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

[0048] The present invention takes the problem above into account, and hence the object is to provide a biodegradable molded article mainly made of starch that has satisfactory strength regardless of a degree of complexity of the shape, and at least satisfactory water resistance, and a very good biodegradation, furthermore excellent moisture absorption strength (moisture resistant strength).

[0060] According to the arrangement above, strength, especially pressure capacity can be further improved, thereby preventing any damage at a fall.

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 to remove the halogenated hydrocarbon used to dissolve the coating agent, and as in the case of the technologies (3) and (4), problems such as a requirement of equipment to prevent diffusion of halogenated hydrocarbon arise.

Many halogenated hydrocarbons are often harmful for a human body and the environment, and moreover the halogenated hydrocarbon that is concretely mentioned in the technology (5) contains CFC so that it should be released to the air as little as possible.

Generally, speaking, it is difficult to paint a water-resistant coating on the surface of the molded article evenly and entirely, while the coating on a flat molded article such as a flat plate is relatively easy.

However, small irregularities are likely to be formed on the surface of the molded article mainly made of starch as described above and obstruct the formation of an uniform film, and furthermore, the molded article or a painting device has to be rotated when the molded article is roughly circular in cross section, for instance formed like a cup or a bowl.

Therefore the painting becomes more difficult.

Besides, even if the coating agent can be painted evenly and entirely by using the dip method, the painted agent runs down before it solidifies and becomes the coating, and an unevenness is likely to show up on the coating.

The wax has a problem of poor heat resistance due to its relatively low melting point.

However, at the same time the method has problems such as: the biodegradation of the pulp-molding takes place slowly since it is made of fiber so that the molded article cannot be disposed together with remaining foods, etc.

; and only limited types of the molded article can be produced because it is difficult to make the molded article thicker, and also the molded article is not suitable for a deep drawing.

Also, the technology does not explain how the biodegradable plastic thin film is actually formed, such as by painting, by attaching preformed film, etc., for instance.

Moreover, the technology (7) does not stipulate the coating state of the biodegradable plastic thin film with respect to the main body of the biodegradable container at all.

Furthermore, as already described, it is difficult to use biodegradable plastics as a thick molded article due to its slow biodegradation, so the speed of the biodegradation also greatly depends on not only the thickness of the molded article but also a total amount of biodegradable plastics contained in the molded article.

As a result, it is not possible to manage the biodegradation of the whole container favorably.

Now, as described in relation to technologies (3) to (5), when -the thermoplastic dissolved in the solvent is used, problems such as a requirement of equipment to prevent diffusion of the solvent arise.

Thus it is impossible to mold molded articles such as a container with deep drawing shape like a cup, molded articles having irregular thickness like a food tray with partitions and a wrapping tray, and molded articles having complex shape like cushioning material for wrapping.

Therefore, even if the biodegradable container derived from starch has sufficient “strength” what is generally called, it does not have sufficient moisture absorption strength and it may soften or disshaped due to moisture absorption during a long-term storage under high humidity due to moisture absorption.

Also, even if an expanded molded article derived from starch is covered with a film or coating made from a biodegradable plastic available at present, it is difficult to block water vapor as the above case unless it is more than hundreds of μm thick.

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