Absorber and absorber production method

Abstract

Disclosed is an absorber comprising one or more water-retaining layers, wherein: at least one layer among the water-retaining layers contains multiple kinds of water-absorbing resin particles having mutually different lock-up 5-minute values; among the multiple kinds of water-absorbing resin particles, the water-absorbing resin particles A having the highest lock-up 5-minute value satisfy the following (1) properties, and the water-absorbing resin particles B having the lowest lock-up 5-minute value satisfy the following (2) properties; the water-retaining amount (g / g) of the water-absorbing resin particles A is higher than the water-retaining amount (g / g) of the water-absorbing resin particles B; and the absorber has at least one water-retaining layer having a water-absorbing resin particle ratio of at least 30 mass%. (1) The lock-up 5-minute value is greater than 2.2 cm and the lock-up 10-minute value is at least 3.0 cm. (2) The lock-up 5-minute value is at most 2.2 cm and the lock-up 10-minute value is at least 2.0 cm.

Description

Absorbent body and method for manufacturing the absorbent body

[0001] The present invention relates to an absorbent body and a method for manufacturing an absorbent body.

[0002] Absorbents containing water-absorbent resin particles are widely used in various fields, such as sanitary materials such as disposable diapers and sanitary products, agricultural and horticultural materials such as water retention agents and soil conditioners, and industrial materials such as waterproofing agents and anti-condensation agents. Among these fields, they are often used in absorbent articles such as disposable diapers, sanitary products, and portable toilet components. Hydrophilic fibers such as pulp may be mixed with the water-absorbent resin particles to form the absorbent.

[0003] International Publication No. 2021 / 049488

[0004] The absorbent body is required to have a high permeation rate and a small amount of return after absorbing liquid.

[0005] An object of the present invention is to provide an absorbent body that has an excellent permeation rate and a small amount of backflow.

[0006] The present disclosure includes the following: [1] An absorbent body having one or more water retention layers, at least one of the water retention layers containing multiple types of water-absorbent resin particles having different 5-minute lock-up values, wherein, among the multiple types of water-absorbent resin particles, water-absorbent resin particles A having the highest 5-minute lock-up value satisfy the following property (1), and water-absorbent resin particles B having the lowest 5-minute lock-up value satisfy the following property (2), the water retention capacity (g / g) of the water-absorbent resin particles A is higher than the water retention capacity (g / g) of the water-absorbent resin particles B, and the water-absorbent resin particle ratio represented by the following formula is 30% by mass or more in at least one water retention layer: (1) The 5-minute lock-up value is more than 2.2 cm, and the 10-minute lock-up value is 3.0 cm or more. (2) The 5-minute lock-up value is 2.2 cm or less, and the 10-minute lock-up value is 2.0 cm or more. Water-absorbent resin particle ratio [mass%] = (total amount of water-absorbent resin particles contained in the water retention layer [g] / amount of water-retention layer [g]) x 100 [2] The absorbent of [1], wherein the 5-minute lock-up value of the water-absorbent resin particles A is 4.6 cm or less. [3] The absorbent of [1] or [2], wherein the water retention capacity of the water-absorbent resin particles B is 25 g / g or more. [4] The absorbent of any one of [1] to [3], wherein the difference in the 5-minute lock-up value of the water-absorbent resin particles A and B is 1.5 cm or more. [5] The absorbent of any one of [1] to [4], wherein in the water retention layer containing the plurality of types of water-absorbent resin particles, the amount of the water-absorbent resin particles B relative to the total amount of the water-absorbent resin particles A and B is 10 to 50 mass%. [6] The absorbent of any one of [1] to [5], wherein the water-absorbent resin particles B are coated resin particles having a polymer particle and a coating layer covering at least a part of the surface of the polymer particle. [7] The absorbent of any one of [1] to [3], wherein the water-retaining layer containing the plurality of types of water-absorbent resin particles further contains hydrophilic fibers. [8] The absorbent of [7], wherein the water-retaining layer containing both the plurality of types of water-absorbent resin particles and the hydrophilic fibers is a mixture of the plurality of types of water-absorbent resin particles and the hydrophilic fibers, and the ratio of the water-absorbent resin particles in the water-retaining layer is 70 mass % or less.[9] The absorbent body according to any one of [1] to [6], which has a first water retention layer as the water retention layer containing the plurality of types of water-absorbent resin particles and further has a second water retention layer, the first water retention layer being provided on the liquid-absorbing side of the absorbent body, and the first water retention layer and the second water retention layer each have a water-absorbent resin particle ratio of 80% by mass or more.

[10] A method for manufacturing an absorbent body having one or more water retention layers, which includes forming water retention layers containing a plurality of types of water-absorbent resin particles each having a different 5-minute lock-up value, wherein, among the plurality of types of water-absorbent resin particles, water-absorbent resin particles A having the highest 5-minute lock-up value satisfy the following property (1), and water-absorbent resin particles B having the lowest 5-minute lock-up value satisfy the following property (2), the water retention capacity (g / g) of the water-absorbent resin particles A is higher than the water retention capacity (g / g) of the water-absorbent resin particles B, and the water retention layer containing the plurality of types of water-absorbent resin particles has a water-absorbent resin particle ratio represented by the following formula of 30% by mass or more. (1) The 5-minute lock-up value is more than 2.2 cm, and the 10-minute lock-up value is 3.0 cm or more. (2) The 5-minute lock-up value is 2.2 cm or less, and the 10-minute lock-up value is 2.0 cm or more. Water-absorbent resin particle ratio [mass%] = (total amount of water-absorbent resin particles contained in the water retention layer [g] / amount of water retention layer [g]) × 100.

[0007] The present invention provides an absorbent article that has an excellent permeation rate and a small amount of backflow.

[0008] 1A and 1B are schematic cross-sectional views of an absorbent body according to one embodiment; 1C are schematic cross-sectional views of an absorbent article according to one embodiment;

[0009] Hereinafter, several embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments.

[0010] In this specification, "acrylic" and "methacrylic" are collectively referred to as "(meth)acrylic." Similarly, "acrylate" and "methacrylate" are also referred to as "(meth)acrylate." In the numerical ranges described in stages in this specification, the upper or lower limit of a certain numerical range can be arbitrarily combined with the upper or lower limit of another numerical range. In the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in the Examples. The materials exemplified in this specification may be used alone or in combination of two or more. When multiple substances corresponding to each component are present in the composition, the content of each component refers to the total amount of the multiple substances present in the composition, unless otherwise specified. "Room temperature" refers to 25±2°C. The term "layer" encompasses structures that are formed over the entire surface as well as structures that are formed only partially when observed in a plan view. "Saline" refers to a 0.9% by mass aqueous solution of sodium chloride.

[0011] The absorbent body according to this embodiment includes one or more water-retaining layers, and at least one of the water-retaining layers contains multiple types of water-absorbent resin particles having different 5-minute lock-up values. Among the multiple types of water-absorbent resin particles, water-absorbent resin particles A having the highest 5-minute lock-up value satisfy the following property (1), and water-absorbent resin particles B having the lowest 5-minute lock-up value satisfy the following property (2): (1) The 5-minute lock-up value is greater than 2.2 cm, and the 10-minute lock-up value is 3.0 cm or more. (2) The 5-minute lock-up value is 2.2 cm or less, and the 10-minute lock-up value is 2.0 cm or more.

[0012] In the absorbent body according to this embodiment, the water-retaining capacity (g / g) of the water-absorbent resin particles A is higher than the water-retaining capacity (g / g) of the water-absorbent resin particles B.

[0013] The absorbent body according to this embodiment has at least one water retention layer in which the water-absorbent resin particle ratio, represented by the following formula, is 30% by mass or more. When the absorbent body has two or more water retention layers, the water-absorbent resin particle ratio is calculated for each water retention layer: Water-absorbent resin particle ratio [mass %] = (total amount of water-absorbent resin particles contained in water retention layer [g] / amount of water retention layer [g]) × 100

[0014] The absorbent body according to this embodiment has the above-described configuration, and therefore has a high permeation rate and a low return amount.

[0015] In recent years, there has been a demand for reducing waste from the perspective of carbon neutrality, and efforts have been made to reduce the amount of components used in absorbent articles. However, if the amount of water-absorbent resin particles used in the absorbent body is reduced, absorbed liquids such as urine are less likely to be retained in the absorbent body during use, making them more likely to return to their original state, resulting in stuffiness when the absorbent article is worn. Furthermore, if the amount of hydrophilic fiber used in the absorbent body is reduced, the distance between the water-absorbent resin particles is reduced, which can lead to the water-absorbent resin particles swollen by the absorption of liquid blocking the liquid flow path, resulting in a slower permeation rate of the liquid in the absorbent body (gel blocking). The absorbent body according to this embodiment can achieve a high permeation rate and a low amount of return to its original state while reducing the amount of water-absorbent resin particles and / or hydrophilic fiber used.

[0016] Usually, when an absorbent body is produced using only one type of water-absorbent resin particles, the following problems arise. For example, in order to reduce the amount of water-absorbent resin particles used while reducing the amount of backflow, a method of using water-absorbent resin particles with high water-retention capacity is conceivable. However, water-absorbent resin particles with high water-retention capacity are prone to gel blocking, which tends to result in a deterioration in the permeation rate. Furthermore, in order to maintain the permeation rate while reducing the amount of hydrophilic fibers used in the absorbent body, a method of using water-absorbent resin particles with high liquid permeability is conceivable. However, water-absorbent resin particles with high liquid permeability generally tend to have low water-retention capacity and are difficult to retain absorbed liquid, which has the disadvantage of increasing the amount of backflow and causing stuffiness.

[0017] The absorbent body according to the present embodiment is provided with a water retention layer containing multiple types of water-absorbent resin particles with different absorption performances, and thereby can achieve a reduction in the amount of components used, a high permeation rate, and a low return flow rate, which are difficult to achieve when using only one type of water-absorbent resin particle. The inventors of the present invention speculate that the reason for these effects is as follows. However, the present invention is not limited to the following mechanism.

[0018] A large 5-minute lock-up value indicates a fast water absorption rate in the initial stage of water absorption. By including water-absorbent resin particles A with a high 5-minute lock-up value, i.e., a fast water absorption rate in the initial stage of water absorption, and water-absorbent resin particles B with a low 5-minute lock-up value, i.e., a slow water absorption rate in the initial stage of water absorption, in one water retention layer, when the water-absorbent resin particles A absorb water and swell faster in the initial stage of water absorption, the presence of the water-absorbent resin particles B in the same water retention layer makes it difficult for the water-absorbent resin particles A to fill the gaps between the particles. In other words, the water-absorbent resin particles B can suppress the gel-blocking phenomenon caused by the water-absorbent resin particles A present in the same water retention layer. This makes it easier for liquid to permeate the entire absorbent body, increasing the permeation rate of the absorbent body. Furthermore, by diffusing the liquid throughout the absorbent body, the amount of liquid not absorbed by the water-absorbent resin particles (excess water) is reduced, reducing the amount of backflow.

[0019] A large 10-minute lock-up value indicates the ability to retain more liquid at the end of the water absorption stage. When both the water-absorbent resin particles A and the water-absorbent resin particles B have high 10-minute lock-up values, the absorbent tends to be able to easily suppress the amount of backflow. Furthermore, since the water-absorbent resin particles A have a higher water retention capacity than the water-absorbent resin particles B, it is easier to prevent the gel-blocking phenomenon when the water-absorbent resin particles B begin to absorb water and swell during the water-absorption stage to the end (for example, after several repeated absorptions). Furthermore, by having one or more water-retaining layers with a relatively high ratio of water-absorbent resin particles, it is easier to achieve a reduction in the amount of components used, a high permeation rate, and a low amount of backflow.

[0020] The absorbent body according to the present embodiment contains multiple types of water-absorbent resin particles with different absorption performances and is provided with one or more water-retaining layers with a relatively high ratio of water-absorbent resin particles, thereby more suitably achieving a reduction in the amount of materials used, a high permeation rate, and a low backflow amount. In other words, it is preferable that the water-retaining layer containing multiple types of water-absorbent resin particles with different absorption performances and the water-retaining layer with a relatively high ratio of water-absorbent resin particles are the same water-retaining layer.

[0021] The lock-up 5-minute value of the water-absorbent resin particles A is more than 2.2 cm, and may be 2.5 cm or more, 3.0 cm or more, 3.5 cm or more, 4.0 cm or more, 4.5 cm or more, or 4.8 cm or more and 6.0 cm or less, or 2.5 cm or more, 3.0 cm or more, 3.5 cm or more, 4.0 cm or more, 4.5 cm or more, or 4.8 cm or more and 5.8 cm or less, or 2.5 cm or more, 3.0 cm or more, 3.5 cm or more, 4.0 cm or more, 4.5 cm or more, or 4.8 cm or more and 5.5 cm or less, or 2.5 cm or more, 3.0 cm or more, 3.5 cm or more, 4.0 cm or more, 4.5 cm or more, or 4.8 cm or more and 5.2 cm or less, or 2.5 cm or more, 3.0 cm or more, 3.5 cm or more, 4.0 cm or more, 4. It may be 5 cm or more, or 4.8 cm or more and 5.0 cm or less; it may be 2.5 cm or more, 3.0 cm or more, 3.5 cm or more, 4.0 cm or more, or 4.5 cm or more and 4.8 cm or less; it may be 2.5 cm or more, 3.0 cm or more, 3.5 cm or more, 4.0 cm or more, or 4.5 cm or more and 4.6 cm or less; it may be 2.5 cm or more, 3.0 cm or more, 3.5 cm or more, or 4.0 cm or more and 4.5 cm or less; it may be 2.5 cm or more, 3.0 cm or more, 3.5 cm or more, or 4.0 cm or more and 4.3 cm or less; it may be 2.5 cm or more, 3.0 cm or more, or 3.5 cm or more and 4.0 cm or less; it may be 2.5 cm or more, 3.0 cm or more, or 3.5 cm or more and 3.8 cm or less. Since the amount of backflow is more likely to be reduced, it is preferable that the 5-minute lock-up value of the water-absorbent resin particles A is high. Furthermore, since gel blocking is more likely to be suppressed, it is preferable that the 5-minute lock-up value of the water-absorbent resin particles A is not too high. From the above-mentioned viewpoint, the 5-minute lock-up value of the water-absorbent resin particles A is preferably 2.5 to 6.0 cm, more preferably 2.5 to 5.5 cm, even more preferably 2.8 to 5.0 cm, and particularly preferably 2.8 to 4.6 cm.

[0022] The lock-up 10-minute value of the water-absorbent resin particles A is 3.0 cm or more, and may be 3.3 cm or more, 3.5 cm or more, 3.8 cm or more, 4.0 cm or more, 4.3 cm or more, 4.5 cm or more, 4.8 cm or more, or 5.0 cm or more and 6.0 cm or less, and may be 3.3 cm or more, 3.5 cm or more, 3.8 cm or more, 4.0 cm or more, 4.3 cm or more, 4.5 cm or more, 4.8 cm or more, or 5.0 cm or more and 5.8 cm or less, and may be 3.3 cm or more, 3.5 cm or more, 3.8 cm or more, 4.0 cm or more, 4.3 cm or more, 4.5 cm or more, 4.8 cm or more, or 5.0 cm or more and 5.5 cm or less, and may be 3.3 cm or more, 3.5 cm or more, 3.8 cm or more, It may be 4.0 cm or more, 4.3 cm or more, 4.5 cm or more, 4.8 cm or more, or 5.0 cm or more and 5.2 cm or less; it may be 3.3 cm or more, 3.5 cm or more, 3.8 cm or more, 4.0 cm or more, 4.3 cm or more, 4.5 cm or more, or 4.8 cm or more and 5.0 cm or less; it may be 3.3 cm or more, 3.5 cm or more, 3.8 cm or more, 4.0 cm or more, 4.3 cm or more, or 4.5 cm or more and 4.8 cm or less; it may be 3.3 cm or more, 3.5 cm or more, 3.8 cm or more, 4.0 cm or more, or 4.3 cm or more and 4.5 cm or less; or it may be 3.3 cm or more, 3.5 cm or more, 3.8 cm or more, 4.0 cm or more, or 4.3 cm or more and 4.5 cm or less.

[0023] The lockup 5-minute value of the water-absorbent resin particles B is 2.2 cm or less, and may be 2.0 cm or less, 1.8 cm or less, 1.6 cm or less, 1.4 cm or less, 1.2 cm or less, 1.0 cm or less, or 0.8 cm or less and 0.5 cm or more, and may be 2.0 cm or less, 1.8 cm or less, 1.6 cm or less, 1.4 cm or less, 1.2 cm or less, 1.0 cm or less, or 0.8 cm or less and 0.7 ...8 cm or less, 1.6 cm or less, 1.4 cm or less, 1.2 cm or less, 1.0 cm or less, or 0.8 cm or less and 0.7 cm or more. The lock-up value may be 0.6 cm or less, 1.4 cm or less, 1.2 cm or less, or 1.0 cm or less, and 0.8 cm or more; 2.0 cm or less, 1.8 cm or less, 1.6 cm or less, 1.4 cm or less, or 1.2 cm or less, and 1.0 cm or more; 2.0 cm or less, 1.8 cm or less, 1.6 cm or less, or 1.4 cm or less, and 1.2 cm or more; 2.0 cm or less, 1.8 cm or less, or 1.6 cm or less, and 1.4 cm or more. The lock-up value may be low for the water-absorbent resin particles B, since gel blocking caused by the water-absorbent resin particles A is easily alleviated. On the other hand, the lock-up value of the water-absorbent resin particles B is preferably not too low, since excess water in the absorbent is easily absorbed and an absorbent with excellent permeation rate is easily obtained. From the above-mentioned viewpoint, the 5-minute lock-up value of the water-absorbent resin particles B is preferably 0.5 to 2.2 cm, more preferably 0.5 to 2.0 cm, still more preferably 0.7 to 2.0 cm, and particularly preferably 0.7 to 1.8 cm.

[0024] The lock-up value of the water-absorbent resin particles B at 10 minutes is 2.0 cm or more, and may be 2.5 cm or more, 2.6 cm or more, 2.8 cm or more, 3.0 cm or more, 3.5 cm or more, 4.0 cm or more, or 4.5 cm or more and 5.5 cm or less, or may be 2.5 cm or more, 2.6 cm or more, 2.8 cm or more, 3.0 cm or more, 3.5 cm or more, 4.0 cm or more, or 4.5 cm or more and 5.3 cm or less, It may be 5 cm or more, 2.6 cm or more, 2.8 cm or more, 3.0 cm or more, 3.5 cm or more, 4.0 cm or more, or 4.5 cm or more and 5.0 cm or less, 2.5 cm or more, 2.6 cm or more, 2.8 cm or more, 3.0 cm or more, 3.5 cm or more, 4.0 cm or more, or 4.5 cm or more and 4.8 cm or less, 2.5 cm or more, 2.6 cm or more, 2.8 cm or more, 3.0 cm or more, 3.5 cm or more, or 4.0 cm or more and 4.5 cm or less, or 2.5 cm or more, 2.6 cm or more, 2.8 cm or more, 3.0 cm or more, 3.5 cm or more, or 4.0 cm or more and 4.3 cm or less, or 2.5 cm or more, 2.6 cm or more, 2.8 cm or more, 3.0 cm or more, or 3.5 cm or more and 4.0 cm or less, or 2.5 cm or more, 2.6 cm or more, 2.8 cm or more, 3.0 cm or more , or 3.5 cm or more and 3.9 cm or less, or 2.5 cm or more, 2.6 cm or more, 2.8 cm or more, 3.0 cm or more, or 3.5 cm or more and 3.8 cm or less, or 2.5 cm or more, 2.6 cm or more, 2.8 cm or more, or 3.0 cm or more and 3.5 ...3 cm or less. Since it is easy to retain more liquid at the end of the absorption period and to suppress the amount of return of the absorbent body low, it is preferable that the lock-up 10-minute value of the water-absorbent resin particles B is high. On the other hand, it is easy to obtain the effect of alleviating gel blocking when liquid is added multiple times (it is easy to increase the permeation rate at the end of the absorption period), so it is preferable that the lock-up 10-minute value of the water-absorbent resin particles B is not too high.From the above-mentioned viewpoint, the lock-up 10-minute value of the water-absorbent resin particles B is preferably 2.5 to 5.5 cm, more preferably 2.5 to 5.3 cm, still more preferably 2.6 to 5.0 cm, particularly preferably 2.6 to 4.5 cm, and most preferably 2.8 to 3.9 cm.

[0025] The difference in the 5-minute lock-up value between the water-absorbent resin particles A and the water-absorbent resin particles B may be, for example, 1.5 cm or more, 1.8 cm or more, 2.0 cm or more, 2.2 cm or more, 2.5 cm or more, 2.8 cm or more, 3.0 cm or more, 3.3 cm or more, 3.5 cm or more, 3.8 cm or more, or 4.0 cm or more and 5.0 cm or less, and may be 1.5 cm or more, 1.8 cm or more, 2.0 cm or more, 2.2 cm or more, 2.5 cm or more, 2.8 cm or more, 3.0 cm or more, 3.3 cm or more, 3.5 cm or more, 3.8 cm or more, or 4.0 cm or more and 4.8 cm or less, and may be 1.5 cm or more, or more, 1.8 cm or more, 2.0 cm or more, 2.2 cm or more, 2.5 cm or more, 2.8 cm or more, 3.0 cm or more, 3.3 cm or more, 3.5 cm or more, 3.8 cm or more, or 4.0 cm or more and 4.5 cm or less, 1.5 cm or more, 1.8 cm or more, 2.0 cm or more, 2.2 cm or more, 2.5 cm or more, 2.8 cm or more, 3.0 cm or more, 3.3 cm or more, 3.5 cm or more, 3.8 cm or more, or 4.0 cm or more and 4.3 cm or less, 1.5 cm or more, 1.8 cm or more, 2.0 cm or more, 2.2 cm or more, 2.5 cm or more, 2.8 cm or more, 3.0 cm or more, 3.3 cm or more, 3.5 cm or more, or 3.8 cm or more, and 4.0 cm or less; 1.5 cm or more, 1.8 cm or more, 2.0 cm or more, 2.2 cm or more, 2.5 cm or more, 2.8 cm or more, 3.0 cm or more, 3.3 cm or more, or 3.5 cm or more, and 3.8 cm or less; 1.5 cm or more, 1.8 cm or more, 2.0 cm or more, 2.2 cm or more, 2.5 cm or more, 2.8 cm or more, 3.0 cm or more, or 3.3 cm or more, and 3.5 cm or less; 1.5 cm or more, 1.8 cm or more, 2.0 cm or more, 2.2 cm or more, It may be 1.5 cm or more, 1.8 cm or more, 2.0 cm or more, 2.2 cm or more, 2.5 cm or more, or 2.8 cm or more and 3.0 cm or less, or 1.5 cm or more, 1.8 cm or more, 2.0 cm or more, 2.2 cm or more, or 2.5 cm or more and 2.8 cm or less, or 2.0 cm or more, 2.2 cm or more and 2.5 cm or less, or 2.0 cm or more, 1.5 cm or more, 1.8 cm or more and 2.3 cm or less.The difference in the 5-minute lock-up value between the water-absorbent resin particles A and the water-absorbent resin particles B may be 1.5 to 5.0 cm, preferably 1.5 to 4.8 cm, more preferably 1.8 to 4.5 cm, even more preferably 2.0 to 4.3 cm, and particularly preferably 2.2 to 4.3 cm, from the viewpoint that the water-absorbent resin particles B can easily suppress the gel-blocking phenomenon caused by the water-absorbent resin particles A present in the same water retention layer.

[0026] The lock-up 2-minute value of the water-absorbent resin particles A may be, for example, 2.0 cm or more, 2.2 cm or more, 2.5 cm or more, 2.8 cm or more, 3.0 cm or more, 3.3 cm or more, or 3.5 cm or more and 4.8 cm or less; 2.0 cm or more, 2.2 cm or more, 2.5 cm or more, 2.8 cm or more, 3.0 cm or more, 3.3 cm or more, or 3.5 cm or more and 4.5 cm or less; 2.0 cm or more, 2.2 cm or more, 2.5 cm or more, 2.8 cm or more, 3.0 cm or more, 3.3 cm or more, or 3.5 cm or more and 4.3 cm or less; 2.0 cm or more, 2.2 cm or more, 2.5 cm or more, 2.8 cm or more, 3.0 cm or more, 3.3 cm or more, or 3.5 cm or more. and 4.0 cm or less, and may be 2.0 cm or more, 2.2 cm or more, 2.5 cm or more, 2.8 cm or more, 3.0 cm or more, 3.3 cm or more, or 3.5 cm or more and 3.8 cm or less, and may be 2.0 cm or more, 2.2 cm or more, 2.5 cm or more, 2.8 cm or more, 3.0 cm or more, or 3.3 cm or more and 3.5 cm or less, and may be 2.0 cm or more, 2.2 cm or more, 2.5 cm or more, 2.8 cm or more, or 3.0 cm or more and 3.3 cm or less, and may be 2.0 cm or more, 2.2 cm or more, 2.5 cm or more, or 2.8 cm or more and 3.0 cm or less, and may be 2.0 cm or more, 2.2 cm or more, or 2.5 cm or more and 2.8 cm or less. The higher the 2-minute lockup value of the water-absorbent resin particles, the faster the water absorption rate in the very early stage after starting to absorb liquid.

[0027] The lock-up 2-minute value of the water-absorbent resin particles B may be, for example, 0.05 cm or more, 0.1 cm or more, 0.15 cm or more, 0.2 cm or more, or 0.25 cm or more and 1.0 cm or less, 0.05 cm or more, 0.1 cm or more, 0.15 cm or more, 0.2 cm or more, or 0.25 cm or more and 0.8 cm or less, 0.05 cm or more, 0.1 cm or more, 0.15 cm or more, 0.2 cm or more, or may be 0.25 cm or more and 0.5 cm or less, 0.05 cm or more, 0.1 cm or more, 0.15 cm or more, 0.2 cm or more, or 0.25 cm or more and 0.3 cm or less, 0.05 cm or more, 0.1 cm or more, 0.15 cm or more, or 0.2 cm or more and 0.25 cm or less, or 0.05 cm or more, 0.1 cm or more, or 0.15 cm or more and 0.2 cm or less.

[0028] The n-minute value of the lock-up height of a water-absorbent resin particle is a value specified by a measurement method described in Examples below, and is measured by a method including: forming a particle layer having a height H0 [cm] by scattering 0.200 g of water-absorbent resin particles over the entire bottom surface of a cylinder having an inner diameter of 2.0 cm and a depth of 8.0 cm; adding 20 g of physiological saline to the particle layer to swell the particle layer; recording the height of the particle layer at the time when n minutes have elapsed since the entire amount of physiological saline was added as Hn [cm]; and calculating the n-minute value of the lock-up height by the formula: (Hn-H0).

[0029] The water retention capacity of the water-absorbent resin particles A in physiological saline may be, for example, 40 g / g or more, 41 g / g or more, 42 g / g or more, 43 g / g or more, 44 g / g or more, or 45 g / g or more and 60 g / g or less; 40 g / g or more, 41 g / g or more, 42 g / g or more, 43 g / g or more, 44 g / g or more, or 45 g / g or more and 55 g / g or less; 40 g / g or more, 41 g / g or more, 42 g / g or more, 43 g / g or more, It may be 44 g / g or more, or 45 g / g or more and 52 g / g or less, it may be 40 g / g or more, 41 g / g or more, 42 g / g or more, 43 g / g or more, 44 g / g or more, or 45 g / g or more and 51 g / g or less, it may be 40 g / g or more, 41 g / g or more, 42 g / g or more, 43 g / g or more, 44 g / g or more, or 45 g / g or more and 50 g / g or less, it may be 40 g / g or more, 41 g / g or more, 42 g / g or more, 43 g / g or more 40 g / g or more, 41 g / g or more, 42 g / g or more, 43 g / g or more, 44 g / g or more, or 45 g / g or more and 49 g / g or less; 40 g / g or more, 41 g / g or more, 42 g / g or more, 43 g / g or more, 44 g / g or more, or 45 g / g or more and 48 g / g or less; 40 g / g or more, 41 g / g or more, 42 g / g or more, 43 g / g or more, 44 g / g or more, or 45 g / g or more and 47 g / g or less; 40 g / g or more, 41 g / g or more, 42 g / g or more The water-absorbent resin particles A may have a water retention capacity of 40 to 60 g / g, preferably 41 to 60 g / g, more preferably 41 to 60 g / g, more preferably 41 to 55 g / g, and even more preferably 42 to 55 g / g. The water retention capacity of the water-absorbent resin particles A in physiological saline may be 40 to 60 g / g, more preferably 41 to 60 g / g, more preferably 41 to 55 g / g, and even more preferably 42 to 55 g / g, from the viewpoint of more easily reducing the amount of backflow. The water retention capacity of the water-absorbent resin particles in physiological saline is measured by the method described in the Examples below.

[0030] The water retention capacity of the water-absorbent resin particles B in physiological saline may be, for example, 25 g / g or more, 28 g / g or more, 30 g / g or more, 33 g / g or more, 35 g / g or more, 37 g / g or more, 39 g / g or more, 41 g / g or more, 43 g / g or more and 55 g / g or less, It may be 37 g / g or more, 39 g / g or more, 41 g / g or more, 43 g / g or more and 50 g / g or less, 25 g / g or more, 28 g / g or more, 30 g / g or more, 33 g / g or more, 35 g / g or more, 37 g / g or more, 39 g / g or more, 41 g / g or more, 43 g / g or more and 48 g / g or less, 25 g / g or more, 28 g / g or more, 30 g / g or more g or more, 33 g / g or more, 35 g / g or more, 37 g / g or more, 39 g / g or more, 41 g / g or more, 43 g / g or more and 46 g / g or less, or 25 g / g or more, 28 g / g or more, 30 g / g or more, 33 g / g or more, 35 g / g or more, 37 g / g or more, 39 g / g or more, 41 g / g or more, 43 g / g or more and 44 g / g or less, The water retention capacity of the water-absorbent resin particles B for physiological saline solution may be 25 to 55 g / g, preferably 30 to 55 g / g, more preferably 35 to 50 g / g, even more preferably 37 to 50 g / g, and particularly preferably 37 to 48 g / g, from the viewpoint of easily obtaining an absorbent body excellent in permeation rate and return amount.

[0031] The difference in water retention capacity for physiological saline between the water-absorbent resin particles A and the water-absorbent resin particles B may be, for example, 1 g / g or more, 2 g / g or more, 3 g / g or more, 4 g / g or more, or 5 g / g or more, and 10 g / g or less; 1 g / g or more, 2 g / g or more, 3 g / g or more, 4 g / g or more, or 5 g / g or more, and 8 g / g or less; 1 g / g or more, 2 g / g or more, 3 g / g or more, 4 g / g or more, or 5 g / g or more, and 6 g / g or less; 1 g / g or more, 2 g / g or more, or 3 g / g or more, and 4 g / g or less; or 1 g / g or more, and 2 g / g or less.

[0032] A water retaining layer (hereinafter also referred to as a "first water retaining layer") containing water absorbent resin particles A and B as the plurality of types of water absorbent resin particles.In the above, the proportion of the water absorbent resin particles B to the total amount of the water absorbent resin particles A and B may be, for example, 10% by mass or more, 12% by mass or more, 15% by mass or more, 18% by mass or more, 20% by mass or more, 22% by mass or more, 25% by mass or more, 28% by mass or more, or 30% by mass or more and 50% by mass or less, 10% by mass or more, 12% by mass or more, 15% by mass or more, 18% by mass or more, 20% by mass or more, 22% by mass or more, 25% by mass or more, 28% by mass or more, or 30% by mass or more and 45% by mass or less, %, 20% by mass or more, 22% by mass or more, 25% by mass or more, 28% by mass or more, or 30% by mass or more and 40% by mass or less; 10% by mass or more, 12% by mass or more, 15% by mass or more, 18% by mass or more, 20% by mass or more, 22% by mass or more, 25% by mass or more, 28% by mass or more, or 30% by mass or more and 38% by mass or less; 10% by mass or more, 12% by mass or more, 15% by mass or more, 18% by mass or more, 20% by mass or more, 22% by mass or more, 25% by mass or more, 28% by mass or more, or 30% by mass or more and 35 ... or more, 12 mass% or more, 15 mass% or more, 18 mass% or more, 20 mass% or more, 22 mass% or more, 25 mass% or more, 28 mass% or more, or 30 mass% or more and 33 mass% or less; 10 mass% or more, 12 mass% or more, 15 mass% or more, 18 mass% or more, 20 mass% or more, 22 mass% or more, 25 mass% or more, or 28 mass% or more and 30 mass% or less; 10 mass% or more, 12 mass% or more, 15 mass% or more, 18 mass% or more, 20 mass% or more, 22 mass% or more, or 25 mass% or more and 28 mass% or less; 10 mass% or more , 12% by mass or more, 15% by mass or more, 18% by mass or more, 20% by mass or more, or 22% by mass or more and 25% by mass or less; 10% by mass or more, 12% by mass or more, 15% by mass or more, 18% by mass or more, 20% by mass or more, or 22% by mass or more and 23% by mass or less; 10% by mass or more, 12% by mass or more, 15% by mass or more, or 18% by mass or more and 20% by mass or less; 10% by mass or more, 12% by mass or more, or 15% by mass or more and 18 ... and 10% by mass or more, 12% by mass or more and 15% by mass or less.The proportion of the water-absorbent resin particles B relative to the total amount of the water-absorbent resin particles A and B may be 10 to 50% by mass, preferably 10 to 45% by mass, more preferably 10 to 40% by mass, even more preferably 10 to 35% by mass, particularly preferably 12 to 35% by mass, and most preferably 15 to 35% by mass, from the viewpoint that an absorbent excellent in permeation speed and return amount can be easily obtained.

[0033] In order to efficiently exhibit the effect of the first water retaining layer containing both water-absorbent resin particles A and B, it is preferable that the water-absorbent resin particles A and B are mixed, and more preferably mixed uniformly, in the water retaining layer. It is preferable that the water-absorbent resin particles A and B are present over the entire surface of the first water retaining layer.

[0034] The first water retaining layer may further contain water absorbent resin particles other than the water absorbent resin particles A or B. The content of the water absorbent resin particles A and B relative to the total amount of the water absorbent resin particles in the first water retaining layer may be, for example, 80 to 100 mass%, 90 to 100 mass%, 95 to 100 mass%, or 98 to 100 mass%.

[0035] The first water retention layer may further contain hydrophilic fibers. When the first water retention layer contains hydrophilic fibers, the hydrophilic fibers further reinforce the permeability of liquid within the first water retention layer, which tends to further improve the performance of the absorbent body (high permeation rate and low return amount). When the absorbent body has only one water retention layer, it is preferable that the first water retention layer contains hydrophilic fibers. Examples of hydrophilic fibers include cellulosic fibers such as finely ground wood pulp, cotton, cotton linter, rayon, and cellulose acetate.

[0036] The first water retaining layer may be composed of only water-absorbent resin particles, or may be composed of only water-absorbent resin particles and hydrophilic fibers. When the first water retaining layer contains hydrophilic fibers, the water-absorbent resin particles and the hydrophilic fibers are preferably mixed. The mixing of the water-absorbent resin particles and the hydrophilic fibers can be carried out, for example, by air papermaking.

[0037] When the first water retaining layer contains hydrophilic fibers, the amount of the hydrophilic fibers in the water retaining layer relative to the amount of the water retaining layer or the total amount of the water-absorbent resin particles and hydrophilic fibers in the water retaining layer may be, for example, 1% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, 30% by mass or more, 35% by mass or more, 40% by mass or more, 45% by mass or more, 50% by mass or more, 55% by mass or more, 60% by mass or more, or 65% by mass or more and 70% by mass or less, and may be 1% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more or more, 30% by mass or more, 35% by mass or more, 40% by mass or more, 45% by mass or more, 50% by mass or more, 55% by mass or more, or 60% by mass or more and 65% by mass or less; or 1% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, 30% by mass or more, 35% by mass or more, 40% by mass or more, 45% by mass or more, 50% by mass or more, or 55% by mass or more and 60 ... It may be 0% by mass or more, 45% by mass or more, or 50% by mass or more and 55% by mass or less; it may be 1% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, 30% by mass or more, 35% by mass or more, 40% by mass or more, or 45% by mass or more and 50% by mass or less; it may be 1% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, 30% by mass or more, 35% by mass or more, or 40% by mass or more and 45% by mass or less; it may be 1% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more, %, 20% by mass or more, 25% by mass or more, 30% by mass or more, or 35% by mass or more, and 40% by mass or less; 1% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, or 30% by mass or more, and 35% by mass or less; 1% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, or 25% by mass or more, and 30% by mass or less; 1% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more, or 20% by mass or more, and 25% by mass or less; 1% by mass or more,It may be 5% by mass or more, 10% by mass or more, or 15% by mass or more and 20% by mass or less, 1% by mass or more, 5% by mass or more, or 10% by mass or more and 15% by mass or less, 1% by mass or more, or 5% by mass or more and 10% by mass or less, 1% by mass or more and 5% by mass or less, 1% by mass or more and 3% by mass or less, or 0% by mass or more and 1% by mass or less.

[0038] The ratio of water-absorbent resin particles in the first water retention layer (the ratio of the total amount of water-absorbent resin particles in the water retention layer to the amount of the water retention layer) is preferably 30% by mass or more, from the viewpoint of easily obtaining an absorbent body excellent in permeation rate and return amount. The ratio of water-absorbent resin particles in the first water retention layer may be, for example, 10% by mass or more, 20% by mass or more, 30% by mass or more, 33% by mass or more, 35% by mass or more, 38% by mass or more, 40% by mass or more, 45% by mass or more, 50% by mass or more, 55% by mass or more, 60% by mass or more, 65% by mass or more, 70% by mass or more, 75% by mass or more, 80% by mass or more, 85% by mass or more, 90% by mass or more, 95% by mass or more, or 98% by mass or more, but 100% by mass or less, and may be 10% by mass or more. Above, 20% by mass or more, 30% by mass or more, 33% by mass or more, 35% by mass or more, 38% by mass or more, 40% by mass or more, 45% by mass or more, 50% by mass or more, 55% by mass or more, 60% by mass or more, 65% by mass or more, 70% by mass or more, 75 It may be 90% by mass or less, 10% by mass or more, 20% by mass or more, 30% by mass or more, 33% by mass or more, 35% by mass or more, 38% by mass or more, 40% by mass or more, 45% by mass. or more, 50% by mass or more, 55% by mass or more, 60% by mass or more, 65% by mass or more, 70% by mass or more, or 75% by mass or more and 80% by mass or less; 10% by mass or more, 20% by mass or more, 30% by mass or more, 33% by mass or more, 35% by mass or more, 38% by mass or more, 40% by mass or more, 45% by mass or more, 50% by mass or more, 55% by mass or more, 60% by mass or more, or 65% by mass or more and 7 ... The content may be 10% by mass or more, 20% by mass or more, 30% by mass or more, 33% by mass or more, 35% by mass or more, 38% by mass or more, 40% by mass or more, 45% by mass or more, 50% by mass or more, or 55% by mass or more and 60% by mass or less; 10% by mass or more, 20% by mass or more, 30% by mass or more, 33% by mass or more, 35% by mass or more, 38% by mass or more, 40% by mass or more, or 45% by mass or more and 50% by mass or less; or 33% by mass or more, 35% by mass or more, or 38% by mass or more and 40% by mass or less.

[0039] The first water retaining layer may further contain inorganic particles, a deodorant, etc. in addition to the water-absorbent resin particles and hydrophilic fibers.

[0040] The method for forming the first water retention layer may include, for example, preparing water-absorbent resin particles A, preparing water-absorbent resin particles B, and forming a layer containing water-absorbent resin particles A and B.

[0041] The first water retaining layer can be formed, for example, by air papermaking, by mixing water-absorbent resin particles including water-absorbent resin particles A and B, and hydrophilic fibers as necessary. The first water retaining layer may also be formed, for example, by providing an adhesive layer on a sheet-like shape-retaining member and spraying water-absorbent resin particles, which are a pre-mixture of water-absorbent resin particles A and B, onto the adhesive layer, or by spraying water-absorbent resin particles A and B separately onto the adhesive layer. When water-absorbent resin particles A and B are sprayed separately, it is preferable that the spraying locations overlap so that the water-absorbent resin particles A and B are mixed within the same region of the water retaining layer.

[0042] The water-absorbent resin particles A, the water-absorbent resin particles B, and / or other water-absorbent resin particles optionally used (hereinafter, these may be collectively referred to simply as "water-absorbent resin particles") may, for example, contain polymer particles or may be polymer particles. The polymer particles may, for example, contain crosslinked polymer particles containing an ethylenically unsaturated monomer as a monomer unit, or may be crosslinked polymer particles containing an ethylenically unsaturated monomer as a monomer unit. The crosslinked polymer particles can be produced, for example, by a method including a step of polymerizing a monomer containing an ethylenically unsaturated monomer. Examples of the polymerization method include a reverse-phase suspension polymerization method, an aqueous solution polymerization method, a bulk polymerization method, and a precipitation polymerization method.

[0043] The ethylenically unsaturated monomer may be a water-soluble ethylenically unsaturated monomer. The solubility of the water-soluble ethylenically unsaturated monomer in 100 g of water may be 1.0 g or more at 25°C. Examples of water-soluble ethylenically unsaturated monomers include (meth)acrylic acid and salts thereof, 2-(meth)acrylamido-2-methylpropanesulfonic acid and salts thereof, (meth)acrylamide, N,N-dimethyl(meth)acrylamide, 2-hydroxyethyl(meth)acrylate, N-methylol(meth)acrylamide, polyethylene glycol mono(meth)acrylate, N,N-diethylaminoethyl(meth)acrylate, N,N-diethylaminopropyl(meth)acrylate, and diethylaminopropyl(meth)acrylamide. When the ethylenically unsaturated monomer has an amino group, the amino group may be quaternized. The ethylenically unsaturated monomer may be used alone or in combination of two or more types.

[0044] When the ethylenically unsaturated monomer has an acidic group, the acidic group may be neutralized with an alkaline neutralizing agent before use in the polymerization reaction. The degree of neutralization of the ethylenically unsaturated monomer with the alkaline neutralizing agent may be, for example, 10 to 100 mol %, 50 to 90 mol %, or 60 to 80 mol % of the acidic groups in the ethylenically unsaturated monomer. Examples of alkaline neutralizing agents include alkali metal salts such as sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, and potassium carbonate; ammonia, etc. The alkaline neutralizing agents may be used alone or in combination of two or more. The alkaline neutralizing agents may be used in the form of an aqueous solution to simplify the neutralization operation.

[0045] The crosslinked polymer particles may further contain monomer units derived from a monomer other than the above-mentioned ethylenically unsaturated monomer. The proportion of the monomer units derived from the ethylenically unsaturated monomer may be 70 to 100 mol% based on the total amount of monomer units constituting the crosslinked polymer particles. The proportion of the monomer units derived from the ethylenically unsaturated monomer may be 80 to 100 mol%, 85 to 100 mol%, 90 to 100 mol%, or 95 to 100 mol% based on the total amount of monomer units constituting the crosslinked polymer particles. The proportion of the monomer units derived from (meth)acrylic acid and salts thereof may be 70 to 100 mol% based on the total amount of monomer units constituting the crosslinked polymer particles. The proportion of the monomer units derived from (meth)acrylic acid and salts thereof may be 80 to 100 mol%, 85 to 100 mol%, 90 to 100 mol%, or 95 to 100 mol% based on the total amount of monomer units constituting the crosslinked polymer in the polymer particles.

[0046] The crosslinked polymer particles constituting the polymer particles may be crosslinked by an internal crosslinking agent. The internal crosslinking agent is usually added to a reaction solution during a polymerization reaction. The entire particle is crosslinked by the internal crosslinking agent. The use of the internal crosslinking agent makes it easy to control the water absorption properties (water retention capacity of physiological saline, etc.) of the water-absorbent resin particles.

[0047] The crosslinked polymer particles constituting the polymer particles may be crosslinked by a surface crosslinking agent. The surface crosslinking agent mainly crosslinks the vicinity of the surface of the particles. The use of a surface crosslinking agent makes it easy to control the water absorption properties (water retention capacity of physiological saline solution, etc.) of the water-absorbent resin particles.

[0048] The water-absorbent resin particles may be substantially composed of polymer particles alone, but may further contain various additional components selected from, for example, a gel stabilizer, a metal chelating agent, an antibacterial agent, a deodorizer, a flowability improver (lubricant), etc. The additional components may be disposed inside or on the surface of the polymer particles or crosslinked polymer particles constituting the polymer particles, or both.

[0049] The flowability improver may contain inorganic particles or may be inorganic particles. Examples of inorganic particles include silica particles such as amorphous silica; metal oxides such as iron oxide and alumina; activated carbon, etc. When the polymer particles contain inorganic particles, the content of the inorganic particles may be 0.05 parts by mass or more, 0.1 parts by mass or more, 0.2 parts by mass or more, 0.3 parts by mass or more, or 0.4 parts by mass or more and 5.0 parts by mass or less, based on 100 parts by total mass of the crosslinked polymer, or 0.05 parts by mass or more, 0.1 parts by mass or more, 0.2 parts by mass or more, 0.3 parts by mass or more, or 0.4 parts by mass or more and 3.0 parts by mass or less, or 0.05 parts by mass or more , 0.1 parts by mass or more, 0.2 parts by mass or more, 0.3 parts by mass or more, or 0.4 parts by mass or more, and 1.0 parts by mass or less; 0.05 parts by mass or more, 0.1 parts by mass or more, 0.2 parts by mass or more, 0.3 parts by mass or more, or 0.4 parts by mass or more, and 0.7 parts by mass or less; 0.05 parts by mass or more, 0.1 parts by mass or more, 0.2 parts by mass or more, 0.3 parts by mass or more, or 0.4 parts by mass or more, and 0.5 parts by mass or less.

[0050] The shape of the water-absorbent resin particles is not particularly limited, and may be, for example, substantially spherical, crushed or granular, or may be formed as particles formed by agglomeration of primary particles having these shapes.

[0051] The median particle diameter of the water-absorbent resin particles may be 100 to 800 μm, 150 to 700 μm, 200 to 600 μm, or 250 to 500 μm. The median particle diameter can be measured by the following method. JIS standard sieves are combined in the following order from top to bottom: 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 180 μm, a sieve with a mesh size of 150 μm, and a tray. 50 g of water-absorbent resin particles are placed on the top sieve of the combination, and classified in accordance with JIS Z 8815 (1994) using a Rotap type shaker (manufactured by Iida Seisakusho Co., Ltd.). After classification, the mass of the particles remaining on each sieve is calculated as a mass percentage relative to the total mass to determine the particle size distribution. The particles remaining on the sieves are integrated in descending order of particle size in this particle size distribution, and the relationship between the sieve opening and the integrated value of the mass percentage of the particles remaining on the sieve is plotted on a logarithmic probability paper. The particle size corresponding to an integrated mass percentage of 50% by mass is determined as the median particle size by connecting the plots on the probability paper with a straight line.

[0052] The 2-minute, 5-minute, and 10-minute lockup values ​​and water retention capacity of the water-absorbent resin particles A can be adjusted by appropriately changing the production conditions of the water-absorbent resin particles A. For example, by increasing the specific surface area of ​​the water-absorbent resin particles A, the 2-minute and 5-minute lockup values ​​tend to increase, and by lowering the water content, the 5-minute and 10-minute lockup values ​​and water retention capacity tend to increase. In addition, the measured lockup value can also be adjusted by adjusting the crosslink density of the crosslinked polymer particles constituting the water-absorbent resin particles A.

[0053] The water-absorbent resin particles B are preferably coated resin particles having the above-mentioned polymer particles and a coating layer covering at least a portion of the surface of the polymer particles. By forming a coating layer covering at least a portion of the surface of the polymer particles, the polymer particles are less likely to come into contact with liquid, making it easier to obtain water-absorbent resin particles with low 2-minute, 5-minute, and 10-minute lockup values. Such coated resin particles can be obtained, for example, by a method of forming a coating layer covering at least a portion of the surface of the polymer particles. In addition to the coated resin particles, the water-absorbent resin particles B may further contain various additional components selected from, for example, a gel stabilizer, a metal chelating agent, an antibacterial agent, a deodorizer, and a flowability improver (lubricant). On the other hand, the water-absorbent resin particles A preferably do not have a coating layer, i.e., are not coated resin particles.

[0054] The coating layer may contain, for example, the following polymer <1> or <2>, or may contain both the following polymers <1> and <2>: <1> A polymer containing an alkene as a monomer unit (a homopolymer, a copolymer, or a mixture thereof). <2> A polymer containing an alkylene oxide as a monomer unit (a homopolymer, a copolymer, or a mixture thereof).

[0055] <1> In a polymer containing an alkene as a monomer unit, the alkene may be unsubstituted or may have a substituent. The polymer may be a homopolymer or a copolymer. The copolymer containing an alkene as a constituent unit may be a copolymer containing only two or more types of alkenes as monomer units, or a copolymer containing one type of alkene and a monomer other than the alkene as monomer units, or a copolymer containing two or more types of alkenes and a monomer other than the alkene as monomer units.

[0056] Examples of the alkene (unsubstituted alkene) that can constitute the copolymer include at least one selected from ethylene, propylene, and butene. The alkene (unsubstituted alkene) may be ethylene and / or propylene, or may be ethylene.

[0057] The monomer other than the alkene (unsubstituted alkene) constituting the copolymer may be a water-soluble ethylenically unsaturated monomer, which may be the same as the compounds listed as the water-soluble ethylenically unsaturated monomers constituting the polymer particles, or may be (meth)acrylic acid and / or a salt thereof.

[0058] The copolymer containing an alkene (unsubstituted alkene) as a monomer unit may be a copolymer containing ethylene and a water-soluble ethylenically unsaturated monomer as monomer units, a copolymer containing ethylene and (meth)acrylic acid and / or a salt thereof as monomer units, a copolymer containing ethylene and sodium acrylate, potassium acrylate, or ammonium acrylate as monomer units (ethylene-sodium acrylate copolymer, ethylene-potassium acrylate copolymer, or ethylene-ammonium acrylate copolymer), or an ethylene-sodium acrylate copolymer.

[0059] In the case of a copolymer containing ethylene and a water-soluble ethylenically unsaturated monomer as monomer units, if the water-soluble ethylenically unsaturated monomer contains an acidic group (for example, when acrylic acid is used), the acidic group may be neutralized with an alkaline neutralizing agent before and / or after polymerization of the copolymer. The lower the degree of neutralization of the ethylenically unsaturated monomer with the alkaline neutralizing agent, the easier it is to increase the hydrophobicity of the coating layer, so the hydrophobicity of the coating layer can be controlled by the neutralization degree of the ethylene-derived monomer. Furthermore, the higher the degree of neutralization of the water-soluble ethylenically unsaturated monomer, the easier it is for the coating layer to adhere to the polymer particles, so the coatability of the polymer particles can be controlled by the neutralization degree of the water-soluble ethylenically unsaturated monomer. In a copolymer containing ethylene and a water-soluble ethylenically unsaturated monomer as a monomer unit, the degree of neutralization of the water-soluble ethylenically unsaturated monomer may be 5 to 100 mol %, preferably 40 to 100 mol %, more preferably 60 to 100 mol %, and even more preferably 80 to 100 mol %, of the acidic groups in the ethylenically unsaturated monomer. By adjusting the degree of neutralization, the lock-up height can be controlled.

[0060] In a copolymer containing ethylene and a water-soluble ethylenically unsaturated monomer as monomer units, the hydrophobicity of the coating layer tends to increase as the proportion of ethylene-derived monomer units increases, so the hydrophobicity of the coating layer can be controlled by the proportion of ethylene-derived monomer units. Furthermore, the coating layer tends to adhere to polymer particles more easily as the proportion of water-soluble ethylenically unsaturated monomer units increases, so the coatability of the polymer particles can be controlled by the proportion of water-soluble ethylenically unsaturated monomer units. The proportion of ethylene-derived monomer units in a copolymer containing ethylene and a water-soluble ethylenically unsaturated monomer as monomer units may be 72.0 to 98.0 mol %, or 80.0 to 97.0 mol %. Adjusting this proportion can control the lock-up height.

[0061] <2> The polymer containing alkylene oxide as a monomer unit may be a polyalkylene oxide (homopolymer) containing only one type of alkylene oxide as a monomer unit, or may be a polyalkylene oxide (copolymer) containing two or more types of alkylene oxide as monomer units, or may be a copolymer containing one or more types of alkylene oxide and a monomer other than alkylene oxide as a monomer unit.

[0062] The alkylene oxide may be, for example, ethylene oxide and / or propylene oxide.

[0063] The polymer containing alkylene oxide as a monomer unit may be a homopolymer containing ethylene oxide as a monomer unit (polyethylene glycol), a copolymer containing ethylene oxide and propylene oxide as monomer units, or a combination thereof.

[0064] The number average molecular weight of the polymer containing alkylene oxide as a monomer unit may be, for example, 100 to 200,000, or 700 to 50,000. Depending on the number average molecular weight, the solubility of the polymer in water can be adjusted, and the lock-up height can be controlled.

[0065] When the coating layer contains the polymer <1> and the polymer <2>, the lock-up height can also be controlled by adjusting the mass ratio of the two.

[0066] The content of the polymer <1> may be, for example, 5% by mass or more, 10% by mass or more, 15% by mass or more, 35% by mass or more, 55% by mass or more, 75% by mass or more, 85% by mass or more, or 95% by mass or more and 100% by mass or less, or 5% by mass or more, 10% by mass or more, 15% by mass or more, 35% by mass or more, 55% by mass or more, 75% by mass or more, or 85% by mass or more and 95 ... %, 55% by mass or more, or 75% by mass or more to 85% by mass or less, 5% by mass or more, 10% by mass or more, 15% by mass or more, 35% by mass or more, or 55% by mass or more to 75% or less, 5% by mass or more, 10% by mass or more, 15% by mass or more, or 35% by mass or more to 55% or less, 5% by mass or more, 10% by mass or more, or 15% by mass or more to 35% or less, 5% by mass or more, 10% by mass or more to 15% or less, or 5% by mass or more to 10% or less. In the coated resin particles, the content of the polymer <1> relative to the total amount of the polymers <1> and <2> can be regarded as the area of ​​the region in the coating layer where the polymer <1> is present relative to the total area of ​​the coating layer.

[0067] The content of the polymer <2> relative to the total amount of the polymer <1> and the polymer <2> may be 35% by mass or less, 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, 10% by mass or less, 5% by mass or less, or 3% by mass or less, and may be 0% by mass or more; 35% by mass or less, 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, 10% by mass or less, 5% by mass or less, or 3% by mass or less, and may be 1% by mass or more; 35% by mass or less, 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, 10% by mass or less, 5% by mass or less, or 3% by mass or less. In the coated resin particles, the content of the polymer <2> relative to the total amount of the polymer <1> and the polymer <2> can be regarded as the area of ​​the region in the coating layer where the polymer <2> is present relative to the total area of ​​the coating layer.

[0068] The total content of the coating layer may be, for example, 1 to 40 parts by mass relative to 100 parts by mass of the polymer particles on which the coating layer is formed.

[0069] The coating layer may have a sea-island structure composed of a sea portion containing one of the polymers <1> containing an alkene as a monomer unit and the polymer <2> containing an alkylene oxide as a monomer unit, and an island portion containing the other polymer. The island portions may be dispersed in the sea portion. The sea-island structure can be confirmed by an analytical method such as Raman spectroscopy. For example, when forming the coating layer, the sea-island structure is easily formed by using a coating material containing the polymer <1> in an emulsion state.

[0070] The sea-island structure may be composed of a sea portion containing the polymer <1> and an island portion containing the polymer <2>. In this case, even if all of the polymer <2> dissolves during water absorption, the water-absorbent resin particles are maintained to some extent in a restrained state by the polymer <1> constituting the sea portion, and therefore the 2-minute and 5-minute lockup values ​​are likely to be kept low. In coated resin particles whose coating layer has a sea-island structure, the portions where the polymer <2>, which serves as a water channel, are present are localized. Therefore, compared to a case where the polymer <2> is not localized to form island portions, the water channels that serve as the starting points for water absorption are larger, and water absorption can begin more rapidly after a certain period of water absorption delay.

[0071] The region containing the polymer <2> (a sea portion or an island portion, preferably an island portion; hereinafter referred to as the polymer-containing region <2>) extends in the thickness direction of the coating layer. At least a part (preferably the whole) of the polymer-containing region <2> constitutes at least half of the thickness of the coating layer including the region, and more preferably at least a part (preferably the whole) of the polymer-containing region <2> constitutes the entire thickness of the coating layer including the region. The polymer <2> contained in the polymer-containing region <2> (sea portion or island portion) is more water-soluble than the polymer <1>. Therefore, a part of the surface of the water-absorbent resin particle corresponding to the polymer-containing region <2> can come into contact with a liquid earlier than a part of the surface of the water-absorbent resin particle corresponding to the region (island portion or sea portion) containing the polymer <1> due to dissolution of the polymer <2>. That is, although the water-absorbent resin particle is prevented from contacting with a liquid by the coating layer, after a predetermined time has elapsed since contact with the liquid, the water-absorbent resin particle can come into contact with a liquid (becomes capable of absorbing water) due to water channels formed by dissolution of the polymer-containing region <2> (sea portion or island portion).

[0072] The coating layer can be formed on at least a portion of the surface by, for example, contacting the polymer particles with a coating material. The coating material is, for example, a liquid containing the above-mentioned components capable of forming the coating layer and a liquid medium (solvent or dispersion medium), preferably an emulsion containing the components capable of forming the coating layer and a dispersion medium.

[0073] The coating layer can be formed by, for example, (1) a method using an eggplant flask, (2) a method using a sprayer, or (3) a method using various granulators.

[0074] (1) Method using an eggplant flask In the method using an eggplant flask, first, a coating material is placed in an eggplant flask, followed by polymer particles. The eggplant flask is attached to an evaporator and heated while rotating, and the liquid medium contained in the coating material is distilled off under reduced pressure. This yields coated resin particles in which the surfaces of polymer particles are coated with a coating layer.

[0075] (2) Method Using a Sprayer In the method using a sprayer, polymer particles are first added to a separable flask equipped with a stirring blade and stirred. A coating material is sprayed onto the polymer particles that have been stirred up by the stirring blade. The coating material can be sprayed using, for example, a two-fluid nozzle. Since uniform coating can be expected, the coating material is desirably atomized and sprayed using a current of inert gas such as nitrogen. The contents of the separable flask are then removed, heated in a hot air dryer, and cooled to room temperature to obtain coated resin particles.

[0076] (3) Methods Using Various Granulators Granulators that can be used to produce coated resin particles include, for example, a tumbling granulator, an agitation granulator, and a fluidized bed granulator.

[0077] When using a tumbling granulator, a shallow, inclined circular container attached to the tumbling granulator is rotated, and polymer particles are supplied to the circular container while an appropriate amount of coating material is added. Then, the liquid medium contained in the coating material causes some of the particles to aggregate during the tumbling, forming a coating layer on their surfaces. The addition step of adding the polymer particles and the coating material may be performed multiple times if necessary.

[0078] When using an agitation granulator, polymer particles are charged into a mixer attached to the agitation granulator, and the coating material is added while the particles are being mixed by agitation. Then, the liquid medium contained in the coating material causes some of the particles to aggregate during the agitation, forming a coating layer on their surfaces. The addition step of adding the polymer particles and the coating material may be carried out multiple times as necessary. Excessive aggregation of the polymer particles can be suppressed by controlling the shear force of the mixer.

[0079] When using a fluidized bed granulator, first, polymer particles are placed in a container equipped in the fluidized bed granulator that can blow hot air from the bottom, and the polymer particles are fluidized in advance. Then, when a coating material is sprayed from a nozzle equipped in the container, the liquid medium contained in the coating material causes some of the polymer particles to aggregate during stirring, forming a coating layer on their surfaces. The coating material may be sprayed multiple times if necessary. Excessive aggregation of the polymer particles can be suppressed by adjusting the amount and / or frequency of spraying of the coating material. As the fluidized bed granulator, for example, a fluidized bed granulator FBD / SG (manufactured by YENCHEN MACHINERY) can be used.

[0080] The absorbent body may have another water retention layer (for example, a second water retention layer) in addition to the first water retention layer. The other water retention layer may contain only water-absorbent resin particles A, only water-absorbent resin particles B, water-absorbent resin particles A and B, or a combination of these with other water-absorbent resin particles. The other water retention layer may contain hydrophilic fibers in addition to water-absorbent resin particles, or may consist of only hydrophilic fibers.

[0081] The water-absorbent resin particle ratio in the other water retention layer may be, for example, 0% by mass or more, 1% by mass or more, 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more and 100% by mass or less; It may be 60% by mass or more, 70% by mass or more, or 80% by mass or more and 90% by mass or less; it may be 0% by mass or more, 1% by mass or more, 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more and 80% by mass or less; it may be 0% by mass or more, 1% by mass or more, 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, or 60% by mass or more It may be 70% by mass or less, 0% by mass or more, 1% by mass or more, 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, or 50% by mass or more and 60% by mass or less, 0% by mass or more, 1% by mass or more, 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, or 40% by mass or more and 50% by mass or less, 0% by mass or more, 1% by mass or more, 5% by mass or more, 10% by mass or more, 20% by mass or more, or 30% by mass The water-absorbent resin particle ratio in the other water retention layer is preferably 30% by mass or more, from the viewpoint of easily obtaining an absorbent body excellent in permeation rate and return amount.

[0082] In other water retention layers, the amount of hydrophilic fibers in the water retention layer relative to the amount of the water retention layer may be, for example, 0% by mass or more, 1% by mass or more, 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more and 100% by mass or less. % or more, 50% or more, 60% or more, 70% or more, or 80% or more and 90% or less by mass; 0% or more, 1% or more, 5% or more, 10% or more, 20% or more, 30% or more, 40% or more, 50% or more, 60% or more, or 70% or more and 80% or less by mass; 0% or more, 1% or more, 5% or more, 10% or more, 20% or more, 30% or more, 40% or more, 50% or more by mass; It may be 60% by mass or more and 70% by mass or less, 0% by mass or more, 1% by mass or more, 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, or 50% by mass or more and 60% by mass or less, 0% by mass or more, 1% by mass or more, 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, or 40% by mass or more and 50% by mass or less, 0% by mass or more, 1% by mass or more, 5% by mass or more, 10% by mass or more, 20% by mass or more, or 3 It may be 0% by mass or more and 40% by mass or less, 0% by mass or more, 1% by mass or more, 5% by mass or more, 10% by mass or more, or 20% by mass or more and 30% by mass or less, 0% by mass or more, 1% by mass or more, 5% by mass or more, or 10% by mass or more and 20% by mass or less, 0% by mass or more, 1% by mass or more, or 5% by mass or more and 10% by mass or less, 0% by mass or more, or 1% by mass or more and 5% by mass or less, or 0% by mass or more and 1% by mass or less.

[0083] The other water-retaining layer may further contain inorganic particles, a deodorant, etc. in addition to the water-absorbent resin particles and hydrophilic fibers.

[0084] Fig. 1 is a schematic cross-sectional view showing an example of an absorbent body. The absorbent body 50 shown in Fig. 1 includes a water retention layer 10 as a first water retention layer, and sheet-like shape-retaining members 20a and 20b sandwiching both sides of the water retention layer 10. The water retention layer 10 includes water-absorbent resin particles 1 and optionally added hydrophilic fibers 3. The water-absorbent resin particles 1 include water-absorbent resin particles A and water-absorbent resin particles B. The proportion of water-absorbent resin particles in the water retention layer 10 may be, for example, 70 mass% or less.

[0085] The shape retaining member 20a is disposed on one side of the water retaining layer 10 in contact with the water retaining layer 10. The shape retaining member 20b is disposed on the other side of the water retaining layer 10 in contact with the water retaining layer 10. That is, the water retaining layer 10 is disposed between the shape retaining members 20a and 20b. The water retaining layer 10 does not need to be completely surrounded by the shape retaining members 20a and 20b; for example, the end of the water retaining layer 10 may be exposed to the outside. The shape retaining members 20a and 20b may be two separate sheets or a single folded sheet. The shape retaining members 20a and 20b may be, for example, a nonwoven fabric such as an airlaid nonwoven fabric, or tissue paper.

[0086] FIG. 2 is a schematic cross-sectional view showing another example of an absorbent body. The absorbent body 51 shown in FIG. 2 includes sheet-like shape-retaining members 20a and 20b, an adhesive layer 21, a water-retaining layer 10A as a first water-retaining layer, a water-retaining layer 10B as a second water-retaining layer, and an intermediate layer 25. The water-retaining layer 10A is adhered to the shape-retaining member 20a via the adhesive layer 21. The water-retaining layer 10B is adhered to the shape-retaining member 20b via the adhesive layer 21. The water-retaining layer 10A and the water-retaining layer 10B are separated from each other by the intermediate layer 25. Each of the water-retaining layers 10A and 10B contains water-absorbent resin particles 1 and, optionally, hydrophilic fibers 3. The water-retaining layers 10A and 10B may be composed solely of water-absorbent resin particles. The water-absorbent resin particle ratio in the water-retaining layers 10A and 10B may be, for example, 80 to 100% by mass.

[0087] The water retention layer 10B, which is the first water retention layer, is provided on the liquid-absorbing side of the absorbent body 51. The absorbent body 51 absorbs water from the side facing the water retention layer 10B, which is the first water retention layer. That is, when the absorbent body 51 is used in an absorbent article such as a diaper, the side of the absorbent body 51 facing the water retention layer 10B is placed on the wearer's side. The water-absorbent resin particles 1 contained in the water retention layer 10B include water-absorbent resin particles A and B. The water-absorbent resin particles 1 contained in the water retention layer 10A, which is the second water retention layer, may be only water-absorbent resin particles A or B, may be water-absorbent resin particles A and B, may be only water-absorbent resin particles other than the water-absorbent resin particles A and B, or may be a mixture of water-absorbent resin particles A or B and other water-absorbent resin particles.

[0088] By having the absorbent body 51 have the first water retention layer, water retention layer 10B, on the wearer side, the liquid penetrates into the second water retention layer, water retention layer 10A, while the liquid is sufficiently diffused in the surface direction of the absorbent body in water retention layer 10B, so that the occurrence of gel blocking in water retention layer 10A can be suppressed, and the performance of the absorbent body as a whole (high permeation rate and low return amount) can be further improved.

[0089] The intermediate layer 25 may be a nonwoven fabric such as an air-laid nonwoven fabric or an air-through nonwoven fabric, or may be tissue paper. The intermediate layer 25 may be, for example, a single sheet of air-through nonwoven fabric, a laminate of two sheets of tissue paper, or a laminate of tissue paper and air-laid nonwoven fabric.

[0090] The adhesive layer 21 may contain an adhesive. Examples of the adhesive include hot melt adhesives. Examples of the hot melt adhesive include mixtures of a base polymer such as ethylene-vinyl acetate copolymer, styrene-isoprene-styrene block copolymer, styrene-butadiene-styrene block copolymer, styrene-ethylene-butylene-styrene block copolymer, styrene-ethylene-propylene-styrene block copolymer, and amorphous polypropylene with a tackifier, a plasticizer, an antioxidant, and the like.

[0091] In plan view, the water-absorbent resin particles A and B in the first water retention layer (water retention layer 10 or water retention layer 10B) in the absorbent body 50 or 51 are preferably arranged over substantially the entire surface of the first water retention layer.

[0092] 1 and 2 are examples, and the configuration of the absorbent body is not limited to these. The absorbent body may, for example, include one or more other water retention layers. When the absorbent body includes two or more water retention layers, the first water retention layer is disposed on the liquid-absorbing side of the absorbent body (for example, the wearer side in an absorbent article such as a diaper). The number of water retention layers included in the absorbent body may be, for example, 1 to 2 layers, 1 to 3 layers, or 2 to 3 layers. The absorbent body may consist of only a water retention layer.

[0093] The basis weight of the water-absorbent resin particles in the absorbent body 50 or 51 is set to 50 g / m because this further improves the effect of achieving both a high absorption rate and a small amount of return. ２ Above, 75g / m ２ Above, 100g / m ２ Above, 125g / m ２ Above, 150g / m ２ Above, 175g / m ２ Above, 200g / m ２ Above, 225g / m ２ Above, 250g / m ２ Above, 275g / m ２ or more, or 300 g / m ２ Above 450 g / m ２ or less, and ２ Above, 75g / m ２ Above, 100g / m ２ Above, 125g / m ２ Above, 150g / m ２ Above, 175g / m ２ Above, 200g / m ２ Above, 225g / m ２ Above, 250g / m ２ Above, 275g / m ２ or more, or 300 g / m ２ That's 425g / m ２ or less, and ２ Above, 75g / m ２ Above, 100g / m２ Above, 125g / m ２ Above, 150g / m ２ Above, 175g / m ２ Above, 200g / m ２ Above, 225g / m ２ Above, 250g / m ２ Above, 275g / m ２ or more, or 300 g / m ２ Above 400 g / m ２ or less, and ２ Above, 75g / m ２ Above, 100g / m ２ Above, 125g / m ２ Above, 150g / m ２ Above, 175g / m ２ Above, 200g / m ２ Above, 225g / m ２ Above, 250g / m ２ Above, 275g / m ２ or more, or 300 g / m ２ That's 375 g / m ２ or less, and ２ Above, 75g / m ２ Above, 100g / m ２ Above, 125g / m ２ Above, 150g / m ２ Above, 175g / m ２ Above, 200g / m ２ Above, 225g / m ２ Above, 250g / m ２ Above, 275g / m ２ or more, or 300 g / m ２ Above 350 g / m ２ or less, and ２ Above, 75g / m ２ Above, 100g / m ２ Above, 125g / m ２ Above, 150g / m ２ Above, 175g / m ２ Above, 200g / m ２ Above, 225g / m ２ Above, 250g / m ２ Above, 275g / m ２ or more, or 300 g / m ２That's 325g / m ２ or less, and ２ Above, 75g / m ２ Above, 100g / m ２ Above, 125g / m ２ Above, 150g / m ２ Above, 175g / m ２ Above, 200g / m ２ Above, 225g / m ２ Above, 250g / m ２ or more, or 275 g / m ２ Above 300 g / m ２ or less, and ２ Above, 75g / m ２ Above, 100g / m ２ Above, 125g / m ２ Above, 150g / m ２ Above, 175g / m ２ Above, 200g / m ２ Above, 225g / m ２ or more, or 250 g / m ２ That's 275 g / m ２ or less, and ２ Above, 75g / m ２ Above, 100g / m ２ Above, 125g / m ２ Above, 150g / m ２ Above, 175g / m ２ Above, 200g / m ２ Above, 225g / m ２ or more, or 250 g / m ２ That's 260g / m ２ The basis weight of the water-absorbent resin particles is the total mass of the water-absorbent resin particles per unit area of ​​the absorbent body.

[0094] The absorbent according to the present embodiment may contain inorganic powder, deodorant, antibacterial agent, pigment, dye, fragrance, adhesive, etc. These additives can impart various functions to the absorbent. When the water-absorbent resin particles contain inorganic particles, the absorbent may contain inorganic powder in addition to the inorganic particles in the water-absorbent resin particles. Examples of inorganic powders include silicon dioxide (e.g., amorphous silica), zeolite, kaolin, and clay-based powders.

[0095] The absorbent body according to this embodiment may be, for example, in the form of a sheet, and the thickness of the absorbent body (for example, the thickness of a sheet-shaped absorbent body) may be 0.1 to 20 mm or 0.3 to 15 mm.

[0096] The method for manufacturing an absorbent body having one or more water retention layers according to this embodiment may include forming a first water retention layer. The absorbent body can be manufactured, for example, by a method including laminating a water retention layer including the first water retention layer, and, as necessary, a shape retention member and other layers, such that the first water retention layer is located closest to the liquid absorption side of the absorbent body.

[0097] The absorbents exemplified above are used, for example, in various absorbent articles. Examples of absorbent articles include sanitary materials, agricultural and horticultural materials such as water retention agents and soil conditioners, and industrial materials such as waterproofing agents and anti-condensation agents. Examples of sanitary materials include diapers (e.g., disposable diapers), toilet training pants, incontinence pads, sanitary materials (sanitary napkins, tampons, etc.), sweat pads, pet sheets, portable toilet components, and animal waste disposal materials. The absorbent article may be disposable.

[0098] Fig. 3 is a cross-sectional view showing an example of an absorbent article. The absorbent article 100 shown in Fig. 3 includes an absorbent body 50, a liquid-permeable sheet 30, and a liquid-impermeable sheet 40. In the absorbent article 100, the liquid-impermeable sheet 40, the absorbent body 50, and the liquid-permeable sheet 30 are layered in this order.

[0099] The liquid permeable sheet 30 is disposed in the outermost layer position on the liquid absorption side (the side into which the liquid to be absorbed penetrates) of the absorbent article 100. The liquid permeable sheet 30 is disposed outside the shape retention member 20b in a state of contact with the shape retention member 20b. The liquid impermeable sheet 40 is disposed in the outermost layer position on the side opposite the liquid permeable sheet 30 in the absorbent article 100. The liquid impermeable sheet 40 is disposed outside the shape retention member 20a in a state of contact with the shape retention member 20a. The liquid permeable sheet 30 and the liquid impermeable sheet 40 have main surfaces that are wider than the main surface of the absorbent body 50, and the outer edges of the liquid permeable sheet 30 and the liquid impermeable sheet 40 extend around the water retaining layer 10 and the shape retention members 20a, 20b. However, the size relationships among the water retaining layer 10, shape retaining members 20a, 20b, liquid permeable sheet 30, and liquid impermeable sheet 40 are not particularly limited and may be adjusted as appropriate depending on the intended use of the absorbent article.

[0100] The liquid-permeable sheet 30 may be a nonwoven fabric. The nonwoven fabric used as the liquid-permeable sheet 30 may have appropriate hydrophilicity from the viewpoint of the liquid absorption performance of the absorbent article. From that viewpoint, the liquid-permeable sheet 30 may be a nonwoven fabric having a hydrophilicity of 5 to 200 as measured in accordance with the Pulp and Paper Testing Method No. 68 (2000) of the Paper and Pulp Technology Association. The hydrophilicity of the nonwoven fabric may also be 10 to 150. For details of Pulp and Paper Testing Method No. 68, see, for example, International Publication No. 2011 / 086843.

[0101] Hydrophilic nonwoven fabrics may be made from fibers with moderate hydrophilicity, such as rayon, or from fibers obtained by hydrophilizing hydrophobic chemical fibers, such as polyolefin and polyester fibers. Methods for obtaining nonwoven fabrics containing hydrophilized hydrophobic chemical fibers include spunbonding a mixture of hydrophobic chemical fibers and a hydrophilizing agent, adding a hydrophilizing agent to the hydrophobic chemical fibers, and impregnating a spunbond nonwoven fabric obtained from hydrophobic chemical fibers with a hydrophilizing agent. Examples of hydrophilizing agents include anionic surfactants such as aliphatic sulfonates and higher alcohol sulfates, cationic surfactants such as quaternary ammonium salts, nonionic surfactants such as polyethylene glycol fatty acid esters, polyglycerin fatty acid esters, and sorbitan fatty acid esters, silicone surfactants such as polyoxyalkylene-modified silicones, and stain release agents made from polyester, polyamide, acrylic, or urethane resins.

[0102] The basis weight (mass per unit area) of the nonwoven fabric used as the liquid-permeable sheet 30 is 5 to 200 g / m from the viewpoint of imparting good liquid permeability, flexibility, strength, and cushioning properties to the absorbent article, and from the viewpoint of increasing the permeation rate of the absorbent article. ２ , 8 to 150 g / m ２ , or 10 to 100 g / m ２ The thickness of the liquid-permeable sheet 30 may be 20 to 1400 μm, 50 to 1200 μm, or 80 to 1000 μm.

[0103] The liquid-impermeable sheet 40 prevents liquid absorbed by the water-retaining layer 10 from leaking out from the liquid-impermeable sheet 40 side. The liquid-impermeable sheet 40 may be a resin sheet or a nonwoven fabric. The resin sheet may be a sheet made of a synthetic resin such as polyethylene, polypropylene, or polyvinyl chloride. The nonwoven fabric may be a spunbond / meltblown / spunbond (SMS) nonwoven fabric in which a water-resistant meltblown nonwoven fabric is sandwiched between high-strength spunbond nonwoven fabrics. The liquid-impermeable sheet 40 may be a composite sheet of a resin sheet and a nonwoven fabric (e.g., a spunbond nonwoven fabric or a spunlace nonwoven fabric). The liquid-impermeable sheet 40 may be breathable to reduce stuffiness during wear and to alleviate discomfort to the wearer. For example, a low-density polyethylene (LDPE) resin sheet can be used as the breathable liquid-impermeable sheet 40.

[0104] The absorbent article 100 can be manufactured, for example, by a method including placing the absorbent body 50 between a liquid-permeable sheet 30 and a liquid-impermeable sheet 40. A laminate in which the liquid-impermeable sheet 40, the absorbent body 50, and the liquid-permeable sheet 30 are laminated in this order is pressurized as necessary.

[0105] 3 is an example, and the configuration of the absorbent article is not limited to this. The shape of the absorbent article is determined appropriately depending on the application. For example, if the absorbent article is an incontinence pad or a sanitary napkin, the absorbent article may be approximately rectangular, oval, hourglass-shaped, or battledore-shaped.

[0106] The present disclosure will be described in more detail below with reference to examples, although the absorbent body and the method for producing the same of the present invention are not limited to these examples.

[0107] [Production of Water-Absorbent Resin Particles] (Production Example 1) A round-bottomed cylindrical separable flask with an inner diameter of 11 cm and a volume of 2 L was prepared, equipped with a reflux condenser, a dropping funnel, a nitrogen gas inlet tube, and a stirrer (a stirring blade having two stages of four inclined paddle blades with a blade diameter of 5 cm). 293 g of n-heptane (hydrocarbon dispersion medium) and 0.736 g of maleic anhydride-modified ethylene-propylene copolymer (polymer dispersant, Mitsui Chemicals, Inc., Hiwax 1105A) were added to the separable flask to obtain a mixture. The mixture was heated to 80 ° C. while stirring at a rotation speed of 300 rpm to dissolve the dispersant, and then the mixture was cooled to 55 ° C.

[0108] Next, 92.0 g of an 80.5 wt% aqueous acrylic acid solution (acrylic acid: 1.03 mol) was placed in a 500 mL Erlenmeyer flask. Subsequently, while cooling externally, 102.2 g of a 30 wt% aqueous sodium hydroxide solution was added dropwise to neutralize 75 mol% of the acrylic acid. Thereafter, 0.092 g of hydroxyethyl cellulose (thickener, Sumitomo Seika Chemicals Co., Ltd., HEC AW-15F), 0.0736 g (0.272 mmol) of potassium persulfate as a radical polymerization initiator, 0.0101 g (0.0581 mmol) of ethylene glycol diglycidyl ether (internal crosslinking agent), and 32.85 g of ion-exchanged water were added and dissolved to prepare a first-stage aqueous monomer solution.

[0109] The first-stage monomer aqueous solution was then added to the separable flask and stirred for 10 minutes. A surfactant solution was obtained by dissolving 0.736 g of sucrose stearate (surfactant, manufactured by Mitsubishi Chemical Foods Corporation, Ryoto Sugar Ester S-370, HLB: 3) in 6.62 g of n-heptane with heating. A reaction solution was obtained by adding 7.356 g of the surfactant solution to the separable flask. The rotation speed was then changed to 550 rpm, and the system was thoroughly purged with nitrogen while stirring the reaction solution. The separable flask was then immersed in a 70°C water bath to heat the reaction solution, and first-stage polymerization was carried out for 10 minutes to obtain a first-stage reaction mixture.

[0110] Next, 128.8 g of an 80.5% by mass aqueous acrylic acid solution (1.44 mol of acrylic acid) was placed in a separate 500 mL Erlenmeyer flask. Subsequently, while cooling externally, 143.1 g of a 30% by mass aqueous sodium hydroxide solution was added dropwise to neutralize the 75 mol% acrylic acid. Subsequently, 0.1030 g (0.3812 mmol) of potassium persulfate as a radical polymerization initiator, 0.0116 g (0.0655 mmol) of ethylene glycol diglycidyl ether (internal crosslinking agent), and 0.63 g of ion-exchanged water were added and dissolved to prepare a second-stage aqueous monomer solution.

[0111] The rotation speed was then changed to 1000 rpm, and the first-stage reaction mixture was cooled to 25°C while stirring, and then the entire amount of the second-stage aqueous monomer solution was added to the first-stage reaction mixture to obtain a reaction solution. The reaction solution was then stirred while the system was thoroughly purged with nitrogen. The separable flask was then immersed in a 70°C water bath to heat the reaction solution, and second-stage polymerization was carried out for 5 minutes to obtain a second-stage reaction mixture (polymer particles before surface crosslinking).

[0112] After the second-stage polymerization, the temperature of the second-stage reaction mixture was increased in an oil bath at 125°C, and 252.0 g of water was extracted from the system by azeotropic distillation of n-heptane and water while refluxing n-heptane. Subsequently, the oil bath was adjusted so that the internal temperature was 83°C, and 0.0884 g (0.5075 mmol) of ethylene glycol diglycidyl ether was added as a surface cross-linking agent, followed by maintaining the temperature at 83°C for 2 hours to obtain a dispersion of surface-cross-linked polymer particles.

[0113] Thereafter, the temperature of the dispersion liquid of the resin particles after surface crosslinking described above was raised in an oil bath of 125°C, and n-heptane was evaporated and dried to obtain a dried product. The dried product was passed through a sieve having an opening of 850 µm, to obtain 232.8 g of water-absorbent resin particles a.

[0114] Amorphous silica (Toxil NP-S, Oriental Silicas Corporation, hydrophilic) in an amount of 0.2% by mass relative to the mass of the water-absorbent resin particles a was mixed with the water-absorbent resin particles a to obtain water-absorbent resin particles (1).

[0115] (Production Example 2) 236.3 g of water absorbent resin particles b was obtained in the same manner as in Production Example 1, except that the radical polymerization initiator used in the first-stage aqueous monomer solution was changed to a combined use of 0.092 g (0.339 mmol) of 2,2′-azobis(2-amidinopropane) dihydrochloride, which was an azo compound, and 0.028 g (0.102 mmol) of potassium persulfate, the amount of ethylene glycol diglycidyl ether added was changed to 0.0046 g (0.026 mmol), the radical polymerization initiator used in the second-stage aqueous monomer solution was changed to a combined use of 0.129 g (0.475 mmol) of 2,2′-azobis(2-amidinopropane) dihydrochloride, which was an azo compound, and 0.039 g (0.143 mmol), and the amount of water extracted to the outside of the system by azeotropic distillation was changed to 219.8 g.

[0116] Amorphous silica (Toxil NP-S, hydrophilic, manufactured by Oriental Silicas Corporation) in an amount of 0.2% by mass relative to the mass of the water-absorbent resin particles b was mixed with the water-absorbent resin particles b to obtain water-absorbent resin particles (2).

[0117] (Production Example 3) The same procedure as in Production Example 2 was carried out except that the amount of water extracted from the system by azeotropic distillation was changed to 234.2 g, to obtain 227.2 g of water-absorbent resin particles c.

[0118] Amorphous silica (Toxil NP-S, Oriental Silicas Corporation, hydrophilic) in an amount of 0.2% by mass relative to the mass of the water-absorbent resin particles c was mixed with the water-absorbent resin particles c to obtain water-absorbent resin particles (3).

[0119] (Production Example 4) 234.5 g of water absorbent resin particles d were obtained in the same manner as in Production Example 1, except that the amount of ethylene glycol diglycidyl ether (internal crosslinking agent) added was changed to 0.00534 g (0.0306 mmol) when preparing a first-stage aqueous monomer solution.

[0120] Amorphous silica (Toxil NP-S, Oriental Silicas Corporation, hydrophilic) in an amount of 0.5% by mass relative to the mass of water-absorbent resin particles d was mixed with water-absorbent resin particles d to obtain water-absorbent resin particles (4).

[0121] [Production of Coated Water-Absorbent Resin Particles] (Production Example 5) Water-absorbent resin particles a were classified using a sieve with a mesh size of 250 μm to obtain 500 g or more of water-absorbent resin particles a having a particle size of 250 to 850 μm.

[0122] An aqueous polyethylene glycol solution prepared from 5.00 g of polyethylene glycol having a number average molecular weight of 6,000 (Fujifilm Wako Pure Chemical Industries, Ltd., polyethylene glycol 6,000) and 45.00 g of ion-exchanged water was added to 200.00 g of an ethylene-sodium acrylate copolymer emulsion having a degree of neutralization of 75 mol% (Sumitomo Seika Chemicals Co., Ltd., Zaixen N, weight ratio of ethylene-derived and sodium acrylate-derived monomers: 79.5:20.5) with a non-volatile content of 25% by mass, and the mixture was diluted with 250.00 g of ion-exchanged water to obtain 500.00 g of coating material A.

[0123] 500.0 g of the classified water absorbent resin particles a described above was placed in a container of a fluidized bed granulator, and hot air at 50°C was blown from the bottom of the container. Next, the coating material A was sprayed onto the water absorbent resin particles being blown up by the air blown while drying. After spraying the coating material A, the particles were dried at 50°C for 30 minutes to obtain coated resin particles.

[0124] 50.0 g of the obtained coated resin particles were spread on a metal tray measuring 26 cm in length and 20 cm in width, and the tray was covered with aluminum foil. Holes were punched in the aluminum foil, and the coated resin particles were heated for 30 minutes in a hot air dryer (ADVANTEC, FV-320) set to 70°C to obtain coated resin particles (1).

[0125] (Production Example 6) [Preparation of ethylene-sodium acrylate copolymer emulsion] Water and ice were placed in a plastic tray measuring 27 cm in length, 38 cm in width, and 7 cm in depth to prepare an ice bath at 3°C. A glass beaker with an internal volume of 1 L was placed in this ice bath, and 545.78 g of ion-exchanged water was added. The ice bath was placed on a magnetic stirrer, and stirrer chips were added to the beaker, followed by stirring.

[0126] 10.55 g of sodium hydroxide (granules) (Nacalai Tesque, Inc.) was added little by little to a beaker to prepare an aqueous sodium hydroxide solution.

[0127] A round-bottomed, cylindrical, separable flask with an inner diameter of 11 cm and an internal volume of 2 L was prepared, equipped with a reflux condenser, a thermometer, and a stirrer (stirring blades with four inclined paddle blades and a blade diameter of 5 cm). To this flask, 100 g of ethylene-acrylic acid copolymer (SK global chemical: Primacol 5980i) with a weight ratio of ethylene-derived and acrylic acid-derived monomers of 79.5:20.5 was added. The entire amount of the aforementioned aqueous sodium hydroxide solution was then added. The beaker used to prepare the aqueous sodium hydroxide solution was then washed with 50.0 g of ion-exchanged water, and the wash water was added to the separable flask to obtain a reaction solution.

[0128] While stirring the reaction solution with a stirrer at a rotation speed of 500 rpm, the reaction solution was immersed in an oil bath at 103° C., and the internal temperature was raised to 95° C. Thereafter, the temperature of the oil bath was appropriately adjusted so that the internal temperature was 95 to 97° C., and the reaction solution was maintained for 4 hours.

[0129] Thereafter, the separable flask was removed from the oil bath and allowed to cool at room temperature until the internal temperature reached 35° C. After confirming that the internal temperature was 35° C. or lower, the reaction liquid was filtered through a nylon mesh with a mesh size of 108 μm, and an ethylene-sodium acrylate copolymer emulsion with a degree of neutralization of 90 mol% and a nonvolatile content of 15% by mass was obtained as the filtrate.

[0130] An aqueous polyethylene glycol solution prepared from 5.00 g of polyethylene glycol having a number average molecular weight of 6,000 (Fujifilm Wako Pure Chemical Industries, Ltd., polyethylene glycol 6,000) and 45.00 g of ion-exchanged water was added to 89.29 g of an ethylene-sodium acrylate copolymer emulsion having a degree of neutralization of 48 mol% and a non-volatile content of 28% by mass (Sumitomo Seika Chemicals Co., Ltd., Zaixen NC, weight ratio of ethylene-derived and sodium acrylate-derived monomers of 79.5:20.5) and 166.67 g of the ethylene-sodium acrylate copolymer emulsion having a degree of neutralization of 90 mol% and a non-volatile content of 15% by mass produced in the preparation of the ethylene-sodium acrylate copolymer emulsion described above, and the mixture was diluted with 194.04 g of ion-exchanged water to obtain 500.00 g of coating material B.

[0131] [Preparation of coated resin particles] Coated resin particles (2) were obtained in the same manner as in Production Example 5, except that coating material B was used as the coating material and the drying conditions for the coated resin particles using a hot air dryer (FV-320, manufactured by ADVANTEC) were changed to 90°C for 60 minutes.

[0132] (Production Example 7) To 333.33 g of the ethylene-sodium acrylate copolymer emulsion having a non-volatile content of 15% by mass and a degree of neutralization of 90 mol% produced in the preparation of the above ethylene-sodium acrylate copolymer emulsion, an aqueous polyethylene glycol solution prepared from 5.00 g of polyethylene glycol having a number average molecular weight of 6,000 (Fujifilm Wako Pure Chemical Industries, Ltd., polyethylene glycol 6,000) and 45.00 g of ion-exchanged water was added, and the mixture was diluted with 116.67 g of ion-exchanged water to obtain 500.00 g of coating material C. Coated resin particles (3) were obtained in the same manner as in Production Example 5, except that water-absorbent resin particles b were used as the water-absorbent resin particles, coating material C was used as the coating material, and the drying conditions for the coated resin particles using a hot air dryer were changed to a setting of 100°C for 30 minutes.

[0133] (Production Example 8) Coated resin particles (4) were obtained in the same manner as in Production Example 7, except that the drying conditions for the coated resin particles in the hot air dryer were changed to a setting of 100°C for 75 minutes.

[0134] (Production Example 9) To 666.67 g of the ethylene-sodium acrylate copolymer emulsion having a degree of neutralization of 90 mol% and a non-volatile content of 15% by mass, which was produced in the preparation of the ethylene-sodium acrylate copolymer emulsion described above, was added an aqueous polyethylene glycol solution prepared from 25.00 g of polyethylene glycol having a number average molecular weight of 6,000 (Fujifilm Wako Pure Chemical Industries, Ltd., polyethylene glycol 6,000) and 225.00 g of ion-exchanged water, and the mixture was diluted with 83.33 g of ion-exchanged water to obtain 1,000.00 g of coating material D. Coated resin particles (5) were obtained in the same manner as in Production Example 5, except that the water-absorbent resin particles c were used as the water-absorbent resin particles, the coating material D was used as the coating material, and the drying conditions for the coated resin particles using a hot air dryer were changed to a setting of 95°C for 30 minutes.

[0135] (Production Example 10) 25.00 g of polyvinyl chloride (FUJIFILM Wako Pure Chemical Industries, Ltd.) was dissolved in 475.00 g of tetrahydrofuran (TCI) to prepare 500.00 g of coating material E. Coated resin particles (6) were obtained in the same manner as in Production Example 5, except that coating material E was used as the coating material, the temperature of the air blown from the bottom of the container was 40°C, and heating with a hot air dryer was not performed.

[0136] The obtained water-absorbent resin particles and coated resin particles were measured for their saline water retention capacity, and lockup values ​​at 2 minutes, 5 minutes, and 10 minutes by the following methods. The results are shown in Table 1.

[0137] <Measurement of Water Retention Capacity> The water retention capacity was measured in an environment of 25°C ± 2°C and humidity of 50 ± 10%. After adding 500 g of physiological saline to a 500 mL polyethylene beaker, 2.00 g of particles for evaluation were added little by little while rotating a stirring bar (8 mm x 30 mm, no ring) using a stirrer at 600 rpm. After the entire amount of particles for evaluation had been added, the mixture was stirred for 30 minutes. The mixture was then transferred into a cotton bag (membrane No. 60, width 100 mm x length 200 mm), and the top of the cotton bag was closed with a rubber band. Next, the mixture was dehydrated for 1 minute using a centrifuge (manufactured by Kokusan Co., Ltd., product number: H-122) set to a centrifugal force of 167 G, and the mass W of the cotton bag containing the swollen gel after dehydration was measured. Ａ The same procedure was carried out without adding the particles to the cotton bag, and the wet empty mass W Ｂ The water retention capacity of the particles for evaluation in physiological saline (25°C) was calculated using the following formula: Water retention capacity [g / g] = (W Ａ -W Ｂ ) / Mass of particles for evaluation

[0138] <Measurement of Lock-up Height> The measurement of the lock-up height was carried out in an environment of 25°C ± 2°C and humidity 50 ± 10%. 0.200 g of particles for evaluation was precisely weighed and spread in a layer on the bottom of an acrylic cylinder with an inner diameter of 2.0 cm and a depth of 8.0 cm to form a particle layer with a flat upper surface, and the height H0 [cm] of the particle layer was measured. Thereafter, 20 g of physiological saline at 25°C was poured into the top of the acrylic cylinder in one go. Measurement of the particle layer height was started once the entire amount of physiological saline was poured, and H2, H5, and H10 [cm] were read as values ​​after 2 minutes, 5 minutes, and 10 minutes, respectively. The lock-up height was calculated using the following formula. If the upper surface of the particle layer after water absorption was not flat, the height of the highest part was read. Lock-up n-minute height [cm] = Hn - H0

[0139]

[0140] <Preparation of mixing core type absorbent articles> (Constitution for children: Examples 1 to 3, Comparative Examples 1 to 6) A water-retaining layer measuring 40 cm x 12 cm was formed by uniformly mixing the predetermined amounts of water-absorbent resin particles, coated resin particles, and disintegrated pulp (Leonia, Rayflock) shown in Table 2 by air papermaking. Next, the top and bottom of the water-retaining layer were cut into the same size as the water-retaining layer, with a basis weight of 16 g / m². ２ The absorbent body was prepared by sandwiching the absorbent body between two tissue papers and applying a load of 141 kPa to the entire body for 30 seconds. ２ A mixing core type absorbent article was obtained by disposing a polyethylene air-through type porous liquid-permeable sheet of the above. In the mixing core type absorbent article, water-absorbent resin particles having no coating layer were used as water-absorbent resin particles A, and coated resin particles were used as water-absorbent resin particles B.

[0141] (Configuration for adults: Examples 4 to 6, Comparative Examples 7 to 10) Absorbent articles were produced in the same manner as above, except that the predetermined amounts of water-absorbent resin particles, coated resin particles, and crushed pulp shown in Table 3 were used, the sizes of the water-retaining layer, tissue paper, and liquid-permeable sheet were 60 × 12 cm, and the pressing pressure was 282 kPa.

[0142] The types and amounts of water-absorbent resin particles and coated resin particles used, and the amount of disintegrated pulp used in the mixing core type absorbent article are shown in Tables 2 and 3. The water-absorbent resin particle ratio (the ratio [mass %] of the total amount of water-absorbent resin particles and coated resin particles to the total amount of water-absorbent resin particles, coated resin particles, and pulp used) is shown in Tables 2 and 3. Tables 2 and 3 show the reduction amounts of water-absorbent resin particles (total amount of water-absorbent resin particles and coated resin particles), pulp, and the total amount of these used, based on Comparative Example 1 or Comparative Example 7. In the tables, "SAP" represents water-absorbent resin particles.

[0143]

[0144]

[0145] <Preparation of two-layer sheet type absorbent article> (Comparative Example 11) Basis weight 40 g / m ２ An airlaid nonwoven fabric (KNH Enterprise Co., Ltd.) was cut into two pieces measuring 42 cm x 14 cm, which were designated as airlaid nonwoven fabrics 1 and 2, respectively.

[0146] Using a hot melt coater (Harries Co., Ltd., pump: Marshal 150, table: XA-DT, tank set temperature: 150°C, hose interior set temperature: 165°C, gun head set temperature: 170°C), a total amount of 0.2 g of hot melt adhesive (Henkel Japan Co., Ltd., ME-765E, softening point 96°C) was applied to the airlaid nonwoven fabric 2 in 14 linear stripes spaced 10 mm apart. The adhesive application pattern was a spiral stripe. During application, the four outer periphery sides (1 cm wide) of the airlaid nonwoven fabric 2 were masked to prevent the adhesive from being applied.

[0147] 7.2 g of water-absorbent resin particles (1) were uniformly scattered over the central portion (40 cm × 12 cm area) of the adhesive-coated surface of the air-laid nonwoven fabric 2 to provide a first water-retaining layer as a lower layer.

[0148] Using a hot melt coater, a total amount of 0.2 g of hot melt adhesive was applied to the airlaid nonwoven fabric 1 in 14 linear lines spaced 10 mm apart. The adhesive was applied in a spiral stripe pattern. 7.2 g of water-absorbent resin particles (1) was uniformly scattered over the central portion (40 cm × 12 cm area) of the adhesive-coated surface of the airlaid nonwoven fabric 1 to form a second water-retaining layer, which was obtained as an upper layer.

[0149] On the surface where the water-absorbent resin particles were scattered as the lower layer, a 40 cm x 12 cm air-through nonwoven fabric (Guangzhou Jinhan Nonwovens Co., Ltd., basis weight 45 g / m) was used as the middle layer. ２ ), the lower layer and intermediate layer were sandwiched between two sheets of release paper, and the layers were pressed and bonded together using a laminator (Hashima Corporation, Straight Linear Fussing Press, model HP-600LFS) at 110°C and 0.1 MPa to obtain a laminate consisting of the intermediate layer and lower layer. The release paper was then peeled off.

[0150] The upper layer was placed with the surface on which the water-absorbent resin particles had been sprayed facing up, and a laminate consisting of the intermediate layer and the lower layer was placed on the upper layer with the intermediate layer facing down. The upper layer, intermediate layer, and lower layer were sandwiched between two sheets of release paper, and pressed and bonded together using a laminator under conditions of 110°C and 0.1 MPa, to obtain an absorbent body including the upper and lower layers and the intermediate layer. The release paper was peeled off, and a 43 x 16 cm sheet with a basis weight of 22 g / m was further added as the outermost layer. ２ The absorbent article was sandwiched between two polyethylene air-through porous liquid-permeable sheets and the periphery was fused to obtain a two-layer sheet type absorbent article having two water retention layers. In the two-layer sheet type absorbent article, water-absorbent resin particles having no coating layer were used as water-absorbent resin particles A in the upper layer and water-absorbent resin particles in the lower layer, and coated resin particles were used as water-absorbent resin particles B in the upper layer.

[0151] (Example 7) An absorbent article was produced in the same manner as in Comparative Example 11, except that 4.8 g of water-absorbent resin particles (1) was used in the lower layer, and 4.8 g of water-absorbent resin particles (2) and 2.4 g of coated resin particles (4) were used in the upper layer. In forming the upper water-retaining layer, predetermined amounts of water-absorbent resin particles (2) and coated resin particles (4) were weighed and added to a plastic container measuring 5 cm in length, 5 cm in width, and 2.5 cm in depth, and thoroughly mixed using a medicine spoon before use.

[0152] Comparative Example 12 An absorbent article was produced in the same manner as in Comparative Example 11, except that 7.2 g of the water-absorbent resin particles (1) was used in the lower layer and 4.8 g of the water-absorbent resin particles (3) was used in the upper layer.

[0153] The types and amounts of water-absorbent resin particles and coated resin particles used in the two-layer sheet-type absorbent article are shown in Table 4. The amount of reduction in the total amount of water-absorbent resin particles used, based on Comparative Example 11, is also shown in Table 4. Since no hydrophilic fiber (pulp) was used in the water retention layer, the ratio of water-absorbent resin particles in both the upper layer and the lower layer was 100% by mass.

[0154]

[0155] The permeation rate and return amount of the obtained absorbent articles were measured by the following methods. The results are shown in Tables 5 and 6. The following tests were carried out by placing the mixing core type absorbent article with the liquid-permeable sheet facing up, and the two-layer sheet type absorbent article with the upper layer facing up.

[0156] <Evaluation of Permeation Rate> [Preparation of Test Solution (Artificial Urine)] A test solution was prepared by mixing 9866.0 g of distilled water, 100.0 g of sodium chloride, 3.0 g of calcium chloride dihydrate, 6.0 g of magnesium chloride hexahydrate, 25.0 g of 1 mass % Triton X solution (a mixture of Triton X-100 and water manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 0.25 g of Food Blue No. 1 (for coloring).

[0157] [Penetration Rate] The permeation rate was measured in a room conditioned at 25°C and 50% humidity (RH) according to the following procedure. An absorbent article was placed on a horizontal table, and a liquid-injection cylinder (59.80 g) with an opening having an outer diameter of 3.5 cm and an inner diameter of 3 cm was placed in the center of the absorbent article. 80 mL of test liquid at a liquid temperature of 25°C was poured into the cylinder all at once. The time from the start of the test liquid injection to the time the test liquid was completely absorbed into the absorbent article was measured as the first permeation rate (seconds). Immediately after the test liquid was completely absorbed into the absorbent article, the liquid-injection cylinder was removed from the absorbent article.

[0158] Next, 30 minutes after the start of the test liquid injection, the second, third, fourth, and fifth penetration rates (seconds) were measured in the same manner as in the first penetration rate measurement. The five penetration rates were added together to calculate the total penetration rate (seconds).

[0159] <Relapse Evaluation> After the permeation rate evaluation described above, the absorbent article was left to stand for 60 minutes in a room adjusted to 25°C and 50% humidity (RH). Next, a 10 cm square filter paper (ADVANTEC, 51A) with a mass of approximately 75 g (preliminarily measured) was placed on the test liquid input section of the absorbent article, and a weight with a base of 10 cm x 10 cm and a mass of 5.0 kg (approximately 0.7 psi, 4.8 kPa) was placed on top of it. After 5 minutes of loading, the weight and filter paper were removed, and the mass of the test liquid absorbed by the filter paper was measured and recorded as the relapse amount (g).

[0160]

[0161] The mixing core-type absorbent articles of Examples 1 to 3 had higher permeation rates and lower backflow amounts than the absorbent article of Comparative Example 1, while reducing the amount of components used. Comparative Examples 1 and 2 demonstrate that simply reducing the amount of components used tends to result in a decrease in permeation rate and / or backflow amount. In Comparative Example 4, the 5-minute lockup value of the water-absorbent resin particles B was not in the range of 2.2 cm or less, resulting in a decrease in permeation rate. In Comparative Example 5, the 10-minute lockup value of the water-absorbent resin particles B was not in the range of 2.0 cm or more, resulting in a decrease in permeation rate and backflow amount. In Comparative Example 6, the water-retention capacity of the water-absorbent resin particles B was higher than that of the water-absorbent resin particles A, resulting in a decrease in permeation rate. The mixing core-type absorbent articles of Examples 4 to 6 also had higher permeation rates and lower backflow amounts than Comparative Example 7, while reducing the amount of components used compared to the absorbent article of Comparative Example 7.

[0162]

[0163] The two-layer sheet type absorbent article of Example 7 had a higher permeation rate and a lower return amount than the absorbent article of Comparative Example 11 while reducing the amount of components used compared to the absorbent article of Comparative Example 11.

[0164] 1...water-absorbent resin particles, 3...hydrophilic fibers, 10, 10A, 10B...water-retaining layers, 20a, 20b...shape-retaining members, 21...adhesive layer, 25...intermediate layer, 30...liquid-permeable sheet, 40...liquid-impermeable sheet, 50, 51...absorbent body, 100...absorbent article.

Claims

1. An absorbent body having one or more water retention layers, at least one of which contains multiple types of water-absorbent resin particles having different 5-minute lock-up values, and among the multiple types of water-absorbent resin particles, water-absorbent resin particles A having the highest 5-minute lock-up value satisfy the following property (1), and water-absorbent resin particles B having the lowest 5-minute lock-up value satisfy the following property (2), the water retention capacity (g / g) of water-absorbent resin particles A is higher than the water retention capacity (g / g) of water-absorbent resin particles B, and the absorbent body has at least one water retention layer in which the water-absorbent resin particle ratio represented by the following formula is 30 mass% or more. (1) The 5-minute lock-up value is more than 2.2 cm, and the 10-minute lock-up value is 3.0 cm or more. (2) The 5-minute lock-up value is 2.2 cm or less, and the 10-minute lock-up value is 2.0 cm or more. Water-absorbent resin particle ratio [mass %] = (total amount of water-absorbent resin particles contained in the water-retaining layer [g] / amount of water-retaining layer [g]) x 100 2. The absorbent body according to claim 1, wherein the water-absorbent resin particles A have a lock-up value of 4.6 cm or less at 5 minutes.

3. The absorbent according to claim 1 or 2, wherein the water-absorbent resin particles B have a water retention capacity of 25 g / g or more.

4. The absorbent according to claim 1 or 2, wherein the difference in 5-minute lock-up value between the water-absorbent resin particles A and B is 1.5 cm or more.

5. The absorbent body according to claim 1 or 2, wherein in the water retention layer containing multiple types of water-absorbent resin particles, the amount of water-absorbent resin particles B relative to the total amount of water-absorbent resin particles A and B is 10 to 50 mass %.

6. The absorbent body according to claim 1 or 2, wherein the water-absorbent resin particles B are coated resin particles having polymer particles and a coating layer covering at least a part of the surface of the polymer particles.

7. The absorbent body according to claim 1 or 2, wherein the water-retaining layer containing a plurality of types of water-absorbent resin particles further contains hydrophilic fibers.

8. The absorbent body described in claim 7, wherein in a water-retaining layer containing both the multiple types of water-absorbent resin particles and the hydrophilic fibers, the multiple types of water-absorbent resin particles and the hydrophilic fibers are mixed together, and the ratio of water-absorbent resin particles in the water-retaining layer is 70 mass% or less.

9. The absorbent body according to claim 1 or 2, which has a first water retention layer as the water retention layer containing the multiple types of water-absorbent resin particles, and further has a second water retention layer, the first water retention layer being provided on the liquid absorption side of the absorbent body, and the ratio of water-absorbent resin particles in the first water retention layer and the second water retention layer is 80 mass % or more.

10. A method for manufacturing an absorbent body having one or more water retention layers, comprising forming a water retention layer containing multiple types of water absorbent resin particles having different 5-minute lock-up values, wherein, among the multiple types of water absorbent resin particles, water absorbent resin particles A having the highest 5-minute lock-up value satisfy the following property (1), and water absorbent resin particles B having the lowest 5-minute lock-up value satisfy the following property (2), the water retention capacity (g / g) of water absorbent resin particles A is higher than the water retention capacity (g / g) of water absorbent resin particles B, and the water retention layer containing the multiple types of water absorbent resin particles has a water absorbent resin particle ratio represented by the following formula of 30% by mass or more. (1) The 5-minute lock-up value is more than 2.2 cm, and the 10-minute lock-up value is 3.0 cm or more. (2) The 5-minute lock-up value is 2.2 cm or less, and the 10-minute lock-up value is 2.0 cm or more. Water-absorbent resin particle ratio [mass %] = (total amount of water-absorbent resin particles contained in the water-retaining layer [g] / amount of water-retaining layer [g]) x 100

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