Water-absorbing sheets, waterproofing equipment

Abstract

To provide a water-absorbing sheet capable of obtaining a water-impervious facility which hardly deteriorates a water leakage prevention effect even when the salt concentration of inorganic salts is high.SOLUTION: There are provided: a water-absorbing sheet having a water-absorbing material between two layers of base material sheets, wherein the water-absorbing material includes at least one water-absorbing material A selected from the group consisting of sodium polyacrylate and bentonite and a water-absorbing material B which is a polyalkylene oxide and the mass ratio of the water-absorbing material A to the water-absorbing material B is 20 / 80 to 99 / 1; and a water-impervious facility comprises the water-absorbing sheet and a water impervious sheet disposed on the outside of the base material sheet of the water-absorbing sheet.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a water-absorbent sheet and a waterproofing facility. [Background technology]

[0002] Waterproof sheets are sometimes used to prevent water leakage into the ground in coastlines, riverbanks, waste disposal sites, underground structures, reservoirs, etc. With regard to waterproof sheets, the use of a water-absorbing sheet in which a superabsorbent resin is blended between two layers of base sheet to prevent water leakage even if holes appear on the surface has been proposed (for example, Patent Document 1). The superabsorbent resin in the water-absorbing sheet absorbs leaked water and swells, thereby sealing holes in the surface of the waterproof sheet and preventing water leakage into the ground. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-52323 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, for example, in waste disposal sites, there has been a demand for preventing leakage of water containing inorganic salts. However, while polyacrylic acid resins, which have been widely used as superabsorbent polymers, have excellent absorbency for fresh water, their absorbency significantly decreases for water containing high concentrations of inorganic salts, particularly water containing divalent cations. Therefore, if the salt concentration of inorganic salts becomes high, the resin may not swell sufficiently, which may impair its ability to prevent leakage.

[0005] The present invention provides a water-absorbent sheet that can provide a water-leakage facility in which the water-leakage prevention effect is not easily impaired even when the salt concentration of inorganic salts is high. [Means for solving the problem]

[0006] The present invention has the following aspects. [1] A water-absorbent sheet having a water-absorbent material between two layers of base sheet; the water-absorbent material includes water-absorbent material A, which is at least one material selected from the group consisting of sodium polyacrylate and bentonite, and water-absorbent material B, which is a polyalkylene oxide; and the mass ratio of water-absorbent material A to water-absorbent material B is 20 / 80 to 99 / 1. [2] The water-absorbent sheet according to [1], wherein the base sheet is a nonwoven fabric. [3] The total content per unit area of ​​the water-absorbing material A and the water-absorbing material B is 100 g / cm 2 The absorbent sheet of [1] or [2] above. [4] The water-absorbent sheet according to any one of [1] to [3], wherein at least a part of the water-absorbent material is adhered to the base sheet by a heat-fusible resin. [5] The water-absorbent sheet according to any one of [1] to [4], wherein the content of the heat-fusible resin is 3 to 80 mass % based on the total content of the water-absorbent material A and the water-absorbent material B. [6] A waterproofing system comprising: a water-absorbent sheet according to any one of [1] to [5]; and a waterproof sheet disposed on the outside of the base sheet of the water-absorbent sheet. [Effects of the Invention]

[0007] According to the present invention, there is provided a water-absorbent sheet that can provide a water-leakage facility in which the water-leakage prevention effect is not easily impaired even when the salt concentration of inorganic salts is high. DETAILED DESCRIPTION OF THE INVENTION

[0008] In this specification, the use of "to" to indicate a range of values ​​means that the values ​​before and after it are included as the lower and upper limits. The lower and upper limits of the ranges disclosed in this specification can be combined in any way to create new ranges.

[0009] <Water-absorbent sheet> The water-absorbent sheet of the present invention has a water-absorbent material between two layers of base sheet.

[0010] (Base sheet) The substrate sheet is a sheet-like substrate for disposing the water-absorbent material in a planar form. Examples include knitted fabric, woven fabric, nonwoven fabric, porous film, and paper. Among these, nonwoven fabric is preferred from the viewpoints of strength and mass productivity. The base sheet may be a water-permeable sheet that has the property of allowing water molecules to pass through.

[0011] The material of the base sheet is not particularly limited. For example, in the case of knitted fabric, woven fabric, or nonwoven fabric, the fibers may be natural fibers or artificial fibers. In the case of film, examples include polyethylene film, polypropylene film, and polyester film. The film may also be a porous film. Examples of natural fibers include cellulosic plant fibers such as pulp, waste paper, paper, cotton, hemp, straw, bamboo, and sawdust; and animal fibers such as silk and wool. The artificial fibers may be, 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 material of the substrate sheet may be one type alone or two or more types in combination. The fiber may be a single yarn, a multifilament, or a fiber with a core-sheath structure.

[0012] The thickness of the base sheet is not particularly limited. The thickness of the base sheet is, for example, preferably 0.2 to 10 mm, more preferably 0.5 to 5 mm, and even more preferably 1 to 3 mm. When the thickness of the base sheet is equal to or greater than the lower limit of the above-mentioned numerical range, the mechanical properties are excellent. When the thickness of the base sheet is equal to or less than the upper limit of the above-mentioned numerical range, the swelling pressure due to the absorption of water by the water-absorbent material A and the water-absorbent material B is easily obtained. Therefore, holes on the surface of the waterproof sheet are easily sealed, and water leakage into the ground is easily prevented. 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 / cm. 2 It is measured under the following conditions.

[0013] The two base sheet layers may have the same or different configurations. For example, when the base sheet is a nonwoven fabric, the properties of the two nonwoven fabric layers, such as fiber material, fiber form, fiber diameter, fiber length, basis weight, and thickness, may be the same or different.

[0014] (Water absorbent material) The water-absorbing material includes a specific water-absorbing material A and a specific water-absorbing material B. The water-absorbing material A is at least one selected from the group consisting of sodium polyacrylate and bentonite. Therefore, the water-absorbing material A exhibits excellent water absorption in fresh water. In addition, the water-absorbing material A has a high swelling rate in fresh water.

[0015] As the sodium polyacrylate and bentonite, commercially available products may be used. Commercially available sodium polyacrylate products include, for example, "AQUALIC" manufactured by Nippon Shokubai Co., Ltd., "AQUAKEEP" manufactured by Sumitomo Seika Chemicals Co., Ltd., and "SANWET" manufactured by Sanyo Chemical Industries, Ltd. One type of sodium polyacrylate may be used alone, or two or more types may be used in combination. Commercially available bentonite products include, for example, "M-1" manufactured by Nippon Bentonite Kogyo Co., Ltd., "Super Clay" manufactured by Hojun Co., Ltd., and "Odosorb" manufactured by Kurosaki Hakudo Kogyo Co., Ltd. One type of bentonite may be used alone, or two or more types may be used in combination.

[0016] Water-absorbent material B is a polyalkylene oxide. Compared to water-absorbent material A, polyalkylene oxide exhibits relatively high water absorption and swelling ratio even in water containing high concentrations of inorganic salts or water containing divalent cations. Therefore, water-absorbent material B can swell sufficiently even in water containing a high concentration of inorganic salts.

[0017] As the polyalkylene oxide, polyethylene oxide and polypropylene oxide are preferred in terms of availability, with polyethylene oxide being more preferred. Commercially available polyalkylene oxides may be used. Commercially available polyethylene oxides and polypropylene oxides are available from, for example, Sumitomo Seika Chemicals Co., Ltd. and AGC Inc. The polyalkylene oxide may be used alone or in combination of two or more kinds.

[0018] The mass ratio (B / A) of the water-absorbent material B to the water-absorbent material A is 20 / 80 to 99 / 1. Since the mass ratio (B / A) is 20 / 80 or more, the blending ratio of the water-absorbent material A is sufficiently high, thereby ensuring a sufficient swelling rate of the water-absorbent sheet in fresh water or water containing trace amounts of inorganic salts. Since the mass ratio (B / A) is 99 / 1 or less, the blending ratio of the water-absorbing material B is sufficiently high, and therefore a sufficient swelling ratio can be ensured even in water containing high concentrations of inorganic salts or water containing divalent cations.

[0019] The mass ratio (B / A) is preferably 30 / 70 or more. When the mass ratio (B / A) is 30 / 70 or more, a high swelling ratio can be maintained in fresh water or water containing an extremely low concentration of inorganic salts, while also easily ensuring a high swelling ratio in water containing a high concentration of inorganic salts.

[0020] The mass ratio (B / A) is preferably 90 / 10 or less, more preferably 80 / 20 or less, even more preferably 60 / 40 or less, and particularly preferably 40 / 60 or less. When the mass ratio (B / A) is 90 / 10 or less, the swelling ratio of the water-absorbent sheet in fresh water becomes very high, and it is easy to maintain the swelling ratio required for practical use in water containing high concentrations of inorganic salts or divalent cations. When the mass ratio (B / A) is 80 / 20 or less, the water-absorbent sheet has a high swelling ratio in fresh water, and it is easy to ensure a sufficient swelling ratio in water containing high concentrations of inorganic salts or divalent cations. When the mass ratio (B / A) is 60 / 40 or less, the water-absorbent sheet can maintain a high swelling rate in fresh water, while also easily ensuring a high swelling rate in water containing high concentrations of inorganic salts or water containing divalent cations.

[0021] The total content of water-absorbent material A and water-absorbent material B per unit area is 30 g / cm 2 More than 100 to 1000 g / cm is preferable. 2 More preferably, 300 to 600 g / cm 2 It is more preferable that the total content per unit area of ​​water-absorbent material A and water-absorbent material B is at least the lower limit of the above-mentioned range, which makes it easier to ensure a sufficient swelling ratio of the water-absorbent sheet. When the total content per unit area of ​​water-absorbent material A and water-absorbent material B is at most the upper limit of the above-mentioned range, it makes it easier to reduce the production cost of the water-absorbent sheet.

[0022] The water-absorbent material may further contain water-absorbent materials other than water-absorbent material A and water-absorbent material B, as long as the effects of the invention are not impaired. Other water-absorbing materials include, for example, cellulose-acrylonitrile polymers, starch-acrylonitrile polymers, acrylic acid-vinyl alcohol copolymers, acrylic acid-acrylamide copolymers, and isobutylene-maleic anhydride copolymers.

[0023] The total proportion of water-absorbent material A and water-absorbent material B is preferably 20 to 100% by mass, more preferably 50 to 100% by mass, and most preferably 100% by mass, relative to 100% by mass of the water-absorbent material in the water-absorbent sheet. When the total proportion of water-absorbent material A and water-absorbent material B is equal to or greater than the lower limit of the aforementioned range, it is easy to obtain a water-absorbent sheet that swells sufficiently even in water containing a high concentration of inorganic salts. When the water-absorbent material contains other water-absorbent materials, when the total proportion of water-absorbent material A and water-absorbent material B is equal to or less than the upper limit of the aforementioned range, it is easy to adjust the water absorption and swelling rate depending on the other water-absorbent materials.

[0024] (thermal adhesive resin) In conventional waterproof sheets, such as the waterproof sheet for civil engineering described in Patent Document 1, a superabsorbent polymer is supported in a composite sheet formed by needle-punching first and second sheet-like substrates. As a result, the superabsorbent polymer is prone to falling off when the sheet is laid. As a result, workability is reduced and water absorption performance may be impaired. In contrast, in the water-absorbent sheet of the present invention, it is preferable that at least a portion of the water-absorbent material is adhered to the base sheet with a heat-sealing resin. When at least a portion of the water-absorbent material is adhered to the base sheet with a heat-sealing resin, the water-absorbent material containing water-absorbent material A and water-absorbent material B is less likely to fall off the water-absorbent sheet during installation. As a result, workability is improved and a decrease in water-absorbency performance due to the fall-off of the water-absorbent material can be prevented.

[0025] The heat-fusible resin is not particularly limited as long as it is a thermoplastic resin that exhibits heat adhesion in a heating oven when producing the water-absorbent sheet. Examples of heat-fusible 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. The heat-fusible resin may be used alone or in combination of two or more kinds.

[0026] The content of the heat-fusible resin is preferably 3 to 80 mass %, more preferably 10 to 50 mass %, and even more preferably 20 to 40 mass %, of the total content of the water-absorbent material A and the water-absorbent material B. When the content of the heat-fusible resin is equal to or greater than the lower limit of the above-mentioned range, the adhesive effect of the heat-fusible resin is easily exhibited. When the content of the heat-fusible resin is equal to or less than the upper limit of the above-mentioned range, the swelling rate of the water-absorbent sheet is less likely to be affected by the heat-fusible resin.

[0027] From the viewpoint of mass productivity, it is preferable to use a heat-fusible resin so that the fibrous thermoplastic resin is thermally bonded to other materials during the production of the water-absorbent sheet. The heat-fusible resin fiber may be a single yarn, a multifilament, or a fiber with a core-sheath structure. Examples of fibers with a core-sheath structure include the following: Polypropylene / polyethylene sheath-core fiber, which has polypropylene in the core and polyethylene in the sheath. Polyester / polyethylene core-sheath fiber, which has a polyester core and a polyethylene sheath. Polyester / low melting point polyester sheath-core fiber, which has polyester in the core and low melting point polyester in the sheath. Among these, polyester / polyethylene sheath-core fibers and polypropylene / polyethylene sheath-core fibers are preferred because they have excellent adhesive properties when heat-sealed. When a fiber having a core-sheath structure is used, the content of the heat-fusible resin includes the total amount of the resin in the core and the resin in the sheath.

[0028] As the core-sheath fiber, a commercially available product may be used. An example of a commercially available polypropylene / polyethylene core-sheath fiber is "NBF" manufactured by Daiwabo Holdings. An example of a commercially available polyester / polyethylene core-sheath fiber is "ETC" manufactured by ES Fiber Visions. An example of a commercially available polyester / low melting point polyester core-sheath fiber is "Melty" manufactured by Unitika Ltd.

[0029] (Properties of water-absorbent sheet) The thickness of the water-absorbent sheet is not particularly limited. For example, the thickness of the water-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 water-absorbent sheet is equal to or greater than the lower limit of the above-mentioned numerical range, the water-absorbent sheet has excellent mechanical properties. When the thickness of the water-absorbent sheet is equal to or less than the upper limit of the above-mentioned numerical range, the swelling pressure due to the absorption of water by water-absorbent material A and water-absorbent material B is easily obtained. Therefore, holes on the surface of the water-shielding sheet can be easily sealed, and water leakage into the ground can be easily prevented. The thickness of the absorbent sheet was measured using a constant pressure thickness gauge with a probe diameter of 30 mm and a measurable pressure of 20 g / cm. 2 It is measured under the following conditions.

[0030] The basis weight of the absorbent sheet is 30g / m 2 More than 200 to 2000 g / m 2 More preferably, 800 to 1200 g / m 2 When the basis weight of the water-absorbent sheet is at least the lower limit of the above-mentioned range, the water-absorbent sheet has excellent mechanical properties. When the basis weight of the water-absorbent sheet is at most the upper limit of the above-mentioned range, the workability when laying the sheet is excellent. The basis weight of the water-absorbent sheet is a value measured by measuring a 120 mm x 417 mm sample in an atmosphere of 23°C and 50% RH for at least 4 hours, measuring the weight with a weighing scale, and converting it into square meters.

[0031] The water permeability coefficient of the absorbent sheet is 5 x 10 -9 m / s or less is preferable, and 5×10 -10 m / s or less is more preferable, and 5×10 -11 When the water-absorbent sheet has a water permeability coefficient of not more than the upper limit of the above range, the water-absorbent sheet has excellent water-blocking properties. The coefficient of permeability of the water-absorbent sheet is a value measured in accordance with JIS A 1218 (Japanese Industrial Standards "Testing method for soil permeability").

[0032] The swelling ratio of the water-absorbent sheet in accordance with JBAS-104-77 is preferably 24 ml / 2 g or more, more preferably 30 ml / 2 g or more, and even more preferably 50 ml / 2 g or more. When the swelling ratio in accordance with JBAS-104-77 is equal to or greater than the lower limit of the above-mentioned range, it can be said that the water-absorbent sheet exhibits excellent swelling performance in distilled water. The upper limit of the swelling ratio in accordance with JBAS-104-77 is preferably as high as possible, and is not particularly limited. The swelling ratio according to JBAS-104-77 is a value measured in accordance with the "Standard Test Method" of the Japan Bentonite Industry Association.

[0033] The amount of powder shedding from the water-absorbent sheet is preferably 2.0 g or less, more preferably 1.0 g or less, and even more preferably 0.5 g or less. When the amount of powder shedding from the water-absorbent sheet is equal to or greater than the lower limit, the workability when laying the water-absorbent sheet is likely to be improved. In addition, it is easy to prevent a decrease in water absorption performance due to the shedding of the water-absorbent material. The less the amount of powder shedding from the water-absorbent sheet, the better, and there is no particular lower limit. The amount of powder falling off a water-absorbent sheet is measured as follows. That is, one corner of a water-absorbent sheet cut into a 100 mm x 100 mm square is pinched and hung above a tray, and the center of the water-absorbent sheet hanging above the tray is lightly tapped with a finger 10 times. Then, the position (corner) of the corner of the water-absorbent sheet that is pinched is changed, and the center of the water-absorbent sheet hanging above the tray is similarly tapped with a finger 10 times, and this operation is repeated. After hanging the sheet at all four corners and tapping with a finger, i.e., after a total of 40 taps, the amount of powder falling off onto the tray is taken as the amount of powder falling off.

[0034] The tensile strength of the water-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 water-absorbent sheet is equal to or greater than the lower limit, the water-absorbent sheet has excellent mechanical properties. There is no particular upper limit to the tensile strength of the water-absorbent sheet. For example, it is about 40 kN / m. The tensile strength of the water-absorbent sheet is a value measured in accordance with JIS L1908.

[0035] (Manufacturing method) The method for producing the water-absorbent sheet is not particularly limited. For example, a water-absorbent material and a thermoplastic resin are placed between two layers of base sheets. The sheets are then passed through a heating oven, and the water-absorbent material is supported between the two layers of base sheets by the heat-molten thermoplastic resin, thereby producing a water-absorbent sheet. During heating, it is preferable to disperse a heat-sealing resin between the two layers of base sheet together with the water-absorbing material. In this case, at least a portion of the water-absorbing material can be adhered to the base sheet by the heat-sealing resin. For example, a method can be used in which water-absorbing material A and water-absorbing material B, and optionally a heat-sealing resin, are dispersed on the surface of one layer of base sheet on a conveyor, and another layer of base sheet is laminated on top, followed by passing through a heating oven. When a heat-sealing resin is used, a water-absorbent sheet is obtained by heat treatment in which two layers of base sheet are bonded to each other by the heat-sealing resin and at least a portion of the water-absorbent material is bonded to the base sheet by the heat-sealing resin.

[0036] (Mechanism of action) The absorbent sheet described above has an absorbent material between two layers of base sheet, so when a hole appears in the sheet, water passes through the base sheet and comes into contact with the absorbent material, causing the absorbent material to swell and seal the hole in the waterproof sheet. Here, water-absorbent material A exhibits excellent water-absorbency in fresh water and can swell sufficiently, while water-absorbent material B, i.e., polyalkylene oxide, exhibits relatively high water-absorbency and can swell sufficiently even in water containing high concentrations of inorganic salts or divalent cations. In the water-absorbent sheet of the present invention, the mass ratio of water-absorbent material A to water-absorbent material B is within a predetermined range, ensuring sufficient blending amounts of water-absorbent material A and water-absorbent material B. Therefore, the water-absorbent sheet of the present invention can swell sufficiently in both fresh water and water containing a high concentration of inorganic salts. Therefore, the water-absorbent sheet of the present invention can provide a water-leakage equipment whose leakage prevention effect is not easily impaired even when the salt concentration of inorganic salts is high.

[0037] <Waterproofing equipment> The water-blocking equipment of the present invention comprises the above-described water-absorbent sheet of the present invention and a water-blocking sheet disposed on the outside of the base sheet of the water-absorbent sheet. Because the water-blocking equipment of the present invention comprises the water-absorbent sheet of the present invention, the water-absorbent sheet swells sufficiently even when the salt concentration of inorganic salts is high. Therefore, the water-blocking equipment of the present invention is less likely to lose its water leakage prevention effect.

[0038] (Waterproof sheet) The waterproof sheet is not particularly limited as long as it is a sheet-shaped substrate that has water-proof properties, i.e., the property of preventing the permeation of water molecules. Examples include polyethylene sheets, polypropylene sheets, polyester sheets, vinyl chloride sheets, rubber sheets, asphalt-based sheets, and rubber-asphalt-based sheets.

[0039] The waterproofing system may include one waterproof sheet or multiple waterproof sheets. When multiple waterproof sheets are included, the multiple waterproof sheets may be the same or different. Furthermore, the waterproof sheets may be placed on both surfaces of the water-absorbent sheet or on one surface.

[0040] (protective sheet) The waterproofing facility may further comprise one or more protective sheets in addition to the water-absorbing sheet and waterproofing sheet of the present invention. When multiple protective sheets are provided, the multiple protective sheets may be the same as or different from each other.

[0041] The protective sheet is a sheet for protecting the water-absorbent sheet or the water-blocking sheet from damage. Examples of the protective sheet include knitted fabric, woven fabric, and nonwoven fabric. From the viewpoint of strength, a long-fiber nonwoven fabric such as a spunbond nonwoven fabric is preferred as the protective sheet. The material of the protective sheet is not particularly limited, and examples thereof include polyethylene, polypropylene, polyester, vinyl chloride, and composites of these materials.

[0042] The protective sheet may be disposed in contact with the water-absorbent sheet of the present invention. In this case, a laminated structure in which the water-absorbent sheet, the protective sheet, and the water-shielding sheet are laminated in this order can be formed as a water-shielding facility. The protective sheet may be placed on the outside of the water-absorbent sheet with a water-shielding sheet interposed therebetween. In this case, a layered structure in which the water-absorbent sheet, the water-shielding sheet, and the protective sheet are layered in this order can be formed as a water-shielding facility.

[0043] When a plurality of protective sheets are provided, some of the protective sheets may be arranged in contact with the water-absorbent sheet, and the remaining protective sheets may be arranged outside the water-absorbent sheet via a water-shielding sheet. All of the protective sheets may be disposed in contact with the water-absorbent sheet, or all of the protective sheets may be disposed outside the water-absorbent sheet with a water-shielding sheet interposed therebetween.Furthermore, the protective sheets may be used by overlapping each other. <Experimental Example>

[0044] The present invention will be specifically described below with reference to experimental examples, but the present invention is not limited to the following description.

[0045] <Raw materials> (Water absorbent material A) Water-absorbent material A1: Sodium polyacrylate (Oji Kinocloth Co., Ltd. product "SA-GM")

[0046] (Water absorbent material B) Water-absorbent material B1: Polyethylene oxide (Sumitomo Seika Chemicals Co., Ltd. product "Aquacork TWP")

[0047] <Water absorption test> Powders were prepared with the blends shown in Table 1. Each of these powders was tested for water absorption in ion-exchanged water, a 0.9% by mass aqueous solution of calcium chloride, and an 8.1% by mass aqueous solution of calcium chloride. First, a test bag was prepared and the test sample powder was placed in the bag. Next, ion-exchanged water, a 0.9% by mass calcium chloride aqueous solution, or an 8.1% by mass calcium chloride aqueous solution was poured into the test bag, and the mass of the bag was measured after 1 hour, 3 hours, and 24 hours. The swelling ratio (times) based on mass of the powder for each formulation is shown in Table 2.

[0048] [Table 1]

[0049] [Table 2]

[0050] Blend 1 does not contain the water-absorbing material B1. Blend 1 showed a high swelling rate in the test using ion-exchanged water. However, the swelling ratio was significantly lower in tests using a 0.9% by mass calcium chloride aqueous solution and in tests using an 8.1% by mass calcium chloride aqueous solution. These results indicate that when Blend 1 is used in a water-absorbent sheet, sufficient water absorption is not achieved for water containing high concentrations of inorganic salts. In addition, when this water-absorbent sheet is used in water-blocking equipment, it may not be able to achieve sufficient water leakage prevention effects.

[0051] In Blend 2, the mass ratio of water-absorbent material B1 to water-absorbent material A1 (B1 / A1) was 20 / 80. Blend 2 showed a high swelling rate in tests using ion-exchanged water. Furthermore, in tests using a 0.9% by mass calcium chloride aqueous solution and an 8.1% by mass calcium chloride aqueous solution, the swelling rate was 1.5 times that of Blend 1 after 1 hour, and twice that of Blend 1 after 3 and 24 hours. These results show that the water-absorbing sheet and water-blocking equipment using Blend 2 can achieve significant improvements compared to Blend 1.

[0052] In Blend 3, the mass ratio of water-absorbent material B1 to water-absorbent material A1 (B1 / A1) was 40 / 60. Blend 3 maintained a high swelling rate in tests using ion-exchanged water. Furthermore, in tests using 0.9% by mass calcium chloride aqueous solution and 8.1% by mass calcium chloride aqueous solution, Blend 3 showed an even higher swelling rate than Blend 2. These results show that the water-absorbing sheet and water-blocking equipment using Blend 3 can achieve even more significant improvement than Blend 1.

[0053] In Mix 4, the mass ratio of water-absorbent material B1 to water-absorbent material A1 (B1 / A1) is 60 / 40. In tests using ion-exchanged water, Mix 4 showed a lower expansion rate than Mix 1, but maintained performance sufficient for use in waterproofing facilities. Furthermore, in tests using a 0.9% by mass calcium chloride aqueous solution and a 8.1% by mass calcium chloride aqueous solution, it showed an even higher expansion rate than Mix 3. These results show that by using a water-absorbing sheet that employs formulation 4 in waterproofing equipment, it is possible to achieve a good balance of waterproofing against both fresh water and water containing high concentrations of inorganic salts.

[0054] In Mix 5, the mass ratio of water-absorbent material B1 to water-absorbent material A1 (B1 / A1) is 80 / 20. In tests using ion-exchanged water, Mix 5 showed a lower expansion rate than Mix 1, but maintained performance suitable for use in waterproofing facilities. Furthermore, in tests using a 0.9% by mass calcium chloride aqueous solution and a 8.1% by mass calcium chloride aqueous solution, it showed an even higher expansion rate than Mix 4. These results show that by using a water-absorbing sheet that employs Blend 5 in a water-blocking facility, it is possible to create a water-blocking facility that is water-blocking to fresh water and suitable for locations prone to the generation of contaminated water containing high concentrations of inorganic salts. If even greater water absorption to fresh water is required, it will increase costs, but it is also possible to obtain the desired water-absorbing performance by increasing the amount of water-absorbing material used per unit area of ​​the water-absorbing sheet.

[0055] Blend 6 does not contain the water-absorbent material A1. Blend 6 has a low expansion coefficient in ion-exchanged water, and the water-absorbent sheet obtained using Blend 6 has low water absorbency, making it difficult to apply to a waterproof sheet. In the case of Mix 6, if the amount of absorbent material per unit area of ​​the absorbent sheet is increased to achieve the desired absorbency, the strength of the absorbent sheet itself will decrease. Therefore, it is thought that there is a high possibility that the absorbent sheet will be damaged when the waterproofing equipment is installed. [Industrial Applicability]

[0056] According to the present invention, there is provided a water-absorbent sheet that can provide a water-leakage facility in which the water-leakage prevention effect is not easily impaired even when the salt concentration of inorganic salts is high.

Claims

1. A water-absorbent sheet having a water-absorbent material and a fibrous heat-fusible resin dispersed together with the water-absorbent material between two layers of base sheet, The water-absorbing material is a blend of a powder of a water-absorbing material A, which is sodium polyacrylate, and a powder of a water-absorbing material B, which is polyalkylene oxide; At least a portion of the water-absorbing material is adhered to the base sheet by the fibrous heat-fusible resin, a mass ratio of the powder of the water-absorbing material B to the powder of the water-absorbing material A is 20 / 80 to 80 / 20; The water-absorbent sheet has a content of the fibrous heat-fusible resin of 10 to 50% by mass relative to the total content of the powder of the water-absorbent material A and the powder of the water-absorbent material B.

2. 2. The water-absorbent sheet according to claim 1, wherein the base sheet is a nonwoven fabric.

3. The water-absorbent sheet according to claim 1 or 2; A waterproof sheet disposed on the outer side of the base sheet of the water absorbent sheet; Equipped with water-proofing equipment.

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