WACKER® G 795
WACKER® G 795 is a solution of various reactive siloxanes and silicone resins in a mixture of isoalkanes. After the solvent has evaporated, a rigid film of silicone resin is formed on exposure to atmospheric humidity at ambient or elevated temperature and firmly adheres to the substrate. The catalysed silicone rubber applied on top will then form a tight bond to this resin film during vulcanization.
Surfaces to be primed should be dry and free from grease, oil or other contaminants. The surface should first be cleaned with a non-polar solvent such as mineral spirits (at a boiling range of 80 °C up to 140 °C), followed by a polar solvent, preferably acetone. Loose particles must be removed, and very smooth surfaces should be roughened by grinding. The primer is best applied with a brush, although dipping or spraying can also be used. On relatively smooth, non-absorbent surfaces such as aluminum, the primer should be applied as thinly as possible and free of air bubbles. On very rough or absorbent surfaces, such as plywood, the coating should be applied quite liberally.
The reaction time of the primer film is at least 1 hour at ambient temperature (relative atmospheric humidity must be at least 40 % and should be monitored using a hygrometer) or 10 minutes at 100 °C (the latter only applies to metallic substrates).
The catalyzed silicone rubber should be applied to the primer coat immediately after the drying or heating process, if possible, but at the latest after 5 hours since otherwise a drop in adhesive strength may occur.
Important Maximum adhesive strength will only be achieved after 4 days. But usually after 24 hours sufficient adhesion will have developed to allow pad demolding without any problems. Once opened, containers of WACKER® G 795 should be kept well sealed and stored in a cool and dry place.
Bonding agent preferably used with addition-curing RTV-2 silicone rubbers from, among others, the ELASTOSIL® M and ELASTOSIL® RT ranges to achieve adhesion to metallic and non-metallic substrates.
Even silicone rubber formulations modified with large amounts of silicone fluid, of the kind commonly used for making printing pads, will develop excellent adhesion to aluminum or plywood carrier plates when WACKER® G 795 is used.