JP2012219151A - Resin composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin composition which is based on polylactic acid and has improved impact resistance, heat resistance or mechanical characteristics in addition thereto at high temperature, in high humidity and with the lapse of time.SOLUTION: The resin composition contains polylactic acid, natural rubber and a carbodiimide compound having 5,000-15,000 mass-average molecular weight Mw and 2,000-5,000 number-average molecular weight Mn. A molded article of the resin composition is also provided.

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 applicant has proposed to use a hydrolysis inhibitor containing a carbodiimide compound in order to achieve the above-described improvement (Japanese Patent Application No. 2010-115391).
However, the heat retention, particularly the Charpy impact strength (kJ / m ² ) at high temperature, high humidity, and strength retention over time has been a concern for applications such as automobile parts and home appliance parts.
The present invention aims to provide a resin composition mainly comprising polylactic acid, which is improved in impact resistance and heat resistance over time, at high humidity, over time, and further in mechanical properties. is there.

The present invention is as follows.
1) A resin composition comprising polylactic acid, natural rubber, a crystal nucleating agent, and a carbodiimide compound having a mass average molecular weight Mw of 5000 to 15000 and a number average molecular weight Mn of 2000 to 5000.
2) A molded product of the resin composition of 1) above.
The present invention has been studied as a result of the need to improve the heat retention, particularly the Charpy impact strength (kJ / m ² ) at high temperature, high humidity, and strength retention over time, and as a result, the molecular weight range of the carbodiimide compound can greatly affect. It is a headline and made.
In the resin composition of the present invention, each component may be made into a kit, may be simply mixed, or may be partially mixed. A kit may be a mixture of two or more of various components alone, for example, a pelletized rubber component (natural rubber and epoxidized natural rubber, or natural rubber, epoxidized natural rubber, etc.) A combination of the components of the composition of the present invention may be mentioned by a combination of pelletized resin components.

  The resin composition of the present invention has improved impact resistance and heat resistance or further mechanical properties, and can improve the plantiness to about 97%, and is widely used as an alternative to general-purpose plastics, especially as automobile parts and household appliance parts it can. 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.

It is a graph which shows the relationship between the number average molecular weight Mn of a carbodiimide compound, and Charpy impact strength. It is a graph which shows the relationship between the number average molecular weight Mn of a carbodiimide compound and Charpy impact strength retention. It is a graph which shows the relationship between the mass mean molecular weight Mw of a carbodiimide compound, and Charpy impact strength. It is a graph which shows the relationship between the mass mean molecular weight Mw of a carbodiimide compound, and Charpy impact strength retention.

The components of the resin composition of the present invention will be described.
(Carbodiimide compound)
The carbodiimide compound used in the resin composition of the present invention is a compound having one or more carbodiimide groups. In addition to the function of inhibiting hydrolysis by removing moisture contained in the mixture composed of components such as natural rubber, the epoxy described later It has a function of performing a crosslinking reaction or the like via a functional group contained in a component, such as a crosslinking reaction with an epoxy group with a natural rubber. 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. In the present invention, it has been found that the above characteristics can be properly exhibited by specifying the molecular weight range of the carbodiimide compound.
The carbodiimide compound has a mass average molecular weight Mw of 5000 to 15000, more preferably 5500 to 12000, further preferably 6000 to 10000, and 6500 to 9000. The number average molecular weight Mn of the carbodiimide compound is 2000 to 5000, more preferably 2500 to 4500, and 2700 to 4000, and 2900 to 3500. 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. A compound containing three or more carbodiimide groups in one molecule is also referred to as a polycarbodiimide compound.
The amount of the carbodiimide compound used in the resin composition of the present invention is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, particularly 2 parts by mass or more, relative to 100 parts by mass of polylactic acid. The content of 3 parts by mass or more and most preferably 4 parts by mass or more is effective for achieving the object of the present invention. Although there is no particular upper limit, the effect is not improved at about 10 parts by mass or more.
The carbodiimide compound used in the present invention performs crosslinking as described above, and as a compound that performs such a crosslinking reaction, polyamine, polyol, polycarboxylic acid, acid anhydride, organic carboxylic acid ammonium salt, dithiocarbamate, etc. It can also be used together.

(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 bark 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 mass, more preferably 2 to 20 parts by mass, and 3 to 15 parts by mass or 4 to 12 parts by mass with respect to 100 parts by mass of polylactic acid. Further, 5 to 10 parts by mass is 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 promoting crystallization of polylactic acid, either inorganic or organic.
Examples of the inorganic crystal nucleating agent include talc and mica.
Examples of organic acid metal salts as crystal nucleating agents include zinc phenyl phosphate and zinc lactate.
Examples of the organic crystal nucleating agent include a homopolymer or a copolymer containing at least lactic acid having a chirality different from that of the polylactic acid 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 polymerization. It may be difficult to remove.
Further, by using bamboo fiber or bamboo powder in combination, the crystallization speed may be further increased and the heat resistance of the resin may be improved. The same effect can be expected from finely pulverized cellulose.
Among them, an organic acid metal salt is preferable as the crystal nucleating agent.
The addition amount of the crystal nucleating agent in the resin composition of the present invention is not particularly limited, but is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and further 5 parts by mass or less, and more preferably 100 parts by mass of polylactic acid. Is preferably 3 or 2 parts by mass or less, more preferably 1.5 to 0.3 parts by mass, and particularly preferably 1.0 to 0.5 parts by mass depending on the type of crystal nucleating agent. When the amount is less than 0.3 part by mass, a remarkable crystallization promoting effect tends to be hardly obtained, and when the amount exceeds 10 parts by mass, the resin strength tends to decrease. In any case, the addition amount is adjusted to an appropriate amount depending on the kind of the crystal nucleating agent.

(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. 20% to 50% is preferable 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 0.3 to 5 parts by weight with respect to 100 parts by weight of polylactic acid. Part by mass, 0.4 to 3 parts by mass, and 0.5 to 2 parts by mass are particularly preferable. 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, as for the sum of natural rubber and epoxidized natural rubber, 1.5-25 mass parts is more preferable, 2-20 mass parts or 3-15. Part by mass, and further 4 to 12 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.

(Other)
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, for example, ultraviolet absorbers such as titanium oxide, hindered amine light stabilizers, plasticizers such as vegetable oils such as soybean oil and medium chain fatty acid triglycerides, and antioxidants and lubricants. Examples thereof include higher fatty acid alcohols, aliphatic amides, metal soaps and fatty acid esters, fillers such as cellulose or its powder, carbon black (including master batch), and the like.

The means for producing the resin composition and molded body 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 molded body of the resin composition blended and extruded by the above twin screw extruder may be used as a product 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.

(Molded body)
The molded body of the present invention is based on JIS K7111, and preferably has a Charpy impact strength of 15 kJ / m ² or more, more preferably 17 to 28. Further, the retention rate (100 × (after treatment / before treatment)) of Charpy impact strength (kJ / m ² ) at 80 ° C., 95% humidity and 96 hours treatment is preferably 60% or more, and more preferably 65 to 90%. preferable.
Moreover, the molded object of this invention is 40-70 Mpa of tensile strength according to JISK7113, 1-5% of elongation at the maximum load, and 2000-3000 Mpa of elastic modulus.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these.
Comparative 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 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), 6.75 parts by mass of natural rubber pellet, crystal nucleating agent (zinc phenyl phosphate, Nissan Chemical Industries) Ecopromote) 1 part by mass, carbodiimide compound (sample A: see Tables 1 and 2) 5 parts by mass, black masterbatch (black MB) (manufactured by Daiichi Seika Kogyo PT-RM H1016-45 [H]) 2 And pellets of 0.5 parts of stearylamide (NOF Alflow S-10) were weighed and premixed in a PE bag, and then a twin screw extruder set at a resin temperature of 180 ° C ( (S1 KRC kneader made by Kurimoto), 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, the pellets created in b were Charpy impact strength test specimens according to JIS K7111, No. 1 tensile test specimen of JIS K7113 A rod-shaped test piece (120 mm × 12 mm × 4 mm) for load deflection measurement 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. to obtain a final test piece.
The obtained test piece was measured for Charpy impact strength according to JIS K7111. The test pieces were also subjected to Charpy impact strength at 80 ° C., humidity 95%, and 96 hours, and the retention rate was determined. Further, the deflection temperature under load was measured in accordance with JIS K7191-1-B method. However, edgewise test pieces were used. Further, the tensile strength and elongation of JIS K7113 and the elastic modulus were also measured according to JIS K7113. The results are shown in Table 1.

Example 1, Comparative Examples 2-3
Except that the carbodiimide compound of Comparative Example 1 (Sample A) was changed to that of Samples B to D (Table 1), pellets were prepared in the same manner as in Comparative Example 1, and test pieces were prepared and evaluated. The results are shown in Tables 1 and 2 and FIGS. Table 2 and FIGS. 1-4 show the relationship between the number average molecular weight Mn or the mass average molecular weight Mw of the carbodiimide compound and the Charpy impact strength or the retention rate thereof.

  From the above table and FIGS. 1-4, by using the carbodiimide compound in the molecular weight range of the present invention, the Charpy impact strength and its high temperature, high humidity, retention over time are improved while ensuring other mechanical properties. It is understood that you can.

Claims (6)

  A resin composition comprising polylactic acid, natural rubber, and a carbodiimide compound having a mass average molecular weight Mw of 5000 to 15000 and a number average molecular weight Mn of 2000 to 5000.   The resin composition of claim 1 comprising epoxidized natural rubber.   The resin composition of Claim 1 or 2 containing 100 mass parts of polylactic acids, 1-30 mass parts of natural rubber, 10 mass parts or less of crystal nucleating agents, and 0.5 mass part or more of carbodiimide compounds.   The molded object of the resin composition of any one of Claims 1-3. The molded article according to claim 4, wherein the Charpy impact strength is 15 kJ / m ² or more. The molded article according to claim 4 or 5, wherein a retention rate of Charpy impact strength (kJ / m ² ) at a temperature of 80 ° C, a humidity of 95%, and a treatment for 96 hours is 60% or more.

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