CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2019-085656, filed Apr. 26, 2019. The contents of which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present disclosure relates to an aliphatic polyester resin composition, a method for producing the aliphatic polyester resin composition, and a produced product.

Description of the Related Art

In recent years, because aliphatic polyester resins such as polylactic acid and polybutylene succinate have biodegradablility, materials in connection with recent garbage problems have been actively developed, and replacement of non-biodegradable polymers with the aliphatic polyester resins has widely been considered.

Meanwhile, calcium carbonate is used in various fields such as food, paper, and cosmetics because calcium carbonate is an inexpensive pigment having high brightness. Examples of the calcium carbonate include heavy calcium carbonate and precipitated calcium carbonate. Considering that precipitated calcium carbonate and a polymer are kneaded, the precipitated calcium carbonate has a problem that an amount of water in the precipitated calcium carbonate is high due to high hydrophilicity of calcium carbonate. Particularly, it is difficult to stably introduce the precipitated calcium carbonate into an aliphatic polyester resin that easily undergoes hydrolysis.

A particle diameter of the heavy calcium carbonate varies widely. Therefore, when these heavy calcium carbonates are ununiformly introduced into a resin to thereby obtain a sheet, physical properties of the sheet such as brightness, strength, and flexibility cannot be satisfied or a cause of nonuniformity may be caused.

Therefore, in order to introduce heavy calcium carbonate at a high concentration into an aliphatic polyester resin, it is necessary to uniformly disperse it in the aliphatic polyester resin, which is not sufficient because of the following reasons.

(1) The heavy calcium carbonate is alkaline, and a problem such as cleavage of molecular chains may be possibly caused when the heavy calcium carbonate is kneaded with an aliphatic polyester resin. Therefore, shearing energy cannot be applied so much. In order to overcome the aforementioned problem, it is proposed that resins other than the aliphatic polyester resin are blended to adjust the melt viscosity (see, for example, Japanese Patent No. 6401303). However, most of them (e.g., polyolefin such as polyethylene or polypropylene, polystyrene, and polymethyl methacrylate) are copolymerized or blended with such a component that degrades biodegradablility the aliphatic polyester resin has.

(2) The aliphatic polyester resin drastically decreases the viscosity at a temperature that is equal to or higher than the melting point, and is generally considered as a resin that is not suitable for dispersing fillers such as calcium carbonate. Actually, there is description that in the cases where an attempt to disperse calcium carbonate in polylactic acid is performed, when the calcium carbonate has a 50% volume particle diameter D50of less than 0.4 μm, particles of the calcium carbonate cohere, which is not preferable (see, for example, Japanese Patent No. 6174453).

SUMMARY OF THE INVENTION

According to one aspect of the present disclosure, an aliphatic polyester resin composition includes: an aliphatic polyester resin; and calcium carbonate. An amount of the calcium carbonate in the aliphatic polyester resin composition is 20% by mass or more. A number average particle diameter of the calcium carbonate in the aliphatic polyester resin composition is 0.20 μm or more but less than 0.40 μm. A standard deviation of the number average particle diameter is 0.3 or more but 0.6 or less.

