JP3260904B2 - Organic composite coated steel sheet with excellent cationic electrodeposition paintability and corrosion resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic composite coated steel sheet which is excellent in both properties of cationic electrodeposition coating when used on the outer side of an automobile body and corrosion resistance when used on the inner side.

[0002]

2. Description of the Related Art In response to strong social demands for higher corrosion resistance of automobile bodies, the use of surface-treated steel sheets in which zinc or a zinc-based alloy plating is applied to the surface of a cold-rolled steel sheet has been increasing in recent years. .

[0003] Examples of these surface-treated steel sheets include hot-dip galvanized steel sheets, galvannealed steel sheets, electro-galvanized steel sheets, and electro-zinc alloy-coated steel sheets. However, a higher degree of corrosion resistance has been required in a bag structure portion or a bent portion (hemming portion) of a body inner plate in which coating performed after assembling the body is not sufficiently distributed.

As a steel sheet for automobiles corresponding to such uses, for example, Japanese Patent Application Laid-Open Nos. Sho 57-108292 and 58-224174 disclose chromate and organic polymer resin on a zinc or zinc-based alloy-plated steel sheet. Organic composite coated steel sheets provided with layers have been proposed. All of these are intended to exhibit high corrosion resistance by applying a coating containing a water-soluble or water-dispersible organic resin and a water-dispersible silica sol to the upper layer of a zinc-plated steel sheet subjected to chromate treatment. Had problems. (1) Since the water-soluble component remains in the coating film even after film formation, the chromium elution resistance is poor, and chromium is eluted during chemical conversion treatment, causing environmental pollution. (2) Peeling of the resin layer occurs at the time of alkali degreasing, resulting in deterioration of corrosion resistance. (3) In a corrosive environment, moisture penetrates into the resin layer, and soluble components dissolve and become highly alkaline, so that the adhesion between the resin layer and the chromate deteriorates.

In order to solve such problems, Japanese Patent Application Laid-Open No. Sho 63-22637 discloses a method of using a coating composition in which hydrophobic silica having a silica surface organically substituted and an epoxy resin are mixed in an organic solvent. Proposed. In this case, the compatibility between the silica sol and the organic resin is ensured, and excellent adhesion after coating is obtained, but the flexibility of the coating film is not sufficient, so that the coating film layer at the processing portion is formed at the time of forming by pressing or the like. It has been pointed out that there is a problem that damage is caused to the steel and the corrosion resistance of this part is deteriorated.

In order to solve the problem of poor corrosion resistance after such processing, a method of providing a coating layer containing a urethane resin and silicon dioxide as main components is disclosed in Japanese Patent Application Laid-Open No. 62-2892.
No. 74 is proposed. In this case, although a slight improvement effect can be obtained on the workability, there is a problem that the corrosion resistance is also deteriorated when more severe processing is performed.

The above description relates to the performance required when used on the inner surface side of an automobile. When used on the outer surface side of an automobile, it is completely different from the inner surface, and has low temperature chipping resistance and outer rust resistance. And cationic electrodeposition coating properties are required.

When a galvanized steel sheet is used on the outer surface side, a zinc-coated steel sheet, particularly a zinc-nickel plated steel sheet, has poor plating adhesion, and is coated with three coats for the outer surface on the plating. When the pebbles hit the vehicle body at a low temperature due to the stress of these coating films, the plating may be peeled off, and a phenomenon of exposing the steel base material may occur. In order to improve the low-temperature chipping resistance, a method of applying an organic composite coated steel sheet which is more excellent in low-temperature chipping resistance than a galvanized steel sheet on the outer surface side is disclosed in JP-A-4-2753.
No. 9 has been proposed. In this case, although excellent low-temperature chipping resistance can be obtained, when a cationic electrodeposition coating is applied for the outer surface, there is a problem that an electrodeposition coating film having uneven surface irregularities called yuzu skin is generated and appearance defects are caused. there were.

As a method for improving the cationic electrodeposition coating property of the organic composite coated steel sheet, a method of forming a solvent type coating composition comprising a binder resin mixed with silica, a hydrophilic polyamide resin and a polyethylene wax on a chromate film. Are disclosed in JP-A-62-283161 and JP-A-63-357.
No. 98 is proposed. In this case, electrodeposition coating defects such as craters and gas pinholes due to the generation of hydrogen during cationic electrodeposition coating are improved, but the clarity after coating is as good as that of cold rolled steel sheets or galvanized steel sheets required for the outer surface. It does not make it.

[0010] Further, most of the paints currently used are mainly of organic solvents, and aromatic hydrocarbon solvents used in these organic solvents are a source of air pollution. Has become.

[0011]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned various problems of the prior art. An object of the present invention is to provide an organic composite coated steel sheet having excellent corrosion resistance.

[0012]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the problems in the prior art, and has been made as a result of a detailed study on aqueous paints using various combinations of water-dispersible silica and an aqueous organic resin. It has been found that the above problems can be solved by a combination paint of an aqueous binder resin, water-dispersible silica, a hydrophilic polyamide resin and / or a polyamine resin and / or a polyimine resin, and the present invention has been achieved. It is. According to the present invention, using a water-based paint , cationic electrodeposition coating
In this case, it is possible to obtain an organic composite coated steel sheet having a sharpness of PGD value 0.5 or more and having excellent corrosion resistance after processing , and does not pollute the global environment.

That is, according to the present invention, the amount of deposit on the surface of a zinc or zinc-based alloy-coated steel sheet is 5 to 500 mg in terms of Cr.
/ m ² having a chromate coating, and the upper layer of the chromate coating having a dry weight of 0.1 to 3 g / m ² , mainly water-dispersed silica, an aqueous binder resin and a polyamide resin and / or a polyamine An organic composite coated steel sheet having a resin layer formed by blending a resin and / or a polyimine resin.

As the silica constituting the organic composite coated steel sheet, an aqueous silica sol having an average particle diameter of 0.005 to 2 μm is preferably used.

It is preferable to use water-dispersed hydrophobic fumed silica as a deer constituting the organic composite coated steel sheet.

The dry weight ratio of silica to the binder resin in the resin layer is preferably 10 to 100 parts by weight of silica with respect to 100 parts by weight of the resin.

[0017]

The present invention will be described below in more detail. As the material for the steel sheet of the present invention, a zinc or zinc-based alloy-plated steel sheet is used. The types of plating applied to this steel sheet include pure zinc plating, Zn-Ni alloy plating, Zn-Fe
Binary alloy plating such as alloy plating, Zn-Cr alloy plating, Zn-Ni-Cr alloy plating, Zn-Co-Cr
Includes ternary alloy plating such as alloy plating.
n-SiO ₂ plating encompasses broadly the composite dispersion plating, such as _{Zn-Co-Cr-Al 2} O 3 plating. These platings are applied by an electric method, a hot-dip plating method, or a vapor phase plating method.

On these zinc or zinc alloy plated steel sheets, the adhesion to an organic polymer resin layer described later is improved,
In addition, chromate treatment is performed to impart high corrosion resistance.
The amount of chromate attached is 5 to 500 mg / Cr equivalent.
m ² , preferably in the range of 10 to 150 mg / m ² . C
If the r adhesion amount is less than 5 mg / m ^2, it is not preferable because not only corrosion resistance is insufficient, but also adhesion to the resin layer is poor. If it exceeds 500 mg / m ² , there is no further effect of improving the corrosion resistance, the resistance of the insulating film is increased, and the spot welding property and the electrodeposition coating property are impaired.

Such a chromate treatment may be performed by any method such as a coating type chromate method using a roll coater or the like, an electrolytic type chromate method, and a reactive type chromate method.

The Cr ⁶⁺ ratio in the chromate is preferably 70% or less based on the total amount of Cr. If the amount of Cr ⁶⁺ exceeds 70%, the elution resistance of chromium during alkaline degreasing deteriorates, which is not preferable.

The upper layer of such a chromate film is provided with an organic composite film comprising water-dispersed silica, an aqueous binder resin, a polyamide resin and / or a polyamine resin and / or a polyimine resin. As the aqueous binder resin used in the present invention, a water-soluble and water-dispersed resin having a hydrophilic group introduced into a resin skeleton, or an emulsion resin obtained by a forced emulsification method can be used. The type of resin is not particularly limited, for example, acrylic resin,
Epoxy resins, urethane resins, alkyd resins, polyester resins, and the like, or resins in which the resin skeleton is partially modified by a combination of these resins (for example, urethane-modified epoxy resin, acryl-modified epoxy resin, and the like) can be preferably used.

Next, in the present invention, a polyamide resin and / or a polyamine resin and / or a polyimine resin are used as a resin component together with the binder resin. By adding the above resin, the cationic electrodeposition coating property is remarkably improved. The resin used here is not particularly limited as long as it has an amide group and / or an amino group.

The amount of addition of the above resin is preferably 0.01 to 10% by weight in dry weight in the resin layer. If the amount is less than 0.01% by weight, the effect of the addition of the above resin does not appear, and the sharpness after cationic electrodeposition coating does not exceed the standard. Further, if it exceeds 10% by weight, not only is the effect of further improving the sharpness of the electrodeposition coating not large, but also the water-resistant secondary adhesion deteriorates, which is not preferable.

As for the silica in the organic composite coating of the present invention, securing an appropriate amount of silanol groups on the silica surface stably retains zinc-based corrosion products in a corrosive environment and ensures high corrosion resistance. Important for. Water-dispersed silica is very suitable because a sufficient silanol group can be secured.

More specifically, an aqueous silica sol whose charge state on the surface of the water-dispersed silica sol is controlled to an average of 0.005 to 2 μm by controlling the amount of alkali metal ions or polyvalent metal ions, or an appropriate dispersant The hydrophobic fumed silica dispersed in water is preferably used.

The average particle size is 0.005 to 2 μm.
It is preferably in the range of m. Average particle size 0.00
If it is less than 5 μm, spot weldability is deteriorated, which is not preferable. When the average particle diameter exceeds 2 μm, a considerable amount of silica is exposed to the outside of the resin layer, and the electric resistance between the electrode and the steel sheet is significantly increased during spot welding. This also promotes the spot weldability. The silica shape may be a uniform granular shape or a shape in which primary particles are aggregated in the above average particle size range.

By dispersing hydrophobic fumed silica in water, silanol groups are present on the silica surface, so that it is possible to stably retain corrosion products, which is remarkably exhibited in combination with an aqueous resin. ,
It has excellent corrosion resistance after processing.

The dry weight ratio of the binder resin and silica in the resin layer is preferably 10 to 100 parts by weight of silica with respect to 100 parts by weight of the resin. When the amount of silica is less than 10 parts by weight, the ability to stably retain a zinc-based corrosion product formed in the coating when exposed to a corrosive environment is insufficient, and high corrosion resistance cannot be obtained.
On the other hand, if the amount of silica exceeds 100 parts by weight, compatibility with the resin composition cannot be obtained, and it is difficult to apply the coating composition on a steel sheet as a coating material.

As a method of applying an aqueous paint formed by mixing an aqueous binder resin, water-dispersed silica and a hydrophilic polyamide resin onto a chromate film, a roll coater method, an air knife method, etc., which are widely used industrially, are widely used. A method can be used.

The coating amount of the organic composite coating layer in the present invention is limited to 0.1 to 3 g / m ² in terms of dry weight. 0.1g /
If it is less than m ² , the corrosion resistance is poor, and if it exceeds 3 g / m ² , the coating resistance increases and the spot weldability and the electrodeposition coating property deteriorate. When the organic composite coated steel sheet of the present invention is exposed to a corrosive environment while being bare, it is preferable to secure a coating amount of 0.3 g / m ² or more from the viewpoint of corrosion resistance, but furthermore, such as electrodeposition coating on the upper layer It was confirmed that sufficient corrosion resistance could be obtained if 0.1 g / m ² or more of the organic resin layer was present.

Further, the organic composite coating according to the present invention is preferably applied to both sides of the steel sheet. With double-sided treatment, the performance required on the outer and inner surfaces of the vehicle can be simultaneously satisfied.

[0032]

Next, the effects of the present invention will be specifically described based on examples.

(Examples 1 to 10 and Comparative Examples 1 to 3) After degreasing various double-sided zinc-coated steel sheets (thickness 0.75 mm), application type chromate of various adhesion amounts was performed using a roll coater, and the maximum was reached. Baking at a temperature of 130 ° C. Next, a paint prepared by mixing various aqueous resins or partially modified aqueous resins with various silicas having different average particle diameters and various polyamide resins was applied by a roll coater. Then, after baking at a maximum temperature of 160 ° C., it was immediately cooled with water and dried. The silica and additive resin used are as follows.

<Silica Type> A: Water-dispersed uniform granular silica sol B: Water-dispersed aggregated silica sol C: Water-dispersed hydrophobic fumed silica (specific surface area: 70 m ²⁾
/ g) <Type of added resin> A: Eporsion E manufactured by Kanebo UNS Co., Ltd.
B-1 B: Epomin SP-018 manufactured by Nippon Shokubai Co., Ltd. C: PAH-LD manufactured by Otsuka Chemical Co., Ltd .: Epomin SP-200 manufactured by Nippon Shokubai Co., Ltd. To evaluate the performance of these organic composite coated steel sheet products. The following test was conducted.

In order to evaluate the cationic electrodeposition paintability, a cationic electrodeposition paint U-53 (manufactured by Nippon Paint) was used.
Electrodeposition was applied at an applied voltage of 250 V for 3 minutes at a bath temperature of 28 to 30 ° C, and baked at 175 ° C for 30 minutes. At this time, the sharpness was determined by the PGD value of the electrodeposited film thickness and the PGD meter after attaching the transparent tape. The thickness of the electrodeposited film was 20 μm in the case of the cold-rolled steel sheet treated at the same time. The evaluation criteria for sharpness are shown below. ◎: PGD value 0.5 or more (equivalent to cold rolled steel sheet and galvanized steel sheet) ＰＧ: PGD value 0.4 or more and less than 0.5 △: PGD value 0.2 or more and less than 0.4 ×: PGD value 0.2 Less than

To evaluate plate corrosion resistance, 5% NaC
1 We conducted a combined cycle corrosion test in which one cycle consisted of spraying an aqueous solution (35 ° C) for 4 hours, drying (60 ° C) for 2 hours, and wet environment (50 ° C) for 2 hours. did. The evaluation criteria for flat plate corrosion resistance are shown below. ：: No red rust generated ○: Red rust generated area rate less than 10% △: Red rust generated area rate 10 to 20% ×: Red rust generated area rate 20% or more

A test piece subjected to a cylindrical drawing test (drawing ratio 2.0, wrinkle holding pressure 1000 kg) to evaluate corrosion resistance after working was sprayed with a 5% NaCl aqueous solution (35 ° C.) for 4 hours.
Drying (60 ° C) for 2 hours and humid environment (50 ° C) for 2 hours
The specimen was subjected to a combined cycle corrosion test as a cycle, and the state of occurrence of red rust on the test piece side wall at 50 cycles was observed. ：: No red rust generated ○: Red rust generated area rate less than 10% △: Red rust generated area rate 10 to 20% ×: Red rust generated area rate 20% or more

To evaluate chromium elution resistance, degreasing,
Four steps of washing, surface conditioning, and chemical conversion treatment were performed, and the change in the amount of Cr attached before and after the treatment was measured by X-ray fluorescence analysis. The evaluation criteria are shown below. ○: 1mg / m ² or less ^{△: 1~2mg / m 2 ×:} 2mg / m 2 or more

In order to evaluate the spot weldability, the tip 6
Using a welding tip made of an Al ₂ O ₃ dispersed copper alloy of mmφ, a pressure of 200 kgf, welding current of 9 kA, welding time of 10 Hz
, Continuous welding was performed until the nugget diameter became smaller than the reference diameter. The evaluation criteria are shown below. ◎: 3000 points or more ○: 2000 to 3000 points △: 1000 to 2000 points ×: Less than 1000 points

In order to evaluate the water-resistant secondary adhesion, the electrodeposition coating was performed under the same conditions as those of the sample for evaluating the electrodeposition coating property.
In addition, spray coating of automotive middle coat and top coat was performed. This sample was immersed in warm water of 40 ° C. for 240 hours. After each sample was taken out, 100 pieces were cut in a grid pattern at 2 mm intervals within 10 minutes using a cutter knife, and a peeling test was performed using a cellophane tape.
The evaluation was performed by measuring the number of peeled pieces. ：: No peeling ○: Number of peeled 1 or less Δ: Number of peeled 2 to 10 ×: Number of peeled 11 or more Table 1 summarizes the conditions and test results of the chromate layer and the resin layer.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

[Table 3]

[0044]

As described above, the organic composite coated steel sheet according to the present invention has excellent cationic electrodeposition coating properties, flat plate corrosion resistance, post-processing corrosion resistance and spot weldability, and can solve the conventional problems. Therefore, since it can be used for both the outer surface and the inner surface of an automobile body, its industrial value is extremely high.

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kyoko Hamahara 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Prefecture Inside the Technical Research Headquarters, Kawasaki Steel Works Co., Ltd. (72) Ryoichi Muko inventor Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba No. 1 Kawasaki Steel Corporation Research and Development Headquarters (72) Kazuo Mochizuki Inventor Kazuo Mochizuki 1 Kawasaki-cho Chuo-ku and Chiba City Chiba Prefecture Kawasaki Steel Corporation Research and Development Headquarters (72) Inventor Hiroshi Tanabe Sumi Otawara, Tochigi 1382-12 Shimoishigami Inside Dai Nippon Paint Co., Ltd. (72) Inventor Masanori Nagai 1382-12 Shimoishigami, Otawara City, Tochigi Prefecture Inside (72) Inventor Nobuyoshi Kato Shimoishigami, Otawara City, Tochigi Prefecture 1382-12 Dainippon Paint Co., Ltd. (72) Inventor Osamu Ogawa 1382-12 Shimoishigami, Otawara City, Tochigi Prefecture Dainippon Paint Co., Ltd. (56) References JP-A-62-283161 JP, A) JP-A-4-335992 (JP, A) JP-A-2000-226532 (JP, A) JP-A-63-35798 (JP, A) JP-A-3-268939 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) B32B 15/08

Claims (5)

(57) [Claims] The present invention has a chromate film having a coating weight of 5 to 500 mg / m ^{2 in} terms of Cr on the surface of a zinc or galvanized steel sheet. is 1 to 3 g / m ^2, image clarity when mainly blended water-dispersed silica and an aqueous binder resin and a polyamide resin and / or polyamine resin and / or polyimine resin resin layer possess comprising, painted cationic electrodeposition
An organic composite coated steel sheet having a PGD value of 0.5 or more and excellent corrosion resistance. 2. An average particle diameter of the silica constituting the silica is 0.2.
Claim an aqueous silica sol is 005～2Myuemu 1
2. The organic composite coated steel sheet according to item 1 . 3. The organic composite coated steel according to claim 1, wherein a water-dispersed hydrophobic fumed silica is used as the constituent silica.
Board . 4. The dry weight ratio of silica to binder resin in the resin layer is such that silica 1
0-100 parts by weight according to any of claims 1 to 3
Organic composite coated steel sheet . 5. The amount of the polyamide resin and / or polyamine resin and / or polyimine resin added is 0.01 to 10% by weight in terms of dry weight in the resin layer.
The organic composite coated steel sheet according to any one of the above .