JPH0338916B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for painting a vehicle exterior panel, and more particularly, to a method for painting a vehicle exterior panel including a step of applying a vinyl chloride sol-based primer to prevent rust from flying stones on the lower side of the vehicle, which is susceptible to flying stones. . Vehicles, especially automobiles, have their outer panels uniformly painted to maintain a good appearance and prevent rust from forming. Particularly, lower parts of automobiles, such as side sills, lower fenders, and lower ends of skirts, are susceptible to chipping due to falling stones, and there is a need for countermeasures against rusting in the peeled parts. Conventionally, in order to prevent paint from peeling off on the lower parts of automobiles, a solvent-free vinyl chloride sol-based primer based on vinyl chloride resin has been applied prior to intermediate coating and top coating. For example, as shown in Fig. 2a and b, when painting the side sill 1 of an automobile, pretreatment of degreasing, film formation, and washing with water is performed using well-known methods, and then electrodeposition is applied as an undercoat using the depping method. The undercoat film 2 is formed by the following steps. After this, a drying process is performed for about 20 minutes at a coating film temperature of 165°C.
The treatment up to this point is uniformly applied to the entire vehicle body, and then only the side sill 1 is sprayed with a PVC sol-based primer to form a PVC sol-based primer coating 3, and this coating 3 dries. Treatment is carried out at a coating temperature of 100-120°C for approximately 15 minutes. After this, apply an intermediate coat by spraying uniformly over the entire car body.
Subsequently, top coating is performed by spraying to form an intermediate coating film 4 and a top coating film 5. Thereafter, the intermediate coating film 4 and the top coating film 5 are dried for about 20 minutes at a coating temperature of 150° C., and the painting of the side sill 1 is completed. In such a conventional coating method, after drying the PVC sol-based primer coating film 3, intermediate coating and top coating are performed, and baking drying is required twice in addition to the drying treatment after the top coating. This is because if intermediate coating or top coating is applied when the PVC sol-based primer coating 3 is wet, repellency, sagging, or cratering may occur due to poor compatibility between the primer coating 3 and the intermediate coating or top coating. This is because there is a problem in that partial dents a (indicated by two-dot chain lines in FIG. 2b) occur in the intermediate and top coats 4 and 5. An object of the present invention is to provide a method for painting vehicle exterior panels that does not cause dents in the intermediate and top coats as described above even when the intermediate and top coats are applied while the PVC sol-based primer film remains wet. purpose. In order to achieve the above object, the present invention uses a vinyl chloride sol mixed with an adhesion-imparting resin that improves adhesion to the electrodeposition paint as well as a polyester plasticizer that improves the adhesion to the intermediate paint. Continuously apply the primer, intermediate coat and top coat,
It is characterized in that it is then dried. Next, the present invention will be explained with reference to Examples. The side sill 1 located at the lower part of the vehicle body is first subjected to pre-treatments such as degreasing, coating and washing along with other parts by well-known methods (see FIG. 1a). Next, electrodeposition coating is applied mainly for the purpose of preventing rust, and an undercoat film 2 is formed (see FIG. 1b). After this, a drying process is performed for about 20 minutes at a coating film temperature of 165°C. Thereafter, only the side sill 1 is subjected to a spray coating treatment of a vinyl chloride sol-based primer. The weight percentages of the vinyl chloride sol primers used here are shown in the right column of the table below. In the left column of the table, conventional products are similarly shown.

[Table] Here, a phthalic acid ester, which is a phthalic acid plasticizer, is mixed into the vinyl chloride resin (base pair) to soften it, and it also improves the adhesion with the intermediate coating, that is, the compatibility between the two. A phosphate ester, which is a polyester plasticizer, is also mixed in to improve the properties. In addition to this, PVC sol-based primers also contain carbonaceous filler (including those with surface treatment to adjust hygroscopicity and those without treatment), and adhesion promoter to improve adhesion with electrodeposition paint. It contains a polyamide resin, lime as an additive to prevent foaming of the paint film, and a paraffin-based high boiling point solvent as a diluent to make it suitable for spraying. Next, an intermediate coating is applied on the PVC sol-based primer coating 3 along with other parts of the vehicle body to form an intermediate coating 4. At this time, the vinyl chloride sol primer has not yet dried, and an oil-free alkyd as an intermediate coating is applied onto the coating film 3 in this state. This oil-free alkyd has a molecular weight n between 2,800 and 3,400, and a resin component ratio of acrylic:alkyd of 30:70 to 70:30. After the intermediate coating and before drying of the intermediate coating film 4, a top coating is performed and spray coating is performed to form the top coating film 5. In this PVC sol-based primer application process, no drying process is performed during the topcoat, and after that, the drying process is performed at a coating film temperature of 150℃.
After about 20 minutes, painting of side sill 1 was completed. The painted surface of the side sill 1 obtained in this way has improved compatibility between the PVC sol-based primer and the intermediate paint, so dents due to repelling of the intermediate paint do not occur, and the appearance is good. A painted surface is obtained. In addition, Fig. 3 shows three coats of the conventional type and one coat of PVC sol-based primer used in the method of the present invention.
Comparative data on repellency and amount of cratering (number of points/m ² ) when applied using the baking method is shown. As described above, it is clear that the vinyl chloride sol primer used in the method of the present invention can be used up to a film thickness of about 650 μm without causing any problems in terms of the aesthetic appearance of the vehicle.
Although the side sill 1 has been described above as an outer panel of the vehicle, the painting method of the present invention can be similarly applied to the lower part of the fender, the lower part of the skirt, etc. In this way, the conventional painting method required two drying treatments, one after applying the PVC sol-based primer and the other after the top coating, that is, three coats and two baking treatments after applying the PVC sol-based primer, whereas the present invention The coating method uses a PVC sol-based primer that has improved compatibility with the intermediate paint, so there is no need for drying after application.In other words, it only requires 3 coats and 1 bake after applying the PVC sol-based primer, reducing the painting time. The process can be shortened, and the drying equipment is only needed after the top coating, which can also simplify the equipment.

[Brief explanation of drawings]

Figures 1a and b are painting process diagrams and a cross-sectional view of the coating film of the present invention, Figures 2a and b are conventional painting process diagrams and a cross-sectional diagram of the coating film, and Figure 3 is a painting process diagram and a cross-sectional diagram of the coating film of the present invention. Comparative data diagrams of repellency and amount of cratering generated when applied with the invention method are shown. 1... Side sill, 3... PVC sol-based primer coating film, 4... Intermediate coating film, 5... Top coating film.

Claims (1)

[Claims] 1. In a vehicle exterior panel painting method in which the vehicle exterior panel is electrodeposited, dried, and then sequentially coated with a vinyl chloride sol-based primer, an intermediate coat, and a top coat, the vinyl chloride sol-based primer is electrodeposited with vinyl chloride resin. In addition to the adhesion-improving resin that improves the adhesion to the paint, a polyester plasticizer that improves the adhesion to the intermediate coating of the vinyl chloride resin is mixed, and the coating of the vinyl chloride sol primer, intermediate coating, and top coating are successively applied. A method for painting an exterior panel of a vehicle, characterized in that a drying treatment is performed after the coating is applied.