Using a treating solution which is easy to dispose after use, the surface of a plastic material is treated so that the treated surface has good adhesion to a coating film to be formed thereon. An aqueous dispersion containing an abrasive which is harder than a plastic material to be surface-treated, is pressurized to about 1.0-200 kg/cm.sup.2 and then is injected onto the surface of said plastic material through an injection nozzle. An airless spray gun having said injection nozzle is supported by a polyaxis type or articulated type robot. Thus, the surface of a plastic material is ground and converted into a rough surface and then coatings are applied thereon.
Improved methods of removing coating films from resin substrates includes first treating the resin substrates in an aqueous alkali solution with a concentration of 0.1 wt % or more at a temperature of 110.degree. C. or more, which temperature is lower than the melting point of the substrates and then polishing the surfaces of the substrates by either bringing them into contact with each other in suitable equipment such as a screw feeder, or using an abrasive in suitable equipment such as a high-speed vessel type stirrer, or subjecting the substrates to a liquid honing process.
A method of cleaning interior surfaces of fluid delivery systems including (a) passing through the system an abrasive cleaner composition including at least one liquid carrier containing solubilizable abrasive particles, at least some of which are in non-solubilized form, effective to abrade the material to be removed from the interior surfaces, and (b) rinsing the system with at least one fluid effective to (i) displace the carrier and (ii) remove the abrasive particles, at least partially by such chemical means as dissolution or decomposition or neutralization. Optionally, the method can include a first step of contacting the inside surfaces of the fluid delivery system with a pretreatment fluid capable of softening or loosening the material that is to be cleaned from the internal surfaces of the delivery system for a time sufficient to soften or loosen unwanted material. A cleaning kit including the abrasive cleaner and rinsing fluid is also provided.
