Receptacles – Closures – With closure opening arrangements for means
Patent
1989-06-09
1990-08-07
Fidei, David T.
Receptacles
Closures
With closure opening arrangements for means
220269, 220276, B65D 1734
Patent
active
049460633
DESCRIPTION:
BRIEF SUMMARY
This invention relates to metal can ends with metal pull tabs bonded thereto, and more specifically to such can ends which are provided with a score line defining an area of the can end which can be detached by tearing along the score line to form an aperture and with a metal pull tab having a shank portion attached to the upper side of the said area.
BACKGROUND OF THE INVENTION
Conventional "easy-open" can ends have a metal pull tab secured by a rivet formed in the metal of the area defined by the score line. Use of a rivet requires that a relatively soft formable metal be used for the can end, which must consequently be relatively thick to resist internal pressure or vacuum, while the rivet is prone to corrosion due to damage to protective coatings on the metal caused during the formation of the rivet. It has previously been proposed in European Patent Application No. 82305528.0, published under No. 0078625Al, to secure a pull tab to the score-defined area by means of an adhesive, without a rivet. To achieve adequate adhesion and protection, we believe that this would require use of special external lacquers, with attendant cost disadvantages, while the adhesive would have to be accurately located and metered and would be relatively slow to bond, thus increasing process time.
SUMMARY OF THE INVENTION
According to the present invention, in a metal can end provided with a score line defining an area of the can end which can be detached by tearing along the score line to form an aperture and with a metal pull tab having a shank portion attached to the upper side of said area, the upper side of the can end is provided with a protective polymer coating and the under side of the shank of the pull tab is also provided with a polymer coating, the surface at least of said coating on the shank portion being based on the same monomer as the polymer of the surface at least of the coating on the upper side of the can end and said surfaces are directly welded to one another.
By the use of coatings on the can end and pull tab which are directly welded to one another, the disadvantages attendant on the use of adhesives are avoided and good adhesion and protection can be obtained, while the process time for forming the can end can be kept relatively short. Furthermore, the absence of a rivet means that a thinner, harder steel can be used for the can end, and the cost of the metal can accordingly be reduced. The coating on the pull tab may be thermally welded to the coating on the can end, or it may be ultrasonically welded to it. Use of ultrasonic welding enables the weld to be effected without heating the metal or any part of the coatings except that part involved in making the weld, and thus avoids any risk of thermally induced effects adjacent the weld, for example recrystallisation of the polypropylene or polyester, or softening of the coating adjacent the weld during welding which might lead to damage if contacted while soft. It also avoids the need to allow process time for cooling or to provide additional equipment for cooling the affected area.
Preferably the upper and under sides of the can end both have protective polymer coatings which have been applied simultaneously, e.g. by the use of the techniques described and claimed in our copending British Patent Application No. 8724237.
In one embodiment of the invention, the coatings on the upper side of the can end and on the under side of the shank portion of the pull tab both have an outer layer of a polyamide. In this case, the said coatings preferably both consist of a composite film comprising an inner layer of a bonding resin which is an acid-modified polyolefin resin containing carboxyl or anhydride groups and an outer layer of a polyamide adhered to the inner layer of said bonding resin. A preferred bonding resin is a maleic anhydride graft modified polypropylene containing 0.05 to 0.5 maleic anhydride and based on a random ethylene/propylene copolymer.
In an alternative embodiment, the coatings on the upper side of the can end and on the under side o
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Derwent Abstract No. 86-207868.
Heyes Peter J.
Owen Robert A.
CMB Packaging (UK) Limited
Fidei David T.
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