JPH09286870A - Production of biodegradable resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process whereby a biodegradable resin foam which does not shrink just after molding and is excellent in mechanical strengths can be produced whole using a generally used molding machine. SOLUTION: A biodegradable resin compsn, essentially comprising a starch- based biodegradable resin, a biodegradable polyester resin having an m.p. or softening point higher then that of the foregoing resin, and a foaming agent is molded and foamed at a temp, somewhat higher than the m.p. or softening point.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a biodegradable resin foam which can be molded by a general molding machine and has excellent strength.

[0002]

2. Description of the Related Art In recent years, due to increasing environmental problems, measures for discarding synthetic resin molded products are required. In particular, packaging materials are often discarded immediately after use. Among them, foamed moldings used as cushioning materials are bulky for their weight, so they are decomposed from conventional thermoplastic resin foams by microorganisms at the time of disposal. There is a movement to replace biodegradable foam.

[0003]

The biodegradable resins are roughly classified into three types, starch type, chemical synthetic type and microbial synthetic type.
With regard to both sleds, as the thermoplastic resin foam is currently established as foamed styrene, etc., pellets prepared by kneading a volatile gas in resin are pre-expanded and then heat-foamed in a mold. It is difficult to use the method as it is because of the nature of the resin.

Therefore, in a cylinder of an extruder or an injection molding machine, a method is used in which a resin containing a foaming component is heated and melted under pressure and then discharged from a nozzle to foam. In this method, after the resin has been foamed, when it is cooled in the atmosphere, the foaming component in the foamed cell contracts, resulting in a negative pressure, so if the resin has not solidified at that point, the cell that could bend will contract. Therefore, the molding temperature must be set slightly higher than the melting point or softening point of the resin so that the resin solidifies immediately after it comes out of the nozzle. However, most of the biodegradable resins currently on the market have a low melting point or softening point, and in particular, many starch-based resins have relatively low temperatures of 100 to 150 ° C. Since the shearing heat generated by kneading is large and the cylinder temperature rises immediately, in order to keep constant at the optimum molding temperature for foaming, which is slightly higher than the melting point or softening point of the resin that does not cause cell shrinkage after foaming. Is limited by the manufacturing conditions that the kneading speed must be reduced,
The kneading / molding equipment must have a cooling function such as water cooling. However, limiting the conditions of foam molding, which is difficult even by itself, could have a fatal impact on the product characteristics, and even if cooling was performed, ordinary injection molding machines and extruders had a cooling function. There are few things, and even less things have a system to control it, so it is necessary to manufacture or add a special device to perform foam molding, which is a disadvantage that the cost becomes high. It was

The present invention has been made in order to solve the above-mentioned drawbacks, and it is possible to perform foam molding using a general molding machine.
An object of the present invention is to provide a method for producing a biodegradable resin foam which does not shrink immediately after molding and is excellent in mechanical strength.

[0006]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventor has blended a biodegradable polyester resin having a higher melting point or softening point than a starch-based biodegradable resin. It was found that the above-mentioned objects can be achieved by doing so, and the present invention has been completed.

That is, the present invention provides a biodegradable resin composition comprising (A) a starch-based biodegradable resin, (B) a biodegradable polyester resin, and (C) a foaming agent as essential components, wherein The biodegradable polyester resin of B) has a higher melting point or softening point than the starch-based biodegradable resin of (A), and the biodegradable resin composition is molded and foamed at a temperature slightly higher than the melting point or softening point. And a method for producing a biodegradable resin foam, which comprises:

Hereinafter, the present invention will be described in detail.

The biodegradable resin composition used in the present invention is
(A) Starch-based biodegradable resin, (B) Biodegradable polyester resin, and (C) Foaming agent are essential components. Next, each of these components will be described.

As the starch-based biodegradable resin (A), starch refined from corn, potato, tapioca, etc. is used as it is or modified, and polyvinyl alcohol, polyacrylic acid, polycaproic acid are added to improve processability. Examples include blends of biodegradable resins such as lactan, and these can be used alone or in combination of two or more.

Examples of the biodegradable polyester resin (B) include polylactic acid, polybutylene succinate, polybutylene diglycolate, polyhydroxybutyrate-based copolymers, chemically synthesized polyesters such as ester-type polyurethane, and microbial polyesters. Examples thereof include resins, and these can be used alone or in combination of two or more. This biodegradable polyester resin needs to have a higher melting point or softening point than the starch-based biodegradable resin (A) described above.
If the melting point or softening point is lower than that of the starch-based biodegradable resin, the shrinkage of the foam cells cannot be prevented, which is not preferable. Biodegradable as much as possible within the range where the starch biodegradable resin does not deteriorate in the cylinder so that the difference in melting point or softening point between the starch biodegradable resin and the biodegradable polyester resin can be increased and the molding temperature can be increased. It is desirable to increase the melting point or softening point of the water-soluble polyester resin. The method of blending the starch-based biodegradable resin with the biodegradable polyester resin is
Even if blended with an extruder before molding into pellets,
Individually processed pellets may be blended at the time of molding and used. However, when water is used as the foaming agent, it is necessary to blend them under the condition that the biodegradable polyester resin is not hydrolyzed. Examples of the foaming agent (C) include inorganic foaming agents such as sodium bicarbonate, ammonium carbonate and azide compounds, and organic foaming agents such as azo compounds, isocyanate compounds and semicarbazide compounds. These may be used alone or in combination of two kinds. The above can be mixed and used. These foaming agents can be used according to the molding temperature of the above-mentioned resin, but in consideration of contamination after disposal, extra water is added to the resin in advance and vaporized by the heat during molding. It is desirable to perform water bubbling for foaming.

The biodegradable resin composition used in the present invention is
It can be produced by blending (A) starch-based biodegradable resin, (B) biodegradable polyester resin and (C) foaming agent. This biodegradable resin composition can be molded and foamed at a temperature slightly higher than the melting point or softening point of the biodegradable polyester resin to produce a biodegradable resin foam.
In the present invention, a starch-based biodegradable resin is blended with a biodegradable polyester resin having a higher melting point or softening point to foam and mold at a temperature slightly higher than the melting point or softening point of the biodegradable polyester resin. Is to do. By doing so, when the resin is discharged from the nozzle, the starch-based biodegradable resin tries to wither due to the negative pressure generated by the contraction due to the temperature decrease in the foam cell, whereas the biodegradable polyester resin does not Since the temperature is slightly higher than the melting point or softening point, it solidifies immediately, plays a role of a kind of core material, and has an effect of preventing the collapse of the foam cells. As a result, in the conventional foam molding of starch-based biodegradable resin, the molding temperature is kept low to prevent shrinkage, so that it is easily affected by heat generation by shearing, and the cylinder temperature rises immediately. On the other hand, since the molding temperature can be raised from the beginning and the influence of shear heat generation is reduced,
The molding temperature can be kept constant without lowering the screw rotation speed or adding a special cooling function to the cylinder. Furthermore, the core material of the biodegradable polyester resin produced also plays the role of a filler. Therefore, by using a biodegradable polyester resin having a property suitable for the purpose, it is possible to improve the compressive strength of the foam and the product. The brittleness could also be improved. In order to effectively utilize such an action, in combining a starch-based biodegradable resin and a biodegradable polyester resin, it is possible to increase the difference in melting point or softening point between them and increase the molding temperature, It is desirable that the melting point or softening point of the biodegradable polyester resin be as high as possible within the range where the starch-based biodegradable resin does not deteriorate in the cylinder.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. In the following Examples and Comparative Examples,
"Parts" means "parts by weight".

EXAMPLE NOVON-180, a starch-based biodegradable resin prepared by blending solidified starch with a polyvinyl alcohol-based water-soluble polymer.
1 (manufactured by Chisso Co., trade name, softening point 110 ° C.), with 18 parts water absorbed as a foaming agent, Lacty lactic acid-based biodegradable polyester resin (manufactured by Shimadzu Corporation, trade name, melting point) A biodegradable resin composition prepared by blending 30 parts of 170 ° C.) in a pellet state was used as a twin screw extruder PCM30.
Cylinder temperature was set to 180 ° C. and rotation speed was 150 rpm by (Ikegai Co., Ltd.), and extrusion molding was performed to continuously produce a biodegradable resin foam. The apparent specific gravity was 0.05 and the expansion ratio was 25 times.

Comparative Example NOVON-180, a starch-based biodegradable resin prepared by blending solidified starch with a polyvinyl alcohol-based water-soluble polymer.
1 (manufactured by Chisso Co., trade name, softening point 110 ° C) 130 parts absorbed 18 parts of water as a foaming agent, rotation speed 150 rp
When extrusion molding was performed with the m set to m, it initially became a foam, but the cylinder temperature gradually increased, and after the temperature exceeded 130 ° C, the shrinkage phenomenon began to appear, and stable molding was possible. There wasn't. Then, when the extrusion speed was reduced to 75 rpm, a biodegradable resin foam having a poor foaming state was obtained although the increase in the cylinder temperature was moderate. The apparent specific gravity was 0.3 and the expansion ratio was 4 times, and there was no satisfactory cushioning capacity as a packaging material.

[0016]

As described above, according to the method for producing a biodegradable resin foam of the present invention, it can be foam-molded using a general molding machine, does not shrink immediately after molding, and has high strength as a product. It was possible to produce a biodegradable resin foam.

Claims (1)

[Claims] 1. A biodegradable resin composition comprising (A) a starch-based biodegradable resin, (B) a biodegradable polyester resin, and (C) a foaming agent, which are essential components. The degradable polyester resin has a higher melting point or softening point than the starch-based biodegradable resin (A), and the biodegradable resin composition is molded and foamed at a temperature slightly higher than the melting point or softening point. And a method for producing a biodegradable resin foam.