JPH072992B2 - Phosphating method for metal surface - Google Patents

Description

TECHNICAL FIELD The present invention relates to a treatment method for forming a phosphate film on a metal surface, and more specifically, it has coating adhesion and corrosion resistance suitable for cationic electrodeposition coating. The present invention relates to a spray-type processing method for forming a zinc phosphate-based film.

[Prior Art] It is conventionally known to use an acidic phosphating solution containing a large amount of phosphate ions for a small amount of zinc ions for pretreatment of coating (see Japanese Examined Patent Publication No. 50-6418). ). According to this, it is said that it is possible to provide a film having good properties suitable for electrodeposition coating, but when the phosphate treatment is carried out by a spray method, the obtained film is a needle-shaped film containing Hopite, Its particle size is also coarse, and both the amount of coating and the iron content in the coating are low, and as a pretreatment for cationic electrodeposition coating, it has the same or higher performance (especially corrosion resistance) as the coating obtained by the dipping method. No coating could be provided.

[Problems to be Solved by the Invention] As a result of intensive studies conducted by the present inventors in order to solve the above-mentioned problems, the free acidity of phosphorus and the phosphorus content are lower than those of the above-described conventionally known phosphate treatment solutions. It was found that a granular coating with a high iron content in the coating can be obtained even by spraying if a treatment liquid with a high acid ion concentration is used, and by further incorporating a cation such as nickel in addition to zinc ion, the coating can be formed. The inventors have found that the performance can be further enhanced, and have completed the present invention.

[Means and Actions for Solving the Problems] That is, according to the present invention, zinc ions 0.01 to 0.05 W / V%,
Nickel ion and / or manganese ion 0.01-0.
15W / V%, phosphate ion 1.5-3.0W / V% and nitrite ion 0.001-0.02W / V% in free acidity 0.1-0.3 point acid phosphate treatment solution containing no chlorate ion A method for phosphating a metal surface is provided, which comprises spraying the metal surface.

Examples of metals to be subjected to the method of the present invention include iron, zinc and alloys thereof.

The acidic phosphating solution used in the method of the present invention may be prepared based on conventional techniques, except that it contains a specific amount of a specific ion and sets the free acidity to a specific value as described above. 0.01-0.05, preferably 0.02-0.03W / V% for zinc ions
Is. If the amount of ions is too small, a chemical conversion film will be difficult to form, while if it is too large, the desired good film cannot be obtained. As cations other than zinc ions, one or more of nickel ions, manganese ions, and calcium ions may be contained in an amount of 0.01 to 0.15 W / V%, respectively, and these properties of the coating (especially primary and secondary physical properties). , Salt spray resistance, and exposure resistance performance).

As for the phosphate ion, it is 1.5 to 3.0 W / V% as described above, and if this amount is too small, a granular chemical conversion film cannot be obtained,
If it is excessive, only the ions are consumed, which is economically disadvantageous. 0.001 to 0.02W for nitrite ion
If it is / V% and this amount is too small, it causes rusting,
When it is excessive, nitrate ions generated by decomposition are excessively accumulated, which adversely affects the film formation. Complex fluoride ion as an anion other than the above _{^{(eg: BF 4 -, SiF 6 -}} ) and nitrate ions may also contain one or more, in the former 0.02~0.15W / V% as fluorine Is preferable from the viewpoint of making the chemical conversion film finer, and the latter nitrate ion may be contained from the same viewpoint as in the prior art. In addition, it is not preferable to include chlorate ion as an anion. This is because a granular conversion coating cannot be obtained, which is not desirable from the viewpoint of corrosion resistance of the conversion coating.

If the free acidity of the treatment liquid is less than 0.1 point, film formation is not performed, and if it exceeds 0.3 point, a granular crystal film is not obtained and a needle crystal film is formed. Regarding the free acidity, 10 ml of the treated solution was sampled, 1 to 2 drops of bromphenol was added as an indicator to the solution, and the solution was titrated with a 0.1N caustic soda solution until the solution changed color from yellow to blue. Point to the number of ml of the aqueous solution. In the treatment liquid used for the phosphate treatment, caustic soda is added to the treatment liquid until the free acidity reaches a predetermined value.

By adjusting the surface before the chemical conversion treatment with a titanium colloid-containing liquid (0.7 to 3.5 mg / titanium colloid), the crystal grain size of the chemical conversion coating can be made finer as conventionally known, and the coating performance can be further improved. it can.

In the spray treatment using the above-mentioned acidic phosphate treatment liquid, a conventional method may be adopted, for example, the temperature is 40 to 70.
℃, preferably 45 ~ 55 ℃, spray pressure 0.5 ~ 3kg / cm ² ,
The treatment time is preferably 0.8 to 1.5 kg / cm ² , and the treatment time is 40 seconds or more, preferably 90 to 180 seconds. As the post-treatment after the chemical conversion treatment, a conventionally known chromium-based or non-chromium-based treatment may be adopted, which further improves the film performance.

[Effects of the Invention] According to the method of the present invention having the above-mentioned constitution, a conversion coating having a granular and fine particle size and a coating amount of 1.5 g / m ² or more and an iron or iron-manganese content of 9 wt% or more is obtained. The same performance as the chemical conversion coating obtained by the dipping treatment is exhibited, and as a result, excellent coating adhesion and corrosion resistance are achieved in cationic electrodeposition coating.

EXAMPLES Next, the present invention will be specifically described with reference to Examples and Comparative Examples.

Example 1 A commercially available cold-rolled steel (70 × 150 × 0.8 mm) test piece was treated with an alkaline degreasing agent (“Rydrin SD200” manufactured by Nippon Paint Co., Ltd., 2 W /
(V%) at a temperature of 50 ° C for 2 minutes by spray degreasing, washing with water,
Spray with a titanium colloidal surface conditioning solution (Nippon Paint Co., Ltd. "Fixogen 5N-5", 0.03W / V%) for 10 seconds at room temperature.

Next, the test piece was treated with zinc ion 0.04 W / V%, nickel ion 0.03 W / V%, phosphate ion 2.5 W / V% and nitrite ion 0.007 W / V%, and an acid phosphate having a free acidity of 0.1 point. Spray treatment with the treatment liquid at 50 ° C. for 2 minutes, wash with tap water and ion-exchanged water, and dry.

The obtained chemical conversion film has a granular shape, and the particle size is 0.5 to 3
is μ. The photograph of Fig. 1 showing the structure of the film crystal was taken with a scanning electron microscope (JSM-T20 manufactured by JEOL Ltd.) at an angle of 55.
Photographed at a magnification of 1500x (the same applies below). The coating weight is 2.01 g / m ² and the iron content is 9.2 wt%.

The chemical conversion treatment test piece thus obtained was then subjected to a cationic electrodeposition coating (“Power Top U-3” manufactured by Nippon Paint Co., Ltd.).
0 ”), electrodeposition coating at 250V for 3 minutes and baking at 180 ° C for 30 minutes (film thickness 20μ). Next, apply a polyester-based intermediate coating ("52E Sealer" manufactured by Nippon Paint Co., Ltd.) at 140 ℃
Bake for 30 minutes (film thickness 30μ), and then apply a melamine alkyd top coat (“Olga G-25E” manufactured by Nippon Paint Co., Ltd.) and bake at 140 ° C. for 30 minutes (film thickness 40μ).

The test pieces thus obtained were subjected to the tests shown below, and the results are shown in Table 1.

(A) Salt spray test A cross-cut is cut into the surface of the electrodeposition coated plate with a cutter until it reaches the substrate, and a 5% salt spray test (JIS-Z-2371) is performed on this coated plate for 1000 hours. Measure the rust width.

(B) Exposure test Cross-cut is put on the surface of the top coated plate with a cutter until it reaches the substrate, and this coated plate is exposed on the coast for 6 months. After that, the blister width of the coating film from the cut portion of the coated plate is measured.

(C) Bending test A top coated plate is placed on a rod having a diameter of 10 mm, and the state of the coating film after bending is observed (JIS-K-5400-6-11).

Example 2 zinc ions 0.04 W / V%, nickel ions 0.03 W / V%, phosphate 2.5 W / V%, fluoroborate hydride ion (BF ₄ ^-) (as fluorine) 0.035W / V%, nitrate 0.3W / V% and 0.007W / V% nitrite ion, using an acidic phosphating solution with a free acidity of 0.1 point, spray treatment is performed for 2 minutes at 50 ° C, iron with a coating weight of 1.87g / m ² The same procedure as in Example 1 is carried out except that a chemical conversion film having a content of 9.7 wt% is obtained. The formed chemical conversion film is granular and has a particle size of 0.3 to 1 µ. An electron micrograph of the film crystal structure is shown in FIG. The test results after coating are shown in Table 1.

Example 3 Zinc ion 0.04 W / V%, nickel ion 0.03 W / V%, phosphate ion 2.5 W / V%, manganese ion 0.06 W / V% and nitrite ion 0.007 W / V% are contained, and free acidity is 0.2. Spray treatment at 50 ° C for 2 minutes using the acidic phosphate treatment solution of Point to obtain a chemical conversion coating with iron content of 7.2 wt% and manganese content of 4.0 wt% at a coating weight of 2.12 g / m _2. Other than that, it implements like Example 1. The formed chemical conversion film is granular and has a particle size of 0.5 to 3 µ. An electron micrograph of the film crystal structure is shown in FIG. The test results after coating are shown in Table 1.

Comparative Example 1 Acidic phosphoric acid containing zinc ion 0.03 W / V%, phosphate ion 1.0 W / V% and chlorate ion 0.3 W / V% and free acidity 0.3 point and nitrite ion 0.007 W / V% Using salt treatment solution, spray treatment at 50 ° C for 2 minutes, coating weight
Except for obtaining a conversion coating of iron content 8.2 wt% at 1.20 g / m ^2,
The same procedure as in Example 1 is carried out. An electron micrograph of the film crystal structure is shown in FIG. The test results after coating are shown in Table 1.

Comparative Example 2 Zinc ion 0.05 W / V%, phosphate ion 1.2 W / V%, nitrate nitrate
On 0.7 W / V% and 0.007 W / V% nitrite ion
Using an acidic phosphating solution with an acidity of 0.3 points,
Spray treatment at 0 ℃ for 2 minutes, coating weight 1.5g / m With iron
Same as Example 1 except that a chemical conversion coating with a content of 7.8 wt% is obtained.
To carry out. Fig. 5 shows an electron micrograph of the crystal structure of the film.
Show as. The test results after coating are shown in Table 1.

Comparative Example 3 Acidic phosphate treatment solution containing zinc ion 0.01 W / V%, nickel ion 0.05 W / V%, phosphate ion 1.5 W / V% and nitrite ion 0.01 W / V% and free acidity 1.1 points Is carried out at 50 ° C. for 2 minutes to obtain a chemical conversion coating having an iron content of 10.2 wt% at a coating weight of 2.0 g / m ² and is carried out in the same manner as in Example 1. Electron micrograph of crystal structure of film No. 6
Shown as a diagram. The test results after coating are shown in Table 1.

[Brief description of drawings]

1 to 6 are electron micrographs showing crystal structures of the phosphate coatings obtained in Examples and Comparative Examples of the present invention.

Claims (1)

[Claims] 1. Zinc ion 0.01 to 0.05 W / V%, nickel ion and / or manganese ion 0.01 to 0.15 W / V%,
Phosphate ion 1.5 to 3.0 W / V% and nitrite ion 0.001 to
Free acidity containing 0.02 W / V% and no chlorate ion
A phosphating method for a metal surface, which comprises spraying the metal surface with an acidic phosphating solution of 0.1 to 0.3 points.