JPH0216399B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an anti-rust coating method for an outer panel of an automobile body, and more particularly to an improved anti-rust coating method for areas of an outer automobile body where corrosion is likely to occur.

In recent years, corrosion of automobile bodies has become a major social problem.

Corrosion of automobile bodies is caused by water and mud accumulating in the narrow spaces and bag-like structures of the automobile body during driving, and these areas are left in a wet state for a long period of time. external corrosion such as so-called chipping corrosion, which occurs when the outer skin of an automobile body is hit by small stones or other objects at high speed while driving, causing scratches that reach the paint film down to the base material, and corrosion occurs from these scratches. There is.

Therefore, in order to prevent the former type of internal corrosion, improvements to the body design such as reducing narrow gaps and making the bag-like structure difficult for water and mud to accumulate, as well as changes in the steel plates used in these parts, are necessary. Measures such as using anti-corrosion steel sheets such as galvanized steel sheets and changing the electrodeposition paint used as an undercoat from the conventional anionic electrodeposition paint to a cationic electrodeposition paint with greater rust prevention properties are taken. It has been taken.

The latter type of external corrosion usually occurs in very limited areas, such as around the radiator core grille, the tip of the hood, the tip of the roof, and the lower half of the door.

The most effective way to prevent external corrosion is to thicken the paint film, and a paint called chipping primer has been developed for this purpose, and it is a paint that combines the electrodeposition paint film and the intermediate paint film. In between, it is painted with intermediate paint and wet-on-wet.

However, the improvement effect is still insufficient. This is because if a chipping primer is applied until chipping corrosion can be completely prevented, defects such as wrinkles and sagging are likely to occur.

In addition, as mentioned above, chipping corrosion only occurs in very limited areas, but if chipping primer is applied partially to very limited areas, the chipping primer will not be applied. Chipping primer must be applied almost evenly over the entire exterior of the body, as there will be obvious differences in appearance such as smoothness and gloss between coated and unpainted areas even after the topcoat is applied. This, in turn, leads to an increase in painting costs. Additionally, cationic electrodeposition paints, which have been adopted as an alternative to anionic electrodeposition paints, have extremely hard and brittle coatings, so they have the problem of being easily destroyed by impact from collisions with pebbles, etc., and easily peeling off from the base. It is occurring.

As a result of intensive research on methods for preventing the above-mentioned corrosion on the outer panels of automobile bodies and improving the exterior durability of automobiles, the inventors of the present invention discovered that they have developed a method to prevent the above-mentioned corrosion on the outer panels of automobile bodies and to improve the exterior durability of automobiles. The inventors have discovered that the occurrence of external corrosion can be extremely effectively prevented by coating the automobile body with a primer coat and then immersing the car body in an electrocoating paint bath to apply electrocoating. It's old.

That is, the present invention contains 1 to 25 parts by weight of conductive powder based on 100 parts by weight of the solid content of the paint in areas where corrosion is likely to occur on the outer panel of the automobile body,
And the volume resistivity value of the dry coating film is 1×10 ⁶ Ω・cm
The present invention relates to a rust-preventing coating method for automobile body outer panels, which comprises applying the following solvent-based or water-based conductive undercoating paint, followed by electrodeposition coating.

In the present invention, the areas where corrosion is likely to occur on the outer skin of an automobile body include, for example, the areas that can be seen when the automobile body is viewed from the front, such as the radiator core grille, bumper stone deflector, engine hood, front fender, etc. This includes the front edge of the roof around the windshield, the front pillar, etc., the lower half of the front fender, the rocker panel, the lower half of the door, the lower half of the quarter panel, and around the key hole of the door and trunk lid. In addition, the attachment parts of decorative moldings attached to the outer panels of automobile bodies (these attachment parts are damaged due to vibration due to loosening of bolts, nuts, etc.) Corrosion often occurs.).

As the conductive undercoating paint used in the present invention, a solvent-based or water-based conductive paint is used, and the volume resistivity value of the dry coating film is 1×10 ⁶ Ω・cm.
If it exceeds 1×10 ⁶ Ω・cm, the electrodeposited paint will not deposit at all or will not deposit uniformly on the undercoat film, which is the main effect of the present invention. However, a thick coating film or good smoothness after topcoating cannot be obtained.

As a method of imparting conductivity to the undercoat paint,
Although various known techniques can be used, a particularly suitable method is, for example, a method of dispersing an electrically conductive powder material in the paint.

Examples of these electrically conductive powder substances include electrically conductive carbon black (commercially available products such as Conductex 950 and 975 manufactured by Columbia Carbon, Vulcan XC-72 manufactured by Cabot,
Examples include Printex L manufactured by Degussa. ), graphite (commercially available products include scaly graphite 97-300 manufactured by Chuetsu Graphite Co., Ltd.), metal oxide materials (commercially available products such as white conductive powder manufactured by Mitsubishi Metals Co., Ltd.) Examples include W-10 and W-100 (a material in which a tin oxide-based conductive film is formed on the surface of titanium oxide). ], metal powders (for example, zinc powder, copper powder, silver powder, aluminum powder, etc.).

The specific blending amount of the conductive powder substance to obtain the above volume resistivity value is based on the solid content of the paint.
The amount is preferably 1 to 25 parts by weight per 100 parts by weight. If it is less than 1 part by weight, sufficient conductivity may not be obtained, and if it exceeds 25 parts by weight, the physical properties of the resulting coating film may be affected. becomes worse.

As the binder resin used in the conductive undercoat paint, as long as the volume resistivity value of the paint film after dispersing a conductive powder substance to form a paint, painting, and drying satisfies the above range. In principle, any material can be used, but considering the rust-preventing ability of the coating film, epoxy resins, modified epoxy resins made by modifying epoxy resins with organic acids or organic amines, phenoxy resins, polyester resins,
Preferred are liquid rubbers such as polybutadiene, modified liquid rubbers, petroleum resins such as polycyclopentadiene, and vinyl resins such as polyvinyl butyral.

Examples of curing agents to be mixed with these binder resins include alkyl etherified melamine resins, alkyl etherified urea resins, phenol resins, polyisocyanates, blocked isocyanates, polyamide resins, polyamines, polyvalent carboxylic acids, and polyvalent carboxylic acids. Examples include carboxylic acid anhydrides.

Furthermore, this conductive undercoating paint can contain a rust-preventing pigment, like a normal rust-preventing paint.

These anti-corrosion pigments include, for example, sulfate-based pigments such as basic lead sulfate; chromate-based pigments such as basic lead chromate, basic lead silichromate, zinc chromate, and strontium chromate; zinc phosphate, and condensed phosphorus. Phosphates such as aluminum acids;
Examples include borate salts such as barium metaborate; molybdate salts such as calcium molybdate; these may be used alone or in combination of two or more.

Incidentally, this conductive undercoating paint may contain pigments such as coloring pigments and extender pigments, and additives such as surface conditioners and anti-settling agents, as well as ordinary paints.

The form of this conductive undercoating paint may be a solvent-based paint dissolved or dispersed in an organic solvent, or a water-based paint dissolved or dispersed in water or a mixture of water and a hydrophilic organic solvent. It's okay to be hot.

Examples of methods for applying conductive primer paint include brushing, roller coating, spray coating,
Examples include electrostatic coating, but air spray coating, airless spray coating, air spray electrostatic coating, rotary atomization electrostatic coating, etc. are suitable.

The thickness of the dry film of the conductive undercoat is 5 to 5.
Preferably it is 50μ. In the case of a film thickness of less than 5 μm, it is sufficiently effective in preventing the progression of corrosion after the paint film is scratched, but the first advantage of the present invention is that it is effective against collisions with pebbles etc. while driving. The paint film is damaged and cannot be sufficiently effective in preventing the substrate from being exposed. In addition, if the film thickness exceeds 50μ, a large amount of conductive powder substance must be blended in order to obtain sufficient conductivity, and the coating performance such as flexibility may deteriorate or the conductivity may deteriorate. There may be a difference in appearance after the topcoat is applied between the areas coated with the primer coat and the areas not coated.

After applying the conductive undercoat as described above, the resulting coating film is either heated and dried, or dipped in an electrodeposition paint bath in an undried or semi-dry state without any particular heating. Perform electrodeposition coating as shown.

There are two types of electrodeposition paints: anionic electrodeposition paints and cationic electrodeposition paints, and both can be applied to the present invention.

After electrocoating, wash with water to remove excess electrocoat paint, and then heat dry at the specified baking temperature for the electrocoat paint (the thickness of the electrocoat film is usually 10 to
It is 30μ. ).

Note that the automobile body to which the rust-preventing coating method of the present invention has been applied can be coated with an intermediate coat,
Alternatively, a top coat is applied after a wet-on-wet coating of a chipping primer and an intermediate coat is applied.

According to the anti-corrosion coating method of the present invention, the undercoat paint is applied twice to areas where external corrosion is likely to occur, and the coating film in those areas can be thickened, so when driving, Even if a pebble or the like hits at high speed, damage to the paint film that exposes the base material is much less likely to occur than in the past. Also,
There is an advantage that there is no difference in smoothness or shine between the areas coated with the conductive undercoat and those not coated with the topcoat.Furthermore, the conductive undercoat used in the present invention can be applied by spray coating, etc. Because it can be painted using the above method, there are fewer restrictions on paint formulation than with electrodeposition paints.For example, the types and amounts of resins and anti-rust pigments can be selected from a wide range, and the adhesion and anti-rust properties can be improved. Since large paint can be used, even if scratches that reach the substrate occur on the paint film,
Corrosion progresses much more slowly than with electrodeposition coating alone, and the progress of corrosion from damaged areas can be extremely effectively prevented.

Next, the present invention will be explained in further detail by giving examples and reference examples. In the examples, parts are examples and % is weight %.

Example 1 A solvent-based conductive undercoat paint was obtained with the following formulation.

Epoxy resin solution (manufactured by Yuka Ciel Epoxy Co., Ltd., Epicote 1007 cellosolve acetate solution, solid content 50%) 114 parts blocked isocyanate solution (Japan Polyurethane
Co., Ltd., DC-2969, solid content 80%) 16 parts Conductive carbon black (Columbia Carbon Co., Ltd., Conductex 975) 5 parts Tribasic lead sulfate (Kikuchi Shiki Kogyo Co., Ltd.) 5 parts Rutile dioxide Titanium (manufactured by Teikoku Kako Co., Ltd., JR-
602) 23 parts cellosolve acetate 10 parts xylene 8 parts The obtained conductive undercoat paint was heated and dried at 140°C for 5 minutes, and the volume resistivity of the film was determined using a film resistance measuring device (Kawaguchi Electric Industry Co., Ltd.). The value was 0.6 x 10 ⁶ Ω·cm when measured using a teraohmmeter (VE-30, manufactured by Manufacturer, Inc.).

This conductive undercoat paint was diluted with a mixed solvent of equal weights of cellosolve acetate and xylene to a viscosity of 20 seconds (20°C) as measured with a food cup No. 4, and then subjected to chemical conversion treatment (Nihon Parkerizing Co., Ltd.).
A steel plate with a size of 30 cm x 10 cm, manufactured by Bonderite Co., Ltd. (Bonderite 3004), was coated with air spray so that the dry film thickness became a gradient film thickness of 0 to 40 μm.

The obtained test piece was heated and dried at 80°C for 5 minutes, cooled to room temperature, and immersed in a cationic electrodeposition paint (Aqua 4120, manufactured by Nippon Oil & Fats Co., Ltd.) bath with the test piece used as a cathode, and heated at 250V. Apply electricity for 3 minutes and apply electrodeposition coating.
After washing with water, heat dry at 170℃ for 25 minutes,
The conductive undercoat film and the cationic electrodeposition film were cured simultaneously.

The cationic electrodeposited film was smooth and uniformly coated to a dry film thickness of approximately 20 μm, both on the areas coated with the conductive undercoat and on the areas not coated.

After electrodeposition, apply an intermediate coating (Epico 1500CP Sealer, manufactured by Nippon Oil & Fats Co., Ltd.) by air spray to a dry film thickness of 40μ, heat dry at 140℃ for 30 minutes, and harden. I let it happen.

Next, top coat paint (manufactured by Nippon Oil & Fats Co., Ltd., Melami No.
1 White) so that the dry film thickness is 40μ.
It was applied with air spray and dried by heating at 140°C for 30 minutes to harden it.

The condition of the painted surface of the test piece after the above process was that there was no difference in smoothness, gloss, etc. between the areas coated with the conductive undercoat and the areas not coated.
It was good and warm.

Next, using a chipping tester (Graberometer, manufactured by Suga Test Instruments Co., Ltd.), approximately 300 c.c. of No. 7 crushed stone was injected onto the painted surface at an air pressure of 2.0 Kg/cm ² and the test piece was subjected to collision. When the chipping resistance was tested, there were many scratches that reached the base material in the areas where the conductive undercoat was not applied, but the areas where the conductive undercoat was applied from 5 μm to less than 10 μm were scratched. , the number of scratches that reach the substrate is extremely small,
In areas coated with conductive undercoat paint of 10 microns or more, there were no scratches that reached the base material.

Furthermore, after the chipping resistance test, the test pieces were exposed to dust for 6 months at an outdoor dust dew test site (Omaezaki Coast, Shizuoka Prefecture) and the spread of rust from the scratches was investigated. The part that is
No thread rust occurred at all, but thread rust of 3 to 4 mm occurred in the area where only the electrodeposition coating was applied.

Example 2 A solvent-based conductive undercoat paint was obtained with the following formulation.

Epoxy ester resin solution (manufactured by Dainippon Ink and Chemicals Co., Ltd., Petscosol P-786, solid content 50%,
107 parts butylated melamine resin solution (manufactured by Dainippon Ink & Chemicals Co., Ltd., Super Betsukamine L-105-60, solid content 60%) 22 parts conductive carbon black (example 1) 5 parts graphite ( Chuetsu Graphite Co., Ltd., flaky graphite 97-300)
5 parts zinc chromate ZTO (manufactured by Kikuchi Shiki Kogyo Co., Ltd.) 10 parts talc 10 parts zinc white 15 parts rutile titanium dioxide (example 1) 20 parts xylene 10 parts cellosolve acetate 5 parts butyl alcohol 3 parts Obtained The conductive undercoat paint was heat-dried at 140° C. for 5 minutes, and the volume resistivity value of the coating film was measured in the same manner as in Example 1 and showed a value of 0.6×10 ⁶ Ω·cm.

This conductive undercoat paint was diluted in the same manner as in Example 1, and then air sprayed onto the steel plate of Example 1 so that the dry film thickness became a gradient film thickness of 0 to 40 μm.

After setting the obtained test piece at room temperature for 5 minutes, it was immersed in a cationic electrodeposition paint bath (example 1 above) in the same manner as in Example 1, and subjected to electrodeposition coating. The cationic electrodeposited coating was smooth and uniformly coated to a dry film thickness of about 20μ, both on the areas coated with the conductive undercoat and on the areas not coated.

After the electrodeposition coating, in the same manner as in Example 1, an intermediate coating (example 1, described above) and a top coating (example 1, described above) were applied, dried by heating, and cured.

The condition of the painted surface of the test piece after the above process was that there was no difference in smoothness, gloss, etc. between the areas coated with the conductive undercoat and the areas not coated.
It was good and warm.

Next, when this test piece was tested for chipping resistance in the same manner as in Example 1, there were many scratches that reached the base material in the area where only electrodeposition coating was applied, but when the conductive undercoating paint was 5μ Areas coated with less than 10μ are extremely unlikely to cause scratches that reach the base material, and areas coated with 10μ or more are
There were no scratches that reached the base material.

Furthermore, when the test piece after the chipping resistance test was subjected to an outdoor back-dew test for 6 months in the same manner as in Example 1, no thread rust was observed in the area coated with the conductive undercoat. However, thread rust of 3 to 4 mm occurred in the area where only the electrodeposition coating was applied.

Example 3 A water-soluble conductive undercoat paint was obtained with the following formulation.

Water-soluble epoxy modified alkyd resin solution (Hoechst
Co., Ltd., VWE-37L, solid content 70%) 114 parts Methylated melamine resin (Mitsui Toatsu Chemical Co., Ltd., Cymel 303, solid content 100%) 20 parts Conductive carbon black (previous example) 1) 3-part strontium chromate (manufactured by Kikuchi Shiki Kogyo Co., Ltd.,
Strontium S) 5 parts talc 5 parts rutile titanium dioxide (example 1) 35 parts triethylamine 7 parts diethylene glycol monobutyl ether 20 parts deionized water 90 parts The resulting conductive undercoat was heated at 140°C for 5 minutes. The volume resistivity value of the dried coating film was measured in the same manner as in Example 1 and showed a value of 1.0×10 ⁶ Ω·cm.

This conductive undercoat was diluted with deionized water to a viscosity of 30 seconds (20°C) as measured with a food cup No. 4, and applied to the steel plate of Example 1 with a gradient of dry film thickness of 0 to 40 μ Air spray coating was applied to achieve the desired film thickness.

The obtained test piece was dried by heating at 80°C for 5 minutes, then cooled to room temperature, and immersed in an anionic electrodeposition paint (Aqua 2500, manufactured by Nippon Oil & Fats Co., Ltd.) bath with the test piece used as an anode, and heated to 200V. The conductive undercoat film and the anionic electrodeposition film were simultaneously cured by applying electricity for 3 minutes to apply the electrodeposition coating, washing with water, and heating and drying at 165°C for 25 minutes.

The anionic electrodeposited film was smooth and uniformly coated to a dry film thickness of about 20 μm both in the areas coated with the conductive undercoat and in the areas not coated.

After the electrodeposition coating, in the same manner as in Example 1, an intermediate coating (example 1, described above) and a top coating (example 1, described above) were applied, dried by heating, and cured.

The condition of the painted surface of the test piece after the above process was that there was no difference in smoothness, gloss, etc. between the areas coated with the conductive undercoat and the areas not coated.
It was good and warm.

Next, when this test piece was tested for chipping resistance in the same manner as in Example 1, there were many scratches that reached the base material in the area where only electrodeposition coating was applied, but when the conductive undercoating paint was 5μ Areas coated with less than 10μ are extremely unlikely to cause scratches that reach the base material, and areas coated with 10μ or more are
There were no scratches that reached the base material.

Furthermore, when the test piece after the chipping resistance test was subjected to an outdoor dew test for 6 months in the same manner as in Example 1, it was found that the parts where only the electrodeposition coating was applied were not affected by chipping. A scab-like rust had developed from the scratches, but no such rust had developed in the areas coated with conductive undercoat.

Reference Example 1 A non-conductive solvent-based undercoat paint was obtained using the same formulation as in Example 1 except for the conductive carbon black.

The obtained undercoat paint was heated and dried at 140° C. for 5 minutes, and the volume resistivity of the coating film was measured in the same manner as in Example 1 and showed a value of 1×10 ¹⁶ Ω·cm.

After diluting this undercoat paint in the same manner as in Example 1, it was applied to the steel plate of Example 1 to a dry film thickness of 0 to 40 μm.
Air spray coating was performed to obtain a gradient film thickness of .

After setting the obtained test piece at room temperature for 5 minutes, it was immersed in a cationic electrodeposition paint bath (example 1 above) in the same manner as in Example 1, and electrocoated. , cationic electrodeposition paints should not be applied thickly to areas that have been coated with an undercoat, and areas where the undercoat has been applied in a mist form may have dents, holes, or small irregularities on the painted surface. It was hot.

Claims (1)

[Claims] 1. Contain 1 to 25 parts by weight of conductive powder per 100 parts by weight of paint solid content in areas where corrosion is likely to occur on the outer panel of the automobile body, and the volume resistivity of the dry coating film is 1 x 10 ⁶ A rust-preventing coating method for automobile body exterior panels, which comprises applying a solvent-based or water-based conductive undercoating paint having a resistance of Ωcm or less, and then applying electrodeposition coating.