JP3503194B2 - Organic composite coated steel sheet - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to an organic composite coated steel sheet used as a steel sheet for automobile bodies.

[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, galvannealed 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 develop 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. Had some problems. (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 secured, and although excellent adhesion after coating is obtained, the flexibility of the coating film is not sufficient, so that the coating film of the processed portion during molding processing such as press working It has been pointed out that the layer is damaged and the corrosion resistance of this part is deteriorated.

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-62-28927.
No. 4 is proposed. 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 addition, most of the paints currently used are organic solvent-based paints, and such aromatic hydrocarbon-based solvents are air pollutants, and their significant reduction is a problem to be solved on a global scale. ing.

[0007]

SUMMARY OF THE INVENTION Therefore, the 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 the one we are trying to provide.

[0008]

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. By combining two types of aqueous resins having different particle sizes, the above (1) to
The inventors have found that the problem (3) can be solved, and that an organic composite steel sheet having excellent various properties can be obtained, and completed the present invention. According to the invention,
An organic composite steel sheet excellent in chromium elution resistance, corrosion resistance, and adhesion can be obtained by using a water-based paint, and does not pollute the global environment.

That is, according to the present invention, the adhesion amount is 5 to 500 in terms of Cr on the surface of the zinc or zinc alloy plated steel sheet.
Silica having a chromate film of mg / m ² and having a dry weight of 0.1 to 3 g / m ² as the upper layer of the chromate film, mainly dispersed in water, and having a particle size of 1 μm or more 10
An organic composite-coated steel sheet having a resin layer formed by mixing an aqueous resin having a particle size of less than μm and an aqueous resin having a particle size of 0.01 μm or more and less than 1 μm.

The water-based resin constituting the resin layer has a mixing weight ratio of the water-based resin having the particle size of 1 μm or more and less than 10 μm and the water-based resin having the particle size of 0.01 μm or more and less than 1 μm, and the particle size of 1 μm. Water-based resin 1 having a size of 10 μm or more
The particle size is 0.01 μm or more and 1 μm with respect to 00 parts by weight.
Less than 5 to 1900 parts by weight of the aqueous resin.

The silica constituting the resin layer is preferably an aqueous silica sol having an average particle size of 0.005 to 2 μm.

According to another aspect of the present invention, it is preferable to use water-dispersed fumed silica as the silica constituting the resin layer.

Further, silica in the resin layer,
The dry weight ratio of the organic resin composed of the aqueous resin having a particle size of 1 μm or more and less than 10 μm and the aqueous resin having a particle size of 0.01 μm or more and less than 1 μm is 100% or more.
The amount of silica is preferably 10 to 100 parts by weight with respect to parts by weight.

[0014]

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 dip plating method, a vapor phase plating method, or the like.

Chromate treatment is performed on the plated zinc or zinc alloy-plated steel sheet to improve the adhesion to the organic polymer resin layer described later and to impart high corrosion resistance. Chromate adhesion amount is 5 in terms of Cr
To 500 mg / m ² , preferably 10 to 150 mg / m ² . 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 the amount of deposited Cr 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 electrodeposition coatability are impaired, which is not preferable.

Such chromate treatment may be carried out by any of a coating type chromate method using a roll coater, an electrolytic type chromate method and a reactive type chromate method. The Cr ⁶⁺ ratio in the chromate is preferably 70% or less, more preferably 50% or less with respect to the total Cr amount. If the Cr ⁶⁺ content exceeds 70%, the chromium elution resistance during alkaline degreasing deteriorates, which is not preferable. Also, during chromating,
Silica may be added in order to obtain high corrosion resistance.

On the upper layer of such a chromate film, there is an organic composite film formed by mixing water-dispersed silica, an aqueous resin having a particle size of 1 μm or more and less than 10 μm, and an aqueous resin having a particle size of 0.01 μm or more and less than 1 μm. Is given. The particle size is 1 μm
The particle size of the water-based resin having a particle size of 10 μm or more is 1 μm
It is preferable that it is 3 μm or less and the particle size is 0.0
The particle size of the aqueous resin of 1 μm or more and less than 1 μm is
The thickness is preferably 0.05 μm or more and 0.7 μm or less.

The water-solubilized resin is roughly classified into a water-soluble resin having a hydrophilic group introduced into the resin skeleton and a water-dispersible resin, or an emulsion-type resin obtained by a forced emulsification method, depending on the method used. Resins having a particle size of 1 μm or more are emulsion type resins obtained by the forced emulsification method and often contain an emulsifier, but there are also resins having a hydrophilic group in the resin skeleton and not containing an emulsifier. The water-dispersible resin is a resin having a particle size of 0.01 μm or more and less than 1 μm, and is one in which a hydrophilic group is introduced into a resin skeleton and dispersed in water. This may also contain an emulsifier as a dispersion aid. In the present invention, attention is paid to the particle size of the resin, not to the method of making it aqueous. The water-soluble resin has a smaller particle size.

As a result of a detailed study on the water-based resin used in the present invention, an organic composite-coated steel sheet having excellent performance can be obtained by combining two kinds of resins having different particle sizes. Here, the particle size is 1 μm or more 1
A resin having a particle size of less than 0 μm is necessary mainly for obtaining high corrosion resistance, and a resin having a particle size of 0.01 μm or more and less than 1 μm cannot be added only by a resin layer consisting of a resin having a large particle size. This is to improve elution, corrosion resistance after processing, and adhesion.

The above-mentioned two kinds of resins having different particle diameters are added with 5 to 1 resin having a particle diameter of 0.01 μm or more and less than 1 μm with respect to 100 parts by weight of the resin having a particle diameter of 1 μm or more and less than 10 μm.
The mixture is used in the range of 900 parts by weight. The particle size is 1
The resin having a particle size of 0.01 μm or more and less than 1 μm is added to 25 to 40 parts by weight of the resin having a particle diameter of 0.01 μm or more and less than 10 μm.
The mixing ratio is preferably 0 part by weight. Particle size is 1 μm
When the amount of the resin having a particle size of 0.01 μm or more and less than 1 μm is less than 5 parts by weight with respect to 100 parts by weight of the resin having a particle size of 10 μm or more and less than 1 μm, the effect on chromium elution resistance, corrosion resistance after processing, and adhesion is small, and 1900 parts by weight is used. This is because if it exceeds, the resin layer is formed only with the resin component having a relatively small molecular weight, and the corrosion resistance is poor.

It is important for the resin according to the present invention to combine two kinds of resins having different particle diameters. If the resin is made water-based by using an emulsifier or by introducing a hydrophilic group, the kind of resin is There is no particular limitation. For example, a resin in which an acrylic resin, an epoxy resin, a urethane resin, an alkyd resin, a polyester resin, or the like is used alone or a resin skeleton is partially modified by a combination of these resins (for example, urethane-modified epoxy resin, epoxy-modified urethane resin, acrylic-modified resin). Epoxy resin etc.) can be preferably used.

Regarding silica in the organic composite coating layer of the present invention, ensuring 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 high corrosion resistance. It is important to ensure. 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 so that the average size is 0.005 to 2.
Aqueous silica sol having a particle size of μm or fumed silica dispersed in water with an appropriate dispersant can be preferably used.

The average particle size of the aqueous silica sol is 0.005
It is preferably in the range of ˜2 μm. Average particle size is 0.
If it is less than 005 μm, silica is evenly dispersed in the resin layer, and the spot weldability deteriorates. Further, when the average particle diameter exceeds 2 μm, a considerable number of silica aggregates bare to the outside of the resin layer, 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 silica shape may be a uniform particle shape or a shape in which primary particles are aggregated in the above-mentioned average particle size range. For example, silica aggregated in a chain shape or a plane shape can be preferably used.

When the hydrophobic fumed silica (1) is also dispersed in water, silanol groups are present on the silica surface.
Therefore, it becomes possible to stably hold the corrosion product, which is remarkably exhibited in combination with the water-based resin, and the corrosion resistance after processing becomes excellent.

The dry weight ratio of resin to silica is 100% resin.
The amount of silica is preferably 10 to 100 parts by weight, more preferably 10 to 70 parts by weight, based on parts by weight. When the amount of silica is less than 10 parts by weight, the ability to stably hold the zinc-based corrosion product formed in the coating when exposed to a corrosive environment is insufficient, and high corrosion resistance cannot be obtained. Further, if the amount of silica exceeds 100 parts by weight, compatibility with the resin composition will not be obtained and it will be difficult to apply it as a paint on a steel sheet.

As a method for applying an aqueous coating material prepared by mixing an aqueous resin and water-dispersed silica on a chromate film, methods such as a roll coater method and an air knife method which are widely used in industry can be used. .

The coating amount of the organic composite coating layer in the present invention is 0.1 to ³ g / m ² , preferably 0.1 to 3 in dry weight.
Limited to 1.5 g / m ² . This is because if it is less than 0.1 g / m ² , corrosion resistance is poor, and if it exceeds 3 g / m ² , coating 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. Also,
In the resin layer containing the aqueous resin in the present invention, a cross-linking agent may be blended according to the baking conditions during production. Further, the coating with the resin layer may be processed on both sides or one side.

[0029]

EXAMPLES Next, the effects of the present invention will be specifically described based on examples. (Examples 1 to 8 and Comparative Examples 1 to 3) Various double-sided zinc-based plated steel sheets (plate thickness 0.80 mm) were degreased and then coated with various amounts of coating type chromate using a roll coater, and the maximum temperature reached 130 ° C. Burned in. Next, a coating material prepared by mixing aqueous resins having different types and particle diameters and various silicas having different average particle diameters was applied by a roll coater.

The aqueous resins having different particle sizes used in Table 1 are as follows. The particle size was measured by the centrifugal sedimentation method. L resin: Epoxy-modified acrylic resin having a particle size of 1.5 to 2 μm (modification rate 30%, manufactured by Asahi Denka Co., Ltd.) Epoxy-modified urethane resin having a particle size of 1.5 to 2 μm (modification rate 20%, Asahi Denka Kogyo) A urethane resin with a particle size of 1.5 to 4 μm (Asahi Denka Kogyo Co., Ltd.)
S resin: Epoxy resin having a particle size of 0.02 to 0.2 μm (manufactured by Asahi Denka Co., Ltd.) Urethane resin having a particle size of 0.05 to 0.1 μm (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) Particle size 0.1-0.5 μm acrylic resin (manufactured by Nissan Chemical Industries, Ltd.)

Then, after baking at the highest temperature of 160 ° C., it was immediately water-cooled and dried. The silica in the resin used is as follows. A: Water-dispersed uniform granular silica sol (Nissan Chemical Co., Ltd.)
B: Water-dispersed chain silica sol (manufactured by Nissan Chemical Industries, Ltd.) C: Water-dispersed hydrophobic fumed silica (specific surface area: 95 m ² / g, manufactured by Nippon Aerosil Co., Ltd.) These silicas are centrifugally precipitated. The particle size was measured using the method.

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 occurred ○: Red rust occurrence area ratio less than 10% △: Red rust occurrence area ratio 10% or more and less than 20% ×: Red rust occurrence area ratio 20% or more

In order to evaluate the corrosion resistance after processing, a cylindrical drawing test (drawing ratio 2.0, wrinkle holding 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) Two hours was used as a combined cycle corrosion test, and the occurrence of red rust on the side wall of the test piece was observed after 100 cycles. ◎: No red rust occurred ○: Red rust occurrence area ratio less than 10% △: Red rust occurrence area ratio 10% or more and less than 20% ×: Red rust occurrence area ratio 20% or more

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

In order to evaluate the water-resistant secondary adhesion, 20 μm
After applying a m-thick electrodeposition coating film, a top coat paint (Luga Bake White, manufactured by Kansai Paint Co., Ltd.) is applied at a thickness of 35 μm, and after drying, the mixture is placed in warm water (pure water) at 40 ° C. for 10 minutes.
Soak for a day, then cut 100 squares of 2 mm square,
The coating film residual rate after tape peeling was measured. The evaluation criteria are shown below. ○: 100% △: 90% or more and less than 100% ×: less than 90%

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 or more and less than 3000 points △: 1000 or more and less than 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.

[0038]

[Table 1]

[0039]

[Table 2]

[0040]

As described above, the organic composite coated steel sheet of the present invention has excellent flat plate corrosion resistance, post-processing corrosion resistance, chromium elution resistance, water secondary adhesion and spot weldability, Since it can solve problems with 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.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI C08K 3/36 C08K 3/36 C23C 22/24 C23C 22/24 28/00 28/00 C (56) Reference JP-A-63 -107781 (JP, A) JP 5-51768 (JP, A) JP 6-234187 (JP, A) JP 5-138804 (JP, A) JP 5-147155 (JP, A) ) JP-A-62-216671 (JP, A) JP-A-4-62150 (JP, A) JP-A-52-146440 (JP, A) JP-A-2-283749 (JP, A) JP-A-2- 194946 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) B05D 1/00-7/26 B32B 1/00-35/00 C08K 3/00-3/40 C23C 22/00 -30/00

Claims (5)

(57) [Claims] 1. A zinc or zinc-based alloy-plated steel sheet has a chromate film with an adhesion amount of 5 to 500 mg / m ^{2 in} terms of Cr, and the adhesion amount on the upper layer of the chromate film is a dry weight of 0.1. An organic composite coating having a resin layer mainly composed of water-dispersed silica of 1 to 3 g / m ² and an aqueous resin having a particle size of 1 μm to less than 10 μm and an aqueous resin having a particle size of 0.01 μm to less than 1 μm steel sheet. 2. A mixing weight ratio of an aqueous resin having a particle size of 1 μm or more and less than 10 μm and an aqueous resin having a particle size of 0.01 μm or more and less than 1 μm as an aqueous resin forming the resin layer Water-based resin 1 of 1 μm or more and less than 10 μm
The particle size is 0.01 μm or more and 1 μm with respect to 00 parts by weight.
The organic composite-coated steel sheet according to claim 1, wherein the water-based resin content is less than 5 to 1900 parts by weight. 3. The organic composite-coated steel sheet according to claim 1, wherein an aqueous silica sol having an average particle size of 0.005 to 2 μm is used as silica constituting the resin layer. 4. The organic composite-coated steel sheet according to claim 1, wherein water-dispersed fumed silica is used as silica constituting the resin layer. 5. A dry weight ratio of the organic resin comprising silica in the resin layer, an aqueous resin having a particle size of 1 μm or more and less than 10 μm, and an aqueous resin having a particle size of 0.01 μm or more and less than 1 μm, The organic composite-coated steel sheet according to claim 1, wherein the amount of silica is 10 to 100 parts by weight with respect to 100 parts by weight of the organic resin.