JP7174761B2 - Absorbent sheet and absorbent article containing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a water absorbent sheet and absorbent articles including the same.

A water-absorbing resin (SAP/Super Absorbent Polymer) is a water-swellable water-insoluble polymer gelling agent, and is used in sanitary materials such as disposable diapers, sanitary napkins and incontinence products for adults, and soil water retention agents for agricultural and horticultural applications. It is used for various purposes such as industrial waterproofing agents.

These absorbent articles are generally manufactured at a paper diaper manufacturing factory by mixing water-absorbing resin and fibrous materials and forming absorbent bodies individually shaped for each absorbent article. (For example, it is processed into an hourglass shape, a fox shape, an elliptical shape, etc. when viewed in plan). Since these absorbent bodies are individually molded, they can be processed into any shape, and the amounts of fibers and water-absorbent resin can be easily adjusted for each absorbent article.

However, in recent years, in the manufacture of paper diapers, absorbent bodies (usually around 10 cm wide and several (cut into 10 cm rectangles) has come to be manufactured. Disposable diaper manufacturers can simplify the manufacturing process of disposable diapers by purchasing or manufacturing long continuous water-absorbing sheets, and can make the disposable diapers thinner by not using pulp. The water-absorbent sheet has a configuration in which water-absorbent resin particles are sandwiched and fixed between upper and lower sheets (especially nonwoven fabric sheets). It is made into a rectangle with a thickness of 10 cm and incorporated into a paper diaper (for example, Patent Document 1).

Unlike conventional sanitary materials (paper diapers), the history of paper diapers using water-absorbent sheets is short. This is the actual situation, and conventional water absorbent resins for paper diapers are used as they are for water absorbent sheets.

International Publication No. 2010-143635

The inventors of the present invention have found that the so-called "backflow", in which the absorbed liquid is released, may occur due to the structure unique to water absorbent sheets, which are mainly thin. The inventors have also found that the problem becomes significant when the liquid is intermittently introduced a plurality of times (especially, three times or more) in a non-pressurized state and the amount of the liquid introduced increases.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a novel water-absorbing sheet that can significantly reduce the amount of liquid returned even in the environment in which the liquid is introduced.

A water absorbent sheet comprising a first base material, a second base material, and a water absorbent layer positioned between the first base material and the second base material, The first base material is a water-permeable sheet positioned on the side where the liquid to be absorbed is introduced, and the water-absorbing layer faces the intermediate sheet and the second base material of the first base material. a first particulate water-absorbing agent localized on the surface side of the second substrate, and a second particulate water-absorbing agent localized on the surface side of the second substrate facing the first substrate; , the transmittance of the mixture of the first particulate water absorbing agent and the second particulate water absorbing agent to the intermediate sheet is less than 60%, and the GPR of the second particulate water absorbing agent is , 45.0 g/min or more to solve the above problems.

It is a schematic diagram showing the cross section of the water-absorbing sheet which concerns on one Embodiment of this invention. 1 is a schematic diagram showing an apparatus for measuring GPR; FIG. FIG. 4A is a plan view and a right side view showing a sample used for evaluation of the amount of reversion, and shows how the water-absorbing sheet prepared in the example is wrapped with the liquid-impermeable sheet. FIG. 4A is a plan view and a front view of a liquid injection cylinder used for evaluation of the backflow amount; Fig. 10 is a front view showing a state in which a liquid injection tube is placed on the water absorbent sheet used in the examples of the present application; FIG. 6 is a front view and a right side view showing a state in which a funnel is used to pour a sodium chloride aqueous solution from a liquid injection tube into the water absorbent sheet in FIG. 5 ; It is the schematic which shows the apparatus used in the case of the transmittance|permeability measurement.

Hereinafter, the present invention will be described while showing the best mode. It should be understood that throughout this specification, expressions in the singular also include the concept of the plural unless specifically stated otherwise. Thus, articles in the singular (eg, "a," "an," "the," etc. in the English language) should be understood to include their plural forms as well, unless specifically stated otherwise. Also, it should be understood that the terms used in this specification have the meanings commonly used in the relevant field 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 modified in various ways within the scope of the claims.

[1. Definition of terms〕
[1-1. 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 held between two or more long substrates. The water absorbent sheet may use an adhesive or a hot-melt adhesive for bonding at least one of the substrate, the intermediate sheet, and the particulate water absorbent. The water absorbent sheet may contain other components (fiber component, antibacterial agent, deodorant, etc.) in addition to the particulate water absorbent. In addition, the water-absorbing sheet may include other sheets than the two substrates sandwiching the particulate water-absorbing agent.

Usually, the water-absorbing sheet is in the form of a continuous sheet or a roll obtained by winding up the continuous sheet. When using the water absorbent sheet, the continuous sheet is cut into an appropriate shape (rectangular or the like) and then used as an absorbent body for disposable diapers and the like. On the other hand, conventional high-concentration water-absorbing resin disposable diapers (for example, pulpless disposable diapers) use an absorbent body that is individually shaped for each disposable diaper. Therefore, such an absorbent body is technically different from the absorbent sheet of the present invention.

[1-2. Water Absorbent Resin]
As used herein, the term "water absorbent resin" means that the water swellability (CRC) defined by ERT441.2-02 is 5 g / g or more, and the water-soluble component defined by ERT470.2-02 ( Ext) is 50% by mass or less.

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

As used herein, the term "water absorbent resin" is not limited to a mode in which the total amount (100% by mass) is only the water absorbent resin. It may be a water absorbent resin composition containing additives and the like. In addition, the term "water absorbent resin" as used herein is a concept that also includes intermediates in the manufacturing process of the water absorbent resin. For example, a water-containing gel-like crosslinked polymer after polymerization, a dry polymer after drying, a water-absorbent resin powder before surface cross-linking, and the like are sometimes referred to as "water-absorbent resin".

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

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

As used herein, the term "particulate water absorbing agent" means a particulate (powder) water absorbing agent (because the water absorbing agent contains the water absorbing resin as a main component, it corresponds to a particulate water absorbing resin). . The concept of "particulate water absorbing agent" includes both a grain of particulate water absorbing agent and an aggregate of a plurality of particulate water absorbing agents. As used herein, "particulate" means having the form of particles. Here, "particle" refers to a relatively small divided body of a substance, and has a size of several angstroms to several millimeters ("particle", McGraw-Hill Scientific and Technical Terminology Comprehensive Editing Committee, "McGraw-Hill Science Technical Terminology Encyclopedia 3rd Edition, Nikkan Kogyo Shimbun, 1996, p. 1929). In this specification, the "particulate water absorbing agent" may be simply referred to as "water absorbing agent". In the water absorbent sheet according to one embodiment of the present invention, the weight average particle size of the particulate water absorbing agent is preferably 200 to 600 μm, more preferably 250 to 500 μm, and still more preferably 300 to 450 μm. . Further, in the water absorbent sheet of the present invention, it is preferable that 95% or more of the whole particulate water absorbing agent has a particle diameter of 850 μm or less, and 98% or more of the whole particulate water absorbing agent has a particle diameter of 850 μm or less. More preferably, substantially 100% of the entire particulate water absorbing agent has a particle size of 850 μm or less. In the examples of the present application, substantially 100% of the entire particulate water absorbing agent has a particle diameter of 850 μm or less. Here, in the present specification, the weight average particle size measurement method is based on the PSD obtained according to the "PSD" measurement method specified in ERT420.2-02, and is described in US Patent No. 7,638,570. (3) Mass-Average Particle Diameter (D50) and Logarithmic Standard Deviation (σζ) of Particle Diameter Distribution”.

The particulate water-absorbing agent contains a water-absorbing resin (also referred to as a particulate water-absorbing resin or water-absorbing resin particles) as a polymer as a main component. The particulate water-absorbing agent contains 60 to 100% by mass, preferably 70 to 100% by mass, more preferably 80 to 100% by mass, still more preferably 90 to 100% by mass, particularly preferably 90 to 100% by mass, of a water-absorbing resin as a polymer. contains 95 to 100% by mass. The remainder of the particulate water-absorbing agent may optionally contain water, additives (inorganic fine particles, polyvalent metal cations, etc.) 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 the water absorbing resin.

That is, the upper limit of the water absorbent resin in the particulate water absorbent is, for example, 100% by mass, 99% by mass, 97% by mass, 95% by mass, or 90% by mass. Further, preferably, 0 to 10% by mass of components, particularly water, additives (inorganic fine particles, polyvalent metal cations), etc. are further included in addition to the water absorbent resin.

A preferable water content of the particulate water absorbing agent is 0.2 to 30% by mass. As described above, the water-absorbing resin composition in which components such as water and additives are integrated with the water-absorbing resin and/or the water-absorbing resin composition in the form of a mixture is also referred to as the "particulate water-absorbing agent. ”.

Examples of water absorbing resins that are the main component of particulate water absorbing agents include polyacrylic acid (salt) resins, polysulfonic acid (salt) resins, maleic anhydride (salt) resins, polyacrylamide resins, and polyvinyl alcohol. based resins, polyethylene oxide based resins, polyaspartic acid (salt) based resins, polyglutamic acid (salt) based resins, polyalginic acid (salt) based resins, starch based resins, and cellulose based resins. Among these, polyacrylic acid (salt) resin is preferably used as the water absorbent resin.

[1-4. Polyacrylic acid (salt)]
As used herein, "polyacrylic acid (salt)" refers to polyacrylic acid and/or its salt. The polyacrylic acid (salt) contains repeating units of acrylic acid and/or a salt thereof (hereinafter referred to as "acrylic acid (salt)") as a main component, and further contains a graft component as an optional component. is. The above polyacrylic acid (salt) is obtained by polymerization of acrylic acid (salt), hydrolysis of polyacrylamide, polyacrynitrile, or 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 when polymerizing polyacrylic acid (salt) is the total amount of monomers used for polymerization (excluding the internal cross-linking agent) , usually 50 to 100 mol%, preferably 70 to 100 mol%, more preferably 90 to 100 mol%, still more preferably substantially 100 mol%.

[1-5. EDANA and ERT]
" EDANA " is an abbreviation for the European Disposables and Nonwovens Association. "ERT" is an abbreviation for the European standard (substantial global standard) water absorbent resin measurement method (EDANA Recommended Test Methods) established by EDANA. In this specification, the physical properties of the water absorbent resin are measured according to the 2002 edition of ERT unless otherwise specified.

[1-6. others]
In this specification, "X to Y" indicating a range means "X or more and Y or less".

In this specification, the unit of mass, "t (ton)", means "metric ton" unless otherwise noted. "ppm" means "ppm by weight"; "mass" and "weight", "parts by mass" and "parts by weight", "% by mass" and "% by weight", and "ppm by mass" and "ppm by weight" are treated as having the same meaning.

As used herein, "acid (salt)" means "acid and/or its salt". "(Meth)acrylic" means "acrylic and/or methacrylic".

In this specification, the unit of volume "liter" may be written as "l" or "L". "% by mass" may be expressed as "wt%". When measuring a trace component, below the detection limit is defined as N.V. D. (Non Detected).

[2. Absorbent sheet]
A water absorbent sheet of the present invention comprises a first substrate, a second substrate, and a water absorbent layer positioned between the first substrate and the second substrate. wherein the first base material is a water-permeable sheet located on the side where the liquid to be absorbed is introduced, and the water-absorbing layer is composed of an intermediate sheet and the first base material. A first particulate water absorbing agent localized on the surface side facing the second base material, and a surface side of the second base material facing the first base material and a second particulate water absorbing agent, the intermediate sheet of a mixture of the first particulate water absorbing agent and the second particulate water absorbing agent (herein also referred to as a "water absorbing agent mixture"). is less than 60%, and the GPR of the second particulate water absorbing agent is less than 60% as measured by the method described in the Examples section of this application is 45.0 g/min or more. With such a configuration, even if the liquid is intermittently introduced a plurality of times (especially, three or more times) under no pressure condition and the amount of liquid introduced increases, the amount of return can be significantly reduced. In particular, with such a configuration, extremely excellent results can be obtained in the measurement of the amount of return under specific conditions in the examples of the present application (also referred to herein as "evaluation of specific amount of return"). In other words, if the liquid is intermittently introduced several times (especially three times or more), with a normal configuration, the liquid amount will exceed the set absorption amount and excessive "return" will occur. . The inventors of the present invention have found that the transmittance of the intermediate sheet of 60% by mass or more essentially makes the evaluation of the specific amount of return excellent. Hereinafter, mass % is also simply referred to as % with respect to transmittance. The reason for this is that the combination of the particulate water-absorbing agent and the intermediate sheet that can achieve such a transmittance makes it easier for the intermediate sheet to capture 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 diffuses into the water absorbing sheet, and gaps between the particulate water absorbing agents present in the water absorbing sheet are likely to open. If the transmittance is less than 60%, the particulate water absorbing agent existing between the intermediate sheet and the base material is difficult to be captured by the intermediate sheet, and the particulate water absorbing agent is trapped between the intermediate sheet and the base material. The probability of existence is increased, and the particulate water absorbing agent is densely present between the intermediate sheet and the base material. Then, a gel blocking phenomenon occurs between the water-absorbing particulate water-absorbing agents, liquid diffusibility decreases, and excessive "return amount" occurs. In other words, when the transmittance is 60% or more, the particulate water absorbing agent existing between the intermediate sheet and the base material diffuses widely into the intermediate sheet, so that gaps between the particulate water absorbing agents tend to form. , the performance of the particulate water-absorbing agent can be maximized, and the water-absorbing sheet has a technical effect of being able to utilize a wider area for water absorption. However, the present inventors found that even if the permeability of the particulate water absorbing agent to the intermediate sheet is less than 60%, the particulate water absorbing agent combined with the intermediate sheet is the first particulate water absorbing agent and the second particulate water absorbing agent. It was found that by localizing the second particulate water absorbing agent with the water absorbing agent and setting the GPR of the second particulate water absorbing agent to 45.0 g/min or more, the "specific return amount evaluation" can be made excellent. rice field. In addition, when the transmittance is less than 60%, the intermediate sheet becomes soft and has a good texture, which has the technical effect of making the user more comfortable. In addition, the mechanism etc. which were described in this specification do not limit the technical scope of the claim of this application. Here, it should be added that water-absorbing sheets and absorbent articles designed to suppress the amount of return under general conditions do not always give excellent results in the "specific return amount evaluation" of the present application. In addition, the water-absorbent sheet according to one embodiment of the present invention is an absorbent article that is used during a period of time during which an infant with a small bladder who is just beginning to learn to run is actively moving around during the daytime (e.g., It is suitable as a diaper), but the form of use is of course not limited to this. Methods for achieving a transmittance of less than 60% will be described later, but (if the intermediate sheet is made of fibers) the fiber diameter can be controlled, or (if the intermediate sheet is a nonwoven fabric) multiple A method of overlapping non-woven fabrics is considered to be suitable. In other words, it is possible to achieve a transmittance of less than 60% by adjusting the properties of the members constituting the intermediate sheet, their surface conditions, the complexity of the network structure, the fiber diameter, the state of fusion between fibers, the basis weight, the thickness, and the like. can. For example, if an air-through nonwoven fabric is used as the intermediate sheet, those who practice the present invention can adjust the transmittance by changing the heat treatment conditions, fiber diameter, and density of the air-through nonwoven fabric. Even if another type of intermediate sheet is used, a transmittance of less than 60% can be achieved by appropriately changing the factors related to the above transmittance adjustment.

Hereinafter, embodiments of the present invention will be described with reference to the attached drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and overlapping descriptions are omitted. Also, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may differ from the actual ratios.

FIG. 1 is a schematic diagram showing a cross section of a water absorbent sheet 40 according to one embodiment of the present invention. The first base material 11 is located on the side where the liquid to be absorbed is introduced. That is, at least the first base material is arranged on the liquid discharge side (for example, on the skin side in the case of paper diapers). A water absorbing layer 12 is arranged between the first substrate 11 and the second substrate 13 . In FIG. 1, the second base material 13 is positioned only on the opposite side of the absorbent layer 12 from the side where the liquid to be absorbed is introduced. The area of 13 may be designed larger than the first base material 11 and folded so as to wrap the first base material 11 . By doing so, it is possible to prevent the particulate water absorbing agents 14a and 14b from coming off. The water absorbent sheet 40 of FIG. 1 includes an intermediate sheet 16, first particulate water absorbing agents 14a localized on the surface side of the first base material 11 facing the second base material, and and a second particulate water absorbing agent 14b localized on the surface side of the second base material 13 facing the first base material. Although this intermediate sheet 16 has a permeability of the water absorbing agent mixture of less than 60%, it is localized in the particulate water absorbing agent 14a and the particulate water absorbing agent 14a, and the second particulate water absorbing agent 14b Since the GPR is 45.0 g/min or more, a large amount of the particulate water absorbing agent 14a and the particulate water absorbing agent 14b do not exist in the intermediate sheet 16. The intended effect of the present invention is exhibited.

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

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

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, probe: anvil top and bottom φ50 mm). The measurement point was the central portion of each of the three equal parts of the absorber divided in the longitudinal direction (a point located at the intersection of diagonal lines drawn from the ends of the absorber). For example, in the case of a water absorbent sheet with a length of 36 cm and a width of 10 cm, the measurement position is a point (left) 6 cm from the left end of the length direction and 5 cm from both ends of the width direction with respect to the length of 36 cm in the length direction. , 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). . Each point is measured twice, and the measured value of the thickness is the average value of a total of 6 points. As a specific procedure, the water-absorbing sheet is flatly attached to a plate with a uniform thickness so as not to cause wrinkles or distortion at the measurement point, and the plate is set on the lower probe of the thickness measuring device. . Next, after bringing the upper probe of the thickness measuring device close to the water absorbent sheet to a height of 2 to 3 mm, slowly release the handle and measure the combined thickness of the water absorbent sheet and the plate. The thickness of the water-absorbent sheet is determined by the formula: T1 = T2-T0 (T0: thickness of plate (mm), T1: thickness of water-absorbent sheet (mm), T2: thickness of water-absorbent sheet and plate (mm)). .

The surface of the water absorbent sheet may be appropriately embossed in order to impart liquid permeability, diffusibility, flexibility, etc. to the water absorbent sheet. The area to be embossed may be the entire surface of the water-absorbent sheet or a part thereof. By providing a continuous embossed region 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 dispersed over the entire surface of the water absorbing sheet, or a part of the water absorbing sheet may be provided with a non-existing area of the particulate water absorbing agent. When the particulate water-absorbing agent-free region is provided, it is preferably provided in the longitudinal direction of the water absorbent sheet in a channel shape (streak shape). By providing the embossed region and/or the non-particulate water-absorbing agent-free region continuously in the longitudinal direction in this manner, the region serves as a passage (liquid transport passage) for flowing a large amount of liquid. Fulfill. The embossed area and/or the particulate water-absorbing agent-free area may be provided linearly, curvedly, or corrugated.

Each member constituting the water absorbent sheet will be described in detail below.

[2-1. First base material, second base material and intermediate sheet]
The first base material is a water-permeable sheet positioned on the side into which the absorbed liquid is introduced. The liquid to be absorbed is not limited to water, but may be urine, blood, sweat, feces, waste liquid, humidity, steam, ice, a mixture of water and an organic solvent and/or an inorganic solvent, rainwater, groundwater, or the like. It is not particularly limited as long as it contains water. Preferred examples include urine, menstrual blood, sweat, and other body fluids.

The upper limit of the transmittance of the water absorbing agent mixture to the intermediate sheet in the water absorbent sheet according to one embodiment of the present invention is not particularly limited as long as it is less than 60%, but it may be 59% or less, or 57% or less. 55% or less, 53% or less, 51% or less, 49% or less, 47% or less, 45% or less , 43% or less. The lower limit is preferably 10% or more, more preferably 20% or more, still more preferably 30% or more, even more preferably 35% or more, and more than 40%. is more preferably 42% or more, even more preferably 44% or more, even more preferably 46% or more, even more preferably 48% or more, 50 % or more is even more preferable. By having such a lower limit, the capture rate of the particulate water-absorbing agent is increased, and the desired effect of the present invention can be easily exhibited.

In the water absorbent sheet according to one embodiment of the present invention, the void ratio of the water absorbing agent mixture to the intermediate sheet is preferably 80 to 99.9%, more preferably 85 to 99.9%, and still more preferably 90%. ~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, a transmittance of less than 60% can be achieved depending on the properties of the members constituting the intermediate sheet, their surface conditions, the complexity of the network structure, the fiber diameter, the fusion state between fibers, the basis weight, the thickness, etc. Therefore, there is no direct relationship between porosity and transmittance.

The materials of the first base material, the second base material and the intermediate sheet used in the water absorbent sheet according to one embodiment of the present invention are each independently preferably non-woven fabric. The material of the non-woven fabric is not particularly limited, but from the viewpoint of liquid permeability, flexibility, and strength of the water-absorbing sheet, polyolefin fibers (polyethylene (PE), polypropylene (PP), etc.), polyester fibers (polyethylene terephthalate (PET) ), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), etc.), polyamide fibers (nylon, etc.), rayon fibers, pulp (cellulose) fibers, etc. are preferred. Nonwoven fabrics of other synthetic fibers, and nonwoven fabrics produced by mixing synthetic fibers with cotton, silk, hemp, pulp (cellulose) fibers, etc., are similarly preferred. The nonwoven fabric described above may be a nonwoven fabric containing only one type of the above-mentioned fibers, or a nonwoven fabric containing a combination of two or more types of fibers. The nonwoven fabric used for the first base material and the second base material is preferably produced by an airlaid method. Pulp (cellulose) fibers are also preferred.

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. Specifically, the thickness under no load is preferably 1.3 mm or more, more preferably 1.5 mm or more, and further preferably 1.7 mm or more. More preferably 1.9 mm or more, still more preferably 2.1 mm or more, still more preferably 2.3 mm or more, still more preferably 2.5 mm or more, still more preferably 3 mm or more, and even more preferably 5 mm or more, 7 mm or more is even more preferable. The nonwoven fabrics described above may contain a small amount of pulp fibers to the extent that they do not increase the thickness of the absorbent sheet. The upper limit of the thickness of the nonwoven fabric used for the intermediate sheet is not particularly limited, but for example, the thickness under no load is preferably about 14 mm or less, more preferably 13 mm or less, and further preferably 12 mm or less. , 11 mm or less, and even more preferably 10 mm or less.

In the water absorbent sheet according to one embodiment of the present invention, the weight per intermediate sheet is preferably 47 g/m ² or more, more preferably 50 g/m ² or more, and still more preferably 55 g/m ² or more. , more preferably 61 g/m ² or more, still more preferably 70 g/m ² or more, still more preferably 80 g/m ² or more, still more preferably 90 g/m ² or more, still more preferably 95 g /m ² or more. The upper limit is not particularly limited, but is preferably 200 g/m ² or less, more preferably 150 g/m ² or less, and even more preferably 120 g/m ² or less.

In the water absorbent sheet according to one embodiment of the present invention, the thickness of the intermediate sheet is thicker than the thickness of either 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, and 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 done. The ratio of the thickness of the intermediate sheet to the arithmetic average of the thicknesses of the first substrate and the second substrate is preferably 1.5 to 100, more preferably 2 to 80, and even more preferably 3 to 50. , and more preferably 3.2 to 15.

As described above, the nonwoven fabric used for the water absorbent sheet according to one embodiment of the present invention is preferably a hydrophilic nonwoven fabric in order to increase water permeability. , the nonwoven fabric or the fibers that are the material of the nonwoven fabric may be hydrophilized.

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

The first base material used in the water absorbent sheet according to one embodiment of the present invention is a water permeable sheet because it is positioned on the side where the liquid to be absorbed is introduced, but the second base material and The intermediate sheets are also preferably water-permeable sheets, and may be of the same type or of different types. The water permeability of the water-permeable sheet is preferably such that the coefficient of water permeability (JIS A1218:2009) is 1×10 ⁻⁵ cm/sec or more. The hydraulic conductivity is more preferably 1×10 ⁻⁴ cm/sec or more, still more preferably 1×10 ⁻³ cm/sec or more, still more preferably 1×10 ⁻² cm/sec or more, and still more preferably 1. ×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 intended effects of the present invention can be efficiently exhibited.

The thicknesses of the first base material and the second base material are preferably thin as long as they have strength as a water-absorbing sheet, and each base material is independently 0.01 to 2 mm and 0.02 to 1 mm. , 0.03 to 0.9 mm, and 0.05 to 0.8 mm. The basis weight of the first substrate and the second substrate 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. 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 an intermediate sheet and a first particulate water-absorbing layer localized on the side of the first substrate facing the second substrate. and a second particulate water-absorbing agent localized on the side of the second substrate facing the first substrate. By having the intermediate sheet in the water absorbing layer, the first particulate water absorbing agent and the second particulate water absorbing agent are more efficiently transferred to the first substrate side and the second substrate side, respectively. It also has the advantage of being easier to localize. In addition, since the intermediate sheet forms something like an air layer, there is an advantage that even if the water-absorbent sheet is pushed back, 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 described in [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, simply referring to a particulate water-absorbing agent means a mixture of the first particulate water-absorbing agent and the second particulate water-absorbing agent, or a mixture of the first particulate water-absorbing agent and the second particulate water-absorbing agent. means at least one of the particulate water absorbing agents. Further, 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, and means the water absorption capacity without pressure of a particulate water absorbing agent (sometimes referred to as "water absorption capacity"). Specifically, after putting 0.2 g of the particulate water-absorbing agent in a bag made of non-woven fabric, it is immersed in a large excess of 0.9% by mass sodium chloride aqueous solution for 30 minutes to allow free swelling, and then centrifuged ( 250G) refers to the water absorption capacity (unit: g/g) after draining.

The CRC of the second particulate water absorbing agent in the water absorbent sheet according to one embodiment of the present invention is preferably 30 to 50 g/g, more preferably 31 to 45 g/g, and 32 to 42 g. /g is more preferred. With such an embodiment, excellent results can be obtained in the specific return amount evaluation.

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

The lower limit of the CRC of the particulate water absorbing agent (the 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 30 g/g or more. is preferably 32 g/g or more, and even more preferably 33 g/g or more. With such an embodiment, excellent results can be obtained in the specific return amount evaluation. The upper limit is preferably 48 g/g or less, more preferably 45 g/g or less.

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

AAP2.1kPa 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 34 g/g, and 24 More preferably ~33 g/g. With such an embodiment, excellent results can be obtained in the specific return amount evaluation.

AAP2.1kPa of the first 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 36 g/g, and 24 More preferably ~34 g/g. With such an embodiment, excellent results can be obtained in the specific return amount evaluation.

"Water absorption time obtained according to the vortex method"
"Vortex" in the present invention is the water absorption time determined according to the "Water Absorption Rate Test Method for Super Absorbent Polymers" described in JIS K7224-1996. A specific measurement method is to add 0.02 parts by weight of Food Blue No. 1, which is a food additive, to 1000 parts by weight of a 0.90% by weight sodium chloride aqueous solution prepared in advance, and adjust the liquid temperature to 30°C. 50 ml of a blue-colored 0.90% by weight sodium chloride aqueous solution is weighed into a 100 ml beaker and stirred at 600 rpm with a cylindrical stirrer having a length of 40 mm and a thickness of 8 mm, and 2.00 g of particulate water absorbing agent is added. and measure the water absorption time (seconds). The end point is the time until the water absorbing agent absorbs physiological saline and the test solution covers the stirrer tip according to the standards described in JIS K 7224-1996 "Explanation of water absorption rate test method for super absorbent polymer". Time is measured as water absorption time (seconds).

In the water absorbent sheet according to one embodiment of the present invention, the water absorption time of the second particulate water absorbent obtained according to the vortex method is preferably 10 seconds or longer, more preferably 20 seconds or longer, and 25 seconds or longer. More preferably, 28 seconds or more is even more preferable. In the water-absorbing sheet according to one embodiment of the present invention, the upper limit of the water-absorbing time of the second particulate water-absorbing agent obtained according to the vortex method is not particularly limited. It may be 100 seconds or less, 80 seconds or less, or 60 seconds or less.

In the water absorbent sheet according to one embodiment of the present invention, the water absorption time of the first particulate water absorbent obtained according to the vortex method is preferably 10 seconds or longer, more preferably 20 seconds or longer, and 25 seconds or longer. More preferably, 28 seconds or more is even more preferable. By significantly lengthening the water absorption time of the first particulate water absorbing agent obtained according to the vortex method, the diffusibility in the surface direction can be increased, and the water absorption possessed by the first particulate water absorbing agent. The volume can be effectively utilized, and excellent results can be obtained in the specific return amount evaluation. In addition, after the liquid to be absorbed is introduced from the side of the first substrate, it becomes easier to be sent to the second particulate water absorbing agent, so that the second particulate water absorbing agent can be effectively used. effective. In the water absorbent sheet according to one embodiment of the present invention, the upper limit of the water absorption time of the first particulate water absorbent obtained according to the vortex method is not particularly limited, but from the viewpoint of liquid leakage prevention, for example, It may be 100 seconds or less, 80 seconds or less, or 60 seconds or less. The water absorption time obtained according to the vortex method can be controlled by the specific surface area of the water absorbent resin particles and the like. As the specific surface area of the water absorbent resin particles increases, the water absorption time tends to shorten.

"GPR"
Gel Permeation Rate (GPR)
In the present specification, the "liquid permeability" of the particulate water absorbing agent refers to the fluidity of the liquid passing through the swollen gel particles under load. A gel permeation rate (GPR) is used as this index. The gel permeation rate (GPR) of the particulate water absorbing agents (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 With reference to the saline flow conductivity (SFC) test described in the specification, the measurement conditions are changed and the following procedure is performed.

A 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 . A container 410 is provided with a cell 411 (with an inner diameter of 6 cm), in which a swollen gel 414 (a particulate water-absorbing agent is absorbed) can be accommodated and a liquid 423 can be introduced. Also, by fitting the piston 412 into the cell 411 , pressure can be applied to the swelling gel 414 . The bottom surface of the cell 411 and the bottom surface of the piston 412 are covered with wire meshes 413a and 413b (No. 400 stainless wire mesh, mesh size 38 μm) to prevent the passage of the swelling gel 414 (and the particulate water absorbing agent). ing. Here, a 0.90% by mass sodium chloride aqueous solution is used as the liquid 423 . Tank 420 stores liquid 423 inside. Liquid 423 is introduced into cell 411 through cocked L-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 swelling gel 414 was set to 4 cm. In other words, the device 400 allows the introduction of a constant hydrostatic pressure of the liquid 423 into the cell 411 . Since the piston 412 has a hole 415 , the liquid 423 flows through the hole 415 , and also flows through the swelling gel 414 layer to flow out of the cell 411 . The container 410 is placed on a stainless wire mesh 431 that does not block the passage of the liquid 423 . Therefore, the liquid 423 that has flowed 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 top pan balance 433 .

A specific gel permeation rate (GPR) measurement method is as follows. The following operations are performed at room temperature (20 to 25°C).

(1) A particulate water absorbing agent (0.900 g) is uniformly placed in the cell 411 .

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

(3) Place the piston on the swollen gel 414 and apply a pressure of 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 to pass through the swelling gel 414 layer.

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

(6) A gel permeation rate (GPR) [g/min] is calculated by averaging flow velocities 1 to 3 minutes after starting the flow of the liquid 423 .

In the water absorbent sheet according to one embodiment of the present invention, the GPR of the first particulate water absorbing agent is more preferably 20 g/min or more, further preferably 35 g/min or more, further preferably 45 g/min. It is more preferably 50 g/min or more, even more preferably 55 g/min or more, even more preferably 75 g/min or more, and 95 g/min or more. 118 g/min or more is even more preferable, 150 g/min or more is more preferable, 160 g/min or more is more preferable, and 165 g/min or more is more preferable. , 175 g/min or more. With such an embodiment, after the liquid to be absorbed is introduced from the first substrate side, it is easily sent to the second particulate water absorbing agent, and the second particulate water absorbing agent is absorbed. It can be used effectively, and gives an excellent result in the specific return amount evaluation. 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 liquid leakage prevention, it is 500 g / min or less, 400 g / min or less, Or it is 300g/min or less.

In the water absorbent sheet according to one embodiment of the present invention, the second particulate water absorbent has a GPR of 45 g/min or more. Since the present invention uses an intermediate sheet having a transmittance of less than 60%, if the GPR of the second particulate water absorbing agent is less than 45 g/min, the intended problem of the present invention cannot be solved. . More specifically, when the transmittance is 60% or more, the particulate water-absorbing agent is widely distributed in the intermediate sheet to improve the diffusion of the liquid. If this is the case, the liquid diffusibility of the intermediate sheet will be insufficient. Therefore, in the present invention, the second particulate water absorbing agent is responsible for liquid diffusion. That is, after the liquid to be absorbed passes through the first particulate water absorbing agent and is introduced into the second particulate water absorbing agent, the second particulate water absorbing agent can act like a tank. Since the liquid is appropriately diffused and the second particulate water absorbing agent absorbs the liquid without drawing it by effectively utilizing the water absorption area, the desired problem of the present invention is achieved even if the transmittance is less than 60%. can be resolved. In the water absorbent sheet according to one embodiment of the present invention, the GPR of the second particulate water absorbing agent may be 45 g/min or more, preferably 46 g/min or more, more preferably 47 g/min or more, It is preferably 50 g/min or more, more preferably 55 g/min or more, even more preferably 75 g/min or more, still more preferably 95 g/min or more, and 118 g/min or more. More preferably, it is 150 g/min or more, more preferably 160 g/min or more, more preferably 165 g/min or more, and more preferably 175 g/min or more. By having such a lower limit, gel blocking is suppressed, diffusibility is increased, and the liquid is easily absorbed by the absorbent. 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 liquid leakage prevention, it is 500 g / min or less, 400 g / min or less, Or it is 300g/min or less.

In the water absorbent sheet according to one embodiment of the present invention, the GPR of the second particulate water absorbing agent is 50 g / min or more, and the content weight of the second particulate water absorbing agent in the water absorbent sheet The content weight of the first particulate water absorbing agent is 0.4 or less, and the transmittance is more than 40%. With such an embodiment, the intended effects of the present invention can be enhanced. Further, in the present embodiment, the GPR of the first particulate water absorbing agent is 50 g/min or more. Such an embodiment can further enhance the intended effect of the present invention.

"degradable soluble matter"
In the water absorbent sheet according to one embodiment of the present invention, the upper limits of the deteriorated soluble content of the first particulate water absorbing agent and the upper limit of the deteriorated soluble content of the second particulate water absorbing agent are not particularly limited, From the viewpoint of liquid leakage during long-term use, it is independently preferably less than 50%, more preferably 25% or less, and even more preferably 15% or less. Although the lower limit is not particularly limited, it is, for example, about 1% or more, 3% or more, or 5% or more from the viewpoint of liquid leakage during long-term use. The method for measuring the deteriorated soluble matter is as follows.

A deterioration test solution is prepared by adding L-ascorbic acid to 0.05% by mass to physiological saline prepared in advance. 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 particulate water absorbing agent is added thereto to form a swollen gel. The container is covered with plastic wrap and sealed, and the swollen gel is allowed to stand for 16 hours under an atmosphere of 37° C. (manufactured by Kusumoto Kasei Co., Ltd., ETAC trademark, HISPEC series, using HT320, set at 37° C., wind speed variable device scale set to 30). did. After 16 hours, 175 ml of physiological saline and a cylindrical stirrer with a length of 30 mm and a thickness of 8 mm are added for deterioration, and then stirred at 500 rpm for 10 minutes to extract from the hydrous gel.

20.0 g of the filtrate obtained by filtering this extract with a filter paper (ADVANTEC Toyo Co., Ltd., product name: (JIS P 3801, No. 2), thickness 0.26 mm, retained particle size 5 μm) was weighed. , and then add 30 g of physiological saline to obtain a measurement solution.

The measurement method is to titrate physiological saline to pH 10 using 0.1N NaOH aqueous solution, then titrate to pH 2.7 using 0.1N HCl aqueous solution, empty titer ([bNaOH] ml , [bHCl] ml). A titration amount ([NaOH] ml, [HCl] ml) is obtained by performing the same titration operation for the measurement solution. For example, in the case of a particulate water absorbing agent consisting of 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 titration amount obtained by the above operation. The following formula:
Deteriorated soluble matter (% by mass) = 0.1 x (average molecular weight) x 200 x 100 x ([HCl]-[bHCl])/1000/1.0/20.0. If the amount is unknown, the average molecular weight of the monomer is calculated using the neutralization rate determined by titration.

"surface tension"
Surface tension is the work (free energy) required to increase the surface area of a solid or liquid expressed per unit area. The term "surface tension" as used herein refers to the surface tension of an aqueous solution when a particulate water absorbing agent is dispersed in a 0.90% by mass sodium chloride aqueous solution. Incidentally, the surface tension of the water absorbing agent is measured by the following procedure. That is, 50 ml of physiological saline adjusted to 20° C. is put into a sufficiently washed 100-ml beaker, and the surface tension of the physiological saline is measured using a surface tensiometer (K11 automatic surface tensiometer manufactured by KRUSS). to measure. Next, a thoroughly washed 25 mm-long fluororesin rotor and 0.5 g of a particulate water-absorbing agent were added to a beaker containing physiological saline after surface tension measurement and adjusted to 20° C., and the temperature was increased to 500 rpm. Stir at conditions for 4 minutes. After 4 minutes, the stirring is stopped, and after the water-containing particulate water-absorbing agent settles, the surface tension of the supernatant liquid is measured again by performing the same operation. In the present invention, a plate method using a platinum plate is employed, and the plate is thoroughly 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 at least one of the first particulate water absorbing agent and the second particulate water absorbing agent is 65 mN/m or more and 66 mN/m or more in order. , 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 the water-absorbent sheet, the effect of surface tension is more likely to appear than in conventional paper diapers, and by satisfying the above conditions, the return amount of paper diapers can be reduced. In the water absorbent sheet according to one embodiment of the present invention, the upper limit of the surface tension of at least one of the first particulate water absorbing agent and the second particulate water absorbing agent is not particularly limited, but is 73 mN/m or less. is.

"Particle shape"
In the water absorbent sheet according to one embodiment of the present invention, at least one of the first particulate water absorbing agent and the second particulate water absorbing agent preferably has an irregular pulverized particle shape. Here, the irregularly crushed particles are crushed particles having irregular shapes. Compared with spherical particles obtained by reversed-phase suspension polymerization or gas-phase polymerization, irregular crushed particles can be easily fixed to a substrate. The particulate water absorbing agent according to one embodiment of the present invention is preferably pulverized in aqueous solution polymerization. On the other hand, when the pulverization process is not performed, spherical particles or granules of spherical particles, which are typically obtained by reversed-phase suspension polymerization or droplet polymerization in which a polymerization monomer is sprayed and polymerized, are irregularly crushed. not in shape. In the embodiment of the present invention, when the particulate water-absorbing agent has an irregularly pulverized shape, the shape of the water-absorbing sheet can be more easily retained than when the particulate water-absorbing agent has a high average roundness (for example, a spherical shape). In an embodiment of the present invention, the average circularity of at least one of the first particulate water absorbing agent and the second particulate water absorbing agent is preferably 0.70 or less, more preferably 0.60 or less. is more preferable, and 0.55 or less is even more preferable.

The calculation method of the average roundness is as follows. 100 or more particulate water-absorbing agents are randomly selected, and each particulate water-absorbing agent is photographed with an electron microscope (VE-9800 manufactured by Keyence Corporation) (50x magnification) to obtain an image of the particulate water-absorbing agent. , the perimeter and area of each particle were calculated using the attached image analysis software. The formula below:

to obtain the circularity of each particle, and the average value of the obtained values is calculated as the average circularity.

In the water absorbent sheet according to one embodiment of the present invention, the lower limits of the content of the particulate water absorbing agent per unit volume of the water absorbent sheet are, in order of preference, 50 mg/cm ³ or more, 51 mg/cm ³ or more, and 52 mg/cm ³ . 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, 60 mg/cm ³ or more. In addition, in the water absorbent sheet according to one embodiment of the present invention, the upper limit of the content of the particulate water absorbing agent per unit volume of the water absorbent sheet is not particularly limited, but is realistically 600 mg/cm ³ or less. , is preferably 500 mg/cm ³ or less, more preferably 400 mg/cm ³ or less, even 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 within the above range, the water-absorbent sheet efficiently exhibits the effects of the present invention. The content of the particulate water-absorbing agent per unit volume of the water-absorbing sheet of the water-absorbing sheet used in the examples of the present application was 50 mg/cm ³ or more.

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.

Further, 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 even more preferably 0.4 or less. By setting the content of the second particulate water absorbing agent to be the same as, preferably greater than, the content of the first particulate water absorbing agent, the second particulate water absorbing agent is considered to have a function like a so-called tank. The water-absorbing agent functions effectively, resulting in an excellent specific return amount evaluation.

One embodiment of the present invention is a water absorbing substrate comprising a first substrate, a second substrate, and a water absorbing layer positioned between the first substrate and the second substrate. wherein the first base material is a water-permeable sheet located on the side where the liquid to be absorbed is introduced, and the water-absorbing layer is composed of an intermediate sheet and the first base material. A first particulate water absorbing agent localized on the surface side facing the second base material, and a surface side of the second base material facing the first base material a second particulate water absorbing agent, wherein a transmittance of a mixture of the first particulate water absorbing agent and the second particulate water absorbing agent to the intermediate sheet is less than 60%; GPR of the particulate water absorbing agent is 45.0 g/min or more, and the nonwoven fabric permeability index (NPI) is less than 60%. According to this embodiment, with such a configuration, even if the liquid is introduced intermittently a plurality of times (especially, three times or more) under no pressure and the amount of liquid introduced increases, the return amount is significantly increased. It is possible to provide a water-permeable sheet that can be reduced to

In one embodiment of the present invention, the upper limit of the nonwoven fabric permeability index (NPI) is not particularly limited, but is preferably 55 or less, more preferably 50 or less. By having such a lower limit, the intended effects of the present invention are efficiently exhibited. In one embodiment of the present invention, the lower limit of the nonwoven fabric permeability index (NPI) is not particularly limited, but is preferably 10 or more, more preferably 20 or more, and even more preferably 30 or more.

It should be noted that the nonwoven fabric permeability index (NPI) described in the specification of the present application is expressed by the following formula:

is indicated by Here, A is the specific surface area (mm ^-1 ) of the intermediate sheet (e.g., nonwoven fabric) measured by X-ray CT, B is the thickness (mm) of the intermediate sheet (e.g., nonwoven fabric), and C 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 with analysis software as described below.

<X-ray CT imaging>
The intermediate sheet was cut into a square of 10 mm long and 10 mm wide (with the same thickness), and was measured using a microfocus X-ray CT system inspeXio SMX-100CT manufactured by Shimadzu Corporation. 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 focus of X-ray source and X-ray detector) (mm): 500
・ SRD (distance between the focus of the X-ray source and the center of rotation of the measurement sample) (mm): 40
・Scan mode 1: CBCT
・Scan mode 2: normal scan ・Scan angle: full scan ・Number of views: 1200
・Average number: 5
・Smoothing: YZ
・Slice thickness (mm): 0.012
・Distance between slices (mm): 0.010
・Number of scaling: 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>
X-ray CT imaging data was analyzed by the following procedure using analysis software TRI/3D-PRT-LRG manufactured by Ratoc 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. Select LW on the Binarize tab of the EVC panel, change the L value, and select a circular measurement target area. Press 'Execute' to apply this process to all slice images (a globally cylindrical measurement area is selected). Press "ROI OK" on the giant particle separation panel.

3. Select the fibers only by selecting LW and setting the L value to 37580 in the Binarize tab of the EVC panel. Press "Execute". Select bD in the BC panel and press "Save".

4. Select the Labeling tab in the 3D tab of the EVC panel, select "Volume", and run MAX (this operation displays 3DLabel Count=1).

5. From the menu, select Particle measurement>Void in 3D particles>Measure after separation. After separation, the measurement panel will be displayed. Uncheck the edge particle removal, check the surface area calculation of the measurement item, select the Void calculation, select Binary 5ch for the calculation ROI designation, press "Register OK" and select the folder to save the data. Press "Execute latest registered data" to perform calculation processing.

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

Specific surface area (mm ⁻¹ )=Total particle surface area (mm ² )/(Total particle volume (mm ³ )
In addition, although the expression "particles" is used due to the configuration of the calculation software, it is actually the measurement result of the fiber, and there is no problem in measurement and calculation.

[3. Manufacturing method of water absorbent sheet]
A method for producing a water absorbent sheet according to an embodiment of the present invention includes the steps of: (1) spraying a first particulate water absorbing agent on a first base material; (2) applying second particles to a second base material; and (3) spraying the first particulate water absorbing agent and/or the second particulate water absorbing agent on the intermediate sheet. Examples of more specific production methods include the following production methods (a) to (d).

(a) evenly spread the first particulate water absorbing agent (and preferably adhesive) on the first substrate; An intermediate sheet is overlaid thereon and pressed. Furthermore, the second particulate water absorbing agent (and preferably an adhesive) is evenly dispersed on the surface of the intermediate sheet on the side not facing the first particulate water absorbing agent. An intermediate sheet is overlaid thereon and pressed (preferably under heating conditions where the hot-melt melts, or under a state in which the hot-melt melts).

(b) The second particulate water absorbing agent is evenly dispersed on the intermediate sheet. Also, the adhesive is spread over the second substrate. Then, the surface of the intermediate sheet on which the second particulate water absorbing agent is dispersed and the surface of the second base material on which the adhesive agent is dispersed are pressed together. Next, the first particulate water absorbing agent is uniformly dispersed on the surface opposite to the surface on which the second particulate water absorbing agent is dispersed in the intermediate sheet after pressure bonding. Also, the adhesive is spread over the first substrate. Then, the surface of the intermediate sheet on which the first particulate water absorbing agent is sprayed and the surface of the first base material on which the adhesive is sprayed are pressed together. The crimping is preferably performed under a heating condition in which the hot-melt melts or under a state in which the hot-melt melts.

(c) spreading the adhesive over the second substrate; Next, the second particulate water absorbing agent is evenly dispersed thereon. Next, an intermediate sheet is put on it and pressed. Next, the surface of the intermediate sheet not facing the second particulate water absorbing agent is sprayed with an adhesive. Next, the first particulate water absorbing agent is evenly spread thereon. Next, the first base material is placed thereon and crimped. The crimping is preferably performed under a heating condition in which the hot-melt melts, or under a state in which the hot-melt melts.

(d) spreading the adhesive over the second substrate; Next, the second particulate water absorbing agent is evenly dispersed thereon. Next, an intermediate sheet is put on it and pressed. Next, the first particulate water absorbing agent is evenly dispersed on the surface of the intermediate sheet not facing the second particulate water absorbing agent. Also, the adhesive is spread over the first substrate. Then, the surface of the intermediate sheet on which the first particulate water absorbing agent is sprayed and the surface of the first base material on which the adhesive is sprayed are pressed together. The crimping is preferably performed under a heating condition in which the hot-melt melts, or under a state in which the hot-melt melts.

As a process other than those described above, the water absorbent sheet may be embossed for the purpose of improving the tactile feel of the water absorbent sheet and improving the liquid absorption performance. Embossing may be performed at the same time when the first base material and the second base material are pressure-bonded, or may be performed after the sheet is manufactured.

Additives (deodorants, fibers, antibacterial agents, gel stabilizers, etc.) may be added as appropriate in the method for producing a water absorbent sheet according to an embodiment of the present invention. A blending 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 manufacturing method, a particulate water absorbing agent mixed with an additive in advance may be used, or an additive may be added during the manufacturing process.

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

In addition to those exemplified above, methods for manufacturing water absorbent sheets are disclosed in, for example, the following patent documents: International Publication No. 2012/174026, International Publication No. 2013/078109, International Publication No. 2015/041784. , 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. 2010/082373, WO 2010/113754, WO 2010/143635, WO 2011/043256, WO 2011/086841, WO 2011/086842, WO WO 2011/086843, WO 2011/086844, WO 2011/117997, WO 2011/118409, WO 2011/136087, WO 2012/043546, WO 2013/ 099634, International Publication No. 2013/099635, JP 2010-115406, JP 2002-345883, JP 6-315501, JP 6-190003, JP 6-190002, JP 6- 190001, JP-A-2-252558, JP-A-2-252560, JP-A-2-252561. The methods for manufacturing water absorbent sheets disclosed in these documents are also appropriately referred to.

In the water-absorbent sheet according to one embodiment of the present invention, the method of fixing the substrates to each other or the substrate and the particulate water-absorbing agent may be (i) using an adhesive and, if necessary, by crimping, (ii) various binders dissolved or dispersed in water, water-soluble polymer, or solvent may be used; Preferably, it is attached using an adhesive.

The adhesive to be used may be a solution type, but hot-melt adhesives with high productivity and no problem of residual solvent are preferred due to problems of solvent removal, remaining solvent, and productivity. In the present invention, the hot-melt adhesive may be contained in advance on the surface of the base material or the particulate water-absorbing agent, or the hot-melt adhesive may be separately used in the manufacturing process of the water-absorbing sheet. The form and melting point of the hot-melt adhesive can be appropriately selected, and may be particulate, fibrous, net-like, film-like, or liquid melted by heating. The melting temperature or softening point of the hot melt adhesive is preferably 50-200°C, preferably 60-180°C. When a particulate adhesive is used, its particle diameter is about 0.01 to 2 times, 0.02 to 1 time, or 0.05 to 0.5 times the average particle diameter of the particulate water absorbing agent. Adhesive is used.

Examples of methods of using hot melt adhesives in manufacturing water absorbent sheets according to one embodiment of the present invention include the following. A mixture of a particulate water-absorbing agent and a hot-melt adhesive is evenly dispersed on a base material (for example, non-woven fabric), another base material is laminated, and then heated near the melting temperature of the hot-melt adhesive. A water-absorbent sheet can be produced by heat-pressing.

The hot melt adhesive used in the present invention can be appropriately selected, but is preferably selected from ethylene-vinyl acetate copolymer adhesives, styrene elastomer adhesives, polyolefin adhesives, polyester adhesives, and the like. Seeds or more can be used as appropriate.

Specific examples of polyolefin-based adhesives include polyethylene, polypropylene, and atactic polypropylene, and examples of styrene-based 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), etc., and copolymerized polyolefin, etc., and polyester-based adhesives such as polyethylene terephthalate ( PET), polybutylene terephthalate (PBT), copolymer polyester, etc., and ethylene-vinyl acetate copolymer adhesives include ethylene-vinyl acetate copolymer (EVA) adhesive; ethylene-ethyl acrylate 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 (for example, hot melt adhesive) used 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. 0.05 to 2.0 times is more preferable. If the content of adhesive (especially hot- melt adhesive ) is too high, not only will it be disadvantageous in terms of cost and the weight of the absorbent sheet (increase in weight of paper diapers), but the particulate water absorbent will not swell. There is also a possibility that the water absorption capacity of the water absorbent sheet will be reduced.

[4. Absorbent article]
An 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 positioned on the first base material side and the An absorbent article is provided, wherein a liquid impermeable sheet is located on the second substrate side. Specific examples of absorbent articles include disposable diapers, incontinence pads, sanitary napkins, pet sheets, drip sheets for food, and waterproofing agents for power cables. With such a configuration, an excellent result can be 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. Moreover, an absorbent article can be manufactured by a well-known method.

The present invention will be described in more detail with 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, the operations were carried out under the conditions of room temperature (25° C.)/relative humidity of 40 to 50% RH.

<Manufacturing example>
With reference to the production examples, examples, and comparative examples described in the following patents, by appropriately adjusting the CRC depending on the amount of the internal cross-linking agent, the particulate water absorbing agent of polyacrylic acid (salt) resin (1) ~ ( 2) 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 (acrylic acid dimer 2000 ppm, acetic acid 500 ppm, propionic acid 500 ppm, p-methoxyphenol 200 ppm ) was supplied to the bottom of a high-boiling impurity separation column having 50 stages of non-weir perforated plates, and the reflux ratio was adjusted to 1. After removing dimers (acrylic acid dimers) composed of maleic acid and acrylic acid, and further crystallizing, acrylic acid (acrylic acid dimers 20 ppm, acetic acid 50 ppm, propionic acid 50 ppm, furfural 1 ppm or less , less than 1 ppm of protoanemonin), and 50 ppm of p-methoxyphenol was added after distillation.
[Method for producing sodium acrylate aqueous solution]
According to Example 9 of US Pat. No. 5,210,298, 1390 g of the above acrylic acid was neutralized with 48% caustic soda at 20-40° C. to obtain an aqueous sodium acrylate solution with a concentration of 37% and 100% neutralization.

<Particulate water absorbing agent 1>
73 mol% obtained by mixing the acrylic acid obtained in the above acrylic acid production example, the aqueous sodium acrylate solution obtained by the above method for producing an aqueous sodium acrylate solution using the acrylic acid, and deionized water. A reaction solution was prepared by dissolving 5.71 g of polyethylene glycol diacrylate (average addition mole number of ethylene oxide: 9) in 5500 g of an aqueous solution of sodium acrylate having a neutralization rate (monomer concentration: 33.0% by mass). Next, the above reaction liquid is supplied to a reactor formed by attaching a lid to a jacketed double-arm stainless steel kneader having an internal volume of 10 L and having two sigma-type blades, and the reaction liquid is maintained at 30° C. while the system is circulated with nitrogen. 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 mass aqueous solution of sodium persulfate and 32.96 g of a 1% by mass aqueous solution of L-ascorbic acid were added, and polymerization started after about 1 minute. After 40 minutes from the start of polymerization, 184.3 g of water absorbent resin fine powder of 150 μm or less is added, and the kneader blade is rotated at high speed (130 rpm) for 10 minutes to crush the gel, and then the hydrous gel polymer is obtained. I took it out. The obtained hydrous gel-like polymer was subdivided into particles of about 1 to 2 mm. This finely divided water-containing gel-like polymer was spread on a 50-mesh wire 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 pulverized water absorbent resin (1-1) having an average particle size of 350 μm.
0.03 parts by weight of ethylene glycol diglycidyl ether, 0.3 parts by weight of 1,4-butanediol, 0.5 parts by weight of propylene glycol, and water3. 3.83 parts by mass of an aqueous solution of a surface cross-linking agent consisting of 0 parts by mass was mixed by spraying. The above mixture was heat-treated at a heat medium temperature of 210° C. for 40 minutes using a paddle type mixing heat treatment machine to obtain a surface-crosslinked water absorbent resin (1-2). 100 parts by mass of the resulting surface-crosslinked water absorbent resin (1-2) was spray-mixed with 1.0 part by mass of water, and cured at 60° C. for 1 hour in a closed container. A water absorbent resin (1-3) was obtained by passing through a sieve. A particulate water absorbing agent (1) was obtained by adding 0.3 parts by mass of Aerosil 200 (hydrophilic amorphous silica, manufactured by Nippon Aerosil Co., Ltd.) to the water absorbing resin (1-3) and mixing.

<Particulate water absorbing agent 2>
73 mol% obtained by mixing the acrylic acid obtained in the above acrylic acid production example, the aqueous sodium acrylate solution obtained by the above method for producing an aqueous sodium acrylate solution using the acrylic acid, and deionized water. A reaction solution was prepared by dissolving 4.17 g of polyethylene glycol diacrylate (average added mole number of ethylene oxide: 9) in 5500 g of an aqueous solution of sodium acrylate having a neutralization rate (monomer concentration: 33.0% by mass). Next, the above reaction liquid is supplied to a reactor formed by attaching a lid to a jacketed double-arm stainless steel kneader having an internal volume of 10 L and having two sigma-type blades, and the reaction liquid is maintained at 30° C. while the system is circulated with nitrogen. 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 mass aqueous solution of sodium persulfate and 32.96 g of a 1% by mass aqueous solution of L-ascorbic acid were added, and polymerization started after about 1 minute. After 40 minutes from the start of polymerization, 181.5 g of water absorbent resin fine powder of 150 μm or less is added, and the kneader blade is rotated at high speed (130 rpm) for 10 minutes to crush the gel, and then the hydrous gel polymer is obtained. I took it out. The obtained hydrous gel-like polymer was subdivided into particles of about 1 to 2 mm. This finely divided water-containing gel-like polymer was spread on a 50-mesh wire 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 irregularly pulverized water absorbent resin (2-1) having an average particle size of 350 μm.

0.03 parts by weight of ethylene glycol diglycidyl ether, 0.3 parts by weight of 1,4-butanediol, 0.5 parts by weight of propylene glycol, and water3. 3.83 parts by mass of an aqueous solution of a surface cross-linking agent consisting of 0 parts by mass was mixed by spraying. The above mixture was heat-treated at a heat medium temperature of 195° C. for 40 minutes using a paddle type mixing heat treatment machine to obtain a surface-crosslinked water absorbent resin (2-2). 100 parts by mass of the resulting surface-crosslinked water-absorbing resin (2-2) was mixed by spraying 1.0 part by mass of water, and cured at 60° C. for 1 hour in a closed container. A water absorbent resin (2-3) was obtained by passing through a sieve. A particulate water absorbing agent (2) was obtained by adding 0.3 parts by mass of Aerosil 200 (hydrophilic amorphous silica, manufactured by Nippon Aerosil Co., Ltd.) to the water absorbing resin (2-3) and mixing.

[Removal of water absorbent resin from commercially available disposable diaper 1]
A water absorbent resin was taken out from a commercially available disposable diaper (Moony Air Fit (L size, Lot No. 201512163072), manufactured by Unicharm, purchased in May 2016). At the time of taking out, only the water-absorbing resin was taken out so as not to mix cotton-like pulp and the like. The taken out water absorbent resin had a particle shape obtained by agglomeration of spherical particles. This water absorbent resin was used as a particulate water absorbent (T1). Table 1 shows the physical properties of the particulate water absorbing agent (T1).

〔Example〕
[Example 1]
A particulate water absorbing agent (1) is applied to the surface of an air-through nonwoven fabric (1) (corresponding to an intermediate sheet) which is mainly composed of olefin and has a thickness of 8.3 mm under no load and is cut into a length of 10 cm and a width of 40 cm. (corresponding to the second particulate water-absorbing agent) was evenly dispersed at 9.0 g (application amount: 225 g/m ² ).

Next, a nonwoven fabric (B) cut into a length of 10 cm and a width of 40 cm (mainly composed of pulp fibers. Thickness under no load: 0.7 mm. Prepared by the airlaid method. Corresponds to the second base material. 0.3 to 0.5 g of an adhesive containing styrene-butadiene rubber (Spray glue 77, manufactured by 3M Japan Ltd.) was evenly spread on the surface of the surface with a weight per unit area of 42 g/m 2 (spread amount: 7.0 g/m ² ). 5-12.5 g/m ² ).

Next, 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 were overlapped so as to face each other (so as to be in contact) and pressure-bonded.

Next, 3.0 g of the particulate water absorbing agent (1) (corresponding to the first particulate water absorbing agent) (spray amount : 75 g/m ² ) was evenly distributed.

Further, 0.3 to 0.5 g of an adhesive containing styrene-butadiene rubber (Spray glue 77, manufactured by 3M Japan Ltd.) was evenly spread thereon (amount of spray: 7.5 to 12.5 g/m ² ). , Non-woven fabric (A) (mainly composed of pulp fibers. Thickness 0.7 mm under no load. Prepared by the airlaid method. Corresponding to the first base material. Basis weight: 42 g/m ² ). The surface of the nonwoven fabric (1) sprayed with the particulate water-absorbing agent and the surface of the nonwoven fabric (A) sprayed with the adhesive were overlapped (contacted) and pressure-bonded. Thus, a water absorbent sheet (1) was obtained.

[Example 2]
In Example 1, as shown in Table 2, nonwoven fabric (2) (an air-through nonwoven fabric containing olefin as a main component) was used instead of nonwoven fabric (1), and the particulate water absorbing agent corresponding to the second particulate water absorbing agent was used. A water absorbent sheet (2) was obtained by using the particulate water absorbing agent (2) instead of the agent (1).

[Example 3]
A water absorbent sheet (3) was obtained by using the particulate water absorbing agent (2) instead of the particulate water absorbing agent (1) corresponding to the first particulate water absorbing agent in Example 1.

[Example 4]
In Example 3, 6.0 g of the particulate water absorbing agent (1) (application amount: 150 g/m ² ) and 6.0 g of the particulate water absorbing agent (2) (application amount: 150 g/m ² ) were used. A water absorbent sheet (4) was obtained.

[Comparative Example 1]
In Example 1, a particulate water absorbing agent (T1) was used instead of the particulate water absorbing agent (1) corresponding to the second particulate water absorbing agent to obtain a comparative water absorbent sheet (1).

Absorbent evaluation (measurement of backflow amount) of the obtained water absorbent sheet was performed, and Table 3 shows the results.

[Example 5]
In Example 2, as shown in Table 2, the nonwoven fabric (1) was used instead of the nonwoven fabric (2) to obtain a water absorbent sheet (5).

[Example 6]
In Example 1, 6.0 g of the particulate water absorbing agent (1) (application amount: 150 g/m ² ) and 6.0 g of the particulate water absorbing agent (2) (application amount: 150 g/m ² ) were used, A water absorbent sheet (6) was obtained.

[Example 7]
In Example 1, as shown in Table 2, the nonwoven fabric (2) was used instead of the nonwoven fabric (1) to obtain a water absorbent sheet (7).

[Evaluation method for absorbent sheet, etc.]
<Reverse amount>
As shown in FIG. 3, a water-absorbent sheet cut into a length of 10 cm and a width of 40 cm was wrapped with a liquid-impermeable sheet of length 14 cm and width 40 cm so as to form an opening at the top. A water-absorbent sheet wrapped with a liquid-impermeable sheet was placed on a flat surface, and a liquid injection cylinder (FIG. 4) was placed on the water-absorbent sheet in the center thereof as shown in FIG. In this state, 80 g of a 0.9% by weight sodium chloride aqueous solution at 23° C. was introduced into the liquid injection cylinder using a funnel capable of introducing liquid at a flow rate of 7 ml/sec (FIG. 6). 10 minutes after adding the liquid, 20 pieces of pre-weighed filter paper (model No. 2, manufactured by ADVANTEC; circular with a diameter of 110 mm) are placed in the center of the water-absorbing sheet, and a circular weight with a diameter of 100 mm is placed. (1200 g) was added and held for 1 minute. After 1 minute, the weight was removed and the first reversion amount (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 adding the liquid, the filter paper and weight (1200 g) were placed and held for 1 minute. After 1 minute, the weight was removed and the amount of reversion was measured. The measurement was repeated, and the second reversion amount (g) and the third reversion amount (g) were measured.The smaller the third reversion amount (g), the better the evaluation.Each water absorbent sheet, Table 2 shows the reversion amount of each comparative water absorbent sheet.

<Method for measuring transmittance of particulate absorbent>
A nonwoven fabric (1) cut to a diameter of 80 mm (intermediate sheet ) was placed as shown in FIG. 7 and taped around the perimeter (at least a diameter of 75 mm or more ensures an area through which the particles can pass). At this time, in the form of the water absorbent sheet, the nonwoven fabric (1) was placed in the sieve so that the surface of the nonwoven fabric (1) in contact with the nonwoven fabric (A) (first base material) faced upward. The nonwoven fabric (1) may be taken out from the water absorbent sheet by the method described below. 10.0 g of a particulate water-absorbing agent is 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 Co., Ltd.; rotation speed 230 rpm, impact number 130 rpm) is used. and shaken for 5 minutes at room temperature (20-25° C.) and relative humidity of 50% RH. The particulate water-absorbing agent may be taken out from the water-absorbing sheet by the method described below. After shaking, the mass (W (g)) of the particulate water absorbing agent that passed through the nonwoven fabric (1) and the JIS standard sieve was measured, and the transmittance of the particulate absorbent was calculated according to the following formula (i). In addition, the measurement was performed 3 times and the average value was calculated.

The transmittance of the nonwoven fabric (2) was also measured in the same manner.

[Method for removing particulate absorbent from water absorbent sheet and nonwoven fabric used for intermediate sheet]
By peeling off 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, the particulate absorbent and the intermediate sheet were taken out. All the absorbent particulates attached to the upper and lower nonwoven fabrics and the intermediate sheet were also taken out. When peeling off the upper and lower non-woven fabrics, cool the water-absorbing sheet and weaken the adhesion of the adhesive (hot-melt adhesive or spray glue) that adheres the non-woven fabric and particulate water-absorbing agent. peeled off. By following this procedure, it is possible to take out the intermediate sheet without changing the fiber or structural thickness of the intermediate sheet, making it possible to accurately measure the transmittance. Various methods can be considered for cooling the water-absorbent sheet, such as placing it in a constant temperature bath at -10°C or less for a certain period of time, spraying a cooling spray, or applying liquid nitrogen, but without changing the fibers, structure, or thickness of the intermediate sheet. There is no particular limitation as long as the condition is such that the particulate water absorbent contained in the water absorbent sheet does not absorb moisture.

Further, when the particulate water-absorbing agent taken out is moisture-absorbing, for example, by drying, the moisture content is adjusted to 10% by mass or less, preferably 5±2% by mass, and the transmittance and other conditions specified in the present application are adjusted. Physical properties should be measured. Drying conditions for adjusting the water content are not particularly limited as long as the water-absorbing resin (particulate water-absorbing agent) is not decomposed or denatured, but drying under reduced pressure is preferable.

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 sheet,
400 device,
410 container,
411 cells,
412 Piston,
413a, 413b wire mesh,
414 swollen gel (water-absorbed particulate water-absorbing agent),
415 holes,
420 tank,
421 glass tube,
422 L-tube with cocked glass tube,
423 liquids,
431 stainless steel wire mesh,
432 collection vessel,
433 Fine balance.

This application is filed on August 9, 2018, Japanese Patent Application No. 2018-150124, Japanese Patent Application No. 2018-150125, Japanese Patent Application No. 2018-150129, Japanese Patent Application No. 2018, September 28. No. 2018-185706, the disclosure of which is incorporated herein by reference in its entirety.

Claims (13)

a first substrate;
a second substrate;
a water absorbing layer positioned between the first substrate and the second substrate;
A water absorbent sheet having
The first base material is a water-permeable sheet located on the side where the liquid to be absorbed is introduced,
The water absorbing layer comprises an intermediate sheet, a first particulate water absorbing agent localized on the side of the first substrate facing the second substrate, and the water absorbing layer of the second substrate. a second particulate water absorbing agent localized on the side facing the first substrate;
the transmittance of the mixture of the first particulate water absorbing agent and the second particulate water absorbing agent to the intermediate sheet is less than 60%;
A water absorbent sheet, wherein the GPR of the first particulate water absorbing agent is 50 g/min or more, and the GPR of the second particulate water absorbing agent is 45.0 g/min or more. 2. The absorbent sheet according to claim 1, wherein said intermediate sheet is a non-woven fabric. 3. The absorbent sheet according to claim 1, wherein the thickness of the intermediate sheet is thicker than the thickness of either one of the first base material and the second base material. The content of the mixture of the first particulate water absorbing agent and the second particulate water absorbing agent per unit volume of the water absorbent sheet is 50 mg/cm ³ or more, according to any one of claims 1 to 3. The water absorbent sheet described. The water absorbent sheet according to any one of claims 1 to 4, wherein the mixture of the first particulate water absorbing agent and the second particulate water absorbing agent has a weight average particle size of 200 to 600 µm. The water absorbent sheet according to any one of claims 1 to 5, wherein the CRC of the mixture of the first particulate water absorbing agent and the second particulate water absorbing agent is 33 g/g or more. 7. The water absorbent sheet according to any one of claims 1 to 6, wherein the content weight of said first particulate water absorbing agent relative to the content weight of said second particulate water absorbing agent is 0.4 or less. water absorbent sheet. The GPR of the second particulate water absorbing agent is 50 g/min or more, and the content weight of the first particulate water absorbing agent with respect to the content weight of the second particulate water absorbing agent in the water absorbent sheet is 8. The water absorbent sheet according to any one of claims 1 to 7, wherein the transmittance is 0.4 or less and the transmittance is more than 40%. The water absorbent sheet according to any one of claims 1 to 8 , wherein at least one of the first particulate water absorbing agent and the second particulate water absorbing agent has a surface tension of 65 mN/m or more. The water absorbent sheet according to any one of claims 1 to 9 , wherein at least one of the first particulate water absorbing agent and the second particulate water absorbing agent has an average circularity of 0.70 or less. The water absorbent sheet according to any one of claims 1 to 10 , wherein at least one of the first particulate water absorbing agent and the second particulate water absorbing agent includes irregularly crushed particles as a particle shape. . The water absorbent sheet contains an adhesive,
The amount of the adhesive used is 0.05 to 2.0 times the total mass of the first particulate water absorbing agent and the second particulate water absorbing agent. The water absorbent sheet according to any one of items 1 and 2. By sandwiching the water-absorbing sheet according to any one of claims 1 to 12 between a liquid-permeable sheet and a liquid-impermeable sheet, the liquid-permeable sheet is on the first base material side wherein said liquid impermeable sheet is located on said second substrate side.

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