JP2018053043A - Plurality of water-absorbing polymer particles, and method for producing plurality of water-absorbing polymer particles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plurality of water-absorbing polymer particles which have a predetermined water retention ratio to water and a predetermined gel strength at the time of water absorption to water, have high water retention, and resist collapsing under pressurization in a high water retention state.SOLUTION: A plurality of water-absorbing polymer particles have a water retention ratio (mass ratio) of 500-1,000 times to water in a water retention test, and a gel strength at the time of water absorption of 60-200 mN to water in a water-absorbing gel strength test.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a plurality of water-absorbing polymer particles and a method for producing a plurality of water-absorbing polymer particles.

  Water-absorbing polymer particles are used for absorbent articles (for example, disposable diapers, sanitary napkins, etc.), agricultural and horticultural materials (for example, water retention agents, soil conditioners, etc.), industrial materials (for example, water-stopping agents for cables, condensation) It is used in a wide range of fields such as inhibitors. The water-absorbing polymer particles have been improved from various viewpoints.

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

Patent Document 2 describes a water-absorbent resin that has both high water retention ability and high gel strength characteristics that can suppress the gel blocking phenomenon and prevent a decrease in liquid permeation rate. The water absorbent resin described in Patent Document 2 has the following configuration.
Water-absorbent resin that satisfies the following conditions (1) and (2):
(1) The 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 times swelling, the gel strength b at 40 times swelling, and the gel strength c at 50 times swelling is 5500 Pa or more,
However, the gel strength a at 30 times swelling is the gel strength when the gel is swelled by adding physiological saline so that the total mass of the gel and physiological saline is 30 times the mass of the gel, The gel strength b at 40 times swelling is the gel strength when the saline is added to the gel and swollen so that the total mass of the gel and physiological saline is 40 times the mass of the gel, 50 times The gel strength c at the time of swelling is the gel strength when the saline is added to the gel and swollen so that the total mass of the gel and physiological saline is 50 times the mass of the gel.

Japanese Patent Laid-Open 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 that can suppress the gel blocking phenomenon, but even when body pressure is applied in a high water retention state, It does not have such a gel strength that the water-absorbent resin is not crushed.
Accordingly, the present disclosure provides a plurality of water-absorbing polymer particles having a predetermined water retention ratio with respect to water and a predetermined gel strength at the time of water absorption with respect to water, having high water retention and being not easily crushed under pressure in a high water retention state. The purpose is to do.

  The present disclosure has a water retention ratio (mass ratio) of 500 to 1,000 times with respect to water in the water retention test, and a gel strength during water absorption of 60 to 200 mN with respect to water in the gel strength test upon water absorption. A plurality of water-absorbing polymer particles were found.

  The water-absorbing polymer particles of the present disclosure have a predetermined water retention ratio with respect to water and a predetermined water absorption gel strength with respect to water, have high water retention and are not easily crushed under pressure in a high water retention state.

FIG. 1 is a schematic diagram for explaining the polymerization apparatus 1. FIG. 1 is a particle size distribution (number basis). FIG. 2 particle size distribution (number basis). FIG. 3 is a particle size distribution (number basis).

Specifically, the present disclosure relates to the following aspects.
[Aspect 1]
In the water retention test, the water retention ratio (mass ratio) of 500 to 1,000 times the water,
In the gel strength test at the time of water absorption, the gel strength at the time of water absorption of 60 to 200 mN with respect to water,
A plurality of water-absorbing polymer particles.

  The plurality of water-absorbing polymer particles have a predetermined water retention ratio with respect to water and a predetermined water absorption gel strength with respect to water, have high water retention properties, and are not easily crushed under pressure in a high water retention state. Further, the plurality of water-absorbing polymer particles have high water retention and are not easily crushed under pressure in a high water retention state. Inconveniences such as popping out of the substrate on which the polymer particles are used, for example, absorbent articles, agricultural / horticultural materials, industrial materials, and the like are less likely to occur.

[Aspect 2]
The water-absorbing polymer particles have a water retention ratio (mass ratio) of 45 to 110 times with respect to physiological saline in a water retention test and a water absorption rate of 20 to 50 mN with respect to physiological saline in a gel strength test at the time of water absorption. The plurality of water-absorbing polymer particles according to aspect 1, having gel strength.

  The plurality of water-absorbing polymer particles have a predetermined water retention ratio with respect to physiological saline and a predetermined water absorption gel strength with respect to physiological saline, and have a high water retention and high water retention state even with respect to ion-containing water. It is hard to crush under pressure. Further, the plurality of water-absorbing polymer particles have high water retention with respect to ion-containing water and are not easily crushed under pressure in a high water retention state. The water-absorbing polymer particles crushed due to the above are less likely to jump out of a substrate on which the water-absorbing polymer particles are used, for example, absorbent articles, agricultural / horticultural materials, industrial materials, and the like.

[Aspect 3]
The plurality of water-absorbing polymer particles according to the aspect 1 or 2, wherein the plurality of water-absorbing polymer particles have a breaking strength of 20 N or more.

  Since the plurality of water-absorbing polymer particles have a predetermined breaking strength, even if they are subjected to a strong impact during transport, for example, even if they are subjected to a strong impact during transportation, a deficient portion (for example, water absorption) Such as cracks on the surface of the water-soluble polymer particles, chipping of a part of the surface, etc.), and the water-absorbing polymer particles are less likely to be crushed due to a defective portion in a highly water-retaining state. In a state, it becomes difficult to be crushed under pressure.

[Aspect 4]
The plurality of water-absorbing polymer particles according to any one of aspects 1 to 3, wherein the plurality of water-absorbing polymer particles have a dust generation rate of 0.00 to 0.20 mass% in a dust generation test.

  Since the water-absorbing polymer particles have a predetermined dust generation rate, even if the water-absorbing polymer particles are subjected to a force that rubs the water-absorbing polymer particles during use, for example, during transportation, the surface of the water-absorbing polymer particles is Defects (such as cracks on the surface of water-absorbing polymer particles, partial chippings on the surface, etc.) are unlikely to occur in the part, and the water-absorbing polymer particles are crushed due to the defect part in a high water retention state. It becomes difficult to occur, that is, it becomes difficult to be crushed under pressure in a high water retention state.

[Aspect 5]
The plurality of water-absorbing polymer particles according to any one of aspects 1 to 4, wherein the plurality of water-absorbing polymer particles have an average sphericity of 0.90 to 0.99.
Since the water-absorbing polymer particles have a predetermined average sphericity, a deficient portion (for example, cracks on the surface of the water-absorbing polymer particles, partial chipping of the surface, etc.) is formed on a part of the surface before water retention. Is less likely to occur. As a result, the water-absorbing polymer particles are less likely to be crushed from the deficient portion due to the small number of deficient portions in the high water retention state, and less likely to crush under pressure in the high water retention state.

[Aspect 6]
The plurality of water-absorbing polymer particles according to any one of aspects 1 to 5, wherein the plurality of water-absorbing polymer particles have a coefficient of variation in particle diameter of 0.01 to 0.20.
In the water-absorbing polymer particles, since the ratio of the water-absorbing polymer particles having a relatively small particle size is small, the water-absorbing polymer particles are used as a substrate on which the water-absorbing polymer particles are used, for example, absorbent articles, agricultural and horticultural It becomes difficult to jump out from industrial materials and industrial materials.

[Aspect 7]
A polymerization composition containing an ethylenically unsaturated monomer, a radical polymerization initiator and water is discharged as a plurality of droplets into a hydrophobic solvent, and the polymerization composition in the plurality of droplets is discharged in the hydrophobic solvent. To form a plurality of water-absorbing polymer water-containing particles from the plurality of droplets, take out the plurality of water-absorbing polymer water-containing particles from the hydrophobic solvent, and dry the plurality of water-absorbing polymer water-containing particles. A plurality of water-absorbing polymer particles produced by:
The water-absorbing polymer particles have a water retention ratio (mass ratio) of 500 to 1,000 times with respect to water in a water retention test, and a gel strength at water absorption of 60 to 200 mN with respect to water in a gel strength test upon water absorption. And having
The plurality of water-absorbing polymer particles as described above.
The plurality of water-absorbing polymer particles have the same effect as that described in Aspect 1.

[Aspect 8]
The plurality of water-absorbing polymer particles according to aspect 7, wherein the plurality of droplets have a coefficient of variation in droplet diameter of 0.01 to 0.20.
When the plurality of droplets have a predetermined droplet diameter variation coefficient, the produced water-absorbing polymer particles tend to have a narrow particle size variation coefficient, and thus the water-absorbing polymer. In the particles, the ratio of water-absorbing polymer particles having a relatively small particle size is reduced, and the water-absorbing polymer particles are a substrate on which the water-absorbing polymer particles are used, for example, absorbent articles, agricultural and horticultural materials, industrial It becomes difficult to jump out from materials.

[Aspect 9]
The aspect 7 or 8, wherein the radical polymerization initiator is a photo radical polymerization initiator, and the polymerization composition in the plurality of droplets is photopolymerized by irradiating the plurality of droplets with light. A plurality of water-absorbing polymer particles.
When the radical polymerization initiator is a photo radical polymerization initiator, the plurality of water-absorbing polymer particles to be produced have high water retention and are not easily crushed under pressure in a high water retention state.

[Aspect 10]
The plurality of the embodiments according to any one of aspects 7 to 9, wherein 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 less. Water-absorbing polymer particles.
When the temperature of the hydrophobic solvent is in a predetermined range, the plurality of water-absorbing polymer particles produced have high water retention and are not easily crushed under pressure in a high water retention state. Further, the plurality of water-absorbing polymer particles are unlikely to contain bubbles.

[Aspect 11]
A method for producing a plurality of water-absorbing polymer particles, comprising:
Releasing a polymerization composition comprising an ethylenically unsaturated monomer, a radical polymerization initiator and water into a hydrophobic solvent as a plurality of droplets;
Polymerizing the polymerization composition in the plurality of droplets in the hydrophobic solvent to form a plurality of water-absorbing polymer-containing particles from the plurality of droplets; and from the hydrophobic solvent, Removing the water-absorbing polymer water-containing particles and drying the plurality of water-absorbing polymer water-containing particles to form the plurality of water-absorbing polymer particles;
The water-absorbing polymer particles have a water retention ratio (mass ratio) of 500 to 1,000 times with respect to water in the water retention test and a water absorption of 60 to 200 mN with respect to water in the gel strength test during water absorption. Having gel strength,
The above manufacturing method.
The plurality of water-absorbing polymer particles produced by the method for producing the plurality of water-absorbing polymer particles have the same effect as that of the first aspect.

[Aspect 12]
Aspect 11 wherein in the step of releasing, the plurality of droplets are discharged into the hydrophobic solvent such that the plurality of droplets have a coefficient of variation in droplet diameter of 0.01 to 0.20. Manufacturing method.

  In the above manufacturing method, each of the plurality of droplets is released into the hydrophobic solvent so as to satisfy a predetermined variation coefficient of the droplet diameter. It tends to have a coefficient of variation in diameter. As a result, the individual particles of the plurality of water-absorbing polymer particles tend to have uniform characteristics, and as a result, the plurality of water-absorbing polymer particles tend to have a high water retention ratio, a high gel strength during water absorption, and the like.

[Aspect 13]
The radical polymerization initiator is a radical photopolymerization initiator, and in the step of forming the water-absorbing polymer water-containing particles, the polymerization in the plurality of droplets is performed by irradiating the plurality of droplets with light. The production method according to aspect 11 or 12, wherein the composition is photopolymerized.

  In the above production method, since the plurality of water-absorbing polymer particles are produced by photopolymerization, the produced plurality of water-absorbing polymer particles have a predetermined water retention ratio with respect to water and a predetermined water absorption gel strength with respect to water. It becomes easy to have. Moreover, the said manufacturing method is completed in a short time compared with the case where it manufactures by thermal polymerization.

[Aspect 14]
The manufacturing method as described in any one of aspects 11-13 in which the temperature of the said hydrophobic solvent exists in the range of more than 0 degreeC and 30 degrees C or less in the step which forms a some water absorbing polymer water-containing particle | grain.

  In the above production method, the step of forming the water-absorbing polymer water-containing particles is carried out at a predetermined temperature, so that the water-absorbing polymer water-containing particles are less likely to enter air bubbles, and the water in the plurality of droplets is less likely to volatilize and form. Since the plurality of water-absorbing polymer water-containing particles are easily maintained in volume, the plurality of water-absorbing polymer particles to be produced are likely to have a predetermined average sphericity. In addition, it is difficult to chip before water retention, and thus is not easily crushed under pressure in a state of high water retention. In addition, the plurality of water-absorbing polymer particles that are formed are less likely to contain bubbles.

[Aspect 15]
The production method according to any one of aspects 11 to 14, wherein the hydrophobic solvent is selected from the group consisting of silicone oil, oil and hydrocarbon, and any combination thereof.
In the manufacturing method, the plurality of water-absorbing polymer particles to be manufactured are likely to have a predetermined average sphericity and a coefficient of variation of a predetermined particle size.

[Definition]
・ "Water absorbent polymer particles" and "Water absorbent polymer powder"
In the present specification, “water-absorbing polymer particles” and “water-absorbing polymer powder” are used separately.
The “water-absorbing polymer particle” means a particle having a predetermined water retention ratio and a predetermined gel strength at the time of water absorption, which is a target of the present disclosure. “Water-absorbing polymer powder” is a superabsorbent polymer known in the art, manufactured by a known production method such as a reverse phase suspension polymerization method, a solution polymerization method, a gas phase method, or the like. Means.

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

Hereinafter, a plurality of water-absorbing polymer particles of the present disclosure and a method for producing the plurality of water-absorbing polymer particles will be described in detail.
<Multiple water-absorbing polymer particles>
A plurality of water-absorbing polymer particles of the present disclosure (hereinafter may be simply referred to as “water-absorbing polymer particles”) are 500 to 1,000 times, preferably 700 to 950 times, with respect to water, in water retention tests, and More preferably, it has a water retention ratio (mass ratio) of 800 to 900 times. By doing so, the water-absorbing polymer particles can keep a large amount of water inside. As a result, even when force or the like is applied to the water-absorbing polymer particles, it becomes difficult to release the absorbed water.

In the present specification, the water retention test described above is performed as follows.
(1) A sample of water-absorbing polymer particles is allowed to stand for 24 hours in a constant temperature and humidity chamber at a temperature of 20 ± 5 ° C. and a humidity of 65 ± 5% RH.
(2) Mass of sample of about 20 mg: m ₁ (g) is accurately weighed, and about 22 mL of ion-exchanged water (about 1,100 times the mass of the sample) is added to the weighed sample and allowed to stand for 3 hours. Swell the sample.
(3) The sample is put into a bag formed of nylon mesh having an opening of 75 μm, and the bag containing the sample is dehydrated with a centrifuge at 150 G for 90 seconds.

(4) A sample is taken out of the bag and its mass: m ₂ (g) is measured.
(5) Sample water retention ratio (mass ratio): W _HR is _expressed by the following formula:
W _HR = 100 × (m ₂ −m ₁ ) / m ₁
Calculated by
(6) Steps (1) to (5) are repeated three times with different samples, and the water retention magnification of three samples: the arithmetic average of W _HR is adopted as the water retention magnification.

  The water-absorbing polymer particles of the present disclosure have a water-absorbing gel strength of 60 to 200 mN, preferably 80 to 160 mN, and more preferably 100 to 140 mN with respect to water in the water-absorbing gel strength test. By doing so, the water-absorbing polymer particles of the present disclosure are not easily crushed even if a force is applied in a high water retention state. As a result, in use, in a highly water-retaining state, a part of the water-absorbing polymer particles crushed by pressurization is a substrate on which the water-absorbing polymer particles are used, for example, absorbent articles, agricultural and horticultural materials, Problems such as jumping out of industrial materials are less likely to occur.

  Further, in this technical field, it is known that there is a negative correlation between the water retention ratio (water absorption amount) of the water-absorbing polymer particles and the particle strength at the time of swelling. Compared with conventional water-absorbing polymer particles, both a high water retention ratio and a high gel strength at the time of water absorption are achieved.

In this specification, the above-mentioned gel strength test at the time of water absorption is implemented as follows.
(1) Minebea Technograph TG-500N is prepared in a constant temperature and humidity chamber of temperature: 20 ± 5 ° C. and humidity: 65 ± 5% RH.
(2) The sample of water-absorbing polymer particles is left in the constant temperature and humidity chamber for 24 hours.
(3) The weight of a sample of about 10 mg is accurately weighed, 10 g of ion exchange water is added per 10 mg of sample, and the sample is allowed to stand for 3 hours to swell the sample.

(4) One swollen particle from the swollen sample is placed on a sample stage of Technograph TG-500N, and the swollen particle is compressed at a speed 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 an arithmetic average of the above loads for 50 times is adopted as the gel strength during water absorption.

  When the water-absorbing polymer particles of the present disclosure are used for applications that absorb ion-containing water, such as absorbent articles, the water-absorbing polymer particles of the present disclosure are preferably used for physiological saline in water retention tests. It has a water retention ratio (mass ratio) of 45 to 110 times, more preferably 55 to 95 times, and still more preferably 60 to 85 times. By doing so, the water-absorbing polymer particles of the present disclosure can keep a large amount of ion-containing water therein. As a result, even when force or the like is applied to the water-absorbing polymer particles, it becomes difficult to release the absorbed water.

  In the above water retention test, when measuring the water retention ratio with respect to physiological saline, instead of “about 22 mL of ion-exchanged water (about 1,100 times the mass of the sample)”, “physiological saline about 3 0.0 mL (about 150 times the mass of the sample) ”is added.

  When the water-absorbing polymer particles of the present disclosure are used for applications that absorb ion-containing water, such as absorbent articles, the water-absorbing polymer particles of the present disclosure are The gel strength is preferably 20 to 50 mN, more preferably 23 to 45 mN, and even more preferably 25 to 40 mN. By doing so, the water-absorbing polymer particles of the present disclosure are not easily crushed even if force is applied when ion-containing water is retained. As a result, in use, the water-absorbing polymer particles are crushed by pressurization in a highly retained state of ion-containing water, and the water-absorbing polymer particles are used, for example, absorbent articles, agricultural and horticultural materials It becomes difficult to jump out from industrial materials.

  In the gel strength test at the time of water absorption, when measuring the gel strength at the time of water absorption with respect to physiological saline, instead of “10 g of ion-exchanged water” per 10 mg of the sample, about 10 mg of the accurately weighed sample, Add 1g of normal saline.

The water-absorbing polymer particles of the present disclosure preferably have a breaking strength of 20 N or more, more preferably 30 N or more, even more preferably 40 N or more, and even more preferably 50 N or more. By doing so, even when the water-absorbing polymer particles are subjected to a strong impact during transportation, for example, before use, a defect portion (for example, the surface of the water-absorbing polymer particles) Cracks, partial chipping of the surface, etc.), and the water-absorbing polymer particles are less likely to be crushed due to the defective portion in the high water retention state, that is, under pressure in the high water retention state. It becomes difficult to be crushed.
The breaking strength was measured in the same manner as the gel strength test at the time of water absorption except that the step (3) was omitted. In the steps (4) and (5), “swelled sample” and “swelled particles” And “sample” and “particle”, respectively. The upper limit of the load is 50N.

  The water-absorbing polymer particles of the present disclosure are preferably 0.00 to 0.20% by mass, more preferably 0.00 to 0.15% by mass, and still more preferably 0.00 to 0.10% in the dust generation test. %, And even more preferably 0.00 to 0.05% by weight. By doing so, even when the water-absorbing polymer particles are subjected to a force that rubs the water-absorbing polymer particles before use, for example, during transportation, a deficient portion is formed on a part of their surface. And the water-absorbing polymer particles are less likely to be crushed due to the defective portion in the high water retention state, that is, are not easily crushed under pressure in the high water retention state.

  In addition, when the water-absorbing polymer particles are produced, the fine powder generated from the water-absorbing polymer particles may contaminate the production line when the water-absorbing polymer particles are applied to an article, for example, an absorbent article. Becomes lower. Moreover, the possibility that fine powder generated from the water-absorbing polymer particles leaks out from the article to which the water-absorbing polymer particles of the present disclosure are applied is reduced.

In the present specification, the above dust generation test is performed as follows.
(1) Prepare an Excel auto homogenizer manufactured by NISSEI in a constant temperature and humidity chamber of temperature: 20 ± 5 ° C. and humidity: 65 ± 5% RH.
(2) A sample of water-absorbing polymer particles is passed through a sieve having an opening of 150 μm and left in the constant temperature and humidity chamber for 24 hours.
(3) Mass of approximately 10 g of sample: m ₃ (g) is accurately weighed, the sample is put into a homogenizer, and the sample is stirred for 1 minute at a rotation speed of 1,000 rpm.

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

  The water-absorbing polymer particles of the present disclosure preferably have an average sphericity of 0.90 to 0.99, more preferably 0.92 to 0.98, and even more preferably 0.93 to 0.97. By doing so, it becomes difficult to produce a defective part in a part of those surfaces before water retention. As a result, the water-absorbing polymer particles are less likely to be crushed from the deficient portion due to the small number of deficient portions in the high water retention state, and less likely to crush under pressure in the high water retention state.

  The water-absorbing polymer particles of the present disclosure preferably have a coefficient of variation in particle size of 0.01 to 0.20, more preferably 0.03 to 0.15, and even more preferably 0.05 to 0.10. By doing so, in the water-absorbing polymer particles of the present disclosure, the ratio of the water-absorbing polymer particles having a relatively small particle size is reduced. It becomes difficult to jump out from materials such as absorbent articles, agricultural and horticultural materials, industrial materials and the like.

In the present specification, the particle diameter of the water-absorbing polymer particles (particle diameter of each water-absorbing polymer particle), the average particle diameter, the coefficient of variation of the particle diameter, and the average sphericity are measured as follows.
(1) A digital microscope (trade name: VHX-1000, zoom lens: x20 to x200) manufactured by Keyence Co., Ltd. and attached to a constant temperature and humidity chamber of temperature: 20 ± 5 ° C. and humidity: 65 ± 5% RH Prepare the software.
(2) The sample of water-absorbing polymer particles is left in the constant temperature and humidity chamber for 24 hours.
(3) Take a sample with the 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 diameter of each particle means the equivalent circle diameter calculated from the projected area of the projected image of each particle. Specifically, the projected area A of each particle is measured with the attached software, and the equivalent circle diameter CD of each particle is expressed by the following formula:

Calculate from
(5) The average particle diameter means the median diameter ( ⁵⁰ D _p ) in the particle size distribution (number basis). Specifically, the attached software creates a particle size distribution (number basis) of 1,000 circle-equivalent diameter CDs of water-absorbing polymer particles, and the median diameter ( ⁵⁰ D _p ) from the particle size distribution (number basis). To decide.

(6) The coefficient of variation of the particle size is calculated from the particle size distribution (number basis) with the attached software.
(7) Average sphericity: S _p is the arithmetic mean of 1,000 water-absorbing polymer particles or sphericity s _p. Specifically, the sphericity of the water-absorbing polymeric particles: s _p from the outer edge of the water-absorbing polymer particles, the major axis is the longest diameter: k ₁ and minor axis is the shortest diameter: k ₂ and Measure the following formula:
s _p = k ₂ / k ₁
Calculated by The major axis: k ₁ and minor axis: k ₂ of each particle are automatically determined by the attached software.

  The water-absorbing polymer particles of the present disclosure preferably have a particle size dispersion coefficient of 0.05 to 0.50, more preferably 0.10 to 0.30, and even more preferably 0.12 to 0.20. By doing so, in the water-absorbing polymer particles of the present disclosure, the ratio of the water-absorbing polymer particles having a relatively small particle size is reduced, and as a result, the water-absorbing polymer particles are a group in which the water-absorbing polymer particles are used. It becomes difficult to jump out from materials such as absorbent articles, agricultural and horticultural materials, industrial materials and the like.

The above-mentioned particle size dispersion coefficient (δ) is 10% particle diameter: ¹⁰ D _p , median diameter: ⁵⁰ D _{p in the} particle size distribution (number basis) of the equivalent circular diameter CD of the above-mentioned 1,000 water-absorbing polymer particles. And 90% particle size: ⁹⁰ _Dp , the following formula:
_{^{δ = (90 D p - 10}} D p) / 50 D p
Is calculated by

In the water absorption test, the water-absorbing polymer particles of the present disclosure are preferably 700 to 1,500 times, more preferably 800 to 1,200 times, and still more preferably 900 to 1,100 times, (Mass ratio). By doing so, the water-absorbing polymer particles of the present disclosure can achieve both a predetermined water absorption ratio and a predetermined gel strength during water absorption.
In this technical field, it is known that there is a negative correlation between the water absorption capacity (water absorption amount) of the water-absorbing polymer particles and the particle strength at the time of swelling. Compared to conventional water-absorbing polymer particles, both a high water absorption ratio and a high gel strength at the time of water absorption are achieved.

In this specification, the above-mentioned water absorption test is implemented as follows.
(1) A sample of water-absorbing polymer particles is allowed to stand for 24 hours in a constant temperature and humidity chamber at a temperature of 20 ± 5 ° C. and a humidity of 65 ± 5% RH.
(2) Mass of approximately 30 mg of sample: m ₅ (g) is accurately weighed, and about 60 mL of ion-exchanged water (approximately 2,000 times the mass of the sample) is added to the weighed sample and allowed to stand for 3 hours. Swell the sample.
(3) A sample is taken out on a polyamide fiber mesh sheet, the moisture adhering to the surface of the water-absorbent polymer particles is wiped off with filter paper, and the mass of the swollen sample: m ₆ (g) is measured.
(4) Sample water absorption ratio (mass ratio): _WAR , the following formula:
W _AR = 100 × (m ₆ −m ₅ ) / m ₅
Calculated by
(5) in different samples, repeat step (1) to step (4) three times, absorbency of three samples: the arithmetic mean of the W _AR adopted as absorption capacity.

  When the water-absorbing polymer particles of the present disclosure are used for an application that absorbs ion-containing water, such as an absorbent article, the water-absorbing polymer particles of the present disclosure are used for physiological saline in the water absorption test described above. Preferably, it has a water absorption ratio (mass ratio) of 60 to 120 times, more preferably 70 to 100 times, and still more preferably 75 to 90 times. By doing so, the water-absorbing polymer particles of the present disclosure can absorb a large amount of ion-containing water.

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

  The water-absorbing polymer particles of the present disclosure have a wicking 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 wicking test. This is from the viewpoint of water uptake by the water-absorbing polymer particles of the present disclosure.

In the present specification, the above-described suction test is performed as follows.
(1) A sample of water-absorbing polymer particles is allowed to stand for 24 hours in a constant temperature and humidity chamber at a temperature of 20 ± 5 ° C. and a humidity of 65 ± 5% RH.
(2) A 1.0 g sample is weighed, and the sample height is made uniform in a cylinder (inner diameter: 25 mm, height: 30 mm) in which a nylon mesh with an opening of 75 μm is stretched on the bottom. Adjust the position.
(3) Two spacers (length: 25 mm × width: 5 mm × height: 0.5 mm) are put in a petri dish (inner diameter: 90 mm, height: 15 mm), and then in the petri dish, Pour 24 mL of colored ion-exchanged water (containing 1 g of Blue No. 1 per liter of ion-exchanged water).

(4) Place the cylinder on which the sample is placed on the two spacers so that the bottom surface faces downward, and allow the sample to suck up ion-exchanged water that has passed through the nylon mesh on the bottom surface.
When the sample absorbs colored ion-exchanged water, the swollen portion colored in blue rises and the interface between the swollen portion and the unswelled portion also rises.
(5) Two hours after placing the cylinder in the petri dish, the height of the lowest part of the boundary surface is measured from the bottom surface (nylon mesh) of the cylinder.
(6) The test is performed a total of 10 times with different samples, and an arithmetic average of 10 heights is adopted as the suction height.
(7) The uniform wicking property of the boundary surface is evaluated in the following three stages.
○: The boundary surface is almost flat, and the uptake of ion-exchanged water is uniform.
(Triangle | delta): There exists an unevenness | corrugation in a boundary surface, and the suction of ion-exchange water is not uniform.
X: The unevenness | corrugation of a boundary surface is large and the suction of ion-exchange water is very non-uniform | heterogenous.

  The water-absorbing polymer particles of the present disclosure preferably have a wicking height of 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 wicking test. By doing so, the water-absorbing polymer particle of this indication is excellent in the wicking property with respect to ion-containing water.

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

The average particle diameter of the water-absorbing polymer particles of the present disclosure 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. It is. For example, when the water-absorbing polymer particles are used in an absorbent article, they can have an average particle size of 300 to 800 μm.
In addition, the measuring method of an average particle diameter is as the above-mentioned.

  The water-absorbing polymer particles of the present disclosure preferably have an average particle size having a particularly high effect as compared to the water-absorbing polymer powder produced by the reverse phase suspension polymerization method, preferably 300 to 1,000 μm, and more preferably 300-800 micrometers is mentioned. In the reversed-phase suspension polymerization method, as a primary particle, a water-absorbing polymer powder having an average particle size of 50 to 100 μm is produced, and in order to produce a water-absorbing polymer powder having an average particle size higher than that, granulation is performed. It is necessary to do. Since the water-absorbing polymer particles of the present disclosure can have the above average particle size as primary particles without granulation, the water-absorbing polymer produced by the reverse phase suspension polymerization method is within the above average particle size range. Compared to the polymer powder, it has an effect that a deficient portion is hardly formed on a part of the surface before water retention, and is less likely to be crushed under pressure after water retention.

  The water-absorbing polymer particles of the present disclosure can have a monomer skeleton that is generally used in the art. For example, the monomer skeleton exemplified in “Method for producing a plurality of water-absorbing polymer particles” described below, for example, , A skeleton derived from an ethylenically unsaturated monomer, a skeleton derived from a crosslinking agent, and the like.

  In use, the plurality of water-absorbing polymer particles of the present disclosure can exist as a simple substance, can exist as two or more lumps, and can exist in a state where the simple substance and the lumps coexist. . This is because the effects of the present disclosure can be exhibited both in a simple substance and in a lump.

When the plurality of water-absorbing polymer particles of the present disclosure forms a lump upon use, the lump is, for example, 2 times or more, 3 times or more, 4 times the average particle diameter of the water-absorbing polymer particles. Thus, the thickness of the thinnest part can be 5 times or more.
The agglomerate can have a high filling rate, for example, 40% or more, 50% or more, and 60% or more.

  The water-absorbing polymer particles of the present disclosure include absorbent articles (for example, disposable diapers, sanitary napkins, etc.), agricultural and horticultural materials (for example, water retention agents, soil conditioners, etc.), industrial materials (for example, waterstops for cables) Agent, anti-condensation agent, etc.).

<Method for producing a plurality of water-absorbing polymer particles>
The above-described plurality of water-absorbing polymer particles are produced by the method for producing a plurality of water-absorbing polymer particles of the present disclosure (hereinafter, sometimes simply referred to as “the production method of the present disclosure”). The manufacturing method of the present disclosure includes the following steps.
(I) A step of releasing a polymerization composition containing an ethylenically unsaturated monomer, a radical polymerization initiator, and water into a hydrophobic solvent as a plurality of droplets (hereinafter sometimes referred to as a “droplet release step”).
(Ii) 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 (hereinafter referred to as “water-absorbing polymer water-containing”). Sometimes referred to as "particle formation step")
(Iii) removing the plurality of water-absorbing polymer-containing particles from the hydrophobic solvent, and drying the plurality of water-absorbing polymer-containing particles to form the plurality of water-absorbing polymer particles (hereinafter referred to as “water absorption”). May be referred to as a “adhesive polymer particle forming step”)

[Droplet release step]
The polymerization composition in the droplet discharge step includes an ethylenically unsaturated monomer, a radical polymerization initiator, water and the like.
The ethylenically unsaturated monomer is not particularly limited as long as it is used in this technical field, and examples thereof include (meth) acrylic acid monomers. In addition, (meth) acrylic acid means acrylic acid and / or methacrylic acid.
The polymerization composition contains the ethylenically unsaturated monomer in a proportion 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, (meth) acrylic acid non-neutralized product), (meth) acrylic acid neutralized product, and (meth) acrylic acid derivatives. Examples thereof include esterified products.
Examples of the neutralized product of (meth) acrylic acid include alkali metal salts of (meth) acrylic acid. As said alkali metal salt, lithium, sodium, potassium salt etc. are mentioned, for example, Sodium and potassium salt are preferable.

  When the water-absorbing polymer particles formed from the polymerization composition have a monomer skeleton derived from a (meth) acrylic acid monomer, the water-absorbing polymer particles are derived from a derivative of (meth) acrylic acid. Except for the monomer skeleton, 85 to 100 mol% of the acid groups (carboxyl groups) are preferably neutralized.

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

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

  Examples of the crosslinking 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, penta Erythritol 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 include pentaerythritol polyglycidyl ether.

Examples of the radical polymerization initiator include a photo radical polymerization initiator and a thermal radical polymerization initiator. From the viewpoint of the characteristics of the water-absorbing polymer particles to be formed, the radical polymerization initiator is preferably a photo radical polymerization initiator, and when the radical polymerization initiator includes a thermal radical polymerization initiator, It is preferably used in combination with a radical polymerization initiator.
The polymerization composition contains the radical polymerization initiator in an amount of preferably 0.001 to 20% by mass and more preferably 0.1 to 10% by mass with respect to the ethylenically unsaturated monomer.

  As the photo radical polymerization initiator, those capable of generating radicals by light having a wavelength of about 200 nm to about 600 nm are preferable. For example, benzoin, acetoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzophenone, benzyl, Examples include Michler's ketone, xanthone, chlorothioxanthone, isopropylthioxanthone, benzyldimethyl ketal, naphthol, anthraquinone, hydroxyanthracene, acetophenone diethyl ketal, α-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methylphenylpropane, and any combination thereof. It is done.

  Examples of the thermal radical polymerization initiator include azobisisobutyronitrile, 4,4′-azobis (4-cyanovaleric acid), 1,1′-azobis (cyclohexanecarbonitrile), 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-butyl peroxyacetate, t-butyl peroxyisobutyrate, t-butyl peroxypivalate, methyl ethyl ketone peroxide, cyclohexanone peroxide, hydrogen peroxide, ammonium persulfate, Persulfuric acid Potassium, and the like.

  The temperature of the droplets of the polymerization composition is generated by the polymerization of the ethylenically unsaturated monomer due to the fact that the polymerization composition contains water and is released into a hydrophobic solvent kept at a constant temperature. It becomes difficult to rise. Most of the water is removed after forming the water-absorbing polymer-containing particles from the polymerization composition.

The hydrophobic solvent is not particularly limited as long as it is not miscible with the polymerization composition and does not react with the components in the polymerization composition. Moreover, it is preferable that the said hydrophobic solvent has specific gravity close | similar to a polymerization composition from a viewpoint of ensuring time for a 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), those Arbitrary combinations etc. are mentioned.
The temperature of the hydrophobic solvent is preferably in the range of more than 0 ° C. and 30 ° C. or less. By doing so, the water-absorbing polymer particles to be produced have high water retention and are not easily crushed under pressure in a high water retention state. Further, the plurality of water-absorbing polymer particles are unlikely to contain bubbles.

  The release method is not particularly limited as long as the polymerization composition is released as droplets in the hydrophobic solvent. For example, the polymerization composition can be used as droplets using a polymerization apparatus including an injection nozzle. Released into hydrophobic solvent. Specifically, with the tip of the injection nozzle immersed in a hydrophobic solvent, the polymerization composition is directly and quantitatively injected from the injection nozzle into the hydrophobic solvent. The above-described droplet is formed. Examples of the amount of the polymerization composition injected from the injection nozzle include 30 to 60 mL / second. As the injection nozzle, those described in Japanese Patent Application Laid-Open No. 2008-11765 can be used, and will be described later in connection with the polymerization apparatus 1 shown in FIG. The polymerization composition is preferably released as droplets inside the hydrophobic solvent. This is to maintain the shape of the droplet.

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

In addition, since the plurality of droplets have the above-described variation coefficient of the droplet diameter, the individual particles of the plurality of water-absorbing polymer particles tend to have uniform characteristics, and thus the plurality of water-absorbing polymers. The particles tend to have a high water retention ratio, a high gel strength upon water absorption, and the like.
The variation coefficient of the droplet diameter can be measured in the same manner as the measurement method of the variation coefficient of the water-absorbing polymer particles described above.

[Water-absorbing polymer water-containing particle forming step]
In the water-absorbing polymer water-containing particle forming step, the polymer composition in the plurality of droplets is polymerized in a hydrophobic solvent to form a plurality of water-absorbing polymer water-containing particles.

  When the radical polymerization initiator is a photo radical polymerization initiator, light, for example, from about 200 nm to about 200 nm to a light source such as a mercury lamp, a fluorescent lamp, a xenon lamp, a carbon arc lamp, a metal halide lamp, or a UV-LED lamp. For example, light having a wavelength of about 600 nm is irradiated onto a forming tube including a hydrophobic solvent and a plurality of droplets, and the polymerization composition is photopolymerized in each of the plurality of droplets, and from each of the plurality of droplets, Water-absorbing 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 light irradiated from the light source. Moreover, it is preferable that the said formation tube has the high transmittance | permeability with respect to the wavelength of the light irradiated from a light source, for example, is formed from quartz glass.

  When the radical polymerization initiator contains only a photo radical polymerization initiator, the polymerization composition and the hydrophobic solvent are preferably not heated. This is because the plurality of water-absorbing polymer water-containing particles and thus the plurality of water-absorbing polymer particles that are formed are less likely to contain bubbles.

  When the radical polymerization initiator contains only a 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 of 10 hours half-life temperature or higher. It 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, the polymer composition can be thermally polymerized in each of the plurality of droplets, and water-absorbing 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 in the hydrophobic solvent, and the polymerization composition may not easily form droplets.

  When the radical polymerization initiator includes both a photo radical 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 in the hydrophobic solvent, and the polymerization composition may not easily form droplets. In addition, the hydrophobic solvent can be maintained at a temperature at which the thermal radical polymerization initiator can function. Furthermore, for example, a polymerization apparatus including a forming tube and a polymerization tank is prepared, and a 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 performed. In the tank, the polymerization composition may be thermally polymerized by maintaining the hydrophobic solvent at a temperature at which the thermal radical polymerization initiator can function.

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

  In the production method of the present disclosure, the droplet discharge step, the water-absorbing polymer water-containing particle forming step, and the water-absorbing polymer particle forming step described above may be performed sequentially, and each step may be performed independently. Good.

  An example of a polymerization apparatus for carrying out the method for producing a plurality of water-absorbing polymer particles of the present disclosure is shown in FIG. In FIG. 1, a polymerization apparatus 1 includes a polymerization composition tank 3 that holds a polymerization composition 103, a metering pump 5 that adjusts the conveyance speed of the polymerization composition 103, a liquid feeding pipe 7 that conveys the polymerization composition 103, A light irradiation chamber 9 having a light source 11, an injection nozzle 13 for injecting a polymerization composition 103, a rectifying perforated plate 15, a forming tube 17 for holding a hydrophobic solvent 105 and photopolymerizing droplets, and water-absorbing polymer water-containing particles 101 are provided. Separation screen 19 for separating from the hydrophobic solvent 105, a hydrophobic solvent tank 21 for holding the hydrophobic solvent 105, a metering pump 23 for adjusting the conveying speed of the hydrophobic solvent 105, and a temperature regulator for adjusting the temperature of the hydrophobic solvent 105 25 and a liquid feeding tube 27 for transporting the hydrophobic solvent 105.

  The hydrophobic solvent 105 circulates between the forming tube 17, the hydrophobic solvent tank 21, the metering pump 23, the temperature controller 25, the liquid feeding tube 27, and the rectifying perforated plate 15, and the circulation speed is determined by the metering pump 23. The temperature of the hydrophobic solvent 105 is controlled by the temperature regulator 25. Most of the forming tube 17 is disposed inside the light irradiation chamber 9.

The polymer composition 103 is supplied from the polymer composition tank 3 to the injection nozzle 13 via the metering pump 5 and the liquid feeding pipe 7. Next, the polymerization composition 103 is ejected from the ejection nozzle 13 and forms droplets 107 in the forming tube 17. Next, the droplet 107 is exposed to light irradiated from the light source 11 in the forming tube 17, and the polymerization composition 103 in the droplet 107 is photopolymerized to form water-absorbing polymer water-containing particles 101. The water-absorbing polymer water-containing particles 101 are separated from the hydrophobic solvent 105 by the separation screen 19.
Next, the water-absorbing polymer water-containing particles 101 are dried to produce water-absorbing polymer particles (not shown).

In this technical field, production methods such as a solution polymerization method, a reverse phase suspension polymerization method, and a gas phase method are known as methods for producing a water-absorbing polymer powder.
In the solution polymerization method, the water-absorbing polymer powder is produced by pulverizing the polymer mass, but since the solution polymerization method includes a step of pulverizing the polymer mass, the produced water-absorbing polymer powder is , Have an irregular shape and tend to be rich in fines. Therefore, since a plurality of water-absorbing polymer powders produced by the solution polymerization method include a portion having a large gap between particles when a lump is formed, water absorption using a capillary phenomenon or the like is performed. Hateful. Further, in a plurality of water-absorbing polymer powders produced by a solution polymerization method, fine powder tends to inhibit water uptake.

Further, in the reverse phase suspension polymerization method, it is difficult to control the particle diameter of the produced water-absorbing polymer powder, and depending on the application, additional steps such as granulation are required. The structure is fragile, tends to cause a defect in a part of their surface before water retention, and tends to collapse under pressure after water retention.
In the reverse phase suspension polymerization method, it is essential to use a surfactant. However, in the production method of the present disclosure, a surfactant may be used. For example, the polymerization composition may contain a surfactant. However, in the production method of the present disclosure, the surfactant may not be used. For example, the polymerization composition may not include the surfactant.

  When the production method of the present disclosure does not use a surfactant, the formed water-absorbing polymer particles do not have a surfactant on the surface thereof. As a result, on the surface of the produced water-absorbing polymer particles, the surfactant is not disposed with its hydrophobic portion facing outward, and the water-absorbing polymer particles absorb water in the hydrophobic portion of the surfactant. Is not hindered.

Furthermore, in the vapor phase method, there is a problem that heat is transmitted to the injection nozzle for injecting the polymerized composition and is easily clogged with the emitted light. Further, the water-absorbing polymer powder produced by the gas phase method has a tendency to retain air bubbles therein, and there are problems from the viewpoint of water retention magnification, gel strength during water absorption, and the like.
In the production method of the present disclosure, the produced water-absorbing polymer particles hardly contain bubbles therein, and the water-absorbing polymer particles have a water retention ratio as compared with the water-absorbing polymer powder produced by a gas phase method. , It has an advantage of excellent gel strength at the time of water absorption.

  In the present specification, drying means drying performed without sublimating moisture. The drying can be performed usually at 0 ° C. or higher, for example, room temperature, preferably high temperature, for example, 40 to 200 ° C. The drying can be performed at 1 atmosphere or under reduced pressure.

Hereinafter, although an example is given and this indication is explained, this indication is not limited to these examples.
[Production Example 1]
90 parts by mass of 60% by mass potassium acrylate (manufactured by Nippon Shokubai) as an ethylenically unsaturated monomer and 10 parts by mass of acrylamide (manufactured by Wako Pure Chemical Industries), and 1.0 mass of benzoin isobutyl ether as a photo radical polymerization initiator Part and 0.5 part by weight of N, N′-methylenebisacrylamide as a cross-linking agent are mixed. 1 was prepared.

  Using the polymerization apparatus 1 shown in FIG. 1 produced a plurality of water-absorbing polymer particles (hereinafter referred to as “particle No. 1”). Specifically, the polymerization composition No. 1 was ejected as droplets from the ejection nozzle 13 into the hydrophobic solvent of the forming tube 17 at a rate of 30 mL / second. The forming tube 17 has a length of about 1.0 m and an inner diameter of about 12 mm. In the forming tube 17, dimethylpolysiloxane held at about 10 ° C. is about 3 L as a hydrophobic solvent. Circulating at a rate of / min.

Polymerization composition No. injected as droplets into the forming tube 17. 1 is irradiated with ultraviolet rays from a high-pressure mercury lamp (wavelength 320 to 400 nm) as the light source 11, and the polymerization composition No. 1 is polymerized, and a plurality of water-absorbing polymer water-containing particles No. 1 are polymerized. 1 was formed.
From dimethylpolysiloxane, a plurality of water-absorbing polymer water-containing particles No. 1 was taken out and dried at 80 ° C. under reduced pressure. 1 was produced.

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

[Production Example 3]
A water-absorbing polymer powder (commercial product, hereinafter referred to as “powder No. 3”) having a skeleton derived from a (meth) acrylic acid monomer produced by a solution polymerization method was prepared. Powder No. 3 is formed by pulverizing and pulverizing a polymer mass produced by a solution polymerization method.

[Example 1 and Comparative Examples 1 and 2]
Particle No. 1, powder no. 2 and powder no. 3, average particle size, coefficient of variation of particle size, particle size dispersion coefficient, average sphericity, dust generation rate in dust generation test, breaking strength, gel strength during water absorption during water absorption test, water absorption during water absorption test The magnification (mass ratio, water, physiological saline), the water retention magnification (mass ratio, water, physiological saline) in the water retention test, and the suction height and uniform suction performance in the suction test were evaluated. The measuring method is as described in this specification.
The results are shown in Table 1. In addition, particle No. 1, powder no. 2 and powder no. The particle size distribution (number basis) of No. 3 is shown in FIGS. The particle size distribution shown in FIGS. 2 to 4 is measured according to the measurement method of the average particle size and the like in the present specification, and the particle size / μm of “400-450” is “over 400 μm and 450 μm or less”. Means.

  As shown in Table 1, the particle Nos. Of Example 1 1 is powder No. 1 produced by the reverse phase suspension polymerization method of Comparative Example 1. No. 2 and Comparative Example 2 produced by the solution polymerization method No. 2 Compared to 3, it is found that the dust generation rate is low, the breaking strength is high, and the gel strength (water, physiological saline) at the time of water absorption is high. Therefore, the particle No. 1 is powder No. 1; 2 and powder no. Compared with No. 3, it can be seen that a deficient portion is less likely to be formed on a part of the surface before water retention, and that it is less likely to crush under pressure after water retention.

DESCRIPTION OF SYMBOLS 1 Polymerization apparatus 3 Polymerization composition tank 5 Metering pump 7 Liquid feeding tube 9 Light irradiation chamber 11 Light source 13 Injection nozzle 15 Rectification perforated plate 17 Forming tube 19 Separation screen 21 Hydrophobic solvent tank 23 Metering pump 25 Temperature controller 27 Liquid feeding tube 101 Water-absorbing polymer water-containing particles 103 Polymerization composition 105 Hydrophobic solvent 107 Liquid droplets

Claims (15)

In the water retention test, the water retention ratio (mass ratio) of 500 to 1,000 times the water,
In the gel strength test at the time of water absorption, the gel strength at the time of water absorption of 60 to 200 mN with respect to water,
A plurality of water-absorbing polymer particles.   The water-absorbing polymer particles have a water retention ratio (mass ratio) of 45 to 110 times with respect to physiological saline in a water retention test and a water absorption rate of 20 to 50 mN with respect to physiological saline in a gel strength test at the time of water absorption. The plurality of water-absorbing polymer particles according to claim 1, having gel strength.   The plurality of water-absorbing polymer particles according to claim 1 or 2, wherein the plurality of water-absorbing polymer particles have a breaking strength of 20 N or more.   The plurality of water-absorbing polymer particles according to any one of claims 1 to 3, wherein the plurality of water-absorbing polymer particles have a dust generation rate of 0.00 to 0.20 mass% in a dust generation test.   The plurality of water-absorbing polymer particles according to any one of claims 1 to 4, wherein the plurality of water-absorbing polymer particles have an average sphericity of 0.90 to 0.99.   The plurality of water-absorbing polymer particles according to any one of claims 1 to 5, wherein the plurality of water-absorbing polymer particles have a coefficient of variation in particle diameter of 0.01 to 0.20. A polymerization composition containing an ethylenically unsaturated monomer, a radical polymerization initiator and water is discharged as a plurality of droplets into a hydrophobic solvent, and the polymerization composition in the plurality of droplets is discharged in the hydrophobic solvent. To form a plurality of water-absorbing polymer water-containing particles from the plurality of droplets, take out the plurality of water-absorbing polymer water-containing particles from the hydrophobic solvent, and dry the plurality of water-absorbing polymer water-containing particles A plurality of water-absorbing polymer particles produced by:
The water-absorbing polymer particles have a water retention ratio (mass ratio) of 500 to 1,000 times with respect to water in a water retention test, and a gel strength at water absorption of 60 to 200 mN with respect to water in a gel strength test upon water absorption. And having
The plurality of water-absorbing polymer particles, wherein:   The plurality of water-absorbing polymer particles according to claim 7, wherein the plurality of droplets have a coefficient of variation in droplet diameter of 0.01 to 0.20.   The radical polymerization initiator is a radical photopolymerization initiator, and the polymerization composition in the plurality of droplets is photopolymerized by irradiating the plurality of droplets with light. A plurality of water-absorbing polymer particles as described.   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 less, according to any one of claims 7 to 9. A plurality of water-absorbing polymer particles. A method for producing a plurality of water-absorbing polymer particles, comprising:
Releasing a polymerization composition comprising an ethylenically unsaturated monomer, a radical polymerization initiator and water into a hydrophobic solvent as a plurality of droplets;
Polymerizing the polymerization composition in the plurality of droplets in the hydrophobic solvent to form a plurality of water-absorbing polymer-containing particles from the plurality of droplets; and from the hydrophobic solvent, Removing the water-absorbing polymer water-containing particles and drying the plurality of water-absorbing polymer water-containing particles to form the plurality of water-absorbing polymer particles;
The water-absorbing polymer particles have a water retention ratio (mass ratio) of 500 to 1,000 times with respect to water in the water retention test and a water absorption of 60 to 200 mN with respect to water in the gel strength test during water absorption. Having gel strength,
The manufacturing method.   The discharging step includes discharging the plurality of droplets into the hydrophobic solvent such that the plurality of droplets have a coefficient of variation in droplet diameter of 0.01 to 0.20. The manufacturing method as described.   The radical polymerization initiator is a photo radical polymerization initiator, and in the step of forming the water-absorbing polymer water-containing particles, the polymerization in the plurality of droplets is performed by irradiating the plurality of droplets with light. The production method according to claim 11 or 12, wherein the composition is photopolymerized.   The method according to any one of claims 11 to 13, wherein in the step of forming a plurality of water-absorbing polymer-containing particles, the temperature of the hydrophobic solvent is in the range of more than 0 ° C and not more than 30 ° C.   The method according to any one of claims 11 to 14, wherein the hydrophobic solvent is selected from the group consisting of silicone oil, oil and hydrocarbon, and any combination thereof.

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