JP7008170B1 - Waterproof paper and its manufacturing method - Google Patents

Abstract

An object of the present invention is to develop a technique for producing a paper having moisture resistance and waterproofness. According to the present invention, the water absorption of the Cobb for 120 seconds is 5 to 25 g / m2, and the pulp and paper test method No. A waterproof paper in which a coating layer containing at least one of a styrene resin, an acrylic resin, and a polyolefin resin and a waterproofing agent having a wax is provided on a paper substrate having a water repellency of R4 or more specified in 68. Provided.

Description

The present invention relates to waterproof paper and a method for producing the same.

Conventionally, in order to wrap various articles, paper containers and packing materials having various forms using a paper base material have been used. In general, paper containers and packaging materials use a paper base material as a base material, so that water vapor and the like are extremely easy to permeate, and the strength may decrease due to the moisture generated from the packaged articles. .. In addition, depending on the packaging and the articles to be packed, there are some that remarkably dislike water vapor and the like invading from the outside. Furthermore, when transporting ice together, such as in chilled products, paper containers and packaging materials must be waterproof.

Therefore, a method of applying a water-repellent wax composition to the surface of a paper base material to form a wax layer, and a method of laminating a polyethylene film, a polypropylene film, or the like to form a resin film have been proposed. .. For example, in Patent Document 1, a mixture of a wax emulsion and a water-insoluble synthetic resin emulsion and a surfactant is applied to at least one side of a paper, and then heat-treated to form a layer of the surfactant on the outermost layer. The formed moisture-proof paper is described. Further, in Patent Document 2, at least one coating layer is provided on at least one side of the base paper, the coating layer located on the outermost surface contains microcapsules containing wax, and the coating amount is solid. The minute conversion is 0.5 g / m ² or more and 2.5 g / m ² or less, and the coating layer located between the outermost coating layer and the base paper is an acrylic copolymer and / or a styrene-based copolymer. Moisture-proof liners containing polymers are described.

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

Paper containers that replace Styrofoam are required in the flow of deplasticization, and water resistant and water repellent liners are attracting attention for producing such containers.

However, in the method of forming the wax layer of Patent Document 1, it is difficult to sufficiently suppress the moisture permeability even if only one layer of the wax composition is applied, and in order to sufficiently suppress the moisture permeability, It is necessary to apply the wax composition many times, which significantly complicates the manufacturing process. Further, in the method of laminating with a resin film as in Patent Document 2, the manufacturing process becomes complicated due to the laminating process, and the paper or paperboard laminated with the resin film is separated when collected and used as used paper after use. The sex was extremely poor and it was difficult to reuse it.

In addition, simple moisture-proof paper is not sufficiently waterproof, and it is difficult to use it as a container or packing material for transporting ice such as chilled products. Conventionally, a moisture-proof paper having only a surface active agent layer formed on the outermost layer and a moisture-proof liner having at least two coating layers provided have not been sufficiently waterproof.

Further, it is necessary to apply a waterproof paint in order to impart waterproofness to the paper base material, and even if an attempt is made to apply the waterproof paint to a water-repellent paper base material such as a water-repellent liner, conventionally With the technique disclosed in the above, the solvent of the waterproof paint tends to be in the form of water droplets, and the waterproof paint cannot be applied uniformly.

The present invention has been made in view of such 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.

As a result of diligent studies on the above-mentioned problems, the present inventors have found that when a waterproofing agent such as styrene / acrylic resin is applied to a paper substrate having a low Cobb water absorption, the paint does not easily become water droplets, and the paint is made into paper. We succeeded in distributing it uniformly on the substrate. According to the present invention, even in a paper substrate having water repellency because it is coated with a wax-based water repellent, by selectively using a specific waterproofing agent, the waterproofing agent can be uniformly applied on the paper substrate. Since it can be coated, it is possible to improve the waterproofness of the paper.

The present invention includes, but is not limited to, the following aspects.
[1] 120 seconds Cobb water absorption is 5 to 25 g / m ² , pulp and paper test method No. A waterproof paper obtained by applying a waterproofing agent on a paper substrate having a water repellency of R4 or higher specified in 68, wherein the waterproofing agent is at least one component of a styrene resin, an acrylic resin, a polyolefin resin, and a wax. The above waterproof paper containing.
[2] The waterproof paper according to [1], wherein the coating amount of the coating layer is 4 to 20 g / m ² .
[3] The waterproof paper according to [1] or [ ² ], which has a moisture permeability of 50 g / m for 2.24 hours or less.
[4] The waterproofing according to any one of [1] to [3], wherein the Cobb water absorption of the paper substrate is 3 g / m ² or less in 120 seconds or 25 g / m ² or less in 30 minutes. paper.
[5] The waterproof paper according to any one of [1] to [4], wherein the moisture permeability of the paper substrate is 1500 g / ^m for 2.24 hours or more.
[6] The waterproof paper according to any one of [1] to [5], wherein the paper substrate has a smoothness of 13 seconds or more.
[7] The waterproof paper according to any one of [1] to [6], wherein a water repellent agent is applied to at least one side 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 waterproof paper according to any one of [1] to [8], wherein the water absorption of the hump of the waterproof paper is 3 g / m ² or less in 120 seconds or 25 g / m ² or less in 30 minutes.
[10] Cobb water absorption for 120 seconds was 5 to 25 g / m ² , and pulp and paper test method No. A method for manufacturing waterproof paper, which comprises applying a waterproofing agent on a paper substrate having a water repellency of R4 or higher specified in 68, wherein the waterproofing agent is a styrene resin, an acrylic resin, or a polyolefin resin. The above method, which comprises at least one component of the above and a wax.

According to the present invention, it is possible to produce paper having both moisture resistance and waterproofness.

It is an external photograph of the paper container made when evaluating the waterproof property.

The present invention relates to waterproof paper. In the present invention, the waterproof paper refers to a paper having a function that water does not soak even when exposed to water for a long time. Further, in the preferred embodiment of the present invention, 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 does not change or is slightly deformed. It is seen, but the shape of the container is maintained.

The use of the waterproof paper according to the present invention is not particularly limited, and for example, a cardboard box, a packaging piece containing a food product such as fresh fish or vegetables, or a package containing a hygroscopic material such as a detergent. It can be used as a box or the like. The basis weight of the waterproof paper according to the present invention is not particularly limited, but 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 to 350 g / m ² or 50 to 300 g / m ² . When the paper substrate is a multi-layer paperboard having two or more 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 water absorption of 3 g / m ² or less for 120 seconds, more preferably 2 g / m ² or less, and may be 1 g / m ² or less. In the case of paper having a water absorption of less than 1 g / m ² (including the case where it does not absorb water and is less than the measurement limit value) when the water absorption of the Cobb for 120 seconds is measured, in a preferred embodiment, the water absorption of the Cobb for 30 minutes on the surface is 25 g / m / 2. It is m ² or less, more preferably 20 g / m ² or less, and may be 10 g / m ² or less. In the present invention, the Cobb water absorption is measured by bringing 100 ml of distilled water into contact with the coating layer and measuring the weight per unit area of the absorbed water after a specified time in accordance with the Cobb method specified in JIS P8140. Even under the condition that the measurement time is extended, the lower the water absorption of the Cobb, the lower the water absorption of the coating layer.

The waterproof paper of the present invention is also excellent in moisture resistance, and in a preferred embodiment, the moisture permeability is 100 g / m 2.24 h or less, more preferably 75 g / ^m 2.24 h or less, and further preferably 50 g / ^{m 2 .} -It is 24 hours or less. Here, the moisture permeability of the 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.

The waterproof paper of the present invention is also excellent in oil resistance, and in a preferred embodiment, the oil repellency on the coating layer side is preferably kit number 7 or more, more preferably 8 or more, and 9 or more. Is more preferable. Here, the oil repellency of the waterproof paper is determined from the coating layer side of the waterproof paper in accordance with "Paper and Paperboard-Rechargeability Test Method-Kit Method" (JAPAN TAPPI Pulp and Paper Test Method No. 41). It can be measured, and the larger the value of the kit number, the higher the oil resistance. Further, in a preferred embodiment, the drip oil absorption degree on the coating layer side is 500 seconds or more, more preferably 550 seconds or more, and further preferably 600 seconds or more. The longer the number of seconds of this drip oil absorption is, the higher the oil resistance is. The degree of oil absorption of the waterproof paper is the time until one drop of light oil No. 1 whose kinematic viscosity coefficient is adjusted to 3 cSt is dropped on the sample surface using a microsyringe equipped with an injection needle H5 until the surface becomes glossy. Can be evaluated by.

In the waterproof paper of the present invention, the smoothness of the coated surface is preferably 15 seconds or longer, more preferably 20 seconds or longer, still more preferably 25 seconds or longer. When the smoothness of the surface of the coated layer of the waterproof paper is within the above range, high gloss can be obtained on the surface of the coated layer, and a waterproof paper having more cosmetic properties can be obtained.

Paper Substrate The waterproof paper according to the present invention has at least a paper substrate 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 . It can be set in the range of. Further, when the paper substrate is a multi-layer paperboard having two or more layers of paper, the basis weight thereof can be appropriately set in the range of 70 to 800 g / m ² , for example, in the case of a corrugated cardboard liner. The basis weight can be set in the range of 80 to 600 g / m ² .

The paper substrate used in the present invention has a 120-second hump water absorption of 25 g / m ² or less, preferably 20 g / m ² or less, and more preferably 15 g / m ² or less on the surface on which the waterproof coating layer is provided. The paper substrate used in the present invention has a 120-second Cobb water absorption of 5 g / m ² or more, preferably 7 g / m ² or more, and more preferably 10 g / m ² or more. In the present invention, the water absorption of the paper substrate for 120 seconds is adjusted by applying a water repellent such as wax or a coating agent (sealing agent) having no waterproof property such as varnish containing resin. However, since the 120-second hump water absorption of the paper substrate is within the above range, the paper strength is prevented from being lowered due to excessive penetration of the water contained in the solvent of the waterproof paint, and the solid in the waterproof paint. By retaining the solvent on the surface of the paper layer, reliable coating is performed, and both waterproofness and moisture resistance can be improved.

The paper substrate used in the present invention is, in a preferred embodiment, the JAPAN TAPPI pulp and paper test method No. The water repellency measured in accordance with 68 "Paper and Paperboard-Water Repellent Test Method" is R4 or more, more preferably R6 or more, and even more preferably R8 or more. When the water repellency of the paper base material is R4 or higher, when the waterproofing agent is applied, the water contained in the coating liquid does not excessively permeate into the paper base material, and the decrease in the strength of the paper is suppressed. Can be done.

In a preferred embodiment, the paper substrate used in the present invention has a drip oil absorption degree of 5 seconds or more, more preferably 7 seconds or more, still more preferably 10 seconds or more on the surface on which the waterproof coating layer is provided. The upper limit is not particularly limited, but is preferably 80 seconds or less, more preferably 75 seconds or less, and further preferably 70 seconds or less. When the degree of oil absorption is within the above range, the wax contained in the waterproofing agent stays on the paper surface and hardly penetrates into the paper layer, so that the waterproofness and moisture resistance of the paper base material can be improved. The oil absorption of the paper substrate is the time until one drop of light oil No. 1 whose kinematic viscosity coefficient is adjusted to 3 cSt is dropped on the sample surface using a microsyringe equipped with an injection needle H5 until the surface becomes glossy. Can be evaluated by.

The physical characteristics of the paper base material are not particularly limited, and can be appropriately set according to the use of the waterproof paper. In the present invention, for example, the longitudinal elongation is 1.0 to 15.0%, the lateral elongation is 2.0 to 12.0%, the specific compressive strength is 100 to 350 Nm ² / g, and the specific burst strength is 2. It can be set to be 80 to 5.00 kPa · m ² / g.

In a preferred embodiment, the paper substrate used in the present invention has a Wangken-type smoothness of 13 seconds or more, more preferably 15 seconds or more, and further preferably 17 seconds or more on the surface on which the coating layer is provided. The upper limit is not particularly limited, but is preferably 100 seconds or less, more preferably 90 seconds or less, still more preferably 80 seconds or less, and most preferably 70 seconds or less. When the smoothness of the surface on which the waterproof coating layer is provided is within the above range, the waterproof coating layer that uniformly covers the paper substrate can be provided, and the waterproof and moisture-proof properties are improved.

In a preferred embodiment, the paper substrate used in the present invention has a moisture permeability of 1500 g / ^m 2.24 h or more, more preferably 1750 g / ^m 2.24 h or more, still more preferably 1750 g / m 2.24 h or more, as measured from the side where the waterproof coating layer is provided. It is 2000 g / ^m 2.24 hours or more. The upper limit of the water permeation is not particularly limited, but in a preferred embodiment, it is 5000 g / ^m 2.24 h or less, more preferably 4500 g / ^m 2.24 h or less, and further preferably 4000 g / ^m 2.24 h or less. Since the moisture permeability of the surface on which the waterproof coating layer is provided is within the above range, the moisture in the coating agent is efficiently evaporated to the paper layer side in the drying process after coating, so that the waterproof coating is uniformly coated. A work layer can be provided, which makes it easier to improve waterproofness and moisture resistance.

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. When the water contact angle is in the above range, it is possible to prevent the water contained in the coating liquid from excessively permeating into the paper base material and prevent the strength of the paper base material from being lowered.

As the raw material pulp for the paper base material, known materials can be used without particular limitation. Specifically, for example, coniferous bleached kraft pulp (NBKP), broadleaf bleached kraft pulp (LBKP), coniferous unbleached kraft pulp (NUKP), broadleaf bleached kraft pulp (LUKP), crushed wood pulp (GP), refiner ground pulp. Various wood-derived pulps such as (RGP), chemical pulp (CP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), and non-wood pulp obtained from Kenaf, Bagus, bamboo, hemp, straw, etc. Can be mentioned.

The paper base material may contain recycled paper pulp or may not contain recycled paper pulp. When the recycled paper pulp is contained, for example, when the paper base material is a single-layer paper, the blending ratio of the recycled paper pulp in the total pulp is preferably 10% by mass or more, more preferably 25% by mass or more, still more preferable. Can be 50% by mass or more, most preferably 70% by mass or more, and 100% by mass (consisting only of pulp derived from used paper). Further, kraft pulp may be blended as pulp other than used paper pulp, or the entire amount may be kraft pulp. Further, when the paper base material is a multi-layer paperboard having two or more layers of paper, the recycled paper pulp compounding ratio per layer can be as described above, and the recycled paper pulp compounding ratio in each layer is different. There may be.

As used paper pulp, used paper pulp, high-quality paper, high-quality coated paper, medium-quality paper, medium-quality coated paper, shavings, etc. Printed used paper, written used paper, paper such as discarded confidential documents, used magazine paper, used newspaper, and deinked pulp (DIP) can be used.

Further, in the paper-based papermaking, a sizing agent and a water-repellent agent can be added internally or externally, and further, a paper strength enhancing agent can be internally added in order to improve the strength. Examples of the sizing agent include rosin-based sizing agents, rosin emulsion-based sizing agents, α-carboxymethyl saturated fatty acids, neutral rosin-based sizing agents, alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), and the like. Examples thereof include cationic polymer-based sizing agents. Examples of the water repellent include a fluorine-based resin, a polyamide-based resin, and a wax. In addition, examples of the paper strength enhancer include conventionally used paper strength enhancers such as polyacrylamide (PAM) and modified starch. In the present invention, it is preferable to externally add a water-repellent agent containing wax to the side where the waterproof layer is provided, and it is more preferable to externally add a water-repellent agent containing paraffin-based wax. The coating amount when externally added to the water repellent agent is preferably 3 g / m ² or less, and more preferably 2 g / m ² or less.

Further, a known filler can be added to the paper substrate as needed, and an inorganic filler or an organic filler can be used without limitation. Examples of the inorganic filler include kaolin, calcined kaolin, delaminated kaolin, clay, calcined clay, delaminated clay, illite, heavy calcium carbonate, light calcium carbonate, light calcium carbonate-silica complex, magnesium carbonate, and carbonic acid. Examples thereof include barium, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide and the like, and examples of the organic filler include urea-formalin resin and polystyrene resin. , Phenolic resin and the like.

Furthermore, even if a sulfate band, aluminum chloride, sodium aluminate, basic aluminum compound, water-soluble aluminum compound, polyvalent metal compound, silica sol, etc. are used internally as long as the quality of the paper substrate is not affected. good.

The paper substrate can be produced by a known papermaking method. For example, it can be performed using a long net paper machine, a gap former type paper machine, a hybrid former type paper machine, an on-top former type paper machine, a round net paper machine, and the like, but the present invention is not limited thereto.

Further, in order to adjust the smoothness of the paper substrate of the present invention, a smoothing treatment may be performed if necessary. For the smoothing process, a smoothing processing device such as a normal calendar, a super calendar, a gloss calendar, a soft calendar, a thermal calendar, or a shoe calendar can be used. The smoothing processing device may appropriately adjust the form of the pressurizing device, the number of pressurizing nips, heating, linear pressure, and the like.

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

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

Examples of the styrene-based monomer include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, p-tert-butylstyrene, α-methylstyrene, and α. -Methyl-p-methylstyrene and the like can be mentioned.

Examples of the monomer copolymerizable with the styrene monomer include alkyl methacrylate such as methyl methacrylate, cyclohexyl methacrylate and methyl phenyl methacrylate, alkyl acrylate such as methyl acrylate, ethyl acrylate, butyl acrylate and cyclohexyl acrylate, and methacrylic acid. , 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 , Conjugate diene such as 3-butadiene and the like. These can be used alone 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 having a copolymerization ratio of acrylic acid, methacrylic acid, and an acrylic monomer that is a derivative thereof of 50% by mass or more. Yes, it may consist only of a polymer of an acrylic monomer.

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

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

In the present invention, the waterproof coating layer contains wax. Examples of the wax contained in the waterproof coating layer include polyethylene wax, Fishertroph wax, oil-based synthetic wax (fatty acid ester-based, fatty acid amide, ketone / amines), synthetic wax such as hydrogen hardening oil, beeswax, and wood wax. , Paraffin wax, natural wax such as microcrystallin wax and the like. These waxes can be used alone or in combination of two or more, and a hydrocarbon wax containing paraffin is particularly suitable.

In the present invention, the pigment may be contained in the waterproof coating layer as long as the waterproof property is not impaired for the purpose of improving the whiteness. In this case, it is preferable that the whiteness of the surface of the waterproof coating layer is increased by 1% or more as compared with 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 sulphate, calcium sulphate, zinc oxide, silicate, silicate, colloidal silica, satin white, mica, etc. Examples thereof include inorganic pigments such as 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, is particularly suitable because it does not easily impair waterproofness. Such a flat-shaped inorganic pigment preferably has 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% by mass to 35% by mass or less. If the content of the pigment is less than 5% by mass, the effect of improving the whiteness cannot be sufficiently obtained, and if it exceeds 40% by mass, the moisture-proof property of the waterproof coating layer of the synthetic resin component, It is not preferable because the waterproof function may not be fully exhibited. Further, as other coating agents, for example, a binder, a stabilizer, a defoaming agent, a viscosity improving agent, a water retaining agent, a preservative, a coloring agent and the like may be contained.

In the present invention, the waterproof coating layer can be formed by applying a coating agent containing the above components on a paper substrate and drying it. The coating amount of the waterproof coating layer is preferably 4 to 20 g / m ² , and more preferably 5 to 15 g / m ² . If it exceeds 20 g / m ² , further improvement in waterproofness cannot be expected, but the manufacturing cost may increase.

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, still more preferably 5.7 to 12.5 μm. .. Here, the average thickness of the coating layer is an average value of the thickness of the waterproof coating layer measured by cutting a sample into strips and observing the cross section at arbitrary 10 points using an electron microscope.

Further, the waterproof paper according to the present invention preferably has a moisture permeability of 15 (g / m ^2.24h ) / μm or less per unit thickness of the waterproof coating layer, and is preferably 10 (g / m ^2.24h ) / μm or less. Is more preferable, and 7 (g / m ^2.24h ) / μm or less is further preferable. Here, the moisture permeability per unit thickness of the waterproof coated 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.

The waterproof paper of the present invention can be produced by applying a waterproofing agent to at least one surface of a paper base material and drying the coated waterproofing agent. The formation of the waterproof coating layer can be performed 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 simultaneously coated by curtain coating or the like. good. When a plurality of coating layers are provided, at least one coating layer may be a waterproof coating layer, and it is preferable to apply a waterproofing agent as the outermost coating layer. When the coating layer is dried, the temperature of the coating layer at the outlet of the drying step is preferably adjusted to be less than 120 ° C. The coating speed at the time of coating the coating agent can be appropriately set in consideration of the viscosity of the coating agent and the target coating amount.

As a preferred embodiment, by applying the coating agent to the paper substrate by a contour coating method such as air knife coating or curtain coating, the amount of the coating agent applied to the surface of the paper substrate becomes uniform. Therefore, the thickness of the coating film becomes uniform, and the generation of blister in the coating layer can be suppressed in the drying step which is a subsequent step. In addition, the amount of the coating agent used can be reduced as compared with the contact coating method, and the manufacturing cost can be suppressed.

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. May be adjusted to. If the temperature of the coating layer at the outlet is 120 ° C or higher, the incidence of blisters 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., in some cases, blocking may occur in the waterproof paper wound after the coating layer is formed, and the coating layer may dry out. Due to insufficient performance, waterproof and moisture proof performance may not be fully exhibited.

The coating layer temperature at the outlet of the drying process can be set in consideration of the basis weight and the thickness of the paper base material. For example, when the paper base material is a multi-layer paperboard and the liner of corrugated board with a large basis weight and paper thickness, the coating layer is compared with the kraft paper which is a single layer paper and has a relatively small basis weight and paper thickness. Blister tends to occur on the surface of the corrugated cardboard. The reason is not limited, but in the case of corrugated cardboard liners, the basis weight and paper thickness are often larger and the air permeability is lower than that of kraft paper, and even if the moisture content in the paper is the same as that of kraft paper, in the drying process. It is considered that blister is likely to be generated on the surface of the coating layer because a large amount of water vaporized inside the paper substrate cannot sufficiently escape. Therefore, it is preferable to adjust the coating layer temperature at the outlet of the drying step to a lower value within the above range as the basis weight and the thickness of the paper base material become larger.

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

The temperature of the coating layer at the outlet of the drying step 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 of drying zones, the length, the equipment capacity of the drying zones (air volume, infrared output), and the like. Further, 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 type infrared drying method, an electric infrared drying method, and any of these. It can be used alone or in combination of two or more.

Hereinafter, the present invention will be described in more detail with reference to specific examples, but the present invention is not limited to the following specific examples. In the present specification, unless otherwise specified, the concentration and the like are based on weight, and the numerical range includes the end points thereof.

Manufacture of waterproof paper <Sample 1>
Back layer made of 100% recycled paper pulp, middle layer made of 100% recycled paper pulp, surface layer made of 70% unbleached kraft pulp and 30% recycled paper pulp, with a weight ratio of back layer: middle layer: surface layer = 25:60:15. After making and drying with a dryer, a water repellent containing paraffin wax and rosin is applied to the surface layer on one side, dried again with a dryer, and then smoothed using a calender to perform a smoothing treatment on the paper substrate A. (Basis weight: about 280 g / m ² , surface 120-second hump water absorption: 13 g / m ² ). Next, 10.0 g / m ² of a waterproofing agent (Michael Mann VaporCoat2200) containing styrene / acrylic resin and wax was applied to the surface layer side of the paper substrate using an air knife, and the temperature of the coating layer at the exit of the drying process was raised. A liner sample was obtained by hot air drying at 80 ° C.

<Sample 2>
A liner sample was obtained in the same manner as in Sample 1 except that the amount of the waterproofing agent applied was 7.8 g / m ² .

<Sample 3>
A liner sample was obtained in the same manner as in Sample 1 except that the amount of the waterproofing agent applied was 11.3 g / m ² .

<Sample 4>
Back layer made of 100% recycled paper pulp, middle layer made of 100% recycled paper pulp, surface layer made of 35% unbleached kraft pulp and 65% recycled paper pulp, with a weight ratio of back layer: middle layer: surface layer = 25:60:15. After the pulping and drying with a dryer, a water repellent containing paraffin wax and rosin is applied to the surface layer on one side, dried again with a dryer, and then smoothed using a calender to obtain the paper substrate B. Manufactured (basis weight: about 280 g / m ² , surface 120 seconds Cobb water absorption: 16 g / m ² ). Next, 10.5 g / m ² of a waterproofing agent (Michael Mann VaporCoat2200) containing styrene / acrylic resin and wax was applied to the surface layer side of the paper substrate using an air knife, and the temperature of the coating layer at the outlet of the drying process was raised. A liner sample was obtained by hot air drying at 80 ° C.

<Sample 5>
A liner sample was obtained in the same manner as in Sample 4 except that the amount of the waterproofing agent applied was 7.9 g / m ² .

<Sample 6 (comparative example)>
The back layer made of 100% recycled paper pulp, the middle layer made of 100% used paper pulp, the surface layer made of 25% unbleached kraft pulp and 75% recycled paper pulp are back layer: middle layer: surface layer = 25:65:10. After making and drying with a dryer, smoothing treatment was performed using a calender to produce a paper substrate C (basis weight: about 260 g / m ² , surface 120 seconds Cobb water absorption: 28 g / m ² ). .. Next, 8.9 g / m ² of a waterproofing agent (Michael Mann VaporCoat2200) containing styrene / acrylic resin and wax was applied to the surface layer side of the paper substrate using an air knife, and the temperature of the coating layer at the exit of the drying process was raised. A liner sample was obtained by hot air drying at 80 ° C.

<Sample 7 (comparative example)>
A liner sample was produced in the same manner as in Sample 1 except that the waterproofing agent was not applied (basis weight: about 280 g / m ² ).

<Sample 8 (comparative example)>
A liner sample was produced in the same manner as in Sample 4 except that the waterproofing agent was not applied (basis weight: about 280 g / m ² ).

<Sample 9 (comparative example)>
A liner sample was produced in the same manner as in Sample 6 except that the waterproofing agent was not applied (basis weight: about 260 g / m ² ).

Evaluation of waterproof paper For each sample, the paper quality and waterproofness were evaluated according to the following procedure.
(Basis weight) Measured according to JIS P 8124.
(Paper thickness) Measured according to JIS P 8118 and JIS P 8124.
(Average coating layer thickness of waterproof layer) Cut the sample into strips, measure the thickness of the coating layer by observing the cross section at any 10 points with an electron microscope, calculate the average value, and apply the average coating. The work layer thickness was used.

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

(Contact angle) The contact angle 1 second after dropping 1 drop (50 μl) of distilled water onto the sample surface was measured by a contact angle measuring device (manufactured by DAT1100 FIBRO System AB).
(Drip oil absorption) Using a microsyringe equipped with an injection needle H5, one drop of light oil No. 1 whose kinematic viscosity coefficient was adjusted to 3 cSt was dropped on the sample surface, and the time until the surface became glossy was measured. .. However, the measurement time was cut off at 600 seconds (10 minutes), and if the surface was glossy even after 600 seconds had passed, it was evaluated as "600 seconds or more".
(Housekiyu degree) JAPAN TAPPI Paper and pulp test method No. 41 The coating layer side (surface layer side) was measured in accordance with "Paper and Paperboard-Housden Oil Degree Test Method-Kit Method".

(Waterproofness) A paper container (length 28 cm x width 22 cm x depth 13 cm, the coating layer is located on the inner surface side) as shown in FIG. 1 is prepared from the above sample, and 1.0 L of water is poured into this paper container. It was put in and left in an environment with a temperature of 40 ° C. and a humidity of 80%. The state of water seepage and the shape of the box after being left for 1 week, 2 weeks, and 3 weeks were visually observed, and the waterproof property was judged based on the following criteria.
○: Water does not seep into the outer surface of the container or the inner surface of the container above the water surface, and the shape of the box can be maintained. △: Water does not seep into the outer surface of the container, and the shape of the box can be maintained. (However, water has penetrated into the inner surface of the container)
×: Water seeps out to the outer surface of the container and the shape of the box cannot be maintained.

As is clear from the results shown in the table, Samples 1 to 4 provided with a waterproof coating layer of styrene / acrylic resin on a paper substrate with low water absorption and high water repellency have moisture resistance and waterproofness. Even if it was held together and left in a state of water for a long period of 3 weeks, no leakage occurred. On the other hand, in the samples 7 to 9, water had exuded to the extent that the shape of the box could not be maintained after 1 day or 6 hours.

From the above experimental results, it was found that the waterproof paper of the present invention can be suitably used as a packaging material particularly for liquids.

Claims (10)

120 seconds Cobb water absorption is 5 to 25 g / m ² , pulp and paper test method No. A waterproof paper in which a waterproofing agent is applied on a paper substrate having a water repellency of R4 or higher specified in 68.
The waterproof paper has a Cobb water absorption of 25 g / m ² or less in 30 minutes, and the waterproofing agent contains at least one of a styrene resin, an acrylic resin, and a polyolefin resin, and a wax. The waterproof paper according to claim 1, wherein the coating amount of the coating layer is 4 to 20 g / m ² . The waterproof paper according to claim 1 or ² , wherein the moisture permeability is 50 g / m 2.24 hours or less. The waterproof paper according to any one of claims 1 to 3, wherein the Cobb water absorption of the paper substrate is 20 g / m ² or less in 120 seconds. The waterproof paper according to any one of claims 1 to 4, wherein the moisture permeability of the paper substrate is 1500 g / ^m for 2.24 hours or more. The waterproof paper according to any one of claims 1 to 5, wherein the paper substrate has a smoothness of 13 seconds or more. The waterproof paper according to any one of claims 1 to 6, wherein a water repellent agent is applied to at least one side of the paper base material. The waterproof paper according to any one of claims 1 to 7, wherein the paper base material is a multi-layer paperboard. The waterproof paper according to any one of claims 1 to 8, wherein the water absorption of the hump of the waterproof paper is 3 g / m ² or less in 120 seconds or 20 g / m ² or less in 30 minutes. 120 seconds Cobb water absorption is 5 to 25 g / m ² , pulp and paper test method No. A method for manufacturing waterproof paper, which comprises applying a waterproofing agent on a paper substrate having a water repellency of R4 or higher specified in 68.
The method described above, wherein the waterproof paper has a Cobb water absorption of 25 g / m ² or less in 30 minutes, and the waterproofing agent contains at least one of a styrene resin, an acrylic resin, and a polyolefin resin, and a wax.

Images