Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Patent
1995-08-28
1997-10-21
Krynski, William
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
428199, 428204, 428207, 4284111, 428419, 4284735, 4284744, 428480, 428500, 428913, B32B 300
Patent
active
056794428
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a shelf-life indicator for repeatedly sterilizable plastic products.
BACKGROUND OF THE INVENTION AND BRIEF DESCRIPTION OF THE PRIOR ART
In the medical field, in order to contribute to waste reduction, more and more products are used that are only partially disposable and the other parts can be reused. In general, these reusable parts are made of plastic products sterilizable under the action of steam. A problem met by these products is that the shelf-life of the plastic products sterilizable under the action of steam is limited. Thus, the hazard exists that after repeated sterilization they break while being used. The consequences of this could be detrimental under certain circumstances, if broken parts fall in the region of a wound or if an important step of an operation cannot be completed by the surgeon because the instrument is broken.
In general, products of this kind are made so that they can undergo 100 sterilizations without being damaged. It is obvious to find an indicator that signals the user that the product is exhausted and should not be used any more.
However, this problem is not easy to solve. Before the resterilization, the products are in general treated in automatic washing machines with partially very abrasive cleaning products. In each case, the reaction of an indicator set on the outer surface would depend more on the cleaning product than on the sterilization itself. This is why trying to set color indicators on the outer surface has been unsuccessful until now.
According to DE 31 26 275 A1, it is known how to provide medical devices with indicators for sterilization processes. The indicator used is a pigment that changes its color under the influence of the sterilization process used and so indicates that the sterilization has occurred. Such indicators are appropriate only for non-reusable products. Besides, in ZIP 4-364174 A, Patents Abstracts of Japan, See. C, Vol. 17, No. 232 (C-1056), an indicator means for sterilization processes of medical devices is described and this indicator means is appropriate for steam sterilization as well as for sterilization with ethylene oxide.
Moreover, a sterilizable packing for items used in the medical field is known from DE 29 29 582 A1. In its closed internal part, the packing has a humidity indicator in the form of an externally visible color that changes constantly under the penetration of humidity.
Finally, it is known from DE 31 03 936 A1 how to color polymer materials by converting a colorant from a solution or from the gaseous phase into the transparent polymer material by diffusion.
DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
The invention is based on the problem of specifying an indicator that signals that the sterilizable material should not be used any more.
This problem is solved by a shelf-life indicator with the characteristics described infra and in the Figures. The action of the invention, which consists of the diffusion and/or of the modification of the pigments put in the polymer under the repeated action of heat, is based on the following behavior. The pigments diffuse themselves between the molecules in the polymer according to the temperature. The migration of the molecules occurs here in three dimensions, therefore, the original concentration at the location where it had been incorporated decreases. In addition, in the course of the repeated action of heat on the polymer, reactive disintegration products result which engage and so modify the pigments. Under the term modification, any kind of modification and even destruction is understood. The concentration of the pigment decreases in this way too.
The portions that the diffusion and the destruction of the pigments have on their concentration at the original incorporation location depend on the kinds of the pigments and polymer. Since both effects go in the same direction, the knowledge of their portions is of subordinate importance in practice. In each case, the result of each steam sterilization is a furthe
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