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

Abstract

To provide a packaging material using a packaging substrate having excellent balance in cushion property and flexibility.SOLUTION: A packaging material includes a heat seal layer at least on a single side of a packaging substrate containing a natural fiber and having a basis weight of 18 g / m2 or over and has a heat seal strength of 0.5 N / 15 mm or over when heat-sealed at a temperature of 130°C under a pressure of 1.0 kgf / cm2 for a time of 1 s and peeled by T type at a tensile speed of 30 mm / min.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a packaging substrate, a packaging material having the packaging substrate, and a method for producing the packaging material. [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. 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 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 items to be easily removed when used in flexible packaging.

[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. [Prior art documents] [Patent documents]

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

[0009] Packaging materials using heat-sealable paper have been proposed as an alternative to packaging materials using plastic film. However, because paper is less stretchable than plastic film, packaging materials using heat-sealable paper have inferior cushioning properties. Furthermore, because paper is less flexible than plastic film, it is not possible to package contents with complex shapes according to the shape of the contents. An object of the present invention is to provide a packaging substrate that has an excellent balance between cushioning properties and flexibility, a packaging material using this packaging substrate, 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 substrate comprising natural fibers, Basis weight 18g / m 2 More than 50g / m 2 below, Packaging substrate with a tensile strength C / M ratio of 60% or more, tear strength of 450mN or more in MD and 650mN or more in CD. 2. The density of the packaging substrate is 0.2 g / cm 3 More than 0.5g / cm 3 The packaging substrate according to 1., characterized in that: 3. The natural fibers include pulp; 3. The packaging substrate according to 1. or 2., characterized in that it contains 50% by mass or more of non-wood pulp with 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, based on the total amount of pulp. 4. The packaging substrate according to any one of 1. to 3., wherein the packaging substrate contains abaca pulp in an amount of 50% by mass or more based on the total fibers. 5. A packaging substrate according to any one of 1. to 4., having a heat seal layer on at least one surface thereof, Temperature 130℃, pressure 1.0kgf / cm 2 A packaging material characterized by having a heat seal strength of 0.5 N / 15 mm or more when heat sealed in 1 second, peeled off at a pulling speed of 30 mm / min using a T-type sealant. 6. A method for producing a packaging material, characterized in that a heat seal layer is formed by applying a coating liquid containing a thermoplastic resin onto the packaging substrate described in any one of 1. to 4. by a gravure method or a flexographic method. 7. The method for producing a packaging material according to 6., wherein the contact angle between the packaging substrate and the coating liquid is 70° or more and 120° or less. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a packaging substrate and a packaging material that combine cushioning properties and flexibility. A packaging material with excellent cushioning properties can protect contents from shaking during transportation and external impact. A packaging material with excellent flexibility can be packaged to fit the shape of the contents. Therefore, the packaging material of the present invention is suitable for packaging contents that are vulnerable to impact and have complex shapes, such as electronic components. [Brief explanation of the drawings]

[0012] [Figure 1] Graph for explaining a method for calculating compressive strength from the measurement results of the KES-G5 compression tester. DETAILED DESCRIPTION OF THE INVENTION

[0013] "Packaging base material" The packaging substrate of the present invention has a basis weight of 18 g / m 2 More than 50g / m 2 The packaging substrate of the present invention has a basis weight of 18 g / m 2 More than 50g / m 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 is preferable. 2 More than 40 g / m is more preferable. 2 Less than 35 g / m 2 Less than 30 g / m is more preferable. 2 The following is even more preferred:

[0014] The packaging substrate of the present invention has a density of 0.2 g / cm 3 More than 0.5g / cm 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. 3When the density is more than 0.4 g / cm, the packaging material has excellent flexibility but may have poor cushioning properties. 3 Less than 0.3 g / cm is preferred 3 If flexibility is important, a density of 0.25 g / cm is more preferable. 3 More than 0.3 g / cm is preferable. 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 proportion 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 natural cellulose such as pulp, cellulose produced by microorganisms such as acetic acid bacteria, mercerized pulp obtained by treating cellulose with a high concentration of alkali, regenerated cellulose obtained by dissolving cellulose in a solvent such as a cuprammonium solution or a morpholine derivative and then reprecipitating, cellulose-based fibers such as various cellulose derivatives such as acetylated cellulose and carboxylated cellulose, and animal hair such as silk, wool, and goat hair. One or more of these can be used. As the natural fiber, wood pulp and non-wood pulp can be preferably used.

[0017] The average fiber length of the 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 dense and compact, which may result in reduced cushioning properties. The average fiber width of the 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 are soft but the substrate becomes tight, resulting in poor cushioning properties, while if the average fiber width is thick, the fibers themselves become difficult to bend, resulting in poor flexibility. In this specification, the average fiber length and the average fiber width refer to the length-weighted average fiber length and the 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 K.K., a Fractionator manufactured by Valmet K.K., an FS5 manufactured by Valmet K.K., or a Morfi manufactured by Voith Turbo K.K., an optical microscope, an electron microscope, or the like.

[0018] The beating degree of the 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 becomes more beaten, the density increases and the substrate becomes softer, but cushioning properties tend to decrease.

[0019] The packaging substrate of the present invention preferably contains 50% by mass or more of non-wood pulp with 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, based on the total amount of pulp. By containing 50% by mass or more of such non-wood pulp, it becomes easy to obtain a packaging substrate that is low in density and has excellent cushioning and flexibility. The average fiber length of the non-wood 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 non-wood 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 non-wood pulp is more preferably 670 ml CSF or more, even more preferably 690 ml CSF or more, and most preferably unbeaten.

[0020] In the present invention, the amount of non-wood pulp that satisfies the above-mentioned average fiber length, average fiber width, and Canadian Standard Freeness relative to the total fibers is more preferably 60% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 93% by mass or more, even more preferably 96% 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 non-wood pulp that satisfies the above-mentioned average fiber length, average fiber width, and Canadian Standard Freeness relative to the total pulp is more preferably 70% by mass or more, even more preferably 90% by mass or more, even more preferably 93% by mass or more, even more preferably 96% by mass or more, even more preferably 99% by mass or more, and most preferably 100% by mass.

[0021] In the present invention, 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; mechanical pulps such as stone ground pulp (SGP), pressurized 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. In the present invention, examples of non-wood pulp include pulps produced from non-wood materials such as bast fibers of flax (linen), kenaf, jute, paper mulberry, and 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, and one or more of these can be used.

[0022] Among these, the packaging substrate of the present invention preferably contains abaca pulp (Manila hemp pulp). By incorporating abaca pulp, it becomes easy to obtain a packaging substrate with excellent cushioning properties and flexibility. In the present invention, the amount of abaca pulp relative to the total fiber content is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 93% by mass or more, even more preferably 96% 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 the total pulp is more preferably 70% by mass or more, even more preferably 90% by mass or more, even more preferably 93% by mass or more, even more preferably 96% by mass or more, even more preferably 99% by mass or more, and most preferably 100% by mass.

[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 (width / length ratio) of physical properties, and it is more preferable to use an inclined short wire paper machine.

[0024] The drying process can be appropriately selected from a multi-cylinder dryer, Yankee dryer, hot air dryer, etc. Among these, it is preferable to dry using a Yankee dryer, which turns the packaging substrate into one-sided glossy paper. When the packaging substrate is one-sided glossy paper, the heat seal layer may be provided on either the glossy or rough side, but providing the heat seal layer on the smoother side (glossy side) that comes into contact with the Yankee dryer allows for the formation of a more uniform coating layer, thereby imparting high heat seal strength with a smaller coating amount. Furthermore, since the rough side, 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 agents, drainage aids, 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 thereof is not particularly limited, and examples that can be used 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 thereof is not particularly limited, and examples that can be used include carboxymethyl cellulose (CMC), carboxymethyl guar gum, polyacrylamide, glyoxal-modified polyacrylamide, and hydroxypropyl guar gum. In the present invention, the water repellent or sizing agent is not particularly limited, and styrene acrylic acid ester copolymer, styrene-acrylonitrile copolymer, anionic polyurethane, styrene-maleic anhydride copolymer, etc. can be used.

[0027] (Paper quality and characteristics of packaging substrate) The packaging substrate of the present invention has a predetermined compressive strength and bending strength, and therefore has excellent cushioning properties and flexibility as a packaging material. (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 has a C / M ratio (horizontal / vertical ratio) of tensile strength of 60% or more. Paper with a C / M ratio of tensile strength of 60% or more has small differences in tear strength and bending strength in all directions and no direction in which it is prone to tearing, so it has excellent cushioning properties and is resistant to tearing even when subjected to impact. The C / M ratio of tensile strength is preferably 70% or more, more preferably 75% or more, even more preferably 85% or more, even more preferably 90% or more, and even more preferably 95% or more. The upper limit of the C / M ratio of tensile strength is not particularly limited, but is about 115%. In the present invention, 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 MD (machine direction) and CD (cross direction), more preferably 0.4 kN / m or more, and even more preferably 0.5 kN / m or more.

[0028] (Tear strength) The tear strength can be adjusted by the fiber length, beating degree, etc. of the fibers used in the packaging substrate. 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. Having a tear strength of 450 mN or more in MD and 650 mN or more in CD prevents damage to the package when subjected to impact, etc. The tear strength in MD is preferably 550 mN or more, even more preferably 650 mN or more, and even more preferably 680 mN or more, and in CD is 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 Testing Method - Elmendorf Tear Tester Method" using a test specimen 63 mm long, a 20 mm incision, and a 43 mm tear length.

[0029] (Compression 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 used. In particular, the compressive strength value can be adjusted by the thickness and degree of beating of the natural fibers used in the packaging substrate. The packaging substrate of the present invention has a compressive strength (measured on one sheet, deformation speed 0.02 mm / sec, initial compressive 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. There is no particular restriction on the lower limit of this compressive strength, but it is, for example, about 1.1.

[0030] (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 0.6 g cm 2 / cm or less is preferable, and 0.4g·cm 2 / cm or less is preferable, and 0.2g cm 2 The lower limit of this bending strength is not particularly limited, but for example, it is 0.02 g cm 2 / cm.

[0031] (Size) 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 as described in 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 materials" 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 thereof. The packaging material of the present invention is resistant to temperatures of 130°C and pressure of 1.0 kgf / cm 2 The heat seal strength when heat-sealed for 1 second, at a pulling rate of 30 mm / min and peeled 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 surface of the packaging substrate, and may be provided on both surfaces. The dry mass of the heat seal layer on one side is 1 g / m 2 More than 20g / m 2 The dry mass of the heat seal layer (per side) is preferably 1 g / m or less. 2 If the dry mass of the heat seal layer (per side) 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, it 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 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 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.

[0035] 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.

[0036] The packaging substrate of the present invention is made mainly of natural fibers, has excellent cushioning properties and flexibility, and is porous and water-absorbent. Bar coaters and air knife coaters use an applicator roll to supply excess coating liquid to a substrate, and then scrape off the excess coating liquid with a Mayer bar or air knife. However, if the packaging substrate is porous, the coating liquid may penetrate the substrate when it is supplied to the substrate, resulting in an excessive amount of coating and may even bleed through to the other side of the substrate, contaminating the process. On the other hand, gravure coaters and flexo coaters measure out the specified amount to be coated 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 they can form a coating layer limited to the surface of the substrate.For this reason, the coating liquid transferred with a gravure coater, etc., does not easily penetrate into the substrate, even if the substrate has good water absorption, and remains on the surface of the substrate, making it possible to obtain sufficient heat seal strength 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 the 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 deep into the substrate, preventing the thermoplastic resin from being localized on the surface of the substrate, which may result in a weakened 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 them is 70° or more and 120° or less. A contact angle between the packaging substrate and the coating liquid of 70° or more and 120° or less allows the coating liquid to remain appropriately on the packaging substrate, and the thermoplastic resin forms a uniform layer on the surface of the packaging substrate, thereby reducing the amount of thermoplastic resin applied and achieving a packaging material with good heat seal strength. If this contact angle is less than 70°, the applied thermoplastic resin may not penetrate into the packaging substrate and be localized on the surface of the packaging substrate, resulting 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 may be repelled from the surface of the packaging substrate, causing unevenness in the heat seal layer and preventing uniform heat seal strength. This contact angle is preferably 80° or more and 110° or less. When coating is performed using 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, and more preferably 200 mPa·s or less. [Example]

[0038] Test 1: Packaging substrate "Examples 1 to 3" Commercially available abaca pulp was disintegrated in a pulper. The freeness was 730 ml of CSF. The disintegrated abaca pulp was fed into a short-wire paper machine in an unbeaten state to produce paper with a specified basis weight so that the CD / MD ratio of the tensile strength was approximately 80 to 110%, and then 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 disaggregated 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, made into paper with 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 made by mixing commercially available NBKP and LBKP in a mass ratio of 10:90 was beaten to a freeness CSF of 650 ml, made into paper of 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 substrate was evaluated as follows, and 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] (tensile strength) In accordance with JAPAN TAPPI No. 71, the test was performed under the conditions of a test piece width of 15 mm, a test length of 180 mm, and a tensile speed of 180 mm / min. (Tear strength) Measurement was performed using an Elmendorf tear tester (Kumagaya Riki Kogyo Co., Ltd.) in accordance with JIS P8116:2000. The test piece length was 63 mm, the cut was 20 mm, and the tear length was 43 mm.

[0042] (Compression strength) The measurement equipment used was a Kato Tech KES-G5 compression tester, and the support was placed on a single sheet with a pressure plate area of ​​2.0 cm. 2 , compression deformation speed (pressure plate descent speed) 0.02mm / sec (0.002cm / sec), maximum compression load 300gf / 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 (horizontal axis) in the figure indicates the thickness T (mm) of one support. In Figure 1, T0 indicates the pressure P of 50 gf / cm 2 indicates the thickness of one support when T M The pressure P is the maximum compressive load of 300gf / cm 2 The compressive strength is the thickness of one support when the pressure plate is 50 gf / cm 2 to 300gf / cm 2 The pressure on the support until it reaches P (gf / cm 2 ) (the area S of the shaded area in Figure 1) divided by the area of ​​triangle ABC.

[0043] (bending strength) Using a Kato Tech KES-FB2-A pure bending tester, test pieces were 100mm x 100mm, bending speed 0.5cm -1 / sec, maximum curvature 2.5cm -1 Measurements were carried out in both the MD and CD directions under the conditions above.

[0044] [Table 1]

[0045] The packaging substrates obtained in Examples 1 to 4 of the present invention had a C / M ratio of tensile strength of 60% or more and a tear strength of 650 mN or more in both MD and CD, and were excellent in cushioning and flexibility. The packaging substrates obtained in Comparative Examples 1 and 2 had tear strengths of less than 650 mN in both MD and CD, and were poor in cushioning properties. The packaging substrate obtained in Comparative Example 2 also had a bending strength in the MD direction of 0.8 g cm 2 / cm and had poor flexibility. The packaging base material of Example 4 had lower compressive strength and excellent cushioning properties compared to the comparative examples. In Examples 1 to 3, the compressive strength was further reduced and the cushioning properties were significantly improved.

[0046] Test 2: Packaging materials (Packaging base material) The packaging substrate obtained in Example 1 was designated as packaging substrate 1. The coating amount of sizing agent (Seiko PMC Corporation, AD1653, AKD / solid content 20%) on packaging substrate 1 is approximately 0.5 g / m2 in 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 packaging substrate 2.

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

[0048] "Examples 5 to 7, Comparative Examples 3 and 4" Using the combinations of packaging substrate, thermoplastic resin, and gravure plate shown in Table 2, a coating liquid (aqueous dispersion of thermoplastic resin) was applied to the packaging substrate by gravure coating and dried to obtain a packaging material. 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, and the results are shown in Table 2. (pen writing size) The heat sealant coated surface of the packaging substrate was 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. The coating liquid was dropped onto the packaging substrate in a drop size of 12 μL, and the contact angle was measured 0.1 seconds after the drop. The measurement was taken three times and the average value was calculated. (Test environment: 23°C) (Heat seal strength) The sealing agent coated surfaces of the packaging substrates were placed together and heated at 130°C and a pressure of 1.0 kgf / cm. 2 The sample was heat-sealed for 1 second and then peeled off in a T-shape using a universal tensile tester (manufactured by Intesco, IM20-ST model) at a test width of 15 mm and a pulling speed of 30 mm / min.

[0050] [Table 2]

[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 most 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 bled through to the back of the packaging substrate, staining the impression roll and 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, and a sufficient heat seal layer could not be formed on the surface, 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 more, had excellent heat-seal strength. In particular, Example 6 used the same coating liquid as Comparative Examples 3 and 4, but a gravure plate with a coarser mesh, but the packaging substrate had a high sizing property and was able to prevent penetration of the coating liquid, so heat sealing was possible.

Claims

[Request 1] Basis weight 18 g / m containing natural fibers ２ A packaging material having a heat seal layer provided on at least one surface of the packaging substrate, Temperature: 130°C, pressure: 1.0 kgf / cm ２ A packaging material 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 sealant at a pulling rate of 30 mm / min.

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