Selecting then testing polymer for life time exposer to high temp

[GRF]

I am looking for a material to over mold a PCB, there will be a clear PC lens on top, a PVC supporter (with lens captures PCB in the mold) and 2 nylon wires that run through the part. Size is approximately 2"L x .8"W x.25H" We have used a TPE but when exposed to 90C temperature the material on the top surface cracked and started to pull away, it looks like it is drying out.

I now need to find a new material and need some criteria to help select the material based on datasheet information. I also need to establish some testing to validate the material will work.

We have tried to mold ABS and PA612 but the board warps and the PC lens is deformed. That was how we originally ended up with TPE. We thought about using a a TPU but the loading time off all the components is too long for the TPE and it foams in the barrel.

Any information or direction you can give is greatly appreciated.

 

[Compositepro]

Might be a good application for liquid silicone rubber (LSR) molding.

 

[GRF]

I am going to guess the LSR is more expensive than the TPE material but something we can consider.

We are also considering a TEEE and a TPEE.

Do you have any suggestions on how to evaluated if the material is acceptable based on a data sheet. We relied on the contract assembly house to select the material last time. Now my boss wants me to select the material and prove it should work before shooting parts.

 

[patprimmer]

Will the PVC and PC be exposed to the molten polymer and injection pressure during over moulding. If so how well are they supported. Is the distortion purely due to temperature, or is it a component of combined load and temperature.

You do know that often, the plasticisers in PVC can migrate and solvent stress crack any PC in the vicinity.

Can you use a casting resin or two pot.

What temperature resistance does the finished product need.

Regards
Pat
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[unclesyd]

would Ryton be applicable to your product?

http://www.cpchem.com/bl/rytonpps/en-us/Pages/default.aspx

 

[GRF]

patprimmer

Yes, the Sabic rep gave me the heads up on the pc and PVC issue. The two do not touch each other.

 

[GRF]

Thank you all for the material recommendations.

Does anyone have a suggestion on what standard tests (SAE, ASME) are done to evaluate plastic materials for high temperature?

Thank you for your time and help,

 

[patprimmer]

There will be tests for Heat Deflection Temperature or HDT at two different loads. This is a short term test to determine load bearing ability and there will be a Continuous Use Temperature which is a long term test to determine degradation of the polymer over time. I don't remember the ISO or SATM numbers, but they will be on the data sheets when YOU look them up.

UL ratings also exist for temperature ratings of electrical components.

Regards
Pat
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[unclesyd]

To get the different test numbers look at the manufacturer data sheet for a particular polymer. The normal is to list a value and give the particular test used to get that number. To get all the available test you may have to look at several data sheets.

There are also proprietary tests used for specific polymer applications. Like we used one where we made a film and blew a bubble until failure at a specific temperature. The film had to take a certain air pressure on a 5" bubble.