JP7076177B2 - Absorbent article - Google Patents

Description

The present disclosure relates to absorbent articles.

For absorbent articles such as disposable diapers, menstrual napkins, panty liners, etc., the basic performance has been improved by the technological development accumulated over many years, and after absorbing excrement such as menstrual blood, compared to before, after absorbing excrement such as menstrual blood, Leakage and the like are less likely to occur, and at present, further improvement in functionality is required.

For example, Patent Document 1 describes that in water-absorbent polymer particles, there is a negative correlation between the water absorption rate, the amount of water absorption, and the gel strength at the time of swelling.

Patent Document 2 describes a water-absorbent resin having high water-retaining ability and high gel strength characteristics capable of suppressing a gel blocking phenomenon and preventing a decrease in liquid permeation rate, and an absorbent article containing the absorbent resin. Is described. The water-absorbent resin described in Patent Document 2 has the following constitution.
A water-absorbent resin that satisfies the following conditions (1) and (2):
(1) Physiological saline water retention capacity is 40 g / g or more.
(2) The total gel strength represented by the sum of the gel strength a at 30-fold swelling, the gel strength b at 40-fold swelling, and the gel strength c at 50-fold swelling is 5500 Pa or more.
However, the gel strength a at the time of 30-fold swelling is the gel strength when the gel is swelled by adding physiological saline so that the total mass of the gel and the physiological saline is 30 times the mass of the gel. The gel strength b at the time of 40 times swelling is the gel strength when the gel is swelled by adding physiological saline so that the total mass of the gel and the physiological saline is 40 times the mass of the gel, and is 50 times. The gel strength c at the time of swelling is the gel strength when the gel is swelled by adding the physiological saline so that the total mass of the gel and the physiological saline is 50 times the mass of the gel.

Japanese Unexamined Patent Publication No. 2004-329664 Japanese Unexamined Patent Publication No. 06-057010 International Publication No. 2012/144564

The absorbent resin described in Patent Document 2 has high water retention ability and gel strength at the time of water absorption to the extent that the gel blocking phenomenon can be suppressed, but even if body pressure is applied in a high water retention state, even if body pressure is applied. It does not have enough gel strength to prevent the water-absorbent resin from being crushed.
Therefore, the present disclosure comprises an absorber containing a plurality of water-absorbent polymer particles, which has high water retention and is not easily crushed under pressure in a high water-retaining state, has excellent liquid absorbency, and is a water-absorbing polymer in a high water-retaining state. It is an object of the present invention to provide an absorbent article in which particles are difficult to pop out from the absorbent article.

The present disclosures are absorbent articles including a liquid permeable sheet, an absorbent body and a liquid impermeable sheet, wherein the absorbent body has a water retention ratio of 45 to 110 times with respect to physiological saline in a water retention test. We have found an absorbent article characterized by containing a plurality of water-absorbent polymer particles having (mass ratio) and a water-absorbing gel strength of 20 to 50 mN with respect to physiological saline in a water-absorbing gel strength test.

The absorbent article of the present disclosure comprises an absorber containing a plurality of water-absorbing polymer particles, which has high water retention and is not easily crushed under pressure in a high water retention state, has excellent liquid absorbency, and absorbs water in a high water retention state. The sex polymer particles do not easily pop out of the absorbent article.

FIG. 1 is a developed view of the front side of the absorbent article 1 according to the first embodiment. FIG. 2 is an end view of the absorber 5 in the II-II end face of FIG. FIG. 3 is a diagram for explaining the absorbent article 1 according to the second embodiment. FIG. 4 is a schematic diagram for explaining the polymerization apparatus 201. FIG. 5 shows the particle No. It is a particle size distribution (number basis) of 1. FIG. 6 shows the powder No. It is a particle size distribution (number basis) of 2. FIG. 7 shows the powder No. It is a particle size distribution (number basis) of 3.

Specifically, the present disclosure relates to the following aspects.
[Aspect 1]
An absorbent article comprising a liquid permeable sheet, an absorber and a liquid impermeable sheet.
The absorber has a water retention ratio (mass ratio) of 45 to 110 times with respect to physiological saline in the water retention test and a gel strength with water absorption of 20 to 50 mN with respect to physiological saline in the gel strength test during water absorption. Has, contains multiple water-absorbent polymer particles,
The above-mentioned absorbent article.

In the absorbent article, the plurality of water-absorbent polymer particles have a predetermined water-retaining ratio with respect to the physiological saline and a predetermined gel strength at the time of water absorption with respect to the physiological saline, and are added in a highly water-retaining and highly water-retaining state. Hard to collapse under pressure. As a result, in the above-mentioned absorbent article, the water-retaining property of the liquid is high, and even if a pressure due to body pressure or the like is applied in a high water-retaining state, the plurality of water-absorbent polymer particles are hard to be crushed, and the crushed water-absorbent polymer particles are formed. It is difficult to pop out of the absorbent article, especially from the liquid permeable sheet.

[Aspect 2]
The absorbent article according to embodiment 1, wherein the plurality of water-absorbent polymer particles have a breaking strength of 20 N or more.

In the absorbent article, since the plurality of water-absorbent polymer particles have a predetermined breaking strength, when the plurality of superabsorbent polymer particles are subjected to a strong impact before use, for example, during transportation of the absorbent polymer. Even if there is, it is difficult for defective parts (cracks on the surface of the water-absorbent polymer particles, chipping of a part of the surface, etc.) to occur on a part of the surface, and the water-absorbent polymer particles are formed on the defective part in the superabsorbent polymer state. Due to this, it becomes difficult to collapse. As a result, in the absorbent article, the water-retaining property of the liquid is high, and in the high water-retaining state, the plurality of water-absorbent polymer particles are hard to be crushed, and the crushed water-absorbent polymer particles or the fragments generated from the defective portion are formed. It is difficult to pop out of the absorbent article, especially from the liquid permeable sheet.

[Aspect 3]
The absorbent article according to aspect 1 or 2, wherein the plurality of water-absorbent polymer particles have a dust generation rate of 0.00 to 0.20% by mass in a dust generation test.

In the absorbent article, since the water-absorbent polymer particles have a predetermined dust generation rate, a force is applied such that a plurality of superabsorbent polymer particles rub against each other before use, for example, during transportation of the absorbent polymer. Even in some cases, defective portions (cracks on the surface of the superabsorbent polymer particles, chipping of a part of the surface, etc.) are unlikely to occur on a part of their surfaces, and the water-absorbent polymer particles have a defective portion in a superabsorbent polymer state. It is less likely to cause crushing problems due to the above, that is, it is less likely to be crushed under pressure in a high water retention state. As a result, in the absorbent article, the water-retaining property of the liquid is high, and in the high water-retaining state, the plurality of water-absorbent polymer particles are hard to be crushed, and the crushed water-absorbent polymer particles or the fragments generated from the defective portion are formed. It is difficult to pop out of the absorbent article, especially from the liquid permeable sheet.

[Aspect 4]
The absorbent article according to any one of aspects 1 to 3, wherein the plurality of water-absorbent polymer particles have an average sphericity of 0.90 to 0.99.

In the absorbent article, since the plurality of water-absorbent polymer particles have a predetermined average sphericity, a defective portion (a crack on the surface of the water-absorbent polymer particle, one of the surfaces) is partially formed on the surface of the absorbent polymer particles before water retention. (Chips of parts, etc.) are less likely to occur. As a result, the water-absorbent polymer particles are less likely to be crushed from the defective portion due to the small number of defective portions in the superabsorbent polymer state, and are less likely to be crushed under pressure in the high water retention state. As a result, in the absorbent article, the water-retaining property of the liquid is high, and in the high water-retaining state, the plurality of water-absorbent polymer particles are hard to be crushed, and the crushed water-absorbent polymer particles or the fragments generated from the defective portion are formed. It is difficult to pop out of the absorbent article, especially from the liquid permeable sheet.

[Aspect 5]
An absorbent article comprising a liquid-permeable sheet, an absorber and a liquid-impermeable sheet in that order.
The absorber has a water retention ratio (mass ratio) of 45 to 110 times with respect to physiological saline in a water retention test and a gel strength with water absorption of 20 to 50 mN with respect to physiological saline in a gel strength test during water absorption. Contains a water-absorbent polymer particle layer composed of a plurality of water-absorbent polymer particles,
The plurality of water-absorbent polymer particles release the polymerization composition containing an ethylene-based unsaturated monomer, a radical polymerization initiator and water as a plurality of droplets into a hydrophobic solvent, and the plurality of the above-mentioned multiple in the hydrophobic solvent. The polymerization composition in the droplets is polymerized to form a plurality of water-absorbent polymer water-containing particles from the plurality of droplets, the plurality of water-absorbent polymer water-containing particles are taken out from the hydrophobic solvent, and the plurality of water-absorbent polymer water-containing particles are taken out. Manufactured by drying the water-absorbent polymer water-containing particles of
The above-mentioned absorbent article.
The absorbent article has the same effect as that described in aspect 1.

[Aspect 6]
The absorbent article according to aspect 5, wherein the plurality of droplets have a coefficient of variation of a droplet diameter of 0.01 to 0.20.
Since the plurality of droplets have a fluctuation coefficient of a predetermined droplet diameter, the ratio of the water-absorbent polymer particles having a relatively small particle size is reduced in the plurality of water-absorbent polymer particles produced. As a result, in the absorbent article, the water-absorbent polymer particles are less likely to pop out of the absorbent article, especially from the liquid-permeable sheet.

[Aspect 7]
5. The embodiment 5 or 6, wherein the radical polymerization initiator is a photoradical polymerization initiator, and the polymerization composition in the plurality of droplets is photopolymerized by irradiating the plurality of droplets with light. Absorbent article.

Since the radical polymerization initiator is a photoradical polymerization initiator, the plurality of water-absorbent polymer particles produced are less likely to be crushed under pressure under high water retention and high water retention. As a result, in the above-mentioned absorbent article, the water retention of the liquid is high, and in the superabsorbent state, the plurality of water-absorbent polymer particles are hard to be crushed, and the crushed water-absorbent polymer particles are outside the absorbent article, particularly the liquid. It becomes difficult to pop out from the transparent sheet.

[Aspect 8]
The absorption according to any one of aspects 5 to 7, wherein the temperature of the hydrophobic solvent in polymerizing the polymerization composition in the plurality of droplets is in the range of more than 0 ° C. and 30 ° C. or lower. Sex goods.
When the temperature of the hydrophobic solvent is within a predetermined range, the plurality of produced water-absorbent polymer particles have high water retention and are less likely to be crushed under pressure in a high water retention state. In addition, the plurality of water-absorbent polymer particles are less likely to contain bubbles. As a result, in the above-mentioned absorbent article, the water retention of the liquid is high, and in the superabsorbent state, the plurality of water-absorbent polymer particles are hard to be crushed, and the crushed water-absorbent polymer particles are outside the absorbent article, particularly the liquid. It becomes difficult to pop out from the transparent sheet.

[Aspect 9]
The absorbent article according to any one of aspects 1 to 8, wherein the plurality of water-absorbent polymer particles have an average particle size of 300 to 800 μm as primary particles.
In the above-mentioned absorbent article, since the plurality of water-absorbent polymer particles have a predetermined average particle size as primary particles, defects are less likely to occur on a part of their surfaces before water retention, and after water retention, they are added. Hard to collapse under pressure. As a result, in the above-mentioned absorbent article, the water retention of the liquid is high, and in the superabsorbent state, the plurality of water-absorbent polymer particles are hard to be crushed, and the crushed water-absorbent polymer particles are outside the absorbent article, particularly the liquid. It becomes difficult to pop out from the transparent sheet.

[Aspect 10]
The absorbent article according to any one of aspects 1 to 9, wherein the plurality of water-absorbent polymer particles have a coefficient of variation of a particle size of 0.01 to 0.20.
In the absorbent article, since the plurality of water-absorbent polymer particles have a variation coefficient of a predetermined particle size, the ratio of the water-absorbent polymer particles having a relatively small particle size is reduced in the water-absorbent polymer particles. As a result, in the absorbent article, the water-absorbent polymer particles are less likely to pop out of the absorbent article, especially from the liquid-permeable sheet.

[Aspect 11]
The absorber includes a first absorber and a second absorber that is closer to the liquid impermeable sheet than the first absorber.
The absorbent article according to any one of aspects 1 to 10, wherein the first absorber comprises a water-absorbent polymer particle layer composed of the plurality of water-absorbent polymer particles.

In the above-mentioned absorbent article, since the first absorbent body closer to the liquid permeable sheet than the second absorbent body contains a water-absorbent polymer particle layer composed of predetermined water-absorbent polymer particles, the first absorbent body retains liquid water. In addition to being excellent in properties, in a highly water-retaining state, a plurality of water-absorbent polymer particles in the first absorbent body are less likely to be crushed, and the crushed water-absorbent polymer particles are less likely to jump out of the absorbent article, especially from the liquid-permeable sheet. ..

[Aspect 12]
The absorbent article according to aspect 11, wherein the plurality of water-absorbent polymer particles have a suction height of 15 to 40 mm with respect to physiological saline in a suction test.
In the absorbent article, since the plurality of water-absorbent polymer particles have a predetermined suction height, the water-absorbent polymer particle layer of the first absorber transfers the body fluid to the second absorber while absorbing the body fluid. Because it can be used, it has excellent absorption of body fluids.

[Aspect 13]
The item according to any one of aspects 1 to 12, wherein the second absorber comprises a second absorbent core and a second core wrap, and the second absorbent core comprises pulp and a plurality of water-absorbing polymer powders. Absorbent article.
The absorbent article contains a second absorbent body including a second absorbent core and a second core wrap, and is excellent in liquid absorbability.

[Definition]
-"Water-absorbent polymer particles" and "water-absorbent polymer powder"
In the present specification, "water-absorbent polymer particles" and "water-absorbent polymer powder" are used separately.
"Water-absorbent polymer particles" mean those having a predetermined water retention ratio and a predetermined gel strength at the time of water absorption, which is the subject of the present disclosure.
On the other hand, the "superabsorbent polymer powder" is produced by any manufacturing method such as a reverse phase suspension polymerization method, a solution polymerization method, a gas phase method, etc. in addition to the above water-absorbent polymer particles, and has high absorption in the art. Includes what is called a sex polymer, SAP, and the like.

The water-absorbent polymer particles preferably have a water content of 1% by mass or less.
Moisture content is measured as follows.
The water-absorbent polymer particles whose mass: _ma (g) was measured were dried in an oven at 110 ° C. for 10 hours to form particles after drying, and the mass of the dried particles: _mb (g) was measured. Formula:
Moisture content (% by mass) ₌ (ma- _mb ) / _ma
Calculated by

・ "Water retention function" and "Water absorption function"
In the present specification, terms related to the "water retention function" of the water-absorbent polymer powder (for example, water retention, water retention test, water retention ratio, high water retention state, etc.) are contained in the water-absorbent polymer powder. The target is liquids (for example, ion-exchanged water, physiological saline, body fluids) and the like.
Further, in the present specification, terms related to the "water absorption function" of the water-absorbent polymer powder (for example, water absorption, water absorption test, water absorption magnification, etc.) are possessed by the water-absorbent polymer powder inside or on the surface thereof. The target is liquids (for example, ion-exchanged water, physiological saline, body fluid) and the like.

The absorbent articles of the present disclosure will be described in detail below.
FIG. 1 is a development view of the front side of an absorbent article 1 according to one of the embodiments of the present disclosure (hereinafter referred to as “first embodiment”), specifically, a tape-type disposable diaper. FIG. 2 is an end view of the absorber 5 in the II-II end face of FIG.

As shown in FIG. 1, the absorbent article 1 includes a liquid permeable sheet 3, an absorber 5, and a liquid permeable sheet 7 in that order. In the first embodiment, as shown in FIG. 1, the absorbent article 1 is fixed to fix the pair of leak-proof walls 101 including the elastic member 103 and the leak-proof walls 101 to the liquid permeable sheet 3. It has a portion 105, an elastic member 107, a tape fastener 109, and the like, but since these are known in the art, description thereof will be omitted.
As shown in FIG. 2, the absorber 5 includes an absorption core 9 containing a plurality of water-absorbent polymer particles 11 and a plurality of pulp fibers 13, and a core wrap 15 for packaging the absorption core 9.

The plurality of water-absorbent polymer particles 11 have a water retention ratio (mass ratio) of 45 to 110 times with respect to the physiological saline in the water retention test and a water absorption of 20 to 100 mN with respect to the physiological saline in the water absorption gel strength test. Has gel strength. The plurality of water-absorbent polymer particles 11 are excellent in water retention of liquids such as body fluids, and are not easily crushed under pressure such as body pressure in a high water retention state. Therefore, under a high water retention state and under pressure, it is unlikely that the crushed plurality of water-absorbent polymer particles 11 will pass through the core wrap 15 and the liquid-permeable sheet 3 and jump out of the absorbent article 1.

FIG. 3 is a diagram for explaining an absorbent article 1 according to another embodiment of the present disclosure (hereinafter, referred to as “second embodiment”). FIG. 3 corresponds to the II-II cross section of FIG. 1, and the portion not shown is the same as that of the first embodiment.
In the second embodiment, the absorbent article 1 includes a liquid permeable sheet 3, a first absorbent 21, a second absorbent 23, and a liquid permeable sheet 7 in that order. The first absorber 21, which is closer to the liquid permeable sheet 3 than the second absorber 23, has a water-absorbent polymer particle layer 25 composed of a plurality of water-absorbent polymer particles 11 and a first core wrap 27 that covers the water-absorbent polymer particle layer 25. It consists of. The second absorbent 23, which is closer to the liquid impermeable sheet 7 than the first absorbent 21, covers the second absorbent core 33 including the water-absorbent polymer powder 29 and the pulp fiber 31, and the second absorbent core 33. It consists of 2 core wraps 35.

In the absorbent article 1 according to the second embodiment, since the first absorber 21 in the upper layer includes the water-absorbent polymer particle layer 25 composed of the plurality of water-absorbent polymer particles 11, the first absorber 21 retains the liquid. However, the liquid can be delivered to the second absorber 23 in the lower layer. Further, in the absorbent article 1 according to the second embodiment, since the second absorber 23 in the lower layer contains the water-absorbent polymer powder 29 and the pulp fiber 31, the liquid absorbency is excellent. Even when the liquid returns from the second absorber 23 in the lower layer to the first absorber 21 in the upper layer due to the application of body pressure or the like, the first absorber 21 can absorb the liquid. The absorbent article 1 has excellent rewetability.
Further, in the absorbent article 1, even when the first absorber 21 is in a highly water-retaining state, the plurality of water-absorbent polymer particles 11 in the first absorber 21 are difficult to be crushed, and the crushed plurality of water-absorbents. The polymer particles 11 are unlikely to pop out of the absorbent article 1.

In the absorbent article of the present disclosure, the plurality of water-absorbent polymer particles (hereinafter, may be simply referred to as "water-absorbent polymer particles") are 45 to 110 times, preferably 55 times as much as those of physiological saline in the water retention test. It has a water retention ratio (mass ratio) of ~ 95 times, and more preferably 60 to 85 times. By doing so, the water-absorbent polymer particles can continue to retain a large amount of body fluid such as urine and menstrual blood inside thereof. As a result, even when a force or the like is applied to the water-absorbent polymer particles, it becomes difficult to release the absorbed body fluid.

In the water retention test, the water-absorbent polymer particles have a water retention ratio (mass ratio) of preferably 500 to 1,000 times, more preferably 700 to 950 times, and even more preferably 800 to 900 times with respect to water. By doing so, the water-absorbent polymer particles can continue to retain a large amount of body fluid having a low ion concentration inside thereof.

In the above-mentioned water retention test, when measuring the water retention ratio with respect to water, instead of "physiological saline about 3.0 mL (about 150 times the mass of the sample)", "ion exchange water about 22 mL (about 22 mL). About 1,100 times the mass of the sample) ”is added.

In the present specification, the above-mentioned water retention test is carried out as follows.
(1) A sample of the water-absorbent polymer particles is allowed to stand in a constant temperature and humidity chamber having a temperature of 20 ± 5 ° C. and a humidity of 65 ± 5% RH for 24 hours.
(2) Mass of a sample of about 20 mg: Weigh accurately m ₁ (g), add about 3.0 mL of physiological saline (about 150 times the mass of the sample) to the weighed sample, and let stand for 3 hours. , Swell the sample.
(3) The sample is placed in a bag made of nylon mesh having an opening of 75 μm, and the bag containing the sample is dehydrated at 150 G for 90 seconds with a centrifuge.

(4) Take out the sample from the bag and measure its mass: m ₂ (g).
(5) Sample water retention ratio (mass ratio): W _HR , the following formula:
W _HR = 100 × (m ₂ -m ₁ ) / m ₁
Calculated by
(6) Steps (1) to (5) are repeated three times in total for different samples, and the arithmetic mean of the water retention ratios of the three samples: _WHR is adopted as the water retention ratio.

In the absorbent article of the present disclosure, the water-absorbent polymer particles have a water-absorbing gel strength of 20 to 50 mN, preferably 23 to 45 mN, and more preferably 25 to 40 mN with respect to physiological saline in a water-absorbing gel strength test. Has. By doing so, the water-absorbent polymer particles are less likely to be crushed even when a force is applied while holding the body fluid. As a result, in the above-mentioned absorbent article, the water-retaining property of the liquid is high, and even if a pressure due to body pressure or the like is applied in the state where the body liquid is retained, the plurality of water-absorbent polymer particles are hard to be crushed, and the crushed water-absorbent polymer particles are crushed. However, it becomes difficult to jump out of the absorbent article.

Further, in the art, it is known that there is a negative correlation between the water retention ratio (water absorption amount) of the water-absorbent polymer particles and the particle strength at the time of swelling. Compared with the water-absorbent polymer powder of No. 1, it has both a high water retention ratio and a high gel strength at the time of water absorption.

In the present specification, the above-mentioned water absorption gel strength test is carried out as follows.
(1) Prepare Minebea Technograph TG-500N in a constant temperature and humidity chamber with a temperature of 20 ± 5 ° C. and a humidity of 65 ± 5% RH.
(2) A sample of the water-absorbent polymer particles is allowed to stand in the above-mentioned constant temperature and humidity chamber for 24 hours.
(3) The mass of the sample of about 10 mg is accurately weighed, 1 g of physiological saline is added per 10 mg of the sample, and the mixture is allowed to stand for 3 hours to swell the sample.

(4) From the swollen sample, one swollen particle is placed on the sample stage of the technograph TG-500N, and the swollen particle is compressed at a rate of 2 mm / min.
(5) Measure the load when the swollen particles break.
(6) A total of 50 measurements are performed with different swollen particles, and the arithmetic mean of the above loads for 50 times is adopted as the gel strength at the time of water absorption.

In the absorbent article of the present disclosure, the water-absorbent polymer particles are preferably 60 to 200 mN, more preferably 80 to 160 mN, and even more preferably 100 to 140 mN with respect to water in a water absorption gel strength test. Has gel strength. By doing so, the water-absorbent polymer particles are less likely to be crushed even when a force is applied to the body fluid having a low ion concentration in a high water retention state.

In the above-mentioned water absorption gel strength test, when measuring the water absorption gel strength with respect to water, in an accurately weighed sample of about 10 mg, instead of "1 g of physiological saline" per 10 mg of the sample, " Add 10 g of ion-exchanged water.

In the absorbent article of the present disclosure, the water-absorbent polymer particles preferably have a breaking strength of 20 N or more, more preferably 30 N or more, still more preferably 40 N or more, and even more preferably 50 N or more. By doing so, even if the absorbent article containing the water-absorbent polymer particles receives a strong impact before use, for example, during transportation, a portion of the surface of the water-absorbent polymer particles is defective. (For example, cracks on the surface of the superabsorbent polymer particles, chipping of a part of the surface, etc.) are less likely to occur, and the superabsorbent polymer particles are less likely to be crushed due to the defective portion in the superabsorbent polymer state. That is, it is less likely to be crushed under pressure under a high water retention state.
The breaking strength was measured in the same manner as in the gel strength test during water absorption except that step (3) was omitted, and the "swelled sample" and "swelled particles" in steps (4) and (5) were , Read as "sample" and "particle", respectively. The upper limit of the load is 50N.

In the absorbent articles of the present disclosure, the water-absorbent polymer particles are preferably 0.00 to 0.20% by mass, more preferably 0.00 to 0.15% by mass, still more preferably 0. It has a dust generation rate of 00 to 0.10% by mass, and even more preferably 0.00 to 0.05% by mass. By doing so, even if the absorbent article containing the superabsorbent polymer particles is subjected to a force such that the superabsorbent polymer particles rub against each other before use, for example, during transportation, the superabsorbent polymer is subjected to the force. Defects are less likely to occur on a part of the surface of the particles, and the superabsorbent polymer particles are less likely to be crushed due to the deficiencies in the superabsorbent polymer state, that is, they are less likely to be crushed under pressure in the superabsorbent state. Become.

In addition, by doing so, it is less likely that the fine powder generated from the water-absorbent polymer particles contaminates the production line of the absorbent article during the production of the absorbent article. In addition, the possibility that the fine powder generated from the water-absorbent polymer particles leaks out from the absorbent article is reduced.

In the present specification, the above-mentioned dust generation test is carried out as follows.
(1) Prepare an Excel autohomogenizer manufactured by NISSEI in a constant temperature and humidity chamber having a temperature of 20 ± 5 ° C. and a humidity of 65 ± 5% RH.
(2) A sample of the water-absorbent polymer particles is sieved with an opening of 150 μm and allowed to stand in the constant temperature and humidity chamber for 24 hours.
(3) Approximately 10 g of sample mass: m ₃ (g) is accurately weighed, the sample is charged into a homogenizer, and the sample is stirred at a rotation speed of 1,000 rpm for 1 minute.

(4) The sample after stirring is sieved with a mesh opening of 150 μm, and the mass of the fine powder passing through the sieve: m ₄ (g) is measured.
(5) Dust generation rate: D (mass%), the following formula:
D (mass%) = 100 x m ₄ / m ₃
Calculated by
(6) The test is carried out three times in total with different samples, and the arithmetic mean of the dust generation rate is adopted three times.

In the absorbent articles of the present disclosure, the water-absorbent polymer particles are preferably average true of 0.90 to 0.99, more preferably 0.92 to 0.98, and even more preferably 0.93 to 0.97. Has a spherical degree. By doing so, before water retention, defects are less likely to occur on a part of their surfaces. As a result, the water-absorbent polymer particles are less likely to be crushed from the defective portion due to the small number of defective portions in the superabsorbent polymer state, and are less likely to be crushed under pressure in the high water retention state.

In the absorbent articles of the present disclosure, the water-absorbent polymer particles preferably have a particle size of 0.01 to 0.20, more preferably 0.03 to 0.15, and even more preferably 0.05 to 0.10. Has a coefficient of variation of. By doing so, the ratio of the water-absorbent polymer particles having a relatively small particle size becomes small in the water-absorbent polymer particles, and as a result, the water-absorbent polymer particles are less likely to jump out of the absorbent article.

In the present specification, the particle size of the water-absorbent polymer particles (the particle size of each water-absorbent polymer particle), the average particle size, the coefficient of variation of the particle size, and the average sphericity are measured as follows.
(1) A digital microscope (trade name: VHX-1000, zoom lens: × 20 to × 200) manufactured by KEYENCE Co., Ltd. and attached to a constant temperature and humidity chamber with a temperature of 20 ± 5 ° C and a humidity of 65 ± 5% RH. Prepare the software.
(2) A sample of the water-absorbent polymer particles is allowed to stand in the above-mentioned constant temperature and humidity chamber for 24 hours.
(3) Take a sample with the above digital microscope.

から算出する。
（５）平均粒径は、粒度分布（個数基準）におけるメジアン径（⁵⁰Ｄ_p）を意味する。具体的には、付属のソフトウェアにて、吸水性ポリマー粒子１，０００個の円相当径ＣＤの粒度分布（個数基準）を作成し、当該粒度分布（個数基準）からメジアン径（⁵⁰Ｄ_p）を決定する。 (4) The particle size of each particle means the equivalent circle diameter calculated from the projected area of the projected image of each particle. Specifically, the projected area of each particle: A is measured by the attached software, and the equivalent circle diameter of each particle: CD is calculated by the following formula:

Calculate from.
(5) The average particle size means the median diameter ( ⁵⁰ D _p ) in the particle size distribution (number basis). Specifically, the attached software is used to create a particle size distribution (number basis) of a circle-equivalent diameter CD of 1,000 water-absorbent polymer particles, and from the particle size distribution (number basis), the median diameter ( ⁵⁰ _Dp ). To determine.

(6) The coefficient of variation of the particle size is calculated from the above particle size distribution (number basis) by the attached software.
(7) Average sphericity: _Sp is the arithmetic mean of the _sphericity sp of 1,000 water-absorbent polymer particles. Specifically, the _sphericity : sp of each water-absorbent polymer particle is the longest diameter: k ₁ and the shortest diameter: k ₂ from the outer edge of each water-absorbent polymer particle. And the following formula:
_sp = k ₂ / k ₁
Calculated by The major axis: k ₁ and the minor axis: k ₂ of each particle are automatically determined by the attached software.

In the absorbent article of the present disclosure, the water-absorbent polymer particles preferably have a particle size of 0.05 to 0.50, more preferably 0.10 to 0.30, and even more preferably 0.12 to 0.20. It has a dispersion coefficient. By doing so, the ratio of the water-absorbent polymer particles having a relatively small particle size becomes small in the water-absorbent polymer particles, and as a result, the water-absorbent polymer particles are less likely to jump out of the absorbent article.

The above-mentioned particle size dispersion coefficient (δ) is 10% particle size: ¹⁰ D _p and median diameter: ⁵⁰ D _p in the particle size distribution (number basis) of the above-mentioned 1,000 circle-equivalent diameter CDs of the water-absorbent polymer particles. And 90% particle size: ⁹⁰ _Dp , the following equation:
δ = ( ⁹⁰ D _p - ¹⁰ D _p ) / ⁵⁰ D _p
Is calculated by.

In the absorbent article of the present disclosure, the water-absorbent polymer particles have a water absorption of preferably 60 to 120 times, more preferably 70 to 100 times, and even more preferably 75 to 90 times with respect to physiological saline in a water absorption test. It has a magnification (mass ratio). By doing so, the water-absorbent polymer particles, and thus the absorbent article, are excellent in absorbability of body fluids such as urine and menstrual blood.

In the art, it is known that there is a negative correlation between the water absorption magnification (water absorption amount) of the water-absorbent polymer particles and the particle strength at the time of swelling, and the above-mentioned water-absorbent polymer particles are conventional water-absorbing polymer particles. Compared with the sex polymer powder, it has both a high water absorption ratio and a high gel strength at the time of water absorption. Therefore, the absorbent article containing the water-absorbent polymer having a predetermined water-absorbing ratio has high water-absorbing state, and the water-absorbing polymer particles are less likely to pop out in the water-absorbing state.

In the present specification, the above-mentioned water absorption test is carried out as follows.
(1) A sample of the water-absorbent polymer particles is allowed to stand in a constant temperature and humidity chamber having a temperature of 20 ± 5 ° C. and a humidity of 65 ± 5% RH for 24 hours.
(2) Approximately 30 mg sample mass: Weigh accurately m ₅ (g), add approximately 6 mL of physiological saline (approximately 200 times the mass of the sample) to the weighed sample, and allow it to stand for 3 hours. Inflate.
(3) The sample is taken out on a mesh sheet of polyamide fiber, the moisture adhering to the surface of the water-absorbent polymer particles is wiped off with a filter paper, and the mass of the swollen sample: m ₆ (g) is measured.
(4) Water absorption ratio (mass ratio) of the sample: _WAR , the following formula:
_WAR = 100 x (m ₆ -m ₅ ) / m ₅
Calculated by
(5) Steps (1) to (4) are repeated three times in total for different samples, and the water absorption ratio of the three samples: the arithmetic mean of _WAR is adopted as the water absorption ratio.

In the absorbent article of the present disclosure, the water-absorbent polymer particles are preferably 700 to 1,500 times, more preferably 800 to 1,200 times, and even more preferably 900 to 1,500 times water with respect to water in the above water absorption test. It has a water absorption magnification (mass ratio) of 1,100 times. By doing so, the water-absorbent polymer particles, and thus the absorbent article, are excellent in absorbability of body fluid having a low ion concentration.

In the above-mentioned water absorption test, when measuring the water absorption ratio with respect to water, "about 6 mL of physiological saline (about 200 times the mass of the sample)" per 30 mg of the sample in an accurately weighed sample of about 30 mg. Instead, add "about 60 mL of ion-exchanged water (about 2,000 times the mass of the sample)".

In the absorbent article of the present disclosure, the water-absorbent polymer particles have a suction height of preferably 15 to 40 mm, more preferably 18 to 35 mm, and even more preferably 20 to 30 mm with respect to physiological saline in a suction test. Has. By doing so, the water-absorbent polymer particles can draw the body fluid into the inside of the absorber.

The suction function is preferable when the absorber includes a water-absorbent polymer particle layer composed of water-absorbent polymer particles. This is because the water-absorbent polymer particle layer can draw the body fluid into the absorber. In addition, the suction function includes a first absorber close to a liquid permeable sheet and a second absorber close to a liquid impermeable sheet, as shown in the second embodiment. 1 It is more preferable that the absorber contains a water-absorbent polymer particle layer composed of water-absorbent polymer particles. This is because the water-absorbent polymer particle layer of the first absorber can transfer the body fluid to the second absorber while absorbing the body fluid.

In the present specification, the above-mentioned suction test is carried out as follows.
(1) A sample of the water-absorbent polymer particles is allowed to stand in a constant temperature and humidity chamber having a temperature of 20 ± 5 ° C. and a humidity of 65 ± 5% RH for 24 hours.
(2) Weigh 1.0 g of the sample, and make the height of the sample uniform in a cylinder (inner diameter: 25 mm, height: 30 mm) with a nylon mesh with an opening of 75 μm on the bottom. Place while adjusting to.
(3) Insert two spacers (length: 25 mm x width: 5 mm x height: 0.5 mm) into the chalet (inner diameter: 90 mm, height: 15 mm) at intervals, and then put them in the chalet (inside the chalet). Pour 24 mL of colored saline (containing 1 g of Blue No. 1 per liter of saline).

(4) A cylinder on which the sample is placed is placed on the two spacers so that the bottom surface faces downward, and the saline solution that has passed through the nylon mesh on the bottom surface is sucked up by the sample.
In addition, when the sample sucks up the colored physiological saline solution, the swelled portion colored in blue rises, and the boundary surface between the swelled portion and the unswelled portion also rises.
(5) Two hours after the cylinder is placed in the petri dish, the height of the lowest portion of the boundary surface is measured from the bottom surface (nylon mesh) of the cylinder.
(6) The test is carried out 10 times in total with different samples, and the arithmetic mean of the heights of 10 times is adopted as the suction height.
(7) The uniform suction property of the boundary surface is evaluated in the following three stages.
◯: The boundary surface is close to flat, and the suction of physiological saline is uniform.
Δ: The boundary surface is uneven, and the suction of physiological saline is not uniform.
X: The unevenness of the boundary surface is large, and the suction of physiological saline is very uneven.

In the absorbent articles of the present disclosure, the water-absorbent polymer particles have a suction height of preferably 15 to 40 mm, more preferably 18 to 35 mm, and even more preferably 20 to 30 mm with respect to water in a suction test. .. By doing so, the water-absorbent polymer particles can draw the body fluid having a low ion concentration into the inside of the absorber. The structure of the preferable absorber is the same as that described in relation to the physiological saline solution in the suction test.

In the suction test, when measuring the suction height with respect to water, instead of "24 mL of colored physiological saline (including 1 g of blue No. 1 per 1 L of physiological saline)", Add "24 mL of colored ion-exchanged water (1 g of blue No. 1 per liter of ion-exchanged water)" and read "saline" as "ion-exchanged water".

The average particle size of the water-absorbent polymer particles is not particularly limited and may vary depending on the application, but is generally 10 to 5,000 μm, preferably 100 to 1,000 μm, and more preferably 300 to 800 μm. ..
The method for measuring the average particle size is as described above.

The average particle size of the water-absorbent polymer particles having a particularly high effect as compared with the water-absorbent polymer powder produced by the reverse phase suspension polymerization method is preferably 300 to 1,000 μm, and more preferably 300 to 300. 800 μm is mentioned. In the reverse phase suspension polymerization method, in order to produce a water-absorbent polymer powder having an average particle size of 50 to 100 μm as primary particles and to produce a water-absorbent polymer powder having an average particle size higher than that, granulation is performed. Because it is necessary to do. Since the water-absorbent polymer particles can have the average particle size as primary particles without granulation, the water-absorbent polymer powder produced by the reverse phase suspension polymerization method is within the range of the average particle size. In comparison with, before water retention, a part of the surface thereof is less likely to have a defect, and after water retention, it has an effect of being less likely to be crushed under pressure.

The water-absorbent polymer particles can have a monomer skeleton generally used in the art, and for example, a monomer skeleton exemplified in the section of the method for producing a water-absorbent polymer particle described later, for example, an ethylene-based non-polymer. A skeleton derived from a saturated monomer, a skeleton derived from a cross-linking agent, and the like can be included.

In the absorbent article of the present disclosure, the water-absorbent polymer particles may not have bubbles. By doing so, the water-absorbent polymer particles are excellent in water retention ratio, gel strength at the time of water absorption, and the like.

In an absorbent article according to one of the embodiments of the absorbent article of the present disclosure (hereinafter referred to as "third embodiment"), the absorber is a water absorbent as shown in the first embodiment as an absorbent core. It contains a mixture of polymer particles and other components (eg, pulp fibers, etc.). In the third embodiment, the absorber contains the water-absorbent polymer particles and other components as an absorption core in a ratio known in the art, for example, in a ratio of 10 to 90% by mass and 90 to 10% by mass. Can be done. Further, in the embodiment, the absorber may include a core wrap that covers the absorption core.

In an absorbent article according to another embodiment of the present disclosure (hereinafter referred to as "fourth embodiment"), the absorber is a water-absorbent polymer particle containing only the above-mentioned water-absorbent polymer particles (that is, a water-absorbent polymer particle) as an absorbent core. Polymer particle layer) is included. In the fourth embodiment, the water-absorbent polymer particles may be covered with a core wrap and may be adhered to, for example, a substrate sheet.

In an absorbent article according to yet another embodiment of the present disclosure (hereinafter referred to as "fifth embodiment"), the absorber may be partitioned into a plurality of absorbers, that is, for example, in the second embodiment. It comprises a first absorber and a second absorber as shown. Examples of the first absorber include the absorber shown in the fourth embodiment. In addition, examples of the second absorber include an absorber according to the third embodiment, and examples of the absorbent core include an absorber containing a mixture of a water-absorbent polymer powder and other components (for example, pulp fiber and the like).

The absorbent article of the present disclosure is not particularly limited as long as it can contain a water-absorbent polymer powder, and the absorbent article for absorbing urine, for example, a disposable diaper, a urine absorbing pad, a light incontinence pad, a pet. Sheets for women, absorbent articles for women, such as menstrual napkins, panty liners and the like.

An example of the method for producing the water-absorbent polymer particles will be described. The manufacturing method includes the following steps.
(I) A step of discharging a polymerization composition containing an ethylene-based unsaturated monomer, a radical polymerization initiator and water as a plurality of droplets into a hydrophobic solvent (hereinafter, may be referred to as a "droplet discharge step").
(Ii) A step of polymerizing the polymerization composition in the plurality of droplets in the hydrophobic solvent to form a plurality of water-absorbent polymer water-containing particles from the plurality of droplets (hereinafter, “water-absorbent polymer water-containing”). Sometimes referred to as "particle formation step")
(Iii) A step of forming the plurality of water-absorbent polymer particles by taking out the plurality of water-absorbent polymer water-containing particles from the hydrophobic solvent and drying the plurality of water-absorbent polymer water-containing particles (hereinafter, “water absorption”). Sometimes referred to as "superpolymer particle formation step")

[Drop emission step]
The polymerization composition in the droplet emission step contains an ethylene-based unsaturated monomer, a radical polymerization initiator, water and the like.
The ethylene-based unsaturated monomer is not particularly limited as long as it is used in the art, and examples thereof include (meth) acrylic acid-based monomers. In addition, (meth) acrylic acid means acrylic acid and / or methacrylic acid.
The polymerization composition contains the ethylene-based unsaturated monomer in a ratio of generally 40 to 70% by mass, preferably 60 to 70% by mass.

Examples of the (meth) acrylic acid-based monomer include (meth) acrylic acid (that is, a non-neutralized product of (meth) acrylic acid), a neutralized product of (meth) acrylic acid, and a derivative of (meth) acrylic acid. , For example, esterified products and the like.
Examples of the neutralized product of (meth) acrylic acid include alkali metal salts of (meth) acrylic acid. Examples of the alkali metal salt include lithium, sodium, potassium salt and the like, and sodium and potassium salts are preferable.

When the water-absorbent polymer particles formed from the above-mentioned polymerization composition have a monomer skeleton derived from the (meth) acrylic acid-based monomer, the water-absorbent polymer particles are derived from the (meth) acrylic acid derivative. It is preferable that 85 to 100 mol% of the acid group (carboxyl group) is neutralized except for the monomer skeleton.

Therefore, in the water-absorbent polymer particles, when 85 to 100 mol% of the acid group (carboxyl group) of the skeleton derived from the neutralized product of (meth) acrylic acid and (meth) acrylic acid is neutralized, The polymerization composition may contain a (meth) acrylic acid-based monomer in which 85 to 100 mol% of the acid groups have been neutralized, or, for example, the acid groups contained in the water-absorbent polymer water-containing particles have been neutralized. Finally, the water-absorbent polymer particles may include a skeleton derived from a (meth) acrylic acid-based monomer in which 85-100 mol% of acid groups have been neutralized.

The polymerization composition preferably contains a cross-linking agent. Examples of the cross-linking agent include (i) a polymerizable cross-linking agent having at least two polymerizable unsaturated groups, (ii) a reactive cross-linking agent having at least two reactive groups capable of reacting with a carboxyl group, and (iii). ) A polymerizable reactive cross-linking agent having a polymerizable unsaturated group and a reactive group capable of reacting with a carboxyl group can be mentioned. From the viewpoint of the water absorption characteristics of the formed water-absorbent polymer particles, the cross-linking agent is preferably an acrylate-based, allyl-based, or acrylamide-based polymerizable cross-linking agent. When the polymerization composition contains a cross-linking agent, the polymerization composition contains the cross-linking agent at a ratio of preferably 0.02 to 0.15 mol% with respect to the ethylene-based unsaturated monomer.

Examples of the cross-linking agent include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, and penta. Elythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, N, N'-methylenebis (meth) acrylamide, triallyl isocyanurate, (poly) ethylene glycol diglycidyl ether, glycerin polyglycidyl ether, sorbitol polyglycidyl ether, Examples thereof include pentaerythritol polyglycidyl ether and the like.

Examples of the radical polymerization initiator include a photoradical polymerization initiator and a thermal radical polymerization initiator. From the viewpoint of the characteristics of the water-absorbent polymer particles formed, the radical polymerization initiator is preferably a photoradical polymerization initiator, and when the radical polymerization initiator contains a thermal radical polymerization initiator, light It is preferably used in combination with a radical polymerization initiator.
The polymerization composition contains the radical polymerization initiator in a proportion of preferably 0.001 to 20% by mass, more preferably 0.1 to 10% by mass, based on the ethylene-based unsaturated monomer.

As the photoradical polymerization initiator, those capable of generating radicals with light having a wavelength of about 200 nm to about 600 nm are preferable, and for example, benzoin, acetoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzophenone, benzyl, etc. Michler's ketone, xantone, chlorothioxanthone, isopropylthioxanthone, benzyldimethylketal, naphthol, anthraquinone, hydroxyanthracene, acetophenone diethyl ketal, α-hydroxycyclohexylphenylketone, 2-hydroxy-2-methylphenylpropane, any combination thereof, etc. Be done.

Examples of the thermal radical polymerization initiator include azobisisobutyronitrile, 4,4'-azobis (4-cyanovaleric acid), 1,1'-azobis (cyclohexanecarbonitrile), and 2,2'-azobis. (2-Methylpropionitrile), 2,2'-azobis (2-methylpropionamidine) dihydrochloride, t-butyl peroxide, cumene hydroperoxide, di-t-butyl peroxide, acetyl peroxide, lauroyl Peroxide, stearoyl peroxide, benzoyl peroxide, t-butylperoxyacetate, t-butylperoxyisobutyrate, t-butylperoxypivalate, methylethylketone peroxide, cyclohexanone peroxide, hydrogen peroxide, ammonium persulfate, Examples include potassium persulfate.

The temperature of the droplets of the polymerization composition is the heat generated by the polymerization of the ethylene-based unsaturated monomer due to the inclusion of water in the polymerization composition, the release into a hydrophobic solvent maintained at a constant temperature, and the like. Makes it harder to rise. Most of the water is removed after forming the water-absorbent polymer water-containing particles from the polymerization composition.

The hydrophobic solvent is not particularly limited as long as it is immiscible with the polymerization composition and does not react with the components in the polymerization composition. Further, the hydrophobic solvent preferably has a specific gravity close to that of the polymerization composition from the viewpoint of securing a time for the polymerization composition to react.
Examples of the hydrophobic solvent include silicone oil (for example, dimethylpolysiloxane), oil (for example, triglyceride, for example, vegetable oil, for example, medium-chain fatty acid triglyceride), hydrocarbon (for example, liquid paraffin), and the like. Any combination and the like can be mentioned.

The temperature of the hydrophobic solvent is preferably in the range of more than 0 ° C. and 30 ° C. or lower. By doing so, the plurality of water-absorbent polymer particles produced are less likely to be crushed under pressure in a state of high water retention and high water retention. In addition, the plurality of water-absorbent polymer particles are less likely to contain bubbles. As a result, in the above-mentioned absorbent article, the water retention of the liquid is high, and in the superabsorbent state, the plurality of water-absorbent polymer particles are hard to be crushed, and the crushed water-absorbent polymer particles are outside the absorbent article, particularly the liquid. It becomes difficult to pop out from the transparent sheet.

The method of discharging the polymerization composition is not particularly limited as long as it is discharged as droplets in a hydrophobic solvent. For example, the polymerization composition can be used as droplets by using a polymerization apparatus equipped with an injection nozzle. Released into a hydrophobic solvent. Specifically, with the tip of the injection nozzle immersed in a hydrophobic solvent, the polymerization composition is directly and quantitatively injected into the inside of the hydrophobic solvent from the injection nozzle to form a hydrophobic solvent. Form the above-mentioned droplets within. The amount of the polymerization composition ejected from the injection nozzle is, for example, 30 to 60 mL / sec. As the injection nozzle, those described in Japanese Patent Application Laid-Open No. 2008-11765 and the like can be used, and will be described later in connection with the polymerization apparatus 201 shown in FIG.

As a general rule, each of the plurality of droplets forms each of the plurality of water-absorbent polymer water-containing particles and each of the plurality of water-absorbent polymer particles by polymerization. Therefore, from the viewpoint of producing a plurality of water-absorbent polymer particles having a coefficient of variation of a predetermined particle size, it is preferable that the plurality of droplets have a coefficient of variation of a predetermined droplet diameter. Specifically, the plurality of droplets preferably have a variation coefficient of the droplet diameter similar to the variation coefficient of the particle size of the water-absorbent polymer particles, preferably 0.01 to 0.20, and more preferably 0.01 to 0.20. It has a variation coefficient of particle size of 0.03 to 0.15, and more preferably 0.05 to 0.10.

Further, since the plurality of droplets have the above-mentioned fluctuation coefficient of the droplet diameter, the individual particles of the plurality of produced water-absorbent polymer particles tend to have uniform characteristics, and thus are produced. The plurality of water-absorbent polymer particles tend to have a high water retention ratio, a high gel strength at the time of water absorption, and the like.
The coefficient of variation of the droplet diameter can be measured in the same manner as the method for measuring the coefficient of variation of the water-absorbent polymer particles described above.

[Step of forming water-absorbing polymer water-containing particles]
In the water-absorbent polymer water-containing particle forming step, the polymerization composition in the plurality of droplets is polymerized in the hydrophobic solvent to form the plurality of water-absorbent polymer water-containing particles.
When the radical polymerization initiator is a photoradical polymerization initiator, light is emitted from a light source such as a mercury lamp, a fluorescent lamp, a xenon lamp, a carbon arc lamp, a metal halide lamp, a UV-LED lamp, or the like, for example, from about 200 nm. Light having a wavelength of about 600 nm is applied to, for example, a hydrophobic solvent and a forming tube containing a plurality of droplets, and the polymerization composition is photopolymerized in each of the plurality of droplets, from each of the plurality of droplets. Water-absorbent polymer Water-containing particles can be formed. From this point of view, the hydrophobic solvent preferably has a high transmittance with respect to the wavelength of the light emitted from the light source. Further, the forming tube preferably has a high transmittance with respect to the wavelength of the light emitted from the light source, and is formed of, for example, quartz glass.

When the radical polymerization initiator contains only a photoradical polymerization initiator, it is preferable that the polymerization composition and the hydrophobic solvent are not heated. This is because the plurality of water-absorbent polymer water-containing particles, and thus the plurality of water-absorbent polymer particles, are less likely to contain air bubbles.

When the radical polymerization initiator contains only the thermal radical polymerization initiator, the temperature of the hydrophobic solvent is maintained at a temperature at which the thermal radical polymerization initiator can function, for example, a temperature having a half-life temperature of 10 hours or more. Is preferable. When the radical polymerization initiator contains only a thermal radical polymerization initiator, for example, a polymerization tank containing a hydrophobic solvent and a plurality of droplets is heated to a temperature equal to or higher than the 10-hour half-life temperature of the thermal radical polymerization initiator. By maintaining the temperature at, the polymerization composition can be thermally polymerized in each of the plurality of droplets, and water-absorbent polymer water-containing particles can be formed from each of the plurality of droplets.

In this case, it is preferable not to heat the polymerization composition before forming the droplets. This is because the polymerization starts before the polymerization composition is released as droplets into the hydrophobic solvent, and the polymerizable composition may be difficult to form into droplets.

When the radical polymerization initiator contains both a photoradical polymerization initiator and a thermal radical polymerization initiator, it is preferable not to heat the polymerization composition before forming droplets. This is because the polymerization starts before the polymerization composition is released as droplets into the hydrophobic solvent, and the polymerizable composition may be difficult to form into droplets. Also, the hydrophobic solvent can be maintained at a temperature at which the thermal radical polymerization initiator can function. Further, for example, a polymerization apparatus equipped with a forming tube and a polymerization tank is prepared, the hydrophobic solvent is maintained at room temperature in the forming tube, and light is irradiated from a light source to photopolymerize the polymerization composition, and then the polymerization is carried out. In the tank, the hydrophobic solvent may be maintained at a temperature at which the thermal radical polymerization initiator can function, and the polymerization composition may be thermally polymerized.

[Water-absorbent polymer particle formation step]
In the water-absorbent polymer particle forming step, a plurality of water-absorbent polymer water-containing particles are taken out from the hydrophobic solvent, and the plurality of water-absorbent polymer water-containing particles are dried to form the plurality of water-absorbent polymer particles.
The water-absorbent polymer water-containing particles taken out from the hydrophobic solvent are dried under normal temperature or high temperature conditions, for example, at a temperature of 40 to 200 ° C. under normal pressure or reduced pressure to form a plurality of water-absorbent polymer particles.

An example of a polymerization apparatus for carrying out the above manufacturing method is shown in FIG. In FIG. 4, the polymerization apparatus 201 includes a polymerization composition tank 203 holding the polymerization composition 303, a metering pump 205 for adjusting the transport speed of the polymerization composition 303, and a liquid feed tube 207 for transporting the polymerization composition 303. A light irradiation chamber 209 provided with a light source 211, an injection nozzle 213 for injecting a polymerization composition 303, a rectifying porous plate 215, a forming tube 217 for holding a hydrophobic solvent 305 and photopolymerizing droplets, and a water-absorbent polymer water-containing particle 301. A separation screen 219 that separates from the hydrophobic solvent 305, a hydrophobic solvent tank 221 that holds the hydrophobic solvent 305, a metering pump 223 that adjusts the transport speed of the hydrophobic solvent 305, and a temperature regulator that adjusts the temperature of the hydrophobic solvent 305. 225 and a liquid feed tube 227 for transporting the hydrophobic solvent 305 are provided.

The hydrophobic solvent 305 circulates between the forming tube 217, the hydrophobic solvent tank 221, the metering pump 223, the temperature controller 225, the liquid feed tube 227 and the rectifying perforated plate 215, and the circulation speed is determined by the metering pump 223. Controlled, the temperature of the hydrophobic solvent 305 is controlled by the temperature controller 225. Most of the forming tube 217 is arranged inside the light irradiation chamber 209.

The polymerization composition 303 is supplied from the polymerization composition tank 203 to the injection nozzle 213 via the metering pump 205 and the liquid feed pipe 207. The polymerization composition 303 is then ejected from the injection nozzle 213 to form a droplet 307 in the forming tube 217. Next, the droplet 307 is exposed to the light emitted from the light source 211 in the forming tube 217, and the polymerization composition 303 in the droplet 307 is photopolymerized to form the water-absorbent polymer water-containing particles 301. The water-absorbent polymer water-containing particles 301 are separated from the hydrophobic solvent 305 by the separation screen 219.
Next, the water-absorbent polymer water-containing particles 301 are dried to produce water-absorbent polymer particles (not shown).

In the art, as a method for producing a water-absorbent polymer powder, a production method such as a solution polymerization method, a reverse phase suspension polymerization method, and a gas phase method is known.
In the solution polymerization method, the water-absorbent polymer powder is produced by crushing the polymer lumps that have been polymerized. However, since the solution polymerization method includes a step of crushing the polymer lumps, the produced water-absorbent polymer powder is produced. , Has an irregular shape and tends to be high in fine powder. Therefore, since the plurality of water-absorbent polymer powders produced by the solution polymerization method include a portion having large voids between the particles when the water-absorbent polymer powder layer is formed, water absorption utilizing the capillary phenomenon or the like is used. It is difficult to raise. Further, in a plurality of water-absorbent polymer powders produced by a solution polymerization method, the fine powder tends to inhibit the uptake of water.

Further, in the reverse phase suspension polymerization method, it is difficult to adjust the particle size of the produced water-absorbent polymer powder, and in the case of absorbent article applications, additional steps such as granulation are performed to increase the particle size of the water-absorbent polymer powder. However, the granulated water-absorbent polymer powders are fragile in structure, tend to have defects on a part of their surface before water retention, and tend to be crushed under pressure after water retention.
Further, in the reverse phase suspension polymerization method, it is essential to use a surfactant, but in the above production method, a surfactant may be used, for example, the polymerization composition may contain a surfactant. In the above production method, it is not necessary to use a surfactant, for example, the polymerization composition may not contain a surfactant.

When the above-mentioned production method does not use a surfactant, the formed water-absorbent polymer particles do not have a surfactant on the surface thereof. As a result, the surfactant is not arranged on the surface of the produced water-absorbent polymer particles with its hydrophobic portion facing outward, and the water-absorbing and water-retaining properties of the water-absorbent polymer particles are improved. Not inhibited by the hydrophobic part of.

Further, the vapor phase method has a problem that heat is transferred to an injection nozzle for injecting the polymerization composition and is easily clogged with the injection light. Further, the water-absorbent polymer powder produced by the vapor phase method tends to retain air bubbles inside, and has problems in terms of water retention ratio, gel strength at the time of water absorption, and the like.
In the above-mentioned production method, the produced water-absorbent polymer particles are less likely to contain bubbles inside, and the above-mentioned water-absorbent polymer particles have a water retention ratio and water absorption as compared with the water-absorbent polymer powder produced by the vapor phase method. It has an advantage of excellent gel strength and the like.

As used herein, drying means drying without sublimation of moisture. The drying can be carried out at a temperature of 0 ° C. or higher, for example, normal temperature, preferably high temperature, for example, 40 to 200 ° C. The drying can be carried out under 1 atm or reduced pressure.

Hereinafter, the present disclosure will be described with reference to examples, but the present disclosure is not limited to these examples.
[Manufacturing Example 1]
90 parts by mass of a 60% by mass potassium acrylate (manufactured by Nippon Catalyst) aqueous solution as an ethylene-based unsaturated monomer, 10 parts by mass of acrylamide (manufactured by Wako Pure Chemical Industries, Ltd.), and 1.0 part by mass of benzoin isobutyl ether as a photoradical polymerization initiator. The part and 0.5 part by weight of N, N'-methylenebisacrylamide as a cross-linking agent were mixed to obtain the polymerization composition No. I prepared 1.

Using the polymerization apparatus 201 shown in FIG. 4, the polymerization composition No. A plurality of water-absorbent polymer particles (hereinafter referred to as "particle No. 1") were produced from 1. Specifically, the polymerization composition No. 1 was ejected as droplets from the ejection nozzle 213 into the hydrophobic solvent of the forming tube 217 at a rate of 30 mL / sec. The forming tube 217 has a total length of about 1.0 m and an inner diameter of about 12 mm, and in the forming tube 217, about 3 L of dimethylpolysiloxane maintained at about 10 ° C. as a hydrophobic solvent. It was circulating at a speed of / minute.

Polymerization composition No. 2 ejected as droplets into the forming tube 217. No. 1 was irradiated with ultraviolet rays from a high-pressure mercury lamp (wavelength 320 to 400 nm) as a light source 211, and the polymerization composition No. 1 in the droplet was irradiated. No. 1 is polymerized, and a plurality of water-absorbing polymers water-containing particles No. 1 was formed.
From dimethylpolysiloxane, a plurality of water-absorbent polymers, water-containing particles No. No. 1 was taken out and dried at 80 ° C. under reduced pressure to obtain particles No. 1. 1 was manufactured.

[Manufacturing Example 2]
A water-absorbent polymer powder having a skeleton derived from a (meth) acrylic acid-based monomer (commercially available, hereinafter referred to as “powder No. 2”) produced by a reverse phase suspension polymerization method was prepared. Powder No. No. 2 is formed by producing primary particles of about 80 μm by a reverse phase suspension polymerization method and then granulating the primary particles.

[Manufacturing Example 3]
A water-absorbent polymer powder having a skeleton derived from a (meth) acrylic acid-based monomer (commercially available, hereinafter referred to as "powder No. 3") produced by a solution polymerization method was prepared. Powder No. No. 3 is formed by crushing and pulverizing a polymer mass produced by a solution polymerization method.

[Example 1, Comparative Example 1 and Comparative Example 2]
Particle No. 1. Powder No. 2 and powder No. 3. Average particle size, particle size variation coefficient, particle size dispersion coefficient, average sphericity, dust generation rate in dust generation test, breaking strength, water absorption gel strength in water absorption gel strength test, water absorption in water absorption test The magnification (mass ratio, water, physiological saline), the water retention ratio in the water retention test (mass ratio, water, physiological saline), and the suction height and uniform suction property in the suction test were evaluated. The measuring method is as described in the present specification.
The results are shown in Table 1. In addition, the particle No. 1. Powder No. 2 and powder No. The particle size distribution (number basis) of No. 3 is shown in FIGS. 5 to 7. The particle size distributions shown in FIGS. 5 to 7 are measured according to the measuring method such as the average particle size of the present specification, and “400-450” of particle size / μm is “more than 400 μm and 450 μm or less”. Means.

As shown in Table 1, the particle No. 1 of Example 1 is shown. No. 1 is the powder No. 1 produced by the reverse phase suspension polymerization method of Comparative Example 1. Powder No. 2 produced by the solution polymerization method of No. 2 and Comparative Example 2. It can be seen that the dust generation rate is low, the breaking strength is high, and the gel strength at the time of water absorption (water, physiological saline) is high as compared with 3. Therefore, the particle No. 1 is the powder No. 2 and powder No. It can be seen that, as compared with No. 3, before water retention, a part of the surface thereof is less likely to have a defect, and after water retention, it is less likely to be crushed under pressure.

[Manufacturing Example 4]
Air-through non-woven fabric cut to a size of 10 cm x 10 cm on a hydrophilically treated spunbonded non-woven fabric (Eltus Aqua manufactured by Asahi Kasei Corporation, basis weight: 18 g / m ² ) cut to a size of 10 cm x 10 cm. Unicharm Co., Ltd., basis weight: 20 g / m ² ) is stacked, and the particle No. 1 produced in Production Example 1 is placed on top of it (excluding the peripheral portion). 1 was sprayed so that the basis weight was 100 g / m ² , and then a hydrophilically treated spunbonded non-woven fabric (Eltas Aqua manufactured by Asahi Kasei Corporation, basis weight: 18 g) cut into a size of 10 cm × 10 cm was sprayed. / M ² ) was stacked, and the peripheral edge of the stack was sealed and fused to obtain the first absorber No. 1 was formed.

A water-absorbent polymer powder (SA60S manufactured by Sumitomo Seika Co., Ltd.) is placed on a laminated pulp (basis weight: 100 g / m ² ) obtained by crushing and laminating sheet pulp (manufactured by International Paper) and cutting it into a size of 10 cm × 10 cm. Average particle size: 350 μm, basis weight: 100 g / m ² ) was sprayed, and sheet pulp (manufactured by International Paper) was crushed and laminated on it, and laminated pulp cut into a size of 10 cm × 10 cm (weight: basis weight:). 100 g / m ² ) was stacked, and they were covered with a tissue (basis weight: 15 g / m ² ) to obtain the second absorber No. 1 was formed.

SA60S manufactured by Sumitomo Seika Chemical Co., Ltd. is a water-absorbent polymer powder having a skeleton derived from a (meth) acrylic acid-based monomer produced by a reverse-phase suspension polymerization method, and has a large particle size by granulation. It was done.
Second absorber No. On top of 1, the first absorber No. 1 1 is stacked, and an air-through non-woven fabric as a liquid permeable sheet is stacked on the stack to obtain a simple absorbent article No. 1 was manufactured.

[Manufacturing Example 5]
Particle No. produced in Production Example 1. The first absorber No. 1 of Production Example 4 except that the basis weight of 1 was changed from "100 g / m ² " to "200 g / m ² ". In the same manner as in the formation method of No. 1, the first absorber No. 2 was formed. In addition, "1st absorber No. 1" is referred to as "1st absorber No. 1". 2 ”, except for the simple absorbent article No. of Production Example 4. In the same manner as in the production method of No. 1, the simple absorbent article No. 2 was manufactured.

[Manufacturing Example 6]
SA60S manufactured by Sumitomo Seika Chemical Co., Ltd. was screened to form an SA60S-adjusted product having an average particle size of 430 nm. Next, the portion to which "the particle No. 1 produced in Production Example 1 is sprayed so that the basis weight is 100 g / m ² " is "SA60S adjusted product so that the basis weight is 150 g / m ² ". The first absorber No. 1 of Production Example 4 except that it was sprayed. In the same manner as in the formation method of No. 1, the first absorber No. 3 was formed. In addition, "1st absorber No. 1" is referred to as "1st absorber No. 1". 3 ”, except for the simple absorbent article No. of Production Example 4. In the same manner as in the production method of No. 1, the simple absorbent article No. 3 was manufactured.
The SA60S has a water retention ratio (mass ratio) of 38 times with respect to the physiological saline in the water retention test, and has a water absorption ratio (mass ratio) of 58 times with respect to the physiological saline in the water absorption test. Was.

[Manufacturing Example 7]
"The particle No. 1 produced in Production Example 1 is sprayed so that the basis weight is 100 g / m ² ", and the portion where "SA60S adjusted product is sprayed so that the basis weight is 300 g / m ² " is sprayed. Except for the above, the first absorber No. 1 of Production Example 4 was used. In the same manner as in the formation method of No. 1, the first absorber No. 4 was formed. In addition, "1st absorber No. 1" is referred to as "1st absorber No. 1". 4 ”, except for the simple absorbent article No. 4 of Production Example 4. In the same manner as in the production method of No. 1, the simple absorbent article No. 4 was manufactured.

[Examples 2 and 3, and Comparative Examples 3 and 4]
Simple absorbent article No. 1 to No. The absorption time (seconds), rewet (g), and the first absorber retention rate (mass%) and the second absorber retention rate (mass%) of No. 4 were evaluated according to the following measuring methods. The results are summarized in Table 2.

[Measurement of absorption time and rewet]
(1) Simple absorbent article No. 1 to No. A cylinder having an inner diameter of 60 mm is placed on the liquid-permeable sheet of each sample of No. 4, and 50 g of physiological saline (first drop) is dropped into the cylinder (first drop).
(2) 55 minutes after the start of the first dropping, a filter paper having an initial mass measured is placed on a liquid permeable sheet, and a 3.5 kg weight is placed on the filter paper.
(3) 58 minutes after the start of the first dropping (3 minutes after placing the weight), the weight and the filter paper are removed, and the post-test mass of the filter paper that has absorbed the physiological saline is measured, and the increase in the mass of the filter paper is measured. Is the first rewet (g).

(4) 60 minutes after the start of the first dropping, 50 g of physiological saline (second dropping) is dropped into the cylinder (second dropping).
(5) The time from the start of the second dropping to the disappearance of the liquid pool on the liquid permeable sheet in the cylinder is measured and used as the second absorption time (seconds).
(6) 115 minutes after the start of the first drip (55 minutes from the start of the second drip), a filter paper whose initial mass was measured was placed on a liquid-permeable sheet, and a 3.5 kg weight was placed on the filter paper. To put.
(7) 118 minutes after the start of the first drip (58 minutes from the start of the second drip, 3 minutes after the weight is placed), the weight and the filter paper are removed, and the post-test mass of the filter paper that has absorbed the physiological saline solution. Is measured, and the increase in the mass of the filter paper is defined as the second rewet (g).
(8) The steps (1) to (7) are repeated 5 times in total for different samples, and the average value of the second absorption time (seconds) and the average value of the second rewet (g) of all the samples are set to the absorption time, respectively. Adopted as (seconds) and rewet (g).

[Measurement of 1st absorber retention rate (mass%) and 2nd absorber retention rate (mass%)]
(1) Simple absorbent article No. 1 to No. In each sample of No. 4, the initial mass of the first absorber: _{M10 (g) and the initial mass of the second absorber: M2 0 (} g) are measured.
(2) Simple absorbent article No. 1 to No. A cylinder having an inner diameter of 60 mm is placed on the liquid-permeable sheet of each sample of No. 4, and 50 g of physiological saline (first drop) is dropped into the cylinder (first drop).
(3) 60 minutes after the start of the first dropping, 50 g of physiological saline (second dropping) is dropped into the cylinder (second dropping).
(4) 90 minutes after the start of the first dropping (30 minutes from the start of the second dropping), the first absorber and the second absorber are separated, and the mass after the test of the first absorber: M1 ₁ (. g) and the post-test mass of the second absorber: M2 ₁ (g) are measured.

(5) Physiological saline absorption amount of the first absorber: M1 (g) is expressed by the following formula:
M1 (g) = M1 ₁ (g) -M1 ₀ (g)
Calculate from.
Similarly, the amount of physiological saline absorbed by the second absorber: M2 (g) is calculated by the following formula:
M2 (g) = M2 ₁ (g) -M2 ₀ (g)
Calculate from.
(6) The retention rate of the first absorber: M1 _h (mass%) is expressed by the following formula:
M1 _h (mass%) = 100 × M1 / (M1 + M2)
Calculate from.
Similarly, the second absorber retention rate: M2 _h (mass%) is expressed by the following equation:
M2 _h (mass%) = 100 × M2 / (M1 + M2)
Calculate from.
(7) The steps (1) to (6) are repeated 5 times in total for different samples, and the average value of the first absorber retention rate (mass%) and the second absorber retention rate (mass%) of all the samples are calculated. The average value is adopted as the first absorber retention rate (mass%) and the second absorber retention rate (mass%), respectively.

Simple absorbable article No. with close water absorption performance (= [basis weight of water-absorbent polymer powder] x [water absorption ratio of water-absorbent polymer powder to physiological saline]). 1 and the simple absorbent article No. Comparing with No. 3, the simple absorbent article No. No. 1 has a short absorption time and is excellent in rewetability. Simple absorbent article No. 2 and the simple absorbent article No. The same is true when compared with 4.

In addition, the simple absorbent article No. 1 and No. No. 2 is a simple absorbent article No. 3 and No. The second absorber retention rate was higher than that of 4. This means that even if the amount of physiological saline absorbed increases, the particles No. 2 contained in these first absorbers. No. 1 seems to have been able to positively deliver the physiological saline solution to the second absorber. On the other hand, the simple absorbent article No. 3 and No. In No. 4, it is suggested that as the amount of the physiological saline solution increased, the SA60S modifier contained in these first absorbers blocked, making it difficult to deliver the physiological saline solution to the second absorber.

Further, when the first absorber was observed after the measurement of the absorption time and the rewet was completed, the simple absorbent article No. 1 and No. In 2, the particle No. No. 1 did not protrude from the spunbonded non-woven fabric, but the simple absorbent article No. 1. 3 and No. In No. 4, it was observed that a part of the SA60S-adjusted material protruded out of the spunbonded non-woven fabric.

1 Absorbent article 3 Liquid permeable sheet 5 Absorbent 7 Liquid impermeable sheet 9 Absorbent core 11 Water-absorbent polymer particles 13 Pulp fiber 15 Core wrap 21 1st absorber 23 2nd absorber 25 Water-absorbent polymer particle layer 27 1st Core wrap 29 Water-absorbent polymer powder 31 Pulp fiber 33 2nd absorption core 35 2nd core wrap 101 Leakage-proof wall 103 Elastic member 105 Fixed part 107 Elastic member 109 Tape solvent 201 Polymerization device 203 Polymerization composition tank 205 Metering pump 207 Liquid transfer tube 209 Light irradiation chamber 211 Light source 213 Injection nozzle 215 Rectifying perforated board 217 Forming tube 219 Separation screen 221 Hydrophobic solvent tank 223 Metering pump 225 Temperature regulator 227 Liquid transfer tube 301 Water-absorbent polymer water-containing particles 303 Polymerized composition 305 Hydrophobic solvent 307 Liquid drop

Claims (17)

An absorbent article comprising a liquid permeable sheet, an absorber and a liquid impermeable sheet.
The absorber has a water retention ratio (mass ratio) of 45 to 110 times with respect to physiological saline in a water retention test and a gel strength with water absorption of 20 to 50 mN with respect to physiological saline in a gel strength test during water absorption. Contains multiple water-absorbent polymer particles
The plurality of water-absorbent polymer particles include a skeleton derived from an ethylene-based unsaturated monomer and a skeleton derived from a cross-linking agent.
The skeleton derived from the ethylene-based unsaturated monomer contains a skeleton derived from a neutralized product of (meth) acrylic acid.
The absorbent article. The first aspect of the present invention, wherein the plurality of water-absorbent polymer particles contain a skeleton derived from the cross-linking agent at a ratio of 0.02 to 0.15 mol% with respect to a skeleton derived from the ethylene-based unsaturated monomer. The absorbent article described. The absorbent article according to claim 1 or 2 , wherein the plurality of water-absorbent polymer particles have a breaking strength of 20 N or more. The absorbent article according to any one of claims 1 to 3 , wherein the plurality of water-absorbent polymer particles have a dust generation rate of 0.00 to 0.20% by mass in a dust generation test. The absorbent article according to any one of claims 1 to 4 , wherein the plurality of water-absorbent polymer particles have an average sphericity of 0.90 to 0.99. The absorbent article according to any one of claims 1 to 5 , wherein the plurality of water-absorbent polymer particles have an average particle size of 300 to 800 μm. The absorbent article according to any one of claims 1 to 6 , wherein the plurality of water-absorbent polymer particles have a coefficient of variation of a particle size of 0.01 to 0.20. The absorber includes a first absorber and a second absorber that is closer to the liquid impermeable sheet than the first absorber.
The absorbent article according to any one of claims 1 to 7 , wherein the first absorbent contains a water-absorbent polymer particle layer composed of the plurality of water-absorbent polymer particles. The absorbent article according to claim 8 , wherein the plurality of water-absorbent polymer particles have a suction height of 15 to 40 mm with respect to physiological saline in a suction test. The first aspect of any one of claims 1 to 9 , wherein the second absorber comprises a second absorbent core and a second core wrap, and the second absorbent core comprises pulp and a plurality of water-absorbing polymer powders. Absorbent article. A method for producing multiple water-absorbent polymer particles for absorbent articles.
A release step of releasing a polymerization composition containing an ethylene-based unsaturated monomer containing a neutralized product of (meth) acrylic acid , a radical polymerization initiator , a cross-linking agent and water into a hydrophobic solvent as a plurality of droplets.
A polymerization step of polymerizing the polymerization composition in the plurality of droplets in the hydrophobic solvent to form a plurality of water-absorbing polymer water-containing particles from the plurality of droplets.
A step of taking out the plurality of water-absorbent polymer water-containing particles from the hydrophobic solvent, and a particle forming step of drying the plurality of water-absorbent polymer water-containing particles to form the plurality of water-absorbent polymer particles.
Including
The plurality of water-absorbent polymer particles have a water retention ratio (mass ratio) of 45 to 110 times with respect to the physiological saline in the water retention test and a water absorption of 20 to 50 mN with respect to the physiological saline in the gel strength test during water absorption. Has gel strength,
The above-mentioned method. The method according to claim 11 , wherein the polymerization composition contains the cross-linking agent in a ratio of 0.02 to 0.15 mol% with respect to the ethylene-based unsaturated monomer. The method according to claim 11 or 12 , wherein the plurality of droplets have a coefficient of variation of a droplet diameter of 0.01 to 0.20. The claim that the radical polymerization initiator is a photo-radical polymerization initiator, and in the polymerization step, the plurality of droplets are irradiated with light to photopolymerize the polymerization composition in the plurality of droplets. The method according to any one of 11 to 13 . Any of claims 11 to 14 , wherein in the polymerization step, the temperature of the hydrophobic solvent when polymerizing the polymerization composition in the plurality of droplets is in the range of more than 0 ° C. and 30 ° C. or lower. The method described in paragraph 1. The method according to any one of claims 11 to 15 , wherein the plurality of water-absorbent polymer particles have an average particle size of 300 to 800 μm. The method according to any one of claims 11 to 16 , wherein the plurality of water-absorbent polymer particles have a coefficient of variation of a particle size of 0.01 to 0.20.

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