TWI507563B - A chromium-free surface treatment liquid for steel and a steel surface treatment method using the treatment liquid - Google Patents

Description

Chromium-free surface treatment liquid for steel parts and surface treatment method of steel parts using the same

The present invention relates to a surface treatment liquid and a surface treatment method, and more particularly to a chromium-free surface treatment liquid for steel parts and a surface treatment method for steel parts using the same.

Galvanized steel sheets are widely used in the fields of automobiles, home appliances and construction, and the high activity of metal zinc causes the steel sheets to be easily oxidized during storage or transportation to form white rust. In order to solve this problem, it is usually galvanized. The steel plate is subjected to passivation treatment. It is customary to apply a treatment liquid water film to the surface of the steel sheet before the protective film of the galvanized steel sheet is formed. After the baking treatment, the water film of the treatment liquid forms a protective film on the steel sheet. The hexavalent chromium protective film has long been regarded as the most economical and corrosion-resistant passivation treatment, in addition to providing the excellent barrier protection of the steel plate to block the attack of corrosion factors, and the protective film also has self-repairing ability ( Self-repairing ability). The self-repairing ability refers to the fact that when the protective film is broken and the galvanized surface is exposed, it can regenerate a protective film in the damaged area to achieve the repairing effect, and at the same time inhibit the corrosion of zinc.

However, hexavalent chromium is carcinogenic and can seriously pollute the ecological environment. Therefore, the RoHS Directive issued in July 2006 and the OSHA 3320-10N Directive, which came into effect in 2006, all explicitly limit the use of hexavalent chromium or regulate the hexavalent price in related processes. The allowable concentration of chromium, therefore, the development of a non-chromium passivation agent that replaces hexavalent chromium is more urgent.

At present, there are mainly chrome-free surface treatment agents:

The first type is a surface treatment agent obtained by reacting an organic resin such as a polyvinylphenol derivative with an acid component or an epoxy compound, as disclosed in Japanese Laid-Open Patent Publication No. 2003-13252.

The second type is a surface treatment technique composed of an aqueous resin, a thiocarbonyl group, a vanadium oxide compound, and phosphoric acid as proposed in Japanese Patent No. 3549455.

The third type is an organic protective film formed on a phosphate protective film, which is formed of at least one organic resin, which is selected from epoxy resin, as proposed in Japanese Patent No. 2001-105528. , urethane resin or acrylic resin.

The fourth type is proposed in the Republic of China Patent No. I279452. The surface of the steel sheet is made of a protective film of magnesium phosphate, and then an epoxy resin and/or a denatured epoxy resin protective film is coated on the phosphate protective film. . The above patent uses an organic resin to enhance the corrosion resistance of the protective film. However, the organic resin has an insulating property, so that the protective film composed of the organic resin does not have sufficient conductivity, so the steel plate made by the above patent There are doubts that it is difficult to balance both conductivity and corrosion resistance.

The fifth type is proposed by the Japanese Patent Laid-Open Publication No. SHO63-90581, which is a thermosetting coating material using a mixed epoxy resin, an amine resin, and tannic acid.

The sixth type is proposed in Japanese Laid-Open Patent Publication No. Hei 8-325760, which is a mixture of an aqueous resin and a polyvalent phenol carboxylic acid.

The treatment liquid for forming the protective film contains inorganic and organic compounds at the same time, so that the waste liquid generated in the preparation process is not easily recovered. Furthermore, organic The film is easily cracked in the subsequent steel plate welding process to cause discoloration of the steel plate surface, and its high temperature discoloration resistance is not good. Moreover, although the protective film formed by the above method can improve the corrosion resistance of the steel sheet, it does not have self-repairing ability.

In summary, if the film can simultaneously have corrosion resistance, self-repairing ability, electrical conductivity and high temperature discoloration, the practicality of the galvanized steel plate can be effectively improved; further, if environmental protection considerations are further The passivation treatment of galvanized steel sheets with a treatment liquid containing no organic resin will better meet the needs of the industry.

Therefore, it is necessary to provide an innovative and progressive chrome-free surface treatment liquid for steel parts and a steel surface treatment method using the same to solve the above problems.

The present invention provides a chromium-free surface treatment liquid for steel parts, which comprises water, a phosphoric acid solution, a zinc-containing compound, a nitrate salt, a magnesium-containing compound, and a vanadium-containing compound, wherein the total weight of the treatment liquid is 100% by weight, The content of the vanadium-containing compound is from 0.7 to 1.5% by weight.

The invention further provides a method for treating a surface of a steel member, wherein the steel member is provided with a chromium-free surface treatment liquid on a zinc-containing surface of a steel member.

The chromium-free surface treatment liquid of the present invention can form a protective film on the zinc-containing surface of the steel member, and the protective film can improve the corrosion resistance, self-repairing ability, electrical conductivity and high temperature discoloration resistance of the steel member. In addition, the chromium-free surface treatment liquid of the present invention does not contain heavy metal chromium and an organic solvent, and is advantageous for environmental protection and waste liquid recovery.

The chromium-free surface treatment liquid for steel parts of the present invention comprises water, a phosphoric acid solution, a zinc-containing compound, a nitrate salt, a magnesium-containing compound, and a vanadium-containing compound, wherein the vanadium-containing compound is calculated based on 100% by weight of the total weight of the treatment liquid. The content of the compound is from 0.7 to 1.5% by weight, and preferably, the chromium-free surface treatment liquid of the steel member has a pH ranging from 1 to 3.5.

The zinc-containing compound is mainly used for raising the concentration of Zn ²⁺ in the treatment liquid, and the zinc-containing compound is selected from the group consisting of zinc oxide, zinc nitrate and zinc chloride.

The nitrate mainly provides nitrate as a promoter to accelerate the dissolution of the zinc-containing surface to provide Zn ²⁺ , so that Zn ^{2+ is} sufficient to produce zinc phosphate with the phosphate. Preferably, the nitrate is sodium nitrate.

The magnesium-containing compound functions to increase the stability of the protective film and to improve the corrosion resistance of the steel member, and the magnesium-containing compound is selected from the group consisting of magnesium oxide, magnesium nitrate, and magnesium chloride.

The vanadium-containing compound is mainly used to raise the vanadate concentration in the treatment liquid, and the vanadium-containing compound may be a vanadate such as sodium vanadate or ammonium vanadate.

The invention further provides a method for treating a surface of a steel member, wherein the steel member is provided with a chromium-free surface treatment liquid on a zinc-containing surface of a steel member. In this embodiment, the steel member is a galvanized steel sheet, and before the steel member is disposed on the zinc-containing surface of the galvanized steel sheet with a chrome-free surface treatment liquid, a cleaning and degreasing step may be further included to clean the plating. The zinc-containing surface of zinc steel. Moreover, in the embodiment, the steel surface treatment method further comprises performing a baking step on the steel member with a chrome-free surface treatment liquid, and the baking step is performed at a temperature of 220 ° C and a time of 12 seconds. The steel member is coated with a chromium-free surface treatment liquid after the baking step to form a protective film on the zinc-containing surface of the steel member. The protective film contains zinc phosphate, zinc magnesium phosphate, zinc hydroxide, vanadium oxide, vanadate and phosphate.

In this embodiment, the protective film is formed in such a way that when the zinc-containing surface of the steel member is in contact with the treatment liquid, the zinc-containing surface dissolves Zn ²⁺ , accompanied by reduction of hydrogen ions (2H ⁺ +2e ^- →H ₂ ), reduction of nitrate (NO ₃ ^- +2H ⁺ +2e ^- →NO ₂ ^- +H ₂ O) and reduction of vanadate [V ₁₀ O ₂₇ (OH) ^5- +10e ^- +15H ⁺ + 2H ₂ O→10VO(OH) ₂ or v ₁₀ O ₂₈ ^6- +10e ^- +16H ⁺ +2H ₂ O→10VO(OH) ₂ ], VO(OH) ₂ combines with water to form octahedron [VO(OH ₂ +3H ₂ O→VO(OH) ₂ (OH ₂ ) ₃ ], while aqueous VO(OH) ₂ is dehydrated to form vanadium oxide (V ₂ O ₄ ), and reduction of H ⁺ leads to galvanized layer The pH value at the interface of the solution rises upwards, so that dihydrogen phosphate is dissociated into hydrogen phosphate and phosphate (H ₃ PO ₄ →H ⁺ +H ₂ PO ₄ ^- →2H ⁺ +HPO ₄ ^2- →3H ⁺ +PO ₄ ^3- ). Therefore, the following deposition reaction occurs on the surface of the galvanized layer: 3Zn ²⁺ +2PO ₄ ^3- +4H ₂ O → Zn ₃ (PO ₄ ) ₂ ↓; xMg ²⁺ +(3-x)Zn ²⁺ +2PO ₄ ^3- +4H ₂ O → (Mg _x Zn _3-x )(PO ₄ ) ₂ ↓[x=0.62]; Zn ²⁺ +OH ^- → Zn(OH) ₂ ↓; VO(OH) ₂ (OH _{2 3} + VO(OH) ₂ (OH ₂ ) ₃ → V ₂ O ₄ ↓ + 8H ₂ O; and phosphate (PO ₄ ^3- ) and vanadate [V ₁₀ O ₂₇ (OH) ^5- , V ₁₀ O ₂₈ ^6- ] Deposition and adsorption.

Moreover, in the present embodiment, the vanadium content of the protective film is 10% by weight or more based on 100% by weight of the total weight of the protective film. Preferably, the protective film has a vanadium content ranging from 14 to 20% by weight. . Further, in order to provide the steel member with better corrosion resistance and self-repairing ability, the thickness of the protective film is 100 to 300 nm.

The chromium-free surface treatment liquid for the steel member of the invention and the surface treatment method for the steel member can provide good corrosion resistance, self-healing ability, electrical conductivity and high temperature discoloration resistance on the surface of the steel member. Further, the chromium-free surface treatment liquid of the present invention does not contain heavy metal chromium and an organic solvent, and therefore does not pollute the environment and meets environmental protection requirements.

The invention is illustrated in the following examples and comparative examples, but is not intended to be limited to the scope of the invention.

Preparation of treatment liquid:

7.5g, 15g, 0g, 1.875g and 3.75g of sodium vanadate (NaVO ₃ ) and 2.4g of zinc oxide, 30g of sodium nitrate, 22ml of phosphoric acid (concentration of 85%), 5g of magnesium nitrate and 1000g The water was mixed, and the pH was adjusted to 2.5 using sodium hydroxide pellets to prepare treatment liquids A, B, C, D, and E, respectively.

[Example 1]

First, a galvanized steel sheet (manufactured by China Iron and Steel Co., Ltd.) was taken as a test piece, and the test piece was subjected to surface degreasing and decontamination, and then the treatment liquid A was applied to the steel plate by a roll coating rod (winding diameter: 0.07 mm). The surface was then baked in an oven at 200 ° C for 12 seconds to form a protective film on the surface of the test piece, thereby producing a surface-treated steel sheet test piece of Example 1.

[Embodiment 2]

Except that the treatment liquid A was replaced with B, the rest of the preparation process was the same as in Example 1, and finally the surface-treated steel sheet test piece of Example 2 was obtained.

[Comparative Example 1]

Except that the treatment liquid A is replaced by C, the rest of the preparation process is implemented In the same manner as in Example 1, the surface-treated steel sheet test piece of Comparative Example 1 was finally obtained.

[Comparative Example 2]

The preparation process was the same as in Example 1 except that the treatment liquid A was replaced with D, and finally the surface-treated steel sheet test piece of Comparative Example 2 was obtained.

[Comparative Example 3]

Except that the treatment liquid A was replaced with E, the rest of the preparation process was the same as in Example 1, and finally the surface-treated steel sheet test piece of Comparative Example 3 was obtained.

[test]

The following test was performed on the steel plate test pieces of the above Examples 1 to 2 and Comparative Examples 1 to 3, and the results obtained are shown in Table 1:

1. Element content analysis: The content of vanadium element was analyzed by X-ray photoelectron spectroscope (XPS).

2. Corrosion resistance test: The test piece size is 150 mm × 100 mm × 1 mm. First, the end and back are sealed with anti-plating tape, and then the test piece is subjected to a salt spray test according to ASTM B117-03. The salt water concentration was 5% by weight, the test piece was sprayed at an angle of 30 degrees and the spray time was 24 hours. After the salt spray test, the white rust coverage area was observed, and the corrosion resistance was evaluated by the percentage of white rust coverage area. If the coverage area is more than 5%, it is judged that it has no corrosion resistance and is marked as "x". If the coverage area is less than 5%, it is judged to have corrosion resistance, and is marked as "○".

3. Self-healing ability test: The test piece size is 150 mm × 100 mm × 1 mm. First, the end and back are sealed with anti-plating tape, and then the protective film is scratched with a sharp knife to create an "X"-shaped damaged area. (damage area deep to steel bottom The material has a scratch width of about 100 to 120 microns. The sample is then subjected to a salt spray test in accordance with ASTM B117-03. The salt water concentration was 5% by weight, the test piece was sprayed at an angle of 30 degrees, and the spray time was 24 hours. After the salt spray test, the white rust coverage area of the "X"-shaped damaged area was observed, and the self-healing ability was evaluated by the percentage of white rust coverage area. If the coverage area is greater than 5%, it is judged that it has no self-healing ability and is marked as "X"; if the coverage area is less than 5%, it is judged to have self-healing ability, and is marked as "○".

4. Conductivity test: The test piece size was 150 mm × 100 mm × 1 mm, and the resistance value of the surface of the test piece was measured by Loresta surface resistance (taken by three points). The resistance value is less than 10 ^-1 Ω and is marked as "○"; the resistance value is higher than 10 ^-1 Ω and is marked as "X".

5. Resistance to high temperature discoloration test: The test piece was placed in a resistance heating furnace, and the temperature was heated to 450 ° C and baked for 5 minutes. After the test is completed, observe whether the surface of the test piece is discolored. If the test piece is discolored, it is judged that it is not resistant to high temperature, and it is marked as "X"; if the test piece is not discolored, it is judged to have high temperature discoloration resistance, and is marked as "○".

[result]

In the results of Table 1, both of Examples 1 to 2 and Comparative Examples 1 to 3 were tested for resistance to high temperature discoloration and conductivity. For the corrosion-resistant portion, it was found that the corrosion resistance and self-healing ability of the steel plate test piece of Comparative Example 1 were not good, and the steel plate test pieces of Comparative Examples 2 to 3 all had better corrosion resistance, but the self-healing ability was still Not ideal; the corrosion resistance and self-healing ability of Examples 1 to 2 are all good. It can be seen that the steel plate is treated with a solution containing more than 0.3% by weight of vanadate, which can effectively improve its corrosion resistance and self-healing ability. For the self-healing ability part, it can be found that the self-healing ability of the protective film increases as the vanadate content in the treatment liquid increases.

In summary, the present invention penetrates the formation of phosphorus on the zinc-containing surface of the steel sheet. The protective film of zinc acid, zinc magnesium phosphate, zinc hydroxide, vanadium oxide, vanadate and phosphate can make the surface of the steel plate have good corrosion resistance, self-healing ability, electrical conductivity and high temperature discoloration resistance, which is very suitable for application. Uses for automobiles, home appliances, and building materials.

The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the scope of the present invention. The scope of the invention should be as set forth in the appended claims.

Claims (7)

A steel surface treatment method comprises: setting a chromium-free surface treatment liquid for a steel part to a zinc-containing surface of a steel part, the chromium-free surface treatment liquid for the steel part comprises water, a phosphoric acid solution, a zinc-containing compound, a nitrate, a magnesium-containing compound, and a vanadium-containing compound, wherein the content of the vanadium-containing compound is 0.7 to 1.5% by weight based on 100% by weight of the total weight of the treatment liquid; and a chromium-free surface treatment of the steel member The liquid was subjected to a baking step which was carried out at a temperature of 220 ° C and a time of 12 seconds. The method for treating a steel surface according to claim 1, wherein the steel member is coated with a chromium-free surface treatment liquid after the baking step, and a protective film is formed on the zinc-containing surface of the steel member, the protective film containing zinc phosphate, Zinc magnesium phosphate, zinc hydroxide, vanadium oxide, vanadate and phosphate. The steel member surface treatment method according to claim 2, wherein the protective film has a vanadium content of 10% by weight or more based on 100% by weight of the total weight of the protective film. The steel member surface treatment method of claim 3, wherein the protective film has a vanadium content ranging from 14 to 20% by weight. The steel member surface treatment method of claim 2, wherein the protective film has a thickness of 100 to 300 nm. The steel member surface treatment method of claim 1, wherein the steel member has a chrome-free surface treatment liquid having a pH ranging from 1 to 3.5. The steel member surface treatment method of claim 1, wherein the steel member is a galvanized steel sheet.