JPH08243488A - Organic composite steel panel excellent in chemical forming treatment resistance - Google Patents

Abstract

PURPOSE: To keep press moldability and corrosion resistance and to enhance chemical forming treatment resistance, in a steel panel wherein a chromate film, a solvent type org. film and a colloidal silica-containing aq. org. film are successively applied to a zinc plated steel panel, by specifying the thicknesses of the respective films and the thickness and composition of the org. film. CONSTITUTION: A zinc plating film 2 is formed on a steel plate 1 and a chromate film 3 with a thickness of 10-150mg/m<2> is formed thereon and a solvent type org. film 4 with a thickness of 0.1-1.5μm is further formed thereon. Subsequently, an aq. org. film 5 is formed thereon in a thickness of 0.5-1.9μm. The aq. org. film 5 contains 15-40% of colloidal silica with a particle size of 1-10μm and formed from an aq. coating material compsn. wherein olefin and acrylic acid are copolymerized within the range of 70-95% of an olefin copolymer. The sum thickness of the solvent type org. film 4 and the aq. org. film 5 is set to 2.0μm or less.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an organic composite plated steel sheet having a chromate film and a water-based organic film, more specifically, press workability and corrosion resistance are maintained, and at the same time, elution of chromium during chemical conversion treatment is suppressed ( Hereinafter, it is referred to as chemical conversion treatment resistance) organic composite steel sheet.

[0002]

2. Description of the Related Art In recent years, the market needs for steel sheets having excellent corrosion resistance as steel sheets for automobile bodies have increased more and more, and the research and development of new products of surface-treated steel sheets have been actively conducted in recent years. One of such surface-treated steel sheets with high corrosion resistance
One example is a galvanized steel sheet.However, in this type of steel sheet, it is necessary to increase the amount of zinc adhering in order to enhance corrosion resistance, and as a result, there is a problem that press formability and spot weldability deteriorate. is there. On the other hand, as a corrosion-resistant steel plate with a small amount of coating, zinc, Ni, C
O / Cr, Fe, Mn and other plated steel sheets and multilayer plated steel sheets have been developed. However, these steel sheets also do not have sufficient corrosion resistance with respect to the hem portion and the bag structure portion that are exposed to extremely severe corrosive conditions in automobile bodies.

Under such circumstances, as a steel plate having a high degree of corrosion resistance, Japanese Patent Publication Nos. 45-24230 and 47 are available.
A rust preventive steel sheet coated with a zinc-rich coating as disclosed in Japanese Patent No. 6882 has been proposed, and a typical one is known by the name of zinc metal. However, even with this rustproof steel plate, the film may peel off in the processed portion such as press formability. Therefore, it is still hard to say that it is a highly corrosion-resistant rustproof steel sheet that can be used as a material for automobile bodies. Therefore, an organic composite steel sheet in which a zinc-based plated steel sheet is used as a raw material and two layers of a chromate layer and a water-based organic coating are formed on the upper layer and a method for producing the same are disclosed in JP-B-61-3.
It is proposed in Japanese Patent No. 6587, Japanese Patent Laid-Open No. 6-234187, and the like.

[0004]

However, although the organic composite steel sheet having this type of water-based organic coating has excellent workability and corrosion resistance as compared with conventional surface-treated steel sheets, when it is used for automobiles, Chromium elutes into the chemical conversion treatment bath during chemical conversion treatment and the bath is contaminated, resulting in poor chemical conversion treatment.
Problems such as bath change and chrome treatment occur. Therefore, it is necessary to suppress the elution of chromium and improve the chemical conversion treatment resistance.
It is an object of the present invention to provide an organic composite steel sheet having excellent chemical conversion treatment resistance while suppressing elution of chromium during chemical conversion treatment while maintaining performance such as press formability and corrosion resistance.

[0005]

Means for Solving the Problems The inventors of the present invention have made extensive studies to solve the above-mentioned problems, and as a result, by having a solvent-based organic film between the chromate film layer and the water-based organic film layer, It was found that the elution of chromium from the chromate to the organic film can be suppressed and the elution of chromium during the chemical conversion treatment can be eliminated. The gist of the present invention is to have a chromate film with a film thickness of 10 to 150 mg / m ^{2 on} one or both sides of a zinc-based plated steel sheet, and a solvent-based organic film with a film thickness of 0.1 to 1.5 μm on it. Furthermore, on top of that, a particle size of 1-10 mμ
Of colloidal silica of 15 to 40% and an olefin copolymerization ratio in the range of 70 to 95%.
An organic composite steel sheet having a water-based organic coating of 1.9 μm and having a total organic coating thickness of 2.0 μm or less and having excellent chemical conversion treatment resistance.

[0006]

The present invention will be described below in more detail. FIG. 1 shows a coating structure when an organic coating is applied on both sides as an example of the steel sheet of the present invention. Examples of the zinc-based plated steel sheet according to the present invention include Zn, Zn-Ni, Zn-Ni-Co, and Zn-F.
e, Zn-Cr, Zn-Cr-Ni, and other electrogalvanized steel sheets, hot-dip galvanized zinc-iron sheets, galvannealed steel sheets, Zn-Al alloy-plated steel sheets, and the like.
The zinc-based plating film 2 applied on the steel plate 1 is usually 5 to 5.
100 g / m ² is deposited. As the zinc-based plating applied to the present invention, electroplated Zn-Ni or Zn-Fe based SiO ₂ , Al ₂ O ₃ , and Ti are used.
O ₂ and BaCrO metal oxides such as ₄ may be used dispersoid plated steel sheet.

In the present invention, the chromate film 3 is first applied on the above-mentioned various zinc-plated steel sheets. The chromate film 3 of the present invention may be any known coating type chromate, and is not particularly limited, but if the water-soluble content of the chromate film exceeds 5%, the chromate film swells, Since the adhesion to the upper organic film is reduced, the water-soluble content of the chromate film is preferably 3% or less.

When the total amount of chromium is less than 10 mg / m ² , the coating amount of the zinc-based plated steel sheet is incomplete and the corrosion resistance is not exhibited, which is not preferable. On the other hand, if the total amount of chromium exceeds 150 mg / m ² , the chromate coating undergoes cohesive failure due to press working or the like, and the adhesion of the upper organic coating is significantly reduced. Also,
It is not preferable because it lowers the continuous spotting property during spot welding. From the above, the preferable range of the adhesion amount of the chromate film is 10 to 150 mg / m ² as the total chromium amount. In the present invention, 1 to 1 of melamine cyanurate is added to the chromate film for the purpose of improving electrodeposition coatability.
5% by weight may be contained.

Next, a solvent-based organic film 4 is applied on the chromate film 3. In the present invention, as the coating composition for the solvent-based organic coating 4, rust preventive pigments such as BaCrO ₄ and color pigments such as Fe ₂ O ₃ are added to epoxy resin, polyester resin, styrene resin and the like, which are used alone or modified. A known material containing an organic coloring dye or a pigment such as SiO ₂ as necessary is applied. The thickness of the solvent-based organic coating 4 described above is preferably 0.1 to 1.5 μm. If it is less than 0.1 μm, it is impossible to suppress the elution of chromium during the chemical conversion treatment, and if it exceeds 1.5 μm, the weldability and the like are hindered due to the relationship of the total film thickness with the upper aqueous organic film, which is preferable. Absent.

Next, a water-based organic film 5 is applied on the solvent-based organic film 4. As the water-based organic film 5, a coating composition comprising a copolymer of olefin and acrylic acid containing 1 to 10 μm of colloidal silica of 15 to 40% and having an olefin copolymerization ratio of 70 to 95% is used. The film thickness of the film is preferably 0.5 to 1.9 μm. Regarding the above-mentioned copolymerization ratio of olefin and acrylic acid, the corrosion resistance is improved as the copolymerization ratio of olefin is increased, and when it is 70% or more, extremely excellent corrosion resistance is exhibited, but when it is 95% or more, the corrosion resistance is slightly lowered. Therefore, the copolymerization ratio of olefin is preferably 70 to 95%.

The particle size of the colloidal silica contained in the coating composition is 1 to 1
When it is 10 mμ, it shows extremely excellent corrosion resistance after processing. If the particle size of the colloidal silica exceeds 10 mμ, the corrosion resistance after processing decreases, so the particle size of the colloidal silica is 1 to 1
0 mμ is preferable. Regarding the added amount of the colloidal silica, when the added amount is 15 to 40%, excellent corrosion resistance is exhibited. If the addition amount is 15% or less, the corrosion resistance cannot be sufficiently exhibited, and if it is 40% or more, the organic coating becomes brittle and cannot withstand the processing, and the corrosion resistance decreases. Therefore, the addition amount of colloidal silica is 15 to 40%. Is preferred. The film thickness of the water-based organic film 5 of the present invention is 0.5 to 1.9.
μm is preferred. If it is less than 0.5 μm, the corrosion resistance is insufficient, and if it exceeds 1.9 μm, the weldability and the like are impaired due to the relation of the total film thickness with the lower solvent-based organic film, which is not preferable.

In the organic composite steel sheet having the above structure, the total thickness of the solvent-based organic coating 4 and the water-based organic coating 5 is 2.0 μm or less. Total film thickness is 2.0μ
If it exceeds m, the weldability will be poor. Regarding the method for producing the organic composite steel sheet of the present invention, a chromate film is formed by a known chromate treatment method, and then a solvent-based and water-based coating composition is applied by a known roll coater or other method, and a baking treatment is performed. After water cooling or air cooling,
It can be dried.

[0013]

EXAMPLES The present invention will be described in more detail below with reference to examples. First, the outline of the test process will be described. 0.8 mm thick galvanized nickel-plated steel sheet (Zinc-nickel plating amount:
20 g / m ² , Ni%: 12%, plate thickness: 0.8 mm, panel size: 200 × 300 mm) was degreased by a known degreasing method, dried, and then subjected to a known coating chromate treatment. Subsequently, a solvent-based coating composition is applied with a roll coater, baked at 150 ° C. for 20 seconds, cooled with water, and then dried.
Apply a water-based paint on it with a roll coater and
It was baked at ℃ for 15 seconds, cooled with water and dried to produce an organic composite steel sheet.

Next, in the above test process, the performance of each organic composite steel sheet under various test conditions was evaluated. Chromate film thickness: Table 1 shows the relationship between the film thickness and the corrosion resistance and press workability when the chromate film thickness is changed. At that time, the olefin copolymerization ratio was 80%, the amount of colloidal silica added was 20%, the particle size of colloidal silica was 5 to 7 μm, the thickness of the solvent-based organic coating was 0.3 μm, and the thickness of the aqueous organic coating was 1.2 μm. Is. Corrosion resistance is 5% NaC
l Aqueous solution spraying (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, and red rust of the test piece after 200 cycles Observe the occurrence situation and check the results ◎
… No red rust, ○… red rust less than 10%, △… red rust 1
0 to 20%, × ... Red rust was 20% or more. As for press workability, after cylindrical drawing (no oil coating), cellophane tape was attached to the die side surface of the processed portion, and the degree of peeling of the film was evaluated when peeling off. The results are shown by ◯ ... no peeling, Δ: slight peeling, ×: considerable peeling. As is clear from Table 1, the thickness of the chromate film is 10 to 150.
The range of mg / m ² is good in both corrosion resistance and press workability.

[0015]

[Table 1]

Film thickness of solvent-based organic film: FIG. 2 shows the relationship between the film thickness of the solvent-based organic film and the chemical conversion treatment resistance when the film thickness is changed. At that time, the thickness of the water-based organic film is 1.2 μm,
The copolymerization ratio of olefin is 80%, the addition amount of colloidal silica is 20%, and the particle size of colloidal silica is 5 to 7 μm. Evaluation of chemical conversion treatment resistance was performed by degreasing chromium elution during chemical conversion treatment with a 1 liter solution of 48 flat plates (70 × 150 mm) (FC-L4460 / manufactured by Nippon Parkerizing Co., Ltd.), washing with water, and surface tone (Percollene ZTH / After the Nihon Parkerizing) and phosphate treatment (PB3020 / Nihon Parkerizing) treatment, the chromium concentration in each solution is measured by ICP.
Analysis, and the result is ○ ... Chromium elution amount 0.1m
g / m ² or less, Δ ... Chromium elution amount of 0.1 mg / m ² or more and 4.0 mg / m ² or less, × ... Chromium elution amount of 4.0 mg
/ M ² or more. As is clear from FIG. 2, when the film thickness of the solvent-based organic film is 0.1 μm or more, the chemical conversion treatment resistance is remarkably improved.

Olefin copolymerization ratio: FIG. 3 shows the relationship with bare corrosion resistance without coating when the copolymerization ratio of olefin and acrylic acid is changed. At that time, the added amount of colloidal silica is 20%, the particle size of colloidal silica is 5 to 7 mμ,
The film thickness of the solvent-based organic film is 0.3 μm, and the film thickness of the water-based organic film is 1.2 μm. Corrosion resistance was subjected to a combined cycle corrosion test in which 5% NaCl aqueous solution was sprayed (35 ° C) for 4 hours, dried (60 ° C) for 2 hours, and wet environment (RH 95%) (50 ° C) for 2 hours. The state of occurrence of red rust on the test piece was observed, and the results are as follows: ◎ ... no red rust occurred, ○ ... red rust less than 10%, △ ... red rust 10-20%,
X: Red rust was 20% or more. As is clear from FIG. 3, in the copolymer resin of olefin and acrylic acid, when the copolymerization ratio of olefin is 70% or more, extremely excellent corrosion resistance is exhibited, while when it is 95% or more, the corrosion resistance is slightly lowered.

Particle size of colloidal silica: FIG. 4 shows the relationship between the particle size of colloidal silica and the corrosion resistance after processing when the particle size of colloidal silica is changed. At that time, the olefin copolymer ratio was 80%, the amount of colloidal silica added was 20%, the thickness of the solvent-based organic coating was 0.3 μm, and the thickness of the aqueous organic coating was 1.2 μm. After processing, the corrosion resistance was evaluated by a cylindrical drawing test (drawing ratio 2.0, wrinkle holding pressure 100
0 kg) of the test piece was sprayed with a 5% NaCl aqueous solution (3
5 ° C) 4 hours, dry (60 ° C) 2 hours, wet environment (RH
(95%) (50 ° C.) 2 hours as a combined cycle corrosion test and observed the red rust occurrence on the side wall of the test piece at 50 cycles.
○: Less than 10% of red rust occurred, Δ: 10 to 20% of red rust, ×:
The red rust was 20% or more. As is clear from the figure, when the particle size of the colloidal silica is 1 to 10 mμ, it exhibits extremely excellent corrosion resistance, and when it exceeds this value, the corrosion resistance decreases.

Addition amount of colloidal silica: FIG. 5 shows the relationship between the addition amount of colloidal silica and the corrosion resistance after processing when the addition amount of colloidal silica is changed. At that time, the copolymerization ratio of olefin is 80%, the particle size of colloidal silica is 5 to 7 μm, and the film thickness of the solvent-based organic film is 0.3 μm.
m, and the film thickness of the water-based organic film is 1.2 μm. When the amount of colloidal silica added is 15 to 40%, it exhibits extremely excellent corrosion resistance. When it exceeds 40%, the organic coating becomes brittle and it cannot withstand processing, and the corrosion resistance decreases. When it is 15% or less, the corrosion resistance cannot be fully exhibited. .

Total film thickness of organic film: FIG. 6 shows the relationship between the film thickness and the weldability when the film thickness of the solvent-based organic film and the film thickness of the water-based organic film are changed. At that time, the copolymerization ratio of olefin is 80%, the addition amount of colloidal silica is 20%, and the particle size of colloidal silica is 5 to 7 mμ.
Weldability was evaluated by the number of continuous dots until the nugget diameter reached 4 mmφ in the continuous welding test, and the results are: ⊚: 5000 or more continuous dots, ∘: 4500 to 4999 continuous dots
Points: Δ: 4000 to 4499 continuous dots; ×: 3999 or less continuous dots. If the total film thickness of the organic coating exceeds 2 μm, the weldability will deteriorate. As is clear from the above evaluation results, the organic composite steel sheet of the present invention is excellent in chemical conversion treatment resistance, corrosion resistance and weldability, and is excellent in overall performance.

[0021]

As described above, the organic composite steel sheet of the present invention has the solvent-based organic film between the chromate film and the water-based organic film, so that elution of chromium into the bath during chemical conversion treatment is suppressed. It As a result, problems such as poor chemical conversion treatment, bath replacement, and treatment of eluted chromium are eliminated. Also, by applying a coating composition consisting of a copolymer of olefin and acrylic acid as an aqueous organic film, by defining an olefin copolymerization ratio and containing an appropriate colloidal silica, good bare corrosion resistance and after processing Since the corrosion resistance is secured, it can withstand even the extremely severe corrosive conditions of the automobile body. Furthermore, by defining the total film thickness of the solvent-based organic film and the water-based organic film, excellent continuous spot performance is exhibited during welding. INDUSTRIAL APPLICABILITY As described above, the organic composite steel sheet of the present invention is excellent in chemical conversion treatment resistance, corrosion resistance, press workability, and weldability, and can provide an organic composite steel sheet having excellent overall use performance.

[Brief description of drawings]

FIG. 1 is a diagram showing a film structure of an example of the present invention,

FIG. 2 is a diagram showing the relationship between the film thickness and the chemical conversion treatment resistance when the film thickness of the solvent-based organic film and the water-based organic film are changed.

FIG. 3 is a graph showing the relationship between the olefin copolymerization ratio and the bare corrosion resistance without coating when the copolymerization ratio of olefin and acrylic acid is changed.

FIG. 4 is a diagram showing the relationship between the particle size of colloidal silica and the corrosion resistance after processing when the particle size of colloidal silica is changed,

FIG. 5 is a diagram showing the relationship between the amount of colloidal silica added and the corrosion resistance after processing when the amount of colloidal silica added is changed,

FIG. 6 is a diagram showing the relationship between the total film thickness and the weldability when the film thicknesses of the solvent-based organic film and the water-based organic film are changed.

[Explanation of symbols]

 1 Steel plate 2 Zinc-based plating film 3 Chromate film 4 Solvent-based organic film 5 Water-based organic film

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B32B 15/08 B32B 15/08 G 103 7148-4F 103Z

Claims (1)

[Claims] 1. A zinc-based plated steel sheet having a chromate film with a film thickness of 10 to 150 mg / m ^{2 on} one or both sides, and a solvent-based organic film having a film thickness of 0.1 to 1.5 μm on the chromate film. And an aqueous coating composition containing 15-40% colloidal silica having a particle size of 1-10 mμ and having an olefin copolymerization ratio in the range of 70-95%. Film thickness 0.5-1.9μ
An organic composite steel sheet having a water-based organic coating of m and having a total organic coating thickness of 2.0 μm or less and having excellent chemical conversion treatment resistance.