JPH05271960A - Manufacture of blackening treated steel sheet - Google Patents

Abstract

PURPOSE:To obtain a black steel sheet having a uniform appearance without requiring special equipments by heating a Zn-Ni alloy electroplated steel sheet to a specified temp. in an oxygen-contg. atmosphere to form a black oxidized film and then applying a transparent film thereto. CONSTITUTION:A Zn-Ni alloy electroplated steel sheet having 10 to 15wt.% Ni content is heated to 350 to 500 deg.C in an oxygen contg. atmosphere such as an air atmosphere to form a black oxidized film. The surface of the black oxidized film is coated with a transparent organic resin, which is dried to form a transparent film. In this way, need of equipments for preparing drug solutions for water treating or the like are eliminated, and the addition of alloy components for coloring is made needless.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a blackened steel sheet from a Zn-Ni alloy electroplated steel sheet.

[0002]

2. Description of the Related Art Black steel sheets are widely used in office automation equipment and the like. Previously, it was manufactured by painting a black organic coating with a thickness of several microns or more (for example, JP-A-
56-62996). However, such a coated black steel plate has some disadvantages in actual use, such as lack of conductivity or welding.

Therefore, in recent years, a technique for chemically treating a Zn-Ni alloy electroplated steel sheet to blacken it has been developed. (See, for example, Japanese Patent Publication No. 63-46158 and Japanese Patent Publication No. 3-25502).

[0004]

At present, as a technique for producing a black steel sheet using a Zn-Ni alloy electroplated steel sheet, a method using the electrochemical treatment described above is generally used. Since the plated surface is electrolyzed in a chemical solution, special equipment, that is, a tank and power source in the manufacturing line, a tank for preparing the chemical solution, a facility for circulating the solution to the tank in the line, etc. are required. is there.
Furthermore, expensive equipment such as water treatment for discarding the chemical waste liquid is required.

Further, during the electrolytic treatment, zinc in the zinc-nickel plating is dissolved, so that the corrosion resistance as a plating is deteriorated, and especially, the zinc content is reduced, so that the sacrificial rust resistance of the end face is deteriorated. The present invention does not require special large-scale equipment when producing a blackening-treated steel sheet from a Zn-Ni alloy electroplated steel sheet, and a production method that does not require addition of alloying components for coloring to the Zn plating layer. The purpose is to provide.

[0006]

The present invention has a Ni content of 10 to
A 15 wt% Zn-Ni alloy electroplated steel sheet was heated to 350-500 ° C in an oxygen-containing atmosphere to form a black oxide film,
Further, it is a method for producing a blackening-treated steel sheet, which is characterized in that a transparent coating film of an organic resin is further applied thereon.

[0007]

[Function] At present, a large number of steel sheets with Zn-Ni alloy electroplating treated with chromic acid and coated with an organic resin and baked to significantly improve corrosion resistance are used as rustproof steel sheets for automobiles. The inventor, when manufacturing this steel sheet, if the steel sheet is exposed to abnormally high temperatures due to troubles in manufacturing equipment,
It was found that the surface of Zn-Ni alloy electroplating became a dark blue tempered color like cold-rolled steel sheet, and the present invention was completed by thoroughly studying the method of applying this phenomenon to blackening treatment, treatment conditions, etc. did.

It is generally known that when a cold-rolled steel sheet or a hot-rolled steel sheet that is not plated is heated in the presence of oxygen such as in the atmosphere, a brown to dark blue oxide film, so-called temper color, mainly forms. There is. It is also known that when a galvanized steel sheet is heated, zinc reacts with the steel sheet to form a zinc-iron-based gray-black alloy. However, the above findings found by the present inventor have not been known so far.

According to the present invention, a Zn-Ni alloy electroplated steel sheet is heated to a steel sheet temperature of 350 ° C. or higher in an oxygen-containing atmosphere,
After making a dark blue oxidized temper color, a black steel sheet is manufactured by applying a transparent organic film of about 1.0 μm as a protective film. FIG. 1 is a graph showing the results of experiments conducted by the present inventor regarding the relationship between the heating temperature of Zn-Ni alloy electroplated steel sheets and the lightness index L (JIS).
It is recognized that if the L value is 15 or less, it is sensually black. Therefore, 350 ° C. or higher is required to obtain a black steel sheet. However, if the temperature exceeds 500 ° C, the control is difficult and the cost is high, so the upper limit of heating is preferably 500 ° C.

As the oxygen-containing atmosphere at the time of heating, an oxidizing combustion gas can be used in the air or by special oxygen enrichment. However, if the oxygen concentration is 100 ppm or less,
The main color is not uniform and delayed, making it unsuitable for mass production. Note that it is possible to improve the corrosion resistance by performing a chromic acid treatment before applying the organic resin.

[0011]

EXAMPLES Examples and comparative examples of the present invention will be described below.
First, a steel sheet was electroplated with Zn-Ni alloy at 20 g / m ² in an electroplating line. This sample was brought to an ordinary color line, the steel plate was heated to 350 ° C. in an oven in the air atmosphere, and then a 1 μm transparent organic resin was applied with a coater and dried. By this treatment, a uniform black steel plate having a lightness index (L value) of 15 was obtained.

On the other hand, when a sample obtained by subjecting a steel sheet to Zn-Ni alloy electroplating in the same manner is heated to 300 ° C., the color has an L value of 20.
Was a dark blue color, which was not suitable as a black steel plate. Similarly, a sample of Zn-Ni alloy electroplated on a steel plate was heated to a maximum reaching plate temperature of 350 ° C at an ambient temperature of 350 ° C in an annealing line of hydrogen 9% and nitrogen 91%. However, only a light color was applied and no good black color was obtained.

Similarly, when a sample obtained by subjecting a steel plate to Zn-Ni alloy electroplating was heated to a plate temperature of 500 ° C. in an air atmosphere, a dark blue temper color was not obtained, and zinc and iron reacted with each other. The color appears to be a grayish black that appears.

[0014]

As described above, according to the present invention, the chemical liquid-related preparation equipment necessary for the electrolytic treatment using a chemical liquid, the dedicated equipment such as a processing tank, and the water treatment of the chemical liquid are unnecessary. Therefore, it is possible to obtain a black steel plate having a uniform appearance at low cost.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a heating temperature of a Zn-Ni alloy electroplated steel sheet and a lightness index (L value).

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Claims (1)

[Claims] 1. A Zn-Ni alloy electroplated steel sheet having a Ni content of 10 to 15% by weight is heated to 350 to 500 ° C. in an oxygen-containing atmosphere to form a black oxide film, on which a transparent organic resin is formed. A method for producing a blackened steel sheet, which comprises applying a coating.