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Application of Film, Film / Paint Drying Time & Viscosity

Application of Film preparation, Drying Time & Viscosity

A good Wet film preparation is not only important for the durability of the coating when it is dried, but also very crucial in terms of film thickness uniformity, color, and appearance. For the applicator, wet film preparations help determine methods of application and device adjustment. While some paint manufacturers will indicate the amount of wet film to be applied in order to obtain a certain dry film, others prefer not to, as paint applicators differ in the amount of thinner used. There is a wide range of devices used for wet film preparation, ranging from the common drawdown bar to automatic film applicators / machines or paint film applicators. Since Automatic film applicators can be set for constant speed and pressure, they ensure consistency of drawdowns, which is not the case when many operators draw down the same film.

 

Wet film takes time to dry and cure. The different stages of drying and curing can be accurately detected using a recorder under controlled environmental conditions. The wet film drying process begins with the shrinking of the paint and the appearance of a thin film on the surface. The end result of the curing process is a dry film or volume solid on the substrate. Operators often use two methods, depending on whether a thinner is added or not, to calculate the approximate dry film thickness (end result) from wet film thickness applied. Calculation without Thinner: Wet Film Thickness (WFT) = Dry Film Thickness (DFT) ÷ Percent Solids by Volume: Calculation with Thinner: WFT = DFT ÷ (Volume solids content ÷ 100% + % of thinner added).  ASTM D5895 defines the standard test methods for evaluating drying and curing during film formation of organic coating using mechanical recorders.

Higher viscosity of a film means high resistance to flow or deformation. 

 

 

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