Paper container

Abstract

To provide a paper packing material that is used to store and convey refrigerated goods that are typical in a bag-in-box application, in which strength in compressing a box does not decrease even when a difference in temperature between the inside and the outside of the box is large so that dew condensation occurs on contents and the box.SOLUTION: An excellent paper packing material is configured to store refrigerated goods by using sheets constituting an inner container and / or an outer container, where at least one surface of the sheet satisfies the condition that wetting / bursting strength survival rates determined by a ratio of [bursting strength after the sheet is impregnated in water for one hour / bursting strength before the sheet is contacted with water] are 45% or higher and 80% or lower.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a paper container. [Background technology]

[0002] Containers and packaging materials using paper substrates have been widely used for storing and transporting goods. In particular, when transporting liquid or gel-like substances as contents, a plastic bag is often used inside the box. Patent Document 1 describes a paper container with an inner bag, which has a 30-minute Cobb water absorbency of 40 g / m2 measured from the waterproof layer side. 2 The following describes a paper container with an inner bag having a waterproof layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-098685 Summary of the Invention [Problem to be solved by the invention]

[0004] As mentioned above, the applicant has developed a paper container with an inner bag, which has a 30-minute Cobb water absorbency of 40 g / m2 measured from the waterproof layer side. 2 We have invented the following paper container with a paper inner bag having a waterproof layer (Patent Document 1). However, regardless of whether the inner bag is present or not, when the contents are transported in contact with the paper container, the greater the temperature difference between the contents and the surrounding environment, the more likely it is that condensation will form on the surface of the inner bag due to the temperature difference between the packaged items and the paper container. This condensation will penetrate into the paper container, causing a decrease in the strength of the paper container. Therefore, the object of this invention is to provide a box that can stably transport the contents without causing the paper container to deteriorate, even if condensation occurs due to the temperature difference between the contents and the surrounding environment. [Means for solving the problem]

[0005] The inventors have thoroughly investigated the above-mentioned problems and have succeeded in realizing a paper container that can transport the contents stably without deterioration of the paper container, even if condensation occurs due to the temperature difference between the contents and the surrounding environment, by using water-resistant paper on at least one surface of the outer container or inner container.

[0006] The present invention includes, but is not limited to, the following aspects. [1] A paper container having (a) a paper outer container and (b) a paper inner container attached to the inside of the outer container, characterized in that at least one of the inner container or the outer container uses a sheet whose wet burst strength retention rate, calculated by [burst strength after immersion in water for 1 hour] / [burst strength before contact with water], is 45% or more and 80% or less. [2] The paper container according to [1], wherein at least the outer container is box-shaped. [3] The paper container according to [1] or [2], wherein the sheet constituting the inner container and / or the outer container is a cardboard sheet. [4] A method for using a paper container, in which an inner container is placed inside an outer container to store an item, characterized in that at least one of the inner container or the outer container uses a sheet whose wet bursting strength retention rate, calculated by [burst strength after immersion in water for 1 hour] / [burst strength before contact with water], is 45% or more and 80% or less. [5] A method for producing a paper container having a double structure, comprising: (a) producing a paper container for an inner container and / or an outer container using a sheet having a wet bursting strength retention rate of 45% or more and 80% or less, as determined by [burst strength after immersion in water for 1 hour] / [burst strength before contact with water]; and (b) placing the inner container inside the outer container. [Effects of the Invention]

[0007] According to the present invention, by using water-resistant paper for one of the sheets constituting the paper container, a paper container whose strength does not decrease even when condensation occurs inside the container can be obtained. Furthermore, the present invention broadens the range of uses of paper containers, and paper containers suitable for various applications can be provided. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view showing an inner container of a paper container according to the present invention. [Figure 2] This is a photograph taken when evaluating the condensation resistance of paper containers. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention relates to a paper container. The paper container according to the present invention is characterized in that at least one of the outer container and the inner container uses a sheet with a wet burst strength retention rate of 45% or more. The paper container according to the present invention is not particularly limited as long as it is used for transporting in a refrigerated or frozen environment, and can be used for storing food products such as meat, fish, and vegetables, or liquid or gel-like medicines in a bag-in-box format. If necessary, the inner surface of the inner container may be made waterproof, and a cooling agent (refrigerant) may be placed inside the paper container to maintain a refrigerated state inside the paper container when the surrounding temperature reaches room temperature.

[0010] The type of paper used in the paper container of the present invention is not particularly limited, and may be appropriately selected from wrapping paper, processed base paper, corrugated board, paperboard for paper containers, miscellaneous paperboard, thick paper, etc. In a preferred embodiment, the paper container is made of corrugated board. By using corrugated board, accidents such as collapse of cargo during handling, such as transportation, do not occur even when stacked in multiple layers. Furthermore, the paper container of the present invention is preferably in the form of a multiple-structure paper container, in which each paper container is formed using multiple corrugated boards, and then an inner paper container (inner container) is inserted inside the outer paper container (outer container) to form a single paper container.

[0011] Although the thickness of the cardboard sheet is not particularly limited, reducing the thickness of the cardboard sheet improves the temperature adaptability to the surrounding environment in which the paper container is placed and improves loading efficiency. 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 addition, when a paper container is made with multiple structures, in a preferred embodiment, the thickness of the cardboard sheet used for the inner container is equal to or less than the thickness of the cardboard sheet used for the outer container.

[0012] Corrugated cardboard sheets are made by gluing together flat paper (liner) and corrugated paper (core) and are suitable for a variety of uses, including packaging and cushioning for goods, transporting luggage, and storing items.

[0013] The corrugated cardboard sheets used in the paper container of the present invention can generally be produced by bonding a liner and a corrugated medium together using a corrugator. Any known corrugator can be used without limitation, but a typical corrugator is composed of a single facer, a double backer, and a cutter. A glue-making device for bonding the liner and medium base paper, as well as a device for generating heat to melt the glue, are also used.

[0014] Furthermore, when manufacturing the corrugated cardboard sheet used in the paper container of the present invention, an adhesive is used to bond the liner and the corrugating medium. While known adhesives can be used, it is preferable to use a water-resistant adhesive, as this prevents the strength of the corrugated cardboard box from being reduced by water wetting, condensation, humidity, etc., on the cross section of the corrugated cardboard sheet. A water-resistant adhesive is a standard corrugated cardboard adhesive to which a water-resistant agent has been added. The water-resistant agent is not particularly limited, and examples include those containing synthetic resin emulsions, ketone aldehyde resins, etc.

[0015] The liner used for the cardboard sheet will be described later, but depending on the application and the part to be used, kraft liner, jute liner, etc. can be used. The basis weight of the liner is not particularly limited, and for example, the basis weight of the entire liner can be 70 to 550 g / m 2 and can be set to 100 to 500 g / m 2 Or 150~450g / m 2 It may also be possible to use the following.

[0016] The corrugating material that makes up the cardboard can be A-flute, B-flute, C-flute, E-flute, F-flute, G-flute, AAA-flute, AA-flute, W-flute, etc., depending on the application and the part to be used, but as mentioned above, by selecting the configuration of the corrugating material so that the overall thickness of the cardboard sheet can be reduced, the temperature adaptability to the surrounding environment in which the paper container is placed will be good and loading efficiency will also be improved. There are also no particular restrictions on the basis weight of the corrugating material, and it is recommended to use a material with a weight of 120 g / m. 2 , 160g / m 2 , 180g / m 2 , reinforced 180g / m 2 , reinforced 200g / m 2 It is preferable to reduce the basis weight of the liner and / or the medium within a range that ensures the effects of the present invention and that ensures the strength of the paper container at a certain level or above.

[0017] The paper container according to the present invention is produced from a cardboard sheet by, for example, folding a single blank sheet and, if necessary, laminating it with an adhesive. The type of adhesive is not particularly limited, and examples include aqueous, water-dispersed, solution-based, solventless, and solid-based adhesives, which can be selected appropriately depending on the surface condition of the paper material to be bonded.

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

[0019] The shape and size of the paper container used in the present invention are not particularly limited as long as they can adequately store the intended items and ensure strength. Examples include corrugated cardboard boxes exemplified in JIS Z 1507, watertight boxes formed by folding a single blank sheet, in which the bottom and all side walls are connected via fold lines and all side walls are connected via fold lines, polygonal containers or boxes, cylindrical containers or boxes, and curved container-shaped containers or boxes. When a paper container is made with multiple structures, the outer and inner containers may have the same shape, or inner and outer containers with different shapes may be combined. A preferred embodiment of a paper container with multiple structures is a set of paper containers in which the inner and outer dimensions of the outer container are set so that at least a portion of the inner surface of the outer container and a portion of the outer surface of the inner container are in contact with each other at the side of the paper container. In a more preferred embodiment, both the inner and outer containers are box-shaped. In an even more preferred embodiment, the inner container is a watertight box.

[0020] When paper materials are made into boxes to produce paper containers such as boxes, a box-making machine can be used. There are no particular restrictions on the type of box-making machine used, and for example, a vertical or horizontal box-making machine can be used.

[0021] The paper container according to the present invention is characterized in that at least one of the inner container and the outer container uses a sheet having a wet bursting strength retention rate of 45% or more. By using a sheet having a wet bursting strength retention rate of 45% or more, even if the ambient temperature conditions around the paper container storing the contents suddenly change and condensation occurs, the strength of the paper container is less likely to decrease, and since paper, an environmentally friendly material, is used, the environmental burden in waste disposal is also reduced. In this embodiment, the wet bursting strength retention rate is preferably 50% or more, and more preferably 55% or more. There is no particular upper limit, but 80% or less is preferred. The wet bursting strength retention rate can be measured by the following procedure. (1) Prepare two types of samples, one of which is left untreated as a blank, and the other is soaked in water for 60 minutes (1 hour) to undergo a wetting treatment. (2) The burst strength of the two samples is measured in accordance with JIS P 8131, and the wet burst strength residual rate is calculated using the following formula: Wet burst strength remaining rate (%) = burst strength after immersion in water for 1 hour (wet burst strength, kPa) / burst strength before contact with water (kPa) × 100

[0022] Paper sheets that make up paper containers The paper sheet for constituting the paper container according to the present invention is preferably paperboard, more preferably a liner for corrugated cardboard. The basis weight of the paper sheet is not particularly limited, but may be, for example, 10 to 800 g / m 2 When the paper sheet is a single-ply paper, the basis weight is 10 to 300 g / m 2 It can be set appropriately within the range of 30 to 250 g / m 2 In addition, when the paper sheet is a multi-layer paperboard having two or more paper layers, the basis weight is 70 to 800 g / m 2The paper sheet can be appropriately set within the range. The paper sheet can be appropriately selected depending on the use, structure, etc. of the paper container. Furthermore, when a paper container is made of multiple structures, the basis weight of the paper sheet for the inner container and the paper sheet for the outer container may be the same, or paper sheets of different basis weights may be used for the inner container and the outer container. In a preferred embodiment, from the viewpoint of improving the ease of assembling the inner container, the basis weight of the paper sheet for the inner container used in the present invention is smaller than the basis weight of the paper sheet for the outer container.

[0023] (Water-resistant paper sheet for paper containers) In the paper container according to the present invention, the waterproof sheet constituting at least one of the inner container and the outer container is made of water-resistant paper with a wet bursting strength retention rate of 45% or more. The wet bursting strength retention rate of the waterproof sheet is preferably 50% or more, and more preferably 55% or more. The higher the wet bursting strength retention rate, the more difficult it is for water droplets adhering to the paper sheet and its surface to penetrate into the paper, thereby suppressing a decrease in the strength of the paper container.

[0024] The waterproof sheet used in the present invention may be water-repellent, and in a preferred embodiment, the water-repellency level defined in Paper Pulp Test Method No. 68 is R4 or higher, more preferably R6 or higher, and even more preferably R8 or higher. The higher the water-repellency level, the smaller the contact area between the paper sheet and water droplets adhering to the surface of the sheet, making it more difficult for water to penetrate the paper, thereby preventing a decrease in the strength of the paper container.

[0025] In a preferred embodiment, the waterproof sheet used in the present invention may have waterproof properties. For example, the waterproof sheet may have a surface water absorption of 155 g / m2 at 120 seconds. 2 less than 100 g / m 2 Less than 50 g / m is more preferable. 2 Here, the Cobb water absorbency of paper is determined in accordance with JIS P8140 (Cobb method) by contacting the surface side of the paper with 100 ml of distilled water and measuring the weight of water absorbed per unit area after a specified time, and the lower the Cobb water absorbency, the better the water resistance.

[0026] The waterproof sheet used in the present invention preferably has an Oken smoothness of 15 seconds or more on the surface side, more preferably 20 seconds or more, and even more preferably 25 seconds or more. When the surface smoothness of the waterproof sheet is in the above range, a high gloss can be obtained on the surface, resulting in a waterproof paper with better decorative properties.

[0027] (Paper sheets used for other parts) In the sheets constituting the paper container, the paper properties of the paper sheets used in the other parts except for the part using the waterproof sheet are not particularly limited. For example, the 120-second Cobb water absorbency of the surface is 50 g / m 2 It may be less than 45 g / m 2 It may be less than 40 g / m 2 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 of water absorbed per unit area after a specified time.

[0028] The moisture permeability of the paper sheet is not particularly limited, and is 10,000 g / m 2 24 hours or less is acceptable, 7500g / m 2 24 hours 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 the smaller the value, the higher the moisture resistance.

[0029] 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 has been 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.

[0030] Other physical properties of the paper sheet are not particularly limited and can be set appropriately depending on the use and structure of the paper container. For example, the Oken smoothness of the surface 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 2.80~5.00kPa·m 2 / g. In addition, a waterproof layer, which will be described later, may be provided on the surface side of the paper sheet.

[0031] (Paper sheet raw materials and manufacturing) As for the raw pulp of the paper sheet, as will be described later, known materials can be used without any particular restrictions for both the waterproof sheet and the paper sheets used in other parts. The paper sheet may contain recycled paper pulp or may not contain recycled paper pulp. When recycled paper pulp is contained, for example, when the paper sheet is a single-ply paper, the recycled paper pulp content of the total pulp can be preferably 10% by mass or more, more preferably 25% by mass or more, even more preferably 50% by mass or more, and most preferably 70% by mass or more, or can be 100% by mass (consisting only of pulp derived from recycled paper). Furthermore, kraft pulp can be blended as a pulp other than recycled paper pulp, or the entire amount can be kraft pulp. Furthermore, when the paper sheet is a multi-layer paperboard having two or more paper layers, the recycled paper pulp content per layer can be as described above, and the recycled paper pulp content in each layer can be different.

[0032] In the papermaking process for paper sheets, sizing agents and water repellents can be added internally or externally, and furthermore, paper strength agents can be added internally or externally to improve strength. Examples of sizing agents include rosin-based sizing agents, rosin emulsion-based sizing agents, α-carboxymethyl saturated fatty acids, neutral rosin-based sizing agents, alkyl ketene dimers (AKD), alkenyl succinic anhydrides (ASA), cationic polymer-based sizing agents, etc. Furthermore, examples of water repellents include fluorine-based resins, polyamide-based resins, waxes, etc. Furthermore, examples of paper strength agents include conventionally used paper strength agents such as polyacrylamide (PAM) and modified starch. When externally added, the coating amount is not particularly limited, and can be, for example, 10 g / m 2 It may be less than 5g / m 2 It may be less than 3g / m 2 It may be less than 2 g / m 2 The following may also be used.

[0033] If necessary, known fillers can be added to the paper sheet, such as 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, and zinc hydroxide, and organic fillers such as urea-formalin resin, polystyrene resin, and phenolic resin.

[0034] 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 sheet is not affected.

[0035] The paper sheet is produced by a known papermaking method, for example, 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, or the like, but is not limited to these.

[0036] Furthermore, to adjust the smoothness of the paper sheet, a smoothing treatment may be carried out as necessary. For the smoothing treatment, a smoothing treatment device such as a normal calender, super calender, gross calender, soft calender, thermal calender, or shoe calender can be used. The smoothing treatment device may be adjusted as appropriate in terms of the form of the pressure device, the number of pressure nips, heating, line pressure, etc. Furthermore, a coating agent such as latex, starch, pigment, water repellent, or waterproofing material (described below) may be applied to the outermost layer of the paper sheet using a known coating method in a manner depending on the intended use of the paper sheet.

[0037] In the present invention, depending on the use and structure of the paper container, the raw materials, chemicals, papermaking methods, etc. described above may be the same as or different from those of the paper sheets used in other parts of the water-repellent sheet. In a more preferred embodiment, the water-repellent sheet may be in the form of paper (waterproof paper) provided with a waterproof layer having waterproof properties as described below.

[0038] Cord base paper The corrugated board of the present invention can be obtained by laminating corrugated medium base paper to the obtained paper sheet (liner). Generally, medium base paper is corrugated using a corrugator, and liners are laminated to the front and back of the medium to produce high-strength corrugated board, but multi-layered corrugated board and single-faced corrugated board with corrugated medium base paper exposed on the surface are also known. In a preferred embodiment of the present invention, the corrugated board is one in which liners are laminated to both sides of the medium, or one in which the corrugated board is laminated to multiple layers.

[0039] The basis weight of the medium base paper is not particularly limited, but is preferably 60 to 250 g / m 2 is preferred, and 70 to 240 g / m 2 More preferably, 80 to 230 g / m 2Furthermore, depending on the application and structure of the double-walled paper container, the corrugated cardboard sheet for the inner container and the corrugated cardboard sheet for the outer container may have the same basis weight, or corrugated cardboard sheets of different basis weights may be used.

[0040] In the present invention, it is preferable to use reinforced corrug in the corrugated cardboard sheet, and it is more preferable to use water-resistant reinforced corrug. Reinforced corrug refers to a corrug that has improved compressive strength compared to a general corrug that satisfies the performance of corrug base paper specified in JIS P 3904 by adding a paper strength agent or the like during the papermaking process. Furthermore, water-resistant reinforced corrug refers to a corrug that has improved not only compressive strength but also water resistance by further adding a waterproofing agent during the reinforced corrug manufacturing process. Polyacrylamide (PAM) may be used as an internal paper strength agent, and in this case, the amount added is preferably 0.1% to 5.0% of the paper stock solids, more preferably 0.2% to 2.0%.

[0041] The medium base paper may have a clear (transparent) coating layer formed on one or both sides of the base paper by applying a coating liquid containing a starch-based compound. Starch coating refers to applying a coating liquid (surface treatment liquid) containing a starch-based compound onto the base paper using a coater (coating machine) such as a pond-type two-roll size press, a gate roll coater or rod metering size press which are film transfer coating methods, or a curtain coater or spray coater which are non-contact coating methods.

[0042] There are no particular restrictions on the amount of starch coating as long as it does not impair the strength of the medium, and the lower limit is 0.2 g / m2 in solids per side. 2 It may be more than 0.8g / m 2 It may be more than 2.0 g / m 2 It may be more than 3.0 g / m 2 It may be more than 4.0 g / m 2There is no particular upper limit to the coating amount, but if the coating amount is increased, it is necessary to reduce the basis weight of the base paper before the starch clear coating, which reduces the tensile strength and tear strength of the base paper before the starch coating, making it more likely to break. Therefore, the coating amount of the starch-based compound is set to 8.0 g / m per side. 2 Less than 6.0 g / m is preferred 2 The following may also be used.

[0043] In the present invention, various auxiliaries that are typically incorporated into starch coatings, such as dispersants, thickeners, water retention agents, antifoaming agents, water-resistant agents, and colorants, can be used as needed.

[0044] Examples of coaters that can be used to apply the starch-based compound to the medium base paper include a two-roll size press, a gate roll coater, a rod metering size press, a blade coater, a bar coater, a spray coater, an air knife coater, and a curtain coater. In the present invention, film transfer type coaters such as a gate roll coater and a rod metering size press can also be used to produce the desired effect.

[0045] As the raw material pulp for the corrug base paper, any known pulp can be used without any particular restrictions, as will be described later. It is preferable that a large amount of recycled paper pulp is blended as the raw material pulp for the corrug base paper used in the present invention. In the present invention, the blending ratio of recycled paper pulp to the total pulp is preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, and may be 90% by weight or more.

[0046] Fillers and additives to be added to the corrug base paper will be described later, but known ones can be used, and known papermaking methods can also be used. Various surface treatments can be applied to the corrug base paper, for example, surface treatment can be performed by calendering, or a lubricant can be applied to the corrug base paper. Wax-based lubricants are particularly preferred, and the application amount is 0.005 g / m. 2 ~0.1g / m 2In the present invention, it is preferable to spray the lubricant onto the calender rolls and transfer it to the paper when the base paper is passed through the calender. This is because, in addition to applying the lubricant, this method can prevent dirt from adhering to the surface of the calender rolls. As described above, applying a lubricant can more effectively prevent dirt from adhering to the surface of the calender rolls.

[0047] The obtained corrugating medium base paper can be corrugated (fluted) using a known corrugator. Any known corrugation process can be used depending on the application, and for example, A flute, B flute, C flute, E flute, F flute, G flute, AAA flute, AA flute, etc. may be applied to the corrugating medium base paper.

[0048] Processing into cardboard sheets The corrugated cardboard sheet used in the paper container of the present invention is obtained by laminating a paper sheet (liner) and a corrugated medium together using a corrugator.

[0049] Any known corrugator can be used without limitation, but a typical corrugator is composed of a single facer, a double backer, and a cutter. It also uses a glue-making device for bonding the liner and the core paper, and a device for generating heat to melt the glue.

[0050] Furthermore, when producing the corrugated cardboard sheet used in the paper container of the present invention, an adhesive is used to bond the liner and the core. However, it is preferable to use a water-resistant adhesive from the viewpoint of preventing a decrease in the strength of the corrugated cardboard box due to water wetting, condensation, humidity, etc. on the cross section of the corrugated cardboard sheet, and it is particularly preferable to use a water-resistant adhesive when producing the corrugated cardboard sheet for the inner container. A water-resistant adhesive is a normal corrugated cardboard adhesive to which a water-resistant agent has been added. The water-resistant agent is not particularly limited, and examples include those containing synthetic resin emulsion, ketone aldehyde resin, etc.

[0051] Raw material for paper sheets for paper containers and corrugated cardboard cores for paper containers The raw material pulp for the paper sheet (liner) and medium (hereinafter referred to as "paper material") used in paper containers can be any known pulp, without particular limitation, depending on the part to be used and the application. Specific examples include various wood-derived pulps such as bleached softwood kraft pulp (NBKP), bleached hardwood kraft pulp (LBKP), unbleached softwood kraft pulp (NUKP), unbleached hardwood kraft pulp (LUKP), groundwood pulp (GP), refiner ground pulp (RGP), chemical pulp (CP), thermomechanical pulp (TMP), and chemithermomechanical pulp (CTMP), as well as non-wood pulps obtained from kenaf, bagasse, bamboo, hemp, straw, etc.

[0052] The paper material may contain recycled paper pulp, or may not contain recycled paper pulp. When recycled paper pulp is contained, for example, when the paper material is single-ply paper, the recycled paper pulp content of the total pulp is preferably 10% by mass or more, more preferably 25% by mass or more, even more preferably 50% by mass or more, and most preferably 70% by mass or more, or may be 100% by mass (consisting only of pulp derived from recycled paper). Furthermore, kraft pulp may be blended as a pulp other than recycled paper pulp, or the entire amount may be kraft pulp.

[0053] Examples of waste paper pulp that can be used include waste paper pulp obtained by disintegrating unprinted waste paper such as cardboard, white paper, extra white paper, medium white paper, and white damage; printed waste paper such as fine paper, fine coated paper, medium paper, medium coated paper, and recycled paper; written waste paper; paper such as discarded confidential documents; and deinked pulp (DIP) obtained by disintegrating waste magazines and newspapers.

[0054] In the papermaking process, sizing agents and water repellents can be added internally or externally, and paper strength agents can be added internally to improve strength. Examples of sizing agents include rosin-based sizing agents, rosin emulsion-based sizing agents, α-carboxymethyl saturated fatty acids, neutral rosin-based sizing agents, alkyl ketene dimers (AKD), alkenyl succinic anhydrides (ASA), and cationic polymer-based sizing agents. Examples of water repellents include fluorine-based resins, polyamide-based resins, and waxes. Examples of paper strength agents include traditionally used paper strength agents such as polyacrylamide (PAM) and modified starch.

[0055] Furthermore, known fillers can be added to the paper stock as needed, and inorganic and organic fillers can be used without restriction. 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, and zinc hydroxide. Examples of organic fillers include urea-formalin resin, polystyrene resin, and phenolic resin.

[0056] 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 material is not affected.

[0057] The paper stock can be produced by a known papermaking method, for example, 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, or the like, but is not limited to these.

[0058] Furthermore, to adjust the smoothness of the paper material of the present invention, a smoothing treatment may be carried out as necessary. For the smoothing treatment, a smoothing treatment device such as a normal calender, super calender, gross calender, soft calender, thermal calender, or shoe calender can be used. The smoothing treatment device may be adjusted as appropriate by adjusting the shape of the pressure device, the number of pressure nips, heating, line pressure, etc.

[0059] Adding water resistance to paper In the water-resistant sheet constituting the paper container of the present invention, water resistance is imparted to the paper by a known method such as adding a wet strength agent. More preferably, the wet strength agent used in the present invention includes polyacrylamide resins, polyamide resins, polyamine resins, acrylic resins, melamine resins, urea resins, polyamide-epichlorohydrin resins, etc.

[0060] The wet strength agent is preferably added in an amount of 0.1% by mass to 1.5% by mass, more preferably 0.5% by mass to 1.0% by mass, based on the total pulp during the manufacturing process. The amount of the wet strength agent can be determined by elemental analysis such as the Kjeldahl method or energy dispersive X-ray analysis. In the present invention, the amount of the wet strength agent contained in the paper layer refers to a converted value assuming that all of the nitrogen element determined using the Kjeldahl method is derived from the resin contained in the wet strength agent. The paper layer preferably contains the wet strength agent in an amount of 0.05% by mass to 0.70% by mass, based on the total amount of pulp.

[0061] Water-repellent layer A water-repellent layer may be added to the water-resistant sheet of the present invention. This can be achieved by laminating a synthetic resin film to a paper substrate, applying a water-repellent agent such as an acrylic emulsion or a polyester emulsion to the paper substrate, or providing a porous layer containing a polymer of a radically polymerizable monomer on an anchor layer primarily composed of a pigment and a binder. A more preferred embodiment of the present invention is a water-repellent layer containing wax. Examples of waxes that can be included in the water-repellent layer include polyethylene wax, Fischer-Tropsch wax, synthetic oil-based waxes (fatty acid esters, fatty acid amides, ketones, and amines), synthetic waxes such as hydrogenated oils, and natural waxes such as beeswax, Japan wax, paraffin wax, and microcrystalline wax. These waxes can be used alone or in combination, with hydrocarbon waxes containing paraffin being particularly preferred.

[0062] waterproof layer In the waterproof sheet constituting the paper container of the present invention, a waterproof layer may be provided by a known method, such as applying a waterproof material to the paper material and laminating a synthetic resin film. In a preferred embodiment, the waterproof layer is provided by coating, and in a more preferred embodiment, the waterproof layer contains a synthetic resin and wax. The synthetic resin preferably contains at least one of a styrene-based resin, an acrylic-based resin, and a polyolefin-based resin. In particular, the synthetic resin is preferably a styrene-based resin and / or an acrylic-based resin.

[0063] The styrene-based resin that can be contained in the waterproof layer preferably has a copolymerization ratio of 50 mass% or more of a styrene-based monomer having a styrene skeleton in its structure, and may be composed only of a polymer of a styrene-based monomer.

[0064] Examples of styrene-based monomers include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, p-tert-butylstyrene, α-methylstyrene, and α-methyl-p-methylstyrene.

[0065] 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 methacrylic acid and acrylic acid, unsaturated dicarboxylic anhydrides such as maleic acid and itaconic acid, unsaturated nitriles such as acrylonitrile and methacrylonitrile, and conjugated dienes such as 1,3-butadiene and 2-methyl-1,3-butadiene. These can be used alone or in combination of two or more.

[0066] The acrylic resin that can be contained in the waterproof layer is a resin in which the copolymerization ratio of acrylic acid, methacrylic acid, and acrylic monomers that are derivatives of these is 50% by mass or more, and it may be composed only of polymers of acrylic monomers.

[0067] 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, and the acrylic resin may be a polymer of one or more monomers selected from these acrylic monomers.

[0068] 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 may be used alone or in combination of two or more.

[0069] In the present invention, the waterproof layer may contain a wax. Examples of waxes that can be contained in the waterproof layer include synthetic waxes such as polyethylene wax, Fischer-Tropsch wax, oil-based synthetic waxes (fatty acid esters, fatty acid amides, ketones, and amines), and hydrogenated oils, as well as natural waxes such as beeswax, Japan wax, paraffin wax, and microcrystalline wax. These waxes can be used alone or in combination of two or more, with paraffin-containing hydrocarbon waxes being particularly preferred.

[0070] In the present invention, a pigment may be applied to improve whiteness, provided that it does not impair water resistance. It is preferable that the whiteness of the waterproof paper surface be increased by at least 1% compared to the whiteness before coating. 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, silicates, colloidal silica, satin white, mica, and montmorillonite. These pigments can be used alone or in combination of two or more. Among these pigments, kaolin, calcium carbonate, or mica, which have flat particles, are particularly suitable because they do not impair water resistance. It is preferable that such flat-shaped inorganic pigments have an aspect ratio of 10 or more. The pigment content in the waterproof layer is preferably 5 to 40% by mass, more preferably 10 to 35% by mass. If the pigment content is less than 5% by mass, the whiteness improvement effect will not be sufficient, and if it exceeds 40% by mass, the moisture-proof and waterproof functions of the waterproof layer due to the synthetic resin component may not be fully exhibited, which is undesirable.In addition, other coating agents such as binders, stabilizers, antifoaming agents, viscosity improvers, water-retaining agents, preservatives, and colorants may also be contained.

[0071] The waterproof layer can be formed by coating a waterproof material containing the above-mentioned components on a paper substrate and drying it. The coating amount of the waterproof layer is 4 to 20 g / m 2 It is preferable to set the thickness to 5 to 15 g / m 2 It is more preferable to set the thickness to 20 g / m 2 If the temperature exceeds this range, further improvement in waterproofness cannot be expected, and the manufacturing cost may increase.

[0072] In a preferred embodiment, the waterproof layer 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 a sample into strips and observing the cross sections at any 10 points using an electron microscope.

[0073] In addition, the moisture permeability per unit thickness of the waterproof layer is 15 (g / m 2 24h) / μm or less is preferable, and 10 (g / m 2 24h) / μm or less is more preferable, and 7 (g / m 2 ·24h) / μm or less is even more desirable. Here, the moisture permeability per unit thickness of the waterproof layer is calculated by dividing the moisture permeability measured from the waterproof layer side of the waterproof paper in accordance with JIS Z 0208 by the average waterproof layer thickness.

[0074] Waterproof paper can be produced by coating at least one side of a paper stock with a waterproofing material and drying the coated waterproofing material. The waterproof layer can be formed by applying a coating agent using a known coating method, such as air knife coating, curtain coating, blade coating, gate roll coating, or die coating. The coating layer may be a single layer or multiple layers. Multiple coating layers may be applied sequentially, or two or more layers may be applied simultaneously using curtain coating or other methods. When multiple coating layers are applied, at least one layer must be waterproof, and it is preferable for the waterproofing material to be applied as the outermost coating layer. When drying the coating layer, the temperature of the coating layer at the exit of the drying process is preferably adjusted to be less than 120°C. The coating speed when applying the coating agent can be appropriately set taking into account the viscosity of the coating agent and the target coating weight.

[0075] In a preferred embodiment, the coating agent is applied to the paper stock by a contour coating method such as air knife coating or curtain coating, which ensures a uniform amount of coating agent on the paper stock surface, resulting in a uniform coating film thickness and preventing the occurrence of blisters in the coating layer during the subsequent drying process. Furthermore, the amount of coating agent used can be reduced compared to contact coating methods, thereby reducing production costs.

[0076] The coating agent applied to the paper stock is dried to form a coating layer. In this drying process, the coating temperature at the exit is preferably less than 120°C, and may be adjusted to 100°C or less. If the coating temperature at the exit is 120°C or higher, the incidence of blisters in the coating layer may increase, and blocking may occur in the waterproof paper that is wound after the coating layer has been formed. On the other hand, the coating temperature at the exit is preferably 60°C or higher, more preferably 70°C, and can also be 80°C or higher. If the coating temperature at the exit is less than 60°C, not only may blocking occur in the waterproof paper that is wound after the coating layer has been formed, but the coating may not dry sufficiently, resulting in insufficient waterproof and moisture-proof performance.

[0077] The coating temperature at the drying process exit can be set taking into account the basis weight and thickness of the paper stock. For example, paper stock with a high basis weight and thickness requires more heat for drying than paper stock with a low basis weight and thickness, but it also tends to be more susceptible to blisters on the coating surface. The reason for this is not limited to specific factors, but thick paper often has a higher basis weight and thickness and lower air permeability than thin paper. Even with the same moisture content, much of the moisture vaporized inside the paper stock during the drying process cannot fully escape, making it more likely to develop blisters on the coating surface. Therefore, the greater the basis weight and thickness of the paper stock, the higher the coating temperature at the drying process exit, within the above range, and the lower the temperature at the drying process entrance.

[0078] Here, the outlet of the drying process refers to the outlet of the drying zone when there is one drying zone in the drying process, and refers to the outlet of the drying zone on the most downstream side when there are multiple drying zones in the drying process.

[0079] The temperature of the coating layer at the exit of the drying process can be adjusted by adjusting the drying time and the temperature of the drying zone. The drying time is determined by the paper material feed speed, the number and length of the drying zones, and the equipment capacity of the drying zones (air volume, infrared output), etc. Furthermore, any known drying method can be used, such as a steam cylinder heating drying method, a hot air drying method, a gas-type infrared drying method, or an electric infrared drying method. Any one of these methods can be used alone or in combination of two or more. [Example]

[0080] The present invention will be described in more detail below using specific examples, but the present invention is not limited to the following specific examples. In this specification, unless otherwise specified, concentrations and the like are based on weight, and numerical ranges include their endpoints.

[0081] Liner and corrug base paper manufacturing (1) Liner sample A The raw materials for the back layer, made of 100% recycled corrugated paper pulp, the middle layer, made of 100% recycled paper pulp, and the top layer, made of 70% unbleached kraft pulp and 30% recycled corrugated paper pulp, were mixed together in a weight ratio of back layer:middle layer:top layer = 25:60:15, dried in a dryer, and smoothed using a calender to produce liner sample A (basis weight: 282.6 g / m 2 , 120-second Cobb water absorption of the surface: 12.9 g / m 2 ). (2) Liner sample B A waterproofing agent consisting of 100 parts styrene-acrylic resin (Michaelman MC1548A) and 5 parts wax emulsion (Seiko PMC WR3932) was applied to the surface of liner sample A using an air knife at a rate of 10.0 g / m. 2The coating was applied and then dried with hot air so that the temperature of the coating layer at the exit of the drying process was 80°C, to obtain liner sample B (basis weight: 291.4 g / m 2 , 120-second Cobb water absorption of the surface: 0.1 g / m 2 ). (3) Liner sample C Liner sample C was produced in the same manner as liner sample A, except that the amount of wet strength agent added to the raw materials of each layer was 0.25% (basis weight: 281.3 g / m 2 , 120-second Cobb water absorption of the surface: 27.7 g / m 2 ). (4) Cord base paper A pulp slurry containing 100% recycled corrugated pulp was mixed with 0.4% wet strength agent to prepare a paper stock. A single layer of paper was then made from this paper stock, dried in a dryer, and smoothed using a calender to produce corrugating base paper (basis weight: approximately 200 g / m). 2 ).

[0082] Evaluation of liner and corrugating materials. The paper quality of the liner samples and medium base 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 using an electron microscope. The average value was calculated as 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) Oken Smoothness was measured in accordance with JIS P 8155 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 compressive strength was divided by the basis weight to calculate the specific compressive strength. (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. (Wet burst strength residual rate) Each sample was placed in water and left for 60 minutes (1 hour), and then the water was wiped off. The burst strength of the sample was measured in accordance with JIS P 8131, and the burst strength index was calculated by dividing this value by the basis weight. The value obtained by dividing this value by the burst strength index (the burst strength index of the sample before contact with water) was taken as the wet burst strength residual rate. (Cobb Water Absorbency) Measurement was carried out 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 the usual specified time of 120 seconds (2 minutes), and also 30 minutes.

[0083] [Table 1]

[0084] Corrugated cardboard sheet manufacturing Corrugated cardboard sheets for box making were produced from each liner sample. Specifically, for liner samples A to C, the front and back liners were used in the combinations shown in Table 2, and the front and back liners were bonded together via medium base paper so that the front layer was on the outside of the cardboard sheet to produce the cardboard sheet. The thickness of the cardboard 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.

[0085] Manufacturing of double-walled paper containers The resulting cardboard sheets were placed with the outer liner facing inward to create an A-type (JIS Z 1507 0201 format) cardboard box (external dimensions of main body: length 28.1 cm x width 24.6 cm x height 23.5 cm, internal dimensions: length 27.1 cm x width 23.6 cm x depth 22.5 cm) for the outer container, and a B-flute (3 mm thick) sheet was used as the inner container to create a cardboard container as shown in Figure 1 (external dimensions of main body: length 23.8 cm x width 23.6 cm x height 22.3 cm, internal dimensions: length 23.2 cm x width 23 cm x depth 21.7 cm). The inner container was then placed inside the A-type cardboard box that would serve as the outer container, producing a double-walled paper container. The inner / external volume ratio of the double-walled paper container was 71.3%. As a comparative example, a paper container was produced in the same manner as above, without using an A-type cardboard box as the outer container, but as an inner container only.

[0086] [Table 2]

[0087] Condensation resistance evaluation A vinyl bag containing a carboxymethyl cellulose solution (Sunrose (registered trademark) manufactured by Nippon Paper Industries Co., Ltd., product number: F350HC, concentration 1%) that had been sufficiently cooled in advance in a refrigerator at 5°C was placed into each cardboard container, and the lid was then sealed. The sealed cardboard container was left in an environment of 30°C and 85% humidity, and the box compressive strength was measured and evaluated after 1 day, 2 days, and 5 days. The box compressive strength was measured according to the following procedure in accordance with JIS Z 0212. (a) Place the box with the lid on in the center of the compression tester. (b) Start the compression testing machine and gradually apply a downward force evenly across the entire top surface of the box. (c) Read the load when the side of the box is deformed and use this as the box compressive strength. (d) The rate of decrease in box strength before and after storage (=box compressive strength after storage / box compressive strength before storage x 100) was calculated, and the condensation resistance was evaluated based on the following criteria. ○: Box strength reduction rate is less than 50% ×: Box strength reduction rate is 50% or more The results are shown in Table 3.

[0088] [Table 3]

[0089] The above results demonstrate that the paper container of the present invention, regardless of the portion using water-resistant paper, has sufficient box compressive strength compared to the box sample ccCC using only ordinary corrugated cardboard and the case where the inner container is used alone. The liner used in the present invention can be suitably used as a liner for manufacturing boxes for bag-in-box applications. [Explanation of symbols]

[0090] 1 box 2 Flat plate part 3 1st fold line 4 First side wall 5 Second fold line 6 Second side wall 7 Third fold line 8 4th fold line 9 5th fold line 10 Folding section 11a,11b Projection piece 12 recess 13a, 13b protrusion 14 6th fold line 15 Locking piece 16a,16b fitting opening 17 Connection part 18 Cut 19 7th fold line

Claims

1. (a) a paper outer container; (b) A paper container having a paper inner container provided inside the outer container, A paper container characterized in that at least one of the inner container and the outer container uses a sheet having a wet burst strength retention rate of 45% or more and 80% or less, as determined by dividing the burst strength after immersion in water for 1 hour by the burst strength before contact with water.

2. The paper container according to claim 1, wherein at least the outer container is box-shaped.

3. 3. The paper container according to claim 1, wherein the sheet constituting the inner container and / or the outer container is a cardboard sheet.

4. A method for using a paper container, in which an inner container is placed inside an outer container to contain an item, characterized in that at least one of the inner container or the outer container uses a sheet whose wet burst strength retention rate, calculated by [burst strength after immersion in water for 1 hour] / [burst strength before contact with water], is 45% or more and 80% or less.

5. A method for manufacturing a paper container having a double structure, comprising: (a) Producing a paper container for an inner container and / or an outer container using a sheet having a wet burst strength retention rate of 45% or more and 80% or less, calculated by dividing the burst strength after immersion in water for 1 hour by the burst strength before contact with water; (b) Placing the inner container inside the outer container; The above method, comprising:

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