Waterproof cardboard box

Abstract

To develop a technology to make cardboard boxes with excellent waterproof properties.SOLUTION: The present invention provides a paper container made of cardboard, in which at least the inner surface of the box is coated with a waterproof resin layer. The cardboard container of the present invention has a 30-minute Cobb water absorbency of 155 g / m2 or less, and a box strength residual ratio of 50% or more after being filled with water and left for 24 hours.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a waterproof cardboard box and a method for manufacturing 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. 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.

[0006] 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.

[0007] 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.

[0008] In view of the above circumstances, an object of the present invention is to provide a paper container that has sufficient waterproofing properties. [Means for solving the problem]

[0009] The inventors have thoroughly investigated the above-mentioned problems and have succeeded in developing a paper container with sufficient waterproofing by using cardboard having a liner with a waterproof coating layer on at least one side of the paper base material and forming the container so that the waterproof coating layer of the liner forms the inner surface of the box.

[0010] The present invention includes, but is not limited to, the following aspects. [1] A paper container made of corrugated board with a waterproof resin layer applied to at least the inside of the box, and with a 30-minute Cobb water absorption of 155 g / m 2 The above paper container has a box strength remaining rate of 50% or more after being filled with water and left for 24 hours. [2] The paper container according to [1], wherein the cardboard sheet constituting the paper container has a burst strength after contact with water for 30 minutes / burst strength before contact with water of 50% or more. [3] The paper container according to [1] or [2], wherein the waterproof resin layer contains at least one of a styrene-based resin, an acrylic-based resin, and a polyolefin resin, and a water-repellent wax. [4] A paper container according to any one of [1] to [3], in which the cardboard liner and core that make up the paper container are bonded together with a waterproof glue. [5] The paper container according to any one of [1] to [4], wherein a waterproofing agent is added to the central core of the cardboard that constitutes the paper container. [6] The paper container according to any one of [1] to [5], wherein the ratio of inner volume to outer volume of the paper container is 0.70 or more. [7] The paper container according to any one of [1] to [6], wherein the thickness of the cardboard constituting the paper container is 2.5 to 15 mm. [8] A corrugated board sheet consisting of a liner and a core, with a waterproof resin layer coated on at least one side. Effect of the Invention

[0011] According to the present invention, a paper container having sufficient waterproof properties can be obtained. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of a paper container produced for evaluating waterproofness. [Diagram 2] FIG. 2 is a development view of the cardboard sheet before it is folded into a box shape. [Diagram 3] FIG. 3 is a perspective view showing how the cardboard sheets are assembled into a box. [Figure 4] Figure 4 is a photograph of the appearance of the paper container produced when evaluating waterproofing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention relates to a paper container (paper container) having waterproof properties. In the present invention, waterproof properties refer to a function that prevents water from seeping in even when exposed to water for a long period of time. In a preferred embodiment of the present invention, the paper container according to the present invention is one in which water does not seep out and the shape of the container does not change even when the paper container is filled with water and left for three weeks, or the container shape is maintained with some deformation.

[0014] There are no particular limitations on the uses of the paper container of the present invention, and it can be suitably used, for example, as a container for storing food items such as fresh fish and vegetables, or for storing hygroscopic items such as detergents.

[0015] Cardboard paper containers The paper container according to the present invention is made of cardboard, and the thickness of the cardboard is 2.5 to 15 mm in a preferred embodiment. Cardboard is made by bonding flat paper (liner) and corrugated paper (core) with an adhesive, and is suitably used for various purposes such as product packaging and cushioning, transporting luggage, and storing goods.

[0016] The cardboard sheet used in the box of the present invention can generally be manufactured by bonding a liner and a corrugated medium using a corrugator. Any known corrugator can be used without any restrictions, but a typical corrugator is composed of a single facer, a double backer, and a cutter. A glue making device for bonding the liner and medium raw paper, and a device for generating heat to melt the glue, etc. are also used.

[0017] In addition, when manufacturing the cardboard sheet used in the box of the present invention, an adhesive is used to bond the liner and the core, and it is preferable to use a water-resistant adhesive from the viewpoint of preventing the strength of the cardboard box from decreasing due to water wetting, condensation, moisture, etc. on the cross section of the cardboard sheet. A water-resistant adhesive is a normal cardboard adhesive to which a water-resistant agent has been added. The water-resistant agent is not particularly limited, and examples include those containing synthetic resin emulsion, ketone aldehyde resin, etc.

[0018] The cardboard liner will be described later, but depending on the application, a kraft liner, a jute liner, etc. can be used. The basis weight of the liner is not particularly limited, and for example, the basis weight of the entire liner is 70 to 550 g / m 2 The thickness can be set to 100 to 500 g / m 2 Or 150~450g / m 2 It may be also possible to use the following.

[0019] Regarding the medium that constitutes the corrugated board, A-flute, B-flute, C-flute, W-flute, E-flute, etc. can be used without any particular restriction. There is also no particular restriction on the basis weight of the medium, and it is up to 120 g / m 2 , 160g / m 2 , 180g / m 2 , reinforced 180g / m 2 , reinforced 200g / m 2 etc. can be suitably used.

[0020] The paper container according to the present invention is produced from cardboard, for example, by folding one blank sheet and, if necessary, bonding it with an adhesive. The type of adhesive is not particularly limited, and examples thereof include water-based, water-dispersed, solution-based, solventless, and solid-based adhesives, and can be appropriately selected depending on the surface condition of the paper substrate to be bonded.

[0021] The amount of adhesive used is not particularly limited as long as sufficient adhesive strength is obtained, but in the case of surface application, the amount is preferably 0.5 to 2000 g / m 2 It can be 5 to 1500 g / m 2 It may be 10 to 1000 g / m 2 In the case of line application, the application width can be appropriately changed depending on the nozzle diameter of the applicator, the movement speed of the nozzle or the paper substrate, the viscosity of the adhesive during application, the width of the paper substrate to be bonded, etc., and the application amount per unit length is not particularly limited, but may be, for example, 0.1 to 30 g / m, 0.5 to 20 g / m, or 1 to 15 g / m.

[0022] In the present invention, in order to ensure the waterproofness of the box, it is preferable that the main body of the box is a watertight box. The watertight type refers to a box shape formed by folding one blank sheet, in which the bottom and all the side walls are connected via fold lines, and all the side walls are connected via fold lines. With regard to the connection parts of the side walls, it is preferable that 50% or more of the inner height of the box from the bottom is connected, more preferably 70% or more is connected, even more preferably 80% or more is connected, and most preferably the entire height of the side walls is connected.

[0023] When manufacturing a container such as a box by forming a paper base material into a box, a box forming machine can be used. There is no particular limitation on the type of box forming machine used, and for example, a vertical type or horizontal type box forming machine can be used. In a preferred embodiment, the paper container according to the present invention may have a box strength remaining rate of 50% or more, more preferably 60% or more, even more preferably 70% or more, and most preferably 80% or more after pouring water into the paper container and leaving it for 24 hours. In the present invention, the box strength remaining rate is a value obtained by pouring water into a box-shaped paper container, leaving it for 24 hours, and then measuring the box compressive strength using a box compression tester in accordance with JIS Z 0212, and dividing the box compressive strength of a paper container of the same shape and dimensions but not pouring water into it. The higher the box strength remaining rate, the more sufficient strength the paper container can maintain even when liquid is directly poured into the paper container as its contents and the container is transported or stored for a period measured in days.

[0024] Raina The liner of the corrugated board according to the present invention is not particularly limited in terms of basis weight, but when the paper base material of the liner is a multi-layer paperboard having two or more paper layers, the basis weight of the liner is 75 to 800 g / m 2 200~600g / m 2 It can be said that:

[0025] In a preferred embodiment, the liner of the present invention has a surface Cobb water absorption of 3 g / m 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 155 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 100 g / m 2 Less than 50 g / m is more preferable. 2 More preferably, 25 g / m 2 More preferably, less than 10 g / m 2 In the present invention, the Cobb water absorbency is measured according to JIS P8140 (Cobb method), 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 in which the measurement time is extended, the lower the water absorbency of the coating layer is.

[0026] In a preferred embodiment, the liner of the present invention is also excellent in moisture resistance, and for example, has a moisture permeability of 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.

[0027] The liner of the present invention also has excellent oil resistance, and in a preferred embodiment, the oil repellency of the coating layer side is preferably kit number 7 or more, more preferably 8 or more, and even more preferably 9 or more. Here, the oil repellency can be measured from the coating layer side of the liner in accordance with JAPAN TAPPI Paper and Pulp Test Method No. 41 "Paper and Paperboard - Oil Repellency Test Method - Kit Method", and the higher the kit number, the higher the oil resistance.

[0028] The liner of the present invention has an Oken smoothness of the coating surface of preferably 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.

[0029] The liner of the present invention has excellent water resistance at the folded portion under any temperature condition, whether at room temperature, refrigerated or frozen. In a preferred embodiment, the cracking rate of the coating layer of a liner folded and left for 24 hours under storage conditions of 23°C is 15% or less, more preferably 10% or less, and even more preferably 5% or less. The cracking rate of the coating layer under storage conditions of 4°C is preferably 55% or less, more preferably 45% or less, even more preferably 35% or less, and most preferably 25% or less. Furthermore, the cracking rate of the coating layer under storage conditions of -18°C is preferably 75% or less, and even more preferably 65% ​​or less. It is more preferable that the cracking rate of the coating layer is less than 55%, more preferably less than 45%, and most preferably less than 45%. Here, the cracking rate of the coating layer is the value obtained by dividing the length of the crack in the coating layer that occurs when a temperature- and humidity-conditioned sample cut to a certain size is left under a specific temperature condition for 24 hours and then a crease is made on the coating layer side along the paper flow direction that is the same length as the paper, by the total length of the crease (length of the paper). When the cracking rate of the coating layer is within the above range, when the liner and cardboard sheet that have been folded under each temperature condition are used, the seepage of liquid from the folded part is suppressed and strength can be maintained. Also, the smaller the cracking rate of the coating layer, the more the liner can maintain its waterproofness even after folding.

[0030] (Paper base material) The liner used in the cardboard of 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 It can be set appropriately within the range.

[0031] The paper substrate 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 2In the present invention, the 120-second Cobb water absorbency can be adjusted by applying a water repellent such as wax, and by having the 120-second Cobb water absorbency be in the above-mentioned range, it is possible to prevent a decrease in paper strength due to excessive penetration of the water contained in the solvent of the waterproof coating, and the solid content of the waterproof coating is retained on the surface of the paper layer, providing a reliable coating, thereby improving both waterproofness and moisture resistance.

[0032] The paper substrate used in the present invention has a water repellency of R4 or more, preferably R6 or more, and 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.

[0033] 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 is measured 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.

[0034] 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.

[0035] 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 24 hours or more. There is no particular upper limit for moisture permeability. Although not limited thereto, 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 during the drying process after coating, allowing a waterproof coating layer to be formed that covers the paper uniformly, improving waterproofness and moisture resistance.

[0036] 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.

[0037] 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 pulps derived from wood fibers, 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.

[0038] 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.

[0039] Examples of waste paper pulp that can be used include waste paper pulp obtained by disintegrating unprinted waste paper such as cardboard, white, extra white, medium white, and white damage; waste paper printed on fine paper, fine coated paper, medium quality paper, medium quality coated paper, and recycled paper; and written waste paper, papers such as discarded confidential documents, waste magazines, and waste newspapers that have been disintegrated and then deinked (DIP).

[0040] 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), cationic polymer-based sizing agents, and the like. Examples of water repellents include fluorine-based resins, polyamide-based resins, waxes, and the like. Examples of paper strength enhancing agents include conventionally used paper strength enhancing agents such as polyacrylamide (PAM) and modified starch. In the present invention, it is preferable to externally add a water repellent containing wax to the side where the waterproof layer is provided, and it is more preferable to externally add a water repellent containing paraffin-based wax. The coating amount when the water repellent is externally added is 3 g / m. 2 Less than 2 g / m is preferred. 2 The following is more preferred:

[0041] If necessary, known fillers can be added to the paper base material. Examples of fillers include kaolin, calcined kaolin, delaminated kaolin, clay, calcined clay, delaminated clay, illite, heavy calcium carbonate, light calcium carbonate, light calcium carbonate-silica composite, magnesium carbonate, barium carbonate, titanium dioxide, and zinc oxide. Examples of the fillers include inorganic fillers such as lead, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, and zinc hydroxide, and organic fillers such as urea-formaldehyde resin, polystyrene resin, and phenol resin.

[0042] 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.

[0043] The paper base material is 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.

[0044] 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. The smoothing treatment device may be appropriately adjusted in terms of the shape of the pressure device, the number of pressure nips, heating, line pressure, etc.

[0045] (Waterproof resin layer) The liner used in the cardboard according to the present invention has a waterproof resin layer (waterproof coating layer) provided on a paper base material, and in a preferred embodiment of the present invention, the waterproof layer contains a synthetic resin and a water-repellent 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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 acid, methacrylic acid, and acrylic monomers that are derivatives of these is 50 mass% or more, and may be composed only of polymers of acrylic monomers.

[0050] 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 is selected from these acrylic monomers. It may be a polymer of one or more monomers.

[0051] 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.

[0052] In a preferred embodiment of the present invention, the waterproof coating layer contains a water-repellent wax. Examples of the water-repellent wax 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.

[0053] In the present invention, in order to improve the whiteness, a pigment may be contained in the waterproof coating layer to the extent that the waterproofness is not impaired. 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 in that they are unlikely to impair the moisture resistance and waterproofness of the waterproof coating layer. 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 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 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, colorants, etc. may be contained.

[0054] 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 20 g / m 2 If the temperature exceeds this range, no further improvement in waterproofness can be expected, while the manufacturing cost may increase.

[0055] In a preferred embodiment, the waterproof coating layer provided on the liner 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.

[0056] In addition, the liner 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 the moisture permeability measured from the coating layer side of the liner in accordance with JIS Z 0208. It is calculated by dividing by the average coating layer thickness.

[0057] The liner of the present invention can be produced, for example, by coating at least one side of a 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, for example, air knife coating, curtain coating, blade coating, gate roll coating, die coating, and other coating methods 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, etc. When drying the coating layer, the coating layer temperature at the drying step 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.

[0058] 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.

[0059] 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 of blisters in the coating layer may increase, and blocking may occur in the waterproof liner wound up 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 liner wound up after the coating layer is formed, but the coating layer may not be dried sufficiently to fully exhibit waterproof and moisture-proof performance.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] Cord base paper The corrugated board according to the present invention can be obtained by bonding corrugated medium base paper to the obtained liner. Generally, corrugated medium base paper is processed into a corrugated shape using a corrugator, and liners are bonded to the front and back of the corrugated medium base paper to produce high-strength corrugated board, but multi-layer corrugated board and single-face corrugated board with corrugated medium base paper exposed on the surface are also known. In the present invention, a preferred embodiment is a corrugated board in which liners are bonded to both sides of the medium, or a corrugated board processed into a multi-layer.

[0064] The basis weight of the medium base paper is not particularly limited, but is preferably 60 to 250 g / m 2 is preferable, and 70 to 240 g / m 2 More preferably, 80 to 230 g / m 2 is more preferred. In the present invention, it is preferable to use reinforced corrug, and more preferable to use water-resistant reinforced corrug. The reinforced corrug refers to a corrug that has improved compressive strength compared to a general corrug that satisfies the performance of corrug base paper specified in JIS P 3904 by adding a paper strength agent or the like in the papermaking process. The water-resistant reinforced corrug refers to a corrug that has improved not only compressive strength but also water resistance by further adding a water resistance agent in the manufacturing process of the reinforced corrug. Polyacrylamide (PAM) may be used as the internal paper strength agent, and in this case, the amount added is preferably 0.1% to 5.0% based on the paper stock solids, more preferably 0.2% to 2.0%.

[0065] The medium base paper may have a clear (transparent) coating layer formed by applying a coating liquid containing a starch-based compound to one or both sides of the base paper. Starch coating refers to applying a coating liquid (surface treatment liquid) containing a starch-based compound onto the base paper using a coater (coating machine) such as a pond-type two-roll size press, a gate roll coater or a rod metering size press which are film transfer type coating methods, or a curtain coater or a spray coater which are non-contact coating methods.

[0066] There is no particular restriction on the amount of starch coating as long as it does not impair the strength of the core. The lower limit is 0.2 g / m2 in solids per side. 2 or more, 0.8 g / m 2 or more, 2.0 g / m 2 or more, 3.0 g / m 2 or more, 4.0 g / m 2 There is no particular upper limit, but if the coating amount is increased, it is necessary to reduce the basis weight of the base paper before the starch is clear coated, which reduces the tensile strength and tear strength of the base paper before the starch coating, making the paper more susceptible to breakage. Therefore, the coating amount of the starch-based compound is set to 8.0 g / m per side. 2 Less than 6.0 g / m is preferred. 2 The following may also be used.

[0067] In the present invention, various auxiliaries that are typically blended in starch coating, such as dispersants, thickeners, water retention agents, antifoaming agents, water-resistant agents, and colorants, may be used as necessary. In the present invention, examples of the coater that can be used for applying the starch-based compound to the base paper include a two-roll size press, a gate roll coater, a rod metering size press, a blade coater, a bar coater, a spray coater, an air knife coater, and a curtain coater. In the present invention, the effect can also be achieved by using a film transfer type coater such as a gate roll coater or a rod metering size press.

[0068] The core raw paper produced in the present invention preferably contains a large amount of recycled paper pulp as a pulp raw material. In the present invention, the recycled paper pulp content in the total pulp is preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, and may be 90% by weight or more. The core raw paper of the present invention is preferably a multi-layered base paper made from a paper material containing recycled paper pulp.

[0069] Waste paper pulp includes unprinted waste paper such as white, special white, medium white, and white loss, which are waste paper such as cardboard waste paper, waste paper, waste paper that has been cut, lost paper, and width-reduced waste paper generated in bookbinding, printing factories, cutting shops, etc., waste paper pulp, wood free paper, wood free coated paper, medium quality paper, medium quality coated paper, and saw paper, etc., used for lithographic, letterpress, and intaglio printing. Examples of pulp that can be used include waste paper printed by electrophotography, thermal printing, thermal transfer printing, pressure-sensitive printing, inkjet printing, carbon paper, etc., waste paper written on with water-based or oil-based ink or pencil, pulp obtained by disintegrating and deinking waste newspaper (hereinafter sometimes referred to as DIP), papermaking sludge, wastewater scum from papermaking factories, etc. Pulps other than waste paper pulp that can be used include ground pulp (GP), thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), deinked pulp (DIP), softwood kraft pulp (NKP), and other pulps that are generally used as raw materials for papermaking.

[0070] Examples of fillers to be added to medium base paper include inorganic fillers such as heavy calcium carbonate and light calcium carbonate, titanium oxide, clay, silica, talc, kaolin, calcined kaolin, delaminated kaolin, magnesium carbonate, barium carbonate, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, titanium oxide, and bentonite; and organic fillers such as urea-formalin resin, polystyrene resin, melamine resin, phenolic resin, and hollow microparticles; which can be used alone or in combination of two or more kinds as appropriate. Recycled fillers made from papermaking sludge, deinking floss, and the like can also be used.

[0071] In acidic papermaking, fillers other than those used in neutral papermaking, excluding those that are acid-soluble, are used, and these fillers are used alone or in combination of two or more kinds as appropriate. When producing medium base paper, known papermaking additives can be used as internal additives. Papermaking chemicals are not particularly limited, and various chemicals can be used alone or in combination.

[0072] For example, papermaking chemicals such as retention aids, drainage improvers, coagulants, aluminum sulfate, bentonite, silica, sizing agents, dry strength agents, wet strength agents, bulking agents, dyes, fluorescent whitening agents, pH adjusters, defoamers, UV inhibitors, discoloration inhibitors, pitch control agents, slime control agents, etc. Examples of papermaking chemicals that can be suitably used include internal dry strength agents such as polyacrylamide polymers, polyvinyl alcohol polymers, cationic starches, various modified starches, urea-formalin resins, and melamine-formalin resins; internal wet strength agents such as polyamide polyamine epichlorohydrin resins; internal sizing agents such as rosin-based sizing agents, AKD-based sizing agents, ASA-based sizing agents, petroleum-based sizing agents, and neutral rosin sizing agents; and the like.

[0073] These auxiliaries may be added in advance to the slurry of the filler of the present invention before application to the paper machine, or may be applied to the paper machine separately from the slurry of the filler of the present invention. The corrug raw paper may be subjected to various surface treatments, for example, surface treatment may be performed by calendaring, or a lubricant may be applied to the corrug raw paper. As the lubricant, a wax-based lubricant may be used, and the amount of application may be 0.005 g / m. 2 ~0.1g / m 2 In the present invention, it is preferable to spray the lubricant onto the calender rolls and transfer it to the paper when the base paper is passed through the calender. This is because, in addition to applying the lubricant, this makes it possible to prevent dirt from adhering to the surface of the calender rolls. As described above, applying the lubricant can more effectively prevent dirt from adhering to the surface of the calender rolls.

[0074] The obtained corrugating medium base paper can be corrugated (fluted) using a known corrugator. Any known corrugation process can be applied depending on the application, and for example, A-flute, B-flute, C-flute, E-flute, F-flute, G-flute, AAA-flute, AA-flute, etc. may be applied to the corrugating medium base paper.

[0075] Processing into cardboard sheets The corrugated cardboard sheet used in the box of the present invention is obtained by laminating a liner and a corrugated medium together using a corrugator.

[0076] Any known corrugator can be used without any restrictions, but a typical corrugator is composed of a single facer, a double backer, and a cutter. In addition, a glue making device for bonding the liner and the core raw paper, and a device for generating heat to melt the glue are also used.

[0077] In addition, when manufacturing the cardboard sheet used in the box of the present invention, an adhesive is used to bond the liner and the core, and it is preferable to use a water-resistant adhesive from the viewpoint of preventing the strength of the cardboard box from decreasing due to water wetting, condensation, moisture, etc. on the cross section of the cardboard sheet. A water-resistant adhesive is a normal cardboard adhesive to which a water-resistant agent has been added. The water-resistant agent is not particularly limited, and examples include those containing synthetic resin emulsion, ketone aldehyde resin, etc.

[0078] In a preferred embodiment, the cardboard sheet used for the box of the present invention may have a burst strength after contact with water for 30 minutes / burst strength before contact with water of 50% or more, more preferably 60% or more, even more preferably 70% or more, and most preferably 80% or more. The higher this value, the less susceptible the cardboard sheet is to condensation and other effects caused by the temperature difference between the contents and the air temperature around the container when processed into a paper container, and the strength of the paper container can be maintained. EXAMPLES

[0079] 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.

[0080] Liner manufacturing and evaluation (1) Liner sample A 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 coated on one side of the surface with a water repellent agent containing paraffin wax and rosin. After drying again with a dryer, the surface was smoothed using a calendar to produce liner sample A (basis weight: approximately 280 g / m 2 , 120 second Cobb water absorption of the surface: 13g / m 2 , Water repellent coating amount: approx. 1g / m 2 ). (2) Liner sample B A waterproofing agent containing styrene-acrylic resin and paraffin wax (Michaelman, VaporCoat2200) was applied at 10.0 g / m to the surface of liner sample A using an air knife. 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 liner sample B (basis weight: about 290 g / m 2 , 120 second Cobb water absorption of the surface: 0.3g / m 2 ). (3) Liner sample C 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 smoothed using a calendar to produce liner sample C (basis weight: about 280 g / m 2 , 120 second Cobb water absorption of the surface: 30g / m 2 ). (4) Liner sample D The surface layer of liner sample C was made up of 100 parts by weight of styrene-butadiene copolymer (HOJ4072, Zeon Corporation, glass transition temperature: 21°C), 65 parts by weight of delaminated kaolin (average particle size: 3 μm, Capim NP, RCC Corporation), and heavy calcium carbonate (average particle size: 8 μm A waterproof coating solution containing 15 parts by weight of a silica-based defoamer (SN DEFORMER 777, San Nopco) and 0.9 parts by weight of a silica-based defoamer (BF300, Bihoku Funka Kogyo Co., Ltd.) was applied to a 10.0 g / m2 coating layer using an air knife. 2 The liner was obtained by applying the coating and drying with hot air so that the temperature of the coating layer at the exit of the drying process was 80°C (basis weight: 290 g / m 2 , 120 second Cobb water absorption of the surface: 0.1g / m 2 ). (Cracks in coating layer) The liner samples B and D were evaluated for cracking of the coating layer. The samples were cut to a size of 50 x 50 mm, and after conditioning for one day in an environment of 23°C and 50% humidity, they were placed in a transparent plastic bag with a zipper and sealed. Each sealed sample was left in an environment of -18°C, 4°C, or 23°C for 24 hours, and then pressed with a V-shaped press so that the coating layer side was folded at 90° in the paper flow direction, and a crease of 50 mm (the same as the length of the paper) was made. The crease was filled in with a water-based pen and then wiped off with tissue paper, and the length of the stained area due to the cracking of the coating layer was measured, and the cracking rate (%) was calculated using the following formula. ·Crack rate = Total length of dyed area ÷ Fold length (50 mm in this evaluation) × 100

[0081] [Table 1]

[0082] Manufacturing and evaluation of cardboard containers (1) Sample 1 (Comparative Example) A pulp slurry containing 100% corrugated waste pulp and 0.4% waterproofing agent was added to prepare a paper stock. A single layer of paper was then made from this paper stock, which was then dried in a dryer and smoothed using a calendar to produce corrugating medium base paper A (basis weight: approximately 200 g / m 2 ).

[0083] After that, a corrugated board sheet was manufactured from the liner sample A and medium base paper A (with waterproofing agent added) using a corrugator. Specifically, the medium base paper A was processed into an A-flute shape (height of uneven waves: 5 mm) in the single facer section, and a waterproof paste was applied to the flute tops, which were then bonded to the back side (uncoated side) of the liner sample and dried to form a single-sided corrugated board sheet. Then, in the double facer section, the non-adhesive side of the medium base paper A and the back side of the liner sample were bonded with waterproof paste and dried to obtain a corrugated board sheet (total thickness: approximately 6 mm).

[0084] A cardboard box with a lid as shown in Fig. 1 was made from the cardboard sheet with the coated side facing inward (inner dimensions of the main body: length 55 cm x width 27.5 cm x depth 16.2 cm, inner dimensions of the lid: length 57 cm x width 29.5 cm x depth 17.2 cm). Fig. 2 is a development view before folding into a box, and Fig. 3 is a perspective view when assembled into a box. (2) Sample 2 A corrugator was used to produce a cardboard sheet from liner sample B and medium base paper A (with waterproofing agent added). In the single facer, medium base paper A was processed into a B-flute shape (height of uneven waves: 3 mm), and water-resistant glue was applied to the flute tops, which were then bonded to the back side (non-coated side) of the liner sample and dried to produce a single-sided cardboard sheet. In the double facer, the non-adhesive side of medium base paper A and the back side of the liner sample were bonded with water-resistant glue and dried to produce a cardboard sheet (total thickness: about 4 mm). Next, a cardboard box was produced from this cardboard sheet in the same manner as sample 1 (inner dimensions of main body: length 55 cm x width 27.5 cm x depth 16.2 cm, inner dimensions of lid: length 57 cm x width 29.5 cm x depth 17.2 cm). (3) Sample 3 (Comparative Example) A pulp slurry containing 80% by weight of recycled corrugated paper pulp and 20% by weight of recycled magazine paper pulp was mixed with 0.2% aluminum sulfate and 0.2% strength agent in terms of pulp solid content to prepare a paper stock. A single layer of paper was then made from this paper stock, which was then dried in a dryer and smoothed using a calendar to produce corrugating medium base paper B (basis weight: approximately 200 g / m2). 2 ).

[0085] Then, a corrugator was used to produce a cardboard sheet from the liner sample C and the medium base paper B. Specifically, the medium base paper B was processed into an A-flute shape in the single facer section (height of uneven waves: 5 mm), and a waterproof glue was applied to the flute tops, which were then glued to the back side (uncoated side) of the liner sample with synthetic glue and dried to produce a single-sided cardboard sheet. Then, in the double facer section, the non-adhesive side of the medium base paper B and the back side of the liner sample were glued to each other with synthetic glue and dried to produce a cardboard sheet (total thickness: approximately 6 mm). Next, a cardboard box was produced from this cardboard sheet in the same manner as sample 1. (4) Sample 4 (Comparative Example) A corrugator was used to produce a cardboard sheet from liner sample D and medium base paper A (with waterproofing agent added). In the single facer, medium base paper A was processed into a B-flute shape (height of uneven waves: 3 mm), and a waterproof paste was applied to the corrugated tops, which were then bonded to the back side (uncoated side) of the liner sample and dried to produce a single-sided cardboard sheet. In the double facer, the non-adhesive side of medium base paper A and the back side of the liner sample were then bonded with waterproof paste and dried to produce a cardboard sheet (total thickness: approximately 4 mm). Next, a cardboard box was produced from this cardboard sheet in the same manner as sample 1. (5) Sample 5 (Comparative Example) As a control, a commercially available polystyrene foam box was used (internal dimensions of the main body: length 28 cm x width 22 cm x depth 13 cm, external dimensions: length 38 cm x width 32 cm x depth 18 cm).

[0086] Sample evaluation (Basis Weight) Measured in accordance with JIS P 8124. (Cobb Water Absorbency) Measurement was performed 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 of water absorbed per unit area after a specified time was measured. Note that the measurement time was set to 30 minutes, not the usual specified time of 120 seconds (2 minutes), in order to evaluate waterproofness. The same measurement was also performed on Sample 5 made of polystyrene foam. (Burst strength) The coated surface of each cardboard sheet sample was exposed to ice water at 4°C for 30 minutes. The burst strength of the samples before and after contact with ice water was measured in accordance with JIS Z 1516. From the burst strength measurement results, the survival rate (%) was calculated using the following formula. The burst strength of sample 5 made of polystyrene foam was also measured in the same manner as for the cardboard box. Survival rate = Burst strength of sample after contact with ice water (kPa) / Burst strength of sample before contact with ice water (kPa) × 100 (Adhesive strength) Each corrugated cardboard sheet sample was immersed in water for 10 minutes. The adhesive peel strength between the liner and core bonded at the single facer part (SF part) of the corrugated cardboard sheet sample was measured before and after immersion in water in accordance with JIS Z 0402. In addition, the residual rate (%) was calculated from the adhesive peel strength measurement results. Residual rate = peel strength of sample after immersion (N) / peel strength of sample before immersion (N) × 100 (Box Compressive Strength) As shown in FIG. 4, 1 kg of ice was placed in a cardboard box, which was then covered and left to stand in an environment at 5° C. for 24 hours.

[0087] The compressive strength of the box before and after being left standing was measured by the following procedure in accordance with JIS Z 0212. Note that the compressive strength of Sample 5 made of polystyrene foam was also measured in the same manner as for the cardboard box. (a) Place the box with the lid on in the center of the compression tester. (b) Start the compression testing machine and gradually apply downward force evenly over the entire top surface of the box. (c) Read the load when the side of the box is deformed and use this as the box compressive strength.

[0088] In addition, from the measurement results of the box compressive strength, the box strength remaining rate (%) was calculated as an index of the waterproofness of the container. Residual rate = Box compressive strength after storage / Box compressive strength before storage x 100 (Loading Efficiency) For the containers of Samples 1 to 5, the loading efficiency was calculated by dividing the inner volume by the outer volume.

[0089] [Table 2]

[0090] The cardboard container (sample 2) according to the present invention has better crack resistance and resistance to breakage than other samples. It was also clear that the box had excellent water resistance. In addition, the box's compressive strength after being left with ice for 24 hours showed a slight decrease compared to the blank sample before the test, but it still maintained sufficient strength.

[0091] Furthermore, since the cardboard container according to the present invention has a higher loading efficiency than polystyrene foam containers, the present invention can be suitably used as a cardboard box for distribution of food products such as fresh fish and vegetables. [Explanation of symbols]

[0092] 1 Box with lid 2 Boxes 3 Lid 4 Bottom 5 fold line 6 Side part 7 broken line 8 Side part 9, 10, 11 broken line 12 Folding section 13a,13b Projection part 14 Recess 15a, 15b protrusion 16 broken line 17 Locking piece 18a,18b fitting opening 19 Connecting part 20 Cut 21 Top opening 22 Top plate 23 broken line 24 Side part 25 broken line 26 Side part 27 broken line 28 Folded Piece 29 broken line 30 protrusion 31 Cut line section 31a Part of the cutting line 32 Cut 33 Open end D Depth H Height W1 Vertical width

Claims

1. A corrugated cardboard sheet in which a core containing a waterproofing agent is bonded to a liner with water-resistant adhesive, Here, the liner constituting the corrugated cardboard sheet is made by coating at least one side of a paper substrate with a water-repellent resin layer containing styrene resin and / or acrylic resin and water-repellent wax, and the 30-minute Cobb water absorption measured from the side coated with the water-repellent resin layer is 155 g / m². ２ The following is the cardboard sheet mentioned above.

2. The corrugated cardboard sheet according to claim 1, wherein the ratio of [bursting strength after contact with water for 30 minutes] / [bursting strength before contact with water] is 50% or more.

3. The waterproof resin layer contains styrene-acrylic resin, and the 30-minute Cobb water absorption rate is 50 g / m². ２ The corrugated cardboard sheet according to claim 1 or 2, which is as follows:

4. A method for manufacturing a corrugated cardboard sheet according to any one of claims 1 to 3, The method comprising laminating a core to a liner, which has a waterproof resin layer coated on at least one side of a paper substrate using a contour coating method, with a water-resistant adhesive.

5. A box made of corrugated cardboard sheets according to any one of Claims 1 to 3, wherein the strength retention rate after being filled with water and left for 24 hours is 70% or more.

6. The box according to claim 5, wherein the thickness of the corrugated cardboard sheet is 2.5 to 15 mm, the internal volume / external volume ratio of the box is 0.70 or more, and it is a watertight type box.

7. A method for manufacturing the box according to claim 5 or 6, The process of obtaining a corrugated cardboard sheet by laminating a core to the liner, The process of folding cardboard sheets to obtain a box, The above method, including.

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