WO2024043200A1

WO2024043200A1 - Heat seal paper

Info

Publication number: WO2024043200A1
Application number: PCT/JP2023/029915
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 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

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-sealing paper containing PHBH and having excellent heat-sealing strength.

Means for solving the problems of the present invention are as follows.
1. A heat-sealable coating layer containing PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)) and an adhesive is provided on at least one surface of the paper base material,
A heat-sealing paper characterized in that the heat-sealing coating layer is a semi-formed film.
2. The heat-sealable coating layer contains 10 parts by weight or more and 50 parts by weight or less of an adhesive based on 100 parts by weight of PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)). Features 1. 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 seal paper of the present invention has excellent heat seal strength. 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.

Electron microscope image of the surface of the heat-sealable coating layer of the heat-sealable paper obtained in Example 1 and Comparative Example 1.

The heat-sealable paper of the present invention has a heat-sealable coating containing PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)) and an adhesive on at least one surface of a paper base material. It has a construction layer,
This heat-sealable coating layer is characterized by being a semi-formed film.
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.

(filling layer)
The coated paper of the present invention can have a sealing layer between the paper base material and the heat-sealing layer.
The sealing layer prevents the heat-sealing layer coating liquid from sinking into the paper base material, thereby preventing the performance of the heat-sealing layer from deteriorating. The sealing layer is not particularly limited as long as it can suppress sinking of the heat-sealing layer coating liquid into the paper base material, but preferably contains a pigment and a binder, for example. Further, the sealing layer may contain a sizing agent, a water-resistant agent, a water repellent, a dye, a surfactant, etc., if necessary.

Examples of pigments include 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, and sulfide. Inorganic pigments such as zinc, zinc carbonate, satin white, aluminum silicate, calcium silicate, magnesium silicate, aluminum hydroxide, alumina, magnesium carbonate, magnesium hydroxide, kaolinite, antigorite, smectite, vermiculite, mica, acrylic or Methacrylic resin, vinyl chloride resin, vinyl acetate resin, polyester resin, styrene-acrylic resin, styrene-butadiene resin, styrene-isoprene resin, polycarbonate resin, silicone resin, urea resin, melamine resin , organic pigments made of resins such as epoxy resins, phenol resins, and diallyl phthalate resins. As the pigment, one or a mixture of two or more of these can be used.

As the binder, any binder commonly used in the coated paper field can be used as appropriate. 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, (meth)acrylic acid, and monomer components copolymerizable with (meth)acrylic acid. Acrylic resins (excluding olefins), ethylene-acrylic 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 resin, silicone resin, petroleum resin, terpene resin, ketone resin, coumaron resin, and the like. As the binder, one type or a mixture of two or more of these can be used.
In the present invention, by using biodegradable binders such as polyvinyl alcohols, cellulose derivatives, starches, and PHBH in the sealing layer, the biodegradability of the heat seal paper as a whole can be further improved. preferable.

By using a binder with high water vapor barrier properties, water vapor barrier properties can be imparted to the sealing layer. When imparting water vapor barrier properties to the sealing layer, the binder is one or a mixture of two or more selected from ethylene vinyl alcohol copolymer, ethylene-acrylic resin, and styrene-butadiene copolymer. It is preferable to do so.
The amount of pigment in the sealing layer is preferably 1 part by weight or more and 1000 parts by weight or less, more preferably 10 parts by weight or more and 500 parts by weight or less, based on 100 parts by weight of the binder in terms of dry weight. It is.

(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.
The heat-sealable coating layer of the present invention is a semi-formed 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 surface of the coated surface, and voids exist between the particles. When the drying temperature is increased, the melted PHBH particles bond together and harden, filling the voids and providing a more uniform coating film. The semi-formed film of the present invention refers to a bonded film in which a part of PHBH is melted, and specifically, the semi-formed film that exists between PHBH particles in a heat seal layer surface image of 8000 μm ² or more observed with an electron microscope etc. It means a coating layer in which the area ratio of voids (hereinafter also referred to as porosity) is 0.1% or more and 10% or less. The heat-sealable coating layer, which is a semi-formed film, has excellent heat-sealability. The porosity is preferably 8% or less, more preferably 6% or less, even more preferably 5% or less, even more preferably 4% or less. Moreover, it is preferably 0.5% or more, and more preferably 1% or more.

<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.

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.

<Adhesive>
The adhesive bonds the PHBH in the heat seal layer to the paper base material and/or the PHBH in the heat seal layer to each other. The heat-sealing paper of the present invention has a heat-sealing layer containing an adhesive, which allows PHBH to adhere closely to the paper base material, and also provides a uniform coating with suppressed coating defects such as cracks and pinholes. A heat-sealing layer can be obtained.
The adhesive can be used without particular limitation as long as it can be dissolved or dispersed in water and can adhere these materials. 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, esterified starch, hydroxymethyl cellulose, hydroxyethyl cellulose, Cellulose derivatives such as methylcellulose, ethylcellulose, carboxymethylcellulose, acetylcellulose, 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, etc., and one or more of these can be appropriately selected and used. .

Among these, polyvinyl alcohols, starches, cellulose derivatives, partially saponified ethylene-vinyl acetate copolymer, styrene-butadiene copolymer latex, conjugated diene polymer latex of methyl methacrylate-butadiene copolymer, acrylic It preferably contains at least one type selected from the group consisting of polymer latexes, and more preferably it contains at least one type selected from this group. Moreover, since it is biodegradable, it is more preferable to contain at least one kind selected from the group consisting of polyvinyl alcohols, starches, cellulose derivatives, partially saponified ethylene-vinyl acetate copolymers, and fully saponified polyvinyl alcohol It is more preferable that the composition contains at least one selected from the group consisting of , partially saponified polyvinyl alcohol, and partially saponified ethylene-vinyl acetate copolymer.

When at least one of fully saponified polyvinyl alcohol and partially saponified polyvinyl alcohol is included as an adhesive, the adhesion between PHBH in the heat seal layer and the paper base material and/or between PHBH in the heat seal layer becomes even better. It is preferable for this reason, and it is more preferable to include partially saponified polyvinyl alcohol having a degree of saponification of 70 mol% or more and 95 mol% or less because the coating layer has excellent strength. The degree of saponification 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 an adhesive, as the degree of polymerization increases, the viscosity of the coating liquid increases, and handling and coating properties may deteriorate. Therefore, the degree of polymerization of fully saponified polyvinyl alcohol and partially saponified polyvinyl alcohol is preferably 2,000 or less, more preferably 1,500 or less, and even more preferably 1,000 or less.

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

In addition to PHBH and adhesive, the coating layer may contain a dispersant, a viscosity modifier, a water retention agent, an antifoaming agent, a water resistance agent, a fluorescent dye, a coloring dye, a coloring pigment, and a surfactant as necessary. , pH adjusters, cationic resins, anionic resins, ultraviolet absorbers, metal salts, and other various auxiliaries that are blended into coating liquids in the papermaking field.

The heat-sealing layer can exhibit performance derived from PHBH in addition to heat-sealing properties, 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. When a sealing layer is provided, the sealing layer is provided between the paper base material and the heat-sealable coating layer before or at the same time as applying the coating liquid for the heat-sealing layer to the paper base material. Apply the coating liquid for the stop layer.

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, as the coating system, an aqueous coating using a solvent such as water is used so as to form a coating liquid in which PHBH is dispersed.
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 adjusted so that the heat-sealable coating layer obtained after drying becomes a semi-formed film, and specifically, it is preferably 105°C or higher and 150°C or lower. When the drying temperature exceeds 150° C., particulate PHBH is dissolved and a uniform coating layer (film formation) with a porosity of less than 0.1% is likely to be formed. On the other hand, if the drying temperature is less than 105° C., PHBH is difficult to dissolve, so a film is likely to be unformed, and the adhesion between the heat seal layer and the paper base material may be reduced. The drying temperature is preferably 140°C or lower, more preferably 135°C or lower, and even more preferably 130°C or lower.

The coating amount (dry weight) of the sealing layer is preferably 3.0 g/m ² or more and 15.0 g/m ² or less. If the coating amount is less than 3.0 g/m ² , the sealing effect may be insufficient. On the other hand, if the amount is more than 15.0 g/m ² , the drying load during coating becomes large, which is not preferable from both operational and cost standpoints.
The sealing layer may be one layer or two or more layers. When there are two or more filler layers, it is preferable that the total coated amount of all filler layers is within the range described above in terms of dry weight.

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.

The heat-sealing paper of the present invention is easy to shape, maintain shape, and ensure sealing properties, so 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 (soft) packaging materials 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 25 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)
Apply the coating liquid for the coating layer on one side of the paper base material (single gloss paper (white) base paper with a basis weight of 50 g/ ^m2 ) so that the dry weight of the coating solution is 10.0 g/ ^m2 per side. It was coated by a bar blade method and dried at 130°C to obtain heat seal paper.

"Example 2"
Heat seal paper was obtained in the same manner as in Example 1 except that the drying temperature was 110°C.
"Example 3"
Heat seal paper was obtained in the same manner as in Example 1 except that the drying temperature was 105°C.
“Comparative Example 1”
Heat seal paper was obtained in the same manner as in Example 1 except that the drying temperature was 160°C.

(Evaluation method)
The obtained heat seal paper was evaluated as shown below. The results are shown in Table 1.
<Porosity>
The surface of the heat seal layer was imaged using an electron microscope (HITACHI, FlexSEM 1000) at a magnification of 1000 times. FIG. 1 shows electron microscope images of the heat seal papers obtained in Example 1 and Comparative Example 1.
Using an image analysis program (Hakutosha, ImagePro), perform black-and-white binarization processing on an arbitrary 8000 μm ² area of the obtained image with brightness 50, contrast 50, and dark color 0 to 50. The area of the void area) was determined, and the porosity was calculated from the ratio of the void area to the total area subjected to image analysis, as shown in the formula below.
Porosity (%) = Total void area (μm ² )
/Total area where image analysis was performed (μm ² ) x 100

<Heat seal suitability evaluation>
Two square test pieces with a side of 100 mm were cut out from the obtained coated paper, and the coating layers were brought into contact with each other, and the pressure was applied at a temperature of 130°C, a pressure of 2 kgf/cm ² , and a time of 0.5 seconds. It was heat sealed.
When the heat-sealed test piece was peeled off by hand, the peeled portion was visually observed, and heat-sealing suitability was evaluated based on the following criteria. If the evaluation is 〇△, there is no problem in practical use.
[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.

<Heat seal layer adhesion evaluation>
A 5×6 cm test piece is cut out from the obtained coated paper, and the coated surface is brought into contact with water and applied to vinyl tape (NITTO TAPE).
[Evaluation criteria]
○: The heat seal layer is not transferred to the tape.
×: The heat seal layer is transferred to the tape.

Claims

A heat-sealable coating layer containing PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)) and an adhesive is provided on at least one surface of the paper base material,
A heat-sealing paper characterized in that the heat-sealing coating layer is a semi-formed film.
The heat-sealable coating layer contains 10 parts by weight or more and 50 parts by weight or less of an adhesive based on 100 parts by weight of PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)). The heat seal paper according to claim 1, characterized in that:
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.