Conventional Release Systems

Many of the same factors that cause hazing also cause streaking. In our experience, streaking that occurs on application of release is most often the result of contamination, entrapped moisture, or improper application techniques. Presuming that the mold was cleaned properly, how you apply the release can have a big impact. Both sealer and release should be applied in a light even coating, using clean 100% cotton cloths. Do not use synthetic cloths because the solvent in the mold release can dissolve this type of cloth and cause streaking. DO NOT REUSE CLOTHS.

Shop environment and atmospheric conditions can play a major role in aggravating streaking. Hazing can occur when molds are cooler than air temperatures. This can result in condensation being trapped within the mold release coating as it cures.

Haze On The Mold After Applying Release (before molding): This can be caused by reaction of the release with contaminants on the mold surface; styrene in the mold blushing to the surface and becoming entrapped; entrapment of moisture in the curing release (particularly in very humid conditions); contaminated application cloths or wipes; condensation (particularly when molds are cooler than air temperature).

Haze That Appears After Molding: Heat as a catalyst can drive moisture, un-reacted styrene or other un-reacted materials up through the mold matrix during the molding process, entrapping them between the mold surface and the semi permanent film. Over several molding cycles the styrene can also polymerize leaving a tenacious film on the mold surface. Compounding is the preferred method of removing this buildup.

First, evaluate the area that is sticking. Perform a tape test in various spots on the mold to determine if the problem is related to application. Is it a consistent problem in one area or in one mold? Perhaps the sticking is related to abrasion, sheer edges, or draft angles. Is the area that is sticking a difficult area to reach when applying mold release? It may also be an area that simply requires more frequent touch ups of release, such as sheer edges or other areas of abrasion.

Gel Coat Over-Spray: Gel coat over-spray has been catalyzed. Even if the film over-sprayed on the mold is thin, it will eventually get hard. If the over-spray has not cured it can usually be wiped off with a cloth dampened with a high quality mold cleaner and then followed by a re-application of mold release. If the over-spray has cured, and the mold has release agent on it, it can sometimes be wiped off with a cloth saturated with a high quality mold cleaner and then followed with a re-application of the release. Or, simply let it totally cure and just peel it off the mold surface. If the mold surface has no release on it and the over-spray cures, in most cases it must be compounded off.

Raw or un-catalyzed resin: Dampen a cloth with a high quality mold cleaner and wipe the raw resin off the mold surface. Use as little mold cleaner as possible and as little pressure in removal as possible to avoid removing an excessive amount of release from the mold. However, you must ensure that you totally remove the un-catalyzed resin from the mold surface; since a thin uncured film of resin could lead to problems on the next de-molding. Having removed all of the uncured resin from the mold surface, reapply mold release and continue processing.

By taking a few precautions, you can achieve the same production from these types of surfaces as from a polished smooth surface. Buildup in non-skid areas generally can be seen as the same color as the spray-up gel coat. The cause of buildup in the grooves of the pattern usually result from either: 1) failure to apply the release into the tips of deep recesses in the pattern which causes small bits of gel coat or resin to bond in the tips with each cycle, or 2) excess release agent pooling in these areas because of poor application technique. When excess release is present, it does not have a chance to dry or cure thoroughly, or to develop full chemical resistance. The release films over on the surface and can attract free styrene from the gel coat or resin used to mold parts. This can occur because styrene in the resin acts as a solvent, penetrating the heavier areas of release and accelerating the buildup and sticking in these areas. To reduce the buildup and sticking concerns, care should be taken to thoroughly brush out and polish the release into these deep patterns without leaving a heavy residue.