Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
2001-08-02
2003-11-25
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Composite
Of metal
C428S035700, C428S035800, C428S035900, C428S457000, C428S480000, C428S910000, C524S275000, C524S277000, C528S275000, C528S283000, C528S302000, C528S305000, C528S308000, C528S308100, C528S308300, C528S308600, C528S308800
Reexamination Certificate
active
06652979
ABSTRACT:
TECHNICAL FIELD
The present invention relates to biaxially-oriented polyester film used for fabrication, and it relates to film which shows outstanding release properties following repeated use, use after fabrication and use in an aqueous environment and, furthermore, which exhibits stable properties with little variation; in particular, it relates to biaxially-oriented polyester film for fabrication which, when used as the inner face of a fabricated metal can following lamination to metal sheet such as steel or aluminium, is outstanding in its non-stick properties in terms of the contents and provides both heat resistance and processability.
BACKGROUND ART
Polyester film is used in various applications due to its outstanding properties but, on account of the molecular structure of polyester, it has poor release properties, and in order to confer such properties there is generally used the technique of coating the surface with a release component. However, this has disadvantages in that, with the surface being subjected to deformation as a result of processing, the properties deteriorate, and for reasons such as the strength of the coating layer itself being inadequate, performance falls in the case of repeated use. Furthermore, there is also the problem that because of poor adhesive strength between the release layer and the polyester layer, following use in an aqueous environment or following a retort or boiling treatment, there is a marked reduction in performance. In the latter case, there has been proposed overcoming the problem by providing a primer layer or reacting two components in the coating layer with a catalyst, etc, but not only are these methods unsuitable when used in food applications, there is also the problem of a lowering of productivity and it is difficult to stably satisfy the required properties under diverse usage conditions as described above. Now, containers such as metal cans are very popular throughout the world and are essential to our way of life and, hitherto, for the purposes of preventing corrosion, it has been common to apply to the inner and outer faces of the metal can a coating material formed by dissolving or dispersing an epoxy, phenolic or other such thermosetting resin in a solvent, so as to coat the metal surface. However, this kind of thermosetting resin coating method requires a long time for the applied material to dry, so that productivity is reduced, and there is also the problem that such a method is undesirable from the point of view of environmental contamination due to the large amount of organic solvent employed.
As a method for resolving these properties, there is the method of laminating a film to the metal can material, namely steel or aluminium sheet or metal sheet obtained by subjecting such metal sheet to a surface treatment like plating. When a metal can is produced by subjecting the film-laminated metal sheet to deep-drawing or ironing, the following properties are demanded of the film.
(1) It should be outstanding in its lamination to the metal sheet.
(2) It should be outstanding in its adhesion to the metal sheet.
(3) It should be outstanding in its processability and no defects such as pin holes should be produced following fabrication.
(4) The polyester film should not separate away, or show cracking or pin hole generation when the metal can is subject to impact.
(5) There should be no adsorption of aroma components from the can contents by the film, nor will the flavour of the contents be harmed by materials dissolved out of the film (referred to below as the taste characteristics).
(6) The contents will not stick to the can walls or to the can bottom, and it will be possible to remove the contents readily (below this is referred to as the non-stick property).
Many proposals have been made hitherto in order to meet these requirements. For example, in U.S. Pat. No. 5,240,779 and U.S. Pat. No. 5,384,354, there are disclosed copolyester films of specified density and planar orientation coefficient, or polyester films based on a combination of specified polyester components. However, these proposals do not altogether wholly satisfy the aforesaid diverse property requirements and, in particular, in applications where non-stick properties are further demanded along with outstanding lamination, impact resistance and heat resistance, it is difficult to simultaneously provide such characteristics.
Objective of the Present Invention
The objective of the present invention lies in resolving the aforesaid problems of the prior art and providing a biaxially-oriented polyester film for fabrication which shows outstanding release properties following repeated use, use after fabrication or use in an aqueous environment and, furthermore, which exhibits stable properties with little variation and, in particular, is outstanding in its lamination, fabrication, impact resistance and non-adsorption properties.
Disclosure of the Invention
In the present invention, in order for the contact angle to water and the surface free energy to fall within these ranges, it is preferred that a wax compound or silicone compound be added. The amount of wax compound, etc, added is preferably 0.001 to 5 wt %, more preferably 0.1 to 2 wt % and in particular 0.3 to 1.5 wt %. As examples of the wax compounds which can be used here, there are the esters of aliphatic carboxylic acid compounds and aliphatic alcohol compounds, and the amides of aliphatic carboxylic acid compounds and aliphatic amine compounds, and preferably the wax is composed of a compound in which the total number of carbons is 30 to 120, and more preferably 40 to 100. As examples of such compounds, synthetic or natural waxes comprising aliphatic esters like stearyl stearate, carnauba wax, candelilla wax, rice wax, pentaerythritol full ester, behenyl behenate, palmityl myristate and stearyl triglyceride, are preferred from the point of view of compatibility with the polyester. Moreover, as examples of silicone compounds, there can be used those having a silicone structure in the main chain or in side chains, and compounds having a molecular weight of 50 to 10,000 are preferred.
In particular, from the point of view of outstanding release properties following repeated use, use after fabrication and use in an aqueous environment, and from the point of view of manifesting non-adsorption properties and enhancing hygiene in food packaging applications, etc, the addition of carnauba wax is preferred and especially refined carnauba wax. The amount of the carnauba wax compound or the like added to the film is preferably from 0.1 to 2 wt %, more preferably 0.2 to 0.9 wt % and in particular from 0.3 to 0.8 wt %.
As a result of a thorough investigation into methods for adding and incorporating carnauba wax into the polyester in the present invention, it was found that, in terms of enhancing the carnauba wax dispersion properties and manifesting stable properties, and also in terms of suppressing contamination in the film production process, the following methods of addition in the polymerization process are preferred:—
(1) The method of adding the carnauba wax at the time of the polyester polymerization, and
(2) The method of producing, by polymerization, a master batch (a carnauba wax master polyester) to which a large quantity of carnauba wax is added, and then mixing this with a specified amount of polyester containing no, or just a small amount of, carnauba wax (the diluent polyester) and kneading.
In the present invention, in the case of polyester where carnauba wax is added, carrying out the polymerization using a germanium catalyst is especially preferred from the point of view of enhancing the dispersion properties, and it is preferred that the germanium element content be from 1 to 200 ppm, more preferably 10 to 100 ppm and in particular 20 to 80 ppm. Again, in the case of obtaining film by method (2), it is preferred that there be used germanium catalyst as described above for the carnauba wax master polymer but the diluent polymer is not restricted to one employing germanium catalyst. Con
Kimura Masahiro
Matsui Ryosuke
Takahashi Kohzo
Chen Vivian
Kubovcik & Kubovcik
Toray Industries Inc.
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