Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Starting material is nonhollow planar finite length preform...
Reexamination Certificate
1995-05-18
2001-09-18
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Starting material is nonhollow planar finite length preform...
C264S547000, C264S553000, C264S554000
Reexamination Certificate
active
06290896
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART
1. Field of the Invention
The present invention relates to a formed product of an L-lactic acid base polymer and the preparation process of the product. More particularly, the invention relates to a formed product of an L-lactic acid base polymer which has good transparency and can degrade after use in natural environment.
2. Related Art of the Invention
Plastic materials for forming products prepared from plastic sheets are polystyrene, polyvinyl chloride, polypropylene and polyethylene terephthalate. Although some of the formed products prepared from these plastics are excellent in transparency, disposal of the products increases the amount of refuse and they remain semipermanently when buried under the ground, since they almost do not degrade under the natural environment. Disposal of the formed products in the ocean causes aesthetic damage or destruction of the living environment of marine organisms.
On the other hand, polylactic acid and copolymers of lactic acid and hydroxycarboxylic acids other than lactic acid (generic name of the polylactic acid and the copolymers will hereinafter be referred to simply as a lactic acid base polymer) have been developed for thermoplastic and biodegradable polymers. These polymers can be completely biodegraded within a few months to an year in an animal body. When the polymers are placed in most soil or sea water, they start to decompose in a few weeks in a moist environment and disappear within a year to several years. Further, final degradation products of the polymers are lactic acid, carbon dioxide and water which are nontoxic to human body.
Polylactic acid in the lactic acid base polymer is usually prepared from a cyclic dimer of lactic acid which is called lactide, and U.S. Pat. Nos. 1,995,970, 2,362,511, and 2,683,136 have disclosed a polymerization process of lactide. U.S. Pat. Nos. 3,636,956 and 3,797,499 have disclosed a process for copolymerizing lactic acid and glycolic acid. In the copolymerization of lactic acid and the other hydroxy carboxylic acids, lactide and a cyclic ester intermediate, for example glycolide, i.e., a dimer of glycolic acid, are used for polymerization.
Lactic acid which is a raw material of the lactic acid base polymer is prepared by fermentation or chemical syntheses. Recently, L-lactic acid has been cheaply produced in a large amount by fermentation in particular. The polymer obtained has the characteristic of high stiffness. Consequently, the polymer having a high content of L-lactic acid is now under development for use.
Particularly, formed products obtained by preparing a sheet from a polymer having a high content of L-lactic acid and subjecting the sheet thus prepared to vacuum forming or air-pressure forming are expected to have a bright future because forming can be conducted with ease and many kinds of desired shapes can be formed. However, the formed products prepared from the polymer having a high content of L-lactic acid through the above forming method are opaque and are restricted in the fields of use. The opacity is particularly enhanced when the L-lactic acid proportion is 75% or more in the lactic acid base polymer. The phenomenon is thought to be inhibition of transparency by the crystallized lactic component because poly-L-lactic acid is very liable to crystallize in the polymer.
SUMMARY OF THE INVENTION
An object of the invention is to provide a formed product which is primarily composed of L-lactic acid base polymer and is excellent in transparency.
One aspect of the invention is a formed product of an L-lactic acid base polymer, the formed product of which is obtained by vacuum forming or pressure air forming, said polymer having an L-lactic acid proportion of 75% or more and a haze of 5%/2 mm or less.
Another aspect of the invention is a process for forming an L-lactic base polymer comprising the steps of holding a transparent L-lactic acid polymer sheet under conditions wherein {circle around (1)} a holding temperature T
1
is in the range of 55~90° C., {circle around (2)} a holding time m
1
(min) satisfies the formula (1):
log
10
m
1
<−0.083
T
1
+7.66 (1),
the step of forming said polymer sheet by adhering to the internal surface of a mold through vacuum suction or compressed air pressure under a condition wherein {circle around (3)} a mold temperature T
2
is in the range of from the glass transition temperature Tg of the L-lactic acid base polymer to the holding temperature T
1
and the step of taking out a formed product having a thickness of 0.1~2 mm from the mold after reducing the internal temperature of the mold to less than Tg.
The formed product of the L-lactic acid base polymer in the invention has excellent transparency, so that one can clearly examine the conditions of contents accommodated in the formed product, and thus can be suitably used for food trays and beverage cups.
Further, when these trays and cups are buried in the ground as waste or abandoned in rivers and sea after use, they can be degraded into nonhazardous water and carbon dioxide within a relatively short period in the natural environment like natural products such as paper and wood.
Thus the invention has been completed.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The L-lactic acid base polymer used for the invention is a polymer having 75% or more of L-lactic acid ratio in the polymer. Lactic acid used for a raw material of the L-lactic acid base polymer is L-lactic acid, D-lactic acid, a mixture thereof or lactide which is a cyclic dimer of the above L-lactic acid, D-lactic acid or a mixture thereof.
Hydroxycarboxylic acids which can be copolymerized with lactic acid include a hydroxycarboxylic acid such as glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, 6-hydroxycaproic acid and a cyclic ester intermediate of a hydroxycarboxylic acid such as glycolide which is a dimer of glycolic acid and &egr;-caprolactone which is a cyclic ester of 6-hydroxy caproic acid.
The L-lactic acid base polymer can be directly prepared by dehydrating polycondensation of L-lactic acid or dehydrating copolycondensation of L-lactic acid and the other hydroxycarboxylic acids or can be prepared by ring opening polymerization of lactide or a cyclic ester intermediate of a hydroxycarboxylic acid, for example, glycolide which is a dimer of glycolic acid and &egr;-caprolactone which is a cyclic ester of 6-hydroxy caproic acid. Any of these compounds can be used in the invention.
When the polymers are directly prepared by dehydrating polycondensation, L-lactic acid or L-lactic acid and the other hydroxycarboxylic acids raw materials are subjected to azeotropically dehydrating condensation in the presence of an organic solvent, a phenyl ether base solvent in particular. A high molecular weight poly-L-lactic acid base polymer obtained by the method in which water is removed from the azeotropically distilled solvent and the resulting substantially anhydrous solvent is returned to the reaction system has a mechnical strength particularly suitable for the presention invention.
Molecular weight of the lactic acid base polymer is 30,000 or more. Polymers having high molecular weight can be used so long as polymers can be formed. Polymers having a molecular weight of less than 30,000 provide a formed product having low-mechanical strength and is unsuitable for practical use. Polymers having a molecular weight of 1,000,000 or more can also be used for preparing the formed product of the invention by modifying the processing method.
A composition which can used in the invention is prepared by mixing and kneading the above L-lactic acid base polymer with commonly known plasticizers and various other modifiers. In such a case, an L-lactic acid proportion of 75% or more must be maintained in the composition. The L-lactic acid polymer or its composition can be used in the form of pellets, bars and powder and can be prepared by any known kneading techniques.
Next, the preparation process of the formed product b
Ajioka Masanobu
Kitahara Yasuhiro
Suzuki Kazuhiko
Watanabe Takayuki
Burns Doane Swecker & Mathis L.L.P.
Mitsui Chemicals Inc.
Silbaugh Jan H.
LandOfFree
Preparation process of the formed product of L-lactic acid... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Preparation process of the formed product of L-lactic acid..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Preparation process of the formed product of L-lactic acid... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2498349