JP2005232505A - Post-treatment method of phosphate coated film or galvannealed film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple method capable of enhancing corrosion resistance and discoloration resistance of a surface of a phosphate coated film or a galvannealed film, and adhesiveness of the coating film, and containing no compositions harmful to the environment. <P>SOLUTION: The present invention copes with the surface treatment other than the plating. When generally performing the coating or solid lubrication after the phosphate chemical conversion coating or galvannealing processing, a surface of a parts is once dried, and brought to the next step, or if rust is generated during this time, the surface is discolored to give adverse effect to the next step. Thus, protection of the surface of the parts from rust or discoloration affects much on the performance of the next step. Thus, a safe and simple solution is to provide a method effective and simple for the surface stabilization of the parts after the phosphate chemical conversion coating or the galvannealing processing. The surface after the phosphate chemical conversion coating or galvannealing processing is brought into contact with aqueous solution containing a cerium salt by ≥25 ppm, and washed in water and dried. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a post-treatment method for preventing oxidation and discoloration when a phosphate film or a zinc alloyed film is applied as a surface treatment of a steel-based metal part.

  Conventionally, a phosphate film or a zinc alloyed film has been applied as a temporary rust prevention treatment for steel or to improve adhesion before applying an organic film or the like. However, the film formed by the phosphate film treatment is generally porous, and the corrosion resistance is not sufficient particularly in the case of zinc phosphate treatment with a thin film. In the zinc alloying treatment, there may be cases where the zinc deficient portion has insufficient corrosion resistance depending on the film thickness. Before the phosphate film is formed, the surface of the steel part is activated by pickling, etc., so there is a defect in the formed phosphate film or the product layer itself by the phosphate film treatment is thin. In some cases, the surface of the chemical film may be discolored before drying, or oxidation may occur on the surface of the part before the complete rust prevention treatment is applied in the next process such as painting, resulting in poor adhesion of the coating film. May cause. Especially in the process of batch processing of parts with complicated shapes in a barrel, the active film just formed is rubbed between parts while the phosphate-treated film is exposed to water vapor during drying. Depending on the shape of the parts, cleaning water may accumulate depending on the shape of the parts, and drying may be delayed, causing accidents in which minute rust is partially generated on the site. For this reason, an extremely thin chromate film is applied to the phosphate film with an aqueous solution containing a hexavalent chromium salt after the phosphate film treatment at an actual work site.

  The method for stabilizing a phosphate coating with hexavalent chromium is to immerse a component formed with a phosphate coating or a component with a zinc alloyed coating in an aqueous solution containing a very small amount of hexavalent chromium for a short time. Since the processing cost is very small, it is widely used as a very effective oxidation and discoloration prevention method.

However, in recent years, it has become necessary to eliminate hexavalent chromium as a countermeasure for environmental problems. The disposal of liquid containing hexavalent chromium also requires treatment for wastewater treatment, although the chromium content is small. For this reason, a simple and non-polluting treatment is desired in place of the hexavalent chromium aqueous solution immersion method. The present invention provides such a method.

  The problem to be solved is that at the work site where the parts after the phosphate treatment or zinc alloying treatment are washed and dried, the processing cost is low, the work is simple, and a series of work processes are performed. It is to provide an effective post-treatment method that can be carried out as a single step in place of the hexavalent chromium addition dipping method.

  The present invention provides a simple post-treatment method for preventing rusting and discoloration due to oxidation with respect to the phosphate chemical conversion film and zinc alloyed film formed on the surface of steel parts. In this case, since these films have strong pretreatment elements for achieving further long-term rust prevention by subsequently applying an organic film such as coating, it is general that simple and inexpensive treatment is desired. Therefore, the adhesion of the next process such as painting should not be hindered, but the corrosion resistance must be sufficiently maintained until the next process. As a result of repeated experiments, these objects have been achieved by the present invention.

As a method of evaluating corrosion resistance, generally, salt spray test and corrosion time with sulfurous acid gas are measured, but this time the purpose is not final long-term corrosion resistance, but the surface of the part is not rusted until the next process. In addition to protecting against discoloration, it is required to suppress deterioration of the coating adhesion on the surface, or rather improve the adhesion. Therefore, in the corrosion resistance evaluation, after the formation of the phosphate coating or after the formation of the zinc alloy coating The dried part surface was held over heated steam to compare the time until discoloration. Moreover, the coating film was coated on the surface of the dried film, and the adhesion of the coating film was evaluated by applying it to a pin-on-disk friction and wear tester.
From these results, it was found that the corrosion resistance of the treated film was practically sufficient, and the adhesion of the coating film was improved as compared with the untreated film.

1. Preparation method of test piece: Using a mild steel plate (SPC 50 × 60 mm × 1 t), it was prepared by the process described in item 2.
Preparation of treatment liquid: A film is formed under the following conditions using the commercially available phosphate coating agent P637 under the average working conditions described in the instruction manual of the phosphate coating agent, and various liquid concentrations are immediately obtained. The test piece was dipped in a cerium (Ce) salt solution for 2 minutes at room temperature, washed with water and then dried by blowing warm air.
The processing steps are as follows.
2. Process: Degreasing (alkaline degreasing solution) → Washing → 15% hydrochloric acid solution dipping (wt%, room temperature dipping for 2 minutes) → Washing → Zinc phosphate coating agent P637, treated with manufacturer recommended median (stock solution 30 g / L, temperature) : 75 ° C., time: 10 minutes) → post-treatment liquid according to the present invention (concentration: 10 ppm, 25 ppm, 50 ppm, 100 ppm, 200 ppm, 400 ppm, normal temperature immersion for 1 minute) → running water washing → warm water washing → drying (warm air) )
3. Corrosion resistance comparison: Put water in a beaker and heat to boil. Hold the dried specimen in the steam and leave for 2 minutes to remove. The phosphate film is visually observed for discoloration and occurrence. Those with discoloration / generation were marked with x, and those without were marked with ◯. A summary is shown in the following table.

In the case of immersion in pure water only, the surface immediately changed color. The evaluation was x.
In the case of the cerium salt in the lower table according to the present invention, the effective concentration range of the liquid is much wider than that in the case of the dichromate in the upper column. That is, the dilute aqueous solution showed a sufficient antioxidant effect.

Parts cut from sulfur free-cutting steel (diameter 8mmФ × length 20mm, 8000 parts with 1.5mmФ blind holes on the side) are placed in a stainless steel barrel and the barrel is automatically rotated slowly while Degreasing, rinsing, rinsing, pickling with 15% hydrochloric acid, rinsing, rinsing, dipping in a surface conditioning bath, followed by zinc phosphate coating treatment using P637, followed by rinsing with water to a 50 ppm cerium salt solution according to the present invention It was immersed for 2 minutes, washed with water, washed with hot water and dried.
The washing water that normally accumulates in the blind holes may bleed out with hot air when dry and may cause partial discoloration of the phosphate film, but there is no discoloration due to the above process, and a uniform phosphate film is formed. I was able to form. The parts were removed from the barrel after drying and sent to the solid lubrication coating process. The finished parts were subjected to a slidability test and an adhesion test as quality evaluations by sampling, but there was no variation in performance.

  About 500 parts punched from a 1 mm-thick steel plate and bent by one press are put into a 300 mm stainless steel wire cage, and the same process as in Example 2 is performed manually. A zinc phosphate film treatment was performed. When the parts were overlapped and dried, a non-uniform pattern was generated. The film after drying was uniform, and there was no defective appearance in the next coating process.

  When the method according to the present invention was actually applied to various parts, there was no difference in appearance from the surface of the parts that were not treated, and the difference appeared only in the hidden characteristic aspects of corrosion resistance and coating film adhesion. The fact that the appearance is the same between the treated product and the untreated product is advantageous in determining adoption. The merit of industrial use is great for reducing defects.

Claims (1)

  As a surface treatment of steel parts such as steel machined parts and iron casting parts, when a phosphate film treatment or zinc alloyed film is applied, after the phosphate treatment or with a treatment method for zinc alloyed film Soaked in an aqueous solution containing a trace amount of cerium compound that does not contain environmentally harmful components, preventing oxidation and discoloration of the film, and improving adhesion of the film to the phosphate film surface or zinc alloy film Post-treatment method for phosphate film or zinc alloy film characterized by