JPH08127995A - Moistureproof paper - Google Patents

Abstract

PURPOSE: To provide a moistureproof paper for packaging, reutilizable as waste paper after use and exhibiting excellent moistureproofness. CONSTITUTION: A moistureproof layer is formed by applying an emulsion containing a synthetic resin latex and a wax to one surface of a substrate. In the moistureproof paper produced by the above process, an organic solvent is impregnated into the paper from the back of the substrate and dried after contacting the solvent with the moistureproof layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moistureproof paper for packaging which can be easily disintegrated in water after use and reused as recycled pulp.

[0002]

2. Description of the Related Art Conventionally, for absorbing high quality paper, bleached kraft paper, unbleached kraft paper, various coated papers, and packaging such as plain paper of high quality paper or coated paper, moisture absorption of the product To prevent this, moisture- and water-resistant wrapping paper is used that does not cause deterioration of the contents due to moisture absorption even if polyolefin-based polymer compounds such as polyethylene and polypropylene are laminated on paper and stored in a high humidity environment. There is.

[0003] In addition, for heavy-duty base paper such as cement bags, salt bags, feed bags, fertilizer bags, and garbage bags, the bag is made into a bag and then packed, and after that, it absorbs moisture and water while preventing heavy moisture from being conveyed. Therefore, a polyolefin laminated paper in which polyethylene, polypropylene, etc. are laminated on kraft paper (hereinafter referred to as poly-laminated paper) and kraft paper are stacked and used as a bag.

However, since these poly-laminated papers are reused as used papers after use, they are not sufficiently disintegrated in water even if they are recovered, and small pieces of the laminated film remain in the pulp suspension, and these are broken into sheets. Even if it is processed and dried, it cannot be reused because it becomes recycled paper full of defects due to the film. For this reason, used poly-laminated paper can only be incinerated or dumped in landfills, and it is difficult to say that it has a sufficient function in the sense of preserving our livable environment.

Therefore, it is known to try to develop a moisture-proof paper that can be recovered as recycled pulp. For example, an emulsion obtained by dispersing a synthetic hydrocarbon resin and a wax in water in the presence of at least a saponification equivalent of alkali using a styrene-maleic acid copolymer and a surfactant instead of a plastic film such as polyethylene. A method for producing a moisture-proof paper is disclosed in which a moisture-proofing agent comprising a substance and a thermoplastic acrylic emulsion is applied to paper and dried (JP-A-56-1).
No. 48997).

Further, a paraffin wax having a specific melting point, and an emulsion of a maleic or fumarized rosin ester with a polyhydric alcohol, liquid polybutene, and a wax containing a rosin as a main component,
Alternatively, a mixture of the emulsion and the synthetic resin latex is applied to the surface of a fibrous support such as high-quality paper and kraft paper,
A method for producing a moisture-proof paper that is dried under heating has been disclosed (JP-A-61-47896).

However, the moisture-proof paper made of the emulsion containing these disclosed synthetic resins or waxes is easily re-dissolved when placed in water for reuse after use, but the water vapor transmission rate (measured by JIS Z0208). However, the moisture resistance is not sufficient considering the long-term storage conditions.

[0008] Further improvement of the moisture-proof performance is desired in order to popularize the moisture-proof paper having these re-disintegration properties and to keep our living environment comfortable, but the present situation is that the objective has not been achieved yet.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a moistureproof paper for packaging which has high moistureproofness and can be collected as waste paper.

[0010]

The present invention relates to a moisture-proof paper comprising a support and a moisture-proof layer formed by coating an emulsion containing a synthetic resin latex and a wax on one side of the support, and impregnating an organic solvent from the back side of the support. The moisture-proof paper is characterized by being dried after being brought into contact with the moisture-proof layer.

The present inventors have examined in detail the structure of a moisture-proof paper formed by forming a moisture-proof layer made of an emulsion containing a synthetic resin latex and a wax on the surface of a support. That is, when a coating liquid consisting of an emulsion containing a synthetic resin latex and a wax (paraffin component) has been applied to the surface of the support, the paraffin component in the emulsion migrates through the moisture-proof layer during film formation and forms a moisture-proof layer. It has been thought that it selectively gathers on the surface and the pulp surface in contact with the moisture-proof layer to form a wax coating layer, which prevents the ingress of moisture from the outside (packaging technology,
(September 1982, pp. 42-46), as a result of further detailed study of the structure of the moisture-proof layer, a large number due to the deviation from the closest packing of latex particles which is inevitably generated during dry film formation of synthetic resin latex. It was found that the existence of the pores (deposition portion of the film) affected the moisture permeability. The moisture-proof performance of the moisture-proof paper is affected not only by the effect of preventing moisture from entering by the wax coating layer, but also by the presence of these pores.

Generally, when a synthetic resin latex forms a film, the latex particles coagulate and fuse with each other in an attempt to minimize their surface energy, but it is said that the particles never close to each other and generate a large number of film-forming defects. ing. Therefore, the inventors have reached the idea that the moisture-proof performance may be further improved if the number of film-defects can be reduced, and the present invention has been completed. That is, since the moisture-proof performance is not sufficient only by the wax coating layer which has been conventionally considered, the moisture permeability of the moisture-proof paper obtained by the conventional method cannot show a good value equal to or lower than that of the poly-laminated paper.

The inventors of the present invention have conducted extensive studies on a method of eliminating or reducing the film-forming defects of the synthetic resin latex, and as a result, the moisture-proof layer was brought into contact with an organic solvent or a mixed solvent thereof (hereinafter referred to as a solvent solution). It was concluded that higher moisture-proof performance can be obtained by dissolving or swelling a part of the synthetic resin latex contained in the moisture-proof layer so as to eliminate or reduce the defective portion of film formation.

Therefore, the effective effect of the present invention is that a part of the moisture-proof layer is eluted into the solvent liquid and the moisture-proof layer becomes thin or swells, and the color of the moisture-proof layer becomes white. This is the case when changing. When a part of the moisture-proof layer is dissolved, film-forming defects on the surface of the moisture-proof layer which are in contact with the solvent liquid disappear and the film-forming density of the moisture-proof layer increases, so that the moisture-proof property as a whole is remarkably improved.

The present invention is very easy to carry out. For example, by forming a moisture-proof layer on one surface of the support and drying the solution, a solvent solution is prepared and impregnated or coated with the solvent solution from the back surface side of the support. The solvent solution may be introduced in the thickness direction of the body, and a part of the moisture-proof layer on the support side may be brought into contact with the solvent solution, followed by drying.

Examples of the solvent liquid used in the present invention include n-hexane, cyclohexane, acetone, methyl ethyl ketone, isopropanol, toluene, ethyl acetate, etc., but if it can dissolve, swell or whiten a part of the moisture-proof layer. It is not limited to these. When such a solvent solution and a moisture-proof layer made of an emulsion containing a synthetic resin latex and a wax are brought into contact with each other, the shape of the moisture-proof layer resin hardly changes visually, and its color changes from white translucent to white, or At the same time, the moisture-proof layer becomes thin, and at the same time, its color changes from white translucent to colorless transparent.

However, when such a solvent solution is impregnated from the back surface of the support for a long time, a large amount of the components of the moisture-proof layer are dissolved away by the solvent solution, so that a through-hole is formed in the moisture-proof layer and the moisture-proof performance is obtained. May become significantly worse. Therefore, the impregnation time is usually 1 second to 5 minutes, preferably 1 second to
1 minute is preferred.

On the other hand, when the impregnation and coating of the solvent solution are carried out from the surface of the moisture-proof layer, the solvent solution directly contacts the moisture-proof layer, so that a large amount of the constituent components of the moisture-proof layer are dissolved and a through hole is formed in the moisture-proof layer. It is easy to do so, and the moisture proof performance is significantly deteriorated. Therefore, when impregnation and coating with the solvent solution are performed from the surface of the moisture-proof layer, the contact time between the solvent solution and the surface of the moisture-proof layer needs to be extremely short such as 1 second or less, which cannot be practically performed.

Equipment for impregnating and coating with such a solvent solution is not particularly limited, but can be arbitrarily selected from a bar coater, a roll coater, a gravure coater and the like. Also,
The impregnation of the solvent liquid and the drying after coating are preferably performed at a relatively low temperature of 60 to 120 ° C. because of the volatility and flammability of the solvent liquid used.

The synthetic resin latex used in the moisture-proof layer of the present invention is an aqueous emulsion, which contains an aromatic vinyl monomer, an aliphatic conjugated diene monomer, an ethylenically unsaturated fatty acid monomer, and other comonomers. Composed of polymerizable monomers. For example, synthetic rubber latex such as styrene / butadiene latex and methyl methacrylate / butadiene latex, and styrene / acrylic emulsion are used.

The aromatic vinyl monomer imparts appropriate hardness and water resistance to the resulting copolymer resin, and can be selected from, for example, styrene, α-methylstyrene, monochlorostyrene, vinyltoluene and the like. . Styrene is especially preferred.

The aliphatic conjugated diene-based monomer imparts appropriate flexibility to the resulting copolymer resin, for example, 1,3-butadiene, 2-methyl-1,3-butadiene, 2-chloro. Examples thereof include -1,3-dibutadiene, and 1,3-butadiene is particularly preferable.

The ethylenically unsaturated acid monomer is effective for increasing the adhesive strength of the copolymer resin obtained and for improving the stability of the copolymer latex as a colloid. For example, acrylic acid. At least one of unsaturated carboxylic acids such as methacrylic acid, crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid and butenetricarboxylic acid, itaconic acid monoethyl ester, fumaric acid monobutyl ester and maleic acid monobutyl ester. Unsaturated sulfonic acids such as unsaturated polycarboxylic acid alkyl ester having one carboxyl group, acrylamidopropanesulfonic acid, acrylic acid sulfoethyl sodium salt, and methacrylic acid sulfopropyl sodium salt, or a salt thereof can be used. Of which, acrylic acid, methacrylic acid, and itacone And fumaric acid are preferably used.

Other monomers (comonomers) copolymerizable with the above monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, and ethylenically unsaturated carboxylic acid alkyl esters such as butyl acrylate, Ethylenically unsaturated nitriles such as acrylonitrile and methacrylonitrile, β-hydroxyethyl acrylate,
Ethylenically unsaturated carboxylic acid hydroxyalkyl ester such as β-hydroxypropyl acrylate and β-hydroxyethyl methacrylate, ethylenically unsaturated carboxylic acid amide such as acrylamide, methacrylamide, N-methylol acrylamide, and diacetone acrylamide And derivatives thereof, unsaturated carboxylic acid glycidyl esters such as glycidyl acrylate and glycidyl methacrylate, and vinyl compounds such as acrolein and allyl alcohol. Among these monomers (comonomer), methyl methacrylate as an unsaturated carboxylic acid alkyl ester, acrylonitrile as an ethylenically unsaturated nitrile, β-hydroxyethyl acrylate as an unsaturated carboxylic acid hydroxyalkyl ester, and unsaturated carboxylic acid. Acrylamide is preferably used as the amide and its derivative.

In general, these latexes have defects during film formation, but the moisture-proof performance is significantly reduced due to these defects, so it is necessary to reduce film defects in order to improve the moisture-proof performance. Therefore, the glass transition point of latex is -3.
0 to 10 ° C., and the minimum film forming temperature is also preferably 10 ° C. or lower. When the glass transition point of the latex is less than -30 ° C, the resulting latex resin is not preferable because it causes blocking (adhesion is expressed by heat or pressure, and a phenomenon in which a coated surface and a non-coated surface adhere). On the other hand, if the temperature exceeds 10 ° C, the latex resin formed is hard and has low resistance to folds, which is not preferable.

The wax-containing emulsion used in the present invention is not particularly limited as long as the melting point of the wax is about 50 ° C. or higher. For example, a paraffin wax or an esterified product of a modified rosin and a polyhydric alcohol as a main component is used. What is contained is used. In addition to the above, the emulsion containing wax may be an emulsion containing liquid polybutene, rosin, an etherified product of polyoxyalkylene, etc. (see JP-A-61-47896). Further, as the waxes, microcrystalline wax having a melting point of 50 ° C. or higher, polyethylene wax and the like can be emulsified and used similarly to the paraffin wax. The blending amount of the synthetic resin latex and the wax-containing emulsion is preferably a weight ratio of the synthetic resin latex: the wax-containing emulsion = 99: 1 to 50:50 in terms of solid content. If the weight ratio of the wax-containing emulsion is less than 1, sufficient moisture resistance cannot be obtained, and if it exceeds 50, the resistance of the moisture-proof sheet to folds becomes small, and the moisture proof property of the portion where the folds occur is extremely high. Deteriorate.

In the present invention, the coating amount of the moistureproofing agent is 5 to 30 g / m ² in terms of solid content. When the coating amount is less than 3 g / m ² , the irregularities of the support cannot be covered sufficiently and the moisture resistance is extremely reduced. When it is higher than 30 g / m ² , the moisture resistance obtained is only slightly improved with an increase in the coating amount, and the level is reached, resulting in high cost, which is uneconomical.

Although the equipment for applying the moistureproof agent is not particularly limited,
Air knife coater, bar coater, roll coater,
It can be arbitrarily selected from a blade coater, a gate roll coater and the like.

The support may be one that is easily dispersed in water by mechanical disaggregation, such as chemical pulp such as hardwood kraft pulp and softwood kraft pulp, high-quality paper made from pulp selected from mechanical pulp, etc., Examples include medium quality paper, single-gloss kraft paper, Ryosara kraft paper, and kraft stretch paper. There is no particular limitation on the basis weight of these base papers, and those having a basis weight of 30 to 300 g / m ² are appropriately selected and used according to the purpose. In addition, a support having a strong tension such as a non-woven fabric, resin-impregnated paper, or vellum paper can be used for applications that do not particularly require re-disintegration property.

The present invention will be specifically described below with reference to examples, but the following examples do not limit the present invention.

[0031]

【Example】

Example 1 Paraffin wax having a melting point of 70 ° C. and an ester compound of fumarized rosin and glycerin (softening point 100 ° C.)
As a main component, and liquid wax containing polybutene, rosin polyoxyalkylene monoalkylene ether, and ethylene glycol monoalkyl ether (trade name: OKW-40, Arakawa Chemical Co., Ltd., solid content 45) % By weight) and styrene butadiene latex (trade name: OX1007W, manufactured by Nippon Zeon Co., Ltd., solid content 5)
0% by weight), the total solid content concentration becomes 38% by weight,
And the ratio of them in terms of solid content, latex: wax-containing emulsion = 58: 42 to become as mixed and Deki moisture proof agent (hereinafter OX / OKW hereinafter) unbleached both further having a basis weight of 70 g / m ² and Kraft paper with Mayer bar as solid content 1
After coating at 2 g / m ² and drying at 120 ° C. for 30 seconds, the back surface was further impregnated with acetone for 30 seconds and air-dried for 2 minutes to produce a moisture-proof paper.

Example 2 A moisture-proof paper was produced in the same manner as in Example 1 except that the solid coating amount of the moisture-proofing agent was 8 g / m ² .

Examples 3 to 6 Example 1 except that the back surface was impregnated with methyl ethyl ketone (Example 3), n-hexane (Example 4), isopropanol (Example 5) and toluene (Example 6). A moisture-proof paper was manufactured in the same manner.

Example 7 A moisture-proof paper was produced in the same manner as in Example 1 except that a 50% by weight aqueous acetone solution was applied to the back surface by a Mayer bar and then dried by heating at 60 ° C. for 30 seconds.

Example 8 A moisture-proofing agent (trade name: X592-651E, manufactured by Saiden Chemical Co., Ltd., solid content: 42% by weight, hereinafter referred to as X592) composed of an acrylic styrene latex and a wax-containing emulsion is used, and a basis weight of 70 is used. g / m Meyer in unbleached both kraft paper ² - bar - in coated so as to be 12 g / m ² as a solid content, was dried for 30 seconds at 120 ° C., impregnation further 30 seconds acetone from the back surface Then, a moisture-proof paper which was air-dried for 2 minutes was produced.

Example 9 A moisture-proof paper was produced in the same manner as in Example 8 except that the solid content coating amount of the moisture-proofing agent was 8 g / m ² .

Comparative Example 1 A moisture-proof paper was manufactured in the same manner as in Example 1 except that the back surface was not impregnated with an organic solvent.

Comparative Example 2 A moisture-proof paper was produced in the same manner as in Example 1 except that the solid content coating amount of the moisture-proofing agent was 18 g / m ² and the back side was not impregnated with an organic solvent.

Comparative Example 3 A moisture-proof paper was produced in the same manner as in Example 8 except that the back surface was not impregnated with an organic solvent.

Comparative Example 4 A moisture-proof paper was produced in the same manner as in Example 8 except that the solid content coating amount of the moisture-proofing agent was 20 g / m ² and the back side was not impregnated with an organic solvent.

The moisture proof papers obtained in Examples 1 to 9 and Comparative Examples 1 to 4 were evaluated for moisture permeability and disintegration property using the following test methods. As a reference example, the moisture permeability and disintegration property of a commercially available polyethylene laminated paper (polyethylene thickness 20 μm) were also evaluated.

[Test Method] 1) Moisture Permeability Measured by JIS Z0208 (cup method) B method with the coated surface facing outward. 2) Disaggregation: 1 cm to a concentration of 1.6% in 500 ml of water
A sample having a size of 1 cm square was prepared, and this sample was put in a domestic mixer together with water and stirred for 2 minutes, then the contents were taken out, and a sheet was prepared by a laboratory handmade machine. The obtained sheet was placed in a hot air circulation oven at a temperature of 120 ° C. for 20 minutes, taken out, and then visually examined for the presence of undisaggregated substances (film pieces, paper pieces, etc.) to evaluate disaggregation property. The case where no undisintegrated matter was contained and a uniform sheet was formed was regarded as good.

Table 1 shows the moisture vapor transmission rate and disintegration property of the moisture-proof paper having a solid coating amount of the moisture-proofing agent of 12 g / m ² with and without impregnation with acetone from the back surface. Table 1
As is clear from the above, the water vapor transmission rate was lowered by the acetone impregnation, and the moisture-proof performance higher than that of the reference laminated polyamid paper was obtained.

[0044]

[Table 1]

Table 2 shows the solid coating amount of the moisture-proofing agent required to obtain a moisture permeability of about 30 g / m ² · 24 hr for the moisture-proofing paper impregnated with acetone from the back side and the moisture-proofing paper not impregnated with acetone. As is clear from Table 2, the amount of the moisture-proof agent applied was reduced by the impregnation with acetone.

[0046]

[Table 2]

Table 3 shows the moisture vapor transmission rate and disintegration property of the moisture-proof paper having a solid coating amount of the moisture-proofing agent of 12 g / m ² when the type of the organic solvent impregnated from the back side is changed. As is clear from Table 3, the water vapor transmission rate was lowered also in organic solvents other than acetone, and the moisture-proof performance higher than that of the polylaminated paper of Reference Example was obtained.

[0048]

[Table 3]

[0049]

As is clear from Tables 1, 2, and 3, the moisture-proof paper obtained in the present invention has a reduced amount of the moisture-proof agent applied, and has excellent disaggregation properties and moisture-proof performance superior to that of commercially available poly-laminated paper. Have.

Claims (1)

[Claims] 1. A moisture-proof paper having a moisture-proof layer coated with an emulsion containing a synthetic resin latex and a wax on one side of a support, wherein the organic solvent is impregnated from the back side of the support to bring it into contact with the moisture-proof layer. Moisture-proof paper characterized by being dried after being dipped.