Nowadays, nine out of ten packaging for food, pharmaceuticals, medical devices, and technical goods are produced using a heat contact method. The technology, where mostly permanently heated tools melt ther-moplastic layers of composite films and connecting these, is robust and relatively easy to use. Nevertheless, the requirements for thermal joining processes are constantly increasing: higher machine speeds, thinner packaging materials or sealing layers, complex seam geometries, high tightness requirements and optical requirements, traceability of process settings for each individual package, and frequent product changes with adjustment and start-up processes. Thereby, the heat conductive sealing method provides relatively few op-portunities of an inline process control of the seam quality, as well as a sufficient sensitive and highly dy-namic adjustability of process parameters. With a sensitive and rapid, thin-film-based temperature measure-ment (Seebeck effect) near the sealing position, interferences, such as wrinkles or contaminations, can be identified and corrected or faulty products can be immediately discharged. Similarly, the localization of layer steps is possible. Reliable temperature measurement using this technology establishes the basis for being able to promptly respond to an increased or decreased heat requirement in the seam area, e.g. in case of fluctuating machine speeds or during adjustment or start-up processes. Thus, burned or leaky seams can be avoided. Also, a locally deviant heat requirement, amongst others in the field of layer steps, can be met. A prompt process correction with zonally heatable ceramic tools will be in prospect therefore, but is not part of the project.
Classic temperature measurements in industrial environments are mostly based on wire or sheathed ther-mometers and even if positioned close under the tool surface, may result in a rather inert and also only inte-gral measuring system when it comes to high-performance processes. In contrast to this, fine-gauge thermo-couples which can be sealed into the seam are suitable only for laboratory use. The aim of the project is therefore to realize a spatially resolved real-time measurement (response time < 1/10 s) of the real joining zone temperature (temperature deviation from the reference temperature +/-1 K) on a heat conductive sealing tool.
Substantial parts of the project are as follows:
A specific sealing bar pair as a demonstrator marks the end of the project. With it, the validation of the func-tionality and detection limits based on typical process scenarios will be realized.
The simulation model is available for the future design of other tools, such as specific applications by indus-trial partners. The developed anti-adhesion and protective layer(s) can be used for classic sealing bars or other tools, independent from a temperature measurement system, for example for pre-heating plates during thermoforming. The thin film technology is also usable for alternative measurement tasks or the acquisition of other physical quantities. For instance, one approach would be an integrated capacitive measurement of the sealing bar movement.
The IGF project presented here by the Research Association of the Industrial Association for Food Technology and Packaging (IVLV e.V.) is funded by the Federal Ministry for Economic Affairs and Energy via the AiF as part of the program for the promotion of industrial community research (IGF) based on a decision of the German Bundestag.