Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2001-09-12
2003-11-11
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S035700, C428S035900, C428S328000, C428S212000, C428S343000, C428S344000, C428S346000, C428S347000, C428S349000, C428S3550RA, C428S457000, C428S458000, C428S480000, C428S910000, C525S437000, C525S444000, C528S308000, C528S308100, C528S308600, C528S308700
Reexamination Certificate
active
06645589
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a polyester film used for preventing corrosion of metal containers for food, such as soft drinks, beer, canned food etc., and the like, to a film-laminated metal plate having the film laminated on the metal plate, and to a metal container obtained by forming the film-laminated metal plate.
BACKGROUND OF THE INVENTION
It is a general and conventional practice to apply a coating on the inside and outside of a metal can to prevent corrosion, wherein the coating is generally made from a thermosetting resin.
For application of a thermosetting resin coating, a solvent type coating is used in most cases. The formation of a coating film requires heating at a high temperature for a long time, for example, 150-250° C. for several minutes. In addition, a large amount of the organic solvent scatters during baking, giving rise to a demand for an improvement including simplification of the process, prevention of pollution and the like.
The film formed under the aforementioned conditions inevitably contains a small amount of the organic solvent. When, for example, food is filled in a metal can having the above-mentioned film inside the can, the organic solvent may be transferred to the food to spoil the taste and flavor of the food. It also happens that the additive in the coating and a low molecular weight substance in the coating, which has been produced by incomplete crosslinking reaction, may be transferred to the food, thereby causing an adverse influence on the food, like the aforementioned residual organic solvent.
A different method for preventing corrosion is the use of a thermoplastic resin film. For example, a polyolefin film such as a polypropylene film and the like or a polyester film is laminated on a heated tin free steel and the resulting film-laminated metal plate is processed to give a metal can.
The use of the thermoplastic resin film resolves the above-mentioned problems of simplification of the process, prevention of pollution and the like.
Of the thermoplastic resin films, for example, when a polyolefin film, such as polyethylene and polypropylene, is used, heat history from a can forming process or heat history from a retorting treatment after can forming and the like may cause peeling off of the film from the film-laminated metal plate, because this film has poor heat resistance.
A method comprising the use of a polyester film as the thermoplastic resin film is most preferable, because the problems associated with the above-mentioned polyolefin film can be resolved.
A polyester film applied to the inside of a can shows superior heat resistance and allows only a small level of a low molecular weight substance to be generated. Consequently, it shows less occurrence of spoiled taste and flavor of food due to the transferred low molecular weight substance, as compared to a polyolefin film. In other words, this film is superior in preventing occurrence of spoiled flavor. When applied to the outside of a can, a polyester film is superior in heat resistance and when the film is whitened, an undercoat can be omitted.
However, the use of a polyester film containing polyethylene terephthalate as a main component for this end is not free from a problem. This is because a heat treatment during a can forming process after laminate processing, which aims at superior finish of the can, repairing a joint part of a can, and the like could cause dimensional changes only in the film part of the film-laminated metal plate due to the insufficient heat resistance of the polyester film, which in turn results in a loose film and a failure to completely cover the surface of a metal plate.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a polyester film superior in heat resistance, opacifying property, barrier property and corrosion resistance, which is capable of stably covering the surface of a metal plate even after experiencing the heat history during the can forming process and the like, and which is preferably used for producing a metal container for food, a film-laminated metal plate superior in can forming processability, and a metal container having superior corrosion resistance and good appearance.
To achieve this object, the present invention provides a white biaxially oriented polyester film comprising a layer A and a layer B in a two-layer structure, wherein the layer A comprises a polyester having a melting point of 240° C.-260° C. and comprising titanium dioxide in a proportion of 5-30 wt %, the layer B comprises a polyester having a melting point of 210° C.-235° C., and the film shows a dimensional change of not more than 2%, which is obtained by thermally adhering a layer B side of the film to a metal plate to give a laminate, which is heat-treated at 210° C. for 2 minutes, and subjecting the film after the treatment to the measurement.
The film-laminated metal plate of the present invention comprises the above-mentioned polyester film laminated on at least one side of the metal plate.
The metal container of the present invention is obtained by forming the above-mentioned film-laminated metal plate.
DETAILED DESCRIPTION OF THE INVENTION
The white biaxially oriented polyester film of the present invention comprises a layer A and a layer B in a two-layer structure, wherein the layer A comprises a polyester having a melting point of 240° C.-260° C. and comprising titanium dioxide in a proportion of 5-30 wt %, the layer B comprises a polyester having a melting point of 210° C.-235° C., and the film shows a dimensional change of not more than 2%, which is obtained by thermally adhering a layer B side of the film to a metal plate to give a laminate, which is heat-treated at 210° C. for 2 minutes, and subjecting the film after the treatment to the measurement.
In the above definition, the “dimensional change, which is obtained by thermally adhering a layer B side of the film to a metal plate to give a laminate, which is heat-treated at 210° C. for 2 minutes, and subjecting the film after the treatment to the measurement” (hereinafter to be referred to as “dimensional change”) is measured by the method to be mentioned later under “(1) Dimensional change of polyester film”, which is measured as regards the state of a film-laminated metal plate.
The polyester to be used for the above-mentioned polyester film is obtained by condensation polymerization of polycarboxylic acid and polyhydric alcohol as main components. It may comprise only monomers or other components copolymerized according to the object.
Examples of the above-mentioned polycarboxylic acid component include dicarboxylic acid such as aromatic dicarboxylic acid (e.g., terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, diphenyl-dicarboxylic acid and the like), aliphatic dicarboxylic acid (e.g., adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, dimer acid and the like), alicyclic dicarboxylic acid (e.g., cyclohexanedicarboxylic acid and the like), and the like.
Examples of the polyhydric alcohol component include glycol such as aliphatic diol (e.g., ethylene glycol, diethylene glycol, triethylene glycol, propanediol, butanediol, hexanediol, dodecamethylene glycol, neopentyl glycol and the like), alicyclic diol (e.g., cyclohexane dimethanol and the like), aromatic diol (e.g., ethylene oxide adduct of bisphenol derivative and the like), and the like.
The polyester to be used for forming layer A is exemplified by those obtained from the above-mentioned dicarboxylic acid and glycol. Preferred one comprises a terephthalic acid-ethylene glycol component, more preferably a mixture of one containing a terephthalic acid-ethylene glycol component and one containing a terephthalic acid-butanediol component. More preferable one has a weight ratio (one containing a terephthalic acid-ethylene glycol component/one containing a terephthalic acid-butanediol component) of 98/2-50/50, particularly preferably 95/5-70/30.
Examples of the polyester to be used for layer B
Fujii Shingo
Igushi Hideki
Nagano Hiroshi
Chen Vivian
Leydig , Voit & Mayer, Ltd.
Toyo Boseki Kabushiki Kaisha
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