JP2011074354A - Resin composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin composition which principally contains polylactic acid and has improved impact resistance and improved heat resistance. <P>SOLUTION: The resin composition contains polylactic acid, natural rubber, a crystal nucleating agent and a hydrolysis inhibitor. Moreover the resin composition having a carbodiimide compound as the hydrolysis inhibitor is provided. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a resin composition, and in particular, to a polylactic acid resin composition containing natural rubber.

Conventionally, polylactic acid has been used as a material for a (biodegradable) resin composition. However, since polylactic acid is generally hard and has a property of being inferior in impact resistance, its use tends to be limited. To cope with this, natural rubber, a modifier containing natural rubber, etc. are used. Various blending means used have been proposed (Patent Documents 1 to 4). Patent Document 4 includes a step of obtaining a first polylactic acid resin having improved heat resistance by adding a crystal nucleating agent such as calcium carbonate and a crystallization accelerator such as triacetin (acetic acid triglyceride) to polylactic acid resin, Adding a flexible resin such as rubber that reacts with the lactic acid resin to obtain a second polylactic acid resin having improved impact resistance, and mixing and molding the first and second polylactic acid resins And a process for producing a polylactic acid resin molded article having excellent strength, rigidity, heat resistance, and impact resistance, which has progressed in crystallization at a low mold temperature and a short molding cycle. Patent Document 5 discloses a method for producing a molded product containing high heat-resistant polylactic acid, but does not disclose the use of natural rubber.
On the other hand, the present applicants proposed a resin composition excellent in heat resistance and impact resistance, which contains poly-L-lactic acid, a crystallization accelerator, a flexibility imparting agent, and a compatibilizing agent (Patent Document 6). However, it has been found that there is room for further improvement in the impact resistance and heat resistance of the resin composition.

JP 2004-143315 A JP 2005-255722 A JP 2009-84333 A JP 2008-201863 A Japanese Patent No. 4259284 JP 2007-23188 A

  The present invention intends to provide a resin composition mainly containing polylactic acid, which has improved impact resistance and heat resistance or further improved mechanical properties.

The present invention is as follows.
1) A resin composition containing polylactic acid, natural rubber, a crystal nucleating agent, and a hydrolysis inhibitor (hereinafter also referred to as “resin composition of the present invention”).
The resin composition of the present invention preferably contains epoxidized natural rubber and / or medium chain fatty acid triglyceride in addition to the above components, and more preferably contains both.

  The resin composition of the present invention can improve impact resistance and heat resistance or further mechanical properties, and can improve plantiness to about 97%, and can be widely used as an alternative to general-purpose plastics. In addition, the resin composition of the present invention can be produced very easily and economically because a blended blended component can be made into a blend polymer in one step.

The components of the resin composition of the present invention will be described.
(Hydrolysis inhibitor)
The hydrolysis inhibitor used in the present invention is not particularly limited as long as it has a function of suppressing hydrolysis of polymer components such as polylactic acid, natural rubber, and crystal nucleating agent. For example, hindered phenol And antioxidants, ethylene-vinyl alcohol copolymers, phosphate esters or phosphate ester derivatives, oxazolines or oxazoline derivatives, isocyanates or isocyanate derivatives, epoxy compounds or epoxy compound derivatives, carbodiimide compounds, and the like. Among them, a carbodiimide compound is preferable as the hydrolysis inhibitor.
The carbodiimide compound used in the resin composition of the present invention is a compound having one or more carbodiimide groups and mainly has a function capable of suppressing hydrolysis of polylactic acid. The carbodiimide compound may be a low molecule or a polymer, but a polymer compound is preferred. The mass average molecular weight Mw of the carbodiimide compound is preferably 500 to 60,000, and more preferably 1,000 to 40,000. The number average molecular weight of the carbodiimide compound is 500 or more, preferably 1000 or more, more preferably 1300 or more, and still more preferably 2000 or more. If the number average molecular weight is less than 500, it is not preferable because it is difficult to supply the resin composition to the apparatus during the production of the resin composition. The upper limit of the number average molecular weight Mn is about the same as the mass average molecular weight Mw. The polydispersity Mw / Mn is preferably 1.0 to 6.0. Further, the content of the carbodiimide group of the carbodiimide compound is preferably 2 to 2,000 / molecule, more preferably 2 to 500 / molecule. Examples of the carbodiimide compound include stavaxol 1-LF (manufactured by Rhein Chemie) and the like as low molecular compounds having a molecular weight of 500 or less, and commercially available carbodilite LA-1 (manufactured by Nisshinbo) as the polymer compound. A compound containing three or more carbodiimide groups in one molecule is also referred to as a polycarbodiimide compound.
The addition amount of the hydrolysis inhibitor used in the resin composition of the present invention is preferably 0.2 parts by mass or more, more preferably 1 part by mass or more, particularly 1.5 parts per 100 parts by mass of polylactic acid. It is effective to achieve the object of the present invention to contain at least part by mass, and most preferably at least 2.0 parts by mass. There is no particular upper limit, but no improvement is seen at about 10 parts by mass or more. Moreover, the result with preferable 3.0 mass parts or less from Table 3 demonstrated later is also obtained.
In addition to the hydrolysis inhibiting function by moisture removal etc. contained in the mixture consisting of each component such as natural rubber, the hydrolysis inhibitor is added to the component as in the crosslinking reaction with the epoxy group with the epoxidized natural rubber described later. It has a function of performing a crosslinking reaction or the like via the contained functional group. This cross-linking reaction is considered to occur between the rubber dispersed phase composed of natural rubber and epoxidized natural rubber and the resin matrix phase composed of polylactic acid. Impact resistance, heat resistance, and mechanical properties (high temperature and high humidity) It is considered that it contributes to improvement of retention characteristics (including hydrolysis resistance) over time under conditions.
As a compound that performs such a crosslinking reaction, polyamine, polyol, polycarboxylic acid, acid anhydride, organic carboxylic acid ammonium salt, dithiocarbamate, and the like can be used in combination.

(Polylactic acid)
In the present invention, polylactic acid is a polymer composed of monomer units derived from L-lactic acid and / or D-lactic acid. Other monomer units not derived from L-lactic acid or D-lactic acid may be included as long as the effects of the present invention are not impaired. Examples of other monomer units include monosaccharides, oligosaccharides, polysaccharides and the like, and they can be contained in an amount of 10 mol% or less. The mass average molecular weight of polylactic acid is preferably in the range of 50,000 to 300,000. If it falls below this range, mechanical properties and the like may not be fully expressed, and if it exceeds, the processability tends to be inferior.
As polylactic acid used in the present invention, for example, poly L-lactic acid is not particularly limited, but a polymerization catalyst is added to a mixture of 90% fermented lactic acid and starch, and dehydrated polymerization is used. Any of commercially available polylactic acid (such as Lacia H-100 manufactured by Mitsui Chemicals, Inc.) or polylactic acid containing a heat-resistant nanocomposite filler may be used. In addition, in the calculation of the compounding ratio of the resin composition of this invention, this additive of polylactic acid containing additives, such as a filler, is handled separately from polylactic acid.
For example, in the present invention, when poly-L-lactic acid is used as the polylactic acid, it is possible to use a homopolymer or copolymer containing at least D-lactic acid as a monomer unit as the crystal nucleating agent. From the viewpoint of maintaining the impact resistance and heat resistance of the lactic acid resin composition.

(Natural rubber)
The natural rubber used in the resin composition of the present invention includes not only a naturally occurring rubber but also a polyisoprene synthesized. However, in recent years, since it is desired to be derived from plants, natural rubber is mainly used. When synthetic polyisoprene is used, those having a high cis-1,4 bond content are preferred. Examples of natural rubber include sheet rubber such as natural rubber latex, ribbed smoked sheet, white crepe, pale crepe, estate brown crepe, component crepe, thin brown crepe, thick blanket crepe, flat bar crepe, and pure smoked blanket crepe. Examples include block rubber.
In the resin composition of the present invention, the amount of natural rubber added is preferably 1 to 30 parts by weight, more preferably 1.5 to 30 parts by weight, and 2 to 20 parts by weight or 2 to 13 parts per 100 parts by weight of polylactic acid. Part by mass, and further 2.5 to 12.5 parts by mass are particularly preferable. If the amount is less than 1 part by mass, the impact resistance improving effect tends not to be obtained. When added over 30 parts by mass, the heat resistance tends to decrease.

(Crystal nucleating agent)
The crystal nucleating agent used in the resin composition of the present invention is not particularly limited as long as it has a function of accelerating crystallization of polylactic acid, but is preferably an organic type. Examples of the polylactic acid include homopolymers or copolymers containing at least lactic acid having different chirality as a monomer unit. Examples of the copolymerizable monomer include polysaccharides such as starch and glucomannan, monosaccharides such as glucose, disaccharides such as sucrose and maltose, oligosaccharides such as cyclodextrin, and the like. Examples thereof include polylactic acid and lactic acid-starch copolymer resin having different chiralities, and any of these may be used, but the lactic acid-starch copolymer containing 0.1% by mass to 1% by mass of sugar. A resin is more preferable. As described above, in the present invention, when poly L-lactic acid is used as the polylactic acid, the polylactic acid having a different chirality from the polylactic acid is a homopolymer or copolymer containing at least D-lactic acid as a monomer unit. It becomes.
The molecular weight of the crystal nucleating agent is not particularly limited, but is preferably in the range of 1,000 to 2,000,000. In the case of 1,000 or less, a eutectic is formed and the crystallization speed is increased, but the resin may be honey-like and difficult to handle, and if it exceeds 2,000,000, the melt viscosity becomes large and at the end of the polymerization. It may be difficult to remove.
The addition amount of the crystal nucleating agent in the resin composition of the present invention is not particularly limited, but is preferably 1 to 15 parts by weight, more preferably 0.5 to 12 parts by weight, with respect to 100 parts by weight of polylactic acid. Part by mass is particularly preferred. When the amount is less than 1 part by mass, a remarkable crystallization promoting effect tends to be hardly obtained, and when the amount exceeds 15 parts by mass, the resin strength tends to decrease.

(Epoxidized natural rubber)
The epoxidized natural rubber used in the present invention is one in which an epoxy group is introduced into the natural rubber with an epoxidizing agent such as hydrogen peroxide or peracetic acid, and is not particularly limited. It is preferably 20% to 50% with respect to the number of moles of the double bond.
In the resin composition of the present invention, the amount of epoxidized natural rubber added is preferably 0.1 to 30 parts by weight, more preferably 0.2 to 10 parts by weight, and more preferably 0.25 to 5 parts per 100 parts by weight of polylactic acid. Part by mass is particularly preferred. The mass ratio of natural rubber to epoxidized natural rubber is the former: the latter, preferably 98: 2 to 40:60, and more preferably 90:10 to 50:50. Moreover, 1-30 mass parts is preferable with respect to 100 mass parts of polylactic acid, and the sum of natural rubber and epoxidized natural rubber has still more preferable 1.5-30 mass parts, 2-20 mass parts or 2-13. Part by mass, and further 2.5 to 12.5 parts by mass are particularly preferable. According to the preferable range, further improvement in impact resistance can be expected, heat resistance is ensured, and roll workability is also maintained well. As described above, it is considered that the (crosslinking) reaction product of the epoxidized natural rubber and the hydrolysis inhibitor functions as a compatibilizing agent for uniformly dispersing the natural rubber in polylactic acid. .
The resin composition of the present invention preferably uses a general anti-aging agent for rubber in order to suppress degradation of natural rubber and epoxidized natural rubber. This anti-aging agent is preferably used in an amount of 0.05 to 0.5 parts by weight, more preferably 0.1 to 0.3 parts by weight, based on 100 parts by weight of polylactic acid.

(Medium chain fatty acid triglyceride)
In the present invention, medium chain fatty acid triglyceride significantly improves impact resistance in the polylactic acid resin composition of the present invention. This is considered to be mainly due to the anchoring effect of the chain length of the medium chain fatty acid having a very appropriate bulk in the same system when the medium chain fatty acid triglyceride is dispersed in the same system. This is in contrast to the use of triacetin described in Patent Document 4 as a crystallization accelerator, and it is clear that the mechanism of action is different from the comparative examples described later.
The medium chain fatty acid of the medium chain fatty acid triglyceride is preferably a fatty acid having 4 to 12 carbon atoms in order to effectively exhibit the above action, and more preferably 5 to 10 carbon atoms. This medium chain fatty acid molecular moiety may be linear, branched, cyclic, or a combination thereof, and may be saturated or unsaturated. Further, the medium chain fatty acid molecule portion can be substituted with the same or different from the three hydroxyl groups of glycerin as long as the number of carbon atoms is within the above range. The various molecules can be used alone or in combination.
The addition amount of medium chain fatty acid triglyceride for effectively exhibiting the above action is preferably 0.5 to 10 parts by mass with respect to 100 parts by mass of polylactic acid, more preferably 1 to 7 parts by mass, Is 1-5 parts by mass and 1-3 parts by mass. If the addition amount of medium-chain fatty acid triglycerides exceeds 7 parts by mass, the heat resistance of the resin tends to decrease. For example, the heat resistance of 80 ° C. or higher required for automobile interior parts cannot be shown, and it may become impractical. There is sex.

In the present invention, natural rubber may be chemically modified by a method other than the above in order to obtain desired characteristics, or a softness-imparting agent such as polycaprolactone may be used in combination. For example, polycaprolactone or the like is used in combination to improve the heat resistance of the resin composition. However, the addition of polycaprolactone reduces the plantiness of the resin.
Additives other than those described above can be added to the resin composition of the present invention. Specific additives include weather resistance improvers, such as ultraviolet absorbers such as titanium oxide, hindered amine light stabilizers, and antioxidants; lubricants such as higher fatty acid alcohols, aliphatic amides, metal soaps, And fatty acid esters.
In the resin composition of the present invention, the average particle size of the rubber dispersed phase is 3 μm or less, the average particle size of the dispersed phase is more preferably 0.2 to 2.5 μm, and particularly preferably 0.3 to 2.0 μm. This average particle diameter means a value obtained by arithmetically averaging 450 to 550 natural rubber particles measured by visual observation using a polarizing microscope, heated and melted on a hot stage at 200 ° C.

The means for producing the resin composition of the present invention is not particularly limited, such as adjusting conditions such as temperature and pressure. Examples of such means include use of a known apparatus such as a twin screw extruder and a kneader.
In the present invention, it is preferable to add a blend containing the above-described components to a twin screw extruder to obtain a resin composition.
Here, the blending condition of the twin-screw extruder is preferably a temperature of 180 to 200 ° C.
The resin composition blended and extruded by the above twin screw extruder may be used as it is, or may be pelletized for injection molding. Further, the pelletized resin composition of the present invention can be used together with other resins or rubbers to produce a molded body by an injection molding machine or an extruder.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these.
Example 1
a. Natural rubber (NR) pelletization An 8-inch open roll set at a temperature of 40 ° C is loaded with an NR block (Sri Lanka pale crepe) cut into 10 cm square by a guillotine cutter, and an amount of about 1 kg of NR is wound on the roll. , And plasticized for about 10 minutes (roll gap during plasticization: 1.5 mm). This plasticized product was finely cut into the same size as the poly L-lactic acid pellet described later.
b. Pelletization of resin composition 100 parts by mass of polylactic acid (poly L-lactic acid, Lacia H-100 manufactured by Mitsui Chemicals, Inc.), 2.5 parts by mass of natural rubber pellets, D-lactic acid-0.1% by mass-starch Each pellet of 5 parts by mass of polymer resin (crystal nucleating agent) and 3 parts by mass of hydrolysis inhibitor (carbodiimide compound, carbodilite LA-1, manufactured by Nisshinbo Co., Ltd.) is weighed and then premixed in a PE bag. After that, it was put into a twin-screw extruder (S1KRC kneader manufactured by Kurimoto) set at a resin temperature of 180 ° C., extruded into a strand shape on a conveyor, and then pelletized with a pelletizer.
c. Injection molding of pellets Using the injection molding machine SAV-30 manufactured by Yamashiro Seiki Seisakusho Co., Ltd., the pellets prepared in b were JIS K7110 Izod test specimens, JIS 7113 No. 1 tensile test specimens, and rods for load deflection measurement. A test piece (120 mm × 12 mm × 4 mm) was molded. The molding temperature was set to 180 ° C., 170 ° C., 175 ° C., and 180 ° C. in the order of the cylinder temperature, the upper part of the screw, the lower part of the screw, and the nozzle. Further, a test piece was molded at an injection time of 20 seconds, a cooling time of 100 seconds, (a total molding time of injection time and cooling time of 2 minutes), and a mold temperature (molding temperature) of 110 ° C. After taking out the test piece, it was heat-treated at an after-curing temperature of 110 ° C. and an after-curing time of 2 hours to obtain a final test piece. There was no deformation or shrinkage due to heat treatment.
The obtained test piece was measured for Izod impact strength according to JIS K7110. However, No. 2 test piece was used. Further, the deflection temperature under load was measured in accordance with JIS K7191-1-B method. However, edgewise test pieces were used. Further, the maximum tensile strength and elongation at break of JIS K7113 and the elastic modulus were also measured in accordance with JIS K7113. The results are shown in Table 1.
Examples 2 to 15, Reference Example 1, Comparative Examples 1 to 4
Except that the components of Example 1 and the amount (parts by mass) thereof were changed to those shown in Table 1, pellets were prepared and evaluated as in Example 1, and the results are shown in Table 1. Indicated. The epoxidized natural rubber is epoxidized: 50 mol%, ENR50 manufactured by Muang Mai Guthrie Public Company Limited in Thailand. This is because a. During the pelletization of natural rubber (NR), NR was wound around a roll and at the same time the required amount was added.

The following is understood from the above table.
From the comparison with Examples 1 to 4 of the same literature including Examples 1 to 15 and Reference Example 1 (Example 1 of Patent Document 6 is transcribed and molding conditions are according to the same literature), the resin of the present invention It can be understood that the composition can improve heat resistance and impact resistance as compared with the resin composition of Patent Document 6. The flexibility-imparting agent is polycaprolactone, and the compatibilizing agent is poly L-lactic acid-polybutylene succinate block copolymer resin.
From comparison between Examples 1 to 5 and Comparative Examples 2 and 3, the resin composition 1 of the present invention improves both impact resistance and heat resistance, but does not use natural rubber or a hydrolysis inhibitor. Although heat resistance is satisfied, impact resistance is not ensured. If the rubber component is not added as in Comparative Example 2, the moldability is lowered and the molding becomes impossible.
In Examples 6 to 10 of the resin composition 2 of the present invention, when epoxidized natural rubber is added as a rubber component, heat resistance is ensured when 10 parts by mass or more of the rubber component is added compared to the case of natural rubber alone. The impact resistance can be further improved.
In Examples 9 and 11 and Comparative Example 1, if no hydrolysis inhibitor is added, the hydrolysis resistance is lowered and the impact resistance is significantly lowered.
In Examples 9 to 15 and Comparative Example 4, it is suggested that the ratio (mass) of natural rubber to epoxidized natural rubber is preferably in the range of 98: 2 to 40:60. When the ratio of the epoxidized natural rubber exceeds 60%, roll workability is remarkably lowered. Moreover, if the rubber component is entirely epoxidized natural rubber, impact resistance is significantly lowered as shown in Comparative Example 5.
The rubber anti-aging agent used in Examples 12 to 15 and Comparative Example 4 is 2,2,4-trimethyl-1,2-dihydroquinoline (Nonflex RD, manufactured by Seiko Chemical Co., Ltd.).

Example 17
The same polylactic acid, natural rubber, crystal nucleating agent, hydrolysis inhibitor, and epoxidized natural rubber as in Example 9 were used.
a. Pelletization of natural rubber (NR) and epoxidized natural rubber (ENR) An NR block cut into 10 cm square with a guillotine cutter is put into an 8-inch open roll set at a temperature of 40 ° C, and 900 g of NR and 100 g of ENR are put into a roll It was wound and plasticized for about 10 minutes (roll gap during plasticization: 1.5 mm). This plasticized product was finely cut into the same size as the poly L-lactic acid pellet described later.
b. Pelletization of resin composition Each pellet of polylactic acid 100 parts by mass, NR and ENR pellets 10 parts by mass, crystal nucleating agent 5 parts by mass, hydrolysis inhibitor 3 parts by mass and medium chain fatty acid triglyceride (octylic acid triglyceride, NOF After weighing 1 part by mass of each Panacet 800 manufactured by Co., Ltd., premixed, and then put into a twin-screw extruder (S1 KRC kneader made by Kurimoto) set at a resin temperature of 180 ° C. and extruded into a strand on a conveyor And pelletized with a pelletizer.
c. Injection molding of pellets Using the injection molding machine SAV-30 manufactured by Yamashiro Seiki Seisakusho Co., Ltd., the pellets prepared in b were JIS K7110 Izod test specimens, JIS 7113 No. 1 tensile test specimens, and rods for load deflection measurement. A test piece (120 mm × 12 mm × 4 mm) was molded. The molding temperature was set to 180 ° C., 170 ° C., 175 ° C., and 180 ° C. in the order of the cylinder temperature, the upper part of the screw, the lower part of the screw, and the nozzle. Further, a test piece was molded at an injection time of 20 seconds, a cooling time of 100 seconds, (a total molding time of injection time and cooling time of 2 minutes), and a mold temperature (molding temperature) of 110 ° C. After taking out the test piece, it was heat-treated at an after-curing temperature of 110 ° C. and an after-curing time of 2 hours to obtain a final test piece. There was no deformation or shrinkage due to heat treatment.
The obtained test piece was measured for Izod impact strength according to JIS K7110. However, No. 1 test piece was used. Further, the deflection temperature under load was measured in accordance with JIS K7191-1-B method. However, a flatwise test piece was used. The results are shown in Table 2.

Examples 16, 18-22
Except that the components of Example 17 and the blending amount (parts by mass) thereof were changed to those shown in Table 2, pellets were prepared and evaluated as in Example 1, and the results are shown in Table 2. Indicated.

The following is understood from the above table.
Examples 16 to 20: From these examples, the impact resistance is remarkably improved by adding a small amount of medium chain fatty acid triglyceride to Example 16 in comparison with Example 16. Moreover, the heat resistance of 80 degreeC or more suitable for a vehicle interior component is maintained.
Example 21: Addition of 7 parts by mass of medium chain fatty acid triglyceride improves impact resistance but slightly decreases heat resistance.
Example 22: When 5 parts by mass of triacetin (acetic acid triglyceride) described in Patent Document 4 is added to medium chain fatty acid triglyceride, the heat resistance is equivalent to that of Example 20, but the impact resistance is inferior. This is because in this example, the fatty acid of the triglyceride is lower than the medium chain fatty acid having 2 carbon atoms and the medium chain fatty acid triglyceride.

Examples 23 to 33, Comparative Example 5
The molecular weight of the hydrolysis inhibitor (carbodiimide compound) was changed, and using the blending components and blending amounts (parts by mass) according to Table 3, pellets were produced in the same manner as described above, and test pieces were produced and evaluated in the same manner. Are shown in Table 3. However, the Izod impact strength test piece was No. 1 test piece, and the load deflection temperature test piece was measured flat-wise by the JIS K7191-1-B method. Moreover, in order to evaluate the hydrolysis resistance of a test piece, the strength retention was measured. The strength retention rate (%) was obtained by setting the tensile strength retention rate (after treatment) after 6 weeks of treatment of the test piece in an atmosphere of temperature 50 ° C. and humidity 95% as 100 × (after treatment / before treatment). The same polylactic acid, natural rubber, crystal nucleating agent, and epoxidized natural rubber as in Example 1 were used. Details of the carbodiimide compounds (samples A to E) are shown in Table 4. Sample D is the carbodilite LA-1. The molecular weights shown in Table 4 were measured using a GPC chromatograph after dissolving each carbodiimide compound in butanol and stirring at a temperature of 40 ° C. for 72 hours. Sample F is a monomer (bis (dipropylphenyl) carbodiimide) having a molecular weight of 363 (Stabaxol 1-LF manufactured by Rhein Chemie).

The following is understood from Tables 3 and 4.
1) From the comparison between Example 23 and other examples, when epoxidized natural rubber is used in combination, the number average molecular weight Mn of the carbodiimide compound of the hydrolysis inhibitor is 1300 or more, preferably 3000 or more. It can be seen that it is effective in improving the impact resistance while maintaining the mechanical strength (including hydrolysis resistance (strength retention) under high temperature and high humidity conditions) and heat resistance.
2) From Examples 24-31, it can be seen that 1.5-2 parts by mass of the carbodiimide compound is most effective with respect to 100 parts by mass of polylactic acid.

Claims (11)

  A resin composition comprising polylactic acid, natural rubber, a crystal nucleating agent, and a hydrolysis inhibitor.   The resin composition according to claim 1, wherein the hydrolysis inhibitor is a carbodiimide compound.   The resin composition of Claim 1 or 2 containing an epoxidized natural rubber.   The resin composition according to any one of claims 1 to 3, comprising a medium chain fatty acid triglyceride.   The resin composition according to any one of claims 1 to 4, wherein the polylactic acid is poly L-lactic acid, and the crystal nucleating agent is a homopolymer or copolymer containing at least D-lactic acid as a monomer unit. .   The resin composition according to any one of claims 2 to 5, wherein the carbodiimide compound has a number average molecular weight of 500 or more.   The resin composition according to any one of claims 1 to 6, wherein the medium chain fatty acid of the medium chain fatty acid triglyceride is a fatty acid having 4 to 12 carbon atoms.   The resin composition according to any one of claims 1 to 7, comprising 100 parts by mass of polylactic acid, 1 to 30 parts by mass of natural rubber, 1 to 15 parts by mass of a crystal nucleating agent, and 0.2 parts by mass or more of a carbodiimide compound. object.   The resin composition of any one of Claims 1-8 containing 0.1-30 mass parts of epoxidized natural rubbers with respect to 100 mass parts of polylactic acid.   The resin composition of any one of Claims 1-9 containing 0.5-10 mass parts of medium chain fatty acid triglycerides with respect to 100 mass parts of polylactic acid.   11. The resin composition according to claim 1, wherein a mass ratio of the natural rubber to the epoxidized natural rubber is 98: 2 to 40:60 in the former: the latter.