JP2023111251A - Waterproof paper and manufacturing method thereof - Google Patents

Abstract

To develop a technique for manufacturing a paper having excellent waterproof property.SOLUTION: A waterproof paper of the present invention has (a) a paper substrate, (b) an undercoat layer provided on at least one side of the paper substrate and containing a synthetic resin having a glass transition point of 65-260°C, and (c) a waterproof layer containing a styrene-acrylic resin and a wax and provided on the undercoat layer as an outermost layer.SELECTED DRAWING: None

Description

WATERPROOF PAPER AND METHOD OF MANUFACTURING THEREOF TECHNICAL FIELD The present invention relates to a waterproof paper and a method for manufacturing the same.

2. Description of the Related Art Conventionally, in order to package various articles, paper containers, packing materials, and the like in various forms using a paper base material have been used. In general, paper containers and packing materials use a paper base material as a base material, so it is extremely easy for water vapor and the like to permeate, and moisture generated from the packaged goods may cause a decrease in strength. . In addition, depending on the article to be wrapped or packed, there are some that are remarkably averse to water vapor or the like entering from the outside. Furthermore, when transporting chilled products together with ice, paper containers and packing materials must be waterproof.

For this reason, a method of forming a wax layer by coating a water-repellent wax composition on the surface of a paper substrate, and a method of forming a resin coating by laminating a polyethylene film, a polypropylene film, or the like have been proposed. . For example, Patent Literature 1 discloses that a mixture of a wax emulsion, a water-insoluble synthetic resin emulsion, and a surfactant is applied to at least one side of paper, and then heat-treated to form a surfactant layer as the outermost layer. Formed moisture barrier papers are described. Further, in Patent Document 2, at least one surface of a base paper has at least two coating layers, the coating layer located on the outermost surface contains microcapsules encapsulating wax, and the coating amount is solid. It is 0.5 g/m ² or more and 2.5 g/m ² or less in terms of minutes, and the coating layer located between the outermost coating layer and the base paper is an acrylic copolymer and / or a styrene copolymer. Moisture barrier liners containing polymers are described. Furthermore, Patent Document 3 proposes manufacturing paper having both high levels of moisture resistance and water resistance by drying the waterproof coating layer under specific drying conditions.

JP-A-10-266096 JP 2011-162899 A JP 2020-165039 A

Paper containers that can replace styrofoam are demanded in the trend of plastic-free, and water-resistant and water-repellent liners are attracting attention in order to manufacture such containers.
However, in the method of forming the wax layer of Patent Document 1, it is difficult to sufficiently suppress the moisture permeability simply by coating one layer of the wax composition. It is necessary to apply the wax composition many times, which makes the manufacturing process extremely complicated. In addition, in the method of laminating with a resin film as in Patent Document 2, in addition to the complicated manufacturing process due to lamination, paper or paperboard laminated with a resin film is disintegrated when it is recovered and used as waste paper after use. The reusability was remarkably poor, and it was difficult to recycle. Furthermore, the method of Patent Document 3 requires the adoption of specific drying conditions, and cannot be said to be economically advantageous.

In addition, mere moisture-proof paper is not sufficiently waterproof, and it is difficult to use it as a container or packing material for transporting ice-filled products such as chilled products. Conventional moisture-proof papers having only a surfactant layer formed on the outermost layer and moisture-proof liners having only at least two coating layers do not have sufficient waterproofness.

In view of such circumstances, an object of the present invention is to provide waterproof paper having both moisture resistance and water resistance, and a method for producing the same.

As a result of intensive studies on the above problems, the present inventors have found that by coating a paper base material with a specific synthetic resin to adjust the water repellency and then applying a waterproofing agent, moisture resistance and water resistance can be improved. It was found that paper with excellent properties can be produced.

Although not limited to the following, the present invention includes the following aspects.
[1] (a) a paper substrate, (b) an undercoat layer containing a synthetic resin having a glass transition point of 65 to 260° C. provided on at least one side of the paper substrate, and (c) on the undercoat layer A waterproof paper having a waterproof layer containing styrene-acrylic resin and wax provided as the outermost layer, and the water repellency at the stage of applying the undercoat layer before applying the waterproof layer is Paper pulp test method no. The above waterproof paper, which is R7 or less when measured by the method specified in 68.
[2] The waterproof paper according to [1], wherein the undercoat layer does not contain wax.
[3] The waterproof paper according to [1] or [2], wherein the synthetic resin used in the undercoat layer contains polyvinyl alcohol and/or styrene-acrylic resin.
[4] The waterproof paper according to any one of [1] to [3], which has a 30-minute Cobb water absorbency of 7 g/m ² or less.
[5] The waterproof paper according to any one of [1] to [4], wherein the paper substrate is multi-layer paperboard.
[6] Paper pulp test method No. A step of providing an undercoat layer containing a synthetic resin having a glass transition point of 65 to 260 ° C. on at least one side of the paper substrate so that the water repellency specified in 68 is R7 or less, and styrene on the undercoat layer. - A method for producing waterproof paper, comprising the step of providing a waterproof layer containing acrylic resin and wax.

According to the present invention, it is possible to produce paper that is waterproof as well as moisture-proof.

It is a figure which shows the carrier used for waterproof evaluation (assembly drawing). It is a figure which shows the carrier used for waterproof evaluation (development view). It is a figure which shows the carrier used for waterproofing evaluation (folding figure).

The present invention relates to waterproof paper. In the present invention, waterproof paper means paper that ^does not soak in water even when exposed to water for a long time. The paper is called waterproof paper. In a preferred embodiment, the waterproof paper according to the present invention does not allow water to seep out even when water is poured into a paper container and allowed to stand for one week, and the shape of the container does not deform, or the shape of the container is slightly deformed. maintained. In a more preferred embodiment, the waterproof paper according to the present invention does not cause water seepage even when water is put in a paper container and left for 3 weeks, and the shape of the container is not deformed, or the shape of the container is slightly deformed. is maintained.

The use of the waterproof paper according to the present invention is not particularly limited. A hygroscopic thing can be accommodated as a content. Although the basis weight of the waterproof paper according to the present invention is not particularly limited, it can be, for example, 30 to 800 g/m ² . When the paper substrate is a single layer paper, the basis weight of the waterproof paper can be, for example, 30-350 g/m ² or 50-300 g/m ² . Further, when the paper base material is multi-layer paperboard having two or more paper layers, the basis weight of the waterproof paper is 75 to 800 g/m ² , 100 to 700 g/m ² , and further 200 to 600 g/m ² . can be

In a preferred embodiment, the waterproof paper of the present invention has a surface 30-minute Cobb water absorbency of 40 g/m ² or less, more preferably 25 g/m ² or less, more preferably 15 g/m ² or less, or 7 g/m ² or less. good. In the present invention, the Cobb water absorbency is determined by contacting the coating layer with 100 ml of distilled water in accordance with the Cobb method specified in JIS P 8140, and measuring the weight per unit area of water absorbed after a specified time. . Even if the measurement time is extended, the lower the Cobb water absorbency, the lower the water absorbency of the coating layer.

The waterproof paper of the present invention is also excellent in moisture resistance, and in a preferred embodiment, has a moisture permeability of 100 g/m ² ·24h or less, more preferably 75 g/m ² ·24h or less, still more preferably 50 g/m ^{2 .}・It is 24 hours or less. Here, the moisture permeability of paper can be measured from the coating layer side of the waterproof paper according to JIS Z 0208, and the smaller the value, the higher the moisture resistance.

The coated surface of the waterproof paper of the present invention preferably has an Oken smoothness of 15 seconds or more, more preferably 20 seconds or more, and even more preferably 25 seconds or more. When the smoothness of the surface of the coating layer of the waterproof paper is within the above range, the surface of the coating layer is highly glossy, and the waterproof paper with excellent cosmetic properties can be obtained.

Paper Substrate The waterproof paper according to the present invention has at least a paper substrate, and an undercoat layer and a waterproof coating layer provided on at least one surface of the paper substrate. In the present invention, the basis weight of the paper substrate is not particularly limited, and can be, for example, 10 to 800 g/m ² . When the paper base material is single-layer paper, the basis weight can be appropriately set in the range of 10 to 300 g/m ² . For example, when the paper base material is kraft paper, the basis weight is 30 to 250 g/m ^{2 .} can be set in the range of Further, when the paper base material is multi-layered paperboard having two or more paper layers, the basis weight can be appropriately set in the range of 70 to 800 g/m ² . The basis weight can be set in the range of 80-600 g/m ² .

The paper substrate used in the present invention is not particularly limited, but preferably has a 120-second Cobb water absorbency of 100 g/m ² or less, preferably 75 g/m ² or less, more preferably 50 g/m 2 or less on the surface on which the waterproof coating layer is to be provided. ² or less. The paper substrate used in the present invention has a 120-second Cobb water absorbency of 5 g/m ² or more, preferably 7 g/m ² or more, more preferably 10 g/m ² or more. In the present invention, the 120-second Cobb water absorbency of the paper substrate is adjusted by applying a water-repellent agent such as wax or a non-waterproof coating agent (filler) such as varnish containing resin. However, if the 120-second Cobb water absorbency of the paper substrate is within the above range, it is possible to prevent deterioration of paper strength due to excessive penetration of moisture contained in the solvent of the waterproof paint and prevent solids in the waterproof paint. As the moisture stays on the surface of the paper layer, a reliable coating is performed, and both waterproofness and moisture resistance can be improved.

As the raw material pulp for the paper substrate, any known pulp can be used without particular limitation. Specifically, for example, softwood bleached kraft pulp (NBKP), hardwood bleached kraft pulp (LBKP), softwood unbleached kraft pulp (NUKP), hardwood unbleached kraft pulp (LUKP), groundwood pulp (GP), refiner ground pulp (RGP), chemical pulp (CP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP) and other wood-derived pulps, and non-wood pulp obtained from kenaf, bagasse, bamboo, hemp, straw, etc. can be mentioned.

The paper substrate may contain waste paper pulp or may not contain waste paper pulp. When waste paper pulp is contained, for example, when the paper substrate is single-layer paper, the content of waste paper pulp in the total pulp is preferably 10% by mass or more, more preferably 25% by mass or more, and still 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, when the paper base material is a multi-layered paperboard having two or more paper layers, the waste paper pulp blending ratio per layer can be set as described above, and the waste paper pulp blending ratio in each layer is different. There may be.

Waste paper pulp includes waste paper pulp obtained by disaggregating unprinted waste paper such as corrugated waste paper, white paper, special white paper, medium white paper, white loss paper, high quality paper, high quality coated paper, medium quality paper, medium quality coated paper, dry paper, etc. It is possible to use printed waste paper, written waste paper, papers such as discarded confidential documents, magazine waste paper, deinked pulp (DIP) obtained by defibrating and deinking waste newspaper paper, and the like.

Further, in the papermaking of the paper substrate, a sizing agent or a water repellent agent can be added internally or externally, and a paper strength agent can be added internally to improve the strength. Examples of sizing agents include rosin-based sizing agents, rosin emulsion-based sizing agents, α-carboxymethyl saturated fatty acids, etc., as well as neutral rosin-based sizing agents, alkylketene dimer (AKD), alkenyl succinic anhydride (ASA), Examples include cationic polymer sizing agents. Further, examples of water repellents include fluorine-based resins, polyamide-based resins, waxes, and the like. Examples of the paper strength enhancer include conventionally used paper strength enhancers such as polyacrylamide (PAM) and modified starch.

In addition, if necessary, a known filler can be added internally to the paper substrate, and inorganic fillers and organic fillers can be used without limitation. Examples of inorganic fillers include kaolin, calcined kaolin, delaminated kaolin, clay, calcined clay, delaminated clay, illite, ground calcium carbonate, light calcium carbonate, light calcium carbonate-silica composite, magnesium carbonate, carbonate Barium, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, etc. Examples of organic fillers include urea-formalin resin and polystyrene resin. , and phenolic resins.

Furthermore, aluminum sulfate, aluminum chloride, sodium aluminate, basic aluminum compounds, water-soluble aluminum compounds, polyvalent metal compounds, silica sol, etc. may be added internally to the extent that the quality of the paper substrate is not affected. good.

The paper substrate can be produced by a known papermaking method. For example, a Fourdrinier paper machine, a gap former paper machine, a hybrid former paper machine, an on-top former paper machine, a cylinder paper machine, or the like can be used, but not limited to these.

Further, in order to adjust the smoothness of the paper substrate of the present invention, a smoothing treatment may be performed as necessary. For the smoothing process, a smoothing apparatus such as a normal calender, super calender, gross calender, soft calender, thermal calender, and shoe calender can be used. In the smoothing device, the shape of the pressure device, the number of pressure nips, heating, line pressure, etc. may be appropriately adjusted.

Undercoat layer (filler layer)
The waterproof paper according to the present invention is characterized in that the paper substrate is coated with a specific synthetic resin so that the water repellency is R7 or less before the waterproof coating layer is provided. By coating the paper surface with synthetic resin, it is possible to coat the paper surface, which improves the smoothness of the surface and suppresses the penetration of the waterproof coating layer into the paper surface, thereby improving moisture resistance and water resistance. improves.

The water repellency of the paper substrate coated with the undercoat layer is evaluated by the paper pulp test method No. 68, and in the present invention, the water repellency at the stage of coating the undercoat layer before coating the waterproof layer is R7 or less, preferably R5 or less, and R3. The following are more preferable.

The waterproof paper according to the present invention has an undercoat layer provided on the paper substrate, and the undercoat layer is applied in an arbitrary amount in consideration of the final waterproof property and economic efficiency. be able to. In a preferred embodiment, the coating weight of the undercoat layer is 0.1 to 15 g/m ² per side, more preferably 0.5 to 10 g/m ² , and may be 1 to 7 g/m ² .

The undercoat layer according to the present invention contains a synthetic resin having a glass transition point of 65-260°C. The glass transition point of a synthetic resin can be measured by a known method, preferably by thermogravimetric analysis (TGA). The glass transition point of the synthetic resin is preferably 70 to 240°C, more preferably 75 to 220°C. Further, if the glass transition point of the synthetic resin is higher than the glass transition point of the resin of the waterproof layer, the waterproof coating layer is less likely to peel off when heat treatment is performed, which is preferable.

The synthetic resin contained in the undercoat layer according to the present invention includes a synthetic resin having a melting point of 65-260°C. The melting point of the synthetic resin can be measured by a known method, but is preferably measured by differential scanning calorimetry (DSC). The melting point of the synthetic resin is preferably 70 to 240°C, more preferably 75 to 220°C, even more preferably 80 to 200°C.

The synthetic resin used in the undercoat layer of the present invention is not particularly limited as long as it has a glass transition point of 65 to 260° C. Examples include polyvinyl alcohol, polyvinyl alcohol such as carboxy-modified polyvinyl alcohol, styrene-acrylic resin, acrylic resin. , styrene-butadiene copolymer, vinyl acetate resin, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride resin, polyvinyl chloride, water-dispersible polymers such as polyvinylidene chloride, styrene-acrylic acid, styrene -maleic acid, olefin compounds, alkyl (meth)acrylate compounds, casein, polyvinylpyrrolidone, gelatin urea resins, alkyd resins, urethane resins, polyethylene and the like. The synthetic resins of the undercoat layer may be used singly or in combination of two or more. In the present invention, among these, it is preferable to use a synthetic resin containing polyvinyl alcohol, styrene resin, or acrylic resin for the undercoat layer because it facilitates uniform coating when providing the waterproof coating layer described later. .

In addition, when the undercoat layer contains wax, the water repellency of the wax may make it difficult to evenly apply a waterproof coating layer, which will be described later. Therefore, it is preferable that the undercoat layer does not contain wax.

Waterproof coating layer (top coating layer)
The waterproof paper according to the present invention has a waterproof coating layer, and the waterproof coating layer according to the present invention contains synthetic resin and wax. The synthetic resin preferably contains at least one of styrene resin, acrylic resin, and polyolefin resin. In particular, it is preferable that the synthetic resin is a styrene resin and/or an acrylic resin.

As the styrene resin that can be contained in the waterproof coating layer constituting the present invention, it is preferable that the copolymerization ratio of the styrene monomer having a styrene skeleton in the structure is 50% by mass or more. It may consist only of a polymer of monomers.

Styrenic monomers include, for example, 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 styrene monomers 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; , unsaturated carboxylic acids such as acrylic acid, unsaturated dicarboxylic acid anhydrides such as maleic acid and itaconic acid, unsaturated nitriles such as acrylonitrile and methacrylonitrile, 1,3-butadiene, 2-methyl-1 , and conjugated dienes such as 3-butadiene. These can be used singly or in combination of two or more.

The acrylic resin that can be contained in the waterproof coating layer constituting the present invention is a resin in which the copolymerization ratio of acrylic monomers, which are 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 acrylic monomers include cyclohexyl methacrylate, t-butylcyclohexyl methacrylate, methacrylic acid esters such as methyl methacrylate, and acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, and isopropyl acrylate. etc., and the acrylic resin may be obtained by polymerizing one or more monomers selected from these acrylic monomers.

Examples of 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 nitriles such as acrylonitrile and methacrylonitrile, maleimides such as N-phenylmaleimide and N-cyclohexylmaleimide, unsaturated dicarboxylic acids such as maleic anhydride. Unsaturated carboxylic acids such as anhydrides, methacrylic acid and acrylic acid are included. These can be used singly or in combination of two or more.

The resin used for the waterproof coating layer preferably has a glass transition point of 20° C. or higher, more preferably 25° C. or higher, and even more preferably 30° C. or higher. Although the upper limit of the glass transition point is not particularly limited, it is preferably 260° C. or lower, more preferably 240° C. or lower, and even more preferably 220° C. or lower. The resin used for the waterproof coating layer preferably has a melting point of 65° C. or higher, more preferably 70° C. or higher, and even more preferably 75° C. or higher. Although the upper limit of the melting point of the waterproof resin layer is not particularly limited, it is preferably 200° C. or lower, more preferably 190° C. or lower, and even more preferably 180° C. or lower. In the present invention, the glass transition point of the resin used for the waterproof layer is preferably lower than the glass transition point of the resin used for the undercoat layer.

In the present invention, the waterproof coating layer contains wax. The wax contained in the waterproof coating layer may be synthetic wax or natural wax, and may be used alone or in combination of two or more. Examples of synthetic wax include polyethylene wax, Fischer-Tropsch wax, polypropylene wax, fat-based synthetic wax (fatty acid ester, fatty acid amide, ketone/amine), and hydrogenated oil. , animal-derived waxes such as beeswax, shellac and privet wax; plant-derived waxes such as Japan wax, carnapa, candelilla and rice; paraffin waxes, microcrystalline waxes, slack wax, montan wax, ceresin, ozokerite Hydrocarbon waxes containing paraffin are particularly preferred.

In the present invention, for the purpose of improving whiteness, the waterproof coating layer may contain a pigment within a range that does not impair the waterproof property. In this case, it is preferable that the whiteness of the surface of the waterproof coating layer is increased by 1% or more compared to the whiteness of the paper substrate 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, Inorganic pigments such as montmorillonite can be used, 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 suitable because they hardly impede waterproofness. Such flat inorganic pigments preferably have an aspect ratio of 10 or more. The pigment content in the waterproof coating layer is preferably 5 to 40% by mass, more preferably 10 to 35% by mass. If the content of the pigment is less than 5% by mass, the effect of improving the whiteness is not sufficiently obtained, and if it exceeds 40% by mass, the moisture resistance of the waterproof coating layer possessed by the synthetic resin component is deteriorated. It is not preferable because the waterproof function may not be sufficiently exhibited. Further, other coating agents such as binders, stabilizers, antifoaming agents, viscosity improvers, water retention agents, preservatives, colorants and the like may be incorporated.

In the present invention, the waterproof coating layer can be formed by coating a paper substrate with a coating agent containing the above components and drying the coating. The coating amount of the waterproof coating layer is preferably 4-20 g/m ² , more preferably 5-15 g/m ² . If it exceeds 20 g/m ² , it may lead to an increase in manufacturing costs, while no further improvement in waterproofness can be expected.

The waterproof paper of the present invention can be produced by coating at least one surface of a paper substrate with a waterproof agent and drying the coated waterproof agent. Formation of the waterproof coating layer can be carried out by applying a coating agent using a known coating method, for example, air knife coating, curtain coating, blade coating, gate roll coating, die A coating method such as coating can be used. Further, the coating layer may be a single layer or a plurality of layers, a plurality of coating layers may be sequentially coated, or two or more layers may be coated simultaneously by curtain coating or the like. good. When a plurality of coating layers are provided, at least one layer may be a waterproof coating layer, and it is preferable to apply a waterproofing agent as the outermost coating layer. When drying the coating layer, the temperature of the coating layer at the outlet of the drying process is preferably adjusted to be less than 120°C. The coating speed at which the coating agent is applied can be appropriately set in consideration of the viscosity of the coating agent and the target coating amount.

The coating agent applied to the paper substrate is dried to form a coating layer. In this drying step, the temperature of the coating layer at the outlet is preferably less than 120°C, preferably 100°C or less. can be adjusted to If the coating layer temperature at the exit is 120° C. or higher, the rate of blistering in the coating layer may increase, and blocking occurs in the waterproof paper wound after the coating layer is formed. I have something to do. On the other hand, the temperature of the coating layer at the outlet is preferably 60° C. or higher, more preferably 70° C. or higher, and may be 80° C. or higher. If the coating layer temperature at the outlet is less than 60°C, blocking may occur in the waterproof paper wound up after the coating layer is formed, and the coating layer may not be dried. Since it is insufficient, it may not be possible to fully exhibit waterproof and moisture-proof performance.

The coating layer temperature at the outlet of the drying process can be set in consideration of the basis weight and paper thickness of the paper substrate. For example, in the case of a corrugated board liner whose paper base material is multi-layered paperboard and whose basis weight and paper thickness are large, the coating layer is less than that of kraft paper, which is single-layer paper and whose basis weight and paper thickness are relatively small. blisters tend to occur on the surface of The reason for this is not limited, but in the case of corrugated board liners, compared to kraft paper, the basis weight and paper thickness are large, and air permeability is often low. It is thought that blisters tend to occur on the surface of the coating layer because a large amount of water vaporized inside the paper base cannot escape sufficiently. Therefore, it is preferable to adjust the temperature of the coating layer at the outlet of the drying process to be lower within the above range as the basis weight and thickness of the paper substrate are larger.

Here, the outlet of the drying process is the outlet of the drying zone when there is one drying zone in the drying process, and the outlet of the most downstream drying zone when the drying process has a plurality of drying zones. .

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 substrate, the number and length of the drying zones, the equipment capacity of the drying zones (air volume, infrared output), and the like. As the drying method, a known drying method can be used, and examples thereof include a steam cylinder heating drying method, a hot air drying method, a gas infrared drying method, an electric infrared drying method, and the like. can be used singly or in combination of two or more.

The present invention will be described in more detail below with specific examples, but the present invention is not limited to the following specific examples. In this specification, concentrations and the like are based on weight unless otherwise specified, and numerical ranges include end points thereof.

Manufacture of corrugated waterproof paper A back layer made of 100% waste paper pulp, a middle layer made of 100% waste paper pulp, and a surface layer made of 70% unbleached kraft pulp and 30% corrugated waste paper pulp. After drying with a drier, smoothing treatment was performed using a calender to produce a paper base material (liner) (basis weight: about 280 g/m ² , paper moisture: 7.5% , surface 120-second Cobb water absorbency: 30 g/m ² , 30-minute Cobb water absorbency: 173.3 g/m ² , water repellency: R0).

On the surface layer side of the paper substrate, using a bar blade, apply an undercoat layer (filler layer) and a topcoat layer (waterproof layer) as shown in the table below, and the temperature of the coating layer at the exit of the drying process is 80 A sample of waterproof paper was produced by drying with hot air so that the temperature reached ℃.
(Coating agent)
The following coating agents were used. The melting point of the resin was measured using a differential scanning calorimeter (DSC Q200, manufactured by TA Instruments), and the glass transition point was measured using a thermogravimetric analyzer (TGA Q50, manufactured by TA Instruments).
・Synthetic resin A: styrene/acrylic resin (concentration: 10%, glass transition point: 120°C)
・Synthetic resin B: styrene/acrylic resin (concentration: 10%, glass transition point: 60°C)
・ Synthetic resin C: polyvinyl alcohol (Kuraray, RS-2117, concentration: 10%, glass transition point: 80 ° C., melting point: 230 ° C.)
・Paraffin wax (manufactured by Seiko PMC)
・Waterproofing agent: Paint containing styrene/acrylic resin (glass transition point: 39°C) and paraffin wax (Michaelman, VaporCoat 2200)

Evaluation of Waterproof Paper Each sample was evaluated for paper quality according to the following procedure.
(Basis Weight) Measured according to JIS P 8124.
(Cobb Water Absorbency) Measured by the Cobb method in accordance with JIS P 8140. That is, 100 ml of distilled water was brought into contact with the front side (coating layer side), and the weight per unit area of absorbed water was measured after a specified period of time. In order to evaluate the waterproof property, the measurement time was set to 30 minutes instead of the usual prescribed time of 120 seconds (2 minutes).
(Air Permeability) Based on JIS P 8117, it was measured from the coating layer side (front side) using an Oken type air permeability tester (manufactured by Asahi Seiko, EYO-55-1MN). A sample exceeding the upper measurement limit of the testing machine was evaluated as "100,000 seconds or more".
(Glossiness) Measured from the front side (coating layer side) according to JIS P 8142.
(Moisture Permeability) Measured from the front side (coating layer side) according to JIS Z 0208.
(Water repellency) JAPAN TAPPI paper pulp test method No. 68 "Paper and paperboard-Water repellency test method", the coating layer side was measured.
(Waterproofness) A sheet of A4 size sample is folded so that the front side (coating layer side) faces inside to make a box-shaped carrier as shown in Fig. 1, and 200 ml of 0.005% brilliant blue solution is put into it. Then, it was allowed to stand in an environment of 23° C. and 50% RH for 3 weeks. After that, the brilliant blue solution was discarded, and the waterproofness was evaluated according to the following criteria based on the degree of coloring of the carrier.
〇: No coloring seen, △: Coloring seen at folds, etc., ×: Colored overall (moisture at the bottom) A cut-out paper sample for moisture measurement was subjected to paper moisture measurement according to JIS P 8203, and the result was defined as bottom moisture.
(Heat resistance) An aluminum foil of the same size was brought into contact with the front side (coating layer side) of one A5 size sample, and a force of 2 kgf / cm was applied to the central part over a width of 10 mm using a heat sealer heated to 120 ° C. was added, heated and pressurized for 3 seconds, and then the heat resistance was evaluated according to the following criteria based on the releasability when manually peeled off.
○: The aluminum foil is not attached to the coated surface △: The coated surface is thinly attached to the aluminum foil ×: The aluminum foil is adhered to the coated surface and is difficult to peel off

As is clear from the results shown in the above table, according to the present invention, paper with low moisture permeability and high waterproofness could be obtained. For Samples 17 and 18, the water repellency was too high at the stage of applying the undercoat layer (filler layer), so the coating liquid containing the waterproofing agent was repelled, resulting in a uniform topcoat layer (waterproof layer). could not be established.

1 Conveyor 2 Sheet 3 First Reference Line 4 First Folded Line 5 Second Reference Line 6 Second Folded Line 7 Rectangular Section 8 Intersection 9 Corner 10 Third Folded Line 11 Folded Section 12 Rectangular Folded Section 13 Sealed Section 14 Bottoms 15, 16 Side wall L1 Depth dimension L2 Width dimension L3, L4 Height dimension

Claims (6)

(a) a paper substrate;
(b) an undercoat layer containing a synthetic resin having a glass transition point of 65 to 260° C. and provided on at least one side of the paper substrate;
(c) a waterproof layer containing styrene-acrylic resin and wax provided as the outermost layer on the undercoat layer;
A waterproof paper having
The water repellency at the stage of applying the undercoat layer before applying the waterproof layer was determined by the paper pulp test method No. The above waterproof paper, which is R7 or less when measured by the method specified in 68. 2. Waterproof paper according to claim 1, wherein the primer layer is free of wax. 3. The waterproof paper according to claim 1, wherein the synthetic resin used in the undercoat layer contains polyvinyl alcohol and/or styrene-acrylic resin. The waterproof paper according to any one of claims 1 to 3, which has a 30-minute Cobb water absorbency of 7 g/m ² or less. The waterproof paper according to any one of claims 1 to 4, wherein the paper substrate is multi-layered paperboard. Paper pulp test method no. A step of providing an undercoat layer containing a synthetic resin having a glass transition point of 65 to 260° C. on at least one side of the paper substrate so that the water repellency defined in 68 is R7 or less;
A step of providing a waterproof layer containing styrene-acrylic resin and wax on the undercoat layer;
A method of making waterproof paper, comprising: