thermoforming white film on clear parts !!!

[rwolf]

hi all . i work for a sign company and last year i took over the thermoforming process. i know nothing about it. the whole process i am learning as i go. i have a female mold that has an MDF base and i am pulling 3/16" polycarbonate that is clear. i keep getting an white film on the face of my part???? i need ur help. when u get a chance. any ideas??

[spektr]

I'd cruise over to the tk560.com forum and ask there.
while you do that, describe the tool, and the process temps.
Also what masking came on the part, cling film or acrylic glued
clear film. are you forming film on or off, how big a part, what
machine etc......

Scott.

[Geof]

Are you baking the polycarbonate before heating it for forming. Polycarbonate adsorbs water into the surface and if this is not driven out by a low temperature bake before heating to forming temperature it can cause the formation of bubbles.

[rwolf]

the mask on my poly-carb is a cling type mask. i am forming with the film off. the part size is 36"x42". the part is a embossed pan sign face. max depth 2". the top of the mold is made from mahogany, then the draft angle is made from repro, and the bottom plane of the mold "face surface" is made from MDF. this area is where i am having the white film transfer. our mold maker prepped this surface with sanding sealer, then liquid wax . . .is this wrong? is this where my mysterious white film transfer is coming from? THANKS

[spektr]

absolutely wrong. never use something that melts below forming temp on any mold. You might get away with wiping the formed part with NAPTHA. This degreases most lexan smear problems. I also have very good luck with Methanol for cleaning........ Scott.

[rwolf]

I was under the impression that NAPTHA would "melt" my formed part??? This would not be good as is this is a clear sign face and has to be 100% translucent. THANKS

[spektr]

I manufacture lexan windshields, Naptha removes marking inks very well, Methanol is good also. MEK and Acetone will destroy lexan really fast. the reason I said you might get away with it is that I am uncertain of the soluability of your sanding sealer in Naptha, not that that I was concerned for the health of the plastic.....

[rwolf]

Ok so is there a certain brand of naphtha that i should try? also what is the application, and or the removal process. i have tried some and it just doesent seem to be working.

[spektr]

I'm fairly certain you are getting smear off the tool. There are basically 2 possibilities here. 1) that it is removable with the proper plastic friendly solvent. 2) That there is a reaction occuring involving the "stuff", heat and the lexan itself. If tha3ts the case I cant help you.

Naptha is a generic solvent, nothing exotic about it. Wet a cotton cloth wipe the plastic wet and look to see if the smear comes off. Methanol sometimes gets stuff Naptha wont touch, try them both.

But most importantly, fix the tool........