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How to achieve a good bond between RTV silicone rubber and other materials

rtv silicone rubberBecause of the non-stick properties of RTV silicone rubbers, special measures have to be taken to make these materials stick to others, e.g. by applying a suitable primer to promote adhesion. Primers are low-viscosity solutions of reactive silanes or silicone resins. Evaporation of the solvent leaves behind a film, which cures at room temperature through atmospheric humidity, or by application of heat. This film causes adhesion between the substrate and the subsequently applied RTV silicone rubber.

 

The primer used will depend on whether the surface is absorbent or non-absorbent, selection being according to the following criteria:

• To promote adhesion between RTV silicone rubbers and absorbent surfaces, Primers are recommended. Absorbent surfaces generally require the application of several coats of primer.

• To improve adhesion, it is best to roughen the surface with sandpaper. Metals should be sandblasted if possible. This is followed by removing the abrasive dust and thorough degreasing with acetone or white spirit. Plastics can also be cleaned with acetone, provided they are not attacked by it. White spirit can also be used for this purpose. In the case of wood, all that is normally necessary is to ensure that it is clean. If necessary, it can be planed or sanded down with emery paper.

 

Primers may be applied by brushing, spraying or dipping. Drying times vary between 30 and 60 minutes at room temperature. Adhesion may be improved by baking the resin film for 10 minutes at 130 – 150oC after it has air-dried. Maximum adhesion to the primed surface will develop about 48 hours after vulcanisation at the earliest.