Sealing tools

The heat conductive sealing is still among the most used joining processes for flexible polymer composites. Here, tools that are heated permanently melt the thermoplastic layers of ever thinner composite films and have to join these at ever higher machine speeds. In the same way, tightness requirements and optical demands on the seam increase.

The heat conductive sealing technology provides relatively few opportunities for a sufficiently sensitive and highly dynamic inline process control as well as an evaluability of process parameters. Therefore, a suitable, sensitive and rapid temperature measurement near the sealing position is the objective of the AiF IGF project 18470 BR “HePhaiStOs”. Furthermore, the way that the sealing bar sinks into the film material (tool movement) is decisive for the evaluation of the melting displacement as a requirement for a high seam quality. So it would be possible to determine, amongst other things, whether the material displacement in a four-layer area is high enough to guarantee a sufficient tool contact with the film and the corresponding heat transfer into the film in two-layer areas as well. Likewise, the safeguarding of stabile process conditions requires precisely adjusted sealing tool parts. This proofs rather difficult, is often not checked after a format change and can be impaired by contaminations. A distance measurement is all the more essential for an efficient, reliable sealing tool assembling and/or the early identification of wear or contamination.

Previous investigations have shown a direct correlation between the seam strength and the tool movement. Therefore, only sensor elements outside the sealing bars have been installed. This could result in larger measuring deviations and/or vibration-dependent noise as well as requiring more assembly space. Consequently, the perspective aim is the realization of a distance measurement by means of thin-film sensors integrated in the sealing tool.

In the IVLV project the feasibility of this intention is to be initially demonstrated. The project includes:

• Selection of the measuring principle, purchasing of suitable coating materials, development of the deposition processes and masking devices, coating tests
• Development of a safe electrical insulation of the sensors against the electrically conductive carrier material
• Conception and realization of test systems, replacement tests for dimensioning the sensor system relating to the measuring range and achievable local resolution
• Construction of a demonstrator with thin-film distance sensors, calibration
• Evaluation of the sensor detection potential in test series

The intended development aims at improved process monitoring, controlling, and handling during heat conductive sealing. However, it is also useable for other heat or cold joining processes in the future. It can also likely be used for contactless, spatially resolved detection of the film thickness in correlation to a continuous measurement of the web tension distribution.