JP2974878B2 - Black plated steel sheet with excellent adhesion and corrosion resistance and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a black-plated steel sheet, and more particularly to a black-plated steel sheet having excellent adhesion and corrosion resistance and a method for producing the same.

[0002]

2. Description of the Related Art The prior art of black-plated steel sheet is Zn-Ni.
Etching alloy plated steel plate with nitric acid aqueous solution
JP-A-112275) or anodizing in an aqueous nitrate solution (JP-A-61-143594) or performing cathodic electrolysis in zinc-nickel alloy plating containing nitrate ions (JP-B-3-40116). A method is disclosed in which a chromate treatment is performed after the formation of a resin, and a resin is further coated on the upper layer. Each of these techniques has its own characteristics, and cathodic electrolysis is the most efficient and high-speed production process.

[0003]

The conventional black-plated steel sheet has a multi-layer structure formed by the above-described multi-step processing, so that its quality is easily affected by operating conditions, and fine work management is required to obtain a black-plated steel sheet having excellent adhesion and corrosion resistance. There are issues that need to be addressed. In many cases, poor adhesion is observed as peeling between the black film and the chromate, peeling in the chromate, and peeling between the resin and the chromate. An object of the present invention is to provide a black-plated steel sheet capable of obtaining stable adhesion, corrosion resistance and beautiful appearance, and a method for producing the same.

[0004]

SUMMARY OF THE INVENTION The present invention advantageously solves the problems of the prior art. (1) A chromium compound is added to the surface of a zinc alloy plated steel sheet
Excellent adhesion and corrosion resistance, characterized in that a black coating layer of 10 to 50 mg / m ^{2 as} eutectoid, a chromate coating of 5 to 90 mg / m ² as Cr on the upper coating layer, and a resin coating layer on the upper coating layer Black plated steel sheet.

(2) NO ₃ is applied to the surface of a zinc alloy plated steel sheet.
^{-, 10~50mg / m Zn 2+,} Ni 2+, the chromium compound by cathodic electrolysis in an aqueous solution containing Cr ³⁺ as Cr
² Co-deposited black coating layer, 5 to 9 as Cr on top
A black-plated steel sheet having excellent adhesion and corrosion resistance, characterized by having a chromate of 0 mg / m ² and a resin film layer coated thereon.

(3) A black coating layer in which a chromium compound as Cr is co-deposited at 10 to 50 mg / m ^{2 on} the surface of a zinc alloy-plated steel sheet, a chromate coating of 5 to 90 mg / m ² as Cr on the upper layer, In the production of a black plated steel sheet having excellent adhesion and corrosion resistance characterized by coating with a resin film layer, the temperature of the inlet side plate where the resin film is applied is 50 to 80.
A method for producing a black-plated steel sheet having excellent adhesion and corrosion resistance, wherein the ultimate sheet temperature after baking is 150 ° C. or higher.

(4) NO ₃ is applied to the surface of a zinc alloy plated steel sheet.
^-, Zn ^2+, Ni ^2+, black coating layer was 10 to 50 mg / m ² eutectoid chromium compound as Cr by a current density of 30A / dm ² or more cathodic electrolysis in an aqueous solution containing Cr ^3+, the upper layer A chromate of 5 to 90 mg / m ² as Cr, and a resin coating layer coated on top of the chromate. A method for producing a black-plated steel sheet having excellent adhesion and corrosion resistance, characterized in that the ultimate sheet temperature after baking is set to 140 ° C. or higher at 80 ° C.

[0008]

FIG. 1 shows an example of the coating structure of the black plated steel sheet of the present invention. a is a thin steel plate, b is a zinc alloy plating film, c is a black film layer composed of Zn-Ni-Cr, d
Is a chromate coating layer, and e is a resin coating layer. The feature of the present invention is that a chromium compound is co-deposited with 10 to 50 mg / m ² as Cr on the black coating layer to obtain stable adhesion, corrosion resistance and good black appearance, and the upper layer has a Cr adhesion amount of 5 to 50 mg / m ^2. In other words, the coating composition was such that a 90 mg / m ² chromate coating was applied.

The black coating layer (c) is composed of a black compound mainly composed of a black hydrated oxide. However, if the drying is insufficient when the upper chromate and the resin coating are coated, excessive reaction between the interfaces may occur. A brittle film with poor adhesion is easily formed. A film having excellent adhesion can be obtained by the binder effect of the chromium compound to be eutectoid, and good corrosion resistance can be obtained by passivation of the chromium compound. The reason for limiting the amount of deposited chromium to be eutectoid is that the chromium compound has a binder of 10 m in order to obtain a passivation effect.
g / m ² or more is required, and if Cr is more than 50 mg / m ² , the passivation of Cr causes uneven appearance and deteriorates the black appearance, which is not preferable. For the above reasons, the optimum eutectoid Cr adhesion amount range is 15 to 30 mg / m ² .

The reason for limiting the upper chromate film on the black film on which the chromium compound is codeposited is that the amount of Cr attached is 5%.
When the amount is less than mg / m ² , the resin and the black coating are excessively reacted, and it is difficult to obtain good appearance and adhesion. On the other hand, if the Cr adhesion amount exceeds 90 mg / m ² , cohesive failure of the chromate film itself occurs, and no adhesion can be obtained. A preferred range of the amount of the chromate coating is 20 to 50 mg / m ² as Cr. A known chromate film can be used, but in the present invention, chromate is preferably applied. Chromic acid, preferably partially reduced reduced chromic acid or a chromate solution obtained by adding phosphoric acid, silica sol, or the like to reduced chromic acid, is applied. Is desirably dried to 60 ° C. or more.

[0011] Further, in the production of black-plated steel sheet, by setting the temperature of the inlet side plate where the final resin coating is applied to 50 to 80 ° C and the ultimate plate temperature after baking to preferably 150 ° C or higher, excellent adhesion and corrosion resistance are obtained. A black plated steel sheet can be manufactured. The reason for limiting the inlet side plate temperature is that if it is lower than 50 ° C, the adhesion is poor at 80 ° C due to insufficient drying of the black and chromate films.
If the temperature is too high, the viscosity of the resin liquid is increased due to the increase in the temperature of the resin liquid, and the leather coating and the coater surface are undesirably dried. The reason for limiting the sheet temperature after baking is that if the temperature is lower than 140 ° C., poor adhesion is likely to occur due to insufficient baking and stable adhesion cannot be obtained. The process of the present invention incorporating these operating conditions is shown in FIG. The adhesion, corrosion resistance and appearance of the black plated steel sheet can be obtained stably.

[0012]

Embodiments will be described below with reference to embodiments. FIGS. 3, 4, 5, and 6 show that a zinc-nickel alloy-coated steel sheet (coating amount 20 g / m ² ) was zinc ions 55 ± 10 g / l and nickel ions 55 ± 10 g using the electroplating pilot line.
g / l, trivalent chromium ion at 1 ± 0.5 g / l, organic additive at 20 ± 5 g / l, bath temperature 55 ± 5 ° C., pH 2.
Current density 30 ± 10 as a cathode in 5 ± 0.5 aqueous solution
And 20 to 30 coulombs / dm ² current in A / dm ^2, immediately chromic acid concentration reducing chromic acid / phosphoric acid ratio of 10/1 was washed with water 5 to 20 g / l chromate solution plate temperature 80 ° C. In applying hot air to the After drying, the inlet side plate temperature was adjusted to 65 to 75 ° C., and an acrylic emulsion resin coating compounded with silica sol was applied at a dry film thickness of 1 μm, and baked in a baking furnace to the outlet side plate temperature of 160 ° C. It shows the results of adhesion, corrosion resistance, and appearance of a black-plated steel sheet manufactured by water cooling.

FIG. 3 shows the relationship between the amount of chromate deposited and the adhesion.
Is indicated by a solid line a, and the relationship between the amount of Cr eutectoid in the black coating and the adhesion is shown.
The engagement is indicated by a dotted line b. Adhesion after Erichsen 8mm processing
The tape was peeled off and evaluated.
Good ones are indicated by a circle. The results clearly show that
90mg / m^Two Super (eutectoid Cr 25 ± 2m
g / m^Two (Constant) has poor adhesion. Also, eutectoid
Cr content is 10mg / m ^Two (Less than 30 chromate deposits)
± 2mg / m^Two ) Indicates poor adhesion.
Was.

FIG. 4 shows the amounts of eutectoid Cr and chromate (Cr adhesion amount 30 ± 2 mg / m ² ) in the black coating and the lightness (solid line a: blackness) of the surface of the black-plated steel sheet coated with the resin using a color difference meter. And a relationship between normal lightness <20 is required and adhesiveness (dotted line b). Eutectoid Cr content is 50mg / m
^If it exceeds ² , the lightness exceeds 20 and the appearance deteriorates. If the amount of eutectoid Cr is less than 10 mg / m ² , the adhesion is not good.

FIG. 5 shows the amount of eutectoid Cr in the black coating, the chromate (Cr adhesion amount 30 ± 2 mg / m ² ), and the corrosion resistance of the black plated steel sheet coated with the resin using a continuous salt spray tester according to JISZ-2371. This is a visual evaluation of the area ratio of white rust after a day test. White rust was reduced in proportion to the amount of eutectoid Cr, and when the amount of eutectoid Cr exceeded 10 mg / m ² , no white rust was observed and the corrosion resistance was improved.

FIG. 6 shows the effect of the resin coating on the adhesiveness between the inlet plate temperature (a frame) and the outlet plate temperature (b frame) under the conditions of eutectoid Cr content of 30 mg / m ² and chromate adhesion amount of 30 mg / m ^2. FIG. The adhesion was evaluated as x when the tape was peeled after OT bending and peeling was observed, and as good when the tape was peeled.
When the inlet side plate temperature was 40 ° C., peeling occurred, and at 50 ° C. or higher, good adhesion was obtained. In addition, peeling was observed when the exit sheet temperature was 80 ° C, and peeling (estimation △) was established at 30% even at 100 ° C. No peeling was observed at an exit side plate temperature of 150 ° C. or higher.

FIG. 7 is a graph showing the relationship between the current density of the black film, the Erichsen adhesion after the chromate and resin coating (solid line a), and the brightness variation in the plate width direction (dotted line b: ΔL). The amount of eutectoid Cr is 5 to 30 mg / m depending on the current density.
² and a condition of 30 mg / m ² of chromate adhesion amount. By setting the current density to 30 A / dm ² or more, excellent adhesion can be obtained, and brightness fluctuation can be reduced to 0.5.
Below, it is good enough that no unevenness is perceived. But,
At a current density of 10 A / dm ² , the adhesion is poor, and the brightness variation has an uneven appearance of 3. At a current density of 20 A / dm ² , the adhesion was good and the brightness variation was improved to 1, but unevenness was observed.

[0018]

The steel sheet of the present invention has properties different from those of the conventional pre-coated steel sheet, such as weldability, scratch resistance, and inconspicuous fingerprints.
Can be used for quasi-skin. According to the present invention, a black-plated steel sheet having a stable appearance, adhesion and corrosion resistance is ensured under a wide range of operating conditions, and there is an effect that high-speed and high-yield production can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a cross-sectional configuration of a coating film of the present invention;

FIG. 2 is a view showing a manufacturing process and a range of a sheet temperature after black processing according to the present invention;

FIG. 3 Chromate deposition amount and eutectoid Cr in black coating
A diagram showing the relationship between the amount and the adhesion,

FIG. 4 is a diagram showing the relationship between the amount of eutectoid Cr in a black coating and the brightness and adhesion.

FIG. 5 is a diagram showing the relationship between the amount of eutectoid Cr in the black coating and the salt spray corrosion resistance;

FIG. 6 is a diagram showing the relationship between the inlet sheet temperature and the outlet sheet temperature of the resin coating on the adhesion of the black plated steel sheet,

FIG. 7 is a diagram showing the relationship between the current density of the black coating, the adhesion (solid line a), and the brightness variation in the plate width direction (dotted line b).

[Explanation of symbols]

 a Thin steel plate b Zinc alloy plating film c Black coating layer d Chromate coating layer e Resin coating layer

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-69508 (JP, A) JP-A-5-59570 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C 28/00

Claims (4)

(57) [Claims] 1. A black coating layer in which a chromium compound is eutectoidized with 10 to 50 mg / m ² as Cr on a surface of a zinc alloy plated steel sheet, a chromate coating with 5 to 90 mg / m ² as Cr on an upper layer, and a resin on the upper layer A black plated steel sheet with excellent adhesion and corrosion resistance characterized by a coating layer. 2. The method according to claim 1, wherein the surface of the zinc alloy-plated steel sheet has NO ₃ ⁻ ,
A black coating layer obtained by co-depositing a chromium compound as Cr by 10 to 50 mg / m ² by cathodic electrolysis in an aqueous solution containing Zn ²⁺ , Ni ²⁺ , and Cr ^3+.
g / m ² chromate, a black-plated steel sheet having excellent adhesion and corrosion resistance, characterized in that a resin film layer is coated thereon. 3. A black coating layer obtained by codepositing a chromium compound as Cr with 10 to 50 mg / m ^{2 on} the surface of a zinc alloy plated steel sheet, a chromate coating of 5 to 90 mg / m ² as Cr on the upper layer, and a resin on the upper layer. In the production of a black-plated steel sheet having excellent adhesion and corrosion resistance, characterized in that the coating layer is coated, the inlet side sheet temperature at which the resin coating is applied is 50 to 80 ° C,
A method for producing a black-plated steel sheet having excellent adhesion and corrosion resistance, wherein the ultimate sheet temperature after baking is set to 140 ° C. or higher. 4. The method according to claim 1, wherein the surface of the zinc alloy plated steel sheet has NO ₃ ⁻ ,
A current density of 30 in an aqueous solution containing Zn ²⁺ , Ni ²⁺ , and Cr ³⁺
A / dm ² or more cathodic electrolysis converts chromium compound to Cr
10 to 50 mg / m ² eutectoid black coating layer, and a Cr layer of 5 to 90 mg / m ² as Cr on the upper layer,
In the production of a black plated steel sheet having excellent adhesion and corrosion resistance, characterized in that an upper layer is coated with a resin film layer, the temperature of the inlet side sheet where the resin film is applied is 50 to 80 ° C., and the ultimate sheet temperature after baking is 140 ° C. A method for producing a black-plated steel sheet having excellent adhesion and corrosion resistance, characterized in that: