JPS6116438B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a coating method for applying an economically strong anti-rust coating to an automobile body. In recent years, with the development of expressways, driving speeds have increased, resulting in paint film damage (so-called chipping phenomenon) due to the impact of flying debris from own vehicles or oncoming vehicles, and in addition to this, freezing in cold regions during the winter. The problem of corrosion (so-called salt damage) caused by corrosive antifreeze agents such as rock salt that are sprayed to prevent corrosion has become serious, but the present invention provides a rust preventive that provides a strong protective effect against such damage and corrosion. Regarding the painting method. Rust prevention for the car body, especially the lower part of the car body, is
Due to the above-mentioned chipping phenomenon, deterioration of the corrosive environment such as damage to the paint film due to salt damage, increased required lifespan, and increased safety requirements due to high-speed driving, there is an increasing demand for Therefore, improving the rust prevention effect is one of the important issues in the industry. Various rust prevention measures for automobile bodies have been studied.
For example, in the area of paints and painted surfaces, the adoption of anionic electrodeposition paints and the subsequent quality improvement of the paints used, the adoption of cationic electrodeposition coatings, and the development and adoption of powder coatings and powder electrodeposition coatings. be. Furthermore, powder coating, powder electrodeposition coating, thick-film electrodeposition coating, etc. are applied in advance to the outer panel of the automobile body, especially the underside, and then the inner panel and bag structure are coated with regular electrodeposition paint, especially cationic coating. A method of painting with electrodeposition paint is being studied and implemented. This method is called the reverse painting method. In order to put this reverse painting method into practical use, there is a method of applying a thick layer of electrodeposited paint to the lower part of the car body as a pre-process, such as in Japanese Patent Publication No. 56-2159, but in practice, it causes the following inconveniences. It turns out that there is. That is, when a continuous slipper dip method is used as a coating method, the automobile body is generally suspended fixedly on a rod-shaped hanger and moved by a conveyor. This rod-shaped hanger is fixed approximately at right angles to the conveyor. The connection and fixation of these hangers and conveyors prevents the car body from moving unstablely due to the buoyancy and resistance caused by the bath liquid that occurs when the car body is placed in the electroplating bath, and in some cases, short circuits may occur during energization. This is done to prevent accidents and even the vehicle falling from the hanger. However, when painting an automobile body fixed with the above-mentioned hanger, especially the lower part thereof, by the slipper dip method, the following disadvantages occur. In the first place, when applying a rust-preventing coating to the lower part of an automobile body, it is common to apply the coating horizontally to only the required lower part of the car body, and it is clear that this is preferable in terms of the appearance of the coating film. However, when using the energized entry and exit methods in the slipper dip system, the car body is entered and exited from the bathtub in an inclined state with respect to the liquid level of the bathtub. For this reason, avoid submerging the front part (when entering the tank) and rear part (when taking out the tank) of the car body into the bathtub up to the part above the horizontal part (referred to as the unpainted part) of the lower part of the target anti-rust coating. I can't. Between entering and exiting the tank, the unpainted parts that are once immersed appear on the surface of the bath liquid, and the car body is kept horizontally in the bath liquid, and only the lower part is immersed in the bath liquid for electrodeposition painting. At this time, in the above method, since the vehicle body enters and exits the tank while energized, it is inevitable that the above-mentioned unnecessary portions will also be electrodeposited during the insertion. Further, even with the method of energizing the tank and not energizing the tank, or the method of energizing the tank and the energizing tank, the electrodeposition on the unnecessary portions described above during energization cannot be avoided. Compared to the electrodeposition time for the target underbody part, the above-mentioned electrodeposition on unnecessary parts is performed only during immersion, so the electrodeposition time is shorter and the coating film is thinner than the underbody part. Not only does this damage the overall appearance of the film, but when regular electrodeposition coating is applied in the subsequent process, this regular electrodeposition coating is not carried out, resulting in problems that are undesirable from both the film thickness and the aesthetics of the coating film. will occur. For this reason, there is a method that uses non-energized entry and exit methods, and then applies electricity and electrodeposit after the vehicle body is completely horizontal. The bath liquid that adhered to the unnecessary parts during immersion physically adheres as it is, and is not completely removed. For this reason, after keeping the car body horizontal, when electricity is applied for the intended electrodeposition coating, the paint remaining on unnecessary parts will be electrodeposited, and in this case, the previous energization tank entry and/or energization exit method will be applied. The coating amount is more irregular than in the case of , causing spots,
The result is that the appearance of the paint film is seriously impaired. Furthermore, if ordinary electrodeposition is carried out in this step while such a patchy or irregular coating film is formed, a discontinuous coating film will be formed, which is unfavorable in terms of coating performance. The inventors of the present invention have studied to improve this inconvenience, and found that when reverse painting the lower part of an automobile body using the slipper dip method, it is necessary to first immerse it in powder electrocoating paint or thick film electrocoating paint bath liquid. died,
The above-mentioned painting method is characterized in that after cleaning the parts of the automobile body that have been exposed to the bath liquid other than the lower part of the car body that have appeared on the bath liquid surface again, the electrolytic coating is applied by applying an electric current. It has been discovered that such inconveniences can be improved. In addition, in the above-mentioned powder electrodeposition coating or thick film electrodeposition coating, (i) energization is started in the horizontal position after cleaning is completed, (ii) energization is applied only when the vehicle body moves horizontally, and (iii) when the vehicle is taken out of the tank. It has been discovered that the effects of the present invention can be maximized by not applying electricity. The cleaning liquid used in the above-mentioned cleaning of the present invention is one that does not contain components that would be electrodeposited in the normal electrodeposition process in the subsequent process, that is, water or ultrafiltration (UF) liquid that cannot become an active component of the coating film. etc. are used. Cleaning is preferably carried out by spraying a cleaning liquid by installing a nozzle at a position where the car body is horizontal in the electrodeposition tank. Hereinafter, the present invention will be explained in detail with reference to Examples and Comparative Examples. Example 1 A powder electrodeposition paint was prepared as follows. Water-dilutable cationic resin is Epicote #1001
(Trade name: epoxy resin, Ciel product) 488 parts,
150 parts of diethanolamine and 250 parts of isopropyl alcohol were reacted under reflux at 80°C to 85°C for 3 hours to obtain a liquid aminoepoxy resin. Also, as a synthetic resin fine powder, Epicoat #1004
(manufactured by Ciel Corporation) 40 parts, Adduct B-1065 (manufactured by Hueva Corporation) 30 parts, titanium oxide R-550 (manufactured by Ishihara Sangyo Co., Ltd.) 29 parts, and Carbon Black MA-100 (manufactured by Mitsubishi Kasei Corporation) 1 part as powder. By the conventional method of paint manufacturing,
The mixture was melted and kneaded using an extruder and pulverized using an impact pulverizer to obtain a fine powder mainly composed of epoxy resin with an average particle size of 7μ. The liquid aminoepoxy resin (Bi) obtained as above, fine powder (Po), glacial acetic acid, and deionized water were added and mixed and dispersed, Po/Bi=2.8/1, PH52,
A powder electrodeposition paint bath solution with a solid content of 15% was prepared. In addition, cationic electrodeposition paints use a cationic resin obtained by adding blocked isocyanate to an aminoepoxy resin in which the terminal glycidyl group of a urethane-modified epoxy resin is ring-opened with an alkanolamine. It was dispersed using a normal dispersion process and neutralized with an acidic compound, and had a solid content of 15%, a pH of 5.8, and a pigment content of 23%. A boat-shaped electrodeposition tank was filled with the powder electrodeposition paint bath solution so that the center of the tank was immersed up to 20 cm from the lower side of the door of an automobile body. The amount of liquid was approximately 55 tons.
The anode was installed with a distance of 50 cm between the lower part of the car body and the 1/1 pole. The nozzle is installed at a position where the car body is horizontal in the electrodeposition tank, that is, at a position where the fender of the car body immerses once in the tank and then reappears on the liquid surface. Water was sprayed 5 times per unit to wash away the paint adhering to this area into the bath liquid, and then electricity was started. The power was turned off before the vehicle began to tilt due to the slope on the outlet side of the boat-shaped tank. At this time, the energizing condition is liquid temperature 25
℃, voltage 500V, and time 30 seconds. The electrodeposited coating film thus formed was washed with water in a conventional manner, drained and dried, and then painted using a cationic electrodeposition paint as a subsequent step. Electrodeposition coating conditions are liquid temperature 28℃ and voltage.
It was set to 300V. The results are shown in Table 1. Comparative Example 1 Coating was carried out in the same manner as in Example 1, except that washing with deionized water before powder electrodeposition coating was not performed. The results are shown in Table 1.

【table】

[Table] Example 2 Method for preparing thick-film electrodeposition paint bath liquid For the cationic electrodeposition paint for underside coating, the terminal glycidyl group of the urethane-modified epoxy resin was replaced with alkanolamine in order to ensure film thickness without emphasizing the appearance finish. Using a cationic resin made by addition-reacting blocked isocyanate to a ring-opened aminoepoxy resin, the composition further increased the amount of components that are thermoplastic and liquid at room temperature that do not dissociate by electrodeposition, and also increased the amount of solvent. . Solid content 18%, PH=6.0, pigment content 20
%, and the coulombic efficiency was 38 mg/C. The electrodeposition bath was filled with bath liquid so that 10 cm from the bottom of the door of the car body was immersed in the bath liquid. Between poles = 30
cm, the relevant part/anode = 1/1, the car body reaches the horizontal level, once submerged below the liquid surface outside the relevant part, and the paint is removed from the paint due to limit excess (UF) at the part that reappears above the liquid surface. A liquid obtained in a conventional manner was sprayed to wash away the adhering paint. The solid content of this liquid is 0.5
It was %. After that, voltage 300V, 1 minute at 28℃
Power was applied for 30 seconds. The vehicle body position was horizontal at the end of energization. After washing with water and drying at 50 to 70°C using a conventional method, cationic electrodeposition was performed in an energized tank. The same cationic electrodeposition paint as in Example 1 was used. The electrodeposition conditions were a bath temperature of 28°C and a voltage of 300V. The energization time was exactly 3 minutes, which is the time when the car was fully immersed in the bath. The results are shown in Table 2. Comparative Example 2 Using the same cationic thick-film electrodeposition paint as in Example 2, the paint was submerged in the liquid and then resurfaced under other conditions without washing off the paint that had adhered to the area where it reappeared on the liquid surface. was electrodeposited in exactly the same manner as in Example 2, and all post-processes were performed in the same manner as in Example 2. The results are shown in Table 2.

【table】

【table】

Claims (1)

[Claims] 1. When reverse painting the lower part of an automobile body using the slipper dip method, the automobile body is once immersed in a powder electrocoating paint or thick film electrocoating paint bath solution and reappears on the surface of the solution. 1. A method for painting the underside of an automobile body, which comprises cleaning the parts to which bath liquid is attached other than the underside of the car, applying electricity to apply electrodeposition coating, and then applying normal electrodeposition coating.