Painting plastics can often be somewhat a bit tricky. This shouldn't be the case providing the correct products are used and if the method of using them is correct the user can achieve good results.
First lets take a look at some plastics used on vehicles and why they need to be painted using different products compared to other substrates.
There are two key categories to plastics. Thermoset Plastics and Thermoplastics.
Thermoplastics - these can be easily plastic welded, recycled and melted. These are generally more Flexible than Thermoset. Some examples of Thermoplastics are;
ABS (Acrylonitrile Butadiene Styrene)
There are many more but the above are some common examples.
Thermoset Plastics - These are harder to plastic weld ,(but can be done) and cannot be recycled. Thermosets are as the name states, they are set once cured. The curing of this plastic is not too dissimilar to the 2K paints we use today. They are cured by crosslinking of polymers. Some examples of Thermosets are;
Now we understand the two key categories of plastics, one thing to note is they can both be painted.
Plastic adhesion promoters are generally made using polyolefins these are resins that come from a plastic. One way to create a similar product to this is to get a heat gun and warm plastic up until it 'sweats' and the plastic will extrude an oil like resin. This is a polyolefin resin. Which is why some older methods to coating plastics are to use a blow torch to create the above method and then overcoating. Of course this can warp the plastic and cause other defects which is why it is not reccomended to try.
Because plastic adhesion promoters are polyolefin based they are best used on plastics such as PP, EP, TPO or EPDM. There are more. A small test panel should be trialled to make sure you are happy with the adhesion on that substrate.
Are Adhesion promoters that contain silver better quality?
No, this doesnt mean better quality. Adhesion promoters that contain silver is usually so commercial users are able to see where they have applied the adhesion promoter as with this product being clear it is hard to see when applied. The silver highlights this area.
Do not add metallic basecoat to the adhesion promoter!
some users think that all the difference is between clear and silver is by adding a bit of silver basecoat in the primer. This is very bad as solvent basecoat contains a wax to help with metallic orientation. This wax does not have any adhesion properties to plastic and could cause the coating on the plastic to peel off.