Thin Heating Layers

For thermal joining of plastic films, especially when sealing flexible packaging, the heat conductive sealing method is predominantly used. A sustainable production and the product safety pose highest demands on the quality of the sealed seams, particularly their tightness and absence of contamination. Because no defective products should reach the consumer; intelligent, adaptive processes are required.
The IGF project "HePhaiStOs" (BG18470) has already provided the evidence of functionality for innovative, tool-integrated temperature sensors with a very short response time and a high sensitivity. They are able to check each sealed seam inline and identify deviations in the heat flow that are spatially resolved. Based on this, a targeted additional partial heating of affected areas should prevent the production of rejects and take a further step towards an adaptive sealing tool.
According to the state of the art, with a solid sealing tool it is not feasible to locally heat sealed seam areas in a differentiated way, or to compensate local temperature sinks, e.g. due to wrinkles or contamination. Rather, it makes sense to keep the tool at a defined temperature and to make additional local temperature adjust-ments. For this, thin film heaters are suitable, which are sputtered similarly to the temperature sensors in the IGF project named before. Both, thin-film thermocouples as well as thin film heaters, can be combined in per-spective.
The IVLV project aims at realizing an exemplary layer structure on a metal sealing bar and to investigate achievable temperatures. The extent to which the temperature in the composite film can be influenced by this is checked by means of thin-film thermocouples in the opposite sealing bar. The feasibility study includes:

• Technical design, selection and procurement of suitable target or precursor materials, development of deposition processes and masking
• Iterative experiments for the deposition of a layer with sufficient power density
• Construction of a demonstrator
  o Electrical insulation against the metallic sealing bar
  o Realization of two independent heating zones (sealing bar 1)
  o Realization of the thermocouple and protective layer coating (sealing bar 2)
  o Control for the thin film heating layers
• Evaluation of thin film heaters in sealing tests

The described technology development paves the way for a future integration of temperature monitoring, determination of the tool movement (the way that the sealing bar sinks into the film material) respectively the melt displacement, and the local heating, directly on the seal contact surface of the tool. It decisively addresses the process stability and the product safety during heat conductive sealing. With a dedicated temperature control, temperature profiles are able to be imprinted into films or preforms to influence the wall thickness distribution. Furthermore, during injection molding or hot embossing the technology is suitable for producing surface structures and functions of plastic components without post-processing.