Absorbent sheet, method for manufacturing the same, and waterproofing equipment

Abstract

The present invention provides an absorbent sheet that exhibits a stable swelling and water-stopping effect even in water with a high concentration of inorganic salts. [Solution] An absorbent sheet having an absorbent material between two layers of base sheets, wherein the absorbent material comprises a nonionic absorbent resin and granular sodium polyacrylate resin, and the average particle diameter R (μm) of the sodium polyacrylate resin satisfies the following formula 1. However, M is the mass of the nonionic absorbent resin per unit area (g / m²). 2 ) indicates, where d is the density of the nonionic superabsorbent polymer (g / cm³). 3 ) indicates. 10

Description

[Technical Field]

[0001] This invention relates to a water-absorbing sheet, a method for manufacturing the same, and a water-blocking device. [Background technology]

[0002] Waterproofing sheets are sometimes installed in coastal areas, riverbanks, waste disposal sites, underground structures, reservoirs, etc., to prevent water leakage into the ground. Regarding waterproof sheets, the main type is a waterproof sheet with waterproofing properties for stopping water leakage. However, to prevent leakage even if the waterproof sheet is damaged or defective, two or more layers of waterproof sheets are sometimes used. Furthermore, the use of a combination of these waterproof sheets and a water-absorbing sheet containing a superabsorbent resin has been proposed (for example, Patent Document 1). The superabsorbent resin in the water-absorbing sheet absorbs the leaked water and swells, filling the damaged or defective parts of the waterproof sheet and stopping the leakage.

[0003] In recent years, in coastal areas susceptible to damage from storm surges and tsunamis, and in waste disposal sites containing large amounts of incinerated ash, there has been a growing need to prevent water leakage from water containing inorganic salts. However, while polyacrylic acid-based resins, which have been widely used as superabsorbent polymers, exhibit excellent water absorption in pure water, their water absorption capacity decreases significantly in water containing high concentrations of inorganic salts, especially water containing divalent cations. Therefore, when the salt concentration of inorganic salts increases, the swelling of the resin becomes insufficient, and leak prevention measures and equipment using polyacrylic acid-based resins may become ineffective. In response to this, an absorbent sheet has been proposed that combines a polyacrylic acid-based resin with a water-absorbing resin that swells even in water containing inorganic salts (for example, Patent Document 2). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-52323

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, although the water-absorbing sheet obtained by simply mixing and using two types of water-absorbing resins as in Patent Document 2 shows a water leakage prevention effect against water containing inorganic salts at a high concentration, the effect may not be stable. The present invention provides a water-absorbing sheet that can stably exhibit a swelling water-stopping effect even against water having a high salt concentration of inorganic salts.

Means for Solving the Problems

[0006] The present invention has the following aspects. [1] A water-absorbing sheet having a water-absorbing material between two layers of base sheets, where the water-absorbing material contains a nonionic water-absorbing resin and a granular sodium polyacrylate resin, and the average particle diameter R (μm) of the sodium polyacrylate resin satisfies the following formula 1: 10 < R < M ÷ d ··· Formula 1 However, M represents the mass (g / m 2 ) of the nonionic water-absorbing resin per unit area, and d represents the density (g / cm 3 ) of the nonionic water-absorbing resin. [2] The water-absorbing sheet according to [1], wherein the nonionic water-absorbing resin is a modified polyalkylene oxide resin. [3] The water-absorbing sheet according to [1] or [2], wherein at least one of the two layers of base sheets is a nonwoven fabric. [4] The water-absorbing sheet according to any one of [1] to [3], wherein at least a part of the water-absorbing material is adhered to the base sheet. [5] A method for producing the water-absorbing sheet according to any one of [1] to [4], A method for manufacturing a water-absorbent sheet, comprising mixing and spraying a raw material containing the sodium polyacrylate resin and the nonionic water-absorbent resin on a base sheet, laminating another base sheet thereon, and performing a heat treatment. [6][1] The water-absorbent sheet according to any one of [4], and A water-blocking sheet located outside the base sheet of the water-absorbent sheet, and A water-blocking facility comprising the same.

Advantages of the Invention

[0007] According to the present invention, a water-absorbent sheet that stably exhibits a swelling and water-stopping effect even with respect to water having a high salt concentration of inorganic salts is provided.

Brief Description of the Drawings

[0008] [Figure 1] It is a schematic cross-sectional view showing an example of a water-absorbent sheet satisfying Formula 1. [Figure 2] It is a schematic cross-sectional view showing an example of a water-absorbent sheet not satisfying Formula 1. [Figure 3] It is a schematic view showing the configuration of a belt press type thermal laminator used in the examples. [Figure 4] It is a schematic view showing the configuration of an airlaid nonwoven fabric manufacturing apparatus used in the examples.

Embodiments for Carrying Out the Invention

[0009] In this specification, "~" indicating a numerical range means including the numerical values described before and after it as the lower limit value and the upper limit value. The lower limit value and the upper limit value of the numerical range disclosed in this specification can be arbitrarily combined to form a new numerical range.

[0010] <Water-absorbent sheet> The water-absorbent sheet of the present invention has a water-absorbent material between two base sheets.

[0011] (Base sheet) The base sheet is a sheet-like substrate for arranging absorbent material in a planar manner. Examples include knitted fabrics, woven fabrics, nonwoven fabrics, films, and paper. The film may be a porous film. Among these, nonwoven fabrics are preferred in terms of strength and mass productionability. The base sheet may be a water-permeable sheet that possesses water permeability, that is, the property of allowing water molecules to pass through.

[0012] The material of the base sheet is not particularly limited. For example, in the case of a base sheet made of fibers such as knitted fabric, woven fabric, or nonwoven fabric, the fibers may be natural fibers or artificial fibers. In the case of a film, examples include polyethylene film, polypropylene film, and polyester film. Examples of natural fibers include cellulose-based plant fibers such as pulp, recycled paper, paper, cotton, hemp, straw, bamboo, and sawdust; and animal fibers such as silk and wool. Artificial fibers may include, for example, cellulose-based synthetic fibers such as acetate and rayon, resin fibers such as polyethylene, polypropylene, polyester, acrylic, and polyamide, or inorganic fibers such as glass fibers and quartz fibers. The base sheet material may be a single material or a combination of two or more materials. Furthermore, if the base sheet is made of fibers, the fibers may be single filaments, multifilaments, or fibers with a core-sheath structure.

[0013] The thickness of the base sheet is not particularly limited. For example, if the base sheet is a nonwoven fabric, the thickness of the base sheet is preferably 1 to 20 mm, and more preferably 3 to 10 mm. If the base sheet is a film, the thickness of the base sheet is preferably 0.05 to 0.5 mm, and more preferably 0.1 to 0.5 mm. If the thickness is above the lower limit of the above range, the mechanical properties are better. If the thickness of the base sheet is below the upper limit of the above range, the workability during installation is better. The thickness of the base sheet was measured using a constant-pressure thickness gauge with a probe diameter of 30 mm and a measurable pressure of 20 g / cm². 2 It is measured under these conditions.

[0014] The two base sheets may have the same or different composition. For example, one base sheet may be a nonwoven fabric and the other a film. Also, for example, if both base sheets are nonwoven fabrics, the properties of the two nonwoven fabric layers, such as fiber material, fiber morphology, fiber diameter, fiber length, basis weight, and thickness, may be the same or different.

[0015] (Water absorbent material) The water-absorbing material comprises a nonionic water-absorbing resin and granular sodium polyacrylate resin. In this specification, granular includes powder. Sodium polyacrylate resin exhibits excellent water absorption and swelling properties in pure water and water with low ion concentrations. Nonionic superabsorbent resins, compared to sodium polyacrylate resin, exhibit relatively high water absorption and swelling properties in water containing high concentrations of inorganic salts or water containing divalent cations (hereinafter collectively referred to as high-ion-concentration water). Therefore, superabsorbent materials can swell sufficiently in both pure water, water with low ion concentrations, and high-ion-concentration water.

[0016] Examples of nonionic superabsorbent polymers include cross-linked hydrophilic polymers. Examples of hydrophilic polymers include polyalkylene oxide resins such as polyethylene oxide (polyethylene glycol), polypropylene oxide (polypropylene glycol), and copolymers thereof, as well as polyvinylpyrrolidone resin and polyacrylamide resin. As a nonionic superabsorbent polymer, modified polyalkylene oxide resins obtained by crosslinking polyalkylene oxide resins are preferred in terms of availability, and crosslinked polyethylene oxide, polypropylene oxide, or copolymers thereof are more preferred. Commercially available modified polyalkylene oxide resins are available, for example, from Sumitomo Seika Co., Ltd. and AGC Inc. Polyalkylene oxide resins may also be used after being crosslinked. Crosslinking can be carried out, for example, using a polyisocyanate compound.

[0017] Preferably, at least a portion of the nonionic water-absorbing resin is heat-sealable. Conventional waterproofing sheets, such as the waterproofing sheet for civil engineering described in Patent Document 1, have a water-absorbing material supported within a composite sheet formed by sewing together first and second sheet-like base materials using needle punching. As a result, the water-absorbing material tends to fall off when the sheet is laid. Consequently, the ease of laying the sheet is reduced, and the water absorption performance may also be impaired. If at least a portion of the nonionic superabsorbent resin is heat-sealable, then in the manufacturing of the absorbent sheet, the nonionic superabsorbent resin can be melted by heating in an oven, and at least a portion of the nonionic superabsorbent resin can be directly bonded to the base sheet. In addition, at least a portion of the sodium polyacrylate resin can be bonded to the base sheet via the nonionic superabsorbent resin. In this way, if at least a portion of the absorbent material is bonded to the base sheet, the absorbent material is less likely to fall off the absorbent sheet when it is laid. As a result, workability is improved, and a decrease in water absorption performance due to the detachment of the absorbent material can be prevented. Examples of nonionic superabsorbent resins with heat-sealing properties include modified polyalkylene oxide resins and polyvinylpyrrolidone resins. The melting point of a nonionic superabsorbent polymer with heat-sealing properties is preferably 40 to 200°C, and more preferably 60 to 120°C. The melting point is measured using a differential scanning calorimeter (DSC) or a heating microscope. However, sodium polyacrylate resin usually decomposes without exhibiting thermal melting properties when heated, and therefore does not have a clearly defined melting point. Nonionic superabsorbent polymers may be used individually or in combination of two or more types.

[0018] As the sodium polyacrylate resin, commercially available (crosslinked) sodium polyacrylate resin powder, which is used as a water-absorbing resin, can be used as is, or the particle size can be adjusted as needed by grinding, classifying, etc. In this specification, crosslinked sodium polyacrylate resin is referred to as sodium polyacrylate resin. Examples of commercially available sodium polyacrylate resins include "Aqualic" manufactured by Nippon Shokubai Co., Ltd., "Aquakeep" manufactured by Sumitomo Seika Chemicals Co., Ltd., and "Sunwet" manufactured by Sanyo Chemical Industries, Ltd. The sodium polyacrylate resin may be used alone or in combination of two or more.

[0019] The sodium polyacrylate resin has an average particle size R (μm) that satisfies the following formula 1. 10 < R < M ÷ d ··· Formula 1 However, M represents the mass (g / m 2 ) of the nonionic water-absorbing resin per unit area, and d represents the density (g / cm 3 ) of the nonionic water-absorbing resin.

[0020] Generally, the particle size of commercially available sodium polyacrylate resins as water-absorbing materials is often about 500 to 800 μm. This is because when used as a diaper or a water-absorbing sheet, if the particle size is small, powder may fall off, local swelling may occur, and a phenomenon called gel blocking may occur, where water diffusion is inhibited and absorption is delayed. Therefore, the particle size is intentionally increased. When the sodium polyacrylate resin is used alone, it swells with a very high swelling ratio in pure water, blocking water penetration and exhibiting the effect as a water-absorbing and water-stopping material. Conventionally, in order to exhibit a water-absorbing and water-stopping effect even for high-ion-concentration water, it has been proposed to use a combination of a sodium polyacrylate resin and a nonionic water-absorbing resin. However, in this case, it has been found that the water-stopping property for high-ion-concentration water is not stable (water-stopping performance is insufficient at sporadic locations). Therefore, as a result of investigating the cause of the unstable water-stopping property for high-ion-concentration water, it was found that in the water-absorbing sheet, the sodium polyacrylate resin that does not swell in high-ion-concentration water exists in a state of penetrating the layer of the nonionic water-absorbing resin or inhibits the continuity of the layer of the nonionic water-absorbing resin, resulting in insufficient water-stopping and water leakage. As a result of further study in view of the above findings, by making the average particle diameter of the sodium polyacrylate resin smaller than the thickness of the layer of the nonionic water-absorbing resin, the sodium polyacrylate that does not swell in high-ion-concentration water exists in a state of penetrating the layer of the nonionic water-absorbing resin or does not inhibit the continuity of the nonionic water-absorbing resin layer, and it has been found that a water-absorbing sheet that exhibits a stable water absorption and water-stopping effect even in high-ion-concentration water can be obtained.

[0021] The thickness (μm) of the layer of the nonionic water-absorbing resin in the water-absorbing sheet is calculated by M÷d, where M (g / m 2 ) is the mass of the nonionic water-absorbing resin per unit area and d (g / cm 3 ) is the density of the nonionic water-absorbing resin. The sodium polyacrylate resin with an average particle diameter satisfying R<M÷d is less likely to damage the continuity of the layer or penetrate the layer as shown in FIG. 1 because its average particle diameter is smaller than the thickness of the layer of the nonionic water-absorbing resin. In the figure, reference numeral 1 indicates the base sheet, reference numeral 2 indicates the layer of the nonionic water-absorbing resin, and reference numeral 3 indicates the sodium polyacrylate resin. The sodium polyacrylate resin with an average particle diameter not satisfying R<M÷d may cause water leakage by damaging the continuity of the layer or penetrating the layer as shown in FIG. 2.

[0022] On the other hand, the sodium polyacrylate resin with an average particle diameter R less than 10 μm is likely to scatter during spraying onto the base sheet during the production of the water-absorbing sheet, which may deteriorate the working environment during production. Also, when the base material is a non-woven fabric, it may enter the non-woven fabric layer or pass through the non-woven fabric layer and fall off.

[0023] Therefore, a water-absorbing sheet having a layer of a water-absorbing material containing a sodium polyacrylate resin and a nonionic water-absorbing resin with an average particle diameter satisfying Formula 1 exhibits stable water absorption and water-stopping performance for both pure water and high-ion-concentration water. Furthermore, an absorbent sheet having a layer of absorbent material containing sodium polyacrylate resin with an average particle size satisfying Equation 1 and a nonionic absorbent resin can be manufactured without the scattering of fine powder or the permeation and shedding of powder from the substrate.

[0024] The method for obtaining a sodium polyacrylate resin with an average particle size satisfying Equation 1 is not particularly limited. For example, methods include synthesizing a sodium polyacrylate resin so that it has a predetermined average particle size from the time of synthesis, and pulverizing a sodium polyacrylate resin to obtain a predetermined average particle size and classifying it as necessary.

[0025] The average particle size R of sodium polyacrylate resin is measured by the following method. [Method for measuring average particle size R] Multiple cross-sections of the absorbent sheet are imaged using a scanning electron microscope (SEM), and the resulting micrographs are analyzed using image analysis software (e.g., MAC-View (Mountec Co., Ltd.), Image-J (National Institutes of Health, USA)). For more than 200 sodium polyacrylate resin samples, the particle size corresponding to the particle size determined by the classification method specified in JIS Z 8815 "General Rules for Sieving Test Methods" is calculated, and the average value of these values ​​is defined as the average particle size R. For convenience, the particle size of the sodium polyacrylate resin may be measured before manufacturing the absorbent sheet using the classification method specified in JIS Z8815, and this value may be taken as the average particle size R. However, if the measured values ​​differ between the former and the latter, the former value shall be taken as the average particle size R. Since sodium polyacrylate resin is an absorbent resin, particle size measurement methods that involve dispersing it in water are unsuitable, and measurement methods in a dry state are appropriate.

[0026] The water-absorbing material may further contain other water-absorbing materials other than nonionic water-absorbing resins and sodium polyacrylate resins, as long as they do not impair the effects of the invention. The water absorption and swelling rate can be adjusted by the other water-absorbing materials. Examples of other water-absorbing materials include, for example, acrylic acid-vinyl alcohol copolymer, acrylic acid-acrylamide copolymer, and isobutylene-maleic anhydride copolymer.

[0027] In the water-absorbing material, the mass ratio of sodium polyacrylate resin to nonionic water-absorbing resin (sodium polyacrylate resin / nonionic water-absorbing resin) is preferably 20 / 80 to 99 / 1, more preferably 20 / 80 to 50 / 50, and even more preferably 30 / 70 to 50 / 50. When the mass ratio is 20 / 80 or more, the swelling ratio of the sodium polyacrylate resin to pure water or water containing trace amounts of inorganic salts is very high, so that the swelling rate of the water-absorbing sheet to pure water or water containing trace amounts of inorganic salts can be sufficiently ensured. When the mass ratio is 99 / 1 or less, as the blending ratio of the nonionic water-absorbing resin, a sufficient swelling rate can be ensured even for high-ion-concentration water, and a water-stopping effect is exhibited.

[0028] The total content per area of the nonionic water-absorbing resin and sodium polyacrylate resin is preferably 30 g / cm 2 or more, more preferably 100 to 1000 g / cm 2 and even more preferably 300 to 600 g / cm 2 When the total content per area of the nonionic water-absorbing resin and sodium polyacrylate resin is at least the lower limit of the above range, it is easy to sufficiently ensure the swelling rate of the water-absorbing sheet. When the total content per area of the nonionic water-absorbing resin and sodium polyacrylate resin is at most the upper limit of the above range, it is easy to reduce the production cost of the water-absorbing sheet.

[0029] The total ratio of the nonionic water-absorbing resin and sodium polyacrylate resin to​

[0030] (Heat-fusible resin) The absorbent sheet may have a heat-sealable resin (excluding the absorbent material) between two layers of base sheets, in addition to the absorbent material. As mentioned above, conventional waterproofing sheets are prone to shedding their absorbent material during installation. As a result, installation efficiency is reduced, and the water absorption performance may also be compromised. When a heat-sealable resin is present between two layers of base sheets, at least a portion of the water-absorbing material can be bonded to the base sheets by the heat-sealable resin. When at least a portion of the water-absorbing material is bonded to the base sheets, it is less likely to detach from the water-absorbing sheet during installation. As a result, work efficiency is improved, and a decrease in water absorption performance due to the detachment of the water-absorbing material can be prevented. A nonionic water-absorbing resin with heat-sealing properties and a heat-sealing resin may be used in combination.

[0031] The heat-sealable resin is not particularly limited as long as it is a thermoplastic resin that exhibits heat adhesion in a heated oven when manufacturing absorbent sheets. Examples of heat-sealable resins include polyester resin, acrylic resin, polyolefin resin (polyethylene, polypropylene, etc.), styrene-acrylic resin, ethylene-vinyl acetate resin, urethane resin, polyamide resin, polycarbonate resin, and polylactic acid resin. A single type of heat-sealable resin may be used alone, or two or more types may be used in combination.

[0032] The content of the heat-fusible resin is preferably 80% by mass or less, more preferably 50% by mass or less, even more preferably 40% by mass or less, and may be 0% by mass, relative to the total content of the nonionic water-absorbing resin and the sodium polyacrylate resin. When the content of the heat-fusible resin is below the upper limit of the above range, the swelling rate of the water-absorbing sheet is less affected by the heat-fusible resin. When the absorbent sheet contains a heat-sealable resin, the content of the heat-sealable resin is preferably 3% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, relative to the total content of the nonionic absorbent resin and the sodium polyacrylate resin. When the content of the heat-sealable resin is above the lower limit of the above range, the adhesive effect of the heat-sealable resin is more likely to be exhibited.

[0033] (Properties of absorbent sheets) The thickness of the absorbent sheet is not particularly limited. For example, the thickness of the absorbent sheet is preferably 1 to 20 mm, more preferably 2 to 10 mm, and even more preferably 3 to 6 mm. When the thickness of the absorbent sheet is above the lower limit of the above range, the absorbent sheet has excellent mechanical properties. When the thickness of the absorbent sheet is below the upper limit of the above range, the swelling pressure due to water absorption by the nonionic absorbent resin and sodium polyacrylate resin is easily obtained. Therefore, it is easier to seal holes in the surface of the waterproof sheet and prevent water leakage into the ground. The thickness of the absorbent sheet was measured using a constant-pressure thickness gauge with a probe diameter of 30 mm and a measurable load of 20 g / cm². 2 It is measured under these conditions.

[0034] The basis weight of the absorbent sheet is 30 g / m². 2 The above is preferable, and 200-2000 g / m² 2 More preferably, 800-1200 g / m 2 This is even more preferable. If the basis weight of the absorbent sheet is above the lower limit of the above range, the absorbent sheet has excellent mechanical properties. If the basis weight of the absorbent sheet is below the upper limit of the above range, the workability when laying the sheet is excellent. The basis weight of the absorbent sheet is determined by measuring the weight of a 120mm x 417mm sample after it has been conditioned for at least 4 hours at 23°C and 50% RH using a weighing scale, and then converting it to a square meter equivalent.

[0035] The water-blocking performance of a water-absorbing sheet that exhibits water-blocking properties through swelling is indicated by its permeability coefficient. A smaller permeability coefficient is preferable. According to the regulations of the Japan Association of Water-Blocking Construction, 5 × 10 -11 It is stipulated that the speed must be less than or equal to m / s. The permeability coefficient of the absorbent sheet is measured in accordance with JIS A 1218 (Japanese Industrial Standard "Method for Testing Soil Permeability").

[0036] The tensile strength of the absorbent sheet is preferably 1 kN / m or more, more preferably 10 kN / m or more, and even more preferably 20 kN / m or more. When the tensile strength of the absorbent sheet is equal to or greater than the lower limit, the absorbent sheet exhibits excellent mechanical properties. The upper limit of the tensile strength of the absorbent sheet is not particularly limited. For example, it is about 40 kN / m. The tensile strength of the absorbent sheet is measured in accordance with JIS L 1908.

[0037] (Manufacturing method) The method for manufacturing the absorbent sheet is not particularly limited, but the following method is preferred. A method of mixing and spraying raw materials containing a nonionic superabsorbent resin and sodium polyacrylate resin onto a base sheet, laminating another base sheet on top of it, and then heat-treating it.

[0038] It is preferable that at least a portion of the nonionic superabsorbent resin is heat-sealable, or that the raw material further contains a heat-sealable resin. In this case, by heat treatment, two layers of base sheets are bonded to each other by the heat-sealable nonionic superabsorbent resin or heat-sealable resin, and an absorbent sheet is obtained in which at least a portion of the absorbent material is bonded to the base sheet by the heat-sealable nonionic superabsorbent resin or heat-sealable resin.

[0039] The method of mixing and spraying is not particularly limited. Examples include spraying by a roll feeder, spraying by a vibrating screen, electrostatic spraying, and spraying by the airlaid method. A roll feeder sprays the raw material onto a base sheet using rotating rolls to form a layer of raw material. Electrostatic spraying uses static electricity to attract the raw material to the base sheet, forming a layer of raw material. In the airlaid method, the raw material is dispersed and mixed in an airflow, and the airflow is drawn in from the back of the base sheet to form a layer of raw material on the base sheet.

[0040] As the nonionic superabsorbent resin, it is preferable to use a granular form due to its ease of mixing with granular sodium polyacrylate resin and its availability. In this case, the average particle size of the nonionic superabsorbent resin is preferably 40 to 800 μm. If the average particle size is above the lower limit of the above range, the nonionic superabsorbent resin is less likely to scatter or permeate the substrate. If the average particle size is below the upper limit of the above range, it is easier to uniformly mix and spray with the sodium polyacrylate resin.

[0041] When mixing and dispersing raw materials onto a substrate sheet using a roll feeder, vibrating screen, or electrostatic dispersion, it is preferable to use granular heat-fusible resin. In this case, the average particle size of the thermoplastic resin is preferably 40 to 800 μm. If the average particle size is above the lower limit of the above range, the heat-fusible resin is less likely to scatter or permeate the substrate. If the average particle size is below the upper limit of the above range, it is easier to uniformly mix and disperse with the sodium polyacrylate resin. Furthermore, the closer the average particle size is to that of the sodium polyacrylate resin, the easier it is to uniformly mix and disperse the two. If the particle size of the larger particle is less than or equal to twice the particle size of the smaller particle, it is easier to uniformly mix and disperse the two.

[0042] When mixing and spraying raw materials onto a base sheet using the airlaid method, it is preferable to use fibrous material as the heat-fusible resin. In this case, the fibers of the heat-fusible resin may be single filaments, multifilaments, or fibers with a core-sheath structure. Examples of fibers with a core-sheath structure include the following: • A polypropylene / polyethylene core-sheath fiber having polypropylene in the core and polyethylene in the sheath. Polyester / polyethylene core-sheath fiber having polyester in the core and polyethylene in the sheath. A polyester / low-melting-point polyester core-sheath fiber having polyester in the core and low-melting-point polyester in the sheath. Among these, polyester / polyethylene core-sheath fibers and polypropylene / polyethylene core-sheath fibers are preferred due to their excellent adhesion when heat-sealed.

[0043] Commercially available core-sheath fibers may be used. Examples of commercially available polypropylene / polyethylene core-sheath fibers include "NBF" from Daiwabo Holdings Co., Ltd. Examples of commercially available polyester / polyethylene core-sheath fibers include "ETC" from ES Fiber Visions Co., Ltd. Examples of commercially available polyester / low-melting-point polyester core-sheath fibers include "Melty" from Unitika Corporation. When using fibers with a core-sheath structure, the content of heat-fusible resin includes the total amount of resin in the core and the resin in the sheath.

[0044] Heat treatment is performed to bond each layer of the raw material, which is formed by the two layers of base sheets and the mixed spraying process. The heat treatment method may be non-contact heating, such as hot air heating, infrared heating, or induction heating, or contact heating, such as hot pressing by contact with a hot plate. It is also possible to use a combination of these methods. In particular, a belt press method, in which the material is continuously heated and compressed by sandwiching it between endless belts, is preferred. The heating temperature can be, for example, the temperature at which a nonionic water-absorbing resin or a heat-fusible resin with heat-fusibility melts.

[0045] <Waterproofing equipment> The water-blocking device of the present invention comprises the water-absorbing sheet of the present invention described above, and a water-blocking sheet located on the outside of the base sheet of the water-absorbing sheet. Because the waterproofing equipment of the present invention is equipped with the water-absorbing sheet of the present invention, the water-absorbing sheet swells sufficiently even when the salt concentration of inorganic salts is high. Therefore, the waterproofing equipment of the present invention is less likely to have its water leakage prevention effect impaired.

[0046] (Waterproof sheet) The waterproof sheet is not particularly limited as long as it is a sheet-like substrate that possesses waterproofing properties, that is, properties that prevent the permeation of water molecules. Examples include polyethylene sheets, polypropylene sheets, polyester sheets, polyvinyl chloride sheets, rubber sheets, asphalt-based sheets, and rubber-asphalt-based sheets.

[0047] The waterproofing system may consist of one waterproofing sheet or multiple waterproofing sheets. If multiple waterproofing sheets are provided, the sheets may be made of the same material or different materials. Furthermore, the waterproofing sheets may be located on both sides of the surface of the water-absorbing sheet or on one side.

[0048] (Protective sheet) The waterproofing device may further include one or more protective sheets in addition to the water-absorbing sheet and waterproofing sheet of the present invention. If multiple protective sheets are provided, the multiple protective sheets may be identical or different from each other.

[0049] A protective sheet is a sheet used to protect absorbent sheets and waterproof sheets from damage. Examples of protective sheets include knitted fabrics, woven fabrics, and nonwoven fabrics. From the standpoint of strength, long-fiber nonwoven fabrics such as spunbond nonwoven fabrics are preferred as protective sheets. The material of the protective sheet is not particularly limited. Examples include polyethylene, polypropylene, polyester, polyvinyl chloride, and composites of these materials.

[0050] The protective sheet may be positioned in contact with the water-absorbing sheet of the present invention. In this case, a laminated structure in which the water-absorbing sheet, protective sheet, and water-blocking sheet are stacked in this order can be formed as a water-blocking device. The protective sheet may be located outside the water-absorbing sheet via a water-impermeable sheet. In this case, a laminated structure in which the water-absorbing sheet, water-impermeable sheet, and protective sheet are stacked in this order can be formed as a water-impermeable device.

[0051] If multiple protective sheets are provided, some of the protective sheets may be in contact with the water-absorbing sheet, while the remaining protective sheets may be located outside the water-absorbing sheet via a water-blocking sheet. Furthermore, all protective sheets may be positioned in contact with the absorbent sheet, or all protective sheets may be positioned outside the absorbent sheet via a waterproof sheet. Also, the protective sheets may be used overlapping each other. If the absorbent sheet of the present invention has the function and performance of a protective sheet, it is also possible to use the absorbent sheet as a protective sheet as well. [Examples]

[0052] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following description.

[0053] <Raw materials> (Sodium polyacrylate resin) • Sodium polyacrylate resin 1: Sodium polyacrylate (SA-80M manufactured by Sumitomo Seika Co., Ltd., density 1.2 g / cm³) 3 , average particle size 400μm)

[0054] (Nonionic superabsorbent polymer) Nonionic superabsorbent resin 1: Modified polyalkylene oxide resin (ethylene oxide / saturated bismethylenediphenyl diisocyanate copolymer, Sumitomo Seika Co., Ltd. product "Aquacoke TWP", density 1.2 g / cm³) 3 (Average particle size 80 μm, thermoplastic, melting point 80-100°C) Nonionic superabsorbent resin 2: Modified polyalkylene oxide resin (ethylene oxide / hexamethylene diisocyanate copolymer, ADEKA Corporation's "ADEKA NOL GT-700", density 1.2 g / cm³) 3 (Average particle size 80 μm, melting point 150°C)

[0055] (Heat-fusible resin) • Heat-sealable resin 1: Copolymer polyester / polyethylene terephthalate core-sheath fiber (fiber length 5 mm)

[0056] <Example 1> (Preparation of pulverized sodium polyacrylate resin powder) The sodium polyacrylate resin 1 was pulverized in a cutting mill for 2 minutes to obtain pulverized sodium polyacrylate resin powder with an average particle size of 100 μm.

[0057] (Preparation of mixed powders) The pulverized sodium polyacrylate resin powder and the nonionic water-absorbing resin 1 were mixed in a mass ratio of 250:300 to obtain a mixed powder.

[0058] (Base sheet) As the base sheet, a nonwoven polyethylene terephthalate fiber fabric for civil engineering (thickness: 3 mm, basis weight: 210 g / m²) is used. 2 ) was used.

[0059] (Preparation of absorbent sheets) A water-absorbing sheet was manufactured using a belt press type sheet laminating machine with the configuration shown in Figure 3, following the procedure below. This belt press type sheet laminating machine includes a hopper 31 for containing raw materials (mixed powder), a spreader 32 for supplying raw materials onto one of the base sheets, a pair of endless belts 33, and a pair of hot plates 34. The base sheet is unwound from the base sheet roll, and the mixed powder is sprinkled onto it at a rate of 550 g / m². 2 The material was then sprayed in this manner. Furthermore, a base sheet unwound from another base sheet roll was placed on top of it, and then it was introduced between a pair of endless belts 33 and heated with a hot plate 34 to heat-compress it, thereby obtaining an absorbent sheet in which the base sheet, the mixed layer of sodium polyacrylate resin powder and modified polyalkylene oxide resin, and the base sheet were integrated.

[0060] <Example 2> (Preparation of pulverized sodium polyacrylate resin powder) The sodium polyacrylate resin 1 was pulverized in a cutting mill for 2 minutes to obtain pulverized sodium polyacrylate resin powder with a particle size of 100 μm.

[0061] (Preparation of mixed powders) The pulverized sodium polyacrylate resin powder and the nonionic water-absorbent resin 2 were mixed in a mass ratio of 250:300 to obtain a mixed powder.

[0062] (Base sheet) Nonwoven polyethylene terephthalate fiber fabric for civil engineering (thickness: 3mm, basis weight: 210g / m²) 2 ) was used.

[0063] (Preparation of absorbent sheets) An absorbent sheet was manufactured using an airlaid nonwoven fabric manufacturing apparatus configured as shown in Figure 4, following the procedure below. This airlaid nonwoven fabric manufacturing apparatus includes a powder hopper 41 for containing raw materials (mixed powder), a resin hopper 42 for containing heat-fusible resin, an airlaid former 43 for mixing the raw materials and heat-fusible resin in an airflow, a suction box 44 for drawing in the airflow, a hot air oven 45, and a pair of embossing rolls 46. The base sheet is unwound from the base sheet roll, and separately, the mixed powder and the heat-fusible resin 1 are mixed in an airflow. The airflow is then sucked from the back side of the base sheet, thereby distributing the mixed powder at a concentration of 550 g / m². 2 and 100 g / m of the heat-fusible resin 1 2 An airlaid layer was formed by mixing and laminating these materials. Furthermore, a base sheet unwound from another base sheet roll was placed on top of it, heated at 150°C in a hot air oven 45, and then rolled and pressed with an embossing roll 46 to obtain a water-absorbing sheet in which the base sheet, the mixed layer of sodium polyacrylate resin powder, modified polyalkylene oxide resin, and heat-sealable resin, and the base sheet were integrated.

[0064] <Comparative Example 1> An absorbent sheet was prepared in the same manner as in Example 1, except that unground sodium polyacrylate resin particles (Sumitomo Seika AquaKeep SA-60S: average particle size 340 μm) were used instead of ground sodium polyacrylate resin powder.

[0065] <Comparative Example 2> An absorbent sheet was prepared in the same manner as in Comparative Example 1, except that Sanyo Chemical Industries' Sunfresh ST-500M (average particle size 380 μm) was used as unground sodium polyacrylate resin particles.

[0066] <Comparative Example 3> An absorbent sheet was prepared in the same manner as in Example 1, except that polyethylene resin powder (average particle size 150 μm) was used instead of modified polyalkylene oxide resin.

[0067] <Comparative Example 4> In this experiment, the same procedure as in Example 1 was followed, except that pulverized sodium polyacrylate resin powder with an average particle size of 100 μm was used instead of pulverized sodium polyacrylate resin powder with an average particle size of 100 μm. However, due to the fineness of the powder, the total surface area of ​​the powder became excessively large, resulting in incomplete thermal fusion within and between layers. Furthermore, because of the fineness, there was a lot of scattering during the application process, and the deterioration of the working environment due to dust made it impossible to produce an absorbent sheet.

[0068] A water-impermeable test was conducted on each absorbent sheet using the following procedure. The results are shown in Table 1. Table 1 shows the values ​​of M÷d and R in the above formula 1.

[0069] <Waterproofing test> For absorbent sheets (circular, 10 cm in diameter), impermeability tests were conducted against pure water and high-calcium-concentration water in accordance with JIS A 1218 (Japanese Industrial Standard "Method for Testing Water Permeability of Soil"). In the impermeability test against pure water, deionized water was used as the test medium (liquid). In the impermeability test against high-calcium-concentration water, an aqueous solution prepared by dissolving calcium chloride in deionized water to adjust the Ca ion concentration to 40,000 ppm was used as the test medium. The permeability coefficient obtained in the test was 5 × 10 -11 Samples with a reading of m / s or less were considered passable (recorded as OK: O), while those with a reading higher were considered failing (recorded as NG: N). The test was performed five times each for pure water and high-calcium concentration water for each sample.

[0070] [Table 1]

[0071] The absorbent sheets used in Examples 1 and 2 passed all five tests. On the other hand, the absorbent sheets of Comparative Examples 1 and 2, in which the average particle size R of the sodium polyacrylate resin was M÷d or greater, sometimes failed the water-impermeableness test against high-calcium concentration water. Comparative Example 3, which does not contain a nonionic superabsorbent resin, failed the water-impermeableness test against high-calcium concentration water in all five trials. [Industrial applicability]

[0072] According to the present invention, an absorbent sheet is provided that can be used to obtain a leak-proofing device that exhibits a stable leak prevention effect even when the salt concentration of inorganic salts is high. [Explanation of symbols]

[0073] 1…Base sheet, 2…Layer of nonionic water-absorbent resin, 3…Sodium polyacrylate resin

Claims

1. An absorbent sheet having an absorbent material between two layers of base sheets, The water-absorbing material comprises a nonionic water-absorbing resin and granular sodium polyacrylate resin. An absorbent sheet wherein the average particle size R (μm) of the sodium polyacrylate resin satisfies the following formula 1. 10<R<M÷d...Formula 1 However, M is the mass of the nonionic water-absorbing resin per unit area (g / m²). ２ ) is shown, and d is the density of the nonionic superabsorbent polymer (g / cm³). ３ ) indicates.

2. The absorbent sheet according to claim 1, wherein the nonionic absorbent resin is a modified polyalkylene oxide resin.

3. The absorbent sheet according to claim 1, wherein at least one of the two base sheets is a nonwoven fabric.

4. The absorbent sheet according to claim 1, wherein at least a portion of the absorbent material is adhered to the base sheet.

5. A method for manufacturing an absorbent sheet according to any one of claims 1 to 4, A method for manufacturing an absorbent sheet, comprising: mixing and spraying a raw material containing the nonionic absorbent resin and the sodium polyacrylate resin onto a base sheet; laminating another base sheet on top of the mixture; and heat-treating the mixture.

6. an absorbent sheet according to any one of claims 1 to 4, A water-blocking sheet located on the outside of the base sheet of the water-absorbing sheet, A waterproofing device equipped with the necessary features.

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