PTFE BEHAVIOUR
PTFE BEHAVIOUR
(OP)
We have recenty done some work laminating 4 mils of PTFE film to roughened (240 grit) copper plates in a high temperature press (380 deg C). When we cut the now laminated product from 3'X3' sheets into panels of 1'X1' with a saw the edge of the panel show excellent adhesion between the copper and the PTFE. However further in the panel ~1/4" the bond is poor and it is easy to peel the film from the copper plate. If the product is left for 2 weeks the bond further in towards the centre improves. This improvement is accelerated if the product is baked unsupported in an oven for a number of hours above 100 deg C. Can anyone explain this phenomenon . Is there a stress relieve occurring within the material due to cold flow of ptfe, is the bake of the material relieving this stress ?.





RE: PTFE BEHAVIOUR
When designing components made of PTFE, the relatively high degree of thermal expansion must be taken into consideration:
20-100 °C: = 16 · 10-5 1/K
20-200 °C: = 23 · 10-5 1/K
Recordings of the coefficient of linear expansion reveal two conspicuous transitions:
At 19°C there is a conversion within the crystal phase (<19°C triclinic, > 19°C hexagonal), which corresponds to a significant increase in thermal expansion.
At app. 327°C there is even higher unsteadiness, i.e. the crystal melting point
The following chart depicts the correlation between temperature and thermal expansion.
Regards,
Peter P
RE: PTFE BEHAVIOUR
If it is correct to assume that by the edges you are referring to the original sheet edges and not the newly cut edges then I suspect the problem is due to some gas evolving during the bonding process. It is likely to be most apparent towards the centre and least apparent on the edges.