JP2000271529A - Method for forming laminated paint film having chipping- proof property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming an excellent chipping-proof laminated paint film capable of preventing deterioration such as a paint film damage due to flying stone, rusting caused thereby or the like on a surface of a metal- made material to be painted. SOLUTION: A chipping-proof primer 1 containing an amine modified epoxy resin, a block isocyanate, and a rust-proof pigment is applied to a part liable to suffer chipping on a metal-made material to be painted, and a chipping-proof primer paint film 1 is formed. A thermosetting powder coating is applied onto the primer paint film 1, heated at a temperature wherein the powder paint film 2 is completely not thermally set, and the powder paint film 2 is formed. Then, the material to be painted is dipped into an electrolytic coating bath, and an electrolytic deposition paint film 3 is formed. Further, the primer paint film 1, the powder paint film 2, and the electrolytic deposition paint film 3 are simultaneously cured by heating, and a laminated paint film is formed. A face coating paint film 4 is formed on the obtained laminated paint film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the formation of a laminated coating film having excellent chipping resistance (that is, it is possible to prevent damage to the coating film caused by splashing on a metal substrate and the formation of rust caused thereby). About the method.

[0002]

2. Description of the Related Art Metallic objects such as automobile bodies, house building materials, guardrails, road signs, and the like usually have cracks in the coating film that protects the surface of the object to be coated due to splashing from the road surface. Or peeling. Such a phenomenon is generally called chipping. Thereafter, when water or the like enters the crack or peeled portion, rust is generated on the base surface of the object to be coated, and as a result, the object to be coated is corroded. In order to prevent the above-described chipping and the progress of corrosion caused by the chipping, there have been proposed many methods of forming a paint or a composite coating film for imparting chipping resistance.

For example, JP-A-6-41494 discloses (a) a polyisocyanate compound in which polycaprolactone is bound and an active isocyanate group is blocked, and (b) two or more polyisocyanate compounds in one molecule. A coating composition having excellent chipping resistance and comprising a hydroxyl group-containing resin having a hydroxyl group as a main component is disclosed. According to JP-A-6-41494, the chipping-resistant coating composition is used in an electrodeposition coating-topcoat coating system, or in an electrodeposition coating-intermediate coating-topcoat coating laminate coating. The application between the two adjacent coating films improves the chipping resistance of the entire composite coating film. Alternatively, Japanese Patent Application Laid-Open No. 62-4475 discloses that an intermediate coating film using an organic solvent type coating material having specific physical properties is formed between an electrodeposition coating film and a powder top coating film. I have. This intermediate coating film has high chipping resistance, and improves the chipping resistance of the formed composite coating film.

On the other hand, as a method of forming a composite coating film which has recently attracted attention, there is a method called a reverse coating method or an inverse coating method. In this method, instead of forming an electrodeposition coating on a metal object as described above, a powder coating is first formed on a metal object, and then a powder coating is formed. After forming an electrodeposition coating on the area not covered with,
Further, a method of forming a top coat on them (for example, Japanese Patent Publication No. 56-10397 and Japanese Patent Application Laid-Open No. 59-14040).
No. 0). In these methods, the area where the powder coating is difficult to apply or cannot be applied (for example, an inner plate of an automobile).
In addition, since the electrodeposition coating is applied only to the region where the thickness of the powder coating is small, the coating cost can be reduced. Furthermore, since the powder coating and the electrodeposition coating are simultaneously heated and cured, the cost relating to the thermal energy used can be reduced. However, although the above method is extremely effective as a coating method, a part of the surface of the object to be coated which is susceptible to chipping in a region which is not coated with an electrodeposition coating film but is coated only with a powder coating film. In particular, it has been found that the chipping resistance of the site in a strongly salt-damaged area is not always sufficient.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for applying the above-mentioned reverse coating method or inverse coating method, in which the area covered with only a powder coating but not with an electrodeposition coating is used. Novel primer that can express excellent chipping resistance at sites that are susceptible to chipping,
And a method for forming a laminated coating film using the same.

[0006]

The inventors of the present invention have made intensive efforts, and as a result, the above-mentioned Japanese Patent Publication No. 56-10397 and Japanese Patent Application Laid-Open
Method of improving the performance of the obtained laminated coating film by applying a primer coating having excellent chipping resistance to the surface of the metal workpiece before performing the inverse coating method described in JP-140400, etc. Was found. First of the present invention
In the embodiment, on a metal coating object 5, (1) an amine-modified epoxy resin, coated with a chipping-resistant primer containing a blocked isocyanate and a rust-preventive pigment, to form a chipping-resistant primer coating film 1, 2) A thermosetting powder coating is applied on the chipping-resistant primer coating film 1, and the powder coating film is heated to a temperature at which the thermosetting powder coating is not completely cured, and the powder coating film is heated.
Forming 2, (3) immersing the object to be coated 5 in an electrodeposition coating bath to form an electrodeposition coating 3, (4) the chipping-resistant primer coating 1, powder coating 2 And simultaneously heating and curing the electrodeposition coating film 3 to form a laminated coating film 10, and (5) including forming an overcoating film 4 on the laminated coating film 10 obtained in the step (4). This is a method for forming a laminated coating film 10 (see FIG. 1).

A second aspect of the present invention is a chipping-resistant primer comprising an amine-modified epoxy resin, a blocked isocyanate and a rust-preventive pigment.
By using the chipping-resistant primer of the present invention, a laminated coating film having excellent chipping resistance is provided.

The present invention also provides a laminated coating formed by the above method.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Step (1) for forming a laminated coating film : In the method for forming a laminated coating film of the present invention, first, an amine-modified epoxy resin, a blocked isocyanate and a rust-preventive pigment are formed on a metal substrate. Paint the chipping resistant primer contained. Hereinafter, the chipping-resistant primer will be described. The chipping-resistant primer used in the present invention contains, as essential components, an amine-modified epoxy resin, a blocked isocyanate, and a rust preventive pigment.

The amine-modified epoxy resin () is obtained by modifying an oxirane group of an epoxy resin with an amine. The epoxy resin serving as the main skeleton is, for example, a compound having two or more oxirane groups in a molecule. It can be used preferably. Specific examples of such an epoxy resin include:
Glycidyl ester resins; glycidyl ether resins such as condensation products of bisphenol A and epichlorohydrin and condensation products of bisphenol F and epichlorohydrin; alicyclic epoxy resins; cotton-like aliphatic epoxy resins; Brom-containing epoxy resin; phenol-novolak type or cresol-novolak type epoxy resin; and the like. In particular, a condensation reaction product of bisphenol A and epichlorohydrin or a condensation reaction product of bisphenol F and epichlorohydrin And the like.

The amine-modified epoxy resin () may be obtained by modifying the epoxy resin with an amine having a primary hydroxyl group such as diethanolamine and monoethanolamine. The amine modification ratio in the resin () is preferably in the range of 100/50 to 100/120 in equivalent ratio of glycidyl group / amine group. As the amine-modified epoxy resin (), those having a nonvolatile content of 20 to 70% by weight are preferred, but the present invention is not limited to this. Specific examples of the amine-modified epoxy resin () include “EP-909A Varnish” manufactured by Toto Kasei Co., Ltd.

The amine-modified epoxy resin () used in the present invention has a number average molecular weight of 500 to 10,000, preferably 10 to 10,000.
It may be in the range of 00-8000. When the number average molecular weight of the amine-modified epoxy resin () is less than 500, the resulting chipping-resistant primer coating film has disadvantages such as reduced chipping resistance. Alternatively, if the number average molecular weight exceeds 10,000, a uniform coating film cannot be obtained, resulting in poor chipping resistance of the chipping-resistant primer coating film.

The blocked isocyanate () incorporated in the chipping-resistant primer of the present invention acts as a curing agent for forming a cured coating film by reacting with the amine-modified epoxy resin () and causing a thermal crosslinking reaction. The blocked isocyanate () is, for example, by subjecting an active isocyanate group of a polyisocyanate such as hexamethylene diisocyanate, isophorone diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate or the like to an addition reaction with a polyol compound or the like.
Blocked with an alcohol or the like in the polyol compound. Here, the polyol compound may be a polyether polyol or a (hydroxyl-containing) polyester resin.

Examples of the rust preventive pigment () used in the present invention include chromium pigments such as strontium chromate, phosphate pigments such as zinc phosphate, and molybdenum pigments such as zinc molybdate and aluminum phosphomolybdate. Is mentioned. Further, in addition to the rust preventive pigment (), the anti-chipping primer includes coloring pigments such as titanium oxide, red iron oxide, iron oxide, carbon black, phthalocyanine blue, phthalocyanine green, quinacridone pigment, and azo pigment; talc, calcium carbonate, An extender such as precipitated barium sulfate or silica may also be contained.

In the chipping-resistant primer of the present invention, the content of the above components (1) to (10) to 50 parts by weight of an amine-modified epoxy resin () based on 100 parts by weight of the total solid content;
It may be in the range of 2 to 30 parts by weight of the blocked isocyanate () and 1 to 20 parts by weight of the rust preventive pigment (). Here, the weight ratio of the solid content of the amine-modified epoxy resin () and the blocked isocyanate () is preferably in the range of 50:50 to 90:10, and more preferably 70:40 to 90:10. If the solid content weight ratio deviates from the above range, the chipping resistance of the chipping-resistant primer coating film is undesirably reduced. The total pigment content of the rust-preventive pigment () and other pigments is 20
It is preferably between 70 and 70% by weight, preferably between 45 and 65% by weight. If the total content of the rust-preventive pigment () and the pigment other than the rust-preventive pigment is outside the above range, the chipping resistance of the chipping-resistant primer coating film decreases.

The chipping-resistant primer of the present invention may further comprise, as other additives, an anti-settling agent; a curing accelerator,
It may contain a plasticizer, an ultraviolet absorber, an antioxidant, a pigment dispersant, benzoin, benzoins such as benzoin such as a derivative obtained by adding 1 to 3 functional groups to benzoin, and a surface conditioner.

As a solvent for dissolving or dispersing the above components, water or an organic solvent (for example, aromatic hydrocarbon such as benzene, toluene, xylene, etc .; aliphatic hydrocarbon such as hexane, heptane, octane, mineral spirit, etc.); Ester such as ethyl acetate and butyl acetate; ketones such as methyl ethyl ketone and methyl isobutyl ketone). When water is used as the solvent, water alone or a mixture of water and a suitable aqueous organic solvent can be used. Alternatively, the organic solvents can be used alone or in combination. The prepared chipping-resistant primer preferably has a viscosity of
Before use, the mixture may be diluted with a suitable diluent so that the viscosity is in the range of 10 to 35 seconds (# 4 Ford cup / 25 ° C.) or the viscosity at the time of coating falls within the above range.

In the first step of the method of the present invention, the above-mentioned chipping-resistant primer is applied on a metal substrate by a conventional method such as air spray, airless spray, electrostatic coating and the like.

The dry film thickness of the coating of the chipping-resistant primer can be in the range of 2 to 30 μm. If the film thickness is less than 2 μm, the desired rust prevention cannot be sufficiently obtained, and if it exceeds 30 μm, it becomes difficult to apply the powder coating to be applied on the primer coating, and as a result, It is not preferable because the appearance becomes poor.

The resulting chipping-resistant primer coating is
Drying or curing may not be performed before subjecting to a subsequent step, or drying may be performed at a temperature of 30 to 100 ° C. within 30 minutes.

Step (2): As the second step of the method of the present invention, a thermosetting powder coating is applied on the chipping-resistant primer coating film, and the temperature at which the powder coating is not completely thermoset. To form a powder coating.

The thermosetting powder coating which can be used in the present invention is a conventionally known powder coating mainly comprising a thermosetting resin (a thermosetting resin such as an epoxy or polyester resin) and a curing agent. May be. In the thermosetting resin,
Examples of the epoxy thermosetting resin include compounds having two or more oxirane groups in the molecule (for example, glycidyl ester resin, glycidyl ether type resin such as condensation product of bisphenol A and epichlorohydrin, alicyclic resin). Epoxy resins, flocculent aliphatic epoxy resins, bromine-containing epoxy resins, phenol novolak epoxy resins, cresol novolak epoxy resins, etc.); and polyester resins such as ethylene glycol, propanediol, pentanediol, and hexanediol. ,
Polyhydric alcohols such as neopentyl glycol, trimethylolpropane, and pentaerythritol, and carboxylic acids such as maleic acid, terephthalic acid, isophthalic acid, phthalic acid, succinic acid, glutanic acid, adipic acid, sebacic acid, β-oxypropionic acid And the like, but not limited thereto. As the curing agent contained in the thermosetting powder coating, when the thermosetting resin is an epoxy resin, an epoxy resin having a phenolic hydroxyl machine, an amine curing agent (dicyandiamide, imidazoles, imidazolines, etc.) However, in the case of the polyester resin, a block isocyanate, a uretdione curing agent, an amino resin, an epoxy resin and the like can be exemplified, but the present invention is not limited thereto.

Powder coatings include various pigments such as coloring pigments and extender pigments; surface modifiers; foams represented by benzoins such as benzoin and benzoin derivatives in which one to three kinds of functional groups are added to benzoin. Inhibitor; anti-armpit agent;
Curing accelerator (or curing catalyst); plasticizer; antistatic agent;
It may contain various additives such as an ultraviolet absorber, an antioxidant, a pigment dispersant, a flame retardant, and a fluidity-imparting agent.

The powder coatings preferred for use in this step include, for example, “Powax P-100” (polyester powder coating), “Powax P-700” (polyester powder coating) and “Powax P-700” (polyester powder coating). Powderx H-100 "(polyester-epoxy powder coating) (all manufactured by Nippon Paint Co., Ltd.).

The powder coating is applied on the coating film of the chipping-resistant primer by a conventionally known electrostatic powder coating method.
As the electrostatic powder coating method, any of a corona charging method and a friction charging method may be used.

Generally, in the electrostatic powder coating method, an object to be coated is first grounded (grounded), and then a powder coating gun (for example, a corona charging coating gun or a friction charging coating gun) is used. This is performed by spraying a body coating composition onto the object to be coated. Here, the corona-charging type coating gun can be sprayed by corona discharge treatment of the powder coating composition, while the tribo-charging type coating gun is sprayed by friction-charging the powder coating composition. It is possible.
In the electrostatic powder coating method, the discharge rate of the powder coating composition of the present invention from the powder coating gun is preferably set to 50 to 400 g / min. In addition, the distance from the tip of the gun portion of the powder coating gun to the workpiece is 100 mm from the viewpoint of coating efficiency.
It is preferable to set it to 500 mm. Thus, the particles of the powder coating composition adhere electrostatically to the object to be coated, and a particle layer (that is, an uncured powder coating film) is formed. In this step, the powder coating is applied under the condition that the film thickness is in the range of 10 to 80 μm.

Thereafter, the powder coating is heated at a temperature (for example, 70 to 150 ° C., preferably 70 to 120 ° C.) at which it is not completely thermally cured.
Heat for ~ 15 minutes. Such a heat treatment is generally called half bake. By this half bake treatment, in the subsequent electrodeposition coating step (3), when the object to be coated is immersed in an electrodeposition coating bath, it is possible to prevent the powder coating from peeling off from the object to be coated. In addition, by employing the above heating temperature, the number of steps for high-temperature curing required for each coating can be reduced, energy can be saved, and production efficiency can be improved.

Step (3): Next, the object to be coated is immersed in an electrodeposition coating bath to form an electrodeposition coating film. In this step, an electrodeposition paint is applied to a region not covered with the powder coating film.

The electrodeposition paint that can be used in the above step is
Either an anionic or cationic electrodeposition coating commonly used in this field may be used, but from the viewpoint of higher corrosion resistance, a coating using a cationic electrodeposition coating is preferred.

The cationic electrodeposition coating composition is a cathodic deposition type thermosetting electrodeposition coating composition that neutralizes a binder resin having a basic amino group with an acid to make it water-soluble. That is, the cationic electrodeposition paint can be deposited on the surface of the object to be coated by using the object as a cathode. Examples of the binder resin having a basic amino group contained in the cationic electrodeposition coating material include a secondary amine (for example, a secondary amine in which a primary amine is blocked by a ketimination of diethylene triamine or the like) with an epoxy group of a bisphenol epoxy resin. Amine) is preferred. As the crosslinking agent contained in the cationic electrodeposition coating composition, it is preferable to use a blocked polyisocyanate blocked by a blocking agent such as alcohols, phenols, oximes, and lactams.

Alternatively, the electrodeposition paint may be an anion type electrodeposition paint such as a maleated oil type or a polybutadiene type.

The above-mentioned cationic or anionic electrodeposition paints further include pigments such as coloring pigments, extender pigments, rust preventive pigments and the like.
A hydrophilic and / or hydrophobic solvent, an additive, and the like may be contained as necessary. The pigment can be used in an amount of 5 to 150 parts by weight based on 100 parts by weight of the resin solid content in the paint. Electrodeposition paints usually have a film thickness after baking of 10 to 40μ.
m, particularly preferably 15 to 25 μm.

Step (4): The chipping-resistant primer coating, powder coating and electrodeposition coating obtained above are simultaneously heated and cured to form a laminated coating. The thermosetting conditions preferably have a thermosetting temperature of from 10 to 240 at a temperature in the range of 150 to 240 ° C.
90 minutes. Therefore, in the present invention, the thermosetting temperature of each of the uncured chipping-resistant primer coating and the electrodeposition coating must be substantially equal to the thermosetting temperature of the powder coating.

Step (5): A top coat is formed on the obtained laminated coat. As the overcoat film (that is, in the case of only the colored paint or in the case of the combination of the colored paint and the clear paint) that can be formed on the above-mentioned laminated coated film and the method of forming the same, any of those known in the art can be used. The coloring paint basically contains a binder resin, a curing agent and a pigment. The clear paint contains a binder resin and a curing agent, and contains little or no pigment. The pigment includes a coloring pigment, an extender pigment, a glitter pigment and the like, and a coloring paint containing the glitter pigment is particularly called a metallic paint. Usually, the metallic paint is used in combination with a clear paint to form a glittering laminated coating film.

As a specific example of the use of the above-mentioned overcoat paint, at least one kind of colored paint is applied on the laminated paint film comprising the powder paint film and the electrodeposition paint film obtained above, and then the desired paint is applied. Thereby, a clear paint can be applied. Each of the top coats may be cured separately, or the colored coat and the adjacent clear coat may be simultaneously cured.

[0036] Metallic coatings suitable for use in the present invention include, for example, phosphated steel sheets, galvanized steel sheets,
Examples include a cold-rolled steel sheet, an aluminum sheet, a stainless steel sheet, a zinc phosphate treated steel sheet, and an iron phosphate treated steel sheet, but the present invention is not limited to these. The metal coated object may be used as it is or may be surface-treated by another method. These treatments may be performed alone or in combination of two or more. Furthermore, the laminated coating film formed by the above-mentioned method and having good anti-chipping properties and, if desired, good anti-corrosion properties can be used in applications where those properties are required, for example, road materials such as guardrails and road signs; automobile bodies; Applicable to building materials.

[0037]

The present invention will be described below with reference to examples.
The present invention is not limited to the following examples. Example 1 Amine-modified epoxy resin [EP-909 manufactured by Toto Kasei Co., Ltd.
A varnish "; nonvolatile content 40%] 34.1 parts by weight, blocked isocyanate [Nippon Polyurethane Industry Co., Ltd." Coronate 2536 "; nonvolatile content 65%] 5.2 parts by weight, rust preventive pigment (SN
2.3 parts by weight of "PHOSPHINAL PZ-04" manufactured by CZ, 21.7 parts by weight of titanium oxide ("Titanium R-960" manufactured by DuPont), 1.5 parts by weight of extender pigment (Tatsumori "Crystalite 5X") and anti-settling (Benton manufactured by Wilbur Ellis, Inc.
38 ") 0.16 parts by weight in 34.4 parts by weight of ethyl acetate
A chipping-resistant primer was prepared by dispersing for 1 hour in a batch SG mill.

The chipping-resistant primer prepared above was applied to a 0.8 mm thick zinc phosphate-treated steel sheet by air spray so that the film thickness was 10 μm over half the area of the steel sheet surface. Next, the steel sheet was placed on a horizontally moving overhead conveyor. Then, while moving the horizontally moving overhead conveyor at a constant speed, a corona charging type coating gun (“PG-1” manufactured by GEMA) fixed in front of the steel plate was used to perform a corona charging type powder coating method. As shown in FIG. 2, a powder paint “Powax P-100” manufactured by Paint Co., Ltd. was applied to a half area of the steel sheet surface (on the chipping-resistant primer previously applied). The thickness of the formed powder coating was set to 50 μm. The electrostatic powder coating conditions applied here were as follows. Horizontal moving overhead conveyor moving speed: 1.8m
/ Min Applied voltage: -80 kv Discharge amount: 100 g / min Discharge pressure: 1.0 kgf / cm ² Air flow rate: 4.5 m ³ / h

After the electrostatic powder coating, a steel plate was coated at 85 ° C.
For 5 minutes to half-bak the powder coating.

Next, a block isocyanate-curing cationic electrodeposition paint “Power Top V-50” manufactured by Nippon Paint Co., Ltd. was applied to the surface of the steel sheet having no powder coating and the thin powder coating. Was used for electrodeposition coating. 28
The steel sheet was immersed in a bath of the electrodeposition paint set at ° C., and the steel sheet was subjected to electrodeposition coating at a coating voltage of 230 V for 3 minutes. Thereafter, the steel sheet was taken out of the bath of the electrodeposition paint and washed with water. The electrodeposition coating film was formed only in the region where the powder coating film was not formed and in the region where the thickness of the powder coating film was small. After the electrodeposition coating, the steel sheet was heated at 180 ° C. for 25 minutes in a hot-air drying furnace to form a coating film, thereby preparing a test plate. Here, the film thickness of the electrodeposition coating film is 20 μm on a steel plate on which the powder coating is not applied.
The conditions were set to be μm. A color coat paint (“Super Luck M-100 Black” manufactured by Nippon Paint Co., Ltd.) was applied on the powder coat and the electrodeposition coat so as to have a dry film thickness of 15 ± 5 μm, and the mixture was allowed to stand at room temperature for 10 minutes. After that, a clear coat paint (“Super Rack O-100 Clear” manufactured by Nippon Paint Co., Ltd.) is further dried to a thickness of 30 ± 5 μm.
After setting at room temperature for 10 minutes, the coating was baked and cured at 140 ° C. for 20 minutes to form a laminated coating film, which was used as a steel sheet sample.

Examples 2 to 5 A chipping-resistant primer was prepared in the same manner as in Example 1 except that the composition and the amount were as shown in Table 1.
Further, using the chipping-resistant primer, a laminated coating film was formed in the same procedure as in Example 1 to obtain a steel sheet sample.

Comparative Example 1 A powder coating, an electrodeposition coating, and the like were prepared in the same manner as in Example 1 except that the chipping-resistant primer was not applied on the substrate.
A laminated coating film consisting of a color coat and a clear coat was formed to obtain a steel sheet sample.

Comparative Example 2 A primer, a powder coating, an electrodeposition coating, and a color were obtained in the same manner as in Example 1 except that a commercially available primer (“Olga CP-250 Primer” manufactured by Nippon Paint Co., Ltd.) was used. A laminated coating film consisting of a coat and a clear coat was formed and used as a steel sheet sample.

[0044]

[Table 1] The numbers in the table represent the following meanings. 1): Amine-modified epoxy resin [“EP-909A Varnish” manufactured by Toto Kasei Co., Ltd .; nonvolatile content: 40%] 2): Blocked isocyanate [Nippon Polyurethane Industry Co., Ltd. “Coronate 2536”; nonvolatile content: 65%] 3): Protection Rust pigment ("PHOSPHINAL PZ-04" manufactured by SNCZ) 4): Titanium oxide ("Titanium R-960" manufactured by DuPont) 5): extender pigment (Tatsumori "Crystalite 5X") 6): Prevention of sedimentation (Benton manufactured by Wilbur Ellis, Inc.
38 ") 7): Ethyl acetate +): No primer coating. ++): Commercially available primer (“OLGA” manufactured by Nippon Paint Co., Ltd.)
CP-250 primer ") was used.

Evaluation Method Using the steel sheet samples having the laminated coating films formed in Examples 1 to 5 and Comparative Examples 1 and 2, the chipping resistance was tested and evaluated according to the following procedures. The test plate was kept at −20 ° C., and 50 g of No. 7 crushed stone was sprayed from the direction perpendicular to the test plate with an air pressure of 4 kg / cm ² , and the peeling of the primer coating on the steel plate sample was evaluated according to the following criteria. did. Evaluation criteria : ：: There is no peeling reaching the steel sheet base. ×: Peeling reaching the steel sheet base. Table 1 shows the results of the chipping resistance test.

From the results shown in Table 1, it can be seen that the use of the chipping-resistant primer of the present invention provides an excellent chipping-resistant laminated coating film.

[0047]

According to the present invention, the chipping-resistant primer of the present invention is applied to a metal-coated object (for example, a metal-coated object used outdoors such as an automobile body, a building material for a house, a guardrail, a road sign, etc.). By performing body coating, electrodeposition coating, and topcoating, a laminated coating film having excellent chipping resistance and a good coating film appearance can be formed.
In addition, by applying the method for forming a laminated coating film of the present invention, it is possible to reduce the heat curing step (that is, the baking step of the coating film) as compared with the conventionally known method, thereby reducing the energy cost. it can.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a laminated coating film obtained by a method of the present invention.

FIG. 2 is a schematic plan view illustrating a coating film evaluation method for steel sheet samples manufactured in Examples 1 to 5 and Comparative Examples 1 and 2.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Anti-chipping primer coating film of the present invention, 2 ... Powder coating film, 3 ... Electrodeposition coating film, 4 ... Overcoat coating film, 5 ... Coating object, 10
... Laminated coating film obtained by the method of the present invention, 100 ... Boundary portion between powder coating film and electrodeposition coating film.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Seiji Takebe 1-10-1 Shin-Sayama, Sayama City, Saitama Prefecture Honda Engineering Co., Ltd. (72) Kenichiro Kurai 1-10-1 Shin-Sayama, Sayama City, Saitama Prefecture Hong Within Da Engineering Co., Ltd. (72) Inventor Chiharu Senoo 19-17 Ikedanakacho, Neyagawa City, Osaka Japan Paint Co., Ltd. F term in reference (reference) 4D075 AE03 BB26Y BB26Z BB89Y CA04 CA33 DB01 DB04 DB05 DB07 DC01 DC05 DC12 EA02 EB33 4K044 AA02 AA03 AA06 BA12 BA14 BA15 BA17 BA21 BB02 BB11 BC02 BC06 CA16 CA18 CA53

Claims (3)

[Claims] 1. A chip-resistant primer coating containing (1) an amine-modified epoxy resin, a blocked isocyanate and a rust-preventive pigment is applied to a portion of a metal substrate to be easily chipped. (2) Applying a thermosetting powder coating on the chipping-resistant primer coating, and heating the powder coating to a temperature at which the powder coating is not completely thermoset to form a powder coating. (3) immersing the object to be coated in an electrodeposition coating bath to form an electrodeposition coating, (4) simultaneously heat-curing the chipping-resistant primer coating, powder coating and electrodeposition coating. And (5) forming a top coat on the laminated coat obtained in the step (4). 2. The chipping-resistant primer used in step (1) of the method according to claim 1, which comprises an amine-modified epoxy resin, a blocked isocyanate and a rust-preventive pigment. 3. A laminated coating film formed by the method according to claim 1.