Receptacles – Closures – With closure opening arrangements for means
Patent
1988-02-24
1989-05-09
Hall, George T.
Receptacles
Closures
With closure opening arrangements for means
220359, B65D 1734
Patent
active
048281360
DESCRIPTION:
BRIEF SUMMARY
TECHNOLOGICAL FIELD
This invention relates to a can provided with an easily openable closure, and more specifically, to a can for canning provided with an easily openable closure whose inside is formed of a resin film having excellent corrosion resistance and hot water resistance, and to a process for its production.
PRIOR ART
So-called easily openable closure-fitted cans have been widely used in the past as cans for canning which can be easily opened by hand without particularly using a tool. This can closure is made by using an aluminum sheet as a metal blank in view of its processability, providing a score in the aluminum closure so that it reaches halfway in the thickness direction of the aluminum sheet to define an opening portion, forming a rivet in the opening portion from the closure itself and fixing a pull tab by the rivet. In use, the closure is double-seamed to the flange of a can body material.
The easily openable closure may give satisfactory results with regard to contents having little corroding property such as beer and carbonated drinks, but have not been able to be used at all for contents of general food cans, for example contents containing sodium chloride, because of their property of corroding the aluminum material. Of course, it is the practice to coat the inside surface of aluminum cans with an organic protective coating to prevent corrosion of the aluminum material. Inevitably, however, considerable injuries are caused to the protective film during formation of scores and ribs. It was proposed to correct the injuries on the coated film by electrodeposition coating. However, the operation is complex and the cost increases. Moreover, its protective effect is not entirely satisfactory.
In particular, tin plate is used as a can body-making material for cans used for canning foods. From the viewpoint of economy on one hand and of excellent corrosion resistance and excellent adhesion to coated films on the other, can body making materials made of tin-free steel (TFS, i.e. electrolytically chromate-treated steel plate), have been widely used. In a can for foods obtained by seaming an easily openable closure of aluminum to a tin-plate or TFS can body, an electrical cell is formed by the connection of dissimilar metals and the corrosion of the aluminum material occurs heavily.
There has already been known an easily openable closure obtained by attaching a polypropylene film to the inside surface of an aluminum material, and providing scores so that they extend from its outside surface to an intermediate site in the thickness direction of the aluminum material.
However, the aforesaid aluminum closure of the type in which a resin film is laminated to its inside surface still has problems to be solved in regard to industrial production and its utility in a retortable can for foods. In the step of producing closures or a step of seaming a closure to a can body, various processings and transfer are carried out while the resin film layer is in contact with processing devices or a conveying member. During this contacting, formation of cracks, pinholes or the like in the film cannot be avoided. If the injuries in the film reaches the aluminum substrate, pitting corrosion immediately occurs in the closure and results in serious defects such as leakage or intrusion of microorganisms. Even when the injuries in the film are not so deep, tensile deformations which are exerted on the film at the time of pressing the closure, score formation, or rivet formation for attaching an opening tab will deepen the small injuries and result in corrosion, for example the pitting corrosion mentioned above.
Furthermore, thermoplastic resin films have inferior hot water resistance to protective films composed of thermosetting resins, and after being subjected to severe retorting conditions of, for example, 110.degree. C. for 60 minutes, undergo marked peeling or corrosion at the processed parts described above. Furthermore, the thermoplastic resin films, particularly a polypropylene film, have low barrier property
REFERENCES:
patent: 4735336 (1988-04-01), Buchner et al.
patent: 4757914 (1988-07-01), Roth et al.
patent: 4762245 (1988-08-01), Matsuhayashi et al.
patent: 4773558 (1988-09-01), Taira et al.
Hotta Hisashi
Kawahara Masayuki
Otsuka Shinya
Watanabe Toshiaki
Hall George T.
Toyo Seikan Kaisha Ltd.
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