PTFE (Teflon) tape on natural rubber misaligns upon press vulcanization 4

[Thais Bassinello]

We are company that produces rubber profile pieces. We are attempting to produce a music note rubber seal by press vulcanization. On the round side of the profile mold, we apply a PTFE (Teflon) tape, priorly shaped in the needed semi-circular shape. Application needs to be inside the mold, prior to vulcanization, so it is embedded into the profile. Upon vulcanization, however, the PTFE tape misaligns. Any ideas on how to fix this? TIA!

 

[btrueblood]

You need to have a part of the teflon mechanically "key" or lock into a feature in the mold to hold it in place as the rubber fills the mold. The movement of the rubber is pushing the teflon around, and there is no good way to adhesively bond the teflon to the mold to prevent that motion without ruining the properties you probably want the teflon to have. If you can't lock down the teflon preform, then you will need to hand lay-up (manually fill) the area of the mold where the teflon sits...then hope the filling of the mold doesn't shift the material you preloaded.

The only other means I could see to get this to work would be with an extrusion process, or more specifically, a co-extrusion, with a means to feed the teflon strip through the extruded die along with the rubber.

 

[GrahamBennett]

One other important point to remember is that Teflon will not adhere to natural rubber so some form of mechanical bonding is required here also.

http://www.over50schat.com

 

[Thais Bassinello]

, could you please clarify? We do a scratching process on the underside of the teflon tape. Would that be enough?

 

[btrueblood]

No, mechanical abrasion of the ptfe won't do much for adhesive bonding. The only way I know to adhesively bond reliably to ptfe is to chemically etch it (you can google for ptfe/teflon etching to get more info.). The problem is, the etching reduces/removes the slippery-ness and and chemical inertness of the surface layer, so you don't want etching to occur on the area of the part where you need those properties. And the etchant is so ridiculously corrosive, it is nearly impossible to limit the area to be etched by masking. So instead you are looking at a mechanical bond, where macro-scale features in the ptfe part (say a bead) is over-molded by the rubber to give the rubber something to "hang onto".

 

[GrahamBennett]

2 very good posts there btrueblood. Thanks for responding to Thais' request for clarification. I would have answered exactly the same.

http://www.over50schat.com

 

[Thais Bassinello]

Thanks to both of you! I really appreciate it.

 

[btrueblood]

Back at ya, Graham. I've learned a lot on this forum, and from other places, about rubber molding and curing, glad to be able to pay some of it forward.