The paint industry often utilizes light-reflecting flaked pigments in paints or coatings to obtain pleasing aesthetic effects. Coatings containing light-reflecting flaked pigment of such materials as aluminum, bronze, coated mica and the like are characterized by a “two-tone”, “flip”, “flip-flop” or “flop” effect, hereafter referred to as flop effects, whereby the apparent color of the paint changes at different viewing angles. Surface coatings containing a metallic flake pigment (i.e., metallic coatings), for example aluminum flake, are especially favored for the protection and decoration of automobile vehicle bodies for their visual effects, such as differential light reflection effect, exemplified by flop effects and flake appearance effects, as well as the enhancement of depth perception in the coating. The flop effects are due to the orientation of the flakes in the paint film. The degree of the flop effects achieved is a function of the orientation of the metallic flakes with respect to the surface plane of the coating. To attain a maximum flop effect, ideally, the flakes should all lie in planes parallel to the surface plane in a coating. However, in practice it is not possible to obtain more than a proportion of the flakes lying truly parallel, the remainder lies at various angles to the surface plane, i.e. there is a distribution of the orientations of the metallic flakes in the coating. The orientation of the flakes is also affected by a number of other factors, such as the presence of visual effect control agents, curing and drying speed of the coating or temperature of the surface at the time of coating application, etc.
When repairing a coating defect on a vehicle coated with a metallic coating, it is important that not only the color, but also the visual effect of the metallic coating is matched. A number of technologies have been developed to achieve the color and the visual effect match. U.S. Pat. No. 6,952,265 disclosed a method and a device for characterization and selection of metallic flakes to match the visual effect of a metallic coating. US Patent Publication No. 2005/0128484 disclosed a computer-implemented method for determining color match. It is known to the paint industry, especially automobile vehicle refinish industry, that a number of visual effect control agents, such as rheology control agents can be used in a metallic coating to control or modulate orientations of the metallic flakes with respect to the surface plane in the coating. Flop adjusters can also be used for controlling orientations of metallic flakes in a metallic coating. Some typical flop adjusters are glass beads or silica and titanium dioxide pigment. One of ordinary skill in the art, such as a paint technician can select a paint formulation that includes desired metallic flakes, rheology or any other visual effect control agents, and any additional additives to produce a repair paint that generally matches the color and the visual effect of a metallic original coating of the vehicle around the coating defect. The repair paint is then applied to a repair area covering the coating defect after certain surface preparations known to the coating and vehicle repair industry, such as but not limited to, cleaning, priming or sanding. In order to make the repair less distinguishable from the original vehicle coating around the repair area, a blending technique such as edge feathering is usually applied. Edge feathering produces gradually reduced paint thickness at the edge of the repair area so a smooth transition from the repair paint to the original coating is achieved. Feathering can be done by gradually moving a spray gun away from the vehicle surface while spraying. It can also be done by gradual reduction of spray pressure while spraying. A combination of moving the spray gun and reducing spray pressure can also be used.
Current problem for metallic coating repair is that the edge of the repair area shows slightly different visual effect. After drying, the edge of the repair area is visually noticeable producing an undesirable edge effect. This is mainly due to the fact that when thickness of the repair paint is reduced, orientations of the metallic flakes in the repair paint become randomized. Some attempts have been made by refinish industry to reduce the undesirable edge effect. One such attempt is to pre-wet the surface to be repaired with a layer of solvent or solvents and then apply the repair paint over the layer of solvents. However, pre-wet method failed to eliminate the undesirable edge effect.
It is therefore still in need for a method to repair metallic coating defects without undesirable edge effect.