JP2021010303A - Water-retaining material - Google Patents

Abstract

To provide a water-retaining material that is less likely to cause fertilizer burn on plants and allows the plants to grow well.SOLUTION: A water-retaining material comprises a water-absorbing resin. The water-absorbing resin comprises at least one element inside the resin. The element does not constitute a polymer skeleton of the resin and is one or more elements selected from a group consisting of a phosphorus element, a potassium element, and a nitrogen element.SELECTED DRAWING: None

Description

The present invention relates to a water retention material.

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. (See, for example, Patent Documents 1 to 3). These agricultural water-retaining materials contain highly water-absorbent resin (SAP) as a main component, and are effective in extremely small amounts compared to, for example, peat moss used for improving the water-retaining property of the entire soil. Has the advantage of being less burdensome to use.

Even when a water-retaining material is used as a medium, fertilizer is usually required for plant growth, and Patent Document 4 discloses a method in which a water-absorbent resin and fertilizer are mixed and applied to soil.

International Publication No. 1998/005196 Pamphlet Special Table 2013-544929 Special Table 2013-540164 JP-A-59-102888

However, as a result of studies by the present inventors, it was found that the mixture of the water-absorbent resin and the fertilizer disclosed in Patent Document 4 inhibits the good growth of roots. It was presumed that when the fertilizer concentration around the roots was high, water flowed out from the roots due to osmotic pressure, a so-called root burning condition occurred. That is, by adding the water-absorbent resin to the medium, the water content of the medium is remarkably increased, and the fertilizer is more easily dissolved as compared with the medium containing no water-absorbent resin, so that root burning is likely to occur. Do you get it.

Therefore, an object of the present invention is to solve the above-mentioned problems, and to provide a water-retaining material which is less likely to cause root burning due to fertilizer and has good plant growth.

As a result of diligent studies, the present inventors have found that the above problems can be solved, and have completed the present invention.

That is, the present invention includes the following preferred embodiments.
[1] A water-retaining material containing a water-absorbent resin, wherein the water-absorbent resin contains an element that does not constitute a polymer skeleton of the resin, and the elements are phosphorus element and potassium element. A water retention material, which is one or more elements selected from the group consisting of and nitrogen elements.
[2] The content of one or more elements selected from the group consisting of phosphorus element, potassium element and nitrogen element existing inside the resin is 0.001 to 50% by mass with respect to the mass of the resin. A water-retaining material according to [1].
[3] The water-retaining material further contains one or more elements selected from the group consisting of phosphorus element, potassium element and nitrogen element, which are not present inside the resin but are present in the water-retaining material, [1] or. The water retention material according to [2].
[4] The content of one or more elements selected from the group consisting of phosphorus element, potassium element and nitrogen element, which is not present inside the resin but is present in the water retention material, is based on the mass of the resin. The water-retaining material according to any one of [1] to [3], which is 0.001 to 50% by mass.
[5] The water-absorbent resin contains a polymer selected from the group consisting of vinyl alcohol-based polymers, acrylic acid-based polymers, acrylamide-based polymers, methacrylic acid-based polymers, and starch-based polymers [1]. ] To [4].
[6] The water-retaining material according to [5], wherein the vinyl alcohol-based polymer contains a copolymer containing a vinyl alcohol constituent unit and a monomer constituent unit having an ionic group or a derivative thereof.
[7] The water-retaining material according to [5] or [6], wherein the vinyl alcohol-based polymer contains potassium ion or ammonium ion as a counter cation of an ionic group.
[8] The water-retaining material according to any one of [5] to [7], wherein the vinyl alcohol-based polymer has a crosslinked structure.
[9] The water-retaining material according to any one of [1] to [8], which is for agriculture.
[10] The water-retaining material according to any one of [1] to [9], which is used for raising seedlings.

According to the present invention, it is possible to provide a water-retaining material that is less likely to cause root burning due to fertilizer and has good plant growth.

The following is an example of an embodiment of the present invention, and is not intended to limit the present invention to the following embodiments.

<Water retention material>
The water-retaining material of the present invention is a water-retaining material containing a water-absorbent resin, and the water-absorbent resin contains an element that does not constitute a polymer skeleton of the resin inside the resin, and the element is phosphorus. One or more elements selected from the group consisting of elements, potassium elements and nitrogen elements.

<Phosphorus element, potassium element and nitrogen element>
The water-retaining material of the present invention contains one or more elements selected from the group consisting of phosphorus element, potassium element and nitrogen element inside the water-absorbent resin.

In the present specification, the content of elements that do not constitute the polymer skeleton of the resin inside the water-absorbent resin is usually the element content of the untreated resin cross section (included inside the resin) as described in Examples described later. , The total value of the element content constituting the polymer skeleton and the element content not constituting the polymer skeleton), the element content of the resin cross section after washing with water and drying treatment (element content constituting the polymer skeleton) Refers to the value calculated by subtraction.

The origins of the phosphorus element, potassium element and nitrogen element include, for example, potassium sulfate, potassium chloride, potassium carbonate, potassium hydrogen carbonate, ammonium chloride, ammonium nitrate, ammonium sulfate, sodium nitrate, phosphoric acid, diammonium hydrogen phosphate and perphosphate. The atoms such as lime, urea, primary calcium phosphate, potassium nitrate, potassium chloride, potassium hydroxide, ammonium ion, nitrate ion, nitrite ion, phosphate ion, dihydrogen phosphate ion, monohydrogen phosphate ion and potassium ion Examples thereof include compounds or ions, and from the viewpoint of easy utilization in plants, diammonium hydrogen phosphate, potassium sulfate, potassium chloride, potassium hydroxide, potassium nitrate, ammonium sulfate, urea and lime perphosphate are preferable.

The content of one or more elements selected from the group consisting of phosphorus element, potassium element and nitrogen element existing inside the resin shall be 0.001 to 50% by mass with respect to the mass of the resin. Is more preferable, 0.05 to 40% by mass is more preferable, 0.1 to 30% by mass is further preferable, and 1.0 to 25% by mass is even more preferable. It is preferable that the content of one or more elements selected from the group consisting of phosphorus element, potassium element and nitrogen element existing inside the resin is in the above range because the element is easily released from the inside of the resin. The content of one or more elements selected from the group consisting of phosphorus element, potassium element and nitrogen element existing inside the resin is, for example, an energy-dispersed X-ray element as described in Examples described later. It can be measured by analysis or ICP-AES (inductively coupled plasma emission spectrometry) method.
The elements existing inside the resin may be two or more kinds of phosphorus element, potassium element and nitrogen element, and are phosphorus element and potassium element, phosphorus element and nitrogen element, and potassium element and phosphorus element. Any of the above is preferable. Further, all of the phosphorus element, potassium element and nitrogen element are also preferable.
The total content of phosphorus element, potassium element and nitrogen element existing inside the resin is preferably 0.002% by mass or more, more preferably 0.06% by mass or more, based on the mass of the resin. , 0.2% by mass or more is more preferable, and 1.1% by mass or more is most preferable. What is the content? 70% by mass or less is preferable, 45% by mass or less is more preferable, 32% by mass or less is further preferable, 27% by mass or less is further preferable, 10% by mass or less is particularly preferable, and 5% by mass or less is most preferable.

In the present specification, the mass of the resin is the mass in the dry state. As used herein, the term "dry state" refers to an amount (for example, a mass change of the resin before and after heating at 60 ° C. under vacuum) for volatile components such as water or an organic solvent. For example, 0.1% by mass or more) may not be contained.

The water-retaining material of the present invention may further contain one or more elements selected from the group consisting of phosphorus element, potassium element and nitrogen element, which are not present in the resin but are present in the water-retaining material.

One or more elements selected from the group consisting of phosphorus element, potassium element and nitrogen element, which are not present inside the resin but are present in the water retention material, are the same as the elements contained inside the resin. May be different.

The content of one or more elements selected from the group consisting of phosphorus element, potassium element and nitrogen element, which is not present inside the resin but is present in the water retention material, is 0.001 with respect to the mass of the resin. It is preferably ~ 50% by mass, more preferably 0.3 to 20% by mass, further preferably 1.0 to 15% by mass, and even more preferably 1.5 to 10% by mass. If the content of one or more elements selected from the group consisting of phosphorus element, potassium element and nitrogen element, which is not present inside the resin but is present in the water retention material, is within the above range, the plant causes root burning. It is preferable because it is difficult.
The elements that do not exist inside the resin but exist in the water-retaining material may be two or more of phosphorus element, potassium element and nitrogen element, and are phosphorus element and potassium element, phosphorus element and nitrogen element, and potassium. Both the element and the phosphorus element are preferable. Further, all of the phosphorus element, potassium element and nitrogen element are also preferable.
The total content of phosphorus element, potassium element and nitrogen element, which does not exist inside the resin but exists in the water retention material, is preferably 0.4% by mass or more with respect to the mass of the resin, and is preferably 1.1% by mass. It is more preferably mass% or more, and further preferably 1.6 mass% or more. What is the content? It is preferably 70% by mass or less, more preferably 25% by mass or less, further preferably 17% by mass or less, further preferably 11% by mass or less, and most preferably 5% by mass or less.

<Water-absorbent resin>
The water-absorbent resin in the present invention is not particularly limited. Examples of the water-absorbent resin include acrylic acid-based polymers, isobutylene-maleic acid-based copolymers, carboxymethyl cellulose-based polymers, acrylonitrile saponified polymers, alginate ester-based polymers, sulfonic acid-based polymers, and vinyl acetate. -Maleic anhydride-based copolymer, N-vinylacetamide-based polymer, acrylamide-based polymer, methacrylic acid-based polymer, starch-based polymer, ethylene glycol-based polymer, vinyl alcohol-based polymer, and the like may be used. .. These polymers may be used alone or in combination of two or more.

From the viewpoint of ease of production and water retention, the water-absorbent resin is preferably selected from the group consisting of vinyl alcohol-based polymers, acrylic acid-based polymers, acrylamide-based polymers, methacrylic acid-based polymers and starch-based polymers. The water-absorbent resin is a vinyl alcohol-based polymer, and more preferably a vinyl alcohol-based polymer is contained, and in one preferred embodiment, the water-absorbent resin is a vinyl alcohol-based polymer.

<Vinyl alcohol polymer>
As the vinyl alcohol-based polymer [hereinafter, may be referred to as vinyl alcohol-based polymer (A)], for example, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, and their vinyl alcohol units are acetalized by an acetalizing agent. The ones that have been made are listed. From the viewpoint of good affinity with one or more elements selected from the group consisting of phosphorus element, potassium element and nitrogen element, the vinyl alcohol-based polymer (A) has a vinyl alcohol constituent unit and an ionic group or an ionic group thereof. It is preferable to contain a copolymer containing a monomer constituent unit having a derivative. The ionic group or a derivative thereof is preferably a carboxyl group, a sulfonic acid group, an ammonium group or a salt thereof, and more preferably a carboxyl group or a salt thereof. The content of the vinyl alcohol-based 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, still more preferably 95% by mass or more. Yes, it may be 100% by mass. Further, 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. The above is particularly preferable, and it is 100% by mass. That is, in one preferred embodiment, the vinyl alcohol-based polymer (A) is composed of a copolymer of a vinyl alcohol constituent unit and a monomer constituent unit having an ionic group or a derivative thereof.

When the vinyl alcoholic polymer (A) has a carboxyl group, a sulfonic acid group or an ammonium group as an ionic group, the vinyl alcoholic polymer (A) may be, for example, (i-1) a carboxyl group, a sulfonic acid group or A saponified product of a copolymer of a vinyl ester and one or more selected from a monomer having an ammonium group and a derivative of the monomer; (i-2) a vinyl alcohol-based polymer and a functional group capable of reacting with a hydroxyl group (b1). ) And a reaction product of a compound (B) having a carboxyl group and / or a functional group (b2) capable of inducing a carboxyl group; and the like.

In the above (i-1), the monomer having a carboxyl group is not particularly limited, and examples thereof include acrylic acid, methacrylic acid, itaconic acid, and maleic acid. Examples of the derivative of the monomer having a carboxyl group include an anhydride, an esterified product, and a neutralized product of the monomer, and examples thereof include methyl acrylate, methyl methacrylate, dimethyl itaconic acid, monomethyl maleate, and the like. Maleic anhydride or the like is used.

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-methylpropane sulfonic acid, and p-styrene sulfonic acid. 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, sodium 2-acrylamide-2-methylpropane sulfonate and p-. Sodium styrene sulfonate or the like is used.

In the above (i-1), the monomer having an ammonium group is not particularly limited, and for example, diallyldimethylammonium chloride, vinyltrimethylammonium chloride, allyltrimethylammonium chloride, p-vinylbenzyltrimethylammonium chloride, 3- (methacrylamide). ) Propyltrimethylammonium chloride. Examples of the derivative of the monomer having an ammonium group include amines of the monomer, and for example, diallylmethylamine, vinylamine, allylamine, p-vinylbenamine 3- (methacrylamide) propylamine and the like are used.

In the above (i-1), the vinyl ester is not particularly limited, but vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, vinyl stearate, vinyl benzoate, vinyl trifluoroacetate, vinyl pivalate and the like. However, vinyl acetate is preferable.

The method for producing the saponified product of (i-1) is not particularly limited, and one or more selected from a monomer having a carboxyl group and a derivative of the monomer and a vinyl ester are known using a known polymerization initiator. It can be produced by carrying out the polymerization reaction of the above, and then carrying out the saponification reaction by a known method.

The compound (B) used in (i-2) above, which has a functional group (b1) capable of reacting with a hydroxyl group and a functional group (b2) capable of inducing a carboxyl group and / or a carboxyl group, reacts with the hydroxyl group. The possible functional group (b1) is not particularly limited, and examples thereof include an aldehyde group, a carboxyl group, an amino group, and derivatives of these functional groups. Of these, aldehyde groups and aldehyde group derivatives are preferable from the viewpoint of ease of production or durability of the vinyl alcohol polymer. That is, as the compound (B), an aldehyde having a carboxyl group and / or a derivative of the aldehyde is preferable.

That is, the reaction product of the above (i-2) is a vinyl alcohol-based weight in which at least a part of vinyl alcohol units are acetalized by one or more selected from an aldehyde having a carboxyl group and / or a derivative of the aldehyde. A coalescence [hereinafter, may be referred to as a vinyl alcohol polymer (A-1)] is preferable.

The aldehyde having a carboxyl group, which is the compound (B), is not particularly limited, and examples thereof include glyoxylic acid, 2-formylpropanoic acid, 3-formylpropanoic acid, and phthalaldehyde acid. Of these, glyoxylic acid is preferable from the viewpoint of availability and biodegradability. Examples of the derivative of the aldehyde having a carboxyl group, which is the compound (B), include anhydrides, hydrates, esters, acetals, and neutralizers of the aldehydes, and examples thereof include glyoxyphosphate. , Glyoxylic acid monohydrate, glyoxylic acid ester, dimethylacetal glyoxylate and the like are used.

Examples of the counter cation of the glyoxylate include alkali metal ions such as sodium ion, potassium ion, and lithium ion; alkaline earth metal ions such as calcium ion and magnesium ion; and organic cations such as ammonium ion and alkylammonium ion: And so on. Of these, potassium ions, calcium ions, and magnesium ions are preferable from the viewpoint of easily developing a more excellent water absorption rate. Calcium ions are more preferable from the viewpoint of easily maintaining water absorption at the time of contact with divalent ions contained in soil, and potassium ions are more preferable from the viewpoint of plant growth. The above counter cations are considered to constitute the polymer skeleton of the resin.

Examples of the glyoxylic acid ester include methyl glyoxylate, ethyl glyoxylate, propyl glyoxylate, isopropyl glyoxylate, butyl glyoxylate, isobutyl glyoxylate, sec-butyl glyoxylate, tert-butyl glyoxylate, hexyl glyoxylate, and glyoxylic acid. Examples thereof include octyl and 2-ethylhexyl glyoxylate.

The method for producing the vinyl alcohol-based polymer (A-1) is not particularly limited, and at least a part of the vinyl alcohol units of the vinyl alcohol-based polymer produced by a known method can be used in the presence or absence of a catalyst. It can be produced by acetalizing with one or more selected from an aldehyde having a carboxyl group and a derivative of the aldehyde.

Examples of the catalyst include inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid; organic acids such as carboxylic acid and sulfonic acid; solid acids such as cation exchange resins and heteropolyacids; and the like. These catalysts may be used alone or in combination of two or more. Since glyoxylic acid is also an acid that promotes the acetalization reaction, it also acts as a catalyst when producing the vinyl alcohol polymer (A-1). That is, from the viewpoint of ease of treatment after the reaction, a method of using glyoxylic acid as the aldehyde having a carboxyl group is preferable in the production of the vinyl alcohol polymer (A-1).

The vinyl alcohol-based polymer used as a raw material in the production of the vinyl alcohol-based polymer (A-1) is an industrially produced commercial product; vinyl carboxylate such as vinyl acetate and other monomers are allowed to coexist as necessary. Then, a known polymerization reaction was carried out using a known polymerization initiator, and then a saponification reaction was carried out by a known method; a product produced by a cationic polymerization reaction and a hydrolysis reaction of vinyl ether; a direct polymerization of acetaldehyde. However, it is preferable that the product is produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate. The degree of saponification of the vinyl alcohol-based polymer used as the raw material is preferably 30 mol% or more, more preferably 60 mol% or more, and 80 mol from the viewpoint that an appropriate amount of carboxyl group can be easily introduced in one embodiment of the present invention. % Or more is more preferable.

The degree of acetalization of the vinyl alcohol polymer (A-1) is preferably 0.01 mol% or more and 85 mol% or less. When the degree of acetalization is within the above range, water absorption is likely to be improved. From the above viewpoint, the degree of acetalization is preferably 0.1 mol% or more, more preferably 1 mol% or more, further preferably 5 mol% or more, still more preferably 8 mol% or more, and particularly preferably 10 mol% or more. And preferably 80 mol% or less, more preferably 70 mol% or less, still more preferably 60 mol% or less, still more preferably 50 mol% or less, particularly preferably 45 mol% or less, still more preferably 40 mol% or less. Is.

From the viewpoint of easily suppressing elution of the vinyl alcohol polymer during seedling raising, in the production of the vinyl alcohol polymer (A-1), an aldehyde having a carboxyl group and an aldehyde other than the derivative of the aldehyde are used in combination. The acetalization reaction may be carried out. Such other aldehydes include aliphatic aldehydes such as, for example, formaldehyde, acetaldehyde, propionaldehyde, n-butylaldehyde, i-butylaldehyde, sec-butylaldehyde, and tert-butylaldehyde; benzaldehyde, anisaldehyde, silica skin aldehyde, and the like. Aromatic aldehydes such as 4-benzyloxybenzaldehyde, 3-benzyloxybenzaldehyde, 4-amyloxybenzaldehyde, and 3-amyloxybenzaldehyde; and the like. Of these, formaldehyde, acetaldehyde, and n-butyraldehyde are preferable from the viewpoint of ease of production or water absorption of the obtained vinyl alcohol-based polymer. When other aldehydes are used in combination, the amount used is not particularly limited, but is usually 0.01 to 30 mol%, preferably 0.1 to 10 mol%, based on the total of the aldehyde having a carboxylic acid and the derivative of the aldehyde. %, More preferably 1-5 mol%. When the amount of other aldehyde used is not more than the upper limit value, the water absorption of the obtained vinyl alcohol polymer tends to be excellent, and when it is more than the lower limit value, the vinyl alcohol type obtained by using another aldehyde in combination is used. It is easy to obtain the effect of suppressing elution of the polymer during seedling raising. The other aldehyde may be used as a derivative of, for example, an acetal compound.

In one embodiment of the present invention, when the vinyl alcoholic polymer (A) has an ionic group (for example, a carboxyl group), a part or all of the ionic group is a salt (carboxylic when the ionic group is a carboxyl group). It may be in the form of (acetate). Examples of salt countercations 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; Other metal ions such as aluminum ions and zinc ions; onium cations such as ammonium ions, imidazoliums, pyridiniums, and phosphonium ions; and the like. Of these, potassium ions, calcium ions, and ammonium ions are preferable from the viewpoint of easily obtaining desired water absorption, and calcium ions are more preferable from the viewpoint of easily maintaining water absorption at the time of contact with divalent ions contained in soil. Preferably, potassium ions are more preferable from the viewpoint of plant growth. Therefore, in a preferred embodiment of the present invention, the vinyl alcohol-based polymer (A) has potassium ion or ammonium ion, preferably potassium ion, as a counter cation of the salt of the ionic group. When the ionic group is a carboxyl group, as a method for producing the vinyl alcoholic 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. Method using a neutralized product of a monomer (I); Method using a neutralized product of a compound having a functional group capable of reacting with a hydroxyl group and a carboxyl group in the above (i-2) (II); A method (III) of neutralizing after producing a vinyl alcoholic polymer (A) having a carboxyl group is mentioned, and the above method (III) is preferable.

In one embodiment of the present invention, when the vinyl alcohol polymer (A) has an ionic group, the amount of the ionic group in the vinyl alcohol polymer (A) is the vinyl alcohol polymer (A). ) Is preferably 0.1 mol% or more, more preferably 1 mol% or more, particularly preferably 3 mol% or more, most preferably 5 mol% or more, and preferably 80 mol% or less, based on all the constituent units of). It is more preferably 50 mol% or less, more preferably 40 mol% or less, more preferably 30 mol% or less, still more preferably 25 mol% or less, particularly preferably 20 mol% or less, and most preferably less than 18 mol%. When the amount of the ionic group is not less than the lower limit value, the water absorption of the vinyl alcohol polymer used in the present invention is more excellent, and when it is not more than the upper limit value, the divalent ion contained in the soil is used. It is easy to maintain water absorption even when in contact. 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 carboxyl groups is not more than the above upper limit value, it is easy to obtain more excellent weather resistance (particularly ultraviolet resistance). When a part or all of the ionic groups contained in the vinyl alcohol-based polymer (A) is in the form of a derivative (for example, a salt) thereof, the above-mentioned ionic group contents are the ionic groups and The content of the derivative or the content of the derivative of the ionic group.
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.

The content of the ionic group in the vinyl alcohol-based polymer (A), particularly the amount of the above-mentioned carboxyl group and the amount of the carboxyl group derived from acrylic acid or a salt thereof among the carboxyl groups, is, for example, solid ¹³ C-NMR. It can be measured by (nuclear magnetic resonance spectroscopy), FTIR (Fourier transform infrared spectroscopy), acid-base titration, or the like. In the present invention, the "constituent unit" means a repeating unit constituting the polymer. For example, a vinyl alcohol unit is "1 unit" and a structure in which two vinyl alcohol units are acetalized is "2 units". It will be counted as.

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, for example, FTIR (Fourier transform infrared spectroscopy), solid ¹³ C-NMR (nuclear magnetic resonance spectroscopy), etc., and is anhydrous when reacted with a certain amount of anhydrous acetic acid. It can also be calculated from the consumption of acetic acid.

The vinyl alcohol-based polymer (A) may contain a structural unit other than the vinyl alcohol structural unit. Examples of the above other structural units include vinyl acetate and vinyl carboxylate-derived structural units such as vinyl pivalate; olefin-derived structural units such as ethylene, 1-butene, and isobutylene; acrylic acid and its derivatives, and methacryl. Examples thereof include acids and their derivatives, acrylamide and its derivatives, methacrylicamide and its derivatives, maleic acid and its derivatives, and structural units derived from maleimide derivatives and the like. The other structural unit 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 15 mol% or less, based on all the structural units of the vinyl alcohol polymer (A). It may be 0 mol%. When the content of the other structural units is not more than the upper limit value, it is easy to obtain better water absorption and water absorption rate of the water retention material of the present invention.

The viscosity average degree of polymerization of the vinyl alcohol-based polymer (A) is not particularly limited, but from the viewpoint of ease of production, it is preferably 20000 or less, more preferably 10000 or less, still more preferably 4000 or less, and particularly preferably 3000 or less. is there. On the other hand, from the viewpoint of the mechanical properties of the vinyl alcohol polymer (A) and the elution resistance to water, it 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-based polymer (A) can be measured, for example, by a method according to JIS K 6726. When the vinyl alcohol-based copolymer (A) has a crosslinked structure as described later, for example, when the vinyl alcohol-based copolymer (A) has an acetal structure or an ester structure as the crosslinked structure, the measurement of the viscosity average degree of polymerization is performed. , Can be done after cutting the crosslinked 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) used in the present invention preferably contains a crosslinked structure from the viewpoint of preventing elution of the vinyl alcohol-based polymer during seedling raising. When the vinyl alcohol-based polymer (A) used in the present invention contains a crosslinked structure, it becomes a gel state when it absorbs water. The form of the crosslinked structure is not particularly limited, and examples thereof include a crosslinked structure having an ester bond, an ether bond, an acetal bond, and a carbon-carbon bond.

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). 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. Examples thereof include acetal bonds formed by the reaction. The carbon-carbon bond is, for example, carbon-carbon formed by coupling between carbon radicals of the vinyl alcohol polymer (A), which is generated when the vinyl alcohol polymer (A) is irradiated with active energy rays. Includes binding. These crosslinked structures may be contained alone or in combination of two or more. Of these, a crosslinked structure with an ester bond and 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 and UV resistance during seedling raising.
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 with, for example, an aldehyde having a carboxyl group and one or more selected from the aldehyde derivative. Although it may be formed in another 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 glyoxal, malonaldehyde, succinaldehyde, glutaaldehyde, 1,9-nonandial, adipaldehyde, malealdehyde, tartaraldehyde, citraldehyde, phthalaldehyde, isophthalaldehyde, terephthalaldehyde and the like.

When a cross-linking agent is added, the amount of the cross-linking agent in the vinyl alcohol-based polymer (A) is appropriately such that one or more elements selected from the group consisting of phosphorus element, potassium element and nitrogen element are appropriately added to the cross-linked structure. From the viewpoint of easy retention, it is preferably 0.001 mol% or more, more preferably 0.005 mol% or more, still more preferably 0.01 mol% or more, still more preferably 0.03 mol% or more, and preferably 0.03 mol% or more. It is 0.5 mol% or less, more preferably 0.4 mol% or less, still more preferably 0.3 mol% or less.

<Acrylic acid polymer>
Examples of the polymer that the water-absorbent resin may contain include acrylic acid-based polymers. In the present specification, the acrylic acid-based polymer is usually a homopolymer of acrylic acid or an acrylic acid derivative, and an acrylic acid or an acrylic acid derivative as a main monomer (a monomer having the largest mol% of the monomer components). It refers to an acrylic acid-based copolymer obtained by copolymerizing a monomer component. For example, as raw materials, acrylic acid, sodium acrylate, potassium acrylate, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, sec-butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate. And phenyl acrylate and the like, which are obtained by polymerizing one or more of these monomers and a cross-linking agent, or at least one of the above-mentioned monomers, a cross-linking agent, and at least another copolymerizable one. Examples thereof include those obtained by copolymerizing a seed monomer using a known method. Specifically, for example, a crosslinked product of an acrylic acid-sodium acrylate copolymer can be mentioned. Commercially available products include highly absorbent polymers (acrylic acid salt); Wako Pure Chemical Industries, Ltd., Acryhope (registered trademark); Nippon Shokubai Co., Ltd., Sunwet (registered trademark); Sanyo Chemical Industries, Ltd. ) Etc. can be mentioned.

<Acrylamide polymer>
Examples of the polymer that the water-absorbent resin may contain include an acrylamide-based polymer. In the present specification, the acrylamide-based polymer usually includes a homopolymer of acrylamide or an acrylamide derivative and a monomer component having acrylamide or an acrylamide derivative as a main monomer (a monomer having the largest molar% of the monomer components). It refers to an acrylamide-based copolymer obtained by polymerization. For example, examples of the raw material include acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, N-alkylacrylamide, etc., which are copolymerized with one or more of these monomers and a cross-linking agent, or at least one of the above. Examples thereof include those obtained by polymerizing a seed monomer, a cross-linking agent, and at least one other copolymerizable monomer by a known method. Specific examples thereof 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 storage crystal; manufactured by Scotts Miracle Glow, and Aquasorb (registered trademark); manufactured by SNF Co., Ltd.

<Methacrylic acid polymer>
Examples of the polymer that the water-absorbent resin may contain include a methacrylic acid-based polymer. In the present specification, the methacrylic acid-based polymer is usually a copolymer of methacrylic acid or a methacrylic acid derivative, and a methacrylic acid or a methacrylic acid derivative as a main monomer (a monomer having the largest mol% of the monomer components). It refers to a methacrylic acid-based copolymer obtained by copolymerizing a monomer component. For example, as raw materials, methacrylic acid, sodium methacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, propyl methacrylate, isopropyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, methacrylic acid (2-ethylhexyl), methacrylic acid (2-ethylhexyl) (T-Butylcyclohexyl), benzyl methacrylate, methacrylic acid (2,2,2-trifluoroethyl) and the like, which are obtained by polymerizing one or more of these monomers, or at least one of the above-mentioned monomers. , A cross-linking agent and at least one other monomer capable of copolymerization are copolymerized by a known method.

<Starch polymer>
Examples of the polymer that the water-absorbent resin may contain include starch-based polymers. Examples of the starch-based polymer include those obtained by graft-polymerizing starch with acrylic acid, sodium acrylate, potassium acrylate, acrylonitrile and the like.

<Additives>
The water-retaining material of the present invention may optionally contain an additive in addition to one or more elements selected from the group consisting of a water-absorbent resin and a phosphorus element, a potassium element and a nitrogen element. Examples of such additives include polysaccharides such as sodium alginate, chitin, chitosan, cellulose and derivatives thereof; polyethylene, polypropylene, ethylene-propylene copolymers, polystyrene, acrylonitrile-styrene copolymers, acrylonitrile-. Butadiene-styrene copolymer, 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 Resins such as diamine terephthalamide, polyhexamethylene diamine isophthalamide, polynonamethylene diamine terephthalamide, polyphenylene ether, polyoxymethylene, polyethylene glycol, polypropylene glycol, polytrimethylene glycol, polytetramethylene glycol, polyurethane; 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, amide-based thermoplastic elastomer, etc. Rubber / elastomers; UV absorbers, antioxidants, light stabilizers, plasticizers, organic solvents, defoaming agents, thickeners, surfactants, lubricants, antifungal agents, antistatic agents and the like. These additives may be used alone or in combination of two or more. When the water-retaining material contains an additive, the total content thereof may be a range that does not impair the effect of the present invention, and is usually 30% by mass or less, preferably 20% by mass or less, based on the total mass of the water-retaining material. is there. When these additives contain one or more elements selected from the group consisting of phosphorus element, potassium element and nitrogen element, the content thereof is preferably 3% by mass or less.

The shape of the water-retaining material of the present invention is preferably particulate. When the water-retaining material of the present invention is in the form of particles, the volume average particle diameter of the particles is preferably 1 μm or more, more preferably 50 μm or more, still more preferably 100 μm or more, particularly preferably 300 μm or more, and preferably 10,000 μm or less. It is more preferably 2000 μm or less, still more preferably 1500 μm or less. When the volume average particle diameter is at least the lower limit value, excellent handleability is excellent, and when it is at least the upper limit value, an excellent water absorption rate can be easily obtained. The volume average particle size can be measured by laser diffraction / scattering.

<Manufacturing method of water retention material>
The water-retaining material of the present invention includes, for example, a compound or ion containing (ii-1) a water-absorbent resin, one or more elements selected from the group consisting of phosphorus element, potassium element and nitrogen element, and optionally the above-mentioned additive. (Ii-2) A solution in which a compound containing one or more elements selected from the group consisting of a phosphorus element, a potassium element and a nitrogen element is dissolved in an arbitrary solvent in a water-absorbent resin or the element is prepared. A method of spraying and mixing a solution containing ions containing ions, or immersing a water-absorbent resin in the solution and mixing, and optionally mixing the mixed water-absorbent resin and the above additive, (ii-3). ) During the preparation of the water-absorbent resin, a compound and an ion containing one or more elements selected from the group consisting of phosphorus element, potassium element and nitrogen element are left, and optionally, the obtained preparation and the above additive are used. Can be produced by a method of mixing (ii-4) or a method of combining (ii-1) to (ii-3) described above. In the above (ii-1) to (ii-4), by adjusting the amount of the compound containing phosphorus element, potassium element and nitrogen element and the degree of cleaning of the water retention material, the phosphorus element, potassium element and nitrogen element The content of one or more compounds selected from the group consisting of can be adjusted.

In the above (ii-1) to (ii-3), the mixing may be carried out sequentially or simultaneously in a general device (for example, a reaction kettle and a mixer equipped with a stirring blade). In the above (ii-3), as the residue compound and ion, a compound that can be used for preparing a vinyl alcohol-based polymer, for example, potassium hydroxide, nitrate, ammonium nitrate, ammonium sulfate, ammonia, potassium hydrogen sulfate, phosphoric acid. , Potassium dihydrogen phosphate, dipotassium hydrogen phosphate, ammonium dihydrogen phosphate, potassium diammonium hydrogen phosphate ion, ammonium ion, phosphate ion, hydrogen phosphate ion, dihydrogen phosphate ion, nitrate ion, etc. Be done.

In one preferred embodiment, the water retention material of the present invention is for agriculture. In a more preferred embodiment, the water retention material of the present invention is for raising seedlings. Therefore, in one embodiment of the present invention, the water retention material can be used as a medium for raising seedlings. The medium may contain any component other than the water retention material.

<Arbitrary ingredient>
Examples of such an optional component include a resin other than the water-absorbent resin contained in the water-retaining material, hilling, other optional components described later, and a combination thereof. In the following description of the preferable content of the optional component when the medium contains the optional component, other than the compound containing one or more elements selected from the group consisting of phosphorus element, potassium element and nitrogen element. The mass of the medium constituents (water-absorbent resin contained in the water-retaining material, additives when contained in the water-retaining material, and optional components when contained) may be the mass in a dry state.

<Resin other than water-absorbent resin>
Examples of resins other than the water-absorbent resin include polyethylene, polypropylene, alkyd resin, phenol 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.

<Cultivation>
When the medium contains soil, the roots grow in the gaps between the soil, so that the roots are easily entangled with each other, and it is easy to obtain excellent drainage and air permeability of the medium. The soil is not particularly limited, and one type of commercially available soil can be used alone or in combination of two or more. Further, an optional component described later can be attached to the soil by a conventional method (for example, a method of spraying a solution or dispersion of the optional component on the soil and then drying it) and using the soil.

From the viewpoint of obtaining better drainage and air permeability, the soil is preferably granular. The particle size of the granular hilling 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 for paddy rice can be used by sieving. 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 hilling can be measured by the following method. Thirty particles are randomly selected from the granular soil, the diameter of each particle is measured using a caliper, and the average value is taken as the particle size of the granular soil. When the particle is not spherical, the average value of the longest side and the shortest side is taken as the diameter of the particle.

When the medium contains hilling, the content of the hilling is preferably 20 to 99.999% 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.

<Other optional ingredients>
Other optional components include animals and plants such as peat, grass charcoal, peat, peat moss, coco peat, paddy shell, fermented material, charcoal, calcined diatomaceous earth, shell fossil powder, shell powder, crab shell, VA mycorrhizal fungus, and microbial material. Quality; minerals such as vermiculite, perlite, bentonite, natural zeolite, synthetic zeolite, peat, fly ash, rock wool, kaolinite, smectite, montmorillonite, cericite, chlorite, gloconite and talc; and combinations thereof 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 a range that does not impair the effects 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. is there.

Examples of pesticides include insecticides, fungicides, insecticides, herbicides, rodenticides, preservatives, plant growth regulators and the like.

When the water retention material is used in combination with an arbitrary component, it is preferable to use the water retention material and the optional component in combination. The mixing method is not particularly limited. A medium for raising seedlings can be prepared by mixing the water-retaining material and an arbitrary component by a general method.

When the medium is for raising paddy rice seedlings, seed paddy can be sown in the medium. 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).
The medium may be used for either bed soil (soil introduced into the paddy rice seedling box before sowing seeds) or soil covering (soil covered from above after sowing seeds), or both. Good. When used for both, the composition of the medium may or may not be the same for the bed soil and the soil cover.

Hereinafter, the present invention will be described in more detail with reference to Examples and the like, but the present invention is not limited to these Examples and the like.

<Evaluation items and evaluation methods>
(1) Phosphorus element, potassium element and nitrogen element content (1) -1. The total content of the elements that make up the polymer skeleton of the water-absorbent resin and the content of the elements that do not form the polymer skeleton and are contained inside the water-absorbent resin (Fa).
A cross section of the water-absorbent resin was prepared by embedding the water-absorbent resin (diameter 130 μm) contained in the water-retaining material of the present invention in the epoxy resin and then cutting it. It is introduced into a scanning electron microscope equipped with an energy dispersive X-ray analyzer, and as a part of the inside of the resin, 3 points 5 μm from the surface of the resin, the center and their intermediate points are measured, and the average value is calculated. The content of each element was set to Fa (mass%).
(1) -2. Element content (Fb) contained in the polymer skeleton of the water-absorbent resin
0.1 g of the water-absorbent resin contained in the water-retaining material of the present invention was washed 5 times with 100 g of pure water to remove phosphorus element, potassium element and nitrogen element contained in the resin which does not form the polymer skeleton. The washed resin was vacuum-dried at 40 ° C. for 12 hours, embedded in an epoxy resin, and then cut to prepare a cross section of a water-absorbent resin. It was introduced into a scanning electron microscope equipped with an energy dispersive X-ray analyzer, and (1) -1. In the same manner as above, elemental analysis of the cross section of the water-absorbent resin was performed, and the content Fb (mass%) of each element constituting the polymer skeleton of the water-absorbent resin was measured.
(1) -3. Element content (Fc) contained in water retention material
The content of nitrogen element was measured by burning the water retention material with an organic elemental analyzer.
The contents of phosphorus element and potassium element were measured by ICP-AES after microwave decomposition was performed by adding nitric acid to the water retention material.
The content of phosphorus element, potassium element and nitrogen element contained in the water retention material was defined as Fc (mass%).
The phosphorus element, potassium element and nitrogen element content Fi contained inside the water-absorbent resin, which does not constitute the polymer skeleton, was calculated from the following formula.
Fi = Fa-Fb
The phosphorus element, potassium element and nitrogen element Fo, which are not contained in the resin but are contained in the water retention material, were calculated from the following formulas.
Fo = Fc-Fa

(2) Budding rate (2 days after sowing)
In the paddy rice seedling box, the number of shoots (N1) that had sprouted and emerged on the soil cover was visually counted. Using the number of germinated paddy seeds (N2), the emergence rate was calculated according to the following formula.
Budding rate [%] = (N1 / N2) x 100

(3) Plant height (9 days after sowing)
In the paddy rice seedling box, the length from the upper surface of the paddy rice seedling cultivation soil to the upper end of the seedlings was measured for 10 randomly sampled seedlings, and the average value was adopted as the plant height.

<Synthesis of water-absorbent resin>
[Synthetic raw materials]
Glyoxylic acid monohydrate, 40% by mass glyoxal aqueous solution, 25% by mass glutalaldehyde aqueous solution, acetonitrile, methanol, vinyl acetate, sodium hydroxide, methyl acrylate, and azobisisobutyronitrile, acetic acid, sodium acetate, acrylic acid Cross-linked product of -sodium acrylate copolymer (product name: highly water-absorbent polymer (acrylic acid salt type)); cross-linked product of acrylamide-acrylic acid-potassium acrylate copolymer (composition ratio) manufactured by Wako Pure Chemical Industries, Ltd. (Mol) 67: 11: 22) (Product name: Miracle-Gro (registered trademark) water storage crystal); Polyvinyl alcohol A manufactured by Scotts Miracle Glow; ELVANOL (registered trademark) 71-30 manufactured by Claret America.

[Synthesis of water-absorbent resin a-0]
12.55 g of glyoxylic acid monohydrate, 0.11 g of 40 mass% glyoxal aqueous solution, 12.55 g of ion-exchanged water, 150 mL of acetonitrile and polyvinyl in a four-necked separable flask with a capacity of 500 mL equipped with a reflux condenser and a stirring blade. 40.0 g of alcohol A was introduced, and the mixture was stirred at 23 ° C. for 1 hour. After the temperature of the obtained mixture was raised to 70 ° C., 16.87 g of a 25 mass% sulfuric acid aqueous solution was added dropwise over 10 minutes, and the mixture was reacted at 70 ° C. for 6 hours. Then, after cooling to 30 ° C., 150 mL of ion-exchanged water was added, and the resin was taken out by filtration. Subsequently, the resin collected by filtration was washed 5 times with 200 mL of methanol each time (washing 1). The washed resin is introduced into a four-necked separable flask having a capacity of 500 mL equipped with a reflux condenser and a stirring blade, 180 mL of methanol, 11.6 mL of ion-exchanged water and 16.8 mL of an 8 mol / L potassium hydroxide aqueous solution are added to reflux. It was allowed to react for 2 hours below. The resin is taken out by filtration, washed 6 times with 200 mL of methanol each time (washing 2), vacuum dried at 40 ° C. for 6 hours, and the target water-absorbent resin (hereinafter, "water-absorbent resin a-0") is obtained. ") Was obtained.

[Synthesis of water-absorbent resin b-0]
602 g of vinyl acetate, 1.21 g of methyl acrylate, and 254 g of methanol were introduced into a reactor equipped with a stirrer, a reflux condenser, a nitrogen inlet tube, and an initiator addition port, and the reactor was subjected to nitrogen bubbling for 30 minutes. The inside 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., 0.16 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, was calculated with respect to the total mass of the introduced vinyl acetate and methyl acrylate. I asked. When the consumption rate reached 4%, the internal temperature of the reactor was cooled to 30 ° C. to terminate the polymerization. It was connected to a vacuum line, and the remaining 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 constituent units. The content of the acrylic acid constituent unit was measured using ¹³ C-NMR.
Next, 1 g of the obtained polyvinyl acetate containing an acrylic acid constituent unit and 18.2 g of methanol were added to the same reactor as described above to dissolve the polyvinyl acetate containing an acrylic acid constituent unit. The temperature of the reactor was started using a water bath, and the reactor was heated with stirring until the internal temperature of the reactor reached 70 ° C. To this, 0.78 g of a methanol solution of sodium hydroxide (meth caustic, concentration 15% by mass) was added, and saponification was carried out at 70 ° C. for 2 hours. The obtained solution was filtered to obtain polyvinyl alcohol (hereinafter referred to as "polyvinyl alcohol b") containing 5.2 mol% of acrylic acid constituent units.
58.9 g of acetonitrile, 6.28 g of ion-exchanged water, 0.171 g of a 25 mass% glutaraldehyde aqueous solution, and 20 g of polyvinyl alcohol b were introduced into a three-necked separable flask equipped with a reflux condenser and a stirring blade, and stirred at 23 ° C. Then, polyvinyl alcohol b was dispersed. 12.38 g of a 16.9 mass% sulfuric acid aqueous solution was added dropwise over 15 minutes, the temperature was raised to 65 ° C., and the reaction was carried out for 6 hours. After the reaction, the resin was taken out by filtration, and the resin collected by filtration was washed 6 times with 160 g of methanol each time (washing 3). The washed resin is introduced into a three-necked separable flask equipped with a reflux condenser and a stirring blade, 71 g of methanol, 13.3 g of ion-exchanged water, and 5.7 g of potassium hydroxide are added, and the mixture is reacted at 65 ° C. for 2 hours. It was. After the reaction, the resin was taken out by filtration, and the resin collected by filtration was washed 6 times with 160 g of methanol each time (washing 4), vacuum dried at 40 ° C. for 12 hours, and the desired water absorption was achieved. A resin (hereinafter referred to as "water-absorbent resin b-0") was obtained.

[Example 1]
A water-absorbent resin (hereinafter referred to as "water-absorbent resin b-1") was synthesized in the same manner as the water-absorbent resin b-0 except that the number of washings 3 was changed from 6 times to 5 times. The water-absorbent resin b-1 contained 0.11% by mass of a potassium element inside the resin. That is, the water-absorbent resin b-1 corresponds to a water-retaining material (hereinafter referred to as "water-retaining material b-1").
48 g of water-retaining material b-1 and 600 g of granular soil A (without fertilizer, average particle size 3.0 mm) were uniformly mixed to prepare paddy rice seedling soil. 60% by mass of this paddy rice seedling cultivation soil was spread in a paddy rice seedling box having an inner size of 58 cm × 28 cm and 56 holes with a diameter of 2 mm on the bottom surface, and 1000 mL of water was irrigated with a watering can over 5 seconds. After uniformly sprinkling 200 g of germinated paddy (variety: Koshihikari), the remaining paddy rice seedling cultivation soil (40% by mass of the prepared paddy rice seedling cultivation soil) was evenly spread on it, and the paddy rice seedling cultivation soil and water-introduced paddy rice seedling cultivation soil were spread. A box was made. The above operation was performed twice more to prepare three paddy rice seedling raising boxes in which the same paddy rice seedling cultivation soil and water were introduced. After budding in a budding chamber at 30 ° C. and 100% humidity for 2 days, the budding rate was measured. Seedlings were continuously raised and the plant height was measured 9 days after sowing. The measurement was performed in each of the three nursery boxes, and the average value was adopted. The results are shown in Table 1.

[Example 2]
A water-absorbent resin (hereinafter referred to as "water-absorbent resin b-2") was synthesized in the same manner as the water-absorbent resin b-0 except that the number of washings 3 was changed from 6 times to 1 time. The water-absorbent resin b-2 contained 1.08% by mass of a potassium element inside the resin. That is, the water-absorbent resin b-2 corresponds to a water-retaining material (hereinafter referred to as "water-retaining material b-2").
Paddy rice seedling boxes were prepared and measured in the same manner as in Example 1 except that this water-retaining material was used. The results are shown in Table 1.

[Example 3]
After synthesizing the water-absorbent resin (hereinafter referred to as "water-absorbent resin b-3") in the same manner as the water-absorbent resin b-0 except that the number of washings 3 was changed from 6 times to 2 times, sulfuric acid Potassium was mixed. The water-absorbent resin b-3 contained 0.75% by mass of a potassium element inside the resin. That is, the water-absorbent resin b-3 corresponds to a water-retaining material (hereinafter referred to as "water-retaining material b-3").
Paddy rice seedling boxes were prepared and measured in the same manner as in Example 1 except that this water-retaining material was used. The results are shown in Table 1.

[Example 4]
After synthesizing the water-absorbent resin (hereinafter referred to as "water-absorbent resin b-4") in the same manner as the water-absorbent resin b-0 except that the number of washings 3 was changed from 6 times to 1 time, phosphorus was used. Diammonium hydrogen acid was mixed. The water-absorbent resin b-4 contained 1.08% by mass of a potassium element inside the resin. That is, the water-absorbent resin b-4 corresponds to a water-retaining material (hereinafter referred to as "water-retaining material b-4").
Paddy rice seedling boxes were prepared and measured in the same manner as in Example 1 except that this water-retaining material was used. The results are shown in Table 1.

[Example 5]
After the reaction of polyvinyl alcohol b and glutaraldehyde was carried out by adding 5.0 g of diammonium hydrogen phosphate in addition to sulfuric acid, the number of washings 3 was set to 3 in the same manner as the water-absorbent resin b-0. , A water-absorbent resin (hereinafter referred to as "water-absorbent resin b-5") was synthesized. After the synthesis, diammonium hydrogen phosphate and potassium sulfate were mixed. The water-absorbent resin b-5 contained 0.33% by mass of phosphorus element, 0.54% by mass of potassium element, and 0.63% by mass of nitrogen element inside the resin. That is, the water-absorbent resin b-5 corresponds to a water-retaining material (hereinafter referred to as "water-retaining material b-5").
Paddy rice seedling boxes were prepared and measured in the same manner as in Example 1 except that this water-retaining material was used. The results are shown in Table 1.

[Example 6]
After the reaction of polyvinyl alcohol b and glutaraldehyde was carried out by adding 5.0 g of diammonium hydrogen phosphate in addition to sulfuric acid, the procedure was the same as that of the water-absorbent resin b-0 except that the number of washings 3 was once. , A water-absorbent resin (hereinafter referred to as "water-absorbent resin b-6") was synthesized. After the synthesis, diammonium hydrogen phosphate and potassium sulfate were mixed. The water-absorbent resin b-6 contained 0.67% by mass of phosphorus element, 1.08% by mass of potassium element and 1.25% by mass of nitrogen element inside the resin. That is, the water-absorbent resin b-6 corresponds to a water-retaining material (hereinafter referred to as "water-retaining material b-6").
Paddy rice seedling boxes were prepared and measured in the same manner as in Example 1 except that this water-retaining material was used. The results are shown in Table 1.

[Example 7]
Change 12.38 g of 16.9 mass% sulfuric acid aqueous solution to 16.32 g of 10 mass% hydrochloric acid, add 5.0 g of diammonium hydrogen phosphate to carry out the reaction of polyvinyl alcohol b and glutaraldehyde, and then wash. A water-absorbent resin (hereinafter referred to as "water-absorbent resin b-7") was synthesized in the same manner as the water-absorbent resin b-0 except that the number of times of 3 was set to 3. After the synthesis, diammonium hydrogen phosphate and potassium chloride were mixed. The water-absorbent resin b-7 contained 0.33% by mass of phosphorus element, 0.54% by mass of potassium element, and 0.63% by mass of nitrogen element inside the resin. That is, the water-absorbent resin b-7 corresponds to a water-retaining material (hereinafter referred to as "water-retaining material b-7").
Paddy rice seedling boxes were prepared and measured in the same manner as in Example 1 except that this water-retaining material was used. The results are shown in Table 1.

[Example 8]
Change 12.38 g of 16.9 mass% sulfuric acid aqueous solution to 27.06 g of 10 mass% nitric acid, add 5.0 g of diammonium hydrogen phosphate to carry out the reaction of polyvinyl alcohol b and glutaraldehyde, and then wash. A water-absorbent resin (hereinafter referred to as "water-absorbent resin b-8") was synthesized in the same manner as the water-absorbent resin b-0 except that the number of times of 3 was set to 3. After the synthesis, diammonium hydrogen phosphate and potassium nitrate were mixed. The water-absorbent resin b-8 contained 0.33% by mass of phosphorus element, 0.54% by mass of potassium element, and 0.79% by mass of nitrogen element inside the resin. That is, the water-absorbent resin b-8 corresponds to a water-retaining material (hereinafter referred to as "water-retaining material b-8").
Paddy rice seedling boxes were prepared and measured in the same manner as in Example 1 except that this water-retaining material was used. The results are shown in Table 1.

[Example 9]
After the reaction of polyvinyl alcohol b and glutaraldehyde was carried out by adding 2.3 g of urea in addition to sulfuric acid, the water-absorbent resin was the same as the water-absorbent resin b-0 except that the number of washings 3 was once. (Hereinafter referred to as "water-absorbent resin b-9") was synthesized. After the synthesis, diammonium hydrogen phosphate and potassium sulfate were mixed. The water-absorbent resin b-9 contained 1.08% by mass of potassium element and 1.25% by mass of nitrogen element inside the resin. That is, the water-absorbent resin b-9 corresponds to a water-retaining material (hereinafter referred to as "water-retaining material b-9").
Paddy rice seedling boxes were prepared and measured in the same manner as in Example 1 except that this water-retaining material was used. The results are shown in Table 1.

[Example 10]
After synthesizing the water-absorbent resin (hereinafter referred to as "water-absorbent resin a-1") in the same manner as the water-absorbent resin a-0 except that the number of washings 1 was changed from 5 to 2, potassium sulfate was used. Was mixed. The water-absorbent resin a-1 contained 0.66% by mass of a potassium element inside the resin. That is, the water-absorbent resin a-1 corresponds to a water-retaining material (hereinafter referred to as "water-retaining material a-1").
Paddy rice seedling boxes were prepared and measured in the same manner as in Example 1 except that this water-retaining material was used. The results are shown in Table 1.

[Comparative Example 1]
Paddy rice seedling boxes were prepared and measured in the same manner as in Example 1 except that the water-absorbent resin b-0 was used. The results are shown in Table 1.

[Comparative Example 2]
1.2 g of potassium sulfate was mixed with 48 g of the water-absorbent resin b-0. Paddy rice seedling boxes were prepared and measured in the same manner as in Example 1 except that this mixture was used. The results are shown in Table 1.

[Comparative Example 3]
3.1 g of diammonium hydrogen phosphate and 1.2 g of potassium sulfate were mixed with 48 g of the water-absorbent resin b-0. Paddy rice seedling boxes were prepared and measured in the same manner as in Example 1 except that this mixture was used. The results are shown in Table 1.

[Comparative Example 4]
1.2 g of potassium sulfate was mixed with 48 g of the water-absorbent resin a-0. Using this mixture, paddy rice seedling boxes were prepared and measured. The results are shown in Table 1.

[Comparative Example 5]
Except for the fact that no water-retaining material was used and only 3000 g of granular culture soil B (containing 0.33-0.42-0.5 g / kg of phosphorus-potassium-nitrogen as fertilizer, average particle size 3.0 mm) was used. A paddy rice seedling box was prepared and measured in the same manner as in Example 1. The results are shown in Table 1.

Budding when the water-retaining material of Examples 1 to 10 is used inside the resin, which contains one or more elements selected from the group consisting of phosphorus element, potassium element and nitrogen element, which do not constitute the polymer skeleton of the resin. Both the rate (the growth index of the early stage of plant growth) and the plant height (the growth index of the late stage of plant growth) are excellent. On the other hand, in Comparative Examples 1 to 4 in which the element is not contained in the resin, both the emergence rate and the plant height are low values. Further, it can be seen that the emergence rate is low in Comparative Example 5 in which the fertilizer component is contained in the medium without containing the water retention material.

The water-retaining material of the present invention is less likely to cause root burning due to fertilizer and has good plant growth, so that it can be suitably used for agriculture, especially for raising seedlings.

Claims (10)

A water-retaining material containing a water-absorbent resin, wherein the water-absorbent resin contains an element that does not constitute a polymer skeleton of the resin, and the elements are phosphorus element, potassium element, and nitrogen element. A water retention material that is one or more elements selected from the group consisting of. The content of one or more elements selected from the group consisting of phosphorus element, potassium element and nitrogen element existing inside the resin is 0.001 to 50% by mass with respect to the mass of the resin. Item 1. The water retention material according to Item 1. The first or second claim, wherein the water-retaining material further contains one or more elements selected from the group consisting of phosphorus element, potassium element and nitrogen element, which are not present in the resin but are present in the water-retaining material. Water retention material. The content of one or more elements selected from the group consisting of phosphorus element, potassium element and nitrogen element, which is not present inside the resin but is present in the water retention material, is 0.001 with respect to the mass of the resin. The water retention material according to any one of claims 1 to 3, which is ~ 50% by mass. The water-absorbent resin comprises a polymer selected from the group consisting of a vinyl alcohol-based polymer, an acrylic acid-based polymer, an acrylamide-based polymer, a methacrylic acid-based polymer, and a starch-based polymer, claims 1 to 4. Water retention material described in any of. The water-retaining material according to claim 5, wherein the vinyl alcohol-based polymer contains a copolymer containing a vinyl alcohol constituent unit and a monomer constituent unit having an ionic group or a derivative thereof. The water-retaining material according to claim 5 or 6, wherein the vinyl alcohol-based polymer contains potassium ion or ammonium ion as a counter cation of an ionic group. The water-retaining material according to any one of claims 5 to 7, wherein the vinyl alcohol-based polymer has a crosslinked structure. The water retention material according to any one of claims 1 to 8, which is for agriculture. The water-retaining material according to any one of claims 1 to 9, which is used for raising seedlings.