Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-03-25
2004-03-23
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S413000, C525S415000, C525S450000
Reexamination Certificate
active
06710135
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a resin composition comprising a polylactic acid resin and a polyalkylene carbonate and to a use thereof. More particularly, the present invention relates to a resin composition comprising a polylactic acid resin and a polyalkylene carbonate, which is excellent in properties, such as flexibility, transparency, heat resistance and gas barrier properties, and which, after use, exhibits degradability in natural environment, and relates to a use thereof
BACKGROUND ART
Soft polyvinyl chloride, soft polyvinylidene chloride, polypropylene, polyethylene and the like are generally known as resins having flexibility and having high transparency and heat resistance.
However, these resins, when disposed of after use, increase the volume of refuse, and are further scarcely decomposed in natural environment with the result that, when buried, the resins semipermanently remain in the earth. Moreover, dumped plastics cause such problems that the sight is deteriorated and that the living environment for marine organism is damaged.
On the other hand, for example, a polylactic acid and a copolymer of polylactic acid and other aliphatic polyester (hereinafter referred to as “polylactic acids”) and a polyester derived from an aliphatic polyhydric alcohol and an aliphatic polycarboxylic acid have been developed as biodegradable resins.
Some of the above resins are 100% biodegraded in animal bodies within a period of months to one year and also, when placed in soil or seawater, they initiate degradation in moist environment within some weeks and are eliminated within a period of about one year to some years. Biodegradable resins have such a characteristic that degradation products therefrom consist of lactic acid, carbon dioxide and water which are harmless to human health.
Among these biodegradable resins, expansion of the application field of the polylactic acids is especially expected because they have excellent properties such as high rigidity, and L-lactic acid which is the starting material thereof comes to be manufactured in a large amount with reduced cost by the fermentation process.
However, containers and packing materials obtained by molding polylactic acids by means of customary extrusion have poor flexibility although having high rigidity. Therefore, polylactic acids are not suitable for the use in packing materials requiring flexibility, such as a tube and a wrap film.
For imparting flexibility to polylactic acids, general technique for softening resins such as to employ the method of adding a plasticizer, the method of blending a soft polymer, or the method of effecting copolymerization with another monomer could be conceivable.
However, the addition of a plasticizer causes such a problem that the plasticizer bleeds out with the passage of time so as to be likely to bring about quality deteriorations such as stickiness and transparency lowering and to also cause deterioration of physical properties such as gas barrier properties and odor retaining capability. When blending the polylactic acids with a soft polymer, the compatibility is not necessarily satisfactory, so that there occurs such a problem that the transparency is likely to become poor. Further, the method of effecting copolymerization with another monomer necessitates a large reaction apparatus for polymer preparation and requires a prolonged reaction time, so that the method has a disadvantage of lacking simplicity.
Therefore, there is a demand for the development of a resin composition enhanced in flexibility containing a biodegradable resin such as a polylactic acid, which exhibits enhanced gas barrier properties without detriment to the excellent properties of biodegradable resin, and is free from the occurrence of bleedout with the passage of time.
In these circumstances, the inventor has made extensive and intensive investigations. As a result, it has been found that a resin comprising a biodegradable polylactic acid resin and a specified polyalkylene carbonate is biodegradable and is excellent in properties such as flexibility. The present invention has been completed on the basis of this finding.
Japanese Patent Laid-open Publication No. 6(1994)-345956 discloses a resin composition comprising a polyethylene carbonate, and a synthetic polymer that is degraded by microorganism, such as poly(3-hydroxybutyric acid) or polycaprolactone, and/or a natural polymer, such as starch, which is indicated as highly biodegradable. However, satisfactory attention was not paid to the transparency which is an important property for packing materials such as a film. Further, Japanese Patent Laid-open Publication No. 11(1999)-140292 discloses a resin composition containing a polylactic acid and a polycarbonate. However, in JP-A-11-140292, no attention was paid to gas barrier properties. The described polycarbonates would have low glass transition temperature, so that the gas barrier properties of obtained resin composition would be poorer than those of polylactic acid alone.
It is an object of the present invention to provide a resin composition which exhibits not only the high degradability inherently in the biodegradable polylactic acid resins but also high flexibility, transparency, heat resistance and gas barrier properties. It is another object of the present invention to provide a use thereof.
DISCLOSURE OF THE INVENTION
The resin composition of the present invention comprises:
30 to 95 parts by weight of a biodegradable polylactic acid resin (A), and
70 to 5 parts by weight of a polyalkylene carbonate (B) of the following formula (I), providing that the sum of components (A) and (B) is 100 parts by weight, and
satisfying that a pressed film of 0.1 mm thickness formed therefrom has a haze of 40% or less,
wherein R represents at least one group selected from the group consisting of an ethylene group, a propylene group and a group of the general formula (II):
(wherein each of R
1
and R
2
independently represents an alkylene group having 2 to 6 carbon atoms; and p is an integer of 1 to 15);
m is an integer of 1 to 15; and
n is an integer of 3 to 15,000.
It is preferred that the resin composition of the present invention comprise:
40 to 90 parts by weight of the biodegradable polylactic acid resin (A), and
60 to 10 parts by weight of the polyalkylene carbonate (B), providing that the sum of components (A) and (B) is 100 parts by weight, and
satisfying that a pressed film of 0.1 mm thickness formed therefrom has a haze of 40% or less.
In the present invention, it is preferred that the polyalkylene carbonate (B) be polyethylene carbonate.
The resin composition preferably satisfies that a pressed film of 0.5 mm thickness formed therefrom has a Young's modulus at 23° C. of 2500 MPa or less.
Also, preferably, the resin composition satisfies that a pressed film of 0.1 mm thickness formed therefrom has a carbon dioxide permeability coefficient at 25° C. of 85 cc mm/m
2
day atm or less.
The above resin composition of the present invention is preferably employed in the production of a molded article, such as a film, an oriented film, an injection-molded product, a blow-molded product, a laminate, a tape, a nonwoven fabric or a yarn.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will be described in detail below.
The resin composition of the present invention comprises a biodegradable polylactic acid resin (A) and a polyalkylene carbonate (B). First, each of these components will be described.
Biodegradable Polylactic Acid Resin (A)
With respect to the biodegradable polylactic acid resin (A) for use in the present invention, the structure thereof is not limited and any one can appropriately be used as long as it is a polylactic acid resin having biodegradability. The terminology “biodegradable” used herein means that biodegradation can be recognized in, for example, the “Determination of the ultimate aerobic biodegradability and disintegration of plastic materials under controlled composting conditions” according to Iso 14855 (Japanese Industrial Standard
Obuchi Shoji
Tan Junji
Wakimura Kazuo
Burns Doane , Swecker, Mathis LLP
Buttner David J.
Mitsui Chemicals Inc.
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