Stock material or miscellaneous articles – Hollow or container type article – Nonself-supporting tubular film or bag
Reexamination Certificate
2000-02-04
2003-04-08
Nolan, Sandra M. (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Nonself-supporting tubular film or bag
C426S415000, C428S035500, C428S913000, C524S313000
Reexamination Certificate
active
06544607
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART
1. Field of the Invention
The present invention relates to an aliphatic polyester stretched film, an aliphatic polyester composition which is a raw material of the stretched film, and a package using the stretched film. More particularly, the present invention relates to an aliphatic polyester stretched film which has degradability within a natural environment, has excellent flexibility and heat resistance and manifests no bleeding of a plasticizer, an aliphatic polyester composition which is a raw material of the stretched film, and a package using the stretched film.
2. Related Art of the Invention
Recently, treatment of plastic wastes have been featured. Plastic molded articles such as packing materials have been disposed by burning, land reclamation and the like after use thereof. However, when plastic wastes are burned, high combustion heat leads to a durability problem with the incinerator. Substances such as polyvinyl chloride sometimes generate harmful gases causing environmental pollution. Further, in the case of the land reclamation treatment, plastic molded products are not completely degraded and remain semi-permanent in original form, causing problems of influence on the natural environment.
Due to such conditions, various biodegradable plastics which are degraded completely by microorganisms within the natural environment and are degraded into natural by-products, carbonic acid gases, water and the like have been invented, and are used at a practical level. For example, Japanese Laid-Open Patent No. Hei-6-340753 discloses a resin composition mainly comprising polylactic acid which is an aliphatic polyester, or a lactic acid-other hydroxycarboxylic acid copolymer. It has been disclosed that this resin composition, for example, can be used as a raw material of a degradable card (sheet), and this card has a high mechanical strength and manifests practical durability, and the like. However, this resin composition has a high elastic modulus and rigidity, and poor flexibility. Therefore, this resin composition is not suitable for use that requires flexibility in which polyethylene, polypropylene, soft polyvinyl chloride and the like are generally used.
In general, there are known, as methods for softening a resin, (1) addition of a plasticizer, (2) copolymerization, (3) blend of a soft polymer, and the like. Among them, investigations for softening using various plasticizers have been made, as in method (1). For example, Japanese Laid-Open Patent No. Hei-4-335060 discloses a composition obtained by adding a plasticizer to polylactic acid. As specific plasticizers, diisobutyl adipate, dioctyl sebacate and the like are listed. However, these have a low plasticizing effect, and sufficient flexibility is not obtained. Further, when these plasticizers are used, bleeding of a plasticizer occurs directly after molding or over time causing variation in flexibility, transparency and the like.
Method (3) is limited to a method adopting a biodegradable resin having flexibility as a blend resin, if biodegradability is taken into consideration. Regarding a biodegradable resin having flexibility, for example, JP-A Nos. 8-245866 and 9-111107 disclose polybutylene succinate, polyethylene succinate, polycaprolactone and the like. However, for imparting sufficient flexibility (tensile modulus of 1.0 GPa or less) to lactic acid-based polymers, it is necessary that the above-described biodegradable resin is added in large amounts (for example, in the case of polybutylene succinate, 60 wt % or more). Consequently, heat resistance, transparency and the like which are characteristics of lactic acid-based polymers deteriorate.
The object of the present invention is, in view of the above-described problems, to provide an aliphatic polyester stretched film which has excellent flexibility, heat resistance and transparency and manifests no bleeding of a plasticizer, an aliphatic polyester composition which is a raw material of the stretched film, and a package using the stretched film.
SUMMARY OF THE INVENTION
The present inventors have carried out an intensive study to solve the above-described problems, and as a result, have found that an aliphatic polyester composition can be obtained which manifests suppressed bleeding of a plasticizer and is suitable as a raw material of molded products such as a film and the like having excellent transparency, heat resistance and flexibility, by selectively adding a specific plasticizer to an aliphatic polyester. Also, it has been found that an aliphatic polyester stretched film having flexibility can be obtained without decreasing transparency and heat resistance of the film due to bleeding of a plasticizer, by film-molding the above-described polyester composition and then stretching and heat setting the film to control the crystallinity in the specific range. Further, it has been found that this stretched film is suitable as a packing material for foods and the like.
Namely, the first invention of the present invention is an aliphatic polyester composition comprising 10 to 60 parts by weight of at least one compound selected from (A) a compound represented by the general formula (1)
(wherein, at least one of R
1
, R
2
and R
3
represents an acyl group having 6 to 18 carbon atoms, and remaining groups represent a hydrogen atom or an acetyl group.)
and (B) a compound which is a reaction product of a condensate of 1 to 10 glycerin molecules with a carboxylic acid having 6 to 18 carbon atoms, based on 100 parts by weight of an aliphatic polyester.
In this polyester composition, the aliphatic polyester is preferably a lactic acid-based polymer. As the lactic acid-based polymer, polylactic acid, lactic acid-other aliphatic hydroxycarboxylic acid copolymer, or a mixture thereof is preferable. It is preferable that the number of glycerin molecules of a glycerin condensate forming the compound (B) is from 2 to 10. Further, it is preferable that the compound (A) and the compound (B) are included in the composition, and the ratio by weight of (A):(B) is from 1:1 to 4:1.
The second invention is an aliphatic polyester stretched film having a crystallinity of 20 to 60% which is obtained by molding the above-described aliphatic polyester composition. The thickness of the stretched film is preferably from 5 to 1,000 &mgr;m.
The third invention is a package which is obtained by packing a product to be packed using the above-described aliphatic polyester stretched film.
The aliphatic polyester composition of the present invention has excellent flexibility, and in addition, is suitable as a raw material of a stretched film and the like in which a plasticizer does not bleed out onto the surface. The aliphatic polyester stretched film of the present invention has excellent heat resistance and flexibility, and further, manifests no bleeding out of a plasticizer. Further, when the aliphatic polyester is polylactic acid, a lactic acid-other aliphatic hydroxycarboxylic acid copolymer comprising 40 mol % or more of a lactic acid unit, or an aliphatic polyester comprising a polyfunctional polysaccharides and 50 mol % or more of a lactic acid unit, and an aliphatic polyester comprising an aliphatic polyvalent carboxylic acid unit, aliphatic polyvalent alcohol unit and a lactic acid unit, the stretched film has degradability within the natural environment and does not accumulate as industrial waste or household waste even if discarded after use.
Therefore, the stretched film can be suitably used as a material in a wide range such as various packing films for foods, electronic products, medical products, medicines, cosmetics and the like, agricultural films, building and contracting films, adhesive tapes and the like. In particular, the stretched film is suitable as a packing material for foods. When product to be packed in the package of the present invention is a food, composting treatment, for example, or the like is possible without separating the packing material from waste of the product to be packed.
DETAILED DESCRIPTION OF PREFER
Ikado Shuhei
Iwata Masataka
Kuroki Takayuki
Wanibe Hirotaka
Mitsui Chemicals Inc.
Nolan Sandra M.
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