WO2020032281A1

WO2020032281A1 - Absorbent sheet and absorbent article containing same

Info

Publication number: WO2020032281A1
Application number: PCT/JP2019/031783
Authority: WO
Inventors: ゆいか野田; 一司鳥井; 裕子植田; 貴洋北野; 達史平内; 裕一朗堀本; 隆一平岡; 博之池内
Original assignee: 株式会社日本触媒
Priority date: 2018-08-09
Filing date: 2019-08-09
Publication date: 2020-02-13
Also published as: CN112584810B; CN112584810A; JP7174760B2; JPWO2020032281A1

Abstract

The purpose of the present invention is to provide a novel absorbent sheet that can significantly reduce the return quantity even if a liquid is intermittently introduced thereto a plurality of times (particularly three or more times) under non-pressurized conditions and the amount of liquid introduced increases. This absorbent sheet has a first substrate, a second substrate, and an absorption layer positioned between the first substrate and the second substrate. The first substrate is a water-permeable sheet that is positioned on the side to which a liquid to be absorbed is introduced. The absorption layer has a granular absorption agent and an intermediate sheet. The weight-average particle size of the granular absorption agent is 200-600 μm. The CRC of the granular absorption agent is 36 g/g or more. The permeability of the granular absorption agent with respect to the intermediate sheet is 60% or more.

Description

Water absorbing sheet and water absorbing article containing the same

The present invention relates to a water-absorbent sheet and a water-absorbent article including the same.

Water-absorbent resin (SAP / Super Absorbent polymer) is a water-swellable, water-insoluble polymer gelling agent. It is used for various purposes, such as water stoppage agents for industrial use.

These absorbent articles are generally manufactured at a disposable diaper manufacturing plant as absorbents which are mixed with a water-absorbent resin and a fiber material and individually molded for each absorbent article. (For example, an hourglass type, a fox type, an elliptical type, etc. when viewed in a plane). The method of manufacturing these absorbers can be processed into an arbitrary shape because they are individually molded, and the amount of fibers and water-absorbent resin can be easily adjusted for each absorbent article.

However, in recent years, in the manufacture of disposable diapers, an absorbent body (usually having a width of about 10 cm and a length of about 10 cm) obtained by cutting a long water-absorbent sheet in which a water-absorbent resin is fixed between two sheets in a sanitary material manufacturing process. Paper diapers using a 10 cm rectangular shape) have been manufactured. The disposable diaper maker can simplify the production process of the disposable diaper by purchasing or manufacturing a long continuous water-absorbent sheet, and can further reduce the thickness of the disposable diaper by not using pulp. The water-absorbent sheet has a configuration in which the water-absorbent resin particles are sandwiched and fixed between upper and lower sheets (especially a non-woven sheet). Usually, a long continuous sheet is manufactured, and then the long continuous sheet is cut to have a width of about 10 cm. It is made into a rectangle having a length of several 10 cm and incorporated in a paper diaper (for example, Patent Document 1).

Unlike conventional sanitary materials (paper diapers), diapers made of water-absorbent sheets have a short history, and there has been little development of water-absorbent resin suitable for water-absorbent sheets and proposals for parameters. In fact, conventional water-absorbent resins for paper diapers are also used as they are in water-absorbent sheets.

International Publication No. 2010-143635

The present inventors have found out that the so-called “return” in which the absorbed liquid is released may occur due to the structure unique to the mainstream water-absorbent sheet that is thin. Then, it has been found that when the liquid is intermittently introduced a plurality of times (especially three or more times) under the condition of no pressure and the amount of the introduced liquid is increased, the problem is remarkable.

Accordingly, an object of the present invention is to provide a novel water-absorbent sheet that can significantly reduce the amount of return even if the environment for introducing the liquid is as described above.

A water-absorbent sheet, comprising: a first substrate, a second substrate, a first substrate, and a water-absorbing layer located between the second substrate. A base material, which is a water-permeable sheet located on a side where a liquid to be absorbed is introduced, wherein the water-absorbing layer has a particulate water-absorbing agent and an intermediate sheet; Has a weight average particle diameter of 200 to 600 μm, a CRC of the particulate water absorbing agent of 36 g / g or more, and a transmittance of the particulate water absorbing agent to the intermediate sheet of 60% or more. The above-mentioned problem is solved by a conductive sheet.

It is a schematic diagram showing the cross section of the water absorbent sheet according to one embodiment of the present invention. It is a schematic diagram which shows the apparatus for measuring GPR. It is the top view and the right view which showed the sample used for evaluation of the amount of reversion, and is the figure which showed a mode that the water-absorbent sheet produced in the Example was wrapped with the liquid impermeable sheet. It is the top view and front view of the liquid injection cylinder used for evaluation of the amount of return. It is the front view which showed a mode that the liquid injection cylinder was placed on the water-absorbent sheet used in the Example of this application. It is the front view and right side view which showed the mode that sodium chloride aqueous solution was thrown in into the water absorbing sheet from the liquid injection cylinder using the funnel in FIG. It is the schematic which shows the apparatus used at the time of the transmittance | permeability measurement.

Hereinafter, the present invention will be described with reference to the best mode. It should be understood that throughout this specification, the use of the singular includes the plural concept unless specifically stated otherwise. Thus, it is to be understood that singular articles (eg, "a", "an", "the", etc. in English) also include the plural concept unless specifically stated otherwise. It is to be understood that the terms used in the present specification are used in a meaning commonly used in the art unless otherwise specified. Thus, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control. The present invention is not limited to the following embodiments, and can be variously modified within the scope of the claims.

[1. Definition of terms〕
[1-1. Water-absorbent sheet]
The “water-absorbent sheet” in the present invention refers to a structure in which a water-absorbent resin (particulate water-absorbing agent) and an intermediate sheet are supported between two or more long base materials. The water-absorbent sheet may use an adhesive or a hot-melt adhesive to bond at least one of the base material, the intermediate sheet, and the particulate water-absorbing agent. The water absorbing sheet may contain other components (fiber component, antibacterial agent, deodorant, etc.) in addition to the particulate water absorbing agent. In addition, the water-absorbing sheet may include other sheets in addition to the two substrates that sandwich the particulate water-absorbing agent and the like.

Usually, the water-absorbent sheet is in the form of a continuous sheet or a roll in which the continuous sheet is wound. When using the water-absorbent sheet, the continuous sheet is cut into an appropriate shape (such as a rectangle) and then used as an absorbent such as a disposable diaper. On the other hand, a conventional disposable diaper made of a high-concentration water-absorbent resin (for example, a disposable diaper whose absorbent is a palpress) uses an individually molded absorbent for each disposable diaper. Therefore, such an absorber has a different technical property from the water-absorbent sheet of the present invention.

[1-2. Water absorbent resin]
As used herein, the term “water-absorbent resin” refers to a water-swelling component (CRC) defined by ERT441.2-02 of 5 g / g or more, and a water-soluble component defined by ERT470.2-02 ( Ext) refers to a polymer gelling agent having an Ext) of 50% by mass or less.

The water-absorbing resin is preferably a hydrophilic cross-linked polymer obtained by cross-linking and polymerizing an unsaturated monomer having a carboxyl group. The shape of the water-absorbent resin is sheet, fiber, film, particle, gel or the like. The water absorbent sheet according to one embodiment of the present invention uses a particulate water absorbent resin.

において In the present specification, the “water-absorbent resin” is not limited to an embodiment in which the total amount (100% by mass) is only the water-absorbent resin. It may be a water-absorbing resin composition containing additives and the like. Further, in this specification, the term "water-absorbent resin" is a concept that also includes intermediates in the process of producing the water-absorbent resin. For example, a hydrogel cross-linked polymer after polymerization, a dried polymer after drying, a water-absorbing resin powder before surface cross-linking, and the like may also be referred to as “water-absorbing resin”.

Thus, in this specification, in addition to the water-absorbent resin itself, the water-absorbent resin composition and the intermediate may be collectively referred to as “water-absorbent resin”.

[1-3. Water absorbing agent, particulate water absorbing agent]
As used herein, the term "water-absorbing agent" refers to an absorbent gelling agent containing a water-absorbing resin as a main component for absorbing an aqueous liquid (liquid). Here, the aqueous liquid (liquid) is not limited to water, and is not particularly limited as long as it is a liquid containing water. The aqueous liquid absorbed by the water-absorbent sheet according to one embodiment of the present invention is urine, menstrual blood, sweat, and other body fluids.

In the present specification, the “particulate water-absorbing agent” means a particulate (powder-like) water-absorbing agent (corresponding to a particulate water-absorbing resin because the water-absorbing agent contains a water-absorbing resin as a main component). . The concept of “particulate water-absorbing agent” includes both a single particulate water-absorbing agent and an aggregate of a plurality of particulate water-absorbing agents. As used herein, “particulate” means having a particle form. Here, “particle” refers to a relatively small divided body of matter and has a size of several mm to several mm (“particle”, edited by McGraw-Hill Scientific and Technical Dictionary Dictionary, edited by McGraw-Hill Science) Technical Term Dictionary 3rd Edition ”, Nikkan Kogyo Shimbun, 1996, p. 1929). In the present specification, the “particulate water-absorbing agent” may be simply referred to as “water-absorbing agent”. In the water absorbing sheet of the present invention, the weight average particle diameter of the particulate water absorbing agent is 200 to 600 μm. Here, if the weight average particle diameter of the particulate water-absorbing agent is less than 200 μm, the handleability may be reduced. If the weight average particle diameter of the particulate water-absorbing agent is more than 600 μm, the texture of the water-absorbing sheet may be reduced. In the water absorbent sheet according to one embodiment of the present invention, the weight average particle diameter of the particulate water absorbing agent is preferably from 250 to 500 μm, more preferably from 300 to 450 μm. In the water-absorbent sheet of the present invention, it is preferable that 95% by mass or more of the whole particulate water-absorbing agent has a particle size of 850 μm or less, and 98% by mass or more of the whole particulate water-absorbing agent has a particle size of 850 μm or less. It is more preferable that substantially 100% by mass of the whole particulate water-absorbing agent has a particle size of 850 μm or less. In the examples of the present application, substantially 100% by mass of the entire particulate water-absorbing agent has a particle diameter of 850 μm or less. Here, in the present specification, the method for measuring the weight average particle diameter is described in US Pat. No. 7,638,570 based on the PSD obtained according to the method for measuring “PSD” specified in ERT420.2-02. (3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation ((Sigma)) of Particle Diameter Distribution ".

において In the water-absorbent sheet according to one embodiment of the present invention, the weight-average particle diameter of the particulate water-absorbing agent is 400 μm or less. With such an embodiment, the desired effects of the present invention can be improved.

The particulate water-absorbing agent contains a water-absorbing resin as a polymer (or particulate water-absorbing resin or water-absorbing resin particles) as a main component. The particulate water-absorbing agent contains the water-absorbing resin as a polymer in an amount of 60 to 100% by mass, preferably 70 to 100% by mass, more preferably 80 to 100% by mass, further preferably 90 to 100% by mass, and particularly preferably. Contains 95 to 100% by mass. The remainder of the particulate water absorbing agent may optionally include water, additives (inorganic fine particles, polyvalent metal cations, and the like). The particulate water-absorbing agent used in the examples of the present application contains about 95 to about 99% by mass of a water-absorbing resin. That is, the upper limit of the water absorbing resin in the particulate water absorbing agent is, for example, 100% by mass, 99% by mass, 97% by mass, 95% by mass, or 90% by mass. Preferably, the composition further contains 0 to 10% by mass of components other than the water-absorbing resin, particularly water, additives (inorganic fine particles, polyvalent metal cations) and the like.

好ましい The preferred water content of the particulate water-absorbing agent is 0.2 to 30% by mass. As described above, the water-absorbent resin composition in which components such as water and additives are integrated with the water-absorbent resin, and / or the water-absorbent resin composition in a mixed form is also referred to as a “particulate water-absorbing agent”. ].

Examples of the water-absorbing resin which is a main component of the particulate water-absorbing agent include polyacrylic acid (salt) resin, polysulfonic acid (salt) resin, maleic anhydride (salt) resin, polyacrylamide resin, and polyvinyl alcohol. Resin, polyethylene oxide resin, polyaspartic acid (salt) resin, polyglutamic acid (salt) resin, polyalginic acid (salt) resin, starch resin, and cellulose resin. Of these, polyacrylic acid (salt) -based resin is preferably used as the water-absorbing resin.

[1-4. Polyacrylic acid (salt)]
As used herein, “polyacrylic acid (salt)” refers to polyacrylic acid and / or a salt thereof. The polyacrylic acid (salt) contains a repeating unit of acrylic acid and / or a salt thereof (hereinafter, referred to as “acrylic acid (salt)”) as a main component, and further includes a graft component as an optional component. It is. The polyacrylic acid (salt) is obtained by polymerization of acrylic acid (salt), hydrolysis of polyacrylamide, polyacrylonitrile, and the like. Preferably, the polyacrylic acid (salt) is obtained by polymerization of acrylic acid (salt).

Here, “containing as a main component” means that the amount of acrylic acid (salt) used in the polymerization of polyacrylic acid (salt) is the total amount of monomers (excluding the internal crosslinking agent) used in the polymerization. To 100 mol%, preferably 70 to 100 mol%, more preferably 90 to 100 mol%, and still more preferably substantially 100 mol%.

[1-5. EDANA and ERT]
“EDANA” is an abbreviation for European Disposables and Nonvens Associations. “ERT” is an abbreviation of a European standard (substantial global standard) water absorbent resin measurement method (EDANA Recommended Test Methods) established by EDANA. In the present specification, unless otherwise specified, the physical properties of the water-absorbent resin are measured in accordance with the 2002 edition of ERT.

[1-6. Others]
In the present specification, “X to Y” indicating a range means “X or more and Y or less”.

において In this specification, unless otherwise specified, the unit of mass “t (ton)” means “metric ton”. “Ppm” means “mass ppm”. The terms “mass” and “weight”, “parts by weight” and “parts by weight”, “% by weight” and “% by weight”, and “ppm by weight” and “ppm by weight” have the same meaning.

書 In the present specification, “—acid (salt)” means “—acid and / or salt thereof”. “(Meth) acryl” means “acryl and / or methacryl”.

において In this specification, the unit of volume “liter” may be described as “l” or “L”. “Mass%” may be described as “wt%”. When a trace component is measured, N.P. D. (Non @ Detected).

[2. Water-absorbent sheet)
The water-absorbent sheet of the present invention has a first base material, a second base material, and a water-absorbent layer located between the first base material and the second base material. It is a water-permeable sheet, wherein the first base material is located on a side where a liquid to be absorbed is introduced, and the water-absorbing layer has a particulate water-absorbing agent and an intermediate sheet. The weight average particle diameter of the particulate water absorbing agent is 200 to 600 μm, the CRC of the particulate water absorbing agent is 36 g / g or more, and the transmittance of the particulate water absorbing agent to the intermediate sheet is 60%. It is a water-absorbent sheet which is not less than mass%. Hereinafter, regarding the transmittance, mass% is simply referred to as%. With such a configuration, even if the liquid is intermittently introduced a plurality of times (especially three or more times) under a non-pressurized condition and the introduced amount of the liquid is increased, the return amount can be significantly reduced. In particular, with such a configuration, a very excellent result can be obtained in the measurement of the return amount under specific conditions (also referred to as “specific return amount evaluation” in the present specification) in the examples of the present application. That is, if the liquid is intermittently introduced a plurality of times (especially three or more times), the liquid amount becomes equal to or more than the set absorption amount and an excessive “return” occurs in a normal configuration. . On the other hand, in the present invention, the transmittance of the particulate water absorbing agent to the intermediate sheet is 60% or more. According to the combination of the particulate water-absorbing agent and the intermediate sheet capable of achieving such transmittance, the intermediate sheet easily captures the particulate water-absorbing agent present in the water-absorbing sheet. Since the intermediate sheet captures a large amount of the particulate water-absorbing agent, the particulate water-absorbing agent is diffused into the water-absorbing sheet, so that gaps between the particulate water-absorbing agents existing in the water-absorbing sheet are easily vacated. If the transmittance is less than 60%, the particulate water-absorbing agent present between the intermediate sheet and the base material is difficult to be captured by the intermediate sheet, and the particulate water-absorbing agent is located between the intermediate sheet and the base material. The probability of existence increases, and the particulate water-absorbing agent densely exists between the intermediate sheet and the base material. In this case, a gel blocking phenomenon occurs between the water-absorbing particulate water-absorbing agents, the liquid diffusibility is reduced, and an excessive “return amount” occurs. In the present invention, since the transmittance is 60% or more, the particulate water-absorbing agent present between the intermediate sheet and the base material diffuses widely into the intermediate sheet, so that the gaps between the particulate water-absorbing agents become empty. This makes it possible to maximize the performance of the particulate water-absorbing agent, and also has the technical effect that the area in which water can be absorbed as a water-absorbing sheet can be more widely utilized. Therefore, the “specific return amount evaluation” can be made excellent. When the CRC is 36 g / g or more, the liquid diffusibility generally tends to decrease. However, in the present invention, since the transmittance is 60% or more, the water absorption is maintained while maintaining the liquid diffusivity. The intended problem of the present invention can be solved while taking advantage of the advantage of being large. Note that the mechanism and the like described in this specification do not limit the technical scope of the claims of the present application. Here, it should be added that a water-absorbent sheet or a water-absorbent article designed to suppress the amount of return under general conditions does not always provide excellent results in the “specific return amount evaluation” of the present application. In addition, the water-absorbent sheet according to an embodiment of the present invention is, for example, a water-absorbent article used during a time period when a baby whose bladder is still small is actively moving around, such as during the day, when the child begins to learn to run. Although it is suitable as a diaper, the use form is of course not limited to this. Here, it is considered that the transmittance can be increased to 60% or more as long as the porosity is increased. However, the intermediate sheet having a high porosity cannot always transmit a large amount of the particulate water-absorbing agent. As a method for realizing the transmittance so as to be 60% or more, which will be described later, the fiber diameter is controlled (if the intermediate sheet is made of fiber), or a plurality of sheets (if the intermediate sheet is a nonwoven fabric) It is considered that a method of laminating nonwoven fabrics is preferable. That is, the transmittance of 60% or more can be realized by appropriately adjusting the properties of the members constituting the intermediate sheet, the surface state thereof, the complexity of the network structure, the fiber diameter, the fusion state between the fibers, the basis weight, the thickness, and the like. Can be. A person who intends to implement the present invention can adjust the transmittance by changing the heat treatment conditions, the fiber diameter and the density of the air-through nonwoven fabric, for example, if the air-through nonwoven fabric is used as the intermediate sheet. Even when another type of intermediate sheet is used, a transmittance of 60% or more can be realized by appropriately changing the factors related to the transmittance adjustment as described above.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. In addition, the dimensional ratios in the drawings are exaggerated for convenience of description, and may be different from the actual ratios.

FIG. 1 is a schematic diagram showing a cross section of the water absorbent sheet 40 according to one embodiment of the present invention. The first substrate 11 is located on the side where the liquid to be absorbed is introduced. That is, at least the first substrate is disposed on the liquid discharge side (for example, on the skin side in a disposable diaper). The water absorbing layer 12 is disposed between the first base 11 and the second base 13. In FIG. 1, the second base material 13 is located only on the side opposite to the side where the liquid to be absorbed is introduced and with the water absorbing layer 12 interposed therebetween. 13 may be designed to be larger than the first base material 11 and folded so as to surround the first base material 11. By doing so, the falling off of the particulate

water absorbing agents

14a, 14b can be suppressed. In the water-absorbent sheet 40 of FIG. 1, the first particulate water-absorbing agent 14 a localized on the surface of the first substrate 11 facing the second substrate 13, The second particulate water-absorbing agent 14b localized on the surface side facing the first base material 11 is localized to sandwich the intermediate sheet 16, but the particulate water-absorbing agent 14a and the particles The water absorbing agent 14b may be made uniform. The water absorbing layer 12 has a particulate water absorbing agent 14 and an intermediate sheet 16. Since the intermediate sheet 16 has a transmittance of the particulate water-absorbing agent 14 of 60% or more, the intermediate sheet 16 has a structure that easily traps the particulate water-absorbing agent 14a and the particulate water-absorbing agent 14b. Therefore, the intermediate sheet 16 contains many particulate water-absorbing

agents

14a and 14b. That is, the desired effect of the present invention is achieved by the fact that the particulate water-absorbing agent 14a and the particulate water-absorbing agent 14b are diffused into the intermediate sheet 16 and exist in the water-absorbing sheet. In a preferred embodiment of the present invention, the particulate water-absorbing agent 14a and the particulate water-absorbing agent 14b diffuse into the intermediate sheet 16 while maintaining the localized state as much as possible.

As described above, in the embodiment of FIG. 1, the water absorbing layer 12 has the particulate water absorbing agent 14a fixed to the first base material 11 and the particulate water absorbing agent 14b fixed to the second base material. However, some of the particulate

water absorbing agents

14a and 14b can be detached from each sheet. Therefore, the water-absorbing “layer” does not refer only to a continuous body such as a sheet, but may be any layer that has a certain thickness between the first base material 11 and the second base material 13. It may be in a form. As a method of fixing the particulate water-absorbing agent to each substrate, for example, an adhesive may be used. For the method of producing a water-absorbent sheet using an adhesive, see [3. ] Will be described in detail.

水性 The water-absorbent sheet according to one embodiment of the present invention can be made thinner than an absorber used for a conventional absorbent article. When the water-absorbent sheet is used in a disposable diaper, the thickness is preferably 15 mm or less, more preferably 10 mm or less, still more preferably 7 mm or less, particularly preferably 5 mm, for example, at 40% RH to 50% RH. Or less, most preferably 4 mm or less. On the other hand, the lower limit of the thickness is at least 0.2 mm, preferably at least 0.3 mm, more preferably at least 0.5 mm, in view of the strength of the water-absorbent sheet and the diameter of the particulate water-absorbing agent. The thickness of the water-absorbing sheet used in the examples of the present application was 3 mm to 5 mm under the following conditions.

厚み The thickness of the water-absorbent sheet is measured using a dial thickness gauge large type (thickness measuring device) (manufactured by Ozaki Seisakusho Co., Ltd., model number: JB, measuring element: anvil vertical φ50 mm). The measurement location was determined by dividing the absorber into three equal parts in the longitudinal direction, and setting the respective central portions (points where a diagonal line was drawn from the end of the absorber and located at the intersection thereof). For example, in the case of a water-absorbent sheet having a length of 36 cm and a width of 10 cm, the measurement position is a point 6 cm from the left end in the longitudinal direction and 5 cm from both ends in the width direction with respect to the length of 36 cm in the longitudinal direction (left). Three points correspond to the measurement points: a point 18 cm from the left end in the longitudinal direction and 5 cm from both ends in the width direction (center), and a point 30 cm from the left end in the longitudinal direction and 5 cm from both ends in the width direction (right). . The number of measurement points is measured twice for each location, and the measured value of the thickness is an average value of a total of six points. As a specific procedure, so that wrinkles and distortions do not occur at the measurement location of the water-absorbent sheet, the flat sheet is stuck flat on a plate having a constant thickness, and the plate is set on the lower measuring element of the thickness measuring instrument. . Next, after the upper measuring element of the thickness measuring instrument is brought close to the height of 2 to 3 mm from the water-absorbing sheet, the hand is slowly released from the handle, and the thickness of the combined water-absorbing sheet and plate is measured. The thickness of the water-absorbent sheet is determined by the formula: T1 = T2-T0 (T0: thickness of the sheet (mm), T1: thickness of the water-absorbent sheet (mm), T2: thickness of the water-absorbent sheet and the sheet (mm)). .

(4) The surface of the water-absorbent sheet may be appropriately embossed in order to further impart liquid permeability, diffusivity, flexibility and the like to the water-absorbent sheet. The region to be embossed may be the entire surface of the water-absorbent sheet or a part thereof. By providing a continuous embossed area in the longitudinal direction of the water absorbent sheet, the liquid can be easily diffused in the longitudinal direction. Further, the particulate water-absorbing agent may be spread over the entire surface of the water-absorbing sheet, or a region where the particulate water-absorbing agent does not exist may be provided in a part. When the non-existing region of the particulate water absorbing agent is provided, it is preferable to provide the region in a channel shape (streak shape) in the longitudinal direction of the water absorbing sheet. As described above, by providing the embossed region and / or the region where the particulate water-absorbing agent does not exist continuously in the longitudinal direction, the region serves as a passage (liquid transfer passage) for flowing a large amount of liquid. Fulfill. The embossed area and / or the area where no particulate water absorbing agent is present may be provided linearly, curvedly, or corrugated.

各 Hereinafter, each member constituting the water absorbent sheet will be described in detail.

[2-1. First substrate, second substrate and intermediate sheet]
The first substrate is a water-permeable sheet located on the side where the liquid to be absorbed is introduced. The liquid to be absorbed is not limited to water, but may be urine, blood, sweat, feces, waste liquid, moisture, steam, ice, a mixture of water and an organic solvent and / or an inorganic solvent, rainwater, groundwater, and the like. It is not particularly limited as long as it contains water. Preferably, urine, menstrual blood, sweat, and other body fluids can be mentioned.

In the water-absorbing sheet according to one embodiment of the present invention, the lower limit of the transmittance of the particulate water-absorbing agent to the intermediate sheet is not particularly limited as long as it is 60% or more, but is preferably 65% or more, more preferably 70%. Or more, more preferably 75% or more, still more preferably 80% or more, even more preferably 85% or more, still more preferably 87% or more, even more preferably 89% or more, It is still more preferably 90% or more, still more preferably 91% or more, still more preferably 92% or more, still more preferably 93% or more, even more preferably 94% or more, It is more preferably at least 95%. By having such a lower limit, the capture rate of the particulate water-absorbing agent is increased, and the intended effect of the present invention is easily exerted. In addition, the upper limit of the transmittance of the particulate water-absorbing agent to the intermediate sheet in the water-absorbing sheet according to one embodiment of the present invention is 100% in theory, but is preferably 99.9% or less. The content is more preferably 5% or less, further preferably 99% or less, still more preferably 98% or less, and even more preferably less than 97%. By having such a transmittance, the intermediate sheet can capture a large amount of the particulate water absorbing agent.

The porosity of the intermediate sheet in the water-absorbent sheet according to one embodiment of the present invention is preferably 80 to 99.9%, more preferably 85 to 99.9%, and further preferably 90 to 99.9. %, Particularly preferably 98.0 (or 98.1) to 99.9%, most preferably 98.2 (98.3 or 98.4) to 99.5 (or 99.0)%. . As described above, the transmittance of 60% or more is realized by the properties of the members constituting the intermediate sheet, the surface state thereof, the complexity of the network structure, the fiber diameter, the fusion state between the fibers, the basis weight, the thickness, and the like. Therefore, there is no direct relationship between the porosity and the transmittance.

材質 The first base material, the second base material, and the material of the intermediate sheet used in the water-absorbent sheet according to one embodiment of the present invention are each independently preferably a nonwoven fabric. The material of the nonwoven fabric is not particularly limited, but from the viewpoint of liquid permeability, flexibility, and strength of the water absorbent sheet, polyolefin fibers (such as polyethylene (PE) and polypropylene (PP)) and polyester fibers (polyethylene terephthalate (PET)) ), Polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), etc.), polyamide fibers (nylon, etc.), rayon fibers, pulp (cellulose) fibers, and the like. Other nonwoven fabrics made of synthetic fibers, and nonwoven fabrics produced by mixing synthetic fibers with cotton, silk, hemp, pulp (cellulose) fibers, and the like are also preferable. The non-woven fabric described above may be a non-woven fabric containing only one kind of the above-mentioned fibers or a non-woven fabric combining two or more kinds of fibers. The nonwoven fabric used for the first base material and the second base material is preferably formed by an airlaid method. Further, it is preferably pulp (cellulose) fiber.

において In the water absorbent sheet according to one embodiment of the present invention, the nonwoven fabric used for the intermediate sheet is preferably an air-through nonwoven fabric. The nonwoven fabric used for the intermediate sheet is preferably bulky, and specifically, the thickness under no load is preferably 1.3 mm or more, more preferably 1.5 mm or more, and still more preferably 1.7 mm or more. 1.9 mm or more is still more preferred, 2.1 mm or more is even more preferred, 2.3 mm or more is even more preferred, and 2.5 mm or more is even more preferred. The nonwoven fabric described above may contain a small amount of pulp fibers to the extent that the thickness of the water absorbent sheet is not increased.

Although the upper limit of the thickness of the nonwoven fabric used for the intermediate sheet is not particularly limited, for example, the thickness under no load is preferably 4.9 mm or less, more preferably 4.8 mm or less, and 4.7 mm. It is still more preferable that it is not more than 4.6 mm, and it is even more preferable that it is less than 4.0 mm. In absorbent sheet according to an embodiment of the present invention, the basis weight of the intermediate sheet, per one intermediate sheet preferably 30 ~ 60g / ^{m 2,} more preferably 40 ~ 59g / ^{m 2,} more preferably 42 ~ 55 g / M ² .

において In the water-absorbent sheet according to one embodiment of the present invention, the thickness of the intermediate sheet is thicker than any one of the first base material and the second base material. More preferably, the thickness of the intermediate sheet is greater than the thickness of both the first substrate and the second substrate. Such an embodiment contributes to water retention at the initial stage of liquid absorption and contributes to reduction of leakage, the first base material and the second base material can be designed to be thin, and the overall thickness of the water absorbent sheet can be reduced. Can be. The ratio of the thickness of the intermediate sheet to the arithmetic mean of the thicknesses of the first base material and the second base material is preferably 1.5 to 100, more preferably 2 to 80, and still more preferably 3 to 50. And even more preferably 3.2 to 10.

As described above, the nonwoven fabric used in the water-absorbent sheet according to one embodiment of the present invention is preferably a hydrophilic nonwoven fabric in order to increase water permeability, but using a hydrophilic agent (such as a surfactant). Alternatively, the nonwoven fabric or the fiber that is the material of the nonwoven fabric may be made hydrophilic.

Examples of the hydrophilizing agent include anionic surfactants (such as aliphatic sulfonates and higher alcohol sulfates), cationic surfactants (such as quaternary ammonium salts), and nonionic surfactants (such as polyethylene glycol). Fatty acid esters, polyglycerin fatty acid esters, sorbitan fatty acid esters, etc.), silicone surfactants (polyoxyalkylene-modified silicones, etc.), stain release agents containing polyester, polyamide, acrylic, and urethane resins are used. Can be

The first substrate used for the water-absorbent sheet according to one embodiment of the present invention is a water-permeable sheet because it is located on the side where the liquid to be absorbed is introduced, but the second substrate and The intermediate sheet is also preferably a water-permeable sheet having water permeability, and may be of the same type or different types. The water permeability of the water-permeable sheet is preferably 1 × 10 ⁻⁵ cm / sec or more as measured by a water permeability coefficient (JIS A1218: 2009). The water permeability is more preferably 1 × 10 ⁻⁴ cm / sec or more, further preferably 1 × 10 ⁻³ cm / sec or more, still more preferably 1 × 10 ⁻² cm / sec or more, and still more preferably 1 × 10 ⁻² cm / sec or more. × 10 ⁻¹ cm / sec or more. The water absorbent sheet according to one embodiment of the present invention is preferably a hydrophilic nonwoven fabric. By being a hydrophilic nonwoven fabric, the desired effects of the present invention can be efficiently achieved.

The thicknesses of the first base material and the second base material are preferably as thin as possible as long as they have strength as a water-absorbent sheet. Each base material independently has a thickness of 0.01 to 2 mm, and more preferably 0.02 to 0.02 mm. It is appropriately selected within a range of 1 to 1 mm, 0.03 to 0.9 mm, and 0.05 to 0.8 mm. The basis weights of the first base material and the second base material are each independently preferably 5 to 300 g / m ² , more preferably 8 to 200 g / m ² , and still more preferably 10 to 300 g / m ² per substrate. It is 100 g / m ² , even more preferably 11 to 50 g / m ² .

[2-2. Water absorption layer]
The water absorbing layer in the water absorbing sheet according to one embodiment of the present invention includes a particulate water absorbing agent and an intermediate sheet. Since the water absorbing layer has the intermediate sheet, the first particulate water absorbing agent and the second particulate water absorbing agent are more efficiently localized on the first base material and the second base material, respectively. There is also an advantage that it is easy to make it. In addition, since the intermediate sheet forms an air layer, there is also an advantage that even if there is a return from the water-absorbent sheet, the skin does not feel it. Since the description of the intermediate sheet is as described above, the description is omitted here. The localization of the first particulate water absorbing agent and the second particulate water absorbing agent is as follows [3. ], For example, by appropriately using an adhesive.

(Particulate water absorbing agent)
The water absorbing layer in the water absorbing sheet according to one embodiment of the present invention contains a first particulate water absorbing agent and a second particulate water absorbing agent. Unless otherwise specified, when simply referred to as a particulate water absorbing agent, a mixture of a first particulate water absorbing agent and a second particulate water absorbing agent, or a first particulate water absorbing agent, Means at least one of the particulate water-absorbing agents. When the first particulate water absorbing agent and / or the second particulate water absorbing agent is a mixture of a plurality of types of particulate water absorbing agents, the following description relates to the physical properties of the mixture.

"CRC" (ERT441.2-02)
“CRC” is an abbreviation for Centrifuge Retention Capacity (centrifuge holding capacity), and refers to the water absorption capacity of a particulate water-absorbing agent under no pressure (sometimes referred to as “water absorption capacity”). Specifically, 0.2 g of the particulate water-absorbing agent is put into a non-woven bag, then immersed in a large excess of 0.9% by mass aqueous sodium chloride solution for 30 minutes to freely swell, and then centrifuged ( 250G) means the water absorption capacity (unit: g / g) after draining.

The CRC of the second particulate water absorbing agent in the water absorbing sheet according to one embodiment of the present invention is preferably 30 to 50 g / g, more preferably 36 to 45 g / g, and more preferably 37 to 44 g. / G is more preferable. With such an embodiment, excellent results are obtained in the specific return amount evaluation.

The CRC of the first particulate water absorbing agent in the water absorbing sheet according to one embodiment of the present invention is preferably 30 to 50 g / g, more preferably 31 to 48 g / g, and more preferably 32 to 45 g / g. / G is more preferable. With such an embodiment, excellent results are obtained in the specific return amount evaluation.

In the water-absorbent sheet according to one embodiment of the present invention, the CRC of the second particulate water-absorbing agent relative to the CRC of the first particulate water-absorbing agent is preferably more than 1 and less than 2, more preferably 1.03 to 1.0. 5 is more preferable, and 1.05 to 1.4 is further preferable. By setting the CRC of the lower layer (the layer of the second particulate water-absorbing agent) higher than the CRC of the upper layer (the layer of the first particulate water-absorbing agent), the specific return amount evaluation is more excellent. However, the present invention is not limited to such an embodiment.

The lower limit of the CRC of the particulate water-absorbing agent (CRC of the mixture of the first particulate water-absorbing agent and the second particulate water-absorbing agent) in the water-absorbent sheet according to one embodiment of the present invention is 36 g / g or more. It is. If the CRC is less than 36 g / g, the amount of water absorption may be insufficient and an excellent result may not be obtained in the specific return amount evaluation. On the other hand, when the CRC is 36 g / g or more, the diffusivity of the liquid generally tends to decrease easily. However, in the present invention, the transmittance is 60% or more. The desired problem of the present invention can be solved while taking advantage of the advantage of being large. The lower limit of the CRC of the particulate water-absorbing agent (CRC of the mixture of the first particulate water-absorbing agent and the second particulate water-absorbing agent) in the water-absorbent sheet according to one embodiment of the present invention is preferably 36. It is 1 g / g or more, more preferably 36.2 g / g or more, further preferably 36.3 g / g or more, and still more preferably 36.4 g / g or more. With such an embodiment, excellent results are obtained in the specific return amount evaluation. The upper limit is preferably 50 g / g or less, more preferably 48 g / g or less, and even more preferably 45 g / g or less.

"AAP" (ERT442.2-02)
“AAP” is an abbreviation for Absorption Against Pressure and means the water absorption capacity under pressure of a particulate water absorbing agent. Specifically, 0.9 g of the particulate water-absorbing agent was swollen under a load of 2.06 kPa (21 g / cm ² , 0.3 psi) for 1 hour against a large excess of 0.9% by mass aqueous sodium chloride solution. It refers to the subsequent water absorption capacity (unit: g / g). In addition, ERT442.2-02 is described as Absorption Under Pressure (AUP), but has substantially the same contents.

AAP2.1 kPa of the second particulate water-absorbing agent in the water-absorbent sheet according to one embodiment of the present invention is preferably 18 to 40 g / g, more preferably 23 to 33 g / g, and 24. More preferably, it is ３２32 g / g, and even more preferably, it is 25-29 g / g. With such an embodiment, excellent results are obtained in the specific return amount evaluation.

AAP2.1 kPa of the first particulate water-absorbing agent in the water-absorbing sheet according to one embodiment of the present invention is preferably 18 to 40 g / g, more preferably 23 to 33 g / g, and 24. More preferably, it is で 32 g / g. With such an embodiment, excellent results are obtained in the specific return amount evaluation.

The lower limit of AAP2.1 kPa of the particulate water-absorbing agent (AAP2.1 kPa of the mixture of the first particulate water-absorbing agent and the second particulate water-absorbing agent) in the water-absorbent sheet according to one embodiment of the present invention is as follows: It is preferably at least 18 g / g, more preferably at least 20 g / g, even more preferably at least 25 g / g. With such an embodiment, excellent results are obtained in the specific return amount evaluation. The upper limit is preferably 40 g / g or less, more preferably 38 g / g or less, and even more preferably 35 g / g or less.

"GPR"
Gel Permeation Rate (GPR)
In the present specification, the “liquid permeability” of the particulate water-absorbing agent refers to the fluidity of a liquid passing between swollen gel particles under a load. The gel permeation velocity (GPR) is used as this index. The gel permeation rate (GPR) of the particulate water-absorbing agent (the first particulate water-absorbing agent and the second particulate water-absorbing agent) contained in the water-absorbent sheet according to one embodiment of the present invention is described in US Pat. No. 5,849,405. Reference is made to the saline flow conductivity (SFC) test described in the specification and the measurement procedure is changed, and the measurement is performed in the following procedure.

(2) The device 400 shown in FIG. 2 is used as a device for measurement. The device 400 is roughly composed of a container 410 and a tank 420. The container 410 is provided with a cell 411 (inner diameter: 6 cm), in which a swelling gel 414 (having a particulate water-absorbing agent absorbed) is accommodated in the cell 411, and a liquid 423 can be introduced. Further, by fitting the piston 412 into the cell 411, pressure can be applied to the swelling gel 414. Wire meshes 413a and 413b (No. 400 stainless steel wire mesh, mesh size 38 μm) are stretched on the bottom surface of the cell 411 and the bottom surface of the piston 412, so that the swelling gel 414 (and the particulate water absorbing agent) cannot pass through. ing. Here, as the liquid 423, a 0.90% by weight aqueous solution of sodium chloride is used. The tank 420 stores the liquid 423 inside. Liquid 423 is introduced into cell 411 through cocked L-shaped tube 422. A glass tube 421 is inserted into the tank 420, and the inside of the glass tube 421 is filled with air. Thereby, the lower end of the glass tube 421 and the liquid level in the cell 411 can be made the same. That is, while the liquid level of the liquid 423 in the tank 420 is above the lower end of the glass tube 421, the liquid level in the cell 411 can be kept constant. In this measurement, the height difference between the lower liquid surface of the liquid 423 in the tank 420 (that is, the lower end of the glass tube 421) and the bottom surface of the swollen gel 414 was 4 cm. That is, according to the device 400, the liquid 423 having a constant hydrostatic pressure can be introduced into the cell 411. Since a hole 415 is formed in the piston 412, the liquid 423 flows through the hole 415, further flows through the swollen gel 414 layer, and flows out of the cell 411. The container 410 is placed on a stainless steel mesh 431 that does not prevent the passage of the liquid 423. Therefore, the liquid 423 flowing out of the cell 411 is finally collected in the collection container 432. Then, the amount of the liquid 423 collected in the collection container 432 can be weighed by the fine balance 433.

The specific method of measuring the gel permeation velocity (GPR) is as follows. The following operation is performed at room temperature (20 to 25 ° C.).

(1) The particulate water-absorbing agent (0.900 g) is uniformly introduced into the cell 411.

(2) The above particulate water-absorbing agent is allowed to absorb a liquid (0.00 to 0.90% by mass (0.9% by mass in this application) aqueous sodium chloride solution) for 60 minutes under no pressure to form a swelling gel 414. And

(3) Place the piston on the swelling gel 414 and pressurize it at 0.3 psi (2.07 kPa).

(4) While maintaining the hydrostatic pressure at a constant value of 3923 dyne / cm ² , the liquid 423 is introduced into the cell 411 and the swollen gel 414 layer is allowed to flow.

(5) Record the amount of the liquid 423 flowing through the swelling gel 414 layer at 5 second intervals for 3 minutes. That is, the flow velocity of the liquid 423 passing through the swollen gel 414 layer is measured. For the measurement, a precision balance 433 and a computer (not shown) are used.

(6) The gel permeation velocity (GPR) [g / min] is calculated by averaging the flow rates 1 to 3 minutes after the start of the flow of the liquid 423.

In the water-absorbent sheet according to one embodiment of the present invention, the first particulate water-absorbing agent has a GPR of preferably 5 g / min or more, more preferably 35 g / min or more, and more preferably 55 g / min or more. Is more preferably, it is more preferably at least 75 g / min, even more preferably at least 95 g / min, even more preferably at least 112 g / min. According to such an embodiment, after the liquid to be absorbed is introduced from the first base material side, the liquid is easily sent to the second particulate water absorbing agent, and the second particulate water absorbing agent is It can be used effectively and gives excellent results in the evaluation of the specific return amount. In the water-absorbent sheet according to one embodiment of the present invention, the upper limit of the GPR of the first particulate water-absorbing agent is not particularly limited, but from the viewpoint of preventing liquid leakage, is 500 g / min or less, 400 g / min or less. Alternatively, it is preferably at most 300 g / min, more preferably at most 120 g / min.

In the water-absorbent sheet according to one embodiment of the present invention, the GPR of the second particulate water-absorbing agent is preferably 1 g / min or more, more preferably 3 g / min or more, and more preferably 5 g / min or more. Is more preferably 10 g / min or more, even more preferably 35 g / min or 45 g / min. By having such a lower limit, gel blocking is suppressed, the diffusivity is enhanced, and the liquid is easily absorbed by the absorber. In the water-absorbent sheet according to one embodiment of the present invention, the upper limit of the GPR of the first particulate water-absorbing agent is not particularly limited, but from the viewpoint of preventing liquid leakage, 300 g / min or less, 200 g / min or less, Or it is 100 g / min or less.

The GPR of the particulate water-absorbing agent (the GPR of the mixture of the first particulate water-absorbing agent and the second particulate water-absorbing agent) in the water-absorbent sheet according to one embodiment of the present invention is 100 g / min or less. Is preferably 98 g / min or less, more preferably 95 g / min or less. In the water absorbent sheet according to one embodiment of the present invention, the lower limit of the GPR of the particulate water absorbing agent is preferably 1 g / min or more, more preferably 3 g / min or more, and more preferably 5 g / min or more. Is more preferably 10 g / min or more, still more preferably 30 g / min or more, still more preferably 50 g / min or more, and 70 g / min or more. Is even more preferred. According to such an embodiment, liquid leakage can be suppressed, and thereby the specific return amount evaluation can be made excellent. In the water-absorbent sheet according to one embodiment of the present invention, the particulate water-absorbing agent has a GPR of 70 g / min or more and a transmittance of 92% or more.

"Degradable solubles"
The upper limit of the particulate water-absorbing agent in the water-absorbing sheet according to one embodiment of the present invention is not particularly limited. It is more preferably at most 25%, further preferably at most 15%. The lower limit is not particularly limited, but is, for example, about 1% or more, 3% or more, and about 5% or more from the viewpoint of liquid leakage during long-time use. In addition, the measuring method of the degradation soluble component is as follows.

(4) L-ascorbic acid is added to a previously prepared physiological saline to a concentration of 0.05% by mass to prepare a deterioration test solution. Specifically, 0.50 g of L-ascorbic acid was dissolved in 999.5 g of physiological saline to prepare a deterioration test solution. 25 ml of the deterioration test liquid is added to a 250 ml glass beaker container, and 1.0 g of a particulate water absorbing agent is added thereto to form a swollen gel. Cover the container with a plastic wrap and seal, and allow the swollen gel to stand for 16 hours in an atmosphere of 37 ° C (Kusumoto Kasei Co., Ltd., ETAC trademark, HISPEC series, using HT320, 37 ° C setting, wind speed variable scale 30 setting). did. Sixteen hours later, 175 ml of physiological saline and a cylindrical stirrer having a length of 30 mm and a thickness of 8 mm are added, and the mixture is degraded. Then, the mixture is stirred for 10 minutes at 500 rpm to extract from the hydrogel.

20.0 g of a filtrate obtained by filtering this extract using a filter paper (ADVANTEC Toyo Co., Ltd., product name: (JIS P # 3801, No. 2), thickness 0.26 mm, particle diameter of retained particles 5 μm) is weighed. Then, 30 g of physiological saline is added to obtain a measurement solution.

The measurement method is as follows: physiological saline is titrated to pH 10 using a 0.1 N NaOH aqueous solution, and then titrated to pH 2.7 using a 0.1 N HCl aqueous solution. , [BHCl] ml). The same titration operation is performed on the measurement solution to determine the titer ([NaOH] ml, [HCl] ml). For example, in the case of a particulate water-absorbing agent comprising a known amount of acrylic acid and its sodium salt, the soluble content in the particulate water-absorbing agent is determined based on the average molecular weight of the monomer and the titer obtained by the above operation. The following formula:
Degradable soluble matter (% by mass) = 0.1 × (average molecular weight) × 200 × 100 × ([HCl] − [bHCl]) / 1000 / 1.0 / 20.0. In the case of an unknown amount, the average molecular weight of the monomer is calculated using the neutralization ratio obtained by titration.

"surface tension"
The surface tension represents the work (free energy) required to increase the surface area of a solid or a liquid per unit area. The surface tension referred to in the present application refers to the surface tension of an aqueous solution when the particulate water-absorbing agent is dispersed in a 0.90% by mass aqueous solution of sodium chloride. The surface tension of the water absorbing agent is measured according to the following procedure. That is, 50 ml of physiological saline adjusted to 20 ° C. is placed in a well-washed 100 ml beaker, and the surface tension of the physiological saline is first measured using a surface tensiometer (KRUSS K11 automatic surface tensiometer). Measure. Next, a well-washed 25 mm long fluororesin rotor and 0.5 g of a particulate water-absorbing agent were charged into a beaker containing physiological saline after surface tension measurement adjusted to 20 ° C., and 500 rpm. Stir for 4 minutes under conditions. After 4 minutes, the stirring is stopped, and after the water-containing particulate water-absorbing agent has settled, the surface tension of the supernatant is measured again by performing the same operation. In the present invention, a plate method using a platinum plate is adopted, and the plate is sufficiently washed with deionized water before each measurement and heated and washed with a gas burner before use. In the water-absorbent sheet according to one embodiment of the present invention, the surface tension of the particulate water-absorbing agent is, in order, 57 N / m or more, 65 mN / m or more, 66 mN / m or more, 67 mN / m or more, 69 mN / m or more. , 70 mN / m or more, 71 mN / m or more, and most preferably 72 mN / m or more. When the particulate water-absorbing agent is applied to a water-absorbent sheet, the influence of the surface tension is more evident than in a conventional paper diaper.

において In the water absorbing sheet according to one embodiment of the present invention, the upper limit of the surface tension of the particulate water absorbing agent is not particularly limited, but is 73 mN / m or less.

"Particle shape"
It is preferable that the particulate water-absorbing agent according to one embodiment of the present invention includes those having an irregular crushed particle shape. Here, the irregularly crushed particles are crushed particles having irregular shapes. In the case of irregularly crushed particles, fixation to a substrate can be facilitated as compared with spherical particles obtained by reverse phase suspension polymerization or gas phase polymerization. The particulate water-absorbing agent according to one embodiment of the present invention is preferably a pulverized product in aqueous solution polymerization. On the other hand, when the pulverization step is not performed, typically, spherical particles or granules of spherical particles obtained by reverse phase suspension polymerization or droplet polymerization such as spraying and polymerizing a polymerization monomer are irregularly crushed. Not a state. In the embodiment of the present invention, when the shape of the particulate water-absorbing agent is irregularly crushed, the shape of the water-absorbent sheet is more easily maintained than that of a particle having a high average roundness (for example, spherical). In the embodiment of the present invention, the average roundness of the particulate water-absorbing agent is preferably 0.70 or less, more preferably 0.60 or less, and even more preferably 0.55 or less.

方法 The method of calculating the average roundness is as follows. 100 or more particulate water-absorbing agents are selected at random, and each particulate water-absorbing agent is photographed with an electron microscope (Keyence Corporation, VE-9800) (magnification: 50 times) to obtain an image of the particulate water-absorbing agent. The perimeter and area were calculated for each particle using the attached image analysis software. The following formula:

Is used to determine the roundness of each particle, and the average of the obtained values is calculated as the average roundness.

In the water-absorbent sheet according to one embodiment of the present invention, the lower limit of the content of the particulate water-absorbing agent per unit volume of the water-absorbent sheet is, in order of preference, 50 mg / cm ³ or more, 51 mg / cm ³ or more, and 52 mg / cm ^3. above, 53 mg / cm ³ or more, 54 mg / cm ³ or more, 55 mg / cm ³ or more, 57 mg / cm ³ or more, 59 mg / cm ³ or more and 60 mg / cm ³ or more. The upper limit of the content of the particulate water-absorbing agent per unit volume of the water-absorbent sheet in the water-absorbent sheet according to one embodiment of the present invention is not particularly limited, but is actually 600 mg / cm ³ or less. , 500 mg / cm ³ or less, more preferably 400 mg / cm ³ or less, still more preferably 300 mg / cm ³ or less, and even more preferably 150 mg / cm ³ or less. By setting the content of the particulate water-absorbing agent in the above range, the water-absorbing sheet effectively exhibits the effects of the present invention. The content of the particulate water-absorbing agent per unit volume of the water-absorbent sheet of the water-absorbent sheet used in Examples of the present application was 50 mg / cm ³ or more.

製造 The method for producing the particulate water-absorbing agent is not particularly limited as long as it is a method for producing a water-absorbing agent having desired physical properties. For example, the particulate water-absorbing agent can be appropriately produced by referring to the publications described in the Examples.

In the water-absorbent sheet according to one embodiment of the present invention, the content weight of the first particulate water-absorbing agent with respect to the content weight of the second particulate water-absorbing agent is preferably 1.0 or less, It is more preferably 0.5 or less, and further preferably 0.4 or less. By making the content of the second particulate water-absorbing agent the same as the content of the first particulate water-absorbing agent, preferably by increasing it, the second particulate water-absorbing agent is considered to have a so-called tank-like function. The water-absorbing agent functions effectively, resulting in excellent evaluation of the specific return amount.

One embodiment of the present invention has a first base material, a second base material, and a water absorbing layer located between the first base material and the second base material. A sheet, wherein the first base material is a water-permeable sheet located on a side where a liquid to be absorbed is introduced, and the water-absorbing layer has a particulate water-absorbing agent and an intermediate sheet. A water-absorbent sheet wherein the weight-average particle diameter of the particulate water-absorbing agent is 200 to 600 μm and the nonwoven fabric transmission index (NPI) is 60 or more. According to such an embodiment, even if the liquid is intermittently introduced a plurality of times (especially three or more times) under a non-pressurized condition and the introduced amount of the liquid is increased, the return amount is significantly reduced. The water-absorbent sheet can be provided.

において In one embodiment of the present invention, the lower limit of the nonwoven fabric transmission index (NPI) is not particularly limited, but is preferably 70 or more, more preferably 80 or more, and further preferably 90 or more. By having such a lower limit, the desired effect of the present invention is efficiently exhibited. In one embodiment of the present invention, the upper limit of the nonwoven fabric transmission index (NPI) is not particularly limited, but is preferably 120 or less, more preferably 110 or less, and further preferably 100 or less.

The nonwoven fabric permeation index (NPI) described in the present specification is calculated by the following formula:

Indicated by Here, A is the specific surface area (mm ⁻¹ ) of the intermediate sheet (for example, nonwoven fabric) measured by X-ray CT, B is the thickness (mm) of the intermediate sheet (for example, nonwoven fabric), and C is Is the basis weight (g / m ² ) of the intermediate sheet (for example, nonwoven fabric), and D is the average particle diameter (μm) (D50) of the particulate water-absorbing agent.

Here, the specific surface area of the intermediate sheet was obtained by analyzing an image taken by X-ray CT using analysis software as described below.

<X-ray CT imaging>
An intermediate sheet cut into a square of 10 mm in length and 10 mm in width (with the same thickness) was measured using a microfocus X-ray CT system, inspeXio SMX-100CT, manufactured by Shimadzu Corporation. The measurement conditions are described below.

-Image horizontal size (pixel): 512
-Image vertical size (pixel): 512
-X-ray tube voltage (kV): 40
X-ray tube current (μA): 50
-Inch size (inch): 4.0
-X-ray filter: None-SDD (distance between focal point of X-ray source and X-ray detector) (mm): 500
SRD (distance between focal point of X-ray source and rotation center of measurement sample) (mm): 40
・ Scanning mode 1: CBCT
-Scan mode 2: Normal scan-Scan angle: Full scan-Number of views: 1200
・ Number of averages: 5
・ Smoothing: YZ
・ Slice thickness (mm): 0.012
・ Distance between slices (mm): 0.010
-Number of scalings: 50
-BHC data: None-Fine mode: Available-FOV XY (maximum shooting area XY) (mm): 5.0
FOV Z (maximum shooting area Z) (mm): 1.5
-Voxel size (mm / voxel): 0.010.

<Calculation of specific surface area>
The X-ray CT imaging data was analyzed by the following procedure using the analysis software TRI / 3D-PRT-LRG manufactured by Latock System Engineering Co., Ltd.

1. From the menu, select Particle Measurement> 3D Particles> Particle Separation> Giant Particle Separation. An EV panel, a BC panel, an EVC panel, and a giant particle separation panel are displayed.

{2. LW is selected on the Binarize tab of the EVC panel, and the L value is changed to select a circular measurement target area. Press “Execute” to apply this process to all slice images (a cylindrical measurement area as a whole is selected). Press "ROI @ OK" on the giant particle separation panel.

{3. By selecting LW on the Binarize tab of the EVC panel and setting the L value to 37580, only fibers are selected. Press “Execute”. Select the bD on the BC panel and press "Save".

4. In the 3D tab of the EVC panel, select the Labeling tab, select “Volume”, and execute MAX (by this operation, 3DLabel {Count} = 1 is displayed).

5. From the menu, select Particle Measurement> Void in 3D Particle> Measurement after Separation. After separation, the measurement panel is displayed. Remove the check of the edge particle removal, check the surface area calculation of the measurement item, select the void calculation, select Binary $ 5ch in the calculation ROI designation, press the "Registration OK", and select the folder to save the data. Press “Execute latest registration data” to perform calculation processing.

6. From the calculation results, the specific surface area was calculated by the following equation.

Specific surface area (mm ⁻¹ ) = total particle surface area (mm ² ) / (total particle volume (mm ³ )
Although the term “particle” is used in the configuration of the calculation software, it is actually a measurement result of the fiber, and there is no problem in measurement and calculation.

In one embodiment of the present invention, the water-absorbent sheet has a nonwoven fabric permeability index (NPI) of 60 or more, and the CRC of the particulate water-absorbing agent contained in the water-absorbing layer in the water-absorbent sheet is 34 g / g or more. And more preferably 36 g / g or more. In addition, the description including physical properties and the like (for example, CRC, AAP 2.1 kPa, GPR, weight average molecular weight, surface tension) of the particulate water absorbing agent described in the specification of the present application is based on the particulate water absorbing agent in the embodiment. And these can be used as a basis for correction to the present embodiment.

[3. Method for producing water-absorbent sheet]
The method for producing a water-absorbent sheet according to one embodiment of the present invention includes: (1) a step of spraying a first particulate water-absorbing agent on a first substrate; At least one of a step of spraying the particulate water absorbing agent and (3) a step of spraying the first particulate water absorbing agent and / or the second particulate water absorbing agent on the intermediate sheet. Examples of more specific manufacturing methods include the following manufacturing methods (a) to (d).

(A) Spread the first particulate water-absorbing agent (and preferably an adhesive) evenly on the first substrate. The intermediate sheet is placed on top of it and pressed. Further, a second particulate water-absorbing agent (and preferably an adhesive) is uniformly dispersed on the surface of the intermediate sheet not facing the first particulate water-absorbing agent. The intermediate sheet is stacked thereon and pressed (preferably under heating conditions under which the hot melt is melted, or under a state in which the hot melt is melted).

(B) Spread the second particulate water-absorbing agent uniformly on the intermediate sheet. In addition, an adhesive is sprayed on the second base material. Then, the surface of the intermediate sheet on which the second particulate water-absorbing agent has been sprayed and the surface of the second base material on which the adhesive has been sprayed are pressed. Next, the first particulate water-absorbing agent is uniformly sprayed on the surface opposite to the surface on which the second particulate water-absorbing agent has been sprayed on the intermediate sheet after the pressure bonding. Further, an adhesive is sprayed on the first base material. Then, the surface of the intermediate sheet on which the first particulate water-absorbing agent has been sprayed and the surface of the first base material on which the adhesive has been sprayed are pressed. The pressure bonding is preferably performed under heating conditions under which the hot melt is melted, or under a state in which the hot melt is melted.

(C) Spray the adhesive on the second substrate. Next, the second particulate water-absorbing agent is evenly sprayed thereon. Next, the intermediate sheet is placed thereon and pressed. Next, an adhesive is sprayed on the surface of the intermediate sheet not facing the second particulate water-absorbing agent. Next, the first particulate water-absorbing agent is evenly sprayed thereon. Next, the first base material is placed thereon and pressed. The pressing is preferably performed under heating conditions under which the hot melt is melted, or under a state in which the hot melt is melted.

(D) Spray the adhesive on the second substrate. Next, the second particulate water-absorbing agent is evenly sprayed thereon. Next, the intermediate sheet is placed thereon and pressed. Next, the first particulate water-absorbing agent is evenly spread on the surface of the intermediate sheet not facing the second particulate water-absorbing agent. Further, an adhesive is sprayed on the first base material. Then, the surface of the intermediate sheet on which the first particulate water-absorbing agent has been sprayed and the surface of the first base material on which the adhesive has been sprayed are pressed. The pressing is preferably performed under heating conditions under which the hot melt is melted, or under a state in which the hot melt is melted.

工程 As a process other than that described above, the water-absorbent sheet may be embossed for the purpose of improving the feel of the water-absorbent sheet and improving the liquid absorption performance. The embossing may be performed simultaneously when the first base material and the second base material are pressed, or may be performed after the sheet is manufactured.

において In the method for producing a water-absorbent sheet according to one embodiment of the present invention, additives (deodorant, fiber, antibacterial agent, gel stabilizer, etc.) may be appropriately blended. The amount of the additive is preferably 0 to 50% by mass, more preferably 0 to 10% by mass, based on the mass of the particulate water absorbing agent. In the above-mentioned production method, a particulate water-absorbing agent in which an additive is mixed in advance may be used, or the additive may be added during the production process.

寸法 The dimensions of the manufactured water-absorbent sheet can be appropriately designed. Usually, the width is 10 cm to 10 m, and the length is several tens to several thousand m (in the state of a continuous sheet or roll). The manufactured water-absorbent sheet is cut and used according to the purpose (the size of the absorber used).

In addition to the above examples, methods for producing a water-absorbent sheet are disclosed in, for example, the following patent documents: WO2012 / 174046, WO2013 / 078109, and WO2015 / 041784. , International Publication No. 2011/117187, International Publication No. 2012/001117, International Publication No. 2012/024445, International Publication No. 2010/004894, International Publication No. 2010/004895, International Publication No. 2010/076857, International Publication No. Publication No. 2010/0882373, International Publication No. 2010/113754, International Publication No. 2010/143635, International Publication No. 2011/043256, International Publication No. 2011/088641, International Publication No. 2011/086862, International Publication No. 2011/086843, International Publication No. 2011/086844, International Publication No. 2011/117997, International Publication No. 2011/118409, International Publication No. 2011/136087, International Publication No. 2012/043546, International Publication No. 2013/099964, International Publication No. No. 2013/096635, JP-A-2010-115406, JP-A-2002-345883, JP-A-6-315501, JP-A-6-190003, JP-A-6-190002, JP-A-6-190001, JP-A-6-190001 JP-A-2-252558, JP-A-2-252560, JP-A-2-252561. The method for producing a water-absorbent sheet disclosed in these documents is also referred to as appropriate.

In the water-absorbent sheet according to one embodiment of the present invention, as a method of fixing the base material or the base material and the particulate water-absorbing agent, (i) an adhesive may be used, and if necessary, pressure-bonding may be performed. (Ii) Various binders dissolved or dispersed in water, a water-soluble polymer, or a solvent may be used. (Iii) The substrates may be heat-sealed at the melting point of the material of the substrate itself. Preferably, it is fixed using an adhesive.

接着 The adhesive used may be a solution type, but a hot-melt adhesive having high productivity and no problem of the residual solvent is preferable from the trouble of removing the solvent, the problem of the remaining solvent, and the problem of the productivity. In the present invention, the hot melt adhesive may be contained in advance on the surface of the substrate or the particulate water absorbing agent, or the hot melt adhesive may be separately used in the process of producing the water absorbing sheet. The form and melting point of the hot melt adhesive can be appropriately selected, and may be in the form of particles, fibers, nets, films, or liquids melted by heating. The melting temperature or softening point of the hot melt adhesive is preferably from 50 to 200 ° C and from 60 to 180 ° C. When a particulate adhesive is used, its particle size is about 0.01 to 2 times, 0.02 to 1 times, and 0.05 to 0.5 times the average particle size of the above particulate water-absorbing agent. An adhesive is used.

方法 Examples of the method of using a hot melt adhesive in the production of the water absorbent sheet according to one embodiment of the present invention include the following examples. A mixture of a particulate water-absorbing agent and a hot-melt adhesive is evenly spread on a base material (for example, a nonwoven fabric), and another base material is laminated. The water-absorbent sheet can be manufactured by thermocompression bonding.

The hot-melt adhesive used in the present invention can be appropriately selected, but is preferably selected from ethylene-vinyl acetate copolymer adhesive, styrene-based elastomer adhesive, polyolefin-based adhesive, polyester-based adhesive and the like. More than one species can be used as appropriate.

Specifically, polyolefin adhesives include polyethylene, polypropylene, atactic polypropylene, and styrene elastomer adhesives include styrene-isoprene block copolymer (SIS), styrene-butadiene block copolymer (SBS), Styrene-isobutylene block copolymer (SIBS), styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene butadiene rubber (SBR), and the like. PET), polybutylene terephthalate (PBT), copolymerized polyester, and the like. Examples of the ethylene-vinyl acetate copolymer adhesive include ethylene-vinyl acetate copolymer (EVA) adhesive; Ethyl acrylic acid copolymer (EEA), ethylene - butyl acrylate copolymer (EBA), and the like.

In the water-absorbent sheet and / or the method for producing the same according to one embodiment of the present invention, the water-absorbent sheet preferably contains an adhesive, and the adhesive is preferably a hot melt adhesive. The amount (content) of the hot melt adhesive (for example, hot melt adhesive) is more than 0 to 3.0 times the total mass of the first particulate water absorbing agent and the second particulate water absorbing agent. Preferably, the ratio is 0.05 to 2.0 times. If the content of the adhesive (especially hot melt adhesive) is too large, not only is it disadvantageous in terms of cost and mass of the water-absorbent sheet (increase in the weight of paper diapers), but also the swelling regulation of the particulate water-absorbing agent There is also a possibility that the water absorbing ability of the water absorbing sheet may be reduced.

[4. Absorbent article)
The absorbent article according to one embodiment of the present invention has a structure in which the water-absorbent sheet described in [2] is sandwiched between a liquid-permeable sheet and a liquid-impermeable sheet. Therefore, in the present invention, the water-absorbent sheet is sandwiched between a liquid-permeable sheet and a liquid-impermeable sheet, and the liquid-permeable sheet is located on the first base material side, A water absorbent article is provided, wherein a liquid impermeable sheet is located on the second substrate side. Specific examples of the absorbent article include disposable diapers, incontinence pads, sanitary napkins, pet sheets, food drip sheets, water cable waterproofing agents, and the like. With such a configuration, excellent results are obtained in the specific return amount evaluation.

As the liquid-permeable sheet and the liquid-impermeable sheet, those known in the technical field of absorbent articles can be used without particular limitation. Further, the absorbent article can be manufactured by a known method.

The present invention will be described in more detail with reference to the following Examples and Comparative Examples. However, the technical scope of the present invention is not limited only to the following examples. In the following examples, unless otherwise specified, operations were performed under the conditions of room temperature (25 ° C.) / Relative humidity of 40 to 50% RH.

<Production example>
The particulate water-absorbing agents (1) to (1) of the polyacrylic acid (salt) -based resin are appropriately adjusted according to the amount of the internal crosslinking agent with reference to the production examples, examples and comparative examples described in the following patents. 4) was obtained. Table 1 shows the physical properties of the obtained particulate water-absorbing agent.

WO 2014/034897 WO 2017/170605 WO 2016/204302 WO 2014/054656 WO 2015/152299 WO 2018/062539 WO 2012/043821.

(Production example of acrylic acid)
Commercially available acrylic acid (2000 ppm of acrylic acid dimer, 500 ppm of acetic acid, 500 ppm of propionic acid, 200 ppm of p-methoxyphenol) was supplied to the bottom of a high-boiling impurity separation column having 50 nonporous perforated plates and a reflux ratio of 1 After removing the dimer (maleic acid dimer) composed of maleic acid or acrylic acid, and further performing crystallization, acrylic acid (acrylic acid dimer 20 ppm, acetic acid 50 ppm, propionic acid 50 ppm, furfural 1 ppm or less) And 1 ppm or less of protoanemonin), and after distillation, 50 ppm of p-methoxyphenol was added.
(Production method of sodium acrylate aqueous solution)
According to Example 9 of US Pat. No. 5,210,298, 1390 g of the above acrylic acid was neutralized at 48 ° C. with 48% sodium hydroxide to obtain a 100% neutralized aqueous solution of sodium acrylate at a concentration of 37%.

<Particulate water-absorbing agent 1>
Acrylic acid obtained in the above acrylic acid production example, 73 mol% of an aqueous solution of sodium acrylate obtained by the method for producing an aqueous solution of sodium acrylate using the acrylic acid, and deionized water. 4.54 g of polyethylene glycol diacrylate (average number of moles of ethylene oxide 9) of 4.54 g was dissolved in 5500 g of an aqueous solution of sodium acrylate having a neutralization ratio (monomer concentration: 39.0% by mass) to prepare a reaction solution. Next, the reaction solution was supplied to a reactor formed by attaching a lid to a stainless steel double-armed kneader having a capacity of 10 L and having two sigma-type blades and having a capacity of 10 L. Gas replacement was performed to remove dissolved oxygen in the reaction solution. Subsequently, while stirring the reaction mixture, 31.65 g of a 10% by weight aqueous solution of sodium persulfate and 38.95 g of a 1% by weight aqueous solution of L-ascorbic acid were added, and polymerization started about 1 minute later. 40 minutes after the start of the polymerization, the hydrogel polymer was taken out. The obtained hydrogel polymer was finely divided into particles of about 2 to 4 mm. The finely divided hydrogel polymer was spread on a wire mesh of 50 mesh (mesh size: 300 μm) and dried with hot air at 175 ° C. for 65 minutes. Next, the dried product was pulverized using a roll mill, and further classified and blended with a wire mesh having an opening of 600 μm to obtain an irregularly crushed water-absorbent resin (1-1) having an average particle diameter of 380 μm.

To 100 parts by mass of the obtained water-absorbent resin (1-1), 0.03 part by mass of ethylene glycol diglycidyl ether, 0.3 part by mass of 1,4-butanediol, 0.5 part by mass of propylene glycol, and 3. 3.83 parts by mass of an aqueous solution of a surface crosslinking agent consisting of 0 parts by mass was spray-mixed. The above mixture was subjected to a heat treatment at a heating medium temperature of 210 ° C. for 40 minutes using a paddle type mixing and heating treatment machine to obtain a surface-crosslinked water-absorbing resin (1-2). To 100 parts by mass of the resulting surface-crosslinked water-absorbent resin (1-2), 1.0 part by mass of water is spray-mixed, and the mixture is cured at 60 ° C. for 1 hour in a closed container. The mixture was passed through a sieve to obtain a water absorbent resin (1-3). 0.3 parts by mass of Aerosil 200 (hydrophilic amorphous silica, manufactured by Nippon Aerosil Co., Ltd.) was added to and mixed with the water absorbing resin (1-3), and the resulting water absorbing resin was used as a particulate water absorbing agent (1).

<Particulate water absorbing agent 2>
The particulate water-absorbing agent 1 was classified and the particle size was adjusted to obtain a particulate water-absorbing agent (2) having an average particle diameter of 420 μm.

<Particulate water absorbing agent 3>
Acrylic acid obtained in the above acrylic acid production example, 73 mol% of an aqueous solution of sodium acrylate obtained by the method for producing an aqueous solution of sodium acrylate using the acrylic acid, and deionized water. 4.17 g of polyethylene glycol diacrylate (average number of moles of ethylene oxide 9) was dissolved in 5,500 g of an aqueous solution of sodium acrylate having a neutralization ratio (monomer concentration: 33.0% by mass) to prepare a reaction solution. Next, the reaction solution was supplied to a reactor formed by attaching a lid to a stainless steel double-armed kneader having a capacity of 10 L and having two sigma-type blades and having a capacity of 10 L. Gas replacement was performed to remove dissolved oxygen in the reaction solution. Subsequently, while stirring the reaction solution, 26.78 g of a 10% by weight aqueous solution of sodium persulfate and 32.96 g of a 1% by weight aqueous solution of L-ascorbic acid were added, and polymerization started about 1 minute later. Forty minutes after the start of the polymerization, 181.5 g of a water-absorbent resin fine powder of 150 μm or less was added, and the kneader blade was subjected to gel crushing at a high speed (130 rpm) for 10 minutes. I took it out. The obtained hydrogel polymer was finely divided into particles of about 1 to 2 mm. The finely divided hydrogel polymer was spread on a wire mesh of 50 mesh (mesh size: 300 μm) and dried with hot air at 175 ° C. for 65 minutes. Next, the dried product was pulverized using a roll mill, and further classified and blended with a wire mesh having an opening of 600 μm to obtain an irregularly crushed water-absorbent resin (3-1) having an average particle diameter of 350 μm.
0.03 parts by mass of ethylene glycol diglycidyl ether, 0.3 parts by mass of 1,4-butanediol, 0.5 parts by mass of propylene glycol, and 3.30 parts by mass of water were added to 100 parts by mass of the obtained water-absorbent resin (3-1). 3.83 parts by mass of a surface crosslinking agent aqueous solution consisting of 0 parts by mass was spray-mixed. The above mixture was subjected to a heat treatment at a heating medium temperature of 195 ° C. for 40 minutes using a paddle type mixing and heating treatment machine to obtain a surface-crosslinked water-absorbing resin (3-2). To 100 parts by mass of the obtained surface-crosslinked water-absorbent resin (3-2), 1.0 part by mass of water is spray-mixed, and the mixture is cured at 60 ° C. for 1 hour in a closed container. The mixture was passed through a sieve to obtain a water absorbent resin (3-3). 0.3 parts by mass of Aerosil 200 (hydrophilic amorphous silica, manufactured by Nippon Aerosil Co., Ltd.) was added to the water-absorbing resin (3-3), and the mixture was mixed to obtain a particulate water-absorbing agent (3).

<Particulate water absorbing agent 4>
The particulate water-absorbing agent 3 was classified and the particle size was adjusted to obtain a particulate water-absorbing agent (4) having an average particle diameter of 420 μm.

<Particulate water absorbing agent 5>
The water-absorbent resin was removed from a commercially available disposable adult diaper urine collection pad (a urine collection pad for safe paper pants without a life shift, made for night use (made by Unicharm, purchased in September 2018). The water-absorbent resin alone was taken out so as not to be mixed with cotton-like pulp, etc. The taken-out water-absorbent resin had a particle shape obtained by granulating spherical particles. 5).

[Removal of water absorbent resin from commercially available disposable diapers 1]
The water-absorbent resin was taken out from a commercially available disposable diaper (Moony Air Fit (L size, Lot No. 2015121633072), manufactured by Unicharm, purchased in May 2016). At the time of taking out, only the water-absorbing resin was taken out so that floc pulp and the like were not mixed. The removed water-absorbent resin had a particle shape obtained by granulating spherical particles. This water absorbing resin was used as a particulate water absorbing agent (T1). Table 1 shows the physical properties of the particulate water-absorbing agent (T1).

〔Example〕
[Example 1]
A particulate water-absorbing agent (3) is applied to the surface of an air-through nonwoven fabric (1) (corresponding to an intermediate sheet) having a thickness of 2.6 mm under an unloaded condition and having an olefin as a main component and cut to a length of 10 cm and a width of 40 cm. 6.0 g (amount of spraying: 150 g / m ² ) was uniformly dispersed.

Next, a nonwoven fabric (B) cut into a length of 10 cm and a width of 40 cm (mainly pulp fiber. Thickness 0.7 mm under no load. Created by an air laid method. Corresponds to the second base material. An adhesive containing styrene butadiene rubber (spray glue 77, manufactured by 3M Japan Co., Ltd.) was uniformly sprayed on the surface of a basis weight of 42 g / m ² (0.3 to 0.5 g) (spray amount: 7. 5 to 12.5 g / m ² ).

Next, the nonwoven fabric (1) was overlaid so that the surface of the nonwoven fabric (1) on which the particulate water-absorbing agent was sprayed and the surface of the nonwoven fabric (B) on which the adhesive was sprayed faced (contacted), and were pressed under pressure.

Next, 6.0 g of the particulate water-absorbing agent (1) (corresponding to the first particulate water-absorbing agent) was applied to the surface of the nonwoven fabric (1) that did not face the particulate water-absorbing agent. : 150 g / m ₂ ). Furthermore, an adhesive containing styrene-butadiene rubber (spray glue 77, manufactured by 3M Japan Co., Ltd.) was evenly applied in an amount of 0.3 to 0.5 g (amount of application: 7.5 to 12.5 g / m ² ). The nonwoven fabric (A) (having a pulp fiber as a main component, a thickness of 0.7 mm under no load, produced by an air laid method, corresponding to the first base material, and having a basis weight of 42 g / m ² ) The surface of the nonwoven fabric (1) on which the particulate water-absorbing agent was sprayed and the surface of the nonwoven fabric (A) on which the adhesive was sprayed were overlapped with each other (to be in contact with each other), and pressed and pressed. Thus, a water absorbent sheet (1) was obtained.

[Example 2]
In Example 1, as shown in Table 2, a water-absorbent sheet (2) was obtained using a nonwoven fabric (2) (air-through nonwoven fabric containing an olefin as a main component) instead of the nonwoven fabric (1).

[Example 3]
In Example 1, as shown in Table 2, a water-absorbent sheet (3) was obtained by using a nonwoven fabric (3) (air-through nonwoven fabric containing an olefin as a main component) instead of the nonwoven fabric (1).

[Example 4]
In Example 1, as shown in Table 2, a water-absorbent sheet (4) was obtained using a nonwoven fabric (4) (air-through nonwoven fabric containing an olefin as a main component) instead of the nonwoven fabric (1).

[Example 5]
In Example 1, a water absorbent sheet (5) was prepared by using a particulate water absorbent (2) instead of the particulate water absorbent (1) and a particulate absorbent (4) instead of the particulate water absorbent (3). ) Got.

[Example 6]
In Example 1, a water-absorbent sheet (6) was obtained by using a particulate absorbent (5) (air-through nonwoven fabric containing an olefin as a main component) instead of the particulate water-absorbent (3).

[Comparative Example 1]
In Example 6, as shown in Table 2, comparative non-woven fabric (5) was used instead of non-woven fabric (1), and particulate absorbent (T1) was used instead of particulate water absorbent (5). Sheet (1) was obtained.

吸収 The obtained water-absorbent sheet was evaluated for absorbers (measurement of the amount of reversion), and Table 3 shows the results.

[Absorbent sheet evaluation method, etc.]
<Return amount>
As shown in FIG. 3, the water-absorbent sheet cut to a length of 10 cm and a width of 40 cm was wrapped with a liquid-impermeable sheet having a length of 14 cm and a width of 40 cm so as to form an opening at the top. The water-absorbent sheet wrapped with the liquid-impermeable sheet was placed on a flat surface, and a liquid injection cylinder (FIG. 4) was placed on the water-absorbent sheet at the center of the water-absorbent sheet as shown in FIG. In this state, 80 g of a 0.9% by weight aqueous solution of 0.9% by weight of sodium chloride at 23 ° C. was introduced into the liquid injection cylinder using a funnel capable of introducing the liquid at a flow rate of 7 ml / sec (FIG. 6). Ten minutes after the introduction of the liquid, 20 pieces of filter paper (model No. 2, made by ADVANTEC; a circular one having a diameter of 110 mm) whose weight was measured in advance were placed on the center of the water absorbent sheet, and a circular weight having a diameter of 100 mm was placed. (1200 g) was further placed and held for 1 minute. One minute later, the weight was removed, and the first return (g) was measured from the weight increase of the filter paper. One minute after removing the weight, the same operation was performed (10 minutes after the liquid was charged, the filter paper and the weight (1200 g) were placed and held for one minute. After one minute, the weight was removed and the amount of reversion was measured. The measurement was repeated to measure the second reversal amount (g) and the third reversal amount (g). Table 3 shows the amount of reversion of each comparative water absorbent sheet.

<Method for measuring transmittance of particulate absorbent>
Nonwoven fabric (1) cut to a diameter of 80 mm in a JIS standard sieve having an opening of 850 μm (The IIDA TESTING SIEVE: inner diameter 80 mm; JIS Z8801-1 (2000)) or a sieve corresponding to the JIS standard sieve Was set as shown in FIG. 7, and the periphery was stopped with a tape (at least a diameter of 75 mm or more secures an area through which particles can pass). At this time, in the form of the water-absorbent sheet, the nonwoven fabric (1) was placed in the sieve such that the surface of the nonwoven fabric (1) in contact with the nonwoven fabric (A) (first base material) faced upward. As the nonwoven fabric (1), a nonwoven fabric taken out of the water-absorbent sheet by a method described later may be used. 10.0 g of the particulate water-absorbing agent was put on the nonwoven fabric (1) in the sieve, and a low-tap type sieve shaker (ES-65 type sieve shaker manufactured by Iida Seisakusho; rotational speed 230 rpm, impact number 130 rpm) was used. The mixture was shaken under the conditions of room temperature (20 to 25 ° C.) and a relative humidity of 50% RH for 5 minutes. The particulate water-absorbing agent may be one taken out of the water-absorbing sheet by the method described below. After shaking, the mass (W (g)) of the nonwoven fabric (1) and the particulate water-absorbing agent passed through the JIS standard sieve was measured, and the transmittance of the particulate absorbent was calculated according to the following formula (i). The measurement was performed three times, and the average value was calculated. The shaking conditions are set in consideration of realistic manufacturing conditions of the water-absorbent sheet, realistic transport conditions of the manufactured water-absorbent sheet, and the like. Here, when the transmittance of the particulate water-absorbing agent to the intermediate sheet is 100%, it seems that all of the particulate water-absorbing agent is spilled in the water-absorbing sheet without being captured by the intermediate sheet. However, the shaking conditions are set to be stronger than those in actual production, transportation, and the like, and are designed so as not to be too strong. According to the intermediate sheet having a predetermined transmittance in the present invention, a large amount of the particulate water-absorbing agent present in the water-absorbent sheet can be captured by a realistic swaying effect in production and transportation.

透過 The transmittance of the nonwoven fabrics (2) to (5) was measured in the same manner.

[Method of removing particulate absorbent from water-absorbent sheet and nonwoven fabric used for intermediate sheet]
The particulate absorbent and the intermediate sheet were taken out by peeling the upper nonwoven fabric (corresponding to the first base material) and the lower nonwoven fabric (corresponding to the second base material) from the water absorbent sheet. All of the particulate absorbent adhering to the upper and lower nonwoven fabrics and the intermediate sheet were also taken out. When the upper and lower nonwoven fabrics are peeled off, cool the water-absorbent sheet and sufficiently weaken the adhesiveness of the nonwoven fabric and the adhesive (hot melt adhesive or spray glue) to which the particulate water-absorbing agent is attached. I peeled it off. By taking this procedure, the intermediate sheet can be taken out without changing the fiber or the structural thickness, and the transmittance can be measured accurately. There are various methods for cooling the water-absorbent sheet, such as putting it in a thermostat at -10 ° C or lower, spraying a cooling spray, applying liquid nitrogen, etc., without changing the fiber, structure and thickness of the intermediate sheet. There is no particular limitation as long as the process is carried out under the condition that the particulate water-absorbing agent contained in the water-absorbent sheet does not absorb moisture.

When the taken-out particulate water-absorbing agent has absorbed moisture, the moisture content is adjusted to 10% by mass or less, preferably 5 ± 2% by mass, for example, by drying, and the transmittance and various values specified in the present application are adjusted. Physical properties may be measured. Drying conditions for adjusting the water content are not particularly limited as long as the conditions do not cause decomposition or modification of the water-absorbent resin (particulate water-absorbing agent), but drying under reduced pressure is preferred.

The present application was filed on August 9, 2018, Japanese Patent Application No. 2018-150124, Japanese Patent Application No. 2018-150125, Japanese Patent Application No. 2018-150129, and Japanese Patent Application No. 2018-185701, the disclosure of which is incorporated herein by reference in its entirety.

11 first substrate,
12 water absorption layer,
13 a second substrate,
14 particulate water absorbing agent 14a first particulate water absorbing agent 14b second particulate water absorbing agent 16 intermediate sheet,
40 water absorbent sheets,
400 devices,
410 containers,
411 cells,
412 pistons,
413a, 413b wire mesh,
414 swollen gel (absorbed particulate water absorbing agent),
415 holes,
420 tanks,
421 glass tube,
422 L-shaped tube with cock glass tube,
423 liquid,
431 stainless steel wire mesh,
432 collection container,
433 Precision balance.

Claims

A first substrate;
A second substrate;
A water-absorbing layer located between the first substrate and the second substrate;
Having a water-absorbent sheet,
The first substrate is a water-permeable sheet located on the side where the liquid to be absorbed is introduced,
The water absorbing layer has a particulate water absorbing agent and an intermediate sheet,
The weight-average particle diameter of the particulate water-absorbing agent is 200 to 600 μm,
CRC of the particulate water-absorbing agent is 36 g / g or more,
A water-absorbent sheet, wherein the transmittance of the particulate water-absorbing agent to the intermediate sheet is 60% by mass or more.
水性 The water-absorbent sheet according to claim 1, wherein the transmittance is 80% by mass or more.
The water-absorbent sheet according to claim 2, wherein the transmittance is 89% by mass or more.
水性 The water-absorbent sheet according to any one of claims 1 to 3, wherein the intermediate sheet is a nonwoven fabric.
(5) The water-absorbent sheet according to any one of (1) to (4), wherein the thickness of the intermediate sheet is larger than the thickness of any one of the first base material and the second base material.
The water-absorbent sheet according to any one of claims 1 to 5, wherein the content of the particulate water-absorbing agent per unit volume of the water-absorbent sheet is 50 mg / cm 3 or more.
The water-absorbent sheet according to any one of claims 1 to 6, wherein the particulate water-absorbing agent has a GPR of 100 g / min or less.
The water-absorbing sheet according to any one of claims 1 to 7, wherein the particulate water-absorbing agent has an AAP of 2.1 kPa of 20 g / g or more.
The water-absorbing sheet according to any one of claims 1 to 8, wherein the surface tension of the particulate water-absorbing agent is 65 mN / m or more.
The water-absorbent sheet according to any one of claims 1 to 9, wherein the average roundness of the particulate water-absorbing agent is 0.70 or less.
The water-absorbing sheet according to any one of claims 1 to 10, wherein the shape of the particulate water-absorbing agent includes an irregularly crushed shape.
The water-absorbing sheet according to any one of claims 1 to 11, wherein the weight average particle diameter of the particulate water-absorbing agent is 400 μm or less.
The water-absorbent sheet according to any one of claims 1 to 12, wherein the particulate water-absorbing agent has a GPR of 70 g / min or more.
The water-absorbent sheet according to claim 13, wherein the transmittance is 92% by mass or more.
The water-absorbent sheet contains an adhesive,
15. The water-absorbent sheet according to claim 1, wherein the amount of the adhesive used is 0.05 to 2.0 times the total mass of the particulate water-absorbing agent.
A first substrate;
A second substrate;
A water-absorbing layer located between the first substrate and the second substrate;
Having a water-absorbent sheet,
The first substrate is a water-permeable sheet located on the side where the liquid to be absorbed is introduced,
The water absorbing layer has a particulate water absorbing agent and an intermediate sheet,
The weight-average particle diameter of the particulate water-absorbing agent is 200 to 600 μm,
A water-absorbent sheet having a nonwoven fabric transmission index (NPI) of 60 or more.
The water-absorbent sheet according to claim 17, wherein the particulate water-absorbing agent has a CRC of 34 g / g or more.
The liquid-absorbent sheet according to any one of claims 1 to 17, which is sandwiched between a liquid-permeable sheet and a liquid-impermeable sheet, wherein the liquid-permeable sheet is on the first substrate side. Wherein the liquid impermeable sheet is located on the second substrate side.