JPH0621126B2 - Method for producing absorbent composite - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a composite of a fiber base material and a liquid-absorbent polymer, and more specifically, it is free from loss of the polymer and free. The present invention relates to a method for producing an absorbent composite capable of having a shape, wherein the absorbent composite of the present invention is a sanitary napkin, a disposable diaper, a hygiene / medical article such as a bandage, and a vegetable. It can be suitably used for applications requiring liquid retention and liquid retention, such as agricultural and forestry fields and civil engineering fields such as freshness-retaining materials and water-retaining materials.

[Conventional technology and its problems]

In recent years, so-called water-absorbent polymers that absorb several tens to several hundreds of times their own weight of water have been developed, and are used as water-retaining and water-absorbing materials in the fields of agriculture and forestry, civil engineering, etc. It's being used.

The water-absorbent polymer used is generally in the form of granules, and because of its granular form, it is often used in sandwiches with paper, embossed by mixing it with pulp, etc. It is used by being changed into a sheet shape, a film shape, or the like by performing a pressure bonding treatment or a compounding such as fusion sealing with a thermoplastic resin or the like. However, even with these compounding methods, the loss of the polymer cannot be avoided. In the case of complexing by fusion sealing with relatively little loss of polymer, the periphery of the polymer is coated with a thermoplastic resin, which results in blocking contact with liquid such as water,
Therefore, there is a drawback that the absorption performance is significantly reduced.

In order to improve these drawbacks, many proposals have been made for absorbent articles in which the polymer does not fall off, and film-like, fiber-like and the like have been proposed. In the case of a film, the surface area is small and the absorption rate is poor, and since it exists as a surface, it limits the flexibility of the absorbent article. On the other hand, in the fibrous form, there is a drawback that the gel strength at the time of swelling is weak even though the flexibility is satisfied, and it is hard to say that an absorbent article having a good absorption performance and no polymer falling off is obtained. .

In order to further improve these, a method of impregnating a fibrous base material with a water-soluble monomer that can be converted into a water-absorbent polymer, coating using a technique such as spraying, and polymerizing with heat or electromagnetic radiation has been proposed. (JP-A-60-149609, JP-A-59-20497)
5, Japanese Patent Publication No. 57-500546). Although these techniques can prevent the polymer from falling off, the liquid absorption performance is significantly lower than that of the conventional granules, and the appearance of a polymer with excellent liquid absorption and no polymer dropout is desired. It is rare.

[Means for solving problems]

Under the circumstances described above, the inventors of the present invention have conducted extensive studies on a liquid-absorbent material that is excellent in liquid-absorbing property and does not drop out of the polymer. As a result, the fibrous base material has a water-soluble ethylenically unsaturated monomer. By attaching a radical polymerization initiator, an aqueous solution containing a water-soluble crosslink as necessary, and polymerizing the monomer in a specific atmosphere, the liquid absorbability is excellent and the polymer does not fall off even when swollen by a liquid. It was found that a liquid-absorbent composite having a good texture can be obtained without the need to complete the present invention.

That is, in the present invention, a water-soluble ethylenically unsaturated monomer and a water-soluble material containing a radical polymerization initiator are attached to an on-fiber base material at least a part of which is composed of a hydrophobic fiber, and the water-soluble ethylenic unsaturated monomer and the radical polymerization initiator are applied under a polymerization-inert atmosphere. At the time of polymerizing the monomer to convert it into a polymer having a liquid-absorbing property, the polymerization is carried out at a temperature of 80 ° C. or higher and a relative humidity (hereinafter, abbreviated as humidity) of 40% or more. The present invention provides a method for producing the liquid-absorbent composite.

The water-soluble ethylenically unsaturated monomer used in the present invention may be any one as long as it can be converted into a polymer having liquid absorbability. Examples of the water-soluble monomer that gives such performance include ethylenically unsaturated compounds having carboxylic acid or / and its salt, phosphoric acid or / and its salt, sulfonic acid or / or its salt, hydroxyl group and amide group as a functional group. Examples include monomers. For example, (meth) acrylic acid (salt), itaconic acid (salt), vinylsulfonic acid (salt), vinylphosphonic acid (salt), polyethylene glycol (meth) acrylate, acrylamide and the like can be mentioned. These can be used alone or in combination of two or more, and can be selected depending on the properties of the liquid to be absorbed. A water-soluble ethylenically unsaturated monomer having a carboxylic acid (salt) functional group is preferable, and acrylic acid and / or a salt thereof is more preferable.

Examples of the water-soluble radical polymerization initiator include peroxides,
Hydroperoxide, an azo compound or the like is used in a known amount. These polymerization initiators can be used as a mixture of two or more kinds, and can also be used as a redox polymerization initiator by adding chromium ion, sulfite, hydroxylamine, hydrazine and the like. Is.

In addition to the above-mentioned monomers, it is possible to add a crosslinking agent or an additive for the purpose of improving the liquid absorbing property and the prevention of sticking during liquid absorption. Polyfunctional water-soluble ethylenically unsaturated monomers such as methylenebisacrylamide, ethylene glycol diacrylate, polyethylene glycol di (meth) acrylate and polyglycerol poly (meth) acrylate as cross-linking agents, ethynylene glycol diglycidyl ether, polyethylene glycol Polyglycidyl ethers such as diglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether,
Polyols such as glycerin and pentaerythritol and polyamines such as ethylenediamine and polyethyleneimide can be preferably used. Generally, the addition amount is 0.01 to 10 parts by weight with respect to 100 parts by weight of the monomer, and if it exceeds 10 parts by weight, the crosslinking density becomes too high and the liquid absorption amount decreases. Further, if it is less than 0.01 part by weight, the effect of crosslinking cannot be sufficiently exhibited.

Examples of the additive include crushed fillers such as talc, clay and diatomaceous earth.

In the present invention, the fibrous base material to which the aqueous monomer solution is attached needs to have a hydrophobic fiber portion in at least a part thereof.

By mixing hydrophobic fibers into the fibrous base material web, the fibrous base material exhibits hydrophobicity. When the aqueous monomer solution is applied to the fibrous base material, the surface tension of water is also helped because the fibers are hydrophobic. Thus, it becomes possible to make a state in which the aqueous monomer solution is discontinuously attached on the fiber base material. As a fibrous base material capable of having such a form, 5% by weight of hydrophobic fiber is used.
What is necessary is just to contain the above.

Examples of the hydrophobic fiber used include polyester, polypropylene, polyethylene-polypropylene composite fiber, and the like, and those having these hydrophobic fibers as a main component are preferable.
In addition to the above hydrophobic fibers, the surface of hydrophilic fibers such as rayon may be hydrophobized with a rosin-based or alkylketene dimer-based sizing agent or a cationic surfactant.

By applying an aqueous monomer solution onto the fibrous base material in the above-mentioned form and then polymerizing it, there is almost no drop-off of the polymer from the fibrous base material even when the polymer swells. The body is obtained. The discontinuous distribution of the polymer on the fibrous base material also increases the surface area per mass of the polymer, and further, since the planar polymer does not continuously exist between the fibers, the polymer can be used as a liquid-absorbent article. It becomes possible to fully exert liquid absorbency, and it is possible to give high liquid absorbability.

As a method of applying the aqueous monomer solution to the fibrous base material,
For example, it is possible to use a known printing method such as screen printing or gravure printing, or a method such as spraying or spraying using a spray. It is also possible to use a polymerization-inert viscosity adjusting agent or a foaming agent in order to enhance the coating efficiency. Further, the water absorbent composite may be subjected to pattern printing suitable for use.

In the present invention, humidification is essential in polymerizing the fibrous base material to which the monomer and the radical polymerization initiator, and optionally the aqueous monomer solution containing the crosslinking agent are attached. That is, the polymerization reaction is allowed to proceed without delay, and in order to obtain an absorbent liquid having excellent liquid absorption properties, a polymerization inert atmosphere that does not inhibit the polymerization reaction and a humidification method for suppressing water vaporization of the monomer aqueous solution are used. It is necessary to keep it in a state.

As the radical polymerization initiator, a peroxide-based initiator is preferable from the viewpoint of liquid absorption properties. Therefore, the polymerization temperature must be 80 or higher.

As described above, the present invention is characterized in that the aqueous monomer solution is polymerized under humidification. The conditions of the heating chamber differ depending on the polymerization time and the polymerization temperature of the monomer, but it is necessary that the temperature is 80 ° C or higher and the relative humidity is 40% or higher. If the humidity is lower than 40%, the water content of the monomer aqueous solution is volatilized during the polymerization, which is not satisfactory as a liquid absorbing material, which is beyond the scope of the present invention. The water-absorbent composite obtained in this manner is dried to give the final liquid absorption.
Means such as hot air, microwaves, infrared rays and the like can be mentioned.

In addition, it is desirable to apply a modifier before drying to improve wettability of the hydrophobic fiber with the substance to be absorbed before drying. Examples of the improving agent include nonionic activators.

〔Example〕

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

The saturated absorption amount, absorption rate, and polymer dropout property were evaluated by the following methods.

(1) Saturated absorption amount The dried liquid-absorbent composite was immersed in a sufficient amount of physiological saline and left for 1 hour. After that, it was allowed to stand with an 80-mesh gold sardine until water drops did not fall, and the weight was measured. The same operation was performed on a substrate having the same area without polymer to measure the weight. From these, the absorption amount of the polymer was determined by the formula shown below.

W: Adhesion amount of polymer (g) W ₁ : Weight of absorbent article after water absorption (g) W ₀ : Weight of base material after water absorption (g) (2) Absorption rate Sufficient dry liquid-absorbent composite It was immersed in an appropriate amount of physiological saline for 3 minutes, and immediately thereafter, suction filtration was performed to separate interstitial water contained between fibers and particles, and the weight was measured.

The same operation was performed on a substrate having the same area without polymer to measure the weight. From these, the absorption rate of the polymer was defined by the following formula.

W ′: Adhesion amount of polymer (g) W ₁ ′: Weight of liquid-absorbent complex after absorbing water (g) W ₀ ′: Weight of substrate after absorbing water (g) (3) Polymer falling sample Was poured into a large amount of physiological saline to sufficiently swell the polymer, followed by stirring for 5 minutes, and then the weight of the polymer dropped from the substrate was measured, and the drop amount was calculated by the following formula.

Examples 1 and 2 A 70 mol% neutralized sodium acrylate aqueous solution having a solid content of 40% by weight was prepared. 1% by weight of sodium persulfate (to sodium acrylate monomer) and 500 rpm of methylenebisacrylamide (to sodium acrylate monomer) were dissolved in this solution, and then nitrogen gas was blown into the solution to remove dissolved oxygen. Hydrophobic fibrous web (A) consisting only of polyethylene-polypropylene composite fibers (ES fibers) in an amount of 45 g / m ² (Example 1), equal weight of polyethylene-
A fibrous web (B) made of polypropylene composite fiber (ES fiber) and rayon (Example 2) was uniformly sprayed at 150 g / m ² .

The web coated with the monomer was left to polymerize in a 90 ° C., 60% humidity oven completely purged with nitrogen for 10 minutes. Humidification was performed by blowing steam into an oven, and humidity was controlled by a humidity control sensor in the oven.
Then, this composite was dried under reduced pressure at 100 ° C. to obtain a liquid-absorbent composite.

Example 3 It carried out according to Example 1. However, as a method of attaching the aqueous monomer solution to the composite fiber, a screen printing means was used instead of spraying, and the solution was attached in an amount of 70 g / m ² ,
Polymerization was performed by leaving it in an oven at 0 ° C and 50% humidity for 10 minutes. Then, this composite was dried by microwave.

Example 4 Polymerization was carried out according to Example 1. However, polymerization was carried out in the same manner as in Example 1 except that 100 mol% neutralized sodium vinylphosphonate having a solid content of 20% by weight was used instead of sodium acrylate.

Example 5 Polymerization was carried out according to Example 1. However, polymerization was carried out in the same manner as in Example 1 except that polyethylene glycol diacrylate (average oxyethylene chain 14 mol, trade name NK ester A-600 manufactured by Shin-Nakamura Chemical Co., Ltd.) was used at 500 rpm (to monomer) instead of methylenebisacrylamide. went.

Example 6 Polymerization was carried out according to Example 2. However, instead of methylenebisacrylamide as a cross-linking agent, tetraglycerol tetraglycidyl ether (trade name Tenacor EX-51
2, using Nagase & Co., Ltd.) 750 rpm (against monomer), 100
Polymerization was carried out in the same manner as in Example 2 except that the polymerization was carried out at a temperature of 93 ° C. and a humidity of 93% for 5 minutes.

Comparative Examples 1 and 2 Polymerization was carried out according to Example 1. However, during the polymerization, the same procedure as in Example 1 was carried out except that the polymerization was performed at a temperature of 90 ° C. and a humidity of 10% (Comparative Example 1) and at 120 ° C. without humidification (Comparative Example 2).

Table 1 shows the measurement results of the obtained liquid-absorbent composite.

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Claims (2)

[Claims] 1. A fibrous substrate, at least a part of which is composed of hydrophobic fibers, is made to adhere water-solubility containing a water-soluble ethylenically unsaturated monomer and a radical polymerization initiator, and the reaction is performed in a polymerization-inert atmosphere. When the monomer is polymerized to convert it into a polymer having a liquid-absorbing property, the polymerization is carried out at a temperature of 80 ° C. or higher and a relative humidity of 40% or more to produce a liquid-absorbing composite. Method. 2. The method for producing a liquid-absorbent composite according to claim 1, wherein the water-soluble ethylenically unsaturated monomer has acrylic acid or an acrylic acid salt as a main component.