JPH0994916A - Organic composite coated steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve press-molding properties, corrosion resistance, electrodeposition coating properties, etc., by a method wherein a chromate coating containing respectively specific amounts of Cr<6+> and silica is provided on a surface of a zinc or zinc alloy plated steel sheet, and an organic resin layer of a specific amount in coating built-up which contains aqueous resin, water-dispersed silica, and organic pigment is provided thereon. SOLUTION: A chromate coating wherein an amount of Cr<6+> is 25-70% of total Cr, silica is contained by weight ratio of 0.5-3 in silica/Cr, and coating built-up is 5-500mg/m<2> in terms of Cr is formed on a surface of a zinc or zinc alloy plated steel sheet. An organic resin layer containing at least one kinds of an anionic aqueous resin or a nonionic aqueous resin and at least one kind of a condensation polycyclic pigment or an azo pigment is provided on its upper layer. The coating built-up is 0.1-3g/m<2> in dry weight. The silica is aqueous silica sol of 0.005-2μm average particle size, and the water-dispersed silica is preferably water-dispersed hydrophylic fumed silica.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an organic material which is excellent in press formability, corrosion resistance, electrodeposition coating property, water secondary adhesion and spot weldability, and is excellent in distinguishability, and is particularly suitable as a steel sheet for automobile bodies. The present invention relates to a composite coated steel sheet.

[0002]

2. Description of the Related Art In recent years, in response to strong social demands for high corrosion resistance of automobile bodies, the application of surface-treated steel sheets obtained by plating cold-rolled steel sheets with zinc or zinc-based alloy has been 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, in the painting performed after assembling the car body, the bag structure part and the bending part (hemming part) of the inner plate of the car body
Since the coating is not sufficiently spread to the above, steel sheets used in these parts are required to have higher corrosion resistance.

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 layer and an organic layer on a zinc or zinc alloy plated steel sheet. Organic composite coated steel sheets having a polymer resin layer have been proposed. All of these organic composite coated steel sheets exhibit high corrosion resistance by applying a coating containing a water-soluble or water-dispersed organic polymer resin and a water-dispersed silica sol to the upper layer of chromate-treated zinc or zinc-based plated steel sheet. Is intended.
However, these organic composite coated steel sheets have the following problems. (1) Since the water-soluble component remains in the organic polymer resin layer even after the formation of the organic polymer resin layer, the chromium elution resistance is poor, and chromium is eluted 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 forming a resin layer using a coating composition in which a hydrophobic silica whose surface is organically substituted in an organic solvent and an epoxy resin and the like are blended is disclosed. It is proposed in Japanese Patent Laid-Open No. 63-22637. According to this method, the compatibility between hydrophobic silica and an organic resin such as an epoxy resin is secured, and although an organic composite-coated steel sheet having excellent adhesion after coating is obtained, the flexibility of the coating film is sufficient. Therefore, it has been pointed out that the coating layer of the processed part is damaged during the forming process such as the press process and the corrosion resistance of this part is deteriorated.

As a method of improving the corrosion resistance after processing, a method of providing a coating layer containing a urethane resin and silicon dioxide as a main component is proposed in JP-A-62-289274. According to this method, although a slight improvement effect on the post-working corrosion resistance can be obtained, there is a problem that the post-working corrosion resistance also deteriorates when more severe working is performed. In particular, when an aqueous resin is used, the compatibility with silica is poor due to the difference in the charge state of the resin, and the resin and silica cannot be mixed sufficiently and cannot form a uniform film. was there. In addition, even if they could be mixed, there were cases where agglomeration and precipitates were formed during storage.

Most of the paints used at present are mainly organic solvents, and aromatic hydrocarbon solvents used as organic solvents are sources of air pollution. Therefore, the drastic reduction of the use of this solvent has become a global problem in terms of the preservation of the global environment.

By the way, in a processing and assembly line of an automobile manufacturing plant, a surface-treated steel sheet such as an organic composite steel sheet, a cold-rolled steel sheet, or even a surface-treated steel sheet having a different coating weight is used depending on the use site or destination. It is normal to mix and use. Therefore, it is important for quality control to use the steel plate as designed without confusion.
is important. Therefore, in order to distinguish between a cold-rolled steel sheet and a surface-treated steel sheet such as an organic composite-coated steel sheet, an automatic identification means using a photoelectric sensor has been put into practical use by utilizing the difference in light reflection intensity of these steel sheets. There is. According to the means for identifying using this photoelectric sensor, the reflection intensity of light is different.
If only steel sheets of different types are mixed, the objective can be achieved by using a relatively inexpensive photoelectric sensor.

However, when the same type of surface-treated steel sheet differs only in the coating weight, or when the plating surface and the organic coating are applied on the plating surface, there is no change in the light reflection intensity. Even if the above method is applied, there is a problem that it cannot be identified. Therefore, a method has been proposed in which an additive is mixed with an organic resin to positively change the glossiness of the organic composite-coated steel sheet. However, when the type of plating used increases, only the light reflection intensity is increased. Then, there was a problem that the discrimination was insufficient.

[0010]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned various problems of the prior art, to improve press formability,
It has excellent corrosion resistance, electrodeposition paintability, water-resistant secondary adhesion, and spot weldability, as well as excellent identification, and reduces the use of organic solvents that are a source of pollution of the global environment in the manufacturing process. The present invention intends to provide a suitable organic composite coated steel sheet.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems in the prior art. In particular, a chromate film and a water-based coating material comprising a combination of water-dispersed silica and an water-based organic resin have been studied in detail, and particularly identified. The present invention has been accomplished by studying various pigments for imparting properties.

That is, according to the present invention, the amount of Cr ⁶⁺ is 25 relative to the total Cr on the surface of a zinc or zinc alloy plated steel sheet.
~ 70%, silica 0.5 to 3 by weight ratio silica / Cr.
And the amount of adhesion is 5 to 500 mg in terms of Cr.
/ M ² chromate film, and at least one aqueous resin selected from anionic aqueous resins and nonionic aqueous resins, water-dispersed silica, and condensed polycyclic pigments and azos, which are disposed on the upper layer of the chromate film. An organic composite-coated steel sheet comprising an organic resin layer containing at least one organic pigment selected from the group of pigments and having a dry weight of 0.1 to 3 g / m ² .

In this organic composite-coated steel sheet, the organic resin layer comprises the organic pigment 1 to 100 parts by weight of the aqueous resin.
It preferably contains 20 parts by weight.

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

Further, in this organic composite-coated steel sheet, it is preferable that the water-dispersed silica in the organic resin layer is a water-dispersed hydrophilic fumed silica.

Further, in this organic composite-coated steel sheet, it is preferable that the organic resin layer contains, in a dry weight ratio, 10 to 100 parts by weight of water-dispersed silica with respect to 100 parts by weight of the aqueous resin.

Further, in this organic composite coated steel sheet,
The anionic water-based urethane resin has a cured product elongation of 5
It is preferable that the tensile strength is 0 to 1000% and the tensile strength is 200 kgf / cm ² or more.

Hereinafter, the organic composite coated steel sheet of the present invention (hereinafter,
The "steel plate of the present invention" will be described in detail.

The steel sheet of the present invention has a chromate coating and an organic resin layer on the surface of a zinc or zinc alloy plated steel sheet.

Zinc used as a material for the steel sheet of the present invention
Or zinc-based alloy plated steel sheet is a base steel sheet with zinc or
Zinc-based alloy plating is applied.
For lead alloy plating, pure zinc plating, Zn-Ni alloy
Gold plating, Zn-Fe alloy plating, Zn-Cr alloy plating
Binary alloy plating such as wood, Zn-Ni-Cr alloy plating
Ternary alloy plating such as Zn-Co-Cr alloy plating
Etc., also Zn-SiO ₂Plating, Zn-Co-Cr-
Al₂O_ThreeA wide range of products such as complex dispersion plating such as plating
I can mention it. In addition, these platings are
Plating method, hot dipping method, or vapor phase plating method
It may be applied by a method.

In the steel sheet of the present invention, the chromate film formed on the surface of zinc or zinc alloy plating is Cr
^{The 6+} amount is 25 to 70%, preferably 25 to 50%, based on the total Cr amount. If the amount of Cr ⁶⁺ is less than 25%, the self-repairing effect of Cr ⁶⁺ cannot be expected, and the corrosion resistance is poor. Further, if the Cr ⁶⁺ amount exceeds 70%, the chromium elution resistance during alkaline degreasing deteriorates, which is not preferable.

This chromate coating improves the adhesion to the organic resin layer described below and imparts corrosion resistance to silica in a weight ratio of silica / Cr of 0.5 to 3, preferably 0. It is included in a ratio of 8 to 2. silica/
If the weight ratio of Cr is less than 0.5, the water-resistant secondary adhesion is insufficient, and even if the weight ratio of silica / Cr exceeds 3, there is no further improvement effect of the water-resistant secondary adhesion, and the insulating material This is not preferable because the silica deteriorates the spot weldability and the electrodeposition coatability. As the silica contained in the chromate film, either liquid phase silica or vapor phase silica can be preferably used.
In particular, for the adhesion to the organic resin layer, it is necessary that silica is present in the outermost surface layer of the chromate film, and silica having a large particle size or silica in an aggregated form is suitable.

Further, the amount of the chromate film deposited is
5 to 500 mg / m ^{2 in} terms of Cr, preferably 10 to 1
It is in the range of 50 mg / m ² . 5mg / m Cr adhesion amount
^If it is less than ² , not only is the corrosion resistance insufficient, but also the adhesion to the resin layer is poor, which is not preferable. 500 mg / m
^When it exceeds ² , there is no further effect of improving the corrosion resistance, the resistance as an insulating coating increases, and the spot weldability and electrodeposition coatability are impaired, which is not preferable.

In the present invention, the chromate treatment for forming this chromate film may be performed 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. Silica, in any method, it is necessary to blend a predetermined amount in the treatment liquid, especially in the case of electrolytic type and reactive type,
By incorporating a special treating agent for co-depositing silica with Cr, a predetermined silica can be present in the chromate film.

The steel sheet of the present invention has an organic resin layer on the chromate film. This organic resin layer contains an organic pigment, water-dispersed silica and a water-based resin as essential components.

In the present invention, the aqueous resin which is a component of the organic resin layer is at least one selected from anionic aqueous resins and nonionic aqueous resins. here,
The anionic aqueous resin is a resin in which an anionic hydrophilic group is introduced into the resin skeleton, and the nonionic aqueous resin is a resin in which a nonionic hydrophilic group is introduced. Examples of the anionic hydrophilic group include a carboxyl group, a sulfonic acid group, and a phosphoric acid ester group.
Examples of the nonionic hydrophilic group include polyethylene glycol, a hydroxyl group, an amide group, and a methylol group. In the present invention, an anionic water-based resin or a nonionic water-based resin is used because, when the organic resin layer is formed, the water-dispersed silica compounded as an essential component in the water-based coating applied on the chromate film is negative. When the resin has a charge and is dispersed, and there is a cationic resin, electrical repulsion disappears and the water-based paint gels, making it difficult to apply the water-based paint on the chromate film to form a film. is there.

The water-based resin is not particularly limited in kind as long as it is a water-based resin by introducing anionic or 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 the resin skeleton is partially modified by a combination of these resins (for example, a urethane-modified epoxy resin, an acrylic-modified epoxy resin, an epoxy-modified urethane resin). , Acrylic modified urethane resin, etc.) are 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, anionic water-based urethane resin can be preferably used.
Here, the urethane-based resin is a polymer compound having a large number of urethane bonds in its molecule, and may be one obtained by modifying a part of the resin skeleton with acrylic, epoxy, alkyd, ester or the like.

In the present invention, when an anionic water-based urethane resin is used as the water-based resin, the elongation of the cured product of the urethane resin is 50 to 1000% and the tensile strength is 20 in particular.
Anionic water-based urethane resin having 0 kgf / cm ² or more is preferable. Here, an anionic water-based urethane resin having different elongation and tensile strength of a cured product is used as a water-based resin to produce an organic composite-coated steel sheet under the following conditions, and the results of examining the corrosion resistance after processing are shown in FIG. 1. At this time, the evaluation of the corrosion resistance after processing was performed by the same method as that used in Examples described later. Plating: Zn-13.0% Ni (electroplating), basis weight = 20 g / m ² Chromate coating: Cr ⁶⁺ / total Cr ratio = 50%, adhesion =
40 mg / m ² , silica / Cr ratio = 1.5 Aqueous paint layer: anionic aqueous urethane resin and water-dispersed chain silica (ST-UP manufactured by Nissan Chemical Industries, Ltd.), resin: silica = 80: 20, adhesion Amount 0.7 g / m ^{2 From the} results shown in FIG. 1, the elongation of the cured product of the anionic water-based urethane resin as the water-based resin is 50 to 1000%,
Further, it is understood that when an anionic water-based urethane resin having a tensile strength of 200 kgf / cm ² or more is used, an organic composite-coated steel sheet having excellent corrosion resistance after processing can be obtained.

In the steel sheet of the present invention, in order to further improve the chromium elution resistance, the weight ratio of at least one of formic acid, tannic acid and hydrazine hydrate to the organic resin (aqueous resin) is 100%. 0.01 to parts by weight
You may mix | blend in an organic resin layer in the ratio of 3 parts. This may be a combination of two kinds of formic acid and hydrazine hydrate, a combination of tannic acid and hydrazine hydrate, or three kinds.

As a method for making the resin aqueous, 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.

Further, the water-dispersed silica, which is a component of the organic resin layer of the steel sheet of the present invention, has an appropriate amount of silanol groups on the silica surface, and is zinc-based due to corrosion of zinc or zinc-based alloy plating in a corrosive environment. When a corrosion product is generated, it is an important component for stably holding the zinc-based corrosion product and obtaining an organic composite-coated steel sheet having excellent corrosion resistance. Since silica with many silanol groups contributes to the retention of zinc corrosion products, the silica contained in the organic resin layer has a large surface area, that is, silica with a small particle size or aggregates with a small particle size. The one in which silica having a small particle diameter is connected in a chain can be preferably used. Especially,
Chain silica, silica particles form a network in the organic resin layer, the cohesive force of the organic resin layer increases,
Excellent adhesion to chromate film.

As this water-dispersed silica, an aqueous silica sol in which the charge state of the surface of the water-dispersed silica sol is controlled by adjusting the amount of alkali metal ions or the amount of polyvalent metal ions, or hydrophilic fume dispersed in water by an appropriate dispersant. Dosilica can be preferably used.

The above-mentioned aqueous silica sol preferably has an average particle size of 0.005 to 2 μm. When the average particle diameter is less than 0.005 μm, silica is uniformly dispersed in the organic resin layer, which may cause deterioration of spot weldability. Further, when the average particle diameter exceeds 2 μm, a considerable number of silica particles barely reach the outside of the organic resin layer, and the electric resistance between the electrode and the steel plate significantly increases during spot welding, and sparks are generated during welding to cause electrode sparking. This will promote damage and deteriorate spot weldability. The shape of this aqueous silica sol may be a uniform particle shape or a shape in which primary particles are aggregated in the above average particle size range.

When the above-mentioned hydrophilic fumed silica is also dispersed in water, silanol groups are generated on the surface of the silica, so that it becomes possible to stably retain the zinc-based corrosion product, which is remarkable in combination with the aqueous resin. Is demonstrated to
It is an effective component for improving the corrosion resistance of the organic composite coated steel sheet.

In the organic resin layer of the steel sheet of the present invention, the mixing ratio of the water-based resin and the water-dispersed silica is preferably 10 to 100 parts by weight of the water-dispersed silica, more preferably 100 parts by weight of the water-based resin as a dry weight ratio. Is 15 to 70 parts by weight of water-dispersed silica with respect to 100 parts by weight of the aqueous resin. When the blending ratio of the water-dispersed 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 lacking, and high corrosion resistance may be obtained. Can not. The blending ratio of water-dispersed silica is 100.
If it exceeds the parts by weight, the compatibility with the aqueous resin deteriorates, making it 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 becomes extremely high and the spot weldability deteriorates. .

Here, as described below, an organic composite-coated steel sheet obtained by forming a chromate film on the surface of a zinc-based alloy-plated steel sheet and then forming an organic resin layer in which the mixing ratio of the aqueous resin and the water-dispersed silica is different. FIG. 2 shows the result of evaluating the flat plate corrosion resistance of the above. The flat plate corrosion resistance was evaluated by the same method as described in Examples below. Plating: Zn-13.5% Ni (electroplating), basis weight = 20 g / m ² Chromate coating: adhesion amount = 40 mg / m ² , silica / C
r = 2 Organic resin layer: Anionic acrylic resin and water-dispersed fumed silica (AEROSIL 136 manufactured by Nippon Aerosil Co., Ltd., particle diameter = 15 nm), adhesion amount = 0.5 g / m ^{2 From} FIG. 2, 100 weight of aqueous resin It can be seen that the compounding ratio of 10 to 100 parts by weight of water-dispersed silica with respect to parts is effective for obtaining an organic composite-coated steel sheet having excellent flat plate corrosion resistance.

The organic pigment, which is an essential component of the aqueous resin film of the steel sheet of the present invention, is at least one selected from condensed polycyclic pigments and azo pigments. Examples of the condensed polycyclic pigments and azo pigments used include phthalocyanine pigments such as phthalocyanine green, polychlorobrom copper phthalocyanine, metal-free phthalocyanine blue, and phthalocyanine blue; quinacridone pigments such as quinacridone red, quinacridone magenta, and quinacridone scarlet. Flantron yellow, anthrapyrimidine yellow, and other threnic pigments; quinophthalone yellow, phthaloimide, quinophthalone yellow, and other quinophthalone pigments; perylene red, perylene scarlet, perylene maroon, and other perylene pigments, isoindolinone pigments, isoindoline pigments Pigments; Pyrocholine pigments; Azo lake pigments such as Brilliant Carmine, Lake Red, Wocken Red; Disazo Yellow, Permanent Insoluble azo pigments such as oven; other condensed azo pigments such as chromophthal yellow and the like. These may be used alone or in combination of two or more.

In the organic resin layer, it is appropriate that at least one organic pigment selected from the above-mentioned condensed polycyclic pigment and azo pigment is blended in an amount of 1 to 20 parts by weight with respect to 100 parts by weight of the aqueous resin. is there. If the blending ratio of the organic pigment is less than 1 part by weight, it is not possible to obtain an organic composite-coated steel sheet having good distinguishability, while if it exceeds 20 parts by weight, the film-forming property and the adhesiveness of the organic resin layer are deteriorated. To do.

The organic resin layer of the steel sheet of the present invention is formed by coating a composition containing the above-mentioned aqueous resin, water-dispersed silica and organic pigment, and various additives to be added as necessary on a chromate film as a paint. It can be performed by coating and drying. As an additive to be added to the composition, for example, a crosslinking agent depending on the baking conditions of the organic resin layer may be added.

The method for forming the organic resin layer by coating the above composition on the chromate film of a plated steel sheet may be any of roll coating, spraying, shower coating, air knife method, and the like. 90 to 200 ° C. is suitable as the plate temperature of the heat treatment for heat treatment, but since it is sufficiently dried even at a temperature of 160 ° C. or less, the B
A remarkable effect that does not impair the H property can be obtained.

In the steel sheet of the present invention, the dry film thickness of the organic resin layer, that is, the amount of the organic resin layer attached is 0.1 to 3.0.
It is necessary to be g / m ² , especially 0.5 to 2.0 g / m
² is preferred. If the adhesion amount is less than 0.1 g / m ² , sufficient corrosion resistance cannot be obtained, and if it exceeds 3.0 g / m ² , the film resistance increases and spot weldability and electrodeposition coatability deteriorate. Further, when the steel sheet of the present invention is exposed to a corrosive environment as it is naked, it is preferable to secure an adhesion amount of 0.3 g / m ² or more, but when applying an electrodeposition coating or the like to the upper layer thereof. If the organic resin layer of 0.1 g / m ² or more is present, sufficient corrosion resistance can be obtained.

The steel sheet of the present invention has two sides, depending on its application.
Alternatively, it may have an organic resin layer on only one side. When the organic resin layer is provided on only one surface, the non-coated surface may be a zinc-based plating surface, a surface on which a zinc-based plating layer is chromated, or a cold-rolled surface.

[0044]

EXAMPLES The present invention will be specifically described below based on examples.

(Examples 1 to 14 and Comparative Examples 1 to 10)
In each example, degreased various double-sided zinc-plated steel sheets (sheet thickness 0.8 mm) were subjected to coating type chromate treatment with a roll coater and baked at a maximum attainable sheet temperature of 120 ° C. A film was formed. Next, as shown in Table 1, an aqueous coating material prepared by mixing various resins, various silicas having different average particle sizes, and various organic pigments was applied onto the chromate film by a roll coater. Then, it was baked at a maximum reaching plate temperature of 150 ° C. to form a paint film to obtain an organic composite-coated steel plate.

The resins used for forming the paint film are as follows. A: Diethylamine neutralized product of carboxyl group-containing anionic urethane resin (acid value 50, weight average molecular weight 20000) B: Diethylamine neutralized product of carboxyl group-containing anionic epoxy resin (acid value 45, weight average molecular weight 12500) C: Triethylamine neutralized product of carboxyl group-containing anionic urethane resin (acid value 48, weight average molecular weight 15,000) D: nonionic acrylic resin (weight average molecular weight 2800
0, glass transition temperature 18 ° C) E: nonionic acrylic modified epoxy resin (weight average molecular weight 35,000, glass transition temperature 42 ° C) F: carboxyl group-containing anionic urethane resin (acid value 48, weight average molecular weight 7800) in triethylamine K: G: Carboxyl group-containing epoxy-modified urethane resin (acid value 60, weight average molecular weight 38000) neutralized with diethylamine H: Cationic urethane resin (amine value 45, weight average molecular weight 35000) neutralized with acetic acid I: Carboxyl Triethylamine neutralized product of group-containing anionic urethane resin (acid value 48, weight average molecular weight 50,000)

The silica used for forming the paint film is as follows. A: Water-dispersed uniform silica sol (manufactured by Nissan Chemical Industries, Ltd., S
T-20) B: Aqueous dispersion aggregate form silica sol (Nissan Chemical Industry Co., Ltd.)
C: Water-dispersed chain silica sol (manufactured by Nissan Chemical Industries, Ltd., S
T-UP) D: Water-dispersed hydrophilic fumed silica (specific surface area = 200)
m ² / g) (Japan Aerosil Co., Ltd., AEROSIL20
0)

The organic pigments used for forming the paint film are as follows. A: Phthalocyanine green B: Quinacridone red C: Disazo yellow D: Quinophthalene yellow E: Quinacridone magenta F: Phthalocyanine blue

The additives added to the paint film are as follows. A: Formic acid (manufactured by Mitsubishi Gas Chemical Company) B: Tannic acid (manufactured by Fuji Chemical Industry Co., Ltd.) C: Hydrazine hydrate (manufactured by Mitsubishi Gas Chemical Company)

The performance evaluation of the organic composite-coated steel sheets obtained in Examples and Comparative Examples was carried out according to the following method.

Evaluation of distinguishability Color sensor HC1 manufactured by HOYA-SCHOTT Co., Ltd.
The output current value of the organic composite-coated steel sheet was measured using 080 at an extraction angle of 70 degrees, and evaluated based on the following criteria based on the difference between the output values of the zinc-based alloy-plated steel sheet and the organic composite-coated steel sheet, which are raw materials. . ◯: Output value difference 4 mA or more Δ: Output value difference 3 to 4 mA X: Output value difference 3 mA or less

Evaluation of Water-resistant Secondary Adhesion Property After subjecting a test piece of an organic composite-coated steel sheet to chemical conversion treatment using a chemical conversion treatment liquid (SD2500MZL manufactured by Nippon Paint Co., Ltd.), an electrodeposition paint (Nippon Paint Co., Ltd. ), U-26
02) was treated with Zn-Ni plating under the condition of electrodeposition of 20 μm, and baked at 160 ° C. for 10 minutes. After that, intermediate paint (Nippon Paint, TO4825 black)
Is spray-painted to a thickness of about 40 μm, then at 140 ° C for 2
A baking process for 0 minutes was performed. Next, topcoat paint (TO650PZ black manufactured by Nippon Paint Co., Ltd.) is applied to about 40 μm.
It was spray-coated to a thickness of m and baked at 140 ° C. for 20 minutes. The coated test piece was immersed in pure water at 50 ° C. for 10 days, and then taken out for 1 hour and then 2 m in length.
A m-square cross-cut was performed, a cellophane tape peeling test was performed, and the water resistant secondary adhesion was evaluated according to the following criteria. ◎: No peeling ：: Peeling area less than 5% and no cross-cut complete peeling. Δ: Peeling area 5% or more and less than 35 ×: Peeling area 35% or more

Evaluation of Flat Plate Corrosion Resistance A test piece of an organic composite coated steel sheet was sprayed with a 5% NaCl aqueous solution (35 ° C.) for 4 hours, dried (60 ° C.) for 2 hours, and in a humid environment (RH 95%, 50 ° C.). Subjected to a combined cycle corrosion test in which the exposure was performed for 2 hours as one cycle,
The state of occurrence of red rust on the test piece after the cycle was observed. The flat plate corrosion resistance was evaluated according to the following criteria. ◎: No red rust generated ○: Red rust generated area rate 10% or less △: Red rust generated area rate 10 to 20% ×: Red rust generated area rate 20% or more

Evaluation of Corrosion Resistance After Processing After subjecting a test piece of an organic composite coated steel sheet to a cylindrical drawing test (drawing ratio 2.0, wrinkle holding pressure 1000 kg), 5%
Spraying with an aqueous NaCl solution (35 ° C.) for 4 hours and drying (60
C.) for 2 hours and exposed to a wet environment (RH 95%, 50.degree. C.) for 2 hours for a combined cycle corrosion test, and observes the occurrence of red rust on the side wall of the test piece after 200 cycles. did. The corrosion resistance after processing was evaluated according to the following criteria. ◎: No red rust generated ○: Red rust generated area rate 10% or less △: Red rust generated area rate 10 to 20% ×: Red rust generated area rate 20% or more

Evaluation of chromium elution resistance The test pieces of the organic composite coated steel sheet were degreased, washed with water, surface-conditioned,
It was subjected to a process consisting of four treatments of chemical conversion treatment, the change in the amount of chromium deposited before and after the treatment was measured by fluorescent X-ray analysis, and the chromium elution resistance was evaluated according to the following criteria. ○: 1mg / m ² or less ^{△: 1~2mg / m 2 ×:} 2mg / m 2 or more

Evaluation of Spot Weldability Using a welding tip made of an Al ₂ O ₃ dispersed copper alloy with a tip of 6 mmφ, continuous welding of an organic composite coated steel sheet was performed at a pressing force of 200 kgf, a welding current of 9 kA and a welding time of 10 Hz to obtain a nugget diameter. The number of continuous welding spots was measured until the value fell below the reference value. The spot weldability was evaluated according to the following criteria. ◎: 3000 points or more ○: 2000 to 3000 points △: 1000 to 2000 points ×: Less than 1000 points

Table 1 collectively shows the composition of the chromate film, the paint film and the distribution state of silica in the organic composite-coated steel sheets obtained in Examples and Comparative Examples, and the results of performance evaluation.

[0058]

[Table 1]

[0059]

[Table 2]

[0060]

[Table 3]

[0061]

[Table 4]

[0062]

The organic composite coated steel sheet of the present invention has a water-resistant secondary adhesion, flat plate corrosion resistance, post-processing corrosion resistance, chromium elution resistance,
It has excellent cationic electrodeposition paintability and spot weldability, as well as excellent distinguishability, and can be used in a wide range of applications where similar quality characteristics are expected, especially for automobile bodies, so it has an industrial value. Is extremely high. Further, the organic composite-coated steel sheet of the present invention can reduce the use of an organic solvent which is a pollution source of the global environment in the manufacturing process.

[Brief description of drawings]

FIG. 1 is a diagram showing the results of examining the relationship between elongation and tensile strength of an anionic water-based urethane resin and corrosion resistance after processing in an organic composite-coated steel sheet.

FIG. 2 is a diagram showing the results of examining the relationship between the compounding ratio of a water-based resin and water-dispersed silica and plate corrosion resistance in an organic composite-coated steel sheet.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C23C 28/00 C23C 28/00 C

Claims (8)

[Claims] 1. A zinc or zinc-based alloy-plated steel sheet surface, wherein the amount of Cr ⁶⁺ is 25 to 70% with respect to the total Cr, and silica is contained in a weight ratio of silica / Cr of 0.5 to 3; A chromate film having an adhesion amount of 5 to 500 mg / m ² in terms of Cr, and at least one aqueous resin selected from an anionic aqueous resin and a nonionic aqueous resin, which is disposed on the upper layer of the chromate film, and an aqueous dispersion. Silica, and at least one organic pigment selected from condensed polycyclic pigments and azo pigments, and the adhesion amount is 0.1 to 3 by dry weight.
An organic composite-coated steel sheet having an organic resin layer of g / m ² . 2. The surface of zinc or zinc-based alloy plated steel sheet contains Cr ^{6+ in an} amount of 25 to 70% with respect to the total Cr and silica in a weight ratio of silica / Cr of 0.5 to 3, A chromate film having an adhesion amount of 5 to 500 mg / m ² in terms of Cr, and an anionic water-based resin, water-dispersed silica, a condensed polycyclic pigment and an azo pigment, which is disposed on the chromate film. An organic composite-coated steel sheet comprising an organic resin layer containing at least one organic pigment and having a dry weight of 0.1 to 3 g / m ² . 3. A zinc or zinc-based alloy-plated steel sheet surface containing Cr ^{6+ in an} amount of 25 to 70% based on the total Cr and silica in a weight ratio of silica / Cr of 0.5 to 3, A chromate film having an adhesion amount of 5 to 500 mg / m ² in terms of Cr and a nonionic water-based resin, a water-dispersed silica, a condensed polycyclic pigment and an azo pigment, which is disposed on the chromate film. An organic composite-coated steel sheet comprising an organic resin layer containing at least one organic pigment and having a dry weight of 0.1 to 3 g / m ² . 4. The organic composite-coated steel sheet according to claim 1, wherein the organic resin layer contains 1 to 20 parts by weight of an organic pigment with respect to 100 parts by weight of an aqueous resin. 5. The silica has an average particle size of 0.005 to 2
The organic composite-coated steel sheet according to any one of claims 1 to 4, which is an aqueous silica sol having a thickness of µm. 6. The organic composite-coated steel sheet according to claim 1, wherein the water-dispersed silica in the organic resin layer is water-dispersed hydrophilic fumed silica. 7. The organic composite-coated steel sheet according to claim 1, wherein the organic resin layer contains, in a dry weight ratio, 10 to 100 parts by weight of water-dispersed silica with respect to 100 parts by weight of the aqueous resin. . 8. The anionic water-based urethane resin has a cured product having an elongation of 50 to 1000% and a tensile strength of 200 kg.
The organic composite-coated steel sheet according to claim 1, which has a f / cm ² or more.