Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
1999-11-09
2002-04-09
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Composite
Of metal
C428S035700, C428S035800, C428S457000, C428S480000, C428S910000, C528S308000, C528S308100, C528S308600
Reexamination Certificate
active
06368720
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is directed to formable polyester films. More particularly, it is directed to a formable biaxially-oriented polyester film which is highly formable, greatly resistant to impact, and has superior characteristics as a packaging material for storing materials to achieve a good shelf life. This invention is applicable to laminates, particularly to laminates in which metal, paper, or plastic is used as a substrate, and to packaging containers.
2. Description of the Related Art
Polyester films have heretofore been used in flexible packaging in which polyethylene and polypropylene sheets are laminated together with or without an adhesive. In this instance a sealant layer is brought into direct contact with the contents to be packaged. Little consideration has been given to problems which might arise from contact of the polyester film with the contents.
Recently, however, packaging materials have been diversified and improved. To cope with this trend, applications predominate in which the contents are packaged in direct contact with the polyester film.
Prolonged shelf life of the contents is also required. For these reasons, attention has been drawn to improvements in the qualities of the polyester film, among others, in the characteristics such as formability, minimal eluation, and nonadsorptivity.
In particular, in the case where foods or beverages are packaged, problems may occur in that the contents are susceptible to quality changes due to contact with the polyester film. Altered flavors of the beverages or food, for example, result in decreased value.
Recently common packaging containers have a polyester film disposed over the inner surface of a metallic can. A metallic material is laminated to a polyester film, with or without use of an adhesive, followed by fabrication of the laminate to make a packaging metallic can.
As is widely accepted in the art, the inner and outer surfaces of a metallic can are prevented from corroding by being coated with a solution or emulsion in which a thermosetting resin selected from among a number of epoxies, phenols, and the like is dissolved or dispersed in an organic solvent. However, this conventional coating has the disadvantage that it takes a long time to dry the coating, which lowers productivity, and also creates environmental pollution due to use of organic solvents in large amounts.
In order to solve those problems, it is known that a polyester film may be laminated on a metallic material for use in a packaging can, such as a steel sheet, an aluminum sheet, or a metallic sheet derived from surface treatment such as by plating. In the production of a metallic can by draw forming or ironing of the metallic sheet so laminated, such polyester film is required to have special properties:
(1) Excellent lamination of the film with a metallic sheet.
(2) Excellent adhesion of the film to a metallic sheet.
(3) Excellent formability, with freedom from pinholes and other defects after forming.
(4) Freedom from peeling, cracking, and pinholing, even upon application of impact shocks to a metallic can.
(5) Nonadsorptivity by the film of the flavor components of the contents of a metallic can, and freedom of the film from altering the flavors of the contents due to its eluates (hereinafter referred to as the film's “taste property”).
Many proposals have been made to meet the requirements noted above. For example, Japanese Examined Patent Publication No. 64-22530 discloses a polyester film having a specific density and a specific face orientation coefficient, and Japanese Unexamined Patent Publication No. 2-57339 discloses a film resulting from a copolymerized polyester and having a specific crystallinity. These known techniques, however, are not always satisfactory with regard to all of the various characteristics above. In particular, a good balance is difficult to attain between superior taste property and superior formability in applications in which severe forming conditions are necessary with extreme deformation.
SUMMARY OF THE INVENTION
With the foregoing problems in mind, the present invention has created a formable biaxially-oriented polyester film which not only has superior formability, heat resistance, and taste property as a packaging material, but is also suitable for severe modes of forming such as draw forming and ironing, and is excellent in adhesion, impact resistance, and prolonging shelf life.
According to an important feature of the present invention, a formable biaxially-oriented polyester film is provided having a difference of 0.007 or less between the maximum and minimum values of the face orientation coefficient as determined in a 20 square cm region of the film, and an average face orientation coefficient in a range of 0.11 to 0.15 as determined in such a film region.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The term “polyester”, as in the “polyester film” of the present invention, means that the film is constituted of a polymer in which ester linkages chemically bond the main chain. The polyester may usually be obtained by polycondensation of a dicarboxylic acid component and a glycol component. Here, suitable dicarboxylic acid components include, for example, from among aromatic dicarboxylic acids such as terephthalic acid, 2,6-naphthalene dicarboxylic acid, isophthalic acid, diphenyl dicarboxylic acid, diphenylsulfone dicarboxylic acid, diphenoxyethane dicarboxylic acid, 5-sodiumsulfone dicarboxylic acid, phthalic acid and the like, aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, fumaric acid and the like, alicyclic dicarboxylic acids such as cyclohexane dicarboxylic acid and the like, and oxycarboxylic acids such as p-oxybenzoic acid and the like. Suitable glycol components include, for example, aliphatic glycols such as ethylene glycol, propanediol, butanediol, pentanediol, hexanediol, neopentyl glycol and the like, polyoxyalkylene glycols such as diethylene glycol, polyethylene glycol, polypropylene glycol and the like, alicyclic glycols such as cyclohexane dimethanol and the like, and aromatic glycols such as bisphenol A, bisphenol S, and the like.
The structure of the polyester for use in the present invention is not particularly restricted, but it is desired that, in order to improve impact resistance and taste property, an ethylene terephthalate unit and/or an ethylene 2,6-naphthalene dicarboxylate unit be contained in an amount of 95% or more by mol based on the totality of the components of the polyester. Contents of such subunits of 97% or more by mol are more desirable since they permit the film's taste property to be further improved.
The polyester used herein may be copolymerized with another dicarboxylic acid component and/or another glycol component so long as neither taste property nor adherence to a laminate substrate is affected. In such a case, the dicarboxylic acid component and glycol component are chosen from those given above and may be used, respectively, in combination with two or more. Diphenyl dicarboxylic acid and 5-sodiumsulfone dicarboxylic acid are preferred for the purpose of the taste property.
Additionally, the polyester suitable for the present invention may be copolymerizable with a polyfunctional compound such as trimellitic acid, trimesic acid, or trimethylolpropane, provided as no adverse effects are exerted on the advantages intended to be achieved by the invention.
To practice the present invention, the polyester should have a melting point of preferably about 246 to 280° C., and more preferably about 250 to 275° C., with taste property and heat resistance in mind.
To increase formability, lamination, and impact resistance, and to prolong shelf life as desired, the polyester film of the present invention should have a difference (hereinafter called a “variable”) of about 0.007 or less between the maximum and minimum values of face orientation coefficient as determined in a 20 square cm region of such film. The face orientation coeffici
Kimura Masahiro
Matsui Ryousuke
Takahashi Kohzo
Chen Vivian
Schnader Harrison Segal & Lewis LLP
Toray Industries Inc.
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