JPH11319553A - Water absorbent and absorption sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify production work to stabilize quality, and to improve the flexibility and a water absorption rate of an absorption sheet produced with a water absorbent. SOLUTION: A water absorbent 1 is obtained from a gel adhesive agent essentially composed of a polyacrylic acid and/or a polyacrylate, a polyhydric alcohol such as glycerin, and a crosslinking agent such as polyethylene glycol diglycidyl ether. An absorption sheet B having a sandwich structure is obtained by sandwiching this water absorbent 1 between two sheet-like fiber materials 2, in which a hydrophilic fiber such as a rayon polyolefin nonwoven fabric is mixed, so that a part of the fiber materials 2 enter into the water absorbent 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a water absorbing agent and a water absorbing sheet. Specifically, the present invention relates to a water-absorbing sheet used as a sanitary article, a disposable diaper, an operation sheet, an incontinence sheet, a bed sheet, a bed sheet for the elderly, a dewatering sheet for food, and a water-absorbing agent suitable for the water-absorbing sheet.

[0002]

2. Description of the Related Art A water-absorbing sheet is used to absorb and retain moisture. Generally, a water-absorbing agent such as a water-absorbing polymer or a web is sandwiched between two sheets. Alternatively, it is configured to be held in a bag-shaped sheet material. As the sheet-like material, a nonwoven fabric or the like that transmits moisture from the outside but does not leak the water-absorbing agent that has absorbed the transmitted moisture is used. For example, a disposable diaper includes a top sheet that directly contacts the skin, a back sheet that prevents leakage of urine from the disposable diaper, and a water-absorbing agent that absorbs and retains excretions such as urine. It is pinched by the sheet.

As the water-absorbing polymer, those having high liquid absorbing properties are used. For example, acrylic acid-based polymers, starch / acrylate graft-based polymers, isobutylene / maleate copolymer-based polymers, and vinyl alcohol / acrylate copolymers Polymerized polymers and polyvinyl alcohol-based polymers are commercially available. Among them, acrylic acid polymers including graft polymers are dominant.In these polymers, unlike sponges and cottony pulp, unlike moisture taken in by porous holes and capillary action, polymer Has the characteristic that the moisture absorbed in the tub is not pushed out even by pressure and is kept as it is. The water-absorbing polymer is usually 40 to 80 times its own weight as a physiological saline solution (for reference, about 5 to 16 times its own weight for cottony pulp and about 2 to 5 times its own weight for water-absorbing paper for reference). .).

[0004] These water-absorbing polymers are generally produced in a powdered state, and for example, in the above-mentioned disposable diapers, usually 250 particles are used.
A powdery polymer of ４５０450 μm is used. But,
In the powder state, the water-absorbing polymer has a low water-absorbing rate and is not practical.In order to improve the water-absorbing rate, the surface area of the water-absorbing polymer is increased, and a method of supporting the powdery polymer in a web made of cotton-like pulp is used. Various devices have been devised such as utilizing the capillary phenomenon.

It is generally known that the rate of water absorption of a water-absorbing polymer is more affected by physical factors than its chemical composition. For this reason, a method for increasing the surface area capable of achieving the object by a relatively simple method as much as possible has been widely used.

However, if the particle size is reduced in order to increase the surface area, a so-called Mamako phenomenon occurs, and conversely, water absorption is hindered. For this reason, it was difficult to substantially increase the water absorption rate by simply reducing the particle diameter.

Further, in order to utilize the capillary phenomenon, fibers such as cotton-like pulp are used in combination as described above. In this case, the cotton-like pulp and the water-absorbing polymer are uniformly mixed. It is common to use a method such as spraying a water-absorbing polymer between two cotton-like pulp layers.

[0008] However, in such a method, the water-absorbing polymer is merely supported on the floc pulp.
In this state, the powder of the water-absorbing polymer easily moves in the web, and there is a disadvantage that the water-absorbing polymer spills from the web. In addition, there is a problem that there is a limit to the amount of water absorbed only by being supported on fibers.

On the other hand, in order to reduce the loss of the water-absorbing polymer, the water-absorbing polymer may be processed into a sheet by any method, such as a powdery water-absorbing polymer sandwiched between two sheets of paper, A sheet-shaped water-absorbing agent in which the surface of a nonwoven fabric is coated with a fine powder of a water-absorbing polymer has also been developed. In addition, as another method, a method in which an aqueous solution of a monomer is impregnated into a fiber woven into a sheet and then polymerized to impregnate the fiber with a water-absorbing polymer, or an aqueous solution of the monomer is applied to the fiber woven into a sheet A method in which the surface portion of the sheet-like fiber material is converted into a water-absorbent resin by a chemical reaction, for example, by cross-linking, and then the water-absorbent resin itself is converted into a fiber by, for example, forming a water-soluble polyacrylate into a fibrous material and then curing. A method of forming the sheet into a sheet shape has also been devised.

However, the sheet-like water-absorbing agent obtained by these methods is generally hard and lacks flexibility, and requires a high level of technology in the production method, and the quality varies greatly. There were problems such as getting out.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and aims at simplifying the manufacturing operation and attaining a quality which cannot be attained with the conventional sheet-like water absorbing agent. The purpose of the present invention is to stabilize the water and improve the flexibility and water absorption rate of an absorbent sheet produced using the obtained water absorbing agent.

The inventors of the present invention have made intensive efforts to achieve the above-mentioned object, and as a result, by using a gel-like adhesive having a specific composition, the adhesiveness of the adhesive has been reduced to a degree that the adhesiveness to the sheet-like fiber material can be reduced. It has been found that the water absorption rate can be improved by facilitating the alignment and by embedding the fibers in the pressure-sensitive adhesive by pressing the sheet-like fiber material, thereby completing the present invention.

[0013]

The water absorbing agent according to the present invention comprises:
It is characterized by comprising a gel adhesive containing polyacrylic acid and / or polyacrylate, polyhydric alcohol and a crosslinking agent as essential components.

The polyacrylic acid and / or polyacrylic acid salt constituting the gel pressure-sensitive adhesive is the basis of the water-absorbing function, and can sufficiently exhibit the function as an absorbent polymer by crosslinking. . The molecular weight of such polyacrylic acid and / or polyacrylate is preferably from 20,000 to 10,000,000 (weight average molecular weight, the same applies hereinafter). From the viewpoint that can be easily done,
Those having a relatively low molecular weight range of 20,000 to 500,000 are desirable.
Further, it is preferable that the polymer concentration of the polyacrylic acid and / or polyacrylate is 2 to 30% by weight in the gel adhesive.

The polymer may be used alone with polyacrylic acid or polyacrylate. However, from the viewpoint of water absorption ability and irritation due to contact with the skin, an aqueous solution of polyacrylic acid is used in a part of the polymer. It is preferable to add the gel adhesive and adjust the pH to 6 to 7. At this time, a mixture of polyacrylic acid and polyacrylate may be used. In this case, the ratio of polyacrylate to polyacrylic acid is set to be 10: 0 to 6: 4 by weight. It is desirable.

The salt in the polyacrylate is not particularly limited, but it is preferable to use a pharmacologically acceptable salt in consideration of use in humans and food. For example, sodium salts, potassium salts, triethanolamine salts and the like can be mentioned. Among them, it is desirable to use a sodium salt because of its excellent water absorbing ability and inexpensiveness. Therefore, when neutralizing polyacrylic acid, an alkali agent such as sodium hydroxide, potassium hydroxide, or triethanolamine may be used.

Next, polyhydric alcohols usable in the present invention include dihydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol and 1,3-propanediol, and trihydric alcohols such as glycerin. Sorbitol, polyethylene glycol, etc., having at least one or more alcohol groups. These polyhydric alcohols function as a plasticizer for the obtained gel adhesive and also function to promote the diffusion of the polymer into water. In particular, glycerin is advantageous in that it has good affinity for polymers and can be obtained at low cost. Usually, the amount of the polyhydric alcohol used is preferably set to 10 to 70% in terms of dry weight based on the total weight of the gel adhesive. At this time, if it is less than 10%, the gel pressure-sensitive adhesive tends to be hardened when dried, and if it exceeds 70%, the blending ratio of the polymer is reduced by that amount, and the water absorption is undesirably reduced.

The water-absorbing agent according to the present invention is obtained by cross-linking the above polymer with a cross-linking agent to form a gel pressure-sensitive adhesive. The crosslinking agent is not particularly limited as long as it is a crosslinking agent, for example, aluminum hydroxide or dried aluminum hydroxide gel, potassium alum, magnesium chloride, aluminum sulfate, aluminum glycinate, aluminum acetate, aluminum oxide, calcium hydroxide, carbonate Examples thereof include metal salts such as calcium and aluminum metasilicate, amine compounds such as polyethyleneimine, and epoxy compounds. In this case, as the epoxy compound, a compound containing at least two or more epoxy groups in a molecule is preferable because of a large contribution of water absorption ability by a crosslinking effect. For example, as the epoxy compound, polyethylene glycol diglycidyl ether, Glycerin triglycidyl ether, triglycidyl isocyanurate and the like can be mentioned. The amount of these crosslinking agents varies depending on the type of crosslinking agent,
Usually, it is used in the range of 0.1 to 10% in terms of dry weight based on the total weight of the gel adhesive. When used in excess of 10%, the water absorption is rather reduced, and the gel hardness of the gel pressure-sensitive adhesive is increased, so that the tackiness is weakened. on the other hand,
If it is less than 0.1%, there is a risk that the water-absorbing agent leaks from the sheet-like fiber material to be bonded later.

The water absorbing agent of the present invention can be obtained as follows. A predetermined amount of an alkali agent and a polyhydric alcohol are added to an aqueous solution in which polyacrylic acid and polyacrylate are mixed at a predetermined mixing ratio or an aqueous solution of polyacrylic acid, and then a crosslinking agent is added. The acid and / or polyacrylate is cross-linked. Then, if necessary, the composition is applied on a sheet-like fiber material or another sheet-like support as described below, and then dried to obtain a gel adhesive. At this time, the moisture content after drying is preferably 4 to 20% by weight in the water absorbing agent. 4 moisture
%, The obtained gel pressure-sensitive adhesive becomes hard and loses flexibility, and if it exceeds 20%, there is a possibility that the gel pressure-sensitive adhesive will break through from a sheet-like fiber material or other water-permeable sheet-like support. is there.

The water-absorbing agent (gel pressure-sensitive adhesive) thus obtained may contain the above-mentioned components as essential components, and, if necessary, other conventional pressure-sensitive adhesives such as antioxidants, coloring agents and fragrances. Various additives that can be contained in the agent can also be added.

[0021]

Next, an absorbent sheet according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic structural diagram showing one embodiment of the absorbent sheet according to the present invention, FIG. 2 is a schematic structural diagram showing another embodiment of the absorbent sheet according to the present invention, and FIG. It is a schematic structure figure showing a form.

The water-absorbing sheet A shown in FIG. 1 has a water-absorbing agent 1 according to the present invention formed into a sandwich structure by two sheet-like fiber materials 2. The water-absorbing agent 1 is usually used in a state of being applied on the sheet-like fiber material 2 or another sheet-like support as described above. The sheet-shaped support is not particularly limited in material and structure, as long as the sheet-shaped support is permeable to water and does not strike through the applied water-absorbing agent 1 like the sheet-shaped fiber material 2. . For example, aggregates of various fibers such as woven fabric, nonwoven fabric, knitted fabric, felt, paper using natural fibers such as cotton, and synthetic fibers such as rayon, acetate, polyester, polyethylene, and polypropylene, as well as others A single film or sheet of polyester, nylon, Saran, polyethylene, polypropylene, ethylene / vinyl acetate copolymer, ethylene / ethyl acrylate copolymer, polytetrafluoroethylene, ionomer, polyacrylonitrile resin, or a laminate thereof Examples of the film include a moisture-permeable film and a porous film, which are appropriately selected according to the purpose of use of the water-absorbing sheet.

At this time, the water absorbing effect can be further enhanced by combining with the sheet-like fiber material 2. In order to further increase the water absorbing speed, it is preferable to use a hydrophilic fiber such as rayon or cotton. On the other hand, when the sheet-like fiber material 2 composed of only the hydrophilic fibers is used, a sticky feeling is given after absorbing the liquid, and the strength is weakened. Therefore, it gives a dry feel even when absorbing liquid,
In order to increase the strength, it is desirable to use a nonwoven fabric such as rayon polyolefin in which a hydrophobic material such as polyethylene or polypropylene is mixed with these hydrophilic materials. Further, from the viewpoint of prevention of strike-through of the water-absorbing agent 1, the basis weight of the sheet-like fiber material 2 used is 2
0 to 300 g / m ² , preferably 70 to 200 g / m ² , and a thickness of 0.2 to 3 mm, preferably 1 to 2
mm.

At this time, it is preferable that at least a part of the sheet-like fiber material 2, preferably the entire surface of the sheet-like fiber material 2 like the water-absorbing sheet B shown in FIG. The water-absorbent sheet B can be obtained, for example, by applying an aqueous solution of the water-absorbing agent 1 to one of the two sheet-like fiber materials 2, drying the solution, and then pressing the remaining sheet-like fiber material 2. it can. As described above, at least a part of the sheet-like fiber material 2 is penetrated into the water-absorbing agent 1, so that the part of the sheet-like fiber material 2 that has penetrated into the water-absorbing agent 1 exhibits a capillary phenomenon, and a water diffusion rate. And the water absorption speed can be further increased.

Further, in the case of the water absorbing sheet C shown in FIG.
A water-impermeable film 3 is laminated on the outer surface of one of the sheet-like fiber materials 2. The material of the water-impermeable film 3 is not particularly limited, and examples thereof include various synthetic resin films such as a polyethylene film, a polypropylene film, a polyurethane film, and a nylon film, and metal thin films such as aluminum. As described above, by laminating the water-impermeable film 3 on the outer surface of one of the sheet-like fiber materials 2, the moisture or moisture that has penetrated and penetrated through the remaining one of the sheet-like fiber materials 2 was absorbed. The water-absorbing agent 1 can be prevented from leaking from the sheet-like fiber material 2 on the opposite side. Further, by forming a sandwich structure by two sheet-like fiber materials 2, for example, in the case of application to a disposable diaper, an aqueous solution of a gel adhesive may be directly applied to either a top sheet or a back sheet. There is also an advantage that the process can be greatly simplified.

If the absorbent sheet 1 is sandwiched between the two sheet-like fiber materials 2 and the absorbent sheet is made to have a sandwich structure, the water absorption speed can be further increased. However, it is not always necessary to make the sandwich structure. The sheet-like support may be made of the sheet-like fiber material 2 and a water-impermeable sheet-like support may be attached to the remaining exposed surface. Furthermore, it is conceivable that the water-absorbing agent according to the present invention is laminated on the sheet-like support that has been subjected to the easy-peeling treatment, and the sheet-like support is peeled off at the time of use to make it usable.

[0027]

Next, a water absorbing agent and an absorbent sheet according to the present invention were produced. In addition, this invention is not limited to a following example.

Example 1 20 g of polyacrylic acid was added to water 2
4 g, and further added 45 g of glycerin to sufficiently dissolve. Then, 10 g of sodium hydroxide was added to this aqueous solution, and a part of polyacrylic acid (85% of carboxyl groups) was added.
(Equivalent amount). Further, a solution prepared by dissolving 0.1 g of methyl paraoxybenzoate in 0.5 g of ethanol as a preservative was added and stirred. To this solution, 0.34 g of triglycidyl isocyanurate was previously added to 6.5 g of hot water.
Was added and the mixture was stirred and uniformly dissolved to obtain a solution of a water absorbing agent.

Then, the obtained solution is applied to the easily peeled surface of a 50 μm-thick polyester film separator (which is later peeled and discarded) having one surface subjected to an easy peeling treatment, so that the coating thickness after drying is obtained. It was applied so as to have a thickness of 80 μm, and then a non-woven fabric (having a basis weight of 40 g / m ² ) consisting of a mixed fiber of polyester / hemp / pulp was stuck thereon. This was dried at 80 ° C. for 10 minutes using a hot air drier, the separator was peeled off, and another nonwoven fabric made of the same material was stuck to the adhesive surface of the separator to form a sandwich structure of Example 1, Was prepared. Note that, in the absorbent sheet, a part of the nonwoven fabric had entered the water absorbing agent layer (adhesive layer).

Example 2 20 g of polyacrylic acid was added to water 2
4 g, and further added 45 g of glycerin to sufficiently dissolve. Then, 10 g of sodium hydroxide was added to this aqueous solution, and a part of polyacrylic acid (85% of carboxyl groups) was added.
(Equivalent amount). Further, a solution prepared by dissolving 0.1 g of methyl paraoxybenzoate in 0.5 g of ethanol as a preservative was added and stirred. To this solution, 0.1 g of dried aluminum hydroxide gel was added, stirred, and uniformly dissolved to obtain a solution of a water absorbing agent.

Next, the obtained solution is applied to the easily peeled surface of a 50 μm-thick polyester film separator (which is later peeled and discarded), which has been subjected to an easy peeling treatment on one side, and the coated thickness after drying. Is 80 μm,
Next, a non-woven fabric (having a basis weight of 40 g / m ² ) composed of a mixed fiber of rayon / polyolefin was bonded thereon.
This was dried at 80 ° C. for 10 minutes using a hot air drier, then the separator was peeled off, and a laminated film of polyester film (thickness 2 μm thick) / non-woven fabric made of polyester (basis weight 40 g / m ² ) on the adhesive surface Were bonded to each other to produce an absorbent sheet of Example 2 having a sandwich structure. Note that, in the absorbent sheet, a part of the nonwoven fabric had entered the water absorbing agent layer (adhesive layer).

[0032]

The water-absorbing agent according to the present invention comprises a gel adhesive containing polyacrylic acid and / or polyacrylate, a polyhydric alcohol and a crosslinking agent as essential components. Since the polyhydric alcohol is contained, the diffusion rate of water in the water absorbing agent is improved, and the water absorbing rate can be improved. In addition, since it has adhesiveness, it has good adhesion to a support or the like, and can be easily manufactured by the same steps as those for manufacturing an ordinary adhesive.

In particular, by using glycerin as the polyhydric alcohol, it can be produced at low cost and has good affinity with the polymer. In addition, by using an epoxy compound as a cross-linking agent, the water absorption can be further improved.

The absorbent sheet according to the present invention is characterized in that the water-absorbing agent according to the present invention is laminated on one surface of a water-permeable sheet-like support. By laminating the water-absorbing agent of the present invention on a sheet-like support as described above, an absorbent sheet having a high water-absorbing rate can be obtained by a simple process. In addition, since the water-absorbing agent is made of an adhesive, a flexible water-absorbing sheet can be obtained.

Further, by forming the water absorbing agent into a sandwich structure with two sheet-like supports, it becomes possible to absorb water from both sides of the water absorbing sheet. Further, by laminating a water-impermeable film on the outer surface of one of the sheet-like supports, the moisture permeating the sheet-like support or the water-absorbing agent that has absorbed the moisture can be applied to the water-absorbing agent layer (adhesive layer). Agent layer) and does not leak out from the opposite side.

At this time, by using the sheet-like fiber material for the sheet-like support, a capillary phenomenon occurs, and the water absorption speed can be further increased. In particular, when a sandwich structure is used with a sheet-like fiber material, the water absorption rate can be more effectively increased. Further, by using a sheet-like fiber material containing hydrophilic fibers, the water absorption speed is increased and the water absorption capacity is improved.

Further, by causing at least a part of the sheet-like fiber material to enter the laminated water-absorbing agent, the capillary effect is more effectively exhibited, and the water-absorbing speed can be further improved. .

[Brief description of the drawings]

FIG. 1 is a schematic structural view of an absorbent sheet according to an embodiment of the present invention.

FIG. 2 is a schematic structural view of an absorbent sheet according to another embodiment of the present invention.

FIG. 3 is a schematic structural view of an absorbent sheet according to still another embodiment of the present invention.

[Explanation of symbols]

A, B, C Absorbing sheet according to the present invention 1 Water-absorbing agent 2 Sheet-like fiber material (sheet-like support having water permeability) 3 Water-impermeable film

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C08L 101/14 C08L 101/14 // C09J 133/02 C09J 133/02 (72) Inventor Fumiya Shirai 1 Shimohozumi, Ibaraki-shi, Osaka 1-2, Nitto Denko Corporation

Claims (9)

[Claims] 1. A water-absorbing agent comprising a gel adhesive comprising polyacrylic acid and / or polyacrylate, a polyhydric alcohol and a crosslinking agent as essential components. 2. The water-absorbing agent according to claim 1, wherein the polyhydric alcohol is glycerin. 3. The water-absorbing agent according to claim 1, wherein the crosslinking agent is an epoxy compound. 4. An absorbent sheet, wherein the water-absorbing agent according to claim 1, 2 or 3 is laminated on one surface of a sheet-like support having water permeability. 5. The absorbent sheet according to claim 4, wherein said water absorbing agent has a sandwich structure between two sheet-like supports. 6. The absorbent sheet according to claim 5, wherein a water-impermeable film is laminated on the outer surface of one of the sheet-like supports. 7. The absorbent sheet according to claim 4, wherein the sheet-like support is a sheet-like fiber material. 8. The absorbent sheet according to claim 7, wherein the sheet-like fiber material contains a hydrophilic fiber. 9. The absorbent sheet according to claim 7, wherein at least a part of the sheet-like fiber material has penetrated into the laminated water absorbing agent.