JP2007182597A - Phosphating solution - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phosphating solution suitable for forming a coating film superior in workability, corrosion resistance and adhesiveness to a paint film. <P>SOLUTION: The phosphating solution is prepared by adding an polyamine-based organic inhibitor with a molecular weight of 200 to 30,000 having at least one functional group of -NH<SB>2</SB>and =NH in an amount of 0.01 to 5 mass%, to a treatment solution containing phosphate ions in an amount of 0.03 to 0.5 mol/l. The polyamine-based organic inhibitor is preferably an aliphatic amine such as polyethylamine, polyethyleneimine, polyetheramine and polyaminoacrylate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a phosphating solution used for forming a phosphate film that does not contain hexavalent chromium harmful to the environment and is excellent in corrosion resistance, paintability, and workability.

  If a galvanized steel sheet, a zinc alloy plated steel sheet, or the like is used in a sea salt particle scattering atmosphere or a high-temperature and high-humidity atmosphere, white rust that causes the appearance deterioration occurs on the surface of the steel sheet, and the sacrificial anticorrosive action of the plating layer is also impaired. Although the generation of white rust can be prevented by chromate treatment, phosphate treatment, etc., elution of hexavalent chromium from the formed film is unavoidable in chromate treatment, so replacement with phosphate treatment has been studied.

Various treatment liquids that can form fine phosphate crystals have been proposed for phosphating (Patent Documents 1 to 3).
Japanese Patent Laid-Open No. 10-204649 JP-A-8-302477 Japanese Laid-Open Patent Publication No.8-134661

However, although the phosphate crystals are fine, the crystals are densely formed without gaps, so in applications where products are produced by severe processing, the phosphate coating cohesively breaks down during processing, and defects such as peeling occur. Easy to be introduced to. Although cohesive failure can be prevented by providing an appropriate gap between the phosphate crystals, in order to secure the gap, contact with the phosphate treatment solution must be interrupted during the growth process of the phosphate film, It was difficult to stably produce a chemically treated steel sheet that can maintain a good appearance and corrosion resistance.
Moreover, when a treatment liquid for depositing fine phosphate crystals is applied to a highly corrosion-resistant Zn-Al-Mg alloy-plated steel sheet, the [Al / Zn / Zn ₂ Mg ternary eutectic structure] Coarse growth of phosphate crystals is observed in the portion where a large amount of is contained.

In the conventional phosphating solution, a crystal grain refining agent is added in order to make the phosphate crystals deposited on the surface of the plating layer dense and fine. The crystal refining agent is adsorbed on the surface of the plating layer to suppress the phosphate crystal formation reaction at the start of the reaction, but is removed with the progress of the reaction to remove the plating layer surface by etching. It is considered to be desorbed.
In Zn-Al-Mg alloy-plated steel sheets with a multiphase structure, the effect of different adsorption speeds and adsorption forces between the phases makes the crystal refining action non-uniform on the surface of the plated layer, resulting in a large adsorption force [Al / It is considered that the crystal growth of the phosphate crystal is promoted in a portion where there is a Zn / Zn ₂ Mg ternary eutectic structure].

Therefore, the present inventors uniformly adsorbed the crystal refining agent even on the plating layer having the [Al / Zn / Zn ₂ Mg ternary eutectic structure] on the surface to grow phosphate crystals. Various inhibitors have been investigated as additives that can suppress the above-mentioned and can form an appropriate gap between phosphate crystals without etching the plating layer. Carboxylic acid-based, phosphoric acid-based, alcohol-based, amine-based, and mercapto-based compounds are considered as inhibitors, but amine-based compounds are the most effective, and the adsorptive power to the plating layer surface is adjusted by chemical structure and molecular weight. It was clarified that a phosphate film with excellent corrosion resistance, paintability and workability was formed.

  The present invention is based on such knowledge, and by adding a polyamine organic compound having a specified chemical structure and molecular weight as an inhibitor, a plated steel sheet in which a plurality of phases are exposed on the surface, such as a Zn-Al-Mg alloy-plated steel sheet. Even so, an object of the present invention is to provide a phosphating solution capable of uniformly forming a phosphate film excellent in corrosion resistance, paintability and workability.

The phosphating solution of the present invention comprises a polyamine organic inhibitor having a molecular weight of 200 to 30000 having at least one of —NH ₂ ══NH as a functional group in a range of 0.01 to 5 mass%. And As the polyamine organic inhibitor, any of aliphatic, aromatic and alicyclic amines can be used, but aliphatic amines are preferred from the viewpoint of dispersion stability. The phosphating solution can further contain a nonionic surfactant.

  The phosphating solution to which the polyamine organic inhibitor is added contains 0.03 to 0.5 mol / l of phosphate ions, metal ions: 0.01 to 0.5 mol / l, and if necessary, nitric acid Ion: A treatment liquid adjusted to 0.01 to 1.0 mol / l is preferable. Metal ions include Zn, Mg, Mn, Ca, Co, Ni, Fe, etc. other than P.

Effects and embodiments of the invention

The polyamine organic inhibitor added to the phosphating solution of the present invention may have at least one functional group of —NH ₂ ══NH, and a halogen ion such as Cl 2 ^— added to the functional group. Any aliphatic polyamine such as polyethylamine, polyethyleneimine, polyetheramine, polyaminoacrylate, or aromatic such as polyaniline can be used. However, in view of dispersion stability in the phosphating solution, an aliphatic polyamine is preferred when the molecular weight is increased. The polyamine having at least one functional group of —NH ₂ ══NH is adsorbed on the surface of the plating layer during the phosphating treatment with a sufficient adsorbing power as compared with the tertiary amine.

Polyamine organic inhibitors are adsorbed on the surface of the plating layer by the action of —NH ₂ , = NH, and nonpolar groups such as hydrocarbon groups oriented to the treatment liquid form a monomolecular film due to intermolecular force, etching. Suppresses contact between components and plating layer surface. As a result, an unetched part is formed, and an appropriate interval is provided between the phosphate crystals.
Furthermore, when a polyamine organic inhibitor and a halogen ion are allowed to coexist, a halogen ion is adsorbed on a positively charged portion on the surface of the plating layer, and —NH ₂ , = NH is combined with a proton to form an onium ion and Even so, uniform adsorption is facilitated. Even when the halogen ion is added to the phosphating solution in the form of hydrochloric acid or the like without being added to the functional group, the same effect is obtained.

  When the molecular weight of the polyamine-based organic inhibitor is selected in the range of 200 to 30,000, the adsorptive power to the plating layer surface is moderately maintained, the contact of the etching component on the plating layer surface is controlled, and the phosphate crystal has an appropriate amount between the phosphate crystals. An unetched portion that forms a gap remains. If the molecular weight is less than 200, the adsorptive power with respect to the surface of the plating layer is insufficient, and the fineness of phosphate crystals and the formation of gaps between crystals become insufficient, resulting in a decrease in work adhesion. On the other hand, when the molecular weight exceeds 30000, the etching component is excessively suppressed from contacting the surface of the plating layer, and phosphate crystals are difficult to precipitate, so the coverage of the phosphate film covering the surface of the plating layer, and thus corrosion resistance. Decreases.

  The polyamine organic inhibitor is added in the range of 0.01 to 5% by mass in order to refine the phosphate crystals and form gaps between the crystals. When the addition amount is less than 0.01% by mass, the fineness of the phosphate crystals and the formation of gaps between the crystals are insufficient, and the work adhesion decreases. On the other hand, when the addition amount exceeds 5% by mass, the contact of the etching component with the plating layer surface is excessively suppressed, and phosphate crystals are difficult to precipitate, so that the coverage of the plating layer surface with the phosphate film decreases. Corrosion resistance is insufficient.

The phosphating solution may contain phosphate ions, metal ions, and nitrate ions in addition to the polyamine organic inhibitor. Phosphate ions are an essential component for the formation of a phosphate film, and 0.03 to 0.5 mol / l in order to deposit sufficient phosphate crystals without destabilizing the phosphate treatment solution. It is preferable to select within the range.
The metal ions are selected from Zn, Mg, Mn, Ca, Co, Ni, Fe, etc. in order to homogenize the precipitation reaction of phosphate crystals. In particular, when phosphate-treating a Zn—Al—Mg alloy-plated steel sheet having a multiphase structure, Mn, Co, Ni, Fe, etc. are preferentially substituted and deposited on the Zn ₂ Mg phase with the lowest surface potential. By preferentially dissolving the Zn phase, phosphate crystals having deep roots and excellent adhesion can be easily formed. Such an effect becomes remarkable at 0.01 mol / l, but an excess amount exceeding 0.5 mol / l increases the amount of substitutional precipitation of Mn, Co, Ni, Fe, etc., and the corrosion resistance of the phosphate film. On the other hand, it will cause a decline.

Nitrate ion is a component added as necessary for reaction adjustment, and the effect of addition becomes remarkable at 0.01 mol / l or more. However, excessive addition exceeding 1.0 mol / l inactivates the surface of the plating layer due to the oxidizing action of nitric acid, and on the contrary, the precipitation reaction of phosphate crystals decreases.
Furthermore, fluoride may be added to the phosphate treatment solution in order to prevent Al eluted from the plating layer from accumulating in the phosphate treatment solution and inhibiting the phosphate reaction. When adding a fluoride, the addition amount is determined in the range of 0.001 to 0.5 mol / l.

Al: 6.1% by mass, Mg: 3.1% by mass, Zn: The remaining alloy plating layer formed on one side with an adhesion amount of 75 g / m ² : Plate thickness: 0.8 mm Molten Zn—Al—Mg An alloy-plated steel sheet was prepared as a raw sheet for chemical conversion treatment.
The phosphating solution was prepared by adding the amine organic inhibitor of Table 2 and polyoxyethylene nonylphenyl ether (nonionic surfactant) to the aqueous solution of Table 1.

The prepared phosphating solution was heated to 60 ° C., brought into contact with the surface-adjusted plated steel sheet for 10 seconds, washed with water and dried to form a phosphate film on the surface of the plating layer. Then, an aqueous solution of titanium ammonium fluoride having a titanium equivalent concentration of 5 g / l was applied at a coating amount such that the amount of titanium adhered was 5 mg / m ² and dried to seal the phosphate coating.

The stability of the phosphating solution and the physical properties of the phosphatized plated steel sheet were evaluated in the following test.
[Stability test of phosphating solution]
The prepared phosphating solution was sealed in a polyethylene container and allowed to stand in a thermostatic device having an atmospheric temperature of 60 ° C. After heating for a predetermined time, the phosphate treatment solution was observed and compared with the treatment solution before heating. The stability of the phosphating solution was evaluated with ◯ as the processing solution that did not change before and after heating, Δ as the processing solution with reduced transparency, and X as the processing solution with precipitation.

[Flat corrosion test]
The flat portion of the test piece was subjected to a corrosion test by a salt spray test in accordance with JIS Z2371. In the salt spray test, a 5% NaCl aqueous solution at 35 ° C. was sprayed on the test piece whose end face was sealed, and after spraying the salt water for 72 hours, the surface of the test piece was observed to investigate the occurrence of white rust. The area occupancy ratio of white rust on the surface of the test piece is less than 5 area%, ◎, 5-10 area% is ◯, 10-30 area% is △, 30-50 area% is ▲, and 50 area% or more is x. The flat part corrosion resistance was evaluated.

[Processed part adhesion test]
The plated steel sheet treated with phosphate was coated with melamine alkyd to form a coating film having a thickness of 30 μm. The test piece cut out from the coated steel sheet was bent 90 degrees and bent back, and then cellophane tape was applied to the inner side of the bend subjected to compressive deformation and peeled off instantaneously. After the cellophane tape was peeled off, the remaining state of the coating film was observed, and the film adhesion was evaluated with ◎ as the coating film remaining rate of 80% or more, ○ as 60-80%, Δ as 40-60%, and X as less than 40%. .

As seen in the investigation results in Table 3, Test Nos. 1 to 15 according to the present invention were excellent in all of the stability of the phosphating solution, the corrosion resistance of the flat portion, and the work adhesion.
In contrast, Test No. 16 in which the molecular weight of the polyamine organic inhibitor is low and Test No. 18 in which the addition amount of the polyamine organic inhibitor is insufficient are inferior in work adhesion. In Test No. 17 in which the molecular weight of the polyamine organic inhibitor is too large and in Test No. 19 in which the polyamine organic inhibitor is excessively added, phosphate crystals hardly precipitate and the surface of the plating layer cannot be sufficiently covered. In Test Nos. 20 and 21 using an amine compound other than the polyamine organic inhibitor, the effect of reducing the phosphate adhesion amount was insufficient, and the processing adhesion was insufficient.

Using the phosphating solution shown in Table 2, the galvanized steel sheet (plate thickness: 0.8 mm) in Table 4 was subjected to the phosphating treatment under the same conditions as in Example 1 and then sealed.
The flat surface corrosion resistance and work adhesion of the obtained surface-treated steel sheet were investigated by the same method as in Example 1.
As can be seen from the investigation results of Table 5, it is confirmed that by applying the phosphate treatment according to the present invention, not only the plating type but also good flat portion corrosion resistance and work adhesion can be imparted. Among them, a Zn—Al—Mg alloy-plated steel sheet is likely to form phosphate crystals that bite into the surface of the plating layer, and a coated steel sheet with better work adhesion can be obtained.

As explained above, by adding at least one of —NH ₂ and ═NH having a functional group-containing molecular weight of 200 to 30000 polyamine-based organic inhibitor, between the phosphate crystals formed on the surface of the plating layer Therefore, the processing adhesion of the phosphate coating is improved without impairing the corrosion resistance. Phosphates with excellent workability, corrosion resistance, and coating adhesion because a homogeneous phosphate film is formed even on the surface of the plating layer where multiple phases are exposed, such as Zn-Al-Mg alloy-plated steel sheet A treated steel sheet is provided.

Claims (3)

A polyamine organic inhibitor having a molecular weight of at least one functional group of —NH ₂ ══NH: 200 to 30000 in a proportion of 0.01 to 5% by mass, and a phosphate ion concentration of 0.03 to 0.5 mol A phosphating solution characterized by being adjusted to a range of / l.   The phosphating solution according to claim 1, wherein one or more aliphatic amines selected from polyethylamine, polyethyleneimine, polyetheramine, and polyaminoacrylate are used as polyamine organic inhibitors.   The phosphating solution according to claim 1 or 2, further comprising a nonionic surfactant.