Biodegradable molding

Abstract

A bowl-shaped container (10a) which is as a biodegradable molded article adheres a coating film (12) mainly made of biodegradable plastic and having at least hydrophobicity to the surface of the main body (11a) of the container mainly made of starch. The main body (11a) is molded through steam expansion of a slurry or dough molding material containing high-amylose starch and water, or a slurry or dough molding material containing starch, polyvinyl alcohol and water. For these reasons, it is possible to accomplish sufficient strength and at least sufficient water resistance, to exert a very excellent biodegradability and further to provide a biodegradable molded article having excellent moisture absorption strength mainly made of starch even if the biodegradable molded article has a complicated shape.

Description

TECHNICAL FIELD [0001] The present invention relates to a biodegradable expanded molded article mainly derived from starch, and a biodegradable molded article including a coating film bonded on a surface thereof, and particularly to a biodegradable molded article that can suitably be used for disposable expanded molded articles that are disposed after the use as a food container, a molding buffer material, GES, a wrapping tray, etc. BACKGROUND ART [0002] Conventionally, a plastic molded article and a paper / pulp molded article are the mainstream of a disposable molded article that is disposed after the use. This is because in most cases, raw materials of the disposable molded article should be durable and strong and at the same time readily formable depending on usage of the molded article. [0003] However, the plastic molded article and the paper / pulp molded article both have difficulties to be used as the disposable molded article, as shown below. [0004] First, when incinerated, the...

AI Technical Summary

Benefits of technology

[0057] Furthermore, according to the arrangement above, inasmuch as the molding material includes polyvinyl alcohol, it is possible to prevent a reduction of strength caused by moisture absorption of starch under high humidity and to improve physical strength.

[0058] Therefore, according to the arrangement above, as described above, it is possible to provide a biodegradable mol

Problems solved by technology

However, the plastic molded article and the paper/pulp molded article both have difficulties to be used as the disposable molded article, as shown below.

First, when incinerated, the plastic molded article damages an incinerator because of the generation of extremely high heat, or additionally produces environmental pollutants such as dioxin.

Also, when the plastic molded article is buried for reclamation, it is impossible to bury the molded article where once the same is buried, since plastics are rarely decomposed naturally.

Moreover, due to a recent increase of the amount of waste, it has become difficult to secure new dumping sites year after year.

Furthermore, continuous environmental pollution for a long period of time could be caused, since the plastic molded article cannot be decomposed easily.

Also, reserves of fossil fuels such as oil, which are raw materials of plastics, are decreasing year after year, so the plastic molded article could become more expensive in the future.

However, trees, of which paper and pulps are made, grow slowly and thus the mass consumption of paper and pulps substantially reduce forest resources.

The reduction of forest resources brings about not only heavy destruction of an environment of the area but also a great impairment of an ability of forests to absorb CO2, and a spun for global warming because of the increase of CO2 from a broad perspective.

Usually the removal of the residues is washed in water, so this induces another pollution such as an increase of the amount of polluted water and subsequent water-pollution in rivers and the sea.

Also, the recycling requires high cost, because the removal of the residues itself lowers the efficiency of recycling as it needs a lot of time and efforts, and the system of recycling has not been really socially established at the moment.

This is because the various biodegradable plastics have a problem that despite having a fine quality almost comparable to conventional plastics (non-degradable or degradable-retardant), practically they cannot be decomposed quickly enough.

For instance, when the thickness of a molded article made of the biodegradable plastic is heavy, it takes a very long time until the molded article is completely decomposed, so practically it is not possible to produce a molded article with enough volume.

However, actually it is difficult to compost them together since the biodegradable plastic above is only decomposed much slower than the food residues.

Furthermore, it is also difficult to crash the molded article to hasten the decomposition of the biodegradable plastic, because normally the molded article cannot be crushed easily when it has a certain thickness and strength.

Thus it is almost impossible to compost the molded article made of the biodegradable plastic.

However, at the same time the molded article derived from the technology (1) or (2) has the disadvantages that it can be used only for limited purposes and is required to barrier moisture, due to its poor water and humidity resistance.

However, the surface of the molded article (including expanded molded article) mainly made of starch cannot be completely smoothed, and generation of small irregularities cannot be avoided.

Thus small pinholes are likely to be formed on the surface corresponding to the irregularities of the water-resistant coating if the resin is simply painted, so it could be possible to render the molded article water repellent but difficult to make the same complete water proof.

So this introduces problems in terms of a manufacturing facility.

However, in this method, it is required t

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