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

Abstract

This invention provides a water-absorbing resin particle that exhibits high resistance to deformation of the absorbent body when it absorbs water. The water-absorbing resin particle has a gel diffusion distance, measured by the following method, that is greater than 0.0 cm and less than 2.0 cm. (Method for measuring gel diffusion distance) A stainless steel culture dish is placed on a movable platform. A mesh 38 covering the upper opening is provided inside the stainless steel culture dish. μ A cylindrical container (A) with an inner diameter of 75 mm and a height of 20 mm is placed at the center of the stainless steel mesh. A cylindrical container (B) with open ends is then fixed in place using clamps. The stainless steel culture dish has an inner diameter of 60 mm, an outer diameter of 70 mm, and a height of 60 mm. The cylindrical container (B) has an inner diameter of 20 mm, an outer diameter of 30 mm, and a height of 60 mm. Next, 0.20 g of absorbent resin particles are evenly distributed inside the cylindrical container (B), and these absorbent resin particles are placed on the stainless steel mesh. Then, 30 mL of 0.9% (w / w) physiological saline is added at a constant rate of 20 mL / min from the upper part of the cylindrical container (B), at a height of 5.0 cm from the lower end and at the center of the inner diameter. Twenty seconds after the input is completed, with the cylindrical container (B) fixed, the movable platform is lowered by 5.0 cm at a speed of 1.2 cm / s. At this time, the gel diffusion distance is measured at the portion of the swollen gel formed by the water-absorbing resin particles in contact with the stainless steel mesh. Regarding the gel diffusion distance, the maximum distance of the following straight line is measured on the swollen gel on the stainless steel mesh. The value obtained by subtracting the inner diameter (diameter) of the cylindrical container (B) of 2.0 cm from this maximum distance Wa is taken as the gel diffusion distance (cm). The straight line passes through the center point of the swollen gel when it is inside the cylindrical container (B), and the straight line connects the ends of the swollen gel that diffuse to the stainless steel mesh by lowering the movable platform. Gel diffusion distance (cm) = maximum distance Wa - 2.0.

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 in the center that absorbs and retains bodily fluids such as urine and menstrual blood; a liquid-permeable surface sheet (top sheet) on the side in contact with the body; and a liquid-resistant back sheet (back sheet) on the opposite side in contact with the body. Furthermore, the absorbent core is typically made 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

[0006] The technical problem that the invention aims to solve In such absorbent materials, loads caused by deformation such as bending are sometimes applied to the absorbent that has absorbed liquid. Due to this deformation, the absorbent is prone to breakage or other damage after absorbing water. Therefore, it is desirable for the absorbent to have high resistance to deformation after absorbing water.

[0007] In this context, the primary objective of the present invention is to provide absorbent resin particles that exhibit greater resistance to deformation of the absorbent after absorbing water. Furthermore, the present invention also aims to provide absorbents and absorbent articles utilizing these absorbent resin particles.

[0008] Technical solutions for solving technical problems To solve the aforementioned technical problems, the inventors conducted in-depth research. In this research, focusing on the gel diffusion distance, an indicator of the adhesive strength of absorbent resin particles after water absorption, the inventors discovered a correlation between the gel diffusion distance and the absorbent's resistance to deformation when absorbing water containing the absorbent resin particles. Specifically, to achieve higher resistance to deformation of the absorbent after water absorption, the inventors repeatedly studied various methods and found that absorbent resin particles with a gel diffusion distance set within a specific range exhibit appropriate resistance to deformation of the absorbent when absorbing water containing the absorbent resin particles. This invention was completed based on further in-depth research based on this insight.

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

[0010] Item 1. A water-absorbing resin particle whose gel diffusion distance, as determined by the following method, is greater than 0.0 cm and less than 2.0 cm.

[0011] (Method for determining gel diffusion distance) A stainless steel petri dish is placed on a movable platform. The stainless steel petri dish is provided with a mesh 38 covering the upper opening. μA cylindrical container (A) with an inner diameter of 75 mm and a height of 20 mm is placed at the center of the stainless steel mesh. A cylindrical container (B) with open ends is then fixed in place using clamps. The stainless steel culture dish has an inner diameter of 60 mm, an outer diameter of 70 mm, and a height of 60 mm. The cylindrical container (B) has an inner diameter of 20 mm, an outer diameter of 30 mm, and a height of 60 mm. Next, 0.20 g of absorbent resin particles are evenly distributed inside the cylindrical container (B), and these absorbent resin particles are placed on the stainless steel mesh. Then, 30 mL of 0.9% (w / w) physiological saline is added at a constant rate of 20 mL / min from the upper part of the cylindrical container (B), at a height of 5.0 cm from the lower end and at the center of the inner diameter. Twenty seconds after the input is completed, with the cylindrical container (B) fixed, the movable platform is lowered by 5.0 cm at a speed of 1.2 cm / s. At this time, the gel diffusion distance is measured at the portion of the swollen gel formed by the water-absorbing resin particles that comes into contact with the stainless steel mesh. Regarding the gel diffusion distance, the maximum distance of the following straight line is measured on the swollen gel on the stainless steel mesh. The value obtained by subtracting the inner diameter of the cylindrical container (B), i.e., 2.0 cm, from this maximum distance Wa is taken as the gel diffusion distance (cm). The straight line passes through the center point of the swollen gel when it is inside the cylindrical container (B), and the straight line connects the ends of the swollen gel that diffuse to the stainless steel mesh by lowering the movable platform.

[0012] Gel diffusion distance (cm) = Maximum distance Wa - 2.0 Item 2. The absorbent resin particles according to Item 1, wherein the saline conductivity (SFC, ×10) of the absorbent resin particles is... -7 cm 3 (·s / g) is below 50.0.

[0013] Item 3. The absorbent resin particles according to Item 1, wherein the unpressurized DW3-minute value of the absorbent resin particles is 15 mL / g or more.

[0014] Item 4. An absorbent comprising the absorbent resin particles described in any one of items 1 to 3.

[0015] Item 5. An absorbent article comprising the absorbent described in item 4.

[0016] Invention Effects According to the present invention, a water-absorbing resin particle can be provided that exhibits higher resistance to deformation of the absorbent when the absorbent containing the water-absorbing resin particle absorbs water. Furthermore, the present invention can provide absorbents and absorbent articles utilizing the water-absorbing resin particle. Attached Figure Description

[0017] Figure 1 A schematic diagram of an apparatus for measuring the gel diffusion distance of absorbent resin particles.

[0018] Figure 2 A schematic diagram of an apparatus for determining the saline conductivity (SFC) of absorbent resin particles.

[0019] Figure 3 This is a schematic diagram of an apparatus used to determine the 3-minute DW value of absorbent resin particles without pressure.

[0020] Figure 4 This is a schematic diagram illustrating a method for evaluating the deformation resistance of an absorbent after water absorption. Figure 4 (a), (b)). Detailed Implementation

[0021] In this specification, "comprising" means both "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 solubility" means a solubility of 5% by mass or more in water at 25°C.

[0022] In this specification, the value connected by "~" refers to the range of values ​​before and after "~" as the lower and upper limits. When multiple lower and upper limits are specified separately, any lower and upper limits can be selected and connected by "~".

[0023] 1. Water-absorbent resin particles The gel diffusion distance of the absorbent resin particles of the present invention, measured by the following method, is greater than 0.0 cm and less than 2.0 cm. The absorbent resin particles of the present invention possess the characteristic of high resistance to deformation of the absorbent body when absorbing water. The absorbent resin particles of the present invention will be described in detail below.

[0024] (Method for determining gel diffusion distance) A stainless steel petri dish is placed on a movable platform. A mesh 38 covering the upper opening is provided inside the stainless steel petri dish. μ A cylindrical container (A) with a stainless steel mesh is prepared. Next, a cylindrical container (B) with open ends along the axial direction is placed at the center of the stainless steel mesh, and the cylindrical container (B) is fixed with clamps. The stainless steel culture dish has an inner diameter of 75 mm and a height of 20 mm. The cylindrical container (A) has an inner diameter of 60 mm, an outer diameter of 70 mm, and a height of 60 mm. The cylindrical container (B) has an inner diameter of 20 mm, an outer diameter of 30 mm, and a height of 60 mm. Next, 0.20 g of absorbent resin particles are evenly distributed inside the cylindrical container (B), and the absorbent resin particles are placed on the stainless steel mesh. Next, 30 mL of 0.9% physiological saline is added from a height of 5.0 cm from the bottom of the cylindrical container (B) and above the center of its inner diameter, at a constant rate of 20 mL / min. Twenty seconds after the input is completed, with the cylindrical container (B) fixed, the movable platform is lowered by 5.0 cm at a speed of 1.2 cm / s. At this time, the gel diffusion distance is measured at the portion of the swollen gel formed by the water-absorbing resin particles that comes into contact with the stainless steel mesh. Regarding the gel diffusion distance, the maximum distance of the following straight line is measured on the swollen gel on the stainless steel mesh. The value obtained by subtracting the inner diameter (diameter) of the cylindrical container (B) of 2.0 cm from the maximum distance Wa is taken as the gel diffusion distance (cm). The straight line passes through the center point of the swollen gel when it is inside the cylindrical container (B), and the straight line connects the ends of the swollen gel that diffuse to the stainless steel mesh by lowering the movable platform.

[0025] Gel diffusion distance (cm) = Maximum distance Wa - 2.0 The gel diffusion distance measured for the absorbent resin particles can be considered an indicator of the adhesive strength of the absorbent resin particles after water absorption. As described above, the inventors have discovered a correlation between the gel diffusion distance, which serves as an indicator of the adhesive strength of the absorbent resin particles after water absorption, and the resistance of the absorbent containing the absorbent resin particles to deformation when absorbing water. That is, absorbent resin particles with a gel diffusion distance set within a specific range of more than 0.0 cm and less than 2.0 cm exhibit appropriate resistance to deformation of the absorbent containing the absorbent resin particles when absorbing water. It is believed that absorbent resin particles with a gel diffusion distance of more than 0.0 cm and less than 2.0 cm have a high adhesive strength between themselves after water absorption. Therefore, even when bent within the absorbent, the absorbent resin particles adhere to each other and to the hydrophilic fibers, making it less prone to breakage due to deformation, thus achieving such excellent results.

[0026] The gel diffusion distance of the absorbent resin particles of the present invention is only required to be in the range of more than 0.0 cm and less than 2.0 cm. From the viewpoint of further appropriately exerting the effects of the present invention, it is preferable to be more than 0.0 cm, more preferably more than 0.1 cm, and even more preferably more than 0.2 cm. In addition, from the same viewpoint, the gel diffusion distance of the absorbent resin particles is preferably less than 2.0 cm, more preferably less than 1.5 cm, even more preferably less than 1.0 cm, particularly preferably less than 0.7 cm, and even more particularly preferably less than 0.5 cm. Examples of preferred ranges include: greater than 0.0cm to 2.0cm, greater than 0.0cm to 1.5cm, greater than 0.0cm to 1.0cm, greater than 0.0cm to 0.7cm, greater than 0.0cm to 0.5cm, 0.1cm to 2.0cm, 0.1cm to 1.5cm, 0.1cm to 1.0cm, 0.1cm to 0.7cm, 0.1cm to 0.5cm, 0.2cm to 2.0cm, 0.2cm to 1.5cm, 0.2cm to 1.0cm, 0.2cm to 0.7cm, and 0.2cm to 0.5cm.

[0027] The gel diffusion distance of the superabsorbent polymer particles can be adjusted to a range greater than 0.0 cm and less than 2.0 cm, for example, by drying and crushing the polymer particles obtained through polymerization processes such as reverse suspension polymerization (described later). Alternatively, by adding a water-soluble polymer (e.g., a thickener such as polyethylene glycol) to the superabsorbent polymer particles to increase their viscosity after absorbing liquid, the gel diffusion distance of the superabsorbent polymer particles can also be adjusted to a range greater than 0.0 cm and less than 2.0 cm.

[0028] From the viewpoint of more effectively utilizing the effects of the present invention, the saline conductivity (SFC) of the absorbent resin particles of the present invention is preferably 0.0 × 10⁻⁶. -7 cm 3 • s / g or higher, more preferably 0.3 × 10 -7 cm 3 • s / g or higher, more preferably 1.0 × 10 -7 cm 3 • s / g or higher, especially preferably 5.0 × 10 -7 cm 3 • s / g or higher, more preferably 10.0 × 10 - 7 cm 3• s / g or higher. Furthermore, from the viewpoint of suppressing liquid leakage from the absorbent, an absorbent with a short diffusion length is desirable. From the viewpoint of shortening the diffusion length of the absorbent, the saline conductivity (SFC) of the absorbent resin particles is preferably 50.0 × 10⁻⁶. -7 cm 3 • s / g or less, more preferably 30.0 × 10 -7 cm 3 Below ·s / g, further preferably 25.0 × 10⁻⁶ -7 cm 3 • s / g or less, especially preferably 20.0 × 10 -7 cm 3 • s / g or less. A preferred range is 0.0 × 10⁻⁶. -7 cm 3 ·s / g~50.0×10 -7 cm 3 ·s / g, 0.0×10 -7 cm 3 ·s / g~30.0×10 -7 cm 3 ·s / g, 0.0×10 -7 cm 3 ·s / g~25.0×10 -7 cm 3 ·s / g, 0.0×10 -7 cm 3 ·s / g~20.0×10 -7 cm 3 ·s / g, 0.3×10 -7 cm 3 ·s / g~50.0×10 - 7 cm 3 ·s / g, 0.3×10 -7 cm 3 ·s / g~30.0×10 -7 cm 3 ·s / g, 0.3×10 -7 cm 3 ·s / g~25.0×10 -7 cm 3 ·s / g, 0.3×10 -7 cm 3 ·s / g~20.0×10 -7 cm 3 ·s / g, 1.0×10 -7 cm 3 ·s / g~50.0×10 -7 cm 3·s / g, 1.0×10 -7 cm 3 ·s / g~30.0×10 -7 cm 3 ·s / g, 1.0×10 -7 cm 3 ·s / g~25.0×10 -7 cm 3 ·s / g, 1.0×10 -7 cm 3 ·s / g~20.0×10 -7 cm 3 ·s / g, 5.0×10 -7 cm 3 ·s / g~50.0×10 -7 cm 3 ·s / g, 5.0×10 - 7 cm 3 ·s / g~30.0×10 -7 cm 3 ·s / g, 5.0×10 -7 cm 3 ·s / g~25.0×10 -7 cm 3 ·s / g, 5.0×10 -7 cm 3 ·s / g~20.0×10 -7 cm 3 ·s / g, 10.0×10 -7 cm 3 ·s / g~50.0×10 -7 cm 3 ·s / g, 10.0×10 -7 cm 3 ·s / g~30.0×10 -7 cm 3 ·s / g, 10.0×10 -7 cm 3 ·s / g~25.0×10 -7 cm 3 ·s / g, 10.0×10 -7 cm 3 ·s / g~20.0×10 -7 cm 3 ·s / g.

[0029] The saline conductivity (SFC) of the absorbent resin particles was determined by the method described in the examples.

[0030] Furthermore, from the viewpoint of shortening the diffusion length of the absorbent, the unpressurized diffusion time (DW) of the superabsorbent resin particles is preferably 15 mL / g or more, more preferably 20 mL / g or more, even more preferably 25 mL / g or more, particularly preferably 28 mL / g or more, even more preferably 30 mL / g or more, and even more preferably 32 mL / g or more. Additionally, the unpressurized DW of the superabsorbent resin particles is preferably 60 mL / g or less, more preferably 55 mL / g or less, even more preferably 50 mL / g or less, particularly preferably 48 mL / g or less, and even more preferably 45 mL / g or less. Preferred ranges include 15–60 mL / g, 15–55 mL / g, 15–50 mL / g, 15–48 mL / g, 15–45 mL / g, 20–60 mL / g, 20–55 mL / g, 20–50 mL / g, 20–48 mL / g, 20–45 mL / g, 25–60 mL / g, 25–55 mL / g, 25–50 mL / g, 25–48 mL / g, 25–40 mL / g, 25–40 mL / g, 25–40 mL / g, 25–40 mL / g, 25–40 mL / g, 25–50 ... 5mL / g, 28~60mL / g, 28~55mL / g, 28~50mL / g, 28~48mL / g, 28~45mL / g, 30~60mL / g, 30~55mL / g, 30 ~50mL / g, 30~48mL / g, 30~45mL / g, 32~60mL / g, 32~55mL / g, 32~50mL / g, 32~48mL / g, 32~45mL / g.

[0031] The unpressurized DW3-minute value of the water-absorbing resin particles was determined by the method described in the examples.

[0032] Furthermore, the water absorption rate of the absorbent resin particles relative to physiological saline is preferably 10 seconds or more, more preferably 15 seconds or more, further preferably 20 seconds or more, particularly preferably 22 seconds or more, and even more preferably 24 seconds or more. Additionally, from the viewpoint of shortening the diffusion length of the absorbent, the water absorption rate of the absorbent resin particles relative to physiological saline is preferably 70 seconds or less, more preferably 60 seconds or less, further preferably 55 seconds or less, particularly preferably 50 seconds or less, even more preferably 45 seconds or less, and even more preferably 42 seconds or less. Preferred ranges include 10–70 seconds, 10–60 seconds, 10–55 seconds, 10–50 seconds, 10–45 seconds, 10–42 seconds, 15–70 seconds, 15–60 seconds, 15–55 seconds, 15–50 seconds, 15–45 seconds, 15–42 seconds, 20–70 seconds, 20–60 seconds, 20–55 seconds, 20–50 seconds, 20–45 seconds, 20–42 seconds, 22–70 seconds, 22–60 seconds, 22–55 seconds, 22–50 seconds, 22–45 seconds, 22–42 seconds, 24–70 seconds, 24–60 seconds, 24–55 seconds, 24–50 seconds, 24–45 seconds, and 24–42 seconds.

[0033] The rate at which the absorbent resin particles absorb water relative to physiological saline was determined using the method described in the examples.

[0034] Furthermore, from the viewpoint of shortening the diffusion length of the absorbent, the saline water retention capacity of the absorbent resin particles is preferably 15 g / g or more, more preferably 20 g / g or more, even more preferably 25 g / g or more, and particularly preferably 27 g / g or more. Additionally, it is preferably 80 g / g or less, more preferably 60 g / g or less, even more preferably 50 g / g or less, particularly preferably 45 g / g or less, and even more preferably 40 g / g or less. Preferred ranges include 15–80 g / g, 15–60 g / g, 15–50 g / g, 15–45 g / g, 15–40 g / g, 20–80 g / g, 20–60 g / g, 20–50 g / g, 20–45 g / g, 20–40 g / g, 25–80 g / g, 25–60 g / g, 25–50 g / g, 25–45 g / g, 25–40 g / g, 27–80 g / g, 27–60 g / g, 27–50 g / g, 27–45 g / g, and 27–40 g / g.

[0035] The water retention capacity of the absorbent resin particles in physiological saline was determined by the method described in the examples.

[0036] The water-absorbing resin particles of the present invention are composed of a substance formed by cross-linking a polymer of a water-soluble olefinic unsaturated monomer, that is, a cross-linked polymer having structural units derived from the water-soluble olefinic unsaturated monomer.

[0037] The absorbent resin particles of the present invention are irregularly shaped, fragmented particles. Examples of the shape of the absorbent resin particles include granular, approximately spherical, irregularly shaped, fragmented, plate-like, fibrous, flake-like, or shapes formed by the aggregation of these resins.

[0038] From the viewpoint of setting the gel diffusion distance of the absorbent resin particles of the present invention to a range of more than 0.0 cm and less than 2.0 cm, the shape of the absorbent resin particles is preferably an irregularly shaped, fragmented form, or a form formed by the aggregation of irregularly shaped, fragmented particles, and more preferably an irregularly shaped, fragmented form. As described above, for example, by drying and then crushing the polymer particles obtained through polymerization processes such as reverse suspension polymerization described later, the gel diffusion distance of the resulting irregularly shaped, fragmented absorbent resin particles can be adjusted to a range of more than 0.0 cm and less than 2.0 cm.

[0039] From the viewpoint of more effectively utilizing the effects of the present invention, the median particle size of the water-absorbing resin particles is preferably 200 μm. μ m or more, 250 μ m or more, 300 μ m or more, 320 μ m or above or 350 μ Above m. Furthermore, from the same perspective, the median particle size is preferably 700 μm. μ Below m, 600 μ Below m, 550 μ Below m, 500 μ Below m or 450 μ Below m. As a preferred range, a median particle size of 200–700 μm can be cited. μ m, 200~600 μ m, 200~550 μ m, 200~500 μ m, 200~450 μ m, 250~700 μ m, 250~600 μ m, 250~550 μ m, 250~500 μ m, 250~450 μ m, 300~700 μ m, 300~600 μ m, 300~550 μ m, 300~500 μ m, 300~450 μ m, 350~700 μ m, 350~600 μ m, 350~550μ m, 350~500 μ m, 350~450 μ m.

[0040] The median particle size of the water-absorbing resin particles can be determined using JIS standard sieves, specifically, by the method described in the examples.

[0041] 2. Method for producing water-absorbent resin particles The method for manufacturing the absorbent resin particles of the present invention is not particularly limited as long as it can produce absorbent resin particles with a gel diffusion distance of more than 0.0 cm and less than 2.0 cm as measured by the above method. The method for manufacturing the absorbent resin particles of the present invention, for example, sequentially comprises: a step of polymerizing a water-soluble olefinic unsaturated monomer to obtain polymer particles; a surface crosslinking step of performing surface crosslinking on the polymer particles; a step of pulverizing the polymer particles; and a step of classifying the polymer particles.

[0042] As described above, methods for adjusting the gel diffusion distance of the absorbent resin particles of the present invention to a range exceeding 0.0 cm and less than 2.0 cm include, for example, drying and crushing polymer particles obtained through polymerization processes such as reverse suspension polymerization (described later); and adding a water-soluble polymer (e.g., a thickener such as polyethylene glycol) to the absorbent resin particles to increase their viscosity after absorbing liquid. Using these methods, the adhesive force of the absorbent resin particles after absorbing liquid can be improved, and the gel diffusion distance can be shortened. Hereinafter, a method for manufacturing the absorbent resin particles of the present invention will be described in detail.

[0043] <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 while stirring an aqueous solution of the water-soluble olefinically unsaturated monomer as needed. Reverse suspension polymerization involves heating the water-soluble olefinically unsaturated monomer in a hydrocarbon dispersion medium under stirring. From the viewpoint of appropriately producing water-absorbent resin particles with a gel diffusion distance of more than 0.0 cm and less than 2.0 cm, reverse suspension polymerization is preferred. In the polymerization process, an internal crosslinking agent can be added to the water-soluble olefinically unsaturated monomer 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.

[0044] [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.

[0045] 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 70–100 mol% relative to the total water-soluble olefinic unsaturated monomers as the primary water-soluble olefinic unsaturated monomer.

[0046] Water-soluble olefinic unsaturated monomers can 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 monomers 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 monomers 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 monomers is more preferably 25% by mass or more, further preferably 28% by mass or more, and even more preferably 30% by mass or more.

[0047] Water-soluble olefinic unsaturated monomers, such as (meth)acrylic acid and 2-(meth)acrylamide-2-methylpropanesulfonic acid, 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, for ease of neutralization, these alkaline neutralizing agents can 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.

[0048] The degree of neutralization of the water-soluble olefinic unsaturated monomer using an alkaline neutralizing agent, as a percentage of the total acid groups present in the water-soluble olefinic unsaturated monomer, is preferably 40 to 100 mol%, more preferably 50 to 90 mol%, even more preferably 60 to 85 mol%, and even more preferably 70 to 80 mol%.

[0049] [Free radical polymerization initiator] From the viewpoint of adjusting the gel diffusion distance, SFC, DW 3-minute value without pressure, water absorption rate of physiological saline, and water retention capacity of physiological saline particles to an appropriate range, 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(2,2'-) Azo compounds such as 2-amidinylpropane dihydrochloride, 2,2'-azobis[2-(N-phenylamidinyl)propane] dihydrochloride, 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]propamide}, 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propamide], and 4,4'-azobis(4-cyanopentanoic acid) are preferred among these free radical polymerization initiators, from the viewpoint of ease of acquisition and operation. These free radical polymerization initiators can be used alone or in combination of two or more. Furthermore, these free radical polymerization initiators can also be used in conjunction with reducing agents such as sodium sulfite, sodium bisulfite, ferrous sulfate, and L-ascorbic acid as redox polymerization initiators.

[0050] The amount used as a free radical polymerization initiator is, for example, 0.00005 to 0.01 moles relative to 1 mole of a water-soluble olefinic unsaturated monomer. By meeting this amount, rapid polymerization can be avoided, and the polymerization can be terminated at an appropriate time.

[0051] [Internal cross-linking agent] As internal crosslinking agents, examples include crosslinking agents for polymers of water-soluble olefinic unsaturated monomers that can be crosslinked. Examples include unsaturated polyesters obtained by reacting diols and triols such as (poly)ethylene glycol [the expression "(poly)" indicates both cases with and without the "poly" prefix. The same applies below], (poly)propylene glycol, 1,4-butanediol, 1,6-hexanediol, trimethylolpropane, and (poly)glycerol with unsaturated acids such as (meth)acrylic acid, maleic acid, and fumaric acid; bisacrylamides such as N,N-methylenebisacrylamide; di(meth)acrylates or tri(meth)acrylates obtained by reacting polyepoxides with (meth)acrylic acid; and polyisocyanates such as toluene diisocyanate and hexamethylene diisocyanate with (meth)acrylic acid. Di(meth)acrylate carbamoyl esters obtained by the reaction of hydroxyethyl methacrylate; allylated starch, allylated cellulose, diallyl phthalate, N,N',N''-triallyl isocyanurate, divinylbenzene, and other compounds with two or more polymerizable unsaturated groups; diglycidyl compounds such as polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and polyglycerol diglycidyl ether; polyglycidyl compounds such as triglycidyl compounds; epichlorohydrin, epibromohydrin, etc. α Compounds with two or more reactive functional groups, such as epihalohydrins like methylepimercohydrin; isocyanate compounds like 2,4-toluene diisocyanate and hexamethylene diisocyanate; and oxetane compounds such as 3-methyl-3-hydroxymethyloxetane, 3-ethyl-3-hydroxymethyloxetane, 3-butyl-3-hydroxymethyloxetane, 3-methyl-3-hydroxyethyloxetane, 3-ethyl-3-hydroxyethyloxetane, and 3-butyl-3-hydroxyethyloxetane. 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 even more preferred. These internal crosslinking agents can be used alone or in combination of two or more.

[0052] From the viewpoint of adjusting the gel diffusion distance, SFC, DW 3-minute value without pressure, water absorption rate relative to physiological saline, and water retention capacity of the absorbent resin particles to an appropriate range, the amount of internal crosslinking agent used is preferably 0.02 mol or less relative to 1 mol of water-soluble olefinic unsaturated monomer, more preferably 0.000001 to 0.01 mol, further preferably 0.000005 to 0.005 mol, and even more preferably 0.00001 to 0.00005 mol.

[0053] [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-ethylpentane, 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 75-85% by mass of heptane and its isomers) also yield suitable results.

[0054] 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 relative to 100 parts by mass of the first-stage water-soluble olefinic unsaturated monomer. More preferably, it is 200 to 1400 parts by mass. It should be noted that, as described below, the reverse suspension polymerization is carried out in one stage (single stage) or two or more stages. The first-stage polymerization mentioned above refers to the first-stage polymerization reaction in single-stage polymerization or multi-stage polymerization (the same applies below).

[0055] [Dispersion stabilizer] (surfactant) In reverse suspension polymerization, dispersion stabilizers can also 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.

[0056] 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 condensation 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.

[0057] 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.

[0058] (Polymer-based dispersants) In addition, as a dispersant stabilizer used in reverse suspension polymerization, it can be used together with the surfactants mentioned above and with a polymeric dispersant.

[0059] Examples of polymeric dispersants include, for instance, 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, 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 particularly preferred. These polymeric dispersants can be used alone or in combination of two or more.

[0060] 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.

[0061] [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.

[0062] 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 adding a thickener and adjusting the viscosity of the aqueous solution, the median particle size obtained in the reverse suspension polymerization can be controlled.

[0063] As thickeners, options include: 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. It should be noted that if the stirring speed during polymerization is the same, there is a tendency for the higher the viscosity of the aqueous solution of the water-soluble olefinically unsaturated monomer, the larger the primary and / or secondary particles obtained.

[0064] [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 dispersant stabilizer. In this case, if the polymerization reaction is to begin, the dispersant stabilizer (surfactant, polymeric dispersant) can be added either before or after the addition of the monomer aqueous solution.

[0065] 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.

[0066] Such reverse suspension polymerization can be carried out in one or more stages. Furthermore, from the viewpoint of improving productivity, a two- to three-stage process is preferred.

[0067] In the case of 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, it is preferable that, 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.

[0068] From the viewpoint of enabling rapid polymerization, shortening polymerization time, thereby improving economy, and easily removing the heat of polymerization to ensure smooth reaction, the reaction temperature is preferably 20 to 110°C, more preferably 40 to 90°C.

[0069] <Dehydration Process> Following the aforementioned reverse suspension polymerization, a dehydration step may be included, in which water and the hydrocarbon dispersion medium are removed by distillation using externally applied heat or other energy. In the case of dehydration from the aqueous gel-like material after reverse suspension polymerization, the system containing the aqueous gel-like material dispersed in the hydrocarbon dispersion medium is heated, thereby temporarily removing water and the hydrocarbon dispersion medium from the system via azeotropic distillation. At this point, 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 post-polymerization dehydration step to adjust the amount of water removed (i.e., adjusting the moisture content of the polymer particles), various properties of the resulting water-absorbing resin particles can be controlled.

[0070] In the dehydration process, dehydration treatment by distillation can be carried out under normal pressure. When dehydration treatment is carried out under normal pressure, the dehydration temperature is preferably 70 to 250°C, more preferably 80 to 180°C, even more preferably 80 to 140°C, and even more preferably 90 to 130°C.

[0071] <Surface Crosslinking Process> The surface crosslinking process is a process of performing surface crosslinking on the polymer particles obtained in the polymerization process. When the polymer particles are crosslinked polymer particles (including hydrogel-like substances), this process involves adding a surface crosslinking agent to the hydrogel-like substance with an internal crosslinked structure obtained by polymerizing water-soluble olefinic unsaturated monomers to perform a crosslinking reaction (surface crosslinking reaction). This surface crosslinking reaction is preferably carried out after the polymerization of the water-soluble olefinic unsaturated monomers in the presence of the surface crosslinking agent.

[0072] Compounds having two or more reactive functional groups can be cited as surface crosslinking agents. Examples include: ethylene glycol, propylene glycol, 1,4-butanediol, diethylene glycol, triethylene glycol, trimethylolpropane, glycerol, polyethylene glycol, polypropylene glycol, polyglycerol, and other polyglycerols; (poly)ethylene glycol diglycidyl ether, (poly)glycerol diglycidyl ether, (poly)glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, (poly)propylene glycol polyglycidyl ether, (poly)glycerol polyglycidyl ether, and other polyglycidyl compounds; epichlorohydrin, epibromohydrin, etc. αHalogenated epoxy compounds such as methylepimerol; isocyanate compounds such as 2,4-toluene diisocyanate and hexamethylene diisocyanate; oxacyclobutane compounds such as 3-methyl-3-hydroxymethyloxacyclobutane, 3-ethyl-3-hydroxymethyloxacyclobutane, 3-butyl-3-hydroxymethyloxacyclobutane, 3-methyl-3-hydroxyethyloxacyclobutane, 3-ethyl-3-hydroxyethyloxacyclobutane, and 3-butyl-3-hydroxyethyloxacyclobutane; oxazoline compounds such as 1,2-ethylidene dioxazoline; ethylene carbonate. Esters, propylene carbonates, 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, 1,3-dioxolane-2-one and other carbonate compounds (e.g. alkylene carbonates); bis[N,N-di( β Hydroxyalkylamide compounds such as hexamethylene glycol diglycidyl ether, polyglycerol diglycidyl ether, polyglycerol triglycidyl ether, trimethylolpropane triglycidyl ether, polypropylene glycol polyglycidyl ether, and polyglycerol polyglycidyl ether are preferred among these surface crosslinking agents. These surface crosslinking agents can be used alone or in combination of two or more.

[0073] The amount of surface crosslinking agent used is preferably 0.00001 to 0.01 mol relative to 1 mol of the total amount of water-soluble olefinic unsaturated monomers used in the polymerization, more preferably 0.00005 to 0.005 mol, even more preferably 0.0001 to 0.001 mol, and even more preferably 0.0002 to 0.0009 mol.

[0074] As a method of adding surface crosslinking agents, the surface crosslinking agent can be added as is or added in an aqueous solution, or it can be added as needed as a solution in which a hydrophilic organic solvent is used as a 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 in a mixed solvent with water.

[0075] From the viewpoint of adjusting the gel diffusion distance, SFC, DW 3-minute value without pressure, water absorption rate relative to physiological saline, and water retention capacity of the water-absorbing resin particles to an appropriate range, the addition time of the surface crosslinking agent can be as soon as the polymerization reaction of the water-soluble olefinic unsaturated monomer is almost completely completed. It is preferable to add the agent 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, further preferably in the presence of water in the range of 10 to 100 parts by mass, even more preferably in the presence of water in the range of 15 to 60 parts by mass, and particularly preferably in the presence of water in the range of 35 to 50 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 amount of water required when adding the surface crosslinking agent.

[0076] The reaction temperature for the surface crosslinking reaction is preferably 50–250°C, more preferably 60–180°C, even more preferably 60–140°C, and still more preferably 70–120°C. The reaction time for the surface crosslinking reaction is preferably 1–300 minutes, more preferably 5–200 minutes.

[0077] <Drying Process> After the above surface crosslinking is performed, a drying process may be included, in which energy such as heat is applied from the outside, and water, hydrocarbon dispersion medium, etc. are removed 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.

[0078] In the drying process, drying 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 70–250°C, more preferably 80–180°C, even more preferably 80–140°C, and still more preferably 90–130°C. When drying is carried out under reduced pressure, the preferred drying temperature is 40–160°C, more preferably 50–110°C.

[0079] 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 using distillation is performed after the surface crosslinking step is completed. Alternatively, the surface crosslinking step and the drying step can be performed simultaneously.

[0080] After the drying process, the polymer particles are crushed to obtain angularly shaped fragments, which improves the binding force of the water-absorbing resin particles. This allows the gel diffusion distance of the resulting water-absorbing resin particles to be adjusted to a range greater than 0.0 cm and less than 2.0 cm. There are no particular limitations on the method of crushing the polymer particles; for example, centrifugal mills, roller mills, pulverizers, jet mills, high-speed rotary mills, and container-driven mills can be used to crush the polymer particles.

[0081] From the perspective of adjusting the median particle size of the superabsorbent resin particles to an appropriate range, polymer particles obtained through pulverization can be classified. Classification refers to the operation of separating a group of particles (powder) into two or more groups with different particle size distributions. A portion of the classified polymer particles can be pulverized and classified again. There are no particular limitations on the classification method; for example, it can be sieve classification or air classification. Sieve classification is a method of classifying particles on a sieve by vibrating the sieve into particles that pass through the sieve mesh and particles that do not pass through the sieve mesh. Sieve classification can be performed using, for example, vibrating screens, drum screens, cylindrical stirred screens, blower sifters, or ro-tap vibrators. Air classification is a method of classifying particles using the flow of air.

[0082] The absorbent resin particles of the present invention may contain additives appropriate to the intended purpose. Examples of such additives include surfactants, oxidizing agents, reducing agents, metal chelating agents, free radical chain terminators, antioxidants, and antibacterial agents. It should be noted that the above-mentioned additives are preferably hydrophilic or water-soluble.

[0083] From the viewpoint of adjusting the absorbency rate relative to physiological saline within an appropriate range for the unpressurized DW 3-minute value, the absorbent resin particles may contain inorganic powder. The inorganic powder is preferably hydrophilic or water-soluble, for example, amorphous silica. The inorganic powder is preferably contained in 0.05 to 5 parts by weight of water-absorbing resin particles, and more preferably in 0.1 to 2.5 parts by weight.

[0084] By including a thickener in the absorbent resin particles, the viscosity of the particles after absorbing liquid is increased, thereby improving the adhesion of the absorbent resin particles after water absorption and adjusting the gel diffusion distance of the absorbent resin particles to a range of more than 0.0 cm and less than 2.0 cm. As a thickener, any water-soluble agent is acceptable, and a water-soluble polymer is preferred. For example, polyethylene glycol, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl ethyl cellulose, methyl cellulose, carboxymethyl cellulose, polyacrylamide, polyethyleneimine, dextrin, sodium alginate, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide, etc., are preferred, with polyethylene glycol being more preferred. As a thickener, 0.01 to 5 parts by weight of the thickener are preferred per 100 parts by weight of the absorbent resin particles. Furthermore, the thickener is preferably included in solid form relative to the absorbent resin particles.

[0085] 3. Absorbent body, absorbent article The absorbent resin particles of the present invention constitute an absorbent material used in sanitary materials such as menstrual 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 structures comprising the absorbent 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 adhesive binders to improve the shape retention performance of the absorbent.

[0087] The water-absorbing resin particles in the absorbent 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. 2 The above, more preferably 120g / m 2 The above is further optimized to 140g / m 2 In addition, the preferred value is 400g / m³. 2 The following is more preferably 350g / m 2 The following is a further preferred value: 300g / m 2 the following.

[0088] Examples of hydrophilic fibers include at least one selected from 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 derived from wood; man-made cellulose fibers such as rayon and acetate rayon; and fibers containing synthetic resins such as polyamide, polyester, and polyolefins that have undergone hydrophilic treatment. The average fiber length of hydrophilic fibers is typically 0.1–10 mm, or 0.5–5 mm.

[0089] 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 weight per unit area: 50 g / m². 2 The above, more preferably 70g / m 2 The above is further preferred to be 90g / m 2 The above is further preferred to be 100g / 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.

[0090] 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.

[0091] 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) and a liquid-impermeable sheet (back sheet). 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.

[0092] Examples of liquid-permeable sheets include nonwoven fabrics containing fibers such as polyethylene, polypropylene, and polyester, such as hot-air type, spunbond type, chemically bonded type, and needle-punched type, as well as porous synthetic resin sheets. Examples of non-liquid-permeable 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 thermally bonded nonwoven fabrics, hot-air nonwoven fabrics, spunbond nonwoven fabrics, and spunbond / meltblown / spunbond nonwoven fabrics.

[0093] 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 of the liquid, embossing or perforation can be performed on the surface of the liquid-permeable sheet. These embossing or perforation processes can be carried out using known methods.

[0094] Examples of liquid-permeable sheets include: sheets containing synthetic resins such as polyethylene, polypropylene, and polyvinyl chloride; sheets containing 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 containing composite materials of these synthetic resins and nonwoven fabrics (e.g., spunbond nonwoven fabrics and spunlace nonwoven fabrics). Sheets containing synthetic resins primarily composed of low-density polyethylene (LDPE) resin can also be used as liquid-permeable sheets. For example, a liquid-permeable sheet may contain a weight per unit area of ​​10–50 g / m². 2 Sheets made of synthetic resin.

[0095] The absorbent article preferably comprises: a laminate, a liquid-permeable sheet, and a liquid-impermeable sheet, wherein the laminate has an absorbent containing absorbent resin particles and a core packing material sandwiching the absorbent between the upper and lower parts; the liquid-permeable sheet is disposed on the upper surface of the laminate; and the liquid-impermeable sheet is disposed on the side of the laminate opposite to the side of the liquid-permeable sheet.

[0096] 4. Supplementary notes This specification includes at least the inventions shown in (1) to (6) below. (1) A water-absorbing resin particle with a gel diffusion distance of more than 0.0cm to 2.0cm, more than 0.0cm to 1.5cm, more than 0.0cm to 1.0cm, more than 0.0cm to 0.7cm, more than 0.0cm to 0.5cm, 0.1cm to 2.0cm, 0.1cm to 1.5cm, 0.1cm to 1.0cm, 0.1cm to 0.7cm, 0.1cm to 0.5cm, 0.2cm to 2.0cm, 0.2cm to 1.5cm, 0.2cm to 1.0cm, 0.2cm to 0.7cm, and 0.2cm to 0.5cm. (2) According to the water-absorbing resin particles described in (1) above, the saline conductivity (SFC) of the water-absorbing resin particles is 0.0 × 10⁻⁶. -7 cm 3 ·s / g~50.0×10 -7 cm 3 ·s / g, 0.0×10 -7 cm 3 ·s / g~30.0×10 -7 cm 3 ·s / g, 0.0×10-7 cm 3 ·s / g~25.0×10 -7 cm 3 ·s / g、0.0×10 -7 cm 3 ·s / g~20.0×10 -7 cm 3 ·s / g、0.3×10 -7 cm 3 ·s / g~50.0×10 -7 cm 3 ·s / g、0.3×10 -7 cm 3 ·s / g~30.0×10 -7 cm 3 ·s / g、0.3×10 - 7 cm 3 ·s / g~25.0×10 -7 cm 3 ·s / g、0.3×10 -7 cm 3 ·s / g~20.0×10 -7 cm 3 ·s / g、1.0×10 -7 cm 3 ·s / g~50.0×10 -7 cm 3 ·s / g、1.0×10 -7 cm 3 ·s / g~30.0×10 -7 cm 3 ·s / g、1.0×10 -7 cm 3 ·s / g~25.0×10 -7 cm 3 ·s / g、1.0×10 -7 cm 3 ·s / g~20.0×10 -7 cm 3 ·s / g、5.0×10 -7 cm 3 ·s / g~50.0×10 -7 cm 3 ·s / g、5.0×10 -7 cm 3 ·s / g~30.0×10 -7 cm 3 ·s / g、5.0×10 -7 cm 3 ·s / g~25.0×10- 7 cm 3 ·s / g, 5.0×10 -7 cm 3 ·s / g~20.0×10 -7 cm 3 ·s / g, 10.0×10 -7 cm 3 ·s / g~50.0×10 - 7 cm 3 ·s / g, 10.0×10 -7 cm 3 ·s / g~30.0×10 -7 cm 3 ·s / g, 10.0×10 -7 cm 3 ·s / g~25.0×10 - 7 cm 3 ·s / g, 10.0×10 -7 cm 3 ·s / g~20.0×10 -7 cm 3 ·s / g. (3) According to the absorbent resin particles described in (1) or (2) above, wherein the absorbent resin particles have a DW3-minute unpressurized value relative to physiological saline of 15 mL / g or more, 15–60 mL / g, 15–55 mL / g, 15–50 mL / g, 15–48 mL / g, 15–45 mL / g, 20–60 mL / g, 20–55 mL / g, 20–50 mL / g, 20–48 mL / g, 20–45 mL / g, 25–60 mL / g, or 25–55 mL / g. , 25~50mL / g, 25~48mL / g, 25~45mL / g, 28~60mL / g, 28~55mL / g, 28~50mL / g, 28~48mL / g, 28~45mL / g, 30~60mL / g , 30~55mL / g, 30~50mL / g, 30~48mL / g, 30~45mL / g, 32~60mL / g, 32~55mL / g, 32~50mL / g, 32~48mL / g, 32~45mL / g. (4) The absorbent resin particles according to any one of (1) to (3) above, wherein the absorbent resin particles absorb water relative to physiological saline at a rate of 10-70 seconds, 10-60 seconds, 10-55 seconds, 10-50 seconds, 10-45 seconds, 10-42 seconds, 15-70 seconds, 15-60 seconds, 15-55 seconds, 15-45 seconds, 15-42 seconds, 20-70 seconds, 20-60 seconds, 20-55 seconds, 20-50 seconds, 20-45 seconds, 20-42 seconds, 22-70 seconds, 22-60 seconds, 22-55 seconds, 22-50 seconds, 22-45 seconds, 22-42 seconds, 24-70 seconds, 24-60 seconds, 24-55 seconds, 24-50 seconds, 24-45 seconds, 24-42 seconds. (5) The water-absorbing resin particles according to any one of (1) to (4) above, wherein the saline water retention capacity of the water-absorbing resin particles is 15-80 g / g, 15-60 g / g, 15-50 g / g, 15-45 g / g, 15-40 g / g, 20-80 g / g, 20-60 g / g, 20-50 g / g, 20-45 g / g, 20-40 g / g, 25-80 g / g, 25-60 g / g, 25-50 g / g, 25-45 g / g, 25-40 g / g, 27-80 g / g, 27-60 g / g, 27-50 g / g, 27-45 g / g, 27-40 g / g. (6) The water-absorbing resin particles according to any one of (1) to (5) above, wherein the median particle size of the water-absorbing resin particles is 200 to 700 mm. μ m, 200~600 μ m, 200~550 μ m, 200~500 μ m, 200~450 μ m, 250~700 μ m, 250~600 μ m, 250~550 μ m, 250~500 μ m, 250~450 μ m, 300~700 μ m, 300~600 μ m, 300~550 μ m, 300~500 μ m, 300~450 μ m, 350~700 μ m, 350~600 μ m, 350~550 μ m, 350~500 μm, 350~450 μ m. (7) The water-absorbing resin particles according to any one of (1) to (6) above, wherein the shape of the water-absorbing resin particles is an irregularly shaped broken shape or a shape formed by the aggregation of irregularly shaped broken particles, or an irregularly shaped broken shape.

[0104] Example The present invention will be described in detail below with examples and comparative examples. However, the present invention is not limited to the examples. It should be noted that, unless otherwise specified, the manufacturing examples, examples, comparative examples, and measurements were carried out in an environment with a temperature of 25±2°C and a humidity of 50±10%.

[0105] <Production of Polymer Particles> (Manufacturing Example 1) [First stage of polymerization process] Prepare a separable cylindrical flask with an inner diameter of 11 cm and an internal volume of 2 L, equipped with a reflux condenser, dropping funnel, nitrogen inlet tube, and stirrer. Use a stirrer with two sections of four inclined blades each with a 5 cm blade diameter. Add 293 g of n-heptane and 0.736 g of maleic anhydride-modified ethylene-propylene copolymer (manufactured by Mitsui Chemicals, HI-WAX 1105A) as a dispersant to the separable flask and mix. While stirring the mixture in the flask, heat to 80°C to dissolve the dispersant in the n-heptane. Cool the resulting n-heptane solution to 50°C.

[0106] Add 92.0 g (1.03 mol) of an 80.5% by mass aqueous solution of acrylic acid, a water-soluble olefinic unsaturated monomer, to a 300 mL beaker. While cooling from the outside, add 147.7 g of a 20.9% by mass aqueous solution of sodium hydroxide dropwise to neutralize 75 mol% of the acrylic acid. Add 0.092 g of hydroxyethyl cellulose (Sumitomo Seika Co., Ltd., HEC AW-15F) as a thickener, 0.0736 g (0.272 mmol) of potassium persulfate as a free radical polymerization initiator, and 0.0156 g (0.090 mmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent, and dissolve them to prepare the first-stage aqueous solution.

[0107] The aqueous solution from the first stage was added to the n-heptane solution in a separable flask, and the resulting reaction mixture was stirred for 10 minutes. Separately, a surfactant solution was prepared, in which 0.736 g of sucrose stearate (Mitsubishi Chemical Foods Co., Ltd., Ryoto Sugar Ester S-370, HLB:3) was dissolved in 6.62 g of n-heptane. This surfactant solution was added to the reaction mixture, and the stirrer was set to 550 rpm. While stirring, the system was thoroughly purged with nitrogen. Then, the separable flask was immersed in a 70°C water bath to raise the temperature of the reaction mixture and carry out the polymerization reaction for 60 minutes, thereby obtaining the polymerization slurry of the first stage.

[0108] [Second stage polymerization process] 128.8 g (1.44 mol) of an 80.5% by mass aqueous solution of acrylic acid was added to a 500 mL beaker. While cooling from the outside, 159.0 g of a 27% by mass aqueous solution of sodium hydroxide was added dropwise to neutralize 75 mol% of the acrylic acid. 0.103 g (0.381 mmol) of potassium persulfate and 0.0116 g (0.067 mmol) of ethylene glycol diglycidyl ether were added to the beaker containing the neutralized acrylic acid aqueous solution and dissolved to prepare the second-stage aqueous solution.

[0109] While stirring at 1000 rpm, the first-stage polymerization slurry in the separable flask was cooled to 25°C, and the total amount of the second-stage aqueous solution was added. After purging the separable flask with nitrogen for 30 minutes, the flask was immersed again in a 70°C water bath to raise the temperature of the reaction solution. Through the second-stage polymerization reaction for 60 minutes, a hydrogel-like polymer was formed.

[0110] [Surface crosslinking] 0.589 g of a 45% by mass aqueous solution of diethylenetriaminepentaacetic acid pentasodium salt was added to the reaction solution containing the hydrogel polymer under stirring. Next, a separable flask was immersed in an oil bath set to 125°C, and 256.1 g of water was removed from the system by azeotropic distillation of n-heptane and water. 4.42 g of a 2% by mass aqueous solution containing 0.508 mmol of ethylene glycol diglycidyl ether as a surface crosslinking agent was added to the separable flask, and the temperature was maintained at 83°C for 2 hours.

[0111] Then, n-heptane was removed by drying at 125°C, thereby obtaining 232.06 g of polymer particles (1).

[0112] (Manufacturing Example 2) [First stage of polymerization process] Prepare a separable cylindrical flask with an inner diameter of 11 cm and an internal volume of 2 L, equipped with a reflux condenser, dropping funnel, nitrogen inlet tube, and stirrer. Use a stirrer with two sections of four inclined blades each with a 5 cm blade diameter. Add 293 g of n-heptane and 0.736 g of maleic anhydride-modified ethylene-propylene copolymer (manufactured by Mitsui Chemicals, HI-WAX1105A) as a dispersant to the separable flask and mix. While stirring the mixture in the flask, heat to 80°C to dissolve the dispersant in the n-heptane. Cool the resulting n-heptane solution to 50°C.

[0113] Add 92.0 g (1.03 mol) of an 80.5% by mass aqueous solution of acrylic acid, a water-soluble olefinic unsaturated monomer, to a 300 mL beaker. While cooling from the outside, add 147.7 g of a 20.9% by mass aqueous solution of sodium hydroxide dropwise to neutralize 75 mol% of the acrylic acid. Add 0.092 g of hydroxyethyl cellulose (Sumitomo Seika Co., Ltd., HEC AW-15F) as a thickener, 0.092 g (0.339 mmol) of 2,2'-azobis(2-amidinylpropane) dihydrochloride and 0.028 g (0.102 mmol) of potassium persulfate as free radical polymerization initiators, and 0.0046 g (0.026 mmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent, and dissolve them to prepare the first-stage aqueous solution.

[0114] The aqueous solution from the first stage was added to the n-heptane solution in a separable flask, and the resulting reaction mixture was stirred for 10 minutes. Separately, a surfactant solution was prepared, in which 0.736 g of sucrose stearate (Mitsubishi Chemical Foods Co., Ltd., Ryoto Sugar Ester S-370, HLB:3) was dissolved in 6.62 g of n-heptane. This surfactant solution was added to the reaction mixture, and the stirrer was set to 550 rpm. While stirring, the system was thoroughly purged with nitrogen. Then, the separable flask was immersed in a 70°C water bath to raise the temperature of the reaction mixture and carry out the polymerization reaction for 60 minutes, thereby obtaining the polymerization slurry of the first stage.

[0115] [Second stage polymerization process] 128.8 g (1.44 mol) of an 80.5% by mass aqueous solution of acrylic acid was added to a 500 mL beaker. While cooling from the outside, 159.9 g of a 27% by mass aqueous solution of sodium hydroxide was added dropwise to neutralize 75 mol% of the acrylic acid. In the beaker containing the neutralized acrylic acid aqueous solution, 0.129 g (0.476 mmol) of 2,2'-azobis(2-amidinepropane) dihydrochloride, 0.039 g (0.143 mmol) of potassium persulfate, and 0.0116 g (0.067 mmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent were added and dissolved to prepare the second-stage aqueous solution.

[0116] While stirring at 1000 rpm, the first-stage polymerization slurry in the separable flask was cooled to 25°C, and the total amount of the second-stage aqueous solution was added. After purging the separable flask with nitrogen for 30 minutes, the flask was immersed again in a 70°C water bath to raise the temperature of the reaction solution. Through the second-stage polymerization reaction for 60 minutes, a hydrogel-like polymer was formed.

[0117] [Surface crosslinking] 0.589 g of a 45% by mass aqueous solution of diethylenetriaminepentaacetic acid pentasodium salt was added to the reaction solution containing the hydrogel polymer under stirring. Next, a separable flask was immersed in an oil bath set to 125°C, and 218.2 g of water was removed from the system by azeotropic distillation of n-pentane and water. 4.42 g of a 2% by mass aqueous solution containing 0.508 mmol of ethylene glycol diglycidyl ether as a surface crosslinking agent was added to the separable flask, and the temperature was maintained at 83°C for 2 hours.

[0118] Then, n-heptane was removed by drying at 125°C, thereby obtaining polymer particles (2) 247.6 g.

[0119] <Manufacturing of Water-Absorbent Resin Particles> (Example 1) The polymer particles (1) produced in Manufacturing Example 1 are processed with a 500 mesh screen. μ The particles were classified using a sieve with a diameter of 500 μm to obtain particles with a diameter of 500 μm. μ Polymer particles larger than m.

[0120] [Crush] A centrifugal grinder (Retsch ZM200, 1.5 mm screen) was used. μ 100g of the above polymer particles were pulverized at 12000rpm (m, rotation speed 12000rpm) to obtain polymer particles. Next, the obtained polymer particles were strung through a 150-mesh screen. μ The particles were classified using a sieve with a diameter of 150 μm to obtain particles with a diameter of 150 μm. μPolymer particles larger than μm were mixed with 0.5% by mass of amorphous silica (Oriental Silicas Corporation, Tokusil NP-S) to obtain 50.71 g of irregularly shaped, fragmented absorbent resin particles of Example 1. The median particle size of the absorbent resin particles of Example 1 was 399 μm. μ m.

[0121] (Example 2) Add 50.0 g of the absorbent resin particles from Example 1 and 0.5% by weight of polyethylene glycol (Tokyo Kasei Corporation, PEG20000) relative to the absorbent resin particles from Example 1 to a 1.0 L SUS bottle. Pulverize the pulverized polyethylene glycol using a mortar and pestle, then pass it through a 400 mesh screen. μ Polyethylene glycol obtained by sieving through a sieve was mixed for 30 minutes using a cross-rotation mixer (manufactured by Meiwa Kogyo Co., Ltd.) (50 rpm revolution speed and 50 rpm rotation speed) to obtain 50.25 g of irregularly shaped, fragmented water-absorbing resin particles of Example 2. The median particle size of the water-absorbing resin particles of Example 2 was 382 μm. μ m.

[0122] (Example 3) The polymer particles (1) used were changed to polymer particles (2) prepared in Manufacturing Example 2. Otherwise, the process was the same as in Example 1, yielding 55.20 g of irregularly shaped, fragmented, water-absorbing resin particles of Example 3. The median particle size of the water-absorbing resin particles of Example 3 was 385 μm. μ m.

[0123] (Example 4) The polymer particles (1) used were changed to polymer particles (2) prepared in Manufacturing Example 2. Otherwise, the process was the same as in Example 2, yielding 50.25 g of irregularly shaped, fragmented, water-absorbing resin particles of Example 4. The median particle size of the water-absorbing resin particles of Example 4 was 393 mm. μ m.

[0124] (Comparative Example 1) The polymer particles (1) of manufacturing Example 1 are passed through a mesh 850. μ A sieve was used to sieve a layer of amorphous silica (Oriental Silicas Corporation, Tokusil NP-S) at a mass of 0.5% relative to the polymer particles (1), resulting in 215.6 g of comparative example 1 water-absorbing resin particles in the shape of approximately spherical resin aggregates. The median particle size of the water-absorbing resin particles of comparative example 1 was 351 μm. μ m.

[0125] [Determination of gel diffusion distance] The gel diffusion distance of the water-absorbing resin particles is used Figure 1 The apparatus shown in the figure was used for measurement. As part of the apparatus, a stainless steel petri dish 61 was placed on the movable platform 60 of a Curdmeter-MAX ME-500 (Asuka Machinery Manufacturing Co., Ltd.). Inside the stainless steel petri dish 61, a mesh 38 covering the upper opening was provided. μ A cylindrical container (A) 62 is formed from a stainless steel mesh 63. Next, a cylindrical container (B) 64 with open ends along the axial direction is placed at the center of the stainless steel mesh 63, and the cylindrical container (B) 64 is fixed with a clamp 65. The stainless steel petri dish 61 has an inner diameter of 75 mm and a height of 20 mm. The cylindrical container (A) 62 has an inner diameter of 60 mm, an outer diameter of 70 mm, and a height of 60 mm. The cylindrical container (B) 64 has an inner diameter of 20 mm, an outer diameter of 30 mm, and a height of 60 mm. 0.20 g of superabsorbent polymer (SAP) particles were uniformly dispersed inside the cylindrical container (B) 64. A silicone tubing with a 2.0 mm inner diameter and 8.0 cm long stainless steel inlet, vertically positioned at a height of 5.0 cm from the bottom of the cylindrical container (B) 64 and at the center of the inner diameter of the container (B) 64, was connected to a delivery pump (INTEGRA Biosciences, DOSE IT P910). 30 mL of 0.9% saline solution was added at a constant rate of 20 mL / min. Twenty seconds after the addition, the movable platform 60 was lowered by 5.0 cm at a speed of 1.2 cm / s. At this time, the gel diffusion distance was measured at the point where the swollen gel formed by the superabsorbent polymer particles contacted the stainless steel mesh. Regarding the gel diffusion distance, the maximum distance of the following straight line was measured on the swollen gel on the stainless steel mesh. The gel diffusion distance (cm) was obtained by subtracting the inner diameter (diameter) of the cylindrical container (B) of 2.0 cm from this maximum distance Wa. The straight line passes through the center point of the swollen gel when it is located inside the cylindrical container (B), and the straight line connects the ends of the swollen gel that diffuse to the stainless steel mesh by lowering the movable platform. The results are shown in Table 1.

[0126] Gel diffusion distance (cm) = Maximum distance Wa - 2.0 [Salt conductivity (SFC) of absorbent resin particles] (a) Preparation of synthetic urine Add 2.0g of potassium chloride, 2.0g of anhydrous sodium sulfate, 0.25g of calcium chloride dihydrate, 0.50g of magnesium chloride hexahydrate, 0.85g of ammonium dihydrogen phosphate, 0.15g of ammonium monohydrogen phosphate, and an appropriate amount of distilled water to a 1L container and dissolve completely. Add more distilled water to adjust the total volume of the aqueous solution to 1L.

[0127] (b) Setup of the measuring device As a measuring device, it is used in Figure 2 The apparatus, with its general structure shown, includes a glass tube 38 for hydrostatic adjustment in tank 39. The lower end of the glass tube 38 is fitted with a 0.69% by mass sodium chloride aqueous solution 40, positioned such that the liquid level in cylinder 32 is maintained at a height of at least 5 cm above the bottom of the swollen gel 35. The 0.69% by mass sodium chloride aqueous solution 40 in tank 39 is supplied to cylinder 32 through an L-shaped tube 37 with a stopcock. A container 43 for collecting the passing liquid is positioned below cylinder 32, above a balance 44. Cylinder 32 has an inner diameter of 6 cm, and its bottom surface is fitted with a No. 400 stainless steel mesh (mesh size 38). μ m)36. The lower part of the piston-type counterweight 31 has a hole 33 large enough to allow liquid to pass through, and a highly permeable glass filter 34 is installed at the bottom in such a way that water-absorbing resin or their swelling gel does not enter the hole 33.

[0128] (c) Determination of saline conductivity (SFC) 0.90 g of absorbent resin particles uniformly placed in a cylindrical container 30 were swollen in the aforementioned synthetic urine under a load of 2.07 kPa for 60 minutes. The height of the swollen gel layer 35 was recorded. Then, under a load of 2.07 kPa, a 0.69% (w / w) sodium chloride aqueous solution 40 was supplied from container 39 to the swollen gel layer at a constant hydrostatic pressure. This SFC test was conducted at room temperature (20–25 °C). Using a computer and a balance, the amount of liquid passing through the gel layer was recorded at 20-second intervals for 10 minutes. The flow rate F through the swollen gel 35 (primarily between the particles) was determined in g / s by dividing the increase in mass (g) of liquid passing through the gel layer by the increase in time (s). s (t). Let t be the time it takes to achieve constant hydrostatic pressure and stable flow velocity. s , only t s Data obtained between 10 and 10 minutes is used for flow rate calculation, using t s Calculate F based on the flow rate obtained between 10 minutes and 10 minutes. s The value of (t=0), i.e., the initial flow rate through the gel layer. F s (t=0) By F s(t) The result of the least squares method over time is extrapolated to t=0. The results are shown in Table 1.

[0129] SFC = (F s (t=0)×L0) / ( ρ ×A×ΔP) =(F s (t=0)×L0) / 139506 in, F s (t=0): Flow velocity in g / s L0: Initial height of the gel layer, expressed in cm ρ The density of a 0.69% (w / w) sodium chloride aqueous solution is 1.003 g / cm³. 3 A: The area of ​​the upper side of the gel layer in cylinder 32 = 28.27 cm² 2 ΔP: Hydrostatic pressure applied to the gel layer = 4920 dyne / cm 2 The unit of SFC is "×10" -7 cm 3 ·s / g”.

[0130] [Determination of 3-minute values ​​for unpressurized demand wettability (DW)] 3-minute value of unpressurized DW for water-absorbing resin particles Figure 3 The measurement was performed using the apparatus shown. The measurement was conducted five times on a type of absorbent resin particles, and the average of the three measured values ​​(excluding the lowest and highest values) was calculated. The results are shown in Table 1.

[0131] 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.

[0132] First, close stopcocks 22 and 24 of burette section 1, and inject 0.9% saline solution 50, adjusted to 25°C, into burette 21 through the opening at the top. The 0.9% concentration of the saline solution 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 of burette 21, and take this position as the zero point (the reading at 0 seconds).

[0133] A nylon mesh 15 (100mm × 100mm, 250 mesh, approximately 50mm thick) is laid near the through hole 13a on the measuring platform 13. μ A cylinder with an inner diameter of 30 mm and a height of 20 mm was placed in the center of the nylon mesh 15. 1.00 g of absorbent resin particles 10a were evenly dispersed in the cylinder. The cylinder was 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 was rapidly moved until the particles were no longer dispersed, with its center positioned as a through-hole 13a, and the measurement began. The moment when the air bubble was initially introduced from the air inlet tube 25 into the burette 21 was defined as the start of absorption (0 seconds).

[0134] Read the decrease in 0.9% saline solution 50 in burette 21 in 0.1 mL units (i.e., the amount of 0.9% saline solution absorbed by the absorbent resin particles 10a). Read the decrease in 0.9% saline solution 50, Wb (mL), after 3 minutes from the start of water absorption by the absorbent resin particles 10a. Calculate the 3-minute unpressurized DW value based on Wb using the following formula. Unpressurized DW is the amount of water absorbed by each 1.00 g of absorbent resin particles 10a.

[0135] The 3-minute DW value without pressurization (mL / g) = Wb / 1.00 [Water absorption rate (Vortex method)] The water absorption rate of physiological saline in the superabsorbent resin particles was determined using the Vortex method according to the following steps. First, 50 ± 0.1 g of physiological saline, adjusted to a temperature of 25 ± 0.2 °C, was measured into a 100 mL beaker in a constant temperature water bath. Next, a magnetic stirring rod (8 mm) was used... φ(×30mm, non-ring) The mixture was stirred at 600 rpm to generate a vortex. 2.0 ± 0.002 g of absorbent resin particles were added to physiological saline in a single addition. The time (in seconds) from the addition of the absorbent resin particles to the moment the vortex on the liquid surface converged was measured and taken as the water absorption rate of the absorbent resin particles. The results are shown in Table 1.

[0136] [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% sodium chloride aqueous solution (physiological saline) was injected into the cotton bag without clumping, and the top of the bag was secured with a rubber band. 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 Wc (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 Wd (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.

[0137] The water retention capacity of physiological saline (g / g) = [Wc - Wd] / 2.0 [Method for determining median particle size] The test uses a continuous fully automatic acoustic vibration sieving machine (Robot Shifter RPS-205, manufactured by Seishin Corporation), with a JIS standard mesh size of 850. μ m, 710 μ m, 600 μ m, 500 μ m, 425 μ m, 300 μ m, 250 μ m and 150 μ Using a sieve and receiving tray of size m, 10g of absorbent resin particles are sieved. The percentage of the mass of particles remaining on each sieve relative to the total mass is calculated. The percentage of the mass of particles remaining on each sieve is accumulated sequentially, starting with the largest particle size. The relationship between the sieve mesh size and the cumulative percentage of the mass of particles remaining on the sieve is plotted on logarithmic probability paper. By connecting the plotted points on the probability paper with a straight line, the particle size equivalent to 50% of the cumulative mass percentage is determined and taken as the median particle size. μ m).

[0138] [The creation of absorbers] Using an airflow mixing device (manufactured by O-tec Ltd., pad former), 12.0g of absorbent resin granules and 6.4g of pulverized paper pulp were uniformly mixed by air forming to create an absorbent core measuring 12cm x 40cm. Next, two sheets of thin paper of the same size as the absorbent core (weight per unit area: 16g / m²) were used... 2 With the absorber core sandwiched between the top and bottom, apply a load of 141 kPa to the whole for 30 seconds, and then cut off the part 5.0 cm wide from both ends in the length direction to make the absorber.

[0139] [Methods for determining deformation resistance and diffusion length] A hydrophilic top sheet (12cm×30cm, weight per unit area 21g / m²) is placed on the upper surface of the fabricated absorbent. 2 (Lengo Co., Ltd.) obtained absorbent articles. The absorbent articles were placed on a horizontal table in a room at 25±2°C, and 150 mL of artificial urine was poured into the center of the absorbent articles through a liquid injection cylinder with an inner diameter of 3 cm. Five minutes after the artificial urine was poured in, the hydrophilic top sheet was removed from the absorbent articles, and the length of the absorbent along its length through the center of the blue area that became wet due to the test solution was measured as the diffusion length (cm). Ten minutes after the artificial urine was poured in, the absorbent that had absorbed the artificial urine was used to evaluate the deformation resistance of the absorbent. The composition of the artificial urine used is as described below.

[0140] (Composition of artificial urine) · Deionized water 5919.6g ·NaCl 60.0g ·CaCl2·H2O 1.8g ·MgCl2·6H2O 3.6g Edible Blue No. 1 (for coloring) 1% Triton X-100 15.0g Figure 4This is a schematic diagram illustrating a method for evaluating the deformation resistance of an absorbent. Two corrugated cardboard sheets 71 and 72, each 40cm x 20cm in size, are prepared, entirely covered by a non-permeable resin sheet. The corrugated cardboard sheets 71 and 72 are fixed together with their long edges touching using adhesive tape, creating a test board 73 with a bendable central joint 75. The absorbent 70 is attached to the test board 73 with its length perpendicular to the joint 75, the side containing artificial urine, and the center of the absorbent 70 overlapping the joint 75, using adhesive tape. Next, the test board 73 is slowly and evenly bent at a speed of 10 degrees per second, creating a mountain fold with the joint 75 as the apex. Bending is stopped at the moment the absorbent 70 breaks, and the angle of the bend up to that moment is measured. θ (degrees). If the angle θ If the value is large, then it can be said to have excellent resistance to deformation. The results are shown in Table 1.

[0141] [Table 1]

[0142] Explanation of reference numerals in the attached figures 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 30 Cylindrical containers 31 Piston-type counterweight 32 cylinders 33 holes 34 Glass Filter 35 Swelling Gel 36 Stainless Steel Mesh 37. L-shaped tube with stopcock 38 Glass tube for static pressure adjustment 39 cans 40 0.69% by mass sodium chloride aqueous solution 41 Funnel 42 Support platform 43 Containers 44. Pallet Balance 60 Movable Platform 61 Stainless Steel Petri Dishes 62. Cylindrical container (A) 63 Stainless Steel Mesh 64. Cylindrical container (B) 65 Fixture 70 Absorbers 71 Corrugated Cardboard 72 Corrugated Cardboard 73 Test Plate 75 Joint.

Claims

1. A water-absorbing resin particle, characterized in that, The gel diffusion distance, determined by the following method, is greater than 0.0 cm and less than 2.0 cm: Methods for determining gel diffusion distance: A stainless steel petri dish is placed on a movable platform, and a mesh 38 covering the upper opening is provided inside the stainless steel petri dish. μ A cylindrical container (A) with a stainless steel mesh is formed. Next, a cylindrical container (B) with open ends is placed at the center of the stainless steel mesh, and the cylindrical container (B) is fixed with clamps. The stainless steel culture dish has an inner diameter of 75 mm and a height of 20 mm. The cylindrical container (A) has an inner diameter of 60 mm, an outer diameter of 70 mm, and a height of 60 mm. The cylindrical container (B) has an inner diameter of 20 mm, an outer diameter of 30 mm, and a height of 60 mm. Next, 0.20 g of absorbent resin particles are evenly distributed inside the cylindrical container (B), and the absorbent resin particles are placed on the stainless steel mesh. Next, water is added from a height of 5.0 cm from the bottom of the cylindrical container (B) and above the center of its inner diameter, at a constant rate of 20 mL / min. 30 mL of 0.9% (w / w) physiological saline was added. Twenty seconds after the addition, with the cylindrical container (B) fixed, the movable platform was lowered by 5.0 cm at a speed of 1.2 cm / s. At this time, the gel diffusion distance was measured at the portion of the swollen gel formed by the water-absorbing resin particles in contact with the stainless steel mesh. Regarding the gel diffusion distance, the maximum distance of the following straight line was measured on the swollen gel on the stainless steel mesh. The gel diffusion distance (cm) was obtained by subtracting the inner diameter (2.0 cm) of the cylindrical container (B) from this maximum distance Wa. This straight line passes through the center point of the swollen gel inside the cylindrical container (B) and connects the ends of the swollen gel that diffused onto the stainless steel mesh by lowering the movable platform. Gel diffusion distance (cm) = maximum distance Wa - 2.

0.

2. The water-absorbing resin particles according to claim 1, wherein, The saline conductivity (SFC) of the absorbent resin particles is below 50.0, and the unit of saline conductivity is ×10. -7 cm 3 ·s / g.

3. The water-absorbing resin particles according to claim 1, wherein, The unpressurized DW 3-minute value of the water-absorbing resin particles is above 15 mL / g.

4. An absorber, characterized in that, It comprises the absorbent resin particles according to any one of claims 1 to 3.

5. An absorbent article, characterized in that, It includes the absorber as described in claim 4.

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