JP7366568B2 - Moisture-proof paper and its manufacturing method - Google Patents

Description

The present invention relates to moisture-proof paper, and more particularly to moisture-proof paper that is both waterproof and cosmetic, and a method for producing the same.

2. Description of the Related Art Conventionally, paper containers, packaging materials, and the like made of paper base materials in various forms have been used to package various articles. In general, paper containers and packaging materials are based on paper, so water vapor can permeate through them extremely easily, and moisture generated from the packaged item can cause a decrease in strength. . Furthermore, some items to be packaged or packaged are extremely sensitive to water vapor or the like entering from the outside. Furthermore, when transporting chilled products with ice, the paper containers and packaging materials need to be waterproof.

For this reason, a method of forming a wax layer by coating the surface of a paper base material with a water-repellent wax composition, and a method of forming a resin film by laminating polyethylene film, polypropylene film, etc. have been proposed. .

In addition, a moisture-proof paper (with a surfactant layer formed on the outermost layer by applying a mixture of a wax emulsion, a water-insoluble synthetic resin emulsion, and a surfactant to at least one side of the paper, and then applying a heat treatment to the paper) Patent Document 1) is known. Furthermore, at least one side of the base paper has at least two coating layers, and the coating layer located on the outermost surface contains microcapsules encapsulating wax, and the coating amount is 0.5 g/solid content. m ² or more and 2.5 g/m ² or less, and the coating layer located between this outermost coating layer and the base paper is a moisture-proof coating containing an acrylic copolymer and/or a styrene copolymer. A liner (Patent Document 2) is known.

Japanese Patent Application Publication No. 10-266096 Japanese Patent Application Publication No. 2011-162899

However, with the method of forming a wax layer, it is difficult to sufficiently suppress moisture permeability even if a single layer of wax composition is applied. It is necessary to apply the coating multiple times, but in that case, the process becomes extremely complicated. In addition, the method of forming a resin film requires lamination, which makes the process complicated. Furthermore, the paper or paperboard on which the resin film has been formed has extremely poor disintegration properties when collected and used as waste paper after use, making it difficult to recycle. is difficult.

In addition, moisture-proof paper with a surfactant layer formed on the outermost layer or moisture-proof liner with at least two coated layers have good moisture-proof properties, but do not have waterproof properties. It is difficult to use it as a container or packaging material for transporting ice products, etc.

Furthermore, in paper or paperboard that has been made moisture-proof by providing a coating layer on the surface of the base paper, as in the past, pigments are contained in the coating agent in order to increase whiteness and improve cosmetic properties. things were being done. However, when the coating agent contains pigments, the functions of the coating agent are not fully demonstrated, and as a result, it is necessary to increase the moisture resistance by thickening the coating layer, resulting in an increase in manufacturing costs. There was the problem of inviting.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a moisture-proof paper that has both moisture-proof and waterproof properties and has excellent cosmetic properties, and a method for producing the same.

That is, the invention according to claim 1 for solving the above problem comprises: a paper base material having a waste paper pulp content ratio of 10% by mass or more; a coating layer located on at least one surface of the paper base material; , the moisture permeability is 50 g/m ² ·24 h or less, the coating layer contains a synthetic resin and wax, the whiteness of the coating layer surface is 20% or more, and the coating layer surface has a The 120 second Cobb water absorption is 1 g/ ^m2 or less, the surface smoothness of the coating layer is 40 seconds or more , and the coating amount of the coating layer is 20 g/m2 ^or less . It is a moisture-proof paper.

In one embodiment, the coating layer contains a pigment. Further, the pigment includes at least an inorganic pigment . Moreover , the basis weight of the paper base material is 10 g/m ² or more and 750 g/m ² or less.

Further, the invention according to claim 5 for solving the above problem includes a paper base material and a coating layer located on at least one surface of the paper base material, and has a moisture permeability of 50 g/m ² · 24 hours or less, the whiteness of the surface of the coating layer is 20% or more, the 120 second Cobb water absorption of the surface of the coating layer is 1 g/m ² or less, and the smoothness of the surface of the coating layer is 40%. A method for producing moisture-proof paper having a moisture-proofing time of 10% or more, wherein a coating amount of a coating agent containing a synthetic resin and a wax is applied to at least one surface of the paper base material having a content of waste paper pulp of 10% by mass or more. 20 g/m ² or less using a blade coating method, and drying the applied coating agent to form the coating layer. .

The moisture-proof paper according to the present invention is as described above, and has moisture-proof properties as well as waterproof properties.This suppresses a decrease in strength in applications where it comes into contact with moisture or moisture, and also suppresses the decrease in strength of the coated layer surface. It has the effect of having excellent cosmetic properties. Furthermore, the method for producing moisture-proof paper according to the present invention is as described above, and it is possible to produce moisture-proof paper that is both moisture-proof and waterproof and has excellent cosmetic properties.

[Moisture-proof paper]
The moisture-proof paper according to the present invention includes a paper base material and a coating layer located on at least one surface of the paper base material, and has a moisture permeability of 50 g/m ² ·24 h or less, preferably 20 g/m ^2.24 h or less, more preferably 10 g/m ^2.24 h or less, the coating layer contains synthetic resin and wax, and the whiteness of the coating layer surface is 20% or more, more preferably 30% or more, more Preferably it is 45% or more, more preferably 55% or more.

The moisture-proof paper according to the present invention has an excellent moisture-proof property because the moisture permeability is 50 g/m ² ·24 h or less. Furthermore, the moisture-proof paper of the present invention also has excellent waterproof properties.

Here, the moisture permeability of the moisture-proof paper is a value measured from the coating layer side of the moisture-proof paper in accordance with JIS Z 0208. In addition, the waterproofness of moisture-proof paper means that even if a container is made using moisture-proof paper, water is poured into the container, and the container is left for three weeks, the water will not seep out and the shape of the container will not change. Or, it means that the container shape is maintained although there is some deformation.

In addition, the whiteness is a value measured in accordance with JIS P8148 using an optical colorimetry system CMS-35SPXM compatible with ISO whiteness manufactured by Murakami Color Research Institute Co., Ltd.

<Paper base material>
The paper base material constituting the moisture-proof paper of the present invention can have an optimum basis weight depending on the use of the moisture-proof paper. When the paper base material is single-layer paper, the lower limit of the basis weight can be set appropriately in the range of 10 g/m ² or more and the upper limit 250 g/m ² or less. For example, when the paper base material is kraft paper The lower limit of the basis weight can be set in a range of 30 g/m ² or more, and the upper limit can be set in a range of 250 g/m ² or less. In addition, when the paper base material is a multilayer paperboard having two or more paper layers, the lower limit of the basis weight can be set as appropriate within the range of 100 g/ ^m2 or more and the upper limit of 750 g/ ^m2 or less. For example, in the case of a corrugated liner, the lower limit of the basis weight can be set in a range of 100 g/m ² or more, and the upper limit can be set in a range of 550 g/m ² or less.

In addition, the physical properties of the paper base material can be set as appropriate depending on the use of the moisture-proof paper. For example, the lower limit of longitudinal elongation is 1.0% or more, the upper limit is 15.0% or less, and the lower limit of horizontal elongation is Set the specific compressive strength so that the lower limit is 100 N・m ² /g or more and the upper limit is 350 N・m ² /g or less. be able to.

Raw material pulps for such paper base materials include bleached softwood kraft pulp (NBKP), bleached hardwood kraft pulp (LBKP), unbleached softwood kraft pulp (NUKP), unbleached hardwood kraft pulp (LUKP), and groundwood pulp (GP). ), various pulps derived from wood fibers such as refined ground pulp (RGP), chemical pulp (CP), thermomechanical pulp (TMP), and chemi-thermomechanical pulp (CTMP), kenaf, bagasse, bamboo, hemp, straw, etc. Non-wood pulps produced by wood can be mentioned.

The paper base material may contain waste paper pulp or may not contain waste paper pulp. When containing waste paper pulp, for example, when the paper base material is single-layer paper, the proportion of waste paper pulp in the total pulp is preferably 10% by mass or more, more preferably 25% by mass or more, and even more preferably can be 50% by mass or more, most preferably 70% by mass or more, and can be 100% by mass (consisting only of pulp derived from waste paper). Further, kraft pulp may be blended as a pulp other than waste paper pulp, and the entire amount may be kraft pulp. Furthermore, if the paper base material is a multilayer paperboard having two or more paper layers, the content ratio of waste paper pulp per layer can be as described above, and the content ratio of waste paper pulp in each layer may be different. There may be.

Waste paper pulp includes waste paper pulp obtained by disintegrating unprinted waste paper such as corrugated cardboard, white paper, special white paper, middle white paper, white loss, etc., wood-free paper, wood-free coated paper, medium-quality paper, medium-quality coated paper, and recycled paper. It is possible to use pulp (DIP) obtained by disintegrating and deinking printed waste paper, used paper with written notes, paper such as discarded confidential documents, used magazine paper, and used newspaper paper.

<Coating layer>
As mentioned above, the coating layer constituting the moisture-proof paper of the present invention contains a synthetic resin and wax, and the whiteness of the coating layer surface is 20% or more, more preferably 30% or more, and more preferably 45% or more. % or more, more preferably 55% or more.

If the whiteness of the surface of the coating layer is less than 20%, the whiteness of the coating layer surface of the moisture-proof paper will be insufficient, and the cosmetic properties of the moisture-proof paper will decrease, resulting in poor cosmetic properties as well as moisture-proof and waterproof properties. This makes it difficult to use moisture-proof paper in applications that require

In the present invention, the coating layer may contain a pigment for the purpose of improving whiteness. In this case, it is preferable that the whiteness of the surface of the coating layer is 1% or more higher than the whiteness of the paper base material by containing the pigment. Such pigments include calcium carbonate, titanium oxide, kaolin, clay, engineered kaolin, delaminated clay, talc, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, satin white, mica, Examples include inorganic pigments such as montmorillonite, and these pigments can be used singly or in combination of two or more. Among these pigments, kaolin, calcium carbonate, or mica, which have flat particles, are particularly preferred because they do not easily impede the moisture-proofing and waterproofing properties of the coating layer. It is preferable that such a flat-shaped inorganic pigment has an aspect ratio of 10 or more. The pigment content in the coating layer can be 5% by mass or more and 40% by mass or less, preferably 10% by mass or more and 35% by mass or less. If the pigment content is less than 5% by mass, the effect of improving whiteness cannot be sufficiently obtained, and if it exceeds 40% by mass, the moisture-proof and waterproof functions of the coating layer possessed by the synthetic resin component will not be sufficient. This is not desirable because it may not be able to perform to its full potential.

Examples of the synthetic resin contained in the coating layer include styrene resin, acrylic resin, butadiene resin, polyolefin resin, polyvinyl alcohol resin, polylactic acid resin, polyester resin, and polyethylene resin. These synthetic resins can be used alone or in combination of two or more, and it is particularly preferable that the synthetic resin is a styrene resin and/or an acrylic resin.

(Styrene resin)
The styrenic resin that can be contained in the coating layer constituting the present invention is a resin in which the copolymerization ratio of a styrene monomer having a styrene skeleton in its structure is 50% by mass or more, and It may be composed only of a polymer of 1-mer.

Examples of styrenic monomers include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, p-tert-butylstyrene, α-methylstyrene, α -Methyl-p-methylstyrene and the like.

Examples of monomers copolymerizable with the styrene monomer include alkyl methacrylates such as methyl methacrylate, cyclohexyl methacrylate, and methylphenyl methacrylate; alkyl acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, and cyclohexyl acrylate; acids, unsaturated carboxylic acids such as acrylic acid, unsaturated dicarboxylic anhydrides such as maleic acid and itaconic acid, unsaturated nitriles such as acrylonitrile and methacrylonitrile, 1,3-butadiene, 2-methyl- Examples include conjugated dienes such as 1,3-butadiene. These can be used alone or in combination of two or more.

(acrylic resin)
The acrylic resin that can be contained in the coating layer constituting the present invention is a resin in which the copolymerization ratio of acrylic monomers such as acrylic acid, methacrylic acid, and derivatives thereof is 50% by mass or more. , it may be composed only of a polymer of acrylic monomers.

Examples of the acrylic monomer include methacrylic acid esters such as cyclohexyl methacrylate, t-butylcyclohexyl methacrylate, and methyl methacrylate; acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, and isopropyl acrylate; The acrylic resin may be one obtained by polymerizing one or more monomers selected from these acrylic monomers.

Monomers copolymerizable with acrylic monomers include styrene, o-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, p-tert-butylstyrene, α-methylstyrene, Aromatic vinyl compounds such as styrene and α-methyl-p-methylstyrene, unsaturated nitrites such as acrylonitrile and methacrylonitrile, maleimides such as N-phenylmaleimide and N-cyclohexylmaleimide, and unsaturated dicarboxylic acids such as maleic anhydride. Examples include anhydrides, unsaturated carboxylic acids such as methacrylic acid, and acrylic acid. These can be used alone or in combination of two or more.

(wax)
The waxes contained in the coating layer include, for example, polyethylene wax, Fischer-Tropsch wax, oil-based synthetic waxes (fatty acid esters, fatty acid amides, ketones/amines), synthetic waxes such as hydrogenated oils, beeswax, Japanese wax, Examples include natural waxes such as paraffin wax and microcrystalline wax. These waxes can be used alone or in combination of two or more, and hydrocarbon waxes containing paraffin are particularly preferred.

The coating layer of the moisture-proof paper of the present invention is formed by applying a coating agent containing the above-mentioned synthetic resin and wax and, if necessary, a pigment using a blade coating method and drying the coating layer. I can do it. The coating amount of the coating agent is preferably 20 g/m ² or less; if it exceeds 20 g/m ² , further improvement of the moisture-proof and waterproof properties of the moisture-proof paper cannot be expected, but the production cost may be reduced. This will result in an increase.

Further, the coating layer of the moisture-proof paper of the present invention may have a surface smoothness of 25 seconds or more, preferably 30 seconds or more, and more preferably 40 seconds or more. When the surface smoothness of the coating layer of the moisture-proof paper is within the above range, high gloss can be obtained on the surface of the coating layer, and a moisture-proof paper with better cosmetic properties can be obtained.

The above smoothness is Oken type smoothness measured in accordance with JIS P8155.

Furthermore, the coating layer of the moisture-proof paper of the present invention has a water contact angle on the surface of 45 degrees or more, preferably 50 degrees or more, more preferably 55 degrees or more, and the upper limit of the 120 second Cobb water absorption of the surface is 3 g. /m ² or less, preferably 2 g/m ² or less, more preferably 1 g/m ² or less, and the lower limit is not particularly limited, but 0 g/m ² (no water absorption and less than the measurement limit) is preferable. . When the water contact angle and 120 second Cobb water absorption on the surface of the coating layer of the moisture-proof paper are within the above ranges, the coating layer has excellent moisture-proofing and waterproofing properties.

The above 120 second Cobb water absorption is determined by bringing 100 ml of distilled water into contact with the coating layer and measuring the weight per unit area of absorbed water after 120 seconds in accordance with JIS P8140 (Cobb method). The lower the 120 second Cobb water absorption, the lower the water absorption of the coating layer.

In addition, the coating layer of the moisture-proof paper of the present invention should have a lower limit of average coating layer thickness of 5.5 μm or more, preferably 5.7 μm or more, in order to have moisture-proof and waterproof properties. desirable. The upper limit of the average coating layer thickness is preferably 20 μm or less, preferably 15 μm or less, and more preferably 12.5 μm or less. Here, the average coating layer thickness is the average value of the coating layer thicknesses measured at ten arbitrary locations.

Further, the coating layer of the moisture-proof paper of the present invention has an upper limit of moisture permeability per unit thickness of the coating layer of 10 (g/m ² · 24 h)/μm or less, preferably 8 (g/m ² · 24 h)/μm or less is desirable in terms of providing moisture proofing and waterproofing properties. Here, the moisture permeability per unit thickness of the coating layer is a value calculated by dividing the moisture permeability measured from the coating layer side of moisture-proof paper in accordance with JIS Z 0208 by the average coating layer thickness. be.

The moisture-proof paper of the present invention has excellent moisture-proof properties, waterproof properties, and high whiteness, which suppresses a decrease in strength in applications where it comes into contact with moisture or moisture. At the same time, the effect of having excellent cosmetic properties on the surface of the coating layer is achieved.

[Method for manufacturing moisture-proof paper]
The method for producing moisture-proof paper of the present invention involves applying a coating agent containing synthetic resin and wax to at least one side of a paper base material using a blade coating method, and drying the applied coating agent. Moisture-proof paper is produced by forming a coating layer.

As the paper base material used in the present invention, a desired paper base material can be used depending on the use of the moisture-proof paper. When manufacturing the paper base material used in the present invention, raw material pulps include, for example, softwood bleached kraft pulp (NBKP), hardwood bleached kraft pulp (LBKP), softwood unbleached kraft pulp (NUKP), and hardwood unbleached kraft pulp ( Various pulps derived from wood fibers such as LUKP), groundwood pulp (GP), refined ground pulp (RGP), chemical pulp (CP), thermomechanical pulp (TMP), and chemithermomechanical pulp (CTMP), kenaf, bagasse, and bamboo. Non-wood pulp obtained from , hemp, straw, etc. can be used.

Waste paper pulp can be used in paper making of the paper base material, and the content ratio of the waste paper pulp in the paper base material can be appropriately set depending on the use of the moisture-proof paper. Waste paper pulp includes waste paper pulp obtained by disintegrating unprinted waste paper such as corrugated cardboard, white paper, special white paper, middle white paper, white loss, etc., wood-free paper, wood-free coated paper, medium-quality paper, medium-quality coated paper, and recycled paper. It is possible to use pulp (DIP) obtained by disintegrating and deinking paper such as printed waste paper, written waste paper, paper such as discarded confidential documents, used magazine paper, and waste newspaper paper.

Furthermore, in papermaking of paper base materials, sizing agents and water repellents for preventing moisture absorption can be added internally or externally, and furthermore, paper strength enhancers can be internally added to improve strength. Sizing agents include, for example, rosin-based sizing agents, rosin emulsion-based sizing agents, α-carboxylmethyl saturated fatty acids, and neutral rosin-based sizing agents, alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), Examples include cationic polymer sizing agents. Furthermore, examples of the water repellent include fluororesins, polyamide resins, wax emulsions, and the like. Examples of the paper strength enhancer include conventionally used paper strength enhancers such as polyacrylamide (PAM) and modified starch.

Further, a known filler can be internally added to the paper base material if necessary. Examples of fillers include kaolin, calcined kaolin, delaminated kaolin, clay, calcined clay, delaminated clay, illite, heavy calcium carbonate, light calcium carbonate, light calcium carbonate-silica composite, magnesium carbonate, barium carbonate. , inorganic fillers such as titanium dioxide, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, and organic fillers such as urea-formalin resin, polystyrene resin, and phenolic resin. etc.

Furthermore, as long as the quality of the paper base material is not affected, aluminum sulfate, aluminum chloride, sodium aluminate, basic aluminum compounds, water-soluble aluminum compounds, polyvalent metal compounds, silica sol, etc. may be added internally. good.

The paper substrate used may be a single layer paper or a multilayer paperboard having two or more paper layers. Furthermore, the basis weight of the paper base material can be appropriately set depending on the use of the moisture-proof paper. When the paper base material is single-layer paper, the lower limit of the basis weight can be set appropriately in the range of 10 g/m ² or more and the upper limit 250 g/m ² or less. For example, when the paper base material is kraft paper The lower limit of the basis weight can be set in a range of 30 g/m ² or more, and the upper limit can be set in a range of 250 g/m ² or less. In addition, when the paper base material is a multilayer paperboard having two or more paper layers, the lower limit of the basis weight can be set as appropriate within the range of 100 g/ ^m2 or more and the upper limit of 750 g/ ^m2 or less. For example, in the case of a corrugated liner, the lower limit of the basis weight can be set in a range of 100 g/m ² or more, and the upper limit can be set in a range of 550 g/m ² or less.

In the present invention, a coating agent containing a synthetic resin and wax is applied to one or both desired surfaces of the paper base material as described above by a blade coating method.

By applying the coating agent to the paper base material using the blade coating method, the surface of the coating layer that is formed has a high degree of smoothness, and high gloss can be obtained on the surface of the coating layer. Moisture-proof paper with excellent cosmetic properties can be obtained.

The coating amount of the coating agent by the blade coating method is such that the moisture permeability of the produced moisture-proof paper is 50 g/m ² ·24 h or less, preferably 20 g/m ² ·24 h or less, more preferably 10 g/m ² · Set it so that it is 24 hours or less. For example, it is preferable that the coating amount of the coating agent be 20 g/m ² or less. If the coating amount of the coating agent exceeds 20 g/m ² , further improvement in the moisture-proofing and waterproofing properties of the moisture-proof paper cannot be expected, but the manufacturing cost will increase.

Further, the feeding speed of the paper base material during application of the coating agent by the blade coating method can be appropriately set in consideration of the viscosity of the coating agent and the target coating amount.

As the coating agent for the coating layer, for example, one in which a synthetic resin and wax are mixed and dispersed in a solvent can be used. The coating agent may contain pigments, binders, stabilizers, antifoaming agents, water resistance agents, viscosity modifiers, water retention agents, preservatives, coloring agents, and the like. Pigments are contained for the purpose of improving the whiteness of the surface of the coating layer to be formed, and examples include calcium carbonate, titanium oxide, kaolin, clay, engineered kaolin, delaminated clay, talc, and sulfuric acid. Examples include inorganic pigments such as barium, calcium sulfate, zinc oxide, silicic acid, silicate, colloidal silica, satin white, mica, and montmorillonite, and these pigments may be used singly or in combination of two or more. can be used. Among these pigments, kaolin, calcium carbonate, or mica, which have flat particles, are particularly preferably used because they do not easily impede the moisture-proofing and waterproofing properties of the coating layer. It is preferable that such a flat-shaped inorganic pigment has an aspect ratio of 10 or more. The amount of pigment added to the coating agent can be 5% by mass or more and 40% by mass or less, preferably 10% by mass or more and 35% by mass or less in the solid content. If the amount of pigment added to the coating agent is less than 5% by mass based on the solid content, a sufficient effect of improving whiteness cannot be obtained, and if it exceeds 40% by mass, the moisture resistance of the formed coating layer will be reduced. , it is not preferable because the waterproof property may become insufficient.

According to the method for producing moisture-proof paper of the present invention, it is possible to produce moisture-proof paper whose moisture permeability is 50 g/m ² · 24 h or less and the whiteness of the surface of the coating layer is 20% or more. be. This type of moisture-proof paper has excellent moisture-proof properties, and even if you make a container using moisture-proof paper, fill it with water and leave it for 3 weeks, water will not seep out, and the shape of the container will remain the same. The container does not deform, or the container shape is maintained although it is slightly deformed. Furthermore, since it has a high degree of whiteness, the surface of the coating layer has excellent cosmetic properties.

There are no particular limitations on the use of the moisture-proof paper according to the present invention, and it can be used, for example, as a cardboard box, an individual packaging box containing a hygroscopic substance such as a detergent, or the like.

EXAMPLES The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited thereto.

[Example 1]
(Preparation of paper base material)
By using 63% by mass of softwood unbleached kraft pulp (NUKP) and 37% by mass of waste paper pulp, and coating the surface with a water resistance agent, viscosity improver, water retention agent, preservative, and coloring agent, 3. Paperboard for the liner was made by layer papermaking to have a basis weight of 280 g/m ² and was used as a paper base material (Reference Sample 1).

(Formation of coating layer)
0.46 parts by mass of an antifoaming agent was added to 100 parts by mass of a desiccant agent (VAPORCOAT 2200.S, manufactured by Michael Mann), in which a styrene resin, an acrylic resin, and a hydrocarbon wax containing paraffin were mixed and dispersed in a solvent. Coating agent A was prepared. Using this coating agent A, coat it on one side of the paper base material (reference sample 1) using a blade coating method so that the three coating amounts shown in Table 1 below are obtained. A coating layer was formed by drying so that the coating layer temperature was 90°C. As a result, three types of moisture-proof paper (Sample 1-1 to Sample 1-3) were produced.

Further, a coating agent B was prepared by adding 0.46 parts by mass of an antifoaming agent, 40 parts by mass of high flat kaolin, and 10 parts by mass of synthetic mica to 100 parts by mass of the above desiccant agent. Using this coating agent B, coat it on one side of the above paper base material (reference sample 1) by a blade coating method so that the coating amount becomes 4 types as shown in Table 1 below, A coating layer was formed by drying so that the coating layer temperature was 90°C. As a result, four types of moisture-proof papers (Sample 1-4 to Sample 1-7) were produced.

(Measurement of physical properties)
Regarding the seven types of moisture-proof paper (Samples 1-1 to 1-7) and paper base material (Reference Sample 1) produced as described above, moisture permeability, smoothness of the coating layer surface, whiteness, Water absorption and moisture-proofing The waterproofness of the paper was measured and evaluated as follows, and the results are shown in Table 1 below.

<Moisture permeability>
Measured in accordance with JIS Z 0208. In the case of moisture-proof paper, measurements are taken from the coating layer side.

<Smoothness>
In accordance with JIS P8155, the Oken type smoothness is measured using a digital Oken type air permeability smoothness tester manufactured by Asahi Seiko Co., Ltd.

<Whiteness>
Measurement is performed in accordance with JIS P8148 using an optical colorimetry system CMS-35SPXM manufactured by Murakami Color Research Institute Co., Ltd. that supports ISO whiteness.

<Water absorption>
In accordance with JIS P8140 (Cobb method), 100 ml of distilled water is brought into contact with the coating layer, and the weight of absorbed water per unit area is measured after 120 seconds.

<Waterproof>
A container with a length of 28 cm, a width of 22 cm, and a depth of 13 cm was made using moisture-proof paper (the coating layer is located on the inner surface), and 1.0 L of water was poured into this container, at a temperature of 40°C and a humidity of 80%. After being left in this environment for 3 weeks, the state of water seepage is observed and judged based on the following criteria.
(Waterproof judgment criteria)
○: Water does not seep into the outer surface of the container or the inner surface of the container above the water surface.
△: Water does not seep out to the outer surface of the container, but it seeps out to the inner surface of the container above the water surface.
×: Water seeps into the outer surface of the container or the inner surface of the container above the water surface.

As shown in Table 1, the moisture permeability of the moisture-proof paper produced by applying the coating agent using the blade coating method is 50 g/ ^m2.24 h or less, and the coating layer contains synthetic resin and Samples 1-1 to 1-3 (using coating agent A) containing wax and having a surface whiteness of the coating layer of 20% or more, and Samples 1-6 to 1-7 (coating It was confirmed that the material (using agent B) had both good moisture resistance and excellent waterproofness, and also had a smoothness of 25 seconds or more and high gloss, and had excellent cosmetic properties.

The moisture-proof paper according to the present invention is as described above, and has moisture-proof properties as well as waterproof properties, which has the effect of suppressing a decrease in strength in applications where it comes into contact with moisture or water. Since it has excellent cosmetic properties, it is suitable for use in various applications such as liners for corrugated cardboard, box making, and wrapping paper, and has great industrial applicability.

Claims (5)

A paper base material having a waste paper pulp blending ratio of 10% by mass or more, and a coating layer located on at least one surface of the paper base material, and having a moisture permeability of 50 g/m ² · 24 h or less, The coating layer contains a synthetic resin and wax, the whiteness of the coating layer surface is 20% or more, the 120 second Cobb water absorption of the coating layer surface is 1 g/m ² or less, and the coating layer A moisture-proof paper characterized in that the smoothness of the layer surface is 40 seconds or more , and the coating amount of the coating layer is 20 g/m ² or less . The moisture-proof paper according to claim 1, wherein the coating layer contains a pigment. The moisture-proof paper according to claim 1 or 2, wherein the pigment includes at least an inorganic pigment. The moisture-proof paper according to any one of claims 1 to 3, wherein the paper base material has a basis weight of 10 g/m ² or more and 750 g/m ² or less. Comprising a paper base material and a coating layer located on at least one surface of the paper base material, the moisture permeability is 50 g/m ² · 24 h or less, and the whiteness of the surface of the coating layer is 20% or more. A method for producing moisture-proof paper, wherein the 120 second Cobb water absorption of the surface of the coating layer is 1 g/m ² or less, and the smoothness of the surface of the coating layer is 40 seconds or more, the method comprising using recycled paper pulp. Coating a coating agent containing synthetic resin and wax on at least one side of the paper base material having a coating rate of 10% by mass or more using a blade coating method in a coating amount of 20g/m2 ^or less. and drying the applied coating agent to form the coating layer.