JPH04247882A - Manufacturing method of chromate-treated plated steel material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing chromate-treated plated steel that enhances the rust prevention properties of zinc or zinc-based alloy plated steel.

0002

[Prior Art] Various chromate treatment methods have been put to practical use and used as rust prevention treatments for zinc or zinc-based alloy coated steel materials. Methods of adding silica sol and trivalent chromium ions were known (for example, Japanese Patent Publication No. 42-14050, Japanese Patent Publication No. 52-285
(See Publication No. 1).

[0003] Furthermore, a method for improving adhesion and corrosion resistance by improving these is disclosed, for example, in Japanese Patent Publication No. 58552/1983.

[0004] However, chromate-treated steel sheets manufactured by these methods suffer from chromium being eluted during alkaline degreasing after pressing, and in recent years, these chromate-treated steel sheets have been used as they are in home appliances, furniture, automobile parts, etc. As the number of cases has increased, the beauty of the appearance has become important to these customers, and in this respect, the chromate-treated steel sheets manufactured by these methods are completely inadequate due to the strong yellowing characteristic of chromate. It became clear that.

[0005] Among these drawbacks, Japanese Patent Application Laid-open No. 137180/1983 is a method for improving chromium elution, but it is still insufficient for improving the appearance, and the present inventors have attempted to solve this problem. previously disclosed in Japanese Patent Application No. 01-204346 a method in which a chromate treatment solution containing phosphoric acid and silica is applied and then dried at a high temperature of 220° C. or higher.

Although this high-temperature drying method is satisfactory in terms of the performance of chromate-treated steel sheets, it has the drawback of requiring additional equipment for high-temperature drying, which increases productivity and cost.

[0007]

[Problems to be Solved by the Invention] A chromate solution made by adding silica sol and trivalent chromium (hereinafter referred to as Cr3+) to chromic acid, which is a conventional method, is applied to a plated steel sheet and the plate temperature is raised to 40℃.
The method of raising the temperature to ~150℃ and drying has almost reached the required level in terms of corrosion resistance and adhesion, but the chromium elution property has not been improved and the appearance, especially the yellowish characteristic of chromate, is strong. However, it had the disadvantage of detracting from the beauty of its appearance.

[0008] Furthermore, patent application No. 01-
204346 has the disadvantage that it is more expensive than the conventional method in terms of productivity and cost.

The present invention improves the shortcomings of these conventional methods, solves the above problems at a lower cost, and provides a chromate-treated plated steel material that does not elute chromium and has excellent corrosion resistance with less yellowing characteristic of chromate. The purpose is to provide a manufacturing method.

0010

[Means for Solving the Problems] The present inventors have already applied a chromate treatment solution containing silica to the steel plate surface by drying at a high temperature of 220°C or higher in order to improve corrosion resistance, chromium elution properties, and appearance. It was discovered that the amount of residual Cr6+ needs to be 30% or less of the total amount of chromium, and an application was filed as Japanese Patent Application No. 01-204346.

However, this high-temperature drying imposes a large burden on productivity and cost, so we investigated various additives that would reduce the amount of Cr6+ remaining on the surface to 30% or less even when dried at lower temperatures. carboxylic acid and/or
Alternatively, the present invention was completed by discovering that carboxylic acid derivatives act as reducing agents for Cr6+ during drying, and that these additives have the effect of simultaneously improving corrosion resistance by increasing the chromate film. It is something that

That is, in order to achieve the above object, according to the present invention, trivalent chromium/hexavalent chromium (weight ratio) is 1/2 to 1/2 on the surface of zinc or zinc-based alloy coated steel.
It contains chromic acid and/or chromic acid reduction products in the range of 1 to 15% by weight as metallic chromium, and silica sol is added to this in a ratio of silica sol (SiO2 equivalent)/total chromium amount (weight ratio) of 1/2 to 6. After applying an aqueous solution containing a total of 0.1 to 10% by weight of one or more carboxylic acids and/or carboxylic acid derivatives that are stable in the aqueous solution, the steel material 150℃~3
It is characterized by heating and baking in a temperature range of 00℃ to form a chromate treatment film with a surface hexavalent chromium/total chromium amount (weight ratio) of 20% or less and a chromium adhesion amount of 10 to 150 mg/m2. A method of manufacturing a chromate-treated plated steel material is provided.

The carboxylic acids and/or carboxylic acid derivatives include benzoic acid, propionic acid, butyric acid, oxalic acid, succinic acid, lactic acid, acetic acid, formic acid, citric acid, acrylic acid, malonic acid, maleic acid, malic acid, valeric acid, Preferred are acetoacetic acid, butyramide, succinimide, succiamide, and succinic monoamide.

The present invention will be explained in more detail below.

First, regarding chromic acid and/or chromic acid reduction products, an aqueous solution containing chromic anhydride as a main ingredient is usually used in chromate treatment to ensure corrosion resistance and to enable uniform application to steel materials. However, in order to obtain a beautiful appearance, this chromic acid must be reduced to Cr.
Since it is necessary to secure 3+ at a certain rate, Cr3+
/Cr6+ (weight ratio) was set to 1/2 to 1/1.

That is, Cr3+/Cr6+ (weight ratio)
If it is less than 1/2, it is difficult to reduce the ratio of Cr6+ on the surface of the steel material after drying to 20% or less with respect to the total amount of chromium (hereinafter referred to as T-Cr). become unable to do so. Furthermore, if the amount of Cr3+ becomes too large and exceeds 1/1, precipitates are likely to form in the aqueous solution, causing inconvenience in storage of the aqueous solution, coating work, etc.

The content of chromic acid and/or chromic acid reduction product in the chromate treatment solution is required to be 1 to 15% by weight. This is because if it is less than 1%, it will be difficult to obtain a sufficient amount of chromium deposited, and if it exceeds 15%, there will be concerns about the stability of the liquid.

Next, silica sol will be described.

It is already known that adding silica to a chromate solution has the effect of improving corrosion resistance and preventing uneven chromate coating. Unable to satisfy sexual needs. However, according to the research conducted by the present inventors, a steel plate coated with a silica-added chromate solution was
Drying at temperatures below 0°C has little effect, but 2
By baking at a high temperature of 20°C or higher, preferably 240°C or higher, Cr6+ on the steel surface is reduced, and a strong chromate film is formed through dehydration and condensation reaction with silica, eliminating the yellowish tinge caused by Cr6+, resulting in a beautiful appearance. It was found that the improvement was achieved. It was also discovered that the corrosion resistance was further improved by the above-mentioned high temperature drying.

However, the effect of such silica addition is
If the amount of silica added is less than 1/2 of the total chromium amount of 1 in terms of SiO2, it is not sufficient, and if it exceeds 6, other adverse effects such as increasing the surface resistance of the steel surface will occur.
-Limited to a range of 1/2 to 6 of Cr.

Next, carboxylic acids and carboxylic acid derivatives will be described.

[0022] Carboxylic acids or carboxylic acid derivatives are stable in the chromate treatment solution at room temperature, but decompose when dried at high temperatures and change to lower molecular weight hydrocarbons, but in the process they have the effect of reducing Cr6+ to Cr3+. . In addition, the remaining hydrocarbons are incorporated into the chromate film and have the effect of thickening the chromate film. For this reason, it is necessary to add 0.1% by weight or more to eliminate the yellowing caused by Cr6+ and improve the appearance, and to thicken the chromate film and ensure corrosion resistance, but addition of more than 10% by weight is required. Since the carboxylic acid causes uneven drying, the amount was limited to a range of 0.1 to 10% by weight.

[0023] Conventionally, so-called resin chromate treatment, in which chromate treatment is carried out by adding polycarboxylic acid or its derivatives such as polyacrylic acid or its ester to a chromate treatment solution, has been known, but the carboxylic acid used in the present application The acid and/or its derivatives do not form a resin film through such copolymerization, but rather are oxidized and decomposed by reducing Cr6+ to Cr3+ as described above. Their technical philosophy is completely different.

[0024] Carboxylic acids and/or
Or its derivatives include benzoic acid, propionic acid,
Preferred are butyric acid, oxalic acid, succinic acid, lactic acid, acetic acid, formic acid, citric acid, acrylic acid, malonic acid, maleic acid, malic acid, valeric acid, acetoacetic acid, butyramide, succinimide, succiamide, and succinic monoamide. Can be used.

[0025] As mentioned above, the baking temperature is Cr
In order to suppress the yellowing caused by 6+, form a strong chromate film, and ensure corrosion resistance, a temperature of at least 150°C or higher, preferably 200°C or higher is required.
Temperatures above 00°C increase manufacturing costs, so 150°C
The temperature was limited to 300°C.

[0026] Such baking involves a reduction reaction of Cr6+ in the chromate treatment solution adhering to the steel surface to Cr3+, and is a very different process that has an essentially different effect from drying, which merely aims to evaporate water. This is an important process, and by going through this process, the weight ratio of Cr6+/T-Cr in the chromate film is reduced to 20% or less, and the chromate-treated steel material has a beautiful appearance and extremely high resistance to chromium elution. This makes manufacturing possible.

[0027]The amount of chromium deposited is 10 to 150 mg.
/m2 is required. This is because if it is too small, corrosion resistance will be insufficient, and if it is too large, it will not be possible to obtain a good appearance.

Further, the steel materials to which the present invention is applied are not limited by the type of plating method such as hot-dip plating, electroplating, or vapor deposition plating, but include zinc, Zn-Ni, Zn-
Binary alloys such as Fe, Zn-Al, and even Zn-Ni
- It is a steel material coated with a zinc-based alloy that widely includes multi-component alloys such as Co, Zn-Al-Cr, etc. The types of steel materials can be applied to steel plates, sections, steel pipes, wire rods, etc., and are limited by the type of steel material. It is not something that is received.

[0029]

EXAMPLES The present invention will be specifically explained below based on examples.

(Example 1) In order to clarify the effects of the present invention, a pure zinc electroplated steel sheet with a basis weight of 20 g/m2, 6
Chromic anhydride, distilled water, ethylene glycol, silica sol (
A basic chromate solution was prepared by blending Nissan Chemical's Snowtex 0), and various carboxylic acids and/or carboxylic acid derivatives were added to this to create each chromate treatment solution with the composition shown in Tables 1 and 2. The coating was applied with a bar coater, and the heating temperature of the steel plate was varied from 50 to 300℃, and the corrosion resistance, appearance, chromium elution property, etc. of each steel plate were evaluated.
The results are shown in Table 3.

Corrosion resistance was determined by salt spray test (JIS Z 23
71) Evaluated by the incidence of white rust on galvanized steel sheets over 240 hours. Appearance was visually checked for unevenness, and yellowness was determined by measuring L, a, and b values using an SM color computer (manufactured by Suga Test Instruments). The b value was used.

[0032] The amount of chromium eluted was determined by immersing it in an alkaline degreasing solution (CL364S 2% solution manufactured by Nippon Parker, 60°C) for 2 minutes, measuring the amount of chromium deposited before and after using fluorescent X-rays, and showing the amount of eluted chromium as a percentage. .

[0033] Furthermore, quantitative analysis of Cr3+ and Cr6+ on the surface of the steel plate was performed by ESCA.

[0034] The amount of chromium deposited was all measured using fluorescent X-rays and expressed in mg/m2.

FIGS. 1 and 2 show No. 1 in Table 1. After performing chromate treatment using the same steel plate and chromate treatment liquid as in Example 1 of the present invention, the heating temperature was variously changed to determine the heating temperature, corrosion resistance, b value, and surface Cr6-(%).
) is a graph showing the results of examining the relationship between The amount of chromium deposited at this time was approximately 45 mg/m2.

From Figure 1, the temperature at 200°C without carboxylic acid additive
From the above, hexavalent chromium decreases and remains at around 10% even at 300°C, whereas in the carboxylic acid additive of the present invention,
The effect of the present invention can be seen from the fact that at temperatures above 150°C, hexavalent chromium decreases, and at temperatures above 220°C, hexavalent chromium becomes almost 0 and the b value also becomes 0 or less.

FIG. 2 shows the results of the corrosion resistance test. In the case of no addition of carboxylic acid, it takes 2 to obtain sufficient corrosion resistance.
Although a drying temperature of 00°C or higher is required, it can be seen that sufficient corrosion resistance is exhibited at a temperature of 150°C or higher in the case of carboxylic acid addition.

Furthermore, from the results shown in Tables 1, 2, and 3, the steel sheets produced by the method of the present invention all have excellent appearance (no unevenness and b value of 3.5 or less) and corrosion resistance (
After 240 hours of salt water spraying, white rust generation rate is 5% or less) and chromium elution amount (5% or less), but when drying at a low temperature of less than 150°C, the b value is high at over 3.5, and chromium elution rate is 5% or less. (
10% or more) and corrosion resistance (5% or more) (Comparative Steels 33 and 38).

Further, when the Cr3+/Cr6+ ratio is less than 1/2, the surface Cr6+ concentration after drying is high and the b value is 3.
5, the appearance is poor (No. 25 Comparative Example).

On the other hand, when the Cr3+/Cr6+ ratio exceeds 1, the chromate solution becomes unstable and uneven coating tends to occur (Comparative Example No. 34).

Furthermore, if the amount of silica added is too small, sufficient corrosion resistance cannot be obtained (Comparative Example No. 27), and if it is too large, unevenness tends to occur (Comparative Example No. 26).

[0042] When the amount of carboxylic acid added is small, the surface C
The r6+ concentration is high and good appearance (b value 3.5 or less) and chromium elution resistance (5% or less) cannot be obtained (Comparative Example No. 21), and if it is too high, unevenness tends to occur (No. 22
comparative example).

[0043] If the chromium weight is too small, sufficient corrosion resistance cannot be obtained (Comparative Example No. 28), and if it is too large, the b value exceeds 3.5 and a good appearance cannot be obtained (No.
．． 29 Comparative Example).

From the above, it is clear that the present invention can produce a chromate-treated plated steel material with excellent corrosion resistance and beautiful appearance.

[0045]

[Table 1]

[0046]

[Table 2]

[0047]

[Table 3]

[0048]

Effects of the Invention Since the present invention is constructed as described above, it is possible to improve the beauty of the appearance, which has been difficult in the past, in particular, to reduce the yellow tinge peculiar to chromate, and to improve corrosion resistance at the same time. It has become possible to manufacture chromate-treated plated steel materials at a lower cost.

[Brief explanation of the drawing]

[Figure 1] Drying temperature and surface Cr in chromate treatment
FIG. 6 is a diagram showing the relationship between 6+ (%) and b value when 1% of carboxylic acid is added and when it is not added.

FIG. 2 is a diagram showing the relationship between drying temperature and corrosion resistance in chromate treatment with and without addition of 1% carboxylic acid, respectively.

Claims (2)

[Claims] [Claim 1] Trivalent chromium/hexavalent chromium (weight ratio) is 1/2 to 1 on the surface of zinc or zinc-based alloy plated steel.
chromic acid and/or chromic acid reduction products in the range of 1 to 15% by weight as metallic chromium, and silica sol (SiO2 equivalent)/total chromium amount (weight ratio) of 1/2 to 15% by weight. After coating an aqueous solution containing a total of 0.1 to 10% by weight of one or more carboxylic acids and/or carboxylic acid derivatives that are stable in the aqueous solution, Steel materials from 150℃
It is characterized by being heated and baked in a temperature range of 300°C to form a chromate treatment film with a surface hexavalent chromium/total chromium amount (weight ratio) of 20% or less and a chromium adhesion amount of 10 to 150 mg/m2. A method for producing chromate-treated plated steel. 2. The carboxylic acid and/or carboxylic acid derivative is benzoic acid, propionic acid, butyric acid, oxalic acid, succinic acid, lactic acid, acetic acid, formic acid, citric acid, acrylic acid, malonic acid, maleic acid, malic acid, Grass acid, acetoacetic acid,
The method for producing a chromate-treated plated steel material according to claim 1, which is butylamide, succinimide, succiamide, or succinic monoamide.