Лако-красочные материалы — производство

One of the important characteristics of a pigment is its inertness to chemicals it may come in contact with. These chemicals may be paint ingredients or others that come in contact with the coating film. Resins, cross-linkers or certain additives may show reactivity toward a pig­ment, causing noticeable change in its performance. The chemicals that may come in contact with the coating film include water, soap or detergent in domestic situations, while in some industrial coatings, it may be strong acids or bases, acidic sulfide fumes or some oxidizing or reducing agents. This exposure may result in discoloration, fading or, in the worst cases, degradation of the pigment. Reactivity of pigments with paint ingredients may result in unacceptable viscosity increases or even gelation. For coatings that come in contact with food materials, it is essential that not only the coating but also the food is unaffected.

Evaluation

Chemical resistance tests are classified as short, medium or long­term resistance properties. Because of diverse and unique demands of coatings, limited published data is not reliable, and therefore it may be necessary to design special tests to reproduce conditions found in practice. Most test methods for chemical resistance of a pigment involve incorporation of the pigment in a coating prior to analysis, and seldom is the pigment analyzed as such. The test is carried out by kee­ping the coating surface in contact with the chemical for a predefined time and then examining for discoloration or staining.