JP2022126275A - waterproof cardboard box - Google Patents

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 The present invention relates to a waterproof cardboard box and a manufacturing method thereof.

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

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

JP-A-10-266096 JP 2011-162899 A

Paper containers that can replace styrofoam are demanded in the trend of plastic-free, and water-resistant and water-repellent liners are attracting attention for manufacturing such containers.
However, in the method of forming the wax layer of Patent Document 1, it is difficult to sufficiently suppress the moisture permeability simply by coating one layer of the wax composition. It is necessary to apply the wax composition many times, which makes the manufacturing process extremely complicated. In addition, in the method of laminating with a resin film as in Patent Document 2, in addition to the complicated manufacturing process due to lamination, paper or paperboard laminated with a resin film is disintegrated when it is recovered and used as waste paper after use. The reusability was remarkably poor, and it was difficult to recycle.

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

Furthermore, in order to impart waterproofness to a paper substrate, it is necessary to apply a waterproof coating. In the technique disclosed by, the solvent of the waterproof paint tends to form droplets, and the waterproof paint cannot be applied uniformly.

In view of such circumstances, an object of the present invention is to provide a sufficiently waterproof paper container.

As a result of intensive studies on the above problem, the present inventors have found that corrugated board having a liner provided with a waterproof coating layer on at least one side of the paper base material is used so that the waterproof coating layer of the liner is the inner surface of the box. We succeeded in developing a paper container with sufficient waterproofness by forming a container in

Although not limited to the following, the present invention includes the following aspects.
[1] A paper container made of cardboard in which at least the inner surface of the box is coated with a waterproof resin layer, the 30-minute Cobb water absorbency is 155 g/m ² or less, and the container is filled with water and left for 24 hours. The above paper container having a box strength residual rate of 50% or more.
[2] The paper 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. container.
[3] The paper container according to [1] or [2], wherein the waterproof resin layer contains at least one of styrene resin, acrylic resin, polyolefin resin, and water-repellent wax.
[4] The paper container according to any one of [1] to [3], wherein the corrugated cardboard liner and the corrugated core constituting the paper container are laminated with a waterproof glue.
[5] The paper container according to any one of [1] to [4], wherein a waterproof agent is internally added to the corrugated cardboard core constituting the paper container.
[6] The paper container according to any one of [1] to [5], wherein the ratio of internal volume/external volume of the paper container is 0.70 or more.
[7] The paper container according to any one of [1] to [6], wherein the cardboard constituting the paper container has a thickness of 2.5 to 15 mm.
[8] A corrugated cardboard sheet comprising a liner coated with a waterproof resin layer on at least one side thereof and a core.

ADVANTAGE OF THE INVENTION According to this invention, the paper container provided with sufficient waterproofness is obtained.

FIG. 1 is a schematic diagram of a paper container produced when evaluating waterproofness. FIG. 2 is an expanded view of the corrugated cardboard sheet before being folded into a box shape. FIG. 3 is a perspective view when corrugated cardboard sheets are assembled into a box shape. FIG. 4 is an appearance photograph of a paper container produced when evaluating waterproofness.

The present invention relates to a waterproof paper container (paper container). In the present invention, the waterproofness means the ability to prevent water from penetrating even when exposed to water for a long period of time. Further, in a preferred embodiment of the present invention, the paper container according to the present invention does not cause water seepage even when the paper container is filled with water and left for 3 weeks. It means that the shape of the container is maintained even though it can be seen.

The use of the paper container according to the present invention is not particularly limited. For example, it can be suitably used as a container for storing foodstuffs such as fresh fish and vegetables, or for storing hygroscopic articles such as detergents. be able to.

Paper container made of cardboard 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. Corrugated cardboard is made by bonding flat paper (liner) and corrugated paper (medium) together with an adhesive, and is used for various purposes such as product packaging, cushioning, transportation of goods, and storage of goods. is preferably used for

The corrugated cardboard sheet used for the box of the present invention can generally be produced by laminating a liner and corrugated corrugated medium together using a corrugator. A known corrugator can be used without limitation, but a general corrugator is composed of a single facer, a double backer, and a cutter. In addition, a paste-making device for bonding the liner and corrugating medium together and a device for generating heat for melting the paste are used together.

In addition, when the corrugated cardboard sheet used for the box of the present invention is manufactured, an adhesive is used to bond the liner and the corrugating medium. From this point of view, it is preferable to use a waterproof adhesive. The water-resistant adhesive is an ordinary corrugated cardboard adhesive added with a water-resistant agent. The waterproofing agent is not particularly limited, and examples thereof include synthetic resin emulsions, ketone aldehyde resins, and the like.

The cardboard liner will be described later, but a kraft liner, a jute liner, or the like can be used depending on the application. ^The basis ^weight of the ^liner is also not particularly limited. good.

As for the corrugated medium, A-flute, B-flute, C-flute, W-flute, E-flute, etc. can be used without particular limitation. The basis weight of the medium is also not particularly limited, and 120 g/m ² , 160 g/m ² , 180 g/m ² , reinforced 180 g/m ² , reinforced 200 g/m ² and the like can be preferably used.

The paper container according to the present invention is manufactured from corrugated cardboard by, for example, folding a single blank sheet and, if necessary, bonding with an adhesive. The type of adhesive is not particularly limited, and includes water-based, water-dispersed, solution-based, non-solvent-based, solid-based, etc., and can be appropriately selected according to the surface condition of the paper substrate to be adhered. can be done.

The amount of adhesive used is not particularly limited as long as it has sufficient adhesive strength, but in the case of surface coating, it may be 0.5 to 2000 g/m ² , 5 to 1500 g/m ² , or 10 to 1000 g. / ^m2 . In the case of line application, the application width can be appropriately changed according to the nozzle diameter of the applicator, the moving speed of the nozzle or the paper substrate, the viscosity of the adhesive during application, the width of the paper substrate to be adhered, and the like. The coating amount per unit length is also 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.

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 is formed by folding one blank sheet, the bottom and all side walls are connected via folding lines, and all the side walls are connected via folding lines. Refers to the shape of the box. Regarding the connection part of the side wall, it is preferable that 50% or more of the box inner surface height is connected from the bottom, more preferably 70% or more is connected, and 80% or more is connected. are more preferably continuous, and most preferably, the entire height of the side wall is continuous.

A box making machine can be used when manufacturing a container such as a box by making a paper base material into a box. The box making machine to be used is not particularly limited, and for example, a vertical or horizontal box making machine can be used.
In a preferred embodiment, the paper container according to the present invention has a box strength residual rate of 50% or more after being left for 24 hours after adding water, more preferably 60% or more, further preferably 70% or more, and most preferably 80%. % or more. In the present invention, the box strength residual rate is measured by using a box compression tester in accordance with JIS Z 0212 after pouring water into a box-shaped paper container and leaving it for 24 hours. It is the value divided by the box compressive strength of a paper container that does not contain water. The higher the box strength residual rate, the more sufficient strength can be maintained even when liquid is directly put into the paper container and transported or stored for a period of days.

Liner The basis weight of the liner of the corrugated cardboard according to the present invention is not particularly limited. m ² or 200-600 g/m ² .

In a preferred embodiment, the liner 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. For 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 155 g/m 2 . m ² or less, more preferably 100 g/m ² or less, even more preferably 50 g/m ² or less, even more preferably 25 g/m ² or less, and most preferably 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.

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

The liner of the present invention is also excellent in oil resistance. It is even more preferable to have Here, oil repellency is determined by JAPAN TAPPI paper pulp test method No. 41 "Paper and Paperboard--Oil Repellency Test Method--Kit Method", it can be measured from the coating layer side of the liner, and the larger the value of the kit number, the higher the oil resistance.

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

The liner of the present invention has excellent water resistance at the bent portion under any temperature conditions, such as room temperature, refrigeration, and freezing. In a preferred embodiment, the crack rate of the coating layer of the liner after being bent 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 crack rate of the coating layer under storage conditions of 4° C. is preferably 55% or less, more preferably 45% or less, still more preferably 35% or less, and most preferably 25% or less. Furthermore, the crack rate of the coating layer under storage conditions of -18°C is preferably 75% or less, more preferably 65% or less, even more preferably 55% or less, and most preferably 45% or less. Here, the rate of cracking of the coating layer is measured by cutting a sample of temperature and humidity control into a certain size and leaving it under specific temperature conditions for 24 hours. It is the value obtained by dividing the length of cracks in the coating layer that occurred when a crease having the same length as the length of is divided by the length of the entire crease (the length of the paper). Because the coating layer has a cracking rate within the above range, when using a liner and corrugated cardboard sheets that have been bent under the respective temperature conditions, it is possible to suppress the seepage of liquid from the bent portion and maintain the strength. It becomes possible. In addition, the smaller the crack rate of the coating layer, the more waterproof the liner can maintain even after bending.

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

The paper substrate used in the present invention has a 120-second Cobb water absorbency of 25 g/m ² or less, preferably 20 g/m ² or less, and more preferably 15 g/m ² or less on the surface provided with the waterproof coating layer. The paper substrate used in the present invention has a 120-second Cobb water absorbency of 5 g/m ² or more, preferably 7 g/m ² or more, more preferably 10 g/m ² or more. In the present invention, the 120-second Cobb water absorbency can be adjusted by applying a water repellent agent such as wax. It is possible to prevent deterioration of paper strength due to excessive penetration of moisture contained in water, and solid content in the waterproof paint stays on the surface of the paper layer, ensuring a reliable coating and improving waterproofness and moisture resistance. .

The paper substrate used in the present invention was tested according to JAPAN TAPPI Paper Pulp Test Method No. 68 "Paper and Paperboard--Water Repellency Test Method" is R4 or higher, preferably R6 or higher, more preferably R8 or higher. When the water repellency of the paper substrate is R4 or higher, the moisture contained in the coating solution does not excessively penetrate into the paper substrate when the waterproofing agent is applied, thereby suppressing the strength reduction of the paper. can be done.

In a preferred embodiment, the paper substrate used in the present invention has a drip oil absorbency of 5 seconds or more, more preferably 7 seconds or more, and still more preferably 10 seconds or more on the surface on which the waterproof coating layer is to be provided. Although the upper limit is not particularly limited, it is preferably 80 seconds or less, more preferably 75 seconds or less, and still more preferably 70 seconds or less. When the oil absorbency is within the above range, the wax contained in the waterproofing agent stays on the paper surface and hardly permeates into the paper layer, so that the waterproofness and moisture resistance of the paper substrate can be improved. The oil absorption of the paper substrate is measured by using a microsyringe equipped with a No. H5 injection needle to drop one drop of light oil No. 1 adjusted to a kinematic viscosity of 3 cSt on the sample surface, and measuring the time until the surface gloss disappears. to measure.

The physical properties of the paper substrate are not particularly limited, and can be appropriately set according to the use of the waterproof paper. In the present invention, for example, the longitudinal elongation is 1.0 to 15.0%, the 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 be 80 to 5.00 kPa·m ² /g.

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

In a preferred embodiment, the paper substrate used in the present invention has a water contact angle of 75 degrees or more, more preferably 77 degrees or more, on the surface on which the waterproof coating layer is provided. When the water contact angle is within the above range, excessive penetration of water contained in the coating liquid into the paper substrate can be prevented, and reduction in the strength of the paper substrate can be prevented.

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 calendar, super calendar, gross calendar, soft calendar, thermal calendar, shoe calendar, or the like 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.

(Waterproof resin layer)
The liner used for the corrugated board according to the present invention has a waterproof resin layer (waterproof coating layer) provided on a paper base material. In a preferred embodiment of the present invention, the waterproof layer comprises a synthetic resin and a water repellent Contains wax. The synthetic resin preferably contains at least one of styrene resin, acrylic resin, and polyolefin resin. In particular, it is preferable that the synthetic resin is a styrene resin and/or an acrylic resin.

The styrene resin that can be contained in the 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 only of a polymer of monomers.

Styrenic monomers include, for example, styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, p-tert-butylstyrene, α-methylstyrene, α -methyl-p-methylstyrene and the like.

Examples of monomers copolymerizable with styrene monomers include alkyl methacrylates such as methyl methacrylate, cyclohexyl methacrylate and methylphenyl methacrylate; alkyl acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate and cyclohexyl acrylate; , Unsaturated carboxylic acids such as acrylic acid, unsaturated dicarboxylic acid anhydrides such as maleic acid and itaconic acid, unsaturated nitriles such as acrylonitrile and methacrylonitrile, 1,3-butadiene, 2-methyl-1 , and conjugated dienes such as 3-butadiene. These can be used singly or in combination of two or more.

The acrylic resin that can be contained in the waterproof coating layer constituting the present invention is a resin in which the copolymerization ratio of acrylic monomers, which are acrylic acid, methacrylic acid and derivatives thereof, is 50% by mass or more. , and it may consist of only a polymer of acrylic monomers.

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

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

In a preferred embodiment of the present invention, the waterproof coating layer contains a water-repellent wax. The water-repellent wax contained in the waterproof coating layer includes, for example, polyethylene-based wax, Fischer-Tropsch wax, oil-based synthetic wax (fatty acid ester, fatty acid amide, ketone/amine), synthetic wax such as hydrogenated oil, and beeswax. , Japanese wax, paraffin wax, and natural wax such as microcrystalline wax. 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, for the purpose of improving the whiteness, the waterproof coating layer may contain a pigment within a range that does not impair the waterproof property. In this case, it is preferable that the whiteness of the surface of the waterproof coating layer is increased by 1% or more compared to the whiteness of the paper substrate by containing the pigment. Such pigments include calcium carbonate, titanium oxide, kaolin, clay, engineered kaolin, delaminated clay, talc, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, satin white, mica, Inorganic pigments such as montmorillonite can be used, and these pigments can be used singly or in combination of two or more. Among these pigments, kaolin, calcium carbonate, and mica, which have flat particles, are particularly preferable because they do not impair the moisture resistance and waterproofness of the 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 waterproof coating layer possessed by the synthetic resin component are lost. It is not preferable because it may not be fully demonstrated. 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 waterproof coating layer can be formed by coating a paper substrate with a coating agent containing the above components and drying the coating. The coating amount of the waterproof coating layer is preferably 4 to 20 g/m ² . If it exceeds 20 g/m ² , further improvement in waterproofness cannot be expected, but the manufacturing cost increases. There is

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

In the liner according to the present invention, the moisture permeability per unit thickness of the waterproof coating layer is preferably 15 (g/m ² ·24h)/μm or less, and preferably 10 (g/m ² ·24h)/μm or less. More preferably, 7 (g/m ² ·24 h)/μm is even more desirable. Here, the moisture permeability per unit thickness of the waterproof coating layer is calculated by dividing the moisture permeability measured from the coating layer side of the liner according to JIS Z 0208 by the average coating layer thickness.

The liner of the present invention can be produced, for example, by coating at least one surface of a paper substrate with a waterproof agent and drying the coated waterproof agent. Formation of the waterproof coating layer can be carried out by applying a coating agent using a known coating method, for example, air knife coating, curtain coating, blade coating, gate roll coating, die A coating method such as coating can be used. Further, the coating layer may be a single layer or a plurality of layers, a plurality of coating layers may be sequentially coated, or two or more layers may be coated simultaneously by curtain coating or the like. good. When 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 substrate is dried to form a coating layer. In this drying step, the temperature of the coating layer at the outlet is preferably less than 120°C, preferably 100°C or less. can be adjusted to If the coating layer temperature at the outlet is 120°C or higher, the rate of blistering in the coating layer may increase, and blocking may occur in the waterproof liner wound after the coating layer is formed. I have something to do. On the other hand, the temperature of the coating layer at the outlet is preferably 60°C or higher, more preferably 70°C or higher, and may be 80°C or higher. If the coating layer temperature at the outlet is less than 60°C, blocking may occur in the waterproof liner wound after the coating layer is formed, and the coating layer may not be dried. Since it is insufficient, it may not be possible to fully exhibit waterproof and moisture-proof performance.

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

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

The coating layer temperature at the exit of the drying process can be adjusted by adjusting the drying time and the temperature of the drying zone. The drying time is determined by the feeding speed of the paper substrate, the number and length of the drying zones, the equipment capacity of the drying zones (air volume, infrared output), and the like. As the drying method, a known drying method can be used, and examples thereof include a steam cylinder heating drying method, a hot air drying method, a gas infrared drying method, an electric infrared drying method, and the like. can be used singly or in combination of two or more.

Corrugated board according to the present invention can be obtained by laminating corrugated corrugated base paper to the obtained liner. In general, corrugating base paper is corrugated by a corrugator, and a liner is attached to the front and back to produce corrugated board with high strength. Single face corrugated board is also known. A preferred embodiment of the present invention is a corrugated board in which liners are attached to both sides of a core, or a corrugated board processed into multiple layers.

The basis weight of the corrugating base paper is not particularly limited, but is preferably 60 to 250 g/m ² , more preferably 70 to 240 g/m ² , and even more preferably 80 to 230 g/m ² .
In the present invention, it is preferable to use a reinforced midsole, and more preferably a water resistant reinforced midsole. Reinforced corrugating medium refers to corrugating medium that has improved compressive strength compared to general corrugating medium that satisfies the performance of corrugating base paper specified in JIS P 3904 by adding a paper strength agent or the like in the papermaking process. In addition, the water-resistant medium is a medium in which not only the compressive strength but also the water resistance is improved by adding a water-resistant agent in the manufacturing process of the reinforced medium. As the internal paper strength agent, polyacrylamide (PAM) may be used, and the amount added in that case is preferably 0.1% to 5.0%, preferably 0.2% to 2.0% is more preferred.

The corrugating base paper may have a clear (transparent) coating layer provided on one or both sides of the base paper by applying a coating liquid containing a starch-based compound. Starch coating includes, for example, pound-type two-roll size presses, gate roll coaters and rod metering size presses that are film transfer type coating methods, and coaters such as curtain coaters and spray coaters that are non-contact coating methods ( coating machine) to apply a coating solution (surface treatment solution) containing a starch-based compound onto the base paper.

^The amount of starch coating is not particularly limited as long as it does not ^impair the strength of the medium. It may be 2.0 g/m ² or more, 3.0 g/m ² or more, or 4.0 g/m ² or more. The upper limit is not particularly limited, but if the amount of coating is increased, it is necessary to lower the basis weight of the base paper before clear coating with starch. The coating amount of the starch-based compound is preferably 8.0 g/m ² or less per side, and may be 6.0 g/m ² or less.

In the present invention, if necessary, various auxiliary agents such as dispersants, thickeners, water retention agents, antifoaming agents, water resistance agents, colorants, etc., which are commonly used in starch coating, can be used.
In the present invention, the coating machine for applying the starch-based compound to the base paper includes, for example, 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, A curtain coater can be used. In the present invention, the effect can be exhibited even by using a film transfer coating machine such as a gate roll coater and a rod metering size press.

It is preferable to mix a large amount of waste paper pulp as the pulp raw material for the core raw paper produced in the present invention. In the present invention, the content of waste paper pulp in the total pulp is preferably 50% by weight or more, more preferably 70% by weight or more, still 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 raw paper made from paper stock containing waste paper pulp.

Waste paper pulp is dissociated from unprinted waste paper such as cardboard waste paper, bookbinding, printing factories, cutting plants, etc. Waste paper pulp, high quality paper, high quality coated paper, medium quality paper, medium quality coated paper, planographic printing, letterpress printing, intaglio printing, etc., electrophotographic method, thermal method, thermal transfer method, pressure sensitive recording method, inkjet recording method, Waste paper printed with carbon paper, etc., water-based, oil-based ink, waste paper written with a pencil, etc., de-inked pulp after disintegration of old newspaper paper (hereinafter sometimes referred to as DIP), paper sludge, paper factory wastewater Scum or the like can be used. Pulp other than waste paper pulp, such as ground pulp (GP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), deinked pulp (DIP), and softwood kraft pulp (NKP), is generally used as a raw material for papermaking. can also be used.

Fillers added to corrugating base paper include, for example, calcium carbonate such as heavy calcium carbonate and light calcium carbonate, titanium oxide, clay, silica, talc, kaolin, calcined kaolin, delaminated kaolin, magnesium carbonate, barium carbonate, and zinc oxide. , silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, titanium oxide, inorganic fillers such as bentonite; urea-formalin resin, polystyrene resin, melamine resin, phenol resin, micro hollow Organic fillers such as particles; can be used alone or in combination of two or more. Recycled fillers made from papermaking sludge, deinked floss, etc. can also be used.

In acidic papermaking, the fillers used in neutral papermaking are removed from the fillers soluble in acid, and these fillers may be used alone or in combination of two or more.
A known papermaking additive can be used as an internal additive when producing a corrugating medium. Papermaking chemicals are not particularly limited, and various chemicals can be used alone or in combination.

For example, retention agents, drainage improvers, coagulants, aluminum sulfate, bentonite, silica, sizing agents, dry strength agents, wet strength agents, bulking agents, dyes, fluorescent whitening agents, pH adjusters, antifoaming agents Papermaking chemicals such as agents, anti-ultraviolet agents, anti-fading agents, pitch control agents, slime control agents can be used. Chemicals suitable for papermaking include polyacrylamide-based polymers, polyvinyl alcohol-based polymers, cationic starches, various modified starches, urea/formalin resins, melamine/formalin resins, and other internal dry paper strength enhancers. internal wet strength agents such as polyamide polyamine epichlorohydrin resin; 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; etc. can be mentioned.

These auxiliaries may be added in advance to the slurry of the filler of the present invention and then applied to the paper machine, or may be applied to the paper machine separately from the slurry of the filler of the present invention.
Further, the corrugating medium may be subjected to various surface treatments. For example, the corrugating medium may be surface-treated by calendering, or the corrugating medium may be coated with a lubricant. As the lubricant, a wax-based lubricant may be used, and the coating amount is preferably 0.005 g/m ² to 0.1 g/m ² . In the present invention, the lubricating agent is preferably transferred to the paper by spraying the lubricating agent on the calender roll when the base paper is passed through the calender. By doing so, it is possible to prevent dirt from adhering to the surface of the calender roll in addition to the application of the lubricant. As described above, by applying a lubricant, it is possible to more effectively prevent dirt from adhering to the surface of the calender roll.

The resulting corrugating base paper can be corrugated (fluted) using a known corrugator. As the corrugation process, any known process can be applied depending on the application. may be applied to

Processing into Corrugated Cardboard Sheet The corrugated cardboard sheet used for the box of the present invention is obtained by bonding together a liner and a corrugated corrugated medium using a corrugator.

A known corrugator can be used without limitation, but a general corrugator is composed of a single facer, a double backer, and a cutter. In addition, a paste-making device for bonding the liner and corrugating medium together and a device for generating heat for melting the paste are used together.

In addition, when the corrugated cardboard sheet used for the box of the present invention is manufactured, an adhesive is used to bond the liner and the corrugating medium. From this point of view, it is preferable to use a waterproof adhesive. The water-resistant adhesive is an ordinary corrugated cardboard adhesive added with a water-resistant agent. The waterproofing agent is not particularly limited, and examples thereof include synthetic resin emulsions, ketone aldehyde resins, and the like.

In a preferred embodiment, the cardboard sheet used for the box of the present invention has a [bursting strength after contact with water for 30 minutes] / [bursting strength before contact with water] of 50% or more, and 60% or more More preferably, it may be 70% or more, and most preferably 80% or more. The higher this value, the less likely the paper container will be affected by dew condensation caused by the temperature difference between the contents and the temperature around the container when processed into a paper container, and the strength of the paper container can be maintained.

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

Production and Evaluation of Liners (1) Liner Sample A
A back layer made of 100% corrugated waste paper pulp, a middle layer made of 100% waste paper pulp, and a surface layer made of 70% unbleached kraft pulp and 30% corrugated waste paper pulp in a weight ratio of back layer: middle layer: surface layer = 25:60:15. After drying with a dryer, a water repellent agent containing paraffin wax and rosin is applied to one side of the surface layer, dried again with a dryer, and smoothed with a calendar. was manufactured (basis weight: about 280 g/m ² , surface 120-second Cobb water absorbency: 13 g/m ² , coating amount of water repellent agent: about 1 g/m ² ).
(2) Liner sample B
Using an air knife, 10.0 g/m ² of a waterproofing agent (Michaelman, VaporCoat 2200) containing styrene-acrylic resin and paraffin wax was applied to the surface layer of liner sample A, and the temperature of the coating layer at the exit of the drying process was was dried with hot air at 80° C. to obtain liner sample B (basis weight: about 290 g/m ² , 120-second Cobb water absorbency on the surface: 0.3 g/m ² ).
(3) Liner sample C
A back layer made of 100% corrugated waste paper pulp, a middle layer made of 100% waste paper pulp, and a surface layer made of 70% unbleached kraft pulp and 30% corrugated waste paper pulp in a weight ratio of back layer: middle layer: surface layer = 25:60:15. After drying with a dryer, smoothing treatment was performed using a calendar to produce liner sample C (basis weight: about 280 g/m ² , 120-second Cobb water absorbency of surface: 30 g/m ² ). .
(4) Liner sample D
On the surface layer side of liner sample C, 100 parts by weight of a styrene-butadiene copolymer (HOJ4072, Nippon Zeon, glass transition point: 21° C.) and 65 parts by weight of delaminated kaolin (average particle size 3 μm, Capim NP, RCC) were added. , Heavy calcium carbonate (average particle size 8 μm, BF300, Bihoku Funka Kogyo Co., Ltd.) 15 parts by weight, silica-based antifoaming agent (SN Deformer 777, San Nopco) 0.9 parts by weight waterproof coating liquid , 10.0 g/m ² was applied using an air knife, and dried with hot air so that the temperature of the coating layer at the exit of the drying process was 80 ° C. to obtain a liner (basis weight: 290 g/m ² , surface 120 seconds Cobb water absorbency: 0.1 g/m ² ).
(Cracking of coating layer)
Liner samples B and D were evaluated for fold cracking of the coating layer. A sample was cut into a size of 50×50 mm, conditioned in an environment of 23° C. and 50% humidity for one day, and then placed in a transparent plastic bag with a zipper and sealed. After leaving each sealed sample in an environment of -18°C, 4°C or 23°C for 24 hours, it is pressed with a V-shaped press so that the coating layer side is folded at 90° in the paper flow direction. Pressure was applied and a crease of 50 mm in length (equivalent to the length of the paper) was made. The crease was painted over with a water-based pen, wiped off with a tissue paper, the length of the dyed portion due to cracks in the coating layer was measured, and the crack rate (%) was calculated using the following formula.
・ Crack rate = total length of dyed part / fold length (50 mm in this evaluation) x 100

Manufacture and evaluation of cardboard containers (1) Sample 1 (comparative example)
A paper stock was prepared by adding 0.4% of a waterproofing agent to a pulp slurry containing 100% by weight of corrugated waste paper pulp. Next, a single layer was made from this stock, dried with a dryer, and smoothed with a calender to produce a medium base paper A (basis weight: about 200 g/m ² ).

After that, a corrugated board sheet was produced from the liner sample A and the corrugating medium base paper A (internally containing the waterproofing agent) using a corrugator. Specifically, the medium base paper A was processed into an A flute shape (height of uneven waves: 5 mm) at the single facer section, water resistant paste was applied to the flute tops, and then the back side of the liner sample (uncoated) was applied. After bonding and drying to a single-sided corrugated board sheet, the non-bonded side of the corrugating medium base paper A and the back side of the liner sample were bonded and dried with a waterproof glue in the double facer section to obtain a corrugated board sheet (total thickness: about 6 mm).

From the cardboard sheet, a cardboard box with a lid as shown in FIG. Dimensions: length 57 cm x width 29.5 cm x depth 17.2 cm). FIG. 2 is a developed view before being folded into a box shape, and FIG. 3 is a perspective view when assembled into a box shape.
(2) Sample 2
A corrugated cardboard sheet was produced from the liner sample B and the corrugating medium base paper A (containing a waterproofing agent) using a corrugator. In the single facer section, the medium base paper A is processed into a B flute shape (height of uneven waves: 3 mm), waterproof glue is applied to the tops of the flutes, and the back side (non-coated surface) of the liner sample is adhered and adhered. After drying to form a single-faced cardboard sheet, the non-bonded side of the corrugating medium base paper A and the back side of the liner sample were bonded to the back side of the liner sample with a waterproof glue in the double facer section, and dried to obtain a corrugated board sheet (total thickness: about 4 mm). ). Next, from this cardboard sheet, a cardboard box was produced in the same manner as Sample 1 (body size: length 55 cm x width 27.5 cm x depth 16.2 cm, lid size: length 57 cm x width 29.5 cm). x depth 17.2 cm).
(3) Sample 3 (comparative example)
A paper stock was prepared by adding 0.2% aluminum sulfate and 0.2% paper strength agent to a pulp slurry containing 80% by weight corrugated waste paper pulp and 20% by weight magazine waste paper pulp. did. Next, a single layer was made from this stock, dried with a dryer, and smoothed with a calender to produce a medium base paper B (basis weight: about 200 g/m ² ).

Thereafter, a corrugated board sheet was produced from the liner sample C and the corrugating medium base paper B using a corrugator. Specifically, the single facer part processed the corrugating medium base paper B into an A flute shape (height of uneven waves: 5 mm), applied water-resistant glue to the flute tops, and then the back side of the liner sample (uncoated). After bonding and drying with synthetic glue to make a single-sided corrugated cardboard sheet, the non-bonded side of the corrugating medium base paper B and the back side of the liner sample are bonded with synthetic glue and dried to obtain a corrugated cardboard sheet at the double facer part. (total thickness: about 6 mm). Next, a corrugated cardboard box was produced from this corrugated cardboard sheet in the same manner as Sample 1.
(4) Sample 4 (comparative example)
A corrugated cardboard sheet was produced from the liner sample D and the corrugating medium base paper A (containing a waterproofing agent) using a corrugator. In the single facer section, the medium base paper A is processed into a B flute shape (height of uneven waves: 3 mm), waterproof glue is applied to the tops of the flutes, and the back side (non-coated surface) of the liner sample is adhered and adhered. After drying to form a single-faced cardboard sheet, the non-bonded side of the corrugating medium base paper A and the back side of the liner sample were bonded to the back side of the liner sample with a waterproof glue in the double facer section, and dried to obtain a corrugated board sheet (total thickness: about 4 mm). ). Next, a corrugated cardboard box was produced from this corrugated cardboard sheet in the same manner as Sample 1.
(5) Sample 5 (comparative example)
As a control, a commercially available styrofoam box was used (inner dimensions of main body: length 28 cm x width 22 cm x depth 13 cm, outer dimensions: length 38 cm x width 32 cm x depth 18 cm).

Evaluation of sample (basis weight) Measured according to JIS P8124.
(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 order to evaluate the waterproof property, the measurement time was set to 30 minutes instead of the usual prescribed time of 120 seconds (2 minutes). Further, the same measurement was performed for sample 5 made of foamed polystyrene.
(Burst Strength) The coated surface of each corrugated cardboard sheet sample was brought into contact with ice water at 4°C for 30 minutes. Bursting strength was measured according to JIS Z 1516 for samples before and after contact with ice water. Also, the residual rate (%) was calculated based on the following formula from the measurement result of the bursting strength. The rupture strength of Sample 5 made of polystyrene foam was also measured in the same manner as for the corrugated cardboard box.
・ Residual rate = Burst strength of sample after contact with ice water (kPa) / Burst strength of sample before contact with ice water (kPa) × 100
(Adhesion Strength) Each corrugated board sample was immersed in water for 10 minutes. Before and after immersion in water, the adhesive peel strength between the liner and the core adhered at the single facer portion (SF portion) of the corrugated cardboard sheet sample was measured according to JIS Z 0402. Also, the residual rate (%) was measured from the measurement results of the adhesive peel strength.
・ 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 corrugated cardboard box, and after the lid was closed, the box was left for 24 hours in an environment at a temperature of 5°C.

The box compression strength before and after standing was measured according to JIS Z 0212 by the following procedure. The compressive strength of Sample 5 made of polystyrene foam was also measured in the same manner as the corrugated cardboard box.
(a) Set the box with the lid on in the center of the compression tester.
(b) Start the compression tester, and gradually apply downward force evenly over the entire upper surface of the box.
(c) Read the load when the box side surface is deformed, and use it as the box compressive strength.

Further, from the measurement results of the box compressive strength, the box strength residual rate (%) was calculated as an indicator of the waterproofness of the container.
・Residual rate = Compressive strength of box after leaving / Compressive strength of box before leaving x 100
(Loading Efficiency) For the containers of Samples 1 to 5, the loading efficiency was calculated by dividing the internal volume by the external volume.

It was found that the corrugated cardboard container (Sample 2) according to the present invention was superior to the other samples in breaking resistance and water resistance. It was also found that the box compressive strength after being left for 24 hours after adding ice was slightly lower than that of the blank product before the test, but still maintained sufficient strength.

In addition, since the cardboard container according to the present invention has higher loading efficiency than a styrofoam container, the present invention can be suitably used as a cardboard box for distribution of foods such as fresh fish and vegetables.

1 Box with Lid 2 Box Body 3 Lid 4 Bottom 5 Folding Line 6 Side Section 7 Folding Line 8 Side Sections 9, 10, 11 Folding Line 12 Folding Sections 13a, 13b Projecting Piece 14 Recesses 15a, 15b Projecting 16 Folding Line 17 Locking Piece Parts 18a, 18b Fitting opening 19 Connecting part 20 Notch 21 Upper opening 22 Top plate part 23 Folding line 24 Side part 25 Folding line 26 Side part 27 Folding line 28 Folded piece 29 Folding line 30 Protruding piece 31 Cutting line 31a One part of the cutting line Part 32 Notch 33 Opening end D Depth H Height W1 Vertical width

Claims (8)

A paper container made of corrugated board having a waterproof resin layer coated on at least the inner surface of the box, having a 30-minute Cobb water absorption of 155 g/m ² or less, and remaining box strength after being left for 24 hours after being filled with water. The above paper container having a rate of 50% or more. 2. The paper container according to claim 1, wherein the cardboard sheet constituting the paper container has a [burst strength after 30 minutes contact with water]/[burst strength before contact with water] of 50% or more. 3. The paper container according to claim 1, wherein the waterproof resin layer contains at least one of styrene resin, acrylic resin, polyolefin resin, and water-repellent wax. 4. The paper container according to any one of claims 1 to 3, wherein the corrugated cardboard liner and core forming the paper container are bonded together with a waterproof glue. 4. The paper container according to any one of claims 1 to 3, wherein a waterproof agent is internally added to the core of the corrugated cardboard constituting the paper container. The paper container according to any one of claims 1 to 5, wherein the ratio of internal volume/external volume of the paper container is 0.70 or more. The paper container according to any one of claims 1 to 6, wherein the thickness of the cardboard constituting the paper container is 2.5 to 15 mm. A corrugated cardboard sheet comprising a liner coated with a waterproof resin layer on at least one side and a core.

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