JP2737603B2 - Surface treated steel sheet with excellent workability and corrosion resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel sheet having excellent workability and corrosion resistance and a beautiful dark gray appearance, which is suitable as a material for home electric appliances, office equipment, steel furniture, building materials and the like. .

[0002]

2. Description of the Related Art In recent years, needs for steel sheets used in fields such as home appliances and office equipment have diversified, and
High quality things have been required. For example, in the past, steel sheets that had been subjected to chromate treatment after being subjected to zinc plating or zinc-based alloy plating were often used.After that, a thin organic film layer was further formed thereon to prevent fingerprint adhesion and Steel sheets with improved corrosion resistance have been used.

Recently, a lubricating steel sheet having improved press formability by adding a solid lubricant to a resin film layer (for example, JP-A-4-94771, JP-A-3-16726, etc.) Have been mass-produced, and a steel sheet in which a resin film is colored by adding a dye, a pigment, or the like has been proposed. For example, conventionally, a method of forming a resin film having a film thickness of several tens of μm containing a black pigment such as carbon black on the surface of a steel sheet by spraying or roll coating is known, and JP-A-4-354884 discloses a method. A black steel sheet which is colored by adding a black dye to the resin film, or which is further improved in press formability by adding a solid lubricant, is disclosed in JP-A-4-355127. The steel sheet is disclosed.

However, in the conventional method of forming a resin film containing a black pigment such as carbon black on the surface of a steel plate by spraying or the like, a problem arises in that spot welding cannot be performed because the film thickness is increased when the degree of blackness is increased. was there. Further, in the black steel sheet described in JP-A-4-354884, the resin film of the base is not improved at all, so when the molding conditions become severe, the resin film and the solid lubricant on the steel sheet surface are scraped off. In addition, there is a problem that the dye adheres to the mold, and the use of a dye as a coloring agent increases the production cost. JP 4
The colored steel sheet described in Japanese Patent No. 355127 also has the same problem as the black steel sheet.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems in a colored steel sheet having a colored resin layer formed on the surface, has excellent workability and corrosion resistance, has good spot weldability, and An object of the present invention is to provide a surface-treated steel sheet having a dark gray uniform and beautiful appearance.

[0006]

The gist of the present invention resides in the following surface-treated steel sheet.

[0007] At least one side of the steel sheet has an organic film mainly composed of a thermosetting resin, and the organic film has a thickness of at least one.
A solid lubricant having a particle size of 0.5 to 5 μm and a particle size of 0.5 to 5 μm is used in an amount of 5 to 30% by weight based on the weight of the organic film.
A surface-treated steel sheet containing 0.5 to 5% by weight and satisfying the following expression (1), having a Vickers hardness of 5 to 30 and a lightness L value of 45 to 55, and having excellent workability and corrosion resistance. .

0.2 ≦ B / A ≦ 2 (1) where A is the thickness of the organic film (μm) B is the average particle size of the solid lubricant (μm)

[0009]

Hereinafter, the present invention will be described in detail.

In the surface-treated steel sheet of the present invention, a steel sheet before an organic film is formed on its surface (hereinafter referred to as a base steel sheet) is generally a SP steel sheet specified in JIS G 3141.
The surface of CC or the like is plated with zinc or a zinc-based alloy, and further subjected to a chromate treatment. Chromate treatment may be performed on other plated steel plates or stainless steel plates. The chromate treatment may be any of coating type chromate, reactive type chromate and electrolytic type chromate.

The thermosetting resin which is a main component of the organic film includes an acrylic resin, an epoxy resin, a urethane resin, an alkyd resin, a phenol resin, or the like, a resin in which two or more of these are mixed, and other monomers. An addition condensate or a derivative modified with another resin may be used. Also,
Silica or a sparingly soluble chromate may be contained as a rust preventive pigment.

The solid lubricant contained in the organic film is, for example, polyolefin wax, polytetrafluoroethylene (Teflon = trade name) or the like. If the particle size of the solid lubricant is smaller than 0.5 μm, the lubricity at the time of press molding is insufficient, while if it exceeds 5 μm, it tends to be peeled off at the time of molding, so it must be 0.5 to 5 μm.

Further, assuming that the thickness of the organic film is A (μm) and the average particle size of the solid lubricant is B (μm), 0.2 ≦ B /
It is necessary that A ≦ 2. This means that B / A is 2
If the ratio exceeds 0.2, the adhesion between the resin and the solid lubricant deteriorates, so that the solid lubricant tends to peel off and adhere to the mold during press molding, while if it is less than 0.2, the workability tends to deteriorate. .

The content of the solid lubricant must be in the range of 5 to 30% by weight based on the weight of the cured organic film, and if it is less than 5% by weight, sufficient lubricity at the time of molding is obtained. If the content exceeds 30% by weight, the production cost is increased but the effect corresponding thereto cannot be obtained.

If the particle size of the carbon black exceeds 0.5 μm, it tends to be in a state of aggregation or precipitation, and an organic film having a good appearance cannot be obtained. In addition, the content of carbon black is 0.5% with respect to the weight of the cured organic film.
When the content is less than 5% by weight, uniform and beautiful dark gray is not obtained within the thickness range of the present invention. On the other hand, when the content is more than 5% by weight, the conductivity of the organic film becomes large and the corrosion resistance is deteriorated.
Its content should be in the range of 0.5 to 5% by weight.

The thickness of the organic film must be 0.5 to 5 μm. If the film thickness is less than 0.5 μm, the corrosion resistance is not sufficient, and if it exceeds 5 μm, the spot weldability decreases.

This organic film has a Vickers hardness (Hv) of 5
Must have a hardness of ~ 30. If the Vickers hardness is less than 5, the sliding property of the film becomes worse at the time of press working. Therefore, the content of the solid lubricant must be increased, and the coating film is easily damaged. On the other hand, if the Vickers hardness exceeds 30, the coating becomes brittle, and the corrosion resistance after processing deteriorates.

The brightness of this organic film must be 45 to 55 in L value. Outside this range, a desirable dark gray color tone cannot be obtained.

The organic film may be formed on at least one side of the base steel sheet according to the application.

In order to manufacture the surface-treated steel sheet of the present invention, the surface of the above-mentioned base steel sheet, that is, a base steel sheet such as SPCC specified in JIS is coated with zinc or a zinc-based alloy, Treated steel sheet, other plated steel sheet, or the surface of a steel sheet subjected to chromate treatment on a stainless steel sheet or the like, a resin containing a solid lubricant and carbon black so as to satisfy the above predetermined conditions. What is necessary is just to apply. As a coating method, a conventionally used method can be applied. The L value of the formed organic film can be set within a predetermined range by adjusting the amount of carbon black and the thickness of the resin. In order to set the hardness of the film to a predetermined value, the composition of the resin and the crosslinking density may be appropriately selected.

[0021]

EXAMPLE An electrogalvanized (Zn) -plated steel sheet shown in Table 1 and a Zn-Ni alloy-plated steel sheet containing 13% by weight of nickel (Ni) in a plating film were subjected to a chromate treatment to an undercoated steel sheet (both of which are shown below). The base material is a material equivalent to SPCC specified in JIS, with a plate thickness of 0.8 mm). The surface is made of the resin shown in Table 2 as a main component (this is called basic resin). An organic film containing the agent and carbon black was formed.

The coating weight was 20 g / m ² . As shown in Table 4, the chromate treatment is performed by reactive chromate treatment for the electro-zinc plated steel sheet, and the amount of the chromate film deposited is converted to metallic chromium (Cr) by 10 to 100 m.
g / m ^2, and electro-Zn—Ni alloy plating was performed by a coating type chromate treatment, and the adhesion amount was also 50 mg / m ² .

As shown in Table 4, a treatment liquid (paint) containing a basic resin containing a solid lubricant and carbon black under various conditions was applied by a roll coater, and the organic film was formed at 200 ° C. as shown in Table 4. This was done by heating for 2 seconds to cure. The thickness of the organic film was adjusted by changing the paint concentration and the peripheral speed ratio between the pickup roll and the applicator roll.

The surface-treated steel sheets prepared as described above (Nos. 1 to 25 of the present invention shown in Table 4 and Nos. 1 to 25 of the comparative examples)
Using 13) as a test material, tests were performed for the following various properties.

(1) Corrosion resistance A plate test piece was cut out from the test material and subjected to a salt spray test specified in JIS Z 2371. Evaluation was made at a time when the white rust occurrence rate became 5% during 360 hours. The evaluation criteria were as follows, and the case of ◎ or 印 was regarded as good.

◎: no white rust generated in 360 hours, ：: 240
Time to less than 360 hours △: 72 hours to less than 240 hours, ×: less than 72 hours (2) Workability For a given test piece, blank diameter 90 mm, die diameter 42 mm
(Shoulder 8R), punch diameter 40 mm (shoulder 8R), and a cylindrical holder with a blank holder pressure of 1 ton (drawing out) were performed. The evaluation criteria were as follows, and the case of ◎ or 印 was regarded as good.

◎: no galling, ○: galling but extremely slight △: galling is noticeable, ×: galling on the entire surface (3) Peeled coating after processing Gold when 10 pieces were continuously formed under the above cylindrical drawing conditions. The evaluation was based on the state of adhesion of the release film to the mold. That is, the tape was stuck to the mold (die side), peeled off, and the adhesion of the release film was visually observed. The evaluation criteria are as follows,
The case of ○ or △ was regarded as good.

：: No adhesion of release film, Δ: Light adhesion of release film ×: Large adhesion of release film (4) Color tone Brightness L of the film using a color tester (manufactured by Suga Test Instruments)
The value was measured. The evaluation criteria are as follows.

：: 45 ≦ L value ≦ 55 (the surface of the film presents a dark gray) ×: L value <45 or L value> 55 (5) Spot weldability The score was evaluated.

[Spot welding conditions] Electrode: Cu-Cr alloy, R type Electrode diameter: 6 mmφ Welding current: 10 kA Pressure: 200 kg Conduction time: 12 cycles / 50 Hz The evaluation criteria are as follows. Was regarded as good.

○: 1000 points or more, Δ: 500 points or more and less than 1000 points ×: less than 500 points (6) Corrosion resistance after processing A salt water spray test specified in JIS Z 2371 is performed on a cylindrical drawn test piece, and 72 hours have passed. The evaluation was made based on the presence or absence of white rust between the spaces. The evaluation criteria are as follows.

：: no white rust occurred, ×: white rust occurred Table 4 also shows the test results. In this table,
The types of the base steel sheet, the organic film, and the solid lubricant are represented by the symbols used in Tables 1, 2, and 3, respectively. As is clear from the results in Table 4, in the present invention example, good results were obtained for each of the performances tested.
When any of the conditions specified in the present invention was missing, at least one of the test items was defective.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

[Table 3]

[0036]

[Table 4 (1)]

[0037]

[Table 4 (2)]

[0038]

[Table 4 (3)]

[0039]

The surface-treated steel sheet of the present invention is excellent in workability and corrosion resistance and has good spot weldability.
Moreover, it has a dark gray uniform and beautiful appearance, and is suitable as a material for home electric appliances, office equipment, steel furniture, building materials, and the like.

Claims (1)

(57) [Claims] 1. A steel sheet having on at least one surface thereof an organic film mainly composed of a thermosetting resin, and the organic film has a thickness of
A solid lubricant having a particle size of 0.5 to 5 μm and a particle size of 0.5 to 5 μm is used in an amount of 5 to 30% by weight based on the weight of the organic film.
A surface-treated steel sheet containing 0.5 to 5% by weight and satisfying the following expression (1), having a Vickers hardness of 5 to 30 and a lightness L value of 45 to 55, and having excellent workability and corrosion resistance. . 0.2 ≦ B / A ≦ 2 (1) where A is the thickness of the organic film (μm) B is the average particle size of the solid lubricant (μm)