JP2793945B2 - Organic composite coated steel sheet with excellent corrosion resistance after processing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic composite coated steel sheet which is excellent in corrosion resistance after working and is mainly used as a steel sheet for an automobile body.

[0002]

2. Description of the Related Art In response to strong social demands for higher corrosion resistance of automobile bodies, the use of surface-treated steel sheets in which zinc or a zinc-based alloy plating is applied to the surface of a cold-rolled steel sheet has been increasing in recent years. .

[0003] Examples of these surface-treated steel sheets include hot-dip galvanized steel sheets, galvannealed steel sheets, electro-galvanized steel sheets, and electro-zinc alloy-coated steel sheets. However, a higher degree of corrosion resistance has been required in a bag structure portion or a bent portion (hemming portion) of a body inner plate in which coating performed after assembling the body is not sufficiently distributed.

For example, Japanese Patent Application Laid-Open Nos. Sho 57-108292 and 58-224174 disclose a chromate and an organic polymer on a zinc- and zinc-based alloy-plated steel sheet. An organic composite coated steel sheet provided with a resin layer has been proposed. All of these are intended to exhibit high corrosion resistance by applying a coating containing a water-soluble or water-dispersible organic resin and a water-dispersible silica sol to the upper layer of a zinc-plated steel sheet subjected to chromate treatment. Had problems. (1) Since the water-soluble component remains in the coating film even after film formation, the chromium elution resistance is poor, and chromium is eluted during chemical conversion treatment, causing environmental pollution. (2) Peeling of the resin layer occurs at the time of alkali degreasing, resulting in deterioration of corrosion resistance. (3) In a corrosive environment, moisture penetrates into the resin layer, and soluble components dissolve and become highly alkaline, so that the adhesion between the resin layer and the chromate deteriorates.

In order to solve such problems, Japanese Patent Application Laid-Open No. Sho 63-22637 discloses a method of using a coating composition in which hydrophobic silica having a silica surface organically substituted and an epoxy resin are mixed in an organic solvent. 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. It has been pointed out that there is a problem that damage is caused to the steel and the corrosion resistance of this part is deteriorated.

In order to solve the problem of poor corrosion resistance after such processing, a method of providing a coating layer containing a urethane resin and silicon dioxide as main components is disclosed in Japanese Patent Application Laid-Open No. 62-2892.
No. 74 is proposed. In this case, although a slight improvement effect can be obtained on the workability, there is a problem that the corrosion resistance is also deteriorated when more severe processing is performed.
In particular, when an aqueous resin is used, there is a problem that depending on the combination with the water-dispersed silica, compatibility cannot be obtained and a coating cannot be formed.

On the other hand, as a fingerprint-resistant steel sheet for home electric appliances, a chromate film is formed on a zinc-based alloy electroplated steel sheet, and an aqueous liquid comprising a carboxylated polyethylene resin dispersion and colloidal silica is applied and dried to form a film. Japanese Patent Publication No. 61-36587 discloses a method of performing
No. 44387. In this case, it is evaluated by a salt spray test, and since it is significantly different from the environment when used as a steel sheet for automobiles, in the corrosion resistance test of the present invention, there is a problem that these methods are insufficient in corrosion resistance. . Similarly, spot weldability does not give excellent results according to the test of the present invention.

[0008] In addition, organic solvents are mainly used in paints currently used, and aromatic hydrocarbon solvents are a source of air pollution, and the drastic reduction of these solvents has become a global problem.

[0009]

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

[0010]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the problems in the prior art, and has been made as a result of a detailed study on aqueous paints using various combinations of water-dispersible silica and an aqueous organic resin. The combination of an anionic or nonionic aqueous urethane resin and water-dispersible silica can solve the above-mentioned problems (1) to (3), provide compatibility as a paint, and have excellent corrosion resistance after processing. This has led to the present invention. According to the present invention, an organic composite coated steel sheet having excellent corrosion resistance after processing can be obtained 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 a zinc or zinc-based alloy-plated steel sheet is 70% of the total amount of Cr.
% Or less, and has a chromate coating with an adhesion amount of 5 to 500 mg / m ^{2 in} terms of Cr, and the upper layer of the chromate coating has an adhesion amount of 0.1 to 3 g / m ² on a dry weight basis. Dispersed silica and one of anionic urethane aqueous resin and nonionic urethane aqueous resin are blended, and dried
The present invention provides an organic composite coated steel sheet having a resin layer of 10 to 60 parts by weight of silica with respect to 100 parts by weight of fat .

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

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

In the case of an anionic or nonionic aqueous urethane resin, it is preferable to use a resin having an elongation of 50 to 1000% and a tensile strength of 200 kgf / cm ² or more.

[0015]

The present invention will be described below in more detail. As the material for the steel sheet of the present invention, a 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, Zn-Fe
Binary alloy plating such as alloy plating, Zn-Cr alloy plating, Zn-Ni-Cr alloy plating, Zn-Co-Cr
Includes ternary alloy plating such as alloy plating.
n-SiO ₂ plating encompasses broadly the composite dispersion plating, such as _{Zn-Co-Cr-Al 2} O 3 plating. These platings are applied by an electric method, a hot-dip plating method, or a vapor phase plating method.

On these zinc or zinc alloy-plated steel sheets, the adhesion to an organic polymer resin layer described later is improved,
In addition, chromate treatment is performed to impart high corrosion resistance.
The amount of chromate attached is 5 to 500 mg / Cr equivalent.
m ² , preferably in the range of 10 to 150 mg / m ² . C
If the r adhesion amount is less than 5 mg / m ^2, it is not preferable because not only corrosion resistance is insufficient, but also adhesion to the resin layer is poor. If it exceeds 500 mg / m ² , there is no further effect of improving the corrosion resistance, the resistance of the insulating film is increased, and the spot welding property and the electrodeposition coating property are impaired.

Such a chromate treatment may be performed by any method such as a coating type chromate method using a roll coater or the like, an electrolytic type chromate method, and a reactive type chromate method. The Cr ⁶⁺ ratio in the chromate is preferably 70% or less based on the total Cr content. If the amount of Cr ⁶⁺ exceeds 70%, the elution resistance of chromium during alkaline degreasing deteriorates, which is not preferable.

The upper layer of such a chromate film is provided with an organic composite film comprising a water-dispersed silica and one of anionic or nonionic aqueous urethane resins.

As a method for making the resin aqueous, water-soluble and water-dispersible resins in which a hydrophilic group is introduced into the resin skeleton, or emulsion resins by a forced emulsification method can be used. The emulsifier remains in the emulsion type resin by the forced emulsification method, while
The water-soluble resin is more preferably a water-dispersed resin because of a concern about insufficient corrosion resistance due to its low molecular weight. Further, a water-dispersed resin containing an emulsifier can also be suitably used.

The result of detailed studies with respect to the aqueous resin used in the present invention, anionic and nonionic aqueous U
It has been found that a urethane resin can be suitably used.

[0021] The hydrophilic group of anionic in the resin skeleton and anionic aqueous urethane resin, the nonionic aqueous urethane <br/> resin with an aqueous urethane tree <br/> fat obtained by introducing a hydrophilic group nonionic is there. The anionic hydrophilic group is a carboxyl group,
Examples of the nonionic hydrophilic group such as a sulfonic acid group or a phosphate group include polyethylene glycol, a hydroxyl group, an amide group, and a methylol group. In the present invention urethane these anionic hydrophilic group or a nonionic hydrophilic group
The resin introduced into the tan resin. The reason for using an anionic aqueous resin and a nonionic aqueous resin is that the aqueous silica sol has a negative charge and is dispersed in the coating. This makes it difficult to apply a paint on the steel sheet.

The urethane resin is not particularly limited as long as it is an aqueous urethane resin in which anionic or nonionic hydrophilic groups are introduced. However, carboxylated polyethylene-based resins are inferior in corrosion resistance and spot weldability in tests in the present invention, and are excluded.

The urethane resin is a polymer compound having a large number of urethane bonds in the molecule, and a resin in which a part of the resin skeleton is modified with acryl, epoxy, alkyd, ester, or the like can be suitably used.

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

After the processing, a test piece subjected to a cylindrical drawing test (drawing ratio 2.0, wrinkle holding pressure 1000 kg) to evaluate corrosion resistance was sprayed with a 5% NaCl aqueous solution (35 ° C.) for 4 hours, and dried (60 ° C.) 2 Time, humid environment (RH 95%) (50 ° C)
The test was subjected to a combined cycle corrosion test in which two cycles were defined as one cycle, and the red rust generation area ratio of the test piece side wall at 50 cycles was measured.

FIG. 1 shows that the anionic aqueous urethane resin and the water-dispersed silica were mixed with silica 10 to 100 parts by weight based on the weight of the resin.
It can be seen that the corrosion resistance after processing is good with a mixing ratio of 60 parts by weight.

In the case of an anionic or nonionic aqueous urethane resin, the balance between resin elongation and tensile strength is important. That is, the range is 50 to 1000 elongation.
% And the tensile strength is 200 kgf / cm ² or more. FIG. 2 shows the results of a post-work corrosion resistance test performed by changing the elongation and tensile strength of the resin under the following conditions. The evaluation method is as described in Examples. Plating: Zn-12.5% Ni (electric), basis weight = 20 (g / m ² ) Chromate: Cr ⁶⁺ / total Cr ratio = 65 (%), adhesion amount = 50 mg / m ² Resin layer: anionic water-dispersed aqueous urethane resin other water dispersible homogeneous particulate silica sol (manufactured by Nissan Chemical Industries, Ltd. ST-20) (average particle size = 0.01 [mu] m) other resin: silica = 80: 20, deposition amount = 0 .9 (g / m ² )

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

As for the silica in the organic composite coating of the present invention, securing an appropriate amount of silanol groups on the silica surface stably holds zinc-based corrosion products in a corrosive environment and ensures high corrosion resistance. Important for. Water-dispersed silica is very suitable because a sufficient silanol group can be secured.

Specifically, the charge state of the surface of the water-dispersed silica sol is controlled by adjusting the amount of alkali metal ions or polyvalent metal ions to an average of 0.005 to 2 μm, or water with an appropriate dispersant. Dispersed hydrophobic fumed silica can be suitably used.

Preferably, the average particle size is in the range of 0.005 to 2 μm. 0.005 μm average agglomerated particle size
If it is less than m, silica was uniformly dispersed in the resin layer, and spot weldability deteriorated. If the average agglomerated particle size exceeds 2 μm, a considerable number of silica agglomerates are exposed to the outside of the resin layer, and the electrical resistance between the electrode and the steel sheet is significantly increased during spot welding, and sparks are generated during welding. This promotes damage to the steel, deteriorating the spot weldability. The silica shape may be a uniform granular shape or a shape in which primary particles are aggregated in the above average particle size range.

By dispersing the hydrophobic fumed silica in water as well, silanol groups are present on the silica surface, so that it is possible to stably retain corrosion products, which is remarkably exhibited in combination with an aqueous resin. And
It has excellent corrosion resistance after processing.

The dry weight ratio of the resin and silica in the resin layer containing the anionic aqueous urethane resin or the nonionic aqueous urethane resin is preferably from 10 to 100 parts by weight of silica to 100 parts by weight of the resin. preferable. When the amount of silica is less than 10 parts by weight, a high corrosion resistance cannot be obtained due to lack of ability to stably retain a zinc-based corrosion product formed in the film when exposed to a corrosive environment. When the amount of silica exceeds 100 parts by weight,
This is because compatibility with the resin composition cannot be obtained, and it becomes difficult to apply a coating composition on a steel sheet.

FIG. 3 shows the results of a flat plate bare corrosion resistance test performed under the following conditions while changing the mixing ratio of the resin and silica. The evaluation method is as described in Examples. Plating: Zn-13.2% Ni (electricity), basis weight = 20 (g / m ² ) Chromate: Cr ⁶⁺ / total Cr ratio = 60 (%), adhesion amount = 50 mg / m ² Resin layer: anionic Acrylic (anionic acrylic resin obtained by mixing poly (methyl methacrylate) and polyacrylic acid) and water-dispersed fumed silica (AEROSIL 136 manufactured by Nippon Aerosil Co., Ltd.) (particle size = 15 nm), adhesion amount = 0.8 (g / m ² ) From FIG. 3, silica 10 to 10 was added to 100 parts by weight of resin.
The flat plate corrosion resistance is improved with a mixing ratio of 0 parts by weight.

Further, in the water-based paint of the present invention, a crosslinking agent may be blended according to the baking conditions of the production.

As a method for applying an aqueous coating composition containing an aqueous resin and water-dispersed silica on a chromate film, a method such as a roll coater method and an air knife method which are widely used industrially can be used. .

The coating amount of the organic composite coating layer in the present invention is limited to 0.1 to 3 g / m ² in terms of dry weight. 0.1g /
If it is less than m ² , the corrosion resistance is poor, and if it exceeds 3 g / m ² , the coating resistance increases and the spot weldability and the electrodeposition coating property deteriorate. When the organic composite coated steel sheet of the present invention is exposed to a corrosive environment while being bare, it is preferable to secure a coating amount of 0.3 g / m ² or more from the viewpoint of corrosion resistance, but furthermore, such as electrodeposition coating on the upper layer It was confirmed that sufficient corrosion resistance could be obtained if 0.1 g / m ² or more of the organic resin layer was present.

The organic resin layer may be a double-sided or single-sided coating depending on its use. In the case of coating on one side only, the non-coated side is zinc-based plating, a surface obtained by chromate-treating an upper layer of zinc-based plating, or a cold-rolled surface.

[0039]

Next, the effects of the present invention will be specifically described based on examples. (Example 1 and Comparative Examples 1 to 3) After degreasing various types of double-sided zinc-coated steel sheets (0.80 mm in thickness), using a roll coater, various types of Cr ⁶⁺ / total Cr ratios and various types of adhesion type coating chromates were applied. Alms, maximum temperature 13
Bake at 0 ° C. Next, paints prepared by mixing various aqueous resins with various silicas having different average particle diameters were applied by a roll coater. After that, the maximum temperature reached 160
After baking at ℃, it was immediately cooled with water and dried. The silica in the resin is as follows. A: Water-dispersed uniform granular silica sol (manufactured by Nissan Chemical Industries, Ltd.) B: Water-dispersed aggregated silica sol (manufactured by Nissan Chemical Industries, Ltd.) C: Water-dispersed chain-shaped silica sol (manufactured by Nissan Chemical Industries, Ltd.) D: Water-dispersed hydrophobic fumed silica (specific surface area: 200 m ² / g) (manufactured by Nippon Aerosil Co., Ltd.)

The following tests were performed to evaluate the performance of these organic composite coated steel sheet products. 5% NaCl aqueous solution spray (35 ° C.) for 4 hours to evaluate plate corrosion resistance
Drying (60 ° C) for 2 hours, humid environment (RH 95%) (50
(° C.) 2 hours was used as one cycle for a combined cycle corrosion test, and the state of red rust generation of the test specimen at 200 cycles was observed. The evaluation criteria for flat plate corrosion resistance are shown below. ：: No red rust generated ○: Red rust generated area rate less than 10% △: Red rust generated area rate 10 to 20% ×: Red rust generated area rate 20% or more

A test piece subjected to a cylindrical drawing test (drawing ratio 2.0, wrinkle holding pressure 1000 kg) to evaluate corrosion resistance after processing was sprayed with a 5% aqueous NaCl solution (35 ° C.) for 4 hours.
Drying (60 ° C) for 2 hours, humid environment (RH 95%) (50
(° C.) 2 hours was taken as one cycle and subjected to a combined cycle corrosion test, and the occurrence of red rust on the side wall of the test piece at 50 cycles was observed. ：: No red rust generated ○: Red rust generated area rate less than 10% △: Red rust generated area rate 10 to 20% ×: Red rust generated area rate 20% or more

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

To evaluate the spot weldability, the tip 6
Using a welding tip made of Al ₂ O ₃ dispersed copper alloy of mmφ,
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 became smaller than the reference diameter was measured. The evaluation criteria are shown below. ◎: 3000 points or more ○: 2000 to less than 3000 points Δ: 1000 to less than 2000 points ×: less than 1000 points

Table 1 summarizes the conditions of the chromate layer and the resin layer, the distribution of silica in the organic resin layer of the product, and the test results. (Examples 2 to 10 and Comparative Examples 4 to 8) Coating types of various Cr ⁶⁺ / total Cr ratios and various adhesion amounts using a roll coater after degreasing various double-sided zinc-coated steel sheets (plate thickness 0.75 mm). Chromate, maximum temperature 13
Bake at 0 ° C. Next, a paint prepared by mixing an aqueous urethane resin having different elongation and strength with an aqueous method and silica was applied by a roll coater. Then, after baking at a maximum temperature of 160 ° C., it was immediately cooled with water and dried. Silica in the resin is the same as in Example 1 and Comparative Examples 1 to 3. The performance evaluation of these organic composite coated steel sheet products was performed in the same manner as in Table 1. Table 2 summarizes the conditions of the chromate layer and the resin layer, the distribution of silica in the organic resin layer of the product, and the test results.

[0045]

[Table 1]

[0046]

[0047]

[Table 2]

[0048]

[Table 3]

[0049]

[Table 4]

[0050]

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

[Brief description of the drawings]

FIG. 1 is a view showing the effect of the mixing ratio of a resin and silica on corrosion resistance after processing.

FIG. 2 is a view showing the effect on corrosion resistance after processing when elongation and tensile strength of an anionic aqueous urethane resin are changed.

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

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Kazuo Mochizuki 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Engineering Co., Ltd. (72) Inventor Nobuyuki Morito Kawasaki, Chuo-ku, Chiba-shi No. 1 town Kawasaki Steel Corp. Technical Research Division (56) References JP-A-2-263633 (JP, A) JP-A-4-74872 (JP, A) JP-A-4-71839 (JP, A) ( 58) Field surveyed (Int.Cl. ⁶ , DB name) B32B 15/08 B05D 7/14 B05D 7/24 302

Claims (5)

(57) [Claims] 1. The method according to claim 1, wherein the amount of Cr ⁶⁺ on the surface of the zinc or zinc-based alloy plated steel sheet is 70% or less of the total amount of Cr, and
It has a chromate film of 5 to 500 mg / m ^{2 in} terms of r, and the amount of adhesion on the upper layer of the chromate film is 0.
1 to 3 g / m ² , mainly containing water-dispersed silica and an anionic aqueous urethane resin, and drying the resin 100 weight
An organic composite coated steel sheet having excellent corrosion resistance after processing and having a resin layer of 10 to 60 parts by weight of silica based on parts by weight . 2. The method according to claim 1, wherein the amount of Cr ⁶⁺ is less than 70% of the total amount of Cr and the amount of C
It has a chromate film of 5 to 500 mg / m ^{2 in} terms of r, and the amount of adhesion on the upper layer of the chromate film is 0.
1 to 3 g / m ² , mainly containing water-dispersed silica and nonionic aqueous urethane resin, and dried
An organic composite coated steel sheet having excellent corrosion resistance after processing and having a resin layer of 10 to 60 parts by weight of silica based on parts by weight . Wherein as the silica constituting the resin layer, excellent organic composite coated steel sheet after processing corrosion resistance according to claim 1 or 2 average particle size an aqueous silica sol is 0.005 ~2μm. 4. As the silica constituting the resin layer, excellent organic composite coated steel sheet after processing corrosion resistance according to claim 1 or 2 using a water-dispersed hydrophobic fumed silica. 5. An anion or nonionic compound constituting said resin layer.
Elongation of 50 to 1000 as on- based aqueous urethane resin
The organic composite coated steel sheet having excellent corrosion resistance after processing according to any one of claims 1 to 4 , wherein an anionic aqueous urethane resin having a tensile strength of 200 kgf / cm ² or more is used.