Base material for packaging, material for packaging, and method for manufacturing material for packaging

Abstract

To provide a base material for packaging which is excellent in cushioning property, a base material for packaging which is excellent in flexibility, a material for packaging using the base materials for packaging, and a method for manufacturing a material for packaging.SOLUTION: There are provided a base material for packaging containing natural fibers in which a basis weight is 18 g / m2 or more and 50 g / m2 or less, and compressive strength (one base material to be measured, deformation rate of 0.02 mm / sec, initial compression load of 50 gf / cm2, and maximum compressive load of 300 gf / cm2) that is measured using a KES-G5 compression testing machine is 1.5 or less; a material for packaging which has a heat seal layer on at least one surface of the base material for packaging, and heat seal strength when being heat sealed at a temperature of 130°C and a pressure of 1.0 kgf / cm2 for 1 second, and being peeled at a tension rate of 30 mm / min by a T type of 0.5 N / 15 mm or more; and a method for manufacturing a material for packaging which coats a coating liquid containing a thermoplastic resin onto the base material for packaging by a gravure method or a flexographic method, and thereby forms a heat seal layer.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Conventionally, plastic materials have mainly been used for packaging containers such as food trays and packaging bodies such as bags for pillow packaging. However, in recent years, due to environmental problems such as those related to plastic waste in the ocean, there has been an increasing trend towards plastic reduction, and it is desired to minimize the use of resin materials in industrial products. Under such a trend, for packaging bodies as well, in order to reduce the environmental load, packaging materials using paper have been studied.

[0003] Patent Document 1 discloses a paper base material mainly composed of unbleached softwood kraft pulp and a heat-sealing layer laminated on one side of the paper base material. The folding endurance in the flow direction of the paper base material 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 Bekk smoothness of the surface of the heat-sealing layer laminated surface is 3 seconds or more and 230 seconds or less, the main component of the heat-sealing layer is an alkali-neutralized product of ethylene (meth)acrylic acid copolymer, and the coating amount of the heat-sealing layer is 1.5 g / m 2 or more and 10.0 g / m 2 or less. There has been proposed a heat-sealing paper that is environmentally friendly, ensures heat-sealing strength, and has an excellent effect of suppressing cracks due to folds and water resistance in the region where the heat-sealing layer is laminated.

[0004] Patent Document 2 includes a paper base material mainly composed of pulp and a heat-sealing layer laminated on one side of the paper base material. The main component of the heat-sealing layer is an alkali-neutralized ethylene (meth)acrylic acid copolymer. The Bek smoothness of the surface of the heat-sealing layer lamination surface on the paper base material is 5 seconds or more and 50 seconds or less, the Parker Print Surf smoothness is 3.8 μm or more and 8.0 μm or less, the Bek smoothness of the surface of the non-heat-sealing layer lamination surface on the paper base material is 50 seconds or more and 500 seconds or less, and the Parker Print Surf smoothness is 2.0 μm or more and 4.2 μm or less. A heat-sealing paper that does not contain high-environmental-impact laminated paper or plastic film and is excellent in water resistance and printability of the non-heat-sealing layer surface has been proposed.

[0005] Patent Document 3 discloses a heat-sealing paper having one or more heat-sealing layers on at least one surface of a paper base material. The heat-sealing layer contains a water-dispersible resin binder. The ISO stiffness in the longitudinal direction of the heat-sealing paper measured in accordance with ISO 2493-1:2010 is 0.55 mNm or less, the ISO stiffness in the transverse direction of the heat-sealing paper is 0.45 mNm or less, and the puncture strength of the heat-sealing paper measured in accordance with JIS Z 1707:2019 is 7.5 N or more. A heat-sealing paper having excellent drop impact resistance, flexibility, and heat-sealing property has been proposed.

[0006] Patent Document 4 discloses a paper for flexible packaging materials having a paper base material and a heat-sealing layer provided on at least one side of the paper base material. The paper base material has a filler content of 1 mass% or less, a basis weight of 25 g / m 2 or more and 50 g / m 2 or less, and a density of 0.85 g / m 3 or more and 1.35 g / m 3 or less. The dry mass (per side) of the heat-sealing layer is 4 g / m 2 or more and 20 g / m 2 or less. The paper for flexible packaging materials has a tear strength (MD direction and CD direction) of 100 mN or more and 650 mN or less, can be easily torn from any direction, and can easily take out the packaged product when made into a flexible package. A paper for flexible packaging materials has been proposed.

[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% or more by mass of an organic material, in which 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, has breathability and moisture permeability, generates little dust, and is recyclable. [Prior art documents] [Patent documents]

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

[0009] Packaging materials using heat-sealing paper have been proposed as an alternative to packaging materials using plastic films. However, since paper is less stretchable than plastic films, packaging materials using heat-sealing paper have inferior cushioning properties. Furthermore, since paper is less flexible than plastic films, 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 having excellent cushioning properties, a packaging substrate having excellent flexibility, a packaging material using these packaging substrates, 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 base material containing natural fibers, with a basis weight of 18 g / m 2 or more and 50 g / m 2 or less, and the compression strength (measured with 1 sheet, deformation speed 0.02 mm / sec, initial compression load 50 gf / cm 2 , maximum compression load 300 gf / cm 2 ) measured using a KES-G5 compression tester is 1.5 or less. A packaging base material characterized by this. 2. The packaging base material according to 1., characterized in that the bending strength in the MD and CD directions measured with a KES-FB2-A pure bending tester is both 0.8 g·cm 2 / cm or less. 3. The packaging base material according to 1. or 2., characterized in that the density of the packaging base material is 0.2 g / cm 3 or more and 0.5 g / cm 3 or less. 4. The natural fiber contains pulp, and contains 50 mass% or more of non-wood pulp having an average fiber length of 2.5 mm or more, an average fiber diameter of 15 μm or more and 25 μm or less, and a Canadian standard freeness of 650 ml CSF or more with respect to the total amount of pulp. The packaging base material according to any one of 1. to 3. 5. The packaging base material according to any one of 1. to 4., characterized in that the packaging base material contains 50 mass% or more of abaca pulp with respect to all fibers. 6. Having a heat seal layer on at least one side of the packaging base material according to any one of 1. to 5., heat-sealed at a temperature of 130°C, a pressure of 1.0 kgf / cm 2 , for 1 second, and the heat seal strength when peeled in a T-shape at a tensile speed of 30 mm / min is 0.5 N / 15 mm or more. A packaging material characterized by this. A method for manufacturing a packaging material, characterized in that a heat-sealing layer is formed by applying a coating liquid containing a thermoplastic resin onto a packaging base material according to any one of 7.1 to 5. by a gravure method or a flexographic method. 8. The method for manufacturing a packaging material according to 7., wherein the contact angle between the packaging base material and the coating liquid is 70° or more and 120° or less.

Advantages of the Invention

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

Brief Description of the Drawings

[0012]

Figure 1

Embodiments for Carrying Out the Invention

[0013] "Packaging base material" The packaging base material of the present invention has a basis weight of 18 g / m 2 or more and 50 g / m 2 or less. The packaging base material of the present invention can achieve both cushioning properties and flexibility at a high level by having a basis weight of 18 g / m 2 or more and 50 g / m 2 or less. In the packaging base material of the present invention, when emphasizing cushioning properties, a basis weight of 20 g / m 2 or more is preferable, and 22 g / m 2 or more is more preferable. When emphasizing flexibility, a basis weight of 40 g / m 2 or less is preferable, 35 g / m 2 or less is more preferable, and 30 g / m 2 or less is even more preferable.

[0014] The base material for packaging of the present invention has a density of 0.2 g / cm 3 or more and 0.5 g / cm 3 or less, which is preferable. When the density is less than 0.2 g / cm 3 , it becomes bulky and has excellent cushioning properties, but the flexibility may decrease. When the density exceeds 0.5 g / cm 3 , it has excellent flexibility, but may become a packaging material with poor cushioning properties. In the base material for packaging of the present invention, when emphasizing cushioning properties, a density of 0.4 g / cm 3 or less is preferable, and 0.3 g / cm 3 or less is more preferable. Also, when emphasizing flexibility, a density of 0.25 g / cm 3 or more is preferable, and 0.3 g / cm 3 or more is more preferable.

[0015] The base material for packaging of the present invention contains natural fibers, and for example, paper and wet non-woven fabrics can be preferably used. The base material for packaging of the present invention only needs to contain natural fibers, and can also contain resin fibers other than natural fibers. However, from the viewpoint of reducing the resin usage amount in the base material for packaging of the present invention, the proportion of natural fibers in all fibers is preferably 80% by mass or more, more preferably 90% by mass or more, further 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. Also, when containing resin fibers, it is preferable to use biodegradable resin fibers made of biodegradable resins 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 natural fibers, fibers derived from plants, microorganisms, and animals can be used without particular limitation. Specifically, examples include cellulose-based fibers such as pulp, natural cellulose such as cellulose produced by microorganisms such as acetic acid bacteria, mercerized pulp obtained by treating cellulose with high-concentration alkali, regenerated cellulose obtained by dissolving cellulose in a solvent such as a copper ammonia solution or a morpholine derivative and then reprecipitating it, and various cellulose derivatives such as acetylated modified cellulose and carboxylated modified cellulose. Examples also include silk, wool, and animal hairs such as goat hair, and one or more of these can be used. As natural fibers, wood pulp and non-wood pulp can be preferably used.

[0017] The average fiber length of the pulp contained in the packaging base material 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 base material becomes flexible, but the packaging base material becomes dense and tightened, so there is a risk of reduced cushioning properties. The average fiber width of the pulp contained in the packaging base material of the present invention is preferably 15 μm or more and 30 μm or less. The average fiber width is a factor that affects the cushioning properties of the base material. If the average fiber width is small, the fiber itself is soft, but the base material becomes tightened, so the cushioning properties are inferior. If the average fiber width is large, the fiber itself becomes difficult to bend, so there is a tendency for inferior flexibility. In this specification, the average fiber length and the average fiber width respectively mean the length-weighted average fiber length and the length-weighted average fiber width. For example, they can be measured by observing the fibers using an image analysis device such as a fiber tester manufactured by ABB Co., Ltd., a fractionator manufactured by Valmet Co., Ltd., FS5 manufactured by Valmet Co., Ltd., or Morfi manufactured by Voith Turbo Co., Ltd., or an optical microscope, an electron microscope, or the like.

[0018] The beating degree of the pulp contained in the packaging base material of the present invention is preferably 650 ml CSF or more, more preferably 670 ml CSF or more, even more preferably 690 ml CSF or more, and most preferably unbleached. As the beating of the pulp progresses, the density increases and the base material becomes flexible, but there is a tendency for the cushioning properties to decrease.

[0019] The base material for packaging of the present invention preferably contains 50% by mass or more of non-wood pulp having an average fiber length of 2.5 mm or more, an average fiber diameter of 15 μm or more and 25 μm or less, and a Canadian standard freeness of 650 ml CSF or more with respect to the total amount of pulp. By containing 50% by mass or more of such non-wood pulp, it becomes easy to obtain a base material for packaging having a low density and excellent cushioning properties and flexibility. The average fiber length of the non-wood pulp is more preferably 2.8 mm or more, further 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, further 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, further preferably 690 ml CSF or more, and most preferably it is unbeaten.

[0020] In the present invention, the blending amount of the non-wood pulp satisfying the above-described average fiber length, average fiber width, and Canadian standard freeness with respect to all fibers is more preferably 60% by mass or more, further 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 blending amount of the non-wood pulp satisfying the above-described average fiber length, average fiber width, and Canadian standard freeness with respect to all pulp is more preferably 70% by mass or more, further 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, as the wood pulp, there are chemical pulps such as bleached kraft pulp (BKP) using softwood and / or hardwood as the material, unbleached kraft pulp (UKP), semi-bleached kraft pulp (SBKP), sulfite pulp, etc., and mechanical pulps such as stone ground pulp (SGP), thermo-mechanical pulp (TMP), chemiground pulp (CGP), groundwood pulp (GP), thermo-mechanical pulp (TMP), etc., dissolving pulp, mercerized pulp, etc. One or more of these can be used. In the present invention, as the non-wood pulp, there are pulps made from non-wood such as flax (linen), kenaf, jute, paper mulberry, bast fibers such as Mitsumata, hard fibers such as bagasse, bamboo, esparto, seed hair fibers such as cotton (linter), and leaf sheath / leaf fibers such as Manila hemp (abaca), sisal hemp, etc. One or more of these can be used.

[0022] Among these, the base material for packaging of the present invention preferably contains abaca pulp (Manila hemp pulp). By blending abaca pulp, it becomes easy to obtain a base material for packaging excellent in cushioning properties and flexibility. In the present invention, the blending amount of abaca pulp with respect to all fibers preferably contains 50% by mass or more, more preferably 60% by mass or more, still 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 blending amount of abaca pulp with respect to all pulps is more preferably 70% by mass or more, still 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 papermaking method of the base material for packaging is not particularly limited and can be carried out using a Fourdrinier paper machine, a cylinder mold paper machine, a twin-wire paper machine, an inclined twin-wire paper machine, etc. Among these, it is preferable to use a twin-wire paper machine, an inclined twin-wire paper machine or a Fourdrinier paper machine that has a small fiber orientation and can increase the C / M ratio (cross / longitudinal ratio) of physical properties, and it is more preferable to use an inclined twin-wire paper machine.

[0024] For the drying process, a multi-cylinder cylinder dryer, a Yankee dryer, a hot air dryer, etc. can be appropriately selected. Among these, it is preferable to dry with a Yankee dryer in which the base material for packaging becomes single-sided glazed paper. When the base material for packaging is single-sided glazed paper, the heat seal layer may be provided on either the glazed surface or the rough surface. However, when the heat seal layer is provided on the smoother surface (glazed surface) facing the Yankee dryer, a more uniform coating layer can be formed, so high heat seal strength can be imparted with a small coating amount. In addition, since the rough surface, which is the opposite surface of the glazed surface, has fewer fibrils compared to the glazed surface, when the heat seal layer is provided on the glazed surface, the fibrils on the glazed surface are suppressed by the heat seal layer, and as a result, a packaging material with fewer fibrils can be obtained.

[0025] In the present invention, examples of various auxiliaries include sizing agents such as rosin, alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), styrene acrylic resin, polyacrylamide-based polymers, polyvinyl alcohol-based polymers, cationized starch, various modified starches, dry paper strength enhancers such as urea-formalin resin and melamine-formalin resin, wet paper strength enhancers, water repellents, retention aids, drainage improvers, coagulants, sulfate bands, bulking agents, dyes, fluorescent brighteners, pH adjusters, defoamers, ultraviolet ray inhibitors, anti-fading agents, pitch control agents, slime control agents, etc., and they can be appropriately selected and used as necessary.

[0026] When using a wet paper strength enhancer in the present invention, the type thereof is not particularly limited, and dialdehyde guar gum, glyoxal-modified polyacrylamide, polyamide epichlorohydrin, polyamide polyamine epichlorohydrin, polyamine epichlorohydrin, polyethyleneimine, etc. can be used. When using a dry paper strength enhancer in the present invention, the type thereof is not particularly limited, and carboxymethyl cellulose (CMC), carboxymethyl guar gum, polyacrylamide, glyoxal-modified polyacrylamide, hydroxypropyl guar gum, etc. can be used. In the present invention, the water repellent or sizing agent is not particularly limited, and styrene acrylate copolymer, styrene-acrylonitrile copolymer, anionic polyurethane, styrene-maleic anhydride copolymer, etc. can be used.

[0027] (Paper quality and characteristics of the packaging base material) The packaging base material of the present invention has a predetermined compressive strength and bending strength, and thus is excellent in cushioning property and flexibility as a packaging material. (Compressive strength) The compressive strength is correlated with the density (porosity), thickness, beating degree, thickness, etc. of the natural fibers incorporated in the packaging base material. In particular, the thickness, beating degree, etc. of the natural fibers incorporated in the packaging base material can be used to adjust the value of the compressive strength. The packaging base material of the present invention has a compressive strength (number of measurement sheets: 1, deformation speed: 0.02 mm / sec, initial compressive load: 50 gf / cm 2 , maximum compressive load: 300 gf / cm 2 ) measured using a KES-G5 compression tester manufactured by Kato Tech Co., Ltd. of 1.5 or less. The smaller this value of the compressive strength, the better the cushioning property. In the present invention, this compressive strength of the packaging base material is preferably 1.45 or less, more preferably 1.4 or less, and even more preferably 1.35 or less. The lower limit value 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 base material, and the value of the bending strength can be adjusted particularly by the thickness of the natural fiber incorporated in the packaging base material. The packaging base material of the present invention preferably has a bending strength in both the MD and CD directions measured by a KES-FB2-A pure bending tester manufactured by Kato Tech Co., Ltd. of 0.8 g·cm 2 / cm or less. The smaller this value of the bending strength, the better the flexibility. In the present invention, this bending strength of the packaging base material is preferably 0.6 g·cm 2 / cm or less, more preferably 0.4 g·cm 2 / cm or less, still more preferably 0.2 g·cm 2 / cm or less. The lower limit value of this bending strength is not particularly limited, but is, for example, about 0.02 g·cm 2 / cm.

[0029] (Tensile strength) The tensile strength can be adjusted by the fiber length of the fiber used in the packaging base material, the beating degree, etc. For the packaging base material of the present invention, the C / M ratio (transverse / longitudinal ratio) of the tensile strength is preferably 60% or more, more preferably 70% or more, and still more preferably 75% or more. By setting the C / M ratio of the tensile strength to 30% or more, the difference in the tear strength and bending strength in all directions becomes small, and paper suitable for packaging applications can be obtained. The upper limit of the C / M ratio of the 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. For the packaging base material of the present invention, the tensile strength is preferably 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 still more preferably 0.5 kN / m or more.

[0030] (Tear strength) The tear strength can be adjusted by the fiber length of the fiber used in the packaging base material, the beating degree, etc. For the base material for packaging of the present invention, it is preferable from the viewpoint of preventing damage to the package when it is subjected to impact or the like that the tear strength is 450 mN or more in the MD direction and 650 mN or more in the CD direction. The tear strength is more preferably 550 mN or more in the MD direction, still more preferably 650 mN or more, even more preferably 680 mN or more, more preferably 700 mN or more in the CD direction, still more preferably 750 mN or more, and even more preferably 780 mN or more. In this specification, the tear strength means a value measured in accordance with JIS P8116:2000 "Paper - Test method for tear strength - Elmendorf type tear tester method" with a test piece length of 63 mm, a notch of 20 mm, and a torn length of 43 mm.

[0031] (Sizing property) When forming a heat - seal layer on the base material for packaging by coating, it preferably has an appropriate sizing property or water - repellency suitable for coating. Specifically, it is preferable that the pen writing sizing degree described in JAPAN TAPPI No.12 is 1 or more because it can be preferably coated with a gravure coater, a flexo coater, etc. The pen writing sizing degree is more preferably 2 or more, still more preferably 3 or more, even more preferably 4 or more, and even more preferably 5 or more.

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

[0033] The heat - seal layer is provided on at least one surface of the base material for packaging and can also be provided on both surfaces. The dry mass per side of the heat-sealing layer is 1 g / m 2 or more and 20 g / m 2 or less, preferably. If the dry mass (per side) of the heat-sealing layer is less than 1 g / m 2 , the heat-sealing suitability may deteriorate. If the dry mass (per side) of the heat-sealing layer exceeds 20 g / m 2 , the heat-sealing suitability saturates and hardly improves. Also, since the amount of resin used increases, it becomes costly and is not preferable from the viewpoint of environmental load. The dry mass (per side) of the heat-sealing layer is preferably 1.5 g / m 2 or more, more preferably 2 g / m 2 or more. The dry mass (per side) of the heat-sealing layer is preferably 15 g / m 2 or less, more preferably 12 g / m 2 or less, even more preferably 9 g / m 2 or less. In particular, for a packaging base material with excellent sizing properties, for example, a packaging base material with a pen writing size degree of 2 or more, it is easy to form a heat-sealing layer even with a small coating amount. Therefore, the dry mass (per side) of the heat-sealing layer can be, for example, 6 g / m 2 or less, 5 g / m 2 or less, 4 g / m 2 or less, 3 g / m 2 or less, etc.

[0034] The thermoplastic resin for forming the heat-sealing layer is not particularly limited, and thermoplastic resins used for heat-sealing applications such as ethylene-vinyl acetate resins, styrene-acrylic ester copolymer resins, acrylic resins, polyethylene, polypropylene, polyester resins such as polyethylene terephthalate, polyvinyl alcohol, polyvinyl acetate, polylactic acid, polyhydroxyalkanoic acid (PHBH), polybutylene succinate, and polyglycolic acid can be used without particular limitation. Among these, ethylene-vinyl acetate resins and acrylic resins are preferable from the viewpoint of heat-sealing strength. Also, biodegradable resins such as polyvinyl alcohol, polylactic acid, polyhydroxyalkanoic acid, polybutylene succinate, and polyglycolic acid are preferable from the viewpoint of reducing the environmental load when they flow out as garbage.

[0035] The heat-sealing 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 (re-dissociability). When the heat-sealing layer is a coating layer, either water-based coating using a solvent such as water or solvent-based coating using a solvent such as an organic solvent may be used, but water-based coating is preferable from the viewpoint of safety and hygiene. When performing water-based 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 with known coating apparatuses and coating systems. For example, coating apparatuses include gravure coaters, flexo coaters, blade coaters, bar coaters, air knife coaters, curtain coaters, spray coaters, roll coaters, reverse roll coaters, size press coaters, gate roll coaters, etc. However, as described later, it is preferable to perform coating with a gravure coater or a flexo coater. When forming the heat-sealing layer by lamination, either extrusion lamination or dry lamination may be used.

[0036] The packaging base material of the present invention is mainly made of natural fibers, and is a packaging base material that is excellent in cushioning properties, further excellent in flexibility, porous, and water-absorbent. Bar coaters and air knife coaters supply excess coating liquid to the substrate with an applicator roll and scrape off the excess coating liquid with a Meyer bar or an air knife. However, when the packaging substrate is porous, not only does the coating liquid penetrate into the substrate when it is supplied to the substrate, resulting in an excessive coating amount, but it may also seep through to the opposite side of the substrate, soiling the process. On the other hand, a gravure coater or a flexo coater measures the specified amount of coating to be applied with the embossing pattern of the gravure roll and directly transfers and applies the coating liquid to the substrate, or first transfers the coating liquid to an application roll and then applies it to the substrate. Therefore, a coating layer can be formed only on the surface of the substrate. For this reason, in a gravure coater or the like, the transferred coating liquid is less likely to penetrate into the substrate even on a substrate with good water absorption and remains on the substrate surface. Therefore, even if the dry mass (per side) of the heat-seal layer is small, it is possible to obtain sufficient heat-seal strength. The embossing pattern of the gravure roll can be appropriately selected for the mesh number and cup depth according to the concentration of the aqueous dispersion or aqueous solution for forming the heat-seal layer and the dry mass of the heat-seal layer.

[0037] When forming the heat-seal layer as a coating layer by aqueous coating, an aqueous dispersion of a thermoplastic resin or an aqueous solution of a thermoplastic resin is used. When the packaging substrate is porous and has good water absorption, the aqueous dispersion or aqueous solution of the thermoplastic resin may penetrate into the substrate, and the thermoplastic resin may not be localized on the substrate surface, resulting in a possible weakening of the heat-seal strength. Also, when trying to achieve sufficient heat-seal strength, it is necessary to increase the dry mass of the heat-seal layer. Therefore, particularly when coating with a gravure coater, a flexo coater, etc., it is preferable to combine so that the contact angle between the packaging base material and the coating liquid is 70° or more and 120° or less. When the contact angle between the packaging base material and the coating liquid is 70° or more and 120° or less, the coating liquid remains appropriately on the packaging base material, and the thermoplastic resin forms a uniform layer on the surface of the packaging base material. Therefore, it is possible to obtain a packaging material with good heat seal strength while suppressing the coating amount of the thermoplastic resin. If this contact angle is less than 70°, the applied thermoplastic resin penetrates into the packaging base material and does not localize on the surface of the packaging base material, so the heat seal strength may become weak. Also, when trying to achieve sufficient heat seal strength, it is necessary to increase the dry mass of the heat seal layer. On the other hand, if this contact angle exceeds 120°, the coating liquid is repelled from the surface of the packaging base material, resulting in unevenness in the heat seal layer, and it may not be possible to obtain a uniform heat seal strength. This contact angle is preferably 80° or more and preferably 110° or less. Also, when coating with a gravure coater, a flexo coater, etc., 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 base material 「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 to a Fourdrinier paper machine in an unbeaten state and paper was made at a predetermined basis weight so that the CD / MD ratio of the tensile strength was about 80 to 110%, and it was dried with a Yankee dryer to obtain a packaging base material. 「Example 4」 Paper was made with a Fourdrinier paper machine in the same manner as in Example 1, except that a mixed pulp (CSF 650 ml) in which the disintegrated abaca pulp (CSF 730 ml) and a pulp obtained by beating commercially available NBKP to CSF 500 ml were mixed at a mass ratio of 50:50 was used, and a packaging base material was obtained.

[0039] 「Comparative Example 1」 The commercially available NBKP was beaten to a freeness of 650 ml CSF, formed into a sheet of a predetermined basis weight on a Fourdrinier paper machine, dried with a multi-cylinder dryer, and a base material for packaging was obtained. "Comparative Example 2" A pulp obtained by mixing commercially available NBKP and LBKP at a mass ratio of 10:90 was beaten to a freeness of 650 ml CSF, formed into a sheet of a predetermined basis weight on a Fourdrinier paper machine, and dried with a Yankee dryer to obtain a base material for packaging.

[0040] Evaluation Items and Evaluation Methods The following evaluations were performed on the obtained base material for packaging. 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 FS5 manufactured by Valmet Corporation. (Basis weight, thickness, density) Basis weight: Measured in accordance with JIS P8124. Thickness: Measured in accordance with JIS P8118. Density: Calculated from the basis weight and thickness.

[0041] (Compressive strength) As a measuring instrument, using a KES-G5 compression tester manufactured by Kato Tech Co., Ltd., with the support in a single sheet state, the area of the pressure plate was 2.0 cm 2 , the compression deformation speed (pressure plate descent speed) was 0.02 mm / sec (0.002 cm / sec), and the measurement was carried out under the measurement conditions of a maximum compression load of 300 gf / cm 2 . The graph shown in Figure 1 was prepared. In Figure 1, the y-axis direction (vertical axis direction) indicates the pressure P (gf / cm 2 ) on the support, and the x-axis direction (horizontal axis direction) in the figure indicates the thickness T (mm) of a single sheet of the support. In Figure 1, T0 indicates the thickness of a single sheet of the support when the pressure P is 50 gf / cm 2 , and T M indicates the thickness of a single sheet of the support when the pressure P is the maximum compression load of 300 gf / cm 2 . The compressive strength is the pressure P (gf / cm 2 ) on the support from when the pressure plate reaches 50 gf / cm 2 to 300 gf / cm 2)It is a value obtained by dividing the integrated value of the change (the area S of the hatched portion in Fig. 1) by the area of triangle ABC.

[0042] (Flexural strength) Using a KES-FB2-A pure bending tester manufactured by Kato Tech Co., Ltd., for test pieces of 100 mm × 100 mm and a bending speed of 0.5 cm -1 / sec and a maximum curvature of 2.5 cm -1 measurements were taken in the MD and CD directions respectively under these conditions.

[0043] (Tensile strength) In accordance with JAPAN TAPPI No.71, measurements were taken 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) In accordance with JIS P8116:2000, measurements were taken using an Elmendorf tear tester (Kumagai Riki Kogyo Co., Ltd.). The test piece had a length of 63 mm, a cut of 20 mm, and a length to be torn of 43 mm for the measurement.

[0044]

Table 1

[0045] The packaging base materials obtained in Examples 1 to 4 of the present invention had a compressive strength (number of measurement pieces: 1, deformation speed: 0.02 mm / sec, initial compressive load: 50 gf / cm 2 , maximum compressive load: 300 gf / cm 2 ) measured using a KES-G5 compression tester of 1.5 or less and were excellent in cushioning properties. Also, the packaging base materials obtained in Examples 1 to 4 of the present invention had a flexural strength in the MD and CD directions measured with a KES-FB2-A pure bending tester of 0.8 g·cm 2 / cm or less and were excellent in flexibility. The packaging base materials obtained in Comparative Examples 1 and 2 had a compressive strength greater than 1.5 and were inferior in cushioning properties. Also, the packaging base material obtained in Comparative Example 2 had a flexural strength in the MD direction exceeding 0.8 g·cm 2 / cm and was inferior in flexibility. Example 4 was a packaging base material with a lower compression strength and better cushioning properties compared to the comparative examples. In Examples 1 to 3, the compression strength was even lower and the 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 sizing agent (AD1653, manufactured by Seiko PMC Co., Ltd., AKD / solid content 20%) was applied to Packaging Base Material 1 at a coating concentration of 3.5% so that the coating amount was approximately 0.5 g / m in terms of solid content, 2 and dried with an air heater + rotary dryer to produce Packaging Base Material 2.

[0047] (Thermoplastic resin) Thermoplastic resin 1: Chem Pearl S-500 (Mitsui Chemicals, Inc., ethylene acrylic type) Thermoplastic resin 2: Arowbase SE-1015J2 (Unitika Ltd., crosslinked polyolefin type) 100 parts with 2.3 parts of thickener SN thickener 929S (manufactured by San Nopco Ltd., sodium polycarboxylate) added for thickening Thermoplastic resin 3: Arowbase AA-1462 (Unitika Ltd., crosslinked polyolefin type)

[0048] "Examples 5 to 7, Comparative Examples 3 and 4" Using the combinations of the packaging base material, thermoplastic resin, and gravure plate described in Table 2, a coating liquid (aqueous dispersion of thermoplastic resin) was applied to the packaging base material by the gravure method and dried to obtain a packaging material. The viscosity of the coating liquid was measured using a B-type viscometer with a No. 2 rotor at 60 rpm.

[0049] The packaging base material and the packaging material were evaluated. The results are shown in Table 2. (Pen writing size degree) The heat-sealing agent-coated surface of the packaging base material was measured in accordance with JAPAN TAPPI Paper Pulp Test Method No. 12. (Contact angle) The dynamic contact angle meter FIBRO 100 DAT MKII was used. The coating liquid was dropped onto the base material for packaging at a drop size of 12 μL, and the contact angle 0.1 second after the drop was measured as the measured value. The measurement was repeated three times and the average value was obtained. (Test environment: 23°C) (Heat seal strength) The sealant-coated surfaces of the base material for packaging were brought together, heat-sealed at a temperature of 130°C, a pressure of 1.0 kgf / cm 2 , and for 1 second, and then peeled in a T-shape using a universal tensile testing machine (manufactured by Intesco Co., Ltd., model IM20-ST) with a test width of 15 mm and a tensile speed of 30 mm / min.

[0050]

Table 2

[0051] In Comparative Example 3 where the contact angle between the base material for packaging and the coating liquid was less than 70°, coating was possible, but most of the coating liquid penetrated into the base material for packaging, and a sufficient heat-seal layer could not be formed on its surface, so heat-sealing could not be performed. In Comparative Example 4 where the mesh of the gravure plate was coarser than that of Comparative Example 3, the coating liquid penetrated through the base material for packaging and soiled the impression roll, and continuous coating could not be performed. Also, although the coating amount increased compared to Comparative Example 3, most of the coating liquid penetrated into the base material for packaging as in Comparative Example 3, and a sufficient heat-seal layer could not be formed on its surface, so heat-sealing could not be performed. The packaging materials obtained in Examples 5 to 7 where the contact angle between the base material for packaging 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 and a gravure plate with a coarser mesh, but because the sizing property of the base material for packaging was high and the penetration of the coating liquid could be suppressed, heat-sealing was possible.

Claims

Claim 1 A base material for packaging containing natural fibers, Grammage: 18 g / m² ２ 50 g / m² or more ２ and below Compressive strength measured using a KES-G5 compression tester (number of specimens measured: 1, deformation rate: 0.02 mm / sec, initial compressive load: 50 gf / cm ２ , maximum compressive load: 300 gf / cm ２ ) is 1.5 or less, and a base material for packaging characterized by this. Claim 2 The bending strength in the MD and CD directions measured with a KES-FB2-A pure bending tester is both 0.8 g·cm ２ / cm or less, and the packaging base material according to claim 1, characterized in that Claim 3 The density of the base material for packaging is 0.2 g / cm ３ or more and 0.5 g / cm ３ or less, and the base material for packaging according to claim 1, characterized in that. Claim 4 wherein the natural fibers contain pulp, The base material for packaging according to claim 1, characterized in that it contains 50% by mass or more of non-wood pulp having an average fiber length of 2.5 mm or more, an average fiber diameter of 15 μm or more and 25 μm or less, and a Canadian standard drainage degree of 650 ml CSF or more with respect to the total amount of pulp. Claim 5 The base material for packaging according to claim 1, characterized in that the base material for packaging contains 50% by mass or more of abaca pulp with respect to all fibers. Claim 6 having a heat-sealing layer on at least one side of the base material for packaging according to any one of claims 1 to 5, Temperature: 130°C, Pressure: 1.0 kgf / cm ２ , heat-sealed at a time of 1 second, and the heat-sealing strength when peeled in a T-shape at a tensile speed of 30 mm / min is 0.5 N / 15 mm or more. A packaging material characterized by this. Claim 7 A method for manufacturing a packaging material, characterized in that a heat-sealing layer is formed by applying a coating liquid containing a thermoplastic resin on the base material for packaging according to any one of claims 1 to 5 by a gravure method or a flexo method. Claim 8 The method for manufacturing a packaging material according to claim 7, characterized in that the contact angle between the base material for packaging and the coating liquid is 70° or more and 120° or less.

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