JPS5953694A - Reverse coating method - Google Patents

Abstract

PURPOSE:To prevent the formation of a water mark by washing a reverse coated body in water, predrying it at a temp. below the softening point of the powder, and carrying out baking. CONSTITUTION:Part of a body to be coated is coated with a powder paint, a wet powder paint or a powder paint for electrodeposition, and the paint film is melted and passivated by heating at a temp. above the softening point of the powder and below the cross-linking and curing temp. Other part of the body is then coated with an ordinary paint for electrodeposition. The coated body is washed in water and predried at a temp. below the softening point of the powder to remove washing water sticking to the paint film formed from the powder paint, and baking is carried out. The formation of water mark is prevented, and the appearance of the paint film is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reverse coating method in which a part of the object to be coated is coated with synthetic resin powder and the remaining part of the object to be coated is further coated by electrodeposition.

The reverse painting method is a painting method that is effective in saving labor and resources, and is a highly corrosion-resistant painting method, so it is a painting method that has been attracting attention in recent years, especially in the field of painting automobile bodies.

In the reverse coating method, a part of the object to be coated is generally dry (static N) powder coated (dry powder), wet powder (slurry) coated, or powder electrodeposition (EPO) coated, and then! In this method, pHGj is thermally fused at a temperature above its softening point and at a humidity that does not cause crosslinking and hardening to make it immobile, and then the other parts of the object are coated by regular electrodeposition.

To take an example of painting an automobile body, the (+) heavy body outer panel is coated with a paint containing the above powder for 17 coats in advance,
This coating film is heat fused and a high-performance coating film that is immobile and has excellent corrosion resistance is applied. (11) After that, +1 (inside and internal parts are coated) by ordinary electrodeposition coating.

According to this method, it is possible to easily apply a thick film coating to the outer panel part 1, and furthermore, since powder etc. can be used, it is possible to reduce the number of coatings required for the final coating length of the automobile body. A coating film of high quality can be obtained.It also has advantages such as good throwing power in electrodeposition coating of the inner plate.

In such a reverse coating method, after a part of the object to be coated is coated with the above-mentioned powder-containing paint, the coating film on the area coated with the above-mentioned powder-containing paint is made immovable before the next electrodeposition coating.・For this reason, it is usually necessary to heat-fuse the coating film to the object to be coated at a temperature that is above the softening point of the powder but does not cause crosslinking and hardening. Next, other parts of the object to be coated are usually electrocoated, and after passing through a water washing process, a baking drying process is carried out to bake the entire coating film.

In the reverse coating method described above, after the coating film is formed with the powder-containing paint in the first stage, the portion where the coating film is thermally fused has become hydrophobic at this stage.

For this reason, after the subsequent ordinary electrodeposition coating process is completed, the washing water after washing adheres in the form of large water droplets or puddles on the coating film formed by the powder-containing paint. It has been found that if the film is subjected to the final baking step as it is, problems in coating film performance will occur due to the water pooling. In other words, it has been found that the water puddles give a concave finish, impairing the appearance of the coating film, and in terms of performance, the moisture resistance may deteriorate.

The reason for this is that in the dry powder, slurry coating, or EPO coating described above, in the post-painting heat fusion process, the powder, which is a component of the coating film, is heat fused and flows, resulting in an even and uniform coating.
brings about θ. As a result, the coating film adheres to the object being coated and becomes hydrophobic in terms of performance. The water that is applied to this hydrophobic coating film in the next normal electrodeposition and water washing process is removed in the final baking and drying process. : It prevents the heat conduction of S and smooths the S paint film (J is locally applied by 4. Also, the moisture becomes boiling and prevents the smoothing of the sticky paint film. For these reasons, it is thought that defects in the coating film will eventually occur.

This paint film defect caused by water is generally referred to as water splash, water drop trace, water mark, etc.

As a method for solving the above-mentioned water jump problem in the reverse coating method, a method can be considered in which a coating film made of a powder-containing paint is cured by baking, and then ml Changtunnan coating is applied. However, even in this case, it is necessary to bake and dry the coating film after the subsequent ordinary electrodeposition coating, and carrying out baking and drying twice is a big disadvantage from the point of view of energy saving. Furthermore, if such intermediate baking and drying is performed, there will be problems such as the boundary line between the powder coating in the first stage and the electrodeposited coating in the second stage. It turns out that the problem of moisture resistance due to water evaporation cannot be completely solved.

In order to solve the above-mentioned drawbacks of the conventional reverse coating method, the inventors of the present invention coated a part of the object with a powder coating, and then coated it with a powder coating at a temperature above the soft point of the powder that would not harden the coating. The above-mentioned water jump ( They discovered that scales can prevent the formation of watermarks.

Further, according to the method of the present invention, since the amount of water that is normally injected into the baking drying oven after electrodeposition coating is reduced, it is possible to prevent coating defects due to tar sag that occurs in the oven.

The vine powder electrodeposition paint used in the method of the present invention includes, for example, Japanese Patent Publication No. 51-4osss-@1 as a powder paint, and Japanese Patent Publication No. 48-29836 as a wet powder paint.
Reference may be made to No. 5-50514. Further, any known electrodeposition paint can be used as the electrodeposition paint.

Examples are described below. All parts and percentages herein are by weight. Note that the present invention is not limited to these Examples.

Example 1 Cachimene moisture PIJ1. Preparation of resin: Ebicoat #1
001 (manufactured by Shell) 488 parts Isopropyl alcohol 25o Day ethanolamine 1o5 Lactic acid 765 Ion-exchanged water 1057#Amine-added organic acid neutralized epoxy cationic electrodeposition resin A solid content 30 % binder was obtained.

Preparation of powder coating: Bicoat #1004 (Shell 12F period)
40 part adduct B-1065 (Hülss ritual 1st harvest)
3Q part titanium oxide R-550 (manufactured by Ishihara San Shibasha)
]9〃Kaolin ASP-200 (manufactured by Hayashi Kasei Co., Ltd.) 1. O# Carbon black MA-10
0 (manufactured by Mitsubishi Kasei) 1 Benzoin
0.5 Premix the incyanate-cured epoxy thermosetting powder coating with the above formulation, heat knead,
It was prepared according to a conventional method that includes steps of cooling, coarsely pulverizing, and finely pulverizing.

848 tons of the above powder coating and the above cationic electrodeposition resin A
binder 21.70) and ion exchange water 69.8
2) 100 tons of a powder electrodeposition paint bath solution with a solid content concentration of 15% and I) H5.3 was prepared and built.

Preparation of cationic electrodeposition coating: Ebicoat #1oo1 (manufactured by Shell) 100
0 parts Tetrahydrophthalic anhydride 30
4〃Hydroxyethyl methacrylate 2
60/Cellosolve acetate
919.7 Diethylethanolamine
234 Trilene diisocyanate
3481111 Hydroquinone
10 Triedylamine
3 Formic acid
494 top; (
Based on the own formulation, a cationic fat B with a solid content of 70% was obtained by the 'woven method'.

Cathioco/resin B 50
titanium oxide
7 Carbon black
O75 Strontium chromate
03 Lead silicate
07 Ion exchange water
87.1 According to the above formulation, a cationic [1 paint solids content of 30%] was obtained through the conventional process of premixing, ball mill dispersion, and red down.

A bath was prepared using 90 tons of the above cationic electrodeposition coating and 90 tons of ion-exchanged water to prepare a bath of 180 tons of cationic electrodeposition coating with a solid content concentration of 15% and pi(,6.0) manufactured by 11.d.

1 800 CC17I'ki rat treated with zinc phosphate,
Conveyor speed 4m for car body with coating area of 70y
At 1 body pitch of 5.5 m, 1 in 100 tons of powder electrodeposition paint bath liquid. 11 Arrival vorticity 25°C/mole spacing t
i960 cm, electrodeposition time 15-30 seconds? ! Ii”
X (under the condition of voltage 500V, cationic powder 'i
ff.

I did some painting.

Then, after washing with water and setting it to drain for 3 minutes,
It was passed through a drain drying oven for about 10 minutes in an atmosphere of ~85°C. It is important that the outer panel is made immobile.
Ii was edicted.

Next, powder electrodeposition was carried out in 180 tons of the above-mentioned cationic electrodeposition coating solution Z1 under the following conditions: electrodeposition temperature 25°C, interelectrode distance 50 cm, total electrodeposition time 120 seconds, electrodeposition voltage 250V. Unpainted interior +) Is.

The bag portion and the gap portion were coated with cationic ITF coating using an energized bath method, and then washed with water.

Passage time 8 minutes, 1500 m/min, 60 m through the automobile body coated with powder electrodeposition and cationic electrodeposition as described above.
1llAqs 50KW circulation fan, 150X I
O' Kcal/Hr burner thermoelectric, 300n
r/min, 30 + A + Aq, 7.5 xw exhaust fan, effective length 35 m1 capacity with 3 nt air curtain zones front and rear each 3'], 5 nr z furnace temperature 70-7
It was passed through a drain drying oven at 5°.

After taking it out of the drain drying oven and moving it through an open space of about 177L, it was introduced into a drying oven with an atmosphere of 185-190°C and a residence time of 25 minutes. Powder ゛111 coating j1σj coated on the outer panel of
The cationic electrodeposition coating applied to the disc was simultaneously baked and N-cured. At this time, the specification of the drying oven was 1000 m/min.
70 wnAq, 25KW &4 Noga fans-11
Burner heat capacity of 10 x 10' Kcal/Hr, 1
05 yd,/min burner blower, 60nj
It has three series of exhaust fans of 30 Aq/min, 1.5 x W, and has an effective length of 90 nm and a volume of 810 nt, with air curtain zones of 3 m each at the front and rear.

1 to 1
No problems such as one water drop or 'water mark a' were observed.

Comparative Example 1 As shown in Example 1, the 0 body was automatically coated using the same painting process as Example 1, without installing a drying oven after landing on water, and under all other conditions. Many water marks were observed on the outer panel, and a polishing process was required to obtain a good appearance.

Example 2 The powder coating shown in Example 1 was ground to an average particle size of 25μ,
The outer panel of the body was electrostatically coated to a coating thickness of 50 ti using a conventional method. Body size, shape, conveyor speed,
The body pitch etc. were the same as in Example 1. Drying to make the outer panel into a passivation body is carried out at 170°XIO at the same temperature as the body.
It was a minute.

After this, the body was put on T4L, washed with water, under the same conditions as Example 1.
Mizukiri: Drying, final baking drying. The fine finish on the outer panel was good.

Comparative Example 2 Reverse painting was carried out in the same manner as in Example 2, except that the drain drying oven was not used.

Many watermarks are observed on the outer skin of the body.
Buko.

Patent applicant Chair! Self 1 (Q-+i4 to Shinto Nuriku Co., Ltd. 1 Co., Ltd. I?εyo-49 ( )

Claims (1)

[Claims] 1. Part of the object to be coated is powder, wet powder or powder TI
After coating with the L-coating paint, the coating film is heat fused at a temperature above the softening point of the powder and at a temperature that does not cause crosslinking and hardening, then the other parts of the object to be coated are coated with a normal electrodeposition paint, washed with water, A reverse coating method characterized by pre-drying at a temperature below the softening point of the powder and then baking.