JPH06320664A - Organic composite coated steel panel excellent in cation electrodeposition painting properties and corrosion resistance - Google Patents

Abstract

PURPOSE:To provide an org. composite coated steel panel excellent in both of cation electrodeposition painting properties in the case used on the outer surface side of a car body and corrosion resistance in the case used on the inner surface side of the car body. CONSTITUTION:In an org. composite coated steel panel excellent in cation electrodeposition painting properties and corrosion resistance, a chromate film with an adhesion amt. of 5-500mg/m<2> in terms of Cr is provided on the surface of a zinc plated steel panel and a resin layer mainly compounded with water- dispersible silica, an aq. binder resin and a polyamide resin and/or a polyamide resin and/or a polyimide resin is provided on the chromate film in a dry adhesion amt. of 0.1-3g/m<2>.

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 cationic electrodeposition coating property when used on the outer surface side of an automobile body and corrosion resistance when used on the inner surface side.

[0002]

2. Description of the Related Art In response to a strong social demand for high corrosion resistance of automobile bodies, application of surface-treated steel sheets having a surface of cold-rolled steel sheet plated with zinc or a zinc-based alloy to automobile bodies has been expanding in recent years. .

Examples of these surface-treated steel sheets include hot-dip galvanized steel sheets, alloyed hot-dip galvanized steel sheets, electrogalvanized steel sheets, and electrogalvanized alloy-plated steel sheets. However, even higher corrosion resistance has been required in the bag structure portion and the bending portion (hemming portion) of the inner plate of the vehicle body where the coating performed after the vehicle body assembly is not sufficiently spread.

As a steel sheet for automobiles corresponding to such use, for example, in JP-A-57-108292 and JP-A-58-224174, chromate and an organic polymer resin are coated on a zinc or zinc alloy plated steel sheet. Layered organic composite coated steel sheets have been proposed. All of these are intended to express high corrosion resistance by applying a coating containing a water-soluble or water-dispersed organic resin and a water-dispersed silica sol to the upper layer of a chromate-treated zinc-plated steel sheet, but I had a problem. (1) Since the water-soluble component remains in the film even after the film is formed, the chromium elution resistance is poor, and chromium elutes during the chemical conversion treatment, which causes environmental pollution. (2) The resin layer is peeled off at the time of degreasing with alkali, resulting in deterioration of corrosion resistance. (3) In a corrosive environment, water penetrates into the resin layer and soluble components are dissolved to become highly alkaline, so that the adhesion between the resin layer and the chromate deteriorates.

In order to solve such a problem, a method of using a coating composition in which a hydrophobic silica whose silica surface is organically substituted in an organic solvent and an epoxy resin are blended is disclosed in JP-A-63-22637. 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 layer of the processed portion during molding processing such as pressing is performed. It has been pointed out that there is a problem that damage occurs to the steel and the corrosion resistance of this part deteriorates.

Regarding the problem that the corrosion resistance is poor after such processing, a method of providing a coating layer containing urethane resin and silicon dioxide as main components is disclosed in JP-A-62-2892.
No. 74 publication. In this case, although a slight improvement effect on workability can be obtained, there is a problem that the corrosion resistance also deteriorates when more severe work is performed.

The above is the performance required when used on the inner surface of an automobile, but when used on the outer surface of an automobile, it is completely different from the inner surface in low temperature chipping resistance and outer surface rust resistance. , Cationic electrodeposition coating property, etc. are required.

When a zinc-based plated steel sheet is used on the outer surface side, a zinc-based plated steel sheet, particularly a zinc-nickel-plated steel sheet, has poor plating adhesion, and therefore is coated with 3 coats for the outer surface on the plating. Then, due to the stress of these coating films, when a small stone hits the vehicle body at a low temperature, the plating may peel off and the steel sheet substrate may be exposed. In order to improve this low temperature chipping resistance, there is a method of applying an organic composite coated steel sheet, which is more excellent in low temperature chipping resistance than a galvanized steel sheet, to the outer surface side as well.
It is proposed in Japanese Patent Publication No. 9 and the like. In this case, although excellent low-temperature chipping resistance can be obtained, when subjected to cationic electrodeposition coating for the outer surface, there is a problem that it becomes an electrodeposition coating film having uneven surface unevenness called Yuzu skin and causes poor appearance. there were.

As a method for improving the cationic electrodeposition coating property of this organic composite coated steel sheet, a method of forming a solvent type coating composition in which a binder resin is mixed with silica, a hydrophilic polyamide resin and a polyethylene wax on a chromate coating film. JP-A-62-283161 and JP-A-63-357.
No. 98 proposed. In this case, cations such as craters and gas pinholes caused by hydrogen generation during cation electrodeposition coating will be improved, but the post-painting image clarity equivalent to that of cold-rolled steel sheet or galvanized steel sheet required for the outer surface will be satisfied. It does not make one.

Furthermore, the paints currently in use are mainly organic solvent-based, and the aromatic hydrocarbon solvent used for this organic solvent is a source of air pollution, and its significant reduction is a global problem. Has become.

[0011]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned various problems of the prior art, and in particular, the cationic electrodeposition coating can be performed without polluting the global environment during the manufacturing process. It is intended to provide an organic composite coated steel sheet having excellent corrosion resistance.

[0012]

The present invention has been made to solve these problems in the prior art. As a result of detailed investigations on water-based paints containing various combinations of water-dispersible silica and water-based organic resins. It has been found that the above-mentioned problems can be solved in a combined coating of an aqueous binder resin, a water-dispersible silica, a polyamide resin and / or a polyamine resin and / or a polyimine resin, and has arrived at the present invention. . According to the present invention, it is possible to obtain an organic composite-coated steel sheet excellent in cationic electrodeposition coating property and corrosion resistance after processing by using a water-based paint, and further, it does not pollute the global environment.

That is, according to the present invention, the amount of adhesion on the surface of zinc- or zinc-based alloy-plated steel sheet is 5 to 500 mg in terms of Cr.
/ m has a ^second chromate film, the adhesion amount on the upper layer of the chromate coating in the dry weight, 0.1 to 3 g / m ^2, largely water-dispersed silica and an aqueous binder resin and a polyamide resin and / or polyamines It is an organic composite coated steel sheet having a resin layer formed by mixing a resin and / or a polyimine resin.

It is preferable to use an aqueous silica sol having an average particle size of 0.005 to 2 μm as the silica constituting the organic composite-coated steel sheet.

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

The dry weight ratio of silica to binder resin in this resin layer is preferably 10 to 100 parts by weight of silica relative to 100 parts by weight of resin.

[0017]

The present invention will be described in more detail below. As the material for the steel sheet of the present invention, 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, and Zn-Fe.
Binary alloy plating such as alloy plating and Zn-Cr alloy plating, Zn-Ni-Cr alloy plating, Zn-Co-Cr
Including ternary alloy plating such as alloy plating, Z
It also broadly includes composite dispersion plating such as n-SiO ₂ plating and Zn-Co-Cr-Al ₂ O ₃ plating. These platings are performed by an electric method, a hot dipping method, or a vapor phase plating method.

On these zinc- or zinc-alloy-plated steel sheets, the adhesion with an organic polymer resin layer described later is improved,
In addition, chromate treatment is performed to impart high corrosion resistance.
Chromate adhesion amount is 5 to 500 mg / in terms of Cr
The range is m ² , preferably 10 to 150 mg / m ² . C
When the amount of r adhered is less than 5 mg / m ² , not only the corrosion resistance is insufficient, but also the adhesion to the resin layer is poor, which is not preferable. Even if it exceeds 500 mg / m ² , there is no further effect of improving the corrosion resistance, the resistance of the insulating coating increases, and the spot weldability and the electrodeposition coatability are impaired, which is not preferable.

Such chromate treatment may be carried out by any of a coating type chromate method using a roll coater, an electrolytic type chromate method, a reactive type chromate method and the like.

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

On the upper layer of such a chromate film, an organic composite film formed by mixing water-dispersed silica, an aqueous binder resin, a polyamide resin and / or a polyamine resin and / or a polyimine resin is applied. As the aqueous binder resin used in the present invention, a water-soluble resin and a water-dispersible resin in which a hydrophilic group is introduced into the resin skeleton, or an emulsion resin 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, etc.) 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 coatability 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 the above resin added is preferably 0.01 to 10% by weight of the dry weight of the resin layer. If it is less than 0.01% by weight, the effect of adding the above resin does not appear, and the image clarity after cationic electrodeposition coating does not exceed the standard. Further, if it exceeds 10% by weight, not only the effect of improving the image clarity of the electrodeposition coating is not great, but also the water-resistant secondary adhesion is deteriorated, which is not preferable.

With respect to silica in the organic composite coating of the present invention, securing an appropriate amount of silanol groups on the surface of the silica will stably retain zinc-based corrosion products in a corrosive environment and ensure high corrosion resistance. Is important for. Water-dispersed silica is very suitable because it can secure sufficient silanol groups.

Specifically, the charge state of the surface of the water-dispersed silica sol is controlled by adjusting the amount of alkali metal ions and the amount of polyvalent metal ions to obtain an average of 0.005 to 2 μm, an aqueous silica sol, or a suitable dispersant. Thus, hydrophobic fumed silica dispersed in water can be preferably used.

The average particle size of 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, the spot weldability is deteriorated, which is not preferable. Further, if the average particle size exceeds 2 μm, a considerable number of silica bares out to the outside of the resin layer, the electric resistance between the electrode and the steel plate remarkably increases during spot welding, and sparks are generated during welding to damage the electrode. It also promotes the deterioration of spot weldability. The silica shape may be a uniform particle shape or a shape in which primary particles are aggregated in the above average particle diameter range.

Since hydrophobic fumed silica also has water-dispersed silanol groups on the silica surface, it becomes 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 based on 100 parts by weight of the resin. When the amount of silica is less than 10 parts by weight, the ability to stably hold the zinc-based corrosion product formed in the coating when exposed to a corrosive environment is insufficient, and high corrosion resistance cannot be obtained.
Further, if the amount of silica exceeds 100 parts by weight, compatibility with the resin composition will not be obtained and it will be difficult to apply it as a paint on a steel sheet.

As a method for applying an aqueous coating composition containing an aqueous binder resin, water-dispersed silica and a hydrophilic polyamide resin onto a chromate film, a roll coater method or an air knife method which are widely used in the industry are used. Any 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. 0.1 g /
This is because if it is less than m ² , corrosion resistance is poor, and if it exceeds 3 g / m ² , film resistance increases and spot weldability and electrodeposition coatability 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 the upper layer thereof is further electrodeposition coated, etc. It was confirmed that sufficient corrosion resistance can be obtained if an organic resin layer of 0.1 g / m ² or more is present.

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

[0032]

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

(Examples 1 to 10 and Comparative Examples 1 to 3) Various types of double-sided zinc-based plated steel sheets (sheet thickness 0.75 mm) were degreased and then coated with various amounts of coating type chromate using a roll coater to reach the maximum. It was baked 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. After that, it was baked at the maximum attainable temperature of 160 ° C., immediately cooled with water and dried. The silica and the added resin used are as follows.

<Type of Silica> 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: Epollon E manufactured by Kanebo UNC Co., Ltd.
B-1 B: Nippon Shokubai Co., Ltd. Epomin SP-018 C: Otsuka Chemical Co., Ltd. PAH-LD: Nippon Shokubai Co., Ltd. Epomin SP-200 For performance evaluation of these organic composite coated steel sheet products. The following test was conducted.

In order to evaluate the cationic electrodeposition coating property, a cationic electrodeposition coating U-53 (manufactured by Nippon Paint Co., Ltd.) was used.
The applied voltage was 250 V, the time was 3 minutes, the bath temperature was 28 to 30 ° C., and the electrodeposition coating treatment was performed, followed by baking at 175 ° C. for 30 minutes. At this time, the image clarity was determined by the PGD value by a PGD meter after the electrodeposition film thickness and the transparent tape were attached. The electrodeposited film thickness was 20 μm in the case of the cold-rolled steel sheet processed at the same time. The evaluation criteria for the sharpness are shown below. ⊚: PGD value of 0.5 or more (equivalent to cold-rolled steel sheet and galvanized steel sheet) ○: PGD value of 0.4 or more and less than 0.5 Δ: PGD value of 0.2 or more and less than 0.4 ×: PGD value of 0.2 Less than

In order to evaluate flat plate corrosion resistance, 5% NaC
1 Aqueous solution spraying (35 ° C.) 4 hours, drying (60 ° C.) 2 hours, wet environment (50 ° C.) 2 hours were subjected to a combined cycle corrosion test, and the occurrence of red rust on the test piece at 200 cycles was observed. did. The evaluation criteria for flat plate corrosion resistance are shown below. ◎: No red rust generation ○: Red rust generation area ratio less than 10% △: Red rust generation area ratio 10 to 20% ×: Red rust generation area ratio 20% or more

In order to evaluate the corrosion resistance after processing, a cylindrical drawing test (drawing ratio 2.0, wrinkle pressing pressure 1000 kg) was applied to a test piece, which was sprayed with a 5% NaCl aqueous solution (35 ° C.) for 4 hours.
Dry (60 ℃) 2 hours, wet environment (50 ℃) 2 hours 1
It was subjected to a combined cycle corrosion test as a cycle, and the occurrence of red rust on the side wall of the test piece was observed after 50 cycles. ◎: No red rust generation ○: Red rust generation area ratio less than 10% △: Red rust generation area ratio 10 to 20% ×: Red rust generation area ratio 20% or more

In order to evaluate the chromium elution resistance, degreasing,
Four steps of washing with water, surface adjustment, and chemical conversion treatment were performed, and changes in the Cr adhesion amount before and after the treatment were measured by fluorescent X-ray analysis. The evaluation criteria are shown below. ○: 1mg / m ² or less ^{△: 1~2mg / m 2 ×:} 2mg / m 2 or more

To evaluate the spot weldability, the tip 6
Using welding tip made of Al ₂ O ₃ dispersed copper alloy of mmφ, pressure 200 kgf, welding current 9 kA, welding time 10 Hz
Was continuously welded, and the number of continuous welding points until the nugget diameter fell below the reference diameter was measured. 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, electrodeposition coating was performed under the same conditions as the sample for evaluating the electrodeposition coating property,
Furthermore, spray coating of intermediate coating and top coating for automobiles was performed. This sample was immersed in warm water at 40 ° C. for 240 hours. Within 10 minutes after taking out each sample, 100 pieces were cut in a grid pattern at intervals of 2 mm using a cutter knife, and a peeling test was performed using cellophane tape.
The evaluation was performed by measuring the number of peeled pieces. ⊚: No peeling ○: Peeling number of 1 or less Δ: Peeling number of 2 to 10 ×: Peeling number of 11 or more Table 1 shows the conditions of the chromate layer and the resin layer and the test results.

[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 property, 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.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kyoko Hamahara Inventor 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Technical Research Division (72) Ryoichi Mukai Kawasaki, Chuo-ku, Chiba Town No. 1 Kawasaki Steel Co., Ltd. Technical Research Division (72) Inventor Kazuo Mochizuki No. 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Co., Ltd. Technical Research Division (72) Inventor Hiroshi Tanabe Sumitomo Tochigi 1382-12 Shimoishigami, Otawara, Oita Prefecture (72) Inventor, Masanori Nagai Masanori Nagai, 1382-12 Shimoishiue, Otawara, Tochigi (72) Inventor, Shinka Kato Tochigi 1382-12 Shimoishigami, Otawara, Oita Prefecture (72) Inventor Osamu Ogawa 1382-12, Shimoishiue, Otawara, Tochigi Dainihon Paint Co., Ltd.

Claims (5)

[Claims] 1. A chromate film having an adhesion amount of 5 to 500 mg / m ^{2 in} terms of Cr is provided on the surface of zinc or zinc-based plated steel sheet, and the amount of adhesion to the upper layer of the chromate film is a dry weight of 0. An organic composite excellent in cationic electrodeposition coating property and corrosion resistance having a resin layer containing 1 to 3 g / m ² of mainly water-dispersed silica, an aqueous binder resin and a polyamide resin and / or a polyamine resin and / or a polyimine resin. Coated steel sheet. 2. The silica as a constituent has an average particle diameter of 0.
An aqueous silica sol having a diameter of 005 to 2 μm is used.
The organic composite coated steel sheet having excellent cationic electrodeposition coatability and corrosion resistance as described in 1. 3. An organic composite coated steel sheet having excellent cationic electrodeposition coating property and corrosion resistance according to claim 1, wherein water-dispersed hydrophobic fumed silica is used as the constituent silica. 4. The dry weight ratio of silica to the binder resin in the resin layer is 1 part by weight of silica based on 100 parts by weight of the resin.
The organic composite coated steel sheet having excellent cationic electrodeposition coating property and corrosion resistance according to claim 1, which is 0 to 100 parts by weight. 5. The polyamide resin and / or polyamine resin and / or polyimine resin is added in an amount of 0.01 to 10% by weight based on the dry weight of the resin layer.
2. An organic composite coated steel sheet having excellent cationic electrodeposition coatability and corrosion resistance according to any one of 1.