CN111868144B - Water-absorbent resin particles and method for producing same - Google Patents

Abstract

Provided are water-absorbent resin particles which have both apparent density and absorption rate without reducing mechanical strength. The present invention relates to water-absorbent resin particles, wherein particles having a particle defect degree (CONV) defined by the following formula (1) of not more than 1% are classified into particles having a particle size in the range of 300 to 600 [ mu ] m, not more than 50% by volume, and particles having a CONV of not less than 8% are not more than 5% by volume. CONV (%) = { B/(a+b) } ×100 (1) (a represents the projection area of the object particle obtained by the image analysis method, B represents a value obtained by subtracting the projection area represented by a from the projection area surrounded by the envelope line connecting the convex portions of the object particle obtained by the image analysis method).

Description

Water-absorbent resin particles and method for producing same

Technical Field

The present invention relates to water-absorbent resin particles and a method for producing the same.

Background

As sanitary materials such as paper diapers, sanitary napkins, and incontinence pads, a mixture of hydrophilic fibers such as pulp and a water-absorbent resin mainly composed of acrylic acid (salt) is widely used as an absorber. In view Of recent improvement in QOL (Quality Of Life), there is a demand for these sanitary materials to be lighter and thinner, and along with this, it is desired to reduce the amount Of hydrophilic fibers. Therefore, the water-absorbent resin itself is required to function as the liquid diffusibility and initial absorption in the absorber which have been heretofore carried by the hydrophilic fiber, and there is a need for a water-absorbent resin having high liquid permeability and absorption rate.

As a method for increasing the absorption rate, there is generally a method of physically increasing the surface area of the water-absorbent resin. For example, it is known that: a method of increasing the drying rate of the water-absorbent resin to reduce the apparent density (patent document 1); a method of foaming the inside of the water-absorbent resin to reduce the apparent density in the drying step of the water-absorbent resin (patent document 2). In addition, a method of granulating water-absorbent resin particles is also known (patent document 3). However, in either method, the mechanical strength of the particles is weak, and fine powder is easily generated in the process of manufacturing diapers. The fine powder causes gel blocking in the diaper manufacturing process, which causes a problem of process clogging. In addition, a method of reducing the particle size of the water-absorbent resin particles in the sieving step to increase the absorption rate is also known (patent document 4), but if the particle size of the water-absorbent resin is reduced, the moisture absorption resistance is lowered, and there is a problem that the step in the diaper manufacturing step is blocked as described above.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 2013-132434

Patent document 2: japanese patent application laid-open No. 2015-508836

Patent document 3: japanese patent publication No. 2008-533213

Patent document 4: japanese patent laid-open No. 2006-143972

Disclosure of Invention

Problems to be solved by the invention

The purpose of the present invention is to provide water-absorbent resin particles that have both apparent density and absorption rate without reducing mechanical strength.

Means for solving the problems

The present invention relates to water-absorbent resin particles, wherein, among particles which are sieved to a range of 300 to 600 [ mu ] m using a JIS standard sieve, particles having a particle defect degree (CONV) defined by the following formula (1) of 1% or less are 50% or less by volume, and particles having a particle defect degree (CONV) of 8% or more are 5% or less by volume.

CONV(％)＝{B/(A+B)}×100 (1)

In the formula (1), CONV represents the particle defect degree, a represents the projection area of the target particle obtained by the image analysis method, and B represents a value obtained by subtracting the projection area of the target particle represented by a from the projection area surrounded by the envelope in which the convex portions of the target particle obtained by the image analysis method are connected.

The present invention also relates to a method for producing water-absorbent resin particles, comprising the steps of: a polymerization step of polymerizing a monomer composition containing a water-soluble vinyl monomer (a 1) and/or a vinyl monomer (a 2) which is hydrolyzed to form the water-soluble vinyl monomer (a 1) and an internal crosslinking agent (b) as essential structural units to obtain an aqueous gel of a crosslinked polymer (A); a step of subdividing the aqueous gel of the crosslinked polymer (A); mixing and cutting finely-divided gel at a gel temperature of 40-120 ℃; and a step of surface-crosslinking the surface of the resin particles (B) containing the crosslinked polymer (A) with a surface-crosslinking agent (c).

ADVANTAGEOUS EFFECTS OF INVENTION

The water-absorbent resin particles of the present invention and the water-absorbent resin particles obtained by the production method of the present invention form irregularities on the surfaces of the water-absorbent resin particles, and the particles are formed in a controlled ratio, whereby both the apparent density and the absorption rate can be achieved without reducing the mechanical strength. Therefore, the diaper can be stably manufactured even under high humidity, and excellent absorption performance (such as liquid diffusibility, absorption rate, absorption amount, and the like) can be stably exhibited under various use conditions.

Drawings

FIG. 1 is a schematic diagram illustrating a method of determining a degree of defective granules (CONV). (1) shows the particle projection area. (2) The projection area surrounded by the envelope line formed by connecting the convex portions of the particle projection region is shown.

Fig. 2 is a view schematically showing a cross-sectional view of a filtration cylindrical tube for measuring a gel flow rate.

Fig. 3 is a perspective view schematically showing a pressing shaft and a weight for measuring the gel liquid passing speed.

Detailed Description

Among the water-absorbent resin particles of the present invention, particles having a particle defect level (CONV) defined by the following formula (1) of not more than 1% and particles sieved to a range of 300 to 600 μm using a JIS standard sieve are not more than 50% by volume. In addition, in the particles of the range of 300 to 600 μm, the volume ratio of the particles having a particle defect degree of 8% or more is 5% or less.

CONV(％)＝{B/(A+B)}×100 (1)

In the formula (1), CONV represents the particle defect degree, a represents the projected area of the target particle obtained by the image analysis method, B represents the value obtained by subtracting the projected area of the target particle represented by a from the projected area surrounded by the envelope line formed by connecting the convex portions of the target particle obtained by the image analysis method, and represents the area of the defect portion of the particle. The particles having a defect degree of 0% or more and less than 100% and a particle size of closer to 0% show that the particles have no irregularities and have a smooth surface.

FIG. 1 is a schematic diagram illustrating a method for determining a defective degree of particles. The projection area (a) of the object particles is obtained from the "particle projection area" of fig. 1. Then, the projection area (a+b) surrounded by the envelope line connecting the convex portions of the particle projection area is obtained as the area including the projection area (a) of the target particle, that is, the a portion and the defect portion, that is, the B portion. The area of the B portion was obtained from these values.

If the volume ratio of particles having a particle defect of 1% or less to particles having a particle size of 50% or less, the particles having a smooth surface are small in proportion and the water-absorbent resin particles have sufficient irregularities, and therefore exhibit good absorption performance, excellent absorption performance is exhibited when an absorbent article is produced, leakage is less likely to occur, and skin irritation resistance is good, preferably 46% or less, more preferably 40% or less. On the other hand, as the particle size is larger, the roughness of the particles increases and the absorption rate increases, but the destructiveness of the water-absorbent resin particles increases, and the fine powder increases in the diaper manufacturing process, so that the volume ratio of particles having a particle size of 8% or more to particles having a particle size of 8% or more is 5% or less, preferably 3% or less, more preferably 2% or less, among particles classified into a range of 300 to 600 μm by using a JIS standard sieve. The volume ratio of particles having a particle defect degree of 8% or more to the total particles is preferably 5% or less. This can suppress the decrease in mechanical strength of the water-absorbent resin particles.

The water-absorbent resin particles of the present invention may be any type as long as they have the above-mentioned characteristics, and are preferably crosslinked polymer (a) obtained by polymerizing a monomer composition comprising water-soluble vinyl monomer (a 1) and/or vinyl monomer (a 2) which is hydrolyzed to form water-soluble vinyl monomer (a 1) and internal crosslinking agent (B) as essential structural units, and more preferably water-absorbent resin particles obtained by surface-crosslinking the surface of resin particles (B) containing crosslinked polymer (a) with surface crosslinking agent (c).

The water-soluble vinyl monomer (a 1) in the present invention is not particularly limited, and a known monomer may be used, for example, a vinyl monomer having at least 1 water-soluble substituent and an ethylenically unsaturated group (for example, an anionic vinyl monomer, a nonionic vinyl monomer, and a cationic vinyl monomer) disclosed in paragraphs 0007 to 0023 of Japanese patent application publication No. 3648553, an anionic vinyl monomer, a nonionic vinyl monomer, and a cationic vinyl monomer disclosed in paragraphs 0009 to 0024 of Japanese patent application publication No. 2003-165883, and a vinyl monomer having at least one selected from the group consisting of a carboxyl group, a sulfo group, a phosphono group, a hydroxyl group, a carbamoyl group, an amino group, and an ammonium group disclosed in paragraphs 0041 to 0051 of Japanese patent application publication No. 2005-75982.

The vinyl monomer (a 2) to be a water-soluble vinyl monomer (a 1) by hydrolysis (hereinafter also referred to as a hydrolyzable vinyl monomer (a 2)) is not particularly limited, and a known vinyl monomer or the like (for example, a vinyl monomer having at least 1 hydrolyzable substituent to be a water-soluble substituent by hydrolysis disclosed in paragraphs 0024 to 0025 of Japanese patent application laid-open No. 3648553, a vinyl monomer having at least 1 hydrolyzable substituent (1, 3-oxo-2-oxapropylene (-CO-O-CO-) group, acyl group, cyano group or the like) disclosed in paragraphs 0052 to 0055 of Japanese patent application laid-open No. 2005-75982) can be used. The water-soluble vinyl monomer means a vinyl monomer having a property of dissolving at least 100g in 100g of water at 25 ℃. The hydrolyzability means a property of being hydrolyzed to be water-soluble by water at 50 ℃ and a catalyst (acid, alkali, etc.) used as needed. The hydrolysis of the hydrolyzable vinyl monomer may be carried out during the polymerization, after the polymerization, or both, and is preferably carried out after the polymerization in view of the molecular weight of the water-absorbent resin particles obtained.

Among these, the water-soluble vinyl monomer (a 1) is preferable from the viewpoint of absorption characteristics and the like. The water-soluble vinyl monomer (a 1) is preferably an anionic vinyl monomer, and more preferably a vinyl monomer having a carboxylic (acid salt) group, a sulfonic (acid salt) group, an amino group, a carbamoyl group, an ammonium group, or a monoalkylammonium group, a dialkylammonium group, or a trialkylammonium group. Among these, vinyl monomers having a carboxyl group (salt) or a carbamoyl group are more preferable, (meth) acrylic acid (salt) and (meth) acrylamide are further preferable, (meth) acrylic acid (salt) is particularly preferable, and acrylic acid (salt) is most preferable.

The "carboxyl (salt) group" means "carboxyl" or "carboxylate group", and the "sulfo (salt) group" means "sulfo" or "sulfonate group". In addition, (meth) acrylic acid (salt) means acrylic acid, acrylic acid salt, methacrylic acid or methacrylic acid salt, and (meth) acrylamide means acrylamide or methacrylamide. In addition, as the salt, alkali metal (lithium, sodium, potassium, etc.) salts, alkaline earth metal (magnesium, calcium, etc.) salts or ammonium (NH) ₄ ) Salts, and the like. Among these salts, alkali metal salts and ammonium salts are preferable from the viewpoint of absorption characteristics and the like, alkali metal salts are more preferable, and sodium salts are particularly preferable.

In the case where either one of the water-soluble vinyl monomer (a 1) and the hydrolyzable vinyl monomer (a 2) is used as a structural unit, each of the structural units may be used alone, or 2 or more kinds of structural units may be used as required. The same applies to the case where the water-soluble vinyl monomer (a 1) and the hydrolyzable vinyl monomer (a 2) are used as the structural units. In the case where the water-soluble vinyl monomer (a 1) and the hydrolyzable vinyl monomer (a 2) are used as the structural units, the molar ratio (a 1/a 2) of these components is preferably 75/25 to 99/1, more preferably 85/15 to 95/5, particularly preferably 90/10 to 93/7, and most preferably 91/9 to 92/8. At this range, the absorption performance becomes better.

As the structural unit of the crosslinked polymer (a), in addition to the water-soluble vinyl monomer (a 1) and the hydrolyzable vinyl monomer (a 2), another vinyl monomer (a 3) copolymerizable with them may be used as the structural unit.

The other copolymerizable vinyl monomer (a 3) is not particularly limited, and known hydrophobic vinyl monomers and the like (for example, hydrophobic vinyl monomers disclosed in paragraphs 0028 to 0029 of Japanese patent application laid-open No. 3648553, vinyl monomers disclosed in paragraph 0058 of Japanese patent application laid-open No. 2003-165883 and Japanese patent application laid-open No. 2005-75982) can be used, and vinyl monomers of the following (i) to (iii) and the like can be used.

(i) Aromatic vinyl monomer with 8-30 carbon atoms

Styrene such as styrene, α -methylstyrene, vinyltoluene and hydroxystyrene, and halogen substituted styrenes such as vinylnaphthalene and dichlorostyrene.

(ii) Aliphatic ethylenic monomer having 2 to 20 carbon atoms

Olefins [ ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutene, octene, dodecene, octadecene, etc ]; diene [ butadiene, isoprene, etc. ], and the like.

(iii) Alicyclic ethylenic monomer having 5 to 15 carbon atoms

Monoethylenically unsaturated monomers [ pinene, limonene, indene, etc ]; and polyethylenic vinyl polymerizable monomers [ cyclopentadiene, dicyclopentadiene, ethylidenenorbornene, etc. ], etc.

When the other vinyl monomer (a 3) is used as a structural unit, the content (mol%) of the other vinyl monomer (a 3) unit is preferably 0.01 to 5, more preferably 0.05 to 3, still more preferably 0.08 to 2, and particularly preferably 0.1 to 1.5 based on the mole number of the water-soluble vinyl monomer (a 1) unit and the hydrolyzable vinyl monomer (a 2) unit. Although as described above, the content of the other vinyl monomer (a 3) unit is most preferably 0 mol% in view of absorption characteristics and the like.

The internal crosslinking agent (b) (hereinafter also simply referred to as the crosslinking agent (b)) is not particularly limited, and a known crosslinking agent or the like (for example, a crosslinking agent having 2 or more ethylenically unsaturated groups as disclosed in paragraphs 0031 to 0034 of japanese patent No. 3648553, a crosslinking agent having at least 1 functional group reactive with a water-soluble substituent and having at least 1 ethylenically unsaturated group, a crosslinking agent having at least 2 functional groups reactive with a water-soluble substituent, a crosslinking agent having 2 or more ethylenically unsaturated groups as disclosed in paragraphs 0028 to 0031 of japanese patent application laid-open No. 2003-165883, a crosslinking agent having an ethylenically unsaturated group and a reactive functional group, and a crosslinking monomer having 2 or more reactive substituents as disclosed in paragraph 0059 of japanese patent application laid-open No. 2005-75982, and a crosslinking monomer as disclosed in paragraphs 0015 to 0016 of japanese patent application laid-open No. 2005-95759) can be used. Of these, a crosslinking agent having 2 or more ethylenically unsaturated groups is preferable from the viewpoint of absorption properties and the like, triallyl cyanurate, triallyl isocyanurate and poly (meth) allyl ether of a polyhydric alcohol having 2 to 10 carbon atoms are more preferable, triallyl cyanurate, triallyl isocyanurate, tetraallyloxyethane and pentaerythritol triallyl ether are particularly preferable, and pentaerythritol triallyl ether is most preferable. The crosslinking agent (b) may be used alone or in combination of two or more.

The content (mol%) of the crosslinking agent (b) unit is preferably 0.001 to 5, more preferably 0.005 to 3, and particularly preferably 0.01 to 1 based on the total mole number of the water-soluble vinyl monomer (a 1) unit and the hydrolyzable vinyl monomer (a 2) unit (based on the total mole number of (a 1) to (a 3) in the case of using the other vinyl monomer (a 3)). At this range, the absorption performance becomes better.

As a method for producing the crosslinked polymer (A), there can be mentioned a method in which an aqueous gel polymer (composed of a crosslinked polymer and water) obtained by a known solution polymerization (adiabatic polymerization, film polymerization, spray polymerization, etc., japanese patent application laid-open No. 55-133413, etc.), a known suspension polymerization, or a known reverse-phase suspension polymerization (Japanese patent application laid-open No. 54-30710, japanese patent application laid-open No. 56-26909, japanese patent application laid-open No. 1-5808, etc.) is dried by heating and pulverized as required. The crosslinked polymer (A) may be used alone or in a mixture of two or more.

Among the polymerization methods, the solution polymerization method is preferable, and the aqueous solution polymerization method is particularly preferable because an organic solvent or the like is not necessary, and the production cost is advantageous, and the aqueous solution adiabatic polymerization method is most preferable because a water-absorbent resin having a large water retention capacity and a small amount of water-soluble components can be obtained, and the temperature control at the time of polymerization is not necessary.

In the case of performing aqueous solution polymerization, a mixed solvent containing water and an organic solvent may be used, and examples of the organic solvent include methanol, ethanol, acetone, methyl ethyl ketone, N-dimethylformamide, dimethyl sulfoxide, and a mixture of 2 or more thereof.

In the case of performing aqueous solution polymerization, the amount (wt%) of the organic solvent is preferably 40 or less, more preferably 30 or less based on the weight of water.

In the case of using a catalyst for polymerization, conventionally known catalysts for radical polymerization can be used, and examples thereof include azo compounds [ azobisisobutyronitrile, azobiscyanovaleric acid, 2' -azobis (2-amidinopropane) hydrochloride, etc. ], inorganic peroxides (hydrogen peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, etc.), organic peroxides [ benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, succinic acid peroxide, bis (2-ethoxyethyl) peroxydicarbonate, etc. ], and redox catalysts (catalysts composed of a combination of a reducing agent such as an alkali metal sulfite or bisulfite, ammonium sulfite, ascorbic acid, etc., and an oxidizing agent such as alkali metal persulfate, ammonium persulfate, hydrogen peroxide, organic peroxide, etc.), and the like. These catalysts may be used alone or in combination of two or more thereof.

The amount (wt%) of the radical polymerization catalyst to be used is preferably 0.0005 to 5, more preferably 0.001 to 2, based on the total weight of the water-soluble vinyl monomer (a 1) and the hydrolyzable vinyl monomer (a 2) (based on the total weight of (a 1) to (a 3) in the case of using the other vinyl monomer (a 3)).

In the case where the polymerization method is a suspension polymerization method or a reverse suspension polymerization method, the polymerization may be carried out in the presence of a conventionally known dispersing agent or surfactant, as required. In the case of the reversed-phase suspension polymerization method, polymerization can be carried out using a conventionally known hydrocarbon solvent such as xylene, n-hexane, and n-heptane.

The polymerization initiation temperature may be appropriately adjusted depending on the kind of the catalyst used, and is preferably 0 to 100 ℃, more preferably 5 to 80 ℃.

In the case where a solvent (an organic solvent, water, or the like) is used in the polymerization, the solvent is preferably distilled off after the polymerization. When the organic solvent is contained in the solvent, the content (wt%) of the organic solvent after distillation is preferably 0 to 10, more preferably 0 to 5, particularly preferably 0 to 3, and most preferably 0 to 1, based on the weight of the crosslinked polymer (a). When the amount is within this range, the absorption properties of the water-absorbent resin particles become better.

When water is contained in the solvent, the water content (% by weight) after distillation is preferably 0 to 20, more preferably 1 to 10, particularly preferably 2 to 9, and most preferably 3 to 8 based on the weight of the crosslinked polymer (a). At this range, the absorption performance becomes better.

The content and moisture of the organic solvent were measured by an infrared moisture meter [ JE400 manufactured by KETT Co., ltd., etc.: the weight reduction of the measurement sample was determined when the sample was heated at 120.+ -. 5 ℃ for 30 minutes, the atmospheric humidity before heating was 50.+ -.10% RH, and the lamp specifications were 100V and 40W.

The hydrogel polymer obtained by polymerization is kneaded, chopped and dried, whereby a crosslinked polymer (A) can be obtained. In the present invention, kneading and cutting means a step of making the aqueous gel fine while repeating cutting of the aqueous gel and aggregation of the cut aqueous gel particles by shear force (shear), and the aqueous gel obtained by the fine aggregation of the aqueous gel particles is obtained by the kneading and cutting step, whereby irregularities can be formed on the surfaces of the water-absorbent resin particles. The size (longest diameter) of the gel after kneading and chopping is preferably 50 μm to 10cm, more preferably 100 μm to 2cm, particularly preferably 1mm to 1cm. When the content is within this range, the drying property in the drying step is improved.

The kneading and chopping may be performed by a known method, and kneading and chopping may be performed using a kneading and chopping device (for example, a kneader, a universal mixer, a single-screw or twin-screw kneading extruder, a chopper, a meat grinder, or the like). The temperature of the aqueous gel during kneading and chopping is preferably 40 to 120 ℃, more preferably 60 to 100 ℃. When the particle size is within this range, the adhesion of the hydrogel in the kneading and chopping device can be prevented, and the hydrogel can be uniformly treated, so that the particle defect degree of the water-absorbent resin particles tends to be uniform. In addition, in view of uniformly forming the irregularities of the water-absorbent resin particles as a whole, the kneading and chopping may be performed a plurality of times, and the number of times of kneading and chopping is preferably 1 to 4 times, more preferably 2 to 3 times. The kneading and chopping devices used in the multiple treatments may be of the same kind or may be of different kinds.

In addition, the hydrogel polymer obtained by polymerization is preferably finely divided before kneading and chopping. In the present invention, the subdivision means a step of cutting the hydrogel into small pieces while maintaining the internal structure of the hydrogel, and is different from the kneading and kneading in terms of the internal structure. By conducting the subdivision before the kneading and crushing step, excessive stress applied to the hydrogel can be relaxed during the kneading and crushing step, and deterioration of the hydrogel polymer can be suppressed, so that the absorption performance becomes good, and an extreme increase in the particle defect degree of the water-absorbent resin particles can be prevented.

The method of the subdivision is not particularly limited, and for example, subdivision may be performed by scissors, and the frozen aqueous gel may be pulverized by a pulverizing device (for example, a hammer mill, an impact mill, a drum mill, and a jet mill).

The size (longest diameter) of the gel after the division is preferably 50 μm to 10cm, more preferably 100 μm to 2cm, particularly preferably 500 μm to 1cm.

When an acid group-containing monomer such as acrylic acid or methacrylic acid is used as the water-soluble vinyl monomer (a 1), the acid group-containing crosslinked polymer (a) obtained after polymerization may be neutralized by adding a base in the state of an aqueous gel. The neutralization degree of the acid groups of the crosslinked polymer (A) is preferably 50 to 80 mol% relative to the total mole number of the acid groups. When the neutralization degree is less than 50 mol%, the adhesiveness of the resulting hydrogel polymer increases, the workability at the time of production and use may be deteriorated, or the water retention amount of the resulting water-absorbent resin particles may be lowered. On the other hand, in the case where the neutralization degree exceeds 80%, the pH of the resulting water-absorbent resin may be raised, the safety to human skin may be worried, or the liquid permeability of the water-absorbent resin particles may be lowered. As the base, a known base may be used { Japanese patent publication No. 3205168, etc. }. Among these, lithium hydroxide, sodium hydroxide and potassium hydroxide are preferable, sodium hydroxide and potassium hydroxide are more preferable, and sodium hydroxide is particularly preferable, from the viewpoint of water absorption properties. The alkali is preferably added before the step of kneading and cutting the aqueous gel or in the step of kneading and cutting the aqueous gel, more preferably before the step of kneading and cutting the aqueous gel, even more preferably after the step of subdividing the aqueous gel and before the step of kneading and cutting the aqueous gel, in terms of uniformity of neutralization. The alkali may be added as an aqueous solution of the above-mentioned alkali.

As a method for removing the solvent (including water) from the aqueous gel by distillation, the following method can be applied: a method of removing (drying) by distillation with hot air at a temperature of 80 to 230 ℃, a film drying method with a drum dryer or the like heated to 100 to 230 ℃, (heating) reduced pressure drying method, freeze drying method, drying method with infrared rays, decantation, filtration, and the like.

The crosslinked polymer (A) may be further pulverized after kneading and chopping the aqueous gel and then drying the kneaded product. The pulverizing method is not particularly limited, and a pulverizing device (e.g., a hammer mill, an impact mill, a drum mill, and a jet mill) or the like may be used. The crosslinked polymer after pulverization may be subjected to particle size adjustment by sieving or the like as needed.

The weight average particle diameter (μm) of the crosslinked polymer (A) which is optionally classified is preferably 100 to 800, more preferably 200 to 700, still more preferably 250 to 600, particularly preferably 300 to 500, and most preferably 350 to 450. At this range, the absorption performance becomes better.

The weight average particle diameter was measured by a method described in the Pery's Chemical Engineer's Handbook 6 th edition (Maglao-Hill book Co., 1984, page 21) using a Ro-Tap type test Sizer (i.e., takara Shuzo) with a pair of instrument (i.e., umbelliferae) and a standard sieve (JIS Z8801-1:2006). That is, JIS standard sieves were combined in the order of 1000 μm, 850 μm, 710 μm, 500 μm, 425 μm, 355 μm, 250 μm, 150 μm, 125 μm, 75 μm and 45 μm, and trays, etc. from above. About 50g of the test particles were placed in the uppermost screen, and the mixture was vibrated for 5 minutes by a Ro-Tap type test sieve. The weight of the particles measured on each sieve and tray was measured and the total weight was set to 100% by weight, the weight fraction of the particles on each sieve was obtained, the value was plotted on a logarithmic probability paper [ the horizontal axis represents the mesh (particle size) of the sieve and the vertical axis represents the weight fraction ], and then the points were connected to each other to obtain the particle size corresponding to 50% by weight of the weight fraction, which was defined as the weight average particle size.

Further, the smaller the content of the fine particles contained in the crosslinked polymer (a), the better the absorption performance, and thus the content (wt%) of fine particles of 150 μm or less in the total weight of the crosslinked polymer (a) is preferably 3.0 or less, more preferably 1.0 or less. The content of the fine particles can be determined using a graph prepared when the weight average particle diameter is determined.

The shape of the crosslinked polymer (A) is not particularly limited, and examples thereof include amorphous crushed, scaly, pearl-like and rice-like ones. Among these, amorphous crushed forms are preferable in terms of good entanglement with fibrous materials and no fear of falling off from the fibrous materials in the use of paper diapers or the like.

The crosslinked polymer (A) or the above-mentioned polymer gel may be treated with a hydrophobic substance by a method described in Japanese patent application laid-open No. 2013-231199 or the like, if necessary.

The crosslinked polymer (A) is preferably surface-crosslinked. By performing surface crosslinking, the gel strength can be further improved, and the water retention capacity and the absorption capacity under load expected in practical use can be satisfied.

As a method for surface-crosslinking the crosslinked polymer (a), there is a conventionally known method, for example, a method in which a water-absorbent resin is formed into particles, and then a mixed solution of the surface-crosslinking agent (c), water and a solvent is mixed and heated for reaction. Examples of the method of mixing include a method of spraying the mixed solution onto the crosslinked polymer (a) and a method of immersing the crosslinked polymer (a) in the mixed solution, and preferably a method of spraying the mixed solution onto the crosslinked polymer (a) and mixing.

Examples of the surface cross-linking agent (c) include polyglycidyl compounds such as ethylene glycol diglycidyl ether, glycerol diglycidyl ether and polyglycidyl ether, polyols such as glycerol and ethylene glycol, ethylene carbonate, polyamines, and polyvalent metal compounds. Among these, polyglycidyl compounds are preferred in that they can undergo a crosslinking reaction at a relatively low temperature. These surface cross-linking agents may be used alone or in combination of two or more.

The amount of the surface cross-linking agent (c) used is preferably 0.001 to 5% by weight, more preferably 0.005 to 2% by weight, based on the weight of the water-absorbent resin before cross-linking. When the amount of the surface cross-linking agent (c) is less than 0.001 wt%, the degree of surface cross-linking is insufficient, and the effect of improving the absorption under load may be insufficient. On the other hand, when the amount of the surface cross-linking agent (c) exceeds 5% by weight, the degree of cross-linking of the surface becomes excessive, and the water retention may be lowered.

The amount of water used in the surface crosslinking is preferably 0.5 to 10% by weight, more preferably 1 to 7% by weight, based on the weight of the water-absorbent resin before crosslinking. When the amount of water is less than 0.5% by weight, the permeability of the surface cross-linking agent (c) into the water-absorbent resin particles may be insufficient, and the effect of improving the absorption under load may be insufficient. On the other hand, if the amount of water exceeds 10% by weight, the penetration of the surface cross-linking agent (c) into the interior becomes excessive, and although it is confirmed that the absorption under load is increased, the water retention may be reduced.

As the solvent used for the surface crosslinking and the hydration, conventionally known solvents can be used, and the solvent can be appropriately selected and used in consideration of the penetration degree of the surface crosslinking agent (c) into the water-absorbent resin particles, the reactivity of the surface crosslinking agent (c), and the like, and is preferably a hydrophilic organic solvent soluble in water such as methanol, diethylene glycol, and propylene glycol. The solvent may be used alone or in combination of two or more.

The amount of the solvent to be used may be appropriately adjusted depending on the kind of the solvent, and is preferably 1 to 10% by weight based on the weight of the water-absorbent resin before surface crosslinking. The proportion of the solvent to water may be arbitrarily adjusted, and is preferably 20 to 80% by weight, more preferably 30 to 70% by weight.

For surface crosslinking, a mixed solution of the surface crosslinking agent (c) and water and a solvent is mixed with the water-absorbent resin particles by a conventionally known method, and a heating reaction is performed. The reaction temperature is preferably 100 to 230℃and more preferably 120 to 180 ℃. The reaction time may be appropriately adjusted depending on the reaction temperature, and is preferably 3 to 60 minutes, more preferably 10 to 45 minutes. The particulate water-absorbent resin obtained by surface-crosslinking may be further surface-crosslinked by a surface-crosslinking agent of the same kind or different kind from the surface-crosslinking agent used initially.

After surface crosslinking, screening can be performed to adjust particle size as needed.

The water-absorbent resin particles of the present invention may further contain a polyvalent metal salt (d), and for this purpose, the production method of the present invention described later may further include a step of mixing with the polyvalent metal salt (d). By containing the polyvalent metal salt (d), the water-absorbent resin particles are improved in blocking resistance and liquid permeability. The polyvalent metal salt (d) may be a salt of at least one metal selected from the group consisting of magnesium, calcium, zirconium, aluminum and titanium with the above inorganic acid or organic acid.

The polyvalent metal salt (d) is preferably an inorganic acid salt of aluminum or an inorganic acid salt of titanium, more preferably aluminum sulfate, aluminum chloride, aluminum potassium sulfate and aluminum sodium sulfate, particularly preferably aluminum sulfate and aluminum sodium sulfate, and most preferably aluminum sodium sulfate, from the viewpoints of easiness of obtaining and solubility. One kind of them may be used alone, or two or more kinds may be used in combination.

The amount (wt%) of the polyvalent metal salt (d) used is preferably 0.01 to 5, more preferably 0.05 to 4, particularly preferably 0.1 to 3, based on the weight of the crosslinked polymer (a), from the viewpoints of absorption properties and blocking resistance.

The timing of mixing with the polyvalent metal salt (d) is not particularly limited, and it is preferable to dry the hydrogel polymer to obtain a crosslinked polymer and then mix the crosslinked polymer in terms of absorption performance and blocking resistance.

The water-absorbent resin particles of the present invention may be further coated with an inorganic powder (D) on the surface. The inorganic powder (D) includes hydrophilic inorganic particles (D1) and hydrophobic inorganic particles (D2).

Examples of the hydrophilic inorganic particles (D1) include particles of glass, silica gel, silica, clay, and the like.

Examples of the hydrophobic inorganic particles (D2) include particles of carbon fibers, kaolin, talc, mica, bentonite, sericite, asbestos, volcanic ash, and the like.

Among these, hydrophilic inorganic particles (D1) are preferable, and silica is most preferable.

The shape of the hydrophilic inorganic particles (D1) and the hydrophobic inorganic particles (D2) may be any of amorphous (crushed), spherical, film-like, rod-like, fibrous, and the like, and is preferably amorphous (crushed) or spherical, and more preferably spherical.

The content (wt%) of the inorganic powder (D) is preferably 0.01 to 3.0, more preferably 0.05 to 1.0, still more preferably 0.1 to 0.8, particularly preferably 0.2 to 0.7, and most preferably 0.3 to 0.6, based on the weight of the crosslinked polymer (a). When the content is within this range, the skin irritation resistance of the absorbent article becomes better.

The water-absorbent resin particles of the present invention may contain other additives { for example, known (Japanese patent application laid-open No. 2003-225565, japanese patent application laid-open No. 2006-131767, etc. }) such as a preservative, a mold inhibitor, an antibacterial agent, an antioxidant, an ultraviolet absorber, a coloring agent, a fragrance, a deodorant, an organic fibrous material, etc. In the case of containing these additives, the content (wt%) of the additives is preferably 0.001 to 10, more preferably 0.01 to 5, particularly preferably 0.05 to 1, most preferably 0.1 to 0.5, based on the weight of the crosslinked polymer (A1).

The water-absorbent resin particles of the present invention preferably have a weight average particle diameter (μm) of 100 to 800, more preferably 200 to 700, still more preferably 250 to 600, particularly preferably 300 to 500, and most preferably 350 to 450. If the absorption rate is higher than this range, the absorption rate may be low, and if the absorption rate is lower than this range, the liquid permeability may be poor, and the spot absorption and gel blocking may occur, thereby facilitating the generation of liquid leakage. The content of the fine particles is preferably small, and the content of particles of 150 μm or less is preferably 3.0 wt% or less, more preferably 1.0 wt% or less. If the particles are large, the particles may be absorbed by spots or gel blocking, which may easily cause leakage or may cause process clogging in the process of manufacturing the diaper.

The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water-absorbent resin particles of the present invention is preferably 50% by weight or more, more preferably 60% by weight, particularly preferably 70% by weight. The higher the upper limit value, the more preferable is, without particular limitation, and from the viewpoint of productivity, the more preferable is 100% by weight or less, and the more preferable is 90% by weight or less.

The particle shape of the water-absorbent resin particles of the present invention is not particularly limited, and examples thereof include amorphous crushed, scaly, pearl-like, rice-like, and the like. Among these, amorphous crushed forms are preferable in terms of good entanglement with fibrous materials and no fear of falling off from the fibrous materials in the use of paper diapers or the like.

The apparent density (g/ml) of the water-absorbent resin particles of the present invention is preferably 0.5 to 0.7, more preferably 0.52 to 0.69, particularly preferably 0.54 to 0.68. When the content is within this range, the skin irritation resistance of the absorbent article becomes better. The apparent density of the water-absorbent resin particles was measured at 25℃in accordance with JIS K7365:1999.

The water retention amount of 0.9% by weight of physiological saline of the water-absorbent resin particles of the present invention is preferably 30 to 50g/g. The water retention amount can be measured by a method described later, and is more preferably 33 to 49g/g, still more preferably 36 to 48g/g, and particularly preferably 39 to 47g/g, from the viewpoint of suppressing leakage of the absorbent article. If the concentration is less than 30g/g, leakage is likely to occur during repeated use, which is not preferable. In addition, if the content exceeds 50g/g, blocking tends to occur, which is not preferable. The water retention amount can be appropriately adjusted by the kind and amount of the crosslinking agent (b) and the surface crosslinking agent (c). Therefore, for example, in the case where an increase in the water retention amount is required, it can be easily achieved by reducing the amounts of the crosslinking agent (b) and the surface crosslinking agent (c).

The water-absorbent resin particles of the present invention preferably have an absorption rate (seconds) of 50 or less as measured by the vortex method and an absorption rate (seconds) of 130 or less as measured by the lock method. The vortex flow method can be measured by a method described later, and is more preferably 48 or less, still more preferably 46 or less, and particularly preferably 44 or less, from the viewpoint of suppressing leakage of the absorbent article. The locking method can be measured by a method described later, and is preferably 130 or less, more preferably 120 or less, and particularly preferably 110 or less, from the viewpoint of suppressing leakage of the absorbent article.

The absorption capacity of the water-absorbent resin particles of the present invention under load is preferably 10 to 27g/g. The absorption capacity under load can be measured by a method described later, and is more preferably 13 to 27, still more preferably 16 to 27, and particularly preferably 19 to 27, from the viewpoint of absorption characteristics.

The gel flow rate (ml/min) of the water-absorbent resin particles of the present invention is preferably 5 to 250. The gel flow rate can be measured by a method described later, and is more preferably 10 to 230, particularly preferably 30 to 210, from the viewpoint of absorption characteristics.

The increase (%) of the particulate content after the crushing test of the water-absorbent resin particles of the present invention is preferably 0.0 to 3.0. The amount of increase in the content of fine particles after the crushing test can be measured by a method described later, and is more preferably 0.0 to 2.0, particularly preferably 0.0 to 1.5, from the viewpoint of mechanical strength.

The water-absorbent resin particles of the present invention can be preferably produced by a method for producing water-absorbent resin particles comprising the steps of: a polymerization step of polymerizing a monomer composition containing a water-soluble vinyl monomer (a 1) and/or a vinyl monomer (a 2) which is hydrolyzed to form the water-soluble vinyl monomer (a 1) and an internal crosslinking agent (b) as essential structural units to obtain an aqueous gel of a crosslinked polymer (A); a step of subdividing the aqueous gel of the crosslinked polymer (A); mixing and cutting finely-divided gel at a gel temperature of 40-120 ℃; and a step of surface-crosslinking the surface of the resin particles (B) containing the crosslinked polymer (A) with a surface-crosslinking agent (c). In the production method of the present invention, the internal shape of the water-absorbent resin particles can be maintained by the subdivision before the kneading and chopping step, and the decrease in mechanical strength of the water-absorbent resin particles can be prevented, and the absorption performance of the produced water-absorbent resin particles is excellent.

The absorbent body of the present invention contains the water-absorbent resin particles of the present invention. The absorbent material may be formed by using the water-absorbent resin particles alone or by using the water-absorbent resin particles together with other materials.

As the other material, a fibrous material or the like can be mentioned. The structure and the manufacturing method of the absorber when used together with the fibrous material are the same as those of the known absorber (Japanese patent application laid-open No. 2003-225565, japanese patent application laid-open No. 2006-131767, japanese patent application laid-open No. 2005-097569, etc.).

The fibrous material is preferably cellulose fibers, organic synthetic fibers, or a mixture of cellulose fibers and organic synthetic fibers.

Examples of the cellulose-based fibers include natural fibers such as fluff pulp, cellulose-based chemical fibers such as viscose rayon, acetate, and cuprammonium rayon. The raw material (needle-leaved tree, broad-leaved tree, etc.), the production method (chemical pulp, semi-chemical pulp, mechanical pulp, CTMP, etc.), the bleaching method, etc. of the cellulose-based natural fiber are not particularly limited.

Examples of the organic synthetic fibers include polypropylene fibers, polyethylene fibers, polyamide fibers, polyacrylonitrile fibers, polyester fibers, polyvinyl alcohol fibers, polyurethane fibers, and hot-melt adhesive composite fibers (fibers in which at least 2 of the fibers having different melting points are composited with a core-sheath type, a core-shift type, a side-by-side type, or the like, fibers in which at least 2 of the fibers are mixed, and fibers in which a surface layer of the fibers is modified).

Among these fibrous materials, cellulose-based natural fibers, polypropylene-based fibers, polyethylene-based fibers, polyester-based fibers, hot-melt adhesive composite fibers, and mixed fibers thereof are preferable, and from the viewpoint of excellent shape retention of the obtained water absorbing agent after water absorption, fluff pulp, hot-melt adhesive composite fibers, and mixed fibers thereof are more preferable.

The length and thickness of the fiber are not particularly limited, and may be suitably used as long as the length is 1 to 200mm and the thickness is 0.1 to 100 denier. The shape is not particularly limited as long as it is fibrous, and a thin cylindrical shape, split filaments, short fibers, filaments, net shape, and the like can be exemplified.

When the water-absorbent resin particles are formed into an absorbent body together with the fibrous material, the weight ratio of the water-absorbent resin particles to the fibers (weight of the water-absorbent resin particles/weight of the fibers) is preferably 40/60 to 90/10, more preferably 70/30 to 80/20.

The absorbent article of the present invention uses the above-described absorber. The absorbent article can be used not only as a sanitary article such as a disposable diaper or a sanitary napkin, but also as an absorbent or a retention agent for various aqueous liquids, a gelling agent, and the like, which will be described later. The method for producing the absorbent article is similar to known methods (methods described in Japanese patent application laid-open No. 2003-225565, japanese patent application laid-open No. 2006-131767, japanese patent application laid-open No. 2005-097569, and the like).

Examples

The present invention will be further described with reference to examples and comparative examples, but the present invention is not limited thereto. Hereinafter, unless otherwise specified, parts means parts by weight and% means% by weight.

The particle defect degree, the water retention amount, the absorption rate by the vortex method, the absorption rate by the lock method, the absorption amount under load, and the gel flow rate were measured in the chambers having a temperature of 25.+ -. 2 ℃ and a humidity of 50.+ -. 10%, respectively, by the following methods. The physiological saline to be used was used after the temperature of the physiological saline was previously adjusted to 25.+ -. 2 ℃.

< method for measuring particle defect degree >

The particle defect degree of the water-absorbent resin particles was measured by using a Camsizer (registered trademark) image analysis system (manufactured by Retsch Technology GmbH). From the sample feeder at the upper part of the apparatus, 5.00g of the measurement sample sieved to a range of 300 to 600 μm by a standard sieve (JIS Z8801-1:2006) was allowed to fall freely in small portions, and the fallen measurement sample was continuously photographed by a CCD camera. The captured image is analyzed to derive a particle defect level of the measurement sample. The arithmetic average of the granule defect degrees derived from the analysis point n=3 was used as the granule defect degree of the present invention. All particles were measured in the same manner as described above except that sieving was not performed.

< method for measuring Water retention >

A teabag (length 20cm, width 10 cm) made of nylon mesh with mesh opening of 63 μm (JIS Z8801-1:2006) was filled with 1.00g of a measurement sample, immersed in 1,000ml of physiological saline (salt concentration 0.9%) without stirring for 1 hour, lifted, and suspended for 15 minutes to remove water. Thereafter, the mixture was placed in a centrifugal separator together with the tea bag, and centrifugal dehydration was carried out at 150G for 90 seconds to remove the remaining physiological saline, and the weight (h 1) including the tea bag was measured to determine the water retention amount by the following formula. The temperature of the physiological saline and the measurement atmosphere used was 25.+ -. 2 ℃.

Water retention (g/g) = (h 1) - (h 2)

(h2) The weight of the tea bag was measured by the same procedure as described above without the measurement sample.

< absorption Rate measured by vortex flow method >

The time (unit: seconds) required for the absorption of 2.000g of the measurement sample sieved to a range of 300 to 600 μm using a standard sieve to complete 50g of physiological saline was measured in accordance with JIS K7224-1996, and the physiological saline was stirred at 600 times per minute in a 100ml high beaker having a flat bottom surface defined in JIS R3503 as the absorption rate measured by the vortex method.

< absorption Rate measured by Lock method >

1.000g of the measurement sample was placed in a 100ml high beaker having a flat bottom surface defined in JIS R3503. At this time, the upper surface of the water-absorbent resin filled in the beaker was made horizontal. Then, 40g of physiological saline having a temperature of 23.+ -. 2 ℃ was measured in a 100ml glass beaker, and carefully and rapidly poured into the 100ml beaker containing the water-absorbent resin. The time measurement was started while the injected physiological saline was in contact with the water-absorbent resin. Then, the beaker filled with physiological saline was turned to the side at an angle of about 90 °, the point where the flow did not ooze out from the surface of the water-absorbent resin was set as the end point, and the time (unit: seconds) was set as the absorption rate measured by the lock-up method.

< method for measuring absorption under load >

A measurement sample of 0.16g, which was sieved to a range of 250 to 500 μm using a standard sieve, was weighed in a cylindrical plastic tube (inner diameter: 25mm, height: 34 mm) having a nylon mesh with a mesh size of 63 μm (JIS Z8801-1:2006) adhered to the bottom surface, and the cylindrical plastic tube was set so as to be perpendicular to the measurement sample and adjusted so that the measurement sample had a substantially uniform thickness on the nylon mesh, and then a weight (weight: 310.6g, outer diameter: 24.5 mm) was placed on the measurement sample. After measuring the weight (M1) of the whole cylindrical plastic tube, the cylindrical plastic tube with the measurement sample and weight added thereto was vertically set up in a plate (diameter: 12 cm) with 60ml of physiological saline (salt concentration: 0.9%) added thereto, and the nylon net side was immersed with the nylon net side as the bottom, and allowed to stand for 60 minutes. After 60 minutes, the cylindrical plastic tube was lifted from the dish and tilted, and the water attached to the bottom was collected in one place and dropped as a water droplet, thereby removing the excess water, and then the weight (M2) of the entire cylindrical plastic tube to which the measurement sample and the weight were added was measured, and the absorption under load was determined by the following formula. The temperature of the physiological saline and the measurement atmosphere used was 25.+ -. 2 ℃.

Absorption under load (g/g) = { (M2) - (M1) }/0.16

< method for measuring gel flow Rate >

The following operations were performed using the apparatus shown in fig. 2 and 3.

A measurement sample (0.32 g) was immersed in 150ml of physiological saline (1) (salt concentration: 0.9%) for 30 minutes to prepare swollen gel particles (2). Then, a filtration cylindrical tube having a metal mesh 6 (mesh opening 106 μm, JIS Z8801-1:2006) and a freely openable cock 7 (inner diameter 5mm of the liquid passing portion) at the bottom of a vertically standing cylinder 3{ diameter (inner diameter) 25.4mm, length 40cm, scale mark 4 and scale mark 5} provided at a position 60ml from the bottom and a position 40ml, respectively, was used, the prepared swollen gel particles 2 were transferred into the filtration cylindrical tube together with physiological saline in a state where the cock 7 was closed, and then a circular metal mesh 8 (mesh opening 150 μm, diameter 25 mm) having a pressurizing shaft 9 (weight 22g, length 47 cm) vertically bonded to the metal mesh surface was placed on the swollen gel particles 2 in such a manner that the metal mesh was in contact with the swollen gel particles, and further a weight 10 (88.5 g) was placed on the pressurizing shaft 9, and allowed to stand for 1 minute. Then, the cock 7 was opened, and the time (T1; sec) required for the liquid surface in the cylindrical tube to pass from the 60ml scale mark 4 to the 40ml scale mark 5 was measured, and the gel flow rate (ml/min) was determined by the following formula.

Gel flow rate (ml/min) =20ml×60/(T1-T2)

The measurement was performed at 25±2 ℃ for the physiological saline and the measurement atmosphere, and T2 was the time measured by the same procedure as described above without the measurement sample.

Example 1 ]

Acrylic acid (a 1) { Mitsubishi chemical corporation, purity 100% }131 parts, internal crosslinking agent (b-1) { pentaerythritol triallyl ether, OSAKA SODA CO., LTD. Manufactured }0.44 parts, and deionized water 362 parts were stirred and mixed, and maintained at 3 ℃. After nitrogen was introduced into the mixture so that the amount of dissolved oxygen was 1ppm or less, 0.5 part of a 1% hydrogen peroxide solution, 1 part of a 2% aqueous ascorbic acid solution, and 0.1 part of a 2% aqueous 2,2' -azobis amidinopropane dihydrochloride solution were mixed and added to initiate polymerization. After the temperature of the mixture reached 80 ℃, polymerization was carried out at 80±2 ℃ for about 5 hours, thereby obtaining an aqueous gel.

Next, the hydrogel was subdivided into approximately 1mm squares with scissors, and 162 parts of 45% aqueous sodium hydroxide solution was added. Further, the mixture was kneaded and chopped 4 times at a gel temperature of 80℃by using a chopper having a grid diameter of 16mm (12 VR-400K manufactured by ROYAL Co.), and then dried by using a vented dryer {150℃at a wind speed of 2 m/s }, to obtain a dried body. The dried product was crushed by a juicer mixer (OSTERIZER BLENDER, manufactured by Oster Co.), and then sieved to adjust the particle size to a range of 710 to 150 μm in mesh (400 μm in weight average particle size), thereby obtaining resin particles containing crosslinked polymer particles.

Next, 100 parts of the obtained resin particles were stirred at a high speed (the same applies hereinafter under the trade name of Hosokawa Micron) and a mixed solution obtained by mixing 0.6 part by weight of aluminum sodium sulfate alum dodecahydrate as the inorganic acid salt (d), 0.08 part by weight of ethylene glycol diglycidyl ether as the surface cross-linking agent and 3.3 parts by weight of a 45% propylene glycol aqueous solution as the solvent was added thereto, followed by standing at 130℃for 60 minutes, followed by drying, to obtain water-absorbent resin particles (P-1) of the present invention. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water-absorbent resin particles (P-1) was 71% by weight.

Example 2 ]

Water-absorbent resin particles (P-2) were obtained in the same manner as in example 1, except that the aqueous gel was finely divided into 5mm squares with scissors. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water-absorbent resin particles (P-2) was 70% by weight.

Example 3 ]

Water-absorbent resin particles (P-3) were obtained in the same manner as in example 1, except that the neutralized aqueous gel was kneaded and chopped 4 times at a gel temperature of 80℃with a chopper having a grid diameter of 8mm (12 VR-400K manufactured by ROYAL Co.). The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water-absorbent resin particles (P-3) was 70% by weight.

Example 4 ]

Water-absorbent resin particles (P-4) were obtained in the same manner as in example 1, except that the neutralized aqueous gel was kneaded and chopped 2 times at a gel temperature of 80℃with a chopper having a grid diameter of 16mm (12 VR-400K manufactured by ROYAL Co.). The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water-absorbent resin particles (P-4) was 71% by weight.

Example 5 ]

Water-absorbent resin particles (P-5) were obtained in the same manner as in example 1, except that the kneading and chopping temperature of the aqueous gel was changed to 60℃at 80 ℃. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water-absorbent resin particles (P-5) was 71% by weight.

Example 6 ]

Water-absorbent resin particles (P-6) were obtained in the same manner as in example 1, except that the kneading and chopping temperature of the aqueous gel was changed to 80℃to 100 ℃. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water-absorbent resin particles (P-6) was 71% by weight.

Example 7 ]

Water-absorbent resin particles (P-7) were obtained in the same manner as in example 1, except that the size of the hydrogel particles was reduced to about 1mm square to about 5mm square, the grid diameter of the chopper was 16mm to 8mm, and the kneading and chopping temperature of the hydrogel particles was 80℃to 100 ℃. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water-absorbent resin particles (P-7) was 71% by weight.

Example 8 ]

Acrylic acid (a 1) { Mitsubishi chemical corporation, purity 100% }131 parts, internal crosslinking agent (b-1) { pentaerythritol triallyl ether, OSAKA SODA CO., LTD. Manufactured }0.44 parts, and deionized water 362 parts were stirred and mixed, and maintained at 3 ℃. After nitrogen was introduced into the mixture so that the amount of dissolved oxygen was 1ppm or less, 0.5 part of a 1% hydrogen peroxide solution, 1 part of a 2% aqueous ascorbic acid solution, and 0.1 part of a 2% aqueous 2,2' -azobis amidinopropane dihydrochloride solution were mixed and added to initiate polymerization. After the temperature of the mixture reached 80 ℃, polymerization was carried out at 80±2 ℃ for about 5 hours, thereby obtaining an aqueous gel.

Next, the hydrogel was subdivided into approximately 5mm squares with scissors, and 162 parts of 45% aqueous sodium hydroxide solution was added. Further, after kneading and chopping 4 times at a gel temperature of 100℃by using a chopper having a grating diameter of 8mm (12 VR-400K manufactured by ROYAL Co., ltd.), the whole amount was put into a kneader (Table kneader PNV-1, kyowa Kagaku Co., ltd.) equipped with a Sigma-type rotary blade and a heat-insulating jacket, and dried at a rotation speed of 40rpm and a jacket temperature of 180℃for 60 minutes, to obtain a dried body containing a crosslinked polymer. The dried product was crushed by a juicer mixer (OSTERIZER BLENDER, manufactured by Oster Co.), and then sieved to adjust the particle size to a range of 710 to 150 μm in mesh (400 μm in weight average particle size), thereby obtaining resin particles containing crosslinked polymer particles.

Next, 100 parts of the obtained resin particles were stirred at a high speed (a high speed stirring paddle mixer manufactured by Hosokawa Micron: rotation speed 2000 rpm), and a mixed solution obtained by mixing 0.6 part by weight of aluminum sodium sulfate alum dodecahydrate as the inorganic acid salt (d), 0.08 part by weight of ethylene glycol diglycidyl ether as the surface cross-linking agent and 3.3 parts by weight of a 45% aqueous propylene glycol solution as the solvent was added thereto, followed by standing at 130℃for 60 minutes, followed by drying, to obtain water-absorbent resin particles (P-8) of the present invention. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water-absorbent resin particles (P-8) was 70% by weight.

Example 9 ]

While stirring and mixing acrylic acid (a 1) { Mitsubishi chemical Co., ltd., purity 100% }131 parts, an internal crosslinking agent (b-2) { polyethylene glycol diacrylate (Mw=508), 0.4 part of Xinzhongcun chemical industry Co., ltd. }, 162 parts of 45% aqueous sodium hydroxide solution, and 362 parts of deionized water, the mixture was kept at 3 ℃. After nitrogen was introduced into the mixture so that the amount of dissolved oxygen was 1ppm or less, 0.5 part of a 1% hydrogen peroxide solution, 1 part of a 2% aqueous ascorbic acid solution, and 0.1 part of a 2% aqueous 2,2' -azobis amidinopropane dihydrochloride solution were mixed and added to initiate polymerization. After the temperature of the mixture reached 80 ℃, polymerization was carried out at 80±2 ℃ for about 5 hours, thereby obtaining an aqueous gel.

Next, the hydrogel was finely divided into about 1mm squares by scissors, kneaded and minced 4 times at a gel temperature of 80℃by a chopper (12 VR-400K manufactured by ROYAL Co.) having a grid diameter of 16mm, and dried by a vent dryer {150℃at a wind speed of 2 m/s } to obtain a dried body. The dried product was crushed by a juicer mixer (OSTERIZER BLENDER, manufactured by Oster Co.), and then sieved to adjust the particle size to a range of 710 to 150 μm in mesh (400 μm in weight average particle size), thereby obtaining resin particles containing crosslinked polymer particles.

Next, 100 parts of the obtained resin particles were stirred at a high speed (a high speed stirring paddle mixer manufactured by Hosokawa Micron: rotation speed 2000 rpm), and a mixed solution obtained by mixing 0.6 part by weight of aluminum sodium sulfate alum dodecahydrate as the inorganic acid salt (d), 0.08 part by weight of ethylene glycol diglycidyl ether as the surface cross-linking agent and 3.3 parts by weight of a 45% aqueous propylene glycol solution as the solvent was added thereto, followed by standing at 130℃for 60 minutes, followed by drying, to obtain water-absorbent resin particles (P-9) of the present invention. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water-absorbent resin particles (P-9) was 70% by weight.

Example 10 ]

Water-absorbent resin particles (P-10) were obtained in the same manner as in example 9, except that the aqueous gel was finely divided into 5mm squares with scissors. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water-absorbent resin particles (P-10) was 71% by weight.

Example 11 ]

Water-absorbent resin particles (P-11) were obtained in the same manner as in example 9, except that the aqueous gel finely divided into about 1mm square was kneaded and chopped 4 times at a gel temperature of 80℃by a chopper (12 VR-400K manufactured by ROYAL Co.) having a grid diameter of 8 mm. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water-absorbent resin particles (P-11) was 70% by weight.

Example 12 ]

Water-absorbent resin particles (P-12) were obtained in the same manner as in example 9, except that the aqueous gel finely divided into about 1mm square was kneaded and chopped 2 times at a gel temperature of 80℃with a chopper (12 VR-400K manufactured by ROYAL Co.) having a grid diameter of 16 mm. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water-absorbent resin particles (P-12) was 71% by weight.

Comparative example 1 ]

A comparative water-absorbent resin particle (R-1) was obtained in the same manner as in example 1 except that the neutralized aqueous gel was not kneaded and chopped by a chopper (12 VR-400K manufactured by ROYAL Co.) and dried by a vented dryer {150 ℃ C., air velocity: 2 m/s }, to obtain a dried product. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water-absorbent resin particles (R-1) was 71% by weight.

Comparative example 2 ]

A comparative water-absorbent resin particle (R-2) was obtained in the same manner as in example 9 except that the aqueous gel was not kneaded and chopped by a chopper (12 VR-400K manufactured by ROYAL Co.) and dried by a ventilating dryer {150 ℃ C., air speed: 2 m/s }, to obtain a dried body. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water-absorbent resin particles (R-2) was 71% by weight.

Comparative example 3 ]

According to the method disclosed in paragraphs 0088 to 0091 of Japanese patent application laid-open No. 2017-222875, a dried body of an aqueous gel is obtained. Namely, 100g of acrylic acid, 0.5g of polyethylene glycol diacrylate (Mw=523) as a crosslinking agent, 0.033g of diphenyl (2, 4, 6-trimethylbenzoyl) phosphine oxide as a UV initiator, 50% hydrogen83.3g of sodium oxide aqueous solution (NaOH) and 89.8g of water were mixed to prepare a monomer aqueous solution composition having a monomer concentration of 45% by weight. Next, the aqueous monomer solution composition was fed to a supply section of a polymerizer constituted by a continuously moving conveyor belt, and then irradiated with ultraviolet rays (irradiation amount: 2 mW/cm) ² ) UV polymerization was carried out for 2 minutes to produce an aqueous gel polymer. The hydrogel polymer was fed to a cutter and cut into 0.2cm pieces. At this time, the water content of the hydrogel polymer after cutting was 50% by weight.

Subsequently, the hydrogel polymer was dried for 30 minutes by a hot air dryer at 160℃to obtain a dried product. The dried product was crushed by a juicer mixer (OSTERIZER BLENDER, manufactured by Oster Co.), and then sieved to adjust the particle size to a range of 710 to 150 μm in mesh (400 μm in weight average particle size), thereby obtaining resin particles containing crosslinked polymer particles.

Next, 100 parts of the obtained resin particles were stirred at a high speed (a high speed stirring paddle mixer manufactured by Hosokawa Micron: rotation speed 2000 rpm), and a mixed solution obtained by mixing 0.6 part by weight of aluminum sodium sulfate alum dodecahydrate as the inorganic acid salt (d), 0.08 part by weight of ethylene glycol diglycidyl ether as the surface cross-linking agent, and 3.3 parts by weight of a 45% aqueous propylene glycol solution as the solvent was added thereto, followed by standing at 130℃for 60 minutes, followed by drying, to obtain comparative water-absorbent resin particles (R-3). The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water-absorbent resin particles (R-3) was 70% by weight.

Comparative example 4 ]

According to the method disclosed in paragraphs 0075 to 0077 of Japanese patent application laid-open No. 2018-16750, comparative water-absorbent resin particles (R-4) were obtained. That is, the temperature was kept at 3℃while stirring and mixing 270 parts of acrylic acid (a 1) { Mitsubishi chemical Co., ltd., purity 100% }, 270 parts of an internal crosslinking agent (b-1) { pentaerythritol triallyl ether, OSAKA SODA CO., LTD. Manufacturing }0.98 part, and 712 parts of ion-exchanged water. After nitrogen was introduced into the mixture so that the amount of dissolved oxygen was 1ppm or less, 1.1 parts of a 1% hydrogen peroxide solution, 2.0 parts of a 2% aqueous ascorbic acid solution, and 13.5 parts of a 2%, 2' -azobis amidinopropane dihydrochloride aqueous solution were mixed and polymerized. After the temperature of the mixture reached 80 ℃, the mixture was aged at 80±2 ℃ for about 5 hours, thereby obtaining an aqueous gel.

Next, 220 parts of 49% aqueous sodium hydroxide solution was added to the aqueous gel while the aqueous gel was chopped by a chopper (12 VR-400K manufactured by ROYAL Co.), and mixed and neutralized to obtain a neutralized gel. The grating diameter used at this time was 16mm, and 4 times of shredding were performed. In addition, the gel temperature was 60 ℃. Further, the neutralized aqueous gel was air-dried using an air dryer (manufactured by well metal production) at a supply temperature of 150℃and an air speed of 1.5 m/s until the water content reached 4%, to obtain a dried body. The dried product was crushed by a juicer mixer (OSTERIZER BLENDER, manufactured by Oster Co.), and then sieved to adjust the mesh size to a range of 710 to 150 μm, thereby obtaining resin particles containing a crosslinked polymer.

Next, while 100 parts of the obtained resin particles were stirred at a high speed (a high-speed stirring paddle mixer manufactured by Hosokawa Micron: rotation speed 2000 rpm), a mixture of 0.12 part of ethylene glycol diglycidyl ether as a surface cross-linking agent, 1.0 part of propylene glycol, 1.0 part of Klebosol30cal (colloidal silica manufactured by AZ Material Co.) as water-insoluble inorganic fine particles, 1.7 parts of ion-exchanged water, and a mixture of 0.6 part of sodium aluminum sulfate dodecahydrate as inorganic acid salt (d), 0.6 part of propylene glycol, and 1.5 parts of ion-exchanged water were simultaneously added thereto, and after uniform mixing, the mixture was heated at 135℃for 30 minutes, to obtain surface-crosslinked resin particles (R-4). The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water-absorbent resin particles (R-4) was 71% by weight.

Comparative example 5 ]

Water-absorbent resin particles (R-5) were obtained in the same manner as in comparative example 4, except that the drying condition of the aqueous gel after neutralization was changed to a supply temperature of 150℃to 200℃and a wind speed of 1.5 m/s to 5 m/s. The weight ratio of the particles having a particle diameter of 300 to 600 μm to the total weight of the water-absorbent resin particles (R-5) was 70% by weight.

Next, in order to evaluate the mechanical strength of the water-absorbent resin particles, the increase in the particulate content after the crushing test was evaluated as follows using the water-absorbent resin particles obtained in example 1, example 8, comparative example 4 and comparative example 5.

< amount of increase in particle content after crushing test >

50g of the measurement sample was sieved through a JIS standard sieve (JIS Z8801-1:2006) having a particle size of 150 μm or less. All of the particles of 150 μm or more remaining on the sieve were put into a 3L round-bottomed flask (manufactured by AS ONE), a nylon net (JIS Z8801-1:2000) of 63 μm with 6 mm-hole openings in the center was laid on the upper part of the round-bottomed flask, and four-port detachable covers (main tube TS29/42, side tube TS24/40, 15/35 manufactured by AS ONE) were further provided thereon. Next, a stainless steel (outer diameter 6mm, inner diameter 4 mm) tube was set in the main tube TS29/42 of the four-port detachable cover so that the tip end was located 45mm from the bottom surface of the round-bottomed flask through the nylon net. A polyurethane tube (length: 1500mm, inner diameter: 8.5 mm) was attached to the other end of the stainless steel tube, and the tube was connected to an air line capable of reaching a pressure of 0.3MPa or more. Next, the air line was opened at a pressure of 0.2MPa, air was blown for 10 minutes, and then a measurement sample was taken out, and the sample was sieved with a JIS standard sieve of 150 μm (JIS Z8801-1:2006), and the proportion (%) of the weight of particles of 150 μm or less to the total weight was used as the amount of increase in the particulate content.

The evaluation results of the particle defect degrees (1% or less, 8% or more (sieved particles and all particles)), apparent density (g/ml), weight average particle diameter (μm), performance (water retention capacity (g/g), absorption rate (seconds) measured by the vortex method, absorption rate (seconds) measured by the lock method, absorption capacity under load (g/g), and gel flow rate (ml/min)) of the water-absorbent resin particles (P-1) to (P-12) of examples 1 to 12 and the water-absorbent resin particles (R-1) to (R-5) of comparative examples 1 to 5 are shown in Table 1. The evaluation results of the increase in the particle content after the crushing test with respect to the water-absorbent resin particles (P-1), (P-8), (R-4) and (R-5) are shown in Table 2.

TABLE 1

TABLE 2

As is clear from the results shown in Table 1, the water-absorbent resin particles of the present invention have a particle defect rate of 1% or less and a particle fraction of 50% or less by volume ratio, as compared with the water-absorbent resin particles of comparative examples 1 to 3, and the absorption rate measured by the vortex method and the locking method is markedly improved. In comparative examples 4 and 5, the proportion of particles having a particle defect degree of 8% or more did not satisfy the conditions of the present invention. In comparative examples 4 and 5, the properties shown in Table 1 were not inferior to those of the examples, but as shown in Table 2, the increase in the particle content after the crushing test was large. That is, as is typically shown in examples 1 and 8, the water-absorbent resin particles of the present invention were inhibited from increasing in particle content after the crushing test, and the decrease in mechanical strength was inhibited, as shown in Table 2, in which the proportion of particles having a particle defect degree of 8% or more was 5% or less by volume ratio, compared with the water-absorbent resin particles of comparative examples 4 and 5. Further, in all of examples and comparative examples, there was no large difference in apparent density and average particle diameter, and there was no difference in polymerization, and therefore it was found that the shape of the particle surface greatly contributed to the absorption rate.

Industrial applicability

The water-absorbent resin particles of the present invention are formed with irregularities on the surfaces of the water-absorbent resin particles and with a certain controlled proportion of particles, and therefore, the apparent density and the absorption rate can be simultaneously achieved without decreasing the mechanical strength, and therefore, the present invention can be used for absorbent articles having a high absorption rate and excellent rewet properties and surface dryness without causing failures in the production process of various absorbent bodies, and is suitable for use in sanitary articles.

Symbol description

1. Physiological saline

2. Aqueous gel particles

3. Cylinder barrel

4. Graduation marks at a position 60ml from the bottom

5. Graduation marks at a position 40ml from the bottom

6. Metal net

7. Cock plug

8. Round metal net

9. Pressurized shaft

10. Weight

Claims (10)

1. Among the particles screened to a range of 300 μm to 600 μm using a JIS standard sieve, particles having a particle defect degree CONV defined by the following formula (1) of not more than 1% by volume of not more than 50%, particles having a particle defect degree CONV of not less than 8% by volume of not more than 5%, an absorption rate measured by a vortex method of not more than 50 seconds, and an absorption rate measured by a lock method of not more than 130 seconds,

the water-absorbent resin particles are produced by a method for producing water-absorbent resin particles, which comprises the steps of: a polymerization step of polymerizing a monomer composition containing a water-soluble vinyl monomer (a 1) and/or a vinyl monomer (a 2) which is hydrolyzed to form the water-soluble vinyl monomer (a 1) and an internal crosslinking agent (b) as essential structural units to obtain an aqueous gel of a crosslinked polymer (A); a step of subdividing the aqueous gel of the crosslinked polymer (A); further carrying out the procedures of mixing and cutting the finely divided gel at the gel temperature of 40-120 ℃; and a step of surface-crosslinking the surface of the resin particles (B) containing the crosslinked polymer (A) with a surface-crosslinking agent (c);

The size of the gel after subdivision before milling and shredding is 50 μm-10 cm based on the longest diameter,

CONV(％)＝{B/(A+B)}×100 (1)

in the formula (1), CONV represents the particle defect degree, a represents the projection area of the target particle obtained by the image analysis method, and B represents a value obtained by subtracting the projection area of the target particle represented by a from the projection area surrounded by the envelope in which the convex portions of the target particle obtained by the image analysis method are connected.

2. The water-absorbent resin particles according to claim 1, wherein the apparent density of the water-absorbent resin particles is from 0.5g/ml to 0.7g/ml.

3. The water-absorbent resin particles according to claim 1 or 2, wherein the water retention amount of 0.9% by weight of physiological saline is 30g/g to 50g/g per unit weight.

4. The water-absorbent resin particles according to claim 1 or 2, wherein the absorption capacity under load of the water-absorbent resin particles is 10g/g to 27g/g.

5. The water-absorbent resin particles according to claim 1 or 2, wherein the gel flow rate of the water-absorbent resin particles is from 5 ml/min to 250 ml/min.

6. A method for producing water-absorbent resin particles, comprising the steps of: a polymerization step of polymerizing a monomer composition containing a water-soluble vinyl monomer (a 1) and/or a vinyl monomer (a 2) which is hydrolyzed to form the water-soluble vinyl monomer (a 1) and an internal crosslinking agent (b) as essential structural units to obtain an aqueous gel of a crosslinked polymer (A); a step of subdividing the aqueous gel of the crosslinked polymer (A); further carrying out the procedures of mixing and cutting the finely divided gel at the gel temperature of 40-120 ℃; and a step of surface-crosslinking the surface of the resin particles (B) containing the crosslinked polymer (A) with a surface-crosslinking agent (c);

The size of the gel after the subdivision before the kneading and the shredding is 50 μm to 10cm in terms of the longest diameter.

7. The manufacturing method according to claim 6, comprising the steps of: after drying the aqueous gel to obtain a crosslinked polymer, 0.01 to 5 wt% of a polyvalent metal salt (d) based on the weight of the crosslinked polymer (A) is mixed.

8. The production process according to claim 7, wherein the polyvalent metal salt (d) is an inorganic acid salt of aluminum.

9. An absorbent body comprising the water-absorbent resin particles according to any one of claims 1 to 5.

10. An absorbent article comprising the absorber of claim 9.