Spraying of Polymers

a method for producing thin coatings and thin-walled articles through the application of powdered polymer compositions to the surface of parts or molds. A continuous protective coating (or the wall of an article) is formed by heating the article (or mold), to which a layer of powder has been applied, above the melting point of the polymer, or by holding in an atmosphere of a solvent vapor, in which the polymer swells. Among the methods used in industry for spraying of polymers are the flame and fluidized-powder methods, coating in an electric field, and a combination of the two (called the electrostatic fluidized-powder method); the jet and plasma methods are less widespread.

In the flame spraying method, the powder is atomized by a special gun, which is combined with an autogenous burner. As the particles of the powder strike the part being coated, they coalesce to form a continuous film. In the fluidized-powder method, the part or mold is preheated and immersed for several seconds in the polymer, which is in a fluidized state. During spraying in an electric field, charged particles are deposited on the part, which carries the opposite charge. In jet spraying, the powder is atomized by means of a special pneumatic atomizer; in plasma spraying, it is atomized under the short-term action of an ionized gas (plasma) at a temperature of 15,000°-30,000°C. The most widespread industrial method is spraying of polymers in an electric field. It is simple and easily automated, and powder losses are minimal.

Polymer spraying is used to produce anticorrosion, decorative, and electrical, thermal, and acoustic insulation coatings on metals, concrete, glass, and ceramics. Some large hollow articles, such as tanks, are also produced by spraying of polymers. This method is 2–3 times less labor-intensive than the production of paint and varnish coatings and 5–10 times less labor-intensive than the production of galvanic coatings.

Polymer spraying uses a broad range of powdered materials, including those derived from high-melting polymers, such as the polyfluoroethylene resins. These materials do not contain organic solvents, which is important from an economic and health standpoint. Polymer spraying requires observation of the principles of protection from static electricity and the use of airtight equipment, as well as the use of remote monitoring and control. It was implemented in industry during the 1950’s. The method was used in 1972 for the production of about 14 percent of all protective coatings in the industrially developed countries of Western Europe.