JPH09206664A - Coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the evenness and corrosion resistance in boundary parts by coating the portions to be the boundary parts of a coating film of a powder coating material and a coating film formed by electrodeposition with a conductive primer after formation of the coating film of the powder coating material and before formation of the coating film by electrodeposition in an object to be coated on which a coating film of a powder coating material is formed at first and uncoated parts are coated by electrodeposition. SOLUTION: In a coating method wherein an object to be coated 1 such as an automotive body is coated with a powder coating material 5 to form a powder coating film 5 at first and then uncoated parts are coated by electrodeposition to form an electrodeposition coating film 7, a conductive primer 2 is applied to portions to be boundary parts of the powder coating film 5 and the electrodeposition coating film 7 after formation of the powder coating film 5 and before formation of the electrodeposition coating film 7. Conductive powder primers consisting of powder resin and conductive liquid primers consisting of conductive materials are used as the conductive primer 2 and metal powders, e.g. copper powder, silver powder, zinc powder, etc., and non- metal powders, e.g. carbon black, acetylene black, etc., are usable as the conductive material. Moreover, cationic electrodeposition coating is preferable as that coating.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a novel coating method.

[0002]

2. Description of the Related Art
Since powder coating contains almost no volatile components such as organic solvents, it has attracted attention as a coating excellent in pollution prevention and global environment protection. However, this coating method has a drawback that it is difficult to coat the back surface, the corner portion, or the slit portion of the object to be coated, and it is difficult to coat the object to be coated having a complicated shape.

As a method for preventing such a defect, there has been considered an undercoat coating method in which an uncoated portion is electrodeposited after powder coating on an object to be coated. According to this method, the electrodeposition coating film is not formed on the dust portion (boundary portion) of the powder coating film.
For this reason, there is a drawback that the corrosion resistance is poor because the coating film thickness at the boundary portion becomes thin.

Further, as a method of increasing the film thickness of the boundary portion, a powder coating material containing a conductive powder is applied to an object to be coated,
Next, a method of coating an anion electrodeposition coating material such as maleated polybutadiene having a re-dissolution rate in a specific range on the unpainted portion is proposed in JP-A-51-133333.
However, in this method, since the powder coating material contains the conductive powder, the fluidity is poor. Therefore, there is a problem that the smoothness of the coating film is deteriorated even in the continuous coating film other than the boundary portion, and as a result, the smoothness of the top coating film is poor.
Further, in this method, since the electrodeposition coating film is formed on the surface of the continuous powder coating film other than the dust portion (boundary portion), it is necessary to use the powder coating material whose volume specific electric resistance value is adjusted within a specific range. Also, there is a problem that it is troublesome because the electrodeposition coating material whose redissolution rate is adjusted to a specific range needs to be used, and the coating material has a narrow selection range, so that only limited coating materials can be used. In addition, the above-mentioned method does not have sufficient corrosion resistance and has a problem in practical use.

[0005]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention applied a powder coating to an object to be coated, such as an automobile body, and preferably electrostatically. In a coating method in which after coating and forming a powder coating film, the uncoated portion is electrodeposited to form an electrodeposition coating film, after the powder coating film is formed and before the electrodeposition coating film is formed, the powder coating film is formed. It was found that a coating film excellent in corrosion resistance, finished appearance, etc. can be formed by applying a conductive primer to the boundary between the coating film and the electrodeposition coating film, and the present invention has been completed. .

That is, according to the present invention, a powder coating material is applied to an object to be coated such as an automobile body, preferably after electrostatic coating to form a powder coating film, and then an unpainted portion is electrodeposited to be electrodeposition coated. In the coating method for forming a film, after forming the powder coating film and before forming the electrodeposition coating film, a conductive primer should be applied to the part that becomes the boundary between the powder coating film and the electrodeposition coating film. Related to the coating method characterized by.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The article to be coated used in the coating method of the present invention is a conductive article to be coated by powder coating and electrodeposition coating, and specifically, it is an automobile body (door, bonnet, etc.). Those used as (including parts) are preferable. As the article to be coated, the article to be coated conventionally used for these coatings can be used without particular limitation, and specifically, aluminum, alumite, iron or steel, zinc, tin, chromium, aluminum or the like on the surface of steel can be used. Examples include a wide range of metals such as plated steel sheets and those whose surfaces are subjected to chemical conversion treatment with chromic acid, phosphoric acid, or the like.

As the powder coating material used in the coating method of the present invention, a conventionally known thermosetting powder coating material can be used without particular limitation. Examples of the thermosetting powder coating material include epoxy resin, polyester resin (containing functional groups such as hydroxyl group and carboxyl group), acrylic resin (containing functional groups such as hydroxyl group, carboxyl group and epoxy group). As a base resin, and as a cross-linking agent (block polyisocyanate, tetramethoxymethyl glycoluril, etc. as a cross-linking agent that reacts with hydroxyl groups, polyepoxide, β
-A thermosetting powder prepared by blending a polycarboxylic acid, an acid anhydride, a phenolic resin, dicyandiamide, an organic acid dihydrazide, an aromatic sulfonium salt cationic polymerization catalyst, etc.) as a cross-linking agent that reacts with an epoxy group such as hydroxyalkylamide. A paint can be used suitably.

In the powder coating material, in addition to the above-mentioned components, for example, a coloring pigment, a filler, a fluidity adjusting agent, an antiblocking agent, a surface adjusting agent, an anti-arming agent, an antioxidant,
Other compounds such as a curing accelerator, a charge control agent and other resins can be blended as necessary. As the powder coating material, one that has passed through about 150 mesh can be preferably used. The powder coating material is a conventionally known method for producing a powder coating material, for example, a base resin, a cross-linking agent, and if necessary, other blending is performed, followed by dry blending, and then melt blending, It can be manufactured by cooling, coarsely pulverizing, finely pulverizing and filtering.

The coating of the powder coating material can be carried out by a powder coating method known per se, preferably an electrostatic powder coating method, for example, a corona charging type, a friction charging type or the like. The powder coating film thickness is usually about 20 to 100 μm, preferably about 30 to 80, in a portion other than the boundary portion (continuous coating film).
The micron range is preferred.

When the conductive primer to be applied next is the conductive powder primer described later, the powder coating is not baked or the powder is not baked when the electrodeposition coating film is baked. The baking can be carried out under conditions such that the coating film reflows (unhardened or not completely hardened), or under baking conditions in which the powder coating material is completely hardened. In the baking of the above powder coating, if the baking is not performed at all or if the coating is formed uncured, the smoothness and the corrosion resistance of the boundary portion between the powder coating and the electrodeposition coating are improved. There are advantages.

Further, when the conductive primer is a conductive liquid primer which will be described later, the powder coating material needs to be baked. Similar to the above, the baking is performed under the conditions (the uncured or not completely cured) such that the powder coating reflows when the electrodeposition coating is baked, or the powder coating is completely cured. However, the former method is preferable.

The baking conditions for the powder coating material in which the powder coating film reflows are different depending on the type of the powder coating material.
About 100 to 140 ° C, about 1 to 10 minutes, about 150
At ~ 170 ° C, it is considered to be about 30 seconds to 5 minutes.

The conductive primer used in the coating method of the present invention is to be applied to the dust portion of the powder coating film (the boundary portion with the electrodeposition coating film) before being subjected to the cationic electrodeposition coating. is there. As the conductive primer, any conventionally known one can be used without particular limitation, as long as the electrodeposition coating film is deposited on the surface of the coating film formed from the primer by electrodeposition coating. As the conductive primer, for example, a conductive powder primer composed of a powder resin and a conductive material, a conductive liquid primer composed of a resin component containing an organic solvent or water as a medium, and a conductive material can be used.

Examples of the conductive material used in the conductive powder primer and the conductive liquid primer include metal powder such as copper powder, silver powder, zinc powder, aluminum powder and bronze powder, and carbon black, acetylene black, graphite and the like. Non-metal powders are included. The mixing ratio of the conductive material may be such that the above-mentioned object is achieved, but normally, the range of about 3 to 50 parts by weight is preferable with respect to 100 parts by weight of the resin component (solid content). The conductive powder primer is 20 from the viewpoint of powder coating workability and electrodeposition coating film deposition.
1 × 10 ³ to 1 × 10 ⁸ Ω · cm at 20 ° C. and 20 V (JIS
It is preferable to have a volume specific electric resistance value in the range of K6911).

As the powder resin used in the conductive powder primer, a thermosetting powder resin prepared by mixing an epoxy resin and a polyester resin as a base resin with a crosslinking agent can be used.

The above epoxy resin has an epoxy equivalent of about 200 to 5000 and an average molecular weight of about 1000 to 8000.
A powder resin having a softening temperature of about 60 to 150 ° C. can be used. Specifically, as the product name, for example, Epicote 1
004, same as left 1002, same as left 1007 (above, Yuka Shell Epoxy Co., Ltd.), Araldite GY-608.
4, same as the left 6097 (manufactured by Ciba-Geigy), DER-6
62, same as left 664, same as left 667 (manufactured by Dow Chemical Co.)
Bisphenol to epichlorohydrin type epoxy resin, EPPN-201, same as the left 202, EOCN-102
No. 0, same as 102S (above, manufactured by Nippon Kayaku Co., Ltd.) and other novolac type epoxy resins, vinyl polymers (eg, glycidyl (meth) acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate and other epoxies. Radical homopolymers of group-containing unsaturated monomers and, if necessary, alkyl or cycloalkyl esters of (meth) acrylic acid such as methyl (meth) acrylate, ethyl (meth) acrylate, cyclohexyl (meth) acrylate, etc. Hydroxyl radical-containing unsaturated monomers such as hydroxyethyl (meth) acrylate, aromatic compounds such as styrene, and radical copolymers with other unsaturated monomers such as nitrile compounds such as (meth) acrylonitrile) Can be mentioned. Among these, bisphenol-epichlorohydrin type epoxy resin and novolac type epoxy resin are preferable because they have excellent corrosion resistance and the like.

As the cross-linking agent for the epoxy resin, any conventionally known one can be used without particular limitation as long as it cross-links and cures with respect to the epoxy groups of the epoxy resin. Specifically, for example, (anhydrous) polycarboxylic acid compound (adipic acid, dodecanedioic acid, (anhydrous) trimellitic acid, (anhydrous) succinic acid, etc.), phenol resin, dicyandiamide, organic acid dihydrazide (adipic acid dihydrazide, Sebacic acid dihydrazide, etc.), cationic polymerization catalyst of aromatic sulfonium salt (benzyl-4-
Hydroxyphenylmethylsulfonium hexafluoroantimonate, benzyl-4-methoxyphenylmethylsulfonium hexafluoroantimonate, 4-acetoxyphenyldimethylsulfonium hexafluoroantimonate and the like).

As the above polyester resin, a hydroxyl group- and / or carboxyl group-containing polyester resin can be used, and the carboxyl equivalent and / or hydroxyl group equivalent is about 200.
˜5,000, an average molecular weight of about 500 to 50,000, and a softening temperature of about 60 to 150 ° C. can be used as a powder resin. The polyester resin is mainly an esterified product of polybasic acid (or methyl ester) and polyhydric alcohol, and examples thereof include phthalic acid, isophthalic acid, terephthalic acid, tetrahydro (anhydrous) phthalic acid, hexahydro (anhydrous) phthalic acid. Aromatic or alicyclic dicarboxylic acid compounds such as dimethyl isophthalate and dimethyl terephthalate and, if necessary, other polycarboxylic acid compounds such as adipic acid, sebacic acid, (anhydrous) maleic acid, (anhydrous) trimellitic acid A polybasic acid such as ethylene glycol, propylene glycol, neopentyl glycol, butanediol, or 1,6-hexanediol which is esterified to have a carboxyl group and / or a hydroxyl group can be used.

As the crosslinking agent for polyester resin, when the polyester resin has a carboxyl group, triglycidyl isocyanurate, polyepoxide (bisphenol (A, F, B) to epichlorohydrin type epoxy resin, novolac epoxy resin, vinyl polymer) Etc.) and β-hydroxyalkylamides. When the polyester resin has a hydroxyl group, blocked polyisocyanates (ε-caprolactam diisocyanate and the like), tetramethoxymethyl glycoluril and the like can be mentioned.

The mixing ratio of the base resin and the cross-linking agent is usually preferably in the range of about 95/5 to 50/50 by weight. However, when the cationic polymerization catalyst of the aromatic sulfonium salt is used, 99.99 / 0.01 to 90 /
A range of 10 weight ratio is sufficient.

In the conductive powder primer, in addition to the above-mentioned components, for example, a coloring pigment, a filler, a fluidity modifier, an antiblocking agent, a surface modifier, an anti-arming agent, an antioxidant, a curing accelerator, Other blends such as a charge control agent and other resins can be blended as necessary. As the powder primer, one that has passed through about 150 mesh can be preferably used.

The electrically conductive powder primer is a conventionally known method for producing a powder coating material, for example, a base resin, a cross-linking agent, an electrically conductive material and, if necessary, other compounds are blended and then dry blended. Next, after melt blending,
It can be manufactured by cooling, coarsely pulverizing, finely pulverizing and filtering.

The conductive powder primer is applied to the dust portion of the powder coating film (boundary portion with the electrodeposition coating film), and the coating method is a known powder coating method, preferably It can be carried out by an electrostatic powder coating method, for example, a corona charging method, a friction charging method or the like.

The conductive powder primer needs to be baked to form a conductive powder primer coating. The coating is a fused or melted uncured powder primer coating or a baked and cured coating. Can be used.

The resin composition used in the above conductive liquid primer may be any of conventionally known lacquer type, heat (including room temperature) curable organic solvent type and water type. As a lacquer type,
For example, acrylic resin-based, polyester (including alkyd resin) resin-based, polyurethane resin-based, silicone resin-based, epoxy resin-based, fibrin resin-based, polyolefin resin-based, phenol resin-based, and the like, and thermosetting type Examples of the epoxy resin include curable epoxy resins (for example, epoxy base resin / phenol resin such as bisphenol to epichlorohydrin type epoxy resin and novolac type epoxy resin, polyamine, polyamide, polycarboxylic acid,
Epoxy resin cross-linking agent such as acid anhydride), acrylic resin-based curing type (for example, hydroxyl group-containing acrylic base resin / amino resin cross-linking agent, hydroxyl group-containing acrylic base resin / (block) polyisocyanate cross-linking agent, epoxy group-containing acrylic resin) / Polycarboxylic acid crosslinking agent, etc., polyester resin type curable type (for example, hydroxyl group-containing polyester (alkyd) base resin / amino resin crosslinking agent, hydroxyl group-containing polyester (alkyd) base resin / (block) polyisocyanate crosslinking agent, air oxidation) Curable alkyd resin, etc.),
Examples thereof include polybutadiene resin-based curable types.

If necessary, the conductive liquid primer may be blended with other compounds such as color pigments, fillers, fluidity modifiers, surface modifiers, anti-armpit agents, curing accelerators and other resins. it can

The conductive liquid primer can be used in a cured or uncured state by applying it by a known application method such as a spray application method, evaporating water or an organic solvent to form a film.

The thickness of the conductive primer coating is preferably about 1 micron or more, preferably about 5 to 100 microns.

As the electrodeposition coating used in the present invention, a cationic electrodeposition coating containing an epoxy resin as a base resin can be preferably used. As the cationic electrodeposition paint, a conventionally known paint can be used. As the cationic electrodeposition coating, for example, an amine-added epoxy resin or an amine-added polyester-modified epoxy resin as a base resin, which is blended or added with a cross-linking agent of block polyisocyanate, and neutralized and dispersed in water can be used. . Among these, electrodeposition coatings using amine-added polyester-modified epoxy resin as a base resin, the corrosion resistance of the electrodeposition coating itself and the smoothness at the boundary portion of the coating, corrosion resistance, weather resistance,
There is an effect such as excellent adhesion. A pigment, an organic solvent, a curing catalyst, a surfactant, and the like can be added to the cationic electrodeposition coating as needed.

The cationic electrodeposition coating method may be a conventionally known method. For example, the cationic electrodeposition coating can be used as an electrodeposition bath, the object to be coated can be used as a cathode, and a material that does not elute metal (carbon plate or the like) can be used as an anode to conduct electricity. It is desirable that the energization condition is such that the thickness of the electrodeposition coating film is about 10 to 40 microns, preferably about 15 to 30 microns. Further, after electrodeposition coating, it is preferable to wash with ultrafiltration filtrate, ultrafiltrate, or the like.

Baking of the cationic electrodeposition coating film is carried out under baking conditions capable of curing the cationic electrodeposition coating film and the powder coating film (in the case of an uncured coating film). The baking depends on the types of the cationic electrodeposition coating film and the powder coating film, but is usually about 140-
In the range of 180 ° C., it can be performed for about 20 to 40 minutes.

The surface of the powder coating film, the electrodeposition coating film and the boundary portion formed by the present invention can be coated with an intermediate coating composition, a top coating composition and the like.

[0034]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 is an explanatory view of a coating method using a conductive powder primer as a conductive primer, FIG. 2 is an explanatory view of a coating method using a conductive liquid primer as a conductive primer, and FIG. 3 is an explanatory view of a conventional coating method. .

Example 1 In FIG. 1, A to E show a coating method using a conductive powder primer. A is a zinc phosphate chemical conversion treated thickness 0.8 x length 300 x width 100
The figure shows the following powder coating material (2) coated with an electrostatic powder coating machine (3) so that the dust of the powder coating material will come near the center of the object (1) of the dull steel plate of (mm). The powder coating film thickness was such that the continuous coating film portion was about 50 microns. The powder coating may or may not be baked. The powder coating was not baked here. B
Is a conductive powder primer coated with an electrostatic powder coating machine (3), and the powder powder dust is coated with a conductive powder primer (4).
The figure which formed is shown. The coating film was applied so that the film thickness was about 10 microns. C is baked (1 at 110 ° C
0 minutes, uncured) powder coating and conductive powder primer (1 × 10 ⁶ Ω · cm, volume specific electric resistance value) flow and powder coating (5) and conductive powder primer coating (6) ) Is formed. D is cationic electrodeposition coating (cationic electrodeposition coating: Electron HG-10R, manufactured by Kansai Paint Co., Ltd., trade name, amine-added epoxy base resin,
The figure shows that a cation electrodeposition coating film (7) was formed by washing with water after (block polyisocyanate crosslinking agent). The thickness of the cation electrodeposition film was such that the continuous coating part had a thickness of about 30 microns. E shows the figure of the coating film after baking.
The baking was performed at 175 ° C. for 20 minutes.

Powder coating: After dry-blending a mixture of 940 g of Epicoat 1004 (trade name, manufactured by Yuka Shell Epoxy Co., Ltd., bisphenol A to epichlorohydrin type epoxy resin), 60 g of adipic dihydrazide, 200 g of titanium white pigment, and 200 g of barita. It was manufactured by melting, kneading and dispersing with a Busco kneader, followed by cooling, coarse pulverization, fine pulverization, and 150 mesh filtration.

Conductive powder primer: Epicoat 100
4 (produced by Yuka Shell Epoxy Co., Ltd., trade name, bisphenol A to epichlorohydrin type epoxy resin) 940
g, adipic acid dihydrazide 60 g, graphite 20
After dry blending 0 g of the mixture, the mixture was melt-kneaded and dispersed in a Busco kneader, followed by cooling, coarse pulverization, fine pulverization, and 150-mesh filtration.

In the coating film formed as described above, the coating film smoothness (smoothness of the coating film smoothness is visually evaluated, hereinafter the same meaning) means that the powder coating part, the electrodeposition coating part and It is good in any of the boundary portions, and has salt spray resistance (JIS K-5400 salt spray test 500.
The rust generation on the flat surface portion after the elapse of time was visually evaluated, and the same meanings will be applied hereinafter), and no rust was generated on the powder coating portion, the electrodeposition coating portion, and the boundary portion thereof, which was good.

[Embodiment 2] In FIG. 2, F to I show a coating method using a conductive organic solvent-based primer. The figure which applied the powder coating material (2) (same as the above) with the electrostatic powder coating machine (3) so that the dust of powder coating material may come near the center of the to-be-coated article (1) is shown. The powder coating film thickness was such that the continuous coating film portion was about 50 microns. G shows the figure which formed the powder coating film (5) by baking (110 degreeC, uncured for 10 minutes). H shows the figure which applied the following conductive organic solvent type | system | group primers (8) with the spray coating machine (9). The coating film was applied so that the film thickness was about 10 microns. The conductive organic solvent-based primer (8) needs to evaporate and dry the organic solvent after coating, but the coating may or may not be cured. No curing was done here. I is a conductive organic solvent-based primer (8) (baked at 80 ° C. for 10 minutes, uncured) (1 ×
10 ⁶ Ω · cm, volume specific electric resistance value) Cationic electrodeposition coating (same as above) on the surface, followed by washing with water to form a cationic electrodeposition coating film (7), then at 20 ° C. at 175 ° C.
The figure which baked for minute and formed the coating film is shown. The coating thickness of the cationic electrodeposition film was such that the continuous coating film portion was about 30 microns.

Conductive organic solvent-based primer: A mixture of 313 g of an organic solvent solution having a solid content of 30% by weight, Epicoat 1004 (the same as the above) dissolved in a xylol solvent (solid content: 94 g), 6 g of adipic acid dihydrazide, and 20 g of graphite. Dispersed and mixed with a paint shaker.

In the coating film formed as described above, the smoothness of the coating film is good both in the powder coating portion, the electrodeposition coating portion and its boundary portion, and the salt spray resistance is in the powder coating portion. No rust was generated in both the electrodeposition coated portion and the boundary portion, which was good.

[Comparative Example 1] In FIG. 3, J to L show a conventional coating method in which a conductive primer is not used. J
Shows a figure in which the powder coating material (2) (the same as the above) is applied by the electrostatic powder coating machine (3) so that the dust of the powder coating material may come near the center of the article to be coated (1). The powder coating film thickness was such that the continuous coating film portion was about 50 microns. K shows a figure in which baking was performed (110 ° C. for 10 minutes, uncured) and the powder coating material flowed to form a coating film. L shows a figure after performing cationic electrodeposition coating (the same as the above), washing with water to form a cationic electrodeposition coating film, and then baking. The thickness of the cationic electrodeposition coating film is about 30 for the continuous coating film part.
Painted to be micron. Baking at 175 ° C for 2
Performed for 0 minutes.

In the coating film formed as described above, the smoothness of the coating film was good in the powder coating portion and the electrodeposition coating portion, but the boundary portion was uneven and poor. The salt spray resistance was good in the powder-coated part and the electrodeposition-coated part, but bad at the boundary part because rust was remarkably generated.

[0044]

According to the coating method of the present invention, the smoothness and corrosion resistance of the boundary portion between the powder coating film and the electrodeposition coating film are excellent.

[Brief description of drawings]

FIG. 1 is an explanatory view of a coating method of the present invention using a conductive powder primer as a conductive primer.

FIG. 2 is an explanatory view of the coating method of the present invention using a conductive liquid primer as the conductive primer.

FIG. 3 is an explanatory view of a conventional coating method.

[Explanation of symbols]

 1 coated object 2 powder coating 3 electrostatic powder coating machine 4 conductive powder primer 5 powder coating 6 conductive powder primer coating 7 cationic electrodeposition coating 8 conductive liquid primer 9 spray coating machine

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshio Tomioka 1-10-1 Shin-Sayama, Sayama City, Saitama Prefecture Honda Motor Co., Ltd. (72) Hiroshi Arai 1-10-1 Shin-Sayama City, Sayama City, Saitama Prefecture HondaE Engineering Co., Ltd.

Claims (4)

[Claims] 1. A coating method for forming an electrodeposition coating film by applying a powder coating material to an object to be coated such as an automobile body to form a powder coating film, and forming an electrodeposition coating film by a powder coating method. A coating method characterized in that a conductive primer is applied to a portion which becomes a boundary portion between the powder coating film and the electrodeposition coating film after forming the film and before forming the electrodeposition coating film. 2. The coating method according to claim 1, wherein the powder coating material is electrostatically coated. 3. The coating method according to claim 1, wherein the conductive primer is a powder coating material. 4. The coating method according to claim 1, wherein the electrodeposition coating is cationic electrodeposition coating.