Package making – Methods – With contents treating
Patent
1996-08-14
1998-09-08
Moon, Daniel
Package making
Methods
With contents treating
53423, 53471, B65B 5514
Patent
active
058028153
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for the self-sealing of tin containers and drums which may be used with advantage for fusible materials, more especially for moisture-reactive polyurethane hotmelts.
2. Discussion of Related Art
Moisture-reactive polyurethane hotmelts are formulated in such a way that they react even with traces with moisture and form crosslinked, infusible polymers. Accordingly, in the packaging and storage of polyurethane hotmelts, the moisture tightness of the containers used has to meet very stringent requirements, as demonstrated in the following. Around 1 kg of water is required for completely curing 1 kg of a polyurethane hotmelt containing 1% of isocyanate, i.e. for reacting all the isocyanate groups. Accordingly, a skin is formed on the surface of the hotmelt even if only fractions of this quantity of water reach the surface of the product.
Accordingly, in the packaging of polyurethane hotmelts in tin containers or drums, even traces of moisture diffusing into the container can render the entire contents thereof unusable as a result of skin formation.
In order, therefore, to ensure that the packaged polyurethane hotmelt has a storage life of 9 months or longer, the containers used have to meet stringent requirements, particularly in regard to the tightness of the seal used and in regard to dimensional stability. Since the tightness of the container cannot be satisfactorily tested, even with 100% incoming goods control, it happens fairly often in the present state of the art that individual containers are found to be leaking after packaging of the hotmelt. It is a considerable disadvantage in this regard that even the customer is unable to detect such defective containers because the crosslinked skin is impossible to distinguish from the uncrosslinked reactive hotmelt at room temperature. Although it is possible to melt the surface each time the container is changed and to determine whether a skin has already formed, this step is both labor-intensive and time-consuming, especially since, in industrial application, the time available to change a container is generally very short. In general, the processor only notices the formation of a skin in the container through a marked reduction in the amount of molten hotmelt transported through the plant. Since the skin can block the throughflow pipes, defective bonds and expensive, time-consuming breaks in production are the outcome.
There has been no shortage of attempts to develop suitable packs for reactive polyurethane hotmelts in which the skin formation and hardening mentioned above can be avoided. Thus, EP-A-102 804 describes a cylindrical container which is heated at its base and which is provided at its base with a removal opening and, at its upper end, with a displaceable piston head as closure. During removal of the hotmelt adhesive, the base of the container is heated so that the hotmelt is only melted at the base of the container. The plunger of a drum press applies pressure to the displaceable piston head of the container so that the entire non-melted block of hotmelt adhesive is pushed downwards and the molten part of the hotmelt adhesive is pressed through the removal opening to the applicator for the hotmelt adhesive connected to the removal opening. This solution has two major disadvantages. Firstly, it requires special containers with a lower outlet opening which are complicated and therefore expensive; secondly, application difficulties are involved where amorphous hotmelts are used. Whereas, in the case of hotmelt adhesives which are crystalline at room temperature, the considerable contraction which the adhesive undergoes on solidification results in the formation of a narrow gap between the wall of the container and the block of solid hotmelt adhesive composition, amorphous hotmelt adhesives shrink to a far lesser extent on solidification so that, in their case, the above-mentioned formation of a gap between the body of the hotmelt adhesive and the wall of the c
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Lohr Christoph
Magunia Robert
Michael Krebs
Henkel Kommanditgesellschaft auf Aktien
Jaeschke Wayne C.
Moon Daniel
Tolan Ed
Trzaska Steven J.
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