JP7606304B2 - Polyester resin composition for injection molding, and injection molded article - Google Patents

Description

The present invention relates to a polyester resin composition for injection molding and an injection molded article, and in particular to a polyester resin composition for injection molding and an injection molded article that contains a large amount of poly(3-hydroxyalkanoate), which has excellent biodegradability, and has excellent impact strength at low temperatures.

In recent years, environmental problems caused by waste plastics have been highlighted, and the realization of a recycling-oriented society on a global scale is eagerly awaited. In this environment, biodegradable plastics that are decomposed into water and carbon dioxide by the action of microorganisms after use have attracted attention. In addition, in the composting of food waste practiced in Europe and other places, there is a demand for garbage bags that can be thrown into the compost together with the garbage. Biodegradable plastics include poly(3-hydroxyalkanoate) (hereinafter sometimes referred to as P3HA), polycaprolactone, polybutylene adipate terephthalate, polybutylene succinate adipate, polybutylene succinate, etc., and the development of compositions and molded articles using these biodegradable resins is underway. In particular, of these biodegradable resins, P3HA has the highest biodegradability, and various biodegradation processes such as composting and anaerobic decomposition at around room temperature are possible. Therefore, from the viewpoint of biodegradability, it is preferable to incorporate a large amount of P3HA alone or in a resin composition with other biodegradable resins.

For example, Patent Document 1 gives an example of an injection molded article of an aliphatic polyester resin composition that contains a polyhydroxyalkanoate (3-hydroxybutyrate-co-3-hydroxyhexanoate, abbreviated as PHBH) and a filler such as pentaerythritol or talc as a crystallization nucleating agent. However, there is room for improvement in terms of impact strength at low temperatures (5°C or less, particularly in the temperature range of 0°C or less), and applications are limited.

Patent Document 2 also lists an aliphatic polyester resin composition that has excellent moldability and impact resistance and contains an aliphatic polyester resin containing repeating units derived from an aliphatic diol and an aliphatic dicarboxylic acid, polyhydroxyalkanoate, and an inorganic filler. However, there is room for improvement in terms of low-temperature impact strength.

International Publication No. 2015/052876 JP 2019-178206 A

In view of the above, the present invention is the result of extensive research and an objective of the present invention to provide a polyester resin composition for injection molding that has excellent low-temperature impact strength and an injection-molded article made from the same.

As a result of intensive research aimed at solving the above problems, the present inventors discovered that low-temperature impact strength is significantly improved in a composition containing a poly(3-hydroxyalkanoate) resin (P3HA), an aliphatic aromatic polyester resin, and a layered clay mineral, and thus completed the present invention.
That is, in order to solve the above problems, the polyester resin composition of the present invention comprises a polyester resin represented by the following general formula (1):

(wherein R is an alkyl group represented by C _n H _2n+1 , and n is an integer of 1 to 15), aliphatic aromatic polyester resin (B), and layered clay mineral (C). The polyester resin composition for injection molding contains a poly(3-hydroxyalkanoate) resin (A) having a repeating unit represented by the formula: (wherein R is an alkyl group represented by C n H 2n+1, and n is an integer of 1 to 15), an aliphatic aromatic polyester resin (B), and a layered clay mineral (C), characterized in that the proportion of the resin (A) is 55 to 75% by weight and the proportion of the resin (B) is 25 to 45% by weight relative to the total of the resins (A) and (B), and the content of the clay mineral (C) is 5 to 35 parts by weight when the total of the resins (A) and (B) is 100 parts by weight.

It is also preferable that the poly(3-hydroxyalkanoate)-based resin (A) is at least one selected from the group consisting of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate).

It is also preferable that the aliphatic aromatic polyester resin (B) is at least one selected from the group consisting of polybutylene adipate terephthalate resins, polybutylene sebacate terephthalate resins, and polybutylene succinate terephthalate resins.

The layered clay mineral (C) is preferably at least one selected from the group consisting of smectite, mica, talc, pyroferrite, vermiculite, chlorite, kaolinite and serpentine.
The present invention is also characterized by being an injection molded article containing the polyester resin composition for injection molding.

The present invention provides a polyester resin composition for injection molding that has excellent low-temperature impact strength and an injection-molded article made from the same.

One embodiment of the polyester resin composition for injection molding of the present invention is described below, but the present invention is not limited thereto.

The polyester resin composition for injection molding according to the present invention contains, as a resin component, a compound represented by the following general formula (1):
[-CHR-CH ₂ -CO-O-] (1)
(wherein R is an alkyl group represented by _{CnH2n +1} , and n is an integer of 1 to 15.)) and an aliphatic aromatic polyester resin (B) having a repeating unit represented by the formula (1), and further comprising a layered clay mineral (C).

The poly(3-hydroxyalkanoate) resin (P3HA) used in the present invention is a polyester resin produced from microorganisms.

There is no particular limitation on the microorganism that produces P3HA, so long as it is a microorganism that has the ability to produce P3HAs. For example, examples of bacteria that produce copolymers of hydroxybutyrate and other hydroxyalkanoates include Aeromonas caviae, which produces a copolymer having 3-hydroxybutyrate and 3-hydroxyvalerate as monomer units (hereinafter abbreviated as "PHBV") and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate (hereinafter abbreviated as "PHBH"), and Alcaligenes eutrophus, which produces poly(3-hydroxybutyrate-co-4-hydroxybutyrate). In particular, with regard to PHBH, Alcaligenes eutrophus AC32 strain (FERM), into which genes of a PHA synthase group have been introduced in order to increase the productivity of PHBH, has been used. BP-6038) (J. Bateriol., 179, p. 4821-4830 (1997)) are more preferred, and microbial cells in which these microorganisms have been cultured under appropriate conditions and PHBH has accumulated within the cells are used.

From the viewpoint of the balance between moldability and physical properties, the weight average molecular weight of the P3HA used in the present invention is preferably 50,000 to 3,000,000, more preferably 100,000 to 1,500,000. It is further preferably 150,000 to 1,000,000, and particularly preferably 200,000 to 600,000. The weight average molecular weight here refers to that measured from the polystyrene equivalent molecular weight distribution using gel permeation chromatography (GPC) using a chloroform solution. If the weight average molecular weight is less than 50,000, the molded product may be too brittle, and if it exceeds 3,000,000, the melt viscosity may be too high, making injection molding difficult.

The P3HA used in the present invention is preferably one consisting of repeating units in which n of the alkyl group (R) in the general formula (1) is 1, or one consisting of repeating units in which n is 1 and at least one of repeating units in which n is 2, 3, 5, and 7, and more preferably one consisting of repeating units in which n is 1 and repeating units in which n is 3. Specific examples of P3HA include poly(3-hydroxybutyrate) (abbreviation: P3HB), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (abbreviation: PHBH), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (abbreviation: PHBV), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (abbreviation: P3HB4HB), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate). Among these, P3HB, PHBH, PHBV, and P3HB4HB are the easiest to produce industrially.

Among these, PHBH, which is composed of a repeating unit in which n in the alkyl group (R) is 1 and a repeating unit in which n is 3 in the general formula (1) in the above, is preferred from the viewpoints that by changing the composition ratio of the repeating units, it is possible to change the melting point, the degree of crystallinity, and physical properties such as Young's modulus and heat resistance, and it is possible to impart physical properties between polypropylene and polyethylene, and that it is a plastic that is easy to produce industrially and has useful physical properties as described above. A specific method for producing PHBH is described in, for example, International Publication No. 2010/013483. In addition, a commercially available product of PHBH is Kaneka Biodegradable Polymer PHBH (registered trademark) from Kaneka Corporation.

From the viewpoint of the balance between flexibility and strength, the composition ratio of the repeating units of PHBH is preferably poly(3-hydroxybutyrate)/poly(3-hydroxyhexanoate) of 80/20 to 99/1 (mol/mol), more preferably 85/15 to 97/3 (mol/mol), further preferably 90/10 to 97/3 (mol/mol), and particularly preferably 93/7 to 96/4 (mol/mol). If the composition ratio of the repeating units of PHBH is less than 80/20, solidification may be slow and the molding cycle may be short. If it is more than 99/1, the moldable temperature may exceed the decomposition temperature, making molding impossible.

The aliphatic aromatic polyester resin (B) used in the present invention is a polyester resin containing one or more dicarboxylic acid units selected from the group consisting of aliphatic dicarboxylic acid units and aromatic dicarboxylic acid units, and one or more diol units selected from the group consisting of aliphatic diol units and aromatic diol units, and is a polyester resin having both aliphatic units and aromatic units.

As the aliphatic aromatic polyester resin (B) used in the present invention, polybutylene adipate terephthalate resin, polybutylene sebacate terephthalate resin, and polybutylene succinate terephthalate resin are preferred, with polybutylene adipate terephthalate resin (PBAT) being particularly preferred. Polybutylene adipate terephthalate resin (PBAT) refers to a random copolymer of 1,4-butanediol, adipic acid, and terephthalic acid. Among them, PBAT obtained by reacting (a) a mixture consisting mainly of 35 to 95 mol % of adipic acid or its ester-forming derivative or a mixture of these, and 5 to 65 mol % of terephthalic acid or its ester-forming derivative or a mixture of these (the sum of the individual mol % is 100 mol %) with (b) a mixture containing butanediol (wherein the molar ratio of (a) to (b) is 0.4:1 to 1.5:1), as described in JP-A-10-508640, is preferred. Commercially available PBAT products include "Ecoflex" (registered trademark) manufactured by BASF.

The mixing ratio of the P3HA (A) and the aliphatic aromatic polyester resin (B) in the polyester of the present invention is 55 to 75% by weight of resin (A) and 25 to 45% by weight of resin (B) relative to the total of resin (A) and resin (B), in order to obtain excellent low-temperature strength of the molded product.

The layered clay mineral (C) used in the present invention is a mineral mainly composed of layered silicate, and can provide effects such as improved heat resistance and improved workability. In particular, in terms of the ease with which the effect of improving workability can be obtained, the layered clay mineral (C) is preferably one or more selected from the group consisting of smectite, mica, talc, pyroferrite, vermiculite, chlorite, kaolinite, and serpentine. From the viewpoint of versatility, mica, talc, and kaolinite are preferred, and talc is particularly preferred.

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.

Examples of the talc include general-purpose talc and surface-treated talc. Specific examples include "Microace" (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.

Examples of kaolinite include dry kaolin, calcined kaolin, wet kaolin, etc., and specific examples include "TRANSLINK" (registered trademark), "ASP" (registered trademark), "SANTINTONE" (registered trademark), and "ULTREX" (registered trademark) from Hayashi Kasei Co., Ltd., and kaolinite manufactured by Keiwa Rozai Co., Ltd.

The content of the layered clay mineral (C) is preferably 5 to 35 parts by weight, more preferably 6 to 25 parts by weight, and particularly preferably 7 to 15 parts by weight, when the total of the poly(3-hydroxyalkanoate) resin (A) and the aliphatic aromatic polyester resin (B) is 100 parts by weight. If the layered clay mineral (C) is less than 5 parts by weight, solidification may be slow and moldability may be poor. Also, if the layered clay mineral (C) is more than 35 parts by weight, the melt viscosity may be too high, resulting in poor moldability.

The resin composition of the present invention may also contain one or more of the following secondary additives, as long as they do not impair the effects of the present invention: fillers other than layered clay minerals that are commonly used as additives, colorants such as pigments and dyes, odor absorbents such as activated carbon and zeolite, fragrances such as vanillin and dextrin, antioxidants, weather resistance improvers, UV absorbers, crystallization nucleating agents, lubricants, release agents, water repellents, antibacterial agents, sliding improvers, and other secondary additives.

Examples of crystallization nucleating agents include pentaerythritol, orotic acid, aspartame, cyanuric acid, glycine, zinc phenylphosphonate, and boron nitride. Among them, pentaerythritol is preferred because of its particularly excellent effect of promoting the crystallization of poly(3-hydroxyalkanoate) resins. The amount of crystallization nucleating agent used is not particularly limited, but is preferably 0.1 to 5 parts by weight, more preferably 0.5 to 3 parts by weight, and even more preferably 0.7 to 1.5 parts by weight, per 100 parts by weight of poly(3-hydroxyalkanoate) resin. In addition, not only one type of crystallization nucleating agent but also two or more types may be mixed, and the mixing ratio can be appropriately adjusted depending on the purpose.

Examples of lubricants include behenamide, oleamide, erucamide, stearamide, palmitamide, N-stearylbehenamide, N-stearylerucamide, ethylenebisstearamide, ethylenebisoleamide, ethylenebiserucamide, ethylenebislauramide, ethylenebiscapricamide, p-phenylenebisstearamide, and polycondensates of ethylenediamine, stearic acid, and sebacic acid. Among these, behenamide and erucamide are preferred because of their particularly excellent lubricant effect on poly(3-hydroxyalkanoate) 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) resin. In addition, the lubricant may be a mixture of one or more types, and the mixing ratio can be adjusted appropriately depending on the purpose.

Examples of the plasticizer include glycerin ester compounds, citrate compounds, sebacic acid ester compounds, adipate compounds, polyether ester compounds, benzoic acid ester compounds, phthalic acid ester compounds, isosorbide ester compounds, polycaprolactone compounds, and dibasic acid ester compounds. Among them, glycerin ester compounds, citrate compounds, sebacic acid ester compounds, and dibasic acid ester compounds are preferred because of their particularly excellent plasticizing effect on poly(3-hydroxyalkanoate) resins. Examples of the glycerin ester compounds include glycerin diacetomonolaurate. Examples of the citrate compounds include acetyl tributyl citrate. Examples of the sebacic acid ester compounds include dibutyl sebacate. Examples of the dibasic acid ester compounds include benzyl methyl diethylene glycol adipate. The amount of the plasticizer used is not particularly limited, but is preferably 1 to 20 parts by weight, more preferably 2 to 15 parts by weight, and even more preferably 3 to 10 parts by weight, per 100 parts by weight of the total of the poly(3-hydroxyalkanoate) resin and the polylactic acid. In addition, the plasticizer may be used alone or in combination of two or more kinds, and the mixing ratio can be appropriately adjusted depending on the purpose.
Next, one embodiment of the method for producing the polyester resin composition for injection molding of the present invention will be described, but the present invention is not limited thereto.

The resin composition of the present invention can be produced using a known kneader such as a single screw extruder, a twin screw extruder, or a Banbury mixer. Of these, a twin screw extruder is preferred as the kneader because it can disperse the layered clay mineral (C) in the resin without applying excessive shear to the resin. As for the setting conditions of the kneader, it is preferred to set the cylinder temperature to 180° C. or less because it can suppress the thermal decomposition of P3HA.
When each component is fed to the kneader, it may be added all at once, or a portion of the components may be kneaded and then the remaining components may be kneaded. Since the layered clay mineral (C) may damage the resin, it is preferable to add the layered clay mineral (C) by using a side feed or the like after melt-kneading the resin components.
As a molding method when processing the polyester resin composition for injection molding of the present invention into an injection molded article, a general injection molding method can be used, for example, an injection molding method generally used when molding a thermoplastic resin, as well as a gas-assisted molding method, an injection compression molding method, etc. can be used. In-mold molding, gas press molding, two-color molding, sandwich molding, PUSH-PULL, SCORIM, etc. can also be used, but the injection molding method usable in the present invention is not limited to the above methods, and specific conditions may be appropriately set.
Applications of the injection molded articles obtained by the present invention are not particularly limited, and examples thereof include tableware such as plates, cups, cutlery, etc., coffee capsules, agricultural materials, office automation parts, home appliance parts, automotive parts, toys, daily necessities such as boxes and containers, stationery such as ballpoint pens, mechanical pencils, rulers, etc., molded articles such as bottles, caps, lids, extruded sheets and films, irregularly shaped extruded products, etc. In addition, the injection molded articles obtained by the present invention have seawater degradability because the resin component is mainly composed of poly(3-hydroxyalkanoate)-based resin, and therefore can solve environmental problems caused by ocean dumping of plastics.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples in any way.
(Ingredients used)
The raw materials used in the present examples and comparative examples are summarized in Table 1.

The evaluation methods used in the examples and comparative examples are described below.

(Releasability)
Using the injection molding conditions described below and a three-plate, pin-gate, single-cavity coffee capsule mold with a thickness of 0.4 mm, the cooling time was shortened and the minimum cooling time during which no release problems occurred was measured, and the releasability was evaluated based on the following criteria.
◎: Less than 10 seconds 〇: 10 to 20 seconds △: 20 to 25 seconds ×: 25 seconds or more

(Appearance Evaluation)
The appearance of the molded article obtained by injection molding as described below was visually inspected and judged based on the following criteria.
○: Good appearance ×: One or more molding defects such as burrs or flow marks are observed

(surface impact test)
From an 8 cm x 8 cm x 1 mm plate obtained by injection molding as described below, a 4 cm x 4 cm x 1 mm plate was cut out and cured for one day in a thermostatic chamber at 23°C and 0°C. After that, a 300 g impact core was dropped from a height of 50 cm and 10 test pieces were tested to calculate the non-destructive rate using the following formula.
Non-destructive rate (%) = Number of unbroken test pieces (pieces) / Total number of test pieces (pieces) × 100

Example 1
(Preparation of PHBH Blends)
Using a 75 L Super Mixer manufactured by Kawata Corporation, 10 kg of PHBH, 100 g of PETL, 50 g of BA, and 50 g of EA were stirred at 300 rpm for 3 minutes to obtain a PHBH blend.

(Compounding using a twin-screw extruder)
A TEM26SS (L/D=60) manufactured by Toshiba Machine was used with the screw configuration shown in Table 2, and the screw rotation speed was set to 100 rpm. The PHBH blend was fed from the screw root at 7.14 kg/hr, and simultaneously, PBAT was fed from the screw root at 3.0 kg/hr, and further, talc was side-fed at 1.0 kg/hr. The strands were solidified by passing through a water tank filled with hot water at 45° C., and cut with a pelletizer to obtain pellets.

(Acquisition of injection molded bodies)
Using a plate mold of 8 cm x 8 cm x 1 mm and a Toyo Machinery Metal injection molding machine Si-30V, nozzle/T1/T2/T3 = 155/145/135/125°C and mold temperature of 35°C, a plate-shaped molded body of 8 cm x 8 cm x 1 mm was obtained.
The obtained injection molded articles were subjected to an appearance evaluation and a surface impact test, and the results are shown in Table 3. Furthermore, the mold releasability was evaluated, and the results are shown in Table 3.

Example 2
An experiment was carried out in the same manner as in Example 1, except that the PHBH blend was fed at 6.12 kg/hr, PBAT was fed at 4.0 kg/hr, and talc was fed from the side feed at 1.0 kg/hr from the base of the screw. Appearance, surface impact test, and demolding properties were evaluated, and the results are shown in Table 3.

Example 3
An experiment was carried out in the same manner as in Example 1, except that the PHBH blend was fed at 7.14 kg/hr, PBAT was fed at 3.0 kg/hr, and talc was fed from the side feed at 2.0 kg/hr from the base of the screw. Appearance, surface impact test, and demolding properties were evaluated, and the results are shown in Table 3.

Example 4
The experiment was carried out in the same manner as in Example 1, except that the PHBH blend was fed at 6.12 kg/hr, PBAT was fed at 4.0 kg/hr, and talc was fed at 2.0 kg/hr from the side feed through the screw root. Appearance evaluation, surface impact test, and mold releasability were evaluated, and the results are shown in Table 3.

Example 5
An experiment was carried out in the same manner as in Example 1, except that the PHBH blend was fed at 7.14 kg/hr, PBAT was fed at 3.0 kg/hr from the base of the screw, and talc was fed from the side feed at 3.0 kg/hr. Appearance evaluation, surface impact test, and demolding properties were evaluated, and the results are shown in Table 3.

<Comparative Example 1>
The experiment was carried out in the same manner as in Example 1, except that the PHBH blend was fed from the base of the screw at 10.20 kg/hr and PBAT and talc were not fed. Appearance evaluation, surface impact test, and demolding properties were evaluated. The results are shown in Table 3.

<Comparative Example 2>
From the base of the screw, the PHBH blend was fed at 8.16 kg/hr and PBAT was fed at 2.0 kg/hr. Except for not feeding talc, an experiment was carried out in the same manner as in Example 1. Appearance evaluation, surface impact test, and demolding properties were evaluated. The results are shown in Table 3.

<Comparative Example 3>
From the base of the screw, the PHBH blend was fed at 7.14 kg/hr and PBAT was fed at 3.0 kg/hr. Except for not feeding talc, an experiment was carried out in the same manner as in Example 1. Appearance evaluation, surface impact test, and demolding properties were evaluated. The results are shown in Table 3.

<Comparative Example 4>
From the base of the screw, the PHBH blend was fed at 6.12 kg/hr and PBAT was fed at 4.0 kg/hr. Except for not feeding talc, an experiment was carried out in the same manner as in Example 1. Appearance evaluation, surface impact test, and demolding properties were evaluated. The results are shown in Table 3.

<Comparative Example 5>
The experiment was carried out in the same manner as in Example 1, except that the PHBH blend was fed at 8.16 kg/hr and PBSA was fed at 2.0 kg/hr from the base of the screw, and no talc was fed. The appearance, surface impact test, and demolding properties were evaluated, and the results are shown in Table 3.

<Comparative Example 6>
From the base of the screw, the PHBH blend was fed at 7.14 kg/hr and PBSA was fed at 3.0 kg/hr. Except for not feeding talc, an experiment was carried out in the same manner as in Example 1. Appearance evaluation, surface impact test, and demolding properties were evaluated. The results are shown in Table 3.

<Comparative Example 7>
From the base of the screw, the PHBH blend was fed at 6.12 kg/hr and PBSA was fed at 4.0 kg/hr. Except for not feeding talc, an experiment was carried out in the same manner as in Example 1. Appearance evaluation, surface impact test, and demolding properties were evaluated. The results are shown in Table 3.

<Comparative Example 8>
An experiment was carried out in the same manner as in Example 1, except that the PHBH blend was fed from the base of the screw at 7.14 kg/hr, PBAT was fed at 3.0 kg/hr, and talc was fed from the side feed at 4.0 kg/hr. Appearance evaluation, surface impact test, and demolding properties were evaluated, and the results are shown in Table 3.

<Comparative Example 9>
The experiment was carried out in the same manner as in Example 1, except that the PHBH blend was fed at 7.14 kg/hr, PBSA at 3.0 kg/hr, and talc was fed from the side feed at 1.0 kg/hr from the base of the screw. Appearance, surface impact test, and demolding properties were evaluated, and the results are shown in Table 3.

<Comparative Example 10>
The experiment was carried out in the same manner as in Example 1, except that the PHBH blend was fed from the base of the screw at 6.12 kg/hr, PBSA was fed at 4.0 kg/hr, and talc was fed from the side feed at 1.0 kg/hr. Appearance, surface impact test, and demolding properties were evaluated, and the results are shown in Table 3.

Table 3 shows the results of various evaluations of resin compositions containing the contents of resin (A) and resin (B) relative to the total of poly(3-hydroxyalkanoate) resin (A) and aliphatic aromatic polyester (B), and the content (parts by weight) of layered clay mineral (C) when the total of resin (A) and resin (B) is taken as 100 parts by weight.
From these results, it can be seen that, compared to Comparative Examples 1 to 10, Examples 1 to 5 have excellent low-temperature impact strength and a short cooling time for demolding, which results in high productivity and the production of injection-molded articles with good appearance.

Claims (5)

The following general formula (1)

(wherein R is an alkyl group represented by C _n H _2n+1 , n being an integer of 1 to 15), a poly(3-hydroxyalkanoate) resin (A) having a repeating unit represented by the formula:
The ratio of the resin (A) is 55 to 75% by weight, and the ratio of the resin (B) is 25 to 45% by weight, based on the total weight of the resin (A) and the resin (B);
A polyester-based resin composition for injection molding, in which the clay mineral (C) is 5 to 30 parts by weight when the total of the resin (A) and the resin (B) is 100 parts by weight (however, excluding compositions containing 30 parts by weight or more and 60 parts by weight or less of polylactic acid out of a total of 100 parts by weight of polylactic acid, the resin (A), and the resin (B)) . The polyester resin composition for injection molding according to claim 1, characterized in that the poly(3-hydroxyalkanoate)-based resin (A) is at least one selected from the group consisting of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate). The polyester resin composition for injection molding according to claim 1 or 2, characterized in that the aliphatic aromatic polyester resin (B) is at least one selected from the group consisting of polybutylene adipate terephthalate resins, polybutylene sebacate terephthalate resins, and polybutylene succinate terephthalate resins. The polyester resin composition for injection molding according to any one of claims 1 to 3, characterized in that the layered clay mineral (C) is at least one selected from the group consisting of smectite, mica, talc, pyroferrite, vermiculite, chlorite, kaolinite and serpentine. An injection molded article comprising the polyester resin composition for injection molding according to any one of claims 1 to 4.