JPH06234187A - Organic composite coated steel plate excellent in corrosion resistance after processing - Google Patents

Abstract

PURPOSE:To provide an organic composite coated steel plate excellent in corrosion resistance by a manufacturing process wherein earth environment is kept free from pollution. CONSTITUTION:The organic composite coated steel plate comprises a chromate film formed on its zinc or zinc alloy plated surface in such an amount that Cr<6+> accounts for at most 70% of total Cr and in a weight of 5-500mg/m<2> based on converted Cr amount and a resin layer consisting mainly of any one of anionic aqueous resin containing water-dispersed silica, nonionic aqueous resin and anionic aqueous urethane resin formed on the chromate film in a dry weight 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 having excellent post-work corrosion resistance, which is mainly used as a steel sheet for automobile bodies by press forming.

[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 a use, for example, JP-A-57-108292 and JP-A-58-224174 disclose a chromate and an organic polymer on zinc and a zinc alloy plated steel sheet. An organic composite-coated steel sheet provided with a resin layer has 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 although excellent adhesion after coating is obtained, the flexibility of the coating film is not sufficient, so that the coating layer of the processed portion during molding such as press working is not sufficient. 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.
In particular, when an aqueous resin is used, there is a problem that compatibility cannot be obtained and it cannot be made into a paint depending on the combination with water-dispersed silica.

On the other hand, as a fingerprint-proof steel plate for home electric appliances, a chromate film is formed on a zinc-based alloy electroplated steel plate, and an aqueous liquid consisting of carboxylated polyethylene-based resin dispersion and colloidal silica is applied and dried to form a film. The method for doing this is as follows: Japanese Examined Patent Publication No. 61-36587
It is proposed in Japanese Patent No. 44387. In this case, it has been evaluated in the salt spray test, because it is significantly different from the environment when used as a steel sheet for automobiles, there is a problem that the corrosion resistance is insufficient in these methods in the corrosion resistance test of the present invention . Further, similarly, regarding the spot weldability, an excellent result is not obtained according to the test of the present invention.

In addition, the paints currently used are mainly organic solvent-based paints, and this aromatic hydrocarbon-based solvent is a source of air pollution, and a large reduction of this is a global problem.

[0009]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned various problems of the prior art, and particularly to an organic material excellent in corrosion resistance which does not pollute the global environment in the manufacturing process. It is intended to provide a composite coated steel sheet.

[0010]

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. In the combination of the anionic, nonionic or anionic aqueous urethane resin and the water-dispersed silica, the above problems (1) to (3) can be solved, and compatibility as a paint is obtained, and after processing, The inventors have found that the corrosion resistance is also excellent, and have reached the present invention. According to the present invention, an organic composite-coated steel sheet having excellent corrosion resistance after processing can be obtained by using a water-based paint, and does not pollute the global environment.

That is, according to the present invention, the Cr ⁶⁺ amount is 70% of the total Cr amount on the surface of the zinc- or zinc-based alloy-plated steel sheet.
% Or less, and has a chromate film having an adhesion amount of 5 to 500 mg / m ^{2 in} terms of Cr, and an adhesion amount on the upper layer of the chromate film is 0.1 to 3 g / m ² in terms of dry weight, mainly water. It is intended to provide an organic composite-coated steel sheet having a resin layer formed by mixing dispersed silica with one of an anionic aqueous resin, a nonionic aqueous resin, and an anionic aqueous urethane resin.

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

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

The dry weight ratio of silica to organic resin in the resin layer of the organic composite-coated steel sheet is 100% in the case of anionic aqueous resin and nonionic aqueous resin.
The amount of silica is preferably 10 to 100 parts by weight with respect to parts by weight. Resin 1 for anionic water-based urethane resin
The amount of silica is preferably 10 to 60 parts by weight with respect to 00 parts by weight.

Further, in the case of an anionic water-based urethane resin, the elongation is 50 to 1000% and the tensile strength is 200 kg.
It is preferable to use a resin having f / cm ² or more.

[0016]

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 the organic polymer resin layer described below 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 chromate method using a roll coater, an electrolytic chromate method, a reactive 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 and one of an anionic aqueous resin, a nonionic aqueous resin and an anionic aqueous urethane resin is applied. To be done.

As a method for water-solubilizing, water-soluble and water-dispersible resins in which a hydrophilic group is introduced into a resin skeleton, or emulsion-type resin by a forced emulsification method can be used. The emulsifier remains in the emulsion type resin by the forced emulsification method, on the other hand,
Since the water-soluble resin is feared to have insufficient corrosion resistance due to its low molecular weight, a water-dispersible resin can be used more preferably. Further, a water-dispersed resin containing an emulsifier can also be preferably used.

As a result of detailed studies on the aqueous resin used in the present invention, it was found that anionic aqueous resin and nonionic aqueous resin can be preferably used.

The anionic aqueous resin is an aqueous resin having an anionic hydrophilic group introduced into the resin skeleton thereof, and the nonionic aqueous resin is an aqueous resin having a nonionic hydrophilic group introduced therein. Examples of the anionic hydrophilic group include a carboxyl group, a sulfonic acid group and a phosphoric acid ester group, and examples of the nonionic hydrophilic group include polyethylene glycol, a hydroxyl group, an amide group and a methylol group. In the present invention, these anionic hydrophilic groups or nonionic hydrophilic groups are introduced into the resin.
Anionic water-based resins and nonionic water-based resins are used because the aqueous silica sol has a negative charge and is dispersed in the paint, so if it is a cationic resin, electrical repulsion will disappear and the paint will gel. This is because it becomes difficult to apply the paint on the steel sheet in order to realize the above-mentioned changes.

The type of resin is not particularly limited as long as it is an aqueous resin by introducing anionic and nonionic hydrophilic groups. For example, an acrylic resin, an epoxy resin, a urethane resin, an alkyd resin, a polyester resin, or a resin in which a resin skeleton is partially modified by a combination of these resins (for example, a urethane-modified epoxy resin, an epoxy-modified urethane resin, an acrylic-modified epoxy resin, etc.) is used. It can be preferably used. However, the carboxylated polyethylene resin is inferior in corrosion resistance and spot weldability in the test of the present invention, and is excluded.

Further, as the water-based resin used in the present invention, an anion-based water-based urethane resin can also be preferably used.
The urethane-based resin is a polymer compound having a large number of urethane bonds in its molecule, and a resin in which a part of the resin skeleton is modified with acrylic, epoxy, alkyd, ester or the like can also be preferably used.

In the present invention, the compounding ratio of the anionic aqueous urethane resin and the water-dispersed silica is in the range of 10 to 60 parts by weight of silica based on 100 parts by weight of the resin. FIG. 1 shows the results of a corrosion resistance test after processing with the resin and silica compounding ratios changed under the following conditions. The evaluation method is as described in the examples. Plating: Zn-13.0% Ni (electric), basis weight = 20 (g / m ² ) Chromate: Cr ⁶⁺ / total Cr ratio = 65 (%), adhesion amount =
45 mg / m ² resin layer: anionic aqueous urethane emulsion (HUX-29OH manufactured by Asahi Denka Co., Ltd.) (elongation: 700
%, Tensile strength: 350: kgf / cm ² ) and water-dispersed uniform granular silica sol (ST-30 manufactured by Nissan Chemical Industries, Ltd.) (average particle size = 0.01 μm), adhesion amount = 0.9 (g / m ² )

In order to evaluate the corrosion resistance after processing, a test piece subjected to a cylindrical drawing test (drawing ratio 2.0, wrinkle pressing pressure 1000 kg) was sprayed with a 5% NaCl aqueous solution (35 ° C.) for 4 hours and dried (60 ° C.) 2 Time, wet environment (RH 95%) (50 ° C)
It was subjected to a combined cycle corrosion test with 2 hours as one cycle, and the area ratio of red rust on the side wall of the test piece was measured after 50 cycles.

From FIG. 1, anionic water-based urethane resin and water-dispersed silica are 10 to 10 parts by weight of silica based on 100 parts by weight of the resin.
It can be seen that the corrosion resistance after processing becomes good with the compounding ratio of 60 parts by weight.

Further, in the case of an anionic water-based urethane resin, it is important to balance the elongation and tensile strength of the resin. That is, the range is such that the elongation is 50 to 1000% and the tensile strength is 200 kgf / cm ² or more. FIG. 2 shows the results of a corrosion resistance test after processing with the elongation and tensile strength of the urethane resin changed under the following conditions. The evaluation method is as described in the examples. Plating: Zn-12.5% Ni (electricity), basis weight = 20 (g / m ² ) Chromate: Cr ⁶⁺ / total Cr ratio = 65 (%), adhesion amount =
50 mg / m ² resin layer: Anionic water-dispersion type aqueous urethane resin and water-dispersion uniform granular silica sol (ST-manufactured by Nissan Chemical Industries, Ltd.)
20) (average particle size = 0.01 μm), resin: silica = 8
0:20, adhesion amount = 0.9 (g / m ² )

The evaluation method of the corrosion resistance after processing is 5 as in FIG.
The area ratio of red rust generation on the side wall of the test piece at 0 cycle was measured. From FIG. 2, it can be seen that the corrosion resistance after processing becomes good in the range of elongation of 50 to 1000% and tensile strength of 200 kgf / cm ² or more.

Regarding the silica in the organic composite coating of the present invention, securing an appropriate amount of silanol groups on the surface of the silica ensures stable retention of zinc-based corrosion products in a corrosive environment and ensures high corrosion resistance. Is important for. Water-dispersed silica is very suitable because it can secure sufficient silanol groups.

Specifically, the state of charge on 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 give an average of 0.005 to 2 μm, or an aqueous silica sol or a suitable dispersant for water. Dispersed hydrophobic fumed silica can be preferably used.

The average particle size of is preferably in the range of 0.005 to 2 μm. Average aggregate particle size 0.005 μ
When it is less than m, the silica is uniformly dispersed even in the resin layer, and the spot weldability is deteriorated. Further, when the average aggregate particle size exceeds 2 μm, a considerable number of silica aggregates bare to the outside of the resin layer, and the electric resistance between the electrode and the steel plate during spot welding significantly increases, and sparks are generated during welding to cause electrode Damage to the spot weldability and deteriorate 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.

The hydrophobic fumed silica also has a silanol group on the silica surface when dispersed in water, so that it is possible to stably hold the corrosion product, which is remarkably exhibited in combination with the aqueous resin. Is
It has excellent corrosion resistance after processing.

The dry weight ratio of the resin to silica in the resin layer containing the anionic aqueous resin or the nonionic aqueous resin is 1 part by weight of silica based on 100 parts by weight of the resin.
It is preferably from 0 to 100 parts by weight. Silica amount is 10
When the amount is less than the weight part, the ability to stably retain the zinc-based corrosion product formed in the film 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.

FIG. 3 shows the results of a flat plate bare corrosion resistance test conducted by changing the compounding ratio of resin and silica under the following conditions. The evaluation method is as described in the examples. Plating: Zn-13.2% Ni (electric), basis weight = 20 (g / m ² ) Chromate: Cr ⁶⁺ / total Cr ratio = 60 (%), adhesion =
50 mg / m ² resin layer: Anionic acrylic (anionic acrylic resin mixed with polymethylmethacrylate and polyacrylic acid) and water-dispersed fumed silica (Japan Aerosil Co., Ltd.)
Manufactured by AEROSIL 136) (particle size = 15 nm), adhesion amount = 0.8 (g / m ² ) From FIG. 3, silica 10 to 10 relative to 100 parts by weight of resin.
A flat plate corrosion resistance becomes good with a compounding ratio of 0 parts by weight.

Further, the water-based paint of the present invention may contain a cross-linking agent depending on the baking conditions for production.

As a method for coating an aqueous coating material containing an aqueous resin and water-dispersed silica on a chromate film, a method such as a roll coater method or an air knife method widely used in the industry 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 exposing the organic composite-coated steel sheet of the present invention 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 electrodeposited or the like. 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.

The organic resin layer may be coated on both sides or only one side, depending on its use. In the case of coating on only one surface, the non-coated surface is a zinc-based plating, a surface obtained by chromating the upper layer of the zinc-based plating, a cold-rolled surface, or the like.

[0040]

EXAMPLES Next, the effects of the present invention will be specifically described based on examples. Examples 1 to 5 and Comparative Examples 1 to 3 Various double-sided zinc-based plated steel sheets (plate thickness 0.80 mm) after degreasing, using a roll coater, various Cr ⁶⁺ / total Cr ratios and various coating amounts It was chromated and baked at a maximum attainable temperature of 130 ° C. Next, a coating material prepared by mixing various aqueous resins and various silicas having different average particle diameters 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 in the resin is as follows. A: Water-dispersed uniform granular silica sol (Nissan Chemical Co., Ltd.)
B): Water-dispersed aggregated silica sol (Nissan Chemical Co., Ltd.)
C: Water-dispersed chain silica sol (manufactured by Nissan Chemical Industries, Ltd.) D: Water-dispersed hydrophobic fumed silica (specific surface area: 200)
m ² / g) (manufactured by Nippon Aerosil Co., Ltd.)

The following tests were conducted to evaluate the performance of these organic composite coated steel sheet products. To evaluate the flat plate corrosion resistance, 5% NaCl aqueous solution spraying (35 ° C.) for 4 hours,
Dry (60 ° C) for 2 hours, wet environment (RH 95%) (50
It was subjected to a combined cycle corrosion test with 2 hours as one cycle, and the occurrence of red rust on the test piece at 200 cycles was observed. 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 and sprayed with a 5% NaCl aqueous solution (35 ° C.) for 4 hours.
Dry (60 ° C) for 2 hours, wet environment (RH 95%) (50
(° C) Two hours was used as a cycle for a combined cycle corrosion test, and the occurrence of red rust on the side wall of the test piece at 50 cycles was observed. ◎: 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

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 a welding tip made of Al ₂ O ₃ dispersed copper alloy of mmφ,
Welding pressure 200kgf, welding current 9kA, welding time 10H
Continuous welding was performed at z, 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

Table 1 shows the conditions of the chromate layer and the resin layer, the distribution of silica in the organic resin layer of the product, and the test results. (Examples 6 to 14 and Comparative Examples 4 to 8) Various double-sided zinc-based plated steel sheets (sheet thickness 0.75 mm) were coated with various Cr ⁶⁺ / total Cr ratios and various amounts of adhesion using a roll coater after degreasing. It was chromated and baked at a maximum attainable temperature of 130 ° C. Next, a coating material prepared by mixing an aqueous urethane resin having different aqueous methods and elongations and strengths with silica was applied with a roll coater. After that, the highest temperature reached 16
After baking at 0 ° C., it was immediately water-cooled and dried. The silica in the resin is the same as in Examples 1-5 and Comparative Examples 1-3. Performance evaluation of these organic composite coated steel sheet products was performed in the same manner as in Table 1. Table 2 shows the conditions of the chromate layer, the resin layer, the distribution state of silica in the organic resin layer of the product, and the test results.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

[Table 3]

[0049]

[Table 4]

[0050]

[Table 5]

[0051]

[Table 6]

[0052]

As described above, the organic composite coated steel sheet of the present invention has excellent flat plate corrosion resistance, post-processing corrosion resistance and spot weldability, and can solve the problems with conventional water-based paints. Since it can be used in a wide range of applications where similar quality characteristics are expected, including those for automobile bodies, its industrial value is extremely high.

[Brief description of drawings]

FIG. 1 is a diagram showing the effect of a compounding ratio of a resin and silica on post-processing corrosion resistance.

FIG. 2 is a diagram showing the influence on corrosion resistance after processing when the elongation and tensile strength of an anionic water-based urethane resin are changed.

FIG. 3 is a diagram showing the effect of the compounding ratio of resin and silica on the flat plate corrosion resistance.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kyoko Hamahara Inventor 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation Technical Research Division (72) Inventor Kazuo Mochizuki Chuo-ku, Chiba-shi, Chiba Kawasaki-cho 1 Technical Research Headquarters Kawasaki Steel Co., Ltd. (72) Inventor Morito Extension No. 1 Kawasaki-cho Chuo-ku, Chiba City Chiba Prefecture Kawasaki Steel Co., Ltd. Technical Research Headquarters

Claims (7)

[Claims] 1. The amount of Cr ⁶⁺ on the surface of a zinc- or zinc-based alloy-plated steel sheet is 70% or less of the total amount of Cr, and the amount of adhesion is C.
It has a chromate film of 5 to 500 mg / m ^{2 in} terms of r, and the amount adhering to the upper layer of the chromate film is a dry weight of 0.
An organic composite-coated steel sheet having excellent corrosion resistance after processing, which has a resin layer mainly composed of water-dispersed silica and an anionic water-based resin, which is 1 to 3 g / m ² . 2. The amount of Cr ⁶⁺ on the surface of a zinc or zinc-based alloy plated steel sheet is 70% or less of the total amount of Cr, and the amount of adhesion is C
It has a chromate film of 5 to 500 mg / m ^{2 in} terms of r, and the amount adhering to the upper layer of the chromate film is a dry weight of 0.
An organic composite-coated steel sheet excellent in post-processing corrosion resistance, having a resin layer mainly composed of water-dispersed silica and a nonionic aqueous resin of 1 to 3 g / m ² . 3. The amount of Cr ⁶⁺ on the surface of a zinc or zinc-based alloy plated steel sheet is 70% or less with respect to the total amount of Cr, and the amount of adhesion is C
It has a chromate film of 5 to 500 mg / m ^{2 in} terms of r, and the amount adhering to the upper layer of the chromate film is a dry weight of 0.
It has a resin layer mainly composed of water-dispersed silica and anionic water-based urethane resin of 1 to 3 g / m ² , and the dry weight ratio of silica and organic resin in the resin layer is 100 parts by weight of the resin. An organic composite-coated steel sheet having 10 to 60 parts by weight of silica and excellent in corrosion resistance after processing. 4. The silica as a constituent has an average particle size of 0.00.
An aqueous silica sol having a particle size of 5 to 2 μm is used.
2. An organic composite coated steel sheet having excellent corrosion resistance after processing according to any one of 1. 5. An organic composite-coated steel sheet excellent in corrosion resistance after processing according to claim 1, wherein water-dispersed hydrophobic fumed silica is used as the constituent silica. 6. The dry weight ratio of silica to organic resin in the resin layer is 10 to 1 with respect to 100 parts by weight of resin.
It is 100 parts by weight, and the organic composite-coated steel sheet excellent in corrosion resistance after working according to claim 1, 2, 4, or 5. 7. The anionic water-based urethane resin constituting the composition has an elongation of 50 to 1000% and a tensile strength of 200 kgf /.
The organic composite-coated steel sheet excellent in corrosion resistance after processing according to claim 3, wherein an anionic water-based urethane resin having a cm ² or more is used.