Coated paper

Abstract

To provide a coated paper having good heat sealability.SOLUTION: The coated paper has a coating layer containing PHBH (poly (3-hydroxybutyrate-co-3-hydroxyhexanoate)) and EVA (ethylene-vinyl acetate copolymer resin) on at least one surface of a paper base material and a second coating layer containing PHBH on the coating layer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to coated paper coated with a coating liquid containing PHBH. [Background technology]

[0002] In recent years, there has been a growing movement to prevent environmental destruction caused by plastic waste, and there is a demand to replace disposable plastic products with materials that have a lower environmental impact, such as biodegradable plastics, wood, and paper. Aliphatic polyesters such as polylactic acid and polycaprolactone are known as biodegradable plastics. However, aliphatic polyesters have the problem that they take a long time to biodegrade at low temperatures and decompose slowly in natural environments such as the ocean.

[0003] Poly(3-hydroxybutyrate) resins are microbially produced thermoplastics that are highly degradable under both aerobic and anaerobic conditions, and have the remarkable ability to be decomposed by microorganisms in a short period of time even in water, such as the ocean. Patent Document 1 describes that a biodegradable polyester aqueous dispersion containing poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (hereinafter also referred to as PHBH), which is a copolymer of 3-hydroxybutyrate and 3-hydroxyhexanoate, has excellent film-forming properties and gives a resin coating film that is flexible, stretches well, and is strong against bending when used in paints, adhesives, fiber processing, sheet / film processing, paper processing, etc. Patent Documents 2 and 3 describe that when PHBH is coated on the surface of a paper substrate, the fixation of PHBH to the surface of the paper substrate is improved by adding an adhesive to the coating liquid. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2004 / 041936 [Patent Document 2] Patent Publication No. 2021-195716 [Patent Document 3] Patent Publication No. 2021-195717 Summary of the Invention [Problem to be solved by the invention]

[0005] It is known that increasing the blending ratio of adhesive in the coating solution improves the adhesion of the coating layer to the paper substrate surface, but at the same time, the heat-sealing properties deteriorate due to the influence of the blending of adhesive (see the examples in Patent Documents 2 and 3). This is thought to be because the adhesive (PVA or starch) in the coating layer does not have thermal fusion properties and therefore inhibits heat sealing. The present invention has been developed based on the above background, and has as its object to provide a coated paper having good heat-sealing properties. [Means for solving the problem]

[0006] The means for solving the problems of the present invention are as follows. 1. A coating layer containing PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)) and EVA (ethylene-vinyl acetate copolymer resin) on at least one surface of a paper substrate; A coated paper having a second coating layer containing PHBH on the coating layer. 2. Coated paper according to 1., characterized in that the coating layer further contains an adhesive. 3. The coating layer further contains an inorganic pigment, 3. Coated paper according to 1. or 2., characterized in that the solids mass ratio of PHBH to inorganic pigment (PHBH:inorganic pigment) is 99:1 to 5:95. 4. Coated paper according to 3, characterized in that the inorganic pigment has a 50% volume average particle size (D50) of 0.1 μm or more. 5. Coated paper according to 3. or 4., characterized in that the inorganic pigment is one or more selected from the group consisting of kaolin, clay, engineered kaolin, and delaminated clay. 6. The coated paper according to any one of 1. to 5., wherein the second coating layer further contains an adhesive. [Effects of the Invention]

[0007] The coated paper of the present invention has excellent heat seal strength and can be suitably used as heat seal paper. DETAILED DESCRIPTION OF THE INVENTION

[0008] The coated paper of the present invention comprises a paper substrate and a coating layer on at least one side thereof, the coating layer comprising PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)) and EVA (ethylene-vinyl acetate copolymer resin); A second coating layer containing PHBH is provided on the 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.

[0009] (Paper base material) The paper base material is a sheet made mainly of pulp (hereinafter also referred to as "base paper") and is obtained by papermaking a paper stock that further contains fillers, various auxiliaries, and the like. 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.

[0010] Examples of fillers that can be used include known fillers such as inorganic fillers such as talc, kaolin, calcined kaolin, clay, heavy calcium carbonate, light calcium carbonate, white carbon, zeolite, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, barium sulfate, and calcium sulfate, and organic fillers such as urea-formalin resin, polystyrene resin, phenolic resin, and hollow microparticles. Note that fillers are not essential materials and may not be used.

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

[0012] The surface of the paper substrate may be treated with various chemicals. Examples of such chemicals include oxidized starch, hydroxyethyl etherified starch, enzyme-modified starch, polyacrylamide, polyvinyl alcohol, surface sizing agents, water-resistant agents, water-retention agents, thickeners, and lubricants. These may be used alone or in combination of two or more. Furthermore, these chemicals may be used in combination with pigments. Examples of pigments include inorganic pigments such as kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin white, as well as organic pigments such as solid, hollow, and core-shell pigments, which may be used alone or in combination of two or more.

[0013] The basis weight of the paper base material can be selected appropriately depending on the desired quality and its application, but is usually 20 g / m 2 More than 600g / m 2 Less than 25 g / m 2 More than 600g / m 2 The following is more preferred: For example, when used for wrapping paper, paper bags, lids, lining paper, packaging materials for liquid paper containers such as milk cartons, posters to be used outdoors, etc., the basis weight of the paper base material is 20 g / m 2 More than 350g / m 2 When used as a flexible packaging material, the paper substrate preferably has a basis weight of 20 g / m 2 More than 100g / m 2Less than 20 g / m is preferred 2 More than 80g / m 2 The following is more preferable. The soft packaging material is a packaging material, particularly a material having a density of 20 g / m 2 from 100g / m 2 It is a flexible packaging material made of thin paper of about 150 g / m². When used for paper cups, paper containers, paper boxes, paper plates, paper trays, etc., the paper base material has a basis weight of 150 g / m². 2 More than 300g / m 2 The following is preferred: The density of the paper substrate can be selected appropriately depending on the desired quality, handling, etc., but is usually 0.5 g / cm 3 More than 1.0g / cm 3 The following are preferred:

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

[0015] (coating layer) The coating layer includes PHBH and EVA. <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.

[0016] Microorganisms that produce PHBH are not particularly limited as long as they accumulate PHBH intracellularly, but examples 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 accumulate PHBH within the cells. The carbon source and culture conditions used for the culture can be obtained according to the methods described in Japanese Patent Application Laid-Open Nos. 05-093049 and 2001-340078, but are not limited thereto.

[0017] The PHBH composition ratio (mol %) is preferably 3HB:3HH = 97:3 to 75:25, more preferably 95:5 to 85:15. If the 3HH composition is less than 3 mol %, the properties of PHBH become similar to those of the 3HB homopolymer, resulting in a loss of flexibility and an undesirable tendency for the film-forming processing temperature to become too high. If the 3HH composition exceeds 25 mol %, the crystallization rate becomes too slow to be suitable for film-forming processing, and the reduced crystallinity tends to make the resin flexible and reduce the flexural modulus. The PHBH composition ratio can be measured by centrifuging the aqueous dispersion and then drying the resulting powder, followed by NMR analysis. Microbial PHBH is a random copolymer. The molar ratio of the copolymer can be adjusted by selecting the bacterial cells, the carbon source, blending with PHBH of different molar ratios, or blending with 3HB homopolymer.

[0018] The weight-average molecular weight of PHBH is preferably 50,000 to 1,500,000. When the weight-average molecular weight of PHBH is within this range, film formation at low temperatures is possible when drying after coating. The weight-average molecular weight of PHBH is more preferably 100,000 to 500,000, and even more preferably 150,000 to 450,000. The weight-average molecular weight of PHBH can be determined as a polystyrene-equivalent molecular weight by gel permeation chromatography (GPC, such as Showa Denko K.K.'s "Shodex GPC-101") using a polystyrene gel (such as Showa Denko K.K.'s "Shodex K-804") as a column and chloroform as the mobile phase. The measurement sample used is a powder obtained by centrifuging an aqueous dispersion containing PHBH and then drying it.

[0019] 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 Co., Ltd., FRA). The solid content of PHBH in the coating solution is not particularly limited and can be adjusted to a viscosity suitable for the coating method, but is preferably 5 to 70% by mass. If the solid content is less than 5% by mass, the coating film tends to be poorly formed, while if it exceeds 70% by mass, the viscosity of the coating solution becomes too high, making coating difficult. The solid content of PHBH in the coating solution is more preferably 10 to 55% by mass.

[0020] <eva> EVA (ethylene-vinyl acetate copolymer) is a copolymer containing ethylene and vinyl acetate as monomers, and may contain other monomers as well. However, it is preferable that the EVA of the present invention is not saponified and does not contain vinyl alcohol units resulting from the saponification of vinyl acetate. When the EVA contains other monomers as monomers, the content of structural units derived from other monomers in the EVA is preferably 30 mol% or less. This content is not particularly limited as long as it does not impair the effects of the present invention, and can be, for example, 20 mol% or less, 10 mol% or less, 5 mol% or less, 3 mol% or less, or 1 mol% or less.

[0021] From the viewpoint of heat seal strength, the glass transition temperature of the EVA is preferably −50 to 30° C. This glass transition temperature is more preferably −40° C. or higher, even more preferably −35° C. or higher, even more preferably −30° C. or higher, even more preferably −25° C. or higher, and more preferably 20° C. or lower, even more preferably 10° C. or lower. In this specification, the glass transition temperature refers to the midpoint glass transition temperature measured in accordance with JIS K 7121-1987. From the viewpoint of heat seal strength, the molar ratio of ethylene to vinyl acetate in the EVA (structural units derived from ethylene:structural units derived from vinyl acetate, also expressed as ethylene:vinyl acetate, the total being 100) is preferably 1:99 to 60:40, more preferably 3:97 to 50:50, and even more preferably 5:95 to 45:55.

[0022] <Adhesive> The coating layer of the present invention may contain an adhesive. The adhesive bonds together PHBH, EVA, an optional inorganic pigment, a paper substrate, etc. Any adhesive can be used without particular limitations as long as it is soluble or dispersible in water and can bond these components. Examples of the polyvinyl alcohol include 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 alcohol copolymers, starches such as oxidized starch, etherified starch, and esterified starch, cellulose derivatives such as hydroxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, acetyl cellulose, and nanocellulose, styrene-butadiene copolymer latex, conjugated diene polymer latex of methyl methacrylate-butadiene copolymer, acrylic polymer latex, styrene-maleic anhydride copolymer latex, polyvinyl chloride latex, and polyvinyl acetate latex. One or more of these may be appropriately selected and used.

[0023] Among these, it is preferable to include at least one selected from the group consisting of polyvinyl alcohols, starches, cellulose derivatives, styrene-butadiene copolymer latex, conjugated diene polymer latex such as methyl methacrylate-butadiene copolymer, and acrylic polymer latex, and more preferably to consist of at least one selected from this group. Furthermore, because it is biodegradable, it is more preferable to include at least one selected from the group consisting of polyvinyl alcohols, starches, and cellulose derivatives, and even more preferable to include at least one selected from the group consisting of fully saponified polyvinyl alcohol and partially saponified polyvinyl alcohol.

[0024] In terms of fixation to the paper substrate, the adhesive preferably contains at least one of fully saponified polyvinyl alcohol and partially saponified polyvinyl alcohol, and more preferably consists of at least one of fully saponified polyvinyl alcohol and partially saponified polyvinyl alcohol.

[0025] <Inorganic pigments> The coating layer can contain an inorganic pigment. By incorporating an inorganic pigment into the coating layer, the adhesion of the coating layer and the heat sealability of the coated paper can be improved. Although the mechanism is unclear, when the coating layer contains both an adhesive and an inorganic pigment, the heat sealability is further improved. The inorganic pigment can be any inorganic pigment used for coating paper, 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 selected from the group consisting of kaolin, clay, engineered kaolin, and delaminated clay are preferred.

[0026] From the viewpoint of dispersibility, the inorganic pigment preferably has a 50% volume average particle size (D50) (hereinafter also referred to as "average particle size") of 0.1 μm or more, as measured by a laser diffraction / scattering method. 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. The average particle size of the inorganic pigment is more preferably 0.2 μm or more, and even more preferably 0.3 μm or more. From the viewpoint of adhesion of the coating layer, the upper limit of the average particle size of the inorganic pigment is preferably 10 μm or less, and more preferably 9 μm or less. When two or more inorganic pigments are used, 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 is preferably 50 mass% or more, and more preferably 70 mass% or more.

[0027] In order to improve the heat-sealing properties of coated paper, inorganic pigments preferably have an aspect ratio of 5 or greater. The aspect ratio can be calculated using measurements obtained with 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 Technical Association. The aspect ratio of inorganic pigments is preferably 8 or greater, more preferably 10 or greater, and even more preferably 12 or greater. There is no particular upper limit to the aspect ratio of inorganic pigments, but it is, for example, approximately 120 or less. When two or more inorganic pigments are used, it is preferable that the aspect ratio of at least one of the inorganic pigments be within the above-mentioned range, and the proportion of inorganic pigments satisfying this aspect ratio relative to the total inorganic pigments is preferably 50% by mass or greater, more preferably 70% by mass or greater.

[0028] In addition to PHBH, EVA, adhesive, and inorganic pigment, the coating layer may contain, as necessary, various auxiliaries that are blended into coating solutions in the papermaking field, such as other biodegradable resins such as polybutylene succinate, polycaprolactone, and polylactic acid, dispersants, viscosity modifiers, water retention agents, defoamers, water-resistant agents, fluorescent dyes, coloring dyes, coloring pigments, surfactants, pH adjusters, cationic resins, anionic resins, ultraviolet absorbers, and metal salts.

[0029] The ratio of EVA to 100 parts by mass of PHBH in the coating layer is not particularly limited as long as the effects of the present invention are achieved, but is preferably 10 parts by mass or more and 500 parts by mass or less, more preferably 14 parts by mass or more, even more preferably 18 parts by mass or more, even more preferably 22 parts by mass or more, and more preferably 400 parts by mass or less, even more preferably 350 parts by mass or less, even more preferably 300 parts by mass or less, even more preferably 250 parts by mass or less, even more preferably 200 parts by mass or less, and even more preferably 150 parts by mass or less. The proportion of EVA relative to the total solid content of the coating layer is not particularly limited as long as the effects of the present invention are achieved, but is preferably, for example, 0.1% by mass or more and 75% by mass or less, more preferably 1% by mass or more, even more preferably 5% by mass or more, even more preferably 10% by mass or more, and more preferably 60% by mass or less, even more preferably 50% by mass or less, and even more preferably 40% by mass or less.

[0030] The solid mass ratio of PHBH to inorganic pigment in the coating layer (PHBH:inorganic pigment, total 100) is preferably 99:1 to 5:95 in terms of improving fixability and heat sealability, more preferably 90:10 to 10:90, even more preferably 80:20 to 15:85, and even more preferably 70:30 to 20:80. The proportion of adhesive relative to 100 parts by mass of the total of PHBH and inorganic pigment in the coating layer is not particularly limited as long as the effects of the present invention are achieved, but is preferably, for example, 0.1 parts by mass or more and 50 parts by mass or less, more preferably 5 parts by mass or more, even more preferably 10 parts by mass or more, more preferably 40 parts by mass or less, even more preferably 35 parts by mass or less, even more preferably 30 parts by mass or less, and even more preferably 25 parts by mass or less.

[0031] (Second coating layer) The second coating layer contains PHBH and is formed on the coating layer. The second coating layer may contain a PHBH equivalent to that contained in the coating layer described above, but the PHBH in the second coating layer preferably has a higher weight-average molecular weight than the PHBH in the coating layer. The higher the molecular weight of PHBH, the lower the MFR and the higher the temperature required for heat sealing. However, because the coated paper of the present invention has excellent heat sealing properties, high-molecular-weight PHBH can also be used. Furthermore, by including PHBH with a high weight-average molecular weight in the second coating layer, the physical properties inherent to PHBH, such as oil resistance and water resistance, can be more effectively exhibited.

[0032] From the viewpoint of heat-sealing properties, the second coating layer preferably contains an adhesive. The adhesive may be the same as the adhesive that can be contained in the coating layer described above. The proportion of adhesive relative to the total solid content of the second coating layer is not particularly limited as long as the effects of the present invention are achieved, but is preferably 0.1% by mass or more and 40% by mass or less. This proportion is more preferably 30% by mass or less, even more preferably 20% by mass or less, and even more preferably 10% by mass or less. In addition to PHBH, the second coating layer may optionally contain various additives commonly used in coating solutions in the papermaking industry, such as EVA, adhesives, inorganic pigments, other biodegradable resins (e.g., polybutylene succinate, polycaprolactone, polylactic acid), dispersants, viscosity modifiers, water retention agents, defoamers, water resistance agents, fluorescent dyes, coloring dyes, coloring pigments, surfactants, pH adjusters, cationic resins, anionic resins, UV absorbers, and metal salts. However, the second coating layer preferably contains 50% by mass or more of PHBH based on the total solids content of the layer, 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.

[0033] (Coating layer, coating of second coating layer) In the present invention, the coating method for the first coating layer and the second coating layer is not particularly limited, and coating can be performed using a known coating device and coating system. Examples of coating devices include a blade coater, a bar coater, a roll coater, an air knife coater, a reverse roll coater, a curtain coater, a spray coater, a size press coater, and a gate roll coater. Examples of coating systems include aqueous coating using a solvent such as water, and solvent-based coating using a solvent such as an organic solvent, with aqueous systems being preferred. The coating layer and the second coating layer can be dried using conventional methods such as a steam heater, gas heater, infrared heater, electric heater, hot air heater, microwave, or cylinder dryer. The second coating layer can be applied simultaneously with the first coating layer, before the first coating layer has dried, or after the first coating layer has dried.

[0034] The coating amount of the coating layer is 1 g / m2 in dry mass per side. 2 More than 50g / m 2 The coating weight of the coating layer is preferably 1 g / m or less. 2 If the thickness is less than 50 g / m, the effect of the coating layer may be almost nonexistent. 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:

[0035] The coating weight of the second coating layer is 0.5 g / m2 on each side in dry weight. 2 More than 30g / m 2 The coating weight of the second coating layer is preferably 0.5 g / m or less. 2 If the thickness is less than 30 g / m, the effect of the second coating layer may be almost nonexistent. 2 If the amount is more than this, the drying load during coating will increase. The coating amount of the second coating layer is 1 g / m 2 More preferably, 3 g / m 2 More preferably, 25 g / m 2 Less than 20 g / m is more preferable. 2 More preferably, 15 g / m 2 Even more preferred are the following:

[0036] Coated paper Because the coating layer and the second coating layer contain PHBH, the functionality of PHBH can be utilized, and they can be used, for example, as a heat-seal layer, an oil-resistant layer, a water-resistant layer, etc. The coating layer can be provided on only one side or both sides of the paper substrate. Furthermore, when coating layers are provided on both sides, the second coating layer can be provided on only one of the coating layers.

[0037] The heat-sealable layer is a layer that has heat-sealing properties, specifically, a layer that can be adhered to an object by heating and pressing. The coated paper of the present invention has improved heat-sealability compared to a paper that does not contain EVA. The coated paper of the present invention has improved heat-sealability when pressed at a pressing temperature of 160°C and a pressing pressure of 2 kgf / cm. 2 When heat-sealed with a pressure applied for 0.5 seconds, and peeled at a tension speed of 200 mm / min using a T-shaped strip, the heat-seal strength is preferably at least 0.4 N / 15 mm higher than that of a paper containing no EVA, more preferably at least 0.6 N / 15 mm, even more preferably at least 0.8 N / 15 mm, and even more preferably at least 0.9 N / 15 mm. Furthermore, the heat-seal strength of the coated paper of the present invention under the above conditions is preferably at least 3.0 N / 15 mm, more preferably at least 3.5 N / 15 mm, even more preferably at least 4.0 N / 15 mm, even more preferably at least 4.5 N / 15 mm, even more preferably at least 5.0 N / 15 mm, and even more preferably at least 5.5 N / 15 mm. There is no particular upper limit to this heat-seal strength, but it is, for example, about 15.0 N / 15 mm.

[0038] An oil-resistant layer is a layer whose average kit number, measured at any five points on the layer surface in accordance with J.TAPPI No. 41:2000 "Paper and Paperboard - Oil Repellency Testing Method - Kit Method," is 4 or greater. When imparting oil resistance to the coated paper of the present invention, the average kit number is preferably 6 or greater, more preferably 8 or greater, even more preferably 10 or greater, even more preferably 11 or greater, and most preferably 12. The water-resistant layer is a layer that has a water absorption (Cobb value) of 20 g / m2 measured with a contact time of 120 seconds in accordance with JIS P 8140:1998 "Paper and paperboard - Water absorption test method - Cobb method." 2 In order to impart water resistance to the coated paper of the present invention, the water absorbency is 10 g / m 2 Less than 5g / m is preferred 2 Less than 3g / m is more preferable. 2 More preferably, 2 g / m 2 Even more preferably, 1 g / m 2 Even more preferred are the following:

[0039] The coated paper of the present invention is easy to form, maintain its shape, and ensure airtightness, and can therefore be suitably used as paper bags, paper containers, paper boxes, paper cups, (soft) packaging materials, lid materials, etc. The coated paper of the present invention, in which the coating layer is a heat-sealable layer, can be suitably used as wrapping paper, paper containers, paper boxes, paper cups, (soft) packaging materials, paper plates, paper trays, etc. The coated paper of the present invention, in which the coating layer is both a heat-sealing layer and an oil-resistant layer, can be suitably used as (soft) packaging material or wrapping paper for foods that contain a lot of oil, such as hamburgers, hot dogs, French fries, fried chicken, and potato chips, as lining paper for deep-fried foods such as tempura, paper plates, paper trays, paper cups, etc. [Example]

[0040] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, parts and % in the examples represent parts by mass and % by mass, respectively.

[0041] PHBH An aqueous PHBH dispersion having a PHBH solids concentration of 50% by mass was obtained by the method described in Patent Document 1. Next, this aqueous PHBH dispersion was hydrolyzed at 60°C to adjust the molecular weight, thereby obtaining the following aqueous PHBH dispersion having a PHBH solids concentration of 50%. PHBH1: Weight average molecular weight 200,000 PHBH2: Weight average molecular weight 600,000

[0042] Inorganic pigments Inorganic pigment 1: Shiraishi Kogyo Co., Ltd., KCS (kaolin) Average particle size 3.6 μm, aspect ratio 10-15 Inorganic pigment 2: CADAM, Amazon Plus (kaolin) Average particle size 0.4 μm, aspect ratio 9 Inorganic pigment 3: Rio Kapim, Kapim DG (kaolin) Average particle size 1.2 μm, aspect ratio 13 Inorganic pigment 4: Shiraishi Kogyo Co., Ltd., Balisurf HX (kaolin) Average particle size: 8.7 μm, aspect ratio: 80-100 Inorganic pigment 5: Engelhard New Surf (delaminated kaolin) Average particle size 6.3 μm, aspect ratio 16 Inorganic pigment 6: Bihoku Funka Kogyo Co., Ltd., Hydrocarb 90 (heavy calcium carbonate) Average particle size <2μm, spherical

[0043] EVA EVA1: Sumika Chemtex Co., Ltd., S-400HQ Tg 0℃, ethylene:vinyl acetate=20:80 EVA2: Sumika Chemtex Co., Ltd., S-305HQ Tg 7℃, ethylene:vinyl acetate=10:90 EVA3: Sumika Chemtex Co., Ltd., S-410HQ Tg -18℃, ethylene:vinyl acetate = 30:70 EVA4: Sumika Chemtex Co., Ltd., S-408HQE Tg-30℃, ethylene:vinyl acetate=40:60 EVA5: Sumika Chemtex Co., Ltd., S-355HQ Tg 10℃, ethylene:vinyl acetate=10:90 ·glue PVA: Japan Vinyl Acetate & Poval Co., Ltd., JF-17 (fully saponified type)

[0044] (Evaluation method) Heat seal strength (HS 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 resulting coated paper. The coating layers were placed in contact with each other and pressed at a pressure of 0.2 MPa (20.0 N / cm) at a pressure of 130°C or 160°C. 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 test sample was peeled (T-type) from the long edge side at a speed of 200 mm / min to measure the peel strength, i.e., HS strength (N / 15 mm). The peeled surface was visually observed and evaluated according to the following criteria. The measurement was carried out twice, and the peel strength is shown as the average value. If the evaluation results differ based on visual observation, both the results are shown. 〇: Breakage on the entire heat-sealed surface (the paper layer breaks completely). Good and Fair: Partial breakage on the heat-sealed surface (partial breakage of the paper layer). △: Peeling occurs between coating layers (no material breakage). △ * : Peeling occurs between the paper base material and the coating layer (no material breakage). ×: Not heat sealed.

[0045] Each agent was blended to obtain the solid content mass ratio shown in Tables 1 to 6 below, to obtain coating solutions (solid content concentration: 40% by mass) for the coating layer and the second coating layer. Paper base material (basis weight 50g / m 2 The coating solution for forming a coating layer was applied to one side of the paper by the bar blade method and dried at 105°C for 1 minute. The coating solution for forming a second coating layer was table-coated onto the coating layer by the bar blade method and dried at 160°C for 3 minutes to obtain coated paper. The heat seal strength of the resulting coated paper was measured.

[0046] [Table 1]

[0047] As shown in Table 1, it was confirmed that the inclusion of EVA in the coating layer improved the HS strength. It was also confirmed that the decrease in HS strength was suppressed even when the coating layer contained an adhesive.

[0048] [Table 2]

[0049] [Table 3]

[0050] As shown in Tables 2 and 3, the HS properties were good even when inorganic pigments were added to the coating layer. The results in Table 2 indicate that when the coating layer does not contain an adhesive, the less pigment there is, the better the HS strength tends to be. However, the results in Table 3 indicate that when the coating layer contains an adhesive, the correlation between the amount of pigment and HS strength becomes weaker, and HS strength is particularly excellent when the PHBH:inorganic pigment ratio is in the range of 65:35 to 25:75. The results of Examples 20 and 21 and Comparative Example 4 confirm that HS strength improves when the coating layer contains EVA, and that HS strength improves when the second coating layer contains an adhesive. Furthermore, as shown in Table 3, the coated paper of the present invention has HS strength sufficient for practical use even at 130°C.

[0051] [Table 4]

[0052] As shown in Table 4, the coated papers obtained in Examples 17 and 25 to 28, which used inorganic pigments with aspect ratios of 5 or more, had improved HS strength compared to Example 29, which used spherical inorganic pigments.

[0053] [Table 5]

[0054] As shown in Table 5, it was confirmed that the HS strength was improved when the coating layer contained EVA compared to when the coating layer contained only PHBH or only PHBH and adhesive. From Examples 30 to 33, it was confirmed that good HS properties were exhibited over a wide range of EVA content in the coating layer. Examples 32 and 34 to 37 confirmed that good HS properties were exhibited even when different EVAs were used.

[0055] [Table 6]

[0056] As shown in Table 6, when the coating layer contained an inorganic pigment, the HS strength improved over a wide range of adhesive content in the coating layer by further including an adhesive.< / eva> < / phbh>

Claims

1. A coating layer containing PHBH (poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)) and EVA (ethylene-vinyl acetate copolymer resin) on at least one surface of a paper substrate; A coated paper characterized by having a second coating layer containing PHBH on the coating layer.

2. 2. The coated paper of claim 1, wherein the coating layer further comprises an adhesive.

3. the coating layer further contains an inorganic pigment, 3. The coated paper according to claim 1, wherein the solids mass ratio of PHBH to inorganic pigment (PHBH:inorganic pigment) is 99:1 to 5:

95.

4. 4. Coated paper according to claim 3, characterized in that the inorganic pigment has a 50% volume average particle size (D50) of 0.1 μm or more.

5. 4. The coated paper according to claim 3, wherein the inorganic pigment is at least one selected from the group consisting of kaolin, clay, engineered kaolin, and delaminated clay.

6. 3. The coated paper according to claim 1, wherein the second coating layer further comprises an adhesive.

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