Heretofore, a lot of biodegradable resins and biodegradable compositions, containing, as main components, biodegradable resins such as polylactic acid and fatty acid polyester as well as natural materials such as starch, have hitherto been proposed, and processed biodegradable articles using these biodegradable resins and biodegradable compositions have been provided.
For example, JP-A-Hei07-17571 (Patent Document 1) discloses a biodegradable buffer material which contains starch as a main component, and is obtained by adding vegetable fibers and/or protein, followed by blow molding. JP-A-2005-119708 (Patent Document 2) discloses a biodegradable resin composition obtained by blending starch and polyol, monosaccharide or oligosaccharide, and protein. JP-A-Hei05-320401 (Patent Document 3) discloses a biodegradable molded article obtained by blending wheat flour, starch and cellulose, followed by foaming and further firing.
However, when natural materials such as starch are used, the resultant product often has poor water resistance and tends to have poor strength. Therefore, JP-A-Hei05-278738 (Patent Document 4) and JP-A-Hei05-57833 (Patent Document 5) and JP-A-2002-355932 (Patent Document 6) each discloses a method of coating the surface of a processed article molded from a biodegradable composition with a water-resistant resin. However, according to this method, coating must be conducted again, resulting in increase of the number of steps.
On the other hand, JP-A-Hei06-248040 (Patent Document 7) discloses, as a biodegradable composition having improved impact resistance and improved heat resistance, a composition composed of phenols, sugar and starch. This composition is obtained by applying formation of a resin by the reaction between phenols and sugar. JP-A-2004-137726 (Patent Document 8) discloses a composition for a biodegradable gravel product, which is composed of starch and tannin or polyphenol and, furthermore, protein and a crushed mineral powder, and a divalent metal powder having the chelate mordanting effect with tannin or polyphenol. However, this composition is obtained by supporting a condensation compound of a metal salt and a polyphenol on starch and also contains a divalent metal salt, and therefore it is not suitable for applications such as tablewares. Also, tannins and polyphenols used herein are condensed tannins such as persimmon tannin, tea tannin and bark tannin, and are suitable for use as a substitute of gravel, but are not suitable for processed articles such as tablewares because condensed tannins and divalent metal salts are used and therefore the strength becomes too higher. Furthermore, since the metal salts are used, metals thereof remain after decomposition and thus it is considered that an adverse influence may be exerted on the environment.
JP-A-2005-23262 (Patent Document 9) discloses a biodegradable composition using main materials obtained by finely dividing 100% natural materials, for example, grains such as maize, dietary fibers such as weeds, and sugar cane, and natural binders such as persimmon tannin and konjac powder. However, a specific composition ratio is unclear and also it is unclear whether or not the product is actually produced. Since this composition is composed only of natural materials such as cereals, quality of the resultant molded article is not maintained and the molded article is not suitable for use as an industrial product.
Furthermore, translation of PCT application No. 9-500924 (Patent Document 10) discloses a biodegradable composition containing starch, protein, cellulose, phenol and tannin, and tall oil or wax. However, this composition contains tall oil or wax, there is a fear of ooze of wax or the like. Therefore, the composition is suitable for production of woodworks. However, when applied to processed articles such as tablewares, there is a possibility that problems for safety may arise.    Patent Document 1: JP-A-Hei07-17571    Patent Document 2: JP-A-2005-119708    Patent Document 3: JP-A-Hei05-320401    Patent Document 4: JP-A-Hei05-278738    Patent Document 5: JP-A-Hei05-57833    Patent Document 6: JP-A-2002-355932    Patent Document 7: JP-A-Hei06-248040    Patent Document 8: JP-A-2004-137726    Patent Document 9: JP-A-2005-23262    Patent Document 10: Translation of PCT application No. 9-500924