Process for the preparation of closures for packaging containers

Details Process for the preparation of closures for packaging containers Process for the preparation of closures for packaging containers

1991-09-27

1995-01-24

Nold, Charles R.

Stock material or miscellaneous articles

Hollow or container type article

428 357, 428355, 206813, 220359, 156182, 1562753, 1562757, 1563084, 1563317, B29D 2200, B32B 3100

Patent

active

053841697

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a process for the preparation of closures for imperviously sealing packaging containers, by which a sealing composition is applied and stoved onto the inside of the closures.
The invention furthermore relates to closures for packaging containers, where a sealing composition has been applied and stored onto the inside of the said closures, and also relates to packaging containers with these closures.
The purpose of the various packaging materials is to hermetically seal the contents from the environment and to do this also under extreme conditions such as, for example, those prevailing when heat-sterilizing foodstuffs. Isolation of the contents from the environment is ensured by introducing suitable sealing compositions to the lid and closures with which the packaging container is sealed. Commercially, i.e. economically, attractive sealing compositions for closures must have a number of critical properties and are therefore highly specialized materials and compositions. The required properties of the sealing compositions are moreover also determined to some extent by the intended use of the packagings.
With foodstuffs packagings, for instance, particular importance attaches to the resistance of the sealing compositions to the contents during sterilization or pasteurization and also during storage of the packaged foodstuffs for a period often extending to years. In the case of industrial packagings, the contents are often chemically highly reactive or agressive, and the sealing compositions must likewise be resistant to these contents. Normally, for closures and lids of glass and metal packagings, sealing compositions made from plasticizer-containing PVC plastisols are used, as described in the case of closures for glass jars in DE-B-2,003,693 for example. As a rule, the PVC plastisols used as a sealing composition are composed of a paste-making polyvinyl chloride which has in particular a defined swelling power in plasticizer, and of one or more plasticizers and optional fillers, stabilizers, pigments and polyvinyl chloride processing auxiliaries.
The formulation of plasticizer-containing PVC plastisols, their preparation and processing, is substantially described in K. Weinmann, Beschichten mit Lacken und Kunststoffen, 1967, published by Verlag W.A. Colomb, Stuttgart.
It is known that with PVC sealing compositions of this type exposed to contents, in particular fatty and oily substances, and thermal stress (pasteurization, sterilization), it is basically impossible to prevent plasticizer migration from the sealing composition and also partial dissolving and swelling of the sealing composition where solvent-containing contents are concerned. The magnitude of the plasticizer migration can exceed foodstuffs regulations which are current or under discussion. Furthermore, under certain circumstances, the plasticizer migration can result in a loss of vacuum in pasteurized and sterilized packagings and also a loss of solvents due to increased gas permeability where industrial packagings are concerned. With industrial packagings, there is likewise basically the problem of contamination of the contents due to the plasticizer migration and swelling or partial dissolving of the polyvinyl chloride. A further disadvantage of these sealing compositions is that the disposal of PVC-containing waste materials is becoming increasingly difficult and cost intensive. However, in addition to the customarily used PVC sealing compositions there are also sealing compositions based on polyurethane. For instance, U.S. Pat. No. 3,971,785 and GB-B-1,374,745 describe sealing compositions for packaging containers, which comprise blocked or unblocked polyisocyanate prepolymers and, as crosslinking agents, carbon dioxide-blocked amines. DE-A-1,957,827 and DE-A-2,203,730 disclose sealing compositions comprising hydroxyl-containing polymers and polyisocyanates or blocked prepolymers and also an activator with hydroxyl-containing polymers and aluminum silicate compounds.
The object of the present invention wa

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