JP2753666B2 - Resin-coated steel sheet with excellent electrodeposition coating properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to home electric appliances and building materials,
The present invention relates to a resin-coated steel sheet having excellent electrodeposition coatability suitably used for automobile parts and the like.

[0002]

2. Description of the Related Art Conventionally, spray coating and powder coating are widely used for coating steel sheets for household electric appliances and building materials. However, in recent years, from the viewpoint of work environment and pollution problems, a coating method has been used. Electrodeposition coating is being adopted, and in the field of automobile parts, electrodeposition coating is already dominant.

[0003] On the other hand, as a base of an electrodeposition coated steel sheet, a cold rolled steel sheet or a zinc-based plated steel sheet has been widely used. Since these steel sheets are rusted before being electrodeposited by a customer after production, oil is conventionally applied in the production process. Further, at the time of coating, pretreatment such as phosphate treatment is also performed in order to improve the adhesion between the steel sheet and the coating film.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a resin-coated steel sheet which can be subjected to electrodeposition coating without the above-mentioned pretreatment such as oil coating and phosphate treatment.

[0005]

According to the present invention, there is provided a resin-coated steel sheet having excellent electrodeposition coatability.
Resin coating containing 5 to 50% by weight of silica fine particles mainly composed of acrylic resin containing 5% by weight
It is characterized in that it is formed on the steel sheet surface at 0.2 to 2.5 g / m ² .

[0006] According to the present invention, the ionic monomer is 1 to
Applying a water-dispersible water-based resin paint containing 5 to 50% by weight of silica fine particles mainly to an acrylic resin containing 20% by weight to a steel plate, drying, and forming a resin film with a predetermined adhesion amount. Accordingly, a resin-coated steel sheet having excellent electrodeposition coating properties can be obtained. As the ionic monomer, a low molecular weight compound having a carboxyl group is particularly suitable, and for example, acrylic acid, methacrylic acid, maleic acid and the like are preferably used.

According to the resin-coated steel sheet according to the present invention, by forming the resin coating as described above, first, it is possible to have a primary rust prevention effect of preventing the generation of white rust, and thus, Conventionally, the oiling and degreasing steps required for primary rust prevention can be omitted. Next, regarding the electrodeposition coating property, in the electrodeposition coating liquid, the ionic monomer and the silica fine particles in the resin film are eluted, and extremely fine pinholes are formed in the resin film. In addition to the improved properties, the current flows uniformly on the coating surface, and the formation of pinholes allows hydrogen gas generated by the electrolysis of water to easily escape to the outside of the coating when energized. In addition, the occurrence of cratering and the like is suppressed. Thus, according to the present invention, it is possible to perform electrodeposition coating with a uniform and excellent appearance.

Further, according to the present invention, the resin film is formed on the surface of the steel sheet, so that it has excellent adhesion to the electrodeposition paint, and thus no pretreatment such as phosphate treatment is required. In addition, the physical properties of the coating film after the electrodeposition coating are remarkably improved as compared with the prior art. In the present invention, the acrylic resin that is the main component of the coating film contains the ionic monomer in a range of 1 to 20% by weight. When the amount of the ionic monomer contained in the acrylic resin is less than 1% by weight, it is difficult to form a uniform pinhole in the resin film. Since there are too many hydrophilic groups inside, the corrosion resistance required for primary rust prevention cannot be obtained.

Further, the resin paint used in the present invention is:
Silica fine particles are contained in the range of 5 to 50% by weight in solid content. The silica fine particles have excellent corrosion resistance as primary rust prevention and, as described above, are eluted from the film in the electrodeposition paint and have an effect of forming extremely fine pinholes. However, when the amount of silica is less than 5% by weight, the corrosion resistance of the obtained resin film is not sufficient, and an effective effect cannot be obtained even in pinhole formation. On the other hand, if it exceeds 50% by weight, cracks occur in the resin film, and the corrosion resistance and the electrodeposition coating property deteriorate. In particular, in the present invention, the amount of the silica fine particles in the resin paint is preferably in the range of 20 to 40% by weight in solid content.

In order to maximize the effect of silica as described above, the silica preferably has a particle size in the range of 4 to 50 nm. As the particle size of silica becomes smaller,
Although the corrosion resistance is improved, the use of extremely fine particles does not particularly enhance the effect. Therefore, in the present invention, the silica may have a particle diameter of 4 nm or more. However, when the thickness exceeds 50 nm, the surface of the coating is roughened, so that a dense coating cannot be formed, the corrosion resistance is deteriorated, and the effect as the primary rust prevention is inferior.

Although there are many unclear points about the effect of the silica particle diameter on the formation of pinholes during electrodeposition coating,
It is clear that the state of formation of pinholes varies greatly depending on the amount of silica, and within the above range, pinholes sufficient for electrodeposition coating are formed. In particular, the particle size of the silica fine particles used in the present invention is preferably in the range of 10 to 20 nm. Such silica is generally known as colloidal silica.
Commercial products can be obtained as 0, 40, and XS (all manufactured by Nissan Chemical Industries, Ltd.).

The resin-coated steel sheet according to the present invention is obtained by applying the above-described resin coating to the surface of the steel sheet, drying the coated steel sheet, and mainly comprising an acrylic resin containing 1 to 20% by weight of an ionic monomer and silica fine particles 5 It can be obtained by forming a resin coating containing 50 to 50% by weight on the steel sheet surface with a coating weight of 0.2 to 2.5 g / m ² . The adhesion amount of the resin coating is in the range of 0.2 to 2.5 g / m ² . When the amount of the resin film attached is less than 0.2 g / m ² , the corrosion resistance of the resin film cannot be sufficiently exhibited, and the pinholes formed at the time of electrodeposition coating become non-uniform. The performance which is the characteristic of cannot be obtained. When the amount of the resin coating is more than 2.5 g / m ² , the corrosion resistance is improved, but the conductivity and pinholes of the coating do not reach the base steel sheet, and the electrodeposition coating property is significantly deteriorated. Excellent paint appearance cannot be obtained. Further, the production cost is increased, which is not economically preferable. In particular, in the present invention,
The adhesion amount of the resin film is preferably in the range of 0.5 to 1.5 g / m ² .

In the present invention, the material of the steel sheet is not particularly limited. For example, a cold-rolled steel sheet, a steel sheet coated with zinc or a zinc alloy, or a sheet obtained by chemically treating such a steel sheet with a chromate treatment or the like is preferable. Used for

[0014]

As described above, according to the present invention, a resin film containing 5 to 50% by weight of silica fine particles mainly composed of an acrylic resin containing 1 to 20% by weight of an ionic monomer is applied. By forming on the steel sheet surface at 0.2 to 2.5 g / m ^{2, the} oiling and degreasing steps as primary rust prevention can be omitted. Processing steps can be omitted. Furthermore,
Excellent coating film performance after electrodeposition coating can also be obtained. Therefore, the resin-coated steel sheet according to the present invention,
For example, it can be suitably used for household electric appliances, building materials, automobile parts, etc., which are subjected to electrodeposition coating.

[0015]

EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited by these examples. In the examples, a steel plate having an electro-galvanized steel plate (a zinc adhesion amount of 20 g / m ² and a chromium adhesion amount of 20 mg / m ² ) subjected to a chromate treatment was used. As a comparative material, a GI material (zinc adhesion amount: 30 g / m ² ) having a hot-dip galvanized steel sheet without resin coating was used.

The evaluation of the performance of the resin-coated steel sheet and the comparative material according to the present invention was performed as follows. Corrosion resistance According to the method specified in JIS Z-2371, evaluation was made by the time until 1% of white rust occurred on the flat plate. Electrodeposition coating manufactured by NOF acrylic cationic electrodeposition paint (Aqua 480
0). The coating conditions and methods for evaluating the properties of the coated film after coating are shown below.

Coating conditions Bath temperature 28 ° C. Polar ratio (+/−) 1/4 to 1/6 Energizing time 2 minutes Energizing voltage 160 to 230 V Film thickness 25 μm Rinsing Rinse shower water Rinse baking conditions 180 ° C. × 20 minutes

Evaluation of physical properties of coating film After grid coating , grids were cut at 1 mm intervals on a steel plate, and a tape peeling test was performed to examine the peeling of the coating film. Ericksen test Using an Erichsen test device, the coated steel sheet was extruded by 4.5 mm, and the occurrence of cracks in the coating film was examined. DuPont Impact Test DuPont Impact Tester (Height 300mm x Weight 500g x
Using a punch test (1/2 inch diameter), a hammer test was conducted to examine the occurrence of cracks in the coating film and the peeling of the coating film by a tape peeling test. Salt spray test A 60 ° cross cut was performed on a flat plate, and a salt spray test 24
After 0 hour, the blister width of the coating film, the peeling of the coating film by a tape peeling test and the occurrence of red rust were examined. In the above test, ◎ indicates very good, ○ indicates good, Δ indicates slightly inferior, and × indicates inferior.

Example 1 0.5 to 25% by weight of acrylic acid as an ionic monomer
Colloidal silica having a particle diameter of 10 to 20 nm was added to the contained acrylic resin at a solid content of 40% by weight to prepare a water-dispersible resin coating. This resin paint was applied to the surface of the electroplated steel sheet subjected to the above chromate treatment and dried to obtain a resin-coated steel sheet having a coating weight of 1 g / m ² . Table 1 shows the corrosion resistance of the obtained resin-coated steel sheet and the physical properties of the film after electrodeposition coating.

[0020]

[Table 1]

Example 2 A water-dispersible resin was prepared by adding colloidal silica having a particle size of 10 to 20 nm in a solid content of 0 to 60% by weight to an acrylic resin containing 5% by weight of acrylic acid as an ionic monomer. A paint was prepared. This resin paint was applied to the surface of the electroplated steel sheet subjected to the above chromate treatment and dried to obtain a resin-coated steel sheet having a coating weight of 1 g / m ² .

In the same manner as in Example 1, the corrosion resistance of the obtained resin-coated steel sheet and the physical properties of the film after electrodeposition coating were examined. Table 2 shows the results.

[0023]

[Table 2]

Example 3 A water-dispersible resin coating was prepared by adding 40% by weight of solid content of colloidal silica having a particle diameter of 4 to 70 nm to an acrylic resin containing 5% by weight of acrylic acid as an ionic monomer. This resin paint was applied to the surface of the electroplated steel sheet subjected to the above chromate treatment and dried to obtain a resin-coated steel sheet having a coating weight of 1 g / m ² .

In the same manner as in Example 1, the corrosion resistance of the obtained resin-coated steel sheet and the physical properties of the film after electrodeposition coating were examined. Table 3 shows the results.

[0026]

[Table 3]

Example 4 A colloidal silica having a particle diameter of 10 to 20 nm was added to an acrylic resin containing 5% by weight of acrylic acid as an ionic monomer at a solid content of 40% by weight to prepare a water-dispersible resin paint. This resin paint was applied to the surface of the electroplated steel sheet subjected to the above-mentioned chromate treatment, and dried to obtain a resin-coated steel sheet having a coating amount of 0.1 to 3 g / m ² .

In the same manner as in Example 1, the corrosion resistance of the obtained resin-coated steel sheet and the physical properties of the film after electrodeposition coating were examined. Table 4 shows the results.

[0029]

[Table 4]

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Claims (3)

(57) [Claims] An acrylic resin containing 1 to 20% by weight of an ionic monomer, and silica fine particles of 5 to 50%.
Weight% of the resin coating is 0.2 to 2.5 g /
lacquered steel sheet excellent in electrodeposition paintability, characterized in that it is formed on the surface of the steel sheet at m ^2. 2. The resin-coated steel sheet having excellent electrodeposition coating properties according to claim 1, wherein the silica fine particles have a particle diameter of 4 to 50 nm. 3. The method according to claim 1, wherein the ionic monomer is acrylic acid, methacrylic acid or maleic acid.
A resin-coated steel sheet with excellent electrodeposition coating properties as described.