Resin composition for injection molding and injection molded article

Abstract

This resin composition for injection molding contains a poly(3-hydroxyalkanoate)-based resin. The poly(3-hydroxyalkanoate)-based resin includes at least one copolymer of a 3-hydroxybutyrate unit and another hydroxyalkanoate unit. The average content ratio of the 3-hydroxybutyrate unit in the poly(3-hydroxyalkanoate)-based resin is 92-99 mol%. The weight-average molecular weight of the poly(3-hydroxyalkanoate)-based resin in terms of polystyrene, as measured by gel permeation chromatography using a chloroform solvent, is 210,000-380,000, and the proportion of a component having a weight molecular weight of at most 200,000 in the weight molecular weight distribution is 35-60 wt%.

Description

[Technical Field]

[0001] The present invention relates to a resin composition for injection molding containing a poly(3-hydroxyalkanoate) resin, and an injection-molded article. [Background technology]

[0002] In recent years, environmental problems caused by discarded plastics have come into the spotlight, and it has become clear that large amounts of plastic, particularly plastics dumped in the ocean or that have entered the ocean via rivers, are drifting in the oceans on a global scale. Because such plastics retain their shape for long periods of time, they can trap and capture marine organisms, a phenomenon known as ghost fishing, and if ingested by marine organisms, can remain in their digestive tracts, causing feeding disorders, and other problems have been pointed out as having an impact on the ecosystem.

[0003] Furthermore, it has been pointed out that microplastics, which are plastics that have broken down and broken down into tiny particles due to ultraviolet rays, adsorb harmful compounds in the ocean, and when marine organisms ingest these, harmful substances are introduced into the food chain.

[0004] The use of biodegradable plastics is expected to combat this type of marine pollution caused by plastics, but a report compiled by the United Nations Environment Programme in 2015 pointed out that plastics that can be biodegraded through compost, such as polylactic acid, cannot be expected to decompose in a short period of time in the cold ocean, and therefore cannot be used to combat marine pollution.

[0005] In this context, poly(3-hydroxyalkanoate) resins have attracted attention as a material that can resolve the above issues because they are biodegradable even in seawater. However, poly(3-hydroxyalkanoate) resins have a slow solidification rate, which means they are prone to flashing during injection molding.

[0006] Patent Document 1 discloses a resin composition containing a poly(3-hydroxyalkanoate) resin such as poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), pentaerythritol, and a filler, which improves the solidification properties of the poly(3-hydroxyalkanoate) resin and suppresses flash during injection molding.

[0007] Patent Document 2 discloses a resin composition containing a polyhydroxyalkanoate such as poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) and a low-melting-point polyhydroxybutyrate having a weight-average molecular weight of 5,000 to 50,000 and a melting point of 140°C to 170°C. It is described that this improves the crystallization rate of the polyhydroxyalkanoate. There is no mention of flash during injection molding. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2015 / 052876 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-227543 Summary of the Invention [Problem to be solved by the invention]

[0009] The techniques disclosed in Patent Documents 1 and 2 improve the solidification properties of poly(3-hydroxyalkanoate) resins, but may not be able to sufficiently suppress flash that can occur during injection molding. Furthermore, the mechanical properties of the resulting injection-molded articles tend to deteriorate when exposed to high temperatures, making them unsuitable for use at high temperatures.

[0010] Here, burrs are formed when molten resin penetrates into gaps that exist in the mating parts of the cavity of an injection molding die (for example, parting lines, inserts, slide core sliding parts, etc.), and are formed on the surface of the injection-molded article produced along the locations where the mating parts were located, which can cause problems in terms of the appearance of the injection-molded article.

[0011] In view of the above-mentioned current situation, the object of the present invention is to provide a resin composition containing a poly(3-hydroxyalkanoate)-based resin, which suppresses the generation of flash and can form an injection-molded article suitable for use at high temperatures. [Means for solving the problem]

[0012] As a result of extensive research conducted by the inventors to solve the above-mentioned problems, they discovered that by setting the monomer composition, average molecular weight, and proportion of low molecular weight components of a poly(3-hydroxyalkanoate) resin within specific ranges, it is possible to suppress the generation of flash and form an injection-molded article suitable for use at high temperatures, and thus completed the present invention.

[0013] Specifically, the present invention relates to a resin composition for injection molding containing a poly(3-hydroxyalkanoate) resin, wherein the poly(3-hydroxyalkanoate) resin contains 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 has a weight-average molecular weight of 210,000 or more and 380,000 or less in terms of polystyrene, as determined by gel permeation chromatography using chloroform solvent, 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. Preferably, the poly(3-hydroxyalkanoate) resin is one or more selected from the group consisting 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). Preferably, the poly(3-hydroxyalkanoate) resin is poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). Preferably, the content of resins other than the poly(3-hydroxyalkanoate)-based resin is 0 to 35 parts by weight per 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin. Preferably, the resin composition for use in injection molding further contains a crystal nucleating agent and / or a lubricant. Preferably, the resin composition for injection molding further contains 1 part by weight to 50 parts by weight of an inorganic filler relative to 100 parts by weight of the total of resin components including the poly(3-hydroxyalkanoate) resin. Preferably, the inorganic filler is a silicate, and more preferably, the silicate is one or more selected from the group consisting of talc, mica, kaolinite, montmorillonite, and smectite. The present invention also relates to an injection-molded article made from the above-mentioned resin composition for injection molding. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a resin composition containing a poly(3-hydroxyalkanoate)-based resin, which is capable of forming an injection-molded article that is suppressed in the generation of flash and is suitable for use at high temperatures. The resin composition or injection-molded article according to a preferred embodiment of the present invention has the advantage that the main resin component is a poly(3-hydroxyalkanoate)-based resin that is degradable in seawater, and therefore can solve the environmental problem caused by the dumping of plastics into the ocean. [Brief explanation of the drawings]

[0015] [Figure 1] An example of the cumulative molecular weight distribution used to calculate the content of low molecular weight components with a molecular weight of 200,000 or less DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0017] The resin composition according to the present embodiment is a resin composition used to produce a molded article by injection molding, and contains at least a poly(3-hydroxyalkanoate) resin as a resin component.

[0018] [Poly(3-hydroxyalkanoate) resin] The poly(3-hydroxyalkanoate) resin (abbreviated as P3HA), which constitutes the main resin component of the resin composition for injection molding, 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) resins may be used in combination.

[0019] Specifically, the 3-hydroxyalkanoate structural unit is preferably a structural unit represented by the following general formula (1). [-CHR-CH2-CO-O-] (1)

[0020] In the general formula (1), R is C p H 2p+1 where p is an integer of 1 to 15. Examples of R include linear or branched alkyl groups such as methyl, ethyl, propyl, methylpropyl, butyl, isobutyl, t-butyl, pentyl, and hexyl. p is preferably 1 to 10, and more preferably 1 to 8.

[0021] The poly(3-hydroxyalkanoate) resin is preferably a poly(3-hydroxyalkanoate) resin produced by a microorganism, in which all 3-hydroxyalkanoate structural units are contained as (R)-3-hydroxyalkanoate structural units.

[0022] The poly(3-hydroxyalkanoate) resin preferably contains 3-hydroxyalkanoate structural units (particularly structural units represented by the above general formula (1)) in an amount of 50 mol % or more, more preferably 60 mol % or more, and even more preferably 70 mol % or more of the total structural units. The poly(3-hydroxyalkanoate) resin may contain only one or more types of 3-hydroxyalkanoate structural units as repeating units constituting the polymer, or may contain one or more types of 3-hydroxyalkanoate structural units as well as other structural units (e.g., 4-hydroxyalkanoate structural units).

[0023] Specific examples of poly(3-hydroxyalkanoate) resins include poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxypropionate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (abbreviation: P3HB3HV), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-3-hydroxyhexanoate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (abbreviation: 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), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (abbreviation: P3HB4HB), and the like.

[0024] In this embodiment, the poly(3-hydroxyalkanoate)-based resin contains at least a copolymer of 3-hydroxybutyrate units (hereinafter sometimes referred to as 3HB) and other hydroxyalkanoate units. The poly(3-hydroxyalkanoate)-based resin may contain only one type of copolymer, or may contain two or more types of copolymers. Furthermore, the poly(3-hydroxyalkanoate)-based resin may consist of only at least one type of copolymer, or may contain poly(3-hydroxybutyrate), i.e., a homopolymer of 3-hydroxybutyrate, in addition to at least one type of copolymer.

[0025] From the viewpoints of processability, mechanical properties, and the like, the copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units is preferably one or more selected from the group consisting 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).

[0026] The average content ratio of 3-hydroxybutyrate units and other hydroxyalkanoate units in the entire poly(3-hydroxyalkanoate) resin contained in the injection molding resin composition is 3-hydroxybutyrate units / other hydroxyalkanoate units = 92 / 8 to 99 / 1 (mol % / mol %). If the average content ratio of 3-hydroxybutyrate units is less than 92 mol %, the crystallization rate of the resin is slow, which makes it easy for the molten resin to penetrate into gaps present in the mating parts of the mold cavity, resulting in the formation of flash in the injection-molded article. On the other hand, if the average content ratio of 3-hydroxybutyrate units exceeds 99 mol %, the mechanical properties of the injection-molded article tend to deteriorate. The average content ratio is preferably 93 / 7 to 98 / 2 (mol % / mol %), and more preferably 94 / 6 to 97 / 3 (mol % / mol %).

[0027] The average content of each monomer unit in the entire poly(3-hydroxyalkanoate) resin can be determined by a method known to those skilled in the art, for example, the method described in paragraph

[0047] of WO 2013 / 147139. The average content refers to the proportion of each monomer unit among all monomer units contained in the entire poly(3-hydroxyalkanoate) resin contained in the resin composition for injection molding. When the poly(3-hydroxyalkanoate) resin is a mixture of two or more poly(3-hydroxyalkanoate) resins, the average content refers to the proportion of each monomer contained in the entire mixture.

[0028] In this embodiment, to achieve both suppression of flash formation in injection-molded articles and suitability for use at high temperatures, the weight-average molecular weight of the poly(3-hydroxyalkanoate) resin is controlled to a range of 210,000 to 380,000. If the weight-average molecular weight exceeds 380,000, the injection pressure increases, making flash formation more likely in the resulting injection-molded articles. By setting the weight-average molecular weight of the poly(3-hydroxyalkanoate) resin to 380,000 or less, the melt viscosity of the resin when melted decreases, thereby reducing the injection pressure required for injection molding. As a result, it is believed that penetration of the molten resin into gaps in the mold is suppressed, thereby suppressing flash formation. On the other hand, if the weight-average molecular weight is less than 210,000, the mechanical strength of the injection-molded article tends to decrease at high temperatures. Furthermore, if the melt viscosity of the resin is too low, the molten resin may easily penetrate into gaps in the mold, potentially increasing the likelihood of flash 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. It is particularly preferable that the weight average molecular weight is 240,000 or less, since this can further suppress the occurrence of burrs.

[0029] When the poly(3-hydroxyalkanoate) resin is a mixture of two or more poly(3-hydroxyalkanoate) resins, the weight-average molecular weight measured for the entire mixture of poly(3-hydroxyalkanoate) resins should be within the above range. In this case, the weight-average molecular weight of each poly(3-hydroxyalkanoate) resin is not particularly limited.

[0030] The weight-average molecular weight of the poly(3-hydroxyalkanoate) resin can be measured in terms of polystyrene using gel permeation chromatography with a chloroform solvent, using a column suitable for measuring the weight-average molecular weight.

[0031] Furthermore, in this embodiment, to achieve both suppression of flash formation in injection-molded articles and suitability for use at high temperatures, the content of low-molecular-weight components in the poly(3-hydroxyalkanoate) resin, which have a weight-weight molecular weight of 200,000 or less in the weight-weight molecular weight distribution, is controlled to 35% by weight or more and 60% by weight or less. If the content of the low-molecular-weight components is less than 35% by weight, flash is likely to occur in the resulting injection-molded article. On the other hand, if the content of the low-molecular-weight components exceeds 60% by weight, the mechanical strength of the injection-molded article at high temperatures tends to decrease, flash may be more likely to occur, and the low-molecular-weight components may be more likely to leach out when the injection-molded article is used at high temperatures. The content of the low-molecular-weight components is preferably 35 to 55% by weight, more preferably 37 to 52% by weight.

[0032] When the poly(3-hydroxyalkanoate) resin is a mixture of two or more poly(3-hydroxyalkanoate) resins, the content of low-molecular-weight components in the weight molecular weight distribution measured for the entire mixture of poly(3-hydroxyalkanoate) resins should be within the above range. In this case, the content of low-molecular-weight components in each poly(3-hydroxyalkanoate) resin is not particularly limited.

[0033] The content of the low molecular weight component can be determined by converting the weight molecular weight distribution obtained by measuring the weight average molecular weight as described above into the cumulative weight molecular weight distribution shown in Figure 1 and calculating the proportion of low molecular weight components having a weight molecular weight of 200,000 or less to the total amount. However, in order to eliminate the influence of components such as additives, the portion having a weight molecular weight of 1,000 or less is not taken into consideration in the calculation.

[0034] The method for producing poly(3-hydroxyalkanoate) resins is not particularly limited, and may be a production method using chemical synthesis or a production method using a microorganism. Among these, a production method using a microorganism is preferred. Known methods can be applied to the production method using a microorganism. For example, known bacteria that produce copolymers of 3-hydroxybutyrate and other hydroxyalkanoates include Aeromonas caviae, which produces P3HB3HV and P3HB3HH, and Alcaligenes eutrophus, which produces P3HB4HB. In particular, for P3HB3HH, to increase P3HB3HH productivity, Alcaligenes eutrophus AC32 (FERM BP-6038) (T. Fukui, Y. Doi, J. Bateriol., 179, pp. 4821-4830 (1997)) or the like, into which genes encoding P3HA synthases have been introduced, is preferred. Microbial cells obtained by culturing these microorganisms under appropriate conditions and allowing P3HB3HH to accumulate within the cells, can be used. Alternatively, genetically modified microorganisms incorporating various poly(3-hydroxyalkanoate) resin synthesis-related genes may be used depending on the poly(3-hydroxyalkanoate) resin to be produced, or culture conditions, including the type of substrate, may be optimized. This allows the content of 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin to be adjusted.

[0035] The method for obtaining a poly(3-hydroxyalkanoate) resin that satisfies the above-mentioned conditions of weight-average molecular weight and content of low-molecular-weight components is not particularly limited, and known techniques for adjusting the molecular weight of polyesters can be applied as appropriate. One example is a method in which two or more poly(3-hydroxyalkanoate) resins with different molecular weights are mixed together, and the molecular weights are adjusted as necessary.

[0036] Specifically, a high-molecular-weight poly(3-hydroxyalkanoate) resin having a weight-average molecular weight in the range of 300,000 to 600,000 (preferably 350,000 to 500,000) is blended with a low-molecular-weight poly(3-hydroxyalkanoate) resin having a weight-average molecular weight in the range of 80,000 to 220,000 (preferably 100,000 to 200,000) to adjust the overall weight-average molecular weight and the content of low-molecular-weight components. The ratio of the high-molecular-weight resin to the low-molecular-weight resin can be appropriately set, and is preferably, for example, 10:90 to 90:10 by weight, more preferably 20:80 to 80:20, and even more preferably 30:70 to 70:30.

[0037] The resin component of the injection molding resin composition may consist solely of a poly(3-hydroxyalkanoate)-based resin, or may contain, in addition to the poly(3-hydroxyalkanoate)-based resin, other resins that do not fall under the category of poly(3-hydroxyalkanoate)-based resins. Examples of such other resins include aliphatic polyester-based resins such as polylactic acid, polybutylene succinate adipate, polybutylene succinate, and polycaprolactone, and aliphatic aromatic polyester-based resins such as polybutylene adipate terephthalate, polybutylene sebatate terephthalate, and polybutylene azelate terephthalate. Only one type of other resin may be included, or two or more types may be included.

[0038] The content of the other resin is not particularly limited, but from the viewpoint of the seawater decomposability of the injection molding resin composition and the injection-molded article, the lower the content, the better. Specifically, the content of the other resin is preferably 35 parts by weight or less, more preferably 30 parts by weight or less, even more preferably 20 parts by weight or less, and even more preferably 10 parts by weight or less, per 100 parts by weight of the poly(3-hydroxyalkanoate) resin. The lower limit of the content of the other resin is not particularly limited, and may be 0 parts by weight.

[0039] [Inorganic filler] The resin composition for use in injection molding may not contain an inorganic filler, but preferably contains an inorganic filler from the viewpoint of improving the strength of the injection molded article.

[0040] The inorganic filler is not particularly limited as long as it can be added to a resin material for injection molding, and examples thereof include silica-based inorganic fillers such as quartz, fumed silica, silicic anhydride, fused silica, crystalline silica, amorphous silica, fillers obtained by condensing alkoxysilanes, and ultrafine amorphous silica, as well as 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, clay, talc, calcium carbonate, manganese carbonate, magnesium carbonate, barium sulfate, and silver powder. These may be used alone or in combination of two or more.

[0041] The inorganic filler may be surface-treated to improve dispersibility in the resin composition for injection molding. Examples of the surface treatment agent include higher fatty acids, silane coupling agents, titanate coupling agents, sol-gel coating agents, and resin coating agents.

[0042] The water content of the inorganic filler is preferably 0.01 to 10%, more preferably 0.01 to 5%, and even more preferably 0.01 to 1%, because this easily inhibits hydrolysis of the poly(3-hydroxyalkanoate) resin. The water content can be determined in accordance with JIS-K5101.

[0043] The average particle size of the inorganic filler is preferably 0.1 to 100 μm, more preferably 0.1 to 50 μm, even more preferably 0.1 to 30 μm, and particularly preferably 0.1 to 15 μm, in order to provide excellent properties and processability for the resin composition for injection molding. The average particle size can be measured using a laser diffraction / scattering device such as the "Microtrac MT3100II" manufactured by Nikkiso Co., Ltd.

[0044] Among inorganic fillers, inorganic fillers belonging to silicates are preferred because they can provide effects such as improved heat resistance and improved processability. Furthermore, among silicates, one or more selected from the group consisting of talc, mica, kaolinite, montmorillonite, and smectite are preferred because they have a significant effect of improving the mechanical strength of injection-molded articles, have a narrow particle size distribution, and are less likely to impair surface smoothness or mold transferability. Two or more silicates may be used in combination, in which case the type and ratio of silicates used can be adjusted as appropriate.

[0045] Examples of the talc include general-purpose talc and surface-treated talc. Specific examples include "Micro Ace" (registered trademark) from Nippon Talc Co., Ltd., "Talc Powder" (registered trademark) from Hayashi Kasei Co., Ltd., and talc manufactured by Takehara Chemical Industry Co., Ltd. and Maruo Calcium Co., Ltd.

[0046] Examples of the mica include wet-ground mica and dry-ground mica, and specific examples include mica manufactured by Yamaguchi Mica Co., Ltd. and Keiwa Rozai Co., Ltd.

[0047] Examples of the kaolinite include dry kaolin, calcined kaolin, and wet kaolin. Specific examples include "TRANSLINK" (registered trademark), "ASP" (registered trademark), "SANTINTONE" (registered trademark), and "ULTREX" (registered trademark) manufactured by Hayashi Kasei Corporation, and kaolinite manufactured by Keiwa Rozai Co., Ltd.

[0048] When the inorganic filler is contained, the blending amount thereof is preferably 1 to 50 parts by weight, more preferably 5 to 40 parts by weight, and even more preferably 10 to 30 parts by weight, per 100 parts by weight of the total resin components including the poly(3-hydroxyalkanoate) resin, from the viewpoint of improving the strength of the injection-molded article and ensuring the fluidity of the resin composition.

[0049] (additives) The resin composition for injection molding may contain additives other than inorganic fillers, as long as the effects of the invention are not impaired. Examples of additives that can be used depending on the purpose include nucleating agents, lubricants, plasticizers, antistatic agents, flame retardants, conductive agents, heat insulating agents, crosslinking agents, antioxidants, ultraviolet absorbers, colorants, organic fillers, and hydrolysis inhibitors. Biodegradable additives are particularly preferred.

[0050] Examples of nucleating agents include pentaerythritol, orotic acid, aspartame, cyanuric acid, glycine, zinc phenylphosphonate, and boron nitride. Poly(3-hydroxybutyrate) can also be added as a nucleating agent. Among these, pentaerythritol is preferred because of its particularly excellent effect of promoting the crystallization of poly(3-hydroxyalkanoate)-based resins. The nucleating agent may be a single agent or a mixture of two or more agents, and the mixing ratio can be appropriately adjusted depending on the purpose. However, the resin composition for injection molding may not contain a nucleating agent (especially pentaerythritol), and even in this case, flashing of the injection-molded article can be suppressed.

[0051] When a nucleating agent other than poly(3-hydroxybutyrate) is used as the nucleating agent, the amount of the nucleating agent added is not particularly limited, but is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 8.5 parts by weight, even more preferably 0.7 to 6 parts by weight, and particularly preferably 0.8 to 3 parts by weight, per 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin. On the other hand, when poly(3-hydroxybutyrate) is added as the nucleating agent, the amount is not particularly limited, but is preferably 0.1 to 15 parts by weight, more preferably 1 to 10 parts by weight, even more preferably 3 to 8 parts by weight, and particularly preferably 4 to 7 parts by weight, per 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin excluding the poly(3-hydroxybutyrate).

[0052] Examples of lubricants include behenamide, oleamide, erucamide, stearamide, palmitamide, N-stearylbehenamide, N-stearylerucamide, ethylenebisstearamide, ethylenebisoleamide, ethylenebiserucamide, ethylenebislauricamide, ethylenebiscapricamide, p-phenylenebisstearamide, and polycondensates of ethylenediamine, stearic acid, and sebacic acid. Among these, behenamide and erucamide are preferred because of their particularly excellent lubricating effect on poly(3-hydroxyalkanoate)-based resins. 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, per 100 parts by weight of poly(3-hydroxyalkanoate)-based resin. Furthermore, lubricants may be used singly or in combination, and the mixing ratio can be adjusted appropriately depending on the purpose.

[0053] Examples of plasticizers include glycerin ester compounds, citrate ester compounds, sebacate compounds, adipate compounds, polyether ester compounds, benzoate ester compounds, phthalate ester compounds, isosorbide ester compounds, polycaprolactone compounds, and dibasic acid ester compounds. Among these, glycerin ester compounds, citrate ester compounds, sebacate compounds, and dibasic acid ester compounds are preferred because of their particularly excellent plasticizing effect on poly(3-hydroxyalkanoate) resins. Examples of glycerin ester compounds include glycerin diacetomonolaurate. Examples of citrate ester compounds include acetyl tributyl citrate. Examples of sebacate ester compounds include dibutyl sebacate. Examples of dibasic acid ester compounds include benzyl methyl diethylene glycol adipate. The amount of plasticizer used is not particularly limited, but is preferably 0 to 20 parts by weight, more preferably 0 to 15 parts by weight, even more preferably 0 to 10 parts by weight, and particularly preferably 0 to 5 parts by weight, per 100 parts by weight of the total resin components including the poly(3-hydroxyalkanoate) resin. Furthermore, the plasticizer may be a single type or a mixture of two or more types, and the mixing ratio can be adjusted appropriately depending on the purpose.

[0054] [Method for manufacturing injection molded products] A method for producing an injection-molded article made from the resin composition for injection molding will be specifically described below.

[0055] First, a poly(3-hydroxyalkanoate) resin containing at least a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units is melt-kneaded using an extruder, kneader, Banbury mixer, roll, or the like to produce a resin composition, which is then extruded into strands and cut to obtain pellets with particle shapes such as cylindrical, elliptical, spherical, cubic, or rectangular prism. The pellets are then thoroughly dried at 40-80°C to remove moisture and then injection molded.

[0056] The temperature at which the melt-kneading is carried out cannot be generally defined because it depends on the melting point, melt viscosity, etc. of the resin used, but the resin temperature of the melt-kneaded product at the die outlet is preferably 140 to 190° C., more preferably 145 to 185° C., and even more preferably 150 to 180° C. If the resin temperature of the melt-kneaded product is less than 140° C., the resin components containing the poly(3-hydroxyalkanoate) resin may remain unmelted, and if it exceeds 190° C., the resin components containing the poly(3-hydroxyalkanoate) resin may undergo thermal decomposition.

[0057] The pellets thus prepared are then subjected to injection molding to produce an injection-molded article. Injection molding is a method in which a heated and melted resin composition is injected into a mold, the resin composition is cooled and solidified in the mold, the mold is opened, and the molded article is demolded to obtain a molded article. Injection molding methods that can be used include those commonly used in molding thermoplastic resins, as well as gas-assisted molding, injection compression molding, and injection blow molding (including one-step and two-step). Other methods that can be used include in-mold molding, gas press molding, two-color molding, sandwich molding, push-pull molding, and scorim molding. However, the injection molding methods that can be used are not limited to those described above.

[0058] The temperature at which the mixture is cooled in the mold after injection is, for example, preferably 20 to 70°C, more preferably 25 to 60°C, even more preferably 30 to 50°C, and particularly preferably 35 to 45°C.

[0059] The resulting injection-molded articles have high heat resistance and a good appearance due to the suppression of burrs, and the labor required for burr removal in post-processing can be omitted or simplified. Furthermore, because the resin component is primarily composed of poly(3-hydroxyalkanoate) resin, it is seawater degradable, which can solve the environmental problems caused by the dumping of plastics into the ocean.

[0060] The uses of the injection molded articles are not particularly limited, but examples include tableware such as plates, cups, cups, and lid trays; cutlery such as spoons, forks, knives, and stirrers; capsules such as coffee capsules and toy containers; toys; agricultural materials; office automation parts; home appliance parts; automotive parts; various containers and boxes; daily necessities; stationery; and molded bottles. [Example]

[0061] The present invention will be specifically explained below with reference to examples, but the technical scope of the present invention is not limited to these examples.

[0062] (raw materials) As raw materials, commercially available products shown in Table 1 were used.

[0063] [Table 1]

[0064] (Adjusting the molecular weight of the resin) Each poly(3-hydroxyalkanoate) resin shown in Table 1 was placed as a raw material in a metal container, which was then placed in a pressure cooker tester (HAST CHAMBER EHS-221M, manufactured by ESPEC Corporation). The resin was hydrolyzed at the temperature and for the time shown in Table 2 to adjust the molecular weight of each resin.

[0065] [Table 2]

[0066] (Method for measuring weight-average molecular weight of poly(3-hydroxyalkanoate) resin before blending) The weight-average molecular weight of each poly(3-hydroxyalkanoate) resin shown in Tables 1 and 2 was measured as follows. First, the poly(3-hydroxyalkanoate) resin was left to stand in chloroform at 60°C for 30 minutes, and then stirred for an additional 30 minutes to dissolve. The solution was filtered through a disposable PTFE filter with a 0.45 μm pore size, and the weight-average molecular weight was measured using the filtrate by GPC measurement under the following conditions. The results are shown in Tables 1 and 2. GPC measurement device: Hitachi RI monitor (L-3000) Column: Showa Denko KG (1 column), K-806L (2 columns) Sample concentration: 3mg / ml Free solution: chloroform solvent Free liquid flow rate: 1.0ml / min Sample injection volume: 100 μL Analysis time: 30 minutes Standard sample: polystyrene

[0067] (Measurement of weight-average molecular weight of poly(3-hydroxyalkanoate) resin after compounding) The weight-average molecular weight of the poly(3-hydroxyalkanoate) resin after compounding in each Example or Comparative Example was measured in the same manner as the weight-average molecular weight of the poly(3-hydroxyalkanoate) resin before blending, except that each pellet described below was used as the poly(3-hydroxyalkanoate) resin and insoluble matter was removed by centrifugation before filtering through a PTFE disposable filter with a 0.45 μm pore size. The results are shown in Table 4.

[0068] (Method for calculating the proportion of components with a molecular weight of 200,000 or less contained in poly(3-hydroxyalkanoate) resin after compounding) In the cumulative molecular weight distribution obtained by GPC measurement, which was created by converting the horizontal axis to the logarithm of the molecular weight and the vertical axis to the cumulative percentage (%), the cumulative percentage (%) at a molecular weight of 200,000 (its logarithm is 5.3) was read as the percentage (by weight%) of components with a molecular weight of 200,000 or less (Figure 1). However, to eliminate the influence of additives, etc., portions with a molecular weight of 1,000 or less were excluded. The results are shown in Table 4.

[0069] <Production example of polymer nucleating agent> Poly(3-hydroxybutyrate), a polymer nucleating agent, was produced by cultivation of C. necator H16 (ATCC17699). The composition of the seed culture medium was 1 w / v% meat extract, 1 w / v% Bacto-Tryptone, 0.2 w / v% yeast extract, 0.9 w / v% Na2HPO4·12H2O, and 0.15 w / v% KH2PO4 (pH 6.8). 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 olein oil, and 0.5 v / v% trace metal salt solution (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 dissolved in 0.1 N hydrochloric acid). Palm olein oil was added as a carbon source at a concentration of 10 g / L. The PHB production medium consisted 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 v / v% trace metal salt solution (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 dissolved in 0.1 N hydrochloric acid). First, glycerol stocks (50 μl) of the H16 strain were inoculated into 10 ml of seed medium and cultured for 24 hours. The seed culture was then inoculated at 1.0 v / v% into a 3 L jar fermenter (Marubishi Bioengine MDL-300) containing 1.8 L of preculture medium. The operating conditions were a culture temperature of 33°C, an agitation speed of 500 rpm, and an aeration rate of 1.8 L / min. The pH was controlled between 6.7 and 6.8 for 28 hours. A 14% aqueous ammonium hydroxide solution was used for pH control. Next, the preculture solution was inoculated at 5.0 v / v% into a 5 L jar fermenter (Marubishi Bioengine MDS-U50 model) containing 2.5 L of PHB production medium. The operating conditions were a culture temperature of 33°C, an agitation speed of 420 rpm, and an aeration rate of 2.1 L / min. The pH was controlled between 6.7 and 6.8. A 25% aqueous solution of ammonium hydroxide was used for pH control. The carbon source was added intermittently. Palm olein oil was used as the carbon source, and the culture was continued for 48 hours. At the end of the culture, a culture sample was taken and confirmed to be poly(3-hydroxybutyrate) by HPLC analysis. After the culture was completed, the cells were collected by centrifugation, washed with methanol, and freeze-dried. The dry cell weight was measured. 100 ml of chloroform was added per 1 g of the obtained bacterial cells, and the mixture was stirred overnight at room temperature to extract the polymer nucleating agent from the bacterial cells. The bacterial cell residue was filtered off, and the mixture was concentrated in an evaporator until the total volume reached 30 vol%, after which 90 ml of hexane was gradually added per 1 g of bacterial cells, and the mixture was left to stand for 1 hour with slow stirring. The precipitated polymer nucleating agent was filtered off and vacuum dried at 50°C for 3 hours to obtain the polymer nucleating agent.

[0070] Example 1 (Preparation of PHBH Blend) Using a 75L Super Mixer manufactured by Kawata Corporation, 5 kg of PHA-A, 5 kg of PHA-C5, and 100 g of BA were added and stirred at 300 rpm for 3 minutes to obtain a PHBH blend.

[0071] (Compounding) A Toshiba Machine TEM26SS (L / D=60) was used with the screw configuration shown in Table 3, and the screw rotation speed was set to 100 rpm. The PHBH blend was fed from the base of the screw at 10.1 kg / hr, and talc was further side-fed at 2.0 kg / hr. The strands were solidified by passing them through a water tank filled with warm water at 45°C, and then cut into pellets by a pelletizer.

[0072] [Table 3]

[0073] (Acquisition of injection molded products) The pellets were injection molded as follows: Using a spoon-shaped mold, a Toyo Machinery & Metal injection molding machine Si-30V was used, with nozzle / T1 / T2 / T3 settings of 155 / 145 / 135 / 125°C, an injection speed of 20 mm / sec, and a mold temperature of 35°C. The smallest shot size that would not result in a short shot was used to produce a large spoon 13.3 cm long, with a 1 mm thick dish and a 2 mm thick handle, and a small spoon 9.8 cm long, with a 1 mm thick dish and a 1.5 mm thick handle. The following evaluation of burrs was carried out using the large spoon, and the following evaluation of high-temperature breakage was carried out using the small spoon. The results are shown in Table 4.

[0074] (Burring evaluation method) The tip of the large spoon, excluding the gas release portion, was observed under an optical microscope, and the occurrence of burrs was evaluated according to the following criteria. ◎: Burr level less than 5μm ○: Burr level between 5μm and 15μm △: Burr level between 15μm and 30μm ×: Burr level of 30 μm or more

[0075] (High temperature breakage evaluation method) A small spoon was immersed in 90°C hot water. It was held upright with the bowl facing downwards, the tip of the bowl touching the bottom of the tank, and the top 2 cm of the handle protruding from the water surface. It was then held in this position for 20 seconds. After that, force was applied to the end of the handle, pushing it in 5 mm and then returning it to its original position. This process was repeated 20 times. If the spoon did not break, it was marked with a 〇, and if it did break, it was marked with an ×.

[0076] Example 2 (Preparation of PHBH Blend) An injection molded article was obtained and evaluated in the same manner as in Example 1, except that PHA-C5 was changed to PHA-C4.

[0077] Example 3 (Preparation of PHBH Blend) An injection molded article was obtained and evaluated in the same manner as in Example 1, except that PHA-C5 was changed to PHA-C3.

[0078] Example 4 (Preparation of PHBH Blend) An injection molded article was obtained and evaluated in the same manner as in Example 1, except that PHA-C5 was changed to PHA-C2.

[0079] <Example 5> (Preparation of PHBH Blend) An injection molded article was obtained and evaluated in the same manner as in Example 1, except that PHA-A was changed to PHA-B.

[0080] Example 6 (Preparation of PHBH Blend) An injection molded article was obtained and evaluated in the same manner as in Example 1, except that PHA-C5 was changed to PHA-F.

[0081] Example 7 (Preparation of PHBH Blend) An injection-molded article was obtained and evaluated in the same manner as in Example 1, except that 5.0 kg of PHA-A was changed to 3.5 kg of PHA-A and 1.5 kg of PHA-E2.

[0082] Example 8 (Preparation of PHBH Blend) An injection-molded article was obtained and evaluated in the same manner as in Example 1, except that 100 g of PETL was further added during blending and the discharge rate from the base of the screw in the compounding process was set to 10.15 kg / hr.

[0083] Example 9 (Preparation of PHBH Blend) An injection molded article was obtained and evaluated in the same manner as in Example 8, except that PHA-C5 was changed to PHA-A2 and the discharge rate from the base of the screw in the compounding process was changed to 10.15 kg / hr.

[0084] Example 10 (Preparation of PHBH Blend) An injection-molded article was obtained and evaluated in the same manner as in Example 9, except that 400 g of a polymer nucleating agent was added instead of PETL and the discharge rate from the base of the screw in the compounding process was set to 10.45 kg / hr.

[0085] Example 11 (Preparation of PHBH Blend) An injection-molded article was obtained and evaluated in the same manner as in Example 9, except that 550 g of a polymer nucleating agent was added instead of PETL and the discharge rate from the base of the screw in the compounding process was set to 10.6 kg / hr.

[0086] Comparative Example 1 (Preparation of PHBH Blend) An injection molded article was obtained and evaluated in the same manner as in Example 1, except that PHA-C5 was changed to PHA-C7.

[0087] Comparative Example 2 (Preparation of PHBH Blend) An injection molded article was obtained and evaluated in the same manner as in Example 1, except that PHA-C5 was changed to PHA-C6.

[0088] Comparative Example 3 (Preparation of PHBH Blend) An injection molded article was obtained and evaluated in the same manner as in Example 1, except that PHA-C was used instead of PHA-C.

[0089] Comparative Example 4 (Preparation of PHBH Blend) An injection molded article was obtained and evaluated in the same manner as in Example 1, except that PHA-A was changed to PHA-D.

[0090] Comparative Example 5 (Preparation of PHBH Blend) An injection molded article was obtained and evaluated in the same manner as in Example 1, except that PHA-A was changed to PHA-E2 and PHA-C5 was changed to PHA-C3.

[0091] Comparative Example 6 (Preparation of PHBH Blend) An injection molded article was obtained and evaluated in the same manner as in Example 2, except that the amount of PHA-A was changed from 5 kg to 4 kg and that PHA-C4 was changed from 5 kg to 6 kg.

[0092] Comparative Example 7 (Preparation of PHBH Blend) An injection molded article was obtained and evaluated in the same manner as in Example 2, except that the amount of PHA-A was changed from 5 kg to 3 kg and that of PHA-C4 was changed from 5 kg to 7 kg.

[0093] Comparative Example 8 (Preparation of PHBH Blend) An injection-molded article was obtained and evaluated in the same manner as in Example 1, except that 10 kg of PHA-C was used instead of PHA-A and PHA-C5. Table 4 summarizes the type and amount (parts by weight) of materials used in each example and comparative example, the average content of 3-hydroxybutyrate units in the resin (average HB content), weight-average molecular weight, content of low molecular weight components, and evaluation results for burrs and high-temperature breakage.

[0094] [Table 4]

[0095] The following can be seen from Table 4: The injection molded articles obtained in Examples 1 to 11 have small flashing, are less likely to break at high temperatures, and are therefore suitable for use at high temperatures. On the other hand, the injection-molded articles obtained in Comparative Examples 1 to 8 did not satisfy at least one of the conditions of the average HB ratio, weight-average molecular weight, and content ratio of low molecular weight components in the poly(3-hydroxyalkanoate) resin, and it was found that they had large flash or were prone to breakage at high temperatures and were not suitable for use at high temperatures.

Claims

1. A resin composition for injection molding containing a poly(3-hydroxyalkanoate)-based resin, the poly(3-hydroxyalkanoate)-based resin contains 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 has a weight average molecular weight of 210,000 or more and 270,000 or less in terms of polystyrene, as determined by gel permeation chromatography using a chloroform solvent, and the proportion of components having a weight molecular weight of 200,000 or less in the weight molecular weight distribution is 35% by weight or more and 60% by weight or less.

2. 2. The resin composition for injection molding according to claim 1, wherein the poly(3-hydroxyalkanoate)-based resin is at least one selected from the group consisting 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. 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. 4. The resin composition for injection molding according to claim 1, wherein the content of the resin other than the poly(3-hydroxyalkanoate)-based resin is 0 parts by weight or more and 35 parts by weight or less per 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin.

5. The resin composition for injection molding according to any one of claims 1 to 4, 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 5, further comprising 1 part by weight or more and 50 parts by weight or less of an inorganic filler per 100 parts by weight of a total of resin components including the poly(3-hydroxyalkanoate) resin.

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

8. 8. The resin composition for injection molding according to claim 7, wherein the silicate is at least one selected from the group consisting of talc, mica, kaolinite, montmorillonite, and smectite.

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

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