Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2001-09-25
2003-02-18
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S346000, C428S347000, C428S3550EN, C428S480000, C428S481000, C524S270000, C524S271000, C525S184000, C525S437000, C525S444000
Reexamination Certificate
active
06521336
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an aliphatic polyester composition suitable for obtaining films provided with biodegradable property which are excellent in transparency, interlaminar adhesiveness and heat sealing strength as well as films and laminates made thereof.
2. Description of the Prior Art
Polylactic acid and an aliphatic polyester, which are representative examples of a biodegradable polymer, are higher in crystallinity and rigid in molecular structure so that they are greater in heat of fusion on heat sealing and thus poor in heat-sealing property. All of the biodegraoable polymers have a melting point of at most about 200° C. Thus, a difference in melting point is not distinct among the materials in a multi-layer film of a substrate/binder/sealant.
As heating of the film is effected from the side of the substrate, transmission of heat toward the sealant is insufficient if the heat sealing temperature is low, so that heat sealing strength of the resultant laminated film becomes poor. On the other hand, if the heat sealing temperature is elevated to enable transmission of heat to the sealant sufficiently, the substrate may also be molten so that thickness of the whole laminated film becomes thin to cause a phenomenon called “edge breaking” which means breaking of the: film from the side of edge. Accordingly, it is impossible to manufacture a film container (bag) for packing liquid from such film. Even if a bag is manufactured, it utterly fails to satisfy the demand for packing liquid. As a means for overcoming such problems, a method wherein polylactic acid is mixed with an aliphatic polyester in a composition to improve heat sealing property (Japanese Laid-open Patent Applns. Nos. Hei. 9-157408 and Hei. 11-222528) or a biodegradable packaging material wherein such composition is utilized as a heat sealing layer (Japanese Laid-open Patent Appln. Hei. 11-20084) are proposed hitherto.
PROBLEMS TO BE SOLVED BY THE INVENTION
Such methods are effective for improving heat sealing property but are still insufficient in the effect and involves in some cases damaging transparency that is a character of the biodegradable polymer. In addition, such compositions are insufficient in a good balance of heat sealing strength and peelability when used as a cover or lid material for plastic containers comprised of polylactic acid.
In case two multilayer films made of a stretched polylactic acid film laminated with a heat sealing layer of a composition of the polylactic acid and an aliphatic polyester is heat-sealed mutually, for example, the heat sealing strength may significantly be enhanced. However, when the aforesaid composition layer is heat sealed with a polylactic acid film, the heat sealing strength is still low so that the effect of improving in heat sealability at low temperature is insufficient. Thus, its packaging application is inevitably limited as compared with the conventional polyolefin packaging materials. In addition, there may be the case wherein a covering material excellent in peelability is not obtained by using a heat sealing layer of the aforesaid composition layer on a container obtained, for example, by thermally molding polylactic acid sheet.
Under the above circumstances, there is a great demand in this art to develop a new type biodegradable aliphatic polyester composition which overcomes the problems seen in the prior art compositions and can be furnished with excellent heat sealable property at low temperatures and peelability in addition to the inherent biodegradable property and transparency.
BRIEF SUMMARY OF THE INVENTION
1. Objects of the Invention
It is an object of the present invention to improve heat sealing property at low temperatures without spoiling biodegradable property which is an inherent character of biodegradable polymers as well as transparency.
It is another object of the present invention to provide an aliphatic polyester composition possessing excellent heat sealing strength and peelability as well as the inherent biodegradable property and transparency.
It is still another object of the present invention to provide a film made of the aliphatic polyester composition by way of any suitable molding method.
It is still further object of the present invention to provide a laminate possessing sufficient heat sealing strength and peelability as a thermally fusible layer of a biodegradable polymer as well as excellent adhesiveness to a substrate.
Other and further objects, features and advantages of the present invention will become apparent more fully from the following description.
2. Means of Solving the Problems
Taking the aforementioned circumstances into consideration, the present inventors have made extensive research for developing a new type aliphatic polyester composition which overcomes the various drawbacks seen in the prior art biodegradable polymer compositions and enables the production of a biodegradable composition enhanced in heat seal strength and peelability without spoiling the inherent biodegradable property and transparency. As a result of such extensive research, it has now been found surprisingly that an aliphatic polyester composition composed of a specific proportion of polylactic acid, an aliphatic polyester and a tackifier exhibits a remarkably high heat sealing strength and peelability while maintaining good adhesion to a substrate. The present invention has been accomplished on the basis of the above finding.
In accordance with an embodiment of the present invention, there is provided an aliphatic polyester composition possessing excellent heat sealable property, which comprises 9-90% by weight of polylactic acid (A), 90-9% by weight of an aliphatic polyester (B), and 1-209% by weight of a tackifier (C).
In accordance with another embodiment of the present invention, there is provided a film made of the aforesaid aliphatic polyester composition by way of any suitable molding method.
In accordance with still another embodiment of the present invention, there is provided a laminate which comprised of a substrate and an aliphatic polyester composition on at least one surface of the substrate, the aliphatic polyester composition possessing excellent heat sealable property and comprising 9-90% by weight of polylactic acid (A), 90-9% by weight of an aliphatic polyester (B) and 1-20% by weight of a tackifier (C).
In a preferred embodiment of the present invention, the aliphatic polyester (B) is an ester obtained by ring-opening polymerization of a cyclic lactone and the tackifier (C) is a rosin derivative or an aliphatic cyclic hydrocarbon resin.
DETAILED DESCRIPTION OF THE INVENTION
Below is a detailed description on the individual components constituting the aliphatic polyester composition of the present invention.
Polylactic Acid (A):
Polylactic acid (A) used in the aliphatic polyester composition generally stands for homopolymers of lactic acid, including poly(L-lactic acid) in which the structure unit is L-lactic acid, poly(D-lactic acid) in which the structure unit is D-lactic acid and poly(DL-lactic acid) in which the structure unit is DL-lactic acid, 1.e. a racemic equiamount mixture of D-lactic acid and L-lactic acid; copolymers of lactic acid containing lactic acid as the predominant component and a small proportion of a copolymerizable comonomer, for example, a copolymer of lactic acid with less than 50% by weight, preferably not more than 30% by weight, more preferably not more than 10% by weight of glycolic acid; and a mixture of these. Illustrative of the comonomer copolymerizable with lactic acid are, for example, a 3-hydroxybutyrate, caprolactone, glycolic acid and the like. Among these polymers, a homopolymer of lactic acid can preferably be used as it excels in transparency.
Any of the known polymerization methods, such as polycondensation method and ring-opening polymerization can be adopted for polymerization of lactic acid. In polycondensation method, for example, L-lactic acid, D-lactic acid or a mixture of these is directly subjected to d
Itoh Suekazu
Narita Junichi
Sawai Tohru
Takeishi Ichiro
Armstrong Westerman & Hattori, LLP
Chen Vivian
Tohcello Co. Ltd.
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