Paper for flexible packaging materials, and flexible packages

Abstract

To provide a soft packaging sheet that can be made into bags with a bag-making machine, and a soft package using the soft packaging sheet.SOLUTION: A soft packaging sheet includes a paper substrate and a heat seal layer on at least one outermost surface. The paper substrate has a thickness of 25 μm or more and 100 μm or less, and a Young's modulus in the MD direction of 3 GPa or more and 15 GPa or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to paper for flexible packaging materials and flexible packages using the same.

Background Art

[0002] In recent years, there has been an increasing trend towards de-oiling and de-plasticizing, triggered by environmental problems such as plastic waste and global warming, and it is desired to minimize the use of resin materials derived from fossil resources and non-biodegradable resin materials in industrial products. Under such a trend, it is also desired to reduce the environmental impact of packages. For example, methods such as reducing the thickness of packaging materials using plastic films are conceivable. However, such thin packaging materials have reduced handleability in the process of forming packages, etc., and are likely to cause defects and tears at the heat-sealed parts. In addition, although the amount of resin used is reduced, the problem that it remains semi-permanently without being decomposed when it flows out into the environment remains.

[0003] Patent Documents 1 and 2 propose using heat-sealing paper in which a heat-sealing layer is laminated on a paper substrate as a packaging material. Since these are decomposed in the environment depending on the type of heat-sealing resin, the environmental impact can be significantly reduced. However, since the physical properties of heat-sealing paper are significantly different from those of plastic films, when passing heat-sealing paper through a bag-making machine under the same operating conditions as plastic films, problems such as the paper meandering, breaking, the resulting flexible package having folds and wrinkles, and being unable to make a bag in the desired shape may occur, and it was necessary to optimize operating conditions such as slowing down the line speed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a paper for a flexible packaging material that can be formed into a bag by a bag-making machine, and a flexible package using this paper for a flexible packaging material.

Means for Solving the Problems

[0006] Means for solving the problems of the present invention are as follows. 1. A paper for a flexible packaging material, having a paper base material and a heat-sealing layer on at least one outermost surface, wherein the paper base material has a thickness of 25 μm or more and 100 μm or less, and a Young's modulus in the MD direction of 3 GPa or more and 15 GPa or less. 2. The paper for a flexible packaging material according to 1., wherein the basis weight of the paper base material is 20 g / m 2 or more and 70 g / m 2 or less. 3. The paper for a flexible packaging material according to 1. or 2., wherein the density of the paper base material is 0.5 g / cm 3 or more and 0.95 g / cm 3 or less. 4. A flexible package, wherein the object to be packaged is enclosed in a packaging material made of the paper for a flexible packaging material according to any one of 1. to 3.

Effects of the Invention

[0007] The paper for a flexible packaging material of the present invention can be used as an alternative to a packaging material made of a conventional resin film. The paper for a flexible packaging material of the present invention can be passed through a bag-making machine under the same operating conditions as a conventional plastic film to produce a flexible package. Since it is not necessary to change the operating conditions, it is easy to switch between a resin film and the paper for a flexible packaging material of the present invention to produce flexible packages made of different materials. Since the paper for a flexible packaging material of the present invention is mainly made of paper, the amount of resin material used can be significantly reduced.

Embodiments for Carrying Out the Invention

[0008] "Paper for flexible packaging materials" The paper for flexible packaging materials has a paper substrate and a heat-sealing layer on at least one of its outermost surfaces.

[0009] · Paper substrate The paper substrate is a substrate on which a heat-sealing layer is formed on at least one of its surfaces. The paper substrate is mainly a sheet made of pulp, and the base paper obtained by papermaking a papermaking stock containing pulp, fillers, various auxiliaries, etc. can be used as it is, or on at least one surface of the base paper, a functional layer such as a blocking layer, an ink-receiving layer, a water-resistant layer, an oil-resistant layer, a water vapor barrier layer, a gas barrier layer, etc. can be used. One or two or more layers can be formed. The paper substrate used in the present invention has a thickness of 25 μm or more and 100 μm or less. The thickness of the paper substrate is measured in accordance with JIS P8118:2014. When the thickness of the paper substrate is 25 μm or more and 100 μm or less, it is easy to pass through a bag-making machine using a conventional plastic film. The thickness of the paper substrate is preferably 30 μm or more, more preferably 35 μm or more, further preferably 40 μm or more, and preferably 90 μm or less, more preferably 80 μm or less, and further preferably 70 μm or less.

[0010] The paper base material of the present invention has a Young's modulus in the MD direction of 3 GPa or more and 15 GPa or less. If this Young's modulus is less than 3 GPa, the paper base material is likely to deform, and due to the tension during manufacturing, the paper base material will be bagged in a stretched state. Therefore, after bagging, it is likely to shrink and cause a deviation in the longitudinal dimension, and wrinkles are also likely to occur. On the other hand, if this Young's modulus exceeds 15 GPa, since the tension cannot be increased during manufacturing, conveyance failures are likely to occur where the paper for flexible packaging materials cannot be conveyed as intended, and deviations in cutting intervals are likely to occur. This Young's modulus is preferably 4 GPa or more, more preferably 5 GPa or more, and preferably 12 GPa or less, more preferably 10 GPa or less. The Young's modulus in the MD direction of the paper base material is measured in accordance with JIS P8113:2006, Part 2, constant speed elongation method.

[0011] The paper base material of the present invention has a basis weight of 20 g / m 2 or more and 70 g / m 2 or less, which is preferable from the viewpoints of flexibility and strength. The basis weight of the paper base material is more preferably 24 g / m 2 or more, even more preferably 28 g / m 2 or more, and more preferably 65 g / m 2 or less, even more preferably 60 g / m 2 or less, and even more preferably 55 g / m 2 or less. The basis weight of the paper base material is measured in accordance with JIS P8124:2011.

[0012] The paper base material of the present invention has a density of 0.5 g / cm 3 or more and 0.95 g / cm 3 or less, which is preferable from the viewpoints of flexibility and strength. The density of the paper base material is more preferably 0.55 g / cm 3 or more, and more preferably 0.9 g / cm 3 or less, even more preferably 0.85 g / cm 3 or less, and even more preferably 0.75 g / cm 3 or less. The thickness of the paper base material is calculated from the density and the basis weight.

[0013] The paper base material of the present invention preferably has a puncture strength of 1.0 N or more. When the puncture strength of the paper base material is 1.0 N or more, it is possible to make the flexible package difficult to break when a protrusion or the like comes into contact. This puncture strength of the paper base material is more preferably 1.1 N or more, and even more preferably 1.2 N or more. The puncture strength of the paper base material is measured in accordance with the 7.5 Puncture Strength Test of JIS Z1707:2019.

[0014] The paper base material of the present invention preferably has a bending rigidity B in the MD direction by the KES method of 0.10 g·cm 2 / cm or more and 1.8 g·cm 2 / cm or less. Also, the bending hysteresis 2HB in the MD direction by the KES method is preferably 0.01 g·cm / cm or more and 1.2 g·cm / cm or less. Incidentally, the KES method is an abbreviation of Kawabata Evaluation System, and is one of the methods for measuring the physical properties of flexible materials such as non-woven fabrics and fabrics. The bending rigidity B and the bending hysteresis 2HB by the KES method can be measured, for example, by an automated pure bending tester KES-FB2-S manufactured by Kato Tech Co., Ltd.

[0015] The smaller the value of the bending rigidity B, the softer it indicates. If this bending rigidity B is less than 0.10 g·cm 2 / cm, the paper for the flexible packaging material is too soft, and when made into a flexible package, the tension is lost, and it may be difficult to maintain a predetermined packaging form. On the other hand, if this bending rigidity B exceeds 1.8 g·cm 2 / cm, it becomes difficult to bend during bag making, and in particular, the lateral dimension may deviate from the designed dimension. This bending rigidity B is more preferably 0.2 g·cm 2 / cm or more, even more preferably 0.3 g·cm 2 / cm or more, even more preferably 0.4 g·cm 2 / cm or more, and more preferably 1.7 g·cm 2 / cm or less, and more preferably 1.5 g·cm 2More preferably, it is 1.2 g·cm / cm or less, and even more preferably, it is 2 1.0 g·cm / cm or less, and even more preferably, it is 2 0.8 g·cm / cm or less, and even more preferably, it is 2 0.8 g·cm / cm or less.

[0016] Hysteresis 2HB indicates that the smaller the value, the easier it is to return to the original state after bending. When this hysteresis 2HB is less than 0.01 g·cm / cm, bending, ruling, folding, etc. become difficult, and a force to return to the original shape (flat or roll shape) occurs after bag making, so warping or rounding may occur in the flexible package, and the cosmetic appearance and shape retention may deteriorate. On the other hand, when this hysteresis 2HB exceeds 1.2 g·cm / cm, it becomes difficult to return to the original state after bending. In particular, wrinkles are likely to occur in the part where a load occurs during bending or folding in contact with the former of the bag making machine, and it may also be easily torn. This hysteresis 2HB is more preferably 0.02 g·cm / cm or more, further preferably 0.025 g·cm / cm or more, even more preferably 0.035 g·cm / cm or more, even more preferably 0.055 g·cm / cm or more, and more preferably 1.1 g·cm / cm or less, further preferably 1.05 g·cm / cm or less, even more preferably 1.0 g·cm / cm or less, even more preferably 0.9 g·cm / cm or less, even more preferably 0.8 g·cm / cm or less, and even more preferably 0.7 g·cm / cm or less.

[0017] In the present invention, when the paper base material is exposed on one side of the flexible packaging paper, the smoothness (Kingsbury method) of the exposed surface (front surface) of the paper base material is preferably 50 seconds or more and 700 seconds or less. The flexible packaging paper of the present invention is wound in a roll form, fed out from the roll, passed through a bag-making machine, and processed into a flexible package. At this time, if the smoothness (Kingsbury method) of the exposed surface of the paper base material is 50 seconds or more and 700 seconds or less, the friction and slipperiness between the paper base material and the bag-making machine will be good, and production defects can be reduced. If the smoothness (Kingsbury method) is less than 50 seconds, the friction is large, and a large burden is applied to the flexible packaging paper during paper feeding, and the paper base material may be torn. On the other hand, if the smoothness (Kingsbury method) exceeds 700 seconds, the friction is small and the flexible packaging paper is likely to slip, so the flexible packaging paper is likely to meander when passing through the bag-making machine, and misalignment may occur in the heat-sealing part or the cutting part. The smoothness (Kingsbury method) of the exposed surface of the paper base material is more preferably 70 seconds or more, further preferably 100 seconds or more, more preferably 650 seconds or less, further preferably 600 seconds or less, even more preferably 500 seconds or less, and even more preferably 450 seconds or less. In addition, since a heat-sealing layer or the like is laminated on the other side (back surface) of the paper base material, the value of the smoothness (Kingsbury method) is not particularly limited. However, in order to improve the adhesion with the layer laminated on the other side, the smoothness (Kingsbury method) of the other side of the paper base material is preferably smaller (rougher surface) than the smoothness (Kingsbury method) of the exposed surface of the paper base material. Specifically, it is preferable that the value of the smoothness (Kingsbury method) is 30 seconds or more smaller.

[0018] As the pulp, chemical pulps such as hardwood bleached kraft pulp (LBKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), softwood unbleached pulp (NUKP), sulfite pulp, mechanical pulps such as stone ground pulp, thermomechanical pulp, deinked pulp, wood fibers such as wastepaper pulp, and non-wood fibers obtained from kenaf, bamboo, hemp, etc. can be used, and two or more of them can be mixed and used. Among these, for reasons such as being less likely to have foreign matter mixed in, being less likely to have discoloration over time when used as a wastepaper raw material for recycling after use, and having a good surface feel during printing due to having a high whiteness, it is preferable to use chemical pulps and mechanical pulps of wood fibers, and it is more preferable to use chemical pulps. Specifically, it is preferable that the blending amount of chemical pulps such as LBKP and NBKP is 80% by weight or more, and it is more preferable that the blending amount of chemical pulp is 100% by weight. Also, the blending ratio of hardwood pulp in the pulp is preferably 30% by weight or more, and more preferably 50% by weight or more. From the viewpoint of the strength of the paper base material, etc., the drainage degree of the pulp (Canadian standard drainage degree: CSF) is preferably 600 ml or less, more preferably 550 ml or less, and even more preferably 500 ml or less.

[0019] As the filler, fillers known for papermaking such as inorganic fillers such as talc, kaolin, calcined kaolin, clay, heavy calcium carbonate, light calcium carbonate, white carbon, zeolite, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, barium sulfate, calcium sulfate, and organic fillers such as urea-formalin resin, polystyrene resin, phenolic resin, and micro hollow particles can be used. Note that the filler is not an essential material and may not be used.

[0020] Examples of various auxiliaries include sizing agents such as rosin, alkyl ketene dimer (AKD), and alkenyl succinic anhydride (ASA), 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, retention aids, drainage improvers, coagulants, sulfate bands, bulking agents, dyes, fluorescent brighteners, pH adjusters, defoamers, ultraviolet light inhibitors, anti-fading agents, pitch control agents, slime control agents, etc. These can be appropriately selected and used as necessary.

[0021] The method for manufacturing (papermaking) the base paper is not particularly limited, and known manufacturing (papermaking) methods and papermaking machines such as fourdrinier machines, cylinder machines, twin-wire machines such as gap former type and hybrid former type (ontopper former type), etc. can be selected. Also, the pH during papermaking can be in any of the acidic region (acidic papermaking), pseudo-neutral region (pseudo-neutral papermaking), neutral region (neutral papermaking), or alkaline region (alkaline papermaking). After papermaking in the acidic region, an alkaline agent can be coated on the surface of the paper layer. Further, the base paper may be a single layer or may be composed of multiple layers of two or more layers.

[0022] Furthermore, it is possible to treat the surface of the base paper with various chemicals. Examples of the chemicals used include oxidized starch, hydroxyethyl etherified starch, enzyme-modified starch, polyacrylamide, polyvinyl alcohol, surface sizing agents, water resistance agents, water retention agents, thickening agents, lubricants, etc. These can be used alone or in combination of two or more. Further, these various chemicals and pigments may be used in combination. As pigments, inorganic pigments such as kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicate, colloidal silica, satin white, etc. and organic pigments such as solid type, hollow type, or core-shell type can be used alone or in combination of two or more. The method for surface treatment of the base paper is not particularly limited, and known coating devices such as rod metering size press, pond size press, gate roll coater, spray coater, blade coater, curtain coater, etc. can be used.

[0023] Furthermore, one or more functional layers such as a blocking layer, an ink receiving layer, a water-resistant layer, an oil-resistant layer, a water vapor barrier layer, a gas barrier layer, etc. can be formed on at least one surface of the base paper. The functional layer may be either a coating layer or a laminate layer, but a coating layer is preferable in terms of maintaining the flexibility of the paper substrate.

[0024] · Heat seal layer The heat seal layer is a layer that imparts heat sealability, specifically, a layer that can adhere to an adhesion target by heating and pressurizing. The paper for flexible packaging material of the present invention has heat sealability, which facilitates forming into a flexible packaging material, maintaining the shape, and ensuring the sealing property.

[0025] The heat seal layer is provided on at least one outermost surface of the paper for flexible packaging material. The heat seal layer may be either a coating layer or a laminate layer. The thermoplastic resin contained in 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, ethylene-acrylic resins, polyolefin resins (such as polyethylene and polypropylene), polyester resins (such as polyethylene terephthalate, polyethylene succinate, polybutylene terephthalate, and polyethylene naphthalate), polyvinyl alcohol resins, polyvinyl acetate resins, and polylactic acid resins can be used without particular limitation. Among these, ethylene-vinyl acetate resins, styrene-acrylic ester copolymer resins, acrylic resins, and ethylene-acrylic resins are preferable in terms of heat-sealing strength. Also, biodegradable resins such as polyvinyl alcohol, polylactic acid, and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) are preferable from the viewpoint of reducing the environmental load when they flow out as garbage. The heat-sealing layer can contain additives such as antiblocking agents and silane coupling agents. As the antiblocking agent, pigments, waxes, metal soaps, etc. can be used without particular limitation. However, in the paper for flexible packaging materials of the present invention, from the viewpoint of cost, it is preferable that the heat-sealing layer does not contain additives.

[0026] When the heat-sealing layer is a coating layer, the dry weight of the heat-sealing layer is preferably 3 g / m 2 or more and 20 g / m 2 or less per side. If the dry weight is less than 3 g / m 2 , the heat-sealing suitability may decrease. Also, even if the dry weight exceeds 20 g / m 2 , the heat-sealing suitability hardly improves, and the cost increases. The heat-sealing layer may be a single layer or may be composed of two or more layers. By forming the heat-sealing layer into two or more layers, defects such as coating unevenness can be reduced compared to the case of a single layer. When the heat-sealing layer is composed of two or more layers, it is preferable that the total dry weight of all the heat-sealing layers is within the above range, and also, the coating amount of the dry weight is 2 g / m 2It is preferably as described above. When the heat seal layer is a laminate layer, the thickness of the heat seal layer is preferably 20 μm or more and 100 μm or less. If the thickness is less than 20 μm, heat sealability may not be ensured. Also, if the thickness exceeds 100 μm, it is not preferable from the viewpoint of cost.

[0027] When the heat seal layer is a coating layer, the coating method is not particularly limited, and it can be coated with a known coating apparatus and coating system. For example, as the coating apparatus, a blade coater, a bar coater, an air knife coater, a curtain coater, a spray coater, a roll coater, a reverse roll coater, a size press coater, a gate roll coater, etc. can be mentioned. As the coating system, either an aqueous coating using a solvent such as water or a solvent-based coating using a solvent such as an organic solvent may be used, but aqueous coating is preferable from the viewpoint of safety and hygiene. When performing aqueous coating, since a water-dispersible resin or a water-soluble resin is used as the thermoplastic resin, the heat seal layer is preferably a coating layer of a water-dispersible resin or a water-soluble resin. When the heat seal layer is a laminate layer, the forming method thereof is not particularly limited, and for example, it can be laminated by appropriately using various methods such as an extrusion lamination method, a wet lamination method, and a dry lamination method.

[0028] "Flexible package" The flexible package of the present invention contains an object to be packaged in a packaging material made of the above-described paper for a flexible packaging material of the present invention. The shape of the flexible package is not particularly limited, and it can be a vertical pillow packaging bag, a horizontal pillow packaging bag, a side seal bag, a two-side seal bag, a three-side seal bag, a gusset bag, a bottom gusset bag, a stand bag, etc. Since the packaging material of the flexible package of the present invention is mainly made of paper, it is easier to tear compared to those using a conventional resin packaging material and can be easily torn from anywhere. In addition, the flexible packaging paper of the present invention can be used in place of conventional plastic films in packaging machines that use such films with almost no change in manufacturing conditions. The flexible packaging material of the present invention can be manufactured using conventional manufacturing machines as is, so no new equipment is required. EXAMPLES

[0029] "Example 1" As pulp raw materials, 80 parts by weight of hardwood bleached kraft pulp (LBKP, CSF: 500 ml) and 20 parts by weight of softwood bleached kraft pulp (NBKP, CSF 530 ml) were used. A stock was prepared by mixing 0.1 parts by weight (relative to the dry weight of the pulp) of polyacrylamide (PAM) with a molecular weight of 2.5 million as a dry strength agent, 0.35 parts by weight of alkyl ketene dimer (AKD) as a sizing agent, 0.15 parts by weight of polyamide epichlorohydrin (PAEH) resin as a wet strength agent, and 0.08 parts by weight of polyacrylamide (PAM) with a molecular weight of 10 million as a retention agent, with 10 parts by weight of the mixed pulp. A wet paper was made from this stock using a papermaking machine, and the wet paper was dried using a Yankee dryer to obtain a paper base material (base paper). The smoothness (Oken method) of the obtained paper base material was 83 seconds on the surface and 10 seconds on the back. A heat seal layer made of low density polyethylene having a thickness of 25 μm was provided on this paper base material by extrusion lamination to obtain a flexible packaging paper.

[0030] "Example 2" As pulp raw materials, 50 parts by weight of softwood bleached kraft pulp (NBKP, CSF: 460 ml) and 50 parts by weight of hardwood bleached kraft pulp (LBKP, CSF: 300 ml) were used. A stock was prepared by mixing 100 parts by weight of this mixed pulp with 0.9 parts by weight (based on the dry weight of the pulp) of polyamine epichlorohydrin resin (WS4010, a wet strength agent made by Seiko PMC) activated with caustic soda, 0.3 parts by weight of polyacrylamide (a dry strength agent), aluminum sulfate, and a sizing agent. A wet paper was made from this stock using a papermaking machine, and the wet paper was dried using a Yankee dryer to obtain a paper base material. The smoothness (Oken method) of the obtained paper base material was 197 seconds on the surface and 9 seconds on the back. A heat seal layer made of low density polyethylene having a thickness of 25 μm was provided on this paper base material by extrusion lamination to obtain a flexible packaging paper.

[0031] "Example 3" The pulp raw material was a mixture of 60 parts by weight of softwood bleached kraft pulp (NBKP, CSF: 40ml) and 40 parts by weight of hardwood bleached kraft pulp (LBKP, CSF: 40ml), and the paper was made on a fourdrinier papermaking machine with a basis weight of 30.0g / m 2 The base paper was made of the above and was then pressed using an on-machine two-roll size press with a modified PVA (RS4104 (Kuraray) content of 1.0 g / m 2 ) and wet strength agent (WS-4020 (Seiko PMC) content 0.05g / m 2 ) and dried with a dryer to obtain a base paper with a moisture content of 8.0%. After that, moisture was added to this base paper to make it a wet paper with a moisture content of 15.0%, and it was treated with a super calendar at a temperature of 130°C and a linear pressure of 250 kg / cm to obtain a paper base material. The smoothness (Oken method) of the obtained paper base material was 1234 seconds on the front side and 1085 seconds on the back side. A heat seal layer made of low density polyethylene having a thickness of 25 μm was provided on this paper base material by extrusion lamination to obtain a flexible packaging paper.

[0032] "Example 4" As pulp raw materials, 50 parts by weight of softwood bleached kraft pulp (NBKP, CSF: 500 ml) and 50 parts by weight of hardwood bleached kraft pulp (LBKP, CSF: 350 ml) were used. To 100 parts by weight of this mixed pulp, 0.9 part by weight (based on the dry weight of the pulp) of a polyamine epichlorohydrin resin (WS4010, a wet paper strength enhancer manufactured by Starlight PMC) activated with caustic soda, 0.3 part by weight of polyacrylamide (a dry paper strength enhancer), aluminum sulfate, and a sizing agent were added to prepare a papermaking stock. Using a paper machine, wet paper was made from this papermaking stock, and the wet paper was dried with a Yankee dryer to obtain a paper substrate. The smoothness (Oken method) of the obtained paper substrate was 299 seconds on the front surface and 10 seconds on the back surface. On this paper substrate, a heat-sealing layer made of low-density polyethylene with a thickness of 25 μm was provided by extrusion lamination to obtain a paper for flexible packaging.

[0033] "Example 5" Sodium polyacrylate was added as a dispersant to engineered kaolin (manufactured by Imerys, Val Surf HX, average particle size 9.0 μm, aspect ratio 80 - 100) (0.2% based on the pigment), and it was dispersed with a Serie mixer to prepare a kaolin slurry with a solid content concentration of 55%. Into the obtained kaolin slurry, 200 parts (solid content) of a styrene-butadiene latex (manufactured by Nippon Zeon Co., Ltd., PNT7868) as a water vapor barrier resin was blended so as to be 200 parts (solid content) with respect to 100 parts (solid content) of the pigment, and a coating liquid for a water vapor barrier layer with a solid content concentration of 50% was obtained. An aqueous solution of polyvinyl alcohol (manufactured by Kuraray Co., Ltd., PVA117) was prepared to have a solid content concentration of 10% to obtain a coating liquid for a gas barrier layer.

[0034] On the back surface of the base paper obtained in Example 1, the coating liquid for the water vapor barrier layer was applied unilaterally using a blade coater so that the coating amount was 12 g / m² in terms of dry weight, dried at 105°C for 2 minutes, and then the coating liquid for the gas barrier layer was applied unilaterally using a roll coater so that the coating amount was 3.0 g / m² in terms of dry weight, and dried at 105°C for 2 minutes to obtain a paper substrate having a functional layer. The smoothness (Oken method) of the obtained paper substrate was 83 seconds on the front surface and 34 seconds on the back surface. 2 2 ​ A 25 μm-thick heat seal layer made of low-density polyethylene was provided by extrusion lamination on the surface of the paper base material on the functional layer side, to obtain a flexible packaging paper.

[0035] "Comparative Example 1" The paper substrate was a commercially available kraft paper (Shin Tokai Paper Co., Ltd.). The smoothness (Oken method) of this paper substrate was 14 seconds on the front side and 4 seconds on the back side. A heat seal layer made of low density polyethylene having a thickness of 25 μm was provided on this paper base material by extrusion lamination to obtain a flexible packaging paper. "Comparative Example 2" The paper substrate was a commercially available glassine paper (Nippon Paper Papylia Co., Ltd.). The smoothness (Oken method) of this paper substrate was 1756 seconds on the front side and 1424 seconds on the back side. A heat seal layer made of low density polyethylene having a thickness of 25 μm was provided on this paper base material by extrusion lamination to obtain a flexible packaging paper.

[0036] The obtained paper base material or flexible packaging paper was evaluated as follows, and the results are shown in Table 1. ·Smoothness (Ouken style) The surface of the paper base opposite to the surface on which the heat seal layer was to be formed (front surface) and the surface on which the heat seal layer was to be formed (back surface) were measured using a digital Oken type air permeability and smoothness tester (manufactured by Asahi Seiko Co., Ltd.) in accordance with JIS P8155. -Puncture strength The paper base side of the flexible packaging paper was measured using an IMADA texture analyzer in accordance with JIS Z1707:2019 7.5 puncture strength test. Young's Modulus Measurement was performed using an L&W tensile tester in accordance with JIS P8113:2006, Part 2, constant rate of extension method. ·B, 2HB by KES method Using the automated pure bending tester KES-FB2-S manufactured by Totec Co., Ltd., the test piece was 100 mm x 100 mm, bending speed was 0.5 cm. -1 / sec, maximum curvature 2.5cm -1 The measurements were performed under the following conditions.

[0037] ·Bag-making property The obtained paper for flexible packaging was cut into a width of 250 mm and wound into a roll. Using a horizontal pillow packaging machine (Omori Machinery Co., Ltd., S-5000X BX) and a product dummy with a width of 75 mm × length of 75 mm × height of 28 mm (weight 45 g), the width between the bag-making devices was set to 80 - 85 mm × height of 35 mm, and 1000 horizontal pillow bags were created under the conditions of a cut pitch of 150 mm and a rotation speed of 60 cpm, and evaluated according to the following criteria. Also, the center seal temperature was 140°C and the top seal temperature was 110°C. In the case where the paper for flexible packaging was broken, the production was stopped at that point.

[0038] ·Breaking OK: The paper for flexible packaging does not break during production. NG: The paper for flexible packaging breaks during production. ·Transportability OK: The paper for flexible packaging can be transported as specified. NG: Deviation occurs in the transport of the paper for flexible packaging. ·Longitudinal dimensional stability (N = 30) 1: All longitudinal dimensions are less than ±3% from the design. 2: All longitudinal dimensions are less than ±5% from the design. 3: One or more longitudinal dimensions deviate from the design by 5% or more.

[0039]

Table 1

[0040] Results The papers for flexible packaging obtained in Examples 1 to 5 could be transported as specified without breaking. Also, the obtained horizontal pillow bags were excellent in longitudinal dimensional stability. On the other hand, the paper for flexible packaging material obtained in Comparative Example 1 was broken during production, so the production of the horizontal pillow bag was discontinued halfway. In addition, when the horizontal pillow bags produced until breakage were inspected, the longitudinal dimension was short and shrank compared to the designed dimension. This is presumably because the Young's modulus of the paper substrate was as small as 2.81 GPa, so it was conveyed in a stretched state in the longitudinal direction by the bag-making machine and shrank when the tension was no longer applied. The paper for flexible packaging material of Comparative Example 2 had good longitudinal dimensional stability although it was cut at 150 mm intervals, but conveyance failure occurred in the bag-making machine, and there were products that were not cut at 150 mm intervals in the longitudinal direction. This is presumably because the Young's modulus of the paper substrate was as large as 15.1 GPa, so the tension could not be applied strongly and conveyance failure occurred.

Claims

1. A paper substrate and a heat seal layer on at least one outermost surface thereof, The paper base material is a flexible packaging paper having a thickness of 30 μm or more and 100 μm or less, a Young's modulus in the MD direction of 5 GPa or more and 12.8 GPa or less, and a bending rigidity B in the MD direction according to the KES method of 0.10 g·cm 2 / cm or more and 0.80 g·cm 2 / cm or less (excluding those containing core-sheath structure fibers).

2. The basis weight of the paper substrate is 20 g / m ２ or more and 70 g / m ２ or less, and the paper for flexible packaging material according to claim 1, characterized in that it is as described above.

3. The density of the paper base material is 0.5 g / cm ３ or more and 0.95 g / cm ３ or less, and the paper for a flexible packaging material according to claim 1, characterized in that it is as described above.

4. The flexible packaging paper as described in claim 1, wherein the paper substrate has a functional layer selected from a sealing layer, an ink-receiving layer, a water-resistant layer, an oil-resistant layer, a water vapor barrier layer, and a gas barrier layer on at least one side of the base paper.

5. The flexible packaging paper according to claim 1, wherein the heat seal layer is a coating layer and has a dry weight of 3 g / m 2 or more and 20 g / m 2 or less per side.

6. The flexible packaging paper according to claim 1, characterized in that the heat seal layer contains a thermoplastic resin selected from ethylene-vinyl acetate resins, styrene-acrylate copolymer resins, acrylic resins, ethylene-acrylic resins, polyolefin resins, polyester resins, polyvinyl alcohol resins, polyvinyl acetate resins, polylactic acid resins, and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

7. A flexible packaging paper as described in claim 1, wherein the hysteresis 2HB of bending in the MD direction as measured by the KES method is 0.01 g·cm / cm or more and 1.2 g·cm / cm or less.

8. A flexible packaging paper as described in claim 1, in which a paper base material is exposed on one side of the flexible packaging paper, and the smoothness (Oken method) of the exposed surface of the paper base material is 50 seconds or more and 700 seconds or less.

9. A flexible packaging body, comprising an article to be packaged, the article being packaged in a packaging material made of the flexible packaging paper according to any one of claims 1 to 8.

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