JPH0827363A - Lactic acid polymer composition - Google Patents

Abstract

PURPOSE:To obtain a biodegradable lactic acid polymer composition excellent in mold releasing, transparency and strengths and capable of being decomposed into H2O and CO2 under the natural environment within a short time by mixing a specified thermoplastic polymer composition with a fatty acid and/or a fatty acid amide in a specified mixing ratio. CONSTITUTION:100 pts.wt. thermoplastic polymer composition mainly consisting of a copolymer of a (poly)lactic acid (e.g. l.-lactic acid) with a hydroxycarboxylic acid (e.g. 6-hydroxy-caproic acid) is mixed with 0.051-1.0pt.wt. fatty acid and/or fatty acid amide (e.g. stearic acid). The obtained mixture is melt-kneaded and injection-molded with a mold having a draft of 0.1-2 deg. in the direction of infection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lactic acid polymer composition and a molding method comprising the same. More specifically, it relates to a composition having excellent releasability, transparency and strength, and an injection molding method comprising the same.

[0002]

2. Description of the Related Art Generally, polystyrene and hard vinyl chloride resins are known as resins having excellent transparency and strength. However, since they increase the amount of dust when they are discarded and have almost no decomposition rate in a natural environment, they remain in the ground semipermanently even if they are buried. Moreover, the discarded resin causes problems such as damage to the landscape and destruction of the living environment of marine life.

Therefore, polylactic acid or a copolymer of lactic acid and hydroxycarboxylic acid (hereinafter, abbreviated as lactic acid-based polymer) has been developed as a biodegradable thermoplastic polymer that decomposes in a natural environment. . These polymers are found in animals within a few months to a year within 1
00% biodegradable and when placed in soil or seawater,
In a moist environment, it begins to decompose in a few weeks and disappears in about 1 to several years, and the decomposition products have the characteristics of lactic acid, carbon dioxide and water, which are harmless to the human body.

Lactic acid, which is a raw material for a lactic acid-based polymer, is produced by a fermentation method or chemical synthesis, but recently, a large amount of L-lactic acid has been produced especially by the fermentation method and the cost has become low. Fork
The obtained polymer is characterized by having a high rigidity, and a molded product obtained by injection molding is characterized by excellent transparency. For these reasons, various applications are currently being developed.

However, the lactic acid type polymer has a drawback that the releasability is deteriorated depending on the shape of the mold. If the draft of the mold in the injection direction is about 2 ° or less, when the molded product is released from the mold, the mold release resistance is so large that mold release failure occurs and a molded product with a good appearance should be obtained continuously. Is difficult.

On the other hand, a method of kneading a lubricant such as metal soap is used to produce a polymer having a mold release property in injection molding. However, when a lubricant such as a metal soap is used as the lactic acid-based polymer, the transparency of the molded product is likely to be lost depending on the kind of the lubricant and the addition amount thereof, and the strength is often deteriorated due to the decrease in the molecular weight.

[0007]

SUMMARY OF THE INVENTION With respect to the above problems, it is an object of the present invention to obtain a molded article having improved releasability during injection molding without lowering transparency and strength.

[0008]

The inventors of the present invention have made extensive studies in order to achieve the above object, and as a result, the present invention has been achieved. That is, 0.05% of fatty acid or fatty acid amide is added to a thermoplastic polymer composition containing a lactic acid-based polymer as a main component.
The present invention relates to a method for molding a lactic acid-based polymer, which comprises adding 1 to 1.0 part by weight and performing injection molding.

The lactic acid-based polymer in the present invention is polylactic acid, lactic acid-hydroxycarboxylic acid copolymer, and a mixture of polylactic acid and lactic acid-hydroxycarboxylic acid copolymer. Lactic acids and hydroxycarboxylic acids are used as raw materials for the polymer. As lactic acid, L
Lactic acid, D-lactic acid, DL-lactic acid or mixtures thereof or lactide which is a cyclic dimer of lactic acid can be used.

Hydroxycarboxylic acids that can be used in combination with lactic acids include glycolic acid, 3-hydroxybutyric acid,
4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, 6-hydroxycarboxylic acid can be used, and further cyclic ester intermediates of hydroxycarboxylic acid, for example, glycolide and 6 which are dimers of glycolic acid. Ε, a cyclic ester of hydroxycaproic acid
-Caprolactone can also be used.

The lactic acid-based polymer used in the present invention is a method of direct dehydration polycondensation using lactic acid or a mixture of lactic acid and carboxylic acid and hydroxycarboxylic acid as a raw material, or a cyclic dimer of the above lactic acid and hydroxycarboxylic acid, For example, it can be obtained by a method of ring-opening polymerization using a cyclic ester intermediate such as lactide, glycolide, or ε-caprolactone.

In the case of production by direct dehydration polycondensation, lactic acid or lactic acid as a raw material and hydroxycarboxylic acid are preferably subjected to azeotropic dehydration condensation in the presence of an organic solvent, particularly a phenyl ether solvent, and particularly preferably. By removing water from the solvent distilled by azeotropic distillation and returning the solvent in a substantially anhydrous state to the reaction system, polymerization is carried out to obtain a high molecular weight L-lactic acid-based polymer having strength suitable for the present invention. To be

The weight average molecular weight of the lactic acid-based polymer is preferably a high molecular weight in the range where moldability is possible, and more preferably 30,000 or more and 5,000,000 or less. If the molecular weight is less than 30,000, the strength of the molded product becomes small, which is not suitable for practical use. Also,
If the molecular weight is 5,000,000 or more, the moldability is poor.

The amount of fatty acid and fatty acid amide used in the present invention has a releasing effect and maintains the stability of molding.
In order to maintain the transparency of the molded product, 0.051 to 1.0% by weight is preferable, and 0.2 to 0.5% by weight is more preferable. When a fatty acid or a fatty acid amide is used in this range, the releasing force at the time of injection molding is greatly reduced and a molded product can be obtained stably, and the molded product has good transparency, and further, by the additive at the time of injection molding. It is possible to obtain a molded product in which the decrease in the molecular weight hardly occurs and the clouding phenomenon of the molded product due to the solubility or the like does not occur.

The fatty acid is not particularly limited, but stearic acid is particularly preferable. The fatty acid amide is not particularly limited, but methylene bis-stearic acid amide, ethylene bis-stearic acid amide, ethylene bis-balmitic acid amide, ethylene bis-oleic acid amide and the like are preferable, and ethylene bis-stearic acid amide (EBS) is particularly preferable. preferable. Any known kneading technique can be applied to the mixing of the lactic acid-based polymer with the fatty acid or the fatty acid amide. These shapes are preferably pellets, rods, powders and the like.

Next, the method for producing a molded article using the lactic acid-based polymer according to the present invention will be described in detail. The lactic acid-based polymer molded article for the purpose of the present invention is produced by homogenizing a lactic acid-based polymer with a lubricant with a mixer, pelletizing with an extruder, and then injection molding.

The molded product is obtained, for example, by the following method. A lubricant is mixed with a lactic acid-based polymer having an average particle size of 15 to 100 μm with a ribbon blender or the like, and pelletized by setting a temperature of a 36 mmφ co-rotating twin-screw extruder at 150 to 230 ° C. and a screw at 100 rpm. Further, in order to improve extrusion stability during molding, the pellets are heat-treated in an oven heated to 80 to 120 ° C. to be crystallized.
In the case of injection molding, it can be obtained by melting the barrel temperature at 150 to 230 ° C. and setting the mold temperature at 10 to 30 ° C. with an ordinary molding machine.

The shape of the molded product of the present invention can be any angle with a draft in the injection direction of the mold being lower than 90 °. Even if the draft in the injection direction of the mold is 2 ° or less, the injection molding can be effectively performed. Draft in the die injection direction is 0.1
In the case of ~ 2.0 °, especially 0.1 ~ 0.9 °, the effectiveness is remarkably exhibited. Molded products can be efficiently molded with a molding machine that molds polystyrene resin, which is a general-purpose resin, for use in containers such as cosmetics, daily necessities, sundries, stationery (ballpoint pens, pencil shafts, cases, etc.), etc. used.

[0019]

EXAMPLES Next, the present invention will be specifically described with reference to examples. In the text, all parts are based on weight. First, the production of the L-lactic acid-based polymer used in the present invention will be described. The average molecular weight (weight average molecular weight) of the polymer was measured by gel permeation chromatography using polystyrene as a standard under the following conditions. Device: Shimadzu LC-10AD Detector: Shimadzu RID-6A Column: Hitachi Chemical GL-S350DT-5, GL-S3
70DT-5 Solvent: Chloroform Concentration: 1% Injection volume: 20 μl Flow rate: 1.0 ml / min

Production Example 1 100 parts of L-lactide and stannous octoate.
01 parts and 0.03 parts of lauryl alcohol were sealed in a thick cylindrical polymerization container made of stainless steel equipped with a stirrer, deaerated under vacuum for 2 hours, and then replaced with nitrogen gas. The mixture was heated at 200 ° C. for 3 hours with stirring under a nitrogen atmosphere. While maintaining the temperature as it was, the inside of the reaction vessel was depressurized to 3 mmHg by gradually degassing with a vacuum pump through an exhaust pipe and a glass receiver. 1 hour after the start of degassing,
Since distillation of the monomer and low-molecular-weight volatile matter disappeared, the inside of the container was replaced with nitrogen, and the monomer was extracted from the lower part of the container into a string and pelletized to obtain L-lactic acid-based polymer A. The weight average molecular weight of this polymer was about 100,000.

Production Example 2 10 kg of 90% L-lactic acid was placed in a 100-liter reactor equipped with a Dien-Stark trap at 150 ° C./50 m.
After distilling water while stirring at mHg for another 2 hours,
Tin powder 6.2 g was added, and the mixture was further stirred at 150 ° C./30 mmHg for 2 hours for oligomerization. To this oligomer, 28.8 g of tin powder and 21.1 kg of diphenyl ether were added, an azeotropic dehydration reaction was carried out at 150 ° C./30 mmHg, and distilled water and the solvent were separated by a water separator, and only the solvent was returned to the reactor. After 2 hours, the organic solvent to be returned to the reactor was passed through a column packed with 4.6 kg of Monocular Sieve 3A and then returned to the reactor to carry out a reaction at 150 ° C./35 mmHg for 40 hours to obtain a weight average molecular weight of 110,000. A polylactic acid solution was obtained. To this solution, 44 kg of dehydrated diphenyl ether was added and diluted, then cooled to 40 ° C., the precipitated crystals were filtered, washed with 10 kg of n-hexane three times, and 60 ° C. /
It was dried at 50 mmHg. This powder was added with 0.5N hydrochloric acid 1
After adding 2 kg and 12 kg of ethanol, stirring at 35 ° C. for 1 hour, filtering, and drying at 60 ° C./50 mmHg, 6.1 kg of polylactic acid powder having an average particle diameter of 30 μm (yield 85
%) L-lactic acid polymer B was obtained. The weight average molecular weight of this polymer was 110,000.

Production Example 3 Production Example 2 with 100 parts of L-lactic acid and 100 parts of DL-lactic acid
At the same time, DL-lactic acid polymer C was obtained. The weight average molecular weight of this polymer was about 110,000.

Production Example 4 Lactic acid and hydroxycarboxylic acid copolymer D were prepared in the same manner as in Production Example 2 except that 100 parts of L-lactic acid was replaced with 90 parts of L-lactic acid and 10 parts of glycolic acid as a hydroxycarboxylic acid component. Obtained. The weight average molecular weight of this polymer was about 100,000.

Production Example 5 The same procedure as in Production Example 2 was repeated except that 100 parts of L-lactic acid was replaced with 90 parts of L-lactic acid and 10 parts of 6-hydroquincaproic acid as a hydroxycarboxylic acid component. Polymer E was obtained. The weight average molecular weight of this polymer was about 100,000.

Hereinafter, examples of the method for producing a lactic acid-based polymer according to the present invention will be described using the L-lactic acid-based polymers obtained in Production Examples 1 to 5. The measurement conditions for the main physical properties are as follows. 1) Haze is made by Tokyo Denshoku Haze Meter
The haze value when the thickness was 1 mm was determined from the relationship between the thickness and the haze. 2) The bending strength was measured with a span of 50 mm by making a test piece having a width of 10 mm and a length of 100 mm from the container. 3) The mold release force is obtained by using an injection molding machine to mold a polymer into a mold when forming a cylindrical container having a diameter of 60 mm, a bottom diameter of 58.3 mm, a height of 100 mm and a thickness of 2 mm (draft angle 0.5 °). After the filling and cooling, the force at the time of extruding the container mouth part with a stripper plate was measured as a mold releasing force at the time of mold opening with a load cell (2 tons) installed between the stripper plate and the extrusion pin. 4) In the degradability test, a 2 × 5 cm test piece was sampled, and the test piece was embedded in soil at a temperature of 35 ° C. and a water content of 30% to carry out a decomposition test to determine the appearance change and the weight reduction rate. Examples 1 to 5 Lactic acid-based polymers A to E obtained in Production Examples 1 to 5 and stearic acid and ethylebisbisstearic acid amide as a lubricant at a ratio shown in Table 1 were mixed in a ribbon blender and then twin-screw extruder barrel Pellets were formed under the conditions of a temperature of 170 to 210 ° C, and the pellets were heat-treated in an oven at 80 ° C. Molded under the conditions of barrel temperature 160-210 ° C, mold temperature 20 ° C, cooling time 25 seconds by Japan Steel Works, Ltd., injection molding machine 100S, outer diameter about 60 mm, height 100 mm, wall thickness 2
A container having a transparency of 0.5 mm and a draft of 0.5 ° was obtained.

Comparative Example 1 The L-lactic acid polymer B obtained in Production Example 2 was used for injection molding. The test results are shown in Table 2. Since the polymer contained no lubricant, the mold release force was large and the molding processability was unstable.

Comparative Example 2 Using the L-lactic acid-based polymer B obtained in Production Example 2,
Zinc stearate was added as a lubricant in the proportion shown in Table 2, and injection molding was carried out in the same manner as in Example 1. Table 2 shows the test results
Shown in The moldability was good, but the molded product obtained was inferior in practical use due to insufficient strength due to a decrease in molecular weight.

Comparative Example 3 Same as Example 2 except that the range of 0.051 to 1.0 parts by weight of the L-lactic acid polymer B and stearic acid obtained in Production Example 2 was changed to less than 0.051 parts by weight. And injection molded.
The test results are shown in Table 2. Since the polymer contained a small amount of lubricant, the mold release force was high and the molding processability was unstable.

Comparative Example 4 The procedure of Example 2 was repeated except that the amount of the L-lactic acid-based polymer B obtained in Production Example 2 and stearic acid was more than 1.0 part by weight in the range of 0.051 to 1.0 part by weight. Injection molded. The test results are shown in Table 2. Since the polymer contained a large amount of lubricant, the biteability was unstable, and a stable molded product could not be obtained.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

The biodegradable lactic acid-based polymer composition of the present invention maintains transparency and strength to improve the releasability of injection molding, and is buried as waste in the ground or in the sea or river. When discarded, it decomposes into harmless water and carbon dioxide within a relatively short period of time in a natural environment like natural products such as paper and wood.

 ─────────────────────────────────────────────────── (72) Inventor Yasuhiro Kitahara Yasuhiro Kitahara 1190 Kasama-cho, Sakae-ku, Yokohama, Kanagawa Mitsui Toatsu Chemical Co., Ltd. (72) Masanobu Amioka 1190 Kasama-cho, Sakae-ku, Yokohama, Kanagawa Mitsui Toatsu Chemical Within the corporation

Claims (3)

[Claims] 1. 0.051 to 1.0 part by weight of a fatty acid, a fatty acid amide, or a mixture of a fatty acid and a fatty acid amide in 100 parts by weight of a thermoplastic polymer composition containing polylactic acid or a copolymer of lactic acid and a hydroxycarboxylic acid as a main component. Biodegradable lactic acid-based polymer composition characterized by being mixed 2. 0.051 to 1.0 part by weight of 100 parts by weight of a thermoplastic polymer composition containing polylactic acid or a copolymer of lactic acid and hydroxycarboxylic acid as a main component and a fatty acid, a fatty acid amide, or a mixture of a fatty acid and a fatty acid amide. 1. A method for molding a biodegradable lactic acid-based polymer, which comprises melt-kneading a part and injection molding. 3. 0.051 to 1.0 part by weight of 100 parts by weight of a thermoplastic polymer composition containing polylactic acid or a copolymer of lactic acid and hydroxycarboxylic acid as a main component and a fatty acid, a fatty acid amide, or a mixture of a fatty acid and a fatty acid amide. A method for molding a biodegradable lactic acid-based polymer, which comprises melt-kneading with a part and performing injection molding using a mold having a draft in the injection direction of 0.1 to 2 °.