Waterproof paper and its manufacturing method

Abstract

The object of the present invention is to develop a technique for producing paper that is moisture-proof and waterproof. According to the present invention, the 120-second Cobb water absorbency is 5 to 25 g / m 2 The waterproof paper is provided by providing a coating layer containing a waterproofing agent having at least one of a styrene resin, an acrylic resin, and a polyolefin resin and a wax on a paper substrate having a water repellency of R4 or more as specified in Paper Pulp Test Method No. 68.

Description

[Technical field]

[0001] The present invention relates to a waterproof paper and a method for producing the same. [Background technology]

[0002] Conventionally, paper containers and packaging materials of various shapes using a paper base material have been used to package various items. In general, paper containers and packaging materials are very easy to permeate because they are based on a paper base material, and the strength of the containers and packaging materials may be reduced due to moisture generated from the packaged items. In addition, some items to be packaged or wrapped are highly sensitive to water vapor entering from the outside. Furthermore, when ice is packed and transported together with refrigerated products, the paper containers and packaging materials need to be waterproof.

[0003] For this reason, methods have been proposed in which a wax layer is formed by coating the surface of a paper substrate with a water-repellent wax composition, and a resin coating is formed by laminating a polyethylene film, a polypropylene film, or the like. For example, Patent Document 1 describes a moisture-proof paper in which a mixture of a wax emulsion, a water-insoluble synthetic resin emulsion, and a surfactant is applied to at least one side of the paper, and then a heat treatment is performed to form a surfactant layer on the outermost layer. Patent Document 2 also describes a paper substrate having at least two coating layers on at least one side, the outermost coating layer containing microcapsules encapsulating wax, with a coating amount of 0.5 g / m2 calculated as solid content. 2 More than 2.5g / m 2 The document describes a moisture-proof liner in which the coating layer located between the outermost coating layer and the base paper contains an acrylic copolymer and / or a styrene copolymer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-266096 [Patent Document 2] JP 2011-162899 A Summary of the Invention [Problem to be solved by the invention]

[0005] As part of the move away from plastics, there is a demand for paper containers to replace polystyrene foam, and water-resistant and water-repellent liners for producing such containers are attracting attention.

[0006] However, in the method of forming a wax layer in Patent Document 1, simply applying one layer of the wax composition makes it difficult to sufficiently suppress the moisture permeability, and in order to sufficiently suppress the moisture permeability, it is necessary to apply the wax composition multiple times, which makes the manufacturing process extremely complicated. Also, in the method of laminating with a resin film as in Patent Document 2, in addition to the manufacturing process being complicated due to the lamination process, the paper or paperboard laminated with a resin film has extremely poor disintegration properties when recovered and used as waste paper after use, making it difficult to reuse it.

[0007] Furthermore, simple moisture-proof paper does not have sufficient waterproofing, and is difficult to use as a container or packaging material for transporting ice for refrigerated products, etc. Existing moisture-proof paper that only has a surfactant layer formed on the outermost layer and moisture-proof liners that only have at least two coating layers do not have sufficient waterproofing.

[0008] Furthermore, in order to make a paper substrate waterproof, it is necessary to apply a waterproof paint. However, even when attempting to apply a waterproof paint to a paper substrate having water repellency, such as a water-repellent liner, the previously disclosed technologies tend to cause the solvent of the waterproof paint to form droplets, making it impossible to apply the waterproof paint evenly.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a waterproof paper having both moisture-proof and waterproof properties, and a method for manufacturing the same. [Means for solving the problem]

[0010] The inventors of the present invention have conducted extensive research into the above-mentioned problems and have succeeded in coating a waterproofing agent such as a styrene-acrylic resin on a paper substrate with low Cobb water absorbency, which makes it difficult for the paint to form droplets and allows the paint to be distributed evenly on the paper substrate. According to the present invention, even on a paper substrate that is water-repellent because it is coated with a wax-based water repellent agent, by selectively using a specific waterproofing agent, it is possible to coat the waterproofing agent evenly on the paper substrate, thereby improving the waterproofing of the paper.

[0011] The present invention includes, but is not limited to, the following aspects. [1] 120-second Cobb absorbency of 5 to 25 g / m 2 A waterproof paper having a waterproofing agent applied to a paper substrate having a water repellency of R4 or higher as specified in Paper Pulp Test Method No. 68, wherein the waterproofing agent contains at least one component selected from the group consisting of styrene resin, acrylic resin, and polyolefin resin, and wax. [2] The coating weight of the coating layer is 4 to 20 g / m 2 The waterproof paper described in [1]. [3] Moisture permeability of 50g / m 2 - Waterproof paper described in [1] or [2], which lasts for 24 hours or less. [4] The Cobb water absorbency of the paper base material is 3 g / m in 120 seconds. 2 or less, or 25 g / m2 in 30 minutes 2 The waterproof paper according to any one of [1] to [3] below. [5] The moisture permeability of the paper base material is 1500g / m 2 -Waterproof paper according to any one of [1] to [4], which has a durability of 24 hours or more. [6] The waterproof paper according to any one of [1] to [5], wherein the paper base material has an Oken smoothness of 13 seconds or more. [7] The waterproof paper according to any one of [1] to [6], wherein a water repellent is applied to at least one surface of the paper base material. [8] The waterproof paper according to any one of [1] to [7], wherein the paper base material is a multi-layer paperboard. [9] The Cobb water absorption of waterproof paper is 3 g / m in 120 seconds. 2or less, or 25 g / m2 in 30 minutes 2 The waterproof paper according to any one of [1] to [8] below.

[10] 120-second Cobb absorbency of 5 to 25 g / m 2 A method for producing waterproof paper, comprising applying a waterproofing agent to a paper substrate having a water repellency of R4 or more as specified in Paper Pulp Test Method No. 68, wherein the waterproofing agent contains at least one component selected from the group consisting of styrene-based resin, acrylic-based resin, and polyolefin resin, and wax. Effect of the Invention

[0012] According to the present invention, it is possible to produce paper that is moisture-proof as well as waterproof. [Brief description of the drawings]

[0013] [Figure 1] 1 is a photograph showing the appearance of a paper container produced for evaluating waterproofing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention relates to waterproof paper. In the present invention, waterproof paper refers to paper that has a function of not allowing water to seep in even when exposed to water for a long period of time. In a preferred embodiment of the present invention, the waterproof paper according to the present invention refers to a paper container that, even if filled with water and left for three weeks, does not leak water and does not deform the shape of the container, or, although it does deform slightly, maintains the shape of the container.

[0015] The waterproof paper according to the present invention can be used for any purpose, for example, as a cardboard box, for storing foodstuffs such as fresh fish and vegetables, or as a packaging box for hygroscopic items such as detergents. The basis weight of the waterproof paper according to the present invention is not particularly limited, but may be, for example, 30 to 800 g / m 2 When the paper base material is a single-ply paper, the basis weight of the waterproof paper can be, for example, 30 to 350 g / m 2 50~300g / m 2In addition, when the paper base material is a multi-layer paperboard having two or more paper layers, the basis weight of the waterproof paper is 75 to 800 g / m 2 or 100~700g / m 2 , and even 200-600g / m 2 It can be said that:

[0016] In a preferred embodiment, the waterproof paper of the present invention has a surface Cobb water absorbency of 3 g / m at 120 seconds. 2 Less than or equal to 2 g / m 2 Less than 1 g / m is more preferable. 2 The absorbency may be less than 1 g / m when the 120-second Cobb water absorbency is measured. 2 In a preferred embodiment, the 30-minute Cobb water absorbency of the surface of the paper is less than 25 g / m2 (including the case where the paper does not absorb water and is less than the measurement limit). 2 Less than or equal to 20 g / m 2 Less than 10 g / m is more preferable. 2 In the present invention, the Cobb water absorbency is measured according to the Cobb method specified in JIS P8140, in which 100 ml of distilled water is brought into contact with a coating layer, and the weight of water absorbed per unit area after a specified time is measured. The lower the Cobb water absorbency is, even under conditions where the measurement time is extended, the lower the water absorbency of the coating layer.

[0017] The waterproof paper of the present invention also has excellent moisture resistance, and in a preferred embodiment, the moisture permeability is 100 g / m 2 - 24h or less, preferably 75g / m 2 24h or less, preferably 50g / m 2 The moisture permeability of paper can be measured from the coating layer side of the waterproof paper in accordance with JIS Z 0208, and the smaller the value, the higher the moisture resistance.

[0018] The waterproof paper of the present invention is also excellent in oil resistance, and in a preferred embodiment, the oil repellency of the coating layer side is preferably 7 or more, more preferably 8 or more, and even more preferably 9 or more. Here, the oil repellency of the waterproof paper can be measured from the coating layer side of the waterproof paper in accordance with "Paper and Paperboard - Oil Repellency Testing Method - Kit Method" (JAPAN TAPPI Paper Pulp Testing Method No. 41), and the higher the kit number, the higher the oil resistance. In a preferred embodiment, the drop oil absorption of the coating layer side is 500 seconds or more, more preferably 550 seconds or more, and even more preferably 600 seconds or more. The longer the number of seconds of the drop oil absorption, the higher the oil resistance. The oil absorption of the waterproof paper can be evaluated by dropping a drop of diesel No. 1, whose dynamic viscosity coefficient has been adjusted to 3 cSt, onto the sample surface using a microsyringe equipped with an H5 needle, and measuring the time until the surface gloss disappears.

[0019] The waterproof paper of the present invention preferably has an Oken smoothness of the coating surface 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 in the above range, a high gloss can be obtained on the surface of the coating layer, and a waterproof paper with excellent cosmetic properties can be obtained.

[0020] paper base material The waterproof paper according to the present invention has at least a paper base material and a waterproof coating layer provided on at least one side of the paper base material. In the present invention, the basis weight of the paper base material is not particularly limited, and is, for example, 10 to 800 g / m 2 When the paper base material is a single-ply paper, the basis weight is 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 In addition, when the paper base material is a multi-layer paperboard having two or more paper layers, the basis weight is 70 to 800 g / m 2 For example, in the case of a cardboard liner, the basis weight is set to 80 to 600 g / m 2 The range can be set as follows:

[0021] The paper base material used in the present invention has a 120-second Cobb water absorbency of 25 g / m on the surface on which the waterproof coating layer is to be formed. 2 Less than 20 g / m 2 Less than 15g / m 2 The paper base material used in the present invention has a 120-second Cobb water absorbency of 5 g / m 2 More than 7 g / m 2 More preferably, 10 g / m 2 In the present invention, the 120-second Cobb water absorbency of the paper base material can be adjusted by applying a water repellent such as wax, or a coating agent (sealing agent) that does not have waterproofing such as a varnish containing a resin, and by having the 120-second Cobb water absorbency of the paper base material be in the above-mentioned range, it is possible to prevent a decrease in paper strength due to excessive penetration of the moisture contained in the solvent of the waterproof paint, and the solid content of the waterproof paint is retained on the surface of the paper layer, thereby providing a reliable coating and improving both waterproofness and moisture resistance.

[0022] In a preferred embodiment, the paper substrate used in the present invention has a water repellency of R4 or more, more preferably R6 or more, and even more preferably R8 or more, measured according to JAPAN TAPPI Paper and Pulp Test Method No. 68 "Paper and Paperboard - Water Repellency Test Method." If the water repellency of the paper substrate is R4 or more, when a waterproofing agent is applied, the moisture contained in the coating liquid does not excessively penetrate into the paper substrate, and a decrease in the strength of the paper can be suppressed.

[0023] In a preferred embodiment, the paper substrate used in the present invention has a drop oil absorption of 5 seconds or more on the surface on which the waterproof coating layer is to be provided, more preferably 7 seconds or more, and even more preferably 10 seconds or more. The upper limit is not particularly limited, but is preferably 80 seconds or less, more preferably 75 seconds or less, and even more preferably 70 seconds or less. By having an oil absorption within the above range, the wax contained in the waterproofing agent remains on the paper surface and is less likely to penetrate into the paper layer, thereby improving the waterproofness and moisture resistance of the paper substrate. The oil absorption of the paper substrate can be evaluated by dropping a drop of diesel No. 1, whose dynamic viscosity coefficient has been adjusted to 3 cSt, onto the sample surface using a microsyringe equipped with an H5 needle, and measuring the time it takes for the surface gloss to disappear.

[0024] The physical properties of the paper base material are not particularly limited and can be appropriately set according to the application of the waterproof paper. In the present invention, for example, the longitudinal elongation is 1.0 to 15.0%, the transverse elongation is 2.0 to 12.0%, and the specific compressive strength is 100 to 350 N·m 2 / g, specific burst strength is 2.80~5.00kPa m 2 / g.

[0025] In a preferred embodiment, the paper substrate used in the present invention has an Oken smoothness of 13 seconds or more, more preferably 15 seconds or more, and even more preferably 17 seconds or more on the surface on which the coating layer is to be formed. There is no particular upper limit, but it is preferably 100 seconds or less, more preferably 90 seconds or less, even more preferably 80 seconds or less, and most preferably 70 seconds or less. By having the smoothness of the surface on which the waterproof coating layer is to be formed within the above range, it is possible to form a waterproof coating layer that uniformly covers the paper substrate, improving waterproofness and moisture resistance.

[0026] In a preferred embodiment, the paper substrate used in the present invention has a moisture permeability of 1500 g / m2 measured from the side on which the waterproof coating layer is provided. 2 - 24h or more, preferably 1750g / m 2 24h or more, preferably 2000g / m 2 The upper limit of the moisture permeability is not particularly limited, but in a preferred embodiment, it is 5000 g / m 2- 24h or less, preferably 4500g / m 2 24h or less, preferably 4000g / m 2 By having the moisture permeability of the surface on which the waterproof coating layer is to be formed within the above range, the moisture in the coating agent can be efficiently evaporated to the paper layer side in the drying process after coating, so that a waterproof coating layer that covers the paper uniformly can be formed, which tends to improve waterproofness and moisture resistance.

[0027] In a preferred embodiment, the paper substrate used in the present invention has a water contact angle of 75 degrees or more, more preferably 77 degrees or more, on the surface on which the waterproof coating layer is provided. Having a water contact angle in the above range prevents the water contained in the coating liquid from excessively penetrating into the paper substrate, and prevents a decrease in the strength of the paper substrate.

[0028] The raw material pulp for the paper base material can be any known one without any particular limitation.Specific examples of the raw material pulp include various wood-derived pulps such as bleached softwood kraft pulp (NBKP), bleached hardwood kraft pulp (LBKP), unbleached softwood kraft pulp (NUKP), unbleached hardwood kraft pulp (LUKP), groundwood pulp (GP), refiner ground pulp (RGP), chemical pulp (CP), thermomechanical pulp (TMP), and chemi-thermomechanical pulp (CTMP), and non-wood pulps obtained from kenaf, bagasse, bamboo, hemp, straw, etc.

[0029] The paper base material may contain recycled paper pulp or may not contain recycled paper pulp. When recycled paper pulp is contained, for example, when the paper base material is a single-layer paper, the recycled paper pulp content of the total pulp can be preferably 10% by mass or more, more preferably 25% by mass or more, even more preferably 50% by mass or more, and most preferably 70% by mass or more, and can be 100% by mass (consisting only of recycled paper-derived pulp). In addition, kraft pulp may be blended as a pulp other than recycled paper pulp, and the total amount may be kraft pulp. In addition, when the paper base material is a multi-layer paperboard having two or more paper layers, the recycled paper pulp content per layer can be as described above, and the recycled paper pulp content in each layer may be different.

[0030] Examples of waste paper pulp that can be used include waste paper pulp obtained by disintegrating unprinted waste paper such as cardboard, white upper, extra white, medium white, and white damaged paper; printed waste paper such as fine paper, fine coated paper, medium quality paper, medium quality coated paper, and recycled paper; written waste paper; papers such as discarded confidential documents; and pulp (DIP) obtained by disintegrating and deinking waste paper such as magazines and newspapers.

[0031] In addition, in the papermaking process of the paper base material, sizing agents and water repellents can be added internally or externally, and further, a paper strength enhancing agent can be added internally to improve strength. Examples of sizing agents include rosin-based sizing agents, rosin emulsion-based sizing agents, α-carboxymethyl saturated fatty acids, neutral rosin-based sizing agents, alkyl ketene dimers (AKD), alkenyl succinic anhydrides (ASA), and cationic polymer-based sizing agents. Examples of water repellents include fluorine-based resins, polyamide-based resins, and waxes. Examples of paper strength enhancing agents include conventional paper strength enhancing agents such as polyacrylamide (PAM) and modified starch. In the present invention, it is preferable to add a water repellent containing wax externally to the side where the waterproof layer is provided, and it is more preferable to add a water repellent containing paraffin-based wax externally. The coating amount when the water repellent is added externally is 3 g / m. 2 Less than 2 g / m is preferred. 2 The following is more preferred:

[0032] Also, known fillers can be added to the paper base material as necessary, and inorganic fillers and organic fillers can be used without restrictions. Examples of inorganic 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, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, etc., and examples of organic fillers include urea-formaldehyde resin, polystyrene resin, phenol resin, etc.

[0033] Furthermore, aluminum sulfate, aluminum chloride, sodium aluminate, basic aluminum compounds, water-soluble aluminum compounds, polyvalent metal compounds, silica sol, etc. may be added internally within the limits that do not affect the quality of the paper base material.

[0034] The paper substrate can be produced by a known papermaking method, for example, using a Fourdrinier papermaking machine, a gap former type papermaking machine, a hybrid former type papermaking machine, an on-top former type papermaking machine, a cylinder papermaking machine, etc., but is not limited thereto.

[0035] In addition, in order to adjust the smoothness of the paper base material of the present invention, a smoothing treatment may be performed as necessary. For the smoothing treatment, a smoothing treatment device such as a normal calender, a super calender, a gloss calender, a soft calender, a thermal calender, or a shoe calender may be used. In the smoothing treatment device, the shape of the pressure device, the number of pressure nips, heating, line pressure, etc. may be appropriately adjusted.

[0036] Waterproof coating layer The waterproof paper according to the present invention has a waterproof coating layer provided on a paper substrate, and the waterproof coating layer in the present invention contains a synthetic resin and a wax. The synthetic resin preferably contains at least one of a styrene-based resin, an acrylic-based resin, and a polyolefin-based resin. In particular, the synthetic resin is preferably a styrene-based resin and / or an acrylic-based resin.

[0037] The styrene-based resin that can be contained in the waterproof coating layer constituting the present invention preferably has a copolymerization ratio of 50 mass% or more of a styrene-based monomer having a styrene skeleton in its structure, and may be composed only of a polymer of a styrene-based monomer.

[0038] Examples of the styrene monomer include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, p-tert-butylstyrene, α-methylstyrene, and α-methyl-p-methylstyrene.

[0039] 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, unsaturated carboxylic acids such as methacrylic acid and acrylic acid, unsaturated dicarboxylic anhydrides such as maleic acid and itaconic acid, unsaturated nitriles such as acrylonitrile and methacrylonitrile, and conjugated dienes such as 1,3-butadiene and 2-methyl-1,3-butadiene. These can be used alone or in combination of two or more.

[0040] 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, such as acrylic acid, methacrylic acid, and their derivatives, is 50 mass% or more, and may be composed only of polymers of acrylic monomers.

[0041] Examples of the acrylic monomer include methacrylic acid esters such as cyclohexyl methacrylate, t-butylcyclohexyl methacrylate, and methyl methacrylate, and acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, and isopropyl acrylate. The acrylic resin may be a polymer of one or more monomers selected from these acrylic monomers.

[0042] Examples of monomers copolymerizable with acrylic monomers include aromatic vinyl compounds such as styrene, o-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, p-tert-butylstyrene, α-methylstyrene, and α-methyl-p-methylstyrene, unsaturated nitriles such as acrylonitrile and methacrylonitrile, maleimides such as N-phenylmaleimide and N-cyclohexylmaleimide, unsaturated dicarboxylic anhydrides such as maleic anhydride, and unsaturated carboxylic acids such as methacrylic acid and acrylic acid. These can be used alone or in combination of two or more.

[0043] In the present invention, the waterproof coating layer contains wax. Examples of waxes contained in the waterproof coating layer include synthetic waxes such as polyethylene wax, Fischer-Tropsch wax, oil-based synthetic waxes (fatty acid esters, fatty acid amides, ketones and amines), hydrogenated oil, and natural waxes such as beeswax, wood wax, paraffin wax, and microcrystalline wax. These waxes can be used alone or in combination of two or more, and paraffin-containing hydrocarbon waxes are particularly suitable.

[0044] In the present invention, for the purpose of improving the whiteness, etc., a pigment may be contained in the waterproof coating layer within a range that does not impair waterproofing. In this case, it is preferable that the whiteness of the surface of the waterproof coating layer is 1% or more higher than that of the paper substrate by containing the pigment. Examples of such pigments include inorganic pigments such as calcium carbonate, titanium oxide, kaolin, clay, engineered kaolin, delaminated clay, talc, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicate salts, colloidal silica, satin white, mica, and montmorillonite, and these pigments can be used alone or in combination of two or more. Among these pigments, kaolin, calcium carbonate, or mica, which have flat particles, are particularly suitable because they do not easily impair waterproofing. It is preferable that such flat inorganic pigments have an aspect ratio of 10 or more. The content of the pigment in the waterproof coating layer is preferably 5 to 40% by mass or less, more preferably 10 to 35% by mass or less. If the pigment content is less than 5% by mass, the whiteness improvement effect is not sufficiently obtained, and if it exceeds 40% by mass, the moisture-proof and waterproof functions of the waterproof coating layer that the synthetic resin component has may not be fully exhibited, which is not preferable. In addition, other coating agents such as binders, stabilizers, defoamers, viscosity improvers, water retention agents, preservatives, and colorants may be contained.

[0045] In the present invention, the waterproof coating layer can be formed by applying a coating agent containing the above-mentioned components onto a paper substrate and drying it. The coating amount of the waterproof coating layer is 4 to 20 g / m 2 It is preferable to set the thickness to 5 to 15 g / m 2 It is more preferable to set the thickness to 20 g / m 2 If the temperature exceeds this range, no further improvement in waterproofness can be expected, while the manufacturing cost may increase.

[0046] In a preferred embodiment, the waterproof coating layer provided on the waterproof paper of the present invention has an average thickness of 5.5 to 20 μm, more preferably 5.6 to 15 μm, and even more preferably 5.7 to 12.5 μm. Here, the average thickness of the coating layer is the average value of the thicknesses of the waterproof coating layer measured by cutting a sample into strips and observing the cross sections at any 10 points using an electron microscope.

[0047] In addition, the waterproof paper according to the present invention has a moisture permeability of 15 (g / m 2 24h) / μm or less is preferable, and 10(g / m 2 24h) / μm or less is more preferable, and 7 (g / m 2 Here, the moisture permeability per unit thickness of the waterproof coating layer is calculated by dividing the moisture permeability measured from the coating layer side of the waterproof paper in accordance with JIS Z 0208 by the average coating layer thickness.

[0048] The waterproof paper of the present invention can be produced by coating at least one side of the paper substrate with a waterproofing agent and drying the coated waterproofing agent. The formation of the waterproof coating layer can be carried out by coating the coating agent using a known coating method, and for example, coating methods such as air knife coating, curtain coating, blade coating, gate roll coating, and die coating can be used. The coating layer may be a single layer or multiple layers, and multiple coating layers may be coated sequentially, or two or more layers may be coated simultaneously by curtain coating or the like. When multiple coating layers are provided, at least one layer may be a coating layer having waterproof properties, and it is preferable to coat the waterproofing agent as the outermost coating layer. When drying the coating layer, the coating layer temperature at the drying process outlet is preferably adjusted to be less than 120°C. The coating speed when coating the coating agent can be appropriately set in consideration of the viscosity of the coating agent and the target coating amount.

[0049] In a preferred embodiment, the coating agent is applied to the paper substrate by a contour coating method such as air knife coating or curtain coating, which allows the amount of coating agent applied to the paper substrate surface to be uniform, thus resulting in a uniform coating thickness, and suppressing the occurrence of blisters in the coating layer in the subsequent drying process. In addition, the amount of coating agent used can be reduced compared to contact coating methods, thereby reducing production costs.

[0050] The coating agent applied to the paper substrate is dried to form a coating layer. In this drying process, the temperature of the coating layer at the outlet is preferably less than 120°C, and may be adjusted to be 100°C or less. If the temperature of the coating layer at the outlet is 120°C or more, the incidence rate of blisters in the coating layer may increase, and blocking may occur in the waterproof paper wound after the coating layer is formed. On the other hand, the temperature of the coating layer at the outlet is preferably 60°C or more, more preferably 70°C, and may be 80°C or more. If the temperature of the coating layer at the outlet is less than 60°C, not only may blocking occur in the waterproof paper wound after the coating layer is formed, but the coating layer may not be dried sufficiently to fully exhibit waterproof and moisture-proof performance.

[0051] The coating temperature at the exit of the drying process can be set in consideration of the basis weight and thickness of the paper substrate. For example, in the case of a cardboard liner in which the paper substrate is a multi-layered paperboard and has a large basis weight and thickness, blisters tend to occur more easily on the surface of the coating layer than in the case of a single-layered paper, kraft paper, which has a relatively small basis weight and thickness. The reason is not limited, but in the case of a cardboard liner, the basis weight and thickness are often larger and the air permeability is lower than that of kraft paper, and even if the moisture content of the paper is the same as that of kraft paper, it is considered that blisters tend to occur more easily on the surface of the coating layer because a large amount of moisture evaporated inside the paper substrate during the drying process cannot escape sufficiently. For this reason, the larger the basis weight and thickness of the paper substrate, the lower the coating temperature at the exit of the drying process is preferably adjusted within the above range.

[0052] Here, the outlet of the drying step refers to the outlet of the drying zone when there is one drying zone in the drying step, and refers to the outlet of the drying zone on the most downstream side when there are multiple drying zones in the drying step.

[0053] The temperature of the coating layer 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 feed speed of the paper substrate, the number and length of the drying zones, the equipment capacity of the drying zone (air volume, infrared output), etc. In addition, the drying method can be a known drying method, 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., and any one of these can be used or a combination of two or more of them can be used. EXAMPLES

[0054] The present invention will be described in more detail below with reference to specific examples, but the present invention is not limited to the following specific examples. In this specification, unless otherwise specified, concentrations and the like are based on weight, and numerical ranges include their endpoints.

[0055] Waterproof paper manufacturing <Sample 1> A back layer made of 100% recycled corrugated paper pulp, a middle layer made of 100% recycled paper pulp, and a surface layer made of 70% unbleached kraft pulp and 30% recycled corrugated paper pulp were combined in a weight ratio of back layer:middle layer:surface layer = 25:60:15, dried with a dryer, and then a water repellent agent containing paraffin wax and rosin was applied to one side of the surface layer, dried again with a dryer, and smoothed using a calendar to produce paper base A (basis weight: approximately 280 g / m 2 , 120 second Cobb water absorption of the surface: 13g / m 2 Next, a waterproofing agent (Michaelman VaporCoat 2200) containing styrene-acrylic resin and wax was applied to the surface of the paper substrate using an air knife at a rate of 10.0 g / m. 2 The coating was applied and then dried with hot air so that the temperature of the coating layer at the exit of the drying process was 80°C, to obtain a liner sample.

[0056] <Sample 2> Waterproofing agent coating weight: 7.8g / m 2 A liner sample was obtained in the same manner as in Sample 1, except that:

[0057] <Sample 3> The coating weight of the waterproofing agent is 11.3g / m 2 A liner sample was obtained in the same manner as in Sample 1, except that:

[0058] <Sample 4> A back layer made of 100% recycled corrugated paper pulp, a middle layer made of 100% recycled paper pulp, and a surface layer made of 35% unbleached kraft pulp and 65% recycled corrugated paper pulp were combined in a weight ratio of back layer:middle layer:surface layer = 25:60:15, dried with a dryer, and a water repellent agent containing paraffin wax and rosin was applied to one side of the surface layer, dried again with a dryer, and smoothed using a calendar to produce paper base material B (basis weight: approximately 280 g / m 2 , 120 second Cobb water absorption of the surface: 16g / m 2 Next, a waterproofing agent (Michaelman VaporCoat 2200) containing styrene-acrylic resin and wax was applied to the surface of the paper substrate using an air knife at a rate of 10.5 g / m. 2 The coating was applied and then dried with hot air so that the temperature of the coating layer at the exit of the drying process was 80°C, to obtain a liner sample.

[0059] <Sample 5> The coating weight of the waterproofing agent is 7.9g / m 2 A liner sample was obtained in the same manner as Sample 4, except that:

[0060] <Sample 6 (Comparative Example)> A back layer made of 100% corrugated recycled paper pulp, a middle layer made of 100% recycled paper pulp, and a surface layer made of 25% unbleached kraft pulp and 75% corrugated recycled paper pulp were combined in a weight ratio of back layer:middle layer:surface layer = 25:65:10, dried with a dryer, and smoothed using a calendar to produce paper base C (basis weight: about 260 g / m 2 , 120 second Cobb water absorption of the surface: 28g / m2 Next, a waterproofing agent (Michaelman VaporCoat 2200) containing styrene-acrylic resin and wax was applied to the surface of the paper substrate using an air knife at a rate of 8.9 g / m. 2 The coating was applied and then dried with hot air so that the temperature of the coating layer at the exit of the drying process was 80°C, to obtain a liner sample.

[0061] <Sample 7 (Comparative Example)> A liner sample was produced in the same manner as sample 1, except that no waterproofing agent was applied (basis weight: approximately 280 g / m 2 ).

[0062] <Sample 8 (Comparative Example)> A liner sample was produced in the same manner as sample 4, except that no waterproofing agent was applied (basis weight: approximately 280 g / m 2 ).

[0063] <Sample 9 (Comparative Example)> A liner sample was produced in the same manner as sample 6, except that no waterproofing agent was applied (basis weight: approximately 260 g / m 2 ).

[0064] [Table 1]

[0065] Evaluation of waterproof paper The paper quality and waterproofness of each sample were evaluated according to the following procedures. (Basis Weight) Measured in accordance with JIS P 8124. (Paper Thickness) Measured in accordance with JIS P 8118 and JIS P 8124. (Average Coating Thickness of Waterproof Layer) A sample was cut into a rectangular shape, and the thickness of the coating layer was measured at any 10 points on the cross section by observation using an electron microscope, and the average value was calculated to obtain the average coating thickness.

[0066] (Smoothness) In accordance with JIS P 8155, the Oken type smoothness of the coating layer side (surface layer side) was measured using a digital Oken type air permeability smoothness tester (Asahi Seiko). (Water repellency) The coating layer side (surface side) was measured in accordance with JAPAN TAPPI Paper and Pulp Test Method No. 68 "Paper and Paperboard - Water Repellency Test Method." (Moisture permeability) Measured from the coating layer side (surface layer side) in accordance with JIS Z 0208. (Cobb Water Absorbency) Measurement was performed from the coating layer side (surface layer side) by the Cobb method in accordance with JIS P 8140. That is, 100 ml of distilled water was brought into contact with the coating layer (surface layer), and the weight of water absorbed per unit area after a specified time was measured. The measurement time was not only the usual specified time of 120 seconds (2 minutes), but also 30 minutes.

[0067] (Contact Angle) One drop (50 μl) of distilled water was dropped onto the sample surface, and the contact angle was measured one second later using a contact angle measuring device (DAT1100, manufactured by FIBRO System AB). (Oil drop absorbency) Using a microsyringe equipped with an H5 needle, one drop of diesel No. 1, whose dynamic viscosity coefficient was adjusted to 3 cSt, was dropped onto the surface of the sample, and the time until the surface no longer became glossy was measured. However, the measurement time was stopped at 600 seconds (10 minutes), and if the surface was still glossy after 600 seconds, it was evaluated as "600 seconds or more." (Oil repellency) The coating layer side (surface side) was measured in accordance with JAPAN TAPPI Paper and Pulp Test Method No. 41 "Paper and paperboard - Oil repellency test method - Kit method."

[0068] (Waterproofness) From the above samples, paper containers (28 cm long × 22 cm wide × 13 cm deep, coating layer located on the inside) as shown in Figure 1 were made, and 1.0 L of water was poured into the paper container and left in an environment with a temperature of 40°C and a humidity of 80%. After leaving it for 1, 2, and 3 weeks, the state of water seepage and the shape of the box were visually observed, and waterproofness was judged based on the following criteria. ○: Water has not seeped onto the outside of the container or onto the inside of the container above the water level, and the box shape is maintained. △: Water has not seeped onto the outside of the container and the shape of the box has been maintained (however, water has seeped into the inside of the container) ×: Water has seeped out onto the outside of the container, and the box shape cannot be maintained.

[0069] [Table 2]

[0070] As is clear from the results shown in the table, samples 1 to 4, which have a waterproof coating layer of styrene-acrylic resin on a paper substrate with low Cobb water absorption and high water repellency, are both moisture-proof and waterproof, and did not leak even when left filled with water for a long period of three weeks. On the other hand, samples 7 to 9 had leaked water to the point that they could no longer maintain the shape of the box after one day or six hours.

[0071] From the above experimental results, it is clear that the waterproof paper of the present invention can be suitably used as a packaging material, particularly for liquids.

Claims

1. 120-second Cobb absorbency of 5 g / m ２ 20g / m or more ２ A waterproof paper having a coating layer in which a waterproofing agent is applied onto a paper base material having an Oken smoothness of 13 seconds or more, The waterproof paper has a Cobb water absorption of 25 g / m2 in 30 minutes. ２ The waterproof paper is as follows: wherein the waterproofing agent contains at least one of a styrene-based resin, an acrylic-based resin, and a polyolefin resin, and a wax.

2. The coating weight of the coating layer is 4 to 20 g / m ２ The waterproof paper according to claim 1 ,

3. Moisture permeability is 50g / m ２ The waterproof paper according to claim 1 or 2, which has a shelf life of 24 hours or less.

4. The waterproof paper according to any one of claims 1 to 3, wherein the waterproofing agent contains at least one of a styrene-based resin and an acrylic-based resin, and a wax.

5. The moisture permeability of the paper base material is 1500 g / m ２ - Waterproof paper according to any one of claims 1 to 4, having a durability of 24 hours or more.

6. The waterproof paper according to any one of claims 1 to 5, wherein the paper base material has an Oken smoothness of 15 seconds or more.

7. A water repellent agent is applied to at least one surface of the paper base material, and the water repellency of the paper base material is R4 or more. The waterproof paper according to any one of claims 1 to 6.

8. The waterproof paper according to any one of claims 1 to 7, wherein the paper base material is a multi-layer paperboard.

9. The Cobb water absorption of waterproof paper is 3 g / m in 120 seconds. ２ or less, and 20 g / m in 30 minutes ２ The waterproof paper according to any one of claims 1 to 8, wherein the water repellency of the paper base material is R6 or more.

10. 120-second Cobb absorbency of 5 g / m ２ 20g / m or more ２ A method for producing waterproof paper, comprising: applying a waterproofing agent to a paper substrate having an Oken smoothness of 13 seconds or more; The waterproof paper has a Cobb water absorption of 25 g / m2 in 30 minutes. ２ The above method, wherein the waterproofing agent contains at least one of a styrene-based resin, an acrylic-based resin, and a polyolefin resin, and a wax.

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