Coated paper

Abstract

To provide coated paper that is less prone to cracking of the coating layer even when subjected to bending loads during the bag-making process for flexible packaging. [Solution] Basis weight 100g / m 2 A paper substrate less than 100 mm in thickness, and a coating layer containing PHBH and EVA on at least one of its surfaces, The coating amount (dry mass) of the aforementioned coating layer is 5 g / m² per side. 2 That's all. The coating layer contains 5 to 120 parts by mass of EVA per 100 parts by mass of PHBH, The aforementioned EVA is a coated paper having a tensile strength of 5.5 to 25.0 MPa and an elongation of 400 to 850%.

Description

[Technical Field]

[0001] The present invention relates to coated paper having a coating layer containing PHBH. [Background technology]

[0002] In recent years, efforts have begun to prevent environmental damage caused by plastic waste, and there is a growing demand to replace single-use plastic products with materials that have a smaller environmental impact. Examples of alternative materials to plastic include biodegradable plastics, wood, and paper. Aliphatic polyesters such as polylactic acid and polycaprolactone are known as biodegradable plastics. However, aliphatic polyesters have the problem that they take a long time to biodegrade at low temperatures, and their decomposition rate in natural environments such as the ocean is slow.

[0003] Poly(3-hydroxybutyrate) resins are microbially produced thermoplastics with excellent biodegradability under both aerobic and anaerobic conditions, and possess the remarkable property of being rapidly decomposed by microorganisms even in water such as oceans. Furthermore, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (hereinafter also referred to as PHBH), a copolymer of 3-hydroxybutyrate and 3-hydroxyhexanoate, is attracting attention due to its biodegradability and resin properties.

[0004] Patent Document 1 describes a coated paper having a coating layer containing PHBH and an adhesive on at least one surface of a paper substrate, wherein the solid content mass ratio of PHBH to adhesive in the coating layer is 99.9 / 0.1 to 60.0 / 40.0, and which has few coating defects, and which can be used as heat-sealable paper, water-resistant paper, oil-resistant paper, etc.

[0005] Here, a flexible packaging material using heat-sealable paper has been proposed (see Patent Documents 2, 3, etc.). These flexible packaging materials are used as wrapping sheets and pillow packaging materials. When used as wrapping sheets, the flexible packaging material is used to cover a cardboard box with its glossy side (coated side) facing outwards, and is folded along the edges of the cardboard box. In the case of pillow packaging, when forming vertical pillow packaging bags, horizontal pillow packaging bags, etc., from a long sheet, the coated side is facing inwards and the material is folded in the CD direction via folds along the direction of travel (MD direction) to form a cylindrical shape. Thus, flexible packaging materials require at least folding in order to enclose their contents. While evaluating the suitability of heat-sealable paper having a coating layer made of PHBH as a flexible packaging material, the inventors discovered that the coating layer is weak against bending and prone to cracking at the bent portion of the coating layer. When cracks occur at the bent portion of a flexible packaging material, water adhering to the outer surface of the packaging material can reach the interior through the cracks, and microorganisms such as mold and E. coli, as well as fine particles such as PM2.5 adhering to the outer surface of the flexible packaging material, may penetrate the interior through the cracks. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2021 / 256381 [Patent Document 2] Japanese Patent Publication No. 2023-011579 [Patent Document 3] Japanese Patent Publication No. 2023-081594 [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to provide coated paper that is less prone to cracking of the coating layer even when a bending load is applied during the bag-making process for flexible packaging. [Means for solving the problem]

[0008] The means for solving the problems of the present invention are as follows. 1. A paper substrate with a basis weight of less than 100 g / mand having a coating layer containing PHBH and EVA on at least one surface, where the coating amount (dry mass) of the coating layer is 5 g / m or more per side, 2 and the coating layer contains 5 to 120 parts by mass of EVA with respect to 100 parts by mass of the PHBH, and the EVA has a tensile strength of 5.5 to 25.0 MPa and an elongation of 400 to 850%, characterized coating paper. 2. The coating paper according to 1., characterized in that the molar ratio of ethylene to vinyl acetate of the EVA (ethylene:vinyl acetate, total 100) is 5:95 to 35:65. 3. The coating paper according to 1. or 2., characterized in that the glass transition temperature (Tg) of the EVA is -25°C or higher and 10°C or lower. 4. A flexible package having the coating paper according to any one of 1. to 3.

Effects of the Invention

[0009] The coating paper of the present invention is less likely to crack during bag making for a flexible package. Since moisture, microorganisms, etc. are less likely to penetrate from the outside through the cracks in the coating paper of the present invention, it is suitable for flexible packages for packaging sanitary products, foods, supplements, pharmaceuticals, etc. The coating paper of the present invention has a high ratio of biodegradable materials and is rapidly decomposed even if it flows out into the environment.

Modes for Carrying Out the Invention

[0010] The coating paper of the present invention has a paper substrate with a basis weight of less than 100 g / m 2 and has a coating layer containing PHBH and EVA on at least one surface, the coating amount (dry mass) of the coating layer is 5 g / m or more per side, 2 and the coating layer contains 5 to 120 parts by mass of EVA with respect to 100 parts by mass of the PHBH, The EVA has a tensile strength of 5.5 to 25.0 MPa and an elongation at break of 400 to 850%. In this specification, the tensile strength and elongation at break are the values evaluated according to 3.4 and 3.5 of JIS-K-6251:2017, respectively. Also, in this specification, the description of "A to B" (A and B are numerical values or ratios) means a numerical range including A and B.

[0011] The coated paper of the present invention only needs to have a coating layer on one outermost surface, and it can also have coating layers on both outermost surfaces. Further, other layers such as an anchor layer, a water vapor barrier layer, a gas barrier layer, and an ink receiving layer may be provided between the paper base material and the coating layer.

[0012] (Paper base material) The paper base material is a sheet mainly made of pulp, and is obtained by papermaking a pulp slurry containing fillers, various additives, etc. Examples of the pulp include chemical pulps such as hardwood bleached kraft pulp (LBKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), softwood unbleached pulp (NUKP), and sulfite pulp; mechanical pulps such as stone ground pulp and thermomechanical pulp; deinked pulp; wood fibers such as wastepaper pulp; and non-wood fibers obtained from kenaf, bamboo, hemp, etc. One or more of these can be appropriately blended and used. Among these, it is preferable to use chemical pulp of wood fibers or mechanical pulp of wood fibers, and it is more preferable to use chemical pulp of wood fibers, because it is difficult for foreign matter to mix into the paper base material, it is difficult for discoloration over time to occur when recycled as a wastepaper raw material, it has a high whiteness and thus has a good surface feeling during printing, and especially the use value when used as a packaging material is high. Specifically, the blending amount of chemical pulp of wood fibers such as LBKP and NBKP with respect to the total pulp is preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and most preferably 100% by mass.

[0013] As fillers, known 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 dioxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, barium sulfate, calcium sulfate, and other inorganic fillers, as well as organic fillers such as urea-formaldehyde resin, polystyrene resin, phenolic resin, and fine hollow particles can be used. Note that fillers are not essential materials and may not be used.

[0014] Examples of various additives include sizing agents such as rosin, alkyl ketene dimer (AKD), and alkenyl succinic anhydride (ASA); dry strength enhancers such as polyacrylamide polymers, polyvinyl alcohol polymers, cationized starch, various modified starches, urea-formaldehyde resins, and melamine-formaldehyde resins; wet strength enhancers; yield enhancers; water drainage enhancers; coagulants; aluminum sulfate; bulk enhancers; dyes; fluorescent whitening agents; pH adjusters; defoamers; UV inhibitors; fade inhibitors; pitch control agents; and slime control agents. These can be selected and used as needed.

[0015] The paper substrate may have its surface treated with various chemicals. Examples of chemicals include oxidized starch, hydroxyethyl etherified starch, enzyme-modified starch, polyacrylamide, polyvinyl alcohol, surface sizing agents, water-resistant agents, water-retaining agents, thickeners, and lubricants, which can be used individually or in combination of two or more. Furthermore, these various chemicals may be used in combination with pigments. Examples of pigments include 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, silicates, colloidal silica, and satin white, as well as organic pigments such as solid, hollow, or core-shell types, which can be used individually or in combination of two or more.

[0016] In this invention, the basis weight of the paper substrate is 100 g / m². 2is less than. The basis weight of the paper substrate is 100 g / m 2 A paper substrate with a basis weight less than 90 g / m 2 is preferably as follows, 80 g / m 2 is more preferably as follows, 70 g / m 2 is even more preferably as follows, 60 g / m 2 is still more preferably as follows. The lower limit of the basis weight of the paper substrate is not particularly limited, but from the viewpoint of strength, 20 g / m 2 or more is preferable, 25 g / m 2 or more is more preferable, 30 g / m 2 or more is even more preferable. In addition, the density of the paper substrate can be appropriately selected according to various desired qualities, handling properties, etc., but usually it is 0.5 g / cm 3 or more and 1.0 g / cm 3 or less is preferable. In the present invention, the paper substrate may be either a paper consisting of only a single paper layer or a multi-layer paper having two or more paper layers. When the paper substrate is a multi-layer paper, the paper material, basis weight, etc. of each paper layer may be the same or different.

[0017] The method for manufacturing (papermaking) the paper substrate is not particularly limited, and known manufacturing (papermaking) methods and papermaking machines such as a fourdrinier papermaking machine, a cylinder papermaking machine, a twin-wire papermaking machine such as a gap former type, a hybrid former type (ontopper former type), etc. can be selected. Also, the pH during papermaking may be in any of the acidic region (acid papermaking), pseudo-neutral region (pseudo-neutral papermaking), neutral region (neutral papermaking), alkaline region (alkaline papermaking), and an alkaline agent may be applied to the surface of the paper layer after papermaking in the acidic region. In addition, when treating the surface of the paper substrate with a chemical, the surface treatment method is not particularly limited, and known coating devices such as a rod metering size press, a pond size press, a gate roll coater, a spray coater, a blade coater, a curtain coater, etc. can be used.

[0018] (Coating layer) The coating layer is located on at least one of the outermost surfaces of the coated paper, contains at least PHBH and EVA, and has a coating amount (dry mass) of 5 g / m² per side. 2 The above is true, and the mixture contains 5 to 120 parts by mass of EVA per 100 parts by mass of PHBH.

[0019] <phbh> PHBH is a copolymer of 3-hydroxybutyrate (hereinafter also referred to as 3HB) and 3-hydroxyhexanoate (hereinafter also referred to as 3HH), and is a biodegradable resin known to be produced by microorganisms. In the present invention, PHBH may be derived from microorganisms or from petroleum resources, but it is preferable to use PHBH derived from microorganisms from the viewpoint of reducing environmental impact.

[0020] Microorganisms that produce PHBH are not particularly limited to any microorganism that accumulates PHBH within its cells, but examples include bacteria of the genera Alcaligenes (such as A. lipolytica, A. eutrophus, and A. latus), Pseudomonas, Bacillus, Azotobacter, Nocardia, and Aeromonas. In particular, in terms of PHBH productivity, strains such as Aeromonas caviae, and even Alcaligenes eutrophas AC32 (accession number FERM BP-6038, deposit date August 7, 1997, National Institute of Advanced Industrial Science and Technology, Patent Organism Depositary Center, address: 1-1-1 Higashi, Tsukuba, Ibaraki Prefecture, Japan, Central No. 6) (J. Bacteriol., 179, pp. 4821-4830 (1997)) are preferred. Furthermore, a method for obtaining PHBH from Aeromonas caviae, a microorganism of the genus Aeromonas, is disclosed, for example, in Japanese Patent Publication No. 05-093049. These microorganisms are cultured under appropriate conditions to accumulate PHBH within the cells before use. The carbon source and culture conditions used for cultivation can be obtained according to the methods described in Japanese Patent Publication No. 05-093049, Japanese Patent Publication No. 2001-340078, etc., but are not limited thereto.

[0021] The composition ratio (mol%) of PHBH is preferably 3HB:3HH = 97:3 to 75:25, and more preferably 95:5 to 85:15. If the 3HH composition is less than 3 mol%, the properties of PHBH become similar to those of the 3HB homopolymer, resulting in a loss of flexibility and an undesirable tendency for the film deposition temperature to become too high. If the 3HH composition exceeds 25 mol%, the crystallization rate becomes too slow, making it unsuitable for film deposition, and the degree of crystallinity decreases, which tends to make the resin more flexible and reduce its flexural modulus. The composition ratio of PHBH can be measured by NMR analysis of the powder obtained by centrifuging an aqueous dispersion and drying it. Microbially produced PHBH is a random copolymer. Methods to adjust the molar ratio of the copolymer include selecting the microbial cells, selecting the carbon source as the raw material, blending with PHBH of different molar ratios, and blending with 3HB homopolymer.

[0022] The weight-average molecular weight of PHBH is preferably between 50,000 and 1,500,000. When the weight-average molecular weight of PHBH is within this range, film formation at low temperatures is possible when coating with PHBH. A weight-average molecular weight of 100,000 to 500,000 is more preferable, and 150,000 to 450,000 is even more preferable. The weight-average molecular weight of PHBH can be determined by gel permeation chromatography (GPC, such as Showa Denko's "Shodex GPC-101") using a polystyrene gel column (such as Showa Denko's "Shodex K-804") with chloroform as the mobile phase, and the molecular weight converted to polystyrene equivalent. For measurement, a powder obtained by centrifuging and drying an aqueous dispersion containing PHBH is used.

[0023] The average particle size of PHBH is preferably 0.1 to 50 μm. PHBH with an average particle size of less than 0.1 μm is difficult to produce by microorganisms, and even when obtained by chemical synthesis, a process of micronization is required. If the average particle size exceeds 50 μm, uneven coating may occur on the surface when a coating solution containing PHBH is applied. The average particle size of PHBH is more preferably 0.5 to 10 μm. The average particle size of PHBH refers to the particle size corresponding to the 50% accumulation of all particles measured by adjusting an aqueous suspension of PHBH to a predetermined concentration using a general-purpose particle size analyzer such as a Microtrac particle size analyzer (Nikkiso, FRA).

[0024] <eva> The EVA used in this invention has a tensile strength of 5.5 to 25.0 MPa and an elongation of 400 to 850%. The coated paper of this invention has a coating layer that contains 5 to 120 parts by mass of EVA that satisfies specific tensile strength and elongation values ​​per 100 parts by mass of PHBH, and although the mechanism is unknown, it exhibits excellent crack resistance. From the viewpoint of crack resistance, the tensile strength of the EVA is preferably 5.7 to 23.0 MPa, more preferably 5.9 MPa or higher, even more preferably 7 MPa or higher, even more preferably 8 MPa or higher, and most preferably 21.0 MPa or lower. The elongation of the EVA is preferably 410 to 750%, and more preferably 420 to 700%.

[0025] EVA (ethylene vinyl acetate copolymer) is a copolymer in which ethylene and vinyl acetate are monomers, and other monomers may also be used as monomers. However, it is preferable that the EVA of the present invention is not saponified and does not have vinyl alcohol units produced by the saponification of vinyl acetate units. When the EVA has other monomers as monomers, it is preferable that the content of constituent units derived from other monomers relative to the total EVA is 30% by mass or less. This content is not particularly limited as long as it does not impair the effects of the present invention, and can be, for example, 20% by mass or less, 10% by mass or less, 5% by mass or less, 3% by mass or less, 1% by mass or less, etc.

[0026] The molar ratio of ethylene to vinyl acetate in EVA (component units derived from ethylene:component units derived from vinyl acetate, also expressed as ethylene:vinyl acetate, with a total of 100) is preferably 5:95 to 35:65, more preferably 7:93 to 33:67, even more preferably 10:90 to 30:70, and even more preferably 15:85 to 25:75, from the viewpoint of crack resistance. Furthermore, the glass transition temperature (Tg) of EVA is preferably -25°C to 10°C, more preferably -22°C or higher, even more preferably -20°C or higher, even more preferably 5°C or lower, and even more preferably 0°C or lower, from the viewpoint of crack resistance. In this specification, the glass transition temperature refers to the intermediate glass transition temperature measured in accordance with JIS K 7121-1987.

[0027] The coated paper of the present invention has a coating layer containing 5 to 120 parts by mass of EVA per 100 parts by mass of PHBH. The coating layer has excellent crack resistance due to the inclusion of PHBH and EVA in this ratio. The ratio of EVA to 100 parts by mass of PHBH is preferably 7 parts by mass or more, more preferably 10 parts by mass or more, preferably 110 parts by mass or less, and more preferably 105 parts by mass or less.

[0028] The coating layer may contain PHBH and EVA, and may also contain other thermoplastic resins or inorganic pigments. <Other thermoplastic resins> Other thermoplastic resins that have heat-seal properties at the temperature at which PHBH is fused can be used without particular limitation, but biodegradable resins such as aliphatic polyester resins such as polycaprolactone, polybutylene succinate adipate, polybutylene succinate, and polylactic acid, and aliphatic aromatic polyester resins such as polybutylene adipate terephthalate and polybutylene azelate terephthalate are preferred.

[0029] When the coating layer contains other thermoplastic resins, the total ratio of PHBH and EVA to the total thermoplastic resins contained in the coating layer is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and most preferably 100% by mass.

[0030] <Inorganic pigments> As inorganic pigments, those used in coating paper can be used without particular limitations. Examples include kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, bentonite, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin white. One or more of these can be used. Among these, one or more of kaolin, heavy calcium carbonate, light calcium carbonate, mica, talc, and bentonite are preferred.

[0031] From the viewpoint of adhesion to the coating layer, it is preferable that the inorganic pigment has a 50% volume average particle diameter (D50, hereinafter also referred to as "average particle diameter") of 6.0 μm or less, as measured by laser diffraction / scattering. Examples of laser diffraction / scattering measurement devices include Horiba's particle size distribution analyzer "Partica" and Malvern's particle size distribution analyzer "MASTER SIZER S". From the viewpoint of adhesion to the coating layer, the average particle diameter of the inorganic pigment is more preferably 5.0 μm or less, even more preferably 4.0 μm or less, even more preferably 3.0 μm or less, and even more preferably 2.0 μm or less. There is no particular lower limit to the average particle diameter of the inorganic pigment, but from the viewpoint of dispersibility, for example, it is preferably 0.1 μm or more, and more preferably 0.2 μm or more. When two or more inorganic pigments are included, it is preferable that the average particle size of at least one of them is within the numerical range described above, and it is preferable that the proportion of inorganic pigments satisfying this average particle size to the total inorganic pigments is 50% by mass or more, and more preferably 70% by mass or more.

[0032] When the coating layer contains an inorganic pigment, the solid content mass ratio of PHBH to the inorganic pigment (PHBH:inorganic pigment, total 100) is preferably 90:10 to 0.01:99.99. By further incorporating an inorganic pigment into a coating solution containing PHBH and EVA, the adhesion of the resulting coating layer is improved. Although the mechanism is unknown, the inventors speculate that because the inorganic pigment has better thermal conductivity than the organic PHBH and adhesive, the inorganic pigment heats up quickly when heated, and this heat is transferred from the inorganic pigment to the PHBH, causing the PHBH to heat up and melt sufficiently, making it easier to form a film. The solid content mass ratio of PHBH to inorganic pigment (PHBH:inorganic pigment, total 100) is more preferably 70:30 to 1:99, even more preferably 60:40 to 2:98, and even more preferably 50:50 to 3:97, from the viewpoint of adhesion of the coating layer.

[0033] The coating layer may contain PHBH, EVA, other thermoplastic resins and inorganic pigments, as well as other water-soluble resins, water-dispersible resins, and adhesives. Furthermore, it may optionally contain various additives used in coating solutions in the papermaking field, such as dispersants, viscosity modifiers, defoamers, water-resistant agents, pH adjusters, cationic resins, anionic resins, UV absorbers, metal salts, lubricants, coloring dyes, and pigments. Polyvinyl alcohol is an example of an adhesive.

[0034] (Manufacturing method) The coated layer can be manufactured by conventionally known coating methods. For example, coating equipment includes blade coaters, bar coaters, roll coaters, air knife coaters, reverse roll coaters, curtain coaters, spray coaters, size press coaters, and gate roll coaters. Coating systems include water-based coatings using solvents such as water, and solvent-based coatings using solvents such as organic solvents, but water-based coatings are preferred.

[0035] The coating amount (dry mass) of the coating layer is 5 g / m² per side. 2 That's all. This coating amount is 5g / m 2 If the amount is less than 6 g / m², cracks are likely to occur in the coating layer during folding. 2 The above is more preferable: 10 g / m 2 The above is even more preferable. There is no particular upper limit to this coating amount, but for example, 50 g / m 2 The following is preferable: This coating amount is 50 g / m². 2 Beyond a certain point, crack resistance saturates and hardly improves further, while material costs increase and the drying load during coating becomes greater. The coating layer may consist of one or more layers. If there are two or more layers, the total coating amount (dry mass) must be within the range specified above.

[0036] The coated paper of the present invention was measured in accordance with JIS Z1707:2019 7.4 "Heat seal strength test" at a pressurized temperature of 130°C and a pressurized pressure of 0.2 MPa (20.0 N / cm²). 2 ) When a heat-sealed product that has been heat-sealed for a pressurizing time of 1.0 second is peeled off in a T-shape, the heat seal strength is preferably 4.0 N / 15 mm or more, more preferably 5.0 N / 15 mm or more, even more preferably 6.0 N / 15 mm or more, and even more preferably 6.5 N / 15 mm or more.

[0037] ·Soft packaging The coated paper of the present invention has excellent foldability and heat-sealability, and is less prone to cracking when folded during bag making, making it suitable for processing into flexible packaging. The shape of the flexible packaging is not particularly limited and can be vertical pillow bags, horizontal pillow bags, side-seal bags, two-side-seal bags, three-side-seal bags, four-side-seal bags, gusset bags, bottom-gusset bags, stand-up pouches, etc. [Examples]

[0038] The present invention will be specifically described below with reference to examples, but the present invention is of course not limited to these examples. Unless otherwise specified, parts and % in the examples refer to parts by mass and mass%, respectively.

[0039] (Evaluation method) Tape pick The prepared coated paper was subjected to two processes: heating the uncoated paper at 105°C for 1 minute (where the PHBH in the coating layer does not melt) and heating the uncoated paper at 160°C for 1 minute (where the PHBH in the coating layer melts). The uncoated paper was then left to stand on a horizontal platform and subjected to temperature and humidity control (conditions: 23°C, 50% humidity) for at least 24 hours. A 24mm wide cellophane tape (Nichiban Co., Ltd., Cellotape® No. 405) was then applied to the surface of the coating layer of the coated paper. A 130mm wide, 1.8kg rubber roller was then moved back and forth 20 times under its own weight to ensure the cellophane tape adhered tightly to the surface of the coating layer. Immediately afterward, the cellophane tape was quickly peeled off, and the ratio of the area where the coating layer adhered to the cellophane tape and peeled away from the surface of the paper substrate (area of ​​interfacial failure) to the area where the cellophane tape was applied, or the ratio of the area where part of the paper substrate adhered to the cellophane tape along with the coating layer and the paper substrate was damaged (area of ​​internal failure of the paper substrate), was calculated, and the adhesion to the paper substrate was evaluated according to the following criteria. An evaluation of 5 or 4 indicates no practical problems. 5: No peeling 4: Less than 0-10% peeling of the adhesive surface. 3: Less than 10-50% of the adhesive surface is peeled off. 2: Less than 50-90% of the adhesive surface is peeled off. 1: 90-100% of the adhesive surface has peeled off.

[0040] ·Bending resistance The film-forming material was folded in a mountain fold with the paper substrate facing inward and the coating layer facing outward, so that the fold line was in the MD direction. A 400g roller was then used to apply pressure to the fold by moving it back and forth 10 times under its own weight. After that, a 0.05% New Coccine dye solution was applied to the fold, left to stand for 30 seconds, and then wiped off with a JK wiper. The penetration level was evaluated according to the following criteria. An evaluation sample is shown in Table 1. An evaluation of 5 to 3 indicates no practical problems. 5: No seepage 4. Check for penetration into the surface layer of the coating and the base paper layer at less than 5% of the folded area. 3. Check for penetration into the surface layer of the coating and the base paper layer in the folded area, covering 5% to less than 30% of the area. 2. Check for penetration into the surface layer of the coating and the base paper layer in 30% to less than 70% of the folded area. 1: Confirm penetration into the surface layer of the coating and the base paper layer in over 70% of the folded area.

[0041] [Table 1]

[0042] • Heat seal strength The test was conducted in accordance with JIS Z1707:2019 7.4 "Heat seal strength test". Two 100mm square test pieces were cut from the obtained coated paper (film-forming material), and the coated layers were brought into contact with each other. The test was then conducted at a pressurized temperature of 130°C and a pressurized pressure of 0.2 MPa (20.0 N / cm²). 2 After heat-sealing with a pressurization time of 1.0 second, the specimen was left to stand for 24 hours in an environment of 23°C and 50% humidity. Then, a measurement sample was cut from the heat-sealed 100mm square test piece so that the long side was 100mm and the short side was 15mm. Subsequently, the peeled long edge was clamped in the upper and lower fixtures of a vertical tensile testing machine (Tensilon, manufactured by A&D Company, Ltd.), and the sample was peeled from the long edge side at a speed of 200 mm / min (T-type), while measuring the peel strength, i.e., the HS strength (N / 15 mm). Furthermore, the detached surface was visually inspected and evaluated according to the following criteria. Measurements are taken twice, and the average value of the peel strength is shown. If the evaluation results differ based on visual observation, both results are shown. ○: The entire surface of the heat-sealed area is damaged. △: Partial material damage on the heat-sealed surface ×: Delamination occurs between coating layers (no material breakage). -: Without heat sealing

[0043] ·Abrasion resistance Test specimens of uncoated and coated materials (paper pieces cut to 25 mm in the CD direction x 240 mm in the MD direction) were placed on the specimen stand of the JSPS Fastening Tester with the coated surface facing upwards. Sandpaper (cut to 20 mm x 50 mm) was then placed on the friction element opposite the sandpaper, with its uneven surface facing the coated surface of the specimen, and the abrasion resistance was evaluated. The sandpaper used was NCA waterproof paper, DC-1000, grit #1000, manufactured by Nippon Resibon Co., Ltd., and the JSPS Fastening Tester was the AB-301, a JSPS-type friction fastening tester manufactured by Tester Sangyo Co., Ltd. For the abrasion resistance test, the coated surface was abraded once back and forth at a reciprocating speed of 30 cpm and with a friction element load of 200 gf. The degree of abrasion on the coated surface of the specimen was then held up to a fluorescent light on the ceiling, and the resulting scratches were evaluated relatively by sensory perception. In the event of scratches, streaky scratches appeared on the coated surface along the reciprocating direction (MD direction). The ratio of the total area of ​​multiple streaks caused by wear on the coated surface within the test area (a 20mm x 20mm region in the CD and MD directions of the test specimen after testing) was evaluated by visually comparing it horizontally, using the following criteria as a guideline. If the evaluation is ○, there are no practical problems. ○: Minimal scratches (Guideline: Less than 20% wear on the test area) △: Some scratches (guideline: wear of 20% to less than 50% of the test area) ×: Many scratches (Guideline: More than 50% of the test area is worn)

[0044] (material) Paper base material: Nippon Paper Industries, basis weight 56 ​​g / m² 2 The base paper, ED-WA PHBH: Kaneka Corporation, mass-average molecular weight 200,000 EVA1: Sumika Chemtex Co., Ltd., S-400HQ: Tensile strength 12.7 MPa, elongation 550%, Ethylene:Vinyl acetate = 20:80, Tg 0℃, EVA2: Sumika Chemtex Co., Ltd., S-305HQ: Tensile strength 18.0 MPa, elongation 420%, ethylene:vinyl acetate = 10:90, Tg 7℃ EVA3: Sumika Chemtex Co., Ltd., S-408HQE: Tensile strength 5.0 MPa, elongation 650%, ethylene:vinyl acetate = 40:60, Tg -30℃ EVA4: Sumika Chemtex Co., Ltd., S-401HQ: Tensile strength 6.2 MPa, elongation 850%, ethylene:vinyl acetate = 30:70, Tg -18℃ EVA5: Sumika Chemtex Co., Ltd., S-500HQ: Tensile strength 8.0 MPa, elongation 500%, Ethylene:Vinyl acetate = 20:80, Tg -10℃ EVA6: Sumika Chemtex Co., Ltd., S-355HQ: Tensile strength 20.6 MPa, elongation 420%, ethylene:vinyl acetate = 10:90, Tg 10℃ PVA1: Kuraray Co., Ltd., RS2117, degree of saponification 97.5~99.0, viscosity (4%, 20℃) 25.0~30.0 mPa·s PVA2: Nippon Vioval Vinegar Co., Ltd., JF-17, 1700, Saponification degree 98.0~99.0, Viscosity (4%, 20℃) 28.0~32.0 mPa·s

[0045] (Formation of the coating layer) PHBH, EVA, or PVA were mixed and stirred in the parts by mass shown in Table 1 to obtain a coating solution with a solid content concentration of 40% by mass. In Table 1, the numbers in parentheses for EVA represent, from left to right, tensile strength, elongation, molar ratio of ethylene:vinyl acetate, and Tg. The coating liquid was applied to one surface of the paper substrate using the bar-blade method to achieve the dry mass per surface shown in Table 1. After drying at 105°C for 1 minute, it was heat-treated at 140°C for 1 minute to form a coating layer on the outermost surface of one side of the paper substrate. The dry coating amount in Example 2 was 4 g / m². 2 This means that two layers of the coating have been laminated together.

[0046] [Table 1]

[0047] <Bending resistance> Comparative Example 1, coated with PHBH (without EVA), received a flexural resistance rating of "2". On the other hand, in Examples 1, 3-6, and Comparative Example 2, where EVA was added, the flexural resistance rating was significantly improved to "4" or "5" by adding EVA, which has a tensile strength of 5.5-25.0 MPa and an elongation of 400-850%, to the coating solution. Comparative Example 3, coated with EVA alone, received a flexural resistance rating of "1". These results confirm that the combined use of PHBH and EVA is essential for improving flexural resistance, and that EVA has an optimal range for tensile strength and elongation. The optimal mixing ratio of PHBH to EVA in the coating solution (Examples 1, 7-11) and the coating amount (Examples 12, 1, 13, 14) were found to have a wide range of flexibility and improve flexibility. Examples 1 and 2 showed that the effect was observed in both single and double coatings, and the same was true with the addition of an adhesive (PVA).

[0048] <Abrasion resistance> Comparative Example 1, coated with PHBH (without EVA), received abrasion resistance evaluation of "× (no film formation)" and "△ (film formation)". However, by adding EVA with a tensile strength of 8.0 MPa or higher and an elongation of 420% or higher (Examples 1, 3, 5, and 6), improvements were observed, with evaluations of "△ (no film formation)" and "〇 (film formation)" respectively. <Flexibility and abrasion resistance> In Comparative Example 3, where only EVA was applied, the abrasion resistance evaluation was "○ (no film formation)" and "○ (film formation)," but the flexural resistance evaluation was "1." Comparative Example 3 confirmed that it is difficult to achieve both flexural resistance and abrasion resistance with EVA alone. Examples 1, 3, 5, and 6 showed improved flexibility and abrasion resistance compared to Comparative Example 1, demonstrating a balance between flexibility and abrasion resistance. This further confirms that the addition of EVA with a tensile strength of 8.0 MPa or higher and an elongation of 420% or higher is particularly effective.< / eva> < / phbh>

Claims

1. Basis weight 100g / m ２ A paper substrate less than 100 mm thick, and a coating layer containing PHBH and EVA on at least one surface, The coating amount (dry mass) of the aforementioned coating layer is 5 g / m² per side. ２ That's all. The coating layer contains 5 to 120 parts by mass of EVA per 100 parts by mass of PHBH, Coated paper characterized in that the EVA has a tensile strength of 5.5 to 25.0 MPa and an elongation of 400 to 850%.

2. The coated paper according to claim 1, characterized in that the molar ratio of ethylene to vinyl acetate in the EVA (ethylene:vinyl acetate, total 100) is 5:95 to 35:

65.

3. The coated paper according to claim 1, characterized in that the glass transition temperature (Tg) of the EVA is -25°C or higher and 10°C or lower.

4. A flexible packaging body having coated paper according to any one of claims 1 to 3.

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