JP2000001796A - Formation of coating film and coated article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cost effective coating film forming method which is improved in the corrosion preventiveness in the thin film parts and edges of an electrodeposition coating film. SOLUTION: This coating film forming method consists in forming a first electrodeposition coating film and a second electrodeposition coating film under the conditions satisfying the following relations: The relations; 200<=B2<=1,000, 1.1<=B1/B2, 130<=T1<=250, 100<T2<=2<=200, when B1=(T1-100)×t1 (where, T1 is the baking temp. ( deg.C) at the time of forming the first electrodeposition coating film, t1 is the baking time (min) at the time of forming the first electrodeposition coating film) and B2=(T2-100)×t2 (where, T2 is the baking temp. ( deg.C) at the time of forming the second electrodeposition coating film, t2 is the baking time (min) at the time of forming the second electrodeposition coating film).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a coating film applied to an automobile body and the like, and a coated article. In particular, the present invention relates to the improvement of the anticorrosion property of a thin film portion and an edge portion of an electrodeposition coating film.

[0002]

2. Description of the Related Art A coating film applied to an automobile body or the like is composed of an electrodeposition coating film and a top coating film, or a laminated coating film composed of an electrodeposition coating film, an intermediate coating film and a top coating film. Among these, the electrodeposition coating film is formed by immersing the object to be coated in an electrodeposition paint in an electrodeposition tank, performing electrodeposition coating, and then baking.

[0003]

The electrodeposited coating film after completion of baking often has so-called "see-through" in which a coating film defect is large in a thin film portion and a base material is transparent in an edge portion.
In order to solve this problem, there has been proposed a method of performing a so-called two-coat one-bake type double-coat electrodeposition in which an electrodeposition coating film of a different component is applied twice and then baked. However, even with this method, no satisfactory improvement results have been obtained.

[0004] For example, in Japanese Patent Application Laid-Open No. Hei 3-193898, after coating and baking a cationic electrodeposition coating material (A) having good thermal fluidity, a coating composition comprising a cationic electrodeposition resin and a particulate component as main components and obtained. A method of applying and baking a cationic electrodeposition coating material (B) having a predetermined minimum melt viscosity at the time of curing of a film has been proposed. However, such a method of performing two-layer double electrodeposition with different components has disadvantages in terms of management and economy since two electrodeposition tanks have to undergo separate electrodeposition steps. In addition, there is a problem that usable electrodeposition paints are limited.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and provides an economical method for forming a coating film and a coating product which improve the corrosion resistance of a thin film portion and an edge portion of an electrodeposition coating film. The purpose is to provide.

[0006]

According to the first aspect of the present invention,
Akira is an electrodeposition coating consisting of a first electrodeposition coating and a second electrodeposition coating
A method for forming₁= (T₁−100) × t₁  (However, T₁Is the baking temperature for forming the first electrodeposition coating film
(° C), t₁Is the baking time for forming the first electrodeposition coating film
(Min)) and B₂= (T₂−100) × t₂  (However, T₂Is the baking temperature for forming the second electrodeposition coating film
(° C), t₂Is the baking time for forming the second electrodeposition coating film
(Min)), the following relational expression 200 ≦ B₂≦ 1000, 1.1 ≦ B₁/ B₂  130 ≦ T₁≤250,100 <T₂Form the first electrodeposition coating film and the second electrodeposition coating film under the condition satisfying ≦ 200
And a method of forming a coating film.

The invention according to claim 2 of the present application provides a method for forming a coating film according to claim 1, wherein the second electrodeposition coating film has the same composition as the first electrodeposition coating film.

According to a third aspect of the present invention, an electrodeposition coating film is formed by the method according to the first or second aspect, and then both an intermediate coating film and a top coating film or a top coating film is formed. A method for forming a coating film, characterized in that only a coating film is formed.

According to a fourth aspect of the present invention, there is provided a coated article formed by the method for forming a coating film according to any one of the first to third aspects.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Object to be Coated) The object to which the coating film forming method of the present invention is applied may be a metal member or various members subjected to a conductive treatment, for example, an automobile body, an automobile part, a building material,
Examples include a steel structure and household electric appliances.

(Undercoating) Prior to electrodeposition coating, the substrate is preferably subjected to a degreasing treatment, followed by an undercoating treatment such as a zinc phosphate conversion treatment, according to a usual method.

(Electrodeposition paint) For both the first electrodeposition coating film and the second electrodeposition coating film, a known cationic electrodeposition coating or anion electrodeposition coating can be used.
The above-mentioned cationic electrodeposition coating material is a resin having a large number of basic functional groups such as amino groups in a molecule as a coating film forming resin. For example, a glycidyl group of an epoxy resin is added and opened with a primary or secondary amine. A ring-forming resin, an amino group-containing acrylic resin or the like, and a cross-linking agent, if necessary, can be used as a film-forming resin. Examples of commercially available products include “Power Top”, “Power Nicks” and the like (both are trade names, manufactured by Nippon Paint Co., Ltd.). As the above-mentioned anionic electrodeposition paint, a resin having a large number of acidic functional groups such as carboxyl groups in the molecule is used as a film-forming resin. For example, maleated oil and its half-esterified product, phenolic resin-modified maleated oil, If necessary, a film-forming resin with a crosslinking agent, such as an alkyd resin, a maleated fatty acid-modified epoxy resin, a carboxyl group-containing polybutadiene resin, and a carboxyl group-containing acrylic resin, may be used. As a commercially available product, “Power Coat” (trade name, manufactured by Nippon Paint Co., Ltd.) may be mentioned. The first electrodeposition coating film and the second electrodeposition coating film may be formed using electrodeposition paints of different components, but when electrodeposition coatings of the same component are used, one electrodeposition tank is used. Since both electrodeposition coating films can be formed, it is advantageous in terms of management and economy.

[0013] These electrodeposition coatings may contain pigments, additives and organic solvents, if necessary, in addition to water as a medium.

Examples of the pigment include coloring pigments such as titanium dioxide, carbon black, graphite and zinc white, extender pigments such as aluminum silicate and kaolin, strontium chromate, basic lead sulfate, basic lead silicate, aluminum phosphomolybdate and the like. Antirust pigments can be used alone or in combination.

As the additives, acids such as formic acid, butyric acid, lactic acid, and sulfamic acid are used when a cationic electrodeposition paint is used, and ammonia, amine, inorganic alkali salts and the like are used when an anion electrodeposition paint is used. it can. Also, surfactants, curing accelerators, defoamers, ultraviolet absorbers,
Antioxidants and the like can also be used.

As the organic solvent, hydrocarbons, alcohols, ethers, ketones, esters and the like can be used in combination for the purpose of dissolving the resin, adjusting the viscosity of the coating film, adjusting the paint, and the like.

(Coating Method) The coating of the electrodeposition paint can be performed by general electrodeposition coating. For example, the object to be coated is a cathode, stainless steel is used as an anode, the object to be coated is immersed in an electrodeposition paint in an electrodeposition tank, a bath temperature of 15 to 35 ° C., a voltage of 100 to 400 V, and an energizing time of 30 seconds to 10 minutes. Electrodeposition is performed under the following conditions.

(Post-coating treatment) After the electrodeposition coating, it is preferable to perform a water-washing treatment. Examples of such a water-washing treatment include a spraying treatment and a dipping treatment. In addition, it is preferable to perform a setting process such as air drying, which is a draining process, when a high appearance is particularly required or when the shape of the object to be coated is complicated. Drying conditions are usually 130 to 190
The composition is baked and cured at 10 ° C. for 10 to 60 minutes. In the present invention, it is necessary to satisfy the baking conditions described later. The dry film thickness is preferably 15 to 40 μm.

(Baking conditions) In the present invention, the first
The baking of the electrodeposition coating film and the second electrodeposition coating film is represented by the following relational expression.
Perform under satisfactory conditions. That is, B₁= (T₁−100) × t₁  (However, T₁Is the baking temperature for forming the first electrodeposition coating film
(° C), t₁Is the baking time for forming the first electrodeposition coating film
(Min)) and B₂= (T₂−100) × t₂  (However, T₂Is the baking temperature for forming the second electrodeposition coating film
(° C), t₂Is the baking time for forming the second electrodeposition coating film
(Min)), the following relational expression 200 ≦ B₂≦ 1000, 1.1 ≦ B₁/ B
₂  130 ≦ T₁≤250,100 <T₂Baking of the first electrodeposition coating film and the second electrodeposition coating film under a condition satisfying ≦ 200
Is attached.

The value of _{B 2} is required to be 200 to 1,000. If the value of B ₂ is less than 200, sometimes the curing reaction of the second electrodeposition coating film does not occur. The value of B ₂ 1
If it exceeds 000, reflow of the edge portion occurs due to baking of the second electrodeposition coating film, and this portion is thinned, so that “see-through” may occur. In addition, a problem of overbaking may occur. A preferred range of values of B ₂ is 400 or more and 600 or less.

The value of B ₁ / B ₂ needs to be 1.1 or more. When the value of B ₁ / B ₂ is less than 1.1, reflow of the edge portion occurs due to baking of the second electrodeposition coating film, and “see-through” may occur as described above. A preferred range of values of B ₁ / _{B 2} is 1.1 to 4.

T ₁ (baking temperature at the time of forming the first electrodeposition coating film) must be 130 ° C. or more and 250 ° C. or less. T
_{If 1} is lower than 130 ° C., the first electrodeposition coating film may not be cured. If T ₁ exceeds 250 ° C., the first electrodeposition coating film may be overbaked. The preferred range of T ₁ is 180 ° C. or less 160 ° C. or higher.

T ₂ (baking temperature at the time of forming the second electrodeposition coating film) must be higher than 100 ° C. and 200 ° C. or lower. If T ₂ is at 100 ° C. or less, a second electrodeposition coating film may not be cured. When T ₂ exceeds 200 ° C., occur reflow of the edge portion in the baking of the second electrodeposition coating, as described above, "transparent" may occur. The preferred range of T ₂ are equal to or less than 160 ° C. 140 ° C. or higher.

(Intermediate coating) An alkyd resin, polyester resin, acrylic resin or the like and a crosslinking agent are used as a vehicle. These resins may be any of an organic solvent type, an aqueous type, and a powder. Painting can be performed by a usual method, for example, electrostatic painting. Baking can also be performed by a conventional method. The dry film thickness of the intermediate coating is preferably 20 to 60 μm. As the intermediate coating, a chipping primer can be used in combination, or a chipping primer can be used as the intermediate coating. Further, in order to exhibit a design property with the top coat, a “color intermediate coating composition” containing a color pigment can be used. In some cases, after forming the electrodeposition coating film, an overcoating film may be formed without forming an intermediate coating film.

(Overcoat) An acrylic resin, a polyester resin, a fluororesin or the like and a crosslinking agent are used as a vehicle. These resins may be any of an organic solvent type, an aqueous type, and a powder. The dry film thickness of the top coat is 10 to 60 μm
Is preferred. As a top coating, a color pigment and / or a glitter pigment (aluminum flake pigment, mica pigment, etc.) is applied. If necessary, a clear coating or a color clear coating containing a colorant that does not impair transparency is applied. Can be stacked.

[0026]

Embodiments of the present invention will be described below.

(Coating Material) A cold-rolled steel sheet (SPCC-S) treated with zinc phosphate chemical conversion as a coating material for evaluating the anticorrosion property of a thin film portion.
D) was treated with zinc phosphate chemical conversion as a coating material for evaluating the rust prevention and corrosion resistance of the edge portion.
0K ", manufactured by Olfer Corporation).

(Electrodeposition paint) A low-temperature-curable cationic electrodeposition paint “Power Top V-6 Gray” (trade name, manufactured by Nippon Paint Co., Ltd.) was used as the electrodeposition paint A, and The electrodeposition paint "Power Top U-600 Gray" (trade name, manufactured by Nippon Paint Co., Ltd.) was used.

(Coating Film Forming Method) For Examples 1 to 5 and Comparative Examples 1 to 4, the conditions shown in Table 1 were selected for the first and second electrodeposition paints, baking temperature and baking time, and the first and second electrodeposition paints were selected. (2) An electrodeposition coating film was formed.

[0030]

[Table 1]

(Evaluation Method and Evaluation Criteria for Corrosion Protection of Thin Film Part)
The first and second electrodeposition coating films were formed in a total thickness of 8 to 10 μm on a SPCC-SD steel sheet in a dry film thickness, and evaluated by the number of rusts generated on a general surface after 300 hours of a salt spray test based on JIS Z-2371 ( Average of 3 steel plates). The evaluation criteria are as follows. ◎: Rust generation 5 or less ○: Rust generation 6 to 15 △: Rust generation 16 to 30 ×: Rust generation 31 or more

(Evaluation Method and Evaluation Criteria of Edge Corrosion Resistance) First and second electrodeposited coatings were formed on the blade of a cutter knife (LB-10K) in a dry film thickness of 20 μm in total, according to JIS.
The number of rust spots after 168 hours of the salt spray test based on Z-2371 was evaluated in accordance with the evaluation criteria described above (average of five cutter knives).

(Economic Evaluation Criteria) The economic efficiency was evaluated according to the following criteria. ○: Can be implemented with existing equipment as is △: Two types of electrodeposition tanks are required (management costs are doubled)

(Results) Table 2 shows the evaluation results of Examples 1 to 5 and Comparative Examples 1 to 4.

[Table 2]

[0035]

As described above, according to the present invention, the corrosion resistance of the thin film portion and the edge portion of the electrodeposition coating film can be improved, and it is economically advantageous because it can be carried out as it is with existing equipment. .

Claims (4)

[Claims] 1. A first electrodeposition coating film and a second electrodeposition coating film.
A method for forming an electrodeposition coating film, comprising:₁= (T₁−100) × t₁  (However, T₁Is the baking temperature for forming the first electrodeposition coating film
(° C), t₁Is the baking time for forming the first electrodeposition coating film
(Min)) and B₂= (T₂−100) × t₂  (However, T₂Is the baking temperature for forming the second electrodeposition coating film
(° C), t₂Is the baking time for forming the second electrodeposition coating film
(Min)), the following relational expression 200 ≦ B₂≦ 1000, 1.1 ≦ B₁/ B₂  130 ≦ T₁≤250,100 <T₂Form the first electrodeposition coating film and the second electrodeposition coating film under the condition satisfying ≦ 200
A method for forming a coating film. 2. The method according to claim 1, wherein the second electrodeposition coating has the same composition as the first electrodeposition coating. 3. After forming an electrodeposition coating film by the method according to claim 1 or 2, both an intermediate coating film and a top coating film or only a top coating film is formed. Coating film forming method. 4. A coated article formed by the coating film forming method according to any one of claims 1 to 3.