Packaging base material, packaging material, and method for manufacturing packaging material

Abstract

[Problem] To provide a packaging base material having excellent cushioning properties, a packaging base material having excellent flexibility, a packaging material using the packaging base materials, and a method for manufacturing the packaging material. [Solution] Provided are: a packaging base material containing natural fibers that has a basis weight of 18 g / m2 or more and 50 g / m2 or less and in which the natural fibers include a hemp pulp; a packaging material that has a heat seal layer on at least one surface of the packaging base material, and that has a heat seal strength of 0.5 N / 15 mm or more when heat-sealed at a temperature of 130°C, a pressure of 1.0 kgf / cm2, and a time of 1 sec, and peeled off with a T-die at a tensile speed of 30 mm / min; and a method for manufacturing the packaging material in which the heat seal layer is formed by applying a coating liquid containing a thermoplastic resin on the packaging base material by a gravure method or a flexographic method.

Description

Packaging substrate, packaging material, and method for manufacturing packaging material

[0001] The present invention relates to a packaging substrate, a packaging material having the packaging substrate, and a method for producing the packaging material.

[0002] Conventionally, plastic materials have been mainly used for packaging containers such as food trays and packaging bodies such as pillow packaging bags. However, in recent years, there has been a growing trend toward eliminating plastic, triggered by environmental issues such as the problem of plastic waste in the ocean, and it is desired 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 endurance in the machine direction of the paper substrate is 500 times or more and 1,000 times or less, the folding endurance in the width direction is 80 times or more and 200 times or less, the Beck smoothness of the surface of the heat seal layer laminated surface is 3 seconds or more and 230 seconds or less, the main component of the heat seal layer is an alkali-neutralized ethylene (meth)acrylic acid copolymer, and the coating amount of the heat seal layer is 1.5 g / m ２ 10.0g / m or more 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 heat-seal layer being mainly composed of 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 that 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 ISO 2493-1:2010, 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 50g / m or more ２ Below, density 0.85g / m ３ 1.35g / m or more ３ The dry mass of the heat seal layer (per side) is 4 g / m or less. ２ 20g / m or more ２ The proposed flexible packaging paper has a tear strength (MD direction and CD direction) 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 seal 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 a 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.

[0008] JP 2023-107689 A JP 2023-107678 A JP 7243901 A JP 2023-81594 A JP 2018-053400 A

[0009] Packaging materials using heat-sealable paper have been proposed as an alternative to packaging materials using plastic films. However, because paper is less stretchable than plastic films, packaging materials using heat-sealable paper have inferior cushioning properties. Furthermore, because paper is less flexible than plastic films, it has been impossible to package contents with complex shapes according to the shape of the contents. The present invention aims to provide a packaging substrate with excellent cushioning properties, a packaging substrate with excellent flexibility, packaging materials using these packaging substrates, and a method for manufacturing the packaging material.

[0010] The means for solving the problems of the present invention are as follows: 1. A packaging substrate containing natural fibers, having a basis weight of 18 g / m ２ 50g / m or more ２ The following are packaging substrates characterized in that the natural fibers contain hemp pulp: 2. The packaging substrate described in 1., characterized in that the hemp pulp has an average fiber length of 2.5 mm or more, an average fiber diameter of 15 μm to 25 μm, and a Canadian Standard Freeness of 650 ml CSF or more. 3. The packaging substrate described in 1. or 2., characterized in that the hemp pulp contains 40 mass% or more of hemp pulp based on the total fibers. 4. The packaging substrate described in any one of 1. to 3., characterized in that the hemp pulp is abaca. 5. The compressive strength measured using a KES-G5 compression tester (number of sheets measured: 1, deformation speed: 0.02 mm / sec, initial compression load: 50 gf / cm２ , maximum compression load 300gf / cm ２ 6. The packaging substrate according to any one of 1. to 4., characterized in that the bending strength in both the MD and CD directions measured with a KES-FB2-A pure bending tester is 0.8 g cm ２ 7. The packaging substrate according to any one of 1. to 5., characterized in that the C / M ratio of the tensile strength is 60% or more, and the tear strength is 450 mN or more in the MD and 650 mN or more in the CD. 8. The packaging substrate according to any one of 1. to 6., characterized in that the density of the packaging substrate is 0.2 g / cm ３ 0.5g / cm or more ３ The packaging substrate according to any one of 1. to 7., characterized in that: 9. The packaging substrate according to any one of 1. to 8., which has a heat seal layer on at least one surface thereof, and is heated at a temperature of 130°C and a pressure of 1.0 kgf / cm ２ 10. A packaging material characterized by having a heat seal strength of 0.5 N / 15 mm or more when heat-sealed for 1 second, and peeled off using a T-type mold at a tensile speed of 30 mm / min. 11. A method for producing a packaging material characterized by forming a heat seal layer by applying a coating liquid containing a thermoplastic resin to the packaging substrate described in any of 1. to 8. by a gravure method or a flexographic method. 12. A method for producing a packaging material described in 10., characterized in that the contact angle between the packaging substrate and the coating liquid is 70° or more and 120° or less.

[0011] According to the present invention, it is possible to provide a packaging substrate and a packaging material having excellent cushioning properties. In particular, it is possible to provide a packaging substrate and a packaging material having both cushioning properties and flexibility. A packaging material having excellent cushioning properties can protect contents from shaking during transportation and external impacts. A packaging material having excellent flexibility can be packaged to fit the shape of the contents.

[0012] Graph for explaining a method for calculating compressive strength from the measurement results of a KES-G5 compression tester.

[0013] "Packaging substrate" The packaging substrate of the present invention has a basis weight of 18 g / m ２ 50g / m or more ２The packaging substrate of the present invention has a basis weight of 18 g / m ２ 50g / m or more ２ When cushioning property is important in the packaging substrate of the present invention, a basis weight of 20 g / m or less can be achieved. ２ More than 22 g / m ２ More preferably, when flexibility is important, a basis weight of 40 g / m ２ Preferably, 35 g / m or less ２ More preferably, 30 g / m or less ２ The following is even more preferred:

[0014] The packaging substrate of the present invention has a density of 0.2 g / cm ３ 0.5g / cm or more ３ It is preferable that the density is 0.2 g / cm or less. ３ If the density is less than 0.5 g / cm, the foam becomes bulky and has excellent cushioning properties, but flexibility may decrease. ３ When the density is more than 0.4 g / cm, the packaging material has excellent flexibility but may have poor cushioning properties. ３ Preferably, 0.3 g / cm or less ３ Furthermore, when flexibility is important, the density is preferably 0.25 g / cm or less. ３ More than 0.3 g / cm ３ The above is more preferable.

[0015] The packaging substrate of the present invention contains natural fibers, and for example, paper and wetlaid nonwoven fabrics can be suitably used. The packaging substrate of the present invention may contain natural fibers, and may also contain resin fibers other than natural fibers. However, from the viewpoint of reducing the amount of resin used in the packaging substrate of the present invention, the ratio of natural fibers to all fibers is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 92% by mass or more, even more preferably 94% by mass or more, even more preferably 96% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and most preferably 100% by mass. Furthermore, when resin fibers are contained, it is preferable to use biodegradable resin fibers made of a biodegradable resin, such as polylactic acid fibers, polycaprolactone fibers, polybutylene succinate fibers, polyethylene succinate fibers, polyvinyl alcohol fibers, polyglycolic acid fibers, poly(caprolactone / butylene succinate) fibers, poly(butylene succinate / adipate) fibers, and 3-hydroxybutyrate-co-3-hydroxyhexanoate fibers.

[0016] As the natural fiber, fibers derived from plants, microorganisms, and animals can be used without any particular limitation. Specific examples include pulp, natural cellulose such as cellulose produced by microorganisms such as acetic acid bacteria, mercerized pulp obtained by treating natural cellulose with a high concentration of alkali, regenerated cellulose obtained by dissolving natural cellulose in a solvent such as a cuprammonium solution or a morpholine derivative and then reprecipitating, cellulosic fibers such as various cellulose derivatives such as acetylated modified cellulose and carboxylated modified cellulose derived from natural cellulose, and animal hair such as silk, wool, and goat hair, and one or more of these can be used. As the natural fiber, wood pulp and non-wood pulp can be suitably used.

[0017] Examples of wood pulp include chemical pulps such as bleached kraft pulp (BKP), unbleached kraft pulp (UKP), semi-bleached kraft pulp (SBKP), and sulfite pulp, which are made from softwood and / or hardwood trees; mechanical pulps such as stone ground pulp (SGP), pressed stone ground pulp (TGP), chemi-ground pulp (CGP), groundwood pulp (GP), and thermomechanical pulp (TMP); dissolving pulp; and mercerized pulp, and one or more of these may be used. Examples of non-wood pulp include pulps made from non-wood fibers such as flax (linen), kenaf, jute, mulberry, and mitsumata (mitsumata), hard fibers such as bagasse, bamboo, and esparto, seed fibers such as cotton (linter), and leaf sheath and leaf fibers such as abaca and sisal. One or more of these may be used.

[0018] The packaging substrate of the present invention contains hemp pulp as natural fibers. Examples of raw materials for hemp pulp include abaca (Manila hemp), flax (linen), kenaf (western hemp), jute (jute), and sisal. One or more of these can be used. In the packaging substrate of the present invention, the proportion of hemp pulp to the total fibers is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and most preferably 100% by mass.

[0019] The packaging substrate of the present invention preferably contains abaca pulp (Manila hemp pulp) as the hemp pulp. The inclusion of abaca pulp facilitates the production of a packaging substrate with excellent cushioning and flexibility. In the packaging substrate of the present invention, the amount of abaca pulp relative to the total fibers is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and most preferably 100% by mass. In the present invention, the amount of abaca pulp relative to all natural fibers is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and most preferably 100% by mass.

[0020] The average fiber length of all pulp contained in the packaging substrate of the present invention is preferably 2.5 mm or more, more preferably 3.0 mm or more, and even more preferably 3.5 mm or more. If the average fiber length is less than 2.5 mm, the packaging substrate will be flexible, but the packaging substrate will become denser and tighter, which may result in reduced cushioning. The average fiber width of all pulp contained in the packaging substrate of the present invention is preferably 15 μm or more and 30 μm or less. The average fiber width is a factor that determines the cushioning properties of the substrate. If the average fiber width is narrow, the fibers themselves will be soft but the substrate will become tighter, resulting in poor cushioning properties. If the average fiber width is wide, the fibers themselves will be difficult to bend, which tends to result in poor flexibility. In this specification, the average fiber length and average fiber width refer to the length-weighted average fiber length and length-weighted average fiber width, respectively, and can be measured by observing the fibers using, for example, an image analyzer such as a Fiber Tester manufactured by ABB Corporation, a Fractionator manufactured by Valmet Corporation, an FS5 manufactured by Valmet Corporation, or a Morfi manufactured by Voith Turbo Co., Ltd., or an optical microscope or an electron microscope.

[0021] The beating degree of all pulp contained in the packaging substrate of the present invention is preferably a Canadian Standard Freeness of 650 ml CSF or more, more preferably 670 ml CSF or more, even more preferably 690 ml CSF or more, and most preferably unbeaten. As the pulp is beaten more, the density increases and the substrate becomes softer, but cushioning properties tend to decrease.

[0022] In the present invention, the hemp pulp preferably has an average fiber length of 2.5 mm or more, an average fiber diameter of 15 μm to 25 μm, and a Canadian Standard Freeness of 650 ml CSF or more. By having the average fiber length, average fiber width, and Canadian Standard Freeness of the hemp pulp within the above ranges, it becomes easy to obtain a packaging substrate that is low-density and has excellent cushioning and flexibility. The average fiber length of the hemp pulp is more preferably 2.8 mm or more, even more preferably 3.2 mm or more, and even more preferably 3.6 mm or more. The average fiber width of the hemp pulp is more preferably 17 μm or more, even more preferably 19 μm or more, and more preferably 23 μm or less. The Canadian Standard Freeness of the hemp pulp is more preferably 670 ml CSF or more, even more preferably 690 ml CSF or more, and most preferably unbeaten.

[0023] The method for making the packaging 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, etc. Among these, it is preferable to use a short wire paper machine, an inclined short wire paper machine, or a Fourdrinier paper machine, which can reduce fiber orientation and increase the C / M ratio (horizontal / vertical ratio) of physical properties, and it is more preferable to use an inclined short wire paper machine.

[0024] The drying process can be carried out using a suitable dryer, such as a multi-cylinder dryer, a Yankee dryer, or a hot air dryer. Among these, a Yankee dryer, which produces a one-sided glossy paper, is preferred. When the packaging substrate is a one-sided glossy paper, the heat seal layer may be provided on either the glossy or rough side. However, providing the heat seal layer on the smoother side (glossy side) that is exposed to the Yankee dryer allows for the formation of a more uniform coating layer, thereby achieving high heat seal strength with a smaller coating amount. Furthermore, since the rough side, which is the side opposite the glossy side, has less fuzz than the glossy side, providing a heat seal layer on the glossy side reduces fuzz on the glossy side, resulting in a packaging material with less fuzz.

[0025] In the present invention, examples of various auxiliaries include sizing agents such as rosin, alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), and styrene acrylic resins, 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, water repellents, retention aids, drainage improvers, coagulants, aluminum sulfate, bulking agents, dyes, fluorescent whitening agents, pH adjusters, antifoaming agents, ultraviolet inhibitors, anti-fading agents, pitch control agents, and slime control agents, and can be appropriately selected and used as needed.

[0026] When a wet strength agent is used in the present invention, the type is not particularly limited, and examples of usable agents include dialdehyde guar gum, glyoxal-modified polyacrylamide, polyamide epichlorohydrin, polyamide polyamine epichlorohydrin, polyamine epichlorohydrin, and polyethyleneimine. When a dry strength agent is used in the present invention, the type is not particularly limited, and examples of usable agents include carboxymethyl cellulose (CMC), carboxymethyl guar gum, polyacrylamide, glyoxal-modified polyacrylamide, and hydroxypropyl guar gum. When a water repellent or sizing agent is used in the present invention, the type is not particularly limited, and examples of usable agents include styrene-acrylic acid ester copolymers, styrene-acrylonitrile copolymers, anionic polyurethanes, and styrene-maleic anhydride copolymers.

[0027] (Paper quality and characteristics of packaging substrate) The packaging substrate of the present invention has predetermined compressive strength and bending strength, and is therefore excellent in cushioning and flexibility as a packaging material. (Compressive strength) The compressive strength is correlated with the density (porosity) and thickness of the packaging substrate, and the degree of beating and thickness of the natural fibers blended therein, and the value of the compressive strength can be adjusted particularly by the thickness and degree of beating of the natural fibers blended in the packaging substrate. The packaging substrate of the present invention has a compressive strength (measured sheet: 1, deformation speed: 0.02 mm / sec, initial compression load: 50 gf / cm) measured using a KES-G5 compression tester manufactured by Kato Tech Co., Ltd. ２ , maximum compression load 300gf / cm ２ ) is preferably 1.5 or less. The smaller the value of this compressive strength, the better the cushioning properties. In the present invention, the compressive strength of the packaging substrate is more preferably 1.45 or less, even more preferably 1.4 or less, and even more preferably 1.35 or less. The lower limit of this compressive strength is not particularly limited, but is, for example, about 1.1.

[0028] (Bending strength) The bending strength is correlated with the basis weight, thickness, fiber thickness, etc. of the packaging substrate, and the value of the bending strength can be adjusted particularly by the thickness, etc. of the natural fibers blended into the packaging substrate. The packaging substrate of the present invention has a bending strength of 0.8 g cm in both the MD and CD directions as measured using a KES-FB2-A pure bending tester manufactured by Kato Tech Co., Ltd. ２ The smaller the value of this bending strength, the better the flexibility. In the present invention, the bending strength of the packaging substrate is preferably 0.6 g cm ２ / cm or less is preferable, and 0.4 g cm ２ / cm or less is more preferable, and 0.2 g cm ２ The lower limit of this bending strength is not particularly limited, but for example, it is preferably 0.02 g cm ２ / cm.

[0029] (Tensile Strength) The tensile strength can be adjusted by the fiber length and beating degree of the fibers used in the packaging substrate. The packaging substrate of the present invention preferably has a C / M ratio (horizontal / vertical ratio) of tensile strength of 60% or more, more preferably 70% or more, and even more preferably 75% or more. By setting the C / M ratio of tensile strength to 30% or more, the difference in tear strength and bending strength in all directions is reduced, making it possible to produce paper suitable for packaging applications. The upper limit of the C / M ratio of tensile strength is not particularly limited, but is about 115%. In the present invention, the tensile strength is measured in accordance with JAPAN TAPPI No. 71. The packaging substrate of the present invention preferably has a tensile strength of 0.3 kN / m or more in both the MD (longitudinal direction) and CD (transverse direction), more preferably 0.4 kN / m or more, and even more preferably 0.5 kN / m or more.

[0030] (Tear Strength) The tear strength can be adjusted by the fiber length, beating degree, etc. of the fibers used in the packaging substrate. It is preferable that the packaging substrate of the present invention has a tear strength of 450 mN or more in MD and 650 mN or more in CD, from the viewpoint of preventing breakage of the package when subjected to impact, etc. The tear strength in MD is more preferably 550 mN or more, even more preferably 650 mN or more, and even more preferably 680 mN or more, and the CD is more preferably 700 mN or more, even more preferably 750 mN or more, and even more preferably 780 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 with a length of 63 mm, a slit of 20 mm, and a tear length of 43 mm.

[0031] (Sizing) When a heat seal layer is formed by coating, the packaging substrate preferably has appropriate sizing or water repellency suitable for coating. Specifically, a pen-writing sizing degree of 1 or more according to JAPAN TAPPI No. 12 is preferred because it allows for suitable coating using a gravure coater, flexo coater, or the like. The pen-writing sizing degree is more preferably 2 or more, even more preferably 3 or more, even more preferably 4 or more, and even more preferably 5 or more.

[0032] "Packaging Material" The packaging substrate of the present invention can be made into a heat-sealable packaging material by providing a heat-sealable layer on at least one surface. The packaging material of the present invention can be heat-sealed at a temperature of 130°C and a pressure of 1.0 kgf / cm. ２ The heat seal strength when heat-sealed for 1 second at a pulling speed of 30 mm / min and peeled off using a T-type sealant is 0.5 N / 15 mm or more. This heat seal strength is preferably 0.8 N / 15 mm or more, more preferably 1.5 N / 15 mm or more, even more preferably 2 N / 15 mm or more, still more preferably 2.5 N / 15 mm or more, even more preferably 3 N / 15 mm or more, and still more preferably 3.5 N / 15 mm or more.

[0033] The heat seal layer is provided on at least one side of the packaging substrate, and may be provided on both sides. The dry mass of the heat seal layer per side is 1 g / m ２ 20g / m or more ２ The dry mass of the heat seal layer (per side) is preferably 1 g / m or less. ２ If the dry mass (per side) of the heat seal layer is less than 20 g / m, the heat sealability may be deteriorated. ２ If the dry mass of the heat seal layer (per side) 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 dry mass of the heat seal layer (per side) is preferably 15 g / m or more. ２ Preferably, the weight is 12 g / m or less. ２ More preferably, it is 9 g / m or less. ２ In particular, in a packaging substrate having excellent sizing properties, for example, a packaging substrate having a pen size of 2 or more, it is easy to form a heat seal layer even with a small coating amount, so the dry mass of the heat seal layer (per side) is preferably, for example, 6 g / m or less. ２ Below, 5g / m ２ Below, 4g / m ２ Below, 3g / m ２ It may be possible to do the following:

[0034] The thermoplastic resin forming the heat seal layer is not particularly limited, and thermoplastic resins used in heat seal 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 acrylic resins are preferred from the viewpoint of heat seal strength. Furthermore, biodegradable resins such as polyvinyl alcohol, polylactic acid, polyhydroxyalkyl acid, polybutylene succinate, and polyglycolic acid are preferred from the viewpoint of reducing the environmental impact if they are discharged as waste.

[0035] The heat seal layer may be either a coated layer or a laminate layer, but is preferably a coated layer from the viewpoints of production efficiency and recyclability (redisintegrability). When the heat seal layer is a coated 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 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.

[0036] The packaging substrate of the present invention is primarily made of hemp pulp, has excellent cushioning properties and flexibility, and is porous and absorbent. Bar coaters and air knife coaters apply excess coating liquid to the substrate using an applicator roll and then scrape off the excess coating liquid using a Mayer bar or air knife. However, if the packaging 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 bleed-through to the opposite side of the substrate, contaminating the process. On the other hand, gravure coaters and flexo coaters measure the specified amount to be coated using an embossed pattern on a gravure roll, and then either transfer the coating liquid directly to the substrate and apply it, or transfer the coating liquid to a coating roll and then apply it to the substrate. This allows for the formation of a coating layer limited to the surface of the substrate. Therefore, with gravure coaters and the like, the transferred coating liquid remains on the surface of the substrate rather than penetrating into the substrate, even with substrates with good absorbency, allowing for sufficient heat seal strength to be achieved even with a small dry mass (per side) of the heat seal layer. The number of meshes and cup depth of the embossing pattern of the gravure roll can be appropriately selected depending on the concentration of the aqueous dispersion or solution forming the heat seal layer and the dry mass of the heat seal layer.

[0037] When aqueous coating is used to form a heat seal layer as a coating layer, an aqueous dispersion of a thermoplastic resin or an aqueous solution of a thermoplastic resin is used. If the packaging substrate is porous and has good water absorption, the aqueous dispersion or solution of the thermoplastic resin may penetrate into the substrate, preventing the thermoplastic resin from localizing on the substrate surface, potentially resulting in weak heat seal strength. Furthermore, to achieve sufficient heat seal strength, the dry mass of the heat seal layer must be increased. Therefore, particularly when coating using a gravure coater, flexo coater, or the like, it is preferable to combine the packaging substrate and the coating liquid so that the contact angle between the packaging substrate and the coating liquid is 70° or more and 120° or less. By ensuring a contact angle between the packaging substrate and the coating liquid of 70° or more and 120° or less, the coating liquid remains appropriately on the packaging substrate, and the thermoplastic resin forms a uniform layer on the packaging substrate surface, thereby enabling a packaging material with good heat seal strength to be obtained while reducing the amount of thermoplastic resin applied. If this contact angle is less than 70°, the coated thermoplastic resin will not penetrate deep into the packaging substrate and will not be localized on the surface of the packaging substrate, which may result in weak heat seal strength. Furthermore, to achieve sufficient heat seal strength, the dry mass of the heat seal layer must be increased. On the other hand, if this contact angle exceeds 120°, the coating liquid will be repelled from the surface of the packaging substrate, resulting in unevenness in the heat seal layer and making it difficult to obtain uniform heat seal strength. This contact angle is preferably 80° or more and 110° or less. Furthermore, when coating with a gravure coater, flexo coater, or the like, the viscosity of the coating liquid (B-type viscosity, No. 2 rotor, 60 rpm) is preferably 500 mPa·s or less, more preferably 200 mPa·s or less.

[0038] Test 1: Packaging substrate "Examples 1 to 3" Commercially available abaca pulp was disintegrated using a pulper. The freeness was 730 ml CSF. The disintegrated abaca pulp was fed into a short wire paper machine in an unbeaten state to produce paper at a predetermined basis weight so that the CD / MD ratio of tensile strength was approximately 80 to 110%, and the paper was dried in a Yankee dryer to obtain a packaging substrate. "Example 4" A packaging substrate was obtained by papermaking using a short wire paper machine in the same manner as in Example 1, except that a mixed pulp (CSF 650 ml) was used, which was a 50:50 mixture by mass of disintegrated abaca pulp (CSF 730 ml) and commercially available NBKP pulp beaten to a CSF of 500 ml.

[0039] "Comparative Example 1" Commercially available NBKP was beaten to a freeness CSF of 650 ml, paper made to a predetermined basis weight using a Fourdrinier paper machine, and dried in a multi-cylinder dryer to obtain a packaging substrate. "Comparative Example 2" A pulp obtained by mixing commercially available NBKP and LBKP in a mass ratio of 10:90 was beaten to a freeness CSF of 650 ml, paper made to a predetermined basis weight using a Fourdrinier paper machine, and dried in a Yankee dryer to obtain a packaging substrate.

[0040] Evaluation items and evaluation methods The resulting packaging substrates were evaluated as follows. The results are shown in Table 1. (Fiber length, fiber width) The length-weighted average fiber length and length-weighted average fiber width were measured using an FS5 manufactured by Valmet Co., Ltd. (Basis weight, thickness, density) Basis weight: Measured in accordance with JIS P8124. Thickness: Measured in accordance with JIS P8118. Density: Calculated from basis weight and thickness.

[0041] (Compression strength) As a measuring instrument, a KES-G5 compression tester manufactured by Kato Tech Co., Ltd. was used. With one support, a pressure plate with an area of ​​2.0 cm ２ , compression deformation speed (pressure plate descending speed) 0.02 mm / sec (0.002 cm / sec), maximum compression load 300 gf / cm ２ The measurement was carried out under the measurement conditions, and the graph shown in Figure 1 was prepared. In Figure 1, the y-axis (vertical axis) direction represents the pressure P (gf / cm ２ ) and the x-axis direction (horizontal axis direction) in the figure indicates the thickness T (mm) of one support. ０ is the pressure P is 50 gf / cm ２and T Ｍ The pressure P is the maximum compressive load of 300 gf / cm ２ The compressive strength is the thickness of one support when the pressure plate is 50 gf / cm ２ to 300 gf / cm ２ The pressure P (gf / cm ２ ) (area S of the shaded area in FIG. 1) divided by the area of ​​triangle ABC.

[0042] (Flexural strength) Using a pure bending tester KES-FB2-A manufactured by Kato Tech Co., Ltd., a test piece of 100 mm x 100 mm was used at 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 given above.

[0043] (Tensile strength) Measured in accordance with JAPAN TAPPI No. 71 under the conditions of a test piece width of 15 mm, a test length of 180 mm, and a pulling speed of 180 mm / min. (Tear strength) Measured in accordance with JIS P8116:2000 using an Elmendorf tear tester (Kumagaya Riki Kogyo Co., Ltd.). The test piece length was 63 mm, the incision depth was 20 mm, and the tear length was 43 mm.

[0044]

[0045] The packaging substrates obtained in Examples 1 to 4 of the present invention had a compressive strength measured using a KES-G5 compression tester (measurement number: 1, deformation rate: 0.02 mm / sec, initial compression load: 50 gf / cm ２ , maximum compression load 300gf / cm ２ The packaging substrates obtained in Examples 1 to 4 of the present invention had a bending strength of 0.8 g cm in both the MD and CD directions as measured with a KES-FB2-A pure bending tester. ２ The packaging substrates obtained in Comparative Examples 1 and 2 had a compressive strength of more than 1.5 and were poor in cushioning properties. The packaging substrate obtained in Comparative Example 2 had a bending strength in the MD direction of 0.8 g cm ２ / cm and was inferior in flexibility. Example 4 was a packaging substrate with lower compressive strength and excellent cushioning properties compared to the comparative examples. In Examples 1 to 3, the compressive strength was further reduced and cushioning properties were significantly improved.

[0046] Test 2: Packaging Material (Packaging Base Material) The packaging base material obtained in Example 1 was designated as Packaging Base Material 1. The coating amount of a sizing agent (manufactured by Seiko PMC Corporation, AD1653, AKD / solid content 20%) on Packaging Base Material 1 was approximately 0.5 g / m2 in terms of solid content. ２ The coating was carried out at a coating concentration of 3.5% so that the coating density was 3.5% and then dried using an air heater and a rotary dryer to produce a packaging substrate 2.

[0047] (Thermoplastic resins) Thermoplastic resin 1: Chemipearl S-500 (Mitsui Chemicals, Inc., ethylene acrylic type) Thermoplastic resin 2: Arrowbase SE-1015J2 (Unitika Ltd., cross-linked polyolefin type) thickened by adding 2.3 parts of thickener SN Thickener 929S (San Nopco Ltd., sodium polycarboxylate) to 100 parts Thermoplastic resin 3: Arrowbase AA-1462 (Unitika Ltd., cross-linked polyolefin type)

[0048] Examples 5 to 7, Comparative Examples 3 and 4: Packaging materials were obtained by applying a coating liquid (aqueous dispersion of thermoplastic resin) to the packaging substrate by gravure coating and drying using the combinations of packaging substrate, thermoplastic resin, and gravure plate shown in Table 2. The viscosity of the coating liquid was measured using a Brookfield viscometer with a No. 2 rotor at 60 rpm.

[0049] The packaging substrates and packaging materials were evaluated. The results are shown in Table 2. (Pen-writing sizing degree) The heat-sealing agent-coated surfaces of the packaging substrates were measured in accordance with JAPAN TAPPI Paper Pulp Test Method No. 12. (Contact angle) A dynamic contact angle meter FIBRO 100 DAT MKII was used. A drop of 12 μL of coating liquid was dropped onto the packaging substrate, and the contact angle 0.1 seconds after dropping was taken as the measured value. Three measurements were taken and the average value was calculated. (Test environment: 23°C) (Heat seal strength) The sealant-coated surfaces of the packaging substrates were placed together, and the temperature was 130°C and the pressure was 1.0 kgf / cm. ２The sample was heat-sealed for 1 second and then peeled off using a universal tensile tester (IM20-ST model, manufactured by Intesco Co., Ltd.) at a test width of 15 mm and a pulling speed of 30 mm / min with a T-type peeler.

[0050]

[0051] In Comparative Example 3, in which the contact angle between the packaging substrate and the coating liquid was less than 70°, coating was possible, but much of the coating liquid soaked into the packaging substrate, preventing the formation of a sufficient heat-sealing layer on the surface and making heat sealing impossible. In Comparative Example 4, in which the gravure plate mesh was coarser than in Comparative Example 3, the coating liquid bleed through the packaging substrate, contaminating the impression roll, making continuous coating impossible. Furthermore, although the coating amount was greater than in Comparative Example 3, much of the coating liquid soaked into the packaging substrate, as in Comparative Example 3, preventing the formation of a sufficient heat-sealing layer on the surface and making heat sealing impossible. The packaging materials obtained in Examples 5 to 7, in which the contact angle between the packaging substrate and the coating liquid was 70° or greater, had excellent heat-sealing strength. In particular, Example 6 used the same coating liquid as Comparative Examples 3 and 4 but a coarser-mesh gravure plate, but the packaging substrate had high sizing properties, preventing the penetration of the coating liquid, making heat sealing possible.

Claims

1. A packaging substrate containing natural fibers and having a basis weight of 18 g / m ２ 50g / m or more ２ Hereinafter, the packaging substrate characterized in that the natural fibers include hemp pulp.

2. The packaging substrate according to claim 1, characterized in that the hemp pulp has an average fiber length of 2.5 mm or more, an average fiber diameter of 15 μm to 25 μm, and a Canadian Standard Freeness of 650 ml CSF or more.

3. The packaging substrate according to claim 1 or 2, characterized in that it contains hemp pulp in an amount of 40% by mass or more based on the total fibers.

4. The packaging substrate according to any one of claims 1 to 3, characterized in that the hemp pulp is abaca.

5. Compressive strength measured using a KES-G5 compression tester (measurement number 1, deformation speed 0.02 mm / sec, initial compression load 50 gf / cm ２ , maximum compression load 300gf / cm ２ 5. The packaging substrate according to claim 1, wherein the value of the linearity of the surface roughness of the packaging substrate is 1.5 or less.

6. The bending strength in both MD and CD measured with a KES-FB2-A pure bending tester is 0.8 g cm ２ The packaging substrate according to any one of claims 1 to 5, characterized in that the thickness of the packaging substrate is 1 / cm or less.

7. The packaging substrate according to any one of claims 1 to 6, wherein the C / M ratio of the tensile strength is 60% or more, the tear strength is 450 mN or more in the MD and 650 mN or more in the CD.

8. The density of the packaging substrate is 0.2 g / cm ３ 0.5g / cm or more ３ The packaging substrate according to any one of claims 1 to 7, characterized in that:

9. The packaging substrate according to any one of claims 1 to 8, having a heat seal layer on at least one side thereof, and a temperature of 130°C and a pressure of 1.0 kgf / cm ２ 1. A packaging material characterized in that the heat seal strength when heat sealed for 1 second and peeled off with a T-shaped strip at a tensile speed of 30 mm / min is 0.5 N / 15 mm or more.

10. A method for producing a packaging material, comprising applying a coating liquid containing a thermoplastic resin onto the packaging substrate according to any one of claims 1 to 8 by a gravure or flexographic method to form a heat seal layer.

11. The method for producing a packaging material according to claim 10, characterized in that the contact angle between the packaging substrate and the coating liquid is 70° or more and 120° or less.

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