Resin composition for injection molding and injection molded body

Abstract

This invention relates to a resin composition for injection molding, comprising a poly(3-hydroxyalkanoate) resin. The poly(3-hydroxyalkanoate) resin comprises at least one copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units. The average content of 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin is 92 mol% or more and 99 mol% or less. The poly(3-hydroxyalkanoate) resin, obtained by gel permeation chromatography using chloroform solvent, has a polystyrene-converted weight-average molecular weight of 210,000 or more and 380,000 or less, and the proportion of components with a weight molecular weight of 200,000 or less in the weight molecular weight distribution is 35 wt% or more and 60 wt% or less.

Description

Technical Field

[0001] This invention relates to resin compositions for injection molding containing poly(3-hydroxyalkanoate) resins 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 therefore have attracted much attention as raw materials for solving the aforementioned problems. However, poly(3-hydroxyalkanoate) resins have a slow curing speed, which makes them prone to producing burrs during injection molding.

[0006] Patent Document 1 discloses a resin composition containing poly(3-hydroxyalkanoate) resins such as poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), pentaerythritol, and fillers. It describes how this improves the curability of the poly(3-hydroxyalkanoate) resin and suppresses burrs during injection molding.

[0007] Patent Document 2 discloses a resin composition containing polyhydroxyalkanoates such as poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) and low-melting-point polyhydroxybutyrates with a weight-average molecular weight of 5,000 to 50,000 and a melting point of 140°C to 170°C. It describes how this improves the crystallization rate of the polyhydroxyalkanoates. There is no mention of burrs generated during injection molding.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: International Publication No. 2015 / 052876

[0011] Patent Document 2: Japanese Patent Application Publication No. 2014-227543 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] According to the technology disclosed in Patent Documents 1 and 2, although the curability of poly(3-hydroxyalkanoate) resins is improved, it is sometimes not sufficient to suppress burrs that may occur during injection molding. In addition, the resulting injection molded articles tend to have reduced mechanical properties when exposed to high temperatures, and are sometimes unsuitable for use at high temperatures.

[0014] Here, burrs refer to the portion formed due to molten resin intruding into the gaps in the joints (e.g., mold closing part, insertion part, sliding magnetic core sliding part, etc.) of the cavity of the injection mold. Burrs form on the surface of the injection molded body along the location of the joints and become a problem in the appearance of the injection molded body.

[0015] In view of the above, the object of the present invention is to provide a resin composition containing a poly(3-hydroxyalkanoate) resin, which can suppress the formation of burrs and is suitable for use at high temperatures in injection molded articles.

[0016] Problem Solving Methods

[0017] In order to solve the above problems, the inventors have repeatedly conducted in-depth research and found that by setting the monomer composition, average molecular weight and low molecular weight components of poly(3-hydroxyalkanoate) resin within a specific range, it is possible to form an injection molded body that suppresses the generation of burrs and is suitable for use at high temperatures, thus completing the present invention.

[0018] Specifically, the present invention relates to a resin composition for injection molding containing a poly(3-hydroxyalkanoate) resin, wherein the poly(3-hydroxyalkanoate) resin comprises at least one copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units, the average content of 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin is 92 mol% or more and 99 mol% or less, the poly(3-hydroxyalkanoate) resin obtained by gel permeation chromatography using chloroform solvent has a polystyrene equivalent weight average molecular weight of 210,000 or more and 380,000 or less, and the proportion of components with a weight molecular weight of 200,000 or less in the weight molecular weight distribution is 35 wt% or more and 60 wt% or less.

[0019] Preferably, the poly(3-hydroxyalkanoate) resin is selected from one or more of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

[0020] Preferably, the above-mentioned poly(3-hydroxyalkanoate) resin is poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

[0021] Preferably, relative to 100 parts by weight of the above-mentioned poly(3-hydroxyalkanoate) resin, the content of resin other than the above-mentioned poly(3-hydroxyalkanoate) resin is 0 parts by weight or more and 35 parts by weight or less.

[0022] Preferably, the above-mentioned resin composition for injection molding further contains a crystal nucleating agent and / or a lubricant.

[0023] Preferably, relative to a total of 100 parts by weight of the resin component comprising the above-mentioned poly(3-hydroxyalkanoate) resin, the above-mentioned resin composition for injection molding further contains 1 part by weight and 50 parts by weight of inorganic filler.

[0024] Preferably, the inorganic filler is silicate, and more preferably, the silicate is selected from one or more of talc, mica, kaolin, smectite and montmorillonite.

[0025] In addition, the present invention relates to an injection-molded article formed from the above-described resin composition for injection molding.

[0026] The effects of the invention

[0027] According to the present invention, a resin composition containing a poly(3-hydroxyalkanoate) resin can be provided, which can form an injection-molded article that suppresses the formation of burrs and is suitable for use at high temperatures. In the resin composition or injection-molded article of a preferred embodiment of the present invention, the main material of the resin component is a poly(3-hydroxyalkanoate) resin that is degradable by seawater, and therefore also has the advantage of solving the environmental problems caused by ocean dumping of plastics. Attached Figure Description

[0028] Figure 1 This is an example of the cumulative distribution of molecular weight used when calculating the content of low molecular weight components with a molecular weight of less than 200,000. Detailed Implementation

[0029] The embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments.

[0030] The resin composition of this embodiment is a resin composition for manufacturing molded articles by performing injection molding. This resin composition contains at least a poly(3-hydroxyalkanoate) resin as a resin component.

[0031] [Poly(3-hydroxyalkanoate) resins]

[0032] The poly(3-hydroxyalkanoate) resin (abbreviated as P3HA), which constitutes the main resin component of the above-mentioned injection molding resin composition, is a polymer containing 3-hydroxyalkanoate structural units (monomer units). One type of poly(3-hydroxyalkanoate) resin may be used, or two or more types of poly(3-hydroxyalkanoate) resin may be used in combination.

[0033] Specifically, the 3-hydroxyalkanoate structural unit described above is preferably represented by the following general formula (1).

[0034] [-CHR-CH2-CO-O-](1)

[0035] 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. P is preferably 1 to 10, and more preferably 1 to 8.

[0036] As for the aforementioned poly(3-hydroxyalkanoate) resins, poly(3-hydroxyalkanoate) resins produced by microorganisms are particularly preferred. In poly(3-hydroxyalkanoate) resins produced by microorganisms, 3-hydroxyalkanoate structural units are contained as all (R)-3-hydroxyalkanoate structural units.

[0037] Poly(3-hydroxyalkanoate) resins preferably contain 3-hydroxyalkanoate structural units (especially those represented by the above general formula (1)) at least 50 mol% of all structural units, more preferably at least 60 mol% of such structural units, and even more preferably at least 70 mol% of such structural units. Poly(3-hydroxyalkanoate) resins may contain only one or more 3-hydroxyalkanoate structural units as repeating units constituting the polymer, or may contain other structural units (e.g., 4-hydroxyalkanoate structural units, etc.) in addition to one or more 3-hydroxyalkanoate structural units.

[0038] 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).

[0039] In this embodiment, the poly(3-hydroxyalkanoate) resin comprises at least a copolymer of 3-hydroxybutyrate units (hereinafter, sometimes referred to as 3HB) and other hydroxyalkanoate units. The poly(3-hydroxyalkanoate) resin may contain only one of the copolymers described above, or it may contain two or more. Furthermore, the poly(3-hydroxyalkanoate) resin may contain only at least one of the copolymers described above, or it may contain, in addition to at least one of the copolymers described above, a homopolymer of poly(3-hydroxybutyrate), i.e., 3-hydroxybutyrate.

[0040] In particular, from the viewpoint of processability and mechanical properties, the copolymer of the above-mentioned 3-hydroxybutyrate unit with other hydroxyalkanoate units is preferably selected from one or more of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate), more preferably poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) and / or poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and even more preferably poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

[0041] The average content ratio of 3-hydroxybutyrate units and other hydroxyalkanoate units in the poly(3-hydroxyalkanoate) resin composition for injection molding is 92 / 8 to 99 / 1 (mol%). When the average content ratio of 3-hydroxybutyrate units is less than 92 mol%, the resin crystallization rate is slow, and therefore, the molten resin easily penetrates the gaps in the joints of the cavity portion of the mold, making the injection molded body prone to burrs. On the other hand, if the average content ratio of 3-hydroxybutyrate units exceeds 99 mol%, there is a tendency for the mechanical properties of the injection molded body to decrease. The above-mentioned average content ratio is preferably 93 / 7 to 98 / 2 (mol%), and more preferably 94 / 6 to 97 / 3 (mol%).

[0042] The average content of each monomer unit in the poly(3-hydroxyalkanoate) resin moiety 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 refers to the proportion of each monomer unit contained in the poly(3-hydroxyalkanoate) resin moiety contained in the injection molding resin composition to all monomer units. In the case where the poly(3-hydroxyalkanoate) resin is a mixture of two or more poly(3-hydroxyalkanoate) resins, it refers to the proportion of each monomer contained in the mixture moiety.

[0043] In this embodiment, to balance the suppression of burr formation in the injection-molded body and its suitability for use at high temperatures, the weight-average molecular weight of the poly(3-hydroxyalkanoate) resin is controlled to be between 210,000 and 380,000. When the weight-average molecular weight exceeds 380,000, the injection pressure becomes higher, and the resulting injection-molded body is prone to burr formation. By setting the weight-average molecular weight of the poly(3-hydroxyalkanoate) resin to 380,000 or less, the melt viscosity of the resin decreases, thus reducing the injection pressure required for injection molding. This is believed to suppress the intrusion of molten resin into the mold gaps, thereby suppressing burr formation. On the other hand, when the weight-average molecular weight is less than 210,000, there is a tendency for the mechanical strength of the injection-molded body to decrease at high temperatures. Furthermore, if the melt viscosity of the resin is too low, the molten resin easily intrudes into the mold gaps, sometimes even leading to burr formation. The weight-average molecular weight is preferably 220,000 to 350,000, more preferably 220,000 to 300,000, and even more preferably 220,000 to 270,000. In order to further suppress the formation of burrs, the weight-average molecular weight is preferably below 240,000.

[0044] When the above-mentioned poly(3-hydroxyalkanoate) resin is composed of a mixture of two or more poly(3-hydroxyalkanoate) resins, the weight-average molecular weight obtained by measuring the mixture of poly(3-hydroxyalkanoate) resins as a whole is sufficient to meet the above-mentioned range. In this case, the weight-average molecular weight of each poly(3-hydroxyalkanoate) resin is not particularly limited.

[0045] It should be noted that the weight-average molecular weight of poly(3-hydroxyalkanoate) resins can be determined by conversion to polystyrene using gel permeation chromatography with chloroform solvent. A column suitable for determining weight-average molecular weight can be used as the chromatographic column for this gel permeation chromatography.

[0046] Furthermore, in this embodiment, in order to balance the suppression of burr formation in the injection-molded body and its suitability for use at high temperatures, the content of the low molecular weight component with a molecular weight of 200,000 or less in the poly(3-hydroxyalkanoate) resin is controlled to be 35% by weight or more and 60% by weight or less. When the content of the aforementioned low molecular weight component is less than 35% by weight, the injection-molded body is prone to burr formation. On the other hand, when the content of the aforementioned low molecular weight component exceeds 60% by weight, there is a tendency for the mechanical strength of the injection-molded body to decrease at high temperatures. In addition, there is a possibility that the low molecular weight component is prone to burr formation or easy dissolution when the injection-molded body is used at high temperatures. The content of the aforementioned low molecular weight component is preferably 35 to 55% by weight, more preferably 37 to 52% by weight.

[0047] When the aforementioned poly(3-hydroxyalkanoate) resin is composed of a mixture of two or more poly(3-hydroxyalkanoate) resins, the content of low molecular weight components in the weight molecular weight distribution obtained by measuring the mixture of poly(3-hydroxyalkanoate) resins as a whole is acceptable as long as it meets the above-mentioned range. In this case, the content of low molecular weight components in each poly(3-hydroxyalkanoate) resin is not particularly limited.

[0048] It should be noted that the content of the aforementioned low molecular weight components can be determined as follows: the weight molecular weight distribution obtained through the above-mentioned determination of weight-average molecular weight is converted into... Figure 1 The cumulative molecular weight distribution shown is determined by calculating the proportion of low molecular weight components (those with a molecular weight of less than 200,000) in the total amount. However, to eliminate the influence of additives and other components, the portion with a molecular weight of less than 1,000 is not considered in the above calculation.

[0049] 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 for the P3HA synthase group introduced to improve the productivity of P3HB3HH. Microbial cells from these strains can be cultured under appropriate conditions to allow P3HB3HH to accumulate within the cells. In addition to the above, recombinant microorganisms with genes introduced to synthesize various poly(3-hydroxyalkanoate) resins can also be used, and the culture conditions, including the type of substrate, can be optimized. This allows for adjustment of the proportion of 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin.

[0050] There are no particular limitations on the method for obtaining poly(3-hydroxyalkanoate) resins that meet the above-mentioned conditions of weight-average molecular weight and content of low molecular weight components; well-known polyester molecular weight adjustment techniques can be appropriately applied. As an example, a method can be given in which the molecular weights of two or more poly(3-hydroxyalkanoate) resins with different molecular weights are adjusted and mixed as needed.

[0051] Specifically, a method can be described as blending a high molecular weight poly(3-hydroxyalkanoate) resin with a weight average molecular weight in the range of 300,000 to 600,000 (preferably 350,000 to 500,000) with a low molecular weight poly(3-hydroxyalkanoate) resin with a weight average molecular weight in the range of 80,000 to 220,000 (preferably 100,000 to 200,000) and adjusting the overall weight average molecular weight and the content of the low molecular weight component. The ratio of the high molecular weight resin to the low molecular weight resin can be appropriately set; for example, a weight ratio preferably of 10:90 to 90:10, more preferably 20:80 to 80:20, and even more preferably 30:70 to 70:30.

[0052] The resin composition of the above-mentioned injection molding resin composition may consist solely of a poly(3-hydroxyalkanoate) resin, but it may also include other resins that are not poly(3-hydroxyalkanoate) resins. Examples of such other resins include aliphatic polyester resins such as polylactic acid, polybutylene adipate, polybutylene succinate, and polycaprolactone; aliphatic aromatic polyester resins such as polybutylene adipate, polybutylene sebacate, and polybutylene azelaate. These other resins may include only one type or two or more types.

[0053] The content of the other resins mentioned above is not particularly limited, but from the viewpoint of the seawater decomposability of the resin composition for injection molding and the injection molded article, the lower the content, the better. Specifically, relative to 100 parts by weight of the poly(3-hydroxyalkanoate) resin, the content of the other resins mentioned above is preferably 35 parts by weight or less, more preferably 30 parts by weight or less, further preferably 20 parts by weight or less, and even more preferably 10 parts by weight or less. The lower limit of the content of the other resins is not particularly limited, and can be 0 parts by weight.

[0054] [Inorganic packing]

[0055] The above-mentioned resin composition for injection molding may not contain inorganic fillers, but from the viewpoint of improving the strength of the injection molded article, it is preferable to contain inorganic fillers.

[0056] As inorganic fillers, any inorganic filler that can be added to the resin material used in injection molding is acceptable, without particular limitations. Examples include: quartz, fumed silica, anhydrous silica, fused silica, crystalline silica, amorphous silica, fillers formed by the condensation of alkoxysilanes, ultrafine amorphous silica and other silica-based inorganic fillers, alumina, zircon, iron oxide, zinc oxide, titanium oxide, silicon nitride, boron nitride, aluminum nitride, silicon carbide, glass, silicone rubber, silicone resin, titanium oxide, carbon fiber, mica, graphite, carbon black, ferrite, graphite, diatomaceous earth, kaolin, clay, talc, calcium carbonate, manganese carbonate, magnesium carbonate, barium sulfate, silver powder, etc. These can be used individually or in combination of two or more.

[0057] The aforementioned inorganic fillers can be surface-treated to improve their dispersibility in resin compositions for injection molding. Examples of treatment agents used in surface treatment include: higher fatty acids, silane coupling agents, titanate coupling agents, sol-gel coating agents, and resin coating agents.

[0058] To suppress the hydrolysis of poly(3-hydroxyalkanoate) resins, the moisture content of the inorganic filler is preferably 0.01–10%, more preferably 0.01–5%, and even more preferably 0.01–1%. This moisture content can be determined according to JIS-K5101.

[0059] To facilitate the suppression of hydrolysis of poly(3-hydroxyalkanoate) resins, the moisture content of the inorganic filler is preferably 0.01–10%, more preferably 0.01–5%, and even more preferably 0.01–1%. This moisture content can be determined according to JIS-K5101.

[0060] To ensure the superior properties and processability of the aforementioned resin composition for injection molding, the average particle size of the inorganic filler is preferably 0.1–100 μm, more preferably 0.1–50 μm, even more preferably 0.1–30 μm, and particularly preferably 0.1–15 μm. This average particle size can be measured using a laser diffraction / scattering apparatus such as the Nikkiso Corporation's "MICROTRAC MT3100II".

[0061] To achieve improved heat resistance and processability, silicate-based inorganic fillers are preferred among the inorganic fillers used. Furthermore, due to their significant improvement in the mechanical strength of injection-molded parts, small particle size distribution, and minimal impact on surface smoothness and mold transferability, silicates preferably selected from one or more of talc, mica, kaolin, montmorillonite, and saponite. Two or more silicates can be used in combination; in this case, the types and ratios of silicates used can be appropriately adjusted.

[0062] Examples of the aforementioned talc include general-purpose talc and surface-treated talc. Specific examples include NipponTalc's "Micro Ace" (registered trademark), Hayashi Kasei Corporation's "Talcan Pawder" (registered trademark), Takehara Chemical Industry Co., Ltd., and MARUO CALCIUM.

[0063] 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.

[0064] 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," as well as kaolin produced by Keiwa Furnace Materials Co., Ltd.

[0065] In the case of containing the above-mentioned inorganic filler, from the viewpoint of improving the strength of the injection molded article and ensuring the flowability of the resin composition, the amount of the compound is preferably 1 part or more and 50 parts or less, more preferably 5 to 40 parts by weight, and even more preferably 10 to 30 parts by weight, relative to a total of 100 parts by weight of the resin component containing the poly(3-hydroxyalkanoate) resin.

[0066] (additive)

[0067] To the extent that it does not impair the effects of the invention, the above-described resin composition for injection molding may contain additives other than inorganic fillers. As additives, depending on the purpose, examples such as crystal nucleating agents, lubricants, plasticizers, antistatic agents, flame retardants, conductive agents, heat insulating agents, crosslinking agents, antioxidants, ultraviolet absorbers, colorants, organic fillers, hydrolysis inhibitors, etc., may be used. Biodegradable additives are particularly preferred.

[0068] Examples of crystal nucleating agents include pentaerythritol, orotic acid, aspartame, cyanuric acid, glycine, zinc phenylphosphonate, and boron nitride. Poly(3-hydroxybutyrate) can also be added as a crystal nucleating agent. Among these, pentaerythritol is preferred due to its particularly excellent effect on promoting the crystallization of poly(3-hydroxybutyrate) resins. Furthermore, only one crystal nucleating agent may be used, or two or more may be mixed; the mixing ratio can be appropriately adjusted according to the purpose. However, the above-described resin composition for injection molding may not contain a crystal nucleating agent (especially pentaerythritol), in which case burrs in the injection-molded article can still be suppressed.

[0069] When using a substance other than the aforementioned poly(3-hydroxybutyrate) as a crystal nucleating agent, the amount of the crystal nucleating agent added is not particularly limited. It is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 8.5 parts by weight, further preferably 0.7 to 6 parts by weight, and particularly preferably 0.8 to 3 parts by weight, relative to 100 parts by weight of the poly(3-hydroxybutyrate) resin. On the other hand, when adding a crystal nucleating agent as poly(3-hydroxybutyrate), its amount added is not particularly limited. It is preferably 0.1 to 15 parts by weight, more preferably 1 to 10 parts by weight, further preferably 3 to 8 parts by weight, and particularly preferably 4 to 7 parts by weight, relative to 100 parts by weight of the poly(3-hydroxybutyrate) resin other than this poly(3-hydroxybutyrate).

[0070] 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) resins. The amount of lubricant 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 poly(3-hydroxyalkanoate) resin. Furthermore, the lubricant can be a single type or a mixture of two or more types, and the mixing ratio can be adjusted appropriately according to the purpose.

[0071] 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) resins. 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 is not particularly limited, but is preferably 0 to 20 parts by weight, more preferably 0 to 15 parts by weight, further preferably 0 to 10 parts by weight, and particularly preferably 0 to 5 parts by weight, relative to 100 parts by weight of the total resin component containing poly(3-hydroxyalkanoate) resin. Furthermore, the plasticizer may be a single type or a mixture of two or more types, and the mixing ratio may be adjusted appropriately according to the purpose.

[0072] [Manufacturing method of injection molded parts]

[0073] The following describes in detail the method for manufacturing an injection molded body composed of the above-described resin composition for injection molding.

[0074] First, a poly(3-hydroxyalkanoate) resin containing at least a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units, along with other resins, inorganic fillers, and other additives as needed, is added and melt-blended using an extruder, kneader, Banbury mixer, rollers, etc., to prepare a resin composition. This composition is then extruded in filament 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.

[0075] 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 outlet of the melt-mixed compound is preferably 140–190°C, more preferably 145–185°C, and even more preferably 150–180°C. When the resin temperature of the melt-mixed compound is below 140°C, the resin component containing poly(3-hydroxyalkanoate) resin may become unmelted; when it exceeds 190°C, the resin component containing poly(3-hydroxyalkanoate) resin may undergo thermal decomposition.

[0076] Next, by injection molding the prepared granules, an injection molded body can be formed. Injection molding refers to the method of injecting a heated and molten resin composition into a mold, allowing the resin composition to cool and solidify inside the mold, opening the mold, and demolding the molded body to obtain the molded body. Besides the injection molding method generally used when molding thermoplastic resins, other injection molding methods include gas-assisted molding, injection compression molding, and injection blow molding (including one-step and two-step methods). In addition, in-mold molding, air compression molding, two-color molding, sandwich molding, push-pull molding, and scorim molding can also be used. However, the injection molding methods that can be used are not limited to the methods mentioned above.

[0077] The temperature at which the mold is used for cooling after injection is preferably 20–70°C, more preferably 25–60°C, even more preferably 30–50°C, and particularly preferably 35–45°C.

[0078] The resulting injection-molded parts exhibit high heat resistance and suppress burr formation, resulting in a good appearance. Furthermore, the labor required for burr removal through post-processing can be eliminated or simplified. Additionally, since the resin composition is primarily composed of poly(3-hydroxyalkanoate) resins, it is seawater-degradable, thus addressing the environmental problems caused by ocean dumping of plastics.

[0079] The applications of the above-mentioned injection molded parts are 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 molded products, etc.

[0080] Example

[0081] The present invention will be specifically described below through embodiments, but the present invention is not limited to its technical scope by these embodiments.

[0082] (raw material)

[0083] The commercially available products shown in Table 1 were used as raw materials.

[0084] [Table 1]

[0085]

[0086] (Molecular weight adjustment of resin)

[0087] The poly(3-hydroxyalkanoate) resins shown in Table 1 were added to a metal container as raw materials, and then further added to an autoclave tester (ESPEC Corporation HAST CHAMBER EHS-221M) to hydrolyze the resins at the temperatures and times shown in Table 2, thereby adjusting the molecular weight of each resin.

[0088] [Table 2]

[0089]

[0090] (Method for determining the weight-average molecular weight of poly(3-hydroxyalkanoate) resins before blending)

[0091] The weight-average molecular weights of the poly(3-hydroxyalkanoate) resins shown in Tables 1 and 2 were determined as follows. First, the poly(3-hydroxyalkanoate) resins were dissolved in chloroform at 60°C for 30 minutes, followed by stirring for another 30 minutes. The solution was then filtered through a disposable PTFE sample filter with a 0.45 μm pore size. The filtrate was used for GPC analysis under the following conditions to determine the weight-average molecular weight. The results are shown in Table 1 or Table 2.

[0092] GPC measuring device: Hitachi, Ltd. RI monitor (L-3000)

[0093] Pillars: Showa Denko Co., Ltd., KG (1 piece), K-806L (2 pieces)

[0094] Sample concentration: 3 mg / ml

[0095] Eluent: Chloroform solvent

[0096] Elution buffer flow rate: 1.0 ml / min

[0097] Sample injection volume: 100 μL

[0098] Analysis time: 30 minutes

[0099] Standard sample: polystyrene

[0100] (Determination of the weight-average molecular weight of the mixed poly(3-hydroxyalkanoate) resin)

[0101] For the weight-average molecular weight of the mixed poly(3-hydroxyalkanoate) resins in each example or comparative example, the individual particles described later were used as the poly(3-hydroxyalkanoate) resins. Before filtration through a disposable sample filter with a 0.45 μm pore size made of PTFE, insoluble matter was removed by centrifugation. Otherwise, the weight-average molecular weight was determined using the same method as described above for determining the weight-average molecular weight of the unmixed poly(3-hydroxyalkanoate) resins. The results are shown in Table 4.

[0102] (Method for calculating the proportion of components with a molecular weight of less than 200,000 in the mixed poly(3-hydroxyalkanoate) resin)

[0103] In the cumulative weight molecular weight distribution (CMB) obtained by GPC, the horizontal axis is replaced with the logarithm of weight molecular weight (log), and the vertical axis is replaced with the cumulative percentage (%). The cumulative percentage (%) at a weight molecular weight of 200,000 (logarithm 5.3) is taken as the proportion (wt%) of components with a weight molecular weight of less than 200,000. Figure 1 However, to remove the influence of additives, the portion with a molecular weight below 1000 was removed. The results are shown in Table 4.

[0104] <Example of manufacturing polymer nucleating agents>

[0105] The production of poly(3-hydroxybutyrate) as a polymer nucleating agent was carried out using C. necator H16 strain (ATCC17699 strain).

[0106] The mother culture medium was composed of 1 w / v% Meat-extract, 1 w / v% Bacto-Tryptone, 0.2 w / v% Yeast-extract, 0.9 w / v% Na2HPO4·12H2O, 0.15 w / v% KH2PO4 (pH 6.8).

[0107] The pre-culture medium consisted of 1.1 w / v% Na₂HPO₄·12H₂O, 0.19 w / v% KH₂PO₄, 1.29 w / v% (NH₄)₂SO₄, 0.1 w / v% MgSO₄·7H₂O, 2.5 w / v% palm oil, and 0.5 w / v% trace metal salt solution (a solution obtained by dissolving 1.6 w / v% FeCl₃·6H₂O, 1 w / v% CaCl₂·2H₂O, 0.02 w / v% CoCl₂·6H₂O, 0.016 w / v% CuSO₄·5H₂O, and 0.012 w / v% NiCl₂·6H₂O in 0.1N hydrochloric acid). Palm oil was added as a carbon source at a concentration of 10 g / L.

[0108] The PHB production medium was composed of 0.385 w / v% Na2HPO4·12H2O, 0.067 w / v% KH2PO4, 0.291 w / v% (NH4)2SO4, 0.1 w / v% MgSO4·7H2O, and 0.5 w / v% trace metal salt solution (obtained by dissolving 1.6 w / v% FeCl3·6H2O, 1 w / v% CaCl2·2H2O, 0.02 w / v% CoCl2·6H2O, 0.016 w / v% CuSO4·5H2O, and 0.012 w / v% NiCl2·6H2O in 0.1N hydrochloric acid).

[0109] First, 50 μl of the stock solution of strain H16 glycerol was inoculated into 10 ml of mother culture medium and cultured for 24 hours for mother culture. Next, the mother culture was inoculated at 1.0 v / v% into a 3 L fermenter (BEMARUBISHI MDL-300 model) containing 1.8 L of pre-culture medium. Operating conditions were set at 33 °C, stirring speed 500 rpm, aeration rate 1.8 L / min, and pH maintained between 6.7 and 6.8 for 28 hours for pre-culture. A 14% ammonium hydroxide aqueous solution was used for pH control.

[0110] Next, the pre-culture medium was inoculated at 5.0 v / v% into a 5L fermenter (BEMARUBISHI MDS-U50 model) containing 2.5L of PHB production medium. Operating conditions were set at a culture temperature of 33°C, a stirring speed of 420 rpm, an aeration rate of 2.1 L / min, and pH maintained between 6.7 and 6.8. A 25% ammonium hydroxide aqueous solution was used for pH control. A carbon source was added intermittently. Palm oil was used as the carbon source, and the culture was carried out for 48 hours. At the end of the culture, a culture sample was obtained and confirmed by HPLC to be poly(3-hydroxybutyrate). After the culture was completed, the bacterial cells were recovered by centrifugation, washed with methanol, and freeze-dried. The weight of the dried bacterial cells was determined.

[0111] 100 ml of chloroform was added to every 1 g of bacterial cells, and the mixture was stirred at room temperature for 24 hours to extract the polymer nucleating agent from the cells. After filtering the remaining bacterial cells, the mixture was concentrated to a total volume of 30 vol% using an evaporator. Then, 90 ml of hexane was added incrementally per 1 g of bacterial cells, with slow stirring, and the mixture was allowed to stand for 1 hour. After filtering the precipitated polymer nucleating agent, it was vacuum dried at 50°C for 3 hours to obtain the polymer nucleating agent.

[0112] <Example 1> (Preparation of PHBH admixture)

[0113] Using a 75L high-speed mixer manufactured by KAWATA Corporation, 5kg of PHA-A, 55kg of PHA-C, and 100g of BA were added and stirred at 300rpm for 3 minutes to obtain the PHBH blend.

[0114] (Hybridization)

[0115] The screw structure described in Table 3 was used in the Toshiba Machinery TEM26SS (L / D=60), and the screw speed was set to 100 rpm. The above-mentioned PHBH admixture was fed from the root of the screw at 10.1 kg / hr, and talc was further fed from the side at 2.0 kg / hr. The mixture was then introduced into a water tank filled with warm water at 45°C to solidify the filaments. The filaments were then cut using a granulator to obtain granules.

[0116] [Table 3]

[0117]

[0118] (Obtaining the injection-molded part)

[0119] Injection molding was performed using the aforementioned granules as described below. Using a spoon-shaped mold, a Toyo Machinery Si-30V metal injection molding machine was used with the following settings: nozzle / T1 / T2 / T3 = 155 / 145 / 135 / 125℃, injection speed 20mm / sec, mold temperature 35℃, and the minimum injection size that would not result in under-injection. This yielded a large spoon with a length of 13.3cm, a head thickness of 1mm, and a handle thickness of 2mm, and a small spoon with a length of 9.8cm, a head thickness of 1mm, and a handle thickness of 1.5mm.

[0120] The following rough edge evaluation was conducted using a large spoon, and the following high-temperature bending evaluation was conducted using a small spoon. The results are shown in Table 4.

[0121] (Method for evaluating rough edges)

[0122] The front part of the large spoon, which is not the venting part, was observed using an optical microscope, and the occurrence of burrs was evaluated according to the following criteria.

[0123] ◎: Horizontal burr size less than 5μm

[0124] 〇: burr level of 5μm or larger and less than 15μm

[0125] △: Horizontal burr size of 15μm or larger and less than 30μm

[0126] ×: Burr level above 30μm

[0127] (High-Temperature Bending Evaluation Method)

[0128] Immerse a small spoon in 90℃ hot water. Hold the spoon upright, head down, with the tip touching the bottom of the tub and the top 2cm of the handle above the water surface. Hold this position for 20 seconds. Then, apply force to the end of the handle, bending it by 5mm and then allowing it to straighten. Repeat this process 20 times. Record the case where the spoon does not bend as 0 and the case where it bends as ×.

[0129] <Example 2> (Preparation of PHBH admixture)

[0130] PHA-C5 was changed to PHA-C4, and otherwise, injection molded articles were obtained and evaluated in the same manner as in Example 1.

[0131] <Example 3> (Preparation of PHBH admixture)

[0132] PHA-C5 was changed to PHA-C3, and otherwise, injection molded articles were obtained and evaluated in the same manner as in Example 1.

[0133] <Example 4> (Preparation of PHBH admixture)

[0134] PHA-C5 was changed to PHA-C2, and otherwise, injection molded articles were obtained and evaluated in the same manner as in Example 1.

[0135] <Example 5>

[0136] By changing PHA-A (the preparation of the PHBH admixture) to PHA-B, injection molded articles were obtained and evaluated in the same manner as in Example 1.

[0137] <Example 6> (Preparation of PHBH admixture)

[0138] PHA-C5 was changed to PHA-F, and otherwise, injection molded articles were obtained and evaluated in the same manner as in Example 1.

[0139] <Example 7> (Preparation of PHBH admixture)

[0140] The PHA-A 5.0 kg was changed to PHA-A 3.5 kg and PHA-E2 1.5 kg. Otherwise, the injection molded articles were obtained and evaluated in the same manner as in Example 1.

[0141] <Example 8>

[0142] (Preparation of PHBH admixtures)

[0143] An additional 100g of PETL was added during mixing, and the ejection rate from the screw root during the mixing process was set to 10.15kg / hr. Otherwise, injection molded articles were obtained and evaluated in the same manner as in Example 1.

[0144] <Example 9>

[0145] (Preparation of PHBH admixtures)

[0146] PHA-C5 was changed to PHA-A2, and the ejection rate from the screw root during the mixing process was set to 10.15 kg / hr. Otherwise, injection molded articles were obtained and evaluated in the same manner as in Example 8.

[0147] <Example 10>

[0148] (Preparation of PHBH admixtures)

[0149] An additional 400g of polymer nucleating agent was added to replace PETL, and the ejection rate from the screw root during the mixing process was set to 10.45kg / hr. Otherwise, injection molded articles were obtained and evaluated in the same manner as in Example 9.

[0150] <Example 11>

[0151] (Preparation of PHBH admixtures)

[0152] An additional 550g of polymer nucleating agent was added to replace PETL, and the ejection rate from the screw root during the mixing process was set to 10.6kg / hr. Otherwise, injection molded articles were obtained and evaluated in the same manner as in Example 9.

[0153] <Comparative Example 1> (Preparation of PHBH admixture)

[0154] PHA-C5 was changed to PHA-C7, and otherwise, injection molded articles were obtained and evaluated in the same manner as in Example 1.

[0155] <Comparative Example 2> (Preparation of PHBH admixture)

[0156] PHA-C5 was changed to PHA-C6, and otherwise, injection molded articles were obtained and evaluated in the same manner as in Example 1.

[0157] <Comparative Example 3> (Preparation of PHBH admixture)

[0158] PHA-C5 was changed to PHA-C, and otherwise, injection molded articles were obtained and evaluated in the same manner as in Example 1.

[0159] <Comparative Example 4> (Preparation of PHBH admixture)

[0160] PHA-A was changed to PHA-D, and otherwise, injection molded articles were obtained and evaluated in the same manner as in Example 1.

[0161] <Comparative Example 5> (Preparation of PHBH admixture)

[0162] PHA-A was changed to PHA-E2, and PHA-C5 was changed to PHA-C3. Otherwise, injection molded articles were obtained and evaluated in the same manner as in Example 1.

[0163] <Comparative Example 6> (Preparation of PHBH admixture)

[0164] The PHA-A was changed from 5 kg to 4 kg, and the PHA-C4 was changed from 5 kg to 6 kg. Otherwise, injection molded articles were obtained and evaluated in the same manner as in Example 2.

[0165] <Comparative Example 7> (Preparation of PHBH admixture)

[0166] The PHA-A was changed from 5 kg to 3 kg, and the PHA-C4 was changed from 5 kg to 7 kg. Otherwise, injection molded articles were obtained and evaluated in the same manner as in Example 2.

[0167] <Comparative Example 8> (Preparation of PHBH admixture)

[0168] PHA-C 10kg was used instead of PHA-A and PHA-C5. Otherwise, injection molded articles were obtained and evaluated in the same manner as in Example 1.

[0169] Table 4 summarizes the types and amounts (parts by weight) of materials used in each embodiment and comparative example, the average content of 3-hydroxybutyrate units in the resin (average HB ratio), weight-average molecular weight, content of low molecular weight components, and evaluation results of burrs and high-temperature bending.

[0170]

[0171] Table 4 shows the following: The injection molded bodies obtained in Examples 1-11 have small burrs and are not easily bent at high temperatures, making them suitable for use at high temperatures.

[0172] On the other hand, it can be seen that the injection molded articles obtained in Comparative Examples 1 to 8 do not meet at least one of the following conditions: average HB ratio, weight-average molecular weight, and content of low molecular weight components in poly(3-hydroxyalkanoate) resins. They have large burrs or are easily bent at high temperatures and are not suitable for use at high temperatures.

Claims

1. A resin composition for injection molding, comprising a poly(3-hydroxyalkanoate) resin, wherein, The poly(3-hydroxyalkanoate) resin comprises at least one type of copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units. The poly(3-hydroxyalkanoate) resin contains an average of 92 mol% to 99 mol% of 3-hydroxybutyrate units. The poly(3-hydroxyalkanoate) resin obtained by gel permeation chromatography using chloroform solvent has a weight-average molecular weight of 210,000 or more and 270,000 or less, and the proportion of components with a weight molecular weight of less than 200,000 in the weight molecular weight distribution is 35% or more and 60% or less.

2. The resin composition for injection molding according to claim 1, wherein, The poly(3-hydroxyalkanoate) resin is selected from one or more of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

3. The resin composition for injection molding according to claim 2, wherein, The poly(3-hydroxyalkanoate) resin is poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

4. The resin composition for injection molding according to any one of claims 1 to 3, wherein, The content of resins other than the poly(3-hydroxyalkanoate) resin is 0 parts by weight or more and 35 parts by weight or less, relative to 100 parts by weight of the poly(3-hydroxyalkanoate) resin.

5. The resin composition for injection molding according to any one of claims 1 to 3, further comprising a crystal nucleating agent and / or a lubricant.

6. The resin composition for injection molding according to any one of claims 1 to 3, wherein, The resin composition comprising the poly(3-hydroxyalkanoate) resin further comprises 1 part by weight and 50 parts by weight of inorganic filler, relative to a total of 100 parts by weight of the resin component comprising the poly(3-hydroxyalkanoate) resin.

7. The resin composition for injection molding according to claim 6, wherein, The inorganic filler is silicate.

8. The resin composition for injection molding according to claim 7, wherein, The silicate is selected from one or more of talc, mica, kaolin, montmorillonite and saponite.

9. An injection-molded article formed from the injection-molding resin composition according to any one of claims 1 to 8.

Images