JP2013129777A - Polylactic acid-containing polypropylene-based resin composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polylactic acid-containing polypropylene-based resin composition that excels in not only the harmony of rigidity and impact resistance but also heat resistance, and thereby that is desirably suitable to form an interior part for an automobile that is irradiated directly to sunlight and exposed to a high temperature environment.SOLUTION: The polylactic acid-containing polypropylene-based resin composition includes: polypropylene; a polylactic acid-based resin; and a polystyrene elastomer, wherein the polylactic acid-based resin comprises combining a nucleating agent of a plant origin into polylactic acid.

Description

  The present invention relates to a polylactic acid-containing polypropylene-based resin composition, and in particular, by blending a plant-derived crystal nucleating agent in addition to a styrene-based thermoplastic elastomer to harmonize impact resistance and heat-resistant deformation temperature, in particular, an automobile. The present invention relates to a resin composition suitable for use as an interior part molding resin material.

With the expansion of the economic scale of developing industrial countries such as BRICs, the oil demand is expected to increase rapidly, leading to a surge in crude oil prices and the depletion of fossil resources. In addition, automobiles are required not only to improve environmental performance such as fuel efficiency in order to reduce CO _{2 and} save energy, but also to have environmental performance that reduces the environmental load on the materials used in products. Due to such industrial trends, the transition from fossil resources to renewable resources is inevitably required, and the use of plastics derived from plant materials has attracted much attention.

  Polylactic acid is made from lactic acid obtained by fermentation from plant resources, and is excellent in strength and rigidity, and is manufactured and commercialized in a commercial plant. However, polylactic acid has a problem that heat resistance and impact resistance are inferior to those of resins used in automobiles. Various attempts have been made to improve heat resistance, such as a technique for controlling optical isomers (L-form, D-form) of polylactic acid and addition of a crystal nucleating agent (Patent Document 1).

  As a technique for improving impact resistance, resin, rubber, thermoplastic elastomer and polymer blend, and polymer alloy are generally used. Polypropylene is used in large quantities in automotive interior and exterior parts such as bumpers, instrument panels, and door trims because of its stable material performance and inexpensive material price. Polypropylene is the most used resin material for automobiles. It is suitable for polymer blends and is used in some interior parts for automobiles. However, the polypropylene resin composition containing polylactic acid has high impact resistance as compared with polylactic acid alone, but is insufficient for interior parts for automobiles. Patent Document 2 describes that a molded article excellent in heat resistance and impact resistance can be obtained using polylactic acid-containing polypropylene. However, the polylactic acid-containing polypropylene resin composition formed in this way is still insufficient for the harmony between rigidity and impact resistance required for automotive parts. In order to solve this problem, blending of styrenic elastomers has been proposed (Patent Document 3), and the present inventors have also described blending of styrenic elastomers having a specific styrene content and melt fluidity (molecular weight). One proposal has been made based on the knowledge that it is effective in solving this problem (Patent Document 4). However, as described above, the polylactic acid-containing polypropylene-based resin composition that achieves a balance between rigidity and impact resistance by blending a styrene-based elastomer has a tendency to decrease the heat resistance, and the top panel of the instrument panel of an automobile It is difficult to achieve both high heat resistance and impact resistance required for parts exposed directly to sunlight and exposed to high temperature environments, as represented by the upper parts of door trims. In order to improve heat resistance, it is known that addition of a crystal nucleating agent is an inexpensive and efficient solution, but there is a problem that impact resistance is significantly lowered. Patent Document 5 discloses that a crystal nucleating agent selected from the group consisting of carboxylic acid amides and N-substituted urea is excellent in heat resistance of polylactic acid-based films and resin compositions. According to the above, it is difficult to achieve both heat resistance and impact resistance of the polylactic acid-containing polypropylene. In addition, the addition of an inorganic crystal nucleating agent having a crystal nucleating agent effect and a physical property reinforcing effect reduces the increase in specific gravity and scratch resistance of the resin composition. I want to avoid it.

JP 2005-146261 A JP 2010-265444 A JP 2008-260861 A Japanese Patent Application No. 2011-131200 JP 2009-249443 A

  The main object of the present invention is to contain not only excellent harmony of rigidity and impact resistance, but also polylactic acid content suitable for molding automotive interior parts that are preferably exposed to high temperature by improving heat resistance. To provide a polypropylene resin composition.

  According to the research of the present inventors, in a polylactic acid-containing polypropylene resin composition mainly composed of polypropylene, polylactic acid and a styrene-based elastomer as shown in Patent Document 4 already developed by the present inventors, By using a polylactic acid resin in which a plant-derived crystal nucleating agent is blended with polylactic acid instead of lactic acid, heat resistance can be effectively improved without reducing the degree of plant components, and conventional crystals It has been found that the cooling time during molding can be effectively shortened compared to the case where a nucleating agent is added. The polylactic acid-containing polypropylene resin composition of the present invention is based on the above-mentioned knowledge, and includes polypropylene, a polylactic acid resin, and a styrene elastomer, and the polylactic acid resin adds a plant-derived crystal nucleating agent to polylactic acid. It is characterized by being blended.

  The polypropylene resin composition of the present invention contains, as main resin components, polypropylene, a polylactic acid resin containing a plant-derived crystal nucleating agent, and a styrene elastomer.

(polypropylene)
Polypropylene, which is the main component of the composition of the present invention, is a homopolypropylene (propylene homopolymer) superior in rigidity and surface hardness as compared to a copolymer, and particularly has a flexural modulus (ISO 178: 1993) of 2000 MPa or more. Things are used. If the flexural modulus is less than 2000 MPa, the flexural modulus of the polypropylene resin composition containing polylactic acid tends to decrease. The melt flow value (MFR; measured at 230 ° C. and 2.16 kgf according to JIS K7210; hereinafter the same unless otherwise specified) is preferably 20 g / 10 min or more, more preferably 30 g / 10 min or more.

(Polylactic acid resin)
The polylactic acid serving as the base of the polylactic acid-based resin preferably has a D-lactic acid unit (D form) of less than 5 mol%, particularly 2 mol% or less. When the D-lactic acid unit is 5 mol% or more, the flexural modulus of the resin composition tends to decrease. MFR (JIS K7210, 190 ° C., 2.16 kgf) is preferably 20 g / 10 min or more, particularly 30 g / 10 min or more. As an example of a commercial item, the grades “3001D” for injection molding manufactured by NatureWorks, “REVODE 110” manufactured by Kaisho Biological Materials Co., Ltd., and the like can be given.

(Plant-derived crystal nucleating agent)
The plant-derived crystal nucleating agent blended with polylactic acid to constitute a polylactic acid-based resin is generally a polyhydroxycarboxylic acid obtained by polymerizing a plant-derived hydroxycarboxylic acid, preferably polylactic acid (based on polylactic acid). Similarly, the terminal hydroxyl group of the D-lactic acid unit (D-form less than 5 mol%, particularly 2 mol% or less) preferably has a structure in which the terminal hydroxyl group is ester-bonded with a dicarboxylate, and the remaining terminal carboxyl The group may form a salt with the cation. Particularly preferably, it is obtained by polymerizing a compound having at least 3 (more preferably 3 to 8) hydroxyl groups in the molecule, such as triacylglycerol, as a main component, for example, castor oil. The branched polylactic acid-based crystal nucleating agent obtained by performing the above esterification and further chlorination as necessary at the end of the branched polylactic acid chain utilizes the improved molecular mobility due to its branching property. It is preferably used because it exhibits rapid crystal nucleation and acts as a good crystal nucleating agent not only on polylactic acid but also on polypropylene. More details of the branched polylactic acid-based crystal nucleating agent as a preferable example of such a plant-derived crystal nucleating agent are described in JP-A-2009-24058. The branched polyester chain constituting the crystal nucleating agent preferably has a weight average molecular weight (Mw) of 5,000 to 15,000 and 3 to 8 branches.

  These plant-derived crystal nucleating agents have a structure similar to that of the base polylactic acid, and can be mixed in a wide range using their compatibility, but in general, with respect to 100 parts by weight of polylactic acid, It is preferable to mix | blend in the ratio of 3-20 weight part, especially 4-20 weight part. If it is less than 3 parts by weight, the effect as a crystal nucleating agent is poor, and if it exceeds 20 parts by weight, the effect as a crystal nucleating agent is almost saturated. As described above, since this plant-derived crystal nucleating agent acts as a good crystal nucleating agent for polypropylene, when forming the composition of the present invention, it is added separately from polylactic acid, Polylactic acid-based resin may be formed in situ by melt-kneading with polypropylene and styrene-based elastomer to form a composition. However, by using good compatibility with polylactic acid, it is melt-kneaded in advance to form polylactic acid. It is preferable to form a resin and then melt-knead with polypropylene and a styrene elastomer to quickly form a homogeneous composition as a whole.

(Styrene elastomer)
As the styrene-based elastomer, hydrogenated products of styrene-butadiene copolymer and styrene-isoprene copolymer are used. Among them, the degree of hydrogenation of double bonds derived from butadiene or isoprene is 90 mol% or more, particularly 95 mol% or more, and styrene / ethylene / butene / styrene block copolymer (SEBS) and styrene / ethylene / propylene. What is commonly referred to as a styrene block copolymer (SEPS) is preferable because, for example, it has excellent weather resistance (light) performance in an automobile use environment.

  The hydrogenated styrenic elastomer itself has the effect of improving the affinity between polypropylene and polylactic acid. The smaller the styrene content (more specifically, the content of polystyrene segment in the polymerized block copolymer elastomer), the stronger the elastomeric properties, and the greater the amount, the more the elastomeric properties are lost. In the present invention, those having a styrene content of 14 to 21% by weight, particularly 15 to 18% by weight are preferably used. When the styrene content exceeds 21% by weight, the impact resistance of the resulting resin composition tends to decrease, and when the styrene content is less than 14% by weight, the rigidity of the resin composition tends to decrease.

  As the hydrogenated styrene-based elastomer, those having a melt flow value (MFR: JIS K7210, 230 ° C., 2.16 kgf) as a standard for determining the molecular weight is preferably 2 to 10 g / 10 minutes, particularly 4 to 6 g / 10 minutes. It is done. Within the above melt flow value range, the dispersed particle size of the styrenic elastomer in the polypropylene matrix becomes an optimum size, approximately 0.3 to 3 μm, that contributes to both the flexural modulus and the impact resistance.

(composition)
When the polypropylene resin composition of the present invention is used as a material for forming automobile interior parts, the following composition is preferably maintained among the three main resin components, that is, polypropylene, polylactic acid resin, and styrene elastomer. composition.

  Polypropylene is preferably used in an amount occupying 44 to 55% by weight, particularly 46 to 55% by weight, of the above three resin components. When the content is less than 44% by weight, polypropylene does not become a matrix phase in the resin composition, and a significant decrease in moldability and durability is observed. On the other hand, if it exceeds 55% by weight, the content of the polylactic acid resin and the styrene elastomer decreases, and it becomes difficult to achieve both rigidity and impact resistance of the resin composition.

  The polylactic acid resin is preferably 25 to 32% by weight, particularly 25 to 30% by weight. If it is less than 25% by weight, the rigidity of the resin composition is lowered, and if it exceeds 32% by weight, the impact resistance tends to be lowered depending on the content of the styrene elastomer.

  The content of the styrene-based elastomer varies depending on the strength of the elastomer that varies depending on the value of the styrene content contained, but is preferably in the range of 16 to 24% by weight, particularly 18 to 23% by weight. If it is less than 16% by weight, the impact resistance of the resin composition is lowered, and if it exceeds 24% by weight, the rigidity is lowered.

(Other ingredients)
Depending on the use of the molded article, the polypropylene resin composition of the present invention may be added to a lubricant, an antioxidant, an antistatic agent, a stabilizer, an ultraviolet absorber, a colorant (pigment, metal powder, etc.), a foaming agent, a flame retardant, etc. The additive may be contained to the extent that the purpose is not impaired.

(Composition)
The polypropylene resin composition of the present invention kneads the above components at a temperature of, for example, 180 to 230 ° C. using a kneader such as a single screw extruder, a twin screw extruder, a Banbury mixer, a roll mixer, a kneader, and the like. It can be formed by granulation. In consideration of productivity, it is preferable to use a twin-screw kneading extruder and set the residence time to 20 minutes or less.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. In the following description, “ratio”, “%” and “part” relating to the composition are all based on weight unless otherwise specified. Moreover, the physical property values described in this specification including the following description are based on the measured values by the following methods.

1) Molding of test piece Using a twin screw extruder (Kobe Steel Co., Ltd., screw diameter D: 32 mm, screw length L / D = 44), it is melt-kneaded at 200 ° C. and a residence time of 20 minutes for pelletization. After that, using an injection molding machine with a clamping pressure of 130 tons, various test pieces (for measuring deflection temperature under load, for measuring flexural modulus, for measuring Charpy impact strength) and heat resistance at a molding temperature of 200 ° C. A molded article for evaluation was molded.

2) Measurement test <Load deflection temperature>
The deflection temperature under load, which is an index of heat resistance, is in accordance with JIS K 7191-1 “Plastics – Determination of deflection temperature under load”, and gripping a test piece with dimensions of 80 mm × 10 mm × 4 mmt held horizontally with a gripping tool spacing of 64 mm When the ambient temperature is increased at a rate of 120 ° C./hour in a state where a downward load of 0.45 MPa is applied to the central portion of the tool interval, the downward displacement amount at the load application portion reaches 0.35 mm. The ambient temperature at was measured as the deflection temperature under load. In general, the acceptance standard value of the deflection temperature under load is determined to be 95 ° C. or higher by comparison with the result of evaluation of heat resistance of molded products for interior parts for automobiles.

<Bending elastic modulus>
The flexural modulus is in conformity with ISO 178 (JIS K7171 “Plastics-Determination of bending characteristics-”), using a test piece of 80 mm × 10 mm × 4 mmt at an bending temperature of 2 mm / min in an environment with an ambient temperature of 23 ° C. It was measured. The bending elastic modulus is empirically required to be 1500 MPa or more in order to prevent dent deformation as an automobile interior part.

<Charpy impact strength>
Charpy impact strength conforms to JIS K7111-2 "Plastics-How to determine Charpy impact properties-", using 80mm x 10mm x 4mmt test piece with type A notch (ISO 179 / 1eA), atmosphere Evaluation was performed under an environment of a temperature of 23 ° C. Avoiding undesirable brittle fracture from the viewpoint of occupant protection at the time of collision, the ductile fracture mode typified by PP resin for automobiles, that is, the mode of impact fracture is YS (yield caused by stable crack) or YD (yield caused by deep drawing) ) Is empirically required to have a Charpy impact strength of 15 kJ / m ² or more.

<Cooling rate>
The cooling rate is the same as that of a general four-wheel vehicle door trim PP resin except for the cooling time, and the cooling time is changed to 15, 30, 45, 60 seconds. X length 300 mm x thickness 2 mm x height 50 mm), and determined by the dimensional change rate of the molded product. The rate of dimensional change is the same position as the maximum length and width of the molded product measured after leaving the molded product after injection molding in a constant temperature environment of 23 ° C and 50% relative humidity for 24 hours or longer. The absolute value of the difference between the numerical value obtained by multiplying the ratio of the mold length by 100 and 100 was used. With respect to a molded product having a dimensional change rate of less than 2%, it was judged that there was no problem in molding stability and cooling was completely completed. That is, the cooling time when the dimensional change rate was less than 2% in both the vertical and horizontal directions was defined as the cooling rate.

[Preparation of composition]
The following was prepared as a raw material constituting the polylactic acid-containing polypropylene-based fat composition.
Polypropylene: Commercially available homopolypropylene (“Novatec MA04A” manufactured by Nippon Polypro Co., Ltd .; MFR = 30 g / 10 min, flexural modulus = 2300 MPa, Charpy impact strength (23 ° C.) = 1.0 kJ / m ² ).

Polylactic acid: Grade “3001D” for injection molding manufactured by NatureWorks; MFR = 30 g / 10 min, flexural modulus = 3500 MPa, Charpy impact strength (23 ° C.) = 2.0 kJ / m ² ).

Styrene elastomer (styrene / ethylene / propylene / styrene block copolymer (SEPS) “Septon 2004” manufactured by Kuraray Co., Ltd .; styrene content: 18% by weight, MFR = 5 g / 10 min).

-Plant-derived crystal nucleating agent: Branched polylactic acid based crystal nucleating agent (made by Biobase Co., Ltd.) obtained by polymerizing terminal hydroxyl groups of branched polylactic acid obtained by polymerizing lactic acid with castor oil as the initiator. Essentially produced by the method described in Example 10 of JP-A-2009-24058. The main component was α, α ′, α ″ -tri-O-ricinoylglycerin-triyltris (−ω-sodium phthaloyl polylactic acid) ester. The weight average molecular weight was about 10,000.

-Polylactic acid-based resin: A blend of 5 parts by weight of the branched polylactic acid-based crystal nucleating agent melted and mixed with 100 parts by weight of the polylactic acid was used.

(Comparative Example 1)
A mixture of the above three basic resins of 50 parts by weight of polypropylene, 30 parts by weight of polylactic acid and 20 parts by weight of styrene elastomer was converted into a twin screw extruder (manufactured by Kobe Steel Co., Ltd., screw diameter D: 32 mm, screw length L / D). = 44) to obtain a pelletized composition by melt kneading at 200 ° C. and a residence time of 20 minutes.

Example 1
In Comparative Example 1, in the same manner as Comparative Example 1, except that 30 parts by weight of the polylactic acid resin (polylactic acid mixed with a branched polylactic acid crystal nucleating agent) was used instead of 30 parts by weight of polylactic acid. A pelletized composition was obtained.

(Comparative Examples 2 to 4)
With respect to 100 parts by weight of the resin mixture of Comparative Example 1, an appropriate amount of commercially available crystal nucleating agent, that is, N, N ′, N ″ -Tris (to 2-methyl), which is typical as a commercially available crystal nucleating agent for polylactic acid (Xyl)-(1,2,3-propanetricarboxamide) (“Rikaclear PC-1” manufactured by Shin Nippon Rika Co., Ltd.) 0.4 parts by weight (Comparative Example 2) and zinc phenylsulfonate (Nissan Chemical Co., Ltd.) 1 part by weight (comparative example 3) and 1 part by weight (comparative example) of organophosphate metal salt (“Adeka Stub NA-11” manufactured by Asahi Denka Co., Ltd.) as a commercially available crystal nucleating agent for polypropylene 3), 3 types of pelletized compositions obtained by blending each were obtained.

  Regarding the five compositions of Example 1 and Comparative Examples 1 to 4, as described above, the deflection temperature under load, the flexural modulus, the Charpy impact strength, the heat resistance and the cooling time, and the degree of plant components (that is, the organism) The results of evaluating the ratio of plant-derived components in the whole are summarized in Table 1 below.

  As shown in Table 1 above, the polylactic acid-containing polypropylene resin composition of Example 1 using a polylactic acid resin containing a plant-derived crystal nucleating agent instead of the polylactic acid in the composition of Comparative Example 1 is a conventional one. Compared to the compositions of Comparative Examples 2 to 4 to which a crystal nucleating agent was added, the impact strength was not significantly reduced, and the remarkable was represented by a significant increase in flexural modulus and deflection temperature under load and a significant shortening of the cooling time. It can be seen that an excellent effect of adding a crystal nucleating agent is obtained.

(Examples 2 to 6)
In contrast to Example 1 above, the amount of the nucleating agent-containing polylactic acid resin is 31.25% by weight (Example 2) to 25% by weight (Example 6) while the polypropylene content is fixed at 50% by weight. Five types of compositions obtained by changing the content and changing the content of the styrene-based elastomer from 18.75% by weight to 25% by weight were evaluated in the same manner as described above. The results are shown in Table 2 together with the results of Example 1 and Comparative Example 1.

As shown in Table 2 above, bending elasticity while changing the plant component degree by changing the nucleating agent-containing polylactic acid resin amount and the styrene elastomer content while fixing the polypropylene content at 50% by weight. It can be seen that the rate (bending strength), impact strength, and deflection temperature under load can be changed. In particular, it can be seen that when the polylactic acid resin content in Examples 1 and 3 to 5 is in the range of 30% by weight to 26.25% by weight, the characteristics as the automobile interior part material are well harmonized. However, in Example 2 where the polylactic acid resin content is 31.25 wt%, it is desirable to reduce the polypropylene content in the range of 44 wt% or more and correspondingly increase the styrene elastomer content. Achieving an impact strength of 15 kJ / m ² or more, and in Example 6 in which the polylactic acid resin content is 25% by weight, the polypropylene content is increased in the range of 55% by weight or less, correspondingly styrene By reducing the content of the system elastomer, it is possible to easily achieve any desired flexural modulus of 1500 MPa or more.

  As described above, according to the present invention, in the polylactic acid-containing polypropylene resin composition mainly composed of polypropylene, polylactic acid and styrene elastomer, a polylactic acid-based compound containing a plant-derived crystal nucleating agent instead of polylactic acid By using a resin, the bending modulus and the deflection temperature under load are significantly increased and the cooling time is significantly shortened (improving the molding efficiency) without reducing the degree of plant components and without significantly reducing the impact strength. A polylactic acid-containing polypropylene-based resin composition having a representative effect of adding a crystal nucleating agent is obtained. In particular, by satisfying the preferred composition requirements, the balance between rigidity and impact resistance is excellent, and because heat resistance has been improved, it has been difficult to use with conventional biomass plastics. Therefore, it is possible to form a composition suitable as an automotive interior member material such as a door trim upper member that requires high heat resistance. In combination with the above-described parts examples, it is possible to replace conventional polypropylene resin compositions for automobile parts that require compatibility of mechanical properties at a high level such as instrument panels (particularly top panels). In addition, components other than the crystal nucleating agent are commercially available products, and can be realized at low material costs in the case of biomass plastics that are generally concerned about cost. Therefore, it is more versatile than conventional biomass plastics. In addition, the polypropylene resin composition of the present invention is expected to be widely deployed not only in automobile interior and exterior parts and motorcycle parts, but also in home appliances, AV equipment, OA equipment, cosmetics, daily necessities, office supplies, and the like.

Claims (9)

A polylactic acid-containing polypropylene resin composition comprising a polypropylene, a polylactic acid resin and a styrene elastomer, wherein the polylactic acid resin comprises polylactic acid and a plant-derived crystal nucleating agent. The polypropylene resin composition according to claim 1, comprising 44 to 55% by weight of polypropylene, 25 to 32% by weight of a polylactic acid resin and 16 to 24% by weight of a styrene elastomer. The plant-derived crystal nucleating agent has a terminal end of a branched polylactic acid chain obtained by polymerizing plant-derived lactic acid using an oil and fat mainly composed of a compound having at least three hydroxyl groups in the molecule. 3. The polypropylene-based resin composition according to claim 1 or 2, which is a branched polylactic acid-based crystal nucleating agent obtained by ester-bonding with a dicarboxylate and further chlorinating a terminal carboxyl with a cation if necessary. A plant-derived crystal nucleating agent is a branched polylactic acid-based crystal nucleating agent mainly composed of α, α ′, α ″ -tri-O-ricinoylglycerin-triyltris (−ω-sodium phthaloyl polylactic acid) ester. The polypropylene resin composition according to claim 3. The polypropylene resin composition according to any one of claims 1 to 4, wherein the polypropylene is a homopolypropylene having a flexural modulus of 2000 MPa or more, and the polylactic acid has a D-form content of less than 5 mol%. The polypropylene resin composition according to any one of claims 1 to 5, wherein the styrene elastomer has a styrene content of 15 to 18% by weight and a melt flow value of 4 to 6 g / 10 min. The polypropylene resin composition according to claim 6, wherein the styrene elastomer is styrene / ethylene / propylene / styrene block copolymer (SEPS) or styrene / ethylene / butene / styrene block copolymer (SEBS). The polypropylene resin composition according to any one of claims 1 to 7, which has a flexural modulus of 1500 MPa or more, a Charpy impact strength of 15 kg / cm ² or more, and a deflection temperature under load of 95 ° C or more. An automotive interior part comprising the polylactic acid-containing polypropylene resin composition according to any one of claims 1 to 8.