Heat-sealable paper, packaging bags

Abstract

To provide heat seal paper having excellent visibility of contents when used as a packaging bag and having good heat sealability.SOLUTION: There is provided heat seal paper with a heat seal layer on at least one side of a paper substrate, in which a total light transmittance measured in accordance with JIS K 7361-1:1997 is 65% or more, and an arithmetic mean height of a surface on the heat seal layer side measured in accordance with JIS B 0601:2001 is 75 μm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to heat-sealable paper and packaging bags made using the same. [Background technology]

[0002] Packaging bags using the heat-sealing method are widely used not only for packaging general industrial products, but also for packaging food, pharmaceuticals, and medical devices.

[0003] In recent years, the plastic waste problem has become increasingly serious. The packaging sector accounts for a large portion of global plastic production, making it a major source of plastic waste. Plastic does not decompose almost indefinitely, and its waste breaks down into microplastics in the natural environment, severely impacting ecosystems. As a solution, replacing plastic with paper has been proposed.

[0004] For example, Patent Document 1 describes a heat-sealable paper in which two or more heat-sealable layers containing an ionomer are formed on at least one surface of a paper substrate. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6580291 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Packaging bags sometimes require visibility of the contents so that the contents and remaining amount can be seen from the outside. However, the heat-sealable paper described in Patent Document 1 has low transparency, which is a problem when used as packaging bags because it makes the contents difficult to see.

[0007] Therefore, the present invention aims to provide heat-sealable paper that offers excellent visibility of the contents when used as a packaging bag, and also has good heat-sealing properties. [Means for solving the problem]

[0008] The problems of the present invention can be solved by the following configuration. <1> A heat-sealable paper having a heat-seal layer on at least one side of a paper substrate, wherein the total light transmittance measured in accordance with JIS K 7361-1:1997 is 65% or more, and the arithmetic mean height of the heat-seal layer side surface measured in accordance with JIS B 0601:2001 is 75 μm or less. <2> The haze measured in accordance with JIS K 7361-1:1997 is 90% or less. <1> The heat-sealing paper described above. <3> The maximum height of the heat seal layer side surface, measured in accordance with JIS B 0601:2001, is 550 μm or less. <1> or <2> The heat-sealing paper described above. <4> The irregular freeness of the pulp fibers constituting the paper substrate is 100 mL or more and 600 mL or less. <1> ~ <3> Heat seal paper as described in one of the following. <5> The coating amount of the heat seal layer is 2 g / m². 2 More than 8g / m 2 The following is: <1> ~ <4> Heat seal paper as described in one of the following. <6> The peel strength when heat-sealing two heat-seal layers together under the conditions of 120°C, 1 second, and 0.2 MPa is 0.9 N / 15 mm or higher. <1> ~ <5> Heat seal paper as described in one of the following. <7> The oxygen permeability at 23°C and 50% RH is 5 mL / (m³). 2 (24 hours / atm) or less. <1> ~ <6> Heat seal paper as described in one of the following. <8> Packaging material, <1> ~ <7> Heat seal paper as described in one of the following. <9> <1> ~ <7> A packaging bag made using heat-sealable paper as described in any of the above. [Effects of the Invention]

[0009] According to the present invention, a heat-sealing paper can be obtained which has excellent visibility of the contents when used as a packaging bag and has good heat-sealing properties.

Mode for Carrying Out the Invention

[0010] Hereinafter, preferred embodiments of the present invention will be described. In this specification, "X to Y" indicating a range means "X or more and Y or less". Also, in this specification, unless otherwise specified, measurements of operations and physical properties are performed under the conditions of room temperature (20 to 25°C) / relative humidity 40 to 50%RH.

[0011] <Heat-sealing paper> The heat-sealing paper according to an embodiment of the present invention (hereinafter, also simply referred to as "heat-sealing paper") has a heat-sealing layer on at least one surface of a paper substrate, and the total light transmittance measured in accordance with JIS K 7361-1:1997 is 65% or more, and the arithmetic mean height of the surface on the heat-sealing layer side measured in accordance with JIS B 0601:2001 is 75 μm or less. The heat-sealing paper of this embodiment has excellent visibility of the contents when used as a packaging bag and has good heat-sealing properties. Hereinafter, this embodiment will be described in detail.

[0012] [Paper substrate] In the heat-sealing paper of this embodiment, the irregular freeness of the pulp fibers constituting the paper substrate is preferably 100 mL or more, more preferably 150 mL or more, and still more preferably 200 mL or more from the viewpoint of the dimensional stability of the paper substrate. Also, the irregular freeness of the pulp fibers constituting the paper substrate is preferably 600 mL or less, more preferably 500 mL or less, and still more preferably 400 mL or less from the viewpoint of the transparency of the paper substrate. For the method of beating the pulp to prepare the irregular freeness, a known method can be used. Here, "irregular freeness" refers to the freeness (filtration efficiency) measured using the Canadian standard filtration efficiency 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. The irregular freeness of the pulp constituting the paper substrate is measured using the method described above, with pulp disintegrated in accordance with JIS P 8220-1:2012 as the sample. In this specification, the irregular freeness of the pulp fibers constituting the paper substrate is also referred to as "irregular freeness of disintegrated pulp." Examples of paper substrates in which the irregular freeness of the constituent pulp fibers is 100 mL to 600 mL include glassine paper. Among glassine papers, glassine paper that exhibits particularly high total light transmittance with high beating is also called Graphan paper. From the viewpoint of improving the gas barrier properties of heat-sealable paper, it is preferable to use Graphan paper as the paper substrate.

[0013] Generally, glassine paper is made primarily from softwood chemical pulp as the pulp raw material. It is highly beaten, paper is made in an acidic to neutral environment, and then compressed using a supercalender or similar device. Specific examples of pulp include chemical pulp made from softwoods such as spruce and hemlock, which is ideal. However, other types of pulp, such as chemical pulp made from hardwoods, mechanical pulp, recycled paper, and synthetic pulp, may also be mixed in.

[0014] Additives may be added to the paper substrate. Examples of additives include pH adjusters (sodium bicarbonate, sodium hydroxide, etc.), drying agents (polyacrylamide, starch, etc.), wetting agents (any of polyamide polyamine epichlorohydrin resin, melamine-formaldehyde resin, or urea-formaldehyde resin), internal sizing agents (rosin-based, alkyl ketene dimer, etc.), filtration yield improvers, defoamers, fillers (calcium carbonate, talc, etc.), dyes, etc. These additives may be used individually or in combination of two or more. The content of additives is not particularly limited and may be within the range commonly used.

[0015] (Basic weight) The basis weight of the paper substrate is not particularly limited. For example, in the case of packaging bag applications, it is preferably 20 g / m 2 or more and 150 g / m 2 or less, more preferably 50 g / m 2 or more and 100 g / m 2 or less, even more preferably 30 g / m 2 or more and 50 g / m 2 or less. The basis weight of the paper substrate is measured in accordance with JIS P 8124:2011.

[0016] (Paper thickness) The paper thickness of the paper substrate is not particularly limited. For example, in the case of packaging bag applications, it is preferably 20 μm or more and 150 μm or less, more preferably 25 μm or more and 100 μm or less, even more preferably 30 μm or more and 50 μm or less. The paper thickness of the paper substrate is measured in accordance with JIS P 8118:2014.

[0017] (Total light transmittance) From the viewpoint of obtaining a heat-sealing paper with excellent visibility of the contents when made into a packaging bag, the total light transmittance of the paper substrate is preferably 65% or more, more preferably 70% or more, even more preferably 75% or more, and even more preferably 80% or more, and it may be 100%. From the viewpoint of easy availability, it is preferably 95% or less, more preferably 90% or less. The total light transmittance of the paper substrate is measured in accordance with JIS K 7375:2008.

[0018] (Method for manufacturing the paper substrate) Examples of the method for manufacturing the paper substrate include a method of papermaking using a paper stock containing pulp. The paper stock may further contain an additive. Examples of the additive include the additives mentioned above.

[0019] The paper stock can be prepared by adding additives to a pulp slurry. The pulp slurry is obtained by beating pulp in the presence of water. The method and apparatus for beating the pulp are not particularly limited and may be the same as known methods and apparatus. The pulp content in the paper stock is not particularly limited and may be within the range commonly used. For example, it may be 60% by mass or more and less than 100% by mass of the total mass of the paper stock.

[0020] Papermaking can be carried out by conventional methods. For example, the paper pulp can be cast onto a wire or the like, dewatered to obtain wet paper, and if necessary, multiple layers of wet paper can be stacked, and this single or multi-layer wet paper can be pressed and dried. In this case, if multiple layers of wet paper are not stacked, single-layer paper can be obtained, and if multiple layers of wet paper are stacked, multi-layer paper can be obtained. When stacking multiple layers of wet paper, an adhesive may be applied to the surface of the wet paper (the surface on which other wet papers are stacked).

[0021] [Heat seal layer] The heat-sealable paper of this embodiment has a heat-seal layer on at least one surface of the paper substrate. The heat-seal layer is a layer that is melted and adhered by heating, ultrasound, or the like. The heat-sealable paper of this embodiment may have the heat-seal layer on both surfaces of the paper substrate. Furthermore, from the viewpoint of providing heat-sealability, the heat-seal layer may be formed on the uppermost layer of at least one surface, and two or more heat-seal layers may be formed on one surface.

[0022] The resin constituting the heat seal layer (hereinafter also referred to as the "heat seal layer resin") is not particularly limited, but examples include vinyl chloride resin, vinyl acetate resin, vinyl chloride-vinyl acetate copolymer, acrylic resin, polyester resin, olefin resin, styrene resin, styrene-acrylic resin, ethylene acrylic resin, and modified versions thereof. The heat seal layer resin may be used alone or in combination of two or more types.

[0023] For the heat seal layer resin, either a synthetic product or a commercially available product may be used, and commercially available products such as those used in the examples can be used.

[0024] The heat seal layer may contain other components in addition to the heat seal resin described above. Examples of other components include pigments, lubricants, defoamers, viscosity modifiers, leveling agents such as surfactants and alcohols, and colorants such as coloring dyes. However, since these other components tend to worsen the heat sealability, the total content of these other components is preferably 30% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, of the solid content of the heat seal layer.

[0025] (Method for forming a heat seal layer) The method for forming the heat seal layer is not particularly limited, but for example, a heat seal layer can be formed by preparing a heat seal layer coating solution containing at least a heat seal layer resin, applying the coating solution to at least one surface of a paper substrate, and drying it. In this method, it is preferable to prepare the heat seal layer coating solution by dissolving or dispersing the heat seal layer resin in an organic solvent or a mixed solvent of an organic solvent and water for the following reasons.

[0026] To obtain heat-sealable paper with excellent visibility of contents when used as a packaging bag, it is conceivable to select a highly transparent paper substrate. However, highly transparent paper substrates (especially graphite paper) have undergone extensive beating, resulting in a large specific surface area of ​​cellulose. Therefore, there are many hydrogen bonds between cellulose molecules, and water easily penetrates these areas. Consequently, when a water-based heat-seal coating solution is applied to a highly transparent paper substrate, the coating solution penetrates the paper substrate, causing numerous wrinkles during the drying process (i.e., increasing the surface roughness of the heat-seal layer side surface). As a result, the resulting heat-sealable paper has poor visibility of contents when used as a packaging bag (see Comparative Example 1 below). In contrast, by applying a solvent-based heat-seal coating solution to a highly transparent paper substrate, the penetration of the coating solution into the paper substrate is suppressed, reducing the occurrence of wrinkles during the drying process (i.e., decreasing the surface roughness of the heat-seal layer side surface). As a result, the resulting heat-sealable paper has excellent visibility of contents when used as a packaging bag.

[0027] For the reasons stated above, it is preferable to use an organic solvent or a mixed solvent of an organic solvent and water as the solvent for the heat seal layer coating solution. The organic solvent is not particularly limited and includes acetone, methanol, ethanol, isopropanol, n-propanol, butanol, ethyl acetate, propyl acetate, methyl ethyl ketone, methyl isobutyl ketone, toluene, propylene glycol monomethyl ether, hexane, etc. In the case of a mixed solvent of water and an organic solvent, it is preferable that the mass ratio of the organic solvent to water (organic solvent / water) in the heat seal layer coating solution is 99 / 1 or more and less than 20 / 80.

[0028] Furthermore, as will be described later, if an anchor coat layer is provided between the paper substrate and the heat seal layer, an aqueous solvent may be used as the solvent for the heat seal layer coating liquid. In this specification, "aqueous solvent" means that the water content in the solvent is 80% by mass or more.

[0029] The equipment used for coating the heat seal layer coating liquid is not particularly limited, and can be appropriately selected from commonly used coating equipment. Examples include various known coating equipment such as air knife coaters, blade coaters, gravure coaters, rod blade coaters, roll coaters, reverse roll coaters, Meyer bar coaters, curtain coaters, die slot coaters, champlex coaters, metering blade type size press coaters, short dwell coaters, spray coaters, gate roll coaters, and lip coaters.

[0030] The drying conditions for the heat seal layer are not particularly limited, but the drying temperature is preferably 50 to 120°C, and the drying time is preferably 5 to 120 seconds.

[0031] The drying equipment for drying the coated heat-seal layer is not particularly limited, and known equipment can be used. Examples of drying equipment include hot air dryers, infrared dryers, explosion-proof dryers, gas burners, and hot plates.

[0032] (Amount of heat seal layer coating) From the viewpoint of heat seal peel strength, the amount of heat seal layer coating is preferably 1 g / m². 2 More than 2g / m 2 The above applies, and preferably 12 g / m². 2 More preferably 10 g / m 2 More preferably 8 g / m 2 The following applies. Note that the amount of heat-seal layer coating refers to the amount of coating after drying, and if the heat-seal paper has two or more heat-seal layers, it refers to the total amount of coating.

[0033] [Anchor coat layer] When applying a water-based heat-seal layer coating solution to a paper substrate, it is preferable to provide an anchor coat layer between the paper substrate and the heat-seal layer in order to suppress the penetration of the coating solution into the paper substrate.

[0034] The resin constituting the anchor coat layer (hereinafter also referred to as "resin for anchor coat layer") is not particularly limited as long as it can exhibit the above-mentioned effects, but preferred examples include polyester resin, urethane resin, acrylic resin, vinyl chloride-vinyl acetate copolymer, ethylene-vinyl acetate resin, ethylene acrylic resin, and modified versions thereof. The resin for anchor coat layer may be used alone or two or more types may be used in combination.

[0035] The anchor coat layer may contain other components in addition to the resin for the anchor coat layer described above. Examples of other components include pigments, lubricants, defoamers, viscosity modifiers, leveling agents such as surfactants and alcohols, and colorants such as coloring dyes. The total content of the other components is preferably 30% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, of the solid content of the anchor coat layer.

[0036] (Method for forming the anchor coat layer) The method for forming the anchor coat layer is not particularly limited, but for example, an anchor coat layer can be formed by preparing an anchor coat layer coating solution containing at least an anchor coat layer resin, applying the coating solution to at least one surface of a paper substrate, and drying it. In this method, it is preferable to prepare the anchor coat layer coating solution by dissolving or dispersing the anchor coat layer resin in an organic solvent or a mixed solvent of an organic solvent and water in order to suppress the penetration of the anchor coat layer coating solution into the paper substrate and the occurrence of wrinkles.

[0037] The organic solvent is not particularly limited, but examples include those exemplified in the section on (Method for forming the heat seal layer) above. In the case of a mixed solvent of water and an organic solvent, the mass ratio of the organic solvent to water (organic solvent / water) in the anchor coat layer coating liquid is preferably 99 / 1 or more and less than 20 / 80.

[0038] The apparatus used for coating and drying the anchor coat layer is not particularly limited, and examples include those described in the section on (method for forming the heat seal layer) above.

[0039] The drying conditions for the anchor coat layer are not particularly limited, but the drying temperature is preferably 50 to 100°C, and the drying time is preferably 5 to 60 seconds.

[0040] (Amount of anchor coat layer applied) From the viewpoint of suppressing the penetration of the heat seal layer coating liquid into the paper substrate, the amount of anchor coat layer applied is preferably 0.1 g / m². 2 More than 0.3 g / m 2 That concludes the explanation. The upper limit of the amount of anchor coat layer applied is not particularly limited, but is preferably 3.0 g / m². 2 More preferably, 2.0 g / m 2 More preferably, 1.0 g / m 2 The following applies. Note that the amount of anchor coat layer applied is the amount after drying.

[0041] <Physical properties of heat-sealable paper> (Peel strength) The heat-sealable paper of the present invention has a peel strength of preferably 0.9 N / 15 mm or more, more preferably 1.5 N / 15 mm or more, even more preferably 2.0 N / 15 mm or more, and even more preferably 2.5 N / 15 mm or more when heat-sealed layers are heat-sealed together at 120°C, 0.2 MPa, and 1 second. The upper limit is not particularly limited, but is preferably 20.0 N / 15 mm or less, more preferably 18.0 N / 15 mm or less, and even more preferably 15.0 N / 15 mm or less.

[0042] (Total light transmittance) The total light transmittance of the heat-seal paper according to this embodiment is 65% or more, preferably 70% or more, more preferably 75% or more, even more preferably 80% or more, and even more preferably 82% or more, from the viewpoint of visibility of the contents when used as a packaging bag. The upper limit of the total light transmittance of the heat-seal paper is not particularly limited, but is usually 100% or less, preferably 95% or less, and more preferably 90% or less. The total light transmittance of the heat-seal paper is measured in accordance with JIS K 7361-1:1997.

[0043] (Hayes) The haze of the heat-sealable paper according to this embodiment is preferably 90% or less, more preferably 85% or less, from the viewpoint of visibility of the contents when used as a packaging bag. The lower limit of the haze of the heat-sealable paper is not particularly limited, but is usually 0% or more, preferably 10% or more, and more preferably 20% or more. The haze of the heat-sealable paper is measured in accordance with JIS K 7361-1:1997.

[0044] (Surface roughness) The surface roughness of the heat-seal paper according to this embodiment is such that, from the viewpoint of visibility of the contents when used as a packaging bag, the arithmetic mean height of the heat-seal layer side surface, measured in accordance with JIS B 0601:2001, is 75 μm or less, preferably 60 μm or less, more preferably 50 μm or less, even more preferably 40 μm or less, even more preferably 30 μm or less, and particularly preferably 25 μm or less, with a lower limit of 0 μm.

[0045] The surface roughness of the heat-seal paper according to this embodiment is preferably 550 μm or less, more preferably 400 μm or less, even more preferably 300 μm or less, even more preferably 250 μm or less, and particularly preferably 200 μm or less, with a lower limit of 0 μm, from the viewpoint of visibility of the contents when used as a packaging bag.

[0046] (Oxygen permeability) In this embodiment, the oxygen permeability of the heat-sealing paper should be as low as possible to minimize oxygen penetration. Preferably, the oxygen permeability at 23°C and 50% RH is 20 mL / m². 2 • 24h·atm or less, more preferably 10 mL / m² 2 • 24h·atm or less, more preferably 5 mL / m² 2 • 24h·atm or less, and particularly preferably 3 mL / m² 2 • 24h·atm or less, particularly preferably 2 mL / m² 2 The oxygen permeability is less than 24h·atm. The oxygen permeability of the barrier laminate is measured using an oxygen permeability measuring device (MOCON, OX-TRAN2 / 20) under the above conditions.

[0047] <Application> The heat-sealable paper according to the present invention is suitable for use as a packaging material for food, cosmetics, daily necessities, detergents, soaps, powders, precision machinery, and the like, taking advantage of its excellent visibility of contents when used as a packaging bag. Accordingly, the present invention also provides a packaging bag made using the above-mentioned heat-sealable paper. [Examples]

[0048] The present invention is described below in detail by giving examples, but the present invention is based on these examples. This is not limited to the above. Unless otherwise specified, the following operations were performed under conditions of 25°C and 50% RH relative humidity. In addition, unless otherwise specified, "parts" and "%" in the examples and comparative examples refer to "parts by mass" and "mass%", respectively.

[0049] <Example 1> A heat sealant mainly composed of a vinyl chloride-vinyl acetate copolymer (solvent: ethyl acetate, solids content: 27.5%, product name: DIC Seal A-100ES-G2, manufactured by DIC Graphics Co., Ltd.) was diluted with ethyl acetate to obtain a heat seal layer coating solution 1 with a solids content of 15%. This was then used with Graphan paper (manufactured by Oji F-Tex Co., Ltd., irregular freeness of disintegrated pulp 250 mL, basis weight 35 g / m²), which was a paper substrate. 2 On paper with a thickness of 32 μm and a total light transmittance of 82.5%, the coating amount after drying is 6 g / m². 2 After coating with a Meyer bar in this manner, the paper was dried in an explosion-proof dryer at 80°C for 10 seconds to obtain heat-sealable paper.

[0050] <Example 2> Heat-sealable paper was prepared in the same manner as in Example 1, except that heat-sealable coating liquid 2 (solvent: ethyl acetate / MEK, solids content: 28%, product name: DIC Seal A-450LT, manufactured by DIC Graphics Co., Ltd.), whose main component is an acrylic resin, was used instead of heat-sealable coating liquid 1.

[0051] <Example 3> A heat sealant whose main component is a polyester resin (solvent: ethyl acetate / MEK, product name: DIC Seal A-970-5NT, manufactured by DIC Graphics Co., Ltd.) was diluted with ethyl acetate to obtain a heat seal layer coating solution 3 with a solid content of 25%. Heat seal paper was prepared in the same manner as in Example 1, except that heat seal layer coating solution 3 was used instead of heat seal layer coating solution 1.

[0052] <Example 4> A heat-sealable paper was prepared in the same manner as in Example 1, except that a modified polyolefin resin dispersion (solvent: isopropyl alcohol / water (27 / 73), solids content: 25%, product name: Arrowbase SB-1200, manufactured by Unitika Ltd.) was used instead of the heat-sealable layer coating liquid 1, and the drying conditions were set to 100°C for 40 seconds.

[0053] <Example 5> Heat-sealable paper was prepared in the same manner as in Example 4, except that a modified polyolefin resin dispersion (solvent: isopropyl alcohol / water (27 / 73), solids content: 20%, product name: Arrowbase AA-1152, manufactured by Unitika Ltd.) was used instead of heat-sealable layer coating liquid 1.

[0054] <Example 6> A heat sealant whose main component is an olefin copolymer (solvent: water, solids content: 48.3%, product name: EA-H700, manufactured by Toyo Morton Co., Ltd.) was diluted with methanol to obtain heat seal layer coating solution 6 (methanol / water = 26 / 74) with a solids content of 20%. Heat seal paper was prepared in the same manner as in Example 4, except that heat seal layer coating solution 6 was used instead of heat seal layer coating solution 1.

[0055] <Example 7> A solvent-based anchor coating agent containing polyester resin (solvent: ethyl acetate, propyl acetate, methyl ethyl ketone, solids content: 5-10%) is applied to Graphan paper (manufactured by Oji F-Tex Corporation, 250 mL of irregular freeness of disintegrated pulp, basis weight 35 g / m²) which is a paper substrate. 2 On paper with a thickness of 32 μm and a total light transmittance of 82.5%, the coating amount after drying is 0.5 g / m². 2 After coating with a Meyer bar, the material was dried in an explosion-proof dryer at 80°C for 10 seconds. Furthermore, a heat seal layer coating liquid (solvent: water, solids content: 49%, product name: Hi-Loss-X·NE-2260, manufactured by Seikoh PMC Co., Ltd.) mainly composed of styrene acrylic resin was applied to the anchor coat layer, with a coating amount of 3.0 g / m² after drying. 2 After coating with a Meyer bar in this manner, the paper was dried in a hot air dryer at 120°C for 1 minute to obtain heat-sealable paper.

[0056] <Comparative Example 1> In Example 6, heat-sealable paper was prepared in the same manner as in Example 6, except that water was used instead of methanol as the diluting solvent for the heat-sealing agent.

[0057] <Comparative Example 2> In Example 2, the paper substrate was bleached kraft paper (manufactured by Oji Materia Co., Ltd., with an irregular freeness of 700 mL of disintegrated pulp and a basis weight of 50 g / m²). 2 Heat-sealable paper was prepared in the same manner, except that the paper thickness was 60 μm and the total light transmittance was 47%.

[0058] <Rating> (1) Total light transmittance In accordance with JIS K 7361-1:1997, the total light transmittance of the heat-seal paper was measured with the light-receiving surface facing the heat-seal layer, and this was used as an indicator of transparency. A total light transmittance of 65% or higher was judged to be good.

[0059] (2) Hayes In accordance with JIS K 7136-1:1997, the haze of the heat-sealing paper was measured with the light-receiving surface facing the heat-sealing layer, and this was used as an indicator of transparency. A haze of 90% or less was judged to be good.

[0060] (3) Surface roughness Using a one-shot 3D shape measuring machine (Keyence Corporation, VR-3000), the arithmetic mean height and maximum height of the heat-sealing layer surface were measured in accordance with JIS B 0601:2001, and these were used as indicators of the surface roughness of the heat-sealing paper. The larger the values ​​for each, the more wrinkled the paper is, and it was judged that there were few wrinkles if the arithmetic mean height was 75 μm or less and the maximum height was 550 μm or less.

[0061] (4) Heat seal peel strength A pair of heat-sealable papers were stacked with the heat-seal layers facing each other, and heat-sealed using a heat-seal tester (Tester Industry Co., Ltd., TP-801-B) under the conditions of 120°C, 0.2 MPa, and 1 second. Subsequently, the heat-sealed test pieces were cut to a width of 15 mm, and a tensile testing machine was used to perform a T-shaped peel test at a tensile speed of 300 mm / min. The average value of six such tests was taken as the heat-seal peel strength. A heat-seal peel strength of 0.9 N / 15 mm or higher was considered to indicate good heat-sealability.

[0062] (5) Oxygen permeability The oxygen permeability of a paper laminate was measured using an oxygen permeability measuring device (MOCON, OX-TRAN2 / 22) under atmospheric pressure, a temperature of 23°C, and a relative humidity of 50% (low humidity conditions). A lower oxygen permeability value indicates superior oxygen barrier performance.

[0063] (6) Visibility The visibility of the heat-sealable paper obtained in the examples and comparative examples was evaluated by visually checking how easily the contents were visible when the paper was formed into a bag. ◎: It is transparent, and the contents can be easily seen (the contents can be seen even from a distance of 50 cm). ○: It is transparent and the contents can be seen (it is difficult to see the contents from a distance of 50cm). △: Although it has transparency, the paper has wrinkles and other imperfections, making it a little difficult to see. ×: It lacks transparency, making it impossible to see the contents.

[0064] [Table 1]

[0065] The results are shown in Table 1 above. The heat-sealable papers of Examples 1 to 7 had excellent visibility of the contents when used as packaging bags, and also possessed good heat-sealability and gas barrier properties. On the other hand, the heat-sealable paper of Comparative Example 1, which was obtained by forming a heat-sealable layer on graphan paper with a water-based coating, developed wrinkles during the drying process and had poor visibility of the contents when used as packaging bags. Furthermore, the heat-sealable paper of Comparative Example 2, which was made using bleached kraft paper instead of graphan paper as the paper substrate, had poor visibility of the contents when used as packaging bags and also had low gas barrier properties.

Claims

1. A heat-sealable paper having an anchor coat layer and a heat-seal layer in this order on at least one surface of a paper substrate, The paper substrate and the heat seal layer are separated by an anchor coat layer. The anchor coat layer comprises at least one of polyester resin, urethane resin, vinyl chloride-vinyl acetate copolymer, and ethylene-vinyl acetate resin. The basis weight of the paper substrate is 20 g / m². ２ 150g / m or more ２ The following: The total light transmittance measured in accordance with JIS K 7361-1:1997 is 65% or higher. A heat-sealable paper having an arithmetic mean height of the heat-sealing layer side surface measured in accordance with JIS B 0601:2001 of 75 μm or less.

2. The heat-sealable paper according to claim 1, wherein the haze measured in accordance with JIS K 7361-1:1997 is 90% or less.

3. The heat-seal paper according to claim 1 or 2, wherein the maximum height of the heat-seal layer side surface, as measured in accordance with JIS B 0601:2001, is 550 μm or less.

4. The heat-sealable paper according to any one of claims 1 to 3, wherein the irregular freeness of the pulp fibers constituting the paper substrate is 100 mL or more and 600 mL or less.

5. The coating amount of the heat seal layer is 2 g / m². ２ 8g / m or more ２ The heat-sealable paper according to any one of claims 1 to 4, which is as follows:

6. The heat-sealable paper according to any one of claims 1 to 5, wherein the peel strength when heat-sealing the heat-sealable layers together under the conditions of 120°C, 1 second, and 0.2 MPa is 0.9 N / 15 mm or more.

7. The oxygen permeability at 23°C and 50% RH conditions is 5 mL / (m³). ２ The heat-sealing paper according to any one of claims 1 to 6, wherein the temperature is 24 h·atm or less.

8. A heat-sealable paper according to any one of claims 1 to 7, which is a packaging material.

9. A packaging bag made using heat-sealable paper according to any one of claims 1 to 7.

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