JPH0366030B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for undercoating an automobile body.

The usual method of painting car bodies currently in use is (a) first applying electrodeposition coating to the entire car body with an anionic or cationic ionic paint for the purpose of rust prevention, and then baking the formed coating film. harden and then
(b) Spray a so-called guard coating paint for the purpose of chipping resistance on the outside of the side seal or the area from the bottom of the door to the side seal, and after hardening the formed coating film (c) Exterior of the vehicle body. Apply an intermediate coat of paint to give the board a beautiful finish and maintain the film thickness when the top coat is applied, and if necessary, after air-drying this, spray a door sash paint for design purposes on the (d) door sash area. The resulting coating film is baked and cured at the same time as the intermediate coating film in the previous step to form an undercoat (including intermediate coating). Finally, a step (e) of applying a top coat to the outer panel of the vehicle body and curing the formed coating film is performed.

In this way, conventional undercoat painting (including intermediate coat painting) before topcoat painting of automobile bodies is done through four painting processes and three baking processes. In addition to being complicated, the above (d) door sash paint and the above
Since the guard coat paint in (b) is applied after baking the electrodeposited film in (a) above, the dust from these coatings adheres to the baked paint film, causing unevenness on the paint film. It had drawbacks that affected the appearance of the final coating. For this reason, it is necessary to apply these paints after sealing other parts where the dust should not adhere, which poses problems in terms of productivity and economy.

In view of the above-mentioned circumstances, the inventors of the present invention have conducted extensive research and have found a coating method that can greatly simplify the conventional process in the undercoating process prior to topcoating, and have completed the present invention.

In other words, the present invention provides an undercoat coating system for an automobile body, in which (1) the entire automobile body is solid at room temperature;
A coating containing synthetic resin fine powder that melts when heated (powder-based coating) is applied, and the coating film formed is heated at a temperature that causes the coating film to melt but does not cause crosslinking and hardening. (2) Electrodeposit the parts that were not painted in (1) above with ionic paint (electrodeposition paint), wash the formed coating film with water, then air blow or drain and dry. 3) Paint the door sash with door sash paint and/or
(4) The present invention provides a method for undercoating an automobile body, in which the side seal portion is coated with a guard coating paint, and then each coating film formed in (1) to (4) is baked and cured at the same time.

In the present invention, the step (1) above is mainly to apply a powder-based paint with excellent performance that has both the performance of an undercoat and an intermediate paint to the outer panel of the car body, so that it can be applied once as an undercoat. It does not require two or more overcoatings, that is, intermediate coatings.

Powder-based paints are preferred because of their low pollution properties, workability that allows thick film coating, and excellent coating performance. Examples of such powder coatings include dry powder coatings used in electrostatic powder coating and fluidized dipping coating methods, and powders used in electrodeposition coating methods in which fine synthetic resin powder is dispersed in an aqueous solution of an ionic binder resin. Known paints such as electrodeposition paints and wet powder paints (slurry paints) used in electrostatic or spray painting methods can be used. Although these paints and coating methods each have their own advantages and disadvantages, they share the characteristics of the powder-based paints described above.

The above powder-based paints differ in their form and coating method depending on their type, but all of them contain as an essential component synthetic resin fine powder that is solid at room temperature and melts when heated, and each is a well-known method. It is applied by an appropriate method, and the applied paint is kept under temperature conditions that cause thermal melting of the coating film, but that do not cause crosslinking reactions in the coating film (for example, 70 to 150℃).
℃ x 5 to 20 minutes), or proceed to the next (2) electrodeposition coating step using an ionic paint without performing any heating as described above.

This process is a process in which an ionic paint is electro-deposited as an undercoat on areas where the powder-based paint was not sufficiently applied in the previous process and unpainted areas (mainly inside the car body). As the ionic paint, any known anionic or cationic electrodeposition paint can be used.

The electrodeposited film applied here is washed with water and then air blown or drained and dried (e.g. 50-100℃ x 5-15 minutes)
Then, (3) coat the door sash with a known door sash paint such as melamine-alkyd resin solvent-based paint, acrylic-melamine resin water-soluble paint, polyester resin slurry paint, etc., and/or (4) apply side seals. Apply a guard coat paint such as a known polyol resin solvent-based paint, emulsion paint, or epoxy resin slurry paint to the outside part of the door or the area from the bottom of the door to the side seal part by spraying or the like.

After that, the powder-based paint film, electrodeposited paint film, door sill paint film, and guard coat paint film formed in steps (1) to (4) are baked and cured simultaneously in one oven to form an undercoat. Finish painting.

The baking hardening process varies depending on the type of paint used and the shape of the object to be coated, but generally it is 170 to 200
This is done by passing through a hot air oven for 30 to 10 minutes at °C.

As explained above, when the method of the present invention is adopted in the undercoat coating system of an automobile body, the number of baking steps is only one compared to the conventional method, and furthermore, even if dust is generated during the application of door sash paint and guard coat paint, Since the coating film from the previous coatings (1) and (2) has not been baked and hardened, it does not create any unevenness, making seals unnecessary and it has been found that productivity and economic efficiency are greatly improved. .

The present invention will be explained in detail below with reference to Examples.

Example 1 A powder electrodeposition coating solution was prepared as follows.

Water-dilutable cationic resin is Epicote #1001
(Product name of epoxy resin manufactured by Ciel) 488 parts, diethanolamine 105 parts, isopropyl alcohol 250 parts
A portion of the mixture was reacted under reflux at 80-85°C for 3 hours to obtain a liquid aminoepoxy resin.

Also, as a synthetic resin fine powder, Epicoat #1004
(epoxy resin trade name manufactured by Ciel Corporation) 400 parts, Adduct B-1065 (blocked isocyanate trade name manufactured by Fueva Corporation) 300 parts, titanium oxide R-550 (manufactured by Ishihara Sangyo Co., Ltd.) 290 parts, and Carbon Black MA-100 (Mitsubishi Kasei Co., Ltd.) Co., Ltd.) 10 parts by the conventional method of powder coating 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 7 μm.

Add 6.2 parts of glacial acetic acid and 500 parts of deionized water to 143 parts of the water-dilutable cationic resin as a binder, stir well with a dissolver, then add 280 parts of the fine powder and stir and mix with a dissolver for 30 minutes to disperse. It was then diluted with deionized water to a solids content of 15% by weight.

This bath liquid had a pH of 5.2 and a fine powder/binder resin ratio of 2.8/1.

A cationic electrodeposition bath was prepared as follows.

Epicote #1004 336 copies, Epicote #1001
Mix and stir 143 parts of ethyl cellosolve and 140 parts of ethyl cellosolve to completely dissolve. Raise the temperature to 50℃ and add 1 part of a solution of 59 parts of diethanolamine and 20 parts of isopropyl alcohol.
The mixture was added to the mixture over a period of time with stirring. After charging, the temperature was maintained at 80-85°C for 3 hours. 202 parts of Adduct B-1065 and 100 parts of ethyl cellosolve were added to the above solution over 30 minutes with stirring, and the mixture was further maintained at 80 to 85°C for 1 hour and 30 minutes to obtain an aminoepoxy isocyanate resin.

A cationic electrodeposition bath was obtained by using the above cationic resin and using acetic acid as a neutralizing agent and titanium oxide and carbon black as pigments by a conventional method for producing electrodeposition paints, and diluting it with pure water to a predetermined concentration. Ta. The bath liquid had a pH of 5.4, an ash content of 25% by weight, a degree of neutralization of 7.5%, and a heating residue of 13% by weight.

A paint for door sills was prepared as follows.

290 parts of acrylic resin (trade name Aron #76 manufactured by Nippon Kaihatsu Kagaku Co., Ltd.), 30 parts of melamine resin (trade name Cymel #300 manufactured by Union Carbide & Carbon Co., Ltd.), 30 parts of dimethylethanolamine,
40 parts of carbon black, 15 parts of extender pigment (trade name: Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.), 5 parts of solvent (butyl carbitol), and 155 parts of water were uniformly mixed and dispersed using a conventional paint manufacturing method to obtain a paint for door sills. .

After the car body to be painted was subjected to zinc phosphate chemical conversion treatment, it was thoroughly washed with pure water and drained and dried in a conventional manner. This car body was immersed in the powder electrodeposition coating bath, and a direct current was passed through the car body using the car body as a cathode to perform powder electrodeposition coating.

The coating conditions were a voltage of 500 V, a current application time of 17 seconds, a bath temperature of 25°C, and a minimum distance between electrodes of 60 cm.

After finishing powder electrodeposition coating, thoroughly rinse with water and heat to 80℃.
After draining and drying at ~100°C for 10 minutes, it was immersed in the cationic electrodeposition coating bath to perform electrodeposition coating. The painting conditions are voltage 250V, energization time (from the start of energization to tank removal) 180 seconds, bath temperature 28℃, distance between electrodes.
It was 60cm long.

After taking out the tank, thoroughly wash with water, remove moisture from the door sash by air blowing, spray paint for door sash, drain and dry at 80 to 100℃, then form powder electrodeposition coating and cationic electrodeposition. All the paint films and the door sash paint film were baked simultaneously in the same oven at 190°C for 20 minutes to crosslink and harden them.
After that, the car body was painted using the usual method.

This method requires approximately 2 man-hours compared to the conventional painting method.
The reduction in the number of seizures resulted in resource savings of about 30 to 40% in terms of fuel.

Furthermore, there was no effect on the finished surface due to dust during application of the door sash paint, and the product had excellent rust prevention and appearance.

Example 2 The powder coating was prepared as follows.

Mix 100 parts of Epicoat #1004, 5 parts of adipic acid dihydrazide, 0.3 parts of imidazole, 1.5 parts of Miki Leveling (trade name of leveling agent made by Kyoeisha Yushi Co., Ltd.), 36 parts of titanium oxide, and 4 parts of carbon black using a conventional method for manufacturing dry powder coatings. It was manufactured through a process of hot kneading, cooling, and pulverization. The average particle size was 50μ.

An anionic electrodeposition coating bath was prepared as follows.

An electrodeposition bath was prepared containing an anionic resin made of a polybutadiene resin by a known process, triethylamine as a neutralizing agent, and titanium oxide and carbon black as pigments. The special characteristics of the bath liquid are
The pH was 7.8, the ash content was 26% by weight, and the heating residue was 13% by weight.

The guard coating paint was prepared as follows.
Add 400 parts of styrene-butadiene emulsion resin (trade name Luxter 4709A, manufactured by Dainippon Ink Co., Ltd.), 10 parts of carbon black, 220 parts of extender pigment (trade name ASP-200, manufactured by Hayashi Kasei Co., Ltd.), and 60 parts of solvent (ethylene glycol) to the paint. The mixture was uniformly mixed and dispersed using a conventional manufacturing method, and the spraying viscosity was adjusted with water to obtain a guard coat paint.

After the car body to be painted was subjected to zinc phosphate chemical conversion treatment, it was thoroughly washed with pure water and drained and dried in a conventional manner. Powder coating was applied to the outer panel of this vehicle body using a Stadget JR-50 type powder electrostatic coating machine manufactured by Sames Co., Ltd. at -80 KV to a film thickness of 50±5 μm. Next, the obtained coating film was heated at 150℃ for 10 minutes without causing crosslinking and curing, and then the car body was cooled to room temperature and placed in an anionic electrodeposition coating bath at a voltage of 200V and a current application time of 180 seconds.The bath temperature was 28℃. Electrodeposition was carried out under the condition that the distance between the electrodes was 40 cm. 80-100 after thoroughly washing with water
After draining and drying at ℃ for 10 minutes, spray paint the guard coat paint on the outside of the side seal of the car body, and then apply the entire powder coat, anion electrodeposition coat, and guard coat paint that have been formed. The membranes were simultaneously baked in the same oven at 200°C for 20 minutes to crosslink and harden.

After that, the car body was painted using the usual method.

This method requires approximately 2 man-hours compared to the conventional painting method.
The reduction in the number of seizures resulted in resource savings of about 20% in terms of fuel.

Furthermore, there was no effect on the finished surface due to dust during application of the guard coat paint, and the product had excellent rust prevention and appearance.

Example 3 The binder used in Example 1 was diluted with water so that the solid content was 15% by weight, and the powder used in Example 1 was added to this with stirring until the solid content ratio of the binder and powder was adjusted. The mixture was added while adjusting the viscosity by adding water as needed until the ratio was 1:3. The slurry paint thus obtained was mixed with water to a food cup #4 viscosity.
The temperature was adjusted to 30 seconds/25°C and used as a test powder coating.

The above slurry paint was treated in the same manner as in Example 1 using a winder #61 type spray gun (manufactured by Iwata Paint Co., Ltd.) to a dry film thickness of 40~
Paint it to a thickness of 50μ and then apply it for 10 minutes in a 130℃ atmosphere.
Dry for a minute. Next, this car body was electrodeposited in the same cationic electrodeposition bath as in Example 1, and then thoroughly washed with water. After that, the same door sash paint as in Example 1 was applied to the door sash area, and the same guard coat paint as in Example 2 was applied to the outside of the side seal, and then the slurry coating film and cationic electrodeposition coating were applied. All coatings, including the membrane, door sash paint, and guard coat paint, were baked simultaneously in the same oven at 190°C for 20 minutes to crosslink and harden them.

After that, the final coat was applied in the usual manner.

This method requires approximately 2 man-hours compared to the conventional painting method.
The reduction in the number of seizures resulted in resource savings of about 20% in terms of fuel.

Furthermore, the finished surface was not affected by dust during the application of the door sash paint and the guard coat paint, and the rust prevention and appearance were excellent.

Claims (1)

[Claims] 1. In the undercoat coating system for automobile bodies, first (1)
Paint for the entire car body that contains synthetic resin fine powder that is solid at room temperature and melts when heated (powder-based paint)
(2) The coating film formed is heated at a temperature that causes melting of the coating film but does not cause crosslinking hardening, or without heating, and then (2) is coated with the coating described in (1) above. Electrodeposit the missing parts with ionic paint (electrodeposition paint), wash the formed coating film with water, then air blow or drain and dry, then (3) paint the door sash area with door sash paint and/or (4) paint the sides. Paint the seal part with door coating paint, and then (1) to (4)
A method for undercoating an automobile body, characterized by simultaneously baking and curing each coating film formed in the step.