Stock material or miscellaneous articles – Structurally defined web or sheet
Reexamination Certificate
1998-12-08
2001-08-07
Ahmad, Nasser (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
C428S458000, C428S480000, C428S623000, C428S626000
Reexamination Certificate
active
06270874
ABSTRACT:
TECHNOLOGICAL FIELD
The present invention relates to polyethylene terephthalate resin covered metal sheet having remarkably excellent formability, which is applicable to heavily formed use such as drawing, drawing and ironing, drawing and stretch forming, and ironing after drawing and stretch forming.
BACKGROUND OF INVENTION
Metal containers such as beverage can or battery container are formed by drawing, drawing and ironing, drawing and stretch forming, or ironing after drawing and stretch forming with the object of material reduction and extension of inside measurement by reduction of wall thickness of container. These metal containers are generally coated inside to give corrosion resistance for content and printed after being coated outside to show content. However, a metal sheet previously covered with organic resin is tried to apply to above-mentioned heavily formed use with a view to reduce coating cost and to eliminate environmental pollution caused by dispersing of solvent during coating operation. And cans formed of metal sheet covered with organic resin has already been placed on sale in beverage can market.
In the organic resin covered metal sheet applied to the above-mentioned heavily formed use, a biaxially oriented film, which is manufactured by biaxial elongation of a thermoplastic polyester resin and subsequent heat-setting of it, is heat bonded to a metal sheet. The biaxial orientation of the film before heat bonding is partially or entirely lost from the contacting portion of the film to the metal sheet to the free surface (the surface not contacting to the metal sheet) in the thickness direction of the film by the heat conducted from the metal sheet when the film is heat bonded to the metal sheet. When the biaxial orientation of the film is totally lost after heat bonding, it causes the excellent adhesion between the film and the metal sheet for the above-mentioned heavily formed use, which is favorable for preventing peeling-off of the film and generation of film cracks during forming operation. On the other hand, the film without orientation has so large permeability that the content permeates the film and corrodes the metal substratum, and furthermore, it has faults that coarse spherlites are generated in the film by post heating during the operation of printing which shows the content or the like and cracks are easily caused in the film by falling of container or collision of each container.
Therefore, in the metal sheet covered with polyester resin film having biaxial orientation applied to the above-mentioned heavily formed use, the biaxial orientation of the film after the heat bonding is controlled to have formability compatible with permeation resistance and impact resistance (Laid open Japanese patent Hei 6-329669).
So far, copolyester resin obtained by copolymerization of ethylene terephthalate and ethylene isophthalate has been used in the organic resin covered metal sheet applied to the above-mentioned heavily formed use, and polyethylene terephthalate without copolymerized component has not been used in that field. The following is the reason. That is, copolyester resin obtained by copolymerization of ethylene terephthalate and ethylene isophthalate has small crystallization velocity, which undergoes little change of biaxial orientation by the temperature change of the metal sheet when a resin film is covered on a metal sheet by a heat bonding method consisting of contacting a resin film to a metal sheet heated to a temperature more than melting temperature of covering resin and pressing both, and it is rather easy to make biaxially oriented film structure having aforementioned formability compatible with permeation resistance and impact resistance by partially losing biaxial orientation before heat bonding as mentioned before. On the other hand, polyethylene terephthalate has large crystallization velocity, which causes extreme difficulty making biaxially oriented film structure having aforementioned formability compatible with permeation resistance and impact resistance by partially losing biaxial orientation before heat bonding when the film is covered on a metal sheet by heat bonding method. That is, as the biaxial orientation largely changes by a little temperature change of the metal sheet, it is extremely hard to make a prescribed film structure after covering. However, as copolyester resin has small crystallization velocity, it has a fault that crystal is apt to grow into coarse spherlite when it is post heated in the aforementioned printing operation or the like, which causes larger extent of deterioration of impact resistance. Furthermore, the price of copolyester resin film is high. Therefore, a polyester resin film of which film structure is easily made into favorable state after heat bonding as that of copolyester resin film and of which price is low is required.
THE OBJECTIVE OF THE PRESENT INVENTION
It is the objective of the present invention to produce a polyethylene terephthalate resin covered metal sheet having extremely excellent formability which can be applied to severely formed use such as drawing, drawing and ironing, drawing and stretch forming, or ironing after drawing and stretch forming.
THE METHOD TO REALIZE THE OBJECTIVE OF THE PRESENT INVENTION
Polyethylene terephthalate resin covered metal sheet of the present invention is one, wherein a biaxially oriented film consisting of polyethylene terephthalate having a low temperature crystallization temperature ranging from 130° to 165° C. is covered at least on one side of a metal sheet by heat bonding, which is characterized by that the low temperature crystallization temperature more preferably ranges from 140° to 150° C. It is further characterized by that the biaxial orientation of the polyethylene terephthalate resin film after being covered on the metal sheet by heat bonding is gradually increasing from the contacting portion of the film to the metal sheet to the surface portion of the film. And it is still further characterized by that the planar orientation coefficient of the film consisting of the polyethylene terephthalate resin after being covered on the metal sheet by heat bonding is ranging from 0 to 0.05 (referred as n
1
) at the contacting portion of the film to the metal sheet and that is ranging from 0.03 to 0.15 (referred as n
2
) at the surface portion of the film.
THE BEST MANNER TO PRACTICE THE PRESENT INVENTION
In the present invention, a film which is manufactured by biaxial elongation of poyethylene terephthalate resin having a low temperature crystallization temperature ranging 130° to 165° C., more preferably 140° to 155° C. is covered on a metal sheet by heat bonding consisting of contacting the resin film to one or either side of the metal sheet heated to a temperature more than melting temperature of the resin, inserting both into a couple of laminating roll, pressing both with the laminating roll, and quenching both immediately after that. The thus manufactured polyethylene terephthalate covered metal sheet can be applied to severely formed use because the biaxial orientation of the film is lost at the portion contacting to the metal sheet, which secures excellent adhesion of the film to the metal sheet, while the biaxial orientation remains higher at the nearer portion to the surface in the thickness direction of the film, which makes orientation structure of the film securing excellent permeation resistance and impact resistance.
EMBODIMENT
Hereinafter, the present invention is explained in detail referring embodiment.
At first, the polyethylene terephthalate resin composing the biaxially oriented film used in the present invention preferably has a low temperature crystallization temperature ranging 130° to 165° C., more preferably 140° to 155° C. A low temperature crystallization temperature is explained hereinafter. When an amorphous polyester resin such as polyethylene terephthalate which is obtained by heating it to a temperature more than melting temperature of it and quenching immediately after that is gradually heated using a diff
Gotoh Fumiko
Iwashita Hiroyuki
Tanaka Atsuo
Ahmad Nasser
Browdy and Neimark
Toyo Kohan Co. Ltd.
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