I will explain the reasons why the coating peels off.
We compared samples with and without a primer. For surface preparation, we degreased with cleaning thinner and roughened the surface with sandpaper. The painting specifications used an epoxy-modified resin paint for the primer and an acrylic-modified phthalic resin paint for the topcoat. After allowing sufficient drying time, tests were conducted. When removing the masking tape, the area without primer had the paint peel off with it. The primer has a high adhesion to the substrate, and when used together with the topcoat, it maximizes the performance of the paint. Skipping the primer may result in a visually appealing finish, but the performance of the paint is compromised. By performing blast treatment, a stronger paint film can be formed. Omitting the primer reduces the adhesion of the paint, making it more prone to peeling and deterioration. The combination of primer and topcoat allows the paint to adhere to the surface, enhancing the strength and durability of the paint film. The primer is an essential process for maximizing the performance of the paint and ensuring quality. While it is possible to shorten the process by omitting it, this will affect the durability and quality of the coating.