Water-absorbent resin particles, absorbent body, and absorbent article

Abstract

The present application provides a water-absorbing resin particle, which, when applied to an absorbent, can inhibit the backflow of a liquid after the liquid is absorbed under pressure in a state in which the absorbent is bent. A water-absorbing resin particle, wherein the 15-minute value of the saline water absorption under a load of 0.69 kPa is 30 mL / g or more and 60 mL / g or less.

Description

Technical Field

[0001] This invention relates to absorbent resin particles, absorbent bodies, and absorbent articles, and more specifically, to absorbent resin particles constituting absorbent bodies suitable for use in sanitary materials such as diapers, sanitary napkins, and incontinence pads, absorbent bodies using the absorbent resin particles, and absorbent articles. Background Technology

[0002] Absorbent polymer particles have been widely used in recent years in the field of sanitary materials such as diapers, sanitary napkins, and incontinence pads.

[0003] As such absorbent resin particles, cross-linked polymers of water-soluble olefinic unsaturated monomers, and more specifically, cross-linked polymers of partially neutralized polyacrylic acid, have excellent water absorption capacity. Acrylic acid, as their raw material, is readily available industrially. Therefore, they have many advantages such as stable quality, low cost, and resistance to spoilage and deterioration, and are thus considered preferred absorbent resin particles (see, for example, Patent Document 1).

[0004] Absorbent products such as diapers, sanitary napkins, and incontinence pads mainly consist of an absorbent core, a liquid-permeable surface sheet (top sheet), and a liquid-impermeable back sheet (back sheet). The absorbent core is located in the center to absorb and retain bodily fluids such as urine and menstrual blood. The surface sheet is located on the side that contacts the body, and the back sheet is located on the opposite side. Furthermore, the absorbent core is typically composed of hydrophilic fibers such as pulp and absorbent resin particles.

[0005] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 3-227301 Summary of the Invention The technical problem that the invention aims to solve In such absorbent articles, when the absorbent is bent or under pressure, after the absorbent has absorbed liquid, a so-called backflow sometimes occurs, where the liquid flows back from the absorbent to the wearer's side of the diaper.

[0006] The inventors have repeatedly studied techniques for suppressing backflow after liquid absorption in a bent state or under pressure. Specifically, referring to existing technologies, they investigated techniques for suppressing backflow by adjusting various characteristics of the absorbent resin particles, such as the saline absorbency under load, the unpressurized DW value, the absorption rate relative to saline, and the saline retention capacity. However, even when these techniques are applied to the absorbent, it is difficult to sufficiently suppress backflow when the absorbent is in a bent and pressurized state while absorbing liquid.

[0007] Under these circumstances, the main objective of the present invention is to provide a water-absorbing resin particle that, when applied to an absorbent, can suppress the backflow of liquid after absorption under pressure while the absorbent is in a bent state. Furthermore, another objective of the present invention is to provide an absorbent and an absorbent article utilizing this water-absorbing resin particle.

[0008] Technical solutions for solving technical problems The inventors conducted in-depth research to solve the aforementioned problems. The results showed that by setting the 15-minute saline absorption capacity of the absorbent resin particles under a 0.69 kPa load to a specific range of 30 mL / g or more and 60 mL / g or less, when the absorbent resin particles were applied to the absorbent body, backflow of the absorbed liquid after absorption under pressure and in a bent state of the absorbent body could be suppressed. This invention was completed based on further repeated and in-depth research based on this insight.

[0009] That is, the present invention provides an invention having the following structure.

[0010] Item 1. A water-absorbing resin particle, wherein the 15-minute value of the water absorption capacity of physiological saline under a load of 0.69 kPa is more than 30 mL / g and less than 60 mL / g.

[0011] Item 2. The absorbent resin particles according to Item 1, wherein the unpressurized DW3-minute value of the absorbent resin particles is 20 mL / g or more and 50 mL / g or less.

[0012] Item 3. The absorbent resin particles according to Item 2, wherein the absorbent resin particles absorb water relative to physiological saline at a rate of less than 60 seconds.

[0013] Item 4. The absorbent resin particles according to Item 2, wherein the physiological saline water retention capacity of the absorbent resin particles is 30 g / g or more.

[0014] Item 5. An absorbent comprising the absorbent resin particles described in any one of Items 1 to 4.

[0015] Item 6. An absorbent article comprising the absorbent described in Item 5.

[0016] Invention Effects According to the present invention, a water-absorbing resin particle can be provided that, when applied to an absorbent, suppresses backflow of liquid after the absorbent has absorbed liquid under pressure while in a bent state. Furthermore, the present invention can provide an absorbent and an absorbent article utilizing this water-absorbing resin particle. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a device for measuring the water absorption of physiological saline under a load of 0.69 kPa.

[0018] Figure 2 This is a schematic diagram of a measuring apparatus for determining the 3-minute and 10-minute values ​​of the pressureless DW of absorbent resin particles. Detailed Implementation

[0019] In this specification, "comprising" means "consisting essentially of" and "consisting of". Additionally, in this specification, "(meth)acrylic acid" means "acrylic acid or methacrylic acid", "(meth)acrylate" means "acrylate or methacrylate", and "(poly)" refers to both the presence and absence of the prefix "poly". Furthermore, in this specification, "water-soluble" means having a solubility of 5% by mass or more in water at 25°C.

[0020] In this specification, the values ​​connected by "~" refer to the range of values ​​before and after "~" as the lower and upper limits. When multiple lower and upper limits are recorded separately, any lower and upper limits can be selected and connected by "~".

[0021] 1. Water-absorbing resin particles The 15-minute water absorption capacity of the hydrophobic resin particles of the present invention under a 0.69 kPa load is 30 mL / g or more and 60 mL / g or less. The hydrophobic resin particles of the present invention, by possessing the characteristic of suppressing backflow of liquid after absorption under pressure in a bent state of the absorbent body, are applied to the absorbent body. The hydrophobic resin particles of the present invention will be described in detail below.

[0022] As described above, the inventors, referring to existing technologies, investigated techniques to suppress liquid backflow by adjusting various characteristics of absorbent resin particles, such as saline absorbance under load, DW value without pressure, absorption rate relative to saline, and saline retention capacity. However, even when these techniques are applied to the absorbent body, it is difficult to sufficiently suppress backflow when the absorbent body is in a bent state and under pressure. In contrast, the inventors focused on the 15-minute value of saline absorbance under a 0.69 kPa load of absorbent resin particles and found that if this value is set within a specific range of 30 mL / g or more and 60 mL / g or less, backflow of liquid is suppressed when absorbent resin particles are applied to the absorbent body, even when the absorbent body is bent and under pressure. This mechanism can be considered, for example, as follows. That is, in absorbent articles under pressure and in a bent state, the load applied to the actual absorbent resin particles is lighter than the load applied to the absorbent article due to the influence of liquid-permeable surface sheets (top sheets), hydrophilic fibers, etc. Therefore, it is believed that for absorbent resin particles, by setting the 15-minute value of saline absorbency under such a low load condition of 0.69 kPa to a specified range, the aforementioned backflow can be suppressed.

[0023] From the viewpoint of further and appropriately maximizing the effects of the present invention, the 15-minute value of the saline water absorption capacity of the absorbent resin particles under a 0.69 kPa load is preferably 30 mL / g or more, more preferably 32 mL / g or more, even more preferably 34 mL / g or more, particularly preferably 35 mL / g or more, and preferably 60 mL / g or less, more preferably 58 mL / g or less, even more preferably 55 mL / g or less. As a preferred range, 30 mL / g is an example. L / g~60mL / g, 30mL / g~58mL / g, 30mL / g~55mL / g, 32mL / g~60mL / g, 32mL / g~58mL / g, 32mL / g~55mL / g, 34 mL / g~60gmL / g, 34mL / g~58mL / g, 34mL / g~55mL / g, 35mL / g~60mL / g, 35mL / g~58mL / g, 35mL / g~55mL / g.

[0024] The method for determining the 15-minute value of physiological saline absorbency of the absorbent resin particles under a load of 0.69 kPa is based on the method described in the examples.

[0025] As a method for adjusting the 15-minute value of saline water absorption by the superabsorbent resin particles under a 0.69 kPa load, examples include: increasing the amount of surface crosslinking agent used in the manufacturing method of the superabsorbent resin particles described later; increasing the ratio of water-soluble olefinic unsaturated monomers in the second-stage monomer aqueous solution to water-soluble olefinic unsaturated monomers in the first-stage monomer aqueous solution, etc. This strengthens the surface crosslinking layer of the superabsorbent resin particles, enabling them to appropriately absorb and retain liquid even under a low load of 0.69 kPa and within a short 15-minute timeframe.

[0026] Furthermore, from the viewpoint of further appropriately maximizing the effects of the present invention and accelerating the water absorption rate of the absorbent (shortening the absorption time), the unpressurized DW3-minute value of the absorbent resin particles is preferably 20 mL / g or more, more preferably 30 mL / g or more, further preferably 33 mL / g or more, particularly preferably 36 mL / g or more, even more preferably 39 mL / g or more, and preferably 50 mL / g or less, more preferably 48 mL / g or less, and further preferably 46 mL / g or less. A preferred range is 20 mL / g to 50 mL / g. L / g, 20mL / g~48mL / g, 20mL / g~46mL / g, 30mL / g~50mL / g, 30mL / g~48mL / g, 30mL / g~46mL / g, 33mL / g~50mL / g, 33mL / g~48m L / g, 33mL / g~46mL / g, 36mL / g~50mL / g, 36mL / g~48mL / g, 36mL / g~46mL / g, 39mL / g~50mL / g, 39mL / g~48mL / g, 39~46mL / g.

[0027] Furthermore, from the viewpoint of further and appropriately maximizing the effects of the present invention, the unpressurized DW10-minute value of the water-absorbing resin particles is preferably 30 mL / g or more, more preferably 45 mL / g or more, further preferably 50 mL / g or more, particularly preferably 54 mL / g or more, even more preferably 56 mL / g or more, and preferably 80 mL / g or less, more preferably 75 mL / g or less, and even more preferably 72 mL / g or less. Examples of preferred ranges include 30 mL / g to 80 mL / g and 30 mL / g to 70 mL / g. 5mL / g, 30mL / g~72mL / g, 45mL / g~80mL / g, 45mL / g~75mL / g, 45mL / g~72mL / g, 50mL / g~80mL / g, 50mL / g~75mL / g, 50mL / g~72mL / g, 54mL / g~80mL / g, 54mL / g~75mL / g, 54mL / g~72mL / g, 56mL / g~80mL / g, 56mL / g~75mL / g, 56mL / g~72mL / g.

[0028] The methods for determining the unpressurized DW 3-minute and unpressurized DW 10-minute values ​​of the water-absorbing resin particles are based on the methods described in the examples.

[0029] Furthermore, from the viewpoint of further appropriately maximizing the effects of the present invention and accelerating the water absorption rate of the absorbent (shortening the absorption time), the water absorption rate of the absorbent resin particles relative to physiological saline is preferably 60 seconds or less, more preferably 55 seconds or less, even more preferably 50 seconds or less, and preferably 20 seconds or more, more preferably 25 seconds or more, even more preferably 30 seconds or more. Examples of preferred ranges include 20 seconds to 60 seconds, 20 seconds to 55 seconds, 20 seconds to 50 seconds, 25 seconds to 60 seconds, 25 seconds to 55 seconds, 25 seconds to 50 seconds, 30 seconds to 60 seconds, 30 seconds to 55 seconds, and 30 seconds to 50 seconds.

[0030] The method for determining the water absorption rate of the absorbent resin particles relative to physiological saline is based on the method described in the examples.

[0031] Furthermore, from the viewpoint of further and appropriately maximizing the effects of the present invention, the saline water retention capacity of the absorbent resin particles is preferably 30 g / g or more, more preferably 36 g / g or more, even more preferably 41 g / g or more, and preferably 70 g / g or less, more preferably 65 g / g or less, even more preferably 60 g / g or less. Examples of preferred ranges include 30 g / g to 70 g / g, 30 g / g to 65 g / g, 30 g / g to 60 g / g, 36 g / g to 70 g / g, 36 g / g to 65 g / g, 36 g / g to 60 g / g, 41 g / g to 70 g / g, 41 g / g to 65 g / g, and 41 g / g to 60 g / g.

[0032] The method for determining the saline water retention capacity of the absorbent resin particles is based on the method described in the examples.

[0033] Furthermore, from the viewpoint of more effectively utilizing the effects of the present invention, the saline water absorption capacity of the water-absorbing resin particles is preferably 45 g / g or more, 52 g / g or more, or 59 g / g or more, and more preferably 80 g / g or less, 74 g / g or less, or 69 g / g or less. Examples of preferred ranges for the saline water absorption capacity of the water-absorbing resin particles include 45 g / g to 80 g / g, 45 g / g to 74 g / g, 45 g / g to 69 g / g, 52 g / g to 80 g / g, 52 g / g to 74 g / g, 52 g / g to 69 g / g, 59 g / g to 80 g / g, 59 g / g to 74 g / g, and 59 g / g to 69 g / g.

[0034] The method for determining the amount of physiological saline absorbed by the water-absorbing resin particles is based on the method described in the examples.

[0035] Furthermore, from the viewpoint of further and appropriately maximizing the effects of the present invention, the difference between the amount of water absorbed by physiological saline and the amount of water retained by physiological saline is preferably 5 or more or 10 or more, and preferably 30 or less, 25 or less or 20 or less. Examples of preferred ranges include 5 to 30, 5 to 25, 5 to 20, 10 to 30, 10 to 25, and 10 to 20.

[0036] Furthermore, from the viewpoint of further and appropriately maximizing the effects of the present invention, the reflux rate of the absorbent resin particles of the present invention, measured according to the provisions of "GB / T 28004.1-2021 NATIONAL STANDARD OF THE PEOPLE'S REPUBLIC OF CHINA, Disposable diapers - Part 1: Disposable diapers for baby", under bending and pressure is preferably 10g or less, more preferably 8g or less, and the lower limit is preferably 0g. As preferred ranges, 0g to 10g and 0g to 8g can be cited.

[0037] Furthermore, from the viewpoint of further and appropriately maximizing the effects of the present invention, the total absorption time (the sum of the first and second absorption times of the test solution) of the absorbent resin particles of the present invention, as measured according to the provisions of "GB / T 28004.1-2021 NATIONAL STANDARD OF THE PEOPLE'S REPUBLIC OF CHINA, Disposable diapers - Part 1: Disposable diapers for baby", is preferably 90 seconds or less, more preferably 80 seconds or less, even more preferably 75 seconds or less, and preferably 20 seconds or more. Examples of preferred ranges include 20 seconds to 90 seconds, 20 seconds to 80 seconds, and 20 seconds to 75 seconds.

[0038] The determination methods for the reflux flow rate under bending and pressure and the total absorption time (the sum of the first absorption time (seconds) and the second absorption time (seconds) of the test solution) determined according to the provisions of "GB / T 28004.1-2021 NATIONAL STANDARD OF THE PEOPLE'S REPUBLIC OF CHINA, Disposable diapers - Part 1: Disposable diapers for baby" are based on the methods described in the examples.

[0039] The water-absorbing resin particles of the present invention are composed of a cross-linked polymer formed by cross-linking a polymer of a water-soluble olefinic unsaturated monomer, that is, a cross-linked polymer having structural units derived from a water-soluble olefinic unsaturated monomer.

[0040] The absorbent resin particles of the present invention are in the form of aggregates of fine particles (primary particles) (secondary particles). Examples of primary particle shapes include approximately spherical, irregularly broken, and plate-like shapes. The absorbent resin particles of the present invention, as secondary particles, can have various shapes. Examples of absorbent resin particle shapes include granular, approximately spherical, irregularly broken, plate-like, fibrous, flake-like, or aggregated forms of these resins. Preferably, the absorbent resin particles are granular, approximately spherical, irregularly broken, fibrous, or aggregated forms of these resins.

[0041] From the viewpoint of further and appropriately maximizing the effects of the present invention while accelerating the water absorption rate of the absorbent (shortening the absorption time), the median particle size of the absorbent resin particles is preferably 200 μm or more, 250 μm or more, 300 μm or more, 320 μm or more, or 350 μm or more. Furthermore, from the same viewpoint, the median particle size is preferably 700 μm or less, 600 μm or less, 550 μm or less, 500 μm or less, or 450 μm or less. Preferred ranges include median particle sizes of 200 μm to 700 μm, 200 μm to 600 μm, 200 μm to 550 μm, 200 μm to 500 μm, 200 μm to 450 μm, 250 μm to 700 μm, 250 μm to 600 μm, 250 μm to 550 μm, 250 μm to 500 μm, and 250 μm to 500 μm. m~450μm, 300μm~700μm, 300μm~600μm, 300μm~550μm, 300μm~500μm, 300μm~45 0μm, 350μm~700μm, 350μm~600μm, 350μm~550μm, 350μm~500μm, 350μm~450μm.

[0042] The median particle size of the superabsorbent resin particles can be determined using JIS standard sieves, specifically, through the method described in the examples. The value determined by the method.

[0043] 2. Method for manufacturing water-absorbing resin particles The method for manufacturing the superabsorbent resin particles of the present invention is not particularly limited as long as it can produce superabsorbent resin particles with a 15-minute water absorption value of 30 mL / g or more and 60 mL / g or less for physiological saline under a load of 0.69 kPa. The method for manufacturing the superabsorbent resin particles of the present invention, for example, sequentially comprises: a step of polymerizing a water-soluble olefinic unsaturated monomer to obtain polymer particles, and a surface crosslinking step of performing surface crosslinking on the polymer particles.

[0044] As described above, methods for adjusting the 15-minute value of saline water absorption capacity of the absorbent resin particles of the present invention under a 0.69 kPa load can include, for example, increasing the amount of surface crosslinking agent used in the manufacturing method of the absorbent resin particles; increasing the ratio of water-soluble olefinic unsaturated monomers in the monomer aqueous solution of the second stage to water-soluble olefinic unsaturated monomers in the monomer aqueous solution of the first stage, etc. This strengthens the surface crosslinking layer of the absorbent resin particles, enabling them to adequately absorb and retain liquid even under a low load of 0.69 kPa and within a short time of 15 minutes. The manufacturing method of the absorbent resin particles of the present invention will be described in detail below.

[0045] <Polymerization Process> The polymerization process is the process of polymerizing water-soluble olefinically unsaturated monomers to obtain polymer particles. Representative methods for polymerizing water-soluble olefinically unsaturated monomers include aqueous solution polymerization, spray-drop polymerization, emulsion polymerization, and reverse suspension polymerization. Aqueous solution polymerization involves heating an aqueous solution of water-soluble olefinically unsaturated monomers while stirring, as needed. Reverse suspension polymerization involves heating water-soluble olefinically unsaturated monomers in a hydrocarbon dispersion medium while stirring. From the viewpoint of setting the 15-minute water absorption capacity of the absorbent resin particles under a 0.69 kPa load in the range of 30 mL / g to 60 mL / g, while simultaneously improving general water absorption performance (water retention capacity of physiological saline, water absorption capacity of physiological saline, etc.), reverse suspension polymerization is preferred. In the polymerization process, an internal crosslinking agent can also be added to the water-soluble olefinically unsaturated monomers as needed to produce crosslinked polymer particles (including hydrogel-like substances) with an internal crosslinking structure. An example of the polymerization process is described below.

[0046] [Water-soluble olefinic unsaturated monomer] Examples of water-soluble olefinically unsaturated monomers include (meth)acrylic acid (in this specification, "acrylic acid" and "methacrylic acid" are collectively referred to as "(meth)acrylic acid"; the same applies hereinafter) and its salts; 2-(meth)acrylamide-2-methylpropanesulfonic acid and its salts; nonionic monomers such as (meth)acrylamide, N,N-dimethyl(meth)acrylamide, (meth)acrylic acid-2-hydroxyethyl ester, N-hydroxymethyl(meth)acrylamide, and polyethylene glycol mono(meth)acrylic acid ester; and amino-containing unsaturated monomers and their quaternary ammonium compounds such as N,N-diethylaminoethyl(meth)acrylic acid ester, N,N-diethylaminopropyl(meth)acrylic acid ester, and diethylaminopropyl(meth)acrylamide. From the viewpoint of easy industrial availability, (meth)acrylic acid or its salts, (meth)acrylamide, and N,N-dimethylacrylamide are preferred, and (meth)acrylic acid and its salts are more preferred. It should be noted that these water-soluble olefinic unsaturated monomers can be used alone or in combination of two or more.

[0047] Acrylic acid and its salts are widely used as raw materials for water-absorbing resin particles. Sometimes, these acrylic acids and / or their salts are used in combination with other water-soluble olefinic unsaturated monomers. In this case, acrylic acid and / or its salts are preferably used at 70 mol% to 100 mol% of the total water-soluble olefinic unsaturated monomers as the main water-soluble olefinic unsaturated monomer.

[0048] Water-soluble olefinic unsaturated monomers can also be dispersed in a hydrocarbon dispersion medium in an aqueous solution for reverse-phase suspension polymerization. By forming an aqueous solution, the dispersion efficiency of the water-soluble olefinic unsaturated monomers in the hydrocarbon dispersion medium can be improved. The concentration of the water-soluble olefinic unsaturated monomer in this aqueous solution is preferably in the range of 20% by mass to below the saturation concentration. Furthermore, the concentration of the water-soluble olefinic unsaturated monomer is more preferably 55% by mass or less, further preferably 50% by mass or less, and even more preferably 45% by mass or less. On the other hand, the concentration of the water-soluble olefinic unsaturated monomer is more preferably 25% by mass or more, further preferably 28% by mass or more, and even more preferably 30% by mass or more.

[0049] The ratio of water-soluble olefinic unsaturated monomers in the second-stage monomer aqueous solution to water-soluble olefinic unsaturated monomers in the first-stage monomer aqueous solution (water-soluble olefinic unsaturated monomers in the second stage / water-soluble olefinic unsaturated monomers in the first stage) is preferably 0.1 to 3.0, more preferably 0.5 to 2.5, further preferably 1.0 to 2.0, and even more preferably 1.5 to 1.8, from the viewpoint of adjusting the 15-minute value of physiological saline water absorption under a 0.69 kPa load to an preferred range.

[0050] Water-soluble olefinically unsaturated monomers, such as (meth)acrylic acid and 2-(meth)acrylamide-2-methylpropanesulfonic acid, which contain acid groups, can also be used if their acid groups have been pre-neutralized with an alkaline neutralizing agent. Examples of such alkaline neutralizing agents include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, and potassium carbonate; and ammonia. Furthermore, to simplify the neutralization process, these alkaline neutralizing agents can also be used in aqueous solution form. It should be noted that the above-mentioned alkaline neutralizing agents can be used alone or in combination of two or more.

[0051] The degree of neutralization of the water-soluble olefinic unsaturated monomer using an alkaline neutralizing agent, relative to the degree of neutralization of all acid groups in the water-soluble olefinic unsaturated monomer, is preferably 40 mol% to 100 mol%, more preferably 50 mol% to 90 mol%, further preferably 60 mol% to 85 mol%, and even more preferably 70 mol% to 80 mol%.

[0052] [Free radical polymerization initiator] Examples of free radical polymerization initiators added in this polymerization process include: persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate; peroxides such as methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, di-tert-butyl peroxide, tert-butyl cumene peroxide, tert-butyl peracetate, tert-butyl perisobutyrate, tert-butyl perpentyl peroxide, and hydrogen peroxide; and 2,2'-azobis(2-amidinylpropane) dihydrochloride and 2,2'-azobis[2-(N-phenylamidinyl)propane]. Azo compounds such as dihydrochlorides, 2,2'-azobis[2-(N-allylamidinyl)propane] dihydrochloride, 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane} dihydrochloride, 2,2'-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamide}, 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], and 4,4'-azobis(4-cyanopentanoic acid) are among these free radical polymerization initiators. From the viewpoint of ease of acquisition and operation, potassium persulfate, ammonium persulfate, sodium persulfate, and 2,2'-azobis(2-amidinylpropane) dihydrochloride are preferred. These free radical polymerization initiators can be used alone or in combination of two or more. In addition, the above-mentioned free radical polymerization initiators can also be used in combination with reducing agents such as sodium sulfite, sodium bisulfite, ferrous sulfate, and L-ascorbic acid as redox polymerization initiators.

[0053] The amount used as a free radical polymerization initiator can be, for example, 0.00005 mol to 0.01 mol relative to 1 mol of a water-soluble olefinic unsaturated monomer. By meeting such a dosage, rapid polymerization can be avoided, and the polymerization reaction can be terminated at an appropriate time.

[0054] [Internal cross-linking agent] As an internal crosslinking agent, examples include crosslinking agents that can crosslink polymers of water-soluble olefinic unsaturated monomers, such as (poly) glycol [the expression "(poly)" indicates both the case with and without the prefix "poly"]. [The following are the same]: unsaturated polyesters obtained by reacting diols and triols such as poly(poly)propylene glycol, 1,4-butanediol, 1,6-hexanediol, trimethylolpropane, and poly(poly)glycerol with unsaturated acids such as methacrylic acid, maleic acid, and fumaric acid; bisacrylamides such as N,N-methylenebisacrylamide; di(meth)acrylates or tri(meth)acrylates obtained by reacting polyepoxides with methacrylic acid; carbamoyl dimethacrylates obtained by reacting polyisocyanates such as toluene diisocyanate and hexamethylene diisocyanate with hydroxyethyl methacrylate; allylated starch, allylated cellulose, diallyl phthalate, N,N',N''-triallyl isocyanurate, divinylbenzene, etc. Compounds having two or more polymerizable unsaturated groups; diglycidyl compounds such as (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, and (poly)glycerol diglycidyl ether; polyglycidyl compounds such as triglycidyl compounds; epihalohydrins such as epichlorohydrin, epibromohydrin, and α-methylepiochlorohydrin; isocyanate compounds such as 2,4-toluene diisocyanate and hexamethylene diisocyanate; and compounds having two or more reactive functional groups such as 3-methyl-3-oxetane methanol, 3-ethyl-3-oxetane methanol, 3-butyl-3-oxetane methanol, 3-methyl-3-oxetane ethanol, 3-ethyl-3-oxetane ethanol, and 3-butyl-3-oxetane ethanol, etc. Among these internal crosslinking agents, polyglycidyl compounds are preferred, diglycidyl ether compounds are more preferred, and (poly)ethylene glycol diglycidyl ether, (poly)propylene glycol diglycidyl ether, and (poly)glycerol diglycidyl ether are particularly preferred. These internal crosslinking agents can be used alone or in combination of two or more.

[0055] The amount of internal crosslinking agent used in the monomer aqueous solution of the first stage is preferably 0.000001 mol to 0.005 mol relative to 1 mol of water-soluble olefinic unsaturated monomer, more preferably 0.00001 mol to 0.002 mol, even more preferably 0.00001 mol to 0.001 mol, and even more preferably 0.00005 mol to 0.0005 mol.

[0056] The amount of internal crosslinking agent used in the monomer aqueous solution of the second stage, from the viewpoint of improving general water absorption performance (water retention capacity of physiological saline, water absorption capacity of physiological saline, etc.), is preferably 0 to 0.005 moles relative to 1 mole of water-soluble olefinic unsaturated monomer, more preferably 0 to 0.0005 moles, even more preferably 0 to 0.0001 moles, and particularly preferably 0 to 0.00004 moles.

[0057] [Hydrocarbon dispersion medium] Examples of hydrocarbon dispersion media include: aliphatic hydrocarbons with 6 to 8 carbon atoms, such as n-hexane, n-heptane, 2-methylhexane, 3-methylhexane, 2,3-dimethylpentane, 3-hexylpentane, and n-octane; alicyclic hydrocarbons, such as cyclohexane, methylcyclohexane, cyclopentane, methylcyclopentane, trans-1,2-dimethylcyclopentane, cis-1,3-dimethylcyclopentane, and trans-1,3-dimethylcyclopentane; and aromatic hydrocarbons, such as benzene, toluene, and xylene. Among these hydrocarbon dispersion media, n-hexane, n-heptane, and cyclohexane are particularly suitable from the perspective of being readily available industrially, having stable quality, and being inexpensive. These hydrocarbon dispersion media can be used alone or in combination of two or more. It should be noted that, as an example of a mixture of hydrocarbon dispersion media, commercially available products such as Exxsol heptane (manufactured by Exxon Mobil: containing 75% to 85% by mass of heptane and its isomers) also yield suitable results.

[0058] From the viewpoint of uniformly dispersing the water-soluble olefinic unsaturated monomer and easily controlling the polymerization temperature, the amount of water-soluble olefinic unsaturated monomer used as the hydrocarbon dispersion medium is preferably 100 to 1500 parts by mass, and more preferably 200 to 1400 parts by mass, relative to 100 parts by mass of the water-soluble olefinic unsaturated monomer in the first stage. It should be noted that, as described below, reverse suspension polymerization is carried out in one stage (single stage) or multiple stages (two or more stages). The aforementioned first-stage polymerization refers to the first-stage polymerization reaction in single-stage polymerization or multi-stage polymerization (the same applies below).

[0059] [Dispersion stabilizer] (surfactant) In reverse suspension polymerization, dispersion stabilizers can be used to improve the dispersion stability of water-soluble olefinic unsaturated monomers in hydrocarbon dispersion media. Surfactants can be used as such dispersion stabilizers.

[0060] As surfactants, examples include sucrose fatty acid esters, polyglycerol fatty acid esters, dehydrated sorbitan fatty acid esters, polyoxyethylene dehydrated sorbitan fatty acid esters, polyoxyethylene glycerol fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene castor oil, polyoxyethylene hydrogenated castor oil, alkylallyl formaldehyde condensed polyoxyethylene ethers, polyoxyethylene polyoxypropylene block copolymers, polyoxyethylene polyoxypropylene alkyl ethers, polyethylene glycol fatty acid esters, alkyl glucosides, N-alkyl glucosamides, polyoxyethylene fatty acid amides, polyoxyethylene alkylamines, phosphate esters of polyoxyethylene alkyl ethers, and phosphate esters of polyoxyethylene alkylallyl ethers. Among these surfactants, dehydrated sorbitan fatty acid esters, polyglycerol fatty acid esters, and sucrose fatty acid esters are particularly preferred from the perspective of monomer dispersion stability. These surfactants can be used alone or in combination of two or more.

[0061] The amount of surfactant used is preferably 0.1 to 30 parts by mass relative to 100 parts by mass of the water-soluble olefinic unsaturated monomer in the first stage, and more preferably 0.3 to 20 parts by mass.

[0062] (Polymer-based dispersants) In addition, as a dispersant stabilizer used in reverse suspension polymerization, it can also be used together with the surfactants mentioned above and with a polymeric dispersant.

[0063] Examples of polymeric dispersants 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 polybutadiene, 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, and ethyl hydroxyethyl cellulose. Among these polymeric dispersants, particularly from the perspective of monomer dispersion stability, maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-ethylene copolymer, maleic anhydride-propylene copolymer, maleic anhydride-ethylene-propylene copolymer, polyethylene, polypropylene, ethylene-propylene copolymer, oxidized polyethylene, oxidized polypropylene, and oxidized ethylene-propylene copolymer are preferred. These polymeric dispersants can be used alone or in combination of two or more.

[0064] The amount of polymeric dispersant used is preferably 0.1 to 30 parts by mass relative to 100 parts by mass of the water-soluble olefinic unsaturated monomer in the first stage, and more preferably 0.3 to 20 parts by mass.

[0065] [Other ingredients] In the manufacturing method of water-absorbent resin particles, other components can be added to an aqueous solution containing water-soluble olefinically unsaturated monomers as needed to carry out reverse-phase suspension polymerization. Various additives such as thickeners and chain transfer agents can be added as these other components.

[0066] As an example, a thickener can be added to an aqueous solution containing a water-soluble olefinically unsaturated monomer to induce reverse suspension polymerization. By adjusting the viscosity of the aqueous solution through the addition of a thickener, the median particle size obtained in the reverse suspension polymerization can be controlled.

[0067] As thickeners, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, carboxymethyl cellulose, polyacrylic acid, partially neutralized polyacrylic acid, polyethylene glycol, polyacrylamide, polyethyleneimine, dextrin, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone, and polyethylene oxide can be used, for example. It should be noted that if the stirring speed during polymerization is the same, there is a tendency that the higher the viscosity of the aqueous solution of the water-soluble olefinically unsaturated monomer, the larger the primary and / or secondary particles will be.

[0068] [Reverse suspension polymerization] In reverse suspension polymerization, for example, an aqueous solution of a monomer containing a water-soluble olefinically unsaturated monomer is dispersed in a hydrocarbon dispersion medium in the presence of a dispersion stabilizer. In this case, if the polymerization reaction is to begin, the dispersion stabilizer (surfactant or polymeric dispersant) can be added either before or after the addition of the monomer aqueous solution.

[0069] From the viewpoint of easily reducing the amount of residual hydrocarbon dispersion medium in the obtained water-absorbing resin particles, it is preferable to disperse the monomer aqueous solution in a hydrocarbon dispersion medium in which a polymeric dispersant is dispersed, and then disperse the surfactant before polymerization.

[0070] Such reverse suspension polymerization can be carried out in one or more stages. Furthermore, from the viewpoint of improving productivity, it is preferable to carry out the process in two to three stages.

[0071] When performing multi-stage reverse suspension polymerization with two or more stages, after the first stage of reverse suspension polymerization, a water-soluble olefinic unsaturated monomer is added to the reaction mixture obtained from the first stage polymerization reaction and mixed. The second and subsequent stages of reverse suspension polymerization are then carried out using the same method as the first stage. In each stage of reverse suspension polymerization after the second stage, preferably, in addition to the water-soluble olefinic unsaturated monomer, the free radical polymerization initiator is added based on the amount of water-soluble olefinic unsaturated monomer added in each stage of reverse suspension polymerization after the second stage, within the range of the above-mentioned molar ratios of each component relative to the water-soluble olefinic unsaturated monomer, and reverse suspension polymerization is carried out. It should be noted that, in the polymerization after the second stage, an internal crosslinking agent may also be added to the water-soluble olefinic unsaturated monomer, if necessary.

[0072] From the viewpoint of improving economy by enabling rapid polymerization and shortening polymerization time, and facilitating smooth reaction by easily removing the heat of polymerization, the reaction temperature is preferably 20°C to 110°C, and more preferably 40°C to 90°C.

[0073] <Dehydration Process> Alternatively, after the aforementioned reverse suspension polymerization, a dehydration step can be included: applying heat or other energy from the outside to remove water, hydrocarbon dispersion medium, etc., by distillation. In the case of dehydrating the aqueous gel-like material after reverse suspension polymerization, the system in which the aqueous gel-like material is dispersed in a hydrocarbon dispersion medium is heated, and water and the hydrocarbon dispersion medium are temporarily removed from the system by azeotropic distillation. At this time, if only the distilled hydrocarbon dispersion medium is returned to the system, continuous azeotropic distillation can be performed. In this case, the temperature within the drying system is maintained below the azeotropic temperature with the hydrocarbon dispersion medium, which is preferable from the viewpoint of minimizing resin degradation. By controlling the processing conditions of this dehydration step after polymerization to adjust the amount of water removed (i.e., adjusting the moisture content of the polymer particles), various properties of the obtained water-absorbing resin particles can be controlled.

[0074] In the dehydration process, dehydration treatment by distillation can also be carried out under normal pressure. When dehydration treatment is carried out under normal pressure, the dehydration temperature is preferably 70°C to 250°C, more preferably 80°C to 180°C, even more preferably 80°C to 140°C, and even more preferably 90°C to 130°C.

[0075] <Surface Crosslinking Process> The surface crosslinking process is a process of performing surface crosslinking on polymer particles obtained in the polymerization process. When the polymer particles are crosslinked polymer particles (including hydrogel-like substances), it becomes a process of adding a surface crosslinking agent to a hydrogel-like substance with an internal crosslinked structure obtained by polymerizing a water-soluble olefinically unsaturated monomer, thereby performing a surface crosslinking reaction. This surface crosslinking reaction is preferably carried out in the presence of a surface crosslinking agent after the polymerization of the water-soluble olefinically unsaturated monomer has been completed. In this way, after polymerization, by performing a surface crosslinking reaction on the hydrogel-like substance with an internal crosslinked structure, the crosslinking density near the surface of the water-absorbing resin particles is set to a specific range, thereby obtaining water-absorbing resin particles with improved water absorption capacity under load and other properties.

[0076] Compounds having two or more reactive functional groups can be cited as surface crosslinking agents. Examples include: polyols such as ethylene glycol, propylene glycol, 1,4-butanediol, diethylene glycol, triethylene glycol, trimethylolpropane, glycerol, polyoxyethylene glycol, polyoxypropylene glycol, and polyglycerol; polyglycidyl compounds such as (poly)ethylene glycol diglycidyl ether, (poly)glycerol diglycidyl ether, (poly)glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, (poly)propylene glycol polyglycidyl ether, and (poly)glycerol polyglycidyl ether; halogenated epoxy compounds such as epichlorohydrin, epibromohydrin, and α-methylepiochlorohydrin; isocyanate compounds such as 2,4-toluene diisocyanate and hexamethylene diisocyanate; 3-methyl-3-oxetane methanol, 3-ethyl-3-oxetane methanol, 3-butyl-3-oxetane methanol, and 3-methyl-3-oxetane methanol. Oxybutane compounds such as alcohols, 3-ethyl-3-oxetane ethanol, and 3-butyl-3-oxetane ethanol; oxazoline compounds such as 1,2-ethylidene bisoxazoline; ethylene carbonate; propylene carbonate, carbonates such as 4,5-dimethyl-1,3-dioxolane-2-one, 4,4-dimethyl-1,3-dioxolane-2-one, 4-ethyl-1,3-dioxolane-2-one, 4-hydroxymethyl-1,3-dioxolane-2-one, 1,3-dioxane-2-one, 4-methyl-1,3-dioxane-2-one, 4,6-dimethyl-1,3-dioxane-2-one, and 1,3-dioxolane-2-one (e.g., alkylene carbonates); hydroxyalkylamide compounds such as bis[N,N-di(β-hydroxyethyl)]hexamethylenediamide. Among these surface crosslinking agents, polyglycidyl compounds such as (poly)ethylene glycol diglycidyl ether, (poly)glycerol diglycidyl ether, (poly)glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, (poly)propylene glycol polyglycidyl ether, and (poly)glycerol polyglycidyl ether are preferred. These surface crosslinking agents can be used alone or in combination of two or more.

[0077] From the viewpoint of adjusting the 15-minute value of saline water absorption under a load of 0.69 kPa to a preferred range, the amount of surface crosslinking agent used is preferably 0.00001 mol to 0.01 mol, more preferably 0.00005 mol to 0.005 mol, even more preferably 0.0001 mol to 0.001 mol, and even more preferably 0.0004 mol to 0.0009 mol, relative to 1 mol of the total amount of water-soluble olefinic unsaturated monomers used in the polymerization.

[0078] As a method of adding a surface crosslinking agent, it can be added directly, as an aqueous solution, or, as needed, as a solution using a hydrophilic organic solvent. Examples of hydrophilic organic solvents include: lower alcohols such as methanol, ethanol, n-propanol, and isopropanol; ketones such as acetone and methyl ethyl ketone; ethers such as diethyl ether, dioxane, and tetrahydrofuran; amides such as N,N-dimethylformamide; and sulfoxides such as dimethyl sulfoxide. These hydrophilic organic solvents can be used alone, in combination of two or more, or as a mixed solvent with water.

[0079] The surface crosslinking agent can be added once the polymerization reaction of the water-soluble olefinic unsaturated monomer is almost completely completed. It is preferably added in the presence of water in the range of 1 to 400 parts by mass relative to 100 parts by mass of the water-soluble olefinic unsaturated monomer used in the polymerization; more preferably in the presence of water in the range of 5 to 200 parts by mass; even more preferably in the presence of water in the range of 10 to 100 parts by mass; and even more preferably in the presence of water in the range of 15 to 60 parts by mass. It should be noted that the amount of water refers to the total amount of water contained in the reaction system and the water required for adding the surface crosslinking agent.

[0080] The preferred reaction temperature for the surface crosslinking reaction is 50°C to 250°C, more preferably 60°C to 180°C, even more preferably 60°C to 140°C, and even more preferably 70°C to 120°C. The preferred reaction time for the surface crosslinking reaction is 1 minute to 300 minutes, more preferably 5 minutes to 200 minutes.

[0081] <Drying Process> Alternatively, after the above-mentioned surface crosslinking, the following drying process can be included: removing water, hydrocarbon dispersion medium, etc. by applying energy such as heat from the outside and by distillation. The surface-crosslinked polymer particles are dried, and water and hydrocarbon dispersion medium are removed by distillation, thereby obtaining water-absorbing resin particles.

[0082] In the drying process, the drying treatment by distillation can be carried out under atmospheric pressure or under reduced pressure. Alternatively, from the viewpoint of improving drying efficiency, it can also be carried out under a gas stream such as nitrogen. When drying is carried out under atmospheric pressure, the preferred drying temperature is 70°C to 250°C, more preferably 80°C to 180°C, even more preferably 80°C to 140°C, and even more preferably 90°C to 130°C. When drying is carried out under reduced pressure, the preferred drying temperature is 40°C to 160°C, more preferably 50°C to 110°C.

[0083] It should be noted that when a surface crosslinking step using a surface crosslinking agent is performed after monomer polymerization via reverse suspension polymerization, the aforementioned drying step by distillation is performed after the surface crosslinking step is completed. Alternatively, the surface crosslinking step and the drying step can be performed simultaneously.

[0084] The absorbent resin particles of the present invention may also contain additives appropriate to the intended purpose. Examples of such additives include inorganic powders, surfactants, oxidizing agents, reducing agents, metal chelating agents, free radical chain reaction terminators, antioxidants, and antibacterial agents. For example, by adding 0.05 to 5 parts by weight of amorphous silica as an inorganic powder relative to 100 parts by weight of the absorbent resin particles, the flowability of the absorbent resin particles can be further improved. It should be noted that the above-mentioned additives are preferably hydrophilic or water-soluble.

[0085] 3. Absorbent materials The absorbent resin particles of the present invention constitute an absorbent material used in hygiene materials such as sanitary products and diapers, and are suitable for absorbent articles containing the above-mentioned absorbent material.

[0086] The absorbent of the present invention comprises the absorbent resin particles of the present invention. The absorbent may further comprise hydrophilic fibers. Examples of absorbent structures include sheet-like structures in which absorbent resin particles are fixed on or between multiple nonwoven fabrics; mixed dispersions obtained by mixing absorbent resin particles and hydrophilic fibers into a uniform composition; sandwich structures in which absorbent resin particles are sandwiched between layered hydrophilic fibers; and structures formed by wrapping absorbent resin particles and hydrophilic fibers in thin paper. It should be noted that other components may be incorporated into the absorbent, such as heat-melt synthetic fibers, heat-melt adhesives, adhesive emulsions, and other adhesives to improve the shape retention performance of the absorbent.

[0087] The absorbent resin particles in the absorbent body of this invention have a unit area weight of 30 g / m³. 2 Above and 500g / m 2 The following is a preferred weight per unit area: 100 g / m². 2Above and 400g / m 2 the following.

[0088] The water-absorbing resin particles in the mixed dispersion of the present invention have a unit area weight of 30 g / m³. 2 Above and 500g / m 2 The following is a preferred weight per unit area: 100 g / m². 2 The above, more preferably 120g / m 2 The above is further optimized to 140g / m 2 In addition, the preferred value is 300g / m³. 2 The following is more preferably 250g / m 2 The following is a further preferred value: 200g / m 2 the following.

[0089] The water-absorbing resin particles in the sheet-like structure of this invention have a unit area weight of 150 g / m². 2 Above and 500g / m 2 The preferred weight per unit area is 250 g / m². 2 The above, more preferably 300g / m 2 The above is further preferred to be 350g / m 2 In addition, the preferred value is 450g / m³. 2 The following is more preferably 400g / m 2 The following is a further preferred value: 350g / m 2 the following.

[0090] Examples of hydrophilic fibers include at least one selected from the group consisting of finely ground wood pulp, cotton, cotton linters, rayon, cellulose acetate, polyamide, polyester, and polyolefins. Examples include cellulose fibers such as cotton-like pulp, mechanical pulp, chemical pulp, and semi-chemical pulp obtained from wood; man-made cellulose fibers such as rayon and acetate; and fibers made from synthetic resins such as polyamide, polyester, and polyolefins that have undergone hydrophilic treatment. The average fiber length of hydrophilic fibers is typically 0.1 mm to 10 mm, or 0.5 mm to 5 mm.

[0091] The hydrophilic fibers in the absorbent of this invention have a surface area weight of 0 g / m². 2 Above and 800g / m 2 The following is a preferred value: the weight per unit area is 0 g / m². 2 Above and 500g / m 2 the following.

[0092] The hydrophilic fibers in the mixed dispersion of the present invention have a unit area weight of 50 g / m². 2 Above and 800g / m 2The following is a preferred weight per unit area: 100 g / m². 2 The above, more preferably 120g / m 2 The above is further optimized to 140g / m 2 In addition, the preferred value is 700g / m³. 2 The following is more preferably 600g / m 2 The following is a further preferred value: 500g / m 2 the following.

[0093] The hydrophilic fibers in the sheet-like structure of this invention have a unit area weight of 0 g / m². 2 Above and 100g / m 2 The following is a preferred value: the weight per unit area is 0 g / m². 2 Above and 80g / m 2 The following is more preferably 0 g / m 2 Above and 50g / m 2 The following is further preferred: 0 g / m 2 .

[0094] The content of water-absorbing resin particles in the absorbent is preferably 5% to 100% by mass, more preferably 10% to 95% by mass, even more preferably 20% to 90% by mass, and even more preferably 30% to 80% by mass.

[0095] The absorbent article of the present invention can be manufactured by holding an absorbent body using the absorbent resin particles of the present invention between a liquid-permeable sheet (top sheet) through which liquid can pass and a liquid-impermeable sheet (back sheet) through which liquid cannot pass. The liquid-permeable sheet is disposed on the side in contact with the body, and the liquid-impermeable sheet is disposed on the opposite side in contact with the body.

[0096] Examples of liquid-permeable sheets include nonwoven fabrics such as hot-air type, spunbond type, chemically bonded type, and needle-punched type made of fibers such as polyethylene, polypropylene, and polyester, as well as porous synthetic resin sheets. Examples of liquid-impermeable sheets include synthetic resin films containing resins such as polyethylene, polypropylene, and polyvinyl chloride. The liquid-permeable sheet is preferably selected from at least one of the following groups: thermally bonded nonwoven fabric, hot-air nonwoven fabric, spunbond nonwoven fabric, and spunbond / meltblown / spunbond nonwoven fabric.

[0097] The preferred weight per unit area of ​​the liquid-permeable sheet is 5 g / m². 2 Above and 100g / m 2 The following is more preferably 10g / m 2 Above and 60g / m 2Furthermore, to improve the diffusion properties of the liquid, the surface of the liquid-permeable sheet can be embossed or perforated. These embossing and perforation processes can be performed using known methods.

[0098] Examples of liquid-impermeable sheets include: sheets made of synthetic resins such as polyethylene, polypropylene, and polyvinyl chloride; sheets made of nonwoven fabrics such as spunbond / meltblown / spunbond (SMS) nonwoven fabrics made by sandwiching water-resistant meltblown nonwoven fabric with high-strength spunbond nonwoven fabric; and sheets made of composite materials of these synthetic resins and nonwoven fabrics (e.g., spunbond nonwoven fabrics, spunlace nonwoven fabrics). Sheets made of synthetic resins primarily composed of low-density polyethylene (LDPE) resin can also be used as liquid-impermeable sheets. For example, a liquid-impermeable sheet may also be made of a material with a weight per unit area of ​​10 g / m². 2 ~50g / m 2 Sheets made of synthetic resin.

[0099] The absorbent article preferably has a laminate, a liquid-permeable sheet disposed on the upper surface of the laminate, and a liquid-impermeable sheet disposed on the side of the laminate opposite to the side of the liquid-permeable sheet. The laminate has an absorbent containing absorbent resin particles and upper and lower core-packing materials (core-packing sheets) that hold the absorbent.

[0100] 4. Additional Notes This specification includes at least the inventions shown in (1) to (8) below. (1) A water-absorbing resin particle with physiological saline absorbance values ​​over 15 minutes at a load of 0.69 kPa of 30 mL / g~60 mL / g, 30 mL / g~58 mL / g, 30 mL / g~55 mL / g, 32 mL / g~60 mL / g, 32 mL / g~58 mL / g, 32 mL / g~55 mL / g, 34 mL / g~60 mL / g, 34 mL / g~58 mL / g, 34 mL / g~55 mL / g, 35 mL / g~60 mL / g, 35 mL / g~58 mL / g, and 35 mL / g~55 mL / g. (2) According to the water-absorbing resin particles described in (1) above, the unpressurized DW 3-minute values ​​of the above water-absorbing resin particles are 20mL / g~50mL / g, 20mL / g~48mL / g, 20mL / g~46mL / g, 30mL / g~50mL / g, 30mL / g~48mL / g, 30mL / g~46mL / g, 33mL / g~50mL / g, 33mL / g~48mL / g, 33mL / g~46mL / g, 36mL / g~50mL / g, 36mL / g~48mL / g, 36mL / g~46mL / g, 39mL / g~50mL / g, 39mL / g~48mL / g, and 39mL / g~46mL / g. (3) According to the water-absorbing resin particles described in (1) or (2) above, the water absorption rate of the water-absorbing resin particles relative to physiological saline is less than 60 seconds, 20 to 60 seconds, 20 to 55 seconds, 20 to 50 seconds, 25 to 60 seconds, 25 to 55 seconds, 25 to 50 seconds, 30 to 60 seconds, 30 to 55 seconds, and 30 to 50 seconds. (4) The water-absorbing resin particles described in any one of (1) to (3) above, wherein the saline water retention capacity of the above-mentioned water-absorbing resin particles is 30 g / g or more, 30 g / g to 70 g / g, 30 g / g to 65 g / g, 30 g / g to 60 g / g, 36 g / g to 70 g / g, 36 g / g to 65 g / g, 36 g / g to 60 g / g, 41 g / g to 70 g / g, 41 g / g to 65 g / g, 41 g / g to 60 g / g. (5) According to any one of (1) to (4) above, the water-absorbing resin particles have a DW 10-minute value of 30 mL / g to 80 mL / g, 30 mL / g to 75 mL / g, 30 mL / g to 72 mL / g, 45 mL / g to 80 mL / g, 45 mL / g to 75 mL / g, 45 mL / g to 72 mL / g, 50 mL / g to 80 mL / g, 50 mL / g to 75 mL / g, 50 mL / g to 72 mL / g, 54 mL / g to 80 mL / g, 54 mL / g to 75 mL / g, 54 mL / g to 72 mL / g, 56 mL / g to 80 mL / g, 56 mL / g to 75 mL / g, and 56 mL / g to 72 mL / g. (6) According to any one of (1) to (5) above, the water-absorbing resin particles of the above water-absorbing resin particles have a saline water absorption capacity of 30 g / g or more, 45 g / g to 80 g / g, 45 g / g to 74 g / g, 45 g / g to 69 g / g, 52 g / g to 80 g / g, 52 g / g to 74 g / g, 52 g / g to 69 g / g, 59 g / g to 80 g / g, 59 g / g to 74 g / g, and 59 g / g to 69 g / g. (7) According to any one of (1) to (6) above, the difference between the amount of water absorbed by the above-mentioned water-absorbing resin particles and the amount of water retained by the physiological saline is 5-30, 5-25, 5-20, 10-30, 10-25, or 10-20. (8) According to any one of (1) to (7) above, the median particle size of the above-mentioned water-absorbing resin particles is 200μm to 700μm, 200μm to 600μm, 200μm to 550μm, 200μm to 500μm, 200μm to 450μm, 250μm to 700μm, 250μm to 600μm, 250μm to 550μm, 2 50μm~500μm, 250μm~450μm, 300μm~700μm, 300μm~600μm, 300μm~550μm, 300μm~500μm, 300μm~450μm, 350μm~700μm, 350μm~600μm, 350μm~550μm, 350μm~500μm, 350μm~450μm.

[0109] Example The present invention will now be described in detail with examples and comparative examples. However, the present invention is not limited to the examples. It should be noted that, unless otherwise specified, the measurements were conducted in an environment with a temperature of 25±2°C and a humidity of 50±10%.

[0110] Manufacturing of Water-Absorbent Resin Particles (Example 1) [First stage of polymerization process] A round-bottomed, cylindrical, separable flask with an inner diameter of 11 cm and a capacity of 2 L was prepared. It was equipped with a reflux condenser, a dropping funnel, a nitrogen inlet tube, and a two-section stirring blade with four inclined blades, each with a blade diameter of 5 cm. 292 g of n-heptane was added to the flask as a hydrocarbon dispersion medium, and 0.782 g of maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals, HI-WAX 1105A) was added as a polymeric dispersant. The mixture was stirred and heated to 80 °C to dissolve the dispersant, then cooled to 50 °C.

[0111] In a 300 mL beaker, 92.0 g (1.03 mol) of an 80.5% by mass aqueous solution of acrylic acid, a water-soluble olefinic unsaturated monomer, was added. While cooling from the outside, 110.1 g of a 28.0% by mass aqueous solution of sodium hydroxide was added dropwise. After neutralization to 75 mol%, 0.092 g (0.339 mmol) of 2,2'-azobis(2-amidinepropane) dihydrochloride, a water-soluble free radical polymerization initiator, 0.028 g (0.102 mmol) of potassium persulfate, 0.0101 g (0.058 mmol) of ethylene glycol diglycidyl ether, an internal crosslinking agent, and 37.2 g of deionized water were added and dissolved to prepare the monomer aqueous solution for the first stage.

[0112] Then, the aqueous solution prepared above was added to a separable flask, and after stirring for 10 minutes, a surfactant solution was further added, which was obtained by heating 7.45 g of n-heptane to dissolve 0.828 g of sucrose stearate (Mitsubishi Chemical Foods Co., Ltd., Ryoto Sugar Ester S-370) as a surfactant. While stirring at 500 rpm, the system was fully purged with nitrogen, and the flask was immersed in a 70°C water bath for 60 minutes to polymerize, thereby obtaining a first-stage polymerization slurry containing primary particles.

[0113] [Second stage polymerization process] 128.8 g (1.44 mol) of an 80.5% by mass aqueous solution of acrylic acid, which is a water-soluble olefinic unsaturated monomer, was added to a 500 mL beaker. While cooling from the outside, 154.2 g of a 28.0% by mass aqueous solution of sodium hydroxide was added dropwise. After neutralization to 75 mol%, 0.064 g (0.237 mmol) of 2,2'-azobis(2-amidinepropane) dihydrochloride, which is a water-soluble free radical polymerization initiator, 0.039 g (0.143 mmol) of potassium persulfate, and 6.49 g of deionized water were added to dissolve the monomer in the second stage.

[0114] While stirring at 1000 rpm, the internal temperature of the separable flask system was cooled to 25°C. Then, all of the second-stage aqueous solution was added to the first-stage polymerization slurry. The system was purged with nitrogen for 30 minutes, and then the flask was immersed again in a 70°C water bath for 60 minutes to allow for polymerization. Through these steps, the hydrogel resulting from the second-stage polymerization was obtained.

[0115] [Surface crosslinking] Then, the flask was immersed in an oil bath set to 125°C, and 176.6 g of water was discharged from the system through azeotropic distillation of n-heptane and water while the n-heptane was refluxed. Then, under stirring, 4.91 g of a 4.5% by mass aqueous solution of diethylenetriaminepentaacetic acid pentasodium and 2.58 g of a 3% by mass aqueous solution of sodium sulfite were added to the flask to obtain a second-stage polymerization slurry containing secondary particles.

[0116] Then, the flask was immersed again in an oil bath set at 125°C, and azeotropic distillation of n-heptane and water was performed, with the n-heptane being refluxed while 99.5 g (total 276.1 g) of water was further discharged from the system. Then, 16.6 g (1.90 mmol) of a 2% by mass aqueous solution of ethylene glycol diglycidyl ether as a surface crosslinking agent was added to the flask, and the mixture was kept at 83°C for 2 hours.

[0117] Then, n-heptane was evaporated at 125°C to dry it, thereby obtaining a dried product. The dried product was passed through a sieve with a mesh size of 850 μm, and 0.2% by mass of amorphous silica (Oriental Silicas Corporation, Tokusil NP-S) was mixed relative to the dried product to obtain 210.4 g of the water-absorbing resin particles of Example 1.

[0118] (Example 2) The amount of water discharged from the system through the second azeotropic distillation was changed to 100.9g (total 277.5g). Otherwise, the process was carried out in the same manner as in Example 1, resulting in 218.6g of the water-absorbing resin particles of Example 2.

[0119] (Example 3) [First stage of polymerization process] Prepare a round-bottomed, separable cylindrical flask with an inner diameter of 11 cm and a capacity of 2 L. The flask is equipped with a reflux condenser, a dropping funnel, a nitrogen inlet tube, and a two-section stirring blade with four inclined blades, each with a blade diameter of 5 cm. Add 315 g of n-heptane as the hydrocarbon dispersion medium and 0.782 g of maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals, HI-WAX 1105A) as the polymeric dispersant. While stirring, heat to 80 °C to dissolve the dispersant, then cool to 50 °C.

[0120] In a 300 mL beaker, 92.0 g (1.03 mol) of an 80.5% by mass aqueous solution of acrylic acid, a water-soluble olefinic unsaturated monomer, was added. While cooling from the outside, 110.1 g of a 28.0% by mass aqueous solution of sodium hydroxide was added dropwise. After neutralization to 75 mol%, 0.092 g (0.339 mmol) of 2,2'-azobis(2-amidinepropane) dihydrochloride, a water-soluble free radical polymerization initiator, 0.028 g (0.102 mmol) of potassium persulfate, 0.0101 g (0.058 mmol) of ethylene glycol diglycidyl ether, an internal crosslinking agent, and 37.2 g of deionized water were added and dissolved to prepare the monomer aqueous solution for the first stage.

[0121] Then, the aqueous solution prepared above was added to a separable flask, and after stirring for 10 minutes, a surfactant solution was further added, which was obtained by heating 7.45 g of n-heptane to dissolve 0.828 g of sucrose stearate (Mitsubishi Chemical Foods Co., Ltd., Ryoto Sugar Ester S-370) as a surfactant. While stirring at 500 rpm, the system was fully purged with nitrogen, and the flask was immersed in a 70°C water bath for 60 minutes to polymerize, thereby obtaining a first-stage polymerization slurry containing primary particles.

[0122] [Second stage polymerization process] 147.2 g (1.64 mol) of an 80.5% by mass aqueous solution of acrylic acid, a water-soluble olefinic unsaturated monomer, was added to a 500 mL beaker. While cooling from the outside, 176.2 g of a 28.0% by mass aqueous solution of sodium hydroxide was added dropwise for 75 mol% neutralization. Then, 0.074 g (0.271 mmol) of 2,2'-azobis(2-amidinepropane) dihydrochloride, a water-soluble free radical polymerization initiator, 0.044 g (0.163 mmol) of potassium persulfate, and 7.41 g of deionized water were added to dissolve the monomer in the second stage.

[0123] While stirring at 1000 rpm, the internal temperature of the separable flask system was cooled to 25°C. Then, all of the second-stage aqueous solution was added to the first-stage polymerization slurry. The system was purged with nitrogen for 30 minutes, and then the flask was immersed again in a 70°C water bath for 60 minutes to allow for polymerization. Through these steps, the hydrogel resulting from the second-stage polymerization was obtained.

[0124] [Surface crosslinking] Then, the flask was immersed in an oil bath set to 125°C, and 191.4 g of water was discharged from the system through azeotropic distillation of n-heptane and water while the n-heptane was refluxed. Then, under stirring, 5.32 g of a 4.5% by mass aqueous solution of diethylenetriaminepentaacetic acid pentasodium and 2.79 g of a 3% by mass aqueous solution of sodium sulfite were added to the flask to obtain a second-stage polymerization slurry containing secondary particles.

[0125] Then, the flask was immersed again in an oil bath set to 125°C, and azeotropic distillation of n-heptane and water was performed, with the n-heptane being refluxed while 84.6 g (total 276.0 g) of water was further discharged from the system. Then, 5.98 g (0.69 mmol) of a 2% by mass aqueous solution of ethylene glycol diglycidyl ether as a surface crosslinking agent was added to the flask, and the mixture was kept at 83°C for 2 hours.

[0126] Then, n-heptane was evaporated at 125°C to dry it, thereby obtaining a dried product. The dried product was passed through a sieve with a mesh size of 850 μm, and 0.2% by mass of amorphous silica (Oriental Silicas Corporation, Tokusil NP-S) was mixed relative to the dried product to obtain 223.3 g of the water-absorbing resin particles of Example 3.

[0127] (Comparative Example 1) [First stage of polymerization process] Prepare a round-bottomed, separable cylindrical flask with an inner diameter of 11 cm and a capacity of 2 L. The flask is equipped with a reflux condenser, a dropping funnel, a nitrogen inlet tube, and a two-section stirring blade with four inclined blades, each with a blade diameter of 5 cm. Add 292 g of n-heptane as the hydrocarbon dispersion medium and 0.736 g of maleic anhydride-modified ethylene-propylene copolymer (Mitsui Chemicals, HI-WAX 1105A) as the polymeric dispersant. While stirring, heat to 80 °C to dissolve the dispersant, then cool to 50 °C.

[0128] In a 300 mL beaker, 92.0 g (1.03 mol) of an 80.5% by mass aqueous solution of acrylic acid, which is a water-soluble olefinic unsaturated monomer, was added. While cooling from the outside, 110.1 g of a 28.0% by mass aqueous solution of sodium hydroxide was added dropwise to neutralize to 75 mol%. Then, 0.074 g (0.272 mmol) of potassium persulfate, which is a water-soluble free radical polymerization initiator, 0.0101 g (0.058 mmol) of ethylene glycol diglycidyl ether, which is an internal crosslinking agent, and 37.2 g of deionized water were added to dissolve the monomer aqueous solution in the first stage.

[0129] Then, the aqueous solution prepared above was added to a separable flask and stirred for 10 minutes. Then, a surfactant solution containing 0.736 g of sucrose stearate (Mitsubishi Chemical Foods Co., Ltd., Ryoto Sugar Ester S-370) as a surfactant, which was dissolved in 7.45 g of n-heptane by heating, was added. While stirring at 500 rpm, the system was fully purged with nitrogen. The flask was then immersed in a water bath at 70°C and heated for 60 minutes to polymerize, thereby obtaining a first-stage polymerization slurry containing primary particles.

[0130] [Second stage polymerization process] In a 500 mL beaker, 128.8 g (1.44 mol) of an 80.5% by mass aqueous solution of acrylic acid, which is a water-soluble olefinic unsaturated monomer, was added. While cooling from the outside, 154.2 g of a 28.0% by mass aqueous solution of sodium hydroxide was added dropwise. After neutralization to 75 mol%, 0.103 g (0.381 mmol) of potassium persulfate, which is a water-soluble free radical polymerization initiator, 0.012 g (0.067 mmol) of ethylene glycol diglycidyl ether, which is an internal crosslinking agent, and 6.48 g of deionized water were added to dissolve the monomer aqueous solution in the second stage.

[0131] While stirring at 1000 rpm, the internal temperature of the separable flask system was cooled to 25°C. Then, all of the second-stage aqueous solution was added to the first-stage polymerization slurry. The system was purged with nitrogen for 30 minutes, and then the flask was immersed again in a 70°C water bath for 60 minutes to allow for polymerization. Through these steps, the hydrogel resulting from the second-stage polymerization was obtained.

[0132] [Surface crosslinking] Then, the flask was immersed in an oil bath set at 125°C, and 176.6 g of water was discharged from the system through azeotropic distillation of n-heptane and water while the n-heptane was refluxed. Then, under stirring, 4.91 g of a 4.5% by mass aqueous solution of diethylenetriaminepentaacetic acid pentasodium and 2.58 g of a 3% by mass aqueous solution of sodium sulfite were added to the flask to obtain a second-stage polymerization slurry containing secondary particles.

[0133] Then, the flask was immersed again in an oil bath set at 125°C, and azeotropic distillation of n-heptane and water was performed, with the n-heptane being refluxed while 89.6 g (total 266.3 g) of water was further discharged from the system. Then, 4.42 g (0.51 mmol) of a 2% by mass aqueous solution of ethylene glycol diglycidyl ether as a surface crosslinking agent was added to the flask, and the mixture was kept at 83°C for 2 hours.

[0134] Then, n-heptane was evaporated at 125°C to dry it, thereby obtaining a dried product. The dried product was passed through a sieve with a mesh size of 850 μm, and 0.5% by mass of amorphous silica (Oriental Silicas Corporation, Tokusil NP-S) was mixed relative to the dried product to obtain 227.3 g of water-absorbing resin particles of Comparative Example 1.

[0135] (Comparative Example 2) In the second stage of the polymerization process, the amount of ethylene glycol diglycidyl ether added as an internal crosslinking agent was changed to 0.026 g (0.148 mmol), the amount of ion-exchanged water added was changed to 6.46 g, the amount of water extracted from the system by the second azeotropic distillation was changed to 97.4 g (total 274.1 g), and the amount of 2% by mass aqueous solution of ethylene glycol diglycidyl ether added as a surface crosslinking agent was changed to 5.52 g (0.63 mmol). Otherwise, the process was carried out in the same manner as in Example 1, and 225.8 g of the water-absorbing resin particles of Comparative Example 2 were obtained.

[0136] For the absorbent resin particles obtained in each embodiment and comparative example, the water absorption capacity of physiological saline, the water retention capacity of physiological saline, the water absorption capacity of physiological saline, the 3-minute and 10-minute values ​​of unpressurized DW under a load of 0.69 kPa, the water absorption rate (Vortex method), the median particle size, the absorption time of the absorbent article, and the reflux rate were determined using the following methods. Unless otherwise specified, the measurements were conducted at 25°C ± 2°C and 50 ± 10% humidity. The results are shown in Table 1.

[0137] [Saline water absorption under a load of 0.69 kPa] use Figure 1 The apparatus shown in the diagram is for measuring the amount of water absorbed by physiological saline by absorbent resin particles under a load of 0.69 kPa (water absorption under 0.69 kPa load). The water absorption of a single absorbent resin particle was measured twice under the same load, and the average value was calculated. Figure 1 The apparatus comprises a burette section 1, a clamp 3, a conduit 5, a stand 11, a measuring stage 13, and a measuring part 4 placed on the measuring stage 13. The burette section 1 includes: a graduated burette 21, a rubber stopper 23 that seals the opening at the top of the burette 21, a stopcock 22 connected to the lower front end of the burette 21, an air inlet tube 25 connected to the lower part of the burette 21, and a stopcock 24. The burette section 1 is fixed by the clamp 3. The flat measuring stage 13 has a through hole 13a with a diameter of 2 mm formed in its center and is supported by a height-variable stand 11. The through hole 13a of the measuring stage 13 is connected to the stopcock 22 of the burette section 1 via the conduit 5. The inner diameter of the conduit 5 is 6 mm.

[0138] The measuring unit 4 includes: an acrylic resin cylinder 31, a polyamide mesh 32 bonded to one opening of the cylinder 31, and a counterweight 33 movable in the vertical direction inside the cylinder 31. The cylinder 31 is placed on the measuring stage 13 through the polyamide mesh 32. The inner diameter of the cylinder 31 is 20 mm. The mesh size of the polyamide mesh 32 is 75 μm (200 mesh). The counterweight 33 has a diameter of 19 mm and a mass of 20.5 g, and as described later, can apply a load of 0.69 kPa to the water-absorbing resin particles 10a uniformly disposed on the polyamide mesh 32.

[0139] First, close stopcocks 22 and 24 of burette section 1, and inject 0.9% saline solution (adjusted to 25°C) into burette 21 through the opening at the top. Next, after sealing the top opening of burette 21 with rubber stopper 23, open stopcocks 22 and 24. Fill the delivery tube 5 with 0.9% saline solution 50, ensuring no air bubbles enter. Adjust the height of the measuring stage 13 so that the water level of the 0.9% saline solution in the through-hole 13a is the same as the height of the upper surface of the measuring stage 13. After adjustment, read the water level of the 0.9% saline solution 50 in burette 21 using the scale, and take this position as the zero point (the reading at 0 seconds).

[0140] In the measuring unit 4, 0.10 g of absorbent resin particles 10a are uniformly arranged on the polyamide mesh 32 inside the cylinder 31, and a counterweight 33 is placed on the absorbent resin particles 10a. The cylinder 31 is set so that its center is aligned with the conduit opening at the center of the measuring stage 13. The amount of physiological saline in the burette 21 reduced after 15 minutes from when the absorbent resin particles 10a begin to absorb physiological saline from the conduit 5 (i.e., the amount of physiological saline absorbed by the absorbent resin particles 10a) Wa (mL) is read. The amount of physiological saline absorbed by the absorbent resin particles 10a under a load of 0.69 kPa is calculated using the following formula. The results are shown in Table 1.

[0141] The amount of physiological saline absorbed under a load of 0.69 kPa (mL / g) = Wa (mL) / mass of absorbent resin particles (g) <Water retention capacity of physiological saline> A cotton bag (cotton broad, size 60, 100mm wide x 200mm long) containing 2.0g of absorbent resin granules was placed in a 500mL beaker. 500g of 0.9% (w / w) sodium chloride aqueous solution (physiological saline) was injected into the cotton bag containing the absorbent resin granules in a single injection, ensuring no clumping. The top of the cotton bag was secured with a rubber band, and the bag was left to stand for 30 minutes to allow the absorbent resin granules to swell. After 30 minutes, the cotton bag was dehydrated for 1 minute using a dehydrator (manufactured by Kokusan Co., Ltd., product number: H-122) set to a centrifugal force of 167G. The mass Wb (g) of the cotton bag containing the swollen gel after dehydration was measured. The same procedure was performed without adding absorbent resin granules, and the empty mass Wc (g) of the wet cotton bag was measured. The water retention capacity of the physiological saline was calculated using the following formula. The results are shown in Table 1.

[0142] The water retention capacity of physiological saline (g / g) = [Wb - Wc] / 2.0 <Water absorption of physiological saline> Weigh 500g of 0.9% physiological saline into a 500mL beaker. Then, while stirring at 600rpm with a magnetic stir bar (8mmφ×30mm length, without rings), disperse 2.0g of water-absorbing resin particles in the physiological saline in a non-clumping manner. Allow the particles to swell fully by stirring for 60 minutes, thereby obtaining a dispersion containing swollen gel. Next, measure the mass Wd[g] of a 75μm mesh standard sieve, and pass the dispersion through the standard sieve. Then, place the sieve at an angle of approximately 30 degrees relative to the horizontal for 30 minutes to remove residual water. Measure the mass We[g] of the sieve containing the remaining swollen gel, and calculate the water absorption capacity (g / g) of the physiological saline using the following formula.

[0143] Physiological saline water absorption (g / g) = (We - Wd) / 2.0 [Determination of 3-minute and 10-minute values ​​for unpressurized demand wettability (DW)] Use of unpressurized DW values ​​for water-absorbing resin particles at 3-minute and 10-minute intervals. Figure 2 The measurement was performed using the apparatus shown. The measurement was conducted five times on a water-absorbing resin particle, and the average value of the three measured points after removing the lowest and highest values ​​was obtained.

[0144] The measuring apparatus comprises a burette section 1, a conduit 5, a measuring stage 13, a nylon mesh 15, a stand 11, and a clamp 3. The burette section 1 includes: a graduated burette 21, a rubber stopper 23 that seals the opening at the top of the burette 21, a stopcock 22 connected to the lower front end of the burette 21, an air inlet tube 25 connected to the lower part of the burette 21, and a stopcock 24. The burette section 1 is fixed by the clamp 3. The flat measuring stage 13 has a through hole 13a with a diameter of 2 mm formed in its center and is supported by a height-variable stand 11. The through hole 13a of the measuring stage 13 is connected to the stopcock 22 of the burette section 1 via the conduit 5. The inner diameter of the conduit 5 is 6 mm.

[0145] First, close stopcocks 22 and 24 of burette section 1. Pour 0.9% saline solution 50, adjusted to 25°C, into burette 21 through the opening at the top. The 0.9% saline concentration is based on the mass of the saline solution. After sealing the opening of burette 21 with rubber stopper 23, open stopcocks 22 and 24. Fill the tube 5 with 0.9% saline solution 50, ensuring no air bubbles enter. Adjust the height of the measuring stage 13 so that the water level of the 0.9% saline solution in the through-hole 13a is the same as the height of the upper surface of the measuring stage 13. After adjustment, read the water level of the 0.9% saline solution 50 in burette 21 using the scale, and take this position as the zero point (the reading at 0 seconds).

[0146] A nylon mesh 15 (100mm × 100mm, 250 mesh, approximately 50μm thick) is laid near the through hole 13a on the measuring stage 13, and a cylinder with an inner diameter of 30mm and a height of 20mm is placed in its center. 1.00g of absorbent resin particles 10a are uniformly dispersed in this cylinder. The cylinder is then carefully removed, yielding a sample with the absorbent resin particles 10a dispersed in a circular pattern in the center of the nylon mesh 15. Next, the nylon mesh 15 containing the absorbent resin particles 10a is moved rapidly to a point where the absorbent resin particles 10a will not disperse, so that its center reaches the position of the through hole 13a, and the measurement begins. The moment when the air bubble is initially introduced from the air inlet tube 25 into the burette 21 is defined as the start of water absorption (0 seconds).

[0147] The decrease in 0.9% saline solution 50 in burette 21 is recorded sequentially in 0.1 mL increments (i.e., the amount of 0.9% saline solution absorbed by the absorbent resin particles 10a). The decrease in 0.9% saline solution 50 is recorded as Wf (mL) after 3 minutes from the start of absorption by the absorbent resin particles 10a, and as Wg (mL) after 10 minutes from the start of absorption by the absorbent resin particles 10a. The 3-minute unpressurized DW value is calculated from Wf using the following formula. The 10-minute unpressurized DW value is calculated from Wg using the following formula. Unpressurized DW is the amount of water absorbed per 1.00 g of absorbent resin particles 10a.

[0148] The 3-minute DW value (mL / g) without pressurization = Wf / 1.00 The 10-minute DW value without pressurization (mL / g) = Wg / 1.00 [Vortex method] The water absorption rate of physiological saline containing superabsorbent resin particles was determined using the Vortex method according to the following steps. First, 50±0.1 g of physiological saline, which was to be adjusted to a temperature of 25±0.2℃ in a constant temperature water bath, was weighed into a 100 mL beaker. Next, the saline solution was stirred at 600 rpm using a magnetic stir bar (8 mm φ × 30 mm, without rings) to generate eddies. Then, 2.0±0.002 g of superabsorbent resin particles were added to the physiological saline solution in a single addition. The time (in seconds) from the addition of the superabsorbent resin particles until the eddies on the liquid surface converged was measured and taken as the water absorption rate of the superabsorbent resin particles.

[0149] [Method for determining median particle size] 10g of absorbent resin particles were sieved using a continuous fully automatic acoustic vibration sieving apparatus (Robot Shifter RPS-205, manufactured by Seishin Corporation) with JIS standard mesh sizes of 850μm, 710μm, 600μm, 500μm, 425μm, 300μm, 250μm, and 150μm, and receiving trays. The percentage of the mass of particles remaining on each sieve relative to the total mass was calculated. The percentage of the mass of particles remaining on each sieve was accumulated sequentially from the largest particle size, and the relationship between the sieve mesh size and the cumulative percentage of the mass of particles remaining on the sieve was plotted on logarithmic probability paper. By connecting the plots on the probability paper with straight lines, the particle size equivalent to 50% of the cumulative mass percentage was determined and taken as the median particle size (μm).

[0150] [Crafting Absorbents and Absorbent Items] (Absorbents and absorbent materials in mixed dispersions) Using an airflow mixing device (manufactured by OTEC.Co.,Ltd., pad former), 8.11g of absorbent resin particles and 12.38g of pulverized paper pulp were uniformly mixed by air forming to create an absorbent core measuring 12cm × 40cm. Next, two sheets of thin paper of the same size as the absorbent core (weight per unit area: 16g / m²) were... 2 While the absorbent core is held in a clamping position, a load of 141 kPa is applied to the entire structure for 30 seconds to compress it, thereby creating the absorbent core. Then, hydrophilic hot-air nonwoven fabric (RENGO NONWOVEN PRODUCTS) (weight per unit area: 21 g / m²) is placed on the upper surface of the absorbent core, with the same size as the absorbent core. 2 The original top sheet and absorbent core were removed from a diaper manufactured by Daio Paper Co., Ltd. (trade name: GOO.N PLUS Sensitive Skin Design, band type, size L, purchased in 2022) to obtain a back sheet with a pair of side pleats bonded to both ends in the short side direction. A hydrophilic hot-air nonwoven fabric and absorbent core were then disposed on this back sheet with their central portions overlapping, thereby obtaining an absorbent article for evaluation. In the absorbent article, the basis weight of the absorbent resin particles was 169 g / m². 2 The unit area weight of the pulverized pulp (hydrophilic fiber) is 258 g / m². 2 .

[0151] (Absorbent materials and absorbent substances with sheet-like structures) The spunlace nonwoven fabric (Zhejiang Wangjin Nonwoven Fabric Co., Ltd., unit area weight: 35g / m²) 2 Cut into two pieces of 14cm×42cm each, which will be used as spunlace nonwoven fabric 1 and 2 respectively.

[0152] A hot melt adhesive (Henkel Japan Co., Ltd., ME-765E) with a total weight of 0.2g was applied to the spunlace nonwoven fabric 1 in 14 straight lines at 10mm intervals along the long side, using a hot melt coating machine (HALLYS Co., Ltd., pump: Marshal150, gauge: XA-DT, tank temperature setting: 150℃, hose temperature setting: 165℃, gun head temperature setting: 170℃). The adhesive coating pattern was a spiral stripe. During coating, the outer four sides (1cm wide) of the spunlace nonwoven fabric 1 were masked without adhesive.

[0153] 6.5g of absorbent resin particles are evenly distributed in a 12cm×40cm area at the center of the surface of the spunlace nonwoven fabric 1 with the hot melt adhesive attached, to obtain absorbent layer A.

[0154] A total of 0.2 g of hot melt adhesive is applied to the spunlace nonwoven fabric 2 in 14 straight lines spaced 10 mm apart. The adhesive coating pattern is a spiral stripe. 13.5 g of absorbent resin particles are evenly distributed in the central part (12 cm x 40 cm area) of the adhesive-coated surface of the spunlace nonwoven fabric 2 to obtain absorbent layer B.

[0155] A 12cm × 40cm hot-air nonwoven fabric (Guangzhou Jinhan Nonwoven Fabric Co., Ltd., unit area weight: 45g / m²) is placed on the surface of the spunlace nonwoven fabric 1 where absorbent resin particles are dispersed. 2 Afterwards, the ends of spunlace nonwoven fabric 1 and spunlace nonwoven fabric 2 are aligned with the adhesive-coated surface facing inwards, clamped with release paper, and pressed together using a laminator (HASHIMA, Straight Linear Fussing Press, model HP-600 LFS) at 110°C and 0.1MPa. The release paper is then peeled off, thus obtaining the absorbent body. The absorbent body contains water-absorbing resin particles in an area of ​​12cm × 40cm.

[0156] Furthermore, on the upper surface of the absorber, 12cm × 40cm hydrophilic hot-air nonwoven fabrics (RENGO NONWOVEN PRODUCTS) (weight per unit area: 21g / m²) are arranged with their central portions overlapping. 2 The original top sheet and absorbent core were removed from a diaper manufactured by P&G Japan Co., Ltd. (trade name: Pampers Dry Care, belt type, size L, purchased in 2022) to obtain a back sheet with a pair of side pleats bonded to both ends in the short side direction. A hydrophilic hot-air nonwoven fabric and absorbent core were then disposed on this back sheet, overlapping at the center, thereby obtaining an absorbent article for evaluation. In the absorbent article, the basis weight of the absorbent resin particles is 340 g / m². 2 The absorbent material comprises, in order, hydrophilic hot-air nonwoven fabric, absorbent layer A, hot-air nonwoven fabric, and absorbent layer B.

[0157] [Determination of absorption time / reflux rate] The determination of liquid reflux and absorption time in absorbent materials is carried out in accordance with the provisions of GB / T28004.1-2021 NATIONAL STANDARD OF THE PEOPLE'S REPUBLIC OF CHINA, Disposable diapers - Part 1: Disposable diapers for baby, which is a Chinese GB standard. The specific method is as follows.

[0158] Prepare a U-shaped sample base (Figure A.1 of the aforementioned GB standard), a sample holder (Figure A.2 of the aforementioned GB standard), a test solution injection module (Figure A.3 of the aforementioned GB standard), and a pressurization module (Figure A.4 of the aforementioned GB standard). The test solution is prepared by mixing 90.0g of sodium chloride, 9910g of deionized water, and edible blue No. 1 (for coloring). The test solution is then adjusted to a temperature of 36±1 degrees Celsius in a constant temperature bath. The absorbent material is placed on the U-shaped sample base and sample holder, which are positioned on a horizontal platform. The dimensions of each fixture are as follows.

[0159] U-shaped sample base: B2 L136mm, W135mm Sample holder: T2 Test liquid dispensing module: M2 W85mm, L108mm Pressure module: Y2 W85mm, L108mm Using a liquid delivery pump and the test solution delivery module shown in Figure A.3 of the GB specification above, add 80 mL of test solution at a rate of 480 mL / min. The first absorption time (in seconds) is measured from the point where the liquid level disappears from the lowest point of the absorption area after the test solution has been added. At this time, adjust the test solution delivery module to apply a pressure of 2.00 kPa to the sample surface and continue applying pressure for 1 minute from the start of liquid addition. After 1 minute, remove the test solution delivery module. If the absorption time is more than 1 minute, wait until absorption is complete, then remove the test solution delivery module again, thus ending the first absorption test.

[0160] Eight minutes after the first application of the test solution, the second absorption time (in seconds) was measured using the same procedure as the first measurement. The sum of the first and second absorption times was then recorded as the total absorption time (in seconds). Fifteen minutes after the first application of the test solution, ten 11.0 cm × 7.0 cm sheets of filter paper were stacked, with the center of the filter paper overlapping the center of the sample surface. Sixteen minutes after the first application of the test solution, the filter paper was used to press the pressure module, applying a pressure of 4.00 kPa. After one minute of pressurization, the pressure module and filter paper were removed, and the weight of the filter paper was measured using a balance. The weight difference of the filter paper before and after the test was calculated as the mass of the test solution absorbed by the filter paper, and this was recorded as the reflux rate (g).

[0161] [Table 1] Symbol Explanation 1. Burette Section 3. Fixture 4. Measurement Section 5 catheters 10a water-absorbing resin particles 11 racks 13 Measuring Platform 13a Through hole 15 Nylon mesh 21 Burette 22. Cocktail 23 Rubber stoppers 24. Cocktail 25 Air inlet tube 31. Cylinder 32 Polyamide mesh 33 counterweight 50g salt water.

Claims

1. A water-absorbing resin particle, characterized in that, The 15-minute water absorption capacity of the absorbent resin particles under a load of 0.69 kPa is above 30 mL / g and below 60 mL / g.

2. The water-absorbing resin particles according to claim 1, wherein, The unpressurized DW 3-minute value of the water-absorbing resin particles is above 20 mL / g and below 50 mL / g.

3. The water-absorbing resin particles according to claim 2, wherein, The absorbent resin particles absorb water from physiological saline at a rate of less than 60 seconds.

4. The water-absorbing resin particles according to claim 2, wherein, The water-absorbing resin particles have a saline water retention capacity of more than 30g / g.

5. An absorber, characterized in that, It comprises the water-absorbing resin particles according to any one of claims 1 to 4.

6. An absorbent article, characterized in that, It includes the absorber as described in claim 5.

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