Heat sealing paper

Abstract

The present invention addresses the problem of providing a heat sealing paper that contains PHBH and has superior coating layer strength. As a solution to the problem, provided is a heat sealing paper which has, on at least one surface of a paper base material, a heat-sealable coating layer containing 7-35 parts by weight of polyvinyl alcohol (PVA) with respect to 100 parts by weight of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), and in which the degree of saponification of the PVA is 70-95 mol%.

Description

heat seal paper

[0001] The present invention relates to heat seal paper.

[0002] In recent years, there has been a growing movement to prevent environmental destruction caused by plastic waste, and there is a demand for replacing disposable plastic products with materials that have a lower environmental impact. Examples of alternative materials to plastic include biodegradable plastics, wood, and paper. Coated paper, which is paper coated with a resin, can exhibit various functions depending on the resin used. However, if the resin used is derived from fossil resources or is non-biodegradable, the environmental impact reduction effect of using paper is diminished. Therefore, there is a demand for coated paper in which a paper substrate is coated with an aqueous dispersion of biodegradable plastic.

[0003] Aliphatic polyesters such as polylactic acid and polycaprolactone are known as biodegradable plastics. However, aliphatic polyesters have the problem of taking a long time to biodegrade at low temperatures and exhibiting a slow decomposition rate in natural environments such as the ocean. On the other hand, poly(3-hydroxybutyrate)-based resins are microbially produced thermoplastics that exhibit excellent aerobic and anaerobic decomposition properties, and have the remarkable ability to be decomposed by microorganisms in a short period of time even in water, such as the ocean. Patent Document 1 describes that a biodegradable polyester aqueous dispersion containing PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)), a copolymer of 3-hydroxybutyrate and 3-hydroxyhexanoate, has excellent film-forming properties and provides a resin coating film that is flexible, stretchy, and resistant to bending when used in paints, adhesives, fiber processing, sheet / film processing, paper processing, and the like.

[0004] WO 2004 / 041936

[0005] An object of the present invention is to provide a heat seal paper containing PHBH and having excellent coating layer strength.

[0006] The means for solving the problems of the present invention are as follows: 1. A heat-sealable paper having a heat-sealable coating layer on at least one side of a paper substrate, the heat-sealable coating layer containing 7 to 35 parts by weight of PVA (polyvinyl alcohol) per 100 parts by weight of PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)), and the saponification degree of the PVA is 70 to 95 mol %. 2. The heat-sealable paper according to 1., wherein the polymerization degree of the PVA is 2000 or less. 3. The coating amount (dry weight) of the heat-sealable coating layer is 1.0 g / m per side. ２ 50.0g / m or more ２ 4. The heat seal paper according to 1. or 2., characterized in that the basis weight of the paper substrate measured in accordance with JIS P 8124 is 20 g / m or less. ２ 600g / m or more ２ 3. The heat seal paper according to any one of 1. to 3., characterized in that:

[0007] The heat-sealable paper of the present invention has excellent coating strength, and the paper substrate and the heat-sealable coating are firmly bonded. The heat-sealable paper of the present invention can be made biodegradable as a whole, so that even if it is released into the environment, it will decompose quickly.

[0008] The heat-sealable paper of the present invention has a heat-sealable coating layer on at least one side of a paper substrate, which contains 7 to 35 parts by weight of PVA (polyvinyl alcohol) per 100 parts by weight of PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)), and is characterized in that the saponification degree of the PVA is 70 to 95 mol%. In this specification, the expression "A to B" (A and B are numerical values) means a numerical range including A and B, i.e., "A to B".

[0009] (Paper base material) The paper base material is a sheet (hereinafter also referred to as "base paper") mainly made of pulp, and is obtained by papermaking from a paper stock further containing fillers, various auxiliaries, etc. Pulp that can be used includes chemical pulps such as hardwood bleached kraft pulp (LBKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), softwood unbleached kraft pulp (NUKP), and sulfite pulp, mechanical pulps such as stone-ground pulp and thermomechanical pulp, wood fibers such as deinked pulp and recycled paper pulp, and non-wood fibers obtained from kenaf, bamboo, hemp, etc., and these can be used in appropriate combinations. Among these, it is preferable to use chemical pulp or mechanical pulp made from wood fibers, and it is more preferable to use chemical pulp made from wood fibers, for reasons such as the fact that foreign matter is less likely to be mixed into the paper base material, that discoloration over time is less likely to occur when recycled and used as a waste paper raw material, that the high whiteness results in a good surface appearance when printed, and that this has high utility value particularly when used as a packaging material. Specifically, it is preferable that the blending amount of chemical pulp such as LBKP or NBKP relative to the total pulp is 80% or more, and it is particularly preferable that the blending amount of chemical pulp is 100%.

[0010] Examples of fillers that can be used include known fillers 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, and calcium sulfate, and organic fillers such as urea-formalin resin, polystyrene resin, phenolic resin, and hollow microparticles. Note that fillers are not essential materials and may not be used.

[0011] Examples of various auxiliaries include sizing agents such as rosin, alkyl ketene dimer (AKD), and alkenyl succinic anhydride (ASA), polyacrylamide polymers, polyvinyl alcohol polymers, cationized starch, various modified starches, dry strength agents such as urea-formalin resin and melamine-formalin resin, wet strength agents, retention aids, drainage improvers, coagulants, aluminum sulfate, bulking agents, dyes, fluorescent whitening agents, pH adjusters, antifoaming agents, ultraviolet inhibitors, anti-fading agents, pitch control agents, and slime control agents, and can be appropriately selected and used as needed.

[0012] The surface of the paper substrate may be treated with various chemicals. Examples of such chemicals include oxidized starch, hydroxyethyl etherified starch, enzyme-modified starch, polyacrylamide, polyvinyl alcohol, surface sizing agents, water-resistant agents, water-retention agents, thickeners, and lubricants. These may be used alone or in combination of two or more. Furthermore, these 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, and core-shell pigments, which may be used alone or in combination of two or more.

[0013] The basis weight of the paper substrate can be selected appropriately depending on the desired quality and its application, but is usually 20 g / m ２ 600g / m or more ２ Preferably, 25 g / m or less ２ 600g / m or more ２ For example, when used for packaging materials such as wrapping paper, paper bags, lids, and liner papers, and for posters to be used outdoors, the basis weight of the paper base material is preferably 30 g / m ２ 150g / m or more ２ When used as a flexible packaging material, the paper substrate preferably has a basis weight of 20 g / m ２ More than 100g / m ２ Preferably, 35 g / m or less ２ 80g / m or more ２The following is more preferable. The soft packaging material is a packaging material having a density of 20 g / m ２ to 100 g / m ２ It is a flexible packaging material made of thin paper of about 150 g / m2. When used for paper cups, paper containers, paper boxes, paper plates, paper trays, etc., the basis weight of the paper base material is 150 g / m2. ２ More than 300g / m ２ The density of the paper substrate can be appropriately selected depending on the desired qualities and handling properties, but is usually 0.5 g / cm ３ 1.0g / cm or more ３ The following are preferred:

[0014] The method for manufacturing (making) the paper substrate is not particularly limited, and known manufacturing (making) methods and paper machines can be selected, such as a Fourdrinier paper machine, a cylinder paper machine, a short wire paper machine, or a twin-wire paper machine such as a gap former or a hybrid former (on-top former). The pH during papermaking may be in the acidic range (acidic papermaking), a pseudo-neutral range (pseudo-neutral papermaking), a neutral range (neutral papermaking), or an alkaline range (alkaline papermaking). After papermaking in the acidic range, an alkaline agent may be applied to the surface of the paper layer. The paper substrate may be composed of a single layer or two or more layers. When treating the surface of the paper substrate with an agent, the surface treatment method is not particularly limited, and known coating devices such as a rod metering size press, a pond-type size press, a gate roll coater, a spray coater, a blade coater, or a curtain coater can be used.

[0015] (Heat-sealable coating layer) A heat-sealable coating layer (hereinafter also referred to as a heat-sealable layer) is a layer having heat-sealability formed by coating. Whether or not a layer is a coating layer can be determined by observing its cross section with an electron microscope or the like. <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 derived from microorganisms or petroleum resources may be used, but the use of PHBH derived from microorganisms is preferred from the viewpoint of reducing the environmental load.

[0016] The microorganism that produces PHBH is not particularly limited as long as it is a microorganism that accumulates PHBH intracellularly, and examples thereof include bacteria of the genus Alcaligenes such as A. lipolytica, A. eutrophus, and A. latus, as well as bacteria of the genus Pseudomonas, Bacillus, Azotobacter, Nocardia, and Aeromonas. Among these, in terms of PHBH productivity, strains such as Aeromonas caviae are particularly preferred, as are strains of Alcaligenes eutrophus AC32 (accession number FERM BP-6038, date of deposit August 7, 1997, National Institute of Advanced Industrial Science and Technology, International Patent Organism Depositary, address: Central 6, 1-1-1 Higashi, Tsukuba, Ibaraki Prefecture, Japan) (J. Bacteriol., 179, pp. 4821-4830 (1997)), into which genes encoding PHA synthases have been introduced. A method for obtaining PHBH from Aeromonas caviae, a microorganism of the genus Aeromonas, is disclosed, for example, in Japanese Patent Application Laid-Open No. 05-093049. These microorganisms are used by culturing them under appropriate conditions to accumulate PHBH within the cells. The carbon source and culture conditions used for the culture can be obtained according to the methods described in Japanese Patent Application Laid-Open Nos. 05-093049 and 2001-340078, but are not limited thereto.

[0017] The PHBH composition ratio (mol %) is preferably 3HB:3HH = 97:3 to 75:25, 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 3HB homopolymer, resulting in a loss of flexibility and an undesirable tendency for the film-forming processing temperature to become too high. If the 3HH composition exceeds 25 mol %, the crystallization rate becomes too slow, making it unsuitable for film-forming processing. Furthermore, the reduced crystallinity tends to make the resin flexible and reduce the flexural modulus. The PHBH composition ratio can be measured by NMR analysis of the powder obtained by centrifuging the aqueous dispersion and drying it. Microbial-produced PHBH is a random copolymer. Methods for adjusting the molar ratio of the copolymer include selecting the bacterial cells, selecting the carbon source as the raw material, blending with PHBH at different molar ratios, and blending with 3HB homopolymer.

[0018] In one embodiment of the present invention, the weight-average molecular weight of PHBH is preferably 50,000 to 550,000, more preferably 100,000 to 500,000, and even more preferably 150,000 to 450,000. When the weight-average molecular weight of PHBH is within the above range, the coating properties of a coating liquid containing PHBH are excellent. The weight-average molecular weight of PHBH can be determined by gel permeation chromatography (GPC, such as "Shodex GPC-101" manufactured by Showa Denko K.K.) using a polystyrene gel (such as "Shodex K-804" manufactured by Showa Denko K.K.) as a column and chloroform as a mobile phase, as a molecular weight converted into polystyrene. The measurement sample is a powder obtained by centrifuging an aqueous dispersion containing PHBH and then drying it.

[0019] PHBH is water-dispersible. The average particle size of PHBH in the coating solution of the present invention is preferably 0.1 to 50 μm, more preferably 0.5 to 10 μm. PHBH with an average particle size of less than 0.1 μm is difficult to achieve through microbial production, and even when obtained by chemical synthesis, microparticulation 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 refers to the particle size corresponding to 50% of the total particle accumulation amount of a normal distribution when an aqueous suspension of PHBH is adjusted to a predetermined concentration using a general-purpose particle sizer such as a Microtrac particle sizer (manufactured by Nikkiso, FRA). In the present invention, two or more PHBHs with different composition ratios, weight-average molecular weights, etc. can be mixed and used.

[0020] <PVA> PVA with a saponification degree of 70 mol% or more and 95 mol% or less is used. Although the mechanism is unclear, the heat seal paper of the present invention has excellent coating layer strength by using PVA with a saponification degree within this range. The saponification degree of PVA is preferably 75 mol% or more, more preferably 78 mol% or more, even more preferably 85 mol% or more, and preferably 93 mol% or less, more preferably 90 mol% or less. PVA is water-soluble. Therefore, as the polymerization degree increases, the coating liquid containing PVA may become thicker, resulting in reduced handleability and coatability. The polymerization degree of PVA is preferably 2000 or less, more preferably 1500 or less, and even more preferably 1000 or less. In the present invention, two or more PVAs with different saponification degrees, polymerization degrees, etc. may be mixed and used.

[0021] The heat seal layer contains 7 to 35 parts by weight of PVA per 100 parts by weight of PHBH. By containing PHBH and PVA in this ratio, a heat seal layer with excellent coating layer strength can be obtained. The heat seal layer preferably contains 10 or more parts by weight, and more preferably 30 or less parts by weight, of PVA per 100 parts by weight of PHBH.

[0022] The heat seal layer may contain, in addition to PHBH and PVA, other water-soluble resins or water-dispersible resins. Furthermore, the heat seal layer may contain, as necessary, various auxiliaries that are blended into coating solutions in the papermaking field, such as dispersants, viscosity modifiers, water retention agents, antifoaming agents, water-resistant agents, fluorescent dyes, coloring dyes, coloring pigments, surfactants, pH adjusters, cationic resins, anionic resins, ultraviolet absorbers, and metal salts.

[0023] Other water-soluble or water-dispersible resins include, for example, fully saponified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, carboxy-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, olefin-modified polyvinyl alcohol, nitrile-modified polyvinyl alcohol, pyrrolidone-modified polyvinyl alcohol, silicone-modified polyvinyl alcohol, other modified polyvinyl alcohols, polyvinyl alcohols such as ethylene-vinyl alcohol copolymers, starches such as oxidized starch, etherified starch, and esterified starch, cellulose derivatives such as hydroxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, acetyl cellulose, and nanocellulose, partially saponified ethylene-vinyl acetate copolymer, styrene-butadiene copolymer latex, conjugated diene polymer latex of methyl methacrylate-butadiene copolymer, acrylic polymer latex, styrene-maleic anhydride copolymer latex, polyvinyl chloride latex, and polyvinyl acetate latex. In the present invention, the ratio of the total amount of PHBH and PVA to the total amount of the water-soluble resin and the water-dispersible resin is preferably 80% by weight or more, more preferably 90% by weight or more, even more preferably 95% by weight or more, and most preferably 100% by weight.

[0024] The heat seal layer can exhibit properties derived from PHBH and PVA in addition to heat sealability, and can be used as, for example, a water-resistant layer, an oil-resistant layer, etc. The water-resistant layer is a layer having a water absorbency (Cobb value) of 20 g / m2 measured at a contact time of 120 seconds in accordance with "Paper and board - Water absorption test method - Cobb method" specified in JIS P 8140:1998. ２ The water absorption of this layer is 10 g / m ２ Preferably, it is 5 g / m or less. ２ The oil-resistant layer is a layer having a minimum kit number of 10 or more measured at any five points on the layer surface in accordance with "Paper and paperboard - Oil repellency test method - Kit method" specified in J. TAPPI No. 41:2000. The minimum kit number is preferably 11 or more, and more preferably 12.

[0025] <Method for producing heat-sealable paper> The heat-sealable paper of the present invention can be produced by applying a coating liquid for a heat-sealable layer to a paper substrate and drying the coating liquid. The heat-sealable layer can be provided on only one side or both sides of the paper substrate.

[0026] The coating method for the heat-sealable coating layer is not particularly limited, and coating can be performed using known coating equipment and coating systems. Examples of coating equipment include blade coaters, bar coaters, air knife coaters, curtain coaters, spray coaters, roll coaters, reverse roll coaters, size press coaters, and gate roll coaters. Examples of coating systems include aqueous coating using solvents such as water, and solvent-based coating using solvents such as organic solvents. The heat-sealable paper of the present invention has the characteristics that the PHBH is biomass-derived and biodegradable, and the PVA is biodegradable, and therefore has a very low environmental impact. Therefore, aqueous coating, which also has a low environmental impact during the manufacturing process, is preferred. The viscosity, solids concentration, etc. of the heat-sealable layer coating solution can be appropriately adjusted depending on the coating equipment, coating system, etc. used.

[0027] The heat-sealable coating layer can be dried using conventional methods such as a steam heater, gas heater, infrared heater, electric heater, hot air heater, microwave, or cylinder dryer. The drying temperature is not particularly limited, but in the case of aqueous coating, a temperature of 105°C or higher and 160°C or lower is preferred. Since PHBH is dispersed in the aqueous coating solution, it is particulate. As the drying temperature increases, the particulate PHBH dissolves, accelerating film formation and forming a uniform coating film. This tends to improve water resistance and oil resistance, but excessive film formation can result in a decrease in heat-sealability. Therefore, the drying temperature is preferably 150°C or lower, more preferably 140°C or lower, and even more preferably 130°C or lower.

[0028] The coating amount (dry weight) of the heat seal layer is not particularly limited as long as it can exhibit its performance. For example, it is 1.0 g / m per side. ２ 50.0g / m or more ２ The coating amount is preferably 1.0 g / m or less per side. ２ If the coating amount is less than 50.0 g / m per side, the heat sealability may not be fully exhibited. ２ Even if the coating amount exceeds 3.0 g / m, further improvement in properties cannot be expected and the cost increases. ２ More preferably, 5.0 g / m or more ２ More preferably, 7.0 g / m or more ２ More preferably, 40.0 g / m ２ More preferably, 30.0 g / m or less ２ More preferably, 20.0 g / m or less ２ Furthermore, when the heat seal paper of the present invention is used for a flexible packaging material, the coating amount (dry weight) of the heat seal layer is 18.0 g / m ２ More preferably, 15.0 g / m or less ２ More preferably, 13.0 g / m or less ２The following is even more preferable. The heat seal layer may be one layer or two or more layers laminated together. When the heat seal layer is two or more layers, it is preferable that the total coating weight of all the heat seal layers is within the above-mentioned range in dry weight.

[0029] The heat-sealable paper of the present invention is easy to form, maintain its shape, and ensure airtightness, and therefore can be suitably used as paper bags, paper containers, paper boxes, paper cups, (flexible) packaging materials, lid materials, etc. The heat-sealable paper of the present invention, in which the heat-sealable layer is also a water-resistant layer, can be suitably used as wrapping paper, paper bags, paper containers, paper boxes, paper cups, (flexible) packaging materials, paper plates, paper trays, posters for outdoor use, etc. The heat-sealable paper of the present invention, in which the heat-sealable layer is also an oil-resistant layer, can be suitably used as (flexible) packaging materials or wrapping paper for foods that contain a lot of oil, such as hamburgers, hot dogs, French fries, fried chicken, potato chips, etc., as lining paper for fried foods such as tempura, paper plates, paper trays, paper cups, etc.

[0030] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, parts and percentages in the examples are by weight. The coated papers obtained were tested according to the following evaluation methods.

[0031] Example 1 Preparation of Coating Solution for Heat-Seal Layer A PHBH aqueous dispersion having a PHBH solids concentration of 50% by weight was prepared using the method described in Patent Document 1. This PHBH aqueous dispersion was then hydrolyzed at 60°C to adjust the molecular weight, thereby obtaining a PHBH aqueous dispersion having a PHBH weight-average molecular weight of 230,000. The PHBH aqueous dispersion and PVA (manufactured by Kuraray Co., Ltd.: 5-88, saponification degree 88 mol%, polymerization degree 500) were then mixed in a solids weight ratio of 100 parts by weight of PHBH to 15 parts by weight of PVA, and water was further added and the mixture was stirred to prepare a coating solution for a coating layer having a solids concentration of 38% by weight.

[0032] (Preparation of heat seal paper) Paper base material (basis weight 50 g / m ２ The coating solution for the heat seal layer was applied to one side of the unbleached kraft paper (100g / m2 in dry weight).２ The coating was carried out by a bar blade method so that the coating was applied to a thickness of 105°C, and then dried at 105°C to obtain a heat seal paper.

[0033] [Comparative Example 1] Heat-sealable paper was obtained in the same manner as in Example 1, except that PVA (manufactured by Kuraray Co., Ltd.: 5-98, saponification degree 98 mol%, polymerization degree 500) was used. [Example 2] Heat-sealable paper was obtained in the same manner as in Example 1, except that PVA (manufactured by Kuraray Co., Ltd.: 22-88, saponification degree 88 mol%, polymerization degree 1700) was used. [Comparative Example 2] Heat-sealable paper was obtained in the same manner as in Example 1, except that PVA (manufactured by Kuraray Co., Ltd.: 28-98, saponification degree 98 mol%, polymerization degree 1700) was used.

[0034] (Evaluation Method) The obtained heat seal paper was evaluated as follows. The results are shown in Table 1. (1) Coating Layer Strength (Cellopic) Cellophane tape (18 mm wide, 15 cm long) was laminated to the surface of the heat seal layer, and a 130 mm wide, 1.8 kg rubber roller was rolled back and forth under its own weight 10 times on the cellophane tape to adhere the cellophane tape to the surface of the heat seal layer. Immediately afterwards, the cellophane tape was peeled off at a constant speed using a digital force gauge (Shimpo Corporation), and the tensile strength at that time was measured and the average value was calculated. This test separates the heat seal layer into a portion that remains attached to the paper and a portion that is attached to the cellophane tape, so the tensile strength represents the strength of the coating layer.

[0035] (2) Heat-sealability Two square test pieces, each 100 mm on a side, were cut out from the obtained heat-seal paper, and the coating layers were brought into contact with each other and pressed at a temperature of 130°C and a pressure of 2 kgf / cm. ２ The heat-sealed test piece was peeled using a Tensilon tensile tester, and the tensile strength was measured to determine the maximum value. The peeled portion was also visually observed, and the heat-sealability was evaluated according to the following criteria. [Evaluation criteria] ◯: Peeling occurred within the paper substrate (paper substrate was destroyed). △: Peeling occurred mostly within the paper substrate (paper substrate was destroyed). ×: Peeling occurred between the coating layers.

[0036] Comparative Example 3 Heat-sealable paper was obtained in the same manner as in Example 1, except that 5 parts by weight of PVA (5-88 manufactured by Kuraray Co., Ltd., saponification degree 88 mol%, polymerization degree 500) was used relative to 100 parts by weight of PHBH. Example 3 Heat-sealable paper was obtained in the same manner as in Example 1, except that 10 parts by weight of PVA (5-88 manufactured by Kuraray Co., Ltd., saponification degree 88 mol%, polymerization degree 500) was used relative to 100 parts by weight of PHBH. Example 4 Heat-sealable paper was obtained in the same manner as in Example 1, except that 20 parts by weight of PVA (5-88 manufactured by Kuraray Co., Ltd., saponification degree 88 mol%, polymerization degree 500) was used relative to 100 parts by weight of PHBH. Example 5 A heat seal paper was obtained in the same manner as in Example 1, except that 30 parts by weight of PVA (manufactured by Kuraray Co., Ltd.: 5-88, saponification degree 88 mol %, polymerization degree 500) was used per 100 parts by weight of PHBH.

[0037] Comparative Example 4 Heat-sealable paper was obtained in the same manner as in Example 1, except that 40 parts by weight of PVA (5-88 manufactured by Kuraray Co., Ltd., saponification degree 88 mol%, polymerization degree 500) was used per 100 parts by weight of PHBH. Comparative Example 5 Heat-sealable paper was obtained in the same manner as in Example 4, except that PVA (5-98 manufactured by Kuraray Co., Ltd., saponification degree 98 mol%, polymerization degree 500) was used. Comparative Example 6 Heat-sealable paper was obtained in the same manner as in Example 5, except that PVA (5-98 manufactured by Kuraray Co., Ltd., saponification degree 98 mol%, polymerization degree 500) was used.

[0038]

Claims

1. A heat-sealable coating layer is provided on at least one surface of a paper substrate, containing 7 to 35 parts by weight of PVA (polyvinyl alcohol) per 100 parts by weight of PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)), The PVA has a degree of saponification of 70 mol% or more and 95 mol% or less, and a degree of polymerization of 2000 or less. A heat-sealable paper characterized in that the PHBH and PVA are not uniformly distributed in the heat-sealable coating layer.

2. The heat-sealable paper according to claim 1, characterized in that the PVA has a degree of polymerization of 1500 or less.

3. The coating amount (dry weight) of the heat-sealable coating layer is 1.0 g / m² per side. ２ 50.0g / m or more ２ The heat seal paper according to claim 1 or 2, characterized in that it is as follows:

4. The basis weight of the aforementioned paper substrate, measured in accordance with JIS P 8124, was 20 g / m². ２ More than 600g / m ２ The heat seal paper according to claim 1 or 2, characterized in that it is as follows:

5. A method for producing heat-sealable paper having a heat-sealable coating layer on at least one surface of a paper substrate, the coating layer containing 7 to 35 parts by weight of PVA (polyvinyl alcohol) per 100 parts by weight of PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)), The process includes applying a heat-seal layer coating solution, in which PHBH is dispersed and PVA is dissolved, to at least one surface of a paper substrate. A method for producing heat-sealable paper, characterized in that the PVA has a degree of saponification of 70 mol% or more and 95 mol% or less, and a degree of polymerization of 2000 or less.