You will probably have to incinerate the paint solids to remove the latex & acrylic binders. Otherwise you will be trying to do the equivilent of grinding rubber (latex paint) or plastic (acrylic enamel). I am assuming you are really only trying to recover the pigments any way as they are the valuable part.

Then a small ball mill or similar should break up the lumps into a fine powder.

In a similar way, incinerating paper sludge is now being done in order to recover the clays present in fine paper without having to separate the fibre from the clay in a wet state. ■

I doubt if you will have much success grinding to 10 micron without removing the binding chemicals first.

Latex paint can remain paste-like in the middle of a hard lump for a long time. I know, I have cleaned up a lot of paint handling equipment and even after sitting for months it can still be soft underneath, and as soon as you hit it with a grinder or wire wheel the heat seems to soften it up again.

Paint line hooks are often baked in special ovens to drive off the solvents so that they clean up easily. If you can't burn the material, try baking it.

I have seen some rubber/plastics recovery processes which freeze the material with liquid nitrogen before shattering it in a hammermill or granulator type machine but I have my doubts about old paint.

Strongly suggest you try some small scale tests first before buying equipment or believing some salesman's claims.

If you could tell us what you are trying to achieve by grinding this material, the solution may be more obvious. ■

Are you trying to describe size reduction of a dried solvent or water-borne paint ("wet paint"), or a waste "powder paint" (otherwise called "powder coating")? We pulverize powder paint to D50 < 20 microns routinely, and can certainly do 10 microns. These are brittle plastic flakes before being mill in our air-swept classifier mill. Temperature control is an option. Cryogenic or near cryogenic milling is a another option for rubbery materials, if that is the case. ■