JPH0621127B2 - Continuous production method of liquid-absorbent composite - Google Patents

Description

TECHNICAL FIELD The present invention relates to a continuous method for producing a composite of a fiber base material and a liquid-absorbent polymer, and more specifically, there is no loss of the polymer, The present invention relates to a continuous method for producing an absorbent composite capable of having a free shape, and the absorbent composite of the present invention is a sanitary napkin, disposable diaper, bandage, etc. It can be suitably used for applications, such as freshness-retaining materials such as vegetables, water-retaining materials such as agricultural and forestry fields, civil engineering fields, and the like, which require liquid absorption and liquid retention.

[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. ing. (JP-A-60-149609, JP-A-59-2049
75, Tokushi Sho 57-500546). Although these techniques can prevent the polymer from falling off, the liquid-absorbing performance is significantly lower than that of the conventional granular ones, and it is expected that a polymer having excellent liquid-absorbing property and no polymer falling off will appear. 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. An aqueous solution containing an unsaturated monomer, a radical polymerization initiator and a water-soluble cross-linking agent was attached, and the monomer was polymerized by continuously passing it under a specific atmosphere, resulting in excellent liquid absorption and swelling with a liquid. Even when the polymer does not fall off,
The present invention was completed by finding that an absorbent composite having a good texture can be efficiently obtained.

That is, the present invention is a water-soluble ethylenically unsaturated monomer,
A long fibrous base material, at least a part of which is coated with an aqueous solution containing a radical polymerization initiator and a water-soluble cross-linking agent, is composed of hydrophobic fibers. (Hereinafter, abbreviated as "humidity") is continuously passed through a zone having an atmosphere of 40% or more to polymerize a monomer to convert it into a polymer having a liquid absorbing property, and then to dry the polymer. It is intended to provide a continuous manufacturing method.

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 a carboxylic acid or / and a salt thereof, a phosphoric acid or / and a salt thereof, a sulfonic acid or / and a salt, a hydroxyl group or an ethylenic unsaturated group having a 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.

As the cross-linking agent used in the present invention, methylene bis acrylamide or ethylene glycol diacrylate,
Polyfunctional water-soluble ethylenically unsaturated monomers such as polyethylene glycol di (meth) acrylate, polyglycerol poly (meth) acrylate, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl Polyglycidyl ethers such as ethers, polyols such as glycerin and pentaerythritol, and polyamines such as ethylenediamine and polyethyleneimine 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.

In the present invention, a crushed filler such as talc, clay or diatomaceous earth may be further added as an additive.

In the present invention, the long 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 alkyl ketene 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 order to improve productivity, a printing method such as screen printing or gravure printing or an impregnation method is desirable. Product texture,
From the aspects of feel and the like, screen printing,
It is a printing method such as gravure printing.

In order to continuously polymerize the fibrous base material to which the aqueous monomer solution containing the monomer, the radical polymerization initiator and the water-soluble crosslinking agent is thus polymerized, the humidifying condition is essential in the present invention. That is, the polymerization reaction is allowed to proceed without delay, and in order to obtain a liquid absorbent having excellent liquid absorption properties, a polymerization inactive atmosphere that does not inhibit the polymerization reaction is kept, and a humidified state is set to suppress evaporation of water in the monomer aqueous solution. It is necessary to keep it.

The polymerization temperature varies depending on the type and amount of radical polymerization initiator and the type of monomer, but from the viewpoint of productivity, it is desired to complete the polymerization rapidly at a high temperature. Therefore, it is desirable to carry out the polymerization at 80 ° C or higher. Temperature is 80 ℃
If it is lower, the productivity is poor, and the performance of the product as a liquid absorbent is not sufficient, which is not the intention of the present invention.

However, when the polymerization temperature is raised, water-soluble water is volatilized, which hinders the completion of the polymerization and deteriorates the liquid absorbing properties, which is not preferable.

As described above, the present invention is characterized in that the aqueous monomer solution is polymerized under humidification. Humidification conditions differ depending on the polymerization time and polymerization temperature of the monomer, but it is necessary that the temperature is 80 ° C. or higher and the 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 thus obtained water-absorptive liquid-absorbent composite is dried to obtain the final liquid-absorption, and the drying method thereof includes means such as hot air, microwaves, and infrared rays.

It is also 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.

The final liquid-absorbent composite is optionally cut or rolled into a roll according to the application.

The liquid-absorbent composite thus obtained is not only excellent in liquid-absorbing property and having a good texture, but also can be formed into a free form without the polymer falling off.
In addition, since it is manufactured continuously, it has good productivity and is advantageous in terms of cost, and the range of use of the liquid-absorbent polymer can be greatly expanded.

〔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 left to stand with a 80-mesh wire mesh until water drops did not drop, 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 liquid absorption (g) W ₀ : Weight of substrate after absorption (g) (2) Absorption rate A dried liquid-absorbent composite The sample was immersed in a sufficient amount of physiological saline for 3 minutes, and immediately thereafter, suction filtration was performed to separate interstitial water contained between fibers and particles and weighed.

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 composite after absorbing water (g) W ₀ ′: Weight of base material after absorbing (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 An aqueous solution of sodium acrylate having a solid content of 40% by weight and a degree of neutralization of 70 mol% was prepared, and 1% by weight of sodium persulfate (to sodium acrylate monomer) and polyethylene glycol diacrylate ( Average oxyethene chain 14 mol, trade name NK ester A-600 Shin-Nakamura Chemical Co., Ltd.
(Manufactured by Mitsui Chemical Co., Ltd.) was uniformly dissolved in 750 ppm (sodium acrylate monomer), and then nitrogen gas was blown in to remove dissolved oxygen in the aqueous solution.

Hydrophobic fiber web (Example 1) consisting of polyethylene-polypropylene composite fibers (ES fiber) having a basis weight of 45 g / m ² spread on a long roll (Example 1), equal weight of polyethylene-polypropylene composite fibers (ES fiber) ) And rayon (Example 2), the above aqueous solution was continuously applied, polymerized and dried using the apparatus shown in FIG. 1 to obtain a liquid-absorbent composite. The coating was applied on the web by a gravure printing machine (a polka dot plate) at 150 g / m ² . The polymerization was carried out at 100 ° C., 65% RH, and the residence time in the polymerization zone was 2 minutes. Humidification was performed by a method of blowing steam into the polymerization zone, and humidity was controlled by a humidity control sensor. Drying was performed with hot air at 120 degrees. Nitrogen gas was blown into the coating zone (5) and the polymerization zone (6) to make it an inert gas atmosphere, and the line speed at this time was 2 m / min.

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 method is used instead of the gravure printing machine in the coating zone, and the above solution is used.
It was coated at 100 g / m ² and polymerized according to Example 1. The line speed at this time was 10 m / min, and the residence time in the polymerization zone was 1 minute. Drying is performed by microwave instead of hot air,
A liquid-absorbent composite was continuously obtained.

Example 4 It carried out according to Example 1. However, a liquid-absorbent composite was continuously obtained 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 It carried out according to Example 1. However, polyethylene glycol diacrylate (average oxyethylene chain 14 mol, trade name NK ester A-600 manufactured by Shin-Nakamura Chemical Co., Ltd.) was replaced with methylenebisacrylamide at 500 ppm (as a monomer) in the same manner as in Example 1. The liquid-absorbent composite was obtained.

Example 6 It carried out according to Example 2. However, polyethylene glycol diacrylate (average oxyethylene chain 14 mol, trade name NK ester A-600 manufactured by Shin-Nakamura Chemical Co., Ltd.) was used at 750 ppm (against monomer) at 90 ° C. and 100% humidity, and the same as Example 2. Then, the liquid-absorbent composite was continuously obtained.

Comparative Examples 1 and 2 were carried out according to Example 1. However, at the temperature of 90 ° C during polymerization
10% humidity (Comparative Example 1), no humidification at 120 ° C (Comparative Example 2)
A liquid-absorbent composite was continuously obtained in the same manner as in Example 1 except that the polymerization was carried out.

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

[Brief description of drawings]

 FIG. 1 is a schematic view showing an example of the manufacturing method of the present invention. 1 ... Unwinding roll, 2 ... Winding roll 3 ... Guide roll, 4 ... Nip roll 5 ... Coating zone, 6 ... Polymerization zone, 7 ... Drying zone, 8 ... Gravure roll, 9 ... Back Roll, 10 ... Monomer aqueous solution

Claims (2)

[Claims] 1. A long fibrous substrate coated with an aqueous solution containing a water-soluble ethylenically unsaturated monomer, a radical polymerization initiator and a water-soluble crosslinking agent, at least a part of which is composed of hydrophobic fibers. Is continuously passed through a zone of a polymerization-inert, humidified atmosphere at a temperature of 80 ° C or higher and a relative humidity of 40% or higher to polymerize the monomer to convert it into a liquid-absorbent polymer, and then dry it. A method for continuously producing a liquid-absorbent composite, comprising: 2. The continuous 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.