JP3009574B2 - Porous water-absorbing resin and water-absorbing article using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to a porous water-absorbent resin and <br/> sheet absorbent <br/> product articles for hygiene or for foods using the same.

[0002]

2. Prior Art and Problems to be Solved by the Invention
Since the conventional water-absorbent resin is in the form of powder, the water-absorbent article using the same is mostly made of a water-absorbent resin that is easily processed by secondary processing into a sheet shape using a certain holding carrier. For example, there are known a water-absorbent sheet in which a water-absorbent resin powder is mixed and laminated with pulp and used as a paper diaper, and a so-called drip sheet in which the water-absorbent resin powder is sandwiched by paper and used as an underlay of food.

On the other hand, recently, various sheets of water-absorbent resins or water-absorbent articles have been developed and marketed in order to improve the handleability. Such sheet-shaped water-absorbent resin or water-absorbent article is roughly classified as follows. (1) A sheet-like product obtained by sandwiching a particulate water-absorbent resin between sheets (2) A product obtained by processing water-absorbent fibers into a nonwoven fabric (3) A water-absorbent resin polymerized into a film ) Is the most commonly used, but it is easy to move, drop,
There is a problem that the sheet is likely to be deformed (made cylindrical) and decomposed, and the water-absorbent resin is spilled from the cut portion of the sheet, so that the sheet cannot be cut freely. Various measures have been taken to address these problems, but desired performance (fixing of resin before and after water absorption and water absorption speed and amount) cannot be obtained, resulting in high cost.

On the other hand, the method (2) has been adopted in recent years because it can be cut freely and can prevent the resin from falling off from a cutting opening. Representative examples of (2) are as follows. A) Nonwoven fabric using fibers obtained by kneading a fine powder of a water-absorbent resin into a thermoplastic resin (Japanese Patent Laid-Open No. 3-20364) b) Nonwoven fabric using a polymer obtained by directly polymerizing a water-absorbent resin into a fibrous form JP-A-3-45769, 3-9794
No. 8) c) Water-absorbing fibers imparted with water-absorbing ability by hydrolyzing acrylic fibers (Japanese Patent Publication Nos. 52-42916 and 58-1)
No. 0508, No. 5,735,286). However, the non-woven fabric of the above item a) is extremely fine (1).
It is manufactured by kneading a water-absorbent resin (less than 0 μm) into a thermoplastic resin and melt-spinning based on a conventional spinning method.
The fine powdered water-absorbing resin has poor handling properties (dust, moisture absorption, etc.), and the water-absorbing resin is easily detached from the fiber after absorbing water, and the compatibility between the water-absorbing resin and the thermoplastic resin is not good. is there. On the other hand, there has been proposed a method of kneading a copolymer-type water-absorbent resin into a thermoplastic resin and melt-spinning in order to increase compatibility with the thermoplastic resin and prevent the resin from falling off after water absorption ( JP-A-3-93815),
This leads to a decrease in water absorption and an increase in cost. Further, before and after water absorption, the water absorption is not sufficient to maintain the fiber shape due to the limit of the amount of the water-absorbing resin added to the thermoplastic resin.

[0005] On the other hand, the nonwoven fabric of the above item b) has recently been receiving attention, but its practical use is difficult due to the following problems. (a) If the shape of the water-absorbent resin is simply a fiber shape, it can be used only in the form of spraying, mixing on pulp, or sandwiching with paper, non-woven fabric, or the like, like the powdery water-absorbent resin.

(B) When processed into a nonwoven fabric in order to improve the handleability, the number of manufacturing steps increases, and the cost becomes considerably higher than that of a powdery water-absorbent resin. That is, when the steps are roughly classified, the following steps are required. I. Raw resin production process (production of water-soluble resin such as polyacrylic acid) II. Fiber molding process (crosslinking process for water insolubility) III. Non-woven fabric manufacturing process (secondary processing such as inter-fiber bonding) (c) In the case of secondary processing into non-woven fabric, the current water-absorbing fibers are short fibers (mostly 60 mm or less). Fibers are often dropped off, or the strength of the sheet itself is insufficient.

(D) Since the polyacrylate used as the water-absorbing resin is not of the heat-adhesive type, it is difficult to form a sheet of a non-woven fabric or the like by using the fiber alone, and even when mixed with other synthetic fibers, Adhesion must be performed using an adhesive or a heat-sealing fiber (Japanese Unexamined Patent Publication (Kokai) Nos. 3-45769 and 3-45769).
97948). Further, it cannot be said that the prevention of collapse of the adhesive points and the movement and falling off of the resin fibers before and after water absorption of the obtained sheet are still insufficient.

(E) Inexpensive aqueous adhesives and emulsion adhesives cannot be used in the production of nonwoven fabrics (because the water-absorbing resin absorbs water and swells in the bonding step), which not only limits the production method but also Leads to increased costs.
On the other hand, the solvent-based adhesive forms a hydrophobic film on the surface of the water-absorbing resin, and inhibits water absorption. In addition, solvent-based adhesives are not preferable in terms of environmental hygiene.

(F) In order to be processed into a nonwoven fabric, it is necessary to apply a machine, so that in addition to the properties as a water-absorbent resin, the properties as fibers (for example, the fibers are crimped) are required. It is difficult to achieve both. Further, as described in (c) above, the following problems also occur in the water-absorbing fiber having the water-absorbing ability imparted by hydrolyzing the acrylic fiber.

(I) Since a hydrolysis step is required, the cost is increased. (II) In the hydrolysis, only the sheath portion of the fiber is converted into a water-absorbing resin, so that the water absorption amount is insufficient as a whole. (III) If the degree of hydrolysis is increased to increase the water absorption, the ratio of the core of the fiber decreases, and the fiber strength, which is one of the major characteristics of this type of water-absorbing fiber, decreases.

(IV) The same problems as (d) and (e) in (b) remain. Therefore, in the case of this fiber, another member is indispensable for maintaining the shape of the sheet before and after water absorption.
Further, the water-absorbent resin polymerized into a film shape in the above (3) has the following problem. (a) The water absorption rate is low because the surface area per unit weight is smaller than that of a fiber or powder.

(B) In order to increase the absolute amount of water absorption, it is necessary to increase the thickness of the film. However, such a measure further reduces the water absorption speed. (c) It is extremely difficult to make the sheet porous so that the water absorption rate of the sheet is substantially improved. The main object of the present invention is to solve the above-mentioned technical problem, and to form a sheet-shaped porous water-absorbing resin composed of only a water-absorbing resin, having a high water absorption rate and a high porosity, a water-absorbing article and a porous material using the same. An object of the present invention is to provide a method for producing a water-absorbing resin.

[0013] Another object of the present invention is to provide a porous water-absorbing resin which can be easily processed by cutting, etc., without causing collapse of the inter-fiber adhesion points of the water-absorbing resin fiber before and after water absorption, a water-absorbing article using the same, and a porous material. An object of the present invention is to provide a method for producing a water-absorbent resin.

[0014]

The porous water-absorbing resin of the present invention is obtained by directly polymerizing a monomer mixture into a fibrous form.
Fibers made of the resultant water-absorbent resin is substantial completion of the polymerization
Laminated by the time of contact, the fibers contact each other during lamination
Characterized by comprising integrated in the network structure by the self-adhesive or the self-adhesive and entangled been made by also allowed to proceed further polymerized at point. Be more specifically, the porous water-absorbent resin of the present invention, the formation of long fibers consisting of water-absorbent resin into a sheet having a three-dimensional network structure integrated by said self-adhesive or the self-adhesive and entangled It is.

The water-absorbing resin includes, for example, a crosslinked product of a polyacrylate polymer. This cross-linked product has 20 to 95 of the carboxyl groups present in the molecule.
Preferably, mole% is neutralized by alkali metal or ammonia. Examples of the alkali metal include potassium, sodium, and lithium.

The porous water-absorbing resin of the present invention can be used for various water-absorbing articles. Examples of such water-absorbent articles include sanitary articles such as diapers and sanitary articles, drip sheets in the food field described above, humidity control sheets, and (melting ice).
A water-absorbing sheet. Such a porous water-absorbing resin of the present invention is, for example, a polymer composition containing a monomer is dropped while being threaded from a nozzle, a polymerization reaction is started in a falling process, and polymerization is completed in a laminated state while being laminated at a drop point. To form a three-dimensional network structure.

That is, in the present invention, instead of directly making the water-absorbent resin film porous, the fibrous water-absorbent resin is self-adhered to each other three-dimensionally to form a sheet, thereby substantially forming the sheet. To create a porous sheet. Therefore, this sheet has a large surface area,
Therefore, there is an advantage that the water absorption speed and the water absorption amount are large.

In the present invention, since the adhesion between the fibers is impaired by the conventional method of using an adhesive in the production of a nonwoven fabric using chemical fibers, the properties of the water-absorbing resin are impaired. A method of directly bonding the resin itself was used. Therefore, the self-adhesion referred to in the present invention means that no component other than the water-absorbing resin such as an adhesive is used,
Water-absorbing resins are directly adhered to each other, and their adhesion points do not collapse even after absorbing water. In addition, the entanglement means a state in which sliding is possible due to entanglement of the fibers, but free movement is hindered.

In the present invention, the fibers (long fibers) are laminated until the polymerization is substantially completed while the monomer mixture is directly formed and polymerized into a fibrous form. By adopting a method of further promoting polymerization even at the contact point, (A) a step of producing a raw resin from a monomer, (B) a step of processing a resin into a fibrous form, and (C) a step of processing a fiber into a nonwoven fabric. The steps can be performed at once in one step. This eliminates the need for transportation between manufacturing equipment and manufacturers, which is required in each conventional process, thereby reducing costs.

Further, in the present invention, a nonwoven fabric in which the fibers are directly bonded to each other can be obtained by contacting and laminating the fibrous water-absorbing resin in the course of polymerization in a point manner and continuing the polymerization. Hereinafter, the porous water-absorbing resin of the present invention and the method for producing the same will be described in detail. Examples of the water-absorbing resin in the present invention include a polyacrylate polymer, particularly a crosslinked product thereof. Examples of the monomer used for producing this polymer include acrylic acid, methacrylic acid or an ester thereof, and these include 20 to 95 mol%, preferably 20 to 75 mol% of a carboxyl group of an alkali metal. Alternatively, it is preferable to be neutralized with ammonia. If the degree of neutralization is larger than this range, the polymerizability is deteriorated, and if the degree of neutralization is smaller than this range, water absorption is deteriorated. Examples of the alkali metal include a sodium salt, a potassium salt, a lithium salt and the like. Further, in order to improve the properties such as hydrophilicity, a polyacrylate copolymer may be produced by mixing acrylamide, N-vinylpyrrolidone, 2-hydroxyethyl methacrylate, or the like as a monomer.

In the present invention, in order to polymerize the fibrous water-absorbent resin, it is preferable to carry out redox polymerization or ultraviolet polymerization, which has a fast rise rate of polymerization and is relatively easy to control. It is also possible to carry out thermal polymerization using a thermal polymerization initiator used for medium / low temperature thermal polymerization. At that time, since the polymer composition having a low viscosity is inferior in spinnability and it is difficult to obtain a fiber, it is preferable to add a spinnable thickener to the monomer.

In order to bond and integrate the fibers of the water-absorbing resin, the falling speed of the polymerization composition (mixture of monomer and other additives) from the nozzle tip, the polymerization atmosphere temperature, In the case of redox polymerization, polymerization is adjusted by adjusting the combination and concentration of redox, in the case of ultraviolet polymerization, the intensity of UV lamp and the concentration and type of initiator, the amount of crosslinking agent, and in the case of thermal polymerization, the type of initiator and temperature control. It is necessary to control the reaction rate and adjust the degree of adhesion between the fibers.

The spinnable thickener is not simply thickened by adding it, but has an inner diameter of 0.35.
When the polymer composition is extruded from a nozzle hole of about mm, 5
Those having a spinnability of 0 cm or more are preferred. The spinnability is manifested by the interaction between viscosity and elasticity, and a substance having a high thickening effect is not always necessarily high in spinnability.

Examples of the spinnable thickener usable in the present invention include nonionic or weakly ionic high molecular compounds, specifically, hydroxyethylcellulose, polyacrylamide, partially anionized polyacrylamide, polyethylene oxide, Acrylate, polymethacrylate, partially cationized polymethacrylate, partially cationized polyacrylate,
Hydroxypropylated guar gum, ramzan gum and the like can be mentioned.

In general, a strong ionic thickener does not sufficiently swell due to the interaction with a neutralizing solution component of acrylic acid in the production of a polyacrylate water-absorbent resin, and is required as the ionicity increases. It is not preferable because the spinning effect hardly appears. In addition, spinnability can be obtained by causing a chemical bond between the polymers using borax or sodium tetraborate.

The thickener can exhibit a thickening and spinning effect (especially a spinning effect) in a small amount relative to the aqueous monomer solution, usually 3 parts by weight or less based on 100 parts by weight of the monomer. Further, it is preferable that the molecular weight of the thickener used is large. If the molecular weight is small, the spinning effect cannot be exhibited with a small amount. The crosslinking agent that can be used in the present invention is not particularly limited, for example, as long as it is a monomer or oligomer compound capable of imparting water-insolubility by binding the polymer chains of the water-absorbent resin by a cross-reaction. Are (1) those having at least two polymerizable double bonds in the molecule and showing copolymerizability with the monomer, and (2) reacting with the functional group (carboxyl group, etc.) of the monomer during polymerization or during drying after polymerization. (3) those having at least one functional group in the molecule each having two or more functional groups in the molecule, and in the case where the water-absorbing resin is a polyacrylic acid salt, It is a monomer or oligomer compound showing a certain degree of solubility in a neutralizing solution for neutralizing acrylic acid.

The functional group having a polymerizable double bond includes an acryloyl group: CH ₂ ＣＨCHCO—, a methacryloyl group: CH ₂ ＣC (CH ₃ ) CO—, an acrylamide group: CH ₂ ＣＨCH—CONH—, and maleic. Acid diester group: —OCOCH ＝ CH—COO—, allyl group: CH ₂
ＣＨCH—CH ₂ —, vinyl ether group: CH ₂ ＣＨCH—
O-, vinyl thioether group: CH ₂ = CH-S-, vinyl amino group: CH ₂ = CH-NH- and the like. Examples of the functional group capable of reacting with a carboxyl group include a glycidyl group, an amino group, a hydroxyl group,
And a phosphate group.

More specifically, examples of the crosslinking agent having a (meth) acryloyl group include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, and propylene glycol di (meth) acrylate. ) Acrylate, polypropylene glycol di (meth) acrylate, glycerin di (meth) acrylate, glycerin tri (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, trimethylolpropane tri (meth) acrylate, Triacryloyloxyethyl phosphate, dimethacryloyloxyethyl phosphate and the like can be mentioned.

Examples of the crosslinking agent having an acrylamide group include N, N'-methylenebis (meth) acrylamide. Examples of the crosslinking agent having an allyl group include diallyl orthophthalate, diallyl isophthalate, diallyl maleate, diallyl terephthalate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, trimethylolpropane diallyl ether, and pentaerythritol triallyl ether. , Diallyldimethylammonium chloride,
Examples include diethylene glycol diallyl ether, tetraallyl polymellitate, triallyl trimellitate, diallyl maleate, diallylamine, triallylamine and the like.

Examples of the compound having a glycidyl group include ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, , 6-hexanediol diglycidyl ether, adipic acid diglycidyl ester, polytetramethylene glycol diglycidyl ether, trimethylolpropane diglycidyl ether, trimethylolpropane triglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, triglycidyl tris (2-hydroxyethyl) isocyanurate, diglyceride Lumpur polyglycidyl ether, pentaerythritol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether, phthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester.

The components copolymerizable with acrylic acid include:
For example, those having a polymerizable double bond in the molecule and showing copolymerizability with the acrylic acid monomer are mentioned, but it is necessary that the monomer or prepolymer exhibit a certain degree of solubility in the neutralizing solution, For example, an acryloyl group: C
H ₂ ＣＨCHCO—, methacryloyl group: CH ₂ ＣC (C
H ₃ ) CO—, acrylamide group: CH ₂ ＣＨCH—CO
NH—, allyl group: CH ₂ ＣＨCH—CH ₂ —, vinyl ether group: CH ₂ ＣＨCH—O—, vinyl thioether group: CH ₂ ＣＨCH—S—, vinylamino group: CH ₂ ＣC
It is a compound having a functional group such as H-NH-.

Specifically, for example, acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-acryloylethanesulfonic acid, 2-acryloylpropanesulfonic acid, and Examples thereof include salts thereof, and alkyl or alkoxy esters thereof, acrylamide, and vinyl sulfonic acid.

The amount of the crosslinking agent used is 0.0
It is from 0.01 to 10% by weight, preferably from 0.01 to 5% by weight. If the content is less than 0.001% by weight, the crosslinking density is too low, and the water-absorbing resin at the time of water absorption is weak. On the other hand, if it exceeds 10% by weight, the crosslinking density is too high, the water absorption capacity is reduced, and the gel becomes very brittle.

The polymerization method used for obtaining the water-absorbing resin in the present invention may be any method as long as it is a radical polymerization method. In the state, the polymerization reaction is started in a short time (second unit), and the polymerization reaction can be advanced to the extent that the shape of the fiber formed by the polymerization reaction can be maintained before lamination and integration at the drop point. It is not particularly limited as long as it is one. Therefore, in a system using a polymerization initiator, a method of irradiating ultraviolet rays or the like, a method of a redox system or a thermal polymerization system, and a method of irradiating a radiation or an electron beam in a system without using a polymerization initiator can be used. . Among these, an ultraviolet irradiation polymerization method is preferable in terms of the cost of the polymerization apparatus, control of the polymerization rate and quick and easy response, and a redox polymerization method is preferable in terms of the cost of additives such as an initiator and temperature control. In addition, the low / medium temperature thermal polymerization method is advantageous in terms of the cost of additives such as an initiator.

The concentration of the monomer in the polymerization composition is not particularly limited, but is preferably in the range of 20 to 80% by weight in consideration of easy control of the polymerization reaction, yield, economy and the like. As the polymerization initiator to be added to the polymerization composition, commonly used ultraviolet polymerization initiators, thermal polymerization initiators, redox polymerization initiators and the like can be used without any particular limitation. The ultraviolet polymerization initiator is not particularly limited as long as it generates or generates radicals effective for radical polymerization by ultraviolet irradiation.Specifically, acetophenone and acetophenone derivatives, benzophenone and benzophenone derivatives, benzoin derivatives, thioxanthone derivatives, One selected from biacetyl and azo compounds or a mixture thereof. Particularly, acetophenone and acetophenone derivatives, benzoin derivatives, benzophenone and benzophenone derivatives are preferred.

As the acetophenone derivative, for example, 2
-Hydroxy-2-methyl-1-phenylpropane-1
-One, 4- (2-hydroxyethoxy) phenyl-
(2-hydroxy-2-propyl) ketone, 1- (4-
Isopropylphenyl) -2-hydroxy-2-methylpropan-1-one, diethoxyacetophenone, 1-
Hydroxycyclohexyl-phenyl ketone, 2-methyl-2-morpholino (4-thiomethylphenyl) propan-1-one, oligo [2-hydroxy-2-methyl-
1- [4- (1-methylvinyl) phenyl] propanone] and the like.

Examples of the benzoin derivative include benzyl dimethyl ketal, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether and the like, with benzyl dimethyl ketal being particularly preferred. Examples of the benzophenone derivative include, for example, acrylated benzophenone, 2,4,6-trimethylbenzophenone and the like, and it is particularly preferable to use benzophenone.

The UV polymerization initiator is used in an amount of 0.1% based on the monomer.
It is used in an amount of from 0.01 to 5 parts by weight, preferably from 0.05 to 1.0 part by weight. The redox polymerization initiator initiates radical polymerization by generating radicals by an oxidation-reduction reaction between an oxidizing agent and a reducing agent, and adjusts a decomposition rate by the reducing agent. Specific examples include hydrogen peroxide-iron (II) salts and hydrogen peroxide-sulfites as hydroperoxides, and persulfates-persulfates-sulfites, persulfates-iron (II ) Salt and the like.

The thermal polymerization initiator is preferably a low / medium temperature thermal polymerization initiator. Here, the low / medium temperature thermal polymerization initiator is 10
It refers to those having a time half-life temperature of 30 to 100 degrees. Specifically, examples of the low / medium temperature thermal polymerization initiator include diacyl peroxides, ketone peroxides, hydroperoxides, peroxyketals, alkyl peresters, and peroxycarbonates.

The diameter of the fiber made of the water-absorbing resin is 0.05 to
It is preferably in the range of 5 mm. If the diameter is less than 0.05 mm, not only is it difficult to process the nozzle, but also the discharge rate of the resin does not increase, and the individual fibers fuse with each other due to slight turbulence before polymerization, resulting in a large product loss. This does not increase productivity. On the other hand, when the diameter exceeds 5 mm, the water absorption rate of the resin is low and the sheet thickness is large, which is not practical. A more preferred diameter is 0.05 to 3 mm.

The porous water-absorbing resin of the present invention has a porosity of 25
Preferably it is in the range of ~ 99%. If the porosity exceeds 99%, the sheet strength before and after water absorption is not sufficient, and the absolute amount of water absorption is small, which is not practical. On the other hand, the porosity is 25
%, The sheet strength is sufficient, but since the stitch is too fine, the stitch is clogged due to swelling of the resin and gel blocking easily occurs. A more preferred porosity is 5
0-98.5%, especially 80-97%.

Further, the porous water-absorbing resin of the present invention preferably has a specific surface area in the range of 0.1 to 5.5 m ² / g. When the specific surface area is less than 0.1 cm ² / g, the absorption rate is low, and when the specific surface area exceeds 5.5 cm ² / g, the fiber diameter becomes thin,
There is a problem with productivity. Preferably 0.2-4.5 cm
² / g.

[0043]

The present invention will be described below in detail with reference to examples. Example 1 Aqueous solution of partially neutralized acrylic acid (monomer concentration: 45% by weight) in which 73% was neutralized by sodium hydroxide 100
0.05 parts by weight of polyethylene glycol (PEG200) diacrylate, 0.2 parts by weight of polyethylene oxide, and 2 parts by weight of 2-hydroxy-2-methyl-1-phenylpropan-1-one were dissolved in parts by weight. The viscosity of this aqueous monomer solution was measured with a B-type viscometer (at 20 ° C., rotor speed 10) and found to be 600 cps.

The aqueous monomer solution was reduced to a fiber diameter of 150 μm.
While dropping the thread from the nozzle so that
Illuminated from the side with a high-pressure mercury lamp (80 W / cm) for 2 seconds
To initiate the polymerization reaction. Polymerization drawn into long fibers
The objects are stacked at the drop point, and a porous
I got it. The obtained porous sheet weighs 60 g / c.
m ^TwoAnd the porosity was 98%.

The capacity of the porous sheet to absorb ion-exchanged water was 420 g / g in 10 minutes. Example 2 0.05 parts by weight of polyethylene glycol (PEG200) diglycidyl ether-acrylic acid adduct was added to 100 parts by weight of a partially neutralized acrylic acid aqueous solution (monomer concentration: 45% by weight) in which 73% was neutralized with sodium hydroxide; Polyacrylate-acrylamide copolymer 0.2
2 parts by weight of 1-hydroxycyclohexyl phenyl ketone were dissolved. The viscosity of this aqueous monomer solution was measured by a B-type viscometer (20 ° C., rotor rotation speed: 10) and found to be 550 cps.

While the aqueous monomer solution was drawn down from a nozzle so as to have a fiber diameter of 100 μm, it was irradiated with a high pressure mercury lamp (80 W / cm) for 2 seconds from the side surface during the dropping to start a polymerization reaction. . The polymer drawn in a long fiber shape was laminated at the drop point to obtain a porous sheet having a thickness of about 0.5 mm. The obtained porous sheet weighed 55 g /
cm ² and a porosity of 85%.

The water absorption capacity of the porous sheet with respect to ion-exchanged water was 230 g / g in 10 minutes. Example 3 0.05 parts by weight of polyethylene glycol (PEG200) diacrylate, 100 parts by weight of a partially neutralized acrylic acid aqueous solution (monomer concentration: 50% by weight) in which 57% was neutralized with sodium hydroxide, and 0.05% by weight of polyethylene oxide.
24 parts by weight and 2 parts by weight of 2-hydroxy-2-methyl-1-phenylpropan-1-one were dissolved. The viscosity of this aqueous monomer solution was measured by a B-type viscometer (at 20 ° C., rotor speed 10) and found to be 750 cps.

While the monomer aqueous solution was pulled down from the nozzle so as to have a fiber diameter of 150 μm, it was irradiated with a high-pressure mercury lamp (80 W / cm) for 2 seconds from the side surface during dropping to start a polymerization reaction. The polymer drawn in a long fiber form was laminated at the drop point to obtain a porous sheet having a thickness of about 0.6 mm. The obtained porous sheet weighed 60 g / cm ² ,
The porosity was 94%.

The water absorption capacity of the porous sheet with respect to ion-exchanged water was 390 g / g in 10 minutes. Example 4 0.05 parts by weight of polyethylene glycol (PEG200) diacrylate, 100 parts by weight of a partially neutralized acrylic acid aqueous solution (monomer concentration: 73% by weight) in which 20% was neutralized with sodium hydroxide, and polyethylene oxide 0.1 part by weight.
1 part by weight and 1 part by weight of 2-hydroxy-2-methyl-1-phenylpropan-1-one were dissolved. The viscosity of this aqueous monomer solution was measured with a B-type viscometer (at 20 ° C., rotor speed 10) and found to be 680 cps.

While the aqueous solution of the monomer was pulled down from the nozzle so as to have a fiber diameter of 180 μm, it was irradiated with a high pressure mercury lamp (80 W / cm) for 2 seconds from the side surface during the dropping to start a polymerization reaction. The polymer drawn in a long fiber form was laminated at the drop point to obtain a porous sheet having a thickness of about 0.7 mm. The obtained porous sheet weighed 90 g / cm ² ,
The porosity was 96%.

The water absorption capacity of the porous sheet with respect to ion-exchanged water was measured and found to be 300 g / g in 10 minutes.

[0052]

As described above, in the present invention, since the fibers made of the water-absorbing resin are integrated by self-adhesion or self-adhesion and entanglement by polymerization, the fibers swell and deform due to water absorption. But they can follow each other. Therefore, the three-dimensional structure due to the destruction of the bonding point does not collapse. In particular, the part directly joined by polymerization is completely integrated as a single resin, so unlike adhesives mainly composed of hydrogen bonds by different types of adhesives and adhesive components, the adhesive strength may be reduced or peeled off by water absorption. Not
The integrated shape does not collapse.

In the present invention, since the fibers of the water-absorbing resin are not continuous fibers but continuous fibers, they do not fall off before and after water absorption. Since a fibrous water-absorbent resin is laminated to form a porous sheet with a three-dimensional network structure, the surface area of the sheet is large, the water absorption speed is high, and liquid can enter the sheet in a short time. Then, the entire sheet swells uniformly and does not cause deformation or gel blocking. Further, by adjusting the nozzle diameter and the discharge amount, it is easy to change the fiber diameter, porosity, and basis weight of the sheet-shaped article.

In the present invention, since the sheet-like porous body is formed of the fiber laminate, the porosity can be easily adjusted and the porosity can be easily adjusted as compared with the case of forming the film porous body. By dropping and forming the fibers on a substrate such as a nonwoven fabric, a composite material with the substrate can be easily produced. Further, by changing the nozzle interval or the type of the nozzle, it is possible to produce a sheet having a porosity gradient in the width direction of the sheet or a sheet-shaped water-absorbent resin having a plurality of fiber diameters.

Further, in the present invention, the present invention does not require an adhesive component such as a heat-fused fiber or a binder, so that the cost can be reduced, and the component which does not participate in water absorption is not included, so that the actual weight and bulk are reduced. it can. In addition, since the steps from the monomer to the bonding of the fibers are performed at once, the final product can be produced in a short time.

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Claims (2)

(57) [Claims] (1) a method comprising directly polymerizing a monomer mixture into a fibrous form.
Of the water-absorbent resin to be used completes substantial polymerization
Contact points where fibers are in contact with each other during lamination
But it is integrated into a network structure by the self-adhesive or the self-adhesive and entangled was made by advancing the further polymerization
It is Te porous water-absorbent resin according to claim. 2. A sheet-like water-absorbent article for hygiene articles or foods, wherein the porous water-absorbent resin according to claim 1 is used.