Conductive paint is to add conductive powder such as silver, copper, nickel or graphite into the varnish, so that the obtained paint layer has conductivity. Commonly used varnish is polyurethane or acrylic varnish. In addition, anti precipitation agent and dispersant are often added to reduce the sedimentation rate of conductive powder and make it well dispersed. In order to prevent the oxidation of conductive powder, antioxidants are often added. The commonly used conductive powder is nickel powder. The coating process is as follows
1) surface preparation. If the molded surface is clean, it can be coated directly. If mold release agent is used in molding, degrease with a suitable solvent or degreaser. In order to improve the adhesion of the paint layer, the surface should be polished with fine sandpaper.
For foam molded parts, 72h should be degassed to prevent paint from bubbling.
2) apply primer. In order to seal the pores of the plastic surface and improve the adhesion of the paint layer, the primer should be applied first. The primer shall be matched with the conductive paint to prevent cracking, peeling, swelling and other defects.
3) prepare conductive paint. The appropriate paint and diluent shall be selected according to the type of plastic substrate and the requirements for the paint layer. The paint shall be fully mixed after dilution.
4) spraying. Generally, the common spray gun with the diameter of LMM nozzle is used for spraying, and the viscosity of the paint is l4-16s (measured by cone disk viscometer, NO2 cup). In order to make the conductive powder well suspended, it is necessary to use a pressure tank with spiral pulp for stirring.
Since the shielding value of the paint layer is related to the thickness of the paint layer, a minimum value shall be specified. The paint layer should not be too thick, otherwise it will produce nodules and cracks. Generally 40-60 μ M.
5) spray the top coat. From the perspective of decoration, and often spray another layer of finish. At this time, it is necessary to prevent the solvent of the top coat from infiltrating into the conductive paint layer and eroding the solvent sensitive plastic matrix.