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
2000-09-28
2003-02-18
Short, Patricia A. (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...
C525S411000, C525S425000, C525S440030, C525S938000
Reexamination Certificate
active
06521717
ABSTRACT:
BACKGROUND OF THE INVENTION
A. Technical Field
The present invention relates to a biodegradable polyester resin composition and its use. Specifically, the present invention relates to a biodegradable polyester resin composition and its use wherein the biodegradable polyester resin composition exhibits improved molding processability and tearing character.
B. Background Art
It is well-known that a lot of aliphatic and aromatic polyesters are as biodegradable polyesters up to now.
It is acknowledged that the aliphatic polyesters have biodegradability in general. It is proposed in JP-A-11517/1995, JP-A-170941/1994 and so on that the aliphatic polyesters can be utilized for a fiber, a molded product, a sheet and a film by applying a characteristic of the aliphatic polyesters.
On the one hand, the biodegradable aromatic polyesters are disclosed in such as JP-A-507109/1993, JP-A-508640/1998, JP-A-500157/1999.
However, the present inventors found two important problems when studying molding processability of the aliphatic polyesters for some time past. At the first, the aliphatic polyesters are inferior in molding processability because of having a long tack-free time in view of industrial productivity. Namely, there was a problem in injection molding that deformation of the molded products, inferior surface appearance and unrelease from the mold at worst occur because the aliphatic polyesters are not crystallized enough in a mold owing to the aliphatic polyesters having a long tack-free time. In addition, there was a problem in molding a film such as molding an inflationary film that fellow films melt-adhere because of a long tack-free time when winding the molded films extruded from dies.
The inventors diligently studied these problems for some time past. As a result, they obtained some findings and proposed JP-A-120165/1996 as one solution. JP-A-120165/1996 proposed a biodegradable polyester resin composition that exhibited a rapid crystallization rate and was excellent in molding processability. Though the acceleration of the crystallization rate of the polyester resin by this method can be confirmed, it was acknowledged that this method alone was not enough to mold in practice.
Incidentally, the tack-free time referred to in the present invention means a time until that resin in a melting state is cooled and solidified and the surface thereof do not have any adhesion. In addition, a measuring method thereof is described later.
At the second, it was acknowledged that the aliphatic polyesters were inferior in heat resistance and it remained a problem to utilize the aliphatic polyesters as a molded product to be heat-melted and plastic-processed.
Furthermore, it was hoped to improve tearing character when producing films except for the above molding processability. For example, when composting kitchen refuse produced in a food store and a restaurant, there is a problem that: refuse bag made of biodegradable resin was used but the refuse bag was pierced and torn when the kitchen refuse included something sharp such as fish bone.
On the one hand, biodegradable polymer (A) itself containing aromatic dicarboxylic acid as an essential structural unit is already well-known. These already well-known polymers have a short tack-free time and no problem on molding processability practically. However, it was acknowledged that: these already well-known polymers do not have tensile strength enough, and has low biodegradability in soil because the polymer contains a lot of aromatic dicarboxylic acid, especially biodegradability in active sludge that is expected to have biodegradability in river is extremely inferior.
In addition, it was acknowledged that biodegradable polymer (A) is inferior in biodegradability at composing in order to applying in a small composing apparatus that requires a comparatively rapid biodegradable rate. In order to improve biodegradability of biodegradable polymer (A) containing aromatic dicarboxylic acid as an essential structural unit, it is considered to diminish aromatic dicarboxylic acid component. However, in order to be more satisfied with biodegradability, diminishing aromatic dicarboxylic acid component causes a problem to lower melting point, to disorder crystallinity, and to lower heat resistance and molding.
SUMMARY OF THE INVENTION
A. Object of the Invention
Thus, considering the above circumstances, an object of the present invention is to provide a novel and useful biodegradable polyester resin composition and its use wherein the biodegradable polyester resin composition solves the problems of the above conventional aliphatic polyester resin composition, and exhibits a short tack-free time, and is excellent in heat resistance, and exhibits improved molding processability and tearing resistance.
B. Disclosure of the Invention
Considering the present circumstances, the present inventors diligently studied to solve the above-mentioned problems. As a result, they achieved the above object by developing a composition that comprises biodegradable polymer (A) and aliphatic polyester (B) wherein the biodegradable polymer (A) contains aromatic dicarboxylic acid as an essential structural unit.
Accordingly, a biodegradable polyester resin composition, according to the present invention, comprises biodegradable polymer (A) and aliphatic polyester (B) wherein the biodegradable polymer (A) contains aromatic dicarboxylic acid as an essential structural unit.
The reason for coexisting moldability and tearing resistance, and biodegradability in the resin composition of the present invention is considered that component (A) and component (B) form what is called “islands-sea structure” because aliphatic polyester (B) excellent in biodegradability, and biodegradable polymer (A) containing aromatic dicarboxylic acid as an essential structural unit excellent in moldability and tearing resistance are mixed in a fixed ratio into the composition. When molding process and using as a molded product, the composition is excellent in moldability and tearing resistance of component (A). After finishing a mission and when discharging into environment or composting process, component (B) in the composition is biodegraded rapidly. On the one hand, component (A) remains as a fine particle because component (B) vanishes owing that component (B) has biodegradability, and it is considered to biodegrade component (A) in a short time because of enlarging the surface area of component (A).
The tack-free time of the composition is preferably in the range of 3 to 30 seconds, more preferably 5 to 20 seconds.
It is preferable that the molecular-weight-retaining ratio defined in formula (1) shown below is 0.8 or more.
Molecular-weight-retaining ratio=
X/Y
(1)
wherein: X represents a number-average molecular weight after a heating test in a condition of 150° C. and 4 hours; and Y represents a number-average molecular before the heating test.
A molded product, according to the present invention, is obtained from the biodegradable polyester resin composition including biodegradable polymer (A) and aliphatic polyester (B) wherein the biodegradable polymer (A) contains aromatic dicarboxylic acid as an essential structural unit.
Toughness of the molded product is preferably 49 N/mm
2
or more measured in 1,000 mm/minute of testing speed according to plastic tensile test (ASTM-D882-90 (A method)), and more preferably 98 N/mm
2
or more.
These and other objects and the advantages of the present invention will be more fully apparent from the following detailed disclosure.
DETAILED DESCRIPTION OF THE INVENTION
Biodegradable polymer (A) containing aromatic dicarboxylic acid as an essential structural unit, used in the present invention, is not especially limited. Examples thereof is a biodegradable polymer containing aromatic dicarboxylic acid as an essential structural unit and having a number-average molecular weight of 5,000 to 100,000, preferably 10,000 to 80,000, more preferably 20,000 to 50,000. Melting point of the polymer is 60 to 200° C., preferably 80 to 160° C., more preferably
Nippon Shokubai Co. , Ltd.
Roylance Abrams Berdo & Goodman L.L.P.
Short Patricia A.
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