Heat-sealable paper and packaging method

Abstract

To provide heat seal paper and a packaging method which prevent opening of a heat seal portion when packaging contents. The heat-sealable paper (1) comprises a paper substrate (10) and a heat-sealable resin layer (12) in this order, and the mass per unit area of ​​the heat-sealable resin layer (12) is 3 g / m 2 The heat-sealable resin layer 12 contains a water-dispersible resin, and the water-dispersible resin contains a urethane resin, and the content of the urethane resin in the heat-sealable resin layer 12 exceeds 5 mass% relative to 100 mass% of the total amount of the water-dispersible resin.

Description

[Technical Field]

[0001] The present invention relates to heat-sealable paper and packaging methods. [Background technology]

[0002] Conventionally, multilayer sheets having heat-sealing properties have been widely used for food packaging materials, pharmaceutical packaging materials, chemical packaging materials, etc. Such multilayer sheets usually have a substrate and a heat-sealing layer, and a package can be formed by heat-sealing the heat-sealing layers together. Paper substrates, plastic substrates, etc. have been used as the substrates for multilayer sheets. However, with increasing awareness of environmental issues in recent years, environmental pollution caused by the disposal of petroleum-derived plastic substrates has become a concern. Therefore, the use of paper substrates, which have a smaller environmental impact, has been considered.

[0003] As a technique relating to a multilayer sheet using a paper base material, for example, Patent Document 1 describes a multilayer sheet comprising a paper base material mainly composed of unbleached softwood kraft pulp and a heat seal layer laminated on one side of the paper base material, in which the folding endurance of the paper base material in the machine direction is 500 times or more and 1,000 times or less, the folding endurance in the width direction is 80 times or more and 200 times or less, the Beck smoothness of the surface of the heat seal layer laminated surface is 3 seconds or more and 230 seconds or less, the main component of the heat seal layer is an ionomer resin, and the coating amount of the heat seal layer is 1.5 g / m 2 More than 10.0g / m 2 The following heat seal paper is disclosed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-024906 [Overview of the Initiative] [Problem to be solved by the invention]

[0005] Further applications of heat-sealable paper have been proposed, including its use as a packaging material to replace corrugated cardboard. Corrugated cardboard is bulky, making storage difficult, and posing challenges to resource conservation. It is hoped that lightweight and compact heat-sealable paper can solve these problems. From this perspective, heat-sealable paper is required to possess sufficient strength to serve as a substitute for corrugated cardboard.

[0006] However, packaging made of heat-sealable paper generally has poor impact resistance, which can lead to problems such as the heat-sealed portion easily opening up depending on the weight and shape of the product when packaging it. In this regard, for example, the packaging using heat-sealable paper described in Patent Document 1 above does not sufficiently suppress the opening of the heat-sealed portion, and therefore there is room for improvement.

[0007] This invention has been made in view of the above circumstances, and aims to provide heat-sealable paper and a packaging method that prevent the heat-sealed portion from opening when packaging contents. [Means for solving the problem]

[0008] As a result of diligent research to achieve the above-mentioned objective, the inventors have developed a heat-sealable paper comprising a paper substrate and a heat-sealable resin layer in that order, wherein the mass per unit area of ​​the heat-sealable resin layer is 3 g / m². 2 In summary, we have found that the heat-sealable resin layer contains a water-dispersible resin, specifically a urethane resin, and that the content of the urethane resin relative to 100% by mass of the total amount of water-dispersible resin in the heat-sealable resin layer exceeds 5% by mass, thereby completing the present invention.

[0009] That is, the present invention is as follows.

[0010] (1) A heat-sealable paper comprising a paper substrate and a heat-sealable resin layer in this order, wherein the mass per unit area of ​​the heat-sealable resin layer is 3 g / m 2 The heat-sealable paper is as described above, wherein the heat-sealable resin layer contains a water-dispersible resin, and the water-dispersible resin contains a urethane resin, and the content of the urethane resin in the heat-sealable resin layer exceeds 5 mass% relative to 100 mass% of the total amount of the water-dispersible resin. (2) The heat-sealable paper according to (1), wherein the heat-sealable resin layer is located on the outermost surface of the heat-sealable paper. (3) The tensile energy per unit volume of the heat-sealable resin layer is 150 MJ / m 3 The heat seal paper is the heat seal paper described in (1) or (2). (4) The heat seal paper according to (1) or (2) further contains at least one selected from the group consisting of styrene-butadiene rubber and ethylene-vinyl acetate copolymer as the water-dispersible resin. (5) The heat seal paper according to (1) or (2) is for pillow packaging. (6) This is a packaging method in which a package is formed by pillow packaging using the heat seal paper described in (1) or (2), and an article is packaged in the package. [Effects of the Invention]

[0011] The present invention has been made in consideration of the above-mentioned circumstances, and provides heat-sealable paper and a packaging method that do not cause openings in the heat-sealed portion when packaging contents. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view showing an example of the heat seal paper according to the present embodiment. [Figure 2] FIG. 2 is a perspective view showing an example of a state in which contents are packaged with the heat seal paper according to this embodiment. [Figure 3] FIG. 3 is a diagram illustrating a pillow packaging method according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. The following present embodiment is an example for explaining the present invention, and is not intended to limit the present invention to the following content. The present invention can be carried out by appropriately modifying it within the scope of its gist.

[0014] In the drawings, the same elements are given the same reference numerals, and redundant explanations will be omitted. Furthermore, unless otherwise specified, the positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios of the drawings are not limited to the ratios shown in the drawings.

[0015] 1. Heat sealing paper

[0016] FIG. 1 is a cross-sectional view showing an example of a heat seal paper 1 according to this embodiment.

[0017] The heat seal paper 1 according to this embodiment is a heat seal paper 1 including a paper substrate 10 and a heat sealable resin layer 12 in this order, and the mass per unit area of ​​the heat sealable resin layer 12 is 3 g / m 2 The heat-sealable resin layer 12 contains a water-dispersible resin. The water-dispersible resin is a urethane resin, and the content of the urethane resin in the heat-sealable resin layer 12 exceeds 5% by mass relative to 100% by mass of the total amount of the water-dispersible resin. A packaging bag using this heat-sealable paper 1 does not open at the heat-sealed portion when packaging contents.

[0018] From the viewpoint of achieving the above-mentioned effects more effectively, it is preferable that the heat-sealable resin layer 12 of the heat-sealable paper 1 according to this embodiment is located on the outermost surface of the heat-sealable paper 1. Unless otherwise specified, the "heat-sealable paper 1" referred to here is sufficient as long as it includes the paper substrate 10 and the heat-sealable resin layer 12 in this order, and is not necessarily limited to a two-layer configuration. Nor is it limited to a configuration in which these two layers are in contact. For example, it goes without saying that a three-layer or more configuration in which another layer is placed between these two layers may be used, if necessary.

[0019] According to this embodiment, the heat seal paper 1 can be made such that openings do not occur in the heat seal portion when packaging contents. In particular, one of its preferred modes is that when used for pillow packaging in which contents are packaged continuously, openings in the heat seal portion can be effectively prevented even when the contents are heavy, weighing 1 kg or more. This is because the mass per unit area of ​​the heat sealable resin layer 12 is 3 g / m 2 As described above, the heat-sealable resin layer 12 contains a water-dispersible resin, and by containing a urethane resin as the water-dispersible resin, it is possible to obtain sufficient heat-seal strength, and further, by having the urethane resin content in the heat-sealable resin layer 12 exceed 5% by mass relative to 100% by mass of the total amount of water-dispersible resin, it is thought that heat-seal strength can be ensured such that openings do not occur in the heat-sealed portion, even when heavy items are packaged continuously in pillow packaging. The reason why openings do not occur in the heat-sealed portion, even when heavy items are packaged, is thought to be because the urethane resin has excellent extensibility and tough properties (however, the functions and effects of this embodiment are not limited to these).

[0020] The heat seal strength of the heat seal paper 1 according to this embodiment is preferably greater than 6.5 N / 15 mm, more preferably 7.0 N / 15 mm or greater, and even more preferably 7.5 N / 15 mm or greater. A heat seal strength equal to or greater than the aforementioned lower limit allows for better heat sealing during bag production using a pillow packaging machine. The upper limit of the heat seal strength is not particularly limited, but is preferably 30.0 N / 15 mm or less, and more preferably 25.0 N / 15 mm or less. The heat seal strength can be adjusted, for example, by controlling the mass of the heat sealable resin layer 12 per unit area, the basis weight of the paper substrate 10, etc. The heat seal strength can be measured, for example, by pressing the surfaces of the heat seal paper 1 having the heat sealable resin layer 12 together under conditions of 160°C, 0.2 MPa, and 1 second, and then peeling them at a tensile speed of 20 mm / min using a tensile tester (manufactured by Shimadzu Corporation, product name "Autograph AG-500NIS") in accordance with JIS Z 1707, as the maximum load.

[0021] The basis weight of the heat seal paper 1 is not particularly limited, but is preferably 30 to 130 g / m 2 The lower limit is preferably 40 g / m 2 More preferably, it is 50 g / m or more. 2 The upper limit is 120 g / m 2 More preferably, it is 110 g / m or less. 2 It is even more preferable that the basis weight is within the above range. When the basis weight of the heat seal paper 1 is within the above range, the heat seal paper 1 has good lightness and flexibility, making it easier to make bags. There is also a tendency for the balance with strength to be even better. When the basis weight of the heat seal paper 1 is below the above upper limit, the stiffness of the heat seal paper 1 can be prevented from becoming too high, preventing deterioration of transportability. The basis weight can be measured in accordance with JIS P 8124:2011.

[0022] The thickness of the heat seal paper 1 is not particularly limited, but is preferably 40 to 150 μm. The lower limit is more preferably 50 μm or more, and even more preferably 60 μm or more. The upper limit is more preferably 130 μm or less, and even more preferably 120 μm or less. When the thickness of the heat seal paper 1 is equal to or greater than the above-mentioned lower limit, the strength of the heat seal paper 1 tends to be improved, and unintentional tearing tends to be more effectively prevented. Furthermore, when the thickness of the paper substrate 10 is equal to or less than the above-mentioned upper limit, the lightness and flexibility tend to be improved, and bag production tends to be easier. The thickness can be measured in accordance with JIS P 8118:2014.

[0023] Each component of the heat seal paper 1 will be described below.

[0024] (Paper base material 10)

[0025] The paper substrate 10 is not particularly limited and can be appropriately selected depending on the application of the heat seal paper 1. Examples of such paper substrates 10 include fine paper, kraft paper, Clupak paper, glassine paper, parchment paper, rayon paper, gravure paper, art paper, coated paper, recycled paper, etc. Among these, kraft paper, Clupak paper, and glassine paper are more preferred, and unbleached kraft paper is even more preferred. One layer of these paper substrates 10 may be used alone, or two or more layers of the same or different paper substrates 10 may be laminated together.

[0026] The basis weight of the paper substrate 10 is not particularly limited, but is preferably 20 to 200 g / m 2 The lower limit is preferably 30 g / m 2 More preferably, it is 40 g / m or more. 2 The upper limit is 150 g / m 2 More preferably, it is 100 g / m or less. 2 It is more preferable that the basis weight is less than or equal to 1000. When the basis weight of the paper base 10 is within the above range, the balance between lightness and strength of the paper base 10 tends to be better. The basis weight can be measured in accordance with JIS P 8124:2011.

[0027] The thickness of the paper substrate 10 is not particularly limited, but is preferably 20 to 200 μm. The lower limit is more preferably 30 μm or more, and even more preferably 40 μm or more. The upper limit is more preferably 150 μm or less, and even more preferably 100 μm or less. When the thickness of the paper substrate 10 is above the lower limit mentioned above, the strength of the paper substrate 10 is improved, and it tends to be less likely to tear unintentionally. Also, when the thickness of the paper substrate 10 is below the upper limit mentioned above, it tends to be lighter and more flexible. Note that "thickness of the paper substrate 10" refers to the total thickness of the paper substrate 10, and if the paper substrate 10 is a substrate consisting of multiple layers, it refers to the total thickness of all the layers constituting the paper substrate 10. The thickness can be measured in accordance with JIS P 8118:2014.

[0028] The paper substrate 10 is preferably subjected to a surface modification treatment to improve adhesion on the side on which the heat-sealable resin layer 12 is provided. Examples of surface modification treatments include the formation of a primer layer, ozone treatment, corona treatment, plasma treatment, and ultraviolet treatment. Among these, ozone treatment and corona treatment are more preferred. These surface treatments may be performed individually or in combination.

[0029] (Heat-sealable resin layer 12)

[0030] The heat-sealable paper 1 according to this embodiment comprises a paper substrate 10 and a heat-sealable resin layer 12 in that order, but it is preferable that the heat-sealable resin layer 12 be present on at least one side of the paper substrate 10. Furthermore, the heat-sealable paper 1 only needs to have at least one heat-sealable resin layer 12 on one side of the paper substrate 10, but it may have two or more layers. The compositions of the two or more heat-sealable resin layers 12 may be the same or different.

[0031] The heat-sealable resin layer 12 contains a water-dispersible resin. A water-dispersible resin is, for example, a resin that is not water-soluble but becomes finely dispersed in water, such as in an emulsion or suspension.

[0032] In this embodiment, the water-dispersible resin includes a urethane resin. In this embodiment, the water-dispersible resin contained in the heat-sealable resin layer 12 may be only a type of urethane resin, or it may contain other water-dispersible resins other than urethane resin. In this case, the content of urethane resin relative to 100% by mass of the total amount of water-dispersible resin exceeds 5% by mass. By setting the proportion of urethane resin within this range, the heat-sealable resin layer 12 stretches when the contents are filled, resulting in excellent impact resistance. Even when packaging contents weighing 1 kg or more in the heat-sealable paper 1 packaging bag, it is possible to suppress the opening of the heat-sealed portion or tearing of the paper due to the weight of the contents. Furthermore, since the heat-sealable paper 1 according to this embodiment stretches at least the heat-sealable resin layer 12, and as a result has excellent impact resistance, various types of paper substrates 10 can be applied to the heat-sealable paper 1 as described above (however, the effects and benefits according to this embodiment are not limited to these).

[0033] From the viewpoint of exhibiting these effects more effectively, the lower limit of the urethane resin content relative to 100% by mass of the total amount of water-dispersible resin is preferably 6% by mass or more, more preferably 8% by mass or more, even more preferably 10% by mass or more, even more preferably 20% by mass or more, and even more preferably 50% by mass or more. The upper limit of the urethane resin content is not particularly limited, but for example, it is preferably 90% by mass or less, and more preferably 80% by mass or less. This makes it possible to impart more suitable extensibility to the heat-sealable resin layer 12, and effectively suppresses deterioration of the heat-sealable resin layer 12 due to moisture absorption and hydrolysis of the urethane resin during storage.

[0034] As the urethane resin, for example, polyether-based, polyester-based, polycarbonate-based, and other urethane resins are preferred. Among these, polyether-based and polycarbonate-based resins are preferred in terms of flexibility, strength, and hydrolysis resistance. Such urethane resins may be commercially available products. Examples of commercially available products include "Hydran WLS-230" manufactured by DIC Corporation and "Superflex: Variety 470" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. These may be used alone or in combination of two or more types.

[0035] In this embodiment, the heat-sealable resin layer 12 may further contain a water-dispersible resin other than the urethane resin. Preferably, the water-dispersible resin further contains at least one selected from the group consisting of styrene-butadiene rubber and ethylene-vinyl acetate copolymer. This effectively alleviates deterioration due to hydrolysis of the urethane resin contained in the heat-sealable resin layer 12, and more effectively ensures the storage stability of the heat-sealable paper 1.

[0036] The styrene-butadiene rubber is preferably one having a single film elongation rate of 100% or more. Such styrene-butadiene rubber may be a commercially available product. Examples of commercially available products include "Narstar SR-107" manufactured by Nippon A&L Co., Ltd. and "Narstar SR-102" manufactured by Nippon A&L Co., Ltd. These may be used alone or in combination of two or more.

[0037] The ethylene-vinyl acetate copolymer preferably has a free-standing elongation of 100% or more. Commercially available ethylene-vinyl acetate copolymers may be used. Examples of commercially available products include "Sumikaflex (registered trademark) S-510HQ" and "Sumikaflex (registered trademark) S-470HQ" manufactured by Sumika Chemtex Co., Ltd. These may be used alone or in combination of two or more.

[0038] The blending ratio of the above-mentioned urethane resin to the styrene-butadiene rubber and ethylene-vinyl acetate copolymer is not particularly limited, but when it is desired to satisfy the required levels of various physical properties and to more effectively improve extensibility, the total ratio of urethane resin:styrene-butadiene rubber and ethylene-vinyl acetate copolymer is preferably 100:0 to 10:90, more preferably 100:0 to 20:80, even more preferably 100:0 to 30:70, and even more preferably 100:0 to 50:50.

[0039] Furthermore, the tensile energy per unit volume of the heat-sealable resin layer 12 is 150 MJ / m 3 It is preferable that it be greater than or equal to 200 MJ / m. The lower limit is 200 MJ / m 3 It is more preferable that the value be greater than or equal to 250 MJ / m 3 It is even more preferable that the value be greater than or equal to the above. The upper limit is not particularly limited, but is 1000 MJ / m 3 Preferably, it is 900MJ / m or less. 3 It is more preferable that the tensile energy per unit volume is equal to or greater than the above-mentioned lower limit. When the tensile energy per unit volume is equal to or greater than the above-mentioned lower limit, the extensibility of the heat-sealable resin layer 12 is further improved to a range suitable for a packaging bag when filling the contents into the packaging bag, resulting in a packaging bag with even better impact resistance, and more effectively preventing the opening of the heat-sealed portion and paper tearing. Note that the tensile energy per unit volume of the heat-sealable resin layer 12 is the tensile energy of the heat-sealable resin layer 12 alone, excluding other layers such as the paper substrate 10. The "tensile energy of the heat-sealable resin layer 12 alone" refers to the tensile energy of the entire heat-sealable resin layer 12; when the heat-sealable resin layer 12 is composed of multiple layers, it refers to the tensile energy measured for the heat-sealable resin layer 12 composed of multiple layers as a single layer.

[0040] (Content of heat-sealable resin layer 12)

[0041] The mass per unit area of ​​the heat-sealable resin layer 12 contained in the heat-sealable paper 1 according to this embodiment is 3.0 g / m². 2That's all. The lower limit is 4.0 g / m 2 Preferably, it is 6.0 g / m 2 The upper limit is not particularly limited, but for example, it is 15.0 g / m 2 Preferably, it is 12.0 g / m 2 It is more preferable that the mass per unit area of ​​the heat-sealable resin layer 12 is equal to or greater than the above-mentioned lower limit. When the mass per unit area of ​​the heat-sealable resin layer 12 is equal to or greater than the above-mentioned upper limit, sufficient heat-seal strength can be ensured, and the impact resistance of the packaging bag can be further improved. When the mass per unit area of ​​the heat-sealable resin layer 12 is equal to or less than the above-mentioned upper limit, blocking during storage and the occurrence of stains during the bag-making process can be more effectively suppressed, and this is also preferable from the standpoint of environmental consideration.

[0042] Unless otherwise specified, the "mass per unit area of ​​the heat-sealable resin layer 12" refers to the weight of the layer 12 per unit area, and means, for example, the amount of the layer 12 formed on the object to be coated (such as the paper substrate 10 or another layer), and corresponds to the amount of solid components contained in the layer 12 per unit area. In this embodiment, when the layer 12 contains two or more solid components, the "mass per unit area" refers to the total amount of these solid components unless otherwise specified.

[0043] The content of the water-dispersible resin in the heat-sealable resin layer 12 is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 100% by mass (i.e., the heat-sealable resin layer 12 is composed only of the water-dispersible resin). This allows for the production of heat-sealable paper 1 with even higher heat-seal strength.

[0044] The heat-sealable resin layer 12 is made of a water-dispersible resin having a mass per unit area of ​​3.0 g / m 2 The lower limit is preferably 4.0 g / m or more. 2 Preferably, it is 6.0 g / m 2The upper limit is not particularly limited, but for example, it is 15.0 g / m 2 Preferably, it is 12.0 g / m 2 The following is more preferable. This makes it possible to obtain a heat-sealable paper 1 with even higher heat-seal strength.

[0045] The heat-sealable resin layer 12 may further contain various additives in addition to the water-dispersible resin, as needed. While not particularly limited, examples of additives include defoamers, thickeners, polysaccharides, neutralizing agents, plasticizers, preservatives, pH adjusters, crosslinking agents, antiblocking agents, and dyes.

[0046] 2. Heat seal paper manufacturing method

[0047] The heat-sealable paper 1 can be manufactured, for example, by manufacturing the paper substrate 10 described above and forming the heat-sealable resin layer 12 described above on at least one surface of the paper substrate 10.

[0048] The method for manufacturing the paper substrate 10 is not particularly limited, and can be manufactured, for example, by conventionally known methods.

[0049] The method for forming the heat-sealable resin layer 12 is not particularly limited, but an example is a method in which a coating liquid in which a water-dispersible resin is dissolved in a dispersion medium is applied to one surface of the paper substrate 10 and dried. The dispersion medium may be selected appropriately depending on the form of the water-dispersible resin, and examples include water, alcohols such as isopropanol and ethanol, polyhydric alcohols such as diethylene glycol and glycerin, and water-soluble organic solvents such as dimethylformamide, with water being preferred from an environmental perspective. Note that the above-mentioned additives are preferably mixed into the coating liquid as needed.

[0050] The method for applying the coating liquid is not particularly limited, and for example, a method can be employed in which various coating devices are appropriately selected from various types of coating devices such as a blade coater, an air knife coater, a rod blade coater, a bar blade coater, a gravure coater, a bar coater, a multistage roll coater, a roll coater, a reverse roll coater, a curtain coater, a spray coater, a gate roll coater, a size press coater, and a shim sizer.

[0051] The method for drying the applied coating liquid is not particularly limited, and any conventionally known method can be used. The drying temperature and drying time are also not particularly limited, and may be set appropriately, but for example, drying at 100 to 150°C for 30 seconds to 1 minute is preferred.

[0052] The surface to be coated with the heat-sealable resin layer 12 may be smoothed by, for example, super calendering, gloss calendering, soft calendering, etc. Alternatively, the surface may be roughened by embossing.

[0053] The obtained heat seal paper 1 is preferably wound into a roll and stored as a roll. Before or after storage, both ends of the roll may be removed using a slitter, if necessary, to adjust the width of the heat seal paper 1 to the width of a processing machine in a subsequent process.

[0054] The uses of the heat seal paper 1 described above are not particularly limited, but it can be used, for example, as packaging material for pillow packaging, gusset packaging, three-sided seal packaging, four-sided seal packaging, etc. Among these, the heat seal paper 1 according to this embodiment does not open or tear at the heat-sealed portion when packaging contents, and therefore can be suitably used, for example, as a packaging material for pillow packaging, which continuously packages contents in a vertical pillow packaging machine that is susceptible to impacts from the contents when filling.

[0055] FIG. 2 is a perspective view showing an example of a state in which contents are packaged with the heat seal paper according to this embodiment.

[0056] As an example of the packaged form of the above-mentioned packaging material, a packaging bag can be cited. The packaging bag 3 comprises a bag-shaped bag body including heat-sealable paper 2, and it is preferable that the heat-sealable resin layer of the bag body is located on the inner surface. That is, it is more preferable that the packaging bag 3 according to this embodiment is manufactured with the heat-sealable resin layer of the heat-sealable paper 2 located on the inner surface of the bag. Furthermore, the heat-sealable resin layer only needs to be provided on the heat-seal portion (seal portion 34 and center seal portion (not shown)) of the packaging bag 3 on the inner surface of the bag body, but it is preferable that it be provided on the entire inner surface.

[0057] Figure 2 shows the product packaged in pillow packaging, but it goes without saying that the form after packaging is not necessarily limited to this. The form after packaging may be, for example, a gusseted bag, a three-sided sealed bag, a four-sided sealed bag, or other types of packaging bags.

[0058] 3. Packaging method

[0059] FIG. 3 is a diagram illustrating a pillow packaging method according to this embodiment.

[0060] The heat-sealable resin layer of the heat-sealable paper 2 according to this embodiment can be heat-sealed, for example, by applying pressure and heating, making it easier to form and seal bags. The method of forming and sealing bags is not particularly limited and can be carried out by conventionally known methods, but as described above, the heat-sealable paper 2 according to this embodiment is preferably used in a packaging method in which a package is formed by pillow packaging using the heat-sealable paper 2 to package an article.

[0061] Pillow packaging is a packaging format in which, as shown in Figure 3, the heat seal paper 2 is overlapped at both widthwise ends with the inner surfaces facing each other so as to encase the packaged item (contents 4) placed on or below the sheet-like heat seal paper 2 in a cylindrical shape, and this overlapping part is sealed with a center seal part 36 to form a cylindrical shape, and the bottom part or the opening part (insertion opening 38) is sealed in a horizontal line with a seal part 34 to match the length (height) of the bag, and this sealed part is cut into individual bags. This pillow packaging can be performed using conventionally known equipment.

[0062] There are various types of pillow packaging, such as vertical pillow packaging, in which the heat seal paper 2 is fed vertically and the contents 4 are filled in from above while being wrapped, and horizontal pillow packaging, in which the heat seal paper 2 is fed horizontally and the contents 4 is wrapped around it.The heat seal paper 2 of this embodiment is suitable for packaging heavy items, and the packaging bag 3 can effectively withstand the impact of a heavy item being dropped, so it can be used suitably for both vertical pillow packaging and horizontal pillow packaging.

[0063] Furthermore, while there are no particular limitations on the method of heat sealing the seal portion 34 and the center seal portion 36 in this case, it is preferable to heat seal the heat-sealable resin layers together at 120 to 220°C, 0.1 to 0.5 MPa for 0.1 to 1.0 seconds. [Example]

[0064] The present invention will be described in more detail by the following examples and comparative examples, but the present invention is not limited in any way by the following examples. Unless otherwise specified, percentages, etc., are based on mass.

[0065] Example 1

[0066] (Preparation of heat seal paper 1)

[0067] As the paper substrate 10, unbleached kraft paper (manufactured by Daio Paper Co., Ltd., product name "Atlas Light Packaging", basis weight 60 g / m 2) was used, and a water-based urethane resin (abbreviated as "PU", manufactured by DIC Corporation, product name "Hydran WLS-230") was used as the water-dispersible resin. A coating liquid containing the water-dispersible resin and water as a dispersion medium was prepared, and the dry adhesion amount of the solid component (the water-dispersible resin) was set to 6 g / m. 2 The coating liquid was applied to one surface (felt side) of the paper substrate 10 with a Mayer bar so that the mass per unit area of ​​the heat-sealable resin layer 12 was 6 g / m, and the paper substrate 10 was dried at 150°C for 30 seconds to form a heat-sealable resin layer 12 on the surface of the paper substrate 10. In this way, the heat-sealable paper 1 shown in Figure 1 was obtained. That is, the mass per unit area of ​​the heat-sealable resin layer 12 was 6 g / m. 2 In the case of this example, the content of the water-dispersible resin in the heat-sealable resin layer 12 was 100 mass %, and the dry adhesion amount of the water-dispersible resin in the heat-sealable resin layer 12 was 6 g / m 2 It was.

[0068] <Example 2>

[0069] A heat-sealable paper 1 was obtained in the same manner as in Example 1, except that the water-dispersible resin in Example 1 was a combination of 90 mass% styrene-butadiene rubber (abbreviated as "SBR", manufactured by Nippon A&L Co., Ltd., trade name "Nalstar SR-107") and 10 mass% water-based urethane resin (abbreviated as "PU", manufactured by DIC Corporation, trade name "Hydran WLS-230"), in a ratio of these two. That is, the mass per unit area of ​​the heat-sealable resin layer 12 was 6 g / m. 2 In the case of this example, the content of the water-dispersible resin in the heat-sealable resin layer 12 was 100 mass %, and the dry adhesion amount of the water-dispersible resin in the heat-sealable resin layer 12 was 6 g / m 2 It was.

[0070] Example 3

[0071] A heat-sealable paper 1 was obtained in the same manner as in Example 1, except that the water-dispersible resin in Example 1 was a combination of 80 mass% styrene-butadiene rubber (abbreviated as "SBR", manufactured by Nippon A&L Co., Ltd., trade name "Nalstar SR-107") and 20 mass% water-based urethane resin (abbreviated as "PU", manufactured by DIC Corporation, trade name "Hydran WLS-230"), in a ratio of these two. That is, the mass per unit area of ​​the heat-sealable resin layer 12 was 6 g / m. 2 In the case of this example, the content of the water-dispersible resin in the heat-sealable resin layer 12 was 100 mass %, and the dry adhesion amount of the water-dispersible resin in the heat-sealable resin layer 12 was 6 g / m 2 It was.

[0072] Example 4

[0073] A coating solution containing a water-dispersible resin was prepared, and the dry adhesion amount of the water-dispersible resin was set to 8 g / m. 2 The heat sealable paper 1 was obtained in the same manner as in Example 3, except that the coating liquid was applied so that the mass per unit area of ​​the heat sealable resin layer 12 was 8 g / m 2 In the case of this example, the content of the water-dispersible resin in the heat-sealable resin layer 12 was 100 mass %, and the dry adhesion amount of the water-dispersible resin in the heat-sealable resin layer 12 was 8 g / m 2 It was.

[0074] <Example 5>

[0075] A coating solution containing a water-dispersible resin was prepared, and the dry adhesion amount of the water-dispersible resin was set to 4 g / m. 2 The heat sealable paper 1 was obtained in the same manner as in Example 3, except that the coating liquid was applied so that the mass per unit area of ​​the heat sealable resin layer 12 was 4 g / m 2 In the case of this example, the content of the water-dispersible resin in the heat-sealable resin layer 12 was 100% by mass, and the dry adhesion amount of the water-dispersible resin in the heat-sealable resin layer 12 was 4 g / m 2 It was.

[0076] Example 6

[0077] As the paper substrate 10, unbleached Clupak paper (manufactured by Tokushu Tokai Paper Co., Ltd., product name "Kraft Tokai TKK", basis weight 73 g / m 2 Heat seal paper 1 was obtained in the same manner as in Example 3, except that ) was used.

[0078] Example 7

[0079] As the paper substrate 10, unbleached kraft paper (manufactured by Shin Tokai Paper Co., Ltd., product name "Tokai Kraft CF", basis weight 50 g / m 2 Heat seal paper 1 was obtained in the same manner as in Example 3, except that ) was used.

[0080] Example 8

[0081] As the paper substrate 10, bleached glassine paper (manufactured by Lintec Corporation, product name "White Glassine", basis weight 50 g / m 2 Heat seal paper 1 was obtained in the same manner as in Example 3, except that ) was used.

[0082] Example 9

[0083] A heat-sealable paper 1 was obtained in the same manner as in Example 1, except that the water-dispersible resin in Example 1 was a combination of 70 mass% styrene-butadiene rubber (abbreviated as "SBR", manufactured by Nippon A&L Co., Ltd., trade name "Nalstar SR-107") and 30 mass% water-based urethane resin (abbreviated as "PU", manufactured by DIC Corporation, trade name "Hydran WLS-230"), in a ratio of these two. That is, the mass per unit area of ​​the heat-sealable resin layer 12 was 6 g / m 2 In the case of this example, the content of the water-dispersible resin in the heat-sealable resin layer 12 was 100 mass %, and the dry adhesion amount of the water-dispersible resin in the heat-sealable resin layer 12 was 6 g / m 2 It was.

[0084] Example 10

[0085] A heat-sealable paper 1 was obtained in the same manner as in Example 1, except that the water-dispersible resin in Example 1 was a combination of 50 mass% styrene-butadiene rubber (abbreviated as "SBR", manufactured by Nippon A&L Co., Ltd., trade name "Nalstar SR-107") and 50 mass% water-based urethane resin (abbreviated as "PU", manufactured by DIC Corporation, trade name "Hydran WLS-230"), in a ratio of these two. That is, the mass per unit area of ​​the heat-sealable resin layer 12 was 6 g / m 2 In the case of this example, the content of the water-dispersible resin in the heat-sealable resin layer 12 was 100 mass %, and the dry adhesion amount of the water-dispersible resin in the heat-sealable resin layer 12 was 6 g / m 2 It was.

[0086] <Comparative Example 1>

[0087] Heat-sealable paper was obtained in the same manner as in Example 1, except that an ionomer-based resin (abbreviated as "ionomer-based," manufactured by Mitsui Chemicals, trade name "Chemipearl S-100") was used as the water-dispersible resin in Example 1. That is, the mass per unit area of ​​the resin layer was 6 g / m². 2 In the case of this comparative example, the ionomer resin content in the resin layer was 100% by mass, and the dry adhesion amount of the ionomer resin in the resin layer was 6 g / m². 2 It was.

[0088] <Comparative Example 2>

[0089] A heat seal paper was obtained in the same manner as in Example 1, except that the water-dispersible resin in Example 1 was a combination of 95 mass% styrene-butadiene rubber (abbreviated as "SBR", manufactured by Nippon A&L Co., Ltd., trade name "Nalstar SR-107") and 5 mass% water-based urethane resin (abbreviated as "PU", manufactured by DIC Corporation, trade name "Hydran WLS-230"), in a ratio of these two. That is, the mass per unit area of ​​the resin layer was 6 g / m. 2 In the comparative example, the content of water-dispersible resin in the resin layer was 100% by mass, and the dry adhesion amount of water-dispersible resin in the resin layer was 6 g / m².2 It was.

[0090] <Comparative Example 3>

[0091] A heat seal paper was obtained in the same manner as in Example 1, except that styrene-butadiene rubber (abbreviated as "SBR", manufactured by Nippon A&L Co., Ltd., product name "Nalstar SR-107") was used as the water-dispersible resin in Example 1, and no water-based urethane resin was used. That is, the mass per unit area of ​​the resin layer was 6 g / m. 2 In the comparative example, the content of water-dispersible resin in the resin layer was 100% by mass, and the dry adhesion amount of water-dispersible resin in the resin layer was 6 g / m². 2 It was.

[0092] <Comparative Example 4>

[0093] Dry adhesion weight of coating liquid containing water-dispersible resin is 2g / m 2 A heat-sealable paper was obtained in the same manner as in Example 3, except that the coating liquid was applied so that the mass per unit area of ​​the heat-sealable resin layer was 2 g / m. 2 In the case of the comparative example, the content of the water-dispersible resin in the heat-sealable resin layer was 100% by mass, and the dry adhesion amount of the water-dispersible resin in the heat-sealable resin layer was 2 g / m 2 It was.

[0094] <Measurement> The following measurements were carried out for each of the above Examples and Comparative Examples. The measurement results are shown in Table 1.

[0095] (Tensile energy of water-dispersible resin)

[0096] First, a coating solution containing 35% by mass of water-dispersible resin and water as a dispersion medium was applied to the surface of the release agent layer of a release film (Lintec Corporation, product name "AL-5") using a 250 μm applicator, and a resin film with a thickness of 30-50 μm was prepared by heating at 120°C for 5 minutes. Then, the release film was removed from the resin film prepared above to obtain a single-layer test specimen (10 mm x 30 mm) of the heat-sealable resin layer. Next, in accordance with JIS K 7161, the work done on the test specimen (J) was calculated from the area of ​​the stress-strain curve when measured with a chuck distance of 10 mm and a tensile speed of 20 mm / min, and this value was divided by the volume of the test specimen to obtain the tensile energy (J / m²). 3 ) was calculated.

[0097] <Evaluation> The following evaluations were carried out for each of the above Examples and Comparative Examples. The evaluation results are shown in Table 1.

[0098] (Heat seal strength)

[0099] Two test pieces were prepared by cutting the obtained heat-sealable paper to 15 mm x 150 mm. These test pieces were stacked so that the heat-sealable resin layers faced each other, and pressed together under conditions of 160°C, 0.2 MPa, and 1 second. Then, in accordance with JIS Z 1707, the heat-seal strength was defined as the maximum load at which the pressed test pieces were peeled in a T-shape at a tensile speed of 300 mm / min using a tensile testing machine (Shimadzu Corporation, product name "Autograph AG-500NIS").

[0100] (Heavy load test)

[0101] The resulting heat-sealable paper was cut into two 200mm x 200mm test sheets. These two test sheets were stacked together with the heat-sealable resin layers facing each other, and three sides of the two test sheets were heat-sealed at a seal width of 30mm at 160°C, 0.2MPa, and 1 second to create a three-sided bag with a single opening. Next, a 1kg weight (M2 class) was vertically dropped from a height of 30cm from the bottom seal through the opening of the three-sided bag toward the bottom seal. The bottom seal was then evaluated for peeling (opening) after the free fall. ○: No peeling (opening) occurred in the bottom seal portion. ×: Peeling (opening) occurred in the bottom seal portion.

[0102] The compositions and evaluation results of each example and comparative example are shown in Table 1. In the table, the "solid content ratio" is a mass ratio.

[0103] [Table 1]

[0104] From the above, it was at least confirmed that according to this embodiment, openings do not occur in the heat-sealed portions of the packaging bags formed from the heat seal paper 1. [Explanation of symbols]

[0105] 1, 2...Heat seal paper 10…Paper base material 12...Heat-sealable resin layer 3...Packaging bag 4…Contents 34...Seal part 36...Center seal part 38...insertion port

Claims

1. A heat-sealable paper comprising a paper substrate and a heat-sealable resin layer in this order, The mass per unit area of ​​the heat-sealable resin layer is 3 g / m ２ That's all, the heat-sealable resin layer contains a water-dispersible resin, The water-dispersible resin includes a urethane resin, the content of the urethane resin in the heat-sealable resin layer is more than 5% by mass relative to 100% by mass of the total amount of the water-dispersible resin; Heat seal paper.

2. The heat-sealable resin layer is located on the outermost surface of the heat-sealable paper. The heat seal paper according to claim 1.

3. The tensile energy per unit volume of the heat-sealable resin layer is 150 MJ / m ３ That's all. The heat seal paper according to claim 1 or 2.

4. The water-dispersible resin further contains at least one selected from the group consisting of styrene-butadiene rubber and ethylene-vinyl acetate copolymer. The heat seal paper according to claim 1 or 2.

5. For pillow packaging, The heat seal paper according to claim 1 or 2.

6. A packaging method, comprising forming a package using the heat seal paper according to claim 1 or 2 by pillow packaging, and packaging an article.

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