JP3279709B2 - Method for producing foamed extrusion of lactic acid resin - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a lactic acid resin by foam extrusion. More specifically, the present invention relates to a method for producing a foamed extrusion which is composed of a thermoplastic resin composition mainly composed of a lactic acid resin and has decomposability in a natural environment after use, and is extruded, particularly excellent in foamed extrusion stability.

[0002]

2. Description of the Related Art Conventionally, resins such as polystyrene, polyethylene, and polypropylene have been used for foam extrusion molding. Foams made from the resin involved have excellent cell diameter and dimensional stability, but when discarded,
In addition to increasing the amount of garbage, it hardly decomposes in the natural environment, so it remains semi-permanently even when buried. In addition, abandoned plastics have caused problems such as degrading the landscape and destroying the living environment of marine life.

On the other hand, as a thermoplastic resin having biodegradability, polylactic acid or a copolymer of lactic acid and another hydroxycarboxylic acid (hereinafter abbreviated as lactic acid resin) has been developed. These resins are 100% biodegradable in the body of animals within a few months to a year, and when placed in soil or seawater, begin to degrade within a few weeks in a humid environment and about one to one.
It disappears in a few years, and the decomposition products have the property of becoming harmless lactic acid, carbon dioxide and water. Such a lactic acid-based resin has a low softening point, at or above the softening point,
Since the resin melt viscosity change is large, there is a problem in foam extrusion stability, and it has been difficult to obtain a uniform cell diameter and thickness with a smooth surface when forming sheets and rods.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a lactic acid-based resin which can be decomposed in a natural environment and has excellent foam extrusion stability.

[0005]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, have reached the present invention. That is, according to the present invention, the cross-sectional area of the die outlet portion when the barrel cross-sectional area of the extruder is set to 1 by adding 0.01 to 5 parts by weight of a metal salt of a higher fatty acid to 100 parts by weight of a lactic acid resin. This is a method for producing a foamed extrudate of a lactic acid-based resin, which comprises foaming and extruding using a mold of 0.02 to 0.10.

In the present invention, the lactic acid resin is lactic acid or lactic acid and other hydroxycarboxylic acids (eg, glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid,
From hydroxyvaleric acid, 5-hydroxyvaleric acid, 6-hydroxycaproic acid, etc.), or a cyclic ester intermediate of lactide or hydroxycarboxylic acid, which is a cyclic dimer of lactic acid, for example, a dimer of glycolic acid And ring-opening polymerization using a copolymerizable monomer such as glycolide or ε-caprolactone which is a cyclic ester of 6-hydroxycaproic acid.

In the case of direct dehydration condensation, lactic acid or lactic acid and another hydroxycarboxylic acid are azeotropically dehydrated and condensed, preferably in the presence of an organic solvent, especially a phenyl ether solvent.
Particularly preferably, high-molecular-weight polylactic acid having a strength suitable for the present invention can be obtained by polymerizing by removing water from the solvent distilled off by azeotropic distillation and returning the substantially anhydrous solvent to the reaction system. Can be

Lactic acid as a raw material is L-lactic acid or D-lactic acid.
Either lactic acid or a mixture thereof may be used. The average molecular weight of the resin is preferably 10,000 to 1,000,000, and if the molecular weight is 10,000 or less, the strength of the foam is small and is not suitable for practical use. Also,
When the molecular weight is higher than 1,000,000, the viscosity in a molten state is high, and the foaming extrudability is poor. The lactic acid-based resin may be mixed and kneaded with a plasticizer and various improvers as necessary. In this case, the ratio of lactic acid resin is 50%
What is necessary is just to make it above. Also, the shape is pellet,
Any of rod-like, powder, etc. may be used.

[0009] The foam extrusion method of the present invention can be carried out using a usual method. For example, a method of obtaining a foamed product through an extruder after mixing a predetermined amount of a higher fatty acid powder and a foaming agent in a lactic acid-based resin pellet and a foaming agent in some cases with a blender, or a foaming agent such as a volatile foaming agent A method of injecting from the middle of the extruder, extruding and simultaneously obtaining a foam is preferable.

An important point in the present invention is that an extruder is used which uses the raw material to which the above-mentioned higher fatty acid is added and which has a defined sectional area ratio between a barrel and a die outlet. Metal salts of higher fatty acids used in the present invention, olefinic acid, stearic acid, magnesium and higher fatty acids and magnesium,
Calcium and zinc are salts with metals. Of these, calcium stearate is preferred.

The amount of the metal salt of the higher fatty acid is lactic acid based resin.
It is in the range of 0.01 to 5 parts per 100 parts by weight. When the amount is less than 0.01 part, the effect of foaming extrusion stability is small. When the amount exceeds 5 parts by weight, the resins mutually slip and the resin stability is impaired. This is not preferable for adjusting the cell diameter of the foam. The cross-sectional area of the die outlet is the cross-sectional area of the die outlet when the cross-sectional area of the extruder barrel is 1.
If it is in the range of 0.02 to 0.10 and less than 0.02, the resin pressure inside the die is too high, and extrusion failure such as melt fracture occurs.If it exceeds 0.10, poor appearance of foam due to insufficient resin pressure inside the die, bubble diameter Is not preferred because it is difficult to obtain uniformity.

Examples of the foaming agent include evaporative foaming agents which foam by evaporation, for example, hydrocarbons such as butane, pentane and propane, halogen compounds such as methyl chloride and chlorodifluoromethane, carbon dioxide gas, nitrogen gas, and decomposition when heated. Decomposable foaming agent that generates a gas by heating, for example, an inorganic foaming agent such as sodium bicarbonate, azodicarbonamide, N, N｀-
Organic blowing agents such as dinitrosopentanemethylenetetramine and p, p @ oxybis (benzenefonylhydrazide). Whether the organic foaming agent is used alone or added in an appropriate amount to the evaporative foaming agent may be appropriately selected depending on the molded article or molding machine. If necessary, foaming aids or nucleating agents, for example, oxalic acid, salicylic acid, phthalic acid, benzoic acid, citric acid, inorganic acids such as tartaric acid, salts of the organic acids or inorganic acids, carbonates such as sodium carbonate, Appropriate amounts of zinc oxide, calcium oxide, titanium oxide, silica, clay and the like may be added.

For coloring and other modification of the foamed molding,
Pigments, flame retardants and fillers can be added at all. The extrusion temperature of the lactic acid-based resin foam sheet varies depending on the composition of the resin, but is usually at a temperature at which the melt viscosity becomes 10,000 to 100,000 poise. If the viscosity of the resin is higher than this, the generation of air bubbles is slow and the expansion ratio does not increase. Conversely, if the viscosity of the resin is too low, air bubbles cannot be retained, and a uniform quality foam sheet cannot be obtained. The expansion ratio varies depending on the container to be molded, but is preferably from 1.1 to 30 times, and more preferably from 2 to 15 times.

[0014]

【Example】

Production Example 1 Water was distilled while 10.0 kg of 90% L-lactic acid was stirred at 150 ° C./50 mmHg for 3 hours, and 6.2 g of tin powder was added.
The mixture was stirred at a temperature of 30 ° C./30 mmHg for another 2 hours to oligomerize. To this oligomer were added 28.8 g of tin powder and 21.1 kg of diphenyl ether, and an azeotropic dehydration reaction was carried out at 150 ° C./30 mmHg. The distilled water and the solvent were separated by a water separator, and only the solvent was returned to the reactor. Two hours later, the organic solvent to be returned to the reactor was passed through a column packed with 4.6 kg of molecular sieve 3A, and then returned to the reactor.
The reaction was carried out at mHg for 40 hours to obtain a polylactic acid solution having an average molecular weight Mw of 110,000. The solution was diluted by adding 44 kg of dehydrated diphenyl ether, cooled to 40 ° C., and the precipitated crystals were filtered, washed three times with 10 kg of n-hexane, and dried at 60 ° C./50 mmHg. This powder is added to 0.5 N-H
After adding 12.0 kg of Cl and 12.0 kg of ethanol, the mixture was stirred at 35 ° C. for 1 hour, filtered, and dried at 60 ° C./50 mmHg to obtain 6.1 kg of polylactic acid powder (yield: 85%). This powder was melted by extrusion and pelletized to obtain a lactic acid-based resin A. The average molecular weight Mw of this resin was 110,000.

Production Example 2 Production Example 1 except that 100 parts of L-lactic acid was changed to 100 parts of DL lactic acid.
Pellets were obtained in the same manner to obtain lactic acid resin B. The average molecular weight of this resin was Mw = 110,000. Production Example 3 A lactic acid resin-C was obtained in the same manner as in Production Example 1, except that 100 parts of L-lactic acid was changed to 80 parts of L-lactic acid and 20 parts of glycolide as a hydroxycarboxylic acid component. The average molecular weight Mw of this resin was 110,000. Lactic resin A
The average molecular weights (weight average molecular weights) of C to C were measured by gel permeation chromatography using polystyrene as a standard under the following conditions.

Apparatus: Shimadzu LC-10AD Detector: Shimadzu RID-6A Column: Hitachi Chemical GL-S350DT-5, GL-S3
70DT-5 Solvent: chloroform Concentration: 1% Injection amount: 20 μl Flow rate: 10 m / min or less, using the lactic acid-based resins A to C obtained in Production Examples 1 to 3,
An example of the method for producing a foam molded article made of a lactic acid-based resin according to the present invention will be described.

Example 1 Calcium stearate was added to 100 parts by weight of lactic acid resin A.
0.1 weight, talc (Micro Ace; Nippon Talc) 0.6
Parts by weight, p, p'-oxybis (benzenesulfonyl
Drazide) 0.5 parts by weight of raw material
Cross section 1257mm ^TwoThe cross section of the die exit is 88mm^TwoFlat
With a 40mmφ foam extruder equipped with a plate die, the resin viscosity is
Was adjusted to prepare a foamed sheet. The resulting foam is
Diameter is 0.15 ~ 0.20mmφ, thickness 3mm, foaming ratio is 2 times
The extrusion stability was good when molded in a flat plate shape. Obtained
5 × 5 cm test from the sample for the degradability of the molded body
And buried the specimen in soil at 35 ° C and 30% moisture
Then, a disassembly test was performed, and the appearance was observed. Table 1 shows the above results.
Shown in

Examples 2 to 4 Mixtures of lactic acid resins A to C having an average molecular weight of 110,000 as shown in Table 1.
0.1 parts by weight of calcium stearate, 0.5 parts by weight of talc, and 8 parts by weight of Freon 22 (manufactured by Mitsui DuPont Fluorochemicals) are used as raw materials in 100 parts by weight.
3319Mm ² to adjust the resin viscosity at a temperature at the die exit 50-65mmφ tandem sectional area gave a 100 mm ² Sakyuradai of portions foam extruder was created foam sheet. The obtained foamed sheet has a cell diameter of 0.15 to 0.20 mmφ and a thickness of 2
mm, the expansion ratio was about 8 times, and it was stable during extrusion molding.
The obtained foamed sheet was measured in the same manner as in Example 1.

Comparative Examples 1 to 3 Comparative Example 1 shows a case where calcium stearate was not added to 100 parts by weight of the lactic acid-based resin A and the foaming extruder used in Example 2 was used. 0.12 cross section ratio
In the case of Comparative Example 2 and the case where the cross-sectional area of the die exit portion was 0.015, Comparative Example 3 was used to prepare a foamed sheet. The foam extrudability was unstable in the case of Comparative Example 1 and almost excellent in the case of Comparative Example 2, but the obtained foamed sheet had an uneven cell diameter and a rough appearance. . In Comparative Example 3, the sheet was severely corrugated at the exit of the die, and a sheet having a uniform thickness could not be obtained.

[0020]

The method of the present invention for producing a lactic acid resin by foam extrusion is excellent in foam extrusion stability, and the obtained foam has a uniform cell diameter and excellent appearance. In addition, when the obtained foam is buried underground or discarded in the sea or river as waste, it is harmless in a relatively short period of time in the natural environment like natural products such as paper and wood. And decompose into carbon dioxide.

[0021]

[Table 1]

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-304244 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08J 9/04 B29C 47/00

Claims (2)

(57) [Claims] (1) To 100 parts by weight of a lactic acid-based resin, 0.01 to less than 5 parts by weight of a metal salt of a higher fatty acid is added.
A method for producing a foamed extrudate of a lactic acid-based resin, which comprises foaming and extruding using a mold having a size of about 0.10. 2. The method according to claim 1, wherein the metal salt of the higher fatty acid is Mg, Ca or Z.
The method for producing foamed extruded lactic acid resin according to claim 1, wherein n is n.