Testing adhesion is the first measurable test when evaluating performance of a coating material, regardless of the type substrate - metal, wood, plastic, composite, paper, glass or engineered materials. In lay terms, this can be expressed as “does it stick to the substrate,” and if so, “what is the measure of adhesion?” The measurement of adhesion applies to all forms of coatings - liquids, powder coatings, varnishes and inks. A coating’s curing system or mechanism is independent of the measure of adhesion. Regardless of the type of curing - ambient air, thermal energy or radiation energy (UV or electron beam (EB)) - the coating has to “stick” to the substrate. A coating that is applied and cured correctly does not guarantee the coating will adhere to the substrate. Proper preparation of the substrate prior to coating is the most important and determinate factor in achieving the desired measure of adhesion for any coating on any substrate.
Preparing a substrate requires an understanding of the physical properties of the substrate, knowledge of the end use of the coated product, followed by identification, selection and use of the right pretreatment materials. Matching pretreatment materials and processes with the appropriate and desired coating materials assures the desired measure of adhesion is achieved after application and cure. Preparation or pretreatment of ferrous metals is well known; iron phosphate, zinc phosphate and zirconium pretreatment materials are ubiquitous, and these materials are compatible with many liquid and powder coatings. For most common industrial metal and wood substrates, there exists a broad platform of pretreatment materials and processes corresponding with coating materials that work well and comprise the mature general coatings market.