Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-10-14
2001-05-22
Sanders, Kriellion (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S556000, C523S124000
Reexamination Certificate
active
06235825
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a polylactic acid-based resin composition and a film comprising the composition. More specifically, the invention relates to a polylactic acid-based resin composition and a film comprising the composition which are excellent in flexibility and thermal resistance and are further dominant in degradability in compost after use.
BACKGROUND ART
Conventionally, polyethylene, polypropylene, flexible polyvinyl chloride and polyethylene terephthalate and other resins have been known to have excellent flexibility, thermal resistance and water resistance. These resins have been used for garbage bags and packaging bags. However, these resins increase an amount of refuse when disposed after use and furthermore, are scarcely degradable in the natural environment. Thus, these resins semi-permanently remain underground even after burial disposal. These dumped plastics have also led to problems such as impairment of a general view and damage of life environment of marine organisms.
On the other hand, polylactic acid, a copolymer of lactic acid and other aliphatic hydroxycarboxylic acid and polyester derived from aliphatic polyhydric alcohol and aliphatic polybasic acid have been known to have thermoplastic property and biodegradability. Application of these polymers to various uses has been developed.
In these polymers, polylactic acid in particular is completely biodegraded in an animal body in a period of several months to one year. When placed in soil or sea water, these polymers initiate degradation within several weeks in a moist environment and disappear in a period of one to several years. The degradation products are characterized by lactic acid, carbon dioxide and water, which are harmless to the human body.
Further, polylactic acid is expected in recent years to extend its application field because the raw material L-lactic acid can be inexpensively produced in a large scale by a fermentation process, degradation velocity of polylactic acid is high in the compost, and polylactic acid is excellent in resistance to fungus and protection of foods from contamination of odor and color.
However, polylactic acid has high rigidity and is thus unsuited for agricultural multi-films, food packaging bags, garbage bags and other film and packaging uses which require flexibility in particular.
As an example of flexible and biodegradable resin, an inflation film prepared from polybutylene succinate has a large anisotropy in tear strength between longitudinal and transverse directions and is characterized in very weak longitudinal tear strength. Low tear strength and its anisotropy lead to problems depending upon uses. Thus, inflation films of polybutylene succinate are also unsuitable for uses in an agricultural multi-film, food packaging bag, garbage bag and other films or wrapping materials.
Generally known techniques for making resin flexible are (1) addition of plasticizer, (2) copolymerization and (3) blending of flexible polymers. However, the techniques (1) and (2) lower the glass transition temperature of the resin composition, even though sufficient flexibility can be provided. As a result, change of physical properties such as increase in crystallinity and rigidity is found under conventional environmental temperature. Additionally, use of plasticizer leads to a problem of bleeding of the plasticizer. Thus, various problems are substantially encountered for putting these techniques to practical use.
On the other hand, in the technique (3), the resin to be blended is restricted to biodegradable resin having flexibility in view of the biodegradability which is one of the subject of the invention. Such resins include, for example, polybutylene succinate, polyethylene succinate, and polycaprolactone. These resins have been disclosed in Japanese Laid-Open Patent HEI 8-245866 and HEI 9-111107. However, in order to provide sufficient flexibility (an elastic modulus of 1,000 MPa or less) for polylactic acid, the technique requires the addition of a large amount of the resin, for example, 60% by weight or more polybutylene succinate. As a result, the above characteristics of polylactic acid are impaired.
Polylactic acid has less anisotropy in tear strength as compared with polybutylene succinate. In the realities, conventional techniques cannot provide a biodegradable film having flexibility and thermal resistance without impairing characteristics of polylactic acid and further having no anisotropy in tear strength.
Consequently, the subject to be solved by the invention is to provide a biodegradable film characterized by having flexibility and thermal resistance in combination without anisotropy in tear strength.
More specifically, the object of the invention is to provide a biodegradable film having excellent thermal resistance and no anisotropy in tear strength, as a result of excellent flexibility like polypropylene, polyethylene and polyvinyl chloride which are used for garbage bags, packaging materials and outstanding resistance to blocking of film and bleeding out of plasticizer at high temperature.
DISCLOSURE OF THE INVENTION
As a result of an intensive investigation on polylactic acid in order to achieve the above subject, the present inventors have found a film comprising a polylactic acid-based resin composition obtained by mixing polylactic acid with specific flexible aliphatic polyester and blending the resultant mixture with a biodegradable plasticizer having good compatibility with the resultant mixture. Thus, the invention has been completed.
That is, the first object of the invention is a polylactic acid-based resin composition comprising 100 parts by weight of a high molecular ingredient (A) which contains 50 to 90% by weight of polylactic acid (a1) and 10 to 50% by weight of a biodegradable aliphatic polyester (a2) having a melting point of 80 to 250° C., and 5 to 25 parts by weight of a biodegradable plasticizer (B).
The second aspect of the invention is a flexible polylactic acid-based resin film, specifically an inflation film of a polylactic acid-based resin, which comprises a polylactic acid-based resin composition composed of 100 parts by weight of high molecular ingredient (A) which contains 50 to 90% by weight of polylactic acid (a1) and 10 to 50% by weight of a biodegradable aliphatic polyester (a2) having a melting point of 80 to 250° C., and 5 to 25 parts by weight of a biodegradable plasticizer (B), wherein the film has an elastic modulus of 200 to 1,000 MPa and longitudinal/transverse ratio of 0.8 to 1.2 in tear strength, leads to neither plasticizer bleeding nor film blocking at 60 to 120° C., and is excellent in resistance to blocking and bleeding-out at high temperature.
The third aspect of the invention is a preparation process of a flexible polylactic acid-based resin film having excellent resistance to blocking and bleeding-out at high temperature characterized by inflation-molding a polylactic acid-based resin composition, wherein a high molecular ingredient (A) comprises 50 to 90% by weight of polylactic acid (a1) and 10 to 50% by weight of a biodegradable, aliphatic polyester (a2) having a melting point of 80 to 250° C., and the amount of a biodegradable plasticizer (B) is 5 to 25 parts by weight for 100 parts by weight of said high molecular ingredient (A), under processing conditions of 150 to 220° C. in resin extrusion temperature and 1.5 to 3.0 in a film blow-up rate.
BEST MODE FOR EMBODYING THE INVENTION
The present invention will hereinafter be illustrated in detail.
[Flexible Film]
The term “flexible film” in the invention refers to a film having an elastic modulus in the range of 200 to 1,000 MPa in accordance with JIS K-6732. The flexible film can be suitably used for agricultural multi-film, food packaging bags and garbage bags. When the elastic modulus exceeds 1,000 MPa, the film has lower flexibility and becomes rigid.
[Film Having Resistance of Film to Blocking and Bleeding-Out at High Temperature]
The term “resistance of film to blocking and bleeding-out at high temperature”
Aihara Hisashi
Ajioka Masanobu
Kitahara Yasuhiro
Nakata Tomoyuki
Obuchi Shoji
Burns Doane Swecker & Mathis L.L.P.
Mitsui Chemicals Inc.
Sanders Kriellion
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