WO2022145274A1 - Water retention material for agriculture, and production method therefor - Google Patents

Water retention material for agriculture, and production method therefor Download PDF

Info

Publication number
WO2022145274A1
WO2022145274A1 PCT/JP2021/047069 JP2021047069W WO2022145274A1 WO 2022145274 A1 WO2022145274 A1 WO 2022145274A1 JP 2021047069 W JP2021047069 W JP 2021047069W WO 2022145274 A1 WO2022145274 A1 WO 2022145274A1
Authority
WO
WIPO (PCT)
Prior art keywords
water
absorbent resin
retaining material
less
mol
Prior art date
Application number
PCT/JP2021/047069
Other languages
French (fr)
Japanese (ja)
Inventor
正博 馬場
結稀 藤井
裕典 三枝
利典 加藤
Original Assignee
株式会社クラレ
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from JP2020219318A external-priority patent/JP2024022704A/en
Priority claimed from JP2020219320A external-priority patent/JP2024022705A/en
Application filed by 株式会社クラレ filed Critical 株式会社クラレ
Publication of WO2022145274A1 publication Critical patent/WO2022145274A1/en

Links

Classifications

    • A—HUMAN NECESSITIES
    • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01G—HORTICULTURE; CULTIVATION OF VEGETABLES, FLOWERS, RICE, FRUIT, VINES, HOPS OR SEAWEED; FORESTRY; WATERING
    • A01G24/00—Growth substrates; Culture media; Apparatus or methods therefor
    • A01G24/30—Growth substrates; Culture media; Apparatus or methods therefor based on or containing synthetic organic compounds
    • A01G24/35—Growth substrates; Culture media; Apparatus or methods therefor based on or containing synthetic organic compounds containing water-absorbing polymers
    • A—HUMAN NECESSITIES
    • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01G—HORTICULTURE; CULTIVATION OF VEGETABLES, FLOWERS, RICE, FRUIT, VINES, HOPS OR SEAWEED; FORESTRY; WATERING
    • A01G24/00—Growth substrates; Culture media; Apparatus or methods therefor
    • A01G24/40—Growth substrates; Culture media; Apparatus or methods therefor characterised by their structure
    • A01G24/42—Growth substrates; Culture media; Apparatus or methods therefor characterised by their structure of granular or aggregated structure
    • A—HUMAN NECESSITIES
    • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01G—HORTICULTURE; CULTIVATION OF VEGETABLES, FLOWERS, RICE, FRUIT, VINES, HOPS OR SEAWEED; FORESTRY; WATERING
    • A01G7/00—Botany in general

Definitions

  • the present invention relates to a water-retaining material for agriculture and a method for producing the same.
  • Patent Documents 1 and 2 disclose that a water-absorbent resin containing a polyacrylic acid salt gel as a main component can be used as a water-retaining material for agriculture.
  • Patent Document 3 discloses polyvinyl alcohol-based water-absorbent resin particles having complicated surface shape characteristics.
  • Patent Document 4 discloses an aggregated polyacrylic acid-based water-absorbent resin obtained by a reverse-phase suspension polymerization method, and discloses that this resin has high liquid-permeable performance and can be suitably used for sanitary material applications.
  • Patent Document 5 discloses a polyvinyl alcohol-based water-absorbent resin having specific pores, and discloses that this resin has excellent absorbability of water and liquid fertilizer and can be suitably used for agriculture.
  • Patent Document 6 an example in which a polymer containing an acrylic acid unit as a main component is used as a soil water-retaining material (Patent Document 6), and a polymer containing an acrylic acid unit and / or a sulfonic acid group-containing acrylamide monomer unit as a main component is water-absorbent.
  • An example of using a resin Patent Document 7
  • an example of using a polymer particle of 2-acrylamide-2-methylpropanesulfonic acid as a salt-resistant water-absorbing agent with an average particle size of 50 ⁇ m or less on a volume basis Patent Document 7
  • Document 8 an example of using a polymer particle of 2-acrylamide-2-methylpropanesulfonic acid as a salt-resistant water-absorbing agent with an average particle size of 50 ⁇ m or less on a volume basis
  • the water absorption rate of the water-absorbent resin is very important in addition to the water retention amount of the water-absorbent resin and the water supply to the plant.
  • a seeder is used to sow soil, water, and seeds containing a water-absorbent resin in the seedling raising box that flows by a conveyor. If the water absorption of the soil containing the water-absorbent resin is not completed before sowing the seed paddy, the seed paddy may flow or sink and affect the growth. From the viewpoint of work efficiency, the nursery box flows at a very high speed, so that the water-absorbent resin is required to absorb water at a very high speed.
  • water-absorbent resins for sanitary products have been actively studied, and one of the methods is Various methods have been proposed to prevent the occurrence of "mamako" (a phenomenon in which fine particles associate with each other through water and become lumpy when the water-absorbent resin comes into contact with water), which is one of the causes of the reduction in water absorption rate. ing.
  • Patent Document 9 a method of foaming with a foaming agent at the time of polymerization or crosslinking to knead air bubbles into a gel
  • Patent Document 9 a method of adding a monomer to a fine particle dispersion during turbid polymerization and aggregating the gel
  • Patent Document 10 a method of granulating fine particles with an aqueous solution and drying them
  • the polyacrylic acid-based water-absorbent resin disclosed in Patent Documents 1, 2 and 4 has a significantly reduced water-absorbing performance due to the calcium salt contained in the soil, and thus is agricultural.
  • the amount of water absorption is not sufficient, and it is difficult to develop a stable amount of water absorption for a long period of time.
  • the vinyl alcohol-based water-absorbent resin disclosed in Patent Documents 3 and 5 a further improved water absorption rate may be required.
  • the water-absorbent resins disclosed in Patent Documents 1, 2, 4 and 6 to 10 are used for agriculture, the water-absorbing power may be too strong and the amount of water supplied to plants may not be sufficient.
  • the vinyl alcohol-based water-absorbent resin disclosed in Patent Document 3 may be required to have a further improved water absorption rate.
  • the problem to be solved by the present invention is to solve the above-mentioned problems, that the water absorption rate is excellent, the water absorption amount is sufficiently high even in the presence of a calcium salt, and the water absorption amount does not easily decrease for a long period of time. It is to provide water retention materials for agriculture.
  • the present inventors have repeated detailed studies on agricultural water-retaining materials and have completed the present invention. That is, the present invention includes the following preferred embodiments.
  • An agricultural water-retaining material containing a water-absorbent resin containing a water-absorbent resin.
  • the water-absorbent resin has 0.1 mol% or more and 50 mol% or less of ionic groups with respect to all the constituent units of the water-absorbent resin.
  • Rate of change of D 10 (D 10 of water-retaining material after applying ultrasonic waves) / (D 10 of water-retaining material before applying ultrasonic waves) Is 1 or less, water retention material.
  • Water retention material [6]
  • the water-absorbent resin comprises one or more selected from the group consisting of a vinyl alcohol-based polymer, an acrylic acid-based polymer, an acrylamide-based polymer, and a methacrylic acid-based polymer.
  • the process includes a coagulation step of agglomerating the water-absorbent resin existing as primary particles by contacting them in a swollen state, and a drying step of drying the agglomerated water-absorbent resin under a pressure of 0.2 MPa or less.
  • the method for producing a water-retaining material according to any one of [1] to [10].
  • an agricultural water-retaining material having an excellent water absorption rate, a sufficiently high water absorption amount even in the presence of a calcium salt, and the water absorption amount does not easily decrease for a long period of time.
  • the agricultural water-retaining material of the present invention contains a water-absorbent resin.
  • the present invention is characterized in that the water-absorbent resin has an ionic group of 0.1 mol% or more and 50 mol% or less with respect to all the constituent units of the water-absorbent resin.
  • the rate of change of the volume-based 10% particle diameter D 10 of the water-retaining material before and after applying ultrasonic waves in the water-retaining material swelling test Is also characterized by being 1 or less.
  • the volume-based 10% particle diameter means a particle diameter in which the ratio of particles smaller than this is 10% on a volume basis.
  • a D 10 change rate of 1 or less can be achieved, for example, by the presence of the water-absorbent resin as an agglomerate in the water-retaining material.
  • the water-absorbent resin in the water-retaining material, exists as an agglomerate of particles, preferably as an agglomerate of primary particles.
  • primary particles mean particles that are not agglomerated.
  • the present inventors show that the water-retaining material has the above-mentioned characteristics, so that the water-retaining material exhibits an excellent water absorption rate and a sufficiently high water absorption amount even in the presence of a calcium salt.
  • a calcium salt was found to be difficult to decrease over a long period of time.
  • the reason is not clear, but the following reasons are presumed as a non-limiting mechanism of action. Since the water-retaining material of the present invention contains a water-absorbent resin, it swells when it absorbs water. On the other hand, since the cohesive force of the water-absorbent resin in the water-retaining material is moderately weak, the water-retaining material disintegrates with expansion.
  • the surface area of the water-absorbent resin that comes into contact with water increases, so it is presumed that the water absorption rate increases. Further, the water-absorbent resin surface is in contact with water because the water-absorbent resin has an ionic group content that is not too high, that is, an ionic group content of 50 mol% or less with respect to all the constituent units of the water-absorbent resin. Not only does it absorb water rapidly, but water can also enter the voids of the water-absorbent resin inside the water-retaining material well, and as a result, the surface area of the water-absorbent resin expanded due to the collapse of the water-retaining material is brought into contact with water.
  • the water absorption rate will be significantly faster because it can be used more effectively. Furthermore, since the water-absorbent resin has the above-mentioned specific ionic group content, ionic cross-linking due to the calcium salt and the ionic group is unlikely to occur, so that the water absorption of the water-retaining material is sufficient even in the presence of the calcium salt. It is presumed that the amount of water absorption is high and the amount of water absorption is unlikely to decrease over a long period of time.
  • the state of the water-retaining material at the initial stage of water absorption is reproduced by dispersing the water-retaining material in a medium in which the water-retaining material does not absorb much liquid, instead of a medium (for example, water) that is quickly absorbed by the water-retaining material.
  • a medium for example, water
  • a 20% by mass sodium chloride aqueous solution is used as such a medium that is not so absorbed.
  • the water-retaining material can be made to absorb the liquid, whereby the state of swelling and disintegration of the water-retaining material can be reproduced.
  • the water retention material swelling test can be carried out by the following procedure.
  • the water-retaining material as a sample is dispersed in a dispersion medium, and for example, using a laser diffraction / scattering type particle size distribution measuring device, a volume-based 10% particle size D 10 (D 10 of the water-retaining material before applying ultrasonic waves). Equivalent to).
  • the water-retaining material is swelled by absorbing the dispersion medium into the water-retaining material by ultrasonic irradiation for 5 minutes, and then the volume-based 10% particle diameter D 10 of the water-retaining material (of the water-retaining material after applying ultrasonic waves). (Equivalent to D10 ) is measured. The measurement conditions are shown below.
  • the present inventors have found that among the water-absorbent resin particles forming the water-retaining material, particles having a relatively small particle size are one of the factors that determine the water absorption rate of the entire water-retaining material. Therefore, in the present invention, D 10 is used as a constituent requirement for achieving an excellent water absorption rate.
  • the rate of change of the volume-based 10% particle diameter D 10 of the water-retaining material before and after applying ultrasonic waves is 1 or less. If the rate of change of D 10 is greater than 1, it is difficult to obtain the desired water absorption rate.
  • the rate of change of D 10 is preferably 0.95 or less, more preferably 0.94 or less, more preferably 0.93 or less, more preferably 0.92 or less, more preferably 0.91 or less, still more preferably 0. It is .90 or less, more preferably 0.85 or less, particularly preferably 0.80 or less, and particularly more preferably 0.75 or less.
  • the lower limit of the rate of change of D 10 is not particularly limited.
  • the rate of change of D 10 is, for example, 0.30 or more.
  • the rate of change of D 10 is, for example, the presence of the water-absorbent resin as an aggregate in the water-retaining material, the adjustment of the binder amount, pressure, temperature or the amount of the plasticizer in the step of aggregating the water-absorbent resin, and the aggregated water-absorbent resin.
  • the pressure, temperature or amount of plasticizer in the drying step or by adjusting the particle size or shape of the water-absorbent resin particles before aggregation, it can be adjusted to the lower limit value or more and the upper limit value or less.
  • the maximum particle size on the smallest particle size side in the state after applying ultrasonic waves is preferably 1 ⁇ m or more, more preferably 5 ⁇ m or more, still more preferably 10 ⁇ m or more, and particularly preferably 30 ⁇ m or more. It is preferably 1000 ⁇ m or less, more preferably 500 ⁇ m or less, still more preferably 200 ⁇ m or less, and particularly preferably 100 ⁇ m or less.
  • the maximum particle size is 0.011 ⁇ m, 0.013 ⁇ m, 0.015 ⁇ m, 0.017 ⁇ m, 0.02 ⁇ m, 0.023 ⁇ m, 0.026 ⁇ m, 0.03 ⁇ m, 0.034 ⁇ m, 0.039 ⁇ m, 0.044 ⁇ m, 0.051 ⁇ m, 0.058 ⁇ m, 0.067 ⁇ m, 0.076 ⁇ m, 0.087 ⁇ m, 0.1 ⁇ m, 0.115 ⁇ m, 0.131 ⁇ m, 0.15 ⁇ m, 0.172 ⁇ m, 0.197 ⁇ m, 0.226 ⁇ m, 0.
  • the maximum particle size is at least the lower limit value and at least the upper limit value, a more preferable water absorption rate can be easily obtained.
  • the maximum particle size can be adjusted to be equal to or higher than the lower limit value and lower than the upper limit value by adjusting the particle size of the water-absorbent resin particles before aggregation, for example.
  • the water-absorbent resin contained in the water-retaining material exists as an aggregate of primary particles.
  • the average particle size of the primary particles of the water-absorbent resin contained in the water-retaining material is preferably 1 ⁇ m or more, more preferably 10 ⁇ m or more, still more preferably 30 ⁇ m or more, particularly preferably 50 ⁇ m or more, preferably 2000 ⁇ m or less, more preferably 2000 ⁇ m or less. It is 1000 ⁇ m or less, more preferably 700 ⁇ m or less, and particularly preferably 150 ⁇ m or less.
  • the average particle diameter of the primary particles is at least the lower limit value and at least the upper limit value, a more preferable water absorption rate can be easily obtained.
  • the average particle diameter of the primary particles is at least the above lower limit value, it is easy to suppress the generation of dust during the production of the water retention material.
  • the average particle size of the primary particles can be measured, for example, using an electron microscope or a sieve with a specific opening.
  • the water-absorbent resin contained in the water-retaining material is 0.1 mol% or more, preferably 0.5 mol% or more, more preferably 1.0 mol% or more, still more preferably 2 with respect to all the constituent units of the water-absorbent resin. It has an ionic group of 0.0 mol% or more, particularly preferably 3.0 mol% or more.
  • the "constituent unit” means a repeating unit that constitutes the water-absorbent resin. When the ionic group content is at least the above lower limit value, the water-absorbent resin tends to have a higher water absorption amount or water absorption rate.
  • the water-absorbent resin is 50 mol% or less, preferably 40 mol% or less, more preferably 30 mol% or less, still more preferably 20 mol% or less, and particularly preferably 10 mol% or less, based on all the constituent units of the water-absorbent resin.
  • the ionic group content is not more than the above upper limit value, the water-absorbent resin tends to maintain an excellent liquid absorption amount or liquid absorption rate even in the presence of divalent ions (for example, calcium ions) contained in the soil. This liquid absorption amount or liquid absorption rate is unlikely to decrease over a long period of time, and decomposition of the water-absorbent resin by ultraviolet rays is unlikely to occur.
  • the content of ionic groups in the water-absorbent resin and the content of various structural units described later are, for example, solid 13 C-NMR (nuclear magnetic resonance spectroscopy), FTIR (Fourier transform infrared spectroscopy) or acid base. It can be measured by titration or the like. Further, the content of the ionic group in the water-absorbent resin and the content of various structural units described later are, for example, the compounding ratio of the monomer that brings about the ionic group and the monomer that forms various structural units, and those at the time of reaction. It can be adjusted by adjusting the consumption rate or reactivity ratio, reaction temperature, solvent and the like.
  • the ionic group may exist as an ionic group or a derivative thereof.
  • the ionic group is preferably a carboxyl group, a sulfonic acid group, an ammonium group or a salt thereof, more preferably a carboxyl group, an ammonium group or a salt thereof, and particularly preferably a carboxyl group or a salt thereof. Therefore, in a preferred embodiment of the present invention, the water-absorbent resin has one or more selected from the group consisting of a carboxyl group, a sulfonic acid group and an ammonium group as an ionic group.
  • the above-mentioned ionic group content is the content of the ionic group and its derivative or The content of the derivative of the ionic group.
  • the water retention material preferably has a water content of 11% by mass or more and 50% by mass or less and a bulk density of 0.20 g / mL or more and 1.25 g / mL or less.
  • the water content of the water-retaining material of the present invention is preferably 11% by mass or more, more preferably 15% by mass or more, more preferably 16% by mass or more, still more preferably 20% by mass or more.
  • the water content of the water-retaining material of the present invention is preferably 50% by mass or less, more preferably 40% by mass or less, more preferably 33% by mass or less, still more preferably 30% by mass or less.
  • the water-absorbent resins contained in the water-retaining material are less likely to stick to each other, are less likely to form a lump, and are likely to secure a sufficient contact area with water, so that a desired water absorption rate can be easily obtained. ..
  • the water content of the water-retaining material is, for example, the type and content of the ionic group of the water-absorbent resin contained in the water-retaining material; the drying conditions at the time of manufacturing the water-absorbent resin contained in the water-retaining material; the storage conditions of the water-retaining material, etc. as appropriate. By adjusting, it can be adjusted within the above range.
  • the water content can be measured using a halogen moisture meter, for example, by the method described in Examples described later.
  • the bulk density of the water-retaining material of the present invention is preferably 0.20 g / mL or more, more preferably 0.30 g / mL or more, and further preferably 0.35 g / mL or more.
  • the bulk density of the water-retaining material is at least the above lower limit value, the water-retaining material is less likely to float on water, and it is easy to secure a sufficient contact area with water, so that a desired water absorption rate can be easily obtained.
  • dust is less likely to be generated, so that the handleability tends to be excellent.
  • the bulk density of the water-retaining material of the present invention is preferably 1.25 g / mL or less, more preferably 0.95 g / mL or less, still more preferably 0.70 g / mL or less.
  • the bulk density of the water-retaining material is not more than the upper limit, it is difficult for the water-retaining material to be densely filled, and it is easy to secure sufficient water permeability, so that a desired water absorption rate can be easily obtained. Further, when the bulk density of the water-retaining material is not more than the upper limit value, this occurrence is unlikely to occur as it is when mixed with water.
  • the bulk density of the water-retaining material is, for example, the particle size and shape of the water-absorbent resin contained in the water-retaining material; the water content of the water-retaining material; It can be adjusted within the above range by appropriately adjusting the type and amount of the above, pressure, etc.).
  • the bulk density can be measured, for example, by the method described in Examples described later.
  • the water-absorbent resin contained in the water-retaining material has an ionicity of 0.1 mol% or more and 50 mol% or less with respect to all the constituent units of the water-absorbent resin.
  • the water content of the agricultural water-retaining material having a group is preferably 11% by mass or more, preferably 50% by mass or less, and the bulk density is preferably 0.20 g / mL or more, preferably 1.25 g / mL or less. It was found that the water-retaining material showed a better water absorption rate.
  • the water-absorbent resin absorbs water by having an ionic group content that is not too high, that is, an ionic group content of 50 mol% or less with respect to all the constituent units of the water-absorbent resin.
  • the elastic modulus of the water-retaining material is high, it is considered that the water-retaining material is less likely to cause gel blocking, and the water absorption rate is increased by ensuring the water permeability.
  • having an appropriate water content improves the mobility of the polymer chains of the water-absorbent resin in the water-retaining material, thereby suppressing the decrease in water permeability between the water-absorbent resins and increasing the water absorption rate. ..
  • the water-retaining material can efficiently absorb water by ensuring the water permeability between the resins in the water-retaining material by having an appropriate bulk density.
  • the water-retaining material before being used as an agricultural water-retaining material that is, at the time of storage (for example, in a storage container) and immediately before being used in combination with a medium or the like described later, satisfies the above water content and bulk density. Is preferable.
  • the water retention material preferably passes through a sieve with a nominal opening of 3000 ⁇ m, more preferably passes through a sieve with a nominal opening of 2000 ⁇ m, more preferably passes through a sieve with a nominal opening of 1500 ⁇ m, and particularly preferably passes through a sieve with a nominal opening of 1000 ⁇ m. It has a particle size that passes through a sieve, preferably does not pass through a sieve with a nominal opening of 10 ⁇ m, more preferably does not pass through a sieve with a nominal opening of 50 ⁇ m, and more preferably does not pass through a sieve with a nominal opening of 100 ⁇ m, particularly preferably.
  • the water retention material has a particle size that does not pass through a sieve with a nominal opening of 200 ⁇ m.
  • the water retention material has a particle size that passes through a sieve with a nominal opening of 3000 ⁇ m and does not pass through a sieve with a nominal opening of 10 ⁇ m.
  • the water-retaining material has such a particle size, it is easy to obtain better handleability and better water absorption rate.
  • the water-absorbent resin preferably has a crosslinked structure from the viewpoint of suppressing elution of the water-absorbent resin due to irrigation.
  • the water-absorbent resin When the water-absorbent resin has a crosslinked structure, the water-absorbent resin becomes a gel state at the time of water absorption.
  • the form of the crosslinked structure is not particularly limited, and examples thereof include a crosslinked structure formed by an ester bond, an ether bond, an acetal bond, a carbon-carbon bond, and the like.
  • the water-absorbent resin contained in the water-retaining material is not particularly limited. From the viewpoint of ease of production and water retention, the water-absorbent resin is preferably one or more selected from the group consisting of vinyl alcohol-based polymers, acrylic acid-based polymers, acrylamide-based polymers and methacrylic acid-based polymers. It contains, more preferably one or more selected from the group consisting of vinyl alcohol-based polymers and acrylamide-based polymers, and more preferably composed of vinyl alcohol-based polymers or acrylamide-based polymers.
  • the vinyl alcohol-based polymer means a polymer having the highest content of a structural unit derived from vinyl alcohol (hereinafter referred to as “vinyl alcohol unit”) among all the structural units. This also applies to acrylic acid-based polymers, acrylamide-based polymers and methacrylic acid-based polymers.
  • vinyl alcohol-based polymer As an example of the vinyl alcohol-based polymer [hereinafter, may be referred to as vinyl alcohol-based polymer (A)], polyvinyl alcohol, an ethylene-vinyl alcohol copolymer, and their vinyl alcohol units are acetalized by an acetal agent. It can be mentioned as a polymer.
  • the content of the vinyl alcohol polymer (A) in the water-absorbent resin is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 95% by mass or more. , 100% by mass.
  • the vinyl alcohol-based polymer (A) comprises a copolymer of a vinyl alcohol unit and a monomer constituent unit having an ionic group or a derivative thereof.
  • the ionic group or a derivative thereof contained in the vinyl alcoholic polymer (A) is preferably a carboxyl group, a sulfonic acid group, an ammonium group, or a salt thereof, and more preferably a carboxyl group, an ammonium group, or a salt thereof. And particularly preferably a carboxyl group or a salt thereof.
  • the content of the copolymer in the vinyl alcohol-based polymer (A) is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, still more preferably 95% by mass or more. Yes, especially preferably 100% by mass.
  • the vinyl alcohol-based polymer (A) When the vinyl alcohol-based polymer (A) has a carboxyl group, a sulfonic acid group and an ammonium group as ionic groups, the vinyl alcohol-based polymer (A) may be, for example, (i-1) a carboxyl group or a sulfonic acid group. And a saponified product of a polymer of one or more selected from the group consisting of a monomer having an ammonium group and a derivative of the monomer and a vinyl ester; and the like.
  • the monomer having a carboxyl group is not particularly limited, and examples thereof include acrylic acid, methacrylic acid, maleic acid, and itaconic acid.
  • examples of the derivative of the monomer having a carboxyl group include anhydrate, an esterified product, and a neutralized product of the monomer, and examples thereof include methyl acrylate, methyl methacrylate, monomethyl maleate, and itaconic acid. Dimethyl acid, maleic anhydride and the like can be used. Therefore, in one embodiment of the present invention, the vinyl alcohol-based polymer (A) contains one or more monomer constituent units selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, itaconic acid and derivatives thereof. include.
  • the monomer having a sulfonic acid group is not particularly limited, and examples thereof include vinyl sulfonic acid, 2-acrylamide-2-methylpropanesulfonic acid, p-styrenesulfonic acid and the like. be able to.
  • examples of the derivative of the monomer having a sulfonic acid group include an esterified product of the monomer and a neutralized product, and examples thereof include sodium vinyl sulfonate and 2-acrylamide-2-methylpropane sulfonic acid. Sodium, sodium p-styrene sulfonate and the like can be used.
  • the monomer having an ammonium group is not particularly limited, and examples thereof include diallyldimethylammonium chloride, vinyltrimethylammonium chloride, allyltrimethylammonium chloride, p-vinylbenzyltrimethylammonium chloride, and 3. -(Methalamide) propyltrimethylammonium chloride and the like can be mentioned.
  • Examples of the derivative of the monomer having an ammonium group include amines of the monomers, and examples thereof include diallylmethylamine, vinylamine, allylamine, p-vinylbenzyldimethylamine, and 3- (methacrylamide). Propyldimethylamine and the like can be used.
  • the vinyl ester is not particularly limited, and examples thereof include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, vinyl stearate, vinyl benzoate, vinyl trifluoroacetate, and vinyl acetate.
  • vinyl acetate and the like can be mentioned, and vinyl acetate is preferable.
  • the saponified product of (i-1) is, for example, a known polymerization of one or more selected from the group consisting of a monomer having a carboxyl group and a derivative of the monomer and a vinyl ester using a known polymerization initiator. It can be produced by carrying out a reaction and then carrying out a saponification reaction by a known method.
  • a part or all of the ionic group (for example, carboxyl group) contained in the vinyl alcohol polymer (A) is in the form of a salt (carboxylate when the ionic group is a carboxyl group). May be.
  • salt counter cations are alkali metal ions such as lithium ion, sodium ion, potassium ion, rubidium ion, and cesium ion; alkaline earth metal ions such as magnesium ion, calcium ion, strontium ion, and barium ion; Examples thereof include aluminum ions and other metal ions such as zinc ions; onium cations such as ammonium ions, imidazoliums, pyridiniums, and phosphonium ions; and the like.
  • potassium ion, ammonium ion, calcium ion, and magnesium ion are preferable from the viewpoint of easily obtaining a more preferable water absorption amount or water absorption rate.
  • Potassium ions and ammonium ions are more preferable from the viewpoint of plant growth, and calcium ions are more preferable from the viewpoint of easily maintaining the amount of liquid absorbed or the rate of liquid absorption even when in contact with divalent ions contained in the soil.
  • the above (i-1) has a carboxyl group.
  • a method (I) using a neutralized product of a monomer; a method (III) of producing a vinyl alcohol-based polymer (A) having a carboxyl group and then neutralizing the polymer (A) in the above (i-1) can be mentioned. Above all, the above method (III) is preferable.
  • the content of the ionic group in the vinyl alcohol-based polymer (A) is 0.1 mol% or more, preferably 1 mol% or more, more preferably 1 mol% or more, based on all the constituent units of the vinyl alcohol-based polymer (A). 3 mol% or more, more preferably 4 mol% or more, particularly preferably 5 mol% or more, 50 mol% or less, preferably 40 mol% or less, more preferably 30 mol% or less, still more preferably 25 mol% or less. It is even more preferably 20 mol% or less, particularly preferably 15 mol% or less, and even more preferably 10 mol% or less.
  • the vinyl alcohol-based polymer (A) tends to have a higher water absorption amount or water absorption rate.
  • the vinyl alcohol-based polymer (A) maintains an excellent liquid absorption amount or liquid absorption rate even when in contact with divalent ions contained in the soil. The liquid absorption amount or the liquid absorption rate is unlikely to decrease over a long period of time, and the vinyl alcohol-based polymer (A) is less likely to be decomposed by ultraviolet rays.
  • the amount of the carboxyl group derived from acrylic acid or a salt thereof among the above-mentioned carboxyl groups is the total constituent unit of the vinyl alcohol-based polymer. On the other hand, it is preferably 20 mol% or less, more preferably 15 mol% or less, particularly preferably 10 mol% or less, and may be 0 mol%.
  • the amount of the carboxyl group derived from acrylic acid or a salt thereof among the above-mentioned carboxyl groups is not more than the upper limit value, more excellent weather resistance (particularly ultraviolet resistance) can be easily obtained.
  • the ionic groups contained in the vinyl alcohol polymer (A) are in the form of derivatives, and in a more preferred embodiment, the ionicity contained in the vinyl alcohol polymer (A). Most of the groups are in the form of derivatives, and in one particularly preferred embodiment, all of the ionic groups contained in the vinyl alcohol polymer (A) are in the form of derivatives.
  • the "constituent unit” means a repeating unit constituting the polymer.
  • the vinyl alcohol unit is "1 unit” and two vinyl alcohol units are acetalized. The structure is counted as "2 units”.
  • the content of the vinyl alcohol unit of the vinyl alcohol-based polymer (A) is preferably more than 20 mol%, more preferably 50 mol% or more, still more preferably 50 mol% or more, based on all the constituent units of the vinyl alcohol-based polymer (A). Is 60 mol% or more, preferably 98 mol% or less, more preferably 95 mol% or less, still more preferably 90 mol% or less.
  • the content of the vinyl alcohol unit can be measured by FTIR, solid 13 C-NMR, or the like as described above, but it can also be calculated from the consumption of acetic anhydride when reacted with a certain amount of acetic anhydride.
  • the vinyl alcohol-based polymer (A) contains other structural units other than the vinyl alcohol unit.
  • examples of the above other structural units include vinyl acetate and structural units derived from vinyl carboxylate such as vinyl pivalate; structural units derived from olefins such as ethylene, 1-butene, and isobutylene; acrylic acid and its derivatives, methacrylic acid. Examples thereof include acid and its derivatives, acrylamide and its derivatives, methacrylic acid and its derivatives, maleic acid and its derivatives, and structural units derived from maleimide derivatives and the like.
  • the other constituent units may contain one type or a plurality of types.
  • the content of the other structural units is preferably 50 mol% or less, more preferably 30 mol% or less, still more preferably 20 mol% or less, and further, with respect to all the structural units of the vinyl alcohol-based polymer (A). More preferably 10 mol% or less, particularly preferably 5 mol% or less, preferably 0.1 mol% or more, more preferably 0.5 mol% or more, still more preferably 1 mol% or more, still more preferably 2 It is mol% or more, particularly preferably 3 mol% or more.
  • the content of the other structural units is at least the lower limit value and at least the upper limit value, it is easy to obtain a better water absorption amount or water absorption rate of the water retention material of the present invention.
  • the viscosity average degree of polymerization of the vinyl alcohol polymer (A) is not particularly limited, but is preferably 20000 or less, more preferably 10000 or less, still more preferably 4000 or less, and particularly preferably 3000 or less from the viewpoint of ease of production. be.
  • the viscosity average degree of polymerization is preferably 100 or more, more preferably 200 or more, still more preferably 400 or more.
  • the viscosity average degree of polymerization of the vinyl alcohol polymer (A) can be measured by a method based on JIS K 6726.
  • the measurement of the viscosity average degree of polymerization is carried out. It can be done after cutting the structure.
  • the cutting can be performed by a general method (for example, hydrolysis using an acid or an alkali).
  • the vinyl alcohol-based polymer (A) preferably contains a crosslinked structure from the viewpoint of suppressing elution of the vinyl alcohol-based polymer due to irrigation.
  • the form of the crosslinked structure is not particularly limited, and examples thereof include a crosslinked structure formed by an ester bond, an ether bond, an acetal bond, a carbon-carbon bond, and the like.
  • the presence or absence of the crosslinked structure in the vinyl alcohol polymer (A) can be examined, for example, by the elution rate in hot water or dimethyl sulfoxide at 100 ° C.
  • the elution rate represented by the ratio of the mass of the eluted sample to the mass of the sample is a certain value or less (for example, 90% by mass or less). With the presence, the existence of the crosslinked structure can be confirmed.
  • ester bond when the vinyl alcohol polymer (A) has a carboxyl group as an ionic group, an ester formed between the hydroxyl group and the carboxyl group of the vinyl alcohol polymer (A). Bonding can be mentioned.
  • the ether bond include an ether bond formed by dehydration condensation between the hydroxyl groups of the vinyl alcohol polymer (A).
  • Another example of the ether bond is an ether bond formed when a polyvalent epoxy compound having a plurality of epoxy groups in one molecule is used in the production of the vinyl alcohol polymer (A). can.
  • the acetal bond when an aldehyde having a carboxyl group is used in the production of the vinyl alcohol polymer (A), the hydroxyl groups of the two vinyl alcohol polymers (A) are acetalized with the aldehyde.
  • the acetal bond formed by the reaction can be mentioned.
  • Another example of the acetal bond is an acetal bond formed when a polyvalent aldehyde compound having a plurality of aldehyde groups in one molecule is used in the production of the vinyl alcohol polymer (A). can.
  • the carbon-carbon bond is, for example, carbon-carbon formed by coupling between carbon radicals of the vinyl alcohol-based polymer (A), which is generated when the vinyl alcohol-based polymer (A) is irradiated with an active energy ray. Bonding can be mentioned.
  • These crosslinked structures may contain one type or a plurality of types. Of these, a crosslinked structure with an ester bond or an acetal bond is preferable from the viewpoint of ease of production, and a crosslinked structure with an acetal bond is more preferable from the viewpoint of maintaining water retention during seedling raising and UV resistance.
  • Such a crosslinked structure may be formed at the same time as the acetalization reaction in the step of acetalizing at least a part of the vinyl alcohol units by, for example, one or more selected from the polyvalent aldehyde compound, or may be formed at the same time as the acetalization reaction step.
  • the cross-linking agent may be further added before the coagulation step described later to be formed before the coagulation step, or the cross-linking agent may be further added in the coagulation step at the same time as the coagulation step. It may be formed or may be formed after the aggregation step by further adding a cross-linking agent after the aggregation step. In the present invention, it is preferable to form a crosslinked structure by further adding a crosslinking agent.
  • Examples of the cross-linking agent include a polyvalent epoxy compound and a polyvalent aldehyde compound, and among them, a polyvalent aldehyde compound is preferable.
  • Examples of the polyvalent epoxy compound include bifunctional epoxy compounds such as ethylene glycol diglycidyl ether.
  • Examples of the polyhydric aldehyde compound include glyoxal, malonaldehyde, succinaldehyde, glutaaldehyde, 1,9-nonandial, adipaldehyde, malealdehyde, tartaraldehyde, citraldehyde, phthalaldehyde, isophthalaldehyde, and terephthalaldehyde.
  • Bifunctional aldehydes can be mentioned.
  • a polyvalent aldehyde compound When a polyvalent aldehyde compound is used as a cross-linking agent, the hydroxyl group of one of the two vinyl alcoholic polymers (A) undergoes an acetalization reaction with one aldehyde group of the polyvalent aldehyde compound, and also Two acetal bonds can be introduced by the hydroxyl group of the other of the two vinyl alcohol-based polymers (A) undergoing an acetalization reaction with another aldehyde group of the polyvalent aldehyde compound. ..
  • the amount of the cross-linking agent in the vinyl alcohol-based polymer (A) is preferably 0.001 mol% or more, more preferably 0, from the viewpoint of easily maintaining water retention in the soil. It is 005 mol% or more, more preferably 0.01 mol% or more, still more preferably 0.03 mol% or more, preferably 0.5 mol% or less, more preferably 0.4 mol% or less, still more preferably. It is 0.3 mol% or less.
  • acrylic acid-based polymer which may contain the water-absorbent resin in the present invention
  • the structural unit derived from acrylic acid or an acrylic acid derivative (hereinafter referred to as “acrylic acid-derived structural unit”) is the most among all the structural units. Contains in high content.
  • raw materials for acrylic acid-based polymers include acrylic acid, sodium acrylate, potassium acrylate, calcium acrylate, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, sec acrylate.
  • acrylic acid-based polymers include those obtained by copolymerizing one or more of these monomers with at least one other monomer copolymerizable by a known method.
  • examples of other monomers capable of copolymerization include monomers that bring about other structural units other than acrylic acid-derived structural units, which will be described later.
  • the content of the acrylic acid-based polymer in the water-absorbent resin is preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, particularly preferably 95% by mass or more, and 100% by mass. May be.
  • a part or all of the ionic group (for example, carboxyl group) contained in the acrylic acid-based polymer is in the form of a salt (carboxylate when the ionic group is a carboxyl group). May be good.
  • salt counter cations are alkali metal ions such as lithium ion, sodium ion, potassium ion, rubidium ion, and cesium ion; alkaline earth metal ions such as magnesium ion, calcium ion, strontium ion, and barium ion; Examples thereof include aluminum ions and other metal ions such as zinc ions; onium cations such as ammonium ions, imidazoliums, pyridiniums, and phosphonium ions; and the like.
  • potassium ion, ammonium ion, calcium ion, and magnesium ion are preferable from the viewpoint of easily obtaining a more preferable water absorption amount or water absorption rate.
  • Potassium ions and ammonium ions are more preferable from the viewpoint of plant growth, and calcium ions are more preferable from the viewpoint of easily maintaining the amount of liquid absorbed or the rate of liquid absorption even when in contact with divalent ions contained in the soil.
  • the content of the ionic group in the acrylic acid-based polymer is 0.1 mol% or more, preferably 1 mol% or more, more preferably 3 mol% or more, and further, with respect to all the constituent units of the acrylic acid-based polymer. It is preferably 4 mol% or more, particularly preferably 5 mol% or more, 50 mol% or less, preferably 40 mol% or less, more preferably 30 mol% or less, still more preferably 25 mol% or less, still more preferably 20. It is mol% or less, particularly preferably 15 mol% or less, and even more preferably 10 mol% or less.
  • the acrylic acid-based polymer tends to have a higher water absorption amount or water absorption rate.
  • the acrylic acid-based polymer can easily maintain an excellent liquid absorption amount or liquid absorption rate even when in contact with divalent ions contained in the soil. This liquid absorption amount or liquid absorption rate is unlikely to decrease over a long period of time, and decomposition of the acrylic acid-based polymer by ultraviolet rays is unlikely to occur.
  • the amount of the carboxyl group derived from acrylic acid or a salt thereof among the above-mentioned carboxyl groups is based on all the constituent units of the acrylic acid-based polymer. It is preferably 20 mol% or less, more preferably 15 mol% or less, particularly preferably 10 mol% or less, and may be 0 mol%.
  • the amount of the carboxyl group derived from acrylic acid or a salt thereof among the above-mentioned carboxyl groups is not more than the upper limit value, more excellent weather resistance (particularly ultraviolet resistance) can be easily obtained.
  • more than half of the ionic groups contained in the acrylic acid polymer are in the form of derivatives, and in a more preferred embodiment, most of the ionic groups contained in the acrylic acid polymer are derivatives. It is a form, and in a particularly preferable embodiment, all of the ionic groups contained in the acrylic acid-based polymer are in the form of a derivative.
  • the content of the acrylic acid-derived structural unit of the acrylic acid-based polymer is preferably more than 20 mol%, more preferably 50 mol% or more, still more preferably 60 mol% with respect to all the structural units of the acrylic acid-based polymer.
  • the above is preferably 98 mol% or less, more preferably 95 mol% or less, still more preferably 90 mol% or less.
  • the acrylic acid-based polymer contains other structural units other than the acrylic acid-derived structural unit.
  • Examples of the above other building blocks include vinyl alcohol units; building blocks derived from vinyl carboxylates such as vinyl acetate and vinyl pivalate; building blocks derived from olefins such as ethylene, 1-butene, and isobutylene; methacrylic acid and Derivatives thereof, acrylamide and its derivatives, methacrylic acid and its derivatives, maleic acid and its derivatives, structural units derived from maleimide derivatives and the like; and the like can be mentioned.
  • the other constituent units may contain one type or a plurality of types.
  • the content of the other structural units is preferably 50 mol% or less, more preferably 30 mol% or less, still more preferably 20 mol% or less, still more preferably 20 mol% or less, based on all the structural units of the acrylic acid-based polymer. 10 mol% or less, particularly preferably 5 mol% or less, preferably 0.1 mol% or more, more preferably 0.5 mol% or more, still more preferably 1 mol% or more, still more preferably 2 mol% or more. , Particularly preferably 3 mol% or more.
  • the content of the other structural units is at least the lower limit value and at least the upper limit value, it is easy to obtain a better water absorption amount or water absorption rate of the water retention material of the present invention.
  • the weight average molecular weight of the acrylic acid-based polymer is not particularly limited, but from the viewpoint of ease of production, it is preferably 1,000,000 or less, more preferably 5,000,000 or less, still more preferably 3,000,000 or less. Below, it is particularly preferably 1,000,000 or less. On the other hand, from the viewpoint of the mechanical properties of the acrylic acid-based polymer and the elution resistance to water, the weight average molecular weight is preferably 1000 or more, more preferably 5000 or more, still more preferably 10,000 or more.
  • the weight average molecular weight of the acrylic acid-based polymer can be measured by, for example, GPC.
  • the weight average molecular weight should be measured after cutting the crosslinked structure. Can be done.
  • the cutting can be performed by a general method (for example, hydrolysis using an acid or an alkali).
  • the acrylic acid-based polymer preferably contains a crosslinked structure from the viewpoint of suppressing elution of the acrylic acid-based polymer due to irrigation.
  • the form of the cross-linked structure is not particularly limited, and examples thereof include a cross-linked structure using a general cross-linking agent.
  • the presence or absence of the crosslinked structure in the acrylic acid-based polymer can be examined by, for example, the elution rate in hot water or dimethyl sulfoxide at 100 ° C.
  • the crosslinked structure may be formed at the same time as the copolymerization reaction in the copolymerization step of, for example, the monomer which brings about the structural unit derived from acrylic acid and the monomer which brings about the structural unit other than the structural unit derived from acrylic acid, or the copolymerization reaction. It may be formed before the aggregation step by further adding a cross-linking agent before the aggregation step described later in another step other than the step, or it may be formed by further adding the cross-linking agent in the aggregation step. It may be formed at the same time, or may be formed after the aggregation step by further adding a cross-linking agent after the aggregation step. In the present invention, it is preferable to form a crosslinked structure by further adding a crosslinking agent.
  • cross-linking agents examples include N, N'-methylenebisacrylamide, divinylbenzene, ethylene glycol diglycidyl ether, pentaerythritol triallyl ether, pentaerythritol triacrylate, pentaerythritol tetraacrylate, 1,6-hexanediol diacrylate, 1,9-Nonandiol diacrylate, 1,10-decanediol diacrylate, neopentyl glycol diacrylate, 2-hydroxy-3-methacrylicpropyl acrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, trimethyl propanetriacrylate and Tris- (2-acryloxyethyl) isocyanurate and the like can be mentioned.
  • the amount of the cross-linking agent in the acrylic acid-based polymer is preferably 0.001 mol% or more, more preferably 0.01 mol%, from the viewpoint of easily maintaining water retention in the soil.
  • the above is more preferably 1.0 mol% or more, still more preferably 2.0 mol% or more, preferably 10 mol% or less, more preferably 5 mol% or less, still more preferably 3 mol% or less.
  • acrylic acid-based polymer examples include a crosslinked product of an acrylic acid-sodium acrylate copolymer.
  • Commercially available products include highly absorbent polymers (acrylic acid salt type, manufactured by Wako Pure Chemical Industries, Ltd.), Acrihope (registered trademark) (manufactured by Nippon Shokubai Co., Ltd.), and Sunwet (registered trademark) (Sanyo Chemical Industries, Ltd.). Made) and the like.
  • the acrylamide-based polymer that may be contained in the water-absorbent resin in the present invention contains a structural unit derived from acrylamide or an acrylamide derivative (hereinafter referred to as "acrylamide-derived structural unit") at the highest content among all the structural units.
  • acrylamide-derived structural unit a structural unit derived from acrylamide or an acrylamide derivative
  • examples of raw materials for acrylamide-based polymers include acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, N-alkylacrylamide, and trimethyl [3- (acryloylamino) propyl] aminium chloride.
  • Examples of the acrylamide-based polymer include those obtained by copolymerizing one or more of these monomers with at least one other monomer copolymerizable by a known method.
  • Examples of other monomers capable of copolymerization include monomers that bring about other structural units other than the acrylamide-derived structural units, which will be described later.
  • the content of the acrylamide polymer in the water-absorbent resin is preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, particularly preferably 95% by mass or more, and 100% by mass. There may be.
  • some or all of the ionic groups (eg, carboxyl groups) of the acrylamide polymer may be in the form of salts (carboxylates if the ionic groups are carboxyl groups).
  • salt counter cations are alkali metal ions such as lithium ion, sodium ion, potassium ion, rubidium ion, and cesium ion; alkaline earth metal ions such as magnesium ion, calcium ion, strontium ion, and barium ion; Examples thereof include aluminum ions and other metal ions such as zinc ions; onium cations such as ammonium ions, imidazoliums, pyridiniums, and phosphonium ions; and the like.
  • potassium ion, ammonium ion, calcium ion, and magnesium ion are preferable from the viewpoint of easily obtaining a more preferable water absorption amount or water absorption rate.
  • Potassium ions and ammonium ions are more preferable from the viewpoint of plant growth, and calcium ions are more preferable from the viewpoint of easily maintaining the amount of liquid absorbed or the rate of liquid absorption even when in contact with divalent ions contained in the soil.
  • the content of the ionic group in the acrylamide-based polymer is 0.1 mol% or more, preferably 1 mol% or more, more preferably 3 mol% or more, still more preferably 3 mol% or more, based on all the constituent units of the acrylamide-based polymer. 4 mol% or more, particularly preferably 5 mol% or more, 50 mol% or less, preferably 40 mol% or less, more preferably 30 mol% or less, still more preferably 25 mol% or less, still more preferably 20 mol%.
  • it is particularly preferably 15 mol% or less, and further particularly preferably 10 mol% or less.
  • the acrylamide-based polymer tends to have a higher water absorption amount or water absorption rate.
  • the content of the ionic group is not more than the upper limit, the acrylamide polymer can easily maintain an excellent liquid absorption amount or liquid absorption rate even when in contact with divalent ions contained in the soil. The amount of liquid absorbed or the rate of liquid absorption is unlikely to decrease over a long period of time, and decomposition of the acrylamide polymer by ultraviolet rays is unlikely to occur.
  • the amount of the carboxyl group derived from acrylamide or a salt thereof among the above-mentioned carboxyl groups is preferably 20 with respect to all the constituent units of the acrylamide-based polymer. It is mol% or less, more preferably 15 mol% or less, particularly preferably 10 mol% or less, and may be 0 mol%.
  • the amount of the carboxyl group derived from acrylamide or a salt thereof among the above-mentioned carboxyl groups is not more than the upper limit value, more excellent weather resistance (particularly ultraviolet resistance) can be easily obtained.
  • more than half of the ionic groups contained in the acrylamide polymer are in the form of derivatives, and in a more preferred embodiment, most of the ionic groups contained in the acrylamide polymer are in the form of derivatives. Yes, and in one particularly preferred embodiment, all of the ionic groups contained in the acrylamide polymer are in the form of derivatives.
  • the content of the acrylamide-derived structural unit of the acrylamide-based polymer is preferably more than 20 mol%, more preferably 50 mol% or more, still more preferably 60 mol% or more with respect to all the structural units of the acrylamide-based polymer. It is preferably 98 mol% or less, more preferably 95 mol% or less, still more preferably 90 mol% or less.
  • the acrylamide-based polymer contains other structural units other than the acrylamide-derived structural unit.
  • Examples of the above other building blocks include vinyl alcohol units; building blocks derived from vinyl carboxylates such as vinyl acetate and vinyl pivalate; building blocks derived from olefins such as ethylene, 1-butene, and isobutylene; acrylic acid and Derivatives thereof, methacrylic acid and its derivatives, methacrylicamide and its derivatives, maleic acid and its derivatives, structural units derived from maleimide derivatives and the like; and the like can be mentioned.
  • the other constituent units may contain one kind or a plurality of kinds.
  • the content of the other structural units is preferably 50 mol% or less, more preferably 30 mol% or less, still more preferably 20 mol% or less, still more preferably 10 with respect to all the structural units of the acrylamide-based polymer.
  • Mol% or less particularly preferably 5 mol% or less, preferably 0.1 mol% or more, more preferably 0.5 mol% or more, still more preferably 1 mol% or more, still more preferably 2 mol% or more, Particularly preferably, it is 3 mol% or more.
  • the content of the other structural units is at least the lower limit value and at least the upper limit value, it is easy to obtain a better water absorption amount or water absorption rate of the water retention material of the present invention.
  • the weight average molecular weight of the acrylamide polymer is not particularly limited, but from the viewpoint of ease of production, it is preferably 1,000,000 or less, more preferably 5,000,000 or less, still more preferably 3,000,000 or less. , Particularly preferably 1,000,000 or less.
  • the weight average molecular weight is preferably 1000 or more, more preferably 5000 or more, still more preferably 10,000 or more.
  • the weight average molecular weight of the acrylamide polymer can be measured by, for example, GPC.
  • the weight average molecular weight can be measured after the crosslinked structure is cut. ..
  • the cutting can be performed by a general method (for example, hydrolysis using an acid or an alkali).
  • the acrylamide polymer preferably contains a crosslinked structure from the viewpoint of suppressing elution of the acrylamide polymer due to irrigation.
  • the form of the cross-linked structure is not particularly limited, and examples thereof include a cross-linked structure using a general cross-linking agent.
  • the presence or absence of the crosslinked structure in the acrylamide-based polymer can be examined by, for example, the elution rate in hot water or dimethyl sulfoxide at 100 ° C.
  • the crosslinked structure may be formed at the same time as the copolymerization reaction in the copolymerization step of, for example, the monomer resulting in the acrylamide-derived structural unit and the monomer resulting in other structural units other than the acrylamide-derived structural unit, or may be formed at the same time as the copolymerization reaction step. In another step, it may be formed before the aggregation step by further adding a cross-linking agent before the aggregation step described later, or it may be formed at the same time as the aggregation step by further adding a cross-linking agent in the aggregation step. It may be formed after the aggregation step by further adding a cross-linking agent after the aggregation step. In the present invention, it is preferable to form a crosslinked structure by further adding a crosslinking agent.
  • cross-linking agents examples include N, N'-methylenebisacrylamide, divinylbenzene, ethylene glycol diglycidyl ether, pentaerythritol triallyl ether, pentaerythritol triacrylate, pentaerythritol tetraacrylate, 1,6-hexanediol diacrylate, 1,9-Nonandiol diacrylate, 1,10-decanediol diacrylate, neopentyl glycol diacrylate, 2-hydroxy-3-methacrylicpropyl acrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, trimethyl propanetriacrylate and Tris- (2-acryloxyethyl) isocyanurate and the like can be mentioned.
  • the amount of the cross-linking agent in the acrylamide-based polymer is preferably 0.001 mol% or more, more preferably 0.005 mol% or more, from the viewpoint of easily maintaining water retention in the soil. More preferably 0.01 mol% or more, still more preferably 0.03 mol% or more, preferably 0.5 mol% or less, more preferably 0.4 mol% or less, still more preferably 0.3 mol. % Or less.
  • the acrylamide-based polymer include a crosslinked product of an acrylamide-acrylic acid-sodium acrylate copolymer and a crosslinked product of an acrylamide-acrylic acid-potassium acrylate copolymer.
  • examples of commercially available products include Miracle-Gro (registered trademark) water storing crystal (manufactured by ScottsMiracle-Gro) and Aquasorb (registered trademark) (manufactured by SNF Holding Company).
  • methacrylic acid-based polymer that may be contained in the water-absorbent resin in the present invention
  • the structural unit derived from methacrylic acid or a methacrylic acid derivative (hereinafter referred to as “methacrylic acid-derived structural unit”) is the most among all the structural units. Contains high content.
  • Examples of raw materials for methacrylic acid-based polymers include methacrylic acid, sodium methacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, propyl methacrylate, isopropyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, and methacrylic acid ( 2-Ethylhexyl), methacrylic acid (t-butylcyclohexyl), benzyl methacrylate and methacrylic acid (2,2,2-trifluoroethyl) and trimethyl [3- (methacryloylamino) propyl] aminium chloride can be mentioned. ..
  • Examples of the methacrylic acid-based polymer include those obtained by copolymerizing one or more of these monomers with at least one other monomer copolymerizable by a known method.
  • Examples of other monomers capable of copolymerization include monomers that bring about other structural units other than the methacrylic acid-derived structural units, which will be described later.
  • the content of the methacrylic acid polymer in the water-absorbent resin is preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, particularly preferably 95% by mass or more, and 100% by mass. May be.
  • a part or all of the ionic group (for example, carboxyl group) contained in the methacrylic acid polymer is in the form of a salt (carboxylate when the ionic group is a carboxyl group). May be good.
  • salt counter cations are alkali metal ions such as lithium ion, sodium ion, potassium ion, rubidium ion, and cesium ion; alkaline earth metal ions such as magnesium ion, calcium ion, strontium ion, and barium ion; Examples thereof include aluminum ions and other metal ions such as zinc ions; onium cations such as ammonium ions, imidazoliums, pyridiniums, and phosphonium ions; and the like.
  • potassium ion, ammonium ion, calcium ion, and magnesium ion are preferable from the viewpoint of easily obtaining a more preferable water absorption amount or water absorption rate.
  • Potassium ions and ammonium ions are more preferable from the viewpoint of plant growth, and calcium ions are more preferable from the viewpoint of easily maintaining the amount of liquid absorbed or the rate of liquid absorption even when in contact with divalent ions contained in the soil.
  • the content of the ionic group in the methacrylic acid-based polymer is 0.1 mol% or more, preferably 1 mol% or more, more preferably 3 mol% or more, and further, with respect to all the constituent units of the methacrylic acid-based polymer. It is preferably 4 mol% or more, particularly preferably 5 mol% or more, 50 mol% or less, preferably 40 mol% or less, more preferably 30 mol% or less, still more preferably 25 mol% or less, still more preferably 20. It is mol% or less, particularly preferably 15 mol% or less, and even more preferably 10 mol% or less.
  • the methacrylic acid-based polymer tends to have a higher water absorption amount or water absorption rate.
  • the content of the ionic group is not more than the upper limit, the methacrylic acid-based polymer can easily maintain an excellent liquid absorption amount or liquid absorption rate even when in contact with divalent ions contained in the soil. This liquid absorption amount or liquid absorption rate is unlikely to decrease over a long period of time, and decomposition of the methacrylic acid-based polymer by ultraviolet rays is unlikely to occur.
  • the amount of the carboxyl group derived from methacrylic acid or a salt thereof among the above-mentioned carboxyl groups is relative to all the constituent units of the methacrylic acid-based polymer. It is preferably 20 mol% or less, more preferably 15 mol% or less, particularly preferably 10 mol% or less, and may be 0 mol%.
  • the amount of the carboxyl group derived from methacrylic acid or a salt thereof among the above-mentioned carboxyl groups is not more than the upper limit value, more excellent weather resistance (particularly ultraviolet resistance) can be easily obtained.
  • more than half of the ionic groups contained in the methacrylic acid polymer are in the form of derivatives, and in a more preferred embodiment, most of the ionic groups contained in the methacrylic acid polymer are derivatives. In one particularly preferred embodiment, all of the ionic groups contained in the methacrylic acid polymer are in the form of derivatives.
  • the content of the methacrylic acid-derived structural unit of the methacrylic acid-based polymer is preferably more than 20 mol%, more preferably 50 mol% or more, still more preferably 60 mol% with respect to all the structural units of the methacrylic acid-based polymer.
  • the above is preferably 98 mol% or less, more preferably 95 mol% or less, still more preferably 90 mol% or less.
  • the methacrylic acid-based polymer contains other structural units other than the methacrylic acid-derived structural unit.
  • Examples of the above other building blocks include vinyl alcohol units; building blocks derived from vinyl carboxylates such as vinyl acetate and vinyl pivalate; building blocks derived from olefins such as ethylene, 1-butene, and isobutylene; acrylic acids and Constituent units derived from its derivatives, acrylamide and its derivatives, methacrylicamide and its derivatives, maleic acid and its derivatives, maleimide derivatives and the like; and the like can be mentioned.
  • the other constituent units may contain one type or a plurality of types.
  • the content of the other structural units is preferably 50 mol% or less, more preferably 40 mol% or less, still more preferably 30 mol% or less, still more preferably 30 mol% or less, based on all the structural units of the methacrylic acid-based polymer. 20 mol% or less, particularly preferably 10 mol% or less, preferably 0.1 mol% or more, more preferably 0.5 mol% or more, still more preferably 1 mol% or more, still more preferably 2 mol% or more. , Particularly preferably 3 mol% or more.
  • the content of the other structural units is at least the lower limit value and at least the upper limit value, it is easy to obtain a better water absorption amount or water absorption rate of the water retention material of the present invention.
  • the weight average molecular weight of the methacrylic acid polymer is not particularly limited, but from the viewpoint of ease of production, it is preferably 1,000,000 or less, more preferably 5,000,000 or less, still more preferably 3,000,000 or less. Below, it is particularly preferably 1,000,000 or less. On the other hand, from the viewpoint of the mechanical properties of the methacrylic acid polymer and the elution resistance to water, the weight average molecular weight is preferably 1000 or more, more preferably 5000 or more, still more preferably 10,000 or more.
  • the weight average molecular weight of the methacrylic acid polymer can be measured by, for example, GPC.
  • the weight average molecular weight should be measured after the crosslinked structure is cut. Can be done.
  • the cutting can be performed by a general method (for example, hydrolysis using an acid or an alkali).
  • the methacrylic acid-based polymer preferably contains a crosslinked structure from the viewpoint of suppressing elution of the methacrylic acid-based polymer due to irrigation.
  • the form of the cross-linked structure is not particularly limited, and examples thereof include a cross-linked structure using a general cross-linking agent.
  • the presence or absence of the crosslinked structure in the methacrylic acid-based polymer can be examined by, for example, the elution rate in hot water or dimethyl sulfoxide at 100 ° C.
  • the crosslinked structure may be formed at the same time as the copolymerization reaction in the copolymerization step of, for example, a monomer which brings about a structural unit derived from methacrylic acid and a monomer which brings about a structural unit other than the structural unit derived from methacrylic acid, or the copolymerization reaction. It may be formed before the aggregation step by further adding a cross-linking agent before the aggregation step described later in another step other than the step, or it may be formed by further adding the cross-linking agent in the aggregation step. It may be formed at the same time, or it may be formed after the aggregation step by further adding a cross-linking agent after the aggregation step. In the present invention, it is preferable to form a crosslinked structure by further adding a crosslinking agent.
  • cross-linking agents examples include N, N'-methylenebisacrylamide, divinylbenzene, ethylene glycol diglycidyl ether, pentaerythritol triallyl ether, pentaerythritol tri and tetraacrylate, 1,6-hexanediol diacrylate, 1,9.
  • Nonandiol diacrylate 1,10-decanediol diacrylate, neopentyl glycol diacrylate, 2-hydroxy-3-methacrylicpropyl acrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, trimethylolpropane triacrylate and tris- ( 2-Acryloxyethyl) isocyanurate and the like can be mentioned.
  • the amount of the cross-linking agent in the methacrylic acid-based polymer is preferably 0.001 mol% or more, more preferably 0.005 mol%, from the viewpoint of easily maintaining water retention in the soil.
  • the above is more preferably 0.01 mol% or more, still more preferably 0.03 mol% or more, preferably 0.5 mol% or less, more preferably 0.4 mol% or less, still more preferably 0.3. It is less than mol%.
  • methacrylic acid-based polymer examples include a crosslinked product of a methacrylic acid-sodium methacrylate copolymer and a crosslinked product of a methacrylic acid-sodium methacrylate-acrylic acid copolymer.
  • the water-retaining material of the present invention may optionally contain an additive in addition to the water-absorbent resin.
  • additives are polysaccharides such as starch, modified starch, sodium alginate, chitin, chitosan, cellulose and derivatives thereof; ethylene-propylene copolymer, polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-butadiene.
  • additives may be used alone or in combination of two or more. Further, all the resins listed as examples of additives are different from the water-absorbent resin of the present invention.
  • the total content thereof may be as long as it does not impair the effect of the present invention, and is usually 20% by mass or less, preferably 15% by mass or less, based on the total mass of the water-retaining material. More preferably, it is 10% by mass or less, for example, 5% by mass or less.
  • a component in a water-retaining material or a medium described later that is, a water-absorbent resin, an optional additive described above, or an optional component (Z) described later], or a component used in a manufacturing process described later (for example, a water-absorbent resin, etc.)
  • the content or mass is based on the dry mass.
  • the "dry state” means a state in which the constituent component does not contain a volatile component such as water or an organic solvent. For example, they can be put into a dry state by vacuum drying at 40 ° C. until the mass of each of the constituents becomes constant.
  • the agricultural water-retaining material of the present invention can be used as a medium in combination with an arbitrary component (Z) as needed, and among them, for example, it can be used as a medium for raising seedlings. Therefore, in one embodiment, the water-retaining material of the present invention is for raising seedlings. Since the water-retaining material of the present invention can exhibit an excellent water absorption rate, when used as a medium, it suppresses a decrease in water utilization efficiency due to water flowing out before the water-retaining material absorbs water during irrigation. be able to.
  • the medium may exhibit a sufficient water absorption rate. can.
  • Examples of such an arbitrary component (Z) include resins other than the water-absorbent resin contained in the water-retaining material, hilling, other optional components described later, and combinations thereof.
  • Resin other than water-absorbent resin examples include polyethylene, polypropylene, alkyd resin, phenolic resin, polyethylene glycol, and polyurethane. These resins can be used alone or in combination of two or more.
  • the total content thereof is preferably 20% by mass or less, more preferably 10% by mass or less, and particularly preferably 5% by mass or less, based on the total mass of the medium.
  • the roots grow in the gaps of the hilling soil so that the roots can be appropriately entangled with each other, and the excellent drainage and air permeability of the medium can be easily obtained.
  • the hilling is not particularly limited, and for example, one kind of commercially available hilling can be used alone or in combination of two or more kinds.
  • other optional components described later may be attached to the soil by a conventional method (for example, a method of spraying a solution or dispersion of the other optional components on the soil and then drying it) and using the soil.
  • the soil is granular.
  • the particle size of the granular soil is preferably 0.2 to 20 mm, more preferably 0.5 to 10 mm, and particularly preferably 1 to 5 mm.
  • a commercially available granular hilling can be sieved and used.
  • a granulation method such as a compression granulation method, an extrusion granulation method, a rolling granulation method, or a fluidized bed granulation method can be used.
  • the particle size of the granular soil can be measured by the following method.
  • the diameter of each particle is measured using a caliper, and the average value is taken as the particle size of the granular culture soil. If the particle is not spherical, the average value of the longest side and the shortest side is taken as the diameter of the particle.
  • the content of the soil is preferably 20 to 99.9999% by mass, more preferably 70 to 99.95% by mass, and particularly preferably 80 to 99.9, based on the total mass of the medium. It is by mass, most preferably 90 to 99.8% by mass.
  • optional ingredients examples include peat, grass charcoal, peat, peat moss, coco peat, rice husks, fertilizer materials, charcoal, diatomaceous earth calcined grains, shell fossil powder, shell powder, crab shells, VA mycorrhizal fungi, microbial materials, etc. Fauna and flora; vermiculite, pearlite, bentonite, natural zeolite, synthetic zeolite, peat, fly ash, rock wool, kaolinite, smectite, montmorillonite, sericite, chlorite, gloconite and talc and other minerals; fertilizer and these The combination of can be mentioned.
  • the medium may be disinfected or sterilized as needed, or may be used with a pH regulator or pesticide.
  • the total content may be as long as it does not impair the effect of the present invention, and is usually 50% by mass or less, preferably 30% by mass or less, based on the total mass of the medium. be.
  • fertilizers are nitrogen-based fertilizers, phosphorus-based fertilizers, and potassium-based fertilizers; essential elements for plants such as calcium, magnesium, sulfur, iron, copper, manganese, zinc, boron, molybdenum, chlorine, and nickel.
  • nitrogen-based fertilizers include sulfur-an, salt-an, glass-an, sodium nitrate, lime nitrate, ammonia fertilizer, urea, lime nitrogen, ammonia lime nitrate, ammonia sodium nitrate and fertilizer with nitrate; phosphorus.
  • system fertilizers include perphosphate lime, heavy perphosphate lime, molten phosphoric acid fertilizer, rotten phosphate fertilizer, roasted phosphorus, heavy roasted phosphorus, phosphorus star, bitter soil perphosphate, mixed phosphate fertilizer, etc.
  • By-product phosphoric acid fertilizer and high-concentration phosphoric acid can be mentioned;
  • potassium-based fertilizer include potassium sulfate, potassium chloride, potassium sulfate bitter soil, potassium carbonate, potassium bicarbonate and potassium silicate and the like. Can be done.
  • These fertilizers may be used in the form of solids, pastes, liquids, solutions, etc., or may be used as coated fertilizers.
  • pesticides include insecticides, fungicides, insecticides, herbicides, rodenticides, preservatives, plant growth regulators and the like.
  • the fertilizer is used as a coated fertilizer.
  • the coated fertilizer is a fertilizer coated with resin.
  • This resin may be, for example, a polyolefin.
  • the coated fertilizer can be supplied to the medium over time as the resin is decomposed. Further, when mat seedlings are produced using granular coated fertilizer, the strength of the obtained mat seedlings tends to be high.
  • the particle size of the coated fertilizer is preferably 1 mm to 10 mm, more preferably 3 mm to 6 mm.
  • the content of the coated fertilizer in the medium is preferably 10 to 99.99% by mass, more preferably 15 to 90% by mass, particularly preferably 20 to 80% by mass, and most preferably 30 to 60% by mass. %.
  • the water-retaining material of the present invention When the water-retaining material of the present invention is used in combination with an arbitrary component (Z), the water-retaining material and the component (Z) are mixed or used, or the water-retaining material of the present invention is contained and the component (Z) is contained. After budding in a medium, the water-retaining material of the present invention can be sprinkled on the medium for use.
  • the mixing method is not particularly limited.
  • the water retention material and the component (Z) may be mixed by a general method.
  • the sprinkling time is not particularly limited, but it is preferable that the plant is vulnerable to drought during the seedling raising period (approximately one month after sowing).
  • the amount of the water-retaining material varies depending on the type of the component (Z) to be combined, but is usually 0.0001% by mass or more with respect to the total mass of the entire medium. It is 20% by mass, preferably 0.05% by mass to 15% by mass, and more preferably 0.1% by mass to 10% by mass.
  • Seed paddy is often sown in a paddy rice seedling box into which a paddy rice seedling medium has been introduced.
  • the amount of seed paddy is 100 to 500 g per box of paddy rice seedling raising box (length 28 cm ⁇ width 58 cm).
  • the water-retaining material of the present invention can be arbitrarily mixed with the component (Z) and used as a medium for sowing seed rice.
  • This medium may be used for either bed soil (soil introduced into the paddy rice seedling box before sowing seed rice) or soil covering (soil covered from above after sowing seed rice), or both. May be good.
  • composition of the medium may be the same or different for the bed soil and the soil cover.
  • water-retaining material of the present invention or a mixture of the water-retaining material of the present invention and the component (Z) may be sprinkled on the medium in which the seed paddy has sprouted.
  • the water absorption time (T2) of the water retention material is preferably 10 seconds or less, more preferably 7 seconds or less, still more preferably 5 seconds or less.
  • the water absorption time (T2) of the water-retaining material is the water absorption time measured by the measuring method described in Examples described later.
  • the degree of improvement in water absorption rate is preferably 1.0 or more, more preferably 2.0 or more, still more preferably 3.0 or more.
  • the degree of improvement in water absorption rate is a value calculated from the water absorption time (T1) measured by the measurement method described in Examples described later.
  • the water absorption time (T1) of the water retention material is preferably 200 seconds or less, more preferably 30 seconds or less, still more preferably 20 seconds or less.
  • the water absorption time (T1) is the water absorption time measured by the measuring method described in Examples described later.
  • the water absorption amount of the water-retaining material in the presence of the calcium salt is preferably 4 g / g or more, more preferably 6 g / g or more, still more preferably 8 g / g or more.
  • the amount of water absorbed in the presence of the calcium salt of the water-retaining material can be measured by a liquid absorption test using an aqueous solution of calcium chloride as described in Examples described later.
  • the water-retaining material of the present invention is, for example, Manufactured by a manufacturing method including a coagulation step of agglomerating a water-absorbent resin existing as primary particles by contacting them in a swollen state, and a drying step of drying the agglomerated water-absorbent resin under a pressure of 0.2 MPa or less.
  • this manufacturing method may be referred to as a manufacturing method according to the first embodiment of the present invention.
  • the primary particles will be described.
  • particles that are not aggregated are referred to as "primary particles" for convenience.
  • particles obtained by melting or dissolving a water-absorbent resin in a solvent and then drying and pulverizing particles obtained by polymerizing a monomer in a melted or dissolved state in a solvent, drying and pulverizing, or (coagulation). It refers to a commercially available water-absorbent resin (not an aggregate) or particles obtained by crushing it.
  • the primary particles are not limited to spherical particles, but may be irregular particles such as those obtained by pulverization.
  • the particle size of the primary particles is as described in the above-mentioned explanation of "agricultural water retention material”.
  • the water-absorbent resin existing as the primary particles is agglomerated by contacting them in a swollen state.
  • a water-absorbent resin in which the average particle size of the primary particles is adjusted by pulverization and / or sieving may be used, if necessary.
  • any of the above-mentioned additives may be mixed with the water-absorbent resin before the aggregation step, at the same time as the aggregation step, or after the aggregation step.
  • the water content of the water-absorbent resin existing as primary particles before swelling the water-absorbent resin is preferably 15% by mass or less, more preferably 13% by mass or less, still more preferably 10% by mass. % Or less, particularly preferably 5% by mass or less.
  • the lower limit of the water content is not particularly limited and is 0% by mass or more.
  • the water content can be calculated using the mass of the water-absorbent resin and the mass of the water-absorbent resin after it has been dried until it becomes dry.
  • the water-absorbent resin existing as primary particles is swollen with a swelling solvent (for example, water, methanol, ethanol, propanol, dimethyl sulfoxide, N-methylpyrrolidone or acetic acid, preferably water).
  • a swelling solvent for example, water, methanol, ethanol, propanol, dimethyl sulfoxide, N-methylpyrrolidone or acetic acid, preferably water.
  • the water-absorbent resin can be uniformly swelled by spraying the swelling solvent in a mist state using a spray or the like.
  • the amount of the swelling solvent to be sprayed is preferably 1% by mass to 500% by mass, more preferably 5% by mass, based on the mass of the water-absorbent resin, from the viewpoint of easily obtaining a preferable particle size and / or cohesive force of the water-retaining material. It is ⁇ 100% by mass, more preferably 10% by mass to 50% by mass.
  • the resin After spraying, the resin is agitated to improve the uniformity of swelling, but agitation with a high shear force, for example, a stirrer equipped with a stirring blade that rotates at high speed, causes crushing or disintegration of once agglomerated particles.
  • a high shear force for example, a stirrer equipped with a stirring blade that rotates at high speed
  • stirring with a low shearing force for example, stirring by a method of putting in a bag and shaking, or stirring with a conical mixer or the like is preferable.
  • the shear force is preferably 10000 MPa or less, more preferably 100 MPa or less, still more preferably 1 MPa or less.
  • the contact time is preferably 0.001 seconds or longer, more preferably 0.1 seconds or longer, still more preferably 1 second or longer.
  • any additive may be added before the agglomeration step or at the same time as the agglomeration step, and the strength of the agglomeration of the water-absorbent resin can be adjusted by adding a binder.
  • binders include polymer components other than water-absorbent resins, such as polyvinyl alcohol, ethylene-vinyl alcohol copolymers, polyvinyl butyral, starch, cellulose, polyethylene oxide, polyethylene glycol, carboxymethyl cellulose, polyacrylic acid and salts thereof. , Polyacrylamide, acrylic acid and its salts and copolymers of acrylamide, styrene butadiene rubber and the like.
  • One type of binder may be used alone, or two or more types may be used in combination.
  • the amount of the binder added is usually 10% by mass or less, preferably 5% by mass or less, more preferably 5% by mass or less, based on the total mass of the water-absorbent resin, the swelling solvent, the binder, and any additive other than the binder if present. It is 1% by mass or less, more preferably 0.5% by mass or less, and may be 0% by mass.
  • the aggregated water-absorbent resin is dried using a dryer under a pressure of 0.2 MPa or less, preferably 0.15 MPa or less, more preferably 0.1 MPa or less, for example, under vacuum.
  • a general dryer can be used, and examples thereof include a conical dryer and a hot air dryer.
  • the drying temperature depends on the water-absorbent resin used, but is usually 20 to 150 ° C, preferably 40 to 100 ° C.
  • the drying time may be appropriately selected so that the obtained water-retaining material is in a dry state, and is usually 1 to 1440 minutes, preferably 5 to 720 minutes. Further, if necessary, any of the above-mentioned additives may be mixed with the aggregated water-absorbent resin before the drying step, at the same time as the drying step, or after the drying step.
  • the swelling solvent may be completely removed, but from the viewpoint of suppressing disintegration, a part of the swelling solvent may remain.
  • the amount of the swelling solvent to be left is preferably 50% by mass or less with respect to the mass of the water-absorbent resin.
  • the production method may further include a cross-linking step of cross-linking the water-absorbent resin before the agglomeration step, at the same time as the agglomeration step, or after the agglomeration step. From the viewpoint of easily obtaining an excellent water absorption rate, it is preferable to include a cross-linking step of cross-linking the water-absorbent resin before the aggregation step. In this case, the crosslinked water-absorbent resin is agglomerated by contacting it in a swollen state, but the cohesive force is not excessively strong.
  • the expansion and disintegration of the water-retaining material proceed in a well-balanced manner during water absorption, and a more preferable water absorption rate can be obtained. Further, it becomes easy to increase the proportion of the crosslinked structure on the surface of the water-absorbent resin, and as a result, from the viewpoint of easily obtaining a low elution rate of the water-absorbent resin from the water-retaining material and / or from the viewpoint of easily obtaining uniform cross-linking, cross-linking is performed. It is preferable that the particle size of the water-absorbent resin to be made is not more than a specific value. The particle size of the water-absorbent resin to be crosslinked can be adjusted to a desired value by sieving.
  • the particle size of the water-absorbent resin to be crosslinked is preferably 2000 ⁇ m or less, more preferably 1000 ⁇ m or less, still more preferably 700 ⁇ m or less, and particularly preferably 150 ⁇ m or less.
  • the particle size of the water-absorbent resin to be crosslinked is preferably 5000 ⁇ m or less, more preferably 3000 ⁇ m or less, and particularly preferably 2000 ⁇ m or less.
  • the particle size when the cross-linking step is carried out at the same time as the coagulation step refers to the particle size at the time when the cross-linking step and the coagulation step are completed.
  • the water-retaining material of the present invention can also be produced, for example, by a production method including a coagulation step in which water-absorbent resins existing as particles are agglomerated by contacting them in a swollen state.
  • this manufacturing method may be referred to as a manufacturing method according to the second embodiment of the present invention.
  • the "particles" in the production method of the second embodiment include non-aggregated particles such as the primary particles in the production method of the first embodiment, and aggregates in which the primary particles are aggregated (scientifically, secondary particles). Any of the particles (sometimes called) are included as a concept. That is, in the production method of the second embodiment, the "particles" include non-aggregated particles, aggregated particles in which non-aggregated particles are aggregated, or non-aggregated particles and aggregated particles. It is also possible to use any of the mixtures of.
  • the particles include, for example, particles obtained by polymerizing in a suspended or emulsified state, particles obtained by spray-drying a resin solution, commercially available particulate water-absorbent resin, or particles obtained by crushing them. , Primary particles used in the production method of the first embodiment, particles in which primary particles are aggregated, a mixture thereof, and the like.
  • the particles may be not only spherical particles such as those obtained by polymerization in a suspended or emulsified state, but also irregularly shaped particles such as those obtained by grinding.
  • the particle size of the particles is preferably 1 ⁇ m or more, more preferably 10 ⁇ m or more, still more preferably 30 ⁇ m or more, particularly preferably 50 ⁇ m or more, preferably 3000 ⁇ m or less, more preferably 1000 ⁇ m or less, still more preferably 600 ⁇ m or less, and particularly preferably. Is 300 ⁇ m or less.
  • the average particle diameter of the particles is at least the lower limit value and at least the upper limit value, a more preferable water absorption rate can be easily obtained. Further, when the average particle diameter of the particles is at least the above lower limit value, it is easy to suppress the generation of dust during the production of the water-retaining material.
  • the average particle size of the particles can be measured, for example, using an electron microscope or a sieve with a specific opening.
  • the water-absorbent resin existing as particles is agglomerated by contacting them in a swollen state.
  • a water-absorbent resin in which the average particle size of the particles is adjusted by pulverization and / or sieving may be used, if necessary.
  • any of the above-mentioned additives may be mixed with the water-absorbent resin before the aggregation step, at the same time as the aggregation step, or after the aggregation step.
  • the water content of the water-absorbent resin existing as particles before swelling the water-absorbent resin is preferably 15% by mass or less, more preferably 13% by mass or less, and particularly preferably 10% by mass. It is as follows. When the water content is not more than the upper limit value, good handleability can be easily obtained.
  • the lower limit of the water content is not particularly limited and is 0% by mass or more.
  • the water content can be calculated using the mass of the water-absorbent resin and the mass of the water-absorbent resin after it has been dried until it becomes dry, and can be calculated, for example, by the method described in Examples described later.
  • the swelling solvent used in the aggregation step of the production method of the second embodiment, the swelling method, the amount of the swelling solvent with respect to the mass of the water-absorbent resin, the stirring method, the stirrer, and the shearing force at the time of stirring are determined by the manufacturing method of the first embodiment. It is possible to adopt the same process as the aggregation process of.
  • Any additive may be added before the agglomeration step or at the same time as the agglomeration step, and the strength of the agglomeration of the water-absorbent resin can be adjusted by adding a binder.
  • a binder As the type and amount of the binder that can be used, those of the production method of the first embodiment can be adopted.
  • the production method may further include a cross-linking step of cross-linking the water-absorbent resin before the agglomeration step, at the same time as the agglomeration step, or after the agglomeration step. From the viewpoint of easily obtaining an excellent water absorption rate, it is preferable to include a cross-linking step of cross-linking the water-absorbent resin before the aggregation step. In this case, the crosslinked water-absorbent resin is agglomerated by contacting it in a swollen state, but the cohesive force is not excessively strong.
  • the expansion and disintegration of the water-retaining material proceed in a well-balanced manner during water absorption, and a more preferable water absorption rate can be obtained. Further, it becomes easy to increase the proportion of the crosslinked structure on the surface of the water-absorbent resin, and as a result, from the viewpoint of easily obtaining a low elution rate of the water-absorbent resin from the water-retaining material and / or from the viewpoint of easily obtaining uniform cross-linking, cross-linking is performed. It is preferable that the particle size of the water-absorbent resin to be made is not more than a specific value. The particle size of the water-absorbent resin to be crosslinked can be adjusted to a desired value by sieving.
  • the particle size of the water-absorbent resin to be crosslinked is preferably 3000 ⁇ m or less, more preferably 1000 ⁇ m or less, still more preferably 600 ⁇ m or less, and particularly preferably 300 ⁇ m or less.
  • the particle size of the water-absorbent resin to be crosslinked is preferably 5000 ⁇ m or less, more preferably 3000 ⁇ m or less, and particularly preferably 2000 ⁇ m or less.
  • the particle size when the cross-linking step is carried out at the same time as the coagulation step refers to the particle size at the time when the cross-linking step and the coagulation step are completed.
  • Peak derived from methyl carbon of vinyl ester group of vinyl acetate unit (usually observed at 10 to 30 ppm), peak derived from methylene carbon of ethylene unit (usually observed at 30 to 50 ppm), acrylic acid And ions contained in the resin from the peak derived from the carbonyl carbon of the methacrylic acid unit (usually observed at 170-180 ppm) and the peak derived from the carbonyl carbon of the acrylamide unit (usually observed at 160-180 ppm).
  • a water-retaining material as a sample is dispersed in a dispersion medium, and a laser diffraction / scattering type particle size distribution measuring device LA-950V2 (manufactured by Horiba Seisakusho) is used to measure the average particle size and volume-based 10% particle size D 10 (ultrasonic waves). (Equivalent to D10 of the water - retaining material before application) was measured. Next, the water-retaining material is swelled by absorbing the dispersion medium into the water-retaining material by ultrasonic irradiation for 5 minutes, and then the volume-based 10% particle diameter D 10 of the water-retaining material (of the water-retaining material after applying ultrasonic waves).
  • the rate of change of the volume-based 10% particle diameter D 10 of the water-retaining material before and after applying ultrasonic waves was calculated by the following formula.
  • Each of the above-mentioned measurements was performed twice for one sample, and the obtained measured value and the average value of the D 10 rate of change were adopted as the measured value and the D 10 rate of change for the sample.
  • Water absorption time (T1) water absorption speed improvement> 0.12 g of a water-retaining material was put into a petri dish having a diameter of 3.5 cm, and 3.0 g of pure water was added with a pipette over 0.5 seconds. The time from when the water was added until the water-retaining material absorbed water and the water surface disappeared was measured. The shorter this time, the faster the water absorption rate of the water retention material. Further, in order to evaluate the degree of improvement in the water absorption rate due to the D 10 change rate of the water retention material being 1 or less, as shown in the following formula, the D 10 change rate of the water retention material is 1 or less as the water absorption rate improvement degree.
  • Water absorption time (T2)> Put Xg of water-retaining material evenly in a petri dish with a diameter of 3.5 cm so that the mass of the water-absorbent resin is 0.12 g, and add pure water Yg with a pipette so that the water content is 3 mL together with the water contained in the water-retaining material. I put it all at once. The time from when the water was added until the water-retaining material absorbed water and the water surface disappeared was measured and used as the water absorption time (T2). The shorter this time, the faster the water absorption rate of the water retention material.
  • Water-absorbent resin As the water-absorbent resin (A1), Aquasorb 3005KB (acrylamide-based polymer, non-aggregate particulate matter, average particle diameter 644 ⁇ m, crosslinked structure) manufactured by SNF Holding Company was used. The content of the ionic group with respect to all the constituent units of the water-absorbent resin (A1) was 22 mol%. As the water-absorbent resin (A2), Aquasorb 3005KB (acrylamide-based polymer, non-aggregate particulate matter, average particle diameter 644 ⁇ m, crosslinked structure) manufactured by SNF Holding Company was used. The content of the ionic group with respect to all the constituent units of the water-absorbent resin (A2) was 22 mol%. An acrylic acid-based polymer (particulate) was used as the water-absorbent resin (C1). The content of the ionic group with respect to all the constituent units of the water-absorbent resin (C1) was 54 mol%.
  • a vinyl alcohol-based polymer [water-absorbent resin (B1)] was synthesized by the following procedure. 9030 g of vinyl acetate, 18.15 g of methyl acrylate, and 3810 g of methanol were introduced into a reactor equipped with a stirrer, a reflux cooling tube, a nitrogen introduction tube, and an initiator addition port, and the reaction was carried out for 30 minutes while nitrogen bubbling. The inside of the vessel was replaced with an inert gas. The temperature of the reactor was started using a water bath, and when the internal temperature of the reactor reached 60 ° C., 2.40 g of azobisisobutyronitrile (AIBN) was added as an initiator to initiate polymerization. ..
  • AIBN azobisisobutyronitrile
  • the progress of the polymerization was confirmed from the solid content concentration by appropriately sampling, and the consumption rate, which is the total mass of vinyl acetate and methyl acrylate consumed by the polymerization, with respect to the total mass of the introduced vinyl acetate and methyl acrylate was calculated. I asked.
  • the consumption rate reached 4% by mass
  • the internal temperature of the reactor was cooled to 30 ° C. to terminate the polymerization. It was connected to a vacuum line, and the residual vinyl acetate was distilled off under reduced pressure at 30 ° C. together with methanol. While visually checking the inside of the reactor, when the viscosity increased, distillation was continued while appropriately adding methanol to obtain polyvinyl acetate containing 5.2 mol% of acrylic acid-derived structural units.
  • the content of acrylic acid-derived structural units was measured using solid 13 C-NMR.
  • 360 g of the obtained polyvinyl acetate containing a structural unit derived from acrylic acid and 6552 g of methanol were added to the same reactor as described above, and the obtained polyvinyl acetate containing a structural unit derived from acrylic acid was dissolved.
  • the temperature of the reactor was started by using a water bath, and the reactor was heated with stirring until the internal temperature of the reactor reached 70 ° C.
  • 280.8 g of a methanol solution of sodium hydroxide metal-caustic, concentration 15% by mass
  • polyvinyl alcohol (b1) polyvinyl alcohol containing 5.2 mol% of acrylic acid-derived structural units.
  • the washed polymer is introduced into a three-neck separable flask equipped with a reflux condenser and a stirring blade, 245 g of methanol, 40.8 g of pure water, and 24.35 g of 50% by mass potassium hydroxide are added, and the temperature is 65 ° C. It was allowed to react for 2 hours. After the reaction, the polymer was taken out by filtration, and then the collected polymer was dispersed in 330 g of methanol, stirred for 30 minutes, and filtered for washing. Washing was repeated twice. The washed polymer was vacuum dried at 40 ° C. for 12 hours to obtain the desired water-absorbent resin (B1). The content of the ionic group with respect to all the constituent units of the water-absorbent resin (B1) was 5 mol%.
  • a vinyl alcohol-based polymer [water-absorbent resin (B2)] was synthesized by the following procedure. 9030 g of vinyl acetate, 18.15 g of methyl acrylate, and 3810 g of methanol were introduced into a reactor equipped with a stirrer, a reflux cooling tube, a nitrogen introduction tube, and an initiator addition port, and the reaction was carried out for 30 minutes while nitrogen bubbling. The inside of the vessel was replaced with an inert gas. The temperature of the reactor was started using a water bath, and when the internal temperature of the reactor reached 60 ° C., 2.40 g of azobisisobutyronitrile (AIBN) was added as an initiator to initiate polymerization. ..
  • AIBN azobisisobutyronitrile
  • the progress of the polymerization was confirmed from the solid content concentration by appropriately sampling, and the consumption rate, which is the total mass of vinyl acetate and methyl acrylate consumed by the polymerization, with respect to the total mass of the introduced vinyl acetate and methyl acrylate was calculated. I asked.
  • the consumption rate reached 4% by mass
  • the internal temperature of the reactor was cooled to 30 ° C. to terminate the polymerization. It was connected to a vacuum line, and the residual vinyl acetate was distilled off under reduced pressure at 30 ° C. together with methanol. While visually checking the inside of the reactor, when the viscosity increased, distillation was continued while appropriately adding methanol to obtain polyvinyl acetate containing 5.2 mol% of acrylic acid-derived structural units.
  • the content of acrylic acid-derived structural units was measured using solid 13 C-NMR.
  • 360 g of the obtained polyvinyl acetate containing a structural unit derived from acrylic acid and 6552 g of methanol were added to the same reactor as described above, and the obtained polyvinyl acetate containing a structural unit derived from acrylic acid was dissolved.
  • the temperature of the reactor was started by using a water bath, and the reactor was heated with stirring until the internal temperature of the reactor reached 70 ° C.
  • 280.8 g of a methanol solution of sodium hydroxide metal-caustic, concentration 15% by mass
  • polyvinyl alcohol (b2) polyvinyl alcohol containing 5.2 mol% of acrylic acid-derived structural units was obtained.
  • the washed polymer is introduced into a three-neck separable flask equipped with a reflux condenser and a stirring blade, 245 g of methanol, 40.8 g of pure water, and 24.35 g of 50% by mass potassium hydroxide are added, and the temperature is 65 ° C. It was allowed to react for 2 hours. After the reaction, the polymer was taken out by filtration, and then the collected polymer was dispersed in 330 g of methanol, stirred for 30 minutes, and filtered for washing. Washing was repeated twice. The washed polymer was vacuum dried at 40 ° C. for 12 hours to obtain the desired water-absorbent resin (B2). The content of the ionic group with respect to all the constituent units of the water-absorbent resin (B2) was 5 mol%.
  • Examples 1 to 3 Sieved particles were collected from the water-absorbent resin (A1) using a sieve with a nominal opening of 53 ⁇ m.
  • the particle size of the collected particles is described as the particle size of " ⁇ 53" for convenience.
  • the particle size of the sieved particles is similarly described using the value of the nominal opening of the sieve.
  • Example 1 All the pure water was absorbed by the water-absorbent resin (A1) in the bag. Then, after vacuum drying at 40 ° C. for 12 hours, a sieve having a nominal opening of 300 ⁇ m, a sieve having a nominal opening of 600 ⁇ m, a sieve having a nominal opening of 1000 ⁇ m and a sieve having a nominal opening of 1400 ⁇ m were used, and the particle size was used as Example 1. Particles having a particle diameter of 300 ⁇ m to 600 ⁇ m, particles having a particle diameter of 600 ⁇ m to 1000 ⁇ m as Example 2, and particles having a particle diameter of 1000 ⁇ m to 1400 ⁇ m were obtained as Example 3, respectively.
  • Examples 4-6 Particles having a particle diameter of 53 ⁇ m to 106 ⁇ m were collected from the water-absorbent resin (A1) using a sieve having a nominal opening of 53 ⁇ m and a sieve having a nominal opening of 106 ⁇ m. Aggregates were obtained in the same manner as in Examples 1 to 3 except that 28 g of the collected particles and 12 g of pure water were used. At this time, all the pure water was absorbed by the water-absorbent resin (A1) in the bag. Then, after vacuum drying at 40 ° C.
  • Example 4 Particles having a particle diameter of 300 ⁇ m to 600 ⁇ m, particles having a particle diameter of 600 ⁇ m to 1000 ⁇ m as Example 5, and particles having a particle diameter of 1000 ⁇ m to 1400 ⁇ m were obtained as Example 6, respectively.
  • Examples 7-8 Particles having a particle diameter of 212 ⁇ m or more were collected from the water-absorbent resin (A1) using a sieve having a nominal opening of 212 ⁇ m. Aggregates were obtained in the same manner as in Examples 1 to 3 except that 28 g of the collected particles and 12 g of pure water were used. At this time, all the pure water was absorbed by the water-absorbent resin (A1) in the bag. Then, after vacuum drying at 40 ° C.
  • particles having a particle diameter of 600 ⁇ m to 1000 ⁇ m were used as Example 7 using a sieve having a nominal opening of 600 ⁇ m, a sieve having a nominal opening of 1000 ⁇ m, and a sieve having a nominal opening of 1400 ⁇ m.
  • particles having a particle diameter of 1000 ⁇ m to 1400 ⁇ m were obtained.
  • Examples 9-10 Particles having a particle diameter of 53 ⁇ m to 106 ⁇ m were collected from the water-absorbent resin (B1) using a sieve having a nominal opening of 53 ⁇ m and a sieve having a nominal opening of 106 ⁇ m. Aggregates were obtained in the same manner as in Examples 1 to 3 except that 28 g of the collected particles and 12 g of pure water were used. At this time, all the pure water was absorbed by the water-absorbent resin (A1) in the bag. Then, after vacuum drying at 40 ° C.
  • particles having a particle diameter of 300 ⁇ m to 600 ⁇ m were used as Example 9 using a sieve having a nominal opening of 300 ⁇ m, a sieve having a nominal opening of 600 ⁇ m, and a sieve having a nominal opening of 1000 ⁇ m.
  • particles having a particle diameter of 600 ⁇ m to 1000 ⁇ m were obtained.
  • Example 11 Particles having a particle diameter of 300 ⁇ m to 600 ⁇ m were collected from the water-absorbent resin (B1) using a sieve having a nominal opening of 300 ⁇ m and a sieve having a nominal opening of 600 ⁇ m. Aggregates were obtained in the same manner as in Examples 1 to 3 except that 28 g of the collected particles and 12 g of pure water were used. At this time, all the pure water was absorbed by the water-absorbent resin (A1) in the bag. Then, after vacuum drying at 40 ° C. for 12 hours, particles having a particle diameter of 600 ⁇ m to 1000 ⁇ m were obtained using a sieve having a nominal opening of 600 ⁇ m and a sieve having a nominal opening of 1000 ⁇ m.
  • Comparative Example 1 Using a sieve having a nominal opening of 300 ⁇ m and a sieve having a nominal opening of 600 ⁇ m, particles having a particle diameter of 300 ⁇ m to 600 ⁇ m were obtained from the water-absorbent resin (A1).
  • Comparative Example 5 Particles having a particle diameter of 106 ⁇ m to 212 ⁇ m were collected from the water-absorbent resin (C1) using a sieve having a nominal opening of 106 ⁇ m and a sieve having a nominal opening of 212 ⁇ m. Aggregates were obtained in the same manner as in Examples 1 to 3 except that 28 g of the collected particles and 12 g of pure water were used. At this time, all the pure water was absorbed by the water-absorbent resin (A1) in the bag. Then, after vacuum drying at 40 ° C. for 12 hours, particles having a particle size of 300 ⁇ m to 600 ⁇ m were obtained using a sieve having a nominal opening of 300 ⁇ m and a sieve having a nominal opening of 600 ⁇ m.
  • the water-absorbent resin having an ionic group of 0.1 mol% or more and 50 mol% or less with respect to all the constituent units of the water-absorbent resin constitutes a water-retaining material having a D10 change rate of 1 or less.
  • the fact that the water absorption rate was significantly improved was the degree of improvement in the water absorption rate [specifically, the ratio of the water absorption time (T1) of Example 1 or 4 to the water absorption time (T1) of Comparative Example 1 (Example). Water absorption rate improvement degree described in row 1 or 4), ratio of water absorption time (T1) of Example 2 or 5 or 7 to water absorption time (T1) of Comparative Example 2 (row of Example 2 or 5 or 7).
  • the water-retaining material of the example also showed a higher absorption amount of calcium chloride aqueous solution than the water-retaining material of the comparative example. This indicates that the water-retaining material of the present invention has a sufficiently high water absorption even in the presence of a calcium salt. In addition, the amount of water absorbed by the water-retaining material of the present invention in the presence of a calcium salt was unlikely to decrease over a long period of time.
  • Example 12 Sieved particles were collected from the water-absorbent resin (A2) using a sieve having a nominal opening of 106 ⁇ m for the water-absorbent resin (A2).
  • the particle size of the collected particles is described as the particle size of " ⁇ 106" for convenience. In the following, the particle size of the sieved particles is similarly described using the value of the nominal opening of the sieve.
  • the water-absorbent resin (A2) was water-containing at this point, and the water content was 15% by mass. The shape was particulate.
  • water-absorbent resin (A2) having a particle size of 106 ⁇ m or less and a water content of 15% by mass is placed in a bag having a length of 28 cm and a width of 20 cm, and 1.5 g of pure water is sprayed little by little each time. I shook it. At this time, instead of applying pressure to the resins to knead them, the bags were filled with air and rotated to be shaken. As a result, particles of the water-absorbent resin (A2) further contained in water were obtained. All the pure water was absorbed by the water-absorbent resin (A2) in the bag. The obtained water-containing water-absorbent resin was used as a water-retaining material for evaluation.
  • Examples 13-14 The sieve used for classification was appropriately changed to obtain a water-absorbent resin (A2) having the particle size shown in Table 2 in the same manner as in Example 12. Next, a water-retaining material was obtained in the same manner as in Example 12 except that the amount of the water-absorbent resin (A2) mixed with water was changed as shown in Table 2 according to the water content of the water-absorbent resin (A2). rice field.
  • Example 15 The water-absorbent resin (B2) was classified by a sieve having a nominal opening of 106 ⁇ m and a sieve having a nominal opening of 250 ⁇ m to obtain a water-absorbent resin (B2) having a particle size of 106 ⁇ m to 250 ⁇ m.
  • the water-absorbent resin (B2) was water-containing at this point, and the water content was 4% by mass.
  • the shape was particulate. 27 g of a water-absorbent resin (B2) having a particle size of 106 ⁇ m to 250 ⁇ m and a water content of 4% by mass was placed in the same bag as that used in Example 12, and 3 g of pure water was sprayed little by little each time.
  • Examples 16-20 The sieve used for classification was appropriately changed to obtain a water-absorbent resin (B2) having the particle size shown in Table 2 in the same manner as in Example 15. Next, a water-retaining material was obtained in the same manner as in Example 15 except that the amount of the water-absorbent resin (B2) mixed with water was changed as shown in Table 2 according to the water content of the water-absorbent resin (B2). rice field.
  • the water-retaining material of the present invention has an excellent water absorption rate, exhibits a sufficiently high water absorption amount even in the presence of a calcium salt, and the water absorption amount does not easily decrease over a long period of time, so that it can be suitably used as a water-retaining material for agriculture.

Abstract

The present invention pertains to a water retention material that is for agriculture and that contains a water-absorbent resin. The water-absorbent resin has 0.1-50 mol% of an ionic group with respect to all constituent units of the water-absorbent resin. The change rate of the volume-based 10% particle size D10 of the water retention material before and after application of ultrasonic waves as measured in a water retention material-swelling test in which a 20-mass% aqueous sodium chloride solution is allowed to be absorbed by the water retention material by means of application of ultrasonic waves, i.e., the change rate of D10 = (D10 of the water retention material after application of ultrasonic waves)/(D10 of the water retention material before application of ultrasonic waves), is at most 1.

Description

農業用保水材およびその製造方法Agricultural water retention material and its manufacturing method
　本発明は、農業用保水材およびその製造方法に関する。 The present invention relates to a water-retaining material for agriculture and a method for producing the same.
　昨今、慢性的な水資源の枯渇に伴い、農業用水を有効にかつ適切に利用すること、および従来よりも少量の灌漑水量でも農産物の収穫量を維持若しくは増大させる試みが、いわゆる農業用保水材を用いて検討されている（例えば、特許文献１～２を参照）。これらの農業用保水材は高吸水性樹脂（ＳＡＰ）を主要構成成分としており、例えば、土壌全体の保水性の改善に用いられるピートモス等と比べると、極めて少量で保水効果を発現することから、農家が用いる際の負担が少ないという利点がある。 In recent years, with the chronic depletion of water resources, attempts to effectively and appropriately use agricultural water and to maintain or increase the yield of agricultural products even with a smaller amount of irrigation water than before are so-called agricultural water retention materials. (For example, see Patent Documents 1 and 2). These agricultural water-retaining materials contain a highly water-absorbent resin (SAP) as a main component, and since they exhibit a water-retaining effect in an extremely small amount as compared with, for example, peat moss used for improving the water-retaining property of the entire soil. It has the advantage of being less burdensome for farmers to use.
　特許文献１および２には、ポリアクリル酸塩ゲルを主成分とする吸水性樹脂を農業用保水材として使用できることが開示されている。特許文献３には、複雑な表面形状特徴を有するポリビニルアルコール系吸水性樹脂粒子が開示されている。特許文献４には、逆相懸濁重合法によって得られる凝集したポリアクリル酸系吸水性樹脂が開示されており、この樹脂は通液性能が高く、衛生材料用途に好適に使用できることが開示されている。特許文献５には、特定の細孔を有するポリビニルアルコール系吸水性樹脂が開示されており、この樹脂は水および液体肥料の吸収性に優れ、農業用に好適に利用できることが開示されている。
　また、アクリル酸単位を主成分とする重合体を土壌保水材とする例（特許文献６）、アクリル酸単位および／またはスルホン酸基含有アクリルアミド単量体単位を主成分とする重合体を吸水性樹脂とする例（特許文献７）、体積基準のメジアン径が５０μｍ以下の平均粒子径であって、２－アクリルアミド－２－メチルプロパンスルホン酸の重合体粒子を耐塩性吸水剤とする例（特許文献８）なども知られている。 Patent Documents 1 and 2 disclose that a water-absorbent resin containing a polyacrylic acid salt gel as a main component can be used as a water-retaining material for agriculture. Patent Document 3 discloses polyvinyl alcohol-based water-absorbent resin particles having complicated surface shape characteristics. Patent Document 4 discloses an aggregated polyacrylic acid-based water-absorbent resin obtained by a reverse-phase suspension polymerization method, and discloses that this resin has high liquid-permeable performance and can be suitably used for sanitary material applications. ing. Patent Document 5 discloses a polyvinyl alcohol-based water-absorbent resin having specific pores, and discloses that this resin has excellent absorbability of water and liquid fertilizer and can be suitably used for agriculture.
Further, an example in which a polymer containing an acrylic acid unit as a main component is used as a soil water-retaining material (Patent Document 6), and a polymer containing an acrylic acid unit and / or a sulfonic acid group-containing acrylamide monomer unit as a main component is water-absorbent. An example of using a resin (Patent Document 7), an example of using a polymer particle of 2-acrylamide-2-methylpropanesulfonic acid as a salt-resistant water-absorbing agent with an average particle size of 50 μm or less on a volume basis (Patent Document 7). Document 8) and the like are also known.
　吸水性樹脂を水稲育苗培土として用いる場合には、吸水性樹脂の保水量および植物への給水性に加えて、吸水性樹脂の吸水速度が非常に重要である。例えば水稲育苗箱の作製においては、播種機を使用し、コンベヤによって流れていく育苗箱に吸水性樹脂を含む培土、水、種籾を順次蒔いていく。種籾を播く前に吸水性樹脂を含む培土の吸水が完了していないと種籾が流動したり沈んだりして生育に影響するおそれがある。作業効率の観点から育苗箱は非常に高速で流れていくため、吸水性樹脂は非常に高速で吸水することが求められる。 When using the water-absorbent resin as soil for raising seedlings of paddy rice, the water absorption rate of the water-absorbent resin is very important in addition to the water retention amount of the water-absorbent resin and the water supply to the plant. For example, in the production of a paddy rice seedling box, a seeder is used to sow soil, water, and seeds containing a water-absorbent resin in the seedling raising box that flows by a conveyor. If the water absorption of the soil containing the water-absorbent resin is not completed before sowing the seed paddy, the seed paddy may flow or sink and affect the growth. From the viewpoint of work efficiency, the nursery box flows at a very high speed, so that the water-absorbent resin is required to absorb water at a very high speed.
　吸水性樹脂の吸水速度の向上（即ち、通水性と吸水性の両立）については、特におむつなどの衛生用品用の吸水性樹脂でさかんに検討がされてきており、その方法の一つとして、吸水速度の低減の原因の一つである「ままこ」（吸水性樹脂が水と接触したときに微粒子同士が水を介して会合しダマになる現象）の発生を防ぐ種々の方法が提案されている。例えば、重合時または架橋時に発泡剤を用いて発泡させて、ゲル中に気泡を練りこむ方法（特許文献９）、縣濁重合中に微粒子分散液にモノマーを追加して凝集させる方法（特許文献４）、微粉を水溶液等で造粒し乾燥する方法（特許文献１０）が提案されている。 Regarding the improvement of the water absorption rate of the water-absorbent resin (that is, both water permeability and water absorption), water-absorbent resins for sanitary products such as diapers have been actively studied, and one of the methods is Various methods have been proposed to prevent the occurrence of "mamako" (a phenomenon in which fine particles associate with each other through water and become lumpy when the water-absorbent resin comes into contact with water), which is one of the causes of the reduction in water absorption rate. ing. For example, a method of foaming with a foaming agent at the time of polymerization or crosslinking to knead air bubbles into a gel (Patent Document 9), and a method of adding a monomer to a fine particle dispersion during turbid polymerization and aggregating the gel (Patent Document 9). 4), a method of granulating fine particles with an aqueous solution and drying them (Patent Document 10) has been proposed.
国際公開第１９９８／００５１９６号パンフレットInternational Publication No. 1998/005196 Pamphlet 特表２０１３－５４４９２９号公報Special Table 2013-544929 特表２０１３－５４０１６４号公報Special Table 2013-540164 国際公開第２０１２／０２３４３３号パンフレットInternational Publication No. 2012/023433 Pamphlet 特開２０１９－１１９８９１号公報Japanese Unexamined Patent Publication No. 2019-11891 国際公開第２０１８／１５９８０１号パンフレットInternational Publication No. 2018/159801 Pamphlet 特開２０１５－０４８３８６号公報JP-A-2015-048386A 特開２００６－２６５３３５号公報Japanese Unexamined Patent Publication No. 2006-265335 特開平１０－１３０３２４号公報Japanese Unexamined Patent Publication No. 10-13324 特開２００８－０１８３２８号公報Japanese Unexamined Patent Publication No. 2008-018328
　しかしながら、本発明者らの検討によれば、特許文献１、２および４に開示されているポリアクリル酸系吸水性樹脂は、土壌中に含まれるカルシウム塩により吸水性能が著しく低下するため、農業用として用いた場合、吸水量が十分でなく、長期間安定した吸水量を発現することも困難である。また、特許文献３および５に開示されたビニルアルコール系吸水性樹脂では、より一層向上した吸水速度が求められる場合があった。
　加えて、特許文献１、２、４および６～１０に開示されている吸水性樹脂は、農業用として用いた場合、吸水力が強すぎて植物への水の供給量が十分ではない場合があり、また、吸水速度の維持も困難である場合があることが分かった。特許文献３に開示されたビニルアルコール系吸水性樹脂は、より一層向上した吸水速度が求められる場合があった。
　本発明が解決しようとする課題は、上記問題を解決することであり、吸水速度に優れ、カルシウム塩の存在下であっても吸水量が十分高く、この吸水量が長期間にわたって低下しにくい、農業用保水材を提供することである。 However, according to the study by the present inventors, the polyacrylic acid-based water-absorbent resin disclosed in Patent Documents 1, 2 and 4 has a significantly reduced water-absorbing performance due to the calcium salt contained in the soil, and thus is agricultural. When used for use, the amount of water absorption is not sufficient, and it is difficult to develop a stable amount of water absorption for a long period of time. Further, in the vinyl alcohol-based water-absorbent resin disclosed in Patent Documents 3 and 5, a further improved water absorption rate may be required.
In addition, when the water-absorbent resins disclosed in Patent Documents 1, 2, 4 and 6 to 10 are used for agriculture, the water-absorbing power may be too strong and the amount of water supplied to plants may not be sufficient. It was also found that it may be difficult to maintain the water absorption rate. The vinyl alcohol-based water-absorbent resin disclosed in Patent Document 3 may be required to have a further improved water absorption rate.
The problem to be solved by the present invention is to solve the above-mentioned problems, that the water absorption rate is excellent, the water absorption amount is sufficiently high even in the presence of a calcium salt, and the water absorption amount does not easily decrease for a long period of time. It is to provide water retention materials for agriculture.
　本発明者らは、前記課題を解決するために、農業用保水材について詳細に検討を重ね、本発明を完成させるに至った。
　即ち、本発明は、以下の好適な態様を包含する。
［１］吸水性樹脂を含んでなる農業用保水材であって、
吸水性樹脂は、吸水性樹脂の全構成単位に対して０．１モル％以上、５０モル％以下のイオン性基を有しており、
超音波を付与することにより２０質量％塩化ナトリウム水溶液を保水材に吸液させる保水材膨潤試験における、超音波を付与する前後の保水材の体積基準１０％粒子径Ｄ１０の変化率：
　　　Ｄ１０の変化率
　　＝(超音波を付与した後の保水材のＤ１０)／(超音波を付与する前の保水材のＤ１０)
は１以下である、保水材。
［２］前記保水材は、含水率が１１質量％以上、５０質量％以下、嵩密度が０．２０ｇ/ｍＬ以上、１．２５ｇ/ｍＬ以下である、前記［１］に記載の保水材。
［３］前記保水材は、公称目開き３０００μｍの篩を通過し、かつ公称目開き１０μｍの篩を通過しない粒度を有する、前記［１］または［２］に記載の保水材。
［４］前記保水材膨潤試験において超音波を付与した後の状態における、最も小粒子径側の極大粒子径は１μｍ以上、１０００μｍ以下である、前記［１］～［３］のいずれかに記載の保水材。
［５］前記吸水性樹脂は、前記イオン性基として、カルボキシル基、スルホン酸基およびアンモニウム基からなる群から選択される１以上を有する、前記［１］～［４］のいずれかに記載の保水材。
［６］前記吸水性樹脂は、ビニルアルコール系重合体、アクリル酸系重合体、アクリルアミド系重合体およびメタクリル酸系重合体からなる群から選択される１以上を含む、前記［１］～［５］のいずれかに記載の保水材。
［７］前記ビニルアルコール系重合体は、アクリル酸、メタクリル酸、マレイン酸、イタコン酸およびそれらの誘導体からなる群から選択される１種以上のモノマー構成単位を含む、前記［６］に記載の保水材。
［８］前記吸水性樹脂は架橋構造を有する、前記［１］～［７］のいずれかに記載の保水材。
［９］育苗用である、前記［１］～［８］のいずれかに記載の保水材。
［１０］前記吸水性樹脂は、吸水時間（Ｔ２）が１０秒以下である、前記［１］～［９］のいずれかに記載の保水材。
［１１］一次粒子として存在する吸水性樹脂を、膨潤させた状態で接触させることにより凝集させる凝集工程、および
　凝集した吸水性樹脂を、０．２ＭＰａ以下の圧力下で乾燥する乾燥工程
を含む、前記［１］～［１０］のいずれか記載の保水材の製造方法。
［１２］前記凝集工程において、前記吸水性樹脂を膨潤させる前において、一次粒子として存在する吸水性樹脂の含水率は１５質量％以下である、前記［１１］に記載の方法。
［１３］粒子として存在する吸水性樹脂を、膨潤させた状態で接触させることにより凝集させる凝集工程を含む、前記［１］～［１０］のいずれか記載の保水材の製造方法。
［１４］前記凝集工程において、前記吸水性樹脂を膨潤させる前において、粒子として存在する吸水性樹脂の含水率は１５質量％以下である、前記［１３］に記載の方法。
［１５］前記凝集工程の前、前記凝集工程と同時、または前記凝集工程の後に、吸水性樹脂を架橋させる架橋工程を更に含む、前記［１１］～［１４］のいずれかに記載の方法。 In order to solve the above-mentioned problems, the present inventors have repeated detailed studies on agricultural water-retaining materials and have completed the present invention.
That is, the present invention includes the following preferred embodiments.
[1] An agricultural water-retaining material containing a water-absorbent resin.
The water-absorbent resin has 0.1 mol% or more and 50 mol% or less of ionic groups with respect to all the constituent units of the water-absorbent resin.
In the water-retaining material swelling test in which a 20% by mass sodium chloride aqueous solution is absorbed by the water-retaining material by applying ultrasonic waves, the rate of change of the volume-based 10 % particle diameter D10 of the water-retaining material before and after applying ultrasonic waves:
Rate of change of D 10 = (D 10 of water-retaining material after applying ultrasonic waves) / (D 10 of water-retaining material before applying ultrasonic waves)
Is 1 or less, water retention material.
[2] The water-retaining material according to the above [1], wherein the water-retaining material has a water content of 11% by mass or more, 50% by mass or less, and a bulk density of 0.20 g / mL or more and 1.25 g / mL or less.
[3] The water-retaining material according to the above [1] or [2], wherein the water-retaining material has a particle size that passes through a sieve having a nominal opening of 3000 μm and does not pass through a sieve having a nominal opening of 10 μm.
[4] The above-mentioned [1] to [3], wherein the maximum particle diameter on the smallest particle diameter side is 1 μm or more and 1000 μm or less in the state after applying ultrasonic waves in the water retention material swelling test. Water retention material.
[5] The above-mentioned [1] to [4], wherein the water-absorbent resin has one or more selected from the group consisting of a carboxyl group, a sulfonic acid group and an ammonium group as the ionic group. Water retention material.
[6] The water-absorbent resin comprises one or more selected from the group consisting of a vinyl alcohol-based polymer, an acrylic acid-based polymer, an acrylamide-based polymer, and a methacrylic acid-based polymer. ] The water-retaining material described in any of.
[7] The vinyl alcohol-based polymer according to the above [6], wherein the vinyl alcohol-based polymer contains one or more monomer constituent units selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, itaconic acid and derivatives thereof. Water retention material.
[8] The water-retaining material according to any one of [1] to [7], wherein the water-absorbent resin has a crosslinked structure.
[9] The water-retaining material according to any one of the above [1] to [8], which is used for raising seedlings.
[10] The water-retaining material according to any one of [1] to [9] above, wherein the water-absorbent resin has a water absorption time (T2) of 10 seconds or less.
[11] The process includes a coagulation step of agglomerating the water-absorbent resin existing as primary particles by contacting them in a swollen state, and a drying step of drying the agglomerated water-absorbent resin under a pressure of 0.2 MPa or less. The method for producing a water-retaining material according to any one of [1] to [10].
[12] The method according to the above [11], wherein in the aggregation step, the water content of the water-absorbent resin existing as primary particles is 15% by mass or less before the water-absorbent resin is swollen.
[13] The method for producing a water-retaining material according to any one of [1] to [10] above, which comprises an agglomeration step of agglomerating the water-absorbent resin existing as particles by contacting them in a swollen state.
[14] The method according to the above [13], wherein in the aggregation step, the water content of the water-absorbent resin existing as particles is 15% by mass or less before the water-absorbent resin is swollen.
[15] The method according to any one of [11] to [14], further comprising a cross-linking step of cross-linking the water-absorbent resin before, at the same time as, or after the coagulation step.
　本発明によれば、吸水速度に優れ、カルシウム塩の存在下であっても吸水量が十分高く、この吸水量が長期間にわたって低下しにくい、農業用保水材を提供することができる。 According to the present invention, it is possible to provide an agricultural water-retaining material having an excellent water absorption rate, a sufficiently high water absorption amount even in the presence of a calcium salt, and the water absorption amount does not easily decrease for a long period of time.
　以下、本発明の実施態様について説明するが、本発明は、本実施態様に限定されない。 Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the present embodiments.
［農業用保水材］
　本発明の農業用保水材（以下、単に「保水材」とも称する）は吸水性樹脂を含んでなる。本発明は、前記吸水性樹脂が、吸水性樹脂の全構成単位に対して０．１モル％以上、５０モル％以下のイオン性基を有することを特徴とする。また、本発明は、保水材膨潤試験における、超音波を付与する前後の保水材の体積基準１０％粒子径Ｄ１０の変化率：
Figure JPOXMLDOC01-appb-M000001

が１以下であることも特徴とする。ここで、体積基準１０％粒子径とは、これ以下の粒子の比率が体積基準で１０％である粒子径を意味する。 [Agricultural water retention material]
The agricultural water-retaining material of the present invention (hereinafter, also simply referred to as “water-retaining material”) contains a water-absorbent resin. The present invention is characterized in that the water-absorbent resin has an ionic group of 0.1 mol% or more and 50 mol% or less with respect to all the constituent units of the water-absorbent resin. Further, in the present invention, the rate of change of the volume-based 10% particle diameter D 10 of the water-retaining material before and after applying ultrasonic waves in the water-retaining material swelling test:
Figure JPOXMLDOC01-appb-M000001

Is also characterized by being 1 or less. Here, the volume-based 10% particle diameter means a particle diameter in which the ratio of particles smaller than this is 10% on a volume basis.
　１以下のＤ１０変化率は、例えば、保水材において、吸水性樹脂が凝集体として存在することにより達成できる。本発明の好ましい一実施態様では、保水材において、吸水性樹脂は、粒子の凝集体として、好ましくは一次粒子の凝集体として存在する。本明細書において一次粒子とは、凝集していない粒子を意味する。 A D 10 change rate of 1 or less can be achieved, for example, by the presence of the water-absorbent resin as an agglomerate in the water-retaining material. In a preferred embodiment of the present invention, in the water-retaining material, the water-absorbent resin exists as an agglomerate of particles, preferably as an agglomerate of primary particles. As used herein, the term primary particles mean particles that are not agglomerated.
　意外なことに、本発明者らは、保水材が上記特徴を有することにより、保水材が優れた吸水速度を示し、カルシウム塩の存在下であっても十分高い吸水量を示し、この吸水量が長期間にわたって低下しにくいことを見出した。
　その理由は明らかではないが、非限定的な作用機構として下記理由が推定される。本発明の保水材は吸水性樹脂を含むため、吸水すると膨潤する。その一方で、保水材における吸水性樹脂の凝集力が適度に弱いため、膨張に伴って保水材の崩壊が進行する。保水材が崩壊すると、水と接触する吸水性樹脂の表面積が拡大することから、吸水速度が速くなると推定される。また、吸水性樹脂が高すぎないイオン性基含有量、即ち吸水性樹脂の全構成単位に対して５０モル％以下のイオン性基含有量を有することにより、水と接している吸水性樹脂表面だけが急激に吸水するのではなく保水材内部の吸水性樹脂の空隙にも水がうまく入り込むことができ、その結果、保水材の崩壊により拡大した吸水性樹脂の表面積を水との接触に、より有効に利用できたため、吸水速度が著しく速くなると推定される。更に、吸水性樹脂が上述した特定のイオン性基含有量を有することにより、カルシウム塩とイオン性基によるイオン架橋が起こりにくいため、カルシウム塩の存在下であっても保水材の吸水量は十分高く、この吸水量は長期間にわたって低下しにくくなることが推定される。 Surprisingly, the present inventors show that the water-retaining material has the above-mentioned characteristics, so that the water-retaining material exhibits an excellent water absorption rate and a sufficiently high water absorption amount even in the presence of a calcium salt. Was found to be difficult to decrease over a long period of time.
The reason is not clear, but the following reasons are presumed as a non-limiting mechanism of action. Since the water-retaining material of the present invention contains a water-absorbent resin, it swells when it absorbs water. On the other hand, since the cohesive force of the water-absorbent resin in the water-retaining material is moderately weak, the water-retaining material disintegrates with expansion. When the water-retaining material collapses, the surface area of the water-absorbent resin that comes into contact with water increases, so it is presumed that the water absorption rate increases. Further, the water-absorbent resin surface is in contact with water because the water-absorbent resin has an ionic group content that is not too high, that is, an ionic group content of 50 mol% or less with respect to all the constituent units of the water-absorbent resin. Not only does it absorb water rapidly, but water can also enter the voids of the water-absorbent resin inside the water-retaining material well, and as a result, the surface area of the water-absorbent resin expanded due to the collapse of the water-retaining material is brought into contact with water. It is estimated that the water absorption rate will be significantly faster because it can be used more effectively. Furthermore, since the water-absorbent resin has the above-mentioned specific ionic group content, ionic cross-linking due to the calcium salt and the ionic group is unlikely to occur, so that the water absorption of the water-retaining material is sufficient even in the presence of the calcium salt. It is presumed that the amount of water absorption is high and the amount of water absorption is unlikely to decrease over a long period of time.
　保水材膨潤試験において、保水材に速やかに吸収される媒体（例えば水）ではなく、保水材があまり吸液しない媒体に保水材を分散させることにより、吸水初期の保水材の状態を再現することができる。本発明では、そのようなあまり吸液されない媒体として２０質量％塩化ナトリウム水溶液を用いている。その後、前記水溶液中の保水材に超音波を付与することにより、前記水溶液を保水材に吸液させることができ、これにより保水材の膨潤および崩壊の様子を再現することができる。
　保水材膨潤試験は、下記手順にて実施できる。まず、分散媒に試料である保水材を分散させ、例えばレーザー回折／散乱式粒子径分布測定装置を用いて、体積基準１０％粒子径Ｄ１０（超音波を付与する前の保水材のＤ１０に相当）を測定する。次いで、５分間の超音波照射により分散媒を保水材に吸液させることで保水材を膨潤させた後、保水材の体積基準１０％粒子径Ｄ１０（超音波を付与した後の保水材のＤ１０に相当）を測定する。測定条件を以下に示す。
　　装置名：堀場製作所製　レーザー回折／散乱式粒子径分布測定装置ＬＡ－９５０Ｖ２
　　測定方式：湿式（循環式）
　　試料屈折率：１．５１
　　分散媒：２０質量％塩化ナトリウム水溶液（屈折率：１．３６８）
　　循環速度：１０
　　撹拌速度：１０
　　超音波強さ：７
　　透過率：８０～９０％
　　循環液量：２８０ｍＬ
　続いて、下記式により、超音波を付与する前後の保水材の体積基準１０％粒子径Ｄ１０の変化率を求める。
Figure JPOXMLDOC01-appb-M000002

　本発明者らは、保水材を形成している吸水性樹脂粒子のうち、比較的小さい粒子径を有する粒子が、保水材全体の吸水速度を決める因子の１つであることを見出した。そのため、本発明では、優れた吸水速度をもたらすための構成要件に、Ｄ１０を用いている。 In the water-retaining material swelling test, the state of the water-retaining material at the initial stage of water absorption is reproduced by dispersing the water-retaining material in a medium in which the water-retaining material does not absorb much liquid, instead of a medium (for example, water) that is quickly absorbed by the water-retaining material. Can be done. In the present invention, a 20% by mass sodium chloride aqueous solution is used as such a medium that is not so absorbed. After that, by applying ultrasonic waves to the water-retaining material in the aqueous solution, the water-retaining material can be made to absorb the liquid, whereby the state of swelling and disintegration of the water-retaining material can be reproduced.
The water retention material swelling test can be carried out by the following procedure. First, the water-retaining material as a sample is dispersed in a dispersion medium, and for example, using a laser diffraction / scattering type particle size distribution measuring device, a volume-based 10% particle size D 10 (D 10 of the water-retaining material before applying ultrasonic waves). Equivalent to). Next, the water-retaining material is swelled by absorbing the dispersion medium into the water-retaining material by ultrasonic irradiation for 5 minutes, and then the volume-based 10% particle diameter D 10 of the water-retaining material (of the water-retaining material after applying ultrasonic waves). (Equivalent to D10 ) is measured. The measurement conditions are shown below.
Device name: Laser diffraction / scattering particle size distribution measuring device LA-950V2 manufactured by HORIBA, Ltd.
Measurement method: Wet (circulation type)
Sample refractive index: 1.51
Dispersion medium: 20% by mass sodium chloride aqueous solution (refractive index: 1.368)
Circulation speed: 10
Stirring speed: 10
Ultrasonic intensity: 7
Transmittance: 80-90%
Circulating fluid volume: 280 mL
Subsequently, the rate of change of the volume-based 10% particle diameter D 10 of the water-retaining material before and after applying ultrasonic waves is obtained by the following formula.
Figure JPOXMLDOC01-appb-M000002

The present inventors have found that among the water-absorbent resin particles forming the water-retaining material, particles having a relatively small particle size are one of the factors that determine the water absorption rate of the entire water-retaining material. Therefore, in the present invention, D 10 is used as a constituent requirement for achieving an excellent water absorption rate.
　保水材膨潤試験における、超音波を付与する前後の保水材の体積基準１０％粒子径Ｄ１０の変化率は、１以下である。Ｄ１０の変化率が１より大きいと、所望の吸水速度を得ることは困難である。Ｄ１０の変化率は、好ましくは０．９５以下、より好ましくは０．９４以下、より好ましくは０．９３以下、より好ましくは０．９２以下、より好ましくは０．９１以下、更に好ましくは０．９０以下、更により好ましくは０．８５以下、特に好ましくは０．８０以下、特により好ましくは０．７５以下である。Ｄ１０の変化率が前記上限値以下であると、吸水時に保水材の膨張と崩壊とがバランス良く進行し、より好ましい吸水速度を得やすい。
　Ｄ１０の変化率の下限値は特に限定されない。Ｄ１０の変化率は、例えば０．３０以上である。Ｄ１０の変化率が前記下限値以上であると、使用前に保水材が崩壊して粉塵発生を招きやすくなることを抑制しやすい。
　Ｄ１０の変化率は、例えば、保水材において吸水性樹脂を凝集体として存在させること、吸水性樹脂を凝集させる工程におけるバインダー量、圧力、温度若しくは可塑剤量の調整、凝集した吸水性樹脂を乾燥する工程における圧力、温度若しくは可塑剤量の調整、または凝集前の吸水性樹脂粒子の粒子径若しくは形状の調整により、前記下限値以上、前記上限値以下に調整できる。 In the water-retaining material swelling test, the rate of change of the volume-based 10% particle diameter D 10 of the water-retaining material before and after applying ultrasonic waves is 1 or less. If the rate of change of D 10 is greater than 1, it is difficult to obtain the desired water absorption rate. The rate of change of D 10 is preferably 0.95 or less, more preferably 0.94 or less, more preferably 0.93 or less, more preferably 0.92 or less, more preferably 0.91 or less, still more preferably 0. It is .90 or less, more preferably 0.85 or less, particularly preferably 0.80 or less, and particularly more preferably 0.75 or less. When the rate of change of D 10 is not more than the upper limit value, the expansion and disintegration of the water-retaining material proceed in a well-balanced manner at the time of water absorption, and it is easy to obtain a more preferable water absorption rate.
The lower limit of the rate of change of D 10 is not particularly limited. The rate of change of D 10 is, for example, 0.30 or more. When the rate of change of D 10 is at least the above lower limit value, it is easy to prevent the water-retaining material from collapsing before use and easily causing dust generation.
The rate of change of D 10 is, for example, the presence of the water-absorbent resin as an aggregate in the water-retaining material, the adjustment of the binder amount, pressure, temperature or the amount of the plasticizer in the step of aggregating the water-absorbent resin, and the aggregated water-absorbent resin. By adjusting the pressure, temperature or amount of plasticizer in the drying step, or by adjusting the particle size or shape of the water-absorbent resin particles before aggregation, it can be adjusted to the lower limit value or more and the upper limit value or less.
　保水材膨潤試験において超音波を付与した後の状態における、最も小粒子径側の極大粒子径は、好ましくは１μｍ以上、より好ましくは５μｍ以上、更に好ましくは１０μｍ以上、特に好ましくは３０μｍ以上であり、好ましくは１０００μｍ以下、より好ましくは５００μｍ以下、更に好ましくは２００μｍ以下、特に好ましくは１００μｍ以下である。前記極大粒子径は、０．０１１μｍ、０．０１３μｍ、０．０１５μｍ、０．０１７μｍ、０．０２μｍ、０．０２３μｍ、０．０２６μｍ、０．０３μｍ、０．０３４μｍ、０．０３９μｍ、０．０４４μｍ、０．０５１μｍ、０．０５８μｍ、０．０６７μｍ、０．０７６μｍ、０．０８７μｍ、０．１μｍ、０．１１５μｍ、０．１３１μｍ、０．１５μｍ、０．１７２μｍ、０．１９７μｍ、０．２２６μｍ、０．２５９μｍ、０．２９６μｍ、０．３３９μｍ、０．３８９μｍ、０．４４５μｍ、０．５１μｍ、０．５８４μｍ、０．６６９μｍ、０．７６６μｍ、０．８７７μｍ、１．００５μｍ、１．１５１μｍ、１．３１８μｍ、１．５１μｍ、１．７２９μｍ、１．９８１μｍ、２．２６９μｍ、２．５９９μｍ、２．９７６μｍ、３．４０９μｍ、３．９０５μｍ、４．４７２μｍ、５．１２２μｍ、５．８６７μｍ、６．７２μｍ、７．６９７μｍ、８．８１６μｍ、１０．０９７μｍ、１１．５６５μｍ、１３．２４６μｍ、１５．１７２μｍ、１７．３７７μｍ、１９．９０４μｍ、２２．７９７μｍ、２６．１１１μｍ、２９．９０７μｍ、３４．２５５μｍ、３９．２３４μｍ、４４．９３８μｍ、５１．４７１μｍ、５８．９５３μｍ、６７．５２３μｍ、７７．３４μｍ、８８．５８３μｍ、１０１．４６μｍ、１１６．２１μｍ、１３３．１０３μｍ、１５２．４５３μｍ、１７４．６１６μｍ、２００μｍ、２２９．０７５μｍ、２６２．３７６μｍ、３００．５１８μｍ、３４４．２０６μｍ、３９４．２４４μｍ、４５１．５５６μｍ、５１７．２μｍ、５９２．３８７μｍ、６７８．５０４μｍ、７７７．１４１μｍ、８９０．１１６μｍ、１０１９．５１５μｍ、１１６７．７２５μｍ、１３３７．４８１μｍ、１５３１．９１４μｍ、１７５４．６１３μｍ、２００９．６８７μｍ、２３０１．８４１μｍ、２６３６．４６７μｍ、または３０００μｍでの頻度により求めた値である。前記極大粒子径が前記下限値以上であり、前記上限値以下であると、より好ましい吸水速度を得やすい。前記極大粒子径は、例えば、凝集前の吸水性樹脂粒子の粒子径を調整することにより前記下限値以上、前記上限値以下に調整できる。 In the water retention material swelling test, the maximum particle size on the smallest particle size side in the state after applying ultrasonic waves is preferably 1 μm or more, more preferably 5 μm or more, still more preferably 10 μm or more, and particularly preferably 30 μm or more. It is preferably 1000 μm or less, more preferably 500 μm or less, still more preferably 200 μm or less, and particularly preferably 100 μm or less. The maximum particle size is 0.011 μm, 0.013 μm, 0.015 μm, 0.017 μm, 0.02 μm, 0.023 μm, 0.026 μm, 0.03 μm, 0.034 μm, 0.039 μm, 0.044 μm, 0.051 μm, 0.058 μm, 0.067 μm, 0.076 μm, 0.087 μm, 0.1 μm, 0.115 μm, 0.131 μm, 0.15 μm, 0.172 μm, 0.197 μm, 0.226 μm, 0. 259 μm, 0.296 μm, 0.339 μm, 0.389 μm, 0.445 μm, 0.51 μm, 0.584 μm, 0.669 μm, 0.766 μm, 0.877 μm, 1.005 μm, 1.151 μm, 1.318 μm, 1.51 μm, 1.729 μm, 1.981 μm, 2.269 μm, 2.599 μm, 2.976 μm, 3.409 μm, 3.905 μm, 4.472 μm, 5.122 μm, 5.867 μm, 6.72 μm, 7. 697 μm, 8.816 μm, 10.097 μm, 11.565 μm, 13.246 μm, 15.172 μm, 17.377 μm, 19.904 μm, 22.779 μm, 26.111 μm, 29.907 μm, 34.255 μm, 39.234 μm, 44.938 μm, 51.471 μm, 58.953 μm, 67.523 μm, 77.34 μm, 88.583 μm, 101.46 μm, 116.21 μm, 133.103 μm, 152.453 μm, 174.616 μm, 200 μm, 229.075 μm, 262.376 μm, 300.518 μm, 344.206 μm, 394.244 μm, 451.556 μm, 517.2 μm, 592.387 μm, 678.504 μm, 777.141 μm, 890.116 μm, 1019.515 μm, 1167.725 μm, 1337. It is a value obtained by the frequency of 481 μm, 1531.914 μm, 1754.613 μm, 2009.687 μm, 2301.841 μm, 2636.467 μm, or 3000 μm. When the maximum particle size is at least the lower limit value and at least the upper limit value, a more preferable water absorption rate can be easily obtained. The maximum particle size can be adjusted to be equal to or higher than the lower limit value and lower than the upper limit value by adjusting the particle size of the water-absorbent resin particles before aggregation, for example.
　本発明の好ましい一実施態様において、保水材に含まれる吸水性樹脂は、一次粒子の凝集体として存在している。保水材に含まれる吸水性樹脂の一次粒子の平均粒子径は、好ましくは１μｍ以上、より好ましくは１０μｍ以上、更に好ましくは３０μｍ以上、特に好ましくは５０μｍ以上であり、好ましくは２０００μｍ以下、より好ましくは１０００μｍ以下、更に好ましくは７００μｍ以下、特に好ましくは１５０μｍ以下である。一次粒子の平均粒子径が前記下限値以上であり、前記上限値以下であると、より好ましい吸水速度を得やすい。また、一次粒子の平均粒子径が前記下限値以上であると、保水材の製造時に粉塵発生を抑制しやすい。一次粒子の平均粒子径は、例えば、電子顕微鏡または特定の目開きの篩を用いて測定できる。 In a preferred embodiment of the present invention, the water-absorbent resin contained in the water-retaining material exists as an aggregate of primary particles. The average particle size of the primary particles of the water-absorbent resin contained in the water-retaining material is preferably 1 μm or more, more preferably 10 μm or more, still more preferably 30 μm or more, particularly preferably 50 μm or more, preferably 2000 μm or less, more preferably 2000 μm or less. It is 1000 μm or less, more preferably 700 μm or less, and particularly preferably 150 μm or less. When the average particle diameter of the primary particles is at least the lower limit value and at least the upper limit value, a more preferable water absorption rate can be easily obtained. Further, when the average particle diameter of the primary particles is at least the above lower limit value, it is easy to suppress the generation of dust during the production of the water retention material. The average particle size of the primary particles can be measured, for example, using an electron microscope or a sieve with a specific opening.
　保水材に含まれる吸水性樹脂は、吸水性樹脂の全構成単位に対して０．１モル％以上、好ましくは０．５モル％以上、より好ましくは１．０モル％以上、更に好ましくは２．０モル％以上、特に好ましくは３．０モル％以上のイオン性基を有する。ここで、「構成単位」とは、吸水性樹脂を構成する繰り返し単位のことを意味する。イオン性基含有量が前記下限値以上であると、吸水性樹脂は、より向上した吸水量または吸水速度を有しやすい。吸水性樹脂は、吸水性樹脂の全構成単位に対して５０モル％以下、好ましくは４０モル％以下、より好ましくは３０モル％以下、更に好ましくは２０モル％以下、特に好ましくは１０モル％以下のイオン性基を有する。イオン性基含有量が前記上限値以下であると、吸水性樹脂は、土壌中に含まれる二価イオン（例えばカルシウムイオン）の存在下でも優れた吸液量または吸液速度を維持しやすく、この吸液量または吸液速度は、長期間にわたって低下しにくく、紫外線による吸水性樹脂の分解が起こりにくい。
　吸水性樹脂中のイオン性基の含有量、および後述する各種構成単位の含有量は、例えば、固体１３Ｃ－ＮＭＲ（核磁気共鳴分光法）、ＦＴＩＲ（フーリエ変換赤外分光法）または酸塩基滴定等によって測定できる。
　また、吸水性樹脂中のイオン性基の含有量、および後述する各種構成単位の含有量は、例えば、イオン性基をもたらすモノマーおよび各種構成単位を形成するモノマーの配合比、反応時のそれらの消費率若しくは反応性比、反応温度、または溶媒等を調整することによって調整できる。 The water-absorbent resin contained in the water-retaining material is 0.1 mol% or more, preferably 0.5 mol% or more, more preferably 1.0 mol% or more, still more preferably 2 with respect to all the constituent units of the water-absorbent resin. It has an ionic group of 0.0 mol% or more, particularly preferably 3.0 mol% or more. Here, the "constituent unit" means a repeating unit that constitutes the water-absorbent resin. When the ionic group content is at least the above lower limit value, the water-absorbent resin tends to have a higher water absorption amount or water absorption rate. The water-absorbent resin is 50 mol% or less, preferably 40 mol% or less, more preferably 30 mol% or less, still more preferably 20 mol% or less, and particularly preferably 10 mol% or less, based on all the constituent units of the water-absorbent resin. Has an ionic group of. When the ionic group content is not more than the above upper limit value, the water-absorbent resin tends to maintain an excellent liquid absorption amount or liquid absorption rate even in the presence of divalent ions (for example, calcium ions) contained in the soil. This liquid absorption amount or liquid absorption rate is unlikely to decrease over a long period of time, and decomposition of the water-absorbent resin by ultraviolet rays is unlikely to occur.
The content of ionic groups in the water-absorbent resin and the content of various structural units described later are, for example, solid 13 C-NMR (nuclear magnetic resonance spectroscopy), FTIR (Fourier transform infrared spectroscopy) or acid base. It can be measured by titration or the like.
Further, the content of the ionic group in the water-absorbent resin and the content of various structural units described later are, for example, the compounding ratio of the monomer that brings about the ionic group and the monomer that forms various structural units, and those at the time of reaction. It can be adjusted by adjusting the consumption rate or reactivity ratio, reaction temperature, solvent and the like.
　イオン性基は、イオン性基またはその誘導体として存在してよい。イオン性基は、好ましくはカルボキシル基、スルホン酸基、アンモニウム基またはその塩であり、より好ましくはカルボキシル基、アンモニウム基またはその塩であり、特に好ましくは、カルボキシル基またはその塩である。従って、本発明の好ましい一実施態様では、吸水性樹脂は、イオン性基として、カルボキシル基、スルホン酸基およびアンモニウム基からなる群から選択される１以上を有する。
　なお、吸水性樹脂に含まれるイオン性基の一部または全部がその誘導体（例えば塩）の形態をとっている場合、上述のイオン性基含有量は、イオン性基およびその誘導体の含有量またはイオン性基の誘導体の含有量である。 The ionic group may exist as an ionic group or a derivative thereof. The ionic group is preferably a carboxyl group, a sulfonic acid group, an ammonium group or a salt thereof, more preferably a carboxyl group, an ammonium group or a salt thereof, and particularly preferably a carboxyl group or a salt thereof. Therefore, in a preferred embodiment of the present invention, the water-absorbent resin has one or more selected from the group consisting of a carboxyl group, a sulfonic acid group and an ammonium group as an ionic group.
When a part or all of the ionic groups contained in the water-absorbent resin are in the form of a derivative (for example, a salt) thereof, the above-mentioned ionic group content is the content of the ionic group and its derivative or The content of the derivative of the ionic group.
　本発明の好ましい一実施態様において、前記保水材は、含水率が１１質量％以上、５０質量％以下、嵩密度が０．２０ｇ／ｍＬ以上、１．２５ｇ／ｍＬ以下であることが好ましい。 In a preferred embodiment of the present invention, the water retention material preferably has a water content of 11% by mass or more and 50% by mass or less and a bulk density of 0.20 g / mL or more and 1.25 g / mL or less.
　本発明の保水材の含水率は、好ましくは１１質量％以上、より好ましくは１５質量％以上、より好ましくは１６質量％以上、更に好ましくは２０質量％以上である。保水材の含水率が前記下限値以上であると、保水材中の吸水性樹脂のポリマー鎖の十分な運動性が確保されやすく、ポリマー鎖が広がりやすく、ポリマー鎖の間に水が入り込みやすくなるため、所望の吸水速度を得やすい。本発明の保水材の含水率は、好ましくは５０質量％以下、より好ましくは４０質量％以下、より好ましくは３３質量％以下、更に好ましくは３０質量％以下である。含水率が前記上限値以下であると、保水材に含まれる吸水性樹脂同士が膠着しにくく、塊状になりにくく、水との十分な接触面積が確保されやすいため、所望の吸水速度を得やすい。保水材の含水率は、例えば保水材に含まれる吸水性樹脂が有するイオン性基の種類および含有量；保水材に含まれる吸水性樹脂の製造時の乾燥条件；保水材の保管条件等を適宜調整することによって前記範囲内に調整することができる。含水率は、ハロゲン水分計を用いて測定することができ、例えば後述の実施例に記載の方法によって測定することができる。 The water content of the water-retaining material of the present invention is preferably 11% by mass or more, more preferably 15% by mass or more, more preferably 16% by mass or more, still more preferably 20% by mass or more. When the water content of the water-retaining material is at least the above lower limit, sufficient mobility of the polymer chains of the water-absorbent resin in the water-retaining material is likely to be ensured, the polymer chains are likely to spread, and water is likely to enter between the polymer chains. Therefore, it is easy to obtain a desired water absorption rate. The water content of the water-retaining material of the present invention is preferably 50% by mass or less, more preferably 40% by mass or less, more preferably 33% by mass or less, still more preferably 30% by mass or less. When the water content is not more than the above upper limit, the water-absorbent resins contained in the water-retaining material are less likely to stick to each other, are less likely to form a lump, and are likely to secure a sufficient contact area with water, so that a desired water absorption rate can be easily obtained. .. The water content of the water-retaining material is, for example, the type and content of the ionic group of the water-absorbent resin contained in the water-retaining material; the drying conditions at the time of manufacturing the water-absorbent resin contained in the water-retaining material; the storage conditions of the water-retaining material, etc. as appropriate. By adjusting, it can be adjusted within the above range. The water content can be measured using a halogen moisture meter, for example, by the method described in Examples described later.
　本発明の保水材の嵩密度は、好ましくは０．２０ｇ／ｍＬ以上、より好ましくは０．３０ｇ／ｍＬ以上、更に好ましくは０．３５ｇ／ｍＬ以上である。保水材の嵩密度が前記下限値以上であると、保水材が水に浮きにくくなり、水との十分な接触面積を確保しやすいため、所望の吸水速度を得やすい。また、保水材の嵩密度が前記下限値以上であると、粉塵発生が起きにくいため取り扱い性に優れる傾向にある。本発明の保水材の嵩密度は、好ましくは１．２５ｇ／ｍＬ以下、より好ましくは０．９５ｇ／ｍＬ以下、更に好ましくは０．７０ｇ／ｍＬ以下である。保水材の嵩密度が前記上限値以下であると、保水材が密に充填されにくく、十分な通水性を確保しやすいため、所望の吸水速度を得やすい。また、保水材の嵩密度が前記上限値以下であると、水と混合した際の、ままこの発生が起こりにくい。保水材の嵩密度は、例えば保水材に含まれる吸水性樹脂の粒子径および形状；保水材の含水率；後述する保水材の製造方法における凝集工程の条件（膨潤溶媒の種類および量、添加剤の種類および量、圧力等）等を適宜調整することによって、前記範囲内に調整することができる。嵩密度は、例えば後述の実施例に記載の方法によって測定することができる。 The bulk density of the water-retaining material of the present invention is preferably 0.20 g / mL or more, more preferably 0.30 g / mL or more, and further preferably 0.35 g / mL or more. When the bulk density of the water-retaining material is at least the above lower limit value, the water-retaining material is less likely to float on water, and it is easy to secure a sufficient contact area with water, so that a desired water absorption rate can be easily obtained. Further, when the bulk density of the water-retaining material is at least the above lower limit value, dust is less likely to be generated, so that the handleability tends to be excellent. The bulk density of the water-retaining material of the present invention is preferably 1.25 g / mL or less, more preferably 0.95 g / mL or less, still more preferably 0.70 g / mL or less. When the bulk density of the water-retaining material is not more than the upper limit, it is difficult for the water-retaining material to be densely filled, and it is easy to secure sufficient water permeability, so that a desired water absorption rate can be easily obtained. Further, when the bulk density of the water-retaining material is not more than the upper limit value, this occurrence is unlikely to occur as it is when mixed with water. The bulk density of the water-retaining material is, for example, the particle size and shape of the water-absorbent resin contained in the water-retaining material; the water content of the water-retaining material; It can be adjusted within the above range by appropriately adjusting the type and amount of the above, pressure, etc.). The bulk density can be measured, for example, by the method described in Examples described later.
　更には、本発明者らの検討によると、保水材において、保水材に含まれる吸水性樹脂が、吸水性樹脂の全構成単位に対して０．１モル％以上、５０モル％以下のイオン性基を有し、当該農業用保水材の含水率が好ましくは１１質量％以上、好ましくは５０質量％以下、嵩密度が好ましくは０．２０ｇ／ｍＬ以上、好ましくは１．２５ｇ／ｍＬ以下であると、保水材がより優れた吸水速度を示すことが分かった。その理由は明らかではないが、吸水性樹脂が高すぎないイオン性基含有量、即ち吸水性樹脂の全構成単位に対して５０モル％以下のイオン性基含有量を有することにより、吸水した場合でも保水材の弾性率が高いため、保水材がゲルブロッキングを生じにくく、通水性が担保されることによって吸水速度が速くなるものと考えられる。更に、適度な含水率を有することにより、保水材中の吸水性樹脂のポリマー鎖の運動性が向上するため、吸水性樹脂間の通水性の低下が抑制され、吸水速度が速くなると推定される。また、適度な嵩密度を有することによって、保水材における樹脂間の通水性が担保され、保水材が効率よく吸水できるためだと考えられる。 Furthermore, according to the study by the present inventors, in the water-retaining material, the water-absorbent resin contained in the water-retaining material has an ionicity of 0.1 mol% or more and 50 mol% or less with respect to all the constituent units of the water-absorbent resin. The water content of the agricultural water-retaining material having a group is preferably 11% by mass or more, preferably 50% by mass or less, and the bulk density is preferably 0.20 g / mL or more, preferably 1.25 g / mL or less. It was found that the water-retaining material showed a better water absorption rate. The reason is not clear, but when the water-absorbent resin absorbs water by having an ionic group content that is not too high, that is, an ionic group content of 50 mol% or less with respect to all the constituent units of the water-absorbent resin. However, since the elastic modulus of the water-retaining material is high, it is considered that the water-retaining material is less likely to cause gel blocking, and the water absorption rate is increased by ensuring the water permeability. Furthermore, it is presumed that having an appropriate water content improves the mobility of the polymer chains of the water-absorbent resin in the water-retaining material, thereby suppressing the decrease in water permeability between the water-absorbent resins and increasing the water absorption rate. .. Further, it is considered that the water-retaining material can efficiently absorb water by ensuring the water permeability between the resins in the water-retaining material by having an appropriate bulk density.
　本発明の一実施態様において、農業用保水材として使用する前、即ち保管時（例えば保管容器中）および後述する培地等と組み合わせて使用する直前の保水材が、上記含水率および嵩密度を満たすことが好ましい。 In one embodiment of the present invention, the water-retaining material before being used as an agricultural water-retaining material, that is, at the time of storage (for example, in a storage container) and immediately before being used in combination with a medium or the like described later, satisfies the above water content and bulk density. Is preferable.
　保水材は、好ましくは公称目開き３０００μｍの篩を通過し、より好ましくは公称目開き２０００μｍの篩を通過し、更に好ましくは公称目開き１５００μｍの篩を通過し、特に好ましくは公称目開き１０００μｍの篩を通過する粒度を有し、好ましくは公称目開き１０μｍの篩を通過しない、より好ましくは公称目開き５０μｍの篩を通過しない、更に好ましくは公称目開き１００μｍの篩を通過しない、特に好ましくは公称目開き２００μｍの篩を通過しない粒度を有する。好ましい一実施態様において、保水材は、公称目開き３０００μｍの篩を通過し、かつ公称目開き１０μｍの篩を通過しない粒度を有する。保水材がこのような粒度を有すると、より優れた取扱い性およびより優れた吸水速度を得やすい。 The water retention material preferably passes through a sieve with a nominal opening of 3000 μm, more preferably passes through a sieve with a nominal opening of 2000 μm, more preferably passes through a sieve with a nominal opening of 1500 μm, and particularly preferably passes through a sieve with a nominal opening of 1000 μm. It has a particle size that passes through a sieve, preferably does not pass through a sieve with a nominal opening of 10 μm, more preferably does not pass through a sieve with a nominal opening of 50 μm, and more preferably does not pass through a sieve with a nominal opening of 100 μm, particularly preferably. It has a particle size that does not pass through a sieve with a nominal opening of 200 μm. In a preferred embodiment, the water retention material has a particle size that passes through a sieve with a nominal opening of 3000 μm and does not pass through a sieve with a nominal opening of 10 μm. When the water-retaining material has such a particle size, it is easy to obtain better handleability and better water absorption rate.
　吸水性樹脂は、潅水による吸水性樹脂の溶出を抑制する観点から、架橋構造を有することが好ましい。吸水性樹脂が架橋構造を有する場合、吸水性樹脂は吸水時にゲル状態となる。架橋構造の形態に特に制限はなく、その例としては、エステル結合、エーテル結合、アセタール結合、および炭素－炭素結合等による架橋構造を挙げることができる。 The water-absorbent resin preferably has a crosslinked structure from the viewpoint of suppressing elution of the water-absorbent resin due to irrigation. When the water-absorbent resin has a crosslinked structure, the water-absorbent resin becomes a gel state at the time of water absorption. The form of the crosslinked structure is not particularly limited, and examples thereof include a crosslinked structure formed by an ester bond, an ether bond, an acetal bond, a carbon-carbon bond, and the like.
　保水材に含まれる吸水性樹脂は特に限定されない。製造容易性および保水性の観点からは、吸水性樹脂は、好ましくはビニルアルコール系重合体、アクリル酸系重合体、アクリルアミド系重合体およびメタクリル酸系重合体からなる群から選択される１以上を含み、より好ましくはビニルアルコール系重合体およびアクリルアミド系重合体からなる群から選択される１以上を含み、更に好ましくはビニルアルコール系重合体またはアクリルアミド系重合体からなる。
　本明細書において、ビニルアルコール系重合体とは、ビニルアルコールに由来する構成単位（以下、「ビニルアルコール単位」と称する）の含有量が全構成単位の中で最も多い重合体を意味する。このことは、アクリル酸系重合体、アクリルアミド系重合体およびメタクリル酸系重合体についても同様に当てはまる。 The water-absorbent resin contained in the water-retaining material is not particularly limited. From the viewpoint of ease of production and water retention, the water-absorbent resin is preferably one or more selected from the group consisting of vinyl alcohol-based polymers, acrylic acid-based polymers, acrylamide-based polymers and methacrylic acid-based polymers. It contains, more preferably one or more selected from the group consisting of vinyl alcohol-based polymers and acrylamide-based polymers, and more preferably composed of vinyl alcohol-based polymers or acrylamide-based polymers.
In the present specification, the vinyl alcohol-based polymer means a polymer having the highest content of a structural unit derived from vinyl alcohol (hereinafter referred to as “vinyl alcohol unit”) among all the structural units. This also applies to acrylic acid-based polymers, acrylamide-based polymers and methacrylic acid-based polymers.
＜ビニルアルコール系重合体＞
　ビニルアルコール系重合体〔以下、ビニルアルコール系重合体（Ａ）と称することがある〕の例としては、ポリビニルアルコール、エチレン－ビニルアルコール共重合体、およびそれらのビニルアルコール単位がアセタール化剤によりアセタール化されたものを挙げることができる。前記吸水性樹脂におけるビニルアルコール系重合体（Ａ）の含有量は、好ましくは７０質量％以上、より好ましくは８０質量％以上、更に好ましくは９０質量％以上、特に好ましくは９５質量％以上であり、１００質量％であってもよい。 <Vinyl alcohol polymer>
As an example of the vinyl alcohol-based polymer [hereinafter, may be referred to as vinyl alcohol-based polymer (A)], polyvinyl alcohol, an ethylene-vinyl alcohol copolymer, and their vinyl alcohol units are acetalized by an acetal agent. It can be mentioned as a polymer. The content of the vinyl alcohol polymer (A) in the water-absorbent resin is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 95% by mass or more. , 100% by mass.
　本発明における吸水性樹脂はイオン性基を有する。従って、本発明の好ましい一実施態様では、ビニルアルコール系重合体（Ａ）は、ビニルアルコール単位とイオン性基またはその誘導体を有するモノマー構成単位との共重合体からなる。ビニルアルコール系重合体（Ａ）が有するイオン性基またはその誘導体は、好ましくはカルボキシル基、スルホン酸基、アンモニウム基、またはそれらの塩であり、より好ましくはカルボキシル基、アンモニウム基、またはそれらの塩であり、特に好ましくはカルボキシル基またはそれらの塩である。ビニルアルコール系重合体（Ａ）における前記共重合体の含有量は、好ましくは７０質量％以上、より好ましくは８０質量％以上、更に好ましくは９０質量％以上、更により好ましくは９５質量％以上であり、特に好ましくは１００質量％である。 The water-absorbent resin in the present invention has an ionic group. Therefore, in a preferred embodiment of the present invention, the vinyl alcohol-based polymer (A) comprises a copolymer of a vinyl alcohol unit and a monomer constituent unit having an ionic group or a derivative thereof. The ionic group or a derivative thereof contained in the vinyl alcoholic polymer (A) is preferably a carboxyl group, a sulfonic acid group, an ammonium group, or a salt thereof, and more preferably a carboxyl group, an ammonium group, or a salt thereof. And particularly preferably a carboxyl group or a salt thereof. The content of the copolymer in the vinyl alcohol-based polymer (A) is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, still more preferably 95% by mass or more. Yes, especially preferably 100% by mass.
　ビニルアルコール系重合体（Ａ）がイオン性基としてカルボキシル基、スルホン酸基およびアンモニウム基を有する場合、ビニルアルコール系重合体（Ａ）としては、例えば、（ｉ－１）カルボキシル基、スルホン酸基およびアンモニウム基を有するモノマーおよび該モノマーの誘導体からなる群から選択される１種以上とビニルエステルとの共重合体のケン化物；等を挙げることができる。 When the vinyl alcohol-based polymer (A) has a carboxyl group, a sulfonic acid group and an ammonium group as ionic groups, the vinyl alcohol-based polymer (A) may be, for example, (i-1) a carboxyl group or a sulfonic acid group. And a saponified product of a polymer of one or more selected from the group consisting of a monomer having an ammonium group and a derivative of the monomer and a vinyl ester; and the like.
　上記（ｉ－１）において、カルボキシル基を有するモノマーとしては特に制限はなく、その例としては、アクリル酸、メタクリル酸、マレイン酸、およびイタコン酸等を挙げることができる。また、上記カルボキシル基を有するモノマーの誘導体の例としては、該モノマーの無水物、エステル化物、および中和物等を挙げることができ、例えば、アクリル酸メチル、メタクリル酸メチル、マレイン酸モノメチル、イタコン酸ジメチル、および無水マレイン酸等を用いることができる。従って、本発明の一実施態様では、ビニルアルコール系重合体（Ａ）は、アクリル酸、メタクリル酸、マレイン酸、イタコン酸およびそれらの誘導体からなる群から選択される１種以上のモノマー構成単位を含む。 In the above (i-1), the monomer having a carboxyl group is not particularly limited, and examples thereof include acrylic acid, methacrylic acid, maleic acid, and itaconic acid. Examples of the derivative of the monomer having a carboxyl group include anhydrate, an esterified product, and a neutralized product of the monomer, and examples thereof include methyl acrylate, methyl methacrylate, monomethyl maleate, and itaconic acid. Dimethyl acid, maleic anhydride and the like can be used. Therefore, in one embodiment of the present invention, the vinyl alcohol-based polymer (A) contains one or more monomer constituent units selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, itaconic acid and derivatives thereof. include.
　上記（ｉ－１）において、スルホン酸基を有するモノマーとしては特に制限はなく、その例としては、ビニルスルホン酸、２－アクリルアミド－２－メチルプロパンスルホン酸、およびｐ－スチレンスルホン酸等を挙げることができる。また、上記スルホン酸基を有するモノマーの誘導体の例としては、該モノマーのエステル化物、および中和物等を挙げることができ、例えば、ビニルスルホン酸ナトリウム、２－アクリルアミド－２－メチルプロパンスルホン酸ナトリウム、およびｐ－スチレンスルホン酸ナトリウム等を用いることができる。 In the above (i-1), the monomer having a sulfonic acid group is not particularly limited, and examples thereof include vinyl sulfonic acid, 2-acrylamide-2-methylpropanesulfonic acid, p-styrenesulfonic acid and the like. be able to. Examples of the derivative of the monomer having a sulfonic acid group include an esterified product of the monomer and a neutralized product, and examples thereof include sodium vinyl sulfonate and 2-acrylamide-2-methylpropane sulfonic acid. Sodium, sodium p-styrene sulfonate and the like can be used.
　上記（ｉ－１）において、アンモニウム基を有するモノマーとしては特に制限はなく、その例としては、ジアリルジメチルアンモニウムクロライド、ビニルトリメチルアンモニウムクロライド、アリルトリメチルアンモニウムクロライド、ｐ－ビニルベンジルトリメチルアンモニウムクロライド、および３－（メタクリルアミド）プロピルトリメチルアンモニウムクロライド等を挙げることができる。また、上記アンモニウム基を有するモノマーの誘導体の例としては、該モノマーのアミン等を挙げることができ、例えば、ジアリルメチルアミン、ビニルアミン、アリルアミン、ｐ－ビニルベンジルジメチルアミン、および３－（メタクリルアミド）プロピルジメチルアミン等を用いることができる。 In the above (i-1), the monomer having an ammonium group is not particularly limited, and examples thereof include diallyldimethylammonium chloride, vinyltrimethylammonium chloride, allyltrimethylammonium chloride, p-vinylbenzyltrimethylammonium chloride, and 3. -(Methalamide) propyltrimethylammonium chloride and the like can be mentioned. Examples of the derivative of the monomer having an ammonium group include amines of the monomers, and examples thereof include diallylmethylamine, vinylamine, allylamine, p-vinylbenzyldimethylamine, and 3- (methacrylamide). Propyldimethylamine and the like can be used.
　上記（ｉ－１）において、ビニルエステルとしては特に制限はなく、その例としては、酢酸ビニル、プロピオン酸ビニル、酪酸ビニル、吉草酸ビニル、ステアリン酸ビニル、安息香酸ビニル、トリフルオロ酢酸ビニル、およびピバル酸ビニル等を挙げることができ、酢酸ビニルが好ましい。 In the above (i-1), the vinyl ester is not particularly limited, and examples thereof include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, vinyl stearate, vinyl benzoate, vinyl trifluoroacetate, and vinyl acetate. Vinyl acetate and the like can be mentioned, and vinyl acetate is preferable.
　上記（ｉ－１）のケン化物を製造する方法に特に制限はない。上記（ｉ－１）のケン化物は、例えば、カルボキシル基を有するモノマーおよび該モノマーの誘導体からなる群から選択される１種以上とビニルエステルとを、公知の重合開始剤を用いて公知の重合反応を行い、次いで公知の方法でケン化反応を行うことで製造できる。 There are no particular restrictions on the method for producing the saponified product of (i-1) above. The saponified product of the above (i-1) is, for example, a known polymerization of one or more selected from the group consisting of a monomer having a carboxyl group and a derivative of the monomer and a vinyl ester using a known polymerization initiator. It can be produced by carrying out a reaction and then carrying out a saponification reaction by a known method.
　本発明の一実施態様において、ビニルアルコール系重合体（Ａ）が有するイオン性基（例えばカルボキシル基）の一部または全部は、塩（イオン性基がカルボキシル基の場合はカルボン酸塩）の形態であってもよい。塩のカウンターカチオンの例としては、リチウムイオン、ナトリウムイオン、カリウムイオン、ルビジウムイオン、およびセシウムイオン等のアルカリ金属イオン；マグネシウムイオン、カルシウムイオン、ストロンチウムイオン、およびバリウムイオン等のアルカリ土類金属イオン；アルミニウムイオン、および亜鉛イオン等のその他金属イオン；アンモニウムイオン、イミダゾリウム類、ピリジニウム類、およびホスホニウムイオン類等のオニウムカチオン；等を挙げることができる。中でも、より好ましい吸水量または吸水速度を得やすい観点から、カリウムイオン、アンモニウムイオン、カルシウムイオン、およびマグネシウムイオンが好ましい。植物の生育の観点からはカリウムイオン、およびアンモニウムイオンがより好ましく、土壌中に含まれる二価イオンとの接触時にも吸液量または吸液速度を維持しやすい観点からはカルシウムイオンがより好ましい。 In one embodiment of the present invention, a part or all of the ionic group (for example, carboxyl group) contained in the vinyl alcohol polymer (A) is in the form of a salt (carboxylate when the ionic group is a carboxyl group). May be. Examples of salt counter cations are alkali metal ions such as lithium ion, sodium ion, potassium ion, rubidium ion, and cesium ion; alkaline earth metal ions such as magnesium ion, calcium ion, strontium ion, and barium ion; Examples thereof include aluminum ions and other metal ions such as zinc ions; onium cations such as ammonium ions, imidazoliums, pyridiniums, and phosphonium ions; and the like. Of these, potassium ion, ammonium ion, calcium ion, and magnesium ion are preferable from the viewpoint of easily obtaining a more preferable water absorption amount or water absorption rate. Potassium ions and ammonium ions are more preferable from the viewpoint of plant growth, and calcium ions are more preferable from the viewpoint of easily maintaining the amount of liquid absorbed or the rate of liquid absorption even when in contact with divalent ions contained in the soil.
　イオン性基がカルボキシル基である場合、カルボキシル基の一部または全部がカルボン酸塩であるビニルアルコール系重合体（Ａ）の製造方法としては、例えば、上記（ｉ－１）においてカルボキシル基を有するモノマーの中和物を用いる方法（Ｉ）；上記（ｉ－１）においてカルボキシル基を有するビニルアルコール系重合体（Ａ）を製造した後、中和する方法（ＩＩＩ）；等を挙げることができ、中でも上記方法（ＩＩＩ）が好ましい。 When the ionic group is a carboxyl group, as a method for producing the vinyl alcohol polymer (A) in which a part or all of the carboxyl group is a carboxylate, for example, the above (i-1) has a carboxyl group. A method (I) using a neutralized product of a monomer; a method (III) of producing a vinyl alcohol-based polymer (A) having a carboxyl group and then neutralizing the polymer (A) in the above (i-1) can be mentioned. Above all, the above method (III) is preferable.
　ビニルアルコール系重合体（Ａ）中のイオン性基の含有量は、ビニルアルコール系重合体（Ａ）の全構成単位に対して０．１モル％以上、好ましくは１モル％以上、より好ましくは３モル％以上、更に好ましくは４モル％以上、特に好ましくは５モル％以上であり、５０モル％以下、好ましくは４０モル％以下、より好ましくは３０モル％以下、更に好ましくは２５モル％以下、更により好ましくは２０モル％以下、特に好ましくは１５モル％以下、更に特に好ましくは１０モル％以下である。上記イオン性基の含有量が前記下限値以上であると、ビニルアルコール系重合体（Ａ）は、より向上した吸水量または吸水速度を有しやすい。上記イオン性基の含有量が前記上限値以下であると、ビニルアルコール系重合体（Ａ）は、土壌中に含まれる二価イオンとの接触時にも優れた吸液量または吸液速度を維持しやすく、この吸液量または吸液速度は、長期間にわたって低下しにくく、紫外線によるビニルアルコール系重合体（Ａ）の分解が起こりにくい。 The content of the ionic group in the vinyl alcohol-based polymer (A) is 0.1 mol% or more, preferably 1 mol% or more, more preferably 1 mol% or more, based on all the constituent units of the vinyl alcohol-based polymer (A). 3 mol% or more, more preferably 4 mol% or more, particularly preferably 5 mol% or more, 50 mol% or less, preferably 40 mol% or less, more preferably 30 mol% or less, still more preferably 25 mol% or less. It is even more preferably 20 mol% or less, particularly preferably 15 mol% or less, and even more preferably 10 mol% or less. When the content of the ionic group is at least the above lower limit value, the vinyl alcohol-based polymer (A) tends to have a higher water absorption amount or water absorption rate. When the content of the ionic group is not more than the upper limit, the vinyl alcohol-based polymer (A) maintains an excellent liquid absorption amount or liquid absorption rate even when in contact with divalent ions contained in the soil. The liquid absorption amount or the liquid absorption rate is unlikely to decrease over a long period of time, and the vinyl alcohol-based polymer (A) is less likely to be decomposed by ultraviolet rays.
　また、ビニルアルコール系重合体（Ａ）がイオン性基としてカルボキシル基を有する場合、上記カルボキシル基のうちアクリル酸またはその塩に由来するカルボキシル基の量は、ビニルアルコール系重合体の全構成単位に対して、好ましくは２０モル％以下、より好ましくは１５モル％以下、特に好ましくは１０モル％以下であり、０モル％であってもよい。上記カルボキシル基のうちアクリル酸またはその塩に由来するカルボキシル基の量が前記上限値以下であると、より優れた耐候性（特に耐紫外線性）を得やすい。
　好ましい一実施態様において、ビニルアルコール系重合体（Ａ）に含まれるイオン性基の半分以上は誘導体の形態であり、より好ましい一実施態様において、ビニルアルコール系重合体（Ａ）に含まれるイオン性基のほとんどは誘導体の形態であり、特に好ましい一実施態様において、ビニルアルコール系重合体（Ａ）に含まれるイオン性基の全ては誘導体の形態である。
　本明細書では、上述した通り「構成単位」とは重合体を構成する繰り返し単位のことを意味するが、例えば、ビニルアルコール単位は「１単位」、２単位のビニルアルコール単位がアセタール化された構造は「２単位」と数えることとする。 When the vinyl alcohol-based polymer (A) has a carboxyl group as an ionic group, the amount of the carboxyl group derived from acrylic acid or a salt thereof among the above-mentioned carboxyl groups is the total constituent unit of the vinyl alcohol-based polymer. On the other hand, it is preferably 20 mol% or less, more preferably 15 mol% or less, particularly preferably 10 mol% or less, and may be 0 mol%. When the amount of the carboxyl group derived from acrylic acid or a salt thereof among the above-mentioned carboxyl groups is not more than the upper limit value, more excellent weather resistance (particularly ultraviolet resistance) can be easily obtained.
In one preferred embodiment, more than half of the ionic groups contained in the vinyl alcohol polymer (A) are in the form of derivatives, and in a more preferred embodiment, the ionicity contained in the vinyl alcohol polymer (A). Most of the groups are in the form of derivatives, and in one particularly preferred embodiment, all of the ionic groups contained in the vinyl alcohol polymer (A) are in the form of derivatives.
In the present specification, as described above, the "constituent unit" means a repeating unit constituting the polymer. For example, the vinyl alcohol unit is "1 unit" and two vinyl alcohol units are acetalized. The structure is counted as "2 units".
　ビニルアルコール系重合体（Ａ）のビニルアルコール単位の含有量は、上記ビニルアルコール系重合体（Ａ）の全構成単位に対して好ましくは２０モル％超、より好ましくは５０モル％以上、更に好ましくは６０モル％以上であり、好ましくは９８モル％以下、より好ましくは９５モル％以下、更に好ましくは９０モル％以下である。上記ビニルアルコール単位の含有量は、上述した通りＦＴＩＲまたは固体１３Ｃ－ＮＭＲ等により測定できるが、一定量の無水酢酸と反応させた際の無水酢酸の消費量から算出することもできる。 The content of the vinyl alcohol unit of the vinyl alcohol-based polymer (A) is preferably more than 20 mol%, more preferably 50 mol% or more, still more preferably 50 mol% or more, based on all the constituent units of the vinyl alcohol-based polymer (A). Is 60 mol% or more, preferably 98 mol% or less, more preferably 95 mol% or less, still more preferably 90 mol% or less. The content of the vinyl alcohol unit can be measured by FTIR, solid 13 C-NMR, or the like as described above, but it can also be calculated from the consumption of acetic anhydride when reacted with a certain amount of acetic anhydride.
　ビニルアルコール系重合体（Ａ）は、ビニルアルコール単位以外の他の構成単位を含む。上記他の構成単位の例としては、酢酸ビニル、およびピバル酸ビニル等のカルボン酸ビニル由来の構成単位；エチレン、１－ブテン、およびイソブチレン等のオレフィン由来の構成単位；アクリル酸およびその誘導体、メタクリル酸およびその誘導体、アクリルアミドおよびその誘導体、メタクリルアミドおよびその誘導体、マレイン酸およびその誘導体、およびマレイミド誘導体等に由来する構成単位；等を挙げることができる。上記他の構成単位は１種を含有していても複数種を含有していてもよい。上記他の構成単位の含有量は、ビニルアルコール系重合体（Ａ）の全構成単位に対して、好ましくは５０モル％以下、より好ましくは３０モル％以下、更に好ましくは２０モル％以下、更により好ましくは１０モル％以下、特に好ましくは５モル％以下であり、好ましくは０．１モル％以上、より好ましくは０．５モル％以上、更に好ましくは１モル％以上、更により好ましくは２モル％以上、特に好ましくは３モル％以上である。上記他の構成単位の含有量が前記下限値以上であり、前記上限値以下であると、本発明の保水材のより優れた吸水量または吸水速度を得やすい。 The vinyl alcohol-based polymer (A) contains other structural units other than the vinyl alcohol unit. Examples of the above other structural units include vinyl acetate and structural units derived from vinyl carboxylate such as vinyl pivalate; structural units derived from olefins such as ethylene, 1-butene, and isobutylene; acrylic acid and its derivatives, methacrylic acid. Examples thereof include acid and its derivatives, acrylamide and its derivatives, methacrylic acid and its derivatives, maleic acid and its derivatives, and structural units derived from maleimide derivatives and the like. The other constituent units may contain one type or a plurality of types. The content of the other structural units is preferably 50 mol% or less, more preferably 30 mol% or less, still more preferably 20 mol% or less, and further, with respect to all the structural units of the vinyl alcohol-based polymer (A). More preferably 10 mol% or less, particularly preferably 5 mol% or less, preferably 0.1 mol% or more, more preferably 0.5 mol% or more, still more preferably 1 mol% or more, still more preferably 2 It is mol% or more, particularly preferably 3 mol% or more. When the content of the other structural units is at least the lower limit value and at least the upper limit value, it is easy to obtain a better water absorption amount or water absorption rate of the water retention material of the present invention.
　ビニルアルコール系重合体（Ａ）の粘度平均重合度に特に制限はないが、製造容易性の観点から、好ましくは２００００以下、より好ましくは１００００以下、更に好ましくは４０００以下、特に好ましくは３０００以下である。一方、ビニルアルコール系重合体（Ａ）の力学特性および水への耐溶出性の観点からは、粘度平均重合度は、好ましくは１００以上、より好ましくは２００以上、更に好ましくは４００以上である。ビニルアルコール系重合体（Ａ）の粘度平均重合度は、ＪＩＳ　Ｋ　６７２６に準拠した方法により測定できる。ビニルアルコール系重合体（Ａ）が後述のように架橋構造を有する場合、例えばビニルアルコール系重合体（Ａ）が架橋構造としてアセタール構造またはエステル構造を有する場合、粘度平均重合度の測定は、架橋構造を切断した後に行うことができる。前記切断は、一般的な方法（例えば、酸若しくはアルカリを用いた加水分解）により行うことができる。 The viscosity average degree of polymerization of the vinyl alcohol polymer (A) is not particularly limited, but is preferably 20000 or less, more preferably 10000 or less, still more preferably 4000 or less, and particularly preferably 3000 or less from the viewpoint of ease of production. be. On the other hand, from the viewpoint of the mechanical properties of the vinyl alcohol polymer (A) and the elution resistance to water, the viscosity average degree of polymerization is preferably 100 or more, more preferably 200 or more, still more preferably 400 or more. The viscosity average degree of polymerization of the vinyl alcohol polymer (A) can be measured by a method based on JIS K 6726. When the vinyl alcohol-based polymer (A) has a crosslinked structure as described later, for example, when the vinyl alcoholic polymer (A) has an acetal structure or an ester structure as the crosslinked structure, the measurement of the viscosity average degree of polymerization is carried out. It can be done after cutting the structure. The cutting can be performed by a general method (for example, hydrolysis using an acid or an alkali).
　ビニルアルコール系重合体（Ａ）は、潅水によるビニルアルコール系重合体の溶出を抑制する観点から、架橋構造を含むことが好ましい。架橋構造の形態に特に制限はなく、その例としては、エステル結合、エーテル結合、アセタール結合、および炭素－炭素結合等による架橋構造を挙げることができる。ビニルアルコール系重合体（Ａ）中の架橋構造の有無は、例えば１００℃の熱水またはジメチルスルホキシド中での溶出率により調べることができる。具体的には、試料の質量に対する、溶出した試料の質量の割合（溶出した試料の質量の割合×１００／試料の質量）で示される溶出率が一定の値以下（例えば９０質量％以下）であることにより、架橋構造の存在を確認できる。 The vinyl alcohol-based polymer (A) preferably contains a crosslinked structure from the viewpoint of suppressing elution of the vinyl alcohol-based polymer due to irrigation. The form of the crosslinked structure is not particularly limited, and examples thereof include a crosslinked structure formed by an ester bond, an ether bond, an acetal bond, a carbon-carbon bond, and the like. The presence or absence of the crosslinked structure in the vinyl alcohol polymer (A) can be examined, for example, by the elution rate in hot water or dimethyl sulfoxide at 100 ° C. Specifically, when the elution rate represented by the ratio of the mass of the eluted sample to the mass of the sample (ratio of the mass of the eluted sample x 100 / the mass of the sample) is a certain value or less (for example, 90% by mass or less). With the presence, the existence of the crosslinked structure can be confirmed.
　上記エステル結合の例としては、ビニルアルコール系重合体（Ａ）がイオン性基としてカルボキシル基を有する場合に、ビニルアルコール系重合体（Ａ）が有する水酸基とカルボキシル基との間で形成されるエステル結合を挙げることができる。上記エーテル結合の例としては、ビニルアルコール系重合体（Ａ）が有する水酸基間の脱水縮合により形成されるエーテル結合を挙げることができる。上記エーテル結合の別の例としては、ビニルアルコール系重合体（Ａ）の製造において、１分子中に複数のエポキシ基を有する多価エポキシ化合物を用いた場合に形成されるエーテル結合を挙げることができる。上記アセタール結合の例としては、ビニルアルコール系重合体（Ａ）の製造においてカルボキシル基を有するアルデヒドを用いた場合に、２つのビニルアルコール系重合体（Ａ）が有する水酸基同士が上記アルデヒドとアセタール化反応することにより形成されるアセタール結合を挙げることができる。上記アセタール結合の別の例としては、ビニルアルコール系重合体（Ａ）の製造において、１分子中に複数のアルデヒド基を有する多価アルデヒド化合物を用いた場合に形成されるアセタール結合を挙げることができる。上記炭素－炭素結合としては、例えば活性エネルギー線をビニルアルコール系重合体（Ａ）に照射したときに生じる、ビニルアルコール系重合体（Ａ）の炭素ラジカル間のカップリングにより形成される炭素－炭素結合を挙げることができる。これらの架橋構造は１種が含まれていても、複数種が含まれていてもよい。中でも、製造容易性の観点からエステル結合またはアセタール結合による架橋構造が好ましく、育苗時における保水性維持、および耐紫外線性の観点から、アセタール結合による架橋構造がより好ましい。 As an example of the ester bond, when the vinyl alcohol polymer (A) has a carboxyl group as an ionic group, an ester formed between the hydroxyl group and the carboxyl group of the vinyl alcohol polymer (A). Bonding can be mentioned. Examples of the ether bond include an ether bond formed by dehydration condensation between the hydroxyl groups of the vinyl alcohol polymer (A). Another example of the ether bond is an ether bond formed when a polyvalent epoxy compound having a plurality of epoxy groups in one molecule is used in the production of the vinyl alcohol polymer (A). can. As an example of the acetal bond, when an aldehyde having a carboxyl group is used in the production of the vinyl alcohol polymer (A), the hydroxyl groups of the two vinyl alcohol polymers (A) are acetalized with the aldehyde. The acetal bond formed by the reaction can be mentioned. Another example of the acetal bond is an acetal bond formed when a polyvalent aldehyde compound having a plurality of aldehyde groups in one molecule is used in the production of the vinyl alcohol polymer (A). can. The carbon-carbon bond is, for example, carbon-carbon formed by coupling between carbon radicals of the vinyl alcohol-based polymer (A), which is generated when the vinyl alcohol-based polymer (A) is irradiated with an active energy ray. Bonding can be mentioned. These crosslinked structures may contain one type or a plurality of types. Of these, a crosslinked structure with an ester bond or an acetal bond is preferable from the viewpoint of ease of production, and a crosslinked structure with an acetal bond is more preferable from the viewpoint of maintaining water retention during seedling raising and UV resistance.
　このような架橋構造は、例えば、多価アルデヒド化合物から選択される１種以上により少なくとも一部のビニルアルコール単位をアセタール化する工程においてアセタール化反応と同時に形成されてもよいし、アセタール化反応工程以外の別の工程であって後述する凝集工程の前に架橋剤を更に添加することにより凝集工程の前に形成されてもよいし、凝集工程において架橋剤を更に添加することにより凝集工程と同時に形成されてもよいし、凝集工程後に架橋剤を更に添加することにより凝集工程の後に形成されてもよい。本発明においては、架橋剤を更に添加することにより架橋構造を形成することが好ましい。 Such a crosslinked structure may be formed at the same time as the acetalization reaction in the step of acetalizing at least a part of the vinyl alcohol units by, for example, one or more selected from the polyvalent aldehyde compound, or may be formed at the same time as the acetalization reaction step. In another step other than the above, the cross-linking agent may be further added before the coagulation step described later to be formed before the coagulation step, or the cross-linking agent may be further added in the coagulation step at the same time as the coagulation step. It may be formed or may be formed after the aggregation step by further adding a cross-linking agent after the aggregation step. In the present invention, it is preferable to form a crosslinked structure by further adding a crosslinking agent.
　架橋剤の例としては、多価エポキシ化合物および多価アルデヒド化合物が挙げられ、中でも多価アルデヒド化合物が好ましい。
　多価エポキシ化合物としては例えば、エチレングリコールジグリシジルエーテル等の２官能のエポキシ化合物が挙げられる。
　多価アルデヒド化合物としては例えば、グリオキサール、マロンアルデヒド、スクシンアルデヒド、グルタルアルデヒド、１，９－ノナンジアール、アジポアルデヒド、マレアルデヒド、タルタルアルデヒド、シトルアルデヒド、フタルアルデヒド、イソフタルアルデヒド、およびテレフタルアルデヒド等の２官能のアルデヒドを挙げることができる。架橋剤として多価アルデヒド化合物を用いた場合、２つのビニルアルコール系重合体（Ａ）のうち一方が有する水酸基が、上記多価アルデヒド化合物の有する１つのアルデヒド基とアセタール化反応をし、また、２つのビニルアルコール系重合体（Ａ）のうち他方が有する水酸基が、当該多価アルデヒド化合物の有する別の１つのアルデヒド基とアセタール化反応をすることで、アセタール結合を２つ導入することができる。 Examples of the cross-linking agent include a polyvalent epoxy compound and a polyvalent aldehyde compound, and among them, a polyvalent aldehyde compound is preferable.
Examples of the polyvalent epoxy compound include bifunctional epoxy compounds such as ethylene glycol diglycidyl ether.
Examples of the polyhydric aldehyde compound include glyoxal, malonaldehyde, succinaldehyde, glutaaldehyde, 1,9-nonandial, adipaldehyde, malealdehyde, tartaraldehyde, citraldehyde, phthalaldehyde, isophthalaldehyde, and terephthalaldehyde. Bifunctional aldehydes can be mentioned. When a polyvalent aldehyde compound is used as a cross-linking agent, the hydroxyl group of one of the two vinyl alcoholic polymers (A) undergoes an acetalization reaction with one aldehyde group of the polyvalent aldehyde compound, and also Two acetal bonds can be introduced by the hydroxyl group of the other of the two vinyl alcohol-based polymers (A) undergoing an acetalization reaction with another aldehyde group of the polyvalent aldehyde compound. ..
　架橋剤を添加する場合、ビニルアルコール系重合体（Ａ）中の架橋剤量としては、土壌中での保水性を維持しやすい観点から、好ましくは０．００１モル％以上、より好ましくは０．００５モル％以上、更に好ましくは０．０１モル％以上、より更に好ましくは０．０３モル％以上であり、好ましくは０．５モル％以下、より好ましくは０．４モル％以下、更に好ましくは０．３モル％以下である。 When a cross-linking agent is added, the amount of the cross-linking agent in the vinyl alcohol-based polymer (A) is preferably 0.001 mol% or more, more preferably 0, from the viewpoint of easily maintaining water retention in the soil. It is 005 mol% or more, more preferably 0.01 mol% or more, still more preferably 0.03 mol% or more, preferably 0.5 mol% or less, more preferably 0.4 mol% or less, still more preferably. It is 0.3 mol% or less.
＜アクリル酸系重合体＞
　本発明における吸水性樹脂が含んでもよいアクリル酸系重合体は、アクリル酸またはアクリル酸誘導体に由来する構成単位（以下、「アクリル酸由来構成単位」と称する）を、全構成単位の中で最も多い含有量で含む。アクリル酸系重合体の原料の例としては、アクリル酸、アクリル酸ナトリウム、アクリル酸カリウム、アクリル酸カルシウム、アクリル酸メチル、アクリル酸エチル、アクリル酸ｎ－プロピル、アクリル酸ｎ－ブチル、アクリル酸ｓｅｃ－ブチル、アクリル酸２－エチルヘキシル、アクリル酸シクロヘキシル、アクリル酸フェニル、およびアクリル酸－２－ヒドロキシエチル等を挙げることができる。これら１種または２種以上のモノマーと共重合が可能な他の少なくとも１種のモノマーとを公知の方法を用いて共重合させたものを、アクリル酸系重合体の例として挙げることができる。共重合が可能な他のモノマーの例としては、後述する、アクリル酸由来構成単位以外の他の構成単位をもたらすモノマーを挙げることができる。
　吸水性樹脂におけるアクリル酸系重合体の含有量は、好ましくは７０質量％以上、より好ましくは８０質量％以上、更に好ましくは９０質量％以上、特に好ましくは９５質量％以上であり、１００質量％であってもよい。 <Acrylic acid polymer>
In the acrylic acid-based polymer which may contain the water-absorbent resin in the present invention, the structural unit derived from acrylic acid or an acrylic acid derivative (hereinafter referred to as “acrylic acid-derived structural unit”) is the most among all the structural units. Contains in high content. Examples of raw materials for acrylic acid-based polymers include acrylic acid, sodium acrylate, potassium acrylate, calcium acrylate, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, sec acrylate. -Butyl, 2-ethylhexyl acrylate, cyclohexyl acrylate, phenyl acrylate, -2-hydroxyethyl acrylate and the like can be mentioned. Examples of acrylic acid-based polymers include those obtained by copolymerizing one or more of these monomers with at least one other monomer copolymerizable by a known method. Examples of other monomers capable of copolymerization include monomers that bring about other structural units other than acrylic acid-derived structural units, which will be described later.
The content of the acrylic acid-based polymer in the water-absorbent resin is preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, particularly preferably 95% by mass or more, and 100% by mass. May be.
　本発明の一実施態様において、アクリル酸系重合体が有するイオン性基（例えばカルボキシル基）の一部または全部は、塩（イオン性基がカルボキシル基の場合はカルボン酸塩）の形態であってもよい。塩のカウンターカチオンの例としては、リチウムイオン、ナトリウムイオン、カリウムイオン、ルビジウムイオン、およびセシウムイオン等のアルカリ金属イオン；マグネシウムイオン、カルシウムイオン、ストロンチウムイオン、およびバリウムイオン等のアルカリ土類金属イオン；アルミニウムイオン、および亜鉛イオン等のその他金属イオン；アンモニウムイオン、イミダゾリウム類、ピリジニウム類、およびホスホニウムイオン類等のオニウムカチオン；等を挙げることができる。中でも、より好ましい吸水量または吸水速度を得やすい観点から、カリウムイオン、アンモニウムイオン、カルシウムイオン、およびマグネシウムイオンが好ましい。植物の生育の観点からはカリウムイオン、およびアンモニウムイオンがより好ましく、土壌中に含まれる二価イオンとの接触時にも吸液量または吸液速度を維持しやすい観点からはカルシウムイオンがより好ましい。 In one embodiment of the present invention, a part or all of the ionic group (for example, carboxyl group) contained in the acrylic acid-based polymer is in the form of a salt (carboxylate when the ionic group is a carboxyl group). May be good. Examples of salt counter cations are alkali metal ions such as lithium ion, sodium ion, potassium ion, rubidium ion, and cesium ion; alkaline earth metal ions such as magnesium ion, calcium ion, strontium ion, and barium ion; Examples thereof include aluminum ions and other metal ions such as zinc ions; onium cations such as ammonium ions, imidazoliums, pyridiniums, and phosphonium ions; and the like. Of these, potassium ion, ammonium ion, calcium ion, and magnesium ion are preferable from the viewpoint of easily obtaining a more preferable water absorption amount or water absorption rate. Potassium ions and ammonium ions are more preferable from the viewpoint of plant growth, and calcium ions are more preferable from the viewpoint of easily maintaining the amount of liquid absorbed or the rate of liquid absorption even when in contact with divalent ions contained in the soil.
　アクリル酸系重合体中のイオン性基の含有量は、アクリル酸系重合体の全構成単位に対して０．１モル％以上、好ましくは１モル％以上、より好ましくは３モル％以上、更に好ましくは４モル％以上、特に好ましくは５モル％以上であり、５０モル％以下、好ましくは４０モル％以下、より好ましくは３０モル％以下、更に好ましくは２５モル％以下、更により好ましくは２０モル％以下、特に好ましくは１５モル％以下、更に特に好ましくは１０モル％以下である。上記イオン性基の含有量が前記下限値以上であると、アクリル酸系重合体は、より向上した吸水量または吸水速度を有しやすい。上記イオン性基の含有量が前記上限値以下であると、アクリル酸系重合体は、土壌中に含まれる二価イオンとの接触時にも優れた吸液量または吸液速度を維持しやすく、この吸液量または吸液速度は、長期間にわたって低下しにくく、紫外線によるアクリル酸系重合体の分解が起こりにくい。 The content of the ionic group in the acrylic acid-based polymer is 0.1 mol% or more, preferably 1 mol% or more, more preferably 3 mol% or more, and further, with respect to all the constituent units of the acrylic acid-based polymer. It is preferably 4 mol% or more, particularly preferably 5 mol% or more, 50 mol% or less, preferably 40 mol% or less, more preferably 30 mol% or less, still more preferably 25 mol% or less, still more preferably 20. It is mol% or less, particularly preferably 15 mol% or less, and even more preferably 10 mol% or less. When the content of the ionic group is at least the above lower limit value, the acrylic acid-based polymer tends to have a higher water absorption amount or water absorption rate. When the content of the ionic group is not more than the upper limit value, the acrylic acid-based polymer can easily maintain an excellent liquid absorption amount or liquid absorption rate even when in contact with divalent ions contained in the soil. This liquid absorption amount or liquid absorption rate is unlikely to decrease over a long period of time, and decomposition of the acrylic acid-based polymer by ultraviolet rays is unlikely to occur.
　また、アクリル酸系重合体がイオン性基としてカルボキシル基を有する場合、上記カルボキシル基のうちアクリル酸またはその塩に由来するカルボキシル基の量は、アクリル酸系重合体の全構成単位に対して、好ましくは２０モル％以下、より好ましくは１５モル％以下、特に好ましくは１０モル％以下であり、０モル％であってもよい。上記カルボキシル基のうちアクリル酸またはその塩に由来するカルボキシル基の量が前記上限値以下であると、より優れた耐候性（特に耐紫外線性）を得やすい。
　好ましい一実施態様において、アクリル酸系重合体に含まれるイオン性基の半分以上は誘導体の形態であり、より好ましい一実施態様において、アクリル酸系重合体に含まれるイオン性基のほとんどは誘導体の形態であり、特に好ましい一実施態様において、アクリル酸系重合体に含まれるイオン性基の全ては誘導体の形態である。 When the acrylic acid-based polymer has a carboxyl group as an ionic group, the amount of the carboxyl group derived from acrylic acid or a salt thereof among the above-mentioned carboxyl groups is based on all the constituent units of the acrylic acid-based polymer. It is preferably 20 mol% or less, more preferably 15 mol% or less, particularly preferably 10 mol% or less, and may be 0 mol%. When the amount of the carboxyl group derived from acrylic acid or a salt thereof among the above-mentioned carboxyl groups is not more than the upper limit value, more excellent weather resistance (particularly ultraviolet resistance) can be easily obtained.
In one preferred embodiment, more than half of the ionic groups contained in the acrylic acid polymer are in the form of derivatives, and in a more preferred embodiment, most of the ionic groups contained in the acrylic acid polymer are derivatives. It is a form, and in a particularly preferable embodiment, all of the ionic groups contained in the acrylic acid-based polymer are in the form of a derivative.
　アクリル酸系重合体のアクリル酸由来構成単位の含有量は、上記アクリル酸系重合体の全構成単位に対して好ましくは２０モル％超、より好ましくは５０モル％以上、更に好ましくは６０モル％以上であり、好ましくは９８モル％以下、より好ましくは９５モル％以下、更に好ましくは９０モル％以下である。 The content of the acrylic acid-derived structural unit of the acrylic acid-based polymer is preferably more than 20 mol%, more preferably 50 mol% or more, still more preferably 60 mol% with respect to all the structural units of the acrylic acid-based polymer. The above is preferably 98 mol% or less, more preferably 95 mol% or less, still more preferably 90 mol% or less.
　アクリル酸系重合体は、アクリル酸由来構成単位以外の他の構成単位を含む。上記他の構成単位の例としては、ビニルアルコール単位；酢酸ビニル、およびピバル酸ビニル等のカルボン酸ビニル由来の構成単位；エチレン、１－ブテン、およびイソブチレン等のオレフィン由来の構成単位；メタクリル酸およびその誘導体、アクリルアミドおよびその誘導体、メタクリルアミドおよびその誘導体、マレイン酸およびその誘導体、およびマレイミド誘導体等に由来する構成単位；等を挙げることができる。上記他の構成単位は１種を含有していても複数種を含有していてもよい。上記他の構成単位の含有量は、アクリル酸系重合体の全構成単位に対して、好ましくは５０モル％以下、より好ましくは３０モル％以下、更に好ましくは２０モル％以下、更により好ましくは１０モル％以下、特に好ましくは５モル％以下であり、好ましくは０．１モル％以上、より好ましくは０．５モル％以上、更に好ましくは１モル％以上、更により好ましくは２モル％以上、特に好ましくは３モル％以上である。上記他の構成単位の含有量が前記下限値以上であり、前記上限値以下であると、本発明の保水材のより優れた吸水量または吸水速度を得やすい。 The acrylic acid-based polymer contains other structural units other than the acrylic acid-derived structural unit. Examples of the above other building blocks include vinyl alcohol units; building blocks derived from vinyl carboxylates such as vinyl acetate and vinyl pivalate; building blocks derived from olefins such as ethylene, 1-butene, and isobutylene; methacrylic acid and Derivatives thereof, acrylamide and its derivatives, methacrylic acid and its derivatives, maleic acid and its derivatives, structural units derived from maleimide derivatives and the like; and the like can be mentioned. The other constituent units may contain one type or a plurality of types. The content of the other structural units is preferably 50 mol% or less, more preferably 30 mol% or less, still more preferably 20 mol% or less, still more preferably 20 mol% or less, based on all the structural units of the acrylic acid-based polymer. 10 mol% or less, particularly preferably 5 mol% or less, preferably 0.1 mol% or more, more preferably 0.5 mol% or more, still more preferably 1 mol% or more, still more preferably 2 mol% or more. , Particularly preferably 3 mol% or more. When the content of the other structural units is at least the lower limit value and at least the upper limit value, it is easy to obtain a better water absorption amount or water absorption rate of the water retention material of the present invention.
　アクリル酸系重合体の重量平均分子量に特に制限はないが、製造容易性の観点から、好ましくは１０，０００，０００以下、より好ましくは５，０００，０００以下、更に好ましくは３，０００，０００以下、特に好ましくは１，０００，０００以下である。一方、アクリル酸系重合体の力学特性および水への耐溶出性の観点からは、重量平均分子量は、好ましくは１０００以上、より好ましくは５０００以上、更に好ましくは１００００以上である。アクリル酸系重合体の重量平均分子量は、例えばＧＰＣにより測定できる。アクリル酸系重合体が後述のように架橋構造を有する場合、例えばアクリル酸系重合体が架橋構造としてアセタール構造またはエステル構造を有する場合、重量平均分子量の測定は、架橋構造を切断した後に行うことができる。前記切断は、一般的な方法（例えば、酸若しくはアルカリを用いた加水分解）により行うことができる。 The weight average molecular weight of the acrylic acid-based polymer is not particularly limited, but from the viewpoint of ease of production, it is preferably 1,000,000 or less, more preferably 5,000,000 or less, still more preferably 3,000,000 or less. Below, it is particularly preferably 1,000,000 or less. On the other hand, from the viewpoint of the mechanical properties of the acrylic acid-based polymer and the elution resistance to water, the weight average molecular weight is preferably 1000 or more, more preferably 5000 or more, still more preferably 10,000 or more. The weight average molecular weight of the acrylic acid-based polymer can be measured by, for example, GPC. When the acrylic acid-based polymer has a crosslinked structure as described later, for example, when the acrylic acid-based polymer has an acetal structure or an ester structure as the crosslinked structure, the weight average molecular weight should be measured after cutting the crosslinked structure. Can be done. The cutting can be performed by a general method (for example, hydrolysis using an acid or an alkali).
　アクリル酸系重合体は、潅水によるアクリル酸系重合体の溶出を抑制する観点から、架橋構造を含むことが好ましい。架橋構造の形態に特に制限はなく、その例としては、一般的な架橋剤による架橋構造を挙げることができる。アクリル酸系重合体中の架橋構造の有無は、先に述べたように、例えば１００℃の熱水またはジメチルスルホキシド中での溶出率により調べることができる。 The acrylic acid-based polymer preferably contains a crosslinked structure from the viewpoint of suppressing elution of the acrylic acid-based polymer due to irrigation. The form of the cross-linked structure is not particularly limited, and examples thereof include a cross-linked structure using a general cross-linking agent. As described above, the presence or absence of the crosslinked structure in the acrylic acid-based polymer can be examined by, for example, the elution rate in hot water or dimethyl sulfoxide at 100 ° C.
　架橋構造は、例えば、アクリル酸由来構成単位をもたらすモノマーとアクリル酸由来構成単位以外の他の構成単位をもたらすモノマーとの共重合工程において共重合反応と同時に形成されてもよいし、共重合反応工程以外の別の工程であって後述する凝集工程の前に架橋剤を更に添加することにより凝集工程の前に形成されてもよいし、凝集工程において架橋剤を更に添加することにより凝集工程と同時に形成されてもよいし、凝集工程後に架橋剤を更に添加することにより凝集工程の後に形成されてもよい。本発明においては、架橋剤を更に添加することにより架橋構造を形成することが好ましい。 The crosslinked structure may be formed at the same time as the copolymerization reaction in the copolymerization step of, for example, the monomer which brings about the structural unit derived from acrylic acid and the monomer which brings about the structural unit other than the structural unit derived from acrylic acid, or the copolymerization reaction. It may be formed before the aggregation step by further adding a cross-linking agent before the aggregation step described later in another step other than the step, or it may be formed by further adding the cross-linking agent in the aggregation step. It may be formed at the same time, or may be formed after the aggregation step by further adding a cross-linking agent after the aggregation step. In the present invention, it is preferable to form a crosslinked structure by further adding a crosslinking agent.
　架橋剤の例としては、Ｎ，Ｎ’－メチレンビスアクリルアミド、ジビニルベンゼン、エチレングリコールジグリシジルエーテル、ペンタエリスリトールトリアリルエーテル、ペンタエリスリトールトリアクリレート、ペンタエリスリトールテトラアクリレート、１，６－ヘキサンジオールジアクリレート、１，９－ノナンジオールジアクリレート、１，１０－デカンジオールジアクリレート、ネオペンチルグリコールジアクリレート、２－ヒドロキシ－３－メタクリルプロピルアクリレート、ポリエチレングリコールジアクリレート、ポリプロピレングリコールジアクリレート、トリメチロールプロパントリアクリレートおよびトリス－（２－アクリロキシエチル）イソシアヌレート等を挙げることができる。 Examples of cross-linking agents include N, N'-methylenebisacrylamide, divinylbenzene, ethylene glycol diglycidyl ether, pentaerythritol triallyl ether, pentaerythritol triacrylate, pentaerythritol tetraacrylate, 1,6-hexanediol diacrylate, 1,9-Nonandiol diacrylate, 1,10-decanediol diacrylate, neopentyl glycol diacrylate, 2-hydroxy-3-methacrylicpropyl acrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, trimethyl propanetriacrylate and Tris- (2-acryloxyethyl) isocyanurate and the like can be mentioned.
　架橋剤を添加する場合、アクリル酸系重合体中の架橋剤量としては、土壌中での保水性を維持しやすい観点から、好ましくは０．００１モル％以上、より好ましくは０．０１モル％以上、更に好ましくは１．０モル％以上、より更に好ましくは２．０モル％以上であり、好ましくは１０モル％以下、より好ましくは５モル％以下、更に好ましくは３モル％以下である。 When a cross-linking agent is added, the amount of the cross-linking agent in the acrylic acid-based polymer is preferably 0.001 mol% or more, more preferably 0.01 mol%, from the viewpoint of easily maintaining water retention in the soil. The above is more preferably 1.0 mol% or more, still more preferably 2.0 mol% or more, preferably 10 mol% or less, more preferably 5 mol% or less, still more preferably 3 mol% or less.
　アクリル酸系重合体の具体的な例としては、アクリル酸－アクリル酸ナトリウム共重合体の架橋物等を挙げることができる。市販品としては、高吸収性ポリマー（アクリル酸塩系、和光純薬工業株式会社製）、アクリホープ（登録商標）（株式会社日本触媒製）、およびサンウェット（登録商標）（三洋化成工業株式会社製）等を挙げることができる。 Specific examples of the acrylic acid-based polymer include a crosslinked product of an acrylic acid-sodium acrylate copolymer. Commercially available products include highly absorbent polymers (acrylic acid salt type, manufactured by Wako Pure Chemical Industries, Ltd.), Acrihope (registered trademark) (manufactured by Nippon Shokubai Co., Ltd.), and Sunwet (registered trademark) (Sanyo Chemical Industries, Ltd.). Made) and the like.
＜アクリルアミド系重合体＞
　本発明における吸水性樹脂が含んでもよいアクリルアミド系重合体は、アクリルアミドまたはアクリルアミド誘導体に由来する構成単位（以下、「アクリルアミド由来構成単位」と称する）を、全構成単位の中で最も多い含有量で含む。アクリルアミド系重合体の原料の例としては、アクリルアミド、２－アクリルアミド－２－メチルプロパンスルホン酸、Ｎ－アルキルアクリルアミド、およびトリメチル［３－（アクリロイルアミノ）プロピル］アミニウム・クロリドを挙げることができる。これら１種または２種以上のモノマーと共重合が可能な他の少なくとも１種のモノマーとを公知の方法を用いて共重合させたものを、アクリルアミド系重合体の例として挙げることができる。共重合が可能な他のモノマーの例としては、後述する、アクリルアミド由来構成単位以外の他の構成単位をもたらすモノマーを挙げることができる。
　吸水性樹脂におけるアクリルアミド系重合体の含有量は、好ましくは７０質量％以上、より好ましくは８０質量％以上、更に好ましくは９０質量％以上、特に好ましくは９５質量％以上であり、１００質量％であってもよい。 <Acrylamide polymer>
The acrylamide-based polymer that may be contained in the water-absorbent resin in the present invention contains a structural unit derived from acrylamide or an acrylamide derivative (hereinafter referred to as "acrylamide-derived structural unit") at the highest content among all the structural units. include. Examples of raw materials for acrylamide-based polymers include acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, N-alkylacrylamide, and trimethyl [3- (acryloylamino) propyl] aminium chloride. Examples of the acrylamide-based polymer include those obtained by copolymerizing one or more of these monomers with at least one other monomer copolymerizable by a known method. Examples of other monomers capable of copolymerization include monomers that bring about other structural units other than the acrylamide-derived structural units, which will be described later.
The content of the acrylamide polymer in the water-absorbent resin is preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, particularly preferably 95% by mass or more, and 100% by mass. There may be.
　本発明の一実施態様において、アクリルアミド系重合体が有するイオン性基（例えばカルボキシル基）の一部または全部は、塩（イオン性基がカルボキシル基の場合はカルボン酸塩）の形態であってもよい。塩のカウンターカチオンの例としては、リチウムイオン、ナトリウムイオン、カリウムイオン、ルビジウムイオン、およびセシウムイオン等のアルカリ金属イオン；マグネシウムイオン、カルシウムイオン、ストロンチウムイオン、およびバリウムイオン等のアルカリ土類金属イオン；アルミニウムイオン、および亜鉛イオン等のその他金属イオン；アンモニウムイオン、イミダゾリウム類、ピリジニウム類、およびホスホニウムイオン類等のオニウムカチオン；等を挙げることができる。中でも、より好ましい吸水量または吸水速度を得やすい観点から、カリウムイオン、アンモニウムイオン、カルシウムイオン、およびマグネシウムイオンが好ましい。植物の生育の観点からはカリウムイオン、およびアンモニウムイオンがより好ましく、土壌中に含まれる二価イオンとの接触時にも吸液量または吸液速度を維持しやすい観点からはカルシウムイオンがより好ましい。 In one embodiment of the present invention, some or all of the ionic groups (eg, carboxyl groups) of the acrylamide polymer may be in the form of salts (carboxylates if the ionic groups are carboxyl groups). good. Examples of salt counter cations are alkali metal ions such as lithium ion, sodium ion, potassium ion, rubidium ion, and cesium ion; alkaline earth metal ions such as magnesium ion, calcium ion, strontium ion, and barium ion; Examples thereof include aluminum ions and other metal ions such as zinc ions; onium cations such as ammonium ions, imidazoliums, pyridiniums, and phosphonium ions; and the like. Of these, potassium ion, ammonium ion, calcium ion, and magnesium ion are preferable from the viewpoint of easily obtaining a more preferable water absorption amount or water absorption rate. Potassium ions and ammonium ions are more preferable from the viewpoint of plant growth, and calcium ions are more preferable from the viewpoint of easily maintaining the amount of liquid absorbed or the rate of liquid absorption even when in contact with divalent ions contained in the soil.
　アクリルアミド系重合体中のイオン性基の含有量は、アクリルアミド系重合体の全構成単位に対して０．１モル％以上、好ましくは１モル％以上、より好ましくは３モル％以上、更に好ましくは４モル％以上、特に好ましくは５モル％以上であり、５０モル％以下、好ましくは４０モル％以下、より好ましくは３０モル％以下、更に好ましくは２５モル％以下、更により好ましくは２０モル％以下、特に好ましくは１５モル％以下、更に特に好ましくは１０モル％以下である。上記イオン性基の含有量が前記下限値以上であると、アクリルアミド系重合体は、より向上した吸水量または吸水速度を有しやすい。上記イオン性基の含有量が前記上限値以下であると、アクリルアミド系重合体は、土壌中に含まれる二価イオンとの接触時にも優れた吸液量または吸液速度を維持しやすく、この吸液量または吸液速度は、長期間にわたって低下しにくく、紫外線によるアクリルアミド系重合体の分解が起こりにくい。 The content of the ionic group in the acrylamide-based polymer is 0.1 mol% or more, preferably 1 mol% or more, more preferably 3 mol% or more, still more preferably 3 mol% or more, based on all the constituent units of the acrylamide-based polymer. 4 mol% or more, particularly preferably 5 mol% or more, 50 mol% or less, preferably 40 mol% or less, more preferably 30 mol% or less, still more preferably 25 mol% or less, still more preferably 20 mol%. Hereinafter, it is particularly preferably 15 mol% or less, and further particularly preferably 10 mol% or less. When the content of the ionic group is at least the above lower limit value, the acrylamide-based polymer tends to have a higher water absorption amount or water absorption rate. When the content of the ionic group is not more than the upper limit, the acrylamide polymer can easily maintain an excellent liquid absorption amount or liquid absorption rate even when in contact with divalent ions contained in the soil. The amount of liquid absorbed or the rate of liquid absorption is unlikely to decrease over a long period of time, and decomposition of the acrylamide polymer by ultraviolet rays is unlikely to occur.
　また、アクリルアミド系重合体がイオン性基としてカルボキシル基を有する場合、上記カルボキシル基のうちアクリルアミドまたはその塩に由来するカルボキシル基の量は、アクリルアミド系重合体の全構成単位に対して、好ましくは２０モル％以下、より好ましくは１５モル％以下、特に好ましくは１０モル％以下であり、０モル％であってもよい。上記カルボキシル基のうちアクリルアミドまたはその塩に由来するカルボキシル基の量が前記上限値以下であると、より優れた耐候性（特に耐紫外線性）を得やすい。
　好ましい一実施態様において、アクリルアミド系重合体に含まれるイオン性基の半分以上は誘導体の形態であり、より好ましい一実施態様において、アクリルアミド系重合体に含まれるイオン性基のほとんどは誘導体の形態であり、特に好ましい一実施態様において、アクリルアミド系重合体に含まれるイオン性基の全ては誘導体の形態である。 When the acrylamide-based polymer has a carboxyl group as an ionic group, the amount of the carboxyl group derived from acrylamide or a salt thereof among the above-mentioned carboxyl groups is preferably 20 with respect to all the constituent units of the acrylamide-based polymer. It is mol% or less, more preferably 15 mol% or less, particularly preferably 10 mol% or less, and may be 0 mol%. When the amount of the carboxyl group derived from acrylamide or a salt thereof among the above-mentioned carboxyl groups is not more than the upper limit value, more excellent weather resistance (particularly ultraviolet resistance) can be easily obtained.
In one preferred embodiment, more than half of the ionic groups contained in the acrylamide polymer are in the form of derivatives, and in a more preferred embodiment, most of the ionic groups contained in the acrylamide polymer are in the form of derivatives. Yes, and in one particularly preferred embodiment, all of the ionic groups contained in the acrylamide polymer are in the form of derivatives.
　アクリルアミド系重合体のアクリルアミド由来構成単位の含有量は、上記アクリルアミド系重合体の全構成単位に対して好ましくは２０モル％超、より好ましくは５０モル％以上、更に好ましくは６０モル％以上であり、好ましくは９８モル％以下、より好ましくは９５モル％以下、更に好ましくは９０モル％以下である。 The content of the acrylamide-derived structural unit of the acrylamide-based polymer is preferably more than 20 mol%, more preferably 50 mol% or more, still more preferably 60 mol% or more with respect to all the structural units of the acrylamide-based polymer. It is preferably 98 mol% or less, more preferably 95 mol% or less, still more preferably 90 mol% or less.
　アクリルアミド系重合体は、アクリルアミド由来構成単位以外の他の構成単位を含む。上記他の構成単位の例としては、ビニルアルコール単位；酢酸ビニル、およびピバル酸ビニル等のカルボン酸ビニル由来の構成単位；エチレン、１－ブテン、およびイソブチレン等のオレフィン由来の構成単位；アクリル酸およびその誘導体、メタクリル酸およびその誘導体、メタクリルアミドおよびその誘導体、マレイン酸およびその誘導体、およびマレイミド誘導体等に由来する構成単位；等を挙げることができる。上記他の構成単位は１種を含有していても複数種を含有していてもよい。上記他の構成単位の含有量は、アクリルアミド系重合体の全構成単位に対して、好ましくは５０モル％以下、より好ましくは３０モル％以下、更に好ましくは２０モル％以下、更により好ましくは１０モル％以下、特に好ましくは５モル％以下であり、好ましくは０．１モル％以上、より好ましくは０．５モル％以上、更に好ましくは１モル％以上、更により好ましくは２モル％以上、特に好ましくは３モル％以上である。上記他の構成単位の含有量が前記下限値以上であり、前記上限値以下であると、本発明の保水材のより優れた吸水量または吸水速度を得やすい。 The acrylamide-based polymer contains other structural units other than the acrylamide-derived structural unit. Examples of the above other building blocks include vinyl alcohol units; building blocks derived from vinyl carboxylates such as vinyl acetate and vinyl pivalate; building blocks derived from olefins such as ethylene, 1-butene, and isobutylene; acrylic acid and Derivatives thereof, methacrylic acid and its derivatives, methacrylicamide and its derivatives, maleic acid and its derivatives, structural units derived from maleimide derivatives and the like; and the like can be mentioned. The other constituent units may contain one kind or a plurality of kinds. The content of the other structural units is preferably 50 mol% or less, more preferably 30 mol% or less, still more preferably 20 mol% or less, still more preferably 10 with respect to all the structural units of the acrylamide-based polymer. Mol% or less, particularly preferably 5 mol% or less, preferably 0.1 mol% or more, more preferably 0.5 mol% or more, still more preferably 1 mol% or more, still more preferably 2 mol% or more, Particularly preferably, it is 3 mol% or more. When the content of the other structural units is at least the lower limit value and at least the upper limit value, it is easy to obtain a better water absorption amount or water absorption rate of the water retention material of the present invention.
　アクリルアミド系重合体の重量平均分子量に特に制限はないが、製造容易性の観点から、好ましくは１０，０００，０００以下、より好ましくは５，０００，０００以下、更に好ましくは３，０００，０００以下、特に好ましくは１，０００，０００以下である。一方、アクリルアミド系重合体の力学特性および水への耐溶出性の観点からは、重量平均分子量は、好ましくは１０００以上、より好ましくは５０００以上、更に好ましくは１００００以上である。アクリルアミド系重合体の重量平均分子量は、例えばＧＰＣにより測定できる。アクリルアミド系重合体が後述のように架橋構造を有する場合、例えばアクリルアミド系重合体が架橋構造としてアセタール構造またはエステル構造を有する場合、重量平均分子量の測定は、架橋構造を切断した後に行うことができる。前記切断は、一般的な方法（例えば、酸若しくはアルカリを用いた加水分解）により行うことができる。 The weight average molecular weight of the acrylamide polymer is not particularly limited, but from the viewpoint of ease of production, it is preferably 1,000,000 or less, more preferably 5,000,000 or less, still more preferably 3,000,000 or less. , Particularly preferably 1,000,000 or less. On the other hand, from the viewpoint of the mechanical properties of the acrylamide polymer and the elution resistance to water, the weight average molecular weight is preferably 1000 or more, more preferably 5000 or more, still more preferably 10,000 or more. The weight average molecular weight of the acrylamide polymer can be measured by, for example, GPC. When the acrylamide-based polymer has a crosslinked structure as described later, for example, when the acrylamide-based polymer has an acetal structure or an ester structure as the crosslinked structure, the weight average molecular weight can be measured after the crosslinked structure is cut. .. The cutting can be performed by a general method (for example, hydrolysis using an acid or an alkali).
　アクリルアミド系重合体は、潅水によるアクリルアミド系重合体の溶出を抑制する観点から、架橋構造を含むことが好ましい。架橋構造の形態に特に制限はなく、一般的な架橋剤による架橋構造を挙げることができる。アクリルアミド系重合体中の架橋構造の有無は、先に述べたように、例えば１００℃の熱水またはジメチルスルホキシド中での溶出率により調べることができる。 The acrylamide polymer preferably contains a crosslinked structure from the viewpoint of suppressing elution of the acrylamide polymer due to irrigation. The form of the cross-linked structure is not particularly limited, and examples thereof include a cross-linked structure using a general cross-linking agent. As described above, the presence or absence of the crosslinked structure in the acrylamide-based polymer can be examined by, for example, the elution rate in hot water or dimethyl sulfoxide at 100 ° C.
　架橋構造は、例えば、アクリルアミド由来構成単位をもたらすモノマーとアクリルアミド由来構成単位以外の他の構成単位をもたらすモノマーとの共重合工程において共重合反応と同時に形成されてもよいし、共重合反応工程以外の別の工程であって後述する凝集工程の前に架橋剤を更に添加することにより凝集工程の前に形成されてもよいし、凝集工程において架橋剤を更に添加することにより凝集工程と同時に形成されてもよいし、凝集工程後に架橋剤を更に添加することにより凝集工程の後に形成されてもよい。本発明においては、架橋剤を更に添加することにより架橋構造を形成することが好ましい。 The crosslinked structure may be formed at the same time as the copolymerization reaction in the copolymerization step of, for example, the monomer resulting in the acrylamide-derived structural unit and the monomer resulting in other structural units other than the acrylamide-derived structural unit, or may be formed at the same time as the copolymerization reaction step. In another step, it may be formed before the aggregation step by further adding a cross-linking agent before the aggregation step described later, or it may be formed at the same time as the aggregation step by further adding a cross-linking agent in the aggregation step. It may be formed after the aggregation step by further adding a cross-linking agent after the aggregation step. In the present invention, it is preferable to form a crosslinked structure by further adding a crosslinking agent.
　架橋剤の例としては、Ｎ，Ｎ’－メチレンビスアクリルアミド、ジビニルベンゼン、エチレングリコールジグリシジルエーテル、ペンタエリスリトールトリアリルエーテル、ペンタエリスリトールトリアクリレート、ペンタエリスリトールテトラアクリレート、１，６－ヘキサンジオールジアクリレート、１，９－ノナンジオールジアクリレート、１，１０－デカンジオールジアクリレート、ネオペンチルグリコールジアクリレート、２－ヒドロキシ－３－メタクリルプロピルアクリレート、ポリエチレングリコールジアクリレート、ポリプロピレングリコールジアクリレート、トリメチロールプロパントリアクリレートおよびトリス－（２－アクリロキシエチル）イソシアヌレート等を挙げることができる。 Examples of cross-linking agents include N, N'-methylenebisacrylamide, divinylbenzene, ethylene glycol diglycidyl ether, pentaerythritol triallyl ether, pentaerythritol triacrylate, pentaerythritol tetraacrylate, 1,6-hexanediol diacrylate, 1,9-Nonandiol diacrylate, 1,10-decanediol diacrylate, neopentyl glycol diacrylate, 2-hydroxy-3-methacrylicpropyl acrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, trimethyl propanetriacrylate and Tris- (2-acryloxyethyl) isocyanurate and the like can be mentioned.
　架橋剤を添加する場合、アクリルアミド系重合体中の架橋剤量としては、土壌中での保水性を維持しやすい観点から、好ましくは０．００１モル％以上、より好ましくは０．００５モル％以上、更に好ましくは０．０１モル％以上、より更に好ましくは０．０３モル％以上であり、好ましくは０．５モル％以下、より好ましくは０．４モル％以下、更に好ましくは０．３モル％以下である。 When a cross-linking agent is added, the amount of the cross-linking agent in the acrylamide-based polymer is preferably 0.001 mol% or more, more preferably 0.005 mol% or more, from the viewpoint of easily maintaining water retention in the soil. More preferably 0.01 mol% or more, still more preferably 0.03 mol% or more, preferably 0.5 mol% or less, more preferably 0.4 mol% or less, still more preferably 0.3 mol. % Or less.
　アクリルアミド系重合体の具体的な例としては、アクリルアミド－アクリル酸－アクリル酸ナトリウム共重合体の架橋物、およびアクリルアミド－アクリル酸－アクリル酸カリウム共重合体の架橋物等を挙げることができる。市販品としては、Ｍｉｒａｃｌｅ－Ｇｒｏ（登録商標）ウォーターストアーリングクリスタル（Ｓｃｏｔｔｓ　Ｍｉｒａｃｌｅ－Ｇｒｏ社製）、およびアクアソーブ（登録商標）（株式会社ＳＮＦホールディングカンパニー製）等を挙げることができる。 Specific examples of the acrylamide-based polymer include a crosslinked product of an acrylamide-acrylic acid-sodium acrylate copolymer and a crosslinked product of an acrylamide-acrylic acid-potassium acrylate copolymer. Examples of commercially available products include Miracle-Gro (registered trademark) water storing crystal (manufactured by ScottsMiracle-Gro) and Aquasorb (registered trademark) (manufactured by SNF Holding Company).
＜メタクリル酸系重合体＞
　本発明における吸水性樹脂が含んでもよいメタクリル酸系重合体は、メタクリル酸またはメタクリル酸誘導体に由来する構成単位（以下、「メタクリル酸由来構成単位」と称する）を、全構成単位の中で最も多い含有量で含む。メタクリル酸系重合体の原料の例としては、メタクリル酸、メタクリル酸ナトリウム、メタクリル酸メチル、メタクリル酸エチル、メタクリル酸ブチル、メタクリル酸プロピル、メタクリル酸イソプロピル、メタクリル酸シクロヘキシル、メタクリル酸フェニル、メタクリル酸（２－エチルヘキシル）、メタクリル酸（ｔ－ブチルシクロヘキシル）、メタクリル酸ベンジルおよびメタクリル酸（２，２，２－トリフルオロエチル）およびトリメチル［３－（メタクリロイルアミノ）プロピル］アミニウム・クロリドを挙げることができる。これら１種または２種以上のモノマーと共重合が可能な他の少なくとも１種のモノマーとを公知の方法を用いて共重合させたものを、メタクリル酸系重合体の例として挙げることができる。共重合が可能な他のモノマーの例としては、後述する、メタクリル酸由来構成単位以外の他の構成単位をもたらすモノマーを挙げることができる。
　吸水性樹脂におけるメタクリル酸系重合体の含有量は、好ましくは７０質量％以上、より好ましくは８０質量％以上、更に好ましくは９０質量％以上、特に好ましくは９５質量％以上であり、１００質量％であってもよい。 <Methacrylic acid polymer>
In the methacrylic acid-based polymer that may be contained in the water-absorbent resin in the present invention, the structural unit derived from methacrylic acid or a methacrylic acid derivative (hereinafter referred to as “methacrylic acid-derived structural unit”) is the most among all the structural units. Contains high content. Examples of raw materials for methacrylic acid-based polymers include methacrylic acid, sodium methacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, propyl methacrylate, isopropyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, and methacrylic acid ( 2-Ethylhexyl), methacrylic acid (t-butylcyclohexyl), benzyl methacrylate and methacrylic acid (2,2,2-trifluoroethyl) and trimethyl [3- (methacryloylamino) propyl] aminium chloride can be mentioned. .. Examples of the methacrylic acid-based polymer include those obtained by copolymerizing one or more of these monomers with at least one other monomer copolymerizable by a known method. Examples of other monomers capable of copolymerization include monomers that bring about other structural units other than the methacrylic acid-derived structural units, which will be described later.
The content of the methacrylic acid polymer in the water-absorbent resin is preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, particularly preferably 95% by mass or more, and 100% by mass. May be.
　本発明の一実施態様において、メタクリル酸系重合体が有するイオン性基（例えばカルボキシル基）の一部または全部は、塩（イオン性基がカルボキシル基の場合はカルボン酸塩）の形態であってもよい。塩のカウンターカチオンの例としては、リチウムイオン、ナトリウムイオン、カリウムイオン、ルビジウムイオン、およびセシウムイオン等のアルカリ金属イオン；マグネシウムイオン、カルシウムイオン、ストロンチウムイオン、およびバリウムイオン等のアルカリ土類金属イオン；アルミニウムイオン、および亜鉛イオン等のその他金属イオン；アンモニウムイオン、イミダゾリウム類、ピリジニウム類、およびホスホニウムイオン類等のオニウムカチオン；等を挙げることができる。中でも、より好ましい吸水量または吸水速度を得やすい観点から、カリウムイオン、アンモニウムイオン、カルシウムイオン、およびマグネシウムイオンが好ましい。植物の生育の観点からはカリウムイオン、およびアンモニウムイオンがより好ましく、土壌中に含まれる二価イオンとの接触時にも吸液量または吸液速度を維持しやすい観点からはカルシウムイオンがより好ましい。 In one embodiment of the present invention, a part or all of the ionic group (for example, carboxyl group) contained in the methacrylic acid polymer is in the form of a salt (carboxylate when the ionic group is a carboxyl group). May be good. Examples of salt counter cations are alkali metal ions such as lithium ion, sodium ion, potassium ion, rubidium ion, and cesium ion; alkaline earth metal ions such as magnesium ion, calcium ion, strontium ion, and barium ion; Examples thereof include aluminum ions and other metal ions such as zinc ions; onium cations such as ammonium ions, imidazoliums, pyridiniums, and phosphonium ions; and the like. Of these, potassium ion, ammonium ion, calcium ion, and magnesium ion are preferable from the viewpoint of easily obtaining a more preferable water absorption amount or water absorption rate. Potassium ions and ammonium ions are more preferable from the viewpoint of plant growth, and calcium ions are more preferable from the viewpoint of easily maintaining the amount of liquid absorbed or the rate of liquid absorption even when in contact with divalent ions contained in the soil.
　メタクリル酸系重合体中のイオン性基の含有量は、メタクリル酸系重合体の全構成単位に対して０．１モル％以上、好ましくは１モル％以上、より好ましくは３モル％以上、更に好ましくは４モル％以上、特に好ましくは５モル％以上であり、５０モル％以下、好ましくは４０モル％以下、より好ましくは３０モル％以下、更に好ましくは２５モル％以下、更により好ましくは２０モル％以下、特に好ましくは１５モル％以下、更に特に好ましくは１０モル％以下である。上記イオン性基の含有量が前記下限値以上であると、メタクリル酸系重合体は、より向上した吸水量または吸水速度を有しやすい。上記イオン性基の含有量が前記上限値以下であると、メタクリル酸系重合体は、土壌中に含まれる二価イオンとの接触時にも優れた吸液量または吸液速度を維持しやすく、この吸液量または吸液速度は、長期間にわたって低下しにくく、紫外線によるメタクリル酸系重合体の分解が起こりにくい。 The content of the ionic group in the methacrylic acid-based polymer is 0.1 mol% or more, preferably 1 mol% or more, more preferably 3 mol% or more, and further, with respect to all the constituent units of the methacrylic acid-based polymer. It is preferably 4 mol% or more, particularly preferably 5 mol% or more, 50 mol% or less, preferably 40 mol% or less, more preferably 30 mol% or less, still more preferably 25 mol% or less, still more preferably 20. It is mol% or less, particularly preferably 15 mol% or less, and even more preferably 10 mol% or less. When the content of the ionic group is at least the above lower limit value, the methacrylic acid-based polymer tends to have a higher water absorption amount or water absorption rate. When the content of the ionic group is not more than the upper limit, the methacrylic acid-based polymer can easily maintain an excellent liquid absorption amount or liquid absorption rate even when in contact with divalent ions contained in the soil. This liquid absorption amount or liquid absorption rate is unlikely to decrease over a long period of time, and decomposition of the methacrylic acid-based polymer by ultraviolet rays is unlikely to occur.
　また、メタクリル酸系重合体がイオン性基としてカルボキシル基を有する場合、上記カルボキシル基のうちメタクリル酸またはその塩に由来するカルボキシル基の量は、メタクリル酸系重合体の全構成単位に対して、好ましくは２０モル％以下、より好ましくは１５モル％以下、特に好ましくは１０モル％以下であり、０モル％であってもよい。上記カルボキシル基のうちメタクリル酸またはその塩に由来するカルボキシル基の量が前記上限値以下であると、より優れた耐候性（特に耐紫外線性）を得やすい。
　好ましい一実施態様において、メタクリル酸系重合体に含まれるイオン性基の半分以上は誘導体の形態であり、より好ましい一実施態様において、メタクリル酸系重合体に含まれるイオン性基のほとんどは誘導体の形態であり、特に好ましい一実施態様において、メタクリル酸系重合体に含まれるイオン性基の全ては誘導体の形態である。 When the methacrylic acid-based polymer has a carboxyl group as an ionic group, the amount of the carboxyl group derived from methacrylic acid or a salt thereof among the above-mentioned carboxyl groups is relative to all the constituent units of the methacrylic acid-based polymer. It is preferably 20 mol% or less, more preferably 15 mol% or less, particularly preferably 10 mol% or less, and may be 0 mol%. When the amount of the carboxyl group derived from methacrylic acid or a salt thereof among the above-mentioned carboxyl groups is not more than the upper limit value, more excellent weather resistance (particularly ultraviolet resistance) can be easily obtained.
In one preferred embodiment, more than half of the ionic groups contained in the methacrylic acid polymer are in the form of derivatives, and in a more preferred embodiment, most of the ionic groups contained in the methacrylic acid polymer are derivatives. In one particularly preferred embodiment, all of the ionic groups contained in the methacrylic acid polymer are in the form of derivatives.
　メタクリル酸系重合体のメタクリル酸由来構成単位の含有量は、上記メタクリル酸系重合体の全構成単位に対して好ましくは２０モル％超、より好ましくは５０モル％以上、更に好ましくは６０モル％以上であり、好ましくは９８モル％以下、より好ましくは９５モル％以下、更に好ましくは９０モル％以下である。 The content of the methacrylic acid-derived structural unit of the methacrylic acid-based polymer is preferably more than 20 mol%, more preferably 50 mol% or more, still more preferably 60 mol% with respect to all the structural units of the methacrylic acid-based polymer. The above is preferably 98 mol% or less, more preferably 95 mol% or less, still more preferably 90 mol% or less.
　メタクリル酸系重合体は、メタクリル酸由来構成単位以外の他の構成単位を含む。上記他の構成単位の例としては、ビニルアルコール単位；酢酸ビニル、およびピバル酸ビニル等のカルボン酸ビニル由来の構成単位；エチレン、１－ブテン、およびイソブチレン等のオレフィン由来の構成単位；アクリル酸およびその誘導体、アクリルアミドおよびその誘導体、メタクリルアミドおよびその誘導体、マレイン酸およびその誘導体、およびマレイミド誘導体等に由来する構成単位；等を挙げることができる。上記他の構成単位は１種を含有していても複数種を含有していてもよい。上記他の構成単位の含有量は、メタクリル酸系重合体の全構成単位に対して、好ましくは５０モル％以下、より好ましくは４０モル％以下、更に好ましくは３０モル％以下、更により好ましくは２０モル％以下、特に好ましくは１０モル％以下であり、好ましくは０．１モル％以上、より好ましくは０．５モル％以上、更に好ましくは１モル％以上、更により好ましくは２モル％以上、特に好ましくは３モル％以上である。上記他の構成単位の含有量が前記下限値以上であり、前記上限値以下であると、本発明の保水材のより優れた吸水量または吸水速度を得やすい。 The methacrylic acid-based polymer contains other structural units other than the methacrylic acid-derived structural unit. Examples of the above other building blocks include vinyl alcohol units; building blocks derived from vinyl carboxylates such as vinyl acetate and vinyl pivalate; building blocks derived from olefins such as ethylene, 1-butene, and isobutylene; acrylic acids and Constituent units derived from its derivatives, acrylamide and its derivatives, methacrylicamide and its derivatives, maleic acid and its derivatives, maleimide derivatives and the like; and the like can be mentioned. The other constituent units may contain one type or a plurality of types. The content of the other structural units is preferably 50 mol% or less, more preferably 40 mol% or less, still more preferably 30 mol% or less, still more preferably 30 mol% or less, based on all the structural units of the methacrylic acid-based polymer. 20 mol% or less, particularly preferably 10 mol% or less, preferably 0.1 mol% or more, more preferably 0.5 mol% or more, still more preferably 1 mol% or more, still more preferably 2 mol% or more. , Particularly preferably 3 mol% or more. When the content of the other structural units is at least the lower limit value and at least the upper limit value, it is easy to obtain a better water absorption amount or water absorption rate of the water retention material of the present invention.
　メタクリル酸系重合体の重量平均分子量に特に制限はないが、製造容易性の観点から、好ましくは１０，０００，０００以下、より好ましくは５，０００，０００以下、更に好ましくは３，０００，０００以下、特に好ましくは１，０００，０００以下である。一方、メタクリル酸系重合体の力学特性および水への耐溶出性の観点からは、重量平均分子量は、好ましくは１０００以上、より好ましくは５０００以上、更に好ましくは１００００以上である。メタクリル酸系重合体の重量平均分子量は、例えばＧＰＣにより測定できる。メタクリル酸系重合体が後述のように架橋構造を有する場合、例えばメタクリル酸系重合体が架橋構造としてアセタール構造またはエステル構造を有する場合、重量平均分子量の測定は、架橋構造を切断した後に行うことができる。前記切断は、一般的な方法（例えば、酸若しくはアルカリを用いた加水分解）により行うことができる。 The weight average molecular weight of the methacrylic acid polymer is not particularly limited, but from the viewpoint of ease of production, it is preferably 1,000,000 or less, more preferably 5,000,000 or less, still more preferably 3,000,000 or less. Below, it is particularly preferably 1,000,000 or less. On the other hand, from the viewpoint of the mechanical properties of the methacrylic acid polymer and the elution resistance to water, the weight average molecular weight is preferably 1000 or more, more preferably 5000 or more, still more preferably 10,000 or more. The weight average molecular weight of the methacrylic acid polymer can be measured by, for example, GPC. When the methacrylic acid polymer has a crosslinked structure as described later, for example, when the methacrylic acid polymer has an acetal structure or an ester structure as a crosslinked structure, the weight average molecular weight should be measured after the crosslinked structure is cut. Can be done. The cutting can be performed by a general method (for example, hydrolysis using an acid or an alkali).
　メタクリル酸系重合体は、潅水によるメタクリル酸系重合体の溶出を抑制する観点から、架橋構造を含むことが好ましい。架橋構造の形態に特に制限はなく、一般的な架橋剤による架橋構造を挙げることができる。メタクリル酸系重合体中の架橋構造の有無は、先に述べたように、例えば１００℃の熱水またはジメチルスルホキシド中での溶出率により調べることができる。 The methacrylic acid-based polymer preferably contains a crosslinked structure from the viewpoint of suppressing elution of the methacrylic acid-based polymer due to irrigation. The form of the cross-linked structure is not particularly limited, and examples thereof include a cross-linked structure using a general cross-linking agent. As described above, the presence or absence of the crosslinked structure in the methacrylic acid-based polymer can be examined by, for example, the elution rate in hot water or dimethyl sulfoxide at 100 ° C.
　架橋構造は、例えば、メタクリル酸由来構成単位をもたらすモノマーとメタクリル酸由来構成単位以外の他の構成単位をもたらすモノマーとの共重合工程において共重合反応と同時に形成されてもよいし、共重合反応工程以外の別の工程であって後述する凝集工程の前に架橋剤を更に添加することにより凝集工程の前に形成されてもよいし、凝集工程において架橋剤を更に添加することにより凝集工程と同時に形成されてもよいし、凝集工程後に架橋剤を更に添加することにより凝集工程の後に形成されてもよい。本発明においては、架橋剤を更に添加することにより架橋構造を形成することが好ましい。 The crosslinked structure may be formed at the same time as the copolymerization reaction in the copolymerization step of, for example, a monomer which brings about a structural unit derived from methacrylic acid and a monomer which brings about a structural unit other than the structural unit derived from methacrylic acid, or the copolymerization reaction. It may be formed before the aggregation step by further adding a cross-linking agent before the aggregation step described later in another step other than the step, or it may be formed by further adding the cross-linking agent in the aggregation step. It may be formed at the same time, or it may be formed after the aggregation step by further adding a cross-linking agent after the aggregation step. In the present invention, it is preferable to form a crosslinked structure by further adding a crosslinking agent.
　架橋剤の例としては、Ｎ，Ｎ’－メチレンビスアクリルアミド、ジビニルベンゼン、エチレングリコールジグリシジルエーテル、ペンタエリスリトールトリアリルエーテル、ペンタエリスリトールトリおよびテトラアクリレート、１，６－ヘキサンジオールジアクリレート、１，９－ノナンジオールジアクリレート、１，１０－デカンジオールジアクリレート、ネオペンチルグリコールジアクリレート、２－ヒドロキシ－３－メタクリルプロピルアクリレート、ポリエチレングリコールジアクリレート、ポリプロピレングリコールジアクリレート、トリメチロールプロパントリアクリレートおよびトリス－（２－アクリロキシエチル）イソシアヌレート等を挙げることができる。 Examples of cross-linking agents include N, N'-methylenebisacrylamide, divinylbenzene, ethylene glycol diglycidyl ether, pentaerythritol triallyl ether, pentaerythritol tri and tetraacrylate, 1,6-hexanediol diacrylate, 1,9. -Nonandiol diacrylate, 1,10-decanediol diacrylate, neopentyl glycol diacrylate, 2-hydroxy-3-methacrylicpropyl acrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, trimethylolpropane triacrylate and tris- ( 2-Acryloxyethyl) isocyanurate and the like can be mentioned.
　架橋剤を添加する場合、メタクリル酸系重合体中の架橋剤量としては、土壌中での保水性を維持しやすい観点から、好ましくは０．００１モル％以上、より好ましくは０．００５モル％以上、更に好ましくは０．０１モル％以上、より更に好ましくは０．０３モル％以上であり、好ましくは０．５モル％以下、より好ましくは０．４モル％以下、更に好ましくは０．３モル％以下である。 When a cross-linking agent is added, the amount of the cross-linking agent in the methacrylic acid-based polymer is preferably 0.001 mol% or more, more preferably 0.005 mol%, from the viewpoint of easily maintaining water retention in the soil. The above is more preferably 0.01 mol% or more, still more preferably 0.03 mol% or more, preferably 0.5 mol% or less, more preferably 0.4 mol% or less, still more preferably 0.3. It is less than mol%.
　メタクリル酸系重合体の具体的な例としては、メタクリル酸－メタクリル酸ナトリウム共重合体の架橋物、およびメタクリル酸－メタクリル酸ナトリウム－アクリル酸共重合体の架橋物等を挙げることができる。 Specific examples of the methacrylic acid-based polymer include a crosslinked product of a methacrylic acid-sodium methacrylate copolymer and a crosslinked product of a methacrylic acid-sodium methacrylate-acrylic acid copolymer.
＜任意の添加剤＞
　本発明の保水材は、吸水性樹脂に加えて、任意に添加剤を含有してよい。そのような添加剤の例としては、デンプン、変性デンプン、アルギン酸ナトリウム、キチン、キトサン、セルロースおよびその誘導体等の多糖類；エチレン－プロピレン共重合体、ポリスチレン、アクリロニトリル－スチレン共重合体、アクリロニトリル－ブタジエン－スチレン共重合体、ポリ塩化ビニル、ポリカーボネート樹脂、ポリエチレンテレフタレート、ポリブチレンテレフタレート、ポリ乳酸、ポリコハク酸、ポリアミド６、ポリアミド６・６、ポリアミド６・１０、ポリアミド１１、ポリアミド１２、ポリアミド６・１２、ポリヘキサメチレンジアミンテレフタルアミド、ポリヘキサメチレンジアミンイソフタルアミド、ポリノナメチレンジアミンテレフタルアミド、ポリフェニレンエーテル、ポリオキシメチレン、ポリプロピレングリコール、ポリトリメチレングリコール、ポリテトラメチレングリコール、ポリ酢酸ビニル、エチレン－酢酸ビニル共重合体、ポリアクリル酸、ポリアクリル酸エステル、ポリアクリル酸塩、ポリアクリルアミド、ポリメタクリル酸、ポリメタクリル酸エステル、ポリメタクリル酸塩、エチレン－アクリル酸共重合体、エチレン－アクリル酸エステル共重合体、エチレン－アクリル酸塩共重合体、エチレン－メタクリル酸共重合体、エチレン－メタクリル酸エステル共重合体、およびエチレン－メタクリル酸塩共重合体等の樹脂類；天然ゴム、合成イソプレンゴム、クロロプレンゴム、シリコーンゴム、フッ素ゴム、ウレタンゴム、アクリルゴム、スチレン系熱可塑性エラストマー、オレフィン系熱可塑性エラストマー、エステル系熱可塑性エラストマー、ウレタン系熱可塑性エラストマー、およびアミド系熱可塑性エラストマー等のゴム・エラストマー類；タルク、滑石、炭酸カルシウム、クレイ、シリカなどの無機鉱物類；紫外線吸収剤、酸化防止剤、光安定剤、可塑剤、有機溶媒、消泡剤、増粘剤、界面活性剤、滑剤、防カビ剤および帯電防止剤等を挙げることができる。これらの添加剤は、１種を単独でまたは２種以上を組み合わせて使用できる。また、添加剤の例として挙げられている樹脂はいずれも、本発明の吸水性樹脂とは異なる。
　保水材が添加剤を含有する場合、その合計含有量は本発明の効果を損なわない範囲であればよく、保水材の総質量に対して通常は２０質量％以下、好ましくは１５質量％以下、より好ましくは１０質量％以下、例えば５質量％以下である。
　なお、保水材若しくは後述する培地における構成成分〔即ち、吸水性樹脂、上述した任意の添加剤、または後述する任意の成分（Ｚ）〕、または後述する製造工程において用いる成分（例えば吸水性樹脂等）の含有量若しくは質量について述べるとき、その含有量若しくは質量は、乾燥状態の質量に基づく。本発明において「乾燥状態」とは、当該構成成分が水または有機溶媒等の揮発成分を含んでいない状態のことを言う。例えば、当該構成成分それぞれの質量が恒量となるまで４０℃で真空乾燥を行うことで、それらを乾燥状態とすることができる。 <Any additive>
The water-retaining material of the present invention may optionally contain an additive in addition to the water-absorbent resin. Examples of such additives are polysaccharides such as starch, modified starch, sodium alginate, chitin, chitosan, cellulose and derivatives thereof; ethylene-propylene copolymer, polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-butadiene. -Sterethane copolymer, polyvinyl chloride, polycarbonate resin, polyethylene terephthalate, polybutylene terephthalate, polylactic acid, polysuccinic acid, polyamide 6, polyamide 6.6, polyamide 6/10, polyamide 11, polyamide 12, polyamide 6/12, Polyhexamethylene diamine terephthalamide, polyhexamethylene diamine isophthalamide, polynonamethylene diamine terephthalamide, polyphenylene ether, polyoxymethylene, polypropylene glycol, polytrimethylene glycol, polytetramethylene glycol, polyvinyl acetate, ethylene-vinyl acetate Polymer, polyacrylic acid, polyacrylic acid ester, polyacrylic acid salt, polyacrylamide, polymethacrylic acid, polymethacrylic acid ester, polymethacrylate, ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer Resins such as ethylene-acrylate copolymer, ethylene-methacrylic acid copolymer, ethylene-methacrylic acid ester copolymer, and ethylene-methacrylate copolymer; natural rubber, synthetic isoprene rubber, chloroprene rubber. , Silicone rubber, fluororubber, urethane rubber, acrylic rubber, styrene-based thermoplastic elastomer, olefin-based thermoplastic elastomer, ester-based thermoplastic elastomer, urethane-based thermoplastic elastomer, and rubber / elastomers such as amide-based thermoplastic elastomer; Inorganic minerals such as talc, talc, calcium carbonate, clay, silica; UV absorbers, antioxidants, light stabilizers, plasticizers, organic solvents, defoaming agents, thickeners, surfactants, lubricants, antifungal agents. Agents, antistatic agents and the like can be mentioned. These additives may be used alone or in combination of two or more. Further, all the resins listed as examples of additives are different from the water-absorbent resin of the present invention.
When the water-retaining material contains an additive, the total content thereof may be as long as it does not impair the effect of the present invention, and is usually 20% by mass or less, preferably 15% by mass or less, based on the total mass of the water-retaining material. More preferably, it is 10% by mass or less, for example, 5% by mass or less.
In addition, a component in a water-retaining material or a medium described later [that is, a water-absorbent resin, an optional additive described above, or an optional component (Z) described later], or a component used in a manufacturing process described later (for example, a water-absorbent resin, etc.) ), The content or mass is based on the dry mass. In the present invention, the "dry state" means a state in which the constituent component does not contain a volatile component such as water or an organic solvent. For example, they can be put into a dry state by vacuum drying at 40 ° C. until the mass of each of the constituents becomes constant.
　本発明の農業用保水材は、必要に応じて任意の成分（Ｚ）と組み合わせて、培地に使用でき、その中でも例えば育苗のための培地に使用できる。従って、一実施態様において、本発明の保水材は育苗用である。本発明の保水材は、優れた吸水速度を示すことができるため、培地に用いた場合、潅水時に保水材が吸水する前に水が流出することに起因する水の利用効率の低下を抑制することができる。また、ベルトコンベヤー等を用いて流れ作業で製造されることの多い水稲育苗箱の製造において、種籾を播種する培地の構成成分として保水材を用いる場合に、培地は十分な吸水速度を示すことができる。 The agricultural water-retaining material of the present invention can be used as a medium in combination with an arbitrary component (Z) as needed, and among them, for example, it can be used as a medium for raising seedlings. Therefore, in one embodiment, the water-retaining material of the present invention is for raising seedlings. Since the water-retaining material of the present invention can exhibit an excellent water absorption rate, when used as a medium, it suppresses a decrease in water utilization efficiency due to water flowing out before the water-retaining material absorbs water during irrigation. be able to. In addition, in the production of paddy rice seedling boxes, which are often produced by assembly line using a belt conveyor or the like, when a water-retaining material is used as a component of the medium for sowing seeds, the medium may exhibit a sufficient water absorption rate. can.
［任意の成分（Ｚ）］
　そのような任意の成分（Ｚ）の例としては、保水材に含まれる吸水性樹脂以外の樹脂、培土、後述するその他の任意成分、およびそれらの組み合わせを挙げることができる。 [Arbitrary component (Z)]
Examples of such an arbitrary component (Z) include resins other than the water-absorbent resin contained in the water-retaining material, hilling, other optional components described later, and combinations thereof.
＜吸水性樹脂以外の樹脂＞
　吸水性樹脂以外の樹脂の例としては、ポリエチレン、ポリプロピレン、アルキッド樹脂、フェノール樹脂、ポリエチレングリコール、およびポリウレタンを挙げることができる。これらの樹脂は、単独でまたは２つ以上を組み合わせて使用できる。培地が上記樹脂を含む場合、その合計含有量は、培地の総質量に対して好ましくは２０質量％以下、より好ましくは１０質量％以下、特に好ましくは５質量％以下である。 <Resin other than water-absorbent resin>
Examples of resins other than the water-absorbent resin include polyethylene, polypropylene, alkyd resin, phenolic resin, polyethylene glycol, and polyurethane. These resins can be used alone or in combination of two or more. When the medium contains the above resin, the total content thereof is preferably 20% by mass or less, more preferably 10% by mass or less, and particularly preferably 5% by mass or less, based on the total mass of the medium.
＜培土＞
　培地が培土を含む場合、培土の間隙に根が生長することで適当に根が互いに絡み合いやすくなり、また、培地の優れた排水性および通気性を得やすくなる。培土は特に限定されず、例えば、市販の培土の１種を単独でまたは２種以上を組み合わせて用いることができる。また、培土に、後述するその他の任意成分を常法（例えば、その他の任意成分の溶液または分散液を培土に噴霧した後に乾燥させる方法）で付着させ、用いることもできる。 <Hilling>
When the medium contains hilling soil, the roots grow in the gaps of the hilling soil so that the roots can be appropriately entangled with each other, and the excellent drainage and air permeability of the medium can be easily obtained. The hilling is not particularly limited, and for example, one kind of commercially available hilling can be used alone or in combination of two or more kinds. Further, other optional components described later may be attached to the soil by a conventional method (for example, a method of spraying a solution or dispersion of the other optional components on the soil and then drying it) and using the soil.
　より優れた排水性および通気性を得やすい観点から、培土は粒状であることが好ましい。粒状培土の粒径は、好ましくは０．２～２０ｍｍ、より好ましくは０．５～１０ｍｍ、特に好ましくは１～５ｍｍである。粒状培土の粒径を前記範囲内に調整するため、市販の粒状培土を篩過して用いることもできる。粒状培土の製造には、圧縮造粒法、押し出し造粒法、転動造粒法、流動層造粒法等の造粒法を用いることができる。粒状培土の粒径は、次の方法で測定できる。粒状培土から粒子をランダムに３０個選び、ノギスを用いて各粒子の直径を測定し、その平均値を粒状培土の粒径とする。なお、粒子が球状ではない場合、最も長い辺と最も短い辺の平均値をその粒子の直径とする。 From the viewpoint of obtaining better drainage and breathability, it is preferable that the soil is granular. The particle size of the granular soil is preferably 0.2 to 20 mm, more preferably 0.5 to 10 mm, and particularly preferably 1 to 5 mm. In order to adjust the particle size of the granular hilling within the above range, a commercially available granular hilling can be sieved and used. For the production of granular hilling, a granulation method such as a compression granulation method, an extrusion granulation method, a rolling granulation method, or a fluidized bed granulation method can be used. The particle size of the granular soil can be measured by the following method. Thirty particles are randomly selected from the granular culture soil, the diameter of each particle is measured using a caliper, and the average value is taken as the particle size of the granular culture soil. If the particle is not spherical, the average value of the longest side and the shortest side is taken as the diameter of the particle.
　培地が培土を含む場合、培土の含有量は、培地の総質量に対して、好ましくは２０～９９．９９９９質量％、より好ましくは７０～９９．９５質量％、特に好ましくは８０～９９．９質量％、最も好ましくは９０～９９．８質量％である。 When the medium contains soil, the content of the soil is preferably 20 to 99.9999% by mass, more preferably 70 to 99.95% by mass, and particularly preferably 80 to 99.9, based on the total mass of the medium. It is by mass, most preferably 90 to 99.8% by mass.
＜その他の任意成分＞
　その他の任意成分の例としては、泥炭、草炭、ピート、ピートモス、ココピート、籾殻、腐植酵質資材、木炭、珪藻土焼成粒、貝化石粉末、貝殻粉末、カニ殻、ＶＡ菌根菌、微生物資材等の動植物質；バーミキュライト、パーライト、ベントナイト、天然ゼオライト、合成ゼオライト、石こう、フライアッシュ、ロックウール、カオリナイト、スメクタイト、モンモリロナイト、セリサイト、クロライト、グローコナイトおよびタルク等の鉱物質；肥料およびこれらの組み合わせを挙げることができる。これらは、必要に応じて消毒または殺菌して用いてもよく、ｐＨ調整剤または農薬と一緒に用いてもよい。培地がその他の任意成分を含有する場合、その合計含有量は本発明の効果を損なわない範囲であればよく、培地の総質量に対して通常は５０質量％以下、好ましくは３０質量％以下である。 <Other optional ingredients>
Examples of other optional components include peat, grass charcoal, peat, peat moss, coco peat, rice husks, fertilizer materials, charcoal, diatomaceous earth calcined grains, shell fossil powder, shell powder, crab shells, VA mycorrhizal fungi, microbial materials, etc. Fauna and flora; vermiculite, pearlite, bentonite, natural zeolite, synthetic zeolite, peat, fly ash, rock wool, kaolinite, smectite, montmorillonite, sericite, chlorite, gloconite and talc and other minerals; fertilizer and these The combination of can be mentioned. These may be disinfected or sterilized as needed, or may be used with a pH regulator or pesticide. When the medium contains other optional components, the total content may be as long as it does not impair the effect of the present invention, and is usually 50% by mass or less, preferably 30% by mass or less, based on the total mass of the medium. be.
　肥料の例としては、窒素系肥料、リン系肥料およびカリウム系肥料の三大肥料；カルシウム、マグネシウム、硫黄、鉄、銅、マンガン、亜鉛、ホウ素、モリブデン、塩素およびニッケル等の植物に必須の要素を含む肥料；バーク堆肥、牛糞、豚糞、鶏糞、生ごみおよび剪定クズ等の堆肥等を挙げることができる。窒素系肥料の例としては、硫安、塩安、硝安、硝酸ソーダ、硝酸石灰、腐植酸アンモニア肥料、尿素、石灰窒素、硝酸アンモニア石灰、硝酸アンモニアソーダおよび硝酸苦土肥等を挙げることができ；リン系肥料の例としては、過リン酸石灰、重過リン酸石灰、熔性リン肥、腐植酸リン酸肥、焼リン、重焼リン、リンスター、苦土過リン酸、混合リン酸肥料、副産リン酸肥料および高濃度リン酸等を挙げることができ；カリウム系肥料の例としては、硫酸カリ、塩化カリ、硫酸カリ苦土、炭酸カリ、重炭酸カリおよびケイ酸カリ等を挙げることができる。これらの肥料は固形、ペースト、液体または溶液等の状態として用いてもよく、被覆肥料として用いてもよい。
　農薬の例としては、殺虫剤、殺菌剤、殺虫殺菌剤、除草剤、殺鼠剤、防腐剤、および植物生長調整剤等を挙げることができる。 Examples of fertilizers are nitrogen-based fertilizers, phosphorus-based fertilizers, and potassium-based fertilizers; essential elements for plants such as calcium, magnesium, sulfur, iron, copper, manganese, zinc, boron, molybdenum, chlorine, and nickel. Fertilizers containing; Examples include fertilizers such as bark compost, cow manure, pig manure, chicken manure, food waste and pruning waste. Examples of nitrogen-based fertilizers include sulfur-an, salt-an, glass-an, sodium nitrate, lime nitrate, ammonia fertilizer, urea, lime nitrogen, ammonia lime nitrate, ammonia sodium nitrate and fertilizer with nitrate; phosphorus. Examples of system fertilizers include perphosphate lime, heavy perphosphate lime, molten phosphoric acid fertilizer, rotten phosphate fertilizer, roasted phosphorus, heavy roasted phosphorus, phosphorus star, bitter soil perphosphate, mixed phosphate fertilizer, etc. By-product phosphoric acid fertilizer and high-concentration phosphoric acid can be mentioned; examples of potassium-based fertilizer include potassium sulfate, potassium chloride, potassium sulfate bitter soil, potassium carbonate, potassium bicarbonate and potassium silicate and the like. Can be done. These fertilizers may be used in the form of solids, pastes, liquids, solutions, etc., or may be used as coated fertilizers.
Examples of pesticides include insecticides, fungicides, insecticides, herbicides, rodenticides, preservatives, plant growth regulators and the like.
　本発明の保水材を肥料と組み合わせて培地を作製する場合、好ましい一実施態様では、肥料は被覆肥料として用いられる。被覆肥料は肥料を樹脂でコートしたものである。この樹脂は、例えばポリオレフィンであってよい。被覆肥料を用いる場合、樹脂の分解に伴い継時的に培地へ肥料を供給できる。また、粒状の被覆肥料を用いてマット苗を作製した場合、得られるマット苗の強度が高くなる傾向がある。被覆肥料の粒径は好ましくは１ｍｍ～１０ｍｍ、より好ましくは３ｍｍ～６ｍｍである。被覆肥料を用いる場合、培地における被覆肥料の含有量は、好ましくは１０～９９．９９質量％、より好ましくは１５～９０質量％、特に好ましくは２０～８０質量％、最も好ましくは３０～６０質量％である。 When the water-retaining material of the present invention is combined with fertilizer to prepare a medium, in one preferred embodiment, the fertilizer is used as a coated fertilizer. The coated fertilizer is a fertilizer coated with resin. This resin may be, for example, a polyolefin. When the coated fertilizer is used, the fertilizer can be supplied to the medium over time as the resin is decomposed. Further, when mat seedlings are produced using granular coated fertilizer, the strength of the obtained mat seedlings tends to be high. The particle size of the coated fertilizer is preferably 1 mm to 10 mm, more preferably 3 mm to 6 mm. When a coated fertilizer is used, the content of the coated fertilizer in the medium is preferably 10 to 99.99% by mass, more preferably 15 to 90% by mass, particularly preferably 20 to 80% by mass, and most preferably 30 to 60% by mass. %.
　本発明の保水材を任意の成分（Ｚ）と組み合わせて使用する場合、保水材と成分（Ｚ）とを混合して使用するか、または成分（Ｚ）を含み本発明の保水材を含まない培地において出芽を行った後に当該培地の上に本発明の保水材を撒いて使用することができる。保水材と成分（Ｚ）とを混合して使用する場合、その混合方法は特に限定されない。一般的な方法により保水材と成分（Ｚ）とを混合すればよい。出芽後に本発明の保水材を撒いて使用する場合、撒く時期は特に限定されないが、植物が乾燥に弱い育苗期間中（播種から概ね１ヵ月間）であることが好ましい。 When the water-retaining material of the present invention is used in combination with an arbitrary component (Z), the water-retaining material and the component (Z) are mixed or used, or the water-retaining material of the present invention is contained and the component (Z) is contained. After budding in a medium, the water-retaining material of the present invention can be sprinkled on the medium for use. When the water retention material and the component (Z) are mixed and used, the mixing method is not particularly limited. The water retention material and the component (Z) may be mixed by a general method. When the water-retaining material of the present invention is sprinkled and used after emergence, the sprinkling time is not particularly limited, but it is preferable that the plant is vulnerable to drought during the seedling raising period (approximately one month after sowing).
　本発明の保水材を成分（Ｚ）と組み合わせて用いる場合の保水材の量は、組み合わせる成分（Ｚ）の種類によって異なるが、培地全体の総質量に対して、通常は０．０００１質量％～２０質量％、好ましくは０．０５質量％～１５質量％、より好ましくは０．１質量％～１０質量％である。 When the water-retaining material of the present invention is used in combination with the component (Z), the amount of the water-retaining material varies depending on the type of the component (Z) to be combined, but is usually 0.0001% by mass or more with respect to the total mass of the entire medium. It is 20% by mass, preferably 0.05% by mass to 15% by mass, and more preferably 0.1% by mass to 10% by mass.
　種籾の播種は、水稲育苗培地が導入された水稲育苗箱に対して行うことが多い。通常、種籾の量は水稲育苗箱（縦２８ｃｍ×横５８ｃｍ）１箱あたり１００～５００ｇである。
　本発明の保水材が水稲育苗用である場合、本発明の保水材を任意に成分（Ｚ）と混合して、種籾を播種するための培地に使用できる。この培地は、床土（種籾を播種する前に水稲育苗箱に導入されている土）または覆土（種籾を播種した後に上から覆う土）のいずれか一方に用いてもよく、両方に用いてもよい。両方に用いる場合、培地の組成は床土と覆土で同じであっても、異なっていてもよい。また、種籾が出芽した培地の上に、本発明の保水材若しくは本発明の保水材と成分（Ｚ）との混合物を撒いてもよい。 Seed paddy is often sown in a paddy rice seedling box into which a paddy rice seedling medium has been introduced. Usually, the amount of seed paddy is 100 to 500 g per box of paddy rice seedling raising box (length 28 cm × width 58 cm).
When the water-retaining material of the present invention is for raising seedlings of paddy rice, the water-retaining material of the present invention can be arbitrarily mixed with the component (Z) and used as a medium for sowing seed rice. This medium may be used for either bed soil (soil introduced into the paddy rice seedling box before sowing seed rice) or soil covering (soil covered from above after sowing seed rice), or both. May be good. When used for both, the composition of the medium may be the same or different for the bed soil and the soil cover. Further, the water-retaining material of the present invention or a mixture of the water-retaining material of the present invention and the component (Z) may be sprinkled on the medium in which the seed paddy has sprouted.
　本発明において、保水材の吸水時間（Ｔ２）は、好ましくは１０秒以下、より好ましくは７秒以下、更に好ましくは５秒以下である。本発明において、保水材の吸水時間（Ｔ２）は、後述の実施例に記載の測定方法によって測定された吸水時間である。 In the present invention, the water absorption time (T2) of the water retention material is preferably 10 seconds or less, more preferably 7 seconds or less, still more preferably 5 seconds or less. In the present invention, the water absorption time (T2) of the water-retaining material is the water absorption time measured by the measuring method described in Examples described later.
　本発明において、吸水速度向上度は、好ましくは１．０以上、より好ましくは２．０以上、更に好ましくは３．０以上である。吸水速度向上度は、後述の実施例に記載の測定方法によって測定された吸水時間（Ｔ１）から算出した値である。 In the present invention, the degree of improvement in water absorption rate is preferably 1.0 or more, more preferably 2.0 or more, still more preferably 3.0 or more. The degree of improvement in water absorption rate is a value calculated from the water absorption time (T1) measured by the measurement method described in Examples described later.
　保水材の吸水時間（Ｔ１）は、好ましくは２００秒以下、より好ましくは３０秒以下、更に好ましくは２０秒以下である。吸水時間（Ｔ１）は、後述の実施例に記載の測定方法によって測定された吸水時間である。 The water absorption time (T1) of the water retention material is preferably 200 seconds or less, more preferably 30 seconds or less, still more preferably 20 seconds or less. The water absorption time (T1) is the water absorption time measured by the measuring method described in Examples described later.
　本発明において、保水材のカルシウム塩の存在下における吸水量は、好ましくは４ｇ／ｇ以上、より好ましくは６ｇ／ｇ以上、更に好ましくは８ｇ／ｇ以上である。保水材のカルシウム塩の存在下における吸水量は、後述の実施例に記載の通り、塩化カルシウム水溶液を用いた吸液試験により測定できる。 In the present invention, the water absorption amount of the water-retaining material in the presence of the calcium salt is preferably 4 g / g or more, more preferably 6 g / g or more, still more preferably 8 g / g or more. The amount of water absorbed in the presence of the calcium salt of the water-retaining material can be measured by a liquid absorption test using an aqueous solution of calcium chloride as described in Examples described later.
［保水材の製造方法］
　本発明の保水材は、例えば、
一次粒子として存在する吸水性樹脂を、膨潤させた状態で接触させることにより凝集させる凝集工程、および
凝集した吸水性樹脂を、０．２ＭＰａ以下の圧力下で乾燥する乾燥工程
を含む製造方法により製造できる。この製造方法を、以下において、本発明の第一実施態様の製造方法と称することがある。 [Manufacturing method of water retention material]
The water-retaining material of the present invention is, for example,
Manufactured by a manufacturing method including a coagulation step of agglomerating a water-absorbent resin existing as primary particles by contacting them in a swollen state, and a drying step of drying the agglomerated water-absorbent resin under a pressure of 0.2 MPa or less. can. Hereinafter, this manufacturing method may be referred to as a manufacturing method according to the first embodiment of the present invention.
＜凝集工程＞
　最初に、一次粒子について説明する。本発明の第一実施態様の製造方法において、凝集をしていない粒子のことを便宜的に「一次粒子」と表現する。例えば、吸水性樹脂を溶融若しくは溶媒に溶解させた後に乾燥し粉砕することにより得た粒子、モノマーを溶融若しくは溶媒に溶解させた状態で重合させ乾燥し粉砕させることにより得た粒子、または（凝集体でない）市販の吸水性樹脂若しくはそれを粉砕して得た粒子等を指す。一次粒子は、球形の粒子だけでなく、粉砕により得られるような異形の粒子でもよい。一次粒子の粒子径については、上述した「農業用保水材」の説明に記載した通りである。 <Aggregation process>
First, the primary particles will be described. In the production method of the first embodiment of the present invention, particles that are not aggregated are referred to as "primary particles" for convenience. For example, particles obtained by melting or dissolving a water-absorbent resin in a solvent and then drying and pulverizing, particles obtained by polymerizing a monomer in a melted or dissolved state in a solvent, drying and pulverizing, or (coagulation). It refers to a commercially available water-absorbent resin (not an aggregate) or particles obtained by crushing it. The primary particles are not limited to spherical particles, but may be irregular particles such as those obtained by pulverization. The particle size of the primary particles is as described in the above-mentioned explanation of "agricultural water retention material".
　前記凝集工程では、一次粒子として存在する吸水性樹脂を、膨潤させた状態で接触させることにより凝集させる。吸水性樹脂として、必要に応じて粉砕および／または篩過により一次粒子の平均粒子径を調整した吸水性樹脂を使用してよい。また、必要に応じて、凝集工程の前、凝集工程と同時、または凝集工程の後に、上述した任意の添加剤を吸水性樹脂と混合してもよい。
　本発明の一実施態様では、吸水性樹脂を膨潤させる前、一次粒子として存在する吸水性樹脂の含水率は、好ましくは１５質量％以下、より好ましくは１３質量％以下、更により好ましくは１０質量％以下、特に好ましくは５質量％以下である。前記含水率が前記上限値以下であると、良好なハンドリング性を得やすい。前記含水率の下限値は特に限定されず、０質量％以上である。含水率は、吸水性樹脂の質量と吸水性樹脂を乾燥状態になるまで乾燥させた後の質量とを用いて計算できる。 In the agglomeration step, the water-absorbent resin existing as the primary particles is agglomerated by contacting them in a swollen state. As the water-absorbent resin, a water-absorbent resin in which the average particle size of the primary particles is adjusted by pulverization and / or sieving may be used, if necessary. Further, if necessary, any of the above-mentioned additives may be mixed with the water-absorbent resin before the aggregation step, at the same time as the aggregation step, or after the aggregation step.
In one embodiment of the present invention, the water content of the water-absorbent resin existing as primary particles before swelling the water-absorbent resin is preferably 15% by mass or less, more preferably 13% by mass or less, still more preferably 10% by mass. % Or less, particularly preferably 5% by mass or less. When the water content is not more than the upper limit value, good handleability can be easily obtained. The lower limit of the water content is not particularly limited and is 0% by mass or more. The water content can be calculated using the mass of the water-absorbent resin and the mass of the water-absorbent resin after it has been dried until it becomes dry.
　第一実施態様の製造方法の凝集工程では、一次粒子として存在する吸水性樹脂を膨潤溶媒（例えば、水、メタノール、エタノール、プロパノール、ジメチルスルホキシド、Ｎ－メチルピロリドンまたは酢酸、好ましくは水）で膨潤させる際、スプレー等を用いてミスト状態で膨潤溶媒を噴霧することで、吸水性樹脂を均一に膨潤させることができる。噴霧する膨潤溶媒の量は、保水材の好ましい粒子径および／または凝集力を得やすい観点から、吸水性樹脂の質量に対して、好ましくは１質量％～５００質量％、より好ましくは５質量％～１００質量％、更に好ましくは１０質量％～５０質量％である。 In the aggregation step of the production method of the first embodiment, the water-absorbent resin existing as primary particles is swollen with a swelling solvent (for example, water, methanol, ethanol, propanol, dimethyl sulfoxide, N-methylpyrrolidone or acetic acid, preferably water). The water-absorbent resin can be uniformly swelled by spraying the swelling solvent in a mist state using a spray or the like. The amount of the swelling solvent to be sprayed is preferably 1% by mass to 500% by mass, more preferably 5% by mass, based on the mass of the water-absorbent resin, from the viewpoint of easily obtaining a preferable particle size and / or cohesive force of the water-retaining material. It is ~ 100% by mass, more preferably 10% by mass to 50% by mass.
　噴霧後は、膨潤の均一性を高めるために樹脂を撹拌するが、高いせん断力での撹拌、例えば高速回転する撹拌翼を備えた撹拌機では、一度凝集した粒子の粉砕または凝集の崩壊を招くおそれがある。このため、低いせん断力での撹拌、例えば袋に入れて振り混ぜる方法による撹拌、またはコニカルミキサー等による撹拌が好ましい。せん断力は、好ましくは１００００ＭＰａ以下、より好ましくは１００ＭＰａ以下、更に好ましくは１ＭＰａ以下である。接触させる時間は、好ましくは０．００１秒以上、より好ましくは０．１秒以上、更に好ましくは１秒以上である。 After spraying, the resin is agitated to improve the uniformity of swelling, but agitation with a high shear force, for example, a stirrer equipped with a stirring blade that rotates at high speed, causes crushing or disintegration of once agglomerated particles. There is a risk. Therefore, stirring with a low shearing force, for example, stirring by a method of putting in a bag and shaking, or stirring with a conical mixer or the like is preferable. The shear force is preferably 10000 MPa or less, more preferably 100 MPa or less, still more preferably 1 MPa or less. The contact time is preferably 0.001 seconds or longer, more preferably 0.1 seconds or longer, still more preferably 1 second or longer.
　凝集工程の前または凝集工程と同時に任意の添加剤を配合してもよく、バインダーを配合することにより、吸水性樹脂の凝集の強固さを調整できる。バインダーの例としては、吸水性樹脂以外の高分子成分、例えば、ポリビニルアルコール、エチレン－ビニルアルコール共重合体、ポリビニルブチラール、デンプン、セルロース、ポリエチレンオキシド、ポリエチレングリコール、カルボキシメチルセルロース、ポリアクリル酸およびその塩、ポリアクリルアミド、アクリル酸およびその塩とアクリルアミドとの共重合体、並びにスチレンブタジエンゴム等を挙げることができる。バインダーは１種を単独で用いてもよく、２種以上を組み合わせて用いてもよい。バインダーの添加量が多いほど凝集が強固になる。凝集が弱いほど吸水時に保水材が崩壊しやすく、高い吸水速度を発現しやすい。バインダーの添加量は、吸水性樹脂、膨潤溶媒、バインダー、および存在する場合はバインダー以外の任意の添加剤の総質量に対して、通常１０質量％以下、好ましくは５質量％以下、より好ましくは１質量％以下、更に好ましくは０．５質量％以下であり、０質量％でもよい。 Any additive may be added before the agglomeration step or at the same time as the agglomeration step, and the strength of the agglomeration of the water-absorbent resin can be adjusted by adding a binder. Examples of binders include polymer components other than water-absorbent resins, such as polyvinyl alcohol, ethylene-vinyl alcohol copolymers, polyvinyl butyral, starch, cellulose, polyethylene oxide, polyethylene glycol, carboxymethyl cellulose, polyacrylic acid and salts thereof. , Polyacrylamide, acrylic acid and its salts and copolymers of acrylamide, styrene butadiene rubber and the like. One type of binder may be used alone, or two or more types may be used in combination. The larger the amount of the binder added, the stronger the aggregation. The weaker the agglomeration, the easier it is for the water-retaining material to collapse during water absorption, and the higher the water absorption rate. The amount of the binder added is usually 10% by mass or less, preferably 5% by mass or less, more preferably 5% by mass or less, based on the total mass of the water-absorbent resin, the swelling solvent, the binder, and any additive other than the binder if present. It is 1% by mass or less, more preferably 0.5% by mass or less, and may be 0% by mass.
＜乾燥工程＞
　前記乾燥工程では、凝集した吸水性樹脂を、乾燥機を用いて、０．２ＭＰａ以下、好ましくは０．１５ＭＰａ以下、より好ましくは０．１ＭＰａ以下の圧力下、例えば真空下で乾燥する。一般的な乾燥機を使用でき、その例としては、コニカルドライヤー、および熱風乾燥機等を挙げることができる。乾燥温度は、用いる吸水性樹脂に依存するが、通常は２０～１５０℃、好ましくは４０～１００℃である。乾燥時間は、得られる保水材が乾燥状態となるよう適宜選択すればよく、通常は１～１４４０分間、好ましくは５～７２０分間である。また、必要に応じて、乾燥工程の前、乾燥工程と同時、または乾燥工程の後に、上述した任意の添加剤を凝集した吸水性樹脂と混合してもよい。 <Drying process>
In the drying step, the aggregated water-absorbent resin is dried using a dryer under a pressure of 0.2 MPa or less, preferably 0.15 MPa or less, more preferably 0.1 MPa or less, for example, under vacuum. A general dryer can be used, and examples thereof include a conical dryer and a hot air dryer. The drying temperature depends on the water-absorbent resin used, but is usually 20 to 150 ° C, preferably 40 to 100 ° C. The drying time may be appropriately selected so that the obtained water-retaining material is in a dry state, and is usually 1 to 1440 minutes, preferably 5 to 720 minutes. Further, if necessary, any of the above-mentioned additives may be mixed with the aggregated water-absorbent resin before the drying step, at the same time as the drying step, or after the drying step.
　乾燥状態では、高いせん断力で撹拌しながらの乾燥、例えば高速回転する撹拌翼を備えた乾燥機では、一度凝集した粒子の粉砕または凝集の崩壊を招くおそれがある。このため、低いせん断力での乾燥、例えば静置した状態での乾燥、またはコニカルドライヤー等による乾燥が好ましい。この工程では膨潤溶媒を完全に除去してもよいが、崩壊を抑制するという観点からは膨潤溶媒の一部を残存させてもよい。膨潤溶媒を一部残存させる場合、残存させる膨潤溶媒の量は、吸水性樹脂の質量に対して好ましくは５０質量％以下である。 In the dry state, drying while stirring with a high shearing force, for example, in a dryer equipped with a stirring blade that rotates at high speed, there is a risk of crushing particles once aggregated or causing disintegration of aggregation. Therefore, drying with a low shear force, for example, drying in a stationary state, or drying with a conical dryer or the like is preferable. In this step, the swelling solvent may be completely removed, but from the viewpoint of suppressing disintegration, a part of the swelling solvent may remain. When a part of the swelling solvent is left, the amount of the swelling solvent to be left is preferably 50% by mass or less with respect to the mass of the water-absorbent resin.
＜架橋工程＞
　前記製造方法は、前記凝集工程の前、前記凝集工程と同時、または前記凝集工程の後に、吸水性樹脂を架橋させる架橋工程を更に含んでよい。
　優れた吸水速度を得やすい観点からは、前記凝集工程の前に吸水性樹脂を架橋させる架橋工程を含むことが好ましい。この場合、架橋後の吸水性樹脂を膨潤状態で接触させることにより凝集させるが、凝集力は過度に強固ではない。このため、吸水時に保水材の膨張と崩壊とがバランス良く進行し、より好ましい吸水速度を得ることができる。
　また、吸水性樹脂表面における架橋構造の割合を増大しやすくなり、その結果、保水材からの吸水性樹脂の低い溶出率を得やすい観点、および／または均一な架橋を得やすい観点からは、架橋させる吸水性樹脂の粒子径が特定の値以下であることが好ましい。架橋させる吸水性樹脂の粒子径は、篩過により所望の値に調整できる。凝集工程の前に架橋工程を実施する場合、架橋させる吸水性樹脂の粒子径は、好ましくは２０００μｍ以下、より好ましくは１０００μｍ以下、更に好ましくは７００μｍ以下、特に好ましくは１５０μｍ以下である。前記凝集工程と同時、または前記凝集工程の後に架橋工程を実施する場合、架橋させる吸水性樹脂の粒子径は、好ましくは５０００μｍ以下、より好ましくは３０００μｍ以下、特に好ましくは２０００μｍ以下である。前記凝集工程と同時に架橋工程を実施する場合の粒子径は、架橋工程と凝集工程とが終了した時点の粒子径を指す。 <Crosslinking process>
The production method may further include a cross-linking step of cross-linking the water-absorbent resin before the agglomeration step, at the same time as the agglomeration step, or after the agglomeration step.
From the viewpoint of easily obtaining an excellent water absorption rate, it is preferable to include a cross-linking step of cross-linking the water-absorbent resin before the aggregation step. In this case, the crosslinked water-absorbent resin is agglomerated by contacting it in a swollen state, but the cohesive force is not excessively strong. Therefore, the expansion and disintegration of the water-retaining material proceed in a well-balanced manner during water absorption, and a more preferable water absorption rate can be obtained.
Further, it becomes easy to increase the proportion of the crosslinked structure on the surface of the water-absorbent resin, and as a result, from the viewpoint of easily obtaining a low elution rate of the water-absorbent resin from the water-retaining material and / or from the viewpoint of easily obtaining uniform cross-linking, cross-linking is performed. It is preferable that the particle size of the water-absorbent resin to be made is not more than a specific value. The particle size of the water-absorbent resin to be crosslinked can be adjusted to a desired value by sieving. When the crosslinking step is carried out before the aggregation step, the particle size of the water-absorbent resin to be crosslinked is preferably 2000 μm or less, more preferably 1000 μm or less, still more preferably 700 μm or less, and particularly preferably 150 μm or less. When the crosslinking step is carried out at the same time as the aggregation step or after the aggregation step, the particle size of the water-absorbent resin to be crosslinked is preferably 5000 μm or less, more preferably 3000 μm or less, and particularly preferably 2000 μm or less. The particle size when the cross-linking step is carried out at the same time as the coagulation step refers to the particle size at the time when the cross-linking step and the coagulation step are completed.
　本発明の保水材はまた、例えば、粒子として存在する吸水性樹脂を、膨潤させた状態で接触させることにより凝集させる凝集工程を含む製造方法により製造できる。この製造方法を、以下において、本発明の第二実施態様の製造方法と称することがある。 The water-retaining material of the present invention can also be produced, for example, by a production method including a coagulation step in which water-absorbent resins existing as particles are agglomerated by contacting them in a swollen state. Hereinafter, this manufacturing method may be referred to as a manufacturing method according to the second embodiment of the present invention.
＜凝集工程＞
　最初に、粒子について説明する。第二実施態様の製造方法における「粒子」には、例えば第一実施態様の製造方法における一次粒子のような凝集していない粒子、および一次粒子が凝集した凝集体（科学的には二次粒子と呼ばれることもある）の粒子のいずれも、概念として包含される。つまり、第二実施態様の製造方法では、「粒子」として、凝集をしていない粒子、凝集をしていない粒子が凝集した凝集体の粒子、または凝集をしていない粒子と凝集体の粒子との混合物のいずれを用いることも可能である。 <Aggregation process>
First, particles will be described. The "particles" in the production method of the second embodiment include non-aggregated particles such as the primary particles in the production method of the first embodiment, and aggregates in which the primary particles are aggregated (scientifically, secondary particles). Any of the particles (sometimes called) are included as a concept. That is, in the production method of the second embodiment, the "particles" include non-aggregated particles, aggregated particles in which non-aggregated particles are aggregated, or non-aggregated particles and aggregated particles. It is also possible to use any of the mixtures of.
　粒子としては、例えば、懸濁若しくは乳化状態で重合して得られた粒子、樹脂溶液をスプレードライして得られた粒子、市販の粒子状吸水性樹脂、またはそれらを粉砕して得られた粒子、第一実施態様の製造方法で用いられる一次粒子、一次粒子が凝集した粒子、或いはそれらの混合物等が挙げられる。粒子は、懸濁若しくは乳化状態での重合により得られるような球形の粒子だけでなく、粉砕により得られるような異形の粒子でもよい。粒子の粒子径は、好ましくは１μｍ以上、より好ましくは１０μｍ以上、更に好ましくは３０μｍ以上、特に好ましくは５０μｍ以上であり、好ましくは３０００μｍ以下、より好ましくは１０００μｍ以下、更に好ましくは６００μｍ以下、特に好ましくは３００μｍ以下である。粒子の平均粒子径が前記下限値以上であり、前記上限値以下であると、より好ましい吸水速度を得やすい。また、粒子の平均粒子径が前記下限値以上であると、保水材の製造時に粉塵発生を抑制しやすい。粒子の平均粒子径は、例えば、電子顕微鏡または特定の目開きの篩を用いて測定できる。 The particles include, for example, particles obtained by polymerizing in a suspended or emulsified state, particles obtained by spray-drying a resin solution, commercially available particulate water-absorbent resin, or particles obtained by crushing them. , Primary particles used in the production method of the first embodiment, particles in which primary particles are aggregated, a mixture thereof, and the like. The particles may be not only spherical particles such as those obtained by polymerization in a suspended or emulsified state, but also irregularly shaped particles such as those obtained by grinding. The particle size of the particles is preferably 1 μm or more, more preferably 10 μm or more, still more preferably 30 μm or more, particularly preferably 50 μm or more, preferably 3000 μm or less, more preferably 1000 μm or less, still more preferably 600 μm or less, and particularly preferably. Is 300 μm or less. When the average particle diameter of the particles is at least the lower limit value and at least the upper limit value, a more preferable water absorption rate can be easily obtained. Further, when the average particle diameter of the particles is at least the above lower limit value, it is easy to suppress the generation of dust during the production of the water-retaining material. The average particle size of the particles can be measured, for example, using an electron microscope or a sieve with a specific opening.
　前記凝集工程では、粒子として存在する吸水性樹脂を、膨潤させた状態で接触させることにより凝集させる。吸水性樹脂として、必要に応じて粉砕および／または篩過により粒子の平均粒子径を調整した吸水性樹脂を使用してよい。また、必要に応じて、凝集工程の前、凝集工程と同時、または凝集工程の後に、上述した任意の添加剤を吸水性樹脂と混合してもよい。
　第二実施態様の製造方法では、吸水性樹脂を膨潤させる前、粒子として存在する吸水性樹脂の含水率は、好ましくは１５質量％以下、より好ましくは１３質量％以下、特に好ましくは１０質量％以下である。前記含水率が前記上限値以下であると、良好なハンドリング性を得やすい。前記含水率の下限値は特に限定されず、０質量％以上である。含水率は、吸水性樹脂の質量と吸水性樹脂を乾燥状態になるまで乾燥させた後の質量とを用いて計算でき、例えば後述の実施例に記載の方法によって計算することができる。 In the agglomeration step, the water-absorbent resin existing as particles is agglomerated by contacting them in a swollen state. As the water-absorbent resin, a water-absorbent resin in which the average particle size of the particles is adjusted by pulverization and / or sieving may be used, if necessary. Further, if necessary, any of the above-mentioned additives may be mixed with the water-absorbent resin before the aggregation step, at the same time as the aggregation step, or after the aggregation step.
In the production method of the second embodiment, the water content of the water-absorbent resin existing as particles before swelling the water-absorbent resin is preferably 15% by mass or less, more preferably 13% by mass or less, and particularly preferably 10% by mass. It is as follows. When the water content is not more than the upper limit value, good handleability can be easily obtained. The lower limit of the water content is not particularly limited and is 0% by mass or more. The water content can be calculated using the mass of the water-absorbent resin and the mass of the water-absorbent resin after it has been dried until it becomes dry, and can be calculated, for example, by the method described in Examples described later.
　第二実施態様の製造方法の凝集工程で用いる膨潤溶媒、膨潤方法、吸水性樹脂の質量に対する膨潤溶媒の量、撹拌方法、撹拌機、および撹拌時のせん断力は、第一実施態様の製造方法の凝集工程と同様のものをそれぞれ採用できる。 The swelling solvent used in the aggregation step of the production method of the second embodiment, the swelling method, the amount of the swelling solvent with respect to the mass of the water-absorbent resin, the stirring method, the stirrer, and the shearing force at the time of stirring are determined by the manufacturing method of the first embodiment. It is possible to adopt the same process as the aggregation process of.
　凝集工程の前または凝集工程と同時に任意の添加剤を配合してもよく、バインダーを配合することにより、吸水性樹脂の凝集の強固さを調整できる。使用できるバインダーの種類および添加量は、第一実施態様の製造方法のものをそれぞれ採用できる。 Any additive may be added before the agglomeration step or at the same time as the agglomeration step, and the strength of the agglomeration of the water-absorbent resin can be adjusted by adding a binder. As the type and amount of the binder that can be used, those of the production method of the first embodiment can be adopted.
＜架橋工程＞
　前記製造方法は、前記凝集工程の前、前記凝集工程と同時、または前記凝集工程の後に、吸水性樹脂を架橋させる架橋工程を更に含んでよい。
　優れた吸水速度を得やすい観点からは、前記凝集工程の前に吸水性樹脂を架橋させる架橋工程を含むことが好ましい。この場合、架橋後の吸水性樹脂を膨潤状態で接触させることにより凝集させるが、凝集力は過度に強固ではない。このため、吸水時に保水材の膨張と崩壊とがバランス良く進行し、より好ましい吸水速度を得ることができる。
　また、吸水性樹脂表面における架橋構造の割合を増大しやすくなり、その結果、保水材からの吸水性樹脂の低い溶出率を得やすい観点、および／または均一な架橋を得やすい観点からは、架橋させる吸水性樹脂の粒子径が特定の値以下であることが好ましい。架橋させる吸水性樹脂の粒子径は、篩過により所望の値に調整できる。凝集工程の前に架橋工程を実施する場合、架橋させる吸水性樹脂の粒子径は、好ましくは３０００μｍ以下、より好ましくは１０００μｍ以下、更に好ましくは６００μｍ以下、特に好ましくは３００μｍ以下である。前記凝集工程と同時、または前記凝集工程の後に架橋工程を実施する場合、架橋させる吸水性樹脂の粒子径は、好ましくは５０００μｍ以下、より好ましくは３０００μｍ以下、特に好ましくは２０００μｍ以下である。前記凝集工程と同時に架橋工程を実施する場合の粒子径は、架橋工程と凝集工程とが終了した時点の粒子径を指す。 <Crosslinking process>
The production method may further include a cross-linking step of cross-linking the water-absorbent resin before the agglomeration step, at the same time as the agglomeration step, or after the agglomeration step.
From the viewpoint of easily obtaining an excellent water absorption rate, it is preferable to include a cross-linking step of cross-linking the water-absorbent resin before the aggregation step. In this case, the crosslinked water-absorbent resin is agglomerated by contacting it in a swollen state, but the cohesive force is not excessively strong. Therefore, the expansion and disintegration of the water-retaining material proceed in a well-balanced manner during water absorption, and a more preferable water absorption rate can be obtained.
Further, it becomes easy to increase the proportion of the crosslinked structure on the surface of the water-absorbent resin, and as a result, from the viewpoint of easily obtaining a low elution rate of the water-absorbent resin from the water-retaining material and / or from the viewpoint of easily obtaining uniform cross-linking, cross-linking is performed. It is preferable that the particle size of the water-absorbent resin to be made is not more than a specific value. The particle size of the water-absorbent resin to be crosslinked can be adjusted to a desired value by sieving. When the crosslinking step is carried out before the aggregation step, the particle size of the water-absorbent resin to be crosslinked is preferably 3000 μm or less, more preferably 1000 μm or less, still more preferably 600 μm or less, and particularly preferably 300 μm or less. When the crosslinking step is carried out at the same time as the aggregation step or after the aggregation step, the particle size of the water-absorbent resin to be crosslinked is preferably 5000 μm or less, more preferably 3000 μm or less, and particularly preferably 2000 μm or less. The particle size when the cross-linking step is carried out at the same time as the coagulation step refers to the particle size at the time when the cross-linking step and the coagulation step are completed.
　以下、実施例により本発明を更に詳細に説明するが、本発明はかかる実施例により何ら限定されない。 Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.
［評価項目および評価方法］
＜吸水性樹脂におけるイオン性基の含有量＞
　実施例および比較例で用いた樹脂について、固体１３Ｃ－ＮＭＲ測定を行った（日本電子株式会社製　機種名ＥＣＺ－５００Ｒ、５００ＭＨｚ）。得られた１３Ｃ－ＮＭＲスペクトルにおける、イオン性基に由来するピーク（通常１６０～１８０ｐｐｍで観測される）、ビニルアルコール単位の水酸基が結合したメチン炭素に由来するピーク（通常６０～８０ｐｐｍで観測される）、酢酸ビニル単位のビニルエステル基のメチル炭素に由来するピーク（通常１０～３０ｐｐｍで観測される）、エチレン単位のメチレン炭素に由来するピーク（通常３０～５０ｐｐｍで観測される）、アクリル酸およびメタクリル酸単位のカルボニル炭素に由来するピーク（通常１７０～１８０ｐｐｍで観測される）、およびアクリルアミド単位のカルボニル炭素に由来するピーク（通常１６０～１８０ｐｐｍで観測される）から、樹脂中に含まれるイオン性基のモル数、ビニルアルコール単位のモル数、酢酸ビニル単位のモル数、エチレン単位のモル数、アクリル酸およびメタクリル酸単位のモル数、アクリルアミド単位のモル数を求め、下記式にしたがってイオン性基の含有量を算出した。
Figure JPOXMLDOC01-appb-M000003

Figure JPOXMLDOC01-appb-M000004

なお、上述した以外の構成単位を含む場合、その構成単位も全構成単位のモル数に含める。 [Evaluation items and evaluation methods]
<Contents of ionic groups in water-absorbent resin>
Solid 13 C-NMR measurements were performed on the resins used in Examples and Comparative Examples (model name ECZ-500R, 500 MHz manufactured by JEOL Ltd.). In the obtained 13 C-NMR spectrum, a peak derived from an ionic group (usually observed at 160 to 180 ppm) and a peak derived from methine carbon to which a hydroxyl group of a vinyl alcohol unit is bonded (usually observed at 60 to 80 ppm). , Peak derived from methyl carbon of vinyl ester group of vinyl acetate unit (usually observed at 10 to 30 ppm), peak derived from methylene carbon of ethylene unit (usually observed at 30 to 50 ppm), acrylic acid And ions contained in the resin from the peak derived from the carbonyl carbon of the methacrylic acid unit (usually observed at 170-180 ppm) and the peak derived from the carbonyl carbon of the acrylamide unit (usually observed at 160-180 ppm). Obtain the number of moles of the sex group, the number of moles of vinyl alcohol unit, the number of moles of vinyl acetate unit, the number of moles of ethylene unit, the number of moles of acrylic acid and methacrylic acid unit, and the number of moles of acrylamide unit. The content of the group was calculated.
Figure JPOXMLDOC01-appb-M000003

Figure JPOXMLDOC01-appb-M000004

When a structural unit other than the above is included, the structural unit is also included in the number of moles of all the structural units.
＜保水材膨潤試験＞
　分散媒に試料である保水材を分散させ、レーザー回折／散乱式粒子径分布測定装置ＬＡ－９５０Ｖ２（堀場製作所製）を用いて、平均粒子径および体積基準１０％粒子径Ｄ１０（超音波を付与する前の保水材のＤ１０に相当）を測定した。次いで、５分間の超音波照射により分散媒を保水材に吸液させることで保水材を膨潤させた後、保水材の体積基準１０％粒子径Ｄ１０（超音波を付与した後の保水材のＤ１０に相当）および最も小粒子径側の極大粒子径を測定した。測定条件を以下に示す。
　　測定方式：湿式（循環式）
　　試料屈折率：１．５１
　　分散媒：２０質量％塩化ナトリウム水溶液（屈折率：１．３６８）
　　循環速度：１０
　　撹拌速度：１０
　　超音波強さ：７
　　透過率：８０～９０％
　　循環液量：２８０ｍＬ
なお、前記極大粒子径は、０．０１１μｍ、０．０１３μｍ、０．０１５μｍ、０．０１７μｍ、０．０２μｍ、０．０２３μｍ、０．０２６μｍ、０．０３μｍ、０．０３４μｍ、０．０３９μｍ、０．０４４μｍ、０．０５１μｍ、０．０５８μｍ、０．０６７μｍ、０．０７６μｍ、０．０８７μｍ、０．１μｍ、０．１１５μｍ、０．１３１μｍ、０．１５μｍ、０．１７２μｍ、０．１９７μｍ、０．２２６μｍ、０．２５９μｍ、０．２９６μｍ、０．３３９μｍ、０．３８９μｍ、０．４４５μｍ、０．５１μｍ、０．５８４μｍ、０．６６９μｍ、０．７６６μｍ、０．８７７μｍ、１．００５μｍ、１．１５１μｍ、１．３１８μｍ、１．５１μｍ、１．７２９μｍ、１．９８１μｍ、２．２６９μｍ、２．５９９μｍ、２．９７６μｍ、３．４０９μｍ、３．９０５μｍ、４．４７２μｍ、５．１２２μｍ、５．８６７μｍ、６．７２μｍ、７．６９７μｍ、８．８１６μｍ、１０．０９７μｍ、１１．５６５μｍ、１３．２４６μｍ、１５．１７２μｍ、１７．３７７μｍ、１９．９０４μｍ、２２．７９７μｍ、２６．１１１μｍ、２９．９０７μｍ、３４．２５５μｍ、３９．２３４μｍ、４４．９３８μｍ、５１．４７１μｍ、５８．９５３μｍ、６７．５２３μｍ、７７．３４μｍ、８８．５８３μｍ、１０１．４６μｍ、１１６．２１μｍ、１３３．１０３μｍ、１５２．４５３μｍ、１７４．６１６μｍ、２００μｍ、２２９．０７５μｍ、２６２．３７６μｍ、３００．５１８μｍ、３４４．２０６μｍ、３９４．２４４μｍ、４５１．５５６μｍ、５１７．２μｍ、５９２．３８７μｍ、６７８．５０４μｍ、７７７．１４１μｍ、８９０．１１６μｍ、１０１９．５１５μｍ、１１６７．７２５μｍ、１３３７．４８１μｍ、１５３１．９１４μｍ、１７５４．６１３μｍ、２００９．６８７μｍ、２３０１．８４１μｍ、２６３６．４６７μｍ、または３０００μｍでの頻度により求めた。
　続いて、下記式により、超音波を付与する前後の保水材の体積基準１０％粒子径Ｄ１０の変化率を計算した。
Figure JPOXMLDOC01-appb-M000005

　上述したいずれの測定も１つの試料について２回ずつ行い、得られた測定値およびＤ１０変化率それぞれの平均値を、その試料についての測定値およびＤ１０変化率として採用した。 <Water retention material swelling test>
A water-retaining material as a sample is dispersed in a dispersion medium, and a laser diffraction / scattering type particle size distribution measuring device LA-950V2 (manufactured by Horiba Seisakusho) is used to measure the average particle size and volume-based 10% particle size D 10 (ultrasonic waves). (Equivalent to D10 of the water - retaining material before application) was measured. Next, the water-retaining material is swelled by absorbing the dispersion medium into the water-retaining material by ultrasonic irradiation for 5 minutes, and then the volume-based 10% particle diameter D 10 of the water-retaining material (of the water-retaining material after applying ultrasonic waves). (Corresponding to D10) and the maximum particle size on the smallest particle size side were measured. The measurement conditions are shown below.
Measurement method: Wet (circulation type)
Sample refractive index: 1.51
Dispersion medium: 20% by mass sodium chloride aqueous solution (refractive index: 1.368)
Circulation speed: 10
Stirring speed: 10
Ultrasonic intensity: 7
Transmittance: 80-90%
Circulating fluid volume: 280 mL
The maximum particle size is 0.011 μm, 0.013 μm, 0.015 μm, 0.017 μm, 0.02 μm, 0.023 μm, 0.026 μm, 0.03 μm, 0.034 μm, 0.039 μm, 0. 044 μm, 0.051 μm, 0.058 μm, 0.067 μm, 0.076 μm, 0.087 μm, 0.1 μm, 0.115 μm, 0.131 μm, 0.15 μm, 0.172 μm, 0.197 μm, 0.226 μm, 0.259 μm, 0.296 μm, 0.339 μm, 0.389 μm, 0.445 μm, 0.51 μm, 0.584 μm, 0.669 μm, 0.766 μm, 0.877 μm, 1.005 μm, 1.151 μm, 1. 318 μm, 1.51 μm, 1.729 μm, 1.981 μm, 2.269 μm, 2.599 μm, 2.976 μm, 3.409 μm, 3.905 μm, 4.472 μm, 5.122 μm, 5.867 μm, 6.72 μm, 7.697 μm, 8.816 μm, 10.097 μm, 11.565 μm, 13.246 μm, 15.172 μm, 17.377 μm, 19.904 μm, 22.977 μm, 26.111 μm, 29.907 μm, 34.255 μm, 39. 234 μm, 44.938 μm, 51.471 μm, 58.953 μm, 67.523 μm, 77.34 μm, 88.583 μm, 101.46 μm, 116.21 μm, 133.103 μm, 152.453 μm, 174.616 μm, 200 μm, 229. 075 μm, 262.376 μm, 300.518 μm, 344.206 μm, 394.244 μm, 451.556 μm, 517.2 μm, 592.387 μm, 678.504 μm, 777.141 μm, 890.116 μm, 1019.515 μm, 1167.725 μm, It was determined by the frequency of 1337.481 μm, 1531.914 μm, 1754.613 μm, 2009.687 μm, 2301.841 μm, 2636.467 μm, or 3000 μm.
Subsequently, the rate of change of the volume-based 10% particle diameter D 10 of the water-retaining material before and after applying ultrasonic waves was calculated by the following formula.
Figure JPOXMLDOC01-appb-M000005

Each of the above-mentioned measurements was performed twice for one sample, and the obtained measured value and the average value of the D 10 rate of change were adopted as the measured value and the D 10 rate of change for the sample.
＜吸水時間（Ｔ１）、吸水速度向上度＞
　直径３．５ｃｍのシャーレに保水材を０．１２ｇ入れ、ピペットで純水３．０ｇを０．５秒間かけて投入した。投入後から、保水材が吸水し、水面が消失するまでの時間を計測した。この時間が短いほど、保水材の吸水速度が速いことを意味する。
　また、保水材のＤ１０変化率が１以下であることによる吸水速度の向上の程度を評価するため、下記式に示す通り、吸水速度向上度として、保水材が１以下のＤ１０変化率を有しているか否かについてのみ異なる保水材の吸水時間（Ｔ１）の比を求めた。その際、１以下のＤ１０変化率を有していない保水材の吸水時間（Ｔ１）は、後述する比較例で準備した保水材を用いて測定を行った。具体的には、例えば実施例１および４の保水材では、比較例１の保水材と比較することで吸水速度向上度を算出した。
Figure JPOXMLDOC01-appb-M000006
<Water absorption time (T1), water absorption speed improvement>
0.12 g of a water-retaining material was put into a petri dish having a diameter of 3.5 cm, and 3.0 g of pure water was added with a pipette over 0.5 seconds. The time from when the water was added until the water-retaining material absorbed water and the water surface disappeared was measured. The shorter this time, the faster the water absorption rate of the water retention material.
Further, in order to evaluate the degree of improvement in the water absorption rate due to the D 10 change rate of the water retention material being 1 or less, as shown in the following formula, the D 10 change rate of the water retention material is 1 or less as the water absorption rate improvement degree. The ratio of the water absorption time (T1) of the water-retaining material, which differs only with or without possession, was determined. At that time, the water absorption time (T1) of the water-retaining material having no D10 change rate of 1 or less was measured using the water-retaining material prepared in the comparative example described later. Specifically, for example, in the water-retaining materials of Examples 1 and 4, the degree of improvement in the water absorption rate was calculated by comparing with the water-retaining material of Comparative Example 1.
Figure JPOXMLDOC01-appb-M000006
＜保水材１ｇ当たりの純水吸収量＞
　ＪＩＳ　Ｋ　７２２３に準じて、実施例および比較例における保水材の純水吸収量を測定し、下記式に基づいて、保水材１ｇ当たりの純水吸収量［ｇ／ｇ］を算出した。
Figure JPOXMLDOC01-appb-M000007
<Absorption amount of pure water per 1 g of water retention material>
The pure water absorption amount of the water-retaining material in Examples and Comparative Examples was measured according to JIS K 7223, and the pure water absorption amount [g / g] per 1 g of the water-retaining material was calculated based on the following formula.
Figure JPOXMLDOC01-appb-M000007
＜保水材１ｇ当たりの塩化カルシウム水溶液吸収量＞
　ＪＩＳ　Ｋ　７２２３の試料設置方法に準じて、実施例および比較例における保水材を１．４４ｇ／Ｌ塩化カルシウム水溶液に６時間浸漬した。テトロン２８０メッシュを用い、塩化カルシウム水溶液を吸収させた保水材と、保水材に吸収されなかった塩化カルシウム水溶液とを濾別し、下記式を用いて保水材１ｇ当たりの塩化カルシウム水溶液吸収量［ｇ／ｇ］を算出した。
Figure JPOXMLDOC01-appb-M000008
 <Absorption amount of calcium chloride aqueous solution per 1 g of water retention material>
The water-retaining materials in Examples and Comparative Examples were immersed in a 1.44 g / L calcium chloride aqueous solution for 6 hours according to the sample setting method of JIS K 7223. Using the Tetron 280 mesh, the water-retaining material that absorbed the calcium chloride aqueous solution and the calcium chloride aqueous solution that was not absorbed by the water-retaining material were filtered off, and the amount of calcium chloride aqueous solution absorbed per 1 g of the water-retaining material was absorbed using the following formula. / G] was calculated.
Figure JPOXMLDOC01-appb-M000008
＜保水材の含水率＞
　METTLER TOLEDO製HB43－S　Halogen水分計を用い測定を行った。測定では１０５℃で保水材を乾燥させ、質量変化が無くなったところを終点として乾燥後の保水材を得た。保水材の含水率は以下の式で表される。
Figure JPOXMLDOC01-appb-M000009
<Moisture content of water retention material>
Measurements were performed using a METTLER TOLEDO HB43-S Halogen Moisture Meter. In the measurement, the water-retaining material was dried at 105 ° C., and the dried water-retaining material was obtained at the end point where the mass change disappeared. The water content of the water retention material is expressed by the following formula.
Figure JPOXMLDOC01-appb-M000009
＜膨潤させる前の吸水性樹脂の含水率＞
　METTLER TOLEDO製HB43－S　Halogen水分計を用い測定を行った。測定では１０５℃で吸水性樹脂を乾燥させ、質量変化が無くなったところを終点として乾燥後の吸水性樹脂を得た。吸水性樹脂の含水率は以下の式で表される。
Figure JPOXMLDOC01-appb-M000010
<Moisture content of water-absorbent resin before swelling>
Measurements were performed using a METTLER TOLEDO HB43-S Halogen Moisture Meter. In the measurement, the water-absorbent resin was dried at 105 ° C., and the dried water-absorbent resin was obtained at the end point where the mass change disappeared. The water content of the water-absorbent resin is expressed by the following formula.
Figure JPOXMLDOC01-appb-M000010
＜保水材の嵩密度＞
　５０ｍLのビーカーに保水材１０ｇを一気に入れ、その後タップ等は行わずに静置し、保水材の最上面が位置する高さに印を付けた。保水材を取り出し、当該印を付けたところまで水を投入し、その水の質量を測定した。水が１ｇ／ｍＬであることを用い、以下の式から嵩密度を算出した。
Figure JPOXMLDOC01-appb-M000011
<Bulk density of water retention material>
10 g of the water-retaining material was put into a 50 mL beaker at once, and then left to stand without tapping, etc., and the height at which the uppermost surface of the water-retaining material was located was marked. The water-retaining material was taken out, water was poured up to the place marked with the mark, and the mass of the water was measured. The bulk density was calculated from the following formula using the fact that the water content was 1 g / mL.
Figure JPOXMLDOC01-appb-M000011
＜吸水時間（Ｔ２）＞
　直径３．５ｃｍのシャーレに吸水性樹脂の質量が０．１２ｇとなるように保水材をＸｇまんべんなく入れ、保水材に含有される水分と併せて水が３ｍＬとなるよう、ピペットで純水Ｙｇを一気に投入した。投入後から、保水材が吸水し、水面が消失するまでの時間を計測し、吸水時間（Ｔ２）とした。この時間が短いほど、保水材の吸水速度が速いことを意味する。
Figure JPOXMLDOC01-appb-M000012

Figure JPOXMLDOC01-appb-M000013
 <Water absorption time (T2)>
Put Xg of water-retaining material evenly in a petri dish with a diameter of 3.5 cm so that the mass of the water-absorbent resin is 0.12 g, and add pure water Yg with a pipette so that the water content is 3 mL together with the water contained in the water-retaining material. I put it all at once. The time from when the water was added until the water-retaining material absorbed water and the water surface disappeared was measured and used as the water absorption time (T2). The shorter this time, the faster the water absorption rate of the water retention material.
Figure JPOXMLDOC01-appb-M000012

Figure JPOXMLDOC01-appb-M000013
［吸水性樹脂］
　吸水性樹脂（Ａ１）として、ＳＮＦホールディングカンパニー製のアクアソーブ３００５ＫＢ（アクリルアミド系重合体、凝集体ではない粒子状のもの、平均粒子径６４４μｍ、架橋構造有）を用いた。吸水性樹脂（Ａ１）の全構成単位に対するイオン性基の含有量は２２モル％であった。
　吸水性樹脂（Ａ２）として、ＳＮＦホールディングカンパニー製のアクアソーブ３００５ＫＢ（アクリルアミド系重合体、凝集体ではない粒子状のもの、平均粒子径６４４μｍ、架橋構造有）を用いた。吸水性樹脂（Ａ２）の全構成単位に対するイオン性基の含有量は２２モル％であった。
　吸水性樹脂（Ｃ１）として、アクリル酸系重合体（粒子状）を用いた。吸水性樹脂（Ｃ１）の全構成単位に対するイオン性基の含有量は５４モル％であった。 [Water-absorbent resin]
As the water-absorbent resin (A1), Aquasorb 3005KB (acrylamide-based polymer, non-aggregate particulate matter, average particle diameter 644 μm, crosslinked structure) manufactured by SNF Holding Company was used. The content of the ionic group with respect to all the constituent units of the water-absorbent resin (A1) was 22 mol%.
As the water-absorbent resin (A2), Aquasorb 3005KB (acrylamide-based polymer, non-aggregate particulate matter, average particle diameter 644 μm, crosslinked structure) manufactured by SNF Holding Company was used. The content of the ionic group with respect to all the constituent units of the water-absorbent resin (A2) was 22 mol%.
An acrylic acid-based polymer (particulate) was used as the water-absorbent resin (C1). The content of the ionic group with respect to all the constituent units of the water-absorbent resin (C1) was 54 mol%.
　下記手順により、ビニルアルコール系重合体〔吸水性樹脂（Ｂ１）〕を合成した。
　撹拌機、還流冷却管、窒素導入管、および開始剤の添加口を備えた反応器に、酢酸ビニル９０３０ｇ、アクリル酸メチル１８．１５ｇ、およびメタノール３８１０ｇを導入し、窒素バブリングをしながら３０分間反応器内を不活性ガス置換した。水浴を用いて反応器の昇温を開始し、反応器の内部温度が６０℃となったところで、開始剤としてアゾビスイソブチロニトリル（ＡＩＢＮ）を２．４０ｇ添加し、重合を開始させた。適宜サンプリングを行い、その固形分濃度から重合の進行を確認し、導入した酢酸ビニルとアクリル酸メチルの合計質量に対する、重合により消費された酢酸ビニルとアクリル酸メチルの合計質量である、消費率を求めた。消費率が４質量％に到達したところで、反応器の内部温度を３０℃まで冷却して重合を停止させた。真空ラインに接続し、残留する酢酸ビニルをメタノールとともに３０℃で減圧留去した。反応器内を目視で確認しながら、粘度が上昇したところで適宜メタノールを添加しながら留去を続け、５．２モル％のアクリル酸由来構成単位を含有するポリ酢酸ビニルを得た。アクリル酸由来構成単位の含有量は固体１３Ｃ－ＮＭＲを用いて測定した。
　次に、上記と同様の反応器に、得られたアクリル酸由来構成単位含有ポリ酢酸ビニル３６０ｇおよびメタノール６５５２ｇを添加し、アクリル酸由来構成単位含有ポリ酢酸ビニルを溶解させた。水浴を用いて反応器の昇温を開始し、反応器の内部温度が７０℃になるまで撹拌しながら加熱した。ここに水酸化ナトリウムのメタノール溶液（メタ苛性、濃度１５質量％）２８０．８ｇを添加し、７０℃で２時間ケン化を行った。 A vinyl alcohol-based polymer [water-absorbent resin (B1)] was synthesized by the following procedure.
9030 g of vinyl acetate, 18.15 g of methyl acrylate, and 3810 g of methanol were introduced into a reactor equipped with a stirrer, a reflux cooling tube, a nitrogen introduction tube, and an initiator addition port, and the reaction was carried out for 30 minutes while nitrogen bubbling. The inside of the vessel was replaced with an inert gas. The temperature of the reactor was started using a water bath, and when the internal temperature of the reactor reached 60 ° C., 2.40 g of azobisisobutyronitrile (AIBN) was added as an initiator to initiate polymerization. .. The progress of the polymerization was confirmed from the solid content concentration by appropriately sampling, and the consumption rate, which is the total mass of vinyl acetate and methyl acrylate consumed by the polymerization, with respect to the total mass of the introduced vinyl acetate and methyl acrylate was calculated. I asked. When the consumption rate reached 4% by mass, the internal temperature of the reactor was cooled to 30 ° C. to terminate the polymerization. It was connected to a vacuum line, and the residual vinyl acetate was distilled off under reduced pressure at 30 ° C. together with methanol. While visually checking the inside of the reactor, when the viscosity increased, distillation was continued while appropriately adding methanol to obtain polyvinyl acetate containing 5.2 mol% of acrylic acid-derived structural units. The content of acrylic acid-derived structural units was measured using solid 13 C-NMR.
Next, 360 g of the obtained polyvinyl acetate containing a structural unit derived from acrylic acid and 6552 g of methanol were added to the same reactor as described above, and the obtained polyvinyl acetate containing a structural unit derived from acrylic acid was dissolved. The temperature of the reactor was started by using a water bath, and the reactor was heated with stirring until the internal temperature of the reactor reached 70 ° C. To this, 280.8 g of a methanol solution of sodium hydroxide (meta-caustic, concentration 15% by mass) was added, and saponification was carried out at 70 ° C. for 2 hours.
　ケン化後の溶液を濾過し、４０℃で真空乾燥させた。得られた重合体を固形分濃度が１５質量％となるように純水に溶解させた後、テフロントレーに流し込み、９０℃で熱風乾燥を行った。得られた重合体を粉砕して、５．２モル％のアクリル酸由来構成単位を含有するポリビニルアルコール（以下、「ポリビニルアルコール（ｂ１）」と称する）を１６５ｇ得た。 The saponified solution was filtered and vacuum dried at 40 ° C. The obtained polymer was dissolved in pure water so that the solid content concentration was 15% by mass, poured into a Teflon tray, and dried with hot air at 90 ° C. The obtained polymer was pulverized to obtain 165 g of polyvinyl alcohol (hereinafter referred to as "polyvinyl alcohol (b1)") containing 5.2 mol% of acrylic acid-derived structural units.
　還流冷却管および撹拌翼を備えた三つ口セパラブルフラスコに、メタノール４４５．５ｇ、純水４７．４ｇ、２５質量％グルタルアルデヒド水溶液１．２０６ｇ、およびポリビニルアルコール（ｂ１）１５０ｇを導入し、２３℃で撹拌し、ポリビニルアルコール（ｂ１）を分散させた。４７質量％硫酸水溶液５．６６ｇと純水３ｇとの混合液を１０分かけて滴加し、６５℃に昇温して６時間架橋反応させた。反応後、濾過により重合体を取り出し、濾取した重合体を２２０ｇのメタノールに分散して３０分間撹拌して濾過することにより洗浄を行った。洗浄は２回繰り返した。 Into a three-necked separable flask equipped with a reflux condenser and a stirring blade, 445.5 g of methanol, 47.4 g of pure water, 1.206 g of a 25 mass% glutaraldehyde aqueous solution, and 150 g of polyvinyl alcohol (b1) were introduced, and 23 The mixture was stirred at ° C. to disperse polyvinyl alcohol (b1). A mixture of 5.66 g of a 47 mass% sulfuric acid aqueous solution and 3 g of pure water was added dropwise over 10 minutes, the temperature was raised to 65 ° C., and a crosslinking reaction was carried out for 6 hours. After the reaction, the polymer was taken out by filtration, and the collected polymer was dispersed in 220 g of methanol, stirred for 30 minutes, and filtered for washing. Washing was repeated twice.
　洗浄後の重合体を還流冷却管および撹拌翼を備えた三つ口セパラブルフラスコに導入し、メタノール２４５ｇ、純水４０．８ｇ、および５０質量％水酸化カリウム２４．３５ｇを加え、６５℃で２時間反応させた。反応後、濾過により重合体を取り出した後、濾取した重合体を３３０ｇのメタノールに分散して３０分間撹拌して濾過することにより洗浄を行った。洗浄は２回繰り返した。洗浄後の重合体を４０℃で１２時間真空乾燥し、目的の吸水性樹脂（Ｂ１）を得た。吸水性樹脂（Ｂ１）の全構成単位に対するイオン性基の含有量は５モル％であった。 The washed polymer is introduced into a three-neck separable flask equipped with a reflux condenser and a stirring blade, 245 g of methanol, 40.8 g of pure water, and 24.35 g of 50% by mass potassium hydroxide are added, and the temperature is 65 ° C. It was allowed to react for 2 hours. After the reaction, the polymer was taken out by filtration, and then the collected polymer was dispersed in 330 g of methanol, stirred for 30 minutes, and filtered for washing. Washing was repeated twice. The washed polymer was vacuum dried at 40 ° C. for 12 hours to obtain the desired water-absorbent resin (B1). The content of the ionic group with respect to all the constituent units of the water-absorbent resin (B1) was 5 mol%.
　下記手順により、ビニルアルコール系重合体〔吸水性樹脂（Ｂ２）〕を合成した。
　撹拌機、還流冷却管、窒素導入管、および開始剤の添加口を備えた反応器に、酢酸ビニル９０３０ｇ、アクリル酸メチル１８．１５ｇ、およびメタノール３８１０ｇを導入し、窒素バブリングをしながら３０分間反応器内を不活性ガス置換した。水浴を用いて反応器の昇温を開始し、反応器の内部温度が６０℃となったところで、開始剤としてアゾビスイソブチロニトリル（ＡＩＢＮ）を２．４０ｇ添加し、重合を開始させた。適宜サンプリングを行い、その固形分濃度から重合の進行を確認し、導入した酢酸ビニルとアクリル酸メチルの合計質量に対する、重合により消費された酢酸ビニルとアクリル酸メチルの合計質量である、消費率を求めた。消費率が４質量％に到達したところで、反応器の内部温度を３０℃まで冷却して重合を停止させた。真空ラインに接続し、残留する酢酸ビニルをメタノールとともに３０℃で減圧留去した。反応器内を目視で確認しながら、粘度が上昇したところで適宜メタノールを添加しながら留去を続け、５．２モル％のアクリル酸由来構成単位を含有するポリ酢酸ビニルを得た。アクリル酸由来構成単位の含有量は固体１３Ｃ－ＮＭＲを用いて測定した。
　次に、上記と同様の反応器に、得られたアクリル酸由来構成単位含有ポリ酢酸ビニル３６０ｇおよびメタノール６５５２ｇを添加し、アクリル酸由来構成単位含有ポリ酢酸ビニルを溶解させた。水浴を用いて反応器の昇温を開始し、反応器の内部温度が７０℃になるまで撹拌しながら加熱した。ここに水酸化ナトリウムのメタノール溶液（メタ苛性、濃度１５質量％）２８０．８ｇを添加し、７０℃で２時間ケン化を行った。 A vinyl alcohol-based polymer [water-absorbent resin (B2)] was synthesized by the following procedure.
9030 g of vinyl acetate, 18.15 g of methyl acrylate, and 3810 g of methanol were introduced into a reactor equipped with a stirrer, a reflux cooling tube, a nitrogen introduction tube, and an initiator addition port, and the reaction was carried out for 30 minutes while nitrogen bubbling. The inside of the vessel was replaced with an inert gas. The temperature of the reactor was started using a water bath, and when the internal temperature of the reactor reached 60 ° C., 2.40 g of azobisisobutyronitrile (AIBN) was added as an initiator to initiate polymerization. .. The progress of the polymerization was confirmed from the solid content concentration by appropriately sampling, and the consumption rate, which is the total mass of vinyl acetate and methyl acrylate consumed by the polymerization, with respect to the total mass of the introduced vinyl acetate and methyl acrylate was calculated. I asked. When the consumption rate reached 4% by mass, the internal temperature of the reactor was cooled to 30 ° C. to terminate the polymerization. It was connected to a vacuum line, and the residual vinyl acetate was distilled off under reduced pressure at 30 ° C. together with methanol. While visually checking the inside of the reactor, when the viscosity increased, distillation was continued while appropriately adding methanol to obtain polyvinyl acetate containing 5.2 mol% of acrylic acid-derived structural units. The content of acrylic acid-derived structural units was measured using solid 13 C-NMR.
Next, 360 g of the obtained polyvinyl acetate containing a structural unit derived from acrylic acid and 6552 g of methanol were added to the same reactor as described above, and the obtained polyvinyl acetate containing a structural unit derived from acrylic acid was dissolved. The temperature of the reactor was started by using a water bath, and the reactor was heated with stirring until the internal temperature of the reactor reached 70 ° C. To this, 280.8 g of a methanol solution of sodium hydroxide (meta-caustic, concentration 15% by mass) was added, and saponification was carried out at 70 ° C. for 2 hours.
　ケン化後の溶液を濾過し、４０℃で真空乾燥させた。５．２モル％のアクリル酸由来構成単位を含有するポリビニルアルコール（以下、「ポリビニルアルコール（ｂ２）」と称する）を１６５ｇ得た。 The saponified solution was filtered and vacuum dried at 40 ° C. 165 g of polyvinyl alcohol (hereinafter referred to as “polyvinyl alcohol (b2)”) containing 5.2 mol% of acrylic acid-derived structural units was obtained.
　還流冷却管および撹拌翼を備えた三つ口セパラブルフラスコに、メタノール４４５．５ｇ、純水４７．４ｇ、２５質量％グルタルアルデヒド水溶液１．２０６ｇ、およびポリビニルアルコール（ｂ２）１５０ｇを導入し、２３℃で撹拌し、ポリビニルアルコール（ｂ２）を分散させた。４７質量％硫酸水溶液５．６６ｇと純水３ｇとの混合液を１０分かけて滴加し、６５℃に昇温して６時間架橋反応させた。反応後、濾過により重合体を取り出し、濾取した重合体を２２０ｇのメタノールに分散して３０分間撹拌して濾過することにより洗浄を行った。洗浄は２回繰り返した。 Into a three-necked separable flask equipped with a reflux condenser and a stirring blade, 445.5 g of methanol, 47.4 g of pure water, 1.206 g of a 25 mass% glutaraldehyde aqueous solution, and 150 g of polyvinyl alcohol (b2) were introduced, and 23 The mixture was stirred at ° C. to disperse the polyvinyl alcohol (b2). A mixture of 5.66 g of a 47 mass% sulfuric acid aqueous solution and 3 g of pure water was added dropwise over 10 minutes, the temperature was raised to 65 ° C., and a crosslinking reaction was carried out for 6 hours. After the reaction, the polymer was taken out by filtration, and the collected polymer was dispersed in 220 g of methanol, stirred for 30 minutes, and filtered for washing. Washing was repeated twice.
　洗浄後の重合体を還流冷却管および撹拌翼を備えた三つ口セパラブルフラスコに導入し、メタノール２４５ｇ、純水４０．８ｇ、および５０質量％水酸化カリウム２４．３５ｇを加え、６５℃で２時間反応させた。反応後、濾過により重合体を取り出した後、濾取した重合体を３３０ｇのメタノールに分散して３０分間撹拌して濾過することにより洗浄を行った。洗浄は２回繰り返した。洗浄後の重合体を４０℃で１２時間真空乾燥し、目的の吸水性樹脂（Ｂ２）を得た。吸水性樹脂（Ｂ２）の全構成単位に対するイオン性基の含有量は５モル％であった。 The washed polymer is introduced into a three-neck separable flask equipped with a reflux condenser and a stirring blade, 245 g of methanol, 40.8 g of pure water, and 24.35 g of 50% by mass potassium hydroxide are added, and the temperature is 65 ° C. It was allowed to react for 2 hours. After the reaction, the polymer was taken out by filtration, and then the collected polymer was dispersed in 330 g of methanol, stirred for 30 minutes, and filtered for washing. Washing was repeated twice. The washed polymer was vacuum dried at 40 ° C. for 12 hours to obtain the desired water-absorbent resin (B2). The content of the ionic group with respect to all the constituent units of the water-absorbent resin (B2) was 5 mol%.
実施例１～３
　公称目開き５３μｍの篩を用いて、吸水性樹脂（Ａ１）から、篩過した粒子を採取した。なお、採取した粒子の粒子径を、便宜上「＜５３」の粒子径と記載する。以下において、篩分けした粒子の粒子径は、篩の公称目開きの値を用いて同様に記載する。
　採取した粒子２８ｇを縦２８ｃｍ、横２０ｃｍの袋に入れ、純水９ｇを少量ずつスプレー噴霧し、その都度振り混ぜ、凝集体を得た。このとき、樹脂同士に圧力をかけて練るようにするのではなく、袋を空気で満たして回転させるようにして振り混ぜた。袋内で純水は全て吸水性樹脂（Ａ１）に吸収されていた。次いで４０℃で１２時間真空乾燥を行った後、公称目開き３００μｍの篩、公称目開き６００μｍの篩、公称目開き１０００μｍの篩および公称目開き１４００μｍの篩を用いて、実施例１として粒子径３００μｍ～６００μｍの粒子、実施例２として粒子径６００μｍ～１０００μｍの粒子、実施例３として粒子径１０００μｍ～１４００μｍの粒子をそれぞれ得た。 Examples 1 to 3
Sieved particles were collected from the water-absorbent resin (A1) using a sieve with a nominal opening of 53 μm. The particle size of the collected particles is described as the particle size of "<53" for convenience. In the following, the particle size of the sieved particles is similarly described using the value of the nominal opening of the sieve.
28 g of the collected particles were placed in a bag having a length of 28 cm and a width of 20 cm, and 9 g of pure water was sprayed little by little and shaken each time to obtain an aggregate. At this time, instead of applying pressure to the resins to knead them, the bags were filled with air and rotated to be shaken. All the pure water was absorbed by the water-absorbent resin (A1) in the bag. Then, after vacuum drying at 40 ° C. for 12 hours, a sieve having a nominal opening of 300 μm, a sieve having a nominal opening of 600 μm, a sieve having a nominal opening of 1000 μm and a sieve having a nominal opening of 1400 μm were used, and the particle size was used as Example 1. Particles having a particle diameter of 300 μm to 600 μm, particles having a particle diameter of 600 μm to 1000 μm as Example 2, and particles having a particle diameter of 1000 μm to 1400 μm were obtained as Example 3, respectively.
実施例４～６
　公称目開き５３μｍの篩および公称目開き１０６μｍの篩を用いて、吸水性樹脂（Ａ１）から粒子径５３μｍ～１０６μｍの粒子を採取した。採取した粒子２８ｇおよび純水１２ｇを用いたこと以外は実施例１～３と同様にして、凝集体を得た。このとき、袋内で純水は全て吸水性樹脂（Ａ１）に吸収されていた。次いで４０℃で１２時間真空乾燥を行った後、公称目開き３００μｍの篩、公称目開き６００μｍの篩、公称目開き１０００μｍの篩および公称目開き１４００μｍの篩を用いて、実施例４として粒子径３００μｍ～６００μｍの粒子、実施例５として粒子径６００μｍ～１０００μｍの粒子、実施例６として粒子径１０００μｍ～１４００μｍの粒子をそれぞれ得た。 Examples 4-6
Particles having a particle diameter of 53 μm to 106 μm were collected from the water-absorbent resin (A1) using a sieve having a nominal opening of 53 μm and a sieve having a nominal opening of 106 μm. Aggregates were obtained in the same manner as in Examples 1 to 3 except that 28 g of the collected particles and 12 g of pure water were used. At this time, all the pure water was absorbed by the water-absorbent resin (A1) in the bag. Then, after vacuum drying at 40 ° C. for 12 hours, a sieve having a nominal opening of 300 μm, a sieve having a nominal opening of 600 μm, a sieve having a nominal opening of 1000 μm and a sieve having a nominal opening of 1400 μm were used, and the particle size was used as Example 4. Particles having a particle diameter of 300 μm to 600 μm, particles having a particle diameter of 600 μm to 1000 μm as Example 5, and particles having a particle diameter of 1000 μm to 1400 μm were obtained as Example 6, respectively.
実施例７～８
　公称目開き２１２μｍの篩を用いて、吸水性樹脂（Ａ１）から粒子径２１２μｍ以上の粒子を採取した。採取した粒子２８ｇおよび純水１２ｇを用いたこと以外は実施例１～３と同様にして、凝集体を得た。このとき、袋内で純水は全て吸水性樹脂（Ａ１）に吸収されていた。次いで４０℃で１２時間真空乾燥を行った後、公称目開き６００μｍの篩、公称目開き１０００μｍの篩および公称目開き１４００μｍの篩を用いて、実施例７として粒子径６００μｍ～１０００μｍの粒子、実施例８として粒子径１０００μｍ～１４００μｍの粒子をそれぞれ得た。 Examples 7-8
Particles having a particle diameter of 212 μm or more were collected from the water-absorbent resin (A1) using a sieve having a nominal opening of 212 μm. Aggregates were obtained in the same manner as in Examples 1 to 3 except that 28 g of the collected particles and 12 g of pure water were used. At this time, all the pure water was absorbed by the water-absorbent resin (A1) in the bag. Then, after vacuum drying at 40 ° C. for 12 hours, particles having a particle diameter of 600 μm to 1000 μm were used as Example 7 using a sieve having a nominal opening of 600 μm, a sieve having a nominal opening of 1000 μm, and a sieve having a nominal opening of 1400 μm. As Example 8, particles having a particle diameter of 1000 μm to 1400 μm were obtained.
実施例９～１０
　公称目開き５３μｍの篩および公称目開き１０６μｍの篩を用いて、吸水性樹脂（Ｂ１）から粒子径５３μｍ～１０６μｍの粒子を採取した。採取した粒子２８ｇおよび純水１２ｇを用いたこと以外は実施例１～３と同様にして、凝集体を得た。このとき、袋内で純水は全て吸水性樹脂（Ａ１）に吸収されていた。次いで４０℃で１２時間真空乾燥を行った後、公称目開き３００μｍの篩、公称目開き６００μｍの篩および公称目開き１０００μｍの篩を用いて、実施例９として粒子径３００μｍ～６００μｍの粒子、実施例１０として粒子径６００μｍ～１０００μｍの粒子をそれぞれ得た。 Examples 9-10
Particles having a particle diameter of 53 μm to 106 μm were collected from the water-absorbent resin (B1) using a sieve having a nominal opening of 53 μm and a sieve having a nominal opening of 106 μm. Aggregates were obtained in the same manner as in Examples 1 to 3 except that 28 g of the collected particles and 12 g of pure water were used. At this time, all the pure water was absorbed by the water-absorbent resin (A1) in the bag. Then, after vacuum drying at 40 ° C. for 12 hours, particles having a particle diameter of 300 μm to 600 μm were used as Example 9 using a sieve having a nominal opening of 300 μm, a sieve having a nominal opening of 600 μm, and a sieve having a nominal opening of 1000 μm. As Example 10, particles having a particle diameter of 600 μm to 1000 μm were obtained.
実施例１１
　公称目開き３００μｍの篩および公称目開き６００μｍの篩を用いて、吸水性樹脂（Ｂ１）から粒子径３００μｍ～６００μｍの粒子を採取した。採取した粒子２８ｇおよび純水１２ｇを用いたこと以外は実施例１～３と同様にして、凝集体を得た。このとき、袋内で純水は全て吸水性樹脂（Ａ１）に吸収されていた。次いで４０℃で１２時間真空乾燥を行った後、公称目開き６００μｍの篩および公称目開き１０００μｍの篩を用いて、粒子径６００μｍ～１０００μｍの粒子を得た。 Example 11
Particles having a particle diameter of 300 μm to 600 μm were collected from the water-absorbent resin (B1) using a sieve having a nominal opening of 300 μm and a sieve having a nominal opening of 600 μm. Aggregates were obtained in the same manner as in Examples 1 to 3 except that 28 g of the collected particles and 12 g of pure water were used. At this time, all the pure water was absorbed by the water-absorbent resin (A1) in the bag. Then, after vacuum drying at 40 ° C. for 12 hours, particles having a particle diameter of 600 μm to 1000 μm were obtained using a sieve having a nominal opening of 600 μm and a sieve having a nominal opening of 1000 μm.
比較例１
　公称目開き３００μｍの篩および公称目開き６００μｍの篩を用いて、吸水性樹脂（Ａ１）から粒子径３００μｍ～６００μｍの粒子を得た。 Comparative Example 1
Using a sieve having a nominal opening of 300 μm and a sieve having a nominal opening of 600 μm, particles having a particle diameter of 300 μm to 600 μm were obtained from the water-absorbent resin (A1).
比較例２
　公称目開き６００μｍの篩および公称目開き１０００μｍの篩を用いて、吸水性樹脂（Ａ１）から粒子径６００μｍ～１０００μｍの粒子を得た。 Comparative Example 2
Using a sieve having a nominal opening of 600 μm and a sieve having a nominal opening of 1000 μm, particles having a particle diameter of 600 μm to 1000 μm were obtained from the water-absorbent resin (A1).
比較例３
　公称目開き３００μｍの篩および公称目開き６００μｍの篩を用いて、吸水性樹脂（Ｂ１）から粒子径３００μｍ～６００μｍの粒子を得た。 Comparative Example 3
Using a sieve having a nominal opening of 300 μm and a sieve having a nominal opening of 600 μm, particles having a particle diameter of 300 μm to 600 μm were obtained from the water-absorbent resin (B1).
比較例４
　公称目開き６００μｍの篩および公称目開き１０００μｍの篩を用いて、吸水性樹脂（Ｂ１）から粒子径６００μｍ～１０００μｍの粒子を得た。 Comparative Example 4
Using a sieve having a nominal opening of 600 μm and a sieve having a nominal opening of 1000 μm, particles having a particle diameter of 600 μm to 1000 μm were obtained from the water-absorbent resin (B1).
比較例５
　公称目開き１０６μｍの篩および公称目開き２１２μｍの篩を用いて、吸水性樹脂（Ｃ１）から粒子径１０６μｍ～２１２μｍの粒子を採取した。採取した粒子２８ｇおよび純水１２ｇを用いたこと以外は実施例１～３と同様にして、凝集体を得た。このとき、袋内で純水は全て吸水性樹脂（Ａ１）に吸収されていた。次いで４０℃で１２時間真空乾燥を行った後、公称目開き３００μｍの篩および公称目開き６００μｍの篩を用いて、粒子径３００μｍ～６００μｍの粒子を得た。 Comparative Example 5
Particles having a particle diameter of 106 μm to 212 μm were collected from the water-absorbent resin (C1) using a sieve having a nominal opening of 106 μm and a sieve having a nominal opening of 212 μm. Aggregates were obtained in the same manner as in Examples 1 to 3 except that 28 g of the collected particles and 12 g of pure water were used. At this time, all the pure water was absorbed by the water-absorbent resin (A1) in the bag. Then, after vacuum drying at 40 ° C. for 12 hours, particles having a particle size of 300 μm to 600 μm were obtained using a sieve having a nominal opening of 300 μm and a sieve having a nominal opening of 600 μm.
比較例６
　公称目開き３００μｍの篩および公称目開き６００μｍの篩を用いて、吸水性樹脂（Ｃ１）から粒子径３００μｍ～６００μｍの粒子を得た。 Comparative Example 6
Using a sieve having a nominal opening of 300 μm and a sieve having a nominal opening of 600 μm, particles having a particle diameter of 300 μm to 600 μm were obtained from the water-absorbent resin (C1).
　実施例１～１１および比較例１～６においてそれぞれ得た粒子を保水材として評価した。それらの結果を表１に示す。 The particles obtained in Examples 1 to 11 and Comparative Examples 1 to 6 were evaluated as water retention materials. The results are shown in Table 1.
Figure JPOXMLDOC01-appb-T000014
Figure JPOXMLDOC01-appb-T000014
　表１に示されている通り、実施例の保水材はいずれも、同程度の粒子径を有する比較例の保水材より優れた吸水速度を示した。保水材の粒子径は、保水材の粉塵防止に対する要望または保水材投入用ホッパーの構造等により制限されることがあるため、このような優れた吸水速度を達成できたことは、大きな意味を持つ。
　また、保水材において、吸水性樹脂の全構成単位に対して０．１モル％以上、５０モル％以下のイオン性基を有する吸水性樹脂がＤ１０変化率１以下の保水材を構成していることにより、吸水速度が著しく向上したことが、吸水速度向上度〔具体的には、実施例１または４の吸水時間（Ｔ１）と比較例１の吸水時間（Ｔ１）との比（実施例１または４の行に記載の吸水速度向上度）、実施例２または５または７の吸水時間（Ｔ１）と比較例２の吸水時間（Ｔ１）との比（実施例２または５または７の行に記載の吸水速度向上度）、実施例９の吸水時間（Ｔ１）と比較例３の吸水時間（Ｔ１）との比（実施例９の行に記載の吸水速度向上度）、実施例１０または１１の吸水時間（Ｔ１）と比較例４の吸水時間（Ｔ１）との比（実施例１０または１１の行に記載の吸水速度向上度）〕から分かる。一方、保水材のＤ１０変化率が１以下であったとしても、吸水性樹脂が前述した特定のイオン性基含有量を有していないと、吸水速度はあまり向上しないという意外な結果が得られたことが、比較例５の吸水時間（Ｔ１）と比較例６の吸水時間（Ｔ１）との比（比較例５の行に記載の吸水速度向上度）から分かる。
　更に、表１に示されている通り、実施例の保水材は、比較例の保水材より高い塩化カルシウム水溶液吸収量も示した。これは、本発明の保水材は、カルシウム塩の存在下であっても吸水量が十分高いことを示している。また、本発明の保水材の、カルシウム塩の存在下での吸水量は、長期間にわたって低下しにくいものであった。 As shown in Table 1, all of the water-retaining materials of the examples showed better water absorption rates than the water-retaining materials of the comparative examples having the same particle size. Since the particle size of the water-retaining material may be limited by the demand for dust prevention of the water-retaining material or the structure of the hopper for charging the water-retaining material, it is significant that such an excellent water absorption rate can be achieved. ..
Further, in the water-retaining material, the water-absorbent resin having an ionic group of 0.1 mol% or more and 50 mol% or less with respect to all the constituent units of the water-absorbent resin constitutes a water-retaining material having a D10 change rate of 1 or less. The fact that the water absorption rate was significantly improved was the degree of improvement in the water absorption rate [specifically, the ratio of the water absorption time (T1) of Example 1 or 4 to the water absorption time (T1) of Comparative Example 1 (Example). Water absorption rate improvement degree described in row 1 or 4), ratio of water absorption time (T1) of Example 2 or 5 or 7 to water absorption time (T1) of Comparative Example 2 (row of Example 2 or 5 or 7). (Degree of improvement in water absorption rate), ratio of water absorption time (T1) of Example 9 to water absorption time (T1) of Comparative Example 3 (degree of improvement in water absorption rate described in the row of Example 9), Example 10 or It can be seen from the ratio of the water absorption time (T1) of 11 to the water absorption time (T1) of Comparative Example 4 (the degree of improvement in water absorption rate described in the row of Example 10 or 11). On the other hand, even if the D 10 change rate of the water-retaining material is 1 or less, the unexpected result that the water absorption rate does not improve so much is obtained unless the water-absorbent resin has the above-mentioned specific ionic group content. It can be seen from the ratio of the water absorption time (T1) of Comparative Example 5 to the water absorption time (T1) of Comparative Example 6 (the degree of improvement in the water absorption rate described in the row of Comparative Example 5).
Further, as shown in Table 1, the water-retaining material of the example also showed a higher absorption amount of calcium chloride aqueous solution than the water-retaining material of the comparative example. This indicates that the water-retaining material of the present invention has a sufficiently high water absorption even in the presence of a calcium salt. In addition, the amount of water absorbed by the water-retaining material of the present invention in the presence of a calcium salt was unlikely to decrease over a long period of time.
実施例１２
　吸水性樹脂（Ａ２）を公称目開き１０６μｍの篩を用いて、吸水性樹脂（Ａ２）から、篩過した粒子を採取した。なお、採取した粒子の粒子径を、便宜上「＜１０６」の粒子径と記載する。以下において、篩分けした粒子の粒子径は、篩の公称目開きの値を用いて同様に記載する。実施例１２において、この時点で吸水性樹脂（Ａ２）は含水しており、含水率は１５質量％であった。また形状は粒子状であった。
　当該粒子径が１０６μｍ以下で、含水率が１５質量％の吸水性樹脂（Ａ２）２８．５ｇを、縦２８ｃｍ、横２０ｃｍの袋に入れ、純水１．５ｇを少量ずつスプレー噴霧し、その都度振り混ぜた。このとき、樹脂同士に圧力をかけて練るようにするのではなく、袋を空気で満たして回転させるようにして振り混ぜた。これにより、さらに含水した吸水性樹脂（Ａ２）の粒子を得た。袋内で純水は全て吸水性樹脂（Ａ２）に吸収されていた。得られた含水した吸水性樹脂を保水材として、評価を行った。 Example 12
Sieved particles were collected from the water-absorbent resin (A2) using a sieve having a nominal opening of 106 μm for the water-absorbent resin (A2). The particle size of the collected particles is described as the particle size of "<106" for convenience. In the following, the particle size of the sieved particles is similarly described using the value of the nominal opening of the sieve. In Example 12, the water-absorbent resin (A2) was water-containing at this point, and the water content was 15% by mass. The shape was particulate.
28.5 g of water-absorbent resin (A2) having a particle size of 106 μm or less and a water content of 15% by mass is placed in a bag having a length of 28 cm and a width of 20 cm, and 1.5 g of pure water is sprayed little by little each time. I shook it. At this time, instead of applying pressure to the resins to knead them, the bags were filled with air and rotated to be shaken. As a result, particles of the water-absorbent resin (A2) further contained in water were obtained. All the pure water was absorbed by the water-absorbent resin (A2) in the bag. The obtained water-containing water-absorbent resin was used as a water-retaining material for evaluation.
　実施例１３～１４
　分級に用いる篩を適宜変更し、実施例１２と同様にして表２に記載の粒子径を有する吸水性樹脂（Ａ２）を得た。次いで、吸水性樹脂（Ａ２）の含水率に応じて当該吸水性樹脂（Ａ２）と水を混合する量を表２に記載の通り変更した以外は、実施例１２と同様にして保水材を得た。 Examples 13-14
The sieve used for classification was appropriately changed to obtain a water-absorbent resin (A2) having the particle size shown in Table 2 in the same manner as in Example 12. Next, a water-retaining material was obtained in the same manner as in Example 12 except that the amount of the water-absorbent resin (A2) mixed with water was changed as shown in Table 2 according to the water content of the water-absorbent resin (A2). rice field.
　実施例１５
吸水性樹脂（Ｂ２）を公称目開き１０６μｍの篩と公称目開き２５０μｍの篩によって分級し、粒子径が１０６μｍ～２５０μｍの吸水性樹脂（Ｂ２）を得た。実施例１５において、この時点で吸水性樹脂（Ｂ２）は含水しており、含水率は４質量％であった。また形状は粒子状であった。
　当該粒子径が１０６μｍ～２５０μｍで、含水率が４質量％の吸水性樹脂（Ｂ２）２７ｇを、実施例１２で使用したものと同じ袋に入れ、純水３ｇを少量ずつスプレー噴霧し、その都度振り混ぜた。このとき、樹脂同士に圧力をかけて練るようにするのではなく、袋を空気で満たして回転させるようにして振り混ぜた。これにより、さらに含水した吸水性樹脂（Ｂ２）の粒子を得た。袋内で純水は全て吸水性樹脂（Ｂ２）に吸収されていた。得られた含水した吸水性樹脂を保水材として、評価を行った。 Example 15
The water-absorbent resin (B2) was classified by a sieve having a nominal opening of 106 μm and a sieve having a nominal opening of 250 μm to obtain a water-absorbent resin (B2) having a particle size of 106 μm to 250 μm. In Example 15, the water-absorbent resin (B2) was water-containing at this point, and the water content was 4% by mass. The shape was particulate.
27 g of a water-absorbent resin (B2) having a particle size of 106 μm to 250 μm and a water content of 4% by mass was placed in the same bag as that used in Example 12, and 3 g of pure water was sprayed little by little each time. I shook it. At this time, instead of applying pressure to the resins to knead them, the bags were filled with air and rotated to be shaken. As a result, particles of the water-absorbent resin (B2) further contained in water were obtained. All the pure water was absorbed by the water-absorbent resin (B2) in the bag. The obtained water-containing water-absorbent resin was used as a water-retaining material for evaluation.
　実施例１６～２０
分級に用いる篩を適宜変更し、実施例１５と同様にして表２に記載の粒子径を有する吸水性樹脂（Ｂ２）を得た。次いで、吸水性樹脂（Ｂ２）の含水率に応じて当該吸水性樹脂（Ｂ２）と水を混合する量を表２に記載の通り変更した以外は、実施例１５と同様にして保水材を得た。 Examples 16-20
The sieve used for classification was appropriately changed to obtain a water-absorbent resin (B2) having the particle size shown in Table 2 in the same manner as in Example 15. Next, a water-retaining material was obtained in the same manner as in Example 15 except that the amount of the water-absorbent resin (B2) mixed with water was changed as shown in Table 2 according to the water content of the water-absorbent resin (B2). rice field.
　実施例１２～２０においてそれぞれ得た粒子を保水材として評価した。それらの結果を表２に示す The particles obtained in Examples 12 to 20 were evaluated as water retention materials. The results are shown in Table 2.
Figure JPOXMLDOC01-appb-T000015
Figure JPOXMLDOC01-appb-T000015
　表２に示されている通り、実施例１２～２０の保水材はいずれも、優れた吸水速度を示した。また、表２に示されている通り、実施例の保水材は、高い塩化カルシウム水溶液吸収量も示した。また、本発明の保水材の、カルシウム塩の存在下での吸水量は、長期間にわたって低下しにくいものであった。 As shown in Table 2, all the water-retaining materials of Examples 12 to 20 showed excellent water absorption rates. In addition, as shown in Table 2, the water-retaining material of the example also showed a high absorption amount of calcium chloride aqueous solution. In addition, the amount of water absorbed by the water-retaining material of the present invention in the presence of a calcium salt was unlikely to decrease over a long period of time.
　本発明の保水材は、吸水速度に優れ、カルシウム塩の存在下であっても十分高い吸水量を示し、この吸水量は長期間にわたって低下しにくいため、農業用保水材として好適に利用できる。 The water-retaining material of the present invention has an excellent water absorption rate, exhibits a sufficiently high water absorption amount even in the presence of a calcium salt, and the water absorption amount does not easily decrease over a long period of time, so that it can be suitably used as a water-retaining material for agriculture.

Claims (15)

  1. 　吸水性樹脂を含んでなる農業用保水材であって、
    吸水性樹脂は、吸水性樹脂の全構成単位に対して０．１モル％以上、５０モル％以下のイオン性基を有しており、
    超音波を付与することにより２０質量％塩化ナトリウム水溶液を保水材に吸液させる保水材膨潤試験における、超音波を付与する前後の保水材の体積基準１０％粒子径Ｄ１０の変化率：
    　　　Ｄ１０の変化率
    　　＝(超音波を付与した後の保水材のＤ１０)／(超音波を付与する前の保水材のＤ１０)
    は１以下である、保水材。     Agricultural water-retaining material containing a water-absorbent resin.
    The water-absorbent resin has 0.1 mol% or more and 50 mol% or less of ionic groups with respect to all the constituent units of the water-absorbent resin.
    In the water-retaining material swelling test in which a 20% by mass sodium chloride aqueous solution is absorbed by the water-retaining material by applying ultrasonic waves, the rate of change of the volume-based 10 % particle diameter D10 of the water-retaining material before and after applying ultrasonic waves:
    Rate of change of D 10 = (D 10 of water-retaining material after applying ultrasonic waves) / (D 10 of water-retaining material before applying ultrasonic waves)
    Is 1 or less, water retention material.
  2. 　前記保水材は、含水率が１１質量％以上、５０質量％以下、嵩密度が０．２０ｇ/ｍＬ以上、１．２５ｇ/ｍＬ以下である、請求項１に記載の保水材。 The water-retaining material according to claim 1, wherein the water-retaining material has a water content of 11% by mass or more, 50% by mass or less, and a bulk density of 0.20 g / mL or more and 1.25 g / mL or less.
  3. 　前記保水材は、公称目開き３０００μｍの篩を通過し、かつ公称目開き１０μｍの篩を通過しない粒度を有する、請求項１または２に記載の保水材。 The water-retaining material according to claim 1 or 2, wherein the water-retaining material has a particle size that passes through a sieve having a nominal opening of 3000 μm and does not pass through a sieve having a nominal opening of 10 μm.
  4. 　前記保水材膨潤試験において超音波を付与した後の状態における、最も小粒子径側の極大粒子径は１μｍ以上、１０００μｍ以下である、請求項１～３のいずれかに記載の保水材。 The water-retaining material according to any one of claims 1 to 3, wherein the maximum particle size on the smallest particle size side is 1 μm or more and 1000 μm or less in the state after applying ultrasonic waves in the water-retaining material swelling test.
  5. 　前記吸水性樹脂は、前記イオン性基として、カルボキシル基、スルホン酸基およびアンモニウム基からなる群から選択される１以上を有する、請求項１～４のいずれかに記載の保水材。 The water-retaining material according to any one of claims 1 to 4, wherein the water-absorbent resin has one or more selected from the group consisting of a carboxyl group, a sulfonic acid group and an ammonium group as the ionic group.
  6. 　前記吸水性樹脂は、ビニルアルコール系重合体、アクリル酸系重合体、アクリルアミド系重合体およびメタクリル酸系重合体からなる群から選択される１以上を含む、請求項１～５のいずれかに記載の保水材。 The method according to any one of claims 1 to 5, wherein the water-absorbent resin comprises one or more selected from the group consisting of a vinyl alcohol-based polymer, an acrylic acid-based polymer, an acrylamide-based polymer, and a methacrylic acid-based polymer. Water retention material.
  7. 　前記ビニルアルコール系重合体は、アクリル酸、メタクリル酸、マレイン酸、イタコン酸およびそれらの誘導体からなる群から選択される１種以上のモノマー構成単位を含む、請求項６に記載の保水材。 The water-retaining material according to claim 6, wherein the vinyl alcohol-based polymer contains one or more monomer constituent units selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, itaconic acid and derivatives thereof.
  8. 　前記吸水性樹脂は架橋構造を有する、請求項１～７のいずれかに記載の保水材。 The water-retaining material according to any one of claims 1 to 7, wherein the water-absorbent resin has a crosslinked structure.
  9. 　育苗用である、請求項１～８のいずれかに記載の保水材。 The water-retaining material according to any one of claims 1 to 8, which is used for raising seedlings.
  10. 　前記吸水性樹脂は、吸水時間（Ｔ２）が１０秒以下である、請求項１～９のいずれかに記載の保水材。 The water-retaining material according to any one of claims 1 to 9, wherein the water-absorbent resin has a water absorption time (T2) of 10 seconds or less.
  11. 　一次粒子として存在する吸水性樹脂を、膨潤させた状態で接触させることにより凝集させる凝集工程、および
    　凝集した吸水性樹脂を、０．２ＭＰａ以下の圧力下で乾燥する乾燥工程
    を含む、請求項１～１０のいずれか記載の保水材の製造方法。     Claim 1 includes a coagulation step of agglomerating a water-absorbent resin existing as primary particles by contacting them in a swollen state, and a drying step of drying the agglomerated water-absorbent resin under a pressure of 0.2 MPa or less. The method for producing a water-retaining material according to any one of 10.
  12. 　前記凝集工程において、前記吸水性樹脂を膨潤させる前において、一次粒子として存在する吸水性樹脂の含水率は１５質量％以下である、請求項１１に記載の方法。 The method according to claim 11, wherein in the aggregation step, the water content of the water-absorbent resin existing as primary particles is 15% by mass or less before the water-absorbent resin is swollen.
  13. 　粒子として存在する吸水性樹脂を、膨潤させた状態で接触させることにより凝集させる凝集工程を含む、請求項１～１０のいずれか記載の保水材の製造方法。 The method for producing a water-retaining material according to any one of claims 1 to 10, further comprising an agglomeration step of agglomerating a water-absorbent resin existing as particles by contacting them in a swollen state.
  14. 　前記凝集工程において、前記吸水性樹脂を膨潤させる前において、粒子として存在する吸水性樹脂の含水率は１５質量％以下である、請求項１３に記載の方法。 The method according to claim 13, wherein in the aggregation step, the water content of the water-absorbent resin existing as particles is 15% by mass or less before the water-absorbent resin is swollen.
  15. 　前記凝集工程の前、前記凝集工程と同時、または前記凝集工程の後に、吸水性樹脂を架橋させる架橋工程を更に含む、請求項１１～１４のいずれかに記載の方法。 The method according to any one of claims 11 to 14, further comprising a cross-linking step of cross-linking the water-absorbent resin before the aggregating step, at the same time as the aggregating step, or after the aggregating step.
PCT/JP2021/047069 2020-12-28 2021-12-20 Water retention material for agriculture, and production method therefor WO2022145274A1 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
JP2020219318A JP2024022704A (en) 2020-12-28 2020-12-28 Agricultural water retaining material and its manufacturing method
JP2020-219320 2020-12-28
JP2020219320A JP2024022705A (en) 2020-12-28 2020-12-28 Agricultural water retaining material and its manufacturing method
JP2020-219318 2020-12-28

Publications (1)

Publication Number Publication Date
WO2022145274A1 true WO2022145274A1 (en) 2022-07-07

Family

ID=82259252

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2021/047069 WO2022145274A1 (en) 2020-12-28 2021-12-20 Water retention material for agriculture, and production method therefor

Country Status (2)

Country Link
TW (1) TW202239321A (en)
WO (1) WO2022145274A1 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2024024706A1 (en) * 2022-07-27 2024-02-01 三洋化成工業株式会社 Water-absorbent resin composition for plant cultivation

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0279911A (en) * 1988-09-14 1990-03-20 Sanyo Chem Ind Ltd Water-holding agent for soil and water-holding method
JPH08256592A (en) * 1995-03-24 1996-10-08 Showa Denko Kk Artificial culture soil
JP2007513205A (en) * 2003-12-05 2007-05-24 株式会社日本触媒 Water-retaining material for particulate plant growth mainly composed of water-absorbing resin
JP2010041999A (en) * 2008-07-17 2010-02-25 Iej:Kk Botanical mat
JP2015083693A (en) * 2010-04-07 2015-04-30 株式会社日本触媒 Method for manufacturing polyacrylic acid (salt)-based water-absorbing resin powder and polyacrylic acid (salt)-based water-absorbing resin powder
CN106010559A (en) * 2016-05-31 2016-10-12 山东胜伟园林科技有限公司 Bentonite-containing water retaining agent used for corn in saline and alkaline land, and preparation method thereof
JP2018145326A (en) * 2017-03-07 2018-09-20 株式会社クラレ Water-absorbing resin

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0279911A (en) * 1988-09-14 1990-03-20 Sanyo Chem Ind Ltd Water-holding agent for soil and water-holding method
JPH08256592A (en) * 1995-03-24 1996-10-08 Showa Denko Kk Artificial culture soil
JP2007513205A (en) * 2003-12-05 2007-05-24 株式会社日本触媒 Water-retaining material for particulate plant growth mainly composed of water-absorbing resin
JP2010041999A (en) * 2008-07-17 2010-02-25 Iej:Kk Botanical mat
JP2015083693A (en) * 2010-04-07 2015-04-30 株式会社日本触媒 Method for manufacturing polyacrylic acid (salt)-based water-absorbing resin powder and polyacrylic acid (salt)-based water-absorbing resin powder
CN106010559A (en) * 2016-05-31 2016-10-12 山东胜伟园林科技有限公司 Bentonite-containing water retaining agent used for corn in saline and alkaline land, and preparation method thereof
JP2018145326A (en) * 2017-03-07 2018-09-20 株式会社クラレ Water-absorbing resin

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2024024706A1 (en) * 2022-07-27 2024-02-01 三洋化成工業株式会社 Water-absorbent resin composition for plant cultivation

Also Published As

Publication number Publication date
TW202239321A (en) 2022-10-16

Similar Documents

Publication Publication Date Title
JP4133807B2 (en) Composition containing mineral substance and sponge structure water-absorbing anionic polymer, and production method and use thereof
CN100391548C (en) Water absorbent and producing method of same
BRPI0610229A2 (en) water swellable hybrid material with inorganic additives and process for their preparation
US20110094967A1 (en) Composite material composed of polymer materials and a porous mineral matrix and the production and use thereof
JP2005500407A5 (en)
WO2010044281A1 (en) Particulate water-absorbing agent for growth of plant which comprises water-absorptive polyacrylic acid (salt) resin as main ingredient
CN111511778B (en) Water-absorbent resin and agricultural water-retaining material
WO2022145274A1 (en) Water retention material for agriculture, and production method therefor
WO2020075725A1 (en) Paddy rice-raising seedling culture soil
JP7010435B2 (en) Water-absorbent resin and water-retaining material for agriculture
JP2018145326A (en) Water-absorbing resin
JP2009148163A (en) Water-retentive agent for vegetation
WO2021002442A1 (en) Water-retaining material
JP7181842B2 (en) Agricultural water retention material
JPH10191777A (en) Water holding agent for soil or horticulture
JP2012080785A (en) Water swelling pellet-like plant growing medium, and method for producing the same
JP2024022705A (en) Agricultural water retaining material and its manufacturing method
JP2002125457A (en) Water-holding material for raising plant body
JP2024022704A (en) Agricultural water retaining material and its manufacturing method
JP3839411B2 (en) Reusable animal waste treatment material and method for reuse
JP4694810B2 (en) Water-retaining material for plant growth mainly composed of water-absorbent resin
JP7253463B2 (en) Vinyl alcohol crosslinked copolymer
JP2021010303A (en) Water-retaining material
WO2020262382A1 (en) Water-absorbent copolymer
JP2009131165A (en) Water-holding agent for growing plant

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 21915134

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 21915134

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: JP