Heat seal paper and packaging bag

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] The present invention relates to a heat seal paper and a packaging bag using the same. [Background technology]

[0002] Packaging bags using the heat seal method are widely used for packaging general industrial products as well as for packaging food, medicine, medical equipment, and the like.

[0003] In recent years, the problem of plastic waste has become more serious. Of the total amount of plastic produced in the world, a large amount is produced in the packaging container sector, which is the cause of plastic waste. Plastic does not decompose for a long time, and the waste turns into microplastics in the natural environment, causing serious damage to the ecosystem. As a countermeasure, it has been proposed to replace plastic with paper.

[0004] For example, Patent Document 1 describes a heat seal paper in which two or more heat seal 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 Summary of the Invention [Problem to be solved by the invention]

[0006] Packaging bags are sometimes required to have visible contents so that the contents and remaining amount can be seen from the outside, but the heat seal paper described in Patent Document 1 has low transparency, and there is a problem that the contents are poorly visible when used as a packaging bag.

[0007] SUMMARY OF THE PRESENT EMBODIMENTS Accordingly, an object of the present invention is to provide a heat sealable paper which, when made into a packaging bag, allows excellent visibility of the contents and has good heat sealability. [Means for solving the problem]

[0008] The object of the present invention can be achieved by the following configuration. <1> A heat seal paper having a heat seal layer on at least one side of a paper base material, the heat seal paper having a total light transmittance of 65% or more as measured in accordance with JIS K 7361-1:1997 and an arithmetic mean height of the surface of the heat seal layer side of 75 μm or less as measured in accordance with JIS B 0601:2001. <2> The haze measured in accordance with JIS K 7361-1:1997 is 90% or less. <1> 2. The heat seal paper according to claim 1 . <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> 2. The heat seal paper according to claim 1 . <4> The irregular freeness of the pulp fibers constituting the paper base material is 100 mL or more and 600 mL or less; <1> ~ <3> 2. The heat sealable paper according to claim 1 . <5> The coating weight of the heat seal layer is 2 g / m 2 More than 8g / m 2 Below is the <1> ~ <4> 2. The heat sealable paper according to claim 1 . <6> When the heat seal layers are heat sealed together under conditions of 120°C, 1 second, and 0.2 MPa, the peel strength is 0.9 N / 15 mm or more. <1> ~ <5> 2. The heat sealable paper according to claim 1 . <7> Oxygen permeability at 23℃ and 50% RH is 5mL / (m 2 ·24h·atm) or less, <1> ~ <6> 2. The heat sealable paper according to claim 1 . <8> A packaging material, <1> ~ <7> 2. The heat sealable paper according to claim 1 . <9> <1> ~ <7> A packaging bag made using the heat seal paper described in any one of the above. Effect of the Invention

[0009] According to the present invention, it is possible to obtain a heat sealable paper which, when made into a packaging bag, has excellent visibility of the contents and good heat sealability. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

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

[0012] [Paper base material] In the heat seal paper of this embodiment, the irregular freeness of the pulp fiber constituting the paper base material is preferably 100mL or more, more preferably 150mL or more, and even more preferably 200mL or more, from the viewpoint of the dimensional stability of the paper base material. Also, the irregular freeness of the pulp fiber constituting the paper base material is preferably 600mL or less, more preferably 500mL or less, and even more preferably 400mL or less, from the viewpoint of the transparency of the paper base material. A known method can be used to beat the pulp to adjust the irregular freeness. Here, "irregular freeness" refers to the freeness measured in the Canadian Standard Freeness Method prescribed in JIS P 8121:2012, by changing the amount of pulp collected from 3 g to 0.3 g and changing the JIS standard screen plate to an 80 mesh wire. The irregular freeness of the pulp constituting the paper base material is measured by the above-mentioned method using pulp disintegrated in accordance with JIS P 8220-1:2012 as a sample. In this specification, the irregular freeness of the pulp fibers constituting the paper base material is also referred to as "irregular freeness of disintegrated pulp". An example of a paper base material having an irregular freeness of 100 mL or more and 600 mL or less of the pulp fiber that constitutes it is glassine paper. Among glassine papers, glassine paper that shows a high total light transmittance when beaten to a particularly high degree is also called graphene paper. From the viewpoint of improving the gas barrier property of the heat seal paper, it is preferable to use graphene paper as the paper base material.

[0013] Generally, glassine paper contains softwood chemical pulp as the main component of the pulp raw material, and is made by beating the paper at a high level under acidic or neutral conditions, and then compressing the paper using a super calendar, etc. As a specific example of the pulp, chemical pulp made from softwood such as spruce or hemlock is optimal, but other types of pulp such as chemical pulp made from hardwood, mechanical pulp, waste paper, and synthetic pulp may also be mixed and blended.

[0014] Additives may be added to the paper base material. Examples of additives include pH adjusters (sodium bicarbonate, sodium hydroxide, etc.), dry strength agents (polyacrylamide, starch, etc.), wet strength agents (polyamide polyamine epichlorohydrin resin, melamine-formaldehyde resin, or urea-formaldehyde resin), internal sizing agents (rosin-based, alkyl ketene dimer, etc.), drainage retention improvers, antifoaming agents, fillers (calcium carbonate, talc, etc.), dyes, etc. These additives may be used alone or in combination of two or more. The content of the additives is not particularly limited and may be within the range that is usually used.

[0015] (Basic weight) The basis weight of the paper substrate is not particularly limited, but for example, for packaging bag applications, it is 20 g / m 2 More than 150g / m 2 Less than 50 g / m is preferable. 2 More than 100g / m 2 Less than 30 g / m is more preferable. 2 More than 50g / m 2 The following is even more preferred: The basis weight of the paper base material is measured in accordance with JIS P 8124:2011.

[0016] (paper thickness) The thickness of the paper base material is not particularly limited, but for example, for packaging bag applications, it is preferably 20 μm to 150 μm, more preferably 25 μm to 100 μm, and even more preferably 30 μm to 50 μm. The thickness of the paper base material is measured in accordance with JIS P 8118:2014.

[0017] (Total light transmittance) 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 from the viewpoint of obtaining a heat seal paper that has excellent visibility of the contents when made into a packaging bag, and may be 100%, but 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] (Manufacturing method of paper base material) The method for producing the paper base material includes a method of making a paper stock containing pulp. The paper stock may further contain additives. Examples of the additives include the additives listed above.

[0019] The 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 pulp beating method and beating device are not particularly limited, and may be the same as known beating methods and beating devices. The pulp content in the stock is not particularly limited, and may be within a range that is usually used. For example, it is 60% by mass or more and less than 100% by mass with respect to the total mass of the stock.

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

[0021] [Heat seal layer] The heat seal paper of this embodiment has a heat seal layer on at least one side of the paper base material. The heat seal layer is a layer that melts and adheres by heating, ultrasonic waves, etc. The heat seal paper of this embodiment may have heat seal layers on both sides of the paper base material. In addition, from the viewpoint of imparting heat sealability, the heat seal layer is provided on the uppermost layer of at least one side, and two or more heat seal layers may be formed on one side.

[0022] The resin constituting the heat seal layer (hereinafter also referred to as "resin for heat seal layer") is not particularly limited, but examples thereof 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 products thereof. The resin for heat seal layer may be used alone or in combination of two or more kinds.

[0023] The resin for the heat seal layer may be either a synthetic product or a commercially available product. As the commercially available product, the one used in the examples may be used.

[0024] In addition to the resin for the heat seal layer, other components may be added to the heat seal layer. Examples of other components include pigments, lubricants, defoamers, viscosity modifiers, leveling agents such as surfactants and alcohols, and colorants such as coloring dyes. Since these other components tend to deteriorate the heat sealability, 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 in the solid content of the heat seal layer.

[0025] (Method of forming 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 liquid containing at least a resin for the heat seal layer, applying the coating liquid to at least one side of a paper substrate, and drying the coating liquid. In this method, it is preferable to prepare the heat seal layer coating liquid by dissolving or dispersing the resin for the heat seal layer in an organic solvent or a mixed solvent of an organic solvent and water for the following reasons.

[0026] In order to obtain a heat seal paper with excellent visibility of the contents when used as a packaging bag, it is considered to select a paper base material with high transparency as the paper base material. However, a highly transparent paper base material (particularly graphene paper) has a large specific surface area of ​​cellulose due to the progress of beating. Therefore, there are many hydrogen bonds between cellulose, and water is likely to penetrate into these areas. For this reason, when a water-based heat seal layer coating liquid is applied to a highly transparent paper base material, the coating liquid penetrates into the paper base material, and many wrinkles are generated during the drying process (i.e., the surface roughness of the heat seal layer side surface increases). As a result, the obtained heat seal paper has poor visibility of the contents when used as a packaging bag (Comparative Example 1 described later). In contrast, by applying a solvent-based heat seal coating liquid to a highly transparent paper base material, the penetration of the coating liquid into the paper base material can be suppressed, and the generation of wrinkles during the drying process can be reduced (i.e., the surface roughness of the heat seal layer side surface decreases). As a result, the obtained heat seal paper has excellent visibility of the contents when used as a packaging bag.

[0027] For the above reasons, 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 liquid. The organic solvent is not particularly limited, and examples thereof include acetone, methanol, ethanol, isopropanol, n-propanol, butanol, ethyl acetate, propyl acetate, methyl ethyl ketone, methyl isobutyl ketone, toluene, propylene glycol monomethyl ether, and hexane. 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 heat seal layer coating liquid is preferably 99 / 1 or more and less than 20 / 80.

[0028] As described later, when 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" means that the water content in the solvent is 80% by mass or more.

[0029] The device used for applying the heat seal layer coating liquid is not particularly limited, and may be appropriately selected from commonly used coating devices. For example, various known coating devices such as an air knife coater, a blade coater, a gravure coater, a rod blade coater, a roll coater, a reverse roll coater, a Mayer bar coater, a curtain coater, a die slot coater, a champlex coater, a metering blade type size press coater, a short dwell coater, a spray coater, a gate roll coater, and a lip coater may be mentioned.

[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 applied heat seal layer is not particularly limited, and known equipment can be used, such as a hot air dryer, an infrared dryer, an explosion-proof dryer, a gas burner, a hot plate, etc.

[0032] (Coating amount of heat seal layer) The coating amount of the heat seal layer is preferably 1 g / m from the viewpoint of heat seal peel strength. 2 More preferably, 2 g / m 2 and preferably 12 g / m 2 Less than 10 g / m 2 Less than 8 g / m, more preferably 2 The coating amount of the heat seal layer is the coating amount after drying, and when the heat seal paper has two or more heat seal layers, it means the total coating amount.

[0033] [Anchor coat layer] When applying an aqueous heat seal layer coating liquid 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 liquid 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 preferable examples include polyester resin, urethane resin, acrylic resin, vinyl chloride-vinyl acetate copolymer, ethylene-vinyl acetate resin, ethylene acrylic resin, and modified products thereof. The resin for the anchor coat layer may be used alone or in combination of two or more kinds.

[0035] In addition to the above-mentioned resin for the anchor coat layer, other components may be added to the anchor coat layer. 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 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, based on the solid content of the anchor coat layer.

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

[0037] The organic solvent is not particularly limited, but may be one exemplified in the above (Method of forming a heat seal layer). In the case of a mixed solvent of water and an organic solvent, the mass ratio of the organic solvent to the water (organic solvent / water) in the coating liquid for the anchor coat layer 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 thereof include those exemplified in the above section (Method of forming a heat seal layer).

[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) The coating amount of the anchor coat layer is preferably 0.1 g / m from the viewpoint of suppressing the penetration of the heat seal layer coating liquid into the paper substrate. 2 More preferably, 0.3 g / m 2 The upper limit of the coating amount of the anchor coat layer is not particularly limited, but is preferably 3.0 g / m 2 Less than 2.0 g / m 2 More preferably, 1.0 g / m or less 2 The coating amount of the anchor coat layer is the coating amount after drying.

[0041] <Physical properties of heat seal paper> (peel strength) The heat seal 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 the heat seal layers are heat sealed together under conditions of 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 the present 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 made into 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 seal paper according to the present embodiment is preferably 90% or less, more preferably 85% or less, from the viewpoint of visibility of the contents when it is made into a packaging bag. The lower limit of the haze of the heat seal paper is not particularly limited, but is usually 0% or more, preferably 10% or more, more preferably 20% or more. The haze of the heat seal paper is measured in accordance with JIS K 7361-1:1997.

[0044] (Surface roughness) From the viewpoint of visibility of the contents when made into a packaging bag, the surface roughness of the heat seal paper in this embodiment is, in terms of the arithmetic mean height of the heat seal layer side surface measured in accordance with JIS B 0601:2001, 75 μm or less, preferably 60 μm or less, more preferably 50 μm or less, even more preferably 40 μm or less, still more preferably 30 μm or less, and particularly preferably 25 μm or less, with the lower limit being 0 μm.

[0045] From the viewpoint of visibility of the contents when made into a packaging bag, the surface roughness of the heat seal paper in this embodiment is, in terms of the maximum height of the heat seal layer side surface measured in accordance with JIS B 0601:2001, 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 the lower limit being 0 μm.

[0046] (Oxygen permeability) The lower the oxygen permeability of the heat seal paper according to the present embodiment, the less oxygen is permeated, and the oxygen permeability at 23° C. and 50% RH is preferably 20 mL / m 2 ·24h·atm or less, preferably 10mL / m 2 24h atm or less, more preferably 5mL / m 2 24h atm or less, and particularly preferably 3mL / m 2 24h atm or less, preferably 2mL / m 2 The oxygen permeability of the barrier laminate is measured under the above conditions using an oxygen permeability measuring device (OX-TRAN2 / 20, manufactured by MOCON).

[0047] <Application> The heat seal paper of the present invention, when made into a packaging bag, has excellent visibility of the contents and can be suitably used as a packaging material for food, cosmetics, daily necessities, detergents, soaps, powders, precision machinery, etc. Therefore, the present invention also provides a packaging bag made of the above heat seal paper. EXAMPLES

[0048] Examples are given below to specifically explain the present invention, but the present invention is not limited to these examples. However, the present invention is not limited to the above. Unless otherwise specified, the following operations were performed at 25°C and a relative humidity of 50%RH. In the examples and comparative examples, "parts" and "%" refer to "parts by mass" and "% by mass", respectively, unless otherwise specified.

[0049] <Example 1> A heat seal agent mainly composed of vinyl chloride-vinyl acetate copolymer (solvent: ethyl acetate, solid 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 solid content of 15%. This was applied to a paper substrate, Grafan paper (manufactured by Oji F-Tex Co., Ltd., irregular freeness of disintegrated pulp 250 mL, basis weight 35 g / m 2 , paper thickness 32μm, total light transmittance 82.5%), coating weight after drying 6g / m 2 After that, the mixture was dried in an explosion-proof dryer at 80° C. for 10 seconds to obtain a heat seal paper.

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

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

[0052] <Example 4> A heat seal 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 seal layer coating solution 1, and the drying conditions were 100°C and 40 seconds.

[0053] <Example 5> A heat seal 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 the heat seal layer coating solution 1.

[0054] <Example 6> A heat seal agent whose main component is an olefin copolymer (solvent: water, solid content: 48.3%, product name: EA-H700, manufactured by Toyo-Morton Co., Ltd.) was diluted with methanol to obtain a heat seal layer coating solution 6 (methanol / water=26 / 74) with a solid content of 20%. A heat seal paper was produced in the same manner as in Example 4, except that the heat seal layer coating solution 6 was used instead of the 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, solid content: 5-10%) was applied to the paper substrate Graphan paper (manufactured by Oji F-Tex Co., Ltd., disintegrated pulp irregular freeness 250 mL, basis weight 35 g / m 2 , paper thickness 32μm, total light transmittance 82.5%), coating weight after drying 0.5g / m 2 After coating with a Mayer bar so that the thickness was 100 mm, the coating was dried in an explosion-proof dryer at 80°C for 10 seconds. Furthermore, a heat seal layer coating solution (solvent: water, solid content: 49%, product name: Hi-Loss-X NE-2260, manufactured by Seiko PMC Corporation) mainly composed of styrene acrylic resin was applied onto the anchor coat layer so that the coating weight after drying was 3.0 g / m. 2 After that, the mixture was dried in a hot air dryer at 120° C. for 1 minute to obtain a heat seal paper.

[0056] <Comparative Example 1> A heat seal paper was prepared in the same manner as in Example 6, except that water was used instead of methanol as the dilution solvent for the heat sealant.

[0057] <Comparative Example 2> In Example 2, the paper base material was bleached kraft paper (manufactured by Oji Materia Co., Ltd., disintegrated pulp irregular freeness 700 mL, basis weight 50 g / m 2 A heat seal paper was prepared in the same manner, except that the paper thickness was 60 μm and the total light transmittance was 47%).

[0058] <Evaluation> (1) Total light transmittance According to JIS K 7361-1:1997, the total light transmittance of the heat seal paper was measured with the light incident surface facing the heat seal layer, and used as an index of transparency. A total light transmittance of 65% or more was judged to be good.

[0059] (2) Hayes According to JIS K 7136-1:1997, the haze of the heat seal paper was measured with the light incident surface being the heat seal layer surface, and used as an index of transparency. A haze of 90% or less was judged to be good.

[0060] (3) Surface roughness Using a one-shot 3D shape measuring instrument (Keyence Corporation, VR-3000), the arithmetic mean height and maximum height of the heat seal layer side surface were measured in accordance with JIS B 0601: 2001, and used as an index of the surface roughness of the heat seal paper. The larger the respective values, the more wrinkles there are in the paper, and it was determined 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 seal papers was stacked so that the heat seal layers faced each other, and heat sealed using a heat seal tester (TP-801-B, manufactured by Tester Sangyo Co., Ltd.) at 120°C, 0.2 MPa, and 1 second. The heat-sealed test piece was then cut to a width of 15 mm and T-peeled using a tensile tester at a tensile speed of 300 mm / min. The average value of six tests was taken as the heat seal peel strength. If the heat seal peel strength was 0.9 N / 15 mm or more, it was determined that the heat sealability was good.

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

[0063] (6) Visibility The visibility of the heat seal papers obtained in the Examples and Comparative Examples was evaluated by visually checking the visibility of the contents when the papers were molded into bags. ◎: Transparent, so the contents can be easily seen (contents can be seen even at a distance of 50 cm) 〇: Transparent, so the contents can be seen (it is difficult to see the contents from a distance of 50 cm) △: Although it is transparent, there are wrinkles on the paper, making it a little difficult to see. ×: No transparency, and the contents cannot be confirmed.

[0064] [Table 1]

[0065] The results are shown in Table 1 above. The heat seal papers of Examples 1 to 7 had excellent visibility of the contents when used as packaging bags, and also had good heat sealability and gas barrier properties. On the other hand, the heat seal paper of Comparative Example 1, which was obtained by forming a heat seal layer on graphene paper by aqueous coating, wrinkled during the drying process, and had poor visibility of the contents when used as a packaging bag. In addition, the heat seal paper of Comparative Example 2, which was prepared using bleached kraft paper instead of graphene paper as the paper base material, had poor visibility of the contents when used as a packaging bag, and also had low gas barrier properties.

Claims

1. A heat seal paper having an anchor coat layer and a heat seal layer in this order on at least one surface of a paper base material, An anchor coat layer is provided between the paper substrate and the heat seal layer, the anchor coat layer contains at least one of a polyester resin, a urethane resin, a vinyl chloride-vinyl acetate copolymer, and an ethylene-vinyl acetate resin; The paper base material has a basis weight of 20 g / m ２ 150g / m or more ２ is as follows: The total light transmittance measured in accordance with JIS K 7361-1:1997 is 65% or more, A heat seal paper having an arithmetic mean height of the heat seal layer side surface of 75 μm or less as measured in accordance with JIS B 0601:2001.

2. 2. The heat seal paper according to claim 1, having a haze of 90% or less as measured in accordance with JIS K 7361-1:1997.

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

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

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

6. The heat seal paper according to any one of claims 1 to 5, which has a peel strength of 0.9 N / 15 mm or more when the heat seal layers are heat sealed together under conditions of 120°C, 1 second, and 0.2 MPa.

7. Oxygen permeability at 23°C and 50% RH is 5mL / (m ２ The heat seal paper according to any one of claims 1 to 6, wherein the thermal expansion coefficient is 24 h atm or less.

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

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

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