Absorbent materials, absorbent products, and methods for manufacturing absorbent materials.

Abstract

Invention details;

Description

Absorbent body, absorbent article, and method for manufacturing the absorbent body

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to absorbent bodies, absorbent articles, and methods of manufacturing absorbent bodies.

[0002] Patent Document 1 discloses a water-absorbent composite sheet, which is an absorbent article for nursing care, having a substrate and substantially spherical water-absorbent resin particles intermittently fixed to the substrate.

[0003] Japanese Patent Application Laid-Open No. 2005-323842

[0004] When an absorbent article absorbs a water-containing liquid, it is desirable that the area over which the liquid spreads within the absorbent article is small. It is also often desirable that the absorbed liquid not return to the surface of the absorbent article, i.e., so-called backflow, is small, and that a dry surface is quickly formed. However, if the liquid diffusion area in the absorbent article is small, backflow tends to be large and it tends to take a long time for a dry surface to be formed.

[0005] The present disclosure relates to an absorbent article that has a small area for the absorbed liquid to spread over and can quickly form a dry surface with little return, and an absorbent body therefor.

[0006] The present disclosure includes the following: [1] A sheet-like absorbent body comprising a fiber layer containing hydrophilic fibers and a particle layer containing first water-absorbent resin particles formed on one or both surfaces of the fiber layer, the fiber layer optionally containing second water-absorbent resin particles, wherein the basis weight of the first water-absorbent resin particles in one particle layer is 40 g / m ２ the first water-absorbent resin particles have a water absorption rate for physiological saline of 20 seconds or less, and the hydrophilic fibers in the fiber layer have a basis weight of 20 g / m ２ 180g / m or more ２an absorbent body according to [1], wherein the ratio of the amount of the first water-absorbent resin particles is 60% by mass or more and 100% by mass or less based on the total mass of the first water-absorbent resin particles and the second water-absorbent resin particles. [2] The absorbent body according to [1], wherein the ratio of the area of ​​the particle layer to the area of ​​the fiber layer is 70% by mass or more and 100% by mass or less when viewed in the thickness direction of the absorbent body. [3] The absorbent body according to [1] or [2], wherein the first water-absorbent resin particles exhibit a water retention capacity of 30 g / g or more in physiological saline. [4] The absorbent body according to any one of [1] to [3], wherein the first water-absorbent resin particles exhibit a water absorption under load of 5 mL / g or more in physiological saline. [5] The absorbent body according to [1], wherein the total basis weight of the first water-absorbent resin particles and the second water-absorbent resin particles is X g / m ２ and the weight of the hydrophilic fibers in the fiber layer is Yg / m ２

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[0024]

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[0029]

[10] The absorbent body according to any one of [1] to [4], wherein the ratio X / Y is 0.25 or more and 7.0 or less when the ratio is 0.25 or more and 7.0 or less. [6] An absorbent article comprising: a liquid-permeable sheet; and the absorbent body according to any one of [1] to [5], provided inside the liquid-permeable sheet. [7] The absorbent article according to [6], wherein the absorbent body is provided so that the particle layer is located between the fiber layer and the liquid-permeable sheet. [8] A method for producing a sheet-like absorbent body, the method comprising: forming a fiber layer containing hydrophilic fibers; and forming a particle layer containing first water-absorbent resin particles on one or both sides of the fiber layer, the method comprising: forming a fiber layer containing hydrophilic fibers; and forming a particle layer containing first water-absorbent resin particles on one or both sides of the fiber layer, the method comprising: forming a fiber layer containing hydrophilic fibers on one or both sides of the fiber layer; ... ２ or more, and the basis weight of the hydrophilic fibers in the fiber layer is 20 g / m ２ More than 180g / m ２ wherein the water absorption rate of the first water-absorbent resin particles is 20 seconds or less.

[0007] According to the present disclosure, an absorbent article can be provided that has a small area over which absorbed liquid spreads and that can quickly form a dry surface with little return. The absorbent article of the present disclosure is useful, for example, as a waterproof sheet for nursing care.

[0008] Fig. 1 is a partial cross-sectional view showing an example of an absorbent article. Fig. 2 is a partial cross-sectional view showing an example of an absorbent article. Fig. 3 is a plan view showing an example of an agitating impeller. Fig. 4 is a schematic view showing an apparatus for measuring water absorption under load for physiological saline. Fig. 5 is a plan view showing an example of a state in which a test liquid has diffused through an absorbent article in measuring a diffusion area. Fig. 6 is a photograph showing an example of an absorbent article onto which a test liquid has been dropped in measuring a whitening time.

[0009] The present invention is not limited to the following examples. In this specification, "room temperature" means 25±2°C. "Layer" is used as a term that encompasses not only a shaped structure continuously formed in the in-plane direction, but also a shaped structure partially formed in the in-plane direction. "Physiological saline" means an aqueous sodium chloride solution with a concentration of 0.9% by mass, containing 9 g of sodium chloride per 1000 mL of water at room temperature.

[0010] FIG. 1 is a partial cross-sectional view showing an example of an absorbent article. The absorbent article 50 shown in FIG. 1 includes a sheet-like absorbent body 10, a first shape-retaining member 21, a second shape-retaining member 22, a liquid-permeable sheet 30, and an adhesive 35. The absorbent body 10 is a laminate composed of one particle layer 11 containing a plurality of first water-absorbent resin particles 11a and one fiber layer 12 containing hydrophilic fibers, and is provided inside the liquid-permeable sheet 30. The absorbent body 10 is disposed between the sheet-like first shape-retaining member 21 and the sheet-like second shape-retaining member 22. The entire absorbent body 10 may be enclosed by the first shape-retaining member 21 and the second shape-retaining member 22. The first shape-retaining member 21 and the second shape-retaining member 22 may be a single sheet or two separate sheets. The first shape-retaining member 21 and the second shape-retaining member 22 may be, for example, tissue. The adhesive 35 is interposed between the liquid permeable sheet 30 and the second shape-retaining member 22 to bond them together. The adhesive 35 may be, for example, a hot melt adhesive. In the example of Fig. 1, the absorbent body 10 is provided so that the particle layer 11 is located between the liquid permeable sheet 30 and the fibrous layer 12. The absorbent article may further include a liquid impermeable sheet provided on the outside of the first shape-retaining member 21.

[0011] Figures 2 and 3 are partial cross-sectional views showing other examples of absorbent articles. The absorbent article 51 shown in Figure 2 differs from the absorbent article 50 of Figure 1 in that the fiber layer 12 further contains second water-absorbent resin particles 11b. The second water-absorbent resin particles 11b may be the same as or different from the first water-absorbent resin particles 11a. The absorbent article 52 shown in Figure 3 differs from the absorbent article 50 of Figure 1 in that the particle layer 11 is located on the surface of the fiber layer 12 opposite to the side on which the liquid-permeable sheet 30 is located.

[0012] In the absorbent articles 50, 51, and 52 illustrated in Figures 1 to 3, the particle layer 11 is provided on only one side of the fiber layer 12. The configuration of the absorbent article according to the present disclosure is not limited to this, and for example, the particle layer 11 may be provided on both sides of the fiber layer 12. The particle layer 11 does not necessarily need to cover the entirety of one or both sides of the fiber layer 12. For example, when viewed in the thickness direction of the absorbent body 10, the area ratio of the particle layer 11 to the area of ​​the fiber layer may be 70% or more and 100% or less, 80% or more and 100% or less, or 95% or more and 100% or less. When multiple particle layers are provided, the area ratio of one or more of them may be within these ranges.

[0013] The basis weight of the first water-absorbent resin particles 11a in one particle layer 11 is 40 g / m ２ or more. When the basis weight of the first water-absorbent resin particles 11a is large, the diffusion area of ​​the liquid in the absorbent article tends to be small, and backflow of the liquid from the absorbent article tends to be suppressed. When the water absorption rate of the first water-absorbent resin particles 11a is high, a large basis weight tends to exhibit particularly significant effects in terms of the diffusion area and backflow. From the same viewpoint, when the basis weight of the first water-absorbent resin particles 11a in one particle layer 11 is 45 g / m ２ or more than 50 g / m ２ The basis weight of the first water-absorbent resin particles 11a in one particle layer 11 may be 40 g / m or more. ２ Above, 45g / m ２ Above, 50g / m ２ Above, 55g / m ２ Above, 60g / m ２ Above, 65g / m ２ Above, 70g / m ２ or more, or 75 g / m ２ Above 300 g / m ２ The basis weight of the first water-absorbent resin particles 11a in one particle layer 11 may be 40 g / m or less. ２ Above, 45g / m ２ Above, 50g / m ２ Above, 55g / m ２ Above, 60g / m ２ Above, 65g / m ２ Above, 70g / m ２or more, or 75 g / m ２ Above 250 g / m ２ The basis weight of the first water-absorbent resin particles 11a in one particle layer 11 may be 40 g / m or less. ２ Above, 45g / m ２ Above, 50g / m ２ Above, 55g / m ２ Above, 60g / m ２ Above, 65g / m ２ Above, 70g / m ２ or more, or 75 g / m ２ That's 230 g / m ２ When two or more particle layers are provided, the basis weight of the first water-absorbent resin particles 11a in each particle layer may be within these ranges. ２ In addition to the particle layer having a basis weight of 40 g / m ２ In this specification, the basis weight means the mass per unit area of ​​the absorbent body when viewed in the thickness direction of the absorbent body.

[0014] The first water-absorbent resin particles 11a forming the particle layer 11 are water-absorbent resin particles contained in the absorbent 10 that are not held in the fiber layer 12. In this specification, the water-absorbent resin particles that fall off from the absorbent 10 in a falling-off test are considered to be the first water-absorbent resin particles 11a. Specifically, the falling-off test includes holding the absorbent 10 horizontally at a position 50 cm above the bottom of a container with the particle layer 11 as the lowest layer, raising the absorbent 10 upward at a speed of 30 cm per second to a height of 55 cm above the bottom of the container, and subsequently lowering the absorbent 10 downward at a speed of 30 cm per second to a height of 45 cm above the bottom of the container, and then repeating this process nine times. The basis weight of the first water-absorbent resin particles 11a can be calculated from the mass Wa (g) of the water-absorbent resin particles (first water-absorbent resin particles 11a) that have fallen off from the absorbent body 10 and collected on the bottom surface of the container, and the area of ​​the absorbent body when viewed from the thickness direction of the absorbent body 10. The container that collects the fallen water-absorbent resin particles may be one that is sufficiently larger in size than the absorbent body 10. For example, the area of ​​the bottom surface of the container may be about 50 times or more the area of ​​the absorbent body.

[0015] When the proportion of the first water-absorbent resin particles 11a forming the particle layer 11 among the water-absorbent resin particles contained in the absorbent body 10 is large, the time until the absorbent article to which liquid is applied forms a dry surface (whitening time) tends to be shorter while maintaining the high water retention capacity of the fiber layer 12. This is thought to be because there are relatively many voids between the multiple first water-absorbent resin particles 11a that constitute the particle layer 11, making gel blocking less likely to occur when the first water-absorbent resin particles 11a absorb water. A large proportion of the first water-absorbent resin particles 11a can also contribute to the increase in the diffusion area of ​​liquid in the absorbent article and the suppression of backflow. From these viewpoints, the proportion of the amount of the first water-absorbent resin particles 11a may be 60% by mass or more and 100% by mass or less, 65% by mass or more and 100% by mass or less, 70% by mass or more and 100% by mass or less, 75% by mass or more and 100% by mass or less, 80% by mass or more and 100% by mass or less, 85% by mass or more and 100% by mass or less, or 90% by mass or more and 100% by mass or less, based on the total mass of the first water-absorbent resin particles 11a and the second water-absorbent resin particles 11b. Here, a proportion of the amount of the first water-absorbent resin particles 11a of 100% by mass means that the fiber layer 12 does not substantially contain water-absorbent resin particles, as in the examples of FIGS. 1 and 3. The proportion of the amount of the first water-absorbent resin particles 11a can be calculated by the following formula from the mass Wa of the first water-absorbent resin particles 11a obtained by the above-mentioned shedding test and the total mass Wb of the first water-absorbent resin particles 11a and the second water-absorbent resin particles 11b (the total mass of the water-absorbent resin particles contained in the absorbent body 10). Proportion of the amount of the first water-absorbing resin particles 11a [mass %]=(Wa / Wb)×100

[0016] The total basis weight of the first water-absorbing resin particles 11a and the second water-absorbing resin particles 11b is X g / m ２ The weight of the hydrophilic fibers in the fiber layer 12 is Yg / m ２When the ratio X / Y is 0.25 or more and 7.0 or less, the ratio X / Y may be 0.25 or more and 6.0 or less, 5.5 or less, 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, 3.0 or less, or 2.5 or less. The ratio X / Y may be 0.35 or more and 6.0 or less, 5.5 or less, 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, 3.0 or less, or 2.5 or less. The ratio X / Y may be 0.45 or more and 6.0 or less, 5.5 or less, 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, 3.0 or less, or 2.5 or less. The ratio X / Y may be 0.55 or more and 6.0 or less, 5.5 or less, 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, 3.0 or less, or 2.5 or less. The ratio X / Y may be 0.65 or more and 6.0 or less, 5.5 or less, 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, 3.0 or less, or 2.5 or less. The ratio X / Y may be 0.75 or more and 6.0 or less, 5.5 or less, 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, 3.0 or less, or 2.5 or less. The ratio X / Y may be 1.5 or more and 6.0 or less, 5.5 or less, 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, 3.0 or less, or 2.5 or less. The ratio X / Y may be 2.0 or more and 6.0 or less, 5.5 or less, 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, 3.0 or less, or 2.5 or less. When the fiber layer 12 contains the second water-absorbing resin particles 11b, the total basis weight (X g / m ２ ) is calculated based on the larger area of ​​the particle layer 11 or the fiber layer 12.

[0017] The water absorption rate of the first water absorbent resin particles 11a for physiological saline may be 20 seconds or less. When the water absorption rate of the first water absorbent resin particles 11a is 20 seconds or less and the basis weight of the first water absorbent resin particles 11a in one particle layer 11 is 40 g / m ２The combination of the above can exhibit particularly significant effects in terms of suppressing the liquid diffusion area in the absorbent article and suppressing the backflow of liquid from the absorbent article. From the same viewpoint, the water absorption speed of the first water-absorbent resin particles 11a with respect to physiological saline may be 18 seconds or less, 16 seconds or less, 14 seconds or less, 12 seconds or less, 10 seconds or less, 9 seconds or less, 8 seconds or less, 7 seconds or less, 6 seconds or less, 5 seconds or less, or 4 seconds or less. The water absorption speed of the first water-absorbent resin particles 11a with respect to physiological saline may be 0.5 seconds or more and 20 seconds or less, 18 seconds or less, 16 seconds or less, 14 seconds or less, 12 seconds or less, 10 seconds or less, 9 seconds or less, 8 seconds or less, 7 seconds or less, 6 seconds or less, 5 seconds or less, or 4 seconds or less. The water absorption rate of the first water-absorbent resin particles 11a for physiological saline may be 1 second or more and 20 seconds or less, 18 seconds or less, 16 seconds or less, 14 seconds or less, 12 seconds or less, 10 seconds or less, 9 seconds or less, 8 seconds or less, 7 seconds or less, 6 seconds or less, 5 seconds or less, or 4 seconds or less. The water absorption rates of the first water-absorbent resin particles 11a and the second water-absorbent resin particles 11b for physiological saline may be within these numerical ranges. The water absorption rates of the water-absorbent resin particles for physiological saline here are values ​​measured by the Vortex method, as described in the examples described later.

[0018] The first water-absorbent resin particles 11a may have a median particle diameter of 150 μm or more and 600 μm or less. When the median particle diameter of the first water-absorbent resin particles 11a is appropriately large, gel blocking is less likely to occur, and the time until a water-absorbent article to which a liquid has been supplied forms a dry surface can be further shortened. From the same viewpoint, the median particle diameter of the first water-absorbent resin particles 11a may be 180 μm or more, 200 μm or more, 220 μm or more, 250 μm or more, 270 μm or more, 280 μm or more, 290 μm or more, 300 μm or more, 310 μm or more, 320 μm or more, 330 μm or more, or 340 μm or more and 600 μm or less. The first water-absorbing resin particles 11a may have a median particle diameter of 150 μm or more, 180 μm or more, 200 μm or more, 220 μm or more, 250 μm or more, 270 μm or more, 280 μm or more, 290 μm or more, 300 μm or more, 310 μm or more, 320 μm or more, 330 μm or more, or 340 μm or more and 500 μm or less. The first water-absorbing resin particles 11a may have a median particle diameter of 150 μm or more, 180 μm or more, 200 μm or more, 220 μm or more, 250 μm or more, 270 μm or more, 280 μm or more, 290 μm or more, 300 μm or more, 310 μm or more, 320 μm or more, 330 μm or more, or 340 μm or more and 400 μm or less. The first water-absorbing resin particles 11a may have a median particle diameter of 150 μm or more, 180 μm or more, 200 μm or more, 220 μm or more, 250 μm or more, 270 μm or more, 280 μm or more, 290 μm or more, 300 μm or more, 310 μm or more, 320 μm or more, 330 μm or more, or 340 μm or more to 390 μm or less. The first water-absorbing resin particles 11a may have a median particle diameter of 150 μm or more, 180 μm or more, 200 μm or more, 220 μm or more, 250 μm or more, 270 μm or more, 280 μm or more, 290 μm or more, 300 μm or more, 310 μm or more, 320 μm or more, 330 μm or more, or 340 μm or more to 380 μm or less. The first water-absorbing resin particles 11a may have a median particle size of 150 μm or more, 180 μm or more, 200 μm or more, 220 μm or more, 250 μm or more, 270 μm or more, 280 μm or more, 290 μm or more, 300 μm or more, 310 μm or more, 320 μm or more, 330 μm or more, or 340 μm or more and 370 μm or less.The median particle diameters of the first water-absorbing resin particles 11 a and the second water-absorbing resin particles 11 b may be within these numerical ranges. The method for measuring the median particle diameter of the water-absorbing resin particles is as described in the examples described later.

[0019] The first water-absorbent resin particles 11a may have a water retention capacity of 30 g / g or more in physiological saline. When the first water-absorbent resin particles 11a have a large water retention capacity, backflow of liquid from the absorbent article can be further suppressed. From the same viewpoint, the water retention capacity of the first water-absorbent resin particles 11a in physiological saline may be 31 g / g or more, 32 g / g or more, 33 g / g or more, 34 g / g or more, 35 g / g or more, 36 g / g or more, 37 g / g or more, 38 g / g or more, 39 g / g or more, or 40 g / g or more. The water retention capacity of the first water absorbent resin particles 11a in physiological saline may be 30 g / g or more, 31 g / g or more, 32 g / g or more, 33 g / g or more, 34 g / g or more, 35 g / g or more, 36 g / g or more, 37 g / g or more, 38 g / g or more, 39 g / g or more, or 40 g / g or more and 60 g / g or less. The water retention capacity of the first water absorbent resin particles 11a in physiological saline may be 30 g / g or more, 31 g / g or more, 32 g / g or more, 33 g / g or more, 34 g / g or more, 35 g / g or more, 36 g / g or more, 37 g / g or more, 38 g / g or more, 39 g / g or more, or 40 g / g or more and 55 g / g or less. The water retention capacity of the first water-absorbent resin particles 11a in physiological saline may be 30 g / g or more, 31 g / g or more, 32 g / g or more, 33 g / g or more, 34 g / g or more, 35 g / g or more, 36 g / g or more, 37 g / g or more, 38 g / g or more, 39 g / g or more, or 40 g / g or more and 50 g / g or less. The method for measuring the water retention capacity of the water-absorbent resin particles in physiological saline is as described in the examples described later.

[0020] The first water-absorbent resin particles 11a may exhibit a water absorption under load of 5 mL / g or more for physiological saline. When the first water-absorbent resin particles 11a have a high water absorption under load, the time until a water-absorbent article supplied with a liquid forms a dry surface can be further shortened. From the same viewpoint, the water absorption under load of the first water-absorbent resin particles 11a for physiological saline may be 5 mL / g or more, 10 mL / g or more, 15 mL / g or more, or 20 mL / g or more. The water absorption under load of the first water-absorbent resin particles 11a for physiological saline may be 5 mL / g or more, 10 mL / g or more, 15 mL / g or more, or 20 mL / g or more and 40 mL / g or less. The water absorption under load of the first water-absorbent resin particles 11a for physiological saline may be 5 mL / g or more, 10 mL / g or more, 15 mL / g or more, or 20 mL / g or more and 35 mL / g or less. The water absorption under load of the first water-absorbent resin particles 11a in physiological saline may be 5 mL / g or more, 10 mL / g or more, 15 mL / g or more, or 20 mL / g or more and 30 mL / g or less. The water absorption under load of the first water-absorbent resin particles 11a in physiological saline may be 5 mL / g or more, 10 mL / g or more, 15 mL / g or more, or 20 mL / g or more and 25 mL / g or less. The method for measuring the water absorption under load of the water-absorbent resin particles in physiological saline is as described in the examples described later.

[0021] The basis weight of the hydrophilic fiber in the fiber layer 12 (Yg / m ２ ) is 20 g / m ２ 180g / m or more ２ If the basis weight of the hydrophilic fibers in the fiber layer 12 is within this range, the liquid diffusion area in the absorbent article can be suppressed while maintaining an appropriate water retention capacity of the absorbent body 10. From the same viewpoint, it is also preferable that the basis weight of the hydrophilic fibers in the fiber layer 12 is 20 g / m or less. ２ 160 g / m or more ２ Below, 140g / m ２ Below, 120g / m ２ Below, 100g / m ２ Below, 90g / m ２ Below, 80g / m ２ Below, 70g / m ２ Below, 60g / m ２ Below, 55g / m２ Less than or equal to 50g ２ The basis weight of the hydrophilic fibers in the fiber layer 12 may be 25 g / m or less. ２ 160 g / m or more ２ Below, 140g / m ２ Below, 120g / m ２ Below, 100g / m ２ Below, 90g / m ２ Below, 80g / m ２ Below, 70g / m ２ Below, 60g / m ２ Below, 55g / m ２ Less than or equal to 50g ２ The basis weight of the hydrophilic fibers in the fiber layer 12 may be 30 g / m or less. ２ 160 g / m or more ２ Below, 140g / m ２ Below, 120g / m ２ Below, 100g / m ２ Below, 90g / m ２ Below, 80g / m ２ Below, 70g / m ２ Below, 60g / m ２ Below, 55g / m ２ Less than or equal to 50g ２ The basis weight of the hydrophilic fibers in the fiber layer 12 may be 35 g / m or less. ２ 160 g / m or more ２ Below, 140g / m ２ Below, 120g / m ２ Below, 100g / m ２ Below, 90g / m ２ Below, 80g / m ２ Below, 70g / m ２ Below, 60g / m ２ Below, 55g / m ２ Less than or equal to 50g ２ The basis weight of the hydrophilic fibers in the fiber layer 12 may be 40 g / m or less. ２ 160 g / m or more ２ Below, 140g / m ２ Below, 120g / m ２ Below, 100g / m ２ Below, 90g / m ２ Below, 80g / m ２Below, 70g / m ２ Below, 60g / m ２ Below, 55g / m ２ Less than or equal to 50g ２ The basis weight of the hydrophilic fibers in the fiber layer 12 may be 45 g / m or less. ２ 160 g / m or more ２ Below, 140g / m ２ Below, 120g / m ２ Below, 100g / m ２ Below, 90g / m ２ Below, 80g / m ２ Below, 70g / m ２ Below, 60g / m ２ Below, 55g / m ２ Less than or equal to 50g ２ It may be the following:

[0022] Examples of hydrophilic fibers include cellulose fibers such as cotton pulp and chemical pulp, and artificial cellulose fibers such as rayon and acetate. The absorbent body may further contain hydrophobic fibers made of synthetic resins such as polyamide, polyester, and polyolefin as a reinforcing agent.

[0023] The liquid-permeable sheet 30 may be, for example, a nonwoven fabric, a porous resin sheet, tissue, or a combination thereof. The nonwoven fabric may contain resin fibers such as polyethylene, polypropylene, polyester, polyamide, or the like.

[0024] The absorbent body 10 can be manufactured by a method including, for example, forming a fiber layer 12 containing hydrophilic fibers, and forming a particle layer 11 containing first water-absorbent resin particles 11a on one or both sides of the fiber layer 12. When the fiber layer 12 further contains second water-absorbent resin particles 11b as in the absorbent article 51 of Fig. 2, for example, the fiber layer 12 can be formed by mixing and depositing the hydrophilic fibers and the second water-absorbent resin particles 11b.

[0025] The first water-absorbing resin particles 11 a and the second water-absorbing resin particles 11 b can be obtained by, for example, a conventional method including polymerizing a water-soluble ethylenically unsaturated monomer. The polymerization method may be, for example, reverse-phase suspension polymerization in a reaction liquid including an aqueous liquid and an oily liquid, or aqueous solution polymerization in an aqueous solution including the water-soluble ethylenically unsaturated monomer.

[0026] The reversed-phase suspension polymerization method includes, for example, polymerizing the water-soluble ethylenically unsaturated monomer by reversed-phase suspension polymerization in a reaction solution containing a water-soluble ethylenically unsaturated monomer, a radical polymerization initiator, water, a dispersion medium, and a surfactant to form a particulate hydrogel polymer containing a polymer of the water-soluble ethylenically unsaturated monomer and water, extracting a portion of the water from the reaction solution to form a concentrate, and surface-crosslinking the aggregated particles in a mixture containing the concentrate and a surface-crosslinking agent. Prior to surface-crosslinking, the hydrogel polymer may be aggregated in the reaction solution to form aggregated particles containing a plurality of hydrogel polymers. The reaction solution for polymerization may also contain an internal crosslinking agent that crosslinks the polymer.

[0027] The aqueous solution polymerization method includes, for example, polymerizing an ethylenically unsaturated monomer in an aqueous monomer solution containing the ethylenically unsaturated monomer, a radical polymerization initiator, and water to form a massive hydrogel polymer containing the polymer and water, crushing the hydrogel polymer to form a crushed product, drying the crushed product to obtain a dried product, pulverizing the dried product to obtain polymer particles, and surface-crosslinking the polymer particles in a mixture containing the polymer particles and a surface-crosslinking agent. The aqueous monomer solution for polymerization may contain an internal crosslinking agent.

[0028] As will be understood by a person skilled in the art, water absorption properties such as water absorption rate, water retention amount, and water absorption amount under load of a water absorbent resin particle can be adjusted by the amount of an internal crosslinking agent, the amount of a surface crosslinking agent, stirring conditions of a reaction liquid, particle diameter, etc.

[0029] Examples of the water-soluble ethylenically unsaturated monomer include an ethylenically unsaturated monomer having at least one functional group selected from the group consisting of a carboxyl group, a sulfo group, an amide group, an amino group, etc. When the water-soluble ethylenically unsaturated monomer contains an amino group, the amino group may be quaternized.

[0030] The water-soluble ethylenically unsaturated monomer may include, for example, at least one selected from the group consisting of (meth)acrylic acid (hereinafter, "acrylic" and "methacrylic" will be collectively referred to as "(meth)acrylic") and its alkali salt, 2-(meth)acrylamido-2-methylpropanesulfonic acid and its alkali salt, (meth)acrylamide, N,N-dimethyl(meth)acrylamide, 2-hydroxyethyl(meth)acrylate, N-methylol(meth)acrylamide, polyethylene glycol mono(meth)acrylate, N,N-diethylaminoethyl(meth)acrylate, N,N-diethylaminopropyl(meth)acrylate, and diethylaminopropyl(meth)acrylamide. The water-soluble ethylenically unsaturated monomer may include (meth)acrylic acid and its alkali metal salt, or may include acrylic acid and its alkali metal salt. The proportion of (meth)acrylic acid and its alkali metal salts in the water-soluble ethylenically unsaturated monomers in the reaction solution may be 60 mol% or more, 70 mol% or more, 80 mol% or more, 90 mol% or more, or 95 mol% or more, or may be substantially 100 mol%. The proportion of monomer units derived from (meth)acrylic acid or its alkali metal salts in the total amount of monomer units constituting the polymer formed by polymerization may be within the above range.

[0031] The post-drop return amount of the absorbent article may be 8.5 g or less, or may be 0.1 g or more and 8.5 g or less. The post-drop return amount is measured by placing the absorbent article on a horizontal table with the liquid-permeable sheet facing up, and dripping 30 mL of test liquid adjusted to 25 ± 1 °C from a 0.4 mm inner diameter inlet 1 cm above the absorbent article toward the center of the absorbent article over 10 seconds. Immediately after the test liquid dripping is completed, a 100 mm x 100 mm filter paper whose mass has been measured in advance is placed at the location where the test liquid was dripped, and a 0.7 psi weight is applied to it for 3 seconds. The weight and filter paper are then removed, and the mass of the test liquid absorbed by the filter paper is taken as the post-drop return amount [g]. The test liquid is prepared by dissolving 45.0 g of NaCl in 4955.0 g of ion-exchanged water and adding a small amount of Blue No. 1. The amount of backflow after 1 minute, the diffusion area and the whitening time, which will be described below, are also measured using the same test liquid.

[0032] When the test liquid is dropped onto the liquid-permeable sheet side of the absorbent article, the spread area of ​​the test liquid is 150 cm ２ It may be less than 10 cm ２ More than 150cm ２ It may be the following:

[0033] The diffusion area was determined by placing the absorbent article on a horizontal table with the liquid-permeable sheet facing upward, dropping 30 mL of test liquid adjusted to 25±1°C from an inlet with an inner diameter of 0.4 mm from 1 cm above the absorbent article toward the center of the absorbent article over 10 seconds, and measuring the maximum length d1 in the longitudinal direction of the absorbent article and the maximum length d2 in the direction perpendicular to the longitudinal direction for the area where the test liquid has diffused within the absorbent article 50, two minutes after the completion of dropping the test liquid. The diffusion area [cm ２ ] is measured by calculating the diffusion area [cm ２ ]=(d1 / 2)×(d2 / 2)×3.14

[0034] The whitening time when the test liquid is dropped onto the liquid-permeable sheet side of the absorbent article may be 55 seconds or less, or may be 5 seconds or more and 55 seconds or less.

[0035] The whitening time is the time it takes for the absorbent article to re-form a dry surface after the test liquid has been dropped. The whitening time is measured by placing the absorbent article on a horizontal table with the liquid-permeable sheet facing up, dropping 30 mL of test liquid adjusted to 25±1°C from a 0.4 mm inner diameter opening toward the center of the absorbent article from a position 1 cm above the absorbent article over 10 seconds, and recording the time from the completion of dropping the test liquid until the color of the liquid-permeable sheet changes to a color close to its original color as the whitening time. The term "whitening time" is used here because liquid-permeable sheets are often white, but the whitening time can be measured in a similar manner even when the liquid-permeable sheet is of another color.

[0036] The absorbent article may be, for example, a waterproof nursing sheet, a disposable diaper, a sanitary napkin, a tampon, or a pet sheet.

[0037] The present invention is not limited to the following examples.

[0038] 1. Preparation of Water-Absorbent Resin Particles Production Example 1 Polymerization Step A round-bottomed cylindrical separable flask (baffle width: 7 mm, baffle length: 10 cm) with an inner diameter of 11 cm and a capacity of 2 L and equipped with four sidewall baffles (baffle width: 7 mm, baffle length: 10 cm) was prepared, equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a stirrer. A stirring blade A having two stages of four inclined paddle blades with a blade diameter of 5 cm and surface-treated with a fluororesin was attached to the stirrer. 472.3 g of n-heptane and 1.10 g of sorbitan monolaurate (surfactant, Nonion LP-20R, HLB: 8.6, manufactured by NOF Corporation) were placed in the prepared separable flask. The mixture in the separable flask was heated to 50 ° C while stirring with a stirrer at a rotation speed of 300 rpm, thereby dissolving the sorbitan monolaurate in n-heptane. The mixture was then cooled to 45 ° C.

[0039] A 500 mL Erlenmeyer flask was charged with 92.0 g of an 80.5 wt% aqueous acrylic acid solution (1.03 mol of acrylic acid). While cooling with ice from the outside, 147.7 g of a 20.9 wt% aqueous sodium hydroxide solution was added dropwise to neutralize 75 mol% of the acrylic acid. 0.101 g (0.374 mmol) of potassium persulfate was dissolved in the partially neutralized acrylic acid solution formed by the neutralization to form a monomer aqueous solution.

[0040] The resulting aqueous monomer solution was added to the mixture in the separable flask, and the atmosphere in the system containing the resulting reaction solution was thoroughly purged with nitrogen. The reaction solution was then stirred with a stirrer at 700 rpm, while the separable flask was immersed in a water bath at 70°C and maintained in this state for 60 minutes to allow the polymerization reaction to proceed. As the polymerization reaction proceeded, a particulate hydrogel polymer was formed in the reaction solution.

[0041] A dispersion containing 0.014 g of amorphous silica particles (flocculant, Toxil NP-S, Oriental Silicas Corporation) and 100 g of n-heptane was added to the reaction solution containing the produced hydrogel polymer, n-heptane, and surfactant while stirring at 1,000 rpm. The reaction solution was then stirred for 10 minutes. The hydrogel polymer flocculated in the reaction solution to form aggregated particles.

[0042] To the reaction solution containing the aggregated particles, 0.41 g of an aqueous solution of ethylene glycol diglycidyl ether (ethylene glycol diglycidyl ether (intermediate crosslinking agent): 0.048 mmol) with a concentration of 2% by mass was added. Thereafter, the reaction solution in the separable flask was stirred for 30 minutes while being heated in a water bath at 75°C, thereby allowing intermediate crosslinking to proceed.

[0043] Concentration The reaction mixture in the separable flask was heated in an oil bath at 125° C., and 106.1 g of water was extracted from the system by azeotropic distillation of n-heptane and water while refluxing n-heptane.

[0044] Surface crosslinking 4.14 g of a 2 mass% aqueous solution of ethylene glycol diglycidyl ether (ethylene glycol diglycidyl ether (surface crosslinking agent): 0.48 mmol) was mixed with the concentrate formed by removing water. The mixture was kept at an internal temperature of 83±2°C for 2 hours to allow surface crosslinking to proceed in the mixture.

[0045] Drying The mixture after surface cross-linking was heated to 125°C, and water and n-heptane were evaporated until almost no evaporants were distilled from the system, thereby obtaining a powder of dried polymer particles (aggregated particles). This powder was passed through a sieve with an opening of 850 µm, thereby obtaining 86.10 g of water-absorbent resin particles of Production Example 1.

[0046] Preparation Example 2 Polymerization Step A round-bottomed cylindrical separable flask (baffle width: 7 mm, baffle length: 10 cm) with an inner diameter of 11 cm and a capacity of 2 L and equipped with four side wall baffles (baffle width: 7 mm, baffle length: 10 cm) was prepared, equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a stirrer. A stirring blade B, the outline of which is shown in FIG. 4, was attached to the stirrer. The stirring blade B had a shaft 200a and a flat plate portion 200b. The flat plate portion 200b was welded to the shaft 200a and had a curved tip. Four slits S extending along the axial direction of the shaft 200a were formed in the flat plate portion 200b. The four slits S were arranged in the width direction of the flat plate portion 200b. The width of the two inner slits S was 1 cm. The width of the two outer slits S was 0.5 cm. The length of the flat plate portion 200b was approximately 10 cm, and the width of the flat plate portion 200b was approximately 6 cm.

[0047] 472.3 g of n-heptane and 0.74 g of sorbitan monolaurate (surfactant, Nonion LP-20R, HLB: 8.6, manufactured by NOF Corporation) were placed in the prepared separable flask. The mixture in the separable flask was heated to 50°C while being stirred with a stirrer at a rotation speed of 300 rpm, thereby dissolving the sorbitan monolaurate in the n-heptane. The mixture was then cooled to 45°C.

[0048] A 500 mL Erlenmeyer flask was charged with 92.0 g of an 80.5 wt% aqueous acrylic acid solution (1.03 mol of acrylic acid). While cooling with ice from the outside, 147.7 g of a 20.9 wt% aqueous sodium hydroxide solution was added dropwise to neutralize 75 mol% of the acrylic acid. 0.101 g (0.374 mmol) of potassium persulfate was dissolved in the partially neutralized acrylic acid solution formed by the neutralization to form a monomer aqueous solution.

[0049] The resulting monomer aqueous solution was added to the mixture in the separable flask, and the system containing the resulting reaction solution was thoroughly purged with nitrogen. The reaction solution was then stirred with a stirrer at 300 rpm, while the separable flask was immersed in a water bath at 70°C and held in that state for 60 minutes to allow the polymerization reaction to proceed. As the polymerization reaction proceeded, a particulate hydrogel polymer was formed in the reaction solution.

[0050] Aggregation Step: The agitator blade B was replaced with agitator blade A having two stages of four inclined paddle blades with a blade diameter of 5 cm, and while stirring at a rotation speed of 1000 rpm, a dispersion containing 0.0138 g of amorphous silica particles (flocculant, Oriental Silicas Corporation, Toxil NP-S) and 100 g of n-heptane was added to the reaction solution containing the produced hydrogel polymer, n-heptane, and surfactant. The reaction solution was then stirred for 10 minutes. Aggregated particles were formed by aggregation of the hydrogel polymer in the reaction solution.

[0051] To the reaction solution containing the aggregated particles, 0.41 g of an aqueous solution of ethylene glycol diglycidyl ether (ethylene glycol diglycidyl ether (intermediate crosslinking agent): 0.048 mmol) with a concentration of 2% by mass was added. Thereafter, the reaction solution in the separable flask was stirred for 30 minutes while being heated in a water bath at 75°C, thereby allowing intermediate crosslinking to proceed.

[0052] Concentration The reaction solution in the separable flask was heated in an oil bath at 125° C., and 110.7 g of water was extracted from the system by azeotropic distillation of n-heptane and water while refluxing n-heptane.

[0053] Surface crosslinking 4.14 g of a 2 mass% aqueous solution of ethylene glycol diglycidyl ether (ethylene glycol diglycidyl ether (surface crosslinking agent): 0.48 mmol) was mixed with the concentrate formed by removing water. The mixture was kept at an internal temperature of 83±2°C for 2 hours to allow surface crosslinking to proceed in the mixture.

[0054] Drying The mixture after surface crosslinking was heated to 120°C, and water and n-heptane were evaporated until almost no evaporants were distilled out from the system, thereby obtaining a powder of dried polymer particles (aggregated particles). This powder was passed through a sieve with an opening of 850 µm, thereby obtaining 79.7 g of water-absorbent resin particles of Production Example 2.

[0055] Production Example 3 Polymerization Step <First-Stage Polymerization Reaction> A round-bottomed, cylindrical, separable flask with an inner diameter of 11 cm and a capacity of 2 L was prepared, equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a stirrer. A stirring blade A was attached to the stirrer. 293 g of n-heptane and 0.736 g of maleic anhydride-modified ethylene-propylene copolymer (hydrophobic polymer dispersant, Mitsui Chemicals, Inc., Hiwax 1105A) were placed in the separable flask. The mixture in the separable flask was heated to 80°C while stirring with the stirrer at a rotation speed of 300 rpm, thereby dissolving the hydrophobic polymer dispersant in n-heptane. The mixture was then cooled to 50°C.

[0056] A 300 mL beaker was charged with 92.0 g of an 80.5 wt% aqueous acrylic acid solution (1.03 mol of acrylic acid). 147.7 g of a 20.9 wt% aqueous sodium hydroxide solution was added dropwise to the beaker while cooling with ice from the outside, thereby neutralizing 75 mol% of the acrylic acid. 0.092 g of hydroxyethyl cellulose (thickener, Sumitomo Seika Chemicals Co., Ltd., HECAW-15F), 0.0736 g of potassium persulfate (water-soluble radical polymerization initiator, 0.272 mmol), and 0.010 g of ethylene glycol diglycidyl ether (internal crosslinking agent, 0.057 mmol) were dissolved in the partially neutralized acrylic acid solution formed by neutralization to prepare a first-stage monomer aqueous solution.

[0057] The first-stage monomer aqueous solution was added to the mixture in the separable flask, and the resulting reaction solution was stirred for 10 minutes using a stirrer at 300 rpm. Subsequently, a surfactant solution containing 6.62 g of n-heptane and 0.736 g of sucrose stearate (surfactant, HLB: 3, Mitsubishi Chemical Foods Corporation, Ryoto Sugar Ester S-370) was further added. The reaction solution was stirred using a stirrer at 550 rpm while the system was thoroughly purged with nitrogen. The separable flask was then immersed in a 70°C water bath and maintained there for 60 minutes to allow the polymerization reaction to proceed. A first-stage polymerization slurry was formed as a result of the polymerization reaction.

[0058] <Second-stage polymerization reaction> 128.8 g of an 80.5 wt% aqueous acrylic acid solution (acrylic acid: 1.44 mol) was placed in a 500 mL beaker. While cooling with ice from the outside, 159.0 g of a 27 wt% aqueous sodium hydroxide solution was added dropwise to neutralize 75 mol% of the acrylic acid. 0.090 g (0.333 mmol) of potassium persulfate and 0.0116 g of ethylene glycol diglycidyl ether (internal crosslinking agent, 0.067 mmol) were dissolved in the partially neutralized acrylic acid solution formed by neutralization to prepare a second-stage aqueous monomer solution.

[0059] The separable flask was cooled to 25°C while stirring the first-stage polymerization slurry with a stirrer at a rotation speed of 1000 rpm. Thereafter, the entire amount of the second-stage aqueous monomer solution was added to the first-stage polymerization slurry, and the system was purged with nitrogen over 30 minutes. The separable flask was again immersed in a water bath at 70°C and maintained in this state for 60 minutes to allow the polymerization reaction to proceed. A reaction liquid containing a particulate hydrogel polymer was obtained by the polymerization reaction.

[0060] After the polymerization reaction, 0.589 g of a 45% by mass aqueous solution of pentasodium diethylenetriaminepentaacetate (pentasodium diethylenetriaminepentaacetate: 0.527 mmol) was added to the reaction solution containing the hydrous gel polymer under stirring. The separable flask was then immersed in an oil bath set at 125°C, and 256.8 g of water was extracted from the system by azeotropic distillation of n-heptane and water while refluxing the n-heptane.

[0061] To the concentrate (hydrogel polymer) after water removal, 4.42 g of a 2 mass% aqueous solution of ethylene glycol diglycidyl ether (surface cross-linking agent, ethylene glycol diglycidyl ether: 0.507 mmol) was added. The internal temperature of the separable flask was maintained at 83±2°C for 2 hours to allow surface cross-linking to proceed in the mixture.

[0062] Drying The surface-crosslinked mixture was heated in an oil bath at 125°C, and water and n-heptane were evaporated until almost no evaporants were distilled from the system, thereby obtaining a powder of dried polymer particles. This powder was passed through a sieve with an opening of 850 μm. The polymer particles that had passed through the sieve were mixed with 0.5% by mass of amorphous silica particles (lubricant, Oriental Silicas Corporation, Toxil NP-S) relative to the mass of the polymer particles, thereby obtaining 230.2 g of water-absorbent resin particles of Production Example 3 in which amorphous silica particles as a lubricant were attached to the polymer particles.

[0063] Production Example 4

[0123] 77.2 g of water absorbent resin particles of Production Example 4 were obtained under the same conditions as those of Production Example 1, except that the stirring blade for stirring the reaction liquid during the polymerization reaction was changed to the stirring blade B, the rotation speed of the stirrer during the polymerization reaction was changed to 300 rpm, amorphous silica particles for forming aggregated particles after the polymerization reaction were not added, and 107.9 g of water was extracted out of the system while refluxing n-heptane by azeotropic distillation of n-heptane and water.

[0064]

[0123] PRODUCTION EXAMPLE 5

[0124] 86.7 g of water absorbent resin particles of Production Example 5 were obtained under the same conditions as those of Production Example 1, except that the stirring blade stirring the reaction liquid during the polymerization reaction was changed to the stirring blade B, the rotation speed of the stirrer during the polymerization reaction was changed to 300 rpm, and after 106.1 g of water was extracted to the outside of the system by azeotropic distillation, 0.204 g of an aqueous solution of pentasodium diethylenetriaminepentaacetate having a concentration of 45 mass% (pentasodium diethylenetriaminepentaacetate: 0.182 mmol) was added before the addition of a surface crosslinking agent.

[0065]

[0113] Production Example 6

[0114] 87.7 g of water absorbent resin particles of Production Example 6 were obtained under the same conditions as those of Production Example 1, except that the stirring blade stirring the reaction liquid during the polymerization reaction was changed to the stirring blade B, the rotation speed of the stirrer during the polymerization reaction was changed to 300 rpm, the amount of water extracted by azeotropic distillation was 109.9 g, and after the water was extracted to the outside of the system, 0.204 g of an aqueous solution of pentasodium diethylenetriaminepentaacetate having a concentration of 45 mass % (pentasodium diethylenetriaminepentaacetate: 0.182 mmol) was added before the addition of a surface crosslinking agent.

[0066] 2. Evaluation of Water-Absorbent Resin Particles The water-absorbent resin particles of each Production Example were evaluated by the following method. Unless otherwise specified, measurements were carried out in an environment of a temperature of 25±2°C and a humidity of 50±10%. The evaluation results are shown in Table 1.

[0067] Water absorption rate The water absorption rate of the water-absorbent resin particles was measured by the Vortex method. 50±0.1 g of saline solution and a magnetic stirrer bar (8 mmφ×30 mm without ring) were placed in a 100 mL beaker. The beaker was immersed in a thermostatic water bath to adjust the liquid temperature to 25±0.2 ° C. Next, the beaker was placed on a magnetic stirrer, and the saline solution was stirred at a rotation speed of 600 rpm to generate a vortex, and 2.0 g of water-absorbent resin particles were quickly added thereto. The time (seconds) from the time the water-absorbent resin particles were added to the time the vortex on the liquid surface converged due to water absorption by the water-absorbent resin particles was measured, and this was taken as the water absorption rate of the water-absorbent resin particles.

[0068] Water Retention Capacity A cotton bag (membrane broadcloth No. 60, 100 mm wide x 200 mm long) containing 2.0 g of water-absorbent resin particles was placed in a 500 mL beaker. 500 g of saline solution was poured into the cotton bag containing the water-absorbent resin particles all at once, taking care not to allow the bag to become lumpy, and the top of the cotton bag was tied with a rubber band. The cotton bag was left to stand for 30 minutes to allow the water-absorbent resin particles in the cotton bag to swell. The swollen gel in the cotton bag was then dehydrated for 1 minute using a dehydrator (manufactured by Kokusan Co., Ltd., product number: H-122) set to a centrifugal force of 167 G. The mass Wa (g) of the cotton bag containing the swollen gel after dehydration was measured. The same procedure was performed on a cotton bag containing no water-absorbent resin particles, and the empty mass Wb (g) of the cotton bag when wet was measured. The water retention capacity of the water-absorbent resin particles in saline solution was calculated using the following formula: Water retention capacity [g / g] = (Wa - Wb) / 2.0

[0069] Water Absorption Under Load The water absorption under load of the water-absorbent resin particles in physiological saline was measured using a measuring device Y shown in FIG. 5. The measuring device Y is composed of a burette unit 61, a conduit 62, a measurement table 63, and a measurement unit 64 placed on the measurement table 63. The burette unit 61 has a burette 61a extending vertically, a rubber stopper 61b arranged at the upper end of the burette 61a, a cock 61c arranged at the lower end of the burette 61a, an air introduction tube 61d having one end extending into the burette 61a near the cock 61c, and a cock 61e arranged at the other end of the air introduction tube 61d. The conduit 62 is attached between the burette unit 61 and the measurement table 63. The inner diameter of the conduit 62 is 6 mm. A hole with a diameter of 2 mm is drilled in the center of the measurement table 63, and the conduit 62 is connected to it. The measuring unit 64 has a cylinder 64a (made of acrylic resin (Plexiglas)), a nylon mesh 64b adhered to the bottom of the cylinder 64a, and a weight 64c. The inner diameter of the cylinder 64a is 20 mm. The openings of the nylon mesh 64b are 75 μm (200 mesh). During measurement, the water-absorbent resin particles 11a to be measured are uniformly scattered on the nylon mesh 64b. The diameter of the weight 64c is 19 mm, and the mass of the weight 64c is 59.8 g. The weight 64c is placed on the water-absorbent resin particles 11a, and can apply a load of 2.07 kPa to the water-absorbent resin particles 11a.

[0070] 0.100 g of water-absorbent resin particles 11a were placed in the cylinder 64a of the measuring device Y. A weight 64c was placed on the water-absorbent resin particles 11a, and the cocks 61c and 61e were opened to start the measurement. Since air of the same volume as the physiological saline solution absorbed by the water-absorbent resin particles 11a was quickly and smoothly supplied into the burette 61a through the air inlet tube 61d, the decrease in the level of the physiological saline solution inside the burette 61a corresponds to the amount of physiological saline solution absorbed by the water-absorbent resin particles 11a. The scale of the burette 61a is marked from top to bottom in increments of 0 mL to 0.5 mL. The scale Va of the burette 61a before the start of water absorption and the scale Vb of the burette 61a 60 minutes after the start of water absorption were read as the level of the physiological saline solution, and the amount of water absorption under load was calculated using the following formula: Water absorption under load [mL / g] = (Vb - Va) / 0.1

[0071] Median Particle Diameter The water-absorbent resin particles were passed through a JIS Z 8801-1 standard sieve having a mesh size of 250 μm. When the amount remaining on the sieve relative to the total amount was 50 mass% or more, the median particle diameter was measured using the following combination of sieves (A); when the amount remaining on the sieve relative to the total amount was less than 50 mass%, the median particle diameter was measured using the following combination of sieves (B). (A) The JIS standard sieves were combined in the following order from top to bottom: a sieve with a mesh size of 710 μm, a sieve with a mesh size of 600 μm, a sieve with a mesh size of 500 μm, a sieve with a mesh size of 425 μm, a sieve with a mesh size of 300 μm, a sieve with a mesh size of 250 μm, a sieve with a mesh size of 150 μm, and a tray. (B) JIS standard sieves were arranged in the following order from top to bottom: a sieve with a mesh size of 425 μm, a sieve with a mesh size of 250 μm, a sieve with a mesh size of 180 μm, a sieve with a mesh size of 150 μm, a sieve with a mesh size of 106 μm, a sieve with a mesh size of 75 μm, a sieve with a mesh size of 45 μm, and a tray.

[0072] Water-absorbent resin particles were placed in the sieve located at the top stage, and the particles were shaken for 10 minutes using a continuous fully automatic ultrasonic vibration sieving measuring instrument (Robot Sifter RPS-205, manufactured by Seishin Enterprise Co., Ltd.) to classify the water-absorbent resin particles. After classification, the ratio (mass percentage) of the mass of the water-absorbent resin particles remaining on each sieve to the total mass was calculated. By integrating the proportions of the fractions in order from the largest particle diameter, the relationship between the sieve opening and the integrated value of the proportion of the water-absorbent resin particles remaining on the sieve was plotted on logarithmic probability paper. By connecting the plots on the probability paper with a straight line, the particle diameter corresponding to an integrated mass percentage of 50% by mass was determined, and this value was taken as the median particle diameter.

[0073]

[0074] 4. Preparation of absorbent article Example 1: Absorbent article having a size of 20 cm x 60 cm and a basis weight of 16 g / m ２ A first shape-retaining member (tissue) of 10 cm was prepared. 5.4 g of hydrophilic fibers (ground pulp) were deposited on this first shape-retaining member by air-pressure forming using an airflow mixer (Autech Co., Ltd., Pad Former) to form a fiber layer covering the entire upper surface of the first shape-retaining member. 10 cm sections were cut off from both longitudinal ends of the laminate of the first shape-retaining member and the fiber layer. The remaining laminate was divided into two equal parts to obtain two laminates measuring 20 cm x 20 cm.

[0075] 1.0 g of water was uniformly sprayed onto each of the two laminates using a spray bottle, and then a load of 500 kPa was applied for 30 seconds. Thereafter, the water-absorbent resin particles (3.0 g, first water-absorbent resin particles) of Production Example 1 were uniformly scattered on the fiber layer to form a particle layer. ２ The second shape-retaining member (tissue) was layered on the particle layer to obtain a layered body having, from the bottom, the first shape-retaining member, the fiber layer, the particle layer, and the second shape-retaining member.

[0076] On the second shape-retaining member of this laminate, an air-through nonwoven fabric (KNH Enterprise Co., Ltd., basis weight: 25 g / m) having a size of 20 cm x 20 cm and coated with a hot melt adhesive (ME-765E, Henkel Japan Co., Ltd.) was placed. ２) was laminated in a direction in which the hot melt adhesive contacted the second shape-retaining member, thereby obtaining an absorbent article. 0.1 g of the hot melt adhesive was applied to the air-through nonwoven fabric so as to form a spiral stripe pattern of 20 stripes arranged at 10 mm intervals. In the absorbent body of the obtained sheet-like absorbent article, the basis weight of the water-absorbent resin particles was 75 g / m ２ The weight of the hydrophilic fiber (crushed pulp) is 45 g / m ２ It was.

[0077] Example 2 An absorbent article was produced in the same manner as in Example 1, except that the amount of the water-absorbent resin particles (first water-absorbent resin particles) in Production Example 1 was changed to 4.0 g. In the absorbent body of the obtained absorbent article, the basis weight of the water-absorbent resin particles was 100 g / m ２ The weight of the hydrophilic fiber (crushed pulp) is 45 g / m ２ It was.

[0078] Example 3 An absorbent article was produced in the same manner as in Example 1, except that the amount of the water-absorbent resin particles (first water-absorbent resin particles) in Production Example 1 was changed to 8.0 g. In the absorbent body of the obtained absorbent article, the basis weight of the water-absorbent resin particles was 200 g / m ２ The weight of the hydrophilic fiber (crushed pulp) is 45 g / m ２ It was.

[0079] Example 4 An absorbent article was produced in the same manner as in Example 1, except that the amount of hydrophilic fiber (crushed pulp) was changed to 3.6 g. In the absorbent core of the obtained absorbent article, the basis weight of the water-absorbent resin particles was 75 g / m. ２ The weight of the hydrophilic fiber (crushed pulp) is 30 g / m ２ It was.

[0080] Example 5: 20 cm x 60 cm size, basis weight 16 g / m ２A first shape-retaining member (tissue) of 100 mm was prepared. 5.4 g of hydrophilic fibers (ground pulp) were deposited on this first shape-retaining member by air-pressure forming using an airflow mixer (Autech Co., Ltd., Pad Former) to form a fiber layer covering the entire upper surface of the first shape-retaining member. 10 cm sections were cut off from both longitudinal ends of the laminate of the first shape-retaining member and the fiber layer. The remaining laminate was divided into two equal parts, yielding two laminates measuring 20 cm x 20 cm. The fiber layers of each of the two laminates were carefully removed from the first shape-retaining member. 1.0 g of water was evenly sprayed onto the removed fiber layer using a spray bottle, and then a load of 500 kPa was applied for 30 seconds. The water-absorbent resin particles (3.0 g, first water-absorbent resin particles) of Production Example 1 were evenly dispersed on the first shape-retaining member to form a particle layer. The fiber layer is placed on the particle layer, and a 20 cm x 20 cm sheet having a basis weight of 16 g / m is placed on the fiber layer. ２ The second shape-retaining member (tissue) was then layered on the first shape-retaining member to obtain a layered body having, from the bottom, the first shape-retaining member, the particle layer, the fiber layer, and the second shape-retaining member.

[0081] On the second shape-retaining member of this laminate, an air-through nonwoven fabric (KNH Enterprise Co., Ltd., basis weight: 25 g / m) having a size of 20 cm x 20 cm and coated with a hot melt adhesive (ME-765E, Henkel Japan Co., Ltd.) was placed. ２ ) was laminated in a direction in which the hot melt adhesive contacted the second shape-retaining member, thereby obtaining an absorbent article. 0.1 g of the hot melt adhesive was applied to the air-through nonwoven fabric so as to form a spiral stripe pattern of 20 stripes arranged at 10 mm intervals. In the absorbent body of the obtained sheet-like absorbent article, the basis weight of the water-absorbent resin particles was 75 g / m ２ The weight of the hydrophilic fiber (crushed pulp) is 45 g / m ２ It was.

[0082] Example 6 An absorbent article was produced in the same manner as in Example 1, except that the amount of hydrophilic fiber (crushed pulp) was changed to 12.0 g. In the absorbent core of the obtained absorbent article, the basis weight of the water-absorbent resin particles was 75 g / m. ２and the weight of the hydrophilic fiber (crushed pulp) is 100 g / m ２ It was.

[0083] Example 7 An absorbent article was produced in the same manner as in Example 1, except that the water-absorbent resin particles (first water-absorbent resin particles) were changed to the water-absorbent resin particles of Production Example 2. In the absorbent body of the obtained absorbent article, the basis weight of the water-absorbent resin particles was 75 g / m ２ The weight of the hydrophilic fiber (crushed pulp) is 45 g / m ２ It was.

[0084] Example 8: 20 cm x 60 cm size, basis weight 16 g / m ２ A first shape-retaining member (tissue) of 100 mm was prepared. 5.4 g of hydrophilic fibers (ground pulp) and the water-absorbent resin particles (0.9 g, second water-absorbent resin particles) of Production Example 1 were deposited on this first shape-retaining member by air-pressure forming using an airflow mixer (Autech Co., Ltd., Pad Former) to form a fiber layer covering the entire upper surface of the first shape-retaining member and containing a uniform mixture of water-absorbent resin particles in the hydrophilic fibers. 10 cm sections were cut off from both longitudinal ends of the laminate of the first shape-retaining member and the fiber layer. The remaining laminate was divided into two equal parts, yielding two laminates measuring 20 cm x 20 cm.

[0085] 1.0 g of water was uniformly sprayed onto each of the two laminates using a spray bottle, and then a load of 500 kPa was applied for 30 seconds. Thereafter, the water-absorbent resin particles (2.7 g, first water-absorbent resin particles) of Production Example 1 were uniformly spread on the fiber layer to form a particle layer. ２ The second shape-retaining member (tissue) was layered on the particle layer to obtain a layered body having, from the bottom, the first shape-retaining member, the mixed layer, the particle layer, and the second shape-retaining member.

[0086] On the second shape-retaining member of this laminate, an air-through nonwoven fabric (KNH Enterprise Co., Ltd., basis weight: 25 g / m) having a size of 20 cm x 20 cm and coated with a hot melt adhesive (Henkel Japan Co., Ltd., ME-765E) was applied. ２) was laminated in a direction in which the hot melt adhesive contacted the second shape-retaining member, thereby obtaining an absorbent article. 0.1 g of the hot melt adhesive was applied to the air-through nonwoven fabric so as to form a spiral stripe pattern of 20 stripes arranged at 10 mm intervals. In the absorbent body of the obtained sheet-like absorbent article, the total basis weight of the water-absorbent resin particles was 75 g / m ２ The weight of the hydrophilic fiber (crushed pulp) is 45 g / m ２ It was.

[0087] Example 9 An absorbent article was obtained in the same manner as in Example 8, except that the amount of water-absorbent resin particles (second water-absorbent resin particles) mixed in the fiber layer was changed to 2.7 g, and the amount of water-absorbent resin particles (first water-absorbent resin particles) for forming the particle layer was changed to 2.1 g. In the absorbent body of the obtained sheet-like absorbent article, the total basis weight of the water-absorbent resin particles was 75 g / m ２ The weight of the hydrophilic fiber (crushed pulp) is 45 g / m ２ It was.

[0088] Example 10 An absorbent article was produced in the same manner as in Example 1, except that the water-absorbent resin particles (first water-absorbent resin particles) were changed to the water-absorbent resin particles of Production Example 4. In the absorbent body of the obtained absorbent article, the basis weight of the water-absorbent resin particles was 75 g / m ２ The weight of the hydrophilic fiber (crushed pulp) is 45 g / m ２ It was.

[0089] Example 11 An absorbent article was produced in the same manner as in Example 1, except that the water-absorbent resin particles (first water-absorbent resin particles) were changed to the water-absorbent resin particles of Production Example 5. In the absorbent body of the obtained absorbent article, the basis weight of the water-absorbent resin particles was 75 g / m ２ The weight of the hydrophilic fiber (crushed pulp) is 45 g / m ２ It was.

[0090] Example 12 An absorbent article was produced in the same manner as in Example 1, except that the water-absorbent resin particles (first water-absorbent resin particles) were changed to the water-absorbent resin particles of Production Example 6. In the absorbent body of the obtained absorbent article, the basis weight of the water-absorbent resin particles was 75 g / m ２The weight of the hydrophilic fiber (crushed pulp) is 45 g / m ２ It was.

[0091] Comparative Example 1 An absorbent article was produced in the same manner as in Example 1, except that the water-absorbent resin particles (first water-absorbent resin particles) were changed to the water-absorbent resin particles of Production Example 3. In the absorbent body of the obtained absorbent article, the basis weight of the water-absorbent resin particles was 75 g / m ２ The weight of the hydrophilic fiber (crushed pulp) is 45 g / m ２ It was.

[0092] Comparative Example 2 An absorbent article was produced in the same manner as in Example 1, except that the amount of the water-absorbent resin particles (first water-absorbent resin particles) in Production Example 1 was changed to 1.2 g. In the absorbent body of the obtained absorbent article, the basis weight of the water-absorbent resin particles was 30 g / m ２ The weight of the hydrophilic fiber (crushed pulp) is 45 g / m ２ It was.

[0093] Comparative Example 3 An absorbent article was produced in the same manner as in Example 1, except that the water-absorbent resin particles (first water-absorbent resin particles) were changed to the water-absorbent resin particles of Production Example 3, and the amount of the water-absorbent resin particles was changed to 4.0 g. In the absorbent body of the obtained absorbent article, the basis weight of the water-absorbent resin particles was 100 g / m ２ The weight of the hydrophilic fiber (crushed pulp) is 45 g / m ２ It was.

[0094] Comparative Example 4 An absorbent article was produced in the same manner as in Example 1, except that the water-absorbent resin particles (first water-absorbent resin particles) were changed to the water-absorbent resin particles of Production Example 3, and the amount of the water-absorbent resin particles was changed to 8.0 g. In the absorbent body of the obtained absorbent article, the basis weight of the water-absorbent resin particles was 200 g / m ２ The weight of the hydrophilic fiber (crushed pulp) is 45 g / m ２ It was.

[0095] Comparative Example 5 An absorbent article was produced in the same manner as in Example 1, except that the amount of hydrophilic fiber (crushed pulp) was changed to 24.0 g. In the absorbent core of the obtained absorbent article, the basis weight of the water-absorbent resin particles was 75 g / m ２The weight of the hydrophilic fiber (crushed pulp) is 200 g / m ２ It was.

[0096] Comparative Example 6 An absorbent article was produced in the same manner as in Example 8, except that the amount of water-absorbent resin particles (second water-absorbent resin particles) mixed in the fiber layer was changed to 9.0 g and no particle layer was formed. In the absorbent body of the obtained absorbent article, the basis weight of the water-absorbent resin particles was 75 g / m ２ The weight of the hydrophilic fiber (crushed pulp) is 45 g / m ２ It was.

[0097] Comparative Example 7 An absorbent article was obtained in the same manner as in Example 8, except that the amount of water-absorbent resin particles (second water-absorbent resin particles) mixed in the fiber layer was changed to 8.1 g, and the amount of water-absorbent resin particles (first water-absorbent resin particles) for forming the particle layer was changed to 0.3 g. In the absorbent body of the obtained sheet-like absorbent article, the total basis weight of the water-absorbent resin particles was 75 g / m ２ The weight of the hydrophilic fiber (crushed pulp) is 45 g / m ２ It was.

[0098] Comparative Example 8 An absorbent article was obtained in the same manner as in Example 8, except that the amount of water-absorbent resin particles (second water-absorbent resin particles) mixed in the fiber layer was changed to 4.5 g, and the amount of water-absorbent resin particles (first water-absorbent resin particles) for forming the particle layer was changed to 1.5 g. In the absorbent body of the obtained sheet-like absorbent article, the total basis weight of the water-absorbent resin particles was 75 g / m ２ The weight of the hydrophilic fiber (crushed pulp) is 45 g / m ２ It was.

[0099] Comparative Example 9 An absorbent article was obtained in the same manner as in Example 8, except that the water-absorbent resin particles (second water-absorbent resin particles) to be mixed in the fiber layer and the water-absorbent resin particles (second water-absorbent resin particles) for forming the particle layer were changed to the water-absorbent resin particles of Production Example 3. In the absorbent body of the obtained sheet-like absorbent article, the total basis weight of the water-absorbent resin particles was 75 g / m ２ The weight of the hydrophilic fiber (crushed pulp) is 45 g / m ２ It was.

[0100] 5. Evaluation of absorbent articles Test solution A test solution was prepared by dissolving 45.0 g of NaCl in 4955.0 g of ion-exchanged water and further adding a small amount of Blue No. 1. This test solution was used for the following evaluations.

[0101] Amount of backflow after dripping: The absorbent article was placed on a horizontal table with the air-through nonwoven fabric facing upward. 30 mL of test liquid adjusted to 25±1°C was dripped from 1 cm above the absorbent article toward the center of the absorbent article over 10 seconds using a pump (INTEGRA Biosciences, DOSE IT P910) connected to an inlet with an inner diameter of 0.4 mm. Immediately after dripping of the test liquid, a pre-measured mass of approximately 75 g of filter paper (ADVANTEC No. 51A, 100 mm x 100 mm) was placed on the center of the absorbent article, and a weight (100 mm x 100 mm base, 5.0 kg) equivalent to a pressure of approximately 0.7 psi (4.8 kPa) was quickly placed on top of it, and the load was applied for 3 seconds. Thereafter, the weight and the filter paper were removed, and the mass of the test liquid absorbed by the filter paper was measured and recorded as the amount of backflow after dropping [g].

[0102] Whitening Time: The absorbent article was placed on a horizontal table with the air-through nonwoven fabric facing upward. 30 mL of test liquid adjusted to 25±1°C was dripped from 1 cm above the absorbent article toward the center of the absorbent article over 10 seconds using a pump (DOSE IT P910, manufactured by INTEGRA Biosciences) connected to an inlet with an inner diameter of 0.4 mm. A portion of the test liquid was temporarily retained in the air-through nonwoven fabric immediately after dripping and then absorbed into the absorbent body. As the test liquid migrated to the absorbent body, the color of the surface of the air-through nonwoven fabric of the absorbent article changed from the dark blue color caused by the test liquid to its original white color. The time from the completion of dripping of the test liquid until the surface color changed to a color close to white was recorded as the whitening time. Figure 7 is a photograph showing an example of an absorbent article to which the test liquid had been dripped. (a) is a photograph taken immediately after the test liquid was dropped, and (b) is a photograph taken after the air-through nonwoven fabric had turned white.

[0103] Spreading Area The absorbent article was placed on a horizontal table with the air-through nonwoven fabric facing upward. 30 mL of test liquid adjusted to 25±1°C was dripped from 1 cm above the absorbent article toward the center of the absorbent article over 10 seconds using a pump (DOSE IT P910, manufactured by INTEGRA Biosciences) connected to an inlet with an inner diameter of 0.4 mm. The dripped test liquid diffused horizontally within the absorbent article. Figure 6 is a plan view showing an example of the state in which the test liquid diffused within the absorbent article. Two minutes after the completion of dripping of the test liquid, the maximum length d1 in the longitudinal direction of the absorbent article and the maximum length d2 in the lateral direction of the absorbent article were measured for the region DA where the test liquid diffused within the absorbent article 50. The diffusion area [cm ] was calculated using the following formula: ２ ] was calculated. ２ ]=(d1 / 2)×(d2 / 2)×3.14

[0104]

[0105] The evaluation results are shown in Table 2. In the table, X is the total basis weight of the first water-absorbent resin particles and the second water-absorbent resin particles, and Y is the basis weight of the hydrophilic fibers. When the fiber layer contains the second water-absorbent resin particles, the basis weight of the first water-absorbent resin particles is shown in parentheses in the X column. With regard to the particle layer, the relative position with respect to the fiber layer and the ratio of the amount of the first water-absorbent resin particles based on the total mass of the first water-absorbent resin particles and the second water-absorbent resin particles are also shown.

[0106] As shown in Table 2, it was confirmed that the absorbent articles of each Example, which include a particle layer made of water-absorbent resin particles exhibiting a water absorption speed of 20 seconds or less, exhibit a narrow diffusion area upon water absorption and a short whitening time, i.e., can quickly form a dry surface with little backflow.

[0107] The absorbent body of the present disclosure can provide an absorbent article that has a small diffusion area for absorbed liquid and can quickly form a dry surface with little backflow, thereby reducing the frequency of replacing the absorbent article (e.g., a pet sheet or a waterproof sheet for nursing care).As a result, the amount of water-absorbent resin particles and materials other than the water-absorbent resin particles contained in the absorbent article (e.g., natural raw materials (biomass resources) such as pulp and nonwoven fabric) used can be reduced, thereby contributing to the conservation of the global environment.

[0108] 10...absorbent body, 11...particle layer, 11a...first water-absorbent resin particles, 11b...second water-absorbent resin particles, 12...fiber layer, 21...first shape-retaining member, 22...second shape-retaining member, 30...liquid-permeable sheet, 35...adhesive, 50, 51, 52...absorbent article.

Claims

DEPCT6926 / 03 / 25691. A sheet-like absorbent body composed of: a fibrous layer composed of hydrophilic fibers; and a particle layer formed on one or both surfaces of the fibrous layer, a particle layer composed of primary hydrophilic resin particles, and a selective fibrous layer composed of secondary hydrophilic resin particles, where the basis weight of the primary hydrophilic resin particles in one particle layer is 40 g / m² or more; the water absorption rate of the primary hydrophilic resin particles relative to physiological saline is 20 seconds or less; the basis weight of hydrophilic fibers in the fibrous layer is 20 g / m² or more and 180 g / m² or less; and the proportion of the volume of the primary hydrophilic resin particles is 60 percent by mass or more and 100 percent by mass or less relative to the total mass of the primary and secondary hydrophilic resin particles.2.

1. Absorbent according to claim 1, where the particle layer area ratio is 70 percent or more and 100 percent or less compared to the fiber layer area when viewed from the absorbent thickness direction.

3. Absorbent according to claim 1, where the first water-absorbing resin particles exhibit a water retention capacity of 30 g / g or more compared to physiological saline.

4. Absorbent according to claim 1, where the first water-absorbing resin particles exhibit a water absorption capacity under load of 5 ml / g or more. Furthermore, when compared to physiological saline:

5. The absorbent according to claim 1, where the X / Y ratio is 0.25 or more and 7.0 or less, where X g / m² is the total basic weight of the first water-absorbing resin particles and the second water-absorbing resin particles, and Y g / m² is the basic weight of the hydrophilic fibers in the fiber layer.

6. The absorbent product (absorbent particle) which consists of: the permeable pad; and the absorbent according to one of claims 1 through 5 provided on the inside of the permeable pad. 7.The absorbent product under claim 6, where the absorbent is arranged in such a way that the particle layer is situated between the fiber layer and the liquid-permeable sheet.

8. Method for the production of sheet-like absorbents, which includes: the formation of a fiber layer composed of hydrophilic fibers; and the formation of a particle layer composed of primary hydrophilic resin particles on one or both surfaces of the fiber layer, where the fiber layer may be selectively composed of secondary hydrophilic resin particles; the proportion of the volume of primary hydrophilic resin particles is 60 percent by mass or more and 100 percent by mass or less than the total mass of primary and secondary hydrophilic resin particles; the basis weight of primary hydrophilic resin particles in one particle layer is 40 g / m² or more; the basis weight of hydrophilic fibers in the fiber layer is 20 g / m² or more and 180 g / m²; and the water absorption rate of primary hydrophilic resin particles is 20 seconds or less.

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