JPH06316774A - Black plated steel sheet excellent in adhesion and corrosion resistance and its production - Google Patents

Abstract

PURPOSE:To produce a black plated steel sheet excellent in adhesion and corrosion resistance at a high yield by successively coating the surface of a galvanized steel sheet with a black film layer and a chromate film layer of specified coating weight and, furthermore, coating it with a resin film layer. CONSTITUTION:The surface of a thin steel sheet (a) on which a galvannealing film (b) is applied, is subjected to cathode electrolysis in an aq. soln. contg. No3<->, Zn<2+>, Ni<2+> and Cr<3+> and chromate compounds are precipitated as a eutectoid by 10 to 50mg/m<2> as Cr, and is coated with a black film layer (c). The upper layer of this black film layer (c) is coated with a chromate film layer (d) by 5 to 90mg/m<2> as Cr, and the upper layer of the chromate film layer (d) is coated with a resin film layer (e) under the conditions in which the inlet side sheet temp. is regulated to be 50 to 80 deg.C and the arrival sheet temp. after baking is regulated to be >=140 deg.C. In this way, the black plated steel sheet having a stable appearance can be obtd.

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 sheet with nitric acid aqueous solution (JP-A-60
No. 112275) or an aqueous solution of nitrate (Japanese Patent Laid-Open No. 61-143594) or cathodic electrolysis in zinc-nickel alloy plating containing nitrate ions (Japanese Patent Publication No. 3-40116). After the formation of the resin, chromate treatment is performed, and a resin is further coated on the upper layer of the resin. Each of these techniques has its own characteristics, and cathodic electrolysis is the most efficient and high-speed production process.

[0003]

Since the conventional black-plated steel sheet has a multi-layer structure by the above-mentioned multi-stage treatment, the quality is easily affected by operating conditions, and detailed work control is required to obtain a black-plated steel sheet excellent in adhesion and corrosion resistance. There are issues that need to be addressed. Poor adhesion is often observed as peeling between the black coating and the chromate, peeling within the chromate and peeling between the resin and the chromate. An object of the present invention is to provide a black-plated steel sheet that can obtain stable adhesion, corrosion resistance and a 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) The surface of a zinc alloy plated steel sheet is provided with a chromium compound containing Cr.
As 10 to 50 mg / m ² eutectoid is black coating layer was chromate coating 5~90mg / m ² as Cr on the upper layer, the adhesion, characterized in that coated with a resin coating layer thereon, excellent corrosion resistance Black plated steel sheet.

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

[0006] (3) the surface of the black coating layer was 10 to 50 mg / m ² eutectoid chromium compound as Cr zinc alloy plated steel sheet, as Cr thereover chromate coating 5~90mg / m ^2, on the upper layer thereof In the production of a black-plated steel sheet excellent in adhesion and corrosion resistance, which is characterized by being coated with a resin film layer, an inlet side plate temperature for applying the resin film is 50 to 80.
A method for producing a black-plated steel sheet having excellent adhesion and corrosion resistance, characterized in that the ultimate plate temperature after baking is 150 ° C. or higher.

(4) NO _{3 on} the surface of zinc alloy plated steel sheet
^- , Zn ²⁺ , Ni ²⁺ , Cr ³⁺ in the aqueous solution containing a current density of 30 A / dm ² or more by cathodic electrolysis, a black film layer obtained by co-depositing a chromium compound as Cr in an amount of 10 to 50 mg / m ² , and an upper layer thereof. Chromate of 5 to 90 mg / m ² as Cr, and a resin coating layer on the upper layer thereof, which is excellent in adhesion and corrosion resistance. The method for producing a black-plated steel sheet having excellent adhesion and corrosion resistance is characterized in that the ultimate plate temperature after baking is set to 80 ° C. and 140 ° C. or higher.

[0008]

ACTION AND EXAMPLE 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 in order to obtain stable adhesion, corrosion resistance and a good black appearance, a chromium compound is co-deposited with 10 to 50 mg / m ² as Cr in the black coating layer and a Cr adhesion amount of 5 to 5 is deposited on the upper layer thereof. That is, the film constitution was such that a 90 mg / m ² chromate film was coated.

The black coating layer (c) is composed of a black compound containing a black hydrated oxide as a main component, but if the drying is insufficient when coating the upper chromate and resin coating, there will be too much reaction between the interfaces. It is easy to form a brittle film with poor adhesion. Due to the binder effect of the chromium compound to be co-deposited, a film having excellent adhesion can be obtained, and passivation of the chromium compound can provide good corrosion resistance. The reason for limiting the amount of chromium deposited on the eutectoid is 10 m as Cr for obtaining the binder and passivation effect of the chromium compound.
g / m ² or more is required, and Cr exceeding 50 mg / m ² is not preferable because the passivation effect of Cr causes uneven appearance and deteriorates the black appearance. For the above reason, the optimum eutectoid Cr deposition amount range is 15 to 30 mg / m ² .

The reason for limiting the chromate film on the upper layer of the black film in which the chromium compound is co-deposited is that the amount of Cr deposited is 5
If it is less than mg / m ² , the resin and the black coating are overreacted, and it is difficult to obtain good appearance and adhesion. On the other hand, if the amount of deposited Cr exceeds 90 mg / m ² , cohesive failure of the chromate film itself will occur and adhesion will not be obtained. The preferred amount range 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, a coating chromate is desirable, and chromic acid is preferably partially reduced reduced chromic acid or a chromate solution obtained by adding phosphoric acid, silica sol or the like to reduced chromic acid, and the plate temperature is applied. It is desirable to dry at 60 ° C. or higher.

Further, in the production of a black-plated steel sheet, the final plate temperature of the resin coating is 50 to 80 ° C., and the ultimate plate temperature after baking is preferably 150 ° C. or higher, whereby excellent adhesion and corrosion resistance are achieved. A black-plated steel sheet can be manufactured. The reason for limiting the temperature of the inlet side plate is that if the temperature is less than 50 ° C, adhesion is poor due to insufficient drying of the black and chromate coating 80 ° C.
If it exceeds the above range, it is not preferable because the viscosity of the resin liquid increases due to the temperature rise of the resin liquid and the leather covering and the coater surface become dry. Further, the reason for limiting the plate temperature after baking is that if the temperature is lower than 140 ° C., poor adhesion easily occurs due to insufficient baking and stable adhesion cannot be obtained. The process of the present invention in which these operating conditions are introduced is shown in FIG. The adhesion, corrosion resistance and appearance of the black plated steel sheet can be stably obtained.

[0012]

EXAMPLES Examples will be described below. 3, 4, 5, and 6 are zinc ion 55 ± 10 g / l and nickel ion 55 ± 10 for zinc-nickel alloy-plated steel sheet (plating amount 20 g / m ² ) using an electroplating pilot line.
g / l, trivalent chromium ion 1 ± 0.5 g / l, organic additive 20 ± 5 g / l, bath temperature 55 ± 5 ° C., pH 2.
Current density 30 ± 10 as 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 the acrylic emulsion resin coating compounding silica sol was applied to a dry coating film thickness of 1 μm. The results of adhesion, corrosion resistance and appearance of a black-plated steel sheet produced by cooling with water are shown.

FIG. 3 shows the relationship between the adhesion amount of chromate and the adhesion.
Is indicated by the 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 the dotted line b. Adhesion after Erichsen 8mm processing
The tape was peeled off and evaluated.
The good ones are marked with a circle. As you can see from the results,
The amount of mate adhered is 90 mg / m² Super (Eutectoid Cr25 ± 2m
g / m² Those with a certain level do not have good adhesion. Also, eutectoid
Cr amount is 10 mg / m ² Less than (Chromate adhesion amount is 30
± 2 mg / m² ) Indicates that the adhesion is poor.
It was

FIG. 4 shows the amount of eutectoid Cr in the black coating and the chromate (Cr deposit 30 ± 2 mg / m ² ) and the lightness (solid line a: blackness) measured on the surface of the black-plated steel sheet after resin coating with a color difference meter. The normal lightness <20 is required) and the adhesion (dotted line b) is shown. Eutectoid Cr amount is 50 mg / m
^If it exceeds ² , the brightness exceeds 20 and the appearance deteriorates. Further, when 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 and the chromate (Cr deposit amount 30 ± 2 mg / m ² ) and the corrosion resistance of the resin-coated black plated steel sheet measured by a continuous salt spray tester according to JIS Z-2371. It 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 white rust was not observed at all when the amount of eutectoid Cr was more than 10 mg / m ² , and corrosion resistance was improved.

FIG. 6 shows the effect of the resin coating on the adhesion between the inlet side plate temperature (a frame) and the outlet side plate temperature (b frame) under the conditions of an eutectoid Cr amount of 30 mg / m ² and a chromate adhesion amount of 30 mg / m ^2. It is the figure shown. Adhesion is indicated by x when the tape was peeled off after OT bending and peeling was recognized, and by o when good peeling was observed.
Peeling occurred when the inlet plate temperature was 40 ° C, and good adhesion was obtained when the inlet plate temperature was 50 ° C or higher. Further, it was observed that when the outlet plate temperature was 80 ° C, peeling occurred, and even at 100 ° C, peeling occurred (assessment Δ) with a probability of 30%. No peeling was observed at the outlet plate temperature of 150 ° C or higher.

FIG. 7 is a diagram showing the relationship between the current density of the black coating, the Erichsen adhesion after coating with chromate and resin (solid line a), and the lightness 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 chromate coverage of 30 mg / m ² . By setting the current density to 30 A / dm ² or more, excellent adhesion can be obtained, and the brightness variation is 0.5
The following is so good that evenness is not noticeable. But,
When the current density is 10 A / dm ² , the adhesion is poor and the brightness variation is 3 and the appearance is uneven. At a current density of 20 A / dm ² , the adhesion is good and the variation in brightness is improved to 1, but unevenness is observed.

[0018]

EFFECTS OF THE INVENTION The steel sheet of the present invention has characteristics different from those of the conventional precoated steel sheet, such as weldability, scratch resistance, and inconspicuous fingerprints.
Can be used for semi-sheath. INDUSTRIAL APPLICABILITY According to the present invention, a black-plated steel sheet having stable appearance, adhesion and corrosion resistance can be secured under a wide range of operating conditions, and there is an effect that high-speed and high-yield production can be achieved.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a manufacturing process and a plate temperature range after the black treatment of the present invention,

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

FIG. 4 is a diagram showing the relationship between the amount of eutectoid Cr in the 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 salt spray corrosion resistance,

FIG. 6 is a diagram showing the relationship between the resin-coated inlet side plate temperature and outlet side plate temperature that affect the adhesion of a black-plated steel sheet,

FIG. 7 is a diagram showing the relationship between the current density of the black coating and 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 film layer d chromate film layer e resin film layer

Claims (4)

[Claims] 1. A black coating layer in which a chromium compound is codeposited as Cr in an amount of 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 is provided as an upper layer, and a resin is provided as an upper layer. A black-plated steel sheet excellent in adhesion and corrosion resistance, characterized by being coated with a coating layer. Wherein NO ₃ on the surface of the zinc alloy plated steel sheet ^-,
Black film layer obtained by co-depositing a chromium compound as Cr in an amount of 10 to 50 mg / m ² by cathodic electrolysis in an aqueous solution containing Zn ²⁺ , Ni ²⁺ , Cr ^3+, and as an upper layer thereof, Cr as a layer of 5 to 90 m
A black-plated steel sheet excellent in adhesion and corrosion resistance, which is characterized by having a g / m ² chromate and a resin film layer coated on the chromate. 3. A black coating layer in which a chromium compound is codeposited as Cr in an amount of 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 is provided as an upper layer, and a resin is provided as an upper layer. Adhesiveness characterized by coating a coating layer, in the production of a black plated steel sheet excellent in corrosion resistance, the inlet side plate temperature for applying the resin coating is 50 to 80 ° C.,
A method for producing a black-plated steel sheet having excellent adhesion and corrosion resistance, characterized in that the ultimate plate temperature after baking is 140 ° C. or higher. 4. NO ₃ on the surface of the zinc alloy plated steel sheet ^-,
Current density 30 in aqueous solution containing Zn ²⁺ , Ni ²⁺ , Cr ³⁺
Chromium compounds were converted to Cr by A / dm ² or more cathodic electrolysis.
As 10 to 50 mg / m ² eutectoid is black coating layer was, dichromate 5~90mg / m ² as Cr on the upper layer,
Adhesiveness characterized by coating a resin film layer on the upper layer thereof, in the production of a black plated steel sheet excellent in corrosion resistance, the inlet side plate temperature for applying the resin film is 50 to 80 ° C, and the ultimate plate temperature after baking is 140 ° C. A method for producing a black-plated steel sheet excellent in adhesion and corrosion resistance, characterized by the above.