JPH05263208A - Zinc-plated material and its production - Google Patents

Abstract

PURPOSE:To prevent the formation of corrosion products and discoloration and to enhance the resistance to acid and corrosion and adhesiveness to a coating film in a zinc-plated material. CONSTITUTION:An iron-base material is plated with molten zinc or a molten zinc alloy and then plated with chromium. Although many microcracks are usually present in a chromium plating film as the defective part, a chromium plated material having high corrosion resistance is obtained by the combination with the zinc-base plating film. A zinc-tin alloy, a zinc-aluminum alloy, etc., are used as the zinc alloy. The corrosion resistance is improved by heating after plating. Meanwhile, when a coating agent is applied on the chromium plating layer, the adhesiveness to the coating film is enhanced, and the corrosion resistance is further increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zinc-based plated coating coated with a hot-dip zinc or hot-dipped zinc alloy coating and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, steel products are hot dip galvanized in order to prevent corrosion. In addition, zinc-tin alloy plating, zinc-aluminum alloy plating, and the like are performed to further improve corrosion resistance. For example, Shokoku Sho 5
No. 2-19531, zinc 3-97% by weight, tin 9
A molten alloy plating method is disclosed in which 0.005 to 0.3% by weight of aluminum is added to a zinc-tin alloy consisting of 7 to 3% by weight, and hot dipping is performed. JP 63-1
No. 53253 discloses that zinc is 2 to 89% by weight and tin is 98 to
A zinc-tin based plating agent in which 0.0005 to 0.004% by weight of aluminum is added to a zinc-tin alloy consisting of 11% by weight is disclosed.

Further, Japanese Patent Laid-Open No. 57-35672 discloses a method of treating an iron-based base material with a flux, hot dip galvanizing and then hot dip zinc-aluminum alloy plating. Further, JP-A-1-38869 proposes plating a material to be plated having a high silicon content with a hot dip galvanizing bath containing a small amount of aluminum and nickel as a method for reducing the zinc adhesion amount. ing.

However, all zinc-based platings are sacrificial corrosion-proof platings, and corrosion products of so-called white rust and black rust are generated by corrosion of the plated coating itself. Further, if the zinc-based plated coating is left in the atmosphere, it will be discolored and the commercial value will be reduced.

Furthermore, the zinc-based plating film and its oxide are relatively easy to dissolve in acid. Therefore, if a zinc-based plated product is used outdoors, it will be eroded early by acid rain. Therefore, zinc-based plating is unlikely to be an effective corrosion protection against acid rain.

Further, since the surface hardness is relatively small, the zinc-based plated product is easily scratched, the material of the steel product is corroded, and red rust occurs. Further, since the friction coefficient is large, when it is applied to a threaded portion such as a joint, not only a tightening torque is required, but also it is easily damaged and corroded.

In order to solve these problems, it has been proposed to apply a paint on the zinc-based plating film. However, since the adhesion between the zinc-based plating film and the coating film is poor,
High corrosion resistance cannot be maintained for a long time.

[0008]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to prevent the formation and discoloration of corrosion products of a zinc-based plating coating, and to provide a zinc-based plating coating excellent in acid resistance and corrosion resistance, and the same. It is to provide a manufacturing method.

Another object of the present invention is to provide a zinc-based plated coating which exhibits high surface hardness and a small friction coefficient and is excellent in corrosion resistance, and a method for producing the same.

Still another object of the present invention is to provide a zinc-based plated coating having excellent adhesion to a coating film and exhibiting higher corrosion resistance, and a method for producing the same.

[0011]

As a result of intensive studies, the inventors of the present invention showed remarkably high corrosion resistance when a zinc-based hot dip plated layer and a chromium plated layer were formed in combination, and further showed higher corrosion resistance when heat treated after plating. The present invention was completed by discovering that the adhesiveness with the coating film and the corrosion resistance are further improved when the coating film is formed by coating a resin-containing coating agent on the chromium plating layer.

That is, the present invention provides a zinc-based plated coating in which an iron-based base material is sequentially coated with a zinc or zinc alloy layer and a chromium plating layer.

The present invention also provides a method for producing a zinc-based plated coating, which comprises subjecting an iron-based substrate to hot-dip zinc or hot-dip zinc alloy plating and then chromium plating.

The zinc alloy layer may be a zinc-tin alloy layer or a zinc-aluminum alloy layer. Further, it is preferable to heat-treat after plating, and it is preferable that a coating film is formed on the chromium plating layer.

It is known that a large number of microcracks are generated in the process of forming the chromium plating layer.
Since the microcracks function as defective portions, the corrosion resistance of the iron-based base material is significantly reduced. However, when the chrome-plated layer is formed in combination with the zinc-based hot-dip plated layer, both advantages are surprisingly exhibited, and a plated coating having high corrosion resistance can be obtained.

In the present specification, molten zinc and molten zinc alloy may contain unavoidable impurities such as lead, iron and cadmium unless otherwise specified.

The iron-based substrate applicable to the present invention is not particularly limited as long as it contains an iron component and can be hot-dipped. Preferred iron-based base materials include corrosive steel products such as steel plates, steel wires, steel strips, and castings; products that require a uniform and thin plating film to be formed, such as joints and bolts. -Steel products having an uneven surface such as nuts; steel products requiring acid resistance, scratch resistance and the like.

The iron-based base material is covered with a zinc-based plating layer. The zinc-based plating layer may be a zinc layer, but is preferably a zinc alloy layer from the viewpoint of corrosion resistance. The type of zinc alloy is not particularly limited, and various conventional zinc alloys, for example, zinc alloys containing at least one component of tin, aluminum, magnesium, nickel, copper, titanium, zirconium and sodium are exemplified.

Preferred zinc alloys include, for example, zinc-tin alloys, zinc-aluminum alloys and the like.

In the zinc-tin alloy, the ratio of zinc and tin is in a wide range, for example, zinc: tin = 2-98: 98-.
It can be selected in the range of 2 (parts by weight). A preferable zinc-tin alloy contains tin in an amount of 30% by weight or more, preferably about 50 to 70% by weight. The zinc-tin alloy may be an alloy containing 70 to 98% by weight, preferably 80 to 95% by weight of tin. When the zinc-tin alloy having such a composition ratio is used, as the tin content increases, a thin film can be formed, and the corrosion resistance as compared with the case of zinc alone,
Acid resistance and the like can be enhanced. The zinc-tin alloy may include at least one component such as aluminum, magnesium, nickel, copper, titanium, zirconium and sodium. The content of these components is, for example, about 0.01 to 5% by weight.

The zinc-aluminum alloy contains at least 0.5% by weight of aluminum, preferably at least 1% by weight, more preferably about 3 to 7% by weight. In order to further improve the corrosion resistance, the zinc-aluminum alloy is preferably an alloy containing at least 0.1% by weight or more, and preferably 0.2 to 2% by weight of magnesium in addition to the above aluminum. Zinc-aluminum alloys are generally more corrosion resistant than zinc-tin alloys. The zinc-aluminum alloy contains at least one component such as tin, magnesium, nickel, copper, titanium, zirconium and sodium, for example, 0.0
You may contain about 1-5 weight%.

The zinc or zinc alloy layer is not limited to a single layer and may be composed of a plurality of layers. For example, hot dip galvanizing on an iron-based base material, or hot dip zinc containing a large amount of zinc-
Tin alloy plating (for example, zinc content of 30 to 60% by weight,
After the hot dip zinc-tin alloy plating of preferably 35 to 50% by weight, the hot dip zinc-tin alloy plating having a high tin content (for example, the tin content 99 to 70 parts by weight, preferably 98 to 80% by weight). % Hot dip zinc-tin alloy plating). In addition, when the aluminum content of the zinc-aluminum alloy is increased, the wettability with respect to the iron-based base material is lowered, and an unplated portion is likely to be formed. In such a case, zinc or zinc alloy plating with an aluminum content of less than 0.5% by weight (preferably an aluminum content of 0.001 to
0.1% by weight, particularly 0.001 to 0.05% by weight of zinc or zinc alloy plating) may be applied, and the zinc-aluminum alloy plating may be applied.

Further, in the case of thinning the zinc or zinc alloy layer, as disclosed in JP-A-3-229846, a molten zinc-nickel alloy (for example, nickel content of 0. 01-1.0% by weight, preferably 0.05-0.5% by weight, especially 0.1-0.3% by weight
Hot dip galvanizing) or electroless nickel plating, and then the hot dip zinc or hot dip zinc alloy plating may be applied at least once.

The thickness of the zinc or zinc alloy layer may be in the range that does not impair the corrosion resistance, and is, for example, 5 to 75 μm,
Preferably 10 to 50 μm, more preferably 10 to 3
It is about 0 μm. Thickness of molten zinc or alloy layer is 5μm
If it is less than 75 μm, the corrosion resistance tends to be lowered, and if it exceeds 75 μm, the film thickness becomes too large, which is not economical and dross is likely to occur.

Such a molten zinc layer or molten zinc alloy layer can be formed by a conventional method. The iron-based substrate is usually subjected to a conventional pretreatment such as degreasing treatment or acid cleaning treatment prior to hot dipping.

Hot-dip plating can be carried out by immersing the iron-based base material in a hot-dip zinc bath or a hot-dip zinc alloy bath. The bath temperature and immersion time can be appropriately set according to the desired thickness of the plating layer, workability, and the like. The temperature of the bath can be selected according to the composition of the bath, and is usually the melting temperature + 20 ° C. or higher.

More specifically, molten zinc bath and molten zinc-
The temperature of the nickel alloy bath is usually 350 to 500 ° C, preferably about 430 to 480 ° C. Although the temperature of the molten zinc-tin alloy bath varies depending on the tin content, it is usually 22
The temperature is 0 to 450 ° C, preferably about 250 to 400 ° C. The temperature of the molten zinc-aluminum alloy bath also varies depending on the aluminum content, but is usually 400-5.
The temperature is 00 ° C, preferably about 420 to 460 ° C. The immersion time is, for example, about 1 second to 5 minutes, preferably about 15 seconds to 2 minutes.

The hot dip galvanizing may be performed in combination with the hot dip galvanizing and hot dipping zinc alloy plating, or the hot dipping zinc alloy plating having different compositions may be performed in combination.

When hot-dip plating is performed a plurality of times, the temperature of the second bath is set to the first bath in order to prevent the film formed by the hot-dip of the first bath from being eluted in the hot-dip bath of the second bath. It is preferable that the temperature is lower than the temperature.

When the iron-based base material is subjected to electroless nickel plating and hot-dip plated, the electroless nickel plating layer is formed by a conventional electroless plating method such as nickel chloride.
Immersion treatment in an electroless plating solution containing a nickel salt such as nickel sulfate or nickel nitrate and a reducing agent such as hypophosphite, borohydride compound, hydrazine, formaldehyde, glucose, tartaric acid, etc. It can be formed by depositing nickel on the surface. Further, in the electroless plating treatment bath, for example, sodium acetate, propionic acid,
Lactic acid, ammonium chloride, ammonium sulfate, sodium malonate, ethylenediamine, sodium hydroxide and the like may be added.

The thickness of the nickel plating layer can be appropriately set, and is, for example, 0.01 to 5 μm, preferably 0.05 to
2.5 μm, more preferably 0.1 to 1 μm is sufficient.

The iron-based base material on which the electroless nickel plating layer is formed may be treated with a flux containing ammonium chloride or zinc chloride and then subjected to the same hot-dip galvanizing or hot-dip zinc alloy plating as described above.

The zinc-based plating layer is covered with a chrome plating layer. Unlike other electroplating layers, this chrome plating layer produces many defects such as microcracks even if the thickness of the plating layer is increased to about 100 μm. Therefore, even if chromium plating is applied, the corrosion resistance is not usually improved, and red rust is generated from the iron-based base material within a short time. However, when the chromium plating layer is formed in combination with the zinc-based plating layer, the corrosion resistance is significantly improved even if microcracks are present in the chromium plating layer. It is presumed that this is because a chromate film is formed below the microcracks during chrome plating, or the microcracks are closed by zinc oxide whose volume has expanded due to oxidation.

Further, by applying chrome plating, it is difficult for the color to change in the atmosphere, it is resistant to acids such as sulfuric acid, the surface hardness is high, and the friction coefficient is small.

The thickness of the chrome-plated layer may be in the range that does not impair the corrosion resistance, and is, for example, 0.1 to 50 μm.
Preferably 0.5 to 10 μm, more preferably 1 to 5
It is about μm. When the thickness of the chrome plating layer is less than 0.1 μm, the corrosion resistance is not improved so much, and when it exceeds 50 μm, the productivity is likely to decrease.

The chrome plating can be performed by a conventional method. Prior to the chrome plating, the plated coating may be subjected to a degreasing treatment with an organic solvent, an alkali immersion, an alkaline electrolytic degreasing or the like, or a pickling treatment with an acid such as hydrochloric acid or sulfuric acid, if necessary. Further, if necessary, after masking the non-plated portion, an etching treatment by anodic oxidation may be performed.

The composition of the chrome plating bath is not particularly limited,
Conventional plating baths can be used. The plating bath, for example, chromic acid anhydride CrO _3, Sargent bath containing sulfuric acid; chromic acid anhydride CrO _3, in addition to sulfuric acid, may be a silicofluoride bath including silicofluoride sodium or fluorosilicate of potassium reduction. Further, the chromium plating bath may contain at least one component such as silicofluoric acid, ammonium fluoride, strontium sulfate, citric acid, tartaric acid, oxalic acid and formic acid. Usually, the plating bath often contains about 0.1 to 3 g / L of trivalent chromium.

For example, the ratio of chromic anhydride and sulfuric acid in a commonly used Sargent bath is usually chromic anhydride: sulfuric acid = 100: 0.7 to 1.5 (g / L), preferably 100: 0. It is about 8 to 1.5 (g / L). The plating bath may be a high-concentration bath, a standard bath, or a low-concentration bath, and the chromic anhydride concentration is usually 100 to 4
The amount is 00 g / L, preferably 150 to 350 g / L, and more preferably 200 to 300 g / L.

In the chrome plating, a lead alloy, iron or the like can be appropriately arranged and used as an anode, and an auxiliary cathode, a shielding plate or the like can be used in order to make the plating layer uniform.

The plating conditions can be selected according to the composition of the bath, etc., and the plating temperature is usually 20 to 70 ° C., preferably 40.
˜65 ° C., current density 10˜100 A / dm ² , preferably 30˜75 A / dm ² . The plating time can be selected according to the bath temperature, current efficiency, desired plating film thickness, and the like.

Further, it is preferable to perform heat treatment after the chrome plating. The heat treatment further improves the corrosion resistance of the iron-based base material.

The heat treatment can be carried out by a conventional method, for example, baking by using an electric furnace or the like, or induction heating such as high frequency heating. The heating temperature for heat treatment by baking is, for example, 100 to 300 ° C., preferably 150 to 25.
It is about 0 ° C. In the case of high frequency heating, the heat treatment is usually performed at a surface temperature corresponding to the above-mentioned temperature in the baking treatment. The heating time can be appropriately selected depending on the heating temperature, the heating method, the plating film thickness, etc., but is usually 0.5 to 24 hours, preferably about 1 to 15 hours. After the heat treatment, the plated product may be buffed.

Further, it is preferable that a coating film is formed on the chromium plating layer. When a coating film is formed on the chrome plating layer, the adhesion of the coating film and the corrosion resistance of the iron-based base material are significantly improved.

The coating film can be composed of a coating film containing a resin capable of forming a coating film. The resin includes, for example, a thermoplastic resin and a thermosetting resin. Examples of the thermoplastic resin include olefin polymers such as polyethylene and polypropylene, acrylic polymers, styrene polymers, chlorine-containing polymers such as polyvinyl chloride, and fluorine-containing polymers such as polytetrafluoroethylene.
Examples thereof include polyvinyl acetate, ethylene-vinyl acetate, polyester, polyvinyl acetal, polyamide and polycarbonate. As the thermosetting resin, for example, thermosetting acrylic polymer, epoxy resin, epoxy ester resin, unsaturated polyester, alkyd resin, phenol resin, furan resin, urea resin, melamine resin, diallyl phthalate resin, polyurethane, polyimide, Silicone resin etc. are mentioned. Further, the resin may be a light curable resin such as an ultraviolet curable resin or an electron beam curable resin. At least one of these resins is used. Among these resins, fluorine-containing polymers, acrylic polymers, polyesters, thermosetting resins, etc. are frequently used.

The coating film may contain additives such as a plasticizer, a dispersant, a colorant, an antioxidant, an ultraviolet absorber, a filler, a rust preventive and a reinforcing agent.

The thickness of the coating film is not particularly limited as long as it can form a uniform coating film, for example, 1 μm or more.
The thickness of the coating film is usually 5 to 100 μm, preferably 10
˜80 μm, more preferably about 15 to 50 μm. The coating film may be formed of two or more coating films of the same kind or different kinds.

The coating film can be formed by coating a plated product with a coating agent containing a resin. The type of coating agent is not particularly limited, and for example,
It may be any of water-based paints, solvent-based paints, powder paints, and light-curable paints.

The water-based or solvent-based paint contains a solvent such as water, alcohols, aliphatic hydrocarbons, aromatic hydrocarbons, esters, ketones, ethers, etc., depending on its type. Further, it may further contain an antifoaming agent, a viscosity modifier, a surfactant, a leveling agent, the above various additives and the like.

In the coating step, a conventional coating method, for example,
Dipping, roll coating, spray coating, etc. can be adopted.

After the coating agent is applied, it may be subjected to a conventional baking process depending on the kind of the coating material.

[0051]

EFFECTS OF THE INVENTION Since the zinc-based plated coating of the present invention has the zinc or zinc alloy layer and the chromium plated layer formed in this order, it is possible to prevent the formation and discoloration of corrosion products of the zinc-based plated coating. Excellent in acid resistance and corrosion resistance. Also, since the zinc-based plated coating is coated with a chrome-plated layer, it can prevent damage due to its high surface hardness, exhibits a small coefficient of friction, and when applied to threaded parts such as joints, tightly tightens with a small tightening torque. It can be fastened and the sealing property can be improved.

The zinc-based plated coating having a coating film formed on the chromium plating layer has excellent adhesion to the coating film and exhibits high corrosion resistance.

According to the production method of the present invention, it is possible to obtain a zinc-based plated coating having the above-mentioned excellent properties.

[0054]

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples. In the following examples and comparative examples, the iron-based base material was 50 mm × 80 mm × 3.
A 2 mm SS steel plate was used.

Comparative Example 1 The above steel sheet was degreased and acid washed with hydrochloric acid,
It was immersed in an aqueous solution flux containing 30 g / L of zinc chloride and 100 g / L of ammonium chloride for flux immersion treatment. Then, it was immersed in a hot dip zinc bath at 460 ° C. for 1 minute to form a hot dip galvanized film having a film thickness of 50 to 60 μm.

Comparative Example 2 The above steel sheet was subjected to degreasing treatment, acid cleaning treatment, as in Comparative Example 1,
After the flux dipping treatment, it was dipped in a molten zinc-tin alloy bath containing 40% by weight of zinc and 60% by weight of tin at 390 ° C. for 1 minute to form a molten zinc alloy plating film having a film thickness of 15 to 20 μm.

Comparative Example 3 After degreasing and acid cleaning the same as in Comparative Example 1, the steel plate was subjected to a chromium plating bath containing 250 g / L of CrO _{3 and} 2.5 g / L of sulfuric acid at a bath temperature of 50 ° C. and an initial current. Density 60
A / dm ² for 1 minute, then current density 35 A / dm ²
For 10 minutes to form a chrome-plated film having a film thickness of 3 to 4 μm.

Example 1 In the same manner as in Comparative Example 1, a hot-dip galvanized coating having a film thickness of 50 to 60 μm was formed on a steel sheet, and then, in the same manner as in Comparative Example 3, degreasing treatment and acid cleaning treatment were performed to obtain a film thickness. A chrome-plated film of 3 to 4 μm was formed.

Example 2 A hot-dip zinc alloy plating film having a film thickness of 15 to 20 μm was formed on a steel sheet in the same manner as in Comparative Example 2, and then degreasing treatment and acid cleaning treatment were performed in the same manner as in Comparative Example 3. A chromium plating film having a thickness of 3 to 4 μm was formed.

Comparative Example 4 In the same manner as in Comparative Example 1, a hot-dip galvanized film having a film thickness of 50 to 60 μm was formed on a steel sheet, and then a fluororesin-based paint was spray-coated and baked at 190 ° C. for 20 minutes to form a film. A coating film having a thickness of 20 to 30 μm was formed.

Comparative Example 5 In the same manner as in Comparative Example 2, after forming a molten zinc alloy plating film having a film thickness of 15 to 20 μm on a steel sheet, a fluororesin-based paint was spray coated and baked at 190 ° C. for 20 minutes, A coating film having a film thickness of 20 to 30 μm was formed.

Example 3 In the same manner as in Example 1, a hot dip galvanized film having a film thickness of 50 to 60 μm and a chrome plated film having a film thickness of 3 to 4 μm were sequentially formed, and then a fluororesin-based paint was spray-coated, Baking at 190 ℃ for 20 minutes, film thickness 20-30μ
m coating film was formed.

Example 4 In the same manner as in Example 2, a hot dip galvanized film having a film thickness of 15 to 20 μm and a chrome plated film having a film thickness of 3 to 4 μm were sequentially formed, and then fluororesin-based paint was spray-coated, Baking at 190 ℃ for 20 minutes, film thickness 20-30μ
m coating film was formed.

Example 5 In the same manner as in Example 1, a hot-dip galvanized film having a film thickness of 50 to 60 μm and a chrome plated film having a film thickness of 3 to 4 μm were sequentially formed on a steel sheet, and then baked at 180 ° C. for 4 hours. I went.

Example 6 In the same manner as in Example 2, a hot-dip zinc alloy plating film having a film thickness of 15 to 20 μm and a chromium plating film having a film thickness of 3 to 4 μm were sequentially formed on a steel sheet, and then baked at 180 ° C. for 4 hours. Processed.

The samples obtained in the above Examples and Comparative Examples were subjected to a salt spray test according to JIS Z 2371, and the corrosion resistance was evaluated by the time until white rust and red rust were generated. The salt spray test was conducted under the following conditions.

Sodium chloride concentration 50 g / L Spray room temperature 35 ± 1 ° C. Spray amount 1 ml / hr Further, for the samples of Comparative Examples 4 and 5 and Examples 3 and 4, the coating film was cross-cut to 1 mm cross-cut. Was subjected to a cross-cutting test and subjected to the salt spray test, and the adhesion of the coating film was evaluated by the time until blister (blister of the coating film) occurred. The results are shown in the table.

[0068]

[Table 1] From the table, the zinc-based plated coatings of the respective examples have significantly higher corrosion resistance and coating film adhesion than the zinc-based plated coatings of the comparative examples. In addition, the heat-treated product after plating is more excellent in corrosion resistance.

Claims (6)

[Claims] 1. A zinc-based plated article in which an iron-based substrate is sequentially coated with a zinc or zinc alloy layer and a chrome-plated layer. 2. The zinc-based plated coating according to claim 1, wherein the zinc alloy layer is a zinc-tin alloy layer containing at least zinc and tin, or a zinc-aluminum alloy layer containing at least zinc and aluminum. 3. The zinc-based plated coating according to claim 1, wherein a coating film is formed on the chromium plating layer. 4. A method for producing a zinc-based plated coating, which comprises subjecting an iron-based base material to hot-dip zinc or hot-dip zinc alloy plating and then chromium plating. 5. The method for producing a zinc-based plated article according to claim 4, wherein heat treatment is performed after chrome plating. 6. The method for producing a zinc-based plated coating according to claim 4, further comprising coating with a resin-containing coating agent after plating with chromium.