Packaging material and manufacturing method thereof

Abstract

To provide a packaging material having excellent packaging processing suitability and air permeability and a method of manufacturing a packaging material.SOLUTION: A packaging material has a paper substrate including natural fibers and a heat seal layer provided on at least one side of the paper substrate, wherein the packaging material is characterized in that the paper substrate comprises crepe paper including a conifer pulp of 80% or more relative to the total amount of pulps and the conifer pulp has an average lumen ratio of 0.50 or more and 0.70 or less. Also, a method of manufacturing the packaging material is disclosed herein.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to packaging materials and methods for producing the same. [Background technology]

[0002] Conventionally, plastic materials have been mainly used for packaging containers such as food trays and packaging bodies such as pillow packaging bags. Furthermore, packaging bodies have been used in which deodorizers such as activated carbon and desiccants such as silica gel are enclosed in breathable bags made of mainly plastic films, nonwoven fabrics, or laminates thereof. However, in recent years, there has been a growing trend toward eliminating plastics, triggered by environmental issues such as those related to plastic waste in the ocean, and it is desirable to reduce the amount of resin materials used in industrial products as much as possible. In light of this trend, paper-based packaging materials have also been considered for packaging bodies in order to reduce the environmental impact.

[0003] Patent Document 1 describes a paper substrate mainly composed of unbleached softwood kraft pulp and a heat seal layer laminated on one side of the paper substrate, in which the folding strength in the machine direction of the paper substrate is 500 times or more and 1,000 times or less, the folding strength in the width direction is 80 times or more and 200 times or less, the Beck smoothness of the surface of the heat seal layer laminated surface is 3 seconds or more and 230 seconds or less, the main component of the heat seal layer is an alkali-neutralized ethylene (meth)acrylic acid copolymer, and the coating amount of the heat seal layer is 1.5 g / m 2 More than 10.0g / m 2 The following heat seal paper has been proposed, which is environmentally friendly, has excellent water resistance and suppresses cracks caused by folds in the area where the heat seal layer is laminated, while ensuring heat seal strength.

[0004] Patent Document 2 proposes a heat-seal paper that has a paper base whose main component is pulp and a heat-seal layer laminated on one side of the paper base, the main component of which is an alkali-neutralized ethylene (meth)acrylic acid copolymer, the surface of the paper base on which the heat-seal layer is laminated having a Beck smoothness of 5 seconds or more and 50 seconds or less and a Parker Print Surf smoothness of 3.8 μm or more and 8.0 μm or less, and the surface of the paper base on which the heat-seal layer is not laminated having a Beck smoothness of 50 seconds or more and 500 seconds or less and a Parker Print Surf smoothness of 2.0 μm or more and 4.2 μm or less, and that does not contain laminated paper or plastic film, which have a high environmental impact, and has excellent water resistance and printability on the surface on which the heat-seal layer is not laminated.

[0005] Patent Document 3 proposes a heat-sealable paper having one or more heat-sealable layers on at least one side of a paper substrate, the heat-sealable layer containing a water-dispersible resin binder, and having an ISO stiffness of 0.55 mNm or less in the longitudinal direction of the heat-sealable paper measured in accordance with ISO2493-1:2010, an ISO stiffness of 0.45 mNm or less in the transverse direction of the heat-sealable paper, and a puncture strength of 7.5 N or more measured in accordance with JIS Z 1707:2019, which has drop impact resistance, excellent flexibility, and excellent heat-sealing properties.

[0006] Patent Document 4 describes a flexible packaging paper having a paper base material and a heat seal layer provided on at least one side of the paper base material, in which the paper base material has a filler content of 1% by mass or less and a basis weight of 25 g / m 2 More than 50g / m 2 Below, density 0.85g / m 3 More than 1.35g / m 3 The dry mass of the heat seal layer (per side) is 4 g / m or less. 2 More than 20g / m 2 The proposed flexible packaging paper has a tear strength (MD and CD directions) of 100 mN or more and 650 mN or less, and can be easily torn from any direction, allowing the packaged item to be easily removed when used as a flexible package.

[0007] Patent Document 5 proposes a heat-sealable sheet that includes a paper base material and a thermal adhesive layer that is provided on the outermost surface of at least one side of the paper base material and contains 50% by mass or more of an organic material, and the thermal adhesive layer contains styrene-butadiene copolymer latex as at least part of the organic material, and the thermal adhesive surface on which the thermal adhesive layer is provided has an Oken smoothness of 50 seconds or more as measured in accordance with JIS P 8155:2010, and the sheet has breathability and moisture permeability, is low in dust generation, and is recyclable. Patent Document 6 proposes a bag-shaped package having deodorizing properties, in which a physical adsorbent is wrapped in a fabric containing a photocatalyst and a chemical adsorbent, and proposes a spunbond nonwoven fabric made of polypropylene as the fabric for the bag-shaped package. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent Publication No. 2023-107689 [Patent Document 2] Patent Publication No. 2023-107678 [Patent Document 3] Patent No. 7243901 [Patent Document 4] Patent Publication No. 2023-81594 [Patent Document 5] Patent Publication No. 2018-053400 [Patent Document 6] Patent Publication No. 2019-208969 Summary of the Invention [Problem to be solved by the invention]

[0009] Packaging materials using heat-seal paper have been proposed as an alternative to packaging materials using plastic film. However, because paper is inferior in elongation, strength, and flexibility to plastic film and nonwoven fabric, packaging materials using heat-seal paper are prone to wrinkling and tearing when packaged using a pillow packaging machine or the like, and may not be able to package certain contents depending on their shape. Furthermore, for packages containing deodorizers or desiccants, using highly breathable packaging materials can achieve high deodorizing and moisture-absorbing properties. An object of the present invention is to provide a packaging material that is excellent in packaging processability and breathability, and a method for producing the packaging material. [Means for solving the problem]

[0010] The means for solving the problems of the present invention are as follows. 1. A packaging material having a paper substrate containing natural fibers and a heat seal layer provided on at least one side of the paper substrate, The paper base material is made of crepe paper containing 80% or more of softwood pulp based on the total amount of pulp, The softwood pulp is characterized in that the average lumen ratio is 0.50 or more and 0.70 or less. packaging materials. 2. The tensile elongation at break in the MD direction is 5% or more and 15% or less, The tear strength in the MD and CD directions is 400 mN or more, The bending strength in both the MD and CD directions measured using the KES-FB2-A pure bending tester was 1 g cm 2 / cm or less, The breathability measured by CERULEAN-PPM Express is 1000 Coresta units or more. The above packaging material. 3. On the crepe paper, A heat seal layer is formed by applying a coating liquid containing a thermoplastic resin by a gravure method or a flexographic method. A method for producing the packaging material. [Effects of the Invention]

[0011] According to the present invention, a packaging material having excellent packaging processability and breathability can be provided. In particular, a packaging material having elongation, strength, flexibility, and breathability can be provided. Packaging materials with excellent elongation, strength, and flexibility can be packaged according to the shape of the contents. Furthermore, packaging materials with excellent breathability can achieve high deodorizing and moisture absorption properties when a deodorizer or desiccant is enclosed in the packaging material to form a package. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of a cross section of pulp. DETAILED DESCRIPTION OF THE INVENTION

[0013] (softwood pulp) The paper base material used in the packaging material of the present invention is made of crepe paper containing 80% or more softwood pulp relative to the total amount of pulp, and is characterized in that the average lumen ratio of this softwood pulp is 0.50 or more and 0.70 or less. Here, in the present invention, the ratio of softwood pulp to the total amount of pulp can be calculated by performing fiber analysis in which the pulp is dyed and examined under an optical microscope, and identifying the type of pulp for 100 or more fibers.

[0014] The cross-sectional structure of pulp will be explained below with reference to the drawings. What is generally called pulp is actually a tracheid in conifers and a wood fiber in hardwoods, both of which have an internal cavity called a lumen. The lumen ratio (l) is the ratio of the lumen diameter (b) to the pulp fiber diameter (d) (l = b / d). The Runkel ratio is also known as an index of pulp cross-sectional shape, and the Runkel ratio (R) is the ratio of the pulp fiber wall thickness (a) to the lumen diameter (b) (R = 2a / b) (Figure 1).

[0015] The softwood pulp used in the present invention has an average lumen ratio of 0.50 or more and 0.70 or less. More preferably, the average lumen ratio is 0.50 or more and 0.65 or less. Here, the average lumen ratio of general softwood pulp is greater than 0.70 and less than 0.90. It is difficult to produce highly breathable base paper from softwood pulp with an average lumen ratio of greater than 0.70. The softwood pulp used in the present invention has a smaller lumen ratio than general softwood pulp. Softwood pulp with an average lumen ratio of 0.50 or more and 0.70 or less has thick fiber walls and is therefore rigid, and the pulp fibers are less likely to be crushed even when the wet paper is dried. Therefore, by blending this softwood pulp, it is possible to obtain bulky and highly breathable base paper.

[0016] In this specification, the average lumen ratio of pulp is calculated from the average value of the fiber diameter, fiber wall thickness, and lumen diameter of 100 or more pulp pieces measured in the following manner. 1. Pulp suspension prepared by dispersing pulp in water is diluted to a concentration of 0.05%. The pulp suspension can also be prepared in the same manner as the raw material slurry used to measure the pulping freeness described below. 2. Using a dropper tube, drip the diluted solution onto a clean preparation, and if necessary, use a dissecting needle to evenly distribute the fibers. 3. Place a cover glass on the slide, taking care not to trap air bubbles, remove excess water with blotting paper, and prepare the slide. 4. Observe the slide using an optical microscope and move the slide horizontally or vertically on a movable stage to measure the pulp fiber diameter (d), fiber wall thickness (a), and lumen diameter (b).

[0017] The softwood pulp used in the present invention may have an average lumen ratio in the range of 0.50 to 0.70, and may be a blend of one or more of mechanical pulp (MP), thermomechanical pulp (TMP), sulfite pulp (SP), kraft pulp (KP), or bleached pulp (BP) and unbleached pulp (UP) of these. Of the softwood pulps, paper base materials made from kraft pulp (KP) and sulfite pulp (SP) are preferred because they have excellent strength and packaging materials using them are excellent in suitability for packaging processing.

[0018] (Other pulps) The crepe paper used in the present invention needs only to contain 80% or more softwood pulp having an average lumen ratio of 0.50 to 0.70, and other pulps can be blended in within a range of less than 20% as long as the properties required for the packaging material are not impaired. The blending amount of softwood pulp having an average lumen ratio of 0.50 to 0.70 is preferably 85% or more, more preferably 90% or more, and even more preferably 95% or more, and most preferably contains no other pulp.

[0019] As other pulps, in addition to hardwood pulp, non-wood pulps such as bast fibers such as flax, kenaf, paper mulberry, and mitsumata, hard fibers such as bagasse, bamboo, and esparto, seed fibers such as cotton linters, and leaf vein fibers such as Manila hemp and sisal can be used. In particular, blending hemp pulp as the other pulp can further improve breathability and strength. However, because hemp pulp is more expensive than softwood pulp, the blending amount of hemp pulp is preferably less than 10%, and most preferably, no hemp pulp is included.

[0020] The pulp suspension used in the packaging material of the present invention preferably has a freeness (2g Schopper-Rigler freeness: specified in JIS P8121-1) of 7°SR or more and 20°SR or less. By adjusting the freeness within the above range, crepe paper that satisfies the breathability required for packaging materials can be produced. Beating of a pulp suspension is not limited to be performed by beating a suspension consisting of only softwood pulp. Softwood pulp and other pulps may be mixed and then beaten together, or softwood pulp and other pulp may be beaten separately and then mixed (separate beating). In the case of separate beating, the freeness of the other pulp is not particularly limited, but it is preferable to adjust the freeness of the pulp suspension after mixing with beaten softwood pulp in any ratio to be 7°SR or more and 20°SR or less. If the freeness is less than 7°SR, papermaking properties and formation may be deteriorated, and if the freeness is more than 20°SR, breathability may be deteriorated.

[0021] Examples of various auxiliary agents include sizing agents such as rosin, alkyl ketene dimer (AKD), and alkenyl succinic anhydride (ASA), polyacrylamide polymers, polyvinyl alcohol polymers, cationized starch, various modified starches, dry strength agents such as urea-formalin resin and melamine-formalin resin, wet strength agents, retention agents, drainage aids, coagulants, aluminum sulfate, bulking agents, dyes, fluorescent whitening agents, pH adjusters, antifoaming agents, UV inhibitors, anti-fading agents, pitch control agents, and slime control agents, and can be selected and used as needed. The method for making the paper substrate is not particularly limited, and can be carried out using a Fourdrinier paper machine, a cylinder paper machine, a short-wire paper machine, an inclined short-wire paper machine, or the like.

[0022] (crepe paper) The paper substrate of the present invention is crepe paper, which has superior MD elongation, flexibility, and breathability compared to base paper before creping, is less likely to tear during packaging, can be packaged to fit the shape of the contents, and can provide high deodorizing and moisture-absorbing properties when used to package deodorants and desiccants.

[0023] There are no particular limitations on the method for producing crepe paper, and it can be produced by making a base paper from a stock containing softwood pulp and, if necessary, other pulps, wet strength agents, other additives, etc., and then subjecting the base paper to creping. The papermaking method is also not particularly limited, and the paper can be made using a Fourdrinier paper machine including a top wire, an on-top former, a gap former, a cylinder paper machine, a short wire paper machine, an inclined short wire paper machine, etc. The drying process can be carried out using an appropriate dryer, such as a multi-cylinder cylinder dryer, a Yankee dryer, or a hot air dryer. Either a wet method or a dry method can be used for creping, but the wet method is preferred as it produces a small difference between the front and back of the crepe shape.

[0024] The basis weight of the crepe paper is 40 g / m 2 More than 70g / m 2 Preferably less than 50 g / m 2 More than 60g / m 2 More preferably, the crepe paper has a basis weight of 40 g / m 2 If it is smaller than this, the strength may decrease, and the basis weight of the crepe paper is 70 g / m 2 If it is larger, flexibility and breathability may decrease.

[0025] (Tensile elongation at break) The tensile breaking elongation in the MD direction of the paper base material of the present invention is preferably 5% or more and 15% or less. If the tensile breaking elongation in the MD direction is less than 5%, problems such as tearing or rupture may occur during packaging processing. If the tensile breaking elongation in the MD direction exceeds 15%, the drying efficiency in the papermaking process may decrease. In this specification, the tensile breaking elongation refers to the value measured in accordance with JIS P8113:2006 "Paper and paperboard - Test methods for tensile properties - Part 2: Constant rate of extension method" using a test specimen with a width of 15 mm, a test length of 100 mm, and an extension rate of 10 mm / min.

[0026] (bending strength) The bending strength can be adjusted by the basis weight and thickness of the paper substrate, the thickness of the fibers used in the paper substrate, and the like. The packaging substrate of the present invention has a bending strength of 1 g cm in both the MD and CD directions as measured using a Kato Tech KES-FB2-A pure bending tester. 2 / cm or less is preferable, and 0.8g·cm 2 The smaller the bending strength value, the better the flexibility.

[0027] (Tear strength) The tear strength can be adjusted by the basis weight of the paper substrate, the fiber length of the fibers used in the paper substrate, the degree of beating, and the like. The paper substrate of the present invention preferably has a tear strength of 400 mN or more to prevent tearing during packaging processing. The tear strength is more preferably 600 mN or more, and even more preferably 800 mN or more. In this specification, tear strength refers to the value measured in accordance with JIS P8116:2000 "Paper - Tear strength test method - Elmendorf tear tester method" using a test piece 63 mm long, 20 mm incision, and 43 mm tear length.

[0028] (breathability) The breathability can be adjusted by the basis weight, thickness, crepe processing, thickness of the fibers used in the paper base material, degree of beating, etc. The packaging substrate of the present invention preferably has an air permeability of 1000 Coresta units (cu) or more as measured with a PPM Express manufactured by Cerulean Co., Ltd. The higher the air permeability value, the higher the breathability of the packaging substrate. By making the air permeability 1000 c.u. or more, high deodorizing and moisture absorbing properties can be obtained when a deodorizer or desiccant is enclosed in the packaging material to form a package.

[0029] (heat seal layer) The packaging material of the present invention has a heat seal layer on at least one surface. The packaging material of the present invention has a heat seal strength of 0.5 N / 15 mm or more when heat-sealed at a temperature of 160°C, a pressure of 98 kPa, and a time of 1 second, and peeled using a T-shaped mold at a test width of 15 mm and a pulling rate of 300 mm / min. A heat seal strength of 1 N / 15 mm or more is more preferred, and 2 N / 15 mm or more is even more preferred.

[0030] The heat seal layer is provided on at least one side of the paper substrate, and can also be provided on both sides. The coating amount of the heat seal layer on one side is 1 g / m 2 More than 20g / m 2 The coating weight of the heat seal layer is preferably 1 g / m or less. 2 If the coating weight of the heat seal layer is less than 20 g / m, the heat sealability may be deteriorated. 2 If the coating amount exceeds 1.5 g / m, the heat sealability will saturate and there will be almost no improvement, and the amount of resin used will increase, resulting in high costs and being undesirable from the standpoint of environmental load. 2 It is preferable that the content is 2 g / m or more. 2 The coating amount of the heat seal layer on one side is preferably 15 g / m or more. 2 Preferably, it is 12 g / m or less. 2 More preferably, it is 9 g / m or less. 2 It is even more preferable that:

[0031] The thermoplastic resin forming the heat seal layer is not particularly limited, and thermoplastic resins used for heat sealing applications such as ethylene-vinyl acetate resins, styrene-acrylate copolymer resins, acrylic resins, polyester resins such as polyethylene, polypropylene, and polyethylene terephthalate, polyvinyl alcohol, polyvinyl acetate, polylactic acid, polyhydroxyalkyl acid (PHBH), polybutylene succinate, and polyglycolic acid can be used without particular limitation. Among these, ethylene-vinyl acetate resins and ethylene-acrylic resins are preferred in terms of heat seal strength. Furthermore, biodegradable resins such as polyvinyl alcohol, polylactic acid, polyhydroxyalkyl acid, polybutylene succinate, and polyglycolic acid are preferred in terms of reducing the environmental impact if they are discharged as waste.

[0032] The heat seal layer may be either a coating layer or a laminate layer, but is preferably a coating layer from the viewpoints of production efficiency and recyclability (redisintegrability). When the heat seal layer is a coating layer, it may be either an aqueous coating using a solvent such as water or a solvent using a solvent such as an organic solvent, but is preferably an aqueous coating from the viewpoint of safety and hygiene. When using an aqueous coating, it is preferable to use an aqueous dispersion of a thermoplastic resin or a water-soluble thermoplastic resin. The coating method is not particularly limited, and coating can be performed using a known coating device and coating system. Examples of coating devices include gravure coaters, flexo coaters, blade coaters, bar coaters, air knife coaters, curtain coaters, spray coaters, roll coaters, reverse roll coaters, size press coaters, and gate roll coaters. As described below, coating is preferably performed using a gravure coater or flexo coater. When the heat seal layer is formed by lamination, either extrusion lamination or dry lamination may be used.

[0033] The paper substrate of the present invention is made mainly of natural fibers, and is a paper substrate that is excellent in flexibility, porous, and water-absorbent.

[0034] Bar coaters and air knife coaters use an applicator roll to apply excess coating liquid to the substrate, and then scrape off the excess with a wire bar or air knife. However, if the paper substrate is porous, the coating liquid may penetrate the substrate as soon as it is applied, resulting in an excessive coating amount and even causing the coating liquid to strike through to the opposite side of the substrate, contaminating the process. Furthermore, if the paper substrate is crepe paper, the coating liquid may penetrate the substrate as soon as it is applied, stretching the crepe shape of the substrate and making coating difficult. In such cases, a sizing agent may be added to the paper substrate or a sealing layer may be applied before the heat-seal layer is applied to inhibit the coating liquid from penetrating the substrate.

[0035] On the other hand, gravure coaters and flexo coaters measure out a specified amount of coating using the embossed pattern of a gravure roll, and either transfer the coating liquid directly to the substrate and apply it, or first transfer the coating liquid to a coating roll and then apply it to the substrate, so that the coating layer can be formed only on the surface of the paper substrate. For this reason, the coating liquid transferred with a gravure coater or the like does not easily penetrate into the substrate, even if the paper substrate has good water absorption, and remains on the surface of the paper substrate, making it possible to obtain sufficient heat seal strength even with a small amount of heat seal layer coating. The number of meshes and cup depth of the embossed pattern of the gravure roll can be appropriately selected depending on the concentration of the aqueous dispersion or solution that forms the heat-sealable layer and the dry mass of the heat-sealable layer. Also, by partially providing the embossed pattern of the gravure roll and not forming a heat-sealable layer in the areas that are not heat-sealed during bag making, a package with higher breathability can be obtained. [Example]

[0036] The present invention will be described below with reference to examples, but the present invention is not limited to the following examples. Example 1 As the paper base material, softwood pulp (NBKP, average lumen ratio 0.60) was beaten to a freeness of 16°SR using a refiner, and then this paper stock was made into paper using a Fourdrinier paper machine and creped using a wet method to obtain a basis weight of 51.3 g / m 2 Crepe paper was produced. An ethylene-acrylic heat sealing agent (Chemipearl S500, manufactured by Mitsui Chemicals, Inc.) was applied to the crepe paper using a 95 mesh filter with a cell volume of 51 cm. 3 / m 2 The coating was applied using a gravure roll and then dried to obtain the packaging material of Example 1.

[0037] <Example 2> The paper base material was made from softwood pulp (NUKP and NBKP mixed at a mass ratio of 80 / 20, with an average lumen ratio of 0.55) which was refined to a freeness of 18°SR using a refiner. The paper was then made into paper using a Fourdrinier paper machine and creped using a wet method to obtain a basis weight of 51.3 g / m. 2 , density 0.37g / cm 3 A packaging material of Example 2 was obtained in the same manner as in Example 1, except that the wet crepe paper of Example 2 was used.

[0038] <Comparative Example 1> The paper base material was a mixture of softwood pulp (NBKP, lumen ratio 0.85) and hardwood pulp (LBKP) in a mass ratio of 80 / 20, which was then refined to a freeness of 21°SR using a refiner. The resulting paper was then made into paper with a basis weight of 70 g / m2 using a fourdrinier paper machine. 2 , density 0.75g / m 3 A packaging material of Comparative Example 1 was obtained in the same manner as in Example 1, except that the paper base material was changed to the above.

[0039] <Comparative Example 2> The paper base material was a 50 / 50 mixture of softwood pulp (NBKP, lumen ratio 0.85) and hardwood pulp (LBKP), which was then refined to a freeness of 90°SR using a refiner. The paper was then made into paper using a Fourdrinier paper machine and calendered to a basis weight of 35 g / m. 2 , density 0.1.1g / m 3 A packaging material of Comparative Example 2 was obtained in the same manner as in Example 1, except that the paper base material was changed to the above.

[0040] <Comparative Example 3> As the paper base material, softwood pulp (NBKP, lumen ratio 0.85) was beaten to a freeness of 18°SR using a refiner, and then this paper stock was made into paper using a Fourdrinier paper machine, followed by calendering to obtain a basis weight of 35 g / m 2 , density 0.1.1g / m 3 A packaging material of Comparative Example 2 was obtained in the same manner as in Example 1, except that the paper base material was changed to the above.

[0041] <Comparative Example 4> As the paper base material, softwood pulp (average lumen ratio 0.60) was beaten to a freeness of 16°SR using a refiner, and then this paper stock was made into paper using a Fourdrinier paper machine, with a basis weight of 51.4 g / m 2 The paper base material was produced. An ethylene-acrylic heat sealing agent (Chemipearl S500, manufactured by Mitsui Chemicals, Inc.) was applied to this paper substrate using a 95 mesh, cell volume of 51 cm. 3 / m 2 The coating was applied using a gravure roll and then dried to obtain a packaging material of Comparative Example 4.

[0042] <Comparative Example 5> An ethylene-acrylic heat sealing agent (Chemipearl S500, manufactured by Mitsui Chemicals, Inc.) was applied to the crepe paper of Example 1 using a wire bar with a winding diameter of 0.1 mm.

[0043] Evaluation items and evaluation methods The resulting packaging material was evaluated as follows, and the results are shown in Table 1.

[0044] (basis weight, coating amount) The basis weight was measured in accordance with JIS P 8124. The coating amount was defined as the difference between the basis weight of the packaging material coated with the heat-sealing agent and the basis weight of the uncoated paper substrate.

[0045] (tensile strength, tensile elongation at break) The tensile strength and tensile elongation at break were measured in accordance with JIS P8113:2006 using a universal tensile testing machine (A&D Co., Ltd., Tensilon RTG-1210) with a test piece width of 15 mm, a test length of 100 mm, and an extension rate of 10 mm / min.

[0046] (bending strength) The bending strength was measured using a Kato Tech KES-FB2-A pure bending tester with a test piece of 100 mm x 100 mm and a bending speed of 0.5 cm. -1 / sec, maximum curvature 2.5cm -1 Measurements were carried out in both the MD and CD directions under the conditions above.

[0047] (Tear strength) The tear strength was measured in accordance with JIS P8116:2000 using an Elmendorf tear tester (Kumagaya Riki Kogyo Co., Ltd.) with a test piece length of 63 mm, a slit depth of 20 mm, and a tear length of 43 mm.

[0048] (Heat seal strength) Heat seal strength was measured by bringing the sealant-coated surfaces of the packaging substrates into contact with each other and heat sealing them using a heat seal tester (HEAT SEAL TESTER TP-701S, manufactured by Tester Sangyo Co., Ltd.) at a temperature of 160°C, a pressure of 98 kPa, and a time of 1 second, and then peeling them off using a universal tensile tester (Tensilon RTG-1210, manufactured by A&D Co., Ltd.) with a test width of 15 mm and a tensile speed of 300 mm / min using a T-type peeler.

[0049] (breathability) The air permeability was measured using PPM Express manufactured by CERULEAN.

[0050] (Packaging processing suitability 1) Each packaging material sample, 210 mm wide, and a white cardboard laminate (size: 100 mm x 65 mm x 25 mm, weight: 130 g) were prepared as inclusion A, and 100 samples were packaged using a pillow packaging machine (Suzuki Seisakusho, SP-803N) with the long side of the laminate in the flow direction of the packaging machine and the short side in the height direction of the packaging machine at a maximum speed of 40 samples per minute to produce flexible packaging, which was evaluated as follows. ○: Packaging can be done at low speed without tearing the packaging material, and speed can be increased. △: The packaging material can be wrapped without tearing at low speeds, but it breaks when the speed is increased. ×: Packaging material breaks even when operating at low speed

[0051] (Packaging processing suitability 2) Each packaging material sample, 230 mm wide, and a white cardboard laminate (size: 65 mm x 50 mm x 50 mm, weight: 130 g) were prepared as inclusion B, and using a pillow packaging machine (Suzuki Seisakusho, SP-803N), 100 samples were packaged at a maximum speed of 40 samples per minute, with the long side of the laminate running in the direction of the machine's flow and the short side running in the height direction of the machine, to produce flexible packaging, which was evaluated as follows. ○: Packaging can be done at low speed without tearing the packaging material, and speed can be increased. △: The packaging material can be wrapped without tearing at low speeds, but it breaks when the speed is increased. ×: Packaging material breaks during slow operation, making packaging impossible

[0052] [Table 1]

[0053] The packaging materials of Examples 1 and 2 were excellent in elongation, flexibility, strength, breathability, and heat sealability, and had good packaging suitability for the contents A and B. The packaging material of Comparative Example 1 had low flexibility, and during packaging processing, the packaging material got caught in the former that formed the packaging material into a bag shape, and the paper was torn at low speeds, making packaging impossible. The packaging material of Comparative Example 2 was highly flexible and could be packaged at low speeds, but had low tear strength, causing the bag to tear when the packaging machine was operated at high speeds. It also had low breathability.

[0054] The packaging materials of Comparative Examples 3 and 4 were excellent in strength, flexibility, and heat sealability, but had low elongation and broke when containing Item B. In addition, the breathability was low. In Comparative Example 5, the coating liquid was applied to the paper substrate with a Mayer bar, but the crepe of the paper substrate stretched immediately after application, and a packaging material could not be obtained. [Explanation of symbols]

[0055] a...pulp fiber wall thickness b...Lumen diameter d: Pulp fiber diameter

Claims

1. A packaging material having a paper substrate containing natural fibers and a heat seal layer provided on at least one surface of the paper substrate, The paper base material is made of crepe paper containing 80% or more of softwood pulp based on the total amount of pulp, The packaging material is characterized in that the softwood pulp has an average lumen ratio of 0.50 or more and 0.70 or less.

2. The tensile elongation at break in the MD direction is 5% or more and 15% or less, The tear strength in the MD direction and the CD direction is 400 mN or more, The bending strength in both the MD and CD directions measured with the KES-FB2-A pure bending tester was 1 g cm ２ / cm or less, 2. The packaging material according to claim 1, wherein the air permeability measured by Cerulean-PPM Express is 1,000 Coresta units or more.

3. The crepe paper A heat seal layer is formed by applying a coating liquid containing a thermoplastic resin by a gravure method or a flexographic method. A method for producing the packaging material of claim 1 or 2.

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