KR100192829B1 - Method of painting a car body - Google Patents

Abstract

The present invention relates to a coating method during the automobile manufacturing process, comprising a surface treatment step of forming a chemical coating on the vehicle body and an electrodeposition coating step of electrodeposition by dipping the vehicle body in a reaction tank containing a primer paint. The electrodeposition coating step is characterized in that the electrode body is electrodeposited while maintaining the temperature in the reaction vessel at about 35 ° C., which can significantly reduce the film thickness deviation, and additionally, the electrodeposition flushing property is improved, and the workability is improved. This has the effect of being improved.

Description

Method of painting a car body

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating method during a vehicle manufacturing process, and more particularly, to a method for uniformly forming a coating film thickness in an electrodeposition coating step after a surface treatment step of a painting process.

In general, automotive coatings must be durable against direct sunlight, rain, dust, and other contaminants, and must be resistant to extremely harsh conditions such as vibration and friction as moving objects. As high performance is required to be maintained as it is, automotive coatings must be excellent in weatherability such as maintaining color and gloss, maintaining adhesion, water resistance and chemical resistance, so that the durability of the undercoat and the overall coating that provides corrosion resistance It consists of an intermediate coating film which improves the quality, and a top coating film which gives an external appearance.

Representative automotive coating process for forming such automotive coating film is, as shown in Figure 1, the surface treatment step (S100) that is the pre-painting step and the electrodeposition coating step (S200) to coat the primer as a primer on the surface-treated car body, thermosetting electrodeposition paint The first heating and drying step (S300) for curing by heating for about 25-35 minutes at 160-170 ℃, performing performance step (S400) to smooth the coating film, medium coating step (S500), electrostatic coating with a medium paint, The second heating and drying step (S600) of heating the intermediate coating film at 130-140 ° C. for 20-30 minutes, the water polishing step of smoothing the coating film (S700), the top coating step (S800), which is the final finishing step of the coating, It consists of a third heat drying step (S900) for curing by curing about 30 minutes at 140-150 ° C thermosetting top paint and an inspection step (S1000) for checking the abnormality of the finished state.

In the electrodeposition coating step (S200), the surface treated car body is immersed in the electrodeposition paint in a reaction tank maintained at about 30 ° C., and the water body is used as an anode and the paint is used as a cathode to form an electrochemical film, followed by water washing. It consists of a process. At this time, the contaminated water after washing with water is treated with EU (Ultra Filton).

However, there is a problem that the variation in the thickness of the coating film exists for each vehicle body part. In particular, the coating film is deteriorated in the horizontal and vertical portions of the body so that the quality of the coating film is deteriorated.

Accordingly, an object of the present invention is to provide an automobile coating method capable of minimizing the deviation of the coating film formed in the electrodeposition coating step.

Automotive coating method of the present invention for achieving the above object,

In the automobile coating method comprising a surface treatment step of forming a chemical film on the vehicle body and an electrodeposition coating step of electrodepositing the vehicle body in a reaction tank containing a primer paint, the electrodeposition coating step is a temperature of about 35 It is characterized in that the electrode body is deposited while maintaining at ℃.

The temperature change in the reaction tank, which is the core content of the present invention, was found to significantly reduce the film thickness variation when the paint was electrodeposited to about 35 ° C. rather than electrodepositing the paint in the conventional reaction tank maintained at about 30 ° C.

1 is a process chart of a conventional automobile coating method.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

This embodiment is an experiment to determine whether the coating film deviation can be reduced by adjusting the value of the reaction factors affecting the electrodeposition coating without supplementing the conventional electrodeposition coating equipment.

This experiment analyzed the effects and effects of the reaction tank temperature with 20.9% solids, 0.35 P / B (Pigment / Binder), 6.1 pH, and 1490μS conductance. 28 ℃, 30 ℃, 32 ℃, and 35 ℃ were selected as the temperature change, and the film thickness and film thickness variation, THROWPOWER, gas pinhole rupture voltage, UF flux , Surface roughness and flushing were tested.

The results of the above experiments are shown in the table below.

Coating thickness depending on reactor temperature Temperature (℃) Coating thickness (μm) 28 26.5 30 34.4 32 41.7 35 47.0

Coating thickness variation with reactor temperature change Temperature (℃) Coating voltage (V) Coating thickness (μm) MAX. MIN. Average Standard Deviation 28 280 36.3 25.4 29.2 2.5 30 250 34.6 27.2 29.8 1.6 32 220 33.2 28.7 29.1 0.9 35 190 31.9 29.0 29.8 0.7

Throw power according to temperature change of reactor Temperature (℃) Throw power (cm) 28 20.9 30 19.5 32 19.3 35 19.0

Gas pinhole voltage due to reactor temperature change Temperature (℃) Rupture voltage (V) LEGEND G.A. PPG 3/2 G.A. 28 230 220 30 280 240 32 300 280 35 320 320

EU permeation rate according to the change of reactor temperature Temperature (℃) Permeation amount (ml / min) 28 130 30 139 32 152 35 171

Surface Roughness with Reactor Temperature Change Temperature (℃) Roughness (μm) 28 0.204 30 0.184 32 0.184 35 0.182

The surface thickness value in Table 1 above is a result of applying a distance of 16 cm to a pole and energizing a voltage of 260 V for 2 minutes. Table 2 is a result of measuring 7 times and a thickness of 30 μm as a reference. It was measured by the pipe method to test as a pipe of mm, in Table 4 LEGEND GA and PPG 3/2 GA is the experimental steel grade, the conduction time is 2 minutes and the distance between the poles to 16cm, Table 5 is the Lomicon ( ROMICON) results of the experiment with the UF device, Table 6 is measured based on the coating film thickness 30μm.

After the electrodeposition specimens were prepared for each temperature, the specimens were left for 2 minutes and 5 minutes before washing with water, followed by washing with water.

Therefore, when the upward management from the conventional electrodeposition reaction temperature of 30 ℃ to 35 ℃, the film thickness variation is significantly reduced, the permeation of the UPF increases, the electrodeposition flushing ability is improved, the gas pin hole voltage of the galvanized steel sheet is increased As the workability was improved.

In addition, when the temperature is increased, the throw power is slightly reduced but it does not affect the electrodeposition quality.

According to the present invention, when the temperature of the electrodeposition coating reactor is adjusted upward, the film thickness variation can be considerably reduced, and in addition, the electrodeposition water washing property is improved, and the workability is improved.

Claims (1)

In the automotive coating method comprising a surface treatment step of forming a chemical film on the vehicle body and electrodeposition coating step of electrodepositing the vehicle body in a reaction tank containing a primer paint, The electrodeposition coating step, the vehicle coating method characterized in that the electrode body is maintained while maintaining the temperature in the reaction tank to about 35 ℃.