Adhesion to Oil-Contaminated Paint and Varnish Coatings

When tested 8-10 days after painting, the adhesion of glass particles to the chlorinated PVC coating was found to be somewhat greater than when tested after 25-30 days. After 10-12 months, the adhesion again increased as a result of breakdown in continuity of the film. The dust-retaining tendency of an oil-base paint was also found to drop off gradually, but in this case the reversal of the trend and the subsequent rise in adhesion took place in only 2-5 months. 

The tackiness of paint and varnish coatings may be reduced by the use of fast-drying film-formers or by fluid-bed application of a solvent-free paint. 

Influence of Thickness of Oil Layer on Adhesion. Atmospheric dust generally contains not only solid particles, but also oily contaminants, which settle on surfaces and make the surfaces oily. Also, the surfaces of some objects such as motor vehicles may become oily in the operating process. It has been found that 17% of the adherent particles on the surfaces of motor vehicles operating in Moscow do have such a layer of oil. Roughly the same results were obtained in an analysis reported in [234] on the contaminants appearing on exterior surfaces of railroad rolling stock. On a locomotive, for example, 23% of the adherent particles were in contact with oily surfaces, and on the railroad cars the figure was 19%. The presence of oily contaminants on surfaces tends to increase particle adhesion because of tackiness this is illustrated by data shown in Table VIII.8 [11]. 

TABLE VIII.8. Adhesion Number On %) for Spherical Glass Particles with 40-60-Mm Diameter 

The mechanism of adhesion on an oily surface can be represented as follows. The thicker the oil layer, the more deeply will the particles be embedded in this layer. With a certain thickness of the oil layer, equilibrium is reached between the forces tending to bury the particles (weight and inertial forces) and the resistance of the oil layer. Then, within a certain interval of oil layer thickness, the adhesive force will be independent of the degree of oiliness. As the oil layer becomes still thicker, it acquires the property of fluidity, and adherent particles may be removed along with the oil. The adhesion of particles to an oily surface will depend not only on the thickness of the oil layer, but also on its viscosity, i.e., on the content of binder components in the oil (for salt pastes, for example, MgCl2,CaCl2,etc. [235]). 

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