JP3458553B2 - Organic composite coated steel sheet with excellent water-resistant secondary adhesion and post-processing corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an organic composite coated steel excellent in water resisting secondary adhesion and corrosion resistance after working by applying the surface of a galvanized steel sheet with a silica-added chromate film and silica-dispersed water base coating material film both having specified compsns. by specified coating weights. SOLUTION: The surface of a galvanized or galvannealed steel sheet is applied with a silica-added chromate film by 5 to 500mg/m<2> coating weight expressed in terms of Cr. The content of Cr<6+> in this film is regulated to 25 to 70% to the whole Cr, and the ratio of Si/Cr therein is regulated to 1 to 5 by Auger electron spectroscopy. The upper layedr of this chromate film is applied with a water base coating material film formed by blending water- dispersed silica with a anionic or nonionic water base resin by 0.1 to 3g/m<2> coating weight (dry weight). As the water-dispersed silica, a water base silica sol or water-dispersed water base fumed silica having 0.05 to 2&mu;m average particle size is preferably used, and the ratio thereof is preferably regulated to 10 to 100 pts.wt based on 100 pts.wt. of the organic resin.

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 mainly used as a steel sheet for automobile bodies by press forming and is excellent in water resistant secondary adhesion and corrosion resistance after working.

[0002]

2. Description of the Related Art In response to the strong social demand for high corrosion resistance of automobile bodies, the use of surface-treated steel sheets obtained by plating a cold-rolled steel sheet with zinc or a zinc-based alloy is expanding to automobile bodies.

Examples of these surface-treated steel sheets include hot-dip galvanized steel sheets, galvannealed steel sheets, electrogalvanized steel sheets, and electrogalvanized alloy-plated steel sheets. However, a higher degree of 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, in JP-A-57-108292 and JP-A-58-224174, chromate and an organic polymer resin are coated on a zinc and zinc alloy plated steel sheet. Organic composite coated steel sheets having layers 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 formation, 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 surface is silica-substituted in an organic solvent is mixed with an epoxy resin 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 on the surface and the corrosion resistance of this part deteriorates.

In order to solve the problem of poor corrosion resistance after such processing, a method of forming a coating layer containing urethane resin and silicon dioxide as main components is disclosed in Japanese Patent Laid-Open No. 62-28.
It is proposed in Japanese Patent No. 9274. 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 when it is combined with silica due to the difference in charge state of the resin, compatibility cannot be obtained and it cannot be made into a paint.

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]

An object of the present invention is to solve the above-mentioned various problems of the prior art, and particularly to provide an organic composite coated steel sheet which does not pollute the global environment in the manufacturing process. It is what

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems in the prior art, and in particular, regarding the secondary adhesion to water and the corrosion resistance after processing, the combination of chromate and water-dispersed silica with an aqueous organic resin is used. The present invention has been achieved by conducting a detailed study on a water-based paint.
According to the present invention, it is possible to obtain an organic composite-coated steel sheet excellent in water-resistant secondary adhesion and corrosion resistance after processing by using a water-based paint, and does not pollute the global environment.

That is, according to the present invention, the amount of Cr ⁶⁺ on the surface of zinc or zinc-based alloy plated steel sheet is 25% with respect to the total Cr.
~ 70%, the amount of adhesion is 5 to 500 mg / m ^{2 in} terms of Cr
And has a silica-added chromate coating having a Si / Cr ratio of 1 to 5 by Auger electron spectroscopy, and the amount of deposition is mainly 0.1 to 3 g / m ² on the upper layer of the chromate coating.
Mainly 1 out of water-dispersed silica and anionic aqueous resin, nonionic aqueous resin and anionic aqueous urethane resin
It is intended to provide an organic composite-coated steel sheet excellent in water-resistant secondary adhesion and excellent in corrosion resistance after working, which is characterized by having an aqueous paint film formed by mixing seeds. It is preferable to use an aqueous silica sol having an average particle size of 0.005 to 2 μm as silica constituting the organic composite coating.

Further, it is preferable to use water-dispersed hydrophilic fumed silica as the silica constituting the organic composite coating. The dry weight ratio of silica to the organic resin in the resin layer of the organic composite coating is preferably 10 to 100 parts by weight of silica based on 100 parts by weight of the resin. Furthermore, the anionic water-based resin that constitutes the organic composite coating is an anionic water-based urethane resin, and has an elongation of 50 to 10
It is preferable that the tensile strength is 00% and the tensile strength is 200 kgf / cm or more.

[0013]

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 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 electroplating, hot dipping, or vapor phase plating.

On these zinc- or zinc-based alloy-plated steel sheets, silica-added chromate treatment is performed in order to improve the adhesion with the organic polymer resin layer described later and to impart corrosion resistance. Chromate adhesion amount is 5 in terms of Cr
500 mg / m ² , preferably 10-150 mg / m ²
The range is. If the amount of deposited Cr is less than 5 mg / m ² , not only the corrosion resistance is insufficient, but also the adhesion with the resin layer is poor, which is not preferable. Even if it exceeds 500 mg / m ² ,
It is not preferable because there is no further improvement in corrosion resistance, the resistance as an insulating coating increases, and the spot weldability and electrodeposition coatability are impaired. The silica to be added is liquid phase silica,
Either of the vapor phase silicas can be preferably used, but the Si / Cr ratio of the chromate layer by Auger electron spectroscopy is 1 to 5, preferably 1.5 to 4.0. With Auger electron spectroscopy, when the surface of a sample is irradiated with a high-speed electron beam, the electrons on the solid surface are ionized and formed into holes in the inner shell, and the electrons in the upper level are emitted with the energy of this step difference. This is called Auger electron emission, which is a spectroscopic analysis by the characteristic energy of the emitted Auger electrons. The escape depth of Auger electrons is about 30Å, which is an analysis of the extreme surface.

S according to Auger electron spectroscopy defined here
The i / Cr ratio is SiKLL (1606 eV) and Cr in the Auger electron spectrum of silica-added chromate.
The intensity ratio is (529 eV). It is necessary that this ratio be 1-5, preferably 1.5-4.0.

FIG. 1 shows the results of evaluating the water-resistant secondary adhesion and spot weldability of the organic composite coated steel sheet produced using the aqueous resin shown below. Plating: Zn-12.7% Ni (electric), basis weight = 20
g / m ² resin layer: acrylic modified epoxy resin and water-dispersed uniform silica (ST-20 manufactured by Nissan Chemical Industries, Ltd.), resin: silica =
80:20, 0.7 g / m ^{2 of} adhesion amount

In order to evaluate the water-resistant secondary adhesion, chemical conversion treatment was performed with SD2500MZL manufactured by Nippon Paint Co., Ltd.
Nippon Paint Co., Ltd. U-2602 was treated by Zn-Ni plating under the condition of electrodeposition of 20 μm, and was subjected to 10 ° C. at 160 ° C.
I baked the minutes. Thereafter, the intermediate coating TO4825 black manufactured by Nippon Paint Co., Ltd. was spray-coated to a thickness of about 40 μm and baked at 140 ° C. for 20 minutes. After that, top coat paint TO650PZ black made by Nippon Paint is about 40 μm.
It was spray-coated to a thickness and baked at 140 ° C. for 20 minutes. The sample after coating is immersed in pure water at 50 ° C. for 10 days, 1 hour after being taken out, soaked in a 2 mm square cross for 10 days, and 1 hour after being taken out, 2 mm cross cross cut and cellophane tape peeling test The water resistance secondary adhesion was investigated according to the following evaluation criteria. ⊚: No peeling ○: Peeling area is less than 5% and there is no complete peeling of the grid. Δ: Peeling area 5% or more and less than 35 ×: Peeling area 35% 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 value was measured. The evaluation criteria are shown below. ⊚: 3000 points or more ○: 2000 to 3000 points Δ: 1000 to 2000 points x: less than 1000 points As shown in FIG. 1, the Si / Cr ratio by Auger electron spectroscopy is in the range of 1 to 5 and particularly in the range of 1.5 to 4.0. The water-resistant secondary adhesion and spot weldability are improved.

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. Si / by Auger electron spectroscopy of the chromate layer
The method of adjusting the Cr ratio to 1 to 5 is not particularly limited, but in the case of the coating type chromate, the ratio of the total Si amount and the total Cr amount in the chromate to be applied is set to the range of 0.5 to 3.0 and further used. If silica having a three-dimensionally aggregated form or silica having a large particle size is selected, the silica in the chromate layer is likely to concentrate on the extreme surface. In particular, if a method of adding gas phase silica or liquid phase silica in an aggregated form to a chromate solution is used, S of the chromate layer by Auger electron spectroscopy
The i / Cr ratio can be in the range of 1-5.

The ratio of Cr ^{6+ in} the chromate is the total Cr.
25-70% is preferable with respect to the amount. Cr ⁶⁺ amount is 25%
If it is less than this, the self-repairing effect of Cr ⁶⁺ cannot be expected, and the corrosion resistance deteriorates. Further, if the Cr ⁶⁺ amount exceeds 70%, the chromium elution resistance during alkaline degreasing deteriorates, which is not preferable.

On the upper layer of such a chromate film, water-dispersed silica and one kind of anionic water-based resin, nonionic water-based resin and anion-based water-based urethane resin having a surfactant content of 10% or less based on the resin are used. An organic composite film formed by blending is applied.

As a method for making the resin water-based, a water-soluble type and a water-dispersed type in which a hydrophilic group is introduced into the resin skeleton, or an emulsion type resin by a forced emulsification method can be used. The emulsifier remains in the emulsion type resin by forced emulsification,
On the other hand, since the water-soluble resin is likely to have insufficient corrosion resistance due to its low molecular weight, a water-dispersible resin can be preferably used. Further, a water-dispersible resin containing a small amount of an emulsifier as a dispersion aid can also be suitably used.

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

The anionic aqueous resin is an aqueous resin in which an anionic hydrophilic group is introduced into the resin skeleton, and the nonionic aqueous resin is a nonionic hydrophilic group. 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 a 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 resin and nonionic water-based resin 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 makes it difficult to apply the paint on the steel plate.

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, acrylic resin, epoxy resin, urethane resin, alkyd resin, polyester resin, or a resin in which the resin skeleton is partially modified by a combination of these resins (for example, urethane modified epoxy resin, acrylic modified epoxy resin, epoxy modified urethane resin, acrylic modified (Urethane resin etc.) 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 aqueous resin used in the present invention, anionic aqueous urethane resin can 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 be preferably used.

In the case of anionic urethane resin, it is important to balance the elongation and tensile strength of the resin. That is, the range has an elongation of 50 to 1000, preferably 100 to 800.
% And the tensile strength is 200, preferably 250 kgf / cm ² or more. FIG. 2 shows the results of corrosion resistance test after working by producing organic composite-coated steel sheets by changing the elongation and tensile strength of urethane resin under the following conditions. Plating: Zn-13.0% Ni (electric), basis weight = 20
g / m ² Silica-added chromate: Cr ⁶⁺ / total Cr ratio = 50%, adhesion amount = 40 mg / m ² , Si / by Auger electron spectroscopy
Cr ratio = 1.5 Resin layer: Anionic aqueous urethane resin and water-dispersed chain silica (ST-UP manufactured by Nissan Chemical Industries, Ltd., resin: silica =
80:20, 0.7 g / m ^{2 of} adhesion amount

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 ° C) for 2 hours, wet environment (RH 95%, 50
C.) was subjected to a combined cycle corrosion test in which 2 hours were one cycle, and the occurrence of red rust on the side wall of the test piece at 200 cycles was determined. The evaluation method is as described later in Examples.

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.

In order to further improve the chromium elution resistance of the organic composite coating, the weight ratio of at least one of formic acid, tannic acid and hydrazine hydrate to the organic resin is 0 relative to 100 parts by weight of the resin. 1 to 3 parts may be blended in the aqueous resin coating material. This is formic acid and hydrazine hydrate,
A combination of two kinds of tannic acid and hydrazine hydrate or three kinds may be used.

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 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, and the average particle size is 0.005 to 2
An aqueous silica sol having a particle size of μm or a hydrophilic fumed silica dispersed in water with an appropriate dispersant can be preferably used.

The average particle size of is preferably in the range of 0.005 to 2, preferably 0.01 to 1.0 μm. When the average particle diameter is 0.005 μm or more, a current-carrying path can be secured during spot welding, and spot weldability is excellent.

If the average particle diameter exceeds 2 μm, a considerable number of silica particles barely reach the outside of the resin layer, and the electric resistance between the electrode and the steel plate during spot welding remarkably increases, causing sparks during welding. This will promote electrode damage and degrade spot welding. The silica may have a uniform particle shape or may have a shape in which primary particles are aggregated in the above average particle diameter range.

Since the silanol groups are present on the surface of the silica by dispersing the fumed silica in water with water, it becomes possible to stably hold the corrosion product, which is remarkably exhibited in combination with the aqueous resin. It has excellent corrosion resistance.

The dry weight ratio of resin to silica in the resin layer of the above aqueous resin and water-dispersed silica is 10
Silica 10 to 100, preferably 15 to 100 parts by weight
70 parts by weight is preferred. When the amount of silica compounded is less than 10 parts by weight, the ability to stably retain 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 silica content is more than 100 parts by weight, compatibility with the resin composition will not be obtained, and it will be difficult to apply it to the steel sheet as a paint. Even if it can be applied, the electrical resistance of the steel sheet surface will be very high. This is because the spot weldability has increased and the spot weldability has deteriorated.

Mixing of resin and silica under the following conditions in FIG.
We manufacture organic composite coated steel sheets with different ratios and perform flat plate corrosion resistance test.
The result is shown. The evaluation method is as described in the examples.
is there. Plating: Zn-13.5% Ni (electric), basis weight = 20
g / m² Silica-added chromate: Adhesion amount = 40 mg / m², Oh
J / e electron spectroscopy Si / Cr ratio = 2.0 Resin layer: Anionic acrylic resin and water dispersion fumed
Rica (AEROSIL 13 manufactured by Nippon Aerosil Co., Ltd.)
6, particle size = 15 nm), adhesion amount = 0.5 g / m ², Prolapse
Contact angle of ion water: 45 degrees

From FIG. 3, the flat plate corrosion resistance is improved with a compounding ratio of 10 to 100 parts by weight of silica to 100 parts by weight of the resin.

Further, in the water-based paint of the present invention, a cross-linking agent may be added depending on the baking conditions during the production of the organic composite coating.

The method of coating the aqueous paint film of the present invention, which is blended as described above, on the chromate film of the plated steel sheet may be any of roll coating, spraying, shower coating, air knife method and the like. As the plate temperature of the heat treatment for drying, 90 to 200 ° C. is suitable, but since it is sufficiently dried even at a temperature of 160 ° C. or less, a remarkable effect that does not impair the BH (bake hardening resistance) of the steel sheet Is obtained.

The dry film thickness of the resin composition, i.e. as the coating weight of the solid film must be 0.1 to 3.0 g / m ^2, especially 0.5 to 2.0 g / m ² is preferred.
This is because if it is less than 0.1 g / m ² , sufficient corrosion resistance cannot be obtained, and if it exceeds 3.0 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 deposition amount of 0.3 g / m ² or more, but the upper layer thereof is further subjected to electrodeposition coating or the like. In this case, 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 composite coating layer may be coated on both sides or only one side depending on the application. In the case of coating only one surface, examples of the non-coated surface include zinc-based plating, a surface on which zinc-based plating is chromate-treated, or a cold-rolled surface.

[0044]

EXAMPLES The present invention will be specifically described below based on examples. (Examples 1 to 8 and Comparative Examples 1 to 4) Various double-sided zinc-based plated steel sheets (sheet thickness 0.8 mm) were degreased and then subjected to coating type chromate treatment with various amounts of adhesion by a roll coater, and the maximum reached sheet temperature 120 ° C. Burned in. Next, a coating material prepared by mixing various aqueous resins, various silicas having different average particle sizes, and various additives was applied by a roll coater. After that, baking was performed at a maximum reaching plate temperature of 150 ° C. The silica in the resin is as follows. A: Water-dispersed uniform silica sol (manufactured by Nissan Chemical Industries, 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 hydrophilic fumed silica (specific surface area = 200)
m ² / g) (manufactured by Nissan Aerosil Co., Ltd.)

The following tests were conducted to evaluate the performance of these organic composite coated steel sheet products. <Water-resistant secondary adhesion evaluation> SD25 manufactured by Nippon Paint Co., Ltd.
A chemical conversion treatment was performed with 00MZL, and the electrodeposition coating material U-2602 manufactured by Nippon Paint Co., Ltd. was treated with Zn-Ni plating for 20 μm electrodeposition, and baked at 160 ° C. for 10 minutes.
Thereafter, the intermediate coating TO4825 black manufactured by Nippon Paint Co., Ltd. was spray-coated to a thickness of about 40 μm and baked at 140 ° C. for 20 minutes. After that, top paint TO made by Nippon Paint
650PZ black is spray-painted to a thickness of about 40 μm. 14
Baking was performed for 20 minutes at 0 ° C. This coated sample is immersed in pure water at 50 ° C for 10 days, and then taken out for 1
After a lapse of time, a 2 mm cross-cut cross-cut and a cellophane tape peeling test were performed, and the water resistant secondary adhesion was investigated according to the following evaluation criteria. ⊚: No peeling ○: Peeling area is less than 5% and there is no complete peeling of the grid. Δ: Peeling area 5% or more and less than 35 ×: Peeling area 35% or more

<Plate corrosion resistance> A 5% NaCl aqueous solution spray (35 ° C.) for 4 hours, drying (60 ° C.) for 2 hours, wet environment (RH 95%, 50 ° C.) for 2 hours were subjected to a combined cycle corrosion test, The occurrence of red rust on the test piece after 200 cycles was observed. The evaluation criteria for flat plate corrosion resistance are shown below. ◎: No red rust occurred ○: Red rust occurrence area ratio 10% or less △: Red rust occurrence area ratio 10 to 20% ×: Red rust occurrence area ratio 20% or more

<Corrosion resistance after processing> A test piece subjected to a cylindrical drawing test (drawing ratio 2.0, wrinkle holding pressure 1000 kg) was dried (5% NaCl aqueous solution spray liquid (35 ° C)) for 4 hours and dried (6
2 hours at 0 ° C) and 2 hours in a wet environment (RH 95%, 50 ° C) as a combined cycle corrosion test.
The occurrence of red rust on the side wall of the test piece in the 00 cycle was observed. The evaluation criteria for the corrosion resistance after processing are shown below. ◎: No red rust occurred ○: Red rust occurrence area ratio 10% or less △: Red rust occurrence area ratio 10 to 20% ×: Red rust occurrence area ratio 20% or more

<Chromium elution resistance> Four steps of degreasing, washing with water, surface conditioning and chemical conversion treatment were carried out, and changes in the amount of chromium adhering before and after the treatment were measured by fluorescent X-ray analysis. ○: less than ^{1mg / m 2 △: 1~2mg /} m 2 ×: 2mg / m 2 or more

<Spot Weldability> Al _{2 with a} tip of 6 mmφ
Welding tip made of O ₃ dispersed copper alloy, pressure 200k
Continuous welding was performed at gf, a welding current of 9 kA, and a welding time of 10 Hz, and the number of continuous welding points until the nugget diameter fell below the reference value 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 state of silica in the organic resin layer of the product, and the test results.

[0051]

[Table 1]

[0052]

[Table 2]

[0053]

[Table 3]

[0054]

[Table 4]

[0055]

[0056]

[0057]

As described above, the organic composite-coated steel sheet of the present invention has excellent water-resistant secondary adhesion, flat plate corrosion resistance,
Since it has corrosion resistance after processing, chromium elution resistance, cationic electrodeposition coating property and spot weldability, it can be used in a wide range of applications where similar quality characteristics are expected, including for automobile bodies, so it is industrial Value is extremely high.

[Brief description of drawings]

FIG. 1 is a diagram showing the influence of the Si / Cr strength ratio on the water resistant secondary adhesion of the produced organic composite coated steel sheet by Auger electron spectroscopy.

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 front page (72) Inventor Kazuo Mochizuki, 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba, Kawasaki Steel Works Ltd. Technical Research Institute (72) Inventor Noriko Makiishi, Kawasaki-cho, Chuo-ku, Chiba-shi No. 1 Kawasaki Steel Co., Ltd. Technical Research Institute (56) Reference JP-A-8-332695 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C23C 28/00 B05D 7/14 B32B 15/08 C23C 22/30

Claims (6)

(57) [Claims] 1. The amount of Cr ⁶⁺ on the surface of a zinc- or zinc-based alloy-plated steel sheet is 25% to 70% with respect to the total Cr, and the adhesion amount is 5 to 500 mg / m ² in terms of Cr, by Auger electron spectroscopy. It has a silica-added chromate film having a Si / Cr ratio of 1 to 5, and an upper layer of the chromate film is blended with water-dispersed silica having an adhesion amount of 0.1 to 3 g / m ² in dry weight and an anionic water-based resin. An organic composite-coated steel sheet having excellent water-resistant secondary adhesion and excellent corrosion resistance after working, which is characterized by having a water-based paint film formed by 2. The amount of Cr ⁶⁺ on the surface of a zinc- or zinc-based alloy-plated steel sheet is 25% to 70% of the total Cr, and the amount of adhesion is 5 to 500 mg / m ² in terms of Cr, by Auger electron spectroscopy. It has a silica-added chromate coating having a Si / Cr ratio of 1 to 5, and an upper layer of the chromate coating is blended with water-dispersed silica having a dry weight of 0.1 to 3 g / m ² and a nonionic aqueous resin. An organic composite-coated steel sheet having excellent water-resistant secondary adhesion and excellent corrosion resistance after working, which is characterized by having a water-based paint film formed by 3. The water-resistant secondary adhesion and corrosion resistance after processing according to claim 1, wherein the water-dispersed silica in the water-based coating film is an aqueous silica sol having an average particle size of 0.005 to 2 μm. Excellent organic composite coated steel sheet. 4. The organic composite-coated steel sheet excellent in water-resistant secondary adhesion and corrosion resistance after processing according to claim 1 or 2, wherein the water-dispersed silica in the aqueous paint film is water-dispersed hydrophilic fumed silica. . 5. The dry weight ratio of silica to organic resin in the aqueous paint film is 10 parts by weight of silica based on 100 parts by weight of resin.
To 100 parts by weight, the organic composite-coated steel sheet excellent in water-resistant secondary adhesion and corrosion resistance after working according to any one of claims 1 to 4. 6. The water-resistant secondary adhesion according to claim 1, wherein the anionic water-based resin is an anionic water-based urethane resin and has an elongation of 50 to 1000% and a tensile strength of 200 kgf / cm or more. Of organic composite coated steel sheet with excellent heat resistance and corrosion resistance after processing.