Laminates and molded articles

Abstract

A laminate having a base material layer and a coating layer laminated on at least one surface of the base material layer, wherein the coating layer contains a poly(3-hydroxybutyrate)-based resin, the coating layer has, on a crystal fusion curve obtained by differential scanning calorimetry, at least one peak top temperature (Tma) in the range of 100-150°C and at least one peak top temperature (Tmb) in the range of 150-170°C, and the temperature difference between Tma and Tmb is 10°C or more.

Description

[Technical Field]

[0001] The present invention relates to a laminate having a coating layer containing a poly(3-hydroxybutyrate)-based resin, and a molded article containing the laminate. [Background technology]

[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 poly(3-hydroxybutyrate) resins in particular are thermoplastic polyesters that are produced and accumulated as energy storage substances within the cells of many microbial species. Because they are capable of biodegrading not only in soil but also in seawater, they are attracting attention as a material that can solve the above problems.

[0004] Furthermore, a laminate obtained by laminating a layer containing a poly(3-hydroxybutyrate)-based resin onto a biodegradable substrate such as paper is extremely promising from the viewpoint of environmental protection, since both the resin and the substrate are highly biodegradable materials (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2019 / 239913 Summary of the Invention [Problem to be solved by the invention]

[0006] Previously reported laminates in which a layer containing a poly(3-hydroxybutyrate) resin is laminated to a substrate have had a limited range of applicable heating temperatures when the resin layer is bonded by heat sealing during molding. In particular, when heat sealing is performed at high temperatures, a relatively long time must pass after heat sealing to achieve good adhesive strength, resulting in a problem of reduced production efficiency.

[0007] In view of the above-mentioned current situation, the present invention aims to provide a laminate having a layer containing a poly(3-hydroxybutyrate)-based resin, which allows the resin layer to be bonded by heat sealing during molding and processing of the laminate, has a wide range of applicable heat sealing temperatures, and is capable of exhibiting good adhesive strength in a short time after heating, even when the resin is heated to a temperature at which adhesion is sufficient. [Means for solving the problem]

[0008] 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 configuring a coating layer containing a poly(3-hydroxybutyrate)-based resin so that it exhibits a specific peak in a crystalline melting curve determined by differential scanning calorimetry, and have thus completed the present invention.

[0009] That is, the present invention relates to a laminate having a base layer and a coating layer laminated on at least one surface of the base layer, wherein the coating layer contains a poly(3-hydroxybutyrate)-based resin, and the coating 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. Preferably, in a crystalline melting curve of the coating layer obtained by differential scanning calorimetry analysis, the ratio (ΔHb / ΔHa) of the crystalline melting enthalpy (ΔHa) of the peak in the range of 100 to 150°C to the crystalline melting enthalpy (ΔHb) of the peak in the range of 150 to 170°C is 0.01 to 2. Preferably, the poly(3-hydroxybutyrate) resin has a weight average molecular weight of 50,000 to 650,000. Preferably, the poly(3-hydroxybutyrate)-based resin comprises at least one poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). Preferably, the poly(3-hydroxybutyrate)-based resin contains at least two types of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) having different content ratios of constituent monomers. Preferably, the poly(3-hydroxybutyrate)-based resin contains poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) having a 3-hydroxyhexanoate unit content of 8 mol% or more and 25 mol% or less. More preferably, the poly(3-hydroxybutyrate)-based resin further contains poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) having a 3-hydroxyhexanoate unit content of less than 8 mol%, or poly(3-hydroxybutyrate). The present invention also relates to a method for producing the laminate, which includes the steps of applying an aqueous coating liquid containing the poly(3-hydroxybutyrate) resin to a substrate to form a coating film, and heating the coating film at a temperature of 130°C or higher and 170°C or lower to form the coating layer. The present invention also relates to a molded article comprising the laminate. Furthermore, the present invention also relates to a method for producing the molded article, which includes a step of heat-sealing the coating layer. [Effects of the Invention]

[0010] According to the present invention, there is provided a laminate having a layer containing a poly(3-hydroxybutyrate)-based resin, which can be bonded by heat sealing during molding of the laminate, has a wide range of applicable heat sealing temperatures, and can exhibit good adhesive strength within a short time after heating, even when the resin is heated to a temperature at which sufficient adhesion is possible. Use of the laminate of the present invention can shorten the heat sealing cycle time and improve the production efficiency of molded articles. [Brief explanation of the drawings]

[0011] [Figure 1] Crystal melting curve measured by differential scanning calorimetry for Example 1 DETAILED DESCRIPTION OF THE INVENTION

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

[0013] [Laminate] A laminate according to one embodiment of the present invention comprises a substrate layer and a coating layer laminated on at least one surface of the substrate layer, the coating layer containing a poly(3-hydroxybutyrate)-based resin.

[0014] The coating layer may be laminated on only one side of the substrate layer or on both sides. The coating layer may be laminated on the substrate layer via another layer or directly on the substrate layer without any other layer. Another layer may be laminated on the coating layer.

[0015] (base material layer) The substrate layer is not particularly limited as long as it is a layer on which a coating layer can be laminated, but is preferably a biodegradable layer. When the substrate layer is a biodegradable layer, the entire laminate, including the coating layer, is biodegradable, making it more advantageous as a material for solving the problem of marine pollution.

[0016] In addition, from the viewpoint of preventing the coating liquid from flowing over the surface and forming a coating film with an uneven thickness, the substrate layer is preferably water-absorbent.

[0017] The biodegradable substrate layer is not particularly limited, but examples include paper (mainly composed of cellulose), cellophane, cellulose ester; polyvinyl alcohol, polyamino acid, polyglycolic acid, pullulan, or these substrates vapor-deposited with inorganic substances such as aluminum or silica. Among these, paper is preferred because it has excellent heat resistance and is inexpensive. The type of paper is not particularly limited, and examples include cup base paper, kraft paper, fine paper, coated paper, tissue paper, glassine paper, and paperboard. The type of paper can be appropriately selected depending on the application of the laminate. Water-resistant agents, water-repellent agents, inorganic substances, etc. may be added to the paper as needed, and the paper may be surface-treated with an oxygen barrier layer coating, a water vapor barrier coating, etc.

[0018] The substrate layer may be subjected to a surface treatment such as corona treatment, flame treatment, anchor coating treatment, etc. These surface treatments may be performed alone or in combination.

[0019] As described below, the coating layer can be formed by applying an aqueous coating liquid to one or both sides of a substrate layer, heating, drying, and forming a film. Therefore, when the coating layer is laminated directly onto the substrate layer without any other layers, a portion of the aqueous coating liquid penetrates into the substrate layer during the laminate production process, forming an intermediate layer between the coating layer and the substrate layer, which contains a portion of the poly(3-hydroxybutyrate) resin derived from the coating layer and a portion of the substrate derived from the substrate layer. Such an intermediate layer is not found in laminates produced by extrusion molding, such as lamination, and is a characteristic feature of laminates containing a coating layer. The morphology of the intermediate layer in the laminate can be easily observed, for example, using a scanning electron microscope (SEM).

[0020] (coating layer) The coating layer contains at least a poly(3-hydroxybutyrate)-based resin. In this specification, a poly(3-hydroxybutyrate)-based resin (hereinafter also referred to as a P3HB-based resin) is an aliphatic polyester resin that contains 3-hydroxybutyrate as a repeating unit and can be produced from a microorganism.

[0021] The P3HB resin may be a poly(3-hydroxybutyrate) containing only 3-hydroxybutyrate as a repeating unit, or may be a copolymer of 3-hydroxybutyrate and another hydroxyalkanoate.

[0022] The P3HB resin may be a mixture of a homopolymer and one or more copolymers, or a mixture of two or more copolymers. The copolymerization method is not particularly limited and may be random copolymerization, alternating copolymerization, block copolymerization, graft copolymerization, or the like.

[0023] Examples of P3HB resins include poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P3HB3HV), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate) (P3HB3HO), poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate) (P3HB3HOD), poly(3-hydroxybutyrate-co-3-hydroxydecanoate) (P3HB3HD), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (P3HB3HV3HH). Among these, P3HB, P3HB3HH, P3HB3HV, and P3HB4HB are preferred because they are easy to produce industrially.

[0024] Furthermore, P3HB3HH, a copolymer of 3-hydroxybutyric acid and 3-hydroxyhexanoic acid, is more preferred because changing the composition ratio of the repeating units can change the melting point and crystallinity, thereby changing physical properties such as Young's modulus and heat resistance, and it can impart physical properties between those of polypropylene and polyethylene. Furthermore, P3HB3HH is also preferred because it can lower the melting point and enable molding at low temperatures.

[0025] In one embodiment of the present invention, the P3HB-based resin preferably contains at least one type of P3HB3HH, and more preferably contains at least two types of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) with different monomer content ratios. It is also preferable to contain at least one type of P3HB3HH and P3HB.

[0026] Microorganisms capable of producing P3HB resins are not particularly limited as long as they are capable of producing P3HB resins. For example, the first P3HB-producing bacterium was Bacillus megaterium, discovered in 1925. Other examples include naturally occurring microorganisms such as Cupriavidus necator (formerly Alcaligenes eutrophus, Ralstonia eutropha) and Alcaligenes latus. These microorganisms are known to accumulate P3HB within their cells.

[0027] Known microorganisms that produce copolymers of 3-hydroxybutyrate and other hydroxyalkanoates include Aeromonas caviae, which produces P3HB3HV and P3HB3HH, and Alcaligenes eutrophus, which produces P3HB4HB. In particular, Alcaligenes eutrophus AC32 (FERM BP-6038) (T. Fukui, Y. Doi, J. Bateriol., 179, pp. 4821-4830 (1997)), which has been transformed with genes encoding P3HA synthases, is preferred for increasing P3HB3HH productivity. These microorganisms are cultured under appropriate conditions to accumulate P3HB3HH within the cells. In addition to the above, genetically modified microorganisms into which various P3HB resin synthesis-related genes have been introduced may be used depending on the P3HB resin to be produced, and culture conditions, including the type of substrate, may be optimized.

[0028] P3HB3HH can also be produced by the method described in, for example, WO 2010 / 013483. Commercially available P3HB3HH products include Kaneka Biodegradable Polymer PHBH (registered trademark) manufactured by Kaneka Corporation.

[0029] The P3HB-based resin preferably contains P3HB3HH with a 3HH unit content of 8 to 25 mol %. The composition ratio of the constituent monomers in the P3HB3HH is preferably 3HB / 3HH=92 to 75 / 8 to 25 (mol % / mol %), and more preferably 3HB / 3HH=90 to 82 / 10 to 18 (mol % / mol %). When the 3HH unit content in the P3HB3HH is 8 mol % or more, a coating layer having the melting characteristics described below can be easily formed. Furthermore, P3HB3HH with a 3HH unit content of 25 mol % or less does not have an excessively slow crystallization rate and is relatively easy to produce. The composition ratio of the constituent monomers is determined by measuring the P3HB3HH by NMR.

[0030] P3HB3HH containing 8 to 25 mol% of 3HH units may be used alone as a P3HB-based resin, or may be used in combination with P3HB3HH or P3HB (3HB homopolymer) containing less than 8 mol% of 3HH units. This combination allows for a larger ΔHb / ΔHa ratio (described below) than when used alone, and allows for the development of good adhesive strength in a short time after heat sealing, even when the heat sealing temperature is raised to a temperature at which sufficient adhesion is possible. In P3HB3HH having a 3HH unit content of less than 8 mol%, the 3HH unit content 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 3HH unit content in P3HB3HH is not particularly limited, but may be, for example, 0.1 mol% or more.

[0031] The amount of P3HB3HH or P3HB containing less than 8 mol% of 3HH units is not particularly limited, but is preferably 0 to 50 wt% of the total P3HB resin contained in the coating layer. If present, the amount is preferably 1 to 50 wt%, more preferably 3 to 30 wt%, even more preferably 4 to 20 wt%, and particularly preferably 5 to 15 wt%.

[0032] Microbial P3HB3HH is a random copolymer, and the 3HH unit content can be adjusted by, for example, selecting the bacterial cells, the carbon source used as the raw material, blending P3HB3HHs with different 3HH unit contents, or blending 3HB homopolymers.

[0033] According to one embodiment of the present invention, the weight-average molecular weight of the P3HB resin is preferably 50,000 to 650,000, more preferably 100,000 to 600,000, even more preferably 150,000 to 550,000, and particularly preferably 150,000 to 500,000. Having a weight-average molecular weight within the above range enables the coating layer to exhibit high adhesive strength upon heat sealing. The weight-average molecular weight of the P3HB resin can be 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 the mobile phase.

[0034] The coating layer may contain one or more resins other than the P3HB resin, as long as the effects of the invention are achieved. Examples of such other resins include aliphatic polyester resins such as polybutylene succinate, polycaprolactone, and polylactic acid, and aliphatic aromatic polyester resins such as polybutylene adipate terephthalate, polybutylene sebatate terephthalate, and polybutylene azelate terephthalate. To ensure the biodegradability of the coating layer, the amount of these resins added is preferably 10 parts by weight or less per 100 parts by weight of the P3HB resin. The coating layer does not necessarily need to contain any resins other than the P3HB resin.

[0035] The coating layer may contain additives commonly used in the art, as long as the effects of the invention are achieved. Examples of such additives include inorganic fillers such as talc, calcium carbonate, mica, silica, titanium oxide, and alumina; organic fillers such as rice husk, wood flour, recycled paper such as newspaper, various starches, and cellulose; 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, UV absorbers, crystal nucleating agents, lubricants, release agents, water repellents, antibacterial agents, sliding property improvers, tackifiers, fillers, and chemicals. Only one type of additive may be contained, or two or more types may be contained. The content of these additives can be appropriately determined by those skilled in the art depending on the intended use.

[0036] According to one embodiment of the present invention, the coating layer has melting characteristics in which, in a crystalline melting curve measured 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. Because the coating layer has such melting characteristics, it can be bonded by heat sealing during molding and processing of the laminate, and the applicable heat sealing temperature range is wide, so that even if the resin is heated to a temperature that allows for sufficient bonding, good adhesive strength can be achieved in a short time after heating.

[0037] It is presumed that the coating layer has a melting point peak in the relatively high temperature range of 150 to 170°C, and resin crystals containing Tmb act as crystal nuclei, accelerating the solidification of the molten resin during heat sealing. This makes it possible to achieve good adhesive strength in a short time after heat sealing, even when the resin is heated to a temperature at which adhesion is sufficient.

[0038] The temperature difference between Tma and Tmb is 10°C or more, preferably 15°C or more, more preferably 20°C or more, and even more preferably 25°C or more. If the temperature difference is less than 10°C, even if the resin is heated to a temperature at which sufficient adhesion is possible, it may be difficult to achieve the effect of exhibiting good adhesive strength in a short time after heating. 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.

[0039] 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 coating layer separated from the substrate layer is placed in an aluminum pan, and the coating layer is melted using a differential scanning calorimetry analyzer by heating from 20°C to 190°C at a rate of 10°C / min under a nitrogen stream to 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. 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. Figure 1 shows the crystalline melting curve measured for Example 1 as a representative example of a crystalline melting curve having Tma and Tmb.

[0040] In one embodiment of the present invention, in a crystalline melting curve of the coating layer measured by differential scanning calorimetry (DSC), the ratio (ΔHb / ΔHb) of the crystalline melting enthalpy (ΔHa) of the peak in the 100-150°C range to the crystalline melting enthalpy (ΔHb) of the peak in the 150-170°C range is preferably 0.01 to 2. When this ratio is within this range, the resin melted by heating solidifies quickly, and even when heated to a temperature sufficient for adhesion, good adhesive strength is easily achieved within a short time after heat sealing. The ratio is more preferably 0.05 to 1, even more preferably 0.1 to 0.8, even more preferably 0.15 to 0.6, and most preferably 0.2 to 0.4.

[0041] In addition, when multiple melting point peaks are observed in the range of 100 to 150°C, the sum of the crystalline melting enthalpies of all those melting point peaks is defined as ΔHa, and when multiple melting point peaks are observed in the range of 150 to 170°C, the sum of the crystalline melting enthalpies of all those peaks is defined as ΔHb.

[0042] The weight per unit area of ​​the P3HB resin in the coating layer is preferably 5 to 100 g / m 2 and more preferably 10 to 50 g / m 2 and particularly preferably 15 to 30 g / m 2 When the weight per unit of the P3HB resin in the coating layer is within the above range, defects such as pinholes can be prevented, the coating layer can have sufficient strength for use, and the coating layer can efficiently exhibit functions such as water resistance. The weight per unit of the P3HB resin in the coating layer is measured and evaluated by the method described in the Examples.

[0043] The thickness of the coating layer (or each coating layer when the laminate has two or more coating layers) is not particularly limited, but is preferably 5 to 100 μm, more preferably 10 to 30 μm, from the viewpoint of preventing water absorption into the base layer while ensuring sufficient flexibility.

[0044] [Method for manufacturing laminate] The laminate according to one embodiment of the present invention can be produced, for example, by applying an aqueous coating liquid to one or both surfaces of a substrate layer, and then heating and drying the coating liquid to form a film. As a method for producing the coating liquid, any known method can be appropriately used, and there is no particular limitation.

[0045] The method for producing the laminate may include the following steps: (a) a step of producing an aqueous coating liquid, (b) a step of feeding out a substrate layer, (c) a step of applying the aqueous coating liquid to the substrate layer, and (d) a step of drying and forming a coating film.

[0046] Step (a) can be carried out by, but is not limited to, the following method: Step (a) involves producing a P3HB resin from a microorganism, disrupting the microbial cells containing the P3HB resin in an aqueous dispersion, and isolating the P3HB resin from the cells.

[0047] Typically, P3HB resins are recovered from microbial cells by dissolving them in an organic solvent such as chloroform, followed by precipitation recovery using a solvent insoluble in P3HB resin, such as methanol or hexane. However, this method does not produce finely divided P3HB resins, necessitating an additional step of microparticleizing the P3HB resin, which is economically disadvantageous. In contrast, a step of disrupting microbial cells containing P3HB resin in an aqueous dispersion and isolating the P3HB resin within the cells allows for the production of an aqueous dispersion of P3HB resin fine particles that maintains a significant degree of their fine particle size.

[0048] In the process of disrupting microbial cells containing P3HB resin in an aqueous dispersion and separating the P3HB resin from the cells, disruption and alkali addition are preferably performed simultaneously while stirring the microbial cells. The advantages of this method are: (i) preventing an increase in the viscosity of the dispersion due to cell components other than the P3HB resin leaking from the microbial cells; (ii) preventing an increase in the viscosity of the cell dispersion allows for pH control, and furthermore, treatment can be performed at a low alkali concentration by adding alkali continuously or intermittently; and (iii) preventing a decrease in the molecular weight of the P3HB resin, allowing for the separation of a high-purity P3HB resin. The pH of the cell dispersion after alkali addition is preferably 9 to 13.5. A pH of 9 or higher facilitates separation of the P3HB resin from the cells, while a pH of 13.5 or lower tends to suppress decomposition of the P3HB resin.

[0049] Microbial cell disruption can be achieved by ultrasonic disruption or by using an emulsifying disperser, high-pressure homogenizer, mill, or the like. Among these, emulsifying dispersers, such as Silverson Mixer (manufactured by Silverson), Clearmix (manufactured by M-Tech), and Ebara Milder (manufactured by Ebara), are preferred because they can dissolve the P3HB resin from the bacterial cells by alkali treatment, efficiently disrupt nucleic acids, which are the primary cause of increased viscosity, and thoroughly disperse insoluble substances other than the P3HB resin, such as cell walls, cell membranes, and insoluble proteins. However, these are not limiting. Furthermore, the temperature conditions for disrupting the microbial cells and adding the alkali are preferably within the range of room temperature to 50°C. Temperatures above 50°C are preferred because decomposition of the P3HB resin is likely to occur. Furthermore, lowering the temperature below room temperature requires a cooling procedure, which is uneconomical.

[0050] A precipitate is obtained from the dispersion obtained by crushing and alkali-treating the microbial cells by centrifugation. This precipitate is then washed with water, and if necessary, with methanol. Finally, an appropriate amount of water is added to obtain an aqueous coating solution containing a P3HB-based resin at the desired solids concentration.

[0051] After the above steps, it is preferable to include a step of subjecting the aqueous coating liquid to mechanical shearing to separate partially aggregated P3HB resin particles from one another. Applying mechanical shearing is preferable because it substantially eliminates aggregates and allows for the production of an aqueous coating liquid containing a P3HB resin with a uniform particle size. Mechanical shearing of the aqueous coating liquid can be carried out using, for example, a stirrer, a homogenizer, ultrasonic waves, or the like. At this stage, the P3HB resin particles are not very strongly aggregated, so for simplicity's sake, it is preferable to use a stirrer equipped with a conventional stirring blade.

[0052] The solids concentration of the P3HB resin in the aqueous coating solution is preferably 25 to 65 wt %, more preferably 30 to 55 wt %, and particularly preferably 35 to 50 wt %. When the solids concentration of the P3HB resin in the aqueous coating solution is within this range, the viscosity of the solution is not too high, which enables uniform coating and maintains the required coating thickness, thereby reducing the occurrence of coating defects.

[0053] The average particle size of the P3HB resin in the aqueous coating solution is, 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 productivity of the P3HB resin and uniformity during coating. An average particle size of 0.1 μm or more allows the P3HB resin to be easily obtained by either microbial production or chemical synthesis. An average particle size of 50 μm or less prevents uneven coating. The average particle size of the P3HB resin in the aqueous coating solution can be calculated using a general-purpose particle size analyzer such as a Microtrac particle size analyzer (manufactured by Nikkiso Co., Ltd., FRA) by adjusting an aqueous suspension containing the P3HB resin to a predetermined concentration and determining the particle size corresponding to 50% of the total particle size in a normal distribution.

[0054] The aqueous coating liquid may not contain an emulsifier, but preferably contains one to stabilize the coating liquid. 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, and water-soluble polymers such as polyvinyl alcohol and polyvinylpyrrolidone. The amount of emulsifier added is not particularly limited, but is preferably 1 to 10 wt% based on the solid content of the P3HB resin. Adding an amount of emulsifier of 1 wt% or more tends to provide a stabilizing effect, while adding an amount of emulsifier of 10 wt% or less can avoid deterioration in physical properties and discoloration due to excessive emulsifier contamination of the P3HB resin.

[0055] The emulsifier can be added to the aqueous dispersion after microbial cell disruption, alkali treatment, centrifugation, and water washing. If methanol washing is performed, the emulsifier can be added after methanol washing, before or after adjusting the solids concentration of the P3HB-based resin by adding an appropriate amount of water.

[0056] The above steps (b) and (c) can be carried out by any method known in the art without any particular limitation.

[0057] In one embodiment of the present invention, the heating temperature in the drying and film-forming step of the coating film in step (d) is preferably 130 to 170° C., more preferably 135 to 165° C., even more preferably 138 to 162° C., and particularly preferably 140 to 160° C. By heating the coating film at such a temperature for drying and film formation, a coating layer exhibiting the above-mentioned melting properties can be formed, and the laminate can be obtained. The heating time in the drying and film-forming step of the coating film in the step (d) is not particularly limited and can be set appropriately, but may be, for example, 30 seconds to 10 minutes, preferably 1 to 5 minutes.

[0058] The method for producing the laminate may include, after the step (d), (e) a step of winding up the laminate. The step (e) is not particularly limited and may be performed by any method known in the art.

[0059] [Molded body] A molded article according to one embodiment of the present invention includes the laminate described above. The molded article includes a laminate that allows the coating layer to be bonded by heat sealing during secondary processing of the laminate, and that has a wide range of applicable heat sealing temperatures and can exhibit good adhesive strength in a short time after heating even when the resin is heated to a temperature that allows for sufficient adhesion. This allows for a shortened cycle time for heat sealing, thereby improving the production efficiency of molded articles.

[0060] The molded article is not particularly limited as long as it contains the laminate, and examples thereof include paper, film, sheet, tube, plate, rod, packaging material (e.g., bag), container (e.g., bottle container), parts, etc. From the viewpoint of measures against marine pollution, the molded article is preferably a packaging material or a container.

[0061] In one embodiment of the present invention, the molded body may be the laminate itself. Also, in one embodiment of the present invention, the laminate included in the molded body may be a secondary processed laminate.

[0062] 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 includes a coating layer that has high adhesion to substrates and good heat resistance, the laminate can be particularly suitably used as containers 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.

[0063] The secondary processing can be carried out by any method known in the art, such as various bag-making machines, filling and packaging machines, etc. Processing can also be carried out using devices such as paper cup forming machines, punching machines, and box-making machines. In these processing machines, known techniques can be used to bond the laminate, such as heat sealing, impulse sealing, ultrasonic sealing, high-frequency sealing, hot air sealing, and frame sealing. It is particularly preferred that the molded article be secondary processed using a heat sealing method, i.e., that it includes a heat-sealed portion formed by a coating layer. The heat sealing may be carried out between the substrate layer and the coating layer, or between the coating layers.

[0064] The heat-sealing temperature when heat-sealing the laminate varies depending on the adhesive method, substrate, and coating thickness. The heat-sealing temperature when heat-sealing the coating layers of the laminate is typically 250°C or lower, preferably 240°C or lower, and more preferably 220°C or lower, when both sides are heated using a heat-sealing tester equipped with a sealing bar. Within this range, melting of the resin near the sealed portion can be avoided, ensuring an appropriate coating layer thickness and seal strength. Furthermore, the lower limit of the heat-sealing temperature when using a heat-sealing tester equipped with a sealing bar is typically 120°C or higher, preferably 140°C or higher. Within this range, appropriate adhesion at the sealed portion can be ensured. Furthermore, since the laminate according to one embodiment of the present invention can exhibit good adhesive strength within a short time after heat-sealing, even at high heat-sealing temperatures, the heat-sealing temperature may be 180°C or higher, or even 200°C or higher. In a particularly preferred embodiment, the heat-sealing temperature may be 220°C or higher.

[0065] The heat-sealing temperature when heat-sealing the coating layer of the laminate to the paper substrate using a heating-type heat-sealing tester equipped with a sealing bar and heating both sides is typically 250°C or lower, preferably 240°C or lower, and more preferably 220°C or lower. Within this range, melting of the resin near the sealed portion can be avoided, ensuring an appropriate coating layer thickness and seal strength. Furthermore, the lower limit of the heat-sealing temperature when using a heating-type heat-sealing tester equipped with a sealing bar is typically 120°C or higher, preferably 140°C or higher. Within this range, appropriate adhesion at the sealed portion can be ensured. Furthermore, since the laminate according to one embodiment of the present invention can exhibit good adhesive strength within a short time after heat-sealing even at high heat-sealing temperatures, the heat-sealing temperature may be 170°C or higher, or even 180°C or higher. In a particularly preferred embodiment, the heat-sealing temperature may be 190°C or higher.

[0066] The heat-sealing pressure when heat-sealing the laminate varies depending on the adhesion method. When a heat-sealing tester equipped with a seal bar is used, the heat-sealing pressure of the laminate is usually 0.1 MPa or more, preferably 0.3 MPa or more. Within the above range, adequate adhesion at the sealed portion can be ensured.

[0067] In order to improve the physical properties of the molded article according to one embodiment of the present invention, it is also possible to compound the molded article with another molded article (for example, fiber, thread, rope, woven fabric, knitted fabric, nonwoven fabric, paper, film, sheet, tube, plate, rod, container, bag, part, foam, etc.) made of a different material from the molded article. These materials are also preferably biodegradable. [Example]

[0068] 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.

[0069] (peel test) Each coated paper was cut into a 25 mm wide strip. Using a heat sealer (TP-701-B, manufactured by Tester Sangyo Co., Ltd.), the coated layers of the coated paper were pressed together or the coated layers were pressed against the paper at a heating temperature of 120°C, 140°C, 160°C, 170°C, 180°C, 190°C, 200°C, or 220°C, a surface pressure of 0.4 MPa, and a sealing time of 1 second. Two seconds after the heat seal bar left the coated paper, the sealed surfaces were peeled off by hand. The peeled surfaces were visually observed and evaluated according to the following criteria. <Evaluation> ○: The paper was destroyed △: Part of the paper was destroyed ×: The paper did not break down.

[0070] (Resin weight) Each coated paper was cut into a 10 cm x 10 cm piece and weighed. The weight was subtracted from the weight of the base paper and multiplied by 100 to obtain the weight per unit area of ​​the resin content.

[0071] [Manufacturing example] (Method of producing resin dispersion) A resin dispersion liquid with a solid content concentration of P3HB3HH of 50% by weight was obtained in accordance with the method described in WO 2015 / 1461965.

[0072] (Method of manufacturing aqueous coating liquid) A 2% aqueous solution of methylcellulose (Metolose SM-400, manufactured by Shin-Etsu Chemical Co., Ltd.) was added and stirred so that the amount was 1 part by weight per 100 parts by weight of the resin contained in the resin dispersion, to obtain an aqueous coating liquid.

[0073] Example 1 An aqueous coating solution was prepared using an aqueous dispersion containing P3HB3HH, which has a 3-hydroxyhexanoate unit content of 11 mol% and a weight-average molecular weight of 260,000. 2 The A3 size base paper was coated with the aqueous coating liquid using a slit coater with a coating thickness of 90 μm, and then heated in an oven at 160 °C for 3 minutes to form a coating layer. The resin weight was 20 g / m 2 The resulting coated paper was subjected to a peel test.

[0074] Example 2 An aqueous dispersion containing P3HB3HH with a 3-hydroxyhexanoate unit content of 11 mol% and a weight-average molecular weight of 260,000 was blended with an aqueous dispersion containing P3HB3HH with a 3-hydroxyhexanoate unit content of 0.7 mol% and a weight-average molecular weight of 350,000, at a blending ratio of 10 wt% based on the resin. The blended aqueous dispersion was used to produce an aqueous coating solution. Basis weight: 200 g / m 2 The A3 size base paper was coated with the aqueous coating liquid using a slit coater with a coating thickness of 90 μm, and then heated in an oven at 160 °C for 3 minutes to form a coating layer. The resin weight was 20 g / m 2 The resulting coated paper was subjected to a peel test.

[0075] Example 3 An aqueous dispersion containing P3HB3HH with a 3-hydroxyhexanoate unit content of 11 mol% and a weight-average molecular weight of 260,000 was blended with an aqueous dispersion containing P3HB3HH with a 3-hydroxyhexanoate unit content of 0.7 mol% and a weight-average molecular weight of 350,000, at a blending ratio of 5 wt% based on the resin. The blended aqueous dispersion was used to produce an aqueous coating solution. Basis weight: 200 g / m 2 The A3 size base paper was coated with the aqueous coating liquid using a slit coater with a coating thickness of 90 μm, and then heated in an oven at 160 °C for 3 minutes to form a coating layer. The resin weight was 20 g / m 2 The resulting coated paper was subjected to a peel test.

[0076] Example 4 An aqueous dispersion containing P3HB3HH with a 3-hydroxyhexanoate unit content of 11 mol% and a weight-average molecular weight of 260,000 was blended with an aqueous dispersion containing P3HB3HH with a 3-hydroxyhexanoate unit content of 0.7 mol% and a weight-average molecular weight of 350,000, at a blending ratio of 20 wt% based on the resin. The blended aqueous dispersion was used to produce an aqueous coating solution. Basis weight: 200 g / m 2 The A3 size base paper was coated with the aqueous coating liquid using a slit coater with a coating thickness of 90 μm, and then heated in an oven at 160 °C for 3 minutes to form a coating layer. The resin weight was 20 g / m 2 The resulting coated paper was subjected to a peel test.

[0077] Comparative Example 1 An aqueous coating solution was prepared using an aqueous dispersion containing P3HB3HH with a weight-average molecular weight of 250,000 and a content of 3-hydroxyhexanoate units of 6 mol %. 2 The A3 size base paper was coated with the aqueous coating solution using a slit coater with a coating thickness of 90 μm, and then heated in an oven at 160°C for 3 minutes to form a coating layer. The resin weight was 20 g / m 2 The resulting coated paper was subjected to a peel test.

[0078] (Differential Scanning Calorimetry) Each of the aqueous coating solutions used in Examples 1 to 4 and Comparative Example 1 was coated onto a PET film using a slit coater with a coating thickness of 90 μm, and heated at 160° C. for 3 minutes to form a coating layer. The coating layer was peeled off from the PET film and subjected to the following differential scanning calorimetry analysis.

[0079] 2 to 5 mg of the coating layer was placed in an aluminum pan, and the coating layer was melted by heating from 20°C to 190°C at a rate of 10°C / min under a nitrogen stream using a differential scanning calorimeter to obtain a crystal melting curve.

[0080] In the obtained crystalline melting curve, the top temperature of the melting peak present in the range of 100 to 150°C was taken as Tma, and the crystalline melting enthalpy of the peak was taken as ΔHa. When multiple melting peaks were observed in the range of 100 to 150°C, the melting temperature of the highest peak was taken as Tma, and the sum of the crystalline melting enthalpies of each peak was taken as ΔHa.

[0081] Furthermore, the top temperature of the melting point peak present in the range of 150 to 170°C was taken as Tmb, and the crystalline melting enthalpy of this peak was taken as ΔHb. When multiple melting point peaks were observed in the range of 150 to 170°C, the melting point temperature of the highest peak was taken as Tmb, and the sum of the crystalline melting enthalpies of each peak was taken as ΔHb.

[0082] 〔result〕 1 shows the crystalline melting curve measured by differential scanning calorimetry for Example 1. The coating layer of Example 1 had a Tma of 120°C and a Tmb of 154°C. The coating layer of Example 2 had a Tma of 120°C and a Tmb of 152°C. The coating layer of Example 3 had a Tma of 120°C and a Tmb of 165°C. The coating layer of Example 4 had a Tma of 120°C and a Tmb of 165°C. The coating layer of Comparative Example 1 had a Tma of 145°C, but no melting point peak was present in the range of 150 to 170°C.

[0083] Table 1 shows the results of the peel test 2 seconds after heat sealing for Examples 1 and 2 and Comparative Example 1 when the coating layers were pressure-bonded together, as well as the values ​​of Tma, Tmb, and ΔHb / ΔHa. Table 2 shows the results of the peel test 2 seconds after heat sealing for Examples 1 to 4 and Comparative Example 1 when the coating layer was pressure-bonded to paper, as well as the values ​​of Tma, Tmb, and ΔHb / ΔHa.

[0084] [Table 1]

[0085] [Table 2]

[0086] In Example 1, in a peel test 2 seconds after heat sealing, when the coating layers were pressure-bonded together (Table 1), the paper underwent material failure over a wide range of heating temperatures during heat sealing, from 120 to 200°C, and when the coating layer and paper were pressure-bonded together (Table 2), the paper underwent material failure over a wide range of heating temperatures during heat sealing, from 140 to 180°C. This indicates that in these temperature ranges, solidification of the molten resin proceeded 2 seconds after heat sealing, resulting in the development of good adhesive strength.

[0087] In Comparative Example 1, in a peel test conducted 2 seconds after heat sealing, when the coating layers were pressed together, the paper broke at a heating temperature of 140 to 160°C during heat sealing, and when the coating layer was pressed together with paper, the paper broke at a heating temperature of 180°C during heat sealing. However, no breakage of the paper occurred at temperatures other than those mentioned above, indicating that the molten resin had not solidified sufficiently.

[0088] The coating layers of Examples 2 to 4 had Tma and Tmb values ​​that were not significantly different from those of Example 1, but ΔHb / ΔHa values ​​of 0.25 to 0.51, which were larger than the 0.12 of Example 1. In a peel test 2 seconds after heat sealing, the paper material broke even when the heating temperature during heat sealing was 220°C (Table 1) or 190°C (Table 2), and even at temperatures higher than those of Example 1, solidification of the resin immediately after heat sealing proceeded quickly, allowing good adhesive strength to be achieved.

[0089] To summarize the above, Example 1 exhibited good adhesive strength in a short time even when heat-sealed at a lower temperature than Comparative Example 1. Furthermore, Examples 2 to 4 exhibited good adhesive strength in a short time even under higher temperatures than Example 1. This effect is thought to be due to the fact that in coating layers having a melting point peak between 150 and 170°C in addition to a melting point peak between 100 and 150°C, as in Examples 1 to 4, the resin crystals forming the melting point peak between 150 and 170°C act as nuclei, accelerating the solidification of the molten resin. Furthermore, the degree to which this solidification rate is improved is thought to be proportional to the value of ΔHb / ΔHa.

[0090] However, in Example 4, where 20% by weight of P3HB3HH containing 0.7 mol% 3-hydroxyhexanoate units was added, the solidification rate increased, but the area of ​​paper peeling decreased. This is presumably due to the resin's increased melt tension, which worsened its penetration into the paper. Therefore, from the perspective of ensuring the strength of the laminate, it is desirable to adjust the amount of P3HB3HH or P3HB containing less than 8 mol% 3HH units.

Claims

1. A laminate having a substrate layer and a coating layer laminated on at least one surface of the substrate layer, the substrate layer is paper, the coating layer contains a poly(3-hydroxybutyrate)-based resin; the coating 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; The poly(3-hydroxybutyrate)-based resin includes poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) having a 3-hydroxyhexanoate unit content of 8 mol% or more and 25 mol% or less, and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) having a 3-hydroxyhexanoate unit content of 0.1 mol% or more and 1 mol% or less, a laminate in which the content of the poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) having a 3-hydroxyhexanoate unit content of 0.1 mol % or more and 1 mol % or less is 5 to 15 wt % based on the total weight of the poly(3-hydroxybutyrate)-based resin contained in the coating layer.

2. 2. The laminate according to claim 1, wherein in a crystalline melting curve of the coating layer measured by differential scanning calorimetry, the ratio (ΔHb / ΔHa) of the crystalline melting enthalpy (ΔHa) of a peak in the range of 100 to 150°C to the crystalline melting enthalpy (ΔHb) of a peak in the range of 150 to 170°C is 0.01 to 2.

3. 3. The laminate according to claim 1, wherein the poly(3-hydroxybutyrate) resin has a weight average molecular weight of 50,000 to 650,000.

4. A method for producing the laminate according to any one of claims 1 to 3, comprising: a step of applying an aqueous coating liquid containing the poly(3-hydroxybutyrate)-based resin to a substrate to form a coating film; and and heating the applied film at a temperature of 130°C or higher and 170°C or lower to form the coating layer.

5. A molded article comprising the laminate according to any one of claims 1 to 3.

6. A method for producing the molded article according to claim 5, and heat-sealing the coating layer.

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