JPH0734259A - Colored lubrication-treated galvanized steel sheet and its production - Google Patents

Abstract

PURPOSE:To produce a colored lubrication-treated galvanized steel sheet excellent in surface appearance, lubricity and corrosion resistance by forming a resin film having a specified compsn. on the surface of a galvannealed steel sheet having a chromate film. CONSTITUTION:A galvannealed steel sheet having 8 to 13% alloying degree is used as a base metal, and, on the plated face, a chromate film is formed by 10 to 150mg/m<2> expressed in terms of metal Cr. Furthermore, on its surface, a resin film obtd. by dissolving 3 to 30wt.% polyolefine wax and silica grains by 5 to 30wt.% as SiO2 into a base resin such as a polyurethane resin with a solvent such as alcohol is formed by 0.1 to 5g/m2 coating weight, by which the surface treated steel sheet having a quiet gray color tone in which the color tone of the surface is regulated to 50<=L*<=62, -1<=a*<=0 and -2<=b*<=0, free from the need of the application of pressing oil and the removal of pressing oil by ozone layer destroying substance such as trichloroethane and excellent in lubricity, corrosion resistance and designing properties can be produced.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a colored lubricated zinc-based plating having a surface appearance suitable for use as an exterior for automobiles, home appliances, building products, etc., and having excellent lubricity and corrosion resistance. Regarding steel plates.

[0002]

2. Description of the Related Art In recent years, measures to prevent the destruction of the global environment have become a global problem, and prevention of the destruction of the ozone layer, which protects us from intense ultraviolet rays, is an important issue. 1987
The use of halogenated hydrocarbon-based organic solvents such as chlorofluorocarbons and trichlene, which causes water pollution, was introduced in Japan in 1988 when the domestic law was enacted in 1988, including the adoption of the CFC regulation protocol in Montreal. It is becoming regulated.

Generally, when processing a steel sheet, press oil is applied to reduce frictional resistance. The applied press oil is degreased in the degreasing step after processing. Trichloroethane, which is often used in this degreasing process, is an ozone depleting substance, and is scheduled to be completely abolished in 1995.

Further, from the viewpoint of improving the environment of the press work workplace and reducing the cost by omitting the degreasing process, there is an increasing need for a lubricated steel sheet which has been subjected to a lubrication process in advance and which can omit the press oil application-degreasing process.

From the above circumstances, various lubricated steel sheets have been proposed as illustrated below. JP-A-3-96337: A resin-coated steel sheet having excellent press workability in which a resin film containing fluororesin particles and silica particles in an acrylated epoxy resin is formed on a chromate-treated electrogalvanized steel sheet. Japanese Unexamined Patent Publication No. 3-17190: Lubricity in which a coating film of montan wax oxide containing fluororesin particles and silica particles is formed on a chromate-treated galvanized steel sheet,
Surface-treated steel sheet with excellent corrosion resistance. JP-A-3-17189: A resin-coated steel sheet excellent in lubricity and corrosion resistance in which a resin coating containing fluorine resin particles and silica particles in a urethane-modified polyolefin resin is formed on a chromate-treated galvanized steel sheet. JP-A-3-28380: Zinc-based (= zinc or zinc alloy)
A surface-treated steel sheet having excellent lubricity and corrosion resistance, having a chromate film formed on the surface of an electroplated steel sheet and having a coating layer of a carboxylated polyethylene-based dispersion containing a fluororesin thereon. JP-A-3-16726: Forming a chromate film on the surface of a zinc-based electric or hot dip plated steel sheet, and a resin film containing silica and polyolefin wax in the resin having a hydroxyl group and / or a carboxyl group on the chromate film Lubricant resin treated steel sheet with excellent properties.

Each of these uses an electrogalvanized steel sheet or a hot-dip galvanized steel sheet as a base material, and its color tone is inferior in design because the metallic luster peculiar to the underlying zinc-based plating remains as it is. In recent years, from the viewpoint of cost reduction, there have been attempts to apply these lubricated steel sheets to exterior applications where coating or pre-painted pre-coated steel sheets have conventionally been used. However, the conventional lubricated steel sheet has a poor design and is difficult to be applied as an exterior.

As a lubricated steel sheet having a colored appearance, Japanese Patent Laid-Open No. 2-263633 discloses an organic solvent containing a chromate film on the surface of a zinc-based plated steel sheet, on which silica, polyethylene wax and a color pigment are contained. A high corrosion resistant colored thin film coated steel sheet coated with a mold coating composition has been proposed.
This coated steel sheet has a high manufacturing cost because the resin film is colored with a pigment. Furthermore, since it is difficult to uniformly disperse the pigment in the paint, it is difficult to form a uniformly colored resin film in a stable manner. Become.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to apply as an exterior, which can be processed by omitting the press oil application-degreasing step, and is colored to have a preferable appearance without using a pigment. It is to provide a surface-treated steel sheet having excellent lubricity, corrosion resistance, and designability.

A more specific object is to exhibit the same lubricating performance as that of the above-mentioned conventional lubricated steel sheet (that is, it has excellent lubricity and is resistant to extreme pressure during heavy working and temperature rise of the die. At the same time, it is colored and lubricated without the use of pigments and has the same design characteristics as pre-coated steel sheets. Furthermore, it retains high corrosion resistance even after the steel sheets have been processed and can be welded. It is to provide a zinc-based plated steel sheet.

[0010]

[Means for Solving the Problems] As seen in the above-mentioned prior art, when a lubricating resin film containing a lubricating component is formed after chromate treatment on the surface of an electrogalvanized or hot-dip galvanized steel sheet, base metal plating is performed. The lubricity and corrosion resistance of the steel sheet can be improved.

The present inventor has conducted extensive studies to develop a lubricated steel sheet that has the design characteristics of a pre-coated steel sheet and is applicable to the exterior, while taking advantage of the advantages of these conventional techniques. When a chromate treatment and formation of a lubricious resin film are performed using a specific galvannealed steel sheet, it has excellent lubricity and corrosion resistance, and exhibits a calm gray color as a color tone, and it has the same design characteristics as pre-coated steel sheets. It was found that a surface-treated steel sheet was obtained, and the present invention was achieved.

Here, the present invention has a chromate film having a Cr deposit of 10 to 150 mg / m ^{2 on} the plated surface of a galvannealed steel sheet, and a polyolefin wax of 3 to 30% by weight as an upper layer. It contains 5 to 30% by weight of silica particles as SiO ₂ and has a resin film containing no coloring pigment and having an adhesion of 0.1 to 5 g / m ² , and the surface tone is JIS Z8729 L ^* a ^* b ^* color system. In the present invention, a colored lubricated zinc-based plated steel sheet is characterized in that 50 ≦ L ^* ≦ 62, −1 ≦ a ^* ≦ 0, and −2 ≦ b ^* ≦ 0.

The L ^* value is a lightness index. The larger the value, the brighter it is, and the smaller the value, the darker it is. The a ^* value is a perceived chromaticity (chromaticity) index between red and green. Larger values indicate stronger redness, and smaller values indicate stronger greenness. The b ^* value is the perceived chromaticity index between yellow and blue. The larger the value, the stronger the yellowness, and the smaller the value, the stronger the blueness.

The zinc-plated steel sheet treated with colored lubrication is made of an alloyed hot-dip galvanized steel sheet having an alloying degree of 8 to 13% as a base material, and is subjected to chromate treatment and coating with a resin coating composition to form the above chromate on the plated surface. It can be manufactured by sequentially forming a film and a resin film.

[0015]

The colored and lubricated zinc-based plated steel sheet and the method for producing the same according to the present invention will be described in detail below.

The base material of the colored and lubricated steel sheet of the present invention is an alloyed hot-dip galvanized steel sheet (hereinafter abbreviated as GA steel sheet), that is, a hot-dip galvanized steel sheet is plated and then heat-treated to remove Zn in the plating film. It is a zinc-based plated steel sheet that is partially alloyed with Fe as the base material. The GA steel sheet used as the base material has an alloying degree of the plating film (average Fe% in the plating film) of 8 to 13
Those within the range of% are desirable. GA steel sheets have a tendency that as the alloying progresses and the alloying degree of the plating film increases, the unevenness of the plating surface increases and the surface roughness increases.

The lubrication-treated steel sheet of the present invention is one in which a chromate film is formed on the plating film of the GA steel plate, and a resin film containing wax and silica particles and containing no pigment is formed thereon. Even though the upper resin film is a clear type that does not contain pigments, the appearance of the resin film is darkened due to the coating with the resin film, the metallic luster of the GA steel sheet disappears, and a favorable gray color tone is obtained. Change.

The reason why the color tone changes in this way is that light is diffusely reflected by the unevenness of the plating surface of the underlayer and the optical path length in the resin becomes long, so that the proportion of light absorbed in the resin increases. It seems that the base metal GA steel sheet looks darker than when it is directly viewed.

In other platings such as electrogalvanizing plating and hot dip galvanizing plating, the surface is relatively smooth. Therefore, when coated with a chromate film and a transparent resin film, the color tone changes to darkening as described above. It is not allowed. That is, this change in color tone is peculiar to the plating film of the GA steel sheet whose surface roughness is increased by the heat treatment.

The color tone obtained by this darkening changes depending on the surface roughness of the plating film of the GA steel sheet. When the surface roughness becomes large, the darkening progresses and the color tone becomes darker. When the alloying degree of the plating film is 8% or less, the surface roughness is small and the unevenness of the surface of the plating film is insufficient, so that sufficient darkness cannot be obtained. However, the alloying degree of the plating film is 13
If it exceeds%, the color tone will be darker, but the unevenness of the surface will be too large and the plating film will become brittle, and as a result, the powdering phenomenon will easily occur during processing. When the degree of alloying of the GA steel sheet used as the base material is 8 to 13%, the workability is not deteriorated and the aforementioned 50 ≦ L ^* ≦ 62 and −1 ≦ a ^* ≦
It is possible to obtain a preferable gray color tone appearance defined by 0, -2≤b ^* ≤0.

The base GA steel sheet is a gray plate having a L ^* value, a ^* value and b ^* value within the above ranges when a chromate film and a resin film are formed on the plated surface according to the present invention. The color tone is not limited in that sense. However, as described above, when a GA steel sheet having an alloying degree of 8 to 13% is used as a base material, the above-described color tone is generally obtained. Therefore, when the colored lubricated steel sheet of the present invention is manufactured, such an alloying degree is obtained. It is sufficient to use the GA steel sheet as the base material. Since the higher the degree of alloying, the darker the color tone, the degree of alloying of the base GA steel sheet can be selected according to the desired color tone (darkness).

Since the alloying degree of the plating film of the GA steel plate correlates with the surface roughness as described above, instead of the alloying degree,
It is also possible to select the base GA steel plate by using the plating surface roughness of the GA steel plate as a scale. Generally, the surface roughness of the plating film is preferably within the range of Ra = 0.5 to 2.0 μm. Since the larger the surface roughness within this range is, the darker the color tone is, it is possible to select the base GA steel sheet by the plating surface roughness so as to obtain a desired color tone.

As described above, since the coloring of the colored and lubricated steel sheet of the present invention is not obtained by adding the coloring pigment to the resin film of the uppermost layer, there is no need to worry about the dispersibility and stability of the pigment. It is possible to obtain a uniform and stable color tone. Moreover, since an expensive coloring pigment is not used, it is advantageous in terms of cost.

The chromate film formed on the galvannealed galvanized surface (usually both surfaces, but may be one surface) may be a known ordinary chromate film, and the hexavalent chromium compound may be Cr ^{3 The} film is formed by being reduced to ⁺ and becoming insoluble. As the chromate treatment liquid, for example, an aqueous solution-type chromate treatment liquid containing a hexavalent chromium compound such as chromic anhydride, chromate salt, and dichromic acid as a main component, or a mixture of the above aqueous solution with colloidal silica is known. Any of these types can be used, and the treatment method is not particularly limited such as dipping, coating, electrolysis, and spraying. Especially preferred as a chromate film is a coating type chromate treatment liquid with excellent corrosion resistance, of which a partially reduced type (a part of Cr ⁶⁺ is reduced to Cr ³⁺ ) that enables rapid film formation is used. It was formed by. If necessary, heating is performed after the treatment to form a chromate film.

In the present invention, the amount of the chromate film deposited is 10 to 150 mg / m ^{2 in} terms of metallic Cr. If the adhesion amount is less than 10 mg / m ² , sufficient corrosion resistance as an exterior cannot be exhibited. On the other hand, if it exceeds 150 mg / m ² , the effect of improving the corrosion resistance with respect to the rate of increase in the amount of adhesion decreases, the surface appearance deteriorates, and the chromate film becomes thicker, causing cohesive failure of the chromate film during pressing. Occurs, and the press formability deteriorates.

A substantially transparent resin film containing no pigment is formed on the chromate film. This resin film contains 3 to 30% by weight of a polyolefin wax and 5 to 30% by weight of silica particles as SiO ₂ , and its adhesion amount is 0.1.
Within the range of up to 5 g / m ² .

Polyolefin wax as a lubricant,
In particular, it works effectively under severe processing conditions such that the mold becomes hot during continuous processing. The polyolefin wax may be any wax as long as it is composed of olefinic hydrocarbons such as polyethylene, polypropylene and polybutene, and two or more kinds of these may be used in combination. The polyolefin wax is preferably in the form of powder having a particle size of about 0.1 to 5 μm.

The content of the polyolefin wax in the resin film is in the range of 3 to 30% by weight. If the content of this wax is less than 3% by weight, the improvement of lubricity is little, and if it exceeds 30% by weight, the adhesion to the substrate is deteriorated.
The strength of the resin film decreases, and the appearance deteriorates significantly.

This resin film contains, in addition to the polyolefin wax, silica particles as SiO _{2 in} a proportion of 5 to 30% by weight. Silica in the resin film is 5% by weight as SiO _2.
If it is less than the above range, the corrosion resistance is insufficient and it is difficult to apply it as an exterior. On the other hand, if it exceeds 30% by weight, the hardness of the resin film is increased, and mold galling occurs during molding, resulting in deterioration of press moldability.

As the silica particles, colloidal silica is used.
(Aqueous silica), fumed silica (gas phase silica), and further organic silicates (eg, ethyl silicate) can be used. The particle size of silica particles is preferably about 1 to 100 nm. In addition, a silane coupling agent may be used in combination in order to improve the adhesiveness with the resin.

The base resin is not particularly limited as long as it can form an insoluble transparent film having sufficient strength and flexibility to withstand processing. Suitable resins include polyurethane resins, epoxy resins, acrylic resins, phenol resins, polyolefin resins, alkyd resins, melamine resins, polyvinyl butyral resins and the like. These resins may be used alone or in combination of two or more.

The amount of such a lubricating resin film deposited is in the range of 0.1 to 5 g / m ² as a dry weight. Adhesion amount is 0.1
When it is less than g / m ² , the effect of improving lubricity and corrosion resistance is small.
On the other hand, if it exceeds 5 g / m ² , the corrosion resistance is improved, but the press formability is lowered and the cost is increased. In particular, in order to obtain a good appearance even after processing, it is preferable that the adhesion amount is 1.0 g / m ² or more.

The resin coating composition used for forming the resin film contains 3 to 30% by weight of a polyolefin wax and 5 to 30% by weight of silica particles as SiO ₂ based on the total amount of nonvolatile components. The type of solvent may be water, alcohol, or an organic solvent, and is selected according to the type of resin used. You may add additives, such as a crosslinking agent and a defoaming agent, to this coating composition as needed. The drying temperature of the coating film after coating is selected according to the type of resin or solvent.

[0034]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited to the examples.

A hot dip galvanized steel sheet (board thickness 0.6 mm, double-sided plating, coating amount 45 g / m ² per side) produced in an existing hot-dip galvanizing line is changed in temperature and / or treatment time in a salt bath. Then, the steel sheets were dipped in and heat treated to produce GA steel sheets having different alloying degrees. A commercially available partial reduction coating type chromate treatment liquid was applied to one plating surface of each GA steel plate (300 × 200 mm) by a spin coater and dried at 80 ° C. for 30 seconds to form a chromate film. Next, on this chromate film, silica particles (colloidal silica with an average particle size of 20 nm) and polyethylene wax (average particle size of 1 μm) were used.
m) and a resin coating composition containing
After drying, apply the coating so that the specified adhesion amount is obtained, and apply at 120 ° C for 30
It was dried for 2 seconds to form a resin film.

Table 1 shows the alloying degree (Fe%) and surface roughness (Ra value) of the plating film of the base GA steel used, the amount of the chromate film deposited, the base resin of the resin film, and the silica in the resin film. The content of particles and polyethylene wax, and the amount of resin film attached are shown together.

Regarding the obtained colored and lubricated GA steel sheet,
The respective properties of color tone, corrosion resistance, lubricity, and post-processing corrosion resistance were examined in the following manner. [Test method] Color tone : Using a color difference meter (CR-300 manufactured by Minolta Co., Ltd.)
L ^* value, a ^* value, and b ^* value were measured. Corrosion resistance : Corrosion resistance was evaluated by the white rust generation time by a salt spray test (according to JIS Z-2371).

Lubricity : The friction coefficient by the Bowden friction test and the press formability by the hat forming test with beads were evaluated.

Bowden friction test: Using the measuring device shown in FIG. 1 (a), load 1 kg, sliding speed 4 mm / sec, sliding distance 20
The friction coefficient was measured under the condition of mm. Hat forming test with beads: Using a crank press with beads shown in FIG. 1 (b), 250 × 50 mm test pieces were deep-drawn into a hat shape. The bead height was 7 mm, the molding height was 43 mm, and the molding speed was 70 mm / sec. Observing the appearance of the ironing part of the molded product, ◎ (good, no change in appearance) →
The evaluation was made in four grades: ○ → △ → × (impossible, large galling, large powdering).

Corrosion resistance after processing : A test piece with a bending diameter of 10 mm
Bending was performed at 180 °, and then a salt spray test was performed in the same manner as the corrosion resistance to examine the white rust generation time.

[0041]

[Table 1]

[0042]

EFFECTS OF THE INVENTION In the colored lubricating zinc-plated steel sheet according to the present invention, the metallic luster of the GA steel sheet disappears and the appearance is calm, even though the resin coating of the uppermost layer is a transparent coating containing no coloring pigment. It is colored and has the same design as pre-coated steel sheets. Therefore, since it can be applied as it is to automobiles, home electric appliances, building materials, etc., it is possible to significantly reduce the cost of these products.

Further, since it is excellent in lubricity and can sufficiently withstand extreme pressure during strong working and temperature rise of the mold, it is possible to use a lubricating oil such as a press oil at the time of press working. It can be directly pressed. Therefore, it is possible to omit the press oil application work and the degreasing process for removing the press oil, which were conventionally performed by the customer, thereby reducing the cost and avoiding the use of harmful solvents such as trichloroethane. Therefore, it also leads to the prevention of environmental damage.

Further, since the steel sheet of the present invention is colored without using a pigment, the coloring is uniform and stable,
It is easy to apply the paint when forming the resin film, and it is inexpensive because no pigment is used. In addition, since the resin film is thin, desirable properties such as the weldability and press workability of the GA steel sheet are maintained, and high corrosion resistance can be exhibited even when subjected to processing. As described above, the steel sheet of the present invention is suitable for being used as it is for the exterior, but of course, it may be coated and used.

[Brief description of drawings]

FIG. 1 shows an apparatus used for evaluation of lubricity in Examples,
FIG. 1 (a) is an explanatory view of a Bowden friction tester used for measuring a friction coefficient, and FIG. 1 (b) is an explanatory view showing a shape of a crank press in a hat forming test with beads.

Claims (2)

[Claims] 1. A galvanized galvanized steel sheet has a chromate film with a Cr deposit of 10 to 150 mg / m ^{2 on} the plated surface, and 3 to 30 wt% of a polyolefin wax and silica particles are added to the SiO ₂ layer as an upper layer. 5 to 30% by weight, and has a resin coating of 0.1 to 5 g / m ² with no color pigment and has a surface color tone of JIS Z8729 L ^* a ^* b ^* color system of 50 ≦ L ^*. ≤
62, −1 ≦ a ^* ≦ 0, −2 ≦ b ^* ≦ 0. 2. An alloyed hot-dip galvanized steel sheet having an alloying degree of 8 to 13% is subjected to a chromate treatment to obtain a Cr adhesion amount of 10 on the plating surface.
~ 150 mg / m ² of chromate film is formed, and then polyolefin wax 3 ~ 30% by weight based on total nonvolatile content
And 5 to 30% by weight of silica particles as SiO ₂ and not containing a color pigment, to form a resin film having an adhesion amount of 0.1 to 5 g / m ² on the chromate film. A method for producing a zinc-based plated steel sheet subjected to a colored lubrication treatment.