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kilkenny (Mechanical) (OP)
8 Jan 04 17:01
Description of assembly:
I am bonding a polycarbonate overlay to a thick , smooth, acrylic sheet using a PSA (3M 468MP tape).  The overlay is about 15" x 17".  The acrylic has dozens of holes that are about 3/4" dia. for snap dome switches that the overlay covers.  The outer edges of the overlay are sealed.  The overlay/PSA is in contact with the acrylic everywhere except over the switch holes.  There will be a +/- 5psi differential pressure between the two sides of the assembly, which causes the overlay to deflect somewhat over the unsupported switch holes when a differential pressure exists.  The assembly will operate in a -40F to 160F temperature range.

Problem statement:
The overlay is separating from the acrylic when the required test pressure is applied at ambient temperature.  Careful surface cleaning and preparation have been done.  Tests at temperature extremes haven't yet been done.  I expect the performance to worsen at higher and/or lower temperatures.

Seeking advise:
I want recommendations on stronger adhesives that may work.   Heat cured adhesives are acceptable.  Would prefer an adhesive film attached to the overlay as a preferred assembly technique but will also consider a dispensed adhesive.

Quiglejp
magic612 (Materials)
16 Mar 04 10:16
Sorry about the late reply; Scapa Industrial makes a tape that is an unsupported (no carrier) acrylic adhesive tape that is 5 mils thick, can handle operating temps of -40 to +300 and has a peel adhesion of 290 oz/in.  They also make a 2 mil version of the same tape (145 oz/in).  Their sales literature indicates it is a good tape for bonding acrylic and polycarbonate, though they make about 6-8 other tapes that may also work for your needs.  Scapa tape would be less $ than 3M, and likely just as good if not better.

It is Scapa's product number UC505 (and 2mil UC205); likely you wouldn't be able to get it directly from them, but most tape converters would have access to it from Scapa and the ability to convert it to the width you need.  It should be available (probably special order, but lead time should be short) at most any tape converter in the U.S.  (And I'm really not trying to sound like an ad here, because it is available elsewhere, but...) if you don't have luck finding it, we could help you out, if needed.

Hope that helps, even though it's late.
Compositepro (Chemical)
24 Mar 04 20:03
Pressure sensitive adhesives are usually not appropriate for long term tensile loads because they will creep under load until they fail. Your geometry also applies a high peel load on the adhesive at the edges of the holes. Your application is not an easy one to solve.

I would suggest a two part urethane that is applied as a thick film (~0.030") to your applique. The two part system allows room or low temp cure. The curing adhesive prevents creep. The thick bond line and low modulus of the urethane will minimizes the peel stress at the hole edges.
CalculatorDave (Mechanical)
29 Apr 04 20:03
A solvent cement would do a good job, but this is not a PSA.  Solvent cements actually dissolve the substrates, such that they fuse at the bond line.  The solvents then quickly evaporate, and you have a chemical weld.  Very strong.  Look at the Weld-On line of solvent cements from IPS Corporation.

David

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