Heat seal paper

Abstract

To provide heat seal paper which has a heat seal layer containing PHBH on one outermost surface, and has excellent heat sealability to the other surface.SOLUTION: Heat seal paper has a paper base material, a heat seal layer containing PHBH on one outermost surface, and an auxiliary coating layer containing an ethylene-vinyl acetate copolymer or a polyester resin on the other outermost surface.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to heat-sealing paper having a heat-sealing layer containing PHBH.

Background Art

[0002] In recent years, movements have started to prevent environmental destruction caused by plastic waste, and it has been demanded to replace plastic disposable products with materials that have a small environmental impact. Examples of alternative materials for plastics include biodegradable plastics, wood, paper, and the like. As biodegradable plastics, aliphatic polyesters such as polylactic acid and polycaprolactone are known. However, aliphatic polyesters have a problem in that biodegradation takes a long time at low temperatures and the degradation rate is slow in natural environments such as the ocean.

[0003] Poly(3-hydroxybutyrate)-based resins are thermoplastic plastics produced by microorganisms that are excellent in degradability under aerobic and anaerobic conditions, and have a remarkable performance of being degraded by microorganisms in a short period of time even in water such as in the ocean. And poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (hereinafter also referred to as PHBH), which is a copolymer of 3-hydroxybutyrate and 3-hydroxyhexanoate, has attracted attention in terms of its biodegradability, resin physical properties, and the like.

[0004] Patent Document 1 proposes a coated paper having a coating layer containing PHBH and an adhesive on at least one surface of a paper substrate, and having a solid content mass ratio of PHBH and the adhesive in the coating layer of 99.9 / 0.1 to 60.0 / 40.0, and being free from coating defects, and being described as being usable as heat-sealing paper, water-resistant paper, oil-resistant paper, and the like. Patent Document 2 proposes a heat-sealing paper having excellent adhesion, in which a heat-sealing layer made of a film mainly composed of PHBH is laminated on at least one surface of a paper substrate via an anchor layer, and the anchor layer is a coating layer containing a polyester-based resin having a glass transition temperature of -25 to 46°C.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Heat-sealing paper having a heat-sealing layer containing PHBH can firmly heat-seal the heat-sealing layers together. However, when heat-sealing a heat-sealing paper having a heat-sealing layer containing PHBH on one side and a paper surface where the paper base material is exposed on the other side, the heat-sealability between the heat-sealing layer and the paper surface is inferior, and it has been found that adhesion failure is likely to occur. For example, when heat-sealing paper by rolling it to form the body of a paper cup and heat-sealing one side and the other side, such adhesion failure is fatal for the paper cup. The present invention has been studied based on such a background, and an object thereof is to provide heat-sealing paper having a heat-sealing layer containing PHBH on one outermost surface and excellent heat-sealability with the other surface.

Means for Solving the Problems

[0007] Means for solving the problems of the present invention are as follows. 1. A heat-sealing paper characterized by having a paper base material and a heat-sealing layer containing PHBH on one outermost surface, and having an auxiliary coating layer containing an ethylene-vinyl acetate copolymer or a polyester resin on the other outermost surface. 2. The heat-sealing paper according to 1., characterized in that the glass transition temperature of the ethylene-vinyl acetate copolymer is -25°C or higher and 20°C or lower. 3. The heat-sealing paper according to 1. or 2., characterized in that the molar ratio of ethylene to vinyl acetate in the ethylene-vinyl acetate copolymer is 30:70 to 1:99. 4. The hot tack peel distance at 180 °C, 0.2 MPa (20.0 N / cm 2 ) and 1 second is less than 300 mm. The heat-sealing paper according to any one of 1. to 3. 5. When heat-sealed under the conditions of 160 °C, 0.2 MPa (20.0 N / cm 2 ) and 1 second, and peeled at a peeling speed of 200 mm / min in a T-shape, the peeling strength is 6.0 N / 15 mm or more. The heat-sealing paper according to any one of 1. to 4. 6. When heat-sealed under the conditions of 0.2 MPa (20.0 N / cm 2 ) and 1 second, and peeled at a peeling speed of 200 mm / min in a T-shape, the material break critical temperature is 150 °C or less. The heat-sealing paper according to any one of 1. to 5. 7. A package having the heat-sealing paper according to any one of 1. to 6.

Advantages of the Invention

[0008] The heat-sealing paper of the present invention has a heat-sealing layer containing PHBH on one outermost surface, and this heat-sealing layer can be firmly heat-sealed to the other surface. Since the heat-sealing surfaces of the heat-sealing paper of the present invention do not need to be heat-fused to each other, processing into a cylindrical shape, a bag shape, etc. is easy. The heat-sealing paper of the present invention has a high ratio of biodegradable materials and can be rapidly decomposed even if it flows out into the environment.

Embodiments for Carrying Out the Invention

[0009] The heat-sealing paper of the present invention has a paper base material, a heat-sealing layer containing PHBH on one outermost surface, and an auxiliary coating layer containing an ethylene-vinyl acetate copolymer or a polyester resin on the other outermost surface. The heat-sealable paper of the present invention only needs to have a heat-sealable layer on one outermost surface and an auxiliary coating layer on the other outermost surface, and may also have other layers such as an anchor layer, a water vapor barrier layer, a gas barrier layer, or an ink-receiving layer between the paper substrate and the heat-sealable layer, or between the paper substrate and the auxiliary coating layer. In this specification, the expression "A to B" (A and B are numerical values or ratios) means a numerical range including A and B.

[0010] (Paper base material) The paper base material is a sheet made mainly of pulp, and is obtained by papermaking a paper stock containing fillers, various auxiliaries, etc. Examples of pulp include chemical pulps such as bleached hardwood kraft pulp (LBKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), unbleached softwood pulp (NUKP), sulfite pulp, and other such pulps; 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, and the like. One or more of these can be used in combination. Among these, chemical pulp made from wood fiber or mechanical pulp made from wood fiber is preferred, with chemical pulp made from wood fiber being more preferred, for reasons such as the reduced likelihood of foreign matter being mixed into the paper base, the reduced likelihood of discoloration over time when recycled as recycled paper, and the high whiteness that results in a favorable surface appearance during printing, making the paper particularly valuable when used as a packaging material. Specifically, the blending amount of wood fiber chemical pulp such as LBKP or NBKP relative to the total pulp is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and most preferably 100% by mass.

[0011] As fillers, known fillers such as inorganic fillers like 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, calcium sulfate, etc., and organic fillers like urea-formalin resin, polystyrene resin, phenolic resin, micro hollow particles, etc. can be used. Note that the filler is not an essential material and may not be used.

[0012] Examples of various auxiliaries include sizing agents such as rosin, alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), polyacrylamide-based polymers, polyvinyl alcohol-based polymers, cationized starch, various modified starches, dry paper strength enhancers such as urea-formalin resin, melamine-formalin resin, wet paper strength enhancers, retention aids, drainage improvers, coagulants, sulfate bands, bulking agents, dyes, fluorescent brighteners, pH adjusters, defoamers, ultraviolet inhibitors, anti-fading agents, pitch control agents, slime control agents, etc., and they can be appropriately selected and used as needed.

[0013] The surface of the paper base material may be treated with various chemicals. Examples of the chemicals include oxidized starch, hydroxyethyl etherified starch, enzyme-modified starch, polyacrylamide, polyvinyl alcohol, surface sizing agent, water resistance agent, water retention agent, thickening agent, lubricant, etc., and these can be used alone or in combination of two or more. Furthermore, these various chemicals and pigments may be used in combination. As pigments, 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, silicate, colloidal silica, satin white, etc., and organic pigments such as solid type, hollow type, or core-shell type, etc. can be used alone or in combination of two or more.

[0014] The basis weight of the paper substrate can be appropriately selected according to various desired qualities, its uses, etc., but usually it is 20 g / m 2 or more and 600 g / m 2 or less, preferably 25 g / m 2 or more and 600 g / m 2 or less. When used for packaging materials such as wrapping paper, paper bags, lid materials, lining paper, liquid paper containers such as milk cartons, and posters used outdoors, the basis weight of the paper substrate is 20 g / m 2 or more and 350 g / m 2 or less, preferably. When used as a flexible packaging material, the basis weight of the paper substrate is 20 g / m 2 or more and 100 g / m 2 or less, preferably 20 g / m 2 or more and 80 g / m 2 or less. Note that the flexible packaging material is a packaging material made of relatively thin paper in the range of 20 g / m 2 to 100 g / m 2 and is rich in flexibility. When used for paper cups, paper containers, cardboard boxes, paper plates, paper trays, etc., the basis weight of the paper substrate is 150 g / m 2 or more and 300 g / m 2 or less, preferably. Also, the density of the paper substrate can be appropriately selected according to various desired qualities, handling properties, etc., but usually it is 0.5 g / cm 3 or more and 1.0 g / cm 3 or less, preferably.

[0015] The manufacturing (paper-making) method of the paper substrate is not particularly limited, and known manufacturing (paper-making) methods and paper-making machines such as Fourdrinier paper machines, cylinder mould paper machines, twin-wire paper machines such as short-former paper machines, gap former type, hybrid former type (on-top former type), etc. can be selected. Also, the pH during paper-making can be in any of the acidic region (acidic papermaking), pseudo-neutral region (pseudo-neutral papermaking), neutral region (neutral papermaking), and alkaline region (alkaline papermaking). After papermaking in the acidic region, an alkaline agent may be applied to the surface of the paper layer. Also, the paper substrate may be a single layer or may be composed of multiple layers of two or more layers. In addition, when treating the surface of the paper substrate with a chemical agent, the surface treatment method is not particularly limited, and known coating apparatuses such as a rod metering size press, a pond size press, a gate roll coater, a spray coater, a blade coater, and a curtain coater can be used.

[0016] (Auxiliary coating layer) The heat-sealing paper of the present invention has an auxiliary coating layer on the other outermost surface which is the surface opposite to the heat-sealing layer. The auxiliary coating layer contains an ethylene vinyl acetate copolymer or a polyester resin. Note that the ethylene vinyl acetate copolymer and the polyester resin can also be used in combination.

[0017] <Ethylene vinyl acetate copolymer> An ethylene vinyl acetate copolymer (hereinafter also referred to as EVA) is a copolymer having ethylene and vinyl acetate as monomers, and may further have other monomers as monomers. When EVA has other monomers as monomers, the content of the structural units derived from the other monomers with respect to the whole EVA is preferably 30% by mass or less. This content is not particularly limited as long as the effects of the present invention are not impaired, and can be, for example, 20% by mass or less, 10% by mass or less, 5% by mass or less, 3% by mass or less, 1% by mass or less, etc.

[0018] From the viewpoint of heat-sealing strength, the glass transition temperature of EVA is preferably -25 to 20°C. This glass transition temperature is more preferably -23°C or higher, further preferably -20°C or higher, and more preferably 16°C or lower, further preferably 12°C or lower. In the present specification, the glass transition temperature means the midpoint glass transition temperature measured in accordance with JIS K 7121-1987. From the viewpoint of heat-sealing strength, the molar ratio of ethylene to vinyl acetate in EVA (the structural units derived from ethylene: the structural units derived from vinyl acetate, also expressed as ethylene: vinyl acetate, and the total is 100) is preferably 30:70 to 1:99. This molar ratio is more preferably 25:75 to 5:95, and further preferably 20:80 to 10:90.

[0019] <Polyester resin> As the polyester resin, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), etc. can also be used. However, due to its biodegradability, aliphatic polyester resins such as polycaprolactone, polybutylene succinate adipate, polybutylene succinate, and polylactic acid, and aliphatic aromatic polyester resins such as polybutylene adipate terephthalate and polybutylene azelate terephthalate are preferred, and polylactic acid is more preferred.

[0020] In addition to EVA or polyester resin, the auxiliary coating layer can contain other water-soluble resins and water-dispersible resins. Furthermore, if necessary, it can contain various auxiliaries formulated in the coating liquid in the paper-making field, such as dispersants, viscosity improvers, water retention agents, defoamers, waterproofing agents, pH adjusters, cationic resins, anionic resins, ultraviolet absorbers, metal salts, lubricants, coloring dyes, and pigments. However, the auxiliary coating layer preferably contains EVA or polyester resin as the main component, and the total amount of EVA and polyester resin with respect to the entire auxiliary coating layer (solid content) is preferably 70% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, even more preferably 98% by mass or more, and even more preferably 99% by mass or more.

[0021] (Heat seal layer) The heat seal layer is located on one of the outermost surfaces of the heat seal paper. Note that the heat seal layer may be a coating layer or a laminate layer. The heat-sealing layer contains PHBH as a thermoplastic resin. The heat-sealing layer can also contain other thermoplastic resins, but the proportion of PHBH in all the thermoplastic resins contained in the heat-sealing layer is preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, even more preferably 99% by mass or more, and most preferably 100% by mass. When the heat-sealing layer contains other thermoplastic resins, the other thermoplastic resins are preferably biodegradable resins such as aliphatic polyester resins such as polycaprolactone, polybutylene succinate adipate, polybutylene succinate, and polylactic acid, and aliphatic aromatic polyester resins such as polybutylene adipate terephthalate and polybutylene azelate terephthalate.

[0022] <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 environmental impact.

[0023] Microorganisms that produce PHBH are not particularly limited as long as they accumulate 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, strains such as Aeromonas caviae, and Alcaligenes eutrophus AC32, into which genes encoding PHA synthases have been introduced (Accession No. FERM BP-6038, date of deposit on 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)), are particularly preferred in terms of PHBH productivity. 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 allow PHBH to accumulate 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.

[0024] 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 the 3HB homopolymer, losing flexibility and having too high a film-forming processing temperature, which is not preferable. When the composition of 3HH exceeds 25 mol%, the crystallization rate becomes too slow, making it unsuitable for film-forming processing. Also, due to the decrease in crystallinity, the resin tends to become flexible and the flexural modulus decreases. The composition ratio of PHBH can be measured by NMR analysis of the powder obtained by centrifuging the aqueous dispersion and then drying it. Microbially produced PHBH is a random copolymer. To adjust the molar ratio of the copolymer, there are methods such as selection of the bacterial strain, selection of the carbon source as the raw material, blending with PHBH of different molar ratios, and blending with the 3HB homopolymer.

[0025] The mass average molecular weight of PHBH is preferably 50,000 to 1,500,000. When the mass average molecular weight of PHBH is within this range, film formation at a low temperature is possible when coating PHBH, and a film with excellent mechanical properties can be obtained when laminating PHBH. The mass average molecular weight of PHBH is more preferably 100,000 to 500,000, and even more preferably 150,000 to 450,000. The mass average molecular weight of PHBH can be determined as the molecular weight in terms of polystyrene 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.) for the column and chloroform as the mobile phase. As the sample for measurement, the powder obtained by centrifuging the aqueous dispersion containing PHBH and then drying it is used.

[0026] The average particle size of PHBH is preferably 0.1 to 50 μm. PHBH with an average particle size of less than 0.1 μm is difficult to produce by microbial production, and even when obtained by chemical synthesis, a microparticulation process is required. If the average particle size exceeds 50 μm, uneven coating may occur on the surface when a coating liquid containing PHBH is applied. The average particle size of PHBH is more preferably 0.5 to 10 μm. The average particle size of PHBH refers to the particle size corresponding to 50% of the accumulated amount of all particles in 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 (Nikkiso, FRA).

[0027] (coating layer) When the heat seal layer is a coating layer, it preferably contains an inorganic pigment and an adhesive. The coating layer may be a single layer or multiple layers. When the coating layer is multi-layered, the number of layers is preferably three or less, and more preferably two. When the coating layer is multi-layered, it is preferable that the coating layer located on the paper layer side contains an inorganic pigment in order to improve heat seal strength. On the other hand, it is preferable that the coating layer located farther from the paper layer does not contain an inorganic pigment or contains a smaller amount of inorganic pigment than the coating layer located on the paper layer side in order to achieve both water resistance and oil resistance.

[0028] <Inorganic pigments> As the inorganic pigment, any inorganic pigment used for coating paper can be used without any particular limitation, and examples thereof include kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, bentonite, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, satin white, etc., and one or more of these can be used. Among these, one or more of kaolin, heavy calcium carbonate, light calcium carbonate, mica, talc, and bentonite are preferred.

[0029] From the viewpoint of coating layer fixation, the inorganic pigment preferably has a 50% volume average particle size (D50) (hereinafter also referred to as "average particle size") of 6.0 μm or less, as measured by laser diffraction / scattering. Examples of measuring devices for the laser diffraction / scattering method include the particle size distribution measuring device "Partica" from Horiba, Ltd. and the particle size distribution measuring device "MASTER SIZER S" from Malvern Instruments. From the viewpoint of coating layer fixation, the average particle size of the inorganic pigment is more preferably 5.0 μm or less, even more preferably 4.0 μm or less, even more preferably 3.0 μm or less, and even more preferably 2.0 μm or less. There is no particular lower limit for the average particle size of the inorganic pigment, but from the viewpoint of dispersibility and the like, it is, for example, preferably 0.1 μm or more, and more preferably 0.2 μm or more. When two or more inorganic pigments are contained, it is preferable that the average particle diameter of at least one of the inorganic pigments is within the above-mentioned numerical range, and the proportion of the inorganic pigments satisfying this average particle diameter relative to the total inorganic pigments is preferably 50% by mass or more, and more preferably 70% by mass or more.

[0030] Furthermore, from the viewpoint of oil resistance and water resistance when a second coating layer is provided on the coating layer, the average particle size of the inorganic pigment contained in the coating layer is preferably 8.0 μm or less. From the viewpoint of oil resistance and water resistance when a second coating layer is provided, the average particle size of the inorganic pigment contained in the coating layer is more preferably 7.0 μm or less, even more preferably 6.0 μm or less, even more preferably 5.0 μm or less, even more preferably 4.0 μm or less, even more preferably 3.0 μm or less, and even more preferably 2.0 μm or less. There is no particular lower limit for the average particle size of the inorganic pigment contained in the coating layer, but from the viewpoint of dispersibility, for example, it is preferably 0.1 μm or more, more preferably 0.2 μm or more. When the coating layer contains two or more inorganic pigments, it is preferable that the average particle size of at least one of the inorganic pigments is within the above-mentioned numerical range, and the proportion of the inorganic pigments satisfying this average particle size relative to the total inorganic pigments contained in the coating layer is preferably 50 mass% or more, more preferably 70 mass% or more.

[0031] Inorganic pigments preferably have an aspect ratio of 60 or less in terms of oil resistance and water resistance when a second coating layer is applied on top of the coating layer. The aspect ratio can be calculated using measurements from a particle size analyzer using the calculation method described in "Basic Research on the Relationship between Coating Pigment Properties and Coated Paper Quality" in Vol. 65, No. 12, of the Journal of the Japan Paper and Pulp Technology Association. The aspect ratio of inorganic pigments contained in the coating layer is preferably 40 or less, even more preferably 30 or less, even more preferably 25 or less, and even more preferably 20 or less. There is no particular lower limit for the aspect ratio of inorganic pigments contained in the coating layer. When a coating layer contains two or more inorganic pigments, it is preferable that the aspect ratio of at least one of the inorganic pigments is within the above-mentioned numerical range. The proportion of inorganic pigments satisfying this aspect ratio relative to the total inorganic pigments contained in the coating layer is preferably 50% by mass or more, and more preferably 70% by mass or more.

[0032] The solids mass ratio of PHBH to inorganic pigment in the coating layer (PHBH:inorganic pigment, total 100) is preferably 90:10 to 0.01:99.99. Adding an inorganic pigment to a coating solution containing PHBH and an adhesive improves the adhesion of the resulting coating layer. While the mechanism is unclear, the inventors speculate that this is because inorganic pigments have better thermal conductivity than organic PHBH and adhesives, so the inorganic pigments heat up quickly when heated, and this heat is transferred from the inorganic pigment to the PHBH, thereby sufficiently heating the PHBH.

[0033] The solid mass ratio of PHBH to inorganic pigment (PHBH:inorganic pigment, total 100) is more preferably 70:30 to 1:99, even more preferably 60:40 to 2:98, and even more preferably 50:50 to 3:97, from the viewpoint of fixation of the coating layer. Also, from the viewpoint of heat seal strength when a second coating layer is provided on the coating layer, the solid content mass ratio of PHBH to inorganic pigment in the coating layer (PHBH:inorganic pigment, total is 100) is more preferably 90:10 to 5:95, further preferably 80:20 to 10:90, still further preferably 70:30 to 10:90, still further preferably 65:35 to 10:90, still further preferably 60:40 to 15:85, and still further preferably 50:50 to 25:75. In particular, when the average particle diameter of the inorganic pigment contained in the coating layer exceeds 8.0 μm, from the viewpoints of oil resistance and water resistance, the solid content mass ratio of PHBH to inorganic pigment (PHBH:inorganic pigment, total is 100) is more preferably 90:10 to 40:60, and further preferably 90:10 to 50:50. The ratio of the total of PHBH and inorganic pigment to the total solid content of the coating layer is preferably 60% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more.

[0034] <Adhesive> The adhesive is for adhering PHBH, inorganic pigment, paper substrate, etc. By including the adhesive in the heat seal layer, it becomes easy to obtain a uniform heat seal layer in which coating defects such as cracks and pinholes are suppressed. The adhesive can be used without particular limitation as long as it can be dissolved or dispersed in water and can adhere PHBH, inorganic pigments, paper substrates, etc. 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, starches such as oxidized starch, etherified starch, esterified starch, cellulose derivatives such as hydroxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, acetyl cellulose, 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. can be mentioned, and one or more of these can be appropriately selected and used.

[0035] Among these, it is preferable to contain at least one selected from the group consisting of polyvinyl alcohols, starches, cellulose derivatives, partially saponified ethylene-vinyl acetate copolymer, styrene-butadiene copolymer latex, conjugated diene polymer latex of methyl methacrylate-butadiene copolymer, and acrylic polymer latex, and it is more preferable to consist of at least one selected from this group. Also, because of its biodegradability, it is more preferable to contain at least one selected from the group consisting of polyvinyl alcohols, starches, cellulose derivatives, and partially saponified ethylene-vinyl acetate copolymer, and it is even more preferable to contain at least one selected from the group consisting of fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, and partially saponified ethylene-vinyl acetate copolymer.

[0036] From the viewpoint of the fixability to the paper substrate, it is preferable to contain at least one of fully saponified polyvinyl alcohol and partially saponified polyvinyl alcohol as the adhesive. Since it has excellent coating layer strength, it is more preferable to contain a partially saponified polyvinyl alcohol having a saponification degree of 70 mol% or more and 95 mol% or less. The saponification degree of the partially saponified polyvinyl alcohol is preferably 75 mol% or more, more preferably 78 mol% or more, still more preferably 85 mol% or more, and preferably 93 mol% or less, more preferably 90 mol% or less. Here, PHBH is water-dispersible, while fully saponified polyvinyl alcohol and partially saponified polyvinyl alcohol are water-soluble. Therefore, when using fully saponified polyvinyl alcohol or partially saponified polyvinyl alcohol as the adhesive, as the degree of polymerization increases, the coating liquid thickens, and the handleability and coatability may decrease. Therefore, the degree of polymerization of fully saponified polyvinyl alcohol and partially saponified polyvinyl alcohol is preferably 2000 or less, more preferably 1500 or less, and still more preferably 1000 or less.

[0037] Also, from the viewpoint of the water resistance of the coating layer, it is preferable to contain a partially saponified ethylene-vinyl acetate copolymer as the adhesive, and it is more preferable to be composed of a partially saponified ethylene-vinyl acetate copolymer.

[0038] The ratio of the adhesive to the total solid content of the coating layer is preferably 0.1 to 40% by mass. If the adhesive is less than 0.1% by mass, almost no effect of improving the fixability by the adhesive can be expected. If it exceeds 40% by mass, there may be too much adhesive and the performance derived from PHBH cannot be fully exhibited. Also, since the water resistance decreases, it is not preferable depending on the use of the coated paper. The ratio of the adhesive to the total solid content of the coating layer is more preferably 1% by mass or more, still more preferably 3% by mass or more, even more preferably 5% by mass or more, and more preferably 30% by mass or less, still more preferably 25% by mass or less, and even more preferably 20% by mass or less.

[0039] (Second coating layer) In the coated paper of the present invention, a second coating layer containing PHBH can be formed on the coating layer. By forming the second coating layer on the coating layer containing an inorganic pigment, the heat seal strength is improved. Although the mechanism is unclear, the inventors of the present invention presume that the coating layer containing an inorganic pigment takes a short time to reach a high temperature, and the second coating layer is exposed to a high temperature for a longer time during the heat fusion process.

[0040] The second coating layer can contain those equivalent except for the range of the above-mentioned PHBH and the mass average molecular weight. The PHBH in the second coating layer preferably has a mass average molecular weight of 50,000 to 1,500,000. The PHBH in the second coating layer preferably has a larger mass average molecular weight than the PHBH in the coating layer. Although PHBH has a smaller MFR and requires a higher temperature for heat seal processing as the molecular weight increases, when there is a coating layer containing an inorganic pigment between the second coating layer and the paper substrate on which it is coated, the coating layer can efficiently transfer the heat received by the paper substrate to the second coating layer due to the excellent thermal conductivity of the inorganic pigment formulation. Therefore, as a result, since the second coating layer is excellent in heat sealability, high molecular weight PHBH can also be preferably used. And by the second coating layer containing PHBH with a large mass average molecular weight, properties such as oil resistance and water resistance derived from PHBH can be more exerted. From the viewpoints of oil resistance and water resistance, it is preferable that the second coating layer does not contain an inorganic pigment or has a smaller amount of inorganic pigment formulation than the coating layer. The amount of inorganic pigment formulation relative to the total solid content is preferably at least 1% by mass less than that of the coating layer, more preferably at least 3% by mass less, and even more preferably at least 5% by mass less.

[0041] The second coating layer preferably contains 50% by mass or more of PHBH, more preferably 70% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, and even more preferably 99% by mass or more. In addition to PHBH, the second coating layer may optionally contain various auxiliaries that are blended into coating solutions in the papermaking field, such as other biodegradable resins (e.g., polybutylene succinate, polycaprolactone, polylactic acid), the adhesives described above, inorganic pigments, dispersants, viscosity modifiers, water retention agents, defoamers, water-resistant agents, fluorescent dyes, coloring dyes, coloring pigments, surfactants, pH adjusters, cationic resins, anionic resins, UV absorbers, and metal salts.

[0042] (laminate layer) When the heat seal layer is a laminate layer, the heat seal layer may contain, in addition to PHBH, other thermoplastic resins, lubricants, inorganic fillers, plasticizers, antiblocking agents, odor absorbers, fragrances, antioxidants, weather resistance improvers, UV absorbers, crystal nucleating agents, release agents, water repellents, antibacterial agents, sliding property improvers, colorants such as pigments and dyes, etc. However, the proportion of PHBH in the entire heat seal layer, which is the laminate layer, is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, and even more preferably 99% by mass or more.

[0043] As the lubricant, known lubricants can be used, and examples thereof include saturated or unsaturated fatty acid amides such as lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, oleic acid amide, and erucic acid amide; aliphatic amide compounds such as alkylene fatty acid amides such as methylene bisstearic acid amide and methylene bisstearic acid amide; and pentaerythritol. The blending amount of the lubricant is preferably 0.1 to 2 parts by mass, more preferably 0.2 to 1 part by mass, per 100 parts by mass of PHBH.

[0044] Examples of the inorganic filler include talc, calcium carbonate, mica, silica, clay, kaolin, titanium oxide, alumina, zeolite, etc. having an average particle diameter of 0.5 μm or more. The compounding amount of the inorganic filler is preferably 0.5 to 5 parts by mass, more preferably 1 to 3 parts by mass, based on 100 parts by mass of PHBH.

[0045] (Anchor layer) When the heat seal layer is a laminate layer, it is preferable to have an anchor layer between the paper base material and the heat seal layer from the viewpoint of adhesion. The anchor layer is preferably a coating layer containing one or more thermoplastic resins selected from the group consisting of polyethyleneimine-based, styrene-acrylic-based, acrylic-based, polyester-based, and ethylene-vinyl acetate-based copolymer (EVA), and more preferably a coating layer containing a polyester-based resin having a glass transition temperature of -25 to 46°C or an EVA having a glass transition temperature of -50 to 30°C.

[0046] In addition to the above-mentioned thermoplastic resins, the anchor layer can contain other water-soluble resins and water-dispersible resins, and further, if necessary, various auxiliaries formulated in the coating liquid in the paper-making field, such as dispersants, viscosity improvers, water retention agents, defoaming agents, waterproofing agents, pH adjusters, cationic resins, anionic resins, ultraviolet absorbers, metal salts, lubricants, coloring dyes, pigments, etc. However, the anchor layer preferably contains a thermoplastic resin as the main component, and the proportion of the thermoplastic resin in the entire anchor layer (solid content) is preferably 70% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, still more preferably 98% by mass or more, and most preferably 99% by mass or more.

[0047] (Manufacturing method) The heat seal layer of the present invention can be produced by a conventionally known coating method or lamination method. For example, coating devices include blade coaters, bar coaters, roll coaters, air knife coaters, reverse roll coaters, curtain coaters, spray coaters, size press coaters, and gate roll coaters. Examples of coating systems include aqueous coating using a solvent such as water, and solvent coating using a solvent such as an organic solvent, with aqueous coating being preferred. The lamination method may be either dry lamination or extrusion lamination.

[0048] When the heat seal layer is a coating layer, the coating weight (when it consists of multiple coating layers or when a second coating layer is present, this refers to the total coating weight) is 1 g / m2 in dry mass. 2 More than 50g / m 2 The coating weight is preferably 1 g / m or less. 2 If the coating density is less than 50 g / m, it may be difficult to form a coating layer, and heat sealing properties may not be exhibited. 2 If the amount is more than this, the drying load during coating will increase. The coating amount of the coating layer is 3 g / m 2 More preferably, 5 g / m 2 More preferably, 40 g / m 2 Less than 30 g / m is more preferable. 2 The following is even more preferred:

[0049] When the heat-sealing layer is a laminate layer, its thickness is preferably 5 μm or more and 300 μm or less. If the thickness of the heat-sealing layer is less than 5 μm, the heat-sealing property may not be fully exhibited. If the thickness of the heat-sealing layer is more than 300 μm, the heat-sealing layer may become too rigid, which may reduce the processability as heat-sealing paper and increase the cost. The thickness of the heat-sealing layer is preferably 10 μm or more, more preferably 20 μm or more, and preferably 200 μm or less, more preferably 100 μm or less, and even more preferably 60 μm or less.

[0050] The coating weight of the auxiliary coating layer is 0.3 g / m2 in dry weight. 2 It is preferably 20 g / m or less. When the coating amount of the auxiliary coating layer is less than 0.3 g / m 2 , the effect of improving the heat sealability by the auxiliary coating layer may hardly be expected. On the other hand, when it is more than 20 g / m 2 , the drying load during coating increases. The coating amount of the auxiliary coating layer is more preferably 1 g / m 2 or more, still more preferably 3 g / m 2 or more, even more preferably 15 g / m 2 or less, more preferably 10 g / m 2 or less, still more preferably 5 g / m 2 or less, and even more preferably less than or equal to 5 g / m 2 is even more preferably less than or equal to 5 g / m.

[0051] · Heat-sealing paper The heat-sealing paper of the present invention is obtained by heat-sealing a heat-sealing layer and an auxiliary coating layer at 180 °C, 0.2 MPa (20.0 N / cm 2 ), for 1 second, and when peeled with a weight of 30 g, the hot tack peel distance is preferably less than 300 mm. The hot tack peel distance is the peel distance immediately after heat-sealing (within 1 second), and the smaller the value, the stronger the adhesion immediately after heat-sealing. For this hot tack peel distance of the heat-sealing paper of the present invention, it is more preferably 200 mm or less, still more preferably 100 mm or less, even more preferably 80 mm or less, even more preferably 60 mm or less, and even more preferably 40 mm or less.

[0052] The heat-sealing paper of the present invention is obtained by heat-sealing a heat-sealing layer and an auxiliary coating layer at 160 °C, 0.2 MPa (20.0 N / cm 2 ) It is preferable that the one heat-sealed under the condition of 1 second is left standing in an environment of 23°C and 50% humidity for 24 hours, and the peel strength when peeled at a peel rate of 200 mm / min in a T shape is 6.0 N / 15 mm or more. This peel strength is more preferably 6.4 N / 15 mm or more, further preferably 6.8 N / 15 mm or more, still further preferably 7.2 N / 15 mm or more, even still further preferably 7.6 N / 15 mm or more, even still further preferably 8.0 N / 15 mm or more, even still further preferably 8.4 N / 15 mm or more, even still further preferably 8.8 N / 15 mm or more, and even still further preferably 9.2 N / 15 mm or more.

[0053] The heat-sealing paper of the present invention preferably has a material break critical temperature of 150°C or lower. The material break critical temperature refers to the lowest heat-sealing temperature at which the heat-sealing layer and the auxiliary coating layer are heat-sealed at various temperatures under 0.2 MPa (20.0 N / cm 2 ) and peeled at a peel rate of 200 mm / min in a T shape, and material break (destruction of the paper base material) occurs. For example, when the one heat-sealed at 150°C undergoes material break, the material break critical temperature is 150°C or lower. The lower the material break critical temperature, the more possible low-temperature heat-sealing is. The material break critical temperature is more preferably 145°C or lower, and further preferably 140°C or lower.

[0054] The heat-sealing paper of the present invention is easy to heat-seal and can be suitably used for packaging applications. Since the heat-sealing paper of the present invention can firmly attach one surface to the other surface, it is particularly suitable for packaging applications such as tubular and bag-shaped ones in which one surface is bonded to multiple surfaces. Note that the tubular shape includes frustum shapes such as cup shapes.

Examples

[0055] Examples are given below to specifically describe the present invention, but the present invention is of course not limited to these examples. Unless otherwise specified, parts and % in the examples indicate parts by mass and mass %, respectively.

[0056] (Evaluation method) ·Hot tack peel distance The hot tack peel distance was measured using a heat seal tester (TP-701-B, manufactured by Tester Sangyo Co., Ltd.) and a hot tack property measuring jig (TP-704, manufactured by Tester Sangyo Co., Ltd.). Two sheets of heat seal paper cut to a length of 60 cm and a width of 4 cm were stacked so that the heat seal layer and the auxiliary coating layer faced each other, and then tested using a heat seal tester with a 30 cm long, 1 cm wide seal bar at 180°C and 0.2 MPa (20.0 N / cm 2 The heat seal was applied for 1 second at 100°C, and the moment the seal bar separated (within 1 second of heat sealing), a 30g weight attached to each of the two sheets of heat seal paper was applied in the direction that caused the seal to peel. The distance the seal peeled was measured and used as the hot tack peel distance.

[0057] Peel strength The test was conducted in accordance with JIS Z1707:2019 7.4 "Heat seal strength test." Two square test pieces, each 100 mm on a side, were cut out from the obtained heat seal paper, and the heat seal layer and the auxiliary coating layer were brought into contact with each other. The test pieces were then pressed at a temperature of 130°C to 160°C and a pressure of 0.2 MPa (20.0 N / cm). 2 ), and heat-sealed for 1.0 second, then left to stand in an environment of 23°C and 50% humidity for 24 hours. A measurement sample with a long side of 100 mm and a short side of 15 mm was then cut out from the heat-sealed 100 mm square test piece. The peeled long edge was then clamped between the upper and lower jigs of a vertical tensile testing machine (Tensilon, manufactured by A&D Co., Ltd.), and the peel strength, i.e., the heat seal strength, was measured while peeling the measurement sample (T-type) from the long edge side at a speed of 200 mm / min. The peeled surface was visually observed and evaluated according to the following criteria: ⊚ indicates that material destruction has occurred. ◎: The paper base is destroyed on 70% or more of the heat-sealed surface. Good: The paper base material is destroyed on 30% or more but less than 70% of the heat-sealed surface. △: The paper substrate is destroyed in less than 30% of the heat-sealed area. ×: Peels between the heat-sealing layer and the auxiliary coating layer.

[0058] (Material) Paper substrate: Nippon Paper Industries Co., Ltd., basis weight 220 g / m 2 of cup base paper, CUP-HD PHBH: Kaneka Corporation, mass average molecular weight 600,000 Inorganic pigment: Shiraishi Kogyo Co., Ltd., kaolin, KCS, average particle diameter 3.6 μm, aspect ratio 10 - 15 Adhesive: Kuraray Co., Ltd., 28-98, fully saponified PVA, saponification degree 98 mol%, degree of polymerization 1700

[0059] EVA1: Sumika Chemtex Corporation, S-408HQE, Tg -30°C, ethylene: vinyl acetate = 40:60 EVA2: Sumika Chemtex Corporation, S-410HQ, Tg -18°C, ethylene: vinyl acetate = 30:70 EVA3: Sumika Chemtex Corporation, S-401HQ, Tg -18°C, ethylene: vinyl acetate = 30:70 EVA4: Sumika Chemtex Corporation, S-400HQ, Tg 0°C, ethylene: vinyl acetate = 20:80 EVA5: Sumika Chemtex Corporation, S-355HQ, Tg 10°C, ethylene: vinyl acetate = 10:90 Polyester: polylactic acid-based A, Tg 56°C

[0060] Polyethyleneimine: Nippon Shokubai Co., Ltd., Epomin P1000 Modified polyolefin: Unitika Ltd., Arrow Base SA-1010 Styrene acrylic: Daiichi Paint Co., Ltd., Harbil HS-1 Ethylene (meth)acrylic: Mitsui Chemicals, Inc., Chem Pearl S500

[0061] (Formation of the heat-sealing layer (coating layer)) 30 parts by mass of PHBH, 70 parts by mass of inorganic pigment, and 10 parts by mass of adhesive were added, and further water was added and stirred to obtain an undercoating liquid with a solid content concentration of 40% by mass. 100 parts by mass of PHBH and 3 parts by mass of an adhesive were added, and further water was added and stirred to obtain a top coating liquid having a solid content concentration of 40% by mass. An undercoating liquid was applied onto one surface of a paper substrate at a dry mass of 7 g / m 2 by a bar blade method, and dried at 105°C for 1 minute. Further, a top coating liquid was applied onto the undercoating layer at a dry mass of 23 g / m 2 by a bar blade method, dried at 105°C for 1 minute, and then heat-treated at 160°C for 3 minutes to form a two-layer coating layer containing PHBH on one outermost surface of the paper substrate.

[0062] (Formation of auxiliary coating layer) An aqueous dispersion of 22% by mass concentration of each resin was prepared, applied by a bar blade method so as to have the coating amount (dry mass) shown in Table 1, and dried at 105°C for 1 minute to form an auxiliary coating layer.

[0063]

Table 1

[0064] (Formation of heat seal layer (laminate layer)) A coating liquid obtained by mixing PHBH and EVA4 at a dry mass ratio of 50:50 was applied at a dry coating amount of 3 g / m 2 to form an anchor layer, and PHBH was extruded onto the anchor layer to a thickness of 30 μm to form a laminate layer. (Formation of auxiliary coating layer) As Examples 13 to 17, auxiliary coating layers were formed in the same manner as in Examples 3, 4, 5, 7, and 9, respectively.

[0065]

Table 2

[0066] In Comparative Example 1 having no auxiliary coating layer, no adhesion was observed even at 160°, but in the heat-seal papers of Examples 1 to 12 having EVA-based and polyester-based auxiliary coating layers, the heat-seal layer containing PHBH and the auxiliary coating layer were firmly fused. A horizontal comparison of the peel strength and hot tack peel distance at 160°C showed that the auxiliary coating layer containing EVA and polyester with a Tg range of -18°C to 10°C was superior in peel strength and initial adhesive strength. 2 From the results of the peel strength at 140°C on the test pieces (Examples 4, 6, 8, 10, and 12), EVA had a higher peel strength than polyester. 2 In the test pieces (Examples 3, 5, 7, 9, and 11), EVA was superior overall in terms of peel strength and material failure evaluation. These results indicate that EVA is the best auxiliary coating layer and provides good peel strength even when the coating weight is slightly reduced. From an industrial perspective, there is a demand for heat-sealable paper formulations with more stable peel strength. It is believed that EVA can more reliably ensure the desired peel strength than polyester during the manufacturing process of heat-sealable paper, even if the coating weight fluctuates slightly. The same is true during the processing process, where a specified peel strength can be reliably ensured after processing. Furthermore, while the processing temperature is sometimes lowered for energy conservation reasons, a stable peel strength can be achieved even at low temperatures. In contrast, the heat seal papers of Comparative Examples 2 to 9, which had auxiliary coating layers using other resins, showed weak fusion between the heat seal layer containing PHBH and the auxiliary coating layer.

[0067] In Examples 13 to 17, in which the heat seal layer is a laminate layer, it was confirmed that the peel strength at 160°C was excellent, similar to Examples 3, 4, 5, 7, and 9. Even when the pressing temperature was lowered to 150°C, good peel strength and material failure evaluation were obtained. It is clear that Example 14 has better peel strength and material failure evaluation than Example 13, which has a smaller coating amount. From the results in Tables 1 and 2, it was confirmed that when a heat seal paper having a heat seal layer containing PHBH on one side formed by a water-based coating method or an extrusion lamination method is provided with an auxiliary coating layer containing EVA or polyester on the other side, good adhesion can be obtained when one side and the other side are heat sealed.< / phbh>

Claims

1. A heat-sealing paper having a paper base material and a heat-sealing layer containing PHBH on one outermost surface, and an auxiliary coating layer containing an ethylene-vinyl acetate copolymer or a polyester resin on the other outermost surface.

2. The heat-sealing paper according to Claim 1, wherein the glass transition temperature of the ethylene-vinyl acetate copolymer is -25°C or higher and 20°C or lower.

3. The heat-sealing paper according to Claim 1, wherein the molar ratio of ethylene to vinyl acetate in the ethylene-vinyl acetate copolymer (ethylene:vinyl acetate) is 30:70 to 1:

99.

4. 180 °C, 0.2 MPa (20.0 N / cm ２ ), The heat-sealing paper according to claim 1, characterized in that the hot tack peel distance at 1 second is less than 300 mm.

5. Heat-sealed under the conditions of 160°C, 0.2 MPa (20.0 N / cm ２ ), and 1 second, the heat-sealing paper according to claim 1, characterized in that when peeled in a T-shape at a peeling speed of 200 mm / min, the peeling strength is 6.0 N / 15 mm or more.

6. 0.2 MPa (20.0 N / cm ２ ), heat-sealed under the conditions of 1 second, has a material break critical temperature of 150°C or less when peeled in a T-shape at a peeling speed of 200 mm / min. The heat-sealing paper according to claim 1, characterized in that.

7. A package having the heat-sealing paper according to any one of Claims 1 to 6.

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