WO2024043201A1

WO2024043201A1 - Heat sealing paper

Info

Publication number: WO2024043201A1
Application number: PCT/JP2023/029916
Authority: WO
Inventors: 望美吉良; 義雄吉田; 浩佑角田; 雅幸藤田; 五樹日下部; 康則岡田
Original assignee: 日本製紙株式会社; 株式会社カネカ
Priority date: 2022-08-22
Filing date: 2023-08-21
Publication date: 2024-02-29

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

The present invention relates to heat seal paper.

In recent years, there has been a growing movement to prevent environmental destruction caused by plastic waste, and there is a need to replace disposable plastic products with materials that have a smaller impact on the environment. Examples of alternative materials to plastic include biodegradable plastic, wood, and paper.
Coated paper, which is paper coated with resin, can exhibit various functions depending on the resin coated. However, if the resin to be coated is derived from fossil resources or is non-biodegradable, the environmental impact reduction effect achieved by using paper will be diminished. Therefore, there is a need for coated paper in which a paper base material is coated with an aqueous dispersion of biodegradable plastic.

Aliphatic polyesters such as polylactic acid and polycaprolactone are known as biodegradable plastics. However, aliphatic polyesters have a problem in that they take time to biodegrade at low temperatures and have a slow decomposition rate in natural environments such as the ocean.
On the other hand, poly(3-hydroxybutyrate) resin is a thermoplastic plastic produced by microorganisms that has excellent decomposition properties under aerobic and anaerobic conditions. It has the remarkable performance of Patent Document 1 describes a biodegradable product containing PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)), which is a copolymer of 3-hydroxybutyrate and 3-hydroxyhexanoate. Polyester aqueous dispersion has excellent film-forming properties, and when applied to paints, adhesives, fiber processing, sheet/film processing, paper processing, etc., it produces resin coatings that are flexible, stretchable, and resistant to bending. It is stated that it is given.

International Publication No. 2004/041936

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

Means for solving the problems of the present invention are as follows.
1. On at least one side of the paper base material, 7 parts by weight or more and 35 parts by weight of PVA (polyvinyl alcohol) per 100 parts by weight of PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)). It has a heat-sealable coating layer containing the following:
A heat seal paper characterized in that the degree of saponification of the PVA is 70 mol% or more and 95 mol% or less.
2. 1. The degree of polymerization of the PVA is 2000 or less. Heat seal paper as described in .
3. 1. A coating amount (dry weight) of the heat-sealable coating layer is 1.0 g/m ² or more and 50.0 g/m ² or less per side. or 2. Heat seal paper as described in .
4. 1. The basis weight of the paper base material measured according to JIS P 8124 is 20 g/m ² or more and 600 g/m ² or less. ~3. Heat seal paper described in any of the above.

The heat-sealable paper of the present invention has excellent coating layer strength, and the paper base material and the heat-sealable coating layer are firmly bonded. Since the heat-sealable paper of the present invention can be biodegradable as a whole, even if it is released into the environment, it will be rapidly decomposed.

The heat-sealable paper of the present invention contains PVA (polyvinyl alcohol) per 100 parts by weight of PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)) on at least one surface of the paper base material. has a heat-sealable coating layer containing 7 parts by weight or more and 35 parts by weight or less,
The saponification degree of the PVA is 70 mol% or more and 95 mol% or less.
In this specification, the expression "A to B" (A and B are numerical values) means a numerical range including A and B, that is, "A to B".

(Paper base material)
The paper base material is a sheet mainly made of pulp (hereinafter also referred to as "base paper"), and is obtained by paper-making a paper stock that further contains fillers, various auxiliary agents, and the like.
Pulps include chemical pulps such as hardwood bleached kraft pulp (LBKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), softwood unbleached kraft pulp (NUKP), sulfite pulp, stone grind pulp, Mechanical pulp such as thermomechanical pulp, wood fibers such as deinked pulp and waste paper pulp, and non-wood fibers obtained from kenaf, bamboo, hemp, etc. can be used, and can be appropriately blended and used. Among these, it is difficult for foreign matter to enter the paper base material, it is difficult to discolor over time when recycled as a waste paper raw material, and it has a high degree of whiteness, so it has a good surface feel when printing. For reasons such as increased utility value when used as a packaging material, it is preferable to use chemical pulp or mechanical pulp made of wood fibers, and it is more preferable to use chemical pulp made of wood fibers. Specifically, it is preferable that the amount of chemical pulp such as LBKP and NBKP is 80% or more based on the total pulp, and it is particularly preferable that the amount of chemical pulp is 100%.

Fillers include 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. Known fillers such as inorganic fillers such as calcium hydroxide, magnesium hydroxide, zinc hydroxide, barium sulfate, and calcium sulfate, and organic fillers such as urea-formalin resin, polystyrene resin, phenolic resin, and micro hollow particles are used. be able to. Note that the filler is not an essential material and may not be used.

Various auxiliary agents include rosin, alkyl ketene dimer (AKD), sizing agents such as alkenyl succinic anhydride (ASA), polyacrylamide polymers, polyvinyl alcohol polymers, cationized starches, various modified starches, urea, etc. Formalin resin, dry paper strength enhancer such as melamine/formalin resin, wet paper strength enhancer, retention agent, freeness improver, coagulant, sulfuric acid, bulking agent, dye, optical brightener, pH adjuster, Examples include antifoaming agents, ultraviolet inhibitors, antifading agents, pitch control agents, slime control agents, etc., and can be appropriately selected and used as required.

The surface of the paper base material may be treated with various chemicals. Examples of the drug include oxidized starch, hydroxyethyl etherified starch, enzyme-modified starch, polyacrylamide, polyvinyl alcohol, surface sizing agents, water resistance agents, water retention agents, thickeners, lubricants, etc. Alternatively, two or more types can be used in combination. Furthermore, these various drugs and pigments may be used in combination. Pigments include kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicate, colloidal silica, and satin. Inorganic pigments such as white and organic pigments such as solid type, hollow type, or core shell type can be used alone or in combination of two or more types.

The basis weight of the paper base material can be selected as appropriate depending on the desired quality and its use, but it is usually preferably 20 g/m ² or more and 600 g/m ² or less, and 25 g/m ² or more and 600 g/m ² or less. is more preferable.
For example, when used for packaging materials such as wrapping paper, paper bags, lids, and liners, posters used outdoors, etc., the basis weight of the paper base material is preferably 30 g/m ² or more and 150 g/m ² or less. When used as a soft packaging material, the basis weight of the paper base material is preferably 20 g/m ² or more and 100 g/m ² or less, more preferably 35 g/m ² or more and 80 g/m ² or less. Note that the soft packaging material is a highly flexible packaging material that uses thin paper of about 20 g/m ² to 100 g/m ² among packaging materials. Further, when used for paper cups, paper containers, paper boxes, paper plates, paper trays, etc., the basis weight of the paper base material is preferably 150 g/m ² or more and 300 g/m ² or less.
Further, the density of the paper base material can be appropriately selected depending on the desired various qualities, ease of handling, etc., but it is usually preferably 0.5 g/cm ³ or more and 1.0 g/cm ³ or less.

The manufacturing method (paper making) of the paper base material is not particularly limited, and may include a fourdrinier paper machine, cylinder paper machine, short wire paper machine, gap former type, hybrid former type (on-top former type), etc. Known manufacturing (paper making) methods and paper machines can be selected, such as a twin wire paper machine. In addition, the pH during papermaking may be any of the acidic region (acidic papermaking), pseudo-neutral region (pseudo-neutral papermaking), neutral region (neutral papermaking), and alkaline region (alkaline papermaking). Afterwards, an alkaline chemical may be applied to the surface of the paper layer. Further, the paper base material may have one layer or may be composed of two or more layers.
In addition, when treating the surface of the paper base material with a chemical, the surface treatment method is not particularly limited, and can be performed using a rod metal ring size press, a pound type size press, a gate roll coater, a spray coater, a blade coater, or a curtain coater. A known coating device such as the like can be used.

(Heat-sealable coating layer)
The heat-sealing coating layer (hereinafter also referred to as heat-sealing layer) is a layer having heat-sealing properties formed by coating. Note that whether or not it 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 biomolecule known to be produced by microorganisms. It is a degradable resin. In the present invention, PHBH derived from microorganisms or petroleum resources may be used, but it is preferable to use one derived from microorganisms from the viewpoint of reducing environmental burden.

The microorganism that produces PHBH is not particularly limited as long as it is a microorganism that accumulates PHBH in its cells, but A. lipolytica, A. eutrophus, A. Examples include bacteria of the genus Alcaligenes such as P. latus, Pseudomonas, Bacillus, Azotobacter, Nocardia, and Aeromonas. Among them, in terms of PHBH productivity, strains such as Aeromonas caviae and Alcaligenes eutrophus AC32 (accession number FERM BP-6038, deposited August 7, 1997) into which genes for the PHA synthase group have been introduced are particularly preferred. Patent Organism Depositary Center, National Institute of Advanced Industrial Science and Technology, Address: Chuo 6, Higashi 1-1-1, Tsukuba, Ibaraki Prefecture, Japan) (J. Bacteriol., 179, pp. 4821-4830 (1997)), etc. is preferred. Furthermore, a method for obtaining PHBH from Aeromonas caviae, which is a microorganism belonging to the genus Aeromonas, is disclosed in, for example, Japanese Patent Laid-Open No. 05-093049. Note that these microorganisms are used by culturing them under appropriate conditions to accumulate PHBH within their cells.
The carbon source and culture conditions used for culture can be obtained according to the methods described in JP-A-05-093049, JP-A-2001-340078, etc., but are not limited thereto.

The composition ratio (mol%) of PHBH is preferably 3HB:3HH=97:3 to 75:25, more preferably 95:5 to 85:15. When the composition of 3HH is less than 3 mol%, the properties of PHBH become close to those of 3HB homopolymer, resulting in a loss of flexibility and an undesirable tendency for the film-forming temperature to become too high. When the composition of 3HH exceeds 25 mol %, the crystallization rate becomes too slow, making it unsuitable for film forming processing, and the crystallinity decreases, which tends to make the resin soft and reduce its flexural modulus. The composition ratio of PHBH can be measured by NMR analysis of a powder obtained by centrifuging and drying an aqueous dispersion.
Microbially produced PHBH is a random copolymer. In order to adjust the molar ratio of the copolymer, there are methods such as selection of bacterial cells, selection of a carbon source as a raw material, blending with PHBH of a different molar ratio, and blending with a 3HB homopolymer.

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 liquid containing PHBH has excellent coating properties. The weight average molecular weight of PHBH was determined by gel permeation chromatography (GPC, Showa Denko Co., Ltd. "Shodex GPC-101", etc.) using a polystyrene gel column (Showa Denko Co., Ltd. "Shodex K-804" etc.). It can be determined as the molecular weight when converted to polystyrene using chloroform as the mobile phase. Note that, as the sample for measurement, a powder obtained by centrifuging an aqueous dispersion containing PHBH and then drying it is used.

PHBH is water dispersible. The average particle size of PHBH in the coating liquid 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 by microbial production, and even when obtained by chemical synthesis, an operation 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 determined by adjusting the aqueous suspension of PHBH to a predetermined concentration using a general-purpose particle size meter such as Microtrac particle size meter (Nikkiso Co., Ltd., FRA), and calculating the accumulated amount of 50% of all particles in a normal distribution. The particle size corresponding to
In the present invention, two or more PHBHs having different composition ratios, weight average molecular weights, etc. can be used as a mixture.

<PVA>
PVA used has a saponification degree of 70 mol% or more and 95 mol% or less. Although the mechanism is unknown, the heat seal paper of the present invention has excellent coating layer strength by using PVA with a degree of saponification within this range. The degree of saponification 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 degree of polymerization increases, a coating solution containing PVA increases in viscosity, and handling and coating properties may decrease. The degree of polymerization of PVA is preferably 2,000 or less, more preferably 1,500 or less, and even more preferably 1,000 or less.
In the present invention, two or more types of PVA having different saponification degrees, polymerization degrees, etc. can be used as a mixture.

The heat seal layer contains 7 parts by weight or more and 35 parts by weight or less of PVA based on 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 PVA in an amount of 10 parts by weight or more, and preferably 30 parts by weight or less, based on 100 parts by weight of PHBH.

The heat seal layer can contain other water-soluble resins and water-dispersible resins in addition to PHBH and PVA. Furthermore, the heat seal layer may contain a dispersant, a viscosity improver, a water retention agent, an antifoaming agent, a water resistance agent, a fluorescent dye, a colored dye, a colored pigment, a surfactant, a pH adjuster, a cationic resin, as necessary. , anionic resins, ultraviolet absorbers, metal salts, and other various auxiliary agents that are blended into coating liquids in the paper manufacturing field.

Examples of other water-soluble or water-dispersible resins include fully saponified polyvinyl alcohol, acetoacetylated polyvinyl alcohol, carboxy-modified polyvinyl alcohol, amide-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, butyral-modified polyvinyl alcohol, and olefin-modified polyvinyl alcohol. 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, esterified starch, Cellulose derivatives such as hydroxymethylcellulose, hydroxyethylcellulose, methylcellulose, ethylcellulose, carboxymethylcellulose, acetylcellulose, nanocellulose, partially saponified ethylene-vinyl acetate copolymer, styrene-butadiene copolymer latex, methyl methacrylate-butadiene copolymer. Examples include conjugated diene polymer latex, 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 water-soluble resin and water-dispersible resin is preferably 80% by weight or more, more preferably 90% by weight or more, and 95% by weight or more. More preferably, the content is 100% by weight, and most preferably 100% by weight.

In addition to heat-sealability, the heat-sealing layer can exhibit properties derived from PHBH and PVA, and can be used, for example, as a water-resistant layer, an oil-resistant layer, etc.
The water-resistant layer is a layer with a water absorbency (Cobb value) of 20 g/m 2 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. The following layers are included. This water absorption is preferably 10 g/m ² or less, more preferably 5 g/m ² or less.
The oil-resistant layer is defined by J. TAPPI No. The layer has 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 41:2000. The lowest value of this kit number is preferably 11 or more, and more preferably 12.

<Method for manufacturing heat seal paper>
The heat seal paper of the present invention can be produced by applying a heat seal layer coating liquid to a paper base material and drying the coating liquid. Note that the heat seal layer can be provided on only one side or both sides of the paper base material.

The coating method for the heat-sealable coating layer is not particularly limited, and coating can be performed using a known coating device and coating system. For example, examples of the coating device include a blade coater, a bar coater, an air knife coater, a curtain coater, a spray coater, a roll coater, a reverse roll coater, a size press coater, a gate roll coater, and the like. Further, examples of the coating system include water-based coating using a solvent such as water, solvent-based coating using a solvent such as an organic solvent, and the like. The heat-sealing paper of the present invention has the characteristics that PHBH is derived from biomass and is biodegradable, and PVA is biodegradable, and has a very small environmental load, so there is no environmental burden during the manufacturing process. It is preferable to use a water-based coating with a small amount.
The viscosity, solid content concentration, etc. of the coating liquid for the heat seal layer can be adjusted as appropriate depending on the coating device, coating system, etc. used.

As a method for drying the heat-sealable coating layer, a conventional method such as a steam heater, a gas heater, an infrared heater, an electric heater, a hot air heater, a microwave, a cylinder dryer, etc. can be used.
The drying temperature is not particularly limited, but in the case of water-based coating, it is preferably 105°C or higher and 160°C or lower. Since PHBH is dispersed in the aqueous coating liquid, PHBH is in the form of particles. As the drying temperature increases, particulate PHBH dissolves, promoting film formation and forming a uniform coating film, which tends to improve water resistance and oil resistance, but if film formation progresses too much, Heat sealability may be reduced. Therefore, the drying temperature is preferably 150°C or lower, more preferably 140°C or lower, and even more preferably 130°C or lower.

The coating amount (dry weight) of the heat seal layer is not particularly limited as long as its performance can be exhibited, but it is preferably 1.0 g/m ² or more and 50.0 g/m ² or less per side, for example. If the coating amount is less than 1.0 g/m ² per side, sufficient heat sealing properties may not be exhibited. Furthermore, even if the coating amount exceeds 50.0 g/m ² per side, hardly any further improvement in properties can be expected, leading to an increase in cost. The coating amount (dry weight) of the heat seal layer is more preferably 3.0 g/m ² or more per side, even more preferably 5.0 g/m ² or more, even more preferably 7.0 g/m ² or more, and , 40.0 g/m ² or less is more preferable, 30.0 g/m ² or less is even more preferable, and even more preferably 20.0 g/m ² or less. Furthermore, when the heat seal paper of the present invention is used for flexible packaging materials, the coating amount (dry weight) of the heat seal layer is more preferably 18.0 g/m ² or less, and even more preferably 15.0 g/m ² or less. Preferably, 13.0 g/m ² or less is even more preferable.
The heat seal layer may be one layer or two or more layers may be laminated. When there are two or more heat-sealing layers, it is preferable that the total coating amount of all the heat-sealing layers is within the above-mentioned range in terms of dry weight.

Since the heat seal paper of the present invention is easy to shape, maintain shape, and ensure sealing properties, it can be suitably used as paper bags, paper containers, paper boxes, paper cups, (soft) packaging materials, lid materials, etc. .
The heat-sealing paper of the present invention, in which the heat-sealing layer is also a water-resistant layer, is suitable for wrapping paper, paper bags, paper containers, paper boxes, paper cups, (soft) packaging materials, paper plates, paper trays, posters used outdoors, etc. It can be used for.
The heat-sealing paper of the present invention, in which the heat-sealing layer is also an oil-resistant layer, can be used as a (soft) packaging material for foods containing a lot of oil such as hamburgers, hot dogs, french fries, fried chicken, and potato chips, wrapping paper, and tempura. It can be suitably used as paper for frying, paper plates, paper trays, paper cups, etc.

The present invention will be specifically explained below with reference to Examples, but the present invention is of course not limited to these Examples. In addition, unless otherwise specified, parts and % in the examples indicate parts by weight and % by weight, respectively. The obtained coated paper was tested based on the evaluation method shown below.

[Example 1]
(Preparation of coating liquid for heat seal layer)
A PHBH aqueous dispersion having a PHBH solid content concentration of 50% by weight was obtained by the method described in Patent Document 1. Next, this PHBH aqueous dispersion was hydrolyzed at 60° C. to adjust the molecular weight, thereby obtaining a PHBH aqueous dispersion having a weight average molecular weight of 230,000.
Next, the PHBH aqueous dispersion and PVA (manufactured by Kuraray Co., Ltd.: 5-88, degree of saponification 88 mol%, degree of polymerization 500) were mixed so that the solid content weight ratio was 15 parts by weight of PVA to 100 parts by weight of PHBH. Then, water was further added and stirred to prepare a coating liquid for a coating layer having a solid content concentration of 38% by weight.

(Preparation of heat seal paper)
Coating solution for the heat seal layer was coated on one side of the paper base material (unbleached kraft paper with a basis weight of 50 g/m ² ) using a barblade method so that the dry weight coating amount was 10 g/m ² per side. The paper was processed and dried at 105°C to obtain heat seal paper.

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

(Evaluation method)
The obtained heat seal paper was evaluated as shown below. The results are shown in Table 1.
(1) Coating layer strength (seropic)
Laminate cellophane tape (width 18 mm, length 15 cm) on the surface of the heat seal layer, and move a rubber roller with a width of 130 mm and a weight of 1.8 kg over the cellophane tape 10 times using its own weight to attach the cellophane tape to the heat seal layer surface. It was placed in close contact with the Immediately thereafter, the cellophane tape was peeled off at a constant speed using a digital force gauge (SHIMPO), the tensile strength at that time was measured, and the average value was determined.
As a result of this test, the heat-sealing layer is divided into those that are still attached to the paper and those that are attached to the cellophane tape, so the tensile strength represents the strength of the coating layer.

(2) Heat-sealing suitability Two square test pieces of 100 mm on a side were cut out from the obtained heat-sealing paper, and the coating layers were brought into contact with each other at a pressure of 130°C and a pressure of 2 kgf/cm ² . Heat sealing was performed with a pressure time of 0.5 seconds.
The tensile strength was measured when the heat-sealed test piece was peeled off using a Tensilon tensile tester, and the maximum value was determined. In addition, the peeled portion was visually observed, and the suitability for heat sealing was evaluated based on the following criteria.
[Evaluation criteria]
○: Peeling within the paper base material (paper base material is destroyed).
Δ: Most of the sample peels off within the paper base material (the paper base material is destroyed).
×: Peeling occurs between coating layers.

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

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

Claims

On at least one side of the paper base material, 7 parts by weight or more and 35 parts by weight of PVA (polyvinyl alcohol) per 100 parts by weight of PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)). It has a heat-sealable coating layer containing the following:
A heat seal paper characterized in that the degree of saponification of the PVA is 70 mol% or more and 95 mol% or less.
The heat seal paper according to claim 1, wherein the PVA has a polymerization degree of 2000 or less.
The heat seal according to claim 1 or 2, wherein the coating amount (dry weight) of the heat sealable coating layer is 1.0 g/m 2 or more and 50.0 g/m 2 or less per side. paper.
The heat seal paper according to claim 1 or 2, wherein the paper base material has a basis weight of 20 g/m 2 or more and 600 g/m 2 or less, as measured according to JIS P 8124.