JPH08302592A - Moistureproof paper - Google Patents

Abstract

PURPOSE: To produce a moistureproof paper by forming a coated layer comprising a water-repellent resin and a silica modified resin, satisfying both rule mark folding and cracking resistance and blocking resistance and excellent in maceration in reproduction. CONSTITUTION: A moistureproof coating solution is prepared by blending 10-90wt.% of a water-repellent resin such as a styrene/butadiene-based latex, etc., and 10-90wt.% of a silica modified resin such as a silica modified acrylic resin, etc. The objective moistureproof paper is obtained by coating base paper with the coating solution in 4-40μm thickness so as to give 3-15wt.% silica content in the coated layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moisture-proof paper, and more particularly to a moisture-proof coated paper which is excellent in disintegration property during recycling of waste paper and broke.

[0002]

2. Description of the Related Art Paper is a material used for a wide range of purposes, but it has essentially no moisture-proof property. Therefore, when moisture resistance is required, generally, a plastic film having excellent moisture resistance such as polyethylene, polypropylene or vinylidene chloride has been laminated on paper (so-called polylamination). Such poly-laminated paper has excellent moisture resistance and mechanical strength, and has expanded the field of use to paper containers such as newsprint wipes, waterproof packaging paper or liquid containers, paper plates, and paper trays.

In recent years, however, global environmental problems have come to the forefront, and the effective use of wood resources and the motivation for recycling have increased for forest conservation, and therefore used paper products or spoiled paper generated at paper processing plants. There is a strong demand for the return to paper. However, the disintegration property of the poly-laminated paper is extremely poor and it is not easy to obtain a good quality recycled paper.

Another type of moisture-proof paper is wax coated paper. This product also cannot be said to have sufficient disintegration property, and since wax is mixed in re-papermaking, printability is poor.
It is also slippery and may cause trouble such as load collapse during storage or transportation. Further, it has a big drawback that the moisture proof property is significantly lowered at the bent portion.

It has been proposed to blend a wax with a synthetic polymer in order to improve the disintegration property and folding resistance of the wax-coated paper. (For example, regarding a blend of synthetic rubber, Japanese Patent Publication No. 55-22597, styrene /
For a blend of an acrylic copolymer or an ethylene / acrylic copolymer, see Japanese Patent Publication No. 6-200498, etc.). Also, for the purpose of balancing disaggregation and bending resistance, the glass transition point of the acrylic emulsion to be blended ( Tg) is limited (Japanese Patent Application Laid-Open No. 6-287980), and a method of hot pressing after coating (Japanese Patent Application Laid-Open No. 6-184988) is proposed in order to obtain a moisture-proof property with a small coating amount. There is.

With such an improvement, the folding resistance of the moisture-proof paper is improved to some extent, and it has come to a level at which it can be used in applications such as newsprint wamps and water-resistant wrapping paper, but in applications where more severe performance is required. Is not enough yet. Particularly in cardboard or paperboard, the amount of change in expansion / contraction of the paper and the coating layer when folded is large, so that the coating layer is subjected to severe force. For example, in the processing of paper containers, carton boxes, etc., there is a step of putting a ruled line on the paper and bending it along the ruled line, and in the conventional wax-based moisture-proof coated paper, the moisture-proof coating layer is destroyed at this time (hereinafter The property of resisting the breakage of the coating layer when folding along a ruled line is called the ruled line cracking resistance), and in many cases the moisture resistance is significantly impaired.

[0007]

DISCLOSURE OF THE INVENTION The present invention provides a moisture-proof coated paper which has both excellent crease breaking resistance and blocking resistance, which were not sufficient in the conventional moisture-proof coated paper, and which has excellent disaggregation. Intended for development.

[0008]

In the present invention, a water repellent resin is used to obtain moisture resistance. Since the water-repellent resin is a high molecular substance, the dry film is tougher than low-molecular water-repellent agents such as wax, which makes it excellent in crease breakage, but considering the balance with blocking resistance, it is moisture-proof. It is hard to say that it is sufficient as a paint, and it is better for the water-repellent resin to be flexible in order to prevent the line from breaking, but it is better to be hard in terms of blocking resistance. That is, the two properties of crease breaking resistance and blocking resistance are inversely related,
Therefore, it is extremely difficult to satisfy both performances with a single water-repellent resin.

By the way, colloidal silica is well known as a material for improving blocking resistance. However, since colloidal silica has extremely poor compatibility with resins, even if blended, the cracking property of ruled lines will deteriorate.

As a result of intensive studies by the present inventors, when a silica-modified resin having a good compatibility between a water-repellent resin and a resin is used as a paint, a moisture-proof paper excellent in moisture resistance, ruled line breakage resistance and blocking resistance can be obtained. Therefore, the present invention has been completed. That is, the present invention relates to a moisture-proof paper having a coating layer made of a water-repellent resin and a silica-modified resin on the paper surface.

In the present invention, the coating material for forming the moisture-proof coating layer comprises a water-repellent resin and a silica-modified resin. Examples of the water-repellent resin include fluorocarbon vinylated products and long-chain alkyl vinyls. It is a copolymer resin of a monomer that forms a water-repellent polymer by polymerization such as a compound and another monomer, or a block product of wax or polyethylene and another resin.

The water-repellent resin in the coating layer of the moisture-proof paper of the present invention is preferably 10 to 90% by weight. When the water-repellent resin is less than 10% by weight, the coated paper does not show sufficient water repellency, and when it exceeds 90% by weight, it is difficult to achieve both the crease breaking resistance and the blocking resistance of the coated paper. Is becoming.

The silica-modified resin in the present invention is obtained by polymerizing in the presence of colloidal silica, for example, but it is preferably 10 to 90% by weight in the coating layer. 10% by weight of silica-modified resin
If it is less than the above range, the coated paper does not show a sufficient effect of improving the blocking resistance, and if it exceeds 90% by weight, the moisture resistance of the coated paper is deteriorated.

Further, the silica in the coating layer has a solid content of 3-1.
It is preferably 5% by weight. If the silica content is less than 3% by weight, sufficient blocking resistance cannot be obtained.
If it exceeds the weight%, the crease resistance of the crease will be deteriorated.

In the present invention, a resin other than the water-repellent resin and the silica-modified resin can be used in combination in the coating material, and by selecting an appropriate resin, a wider balance of physical properties can be achieved and the cost can be reduced. As the type of resin, acrylic resin,
Examples thereof include vinyl acetate resin, vinyl acetate / ethylene copolymer resin, vinyl chloride resin, vinylidene chloride resin, urethane resin, alkyd resin, polyester resin, natural rubber and synthetic rubber.

The paint used in the present invention also has water repellency,
Water repellent to improve coatability, mechanical properties or appearance,
Thickeners, viscosity modifiers, defoamers, wetting agents, plasticizers, solvents,
A cross-linking agent, pigment, dye or the like may be added.

The coating layer in the present invention is coated with a moisture-proof coating on a base material by a conventional method such as a blade coater, roll coater, air knife coater or size press coater, and dried with hot air. It can be obtained by drying with a container, an infrared dryer or the like.

The thickness of the coating layer is preferably 4 to 50 μm. If the thickness of the coating layer is less than 4 μm, sufficient moisture resistance cannot be obtained, and if it exceeds 50 μm, blocking resistance tends to decrease, which is economically undesirable.

[0019]

EXAMPLES The present invention will now be specifically described with reference to examples, but the present invention is not limited to these examples. In the examples and comparative examples, “parts” and “%” represent “parts by weight” and “% by weight”, respectively, unless otherwise specified.

The evaluation items and evaluation methods in the present invention are as follows. Water repellency: According to JIS P8137. R7 or higher was passed.

Water vapor transmission rate: According to JIS Z208. Three
A value of 00 g / m ² · 24 hours or less was passed.

Ruled line crease cracking property: In the atmosphere of 20 ° C. and 65% RH, a linear pressure of 30 kg / cm for 1 minute was applied to the sample with a width of 10 cm to form a ruled line, and the folded portion was methylene blue / ethanol = 1. / 9 solution was applied, and the presence or absence of cracks was observed, and the following four grades were given, and a rating of Δ or above was passed.

⊚: No cracking. ◯: There are 1 or 2 small cracks. Δ: There are 3 to 5 small cracks. X: 6 or more small cracks or large cracks.

Abrasion resistance: Put a filter paper on the coated surface,
A friction tester (Souza Land Lapotester manufactured by Toyo Seiki Co., Ltd.) is used to perform 50 reciprocating frictions at a load of 4 pounds in an atmosphere of 20 ° C. and 65% RH. The surface condition was observed, and the following four grades were given, and a grade of Δ or above was passed.

⊚: No change is observed. ◯: Gloss slightly changed. Δ: There is a change in gloss. X: Peeling occurs.

Blocking resistance: A test piece of coated paper of 5 cm × 4 cm is put on its coated surfaces at 50 ° C. and 75% RH.
In the atmosphere of, apply a load of 10 kg, leave it for 24 hours,
Leave in an atmosphere of 20 ° C and 65% RH for 1 hour, slowly peel it off by hand, and give the following 5 grades. △
The above was passed.

⊚: No adhesion at all ○: Peels with a slight noise. Δ: A considerable amount of noise was generated when peeling, but the adhesive surface was not roughened. X: When peeled off, a considerable noise was generated and the adhesive surface was roughened. XX: Adhered.

Disaggregation: A coated paper test piece cut into about 1 cm square was added to tap water at room temperature so that the pulp concentration was 4%, and disaggregation was performed at 3000 rpm for 10 minutes using a Tappi standard disintegrator, The disaggregated material was handmade to make a paper, and if no undispersed binding resin was observed with the naked eye, it was determined to be acceptable.

Example 1 As a water-repellent resin, Pateracol HB-604 (styrene / butadiene latex water-repellent resin manufactured by Dainippon Ink and Chemicals, Inc.) and as a silica-modified resin, Almatex S-181 (manufactured by Mitsui Toatsu Chemicals, Inc.) Silica-modified acrylic emulsion, containing 30% silica) at a solid content ratio of 80
The mixture was mixed so as to be / 20 to obtain a paint. (Silica contained in the paint is 6% by weight in solid content) This paint is used as a cup base paper (Tokyo Paper Co., Ltd., basis weight 32
0 g / m ² ) with an applicator dry coating amount of 12 g
/ M ² coating, 120 with a hot air circulation dryer
Drying was performed at 30 ° C. for 30 seconds to obtain a moisture-proof coated paper. This moisture-proof paper has a water repellency of R10 and a penetration of 190 g / m ² · 24 h
r, crease breaking resistance was good, abrasion resistance was good, blocking resistance was good, and disaggregation was acceptable.

Examples 2 and 3 and Comparative Examples 1 and 2 Moisture-proof coated papers were obtained in the same manner as in Example 1 except that the water repellent resin in the coating composition was changed as shown in Table 1.

[0031]

[Table 1]

As is clear from the evaluation results in Table 1, the water repellency and abrasion resistance were reduced by replacing the water repellent resin with a soft acrylic resin. Further, in Comparative Example 2 in which water repellency was imparted by a wax emulsion and blocking resistance was improved by a hard acrylic emulsion (BRIMAL AC-61), the crease breaking resistance and the abrasion resistance were not good.

Examples 4, 5 and Comparative Examples 3, 4 Moisture-proof coated papers were obtained in the same manner as in Example 1 except that the silica-modified resin in the coating composition was changed as shown in Table 2.

[0034]

[Table 2]

As is clear from the evaluation results in Table 2, when the silica-modified resin is reduced, the moisture permeability is improved, but the abrasion resistance and blocking resistance are decreased. Further, when the silica-modified resin was replaced with Korodal silica (Comparative Example 4), the breaking property of ruled lines and the moisture permeability were extremely lowered.

Examples 6 and 7 and Comparative Example 5 A moisture-proof paper was obtained in the same manner as in Example 2 except that the coating amount was changed. Table 3 shows the dry coating amount and the evaluation results.

[0037]

[Table 3]

When the coating amount was reduced too much (Comparative Example 5), the cracking property of ruled lines and the water vapor transmission rate were extremely lowered.

[0039]

As described above, the present invention is constituted and has excellent disaggregation property at the time of recycling of waste paper and broke, and has excellent disaggregation property such as crease line crease resistance and blocking resistance. It is effective in providing a moisture-proof paper.

Claims (4)

[Claims] 1. A moisture-proof paper having a coating layer comprising a water-repellent resin and a silica-modified resin on the surface of the paper. 2. The moisture-proof paper according to claim 1, wherein the coating layer comprises 10 to 90% by weight of a water-repellent resin and 10 to 90% by weight of a silica-modified resin. 3. The moisture-proof paper according to claim 1, wherein the silica in the coating layer is 3 to 15% by weight. 4. The moisture-proof paper according to claim 1, wherein the coating layer has a thickness of 4 to 50 μm.