Heat seal paper

Abstract

The present invention addresses the problem of providing a heat seal paper that contains PHBH and has excellent heat seal strength. The solution is to provide a heat seal paper comprising a heat seal coating layer containing poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) and an adhesive that are disposed on at least one surface of a paper substrate, where the heat-seal coating layer is a semi-permeating film.

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 sealable paper containing PHBH and having excellent heat seal 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 containing PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)) and an adhesive on at least one side of a paper substrate, wherein the heat-sealable coating layer is a semi-film-forming layer. 2. The heat-sealable paper according to 1., wherein the heat-sealable coating layer contains 10 to 50 parts by weight of adhesive per 100 parts by weight of PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)). 3. The heat-sealable paper, wherein 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 More than 600g / m ２ 1. The heat seal paper according to any one of 1. to 3., characterized in that:

[0007] The heat seal paper of the present invention has excellent heat seal strength. The heat seal paper of the present invention can be made biodegradable as a whole, so that even if it is released into the environment, it will be rapidly decomposed.

[0008] Electron microscope images of the surface of the heat-sealable coating layer of the heat-sealable papers obtained in Example 1 and Comparative Example 1.

[0009] The heat-sealable paper of the present invention has a heat-sealable coating layer containing PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)) and an adhesive on at least one side of a paper substrate, and is characterized in that this heat-sealable coating layer is a semi-film-forming layer. In this specification, the expression "A to B" (A and B are numbers) means a numerical range including A and B, i.e., "A or more and B or less."

[0010] (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%.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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 More than 600g / m ２ Preferably, 25 g / m or less ２ More than 600g / m 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:

[0015] 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.

[0016] (Sealing Layer) The coated paper of the present invention can have a sealing layer between the paper substrate and the heat-sealing layer. The sealing layer prevents the heat-sealing layer coating liquid from sinking into the paper substrate, thereby preventing a decrease in the performance of the heat-sealing layer. The sealing layer is not particularly limited as long as it can prevent the heat-sealing layer coating liquid from sinking into the paper substrate, but it preferably contains, for example, a pigment and a binder. Furthermore, the sealing layer can contain a sizing agent, a water-resistant agent, a water-repellent agent, a dye, a surfactant, etc., as necessary.

[0017] Examples of pigments include inorganic pigments such as light calcium carbonate, heavy calcium carbonate, kaolin, calcined kaolin, engineered kaolin, clay, delaminated clay, talc, silica, colloidal silica, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, aluminum silicate, calcium silicate, magnesium silicate, aluminum hydroxide, alumina, magnesium carbonate, magnesium hydroxide, kaolinite, antigorite, smectite, vermiculite, and mica, and organic pigments made of resins such as acrylic or methacrylic resins, vinyl chloride resins, vinyl acetate resins, polyester resins, styrene-acrylic resins, styrene-butadiene resins, styrene-isoprene resins, polycarbonate resins, silicone resins, urea resins, melamine resins, epoxy resins, phenolic resins, and diallyl phthalate resins. These pigments can be used alone or in combination.

[0018] As the binder, any type generally used in the field of coated paper, etc. can be used as appropriate. For example, polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially 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, ethylene-vinyl alcohol copolymers, acrylic resins composed of (meth)acrylic acid and monomer components copolymerizable with (meth)acrylic acid (excluding olefins), ethylene-acrylic resins, etc. Examples of binders include resins, cellulose derivatives such as hydroxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, and acetyl cellulose; starches such as oxidized starch, etherified starch, and esterified starch; poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), styrene-maleic anhydride copolymer, styrene-butadiene copolymer, casein, gum arabic, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic acid ester, polyvinyl butyral, polystyrose and copolymers thereof; polyamide resins, silicone resins, petroleum resins, terpene resins, ketone resins, and coumarone resins. These binders can be used alone or in combination of two or more. In the present invention, the use of biodegradable binders such as polyvinyl alcohols, cellulose derivatives, starches, and PHBH in the filling layer is preferred because it further improves the biodegradability of the heat-sealable paper as a whole.

[0019] By using a binder with high water vapor barrier properties, water vapor barrier properties can be imparted to the filling layer. When water vapor barrier properties are imparted to the filling layer, it is preferable to use one or a mixture of two or more binders selected from ethylene vinyl alcohol copolymers, ethylene-acrylic resins, and styrene-butadiene copolymers. The blending amount of the pigment in the filling layer is preferably in the range of 1 part by weight to 1,000 parts by weight, more preferably 10 parts by weight to 500 parts by weight, per 100 parts by weight of the binder, on a dry weight basis.

[0020] (Heat-sealable coating layer) A heat-sealable coating layer (hereinafter also referred to as heat-sealable layer) is a layer having heat-sealability formed by coating. Whether or not a coating layer is a coating layer can be determined by observing its cross section with an electron microscope or the like. The heat-sealable coating layer of the present invention is a semi-film. Since PHBH is water-dispersible, when a coating liquid in which PHBH is dispersed is applied and dried at a low temperature, particulate PHBH adheres to the coated surface, and voids exist between the particles. When the drying temperature is increased, the melted PHBH particles bond together and solidify, filling the voids and resulting in a more uniform coating film. The semi-film of the present invention means a film in which part of the PHBH is melted and bonded, and specifically, a film of 8000 μm observed with an electron microscope or the like. ２ This refers to a coating layer in which the area ratio of voids present between PHBH particles in the above heat-sealable layer surface image (hereinafter also referred to as porosity) is 0.1% or more and 10% or less. A semi-film-forming heat-sealable coating layer has excellent heat-sealability. This porosity is preferably 8% or less, more preferably 6% or less, even more preferably 5% or less, and even more preferably 4% or less. Also, it is preferably 0.5% or more, more preferably 1% or more.

[0021] <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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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. may be mixed and used.

[0026] <Adhesive> The adhesive bonds the PHBH in the heat-seal layer to the paper substrate and / or bonds the PHBHs together in the heat-seal layer. The heat-seal paper of the present invention allows the PHBH to be adhered to the paper substrate by containing an adhesive in the heat-seal layer, and also allows a uniform heat-seal layer to be obtained in which coating defects such as cracks and pinholes are suppressed. Any adhesive can be used without particular limitations as long as it dissolves or disperses in water and can bond these. For example, fully saponified polyvinyl alcohol, partially 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, hydroxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, acetyl cellulose, cellulose derivatives such as 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, polyvinyl acetate latex, and the like can be mentioned, and one or more of these can be appropriately selected and used.

[0027] Among these, it is preferable to include at least one selected from the group consisting of polyvinyl alcohols, starches, cellulose derivatives, partially saponified ethylene-vinyl acetate copolymers, styrene-butadiene copolymer latexes, conjugated diene polymer latexes such as methyl methacrylate-butadiene copolymers, and acrylic polymer latexes, and more preferably to consist of at least one selected from this group. Furthermore, because it is biodegradable, it is more preferable to include at least one selected from the group consisting of polyvinyl alcohols, starches, cellulose derivatives, and partially saponified ethylene-vinyl acetate copolymers, and even more preferably to include at least one selected from the group consisting of fully saponified polyvinyl alcohols, partially saponified polyvinyl alcohols, and partially saponified ethylene-vinyl acetate copolymers.

[0028] Inclusion of at least one of fully saponified polyvinyl alcohol and partially saponified polyvinyl alcohol as the adhesive is preferred because it further improves adhesion between the PHBH in the heat seal layer and the paper substrate, and / or between the PHBHs in the heat seal layer. Furthermore, in order to achieve excellent coating layer strength, it is more preferred to include partially saponified polyvinyl alcohol with a saponification degree of 70 mol% to 95 mol%. The saponification degree of the partially saponified polyvinyl alcohol 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. Here, PHBH is water-dispersible, but fully saponified polyvinyl alcohol and partially saponified polyvinyl alcohol are water-soluble. Therefore, when fully saponified polyvinyl alcohol or partially saponified polyvinyl alcohol is used as the adhesive, the coating liquid may thicken as the degree of polymerization increases, resulting in reduced handleability and coatability. Therefore, the degree of polymerization of the fully saponified polyvinyl alcohol and the partially saponified polyvinyl alcohol is preferably 2,000 or less, more preferably 1,500 or less, and even more preferably 1,000 or less.

[0029] The heat seal layer preferably contains 10 to 50 parts by weight of an adhesive per 100 parts by weight of PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)). By containing PHBH and an adhesive within this range, it becomes easy to form a coating layer that adheres closely to the paper substrate. The heat seal layer preferably contains 15 or more parts by weight of an adhesive per 100 parts by weight of PHBH, and preferably contains 40 or less parts by weight.

[0030] In addition to PHBH and an adhesive, the coating layer may contain, as necessary, various auxiliaries that are blended into coating solutions in the papermaking field, such as dispersants, viscosity improvers, 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.

[0031] The heat seal layer can exhibit the performance derived from PHBH other than 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.

[0032] <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. When a sealing layer is provided, the coating liquid for a sealing layer is applied to the paper substrate before or simultaneously with applying the coating liquid for a heat-sealable layer so that the sealing layer is present between the paper substrate and the heat-sealable coating layer.

[0033] 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. Furthermore, as the coating system, an aqueous coating system is used in which a solvent such as water is used to obtain a coating solution in which PHBH is dispersed. The viscosity, solids concentration, etc. of the heat-sealable coating solution can be appropriately adjusted depending on the coating equipment, coating system, etc. used.

[0034] 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 adjusted so that the heat-sealable coating layer obtained after drying is a semi-film-formed layer, and specifically, is preferably 105°C or higher and 150°C or lower. If the drying temperature exceeds 150°C, the particulate PHBH dissolves, making it easier to form a uniform coating layer (film-formed layer) with a porosity of less than 0.1%. On the other hand, if the drying temperature is lower than 105°C, the PHBH is less likely to dissolve, making it easier for the film to not be formed, which may reduce the adhesion between the heat-sealable layer and the paper substrate. The drying temperature is preferably 140°C or lower, more preferably 135°C or lower, and even more preferably 130°C or lower.

[0035] The coating amount (dry weight) of the sealing layer is 3.0 g / m ２ 15.0g / m or more ２ The coating amount is preferably 3.0 g / m or less. ２ If the density is less than 15.0 g / m, the sealing effect may be insufficient. ２ If the amount is more than this, the drying load during coating increases, which is undesirable from the viewpoints of both operation and cost. The number of filling layers may be one layer or two or more layers. When the number of filling layers is two or more layers, it is preferable that the total coating amount of all the filling layers is in the above-mentioned range in terms of dry weight.

[0036] 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 ２ The 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.

[0037] 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.

[0038] 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.

[0039] 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 25 parts by weight of PVA to 100 parts by weight of PHBH, 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.

[0040] (Preparation of heat seal paper) Paper base material (basis weight 50 g / m ２ The coating layer coating solution is applied to one side of the single-sided glossy paper (white base paper) in a dry weight amount of 10.0 g / m² per side. ２ The coating was carried out by a bar blade method so that the coating was carried out in the following manner, and then dried at 130°C to obtain a heat seal paper.

[0041] Example 2: Heat-sealable paper was obtained in the same manner as in Example 1, except that the drying temperature was 110°C. Example 3: Heat-sealable paper was obtained in the same manner as in Example 1, except that the drying temperature was 105°C. Comparative Example 1: Heat-sealable paper was obtained in the same manner as in Example 1, except that the drying temperature was 160°C.

[0042] (Evaluation Method) The heat seal papers obtained were evaluated as follows. The results are shown in Table 1. <Porosity> Using an electron microscope (FlexSEM 1000, manufactured by HITACHI Corporation), the surface of the heat seal layer was photographed at a magnification of 1000 times. Electron microscope images of the heat seal papers obtained in Example 1 and Comparative Example 1 are shown in Figure 1. Using an image analysis program (ImagePro, manufactured by Hakutosha), an arbitrary 8000 µm portion of the obtained image was analyzed. ２ The area was subjected to black and white binarization processing with brightness 50, contrast 50, and dark color 0 to 50, and the area of ​​the dark colored portion (void portion) was calculated. The porosity was calculated from the ratio of the void area to the total area subjected to image analysis as shown in the following formula: Porosity (%) = Total void area (μm ２ ) / total area where image analysis was performed (μm ２ ) x 100

[0043] <Evaluation of heat sealability> Two square test pieces, each 100 mm on a side, were cut out from the obtained coated 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 off by hand, and the peeled area was visually inspected, and the heat-sealability was evaluated according to the following criteria. If the evaluation was good or fair, there was no problem in practical use. [Evaluation criteria] Good: Peeling occurred within the paper substrate (paper substrate was destroyed). Fair: Peeling occurred mostly within the paper substrate (paper substrate was destroyed). Poor: Peeling occurred between the coating layers.

[0044] <Evaluation of Heat Seal Layer Adhesion> A 5 ​​x 6 cm test piece was cut out from the obtained coated paper, and the coated surface was brought into contact with water and placed against vinyl tape (NITTO TAPE). [Evaluation Criteria] ◯: The heat seal layer was not transferred to the tape. ×: The heat seal layer was transferred to the tape.

[0045]

Claims

1. A heat-sealable coating layer is provided on at least one surface of a paper substrate, containing 10 to 50 parts by weight of adhesive per 100 parts by weight of PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)), A heat-sealable paper characterized in that the heat-sealable coating layer is semi-film-forming.

2. 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, characterized in that it is as follows.

3. 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: