JP7706318B2 - Polylactic acid resin composition - Google Patents

Description

The present invention relates to a polylactic acid resin composition.

Polylactic acid is a plant-derived resin and is known as a biodegradable resin. Polylactic acid is sometimes crystallized before use to improve its heat resistance, but this polylactic acid has a slow crystallization rate, which results in low productivity during molding, such as a long molding cycle during injection molding.

In addition, attempts have been made to obtain molded bodies with improved properties by blending various fillers into resin compositions. Blending fillers at high concentrations is extremely difficult due to production problems (e.g., a feed neck when feeding filler into a kneader) and filler dispersibility problems. For example, Patent Document 1 discloses a method of obtaining a resin composition by mixing polylactic acid and a filler, but even when the amount of filler blended is about 30% by weight, it is not easy to perform stable melt-kneading with high productivity due to the feed neck.

Furthermore, polylactic acid resin compositions inherently have issues with impact resistance due to the properties of polylactic acid, and when fillers are blended at high concentrations, there is a problem that impact resistance is further reduced.

JP 2004-352844 A

As described above, conventional polylactic acid resin compositions, which have difficulty in containing a high concentration of filler, have the problem that the filler-attributable properties (e.g., rigidity, heat resistance, shape stability) are not fully exhibited. The present invention has been made to solve this problem, and its object is to provide a polylactic acid resin composition that has excellent filler-attributable properties, such as excellent properties such as impact resistance, and also has excellent productivity during molding (e.g., shortened molding cycle), and a method for producing the same.

The polylactic acid resin composition of the present invention is a polylactic acid resin composition comprising a polylactic acid resin, a filler, an impact resistance modifier, and a filler dispersant and/or a filler dispersion polymer, wherein the content of the filler in the polylactic acid resin composition is 20% by weight to 60% by weight, and the content of the impact resistance modifier in the polylactic acid resin composition is 5% by weight to 50% by weight.
In one embodiment, the impact resistance improver is at least one selected from the group consisting of an aliphatic polyester resin, an aliphatic-aromatic polyester resin, a polyvinyl alcohol resin, and a natural rubber.
In one embodiment, the filler dispersing agent is at least one selected from the group consisting of polyhydric alcohol fatty acid esters, fatty acid amides, polyglycerin fatty acid esters, condensed hydroxy fatty acids, and alcohol esters of condensed hydroxy fatty acids.
In one embodiment, the filler dispersion polymer is at least one selected from the group consisting of polyolefin-based resins, polystyrene-based resins, polyvinyl alcohol-based resins, polyalkylene glycol-based resins, polyvinylpyrrolidone-based resins, polyester-based resins, polyamide-based resins, acrylic-based resins, urethane-based resins, epoxy-based resins, and water-soluble polysaccharides.
In one embodiment, the filler dispersion polymer is at least one selected from the group consisting of polyvinyl alcohol-based resins, polyalkylene glycol-based resins, polyvinylpyrrolidone-based resins, and water-soluble polysaccharides.
In one embodiment, the total content of the filler dispersant and the filler dispersion polymer in the polylactic acid resin composition is 0.1% by weight to 30% by weight.
In one embodiment, the filler is at least one selected from talc and mica.
In one embodiment, the polylactic acid resin composition further contains a hydrolysis inhibitor.
In one embodiment, the hydrolysis inhibitor is a compound having at least one functional group selected from the group consisting of a carbodiimide group, an oxazoline group, and an epoxy group.
According to another aspect of the present invention, there is provided a method for producing the polylactic acid resin composition, comprising melt-kneading a polylactic acid resin, a filler granule, and an impact resistance improver, the filler granule containing the filler, the filler dispersant, and/or the filler dispersion polymer, and the filler content in the filler granule is 80 to 99.9 parts by weight per 100 parts by weight of the filler granule.
According to yet another aspect of the present invention, there is provided an injection-molded article, which is formed from the above-mentioned polylactic acid resin composition.
According to yet another aspect of the present invention, there is provided an extrusion molded article formed from the above-mentioned polylactic acid resin composition.
According to yet another aspect of the present invention, there is provided a sheet-shaped material, which is formed from the above-mentioned polylactic acid resin composition.

The present invention provides a polylactic acid resin composition that has excellent filler-attributable properties, such as excellent impact resistance, and also has excellent productivity during molding (e.g., shortened molding cycle), as well as a method for producing the same.

A. Polylactic acid resin composition A-1. Overview of polylactic acid resin composition The polylactic acid resin composition of the present invention contains a polylactic acid resin, a filler, an impact modifier, and a filler dispersant and/or a filler dispersion polymer. The filler content in the polylactic acid resin composition is 20% by weight to 60% by weight. The impact modifier content in the polylactic acid resin composition is 5% by weight to 50% by weight. In this specification, the content ratios of components in the polylactic acid resin composition, including the "filler content ratio in the polylactic acid resin composition" and the "impact modifier content ratio", are weight ratios based on the total solid content in the polylactic acid resin composition.

The polylactic acid resin composition of the present invention contains a high content of filler with good uniformity, so that it is possible to form a molded product with excellent mechanical properties (for example, rigidity, dimensional stability (low molding shrinkage rate, low linear expansion coefficient, low warpage)) even though it is mainly composed of polylactic acid resin. In addition, the polylactic acid resin composition can be advantageously used from the viewpoints of heat resistance (heat distortion temperature resistance), appearance, colorability (ability to be colored to bright colors), filler dispersion, and composition uniformity. In particular, the polylactic acid resin composition is advantageous in that it has a good balance of rigidity, heat resistance, and impact resistance. In addition, the polylactic acid resin composition also has an excellent production speed when manufactured by melt kneading.

In addition, in the above polylactic acid resin composition, the crystallization rate of the polylactic acid resin is fast, and the moldability during injection molding is excellent, and the molding cycle can be shortened. The degree of crystallization of the polylactic acid resin composition can be evaluated by differential scanning calorimetry (DSC). Here, differential scanning calorimetry is a method for measuring the endothermic heat of melting of polylactic acid crystals and the exothermic heat of recrystallization in a series of operations in which 5 to 10 mg of a sample is heated from room temperature to 200 ° C at a constant heating rate, held at 200 ° C for 5 minutes, and then cooled to room temperature under a constant cooling rate condition. Here, the faster the heating peak of recrystallization in the cooling process occurs at a faster cooling rate or in a higher temperature region, the more crystallization becomes possible during molding, and the molding speed (molding cycle) can be increased. In the above polylactic acid resin composition, the exothermic peak derived from this crystallization is preferably 10 J/g or more in polylactic acid equivalent, more preferably 20 J/g or more, and even more preferably 25 J/g or more. If the exothermic peak due to this crystallization is 10 J/g or more in terms of polylactic acid, excellent heat resistance can be exhibited as the crystallization progresses. Note that the term "polylactic acid equivalent" used here refers to the value obtained by dividing the heat generation amount of the exothermic peak by the content of polylactic acid contained in the resin composition sample.

The polylactic acid resin composition of the present invention, which has the above-mentioned excellent properties, can be obtained, for example, by forming a filler granule containing the above-mentioned filler and a filler dispersant and/or a filler dispersion polymer, and then mixing the filler granule with a polylactic acid resin (for example, by melt kneading). By adopting such a manufacturing method, the workability of adding the filler and the filler dispersibility are significantly improved, making it possible to incorporate a high content of filler.

In one embodiment, a molded article is provided that is formed from the polylactic acid resin composition. The molded article has a flexural modulus at 23°C of preferably 3 GPa or more, more preferably 5 GPa or more, and even more preferably 7 GPa or more. The flexural modulus is measured in accordance with ISO 178. The molded article can be obtained, for example, by injection molding using pellets of the polylactic acid resin composition, as described below.

The deflection temperature under load of the molded article formed from the polylactic acid resin composition at a load of 0.45 MPa is preferably 90°C or higher, more preferably 100°C or higher, even more preferably 110°C or higher, and particularly preferably 120°C or higher. The deflection temperature under load is measured in accordance with ISO 75 using a dumbbell-shaped test piece (type 1A multipurpose test piece).

The tensile strength at 23°C of the molded article formed from the polylactic acid resin composition is preferably 35 MPa or more, more preferably 40 MPa or more, and even more preferably 50 MPa or more. The tensile strength and the judgment elongation described below are measured using a dumbbell-shaped test piece (type 1A multipurpose test piece) in accordance with ISO527 at a tensile speed of 5 mm/min.

In the above polylactic acid resin composition, the higher the temperature at which the exothermic peak of recrystallization occurs during the cooling process, the shorter the molding cycle can be, which is preferable. According to the above-mentioned DSC measurement, when the temperature is lowered from 200°C at a rate of 10°C/min, the exothermic peak of recrystallization is preferably 95°C or higher, more preferably 100°C or higher, and even more preferably 105°C or higher.

A-2. Polylactic acid resin Any suitable polylactic acid resin can be used as the polylactic acid resin. Polylactic acid resins can have the same properties as synthetic resins under normal use environments, can be used in the same conditions as synthetic resins, and exhibit degradability in specific waste environments.

The polylactic acid resin may be a copolymer containing structural units derived from lactic acid, in addition to polylactic acid (homopolymer). In one embodiment, the polylactic acid resin may be a copolymer of lactic acid and a hydroxycarboxylic acid. Examples of hydroxycarboxylic acids include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, and 6-hydroxycaproic acid. As the polylactic acid resin, a polylactic acid resin having a high L-lactic acid ratio is preferably used because it has a high melting point. The L-lactic acid ratio of the polylactic acid resin is preferably 96% or more, more preferably 98% or more, and even more preferably 98.6% or more.

The content of polylactic acid resin in the polylactic acid resin composition is preferably 29.8% by weight to 73% by weight, more preferably 35% by weight to 70% by weight, even more preferably 40% by weight to 68% by weight, and particularly preferably 45% by weight to 65% by weight.

A-3. Filler As the filler, any appropriate filler can be used depending on the desired characteristics.

The properties and effects that can be imparted by the above fillers include, for example, weight increase or weight reduction, reinforcement (high rigidity, high elasticity, high strength), dimensional stability, molding cycle (crystallization rate), crystallinity, thermal conductivity, electrical conductivity, magnetism, piezoelectricity, vibration damping, sound insulation, sliding properties, heat insulation, electromagnetic wave absorption, light reflectivity, light scattering, heat radiation, flame retardancy, radiation protection, UV protection, moisture removal, dehydration, deodorization, gas absorption, gas barrier, anti-blocking, oil absorption, antibacterial properties, biodegradation promotion, improved bio content (increased proportion of naturally derived ingredients), etc.

For example, calcium carbonate, talc, silica, and clay are suitable for increasing the weight. For reinforcing purposes, wollastonite, potassium titanate, xonotlite, gypsum fiber, aluminum borate, fibrous magnesium compound (MOS), aramid fiber, various fiber systems, carbon fiber, glass fiber, talc, mica, glass flakes, polyoxybenzoyl whiskers, and the like are suitable. For providing antibacterial properties, catechin, silver ion-supported zeolite, copper phthalocyanine, and the like are suitable. For providing gas barrier properties, synthetic mica systems, clay/synthetic mica nanofillers, and the like are suitable. For reducing weight, balloon systems such as silica balloons, glass balloons, cenospheres, perlite, and shirasu balloons are suitable. For providing electrical conductivity, carbon black, graphite, carbon fiber, metal powder, metal fiber, and metal foil are suitable. For the purpose of imparting magnetism, various magnetic materials, various ferrites, magnetic iron oxide, samacobalt (Sm-Co), Nd-Fe-B, etc. are suitable. For the purpose of imparting thermal conductivity, alumina, AlN, BN, BeO, etc. are suitable. For the purpose of imparting piezoelectricity, barium titanate, lead zirconate titanate (PZT), etc. are suitable. For the purpose of imparting vibration damping properties, mica, graphite, potassium titanate, xonotlite, carbon fiber, ferrite, etc. are suitable. For the purpose of imparting sound insulation properties, iron powder, lead powder, barium sulfate, etc. are suitable. For the purpose of imparting sliding properties, graphite, hexagonal BN, molybdenum sulfide, Teflon (registered trademark) powder, talc, high molecular weight polyethylene, etc. are suitable. For the purpose of imparting electromagnetic wave absorption, electromagnetic wave absorbing ferrite, graphite, charcoal powder, carbon microcoil (CMC), carbon nanotube (CNT), PZT, etc. are suitable. For the purpose of imparting light reflection and light scattering, titanium oxide, glass beads, calcium carbonate, aluminum powder, mica, etc. are suitable. For the purpose of imparting heat radiation, magnesium oxide, hydrotalcite, MOS, alumina, charcoal powder, etc. are suitable. For the purpose of flame retardancy, antimony oxide, aluminum hydroxide, magnesium hydroxide, zinc borate, red phosphorus, zinc carbonate, hydrotalcite, dawsonite, bromine-based flame retardants, phosphorus-based flame retardants, etc. are suitable. For the purpose of radiation protection, lead powder, barium sulfate, etc. are suitable. For the purpose of "ultraviolet light protection", titanium oxide, zinc oxide, iron oxide, etc. are suitable. For the purpose of dehumidification and dehydration, calcium oxide, magnesium oxide, etc. are suitable. For the purpose of deodorization and gas absorption, zeolite, activated clay, etc. are suitable. For the purpose of anti-blocking (prevention of film adhesion), silica, calcium carbonate, talc, spherical particles (silicone or acrylic beads), etc. are suitable. For the purpose of oil absorption (printing ink absorption, quick drying, etc.), algae-shaped calcium carbonate, algae-shaped xonotlite, etc. are suitable. For the purpose of water absorption, water-absorbing polymer gel, calcium oxide, magnesium oxide, etc. are suitable. For the purpose of improving the bio content, cellulosic materials (wood flour, wood fiber, sawdust, wood chips, newsprint, paper, flax, hemp, wheat straw, rice husk, kenaf, jute, sisal, peanut shells, soybean husks, etc.), starch, etc. are suitable.

The size of the filler can be any appropriate size. The particle size of the filler is, for example, 10 nm to 100 μm. The size of the filler can be determined by a laser diffraction method.

In one embodiment, a silicate compound is used as the filler. Examples of silicate compounds that can be preferably used include talc, mica, and wollastonite. In one embodiment, the filler is at least one selected from talc and mica. Talc is particularly preferred. The silicate compound not only acts as a reinforcing material for the polylactic acid resin composition, but also acts as a crystallization nucleating agent for polylactic acid. The use of the silicate compound increases the degree of crystallization of polylactic acid and at the same time increases the crystallization rate. As a result, the heat resistance of the polylactic acid resin composition can be increased, and the solidification time can be shortened, making it possible to improve moldability.

As described above, the filler content in the polylactic acid resin composition is 20% to 60% by weight. The filler content in the polylactic acid resin composition is preferably 25% to 55% by weight, and more preferably 30% to 50% by weight.

A-4. Impact modifiers Impact modifiers are additives used to improve the impact strength of polylactic acid resins by compensating for their brittleness, embrittlement, notch sensitivity, and crack propagation. For example, the impact modifier may be a rubber-like material. By dispersing the rubber material in the polylactic acid resin in the form of domains or microdomains, it is possible to absorb or dissipate impact energy and improve impact resistance and/or toughness.

Examples of the impact resistance improver include aliphatic polyester resins (e.g., homopolymers or copolymers of polycaprolactone, polyethylene succinate, polybutylene succinate adipate, polyhydroxyvalerate, etc., or modified products of these homopolymers or copolymers), aliphatic/aromatic polyester resins (e.g., block polymers or random polymers of aliphatic carboxylic acids or hydroxy acids, aromatic dicarboxylic acids and 1,3-propanediol, etc.), polyvinyl alcohol resins (e.g., polyvinyl alcohol, polyvinyl acetate, polyvinyl butyrate, ethylene-vinyl alcohol copolymers, etc.). Naturally derived biodegradable resins include natural rubber, eucommia elastomer, etc. In one embodiment, the impact resistance improver is at least one selected from the group consisting of aliphatic polyester resins, aliphatic/aromatic polyester resins, polyvinyl alcohol resins, and natural rubber. These resins may be biodegradable resins. In one embodiment, polybutylene adipate terephthalate (PBAT) resin and/or amorphous polyhydroxyalkanoate (amorphous PHA) are preferably used.

In one embodiment, polyolefin elastomers, SEBS, SEPS, core-shell rubber, and the like can be preferably used as impact modifiers. Core-shell rubber is a rubber particle having a rubber core and a polymer shell. In one embodiment, the rubber has a submicron particle size from the viewpoint of imparting toughness. In addition, the polymer shell can provide adhesion and compatibility with the resin component (thermoplastic matrix).

The content of the impact modifier in the polylactic acid resin composition is preferably 5% to 50% by weight, more preferably 10% to 45% by weight, and even more preferably 15% to 40% by weight.

A-5. Filler dispersant In one embodiment, the filler dispersant is a compound composed of a hydrophobic group and a hydrophilic group. The hydrophilic/hydrophobic balance can be controlled by adjusting the degree of esterification of the compound to be the filler dispersant, the type of fatty acid (presence or absence of a hydroxyl group, saturated or unsaturated fatty acid, alkyl chain length), and the degree of polymerization. By using the filler dispersant, it is possible to increase the dispersibility of the filler in the polylactic acid resin composition, and also to improve the productivity (discharge speed) in the production of the filler granules described below, and also to improve the cleanability of the processing machine.

Examples of the filler dispersant include fatty acids, fatty acid metal salts, fatty acid sulfonates, fatty acid amides, acrylamides, polyhydric alcohol fatty acid esters, polyglycerin fatty acid esters, etc. One type of filler dispersant may be used alone, or two or more types may be used in combination.

In one embodiment, the filler dispersant is at least one selected from the group consisting of polyhydric alcohol fatty acid esters, fatty acid amides, polyglycerin fatty acid esters, condensed hydroxy fatty acids, and alcohol esters of condensed hydroxy fatty acids.

The polyhydric alcohol fatty acid ester is an ester compound composed of a polyhydric alcohol and a fatty acid. Examples of polyhydric alcohol fatty acid esters include esters of polyhydric alcohols such as pentaerythritol and glycerin and fatty acids having 8 or more carbon atoms (preferably 8 to 24 carbon atoms, more preferably 10 to 22 carbon atoms).

The fatty acid amide is a compound having a structure formed by dehydration condensation of a fatty acid with ammonia or a primary or secondary amine. Examples of the fatty acid amide include saturated fatty acid monoamides such as lauric acid amide, palmitic acid amide, stearic acid amide, and behenic acid amide.

The polyglycerol fatty acid ester is an ester compound composed of polyglycerol and a fatty acid. Examples of polyglycerol fatty acid ester include diglycerol palmitate, diglycerol stearate, diglycerol oleate, decaglycerol palmitate, decaglycerol stearate, and decaglycerol oleate.

The polyglycerol fatty acid ester, condensed hydroxy fatty acid, and alcohol ester of condensed hydroxy fatty acid may be commercially available products. Examples of commercially available products include "Chirabazole P-4", "Chirabazole VR-01", "Chirabazole VR-08" (polyglycerol fatty acid ester), and "Chirabazole H-818" (alcohol ester of condensed hydroxy fatty acid), all manufactured by Taiyo Kagaku Co., Ltd. These may be used alone or in combination of two or more types.

The content of the filler dispersant in the polylactic acid resin composition is preferably 0.1% by weight to 15% by weight, more preferably 1% by weight to 10% by weight, and even more preferably 1% by weight to 5% by weight.

The total content of the filler dispersant and the filler dispersion polymer in the polylactic acid resin composition is preferably 0.1% by weight to 30% by weight, more preferably 1% by weight to 25% by weight, and even more preferably 1% by weight to 15% by weight. Within such a range, a resin composition having excellent filler-attributable properties can be obtained, and a polylactic acid resin composition having excellent productivity and filler dispersibility can be obtained. Note that the "total content of the filler dispersant and the filler dispersion polymer" means the content of the filler dispersion polymer when the polylactic acid resin composition does not contain a filler dispersant, and means the content of the filler dispersant when the polylactic acid resin composition does not contain a filler dispersion polymer.

A-6. Filler Dispersing Polymer The polylactic acid resin composition may contain a filler dispersing polymer for the purpose of increasing the dispersibility of the filler. The filler dispersing polymer may also have the effect of improving the interfacial adhesion between the filler and the polylactic acid resin.

The filler dispersion polymer may be at least one selected from the group consisting of polyolefin resins, polystyrene resins, polyvinyl alcohol resins, polyalkylene glycol resins, polyvinylpyrrolidone resins, polyester resins, polyamide resins, acrylic resins, urethane resins, epoxy resins, and water-soluble polysaccharides. In one embodiment, the filler dispersion polymer is at least one selected from the group consisting of polyvinyl alcohol resins, polyalkylene glycol resins, polyvinylpyrrolidone resins, and water-soluble polysaccharides. These resins are particularly preferably used because they have excellent compatibility with polylactic acid resins, excellent filler dispersion function, and are themselves biodegradable.

Specific examples of the polyvinyl alcohol resin used as a filler dispersion polymer include ethylene-vinyl alcohol copolymer (EVOH; EVAL (registered trademark) manufactured by Kuraray Co., Ltd.) and butenediol-vinyl alcohol copolymer (BVOH; Nichigo G-Polymer (registered trademark) manufactured by Mitsubishi Chemical Corporation).

The water-soluble polysaccharides refer to water-soluble compounds formed by long chains of monosaccharides such as glucose and mannose. In one embodiment, the water-soluble polysaccharides are water-soluble carbohydrates formed by the binding of 10 or more monosaccharides. In one embodiment, the water-soluble polysaccharides may be naturally derived polymeric substances. For example, water-soluble polysaccharides derived from plants (seeds, sap, fruits, etc.), seaweed, and microorganisms may be used. Specific examples of the water-soluble polysaccharides include pullulan, dextrin, chitosan, tamarind seed gum, guar gum, locust bean gum, gum arabic, karaya gum, pectin, cellulose, konjac mannan, soybean polysaccharides, carrageenan, agar, tragacanth gum, alginic acid, xanthan gum, gellan gum, Agrobacterium succinoglycan, carboxymethylcellulose, and cationized guar gum. Among these, pullulan or dextrin is preferred, and pullulan is more preferred.

Commercially available products may be used as the filler dispersion polymer. Examples of commercially available products include Chemipearl (registered trademark) manufactured by Mitsui Chemicals, Inc., HYPOD (registered trademark) manufactured by Dow Chemical Company, AQUACER (registered trademark) manufactured by BYK Japan, ZAIKXEN (registered trademark) manufactured by Sumitomo Seika Chemicals, Saiden Glue (registered trademark) manufactured by Saiden Chemical, Inc., and Saibinol (registered trademark) manufactured by Saiden Chemical, Inc.

The content of the filler dispersion polymer in the polylactic acid resin composition is preferably 0.1% by weight to 15% by weight, more preferably 1% by weight to 10% by weight, and even more preferably 1% by weight to 5% by weight.

A-7. Hydrolysis Inhibitor The hydrolysis inhibitor may be blended for the purpose of improving the processing stability, long-term heat resistance, and long-term wet heat resistance of the polylactic acid resin composition. The hydrolysis inhibitor has the function of suppressing the decrease in the molecular weight of the polylactic acid resin and stabilizing it by capturing the carboxylic acid generated by the hydrolysis of the polylactic acid resin.

In one embodiment, the hydrolysis inhibitor is a compound having at least one functional group selected from the group consisting of a carbodiimide group, an oxazoline group, and an epoxy group. The compound may be a polymer.

Examples of compounds containing the carbodiimide group include dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, t-butylisopropylcarbodiimide, diphenylcarbodiimide, di-t-butylcarbodiimide, di-β-naphthylcarbodiimide, N,N'-di-2,6-diisopropylphenylcarbodiimide, 2,6,2',6'-tetraisopropyldiphenylcarbodiimide, as well as cyclic carbodiimides and polycarbodiimides such as Carbodilite (registered trademark: manufactured by Nisshinbo Chemical Inc.) and Stavaxol (registered trademark: manufactured by Rhein Chemie AG).

Examples of commercially available products of the above-mentioned compounds having epoxy groups include "Celloxide 2021P" manufactured by Daicel Corporation, "Denacol" manufactured by Nagase ChemteX Corporation, and "Epofriend" manufactured by Daicel Corporation.

An example of a commercially available compound having the above oxazoline group is "Epocross" manufactured by Nippon Shokubai Co., Ltd.

The content of the hydrolysis inhibitor in the polylactic acid resin composition is preferably 0.1% to 5% by weight, more preferably 0.3% to 4% by weight, and even more preferably 0.5% to 3% by weight.

A-8. Other components The polylactic acid resin composition may further contain any appropriate other components (additives) as necessary. Examples of additives include antioxidants, light stabilizers, foaming agents, ultraviolet absorbers, antiblocking agents, heat stabilizers, antibacterial agents, compatibilizers, plasticizers, tackifiers, processing aids, lubricants, coupling agents, flame retardants, oxygen scavengers, colorants, and the like. The additives may be added at any appropriate time in the production process of the polylactic acid resin composition, for example, in the form of liquid, powder, pellets, granules, or in the form of a master batch.

B. Method for Producing a Polylactic Acid Resin Composition In one embodiment, the polylactic acid resin composition can be obtained by melt-kneading the polylactic acid resin, the filler, the filler dispersant and/or the filler dispersion polymer, and the impact resistance improver. Any appropriate method can be adopted as the melt-kneading method. For example, a kneader, a Banbury mixer, a roll, or a single-screw or multi-screw extruder having two or more screws can be used. Preferably, a twin-screw extruder is used. The melt-kneaded composition can be pelletized. In one embodiment, the melt-kneading is performed in a temperature range of 80°C to 170°C (preferably 100°C to 160°C).

In one embodiment, the polylactic acid resin composition is obtained by melt-kneading the filler granules containing the filler and the filler dispersant and/or filler dispersion polymer, and then melt-kneading the filler granules with the polylactic acid resin and the impact resistance improver. By adopting such a manufacturing method, the workability of adding the filler and the filler dispersibility are significantly improved, making it possible to contain a high content of filler. More specifically, since the filler granules are extremely stable when put into an extruder or other device, the productivity (compound processing speed per hour) of the filler-containing resin composition can be dramatically improved by using the filler granules. Furthermore, when the filler granules are used, the filler dispersibility and molding processability (fluidity) are improved, so that the polylactic acid resin composition obtained using the filler granules can be obtained by melt-kneading by low-load extrusion, i.e., melt-kneading in which excessive heat generation of the resin is suppressed, even though the filler is contained at a high concentration. As a result, the polylactic acid resin composition has excellent mechanical properties and moldability, with the thermal degradation of the resin suppressed. The impact modifier can also be added during the granulation process of the filler granules. In particular, when the impact modifier has a powder shape (e.g., core-shell rubber), the impact modifier can be included in the filler granules.

(Filler granules)
The filler granules can be produced by any suitable method. The filler granules can be obtained, for example, by subjecting a mixture containing the filler, the filler dispersant and/or the binder component to a semi-wet granulation method. More preferably, the filler granules can be obtained by subjecting a mixture containing the filler, the filler dispersant and the binder component to a semi-wet granulation method. The filler and filler dispersant described in Section A can be used.

The content of the filler in the filler granules is preferably 80 to 99.9 parts by weight, more preferably 82 to 99 parts by weight, even more preferably 85 to 98 parts by weight, particularly preferably 87 to 97 parts by weight, and most preferably 90 to 96 parts by weight, per 100 parts by weight of the filler granules.

In one embodiment, the filler dispersion polymer is mixed in the form of a polymer liquid (polymer solution or polymer dispersion) containing the filler dispersion polymer.

In one embodiment, the method for producing the filler granules includes a mixing step of mixing the filler with the filler dispersion polymer component and/or the filler dispersant, a granulation step of granulating the mixture obtained through the mixing step to obtain a granule precursor, and a drying step of drying the granule precursor.

In the above mixing step, water may be further mixed. The water to be added is not particularly limited, and for example, tap water, distilled water, ion-exchanged water, hard water, soft water, etc. can be used.

The amount of water mixed is usually 1 to 30 parts by weight, preferably 3 to 25 parts by weight, and more preferably 5 to 20 parts by weight, per 100 parts by weight of filler in the filler granules.

In the mixing process, it is preferable to mix the components at room temperature and homogenize them using any suitable mixer. Examples of mixers include a Henschel mixer, a powder kneader (KDH, KDA, CKD, CPM) (Dalton), a Spartan mixer (SPM) (Dalton), and a SP granulator (SPG) (Dalton).

The mixing time in the mixing process can be any appropriate time depending on the type of components, the type of mixer, the component blending ratio, etc. In the mixing process, the mixing time is set so that each component is uniformly dispersed. With a high-speed mixer such as a Henschel mixer or Spartan mixer, the process can be carried out in a processing time of 1 to 10 minutes. On the other hand, with a powder kneader, a processing time of several minutes to 60 minutes may be required.

In the granulation step, a compression granulation method is preferably used. In addition, in the granulation step, a semi-wet granulation method can be preferably used. Examples of the compression granulation method/semi-wet granulation method include a disk pelleting method, a tableting method, and a briquetting method.
From the viewpoint of the balance between productivity and the quality of the resulting filler granules, the disk pelletizer method is preferably adopted.

The basic structure of a disk pelletizer is one or two disks with many holes of 2 mm to 30 mm, and a roller for pressure-feeding the raw material into the holes of the disk. The raw material supplied between the disk and the roller, or between the two disks, is pressed into the holes of the disk as the roller rotates, forming a cylindrical extrudate. The disk holes are tapered, and as the filler mixture passes through the holes, a compressive stress is applied from the outer periphery of the die hole. The length of this tapered hole is called the effective length. The extruded granulated material precursor is cut by a cutter or the like on the back side of the disk to obtain pellet-shaped filler granulated material. The length of the granulated material precursor (resulting in the filler granulated material) can be adjusted by the distance between the back side of the disk and the cutter, and the number of rotations of the roller.

Specific examples of the disc pelleter system include the roller disc die system, roller ring die system, double die system, and flat die system. An example of a commercially available disc pelleter system granulator is the Disc Pellet F Series manufactured by Dalton.

Any suitable method can be used as the drying method in the drying step. After the drying step, the filler granules from which fine powder has been removed can be obtained using a vibrating sieve or the like. Any suitable drying equipment can be used in the drying step. For example, a vibrating fluidized dryer is preferred because it can perform drying efficiently in a short time, and examples of such equipment include the VDF series vibrating fluidized dryers manufactured by Dalton.

In the present invention, various molded articles are provided using the polylactic acid resin composition. For example, injection molded articles, extrusion molded articles, sheets, 3D printer shaped articles, etc. can be provided. Furthermore, shaped articles (vacuum molded articles, press molded articles, sheet-like shaped articles, etc.) can be obtained from the sheets.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Note that parts and percentages are based on weight unless otherwise specified.

[Production Example 1] Production of filler granule MB-1 20 parts by weight of a filler dispersion polymer (polyolefin aqueous dispersion (aqueous PE dispersion); manufactured by Mitsui Chemicals, Inc., product name "Chemipearl A100"; polyolefin solids concentration: 40% by weight; average particle size of polyolefin particles: 4 μm; in the table, "D-1") and 3 parts by weight of a filler dispersant (polyglycerol condensed hydroxy fatty acid ester; manufactured by Taiyo Kagaku Co., Ltd., product name "Chirabazol H818"; in the table, "C-1") were placed in a 1 L plastic container and stirred for 20 minutes at room temperature using a stirring blade to obtain a mixture A.
Next, 100 parts by weight of a filler (talc powder, manufactured by Asada Flour Milling Co., Ltd., product name "JM-300"; in the table, "B-1") was added to a powder kneader (KDHJ-10), and while stirring with a stirring blade at a rotation speed of 30 rpm, mixture A was added to the powder kneader. Thereafter, stirring was carried out for 6 minutes to obtain mixture B.
Mixture B was fed into a disk pelleter (manufactured by Dalton, product name "Disc Pelleter F-5/11-175") to obtain a pellet-shaped granulated precursor. At this time, the die hole diameter was 3 mmφ, the die plate thickness was 15 mm, the effective length of the die hole was 10 mm, and the roller rotation speed of the disk pelleter was 108 rpm.
The obtained granule precursor was dried at 140° C. for 6 hours using a hot air circulation type dryer to obtain filler granule MB-1.

[Production Example 2] Production of filler granule MB-2 Filler granule MB-2 was obtained in the same manner as in Production Example 1, except that 20 parts by weight of a filler dispersion polymer (a 15% aqueous solution of water-soluble vinyl alcohol resin (BVOH) (manufactured by Mitsubishi Chemical Corporation, product name "Nichigo G-polymer AZF8035Q"; saponification degree 98.0 mol% or more; melting point: 172°C; polymer concentration: 15 wt%: in the table, "D-2")) was used instead of the filler dispersion polymer (polyolefin aqueous dispersion (aqueous PE dispersion); manufactured by Mitsui Chemicals, Inc., product name "Chemipearl A100").
The ingredients used in Production Examples 1 and 2 are shown in Table 2.

<Evaluation>
The filler granules obtained in Production Examples 1 and 2 were subjected to the following evaluations. The results are shown in Table 3.
(1) Bulk density The surface-modified filler granules after drying were allowed to fall naturally into a 1-liter measure until the measure was filled to the brim, and a volume of exactly 1 liter was taken. The weight was then measured to calculate the bulk density (unit: kg/L) of the surface-modified filler granules.

(2) Pellet Size Twenty particles of the surface-modified filler granules were taken out, and the average length and diameter of the particles were measured using a vernier caliper.

(3) Moisture Content The moisture content (unit: weight %) remaining in the surface-modified filler granules was measured using an infrared moisture meter (FD-660 manufactured by Kett Electric Laboratory).

(4) Measurement of collapse strength The collapse stress (unit: kg) of the surface-modified filler granules after drying was measured using a Kiya hardness tester (manufactured by Shiro Sangyo Co., Ltd., product name "WPF1600-B"). The measured value was the average value of 25 granules.

(5) Filler concentration in filler granules 1 to 3 g of the filler granules were sampled and kept in a crucible in an electric furnace at 600° C. for 3 hours, and the filler concentration (wt %) was calculated from the ash weight.

[Example 1]
32 parts by weight of filler granules MB-2, 63 parts by weight of polylactic acid (PLA; Nature Works, Inc., product name "Ingeo 4032D"; melting point 155 to 170°C; in the table, "A-1"), and an impact resistance improver (polybutylene adipate terephthalate (PBAT) resin (BASF, product name "Ecoflex F Blend")) were mixed. C1200"; in the table, "E-1") and 5 parts by weight of 10 ...
[Examples 2 to 6 and Comparative Examples 1 to 3]
Pellets of a polylactic acid resin composition were obtained in the same manner as in Example 1, except that the filler granules, polylactic acid, impact modifier, and hydrolysis inhibitor shown in Table 4 were used in the amounts shown in Table 4. Details of the polylactic acid, impact modifier, and hydrolysis inhibitor used are as shown in Table 2.
In Comparative Examples 1 and 2, no filler dispersion polymer or filler dispersant was used, and no filler granules were formed, but powdered talc ("B-1" in Table 2) was used. In these Comparative Examples, bridging of powder B-1 occurred at the supply port, so pellets of the polylactic acid resin composition could not be stably produced. Comparative Example 3 is an example lacking an impact resistance improver.

<Evaluation>
The polylactic acid resin compositions obtained in the Examples and Comparative Examples were subjected to the following evaluations. The results are shown in Table 5.

(1) Ash content measurement (unit: weight %)
1 to 3 g of pellets of the polylactic acid resin composition were collected and held in a crucible in an electric furnace at 600° C. for 3 hours, and the weight of the ash was calculated.

(2) Dispersibility of Filler Pellets of the polylactic acid resin composition were rolled by a hot press to form a sheet having a thickness of about 0.5 mm. The remaining filler aggregates were visually observed through the sheet and evaluated according to the following criteria.
AA: Good dispersion state with almost no filler agglomerates observed A: A state in which a small amount of relatively small filler agglomerates remain BB: A state in which a considerable amount of relatively small filler agglomerates remain B: A state in which the filler agglomerates are large (Dispersion state ranking: AA>A>BB>B (left good))

(3) Crystallization temperature (Tc) measurement (unit: ° C.)
Using a differential scanning calorimeter (DSC) (Hitachi High-Tech Science Corporation, DSC6220), 5 to 10 mg of a sample was heated from room temperature to 200° C. at a constant heating rate, held at 200° C. for 5 minutes, and then cooled to room temperature at a constant cooling rate of 10° C./min to measure the recrystallization temperature of polylactic acid crystals.

(4) MFR (unit: g / 10 min)
The melt mass flow rate (MFR) was measured using a "Melt Indexer" manufactured by Toyo Seiki Seisakusho Co., Ltd. in accordance with JIS K7210 to evaluate the fluidity. The measurement conditions were 210°C and a load of 2.16 kg.

(5) Tensile Measurement The tensile strength (unit: MPa) and breaking elongation (unit: %) were measured at a pulling speed of 5 mm/min in accordance with ISO 527.
The test pieces used for the measurements were dumbbell-shaped test pieces (Type 1A multipurpose test pieces) molded from pellets of the polylactic acid resin composition using an injection molding machine (Toyo Machinery & Metals "SI-80W", mold clamping 100 tons) with a cylinder setting temperature of 200°C, a mold temperature of 110°C (both the fixed side and the moving side), and a cooling time of 60 seconds.

(6) Bending Measurement A bending test was carried out in accordance with ISO 178 to measure the bending strength (unit: MPa) and bending modulus.
The test specimens for measurement were dumbbell-shaped test specimens cut out from the above-mentioned tensile measurements.

(7) Heat deflection temperature measurement (unit: °C)
The deflection temperature under load was measured under a load of 0.45 MPa in accordance with ISO 75. The test specimens used for the measurement were dumbbell-shaped test specimens cut out from the above tensile measurement.

(8) Charpy impact test (unit: kJ/ ^m2 )
The Charpy impact strength of a notched test piece formed from a polylactic acid resin composition was measured in accordance with ISO 179. The test piece for measurement was a dumbbell-shaped test piece cut out from the tensile measurement described above.

(9) Molding time of injection molded specimen (dumbbell test specimen) (unit: seconds)
In the injection molding of the dumbbell-shaped test piece for the tensile test (Type 1A multipurpose test piece), the total number of seconds was counted, including the cooling time of 60 seconds, the injection time, the pressure holding time, and the molded product ejection time.

(10) Appearance of Molded Product The appearance of the dumbbell-shaped test specimens for the tensile test was classified into the following three categories.
A: Shiny B: Dull C: Rough skin (Appearance ranking: A>B>C (left: good))

(11) Warpage of injection-molded specimen (dumbbell test specimen) The above-mentioned dumbbell-shaped test specimen for the tensile test (Type 1A multipurpose test specimen) was placed on a horizontal plane, and one end of the dumbbell specimen was pressed against the horizontal plane to measure the lift (unit: mm) of the opposite end from the horizontal plane. The warpage was classified into the following three types.
AA: Almost no lifting is observed. A: Lifting is less than 2 mm. B: Lifting is 2 mm to less than 4 mm. C: Lifting is 5 mm or more. (Serration order: AA>A>B>C (left good))

(12) Specific Gravity The specific gravity of the resin composition was measured using a specific gravity meter (DMA220H, manufactured by Shinko Denshi Co., Ltd.).

As shown in Table 5, the polylactic acid resin compositions of Examples 1 to 6 can mold molded articles having excellent rigidity (flexural modulus) and heat distortion temperature. Comparison of Example 1 and Comparative Example 3 shows that the impact strength is improved by the incorporation of an impact modifier. In addition, as shown by the fact that test pieces can be easily obtained by injection molding, the polylactic acid resin composition of the present invention has a high crystallization rate and improved moldability. In addition, the obtained polylactic acid resin composition has high rigidity and heat resistance, but also has excellent surface appearance (smoothness). Furthermore, according to the polylactic acid resin composition of the present invention, a molded article having excellent dimensional stability (shrinkage rate, linear expansion coefficient, low warpage) can be formed. Furthermore, a molded article having improved hydrolysis resistance can be obtained by the incorporation of a hydrolysis inhibitor.

Claims (13)

A polylactic acid resin composition comprising a polylactic acid resin , a filler granule containing a filler and a filler dispersant and/or a filler dispersion polymer, and an impact resistance improver,
The content of the filler in the polylactic acid resin composition is 20% by weight to 60% by weight,
The content of the impact modifier in the polylactic acid resin composition is 5% by weight to 50% by weight.
Polylactic acid resin composition. The polylactic acid resin composition according to claim 1, wherein the impact resistance improver is at least one selected from the group consisting of aliphatic polyester resins, aliphatic/aromatic polyester resins, polyvinyl alcohol resins, and natural rubber. The polylactic acid resin composition according to claim 1 or 2, wherein the filler dispersant is at least one selected from the group consisting of polyhydric alcohol fatty acid esters, fatty acid amides, polyglycerin fatty acid esters, condensed hydroxy fatty acids, and alcohol esters of condensed hydroxy fatty acids. The polylactic acid resin composition according to any one of claims 1 to 3, wherein the filler dispersion polymer is at least one selected from the group consisting of polyolefin resins, polystyrene resins, polyvinyl alcohol resins, polyalkylene glycol resins, polyvinylpyrrolidone resins, polyester resins, polyamide resins, acrylic resins, urethane resins, epoxy resins, and water-soluble polysaccharides. The polylactic acid resin composition according to claims 1 to 3, wherein the filler dispersion polymer is at least one selected from the group consisting of polyvinyl alcohol-based resins, polyalkylene glycol-based resins, polyvinylpyrrolidone-based resins, and water-soluble polysaccharides. The polylactic acid resin composition according to any one of claims 1 to 5, wherein the total content of the filler dispersant and the filler dispersion polymer in the polylactic acid resin composition is 0.1% by weight to 30% by weight. The polylactic acid resin composition according to any one of claims 1 to 6, wherein the filler is at least one selected from talc and mica. The polylactic acid resin composition according to any one of claims 1 to 7, further comprising a hydrolysis inhibitor. The polylactic acid resin composition according to claim 8, wherein the hydrolysis inhibitor is a compound having at least one functional group selected from the group consisting of a carbodiimide group, an oxazoline group, and an epoxy group. The method includes melt-kneading a polylactic acid resin, a filler granule, and an impact resistance improver,
The filler granules contain the filler and the filler dispersant and/or the filler dispersion polymer,
The content of the filler in the filler granules is 80 parts by weight to 99.9 parts by weight based on 100 parts by weight of the filler granules.
A method for producing the polylactic acid resin composition according to any one of claims 1 to 9. An injection molded article formed from the polylactic acid resin composition according to any one of claims 1 to 9. An extrusion molded article formed from the polylactic acid resin composition according to any one of claims 1 to 9. A sheet-like shaped product formed from the polylactic acid resin composition according to any one of claims 1 to 9.