Paper container for refrigerated article

Abstract

To develop a paper packaging material used for storing a refrigerated article, in which not only waterproofness but also followability to temperature changes inside a box relative to a surrounding environment are satisfactory, and box compression strength does not reduce even when the refrigerated article is put therein and conveyance temperature conditions are rapidly changed.SOLUTION: An excellent paper packaging material for storing a refrigerated article can be provided by making a paper container in which a 30-minute Cobb water absorption measured from the inside of the container is 155 g / m2 or lower, and relative to temperature changes of a surrounding environment, a temperature inside a box can also follow a surrounding temperature environment within 10 minutes.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a paper container for refrigerated products.

Background Art

[0002] In the transportation of fresh foods such as fresh fish and vegetables, conventionally, a cold storage agent (cold storage material) and fresh food are put into a polystyrene container and transported widely. Also, when using a paper container from the viewpoint of environmental protection, etc., usually, an inner bag is provided inside a paper container such as cardboard, and a cold storage agent and fresh food are put into the inner bag and transported. However, in order to prevent a decrease in strength due to the moisture of the fresh food itself and condensation, it is necessary to use a plastic bag or the like as the inner bag (Patent Document 1, etc.).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The problem of the present invention is to develop a paper container for use in storing refrigerated products, which has waterproofness on the innermost surface of the container, has good followability of the temperature change inside the box with respect to the surrounding environment, and does not have a decrease in box compression strength even when refrigerated products are put in or when the transport temperature conditions change rapidly.

Means for Solving the Problems

[0005] The inventors of the present invention earnestly studied the above problems, and as a result, by providing a waterproof resin layer on at least the innermost surface of the paper container by coating, an excellent paper container for storing refrigerated products could be realized.

[0006] Although not limited to the following, the present invention includes the following aspects. [1] A paper container for transporting refrigerated products, at least the inner surface of which is coated with a waterproof resin layer, The Cobb water absorption per 30 minutes measured from the inner side of the container is 155 g / m 2 or less, When a storage test is performed under the following conditions, the temperature T inside the paper container b satisfies T ≤ the storage temperature T of the paper container a + 5°C. The paper container is characterized by this. a) After closing the lid of the paper container so that outside air does not enter, move the paper container to an environment of temperature T a . b) After moving to an environment of temperature T a and after 10 minutes have elapsed, measure the temperature T inside the paper container b . [2] The paper container according to [1], characterized in that the remaining rate of the box strength immediately after the paper container is left in an environment of 23°C in air temperature and 50% in humidity for 1 hour or more and then transferred to an environment of 5°C in air temperature and stored for 24 hours is 50% or more. [3] The paper container according to [1] or [2], characterized in that the waterproof resin layer contains at least one of a styrene resin, an acrylic resin, a polyolefin resin and a water-repellent wax. [4] The paper container according to any one of [1] to [3], characterized in that the thickness of the corrugated cardboard sheet constituting the paper container is 0.4 to 15 mm. [5] The paper container according to any one of [1] to [4], characterized in that the inner volume / outer volume of the paper container is 0.70 or more. [6] The paper container according to any one of [1] to [5], characterized in that the thermal conductivity of the liner used for the corrugated cardboard sheet is 0.05 w / mK or more and 0.20 w / mK or less. [7] The paper container according to any one of [1] to [6], characterized in that the corrugated cardboard sheet is any one of single-sided corrugated cardboard, double-sided corrugated cardboard, double-double-sided corrugated cardboard, and double-double-sided corrugated cardboard. [8] The paper container according to any one of [1] to [6], characterized in that the corrugated cardboard sheet used for the paper container is two or more corrugated cardboards, and when the paper container is assembled so that each corrugated cardboard sheet contacts at the bottom and side wall portions of the paper container, the inner surface side of the corrugated cardboard sheet located on the innermost side of the paper container has a waterproof resin layer. [9] A cardboard sheet composed of a liner with a thermal conductivity of 0.05 W / m·K or more and 0.20 W / m·K or less, and a waterproof resin layer coated on at least one side, is used. A paper container characterized by this.

Effect of the Invention

[0007] According to the present invention, not only waterproofness but also good followability of the temperature change inside the box with respect to the surrounding environment, and the box compression strength does not decrease even when refrigerated products are put in or the transport temperature conditions change rapidly. A paper container suitable for use in storing refrigerated products can be obtained.

Brief Explanation of the Drawings

[0008]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0009] The present invention relates to a paper container for storing refrigerated products. The paper container according to the present invention has waterproofness at least on the innermost surface of the container, has good followability of the temperature change inside the container with respect to the surrounding environment even when storing refrigerated products, and the strength of the paper container is not easily reduced even when the transport temperature conditions change rapidly and condensation occurs. It refers to a paper container characterized by this. In particular, the paper container according to the present invention has the characteristic that the temperature inside the container becomes +5°C or less with respect to the temperature of the surrounding environment within 10 minutes after the surrounding temperature environment changes. The paper container according to the present invention is not particularly limited as long as it is used for packaging things including refrigerated products. For example, it can be used for applications such as storing meat, fish, vegetables, etc. as contents. Since the paper container according to the present invention has the characteristic that the temperature inside the paper container easily follows the surrounding temperature environment, unlike conventional polystyrene foam containers, it can also be used for applications such as storing meat, fish, vegetables, etc. and then refrigerating them without containing a cold storage agent (heat storage material) even in a refrigerated environment of 10°C or less. Also, a cold storage agent may be contained for the purpose of maintaining the refrigerated state inside the paper container when the surrounding of the paper container becomes normal temperature.

[0010] The type of paper used for the paper container according to the present invention is not particularly limited, and it may be appropriately selected from wrapping paper, base paper for processing, cardboard base paper, paperboard for paper containers, waste paperboard, thick paper, etc. In a preferred embodiment, the paper container is preferably made of cardboard. By being made of cardboard, even when stacked in multiple layers, accidents such as collapse during handling such as transportation do not occur. Further, the paper container according to the present invention may be made of a single cardboard, or after forming paper containers using a plurality of cardboards respectively, an inner paper container (inner container) may be inserted inside an outer paper container provided outside to form a single paper container, and it may be in the form of a paper container having a plurality of structures.

[0011] The thickness of the cardboard sheet is not particularly limited, but by reducing the thickness of the cardboard sheet, the temperature adaptability to the surrounding environment where the paper container is placed becomes good, and the stacking efficiency is improved. In a preferred embodiment, the thickness of the cardboard sheet used for the paper container is 0.2 to 15 mm, more preferably 0.4 to 5 mm. In the case of a paper container having a plurality of structures, in a preferred embodiment, the thickness of the cardboard sheet used for the inner container is less than or equal to the thickness of the cardboard sheet used for the outer container.

[0012] A cardboard sheet is made by bonding a flat paper (liner) and a corrugated paper (medium) with an adhesive, and is suitably used for various applications such as packaging of goods, cushioning materials, transportation of luggage, and storage of articles.

[0013] The cardboard sheet used for the paper container according to the present invention can generally be manufactured by bonding a liner and a medium processed into a corrugated shape using a corrugator. As the corrugator, known ones can be used without limitation, but a general corrugator is composed of a single facer, a doublebacker, and a cutter. In addition, a pasting device for bonding the liner and the medium base paper, and further, a device for generating heat for melting the paste are used in combination.

[0014] Also, when manufacturing the cardboard sheet used for the paper container according to the present invention, an adhesive is used for adhering the liner and the medium. Known adhesives can be used, but from the viewpoint of making it difficult for the strength of the cardboard box to decrease due to water wetting, condensation, moisture, etc. in the cross-section of the cardboard sheet, it is preferable to use a water-resistant adhesive. A water-resistant adhesive is one obtained by adding a water-proofing agent to an ordinary adhesive for cardboard. The water-proofing agent is not particularly limited, and examples thereof include those containing synthetic resin emulsions, ketone aldehyde resins, and the like.

[0015] The liner used for the cardboard sheet will be described later, and kraft liner, jute liner, etc. can be used according to the application and the part to be used. The basis weight of the liner is not particularly limited either. For example, the basis weight of the entire liner can be 70 to 550 g / m 2 It can be set to, or can be set to 100 to 500 g / m 2 or can be set to 150 to 450 g / m 2 or the like.

[0016] Regarding the medium that constitutes the cardboard, depending on the application and the part to be used, A flute, B flute, C flute, E flute, F flute, G flute, AAA flute, AA flute, W flute, etc. can be used without particular limitation. However, as described above, by selecting the configuration of the medium so that the thickness of the entire cardboard sheet can be reduced, the temperature adaptability to the surrounding environment where the paper container is placed is improved, and the loading efficiency is also improved. The basis weight of the medium is not particularly limited either, and 120 g / m 2 160 g / m 2 180 g / m 2 Reinforced 180 g / m 2 Reinforced 200 g / m 2 etc. can be preferably used. Note that it is preferable to reduce the basis weight of the liner and / or the basis weight of the medium within the range where the effects of the present invention are exhibited and the strength of the paper container is ensured at a certain level or higher.

[0017] The paper container according to the present invention is manufactured from a cardboard sheet by, for example, folding using a single blank sheet and, if necessary, bonding with an adhesive. The type of adhesive is not particularly limited, and examples include aqueous, water-dispersible, solution-based, solvent-free, solid-based, etc., and can be appropriately selected according to the surface state of the paper material that becomes the bonding surface.

[0018] The amount of adhesive used is not particularly limited as long as it has sufficient adhesive strength. In the case of surface coating, it may be 0.5 to 2000 g / m 2 and may also be 5 to 1500 g / m 2 and may also be 10 to 1000 g / m 2 In the case of line coating, the coating width can be appropriately changed according to the nozzle diameter of the applicator, the moving speed of the nozzle or the paper material, the viscosity of the adhesive during coating, the width of the paper to be bonded, etc. The coating amount per unit length is not particularly limited either, but for example, it may be 0.1 to 30 g / m, may be 0.5 to 20 g / m, or may be 1 to 15 g / m.

[0019] The shape and size of the paper container used in the present invention are not particularly limited as long as they can appropriately accommodate the target article and ensure strength. For example, a cardboard box exemplified in JIS Z 1507, a water-tight box formed by folding a single blank sheet, where the bottom and all side wall portions are connected via fold lines and all side wall portions are connected via fold lines, a polygonal container or box, a cylindrical container or box, a curved container or box, etc., can be appropriately selected according to strength and usage. Also, when making a paper container with a plurality of structures, the shapes of the outer container and the inner container may be the same, or different-shaped inner and outer containers may be combined. As a preferred embodiment when forming a paper container with a plurality of structures, it is a set of paper containers in which the inner dimensions of the outer container and the outer dimensions of the inner container are set such that at least a part of the inner surface of the outer container and a part of the outer surface of the inner container are in contact on the side surface of the paper container. In a more preferred embodiment, both the inner and outer containers are in the shape of a box. In an even more preferred embodiment, the inner container is a water-tight box. When manufacturing a paper container such as a box by making a paper material into a box body, a box-making machine can be used. The box-making machine to be used is not particularly limited. For example, a vertical or horizontal box-making machine can be used.

[0020] The paper container according to the present invention is characterized in that the residual rate of the box compression strength after leaving water in the inner container for 24 hours is 30% or more. Further, the paper container according to the present invention is characterized in that, on the innermost surface of the paper container, [burst strength after contacting water for 30 minutes] / [burst strength before contacting water] is 50% or more. By using waterproof paper on the innermost surface of the paper container, even when the transport temperature conditions change rapidly and condensation occurs inside the paper container, the strength of the paper container is less likely to decrease, and it is possible to achieve both the effect of making the paper container less likely to have its strength reduced and the ability of the paper inside to follow the temperature change of the surrounding environment when storing refrigerated products.

[0021] Paper sheet constituting the paper container The paper sheet for constituting the paper container according to the present invention is preferably cardboard, and more preferably a liner for corrugated board. The basis weight of the paper sheet is not particularly limited. For example, it can be 10 to 800 g / m 2 It can be set as appropriate. When the paper sheet is a single-layer paper, the basis weight can be appropriately set within the range of 10 to 300 g / m 2 and can also be in the range of 30 to 250 g / m 2 When the paper sheet is a multi-layered cardboard having two or more paper layers, its basis weight can be appropriately set within the range of 70 to 800 g / m 2 The paper sheet can be appropriately selected according to the use and structure of the paper container, etc. Further, when making a paper container with a plurality of structures, the basis weight of the paper sheet for the inner container and the basis weight of the paper sheet for the outer container may be the same, or paper sheets with different basis weights may be used for the inner container and the outer container. As a preferred form, from the viewpoint of improving the assembly workability of the inner container, the basis weight of the paper sheet for the inner container used in the present invention is preferably smaller than the basis weight of the paper sheet for the outer container.

[0022] (Paper sheet for paper container) The paper sheet (inner sheet) constituting the innermost surface of the paper container according to the present invention has waterproof property in a preferred embodiment, and in a more preferred embodiment, the Cobb water absorption of the surface is 3 g / m 2 or less, and 2 g / m 2 or less is more preferred, and it may be 1 g / m 2 or less. When measuring the Cobb water absorption for 120 seconds, in the case of paper with less than 1 g / m 2 (including the case where water absorption does not occur and is less than the measurement limit value), in a preferred embodiment, the Cobb water absorption of the surface is 155 g / m 2 or less, 100 g / m 2 or less is more preferred, 50 g / m 2 or less is further preferred, 25 g / m 2 or less is further preferred, and most preferably it may be 10 g / m 2 or less. In the present invention, the Cobb water absorption is measured in accordance with JIS P8140 (Cobb method) by bringing 100 ml of distilled water into contact with the waterproof layer and measuring the weight per unit area of the water absorbed after a specified time. The lower the Cobb water absorption under the condition of extending the measurement time, the lower the water absorption property of the waterproof layer.

[0023] The inner sheet according to the present invention is excellent in moisture-proof property in a preferred embodiment. For example, the moisture permeability is 100 g / m 2 ·24 h or less, more preferably 75 g / m 2 ·24 h or less, still more preferably 50 g / m 2 ·24 h or less. Here, the moisture permeability of the paper can be measured from the waterproof layer side of the inner sheet in accordance with JIS Z 0208, and the smaller the numerical value, the higher the moisture-proof property.

[0024] The inner sheet of the present invention also has excellent oil resistance, and in a preferred embodiment, the oil repellency on the waterproof 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 waterproof layer side of the inner sheet in accordance with JAPAN TAPPI Paper and Pulp Test Method No. 41 "Paper and Paperboard - Oil Repellency Test Method - Kit Method", and a higher kit number indicates higher oil resistance.

[0025] The inner sheet of the present invention preferably has an Oken smoothness of the waterproof surface of 15 seconds or more, more preferably 20 seconds or more, and even more preferably 25 seconds or more. When the surface smoothness of the waterproof layer of the waterproof paper is in the above range, a high gloss can be obtained on the surface of the waterproof layer, resulting in a waterproof paper with excellent cosmetic properties.

[0026] (Paper base material for inner sheet) The inner sheet of the present invention has at least a paper base material and a waterproof layer provided on at least one surface 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 The range can be appropriately set.

[0027] The paper base material used for the inner sheet has a 120-second Cobb water absorption of 25 g / m on the side where the waterproof layer is to be provided. 2 Less than 20 g / m 2 Less than 15g / m 2 In the double-walled paper container of the present invention, the paper base material used for the inner sheet has a 120-second Cobb water absorbency of 5 g / m 2 More than 7 g / m 2 More preferably, 10 g / m2 The above is the case. In the present invention, the Cobb water absorption degree at 120 seconds can be adjusted by applying a water repellent such as wax. However, when the Cobb water absorption degree at 120 seconds is within the above range, it is possible to prevent a decrease in paper strength due to excessive penetration of moisture contained in the solvent of the waterproof paint, and to ensure coating by allowing the solid content in the waterproof paint to stay on the surface of the paper layer, thereby achieving both improvement in waterproofness and moisture resistance.

[0028] The paper base material used for the inner surface sheet has a water repellency of R4 or more, preferably R6 or more, and more preferably R8 or more, measured in accordance with JAPAN TAPPI Paper Pulp Test Method No. 68 "Paper and Paperboard - Water Repellency Test Method". When the water repellency of the paper base material is R4 or more, when applying the waterproof material, moisture contained in the waterproof material and / or the solvent of the waterproof material does not excessively penetrate into the paper base material, and a decrease in the strength of the paper can be suppressed.

[0029] In a preferred embodiment, the oil absorption degree of the surface where the waterproof layer is provided on the paper base material used for the inner surface sheet is 5 seconds or more, 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. When the oil absorption degree is within the above range, the wax contained in the waterproof material stays on the paper surface and is less likely to penetrate into the paper layer, so that the waterproofness and moisture resistance of the paper base material can be improved. The oil absorption degree of the paper base material is measured by dropping 1 drop of light oil No. 1 adjusted to a kinematic viscosity coefficient of 3 cSt onto the sample surface using a microsyringe equipped with an injection needle No. H5, and measuring the time until the gloss on the surface disappears.

[0030] In a preferred embodiment, the paper base material used for the inner surface sheet has a moisture permeability of 1500 g / m 2 ·24h or more, more preferably 1750 g / m 2 ·24h or more, even more preferably 2000 g / m 2 ·24h or more, measured from the side where the waterproof layer is provided. The upper limit of the moisture permeability is not particularly limited, but in a preferred embodiment, it is 5000 g / m 2·Less than 24 h, more preferably 4500 g / m 2 ·Less than 24 h, even more preferably 4000 g / m 2 ·It is less than 24 h. When the moisture permeability of the surface where the waterproof layer is provided is within the above range, the moisture in the waterproof material and / or the solvent of the waterproof material can be efficiently evaporated to the paper layer side in the drying process after coating, so that a uniformly coated waterproof layer can be provided, and the waterproof property and moisture-proof property are improved.

[0031] The paper substrate used for the inner surface sheet preferably has a water contact angle of 75 degrees or more, more preferably 77 degrees or more, on the surface where the waterproof layer is provided. When the water contact angle is within the above range, it is possible to prevent the moisture contained in the waterproof material and / or the solvent of the waterproof material from excessively penetrating into the paper substrate and prevent the strength of the paper substrate from decreasing.

[0032] The physical properties of the paper substrate used for the inner surface sheet are not particularly limited and can be appropriately set according to the use and structure of the paper container. 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, and the specific burst strength can be set to be 2.80 to 5.00 kPa·m 2 / g.

[0033] (Paper sheet used for other parts) The paper physical properties of the paper sheet used for other parts except the innermost surface of the paper container are not particularly limited. For example, the Cobb water absorbency of the surface may be 50 g / m 2 or less, may be 45 g / m 2 or less, and may be 40 g / m 2 or less. In the present invention, the Cobb water absorbency is measured in accordance with JIS P8140 (Cobb method) by bringing 100 ml of distilled water into contact with the surface layer and measuring the weight per unit area of the water absorbed after a specified time.

[0034] The moisture permeability of the paper sheet is not particularly limited and may be 10000 g / m 2 ·24 h or less, or may be 7500 g / m 2-24h or less is acceptable, 5000g / m 2 The moisture permeability of paper can be measured from the surface layer side in accordance with JIS Z 0208, and a smaller value indicates higher moisture resistance.

[0035] The drop oil absorbency of the surface of the paper sheet is not particularly limited, and may be 1 second or more, 2 seconds or more, or 3 seconds or more. The oil absorbency is measured by dropping one drop of diesel No. 1, whose dynamic viscosity coefficient is adjusted to 3 cSt, onto the surface of the sample using a microsyringe equipped with an H5 needle, and measuring the time until the surface no longer becomes glossy.

[0036] Other physical properties of the paper sheet are not particularly limited and can be set appropriately depending on the application and structure of the paper container. For example, the Oken smoothness of the front side is 1 second to 100 seconds, 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. In addition, a waterproof layer, which will be described later, may be provided on the surface of the paper sheet that will become the inside of the outer container.

[0037] (Raw materials and manufacturing of paper sheets) As the raw material pulp for the paper sheet, known materials can be used without particular limitation for both the inner sheet and the paper sheets used for other parts, as will be described later. The paper sheet may contain wastepaper pulp or may not contain wastepaper pulp. When it contains wastepaper pulp, for example, when the paper sheet is a single-layer paper, preferably the blending ratio of wastepaper pulp in the total pulp is 10% by mass or more, more preferably 25% by mass or more, still more preferably 50% by mass or more, and most preferably 70% by mass or more, and it can also be 100% by mass (consisting only of pulp derived from wastepaper). Further, kraft pulp may be blended as the pulp other than wastepaper pulp, or it may be all kraft pulp. When the paper sheet is a multi-layered board paper having two or more paper layers, the blending ratio of wastepaper pulp per layer can be as described above, and the blending ratio of wastepaper pulp in each layer may be different.

[0038] Also, in the papermaking of the paper sheet, a sizing agent or a water repellent can be added internally or externally, and further, a paper strength enhancer can be added internally or externally to improve the strength. Examples of the sizing agent include rosin-based sizing agents, rosin emulsion-based sizing agents, α-carboxymethyl saturated fatty acids, etc., as well as neutral rosin-based sizing agents, alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), cationic polymer-based sizing agents, etc. Examples of the water repellent include fluorine-based resins, polyamide-based resins, waxes, etc. Examples of the paper strength enhancer include conventionally used paper strength enhancers such as polyacrylamide (PAM) and modified starch. The coating amount in the case of external addition is not particularly limited, for example, it may be 10 g / m 2 or less, and it may be 5 g / m 2 or less, and it may be 3 g / m 2 or less, and it may be 2 g / m 2 or less.

[0039] Further, if necessary, known fillers can be added to the paper sheet. Examples of the fillers include inorganic fillers such as kaolin, calcined kaolin, delaminated kaolin, clay, calcined clay, delaminated clay, illite, heavy calcium carbonate, light calcium carbonate, light calcium carbonate-silica composite, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, etc., and organic fillers such as urea-formalin resin, polystyrene resin, phenolic resin, etc.

[0040] Furthermore, within a range that does not affect the quality of the paper sheet, sulfuric acid band, aluminum chloride, sodium aluminate, basic aluminum compound, water-soluble aluminum compound, polyvalent metal compound, silica sol, etc. may be added and used.

[0041] The paper sheet is manufactured by a known papermaking method. For example, it can be carried out using a fourdrinier paper machine, a gap former type paper machine, a hybrid former type paper machine, an on-top former type paper machine, a cylinder paper machine, etc., but is not limited thereto.

[0042] Also, in order to adjust the smoothness of the paper sheet, a smoothing treatment may be performed if necessary. For the smoothing treatment, smoothing treatment devices such as a normal calendar, a super calendar, a gloss calendar, a soft calendar, a heat calendar, a shoe calendar, etc. can be used. The smoothing treatment device may appropriately adjust the form of the pressurizing device, the number of pressurizing nips, heating, line pressure, etc. Further, on the outermost layer of the papermade sheet after papermaking, a coating agent such as latex, starch, pigment, water repellent, waterproof material described later, etc. may be coated in a form according to the purpose of use of the paper sheet using a known coating method.

[0043] In the present invention, depending on the use and structure of the paper container, the raw materials, chemicals, papermaking method, etc. described above may be the same or different between the inner sheet and the paper sheet used for other parts. As a more preferable aspect, for the inner sheet, paper (waterproof paper) provided with a waterproof layer having waterproofness described later is used.

[0044] Core base paper By laminating a corrugated medium paper on the obtained paper sheet (liner), the cardboard according to the present invention can be obtained. Generally, the corrugated medium paper is processed into a corrugated shape by a corrugator, and liners are laminated on both its front and back to manufacture a high-strength cardboard. However, multi-layered cardboard and single-sided cardboard with a corrugated medium paper on the surface are also known. As a preferred embodiment in the present invention, it is preferably a cardboard with liners laminated on both sides of the medium or a multi-layered cardboard.

[0045] The basis weight of the corrugated medium paper is not particularly limited, but 60~250 g / m 2 is preferred, 70~240 g / m 2 is more preferred, and 80~230 g / m 2 is even more preferred. Also, depending on the use and structure of the double-structured paper container, the basis weight of the medium used for the cardboard sheet for the inner container and the medium used for the cardboard sheet for the outer container may be the same, or different basis weights of the medium may be used.

[0046] In the present invention, it is preferable to use a reinforced corrugated medium in the cardboard sheet, and it is more preferable to use a water-resistant reinforced corrugated medium. The reinforced corrugated medium refers to a corrugated medium whose compression strength is improved compared to a general corrugated medium that satisfies the performance of the corrugated medium paper specified in JIS P 3904 by adding a paper strength agent or the like in the papermaking process. Also, the water-resistant reinforced corrugated medium refers to a corrugated medium whose water resistance as well as compression strength is improved by further adding a water-resistant agent in the manufacturing process of the reinforced corrugated medium. As the internal paper strength agent, polyacrylamide (PAM) may be used, and in that case, the addition amount is preferably 0.1%~5.0% based on the paper stock solid content, and more preferably 0.2%~2.0%.

[0047] The medium base paper may have a clear (transparent) coating layer provided by applying a coating liquid containing a starch-based compound to one or both sides of the base paper. Starch coating, for example, 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 2-roll size press, a gate roll coater or a rod metering size press which is a film transfer type coating method, or a curtain coater or a spray coater which is a non-contact coating method.

[0048] The amount of starch coating is not particularly limited as long as it does not impair the strength of the medium, and the lower limit may be 0.2 g / m per side in terms of solid content 2 or more, and may be 0.8 g / m 2 or more, and may be 2.0 g / m 2 or more, and may be 3.0 g / m 2 or more, and may be 4.0 g / m 2 or more. Although the upper limit is not particularly limited, if the coating amount is increased, it is necessary to reduce the basis weight of the base paper before clear coating of starch, and the tensile strength and tear strength of the base paper before starch coating will decrease, making paper breakage more likely to occur. Therefore, the coating amount of the starch-based compound is preferably 8.0 g / m or less per side 2 and may be 6.0 g / m 2 or less.

[0049] In the present invention, various auxiliaries usually used in ordinary starch coating, such as a dispersant, a thickener, a water retention agent, an antifoaming agent, a water resistance agent, a colorant, etc., can be appropriately used as necessary.

[0050] As a coater for applying a starch-based compound to the medium base paper, for example, a 2-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, or a curtain coater can be used. In the present invention, a coating machine of a film transfer type such as a gate roll coater or a rod metering size press can also exhibit an effect.

[0051] As the raw material pulp for the middle core base paper, those known without particular limitation can be used as will be described later. As the pulp raw material for the middle core base paper used in the present invention, it is preferable to blend a large amount of waste paper pulp. In the present invention, the blending ratio of waste paper pulp in all the 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.

[0052] Regarding the fillers and additives added to the middle core base paper, those known can be used as will be described later, and a known papermaking method can also be used. In addition, various surface treatments can be applied to the middle core base paper. For example, the surface treatment may be performed by calendering, or a lubricant may be applied to the core base paper. As the lubricant, a wax-based lubricant may be particularly used, and the coating amount is preferably 0.005 g / m 2 ~0.1 g / m 2 is preferable. In the present invention, as the lubricant, when passing the base paper through the calender, a method of spraying the lubricant on the calender roll and transferring it to the paper is preferable. This is because, in addition to applying the lubricant, it becomes possible to prevent dirt from adhering to the surface of the calender roll. As described above, by applying the lubricant, it is possible to more effectively prevent dirt from adhering to the surface of the calender roll.

[0053] The obtained middle core base paper can be processed into a corrugated shape (fluted) using a known corrugator. As the corrugation processing, any known processing can be performed according to the application. For example, A flute, B flute, C flute, E flute, F flute, G flute, AAA flute, AA flute, etc. may be applied to the middle core base paper.

[0054] Processing into cardboard sheet The corrugated cardboard sheet used in the paper container of the present invention is obtained by laminating a paper sheet (liner) and the corrugated middle core using a corrugator.

[0055] As the corrugator, known ones can be used without limitation. Generally, a common corrugator is composed of a single facer, a doublebacker, and a cutter. Also, a pasting device for adhering the liner and the medium paper, and further, a device for generating heat to melt the paste are used together.

[0056] Also, when manufacturing the cardboard sheet used for the paper container of the present invention, an adhesive is used for adhering the liner and the medium. From the viewpoint of making it difficult for the strength of the cardboard box to decrease due to water wetting, condensation, moisture, etc. in the cross-section of the cardboard sheet, it is preferable to use a water-resistant adhesive. In particular, it is more preferable to use a water-resistant adhesive when manufacturing the cardboard sheet for the inner container. A water-resistant adhesive is obtained by adding a water-proofing agent to a normal adhesive for cardboard. The water-proofing agent is not particularly limited, and examples include those containing a synthetic resin emulsion, a ketone aldehyde resin, etc.

[0057] Raw material for the core of the paper sheet for paper containers and the cardboard for paper containers As the raw material pulp of the paper sheet (liner) and the medium (hereinafter referred to as "paper material") used for the paper container, known ones can be used without particular limitation according to the use part and application. Specifically, for example, various wood-derived pulps such as 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 non-wood pulps obtained from kenaf, bagasse, bamboo, hemp, straw, etc. can be mentioned.

[0058] The paper material may contain waste paper pulp or may not contain waste paper pulp. When it contains waste paper pulp, for example, if the paper material is single-layer paper, preferably the blending ratio of waste paper pulp in all pulp is 10% by mass or more, more preferably 25% by mass or more, still more preferably 50% by mass or more, and most preferably 70% by mass or more, and it can also be 100% by mass (consisting only of pulp derived from waste paper). Also, kraft pulp may be blended as pulp other than waste paper pulp, or all may be kraft pulp.

[0059] As the waste paper pulp, waste paper pulp obtained by pulping unprinted waste paper such as cardboard waste paper, high white, extra white, medium white, and white waste, waste paper printed on high-quality paper, coated high-quality paper, medium-quality paper, coated medium-quality paper, and recycled paper, waste paper with writing, papers such as discarded confidential documents, waste magazine paper, and pulp (DIP) obtained by deinking newsprint waste paper after pulping can be used.

[0060] In addition, in the papermaking of the paper material, a sizing agent or a water repellent can be added internally or externally, and further, a paper strength enhancer can be added internally to improve the strength. Examples of the sizing agent include rosin sizing agents, rosin emulsion sizing agents, α-carboxymethyl saturated fatty acids, etc., and also neutral rosin sizing agents, alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), cationic polymer sizing agents, etc. Examples of the water repellent include fluorine-based resins, polyamide-based resins, waxes, etc. Examples of the paper strength enhancer include conventionally used paper strength enhancers such as polyacrylamide (PAM) and modified starch.

[0061] In addition, known fillers can be added to the paper material as needed, and inorganic fillers and organic fillers can be used without limitation. Examples of inorganic fillers include kaolin, calcined kaolin, delaminated kaolin, clay, calcined clay, delaminated clay, illite, heavy calcium carbonate, light calcium carbonate, light calcium carbonate-silica composite, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, etc. Examples of organic fillers include urea-formalin resin, polystyrene resin, phenolic resin, etc.

[0062] Furthermore, within a range that does not affect the quality of the paper material, sulfuric acid band, aluminum chloride, sodium aluminate, basic aluminum compound, water-soluble aluminum compound, polyvalent metal compound, silica sol, etc. can be added and used.

[0063] The paper material can be manufactured by known papermaking methods. For example, it can be carried out using a fourdrinier paper machine, a gap former paper machine, a hybrid former paper machine, an on-top former paper machine, a cylinder paper machine, etc., but it is not limited thereto.

[0064] In addition, in order to adjust the smoothness of the paper material of the present invention, a smoothing treatment may be performed as needed. For the smoothing treatment, smoothing treatment devices such as a normal calendar, a super calendar, a gloss calendar, a soft calendar, a heat calendar, a shoe calendar, etc. can be used. The smoothing treatment device can appropriately adjust the form of the pressing device, the number of pressing nips, heating, line pressure, etc.

[0065] Waterproof paper, waterproof layer The waterproof paper that constitutes the paper container of the present invention has a waterproof layer provided on the paper material. In a preferred embodiment, the waterproof layer of the present invention is provided by coating. In a more preferred embodiment, the waterproof layer contains a synthetic resin and wax. It is preferable that the synthetic resin contains at least one of a styrene-based resin, an acrylic-based resin, and a polyolefin-based resin. In particular, it is preferable that the synthetic resin is a styrene-based resin and / or an acrylic-based resin.

[0066] As for the styrene-based resin that the waterproof layer constituting the present invention can contain, it is preferable that the copolymerization ratio of the styrene-based monomer having a styrene skeleton in the structure is 50% by mass or more, and it may be composed only of a polymer of the styrene-based monomer.

[0067] Examples of the styrene-based monomer include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, p-tert-butylstyrene, α-methylstyrene, α-methyl-p-methylstyrene, and the like.

[0068] Also, as monomers copolymerizable with the styrene monomer, for example, 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 acid anhydrides that are anhydrides such as maleic acid and itaconic acid, unsaturated nitriles such as acrylonitrile and methacrylonitrile, conjugated dienes such as 1,3-butadiene and 2-methyl-1,3-butadiene, and the like can be mentioned. These can be used alone or in combination of two or more.

[0069] The acrylic resin that can be contained in the waterproof layer constituting the present invention is a resin in which the copolymerization ratio of acrylic monomers, which are acrylic acid, methacrylic acid, and their derivatives, is 50% by mass or more, and it may consist only of a polymer of acrylic monomers.

[0070] Examples of acrylic monomers include methacrylic acid esters such as cyclohexyl methacrylate, t-butylcyclohexyl methacrylate, and methyl methacrylate, and acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, and isopropyl acrylate. The acrylic resin may be a polymer of one or more monomers selected from these acrylic monomers.

[0071] 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 combinations of two or more.

[0072] In the present invention, wax is contained in the waterproof layer. Examples of the wax contained in the waterproof layer include synthetic waxes such as polyethylene wax, Fischer-Tropsch wax, oil-based synthetic waxes (fatty acid ester-based, fatty acid amide, ketone-amines), and hydrogenated oils, and natural waxes such as beeswax, wood wax, paraffin wax, and microcrystalline wax. These waxes can be used alone or in combinations of two or more, and in particular, hydrocarbon waxes containing paraffin are suitable.

[0073] In the present invention, for the purpose of improving whiteness or the like, a pigment may be contained in the waterproof layer 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 layer is 1% or more higher than the whiteness of the paper material 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, colloidal silica, satin white, mica, montmorillonite, etc. These pigments can be used alone or in combination of two or more. Among these pigments, in particular, kaolin, calcium carbonate or mica having a flat particle shape is particularly suitable because it is less likely to inhibit the waterproof property. Such a flat-shaped inorganic pigment preferably has an aspect ratio of 10 or more. The content of the pigment in the waterproof layer is preferably 5 to 40% by mass or less, more preferably 10% to 35% by mass or less. If the content of the pigment is less than 5% by mass, the effect of improving whiteness cannot be sufficiently obtained. If it exceeds 40% by mass, the moisture-proof and waterproof functions of the waterproof layer of the synthetic resin component may not be sufficiently exhibited, which is not preferable. Further, as other coating agents, for example, a binder, a stabilizer, an antifoaming agent, a viscosity improver, a water retention agent, a preservative, a colorant, etc. may be contained.

[0074] In the present invention, the waterproof layer can be formed by coating a waterproof material containing the above components on a paper material and drying it. The coating amount of the waterproof layer is preferably 4 to 20 g / m 2 and more preferably 5 to 15 g / m 2 . If it exceeds 20 g / m 2 , further improvement in waterproof property cannot be expected, while the manufacturing cost may increase.

[0075] The waterproof layer provided on the waterproof paper constituting the present invention preferably 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 waterproof layer is the average value of the thicknesses of the waterproof layer measured by cutting the sample into strip shapes and observing the cross-sections at any 10 locations using an electron microscope.

[0076] In addition, the waterproof paper constituting the present invention preferably has a moisture permeability per unit thickness of the waterproof layer of 15 (g / m 2 ·24 h) / μm or less, more preferably 10 (g / m 2 ·24 h) / μm or less, and even more desirably 7 (g / m 2 ·24 h) / μm or less. Here, the moisture permeability per unit thickness of the waterproof layer is calculated by dividing the moisture permeability measured in accordance with JIS Z 0208 from the waterproof layer side of the waterproof paper by the average waterproof layer thickness.

[0077] The waterproof paper constituting the present invention can be manufactured by applying a waterproof material to at least one surface of a paper material and drying the applied waterproof material. The formation of the waterproof layer can be carried out by applying a coating agent using a known coating method. For example, coating methods such as air knife coating, curtain coating, blade coating, gate roll coating, and die coating can be used. Also, the coating layer may be a single layer or a plurality of layers. A plurality of coating layers may be sequentially applied, or two or more layers may be simultaneously applied by curtain coating or the like. When providing a plurality of coating layers, at least one layer may be a coating layer having waterproof properties, and it is preferable to apply a waterproof material as the outermost coating layer. When drying the coating layer, preferably, the temperature of the coating layer at the outlet of the drying process is adjusted to be less than 120°C. The coating speed when applying the coating agent can be appropriately set in consideration of the viscosity of the coating agent and the target coating amount.

[0078] As a preferred embodiment, by applying the coating agent to the paper material by a contour coating method such as air knife coating or curtain coating, the coating amount of the coating agent on the surface of the paper material becomes uniform. Therefore, the coating film thickness becomes uniform, and the generation of blisters in the coating layer in the subsequent drying process can be suppressed. In addition, the amount of the coating agent used can be reduced compared to the contact coating method, and the manufacturing cost can be suppressed.

[0079] The coating agent applied to the paper material is dried to form a coating layer. In this drying process, it is preferable that the temperature of the coating layer at the outlet is less than 120°C, and it may be adjusted to be 100°C or less. When the temperature of the coating layer at the outlet is 120°C or higher, the generation rate of blisters in the coating layer may increase, and blocking may occur on the waterproof paper 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 higher, more preferably 70°C, and can also be 80°C or higher. When the temperature of the coating layer at the outlet is less than 60°C, in some cases, not only may blocking occur on the waterproof paper wound up after the coating layer is formed, but also the drying of the coating layer may be insufficient, so that the waterproof and moisture-proof performance may not be fully exhibited.

[0080] The setting of the temperature of the coating layer at the outlet of the drying process can be set in consideration of the basis weight and paper thickness of the paper material. For example, in the case of a paper material with a large basis weight and paper thickness, more heat is required for drying compared to a paper material with a small basis weight and paper thickness. On the other hand, blisters tend to occur on the surface of the coating layer. The reason is not limited, but in the case of thick paper, the basis weight and paper thickness are generally larger and the air permeability is lower compared to thin paper. Even with the same moisture value in the paper, in the drying process, a large amount of moisture vaporized inside the paper material cannot escape sufficiently, so it is considered that blisters are likely to occur on the surface of the coating layer. Therefore, the larger the basis weight and paper thickness of the paper material, the more preferably the temperature of the coating layer at the outlet of the drying process is adjusted higher within the above range, and it is more preferable to set the temperature at the inlet of the drying process lower.

[0081] Here, the outlet of the drying process, when there is one drying zone in the drying process, is the outlet of that drying zone; when there are multiple drying zones in the drying process, it is the outlet of the most downstream drying zone.

[0082] The adjustment of the coating layer temperature at the outlet of the drying process can be carried out by adjusting the drying time and the temperature of the drying zone. The drying time is determined by factors such as the feeding speed of the paper material, the number and length of the drying zones, and the equipment capabilities (air volume, infrared output) of the drying zones. Also, as the drying method, known drying methods can be used. For example, steam cylinder heating drying method, hot air drying method, gas infrared drying method, electric infrared drying method, etc. can be mentioned, and any one of these, or a combination of two or more, can be used.

Example

[0083] Hereinafter, the present invention will be described in more detail with specific examples, but the present invention is not limited by the following specific examples. In this specification, unless otherwise specified, concentrations, etc. are based on weight, and numerical ranges include their endpoints.

[0084] Manufacture of liner and core base paper (1) Liner sample A A back layer composed of 100% waste paper pulp, a middle layer composed of 100% waste paper pulp, and a surface layer composed of 70% unbleached kraft pulp and 30% waste paper pulp were formed by wet-laying at a weight ratio of back layer: middle layer: surface layer = 25:60:15. After drying with a dryer, a water repellent containing paraffin wax and rosin was applied unilaterally on the surface layer side. After drying again with a dryer, a smoothing treatment was performed using a calendar to produce liner sample A (basis weight: 282.6 g / m 2 , Cobb water absorbency of the surface for 120 seconds: 12.9 g / m 2 , coating amount of the water repellent: about 1 g / m 2 ). (2) Liner sample B Using an air knife on the surface side of the liner sample A, 5 parts of a wax-based emulsion (Starlight PMC WR3932) were mixed with 100 parts of a styrene-acrylic resin (Michaelman MC1548A), and 10.0 g / m of the waterproofing agent was applied. 2 The sample was heat-dried so that the temperature of the coating layer at the exit of the drying process was 80°C to obtain a liner sample B (basis weight: 291.4 g / m 2 , 120-second Cobb water absorption of the surface: 0.1 g / m 2 ). (3) Liner sample C A back layer made of 100% waste paper pulp, a middle layer made of 100% waste paper pulp, and a surface layer made of 70% unbleached kraft pulp and 30% waste paper pulp were combined by weight ratio of back layer: middle layer: surface layer = 25:60:15, dried with a dryer, and then smoothed using a calendar to produce a liner sample C (basis weight: 281.3 g / m 2 , 120-second Cobb water absorption of the surface: 27.7 g / m 2 ). (4) Liner sample D A 10-μm-thick polyethylene film was laminated on the surface side of the liner sample C, and then adhered and laminated using a roller heated to 80°C to obtain a liner sample D (basis weight: 289.7 g / m 2 ). (5) Middle core paper 0.4% of a waterproofing agent was added to a pulp slurry of 100% waste paper pulp to prepare a paper stock. Then, this paper stock was single-layered and dried with a dryer, and then smoothed using a calendar to produce a middle core paper (basis weight: approximately 200 g / m 2 ).

[0085] Evaluation of liner and core base paper The paper quality of the liner samples and the middle core paper is shown in Table 1. (Basis weight) Measured in accordance with JIS P 8124. (Average coating layer thickness, moisture permeability per unit coating layer thickness) The sample was cut into strips, and the thickness of the coating layer (waterproof layer) was measured at 10 random points on the cross section by observation using an electron microscope, and the average value was calculated to obtain the average coating layer thickness. The moisture permeability per unit coating layer was also calculated by dividing the moisture permeability by the average coating layer thickness. (Oken Smoothness) In accordance with JIS P 8155, the Oken smoothness was measured using a digital Oken air permeability smoothness tester (Asahi Seiko). (Longitudinal elongation, transverse elongation) Measured in accordance with JIS P 8113. (Specific Compressive Strength) The compressive strength was measured in accordance with JIS P 8126, and the specific compressive strength was calculated by dividing the measured value by the basis weight. (Burst Ratio) Burst strength was measured in accordance with JIS P 8131, and the burst ratio was calculated by dividing the burst strength by the basis weight. (Rate of Residual Burst Strength after Contact with Water) After leaving the surface of the outer layer of each sample in contact with water for 30 minutes, the water was wiped off and the burst strength of the sample was measured in accordance with JIS P 8131. The burst strength was then divided by the basis weight to calculate the burst strength. The value obtained by dividing the burst strength by the aforementioned burst strength (the burst strength of the sample before contact with water) was taken as the rate of residual burst strength after contact with water. (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 surface (coated surface), and the weight of water absorbed per unit area after a specified time was measured. Note that the measurement time was not only the usual specified time of 120 seconds (2 minutes), but also 30 minutes. (Moisture permeability) Measured from the front side (coated side) in accordance with JIS Z 0208. (Water repellency) The surface side (coated side) was measured in accordance with JAPAN TAPPI Paper and Pulp Test Method No. 68 "Paper and Paperboard - Water Repellency Test Method." (Contact Angle) One drop (50 μl) of distilled water was dropped onto the sample surface, and the contact angle was measured one second later using a contact angle measuring device (DAT1100, manufactured by FIBRO System AB). (Initial oil absorption) In accordance with JAPAN TAPPI Paper Pulp Test Method No. 41, "Paper and Paperboard - Initial Oil Absorption Test Method - Kit Method", the surface side (coated surface side) was measured. (Dropwise oil absorption) Using a microsyringe equipped with a No. 5 hypodermic needle, No. 1 light oil with a kinematic viscosity coefficient adjusted to 3 cSt was dropped one drop at a time onto the sample surface, and the time until the gloss on the surface disappeared was measured. (Thermal conductivity) For each liner sample, after cutting the sample into 50 mm × 50 mm pieces, a measurement sample was prepared by stacking 8 pieces and sandwiching them with graphite paper. After placing the heat flux measurement sensor and the measurement sample in that order on the lower heater of the heat flux meter, the upper heater was lowered and pressed. Using the measured thermal resistance value with the lower heater set to 18 °C and the upper heater set to 42 °C so that the sample surface temperature became 30 °C, the thermal conductivity of the sample was determined by the following formula: Thermal conductivity (W / mK) = sample thickness (m) / thermal resistance value (m 2 ·K / W)

[0086] [Table 1]

[0087] Manufacture of cardboard sheet Corrugated sheets for box making were produced from each liner sample. Specifically, for liner samples A to D, each sample was used with the same liner as the face liner and the back liner, and the face liner and the back liner were adhered through the middle kraft paper so that the surface layer side (waterproof layer side) was on the outside of the corrugated sheet, and the corrugated sheet was manufactured. The thickness of the corrugated sheet was 5 mm (A flute) for the sheet for the outer container and 3 mm (B flute) for the sheet for the inner container. However, for the sheet using liner B for the face liner, in addition to sample B3 (3 mm, B flute), there were three types: sample B1 (0.6 mm, F flute) and sample B5 (5 mm, A flute).

[0088] [Table 2]

[0089] Manufacture of paper container with single-layer structure The obtained cardboard sheets were each made into a cardboard container [1] (inner dimensions: length 45 cm × width 31 cm × depth 24 cm) as shown in Fig. 1 with the surface liner side (waterproof layer side) facing inward.

[0090] Manufacture of paper container with double-layer structure The obtained cardboard sheets were each made into an A-style (0201 format specified in JIS Z 1507) cardboard box for the outer container (outer dimensions of the main body: length 47 cm × width 33 cm × height 27 cm, inner dimensions: length 46 cm × width 32 cm × depth 25 cm) with the surface liner side (waterproof layer side) facing inward, and a cardboard container [2] (outer dimensions of the main body: length 45.6 cm × width 31.6 cm × height 24.6 cm, inner dimensions: length 45 cm × width 31 cm × depth 24 cm) as shown in Fig. 2 using a B flute (thickness 3 mm) sheet for the inner container. Next, the inner container was set inside the A-style cardboard box that serves as the outer container to manufacture a paper container with a double structure. The inner dimension / outer dimension volume ratio of the paper container with a double structure was 86.0%.

[0091] Preparation of foam polystyrene box for comparison As a control, a commercially available expanded polystyrene box was used (outer dimensions of the main body: length 55 cm × width 41 cm × height 29 cm, inner dimensions: length 45 cm × width 31 cm × depth 24 cm, inner dimension / outer dimension volume ratio 51.2%).

[0092] Evaluation of each container (1) Temperature adaptability and dew condensation resistance Two of each cardboard container [1], cardboard container [2], and expanded polystyrene container were prepared per sample, and a commercially available cold insulator (CKB-350 manufactured by Iris Ohyama) was housed in one of them. After that, a data logger was set in both containers so as not to come into contact with the cold insulator, and after closing the lid using gum tape, the containers were moved into a refrigerator at a temperature of 5°C. After 5 minutes, 10 minutes, and 1 hour, the temperature inside the containers was measured with the data logger, and the temperature followability was confirmed by the following evaluation. ○: The temperature inside the box was 7°C or lower. △: The temperature inside the box exceeded 7°C and was 10°C or less. ×: The temperature inside the box exceeded 10°C.

[0093] Also, regarding dew resistance, the box compression strength before storage in the refrigerator and 24 hours after the start of refrigerator storage was measured and evaluated. The box compression strength was measured according to the following procedure in accordance with JIS Z 0212. (a) Set the box with the lid on in the center of the compression tester. (b) Start the compression tester and gradually apply a downward force evenly across the entire upper surface of the box. (c) Read the weight when the side of the box is deformed and use it as the box compression strength. (d) After obtaining the reduction rate of the box strength before and after storage (= box compression strength after refrigerator storage / box compression strength before refrigerator storage × 100), the dew resistance was determined based on the following criteria. ○: The reduction rate of the box strength is less than 50%. ×: The reduction rate of the box strength is 50% or more.

[0094] (2) Mixed recyclability (2-1) Corrugated sheet alone (corrugated box with single-layer structure [1]) For the corrugated sheet sample used in the single-layer structure corrugated box, each obtained liner sample was cut into a size of 25 mm square, then weighed 30 g, added 1.5 L of water at 45°C, diluted to 2%, and then disintegrated for 30 minutes using a Tappi-type disintegrator. Next, after forming a sheet and pressing in accordance with JIS P 8222 to obtain a wet paper, it was dried on a plate heated to 50°C for 2 hours to produce a hand-made sheet (basis weight: about 50 g / m 2 ). Next, based on the following criteria, the appearance of the surface of the hand-made sheet was visually evaluated. 〇: There are no obvious foreign substances on the paper surface, and there are no particular problems regarding recycling. ×: Foreign substances and the like are obvious on the paper surface, which poses a problem regarding recycling.

[0095] (2-2) Double-layer corrugated box [2] Paper sheet samples for the outer container and the inner container (outer corrugated board and inner corrugated board) were each cut into 25 mm square sizes, and weighed out at a ratio of 30 g of the outer container paper sample to 10 g of the inner container paper sample. Except for this, dilution, pulping, and hand-sheeted paper were produced in the same manner as the corrugated board sheet alone, and evaluation was performed in the same manner.

[0096] (3) Ease of disassembly 50 each of the corrugated board boxes [1]-B3, corrugated board boxes [2]-B32, and boxes made of expanded polystyrene used in the temperature adaptability and dew condensation resistance evaluation were prepared. Five adult men in their 30s who received the following disassembly procedure explanation disassembled 10 samples each per person, and measured the average value of the time required to disassemble 10 boxes and the volume occupied by the box materials (corrugated board sheets, expanded polystyrene pieces) after disassembling all 50 boxes. · Disassembly method of the single-layer corrugated board box [1]: In the reverse procedure of the assembly method, with the opening facing up, raise the locking piece portion 15 to release the fixed state with the protruding piece portions 11a and 11b, and then stack the corrugated board sheets in a state where the side wall portions are spread out into a substantially flat shape. · Disassembly method of the double-layer corrugated board box [2]: After taking out and separating the inner container from the outer container, for the inner container, in the reverse procedure of the assembly method, with the opening facing up, raise the locking piece portion 15 to release the fixed state with the protruding piece portions 11a and 11b, and then stack the corrugated board sheets in a state where the side wall portions are spread out into a substantially flat shape. For the outer container, after peeling off the adhesive tape for forming the bottom surface, stack the corrugated board sheets in a state where they are folded into a double-layer with the bottom open. · Disassembly method of the expanded polystyrene box: Manually crush it to approximately a size of 15 cm square, and then put the disassembled expanded polystyrene pieces into a commercially available 90 L garbage bag to the maximum extent that the garbage bag can be sealed. The results are shown in Table 3.

[0097]

Table 3

[0098] From the above results, it was revealed that the paper container of the present invention (with the inner container as Sample B) has sufficient temperature followability and box compressive strength even after being transferred to a refrigerated environment regardless of whether a coolant is included or not, compared to other samples. The liner used in the present invention can be suitably used as a liner for manufacturing boxes for storing refrigerated products.

Explanation of Signs

[0099] 1 Box 2 Bottom 3 First fold line 4 First side wall part 5 Second fold line 6 Second side wall part 7 Third fold line 8 Fourth fold line 9 Fifth fold line 10 Folded part 11a, 11b Protruding piece part 12 Recessed part 13a, 13b Protruding part 14 Sixth fold line 15 Locking piece part 16a, 16b Fitting opening 17 Connecting part 18 Notch 20 Inner lid 21 Fitting piece 22 Inner lid part 23 Seventh fold line 24 Notch 25 Fitting piece 26 Outer lid part 27 Outer lid 28 Top plate 29 Eighth fold line 30 Side wall part

Claims

1. A paper container for transporting refrigerated products, with a waterproof resin layer applied at least to the inner surface of the box, The Cobb water absorption in 30 minutes measured from the inner side of the container is 155 g / m ２ or less, The temperature T inside the paper container when the storage test is conducted under the following conditions ｂ is such that it satisfies the condition that it is equal to or lower than the storage temperature T of the paper container ａ + 5°C. This is the characteristic of the paper container a) After closing the lid of the paper container so that outside air does not enter, move the paper container to an environment at temperature T ａ . b) Temperature T ａ After moving to the environment of ｂ and after 10 minutes have elapsed, measure the temperature T inside the paper container.

2. The paper container according to claim 1, characterized in that the remaining box strength ratio immediately after transferring the paper container to an environment at 5°C and storing it for 24 hours after leaving the paper container in an environment at 23°C and 50% humidity for 1 hour or more is 50% or more.

3. The paper container according to claim 1 or 2, wherein the waterproof resin layer contains at least one of a styrene-based resin, an acrylic-based resin, a polyolefin resin, and a water-repellent wax.

4. The paper container according to claim 1 or 2, wherein the thickness of the corrugated sheet constituting the paper container is 0.4 to 15 mm.

5. The paper container according to claim 1 or 2, wherein the inner volume / outer volume of the paper container is 0.70 or more.

6. The paper container according to claim 1 or 2, wherein the thermal conductivity of the liner used for the corrugated sheet is 0.05 w / mK or more and 0.20 w / mK or less.

7. The paper container according to claim 1 or 2, wherein the corrugated sheet is any one of single-faced corrugated board, double-faced corrugated board, double-double-faced corrugated board, and double-double-double-faced corrugated board.

8. The paper container according to claim 1 or 2, wherein the corrugated sheet used for the paper container is two or more corrugated boards, and when the paper container is assembled so that the corrugated sheets are in contact with each other at the bottom and side walls of the paper container, the waterproof resin layer is provided on the inner surface side of the corrugated sheet located on the innermost side of the paper container.

9. A paper container characterized by using a corrugated sheet composed of a middle liner with a thermal conductivity of 0.05 W / m·K or more and 0.20 W / m·K or less and having a waterproof resin layer applied at least to one side.

Images