JP5197260B2 - Method for producing polylactic acid resin injection molded body - Google Patents

Description

  The present invention relates to a method for producing a polylactic acid resin injection-molded article.

  Among the biodegradable resins, polylactic acid resins are made from saccharides from corn, straw, etc., and a large amount of L-lactic acid is produced by fermentation. The use of the obtained resin is expected because it is extremely rare and has the characteristics that the obtained resin has high rigidity and good transparency. However, the polylactic acid resin has a very low crystallization rate, is in an amorphous state after molding unless a mechanical process such as stretching is performed, and the glass transition temperature (Tg) of the polylactic acid resin is as low as about 60 ° C. Therefore, there is a problem that the heat resistance is inferior and it cannot be used in an environment where the temperature is 55 ° C. or higher.

In order to improve the heat resistance of the polylactic acid resin, it is important to crystallize at the time of molding. For example, a production method in which polylactic acid is crystallized using a supercritical fluid in injection molding has been proposed ( For example, Patent Document 1). However, even this method has a problem that crystallization is difficult to proceed due to a low crystallization rate, and foaming and deformation occur when the mold is removed quickly. In order to prevent this, the mold holding time must be lengthened and the glass must be cooled to a temperature lower than the glass transition temperature, resulting in a problem that the molding time becomes long. In addition, in order to prevent foaming in the mold due to low crystallization speed, it is necessary to pressurize the mold with nitrogen gas or the like above the supercritical pressure, and there are restrictions in terms of equipment and equipment. there were. On the other hand, using a biodegradable resin, a plasticizer, and a crystal nucleating agent that is an aliphatic compound having at least one group selected from a hydroxyl group and an amide group, a biodegradation with a good crystallization rate A method for producing a conductive resin composition has been proposed (for example, Patent Document 2). However, in this method, it is an essential requirement to use a plasticizer.
JP 2003-236944 A JP 2006-176747 A

  The subject of this invention is providing the manufacturing method which can obtain efficiently the polylactic acid resin injection molding which has the outstanding heat resistance, without using a plasticizer by the outstanding moldability.

The present invention provides a method for producing a polylactic acid resin injection-molded article having the following steps (1) and (2).
Step (1): A polylactic acid resin composition containing a polylactic acid resin and at least one organic crystal nucleating agent selected from the group consisting of carbohydrazides, melamine compounds, uracils and N-substituted ureas, Step of melt kneading while making contact with supercritical fluid Step (2): Filling the mold with the melt obtained in Step (1) and injection molding

  The production method of the present invention can efficiently obtain a polylactic acid resin injection-molded article having excellent heat resistance in a short molding time without using a plasticizer, and excellent molding even at a lower mold temperature. Showing gender.

[Polylactic acid resin composition]
The polylactic acid resin composition used in step (1) of the present invention comprises at least one organic crystal nucleating agent selected from the group consisting of polylactic acid resins, carbohydrazides, melamine compounds, uracils, and N-substituted ureas. Containing.

  In the present invention, the polylactic acid resin is polylactic acid or a copolymer of lactic acid and hydroxycarboxylic acid. Examples of the hydroxycarboxylic acid include glycolic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxypentanoic acid, hydroxycaproic acid, hydroxyheptanoic acid and the like, and glycolic acid and hydroxycaproic acid are preferable. The molecular structure of polylactic acid is preferably composed of 80 to 100 mol% of either L-lactic acid or D-lactic acid and 0 to 20 mol% of each enantiomer. The copolymer of lactic acid and hydroxycarboxylic acid is composed of 85 to 100 mol% of either L-lactic acid or D-lactic acid and 0 to 15 mol% of hydroxycarboxylic acid units. These polylactic acid resins can be obtained by dehydrating polycondensation using L-lactic acid, D-lactic acid and hydroxycarboxylic acid as a raw material by selecting those having the required structure. Preferably, it can be obtained by ring-opening polymerization by selecting a desired structure from lactide, which is a cyclic dimer of lactic acid, glycolide, which is a cyclic dimer of glycolic acid, and caprolactone. Lactide includes L-lactide which is a cyclic dimer of L-lactic acid, D-lactide which is a cyclic dimer of D-lactic acid, meso-lactide obtained by cyclic dimerization of D-lactic acid and L-lactic acid, and D-lactide. There is DL-lactide, which is a racemic mixture of lactide and L-lactide. Any lactide can be used in the present invention. However, the main raw material is preferably D-lactide or L-lactide from the viewpoint of improving the crystallization rate and efficiently obtaining a molded article having excellent heat resistance.

  Moreover, as polylactic acid resin in this invention, the polylactic acid unit (A) comprised by 80-100 mol% of L-lactic acid units, 0-20 mol% of units, such as D-lactic acid, and D-lactic acid unit 80 Stereocomplex polylactic acid composed of a mixture of ˜100 mol% and polylactic acid units (B) composed of units of 0 to 20 mol% such as L-lactic acid can also be used. Specifically, two types of polylactic acid may be melt-kneaded in advance, and the melt-kneaded product may be used as a polylactic acid resin for the step (1) of the present invention. Only polylactic acid may be separately melt-kneaded and used, but two types of polylactic acid and raw materials other than the polylactic acid may be melt-kneaded at the same time. From the viewpoint of improving the crystallization rate and efficiently obtaining a molded article having excellent heat resistance, the polylactic acid unit (A) / polylactic acid unit (B) (weight ratio) is preferably 10/90 to 90/10. . The copolymer component unit other than lactic acid used in each of the polylactic acid units (A) and (B) constituting these stereocomplex polylactic acid is a dicarboxylic acid having a functional group capable of forming two or more ester bonds, Examples include polyesters, polyethers, polycarbonates, and the like, which are composed of polyhydric alcohols, hydroxycarboxylic acids, lactones, and the like and various kinds of these structural components and have two or more unreacted functional groups in the molecule.

  Examples of commercially available polylactic acid resins include Toyota Motor Corporation, trade name Eco Plastic U'zS; Mitsui Chemicals, trade name LACEA; Cargill Dow Polymers, trade name Nature. works and the like. Specifically, for example, “Lacia Series” (manufactured by Mitsui Chemicals) such as Lacia H-100, H-280, H-400, H-440, 3001D, 3051D, 4032D, 4042D, 6201D, 6251D, 7000D, “Nature Works” (manufactured by Nature Works) such as 7032D, and “ecoplastic U′z series” (manufactured by Toyota Motor Corporation) such as ecoplastic U′z S-09, S-12, and S-17. Among these, from the viewpoint of the heat resistance of the polylactic acid resin composition, Lacia H-100, H-400 (manufactured by Mitsui Chemicals), 3001D, 3051D, 4032D, 6201D, 6251D, 7000D, 7032D (manufactured by Nature Works) Ecoplastics U'z S-09, S-12, and S-17 (manufactured by Toyota Motor Corporation) are preferable.

  The polylactic acid resin composition in the present invention may contain other resins in addition to the polylactic acid resin from the viewpoint of improving physical properties such as rigidity, flexibility, heat resistance, and durability. Specific examples of other resins include polyethylene, polypropylene, polystyrene, ABS resin, AS resin, acrylic resin, polyamide, polyphenylene sulfide, polyether ether ketone, polyester, polyacetal, polysulfone, polyphenylene oxide, polyimide, polyetherimide, Or thermoplastic resins such as ethylene / glycidyl methacrylate copolymers, polyester elastomers, polyamide elastomers, soft thermoplastic resins such as ethylene / propylene terpolymers, ethylene / butene-1 copolymers, phenol resins, melamine resins, unsaturated Thermosetting resins such as polyester resins, silicone resins, and epoxy resins can be mentioned. Among them, amide bonds and S are preferred from the viewpoint of compatibility with polylactic acid resins. Le coupling, the resin having a bond containing a carbonyl group of a carbonate bond or the like are preferred because structurally polylactic acid resin and affinity tends to be high. Examples of preferable resins include polycarbonate, acrylic resin (PMMA), polyamide, and polyester (polyethylene terephthalate, polybutylene succinate, and the like).

  Also, in the present invention, as the polylactic acid, a polymer alloy by blending polylactic acid and the above resin is used from the viewpoints of compatibility of moldability, flexibility and rigidity, heat resistance, and wear resistance of the polylactic acid resin composition. May be. Specifically, polylactic acid and the above resin may be previously melt-kneaded, and the melt-kneaded product may be used as the polylactic acid resin for the step (1) of the present invention. In addition, you may use what was prepared by melt-kneading polylactic acid and the said resin separately, but you may melt-knead polylactic acid, the said resin, and another raw material simultaneously.

  The blend ratio of polylactic acid and other resin (polylactic acid / other resin) is 95/5 from the viewpoint of compatibility of moldability, flexibility and rigidity, heat resistance, and abrasion resistance of the polylactic acid resin composition. -20/80 is preferable, 95 / 5-50 / 50 is more preferable, and 90 / 10-60 / 40 is more preferable.

  The content of the polylactic acid resin, that is, the polylactic acid or the copolymer of lactic acid and hydroxycarboxylic acid is selected from the viewpoints of compatibility between strength and flexibility of the polylactic acid resin composition, heat resistance, and productivity. The total resin contained in the product is preferably 50% by weight or more, more preferably 80% by weight or more, still more preferably 90% by weight or more, and still more preferably substantially 100% by weight. The polylactic acid resin referred to here includes stereocomplex polylactic acid and a polymer alloy obtained by blending polylactic acid and a resin other than polylactic acid resin.

  The content of the polylactic acid resin is preferably 50% by weight or more, more preferably 60% by weight or more, and further preferably 70% by weight or more in the polylactic acid resin composition.

  In the present invention, at least one organic crystal nucleating agent selected from the group consisting of carbohydrazides, melamine compounds, uracils and N-substituted ureas (hereinafter referred to as the organic crystal nucleating agent of the present invention) is ethylenedicarbonyl. Dibenzoyl hydrazide, tetramethylene dicarbonyl dibenzoyl hydrazide, hexamethylene dicarbonyl dibenzoyl hydrazide, octamethylene dicarbonyl dibenzoyl hydrazide, decamethylene dicarbonyl dibenzoyl hydrazide, dodecamethylene dicarbonyl dibenzoyl hydrazide, cyclohexylene dicarbonyl di Benzoyl hydrazide, octamethylenedicarbonyldi (4-methylbenzoyl) hydrazide, octamethylenedicarbonyldi (4-t-butylbenzoyl) hydrazide, octamethylenedi Carbohydrazides such as rubonyldi (2-methylbenzoyl) hydrazide and octamethylenedicarbonyldi (3-methylbenzoyl) hydrazide; substituted melamine compounds in which the hydrogen of the amino group of melamine or melamine is substituted with an alkyl group, an alkenyl group or a phenyl group , Melamine amino group hydrogen substituted with hydroxyalkyl group, hydroxyalkyl (oxaalkyl) n group, aminoalkyl group substituted melamine compound, melam, melem, melon, melamine deammonia condensate, benzoguanamine, aceto At least one melamine selected from guanamines such as guanamine, isocyanuric acid, formic acid, acetic acid, oxalic acid, malonic acid, lactic acid, citric acid, benzoic acid, isophthalic acid, terephthalic acid and other organic acids, hydrochloric acid, nitric acid, Sulfuric acid, Sulfuric acid, methanesulfonic acid, ethanesulfonic acid, paratoluenesulfonic acid, dodecylbenzenesulfonic acid, sulfamate, phosphate, pyrophosphate, polyphosphate, phosphonate, phenylphosphonate, alkylphosphonate, A melamine compound comprising a salt with at least one acid selected from inorganic acids such as phosphite, borate, tungstate; uracil, 6-methyluracil, 5-methyluracil (thymine), 6-azathymine, 6-azauracil, 5-crouracil, 6-benzyl-2-thiouracil, 5-cyanouracil, ethyl 2-thiouracil-5-carboxylate, 5-ethyluracil, 5,6-dihydro-6-methyluracil, 5- ( Hydroxymethyl) uracil, 5-iodouracil, 5-methyl-2-thiourasi Uracils such as 5-nitrouracil, 5- (trifluoromethyl) uracil, 2-thiouracil, and 5-fluorouracil; N such as xylene bislauryl urea, xylene bismyristyl urea, xylene bispalmityl urea, and xylene bisstearyl urea -Substituted ureas. In this specification, carbohydrazides do not include compounds in which the carbohydrazide group forms part of the ring, and uracils do not include 1,4-diketo-2,5-dihydro-3,6- Diphenyl-pyrrolo [3,4-c] pyrrole, 1,4-diketo-2,5-dihydro-3,6-di- (p-chlorophenyl) pyrrolo [3,4-c] pyrrole, 1,4-diketo -2,5-dihydro-3,6-di- (p-methylphenyl) pyrrolo [3,4-c] pyrrole, 1,4-diketo-2,5-dihydro-3,6-di- (m- Methylphenyl) pyrrolo [3,4-c] pyrrole, 1,4-diketo-2,5-dihydro-3- (p-methylphenyl) -6- (m-methylphenyl) pyrrolo [3,4-c] Pyrrole, 1,4-diketo-2,5-dihydro-3,6-di- (p-tert-butyl) Phenyl) pyrrolo [3,4-c] pyrrole, 1,4-diketo-2,5-dihydro-3,6-di- (p-biphenyl) pyrrolo [3,4-c] pyrrole, 1,4-diketo -2,5-dihydro-3,6-di- (m-cyanophenyl) pyrrolo [3,4-c] pyrrole and 1,4-diketo-2,5-dihydro-3,6-di- (m- Chlorophenyl) pyrrolo [3,4-c] pyrrole does not include organic pigments that are cyclic compounds selected from the group consisting of N-substituted ureas that do not include compounds in which urea forms part of the ring And

  Among these organic crystal nucleating agents, hexamethylene dicarbonyl dibenzoyl hydrazide, octamethylene dicarbonyl dibenzoyl hydrazide, decamethylene dicarbonyl are used from the viewpoint of improving the crystallization speed and efficiently obtaining a molded product having excellent heat resistance. Dibenzoyl hydrazide, melamine cyanurate, melamine polyphosphate, melamine polyphosphate melam melem double salt, paratoluenesulfonate, uracil, 6-methyluracil, xylene bisstearyl urea are preferred, decamethylene dicarbonyldibenzoyl hydrazide, Melamine cyanurate, 6-methyluracil, and xylene bisstearyl urea are more preferable, and decamethylene dicarbonyldibenzoyl hydrazide is still more preferable.

  The organic crystal nucleating agent used in the present invention may be used alone or in combination of two or more.

  In the present invention, a known organic crystal nucleating agent other than the above organic crystal nucleating agent may be used as long as the effects of the present invention are not impaired. In the agent, it is preferably 80% by weight or more, more preferably 90% by weight or more, and substantially 100% by weight.

  The total content of the organic crystal nucleating agent in the polylactic acid resin composition in the present invention is based on 100 parts by weight of the polylactic acid resin, from the viewpoint of improving the crystallization rate and efficiently obtaining a molded product having excellent heat resistance. 0.01 to 5 parts by weight is preferred, 0.05 to 4 parts by weight is more preferred, 0.10 to 3 parts by weight is still more preferred, 0.2 to 3 parts by weight is even more preferred, and 0.3 to 2 parts by weight Part is even more preferred.

  The polylactic acid resin composition in the present invention can obtain good moldability without containing a plasticizer, but can contain a better plasticization rate by containing a plasticizer, which is efficient. Can be molded.

  Although it does not specifically limit as a plasticizer used for this invention, Polyhydric alcohol esters, such as hydroxybenzoic acid ester, such as 2-ethylhexyl hydroxybenzoic acid, the ethylene oxide adduct of glycerol, Di-2-ethylhexyl phthalate Phthalates such as dioctyl adipate, maleates such as di-n-butyl maleate, citrates such as tributyl acetylcitrate, alkyl phosphates such as tricresyl phosphate, succinic acid Ester of triethylene glycol monomethyl ether, ester of adipic acid and diethylene glycol monomethyl ether, tricarboxylic acid ester such as trioctyl trimellitic acid, 1,3,6-hexatricarboxylic acid and butyl diglycol Alkyl ether ester of polyvalent carboxylic acid such as ester with ruthenium, acetylated polyoxyethylene alkyl (alkyl group having 2 to 15 carbon atoms) ether such as acetylated polyoxyethylene hexyl ether, ethylene oxide addition mole number 3 -20 polyethylene glycol diacetate, polyoxyethylene 1,4-butanediol ether diacetate and the like. From the viewpoint of excellent flexibility, transparency and crystallization speed of polylactic acid resin, polyhydric alcohol ester such as acetate ester of ethylene oxide adduct of glycerin, polyethylene glycol diacetate having 3-10 addition moles of ethylene oxide, Alkyl ether esters of polyvalent carboxylic acids such as esters of succinic acid and triethylene glycol monomethyl ether, esters of adipic acid and diethylene glycol monomethyl ether, and esters of 1,3,6-hexatricarboxylic acid and butyl diglycol preferable. From the viewpoint of excellent flexibility, transparency, crystallization speed, and bleed resistance, acetic acid ester of 3 to 6 mol adduct of glycerin, polyethylene glycol diacetate having 5 to 10 mol of ethylene oxide, and succinic acid More preferred are esters of triethylene glycol monomethyl ether and esters of adipic acid and diethylene glycol monomethyl ether.

  The content of the plasticizer in the polylactic acid resin composition in the present invention is preferably 1 to 50 parts by weight with respect to 100 parts by weight of the polylactic acid resin from the viewpoints of flexibility, transparency, crystallization speed and bleed resistance. 5 to 20 parts by weight is more preferable.

  That is, the content ratio of the organic crystal nucleating agent and the plasticizer to the polylactic acid resin composition (organic crystal nucleating agent / plasticizer) is 1 from the viewpoint of improving the crystallization rate and efficiently obtaining a molded article having excellent heat resistance. It is preferably / 10 to 5/1, and more preferably 1/2 to 2/1.

  The polylactic acid resin composition in the present invention preferably contains a hydrolysis inhibitor, that is, a carboxyl group-reactive end capping agent, from the viewpoints of durability and heat and humidity resistance. The carboxyl group-reactive end-blocking agent used in the present invention is not particularly limited as long as it is a compound that can block the carboxyl end group of the polymer, and those used as the carboxyl-terminal blocking agent of the polymer are used. be able to. In the present invention, such a carboxyl group-reactive end-blocking agent is not only used to block the end of a polylactic acid resin, but also an acidic low-molecular compound produced by thermal decomposition or hydrolysis of a polylactic acid resin or a natural organic filler. Carboxyl groups can also be blocked. Further, the end-capping agent is more preferably a compound that can also block the hydroxyl end where an acidic low molecular weight compound is generated by thermal decomposition.

  As such a carboxyl group-reactive endblocker, it is preferable to use at least one compound selected from an epoxy compound, an oxazoline compound, an oxazine compound, and a carbodiimide compound from the viewpoints of durability and heat and humidity resistance. Epoxy compounds and / or carbodiimide compounds are preferred.

  Examples of the carbodiimide compound include carbodiimide compounds such as aromatic and / or aliphatic polycarbodiimide compounds and monocarbodiimide compounds, and a polycarbodiimide compound is preferable from the viewpoint of moldability of a polylactic acid resin molded article.

  Examples of the polycarbodiimide compound include poly (4,4′-diphenylmethanecarbodiimide), poly (4,4′-dicyclohexylmethanecarbodiimide), poly (1,3,5-triisopropylbenzene) polycarbodiimide, and poly (1,3,3). 5-triisopropylbenzene and 1,5-diisopropylbenzene) polycarbodiimide and the like, and examples of the monocarbodiimide compound include N, N′-di-2,6-diisopropylphenylcarbodiimide.

  The carbodiimide compounds may be used alone or in combination of two or more in order to satisfy the moldability, heat resistance, impact resistance, and bloom resistance of the organic crystal nucleating agent of the polylactic acid resin composition. Poly (4,4′-dicyclohexylmethane carbodiimide) is obtained from carbodilite LA-1 (manufactured by Nisshinbo Industries, Inc.), poly (1,3,5-triisopropylbenzene) polycarbodiimide and poly (1,3,5-trimethyl). (Isopropylbenzene and 1,5-diisopropylbenzene) polycarbodiimide are stabuxol P and stabuxol P-100 (manufactured by Rhein Chemie), N, N'-di-2,6-diisopropylphenylcarbodiimide is stabuxol 1, stabuxol 1- LF (manufactured by Rhein Chemie) can be purchased and used.

  In the present invention, the content of the hydrolysis inhibitor in the polylactic acid resin composition is preferably 0.05 to 3 parts by weight with respect to 100 parts by weight of the polylactic acid resin, from the viewpoint of durability and heat and humidity resistance. More preferred is ˜2 parts by weight.

  The polylactic acid resin composition in the present invention preferably further contains an inorganic filler from the viewpoint of improving physical properties such as rigidity. As the inorganic filler used in the present invention, fibers, plates, granules, and powders that are usually used for reinforcing thermoplastic resins can be used. Specifically, glass fiber, asbestos fiber, carbon fiber, graphite fiber, metal fiber, potassium titanate whisker, aluminum borate whisker, magnesium-based whisker, silicon-based whisker, wollastonite, sepiolite, asbestos, slag fiber, zonolite, Elastadite, gypsum fiber, silica fiber, silica-alumina fiber, zirconia fiber, boron nitride fiber, silicon nitride fiber, boron fiber and other fibrous inorganic fillers, glass flakes, non-swellable mica, swellable mica, graphite, metal foil , Ceramic beads, talc, clay, mica, sericite, zeolite, bentonite, organic modified bentonite, organic modified montmorillonite, dolomite, kaolin, fine powder silicic acid, feldspar powder, potassium titanate, shirasu balloon, calcium carbonate Magnesium carbonate, barium sulfate, calcium oxide, aluminum oxide, titanium oxide, aluminum silicate, silicon oxide, gypsum, novaculite, include plate-like or granular inorganic fillers such as dawsonite and white clay. Among these inorganic fillers, carbon fiber, glass fiber, wollastonite, mica, talc and kaolin are particularly preferable. The aspect ratio of the fibrous filler is preferably 5 or more, more preferably 10 or more, and further preferably 20 or more.

  The inorganic filler may be coated or focused with a thermoplastic resin such as an ethylene / vinyl acetate copolymer or a thermosetting resin such as an epoxy resin, or a coupling agent such as aminosilane or epoxysilane. May be processed. Moreover, 1-100 weight part is preferable with respect to 100 weight part of polylactic acid resins, and, as for the compounding quantity of an inorganic filler, 5-50 weight part is more preferable.

  The polylactic acid resin composition in the present invention can further contain high-strength organic synthetic fibers from the viewpoint of improving physical properties such as strength, heat resistance and impact resistance. Specific examples of the high-strength organic synthetic fibers include aramid fibers, polyarylate fibers, PBO fibers, and the like, and aramid fibers are preferable from the viewpoint of heat resistance.

  The polylactic acid resin composition in the present invention can further contain a flame retardant. Specific examples of flame retardants include halogen compounds containing bromine or chlorine, antimony compounds such as antimony trioxide, inorganic hydrates (metal hydroxides such as aluminum hydroxide and magnesium hydroxide) and phosphorus compounds Etc. From the viewpoint of safety, inorganic hydrates are preferred. The flame retardant may have a surface treated with a silane coupling agent or the like. The content of the flame retardant is determined while confirming the effect of the flame retardant, but a good flame retardant effect is obtained, the flow characteristics during processing, the strength of the molded body, the flexibility of the composition, And from a viewpoint of suppressing a heat resistant fall, 30-150 weight part is preferable with respect to 100 weight part of polylactic acid resin, 50-140 weight part is more preferable, 60-130 weight part is further more preferable.

  The polylactic acid resin composition in the present invention is an ordinary additive such as an ultraviolet absorber (benzophenone compound, benzotriazole compound, aromatic benzoate compound, oxalic acid anilide compound, as long as the object of the present invention is not impaired. Colorants including cyanoacrylate compounds and hindered amine compounds), heat stabilizers (hindered phenol compounds, phosphite compounds, thioether compounds), antistatic agents, lubricants, foaming agents, mold release agents, dyes and pigments 1 type, or 2 or more types, such as these, can further be contained.

[Step (1)]
Step (1) of the present invention is a step of melt-kneading the polylactic acid resin, the organic crystal nucleating agent of the present invention, and, if necessary, a polylactic acid resin composition containing other components as necessary in contact with a supercritical fluid.

  The supercritical fluid is a liquid obtained by compressing a gas in a supercritical state, and specifically includes carbon dioxide, water, hydrocarbons, etc. Carbon dioxide is preferred. Carbon dioxide has a critical temperature of 31.2 ° C., and at a temperature higher than that, it exhibits a supercritical state in which no phase change occurs due to pressure. When a gas in a supercritical state is compressed and the density approaches a liquid, the dissolving power increases and the solubility in the polylactic acid resin composition increases rapidly. Therefore, practically, carbon dioxide compressed at a pressure of 7 MPa or more is more preferable.

  In the step (1), as a method of melt-kneading the polylactic acid resin composition in contact with the supercritical fluid, for example, using an extruder or an injection molding machine having a supercritical fluid inlet, carbon dioxide or the like is used. Examples thereof include a method of melt-kneading the polylactic acid resin composition while press-fitting a supercritical fluid. From the viewpoint of improving the crystallization speed of the polylactic acid resin composition, the supercritical fluid is preferably pressed into the polylactic acid resin composition at a ratio of 0.1 to 10% by weight, preferably 0.5 to 8% by weight. It is more preferable to press-fit at a ratio of

  The melt kneading temperature in the step (1) is preferably 170 to 240 ° C., more preferably 170 to 220 ° C., from the viewpoint of increasing the dispersibility of the organic crystal nucleating agent and the like of the present invention and the crystallization speed. The injected supercritical fluid such as carbon dioxide is preferably mechanically kneaded with the molten polylactic acid resin composition, so that a highly concentrated supercritical fluid is uniformly added to the molten polylactic acid resin composition. Dissolve.

[Step (2)]
The step (2) of the present invention is a step of filling the mold with the melt obtained in the step (1) and molding it. The polylactic acid resin injection-molded article of the present invention is preferably non-foamed from the viewpoint of maintaining physical properties. Therefore, the expansion ratio of the polylactic acid resin injection-molded article of the present invention is preferably 1.5 times or less, more preferably 1.2 times or less, further preferably 1.1 times or less, and even more preferably 1.05 times or less. preferable. As a method for suppressing the foaming ratio of the polylactic acid resin injection-molded product of the present invention to be low, the shape of the resulting injection-molded product is designed to be thin, the injection speed is increased, or the inside of the mold is supercritical fluid supercritical fluid. In order to maintain a critical state, it is preferable to pressurize in advance with a gas such as nitrogen gas, and the pressure in the mold is preferably equal to or higher than the critical pressure of the supercritical fluid.

  The mold temperature in the step (2) is preferably from 10 to 90 ° C, more preferably from 20 to 85 ° C, from the viewpoint of improving the crystallization rate of the polylactic acid resin composition and efficiently obtaining a molded article having excellent heat resistance. 50 to 85 ° C. is more preferable.

  The present invention allows a polylactic acid resin injection molded article having excellent heat resistance to be efficiently produced in a short molding time without using a plasticizer by bringing a supercritical fluid into contact with a specific polylactic acid resin composition. It can be obtained and has a particularly excellent effect of exhibiting excellent moldability even at a lower mold temperature. The reason why the exceptional effect of the present invention can be manifested is not clear, but is considered to be due to the synergistic action of the organic crystal nucleating agent contained in the specific polylactic acid resin composition and the supercritical fluid.

Synthesis example 1 of polylactic acid resin composition
As the polylactic acid resin composition, the raw materials of the products of the present invention (A to G) and the comparative product (a) shown in Table 1 are melt-kneaded at 190 ° C. with a twin-screw extruder (PCM-45 manufactured by Ikegai Co., Ltd.). Then, strand cutting was performed to obtain pellets of the polylactic acid resin composition. The obtained pellets were dried at 70 ° C. under reduced pressure for 1 day, and the water content was adjusted to 500 ppm or less.

In addition, the raw material in Table 1 shows the following.
<Polylactic acid resin>
* 1: Polylactic acid resin (manufactured by Toyota Motor Corporation, Eco-Plastic U'zS-12)
(Optical purity 99.6%, weight average molecular weight 112000, residual monomer 173 ppm)
* 2: Polylactic acid resin (manufactured by Toyota Motor Corporation, Eco-Plastic U'zS-17)
(Optical purity 99.7%, weight average molecular weight 110000, residual monomer 327 ppm)
* 3: Polylactic acid resin (manufactured by Mitsui Chemicals, LACEA H-400)
(Optical purity 98.5%, weight average molecular weight 142000, residual monomer 1200 ppm)
<Organic crystal nucleating agent>
* 4: Decamemethylene dicarbonyl dibenzoyl hydrazide (T-1287, manufactured by ADEKA Corporation)
* 5: Xylylene bisstearyl urea (Nippon Kasei Co., Ltd., Haclean SX)
* 6: 6-methyluracil (manufactured by Wako Pure Chemical Industries, Ltd., reagent)
* 7: Melamine cyanurate (MC-6000 manufactured by Nissan Chemical Industries, Ltd.)
<Plasticizer>
* 8: Diester of succinic acid and triethylene glycol monomethyl ether obtained in Synthesis Example 1 of the following plasticizer <Hydrolysis inhibitor>
* 9: Diisopropylphenylcarbodiimide (Rhinchemy Japan Co., Ltd. Starbuxol 1-LF)
* 10: Poly (4,4′-dicyclohexylmethanecarbodiimide) (Carbodilite LA-1 manufactured by Nisshinbo Industries, Ltd.)
<Inorganic filler>
* 11: Talc (Nihon Talc Co., Ltd., MicroAceP-6)
* 12: Glass fiber (manufactured by Nippon Electric Glass Co., Ltd., ECS03T-187)
<Flame retardant>
* 13: Aluminum hydroxide (Nippon Light Metal Co., Ltd., BT703ST)

Synthesis example 1 of plasticizer
A 3 L flask equipped with a stirrer, thermometer and dehydration tube was charged with 500 g of succinic anhydride, 2463 g of triethylene glycol monomethyl ether, and 9.5 g of paratoluenesulfonic acid monohydrate, and nitrogen (500 mL / min) was blown into the space. The reaction was carried out at 4 to 10.7 kPa and 110 ° C. for 15 hours under reduced pressure. The acid value of the reaction solution was 1.6 (KOH mg / g). After adding 27 g of adsorbent Kyoward 500SH (manufactured by Kyowa Chemical Industry Co., Ltd.) to the reaction solution and stirring and filtering at 80 ° C. and 2.7 kPa for 45 minutes, the solution temperature was 115 to 200 ° C. and the pressure was 0.03 kPa. After distilling off ethylene glycol monomethyl ether and cooling to 80 ° C., the remaining liquid was filtered under reduced pressure to obtain a diester of succinic acid and triethylene glycol monomethyl ether as a filtrate. The obtained diester had an acid value of 0.2 (KOHmg / g), a saponification value of 276 (KOHmg / g), a hydroxyl value of 1 or less (KOHmg / g), and a hue of APHA200.

Examples 1-7 and Comparative Example 1
An injection molding machine with a cylinder temperature of 200 ° C. (mucell 85 tons, manufactured by Nippon Steel), which is a pellet of the polylactic acid resin composition (present invention products A to G and comparative product a) obtained in Synthesis Example 1. The supercritical fluid (supercritical carbon dioxide) at a pressure of 8 MPa is press-fitted at a concentration shown in Table 2 from a gas inlet provided in the cylinder part of the injection molding machine, and screwed. And kneaded with a polylactic acid resin composition in a molten state. The temperature in the mold attached to the tip of the injection molding machine is maintained at the temperature shown in Table 2, and the molten polylactic acid resin composition brought into contact with carbon dioxide in a supercritical state in this mold is shown in Table 2. The test piece (150 mm × 30 mm × thickness 1 mm) was obtained by injection molding at the injection pressure required for molding as shown and held until crystallization was completed. The mold holding time required for releasing the obtained test piece was evaluated according to the following criteria. These results are shown in Table 2.

<Evaluation criteria for mold holding time required for mold release>
Under the molding conditions shown in Table 2, the time required until each test piece was not deformed and taken out was determined to be the mold holding time required for mold release. Note that the higher the melt crystallization speed of the test piece in the mold and the runner part, the shorter the mold holding time required for mold release.

Comparative Examples 2-5
As shown in Table 2, the pellets of the polylactic acid resin composition (the products A to D of the present invention) obtained in Synthesis Example 1 were used, and carbon dioxide in a supercritical state was not injected, and the mold temperatures shown in Table 2 were used. A test piece was obtained in the same manner as in Example 1 except that injection molding was performed at an injection pressure required for proper molding, and the mold holding time required for mold release was evaluated in the same manner. These results are shown in Table 2.

  From the results of Table 2, the production of the present invention is compared to Comparative Example 1 that does not contain the organic crystal nucleating agent of the present invention, or Comparative Examples 2 to 5 that were not brought into contact with the supercritical fluid during melt kneading of the polylactic acid resin composition. It has been found that the method can remarkably shorten the mold holding time due to the synergistic effect of the organic crystal nucleating agent of the present invention and the supercritical fluid, and dramatically improve the moldability. The effect became more remarkable as the mold temperature was lowered. It has also been found that the injection pressure during molding is reduced by bringing the polylactic acid resin composition into contact with a supercritical fluid during melt kneading.

Examples 8 to 10, Comparative Example 6
Using the pellets of the polylactic acid resin composition obtained in Synthesis Example 1 (present products A, E, F, comparative product a), the mold temperature, supercritical carbon dioxide concentration and mold holding time shown in Table 3 Except that, injection molding was performed in the same manner as in Example 1. About the obtained test piece [flat plate (70 mm × 40 mm × 3 mm) and prismatic test piece (125 mm × 12 mm × 6 mm)], the prismatic test piece (125 mm × 12 mm × 6 mm) is subjected to a bending test and a thermal deformation temperature. (70 mm × 40 mm × 3 mm) was evaluated for relative crystallinity, bleed resistance and expansion ratio by the following methods. These results are shown in Table 3.

<Evaluation criteria for mold releasability>
A: The test piece is not deformed and can be easily taken out.
B: There is some deformation of the test piece and it is difficult to take it out.
C: The deformation of the test piece is large and does not leave the runner part.
The mold releasability becomes better as the melt crystallization speed of the test piece increases in the mold and in the runner portion.

<Bending test (rigidity)>
The prismatic test piece (125 mm × 12 mm × 6 mm) was subjected to a bending test using Tensilon (Orientec Tensilon Universal Testing Machine RTC-1210A) based on JIS K7203 to obtain the flexural modulus. Crosshead speed is 3mm / min. The higher the flexural modulus, the better the rigidity.

<Heat deformation temperature (heat resistance)>
For a prismatic test piece (125 mm x 12 mm x 6 mm), the temperature at which the heat deflection temperature measuring machine (B-32 manufactured by Toyo Seiki Seisakusho Co., Ltd.) is deflected by 0.025 mm at a load of 0.45 MPa, based on JIS-K7207. It was measured. The higher this temperature, the better the heat resistance.

<Impact resistance>
The Izod impact strength of a prismatic test piece (63 mm × 12 mm × 5 mm) was measured using an impact tester (type 863 manufactured by Ueshima Seisakusho Co., Ltd.) based on JIS-K7110. The higher the strength, the better the impact resistance.

<Relative crystallinity>
A flat test piece (70 mm x 40 mm x 3 mm) after injection molding is pulverized, precisely weighed 7.0-8.0 mg, sealed in an aluminum pan, and then used with a DSC device (Perkin Elmer Diamond DSC). The temperature is increased from 20 ° C. to 200 ° C. at a temperature increase rate of 20 ° C./min, held at 200 ° C. for 5 minutes, and then the temperature is decreased from 200 ° C. to 20 ° C. at a temperature decrease rate of −20 ° C./min. After maintaining for a minute, the temperature was further increased from 20 ° C. to 200 ° C. at a rate of temperature increase of 20 ° C./min as 2nd RUN. The absolute value ΔHcc of the cold crystallization enthalpy of the polylactic acid resin observed at 1st RUN was obtained, and the crystal melting enthalpy ΔHm observed at 2nd RUN was obtained. From the obtained value, the relative crystallinity (%) was obtained by the following formula.
Relative crystallinity (%) = {(ΔHm−ΔHcc) / ΔHm} × 100

<Bleed resistance>
The injection-molded flat plate (70 mm × 40 mm × 3 mm) was left in an oven at 80 ° C. for 1 month, and the presence or absence of organic crystal nucleating agent and / or plasticizer bleed on the surface was observed with the naked eye.

<Foaming ratio>
The expansion ratio was determined by the following formula.

  In addition, the density of the molded object was measured based on JIS K-7112 (B method: pycnometer method).

  From the results of Table 3, the production method of the present invention can achieve high crystallinity by the synergistic effect of the organic crystal nucleating agent of the present invention and the supercritical fluid, and injection of polylactic acid resin having excellent heat resistance. It turned out that a molded object is obtained.

  Moreover, the manufacturing method of this invention can acquire favorable moldability, even if it does not contain a plasticizer. This is because when the production method of the present invention contains a plasticizer, the rigidity is lowered, but good moldability can be obtained without containing a plasticizer, so that polylactic acid having a high rigidity (flexural modulus) is obtained. A resin molded body can be obtained (as can be seen from the fact that a highly rigid polylactic acid resin molded body is obtained by comparing Example 8 with Examples 9 and 10).

  Therefore, it can be seen that the production method of the present invention is an advantageous technique compared to a technique for obtaining good moldability by containing a plasticizer in a field where a highly rigid polylactic acid resin molded body is required. .

Synthesis example 2 of polylactic acid resin composition
As the polylactic acid resin composition, the raw materials of the product of the present invention (H to N) and the comparative product (b) shown in Table 4 are melt-kneaded at 230 ° C. with a twin-screw extruder (PCM-45 manufactured by Ikegai Co., Ltd.). Then, strand cutting was performed to obtain pellets of the polylactic acid resin composition. The obtained pellets were dried at 80 ° C. with a dehumidifying dryer for 5 hours, and the water content was adjusted to 500 ppm or less.

In addition, the raw material in Table 4 shows the same thing as the raw material in Table 1, and other things are shown below.
<Polylactic acid resin>
* 14: Polylactic acid resin obtained in Synthesis Example 1 of the following polylactic acid resin (poly-L-lactic acid resin)
* 15: Polylactic acid resin (poly-D-lactic acid resin) obtained in Synthesis Example 2 of the following polylactic acid resin

Synthesis example 1 of polylactic acid resin (production of poly-L-lactic acid resin)
To 100 parts by weight of L-lactide (manufactured by Musashino Chemical Laboratory, Inc., optical purity: 100%), 0.005 part by weight of octylic acid tin was added, and 180 ° C. in a reactor equipped with a stirring blade in a nitrogen atmosphere. And then reduced pressure to remove the remaining lactide, and chipped to obtain poly-L-lactic acid. The obtained poly-L-lactic acid had a weight average molecular weight of 110,000, a glass transition point (Tg) of 60 ° C., and a melting point of 166 ° C.

Synthesis example 2 of polylactic acid resin (production of poly-D-lactic acid resin)
To 100 parts by weight of D-lactide (manufactured by Musashino Chemical Laboratory, Inc., optical purity 100%), 0.005 part by weight of octylic acid tin was added, and 180 ° C. in a reactor equipped with a stirring blade under a nitrogen atmosphere. The mixture was then reacted for 2 hours and then reduced in pressure to remove the remaining lactide and chipped to obtain poly-D-lactic acid. The obtained poly-D-lactic acid had a weight average molecular weight of 110,000, a glass transition point (Tg) of 60 ° C., and a melting point of 167 ° C.

Examples 11 to 17 and Comparative Example 7
An injection molding machine (manufactured by Nippon Steel Works, Ltd. Mucell 85 tons) of pellets of the polylactic acid resin composition obtained in Synthesis Example 2 (invention products H to N and comparative product b) with a cylinder temperature of 230 ° C. Is supplied and melted, and a supercritical fluid (carbon dioxide in a supercritical state) with a pressure of 8 MPa is press-fitted at a concentration shown in Table 5 from a gas inlet provided in a cylinder portion of an injection molding machine. And kneaded with a polylactic acid resin composition in a molten state. The temperature in the mold attached to the tip of the injection molding machine was maintained at the temperature shown in Table 5, and the molten polylactic acid resin composition brought into contact with carbon dioxide in a supercritical state in this mold is shown in Table 5. The test piece (150 mm × 30 mm × thickness 1 mm) was obtained by injection molding at the injection pressure required for molding as shown and held until crystallization was completed. The mold holding time required for releasing the obtained test piece was evaluated in the same manner as in Example 1. These results are shown in Table 5.

Comparative Examples 8-11
As shown in Table 5, the pellets of the polylactic acid resin composition (Products H to K of the present invention) obtained in Synthesis Example 2 were used, and carbon dioxide in a supercritical state was not injected, and the mold temperatures shown in Table 5 were used. A test piece was obtained in the same manner as in Example 11 except that injection molding was performed at an injection pressure required for proper molding, and the mold holding time necessary for mold release was evaluated in the same manner. These results are shown in Table 5.

  From the results of Table 5, also in the stereocomplex polylactic acid resin, Comparative Example 7 not containing the organic crystal nucleating agent of the present invention, or Comparative Examples 8 to 8 which were not brought into contact with the supercritical fluid at the time of melt kneading of the polylactic acid resin composition On the other hand, it was found that the production method of the present invention can remarkably shorten the mold holding time due to the synergistic effect of the organic crystal nucleating agent of the present invention and the supercritical fluid, and dramatically improve the moldability. . The effect became more remarkable as the mold temperature was lowered. It has also been found that the injection pressure during molding is reduced by bringing the polylactic acid resin composition into contact with a supercritical fluid during melt kneading.

Examples 18-20, Comparative Example 12
Using the pellets of the polylactic acid resin composition obtained in Synthesis Example 2 (the products of the present invention H, L, M, and comparative product b), the mold temperature, supercritical carbon dioxide concentration and mold holding time shown in Table 6 Except that, injection molding was performed in the same manner as in Example 11. About the obtained test piece [flat plate (70 mm × 40 mm × 3 mm) and prismatic test piece (125 mm × 12 mm × 6 mm)], the prismatic test piece (125 mm × 12 mm × 6 mm) is subjected to a bending test and a thermal deformation temperature. (70 mm × 40 mm × 3 mm) was evaluated in the same manner as in Example 8 for relative crystallinity, bleed resistance, and expansion ratio. These results are shown in Table 6.

  From the results of Table 6, the production method of the present invention can achieve high crystallinity by the synergistic effect of the organic crystal nucleating agent of the present invention and the supercritical fluid, and injection of polylactic acid resin having excellent heat resistance. It turned out that a molded object is obtained.

  In addition, the production method of the present invention can obtain good moldability even in a stereocomplex polylactic acid resin without containing a plasticizer. This is because the manufacturing method of the present invention reduces the rigidity when a plasticizer is contained, and can obtain good moldability without containing a plasticizer, so that a stereo complex having a high rigidity (flexural modulus) is obtained. A polylactic acid resin molded body can be obtained (as can be seen from the comparison between Example 18 and Examples 19 and 20, a highly rigid polylactic acid resin molded body is obtained).

  Therefore, the production method of the present invention is an advantageous technique in a field where a stereocomplex polylactic acid resin molded body having high rigidity is required, as compared with a technique for obtaining good moldability by containing a plasticizer. I understand.

Synthesis example 3 of polylactic acid resin composition
As the polylactic acid resin composition, the present invention products (O to R) and the comparative product (c) shown in Table 7 were melt-kneaded at 240 ° C. with a twin-screw extruder (PCM-45 manufactured by Ikegai Co., Ltd.), Strand cutting was performed to obtain a pellet of a polylactic acid resin composition. The obtained pellets were dried at 80 ° C. with a dehumidifying dryer for 5 hours, and the water content was adjusted to 500 ppm or less.

In addition, the raw material in Table 7 shows the same thing as the raw material in Table 1, and other things are shown below.
<Resin>
* 15: Polylactic acid resin (Nature Works, Nature Works 4032D)
(Optical purity 98.5%, weight average molecular weight 141000, residual monomer 1200 ppm)
* 16: Polycarbonate resin (manufactured by Teijin Chemicals Ltd., Panlite L-1250Y)
(0% crystallinity, 120 ° C glass transition point)

Examples 21 to 24 and Comparative Example 13
An injection molding machine with a cylinder temperature of 220 ° C. (mucell 85 tons, manufactured by Nippon Steel Co., Ltd.) using the pellets of the polylactic acid resin composition (the present invention products O to R and comparative product c) obtained in Synthesis Example 3 The supercritical fluid (supercritical carbon dioxide) having a pressure of 8 MPa is press-fitted at a concentration shown in Table 8 from a gas inlet provided in the cylinder part of the injection molding machine, and then screwed. And kneaded with a polylactic acid resin composition in a molten state. The temperature in the mold attached to the tip of the injection molding machine was maintained at the temperature shown in Table 8, and the molten polylactic acid resin composition brought into contact with carbon dioxide in a supercritical state was stored in Table 8 in Table 8. The test piece (150 mm × 30 mm × thickness 1 mm) was obtained by injection molding at the injection pressure required for molding as shown and held until crystallization was completed. The mold holding time required for releasing the obtained test piece was evaluated in the same manner as in Example 1. These results are shown in Table 8.

Comparative Examples 14-17
As shown in Table 8, the pellets of the polylactic acid resin composition (Products O to R of the present invention) obtained in Synthesis Example 3 were used, and carbon dioxide in a supercritical state was not injected, and the mold temperatures shown in Table 8 were used. A test piece was obtained in the same manner as in Example 21 except that injection molding was performed at an injection pressure necessary for proper molding, and the mold holding time necessary for mold release was evaluated in the same manner. These results are shown in Table 8.

  From the results of Table 8, even in a mixed system of polylactic acid resin and other thermoplastic resin, Comparative Example 13 not containing the organic crystal nucleating agent of the present invention, or a supercritical fluid at the time of melt kneading of the polylactic acid resin composition Compared with Comparative Examples 14 to 17 which were not brought into contact, the production method of the present invention can remarkably shorten the mold holding time due to the synergistic effect of the organic crystal nucleating agent of the present invention and the supercritical fluid, and the moldability is greatly improved. It was found that it improved. The effect became more remarkable as the mold temperature was lowered. It has also been found that the injection pressure during molding is reduced by bringing the polylactic acid resin composition into contact with a supercritical fluid during melt kneading.

Examples 25-28, Comparative Example 18
Using the pellets of the polylactic acid resin composition (the products O to R of the present invention, comparative product c) obtained in Synthesis Example 3, the mold temperature, supercritical carbon dioxide concentration and mold holding time shown in Table 9 are set. Except that, injection molding was carried out in the same manner as in Example 21. About the obtained test piece [flat plate (70 mm × 40 mm × 3 mm) and prismatic test piece (125 mm × 12 mm × 6 mm)], the prismatic test piece (125 mm × 12 mm × 6 mm) is subjected to a bending test and a thermal deformation temperature. (70 mm × 40 mm × 3 mm) was evaluated in the same manner as in Example 8 for relative crystallinity, bleed resistance, and expansion ratio. These results are shown in Table 9.

  From the results of Table 9, the production method of the present invention can achieve high crystallinity by the synergistic effect of the organic crystal nucleating agent of the present invention and the supercritical fluid, and injection of polylactic acid resin having excellent heat resistance. It turned out that a molded object is obtained.

  Further, the production method of the present invention can obtain a good moldability even in a mixed system of a polylactic acid resin and another thermoplastic resin without containing a plasticizer and has a high crystallinity. High heat resistance is obtained by blending with lactic acid and other thermoplastic resins having a high Tg. This is because when the production method of the present invention contains a plasticizer, the rigidity is lowered, and even if it does not contain a plasticizer, good formability can be obtained while crystallizing polylactic acid. A polylactic acid resin molded article having a high (flexural modulus) can be obtained (as can be seen from the comparison between Examples 25 to 27 and Example 28, a highly rigid polylactic acid resin molded article is obtained). .

  Accordingly, the production method of the present invention is a polylactic acid resin molded article containing another high-rigidity, high-Tg thermoplastic resin, and contains a plasticizer in a field where higher heat resistance and rigidity are required. It can be seen that this is an advantageous technique compared to a technique for obtaining good moldability while crystallizing polylactic acid.

  The polylactic acid resin composition in the present invention can be suitably used for various industrial applications such as daily goods, household appliance parts, automobile parts and the like.

Claims (6)

The manufacturing method of the polylactic acid resin injection molding which has the following process (1) and process (2).
Step (1): A polylactic acid resin composition containing a polylactic acid resin and at least one organic crystal nucleating agent selected from the group consisting of carbohydrazides, melamine compounds, uracils and N-substituted ureas, Step (2) of melt-kneading while making contact with the supercritical fluid: Step of filling the melt obtained in step (1) into a mold and injection molding with a foaming ratio of 1.1 times or less The method for producing a polylactic acid resin injection-molded article according to claim 1, wherein in the step (2), the injection molding is carried out at a foaming ratio of 1.05 or less. The method for producing a polylactic acid resin injection-molded article according to claim 1 or 2 , wherein the polylactic acid resin composition contains 0.01 to 5 parts by weight of an organic crystal nucleating agent with respect to 100 parts by weight of the polylactic acid resin. The method for producing a polylactic acid resin injection-molded article according to any one of claims 1 to 3 , wherein the supercritical fluid is brought into contact with the polylactic acid resin composition at a ratio of 0.1 to 10% by weight. The method for producing a polylactic acid resin injection-molded article according to any one of claims 1 to 4 , wherein the mold temperature in the step (2) is 10 to 90 ° C. The polylactic acid resin composition further contains a plasticizer, and the content ratio of the organic crystal nucleating agent and the plasticizer to the polylactic acid resin composition (organic crystal nucleating agent / plasticizer) is 1/10 to 5/1. The manufacturing method of the polylactic acid resin injection molding in any one of Claims 1-5 .