Method for producing laminate, and method for producing molded article

Abstract

In the present invention, an aqueous dispersion liquid of a poly(hydroxyalkanoate) resin is applied onto a substrate to form an applied film, and then, the applied film is heated with superheated steam such that the surface temperature of the applied film reaches a temperature that is 10°C to 100°C higher than the melting point (Tm) of the poly(hydroxyalkanoate) resin, allowing the poly(hydroxyalkanoate) resin to fuse to form a resin layer.

Description

Manufacturing method of laminate and manufacturing method of molded body

[0001] The present invention relates to a method for producing a laminate having a resin layer containing a poly(hydroxyalkanoate) resin, and a method for producing a molded article containing the laminate.

[0002] In recent years, environmental problems caused by discarded plastics have been attracting attention. In particular, marine pollution caused by discarded plastics is serious, and there are high hopes for the widespread use of biodegradable plastics that decompose in the natural environment.

[0003] Various types of biodegradable plastics are known, but among them, poly(3-hydroxybutyrate) resin, a type of poly(hydroxyalkanoate) resin, is a thermoplastic polyester that is produced and accumulated as an energy storage substance within the cells of many microbial species. Because it is a material that can biodegrade not only in soil but also in seawater, it has attracted attention as a material that can solve the above-mentioned problems.

[0004] A laminate obtained by laminating a layer mainly composed of a poly(hydroxyalkanoate)-based resin such as a poly(3-hydroxybutyrate)-based resin onto a biodegradable paper substrate is extremely promising from the viewpoint of environmental protection, since both the resin and the substrate are highly biodegradable materials.

[0005] As an example of a method for producing such a laminate, Patent Document 1 describes a method in which an aqueous dispersion containing a copolymer of 3-hydroxybutyrate and 3-hydroxyhexanoate having a specific average molecular weight is applied to a substrate, followed by heating and drying to form a film.

[0006] International Publication No. 2021 / 075412

[0007] According to a manufacturing method described in Patent Document 1, in which an aqueous dispersion of resin is applied to a substrate, a laminate can be produced in which a resin layer composed primarily of a poly(hydroxyalkanoate)-based resin is laminated on a substrate. However, when the cross section of the resin layer of a laminate obtained by the manufacturing method described in Patent Document 1 is observed under an electron microscope, it has been found that the resin particle shape or voids remain, and the resin layer may not be sufficiently uniform. If the particle shape or voids remain in the resin layer, this can cause a decrease in the adhesion of the resin layer to the substrate and a decrease in the water resistance and oil resistance that the resin layer should provide. On the other hand, setting the temperature during heat drying high can significantly decrease the molecular weight of the poly(hydroxyalkanoate)-based resin. A decrease in the molecular weight of the resin can make it difficult to achieve the desired physical properties or make the resin layer more susceptible to cracking.

[0008] In view of the above-described current situation, the present invention aims to provide a method for producing a laminate by applying an aqueous dispersion of a poly(hydroxyalkanoate) resin to a substrate, which method can improve the uniformity of the resin layer without significantly reducing the molecular weight of the resin.

[0009] As a result of intensive research into solving the above-mentioned problems, the inventors have found that the above-mentioned problems can be solved by applying an aqueous dispersion of a poly(hydroxyalkanoate) resin to a substrate, and then heating the coating film to a temperature within a specific range using superheated steam to fuse the resin in the coating film, thereby completing the present invention.

[0010] That is, the present invention relates to a method for producing a laminate including a substrate and a resin layer formed on at least one surface of the substrate, the method comprising the steps of: applying an aqueous dispersion of a poly(hydroxyalkanoate)-based resin to the substrate to form a coating film; and heating the coating film using superheated steam so that the surface temperature of the coating film becomes a temperature 10°C to 100°C higher than the melting point (Tm) of the poly(hydroxyalkanoate)-based resin, thereby fusing the poly(hydroxyalkanoate)-based resin to form the resin layer.

[0011] According to the present invention, there is provided a method for producing a laminate by applying an aqueous dispersion of a poly(hydroxyalkanoate) resin to a substrate, which can improve the uniformity of the resin layer without significantly reducing the molecular weight of the resin. Furthermore, according to the present invention, curling of the laminate, a decrease in tear strength, and changes in the color tone of the substrate that may occur due to heating can be suppressed.

[0012] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0013] A manufacturing method according to one embodiment of the present disclosure is for producing a laminate. The laminate includes at least a substrate and a resin layer formed on one or both sides of the substrate. In a preferred embodiment, the laminate as a whole is biodegradable. The resin layer may be laminated directly onto the substrate or may be laminated via another layer, but it is preferably laminated directly onto the substrate.

[0014] In one embodiment of the present disclosure, the resin layer may be the outermost layer of the laminate, and in this case, the resin layer may function as a heat seal layer, a water-resistant layer, and / or an oil-resistant layer.

[0015] In another aspect of the present disclosure, another layer may be laminated on the resin layer. In this case, the resin layer may function as an anchor coat layer between the substrate and the other layer. The other layer is not particularly limited and may be another resin layer or an inorganic layer, but one example is the second resin layer described below.

[0016] The surface of the substrate opposite to the side on which the resin layer is laminated may be the outermost layer, or may have any other layer laminated thereon. The layer may be a layer that can correspond to the resin layer, or may be a layer other than the first resin layer.

[0017] (Substrate) The material constituting the substrate is not particularly limited, but is preferably biodegradable. Examples include paper, cellophane, cellulose ester, polyvinyl alcohol, polyamino acid, polyglycolic acid, pullulan, and substrates thereof onto which inorganic materials such as aluminum and silica are vapor-deposited. Among these, paper is preferred because of its excellent heat resistance and low cost.

[0018] Paper is composed of a sheet mainly made of pulp. The paper base material can be obtained by papermaking a stock containing pulp, fillers, various auxiliaries, etc. The type of paper that can be used is not particularly limited, and examples include cup base paper, kraft paper, fine paper, coated paper, tissue paper, glassine paper, and paperboard.

[0019] The pulp is not particularly limited, and examples thereof include chemical pulps such as bleached hardwood kraft pulp (LBKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), unbleached softwood pulp (NUKP), and sulfite pulp; mechanical pulps such as stone-ground pulp and thermomechanical pulp; wood fibers such as deinked pulp and recycled paper pulp; and non-wood fibers obtained from kenaf, bamboo, hemp, etc. These can be used in appropriate combinations.

[0020] Among these, it is preferable to use chemical pulp or mechanical pulp made from wood fibers, and it is more preferable to use chemical pulp, for reasons such as the fact that foreign matter is less likely to be mixed into the paper, that discoloration is less likely to occur over time when recycled as a waste paper raw material, that the high whiteness results in a good surface appearance when printed, and that the value is particularly high when used as a packaging material. Specifically, it is preferable that the amount of chemical pulp such as LBKP or NBKP in the pulp is 80% or more, and it is particularly preferable that the amount of chemical pulp is 100%.

[0021] The filler is not particularly limited, and examples thereof include 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.

[0022] The various auxiliaries are not particularly limited and include, for example, sizing agents such as rosin, alkyl ketene dimer (AKD), and alkenyl succinic anhydride (ASA), polyacrylamide polymers, polyvinyl alcohol polymers, cationized starch, various modified starches, dry strength agents such as urea-formalin resin and melamine-formalin resin, wet strength agents, retention aids, drainage aids, coagulants, aluminum sulfate, bulking agents, dyes, fluorescent whitening agents, pH adjusters, antifoaming agents, UV inhibitors, anti-fading agents, pitch control agents, slime control agents, etc. These may be selected and used as needed.

[0023] The surface of the paper may be treated with various chemicals. The chemicals are not particularly limited, and examples thereof include oxidized starch, hydroxyethyl etherified starch, enzyme-modified starch, polyacrylamide, polyvinyl alcohol, surface sizing agents, water-resistant agents, water-retaining agents, thickeners, lubricants, etc. Only one type of chemical may be used, or two or more types may be used in combination. Furthermore, these chemicals may be used in combination with pigments.

[0024] The pigment is not particularly limited, and examples thereof 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, satin white, etc.; organic pigments such as solid, hollow, or core-shell type pigments, etc. Only one type of pigment may be used, or two or more types may be used in combination.

[0025] The basis weight of the substrate, particularly the paper substrate, can be appropriately selected depending on the desired quality and the use of the laminate, but is preferably 40 g / m ２ More than 400g / m ２ Preferably, it is 50 g / m or less. ２ 350g / m or more ２ When the laminate is used for packaging materials such as wrapping paper, paper bags, lids, liner papers, and soft packaging materials, or posters to be used outdoors, the weight of the laminate is preferably 40 g / m or less. ２ 150g / m or more ２ It is more preferable that the soft packaging material is a packaging material having a density of 40 g / m or less. ２ ~100g / m ２ In addition, when the laminate is used for paper tableware such as paper cups, paper boxes, paper plates, paper trays, etc., or for lids and other paper containers, it is recommended to use a paper thickness of 150 g / m or less. ２ More than 400g / m ２ It is more preferable that:

[0026] The density of the substrate, particularly the paper substrate, can be appropriately selected depending on the desired quality, handling, etc., but is usually 0.5 g / cm ３ 1.0g / cm or more ３ It is preferable that:

[0027] The method for manufacturing the substrate is not particularly limited. The method for manufacturing the paper substrate (papermaking) is also not particularly limited, and can be carried out by appropriately selecting a known papermaking machine, 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 type or a hybrid former type (on-top former type). 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 coated on the surface of the paper layer. The paper substrate may be a single layer, or may be composed of two or more layers.

[0028] 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, or a curtain coater can be used.

[0029] (Resin Layer) The resin layer formed on at least one surface of the substrate contains at least a poly(hydroxyalkanoate)-based resin (hereinafter also referred to as PHA). Only one type of PHA may be used, or two or more types may be used in combination. The resin component contained in the resin layer may be only PHA, or may further contain another resin. The other resin may be a biodegradable resin described below.

[0030] The poly(hydroxyalkanoate) resin is a general term for polymers containing hydroxyalkanoic acid as a monomer unit. The hydroxyalkanoic acid constituting the PHA is not particularly limited, but examples thereof include 3-hydroxybutanoic acid, 4-hydroxybutanoic acid, 3-hydroxypropionic acid, 3-hydroxypentanoic acid, 3-hydroxyhexanoic acid, 3-hydroxyheptanoic acid, and 3-hydroxyoctanoic acid. The PHA may be a homopolymer or a copolymer containing two or more types of monomer units.

[0031] The resin layer preferably contains 50% by weight or more of PHA, more preferably 70% by weight or more, even more preferably 80% by weight or more, and even more preferably 90% by weight or more. By using PHA as a main component, the resin layer can exhibit biodegradability.

[0032] The PHA is preferably a poly(3-hydroxybutyrate) resin (hereinafter also referred to as P3HB). P3HB refers to a homopolymer having only 3-hydroxybutyrate units and / or a copolymer containing 3-hydroxybutyrate units and other hydroxyalkanoate units. From the viewpoint of seawater decomposability, it is preferable to include a copolymer containing 3-hydroxybutyrate units and other hydroxyalkanoate units.

[0033] The type of copolymerization in the copolymer is not particularly limited, and may be random copolymerization, alternating copolymerization, block copolymerization, graft copolymerization, etc. Copolymers produced by microorganisms are usually random copolymers.

[0034] The hydroxyalkanoic acid forming the other hydroxyalkanoate unit is not particularly limited, and examples thereof include 4-hydroxybutanoic acid, 3-hydroxypropionic acid, 3-hydroxypentanoic acid, 3-hydroxyhexanoic acid, 3-hydroxyheptanoic acid, and 3-hydroxyoctanoic acid.

[0035] Specific examples of P3HB include poly(3-hydroxybutyrate) (abbreviation: PHB), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (abbreviation: PHBH), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (abbreviation: P3HB3HV), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (abbreviation: P3HB4HB), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate). Examples of suitable P3HBs include poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate) (abbreviation: P3HB3HO), poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate) (abbreviation: P3HB3HOD), poly(3-hydroxybutyrate-co-3-hydroxydecanoate) (abbreviation: P3HB3HD), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (abbreviation: P3HB3HV3HH). Among these, PHB, PHBH, P3HB3HV, and P3HB4HB are preferred due to their ease of industrial production. Only one type of P3HB may be used, or two or more types may be used in combination.

[0036] The resin layer preferably contains P3HB in an amount of 50% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, and even more preferably 90% by weight or more. By using P3HB as a main component, the resin layer can exhibit biodegradability.

[0037] Among P3HB, PHBH is particularly preferred from the viewpoints that it is possible to change the melting point and degree of crystallinity by changing the composition ratio of the repeating units, thereby adjusting physical properties such as Young's modulus and heat resistance, and that it is possible to impart physical properties between those of polypropylene and polyethylene, and that it is easy to produce industrially and is a physically useful plastic.

[0038] The resin layer preferably contains 50% by weight or more of PHBH, more preferably 70% by weight or more, even more preferably 80% by weight or more, and even more preferably 90% by weight or more. By using PHBH as a main component, the resin layer can exhibit biodegradability, particularly seawater degradability.

[0039] The average content ratio of the constituent monomers in P3HB is preferably 3HB units / other hydroxyalkanoate units = 97-70 / 3-30 (mol % / mol %), and more preferably 3HB / 3HH = 94-82 / 6-18 (mol % / mol %). When the average content ratio of other hydroxyalkanoate units in P3HB is 3 mol % or more, good adhesion can be obtained by heat sealing using the resin layer. Furthermore, P3HB with an average content ratio of other hydroxyalkanoate units of 30 mol % or less does not have an excessively slow crystallization rate and is relatively easy to produce.

[0040] When P3HB contains PHBH, P3HB having an average 3HH content of 3 to 30 mol % may be composed of one type of PHBH, may be composed of a mixture of at least two types of PHBH having different content ratios of constituent monomers, or may be composed of a mixture of at least one type of PHBH and PHB.

[0041] A preferred combination of PHBH or PHB in the mixture is a combination of PHBH having a 3HH unit content of 8 to 25 mol % and PHBH or PHB having a 3HH unit content of less than 8 mol %. By using such a combination, in heat sealing using the resin layer, good adhesive strength can be exhibited in a short time after heat sealing, even if the heat sealing temperature rises to a temperature at which sufficient adhesion is possible.

[0042] In the above combination, the content of 3HH units in PHBH having a content of 3HH units of less than 8 mol% is preferably 5 mol% or less, more preferably 3 mol% or less, and even more preferably 1 mol% or less. The lower limit of the content of 3HH units in the PHBH is not particularly limited, but may be, for example, 0.1 mol% or more.

[0043] The amount of PHBH or PHB containing less than 8 mol% of 3HH units is not particularly limited, but is preferably 0 to 50% by weight relative to the total weight of the P3HB-based resin contained in the resin layer. When used, the amount is preferably 1 to 50% by weight, more preferably 3 to 30% by weight, even more preferably 4 to 20% by weight, and particularly preferably 5 to 15% by weight.

[0044] The average content ratio of each constituent monomer in P3HB can be determined by a method known to those skilled in the art, for example, the method described in paragraph

[0047] of WO 2013 / 147139, or by NMR measurement. The average content ratio means the molar ratio of 3HB units to other hydroxyalkanoate units in the entire P3HB contained in the resin layer, and when P3HB is a mixture containing at least two types of PHBH, or a mixture containing at least one type of PHBH and PHB, it means the molar ratio of each monomer unit contained in the entire mixture.

[0045] The weight average molecular weight (hereinafter sometimes referred to as Mw) of the PHA contained in the resin layer can be selected as appropriate, but from the viewpoint of achieving both mechanical properties and processability, it is preferably 50,000 to 900,000, more preferably 100,000 to 800,000, and even more preferably 150,000 to 700,000. When the weight average molecular weight of P3HB is 50,000 or more, good mechanical properties are obtained, and when it is 900,000 or less, good adhesion can be obtained by heat sealing.

[0046] The weight average molecular weight of the PHA can be determined as a molecular weight converted into polystyrene by gel permeation chromatography (GPC) (Shodex GPC-101 manufactured by Showa Denko K.K.) using a polystyrene gel (Shodex K-804 manufactured by Showa Denko K.K.) as a column and chloroform as a mobile phase.

[0047] A specific method for producing PHBH is described in, for example, International Publication No. 2010 / 013483. Commercially available PHBH products include Kaneka Biodegradable Polymer Green Planet (registered trademark) manufactured by Kaneka Corporation.

[0048] The resin layer may contain, to the extent that the effects of the invention are not impaired, one or more of the following: resins other than PHA, adhesives, dispersants or emulsifiers, pH adjusters, inorganic fillers, colorants such as pigments and dyes, odor absorbers such as activated carbon and zeolite, fragrances such as vanillin and dextrin, plasticizers, antioxidants, weather resistance improvers, ultraviolet absorbers, crystal nucleating agents, lubricants, release agents, water repellents, antibacterial agents, and sliding property improvers, etc. However, these are optional components, and the resin layer may not contain these components.

[0049] Resins other than PHA that can be used in the resin layer are not particularly limited, but are preferably biodegradable resins. Specific examples include 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. The blending amount of these resins other than PHA may be 50 parts by weight or less, 30 parts by weight or less, or 10 parts by weight or less, relative to 100 parts by weight of PHA. It may also be 5 parts by weight or less, or 1 part by weight or less.

[0050] The thickness of the resin layer is not particularly limited and can be appropriately determined in consideration of the performance and productivity required of the resin layer, and may be, for example, 0.5 to 100 μm, or 1 to 30 μm.

[0051] (Coating Film Formation Process) In the manufacturing method according to this embodiment, first, an aqueous dispersion of PHA is prepared, and this is applied to one or both surfaces of a substrate to form a coating film. The aqueous dispersion of PHA refers to a liquid in which at least resin particles containing PHA are dispersed in water. If necessary, components other than the resin particles may be dissolved or dispersed in the aqueous dispersion. Applying this aqueous dispersion to a substrate as a coating liquid has the advantage that, particularly when a resin layer is directly laminated on a paper substrate without any other layer interposed therebetween, a portion of the coating liquid permeates the paper substrate, which makes it easier to improve the adhesion of the resin layer to the paper substrate.

[0052] The aqueous dispersion can be prepared by referring to, for example, International Publication No. 2021 / 059592.

[0053] The solids concentration of the PHA in the aqueous dispersion may be set as appropriate, for example, 25 to 65 wt %, preferably 30 to 55 wt %, and more preferably 35 to 50 wt %. When the solids concentration of the PHA in the aqueous dispersion is within the above range, the viscosity of the solution is not too high, which enables uniform application and also makes it possible to maintain the required thickness of the coating film, thereby suppressing defects in the coating film.

[0054] The average particle size of the PHA particles in the aqueous dispersion may be, for example, 0.1 to 50 μm, preferably 0.5 to 30 μm, and more preferably 0.8 to 20 μm, from the viewpoint of achieving both PHA productivity and uniformity during application. An average particle size of 0.1 μm or more allows PHA to be easily obtained by either microbial production or chemical synthesis. An average particle size of 50 μm or less prevents uneven application. The average particle size of the PHA particles in the aqueous dispersion can be calculated using a general-purpose particle size analyzer such as a Microtrac particle size analyzer (manufactured by Nikkiso, FRA) by adjusting an aqueous suspension containing PHA to a predetermined concentration and calculating the particle size corresponding to 50% of the accumulated amount of all particles in a normal distribution.

[0055] The aqueous dispersion may not contain an emulsifier, but preferably contains one to stabilize the dispersion. Examples of emulsifiers include anionic surfactants such as sodium lauryl sulfate and sodium oleate, cationic surfactants such as lauryl trimethylammonium chloride, nonionic surfactants such as glycerin fatty acid esters and sorbitan fatty acid esters, polyvinyl alcohol derivatives such as polyvinyl alcohol, carboxy-modified polyvinyl alcohol, sulfonated polyvinyl alcohol, and ethylene-modified polyvinyl alcohol, cellulose derivatives such as methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose, starch derivatives such as starch, oxidized starch, and etherified starch, and water-soluble polymers such as chitin, chitosan, casein, and gum arabic. These may be used alone or in combination of two or more. Among these, polyvinyl alcohol is preferred because it can be easily added to the dispersion on an industrial scale to prepare an aqueous solution.

[0056] The amount of emulsifier added is not particularly limited, but is preferably 1 to 10% by weight based on the solid content of the PHA. When the amount of emulsifier added is 1% by weight or more, the stabilizing effect of the emulsifier tends to be easily obtained, and when it is 10% by weight or less, deterioration of physical properties, coloration, etc. due to the inclusion of an excess emulsifier in the PHA can be avoided.

[0057] The method for applying the aqueous dispersion to the substrate is not particularly limited, and any known method can be used as appropriate. Specifically, a spraying method, a scattering method, a slit coater method, an air knife coater method, a roll coater method, a bar coater method, a comma coater method, a blade coater method, a screen printing method, a gravure printing method, etc. can be used. Before applying the aqueous dispersion, a step of subjecting the paper substrate to a surface treatment such as a corona treatment may be carried out.

[0058] The coating amount of PHA is not particularly limited and can be determined appropriately in consideration of the performance and productivity required for the resin layer. Specifically, the coating amount of PHA is 1.0 g / m2 in dry weight. ２ 80g / m or more ２Preferably, the amount is 5.0 g / m or less. ２ 60g / m or more ２ More preferably, 10 g / m or less ２ 50g / m or more ２ When the coating amount of PHA is within the above range, defects such as pinholes can be prevented, the resin layer can have sufficient strength to withstand use, and functions such as water resistance and oil resistance can be efficiently exhibited.

[0059] It is also preferable to set the coating weight of the PHA and the basis weight of the substrate so that the value obtained by dividing the coating weight (dry weight) of the PHA by the basis weight of the substrate (coating weight / basis weight of substrate) is 0.05 to 0.45. Within this range, the resin layer efficiently exhibits functions such as water resistance and oil resistance, and the laminate can be efficiently produced by the production method according to the present disclosure.

[0060] (Drying step) After forming the coating film, the coating film may be heated and dried using a method that does not use superheated steam, i.e., a step of reducing the water content in the coating film may be performed. The heating temperature at this time is not particularly limited, but may be a temperature lower than the melting point (Tm) of the PHA. Specifically, the upper limit of the heating temperature may be less than 130°C and may be 125°C or lower. The lower limit of the heating temperature is not particularly limited, but may be, for example, 70°C or higher, preferably 90°C or higher, and more preferably 100°C or higher.

[0061] The heating time in the drying step is not particularly limited and can be set appropriately, but may be, for example, 10 seconds to 10 minutes, and preferably about 30 seconds to 5 minutes.

[0062] This drying step can be carried out using a known heating method, such as hot air heating, infrared heating, ultrasonic irradiation, microwave heating, roll heating, or hot plate heating, which can be used alone or in combination of two or more.

[0063] This drying step does not have to be performed. That is, the step of forming a resin layer using superheated steam may be performed directly after the step of forming a coating film without performing the drying step. This is because the drying of the coating film can proceed simply by heating using superheated steam.

[0064] (Humidity Adjustment Step) After the drying step, a humidity adjustment step of adjusting the moisture content of the dried substrate may be performed, thereby reducing curling of the substrate that occurs in the drying step.

[0065] In this step, it is preferable to increase the moisture content of the substrate by spraying water onto the surface of the substrate. The sprayed water may contain additives such as humectants such as glycerin and propylene glycol, various fragrances, and preservatives.

[0066] The temperature of the sprayed water is not particularly limited, and may be, for example, about 10 to 50°C, or may be room temperature (about 10 to 30°C) without temperature control.

[0067] The amount of water used may be appropriately determined taking into consideration the moisture content of the substrate after the drying step and the moisture content of the target substrate. The moisture content of the target substrate is not particularly limited, but may be, for example, about 5 to 8%, or may be 6 to 7%.

[0068] This humidity conditioning step may not be performed. That is, the step of forming a resin layer using superheated steam may be performed directly after the step of forming a coating film or the step of drying, without performing the humidity conditioning step.

[0069] (Resin layer formation process using superheated steam) After the coating film formation process and the optional drying and humidity adjustment processes are performed, the coating film is heated using superheated steam to fuse the PHA and form a resin layer. In this process, at least a portion of the PHA melts, and the molten portion is cooled and solidified after heating, thereby fusing the PHA.

[0070] In the coating film before heating with superheated steam, the PHA particles contained in the aqueous dispersion are placed on the substrate, but the PHA particles are not sufficiently bonded to each other, and sufficient uniformity is not achieved. In this resin layer formation process, by heating the coating film in a temperature range where at least a portion of the PHA melts, the PHA particles are fused to each other, integrating the resin components, and a resin layer with higher uniformity can be formed.

[0071] In this resin layer forming process, superheated steam is used as a heating means. Superheated steam refers to steam with a high calorific value that is obtained by further heating saturated steam to a temperature above the saturation temperature.

[0072] Heating the coating film using superheated steam can efficiently increase the uniformity of the resin layer, thereby improving the adhesion of the resin layer to the substrate and improving the reliability of the water resistance and oil resistance that the resin layer should provide.

[0073] In contrast, when a resin layer is formed using hot air, which is a common heating method, the fusion between PHA particles is difficult to proceed sufficiently, and particle shapes and voids are observed in the cross section of the resin layer, and the resin layer tends to be insufficiently uniform. A resin layer with insufficient uniformity may result in insufficient adhesion of the resin layer to the substrate, as well as insufficient water resistance and oil resistance.

[0074] Since superheated steam has a larger heat capacity than hot air, its temperature does not drop easily and the resin layer can be heated efficiently, which facilitates the melting of the PHA.

[0075] Furthermore, the heating process using superheated steam causes less damage to the substrate and can also suppress curling of the laminate, a decrease in the tear strength of the laminate, and discoloration of the paper substrate, which can occur with general heating.

[0076] The heating temperature when heating using superheated steam is set so that the surface temperature of the coating film is 10 to 100°C higher than the melting point (Tm) of the PHA (i.e., in the range of Tm + 10°C to Tm + 100°C). This temperature range promotes fusion of the PHA while suppressing decomposition of the PHA. The temperature range is preferably 10 to 80°C higher than Tm, more preferably 10 to 70°C higher than Tm, even more preferably 20 to 60°C higher than Tm, and particularly preferably 30 to 50°C higher than Tm.

[0077] The melting point (Tm) of the PHA refers to the peak top temperature in the crystalline melting curve obtained by differential scanning calorimetry of the PHA before the resin layer formation step. When multiple peaks exist, the melting point (Tm) refers to the lowest peak top temperature.

[0078] In order to set the surface temperature of the coating film within the above temperature range, the amount of superheated steam sprayed, heating time (superheated steam spray time), etc. may be adjusted in addition to the temperature of the superheated steam.

[0079] The superheated steam is usually sprayed from a spray nozzle. In this heating step, it is preferable to spray the superheated steam onto the surface of the coating film. In addition to the surface of the coating film, the superheated steam may also be sprayed onto the surface of the substrate on which the coating film is not formed.

[0080] The heating time using superheated steam is not particularly limited, but may be, for example, 2 seconds to 10 minutes, preferably 20 seconds to 5 minutes, and more preferably 30 seconds to 2 minutes.

[0081] (Second humidity adjustment step) After the heating step using superheated steam, a second humidity adjustment step of adjusting the moisture content of the substrate may be performed. This can reduce curling of the laminate caused by the heating step. It can also promote solidification or crystallization of the PHA. The details of the second humidity adjustment step are the same as those of the humidity adjustment step described above. However, since heating using superheated steam can suppress curling of the laminate, the second humidity adjustment step can be omitted or simplified.

[0082] (Resin Layer) In the laminate that can be produced by this embodiment, the resin layer can constitute the outermost layer. In this case, the resin layer can function as a heat seal layer, a water-resistant layer, and / or an oil-resistant layer, etc.

[0083] The heat seal layer is a layer having heat sealability, specifically, a layer that can be bonded to an object by heat and pressure bonding. The object may be the same heat seal layer, the substrate, or an article made of another material.

[0084] In the laminate that can be produced by this embodiment, the resin layer containing PHA as a main component preferably has melting characteristics in which, in a crystalline melting curve obtained by differential scanning calorimetry, it has at least one peak top temperature (Tma) in the range of 100 to 150°C and at least one peak top temperature (Tmb) in the range of 150 to 170°C, and the temperature difference between Tma and Tmb is 10°C or more. When the resin layer has such melting characteristics, it is possible to bond the resin layer by heat sealing during molding of the laminate, and it has the advantage that the applicable heat sealing temperature range is wide, and even if the resin is heated to a temperature that allows sufficient bonding, good adhesive strength can be exhibited in a short time after heating.

[0085] The resin layer has a melting point peak in the relatively high temperature range of 150 to 170°C, and resin crystals having Tmb act as crystal nuclei, accelerating the solidification of the molten resin during heat sealing. This makes it possible to develop good adhesive strength in a short time after heat sealing, even when the resin is heated to a temperature at which adhesion is sufficient.

[0086] The temperature difference between Tma and Tmb is more preferably 15° C. or more, even more preferably 20° C. or more, and particularly preferably 25° C. or more. There are no particular limitations on the upper limit of the temperature difference between Tma and Tmb, but from the viewpoint of ease of production, it is, for example, 60° C. or less, more preferably 50° C. or less.

[0087] In this specification, the peak top temperature of a crystalline melting curve in differential scanning calorimetry is defined as follows. 2 to 5 mg of the resin to be measured is filled into an aluminum pan, and using a differential scanning calorimetry analyzer, the temperature is raised from 20°C to 190°C at a rate of 10°C / min under a nitrogen stream to melt the resin and obtain a crystalline melting curve. In the obtained crystalline melting curve, the top temperature of the melting peak present in the range of 100 to 150°C is defined as Tma, and the top temperature of the melting peak present in the range of 150 to 170°C is defined as Tmb. Furthermore, if multiple melting peaks are observed in the range of 100 to 150°C, the top temperature of the highest peak is defined as Tma, and if multiple melting peaks are observed in the range of 150 to 170°C, the top temperature of the highest peak is defined as Tmb. A laminate including a resin layer exhibiting such melting characteristics can be produced by carrying out the heating process using superheated steam described above.

[0088] (Second Resin Layer) In a laminate according to another aspect of the present embodiment, a second resin layer may be further laminated on the resin layer described above (referred to as the first resin layer in this aspect). In this aspect, the substrate, the first resin layer, and the second resin layer are laminated in this order.

[0089] In this embodiment, the first resin layer functions as an anchor coat layer between the substrate and the second resin layer. Furthermore, by providing the second resin layer, it is possible to impart a high level of water resistance and oil resistance to the laminate. In this embodiment, the first resin layer only needs to have adhesive properties between the paper substrate and the second resin layer. The thickness of the first resin layer may be 0.5 to 100 μm as described above, but is preferably 0.7 to 15 μm, and more preferably 1 to 10 μm. The second resin layer may be the outermost layer in the laminate, or another layer may be laminated on top of the second resin layer.

[0090] The second resin layer preferably contains a biodegradable resin and exhibits biodegradability. This can enhance the biodegradability of the entire laminate. Usable biodegradable resins include the resins described above for the first resin layer, specifically PHA, as well as aliphatic polyester resins and aliphatic aromatic polyester resins. The second resin layer may also contain additives that are typically added to resin materials, as long as they do not impair the effects of the invention.

[0091] The thickness of the second resin layer is not particularly limited and can be appropriately determined taking into consideration the performance and productivity required of the second resin layer, and may be, for example, about 5 to 100 μm.

[0092] The method for forming the second resin layer on the first resin layer is not particularly limited, and examples thereof include a coating method, an extrusion lamination method, and a thermal lamination method.

[0093] [Molded Product] The laminate that can be produced by this embodiment can be molded into a predetermined shape to form a molded product (hereinafter also referred to as "the molded product"). The molded product includes the laminate and has a desired size and shape. The molded product is formed from a laminate including a resin layer containing PHA, and is therefore advantageous in various applications.

[0094] The present molded article is not particularly limited as long as it contains the present laminate, and examples thereof include paper, film, sheet, tube, plate, rod, container (e.g., bottle container), bag, part, etc. From the viewpoint of measures against marine pollution, the present molded article is preferably a packaging bag, a lid material, or a container such as a cup or a tray.

[0095] In one embodiment of the present disclosure, the present molded article may be the present laminate itself, or may be a product obtained by subjecting the present laminate to secondary processing.

[0096] Because the laminate has been subjected to secondary processing, the molded article containing it can be suitably used as various packaging container materials such as shopping bags, various bags, food and confectionery packaging materials, cups, trays, cartons, etc. (in other words, in various fields such as food, cosmetics, electronics, medicine, and pharmaceuticals.) Because the laminate contains a resin that has high adhesion to substrates and good heat resistance, it is more suitable as a container for holding liquids, particularly containers for holding hot contents such as cups for food and drink such as instant noodles, instant soup, and coffee, and trays for prepared meals, boxed lunches, and microwaveable foods.

[0097] The secondary processing can be carried out in the same manner as conventional resin-laminated paper or coated paper, i.e., using various bag-making machines, filling and packaging machines, etc. Processing can also be carried out using machines such as paper cup forming machines, punching machines, box making machines, etc. In these processing machines, known techniques can be used to bond the present laminate, such as heat sealing, impulse sealing, ultrasonic sealing, high-frequency sealing, hot air sealing, and frame sealing.

[0098] The heat-sealing temperature of the present laminate varies depending on the adhesion method. For example, when a heating-type heat-sealing tester equipped with a sealing bar is used, the heat-sealing temperature of the present laminate can usually be set so that the surface temperature of the resin layer is 180°C or less, preferably 170°C or less, and more preferably 160°C or less. Within the above range, melting of the resin near the sealed portion can be avoided, and an appropriate resin layer thickness and sealing strength can be ensured. Since the present laminate can achieve good adhesion even when heat-sealed at low temperatures, the surface temperature may be 150°C or less or 140°C or less. Furthermore, when a heating-type heat-sealing tester equipped with a sealing bar is used, the lower limit of the surface temperature is usually 100°C or more, preferably 110°C or more, and more preferably 120°C or more. Within the above range, appropriate adhesion at the sealed portion can be ensured.

[0099] The heat-sealing pressure of the present laminate varies depending on the bonding method. For example, when a heat-sealing tester with a seal bar is used, the heat-sealing pressure of the present laminate is usually 0.1 MPa or more, preferably 0.5 MPa or more. Within this range, appropriate adhesion at the sealed portion can be ensured. Furthermore, when a heat-sealing tester with a seal bar is used, the upper limit of the heat-sealing pressure is usually 1.0 MPa or less, preferably 0.75 MPa or less. Within this range, thinning of the film thickness at the sealed end can be avoided, and seal strength can be ensured.

[0100] Furthermore, in order to improve the physical properties of the present molded article, it can also be composited with a molded article made of a material different from the present molded article (for example, fiber, thread, rope, woven fabric, knitted fabric, nonwoven fabric, paper, film, sheet, tube, plate, rod, container, bag, part, foam, etc.). These materials are also preferably biodegradable.

[0101] The following items list preferred aspects of the present disclosure, but the present invention is not limited to them. [Item 1] A method for producing a laminate including a substrate and a resin layer formed on at least one surface of the substrate, comprising: applying an aqueous dispersion of a poly(hydroxyalkanoate)-based resin to the substrate to form a coating film; and heating the coating film with superheated steam so that the surface temperature of the coating film becomes 10°C to 100°C higher than the melting point (Tm) of the poly(hydroxyalkanoate)-based resin, thereby fusing the poly(hydroxyalkanoate)-based resin to form the resin layer. [Item 2] The manufacturing method according to Item 1, wherein the substrate is paper. [Item 3] The manufacturing method according to Item 1 or 2, wherein the value obtained by dividing the coating amount (dry weight) of the poly(hydroxyalkanoate)-based resin by the basis weight of the substrate (coating amount / basis weight of substrate) is 0.05 to 0.45. [Item 4] The coating amount (dry weight) of the poly(hydroxyalkanoate) resin is 1.0 g / m ２ 80g / m or more ２ [Item 5] The manufacturing method according to any one of items 1 to 3, wherein the basis weight of the substrate is 40 g / m or less. ２More than 400g / m ２ The manufacturing method according to any one of Items 1 to 4, wherein the poly(hydroxyalkanoate)-based resin is a poly(3-hydroxybutyrate)-based resin. [Item 7] The manufacturing method according to Item 6, wherein the poly(3-hydroxybutyrate)-based resin contains a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units. [Item 8] The manufacturing method according to Item 7, wherein the average content of 3-hydroxybutyrate units in the poly(3-hydroxybutyrate)-based resin is 70 to 97 mol %. [Item 9] The manufacturing method according to Item 7, wherein the other hydroxyalkanoate units are 3-hydroxyhexanoate units. [Item 10] The manufacturing method according to any one of Items 1 to 9, further comprising, before the step of forming the resin layer, a step of heating and drying the coating film at a temperature lower than the melting point (Tm) of the poly(hydroxyalkanoate)-based resin. [Item 11] The manufacturing method according to Item 10, further comprising a step of adjusting the moisture content of the substrate before the step of forming the resin layer and after the drying step. [Item 12] The manufacturing method according to any one of Items 1 to 11, further comprising a step of adjusting the moisture content of the substrate after the step of forming the resin layer. [Item 13] The manufacturing method according to any one of Items 1 to 12, wherein the resin layer has at least one peak top temperature (Tma) in the range of 100 to 150°C and at least one peak top temperature (Tmb) in the range of 150 to 170°C in a crystalline melting curve measured by differential scanning calorimetry, and the temperature difference between Tma and Tmb is 10°C or more. [Item 14] A manufacturing method for a molded article, comprising a step of manufacturing a laminate by the manufacturing method according to any one of Items 1 to 13, and a step of molding the laminate. [Item 15] The manufacturing method according to Item 14, wherein the molded article is a packaging bag, a lid material, or a container.

[0102] The present invention will be specifically explained below with reference to examples, but the technical scope of the present invention is not limited to these examples.

[0103] (Preparation of an aqueous suspension containing PHBH isolated from a microorganism) First, Ralstonia eutropha (formerly Alcaligenes eutrophus AC32 (deposit number FERM BP-6038)) into which Aeromonas caviae-derived 3-hydroxyalkanoic acid copolymer synthase group genes had been introduced was cultured by the method described in J. Bacteriol., 179, pp. 4821-4830 (1997), to obtain bacterial cells containing approximately 67% by weight of PHBH. In this PHBH, the composition ratio of repeating units (composition ratio of 3-hydroxybutyrate units / 3-hydroxyhexanoate units) was 89 / 11 (mol / mol). Next, paste-like bacterial cells were separated from the culture broth by centrifugation (5000 rpm, 10 min). Water was added to the bacterial cells to prepare a suspension of 75 g dry bacterial cells / L, and aqueous sodium hydroxide solution was added as an alkali to maintain the pH at 11.7. The bacterial constituents other than PHBH were solubilized by stirring and physical disruption, and the mixture was centrifuged (3,000 rpm, 10 min) to obtain a precipitate. The precipitate was further washed with water to separate PHBH with a weight-average molecular weight of approximately 260,000, a 3HH molar fraction of 11%, and a purity of 91%, yielding a suspension containing 75 g / L of PHBH. The suspension was placed in a stirring tank equipped with a pH electrode and maintained at 70°C. The pH electrode was connected to a Marubishi Bioengine Lab Controller Model MDL-6C, and was set so that when the pH fell below the set value, a peristaltic pump would operate and sodium hydroxide aqueous solution would enter the suspension until the set value was reached. The pH of the lab controller was set to 10, and 30% aqueous hydrogen peroxide was added to the suspension so that the hydrogen peroxide concentration was 5 wt% relative to the polymer weight (0.375 wt% relative to the suspension weight), followed by stirring for 1 hour. The suspension was then centrifuged, washed twice with water, and then washed twice with methanol. Furthermore, 30% aqueous hydrogen peroxide was added to the solids (PHBH) of the aqueous suspension as a preservative treatment so that the hydrogen peroxide concentration was 0.1 wt%. This process yielded an aqueous suspension with a PHBH concentration of 52 wt%. The protein content of the aqueous suspension was 1,500 ppm based on the solids, and the purity of the PHBH was 99.8% or higher.

[0104] [Example 1] Coating amount (dry weight) 35 to 40 g / m ２The PHBH aqueous suspension was added to a paper substrate (basis weight 220 g / m ２ ), and then dried for 60 seconds in a hot air drying oven at 120°C. An irreversible thermolabel (5E-125, 5E-170, manufactured by NOF Corporation) was affixed to the surface of the dried coating film. After drying, moisture was applied to the paper surface (opposite the coating film) using a spray bottle and then wiped off with a rag. The moisture content of the paper substrate was adjusted to 6-7%, and the curl was straightened. The laminate after moisture content adjustment and curl straightening was placed in a box-shaped container, and the coating film was sprayed with superheated steam for 60 seconds for heating. Heating was performed by spraying superheated steam so that the irreversible thermolabel displayed a temperature of resin melting point (Tm) + 30°C. This fused the PHBH, yielding a laminate in which a resin layer was formed on the paper substrate. The resin melting point (Tm) refers to the peak-top temperature in the crystalline melting curve obtained by performing differential scanning calorimetry on the PHBH contained in the PHBH aqueous suspension. When multiple peaks exist, the melting point (Tm) of the resin is the lowest peak temperature. In this example, the resin melting point (Tm) was 110°C.

[0105] Example 2 A laminate was obtained in the same manner as in Example 1, except that the superheated steam was sprayed so that the irreversible thermolabel displayed a temperature of the resin melting point + 40°C.

[0106] Example 3 A laminate was obtained in the same manner as in Example 1, except that the superheated steam was sprayed so that the irreversible thermolabel displayed a temperature of the resin melting point + 60°C.

[0107] Example 4 A laminate was obtained in the same manner as in Example 1, except that the superheated steam was sprayed so that the irreversible thermolabel displayed a temperature of the resin melting point + 70°C.

[0108] Comparative Example 1 A laminate was obtained in the same manner as in Example 1, except that the superheated steam was sprayed so that the irreversible thermolabel displayed a temperature of the resin melting point + 120°C.

[0109] [Comparative Example 2] After adjusting the moisture content and straightening the curl in the same manner as in Example 1, the paper substrate was dried by heating in a hot air oven for 120 seconds instead of spraying with superheated steam, to obtain a laminate in which a resin layer was formed on the paper substrate. Heating was carried out in the hot air oven until the irreversible thermolabel displayed a temperature of the resin melting point + 40°C.

[0110] Comparative Example 3 A laminate was obtained in the same manner as in Comparative Example 2, except that the heating in the hot air oven was carried out so that the irreversible thermolabel displayed a temperature of the resin melting point + 50°C.

[0111] Comparative Example 4 A laminate was obtained in the same manner as in Comparative Example 2, except that the heating in the hot air oven was carried out so that the irreversible thermolabel displayed a temperature of the resin melting point + 60°C.

[0112] Comparative Example 5 A laminate was obtained in the same manner as in Comparative Example 2, except that the heating in the hot air oven was carried out so that the irreversible thermolabel displayed a temperature of the resin melting point + 70°C.

[0113] The laminates obtained in Examples 1 to 4 and Comparative Examples 1 to 5 were evaluated for particle fusion state, curl height, molecular weight retention rate after heating, tear strength retention rate after heating, and color change by the methods described below. The results are shown in Table 1.

[0114] [Particle fusion state] The laminate obtained in each example or comparative example was immersed in liquid nitrogen and cooled to below the Tg of the resin, and then cut to expose the cross section of the resin layer. The cross section of the resin layer was observed at 2000x magnification using a scanning electron microscope (SEM). When particle shapes or voids were confirmed in the cross section, it was marked with ×, and when particle shapes or voids were not confirmed, it was marked with ◯.

[0115] [Curl height] A test piece measuring 300 mm in the machine direction and 200 mm in the width direction was cut out from the laminate obtained in each Example or Comparative Example. The test piece was placed on a flat surface with the resin layer facing up, and the maximum height of the end of the test piece from the surface on which it was placed was taken as the curl height.

[0116] [Molecular Weight Retention Rate After Heating] A laminate for evaluation was obtained in the same manner as in each Example or Comparative Example, except that the PHBH aqueous suspension was applied to a 38 μm-thick PET film instead of a paper substrate. The resin layer was peeled from the laminate for evaluation, and the weight-average molecular weight (weight-average molecular weight after heating) of the resulting resin piece was measured. In addition, a coating film was also peeled from the laminate for evaluation before heating using superheated steam or a hot air oven, and the weight-average molecular weight (weight-average molecular weight before heating) of the resulting coating film was similarly measured. The weight-average molecular weight was determined as a polystyrene-equivalent molecular weight by gel permeation chromatography (GPC) (Shodex GPC-101 manufactured by Showa Denko K.K.) using a polystyrene gel (Shodex K-804 manufactured by Showa Denko K.K.) as a column and chloroform as a mobile phase. The molecular weight retention rate after heating was calculated based on the following formula: Molecular weight retention rate after heating (%) = weight-average molecular weight after heating / weight-average molecular weight before heating × 100

[0117] [Tear strength retention rate after heating] The tear strength (tear strength after heating) of the laminates obtained in each Example or Comparative Example was evaluated in accordance with JIS P8116. The tear strength (tear strength before heating) of the laminates of each Example or Comparative Example before heating using superheated steam or a hot air oven was also evaluated in the same manner. The tear strength retention rate after heating was calculated based on the following formula. Formula: Tear strength retention rate after heating (%) = Tear strength after heating / Tear strength before heating × 100

[0118] [Color Change] The paper surface (the surface opposite to the resin layer) of the laminate obtained in each Example or Comparative Example was visually observed to evaluate whether or not there was discoloration of the paper base material (discoloration due to heating).

[0119]

[0120] Table 1 shows that in Examples 1 to 4, in which the coating film was heated using superheated steam within a range of 10 to 100°C above the resin melting point after coating of the aqueous resin dispersion, no particle shapes or voids were observed in the resin layer of the resulting laminate, and the resin was sufficiently fused. Moreover, the molecular weight retention rate after heating was relatively high, and it can be seen that the decrease in molecular weight of the resin due to heating was suppressed.

[0121] On the other hand, in Comparative Example 1, in which superheated steam was used but the heating temperature was set high, the molecular weight retention rate after heating was low, indicating that the molecular weight of the resin was significantly reduced by heating. Furthermore, in Comparative Examples 2 to 5, in which heating was performed using ordinary hot air without using superheated steam, particle shapes and voids were observed in the resin layer of the obtained laminate, despite the fact that the heating temperature was the same as in Examples 1 to 4, indicating that the resin was not sufficiently fused and the uniformity of the resin layer was insufficient.

[0122] It can also be seen that in Examples 1 to 4, compared to Comparative Examples 2 to 5, curling, a decrease in tear strength, and changes in the color tone of the paper base material that may occur during the heating process are suppressed.

Claims

1. A method for producing a laminate comprising a substrate and a resin layer formed on at least one surface of the substrate, A step of applying an aqueous dispersion of poly(hydroxyalkanoate) resin to the substrate to form a coating film, and A manufacturing method comprising the step of heating the coating film by blowing superheated steam onto the surface of the coating film so that the surface temperature of the coating film becomes 10°C to 100°C higher than the melting point (Tm) of the poly(hydroxyalkanoate) resin, thereby fusing the poly(hydroxyalkanoate) resin and forming the resin layer.

2. The manufacturing method according to claim 1, wherein the substrate is paper.

3. The manufacturing method according to claim 1 or 2, wherein the amount of the poly(hydroxyalkanoate) resin coating (dry weight) divided by the basis weight of the substrate (coating amount / basis weight of the substrate) is 0.05 to 0.

45.

4. The coating amount (dry weight) of the aforementioned poly(hydroxyalkanoate) resin is 1.0 g / m². ２ 80g / m or more ２ The manufacturing method according to claim 1 or 2, which is as follows:

5. The basis weight of the aforementioned substrate is 40 g / m². ２ More than 400g / m ２ The manufacturing method according to claim 1 or 2, which is as follows:

6. The manufacturing method according to claim 1 or 2, wherein the poly(hydroxyalkanoate) resin is a poly(3-hydroxybutyrate) resin.

7. The manufacturing method according to claim 6, wherein the poly(3-hydroxybutyrate) resin comprises a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units.

8. The manufacturing method according to claim 7, wherein the average content of the 3-hydroxybutyrate units in the poly(3-hydroxybutyrate) resin is 70 to 97 mol%.

9. The manufacturing method according to claim 7, wherein the other hydroxyalkanoate unit is a 3-hydroxyhexanoate unit.

10. The manufacturing method according to claim 1 or 2, further comprising the step of heating and drying the coating film at a temperature lower than the melting point (Tm) of the poly(hydroxyalkanoate) resin before the step of forming the resin layer.

11. The manufacturing method according to claim 10, further comprising a step of adjusting the moisture content of the substrate before the step of forming the resin layer and after the drying step.

12. The manufacturing method according to claim 1 or 2, further comprising the step of adjusting the water content of the substrate after the step of forming the resin layer.

13. The manufacturing method according to claim 1 or 2, wherein the resin layer has at least one peak top temperature (Tma) in the range of 100 to 150°C and at least one peak top temperature (Tmb) in the range of 150 to 170°C in the crystal melting curve obtained by differential scanning calorimetry, and the temperature difference between Tma and Tmb is 10°C or more.

14. A method for manufacturing a molded article, comprising the steps of manufacturing a laminate by the manufacturing method described in claim 1 or 2, and molding the laminate.

15. The manufacturing method according to claim 14, wherein the molded body is a packaging bag, a lid, or a container.