KR100627029B1 - Treating solution for forming black hexavalent chromium-free chemical coating on zinc or zinc alloy plated substrate, and method for forming black hexavalent chromium-free chemical coating on zinc or zinc alloy plated substrate - Google Patents

Abstract

It is an object of the present invention to provide a processing solution used for forming a hexavalent chromium free, black conversion film, which is applied onto the surface of zinc or zinc alloy plating layers, and which has corrosion resistance identical to or higher than that achieved by the conventional hexavalent chromium-containing conversion film. <??>According to an aspect of the present invention, there is provided a processing solution for forming a hexavalent chromium free, black conversion film on zinc or zinc alloy plating layers, the processing solution comprising: nitrate ions and trivalent chromium in a mole ratio (NO<3->/Cr<3+>) of less than 0.5/1, wherein the trivalent chromium is present in the form of a water-soluble complex with a chelating agent; and cobalt ions and / or nickel ions, wherein the cobalt ions and / or nickel ions are stably present in the processing solution without causing any precipitation by forming a hardly soluble metal salt with the chelating agent; wherein the solution reacts with zinc when it is brought into contact with the zinc or zinc alloy plating to form a hexavalent chromium free, black conversion film containing zinc, chromium, cobalt and / or nickel, and the chelating agent on the plating.

Description

Treatment solution for forming a black hexavalent chromium-free chemical conversion film on zinc and zinc alloy plating, and a method for forming a black hexavalent chromium-free chemical conversion film on zinc and zinc alloy plating. hexavalent chromium-free chemical coating on zinc or zinc alloy plated substrate, and method for forming black hexavalent chromium-free chemical coating on zinc or zinc alloy plated substrate}

The present invention relates to a treatment solution for forming a black hexavalent chromium-free chemical conversion film on zinc and zinc alloy plating and a method for forming a black hexavalent chromium-free chemical conversion film.

As a method of preventing corrosion of metal surfaces, there is a method of performing zinc and zinc alloy plating, but plating alone is not sufficient in corrosion resistance, and after plating, chromic acid treatment containing hexavalent chromium, so-called chromate treatment Is widely used in the industry. However, in recent years, it has been pointed out that hexavalent chromium adversely affects the human body and the environment, and there is an active movement regulating the use of hexavalent chromium.

One alternative technique is a corrosion resistant film using trivalent chromium. For example, Japanese Patent Laid-Open No. 63-015991 discloses a method in which trivalent chromium and metal salts such as fluoride, organic acid, inorganic acid and cobalt sulfate are mixed and treated. However, this bath is environmentally problematic because it uses fluoride. Further, Japanese Patent Application Laid-open No. 03-010714 discloses a method of mixing and treating trivalent chromium and metal salts such as an oxidizing agent, an organic acid, an inorganic acid, and cerium. In this method, since an oxidant and cerium are used, there is a possibility that trivalent chromium is oxidized to hexavalent chromium.

In Japanese Patent Laid-Open No. Hei 10-183364, a hexavalent chromium-free corrosion-resistant treatment containing phosphoric acid, metal salts such as Mo, Cr ³⁺ , Ti and the like and an oxidizing agent is proposed. Since this method also uses a large amount of oxidizing agent, there is a possibility that trivalent chromium is oxidized to hexavalent chromium.

Japanese Patent Laid-Open No. 2000-54157 proposes a chemical conversion treatment containing metals such as phosphorus, Mo, and trivalent chromium, and containing no fluoride. However, as a result of our confirmation test, satisfactory corrosion resistance could not be reproduced.

Further, Japanese Patent Laid-Open No. 2000-509434 discloses a method of treating using trivalent chromium 5 to 100 g / L, metal salts such as nitrate residues, organic acids, and cobalt. This method has the advantage of having a high trivalent chromium concentration and the like and having a high temperature treatment so that a thick film can be obtained and a good corrosion resistance can be obtained, but since it is difficult to form a stable and dense film, stable corrosion resistance is not obtained. There is a flaw. In addition, since the concentration of trivalent chromium in the treatment bath is high, and organic acids are also used in large amounts, drainage treatment is difficult, and the sludge produced after the treatment is also enormous. The environmental advantages of not using hexavalent chromium in the treatment liquid are acknowledged, but on the other hand, they pose a significant drawback because they create a new environmental burden of generating a large amount of waste.

In addition, the external appearance of the coating was obtained only by a colorless or interference color external appearance. In addition, a black chemical conversion film of zinc-nickel (Ni% in the film is 8% or more) and trivalent chromium on zinc-iron is treated in an acidic aqueous solution of a phosphoric acid compound and trivalent chromium in US Pat. It is proposed how to. In addition, as for the interference-chromic coating of zinc-nickel (Ni% in the film is 8% or more) trivalent chromium, in US Pat. No. 5,077,49, the acid containing phosphorus compound, trivalent chromium and halide ion is similarly used. The method of treatment in aqueous solution is shown.

However, the Ni vacancy rate of zinc-nickel alloy plating actually produced is often less than 8%, and there is a practical problem in obtaining a black appearance. Moreover, sufficient corrosion resistance is not acquired about zinc-iron alloy plating.

In addition, US Pat. No. 4,578,122 proposes a method of treating with low concentrations of trivalent chromium and metal salts such as organic acids and nickel, and US Pat. No. 5,368655 proposes a method of treating with low concentrations of trivalent chromium and organic acids. However, these methods do not have sufficient corrosion resistance compared with conventional chromates.

An object of the present invention is to provide a treatment solution for forming a black hexavalent chromium-free chemically resistant film having a corrosion resistance equal to or higher than that of a conventional hexavalent chromium-containing film on zinc and zinc alloy plating.

Another object of the present invention is to provide a method for forming a black hexavalent chromium-free chemical conversion film.

The present invention precipitates zinc or zinc alloy plating on a substrate, and then performs trivalent chromate treatment using a treatment solution having a specific composition containing low concentrations of acetic acid ions, cobalt ions, and nickel ions. It is based on the knowledge that the task can be solved efficiently.

That is, the present invention is a treatment solution for forming a black hexavalent chromium-free chemical conversion film on zinc and zinc alloy plating,

The molar ratio of nitrate ions to trivalent chromium (NO _{3 ⁻} / Cr ³⁺ ) is less than 0.5,

Trivalent chromium is present in the form of a water-soluble complex with a chelating agent,

At least one of cobalt ions and nickel ions,

At least one of cobalt ions and nickel ions forms a poorly soluble metal salt with a chelating agent and does not precipitate, but is stably present in the treatment solution,

When zinc and zinc alloy plating are brought into contact with the treatment solution, they react with zinc to form a zinc hexavalent chromium-free chemical conversion film containing zinc and chromium, at least one of cobalt and nickel, and a chelating agent. It provides to the said process solution characterized by forming on alloy plating.

The present invention also provides a method for forming a black hexavalent chromium-free chemically convertible coating, which is characterized in that zinc and zinc alloy plating are brought into contact with the treatment solution.

Examples of the substrate used in the present invention include various metals such as iron, nickel, and copper, alloys thereof, and plate-shaped objects, such as cuboids, cylinders, cylinders, and spheres of metals or alloys such as aluminum subjected to zinc substitution treatment. And various shapes.

The substrate is subjected to zinc and zinc alloy plating by a conventional method. Precipitation of zinc plating on the gas may be an acidic bath such as a sulfuric acid bath, an ammonium chloride bath or a potassium chloride bath, an alkali bath such as an alkali non-cyanide bath or an alkali cyanide bath. And an alkali non-cyanide plating bath (NZ-98 bath made by Dipsol Corporation) are preferable.

Examples of zinc alloy plating include zinc-iron alloy plating, zinc-nickel alloy plating with a nickel vacancy rate of 5 to 20%, zinc-cobalt alloy plating, and tin-zinc alloy plating. Although the thickness of the zinc or zinc alloy plating which precipitates on a base can be arbitrary, it is good to set it as 1 micrometer or more, Preferably it is 5-25 micrometers in thickness.

In the present invention, in this way, after depositing zinc or zinc alloy plating on the substrate, if necessary, after treatment with water or after washing with nitric acid, the treatment for forming the black hexavalent chromium-free chemically usable film of the present invention is performed. The solution is contacted, for example, using this treatment solution to perform an immersion treatment.

In the treatment solution of the present invention, any chromium compound including trivalent chromium may be used as a source of trivalent chromium, but preferably trivalent chromium salts such as chromium chloride, chromium sulfate, chromium nitrate, chromium phosphate, and chromium acetate It is also possible to reduce hexavalent chromium, such as chromic acid and dichromate, to trivalent using a reducing agent. A particularly preferred source of trivalent chromium is chromium phosphate (Cr (H _n PO ₄ ) _{(3 / (3-n))} ), where n = 0, 1, 2. The source of the trivalent chromium may be one kind or two or more kinds. There is no limitation on the concentration of trivalent chromium in the treatment solution. It is preferable to make it as low as possible from a viewpoint of waste water treatment property, but 0.5-10 g / L is preferable in consideration of corrosion resistance, and 0.8-5 g / L is a more preferable density | concentration. When trivalent chromium is used in this low concentration range in the present invention, it is advantageous both economically and in terms of drainage treatment.

The treatment solution of the present invention contains nitrate ions in a molar ratio of nitrate ions to trivalent chromium (NO ₃ ⁻ / Cr ³⁺ ) of less than 0.5, preferably in the range of 0.02 to 0.25. Preferred nitrate concentrations are from 0.1 to 1 g / L. As a source of nitric acid ion, nitric acid or its salt is mentioned.

Examples of the chelating agent used in the treatment solution of the present invention include hydroxycarboxylic acids such as tartaric acid and malic acid, monocarboxylic acid, oxalic acid, malonic acid, and succinic. dicarboxylic acids such as acid), citric acid, adipic acid, or polycarboxylic acids such as tricarboxylic acid, aminocarboxylic acids such as glycine, and the like. Moreover, 1 type, or 2 or more types of these acids or its salt (for example, salts, such as sodium, potassium, ammonium) can be used as a chelating agent. The concentration in the treatment solution is preferably 1 to 40 g / L in total, more preferably 5 to 35 g / L.

The molar ratio (chelating agent / Cr ³⁺ ) of the chelating agent to trivalent chromium in the treatment solution of the present invention is preferably 0.2 to 4, more preferably 1 to 4.

The treatment solution of the present invention contains at least one of cobalt ions and nickel ions. As a source of cobalt ions and nickel ions, any metal compound containing such a metal can be used. Although these metal compounds may use 1 type, or 2 or more types, Preferably, 1 or more types of metal salts of cobalt and nickel are used, respectively. It is preferable to contain 0.1-2 g / L in total in the process solution, More preferably, it is 0.5-1.5 g / L.

In addition, the treatment solution of the present invention is a metal such as 1 to 6-valent metal ions such as silicon, iron, titanium, zirconium, tungsten, vanadium, molybdenum, strontium, niobium, tantalum, manganese, calcium, barium, magnesium, aluminum, and the like. It may contain ions. You may add 1 type (s) or 2 or more types of said metal ion to the process solution of this invention. As the source of the metal ions, any metal compound containing the metal can be used. Preferably, nitrate, sulfate, or chlorine salt is used. The said metal compound may use 1 type (s) or 2 or more types. The concentration in the treatment solution is preferably 0.05 to 3.0 g / L in total, and more preferably 0.1 to 2.0 g / L.

Chelating agents, such as trivalent chromium and oxalic acid, exist in the treatment solution to form stable water-soluble complexes that are believed to have the following general formula, and metal ions such as cobalt do not precipitate by forming soluble chelating agents and metal salts. It needs to be stable.

[(Cr) _ℓ (A) _m ] ^3ℓ-mn

(Wherein A represents a chelating agent and n represents the valence of the chelating agent.)

For example, when the above stable chromium complex is not formed or when chelating agents such as oxalate ions are contained in the treatment solution, metal ions such as cobalt are free in the treatment solution. ) React with chelating agents to produce poorly soluble precipitates. As a result, a chemical resistant film with good corrosion resistance cannot be obtained.

In order to obtain a favorable black film, it is preferable that the molar ratio (m / L) of trivalent chromium and a chelating agent is in the range of 0.2-4.

Further, better black appearance can be obtained by adding phosphate ions to the treatment solution. Examples of the source of phosphate ions include oxygen acids of phosphorus such as phosphoric acid and phosphorous acid, and salts thereof. These may use 1 type, or 2 or more types. It is preferable that the density | concentration of a phosphate ion is 0.1-50 g / L, More preferably, it is 5-25 g / L.

Further, at least one of sulfate ions, halogen ions, and borate ions may be added to the treatment solution. Examples of the source of these ions include sulfuric acid, hydrochloric acid, boric acid and inorganic salts thereof. It is preferable that the density | concentration of these inorganic acid ion is 1-50 g / L in total, More preferably, it is 1-20 g / L.

It is preferable that pHs of the process solution of this invention are 0.5-4, More preferably, it is 2-3. In order to adjust pH in this range, the said inorganic acid ion may be used, and alkali chemicals, such as alkali hydroxide and ammonia water, may be used.

The remainder of the above components in the treatment solution used in the present invention is water.

When zinc and zinc alloy plating are brought into contact with the treatment solution of the present invention, it is reacted with zinc as is assumed below, and a black hexavalent chromium-free chemical conversion film is formed on the zinc and zinc alloy plating.

As a method of bringing the zinc and zinc alloy plating of the present invention into contact with the treatment solution, it is common to immerse the zinc and zinc alloy plating in the treatment solution. For example, it is preferable to immerse for 5 to 600 second at 10-80 degreeC, More preferably, it is 40-60 degreeC liquid temperature, More preferably, it is immersed for 30 to 120 second.

In order to activate the surface, the object to be treated may be dipped in a dilute nitric acid solution before the chromate treatment.

Conditions and treatment operations other than the above can be carried out in accordance with the conventional chromate treatment method.

In addition, by aging (heating) the chromate treated film, the corrosion resistance of the film can be further improved. In particular, the effect is high in zinc-nickel alloy plating. The conditions of the aging treatment are 100 to 250 ° C. for 10 to 300 minutes. Preferably it is 10 to 300 minutes at 150-200 degreeC. More preferably, an aging process is performed at 200 degreeC for 4 hours.

Moreover, by overcoat (topcoat) treatment on the black hexavalent chromium-free chemical conversion film of this invention, corrosion resistance can be improved once again and it is a very effective means to make it more corrosion resistant. For example, first, the trivalent chromate treatment is performed on zinc and zinc alloy plating, followed by immersion treatment or electrolytic treatment with an overcoat treatment liquid after washing with water, followed by drying. Moreover, after trivalent chromate treatment drying, it is also possible to dry, after immersion treatment or electrolytic treatment with an overcoat process liquid newly. Here, the overcoat is not only inorganic coatings such as silicates and phosphates, but also polyethylene, polyvinyl chloride, polystyrene, polypropylene, methacryl resin, polycarbonate, polyamide, polyacetal, fluorine resin, urea resin, phenol resin, and unsaturated. Organic coatings such as polyester resins, polyurethanes, alkyd resins, epoxy resins and melamine resins are also effective.

As an overcoat process liquid for implementing such an overcoat, the dipcoat W, CC445, etc. made by a dip sole Corporation can be used, for example. Although the thickness of an overcoat film can be arbitrary, it is good to set it as 0.1-30 micrometers.

Reaction mechanism of film formation:

The reaction mechanism of black hexavalent chromium-free chemical conversion film formation of this invention can be estimated as follows.

(1) dissolution reaction of Zn, Fe, Ni, etc. from the coating film by the action of oxidizing agents such as hydrogen ions and nitric acid, supply of metal ions such as zinc to the plating table system and reuse of deposits Harm reaction.

(2) Consumption of hydrogen ions and pH rise at the surface to be plated.

Zn → Zn ²⁺ + 2e-, 2H ⁺ + 2e- → 2H, 2H + 1 / 2O ₂ → H ₂ O (pH rise)

(3) Decreasing the stability of the chelating agent accompanying the increase in pH, formation and deposition of Cr hydroxide, and generation and supply of excess oxalic acid.

(4) Generation and deposition of insoluble metal salts by reaction of metal ions in excess chelate bath.

For example, when the chelating agent is oxalic acid and the metal is cobalt:

[CrC ₂ O ₄ · (H ₂ O) ₄ ] ⁺ → Cr (OH) ₃ ↓ + C ₂ O ₄ ^2- + 3H ⁺ + H ₂ O

C ₂ O ₄ ^2- + Co ²⁺ → CoC ₂ O ₄ ↓

⑤ Forming, adsorption and plating of insoluble metal salts by reaction with anions such as phosphoric acid in the bath and metal ions such as zinc, Fe and Ni eluted from the plating film or Ni, Co and Fe added in the bath. Deposition of other insoluble substances that form upon dissolution of the coating.

For example, when phosphate ions are added to the bath:

X _m Y _n (H ₂ PO ₄ ) ₂ → X _m Y _n (PO ₄ ) ₂ 4H ₂ O ↓

M + n = 3, X, Y: metal ions such as zinc, iron, nickel and manganese

⑥ 화 Martian film grows by repetition of these reactions.

Here, it is thought that the black chemical film is a composite film of (3), (4) and (5).

In the concentration range (0.1-1 g / L) where nitrate ion concentration is suitable, the redissolution reaction of substance (5) is suppressed, and insoluble substance (5) is taken into a film, and it is thought that it shows black appearance.

(Examples 1 to 6)

Using a NZ-98 bath manufactured by Dipsol Co., Ltd., the zinc plated zinc plated with a thickness of 8 µm was immersed in the trivalent chromate treatment solution shown in Table 1.

Example One 2 3 4 5 6 Cr ³⁺ (g / L) 4.5 4.5 4.5 4.5 4.5 2 NO ₃ ^- (g / L) 0.2 0.4 0.1 0.4 0.6 0.4 NO ₃ ^- / Cr ³⁺ molar ratio of 0.04 0.07 0.02 0.07 0.11 0.17 PO ₄ ^3- (g / L) 12 12 0 15 12 12 SO ₄ ^2- (g / L) 15 0 0 2 0 2 Cl ^- (g / L) 10 10 10 0 15 0 Oxalic Acid (g / L) 15 15 7 0 0 0 Malonic acid (g / L) 0 0 7 15 12 12 Succinic Acid (g / L) 0 10 20 0 0 0 Adipic acid (g / L) 0 0 0 20 0 0 Molar ratio of chelating agent / Cr ³⁺ 2.0 3.0 3.7 3.4 1.4 1.4 Co (g / L) One 1.5 0.5 One One One Ni (g / L) 0.1 0 1.0 0 0.3 0.5 Other metal salts Si Si Ti Si Si Si PH of the treatment liquid 2.3 2.3 2.3 2.4 2.6 2.5 Treatment temperature (℃) 50 50 60 50 40 30 Processing time (seconds) 30 60 120 60 60 60

In the table, chromium chloride (Examples 1, 2, 3, 5), chromium phosphate (Examples 4, 6), and chromium nitrate (Example 5) were used for Cr ³⁺ . NO ₃ ⁻ was adjusted by adding HNO ₃ (Examples 1, 2, 3) and NaNO ₃ (Examples 4, 6) or by chromium nitrate (Example 5). In addition, SO ₄ ^2- was added as Na ₂ SO ₄ and PO ₄ ^3- was added as NaH ₂ PO ₄ . Again, the rest is water. As metal salts such as Co and Ni, sulfates (Examples 1, 4 and 6) and chlorine salts (Examples 2 and 3 and 5) were used. Si used colloidal silica and Ti used titanium trichloride. Metal ion concentrations other than Co and Ni were 1 g / L. pH adjustment was made into NaOH.

(Examples 7 to 10)

An alkali zinc nickel (Ni%: 5 to 15%) or zinc iron alloy plating (Fe%: 0.3 to 2.0%) was applied to the steel sheet to a thickness of 8 µm, and immersed in the trivalent chromate treatment solution shown in Table 2.

Example 7 8 9 10 Cr ³⁺ (g / L) 4.5 4.5 4.5 4.5 NO ₃ ^- (g / L) 0.6 0.4 0.2 0.4 NO ₃ ^- / Cr ³⁺ 0.11 0.07 0.04 0.07 PO ₄ ^3- (g / L) 12 12 12 15 SO ₄ ^2- (g / L) 10 0 15 2 Cl ^- (g / L) 0 10 0 0 Oxalic Acid (g / L) 15 7 15 15 Malonic acid (g / L) 0 7 0 0 Succinic Acid (g / L) 10 0 0 0 Adipic acid (g / L) 0 0 0 20 Molar ratio of chelating agent / Cr ³⁺ 3.0 1.7 2.0 3.7 Co (g / L) One One One One Ni (g / L) 0.3 0 0.1 0 Other metal salts Si Si Si Si PH of the treatment liquid 2.6 2.0 2.3 2.5 Treatment temperature (℃) 35 50 50 40 Processing time (seconds) 60 60 60 60 Plating vacancy rate (%) Zn-Ni 6.5 Zn-Ni 15 Zn-Fe 0.5 Zn-Fe 2.0

In the table, chromium chloride (Example 8) and chromium phosphate (Examples 7, 9 and 10) were used for Cr ³⁺ .

NO ₃ ⁻ was adjusted by adding HNO ₃ (Example 8) and NaNO ₃ (Example 7, 9, 10). In addition, SO ₄ ^2- was added as Na ₂ SO ₄ and PO ₄ ^3- was added as NaH ₂ PO ₄ . The balance is water. As metal salts such as Co and Ni, sulfate salts (Examples 7, 9) and chlorine salts (Example 8) were used. Si used colloidal silica and the density | concentration was 1 g / L. pH adjustment was made into NaOH.

(Examples 11 to 14)

After the trivalent chromate treatment of Examples 1, 8 and 9, the overcoat treatment was performed. Table 3 shows the overcoat treatment conditions.

Example 11 12 13 14 Trivalent Chromate Treatment Example 1 Example 8 Example 9 Example 9 Type of overcoat Silicate Inorganic Membrane Silicate Inorganic Film Polyurethane Organic Film Methacrylic resin organic film Treatment concentration 200 mL / L 200 mL / L 100mL / L Undiluted use Treatment condition 45 ℃-45 seconds 45 ℃-45 seconds 25 ℃-60 seconds 25 ℃-60 seconds Drug name Deep Sole CC445 Deep Sole CC445 Jeil Industrial Pharmaceutical Co., Ltd. Superflex Deep Sole Co., Ltd. Deep Coat

(Comparative Example 1)

As a comparative example, the hexavalent chromate treatment was performed on the steel plate subjected to 8 μm zinc plating.

As the hexavalent chromate, ZIP-535A (200 mL / L) and ZB-535B (10 mL / L) manufactured by Dipsol Co., Ltd. were used.

(Comparative Example 2)

As a comparative example, trivalent chromate treatment was performed with the following composition to the steel plate which 8 micrometers zinc plated.

Cr (NO ₃ ) ₃ 15 g / L (3.3 g / L as Cr ³⁺ )

NaNO ₃ 10g / L

Oxalic Acid 10g / L

    pH 2.0

(However, treatment conditions were performed at 30 ° C.-40 seconds.)                 

(Comparative Example 3)

The trivalent chromate treatment was performed with the following composition described in Example 3 of Unexamined-Japanese-Patent No. 2000-509434 by having galvanized steel plate with 8 micrometers.

50 g / L CrCl ₃ · 6H ₂ O (9.8 g / L as Cr ³⁺ )

Co (NO ₃ ) ₂ 3 g / L (0.6 g / L as Co)

NaNO ₃ 100 g / L

Malonic acid 31.2 g / L

pH 2.0

(However, treatment conditions were performed at 30 ° C.-40 seconds.)

fair:

In addition, the said process is as follows.

Plating → washing water → nitric acid activity → washing water → chromate treatment → washing water → (overcoat treatment) ¹ → drying ² → (heat treatment) ³

Note 1: Only when performing overcoat processing

Note 2: Drying is 60-80 degrees Celsius-ten minutes

Note 3: In the case of the test of heating corrosion resistance, it is treated at 200 ° C for 2 hours.

Salt Spray Test ：

Table 4 shows the appearance of the zinc plating obtained in Examples 1 to 14 and Comparative Examples 1 to 3 and the results of the salt spray test (JIS-Z-2371).

As shown in Table 4, the coatings of Examples 1 to 10 obtained almost equivalent or more corrosion resistance compared with the chromate coatings of Comparative Examples 1 to 3. In addition, the overcoat-treated films of Examples 11 to 14 were able to obtain better corrosion resistance than conventional chromates, especially in the time until red rust.

Salt spray test result (JIS-Z-2371) Example Appearance of film Corrosion Resistance 5% White Rust / Red Rust Development Time (Hrs) Heat Corrosion Resistance 5% White Rust Development Time (Hrs) One black 120/600 240 2 black 72/500 240 3 black 72/400 120 4 black 96/500 240 5 black 120/500 240 6 black 120/500 240 7 black 120/800 240 8 black 120/1500 240 9 black 240/1000 240 10 black 240/1000 240 11 black 240/1000 12 black 300/2000 13 black 300/1200 14 black 300/1200 Comparative Example 1 black 120/500 12 Comparative Example 2 Light blue 24/250 24 Comparative Example 3 Interference color 72/300 48

According to the present invention, a black hexavalent chromium-free chemical conversion film can be produced directly on zinc and zinc alloy plating. In addition to the corrosion resistance of zinc and zinc alloy plating itself, the plating material obtained by this method has the outstanding corrosion resistance which the trivalent chromate film newly has. In addition, since trivalent chromium is low in concentration, it is advantageous for wastewater treatment and economically excellent. The film obtained by producing trivalent chromate directly on the plating is widely used in various fields in the future because its corrosion resistance, saline resistance and heat resistance are equivalent to or higher than those of the conventional hexavalent chromate and exhibit black appearance. You can expect

Claims (13)

As a treatment solution for forming a black hexavalent chromium free chemical conversion film on zinc and zinc alloy plating, The molar ratio of nitrate ions to trivalent chromium (NO _{3 ⁻} / Cr ³⁺ ) is less than 0.5, Trivalent chromium is present in the form of a water-soluble complex with a chelating agent, At least one of cobalt ions and nickel ions, At least one of cobalt ions and nickel ions forms a poorly soluble metal salt with a chelating agent and does not precipitate, but is stably present in the treatment solution, When zinc and zinc alloy plating are brought into contact with the treatment solution, they react with zinc to form a zinc hexavalent chromium-free chemical conversion film containing zinc and chromium, at least one of cobalt and nickel, and a chelating agent. The treatment solution, characterized in that formed on the alloy plating. The method of claim 1, The concentration of trivalent chromium is 0.5-10 g / L, The molar ratio (chelating agent / Cr ³⁺ ) of the chelating agent and trivalent chromium is ^0.2-4 . The method according to claim 1 or 2, Wherein said source of trivalent chromium is chromium phosphate (Cr (H _n PO ₄ ) _{(3 / (3-n))} ) (where n = 0, 1, 2). The method according to claim 1 or 2, Said chelating agent is 1 or more types chosen from the group which consists of monocarboxylic acid, dicarboxylic acid, tricarboxylic acid, hydroxycarboxylic acid, aminocarboxylic acid, and their salts, The said treating solution characterized by the above-mentioned. The method according to claim 1 or 2, Said chelating agent is at least one selected from the group consisting of oxalic acid, malonic acid, succinic acid and salts thereof. The method according to claim 1 or 2, Said treatment further comprising one or more metal ions selected from the group consisting of silicon, iron, titanium, zirconium, tungsten, vanadium, molybdenum, strontium, niobium, tantalum, manganese, calcium, barium, magnesium and aluminum solution. The method according to claim 1 or 2, The treatment solution, characterized in that the concentration of nitrate ions in the treatment solution is 0.1 ~ 1g / L. The method according to claim 1 or 2, The treatment solution further comprises a phosphate ion. The method according to claim 1 or 2, The treatment solution further comprises one or more selected from the group consisting of nitrate ions, halogen ions and borate ions. A method of forming a black hexavalent chromium-free chemical conversion film comprising the step of bringing zinc and zinc alloy plating into contact with the treatment solution according to claim 1. The method of claim 10, The forming method, characterized in that it further comprises the step of aging the black hexavalent chromium-free chemical conversion film at 100 ~ 250 ℃ for 30 to 300 minutes. The method of claim 11, The forming method, wherein the aging treatment step is performed at 200 ° C. for 60 to 300 minutes. An antirust method for zinc and zinc alloy plating, further comprising an overcoat treatment on the black hexavalent chromium-free chemical conversion film formed by the method of claim 10.