The coating film rises into blisters or cracks into skins. Defects of cracking, bubbles, and shedding are usually found when the color-coated roll is re-rolled or during customer use. The cracking phenomenon is usually a visual crack or crack found during the use of the color-coated plate. The cracks are small to large, and eventually lead to film layer is completely destroyed. The peeling phenomenon is usually the phenomenon that the coating falls off the steel surface in flakes, accompanied by partial or complete peeling off.
According to the degree of exfoliation, it can be divided into: small pieces with a diameter of about 5mm or less are called scale exfoliation, local exfoliation with a diameter of more than 5mm is called cortex exfoliation, and those that are larger than the exfoliation of the cortex (or torn off) ) is called peeling and peeling, and the peeling between the top coat and the bottom coat is called intercoat peeling.
cause:
(1) Improper coating pre-treatment, the substrate has wax, oil, water, etc., and its pressure will bulge the paint film when it spreads outward, especially for products with poor air permeability, which affects the adhesion between coatings;
(2) Covering the top coat before the primer coat is dry, resulting in poor adhesion between the two layers of the bottom surface, or complete loss of adhesion;
(3) The interval between surface treatment before coating and coating construction is too long;
(4) There are pinholes, missing coatings and bubble defects inside the coating, which make the coating film bear stress, especially when stresses such as the quenching process and the coating film fatigue process exist, the film layer is prone to cracking;
(5) The coating is not suitable, and the base coat or top coat is too thick;
(6) Improper choice of coating or mismatching of the bottom coating will cause poor adhesion between coatings, poor mechanical properties and poor flexibility of the coating, which will cause the film to crack when subjected to drastic temperature changes or compression.
Method of exclusion:
(1) Before coating, ensure that the substrate is free of wax, oil, water and other sundries and that there are no cracks on the surface;
(2) Ensure that the undercoat is completely cured before applying the topcoat;
(3) The variety of bottom coating with good matching should be selected to improve the adhesion between the coatings, and the thickness of the bottom coating should be strictly controlled according to the process requirements during construction;
(4) Strictly control the quality of the coating on the machine to avoid defects such as "pinholes" and "bubbles" during coating construction;
(5) Color-coated rolls should not be used in places with rapid temperature changes immediately after they come off the assembly line.
