JP5341478B2 - Manufacturing method of polylactic acid resin molded product - Google Patents

Description

  The present invention relates to a method for producing a heat-resistant polylactic acid-based resin molded product.

  Resource recycling plastics are attracting attention as one of the environmental countermeasure technologies. Among them, the demand for polylactic acid resin is increasing. Since the polylactic acid resin can be obtained from plants, it can contribute to the construction of a recycling society as a carbon neutral material produced from non-petroleum resources. In addition, since the polylactic acid-based resin is highly biodegradable compared to other resins, the melting point is sufficiently high as 140 to 180 ° C. and excellent in transparency, packaging materials and molded articles that make use of transparency, etc. It is expected to spread in a wide range of fields.

  On the other hand, the polylactic acid resin has a problem that the crystallization rate from the molten state is small and the heat resistance is low because the crystallization is insufficient in the injection molding at a mold temperature of 80 ° C. or less. When sufficient crystallization is not performed, for example, when used as tableware, hot water or a microwave oven cannot be used, and the application is limited. In order to improve heat resistance, methods such as increasing the cooling time of the mold during molding and annealing the molded product after molding are used, but the molded product may be deformed during the crystallization process. There were problems such as poor productivity. As a means for solving such a problem, a technique for improving the crystallization speed by blending an inorganic nucleating agent such as mica or calcium carbonate or an organic nucleating agent into a polylactic acid resin is known. .

  For example, Patent Document 1 discloses a resin composition containing an organic nucleating agent such as a polylactic acid-based resin and a trimesic acid triamide compound, a plasticizer, and a stabilizer, and a molten polylactic acid-based resin as an organic nucleating agent. The manufacturing method of the molded object characterized by kneading | mixing at the temperature more than the melting temperature with respect to and using for a formation process is disclosed.

  Similarly, as an example of blending a nucleating agent of a trimesic acid triamide compound, (Patent Document 2) includes (i) an amide compound such as trimesic acid tricyclohexylamide, (ii) an ester plasticizer, and (iii) ) A lactic acid-based polymer composition containing a lactic acid-based polymer is disclosed, and a dry pellet of this composition is barrel-heated at an injection molding machine (clamping pressure of 40 tons) at a barrel temperature of 160 to 200 ° C. and an injection time of 10 seconds. In addition, it is stated that heat resistance is improved when molding is performed under conditions of a mold temperature of 90 to 100 ° C. However, a standard method such as deflection temperature under load (JIS K7207) is not used as a heat resistance evaluation method, and the test piece is put in a gear oven at 80 ° C., and the deformation state of the test piece after 24 hours is visually determined. Therefore, the actual heat resistance was unclear. In addition, molding is performed at a mold temperature of 90 to 100 ° C. Generally, a molding temperature is required at a mold temperature of 80 ° C., and an oil temperature control is required at a temperature of 90 ° C. or higher. Therefore, molding at a mold temperature of 80 ° C. or less is desired.

  Further, (Patent Document 3) discloses a resin composition in which 0.01 to 5 parts by weight of trimesic acid tris (t-butylamide) or the like is blended with 100 parts by weight of a polylactic acid resin. An example in which molding is performed under conditions of a barrel temperature of 180 to 210 ° C. and a mold temperature of 30 ° C. in an injection molding machine is described. However, since crystallization does not occur at a mold temperature of 30 ° C. lower than Tg (60 ° C.) of polylactic acid, the obtained heat resistance is considered to be considerably low (load deflection temperature (low load): about 80 ° C.).

JP 2006-328163 A International Publication No. 03/042302 Pamphlet Japanese Patent Laid-Open No. 10-87975

  As described above, trimesic acid triamide compounds and the like have been proposed as crystal nucleating agents, but when the mold temperature is 80 ° C. or less, the heat resistance of the molded product is at most about 80 to 90 ° C., which is insufficient. Met. Accordingly, an object of the present invention is to provide a method for producing a polylactic acid-based resin molded product that can obtain unprecedented high heat resistance even when molded at a mold temperature of 80 ° C. or less.

  Usually, the optimum kneading temperature of the resin composition to be introduced into the injection molding machine depends on the type of crystal nucleating agent, the particle size and the amount used, the type of polylactic acid resin, the amount of other additives, etc. Although it changes, generally it is said that 210-250 degreeC, desirably 220-245 degreeC is good. This is determined because there is a problem that if the temperature is too high, thermal decomposition will occur, and if the temperature is too low, the nucleating agent will not dissolve. At this time, the present inventors kneaded at 210 ° C. or lower, and controlled the mold temperature of the nucleating agent, the cylinder temperature, the residence time in the cylinder, etc. within a predetermined range, thereby lowering the mold temperature to 80 ° C. or lower. The present invention has been completed by finding that a high heat resistance unprecedented can be obtained when it is molded by the above method.

That is, the gist of the present invention is as follows.
(1) A method for producing a polylactic acid-based resin molded article by injection molding a resin composition obtained by kneading a polylactic acid-based resin and a trimesic acid triamide compound, which is performed under the following conditions: Production method.
(A) Blending amount of trimesic acid triamide compound in the resin composition: 0.7 to 1.3% by weight
(B) Kneading temperature: 200-210 ° C
(C) Cylinder temperature: 210-240 ° C
(D) Residence time in cylinder: 0.5-2 minutes (e) Mold temperature: 60-85 ° C
(2) The method for producing a polylactic acid-based resin molded article according to (1), wherein the trimesic acid triamide compound is trimesic acid tris (cyclohexylamide).

  According to the present invention, the amount of nucleating agent added and the kneading / injection molding conditions are optimized when a molded product is produced by adding a crystal nucleating agent of a trimesic acid triamide compound to a polylactic acid resin. When injection molding is performed at a mold temperature of ℃ or lower, a molded product having high heat resistance of 130 ℃ or higher can be obtained.

Hereinafter, the present invention will be described in detail.
The resin composition in the present invention contains a polylactic acid resin. Examples of usable polylactic acid-based resins include polylactic acid homopolymers, polylactic acid copolymers, blends of polylactic acid homopolymers and polylactic acid copolymers, and the like. In the case of polylactic acid homopolymer, it is not particularly limited, and polymers having lactic acid units of various optical purities are applicable, but it is substantially composed only of monomer units derived from L-lactic acid or D-lactic acid. A polymer is preferably used. That is, the L-lactic acid unit or the D-lactic acid unit is preferably in the range of 80 to 99.5 mol% with respect to all the structural units constituting the polylactic acid. Such polylactic acid homopolymer is relatively easy to obtain and has a high melting point, so that it becomes easier to obtain better heat resistance.

  The polylactic acid homopolymer can be obtained by any known polymerization method. Specific examples include a method of ring-opening polymerization of lactide, which is an anhydrous cyclic dimer of lactic acid (lactide method), a method of directly condensation polymerization of lactic acid, and the like. For example, in the case of the ring-opening polymerization method, lactide, which is a cyclic dimer of lactic acid, can be obtained by mixing with a polymerization regulator or the like, if necessary, and polymerizing using a catalyst. Here, the lactide includes L-lactide, which is a dimer of L-lactic acid, D-lactide, which is a dimer of D-lactic acid, L-lactic acid, and DL-lactide composed of D-lactic acid. In the case of direct condensation polymerization of lactic acid, the desired polymer can be obtained by direct dehydration condensation polymerization of L-lactic acid, D-lactic acid or a mixture thereof. The lactic acid used for the polymerization is preferably derived from plants because it is easily available, or one produced by microorganisms can be used. Moreover, you may manufacture from lactic acid derivatives, such as L- or D-methyl lactate and L- or D-ethyl lactate, as a raw material.

  The polylactic acid copolymer is obtained by copolymerizing a lactic acid monomer or lactide and another copolymerizable component. The proportion of structural units other than lactic acid residues can be appropriately set within a range not impairing the effects of the present invention. Generally, it is preferable that other structural units are 50 mol% or less, and especially 20 mol% or less in all the structural units. Examples of such other structural units include dicarboxylic acids having two or more ester bond-forming functional groups, polyhydric alcohols, hydroxycarboxylic acids, lactones, and various polyesters and polyethers composed of these various constituents. And polycarbonate.

  Examples of the dicarboxylic acid include aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, and azelaic acid, and aromatic dicarboxylic acids such as terephthalic acid and isophthalic acid.

  Polyhydric alcohols include aromatic polyhydric alcohols such as those obtained by addition reaction of ethylene oxide with bisphenol, ethylene glycol, propylene glycol, butanediol, hexanediol, octanediol, glycerin, sorbitan, trimethylolpropane, neopentyl glycol And aliphatic glycols such as diethylene glycol, triethylene glycol, polyethylene glycol, and polypropylene glycol.

  Examples of hydroxycarboxylic acid include glycolic acid and hydroxybutylcarboxylic acid.

  Examples of the lactone include glycolide, ε-caprolactone glycolide, ε-caprolactone, β-propiolactone, δ-butyrolactone, β- or γ-butyrolactone, pivalolactone, δ-valerolactone, and the like.

  The molecular weight of the polylactic acid homopolymer or copolymer is generally about 50,000 to 500,000, preferably about 100,000 to 250,000 as a weight average molecular weight (Mw) in terms of polystyrene by gel permeation chromatography analysis. However, the present invention is not limited to this. If the molecular weight is too small, it is difficult to obtain practically necessary physical properties such as reduced strength of the molded product or decreased stability due to increased hydrolyzability. Since there is a tendency for the property to deteriorate, it is appropriately set in consideration of these.

  Moreover, in addition to the said polylactic acid-type resin, you may blend other resin with the resin composition in this invention for the purpose of the impact strength improvement, the improvement of a moldability, etc. as needed. Examples of the resin to be blended include ethylene-propylene copolymer rubber, ethylene-propylene-diene copolymer, polyurethane resin, polyamide resin, polyester resin, polycarbonate resin, and acrylic resin. The content of such other resins can be appropriately set within a range that does not impair the crystallinity of the polylactic acid-based resin. Specifically, it is 40% by weight or less, preferably 10% by weight or less in the resin composition. is there.

  Next, the resin composition in the present invention contains a trimesic acid triamide compound as a crystal nucleating agent. Thereby, crystallization of polylactic acid-type resin can be accelerated | stimulated and the heat resistance of a molded article can be improved. As the trimesic acid triamide compound, any triamide compound obtained by reaction of trimesic acid or its acid chloride with various amines can be applied. Specifically, trimesic acid tris (cyclohexylamide), trimesic acid tris ( 2-methylcyclohexylamide), trimesic acid tris (3-methylcyclohexylamide), trimesic acid tris (4-methylcyclohexylamide), trimesic acid tris (2,3-dimethylcyclohexylamide), and the like. Among these, trimesic acid tris (cyclohexylamide) is preferably used because it is particularly excellent in improving the crystallization speed of the polylactic acid resin.

  The average particle size of the trimesic acid triamide compound is not particularly limited, but is generally 80 μm or less, preferably 5 μm or less. When the average particle size of the crystal nucleating agent is small, the specific surface area is increased and the effect as a crystal nucleating agent is enhanced. On the other hand, if the average particle size is too large, the trimesic acid triamide compound will not be sufficiently dissolved in the polylactic acid resin, resulting in a decrease in nucleation and a tendency to decrease the crystallinity and heat resistance of the resulting molded product. This is not preferable.

  The blending amount of the trimesic acid triamide compound in the resin composition is preferably 0.7 to 1.3% by weight, particularly 0.9 to 1.2% by weight. If the blending amount is less than 0.7% by weight or exceeds 1.3% by weight, the crystallization rate tends to decrease, which is not preferable.

  In addition to the polylactic acid-based resin and the trimesic acid triamide compound, various additives can be blended in the resin composition of the present invention as necessary. Examples of additives include stabilizers, antioxidants, ultraviolet absorbers, pigments, colorants, mold release agents, plasticizers, fragrances, antibacterial agents, antistatic agents, lubricants, flame retardants, foaming agents, fillers, etc. Is mentioned. The blending amount of these additives can be appropriately set within a range not impairing the effects of the present invention. Specifically, the total amount of additives other than the trimesic acid triamide compound is 10% by weight with respect to the entire resin composition. In the following, it is particularly preferable to set it to 2 to 5% by weight. Moreover, various fillers can also be mix | blended with the resin composition in this invention. The amount of the various fillers is preferably set so as to be 30% by weight or less, particularly 20% by weight with respect to the entire resin composition.

  A resin composition can be obtained by kneading the above components. The kneading method of each component is not particularly limited and can be kneaded by a conventionally known method. For example, a dry blend method in which each component is charged and kneaded in a V-type blender, a Hell shell mixer, a ribbon blender, a tumbler mixer, etc., and further dry blended is melt kneaded with a single or twin screw extruder, kneader, roll, etc. It can be carried out by a method of cooling and pelletizing into, for example, a spherical shape, a cylindrical shape, or a prism shape, or a solution blending method in which each component is dissolved in a solvent and mixed to remove the solvent.

  The kneading temperature is 200 to 210 ° C, preferably 205 to 210 ° C. Conventionally, kneading was performed at 210 to 250 ° C. from the viewpoint of dissolving the nucleating agent while suppressing thermal decomposition, but in the present invention, kneading was performed at 200 to 210 ° C., which is lower than this, and described later. By performing injection molding under the molding conditions, high heat resistance exceeding 130 ° C. can be obtained.

  The resin composition obtained by kneading can be easily molded into molded products of various shapes using a known injection molding method. Here, injection molding includes injection blow molding, injection extrusion blow molding, injection compression molding, and the like in addition to narrowly-defined injection molding. The cylinder temperature in the injection molding is 210 to 240 ° C., preferably 225 to 235 ° C., and the residence time of the resin composition in the cylinder is 0.5 to 2 minutes, preferably 1 to 1.5 minutes. By molding under these conditions, it is possible to obtain unprecedented high heat resistance in combination with the low kneading temperature. Moreover, the molded product obtained has high strength and excellent thermal stability.

  The mold temperature is 85 ° C. or less, preferably 60 to 85 ° C., more preferably 60 to 80 ° C. A mold temperature of 80 ° C. or lower is preferable from the viewpoint of equipment cost and energy consumption reduction because the molding equipment can be configured with water temperature control instead of oil temperature control. The cooling time of the molded product in the mold varies depending on the type of the polylactic acid resin and the mold temperature, and is not particularly limited, but is generally 20 to 300 seconds, preferably 30 to 180 seconds. Degree.

  If necessary, the molded product can be annealed after injection molding. Annealing treatment promotes microcrystallization of polylactic acid and can further improve heat resistance. The annealing conditions in that case are, for example, about 60 to 160 ° C. for about 1 to 60 minutes, and can be performed using an oven or the like.

  The polylactic acid-based resin molded product obtained by the above production method has excellent heat stability and high heat resistance of more than 130 ° C., so that it can be used as a substitute for resin molded products derived from petroleum resources so far. Applicable to fields. Specifically, automobile parts (interior parts such as instrument panels and consoles), household appliance parts (cases such as personal computers and stereos), gears, general goods, agricultural materials, building materials, civil engineering materials, tableware, toys It can use suitably for uses, such as a kind.

EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, it is not limited to these.
N'z S09 (manufactured by Toyota Motor Co., Ltd., molecular weight Mw = 120,000) is used as a polylactic acid-based resin, and Trigestic acid triamide (Crystal Nucleating Agent) is used as NJESTA-TF which is trimesic acid tris (cyclohexylamide). -1 (New Nippon Rika Co., Ltd.) was used. First, a polylactic acid resin and a trimesic acid triamide compound were mixed by dry blending. The blending amount of the trimesic acid triamide compound in the mixed resin composition was 0.1 wt%, 0.5 wt%, and 1.0 wt%. Next, the mixed resin composition was kneaded with a biaxial kneader. As shown in Table 1, the kneading conditions were set to kneading temperature: 190 to 230 ° C., screw rotation speed: 100 or 200 rpm, and material supply amount: 2.5 kg / h.

  After kneading under each of the above conditions, it was pelletized, introduced into an injection molding machine, and injection molded under predetermined conditions. The molding conditions are as shown in Table 1. The cylinder temperature was set to 190 ° C. or 230 ° C., the residence time of the resin composition in the cylinder was 1 minute or 5 minutes, and the mold holding time was set to 1 minute to 3 minutes. The mold temperature was unified at 80 ° C.

  The obtained molded product was evaluated for heat deformability and represented in Table 1 by symbols ◎ to ×. Further, the deflection temperature under load of the molded product (JIS K7207, low load 0.45 MPa, temperature rising rate 2 ° C./min) was measured, and the heat resistance was evaluated. The results are shown in Table 1.

  As is apparent from Table 1, when a resin composition containing 1.0% by weight of trimesic acid triamide compound and kneaded at 210 ° C. was injection molded under the conditions of a cylinder temperature of 230 ° C. and a residence time of 1 minute, The deflection temperature under load exceeding 130 ° C. was exhibited, and it was found that the film had high heat resistance.

  On the other hand, when the amount of the trimesic acid triamide compound is 0.1% by weight or 0.5% by weight, the heat resistance is generally improved even if the mold is deformed or the releasability is improved. It was as low as about 70 to 80 ° C. and did not meet the requirements.

Claims (4)

A method for producing a polylactic acid-based resin molded product by injection molding a resin composition obtained by kneading a polylactic acid-based resin and a trimesic acid triamide compound, which is performed under the following conditions.
(A) Blending amount of trimesic acid triamide compound in the resin composition: 0.7 to 1.3% by weight
(B) Kneading temperature: 200-210 ° C
(C) Cylinder temperature: 210-240 ° C
(D) Residence time in cylinder: 0.5-2 minutes (e) Mold temperature: 60-85 ° C
(However, the kneading temperature is 210 ° C., the cylinder temperature is 240 ° C., the residence time in the cylinder is 1 minute, and the mold temperature is 80 ° C.) A method for producing a polylactic acid-based resin molded product by injection molding a resin composition obtained by kneading a polylactic acid-based resin and a trimesic acid triamide compound, which is performed under the following conditions.
(A) Blending amount of trimesic acid triamide compound in the resin composition: 0.7 to 1.3% by weight
(B) Kneading temperature: 200-210 ° C
(C) Cylinder temperature: 210-235 ° C
(D) Residence time in the cylinder: 0.5-2 minutes
(E) Mold temperature: 60-85 ° C The method for producing a polylactic acid-based resin molded article according to claim 1 or 2 , wherein the trimesic acid triamide compound is trimesic acid tris (cyclohexylamide). The method for producing a polylactic acid-based resin molded product according to any one of claims 1 to 3, wherein a deflection temperature under load (low load) of the produced polylactic acid-based resin molded product is higher than 130 ° C.