JPH05214268A - Water-absorptive sheet and water-absorptive coating material applied thereto - Google Patents

Abstract

PURPOSE:To obtain a water-absorptive coating material which, when applied to a base sheet, can give a water-absorptive sheet capable of effectively preventing water from infiltrating thereinto and running therethrough, by using a resin binder, a water-insoluble water-absorptive resin powder and a specific compd. CONSTITUTION:A water-absorptive coating material comprises a resin binder (e.g. an acrylic resin), a water-insoluble water-absorptive resin powder (e.g. cross-linked polysodium acrylate), and a water-soluble org. compd. (salt) (e.g. ammonium salicylate), the max. mass of which as a solute soluble in 100g of water is pref. at least 1X10<2>g. This coating material 2 is applied to a base sheet 1 to form a water-absorptive sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water-absorbent sheet which absorbs water or an aqueous solution to swell when contacted with an aqueous solution such as water or a salt to prevent the movement of water, and particularly to its water-absorbing ability. The present invention relates to an improvement of a water-absorbent sheet having improved water content.

[0002]

2. Description of the Related Art As shown in FIG. 2, a water-absorbent sheet of this type comprises a base sheet a and a water-absorbent paint layer b made of a resin binder and a water-insoluble water-absorbent resin powder, which constitutes a main part thereof. It has been known.

These are widely used for products requiring a relatively high water absorption capacity, for example, sanitary products, diapers, disposable rags, paper towels, medical gauze, etc. In recent years, waterproofing which requires a higher water absorption capacity. Application to cables (optical fiber cables, power cables, etc.) has also been put to practical use in some cases.

An optical fiber cable will be described as an example of the waterproof cable to which the water absorbent sheet is applied. As shown in FIG. 3, this optical fiber cable includes a central tensile strength member c formed of a steel wire or fiber reinforced plastic, and a plurality of optical fiber core wires e to e ′ twisted around an intervening buffer layer d of polypropylene yarn.
And a water-absorbent sheet f wound around the outer periphery of the water-absorbent coating layer so that the water-absorbent coating layer is located inside thereof, and a wrap layer g (aluminum tape and polyethylene And a sheath layer h made of polyethylene or the like provided on the outer periphery thereof.

When the sheath layer h or the wrap layer g is damaged, rainwater, seawater or the like entering from the damaged part is absorbed by the water-absorbent paint layer of the water-absorbent sheet f, and the water-absorbent paint layer swells and It will block the damaged part. As a result, it is possible to prevent water from entering the inside of the optical fiber cable i and prevent water from running (running water) in the length direction of the optical fiber cable i.

By the way, most of the water-insoluble water-absorbent resins, such as starch-sodium acrylate graft copolymer, which constitutes the main part of the above-mentioned water-absorbent coating layer, are powders having low adhesiveness, Since it is difficult to apply it directly, conventionally, using a resin binder as described above,
A method of adhering the water-insoluble water-absorbent resin powder to the base sheet through this resin binder is adopted.

The resin binder is, for example, a chlorinated ethylene-vinyl acetate copolymer resin or a chlorinated polypropylene in consideration of the adhesiveness to the base sheet and the affinity with the water-insoluble water-absorbent resin. Resin (Japanese Patent Publication Sho 63-
19545), or a polyamide resin, a linear thermoplastic polyester resin, a vinyl chloride-vinyl acetate copolymer resin, a cyclized rubber, a chlorinated rubber, a urethane resin, etc. (Japanese Patent Publication No. 63-40665). (See Japanese Patent Publication No. 63-63376).

However, these resin binders are hydrophobic resins, and the water-absorbent coating material layer whose main part is composed of the water-absorbent resin and the water-insoluble water-absorbent resin powder is also hydrophobic. There is a problem in that the wettability is poor, and when the water-absorbent coating layer comes into contact with water or an aqueous solution of salt or the like, the water-absorbing performance cannot be sufficiently exhibited.

This is because the incompatibility of the resin binder with respect to water tends to hinder the contact between the water-insoluble water-absorbent resin powder and water, and the water-insoluble water-absorbent resin in the water-absorbent coating layer used for the water-absorbing action. This is because the powder is limited to those existing in a region where it is likely to come into contact with moisture, and reaches a saturated state with a small amount of water absorption, and the water absorption capacity after that is extremely reduced by the initial water absorption.

Therefore, when this water-absorbent sheet is applied to an optical fiber cable or the like which is required to have a high water-absorbing ability, the water-absorbing performance is deteriorated by a slight amount of water absorption as described above, so that running water, etc. However, there is a problem in that even the optical fiber cable in a portion where cracks and the like are not likely to occur is damaged and cannot be used, or equipment and the like connected to this optical fiber cable are deteriorated. Furthermore, if the optical fiber core wire in the optical fiber cable is immersed in the invading seawater for a long time, the strength of the optical fiber core is deteriorated, and in the worst case, the tension applied to the optical fiber core wire breaks the optical fiber core wire. There was a problem.

[0011]

SUMMARY OF THE INVENTION The present invention has been made by paying attention to the above problems, and the problems are as follows.
An object of the present invention is to provide a water absorbent sheet that can sufficiently withstand application to a waterproof cable or the like that requires high water absorption capacity.

[0012]

In order to solve the above problems, the present invention comprises a resin binder, a water-insoluble water-absorbent resin powder, and a water-soluble organic compound, or a salt thereof. The present invention provides a water-absorbing paint, wherein the water-soluble organic compound or its salt is water 1.
The maximum mass of the solute that can be dissolved in 00g is 1 × 10 ² g or more, 100 parts by weight of the resin binder and 120 to 1000 parts by weight of the water-insoluble water-absorbent resin powder, and an organic compound soluble in water, or a salt thereof 2- It is characterized by comprising 100 parts by weight. Then, the present invention provides a water-absorbent sheet characterized in that the water-absorbent coating material is applied onto a substrate sheet.

The present invention will be described in detail below. Examples of the resin binder according to the present invention include acrylic resin, polyurethane resin, unsaturated polyester resin, ethylene copolymer resin, polyamide resin, cellulose resin, chlorinated ethylene-vinyl acetate copolymer and / or chlorinated polypropylene. As the water-insoluble water-absorbent resin powder, a starch-sodium acrylate graft polymer, a starch-acrylonitrile graft polymer hydrolyzate, a partially cross-linked starch-polyacrylic acid copolymer is used. Polymers, partially cross-linked starch-polymethacrylic acid copolymers, partially cross-linked starch-polymethylmethacrylate hydrolysates, and starch-graft polymerization systems such as salts of the above substances, or poly Partially crosslinked acrylate, polyisobutylene-maleic anhydride copolymer, meta Examples thereof include crosslinked synthetic resin-based ones typified by a hydrolyzate of a methyl acetate-vinyl acetate copolymer, but basically, a water-soluble polymer is partially crosslinked to make it insoluble. There is no particular limitation as long as it has a property of rapidly absorbing and swelling water or an aqueous solution when brought into contact with an aqueous solution such as water or a salt, and retaining the water content.

The particle size of the water-insoluble water-absorbent resin powder applied is usually 5 μm or more and 200 μm or less for the following well-known reasons. That is, the particle size is 200
If it is rougher than μm, problems will occur in stability, fluidity, and coating workability when used as a water-absorbent coating. Furthermore, the smoothness and evenness of the coating surface will be lacking, and after application, it will be noticeably dropped from the base sheet. There is a harmful effect. On the other hand, a fine powder having a particle size of less than 5 μm has a problem that the water absorption capacity per 1 g is lowered and the powder easily aggregates, which makes the handling difficult. The water-insoluble water-absorbent resin powder having a shape closer to a sphere is superior in water absorption performance and workability, but is not limited to this shape.

The organic compound soluble in water or its salt is
A solute having a maximum mass of 1 × 10 ² g or more as an anhydride that can be dissolved in 100 g of water is used. Specifically, these are ammonium formate salt, salicylic acid ammonium salt, n-dodecyltrimethylammonium bromide, tetraethylammonium bromide, 4-aminobutyric acid and the like.

The composition of the water-absorbent coating composition of the present invention is such that 1 part of the water-insoluble water-absorbent resin powder is added to 100 parts by weight of the resin binder.
A ratio of 20 parts by weight or more and 1000 parts by weight or less is desirable. That is, the mixing ratio of the water-insoluble water-absorbent resin powder is 1
If the amount is less than 20 parts by weight, when the water-absorbent coating layer is applied to the base material sheet to form a water-absorbent sheet, the blending ratio is too small and the water-absorbing ability is not sufficient. It takes time to do so, and it becomes difficult to effectively exhibit the water absorbing effect. On the other hand, when the blending ratio of the water-insoluble water-absorbent resin powder exceeds 1000 parts by weight, the surface area becomes too large even if the water-insoluble water-absorbent resin powder is coarse particles, so that the addition amount of the resin binder is insufficient and the substrate It becomes difficult to securely hold the sheet. Therefore, it is desirable to set the water-insoluble water-absorbent resin powder to 120 parts by weight or more and 1000 parts by weight or less with respect to 100 parts by weight of the resin binder.

It is desirable that the organic compound or its salt soluble in water is in a proportion of 2 parts by weight or more and 100 parts by weight or less with respect to 100 parts by weight of the resin binder. That is,
When the compounding ratio of the organic compound or its salt that dissolves in water is less than 2 parts by weight, it is difficult for water to enter the water-absorbent coating layer and the water-insoluble water-absorbent resin does not swell sufficiently. The compounding ratio of the organic compound or its salt is 100
This is because if it exceeds the weight part, the water-absorbent coating material layer will be dissolved and fall off or flow out.

The method for producing the water-absorbent coating material of the present invention will be described below. A resin binder, a water-insoluble water-absorbent resin powder, an organic compound soluble in water, or a salt thereof is appropriately blended to obtain a water-absorbent coating material. In this case, the solvent is methanol, alcohol such as ethanol, acetic acid. Acetic acid esters such as ethyl and butyl acetate, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, and hydrocarbon solvents such as n-hexane and toluene can be applied.
The water-absorbent coating is applied as a dispersion-type coating in which a large amount of water-insoluble water-absorbent resin powder is dispersed in a large amount of solvent in which a resin binder is dissolved, but the stability, viscosity, fluidity, and coating of the coating are applied. In order to improve workability and the like, it is desirable to add a non-aqueous dispersant, a viscosity modifier, a colorant, and other additives in an amount of 2% by weight or less based on the total solid content. Further, an antiseptic, a bactericide, a fragrance, a deodorant, etc. may be added depending on the use of the water absorbent sheet.

As a mixing means at the time of compounding, stirring with a disper may be used, but it is desirable to adopt a mixing method having a higher energy such as an attritor or a ball mill.

As a means for applying the water-absorbent coating material to the base sheet, the usual coating method used for solvent-based coating material can be applied as it is, but the water-absorbent coating material contains a large amount of a solvent having a high drying property. In the case of paint-like paint, gravure method, roll coating method, flow coating method,
A dipping method or the like is preferable. The spray method can also be applied by appropriately adjusting the viscosity and nozzle shape of the water-absorbent paint.

Next, polyethylene terephthalate, polyvinyl chloride, metal or the like can be applied as the base material sheet on which the water absorbing coating layer is formed, and these are used in the form of a sheet or a non-woven fabric.

As for the range of application of the water absorbent sheet according to the invention of claim 5, in addition to the conventional products such as sanitary products, diapers, disposable rags, paper towels, medical gauze, etc., which are required to have a high water absorption capacity, It can also be applied to waterproof cables such as optical fiber cables.

When applied as a water-absorbent sheet for optical fiber cables, etc., the water-absorbent sheet is cut into a strip shape and the water-absorbent sheet is spirally wound around the outer peripheral surface of a plurality of optical fiber core wires twisted together with an intervening buffer layer. It is used by wrapping around.

[0024]

[Function] Urethane resin, which is a type of resin binder,
When it comes into contact with water, it repels water at all, does not penetrate, and has poor wettability. Further, the acrylic resin repels water when it comes into contact with water, but the wettability also improves with time,
Infiltration begins. That is, neither the urethane resin nor the acrylic resin allows water to penetrate quickly. When a water-soluble organic compound or a salt thereof is added to a urethane resin or an acrylic resin and the maximum mass of the solute as an anhydride that can be dissolved in 100 g of water is 1 × 10 ² g or more, The wettability is improved and water penetrates quickly. The reason for this is not clear, but it is considered that a kind of passage through which water permeates is formed in the resin layer.

[0025]

Example A water-absorbent coating material was prepared with the composition and parts by weight shown in Table 1.

[0026]

[Table 1]

Examples 1 and 2 and Comparative Examples 1 to 4 were dried on one surface of a non-woven fabric of 50 g / m ² as a base material sheet in a dry state.
The following confirmation test was conducted by applying g / m ² .

<Water absorption amount> Each water-absorbent sheet cut into 100 m x 100 m was placed in a bag made of a polyester nonwoven fabric of 5 μm or less and immersed in seawater, and after a lapse of 2 minutes, a part thereof was taken out. And place it between blotting papers, then 1
The water absorption was measured after the water was drained for 1 minute, and the data was taken as the water absorption after 2 minutes. The amount of water absorption was determined as the difference between the weight of the water absorbent sheet after draining and the weight of the water absorbent sheet itself not immersed in seawater. Further, another water-absorbent sheet soaked for 30 minutes was taken out, sandwiched between absorbent papers, and the same process was followed to obtain water absorption data after 30 minutes.

<Coatability> When the water-absorbent coating composition of each composition is applied on a polyethylene terephthalate film, the workability and coating unevenness are checked, and when the adhesiveness is poor and the workability is poor or there is coating unevenness. Was evaluated as ×, when there was no such a case was evaluated as ○, and the middle thereof was evaluated as Δ.

<Adhesion> The water-absorptive paint layer of each water-absorbent sheet was scratched with a nail and the peeled state was visually confirmed. Then, x was evaluated when peeling was easy, and o was measured when peeling was difficult, and the middle was evaluated as Δ.

<Blocking property> A plurality of water-absorbent sheets laminated on each other are prepared, and at 40 ° C. and 20% RH.
Under the conditions of, applying a pressure of 500 g / cm ² and checking whether the upper and lower water-absorbing sheets are adhered,
The case where there was no adhesion was evaluated as ◯, the case where there was adhesion was evaluated as x, and the middle thereof was evaluated as Δ.

<Flexibility> Whether or not the water absorbing coating layer of the water absorbing sheet has flexibility is checked by winding each water absorbing sheet around the optical fiber cable. The case where it was difficult to wind was evaluated as x, and the middle was evaluated as Δ.

<Water running test> The tape is reticulated to have a width of 1.3 mm, one water absorbent sheet is put in a slit having a cross section of 0.6 mm × 1.6 mm shown in FIG.
The running water distance after a predetermined time (24 hours) was measured over 2 m.

[0034]

[Table 2]

As shown by the results in Table 2, the water-absorbent sheet coated with the water-absorbent coating material of the present invention has a large water absorption amount and is excellent in coating property, adhesiveness, blocking property and flexibility, and thus has a running water. It stopped at a short distance, and it was confirmed that it was effective even when used for optical fiber cables.

[0036]

As described above, in the water-absorbent sheet of the present invention, when it comes into contact with water, water quickly permeates into the water-absorbent coating layer, and subsequently the water-absorbent resin develops a water-absorbing effect and swells. Therefore, when water is in use during use in a narrow space such as an optical fiber cable, invasion of water and running water are effectively prevented. Therefore, the optical fiber cable, in which the optical fiber core wire is protected by the water absorbent sheet coated with the water absorbent coating, is hardly affected by water even if the outer wall of the sheath is damaged and there is water infiltration. In addition, even in the manufacturing method, since the optical fiber core wire is sandwiched between the water-absorbent sheets or wound in a spiral shape, the automation is easy, and the on-site connection work is also easy. The target value is extremely large.

[0037]

[Brief description of drawings]

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

FIG. 2 is a perspective view of a conventional water absorbent sheet.

FIG. 3 is an explanatory view of a cross section of an optical fiber cable to which a conventional water absorbent sheet is applied.

FIG. 4 is an explanatory diagram of a water running test of a water absorbent sheet according to an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate sheet 2 ... Water-absorbent coating layer a ... Substrate sheet b ... Water-absorptive coating layer c ... Central tension body d ... Intervening buffer layer e, e '... Optical fiber layer f ... Water-absorption sheet g ... Wrap layer h ... Sheath layer i ... Optical fiber cable

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location A61F 13/15 A61L 15/60 B32B 27/06 7258-4F C08J 7/04 CFJ 7258-4F C09D 5 / 00 PPG 6904-4J 151/02 PGX 7142-4J 201/00 PDC 6770-4J // H01B 7/28 E 7244-5G C08L 101: 00 7167-4J 7603-4C A61F 13/18 307 A

Claims (4)

[Claims] 1. A water-absorbent coating material comprising a resin binder, a water-insoluble water-absorbent resin powder, and an organic compound soluble in water, or a salt thereof. 2. An organic compound soluble in water, or a salt thereof,
The maximum mass of solute that can be dissolved in 100 g of water is 1 × 10 ² g
The water-absorbing paint according to claim 1, which is as described above. 3. A resin binder of 100 parts by weight, water-insoluble water-absorbent resin powder of 120 to 1000 parts by weight, and an organic compound or a salt thereof dissolved in water of 2 to 100 parts by weight. 1. The water-absorbent paint according to 1. 4. A water-absorbent sheet obtained by applying the water-absorbent coating composition according to claim 1 on a substrate sheet.