Resin composition for injection molding and injection molded body

Abstract

A poly(3-hydroxyalkanoate) resin composition comprising: a copolymer (A) of 3-hydroxybutyrate units and other hydroxyalkanoate units, and a copolymer (B) of 3-hydroxybutyrate units and other hydroxyalkanoate units, wherein the content of other hydroxyalkanoate units in copolymer (A) is 1 to 6 mol%, and the content of other hydroxyalkanoate units in copolymer (B) is 24 mol% or more. The resin composition further comprises layered clay mineral (C). The proportion of (A) is 72 to 93 wt%, and the proportion of (B) is 7 to 28 wt%. The content of (C) is 5 to 45 parts by weight relative to 100 parts by weight of the total poly(3-hydroxyalkanoate) resin composition.

Description

Technical Field

[0001] This invention relates to resin compositions for injection molding containing poly(3-hydroxyalkanoate) resin components and injection molded articles. Background Technology

[0002] In recent years, the environmental problems caused by waste plastics have become increasingly prominent, especially as large quantities of plastics drift in oceans globally through dumping and river flow. Because such plastics retain their shape for extended periods, they are known to have ecosystem-related impacts such as trapping marine life (so-called ghost fishing) and causing feeding difficulties when ingested by marine organisms, as they may remain in their digestive systems.

[0003] Furthermore, it points out the problem that microplastics, formed by the degradation / micronization of plastics by ultraviolet light, can adsorb harmful compounds in the ocean and enter the food chain through ingestion by marine organisms.

[0004] Regarding the marine pollution caused by such plastics, there is hope for the use of biodegradable plastics. However, a report compiled by the United Nations Environment Programme in 2015 pointed out that plastics such as polylactic acid, which can be biodegraded through mixed fertilizers, cannot decompose in the low temperatures of the actual ocean in a short period of time, and therefore cannot be used as a measure to address marine pollution.

[0005] Among such materials, poly(3-hydroxyalkanoate) resins are biodegradable in seawater and are therefore attracting attention as raw materials for solving the aforementioned problems.

[0006] In Patent Document 1, a resin composition containing poly(3-hydroxyalkanoate) resins such as poly(3-hydroxyalkanoate) resins, pentaerythritol, and fillers is disclosed in order to improve the slow crystallization of poly(3-hydroxyalkanoate) resins and to improve the surface smoothness and mold transferability of the obtained molded articles.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: International Publication No. 2015 / 052876 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] For example, there are many cases where a high balance between elastic modulus (rigidity) and toughness (resistance to bending) is required for injection-molded bodies such as spoons.

[0012] However, as described in Patent Document 1, the method of adding fillers only to poly(3-hydroxyalkanoate) resins sometimes results in injection molded articles with reduced toughness and that become easily bent.

[0013] On the other hand, as a method to improve flexibility, adding other soft, biodegradable resins, such as polybutylene succinate resins and polybutylene adipate terephthalate resins, has been considered. However, adding these resins can lead to deterioration in the seawater decomposability of the injection-molded articles, a decrease in the elastic modulus, longer molding cycles, and reduced productivity.

[0014] The aim is to produce injection molded parts that achieve a practical balance between elastic modulus and toughness while using poly(3-hydroxyalkanoate) resins with seawater decomposability as the main resin component, and with excellent manufacturability.

[0015] In view of the above, the object of the present invention is to provide a resin composition containing a poly(3-hydroxyalkanoate) resin component that can be used to form an injection molded article with a practical balance of elastic modulus and toughness with good manufacturability.

[0016] Problem Solving Methods

[0017] In order to solve the above-mentioned problems, the inventors conducted repeated and in-depth research and found that by using two poly(3-hydroxyalkanoate) resins containing different proportions of monomers in a specific ratio and adding a specific amount of filler, it is possible to form an injection molded body with a practical balance of elastic modulus and toughness with good manufacturability, thus completing the present invention.

[0018] That is, the present invention relates to a resin composition for injection molding, which contains a poly(3-hydroxyalkanoate) resin component.

[0019] The poly(3-hydroxyalkanoate) resin composition comprises: a copolymer (A) of 3-hydroxybutyrate units and other hydroxyalkanoate units, and a copolymer (B) of 3-hydroxybutyrate units and other hydroxyalkanoate units, wherein the content of other hydroxyalkanoate units in copolymer (A) is 1-6 mol%, and the content of other hydroxyalkanoate units in copolymer (B) is 24 mol% or more.

[0020] The resin composition further comprises layered clay minerals (C).

[0021] In the poly(3-hydroxyalkanoate) resin composition, the proportion of copolymer (A) is 72-93% by weight, and the proportion of copolymer (B) is 7-28% by weight.

[0022] The content of the layered clay mineral (C) is 5 to 45 parts by weight relative to 100 parts by weight of the total poly(3-hydroxyalkanoate) resin component.

[0023] Preferably, the other hydroxyalkanoate units account for an average of 2 to 35 mol% of all monomer units constituting the poly(3-hydroxyalkanoate) resin component.

[0024] Preferably, the other hydroxyalkyl ester unit is a 3-hydroxyhexanoate unit.

[0025] Preferably, the layered clay mineral (C) is selected from at least one of mica, talc and kaolin.

[0026] In addition, the present invention relates to an injection-molded article formed from the above-described resin composition for injection molding.

[0027] The effects of the invention

[0028] According to the present invention, a resin composition containing a poly(3-hydroxyalkanoate) resin component is provided, which can be used to form an injection molded article with a practical balance of elastic modulus and toughness with good manufacturability. Attached Figure Description

[0029] Figure 1 This figure illustrates the bending test of the injection-molded body (spoon) performed in the embodiments and comparative examples.

[0030] Symbol Explanation

[0031] 10 spoons

[0032] 11. Spoon and dish section

[0033] 12 spoon handles Detailed Implementation

[0034] The embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments.

[0035] One embodiment of the present invention relates to a resin composition for use in injection molding to manufacture a molded article. The resin composition contains at least a poly(3-hydroxyalkanoate) resin component as a resin component.

[0036] (Poly(3-hydroxyalkanoate) resin components)

[0037] As a poly(3-hydroxyalkanoate) resin component, a mixture of at least two poly(3-hydroxyalkanoate) resins containing different proportions of each other is used as the constituent monomers. By using this mixture, injection molded parts with a practical balance of elastic modulus and toughness can be formed with good productivity.

[0038] The above-mentioned poly(3-hydroxyalkanoate) resin is preferably a polymer having 3-hydroxyalkanoate units, and more specifically a polymer containing units represented by the following general formula (1).

[0039] [-CHR-CH2-CO-O-](1)

[0040] In general formula (1), R represents C p H 2p+1 The alkyl group indicated is p, which represents an integer from 1 to 15. Examples of R include straight-chain or branched alkyl groups such as methyl, ethyl, propyl, methylpropyl, butyl, isobutyl, tert-butyl, pentyl, and hexyl. Preferably, p is 1 to 10, more preferably 1 to 8.

[0041] As for the above-mentioned poly(3-hydroxyalkanoate) resin, poly(3-hydroxyalkanoate) resin produced by microorganisms is particularly preferred. In the poly(3-hydroxyalkanoate) resin produced by microorganisms, 3-hydroxyalkanoate units are contained as all (R)-3-hydroxyalkanoate units.

[0042] Poly(3-hydroxyalkanoate) resins preferably contain 50 mol% or more of 3-hydroxyalkanoate units (especially those represented by general formula (1)) of all constituent units, more preferably 60 mol% or more, and even more preferably 70 mol% or more. Poly(3-hydroxyalkanoate) resins may contain only one or two or more 3-hydroxyalkanoate units as constituent units of the polymer, or they may contain other units (e.g., 4-hydroxyalkanoate units, etc.) in addition to one or two or more 3-hydroxyalkanoate units.

[0043] Poly(3-hydroxyalkanoate) resins can be homopolymers or copolymers containing 3-hydroxybutyrate (hereinafter sometimes referred to as 3HB) units. In particular, the 3-hydroxybutyrate units are preferably all (R)-3-hydroxybutyrate units. In addition, poly(3-hydroxyalkanoate) resins are preferably copolymers of 3-hydroxybutyrate units and other hydroxyalkanoate units.

[0044] Specific examples of poly(3-hydroxyalkanoate) resins include: poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxypropionate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (abbreviated as P3HB3HV), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (abbreviated as P3HB3HH), poly(3-hydroxybutyrate-co-3-hydroxyheptanoate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), poly(3-hydroxybutyrate-co-3-hydroxynonanoate), poly(3-hydroxybutyrate-co-3-hydroxydecanoate), poly(3-hydroxybutyrate-co-3-hydroxyundecanoate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (abbreviated as P3HB4HB). In particular, from the viewpoint of the productivity and mechanical properties of the injection molded part, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate) is preferred, and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is more preferred.

[0045] The aforementioned poly(3-hydroxyalkanoate) resin composition contains at least one highly crystalline poly(3-hydroxyalkanoate) resin and at least one low-crystalline poly(3-hydroxyalkanoate) resin. Generally, highly crystalline poly(3-hydroxyalkanoate) resins exhibit excellent productivity but lack mechanical strength, while low-crystalline poly(3-hydroxyalkanoate) resins have poor productivity but excellent mechanical properties. It is speculated that when the two resins are mixed, the highly crystalline poly(3-hydroxyalkanoate) resin forms fine resin crystal particles, while the low-crystalline poly(3-hydroxyalkanoate) resin forms linking molecules that cross-link these resin crystal particles. By combining these resins, good productivity is achieved, and the mechanical properties of the injection-molded articles can be significantly improved.

[0046] The aforementioned highly crystalline poly(3-hydroxyalkanoate) resin is a copolymer (A) of 3-hydroxybutyrate units and other hydroxyalkanoate units. Preferably, the proportion of 3-hydroxybutyrate units in the aforementioned highly crystalline poly(3-hydroxyalkanoate) resin is higher than the average proportion of 3-hydroxybutyrate units in all monomer units constituting the poly(3-hydroxyalkanoate) resin. Specifically, the proportion of other hydroxyalkanoate units in the copolymer (A) is preferably 1 mol% or more and 6 mol% or less, more preferably 2 mol% or more and 5 mol% or less, and even more preferably 3 mol% or more and 5 mol% or less.

[0047] As the copolymer (A) described above, the copolymer containing 3-hydroxybutyrate units described above can be used, preferably poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), or poly(3-hydroxybutyrate-co-4-hydroxybutyrate), more preferably poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

[0048] The aforementioned low-crystallinity poly(3-hydroxyalkanoate) resin is a copolymer (B) of 3-hydroxybutyrate units and other hydroxyalkanoate units. Preferably, the proportion of 3-hydroxybutyrate units in the aforementioned low-crystallinity poly(3-hydroxyalkanoate) resin is lower than the average proportion of 3-hydroxybutyrate units in all monomer units constituting the poly(3-hydroxyalkanoate) resin. Specifically, the proportion of other hydroxyalkanoate units in the copolymer (B) is preferably 24 mol% or more and 99 mol% or less, more preferably 24 mol% or more and 50 mol% or less, further preferably 24 mol% or more and 35 mol% or less, and particularly preferably 24 mol% or more and 30 mol% or less.

[0049] As the copolymer (B) described above, the copolymer containing 3-hydroxybutyrate units described above can be used, preferably poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), or poly(3-hydroxybutyrate-co-4-hydroxybutyrate), more preferably poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

[0050] Relative to the total amount of copolymer (A) and copolymer (B), the proportion of copolymer (A) is 72% by weight or more and 93% by weight or less, and the proportion of copolymer (B) is 7% by weight or more and 28% by weight or less. By using copolymer (A) and copolymer (B) in combination within this range, injection molded parts with excellent balance between elastic modulus and toughness can be formed with good productivity. When the proportion of copolymer (B), which is a low-crystallinity poly(3-hydroxyalkanoate) resin, is less than 7% by weight, there is a tendency for the toughness of the injection molded part to become insufficient; when it exceeds 28% by weight, there is a tendency for the molding cycle of the injection molded part to become longer and for productivity to decrease. Preferably, the proportion of copolymer (A) is 75% or more and 90% or less, and the proportion of copolymer (B) is 10% or more and 25% or less. More preferably, the proportion of copolymer (A) is 77% or more and 88% or less, and the proportion of copolymer (B) is 12% or more and 23% or less. Even more preferably, the proportion of copolymer (A) is 75% or more and 85% or less, and the proportion of copolymer (B) is 15% or more and 25% or less.

[0051] The poly(3-hydroxyalkanoate) resin component may contain only copolymer (A) and copolymer (B), and may further contain other poly(3-hydroxyalkanoate) resins in addition to copolymer (A) and copolymer (B). These other poly(3-hydroxyalkanoate) resins may be homopolymers of 3-hydroxybutyrate, or copolymers of 3-hydroxybutyrate units and other hydroxyalkanoate units, provided that the proportion of these other hydroxyalkanoate units does not conform to any definition in copolymer (A) and copolymer (B).

[0052] From the viewpoint of balancing the mechanical properties and productivity of the injection-molded parts, the average content ratio of 3-hydroxybutyrate units and other hydroxyalkanoate units in all monomer units constituting the poly(3-hydroxyalkanoate) resin components is preferably 3-hydroxybutyrate units / other hydroxyalkanoate units = 98 / 2 to 65 / 35 (mol% / mol%), more preferably 96 / 4 to 75 / 25 (mol% / mol%), even more preferably 95 / 5 to 80 / 20 (mol% / mol%), and particularly preferably 96 / 6 to 85 / 15 (mol% / mol%).

[0053] The average content ratio of each monomer unit in all monomer units constituting the poly(3-hydroxyalkanoate) resin component can be determined by methods known to those skilled in the art, such as those described in paragraph

[0047] of International Publication No. 2013 / 147139. The average content ratio refers to the molar proportion of each monomer unit in the total poly(3-hydroxyalkanoate) resin component, and specifically to the molar proportion of each monomer unit contained in the total mixture of two or more poly(3-hydroxyalkanoate) resins constituting the poly(3-hydroxyalkanoate) resin component.

[0054] The weight-average molecular weight of the poly(3-hydroxyalkanoate) resin component is not particularly limited. From the viewpoint of balancing the mechanical properties and productivity of the injection molded part, it is preferably 50,000 to 3,000,000, more preferably 200,000 to 2,000,000, further preferably 250,000 to 1,500,000, and particularly preferably 300,000 to 800,000.

[0055] Furthermore, the weight-average molecular weight of each poly(3-hydroxyalkanoate) resin constituting the poly(3-hydroxyalkanoate) resin component is not particularly limited. However, from the viewpoint of balancing the mechanical properties and productivity of the injection-molded article, the weight-average molecular weight of the copolymer (A) of the highly crystalline poly(3-hydroxyalkanoate) resin is preferably 200,000 to 1,000,000, more preferably 220,000 to 800,000, and even more preferably 250,000 to 600,000. On the other hand, from the viewpoint of balancing the mechanical properties and productivity of the injection-molded article, the weight-average molecular weight of the copolymer (B) of the low-crystalline poly(3-hydroxyalkanoate) resin is preferably 200,000 to 2,500,000, more preferably 250,000 to 2,300,000, even more preferably 300,000 to 2,000,000, and particularly preferably 350,000 to 1,500,000.

[0056] It should be noted that the weight-average molecular weight of poly(3-hydroxyalkanoate) resins or poly(3-hydroxyalkanoate) resin components can be determined by polystyrene conversion using gel permeation chromatography (HPLC GPC system manufactured by Shimadzu Corporation) with chloroform solvent. A column suitable for determining weight-average molecular weight can be used as the chromatographic column for this gel permeation chromatography.

[0057] The above-mentioned poly(3-hydroxyalkanoate) resin components are preferably not cross-linked using cross-linking agents such as organic peroxides, that is, preferably resin components without cross-linking structures.

[0058] The manufacturing method of poly(3-hydroxyalkanoate) resins is not particularly limited; it can be manufactured using chemical synthesis or microbial methods. Microbial manufacturing is preferred. Known methods can be used for microbial manufacturing. For example, known microorganisms that produce copolymers of 3-hydroxybutyrate and other hydroxyalkanoates include *Aeromonas caviae* as a P3HB3HV and P3HB3HH producer, and *Alcaligenes eutrophus* as a P3HB4HB producer. In particular, regarding P3HB3HH, a more preferred strain is Alcaligenes eutrophus AC32 (FERM BP-6038) (T. Fukui, Y. Doi, J. Bateriol., 179, p4821-4830 (1997)), which has had genes from the P3HA synthase group introduced to improve the productivity of P3HB3HH. Microbial cells of these microorganisms can be used to accumulate P3HB3HH within the cells under appropriate conditions. In addition to the above, recombinant microorganisms with genes introduced to synthesize various poly(3-hydroxyalkanoate) resins can also be used in conjunction with the poly(3-hydroxyalkanoate) resins to be produced, and the culture conditions, including the type of substrate, can be optimized.

[0059] There are no particular limitations on the method for obtaining blends of two or more poly(3-hydroxyalkanoate) resins. Blends can be obtained through microbial production or chemical synthesis. Alternatively, blends can be obtained by melt-blending two or more resins using an extruder, kneader, Banbury mixer, rollers, etc., or by dissolving two or more resins in a solvent and then mixing / drying them.

[0060] (Other resins)

[0061] Without impairing the effects of the invention, the resin composition for injection molding in one embodiment may comprise resins other than poly(3-hydroxyalkanoate) resins. Examples of such other resins include, for instance, aliphatic polyester resins such as polybutylene adipate, polybutylene succinate, polycaprolactone, and polylactic acid, as well as aliphatic aromatic polyester resins such as polybutylene adipate, polybutylene sebacic acid, and polybutylene azelaic acid. These other resins may comprise only one type or two or more types.

[0062] The content of the other resins mentioned above is not particularly limited. From the viewpoint of the seawater decomposability of the injection-molded article, it is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, and even more preferably 5 parts by weight or less, relative to 100 parts by weight of the total poly(3-hydroxyalkanoate) resin component. The lower limit of the content of other resins is not particularly limited and can be 0 parts by weight.

[0063] (Layered clay minerals (C))

[0064] One embodiment of the resin composition for injection molding further contains layered clay minerals (C). This enables the formation of injection molded articles with an excellent balance between elastic modulus and toughness. Here, layered clay minerals refer to minerals whose main component is layered silicate.

[0065] The layered clay mineral (C) is not particularly limited and can be any known layered clay mineral. However, for ease of achieving productive improvement, it is preferably selected from one or more of montmorillonite, mica, talc, pyrophyllite, vermiculite, chlorite, kaolinite, and serpentine. From a generality point of view, mica, talc, and kaolinite are preferred, with talc being particularly preferred.

[0066] Examples of mica mentioned above include wet-processed mica and dry-processed mica, specifically those manufactured by Yamaguchi Mica Co., Ltd. and Keiwa Furnace Materials Co., Ltd.

[0067] Examples of the aforementioned talc include general-purpose talc and surface-treated talc. Specific examples include "Micro Ace" (registered trademark) manufactured by Japan Talc Co., Ltd., "Talcan Pawder" (registered trademark) manufactured by Hayashi Kasei Co., Ltd., and talc manufactured by Takehara Chemical Industry Co., Ltd. and Maruo Calcium Co., Ltd.

[0068] Examples of the aforementioned kaolin include: dry kaolin, calcined kaolin, and wet kaolin. Specific examples include kaolin produced by Rinkasei Corporation under the trademarks "TRANSLINK," "ASP," "SANTINTONE," and "ULTREX," and kaolin produced by Keiwa Furnace Materials Co., Ltd.

[0069] Due to the excellent mechanical properties and manufacturability of the injection-molded articles, the average particle size of the aforementioned layered clay mineral (C) is preferably 0.1 to 50 μm, more preferably 0.3 to 30 μm, even more preferably 0.5 to 15 μm, and particularly preferably 1 to 10 μm. This average particle size can be measured using a laser diffraction / scattering apparatus such as the "MICROTRAC MT3100II" manufactured by Nikkiso Co., Ltd.

[0070] The content of the layered clay mineral (C) is 5 parts by weight or more and 45 parts by weight or less, relative to the total 100 parts by weight of the poly(3-hydroxyalkanoate) resin component. By incorporating the layered clay mineral (C) within this range, an injection-molded article with excellent balance between elastic modulus and toughness can be formed with good manufacturability. When the content of the layered clay mineral (C) is less than 5 parts by weight, there is a tendency for the elastic modulus of the injection-molded article to decrease; when it exceeds 45 parts by weight, the production of the injection-molded article becomes difficult. The above-mentioned content is preferably 10 parts by weight or more and 40 parts by weight or less, more preferably 10 parts by weight or more and 35 parts by weight or less, and even more preferably 15 parts by weight or more and 30 parts by weight or less.

[0071] For the purpose of improving the dispersibility of the above-mentioned layered clay mineral (C), it is preferable to use the above-mentioned layered clay mineral (C) in combination with a dispersing aid.

[0072] Examples of dispersing agents include glyceryl ester compounds, adipate ester compounds, polyether ester compounds, phthalate ester compounds, isosorbide ester compounds, and polycaprolactone compounds. Among these, modified glyceryl ester compounds such as glyceryl diacetyl monolaurate, glyceryl diacetyl monooctanoate, and glyceryl diacetyl monodecanoate are preferred from the perspective of excellent affinity for resin components and low exudation. Adipate ester compounds such as diethylhexyl adipate, dioctyl adipate, and diisononyl adipate are also preferred. Polyether ester compounds such as polyethylene glycol dibenzoate, polyethylene glycol dioctanoate, and polyethylene glycol diisostearate are also preferred. Furthermore, when a large amount of components derived from biomass is included, the overall biomass content of the composition can be improved, and therefore, they are particularly preferred. Examples of such dispersing agents include the "RIKEMAL" (registered trademark) PL series from RIKEN Vitamin Co., Ltd., and the Polysorb series from ROQUETTE Co., Ltd. Dispersing agents can be used alone or in combination of two or more.

[0073] The amount of the dispersing agent (total amount) is not particularly limited, but is preferably 0.1 to 20 parts by weight relative to 100 parts by weight of the poly(3-hydroxyalkanoate) resin components. However, the dispersing agent may be omitted.

[0074] (additive)

[0075] To the extent that it does not impair the effects of the invention, the resin composition for injection molding in one embodiment may contain additives. As additives, for example, crystal nucleating agents, lubricants, plasticizers, antistatic agents, flame retardants, conductive agents, heat insulating agents, crosslinking agents, antioxidants, ultraviolet absorbers, colorants, inorganic fillers, organic fillers, hydrolysis inhibitors, etc., may be used, depending on the purpose. Additives with biodegradability are particularly preferred.

[0076] Examples of crystal nucleating agents include pentaerythritol, orotic acid, aspartame, cyanuric acid, glycine, zinc phenylphosphonate, and boron nitride. Among these, pentaerythritol is preferred due to its particularly excellent effect in promoting the crystallization of poly(3-hydroxyalkanoate) resin components. The amount of crystal nucleating agent used is not particularly limited, but is preferably 0.1 to 5 parts by weight, more preferably 0.5 to 3 parts by weight, and even more preferably 0.7 to 1.5 parts by weight, relative to 100 parts by weight of the total poly(3-hydroxyalkanoate) resin components. Furthermore, one or more crystal nucleating agents can be used, and the ratio can be appropriately adjusted according to the purpose.

[0077] Examples of lubricants include: benzyl amide, oleamide, erucamide, stearamide, palmitamide, N-stearyl benzyl amide, N-stearyl erucamide, ethylene bis-stearamide, ethylene bis-oleamide, ethylene bis-erucamide, ethylene bis-laurate amide, ethylene bis-decanoate amide, p-phenylene bis-stearamide, condensates of ethylenediamine, stearic acid, and sebacic acid, etc. Among these, benzyl amide or erucamide is preferred from the viewpoint that it has particularly excellent lubricating effect on poly(3-hydroxyalkanoate) resin components. The amount of lubricant used is not particularly limited, but is preferably 0.01 to 5 parts by weight, more preferably 0.05 to 3 parts by weight, and even more preferably 0.1 to 1.5 parts by weight relative to 100 parts by weight of the total poly(3-hydroxyalkanoate) resin component. Furthermore, one or more lubricants can be used, and the ratio can be adjusted appropriately according to the purpose.

[0078] Examples of plasticizers include: glyceryl ester compounds, citrate compounds, sebacic acid ester compounds, adipate compounds, polyether ester compounds, benzoate compounds, phthalate compounds, isosorbide compounds, polycaprolactone compounds, and diester compounds. Among these, glyceryl ester compounds, citrate compounds, sebacic acid ester compounds, and diester compounds are preferred from the viewpoint of having particularly excellent plasticizing effects on poly(3-hydroxyalkanoate) resin components. Examples of glyceryl ester compounds include: glyceryl diacetyl monolaurate. Examples of citrate compounds include: acetylated tributyl citrate. Examples of sebacic acid ester compounds include: dibutyl sebate. Examples of diester compounds include: benzyl methyl diethylene glycol adipate. The amount of plasticizer used is not particularly limited, but is preferably 1 to 20 parts by weight, more preferably 2 to 15 parts by weight, and even more preferably 3 to 10 parts by weight, relative to 100 parts by weight of the total poly(3-hydroxyalkanoate) resin component. Furthermore, one type of plasticizer or two or more types can be used, and the ratio can be adjusted appropriately according to the purpose.

[0079] (Manufacturing method of injection molded parts)

[0080] One embodiment of the injection-molded article can be manufactured by melt-blending the various components, obtaining granules as needed, and then using a known injection molding method. This will be described in detail below.

[0081] First, poly(3-hydroxyalkanoate) resin components, layered clay minerals (C), other resins as needed, and any additives are added. The mixture is then melt-blended using an extruder, kneader, Banbury mixer, rollers, etc., to prepare a resin composition. This composition is then extruded as filaments and cut to obtain granules in cylindrical, elliptical, spherical, cubic, and cuboid shapes. The granules are then thoroughly dried at 40–80°C to remove moisture before injection molding.

[0082] The temperature during the above-mentioned melt mixing depends on the melting point and melt viscosity of the resin used, and therefore cannot be determined uniformly. The resin temperature at the die exit of the melt-mixed compound is preferably 135–200°C, more preferably 140–195°C, even more preferably 145–190°C, and particularly preferably 150–185°C. When the resin temperature of the melt-mixed compound is below 135°C, the poly(3-hydroxyalkanoate) resin component may become unmelted; when it exceeds 200°C, the poly(3-hydroxyalkanoate) resin component may undergo thermal decomposition.

[0083] Next, by injection molding the prepared granules, an injection molded body can be formed. Injection molding is a method in which a heated and molten resin composition is injected into a mold, the resin composition is allowed to cool and solidify inside the mold, the mold is opened, and the molded body is demolded, thereby obtaining the molded body. As an injection molding method, in addition to the injection molding method generally used when molding thermoplastic resins, injection blow molding, gas-assisted molding, injection compression molding, and other injection molding methods can also be used. In addition, in-mold molding, air compression molding, two-color molding, sandwich molding, push-pull, scorim, etc. can also be used. However, the injection molding methods that can be used are not limited to the above methods.

[0084] The temperature for cooling using the mold after injection can be appropriately determined by those skilled in the art, preferably 20-70°C, more preferably 25-60°C, further preferably 30-50°C, and particularly preferably 35-45°C.

[0085] In a preferred embodiment, the injection-molded body is composed primarily of poly(3-hydroxyalkanoate) resin, which is seawater degradable, thus solving the environmental problems caused by ocean dumping of plastics.

[0086] The application of the injection-molded body in one embodiment is not particularly limited. Examples include tableware such as plates / cups / handleless cups / trays with lids, cutlery such as spoons / forks / knives / stirring spoons, sealed containers such as coffee capsules / toy containers, toys, agricultural supplies, OA components, home appliance components, automotive components, various containers / boxes, daily necessities, stationery, bottle-shaped products, etc.

[0087] Example

[0088] The present invention will be specifically described below through embodiments, but the present invention is not limited to its technical scope by these embodiments.

[0089] The following shows the substances used in the examples and comparative examples.

[0090] [Poly(3-hydroxyalkanoate) resins]

[0091] PHBH1: P3HB3HH (average content ratio 3HB / 3HH = 95.4 / 4.6 (mol% / mol%), weight-average molecular weight is 380,000 g / mol)

[0092] It was manufactured according to the method described in Example 2 of International Publication No. 2019 / 142845.

[0093] PHBH2: P3HB3HH (average content ratio 3HB / 3HH = 71.8 / 28.2 (mol% / mol%), weight-average molecular weight is 660,000 g / mol)

[0094] It was manufactured according to the method described in Example 9 of International Publication No. 2019 / 142845.

[0095] PBSA: Polybutylene adipate resin, BioPBS FD72PB manufactured by Mitsubishi Chemical.

[0096] PBAT: Polybutylene adipate terephthalate, BASF-made Ecoflex F blended with C1200

[0097] [Layered clay minerals (C)]

[0098] Talc: Micro AceK-1 (Japanese Talc)

[0099] [additive]

[0100] Additive-1: Pentaerythritol (manufactured by Mitsubishi Chemical Corporation: Neutizer-P)

[0101] Additive-2: Succinate (manufactured by Nippon Seika Co., Ltd.: BNT-22H)

[0102] The evaluation methods implemented in the embodiments and comparative examples will be described below.

[0103] [Evaluation of tensile modulus of elasticity]

[0104] (Production of the experimental film)

[0105] The resin particles were dried at 60°C for 24 hours using a dehumidifying dryer. The resulting resin particles were then used in a Toyo Machinery Si-30V metal injection molding machine. The barrel temperature of the injection molding machine was set to nozzle / T1 / T2 / T3 = 155 / 145 / 135 / 125°C, the mold temperature was set to 35°C, and the injection speed was 20 mm / sec. A JIS K7161 1A type dumbbell with a thickness of 4 mm was obtained.

[0106] (Determination of elastic modulus)

[0107] The dumbbells were left to stand at 23°C for 168 hours, and then subjected to a tensile test at 10 mm / sec according to JIS K 7161 to determine the tensile modulus of elasticity. A tensile modulus of elasticity greater than 1400 MPa was rated as 0 (good), and a tensile modulus less than 1400 MPa was rated as × (insufficient).

[0108] [Bending Test]

[0109] (Production of the experimental film)

[0110] Using a dehumidifying dryer, the resin particles were dried at 60°C for 24 hours. Using a Toyo Machinery Si-30V metal injection molding machine, the barrel temperature of the injection molding machine was set to nozzle / T1 / T2 / T3 = 155 / 145 / 135 / 125°C, the mold temperature was set to 35°C, and the injection speed was 20 mm / sec. A dessert spoon with a length of 9.8 cm, a spoon body thickness of 1 mm, and a handle thickness of 1.5 mm was obtained.

[0111] (Bending Evaluation)

[0112] Hold the spoon 10 at the spoon bowl 11 end with your left hand and the spoon handle 12 end with your right hand, and press firmly along... Figure 1 The direction of the arrow shown indicates a bend, thus conducting a bend test. The same bend test was performed on 5 spoons, and the case where none of them bent was rated as 0 (good toughness), while even if one bent, it was rated as × (insufficient toughness).

[0113] [Evaluation of Molding Cycle]

[0114] The resin particles were dried at 60°C for 24 hours using a dehumidifying dryer. Using a Toyo Machinery Si-30V metal injection molding machine, the barrel temperature was set to nozzle / T1 / T2 / T3 = 155 / 145 / 135 / 125°C, the mold temperature was set to 35°C, and the injection speed was 20 mm / sec. Coffee capsules were obtained. Molding cycles of less than 30 seconds were rated as 0 (good productivity), and cycles of more than 30 seconds were rated as × (insufficient productivity).

[0115] [Evaluation of Seawater Decomposition Properties]

[0116] (Production of the experimental film)

[0117] Granules obtained by drying at 60°C for 24 hours using a dehumidifying dryer were used. A film with a thickness of 30 μm was obtained using a single-screw extruder (D2020 type), a T-die (T150C type, die lip thickness 250 μm, die lip width 15 cm), and a film collection device (FT2W20 type, roller temperature 30°C, collection speed 2 m) in a Toyo Seiki Laboratory Plastic Mill 3S150, under molding temperature conditions C1 / C2 / C3 / die = 130 / 140 / 150 / 160°C. (Seawater decomposition test)

[0118] 10L of seawater obtained from the Seto Inland Sea, adjacent to Kaneka Takasago Industrial Co., Ltd., after more than three consecutive days without rainfall, was filtered through an 80-mesh screen. 5g of ammonium chloride and 1g of potassium dihydrogen phosphate were added and stirred until completely dissolved. The prepared seawater was added to a container (37cm high x 30cm deep x 52cm wide) until it reached 60% of its volume. A 10cm x 10cm section of the membrane was cut and immersed in the seawater. The membrane was left to stand for two months while being aerated. The condition where the membrane completely decomposed and disappeared was evaluated as 0 (good seawater decomposition), and the condition where the membrane did not disappear was evaluated as × (insufficient seawater decomposition).

[0119] <Example 1>

[0120] (Preparation of PHBH admixtures)

[0121] The total amount of copolymer (A), copolymer (B), and other biodegradable resins was set at 100 parts by weight, where 100 parts by weight = 10 kg. Based on the formulations (units are parts by weight) described in Table 2, all components except talc were mixed. Specifically, using a 75L high-speed mixer manufactured by KAWATA Co., Ltd., 9.0 kg of PHBH1, 1.0 kg of PHBH2, 1100 g of additive, and 50 g of additive 2 were added and stirred at 300 rpm for 3 minutes to obtain the PHBH blend.

[0122] (Hybridization)

[0123] Using the screw structure, auxiliary equipment, and barrel setting temperature described in Table 1, as described in the Toshiba TEM26SS (L / D=60) machine, the screw speed was set to 100 rpm. The aforementioned PHBH blend was added from the screw root via the main feed section, and 1.0 kg of talc was added via the side feed section. The total supply rate of the main feed section and the side feed section was set to 10 kg / hr, and the respective supply rates of the main feed section and the side feed section were determined based on the following formula.

[0124] Side feed rate = 10 kg / hr × talc weight parts ÷ total weight parts of compounding ingredients

[0125] Main feed section supply rate = 10 kg / hr - Side feed section supply rate

[0126] The wire material exiting from the front of the mold is fed into a water tank filled with 45°C warm water to solidify it. It is then cut into granules by a granulator.

[0127] Using the obtained particles, tensile modulus of elasticity, bending test and molding cycle test were carried out, and the results are summarized in Table 3.

[0128] <Examples 2-16, Comparative Examples 1-22>

[0129] Based on the preparation and mixing of the PHBH admixture as described in Table 2, particles were obtained in the same order as in Example 1, and tensile modulus of elasticity, bending test and molding cycle test were performed. The results are summarized in Table 3.

[0130] Seawater decomposability tests were also conducted on Examples 4 and 8, and Comparative Examples 21 and 22, and the results are recorded in Table 3.

[0131] [Table 1]

[0132]

[0133]

[0134] [Table 3]

[0135]

[0136] As shown in Table 3, the injection molded bodies obtained in Examples 1 to 16 all exhibit good elastic modulus and toughness in bending tests, short molding cycles, and excellent productivity.

[0137] On the other hand, the injection molded articles obtained from Comparative Examples 1, 2, 6, 7, 9, 10, 12, 13, and 15, in which the copolymer (B) content was less than 7% by weight, all lacked sufficient toughness. In addition, the injection molded articles obtained from Comparative Examples 8, 11, 14, and 16, in which the copolymer (B) content was more than 28% by weight, all had long molding cycles and insufficient productivity.

[0138] Although the content of copolymer (B) ranged from 7% to 28% by weight, the elastic modulus of the injection molded articles obtained in Comparative Examples 3 to 5, which did not contain talc, was insufficient. In addition, Comparative Examples 17 to 20, which contained more than 45 parts by weight of talc, could not be granulated, i.e., injection molded articles could not be manufactured.

[0139] The injection molded articles obtained in Comparative Examples 21 and 22, which do not contain copolymer (B) but contain other biodegradable resins as substitutes, have insufficient elastic modulus and insufficient seawater decomposability.

Claims

1. A resin composition for injection molding, comprising a poly(3-hydroxyalkanoate) resin component, The poly(3-hydroxyalkanoate) resin composition comprises: a copolymer (A) of 3-hydroxybutyrate units and other hydroxyalkanoate units, and a copolymer (B) of 3-hydroxybutyrate units and other hydroxyalkanoate units, wherein the content of other hydroxyalkanoate units in copolymer (A) is 1-6 mol%, and the content of other hydroxyalkanoate units in copolymer (B) is 24 mol% or more. The resin composition further comprises layered clay minerals (C). In the poly(3-hydroxyalkanoate) resin composition, the proportion of copolymer (A) is 72-93% by weight, and the proportion of copolymer (B) is 7-28% by weight. The content of the layered clay mineral (C) is 5 to 45 parts by weight relative to 100 parts by weight of the total poly(3-hydroxyalkanoate) resin component. The layered clay mineral (C) is selected from at least one of mica, talc and kaolin.

2. The resin composition for injection molding according to claim 1, wherein, The other hydroxyalkanoate units account for an average of 2 to 35 moles of all monomer units constituting the poly(3-hydroxyalkanoate) resin components.

3. The resin composition for injection molding according to claim 1 or 2, wherein, The other hydroxyalkanoate unit is a 3-hydroxyhexanoate unit.

4. An injection-molded article formed from any one of the injection molding resin compositions according to claims 1 to 3.

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