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Substrates Applicable for Coating with a Wet Film Applicator

A wet film applicator is suitable for coating on a variety of substrates, mainly including metal, glass, plastic, wood, paper and paperboard, as well as composite materials. Each type of substrate has its specific applicability and limitations.

•   Metal Substrates: Such as steel panels, aluminum plates, tinplate, and galvanized sheets. Due to their high surface hardness and good flatness, they are suitable for testing mechanical properties such as adhesion, impact resistance, and bending.

•   Glass Panels: Characterized by an extremely flat and transparent surface, they facilitate the observation of coating defects and the measurement of film thickness. They are commonly used for optical coatings, UV-curable coatings, and laboratory comparative testing.

•   Plastic Substrates: Such as PVC sheets, acrylic sheets, polycarbonate sheets, and PET films, suitable for testing plastic coatings and decorative coatings. It should be noted that some plastics have low surface energy and require pretreatment such as corona or plasma treatment to ensure uniform wetting of the coating.

•   Wood Substrates: Such as solid wood boards and medium-density fiberboard (MDF), suitable for testing wood coatings. Wood surfaces are rough and porous; before coating, they must be sanded smooth and the pores sealed. Otherwise, the coating will penetrate into the wood, resulting in a significantly lower film thickness.

•   Paper and Paperboard: Suitable for testing printing inks and paper coatings. Paper has strong water absorption; after coating, the wet film thickness will change rapidly due to absorption, so measurement must be taken immediately after application.

•   Composite Substrates: Such as copper-clad laminates and fiberglass boards.

Limitations

•   The substrate surface must be flat. An uneven surface will prevent the blade from fitting uniformly, leading to large deviations in coating thickness.

•   Flexible substrates (such as films and paper) must be fixed on a rigid platform using double-sided tape or vacuum suction. Otherwise, the substrate will move along with the applicator blade during coating.

•   The substrate size should be larger than the coating width of the applicator, with at least a 10 mm margin reserved at each end. Otherwise, edge effects will affect coating uniformity.

•   The substrate surface must be clean and dry. Oil stains and moisture can cause cratering (crater defects) and poor adhesion.

•   For substrates with a surface energy lower than 32 dynes (such as certain polyolefin plastics), the coating tends to retract or fail to spread. Pretreatment such as corona or flame treatment is required beforehand.

•   Substrates with excessive roughness are not suitable for use with a wet film applicator, as the blade cannot conform to the substrate surface, resulting in missed coating and severe thickness unevenness. If coating on a rough substrate is unavoidable, it is recommended to first apply a sealer primer or adhere a layer of flat PET film to the substrate before coating.