Overmolding Noryl GFN3 over PC

[joeprocess]

Working on a new project that requires a PC Lens to be over-molded with a Noryl housing or visa versa. The lens must have a water tight seal. Any thoughts or experience with this would be appreciated. The housing is visual and the lens will cover an LCD screen.

[rickbatey]

At a glance with these resins I'd say mold the lens then over mold next. I think the lens melt temp will hurt the housing resin to the point of failure. Just exactly do you plan to over mold them? Transfer from cavity to cavity, rotating platten or table, or in different molds and machines? That might be a bigger point to define.
Rick.

[joeprocess]

It's low volume so it would be two separate molds. I personally don't like the idea at all being low volume and with two materials that I do not believe will bond too well together. Especially to create a waterproof seal.

[JayDub]

If the two materials are not chemically compatible, the only way you are going to get a reliable seal is to mold the hotter PC over the PPE, so you reflow the PPE and get some mixing at the interface. Depending on the design, this could be really ugly looking though, and as Rick says you do risk inducing failure. If you keep the mold temp high, it may help by acting as a cooling/annealing fixture, at the expense of a long cycle. Then again, if you mold the PPE over a rigid PC part, you might get stress cracking as the PPE shrinks, especially if there are sharp corners. Oh well, if it was easy they would have sent it off-shore …

[rickbatey]

You're going to spend weeks finding how long the first part must sit and cool to meet proper dimensions to allow for over molding. Plus trying to first mold good, clean and clear lenses before trying to pack them into something until they shrink enough and then re-handle them to load them into another mold, don't scratch or damage it, and not hurt the over mold. The sealing should be ok since the over mold will shrink tightly around the lens. Even so if put some land and grooves around perimeter to interlock the two parts. May the Molding gods be forever in your favor!!
Rick.

[joeprocess]

Thanks folks. I will let you know what was decided. We are trying to convince them to go with UV glue, which we have had good success with.