Composites

Removal of semi-permanent release agent in composites moulding processes can be more difficult due to the toughness of the cross-linked coating. The recommended procedure is to use a specially designed cleaner or a buffing compound to ensure that all of the coating is removed.

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 mould was cleaned properly, how you apply the release can have a big impact. Both sealer and release agent should be applied in a light even coating, using clean 100% cotton cloths. Do not use synthetic cloths because the solvent in the mould 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 moulds are cooler than air temperatures. This can result in condensation being trapped within the mould release coating as it cures.

Haze On The Mould After Applying Release (before moulding):

This can be caused by reaction of the release with contaminants on the mould surface; styrene in the mould 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 moulds are cooler than air temperature).

Haze That Appears After Moulding:

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

If you are evaluating any mould release, we suggest that you totally strip a test mould and prepare it according to the manufacturer’s instructions. This is the only way you can gauge performance and understand the specific application process.

When testing any mould release, we always suggest that you select a test mould that is representative of your production, and one that is expendable in the event of a mishap occurring while testing. Always perform a tape test in several areas of the mould to assure that it is clean (tape should adhere well). Similarly, always perform a tape test on several areas of the mould after applying sealer and release (tape should release easier than on a clean surface).

Seasoned Test Mould Previously Prepared with Wax

This includes any kind of liquid wax, paste wax and waxed based sealers. Remove all foreign matter from the mould surface with a high quality mould cleaner and a cotton cloth. We do not recommend applying a semi-permanent directly over waxes, as this will compromise the bond of the semi-permanent mould release to the mould surface.

Seasoned Test Mould Previously Prepared with a Semi-Permanent Release

All semi-permanent mould releases are not the same. Many, however, are compatible with each other, which means one can be directly applied over a cured film of the other without stripping or compounding the mould. Test a small area with a high quality mould cleaner. Next, apply a coat of the new semi-permanent release. If the initial coat is difficult to apply (wets poorly), streaks or behaves unusually, STOP, and strip the mould. If everything appears as usual, follow this procedure for the entyre mould.

Pre-releasing is another issue that has many contributing factors. Mould design, laminate schedule, resin formulation, gel coat formulation, improperly calibrated spray equipment, gel coat cure time, under or over catalization, shop temperature, humidity, and external heat sources – to name a few – can all lead to pre-release. Most semi-permanent mould releases have a lower surface coefficient of friction than conventional paste waxes, which is why they are more often implicated in pre-release. If all factors other than mould release have been addressed, you may be able to reduce the incidence of pre-release by lightly wiping areas where the mould is pre-releasing with a high quality mould cleaner to slightly alter the surface tension.

First, evaluate the area that is sticking. Perform a tape test in various spots on the mould to determine if the problem is related to application. Is it a consistent problem in one area or in one mould? 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 mould 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.

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 colour 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 mould 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.