JPH066357B2 - Water absorbent / water retentive sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a water-absorbing / water-retaining sheet, and more specifically, it has high water-absorbing ability not only for pure water but also for aqueous solutions containing high-concentration salts, The present invention relates to a sheet having water retention property.

<Prior art and its problems> Conventional sanitary items, diapers, disposable rags, paper towels, medical gauze, and the like are required to have a relatively high water absorption capacity. Also, interior materials for construction such as wall materials and ceiling materials, soil-holding sheets for agriculture, and covering materials for electric wires and cables are required to have high water absorption and water retention from the viewpoints of dew condensation prevention, water retention and running prevention. ing.

As a material to meet these requirements, cotton,
Sheets that use physical water absorption, such as sponge, pulp, cloth, and felt, are generally used, but their water absorption capacity is limited to several times their own weight to 20 times at most, and water retention capacity is There was the problem of getting out easily.

Further, in recent years, a "water-absorbing polymer" composed of a polyelectrolyte capable of absorbing and retaining several hundred times its own weight of water has been used and is used for the above purpose.

However, the conventional water-absorbing polymer is a polymer electrolyte having a three-dimensional structure and has a mechanism of absorbing water based on the osmotic pressure resulting from the salt effect produced by the functional groups present in the structure to sodium carboxylic acid. Therefore, although the water absorption rate is very fast, the more salt (ions) contained in the water to be absorbed, the smaller the difference from the salt concentration in the water-absorbing polymer, the smaller the osmotic pressure, and the less the absorption amount. There is a problem, and in actual use, pure water is a target for some examples of dew condensation water of steam, and there is a problem that the absorption effect is not exerted so much for seawater, human sweat, and the like.

Further, as another water-absorbing polymer, there is a partially crosslinked non-electrolyte water-soluble polymer, and this polymer exhibits a water-absorbing ability due to the hydrophilicity of the polymer and the tendency to dissolve in water.
Since this polymer has a different water-absorption mechanism, it is not affected by the salt concentration and exhibits a similar absorption amount to almost all aqueous solutions, but unlike the above-mentioned polymer electrolyte, an absorption amount of several hundred times is not obtained, and The absorption rate was also slow.

<Purpose of the Invention> When a water-absorbing / water-retaining sheet is actually applied, particularly in the case of an electric wire or a communication cable, it is difficult to identify the object to which the sheet absorbs / retains water, and it is difficult to identify It is expected that there will be various cases such as from water that is close to pure water to seawater or muddy water that contains salts in soil, and sheets that are coated for water shielding are also required to have the corresponding performance.

In view of the above problems, an object of the present invention is to provide a sheet having high water retention and water absorption even from water close to pure water such as rainwater to seawater, or water containing salts in soil. .

<Structure of the Invention> A coating liquid (A) comprising a fine powder of a three-dimensional partially crosslinked water-soluble polymer electrolyte and a non-aqueous solvent or a solvent-free resin binder.
And a coating liquid (B) comprising a fine powder of a three-dimensional partially crosslinked non-electrolyte water-soluble polymer and a non-aqueous solvent or a solvent-free resin binder, at least partially on at least one surface of a water-resistant substrate. The problem was solved by providing a coated film.

It is more effective to use a coating solution (B) having a larger area or thickness than the coating solution (A).

Examples of the three-dimensional partially crosslinked product of the water-soluble polyelectrolyte used in the present invention include sodium acrylate polymer, starch-sodium acrylate graft polymer, hydrolyzate of starch-acrylonitrile graft polymer, and partially crosslinked. Starch-poly (meth) acrylic acid copolymer, partially crosslinked starch-polymethylmethacrylate hydrolyzate, vinyl acetate-acrylic acid ester copolymer, isobutylene-maleic acid copolymer, vinyl alcohol -Acrylic acid copolymer, vinyl alcohol-maleic anhydride copolymer and the like can be mentioned.

Examples of the three-dimensional partially cross-linked non-electrolyte water-soluble polymer used at the same time include those obtained by partially cross-linking water-soluble polyethylene oxide, polyacrylic acid, polyvinyl alcohol, polyethylene glycol or the like with an isocyanate compound or the like. .

These two types of water-absorbent polymers are used as fine powders to form a paint. The powder particle size is 35 mesh or less, preferably 100 mesh or less and 5 μ or more is suitable, and the shape close to a sphere is more preferable. When the powder particle shape is 35 Mesh or more, it is difficult to obtain a fluid coating solution, and when applied to a substrate, the surface is rough and the powder tends to fall off. On the other hand, when the particle size is 5 μm or less, the powder particles are buried in the binder film, which makes it difficult to obtain high water absorption as the object of the present invention. Alternatively, there is a problem that it is difficult to collect suspended particles.

Resin binders for mixing and dispersing these water-insoluble / water-absorbing polymer fine powders include alcohols such as methanol and ethanol, acetic acid esters such as ethyl acetate and butyl acetate, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, n- Solution-based, dispersion-based, non-aqueous emulsion-based resin liquid based on non-aqueous solvents such as hexane and toluene and other hydrocarbon-based solvents, curable solvent-free resin liquids composed of urethane oligomers, or thermoplastic resins The melt etc. of is used.

The resin binder is basically insoluble in water, for example, polyamide resin, linear thermoplastic polyester resin, vinyl chloride-vinyl acetate copolymer, cyclized rubber, chlorinated rubber,
One or a mixture of chlorinated polypropylene, urethane and the like can be mentioned, and the water-absorbing polymer is at least 200 parts or more, preferably 5 parts or more with respect to 100 parts of the resin binder.
It is necessary to mix more than 00 parts, and if less than 200 parts, the final water absorption amount is not so different, but the water absorption speed becomes extremely slow, and the sheet of the present invention is applied as a covering material for a cable, for example. However, there is a problem that it cannot be applied to applications that expect short-term water absorption, such as applications that prevent running of water.

It is preferable to increase the ratio of the water-absorbing polymer as long as the fluidity as a coating liquid, the coating workability, and the ability to retain and adhere to a substrate are maintained. In this case, since the outside is covered with a sheath made of polyvinyl chloride, polyethylene or the like, there is no possibility of powder falling off. Mixing of the water-absorbent polymer and the resin binder is possible by a normal stirring operation, stability of the coating liquid,
In order to improve the viscosity / fluidity and coating workability, additives such as non-aqueous dispersants / viscosity modifiers and colorants are added to form a coating liquid.

The coating liquid of the present invention can be used a coating method that is usually used for solvent-based coating agents, screen printing method, roll coating method, blade coating method, spray coating method, etc. Controlling the amount of coating that affects, and the coating shape that affects the water absorption speed, that is, to obtain a state in which more water-absorbent polymer sticks its head onto the binder after drying, and the two types of coating liquids are on the same plane. It is most preferable to adopt the gravure printing method by alternately applying stripes, grids, etc. It is particularly preferable that the gravure is applied so that the gravure eyes are clearly visible, rather than the uniform leveling.

The water-resistant substrate used in the present invention is not particularly limited as long as it is a sheet-shaped one such as a biaxially stretched polyethylene terephthalate film, a polymer film such as a biaxially stretched polypropylene film, a nonwoven fabric made of fibers of a water resistant plastic. As a specific example, a material capable of slitting in a unit of several millimeters and capable of being elongated over 1000 m is particularly preferable for use as a cable covering material.

The pattern to be applied may be a striped pattern, a grid pattern, or a non-regular pattern, but when it is used as a water-running prevention material such as a communication cable, the stripe-shaped pattern is particularly used parallel to the water running direction. Is not preferable. The pitch of this pattern is 1 / the width of the tape when slitting and used as a cable tape.
A range of 10-50 is preferred. If it is 1/10 or less of the width of the tape, the properties of each film are difficult to be exhibited, and if it is 50 or more, the effect of alternately coating is difficult to obtain. The ratio of the two types of coatings is preferably such that the non-electrolytic polymer coating has a larger area or thickness than the electrolytic polymer.

<Function> An electrolyte-type water-absorbing polymer, for example, a sodium polyacrylate-based polymer, rapidly absorbs several hundred times to 1,000 times its own weight of pure water.
It decreases about 100 times in 9% aqueous solution, 60 to 70 times in Nac 1.6% aqueous solution, and shows almost no absorbability in seawater with higher salt concentration.

On the other hand, a non-electrolyte-type water-absorbing polymer, for example, a modified product of polyethylene oxide isocyanate, has a maximum water absorption of about 50 times at most.
It shows the same amount of liquid absorption as deionized water for deliquescent liquid of calcium chloride and 40% sulfuric acid for storage batteries. The absorption speed of the electrolyte type is three times faster.

From the above, when the polymer is used alone, depending on the type of water that has penetrated into the cable, water absorption and swelling are insufficient at all, and a water-stopping effect cannot be obtained. However, in the present invention, two types of polymer films are used. By using together, and by changing the area or thickness of the film, it exhibits stable water absorption and water retention from pure water to high-concentration salt solution, and has an excellent swelling and water-stopping effect when used as a cable covering material. Demonstrate.

Examples will be described below.

<Example 1.> A coating material having the following composition was prepared, and 110-on each side of a biaxially stretched polyethylene terephthalate film 50μ.
A sheet (a) of the present invention was obtained by applying and drying using a 85μ lattice engraving gravure plate. The pitch width was such that the coating liquid (A) had a film thickness of 3 mm and the coating liquid (B) had a film thickness of 5 mm. Each coating amount 2.1 g / m ^2, was adjusted to 3.5 g / m ^2.

Coating liquid (A) Sumika gel NP-1010 (~ 10μ) 43.5 parts by weight Super Clone 803MW 8.3 〃 Super Clone B 16.6 〃 Syloid 244 0.5 〃 Toluene / MEK = 1/1 31.1 〃 Coating liquid (B) Sumika gel R-30 Finely pulverized product (up to 15μ) 43.5 parts by weight Super Clone 803MW 8.3 〃 Super Clone B 16.6 〃 Syloid 244 0.5 〃 Toluene / MEK = 1/1 31.1 〃 Note) ・ Sumikagel NP-1010: Sodium polyacrylate cross-linked product [Sumitomo Chemical Industrial Co., Ltd.] ・ 〃 R-03: Crosslinked polyethylene oxide [Sumitomo Chemical Co., Ltd.] ・ Super Clone 803MW: Chlorinated PP20% toluene solution [Sanyo Kokusaku Pulp Co., Ltd.] ・ Super Clone B: Chlorinated EVA20 % Toluene solution [Sanyo Kokusaku Pulp Co., Ltd.]-Syloid 244: fine powder silica-for adjusting viscosity [Fuji Devison Chemical Co., Ltd.] As a comparative example, the coating liquid (A) and the coating liquid (B) were used. Sheet (b) of each comparative example by gravure coating in the same manner, respectively, to give the (c).

The results of the water absorption performance-water running prevention performance of the thus obtained sheets (a), (b) and (c) are tested by the following method.
Shown in 1.

Slit each sheet (a), (b) and (c) to a width of 1.3 mm to make a sample. The thicknesses of (a), (b) and (c) are about 90μ. This sheet is inserted into a polyvinyl chloride rectangular tube 1 having a cross-sectional shape shown in FIG. 1, and the running length is measured when a water head pressure of 1.2 m is applied from one end in the shape shown in FIG. did. The results are shown in Table-1.

(Running water length max, 2 m, measurement time max 24 hours) As water, (a) pure water (deionized water) and (b) ionic water (Nacl 2.7 g, CaCl ₂ 0.8 g / water 1) were used.

<Effects of the Invention> As described in detail above, in the present invention, since a water-absorbing polymer having two different water-absorbing mechanisms and absorption rates is used in combination,
Compared to when used alone, it exhibits stable water absorption capacity from pure water to highly concentrated salts close to seawater. If a value of 200 mm or less is actually obtained by the above-described test method as an example of a cable, it has sufficient performance as a water barrier coating material for an optical fiber cable for subscribers.

[Brief description of drawings]

FIG. 1 is an explanatory view showing the shape of a tube used in the test of the embodiment of the present invention, and FIG. 2 is an explanatory view showing the same test method.

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Claims (2)

[Claims] 1. A coating solution (A) comprising a fine powder of a three-dimensional partially crosslinked water-soluble polymer electrolyte and a non-aqueous solvent or a solventless resin binder, and three-dimensional partially cross-linked non-electrolyte water-soluble polymer. Water-absorbing / water-retaining sheet having a film in which at least one surface of a water-resistant substrate is partially coated with a fine powder of the product and a coating liquid (B) consisting of a non-aqueous solvent or a solvent-free resin binder . 2. A coating liquid (B) as compared with a coating liquid (A) film.
The water absorbent / water retaining sheet according to claim (1), which is a film having a large area or a large thickness.