Surface cleaning processes coating effectiveness

As with adhesive bonding, surface treatment emd cleanliness is of primary importance when decorating plastic parts. Prior to decoration, the svirface of the plastic part must be cleaned of mold release, internal plastics lubricants, and plasticizers. Plastic parts can also become electrostatically charged and attract dust. This could disrupt the even flow of a coating or interfere with adhesion. Solvent or destaticizers may be used to clean and eliminate static from plastic parts prior to decorating. Cleaning of the plastic part requires an understanding of the plastic material to be cleaned and the effect of the solvents and processes on that plastic. 

Fouling of the pH sensor may occur in solutions containing surface-active constituents that coat the electrode surface and may result in sluggish response and drift of the pH reading. Prolonged measurements in blood, sludges, and various industrial process materials and wastes can cause such drift. Therefore, it is necessary to clean the membrane mechanically or chemically at intervals that are consistent with the magnitude of the effect and the precision of the results requited. 

Improved processes and quality control have helped to establish these new coating materials but the care necessary for successful use has to be appreciated. Sections 11.1 and 11.2 have shown how necessary it is to remove millscale before coating and how scale-free surfaces may still retain seeds of further corrosion even when apparently cleaned well. The percentage of premature failures with sophisticated systems is still high, even on apparently well-prepared surfaces and there is a strong case for effective inspection at each stage of coating operations. 

When the direct-on process is utilized, surface preparation requirements are more critical to ensure effective enamel adhesion. The acid etch is often deeper and the nickel deposition is always thicker. Typically, the nickel coating is 0.01 to 0.02 g/m2 for direct-on coating as compared to 0.002 to 0.007 g/m2 for two-coat applications. A few porcelain enamelers prefer to omit the nickel deposition step. Although the nickel enhances enamel bonding, product quality requirements may not require nickel deposition. The omission of the nickel step necessitates the utilization of a heavy acid etch to ensure a clean, properly conditioned surface for enamel bonding.3-6... 

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