KR20220050918A - Absorbent Sheets and Absorbent Articles - Google Patents

Abstract

An absorbent sheet comprising a plurality of absorbent layers comprising absorbent resin particles, wherein one of the outermost absorbent layers contains absorbent resin particles having an absorption absorption amount of 10.5 g/g or more and a permeate absorption amount of 12.5 g/g or more, It relates to an absorbent sheet.

Description

Absorbent Sheets and Absorbent Articles

The present invention relates to an absorbent sheet and an absorbent article.

A thin absorbent body (or absorbent sheet) provided with an absorbent layer capable of absorbing liquid is used these days for absorbent articles for absorbing liquids containing water as a main component, such as urine. there is. In such an absorber or absorbent sheet, a plurality of absorber layers may be provided (for example, Patent Documents 1 to 3).

Japanese Patent Laid-Open No. 10-118117 Japanese Laid-Open Patent Publication No. 2002-113800 Japanese Patent Laid-Open No. 2012-183175

Absorbent articles may leak liquid during use, and as they become thinner, they tend to leak more easily. There was room for further improvement in this regard.

Accordingly, one aspect of the present invention aims to provide an absorbent sheet capable of suppressing liquid leakage in an absorbent article.

One aspect of the present invention is an absorbent sheet including a plurality of absorbent layers, wherein one of the outermost absorbent layers has an absorption absorption amount of 10.5 g/g or more and a permeate absorption amount of 12.5 g/g or more. It relates to an absorbent sheet comprising particles. Here, in accordance with the DW method, the amount of absorption by absorption is 0.5 g of water absorbent resin particles disposed in a container comprising a cylinder having an inner diameter of 25 mm and a mesh sheet adhered to the bottom of the cylinder. When physiological saline is absorbed, the absorbency It is the mass of the physiological saline solution per 1 g of the water-absorbing resin particles that the resin particles absorb until 10 minutes after the start of absorption. In addition, the amount of absorption of the permeate is determined by disposing 0.5 g of water-absorbing resin particles on a mesh sheet in a container made of a cylinder having an inner diameter of 60 mm and a mesh sheet adhered to the bottom of the cylinder, then 30 g of physiological saline is added, It relates to an absorbent sheet, which is the amount of absorption of physiological saline per 1 g of water absorbent resin particles measured 1 minute after the start time.

Another aspect of the present invention provides an absorbent article comprising a liquid-impermeable sheet, an absorbent sheet having a plurality of absorbent layers, and a liquid-permeable sheet, wherein the liquid-impermeable sheet, the absorbent sheet and the liquid-permeable sheet are disposed in this order. , wherein the absorbent layer of the outermost layer on the liquid-impermeable sheet side contains absorbent resin particles having an absorption absorption amount of 10.5 g/g or more and a permeate absorption amount of 12.5 g/g or more. Here, in accordance with the DW method, the amount of absorption by absorption is 0.5 g of water absorbent resin particles disposed in a container comprising a cylinder having an inner diameter of 25 mm and a mesh sheet adhered to the bottom of the cylinder. When physiological saline is absorbed, the absorbency It is the mass of the physiological saline solution per 1 g of the water-absorbing resin particles that the resin particles absorb until 10 minutes after the start of absorption. In addition, the amount of absorption of the permeate is determined by disposing 0.5 g of water-absorbing resin particles on a mesh sheet in a container made of a cylinder having an inner diameter of 60 mm and a mesh sheet adhered to the bottom of the cylinder, then 30 g of physiological saline is added, It is the amount of absorption of physiological saline per 1 g of water-absorbing resin particles, measured 1 minute after the start time.

ADVANTAGE OF THE INVENTION According to this invention, the absorbent sheet which can suppress the liquid leakage in an absorbent article can be provided.

1 is a cross-sectional view showing an example of an absorbent sheet.
2 is a plan view illustrating an example of an adhesive application pattern formed on a core wrap sheet.
It is sectional drawing which shows an example of an absorbent article.
4 is a schematic diagram showing a method for measuring inhalation absorption.
5 is a schematic diagram showing a method for measuring absorption under load.
6 is a schematic diagram showing a method for measuring a liquid leakage test.

Hereinafter, several embodiments of the present invention will be described in detail. However, this invention is not limited to the following embodiment.

In the present specification, "(meth)acryl" is expressed by combining "acryl" and "methacrylic". “Acrylate” and “methacrylate” are also referred to as “(meth)acrylate”. In the numerical range described step by step in this specification, the upper limit or lower limit of the numerical range of a certain step may be arbitrarily combined with the upper limit or lower limit of the numerical range of another step. In the numerical range described herein, the upper limit or lower limit of the numerical range may be substituted with the value shown in Examples. "A or B" may include any one of A and B, and may include both. "Water solubility" means showing solubility of 5 mass % or more in water in 25 degreeC. The material illustrated in this specification may be used independently and may be used in combination of 2 or more type. The content of each component in the composition means the total amount of the plurality of substances present in the composition unless otherwise specified, when a plurality of substances corresponding to each component exist in the composition.

The absorbent sheet according to the embodiment includes a plurality of absorbent layers. In the plurality of absorbent layers, one of the outermost absorbent layers contains water-absorbent resin particles having an absorption absorption amount of 10.5 g/g or more and an absorption amount of a permeate solution of 12.5 g/g or more.

According to the DW method, the absorbent amount is 0.5 g of water absorbent resin particles disposed in a container comprising a cylinder with an inner diameter of 25 mm and a mesh sheet adhered to the bottom of the cylinder. When physiological saline is absorbed, the water absorbent resin particles It is the mass of the physiological saline solution per 1 g of the water-absorbing resin particles absorbed until 10 minutes after the start of absorption. The amount of absorption by inhalation is specifically measured by the method described in Examples to be described later. In the present specification, physiological saline is an aqueous sodium chloride solution having a concentration of 0.9% by mass. The density|concentration 0.9 mass % is a density|concentration based on the mass of physiological saline.

The amount of absorption of the permeate was determined by placing 0.5 g of water-absorbing resin particles on a mesh sheet in a container made of a cylinder having an inner diameter of 60 mm and a mesh sheet adhered to the bottom of the cylinder, then adding 30 g of physiological saline, and starting time of injection It is the amount of absorption of physiological saline per 1 g of water-absorbent resin particles, measured after 1 minute. The amount of absorption of the permeate is specifically measured by the method described in Examples to be described later.

According to the absorbent sheet which concerns on this embodiment, liquid leakage in an absorbent article can be suppressed. Although the cause for which such an effect is acquired is not clear, this inventor estimates as follows. However, the cause is not limited to the following. According to the absorbent resin particles having the absorption absorption amount and the absorption amount of the permeate within the above ranges, in addition to enabling rapid liquid absorption, the occurrence of a phenomenon (blocking) in which the passage of the liquid is blocked due to the concentration of the absorbent water absorbent resin particles is suppressed, and more It is thought that the liquid absorption of many liquids becomes possible. It is thought that liquid leakage can be effectively suppressed by using such an absorbent layer containing the water absorbent resin particles as the absorbent layer located in the outermost layer on the side opposite to the liquid intrusion side of the absorbent article.

In the plurality of absorbent layers, a layer other than one of the outermost layers containing the first water absorbent resin particles (hereinafter, also referred to as "another layer") is the same as or different from the first water absorbent resin particles. (Hereinafter, it may be referred to as "second water-absorbing resin particle.") may be included.

The plurality of absorbent layers may have a layer (other layers) other than the outermost layer containing the first water absorbent resin particles and one or more outermost layers including the second water absorbent resin particles. The absorbent sheet is disposed so that the outermost layer containing the first water absorbent resin particles is on the opposite side to the side where the liquid penetrates. In the absorbent sheet, the number of the absorbent layers may be two or more, for example, 2 to 5, 2 to 4, 2-3, or 2 may be sufficient.

4 is a schematic diagram showing a method for measuring inhalation absorption. The measuring device shown in FIG. 4 has the same configuration as the device for measuring the DW (Demand Wettability) value, and has a burette 1, a conduit 5, a measuring table 13, and a mount 14. ), and a clamp 3 . The burette part 1 is connected to a burette tube 26 with a graduated scale, a rubber stopper 23 for sealing the upper opening of the burette tube 26, and the tip of the lower portion of the burette tube 26. It has a cock 22 and an air introduction pipe 25 and a cock 24 connected to the lower part of the burette pipe 26 . The burette part 1 is fixed with a clamp 3 . The flat plate-shaped measuring table 13 has a through hole 13a having a diameter of 2 mm formed in the central portion thereof, and is supported by a variable height mount 14 . The through hole 13a of the measuring table 13 and the cock 22 of the burette 1 are connected by a conduit 5 . The inner diameter of the conduit 5 is 6 mm.

Inhalation absorption is measured by the method including the following process in the environment of temperature 25 degreeC and humidity of 60±10%.

(1) The cock 22 and the cock 24 of the burette part 1 are closed, and physiological saline 27 at 25° C. is poured into the burette tube 26 from the opening at the top of the burette tube 26 .

(2) After sealing the opening of the burette tube 26 with the rubber stopper 23, the cock 22 and the cock 24 are opened. Fill the inside of the conduit (5) with physiological saline (27) to prevent air bubbles from entering.

(3) The height of the measuring table 13 is adjusted so that the height of the water surface of the physiological saline solution reaching the through hole 13a becomes equal to the height of the upper surface of the measuring table 13 . After adjustment, the height of the water surface of the physiological saline solution 27 in the burette tube 26 is read on the scale of the burette tube 26, and the position is set as the zero point (reading value at the time of 0 second).

(4) 0.5 g of water absorbent resin in a container for measuring suction and absorption, which consists of a cylinder 16 (inner diameter 25 mmφ × height 150 mm) and a nylon mesh sheet 15 (250 mesh, thickness about 60 μm) adhered to the bottom of the cylinder. Distribute the particles evenly.

(5) The nylon mesh sheet 15 on which the water absorbent resin particles 11a are arranged is arranged so that the center thereof is the position of the through hole 13a, and measurement is started. The point at which air bubbles are first introduced into the burette tube 26 from the air introduction tube is regarded as the start of absorption (0 second).

(6) The decrease amount of the physiological saline solution 27 in the burette tube 26 (that is, the amount of physiological saline solution absorbed by the water absorbent resin particles 11a) is sequentially read in units of 0.1 mL. The absorption amount A (loss amount) (mL) of the physiological saline 27 10 minutes after counting from the start of absorption of the water absorbent resin particles 11a is read. From the absorption amount A and the density (1.0028 g/mL) of the physiological saline, the intake absorption amount is calculated by the following formula. The amount of absorption by inhalation is the mass per 1 g of water-absorbing resin particles of the absorbed physiological saline.

Inhalation absorption [g/g] = A [mL] × 1.0028 (density of physiological saline) [g/mL]/0.5 [g]

The suction and absorption amount of the first water absorbent resin particles is 12.0 g/g or more, 14.0 g/g or more, 16.0 g/g or more, 18.0 g/g or more, 20.0 g/g or more, from the viewpoint of further excellent liquid leakage suppression effect. , 22.0 g/g or more, 24.0 g/g or more, 26.0 g/g or more, or 28.0 g/g or more may be sufficient. The absorption amount of the first water absorbent resin particles may be, for example, 50.0 g/g or less, 40.0 g/g or less, 35.0 g/g or less, or 30.0 g/g or less. The absorption and absorption amount of the 2nd water absorbent resin particle may be in the said range, and may be outside the said range.

The water absorbent resin particles having an absorption amount of 10.5 g/g or more include, for example, surface crosslinking and surface modification after surface crosslinking to the polymer particles described later, increasing the surface area of the water absorbent resin particles, or a combination thereof. , can be obtained.

The permeate absorption amount is measured by a method including the following steps.

(1) 0.5 g of water absorbent resin particles are uniformly sprayed on a mesh sheet in a container made of an acrylic resin cylinder having an inner diameter of 60 mmφ and a height of 70 mm and a mesh sheet adhered to the bottom of the cylinder, and Measure the total mass Wc.

(2) After placing the container in which the water absorbent resin particles are placed on a gold mesh (eye size 1.4 mm, 100 mm × 100 mm) placed on an empty petri dish, in the container in which the water absorbent resin particles are placed, 30 g of physiological saline (concentration 0.9) wt% saline) is added at one time, and after 1 minute, the total mass Wd of the container and its contents is measured.

(3) From the total mass Wc of the container and the water absorbent resin particles and the total mass Wd of the container and its contents, the permeate absorption amount is calculated by the following formula.

Permeate absorption [g/g]=(Wd[g]-Wc[g])/0.5[g]

The permeate absorption amount of the first water absorbent resin particles is 15.0 g/g or more, 17.0 g/g or more, 20.0 g/g or more, 25.0 g/g or more, 30.0 g/g or more from the viewpoint of further excellent liquid leakage suppression effect. or more, 35.0 g/g or more, or 40.0 g/g or more may be sufficient. The permeate absorption amount of the first water absorbent resin particles may be, for example, 60 g/g or less, 55 g/g or less, or 50 g/g or less. The permeate absorption amount of the second water absorbent resin particles may be within the above range or outside the above range.

The water-absorbent resin particles having a permeate absorption amount of 12.5 g/g or more include, for example, surface crosslinking and surface modification after surface crosslinking to the polymer particles described later, increasing the surface area of the water absorbent resin particles, or these By combination, it can be obtained.

The absorption amount of the physiological saline solution of the first water absorbent resin particles and the second water absorbent resin particles may be 40 g/g or more, 50 g/g or more, or 55 g/g or more, respectively, from the viewpoint of further suppressing liquid leakage, and 80 g /g or less, 70 g/g or less, or 65 g/g or less may be sufficient. The absorption amount of the physiological saline is measured by the method described in Examples to be described later.

The shapes of the first and second water-absorbing resin particles may be, for example, substantially spherical, crushed, or granular, or a shape in which primary particles having these shapes aggregated. The median particle diameter of the first and second water absorbent resin particles may be 800 μm or less, 600 μm or less, 500 μm or less, 450 μm or less, or 400 μm or less, respectively, 100 μm or more, 150 μm or more, 200 μm or more, 250 μm or more, 300 μm or more, or 350 μm or more. It may be more than The median particle diameter of the first and second water-absorbing resin particles may be 100 to 800 µm, 150 to 600 µm, 200 to 500 µm, or 250 to 450 µm, respectively. Although the 1st and 2nd water absorbing resin particles may have a desired particle size distribution at the time obtained by the manufacturing method mentioned later, you may adjust a particle size distribution by performing operations, such as particle size adjustment using classification by a sieve.

When the water absorbent resin particles are used for sanitary materials, it is generally said that the median particle diameter of the water absorbent resin particles is preferably relatively large from the viewpoint of handleability during production of the absorbent body or absorbent sheet. The water absorbent resin particles (first water absorbent resin particles) contained in the outermost layer may be water absorbent resin particles having a relatively small median particle diameter (for example, 450 µm or less or 300 µm or less) from the viewpoint of further excellent liquid leakage suppression effect.

In the first water absorbent resin particles, the content of particles having a particle diameter of 150 µm or less is 21.0 mass% or less, 15.0 mass% or less, 10.0 mass% based on the total mass of the water absorbent resin particles from the viewpoint of further excellent liquid leakage suppression effect. % or less, 8.0 mass % or less, or 6.0 mass % or less may be sufficient, and 0.5 mass % or more, 1.0 mass % or more, or 1.5 mass % or more may be sufficient. 1st water absorbent resin particle WHEREIN: 0.5-21.0 mass %, 1.0-15.0 mass %, or 1.5-10.0 mass % of particle|grains with a particle diameter of 150 micrometers or less may be sufficient. The content of the water-absorbent resin particles having a particle diameter of 150 µm or less is the content of the water-absorbing resin particles passing through a sieve having an eye size of 150 µm based on the total mass of the water absorbent resin particles.

When the water absorbent resin particles are used for sanitary material applications, the content of particles having a particle diameter of 150 µm or less is generally relatively small (e.g., less than 0.5 mass%) from the viewpoint of reducing voids (loss) during the production of the absorbent body or absorbent sheet. ) is preferable, but the water absorbent resin particles (first water absorbent resin particles) contained in the outermost layer of the absorbent sheet having a plurality of absorbent layers have a particle content of 150 μm or less in particle diameter from the viewpoint of further excellent liquid leakage suppression effect. A relatively large number (eg, 0.5 mass% or more and 21.0 mass% or less) of water-absorbent resin particles may be sufficient.

The absorption amount of the physiological saline solution under a load of 2.07 kPa by the first and second water absorbent resin particles (hereinafter, simply referred to as “absorption under load”) is 15 mL/g or more, 18 mL/g or more, and 20 mL/g, respectively. g or more, 25 mL/g or more, or 30 mL/g or more may be sufficient, and 50 mL/g or less, 45 mL/g or less, 40 mL/g or less, or 34 mL/g or less may be sufficient. When the amount of absorption under load is large, even when the wearer of the absorbent article receives a load, high absorption capacity can be maintained. The water absorption under load is measured by the method described in Examples to be described later.

The absorption rate of the physiological saline by the DW method of the first water absorbent resin particles may be, for example, less than 5.0 g/30 sec/0.3 g, 1.0 g/30 sec/0.3 g or more, or 2.5 g/30 sec/ 0.3 g or more may be sufficient. The absorption rate of physiological saline by the DW method is measured by the method described in Examples to be described later.

The absorption rate of the physiological saline solution by the Vortex method of the first water absorbent resin particles may be, for example, 2 seconds or more, 3 seconds or more, or 4 seconds or more, 30 seconds or less, 25 seconds or less, 20 seconds or less, 16 seconds It may be less than or 13 seconds or less. The absorption rate of physiological saline by the Vortex method is measured by the method described in Examples to be described later.

The liquid permeation time of the second water absorbent resin particles may be, for example, more than 20 seconds, 60 seconds or less, 50 seconds or less, 40 seconds or less, or 35 seconds or less. Liquid permeation time is measured by the method described in the Example mentioned later.

The first and second water absorbent resin particles may include, for example, a crosslinked polymer formed by polymerization of a monomer including an ethylenically unsaturated monomer. The crosslinked polymer has a monomer unit derived from an ethylenically unsaturated monomer.

The 1st and 2nd water absorbing resin particles can be manufactured by the method including the process of polymerizing the monomer containing an ethylenically unsaturated monomer. Examples of the polymerization method include a reverse phase suspension polymerization method, an aqueous solution polymerization method, a bulk polymerization method, and a precipitation polymerization method. From the viewpoints of ensuring good absorption characteristics of the resulting water-absorbing resin particles and facilitating control of polymerization reaction, a reversed-phase suspension polymerization method or an aqueous solution polymerization method may be applied. Below, as a method of superposing|polymerizing an ethylenically unsaturated monomer, the reverse phase suspension polymerization method is mentioned and demonstrated as an example.

The ethylenically unsaturated monomer may be water-soluble. Examples of the water-soluble ethylenically unsaturated monomer include (meth)acrylic acid and salts thereof, 2-(meth)acrylamide-2-methylpropanesulfonic acid and salts thereof, (meth)acrylamide, N,N-dimethyl (meth) Acrylamide, 2-hydroxyethyl (meth) acrylate, N-methylol (meth) acrylamide, polyethylene glycol mono (meth) acrylate, N,N-diethylaminoethyl (meth) acrylate, N , N-diethylaminopropyl (meth)acrylate, diethylaminopropyl (meth)acrylamide, etc. are mentioned. When the ethylenically unsaturated monomer has an amino group, the amino group may be quaternized. An ethylenically unsaturated monomer may be used independently and may be used in combination of 2 or more type. Functional groups, such as a carboxyl group and an amino group of the above-mentioned monomer, can function as a functional group which can bridge|crosslink in the surface crosslinking process mentioned later.

From the viewpoint of industrial availability, the ethylenically unsaturated monomer is at least one selected from the group consisting of (meth)acrylic acid and its salts, acrylamide, methacrylamide, and N,N-dimethylacrylamide. The compound may be included. The ethylenically unsaturated monomer may contain the at least 1 sort(s) of compound chosen from the group which consists of (meth)acrylic acid and its salt, and acrylamide. From the viewpoint of further enhancing water absorption characteristics, the ethylenically unsaturated monomer may contain at least one compound selected from the group consisting of (meth)acrylic acid and salts thereof.

The ethylenically unsaturated monomer can be used for a polymerization reaction as an aqueous solution. The concentration of the ethylenically unsaturated monomer in the aqueous solution containing the ethylenically unsaturated monomer (hereinafter simply referred to as "monomer aqueous solution") is 20 mass % or more and the saturation concentration or less, 25 to 70 mass %, or 30 to 55 mass %. may be As water used in aqueous solution, tap water, distilled water, ion-exchange water, etc. are mentioned.

As the monomer for obtaining the water-absorbing resin particles, a monomer other than the above-mentioned ethylenically unsaturated monomer may be used. Such a monomer can be mixed and used with the aqueous solution containing the above-mentioned ethylenically unsaturated monomer, for example. The usage-amount of an ethylenically unsaturated monomer may be 70-100 mol% with respect to monomer whole quantity. The ratio of (meth)acrylic acid and its salt may be 70-100 mol% with respect to monomer whole quantity.

When an ethylenically unsaturated monomer has an acidic radical, after neutralizing the acidic radical with an alkaline neutralizing agent, you may use a monomer solution for a polymerization reaction. The degree of neutralization by the alkaline neutralizing agent in the ethylenically unsaturated monomer increases the osmotic pressure of the water-absorbing resin particles obtained, and from the viewpoint of further enhancing the absorption characteristics (water absorption, etc.), 10 to 100 moles of the acidic group in the ethylenically unsaturated monomer. %, 50 to 90 mol%, or 60 to 80 mol% may be sufficient. Examples of the alkaline neutralizing agent include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium hydrogencarbonate, potassium hydroxide and potassium carbonate; Ammonia etc. are mentioned. An alkaline neutralizing agent may be used independently and may be used in combination of 2 or more type. The alkaline neutralizing agent may be used in the state of an aqueous solution in order to simplify the neutralization operation. Neutralization of the acid group of an ethylenically unsaturated monomer can be performed by dripping and mixing aqueous solutions, such as sodium hydroxide and potassium hydroxide, to the monomer aqueous solution mentioned above, for example.

In the reversed-phase suspension polymerization method, the monomer aqueous solution is disperse|distributed in a hydrocarbon dispersion medium in presence of surfactant, and superposition|polymerization of an ethylenically unsaturated monomer can be performed using a radical polymerization initiator etc. As the radical polymerization initiator, a water-soluble radical polymerization initiator can be used.

Nonionic surfactants, anionic surfactants, etc. are mentioned as surfactant. As the nonionic surfactant, sorbitan fatty acid ester, (poly)glycerin fatty acid ester ("(poly)" means both with and without the prefix "poly". The same applies hereinafter); Sucrose fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, sorbitol fatty acid ester, polyoxyethylene sorbitol fatty acid ester, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene Castor oil, polyoxyethylene hydrogenated castor oil, alkylallylformaldehyde condensed polyoxyethylene ether, polyoxyethylene polyoxypropylene block copolymer, polyoxyethylene polyoxypropyl alkyl ether, polyethylene glycol fatty acid ester, etc. are mentioned. there is. Examples of the anionic surfactant include fatty acid salts, alkylbenzenesulfonates, alkylmethyltaurates, polyoxyethylenealkylphenylether sulfate ester salts, polyoxyethylenealkylethersulfonates, polyoxyethylenealkylether phosphate esters, and Phosphoric acid ester of polyoxyethylene alkyl allyl ether, etc. are mentioned. Surfactant may be used independently and may be used in combination of 2 or more type.

From the viewpoint of good W/O-type reverse-phase suspension, easy to obtain water-absorbing resin particles having a suitable particle size, and easy industrial availability, surfactants are sorbitan fatty acid ester, polyglycerol fatty acid ester, and sucrose You may also contain the at least 1 sort(s) of compound chosen from the group which consists of fatty acid ester. From the viewpoint of easily improving the absorption characteristics of the water-absorbing resin particles obtained, and from the viewpoint of increasing the surface area of the water-absorbing resin particles, the surfactant is a sorbitan fatty acid ester (eg, sorbitan monolaurate), and/or sucrose Fatty acid esters (eg, sucrose stearic acid esters) may be used. These surfactants may be used independently and may be used in combination of 2 or more type.

0.05-10 mass parts, 0.08-5 mass parts, or 0.1-3 mass parts may be sufficient as the quantity of surfactant with respect to 100 mass parts of monomer aqueous solution.

In reversed-phase suspension polymerization, you may use together a polymer type dispersing agent together with the surfactant mentioned above. Examples of the polymeric dispersant include maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene/propylene copolymer, maleic anhydride-modified EPDM (ethylene/propylene/diene/terpolymer), maleic anhydride-modified pol Reviewtadiene, maleic anhydride/ethylene copolymer, maleic anhydride/propylene copolymer, maleic anhydride/ethylene/propylene copolymer, maleic anhydride/butadiene copolymer, polyethylene, polypropylene, ethylene/propylene copolymer , oxidized polyethylene, oxidized polypropylene, oxidized ethylene/propylene copolymer, ethylene/acrylic acid copolymer, ethyl cellulose, ethyl hydroxyethyl cellulose, and the like. A polymer type dispersing agent may be used independently and may be used in combination of 2 or more type. From the viewpoint of excellent dispersion stability of the monomer, the polymeric dispersant is maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified ethylene/propylene copolymer, maleic anhydride/ethylene copolymer, maleic anhydride/propylene At least one selected from the group consisting of copolymer, maleic anhydride/ethylene/propylene copolymer, polyethylene, polypropylene, ethylene/propylene copolymer, oxidized polyethylene, oxidized polypropylene, and oxidized ethylene/propylene copolymer okay

The quantity of a polymeric dispersing agent may be 0.05-10 mass parts, 0.08-5 mass parts, or 0.1-3 mass parts with respect to 100 mass parts of monomer aqueous solution.

The hydrocarbon dispersion medium may contain at least one compound selected from the group consisting of a chain aliphatic hydrocarbon having 6 to 8 carbon atoms and an alicyclic hydrocarbon having 6 to 8 carbon atoms. Examples of the hydrocarbon dispersion medium include chain aliphatic hydrocarbons such as n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 3-ethylpentane, and n-octane. ; Cyclohexane, methylcyclohexane, cyclopentane, methylcyclopentane, trans-1,2-dimethylcyclopentane, cis-1,3-dimethylcyclopentane, trans-1,3-dimethyl alicyclic hydrocarbons such as cyclopentane; Aromatic hydrocarbons, such as benzene, toluene, and xylene, etc. are mentioned. A hydrocarbon dispersion medium may be used independently and may be used in combination of 2 or more type.

From the viewpoint of industrial availability and stable quality, the hydrocarbon dispersion medium may contain at least one selected from the group consisting of n-heptane and cyclohexane. Further, from the same viewpoint, as the mixture of the hydrocarbon dispersion medium described above, for example, commercially available Exolheptane (manufactured by Exxon Mobil, containing 75 to 85% of hydrocarbons of n-heptane and its isomers) may be used.

The amount of the hydrocarbon dispersion medium may be 30 to 1000 parts by mass, 40 to 500 parts by mass, or 50 to 300 parts by mass relative to 100 parts by mass of the aqueous monomer solution from the viewpoint of appropriately removing the heat of polymerization and controlling the polymerization temperature. When the amount of the hydrocarbon dispersion medium is 30 parts by mass or more, control of the polymerization temperature tends to be easy. When the amount of the hydrocarbon dispersion medium is 1000 parts by mass or less, the productivity of polymerization tends to improve, which is economical.

The radical polymerization initiator may be water-soluble. Examples of the water-soluble radical polymerization initiator include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; Methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, t-butylperoxyacetate, t-butylperoxyisobutyrate, t-butylperoxypival peroxides such as lactate and hydrogen peroxide; 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[2-(N-phenylamidino)propane] dihydrochloride, 2,2'-azobis[2 -(N-allylamidino)propane] dihydrochloride, 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis{2 -[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane} dihydrochloride, 2,2'-azobis{2-methyl-N-[1,1-bis(hydride) Roxymethyl)-2-hydroxyethyl]propionamide}, 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], 4,4'-azobis(4- and azo compounds such as cyanovaleric acid). A radical polymerization initiator may be used independently and may be used in combination of 2 or more type. The radical polymerization initiator is potassium persulfate, ammonium persulfate, sodium persulfate, 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[2-(2-imida) zolin-2-yl)propane] dihydrochloride, and as 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane} dihydrochloride At least 1 type selected from the group which consists of may be sufficient.

0.00005-0.01 mol may be sufficient as the quantity of a radical polymerization initiator with respect to 1 mol of ethylenically unsaturated monomers. If the usage-amount of a radical polymerization initiator is 0.00005 mol or more, a long time is not required for a polymerization reaction, but it is efficient. When the amount of the radical polymerization initiator is 0.01 mol or less, it is easy to suppress the occurrence of a rapid polymerization reaction.

The illustrated radical polymerization initiator may be used as a redox polymerization initiator in combination with a reducing agent such as sodium sulfite, sodium hydrogen sulfite, ferrous sulfate or L-ascorbic acid.

In the case of a polymerization reaction, the monomer aqueous solution may contain the chain transfer agent. As a chain transfer agent, hypophosphite, thiols, thiolic acids, secondary alcohols, amines, etc. are mentioned.

In order to control the particle diameter of water-absorbent resin particles, the aqueous monomer solution used for polymerization may contain a thickener. As the thickener, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, polyacrylic acid, polyethylene glycol, polyacrylamide, polyethyleneimine, dextrin, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone , polyethylene oxide, and the like. When the stirring rate during polymerization is the same, the higher the viscosity of the aqueous monomer solution, the larger the median particle diameter of the obtained particles tends to be.

Although crosslinking by self-crosslinking may occur during polymerization, crosslinking may be further performed by using an internal crosslinking agent. When an internal crosslinking agent is used, it is easy to control the water absorption characteristics of the water absorbent resin particles. An internal crosslinking agent is usually added to the reaction liquid at the time of a polymerization reaction. As an internal crosslinking agent, For example, di or tri of polyols, such as ethylene glycol, propylene glycol, trimethylol propane, glycerol, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerol. (meth)acrylic acid esters; unsaturated polyesters obtained by reacting the above-mentioned polyols with unsaturated acids (maleic acid, fumaric acid, etc.); bis(meth)acrylamides such as N,N'-methylenebis(meth)acrylamide; di or tri (meth)acrylic acid esters obtained by reacting polyepoxide with (meth)acrylic acid; di(meth)acrylic acid carbamyl esters obtained by reacting polyisocyanate (tolylene diisocyanate, hexamethylene diisocyanate, etc.) with hydroxyethyl (meth)acrylate; compounds having two or more polymerizable unsaturated groups, such as allylated starch, allylated cellulose, diallyl phthalate, N,N',N''-triallylisocyanurate, and divinylbenzene; (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) polyglycidyl compounds such as propylene glycol polyglycidyl ether and polyglycerol polyglycidyl ether; haloepoxy compounds such as epichlorohydrin, epibromohydrin and α-methylepichlorohydrin; The compound which has two or more reactive functional groups, such as an isocyanate compound (2, 4- tolylene diisocyanate, hexamethylene diisocyanate, etc.), is mentioned. An internal crosslinking agent may be used independently and may be used in combination of 2 or more type. As an internal crosslinking agent, a polyglycidyl compound may be sufficient and a diglycidyl ether compound may be sufficient. The internal crosslinking agent is at least selected from the group consisting of (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerin diglycidyl ether. You may include 1 type.

The amount of the internal crosslinking agent is 0 mmol or more, 0.01 mmol or more, per 1 mol of the ethylenically unsaturated monomer, from the viewpoint that the water-soluble property is suppressed by appropriately crosslinking the polymer obtained by polymerization of the above-mentioned aqueous monomer solution and a sufficient amount of water absorption is easy to be obtained; 0.015 mmol or more or 0.020 mmol or more may be sufficient, and 0.1 mol or less may be sufficient.

An aqueous phase containing an ethylenically unsaturated monomer, a radical polymerization initiator, and, if necessary, an internal crosslinking agent, etc., and an oil phase containing a hydrocarbon-based dispersant and, if necessary, a surfactant, a polymer-based dispersant, etc. In a state, it can be heated under stirring to perform reverse-phase suspension polymerization in a water-in-oil system.

When performing reverse-phase suspension polymerization, the monomer aqueous solution containing an ethylenically unsaturated monomer is disperse|distributed in a hydrocarbon dispersion medium in presence of surfactant (and a polymer type dispersing agent further as needed). At this time, as long as it is before starting the polymerization reaction, the timing of addition of the surfactant, the polymeric dispersant, etc. may be either before or after the addition of the aqueous monomer solution.

From the viewpoint of easily reducing the amount of the hydrocarbon dispersion medium remaining in the resulting water absorbent resin, the monomer aqueous solution may be dispersed in the hydrocarbon dispersion medium in which the polymeric dispersing agent is dispersed, and then a surfactant may be further dispersed, followed by polymerization.

Reversed-phase suspension polymerization can be performed in one stage or in multiple stages of two or more stages. Reverse phase suspension polymerization may be performed in two or three stages from the viewpoint of increasing productivity.

When performing reverse phase suspension polymerization in two or more stages, after performing reverse phase suspension polymerization in the first stage, an ethylenically unsaturated monomer is added to the reaction mixture obtained by the polymerization reaction in the first stage and mixed, and the second stage is performed in the same manner as in the first stage What is necessary is just to perform the subsequent reverse-phase suspension polymerization. In the reverse phase suspension polymerization in each stage after the second stage, in addition to the ethylenically unsaturated monomer, the above-mentioned radical polymerization initiator is added at the time of reverse phase suspension polymerization in each stage after the second stage The amount of the ethylenically unsaturated monomer As a reference, it may be added within the range of the molar ratio of each component with respect to the above-mentioned ethylenically unsaturated monomer to perform reverse-phase suspension polymerization. In the reversed-phase suspension polymerization in each stage after the 2nd stage|stage, you may use an internal crosslinking agent as needed. When using an internal crosslinking agent, based on the amount of the ethylenically unsaturated monomer provided to each stage, you may add within the range of the molar ratio of each component with respect to the above-mentioned ethylenically unsaturated monomer, You may carry out reverse phase suspension polymerization.

Although the temperature of the polymerization reaction varies depending on the radical polymerization initiator used, the polymerization proceeds rapidly and the polymerization time is shortened, thereby improving economic feasibility, and from the viewpoint of easily removing the heat of polymerization and performing the reaction smoothly. 20-150 degreeC or 40-120 degreeC may be sufficient. Reaction time is 0.5 to 4 hours normally. The completion of the polymerization reaction can be confirmed, for example, by stopping the temperature rise in the reaction system. Thereby, the polymer of an ethylenically unsaturated monomer is obtained in the state of a hydrous gel-like polymer normally.

After polymerization, a crosslinking agent may be added to the obtained hydrogel polymer and heated to perform crosslinking after polymerization. By crosslinking after polymerization, the degree of crosslinking of the hydrogel polymer can be increased, thereby further improving the absorption characteristics of the water absorbent resin particles.

As a crosslinking agent for crosslinking after polymerization, for example, ethylene glycol, propylene glycol, 1,4-butanediol, trimethylol propane, glycerin, polyoxyethylene glycol, polyoxy polyols such as propylene glycol and polyglycerol; compounds having two or more epoxy groups, such as (poly)ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, and (poly) glycerin diglycidyl ether; haloepoxy compounds such as epichlorohydrin, epibromohydrin, and α-methylepichlorohydrin; compounds having two or more isocyanate groups, such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; oxazoline compounds such as 1,2-ethylenebisoxazoline; carbonate compounds such as ethylene carbonate; and hydroxyalkylamide compounds such as bis[N,N-di(β-hydroxyethyl)]adipamide. Crosslinking agents for crosslinking after polymerization are (poly)ethylene glycol diglycidyl ether, (poly)glycerin diglycidyl ether, (poly)glycerin triglycidyl ether, (poly)propylene glycol Polyglycidyl compounds, such as cold polyglycidyl ether and polyglycerol polyglycidyl ether, may be sufficient. These crosslinking agents may be used independently and may be used in combination of 2 or more type.

The amount of the crosslinking agent used for crosslinking after polymerization is 0 to 0.03 moles, 0 to 0.01 moles, or 0.00001 to 0.005 moles per mole of the water-soluble ethylenically unsaturated monomer from the viewpoint of ensuring that the water-soluble gel-like polymer obtained exhibits suitable absorption characteristics by being appropriately crosslinked. may be malleable

The crosslinking agent for crosslinking after polymerization is added to the reaction solution after the polymerization reaction of the ethylenically unsaturated monomer. In the case of multistage polymerization, a crosslinking agent for crosslinking after polymerization may be added after multistage polymerization. In consideration of heat generation during and after polymerization, retention due to process delay, system opening during addition of the crosslinking agent, and fluctuations in moisture due to addition of water according to the addition of the crosslinking agent, the crosslinking agent for crosslinking after polymerization has a moisture content (described later) From a viewpoint, you may add in the area|region of [moisture content +/-3 mass % immediately after polymerization].

Then, moisture is removed from the obtained hydrogel polymer. By drying to remove moisture, polymer particles containing a polymer of an ethylenically unsaturated monomer are obtained. As the drying method, for example, (a) a method of removing moisture by azeotropic distillation in a state in which the hydrogel polymer is dispersed in a hydrocarbon dispersion medium, (b) taking out the hydrous gel polymer by decantation, A method of drying under reduced pressure, (c) a method of separating the water-containing gel polymer by filtration through a filter and drying under reduced pressure, and the like.

The particle size of the water absorbent resin particles can be adjusted by adjusting the rotation speed of the stirrer during the polymerization reaction or by adding a coagulant to the system after the polymerization reaction or at the initial stage of drying. By adding a coagulant, the particle diameter of the water absorbent resin particle obtained can be enlarged. As the coagulant, an inorganic coagulant can be used. Examples of the inorganic coagulant (eg, powdery inorganic coagulant) include silica, zeolite, bentonite, aluminum oxide, talc, titanium dioxide, kaolin, clay, hydrotalcite, and the like. At least 1 type selected from the group which consists of silica, aluminum oxide, a talc, and kaolin may be sufficient as a viewpoint of being excellent in the aggregation effect.

In the reversed-phase suspension polymerization, the coagulant may be previously dispersed in a hydrocarbon dispersion medium or water of the same kind as that used in the polymerization, and then mixed in a hydrocarbon dispersion medium containing an aqueous gel polymer under stirring.

0.001-1 mass part, 0.005-0.5 mass part, or 0.01-0.2 mass part may be sufficient as the quantity of a coagulant with respect to 100 mass parts of ethylenically unsaturated monomers used for superposition|polymerization. When the amount of the coagulant is within these ranges, it is easy to obtain water-absorbing resin particles having a target particle size distribution.

Polymerization reaction can be performed using various stirrers which have stirring blades. As the stirring blade, a flat blade blade, a grid blade, a paddle blade, a propeller blade, an anchor blade, a turbine blade, a Powdler blade, a ribbon blade, a full zone blade, a MaxBlend blade, etc. can be used. The flat blade has a shaft (stirring shaft) and a flat plate portion (stirring portion) arranged around the shaft. The flat plate portion may further include a slit or the like.

In the production of the water-absorbent resin particles, crosslinking (surface crosslinking) of the surface portion of the hydrous gel-like polymer may be performed using a crosslinking agent in the drying step (water removal step) or any subsequent step. By performing surface crosslinking, it is easy to control the water absorption characteristics of water-absorbent resin particles. The water content of the hydrous gel-like polymer to be surface crosslinked may be 5 to 50 mass%, 10 to 40 mass%, or 15 to 35 mass%. The water content (mass %) of the hydrous gel-like polymer is calculated by the following formula.

Moisture content = [Ww/(Ww+Ws)]×100

Ww: Calculated by adding the amount of water used as necessary when mixing the coagulant, the surface crosslinking agent, etc. to the amount obtained by subtracting the amount of water discharged to the outside of the system by the drying process from the amount of water contained in the aqueous monomer solution before polymerization in the entire polymerization process Moisture content of the hydrous gel polymer.

Ws: A solid content calculated from the input amount of materials such as an ethylenically unsaturated monomer, a crosslinking agent, and an initiator constituting the hydrogel polymer.

As a crosslinking agent for surface crosslinking (surface crosslinking agent), the compound which has two or more reactive functional groups is mentioned, for example. Examples of the crosslinking agent include polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, trimethylol propane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerin. Ryu; (poly) ethylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, trimethylol propane triglycidyl ether, (poly) ) polyglycidyl compounds such as propylene glycol polyglycidyl ether and (poly)glycerol polyglycidyl ether; haloepoxy compounds such as epichlorohydrin, epibromohydrin and α-methylepichlorohydrin; isocyanate compounds such as 2,4-tolylene diisocyanate and hexamethylene diisocyanate; 3-methyl-3-oxetanemethanol, 3-ethyl-3-oxetanemethanol, 3-butyl-3-oxetanemethanol, 3-methyl-3-oxetaneethanol, 3-ethyl-3-oxetaneethanol; oxetane compounds such as 3-butyl-3-oxetaneethanol; oxazoline compounds such as 1,2-ethylenebisoxazoline; carbonate compounds such as ethylene carbonate; and hydroxyalkylamide compounds such as bis[N,N-di(β-hydroxyethyl)]adipamide. A surface crosslinking agent may be used independently and may be used in combination of 2 or more type. The surface crosslinking agent may be a polyglycidyl compound, (poly) ethylene glycol diglycidyl ether, (poly) glycerin diglycidyl ether, (poly) glycerin triglycidyl ether, (poly) ) You may contain at least 1 sort(s) chosen from the group which consists of propylene glycol polyglycidyl ether and polyglycerol polyglycidyl ether.

The quantity of a surface crosslinking agent may be 0.00001-0.02 mol, 0.00005-0.01 mol, or 0.0001-0.005 mol with respect to 1 mol of the ethylenically unsaturated monomer used for superposition|polymerization. When the amount of the surface crosslinking agent is 0.00001 mol or more, the crosslinking density in the surface portion of the water absorbent resin particles is sufficiently high, and the gel strength of the water absorbent resin particles is easily increased. When the amount of the surface crosslinking agent is 0.02 mol or less, it is easy to increase the amount of water absorbed by the water absorbent resin particles.

In the production of the water-absorbent resin particles, the surface portion of the water-containing gel polymer may be treated (surface modification) using a surface modifier in the drying step (water removal step) or any subsequent step. The surface modification may be performed, for example, before, during, or after the surface crosslinking step. Above all, surface modification may be performed after surface crosslinking. In particular, in the case of water-containing gel polymers obtained by reverse-phase suspension polymerization, aqueous solution polymerization, and other polymerization methods, when the water-containing gel polymer is treated with a surface modifier after surface crosslinking, the absorption absorption amount and the absorption amount of the permeate are the above. There is a tendency to easily form water-absorbing resin particles within the range.

Surfactants, such as a nonionic surfactant, an anionic surfactant, a cationic surfactant, and an amphoteric surfactant, may be sufficient as a surface modifier, for example. For example, the HLB value of the nonionic surfactant used as a surface modifier may be 3-12 or 6-10, for example. As a nonionic surfactant, sorbitan fatty acid ester, such as sorbitan monolaurate, is mentioned, for example. In particular, when the surface modifier is a nonionic surfactant having an HLB value within the above range, there is a tendency to easily form water absorbent resin particles having an absorption absorption amount and a permeate absorption amount within the above range. The HLB value is measured by the Griffin method.

0.01-0.50 mass part, 0.02-0.40 mass part, or 0.04-0.30 mass part may be sufficient as the quantity of a surface modifier with respect to 100 mass parts of ethylenically unsaturated monomers used for superposition|polymerization.

If necessary, after surface crosslinking and/or surface modification is performed, the dried polymer particles can be obtained by distilling off water and a hydrocarbon dispersion medium from the hydrogel polymer or the like.

The water absorbent resin particles according to the present embodiment may be composed of only polymer particles, but may further contain various additional components selected from, for example, gel stabilizers, metal chelating agents, and fluidity improving agents (lubricating agents). can The additional component may be disposed inside the polymer particle, on the surface of the polymer particle, or both. The additional component may be a fluidity improving agent (lubricating agent). The fluidity improving agent may contain inorganic particles. Examples of the inorganic particles include silica particles such as amorphous silica.

The water absorbent resin particle may contain the some inorganic particle arrange|positioned on the surface of a polymer particle. For example, by mixing a polymer particle and an inorganic particle, an inorganic particle can be arrange|positioned on the surface of a polymer particle. Silica particles, such as amorphous silica, may be sufficient as this inorganic particle. When the water absorbent resin particles include inorganic particles disposed on the surface of the polymer particles, the ratio of the amount of the inorganic particles to the mass of the polymer particles is 0.2% by mass or more, 0.5% by mass or more, 1.0% by mass or more, or 1.5 Mass % or more may be sufficient, 5.0 mass % or less, or 3.5 mass % or less may be sufficient. The inorganic particles here usually have a small size compared with the size of the polymer particles. For example, the average particle diameter of an inorganic particle may be 0.1-50 micrometers, 0.5-30 micrometers, or 1-20 micrometers. The average particle diameter here may be a value measured by a dynamic light scattering method or a laser diffraction/scattering method.

1 is a cross-sectional view showing an example of an absorbent sheet. The absorbent sheet 50 shown in FIG. 1 includes a first absorbent layer 10a, a second absorbent layer 10b, and three core wrap sheets 20a, 20b, and 20c. Core wrap sheets 20a and 20c are disposed on both sides of the first absorbent layer 10a, and core wrap sheets 20b and 20c are disposed on both sides of the second absorbent layer 10b. In other words, the first absorbent layer 10a is disposed inside the core wrap sheets 20a and 20c, and the second absorbent layer 10b is disposed inside the core wrap sheets 20b and 20c. The first absorbent layer 10a and the second absorbent layer 10b are sandwiched between the two core wrap sheets 20a and 20b, thereby retaining shape. The core wrap sheets 20a and 20b may be individual sheets, a single folded sheet, or a single bag body.

The absorbent sheet 50 may further include an adhesive 21 interposed between the core wrap sheet 20a and the first absorbent layer 10a and between the core wrap sheet 20b and the second absorbent layer 10b. do. 2 is a plan view showing an example of an adhesive application pattern formed on a core wrap sheet. The adhesive 21 shown in FIG. 2 forms an application pattern composed of a plurality of linear portions arranged at intervals on the core wrap sheet 20a. The application pattern of the adhesive 21 may be linear, curved, dotted, or a combination thereof. The adhesive 21 may be interposed only between the core wrap sheet 20a and the first absorbent layer 10a or between the core wrap sheet 20b and the second absorbent layer 10b. The absorbent sheet 50 does not need to have the adhesive 21 . The adhesive 21 may be, for example, an aqueous adhesive, a solvent adhesive, an elastic adhesive, an aerosol adhesive, or a hot melt adhesive.

Each of the first absorption layer 10a and the second absorption layer 10b is an absorption layer including the above-described water-absorbing resin particles. The first absorbent layer 10a includes the first water absorbent resin particles 11a. The absorption and absorption of the first water absorbent resin particles 11a is 10.5 g/g or more, and the absorption amount of the permeate of the first water absorbent resin particles 11a is 12.5 g/g or more. The first absorbent layer 10a has, in addition to the first water absorbent resin particles 11a, a fibrous layer 12a made of a fibrous material. The second absorbent layer 10b includes the second water absorbent resin particles 11b and a fibrous layer 12b containing a fibrous material. The first absorbent layer 10a does not need to include the fibrous layer 12a. Similarly, the second absorbent layer 10b does not need to include the fibrous layer 12b. The 2nd water absorbent resin particle 11b may be the same type as the 1st water absorbent resin particle 11a, or a different type may be sufficient as it.

The content of the water absorbent resin particles in the absorbent layer may be 70 to 100 mass%, 80 to 100 mass%, or 90 to 100 mass% based on the mass of the absorbent layer.

The thickness of the first absorption layer 10a and the thickness of the second absorption layer 10b may be, respectively, in a dry state, for example, 20 mm or less, 15 mm or less, 10 mm or less, 5 mm or less, 4 mm or less, or 3 mm or less, and 0.1 mm or more, or 0.3 mm or more may be sufficient. The thickness of the first absorption layer 10a and the thickness of the second absorption layer 10b may be the same or different.

The mass per unit area of the first absorption layer 10a and the second absorption layer 10b may be 800 g/m ² or less, 600 g/m ² or less, or 400 g/m ² or less, respectively, and may be 50 g/m ² or more and 80 g/m 2 or less. m ² or more, or 100 g/m ² or more may be sufficient. The mass per unit area of the first absorption layer 10a and the mass per unit area of the second absorption layer 10b may be the same or different.

The fibrous material constituting the fibrous layers 12a and 12b may be, for example, cellulosic fibers, synthetic fibers, or a combination thereof. Examples of cellulosic fibers include pulverized wood pulp, cotton, cotton linter, rayon, and cellulose acetate. Examples of synthetic fibers include polyamide fibers, polyester fibers, and polyolefin fibers. The fibrous material may be a hydrophilic fiber (for example, pulp).

The first absorption layer 10a and the second absorption layer 10b may further contain inorganic particles (eg, amorphous silica), a deodorant, an antibacterial agent, a perfume, and the like. When the first water absorbent resin particles 11a contain inorganic particles, the first water absorbent layer 10a may contain inorganic particles different from the inorganic particles in the first water absorbent resin particles 11a. Similarly, when the second water absorbent resin particles 11b contain inorganic particles, the second water absorbent layer 10b may contain inorganic particles different from the inorganic particles in the second water absorbent resin particles 11b.

The core wrap sheets 20a, 20b, and 20c may be, for example, non-woven fabric. The core wrap sheets 20a, 20b, and 20c may be the same or different nonwoven fabrics. For example, the core wrap sheets 20a and 20b may be a nonwoven fabric of the same type, and the core wrap sheet 20c may be a nonwoven fabric of a different type from these. The nonwoven fabric may be a nonwoven fabric (short fiber nonwoven fabric) composed of short fibers (ie, staples), or may be a nonwoven fabric composed of long fibers (ie filaments) (long fiber nonwoven fabric). The staple may generally have a fiber length of several hundred mm or less.

The core wrap sheets 20a, 20b, and 20c are a thermal bond nonwoven fabric, an air through nonwoven fabric, a resin bond nonwoven fabric, a spun bond nonwoven fabric, a melt blown nonwoven fabric, an air laid nonwoven fabric, a spun lace nonwoven fabric, a point bond nonwoven fabric, or 2 selected from these A laminate containing more than one type of nonwoven fabric may be used.

The nonwoven fabric used as the core wrap sheets 20a, 20b, and 20c may be a nonwoven fabric formed by synthetic fibers, natural fibers, or a combination thereof. Examples of synthetic fibers include polyolefins such as polyethylene (PE) and polypropylene (PP), polyester such as polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT) and polyethylene naphthalate (PEN), and poly such as nylon and fibers comprising a synthetic resin selected from amide and rayon. Examples of natural fibers include fibers comprising cotton, silk, hemp, or pulp (cellulose). The fibers forming the nonwoven fabric may be polyolefin fibers, polyester fibers, or a combination thereof. The core wrap sheets 20a, 20b, and 20c may be tissues.

The absorbent sheet 50 can be obtained, for example, by the following method. First, the first water absorbent resin particles 11a or a mixture containing the first water absorbent resin particles 11a and the fibrous material is sandwiched between the core wrap sheets 20a and 20c. Next, the second water absorbent resin particles 11b or a mixture containing the second water absorbent resin particles 11b and the fibrous material is sandwiched between the core wrap sheets 20b and 20c. The core wrap sheet 20a, the first absorbent layer 10a, the core wrap sheet 20c, the second absorbent layer 10b, and the core wrap sheet ( 20b) can be obtained in which the absorbent sheet 50 is arranged in this order. If necessary, between the core wrap sheet 20a, the first water absorbent resin particles 11a, or a mixture containing the same, and/or the core wrap sheet 20b and the second water absorbent resin particles 11b; Alternatively, the adhesive 21 is disposed between the mixture containing the same.

The absorbent sheet 50 is used in order to manufacture various absorbent articles, for example. Examples of the absorbent article include diapers (eg, paper diapers), toilet training pants, incontinence pads, sanitary materials (sanitary napkins, tampons, etc.), sweat-absorbing pads, pet sheets, toilet members, and animal excreta disposal materials. can be heard

3 : is sectional drawing which shows an example of an absorbent article. The absorbent article 100 shown in Fig. 3 includes an absorbent sheet 50 having a first absorbent layer 10a and a second absorbent layer 10b, a liquid-permeable sheet 30, and a liquid-impermeable sheet 40. do. In other words, the absorbent sheet 50 is sandwiched between the liquid-permeable sheet 30 and the liquid-impermeable sheet 40 .

The absorbent sheet 50 is disposed in a direction in which the first absorbent layer 10a is on the liquid-impermeable sheet 40 side. That is, the water-absorbing layer of the outermost layer on the liquid-impermeable sheet 40 side contains the first water-absorbing resin particles 11a.

The liquid-permeable sheet 30 is disposed at the position of the outermost layer on the side where the liquid to be absorbed enters. The liquid-permeable sheet 30 is disposed on the outside of the core wrap sheet 20b in a state in contact with the core wrap sheet 20b. The liquid-impermeable sheet 40 is disposed at the position of the outermost layer on the side opposite to the liquid-permeable sheet 30 in the absorbent article 100 . The liquid-impermeable sheet 40 is disposed on the outside of the core wrap sheet 20a in a state in contact with the core wrap sheet 20a. The liquid-permeable sheet 30 and the liquid-impermeable sheet 40 have main surfaces wider than the main surface of the absorbent sheet 50 , and the liquid-permeable sheet 30 and the liquid-impervious sheet 40 have outer edges The portion extends around the first absorbent layer 10a, the second absorbent layer 10b, and the core wrap sheets 20a, 20b. However, the magnitude relationship between the absorbent layers 10a and 10b, the core wrap sheets 20a and 20b, the liquid-permeable sheet 30, and the liquid-impermeable sheet 40 is appropriately adjusted according to the use of the absorbent article or the like.

The liquid-permeable sheet 30 may be a nonwoven fabric. The nonwoven fabric used as the liquid-permeable sheet 30 may have appropriate hydrophilicity from the viewpoint of the liquid absorption performance of the absorbent article. From that point of view, the liquid-permeable sheet 30 is a paper pulp test method No. 1 by the Paper Pulp Technology Association. 68 (2000) may be a nonwoven fabric having a hydrophilicity of 5 to 200 measured according to the measurement method. The hydrophilicity of the nonwoven fabric may be 10-150. Paper Pulp Test Method No. For details of 68, reference can be made, for example to WO2011/086843.

The nonwoven fabric having hydrophilicity may be formed of fibers exhibiting appropriate hydrophilicity, such as rayon fibers, or those formed by fibers obtained by hydrophilizing hydrophobic chemical fibers such as polyolefin fibers and polyester fibers. okay As a method of obtaining a nonwoven fabric containing hydrophobic chemical fibers treated with hydrophilicity, for example, a method of obtaining a nonwoven fabric by a spun bonding method using a mixture of a hydrophobic chemical fiber with a hydrophilizing agent, a spunbonding nonwoven fabric using a hydrophobic chemical fiber A method of entraining a hydrophilicizing agent when producing a spun-bonded nonwoven fabric obtained by using a hydrophobic chemical fiber may be impregnated with a hydrophilicizing agent. Examples of the hydrophilizing agent include anionic surfactants such as aliphatic sulfonates and higher alcohol sulfate ester salts, cationic surfactants such as quaternary ammonium salts, polyethylene glycol fatty acid esters, polyglycerol fatty acid esters, sorbitan fatty acid esters, etc. Silicone surfactants, such as an ionic surfactant and polyoxyalkylene modified silicone, and the stain release agent etc. which consist of polyester-type, polyamide-type, acryl-type, and urethane-type resin are used.

The weight per unit area (mass per unit area) of the nonwoven fabric used as the liquid-permeable sheet 30 is, from the viewpoint of imparting good liquid permeability, flexibility, strength and cushioning properties to the absorbent article, and speeding up the liquid permeation rate of the absorbent article. From the viewpoint of doing, 5-200 g/m ² , 8-150 g/m ² , or 10-100 g/m ² may be sufficient. The thickness of the liquid-permeable sheet 30 may be 20 to 1400 µm, 50 to 1200 µm, or 80 to 1000 µm.

The liquid-impermeable sheet 40 prevents the liquid absorbed in the absorbent layer 10 from leaking from the liquid-impermeable sheet 40 side to the outside. The liquid-impermeable sheet 40 may be a resin sheet or a nonwoven fabric. The resin sheet may be a sheet made of a synthetic resin such as polyethylene, polypropylene, or polyvinyl chloride. The nonwoven fabric may be a spunbonded/meltblown/spunbonded (SMS) nonwoven fabric in which a water-resistant meltblown nonwoven fabric is sandwiched by a high-strength spunbonded nonwoven fabric. Further, the liquid-impermeable sheet 40 may be a composite sheet of a resin sheet and a nonwoven fabric (eg, spunbond nonwoven fabric or spunlace nonwoven fabric). The liquid-impermeable sheet 40 may have air permeability from the viewpoint of reducing moisture during wearing and reducing discomfort to the wearer. As the liquid-impermeable sheet 40 having air permeability, for example, a sheet of low-density polyethylene (LDPE) resin can be used.

The weight per unit area (mass per unit area) of the liquid-impermeable sheet 40 may be 5 to 100 g/m ² , or 10 to 50 g/m ² , from the viewpoint of ensuring flexibility so as not to impair the wearing comfort of the absorbent article.

The absorbent article 100 can be manufactured, for example, by a method comprising disposing the absorbent sheet 50 between the liquid-permeable sheet 30 and the liquid-impermeable sheet 40 . The laminated body laminated in this order of the liquid-impermeable sheet 40, the absorbent sheet 50, and the liquid-permeable sheet 30 is pressed as necessary. Alternatively, the liquid-permeable sheet 30, the core wrap sheet 20b, the first water absorbent resin particles 11a, or a mixture containing the first water absorbent resin particles 11a and a fibrous material, and the core wrap sheet 20c ), the second water absorbent resin particles 11b, or a mixture containing the second water absorbent resin particles 11b and a fibrous material, and the core wrap sheet 20a and the liquid impermeable sheet 40 are arranged in this order, The absorbent article 100 can also be obtained by the method of pressurizing, heating the formed structure as needed. Moreover, you may couple|bond together between each structural unit with an adhesive agent.

Example

Hereinafter, the present invention will be described in more detail by way of Examples. However, the present invention is not limited to these Examples.

1. Preparation of water absorbent resin particles

Preparation Example 1

A reflux condenser, a dropping funnel, a nitrogen gas introduction tube, and a stirrer (agitating blade having two stages of four inclined paddle blades (surface-treated with fluororesin) with a blade diameter of 5 cm) with an inner diameter of 11 cm and an internal volume of 2 L; Four round-bottom cylindrical separable flasks with sidewall baffles (baffle width: 7 mm, baffle length: 10 cm) were prepared. To this flask, 451.4 g of n-heptane as a hydrocarbon dispersion medium was added, and 1.104 g of sorbitan monolaurate (Nonion LP-20R, HLB value: 8.6, manufactured by Nichiyu Corporation) as a surfactant was added to obtain a mixture. . The mixture was heated up to 50°C while stirring at a rotation speed of 300 rpm of a stirrer to dissolve sorbitan monolaurate in n-heptane, and then the mixture was cooled to 40°C.

Next, 92.0 g (acrylic acid: 1.03 mol) of 80.5 mass % acrylic acid aqueous solution was put into the Erlenmeyer flask with an internal volume of 500 mL. Then, an aqueous solution of partially neutralized acrylic acid was obtained by neutralizing acrylic acid by dropping 147.7 g of a 20.9 mass % aqueous sodium hydroxide solution dropwise while cooling from the outside. Next, an aqueous monomer solution was prepared by dissolving 0.1012 g (0.374 mmol) of potassium persulfate as a water-soluble radical polymerization initiator in an aqueous solution of partially neutralized acrylic acid.

After adding the above-mentioned aqueous monomer solution to the above-mentioned separable flask, the inside of the system was sufficiently substituted with nitrogen. Then, while stirring at 700 rpm of rotation speed of the stirrer, the flask was immersed in a water bath at 70° C., and then maintained for 60 minutes to complete polymerization, thereby obtaining a hydrogel polymer.

Then, while stirring at 1000 rpm of rotation speed of the stirrer, amorphous silica (Oriental Silicas Corporation, Tokusil NP-S) as a powdery inorganic coagulant in the resulting polymerization solution containing the hydrous gel-like polymer, n-heptane and surfactant The dispersion obtained by dispersing 0.092 g in 100 g of n-heptane in advance was added, followed by mixing for 10 minutes. Thereafter, the flask containing the reaction solution was immersed in an oil bath at 125°C, and 129.0 g of water was withdrawn out of the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Then, after adding 4.14 g (ethylene glycol diglycidyl ether: 0.475 mmol) of a 2 mass % aqueous solution of ethylene glycol diglycidyl ether as a surface crosslinking agent, 2 at an internal temperature of 83±2 degreeC time kept

Next, a surfactant solution in which 0.074 g of sorbitan monolaurate (trade name: Nonion LP-20R, HLB value 8.6, manufactured by Nichiyu Corporation) as a surfactant was dissolved in 6.62 g of n-heptane was added.

Then, water and n-heptane were evaporated at 120 degreeC, and the dried product was obtained by drying until the vaporized material from the system inside hardly flows out. This dried product was passed through a sieve having an eye size of 850 µm to obtain 90.1 g of water-absorbing resin particles. The median particle diameter of the water-absorbing resin particles was 382 µm.

The absorbent amount of the water absorbent resin particles of Production Example 1 was 60 g/g, and the water absorbent amount of the water absorbent resin particles under load was 32.5 mL/g.

Preparation 2

The amount of sorbitan monolaurate added into the separable flask before addition of the aqueous monomer solution was changed from 1.104 g to 0.97 g, and the amount of water extracted by azeotropic distillation of n-heptane and water was changed from 129.0 g to 131.0 g Except having carried out, it carried out similarly to manufacture example 1, and obtained water absorbing resin particle. The median particle diameter of the water-absorbing resin particles was 384 µm.

The absorbent amount of the water absorbent resin particles of Production Example 2 was 63 g/g, and the water absorbent amount of the water absorbent resin particles under load was 30.5 mL/g.

Preparation 3

Equipped with a reflux condenser, a dropping funnel, a nitrogen gas introduction tube, and a stirring blade having two stages of four inclined paddle blades (surface-treated with fluororesin) with a blade diameter of 5 cm as a stirrer, 11 cm inner diameter, 2 L capacity, Four round-bottom cylindrical separable flasks with sidewall baffles (baffle width: 7 mm) were prepared. To this flask, put 451.4 g of n-heptane as a petroleum hydrocarbon dispersion medium, add 0.984 g of sorbitan monolaurate (Nonion LP-20R, HLB value 8.6, manufactured by Nichiyu Corporation) as a surfactant, and stir The rotation speed was 300 rpm, and it heated to 50 degreeC. After dissolving sorbitan monolaurate in n-heptane by heating, the internal temperature was cooled to 40°C.

In an Erlenmeyer flask with a volume of 500 mL, 92.0 g (1.03 mol) of an 80.5 mass % aqueous acrylic acid solution was put, and 147.7 g of a 20.9 mass % aqueous sodium hydroxide solution was added dropwise while cooling this from the outside to neutralize 75 mol%. Next, 0.101 g (0.374 mmol) of potassium persulfate was added as a radical polymerization initiator to the obtained aqueous solution of partially neutralized acrylic acid, and it was made to melt|dissolve, and the monomer aqueous solution was prepared.

The aqueous monomer solution was added to the separable flask, and the inside of the system was sufficiently substituted with nitrogen, the rotation speed of the stirrer was set to 700 rpm, the flask was immersed in a water bath at 70° C., and held for 60 minutes.

After that, the rotation speed of the stirrer was set to 1000 rpm, and amorphous silica (Oriental Silicas Corporation, Tokusil NP-S) 0.092 as a powdery inorganic coagulant was added to the resulting polymerization solution containing hydrogel, n-heptane and surfactant. g previously dispersed in 100 g of n-heptane was added, followed by mixing for 10 minutes. Thereafter, the flask containing the reaction solution is immersed in an oil bath at 125° C., and 112 g of water is withdrawn out of the system while refluxing n-heptane by azeotropic distillation of n-heptane and water, and then ethylene glycol as a post-crosslinking agent. 4.97 g (2.85 mmol) of 10 mass % aqueous solution of cold diglycidyl ether was added, and it hold|maintained at 83±2 degreeC of internal temperature for 2 hours.

Next, a surfactant solution in which 0.074 g of sorbitan monolaurate (trade name: Nonion LP-20R, HLB value 8.6, manufactured by Nichiyu Corporation) as a surfactant was dissolved in 6.62 g of n-heptane was added.

After that, the water and n-heptane are evaporated and dried until almost no evaporation from the system flows out, the flask is once removed from the oil bath, and 13.8 g of water is sprayed at a flow rate of 0.3 g/sec. sprayed with Thereafter, the system was maintained at 80°C for 30 minutes while spraying nitrogen at a flow rate of 200 mL/min into the system to obtain a dried product. The dried product was passed through a sieve having an eye size of 850 µm to obtain 90.5 g of water-absorbing resin particles. The median particle diameter of the water-absorbing resin particles was 368 µm.

The absorbent amount of the water absorbent resin particles of Production Example 3 was 63 g/g, and the water absorbent amount of the water absorbent resin particles under load was 32.0 mL/g.

Preparation 4

A round-bottomed cylindrical separable flask with an inner diameter of 110 mm equipped with a reflux condenser, a nitrogen gas introduction tube, and a stirring blade (a fluororesin coated on the surface) having two stages of four inclined paddle blades with a blade diameter of 50 mm as a stirrer prepared 451.4 g of n-heptane as a hydrocarbon dispersion medium was taken into this flask, and 1.104 g of sorbitan monolaurate of HLB 8.6 (Nichiyo Co., Ltd., Nonion LP-20R) was added as a surfactant, and stirred in a water bath at 80°C. The temperature was raised by immersion. Next, the inside of the system was sufficiently substituted with nitrogen.

92 g (1.03 mol) of an 80.5 mass % aqueous solution of acrylic acid was put into an Erlenmeyer flask with a volume of 500 mL, and 147.7 g of a 20.9 mass % sodium hydroxide aqueous solution was added dropwise while cooling this from the outside to neutralize. In the solution after neutralization, 0.1104 g (0.407 mmol) of 2,2'-azobis(2-amidinopropane) dihydrochloride as an azo compound and 0.0092 g (0.0528 mmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent ) was added and dissolved to prepare an aqueous monomer solution.

Next, after sufficiently venting nitrogen through the aqueous monomer solution, the number of rotations of the stirrer was set to 1000 rpm, and it was added dropwise to the separable flask at a constant rate so that the dropping time of the entire amount of the aqueous monomer solution was 7 minutes. Then, after the dropwise addition was completed, 0.41 g (0.047 mmol) of a 2% by mass aqueous ethylene glycol diglycidyl ether aqueous solution was added as an intermediate crosslinking agent into the separable flask, and maintained at 80° C. for 20 minutes to obtain an aqueous gel-like polymer. .

Next, the reaction solution was heated in the separable flask with an oil bath of 125° C., and 105 g of water was withdrawn out of the system while refluxing n-heptane into the system by azeotropic distillation of n-heptane and water, and then the separable flask 4.14 g (0.475 mmol) of a 2 mass % ethylene glycol diglycidyl ether aqueous solution was added as a post-crosslinking agent inside, and it hold|maintained at 83 degreeC for 120 minutes.

Next, a surfactant solution in which 0.074 g of sorbitan monolaurate (trade name: Nonion LP-20R, HLB value 8.6, manufactured by Nichiyu Corporation) as a surfactant was dissolved in 6.62 g of n-heptane was added to a separable flask. .

Thereafter, water and n-heptane were evaporated and dried until the evaporated substance from the system hardly flowed out, thereby obtaining a dried product of polymer particles. By passing this dry product through a sieve having an eye size of 850 µm, 70.0 g of granular water-absorbing resin particles were obtained. The median particle diameter of the water absorbent resin particles was 448 µm.

The absorbent amount of the water absorbent resin particles of Production Example 4 was 63 g/g, and the water absorbent amount of the water absorbent resin particles under load was 33.1 mL/g.

Preparation 5

[Preparation of aqueous monomer solution]

130.0 g (1.80 mol) of 100% acrylic acid was placed in a 2L separable flask. After adding 112.3 g of ion-exchanged water while stirring the inside of the separable flask, 112.85 g of 48 mass% sodium hydroxide was added dropwise under an ice bath to prepare a partially neutralized acrylic acid solution having a monomer concentration of 45 mass% and a neutralization rate of 75 mol%. .

[polymerization]

A stirrer (8 mm in diameter, 40 mm in length) is placed in a stainless steel bat (φ 20 cm), and 340.0 g of acrylic acid partially neutralized liquid (monomer concentration: 45 mass%, neutralization rate of acrylic acid: 75 mol%) as a monomer used for polymerization, 32.6 g of ion-exchanged water , and 0.0541 g (0.311 mmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent, and then a stirrer was rotated to uniformly disperse the mixture (acrylic acid partially neutralized solution concentration of 38% by mass) to obtain a mixture. Then, the upper part of the stainless batt was sealed with the polyethylene film, and the inside of the stainless bat was covered. After adjusting the temperature of the said mixture in the stainless steel vat to 25 degreeC, the mixture was replaced with nitrogen and the amount of dissolved oxygen was made into 0.1 ppm or less. Next, 24.75 g (1.831 mmol) of 2 mass % potassium persulfate aqueous solution and 5.20 g of 0.5 mass % L-ascorbic acid aqueous solution were dripped sequentially under stirring at 300 rpm, and the monomer aqueous solution was adjusted. Polymerization was started immediately after the 0.5 mass % L-ascorbic acid aqueous solution was dripped. After 10 minutes from the start of polymerization, the obtained post-polymerization gel was placed in a container and immersed in a water bath at 75° C. and aged for 20 minutes. The thickness of the obtained gel after polymerization was 1.3 cm.

[Pulverization of gel after polymerization]

The whole amount of the hydrous gel-like polymer after aging was taken out from the container, and cut-outs were placed in a grid shape at intervals of 5 cm and cut. The entire amount of the hydrous gel-like polymer cut at 5 cm intervals was sequentially put into a meat chopper 12VR-750SDX manufactured by Gireroyal, and crushed. The diameter of the hole of the plate located at the exit of the meat chopper was 6.4 mm. Crushing was performed until the crushed gel (hydrous gel crushed product) ceased to come out from the meat chopper plate. At this time, the amount of water-containing gel polymer put into the meat chopper was 390 g, and the amount of water-containing gel crushed product that was discharged and recovered was 217 g.

[Drying of crushed gel]

The crushed gel was spread on a sieve having an eye size of 850 μm, and dried for 30 minutes with a hot air dryer (manufactured by ADVANTEC, model number: DRE320DB) set at 180° C. to obtain a dried product.

[Pulverization of dry matter]

The above-mentioned dried product was pulverized with an ultracentrifugal mill (manufactured by Budder Scientific Co., Ltd., ZM200, six-blade rotor, rotor rotation speed: 6000 rpm, screen hole hole: 1.00 mm) to obtain 101 g of crosslinked polymer particles. The same operation was repeated from polymerization to pulverization to obtain a crosslinked polymer having a total weight of 198 g.

[Surface crosslinking]

25.0 g of the pulverized particles were weighed into a round-bottomed cylindrical separable flask with an inner diameter of 11 cm provided with an anchor-type stirring blade made of fluororesin. Next, while stirring at 500 rpm, an aqueous solution of a crosslinking agent obtained by mixing 0.060 g of ethylene glycol diglycidyl ether, 3.6 g of water, 1.20 g of propylene glycol, and 1.20 g of isopropyl alcohol was added into a separable flask. did. The mixture obtained by this addition was spread evenly on a fluororesin-coated tray, and then heated at 180°C for 40 minutes. After cooling to room temperature, crosslinked polymer particles after surface crosslinking were obtained by passing through an 850 µm mesh. The said surface crosslinking operation was performed 7 times in total, and 165g of crosslinked polymer particles were obtained.

[Classification of crosslinked polymer particles]

The crosslinked polymer particles after surface crosslinking described above were classified using a sieve of 850 µm, a sieve of 180 µm, and a tray. Those that passed through a sieve having an eye size of 850 µm and remained on the 180 µm sieve were recovered as raw material particles, and those that passed through a 180 µm sieve were collected as raw material fine particles.

[Granulation of crosslinked polymer particles]

3.75 g of the above-mentioned raw material fine particles were put into a 100 mL New Dispo Cup (manufactured by As One Corporation, CODE1-4620-01). While stirring at 600 rpm with a magnetic stirrer bar (without a ring of 8 mm φ × 45 mm), 5.63 g of ion-exchanged water is added dropwise at 0.1 g/sec using a macropipette (manufactured by Shibata Chemical Co., Ltd., 10 mL volume), dropwise for 1 minute stirred. Then, 8.75g of the raw material particles mentioned above were thrown in, and it further stirred at 600 rpm for 1 minute, and obtained the aggregate.

The whole amount of the above-mentioned aggregate was transferred to a glass petri dish (inner diameter 5.8 cm) using a spatula, and dried for 150 minutes with a hot air dryer (manufactured by ADVANTEC, model number: DRE320DB) set at 80 ° C. to obtain a dried product of the aggregate. This assembly operation was repeated 5 times.

The dried product of the agglomerate obtained above was put into an ultracentrifugal mill (manufactured by Budder Scientific Co., Ltd., ZM200, 6-blade rotor, rotor rotation speed: 6000 rpm, screen formulation hole: 1.00 mm, inlet diameter φ3 cm) and pulverized to obtain polymer particles 60 g was obtained. This polymer particle was passed through a sieve having an eye size of 500 µm. Then, 0.5 mass % of amorphous silica (Oriental Silicas Corporation, Tokusil NP-S) was mixed with the polymer particle with respect to the mass of the polymer particle, and 43.3 g of water absorbing resin particles containing amorphous silica were obtained. The median particle diameter was 208 µm.

The absorbent amount of the water absorbent resin particles of Production Example 5 was 50 g/g, and the water absorbent amount of the water absorbent resin particles under load was 27.0 mL/g.

Preparation 6

[Polymerization reaction in the first stage]

As a reflux condenser, a dropping funnel, a nitrogen gas introduction tube, and a stirrer, a round-bottomed cylindrical separable flask having an inner diameter of 11 cm and a capacity of 2 L equipped with a stirring blade having two stages of four inclined paddle blades with a blade diameter of 5 cm was prepared. To this flask, 293.0 g of n-heptane as a hydrocarbon dispersion medium, 0.736 g of maleic anhydride-modified ethylene/propylene copolymer (Mitsui Chemical Co., Ltd., High Wax 1105A) as a polymeric dispersant was added and stirred to 80° C. After heating up and dissolving a dispersing agent, it cooled to 50 degreeC.

To a 300 mL beaker, take 92.0 g (1.03 mol) of an 80.5 mass % aqueous acrylic acid solution as a water-soluble ethylenically unsaturated monomer, and while cooling from the outside, 147.7 g of a 20.9 mass % aqueous sodium hydroxide solution is added dropwise to neutralize 75 mol% , hydroxyethyl cellulose 0.092 g (Sumitomo Seika Co., Ltd., HECAW-15F) as a thickener, and 2,2'-azobis (2-amidinopropane) dihydrochloride as a water-soluble radical polymerization initiator 0.092 g (0.339 mmol) and 0.018 g (0.067 mmol) of potassium persulfate and 0.010 g (0.057 mmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent were added and dissolved to prepare an aqueous monomer solution in the first stage.

Then, the aqueous solution prepared above was added to a separable flask, stirred for 10 minutes, and then sucrose stearic acid ester of HLB 3 as a surfactant in 6.62 g of n-heptane (Mitsubishi Chemical Foods Co., Ltd., Lyoto Sugar Ester S- 370) A surfactant solution obtained by dissolving 0.736 g by heating is further added, the rotation speed of the stirrer is set to 550 rpm and the inside of the system is sufficiently substituted with nitrogen while stirring, and then the flask is immersed in a water bath at 70 ° C. By carrying out for 60 minutes, the polymerization slurry liquid of a 1st stage|stage was obtained.

[Second stage polymerization reaction]

128.8 g (1.44 mol) of an 80.5 mass % aqueous acrylic acid solution as a water-soluble ethylenically unsaturated monomer was taken into a 500 mL beaker, and while cooling from the outside, 159.0 g of a 27 mass % aqueous sodium hydroxide solution was added dropwise to neutralize 75 mol%. After carrying out, 0.129 g (0.476 mmol) of 2,2'-azobis(2-amidinopropane) dihydrochloride as a water-soluble radical polymerization initiator, 0.026 g (0.096 mmol) of potassium persulfate, and ethylene glycol as an internal crosslinking agent 0.0116 g (0.067 mmol) of diglycidyl ether was added and dissolved to prepare an aqueous monomer solution in the second stage.

After cooling the inside of the separable flask system to 25° C. while stirring the rotation speed of the stirrer at 1000 rpm, the entire amount of the aqueous monomer solution in the second stage is added to the polymerization slurry liquid in the first stage, After replacing with nitrogen for 30 minutes, the flask was again immersed in a water bath at 70°C to raise the temperature, and polymerization reaction was performed for 60 minutes. Thus, a hydrous gel-like polymer was obtained.

After polymerization in the second stage, 0.589 g of a 45% by mass aqueous solution of pentasodium diethylenetriaminepentaacetic acid was added to the hydrogel polymer under stirring. Thereafter, the reaction solution was heated with an oil bath at 125°C, and 239.2 g of water was taken out of the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Then, 4.42 g (0.507 mmol) of a 2 mass % ethylene glycol diglycidyl ether aqueous solution was added to the flask as a post-crosslinking agent, and it hold|maintained at 83 degreeC for 2 hours.

Thereafter, water and n-heptane were evaporated to dryness at 125°C to obtain a dried product of polymer particles. The polymer particles were passed through a sieve having an eye size of 850 μm, and 0.2 mass % of amorphous silica (Oriental Silicas Corporation, Tokusil NP-S) was mixed with respect to the mass of the polymer particles to obtain water absorbent resin particles containing amorphous silica. 228.1 g was obtained. The median particle diameter of the water absorbent resin particles was 362 µm.

The absorbent amount of the water absorbent resin particles of Production Example 6 was 61 g/g, and the water absorbent amount of the water absorbent resin particles under load was 39.5 mL/g. The liquid permeation time of the water absorbent resin particles was 30.8 seconds.

Preparation 7

[Polymerization reaction in the first stage]

As a reflux condenser, a dropping funnel, a nitrogen gas introduction tube, and a stirrer, a round-bottomed cylindrical separable flask having an inner diameter of 11 cm and a capacity of 2 L equipped with a stirring blade having two stages of four inclined paddle blades with a blade diameter of 5 cm was prepared. To this flask, 293 g of n-heptane as a hydrocarbon dispersion medium, 0.736 g of maleic anhydride-modified ethylene/propylene copolymer (Mitsui Chemical Co., Ltd., High Wax 1105A) as a polymeric dispersant was added, and the temperature was raised to 80° C. while stirring. After dissolving the dispersant, it was cooled to 50°C.

To a 300 mL beaker, take 92.0 g (1.03 mol) of an 80.5 mass % aqueous acrylic acid solution as a water-soluble ethylenically unsaturated monomer, and while cooling from the outside, 147.7 g of a 20.9 mass % aqueous sodium hydroxide solution is added dropwise to neutralize 75 mol% After hydroxyethyl cellulose 0.092 g (Sumitomo Seika Co., Ltd., HECAW-15F) as a thickener, sodium persulfate 0.0736 g (0.272 mmol) as a water-soluble radical polymerization agent, ethylene glycol diglycidyl ether as an internal crosslinking agent 0.010 g (0.057 mmol) was added and dissolved to prepare an aqueous monomer solution in the first stage.

Then, the aqueous solution prepared above was added to a separable flask, stirred for 10 minutes, and then sucrose stearic acid ester of HLB 3 as a surfactant in 6.62 g of n-heptane (Mitsubishi Chemical Foods Co., Ltd., Lyoto Sugar Ester S- 370) A surfactant solution in which 0.736 g was dissolved by heating was further added, the rotation speed of the stirrer was set to 500 rpm, and the inside of the system was sufficiently substituted with nitrogen while stirring, and then the flask was immersed in a water bath at 70 ° C. By carrying out for 60 minutes, the polymerization slurry liquid of a 1st stage|stage was obtained.

[Second stage polymerization reaction]

128.8 g (1.44 mol) of an 80.5 mass % aqueous acrylic acid solution as a water-soluble ethylenically unsaturated monomer was taken into a 500 mL beaker, and while cooling from the outside, 159.0 g of a 27 mass % aqueous sodium hydroxide solution was added dropwise to neutralize 75 mol%. After that, 0.090 g (0.333 mmol) of potassium persulfate as a water-soluble radical polymerization initiator and 0.0116 g (0.067 mmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent were added and dissolved to prepare an aqueous monomer solution in the second stage. did.

After cooling the inside of the separable flask system to 44° C. while stirring the rotation speed of the stirrer at 1000 rpm, the entire amount of the aqueous liquid in the second stage is added to the polymerization slurry liquid in the first stage, After replacing with nitrogen for 30 minutes, the flask was again immersed in a water bath at 70° C. to raise the temperature, and polymerization was performed for 60 minutes to obtain a hydrogel polymer.

Thereafter, the flask was immersed in an oil bath set at 125°C, and 260.1 g of water was withdrawn out of the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Then, 4.42 g (0.507 mmol) of a 2 mass % ethylene glycol diglycidyl ether aqueous solution was added to the flask as a surface crosslinking agent, and it hold|maintained at 83 degreeC for 2 hours.

Thereafter, water and n-heptane were evaporated to dryness at 125°C to obtain polymer particles (dry product). This polymer particle was passed through a sieve having an eye size of 850 μm, and 0.2 mass% of amorphous silica (Oriental Silicas Corporation, Tokusil NP-S) with respect to the mass of the polymer particle was mixed with the polymer particles to absorb amorphous silica containing 231.0 g of resin particles were obtained. The median particle diameter of the water-absorbing resin particles was 76 µm.

The water absorbent resin particles of Production Example 7 had an absorption amount of 67 g/g, and the water absorption amount under load of the water absorbent resin particles was 3.3 mL/g.

Preparation 8

[Polymerization reaction in the first stage]

As a reflux condenser, a dropping funnel, a nitrogen gas introduction tube, and a stirrer, a round-bottomed cylindrical separable flask having an inner diameter of 11 cm and a capacity of 2 L equipped with a stirring blade having two stages of four inclined paddle blades with a blade diameter of 5 cm was prepared. To this flask, 293.0 g of n-heptane as a hydrocarbon dispersion medium, 0.736 g of maleic anhydride-modified ethylene/propylene copolymer (Mitsui Chemical Co., Ltd., High Wax 1105A) as a polymeric dispersant was added and stirred to 80° C. After heating up and dissolving a dispersing agent, it cooled to 50 degreeC.

To a 300 mL beaker, take 92.0 g (1.03 mol) of an 80.5 mass % aqueous acrylic acid solution as a water-soluble ethylenically unsaturated monomer, and while cooling from the outside, 147.7 g of a 20.9 mass % aqueous sodium hydroxide solution is added dropwise to neutralize 75 mol% After hydroxyethyl cellulose 0.092 g (Sumitomo Seika Co., Ltd., HECAW-15F) as a thickener, potassium persulfate 0.0736 g (0.272 mmol) as a water-soluble radical polymerization initiator, ethylene glycol diglycidyl ether as an internal crosslinking agent 0.010 g (0.057 mmol) was added and dissolved to prepare an aqueous solution of the first stage.

Then, the aqueous solution prepared above was added to a separable flask, stirred for 10 minutes, and then sucrose stearic acid ester of HLB 3 as a surfactant in 6.62 g of n-heptane (Mitsubishi Chemical Foods Co., Ltd., Lyoto Sugar Ester S- 370) A surfactant solution obtained by dissolving 0.736 g by heating is further added, the rotation speed of the stirrer is set to 550 rpm and the inside of the system is sufficiently substituted with nitrogen while stirring, and then the flask is immersed in a water bath at 70 ° C. By carrying out for 60 minutes, the polymerization slurry liquid of a 1st stage|stage was obtained.

[Second stage polymerization reaction]

128.8 g (1.44 mol) of an 80.5 mass % aqueous acrylic acid solution as a water-soluble ethylenically unsaturated monomer was taken into a 500 mL beaker, and while cooling from the outside, 159.0 g of a 27 mass % aqueous sodium hydroxide solution was added dropwise to neutralize 75 mol%. After that, 0.090 g (0.333 mmol) of potassium persulfate as a water-soluble radical polymerization initiator and 0.0116 g (0.067 mmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent were added and dissolved to prepare an aqueous solution of the second stage. did.

After cooling the inside of the separable flask system to 25° C. while stirring the rotation speed of the stirrer at 1000 rpm, the entire amount of the aqueous liquid in the second stage is added to the polymerization slurry liquid in the first stage, and the After replacing with nitrogen for 30 minutes, the flask was again immersed in a water bath at 70°C to raise the temperature, and polymerization reaction was performed for 60 minutes. Thus, a hydrous gel-like polymer was obtained.

To the hydrous gel after polymerization in the second stage, 0.265 g of a 45% by mass aqueous solution of pentasodium diethylenetriaminepentaacetic acid was added under stirring. Thereafter, the reaction solution was heated with an oil bath at 125°C, and 256.1 g of water was taken out of the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Then, 4.42 g (0.507 mmol) of a 2 mass % ethylene glycol diglycidyl ether aqueous solution was added to the flask as a post-crosslinking agent, and it hold|maintained at 83 degreeC for 2 hours.

Thereafter, water and n-heptane were evaporated to dryness at 125°C to obtain a dry product. This dried product was passed through a sieve having an eye size of 850 µm, and 0.1 mass % of amorphous silica (Oriental Silicas Corporation, Tokusil NP-S) was mixed with respect to the dried product to obtain 230.8 g of water-absorbing resin particles. The median particle diameter of the water absorbent resin particles was 402 µm.

The water absorption amount of the water absorbent resin particles of Production Example 8 was 60 g/g, and the water absorption amount of the water absorbent resin particles under load was 34.5 mL/g. The liquid permeation time of the water absorbent resin particles was 32.2 seconds.

Preparation 9

[Polymerization reaction in the first stage]

As a reflux condenser, a dropping funnel, a nitrogen gas introduction tube, and a stirrer, a round-bottomed cylindrical separable flask having an inner diameter of 11 cm and a capacity of 2 L equipped with a stirring blade having two stages of four inclined paddle blades with a blade diameter of 5 cm was prepared. To this flask, 293 g of n-heptane as a hydrocarbon dispersion medium, 0.736 g of maleic anhydride-modified ethylene/propylene copolymer (Mitsui Chemical Co., Ltd., High Wax 1105A) as a polymeric dispersant was added, and the temperature was raised to 80° C. while stirring. After dissolving the dispersant, it was cooled to 50°C.

To a 300 mL beaker, take 92.0 g (1.03 mol) of an 80.5 mass % aqueous acrylic acid solution as a water-soluble ethylenically unsaturated monomer, and while cooling from the outside, 147.7 g of a 20.9 mass % aqueous sodium hydroxide solution is added dropwise to neutralize 75 mol% , hydroxyethyl cellulose 0.092 g (Sumitomo Seika Co., Ltd., HECAW-15F) as a thickener, and 2,2'-azobis (2-amidinopropane) dihydrochloride as a water-soluble radical polymerization initiator 0.092 g (0.339 mmol) and 0.018 g (0.067 mmol) of potassium persulfate and 0.0046 g (0.026 mmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent were added and dissolved to prepare an aqueous monomer solution in the first stage.

Then, the aqueous solution prepared above was added to a separable flask, stirred for 10 minutes, and then sucrose stearic acid ester of HLB 3 as a surfactant in 6.62 g of n-heptane (Mitsubishi Chemical Foods Co., Ltd., Lyoto Sugar Ester S- 370) A surfactant solution obtained by dissolving 0.736 g by heating is further added, the rotation speed of the stirrer is set to 550 rpm and the inside of the system is sufficiently substituted with nitrogen while stirring, and then the flask is immersed in a water bath at 70 ° C. By carrying out for 60 minutes, the polymerization slurry liquid of a 1st stage|stage was obtained.

[Second stage polymerization reaction]

128.8 g (1.44 mol) of an 80.5 mass % aqueous acrylic acid solution as a water-soluble ethylenically unsaturated monomer was taken into a 500 mL beaker, and while cooling from the outside, 159.0 g of a 27 mass % aqueous sodium hydroxide solution was added dropwise to neutralize 75 mol%. After carrying out, 0.129 g (0.476 mmol) of 2,2'-azobis(2-amidinopropane) dihydrochloride as a water-soluble radical polymerization initiator, 0.026 g (0.096 mmol) of potassium persulfate, and ethylene glycol as an internal crosslinking agent 0.0116 g (0.067 mmol) of diglycidyl ether was added and dissolved to prepare an aqueous monomer solution in the second stage.

After cooling the inside of the separable flask system to 25° C. while stirring the rotation speed of the stirrer at 1000 rpm, the entire amount of the aqueous liquid in the second stage is added to the polymerization slurry liquid in the first stage, and the After replacing with nitrogen for 30 minutes, the flask was again immersed in a water bath at 70°C to raise the temperature, and polymerization reaction was performed for 60 minutes.

To the hydrous gel after polymerization in the second stage, 0.589 g of a 45% by mass aqueous solution of pentasodium diethylenetriaminepentaacetic acid was added under stirring. Thereafter, the reaction solution was heated with an oil bath at 125°C, and 216.7 g of water was taken out of the system while refluxing n-heptane by azeotropic distillation of n-heptane and water. Then, 4.42 g (0.507 mmol) of a 2 mass % ethylene glycol diglycidyl ether aqueous solution was added to the flask as a surface crosslinking agent, and it hold|maintained at 83 degreeC for 2 hours.

Thereafter, n-heptane was evaporated to dryness at 125°C to obtain a dry product. This dried product was passed through a sieve having an eye size of 850 µm, and 0.2 mass % of amorphous silica (Oriental Silicas Corporation, Tokusil NP-S) was mixed with the dried product to obtain 229.0 g of water-absorbing resin particles. The median particle diameter of the water absorbent resin particles was 351 µm.

The absorbent amount of the water absorbent resin particles of Production Example 9 was 56 g/g, and the water absorbent amount of the water absorbent resin particles under load was 35.3 mL/g.

2. Evaluation of water absorbent resin particles

<Absorption amount of physiological saline (g/g)>

In a 500 mL beaker, 500 g of physiological saline (0.9 mass% sodium chloride aqueous solution) was weighed, and while stirring at 600 rpm with a magnetic stirrer bar (without a ring of 8 mm φ × 30 mm), 2.0 g of water-absorbent resin particles were agglomerated. dispersed so as not to It was left to stand for 60 minutes in a stirred state, and the water-absorbent resin particles were sufficiently swollen. Thereafter, the mass Wa (g) of a standard sieve with an eye size of 75 μm is measured in advance, and the contents of the beaker are filtered using this, and the sieve is tilted to an inclination angle of about 30 degrees with respect to the horizontal, and left for 30 minutes. By doing this, excess water|moisture content was separated by filtration. The mass Wb (g) of the sieve containing the swelling gel was measured, and the absorption amount of the physiological saline was calculated by the following formula.

Absorption of physiological saline [g/g]=(Wb[g]-Wa[g])/2.0[g]

<Amount of absorption (g/g)>

Using the measuring device shown in Fig. 4, the amount of absorption was measured in an environment of a temperature of 25±2°C and a humidity of 60±10%. First, the cock 22 and the cock 24 of the burette part 1 are closed, and physiological saline (0.9 mass % saline) 27 adjusted to 25° C. ) was put in After sealing the opening of the burette tube 26 with the rubber stopper 23, the cock 22 and the cock 24 were opened. The inside of the conduit (5) was filled with physiological saline (27) to prevent air bubbles from entering. The height of the measuring table 13 was adjusted so that the height of the water surface of the physiological saline solution reached in the through hole 13a was equal to the height of the upper surface of the measuring table 13 . After adjustment, the height of the water level of the physiological saline solution 27 in the burette tube 26 was read on the scale of the burette tube 26, and the position was set as the zero point (reading value at the time of 0 second).

A container for measuring the suction and absorption amount consisting of an acrylic resin cylinder 16 (inner diameter 25 mmφ × height 150 mm) and a nylon mesh sheet 15 (250 mesh, thickness about 60 μm) adhered to the bottom of the cylinder was prepared. 0.5 g of water-absorbing resin particles were uniformly sprayed into the container for measuring the amount of absorption by inhalation. The nylon mesh sheet 15 on which the water absorbent resin particles 11a were mounted was placed so that the center thereof was the position of the through hole 13a, and measurement was started. The point at which air bubbles were first introduced into the burette tube 26 from the air introduction tube 25 was defined as the start of absorption (0 second).

The amount absorbed by the water absorbent resin particles 11a until 10 minutes after the start of absorption was measured as the absorption amount A. Using Formula (1), the intake and absorption amount was calculated.

Formula (1): inhalation absorption [g/g] = absorption A [mL] × 1.0028 (density of physiological saline) [g/mL]/0.5 [g]

<Permeate absorption (g/g)>

A container for measuring the permeate was prepared, which consisted of an acrylic resin cylinder (inner diameter: 60 mm phi x height: 70 mm) and a mesh sheet (400 mesh made of SUS) adhered to the bottom of the cylinder. 0.5 g of water absorbent resin particles were uniformly spread on the mesh sheet in the container for measuring the permeate, and the total mass Wc of the container for measuring the permeate and the water absorbent resin particles was measured. In a 100 mL plastic beaker, 30 g of physiological saline (concentration 0.9 wt% saline) was weighed. On an empty petri dish, a metal mesh (eye size: 1.4 mm, 100 mm x 100 mm) was placed, and on the metal mesh, a container for measuring the permeate in which the water absorbent resin particles were arranged was installed. The physiological saline solution in the beaker was put into the container for measuring the permeate at once, and the total mass Wd of the container for measuring the permeate and its contents was measured 1 minute after the start of the pouring. Equation (2) was used to calculate the absorption amount of the permeate.

Equation (2): Permeate absorption amount [g/g] = (Wd[g]-Wc[g])/0.5 [g]

<Amount absorbed under load>

The amount of water absorbed by the water absorbent resin particles to physiological saline under a load of 2.07 kPa was measured in an environment of 25°C ± 2°C using the measuring device (Y) shown in FIG. 5 . The measuring device Y is constituted by a burette part 71 , a conduit 72 , a measuring table 73 , and a measuring part 74 placed on the measuring table 73 . The burette part 71 includes a burette 71a extending in the vertical direction, a rubber stopper 71b disposed at the upper end of the burette 71a, and a cock disposed at the lower end of the burette 71a. 71c), an air introduction pipe 71d having one end extending into the burette 71a in the vicinity of the cock 71c, and a cock 71e disposed on the other end side of the air introduction pipe 71d ) has The conduit 72 is attached between the burette part 71 and the measuring table 73 . The inner diameter of the conduit 72 is 6 mm. A hole having a diameter of 2 mm is drilled in the center of the measuring table 73 , and a conduit 72 is connected thereto. The measuring part 74 has a cylinder 74a (made of acrylic resin (plexiglass)), a nylon mesh 74b adhered to the bottom of the cylinder 74a, and a weight 74c. The inner diameter of the cylinder 74a is 20 mm. The eye size of the nylon mesh 74b is 75 μm (200 mesh). Then, during measurement, the water absorbent resin particles 75 to be measured are uniformly spread on the nylon mesh 74b. The diameter of the weight 74c is 19 mm, and the mass of the weight 74c is 59.8 g. The weight 74c is placed on the water absorbent resin particles 75 and can apply a load of 2.07 kPa to the water absorbent resin particles 75 .

After putting 0.100 g of water-absorbing resin particles 75 in the cylinder 74a of the measuring device Y, the weight 74c was lifted and measurement was started. Since the same volume of air as the physiological saline solution absorbed by the water absorbent resin particles 75 is quickly and smoothly supplied to the inside of the burette 71a from the air introduction pipe, the level of the physiological saline solution inside the burette 71a The loss of , becomes the amount of physiological saline absorbed by the water absorbent resin particles 75 . The scale of the burette 71a is engraved in units of 0 mL to 0.5 mL from top to bottom. As the level of the physiological saline, the scale Va of the burette 71a before the start of absorption and the scale Vb of the burette 71a after 60 minutes from the start of absorption are read, and the absorption under load (the amount of absorption under the load of 2.07 kPa) is obtained from the following equation. absorption) was calculated.

Absorption under load [mL/g]=(Vb[mL]-Va[mL])/0.1[g]

<Median particle diameter>

The above-mentioned median particle diameter of the water absorbent resin particles was measured according to the following procedure. That is, a JIS standard sieve is taken from above, an eye size sieve 600 μm, an eye size 500 μm sieve, an eye size 425 μm sieve, an eye size 300 μm sieve, an eye size 250 μm sieve, a 180 μm eye size sieve, an eye size 150 μm sieve , and the saucer were combined in the order of. 50 g of water-absorbing resin particles were put into the combined uppermost sieve, and classification was performed according to JIS Z 8815 (1994) using a low-tap shaker (manufactured by Iida Seisakusho Co., Ltd.). The particle size distribution was calculated|required by calculating the mass of the particle|grains remaining on each sieve after classification as a mass percentage with respect to the whole quantity. Regarding this particle size distribution, by integrating the top of the sieve in order from the one with the largest particle diameter, the relationship between the sieve eye size and the integrated value of the mass percentage of the particles remaining on the sieve was plotted on a logarithmic probability paper. By linking the plots on the probability paper with a straight line, the particle diameter corresponding to the integrated mass percentage of 50 mass % was obtained as a median particle diameter. Table 1 shows the median particle size and the content (mass %) of water-absorbent resin particles with a particle diameter of 150 µm or less (water-absorbent resin particles passing through a sieve having an eye size of 150 µm) based on the total mass of the water-absorbing resin particles.

<Act Penetration Time>

The liquid permeation time (sec) was measured according to the methods described in Japanese Patent Application Laid-Open Nos. 10-118117, 9-276391, and 3311753. Specifically, first, 0.5 g of water-absorbent resin particles are filled into an acrylic resin cylinder having a cross-sectional area of 4.91 cm ² (inner diameter 25 mmφ) and an opening and closing cock (inner diameter 4 mmφ) provided at the bottom, the cock is closed and filled with physiological saline and swelled with the physiological saline until the water absorbent resin particles reached a saturated state. The swelling time of the water absorbent resin particles with physiological saline was 1 hour. After the swollen water-absorbent resin particles were allowed to settle to the top of the filter (glass filter G1), the cock was opened, 50 mL of physiological saline was passed through, and the time required for 50 mL of physiological saline to pass was obtained as the liquid permeation time.

<Absorption rate of physiological saline by DW method>

The absorption rate (g/30 sec/0.3 g) of physiological saline by the DW method was measured based on the method described in Japanese Patent Application Laid-Open No. 10-118117. Specifically, using a device (Demand Wettability Tester) generally known as a device for performing the DW method, a polymer sprayer (70 mmφ, filter paper No. 2 (55 mmφ)) with the liquid level of physiological saline set to an equal water level was filtered through a glass filter. 0.3 g of water absorbent resin particles are sprayed on G1 (60 mmφ)), the absorption amount at the time of spraying the water absorbent resin particles is set to 0, and the absorption amount after 30 seconds (this absorption amount is the decrease in the water level of physiological saline ) was measured, and this value was taken as the absorption rate (unit: g/30 sec/0.3 g).

<Absorption rate by Vortex method>

The absorption rate (seconds) by the Vortex method was measured according to the method described in Unexamined-Japanese-Patent No. 2012-183175. The absorption rate test by the Vortex method was performed in the room adjusted to 25 degreeC ± 1 degreeC. In a 100 mL beaker, 50 ± 0.1 g of physiological saline was weighed, a magnetic stirrer bar (without a ring of 8 mmφ × 30 mm) was put, the beaker was immersed in a constant temperature water bath, and the liquid temperature was adjusted to 25 ± 0.2 ° C. Next, a beaker is placed on a magnetic stirrer, the rotation speed is set to 600 rpm, and a vortex is generated in physiological saline, then 2.0±0.002 g of water absorbent resin particles are quickly added to the beaker, and using a stopwatch, absorbency The time (seconds) from the addition of the resin particles to the time when the vortex of the liquid level is settled was measured, and it was set as the absorption rate of the water-absorbent resin particles.

3. Fabrication and Evaluation of Absorbent Sheets

Three nonwoven fabrics selected from the group consisting of spunlace nonwoven fabric and air through nonwoven fabric were laminated to prepare an absorbent sheet having an absorbent layer containing water absorbent resin particles between each layer on the upper layer side and the lower layer side as viewed from the intermediate nonwoven fabric. Details are shown in Table 2.

Example 1

A spunlace nonwoven fabric (Gurare Co., Ltd., 70% rayon, 20% PET, 10% PP/PE) having a weight per unit area of 35 g/m ² was cut into 2 pieces to a size of 42 cm × 14 cm, did. A 45 g/m ² air-through non-woven fabric (manufactured by Hualong (Nanjing)) cut to a size of 42 cm × 14 cm was placed on the spunlace non-woven fabric-1, and using an air flow mixing device (manufactured by AUTEC Co., Ltd., pad former), 7.2 g of the water-absorbent resin particles obtained in Preparation Example 1 were uniformly sprayed over a central area of 12 cm x 40 cm of the nonwoven fabric.

Hot melt adhesive on spunlace non-woven fabric-2 with a hot melt coating machine (Hariz, Inc., pump: Marshal150, table: XA-DT, tank set temperature: 150 ° C, hose set temperature: 165 ° C, gunhead set temperature: 170 ° C) 0.2 g (Henkel Japan Co., Ltd., ME-765E) was applied (pattern: spiral stripe, 12 pieces at 10 mm intervals). The side of the spunlace nonwoven fabric-2 to which the hot-melt adhesive was attached was aligned with both ends to the side on which the water absorbent resin particles were sprayed of the above-described air-through nonwoven fabric, sandwiched with a release paper, and inverted vertically. At this time, the spunlace nonwoven fabric-1 provided under the air through nonwoven fabric was removed. By the above procedure, a laminate in which the spunlace nonwoven fabric (lower layer core wrap sheet), the absorbent layer (lower layer absorbent layer) made of the water absorbent resin particles obtained in Production Example 1, and the air through nonwoven fabric (intermediate layer core wrap sheet) are arranged in this order got it The removed spunlace nonwoven fabric-1 was cut by 6 cm at both ends in the longitudinal direction and 1 cm at both ends in the short longitudinal direction, and used as an upper core wrap sheet to be described later.

In the air-through nonwoven fabric of the obtained laminate, with respect to the side opposite to the side on which the water absorbent resin particles were sprayed, the water absorbency obtained in Production Example 6 with respect to the central portion of the nonwoven fabric in the range of 12 cm × 40 cm using an air flow mixing device 7.2 g of resin particles were uniformly spread|dispersed. The surface on which the water absorbent resin particles obtained in Preparation Example 6 was sprayed was facing up, and the laminate was cut by 6 cm at both ends in the long longitudinal direction, and 2 cm at both ends in the short longitudinal direction, and cut into 30 cm×10 cm. As the upper core wrap sheet, 0.12 g of a hot melt adhesive was applied to the spun lace nonwoven fabric-1 (30 cm x 12 cm) using a hot melt coating machine as described above. With respect to the surface on which the water absorbent resin particles obtained in Preparation Example 6 of the air-through nonwoven fabric were sprayed, the center of the spunlace nonwoven fabric-1 from above and both ends in the long longitudinal direction were aligned and aligned, and the both ends of the upper core wrap sheet in the short longitudinal direction were It was folded back according to the laminated body. The laminate to which this upper layer core wrap sheet was fitted was sandwiched with release paper, and a laminating machine (Hashima Co., Ltd., Straight Linear Fussing Press, model HP-600LFS) was pressed under the conditions of 110° C. and 0.1 MPa to bond the absorbent sheet. made The obtained absorbent sheet was a spunlace nonwoven fabric (lower layer core wrap sheet), an absorbent layer comprising the water absorbent resin particles obtained in Production Example 1 (lower absorbent layer), an air through nonwoven fabric (intermediate layer core wrap sheet), and the water absorbent resin particles obtained in Production Example 6. The resulting absorbent layer (upper absorbent layer) and spunlace nonwoven fabric (upper layer core wrap sheet) are arranged in this order.

Example 2

An absorbent sheet was obtained in the same manner as in Example 1 except that the water absorbent resin particles used for the lower absorbent layer were changed to those produced in Production Example 2.

Example 3

An absorbent sheet was obtained in the same manner as in Example 1 except that the water absorbent resin particles used for the lower absorbent layer were changed to those produced in Production Example 3.

Example 4

An absorbent sheet was obtained in the same manner as in Example 1 except that the water absorbent resin particles used for the lower absorbent layer were changed to those produced in Production Example 4.

Example 5

An absorbent sheet was obtained in the same manner as in Example 1 except that the water absorbent resin particles used for the lower absorbent layer were changed to those produced in Production Example 5.

Comparative Example 1

An absorbent sheet was obtained in the same manner as in Example 1 except that the water absorbent resin particles used for the lower absorbent layer were changed to those produced in Production Example 6.

Comparative Example 2

An absorbent sheet was obtained in the same manner as in Example 1 except that the water absorbent resin particles used for the lower absorbent layer were changed to those produced in Production Example 7.

Comparative Example 3

An absorbent sheet was obtained in the same manner as in Example 1 except that the water absorbent resin particles used for the lower absorbent layer were changed to those produced in Production Example 8.

Comparative Example 4

An absorbent sheet was obtained in the same manner as in Example 1 except that the water absorbent resin particles used for the lower absorbent layer were changed to those produced in Production Example 9.

Example 6

An absorbent sheet was obtained in the same manner as in Example 1 except that the water absorbent resin particles used for the upper absorbent layer were changed to those produced in Production Example 8.

Example 7

In the same manner as in Example 1, except that the air-through non-woven fabric as the intermediate core wrap sheet was changed to a spun lace non-woven fabric having a weight per unit area of 35 g/m ² (Kurare Co., Ltd., 70% rayon, 20% PET, 10% PP/PE). Thus, an absorbent sheet was obtained.

Example 8

An absorbent sheet was obtained in the same manner as in Example 1, except that the spunlace nonwoven fabric as the upper core wrap sheet and the lower core wrap sheet was changed to an air through nonwoven fabric having a weight per unit area of 45 g/m ² (manufactured by Hualong (Nanjing)).

<Production of artificial urine (test solution)>

Artificial urine was prepared by adding a small amount of Blue No. 1 to ion-exchanged water, mixing and dissolving so that inorganic salts exist as follows. The concentrations shown below are concentrations based on the total mass of artificial urine.

NaCl: 0.777 mass %

CaCl ₂ : 0.022 mass %

MgSO ₄ : 0.038 mass %

Urea: 1.933% by mass

Blue No. 1: 0.002% by mass

<45 degree leakage test>

The liquid leak property was evaluated by a 45 degree leak test. 6 : is a schematic diagram which shows the method of evaluating the leakiness of an absorbent article. A support plate 45 with a length of 45 cm having a flat main surface (herein, an acrylic resin plate, also referred to as an inclined surface S ₁ ), is inclined at 45 ± 2 degrees with respect to the horizontal surface S ₀ by the mount 41 fixed At room temperature with a temperature of 25±2°C, the absorbent sheet 50 for testing is placed on the inclined surface S ₁ of the fixed support plate 45 in a direction in which the longitudinal direction is along the longitudinal direction of the support plate 45 . was pasted with Here, the absorbent sheet 50 for testing was arranged so that the lower absorbent layer was on the support plate side. Next, the test solution 46 (artificial urine) adjusted to 25±1° C. was dripped from the dropping funnel 42 disposed vertically above the absorbent sheet 50 toward a position 2 cm above the center of the absorbent sheet. . 80 mL of the test solution 46 per one time was injected at a rate of 8 mL/sec. The distance between the tip of the dropping funnel 42 and the absorbent sheet was 10±1 mm. After 10 minutes from the start of the first injection of the test solution, the test solution was charged under the same conditions.

When the test liquid that was not absorbed by the absorbent sheet for testing leaked from the lower part of the support plate 45 , the leaked test liquid was collected into a metal tray 44 disposed below the support plate 45 . The weight (g) of the recovered test solution was measured with a balance 43, and the value was recorded as the leakage amount (g). A measurement result is shown in Table 2.

Table 2 shows the evaluation results. The absorbent sheet produced by using water-absorbent resin particles having specific values for absorption by suction and absorption by permeate as the lower absorbent layer had improved liquid leakage.

One… burette part
3… clamp
5… conduit
10a… first absorbent layer
10b… second absorbent layer
11a… first water-absorbent resin particles
11b… 2nd water absorbent resin particle
12a, 12b... fiber layer
13… measuring table
13a… through hole
14… trestle
15… nylon mesh sheet
16… cylinder
20a… core wrap sheet
20b… core wrap sheet
21… glue
22… cock
23… rubber stopper
24… cock
25… air inlet pipe
26… burette tube
27… physiological saline
30… liquid permeable sheet
40… liquid impermeable sheet
41… trestle
42… dropping funnel
43… balance
44… tray
45… support plate
46… test solution
50… absorbent sheet
71… burette part
71a… burette
71b... rubber stopper
71c… cock
71d… air inlet pipe
71e... cock
72… conduit
73... measuring table
74… measuring part
74a… cylinder
74b... nylon mesh
74c... weight
75… absorbent resin particles
100… absorbent article
S ₀ … water level
S ₁ . incline

Claims (8)

An absorbent sheet comprising a plurality of absorbent layers comprising absorbent resin particles, the absorbent sheet comprising:
The absorbent layer of one of the outermost layers contains water-absorbent resin particles having an absorption absorption amount of 10.5 g/g or more and a permeate absorption amount of 12.5 g/g or more,
According to the DW method, when physiological saline is absorbed into 0.5 g of water absorbent resin particles disposed in a container comprising a cylinder having an inner diameter of 25 mm and a mesh sheet adhered to the bottom of the cylinder, the water absorbent resin particles It is the mass of physiological saline solution per 1 g of the water-absorbing resin particle that is absorbed up to 10 minutes after the start of absorption,
After disposing 0.5 g of water-absorbing resin particles on the mesh sheet in a container comprising a cylinder having an inner diameter of 60 mm and a mesh sheet adhered to the bottom of the cylinder, 30 g of physiological saline is added, The absorbent sheet, which is the amount of absorption of physiological saline per 1 g of the absorbent resin particles, measured 1 minute after the start time. The method according to claim 1,
The absorbent sheet, wherein the absorbent resin particles have a median particle diameter of 100 to 800 µm. The method according to claim 1 or 2,
The absorbent sheet, wherein the content of particles having a particle diameter of 150 µm or less of the water absorbent resin particles is 21.0 mass % or less based on the total mass of the water absorbent resin particles. 4. The method according to any one of claims 1 to 3,
The absorbent sheet, wherein the absorbent amount is 15 mL/g or more when the water absorbent resin particles absorb physiological saline under a load of 2.07 kPa. An absorbent article comprising: a liquid-impermeable sheet, an absorbent sheet having a plurality of absorbent layers, and a liquid-permeable sheet, wherein the liquid-impermeable sheet, the absorbent sheet, and the liquid-permeable sheet are arranged in this order,
the absorbent layer of the outermost layer on the liquid-impermeable sheet side contains water-absorbing resin particles having an absorption absorption amount of 10.5 g/g or more and an absorption amount of a permeate liquid of 12.5 g/g or more;
According to the DW method, when physiological saline is absorbed into 0.5 g of water absorbent resin particles disposed in a container comprising a cylinder having an inner diameter of 25 mm and a mesh sheet adhered to the bottom of the cylinder, the water absorbent resin particles It is the mass of physiological saline solution per 1 g of the water-absorbing resin particle that is absorbed up to 10 minutes after the start of absorption,
After disposing 0.5 g of water-absorbing resin particles on the mesh sheet in a container comprising a cylinder having an inner diameter of 60 mm and a mesh sheet adhered to the bottom of the cylinder, 30 g of physiological saline is added, The absorbent article, which is the amount of absorption of physiological saline per 1 g of the absorbent resin particles measured 1 minute after the start time. 6. The method of claim 5,
The absorbent article, wherein the median particle diameter of the water absorbent resin particles is 100 to 800 µm. 7. The method according to claim 5 or 6,
The absorbent article, wherein the content of particles having a particle diameter of 150 µm or less of the water absorbent resin particles is 21.0 mass % or less based on the total mass of the water absorbent resin particles. 8. The method according to any one of claims 5 to 7,
The absorbent article, wherein the absorbent amount is 15 mL/g or more when the absorbent resin particles absorb physiological saline under a load of 2.07 kPa.

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