WO2021049467A1

WO2021049467A1 - Method for producing crosslinked polymer particles, and crosslinked polymer gel

Info

Publication number: WO2021049467A1
Application number: PCT/JP2020/033833
Authority: WO
Inventors: 志保岡澤
Original assignee: 住友精化株式会社
Priority date: 2019-09-09
Filing date: 2020-09-07
Publication date: 2021-03-18
Also published as: JPWO2021049467A1

Abstract

A method for producing crosslinked polymer particles comprising a coarse grinding step for coarse grinding a crosslinked polymer gel that has a structural unit derived from an ethylenically unsaturated monomer, wherein the gel hardness after polymerization, as obtained by the procedures (1) to (3) described below, is not less than 70 N but less than 450 N. (1) A test piece having a rectangular solid shape of 20 mm × 20 mm × 17 mm is obtained from the crosslinked polymer gel. (2) A flat surface of a jig having the flat surface is brought into contact with the 20 mm × 20 mm surface of the test piece from the upper side in the vertical direction. (3) An operation wherein the jig is pressed into the test piece by 15 mm in the vertical direction is performed, and the maximum value of the load undertaken by the jig during this operation is obtained as the above-described gel hardness after polymerization.

Description

Method for producing crosslinked polymer particles and crosslinked polymer gel

The present invention relates to a method for producing crosslinked polymer particles and a crosslinked polymer gel.

Conventionally, an absorber containing water-absorbent resin particles has been used as an absorbent article for absorbing a liquid containing water as a main component (for example, urine) (see, for example, Patent Document 1 below). The water-absorbent resin particles can be obtained, for example, by using crosslinked polymer particles obtained by coarsely crushing, drying, or the like a crosslinked polymer gel obtained by polymerizing an ethylenically unsaturated monomer.

Japanese Unexamined Patent Publication No. 06-345819

When a liquid containing water as a main component is provided to an absorbent article, if the liquid is not sufficiently absorbed by the absorbent body of the absorbent article, the excess liquid flows on the surface of the absorbent article and the absorbent article is used. Problems such as leakage to the outside may occur. Therefore, the water-absorbent resin particles constituting the absorber are required to have excellent water-absorbing ability, and the crosslinked polymer particles used for obtaining such water-absorbent resin particles are also excellent. It is required to have water absorption capacity.

By performing the coarse crushing treatment when obtaining the crosslinked polymer particles, it is easy to uniformly dry the crosslinked polymer particles with a suitable drying efficiency in the subsequent drying treatment, so that the crosslinked polymer particles having stable performance can be obtained in a short time. However, it is required to avoid a decrease in the water absorption capacity of the crosslinked polymer particles due to the coarse crushing.

One aspect of the present invention is to provide a method for producing crosslinked polymer particles capable of suppressing a decrease in water absorption capacity in the crosslinked polymer particles obtained by subjecting the coarsely crushed treatment. Another aspect of the present invention is to provide a crosslinked polymer gel capable of obtaining the crosslinked polymer particles.

The present inventor has found that the water absorption capacity of the crosslinked polymer particles may be lowered by coarsely crushing the crosslinked polymer gel, and then the crosslinked polymer gel to be coarsely crushed in the coarse crushing step is specified. It has been found that it is possible to suppress a decrease in water absorption capacity of the crosslinked polymer particles when a test force is applied.

One aspect of the present invention includes a rough crushing step of coarsely crushing a crosslinked polymer gel having a structural unit derived from an ethylenically unsaturated monomer, and is obtained after polymerization by the following procedures (1) to (3). Provided is a method for producing crosslinked polymer particles having a gel hardness of 70 N or more and less than 450 N.
(1) A rectangular parallelepiped test piece of 20 mm × 20 mm × 17 mm is obtained from the crosslinked polymer gel.
(2) The flat surface of the jig having a flat surface is brought into contact with the 20 mm × 20 mm surface of the test piece from the upper side in the vertical direction.
(3) An operation of pushing the jig into the test piece by 15 mm in the vertical direction is performed, and the maximum value of the load applied to the jig during the operation is obtained as the gel hardness after polymerization.

Another aspect of the present invention is a crosslinked polymer gel having a structural unit derived from an ethylenically unsaturated monomer, which has a post-polymerization gel hardness of 70 N obtained by the following procedures (1) to (3). Provided is a crosslinked polymer gel having a value of more than 450 N and less than 450 N.
(1) A rectangular parallelepiped test piece of 20 mm × 20 mm × 17 mm is obtained from the crosslinked polymer gel.
(2) The flat surface of the jig having a flat surface is brought into contact with the 20 mm × 20 mm surface of the test piece from the upper side in the vertical direction.
(3) An operation of pushing the jig into the test piece by 15 mm in the vertical direction is performed, and the maximum value of the load applied to the jig during the operation is obtained as the gel hardness after polymerization.

According to the above-mentioned method for producing crosslinked polymer particles and the above-mentioned crosslinked polymer gel, it is possible to suppress a decrease in water absorption capacity of the crosslinked polymer particles obtained by performing a coarse crushing treatment.

According to one aspect of the present invention, it is possible to provide a method for producing crosslinked polymer particles capable of suppressing a decrease in water absorption capacity in the crosslinked polymer particles obtained by subjecting the coarse crushing treatment. According to another aspect of the present invention, it is possible to provide a crosslinked polymer gel capable of obtaining the crosslinked polymer particles.

It is a figure for demonstrating the test content of a compression test. It is a figure for demonstrating the test content of a compression test.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be variously modified and implemented within the scope of the gist thereof.

In this specification, "acrylic" and "methacryl" are collectively referred to as "(meth) acrylic". Similarly, "acrylate" and "methacrylate" are also referred to as "(meth) acrylate". In the numerical range described stepwise in the present specification, the upper limit value or the lower limit value of the numerical range of one step can be arbitrarily combined with the upper limit value or the lower limit value of the numerical range of another step. In the numerical range described in the present specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. "Water-soluble" means that it exhibits a solubility in water of 5% by mass or more at 25 ° C. The materials exemplified in the present specification may be used alone or in combination of two or more. The content of each component in the composition means the total amount of the plurality of substances present in the composition when a plurality of substances corresponding to each component are present in the composition, unless otherwise specified. "Saline" refers to a 0.9% by mass sodium chloride aqueous solution. "Room temperature" means 25 ° C ± 2 ° C.

The method for producing crosslinked polymer particles according to the present embodiment includes a roughing step of coarsely crushing a crosslinked polymer gel having a structural unit derived from an ethylenically unsaturated monomer. The crosslinked polymer gel according to this embodiment has a structural unit derived from an ethylenically unsaturated monomer. In the present embodiment, the gel hardness after polymerization (hereinafter, sometimes referred to as “test force”) obtained by the following procedures (1) to (3) is 70 N or more and less than 450 N.
(1) A rectangular parallelepiped test piece of 20 mm × 20 mm × 17 mm is obtained from the crosslinked polymer gel.
(2) The flat surface of the jig having a flat surface is brought into contact with the 20 mm × 20 mm surface of the test piece from the upper side in the vertical direction.
(3) An operation of pushing the jig vertically into the test piece by 15 mm is performed, and the maximum value of the load applied to the jig during the operation is obtained as the above-mentioned post-polymerization gel hardness (test force).

According to this embodiment, it is possible to suppress a decrease in water absorption capacity in the crosslinked polymer particles obtained by performing the coarse crushing treatment. For example, according to the present embodiment, as the reduction rate of the water absorption capacity due to the coarse crushing treatment, the difference B (water absorption capacity before coarse crushing-) of the water absorption capacity due to the rough crushing treatment with respect to the “water absorption capacity A before coarse crushing treatment”. It is possible to keep the ratio ([B / A] x 100) of "water absorption capacity after coarse crushing)" to 10% or less, and increase the water absorption capacity with the rough crushing treatment (the above reduction rate is a negative value). There is also).

Further, the present inventor has found that when the crosslinked polymer gel imparts the above-mentioned test force, it gives an excellent crude crushing yield when the crosslinked polymer gel is roughly crushed. That is, according to the present embodiment, an excellent crude crushing yield (for example, 50% or more) can be obtained when the crosslinked polymer gel is coarsely crushed.

The cause of these effects is not clear, but the present inventor speculates as follows. However, the cause is not limited to the following contents. That is, when the crosslinked polymer gel giving the above-mentioned test force is subjected to the roughing treatment, the retention of the crosslinked polymer particles during the roughing treatment is suppressed, the load of excessive force is suppressed, and the like, so that the crosslinked polymer particles are subjected to the roughing treatment. It is presumed that a decrease in water absorption capacity can be suppressed and an excellent coarse crushing yield can be obtained. When the crosslinked polymer gel that does not give the above-mentioned test force is subjected to the roughing treatment, the crosslinked polymer gel is excessively soft, so that the crosslinked polymer gel is unnecessarily stretched or kneaded in the roughing apparatus. When the crosslinked polymer gel is crushed and unnecessary heat (friction heat, compression heat, etc. in the device) is applied to the crosslinked polymer gel during coarse crushing, the crosslinked polymer gel is altered in quality, and the water absorption capacity is likely to decrease and excellent coarseness is obtained. It is presumed that it is difficult to obtain the crushing yield.

In the step (1) in the compression test for evaluating the above-mentioned test force, a rectangular parallelepiped test piece of 20 mm × 20 mm × 17 mm is obtained from the crosslinked polymer gel according to the present embodiment. The test piece can be obtained by cutting out from a massive crosslinked polymer gel. As the test piece, a solid gel having no visible voids can be used.

In step (2), the flat surface of the jig (pressure sensitive shaft) having a flat surface is brought into contact with the 20 mm × 20 mm surface of the test piece from the upper side in the vertical direction. In the step (2), a jig having a flat surface and capable of transmitting the load applied when it comes into contact with the test piece to the detector can be used. The shape of the flat surface is circular, and the diameter of the circular flat surface is 20 mm. The jig includes a flat plate portion (for example, a disk portion) having a flat surface in contact with the test piece. It is preferable that the entire flat plate portion is not immersed in the test piece during the operation of step (3). The thickness of the flat plate portion is 5 mm. After the jig is brought into contact with the test piece in the step (2), the jig may be moved in the direction of pulling away from the test piece.

In the step (3), the jig is pushed into the test piece by 15 mm in the vertical direction, and the maximum value (unit: N) of the load applied to the jig during the operation is obtained as the above-mentioned test force. By adopting the operation of pushing in by 15 mm, it is possible to prevent the jig from penetrating the test piece (thickness 17 mm). As the test force, a vertical load applied to the jig can be obtained. The load tends to increase as the jig is pushed into the test force, and the maximum value of the load (see reference numeral P in FIG. 1) tends to be obtained when the jig is pushed into the test piece by 15 mm. The scanning speed of the jig is 30 mm / min.

The test force is 80N or more, 85N or more, 88N or more, 90N or more from the viewpoint of easily suppressing a decrease in water absorption capacity of the crosslinked polymer particles due to the coarse crushing treatment and from the viewpoint of easily obtaining an excellent coarse crushing yield. , 95N or more, 100N or more, 103N or more, 105N or more, 110N or more, 120N or more, 130N or more, 140N or more, 150N or more, 160N or more, 170N or more, or 180N or more is preferable. The test force is 400 N or less, 350 N or less, 300 N or less, 250 N or less from the viewpoint of easily suppressing a decrease in water absorption capacity of the crosslinked polymer particles due to the coarse crushing treatment and from the viewpoint of easily obtaining an excellent coarse crushing yield. , 200N or less, 190N or less, or 180N or less is preferable. As the test force, the test force at room temperature can be used.

The method for producing a crosslinked polymer gel according to the present embodiment includes a polymerization step of polymerizing a monomer composition containing an ethylenically unsaturated monomer. The monomer composition may contain water, an organic solvent and the like. The monomer composition may be a monomer aqueous solution. Examples of the polymerization method of the monomer composition include an aqueous solution polymerization method and a bulk polymerization method. Among these, from the viewpoint that good water absorption performance (high water absorption capacity of crosslinked polymer particles, suppression of decrease in water absorption capacity of crosslinked polymer particles due to coarse crushing treatment, etc.) can be easily obtained, an excellent coarse crushing yield is obtained. The aqueous polymerization method is preferable from the viewpoint of easy acquisition and easy control of the polymerization reaction. In the following, a case where the aqueous solution polymerization method is used as an example of the polymerization method will be described.

As the ethylenically unsaturated monomer, a water-soluble ethylenically unsaturated monomer can be used. Examples of the ethylenically unsaturated monomer include α, β-unsaturated carboxylic acids such as (meth) acrylic acid, maleic acid, maleic anhydride and fumaric acid, and carboxylic acid-based monomers such as salts thereof; Nonionic monomers such as meta) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, N-methylol (meth) acrylamide, polyethylene glycol mono (meth) acrylate; N, N -Amino group-containing unsaturated monomers such as diethylaminoethyl (meth) acrylate, N, N-diethylaminopropyl (meth) acrylate, diethylaminopropyl (meth) acrylamide, and quaternary products thereof; vinyl sulfonic acid, styrene sulfone. Examples thereof include acids, 2- (meth) acrylamide-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, and sulfonic acid-based monomers such as salts thereof. The ethylenically unsaturated monomer can contain at least one (meth) acrylic acid compound selected from the group consisting of (meth) acrylic acid and salts thereof. The ethylenically unsaturated monomer may contain both (meth) acrylic acid and a salt of (meth) acrylic acid. Examples of salts of α, β-unsaturated carboxylic acid ((meth) acrylic acid, etc.) include alkali metal salts (sodium salt, potassium salt, etc.), alkaline earth metal salts (calcium salt, etc.) and the like.

The ethylenically unsaturated monomer having an acid group ((meth) acrylic acid, etc.) may have the acid group neutralized in advance with an alkaline neutralizer. Examples of the alkaline neutralizing agent include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, potassium hydroxide and potassium carbonate; ammonia and the like. The alkaline neutralizer may be used in the form of an aqueous solution in order to simplify the neutralization operation. The acid group may be neutralized before the polymerization of the ethylenically unsaturated monomer as a raw material, or during or after the polymerization.

The degree of neutralization of the ethylenically unsaturated monomer by the alkaline neutralizer has good water absorption performance by increasing the osmotic pressure (high water absorption capacity of the crosslinked polymer particles, water absorption of the crosslinked polymer particles due to the coarse crushing treatment). From the viewpoint of easily obtaining (such as suppressing deterioration of ability), from the viewpoint of easily obtaining an excellent crude crushing yield, and from the viewpoint of suppressing defects caused by the presence of excess alkaline neutralizer, 10 to 100 mol%, 30 It is preferably from 90 mol%, 40 to 85 mol%, or 50 to 80 mol%. The "neutralization degree" is the neutralization degree for all the acid groups of the ethylenically unsaturated monomer.

The content of the (meth) acrylic acid compound is preferably in the following range based on the total mass of the monomer composition. The content of the (meth) acrylic acid compound is 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, 30% by mass or more, or from the viewpoint of easily obtaining an excellent crude crushing yield. 35% by mass or more is preferable. The content of the (meth) acrylic acid compound is 60% by mass or less, 55% by mass or less, 50% by mass or less, 50% by mass from the viewpoint that good water absorption performance (high water absorption ability of crosslinked polymer particles, etc.) can be easily obtained. %, 45% by mass or less, or 40% by mass or less is preferable. From these viewpoints, the content of the (meth) acrylic acid compound is preferably 10 to 60% by mass.

The content of the (meth) acrylic acid compound is the total amount of the monomers contained in the monomer composition and / or the total amount of the ethylenically unsaturated monomer contained in the monomer composition. The following range is preferable with reference to. The content of the (meth) acrylic acid compound is preferably 50 mol% or more, 70 mol% or more, 90 mol% or more, 95 mol% or more, 97 mol% or more, or 99 mol% or more. The monomer contained in the monomer composition and / or the ethylenically unsaturated monomer contained in the monomer composition is substantially composed of a (meth) acrylic acid compound (substantially). In addition, 100 mol% of the monomer contained in the monomer composition and / or the ethylenically unsaturated monomer contained in the monomer composition is a (meth) acrylic acid compound). It may be.

The monomer composition may contain a polymerization initiator. The polymerization of the monomer contained in the monomer composition may be started by adding a polymerization initiator to the monomer composition and, if necessary, heating, irradiating with light or the like. Examples of the polymerization initiator include a photopolymerization initiator and a radical polymerization initiator, and a water-soluble radical polymerization initiator is preferable. The polymerization initiator preferably contains at least one selected from the group consisting of azo compounds and peroxides from the viewpoint of easily obtaining good water absorption performance (high water absorption capacity of crosslinked polymer particles, etc.), and is roughly crushed. It is more preferable to contain a peroxide from the viewpoint of easily suppressing a decrease in the water absorption capacity of the crosslinked polymer particles due to the treatment.

Examples of the azo compound include 2,2'-azobis [2- (N-phenylamidino) propane] dihydrochloride and 2,2'-azobis {2- [N- (4-chlorophenyl) amidino] propane} dihydrochloride. Salt, 2,2'-azobis {2- [N- (4-hydroxyphenyl) amidino] propane} dihydrochloride, 2,2'-azobis [2- (N-benzylamidino) propane] dihydrochloride, 2 , 2'-azobis [2- (N-allylamidino) propane] dihydrochloride, 2,2'-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis {2- [N- (2) -Hydroxyethyl) amidino] propane} dihydrochloride, 2,2'-azobis [2- (5-methyl-2-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis [2-( 2-imidazolin-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (4,5,6,7-tetrahydro-1H-1,3-diazepine-2-yl) propane] dihydrochloride Salt, 2,2'-azobis [2- (5-hydroxy-3,4,5,6-tetrahydropyrimidine-2-yl) propane] dihydrochloride, 2,2'-azobis {2- [1-( 2-Hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride, 2,2'-azobis [2- (2-imidazolin-2-yl) propane] disulfate dihydrate, 2, 2'-azobis [N- (2-carboxyethyl) -2-methylpropion amidine] tetrahydrate, 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) propionamide] and the like can be mentioned. Be done. Azo-based compounds are 2,2'-azobis (2-methylpropionamide) dihydrochloride and 2,2'-azobis from the viewpoint that good water absorption performance (high water absorption capacity of crosslinked polymer particles, etc.) can be easily obtained. (2-Amidinopropane) dihydrochloride, 2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride, and 2,2'- It preferably contains at least one selected from the group consisting of azobis [N- (2-carboxyethyl) -2-methylpropionamidine] tetrahydrate.

Peroxides include persulfates such as potassium persulfate, ammonium persulfate, sodium persulfate; methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide, t-butyl. Examples thereof include organic peroxides such as peroxyacetate, t-butylperoxyisobutyrate, and t-butylperoxypivalate. Peroxides are potassium persulfate, ammonium persulfate, and peroxide from the viewpoint that good water absorption performance (high water absorption capacity of crosslinked polymer particles, etc.) can be easily obtained and excellent crude crushing yield can be easily obtained. It preferably contains at least one selected from the group consisting of sodium sulfate.

The content of the polymerization initiator is preferably in the following range with respect to 1 mol of the (meth) acrylic acid compound. The content of the polymerization initiator is excellent from the viewpoint that good water absorption performance (high water absorption capacity of crosslinked polymer particles, suppression of decrease in water absorption capacity of crosslinked polymer particles due to coarse crushing treatment, etc.) can be easily obtained. From the viewpoint of easily obtaining the yield and shortening the polymerization reaction time, 0.001 mmol or more, 0.003 mmol or more, 0.015 mmol or more, 0.03 mmol or more, 0.06 mmol or more, 0. It is preferably 08 mmol or more, 0.1 mmol or more, 0.15 mmol or more, 0.2 mmol or more, or 0.25 mmol or more. The content of the polymerization initiator is excellent from the viewpoint that good water absorption performance (high water absorption capacity of crosslinked polymer particles, suppression of decrease in water absorption capacity of crosslinked polymer particles due to coarse crushing treatment, etc.) can be easily obtained. From the viewpoint of easily obtaining the yield and avoiding a rapid polymerization reaction, 5 mmol or less, 4 mmol or less, 2 mmol or less, 1 mmol or less, 0.8 mmol or less, 0.5 mmol or less, 0. It is preferably 4 mmol or less, or 0.3 mmol or less. From these viewpoints, the content of the polymerization initiator is preferably 0.001 to 5 mmol. It is easy to adjust the test force by adjusting the content of the polymerization initiator.

The monomer composition may contain a reducing agent. Examples of the reducing agent include sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, L-ascorbic acid and the like. A polymerization initiator and a reducing agent may be used in combination.

The monomer composition may contain an oxidizing agent. Examples of the oxidizing agent include hydrogen peroxide, sodium perborate, perphosphoric acid and salts thereof, potassium permanganate and the like.

The monomer composition may contain an internal cross-linking agent. By using the internal cross-linking agent, the obtained cross-linked polymer can have a cross-linked structure by the internal cross-linking agent in addition to the self-cross-linking structure by the polymerization reaction as the internal cross-linking structure.

Examples of the internal cross-linking agent include compounds having two or more reactive functional groups (for example, polymerizable unsaturated groups). Examples of the internal cross-linking agent include di or tri (meth) acrylic acid esters of polyols such as (poly) ethylene glycol, (poly) propylene glycol, trimethylolpropane, glycerin polyoxyethylene glycol, polyoxypropylene glycol, and (poly) glycerin. Class: Unsaturated polyesters obtained by reacting the above polyol with an unsaturated acid (maleic acid, fumaric acid, etc.); (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, (poly) glycerin Glycidyl group-containing compounds such as diglycidyl ether and glycidyl (meth) acrylate; bisacrylamides such as N, N'-methylenebis (meth) acrylamide; di or tri (meth) obtained by reacting polyepoxide with (meth) acrylic acid. Meta) acrylic acid esters; di (meth) acrylic acid carbamil esters obtained by reacting polyisocyanates (tolylene diisocyanate, hexamethylene diisocyanate, etc.) with hydroxyethyl (meth) acrylic acid; allylated starch; allyl Cellified cellulose; diallyl phthalate; N, N', N "-triallyl isocyanurate; divinylbenzene; pentaerythritol; ethylenediamine; polyethyleneimine, etc. The internal cross-linking agent has good water absorption performance (high cross-linked polymer particles). From the viewpoint that water absorption capacity, suppression of decrease in water absorption capacity of crosslinked polymer particles due to coarse crushing treatment, etc.) can be easily obtained, excellent crude crushing yield can be easily obtained, and reactivity at low temperature is excellent. It is preferable to contain at least one selected from the group consisting of (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerin diglycidyl ether.

The content of the internal cross-linking agent is preferably in the following range with respect to 1 mol of the (meth) acrylic acid compound. The content of the internal cross-linking agent is excellent from the viewpoint that good water absorption performance (high water absorption capacity of the cross-linked polymer particles, suppression of deterioration of the water absorption capacity of the cross-linked polymer particles due to the coarse crushing treatment, etc.) can be easily obtained. From the viewpoint of easily obtaining the crude crushing yield, 0.01 mmol or more, 0.05 mmol or more, 0.08 mmol or more, 0.1 mmol or more, 0.15 mmol or more, 0.2 mmol or more, 0.5 mmol As mentioned above, 1 mmol or more, or 1.5 mmol or more is preferable. The content of the internal cross-linking agent is 10 mmol or less from the viewpoint that good water absorption performance (high water absorption capacity of the cross-linked polymer particles, suppression of deterioration of the water absorption capacity of the cross-linked polymer particles due to the coarse crushing treatment, etc.) can be easily obtained. , 8 mmol or less, 5 mmol or less, 3 mmol or less, or 2 mmol or less is preferable. From these viewpoints, the content of the internal cross-linking agent is preferably 0.01 to 10 mmol. It is easy to adjust the test force by adjusting the content of the internal cross-linking agent.

If necessary, the monomer composition may contain additives such as a chain transfer agent, a thickener, and an inorganic filler as components different from the above-mentioned components. Examples of the chain transfer agent include thiols, thiol acids, secondary alcohols, hypophosphorous acid, phosphorous acid, achlorine and the like. Examples of the thickener include carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, polyethylene glycol, polyacrylic acid, neutralized polyacrylic acid, polyacrylamide and the like. Examples of the inorganic filler include metal oxides, ceramics, and viscous minerals.

As a polymerization method for aqueous solution polymerization, a static polymerization method in which the monomer composition is polymerized without stirring (for example, a static state); a stirring polymerization method in which the monomer composition is polymerized while stirring in a reaction apparatus. And so on. In the static polymerization method, when the polymerization is completed, a single block-shaped gel occupying substantially the same volume as the monomer composition present in the reaction vessel is obtained.

The form of polymerization may be batch, semi-continuous, continuous, or the like. For example, when the static polymerization method is carried out by continuous polymerization, the polymerization reaction can be carried out while continuously supplying the monomer composition to the continuous polymerization apparatus to continuously obtain a gel.

The polymerization temperature varies depending on the polymerization initiator used, but from the viewpoint of rapidly advancing the polymerization, increasing the productivity by shortening the polymerization time, removing the heat of polymerization, and facilitating the smooth reaction, 0 to 0 to It is preferably 130 ° C. or 10 to 110 ° C. The maximum value of the polymerization temperature may be 25 ° C. or higher, 30 ° C. or higher, 40 ° C. or higher, 50 ° C. or higher, or 60 ° C. or higher. The maximum value of the polymerization temperature may be 110 ° C. or lower, 105 ° C. or lower, 100 ° C. or lower, or 95 ° C. or lower. From these viewpoints, the maximum value of the polymerization temperature may be 25 to 110 ° C. The polymerization time is appropriately set depending on the type and amount of the polymerization initiator used, the reaction temperature, and the like, but is preferably 1 to 200 minutes or 5 to 100 minutes.

The crosslinked polymer particles according to this embodiment can have a structural unit derived from an ethylenically unsaturated monomer. The crosslinked polymer particles according to the present embodiment are, for example, crosslinked polymer particles obtained by coarsely crushing, drying and pulverizing the crosslinked polymer gel according to the present embodiment, and the coarsely crushed product obtained in the coarse crushing step is used. It can be obtained by drying (for example, hot air drying at 180 ° C. for 30 minutes) and pulverization (for example, pulverization with a centrifugal pulverizer). The crosslinked polymer particles according to the present embodiment may be obtained by drying and pulverizing the coarse crushed product and then classifying the pulverized product with a sieve having an opening of 850 μm and a sieve having an opening of 106 μm. Examples of the shape of the crosslinked polymer particles according to the present embodiment include substantially spherical, crushed, and granular shapes. The crosslinked polymer particles according to the present embodiment may be any as long as they can retain water, and the liquid to be absorbed may contain water. The crosslinked polymer particles according to the present embodiment can absorb body fluids such as urine, sweat, and blood (for example, menstrual blood). The crosslinked polymer particles according to this embodiment can be used as a constituent component of the absorber. This embodiment can be used in the fields of, for example, sanitary materials such as disposable diapers and sanitary products; agricultural and horticultural materials such as water retention agents and soil conditioners; and industrial materials such as water stop agents and dew condensation inhibitors.

The crosslinked polymer particles according to the present embodiment are a gel stabilizer; a metal chelating agent (ethylenediamine tetraacetic acid and a salt thereof, diethylenetriamine 5 acetic acid and a salt thereof (for example, diethylenetriamine 5 sodium acetate), etc.); a fluidity improver (lubricant). Other components such as may be further contained. Other components may be located inside, on the surface, or both of crosslinked polymers having structural units derived from ethylenically unsaturated monomers.

The crosslinked polymer particles according to the present embodiment may contain inorganic particles arranged on the surface of the crosslinked polymer having a structural unit derived from an ethylenically unsaturated monomer. For example, by mixing the crosslinked polymer and the inorganic particles, the inorganic particles can be arranged on the surface of the crosslinked polymer. Examples of the inorganic particles include silica particles such as amorphous silica.

The water absorption capacity of the crosslinked polymer particles according to the present embodiment in the physiological saline solution may be in the following range. Water absorption capacity is 30 g / g or more, 35 g / g or more, 40 g / g or more, 45 g / g or more, 50 g / g or more, 55 g / g or more, 60 g / g or more, 65 g / g or more, 65.3 g / g or more. Or, it may be 70 g / g or more. The water absorption capacity may be 80 g / g or less, 77 g / g or less, 75 g / g or less, or 72 g / g or less. From these viewpoints, the water absorption capacity may be 30 to 80 g / g or 50 to 80 g / g. As the water absorption capacity, the water absorption capacity at room temperature can be used. The water absorption capacity can be measured by the method described in Examples described later.

The medium particle size of the crosslinked polymer particles (crosslinked polymer particles before water absorption) according to the present embodiment may be in the following range. The medium particle size may be 200 μm or more, 250 μm or more, 300 μm or more, or 350 μm or more. The medium particle size may be 600 μm or less, 550 μm or less, 500 μm or less, 450 μm or less, or 400 μm or less. From these viewpoints, the medium particle size may be 100 to 600 μm. The crosslinked polymer particles according to the present embodiment may have a desired particle size distribution at the time of being obtained by the production method described later, but the particle size distribution can be adjusted by performing an operation such as particle size adjustment using classification with a sieve. May be adjusted.

The method for producing the crosslinked polymer particles according to the present embodiment includes a gel preparation step for producing a crosslinked polymer gel by the method for producing a crosslinked polymer gel according to the present embodiment, and a crude product by coarsely crushing the crosslinked polymer gel. A coarse crushing step for obtaining (for example, a gel crushed product), a drying step for drying the crushed product to obtain a dried product, and a crushing step for crushing the dried product to obtain a crushed product may be provided. The method for producing crosslinked polymer particles according to the present embodiment may include a classification step of classifying the pulverized product (for example, classifying the pulverized product with a sieve having an opening of 850 μm and a sieve having an opening of 106 μm) after the pulverization step. ..

As the crushing device in the crushing step, for example, a kneader (pressurized kneader, double-armed kneader, etc.), a meat chopper, a cutter mill, a pharma mill, or the like can be used.

In the drying step, a dried product (for example, gel dried product) can be obtained by removing liquid components (water, etc.) in the pyroclastic material by heating and / or blowing air. The drying method may be natural drying, heat drying, spray drying, freeze drying or the like. The drying temperature is, for example, 70 to 250 ° C.

Crushers in the crushing process include roller mills (roll mills), stamp mills, jet mills, high-speed rotary crushers (hammer mills, pin mills, rotor beater mills, etc.), container-driven mills (rotary mills, vibration mills, planetary mills, etc.). ) And so on.

The water-absorbent resin particles according to the present embodiment can be obtained by cross-linking the crosslinked polymer particles obtained in the coarse crushing step (crosslinking step). The cross-linking may be surface cross-linking to the cross-linked polymer particles. The cross-linking can be performed, for example, by reacting a cross-linking agent (for example, a surface cross-linking agent) with the cross-linked polymer particles. By performing additional cross-linking using a cross-linking agent, the cross-linking density of the cross-linked polymer particles (for example, the cross-linking density near the surface of the cross-linked polymer particles) is increased, so that the water absorption performance (water absorption amount under load in the water-absorbent resin particles, etc.) It is easy to increase the water absorption rate, etc.).

The surface cross-linking agent may contain, for example, two or more functional groups (reactive functional groups) having reactivity with a functional group derived from an ethylenically unsaturated monomer. Examples of the surface cross-linking agent include polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerin; (poly) ethylene glycol di. Polyglycidyl compounds such as glycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) propylene glycol polyglycidyl ether, (poly) glycerol polyglycidyl ether; epichlorohydrin, epibromhydrin, α- Haloepoxy compounds such as methyl epichlorohydrin; compounds having two or more reactive functional groups such as isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; 3-methyl-3-oxetane methanol, 3-ethyl-3- Oxetane compounds such as oxetane methanol, 3-butyl-3-oxetane methanol, 3-methyl-3-oxetane ethanol, 3-ethyl-3-oxetane ethanol, 3-butyl-3-oxetane ethanol; 1,2-ethylenebisoxazoline Oxetane compounds such as; carbonate compounds such as ethylene carbonate; hydroxyalkylamide compounds such as bis [N, N-di (β-hydroxyethyl)] adipamide and the like. Among these, polyglycidyl compounds such as (poly) ethylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) propylene glycol polyglycidyl ether, and (poly) glycerol polyglycidyl ether. And / or polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, polyoxyethylene glycol, polyoxypropylene glycol are preferable, and polyglycidyl compounds are more preferable. These surface cross-linking agents may be used alone or in combination of two or more. For example, a polyglycidyl compound and polyols may be used in combination.

The amount of the surface cross-linking agent added is preferably 0, with respect to 100 mol of the total amount of the ethylenically unsaturated monomer usually used for the polymerization, from the viewpoint of appropriately increasing the cross-linking density in the vicinity of the surface of the cross-linked polymer particles. It is 0001 to 1 mol, more preferably 0.001 to 0.5 mol.

The surface cross-linking step is preferably carried out in the presence of water in the range of 1 to 200 parts by mass with respect to 100 parts by mass of the ethylenically unsaturated monomer. The amount of water can be adjusted by appropriately using a water-soluble organic solvent such as water and / or alcohol. By adjusting the amount of water in the surface cross-linking step, the water-absorbent resin particles can be more preferably cross-linked in the vicinity of the particle surface.

The treatment temperature of the surface cross-linking agent is appropriately set according to the surface cross-linking agent used, and may be 20 to 250 ° C., and the treatment time is preferably 1 to 200 minutes, more preferably 5 to 100 minutes.

According to the present embodiment, it is possible to provide a liquid absorbing method using the crosslinked polymer particles according to the present embodiment. The liquid absorbing method according to the present embodiment includes a step of bringing the liquid to be absorbed into contact with the crosslinked polymer particles according to the present embodiment. According to this embodiment, it is possible to provide the application of the crosslinked polymer particles to the liquid absorbing liquid.

According to the present embodiment, it is a method for adjusting the water absorption capacity of the crosslinked polymer particles (a method for suppressing a decrease in the water absorption capacity due to the coarse crushing treatment), and the crosslinked polymer gel according to the present embodiment is described above (1). It is possible to provide a method for adjusting the water absorption capacity, which comprises an adjusting step for adjusting the test force measured by the procedure of (3). In the adjusting step, the test force can be adjusted to each of the above ranges (for example, 70 N or more and less than 450 N).

According to the present embodiment, the crosslinked polymer gel according to the present embodiment includes a selection step of selecting crosslinked polymer particles based on the test force measured by the above-mentioned procedures (1) to (3). A method for producing coalesced particles can be provided. In the selection step, the test force can be adjusted to each of the above ranges (for example, 70 N or more and less than 450 N).

Hereinafter, the content of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

<Preparation of hydrogel polymer>
(Example 1)
340.0 g (4.72 mol) of 100% acrylic acid was placed in a 2 L separable flask. After adding 293.6 g of ion-exchanged water while stirring the inside of the separable flask, 295.1 g of 48% by mass sodium hydroxide was added dropwise under an ice bath to obtain a monomer concentration of 45% by mass of sodium acrylate. A partially neutralized solution was prepared.

Partial neutralization of the acrylic acid in an 18-8 stainless steel container (stainless steel bat, outer dimensions: 297 mm x 232 mm x height 50 mm) equipped with two stir bars (diameter 8 mm, length 45 mm) and coated with fluororesin. After adding 908.9 g of the liquid, 133.8 g of ion-exchanged water, and 0.141 g of ethylene glycol diglycidyl ether (internal cross-linking agent, 0.809 mmol), rotate the stirrer to uniformly disperse the components. Obtained a mixture. Then, the upper part of the container was covered with a polyethylene film. After adjusting the temperature of the mixture in the container to 25 ° C., the amount of dissolved oxygen was adjusted to 0.1 ppm or less by substituting nitrogen in the mixture. Then, 8.09 g of a 2 mass% potassium persulfate aqueous solution (radical polymerization initiator, 0.599 mmol) and 1.74 g of a 0.5 mass% L-ascorbic acid aqueous solution were sequentially added to a syringe (Termo Co., Ltd.) under stirring at 300 rpm. A monomer aqueous solution was prepared by dropping the mixture using a disposable syringe having a volume of 50 mL. The acrylic acid concentration in the aqueous monomer solution was 38.9%.

As described above, the polymerization started immediately after the 0.5 mass% L-ascorbic acid aqueous solution or the like was added dropwise. As a result of the polymerization reaction proceeding with the aqueous monomer solution, the viscosity of the aqueous monomer solution increased and the stirrer stopped. The polymerization temperature reached a peak temperature of 64 ° C. 22 minutes after the addition of a 0.5 mass% L-ascorbic acid aqueous solution or the like. Then, after confirming that the temperature was lowered, the container was immersed in a water bath at 75 ° C. and aged for 20 minutes to obtain a hydrogel polymer. The thickness of the hydrogel polymer was about 17 mm.

(Example 2)
The amount of ion-exchanged water was changed from 133.8 g to 124.0 g, and the amount of 2 mass% potassium persulfate aqueous solution was changed from 8.09 g (0.599 mmol) to 16.18 g (1.197 mmol). A monomer aqueous solution was prepared by performing the same operation as in Example 1 except that the amount of the 0.5 mass% L-ascorbic acid aqueous solution was changed from 1.74 g to 3.47 g. Then, a hydrogel-like polymer was obtained by performing the same operation as in Example 1. As a result of the polymerization, the polymerization temperature reached a peak temperature of 85 ° C. 11 minutes after the addition of a 0.5 mass% L-ascorbic acid aqueous solution or the like.

(Example 3)
The amount of ion-exchanged water was changed from 133.8 g to 123.8 g, and the amount of 2 mass% potassium persulfate aqueous solution was changed from 8.09 g (0.599 mmol) to 16.18 g (1.197 mmol). That, the amount of 0.5 mass% L-ascorbic acid aqueous solution was changed from 1.74 g to 3.47 g, and the amount of ethylene glycol diglycidyl ether was changed from 0.141 g (0.809 mmol) to 0.283 g. A monomer aqueous solution was prepared by performing the same operation as in Example 1 except that the value was changed to (1.625 mmol). Then, a hydrogel-like polymer was obtained by performing the same operation as in Example 1. As a result of the polymerization, the polymerization temperature reached the peak temperature of 95 ° C. 13 minutes after the addition of a 0.5 mass% L-ascorbic acid aqueous solution or the like.

(Example 4)
The amount of ion-exchanged water was changed from 133.8 g to 127.3 g, and instead of 8.09 g (0.599 mmol) of the 2 mass% potassium persulfate aqueous solution, 14.25 g (1.) of the 2 mass% sodium persulfate aqueous solution. 197 mmol) was used, and the amount of the 0.5 mass% L-ascorbic acid aqueous solution was changed from 1.74 g to 3.47 g. An aqueous solution was prepared. Then, a hydrogel-like polymer was obtained by performing the same operation as in Example 1. As a result of the polymerization, the polymerization temperature reached a peak temperature of 86 ° C. 11 minutes after the addition of a 0.5 mass% L-ascorbic acid aqueous solution or the like.

(Example 5)
The amount of ion-exchanged water was changed from 133.8 g to 122.9 g, and the amount of 2 mass% potassium persulfate aqueous solution was changed from 8.09 g (0.599 mmol) to 16.18 g (1.197 mmol). That, the amount of the 0.5 mass% L-ascorbic acid aqueous solution was changed from 1.74 g to 3.47 g, and the ethylene glycol diglycidyl ether was changed from 0.141 g (0.809 mmol) to 1.240 g (7). A monomer aqueous solution was prepared by carrying out the same operation as in Example 1 except that it was changed to .119 mmol). Then, a hydrogel-like polymer was obtained by performing the same operation as in Example 1. As a result of the polymerization, the polymerization temperature reached a peak temperature of 98 ° C. 10 minutes after the addition of a 0.5 mass% L-ascorbic acid aqueous solution or the like.

(Example 6)
The amount of ion-exchanged water was changed from 133.8 g to 94.5 g, and the amount of 2 mass% potassium persulfate aqueous solution was changed from 8.09 g (0.599 mmol) to 40.44 g (2.992 mmol). A monomer aqueous solution was prepared by performing the same operation as in Example 1 except that the amount of the 0.5 mass% L-ascorbic acid aqueous solution was changed from 1.74 g to 8.68 g. Then, a hydrogel-like polymer was obtained by performing the same operation as in Example 1. As a result of the polymerization, the polymerization temperature reached a peak temperature of 102 ° C. 6 minutes after the addition of a 0.5 mass% L-ascorbic acid aqueous solution or the like.

(Example 7)
The amount of ion-exchanged water was changed from 133.8 g to 65.0 g, and the amount of 2 mass% potassium persulfate aqueous solution was changed from 8.09 g (0.599 mmol) to 64.71 g (4.788 mmol). A monomer aqueous solution was prepared by performing the same operation as in Example 1 except that the amount of the 0.5 mass% L-ascorbic acid aqueous solution was changed from 1.74 g to 13.89 g. Then, a hydrogel-like polymer was obtained by performing the same operation as in Example 1. As a result of the polymerization, the polymerization temperature reached the peak temperature of 107 ° C. 4 minutes after the addition of a 0.5 mass% L-ascorbic acid aqueous solution or the like.

(Comparative Example 1)
The amount of ion-exchanged water was changed from 133.8 g to 65.1 g, and the amount of ethylene glycol diglycidyl ether was changed from 0.141 g (0.809 mmol) to 0.0236 g (0.135 mmol). The amount of the 2 mass% potassium persulfate aqueous solution was changed from 8.09 g (0.599 mmol) to 64.71 g (4.788 mmol), and the amount of the 0.5 mass% L-ascorbic acid aqueous solution was changed to 1. A monomer aqueous solution was prepared by performing the same operation as in Example 1 except that the amount was changed from .74 g to 13.89 g. Then, a hydrogel-like polymer was obtained by performing the same operation as in Example 1. As a result of the polymerization, the polymerization temperature reached the peak temperature of 104 ° C. 4 minutes after the addition of a 0.5 mass% L-ascorbic acid aqueous solution or the like.

(Comparative Example 2)
An acrylic acid partial neutralizing solution was prepared by performing the same operation as in Example 1.

In the sodium acrylate portion in an 18-8 stainless steel container (stainless steel bat, outer dimensions: 297 mm × 232 mm × height 50 mm) provided with two stir bars (diameter 8 mm, length 45 mm) and coated with fluororesin. After adding 908.9 g of Japanese solution, 130.6 g of ion-exchanged water, and 0.141 g of ethylene glycol diglycidyl ether (internal cross-linking agent, 0.809 mmol), the stirrer is rotated to uniformly disperse the components. This gave the mixture. Then, the upper part of the container was covered with a polyethylene film. After adjusting the temperature of the mixture in the container to 25 ° C., the amount of dissolved oxygen was adjusted to 0.1 ppm or less by substituting nitrogen in the mixture. Next, 5.47 g (1.193 mmol) of a 5 mass% V-50 aqueous solution (2,2'-azobis (2-amidinopropane) dihydrochloride, manufactured by Wako Pure Chemical Industries, Ltd.), 0.5 mass% L. -By dropping 3.06 g of an aqueous ascorbic acid solution and 3.43 g of a 0.35 mass% hydrogen peroxide solution in order using a syringe (manufactured by Telmo Co., Ltd., a disposable syringe having a volume of 50 mL) under stirring at 300 rpm. A monomer aqueous solution was prepared. The acrylic acid concentration in the aqueous monomer solution was 38.9%.

As described above, the polymerization started immediately after dropping 0.35% by mass hydrogen peroxide solution or the like. Then, a hydrogel-like polymer was obtained by performing the same operation as in Example 1. As a result of the polymerization, the polymerization temperature reached the peak temperature of 104 ° C. 2 minutes after the addition of 0.35 mass% hydrogen peroxide solution or the like.

<Compression test>
By cutting the hydrogel polymer, a rectangular parallelepiped test piece of 20 mm × 20 mm × 17 mm was obtained. As shown in FIG. 2, a measuring instrument 100 having a load cell 10 having a capacity of 500 N (measurement upper limit setting: 450 N) and a pressure sensitive shaft 20 (a rod-shaped jig having a disk 30 having a diameter of 20 mm and a thickness of 5 mm at the tip). (Manufactured by Shimadzu Corporation, product name: EZtest, model number: EZ-SX) was prepared. The flat surface of the disk 30 was adjusted to be along the horizontal direction. The test piece 40 was placed on the measuring table 50 of the measuring instrument 100 so that the 20 mm × 20 mm surface of the test piece 40 faced upward in the vertical direction. Using the Shimadzu autograph software "Trapezium X" (manufactured by Shimadzu Corporation), the position of the pressure sensitive shaft 20 in the vertical direction is adjusted, and the center of the test piece 40 is located at the center of the disk 30 of the pressure sensitive shaft 20. Adjusted to be positioned.

The pressure sensitive shaft 20 was lowered until the load cell 10 sensed a test force of 0.01 N, and the disk 30 of the pressure sensitive shaft 20 and the surface of the test piece 40 were brought into contact with each other. Next, the position of the pressure sensitive shaft 20 was adjusted to the measurement start position by raising the pressure sensitive shaft 20 by 0.05 mm. Subsequently, the disk 30 was pushed into the test piece 40 by 15 mm at a scanning speed of 30 mm / min, and the maximum value (room temperature) of the test force at this time was measured. The results are shown in Table 1.

<Water absorption capacity of hydrogel before coarse crushing>
A 5 mm × 5 mm × 17 mm hydrogel obtained by cutting the above hydrogel polymer was dried with hot air at 180 ° C. for 30 minutes to obtain a dried product (gel dried product). Next, 15 g of this dried product is crushed using a centrifugal crusher (manufactured by Verder Scientific Co., Ltd., product name: ZM200, 6-blade rotor, rotor rotation speed: 6000 rpm, screen trapezoidal hole: 1.00 mm). As a result, a crushed product was obtained. Subsequently, the pulverized product was classified by a sieve having an opening of 850 μm and a sieve having an opening of 106 μm to recover the dried pulverized product of the pre-grinding hydrogel remaining on the sieve having an opening of 106 μm.

500 g of physiological saline was weighed in a beaker having a volume of 500 mL. Next, while stirring at 600 rpm using a magnetic stirrer bar (8 mmφ × length 30 mm, no ring), 2.0 g of the above-mentioned dried pulverized product was dispersed in physiological saline so as not to generate mamaco. The particles were sufficiently swollen by leaving them to stand for 60 minutes in a stirred state to obtain a dispersion liquid containing a swollen gel. Subsequently, after measuring the mass Wa [g] of the standard sieve having an opening of 75 μm, the above-mentioned dispersion liquid was passed through this standard sieve. Then, the excess water was removed by leaving the sieve at an inclination angle of about 30 degrees with respect to the horizontal for 30 minutes. The mass Wb [g] of the sieve on which the swelling gel remained was measured, and the water absorption capacity Wc [g / g] (room temperature) of the hydrogel before coarse crushing (dry pulverized product) was determined by the following formula. The results are shown in Table 1.
Water absorption capacity of hydrogel before coarse grinding Wc = (Wb-Wa) /2.0

<Coarse crushing of hydrogel polymer>
After taking out the above-mentioned hydrogel polymer from the container, the hydrogel polymer was cut by making cuts in a grid pattern at intervals of 50 mm. The cut hydrogel polymer was sequentially put into a coarse crusher (meat chopper 12VR-750SDX manufactured by Kiren Royal Co., Ltd.) and coarsely crushed to obtain a crude product (hydrous gel coarse crushed product). The diameter of the hole (circular) of the plate located at the outlet of the meat chopper was 6.4 mm. The crushing was carried out until no crushed material came out from the plate of the meat chopper. At this time, the crude crushing yield was calculated from the following formula using the amount Ga [g] (= 200 g) of the hydrogel polymer charged into the meat chopper and the pyroclastic material Gb [g] that was discharged and recovered. did. The results are shown in Table 1.
Crude crushing yield [mass%] = (Gb / Ga) × 100

<Drying and crushing of coarse crushed material>
The above-mentioned pyroclastic material was dried with hot air at 180 ° C. for 30 minutes to obtain a dried product (gel dried product). Next, 15 g of the dried product is crushed using a centrifugal crusher (manufactured by Verder Scientific Co., Ltd., product name: ZM200, 6-flute rotor, rotor rotation speed: 6000 rpm, screen trapezoidal hole: 1.00 mm). Obtained a crushed product. Subsequently, the pulverized product was classified by a sieve having an opening of 850 μm and a sieve having an opening of 106 μm to recover the dried pulverized product (crosslinked polymer particles) of the hydrous gel after coarse crushing remaining on the sieve having an opening of 106 μm. ..

<Water absorption capacity of hydrogel after coarse crushing and rate of change in water absorption capacity>
The water absorption capacity Wd [g / g] (room temperature) of the water-containing gel after coarse crushing was measured by the same method as the water absorption capacity Wc of the water-containing gel before coarse crushing. Further, the rate of change in water absorption capacity was determined from the following formula using the water absorption capacity Wc of the water-containing gel before coarse crushing and the water absorption capacity Wd of the water-containing gel after coarse crushing. The results are shown in Table 1.
Rate of change in water absorption [%] = (Wc-Wd) / Wc × 100

According to Table 1, it is confirmed that when the crosslinked polymer gel coarsely crushed in the coarse crushing step gives a specific test force, it is possible to suppress a decrease in water absorption capacity of the crosslinked polymer particles.

10 ... load cell, 20 ... pressure sensitive shaft, 30 ... disk, 40 ... test piece, 50 ... measuring table, 100 ... measuring instrument.

Claims

A rough crushing step for coarsely crushing a crosslinked polymer gel having a structural unit derived from an ethylenically unsaturated monomer is provided.
A method for producing crosslinked polymer particles, wherein the gel hardness after polymerization obtained by the following procedures (1) to (3) is 70 N or more and less than 450 N.
(1) A rectangular parallelepiped test piece of 20 mm × 20 mm × 17 mm is obtained from the crosslinked polymer gel.
(2) The flat surface of the jig having a flat surface is brought into contact with the 20 mm × 20 mm surface of the test piece from the upper side in the vertical direction.
(3) An operation of pushing the jig into the test piece by 15 mm in the vertical direction is performed, and the maximum value of the load applied to the jig during the operation is obtained as the gel hardness after polymerization.
The method for producing crosslinked polymer particles according to claim 1, wherein the ethylenically unsaturated monomer contains at least one selected from the group consisting of (meth) acrylic acid and a salt thereof.
The method for producing crosslinked polymer particles according to claim 1 or 2, wherein the crosslinked polymer particles obtained by drying and pulverizing the coarsely crushed product obtained in the coarse crushing step have a water absorption capacity of 30 to 80 g / g.
A crosslinked polymer gel having a structural unit derived from an ethylenically unsaturated monomer.
A crosslinked polymer gel having a post-polymerization gel hardness of 70 N or more and less than 450 N obtained by the following procedures (1) to (3).
(1) A rectangular parallelepiped test piece of 20 mm × 20 mm × 17 mm is obtained from the crosslinked polymer gel.
(2) The flat surface of the jig having a flat surface is brought into contact with the 20 mm × 20 mm surface of the test piece from the upper side in the vertical direction.
(3) An operation of pushing the jig into the test piece by 15 mm in the vertical direction is performed, and the maximum value of the load applied to the jig during the operation is obtained as the gel hardness after polymerization.
The crosslinked polymer gel according to claim 4, wherein the ethylenically unsaturated monomer contains at least one selected from the group consisting of (meth) acrylic acid and a salt thereof.
The crosslinked polymer gel according to claim 4 or 5, wherein the crosslinked polymer particles obtained by coarsely crushing, drying and pulverizing the crosslinked polymer gel have a water absorption capacity of 30 to 80 g / g.