JPH09263968A - Chromating process and chromating processed product obtained with this - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the interface stickiness between galvernized layer and chromatic film by applying the galvanizing on the surface of a metal, successive ly, applying the chromatic treatment on the galvanized layer and thereafter, executing heat treatment. SOLUTION: The galvernizing 2 is applied on the surface of the metallic plate 1. The chromatic treatment 3 is applied on the galvanized layer surface 2 and thereafter, the heat treatment is executed at 60-100 deg.C for 10min-5hr. The unnecessary moisture in the chromatic film is removed by the heat treatment. Miscellaneous ions of remained sulfate ion, etc., included in the chromatic film at the time of the chromatic treatment is fixed in the chromatic film. In this result, a brittle layer is not formed at the interface between the galvernized layer and the chromatic film. At the time of once applying this treatment, the chromatic film is difficult to absorb the moisture. If the heat treatment temp. is lower than 60 deg.C, the fixing of sulfate radical is not sufficiently executed, and if this temp. is higher than 100 deg.C, the chromatic film is crazed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a chromate treatment method and a chromate-treated product obtained thereby.

[0002]

2. Description of the Related Art Conventionally, metal pipes, metal plates, etc. of automobiles have been subjected to zinc-based plating as a rust preventive treatment on their metal surfaces. It is usually applied. This chromate treatment is performed for the purpose of further improving the corrosion resistance and appearance of the zinc-based plating and the base treatment of the coating, and at the time of this treatment, for the purpose of forming a chromate film, at 60 to 70 ° C for about 5 minutes. Is also dried.
Regarding such chromate treatment, in the past,
By considering the factors during chromate treatment (treatment liquid, treatment temperature, treatment time, washing process, drying conditions, etc.), we examined how to improve the corrosion resistance and adhesion of the film,
As the evaluation method, salt spray test and cross-cut peeling test have been conducted. Regarding the point of improving corrosion resistance,
These techniques were sufficient.

[0003]

However, in recent years, it has been pointed out that the adhesion of the zinc-based plating / chromate film interface decreases depending on the use environment. The demand for is increasing. However, in the past,
Chromate coatings have been improved with emphasis on corrosion resistance, and it has been difficult to obtain high interfacial adhesion between zinc-based plating / chromate coatings by the conventional chromate treatment method.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a chromate treatment method capable of realizing high interfacial adhesion in addition to corrosion resistance, and a chromate-treated product obtained thereby. .

[0005]

In order to achieve the above object, the present invention provides a chromate treatment in which a metal surface is subjected to zinc plating, the surface of this zinc plating is subjected to chromate treatment, and then heat treatment is performed. The method is the first gist, and the chromate-treated product obtained by this chromate treatment method is the second gist.

[0006] That is, the present inventors
In order to obtain a chromate treatment method capable of achieving high interfacial adhesion of a chromate film, intensive research was conducted. In the middle of the research, if the heat and time factors above a certain level are applied to the metal pipe, metal plate, etc. on which the zinc-based plating / chromate film is formed as the surface treatment, the above-mentioned interfacial adhesion will deteriorate. I found it easy to do. It was also found that the cause of this is that peeling is likely to occur at the zinc-based plating / chromate coating interface when a certain factor of heat and time is added to the chromate coating containing a large amount of water. Therefore, as a result of further research, it is difficult to form a stable chromate film with high adhesion only by conventional drying, and it is difficult to form a chromate film with high adhesion. The inventors have found that it is effective to add steps, and have arrived at the present invention.

The following mechanism can be considered as the mechanism of this chromate treatment method. That is, the above heat treatment removes unnecessary water in the chromate film, and also removes miscellaneous ions in the chromate film (particularly, sulfate ions taken in and remaining in the chromate film during the chromate treatment). Can be immobilized inside. As a result, it is considered that WBL (fragile layer) is prevented from being formed at the interface of the zinc-based plating / chromate coating. Once this treatment is applied, it becomes a chromate film that hardly absorbs water. Therefore, in the product obtained by the chromate treatment method of the present invention, there is no variation in the amount of water in the chromate film, and a stable supply of the product can be achieved. In addition, although the conventional water-absorbing chromate film-treated product was very difficult to control such as storage, the product of the present invention facilitates this control. Moreover, when the metal pipe subjected to the chromate treatment method of the present invention is assembled to the connecting rubber hose, not only peeling of the chromate film does not occur, but also the adhesive force of the rubber to the metal pipe is improved. Moreover, when used as a base treatment for coating and coating, not only does chromate peeling occur, but also the adhesion of coating and coating is improved. When considering the adhesion and adhesion of the interface between the chromate film and the rubber, coating and coating, it is known that dust, water, etc. will reduce the interface. It is considered that since the water content is removed, the adhesive strength and the adhesive strength are consequently improved, and the above-mentioned effects are obtained.

[0008]

Next, the present invention will be described in detail.

The zinc-based plating of the present invention includes Zn plating, Zn-Ni plating, Zn-Fe plating, Sn-Zn.
There are various types such as plating.

When the heat treatment (drying) of the present invention is performed, the heating temperature (drying temperature) is basically the boiling point of water.
The temperature is set to around 00 ° C, but it can be performed without problems within the range of 60 to 100 ° C, and preferably within the range of 80 to 100 ° C. Such a temperature range is set because it is suitable for immobilizing the sulfate group in the chromate film. When the drying temperature is lower than 60 ° C., there is a problem that the sulfate radicals cannot be sufficiently fixed, and when the drying temperature is higher than 100 ° C., the chromate film is cracked. Also, the drying time is 10 minutes ~
It is set within the range of 5 hours, and preferably within the range of 15 minutes to 60 minutes. When the drying time is less than 10 minutes, there is a problem that the sulfate radicals cannot be sufficiently fixed, and when the drying time is more than 5 hours, there is a problem that the chromate film warps or cracks. Such heat treatment is usually performed by a gear oven or high frequency heating.

The heat treatment of the present invention can be applied to a coating formed from any treatment bath as long as it is a chromate coating on zinc-based plating. Further, the thickness of the chromate film has an optimum value depending on the type of base plating. For example, in the case of a colored chromate film on zinc plating, the film thickness is 0.
Within the range of 1 to 0.5 μm, preferably 0.25 to
Within the range of 0.3 μm, a good film can be obtained in terms of corrosion resistance.

In the present invention, for example, the surface of an iron plate is subjected to chromate treatment as follows. That is, first, FIG.
As shown in, the surface of the iron plate 1 is plated with zinc (the thickness of the zinc plating layer 2 is set to about 8 μm). Then, it is dipped in a solution containing chromic acid (5 to 250 g / liter) as a main component and dried at a low temperature (RT to 60 ° C. for 1 to 10 minutes) to form a chromate film 3 (αC on the zinc plating layer 2).
r ₂ O · βCrO ₃ · γH ₂ O) (the thickness of the chromate film 3 is set to 0.1 to 0.5 μm).
Then, after leaving it at room temperature for 24 hours or more, use a gear oven or the like immediately before use at 60 to 100 ° C. for 10 minutes to
Heat treatment (dry) for 5 hours. This heat treatment is 2
It does not need to be performed after 4 hours or more, and may be performed immediately after the chromate treatment or may be performed at any time.

In order to examine the elution of SO ₄ ^2- ions (sulfate) which are presumed to be immobilized by the above heat treatment, a conventional example product which was subjected to chromate treatment after being galvanized (only primary drying) Then, the product of the present invention which was subjected to zinc plating and chromate treatment and then secondarily dried at 100 ° C. for 5 hours was prepared (both the conventional product and the product of the present invention have a surface area of a chromate film of 100,000 mm ² Is 0.3 μm). Then, it was immersed in distilled water for high performance liquid chromatography (1 liter, 80 ° C.) for 24 hours, and the amount of SO ₄ ²⁻ ions in the liquid (extract) was measured using an ion chromatograph. The result is
It is shown in Table 1 below. As is clear from Table 1 below, the amount of SO ₄ ²⁻ ions extracted from the product of the present invention is lower than that of the conventional product (about 1/8 of the conventional product). It can be seen that SO ₄ ²⁻ ions were immobilized.

[0014]

[Table 1]

Next, examples of the present invention will be described.

[0016]

[Examples 1 to 16] Sixteen iron plates were prepared, the surface of each iron plate was galvanized (the film thickness of the plating was 8 µm), and then chromic acid (5 to 10 g / liter) was the main component. It was dipped in the solution and primary dried at 60 ° C. for 5 minutes to form a chromate film on the zinc plating. Next, after leaving at room temperature (20 ° C.) for 24 hours, secondary drying was performed at 100 ° C. using a gear oven. At this time, the thickness of the chromate film is set to 0.1 μm, 0.25 μm, 0.3 μm.
m and 0.5 μm and the drying time was set to 0 minutes, 10 minutes, 1 hour and 5 hours at each film thickness, corrosion resistance evaluation, chromate crack occurrence and interface adhesion were examined. . The corrosion resistance evaluation was carried out by conducting a salt spray test time and checking the rust generation status every 24 hours. In Tables 2 to 5, ○ indicates no abnormality: △
Indicates white rust occurrence: × indicates red rust occurrence. Further, with respect to the generation state of chromate cracks, the size of the generated cracks and whether the cracks were continuous or discontinuous were examined by using a metallographic microscope and a low vacuum SEM. In Tables 6 and 7, [small, discontinuous]
Indicates that small cracks occurred discontinuously, [Medium, continuous] indicates that medium cracks occurred continuously, and [Large, continuous] indicates that large cracks occurred continuously. Also, the interface adhesion is JIS K
By conducting an adhesion test according to 6301, the chromate peeling degree and the sticking force were examined. The results are shown in Tables 6 and 7. In Tables 6 and 7, the film thickness and the drying time of each Example are the same as those of Tables 2 to 5 having the same numbers. Moreover, the numerical value in () has shown the average value.

[0017]

[Table 2]

[0018]

[Table 3]

[0019]

[Table 4]

[0020]

[Table 5]

[0021]

[Table 6]

[0022]

[Table 7]

As is clear from Tables 2 to 5, when the secondary drying time is in the range of 10 minutes to 1 hour, the film thickness is 0.1 to 0.5.
In any case of μm, the corrosion resistance is hardly affected. When the secondary drying time is 5 hours, the film thickness is 0.1
In any case of .about.0.5 .mu.m, the corrosion resistance tends to be slightly lowered. These corrosion resistances are shown in Table 6 and Table 7.
It is shown that there is a correlation with the occurrence of chromate cracks shown in, and that the deterioration of corrosion resistance is not observed unless the situation of chromate cracks changes. On the other hand, Table 6
Also, as is clear from Table 7, when the secondary drying time is in the range of 10 minutes to 5 hours, the adhesion of chromate and the adhesive force are improved in any case of the film thickness of 0.1 to 0.5 μm. From these results, in order to obtain a chromate-treated product having both corrosion resistance and high adhesion, it is necessary that the chromate film thickness is 0.1 to 0.5 μm and the drying time is 1 hour when the drying temperature is 100 ° C. It turns out to be optimal.

[0024]

As described above, according to the method of the present invention,
Since the zinc-based plating is applied to the metal surface, the chromate treatment is then applied to the surface of the zinc-based plating, and then the heat treatment is performed, the high adhesion of the zinc-based plating / chromate coating interface can be realized. Further, in the product obtained by the method of the present invention, there is no variation in the amount of water in the chromate film, and the product can be stably supplied. In addition, although the conventional water-absorbing chromate film-treated product was very difficult to control such as storage, the product of the present invention facilitates this control. Furthermore, when assembling the metal pipe that has been subjected to the chromate treatment method of the present invention to the rubber hose for connection, not only peeling of the chromate film does not occur, but also the effect of improving the adhesion force of the rubber to the metal pipe. Moreover, when used as a base treatment for coating and coating, not only does chromate peeling occur, but also the adhesion of coating and coating is improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

[Explanation of symbols]

 1 Iron plate 2 Zinc-based plating layer 3 Chromate film

Claims (4)

[Claims] 1. A chromate treatment method, which comprises subjecting a metal surface to zinc-based plating, then subjecting the surface of the zinc-based plating to chromate treatment, and then performing heat treatment. 2. The heat treatment comprises heating at 60 to 100 ° C. for 1 time.
The chromate treatment method according to claim 1, which is carried out for 0 minutes to 5 hours. 3. A chromate-treated product obtained by the chromate treatment method according to claim 1. 4. A chromate-treated product obtained by the chromate treatment method according to claim 2.