Resin foam, laminated resin foam, film-covered resin foam, and method for laminating resin foam

Abstract

To provide a resin foam capable of being laminated with another one.SOLUTION: A resin foam 1 is composed of mixed resin particles containing polylactic acid, and is formed by foaming of the heated mixed resin particles through expansion of a foaming agent. The mixed resin particles contain high-melting-point polylactic acid particles and low-melting-point polylactic acid particles having a melting point lower than that of the high-melting-point polylactic acid particles. When a plurality of the resin foams 1 are stacked and heated, the foam of the low-melting-point polylactic acid particles on the surface side where heat is transferred melts, allowing the surface side of the resin foam 1 to be partially melted, and thus, through stacking and heating of a plurality of the resin foams, lamination with one another is achieved.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technical field of the present specification relates to a resin foam for lamination, a laminated resin foam obtained by laminating resin foams, a film-coated resin foam obtained by laminating a resin foam and a resin film, and a method for laminating resin foams. [Background technology]

[0002] Resin foams are used as packaging materials for perishable items such as fresh produce, and for shock-sensitive items such as household appliances. After being used as packaging materials, resin foams are sometimes thrown away and discarded into the natural environment. Resin foams discarded into the natural environment are difficult to decompose by microorganisms and remain in the natural environment semipermanently. In response to this, resin foams that can be decomposed by microorganisms have been proposed, and Patent Documents 1 and 2 describe resin foams using polylactic acid as resin foams that can be decomposed by microorganisms. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. WO2013 / 147400 [Patent Document 2] Japanese Patent Publication No. 2022-83081 Summary of the Invention [Problem to be solved by the invention]

[0004] Depending on the item to be packaged, the packaging material may need to be thick, which necessitates lamination of resin foams. However, the resin foams using polylactic acid described in Patent Documents 1 and 2 have the problem that they cannot be thermally fused together and therefore cannot be laminated.

[0005] The technology of the present specification has been made in view of the above points, and has an object to provide resin foams that can be laminated on each other. [Means for solving the problem]

[0006] A resin foam according to an embodiment of the present specification is a resin foam formed from mixed resin particles containing polylactic acid, the mixed resin particles being heated and foamed by the expansion of a blowing agent, The mixed resin particles contain high-melting-point polylactic acid particles and low-melting-point polylactic acid particles, and are characterized in that the melting point of the low-melting-point polylactic acid particles is lower than the melting point of the high-melting-point polylactic acid particles.

[0007] According to the resin foam of the embodiment, a resin foam is formed by foaming mixed resin particles containing high-melting-point polylactic acid particles and low-melting-point polylactic acid particles through the expansion of a blowing agent. When multiple sheets of the formed resin foam are stacked and heated, the low-melting-point polylactic acid particle foam on the surface side where heat is transferred melts at the stacked interface, while the high-melting-point polylactic acid particle foam does not melt, maintaining the shape of the foam. When heating is completed, the molten low-melting-point polylactic acid particles fuse to the high-melting-point polylactic acid particle foam that maintains the shape of the foam, bonding the stacked interface. Therefore, multiple resin foams can be stacked on top of each other by heating.

[0008] In the resin foam, the high-melting-point polylactic acid particles may have a melting point of 150 to 175°C, and the low-melting-point polylactic acid particles may have a melting point of 50 to 100°C.

[0009] According to this, a plurality of resin foams can be stacked on top of each other by being heated.

[0010] In the resin foam, the foaming agent may contain carbon dioxide and nitrogen.

[0011] This allows the cells formed in the resin foam to be finer.

[0012] Moreover, the laminated resin foam according to the embodiment may be obtained by laminating the above-described resin foams one on top of another.

[0013] This makes it possible to form an integrated laminated resin foam.

[0014] The film-coated resin foam according to the embodiment may be obtained by laminating the above-described resin foam and a resin film.

[0015] This makes it possible to form a film-coated resin foam having at least one surface coated with a resin film.

[0016] In addition, in the method for producing a laminated resin foam according to the embodiment, a plurality of the above-mentioned resin foams can be stacked and heated to a surface temperature of 70 to 140°C, thereby laminating them.

[0017] This makes it possible to form an integrated laminated resin foam. [Effects of the Invention]

[0018] According to the resin foam according to the embodiment of the present specification, a plurality of sheets can be stacked on top of each other by being heated. [Brief explanation of the drawings]

[0019] [Figure 1] 1A is a side view of a laminated resin foam body formed by laminating a plurality of resin foam bodies, and FIG. 1B is a side view of a film-coated resin foam body formed by laminating a resin foam body and a resin film. [Figure 2] 1A shows a differential scanning calorimetry curve of high-melting-point polylactic acid particles A, and FIG. 1B shows a differential scanning calorimetry curve of low-melting-point polylactic acid particles A. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0020] The following describes a resin foam 1 for lamination according to an embodiment of the present specification, a laminated resin foam 10 obtained by laminating resin foams 1, a film-coated resin foam 20 obtained by laminating resin foam 1 and a resin film 2, and a lamination method for laminated resin foam 10. Note that the scope of the present invention is not limited to the scope disclosed in the embodiments.

[0021] The resin foam 1 of the embodiment is formed from mixed resin particles containing polylactic acid. The heated mixed resin particles are foamed by the expansion of a blowing agent mixed into the mixed resin particles, forming the resin foam 1. The resin foam 1 is used as a packaging material for perishable items such as fresh produce, and for shock-sensitive items such as household appliances. Depending on the item to be packaged, thickness may be required, and the resin foam 1 of the embodiment can be laminated by stacking and heating the resin foam 1. In this specification, when expressing the blending amount or blending ratio of the laminated resin foam 10, unless otherwise specified, it is expressed in mass units, including volatile content. Furthermore, the "%" representing the blending unit means "% by mass" unless otherwise specified.

[0022] The resin foam 1 according to the embodiment is formed by melting mixed resin particles containing high-melting-point polylactic acid particles and low-melting-point polylactic acid particles, and then foaming them by the expansion of the mixed blowing agent. The mixed resin particles may contain a chain extender and / or other biodegradable plastics. The mixed resin particles are foamed by mixing the blowing agent into the mixed resin particles and changing the state of the mixed resin particles, such as the temperature or external pressure.

[0023] High-melting-point polylactic acid particles have a melting point higher than that of low-melting-point polylactic acid particles. Lactic acid has enantiomers, and these are L- and D-isomers. Polylactic acid composed of the L-isomer has a high melting point (melting point: approximately 175°C). Polylactic acid composed of the L-isomer can be converted into polylactic acid with a low melting point by adding the other enantiomer, the D-isomer. Adding 10% by mass or more of the D-isomer to polylactic acid composed of the L-isomer makes the polylactic acid amorphous and does not crystallize. Therefore, the melting point of low-melting-point polylactic acid can be considered to be the temperature at which the endothermic reaction peak occurs in the differential scanning calorimetry curve (DSC curve) measured with a differential scanning calorimeter or the like.

[0024] Here, the temperature at which the endothermic reaction peak occurs is the temperature at which the last endothermic reaction peak appears on the high-temperature side from the low-temperature side (25°C) to the high-temperature side (250°C) in the DSC curve shown in Figure 2(A) or 2(B). The endothermic reaction peak can be, for example, a value where the absolute value of the change in heat flow q |Δq| is 0.15 (mW / mg) or more. In Figure 2(A), the melting point of the high-melting-point polylactic acid particles A is approximately 155°C, and in Figure 2(B), the melting point (temperature at which the endothermic reaction peak occurs) of the low-melting-point polylactic acid particles A is approximately 60°C.

[0025] Polylactic acid is amorphous and does not crystallize when the L-isomer:D-isomer ratio is in the range of 90:10 to 10:90 (mass%), but is crystalline and crystallizes outside this range (when the L-isomer or D-isomer exceeds 90 mass%).

[0026] High-melting-point polylactic acid particles and low-melting-point polylactic acid particles can be selected from commercially available polylactic acid pellets, taking into account the difference in melting point. In an embodiment, as a guideline, high-melting-point polylactic acid particles have a melting point of more than 140°C, and low-melting-point polylactic acid particles have a melting point (the temperature at which the endothermic reaction peak occurs) of less than 120°C. In another embodiment, the high-melting-point polylactic acid particles have a melting point of 150 to 175°C, and in yet another embodiment, a melting point of 160 to 175°C. In another embodiment, the low-melting-point polylactic acid particles have a melting point (the temperature at which the endothermic reaction peak occurs) of 50 to 100°C, and in yet another embodiment, a melting point of 50 to 80°C.

[0027] Polylactic acid pellets are made by saccharifying biomass (primarily starch obtained from plants) as a raw material, fermenting it to produce lactic acid, and then polymerizing the lactic acid to produce a polymer (polylactic acid pellets). Polylactic acid is environmentally friendly because it does not use petroleum-derived raw materials, which are at risk of becoming depleted, and the biomass raw material absorbs a large amount of carbon dioxide during growth. Furthermore, because polylactic acid is a biodegradable polymer compound, even if the laminated resin foam 10 according to the embodiment is unintentionally discarded in the natural environment, it will be decomposed by microorganisms, minimizing the impact on the environment.

[0028] The polylactic acid pellets used as the high-melting-point polylactic acid particles and low-melting-point polylactic acid particles can be commercially available products. Commercially available polylactic acid pellets include Luminy L105 (175°C), L130 (175°C), L175 (175°C), LX530 (165°C), LX575 (165°C), LX175 (155°C), LX930 (60°C), LX975 (60°C), D070 (175°C), and D120 (175°C) (manufactured by TotalEnergies Corbion, the Netherlands and Thailand), and REVODE 110 (165°C), 190 (175°C), 210 (165°C), and 290 (175°C) (manufactured by Zhejian Hisun). Polylactic acid pellets can be manufactured by companies such as Zhejiang Haizheng Biomaterials (China). The temperature in parentheses indicates the melting point of the polylactic acid pellets (the temperature at which the endothermic reaction peak occurs). Commercially available polylactic acid pellets are also available from NatureWorks (USA), Anhui Fengyuan Biomaterials (China), weforyou group (Austria, China), Shenzhen Guanhua Weiye (China), Jiujiang Keyuan Biomaterial (China), Jilin COFCO Biomaterials (China), Henan Technology (China), Synbra Technology bv (Netherlands), and Feterro (Belgium).

[0029] When the mixed resin particles are melted and foamed, the high-melting-point polylactic acid particles and low-melting-point polylactic acid particles contained in the mixed resin particles melt without mixing, and each particle foams. As a result, the resin foam 1 contains a mixture of high-melting-point polylactic acid and low-melting-point polylactic acid in the foamed particle units. When resin foams 1 are stacked on top of each other and heated at a temperature above the melting point of the low-melting-point polylactic acid particles, the low-melting-point polylactic acid particles in the foamed particle units on the surface side of the resin foam 1 melt first. When the heating temperature is below the melting point of the high-melting-point polylactic acid particles, the high-melting-point polylactic acid particles in the foamed particle units do not melt and retain their foamed shape. Since the low-melting-point polylactic acid particles are in a molten state, at the surfaces where the resin foams 1 are stacked, the low-melting-point polylactic acid particles fuse to each other and to the high-melting-point polylactic acid particles in the foamed particle units, and solidify when heating is completed, thereby joining the surfaces of the resin foams 1 that are stacked to each other.

[0030] When the polylactic acid particles contained in the mixed resin particles are only high-melting-point polylactic acid particles, if resin foams 1 are stacked on top of each other and heated above the melting point of the high-melting-point polylactic acid particles, all of the foamed polylactic acid particles on the surface of the resin foam 1 will melt, leaving nothing for the molten polylactic acid to bond with, which may prevent the overlapping surfaces of the resin foam 1 from bonding together. On the other hand, when the polylactic acid particles contained in the mixed resin particles are only low-melting-point polylactic acid particles, if resin foams 1 are stacked on top of each other and heated above the melting point of the low-melting-point polylactic acid particles, all of the foamed polylactic acid particles on the surface of the resin foam 1 will melt, leaving nothing for the molten polylactic acid to bond with, which may prevent the overlapping surfaces of the resin foam 1 from bonding together, just as in the case of high-melting-point polylactic acid particles. It has also been confirmed that if the polylactic acid particles contained in the mixed resin particles are only low-melting-point polylactic acid particles, foaming may not occur.

[0031] The polylactic acid particles contained in the mixed resin particles can be in a ratio of high-melting-point polylactic acid particles to low-melting-point polylactic acid particles of 70:30 to 30:70 (mass %). This is because the overlapping surfaces of the resin foams 1 can be bonded by stacking and heating the resin foams 1. If the high-melting-point polylactic acid particles in the polylactic acid particles exceed 70 mass %, when the resin foams 1 are stacked and heated, they will be bonded by 30 mass % of the low-melting-point polylactic acid particles, which may result in insufficient bonding due to insufficient bonding. On the other hand, if the low-melting-point polylactic acid particles in the polylactic acid particles exceed 70 mass %, there will be few targets (high-melting-point polylactic acid particles) for the molten low-melting-point polylactic acid particles to bond to, which may result in insufficient bonding of the overlapping surfaces of the resin foams 1. In another embodiment, the polylactic acid particles contained in the mixed resin particles can be in a ratio of high melting point polylactic acid particles:low melting point polylactic acid particles = 65:35 to 35:65, and in yet another embodiment, the ratio of high melting point polylactic acid particles:low melting point polylactic acid particles = 60:40 to 40:60.

[0032] A foaming agent is a chemical that is mixed into polylactic acid to change the temperature, external pressure, and other conditions of the polylactic acid to foam it. Examples of foaming agents include air components such as hydrogen, nitrogen, oxygen, carbon dioxide, and water; rare gases such as helium, neon, argon, krypton, and xenon; saturated chain hydrocarbons such as methane, ethane, propane, butane, and pentane; alcohols such as methanol, ethanol, propanol, and butanol; and combinations thereof. In another embodiment, the foaming agent may be an inert gas such as nitrogen, carbon dioxide, or a rare gas, or a combination thereof. In yet another embodiment, the foaming agent may be readily available gas such as nitrogen, carbon dioxide, or a combination thereof. The foaming agent may be brought into a supercritical state when mixed into polylactic acid. Bringing the foaming agent into a supercritical state reduces the dielectric constant of the foaming agent, allowing it to be incorporated into polylactic acid as fine bubbles. Nitrogen has a critical temperature of -147.0°C and a critical pressure of 3.89 MPa, while carbon dioxide has a critical temperature of 31.1°C and a critical pressure of 7.38 MPa.

[0033] The amount of foaming agent mixed with polylactic acid can be 3 to 20% by mass. This is because the laminated resin foam 10 formed from polylactic acid can be flexible yet strong. If the amount of foaming agent mixed with polylactic acid is less than 3% by mass, the laminated resin foam 10 formed from polylactic acid may have a low expansion ratio and may lack flexibility. On the other hand, if the amount mixed with polylactic acid exceeds 20% by mass, the laminated resin foam 10 formed from polylactic acid may have a high expansion ratio and may lack strength. In this case, the expansion ratio of the laminated resin foam 10 is 5 to 50 times. In another embodiment, the amount of foaming agent mixed with polylactic acid and the expansion ratio can be 4 to 15% by mass and 10 to 40 times, respectively. In yet another embodiment, the amount of foaming agent mixed with polylactic acid and the expansion ratio can be 5 to 10% by mass and 15 to 30 times, respectively.

[0034] A chain extender is a compound that, when added to a polymer (polylactic acid), can increase the molecular weight of the polymer. This increases the molecular weight (extends the molecular chain) of the polylactic acid forming the laminated resin foam 10, thereby increasing the strength of the laminated resin foam 10 and improving the cell formability. The chain extender is not limited to any particular type, but examples include epoxy chain extenders selected from the group consisting of bisphenol A diglycidyl ether, terephthalic acid diglycidyl ether, trimethylolpropane diglycidyl ether, and 1,6-hexanediol diglycidyl ether; isocyanate chain extenders selected from the group consisting of hexamethylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, and triisocyanate; acrylic chain extenders; maleic anhydride chain extenders; and copolymers containing these compounds. In another embodiment, the chain extender may be an epoxy chain extender.

[0035] The chain extender can be contained in an amount of 0.01 to 10% by mass relative to the polymer (polylactic acid). This is because it increases the molecular weight of the polymer, thereby enhancing the strength of the laminated resin foam 10 and improving the moldability of the cells. If the chain extender content is less than 0.01% by mass, the strength of the laminated resin foam 10 may not be enhanced, and if it exceeds 10% by mass, the biodegradability of the laminated resin foam 10 may be impaired. In another embodiment, the chain extender content relative to the laminated resin foam 10 may be 0.1 to 1% by mass.

[0036] Other biodegradable plastics are plastics that can be decomposed by microorganisms, and examples of such plastics that can be used include BioPBS (polybutylene succinate) (115°C), PBAT (polybutylene adipate terephthalate) (115°C), PHA (polyhydroxyalkanoic acid) (175°C), etc. Other biodegradable plastics are flexible, and by using other biodegradable plastics, the impact resistance of the laminated resin foam 10 can be increased.

[0037] The other biodegradable plastics can be contained in an amount of 0.01 to 10% by mass relative to the polymer (polylactic acid). This is because the impact resistance of the laminated resin foam 10 can be increased. If the content of the other biodegradable plastics is less than 0.01% by mass, the impact resistance of the laminated resin foam 10 may not be increased, and if it exceeds 10% by mass, the foamability of the laminated resin foam 10 may be poor. In another embodiment, the content of the other biodegradable plastics relative to the laminated resin foam 10 may be 0.1 to 1% by mass.

[0038] Next, a method for manufacturing the resin foam 1 according to the embodiment will be described. The method for manufacturing the resin foam 1 includes the following steps, in this order: a mixing step of mixing high-melting-point polylactic acid particles and low-melting-point polylactic acid particles to form mixed resin particles, a melting step of melting the mixed mixed resin particles, a dissolving step of dissolving a foaming agent in the molten mixed resin particles, a pressurizing step of pressurizing the polylactic acid with the foaming agent dissolved therein, and a foaming step of pressurizing and then depressurizing the mixture to cause foaming.

[0039] The mixing step is a step in which high-melting point polylactic acid particles, low-melting point polylactic acid particles, and optionally a chain extender and / or other biodegradable plastics are uniformly mixed (dry blended) in a powder state to form mixed resin particles.

[0040] The melting step is a step in which the uniformly mixed mixed resin particles are heated to melt them. The melting is carried out at a temperature higher than the melting point (150 to 175°C) of the high-melting-point polylactic acid particles. Heating is continued until the pressurizing step.

[0041] The dissolving step is a step of dissolving a foaming agent in the molten mixed resin particles. In the dissolving step, the foaming agent is mixed into the molten mixed resin particles by an extruder and dissolved therein.

[0042] The pressurization step is a step in which the mixed resin particles in which the foaming agent has been dissolved are pressurized using an extruder. The mixed resin particles containing the foaming agent are pressurized, and the temperature exceeds the critical temperature and pressure of the foaming agent, causing the foaming agent to enter a supercritical state. When the foaming agent enters a supercritical state, the dielectric constant of the foaming agent decreases, allowing the foaming agent to be incorporated into the mixed resin particles as countless fine bubbles, resulting in the resin foam 1 formed from the mixed resin particles having fine bubbles (1 to 50 μm in diameter).

[0043] The foaming process is a process in which the pressure of the polylactic acid pressurized in the pressurizing process is reduced to normal pressure to foam it. Specifically, the pressure is reduced by extruding it from a die at the outlet of the extruder. When the mixed resin particles are decompressed, the foaming agent dissolved in the mixed resin particles expands, forming countless bubbles in the mixed resin particles, resulting in resin foam 1. The high-melting point polylactic acid particles and low-melting point polylactic acid particles that make up resin foam 1 (mixed resin particles) melt without being fully mixed together, and each particle foams. As a result, resin foam 1 contains a mixture of high-melting point polylactic acid and low-melting point polylactic acid in each expanded particle.

[0044] The foamed molded product is processed into a sheet to form a resin foam 1. The resin foam 1 is stretched in the direction of extrusion from the die at the outlet of the extruder and has directional properties. The thickness of the resin foam 1 sheet can be 0.5 to 5.0 mm. This is because sufficient sheet strength can be ensured. If the thickness of the resin foam 1 sheet is less than 0.5 mm, the sheet strength may be insufficient and the sheet may be easily torn. On the other hand, if the thickness exceeds 5.0 mm, air bubbles generated in the resin foam 1 (mixed resin particles) may stick together and become larger, which may reduce the strength of the sheet. In another embodiment, the thickness of the laminated resin foam 10 sheet can be 1.0 to 4.0 mm, and in yet another embodiment, it can be 1.5 to 3.0 mm.

[0045] The resin film 2 to be laminated on the resin foam 1 is formed by melting a raw material resin containing high-melting-point polylactic acid particles and molding it into a film shape. The raw material resin may contain low-melting-point polylactic acid particles, a chain extender, and / or other biodegradable plastics.

[0046] The high-melting point polylactic acid particles, low-melting point polylactic acid particles, chain extenders and other biodegradable plastics used as the raw material resin for the resin film 2 can be the high-melting point polylactic acid particles, low-melting point polylactic acid particles, chain extenders and other biodegradable plastics used in the mixed resin particles for the resin foam 1 described above.

[0047] Next, we will describe a method for manufacturing the resin film 2. The resin film 2 is manufactured through a mixing step in which high-melting point polylactic acid particles and low-melting point polylactic acid particles are mixed together to form a raw material resin, and a processing step in which the mixed resin particles are melted and processed into a film, in that order.

[0048] The mixing step is a step in which high-melting-point polylactic acid particles and, if necessary, low-melting-point polylactic acid particles, a chain extender and / or other biodegradable plastics are uniformly mixed in a powder state to obtain a raw material resin.

[0049] The processing step is a process of processing into a film by the die method of extrusion molding. Specifically, raw material resin is fed into an extruder, melted at 180 to 240°C, extruded through a die, and then wound around a cooled rotating roll for rapid cooling, thereby processing into a film.

[0050] Note that the resin film 2 of the embodiment may be a commercially available product made from polylactic acid as a raw material. Examples of commercially available resin films 2 made from polylactic acid as a raw material include the Oysheet series and Yumisheet series (manufactured by Daido Shikko Co., Ltd.).

[0051] Next, we will explain the process of laminating the resin foam 1. Laminating the resin foam 1 includes a lamination process in which resin foams 1 are stacked on top of each other to form a laminated resin foam 10 (laminate), and a film coating process in which resin foam 1 is stacked on a resin film 2 to form a film-coated resin foam 20 (film-coated body).

[0052] Resin foam 1 is a mixture of high-melting point polylactic acid and low-melting point polylactic acid in foamed particle units, and when heated during the lamination process, the low-melting point polylactic acid particles melt from the surface side of the foam, resulting in the surface side of resin foam 1 being partially melted.

[0053] In the lamination process in which resin foams 1 are laminated to form laminated resin foam 10, resin foams 1 are stacked on top of each other and heated to a temperature above the melting point of the low-melting-point polylactic acid particles but below the melting point of the high-melting-point polylactic acid particles, causing the low-melting-point polylactic acid particles on the surface of resin foam 1 to melt. Therefore, at the surfaces where resin foams 1 are stacked, the low-melting-point polylactic acid particles fuse to each other and to the high-melting-point polylactic acid particles, bonding the resin foams 1 together at the surfaces where they are stacked. During production, resin foam 1 is stretched in the direction extruded from the die at the outlet of the extruder, and thus has directional properties. Therefore, by alternately stacking resin foams 1 in the direction extruded from the die and in a direction perpendicular to that direction, the strength of laminated resin foam 10 can be increased.

[0054] In the film-coating process in which the resin foam 1 and the resin film 2 are laminated to form the film-coated resin foam 20, the resin foam 1 and the resin film 2 are laminated together and heated to a temperature above the melting point of the low-melting-point polylactic acid particles and below the melting point of the high-melting-point polylactic acid particles. As a result, the low-melting-point polylactic acid particles on the surface side of the resin foam 1 are melted, and the low-melting-point polylactic acid particles are fused to the resin film 2. When the resin foam 1 and the resin film 2 are heated, the low-melting-point polylactic acid particles are fused to the resin film 2, and the resin foam 1 and the resin film 2 are bonded together. The film-coated resin foam 20 can be further laminated, for example, with a film-coated resin foam 20 formed by laminating the resin foam 1, the resin film 2, and the resin foam 1 in this order, or with a film-coated resin foam 20 formed by laminating the resin foam 1, the resin film 2, and the resin foam 1 in this order.

[0055] In the lamination step or film coating step, multiple sheets of resin foam 1 are stacked on top of each other, or a resin foam 1 is stacked on top of a resin film 2, and the surface temperature of the resin foam 1 is heated to a temperature (specifically, 70 to 140°C) above the melting point of the low-melting-point polylactic acid particles and below the melting point of the high-melting-point polylactic acid particles to laminate them. This allows the low-melting-point polylactic acid particles on the surface of the resin foam 1 to melt, thereby bonding the resin foams 1 together or the resin foam 1 and the resin film 2. If the surface temperature of the resin foam 1 is less than 70°C, the low-melting-point polylactic acid particles may not be sufficiently melted, and bonding the resin foams 1 together or the resin foam 1 and the resin film 2 may not be possible. On the other hand, if the surface temperature of the resin foam 1 exceeds 140°C, the molten low-melting-point polylactic acid particles may also melt the high-melting-point polylactic acid particles or the resin film 2 to which they are attached, and this may prevent bonding the resin foams 1 together or the resin foam 1 and the resin film 2. In another embodiment, the heating temperature of the surface of the resin foam 1 can be 80 to 130°C, and in yet another embodiment, 90 to 120°C. [Example]

[0056] Test examples will be described below as working examples. Details of raw materials used for resin foam 1 of the test examples will be described below.

[0057] High-melting polylactic acid particles A L body:D body=96:4 Melting point: 155℃ Particle size (median diameter d50): 3.2 mm High-melting polylactic acid particles B L body:D body=99:1 Melting point: 175℃ Particle size (median diameter d50): 3.3 mm Low melting point polylactic acid particles A L body:D body=88:12 Melting point (temperature at which the endothermic reaction peaks): 60°C Particle size (median diameter d50): 3.4 mm Low melting point polylactic acid particles B L body:D body=89:11 Melting point (temperature at which the endothermic reaction peaks): 60°C Particle size (median diameter d50): 3.5 mm PHA Melting point: 175℃ Particle size (median diameter d50): 3.2 mm PBAT Melting point: 115℃ Particle size (median diameter d50): 3.3 mm Chain extender Epoxy chain extender foaming agent N2:CO2=10:90 These were commercially available products. The DSC curve of high-melting-point polylactic acid particles A (sample mass: 9.1 mg) is shown in Figure 2(A), and the DSC curve of low-melting-point polylactic acid particles A (sample mass: 11.8 mg) is shown in Figure 2(B).

[0058] Resin foam 1 of the test example was produced to a thickness of 3 mm through the foam production process, which consisted of the above-mentioned mixing, melting, dissolving, pressurizing, and foaming steps. The temperature from the melting to the pressurizing step was approximately 180°C, and the pressure in the pressurizing step was 40 MPa. This put the foaming agent into a supercritical state, and countless fine bubbles with diameters of 1 to 50 μm were formed in resin foam 1. The resin foam 1 produced in the test example was evaluated for foamability.

[0059] <Foaming> The foamability was evaluated as follows: resin foam 1 with an expansion ratio of 5 times or more was rated as ◯; resin foam 1 with an expansion ratio of 2 times or more but less than 5 times was rated as △; resin foam 1 with an expansion ratio of less than 2 times was rated as ×.

[0060] In the lamination process, six sheets of resin foam 1 of the test example were stacked on top of each other and heated to adhere the resin foams 1 together and form an integrated laminated resin foam 10. The six resin foams 1 were stacked so that the direction of extrusion from the die at the outlet of the extrusion molding machine alternated with a direction perpendicular to this direction in the foaming process. The resin foams 1 were heated until the surface temperature reached 95°C; specifically, the six stacked resin foams 1 were left to stand in a hot air circulating oven set at 100°C for 20 minutes.

[0061] The laminated resin foam 10 formed in the lamination step was subjected to the following adhesion strength test and evaluated.

[0062] <Adhesion strength test> An adhesion strength test was conducted in the layering direction (based on 7.10 Adhesion Strength Test for Architectural Finish Coating Materials (JIS A 6909:2014)) and the adhesion strength was 0.2 N / mm 2 Those with an adhesive strength of 0.1 N / mm or more are marked with a circle. 2 More than 0.2N / mm 2 Adhesion strength is less than 0.1N / mm 2 If the value was less than this, it was evaluated as x.

[0063] Furthermore, in the film coating process, the resin foam 1 of the test example was overlaid with a resin film 2 and heated to form an integrated film-coated resin foam 20. Heating was performed using press heaters that sandwiched the resin foam 1 from both sides until the surface temperature of the resin foam 1 reached 95°C. Specifically, the temperature of the press heaters on both sides was set to 150°C, and the resin foam was pressed for 30 seconds.

[0064] The resin film 2 used was a raw material resin consisting of high melting point polylactic acid particles B:PBAT=95:5, which was formed into a film by the above-mentioned method for producing the resin film 2.

[0065] The film-coated resin foam 20 thus formed was subjected to the same adhesive strength test as that used to evaluate the laminated resin foam 10, and its evaluation was carried out.

[0066] Test examples are shown below. Test examples 1 to 6 (Table 1) and Test examples 7 to 12 (Table 2) are obtained by changing the blending of the raw materials of the mixed resin particles that form the resin foam 1. Test examples 2 to 5 and 7 to 12 are working examples, and Test examples 1 and 6 are comparative examples.

[0067] [Table 1]

[0068] [Table 2]

[0069] (Test Example 1) In Test Example 1, 0.7 parts by mass of an epoxy chain extender was added to 100 parts by mass of high-melting-point polylactic acid particles A (polylactic acid) with a melting point of 155°C as the mixed resin particles. 10 parts by mass of a blowing agent with a N2:CO2 ratio of 10:90 was used for 100 parts by mass of polylactic acid. In Test Example 1, during the foam preparation process, the blowing agent entered a supercritical state, lowering its dielectric constant. This enabled the blowing agent to incorporate countless fine bubbles into the mixed resin particles, resulting in the resin foam 1 formed from the mixed resin particles with fine bubbles (1 to 50 μm in diameter). However, in Test Example 1, the heating temperature of the surface of the resin foam 1 during the lamination process was below the melting point of the resin foam 1, making lamination impossible and preventing measurement of adhesion strength. Furthermore, during the film coating process, the heating temperature of the surface of the resin foam 1 was below the melting point of the resin foam 1, making it impossible to coat the resin film 2, preventing measurement of adhesion strength. In Test Example 1, the lamination step was attempted by increasing the surface temperature of the resin foam 1 to 160°C, but lamination was not possible. Although the surface of the resin foam 1 was melted, the molten polylactic acid and the resin foam 1 were not in close contact with each other.

[0070] (Test Examples 2 to 5) In Test Examples 2 to 5, high-melting-point polylactic acid particles A with a melting point of 155°C and low-melting-point polylactic acid particles A with a melting point (the temperature at which the endothermic reaction peaks) of 60°C were used as mixed resin particles, and the mixing ratio was varied. The chain extender and blowing agent were the same as in Test Example 1. Test Examples 2 to 5 were able to be sufficiently foamed in the foam preparation process, and resin foam 1 with satisfactory foamability was obtained. Furthermore, in Test Examples 2 to 5, the low-melting-point polylactic acid particles A melted in the lamination process, and at the overlapping surfaces of the resin foam 1, the low-melting-point polylactic acid particles A fused with each other and bonded to the high-melting-point polylactic acid particles A of the expanded particle units, thereby bonding the overlapping surfaces of the resin foam 1. Furthermore, in the film coating process, the low-melting-point polylactic acid particles A melted and bonded to the resin film 2, and the resin film 2 was able to be bonded to the resin foam 1. Among these, Test Example 2 used high-melting-point polylactic acid particles A:low-melting-point polylactic acid particles A in a ratio of 80:20, and the adhesive strength was slightly inferior, probably due to the low proportion of low-melting-point polylactic acid particles A used for bonding. Test Example 5 used high-melting-point polylactic acid particles A:low-melting-point polylactic acid particles A in a ratio of 20:80, and the foaming property was slightly reduced, probably due to the high proportion of low-melting-point polylactic acid particles A used for bonding.

[0071] (Test Example 6) In Test Example 6, only low-melting-point polylactic acid particles A with a melting point (temperature at which the endothermic reaction peak occurs) of 60°C were used as the mixed resin particles. The chain extender and blowing agent were the same as in Test Example 1. In Test Example 6, foaming could not be achieved in the foam production process, and resin foam 1 could not be obtained. Of course, in Test Example 6, since resin foam 1 could not be obtained, resin foam 1 could not be laminated, and resin film 2 could not be bonded to resin foam 1.

[0072] (Test Examples 7 to 11) In Test Examples 7 to 9, the mixed resin particles used were polylactic acid particles A (L-form:D-form = 96:4) and low-melting-point polylactic acid particles A (L-form:D-form = 88:12), as well as high-melting-point polylactic acid particles B (L-form:D-form = 99:1) with a melting point of 175°C and low-melting-point polylactic acid particles B (L-form:D-form = 89:11) with a melting point (the temperature at which the endothermic reaction peak occurs) of 60°C. In Test Example 10, part of the polylactic acid was replaced with PBAT (polybutylene adipate terephthalate) with a melting point of 115°C, and in Test Example 11, part of the polylactic acid was replaced with PHA (polyhydroxyalkanoic acid) with a melting point of 175°C. Test Examples 7 to 11 were able to be sufficiently foamed in the foam preparation process, and resin foam 1 with satisfactory foamability was obtained. In addition, in Test Examples 7 to 11, the low-melting polylactic acid particles melted in the lamination step, and at the surfaces where the resin foams 1 were stacked, the low-melting polylactic acid particles fused with each other and bonded to the high-melting polylactic acid particles in the foamed particle units, thereby successfully bonding the surfaces where the resin foams 1 were stacked. In addition, in the film covering step, the low-melting polylactic acid particles melted and bonded to the resin film 2, successfully bonding the resin foams 1 and the resin film 2.

[0073] (Test Example 12) Test Example 12 was obtained by removing the chain extender from Test Example 3. Due to the absence of the chain extender, the foam-forming properties of polylactic acid in Test Example 12 were poor, and sufficient foaming was not achieved in the foam production process, resulting in slightly poor foamability of the resulting resin foam 1. In the lamination process, the overlapping surfaces could be bonded together, and in the film coating process, the resin foam 1 and the resin film 2 could be bonded together. [Explanation of symbols]

[0074] 1...resin foam, 2...resin film, 10...laminated resin foam, 20...film-coated resin foam.

Claims

1. A resin foam formed from mixed resin particles containing polylactic acid, the mixed resin particles being heated and foamed by the expansion of a blowing agent, The mixed resin particles contain high-melting-point polylactic acid particles and low-melting-point polylactic acid particles, and the melting point of the low-melting-point polylactic acid particles is lower than the melting point of the high-melting-point polylactic acid particles.

2. The resin foam according to claim 1, wherein the high-melting-point polylactic acid particles have a melting point of 150 to 175°C, and the low-melting-point polylactic acid particles have a melting point of 50 to 100°C.

3. The resin foam according to claim 1 , wherein the foaming agent contains carbon dioxide and nitrogen.

4. A laminated resin foam, characterized in that the resin foams according to claim 1 are laminated together.

5. A film-coated resin foam, which is obtained by laminating the resin foam according to claim 1 and a resin film.

6. A method for laminating resin foams, comprising stacking a plurality of sheets of the resin foam according to claim 1 and heating the surfaces of the resin foams to a temperature of 70 to 140°C.

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