JP2006176652A - Polylactic acid resin composition and molded article produced by molding the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin composition having excellent mechanical strength, heat-resistance durable in practical use and moldability, shortened molding cycle in injection molding and excellent productivity and provide a molded article of the resin composition. <P>SOLUTION: The invention provides a resin composition composed of (A) 50-95 pts.mass of a crosslinked polylactic acid and (B) 50-5 pts.mass of glass fiber surface-treated with a silane coupling agent having epoxy group; the above resin composition wherein the silane coupling agent having epoxy resin is γ-glycidoxypropyltrimethoxysilane or γ-glycidoxypropylmethyldiethoxysilane; the above resin composition compounded further with (C) 0.01-20 pts.mass of a (meth)acrylic acid ester compound based on 100 pts.wt. of the crosslinked polylactic acid (A); and a molded article produced by molding the above resin composition. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a resin composition comprising a crosslinked polylactic acid and a glass fiber treated with a silane coupling agent having an epoxy group, and a molded article obtained by molding the resin composition, and has mechanical strength and heat resistance. The present invention relates to a resin composition having excellent moldability and low dependence on petroleum-based products, and a molded body molded using the resin composition.

Polylactic acid is a resin having crystallinity, but since the crystallization rate is slow, the mechanical strength, heat resistance, moldability and the like are often insufficient with ordinary molded articles. In order to improve the crystallization rate of polylactic acid, a method of adding talc, silica, calcium lactate or the like as a crystal nucleating agent has been proposed (for example, see Patent Document 1). However, this method has a problem that crystallization is insufficient because no heat treatment is performed, and productivity at the time of molding is inferior because a polymer crystallization rate is low. There is also a method of reinforcing polylactic acid by filling it with an inorganic filler or a fibrous reinforcing material (see, for example, Patent Document 2). However, although the rigidity at room temperature is improved to some extent, the crystallinity of polylactic acid itself is not high, so the rigidity and toughness are lowered in the temperature range exceeding the glass transition temperature, and it is difficult to obtain sufficient heat resistance. . Moreover, in order to improve the crystallization rate, a method of adding a glass fiber is also disclosed (for example, refer to Patent Document 3) as long as the biodegradable polyester resin is crosslinked and the properties of the resin composition are not impaired. However, in terms of mechanical strength, heat resistance, and moldability, the improvement effect is not always sufficient.
JP-A-8-193165 JP 2002-105298 A JP 2003-128901 A

  An object of the present invention is to solve the above problems and to stabilize the crystallinity and crystallinity of polylactic acid. An object of the present invention is to provide a resin composition and a practically used molded article that are shortened in the molding cycle at the time of injection molding by accelerating and excellent in productivity.

As a result of intensive studies to solve the above problems, the present inventors use a resin composition comprising a crosslinked polylactic acid and a glass fiber surface-treated with a silane coupling agent having an epoxy group. It has been found that the crystallization of polylactic acid can be promoted remarkably, the mechanical strength of the resin composition and the actual use temperature of the molded product obtained by molding the resin composition are improved, and the moldability is excellent. The present invention has been reached.
That is, the gist of the present invention is as follows.
(1) Resin composition comprising 50 to 95 parts by mass of crosslinked polylactic acid (A) and 50 to 5 parts by mass of glass fiber (B) surface-treated with a silane coupling agent having an epoxy group .
(2) The resin composition according to (1), wherein the silane coupling agent having an epoxy group is γ-glycidoxypropyltrimethoxysilane or γ-glycidoxypropylmethyldiethoxysilane.
(3) 0.01 to 20 parts by mass of (meth) acrylic acid ester compound (C) is blended with 100 parts by mass of crosslinked polylactic acid (A). (1) or (2) The resin composition as described.
(4) A molded article obtained by molding the resin composition according to any one of (1) to (3).

  ADVANTAGE OF THE INVENTION According to this invention, the resin composition with the low dependence on the petroleum-type product which has not only the improvement of mechanical strength but the outstanding heat resistance and moldability is provided. In particular, by blending glass fibers surface-treated with a silane coupling agent having an epoxy group, the molding cycle can be shortened by improving the crystallization speed. This resin composition can be made into various molded articles by various molding methods, and has very high industrial utility value. In addition, since a biodegradable resin derived from a natural product is used, it can contribute to saving of depleted resources such as oil.

Hereinafter, the present invention will be described in detail.
The resin composition of the present invention contains polylactic acid (A) having a crosslinked structure and glass fibers (B) subjected to surface treatment with a silane coupling agent having an epoxy group as main components. The blending ratio (A) / (B) needs to be 50 to 95/50 to 5 (parts by mass), and preferably 70 to 90/30 to 10 (parts by mass). If the amount of the crosslinked polylactic acid (A) exceeds 95 parts by mass, sufficient mechanical properties and heat resistance cannot be obtained. On the other hand, when the glass fiber (B) content exceeds 50 parts by mass, the effect is not only saturated, but the balance of mechanical properties is impaired, which is not preferable. That is, when the blending amount exceeds 50 parts by mass, the specific gravity of the mixture becomes too large, and the fluidity is lowered, so that the moldability is deteriorated. In addition, since the fibers float on the surface at the time of molding, the appearance is deteriorated, which is not preferable. Moreover, if the compounding quantity of glass fiber (B) is less than 5 mass parts, the reinforcement effect by glass fiber is not fully acquired.

  Examples of the polylactic acid used in the present invention include poly (L-lactic acid) and poly (D-lactic acid). From the viewpoint of biodegradation, poly (L-lactic acid) is preferred. Moreover, if it is a small amount, a mixture or copolymer with other polyesters such as polyglycolic acid, polycaprolactone, polybutylene succinate, polyethylene succinate and the like can be used, but from the viewpoint of biodegradability, poly (L -Lactic acid) is preferred.

  Further, the melting point of polylactic acid mainly composed of poly (L-lactic acid) varies depending on the optical purity, but in the present invention, the melting point is 160 ° C. or higher in consideration of the mechanical strength and heat resistance of the molded product. Is desirable. In order to obtain a melting point of 160 ° C. or higher in polylactic acid mainly composed of poly (L-lactic acid), the ratio of the D-lactic acid component may be less than about 3 mol%.

  The melt flow rate of polylactic acid at 190 ° C. and a load of 21.2 N is 0.1 to 50 g / 10 minutes, preferably 0.2 to 20 g / 10 minutes, and optimally 0.5 to 10 g / 10 minutes. When the melt flow rate exceeds 50 g / 10 min, the melt viscosity is too low, and the mechanical strength and heat resistance of the molded product may be inferior. On the other hand, when the melt flow rate is less than 0.1 g / 10 minutes, the load during the molding process becomes too high, and the operability may be lowered.

  Polylactic acid is usually produced by a known melt polymerization method or in combination with a solid phase polymerization method. As a method of adjusting the melt flow rate to a predetermined range, if the melt flow rate is too high, a resin is used by using a small amount of chain extender, for example, a diisocyanate compound, a bisoxazoline compound, an epoxy compound, an acid anhydride, or the like. And a method of increasing the molecular weight of Conversely, when the melt flow rate is too small, a method of mixing with a polyester resin or a low molecular weight compound having a large melt flow rate can be used.

  In the present invention, the crosslinked polylactic acid (A) is obtained by introducing a crosslinked structure into polylactic acid. Although it does not specifically limit as a form of bridge | crosslinking, You may use together what was bridge | crosslinked with polylactic acid alone, indirectly bridge | crosslinked via the crosslinking adjuvant, or both.

  As a method of introducing a crosslinked structure into polylactic acid, known methods such as electron beam irradiation and the use of a polyfunctional compound such as a polyvalent isocyanate compound can be applied. However, radical crosslinking by using a peroxide is possible in terms of crosslinking efficiency. desirable.

  Specific examples of peroxides include benzoyl peroxide, bis (butylperoxy) trimethylcyclohexane, bis (butylperoxy) cyclododecane, butylbis (butylperoxy) valerate, dicumyl peroxide, butylperoxybenzoate, dibutyl Examples thereof include peroxide, bis (butylperoxy) diisopropylbenzene, dimethyldi (butylperoxy) hexane, dimethyldi (butylperoxy) hexyne, and butylperoxycumene. 0.1-20 mass parts is preferable with respect to 100 mass parts of polylactic acids, and, as for the compounding quantity of a peroxide, More preferably, it is 0.1-10 mass parts. Although it can be used even if it exceeds 20 parts by mass, it is disadvantageous in terms of cost. In addition, since such a peroxide decomposes | disassembles at the time of mixing with resin, even if it is used at the time of a mixing | blending, it may not be contained in the obtained resin composition.

  In order to further increase the crosslinking efficiency, it is desirable to use the (meth) acrylic acid ester compound (C) as a crosslinking aid together with the peroxide. Through this component, the polylactic acid component is cross-linked, and mechanical strength, heat resistance, dimensional stability and crystallization speed are improved. As the (meth) acrylic acid ester compound (C), the reactivity with polylactic acid is high, the monomer hardly remains, and the resin is less colored. Therefore, two or more (meth) acrylic groups are contained in the molecule. Compounds having one or more (meth) acryl groups and one or more glycidyl groups or vinyl groups are preferred. Specific compounds include glycidyl methacrylate, glycidyl acrylate, glycerol dimethacrylate, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, allyloxy polyethylene glycol monoacrylate, allyloxy polyethylene glycol monomethacrylate, polyethylene glycol dimethacrylate, polyethylene glycol. Diacrylate, polypropylene glycol dimethacrylate, polypropylene glycol diacrylate, polytetramethylene glycol dimethacrylate, and these alkylene glycol structures may also be copolymers of alkylenes having different numbers of carbon atoms, butanediol methacrylate, butanediol acrylate Etc., among others Polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate are preferred from the high refractory reasons.

  When the (meth) acrylic acid ester compound (C) is blended as a crosslinking aid, the amount thereof is preferably 0.01 to 20 parts by mass, more preferably 0.05 to 10 parts by mass with respect to 100 parts by mass of polylactic acid. Is preferable, and 0.1-5 mass parts is more preferable. If the operability is not particularly hindered, it can be used in excess of 20 parts by mass.

  As a means for blending the polylactic acid with the peroxide and the (meth) acrylic acid ester compound (C), there can be mentioned a method of melt-kneading using a general extruder. In order to improve the kneading state, it is preferable to use a twin screw extruder. The kneading temperature is preferably in the range of (melting point of polylactic acid + 5 ° C.) to (melting point of polylactic acid + 100 ° C.), and the kneading time is preferably 20 seconds to 30 minutes. If the temperature is lower or shorter than this range, kneading or reaction is insufficient, and if the temperature is higher or longer, the resin may be decomposed or colored. In blending, a (meth) acrylic acid ester compound (C) or a method of supplying a solid blend using a dry blend or a powder feeder is preferable. If liquid, extrusion is performed using a pressure pump. A method of injecting from the middle of the machine is preferred.

  As a preferable method when the (meth) acrylic acid ester compound (C) and the peroxide are used in combination, the (meth) acrylic acid ester compound (C) and / or the peroxide is dissolved or dispersed in a medium and mixed in a kneader. The method of inject | pouring is mentioned and operativity can be improved significantly. That is, during melting and kneading of polylactic acid and peroxide, a solution or dispersion of (meth) acrylic ester compound (C) is injected, or during melting and kneading of polylactic acid, (meth) acrylic A solution or dispersion of the acid ester compound (C) and peroxide can be injected and melt kneaded.

  As a medium for dissolving or dispersing the (meth) acrylic acid ester compound (C) and / or peroxide, a conventionally known medium is used and is not particularly limited, but is excellent in compatibility with the polylactic acid of the present invention. A plasticizer is preferred. For example, one or more selected from aliphatic polycarboxylic acid ester derivatives, aliphatic polyhydric alcohol ester derivatives, aliphatic oxyester derivatives, aliphatic polyether derivatives, aliphatic polyether polycarboxylic acid ester derivatives, etc. Examples include plasticizers. Specific examples of the compound include dimethyl adipate, dibutyl adipate, triethylene glycol diacetate, methyl acetyl ricinoleate, acetyl tributyl citric acid, polyethylene glycol, and dibutyl diglycol succinate. As a usage-amount of a plasticizer, 30 mass parts or less are preferable with respect to a total of 100 mass parts of crosslinked polylactic acid (A) and glass fiber (B), and 0.1-20 mass parts is more preferable. When the reactivity of the crosslinking agent is low, it is not necessary to use the plasticizer, but when the reactivity is high, it is preferable to use 0.1 parts by mass or more. In addition, since this medium may volatilize at the time of mixing with resin, even if it uses it at the time of manufacture, this medium may not be contained in the obtained resin composition.

  The glass fiber (B) used in the present invention needs to be surface-treated with a silane coupling agent having an epoxy group. Examples of the silane coupling agent having an epoxy group include β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, β- (3,4-epoxycyclohexyl) ethyltriethoxysilane, and γ-glycidoxypropyltrimethoxy. Examples include silane, γ-glycidoxypropyltriethoxysilane, and γ-glycidoxypropylmethyldiethoxysilane. One or more compounds may be arbitrarily selected from these silane coupling agents. From the viewpoint of reactivity and cost, γ-glycidoxypropyltrimethoxysilane and γ-glycidoxypropylmethyldiethoxysilane are preferred.

    Examples of the method for treating the surface of glass fiber with a coupling agent include the following methods. If necessary, an organic acid such as acetic acid or formic acid is added to water or a mixed solution containing water and an organic solvent such as methyl alcohol or ethyl alcohol to adjust the pH, and the silane coupling agent is added to this. Dissolve or disperse to prepare a treatment solution. The glass fiber is immersed in the treatment liquid, or the treatment liquid is sprayed onto the glass fiber by spraying or the like, and the treatment liquid is attached to the glass fiber surface. Next, after squeezing out the excess treatment liquid, there is a method in which the glass fiber is heated or dried at room temperature. In addition, 0.1-2.0 mass parts is preferable with respect to 100 mass parts of polylactic acid, and, as for the addition amount of a silane coupling agent, 0.5-1.5 mass parts is more preferable.

  The length of the glass fiber (B) used in the present invention is preferably 3 to 25 mm, and more preferably 5 to 15 mm. The longer the fiber length, the greater the reinforcing effect and the higher the flexural modulus. That is, the rigidity is further increased. If the fiber length is less than 3 mm, a sufficient reinforcing effect due to the fiber length cannot be obtained, and if the fiber length exceeds 25 mm, the fluidity is greatly reduced, which is not preferable in terms of moldability.

  As a method for adding the glass fiber (B) used in the present invention, the glass fiber (B) can be added from a hopper or using a side feeder in an extruder. Moreover, it can also use by diluting with a base resin at the time of shaping | molding by carrying out a masterbatch process of glass fiber.

  The resin composition of the present invention can be formed into various molded products by molding methods such as injection molding, blow molding, extrusion molding, inflation molding, and vacuum molding, pressure molding, and vacuum / pressure molding after sheet processing. In particular, an injection molding method is preferable, and in addition to a general injection molding method, gas injection molding, injection press molding, or the like can be employed. As an example of injection molding conditions suitable for the resin composition of the present invention, the cylinder temperature is not less than Tm of polylactic acid or the flow start temperature, preferably 190 to 280 ° C, more preferably 210 to 270 ° C, and The mold temperature is suitably set to (Tm-20 ° C.) or less of the resin composition. If the molding temperature is too low, the operability becomes unstable or overload is likely to occur, such as a short circuit in the molded product. Conversely, if the molding temperature is too high, the resin composition will decompose and the strength of the resulting molded product It tends to cause problems such as a decrease in color and coloring.

  The polylactic acid of the present invention can improve its heat resistance by promoting crystallization. As a method for this, for example, there is a method of promoting crystallization by cooling in a mold at the time of injection molding. In this case, the mold temperature is set to (Tg + 20 ° C.) or more of polylactic acid (Tm− It is preferable that the temperature is kept below 20 ° C. for a predetermined time and then cooled to Tg or less. Further, as a method for promoting crystallization after molding, it is preferable to directly heat the sample at Tg or more and (Tm−20 ° C.) or less after cooling to Tg or less.

  Specific examples of molded articles include resin parts for electrical appliances such as various cases, agricultural materials such as containers and cultivation containers, resin parts for agricultural machinery, resin parts for fishery business such as floats and processed fishery products containers, dishes, Tableware and food containers such as cups and spoons, medical resin parts such as syringes and infusion containers, drain materials, fences, storage boxes, resin parts for housing, civil engineering, and building materials such as construction switchboards, cooler boxes, fan fans, and toys Such as resin parts for miscellaneous goods, automobile parts such as bumpers, instrument panels and door trims. Moreover, it can also be set as extrusion molded articles, such as a film, a sheet | seat, and a pipe, and a hollow molded article.

Hereinafter, the present invention will be described more specifically with reference to examples. The measuring method used for evaluation of the resin composition of an Example and a comparative example is as follows.
(1) Melt flow rate (MFR):
According to JIS standard K-7210 (test condition 4), it measured at 190 degreeC and the load 21.2N.
(2) Molding cycle:
Resin compositions A to O obtained in Examples and Comparative Examples were molded using an injection molding machine (Toshiba Machine IS-80G type) to obtain test pieces. At this time, the resin compositions A to L were melted at a cylinder set temperature of 190 to 170 ° C. and filled in a mold of 105 ° C. with an injection pressure of 100 MPa and an injection time of 30 seconds. Resin compositions N and N were filled in a mold with an injection pressure of 100 MPa and an injection time of 15 seconds. The molding cycle was defined as the time from when the resin composition was injected (filled, pressure-carrying) into the mold until it was cooled and taken out without resistance without the molded body sticking to the mold.
(3) Releasability:
When the molded body was taken out from the mold, the degree of fixing to the mold was evaluated in three stages based on the following criteria. The cooling time in the molding cycle was evaluated at 70 seconds, and ○ was accepted.
○: The molded body did not stick to the mold, could be taken out without resistance, and there was no deformation. Δ: The molded body was slightly fixed to the mold and slightly deformed when taken out, and there was a problem in practical use. X: The molded body was fixed to the mold, and it was necessary to apply a strong load to take out, and the molded body was deformed by the load.
(4) Bending strength, bending elastic modulus, bending breaking strain:
Measured according to ISO 178.
(5) Charpy impact strength:
Measured according to ISO 179.
(6) Thermal deformation temperature:
According to ISO 75, the heat distortion temperature was measured with a load of 0.45 MPa.

The raw materials used in Examples and Comparative Examples of the present invention are shown below.
Polylactic acid: Cargill Dow, NatureWorks 4030D; MFR = 3.0, melting point 166 ° C. (hereinafter abbreviated as “PLA”).
Glass fiber (no coupling agent treatment): manufactured by Unitika Glass Fiber Co., Ltd .: fiber diameter φ10 μm, fiber length 5 mm
Silane coupling agent:
A: Nihon Unicar Co., Ltd., A-187, γ-glycidoxypropyltrimethoxysilane B: GE Toshiba Silicone Co., Ltd., TSL-8350, γ-glycidoxypropylmethyldiethoxysilane C: Nihon Unicar Co., Ltd., A -189, γ-mercaptopropyltrimethoxysilane D: manufactured by Nihon Unicar Co., Ltd., A-1100, γ-aminopropyltriethoxysilane peroxide: manufactured by NOF Corporation, di-t-butyl peroxide methacrylate: Japan Polyethylene glycol dimethacrylate, manufactured by Yushi Co.

Example 1 (resin composition A)
Using a twin screw extruder (TEM-37BS manufactured by Toshiba Machine Co., Ltd.), a treatment liquid (acidic) containing 95 parts by mass of PLA at the top feeder port and 0.3 parts by mass of silane coupling agent A at the side feeder port. 5 parts by mass of the glass fiber surface-treated by spraying an aqueous solution), and 3 parts by mass of di-t-butyl peroxide and 1.5 parts by mass of polyethylene glycol dimethacrylate were supplied from the middle of the kneader using a pump. . Melt kneading extrusion was performed at a processing temperature of 170 to 190 ° C., and the discharged resin was cut into pellets to obtain a resin composition A.

Examples 2 to 4 (resin compositions B to D), Comparative Examples 1 and 2 (resin compositions I and J)
Except for changing the mass ratio of the glass fiber surface-treated with PLA and the silane coupling agent A, melt-kneading extrusion was performed under the same apparatus and conditions as in Example 1 to obtain resin compositions B to D, I, and J. It was.

Example 5 (resin composition E), Comparative Examples 3 to 5 (resin compositions K to M)
Extruded by melt kneading in the same apparatus and conditions as in Example 1 except that the raw material was made into 70 parts by mass of PLA and 30 parts by mass of glass fiber surface-treated with silane coupling agents B, C, and D, respectively. The resin compositions E and K to M were obtained.

Example 6 (resin composition F)
Except for using 70 parts by mass of PLA, 30 parts by mass of glass fiber surface-treated with silane coupling agent A, and 5 parts by mass of di-t-butyl peroxide, melt-kneading extrusion was performed under the same apparatus and conditions as in Example 1. The resin composition F was obtained.

Example 7 (resin composition G)
Except for using 70 parts by mass of PLA, 30 parts by mass of glass fiber surface-treated with silane coupling agent A, and 10 parts by mass of di-t-butyl peroxide, melt-kneading extrusion was performed under the same apparatus and conditions as in Example 1. The resin composition G was obtained.

Example 8 (resin composition H)
The raw material was made into 70 parts by mass of PLA, 30 parts by mass of glass fiber surface-treated with silane coupling agent A, 3 parts by mass of di-t-butyl peroxide, and the same as in Example 1 without supplying polyethylene glycol dimethacrylate. The resin composition H was obtained by performing melt-kneading extrusion using the apparatus and conditions.

Comparative Example 6 (resin composition N)
Except that the raw material was only 100 parts by mass of PLA, melt-kneading extrusion was performed under the same apparatus and conditions as in Example 1 to obtain a resin composition M.

Comparative Example 7 (resin composition O)
The raw material is 70 parts by mass of PLA and 30 parts by mass of glass fiber surface-treated with the silane coupling agent A, and the same apparatus as in Example 1 is used without supplying di-t-butyl peroxide and polyethylene glycol dimethacrylate. The resin composition P was obtained by performing melt-kneading extrusion under the conditions.

  Table 1 summarizes the results of various physical property evaluations.

About resin composition AH obtained in Examples 1-8, it became a result excellent in a molding cycle, heat resistance, and other mechanical characteristics.
In Comparative Example 1, since glass fiber was not used, the molding cycle, mold release property, impact resistance, mechanical strength, and heat resistance were inferior.
Comparative Example 2 was inferior in molding cycle, releasability, impact resistance, mechanical strength, and heat resistance because of less glass fiber blending.
Since Comparative Example 3 and 4 used the glass fiber surface-treated with the silane coupling agent which does not have an epoxy group, it became a result inferior to a shaping | molding cycle and mold release property.
Since the comparative example 5 used the untreated glass fiber, it became a result inferior to a shaping | molding cycle and mold release property.
Since the comparative example 6 used PLA which does not have a crosslinked structure and did not use glass fiber, it resulted in inferior mechanical strength property, heat resistance, and impact resistance.
Since the comparative example 7 used PLA which does not have a crosslinked structure, it was inferior to mechanical strength and heat resistance.

Claims (4)

A resin composition comprising 50 to 95 parts by mass of crosslinked polylactic acid (A) and 50 to 5 parts by mass of glass fiber (B) surface-treated with a silane coupling agent having an epoxy group. The resin composition according to claim 1, wherein the silane coupling agent having an epoxy group is γ-glycidoxypropyltrimethoxysilane or γ-glycidoxypropylmethyldiethoxysilane. The resin composition according to claim 1 or 2, wherein 0.01 to 20 parts by mass of the (meth) acrylic acid ester compound (C) is blended with 100 parts by mass of the crosslinked polylactic acid (A). . The molded object formed by shape | molding the resin composition in any one of Claims 1-3.