JP7366567B2 - Moisture-proof paper and its manufacturing method - Google Patents

Description

The present invention relates to moisture-proof paper, and particularly to a moisture-proof paper that is waterproof and a method for manufacturing 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, moisture-proof paper (patented) is made 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 heating it to form a surfactant layer on the outermost layer. Document 1) is known. In addition, the base paper has at least two coating layers on at least one side, and the coating layer located on the outermost surface contains microcapsules encapsulating wax, and the coating amount is 0.5 g/solid content equivalent. 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, in the method of forming a wax layer, it is difficult to sufficiently suppress moisture permeability even by simply coating one layer of a wax composition. It required multiple coatings, and the process was extremely complicated. In addition, the method of forming a resin film requires lamination, which makes the process complicated, and 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. was difficult.

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

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a moisture-proof paper having both moisture-proof and waterproof properties and a method for manufacturing the same.

The inventors of the present invention, while intensively investigating the possibility of imparting moisture-proofing and waterproofing properties by simply applying a coating agent to a paper base material, discovered that the surface of the coating layer formed by applying the coating agent The present inventors discovered that the presence of minute blisters or bubbles (hereinafter also referred to as "blisters") affects moisture proofing and waterproofing properties, and created the present invention.

That is, the invention according to claim 1 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 coating layer contains at least one synthetic resin of styrene resin and acrylic resin and wax, and the frequency of blisters with a diameter of 50 μm or more on the surface of the coating layer is 30 pieces/cm. It is a moisture-proof paper characterized by having a moisture resistance of ² or less.

In one embodiment, the paper substrate is a single layer paper. Further, the paper base material is a multilayer paper base material. Further, the coating amount of the coating layer is 20 g/m ² or less. Moreover, the basis weight of the paper base material is 10 g/m ² or more and 750 g/m ² or less.

The invention according to claim 6 for solving the above problem includes a coating step of coating a coating agent on at least one side of a paper base material by a contour coating method, and a coating agent applied on at least one surface of a paper base material. a drying step of drying to form a coating layer , the coating agent contains at least one synthetic resin of styrene resin and acrylic resin and wax, and in the coating step, The coating agent is applied in an amount of 20 g/ ^m2 or less, and in the drying step, the temperature of the coating layer at the exit of the drying step is adjusted to be 75°C or more and 100°C or less. This is a method for producing moisture-proof paper, characterized in that the moisture-proof paper has a humidity of 50 g/m ² ·24 hours or less .

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 the paper comes into contact with moisture or moisture. 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.

[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 hours or less, more preferably 10 g/m ^2.24 hours or less, and the frequency of blisters with a diameter of 50 μm or more on the surface of the coating layer is 30 pieces/cm ² or less, preferably 20 pieces/cm ² or less. .

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.

Furthermore, the frequency of blisters can be determined by observing images of locations where blisters occur. That is, five areas of 1 cm x 1 cm in size are arbitrarily set on the surface of the coating layer, and the frequency of blisters is determined by observing images in each of these areas using a microscope, etc., and the average value of these is calculated. This is calculated and used as the frequency of blisters. In order to make it easier to see the areas where blisters occur, the surface of the coating layer is impregnated with a colored dyeing liquid, and after being left for 120 seconds, the density of the coloring on the surface of the area impregnated with the dyeing liquid is checked, making it easier to observe the image. becomes easier. Furthermore, by using a staining solution, the frequency of blister presence can also be calculated by image analysis using color differences in coloring.

<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. I can do it.

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. In addition, if the paper base material is a multilayer paperboard having two or more paper layers, the waste paper pulp content per layer can be as described above, and the waste paper pulp content 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 paper such as printed waste paper, written waste paper, paper such as discarded confidential documents, used magazine paper, and waste newspaper paper.

<Coating layer>
As mentioned above, in the coating layer constituting the present invention, the frequency of blisters having a diameter of 50 μm or more on the surface of the coating layer is 30 pieces/cm ² or less. Due to this requirement and the requirement that the moisture permeability of the moisture-proof paper be 50 g/m ² ·24 h or less, the moisture-proof paper of the present invention has excellent moisture resistance. Furthermore, the moisture-proof paper of the present invention also has excellent waterproof properties. Here, 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, 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.

When the frequency of blisters with a diameter of 50 μm or more on the surface of the coating layer exceeds 30 pieces/cm ² , the moisture permeability of the coating layer decreases, and the moisture permeability of the moisture-proof paper exceeds 50 g/m ² 24 h. This makes it difficult for moisture-proof paper to have both moisture-proof and waterproof properties.

Preferably, such a coating layer contains a synthetic resin and wax. The synthetic resin preferably contains at least one of styrene resin, acrylic resin, butadiene resin, polyolefin resin, polyvinyl alcohol resin, polylactic acid resin, polyester resin, and polyethylene resin. In particular, it is 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.

In addition, monomers copolymerizable with styrene monomers include, for example, alkyl methacrylates such as methyl methacrylate, cyclohexyl methacrylate, and methyl phenyl methacrylate; alkyl acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, and cyclohexyl acrylate; and methacrylic acid. , 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-1 , 3-butadiene, and other conjugated dienes. 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 acid, methacrylic acid, and acrylic monomers that are 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 can be formed by applying a coating agent containing the above components and drying 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.

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 the 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 as well as waterproof properties, and has the effect of suppressing a decrease in strength in applications where it comes into contact with moisture or moisture.

[Method for manufacturing moisture-proof paper]
The method for producing moisture-proof paper of the present invention includes a coating step of applying a coating agent to at least one surface of a paper base material by a contour coating method, and drying the applied coating agent. In the drying step, the temperature of the coating layer at the exit of the drying step is adjusted to be less than 120°C.

<Coating process>
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, in the coating step, a coating agent is applied to one or both desired surfaces of the paper base material as described above by a contour coating method. As the contour coating method, a known contour coating method such as air knife coating, curtain coating, spray coating, die coating, etc. can be used.

By applying the coating agent to the paper base material using the contour coating method, the amount of coating agent applied to the surface of the paper base material is uniform, and the thickness of the coating film is therefore uniform. It is possible to suppress the occurrence of blisters in the coating layer during a certain drying process. Furthermore, the amount of coating agent used can be reduced compared to the contact coating method, and manufacturing costs can be held down.

The amount of coating agent applied using the contour coating method is such that the moisture permeability of the moisture-proof paper produced through the subsequent drying process is 50 g/m ^2.24 h or less, preferably 20 g/m ^2.24 h or less, More preferably, it is set to 10 g/m ² ·24 h 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 when applying the coating agent by the contour coating method can be appropriately set in consideration of the viscosity of the coating agent and the target coating amount.

Coating of the coating agent by such a contour coating method may be a single layer coating, or if necessary, two or more layers may be simultaneously coated by curtain coating.

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, waterproofing agents, viscosity modifiers, water retention agents, preservatives, coloring agents, and the like.

<Drying process>
Next, in a drying step, the coating agent applied to the paper base material is dried to form a coating layer. In this drying step, the temperature of the coating layer at the outlet is adjusted to be less than 120°C, preferably less than 100°C. If the coating layer temperature at the outlet is 120°C or higher, the rate of blistering in the coating layer will increase, and blocking will occur in the moisture-proof paper that is wound up after the coating layer is formed. There is. On the other hand, the lower limit of the coating layer temperature at the exit can be 70°C, preferably 80°C. If the coating layer temperature at the outlet is less than 70°C, not only may blocking occur in the moisture-proof paper wound up after the coating layer is formed, but also the coating layer may not be sufficiently dried. Therefore, it is not possible to sufficiently exhibit waterproof and moisture-proof performance.

The coating layer temperature at the exit of the drying process can be set in consideration of the basis weight and paper thickness of the paper base material. For example, in the case of a corrugated board liner whose paper base is multilayer paperboard and has a large basis weight and paper thickness, compared to kraft paper which is a single layer paper and has a relatively small basis weight and paper thickness, the coating layer is Blisters tend to form on the surface. The reasons for this are not limited, but in the case of corrugated liners, they often have a higher basis weight and paper thickness and lower air permeability than kraft paper, and even if the paper has the same moisture content as kraft paper, it is It is thought that blisters are likely to occur on the surface of the coating layer because much of the moisture vaporized inside the paper base material cannot escape sufficiently. Therefore, the larger the basis weight and paper thickness of the paper base material, the more preferably the coating layer temperature at the exit of the drying process is adjusted to be lower within the above range.

Here, the exit of the drying process is the exit of the drying zone when there is one drying zone in the drying process, and the exit of the most downstream drying zone when there are multiple drying zones in the drying process. .

The coating layer temperature at the exit of the drying process can be adjusted by adjusting the drying time and the temperature of the drying zone. The drying time is determined by the feeding speed of the paper base material, the number and length of drying zones, the equipment capacity of the drying zones (air volume, infrared output), etc. Further, as the drying method, a known drying method can be used, such as a steam cylinder heating drying method, a hot air drying method, a gas type infrared drying method, an electric infrared drying method, etc. They can be used alone or in combination of two or more.

In the method for producing moisture-proof paper of the present invention, the moisture permeability is 50 g/m ² ·24 h or less, and the frequency of blisters with a diameter of 50 μm or more on the surface of the coating layer is 30 pieces/cm ² or less. It is possible to produce moisture-proof paper. This kind 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 three 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.

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 for containing hygroscopic materials such as detergent, and 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).

(Coating process)
Adding 0.46 parts by mass of an antifoaming agent to 100 parts by mass of a moisture-proofing agent (VAPORCOAT 2200.S, manufactured by Michael Mann), which is a mixture and dispersion of a styrene resin, an acrylic resin, and a hydrocarbon wax containing paraffin in a solvent. A coating agent was prepared. This coating agent was coated on one side of the above paper base material (Reference Sample 1) by air knife coating, which is a contour coating method, so that the coating amount was 10 g/m ² .

(drying process)
The coating agent applied to the paper base material as described above was dried to form a coating layer. The drying conditions were five types in which the coating layer temperature at the exit of the drying step was adjusted as shown in Table 1 below. As a result, five types of moisture-proof paper (Sample 1-1 to Sample 1-5) were produced.

[Physical property measurement]
Regarding the five types of moisture-proof papers (Samples 1-1 to 1-5) and the paper base material (Reference Sample 1) produced as described above, the moisture permeability and blisters with a diameter of 50 μm or more on the surface of the coating layer were evaluated. The presence frequency, the blocking resistance of the moisture-proof paper in the rolled state, and the waterproofness of the moisture-proof paper were measured and evaluated as follows, and the results are shown in Table 1 below.

<Moisture permeability>
Measured in accordance with JIS Z 0208. In addition, in the case of moisture-proof paper, measurement is performed from the coating layer side.

<Frequency of blister presence>
Five areas of 1 cm x 1 cm in size were arbitrarily set on the surface of the coating layer, images were observed in each of these areas, the frequency of blisters with a diameter of 50 μm or more (pieces/cm ² ) was determined, and these The average value of is calculated and used as the frequency of blisters (numbers/cm ² ).

<Blocking resistance>
The moisture-proof paper is pulled out from the rolled state, the mutual blocking state of the moisture-proof papers is observed, and the judgment is made according to the following criteria.
(Judgment criteria for blocking resistance)
○: Peeling occurs when the moisture-proof paper on the outside of the roll peels off from the moisture-proof paper on the inside of the roll.
It makes no noise and can be pulled out without resistance.
△: When the moisture-proof paper on the outside of the roll peels off from the moisture-proof paper on the inside of the roll, peeling occurs.
Although it makes some noise, it can be pulled out without resistance and can be used for practical purposes.
×: When the moisture-proof paper on the outside of the roll peels off from the moisture-proof paper on the inside of the roll, it peels off.
There is a sound, and the moisture-proof paper on the outside of the roll is falling to the moisture-proof paper on the inside of the roll.
There is a tendency to

<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 outside of the container, but the inside of the container is above the water surface.
It's seeping out.
×: 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, sample 1 has a moisture permeability of 50 g/m ² ·24 h or less, and the frequency of blisters with a diameter of 50 μm or more on the surface of the coating layer is 30 pieces/cm ² or less It was confirmed that Samples -2 to 1-4 had both good moisture proofing properties and excellent waterproofing properties, and also had good blocking resistance.

[Example 2]
(Preparation of paper base material)
Using unbleached softwood kraft pulp (NUKP), kraft paper was made to have a basis weight of 75 g/m ² to obtain a paper base material (reference sample 2).

(Coating process)
A coating agent was prepared in the same manner as in Example 1. This coating agent was applied to one side of the above paper base material (Reference Sample 2) by air knife coating, which is a contour coating method, so that the coating amount was 12 g/m ² .

(drying process)
The coating agent applied to the paper base material as described above was dried to form a coating layer. The drying conditions were five types in which the coating layer temperature at the exit of the drying step was adjusted as shown in Table 2 below. As a result, five types of moisture-proof papers (Samples 2-1 to 2-5) were produced.

[Physical property measurement]
Regarding the five types of moisture-proof papers (Samples 2-1 to 2-5) and paper base material (Reference Sample 2) produced as described above, moisture permeability and blisters with a diameter of 50 μm or more on the surface of the coating layer were evaluated. The presence frequency, the blocking resistance of the moisture-proof paper in the rolled state, and the waterproofness of the moisture-proof paper were measured and evaluated in the same manner as in Example 1, and the results are shown in Table 2 below.

As shown in Table 2, sample 2-1 has a moisture permeability of 50 g/m ² ·24 h or less, and the frequency of blisters with a diameter of 50 μm or more on the surface of the coating layer is 20 pieces/cm ² or less ~Sample 2-3 was confirmed to have both good moisture proofing properties and excellent waterproofing properties, as well as good blocking resistance.

On the other hand, in Samples 2-4 and 2-5, the frequency of blisters with a diameter of 50 μm or more on the surface of the coating layer was 20 pieces/ ^cm2 or less, but the moisture permeability was 50 g/ ^m2 /24h. , and the waterproofness was poor.

Moreover, when comparing Sample 2-5 and Sample 1-5 of Example 1, it is found that although the coating layer temperature at the exit of the drying process in Sample 2-5 is high, Sample 2-5 has a diameter of 50 μm or more. The frequency of blisters is less than 20/ ^cm2 . This is because the paper base material used in Example 2 (Reference Sample 2) has a smaller paper thickness and higher moisture permeability than the paper base material (Reference Sample 1) used in Example 1, and therefore has higher air permeability. It is thought that the water vaporized inside the paper base material during the drying process easily escapes, which reduces the incidence of blisters on the surface of 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, which has the effect of suppressing a decrease in strength in applications where it comes into contact with moisture or moisture. It is suitable for use in a variety of applications, such as liners for corrugated cardboard, boxes, and wrapping paper, and has great industrial applicability.

Claims (6)

It comprises 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/ ^m2.24h or less, and the coating layer is made of styrene resin, acrylic resin. A moisture-proof paper containing at least one synthetic resin and wax, characterized in that the frequency of blisters with a diameter of 50 μm or more on the surface of the coating layer is 30 pieces/cm ² or less. The moisture-proof paper according to claim 1, wherein the paper base material is a single-layer paper. The moisture-proof paper according to claim 1, wherein the paper base material is a multilayer paper base material. The moisture-proof paper according to any one of claims 1 to 3, wherein the coating amount of the coating layer is 20 g/m ² or less. The moisture-proof paper according to any one of claims 1 to 4, wherein the paper base material has a basis weight of 10 g/m ² or more and 750 g/m ² or less. A coating process of applying a coating agent to at least one surface of a paper base material by a contour coating method, and a drying process of drying the applied coating agent to form a coating layer. The coating agent contains at least one type of synthetic resin such as a styrene resin or an acrylic resin, and wax, and in the coating step, the coating agent is applied so that the coating amount is 20 g/m ² or less. In the drying step, the temperature of the coating layer at the exit of the drying step is adjusted to be 75° C. or higher and 100° C. or lower, and a moisture-proof paper with a moisture permeability of 50 g/m ² · 24 h or lower is prepared. A method for producing moisture-proof paper, characterized by: