Heat-sealing paper, roll, packaging bag, and package

Abstract

The present invention relates to: a heat-sealing paper with which it is possible to obtain a packaging bag and a package that have a reduced load on the environment, are easy to open, and are not easily torn by an operation during opening; and a roll, a packaging bag, and a package that are formed using the heat-sealing paper.　The heat-sealing paper comprises a heat-sealing layer on one face of a paper base material. The content of the paper base material in the heat-sealing paper is 50 mass% or greater. The geometric mean of the pure bending stiffness in the longitudinal direction and the pure bending stiffness in the lateral direction of the heat-sealing paper is 0.80 g·cm2 / cm or less. The vertical tensile strength of the heat-sealing paper is 1.8 kN / m or greater. The coefficient of static friction of a surface of the heat-sealing layer on the opposite side to the paper base material is 0.750 or less.

Description

Heat-sealing paper, roll, packaging bag, and package

[0001] The present invention relates to heat-sealing paper, a roll, a packaging bag, and a package.

[0002] Packages using the heat-sealing method are widely used not only for packaging general industrial products but also for packaging food, medicine, medical devices, etc.

[0003] In recent years, the problem of plastic waste has been worsening. Among the world's plastic production volume, the plastic production volume in the packaging container sector is large, which is the cause of plastic waste. Plastic is not decomposed semi-permanently, and the waste is microplastics in the natural environment, having a serious adverse impact on the ecosystem. As a countermeasure, it has been proposed to replace plastic with paper.

[0004] For example, in Japanese Patent Application Laid-Open No. 2023-182608, for the purpose of providing a paper for a flexible packaging material that can be made into a bag by a bag-making machine and a flexible package using this paper for a flexible packaging material, a paper base material and a heat-sealing layer on at least one outermost surface are provided. The paper base material has a thickness of 25 μm or more and 100 μm or less, and the ratio of pulp to all papermaking fibers contained in the paper base material exceeds 90% by weight, and a paper for a flexible packaging material characterized by satisfying specific conditions is disclosed.

[0005] The packaging bag using the paper for a flexible packaging material described in Japanese Patent Application Laid-Open No. 2023-182608 has insufficient ease of opening when opening. An object of the present invention is to provide heat-sealing paper that can obtain a packaging bag and a package that have a reduced environmental load, are easy to open, and are not easily torn by the operation when opening, a roll, a packaging bag, and a package using the heat-sealing paper.

[0006] The inventors have found that the above problems can be solved by providing a heat-sealable paper having a heat-seal layer on one side of a paper substrate, wherein the content of the paper substrate in the heat-sealable paper, the synergistic mean of the pure bending stiffness in the longitudinal direction and the pure bending stiffness in the transverse direction of the heat-sealable paper, and the tensile strength in the longitudinal direction of the heat-sealable paper are set to a specific value or higher, and the static friction coefficient of the side of the heat-seal layer opposite to the paper substrate is set to a specific value or lower. That is, the present invention relates to the following <1> to <10>. <1> A heat-sealable paper having a heat-seal layer on one side of a paper substrate, wherein the content of the paper substrate in the heat-sealable paper is 50% by mass or more, and the synergistic mean of the pure bending stiffness in the longitudinal direction and the pure bending stiffness in the transverse direction of the heat-sealable paper is 0.80 g・cm ２ Heat-seal paper having a rigidity of 1.80 kN / m or less, a tensile strength in the longitudinal direction of the heat-seal paper of 1.80 kN / m or more, and a static friction coefficient of 0.750 or less on the side of the heat-seal layer opposite to the paper substrate. <2> Heat-seal paper having a pure bending rigidity in the longitudinal direction of 1.20 g·cm ２ The heat-sealing paper described in <1> has a lateral bending stiffness of 0.60 g·cm or less. <3> The heat-sealing paper has a lateral pure bending stiffness of 0.60 g·cm. ２ Heat-sealable paper as described in <1> or <2>, with a basis weight of 80 g / m² or less. <4> Heat-sealable paper as described in any one of <1> to <3>, wherein the heat-seal layer contains a slip agent. <5> Heat-sealable paper as described in any one of <1> to <4>, wherein the heat-seal layer is a laminate layer. <6> Basis weight of 80 g / m² ２ The following are heat-sealable papers as described in any one of <1> to <5>: <7> Heat-sealable paper as described in any one of <1> to <6> for packaging bags having a heat-seal layer on the inside. <8> A roll of heat-sealable paper as described in any one of <1> to <7>, in which both ends where the heat-seal layers overlap are heat-sealed in the vertical direction, and which is wound in the vertical direction. <9> A packaging bag using the heat-sealable paper as described in any one of <1> to <7> or the roll as described in <8>. <10> A package containing contents in the packaging bag as described in <9>.

[0007] [Heat-sealable paper] The heat-sealable paper of this embodiment is a heat-sealable paper having a heat-seal layer on one side of a paper substrate, the paper substrate content in the heat-sealable paper is 50% by mass or more, and the geometric mean of the pure bending stiffness in the longitudinal direction and the pure bending stiffness in the transverse direction of the heat-sealable paper is 0.80 g・cm ２ The coefficient of static friction of the heat-sealing paper is 0.750 or less on the side opposite to the paper substrate, the tensile strength in the longitudinal direction of the heat-sealing paper is 1.80 kN / m or more, and the coefficient of static friction of the heat-sealing layer on the side opposite to the paper substrate is 0.750 or less.

[0008] The heat-sealable paper of this embodiment reduces the environmental burden, is easy to open (excellent ease of opening), and provides packaging bags and packaging bodies that are resistant to tearing during opening. The reason for these effects is that the paper base material content in the heat-sealable paper is 50% by mass or more, resulting in a plastic material content of 50% by mass or less, thus reducing the environmental burden. Furthermore, the geometric mean of the pure bending stiffness in the longitudinal direction and the pure bending stiffness in the transverse direction of the heat-sealable paper is 0.80 g・cm ２ The coefficient of static friction of the heat-seal layer is less than or equal to / cm, and the coefficient of static friction of the heat-seal layer on the side opposite to the paper substrate is 0.750 or less. This allows the opposing heat-seal layers to slide easily against each other when used in packaging, resulting in excellent openability. Furthermore, the tensile strength of the heat-seal paper in the longitudinal direction is 1.80 kN / m or more, making it less likely to tear due to stress during opening. However, the reasons for obtaining the above effects are not limited to these. The present invention will be described in more detail below.

[0009] In this specification, numerical ranges expressed as "X to Y" mean numerical ranges that include X as the lower limit and Y as the upper limit. When numerical ranges are described in steps, the upper and lower limits of each numerical range can be arbitrarily combined. In addition, unless otherwise specified in this specification, operations and measurements of physical properties, etc., shall be performed under conditions of room temperature (20 to 25°C) / relative humidity (RH) 40 to 50%. The longitudinal direction of heat seal paper and paper substrate means the papermaking direction (MD) of the paper substrate, and the transverse direction means the direction perpendicular to the papermaking direction (CD). Each component contained in heat seal paper may be used individually or in combination of two or more. The surface of heat seal paper means the side that will be on the outside when it is made into a packaging bag. The back of heat seal paper means the side that will be on the inside when it is made into a packaging bag.

[0010] <Paper Substrate> The paper substrate is preferably paper that is commonly used with plant-derived pulp as the main component, and more preferably paper that is mainly composed of wood pulp. Furthermore, it is preferable that the paper is mainly composed of pulp that disperses easily in water due to mechanical disintegration. Specifically, examples include bleached or unbleached kraft paper, fine paper, cardboard, liner paper, coated paper, glossy paper, glassine paper, etc. Among these, bleached kraft paper, glassine paper, and Graphan paper are preferred from the viewpoint of obtaining a packaging body with excellent ease of opening and a packaging bag that is resistant to tearing during opening, and glassine paper and Graphan paper are more preferred from the viewpoint of obtaining a packaging body with excellent visibility of the contents. Generally, glassine paper has coniferous chemical pulp as the main component as the pulp raw material, is highly beaten and paper is made in an acidic to neutral environment, and finished by compression treatment with a supercalender or the like. Specific examples of pulp include, for example, chemical pulp made from coniferous woods such as spruce and hemlock, which is preferred, but chemical pulp made from hardwoods, mechanical pulp, recycled paper, synthetic pulp, etc., may also be mixed and blended.

[0011] The paper base material preferably contains softwood chemical pulp and / or hardwood chemical pulp. In the pulp constituting the paper base material, the total content of softwood chemical pulp and hardwood chemical pulp is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and is 100% by mass or less, preferably 100% by mass. When the paper base material is glassine paper or graph paper, from the viewpoints of obtaining a packaging body with excellent easy-opening property, obtaining a packaging bag that is not easily torn by the operation during opening, and obtaining a packaging body with excellent visibility of the contained product, the content of softwood chemical pulp (preferably softwood kraft pulp) in the pulp constituting the paper base material is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and is 100% by mass or less, preferably 100% by mass. When the paper base material is kraft paper, from the viewpoints of obtaining a packaging body with excellent easy-opening property and obtaining a packaging bag that is not easily torn by the operation during opening, the content of hardwood chemical pulp (preferably hardwood kraft pulp) in the pulp constituting the paper base material is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and is 100% by mass or less, preferably 100% by mass.

[0012] (Grammage) The grammage of the paper base material is preferably 22.0 g / m ２ or more and 65.0 g / m ２ or less, more preferably 24.5 g / m ２ or more, still more preferably 28.0 g / m ２ or more, and more preferably 60.0 g / m ２ or less, still more preferably 55.0 g / m ２ or less, even more preferably 50.0 g / m ２ or less, still more preferably 45.0 g / m ２ or less, even more preferably 40.0 g / m ２ or less, still more preferably 35.0 g / m ２The following applies: The basis weight of the paper substrate is preferably above the lower limit from the viewpoint of obtaining a packaging bag that is resistant to tearing during opening, and preferably below the upper limit from the viewpoint of obtaining a packaging body with excellent ease of opening. The basis weight of the paper substrate is measured in accordance with JIS P 8124:2011.

[0013] (Thickness) The thickness of the paper substrate is preferably 22 μm or more and 60 μm or less, more preferably 24.5 μm or more, even more preferably 28 μm or more, and more preferably 55 μm or less, even more preferably 50 μm or less, even more preferably 45 μm or less, even more preferably 40 μm or less, and even more preferably 35 μm or less. From the viewpoint of obtaining a packaging bag that is difficult to tear during opening, the thickness of the paper substrate is preferably above the lower limit, and from the viewpoint of obtaining a packaging body with excellent ease of opening, it is preferably below the upper limit.

[0014] (Density) From the viewpoint of ease of manufacturing heat-sealable paper, the density of the paper substrate is preferably 0.65 g / cm³. ３ 1.25g / cm or more ３ The following, and more preferably 0.70 g / cm³ ３ More preferably, 0.75 g / cm³ ３ More preferably, 0.85 g / cm³ ３ More preferably, 0.90 g / cm³ ３ More preferably, 0.95 g / cm³ ３ The above applies, and more preferably 1.20 g / cm³. ３ More preferably, 1.15 g / cm³ ３ The following applies: The density of the paper substrate is calculated from the basis weight and thickness of the paper substrate, obtained by the measurement method described above.

[0015] (Irregular Freeness) In this embodiment, from the viewpoint of obtaining a packaging bag and packaging body with excellent visibility of the contents, it is preferable that the irregular freeness of the pulp constituting the paper substrate is 100 mL or more and 800 mL or less. Here, irregular freeness refers to the freeness (filtration rate) measured in the Canadian standard filtration rate method specified in JIS P 8121:2012, by changing the pulp sample amount from 3 g to 0.3 g and changing the JIS standard screen plate to an 80 mesh wire. It is preferable that the irregular freeness of the pulp constituting the paper substrate is above the lower limit, as this increases the dimensional stability of the paper substrate and makes it less likely to develop bumps, and that it is below the upper limit, as this maintains the transparency of the paper substrate. It is more preferable that the irregular freeness of the pulp constituting the paper substrate is 300 mL or more and 700 mL or less, even more preferable that it is 400 mL or more and 600 mL or less, and even more preferable that it is 460 mL or more and 550 mL or less. Known methods can be used for beating the pulp to adjust the irregular freeness. The irregular freeness of the pulp constituting the paper substrate is specifically measured by the method described in the examples. Note that "irregular freeness of the pulp constituting the paper substrate" refers to the irregular freeness of the disintegrated pulp obtained by disintegrating the paper substrate.

[0016] When bleached kraft paper is used as the paper substrate, the freeness (Canadian Standard Water Filtration (CSF)) of the disintegrated pulp obtained by disintegrating the pulp constituting the bleached kraft paper is preferably 200 mL to 700 mL, more preferably 300 mL to 600 mL, and even more preferably 350 mL to 550 mL. Specifically, the freeness of the disintegrated pulp obtained by disintegrating the pulp constituting the bleached kraft paper is measured by the method described in the examples.

[0017] The static friction coefficient of the surface (front side) of the heat-sealable paper is preferably 0.100 to 0.500, more preferably 0.150 or higher, even more preferably 0.200 or higher, even more preferably 0.220 or higher, and even more preferably 0.400 or lower, and even more preferably 0.300 or lower, from the viewpoint of making it easier to wind the heat-sealable paper in the longitudinal direction into a roll. The static friction coefficient is measured in accordance with JIS P 8147:2010. When the surface (front side) of the heat-sealable paper of this embodiment is the side opposite to the heat-seal layer of the paper substrate (when the heat-sealable paper of this embodiment does not have any layer on the side opposite to the heat-seal layer of the paper substrate), the static friction coefficient of the surface (front side) can be adjusted by the type of raw pulp, the concentration and degree of pulp slurry during beating, the presence or absence of calendering and the processing conditions, etc. Specifically, during calendering, reducing the linear pressure tends to increase the static friction coefficient of the surface. Also, increasing the pulp's beaten rate tends to decrease the static friction coefficient of the surface. Furthermore, if the surface of the heat-sealable paper of this embodiment is the surface of an arbitrary layer (i.e., the heat-sealable paper of this embodiment has an arbitrary layer on the side opposite to the heat-sealable layer of the paper substrate), the static friction coefficient of the surface can be adjusted by printing methods and conditions, coating methods and conditions, etc. Specifically, forming an arbitrary layer by curtain coating tends to increase the static friction coefficient of the surface. Also, forming an arbitrary layer by blade coating tends to decrease the static friction coefficient of the surface.

[0018] <Heat Seal Layer> The heat seal paper of this embodiment has a heat seal layer on one side of the paper substrate. The heat seal layer is the uppermost layer. The heat seal layer is a layer that is melted and bonded by heating, ultrasound, etc. The heat seal layer may be provided by coating, dry lamination, or extrusion lamination. Among these, it is preferable to provide it by lamination from the viewpoint of ease of manufacturing the heat seal paper. From the viewpoint of obtaining a package with excellent ease of opening, it is preferable that the heat seal layer be formed on the entire surface of one side of the paper substrate. Furthermore, from the viewpoint of ease of manufacturing the heat seal paper and obtaining a package with excellent visibility of the contents, it is preferable that the heat seal layer be directly laminated to the paper substrate or laminated via an adhesive layer.

[0019] The heat seal layer preferably contains a slip agent from the viewpoint of reducing the static friction coefficient on the back surface of the heat seal paper.

[0020] (Laminate layer) When the heat seal layer is provided by lamination, it can be manufactured by appropriately selecting from conventionally known manufacturing methods, such as dry lamination, melt extrusion, melt casting, calendering, etc. Among these, dry lamination is preferred from the viewpoint of ease of manufacturing the heat seal paper of this embodiment.

[0021] Any thermoplastic resin, whether crystalline or amorphous, can be used as the resin constituting the heat seal layer. Examples of thermoplastic resins include polyethylene (low-density polyethylene (LDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), etc.), polyolefin resins such as polypropylene and polymethylpentene, polyester resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), polyamide resins, biodegradable resins such as polylactic acid (PLA), polyhydroxybutyrate (PHB), polybutylene succinate (PBS), poly(butylene adipate-co-butylene terephthalate) (PBAT), polycaprolactone (PCL), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), as well as polystyrene, polyvinyl chloride, acrylonitrile-butadiene-styrene (ABS) resin, acrylic resin, and modified polyphenylene ether (PPE). Among these, it is preferable to use polyethylene (LDPE, MDPE, HDPE, LLDPE, etc.), polyolefin resins such as polypropylene and polymethylpentene, or polylactic acid (PLA) as the thermoplastic resin, and it is more preferable to use polyethylene.

[0022] A resin film containing a slip agent can also be used as the laminate layer. Specific examples of resin films containing a slip agent include LL-XMTN (polyethylene film (PE film), manufactured by Futamura Chemical Co., Ltd.) and LL-MT NR (PE film, manufactured by Futamura Chemical Co., Ltd.).

[0023] The heat seal layer may be formed as a single layer of a single resin, as a single layer formed by mixing multiple resins, or as a multilayer of these (for example, single resin layer / single resin layer, single resin layer / mixed resin layer, mixed resin layer / mixed resin layer).

[0024] (Basis weight) The basis weight of the heat seal layer can be appropriately selected within a range where the paper base material content in the heat seal paper is 50% by mass or more. From the viewpoint of reducing environmental impact and heat sealability, 1 g / m² is preferred. ２ 25g / m or more２ The following is more preferable: 5 g / m ２ More preferably 7 g / m ２ More preferably 10 g / m ２ The above applies, and more preferably 20 g / m² ２ The following applies. In particular, when a heat seal layer is provided by coating, the basis weight of the heat seal layer is preferably 1 g / m² from the viewpoint of reducing environmental impact and heat sealability. ２ 20g / m or more ２ The following is more preferable: 2 g / m ２ The above applies, and more preferably 10 g / m ２ More preferably 5 g / m ２ More preferably, 3 g / m ２ The following applies. Furthermore, when the heat-seal layer is provided by lamination, 5 g / m² is preferred. ２ 25g / m or more ２ The following is more more preferable: 7 g / m ２ More preferably 10 g / m ２ The above applies, and more preferably 20 g / m² ２ The following applies. When the heat seal layer is provided by lamination, the basis weight of the heat seal layer is preferably above the lower limit from the viewpoint of reducing environmental impact and heat sealability, and preferably below the upper limit from the viewpoint of obtaining a package with excellent ease of opening. Furthermore, when the heat seal layer is provided by lamination, the thickness of the heat seal layer is preferably 5 μm or more and 24 μm or less, more preferably 9 μm or more, even more preferably 12 μm or more, and more preferably 21 μm or less from the same viewpoint.

[0025] <Optional Layers> The heat-sealable paper of this embodiment may have an optional layer on the side of the paper substrate opposite to the heat-sealable layer. However, from the viewpoint of making it easier to wind the heat-sealable paper in the vertical direction into a roll, it is preferable that it does not have an optional layer. Specific examples of optional layers include a printing layer, a coating layer, a laminating layer, and a barrier layer.

[0026] <Characteristics of Heat-Sealing Paper> (Paper Substrate Content) In the heat-sealing paper of this embodiment, from the viewpoint of reducing environmental impact, the paper substrate content in the heat-sealing paper is 50% by mass or more, preferably 50% by mass or more and 90% by mass or less, more preferably 53% by mass or more, even more preferably 55% by mass or more, and even more preferably 85% by mass or less, and even more preferably 80% by mass or less. From the viewpoint of heat-sealability, it is preferable that the paper substrate content in the heat-sealing paper is below the above upper limit.

[0027] (Basis weight) The basis weight of the heat-sealing paper in this embodiment is preferably 22 g / m². ２ 80g / m or more ２ The following is more more preferable: 30 g / m ２ More preferably 35 g / m² ２ More preferably 40 g / m² ２ More preferably 45 g / m² ２ The above applies, and more preferably 75 g / m² ２ More preferably, 70 g / m ２ More preferably, 65 g / m ２ More preferably, 60 g / m ２ The following applies. From the viewpoint of obtaining a packaging bag that is difficult to tear during opening, the basis weight of the heat-seal paper is preferably above the lower limit, and from the viewpoint of obtaining a packaging body that is easy to open and has excellent visibility of the contents, it is preferably below the upper limit. The basis weight of the heat-seal paper can be set to a desired range by appropriately adjusting the basis weight of the paper base material and the heat-seal layer. The basis weight of the heat-seal paper is measured by the method described in the examples.

[0028] (Thickness) The thickness of the heat-seal paper in this embodiment is preferably 30 μm or more and 80 μm or less, more preferably 35 μm or more, even more preferably 40 μm or more, and more preferably 75 μm or less, even more preferably 70 μm or less, even more preferably 66 μm or less, even more preferably 62 μm or less, even more preferably 58 μm or less, and even more preferably 54 μm or less. From the viewpoint of obtaining a packaging bag that is difficult to tear during opening, the thickness of the heat-seal paper is preferably above the lower limit value, and from the viewpoint of obtaining a packaging body with excellent ease of opening and excellent visibility of the contents, it is preferably below the upper limit value. The thickness of the heat-seal paper can be set to a desired range by appropriately adjusting the thickness of the paper base material and the heat-seal layer. The thickness of the heat-seal paper is measured by the method described in the embodiment.

[0029] (Density) The density of the heat-sealable paper in this embodiment is preferably 0.70 g / cm³ from the viewpoint of ease of manufacturing the heat-sealable paper. ３ 1.20g / cm or more ３ The following, and more preferably 0.75 g / cm³ ３ More preferably, 0.80 g / cm³ ３ More preferably, 0.85 g / cm³ ３ More preferably, 0.90 g / cm³ ３ More preferably, 0.95 g / cm³ ３ The above applies, and more preferably, 1.15 g / cm³. ３ More preferably, 1.10 g / cm³ ３ The following applies: The density of the heat-sealable paper can be set to a desired range by appropriately adjusting the density of the paper substrate and the type of resin used in the heat-sealing layer. The density of the heat-sealable paper is calculated from the basis weight and thickness of the heat-sealable paper.

[0030] (Pure Bending Stiffness) The synergistic mean of the pure bending stiffness in the longitudinal direction and the pure bending stiffness in the transverse direction of the heat-sealable paper according to this embodiment is 0.80 g / cm², from the viewpoint of obtaining a package with excellent ease of opening. ２ It is less than or equal to / cm, preferably 0.01 g / cm ２ / cm or more 0.80g・cm ２ It is less than or equal to / cm, and more preferably 0.60 g / cm ２ / cm or less, more preferably 0.40 g / cm ２ Less than or equal to 0.20 g / cm, more preferably 0.20 g / cm ２ Less than or equal to 0.16 g / cm, more preferably 0.16 g / cm ２ It is less than or equal to / cm, and more preferably 0.02 g / cm ２ / cm or more, more preferably 0.03 g / cm ２ It is at least / cm. From the viewpoint of ease of manufacturing the heat seal paper, it is preferable that the geometric mean of the pure bending stiffness in the longitudinal direction and the pure bending stiffness in the transverse direction is at or above the above lower limit.

[0031] The longitudinal pure bending stiffness of the heat-sealing paper according to this embodiment is preferably 0.01 g / cm². ２ / cm or more 1.20g・cm ２ less than or equal to 0.80 g / cm², more preferably 0.80 g / cm². ２ / cm or less, more preferably 0.40 g / cm ２ Less than or equal to 0.20 g / cm, more preferably 0.20 g / cm ２ It is less than or equal to / cm, and more preferably 0.03 g / cm ２ / cm or more, more preferably 0.05 g / cm ２ It is 1 cm or more. The pure bending stiffness in the longitudinal direction of the heat-seal paper is preferably less than or equal to the above upper limit value from the viewpoint of obtaining a package with excellent ease of opening, and preferably greater than or equal to the above lower limit value from the viewpoint of ease of manufacturing the heat-seal paper.

[0032] The transverse pure bending stiffness of the heat-sealing paper according to this embodiment is preferably 0.01 g·cm. ２ / cm or more 0.60g・cm ２ / cm or less, more preferably 0.40 g / cm ２ / cm or less, more preferably 0.20 g / cm ２ / cm or less, more preferably 0.15 g / cm ２ Less than or equal to 0.12 g / cm, more preferably 0.12 g / cm ２ It is less than or equal to / cm, and more preferably 0.02 g / cm２ It is 1 / cm or more. The pure bending stiffness of the heat-seal paper in the lateral direction is preferably less than or equal to the above upper limit value from the viewpoint of obtaining a package with excellent ease of opening, and preferably greater than or equal to the above lower limit value from the viewpoint of ease of manufacturing the heat-seal paper.

[0033] The longitudinal and transverse pure bending stiffness of heat-sealable paper can be adjusted by the type of raw pulp, the type and amount of paper strength enhancer, the pulp slurry concentration and degree of beating during beating, the drying conditions during papermaking (e.g., the position of the drying device in the paper machine), the presence or absence of calendering and the conditions of calendering, the basis weight, etc. For example, increasing the basis weight or thickness of the paper substrate tends to increase the longitudinal and transverse pure bending stiffness. The longitudinal and transverse pure bending stiffness of heat-sealable paper is measured by the method described in the examples.

[0034] (Tensile Strength) The longitudinal tensile strength of the heat-seal paper of this embodiment is preferably 1.80 kN / m or more, more preferably 1.80 kN / m to 5.00 kN / m, more preferably 1.90 kN / m or more, even more preferably 2.00 kN / m or more, even more preferably 2.10 kN / m or more, even more preferably 2.20 kN / m or more, and more preferably 4.50 kN / m or less, even more preferably 4.00 kN / m or less, even more preferably 3.50 kN / m or less, and even more preferably 3.00 kN / m or less. From the viewpoint of obtaining a package with excellent ease of opening, the longitudinal tensile strength of the heat-seal paper is preferably less than or equal to the above upper limit. The tensile strength is measured in accordance with JIS P 8113:2006. Tensile strength is adjusted by appropriately selecting the degree of beating of the raw pulp, the basis weight, thickness, and density of the paper substrate, the papermaking conditions for the paper substrate, and the type and thickness of the heat seal layer. For example, increasing the basis weight of the paper substrate or the heat seal layer tends to increase tensile strength.

[0035] (Static friction coefficient) The static friction coefficient on the back surface of the heat-seal paper of this embodiment is 0.750 or less, from the viewpoint of obtaining a package with excellent ease of opening, for example, 0.100 to 0.750, preferably 0.600 or less, more preferably 0.450 or less, even more preferably 0.300 or less, even more preferably 0.250 or less, and more preferably 0.150 or more. From the viewpoint of handling when used as a packaging bag, it is preferable that the static friction coefficient on the back surface of the heat-seal paper is above the above lower limit. The static friction coefficient on the back surface of the heat-seal paper of this embodiment is considered to be isotropic. The static friction coefficient is measured in accordance with JIS P 8147:2010. The static friction coefficient on the back surface of the heat-seal paper of this embodiment is adjusted according to the method of forming the heat-seal layer. When the heat-seal layer is formed by the dry lamination method, for example, it is adjusted by the content of the slip agent in the heat-seal layer. A high content of the slip agent tends to lower the static friction coefficient on the back surface. Furthermore, when the heat seal layer is formed by melt extrusion lamination, the static friction coefficient on the back surface is adjusted, for example, by the surface roughness of the cooling roll. Reducing the surface roughness of the cooling roll tends to decrease the static friction coefficient on the back surface. Also, when the heat seal layer is formed by coating, the static friction coefficient on the back surface is adjusted, for example, by the content of the slip agent. A higher content of the slip agent tends to decrease the static friction coefficient on the back surface.

[0036] (Opacity) The opacity of the heat-seal paper of this embodiment is preferably 5% to 60%, more preferably 55% or less, even more preferably 50% or less, even more preferably 45% or less, even more preferably 40% or less, and even more preferably 35% or less, and from the viewpoint of ease of manufacturing the heat-seal paper, it is more preferably 10% or more, and even more preferably 15% or more. From the viewpoint of obtaining a package with excellent visibility of the contents, the opacity of the heat-seal paper is preferably below the above upper limit, and from the viewpoint of ease of manufacturing the heat-seal paper, it is preferably above the above lower limit. The opacity of the heat-seal paper can be set to a desired range by appropriately adjusting the type of paper substrate, the basis weight and thickness of the paper substrate and heat-seal layer. The opacity of the heat-seal paper is measured by the method described in the examples.

[0037] [Roll] The roll of this embodiment is formed by overlapping the heat-sealing layers of the heat-sealing paper of this embodiment, with both ends heat-sealed in the vertical direction, and then winding it up in the vertical direction. The packaging bags of this embodiment can be efficiently manufactured using the roll of this embodiment.

[0038] [Packaging Bag] The packaging bag of this embodiment is manufactured by heat-sealing the heat-seal layers of the heat-seal paper of this embodiment facing each other, and has the heat-seal layer on the inside. Preferably, the packaging bag of this embodiment is made only of the heat-seal paper of this embodiment. Examples of the forms of the packaging bag of this embodiment include three-side sealed packaging bags, four-side sealed packaging bags, and pillow packaging bags, with three-side sealed packaging bags and four-side sealed packaging bags being preferred.

[0039] [Packaging] The packaging of this embodiment is formed by placing the contents to be contained in the packaging bag of this embodiment. Examples of the contents to be contained include metal fittings, food, stationery, daily necessities, miscellaneous goods, etc. The contents may be one or two or more.

[0040] Examples are given below to illustrate the present invention in detail, but the present invention is not limited to these examples. Unless otherwise specified, the following operations were carried out under conditions of 23°C and 50% relative humidity. In the examples and comparative examples, "parts" and "%" refer to "parts by mass" and "mass%", respectively, unless otherwise specified.

[0041] [Example 1] Paper substrate with a basis weight of 23.0 g / m² ２ Glassine paper (manufactured by Oji F-Tex Co., Ltd., 100% by mass of bleached softwood kraft pulp, irregular freeness of disintegrated pulp 500 mL) was used. On one side of the PE film (manufactured by Futamura Chemical Co., Ltd., LL-XMTN), an adhesive mixture of 10 parts DIC Dry LX-500 (manufactured by DIC Corporation) and 1 part DIC Dry KW-75 (manufactured by DIC Corporation) was applied at a rate of 5 g / m². ２ The coating was applied to a thickness of 5 μm. A PE film coated with adhesive was dry-laminated to one side of the glassine paper to obtain heat-sealable paper.

[0042] [Example 2] Glassine paper with a basis weight of 30.5 g / m² ２ Heat-sealable paper was obtained in the same manner as in Example 1, except that (100% by mass of bleached softwood kraft pulp manufactured by Oji F-Tex Co., Ltd., with an irregular freeness of 500 mL of disintegrated pulp) was used.

[0043] [Example 3] Glassine paper with a basis weight of 50.0 g / m² ２ Heat-sealable paper was obtained in the same manner as in Example 1, except that (100% by mass of bleached softwood kraft pulp manufactured by Oji F-Tex Co., Ltd., with an irregular freeness of 500 mL of disintegrated pulp) was used.

[0044] [Example 4] Heat-seal paper was obtained in the same manner as in Example 2, except that the heat-seal layer was made of a low-slip PE film (manufactured by Futamura Chemical Co., Ltd., LL-MTNR).

[0045] [Example 5] Glassine paper with a basis weight of 30.0 g / m² ２ Heat-sealable paper was obtained in the same manner as in Example 1, except that bleached kraft paper (manufactured by Oji F-Tex Co., Ltd., 100% by mass of bleached hardwood kraft pulp, with a freeness of 420 mL of disintegrated pulp) was used.

[0046] [Comparative Example 1] Heat-sealing paper was obtained in the same manner as in Example 1, except that glassine paper was produced by the following method to have a basis weight of 20.0 g / m ２ Softwood bleached kraft pulp (NBKP) was beaten to a freeness of 250 mL of irregular freeness of the pulped pulp, and then a pulp slurry with a concentration of 3.8% was obtained. In this pulp slurry, 0.9 part of an anionic dry paper strength enhancer mainly composed of polyacrylamide (trade name: PS-NH20B, manufactured by Arakawa Chemical Industries, Ltd.), 0.9 part of a cationic wet paper strength enhancer mainly composed of polyamide polyamine epichlorohydrin (trade name: WS4024, manufactured by Starlight PMC Co., Ltd.), and 0.1 part of an alkyl ketene dimer (trade name: AD1612, manufactured by Starlight PMC Co., Ltd.) as a neutral sizing agent were mixed per 100 parts of pulp solids, and stirred to obtain a paper stock. This paper stock was adjusted to a concentration of 0.5%, and papermaking was carried out using a standard hand sheet former. Drying was performed using a cylinder dryer so that the moisture content in the obtained sheet was 15%. Immediately after drying, it was passed through a heat calendar composed of a metal roll and an elastic roll to obtain glassine paper with a basis weight of 20.0 g / m ２ of glassine paper.

[0047] [Comparative Example 2] Heat-sealing paper was obtained in the same manner as in Example 1, except that the glassine paper had a basis weight of 75.0 g / m ２ (manufactured by Oji Efftex Co., Ltd., 100% by mass of softwood bleached kraft pulp, irregular freeness of the pulped pulp: 500 mL).

[0048] [Comparative Example 3] Heat-sealing paper was obtained in the same manner as in Example 2, except that the heat-sealing layer was changed to a PE film (LF440B, manufactured by Nippon Polyethylene Co., Ltd.) that does not contain a slip agent.

[0049] [Measurement and Evaluation Methods] The following measurements and evaluations were performed on the paper substrate and the obtained heat-sealing paper. <Basis Weight> The basis weights of the paper substrate and the heat-sealing paper were measured in accordance with JIS P 8124:2011. The basis weight of the heat-sealing layer was calculated from the numerical values of the paper substrate and the heat-sealing paper.

[0050] <Thickness> The thickness of the paper substrate and heat-sealing paper was measured in accordance with JIS P 8118:2014. The thickness of the heat-sealing layer was calculated from the values ​​of the paper substrate and heat-sealing paper.

[0051] <Irregular Freeness> The irregular freeness of the pulp constituting the paper substrate was measured using pulp that had been disintegrated in accordance with JIS P 8220-1:2012 as a sample, using the Canadian standard filtration method specified in JIS P 8121:2012, but with the pulp sample amount changed from 3g to 0.3g and the JIS standard screen plate changed to an 80-mesh wire.

[0052] <Freeness> The freeness (Canadian Standard Fluidity (CSF)) of the pulp constituting the paper substrate was measured in accordance with JIS P 8121-2:2012, using pulp that had been disintegrated in accordance with JIS P 8220-1:2012 as a sample.

[0053] <Density> The density of the paper substrate and heat-sealable paper was calculated from the basis weight and thickness.

[0054] <Static friction coefficient> The static friction coefficients of the front and back surfaces of the heat-sealing paper were measured in accordance with JIS P 8147:2010.

[0055] <Tensile Strength> The tensile strength of the heat-sealing paper was measured in accordance with JIS P 8113:2006.

[0056] <Pure Bending Stiffness> After conditioning the heat-sealing paper to 23°C and 50% RH, test pieces were cut to a width of 80 x 80 mm. The pure bending stiffness in the longitudinal direction (MD direction) and transverse direction (CD direction) of the test pieces was measured using a pure bending stiffness tester (manufactured by Kato Tech Co., Ltd.). Note that the pure bending stiffness in the MD direction is the stiffness when bent in the MD direction, and the pure bending stiffness in the CD direction is the stiffness when bent in the CD direction. Specifically, the heat-sealing paper was bent at a deformation speed of 0.5 cm / second. The amount of change in bending moment (per unit test piece width) per change in curvature was determined at two points in the range of curvature 0.5 to 1.5 (front bending) and -0.5 to -1.5 (back bending), and the average value of each value was taken as the pure bending stiffness.

[0057] <Opacity> The opacity of the heat-sealable paper was measured in accordance with JIS P 8149:2000. The lower the opacity, the better the visibility of the packaging using the heat-sealable paper.

[0058] <Easy Opening> Two sheets of heat-sealable paper were overlapped with the heat-sealed layers facing inward, and the sides and bottom were heat-sealed to create a packaging bag measuring 10 cm wide x 12 cm long with three sides sealed. Ten people evaluated how easy it was to open the bag by pinching the opening (near the edge that was not heat-sealed) with their fingers and sliding one side of the heat-sealable paper approximately 3 cm in the vertical direction of the paper. The three-sided sealed packaging bag made using the heat-sealable paper from Example 2 was evaluated first and used as a baseline. The following scores were assigned, and the total scores of the ten people were applied to the evaluation rank below. (Score) 2 points: Easier to open than the baseline 1 point: Equal to the baseline ease of opening 0 points: Difficult to open than the baseline (Evaluation Rank) A: 10 points or more B: 7 points or more and 9 points or less C: 4 points or more and 6 points or less D: 3 points or less

[0059] Packaging bags were prepared with three sides sealed in the same manner as for <tear resistance> and <easy opening>. For five packaging bags, the opening (near the side not heat-sealed) was held between fingers, and one side of the heat-seal paper was slid approximately 3 cm in the vertical direction of the paper 200 times. The number of tears that occurred in the paper base material was evaluated according to the evaluation rank below. The test was conducted by one person. A: 0 packaging bags out of 5 that tore B: 1 packaging bag out of 5 that tore C: 2 or more packaging bags out of 5 that tore

[0060]

[0061] Table 1 shows that the packaging bags obtained using the heat-sealable paper of this embodiment were easy to open and resistant to tearing during opening (Examples 1-5). In contrast, the packaging bags obtained using heat-sealable paper with a longitudinal tensile strength of less than 1.8 kN / m (1.71 kN / m) were easily torn during opening (Comparative Example 1). Furthermore, the geometric mean of the pure bending stiffness in the longitudinal and transverse directions was 0.80 g・cm. ２ / cm over (1.005g・cm ２A packaging bag obtained using heat-seal paper with a coefficient of friction of 0.750 (0.795) on the side of the heat-seal layer opposite to the paper substrate (front side) (Comparative Example 2), and a packaging bag obtained using heat-seal paper with a coefficient of friction of 0.750 (0.795) on the front side of the heat-seal layer, exhibited poor ease of opening. According to this embodiment, it is possible to provide heat-seal paper that reduces the burden on the environment, is easy to open, and is resistant to tearing during opening, as well as rolls, packaging bags, and packaging bodies made using this heat-seal paper.

[0062] The heat-sealable paper of the present invention is suitable as a packaging material, as it provides excellent visibility of the contents when used as a package, is easy to open, and is resistant to tearing when the contents are removed, making it suitable for use in forming packaged goods.

Claims

1. A heat-sealable paper having a heat-seal layer on one side of a paper substrate, wherein the paper substrate content in the heat-sealable paper is 50% by mass or more, and the geometric mean of the pure bending stiffness in the longitudinal direction and the pure bending stiffness in the transverse direction of the heat-sealable paper is 0.80 g・cm². ２ A heat-sealable paper having a thickness of 1.80 kN / m or less, a tensile strength in the longitudinal direction of the heat-sealable paper of 1.80 kN / m or more, and a static friction coefficient of 0.750 or less on the side of the heat-sealable layer opposite to the paper substrate.

2. The longitudinal bending stiffness of the heat-sealable paper is 1.20 g·cm. ２ The heat-sealable paper according to claim 1, wherein the thickness is less than or equal to / cm.

3. The transverse pure bending stiffness of the heat-sealing paper is 0.60 g·cm. ２ The heat-sealable paper according to claim 1 or 2, wherein the thickness is less than or equal to / cm.

4. The heat-seal paper according to any one of claims 1 to 3, wherein the heat-seal layer contains a slip agent.

5. The heat-sealable paper according to any one of claims 1 to 4, wherein the heat-sealable layer is a laminate layer.

6. Basis weight is 80.0 g / m² ２ The heat-sealable paper according to any one of claims 1 to 5, which is as follows:

7. Heat-sealable paper according to any one of claims 1 to 6, for use in packaging bags having a heat-sealable layer on the inside.

8. A roll of heat-sealable paper according to any one of claims 1 to 7, wherein both ends of the overlapping heat-sealable layers are heat-sealed in the vertical direction, and the roll is wound in the vertical direction.

9. A packaging bag using heat-sealable paper according to any one of claims 1 to 7 or a roll according to claim 8.

10. A package comprising a packaging bag according to claim 9, containing an item to be contained.

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