Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1999-05-03
2000-10-03
Dawson, Robert
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
528300, 524605, C08K 336
Patent
active
061274739
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a polyester film. More particularly, the invention concerns a polyester film excellent in can-capping processability, corrosion resistance and mechanical properties, and most suited for the lamination onto the surface that comes in contact with the contents, of the cap of a metallic easy-open can.
BACKGROUND ART
The pull top type or stay-on type cap of an easy-open can is widely used as the cap of a metallic can which can be opened without using a can opener or the like.
The cap of an easy-open can is produced by using aluminum, tin plate, tin-free steel (TFS) or the like as the metallic material; the inner surface of the can cap that comes in contact with the contents is coated with a corrosion proofing membrane; and then the metal sheet is scored at a position where an opening is to be formed to define an openable sector. Inner coatings are damaged or ruptured by the scoring process in many cases, and therefore a repair coating film is placed on the coating film.
Generally, a corrosion proofing coating film is formed, for example, by dissolving or dispersing a coating agent containing a corrosion inhibitor in a solvent such as an organic solvent or the like to prepare a coating liquid, applying the resultant coating liquid on a metal sheet and removing the solvent by drying.
The remaining minute amount of the solvent therefore possibly flows out into the contents of the can to contaminate them. Further, a repair coating is required in many cases, and this causes troubles in productivity.
As measures for preventing the pollution of the contents and dispensing with the repair coating, methods in which specific polyester films are laminated on metallic materials have been disclosed (Japanese Unexamined Patent Publication No. 62-52045, Japanese Unexamined Patent Publication No. 63-12445, Japanese Unexamined Patent Publication No. 1-124551, Japanese Unexamined Patent Publication No. 1-182248 and Japanese Unexamined Patent Publication No. 3-63124).
However, the can caps produced even by these methods are still apt to corrode at the scored parts, and especially when the can is kept hot (higher than 60.degree. C.) before eating or drinking, corrosion may develop at the scored parts.
Problems to Be Solved by the Invention
It is an object of the present invention to solve these shortcomings of the conventional technologies and to provide a polyester film free from corrosion at the scored parts even during holding at high temperature and most suited for the cap of an easy-open can.
Means for Solving the Problems
Such object of the present invention is achieved, according to the present invention, by a polyester film comprises a polyester containing a lubricant having an average particle diameter of 0.001 to 2.5 .mu.m in an amount of 0.01 to 5.0% by weight, wherein the film is characterized in that it has a plane orientation coefficient of 0.115 to 0.140, two or more endothermic peaks in DSC curve in the range of 170 to 270.degree. C. and a peak temperature of 60-120.degree. C. of a complex elastic modulus (E") in water, and the polyester which constitutes the film has an intrinsic viscosity of 0.50 to 0.64 dl/g.
The present invention will be explained hereafter further in detail.
(i) Polyester
The polyester used in the present invention is a linear polyester comprising dicarboxylic acid component(s) and glycol component(s). The examples of the polyester include homopolymers and copolymers such as polyethylene terephthalate, polyethylene isophthalate, polybutylene terephthalate, polyethylene 2,6-naphthalate and the like.
Among them, a polyester having a melting point of 270.degree. C. or less is preferable since film (especially biaxially oriented film) can be easily produced from it on an industrial scale, and a polyethylene terephthalate copolymer is especially preferable. The copolymer component other than terephthalic acid and ethylene glycol in the polyethylene terephthalate copolymer may be either a dicarboxylic acid component or a glycol component. The dica
REFERENCES:
patent: 4931500 (1990-06-01), Okamoto et al.
Kubo Koji
Minamihira Yukihiko
Murooka Hirofumi
Yoshida Tetsuo
Dawson Robert
Peng Kuo-Liang
Teijin Limited
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