JP7085795B2 - 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, there is a demand for further enhanced functionality, for example, a thin and highly absorbent absorbent article.

As such an absorbent article, one aiming at both thinning and high absorbency by increasing the ratio of the water-absorbent polymer powder in the absorber is known. Specifically, for example, an absorbent having two absorbent bodies in the thickness direction of the absorbent article, that is, an absorbent body containing a water-absorbent polymer powder and an absorbent body containing a water-absorbent polymer powder and pulp fibers. Goods are mentioned.

For example, Patent Document 1 describes a disposable absorbent article provided with an absorbent mat between a liquid-permeable front sheet and a liquid-impermeable back sheet, wherein the absorbent mat is a water-absorbent resin powder. A sheet-like water-absorbent layer containing and not containing pulp fibers and a fiber assembly layer containing both pulp fibers and water-absorbent resin powder are provided in order from the surface sheet side, and the fiber assembly layer is a pulp fiber. Described is a disposable absorbent article characterized in that a fiber-presence region containing both the pulp fiber and the water-absorbent resin powder and a fiber-free region in which both the pulp fiber and the water-absorbent resin powder do not exist are formed adjacent to each other. Has been done.

Further, the water-absorbent polymer powder used for the absorbent article has also been improved from various viewpoints.
For example, Patent Document 2 discloses a highly water-absorbent resin having an appropriate average particle size (about 200 to 350 μm) that suppresses the generation of fine particles and is easy to handle, and has a sharp flow distribution. Patent Document 3 discloses water-absorbent resin particles having a small amount of fine powder and coarse powder and a narrow particle size distribution.

Japanese Unexamined Patent Publication No. 2004-329664 Japanese Unexamined Patent Publication No. 8-120019 Japanese Unexamined Patent Publication No. 2006-0892525

In the absorbent article described in Patent Document 1, the water-absorbent resin powder is not present in the sheet-like water-absorbent layer in order to move the body fluid excreted from the wearer from the upper sheet-like water-absorbent layer to the lower fiber assembly layer. A region and a sealing portion are provided, and the design is made to move the body fluid from the upper sheet-like water-absorbing layer to the lower fiber assembly layer through the sealing portion. The reason why the water-absorbent resin powder non-existent region and the sealing portion are provided is that as the body fluid is absorbed, the water-absorbent resin powder in the sheet-like water-absorbent layer is blocked, and it becomes difficult to move the body fluid to the lower fiber assembly layer. Therefore, the purpose is to secure a water passage for body fluid in the sheet-like water absorption layer which is the upper layer. However, in the absorbent article described in Patent Document 1, the sheet-shaped water-absorbing layer itself needs to have a water-absorbent resin powder non-existent region and a sealing portion that serve as a water passage for the body fluid, so that the sheet-shaped water-absorbing layer itself is the body fluid. Was inferior in absorbency. Further, since the structure of the sheet-shaped water absorbing layer is non-uniform in the plane direction, it tends to be inferior in wearing feeling, twisting property and the like.

Further, the highly water-absorbent resin and the water-absorbent resin particles (hereinafter referred to as "particles") described in Patent Documents 2 and 3 have a narrow particle size distribution to some extent and do not contain much fine particles, so that a plurality of particles are layered. Even in the case of forming, since the "water passage" of water to be absorbed is secured to some extent between the particles, the "initial suction property" which is the absorption property of the initial water to be absorbed. Have. However, when a plurality of particles absorb water, the strength of the particles that have absorbed water is insufficient, so that the water passage between the particles is easily crushed, and the water absorption property after absorbing water. It is inferior in "time-lapse suction property".
Therefore, it is an object of the present disclosure to provide an absorbent article having excellent absorbability, including a first absorber having excellent initial sucking property and time-consuming sucking property.

The present disclosures are an absorbent article comprising a liquid permeable sheet, a first absorbent body, a second absorbent body and a liquid impermeable sheet in this order, wherein the first absorbent body is 0.90 to 0. A plurality of gels having an average sphericity of .99, a variation coefficient of particle size of 0.01 to 0.20, and a gel strength of 20 to 50 mN with respect to physiological saline in a gel strength test during water absorption. We have found an absorbent article characterized by comprising a water-absorbent polymer particle layer composed of water-absorbent polymer particles.

The absorbent article of the present disclosure includes a first absorbent body having excellent initial sucking property and time-consuming sucking property, and is excellent in absorbability.

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 first absorber 5 and the second absorber 7 in the II-II end face of FIG. 1. FIG. 3 is a schematic diagram for explaining the polymerization apparatus 201. FIG. 4 shows the particle No. It is a particle size distribution (number basis) of 1. FIG. 5 shows the powder No. It is a particle size distribution (number basis) of 2. FIG. 6 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, a first absorbent body, a second absorbent body, and a liquid-impermeable sheet in that order.
The first absorber has an average sphericity of 0.90 to 0.99, a variation coefficient of a particle size of 0.01 to 0.20, and 20 to 50 mN with respect to physiological saline in a gel strength test during water absorption. Containing a water-absorbent polymer particle layer composed of a plurality of water-absorbent polymer particles, which has a water-absorbing gel strength of
The above-mentioned absorbent article.

In the absorbent article, the plurality of water-absorbent polymer particles have a predetermined average sphericity and a fluctuation coefficient of a predetermined particle size, and each water-absorbent polymer particle is substantially true sphere and is a water-absorbent polymer. The particle size distribution of the particles is very narrow. Therefore, the water-absorbent polymer particle layer composed of a plurality of water-absorbent polymer particles has a gap between the water-absorbent polymer particle and the water-absorbent polymer particle, and the gap functions as a "water passage" for the body fluid to be absorbed. do. The water passage can suck up (suck) the body fluid that has reached the water-absorbent polymer particles due to a capillary phenomenon or the like. Since the plurality of water-absorbent polymer particles do not contain particles (fine particles) having a smaller particle size than the average particle size, the water passage is less likely to be blocked by the fine powder. As a result, the water-absorbent polymer particle layer can suck up the body fluid through the water passage due to the capillary phenomenon or the like, and the water-absorbent polymer particle layer, and eventually the first absorber, sucks up the initial body fluid. It is excellent in "initial suction property" which means property (suction property).

Further, in the absorbent article, since the plurality of water-absorbent polymer particles in the plurality of water-absorbent polymer particle layers have a predetermined water-absorbing gel strength, the plurality of water-absorbent polymer particles retain water while retaining the body fluid. In the state, even if a force is applied to the plurality of water-absorbent polymer particles, their surfaces are less likely to be chipped, and fine powder which is a chipped particle piece is less likely to be generated. Therefore, the plurality of water-absorbent polymer particle layers, and thus the first absorber, easily retains the above-mentioned water passage even in the water-retaining state in which the body fluid is retained, and further absorbs the body fluid after absorbing the body fluid ( It is excellent in "sucking property over time" which means "sucking property".

As a result, in the above-mentioned absorbent article, the water-absorbent polymer particle layer of the first absorber in the upper layer absorbs the body fluid according to the absorption performance of the water-absorbent polymer particles in the initial stage and in the state of holding the body fluid, and temporarily. The body fluid that cannot be completely absorbed can be transferred to the second absorber in the lower layer. Further, thereby, the body fluid can be absorbed up to the upper limit of the absorption capacity of the body fluid of each of the first absorber and the second absorber.

[Aspect 2]
The absorbent article according to embodiment 1, 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 plurality of water-absorbent polymer particles have a predetermined dust generation rate, the absorbent article is worn before use, for example, during the production, transportation, and use of the absorbent article. Even when the water-absorbent polymer particles collide with each other before absorbing the body fluid, fine particle pieces are unlikely to be generated from the water-absorbent polymer particles. Therefore, the fine particle pieces generated from the plurality of water-absorbent polymer particles are less likely to block the water passage, and the first absorber is excellent in initial suction property and time-lapse absorption property.

[Aspect 3]
The absorbent article according to aspect 1 or 2, wherein the plurality of water-absorbent polymer particles have a water-retaining ratio (mass ratio) of 45 to 110 times with respect to physiological saline in a water-retaining test.
In the absorbent article, since the plurality of water-absorbent polymers have a predetermined water-retaining ratio, the first absorbent body is excellent in water-retaining body fluid. Along with this, the absorbent article is excellent in the absorbability of body fluid with respect to its thickness.

[Aspect 4]
The absorbent article according to any one of aspects 1 to 3, wherein the plurality of water-absorbent polymer particles have a water-absorbing ratio (mass ratio) of 60 to 120 times with respect to physiological saline in a water-absorbing test.
In the absorbent article, since the plurality of water-absorbent polymer particles have a predetermined water-absorbing ratio, the first absorbent body is excellent in water-absorbing body fluid. Along with this, the absorbent article is excellent in the absorbability of body fluid with respect to its thickness.

[Aspect 5]
The absorbent article according to any one of aspects 1 to 4, 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 is excellent in initial suction property and time-lapse absorption property.

[Aspect 6]
The absorbent article according to any one of aspects 1 to 5, wherein the plurality of water-absorbent polymer particles have a suction height of 15 to 40 mm with respect to water in a suction test.
In the absorbent article, since the plurality of water-absorbent polymer particles have a predetermined suction height with respect to water, the first absorber containing the water-absorbent polymer particle layer is initially used for a body fluid having a low ion concentration. Excellent in sucking property and sucking property over time.

[Aspect 7]
An absorbent article comprising a liquid-permeable sheet, a first absorbent body, a second absorbent body, and a liquid-impermeable sheet in that order.
The first absorber has an average sphericity of 0.90 to 0.99, a variation coefficient of a particle size of 0.01 to 0.20, and 20 to 50 mN with respect to physiological saline in a gel strength test during water absorption. Containing a water-absorbent polymer particle layer composed of a plurality of water-absorbent polymer particles having a water-absorbing gel strength of
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 plurality 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 8]
The absorbent article according to aspect 7, 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 variation coefficient of a predetermined droplet diameter, the plurality of produced water-absorbent polymer particles are likely to have a variation coefficient of a predetermined particle size, and thus the water-absorbent polymer particle layer, and thus the water-absorbent polymer particle layer. The first absorber tends to be excellent in initial sucking property and time-consuming sucking property.

[Aspect 9]
8. The embodiment 7 or 8, 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.
When the radical polymerization initiator is a photoradical polymerization initiator, the plurality of water-absorbent polymer particles produced are likely to have a predetermined average sphericity and a predetermined gel strength at the time of water absorption, so that water absorption is likely to occur. The sex polymer particle layer, and thus the first absorber, tends to be excellent in initial suction property and time-lapse absorption property.

[Aspect 10]
The absorption according to any one of aspects 7 to 9, 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 water-absorbent polymer particles produced have a predetermined average sphericity, a predetermined variation coefficient of a predetermined particle size, a predetermined gel strength at the time of water absorption, and the like. It becomes easy to hold, and the water-absorbent polymer particle layer, and thus the first absorber, tends to be excellent in initial suction property and time-lapse absorption property. In addition, the plurality of water-absorbent polymer particles are less likely to contain bubbles.

[Aspect 11]
The absorbent article according to any one of aspects 1 to 10, wherein the plurality of water-absorbent polymer particles have an average particle size of 300 to 800 μm as primary particles.
In the absorbent article, since the plurality of superabsorbent polymer particles have a predetermined average particle size as primary particles, they are produced by a conventional superabsorbent polymer powder, for example, a reverse phase suspension polymerization method, and are large by granulation. Compared to the particle size, the above-mentioned water passage is less likely to be blocked. Therefore, the water-absorbent polymer particle layer, and thus the first absorber, is excellent in initial suction property and time-lapse absorption property.

[Aspect 12]
The absorbent article according to any one of aspects 1 to 11, wherein the first absorber comprises the water-absorbent polymer particle layer and a base sheet arranged adjacent to the water-absorbent polymer particle layer.
In the absorbent article, since the first absorber has a predetermined structure, the absorbent article is excellent in absorbability of body fluid with respect to its thickness.

[Aspect 13]
The absorbency 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 water absorbent polymer powder. Goods.

In the absorbent article, since the second absorbent contains pulp, the body fluid that has reached the absorbent article is passed through the first absorbent and temporarily held by the second absorbent containing the pulp. The body fluid temporarily held by the second absorber is supplied from the second absorber to the first absorber according to the rate at which the plurality of water-absorbent polymer particles of the first absorber absorb the body fluid inside the absorber. can do. Therefore, the absorbent article is excellent in rewetability, absorbability and the like.

[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.
The "water-absorbent polymer particle" means a particle having a predetermined average sphericity, a coefficient of variation of a predetermined particle size, 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 first absorber 5 and the second absorber 7 in the II-II end face of FIG. 1.

As shown in FIG. 1, the absorbent article 1 includes a liquid permeable sheet 3, a first absorbent 5, a second absorbent 7, and a liquid impermeable sheet 9 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 upper layer, that is, the first absorber 5 which is closer to the liquid permeable sheet 3 than the second absorber 7, is a water-absorbent polymer particle layer 13 composed of a plurality of water-absorbent polymer particles 11. It is composed of a first core wrap 15 that covers the water-absorbent polymer particle layer 13. The lower layer, that is, the second absorbent body 7 which is closer to the liquid impermeable sheet 9 than the first absorbent body 5, is a second absorbent core 21 containing a water-absorbent polymer powder 17, a pulp fiber 19, and a second absorbent core. It consists of a second core wrap 23 that covers 21.

In the absorbent article 1 according to the first embodiment, the water-absorbent polymer particle layer 13 of the first absorber 5 in the upper layer absorbs the body fluid according to the absorption performance of the water-absorbent polymer particles 11 in the initial stage and in the state of holding the body fluid. However, the body fluid that cannot be absorbed temporarily can be transferred to the second absorber 7 in the lower layer. Thereby, the body fluid can be absorbed up to the upper limit of the absorption capacity of the body fluid of each of the first absorber 5 and the second absorber 7.

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 0.90 to 0.99, preferably 0.92 to 0.98. And more preferably, it has an average sphericity of 0.93 to 0.97. By doing so, the water-absorbent polymer particles can be filled in the water-absorbent polymer particle layer at a high density. Further, since the water-absorbent polymer particles have the above-mentioned average sphericity, the surface of the water-absorbent polymer particles is less likely to be chipped before and after water retention, and fine powder which is a chipped particle piece is less likely to be generated. .. It should be noted that fine powder is not preferable because it tends to block the water passage.

In the absorbent articles of the present disclosure, the water-absorbent polymer particles have a coefficient of variation of particle size of 0.01 to 0.20, preferably 0.03 to 0.15, and more preferably 0.05 to 0.10. Have. By doing so, before water retention, the water to be absorbed between the water-absorbent polymer particles and the water-absorbent polymer particles while being filled with the plurality of water-absorbent polymer particles at high density in the water-absorbent polymer particle layer. A water passage that serves as a passage is secured.

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 variation coefficient 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）のメジアン径（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 ) of 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, before water retention, the plurality of water-absorbent polymer particles are filled in the water-absorbent polymer particle layer at a high density, and the passage of water to be absorbed between the plurality of water-absorbent polymer particles is provided. It becomes easier to secure a water channel.

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 circle-equivalent diameter CD of 1,000 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 are 20 to 50 mN, preferably 23 to 45 mN, and more preferably 25 to 40 mN of water-absorbing gel with respect to physiological saline in a water-absorbing gel strength test. Has strength. By doing so, the water-absorbent polymer particles are less likely to be chipped even when a force is applied in a state where the body fluid is retained, and the chipped particle pieces are less likely to be generated. As a result, the above-mentioned water passage is easily maintained in the above-mentioned water-absorbent polymer particle layer in a state where the body fluid is retained.

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 chipped even when a force is applied in a body fluid having a low ion concentration in a high water retention state, and the chipped particle pieces are less likely to be generated. As a result, the above-mentioned water passage is easily maintained in the water-absorbent polymer particle layer in a superabsorbent polymer particle layer in a state of high water retention of a body fluid having a low ion concentration.

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 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 water-absorbent polymer particles receives a force such that the water-absorbent polymer particles rub against each other before use, for example, during transportation, the water-absorbent polymer particles The surface of the polymer is less likely to be chipped, and fine powder, which is a fragment of particles that has been chipped off, is less likely to be generated. As a result, in the water-absorbent polymer particle layer, the fine powder makes it difficult for the water passage to be blocked.

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 ₁ (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 ₂ (g) is measured.
(5) Dust generation rate: D (mass%), the following formula:
D (mass%) = 100 x m ₂ / m ₁
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 article of the present disclosure, the water-absorbent polymer particles have a breaking strength of preferably 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, the surface of the water-absorbent polymer particles is less likely to be chipped and chipped off even when the absorbent article containing the water-absorbent polymer particles receives a strong impact before use, for example, during transportation. Fine powder, which is a fragment of particles, is less likely to be generated. As a result, when the water-absorbent polymer particles are used, the fine powder makes it difficult for the water passage to be blocked.

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 article of the present disclosure, the water-absorbent polymer particles preferably absorb 60 to 120 times, more preferably 70 to 100 times, and even more preferably 75 to 90 times the water absorption of physiological saline in the 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. Further, even when the absorbent article is formed in a thin shape, it is excellent in the absorbability of body fluid.
In the art, it is known that there is a negative correlation between the water absorption 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-absorbing ratio and a high gel strength at the time of water-absorbing.

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 ₃ (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 ₄ (g) is measured.
(4) Water absorption ratio (mass ratio) of the sample: _WAR , the following formula:
_WAR = 100 × (m ₄ -m ₃ ) / m ₃
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 the body fluid having a low ion concentration. Further, even when the absorbent article is formed thin, it is excellent in absorbability of a 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 of, 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 first absorber containing the water-absorbent polymer particle layer is excellent in initial suction property and time-lapse absorption property for body fluids having a low ion concentration.

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 a petri dish (inner diameter: 90 mm, height: 15 mm) at intervals, and then put them in the petri dish. 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 first absorber containing the water-absorbent polymer particle layer is excellent in initial suction property and time-lapse absorption property for body fluids having a low ion concentration.

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

In the absorbent article of the present disclosure, the water-absorbent polymer particles have a water retention of preferably 45 to 110 times, more preferably 55 to 95 times, and even more preferably 60 to 85 times with respect to physiological saline in a water retention test. It has a magnification (mass ratio). By doing so, the first absorber is excellent in water retention of the body fluid. Along with this, even when the absorbent article is formed thin, the absorbability of body fluid is excellent.
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, and the above-mentioned water-absorbent polymer particles have conventional water absorption. Compared with the sex polymer powder, 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 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 sample of about 20 mg: Weigh accurately m ₅ (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 ₆ (g).
(5) Sample water retention ratio (mass ratio): W _HR , the following formula:
W _HR = 100 x (m ₆ -m ₅ ) / m ₅
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 retention 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 in a water retention test. It has a magnification (mass ratio). By doing so, the first absorber is excellent in water retention of the body fluid having a low ion concentration. Along with this, even when the absorbent article is formed thin, it is excellent in absorbability of a body fluid having a low ion concentration.

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 (sample). Approximately 1,100 times the mass of) ”.

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

In the absorbent article of the present disclosure, the water-absorbent polymer particles preferably have an average particle size of 300 to 1, which has a particularly high effect as compared with the water-absorbent polymer powder produced by the reverse phase suspension polymerization method. 000 μm, and more preferably 300 to 800 μm. 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. Can have a predetermined average sphericity, a predetermined particle size variation coefficient, and a predetermined water-absorbing gel strength, which is difficult to achieve, and the water-absorbent polymer particle layer, and thus the first absorber, Excellent initial suction and time-lapse suction.

In the absorbent article of the present disclosure, the water-absorbent polymer particles can have a monomer skeleton generally used in the art, and are exemplified in "Method for producing a plurality of water-absorbent polymer particles" described later, for example. The monomer skeleton to be used, for example, a skeleton derived from an ethylene-based unsaturated 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 absorption, gel strength at the time of water absorption, and the like.

In the absorbent article of the present disclosure, the first absorber can uniformly hold the water-absorbent polymer particles in the plane direction of the absorbent article. This is because the first absorber is excellent in initial suction property and time-lapse absorption property even if it does not have a region in which the water-absorbent polymer particles do not exist. However, in the absorbent article of the present disclosure, the first absorber may hold the water-absorbent polymer particles non-uniformly in the plane direction of the absorbent article.

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 particles”). 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 low specific gravity in the polymerization composition.
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 likely to have a predetermined average sphericity, a coefficient of variation of a predetermined particle size, a predetermined gel strength at the time of water absorption, and the like, and the water-absorbent polymer particle layer. As a result, the first absorber tends to be excellent in initial suction property and time-lapse absorption property. In addition, the plurality of water-absorbent polymer particles are less likely to contain bubbles.

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. The above-mentioned droplets are formed in the film. The amount of the polymerization composition ejected from the injection nozzle is, for example, 30 to 60 mL / min. 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. The polymerization composition is preferably discharged as droplets inside the hydrophobic solvent. This is to maintain the shape of the droplet.

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 water-absorbent polymer particles tend to have homogeneous properties, and thus the plurality of water-absorbent polymers. The particles tend to have a high average sphericity, a high gel strength at the time of water absorption, a high water retention ratio, 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 a hydrophobic solvent to form a 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 in 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. 3, 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, the plurality of water-absorbent polymer powders produced by the solution polymerization method include a portion where the voids between the particles are large, that is, a portion where the width of the water passage is wide, when the water-absorbent polymer powder layer is formed. It is difficult to suck up water using capillarity. Further, in the plurality of water-absorbent polymer powders produced by the solution polymerization method, the fine powder tends to block a narrow portion of the water passage, and it becomes difficult to suck up water. As a result, the absorbent article containing the plurality of water-absorbent polymer powders produced by the solution polymerization method tends to be inferior in the initial sucking property and the time-consuming sucking property.

Further, in the reverse phase suspension polymerization method, it is difficult to adjust the particle size of the water-absorbent polymer powder to be produced, and for the use of absorbent articles, additional steps such as granulation are performed to increase the particle size of the water-absorbent polymer powder. However, the granulated water-absorbent polymer powder is inferior in particle size variation coefficient, average sphericity, gel strength at the time of water absorption, etc., and primary particles tend to block the water passage as fine powder. As a result, the absorbent article containing the plurality of water-absorbent polymer powders produced by the reverse-phase suspension polymerization method tends to be inferior in the initial sucking property and the time-consuming sucking property.

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 absorption, 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 are water-absorbent and water-absorbent 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 mass 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. 3, 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 305 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, dimethylpolysiloxane held at about 10 ° C. as a hydrophobic solvent 305 is about. It was circulating at a rate of 3 L / min.

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-absorbent polymers such as water-containing particles No. 1 are polymerized. 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. 4 to 6. The particle size distributions shown in FIGS. 4 to 6 are measured according to the measuring method such as the average particle size of the present specification, and “400-450” with a particle size / μm is “more than 400 μm and 450 μm or less”. Means.

As shown in Table 1, the particle No. 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. In comparison with No. 3, it can be seen that in the suction test, the suction height is excellent and the suction property is uniform. Therefore, the particle No. In No. 1, it is suggested that the waterway was continuously secured. On the other hand, powder No. 2 and powder No. In No. 3, both the suction height and the uniform suction property are the particle No. It is inferior to 1 and suggests that the waterway is blocked by fine powder or the like. Particle No. The excellent suction height and uniform suction property of No. 1 are the particles No. This is due to the fact that the coefficient of variation of the particle size of 1 is as small as 0.08, the average sphericity is as high as 0.94, and the gel strength at the time of water absorption is as high as 112 mN.

Although not shown in Table 1, the particle No. 1 is the powder No. 2 and powder No. Compared with No. 3, the cylinder in which the sample was placed was excellent in sucking property immediately after being immersed in physiological saline, that is, initial sucking property. As shown in Table 1, the particle No. 1 is the powder No. 2 and powder No. It is clear that the suction height, that is, the suction property over time is excellent as compared with 3.

[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 (Eltus Aqua manufactured by Asahi Kasei Corporation, basis weight: 18 g) was cut into a size of 10 cm × 10 cm. / 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 (= [water absorption polymer powder basis weight] 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 1st absorber 7 2nd absorber 9 Liquid impermeable sheet 11 Water-absorbent polymer particles 13 Water-absorbent polymer particle layer 15 1st core wrap 17 Water-absorbent polymer powder 19 Pulp fiber 21 2nd Absorption core 23 2nd core wrap 101 Leakage-proof wall 103 Elastic member 105 Fixed part 107 Elastic member 109 Tape fastener 201 Polymerization device 203 Polymer composition tank 205 Metering pump 207 Liquid transfer tube 209 Light irradiation chamber 211 Light source 213 Injection nozzle 215 Rectification perforated board 217 Forming tube 219 Separation screen 221 Hydrophobic solvent tank 223 Metering pump 225 Temperature regulator 227 Liquid feeder tube 301 Super absorbent polymer Water-containing particles 303 Polymerization composition 305 Hydrophobic solvent 307 Droplets

Claims (14)

An absorbent article comprising a liquid permeable sheet, a first absorbent body, a second absorbent body, and a liquid impermeable sheet in that order.
The first absorber has an average particle size of 300 to 1,000 μm, an average sphericity of 0.90 to 0.99, a variation coefficient of a particle size of 0.01 to 0.20, and a gel strength at the time of water absorption. A water-absorbent polymer particle layer composed of a plurality of water-absorbent polymer particles having a gel strength at the time of water absorption of 20 to 50 mN with respect to physiological saline in the test was included .
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 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 3 , wherein the plurality of water-absorbent polymer particles have a water retention ratio (mass ratio) of 45 to 110 times with respect to physiological saline in a water retention test. The absorbent article according to any one of claims 1 to 4 , wherein the plurality of water-absorbent polymer particles have a water absorption ratio (mass ratio) of 60 to 120 times with respect to physiological saline in a water absorption test. The absorbent article according to any one of claims 1 to 5 , 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 absorbent article according to any one of claims 1 to 6 , wherein the plurality of water-absorbent polymer particles have a suction height of 15 to 40 mm with respect to water in a suction test. The absorbent article according to any one of claims 1 to 7 , wherein the first absorber includes the water-absorbent polymer particle layer and a base sheet arranged adjacent to the water-absorbent polymer particle layer. .. The absorption according to any one of claims 1 to 8 , wherein the second absorber comprises a second absorbent core and a second core wrap, and the second absorbent core comprises pulp and a water-absorbing polymer powder. Sex goods. A method of 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-absorbent 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 an average particle size of 300 to 1,000 μm, an average sphericity of 0.90 to 0.99, a coefficient of variation of a particle size of 0.01 to 0.20, and water absorption. It has a gel strength at the time of water absorption of 20 to 50 mN with respect to physiological saline in the gel strength test.
The above-mentioned method. The method according to claim 10 , 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 10 or 11 , 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 photoradical 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 10 to 12 . Any of claims 10 to 13 , 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.

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