PTFE BEHAVIOUR

FrankSmith · May 13, 2004

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 ?.

PrentP · May 15, 2004

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

rnd2 · May 15, 2004

Frank
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.

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

PTFE BEHAVIOUR

FrankSmith

Industrial

Recommended for you

PrentP

Materials

rnd2

Materials

Similar threads

Part and Inventory Search

Sponsor