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

Abstract

To provide a base material for packaging which has an excellent balance between cushioning property and flexibility, a material for packaging using the base material 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, a C / M ratio of tensile strength is 60% or more, MD tear strength is 450 mN or more and CD tear strength is 650 mN or more; a material for packaging which has a heat seal layer on at least one surface of the base material for packaging, and has 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 been mainly used for packaging containers such as food trays and packaging bodies such as bags for pillow packaging. However, in recent years, a trend of plastic reduction has been increasing due to environmental problems such as problems related to plastic waste in the ocean, and it is desired to reduce the usage amount of resin materials in industrial products as much as possible. Under such a trend, for packaging bodies, 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 strength in the flow direction of the paper base material is 500 or more and 1,000 or less times, the folding strength in the width direction is 80 or more and 200 or less times, 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 ethylene (meth) acrylic acid copolymer, and the coating amount of the heat-sealing layer is 1.5 g / m 2 to 10.0 g / m 2 or less. A heat-sealing paper has been proposed 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 discloses a heat-sealing paper comprising 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 is proposed that does not contain high-environmental-impact laminated paper or plastic film and has excellent water resistance and printability on the non-heat-sealing layer side.

[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 is proposed that has excellent drop impact resistance, flexibility, and heat-sealing properties.

[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. A paper for flexible packaging materials is proposed that has a tear strength (in the 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 formed into 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% 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 an excellent balance between cushioning properties and flexibility, a packaging material using the 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 base material containing natural fibers, with a basis weight of 18 g / m 2 or more and 50 g / m 2 or less, and a packaging base material having a C / M ratio of tensile strength of 60% or more, a tear strength of 450 mN or more in the MD direction and 650 mN or more in the CD direction. 2. The packaging base material according to 1., 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. 3. The natural fiber contains pulp, and the packaging base material according to 1. or 2., 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 freeness of 650 ml CSF or more with respect to the total amount of pulp. 4. The packaging base material according to any one of 1. to 3., characterized in that the packaging base material contains 50% by mass or more of abaca pulp with respect to all fibers. 5. A packaging material having a heat seal layer on at least one side of the packaging base material according to any one of 1. to 4., heat-sealed at a temperature of 130 °C, a pressure of 1.0 kgf / cm 2 for 1 second, and having a heat seal strength of 0.5 N / 15 mm or more when peeled in a T-shape at a tensile speed of 30 mm / min. 6. A method for manufacturing a packaging material, characterized in that a heat seal layer is formed by applying a coating liquid containing a thermoplastic resin on the packaging base material according to any one of 1. to 4. by a gravure method or a flexo method. 7. The method for manufacturing a packaging material according to 6., characterized in that 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 both cushioning properties and flexibility. A packaging material with excellent cushioning properties can protect the contents from shaking during transportation or external impacts. A packaging material with excellent flexibility can be used to package according to 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 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 has a basis weight of 18 g / m 2 or more and 50 g / m 2 or less, so that both cushioning properties and flexibility can be achieved at a high level. In the packaging base material of the present invention, when cushioning properties are emphasized, a basis weight of 20 g / m 2 or more is preferable, and 22 g / m 2 or more is more preferable. When flexibility is emphasized, 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 packaging base material of the present invention preferably has a density of 0.2 g / cm 3 or more and 0.5 g / cm 3 or less. If the density is less than 0.2 g / cm 3 , it will be bulky and have excellent cushioning properties, but the flexibility may decrease. If the density is 0.5 g / cm 3If it is too high, it will have excellent flexibility but may become a packaging material with poor cushioning properties. In the packaging base material 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 packaging base material of the present invention contains natural fibers, and for example, paper and wet non-woven fabrics can be preferably used. The packaging base material 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 packaging base material 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, 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 reprecipitated after dissolving cellulose in a solvent such as a copper ammonia solution or a morpholine derivative, and various cellulose derivatives such as acetylated modified cellulose and carboxylated modified cellulose, silk, wool, and animal hairs such as goat hair. 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 since the packaging base material becomes dense and compact, the cushioning property may decrease. 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 property of the base material. When the average fiber width is small, the fiber itself is soft, but the base material becomes compact, resulting in poor cushioning property. When the average fiber width is large, the fiber itself becomes difficult to bend, and thus tends to be inferior in 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., Morfi manufactured by Voith Turbo Co., Ltd., 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 of the Canadian standard freeness, more preferably 670 ml CSF or more, even more preferably 690 ml CSF or more, and most preferably unbeaten. As the beating of the pulp progresses, the density increases and the base material becomes flexible, but the cushioning property tends 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 unbleached.

[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, chemical pulps such as bleached kraft pulp (BKP) using coniferous trees and / or broad-leaved trees as raw materials, unbleached kraft pulp (UKP), semi-bleached kraft pulp (SBKP), sulfite pulp, etc., and mechanical pulps such as stone ground pulp (SGP), pressure stone ground pulp (TGP), chemiground pulp (CGP), groundwood pulp (GP), thermomechanical pulp (TMP), etc., dissolving pulp, mercerized pulp, etc. may be mentioned, and one or more of these can be used. In the present invention, as the non-wood pulp, pulps made from non-wood such as bast fibers like flax (linen), kenaf, jute, paper mulberry, and Mitsumata, hard fibers like bagasse, bamboo, and esparto, seed hair fibers like cotton (linter), and leaf sheath / leaf fibers like Manila hemp (abaca) and sisal can be mentioned, and 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 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 glossy paper. When the base material for packaging is single-sided glossy paper, the heat seal layer may be provided on either the glossy surface or the rough surface. However, when the heat seal layer is provided on the smoother surface (glossy 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 glossy surface, has fewer fibrils compared to the glossy surface, when the heat seal layer is provided on the glossy surface, the fibrils on the glossy 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, flocculants, sulfate bands, bulking agents, dyes, fluorescent brighteners, pH adjusters, defoamers, ultraviolet 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, its type 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, its type 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 properties and flexibility as a packaging material. (Tensile strength) The tensile strength can be adjusted according to the fiber length of the fiber used in the packaging base material and the beating degree, etc. For the packaging base material of the present invention, the C / M ratio (crosswise / longitudinal ratio) of the tensile strength is 60% or more. Paper with a C / M ratio of the tensile strength of 60% or more has a small difference in tear strength and bending strength in all directions and no direction where it is easily torn, so it has excellent cushioning properties and is not easily torn even when an impact or the like is applied. The C / M ratio of the 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 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 (crosswise 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 according to the fiber length, beating degree, etc. of the fibers used in the base material for packaging. For the base material for packaging of the present invention, the tear strength is 450 mN or more in the MD direction and 650 mN or more in the CD direction. By having the tear strength of 450 mN or more in the MD direction and 650 mN or more in the CD direction, it is possible to prevent the package from being damaged when receiving an impact or the like. The tear strength is more preferably 550 mN or more in the MD direction, further preferably 650 mN or more, even more preferably 680 mN or more, more preferably 700 mN or more in the CD direction, further 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.

[0029] Compressive strength The compressive strength is correlated with the density (porosity), thickness, beating degree, thickness, etc. of the natural fibers incorporated in the base material for packaging. In particular, the value of the compressive strength can be adjusted according to the thickness, beating degree, etc. of the natural fibers incorporated in the base material for packaging. The base material for packaging of the present invention has 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 manufactured by Kato Tech Co., Ltd. that is preferably 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 base material for packaging is more preferably 1.45 or less, further 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.

[0030] Bending strength The bending strength is correlated with the basis weight, thickness, thickness of the fibers, etc. of the base material for packaging. In particular, the value of the bending strength can be adjusted according to the thickness of the natural fibers incorporated in the base material for packaging. The base material for packaging of the present invention preferably has a bending strength in both the MD and CD directions, measured with 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 bending strength value, the better the flexibility. In the present invention, the bending strength of the base material for packaging is preferably 0.6 g·cm 2 / cm or less, more preferably 0.4 g·cm 2 / cm or less, even 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.

[0031] (Size property) When forming a heat-sealing layer on the base material for packaging by coating, it preferably has an appropriate size property or water repellency suitable for coating. Specifically, it is preferable that the pen writing size degree described in JAPAN TAPPI No. 12 is 1 or more because it can be suitably coated with a gravure coater, a flexo coater, etc. The pen writing size 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 base material for packaging of the present invention can be made into a heat-sealable packaging material by providing a heat-sealing layer on at least one surface. The packaging material of the present invention has a heat-sealing strength of 0.5 N / 15 mm or more when heat-sealed at a temperature of 130°C, a pressure of 1.0 kgf / cm 2 , for 1 second, and peeled in a T-shape at a tensile speed of 30 mm / min. This heat-sealing 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, 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-sealing layer is provided on at least one surface of the packaging base material, 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. It is preferable that the dry mass (per side) of the heat-sealing layer is less than 1 g / m 2 because the heat-sealing suitability may deteriorate. When the dry mass (per side) of the heat-sealing layer exceeds 20 g / m 2 , the heat-sealing suitability saturates and hardly improves, and 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, and even more preferably 9 g / m 2 or less. In particular, for a packaging base material excellent in sizeability, 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 using 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 using 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 mainly consists of natural fibers, is excellent in cushioning properties and further flexibility, and is a porous and water-absorbent packaging base material. 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 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, gravure coaters or flexo coaters measure the specified amount to be coated with the embossing pattern of the gravure roll and transfer and apply the coating liquid directly to the substrate, or transfer the coating liquid to the coating roll first and then apply it to the substrate. Therefore, a coating layer can be formed limited to the surface of the substrate. For this reason, in the case of a gravure coater or the like, the transferred coating liquid is less likely to penetrate into the substrate even with a substrate having 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 in terms of 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, which may result in weak 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 such 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 with a pulper. The freeness was CSF730 ml. The disintegrated abaca pulp was supplied to a Fourdrinier paper machine in an unbeaten state and paper was made at a predetermined basis weight such 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 (CSF650 ml) obtained by mixing the disintegrated abaca pulp (CSF730 ml) and a pulp obtained by beating commercially available NBKP to CSF500 ml at a mass ratio of 50:50 was used, to obtain a packaging base material.

[0039] 「Comparative Example 1」 Commercially available NBKP was beaten to a freeness of 650 ml CSF, formed into a sheet on a Fourdrinier paper machine at a predetermined basis weight, 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 on a Fourdrinier paper machine at a predetermined basis weight, and dried with a Yankee dryer to obtain a base material for packaging.

[0040] Evaluation Items and Methods The following evaluations were performed on the obtained base material for packaging. The results are shown in Table 1. (Fiber Length, Fiber Width) Using FS5 manufactured by Valmet Corporation, the length-weighted average fiber length and the length-weighted average fiber width were measured. (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 the thickness.

[0041] (Tensile Strength) Measured in accordance with JAPAN TAPPI No.71 under the conditions of a specimen width of 15 mm, a test length of 180 mm, and a tensile speed of 180 mm / min. (Tear Strength) Measured in accordance with JIS P8116:2000 using an Elmendorf tear tester (Kumagai Riki Kogyo Co., Ltd.). The length of the test specimen was 63 mm, the notch was 20 mm, and the length to be torn was 43 mm.

[0042] (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 lowering speed) was 0.02 mm / sec (0.002 cm / sec), and the maximum compression load was 300 gf / cm 2 Measurements were performed under the measurement conditions, and a graph shown in Figure 1 was prepared. In Figure 1, the y-axis direction (vertical axis direction) is the pressure P (gf / cm 2) is shown, and in the figure, the x-axis direction (horizontal axis direction) indicates the thickness T (mm) of a single sheet of the support. In Fig. 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 300 gf / cm, which is the maximum compressive load 2 . The compressive strength is the value obtained by dividing the integral value of the change in the pressure P (gf / cm 2 ) on the support from 50 gf / cm 2 to 300 gf / cm 2 (the area S of the hatched part in Fig. 1) by the area of triangle ABC.

[0043] (Bending strength) Using a KES-FB2-A pure bending tester manufactured by Kato Tech Co., Ltd., measurements were taken for each of the MD and CD directions under the conditions of a test piece of 100 mm × 100 mm, a bending speed of 0.5 cm -1 / sec, and a maximum curvature of 2.5 cm -1 .

[0044]

Table 1

[0045] The packaging base materials 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 the MD and CD directions, and were excellent in cushioning properties and flexibility. The packaging base materials obtained in Comparative Examples 1 and 2 had a tear strength of less than 650 mN in both the MD and CD directions and were inferior in cushioning properties. Also, the packaging base material obtained in Comparative Example 2 had a bending 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 compressive strength and excellent cushioning properties compared to the comparative examples. In Examples 1 to 3, the compressive strength was even lower and the cushioning properties were significantly improved.

[0046] Test 2: Packaging material (Packaging base material) The base material for packaging 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 would be approximately 0.5 g / m 2 in terms of solid content, and it was dried using 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), with 2.3 parts of thickener SN thickener 929S (manufactured by San Nopco Ltd., sodium polycarboxylate) added to 100 parts and thickened 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 base material for packaging, thermoplastic resin, and gravure plate described in Table 2, a coating liquid (aqueous dispersion of thermoplastic resin) was applied to the base material for packaging 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 base material for packaging 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 base material for packaging 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 base material for packaging at a drop size of 12 μL, and the contact angle 0.1 second after the drop was taken as the measured value, and it was measured 3 times and the average value was obtained. (Test environment: 23°C) (Heat-sealing strength) The sealing agent-coated surfaces of the base materials 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-sealing 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-sealing 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-sealing 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

1. A packaging base material containing natural fibers, Grammage 18 g / m² ２ 50 g / m² or more ２ and below The packaging base material has a C / M ratio of tensile strength of 60% or more, a tear strength of 450 mN or more in the MD direction and 650 mN or more in the CD direction.

2. 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.

3. The natural fibers include pulp, The packaging base material 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 freeness of 650 ml CSF or more, based on the total amount of pulp.

4. The packaging base material according to claim 1, characterized in that the packaging base material contains 50% by mass or more of abaca pulp based on all fibers.

5. The packaging base material according to any one of claims 1 to 4 has a heat-sealing layer on at least one side, At a temperature of 130°C, a pressure of 1.0 kgf / cm ２ , heat-sealed for 1 second, and when peeled in a T-shape at a tensile speed of 30 mm / min, the heat-sealing strength is 0.5 N / 15 mm or more. A packaging material characterized by this.

6. 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 to the packaging base material according to any one of claims 1 to 4 by a gravure method or a flexo method.

7. The method for manufacturing a packaging material according to claim 6, characterized in that the contact angle between the packaging base material and the coating liquid is 70° or more and 120° or less.

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