JPH0912748A - Method for molding polylactic acid-based polymer and polylactic acid-based molded article - Google Patents

Abstract

(57) Abstract: [PROBLEMS] To provide a method for molding a polylactic acid-based polymer having excellent dimensional stability and a polylactic acid-based molded article. SOLUTION: The composition ratio of L-form and D-form is 100: 0.
To 94: 6 or 6:94 to 0: 100, a primary molded article made of a polylactic acid-based polymer is molded into a desired shape to obtain a secondary molded article. A method for molding a polylactic acid-based polymer, characterized in that the temperature is maintained in the temperature range from the glass transition temperature Tg to the melting point Tm of the polymer, and a molded article. [Effect] A molded product using polylactic acid can be used in a wide range of fields as a blister processed product or a plastic container such as a bottle.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for molding a polylactic acid-based polymer which is excellent in dimensional stability and decomposes in a natural environment, and a polylactic acid-based molded article.

[0002]

2. Description of the Related Art Plastic resins such as polyvinyl chloride, polyethylene, polystyrene and polyethylene terephthalate have been used for bottles containing blister processed products and drinking water which are widely used for display and packaging of various products. However, since these resins are chemically and biologically stable, they remain and accumulate without being decomposed even if they are left in a natural environment. Then, there is a problem that not only is it scattered in the natural environment to contaminate the living environment of plants and animals, but also it is hardly decomposed when it is buried as garbage, and the life of the landfill is shortened.

Therefore, there is a demand for a material composed of a polymer having a spontaneously decomposing property which does not cause these problems, and many studies and developments have been conducted in practice. Polylactic acid is drawing attention as an example. Polylactic acid is naturally hydrolyzed in the soil and does not remain in its original form in the soil, and becomes a degradable product harmless to microorganisms.

[0004]

At present, a method for obtaining a molded product using polylactic acid is being investigated, and it is disclosed in JP-A-6-23.
No. 828 and JP-A-6-122148 disclose a molded product of polylactic acid, which has improved impact strength, transparency and moldability.

By the way, a blister processed product or a plastic container such as a bottle may shrink when exposed to a high temperature, which causes a problem such as the contents of the container popping out. Therefore, the above-mentioned plastic container may be required to have dimensional stability. That is, in order to use the molded product using polylactic acid in a wide range of fields, it is important to impart dimensional stability.

Therefore, an object of the present invention is to provide a method for molding a polylactic acid polymer excellent in dimensional stability and a polylactic acid molding.

[0007]

The gist of the present invention is that the composition ratio of the L-form and the D-form is 100: 0 to 94: 6 or 6 :.
After molding a primary molded product composed of a polylactic acid-based polymer of 94 to 0: 100 into a desired shape to obtain a secondary molded product,
The glass transition temperature T of the polylactic acid-based polymer
It is a method for molding a polylactic acid-based polymer, which is characterized in that the temperature is maintained in the temperature range from g to melting point Tm. Another gist of the present invention is that the composition ratio of the L-form and the D-form is 100: 0 to 94 :.
A sheet or hollow body made of a polylactic acid-based polymer of 6 or 6:94 to 0: 100 is molded into a desired shape, and then the glass transition temperature Tg to the melting point Tm of the polymer are molded.
It is a polylactic acid type molded product obtained by heat treatment in the temperature range of.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The polylactic acid-based polymer used in the present invention is polylactic acid or a copolymer of lactic acid and other hydroxycarboxylic acid, or a mixture thereof, and does not impair the effects of the present invention. Other polymer materials can be mixed in the range.

Lactic acid includes L-lactic acid and D-lactic acid,
Typical examples of the hydroxycarboxylic acid include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvaleric acid, 4-hydroxyvaleric acid and 6-hydroxycaproic acid.

The constitutional unit of the polylactic acid-based polymer is poly (L-lactic acid) whose structural unit is lactic acid, poly (D-lactic acid) whose structural unit is D-lactic acid, and further L-lactic acid. And poly (DL-lactic acid), which is a copolymer of D-lactic acid.
There are also mixtures of these.

As the polymerization method, any known method such as a condensation polymerization method and a ring-opening polymerization method can be adopted. For example, in the polycondensation method, L-lactic acid, D-lactic acid or a mixture thereof can be directly dehydrated and polymerized to obtain polylactic acid having an arbitrary composition.

In the ring-opening polymerization method, polylactic acid can be obtained by using lactide, which is a cyclic dimer of lactic acid, and a catalyst selected as necessary while using a polymerization modifier and the like. Lactide is L-lactide which is a dimer of L-lactic acid, D-lactide which is a dimer of D-lactic acid, and further L-
There is DL-lactide composed of lactic acid and D-lactic acid, and polylactic acid having an arbitrary composition and crystallinity can be obtained by mixing and polymerizing these as needed.

A small amount of chain extender for the purpose of increasing the molecular weight,
For example, a diisocyanate compound, an epoxy compound, an acid anhydride, etc. can be used. The preferred range of the weight average molecular weight of the polymer is from 60,000 to 700,000. When the weight average molecular weight is less than this range, practical physical properties are scarcely expressed, and when it exceeds the range, the melt viscosity is too high and moldability is poor. Those having a low molecular weight are suitable for injection molding.

Further, additives such as plasticizers, lubricants, inorganic fillers and ultraviolet absorbers, and modifiers may be added for the purpose of adjusting the molding processability and the physical properties of the molded product.

The copolymer has different crystallinity and melting point depending on the ratio of the L-lactic acid structural unit and the D-lactic acid structural unit. The mixing ratio of the polylactic acid-based polymer used in the present invention is as a material for molding. The composition ratio of L-lactic acid and D-lactic acid is 100: 0 to 9
It is 4: 6 or 6:94 to 0: 100. If it falls within this range, the glass transition temperature Tg to the melting point Tm will be described later.
By heat-treating in the temperature range of 1, a secondary molded product having high crystallinity can be obtained.

A method of molding the molded product will be described. First, a sheet or a hollow body (primary molded product) is manufactured using the lactic acid-based polymer described above, and then heat-processed to mold it into a desired shape to obtain a secondary molded product. The heat processing is a so-called thermoforming method, and specifically includes vacuum forming, pressure forming, vacuum pressure forming, plug assist forming, male and female forming, blow forming and the like.

Specific examples of the primary molded product include a sheet or plate formed by melt extrusion or press molding, and a hollow molded product (parison) formed by injection molding or the like.

The method for producing the sheet used as the primary molded article is, for example, after removing water from the polylactic acid-based polymer,
Melt extrusion is performed with an extruder. It is preferable to appropriately select the melting temperature in consideration of the change depending on the composition and the thermal decomposition of the polymer. In practice, a temperature range of 140 ° C to 250 ° C is selected.

It is extruded from a T-die and brought into contact with a casting drum (cooling drum) to form a sheet. The preferred temperature range of the casting roll is below the glass transition temperature Tg of the polymer. If it is higher than the glass transition temperature Tg, the polymer sticks to the casting drum and cannot be removed. Furthermore, crystallization is promoted and spherulites develop, and it is difficult to obtain a molded product having a desired shape.

Before obtaining a secondary molded product from a sheet, the sheet is preheated to a glass transition temperature Tg or higher and softened before molding. Next, the molded product is obtained by bringing it into close contact with a mold having a desired shape to obtain a secondary molded product, and then performing heat treatment.

The method of heat treatment is not particularly limited, but is usually performed in a mold. The temperature of the heat treatment may or may not be the same as the temperature of the mold for obtaining the secondary molded product. In any case, in order to obtain a molded product excellent in dimensional stability, the glass transition temperature Tg To the melting point Tm.

The term "heat treatment" as used in the present invention means that the secondary molded product is maintained in the temperature range from the glass transition temperature Tg to the melting point Tm.
Preferably, it is maintained in the range of 90 ° C to the melting point Tm. The time to be kept in the above range depends on the temperature of the heat treatment, but it is preferable to perform the heat treatment for 3 seconds or more. It is possible to increase the crystallinity of the secondary molded product and impart dimensional stability.

A molded product having high transparency is required for some applications. In order to obtain a highly transparent molded product, the primary molded product is preheated at a relatively low temperature (near the glass transition temperature Tg) and then heat treated. Thereby, the growth of spherulites can be suppressed, and a molded product having excellent transparency and dimensional stability can be obtained.

The case where the molded product is obtained from the primary molded product which is a sheet has been described above, but the same applies when the molded product is obtained from another primary molded product, for example, a parison which is a hollow body.

[0025]

EXAMPLES Examples will be described below, but the present invention is not limited to these examples. The measured values described below were obtained by measuring under the following conditions.

(1) Glass transition temperature Tg and melting temperature Tm Using a differential scanning calorimeter DSC-7 manufactured by Perkin Elmer Co., 10 mg of polylactic acid type polymer was heated according to JIS-K7122 at a heating rate of 10 ° C. / The glass transition temperature Tg and the melting temperature Tm were determined from the thermogram when the temperature was raised in minutes.

(2) Volume Retention Rate The molded product was placed in a box-shaped stainless steel wire mesh of 20 cm × 20 cm and immersed in warm water of 80 ° C. for 5 minutes. After immersion, the molded product is filled with water, the water is measured with a graduated cylinder, and the capacity after contraction (V1) is examined, and the capacity before immersion (V0)
The volume retention rate was calculated in comparison with.

Volume retention rate (%) = (V1 / V0) × 100 (Example 1) The composition ratio of L-lactic acid and D-lactic acid was 98: 2.
The glass transition temperature Tg is 58 ° C. and the melting temperature Tm is 17
A polylactic acid polymer having a weight average molecular weight of 180,000 at 5 ° C is dried at 120 ° C while sending dry air to remove water.
For 3 hours. This polylactic acid polymer was extruded from a T-die at 210 ° C. in a 60 mmφ uniaxial extruder and rapidly cooled by a casting roll (roll temperature 58 ° C.) to obtain a sheet of transparent polylactic acid polymer having a thickness of about 400 μm (primary A molded product) was obtained. The extrudability of the polylactic acid polymer was good.

About 4 cut into 250 mm × 250 mm
A thermoforming machine (PLAVAC-FE36PH type) manufactured by Sanwa Kogyo Co., Ltd. was used to prepare the polylactic acid sheet (primary molded product) having a thickness of 00 μm.
After mounting on the sheet, the sheet was preheated to 68 ° C. with an infrared heater. After lifting the mold from below the polylactic acid sheet and pressing the sheet from the top to the mold bottom by 3 mm with a plug, the inside of the mold is evacuated and the sheet is molded into a cup shape to obtain a secondary molded product. It was At this time, the mold temperature is 70 ° C.

The above secondary molded product is continuously molded at a mold temperature of 70 ° C.
Then, heat treatment was performed by holding for 30 seconds while vacuum suction. After that, water is sprayed on the thermoformed product in the mold to cool it,
The cup-shaped molded product was taken out from the mold.

Example 2 A mold temperature for obtaining a secondary molded product is 100 ° C., and a mold temperature for heat treatment is 100 ° C.
A cup-shaped polylactic acid-based molded article was produced in the same manner as in Example 1 except that the heat treatment time was 20 seconds.

(Example 3) Same as Example 1 except that the mold temperature for obtaining the secondary molded product was 70 ° C, the mold temperature for heat treatment was 160 ° C, and the heat treatment time was 10 seconds. Then, a cup-shaped polylactic acid-based molded product was produced.

Example 4 Polylactic acid having a composition ratio of L-lactic acid and D-lactic acid of 94: 6, a glass transition temperature Tg of 57 ° C., a melting temperature Tm of 152 ° C. and a weight average molecular weight of 130,000. A sheet was obtained from the polymer in the same manner as in Example 1.

The mold temperature for obtaining a secondary molded product from the polylactic acid sheet is 50 ° C., and the mold temperature for heat treatment is 1
A cup-shaped polylactic acid-based molded product was produced in the same manner as in Example 1 except that the heat treatment time was set to 00 ° C. and the heat treatment time was set to 20 seconds.

(Comparative Example 1) The same as Example 1 except that the mold temperature for obtaining the secondary molded product was 50 ° C., the mold temperature for heat treatment was 50 ° C., and the heat treatment time was 60 seconds. Then, a cup-shaped polylactic acid-based molded product was produced.

(Comparative Example 2) The same as Example 1 except that the mold temperature for obtaining the secondary molded product was 70 ° C, the mold temperature for heat treatment was 190 ° C, and the heat treatment time was 10 seconds. Then, a cup-shaped polylactic acid-based molded product was produced.

Comparative Example 3 The mold temperature for obtaining the secondary molded product from the sheet used in Example 4 was 50 ° C., the mold temperature for heat treatment was 50 ° C., and the heat treatment time was 60 seconds. A cup-shaped polylactic acid-based molded product was produced in the same manner as in Example 1 except for the above.

Comparative Example 4 Polylactic acid having a composition ratio of L-lactic acid and D-lactic acid of 93: 7, a glass transition temperature Tg of 57 ° C., a melting temperature Tm of 125 ° C. and a weight average molecular weight of 110,000. A polylactic acid sheet was obtained from the polymer by the same method as in Example 1.

The mold temperature for obtaining the secondary molded product from the above sheet is 100 ° C., and the mold temperature for heat treatment is 100.
A cup-shaped polylactic acid-based molded product was produced in the same manner as in Example 1 except that the temperature was 30 ° C. and the heat treatment time was 30 seconds.

The examples 3 and 4 and the comparative example 2 are the same except that the mold temperature for obtaining the secondary molded product and the mold temperature for the heat treatment are different.

Table 1 shows the above Examples 1 to 4 and Comparative Examples 1 to 1.
L- in the cup-shaped polylactic acid-based molded product obtained in No. 4
The composition ratio of lactic acid and D-lactic acid, the glass transition temperature Tg, the melting point Tm, the heat treatment temperature, and the heat treatment time are shown. In addition, Table 1 shows the volume retention of each cup-shaped polylactic acid-based molded product.

[0042]

[Table 1] Although it depends on the application, in general, when the volume retention is judged by immersing it in warm water of 80 ° C. for 5 minutes, a volume retention of 70% or more is suitable for practical use. . As is clear from Table 1, Examples 1 to 4, which are the present invention, have a retention rate of 70% or more even when immersed, and are suitable for practical use. In particular, Examples 2 and 3 have a volume retention rate of more than 95%, and are excellent in filling a high temperature solution.

On the other hand, in Comparative Examples 1, 3 and 4, the volume retention rate is 7
It is less than 0%, which is insufficient for use as a blister processed product or a plastic container such as a bottle. In Comparative Example 2, the cup-shaped molded product was melted by the heat treatment.

Although the above examples show the case where the amount of L-lactic acid is larger than that of D-lactic acid, similar results are obtained when the amount of D-lactic acid is larger than that of L-lactic acid.

[0045]

As described above, according to the present invention, dimensional stability can be imparted to a polylactic acid-based molded product, so that a molded product using polylactic acid can be used in a wide range of fields as a plastic container such as a blister processed product or a bottle. Can be used.

Claims (2)

[Claims] 1. The composition ratio of L-form and D-form is 100: 0.
To 94: 6 or 6:94 to 0: 100, a primary molded article made of a polylactic acid-based polymer is molded into a desired shape to obtain a secondary molded article. A method for molding a polylactic acid-based polymer, which comprises maintaining the glass transition temperature Tg of the polymer to a melting point Tm. 2. The composition ratio of L-form and D-form is 100: 0.
A sheet or hollow body made of a polylactic acid-based polymer having a molecular weight of ˜94: 6 or 6:94 to 0: 100 in a desired shape, and then having a temperature range from a glass transition temperature Tg to a melting point Tm of the polymer. A polylactic acid-based molded product obtained by heat treatment.