Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Reexamination Certificate
2001-01-08
2002-04-16
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
C428S480000, C525S437000, C525S444000
Reexamination Certificate
active
06372331
ABSTRACT:
TECHNICAL FIELD TO WHICH THE INVENTION BELONGS
The present invention relates to a plastic card that decomposes in natural environment. It particularly relates to a multilayered biodegradable card having superior flexibility and heat resistance.
Prior Art
While various kinds of plastic cards have heretofore been used in an extensive range, for many of them, their purpose of use comes to an end in a relatively short time and they are burned or discarded. On the other hand, from an environmental viewpoint, burning or discarding is not necessarily easy. Thus, various cards have been proposed which are made from biodegradable plastic materials.
For example, in Japanese patent publication 8-267968, it is proposed to form a multilayered structure having over-layers on both sides of a core layer from a biodegradable plastic, and use as the major component of the over-layers a polylactic acid or a copolymer of lactic acid and an oxycarboxylic acid in order to answer the requirement for clearness.
Problems To Be Solved
But even if the requirement for clearness can be answered by such a proposal, the following problems actually remain.
{circle around (1)} A non-orientated sheet of polylactic acid is extremely brittle, so that when it is cut to a predetermined size by a cutter, cracks or chipping may develop, thus making it difficult to finish it beautifully. This is true for laminated sheets too. After such a sheet is formed into cards, embossed letters are sometimes mechanically formed. At such a time too, cracks or chipping may develop.
{circle around (2)} An amorphous sheet of polylactic acid has a glass transition temperature of about 60° C., so that at temperatures over this point, the rigidity (or elastic modulus) drops sharply.
{circle around (3)} Further, in Japanese patent publication 8-267968, it is proposed to use a biaxially orientated sheet of polylactic acid. It is true that this method is effective in improving brittleness while keeping clearness of polylactic acid. But since strains remain in this state, there is a problem that the sheet may shrink due to heat produced during printing, laminating and other steps.
Means to Solve the Problems
The first subject matter of the present invention is to provide a biodegradable card which is a laminated member having over-layers whose major component is a composition comprising 60-100 wt % of a polylactic acid and 40-0 wt % of a biodegradable aliphatic polyester having a glass transition temperature (Tg) of 0° C. or under on both sides of a core layer whose major component is a composition comprising 40-90 wt % of a polylactic acid and 60-10 wt % of a biodegradable aliphatic polyester having a glass transition temperature (Tg) of 0° C. or under, characterized in that for the core layer and the over-layers, the crystallinities {(&Dgr;Hm-&Dgr;Hc))/&Dgr;Hm} converted from the melting calorie after crystallizing (&Dgr;Hm) of the polylactic acid portion when the temperature is raised, and the crystallizing calorie (&Dgr;Hc) of the polylactic acid portion generated due to crystallization during the temperature rise are 0.8 or over and 0.9 or over, respectively.
The second subject matter of the present invention is to provide a core layer of a biodegradable card comprising as its major component a composition comprising 40-90 wt % of a polylactic acid in which the ratio of L-lactic acid to D-lactic acid is 100:0 to 94:6 or 6:94 to 0:100, and 60-10 wt % of a biodegradable aliphatic polyester having a glass transition temperature (Tg) of 0° C. or under, and the crystallinity {(&Dgr;Hm-&Dgr;Hc))/&Dgr;Hm} converted from the melting calorie after crystallizing (&Dgr;Hm) of the polylactic acid portion when the temperature is raised, and the crystallizing calorie (&Dgr;Hc) of the polylactic acid portion generated due to crystallization during the temperature rise being 0.8 or over.
The third subject matter of the present invention is to provide an over-layer of a biodegradable card comprising as its major component a composition comprising 60-100 wt % of a polylactic acid in which the ratio of L-lactic acid to D-lactic acid is 100:0 to 94:6 or 6:94 to 0:100, and 40-0 wt % of a biodegradable aliphatic polyester having a glass transition temperature (Tg) of 0° C. or under, and the crystallinity {(&Dgr;Hm-&Dgr;Hc))/&Dgr;Hm} converted from the melting calorie after crystallizing (&Dgr;Hm) of the polylactic acid portion when the temperature is raised, and the crystallizing calorie (&Dgr;Hc) of the polylactic acid portion generated due to crystallization during the temperature rise being 0.9 or over.
Embodiments of the Invention
In selecting a polylactic acid as one of the polymer components of the composition forming the core layer or the over-layers in the present invention, its crystallizability is important. For example, for an amorphous polylactic acid, since its rigidity drops sharply and it begins to flow above the glass transition temperature, if it is made into cards, heat resistance will be insufficient. This becomes a disadvantage in use. On the other hand, a sufficiently crystallized polylactic acid retains rigidity even above the glass transition temperature, though it slightly softens, and will not flow. That is to say, in the biodegradable card according to the present invention, it is preferable that in at least the core layer and preferably in both the core layer and the over-layers, the polylactic acid component has crystallized. For this purpose, it is important to select a crystallizable polylactic acid.
A The crystallizability of a polylactic acid depends on the types and contents of lactic acids forming it. Among polylactic acids, there are monopolymers of poly-L-lactic acid or poly-D-lactic acid whose structural unit is only L-lactic acid or D-lactic acid, and a copolymer containing both L-lactic acid and D-lactic acid as its structural units. Poly-L-lactic acid and poly-D-lactic acid which are monopolymers are both crystallizable. The copolymer becomes amorphous depending upon the contents of the L-lactic acid and D-lactic acid. That is to say, one in which the ratio between L-lactic acid and D-lactic acid in the copolymer is within the range of 94:6 to 6:94 is amorphous and will not crystallize even by heat treatment. Even if crystalled, its crystallinity is too low to satisfy heat resistance. In short, a crystalline polylactic acid is obtained if the ratio between L-lactic acid and D-lactic acid in the polymer is within the range of 100:0 to 94:6 or 6:94 to 0:100. Heat resistance improves by increasing crystallinity by e.g. heat treatment. But from the viewpoint of bonding sheets, the ratio between L-lactic acid and D-lactic acid in the polylactic acid polymer is preferably within the range of 98:2 to 94:6 or 6:94 to 2:98.
The manufacturing method of such a polylactic acid is not specifically limited, and such methods as condensation polymerization and ring opening polymerization may be used. As a monomer, L-lactic acid, D-lactic acid or their mixture is used for condensation polymerization, and L-lactide, D-lactide or DL-lactide, which are cyclic dimers of lactic acid, or their mixture is used for ring opening polymerization. Also, in order to increase the molecular weight, a small amount of a chain extender such as a diisocyanate compound, an epoxy compound or an acid anhydride may be used during polymerization.
The preferable weight-average molecular weight of the polylatic acid is 60 thousand to one million. If it is too small, practical physical properties will not exhibit. If it is too large, the melt viscosity will increase and formability and workability will be inferior. The glass transition temperature (Tg) of the polylactic acid is 60° C. The melting temperature (Tm) depends upon the ratio between L-lactic acid and D-lactic acid. An amorphous one has no melting temperature, while a crystalline one has a melting temperature of 100-200° C.
Another polymer component in the composition forming the core layer and the over-layers in the present invention is a crystalline aliphatic polyeste
Takagi Jun
Terada Shigenori
Chen Vivian
Mitsubishi Plastics Inc.
Wenderoth Lind & Ponack LLP
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