JPS60211080A - Treatment with zinc phosphate by immersion - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance of the surface of the edge part of a metallic article treated with zinc phosphate by supplying DC at a proper current density for a proper time using the metallic surface immersed in a treating soln. contg. zinc phosphate as a cathode. CONSTITUTION:When a metallic surface is treated with zinc phosphate by immersion, DC is supplied at 2-10A/dm<2> current density on the metallic surface for 10-60sec using the immersed metallic surface as a cathode to form a film different from a conventional zinc phosphate film and having high corrosion resistance in itself on the edge part of the metallic surface to be treated. The DC supply may be suitably carried out during treatment with zinc phosphate by immersion, immediately after immersion or immediately before taking out. By said treatment the corrosion resistance of the edge part of a metallic article is improved. The edge part is coated with a little paint by the flow of a paint film during coating and baking.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] The present invention relates to an improved immersion zinc phosphate treatment method. More specifically, the present invention relates to a zinc phosphate treatment method that can improve the corrosion resistance of the edge surface of metal products.

[Prior Art] In recent years, various improvements regarding phosphate treatment and the introduction of cationic electrodeposition coating have dramatically improved the corrosion resistance of metal products after coating. However, there is a problem in that the paint film forms cracks from the edges (particularly the edges) of metal products after a short period of time. As a result of further investigation, when the edge in question was observed under a microscope, it was found that the phosphate chemical coating was attached to the tip of the edge, but the electrodeposited coating and other coatings were not present during baking. 7
0-, it was confirmed that there was almost no adhesion. Based on this knowledge, we conducted research on improving the chemical conversion coating on the edge portion, and found that during immersion zinc phosphate treatment of the metal surface, the entire surface of the object to be treated, including the edge portion, was treated using the metal surface as a cathode. When a DC current of a predetermined current value is applied for a certain period of time, a larger charge is applied to the edge part than other parts, and as a result, a film different from the conventional zinc phosphate film is formed on the edge part, and this film It was discovered that by itself it exhibits good corrosion resistance performance.

1 Structure and effect of the invention 1 The present invention was completed based on such discovery, and
The gist is a method of immersing a metal surface and treating it with zinc phosphate, using the metal surface as a cathode at a rate of 2 to 10 A/d.
m2 (metal surface, hereinafter the same) is a method characterized by passing a direct current for 10 to 60 seconds.6 Note that the phosphoric acid formed by passing current through the metal surface during immersion phosphating is It is conventionally known to improve the corrosion resistance performance of chloride conversion coatings. For example, special public service in 1977-46
No. 220 and Japanese Unexamined Patent Publication No. 55-41930. In the method disclosed in the former, an alternating current is applied to the metal surface. In the method disclosed in the latter, alternating current or direct current (the metal surface is a cathode or an anode) is applied to the metal surface after a normal immersion treatment. According to these conventional techniques, the corrosion resistance of the formed film is clearly improved compared to a normal immersion treatment that does not carry out energization treatment. However, in these conventional technologies,
In particular, regarding the current value, a lower value is adopted compared to the present invention. For example, in JP-A-55-41930, a current value of 0.05 to 2 A/dm2 is adopted.

However, it is not disclosed that a metal surface is specified as a cathode and that a direct current is applied thereto at 2 to 10 A/dm2 for 10 to 60 seconds. In this case, 2A/d+++2
If it is less than that, the corrosion resistance will improve on the flat parts of the metal surface, but the film according to the present invention will not be formed on the edge parts, and no significant improvement in the corrosion resistance will be observed. Also, 10A/d transport 2
If the value exceeds 100%, the corrosion resistance of the edge portions will be improved by the coating according to the present invention, but the adhesion of the coating on the flat portions will deteriorate due to the formation of an excessive zinc phosphate coating. If the current application time does not reach 10 seconds, the film according to the present invention will not be formed on the edge portions, and if it exceeds 60 seconds, the coating film adhesion performance on the flat portions will deteriorate.

In the method of the present invention, by setting the current value and energization time within the above range, a film different from the conventional zinc phosphate film is formed on the edges of the metal surface, which itself has corrosion resistance. is improved. Although the film obtained by conventional zinc phosphate treatment generally contributes to improving the corrosion resistance after painting, it can hardly be expected to have corrosion resistance alone because the film itself is porous. The film formed on the edge part according to the present invention is a blue-black film in appearance, unlike the gray-white zinc phosphate film on the flat part,
Excellent corrosion resistance on its own. Therefore, the treatment according to the present invention improves the corrosion resistance of parts such as the edges of metal products, which are only slightly covered with a paint film due to the flow of the paint film during baking. Therefore, it is possible to satisfactorily prevent blisters from occurring in the coating film around the edge portions.

In normal immersion treatment without electricity, generally 15 to 1
Although a processing time of 20 seconds is employed, the energization processing of the present invention may be performed in parallel. That is, the energization process may be partially performed during the normal immersion process. Further, the energization treatment of the present invention may be carried out by adding it in series before and after the normal immersion treatment.

In this case, the energizing treatment and the non-energizing treatment may be performed in the same bath or in separate baths. If the treatment is carried out in a separate bath, a water washing treatment may be employed in addition to the bath.

Examples of the anode used as a counter electrode in the current treatment include stainless steel (eg, 5US304.316) and carbon. The distance between the metal surface cathode and anode is not a particularly important factor.

Other conditions in the method of the present invention may be appropriately selected based on the conventionally known immersion zinc phosphate treatment method. For example, if the zinc phosphate treatment is performed as a pretreatment for cationic electrodeposition coating, the treatment solution should contain 0.5 to 2 g/! of Zn ions! , P04 ion 10-30g/II
, Mn ions 0-2g/! , Ni 41rn0-2g/
, e, No3 ton 0-10F1/4. ClO3 ion 0-1g/4, NO2 ion 0.01-0.1g/4,
F ion O~3g/! An aqueous solution containing may be used.

A suitable treatment temperature is 30 to 70°C. A treatment may be employed in which the treatment liquid is sprayed onto the metal surface immediately after it has been taken out from the treatment liquid to remove adhering sludge from the metal surface. After the chemical conversion treatment, the metal surface is then washed with water according to the usual method.
After drying, it may be subjected to a known coating treatment such as electrodeposition coating.

Metal surfaces include steel, zinc and their alloys.

[Example 1] Next, the present invention will be specifically explained with reference to Examples and Comparative Examples.

Examples 1 to 3 A clean steel plate was punched out to a diameter of 10 mm and the edges were approximately 0.0 mm in diameter.
A hole having a paris of about 11QI11 is formed. This test piece was treated with a zinc phosphate treatment solution (Zn ion 0.8g/l, P
O, ion 14g/l, Ni ion 0.5g/It,
NO, ion 3g/! , CIO, ion 0.5g/poor,
It was immersed in an aqueous solution (containing NO2 ion 0.0B, #, total acidity 17 points, free acidity 0.9 points, toner value 1.5 points), and then treated without electricity at 52°C under the conditions shown in Table 1. Continuously conduct direct current treatment using the test piece as a cathode and the carbon electrode as an anode. The specimens are then washed with tap water and then with deionized water and dried.

The obtained phosphate-treated test piece was coated with an amine-modified epoxy resin cationic electrodeposition paint (manufactured by Nippon Paint Co., Ltd. [Power Top Bee 30 Black]) using blocked isocyanate as a crosslinking agent to a film thickness of 20 μm at a voltage of 250 V and a duration of current application. 3 minutes), and bake at 180℃ for 1 minute.

The obtained electrodeposition coating test piece was subjected to a salt spray test (JIS-Z-
2371, 35°C, 2 hours) → dry test (60°C, 2 hours) → wet test (50°C, 95% relative humidity, 4 hours) was subjected to 100 cycles of corrosion test. Measure the 7-fur width of the coating film. The results are shown in Table 1.

Examples 4 to 6 Examples 1 to 3 are carried out in the same manner as in Examples 1 to 3, except that in the zinc phosphate treatment, direct current treatment and then continuous non-current treatment are performed under the conditions shown in Table 2. The results are shown in Table 2.

Example 7 Zinc phosphate treatment solution with different formulations (Zn ion 1g/poor,
PO4 ion 14 g/Jl %Mn ion 0°8
g/! , NO, ion 4 g/night, C10, ion 0.
7g/poor, NO2 ion 0.06g/4, total acidity 17.5 points, free acidity 0.9 points, toner value 2.0 points) was used, and DC current was applied under the conditions shown in Table 3. Examples 1 to 3 are carried out in the same manner as in Examples 1 to 3, except that the energizing treatment is followed by the non-energizing treatment. The results are shown in Table 3.

Example 8 Zinc phosphate treatment solution with different formulations (Zn ion 1g/It
, PO, ion 14 g/(1, Mn ion 0.8 g/
I1%5iFa ion ig/child, NO, ion 4g/l
, ClO3 ion 0.7g/1% NO2 ion 0.06
g/ffi, total acidity 18.5 points, free acidity 0.9 points, and toner value 2°0 points), and was treated with direct current under the conditions shown in Table 3, then continuously without current. Examples 1 to 3 except for the treatment
Execute in the same manner as .

The results are shown in Table 3.

Comparative Example 1 The same procedure as in Example 1 was carried out except that the entire non-current treatment was carried out for 120 seconds. The results are shown in Table 4.

Comparative Example 2 The same procedure as in Example 7 was carried out except that the entire non-energizing process was carried out for 120 seconds. The results are shown in Table 4.

Comparative Example 3 The same procedure as in Example 8 was carried out except that the entire non-current treatment was carried out for 120 seconds. The results are shown in Table 4.

Table 1 Table 2 Table 3 Table 4

Claims (1)

[Claims] 1. A method of immersing a metal surface and treating it with zinc phosphate, characterized by applying a direct current at 2 to IOA/da2 (metal surface) for 10 to 60 seconds using the metal surface as a cathode. How to do it. 2. The method of item 1 above, in which the metal surface is energized immediately after being immersed in the treatment liquid. 3. The method of item 1 above, in which the metal surface is energized immediately before being taken out from the processing solution.