WO2022025122A1

WO2022025122A1 - Method for producing water-absorbing resin particles

Info

Publication number: WO2022025122A1
Application number: PCT/JP2021/027923
Authority: WO
Inventors: 志保岡澤
Original assignee: 住友精化株式会社
Priority date: 2020-07-31
Filing date: 2021-07-28
Publication date: 2022-02-03
Also published as: JPWO2022025122A1

Abstract

The present invention discloses a method for producing water-absorbing resin particles containing polymer particles. This method includes: a step for forming a hydrous gel-like polymer through a polymerization reaction in a reaction solution; and a step for forming a powder of polymer particles by pulverizing a dried product containing the polymer. When five measurement points are arranged in series on a straight line perpendicular to an extension direction X of a side wall surface, among the highest temperatures at which the temperature of the reaction solution reaches during the polymerization reaction, measured respectively at the five measurement points, at a point of time when the maximum value T_max is indicated at any one of the five measurement points, the standard deviation of the temperatures of the reaction solution, measured respectively at the five measurement points, is 12-30, and T_max is 80-100°C.

Description

Method for manufacturing water-absorbent resin particles

The present disclosure relates to a method for producing water-absorbent resin particles.

The water-absorbent resin particles that can be used for absorbent articles such as sanitary products form a massive hydrogel-like polymer by the polymerization reaction of the monomers in the reaction solution contained in the reaction vessel, and contain water. It may be produced by a method including pulverizing a solid dried product containing a polymer, which is obtained by drying a gel-like polymer (for example, Patent Documents 1 and 2).

Japanese Unexamined Patent Publication No. 11-22864 Japanese Unexamined Patent Publication No. 2006-160866

The powder formed by pulverizing a dried product containing a polymer contains fine powder, but in general, fine powder that passes through a sieve having an opening of 180 μm is often difficult to use as it is as a product. Therefore, in order to improve the production yield, it is desirable that the proportion of fine powder in the powder obtained by pulverization is as small as possible.

One aspect of the present disclosure relates to a method for reducing the proportion of fine powder in the powder formed by pulverization in the case of producing water-absorbent resin particles by a method including pulverizing a dried product containing a polymer.

One aspect of the present disclosure provides a method for producing water-absorbent resin particles containing polymer particles. The method according to one aspect of the present disclosure includes a step of forming a hydrogel-like polymer containing water and a polymer by a polymerization reaction in a reaction solution containing a monomer and water contained in a reaction vessel, and the above-mentioned step. The present invention includes a step of obtaining a dried product containing the polymer by removing water from the water-containing gel-like polymer, and a step of forming a powder of polymer particles by pulverizing the dried product.

The reaction vessel has two side wall surfaces extending along a certain direction and facing each other, and a bottom surface forming a recess together with the two side wall surfaces. When five measurement points are arranged in series on a straight line in the liquid surface of the reaction liquid, which is perpendicular to the extending direction of the two side wall surfaces, the temperature of the reaction liquid is the temperature at each of the five measurement points. When the maximum T _max of the maximum temperatures reached during the polymerization reaction is indicated at any of the five measurement points, the standard deviation of the temperature of the reaction solution at each of the five measurement points is 12 to. It is 30 and the T _max is 80 to 100 ° C. The five measurement points are composed of two measurement points at a position 1 cm from each of the two side wall surfaces and three measurement points at a position that divides the two measurement points into four equal parts. The temperature of the reaction solution at each of the five measurement points is measured on the bottom surface at a position directly below each measurement point.

According to one aspect of the present disclosure, when the water-absorbent resin particles are produced by a method including pulverizing a dried product containing a polymer, the proportion of fine powder in the powder formed by the pulverization can be reduced. ..

It is a schematic top view which shows the example of the measurement point arranged in the liquid surface of a reaction liquid in the step of forming a water-containing gel polymer by the polymerization reaction in a reaction liquid. It is a schematic cross-sectional view which shows the example of the measurement point arranged in the liquid surface of a reaction liquid in the step of forming a water-containing gel polymer by the polymerization reaction in a reaction liquid.

The present invention is not limited to the following examples.

In the present specification, "(meth) acrylic" means both acrylic and methacrylic. Similarly, "acrylate" and "methacrylate" are also referred to as "(meth) acrylate". The same is true for other similar terms. "(Poly)" shall mean both with and without the "poly" prefix. Within the numerical range described stepwise herein, the upper or lower limit of the numerical range at one stage may be optionally combined with the upper or lower limit of the numerical range at another stage. 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. The materials exemplified in the present specification may be used alone or in combination of two or more.

One embodiment of the method for producing water-absorbent resin particles includes a step of forming a water-containing gel-like polymer containing water and a polymer by a polymerization reaction in a reaction solution containing a monomer and water, and a water-containing gel-like state. It includes a step of forming a dried product containing the polymer by removing water from the polymer, and a step of forming a powder of water-absorbent resin particles by pulverizing the dried product.

The polymerization reaction is a reaction measured at five measurement points arranged on the liquid surface of the reaction solution in a reaction solution contained in a reaction vessel having a bottom surface and two side wall surfaces extending from the end of the bottom surface. It is performed under the condition that the variation in the temperature of the liquid becomes large to some extent.

FIG. 1 is a schematic top view showing an example of measurement points arranged in the liquid surface of the reaction liquid in the step of forming a water-containing gel-like polymer by a polymerization reaction in a reaction liquid containing a monomer and water. Yes, FIG. 2 is a cross-sectional view of FIG. The reaction vessel 10 containing the reaction solution 1 shown in FIGS. 1 and 2 extends along the same constant direction X, and has two

side wall surfaces

11 and 12 facing each other and two side wall surfaces 11. , 12 two

side wall surfaces

13 and 14 extending along a direction perpendicular to the extending direction X and facing each other, and a bottom surface 15 forming a recess for accommodating the reaction solution 1 together with these side wall surfaces. Has. The

side wall surfaces

11, 12, 13, 14 may be perpendicular to the bottom surface 15 or may be inclined.

Five measurement points P1, P2, P3, P4 and P5 are in series in this order on a straight line 2 in the liquid surface 1S of the reaction liquid 1 perpendicular to the extending direction X of the two

side wall surfaces

11 and 12 facing each other. Is placed in. The five measurement points are the two measurement points P1 and P5 located 1 cm from each of the two

side wall surfaces

11 and 12, and the three measurement points P2 at positions that divide the space between the two measurement points P1 and P5 into four equal parts. It is composed of P3 and P4. The distance W0 between the

side wall surfaces

11 and 12 and the measurement points P1 and P2 is 1 cm. The distance W12 between the measurement point P1 and the measurement point P2, the distance W23 between the measurement point P2 and the measurement point P3, the distance W34 between the measurement point P3 and the measurement point P4, and the distance W45 between the measurement point P4 and the measurement point P5 are It is the same. The measurement point P3 is located in the center between the two

side wall surfaces

11 and 12.

During the polymerization reaction, the temperatures T1, T2, T3, T4 and T5 of the reaction solution at each of the five measurement points P1, P2, P3, P4 and P5 are located directly below the respective measurement points P10, P20, P30, P40. And measured on the bottom surface 15 of P50. When there are inclined

side wall surfaces

11 and 12 at positions directly below the measurement points P1 and P5 at both ends, the temperatures T1 and T5 are measured on the

side wall surfaces

11 and 12 at positions directly below the measurement points P1 and P5 at both ends. The position on the bottom surface 15 where the temperature of the reaction solution 1 is measured can be a position within 0.5 cm in the depth direction of the reaction solution 1 from the bottom surface 15 (or the side wall surfaces 11 and 12).

The temperatures T1, T2, T3, T4 and T5 of the reaction solution 1 shown at each of the five measurement points P1, P2, P3, P4 and P5 rise with the progress of the polymerization reaction to reach the maximum temperature, and then reach the maximum temperature. descend. Of the maximum temperatures T1, T2, T3, T4 and T5 reach in the polymerization reaction of the reaction solution 1 at each measurement point, the maximum value T _max is any of the five measurement points P1, P2, P3, P4 and P5. At the time point indicated by K There is.) Is 12 to 30. For example, the maximum temperature at which the temperature T3 of the reaction solution 1 at the measurement point P3 reaches during the polymerization reaction reaches the maximum temperature at which the temperatures T1, T2, T3, T4 and T5 of the reaction solution 1 at each measurement point reach during the polymerization reaction. When the maximum value T _max is the maximum temperature to be measured, the temperature deviation calculated from the temperatures T1, T2, T3, T4 and T5 at the time when the temperature T3 of the reaction solution 1 at the measurement point P3 reaches T _max is 12 ~ 30.

When the temperature deviation of the reaction solution is large to some extent, such as 12 to 30, the uniformity of the polymerization reaction is lowered, so that the dried product containing the polymer tends to be softened, and as a result, the generation of fine powder in pulverization is suppressed. It is thought that it will be done. From the viewpoint of further reducing the proportion of fine powder in the powder of the polymer particles, the temperature deviation of the reaction solution may be 25 or less, 23 or less or 20 or less at 12 or more, and 30 or less, 25 or less at 13 or more. , 23 or less or 20 or less.

The maximum value T _max among the maximum temperatures reached by the temperatures T1, T2, T3, T4 and T5 of the reaction solution 1 in the polymerization reaction is 80 to 100 ° C. When the T _max is 80 ° C. or higher, the polymerization reaction is sufficiently easy to proceed until the entire reaction solution 1 is gelled. Any one of the temperatures T1, T2, T3, T4 and T5 reaches T _max after the temperature of the reaction solution starts to rise due to the start of the polymerization reaction or when the addition of the cleavage accelerator solution described later is completed. The time to reach may be, for example, 1 to 20 minutes.

The width of the liquid level 1S of the reaction solution 1 in the direction in which the five measurement points P1, P2, P3, P4 and P5 are arranged (direction of the straight line 2) is 10 to 500 cm, 10 to 300 cm, 10 to 100 cm or 10 to It may be 80 cm.

In the case of the reaction vessel 10 shown in FIG. 1, the widths of the

side wall surfaces

11 and 12 are shorter than the widths of the

side wall surfaces

13 and 14. Five measurement points for determining the temperature deviation may be arranged on a straight line in the direction perpendicular to the

side wall surfaces

13, 14. When the reaction vessel has two sets of two side wall surfaces facing each other as in the embodiment of FIG. 1, the reaction measured at five measurement points arranged between the two side wall surfaces of one or both of the two sets. The temperature deviation of the liquid can be 12-30.

The polymerization reaction may proceed while moving the reaction vessel along the extending direction of the side wall surfaces 11 and 12. In that case, the temperature deviation of the reaction solution at any position in the moving direction of the reaction vessel is 12 to 30 at five measurement points arranged in series on a straight line in the direction perpendicular to the moving direction of the reaction vessel. You may.

When the polymerization reaction is started by charging the reaction solution 1 with a cleavage promoter solution containing a cleavage promoter for starting the polymerization reaction at a low temperature as described later, measurement points P1, P2, P3, P4 and P5. The straight line 2 on which the is arranged may be a straight line passing through the position in the liquid surface 1S where the cleavage promoter liquid is poured or its vicinity. For example, the straight line 2 may be a straight line passing through a region within 1 cm from the position where the cleavage promoter liquid is charged in the liquid surface 1S.

The cleavage accelerator liquid may be charged toward one position in the liquid surface 1S, or may be divided into two or more positions in the liquid surface 1S and charged at the same time. When the number of positions where the cleavage accelerator liquid is simultaneously added is small, the temperature deviation tends to be large and the T _max tends to be large. Using a long reaction vessel or a reaction vessel provided on an endless belt, the reaction vessel is moved to change the charging position of the reaction solution in the liquid surface, and the cleavage accelerator solution is sequentially charged twice or more. You may. In that case, for each injection of the cleavage accelerator solution, five measurement points are arranged on a straight line passing through the position where the cleavage accelerator solution is added or its vicinity, and the measurement is performed at each of the five measurement points. The conditions of the polymerization reaction are adjusted so that the temperature deviation of the reaction solution is maintained in the range of 12 to 30.

The entire amount of the cleavage accelerator solution is charged into the reaction solution 1 over a period of, for example, 5 to 120 seconds. If the time required for charging the cleavage accelerator solution into the reaction solution 1 is long, the temperature deviation of the reaction solution tends to be large.

The temperature of the reaction solution 1 before the cleavage accelerator solution is added is adjusted so that the T _max is 80 to 100 ° C., and may be, for example, 0 to 40 ° C. or 10 to 30 ° C. The amount of dissolved oxygen in the reaction solution 1 may be, for example, 0.1 ppm or less.

The reaction solution 1 may be stirred during the polymerization reaction. When the intensity of stirring is small, the standard deviation of the temperature of the reaction solution measured at the five measurement points tends to be large. For example, when the reaction solution 1 is agitated by a stirrer 3 arranged on the bottom surface 15 of the reaction vessel 10, if the number of rotations and / or the number of the stirrers 3 is small, the temperature deviation of the reaction solution 1 tends to be large. .. The rotation speed and number of the stirrer can be adjusted so that the temperature deviation is 12 to 30 depending on the type of the stirrer, the amount of the reaction solution 1, and the like. For example, the number of stirrers installed in one reaction vessel may be 1 to 3, and the rotation speed of the stirrers may be 50 to 300 rpm.

The time of the polymerization reaction is adjusted so that the polymerization reaction proceeds sufficiently and a hydrogel-like polymer is formed. After the temperature of the reaction solution starts to decrease, the polymerization reaction may be completed by keeping the reaction vessel 10 at 50 to 80 ° C.

The reaction vessel 10 is not particularly limited, but may be, for example, a vessel made of stainless steel, ceramics, synthetic resin, or steel. The reaction vessel 10 may be provided on the belt conveyor. The depth of the reaction solution 1 in the reaction vessel 10 may be, for example, 10 to 50 mm, 10 to 40 mm, or 15 to 35 mm.

The reaction solution 1 before the polymerization reaction can be water and a monomer aqueous solution containing a monomer dissolved in water. As the polymerization reaction progresses, the reaction solution 1 thickens and then gels to form a hydrogel polymer. Normally, the reaction solution 1 loses its fluidity as the polymerization reaction progresses, but in the present specification, the mixture after the reaction solution 1 loses its fluidity may also be referred to as a reaction solution for convenience.

The concentration of the monomer in the reaction solution 1 may be, for example, 20 to 50% by mass or 20 to 40% by mass based on the mass of the reaction solution 1.

The monomer is a compound that forms a polymer that imparts water absorption to the polymer particles and the water-absorbent resin particles by polymerization. The polymer may be a crosslinked polymer. The monomer may be an ethylenically unsaturated monomer.

The ethylenically unsaturated monomer is, for example, (meth) acrylic acid and a salt thereof, 2- (meth) acrylamide-2-methylpropanesulfonic acid and a salt thereof, (meth) acrylamide, N, N-dimethyl (meth). Acrylamide, 2-hydroxyethyl (meth) acrylate, N-methylol (meth) acrylamide, polyethylene glycol mono (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-diethylaminopropyl (meth) acrylate, and It may contain at least one compound selected from the group consisting of diethylaminopropyl (meth) acrylamide. When the ethylenically unsaturated monomer contains an amino group, the amino group may be quaternized. At least one compound selected from the group consisting of acrylic acid and its salts, methacrylic acid and its salts, acrylamide, methacrylic acid and N, N-dimethylacrylamide, acrylic acid and its salts, methacrylic acid and its monomers. It may contain at least one compound selected from the group consisting of a salt and acrylamide, or at least one compound selected from the group consisting of acrylic acid and a salt thereof, and methacrylic acid and a salt thereof.

The reaction solution 1 may contain a monomer other than the ethylenically unsaturated monomer. The proportion of ethylenically unsaturated monomers (particularly (meth) acrylic acid and salts thereof) is 70 to 100 mol%, 80 to 100 mol% or 90 to 100 mol% with respect to the total amount of monomers in the reaction solution. May be. The proportion of (meth) acrylic acid and a salt thereof in the ethylenically unsaturated monomer may be 70 to 100 mol%, 80 to 100 mol% or 90 to 100 mol%.

The reaction solution 1 may further contain an initiator (particularly, a radical polymerization initiator). Initiators may include persulfates, azo compounds, organic peroxides or combinations thereof. The amount of initiator may be 0.01-15 mmol per mole of monomer. When two or more initiators are used, the amount of each initiator may be 0.01 to 15 mmol per mole of the monomer.

Examples of persulfate include potassium persulfate, ammonium persulfate, and sodium persulfate.

Examples of azo compounds include 2,2'-azobis [2- (N-phenylamidino) propane] dihydrochloride, 2,2'-azobis {2- [N- (4-chlorophenyl) amidino] propane} 2 Hydrochloride, 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] di Hydrochloride, 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-methylpropionamidine] tetrahydrate, and 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) propionamide] Can be mentioned. From the viewpoint of forming polymer particles showing a large CRC (water absorption ratio under no pressurization), the radical polymerization initiators are 2,2'-azobis (2-amidinopropane) dihydrochloride and 2,2'-azobis {2. -[1- (2-Hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride, 2,2'-azobis [N- (2-carboxyethyl) -2-methylpropionamidine] tetrahydrate It may contain at least one azo compound selected from the product and 2,2'-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride.

Examples of organic peroxides include methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t-butyl cumyl peroxide, t-butyl peroxyacetate, t-butyl peroxyisobutyrate, etc. And t-butylperoxypivalate.

The reaction solution 1 may contain an initiator and a cleavage promoter. The cleavage accelerator is a compound that lowers the temperature at which the polymerization reaction is initiated by the initiator. When the polymerization reaction is started at a low temperature, water-absorbent resin particles having better water-absorbing performance can be easily obtained. The cleavage promoter can be, for example, a reducing agent, an oxidizing agent or a combination thereof. A part or all of the cleavage accelerator may be added later to the reaction solution containing the monomer, the initiator and water to initiate the polymerization reaction. The amount of cleavage promoter may be, for example, 0.01 to 1.0 mol per 1 mol of initiator.

The reducing agent used as the cleavage accelerator may be, for example, at least one compound selected from the group consisting of sodium sulfite, sodium hydrogen sulfite, ferrous sulfate, and L-ascorbic acid. The oxidizing agent used as a cleavage promoter may be, for example, at least one compound selected from the group consisting of hydrogen peroxide, sodium perborate, perphosphate, perphosphate, and potassium permanganate. good.

When two or more kinds of cleavage promoters are used, they may be added to the reaction solution separately. For example, for a reaction solution containing a monomer, an initiator and water, a cleavage accelerator solution containing a reducing agent (for example, L-ascorbic acid) and a cleavage accelerator solution containing an oxidizing agent (for example, hydrogen peroxide) may be used. The polymerization reaction may be started by sequentially charging. Alternatively, the polymerization reaction may be started by adding a cleavage promoter solution containing a reducing agent (for example, L-ascorbic acid) to the reaction solution containing the monomer, the initiator and water. The cleavage-promoting agent solution may be an aqueous solution containing a cleavage-promoting agent and water.

The reaction solution 1 may further contain a chain transfer agent. The chain transfer agent may include, for example, hypophosphorous acid, phosphorous acid or a combination thereof.

The reaction solution 1 may contain an internal cross-linking agent. In that case, a hydrogel-like polymer containing a crosslinked polymer crosslinked by an internal crosslinking agent is formed. The amount of the internal cross-linking agent may be 0.002 to 0.04 mmol per mole of the monomer.

The internal cross-linking agent may be a compound having two or more reactive functional groups (for example, a polymerizable unsaturated group). The internal cross-linking agent may contain a compound having a (meth) acrylic group, an allyl group, an epoxy group, or an amino group as a reactive functional group. Examples of compounds having a (meth) acrylic group include (poly) ethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, and N, N'-methylenebis (meth) acrylamide. Examples of compounds having an allyl group include triallylamine. Examples of compounds having an epoxy group include (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin polyglycidyl ether and epichlorohydrin. Will be. Examples of compounds having an amino group include triethylenetetramine, ethylenediamine, and hexamethylenediamine.

The massive hydrogel-like polymer formed by the polymerization reaction is taken out from the reaction vessel 10. Prior to the step of obtaining a dry product containing the polymer by removing water from the water-containing gel-like polymer, a coarsely crushed product containing a structure having a somewhat small size is formed by coarsely crushing the water-containing gel-like polymer. May be good. By forming the crushed product, water can be efficiently removed. The structure constituting the coarsely crushed product can be, for example, an elongated structure, a granular structure (particle), or a combination thereof. The crushed product may contain a plurality of structures having a shape capable of passing through a circular hole having a diameter of 10 mm or 7 mm. The elongated structure may be bent, and if the maximum width thereof is 10 mm or less, it can be said that the elongated structure has a shape capable of passing through a circular hole having a diameter of 10 mm. The granular structure (particle) may have an amorphous shape, or may have a shape capable of passing through a circular hole having a diameter of 10 mm while changing its direction. Examples of the coarsening apparatus for coarsely crushing the hydrogel-like polymer include kneaders (for example, pressurized kneaders, double-armed kneaders), meat choppers, cutter mills, and pharmacomills.

Most of the water in the hydrogel polymer is removed by drying the hydrogel polymer or its coarse crushed product. The water content of the dried product containing the polymer obtained by drying may be, for example, 20% by mass or less, 10% by mass or less, or 5% by mass or less, or 0% by mass or more. The water content of the dried product here means the ratio of the water content in the polymer particles based on the total mass of the dried product containing water. Usually, when a dried product containing water to be measured is heated at 200 ° C. for 2 hours, the difference in mass of the dried product before and after heating can be regarded as the amount of water in the dried product used for measurement. The drying method may be a general method such as natural drying, heat drying, blast drying, freeze drying or a combination thereof. The crushed product may be dried under normal pressure or reduced pressure. The heating temperature for drying under normal pressure may be 70 to 250 ° C. or 80 to 200 ° C.

The method of crushing the dried product containing the polymer is not particularly limited. For example, a crusher such as a centrifugal crusher, a roller mill, a stamp mill, a jet mill, a high-speed rotary crusher, and a container-driven mill can be used to crush the dried product.

The powder of the polymer particles obtained by pulverization may be classified. Classification means an operation of dividing a particle group (powder) into two or more particle groups having different particle size distributions. A part of the powder of the polymer particles after the classification may be pulverized and classified again.

The classification method is not particularly limited, but may be, for example, screen classification or wind power classification. Screen classification is a method of classifying particles on a screen into particles that pass through the mesh of the screen and particles that do not pass through the screen by vibrating the screen. Screen classification can be performed using, for example, a vibrating sieve, a rotary shifter, a cylindrical stirring sieve, a blower shifter, or a low-tap shaker. Wind power classification is a method of classifying particles using the flow of air.

The medium particle size of the polymer particles obtained by pulverization and, if necessary, classification may be, for example, 200 to 500 μm. The medium particle size of the polymer particles before being mixed with the surface cross-linking agent solution described later may be, for example, 200 to 500 μm. The particle size distribution may be adjusted by mixing two or more powders having different medium particle diameters obtained by classification.

The polymer particles may be surface-crosslinked with a surface-crosslinking agent. By surface cross-linking, the polymer near the surface of the polymer particles is cross-linked by the surface cross-linking agent. For example, the polymer particles can be surface-crosslinked by heating a mixture of the polymer particle powder and the surface cross-linking agent solution. The above-mentioned dissolution for selecting the elapsed time t is measured using the polymer particles before surface cross-linking.

The surface cross-linking agent solution can be water and a solution containing a surface cross-linking agent dissolved in water. The solvent contained in the surface cross-linking agent solution may be substantially only water. The ratio of the solvent other than water may be 10% by mass or less, 5% by mass or less, or 1% by mass or less based on the mass of the surface cross-linking agent solution.

Examples of surface cross-linking agents include alkylene carbonate compounds such as ethylene carbonate; ethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, polyglycerin and the like. Polypoly compounds; (poly) ethylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, trimethylolpropane triglycidyl ether (poly) propylene glycol polyglycidyl ether, and (poly) glycerol polyglycidyl. Polyglycidyl compounds such as ether; haloepoxy compounds such as epichlorohydrin, epibromhydrin, and α-methylepicrolhydrin; isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylenediisocyanate; 3-methyl-3-oxetanemethanol, Oxetane compounds such as 3-ethyl-3-oxetan methanol, 3-butyl-3-oxetane methanol, 3-methyl-3-oxetane ethanol, 3-ethyl-3-oxetane ethanol, and 3-butyl-3-oxetane ethanol; Oxazoline compounds such as 1,2-ethylenebisoxazoline; hydroxyalkylamide compounds such as bis [N, N-di (β-hydroxyethyl)] adipamide can be mentioned. These surface cross-linking agents may be used alone or in combination of two or more. The surface cross-linking agent may contain an alkylene carbonate compound, a polyol compound, or a combination thereof. The ratio of the alkylene carbonate compound in the surface cross-linking agent is 50 to 100% by mass, 60 to 100% by mass, 70 to 100% by mass, 80 to 100% by mass, or 90 to 100% by mass based on the total mass of the surface cross-linking agent. May be.

From the viewpoint of water absorption performance under pressure of the water-absorbent resin particles, the amount of the surface cross-linking agent is 0.001 to 0.10 mol, 0 per mol of the monomer unit constituting the polymer in the polymer particles. It may be .005 to 0.05, or 0.01 to 0.02 mol.

The heating temperature and heating time for surface cross-linking are adjusted so that the cross-linking reaction proceeds appropriately in consideration of the type of surface cross-linking agent and the like. For example, the heating temperature for surface cross-linking may be 80 to 200 ° C. The heating time for surface cross-linking may be, for example, 5 to 90 minutes.

The surface-crosslinked polymer particles may be further dried or classified if necessary. The polymer particles may be used as they are as the water-absorbent resin particles, or the inorganic particles may be attached to the surface of the polymer particles, for example. That is, the water-absorbent resin particles may contain the polymer particles and the inorganic particles adhering to the surface of the polymer particles. Examples of inorganic particles include silica particles such as amorphous silica.

The produced water-absorbent resin particles are used to form an absorbent body constituting an absorbent article such as a diaper, for example.

The present invention is not limited to the following examples.

1. 1. Crosslinked polymer particles (Example 1)
Preparation of Aqueous Monomer Solution 325.9 g (4.52 mol) of acrylic acid was placed in a 2 L separable flask. To the acrylic acid in the separable flask, 280.4 g of ion-exchanged water was added with stirring. Then, by dropping 283.2 g of a 48% by mass sodium hydroxide aqueous solution under an ice water bath at about 3 ° C., a partially neutralized acrylic acid is contained as a monomer, and the monomer concentration is 45% by mass. A monomer aqueous solution of Caustic acid was prepared.

Polymerization reaction 888.10 g of aqueous monomer solution, 150.04 g of ion-exchanged water, 0.930 g of polyethylene glycol diacrylate (n = about 9, internal cross-linking agent, Nichiyu Co., Ltd., Blemmer ADE-400A), concentration 5 6.47 g of a mass% 2,2'-azobis (2-amidinopropane) dihydrochloride (Fujifilm Wako Pure Chemical Industries, Ltd .: V-50) aqueous solution was sequentially added to a 2 L hand-held beaker and inside the beaker. The mixture was stirred.

Fluororesin coated with a height of 5 cm, having a rectangular bottom surface with internal dimensions of 25 cm x 19 cm and four side wall surfaces provided around the bottom surface, and having a rectangular opening with internal dimensions of 28 cm x 22 cm. A stainless steel bat was used as the reaction vessel. A uniform reaction solution was formed by putting the mixture in the beaker into the reaction vessel and stirring the mixture in the reaction vessel with two stirrers (diameter 8 mm, length 45 mm, no ring). Then, the upper part of the reaction vessel was sealed with a polyethylene film.

The width of the liquid surface of the reaction solution was 26 cm in the longitudinal direction of the reaction vessel, and the depth of the reaction solution was 1.7 cm. Two points P1 and P5 located 1 cm from the two side wall surfaces facing each other in the longitudinal direction of the reaction vessel on a straight line perpendicular to the longitudinal direction of the reaction vessel in the liquid surface of the reaction solution, and 4 between these two points. A total of five measurement points, three points P2, P3, and P4, which are equally divided, were determined. At each of the measurement points P1, P2, P3, P4 and P5, a thermometer (CT-320WP, manufactured by Custom Co., Ltd.) was inserted vertically into the reaction solution so as to reach the bottom surface of the reaction vessel. The five measurement points were aligned linearly along the longitudinal direction of the reaction vessel at the center of the reaction vessel in the lateral direction. The two stir bars were installed between the measurement points P1 and P2 and between the measurement points P4 and P5.

The temperature of the reaction solution in the reaction vessel was adjusted to 25 ° C., and the amount of dissolved oxygen in the reaction solution was adjusted to 0.1 ppm or less by nitrogen substitution. Next, 3.40 g of an L-ascorbic acid aqueous solution having a concentration of 0.5% by mass was added to the reaction solution using a syringe (10 mL disposable syringe manufactured by Terumo Corporation, injection needle manufactured by Terumo Corporation), and the reaction solution was added. It was stirred well. While stirring the reaction solution at 100 rpm, use a syringe (Terumo Corporation's 10 mL disposable syringe, Terumo Corporation's injection needle) toward the vicinity of the central measurement point P3 to peroxidize 0.35% by mass. 3.70 g of an aqueous hydrogen solution was added dropwise over 4 seconds.

The polymerization reaction started at the same time as the dropping of the aqueous hydrogen peroxide solution. After the viscosity of the reaction solution increased with the progress of the polymerization reaction, the reaction solution gelled to form a hydrogel-like polymer containing water and a crosslinked polymer. The temperature indicated by each of the five thermometers reached the maximum temperature as the polymerization reaction proceeded, and then decreased. At 3 minutes from the end of the dropping of the hydrogen peroxide aqueous solution, the thermometer at the measurement point P3 showed the maximum value of 99 ° C. among the maximum temperatures shown by each of the five thermometers during the polymerization reaction. When the thermometer at the measurement point P3 showed the maximum temperature of 99 ° C., the temperatures indicated by the five thermometers were recorded, and the standard deviation (temperature deviation) of these five temperatures was calculated. Six minutes after the completion of dropping the hydrogen peroxide solution, the reaction vessel containing the hydrogel polymer was immersed in a water bath at 75 ° C., and the hydrogel polymer was kept warm for 20 minutes in that state to complete the polymerization reaction. ..

Roughing and drying The lumpy hydrogel polymer taken out from the reaction vessel was cut into 5 cm widths. The cut hydrogel polymer was sequentially put into a meat chopper (manufactured by Kiren Royal Co., Ltd., model number: 12VR-750SDX) and coarsely crushed at room temperature. The diameter of the circular discharge hole of the plate located at the outlet of the meat chopper was 6.4 mm. The coarsely crushed hydrogel polymer is spread out on a wire mesh with an opening of 0.8 cm × 0.8 cm and heated at 180 ° C. for 30 minutes using a hot air dryer (ADVANTEC, FV-320). To obtain a dried product containing a crosslinked polymer.

The pulverized dried product was pulverized by a centrifugal pulverizer (ZM200 manufactured by Retsch, screen diameter: 1 mm, 6000 rpm) to obtain a powder of polymer particles.

(Example 2)
Except that the rotation speed of the stirrer when dropping the 0.35% by mass hydrogen peroxide solution was changed to 300 rpm, and 3.70 g of the 0.35% by mass hydrogen peroxide solution was dropped over 63 seconds. The powder of the polymer particles was obtained by the same procedure as in Example 1. At 3 minutes from the end of the dropping of the hydrogen peroxide aqueous solution, the thermometer at the measurement point P2 showed the maximum value of 80 ° C. among the maximum temperatures shown by each of the five thermometers during the polymerization reaction. When the thermometer at the measurement point P2 showed the maximum temperature of 80 ° C., the temperatures indicated by the five thermometers were recorded, and the standard deviation (temperature deviation) of these five temperatures was calculated.

(Example 3)
630.55 g of a monomer aqueous solution prepared in the same manner as in Example 1, 68.30 g of ion-exchanged water, and polyethylene glycol diacrylate (n = about 9, internal cross-linking agent, Nichiyu Co., Ltd., Blemmer ADE-400A). 0.660 g, 1.44 g of potassium persulfate aqueous solution having a concentration of 2% by mass, and 2,2'-azobis (2-amidinopropane) dihydrochloride having a concentration of 5% by mass (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd .: V-50) 4.02 g of the aqueous solution was sequentially put into a 1 L hand-held beaker, and the mixed solution in the beaker was stirred.

Fluororesin-coated 3 cm high stainless steel with a rectangular bottom surface with internal dimensions of 16 cm x 20 cm and four side wall surfaces provided around the bottom surface, with a rectangular opening with internal dimensions of 19 cm x 23 cm. A bat was used as a reaction vessel. A uniform reaction solution was formed by putting the mixture in the beaker into the reaction vessel and stirring the mixture in the reaction vessel with two stirrers (diameter 8 mm, length 30 mm, no ring). Then, the upper part of the reaction vessel was sealed with a polyethylene film.

The width of the liquid surface of the reaction solution was 18 cm in the lateral direction of the reaction vessel, and the depth of the reaction solution was 1.6 cm. Two points P1 and P5 located 1 cm from the two side wall surfaces facing each other in the lateral direction of the reaction vessel on a straight line perpendicular to the longitudinal direction of the reaction vessel in the liquid surface of the reaction solution, and between these two points. A total of five measurement points, three points P2, P3, and P4, which are divided into four equal parts, were determined. At each of the measurement points P1, P2, P3, P4 and P5, a thermometer (CT-320WP, manufactured by Custom Co., Ltd.) was inserted vertically into the reaction solution so as to reach the bottom surface of the reaction vessel. The five measurement points were aligned linearly along the lateral direction of the reaction vessel at the center of the reaction vessel in the lateral direction. The two stir bars were installed between the measurement points P1 and P2 and between the measurement points P4 and P5.

The temperature of the reaction solution in the reaction vessel was adjusted to 25 ° C., and the amount of dissolved oxygen in the reaction solution was adjusted to 0.1 ppm or less by nitrogen substitution. Then, while stirring at 100 rpm, a syringe (Terumo Corporation, 10 mL disposable syringe, Terumo Corporation injection needle) was used toward the vicinity of the central measurement point P3, and the concentration was 0.5% by mass. -2.41 g of the ascorbic acid aqueous solution and 2.62 g of the 0.35 mass% hydrogen peroxide aqueous solution were sequentially added dropwise over 3 seconds.

The polymerization reaction started at the same time as the dropping of the aqueous hydrogen peroxide solution. After the viscosity of the reaction solution increased with the progress of the polymerization reaction, the reaction solution gelled to form a hydrogel-like polymer containing water and a crosslinked polymer. Five minutes after the completion of dropping the hydrogen peroxide solution, the temperature at the measurement point P3 showed the maximum value of 95 ° C. among the maximum temperatures shown by each of the five thermometers during the polymerization reaction. The temperatures indicated by the five thermometers at the time when the thermometer at the measurement point P3 showed the maximum temperature of 95 ° C. were recorded, and the standard deviation (temperature deviation) of these five temperatures was calculated. Eight minutes after the completion of dropping the aqueous hydrogen hydrogen solution, the reaction vessel containing the hydrogel-like polymer was immersed in a water bath at 75 ° C., and the hydrogel-like polymer was kept warm for 20 minutes in that state to complete the polymerization reaction. rice field.

From the formed hydrogel-like polymer, powder of polymer particles was obtained by coarse crushing, drying and crushing in the same manner as in Example 1.

(Comparative Example 1)
Polymer particles were obtained by the same procedure as in Example 1 except that the rotation speed of the stirrer when dropping the 0.35 mass% hydrogen peroxide aqueous solution was changed to 300 rpm. At 3 minutes from the end of the dropping of the hydrogen peroxide aqueous solution, the thermometer at the measurement point P3 showed the maximum value of 98 ° C. among the maximum temperatures shown by each of the five thermometers during the polymerization reaction. When the thermometer at the measurement point P3 showed the maximum temperature of 98 ° C., the temperatures indicated by the five thermometers were recorded, and the standard deviation (temperature deviation) of these five temperatures was calculated.

(Comparative Example 2)
Polymer particles were obtained by the same procedure as in Example 1 except that the rotation speed of the stirrer when dropping the 0.35 mass% hydrogen peroxide aqueous solution was changed to 500 rpm. Two minutes after the completion of dropping the hydrogen peroxide solution, the thermometer at the measurement point P4 showed the maximum value of 94 ° C. among the maximum temperatures shown by each of the five thermometers during the polymerization reaction. When the thermometer at the measurement point P4 showed the maximum temperature of 94 ° C., the temperatures indicated by the five thermometers were recorded, and the standard deviation (temperature deviation) of these five temperatures was calculated.

(Comparative Example 3)
Five syringes (Terumo Corporation, 10 mL disposable syringe, Terumo Corporation injection needle) with a method of dropping a 0.35 mass% hydrogen peroxide solution toward each of the five measurement points. The polymerization reaction was carried out by the same procedure as in Example 1 except that the method was changed to drop 0.74 g of a 0.35 mass% hydrogen peroxide aqueous solution from each syringe all at once over 1 second. rice field. At 3 minutes from the end of the dropping of the hydrogen peroxide aqueous solution, the thermometer at the measurement point P5 showed the maximum value of 63 ° C. among the maximum temperatures shown by each of the five thermometers during the polymerization reaction. When the thermometer at the measurement point P5 showed the maximum temperature of 63 ° C., the temperatures indicated by the five thermometers were recorded, and the standard deviation (temperature deviation) of these five temperatures was calculated. Since a part of the reaction solution did not gel and a liquid part remained, it was not possible to obtain a lumpy hydrogel polymer.

2. Particle size ratio of 180 to 850 μm JIS standard sieves with openings of 850 μm, 500 μm, 425 μm, 300 μm, 250 μm, 180 μm and 106 μm were combined in this order from the top on the saucer. 10 g of crosslinked polymer particle powder is placed in a sieve with an opening of 850 μm at the top, and the powder is powdered using a continuous fully automatic sonic vibration type sieving measuring instrument (Robot Shifter RPS-205, manufactured by Seishin Enterprise Co., Ltd.). Was classified. After the classification, the mass of the polymer particles remaining on each sieve was measured, and the particle size ratio [%] of 180 to 850 μm was calculated by the following formula.
Particle size ratio [%] of 180 to 850 μm = (total mass [g] of crosslinked polymer particles remaining on the sieve with openings of 500 μm, 425 μm, 300 μm, 250 μm and 180 μm) / (crosslinked polymer particles used for measurement) Mass [g]) x 100

Table 1 shows the particle size distribution and the particle size ratio obtained from it. In the table, "850 μm on" means the ratio of the crosslinked polymer particles remaining on the opening 850 μm to the mass of the crosslinked polymer particles used for the measurement. This also applies to "500 μm on" and the like. “Pass” means the ratio of the crosslinked polymer particles that have passed through the sieve having an opening of 106 μm to the mass of the crosslinked polymer particles used for the measurement.

1 ... Reaction solution, 10 ... Reaction vessel, 1S ... Liquid level, 11, 12, 13, 14 ... Side wall surface, 15 ... Bottom surface, P1, P2, P3, P4, P5 ... Measurement points, P10, P20, P30, P40 , P50 ... Position where the temperature of the reaction solution is measured, X ... Extension direction of the side wall surface.

Claims

A method for producing water-absorbent resin particles containing polymer particles, wherein the method is
A step of forming a water-containing gel-like polymer containing water and a polymer by a polymerization reaction in a reaction solution containing a monomer and water contained in a reaction vessel.
A step of forming a dry product containing the polymer by removing water from the hydrogel-like polymer, and a step of forming the dried product.
A step of forming a powder of polymer particles by pulverizing the dried product, and
Including
The reaction vessel has two side wall surfaces extending along a certain direction and facing each other, and a bottom surface forming a recess together with the two side wall surfaces.
When five measurement points are arranged in series on a straight line in the liquid surface of the reaction liquid, which is perpendicular to the extending direction of the two side wall surfaces, the temperature of the reaction liquid is the temperature at each of the five measurement points. When the maximum T max of the maximum temperatures reached during the polymerization reaction is indicated at any of the five measurement points, the standard deviation of the temperature of the reaction solution at each of the five measurement points is 12. ~ 30, T max is 80-100 ° C, and
The five measurement points are composed of two measurement points at a position 1 cm from each of the two side wall surfaces and three measurement points at a position that divides the two measurement points into four equal parts.
A method in which the temperature of the reaction solution at each of the five measurement points is measured on the bottom surface at a position directly below each measurement point.
The method according to claim 1, wherein the width of the liquid surface of the reaction solution in the direction in which the five measurement points are arranged is 10 to 500 cm.
The method according to claim 1 or 2, wherein the monomer contains at least one compound selected from the group consisting of (meth) acrylic acid and a salt thereof.