I need to know what process could be used to bond a part made out of
porous teflon to another plastic part. I know of products that are
made out of either polypropylene or polyethylene that have a teflon
layer applied to it. I need a method where I can take two parts that
are already made, physically put the two parts together, and then
perform some sort of operation to make a seal where the two parts
meet. Note that the bond does not need to have a lot of strength. The
two parts are designed to mate together and will stay in place with
friction. The seal is to stop moisture seeping through the crack.

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Request for Question Clarification by krobert-ga on 05 Nov 2002 16:55 PST

May I ask what you are trying to bond the teflon to?  Would an
adhesive meet your need?

Also, what is the geometry of the parts? Are you trying to bond two
sheets? Or are you trying to put a teflon "gasket" on some larger
part?

krobert-ga

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Request for Question Clarification by seedy-ga on 05 Nov 2002 21:37 PST

Eniac:

Would you consider an adhesive layer between the parts.  You can get
pressure sensitive adhesive that would conform very well to the parts
and would form a good seal (not a structural bond) that would prevent
water seepage.  Available at about 1/400" thickness (.0025").

You amy wish to consider double coated foam products which would tend
to conform very well and provide a great water seal. Available at
about 1/64" thickness (.016")

If you would consider these products, I can supply several alternative
suppliers..What surface cross section do you need to bond?? What
volume in square feet do you anticipate needing?? (answers to these
questions will help determine a vendor)...

Hoping to hear from you..

seedy

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Request for Question Clarification by lot-ga on 06 Nov 2002 06:43 PST

Hello eniac2-ga
If I were designing the part I would not coat the part to be bonded
with teflon and design the join to have a mechanical mating property
which prevents the parts separating, and not rely on the 'bond' alone.
(even though you do not require specific strength, this makes basic
design sense). However your application is unknown so it is hard to
advise.
As one part is plastic and specifically polyprop it can be made into a
one way snap fit join with the teflon piece. The moisture seal can be
provided by a 'rubber' gasket which the plastic part sandwiches.
Alternatively  you could design the plastic piece to join as a screw
and create a thread in the teflon piece to screw in. (depending on
your application).
kind regards
lot-ga

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Clarification of Question by eniac2-ga on 09 Nov 2002 07:00 PST

Sorry for this slow response. I didn't realize there was any activity
on my question because my spam filter caught the email from Google.

The parts in question are very small (several millimeters) and will be
produced in high volume. An adhesive of some sort is an option though
that will add cost in handling and applying etc. Buying equipment is
OK since there will be high volume.

There is a circular teflon piece pushed into a round hole. We have
tried thermoforming the plastic rim around the teflon part, heating it
to melting and forming it over the outer rim of the teflon. We
carefully control the force and temperature so that we get a slight
deformation of the teflon indicating that we have a good compression
between the two plastics. We find that this is not adequate to stop
liquid seeping along the barrier. For this reason I doubt a rubber
gasket would work. Note that we have tested to make sure the seepage
was not through the porous teflon. We need to transmit gases through
the part but not allow ANY liquid to pass.

The preferred plastic is a high temperature variant of ABS. Although
we are open to the idea of using other plastics if they would work
better. I mentioned the poly-pro and poly-e because I have samples of
products that laminate teflon onto those plastics. I also visited a
company once that made tanks for chemical processing where the
interior of the tanks had a poly-e liner coated in teflon. I didn't
know if there was some process of spraying teflon onto a surface so
that you could get the protection teflon offers while minimizing the
amont of (expensive) teflon used.

I hope this helps.

Supercritical CO2 has been used to "weld" plastics together--see
www.pse.umass.edu/lesser/   under work done by grad student Terry
Caskey (specifically,
http://www.pse.umass.edu/lesser/Students/Caskey/presentations/caskey_cumirp2000-1.pdf).
This technique will only be practical for small parts; not, for
example, if you're trying to apply a seal to an already-installed
window.  For larger parts, an adhesive is your best bet.  For
adhesives, www.loctite.com has a good product selection guide and
links to competent technical help.

perhaps can consider option of using Super High Frequency to perform
bonding between Plastic and Teflon.  i.e. check out Ultra sound
adhesion techniques.

Maybe you want to look at adding an additional process that will
render the entire item liquid repellent? This will also allow you to
use cheaper materials. Check out www.p2ilabs.com