It would be helpful to know the reason you are painting the subfloor. Anytime you paint raw wood, IMHO, I use an oil based product for the first coat. Any water based product will raise the grain of the wood be it plywood, mdf, chipboard or the back yard tree. Understanding your goal with the floor will help give you a better answer.
I agree, we need to know what you're doing. Particle board is not a suitable subfloor for just about any kind of flooring. It was pushed back in the '80's because it was cheap, but has proven to be a very bad choice for subfloors.
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