JP2006143829A - Polylactic acid-based resin molding and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polylactic acid-based resin molding obtained by crystallizing a polylactic acid-based resin having excellent impact resistance while maintaining transparency, and a method for producing the same. <P>SOLUTION: This polylactic acid-based resin molding having ≥30% crystallinity comprises 0.1-15.0 pts. by weight castor oil-based fatty acid ester to 100 pts. by weight polylactic acid. This resin molding has such a level of impact resistance as usable for various containers, home electrical appliances, automobile parts, etc., and transparency to an extent not largely impairing transparency originally possessed by the polylactic acid. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a molded article of a polylactic acid resin composition produced by injection molding or the like. More specifically, the present invention relates to a polylactic acid resin molded article whose impact resistance is improved by crystallization and whose transparency is maintained, and a method for producing the same.

  In recent years, from the viewpoint of protecting the natural environment, biodegradable resins that decompose in the natural environment and molded articles thereof have been demanded. In particular, research and development of biodegradable resins such as aliphatic polyesters are actively conducted. In particular, polylactic acid is not only a biodegradable resin, but it does not use petroleum as a raw material, but also uses plants such as corn, which is a renewable resource, as a material for building a recycling society. Is big.

  Polylactic acid is expected to be a molding material because it has a melting point as high as 150 to 180 ° C. compared to other biodegradable resins and is excellent in transparency. However, polylactic acid has high strength due to its rigid molecular structure, but has the disadvantage of being inferior in impact resistance and fragile.

  As a method for improving the impact resistance of polylactic acid, there is a modification by a molding method. This is a method of obtaining impact resistance by crystallizing polylactic acid with various modifiers at the time of molding or after molding. Usually, even if polylactic acid alone is crystallized, the impact resistance is not improved. However, Patent Document 1 discloses a method for improving impact resistance by adding a fatty acid ester to polylactic acid and performing crystallization. Yes. Further, Patent Document 2 describes that impact resistance is improved by blending a modified elastomer with an aliphatic polyester such as polylactic acid and performing an annealing treatment. Furthermore, Patent Document 3 describes that impact resistance is improved by blending an aliphatic polyester with a lactic acid resin and crystallizing it after injection molding.

  However, although these methods can improve impact resistance, there is no description about transparency. This is because if the impact resistance is secured by this method, it is not transparent or the transparency is extremely lowered. Usually, when polylactic acid is crystallized by heat treatment or the like, the crystal size becomes from the micron order to about sub mm, and the polylactic acid crystal itself becomes a factor of light scattering and becomes cloudy.

  On the other hand, Patent Document 4 and Patent Document 5 disclose methods of increasing the crystallization speed by adding a specific crystal nucleating agent to polylactic acid and maintaining transparency even when heat crystallization is performed. However, there is no mention of improvement in impact resistance.

  That is, a polylactic acid resin molded article having excellent impact resistance while maintaining transparency in a molded article obtained by crystallizing a polylactic acid resin has not yet been obtained.

JP-A-11-116784 JP 2004-35691 A JP 2003-335933 A JP-A-11-5849 Japanese Patent Laid-Open No. 11-116783

The problem to be solved by the present invention is a molded product obtained by crystallizing a polylactic acid resin, and has a superior impact resistance and can maintain transparency, and a molded product thereof It is to provide a manufacturing method.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have completed the present invention. That is, by using a polylactic acid resin composition containing 0.1 to 15.0 parts by weight of castor oil fatty acid ester with respect to 100 parts by weight of polylactic acid and crystallizing at the time of molding or after molding, Izod It has been found that a polylactic acid-based resin molded article having an impact resistance of 6 kJ / m ² or more and transparency having a 2 mm thickness Haze value of 50% or less can be obtained.

  The polylactic acid-based resin molded article of the present invention has a level of impact resistance that can be used for various containers, household appliances, automobile parts, etc., and has a transparency that does not significantly impair the transparency inherent in polylactic acid. Have.

  Hereinafter, the present invention will be described in detail.

  The polylactic acid resin molded article of the present invention is a polylactic acid resin molded article obtained by crystallizing a polylactic acid resin composition containing polylactic acid and a castor oil fatty acid ester at the time of molding or after molding.

(Polylactic acid)
The polylactic acid used in the present invention is a polymer composed substantially only of monomer units derived from L-lactic acid or D-lactic acid. Here, “substantially” means that 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. When polylactic acid is composed of only monomer units derived from L-lactic acid or D-lactic acid, the polymer is crystalline and has a high melting point. Furthermore, the crystallinity and melting point can be adjusted freely by changing the ratio of monomer units derived from L-lactic acid and D-lactic acid (abbreviated as D / L ratio). It is possible to control the characteristics.

  Further, it may be a copolymer with another hydroxycarboxylic acid unit or a copolymer with an aliphatic diol or an aliphatic dicarboxylic acid as long as the properties of polylactic acid are not impaired. Examples of the “other hydroxycarboxylic acid units” copolymerized with polylactic acid include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxy-n-butyric acid, 2-hydroxy3,3-dimethylbutyric acid. And bifunctional aliphatic hydroxy-carboxylic acids such as 2-hydroxy-3-methylbutyric acid, 2-methyllactic acid and 2-hydroxycaproic acid, and lactones such as caprolactone, butyrolactone and valerolactone. Examples of the “aliphatic diol” copolymerized with polylactic acid include ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol and the like. Examples of the “aliphatic dicarboxylic acid” copolymerized with polylactic acid include succinic acid, adipic acid, suberic acid, sebacic acid, and dodecanedioic acid.

  Furthermore, if necessary, such as improving heat resistance, a non-aliphatic dicarboxylic acid such as terephthalic acid and / or a non-aliphatic diol such as an ethylene oxide adduct of bisphenol A may be copolymerized as a small amount copolymerization component. Also good. A small amount of a chain extender such as a diisocyanate compound, an epoxy compound, or an acid anhydride can be copolymerized for the purpose of increasing the molecular weight.

As a polymerization method of polylactic acid, a condensation polymerization method, a ring-opening polymerization method, and other known polymerization methods can be employed. For example, in the condensation polymerization method, polylactic acid having an arbitrary composition can be obtained by directly dehydrating condensation polymerization of L-lactic acid, D-lactic acid or a mixture thereof. In the ring-opening polymerization method, polylactic acid can be obtained using a selected catalyst while using lactide, which is a cyclic dimer of lactic acid, with a polymerization regulator or the like as necessary. In this case, the lactide includes L-lactide, which is a dimer of L-lactic acid, D-lactide, which is a dimer of D-lactic acid, or DL-lactide composed of L-lactic acid and D-lactic acid. If necessary, polylactic acid having an arbitrary composition and crystallinity can be obtained by mixing and polymerizing.

  The molecular weight of the polylactic acid used in the present invention is not particularly limited as long as it exhibits substantially sufficient mechanical properties when used in an intended application, for example, an injection molded product. When the molecular weight is low, the strength of the obtained molded product is lowered and the decomposition rate is increased. On the other hand, if it is high, the workability is lowered and molding becomes difficult.

  Considering this point, the preferred range of the weight average molecular weight of the polylactic acid used in the present invention is 50,000 to 400,000, more preferably 100,000 to 250,000. Representative examples of polylactic acid include the Lacia series manufactured by Mitsui Chemicals, the Eco Plastic (U'z) series manufactured by Toyota Motor Corporation, and the Nature Works series manufactured by Cargill Dow.

(Castor oil fatty acid ester)
The castor oil fatty acid ester used in the present invention is a fatty acid ester derived from castor oil. Castor oil is a triglyceride containing less than 3 (more precisely, 2.7) ricinoleic acid as a constituent fatty acid in the molecule, where ricinoleic acid is 9 to 10 positions out of 18 carbon atoms. It is a fatty acid having a double bond between carbon atoms and having an OH group at the 12th carbon atom.

  The castor oil fatty acid ester is purified by, for example, an esterification reaction between castor oil or hydrogenated castor oil and a monovalent fatty acid that is at least partially oxy fatty acid or a condensed fatty acid obtained by condensing the fatty acid. Here, hydrogenated castor oil is obtained by hydrogenating linoleic acid, which is a constituent fatty acid of castor oil, and converting it to 12-hydroxystearic acid. Examples of the monovalent fatty acid include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behemic acid, montanic acid, oleic acid, ricinoleic acid, and 12-hydroxystearic acid.

(Addition amount of castor oil fatty acid ester)
The amount of castor oil fatty acid ester added in the present invention can be added to 0.1 to 15.0 parts by weight, preferably 5.0 to 13.0 parts by weight, relative to 100 parts by weight of polylactic acid. More preferably, it is 7.5-12.5 weight part. When it exceeds 15 parts by weight, the viscosity is lowered, and kneading with polylactic acid becomes difficult.

(Organic and inorganic additives)
The molded article produced by the production method of the present invention improves various physical properties such as an improvement in crystallization speed, an improvement in heat resistance, an improvement in mechanical properties, and an improvement in blocking resistance, as long as the effects of the present invention are not impaired. Therefore, an organic additive or an inorganic additive can also be added.

Organic additives include fatty acid amides, fatty acid salts, fatty alcohols and fatty acid esters. Among these, examples of the fatty acid amide include mono fatty acid amides, N-substituted mono fatty acid amides, bis fatty acid amides, N-substituted fatty acid bisamides, and N-substituted ureas. These may be one kind or a mixture of two or more kinds. Of these, mono-fatty acid amides, N-substituted mono-fatty acid amides, and bis-fatty acid amides are preferable. In particular, palmitic acid amide, stearic acid amide, erucic acid amide, behenic acid amide, ricinoleic acid amide, hydroxy stearic acid amide. N-oleyl palmitic acid amide, N-stearyl erucic acid amide, ethylene biscapric acid amide, ethylene bisoleic acid amide, ethylene bislauric acid amide, ethylene biserucic acid amide, m-xylylene bis stearic acid amide, m- Xylylene bis-12-hydroxystearic acid amide is preferably used.

  Examples of the fatty acid salt include laurate, myristic acid, palmitate, oleate, stearate, isostearate, behenate, and montanate. These may be one kind or a mixture of two or more kinds. Among them, stearic acid salts and montanic acid salts are preferable, and sodium stearate, potassium stearate, calcium stearate, zinc stearate, and calcium montanate are particularly preferably used.

  Examples of the aliphatic alcohol include aliphatic monoalcohols, aliphatic polyhydric alcohols, and cyclic alcohols. These may be one kind or a mixture of two or more kinds. Of these, aliphatic monoalcohols are preferred, and stearyl alcohol is particularly preferred.

  Examples of fatty acid esters include mono fatty acid esters, ethylene glycol monoesters and ethylene glycol diesters, glycerin monoesters, glycerin diesters, and glycerin triesters. These may be one kind or a mixture of two or more kinds. Of these, ethylene glycol diesters are preferred, and ethylene glycol distearate is particularly preferred.

Specific examples of the inorganic additive include, for example, talc, kaolinite, SiO ₂ , clay, calcium carbonate, titanium oxide, zinc oxide, barium sulfate, etc., but the transparency and impact resistance of the molded product are not impaired. Thus, it is necessary to appropriately select conditions (addition amount, particle size).

In addition, when the purpose is to further improve the crystallization speed during molding such as crystallization in the mold during molding or crystallization by heat treatment of the formed molded product, the SiO ₂ component is 10% by weight or more. The crystalline inorganic substance contained is preferable. Specifically, talc TM-30 (manufactured by Fuji Talc), kaolin JP-100 (manufactured by Tsuchiya Kaolin), NN kaolin clay (manufactured by Tsuchiya Kaolin), kaolinite ASP-1170 (Made by Fuji Talc), kaolin UW (made by Engelhard), talc RF (made by Fuji Talc), etc. are mentioned. In this case, those having a small particle size and being well dispersed without being aggregated when melt-kneaded with a resin are preferably used.

(Amount of organic and inorganic additives added)
Although the addition amount of an organic additive or an inorganic additive depends on the kind of additive, generally an amount that does not extremely impair the effects of the present invention can be added.

(Other additives)
As long as the effects of the present invention are not impaired, various types of elastomers (SBR, NBR, SBS type ternary block copolymer thermoplastic elastomers, etc.) and additives (plasticizers, pigments) , Stabilizers, antistatic agents, endblockers, UV absorbers, antioxidants, flame retardants, mold release agents, lubricants, dyes, antibacterial agents, fillers (impact core / shell particles, impact modifiers) Etc.) and pigments (metallic pigments, pearl pigments) can be appropriately used according to the purpose and application.

(Polylactic acid resin molded product)
The polylactic acid-based resin molded product of the present invention is molded by any currently known molding method such as injection molding, injection compression molding, extrusion molding, blow molding, press molding, vacuum pressure molding, etc. It is. In the present invention, when a polylactic acid resin molded product is molded by the above molding method, a polylactic acid resin having excellent impact resistance and transparency is maintained by performing a crystallization operation at the time of molding or after molding. A molded article can be suitably manufactured.

(Production method)
Next, a method for producing a polylactic acid resin molded product of the present invention, particularly a method for producing an injection molded product will be described. Here, the case of injection molding will be mainly described, but a known molding method may be adopted for other molding methods.

  Polylactic acid and castor oil fatty acid ester adopt a method of producing an injection molded product using an injection molding machine after producing pellets by extruding into a strand shape using a twin screw extruder, for example. I can do things. Specifically, for example, after polylactic acid is sufficiently dried to remove moisture, castor oil fatty acid ester is injected and melted and kneaded while melting polylactic acid using a twin screw extruder or the like. What is necessary is just to extrude into a shape and to produce a pellet. At that time, considering that the melting point of polylactic acid changes depending on the composition ratio of L-lactic acid and D-lactic acid, and that the melting point of the mixed resin changes depending on the mixing ratio of castor oil fatty acid ester, It is preferable to appropriately select the melt extrusion temperature. In practice, a temperature range of 100 ° C. to 250 ° C. is selected. The pellets thus produced may be sufficiently dried to remove moisture and then injection molded.

  The method of injection molding is not particularly limited. Typical examples include general injection molding methods for thermoplastic resins, gas assist molding methods, injection compression molding methods, and the like. In addition to the above methods, an in-mold molding method, a gas press molding method, a two-color molding method, a sandwich molding method, PUSH-PULL, or the like can be employed in accordance with other purposes. At this time, the injection molding apparatus is composed of a general injection molding machine, a gas assist molding machine, an injection compression molding machine, etc., and a molding die and ancillary equipment used therefor, a mold temperature control device, a raw material drying device, and the like. It is common to be done. The molding conditions are preferably such that the molten resin temperature is in a temperature range of 170 to 210 ° C. in order to avoid thermal decomposition of the resin in the injection cylinder.

  In the present invention, it is necessary to crystallize the polylactic acid resin composition by some method at the time of molding or after molding. Specific examples thereof include, for example, a method in which a melt of the composition is filled in a mold at the time of molding and crystallized as it is in the mold (hereinafter referred to as in-mold crystallization method), and Examples thereof include a method in which an amorphous molded product is subjected to a dry heat treatment or a wet heat treatment (hereinafter referred to as a post-crystallization method). In the in-mold crystallization method and the post-crystallization method, the optimum temperature conditions for crystallization of the molded product are different.

  In the case of the in-mold crystallization method, the set temperature condition of the mold is preferably a temperature range from the crystallization start temperature at the time of temperature drop to the crystallization end temperature in the differential scanning calorimetry of the composition, A temperature near the apex is more preferable. If the temperature is higher than the crystallization start temperature, the crystallization rate is remarkably slow, the productivity and operability are deteriorated, and further, crystallization may not occur and the desired molded product may not be obtained. At a temperature lower than the end temperature, the crystallization rate is remarkably slow, and the intended molded product may not be obtained. In this method, the holding time in the mold varies depending on the composition, but there is no particular limitation as long as it is longer than the time required for the molded product to sufficiently crystallize in the mold.

On the other hand, in the case of the post-crystallization method (dry heat treatment), the set temperature condition is the temperature range from the glass transition temperature (Tg) to the melting point (Tm) of the composition, more preferably from (Tg + 5 ° C.) to (Tm−2).
0 ° C.), more preferably a temperature range from (Tg + 10 ° C.) to (Tm−30 ° C.). When the set temperature is higher than Tm, the impact resistance may be impaired or the shape may be distorted even if crystallization is performed in a short time, and further melting may occur when heated for a long time. On the other hand, at a temperature lower than Tg, the crystallization rate is remarkably slow, and the intended molded product may not be obtained. In this method, the time for the dry heat treatment of the molded product varies depending on the composition, but is not particularly limited as long as it is longer than the time required for the molded product to be sufficiently crystallized.

  In the case of a post-crystallization method (wet heat treatment), crystallization is performed in a humidified atmosphere in addition to the set temperature in the dry heat treatment. The relative humidity during the wet heat treatment is preferably 60% or more, more preferably 80% or more. In this method, the time for wet heat treatment of the molded product varies depending on the composition, but is not particularly limited as long as it is a time sufficient for the molded product to be sufficiently crystallized.

  When performing the above crystallization operation, the molded product does not have to be fixed. However, in order to prevent deformation of the molded product, it is more preferable to fix the molded product with a mold, a resin mold or the like. Further, in consideration of productivity, heat treatment can be performed in a packed state.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these Examples at all. The evaluation was performed by the following method.

(Evaluation methods)
(1) Impact resistance Izod impact strength was measured by an Izod impact test based on JIS K 7110. The test piece was a JIS No. 1 test piece (with a 3.18 mm (1/8 inch) thickness notch), and was measured using an impact tester “IM-401” (manufactured by Ueshima Seisakusho).

(2) Transparency (hereinafter abbreviated as Haze)
Using a turbidimeter “NDH-2000” (manufactured by Nippon Denshoku Industries Co., Ltd.), the haze of a flat molded product having a thickness of about 2 mm was measured.

(3) Crystallinity With a differential scanning calorimeter “DSC-7” (manufactured by PerkinElmer), the rate of temperature increase is 10 ° C./min, the heat of fusion (ΔHm) and the heat of crystallization caused by the polylactic acid resin ( ΔHc) was measured, and the degree of crystallinity of the polylactic acid resin was calculated by the following formula.
Crystallinity (%) = 100 × (ΔHm + ΔHc) / 93

(Crystallization by wet heat treatment)
(Example 1-1)
100 parts by weight of polylactic acid (D-form ratio 1.0%, relative viscosity 3.1) and 10 parts by weight of castor oil fatty acid ester “Rick Sizer C-401” (manufactured by Ito Oil Co., Ltd.) Using a machine “NR2-22” (manufactured by Nakatani Machinery Co., Ltd.), the mixture was melt-kneaded at a cylinder setting temperature of 170 to 200 ° C., and the resulting polylactic acid-based resin composition was formed into a pellet shape.

Next, the pellets were melted using a small injection molding machine “MINIMAT 14 / 7B” (manufactured by Sumitomo Heavy Industries, Ltd.) at a cylinder set temperature of 170 to 200 ° C., and a mold having a set temperature of 30 ° C. The JIS No. 1 test piece (with a 3.18 mm (1/8 inch) thickness notch) and a 2 mm thick flat plate molded product were obtained with a cooling time of 30 seconds. The obtained molded product was measured and evaluated for crystallinity, impact resistance and transparency. Moreover, the obtained molded article was left still in a constant temperature and high humidity test apparatus “IG400” (manufactured by Yamato Kagaku Co., Ltd.), and wet heat treatment was performed at 50 ° C. and 80% RH (relative humidity) for one week. . The crystallinity, impact resistance and transparency of the molded product after the wet heat treatment were measured and evaluated. The results are shown in Table 1.

(Examples 1-2 to 1-6)
It carried out similarly to Example 1-1 except having changed the kind of castor oil type fatty acid ester, and the addition amount as shown in Table 1. The results are shown in Table 1.

(Comparative Example 1-1)
The same procedure as in Example 1-1 was performed except that the castor oil fatty acid ester was excluded. The results are shown in Table 1.

(Comparative Example 1-2)
The same procedure as in Example 1-1 was performed, except that 100 parts by weight of polylactic acid and 10 parts by weight of a plasticizer “Triacetin” (manufactured by Daihachi Chemical Co., Ltd.) were used. The results are shown in Table 1.

(Comparative Example 1-3)
The same procedure as in Example 1-1 was performed, except that 100 parts by weight of polylactic acid and 20 parts by weight of impact imparting agent “Plamate PD-150” (manufactured by Dainippon Ink & Chemicals, Inc.) were used. The results are shown in Table 1.

(Crystallization by dry heat treatment)
(Example 2-1)
After obtaining an injection molded product by the same method as in Example 1-1, the obtained molded product was allowed to stand in a dryer “DFS82” (manufactured by Yamato Scientific Co., Ltd.) and dried at 60 ° C. for 1 hour. Heat treatment was performed. Measurements and evaluations of crystallinity, impact resistance and transparency of the molded product after the dry heat treatment were performed. The results are shown in Table 2.

(Example 2-2, 2-3)
The same procedure as in Example 2-1 was conducted except that the dry heat treatment conditions were changed as shown in Table 2. The results are shown in Table 2.

(Comparative Examples 2-1 to 2-3)
The same procedure as in Examples 2-1 to 2-3 was performed except that the castor oil fatty acid ester was excluded. The results are shown in Table 2.

(In-mold crystallization)
(Example 3-1)
After obtaining pellets by the same method as in Example 1-1, the pellets were set to a cylinder set temperature of 170 to 200 ° C. using a small injection molding machine “MINIMAT 14 / 7B” (manufactured by Sumitomo Heavy Industries, Ltd.). JIS No. 1 test piece (with 3.18 mm (1/8 inch) thickness notch), 2 mm thick flat plate molded product, melted under the conditions of Got. The obtained molded product was measured and evaluated for crystallinity, impact resistance and transparency. The results are shown in Table 3.

(Comparative Example 3-1)
The same procedure as in Example 3-1 was performed except that the castor oil fatty acid ester was excluded. The results are shown in Table 3.

As is apparent from Tables 1, 2, and 3, the polylactic acid-based resin molded product of the example has a crystallinity of 30% or more, an Izod impact strength of 6 kJ / m ² or more, and a 2 mm thick Haze value of 50%. The following shows that the impact resistance is improved by crystallization and the transparency is maintained.

On the other hand, in the case of a molded product of polylactic acid alone, as in Comparative Examples 2-2 and 2-3, even when the degree of crystallinity is 30% or more, the impact resistance as in Examples is not obtained, and the transparency is lost. In Comparative Examples 1-1, 2-1, and 3-1, crystallization did not occur. In Comparative Example 1-2, the Izod impact strength was N.P. B. (No breakage) and impact resistance is obtained, but transparency is lost. In Comparative Example 1-3, the crystallinity was 30% or more, the Izod impact strength was 5.8 kJ / m ² , and the Haze was 52.9%, and both the impact resistance and the transparency were inferior.

  The polylactic acid-based resin molded product of the present invention has excellent impact resistance by crystallization and also has transparency, so it is suitable for molded products such as various containers, household appliances, and automobile parts. Used for.

Claims (2)

A polylactic acid resin molded article having a crystallinity of 30% or more, comprising a polylactic acid resin composition containing 0.1 to 15.0 parts by weight of castor oil fatty acid ester with respect to 100 parts by weight of polylactic acid. The crystallization is performed using an in-mold crystallization method in which crystallization is performed within a temperature range from a glass transition temperature to a melting point of the polylactic acid-based resin composition, or a post-crystallization method. A method for producing a polylactic acid resin molded product.