You are correct in the intention of primer in general is to help paint to stick to a surface, but this is a slightly different situation. Any Tamiya lacquer will stick to plastic just fine. They are roughly all the same formula except for the gray self etching primer which is primarily for R/C metal parts. What you are referring to is the surface bonding action of a "self etching " primer which is necessary for bonding paint to metal.sky1911 wrote: ↑Mon Feb 01, 2021 4:57 am Pete, does that even work? I mean, isn't the primer supposed to prepare the surface, ie serve as a bonding agent between the plastic and the following layers of colour to give them something to grip onto?
Spraying silver first then primer seems counter intuitive to me in that regard. But I am happy to learn something new every day and if this works, even better
When a self etching primer is applied to plastic it will to some degree or other make a mess of the surface underneath. Try spraying etching primer on plastic and sand it off and you will see what I mean. I have used automotive based self etching primers on plastic for years and it has a profound effect on the underlying plastic. This is most noticeable if you use Super Clean to remove the paint to start over. The surface is no longer smooth plastic.
Having said that, all Tamiya lacquers(TS and LP) will stick the same way to plastic. There is no issue with adhesion of the base. The white has two purposes. The first has to do with acrylics. Acrylics don't chemically bond to plastic the same way as lacquers do, so when using alcohol based paints it is necessary to provide the additional adhesion of a lacquer based primer to assist with the adhesion, but the surface key of the primer is what the acrylic paints use to stick to the plastic. This is not necessary when laying down lacquer top coats.
In the case of lacquer, primer is there to give you a consistent, even colored surface to apply the color over. This becomes particularly important with some colors like reds and yellows. These colors are more translucent that others and the substrate color will significantly impact the look of the color sprayed over the top. Try laying down a coat of white primer, mask off a straight line and spray gray primer next to it. Then top coat it with Tamiya red or yellow and you will immediately see the difference. The gray side looks dead. You will have to spray on a lot of paint on the gray side to get rid of that dead look. This is also the reason that Tamiya offers a pink primer for florescent colors. Just a little fun fact about reds. Ferrari uses either a pink or orange primer in the factory to get the exact shade of "Ferrari" red they want. This can be a real problem in a restoration shop. This is why a lot of model paints don't quite look "right" for the Ferrari colors.
The real problem we are discussing here is the dyes in the plastic bleeding through the base layer and passing through the relatively porous layer of primer. To stop that you need to put a sealer barrier between the plastic and the primer. The metallic pigments in the bright silver provide that layer and white primer will stick well to the silver and give you the color you want. You could just use the silver as a primer but then that changes the look of the paint also. However the silver can give you a spectacular custom color. Try it. Mixing base colors and top coats is fun.