JP2022153750A - Heat-insulating waterproof paper - Google Patents

Abstract

To provide a heat-insulating waterproof paper manufactured by a method easier than conventional methods and having both of heat-insulating property and waterproof property.SOLUTION: A heat-insulating waterproof paper is provided with a coating layer involving a waterproof agent and a heat-insulating material on a paper substrate; the waterproof agent involves at least one selected from a styrenic resin, an acrylic resin, and a polyolefin-based resin, and, the heat-insulating material involves at least one selected from a hollow particle and a thermal expansion microcapsule. The heat-insulating waterproof paper is manufactured by a method that includes applying and drying a coating liquid which is a blend of a waterproof agent and a heat-insulating agent.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a heat-retaining waterproof paper, and more particularly to a heat-retaining waterproof paper suitable for transporting foodstuffs and the like that require waterproofness, heat insulation, and heat retention.

2. Description of the Related Art Styrofoam transport boxes are widely used as packaging means for transporting refrigerated/frozen foods such as fresh fish and heated foods such as lunch boxes while keeping them warm. Styrofoam shipping boxes have the advantage of being lightweight, but they are also highly water-resistant and have heat and heat insulation properties. I had a problem with weight loss.

In recent years, there has been a growing movement to eliminate plastic from the viewpoint of environmental protection, and the packaging and transportation industries are also demanding the development of Styrofoam alternatives. As one of them, a cardboard box made of paper is attracting attention.

Corrugated cardboard boxes can be given various functions according to their uses, one of which is heat insulation and heat retention. Methods of imparting heat insulation and heat retention functions to corrugated cardboard boxes include the use of internal chemicals used mainly during papermaking, the coating of heat insulating materials on the paper surface, and the use of a heat insulating structure during corrugated box processing. Patent document 1 discloses that heat-insulating base paper for corrugated board is provided with heat-insulating and heat-retaining performance by adding heat-expandable particle aggregates to at least the middle layer to form a foam layer. In addition, the base paper for insulating corrugated board described in Patent Document 2 is provided with heat insulation and heat retention by applying a coating liquid containing hollow inorganic particles, thermally expandable particles and a binder to the base paper to provide a coating layer. disclose. Furthermore, in Patent Document 3, an inner box is provided in the outer box, and the U-shaped open portion of the inner box is attached to the outer box so that it faces in the opposite direction to the U-shaped open portion of the outer box. A corrugated box is disclosed that has a thermal insulation function due to the structure in which it is housed.

Moreover, water resistance is mentioned as a function provided to the corrugated cardboard box. Methods for imparting water resistance include coating a paper surface with a water resistant material and coating the surface with a laminate film. For example, water resistance is imparted by applying a water resistant coating solution disclosed in Patent Document 4. and a method of imparting water resistance by coating with a laminate film disclosed in Patent Document 5.

Japanese Patent Application Laid-Open No. 2009-133030 JP 2008-127703 A JP 2018-111521 A JP-A-05-025796 Japanese Patent Application Laid-Open No. 2002-284140

These techniques have had problems in the manufacturing process and process control. When manufacturing the heat-retaining corrugated base paper described in Cited Document 1 that imparts heat-retaining properties, the internal addition of thermally expandable particle suspension tends to accumulate dirt in the paper-making system. requires complicated management. Although existing paper can be used for the corrugated cardboard box described in Cited Document 3, the box itself has a double structure in order to improve heat retention performance, which complicates the processing process and handling when storing articles. Furthermore, the technique described in Patent Document 5, which focuses on imparting water resistance, requires a separate lamination process.

In addition, in the prior art, the provision of heat retention function and the provision of water resistance function are generally performed separately, and in particular, when trying to provide only with coating technology, the desired water resistance and heat retention may not be guaranteed. There are many. The technique described in Patent Document 2 can provide heat retention by applying a coating liquid mixed with a heat insulating material, but does not have water resistance. Further, the technique described in Patent Document 4 imparts a water-resistant function to the coating liquid, but does not have a heat retaining property.

In view of such circumstances, it is an object of the present invention to provide a paper having both heat retention and water resistance by a simpler method than the prior art.

As a result of ingenuity and ingenuity, the inventors have found a technique for imparting heat retention and water resistance at the same time with only a coating layer, which has been difficult to achieve in the past, and have completed the present invention. The present invention includes, but is not limited to, the following aspects.
(1) A paper substrate is provided with a coating layer containing at least one synthetic resin selected from styrene resin, acrylic resin, and polyolefin resin, and at least one selected from hollow particles and thermally expandable microcapsules. Insulation waterproof paper.
(2) The heat insulating waterproof paper according to (1), wherein the coating weight of the coating layer is 4 g/m ² or more.
(3) The heat insulating waterproof paper according to (1) or (2), wherein the Cobb water absorbency of the heat insulating waterproof paper is 3 g/m ² or less after 120 seconds or 25 g/m ² or less after 30 minutes.
(4) The heat-insulating and waterproofing according to any one of (1) to (3), wherein the thermally expandable microcapsules have a thermoplastic resin outer shell and contain therein a low boiling point hydrocarbon as an expansion agent. paper.
(5) The heat-retaining waterproof paper according to any one of (1) to (4), wherein the expansion temperature of the thermally expandable microcapsules is 60°C or higher and 120°C or lower.
(6) The heat-retaining waterproof paper according to any one of (1) to (5), wherein the outer shell of the hollow particles contains an inorganic element.
(7) The heat-retaining waterproof paper according to any one of (1) to (6), wherein the inside of the hollow particles is in a vacuum state.
(8) The heat-retaining waterproof paper according to any one of (1) to (7), wherein the paper base material is multi-layered paperboard.
(9) A coating liquid obtained by mixing a waterproof agent containing at least one synthetic resin selected from styrene resin, acrylic resin, and polyolefin resin, and a heat insulating agent containing at least one hollow particle and thermally expandable microcapsule. A method for producing a heat-retaining waterproof paper, characterized by drying after coating.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide paper provided with a coating layer that achieves both heat retention and water resistance by a simpler method than the conventional method, such as only a coating process.

1 is a photograph showing the back side of a polystyrene foam lid in which a mold in which a sheet is set is fitted, as a method for evaluating heat retention of the sheet of the present invention. 1 is an overall photograph showing a method for evaluating heat retention of a sheet of the present invention.

TECHNICAL FIELD The present invention relates to heat insulating waterproof paper. In the present invention, the term “heat-retaining waterproof paper” refers to paper capable of retaining the heat of the packaged contents and having the function of preventing water from penetrating even when exposed to water for a long period of time. In a preferred embodiment of the present invention, the heat-retaining and waterproof paper according to the present invention maintains the air temperature in the container even when ice is placed in the paper container and left for 20 hours or more, and water is added and left for 3 weeks. It means that the shape of the container does not change due to water leaking out, or the shape of the container is maintained even though it is slightly deformed.

There are no particular restrictions on the use of the heat-insulating waterproof paper according to the present invention. can be used. The basis weight of the heat insulating and 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 heat insulating waterproof paper can be, for example, 30-350 g/m ² or 50-300 g/m ² . Further, when the paper substrate is multi-layered paperboard having two or more paper layers, the basis weight of the heat insulating waterproof paper can be 75-800 g/m ² or 200-600 g/m ² .

In a preferred embodiment, the heat insulating waterproof paper of the present invention has a surface 120-second Cobb water absorbency of 3 g/m ² or less, more preferably ² g/m ² or less, and may be 1 g/m 2 or less. In addition, in a paper whose 120-second Cobb water absorbency is less than 1 g/m ² (including cases where water is not absorbed and is less than the measurement limit value), in a preferred embodiment, the surface has a 30-minute Cobb water absorbency of 25 g/m 2 . 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 absorbency is determined according to JIS P8140 (Cobb method) by contacting the coating layer with 100 ml of distilled water 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.

(Paper substrate)
The heat-retaining waterproof paper according to the present invention has at least a paper base material and a heat-retaining waterproof coating layer provided on at least one surface of the paper base material. 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 120-second Cobb water absorbency of the paper substrate used in the present invention is not particularly limited as long as it can be provided with a heat-retaining waterproof coating layer, but is preferably 25 g/m ² or less. It may be more preferably 20 g/m ² or less, still more preferably 15 g/m ² or less. The paper substrate used in the present invention may preferably have a 120-second Cobb water absorbency of 5 g/m ² or more, more preferably 7 g/m ² or more, still more preferably 10 g/m ² or more. In the present invention, the 120-second Cobb water absorbency of the paper substrate can be adjusted by coating a water repellent agent such as wax, but the 120-second Cobb water absorbency of the paper substrate is within the above range. By doing so, it is possible to prevent deterioration of paper strength due to excessive penetration of moisture contained in the solvent of the heat-retaining waterproof paint, and solid content in the heat-retaining waterproof paint stays on the surface of the paper layer, so that a reliable coating is performed. It can satisfy the improvement of waterproofness and moisture resistance.

The physical properties of the paper substrate are not particularly limited, and can be appropriately set according to the intended use of the heat-retaining 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%, the specific compressive strength is 100 to 350 N·m ² /g, and the specific burst strength is 2.0%. It can be set to 80 to 5.00 kPa·m ² /g, and the water contact angle of the surface on which the waterproof coating layer is provided is 75 degrees or more, more preferably 77 degrees or more. In a preferred embodiment, the surface on which the coating layer is to be provided has an Oken smoothness of 13 seconds or more, more preferably 15 seconds or more, and even more preferably 17 seconds or more. Although the upper limit is not particularly limited, it 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. Furthermore, the moisture permeability measured from the side on which the waterproof coating layer is provided is 1500 g/m ² ·24h or more, more preferably 1750 g/m ² ·24h or more, and still more preferably 2000 g/m ² ·24h or more. Although the upper limit of moisture permeability is not particularly limited, in a preferred embodiment, it may be 5000 g/m ² ·24h or less, more preferably 4500 g/m ² ·24h or less, and still more preferably 4000 g/m ² ·24h or less.

As the raw material pulp for the paper substrate, any known pulp can be used without any 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 fiber-derived pulps, 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, fine white, special white, medium white, and white loss, 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) of newspaper waste 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 enhancer can be added internally to improve the strength. Examples of sizing agents include rosin-based sizing agents, rosin emulsion-based sizing agents, α-carboxylmethyl 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. Moreover, fluorine-based resins, polyamide-based resins, waxes, and the like can be used as water repellents. Examples of paper strength agents include conventionally used paper strength agents such as polyacrylamide (PAM) and modified starch. In the present invention, a water repellent agent containing wax is preferably externally added to the side on which the waterproof layer is provided, and more preferably a water repellent agent containing paraffin wax is externally added. When externally added with a water repellent, the coating amount is preferably 3 g/m ² or less, more preferably 2 g/m ² or less.

In addition, a known filler can be added to the paper substrate as required. Examples of 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, and barium carbonate. , titanium dioxide, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide and other inorganic fillers, and urea-formalin resin, polystyrene resin, phenolic resin and other organic fillers. etc.

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.

A paper substrate is manufactured 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, or 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 adjusted as appropriate.

(Heat insulation waterproof coating layer)
The heat insulating waterproof paper according to the present invention is characterized by having a heat insulating waterproof coating layer provided on a paper substrate. In the present invention, the heat insulating waterproof coating layer comprises a heat insulating material, a synthetic resin and a wax. contains As a result, it is possible to easily provide the paper substrate with a function that achieves both heat retention and waterproofness with a simpler configuration than in the prior art.

Thermally expandable microcapsules or hollow particles are preferably used for the heat insulating material used in the present invention. A thermally expandable microcapsule has an outer shell of a thermoplastic resin and contains a low boiling point hydrocarbon as an expanding agent inside. The thermoplastic synthetic resin constituting the outer shell is not particularly limited, and examples include acrylonitrile, methacrylonitrile, acrylamide, methacrylic acid or salts thereof, isobornyl methacrylate, dicyclopentenyl acrylate, vinylidene chloride, acrylic acid esters, and the like. can be mentioned. In addition, the low boiling point solvent enclosed in the outer shell is not particularly limited, and examples include isobutane, normal butane, normal pentane, isopentane, hexane, cyclohexane, heptane, petroleum ether, neopentane, propane, propylene, butene, and methane. (methyl chloride, methylene chloride, etc.), tetraalkylsilane, etc., and two or more of them may be appropriately selected. In the present invention, when thermally expandable microcapsules are used as a heat insulating material, the foaming start temperature and maximum expansion temperature of the thermally expandable microcapsules are preferably selected according to the drying temperature conditions of the waterproof agent described later, and the waterproof performance is It is more preferable to select a drying temperature within the optimum drying temperature range for expressing the Specifically, the foaming start temperature of the microcapsules is preferably in the range of 60 to 120°C, more preferably 70 to 110°C, even more preferably 75 to 105°C.

Hollow particles are fine particles having a solid outer shell and voids inside (having a so-called balloon structure). The material constituting the outer shell is not particularly limited as long as it does not hinder the implementation and effects of the present invention, but it is preferably an inorganic element or an inorganic compound, such as aluminum and its compounds, silicon and its compounds, Examples include alkali metals and their compounds, group 2 elements and their compounds, group 4 elements and their compounds, boron and their compounds, and the like, and one or more of these groups can be used. Further, in order to increase the effect of improving the heat retaining effect, it is preferable to use hollow particles having a vacuum balloon structure in which the gap is in a vacuum state. The average particle diameter of the hollow particles and the average thickness of the outer shell of the particles are not particularly limited as long as they do not hinder the implementation and effects of the present invention. Hollow particles with a thickness of 0.1 to 20 μm can be used.

In the present invention, when hollow particles are used as a heat insulating material, the heat resistance temperature is preferably selected according to the drying temperature conditions of the waterproofing agent described later, and the drying temperature exceeding the optimum drying temperature for expressing waterproof performance is selected. is more preferable. Specifically, the heat resistance temperature of the hollow particles is preferably 120° C. or higher, more preferably 130° C. or higher, and even more preferably 140° C. or higher.

The synthetic resin used in the present invention 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.

The styrene resin that can be contained in the heat insulating and waterproof coating layer constituting the present invention preferably has a copolymerization ratio of 50% by mass or more of a styrene monomer having a styrene skeleton in its structure. It may consist of only a polymer of system 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 heat insulating and 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 their derivatives, is 50% by mass or more. and may consist of a polymer of acrylic monomers only.

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.

In the present invention, wax may be contained in the heat-retaining and waterproof coating layer. Waxes contained in the heat-retaining waterproof coating layer include, for example, polyethylene-based waxes, Fischer-Tropsch waxes, oil-based synthetic waxes (fatty acid esters, fatty acid amides, ketones and amines), synthetic waxes such as hydrogenated oils, beeswax, Natural waxes such as Japan wax, paraffin wax, and microcrystalline wax can be used. These waxes can be used singly or in combination of two or more, and hydrocarbon waxes containing paraffin are particularly suitable.

In the present invention, it is preferable to add 0.1 to 100 parts by weight of the heat insulating material to 100 parts by weight of the waterproof agent from the viewpoint of achieving both heat insulating properties and waterproof properties. The number of parts of the heat insulating material to be added is more preferably 75 parts by weight or less, more preferably 50 parts by weight or less. If the heat insulating material is added in an amount of 0.1 part by weight or less, the heat insulating property is lost, and if the heat insulating material is added in an amount of 100 parts by weight or more, the waterproof property is lost.

In the present invention, for the purpose of improving the degree of whiteness, the heat-retaining and waterproof coating layer may contain a pigment within a range that does not impair the heat-retaining and water-retaining properties. In this case, it is preferable that the whiteness of the surface of the heat-retaining and 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, and mica, which have flat particles, are particularly preferable because they do not impede the moisture-proof and waterproof properties of the heat-retaining and waterproof coating layer. Such flat inorganic pigments preferably have an aspect ratio of 10 or more. The content of the pigment in the waterproof coating layer can be 5% by mass or more and 40% by mass or less, preferably 10% by mass or more and 35% by mass or less. If the 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-proof and waterproof functions of the heat-insulating and waterproof coating layer possessed by the synthetic resin component are impaired. It is not preferable because it may not be able to exhibit sufficiently. Further, as other coating agents, for example, binders, stabilizers, antifoaming agents, viscosity improvers, water retention agents, preservatives, colorants and the like may be incorporated.

In the present invention, the heat-retaining and waterproof coating layer can be formed by coating a paper substrate with a coating agent containing the components described above and drying the coating agent. The coating amount of the heat insulating and waterproof coating layer is preferably 4 to 20 g/m ² , and if it exceeds 20 g/m ² , further improvement in heat insulating properties and waterproof properties cannot be expected, but manufacturing costs increase. may come.

The heat-retaining and waterproof paper of the present invention can be produced by coating at least one surface of a paper substrate with a heat-retaining and waterproofing agent and drying the coated heat-retaining and waterproofing agent. The heat-retaining and waterproof coating layer can be formed by applying a coating agent using a known coating method, such as air knife coating, curtain coating, blade coating, gate roll coating, A coating method such as die 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 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.

As a preferred embodiment, the application of the coating agent to the paper base material is performed by a contour coating method such as air knife coating or curtain coating, whereby the coating amount of the coating agent on the surface of the paper base material becomes uniform. Therefore, the coating thickness becomes uniform, and the formation of blisters in the coating layer can be suppressed in the subsequent drying step. In addition, the amount of coating agent used can be reduced compared to the contact coating method, and the manufacturing cost can be suppressed.

The coating agent applied to the paper base material is dried to form the coating layer.In this drying process, the temperature of the coating layer at the outlet balances the thermal expansion of the heat insulating material and the suppression of blistering of the waterproof agent. dry conditions are required. The preferable range of the coating layer temperature at the outlet of the drying process is preferably 120° C. or lower, and may be adjusted to 100° C. or lower. If the coating layer temperature at the exit exceeds 120°C, the rate of blistering in the coating layer may increase, and blocking occurs in the heat insulating waterproof paper wound up 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 temperature of the coating layer at the outlet is less than 60°C, blocking may occur in the heat insulating waterproof paper wound up after the coating layer is formed, and the thermal expansion of the heat insulating material may occur. is hindered, and the coating layer is not sufficiently dried, so that heat retention, waterproofing, and moisture resistance may not be sufficiently exhibited. At that time, from the viewpoint of achieving both heat retention, waterproofness, and moisture resistance, when thermally expandable microcapsules are used as the heat insulating material as described above, thermally expandable microcapsules with a foaming start temperature of 60 to 120 ° C. should be used. is preferred. When microcapsules having a foaming initiation temperature exceeding 120° C. are used, the rate of blistering in the coating layer may increase, and the waterproof and moisture-proof properties, which should be compatible with heat retention, may be inferior. When hollow particles are used as the heat insulating material, the heat resistance temperature is preferably 120° C. or higher, more preferably 130° C. or higher, and even more preferably 140° C. or higher. If the heat-resistant temperature is lower than 120°C, the heat-retaining material may be destroyed by heat during the drying process, resulting in poor heat-retaining 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.

By using the heat insulating waterproof paper as a cardboard liner, it may be used as a cardboard box for preserving and transporting fresh fish that requires refrigeration. When transporting fresh fish, a large amount of ice is packed together with the fresh fish in a frozen or refrigerated state. Moreover, since it is waterproof, it does not easily collapse even during long-term transportation, so it can be expected to contribute to resource saving and improvement of transportation efficiency.

The following examples illustrate the present invention, but are not intended to limit the present invention.
[Preparation of paper substrate]
Using 63% by mass of unbleached softwood kraft pulp (NUKP) and 37% by mass of waste paper pulp, paperboard for the liner is made into a three-layered paperboard with a basis weight of 280g/m ² . (paper substrate sample).

[Example 1]

Hollow particles (MFL-100MCA manufactured by Matsumoto Yushi Seiyaku Co., Ltd., heat resistant temperature 150 to 160 ° C.) and a waterproof material (VAPORCOAT2200 manufactured by Michael Mann Co., Ltd.) in which hydrocarbon wax containing styrene resin and acrylic resin and paraffin are mixed and dispersed .S) were mixed at a solid content weight ratio of 1:9 to prepare a coating solution. The prepared coating solution was applied to a paper substrate using a Meyer bar so that the coating amount was 10 g/m ² , and dried at 105°C for 1 minute with a blower dryer to obtain a heat-retaining waterproof paper. (Sample 1).

[Example 2]
A waterproofing agent (VAPORCOAT2200. S) was mixed at a solid content weight ratio of 1:9 to prepare a coating solution. The prepared coating solution was applied to a paper substrate using a Meyer bar so that the coating amount was 10 g/m ² , and dried at 105°C for 1 minute with a blower dryer to obtain a heat-retaining waterproof paper. (Sample 2).

[Example 3]
A thermally expandable microcapsule (F-35D, manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.) and a waterproofing agent (VAPORCOAT2200.S manufactured by Michael Mann Co., Ltd.) in which a hydrocarbon wax containing styrene resin, acrylic resin, and paraffin is mixed and dispersed. were mixed at a solid content weight ratio of 1:9 to prepare a coating solution. The prepared coating solution was applied to a paper substrate using a Meyer bar so that the coating amount was 10 g/m ² , and dried at 140 ° C. for 3 minutes with a blower dryer to obtain a heat insulating waterproof paper. (Sample 3).

[Example 4]
A thermally expandable microcapsule (F-48D manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.) and a waterproofing agent (VAPORCOAT2200.S manufactured by Michael Mann Co., Ltd.) in which a hydrocarbon wax containing styrene resin, acrylic resin and paraffin is mixed and dispersed. A coating liquid was prepared by mixing at a solid content weight ratio of 1:9. The prepared coating solution was applied to a paper substrate using a Meyer bar so that the coating amount was 10 g/m ² , and dried at 160 ° C. for 3 minutes with a blower dryer to obtain a heat-retaining waterproof paper. (Sample 4).

[Example 5]
A heat-expandable microcapsule (F-78D manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.) and a waterproofing agent (VAPORCOAT2200.S manufactured by Michael Mann Co., Ltd.) in which a hydrocarbon wax containing styrene resin, acrylic resin and paraffin is mixed and dispersed. A coating liquid was prepared by mixing at a solid content weight ratio of 1:9. The prepared coating solution was applied to a paper substrate using a Meyer bar so that the coating amount was 10 g/m ² , and dried at 180 ° C. for 3 minutes with a blower dryer to obtain a heat insulating waterproof paper. (Sample 5).

[Comparative Example 1]
Hollow particles (MFL-100MCA manufactured by Matsumoto Yushi Seiyaku Co., Ltd., expansion temperature: 105 ° C.) and a coating liquid containing polyvinyl alcohol (manufactured by Kuraray Co., Ltd., PVA117) are mixed at a solid content weight ratio of 1: 9, A coating solution was prepared. The prepared coating solution was applied to a paper substrate using a Meyer bar so that the coating amount was 10 g/m ² , and dried at 105°C for 1 minute with a blower dryer to obtain a heat-retaining base paper for corrugated board. (Sample 6).

[Comparative Example 2]
A waterproofing agent (VAPORCOAT2200.S manufactured by Michael Mann Co., Ltd.) in which hydrocarbon waxes containing styrene resins and acrylic resins and paraffin are mixed and dispersed is applied using a Meyer bar so that the coating amount is 10 g/m ² on paper. After coating the base material, it was dried at 105° C. for 1 minute in a blower dryer to obtain a waterproof paper (Sample 7).

[Evaluation method]
Each obtained sample was subjected to the following tests and evaluated.
(1) 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 coating layer, and the weight per unit area of water absorbed after a specified time was measured. In addition to the normal prescribed time of 120 seconds (2 minutes), the measurement was also performed for 30 minutes.

(2) Thermal conductivity A measurement sample was prepared by cutting a sample into 50 mm x 50 mm, stacking 8 sheets, and sandwiching between graphite papers. After placing the heat flux measurement sensor and the measurement sample on the lower heater of the heat flux meter in this order, the upper heater is lowered and pressed, and the lower heater is set to 18 ° C and the upper heater to 42 ° C so that the sample surface becomes 30 ° C. Using the measured thermal resistance value, the thermal conductivity of the sample was obtained by the following formula:
Thermal conductivity (W/mK) = sample thickness (m)/thermal resistance (m ² K/W)

(3) Heat Retention The prepared sample was allowed to stand in an environment of 25° C. and 50% RH for 3 hours, then cut into 200 mm length × 150 mm width, layered on a 5 mm thick A-flute cardboard, and placed as shown in FIG. After inserting it into a mold, it was inserted into a polystyrene foam lid with a thermometer on the upper surface so that the sample faced the inside of the box. After putting 2 kg of crushed ice in a styrene foam container, the container was sealed with a lid fitted with a sample, and the temperature inside the container was measured every 10 minutes under an environment of 23°C and 50% humidity. (See Figure 2.)
Table 1 shows the evaluation results.

From the above results, it was clarified that the heat-retaining waterproof papers of the present invention (Samples 1 to 5) have superior heat-retaining properties and waterproofness compared to other samples. INDUSTRIAL APPLICABILITY The heat insulating waterproof paper of the present invention can be suitably used as a paper for manufacturing boxes, bags, etc., which require heat retention of foods and the like and do not leak liquid.

Claims (9)

A paper base material provided with a coating layer containing at least one kind of synthetic resin selected from styrene resin, acrylic resin and polyolefin resin, and containing at least one kind of hollow particles and thermally expandable microcapsules. waterproof paper. The heat insulating waterproof paper according to claim 1, wherein the coating weight of the coating layer is 4 g/ ^m2 or more. 3. The heat insulating waterproof paper according to claim 1, wherein the Cobb water absorbency of said heat insulating waterproof paper is 3 g/m<^{2> or less after 120 seconds or 25 g/m<2 >} or less after 30 minutes. 4. The heat-retaining and waterproof paper according to claim 1, wherein said heat-expandable microcapsules have a thermoplastic resin outer shell and contain therein a low-boiling-point hydrocarbon serving as an expanding agent. The heat-retaining waterproof paper according to any one of claims 1 to 4, wherein the thermally expandable microcapsules have an expansion temperature of 60°C or higher and 120°C or lower. The heat-retaining waterproof paper according to any one of claims 1 to 5, wherein the outer shell of the hollow particles contains an inorganic element. The heat-retaining waterproof paper according to any one of claims 1 to 6, wherein the interior of said hollow particles is in a vacuum state. The heat-insulating and waterproof paper according to any one of claims 1 to 7, wherein the paper substrate is multi-layered paperboard. After coating with a coating liquid mixed with a waterproof agent containing at least one synthetic resin selected from styrene-based resin, acrylic resin, and polyolefin-based resin, and a heat insulating agent containing at least one selected from hollow particles and thermally expandable microcapsules. A method for producing a heat-retaining waterproof paper, characterized by drying.

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