KR960009198B1 - Zn and zn-alloy coated steel sheets with an excellent phosphating galvanized surface - Google Patents

Abstract

This sheet is used for automobile and electric home appliances by a close nucleation of phosphate on the plane of steel sheets and a fine film formation of phosphate. This coating sheet has a coated layer in the quantity of 0.2 to 10mg/m2 copper. The copper coated layer is a substitution coated layer. The sheet provides a improvement of phosphate treatability by a small coated quantity of copper, and homogeneous film of phosphate in continuous plating line.

Description

Zinc and zinc-based alloy coated steel sheet with excellent phosphate treatment

1 is an enlarged structure photograph of a phosphate structure of a conventional zinc-iron alloy plated steel sheet and a zinc-iron alloy plated steel sheet treated by the present invention.

The present invention relates to a zinc- and zinc-based alloy plated steel sheet having excellent phosphate treatment, and particularly, to a zinc- and zinc-based alloy plated steel sheet obtained by obtaining a uniform phosphate coating even in a phosphate treatment in a plating line that continuously produces coiled steel sheets. It is about.

Phosphate treatment has been conventionally performed for the purpose of improving the paint adhesion of the steel sheet and the corrosion resistance after coating. Phosphate treatment for steel sheets includes a method of performing phosphate treatment after assembling parts, such as an automobile phosphate treatment process, and a method of continuously treating coiled steel sheets such as post-treatment of an electroplating line. In the former method, the processing time is less limited and a uniform phosphate coating can be obtained without being greatly influenced by the phosphate treatment property of the steel sheet. However, the processing time is limited to 10 seconds or less in the method of continuously treating the coiled steel sheet. Thus, the phosphate treatability of the steel sheet greatly affects the weave of the phosphate film. In other words, when the reaction rate of phosphate film formation is high, such as a zinc plated layer, a complete film can be formed within the above time. However, in the zinc-based alloy plated steel sheet, the phosphate film formation reaction is late and thus a complete phosphate film cannot be obtained in the above time. There is.

Known techniques for forming a complete film on a zinc-based alloy plated steel sheet in a plating line include a method of increasing the free acidity and free acidity of a phosphate solution and using a separate reaction promoter. However, this method is effective for zinc-based alloy plated steel sheet, but for the galvanized steel sheet, the zinc plated layer is eluted a lot during the formation of the phosphate film, so that a large amount of phosphate sludge is generated, thereby aging the solution.

In addition, as a known technique for obtaining a uniform phosphate coating, a method of performing surface adjustment before phosphate treatment is known. In this method, it is effective when the phosphate treatment time is about 150 seconds, but in a short treatment time within 10 seconds. In the case of zinc-based alloy plated steel sheet, there is no obvious treatment effect.

In addition, a well-known technique for improving the phosphate treatment of the steel sheet is a two-layer plated steel sheet, but the main use of the steel sheet is mainly used for the exterior of a car, and the phosphate coating is well used during the phosphate treatment in a continuous plating line. There is a problem that is not formed.

MEANS TO SOLVE THE PROBLEM The present inventor conducted research and experiment in order to solve the various problems of the conventional methods mentioned above, and by this result, the present invention was proposed, and the present invention provides a small amount (part) of copper on the surface of a plated steel sheet, thereby providing zinc and It is an object of the present invention to provide a zinc and zinc-based alloy plated steel sheet having excellent phosphate treatability, which can obtain a uniform phosphate coating even when the zinc-based alloy plated steel sheet is treated in a continuous plating line.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention relates to a zinc or zinc-based alloy plated steel sheet having excellent phosphate treatment property in which copper is partially coated on the surface thereof with an adhesion amount of 0.2-10 mg / m ² .

Phosphate film formation reaction is caused by phosphate nucleation and crystal growth in the electrical cathode part of the plated steel sheet. Therefore, the physical state and chemical properties of the plated layer (corrosion resistance and other chemical properties according to the plating layer alloy composition, alloy amount and surface oxide film state) Therefore, the phosphate treatment will be different. In the case of zinc plated layer, the plating layer has high reactivity, so the dissolution reaction of the plating layer and the phosphate precipitation reaction are active in the phosphate solution, but the zinc alloy plated layer is less reactive than the zinc plated layer, so the precipitation reaction of the phosphate is not active. It is likely that a coarse and dense phosphate film is formed.

In the constitution of the present invention, the copper attached to the surface generates an electrical difference on the surface of the plating layer to increase the phosphate nucleation area, thereby forming a uniform and dense phosphate film. Particularly, even in the low reactivity zinc-based alloy plated steel sheet, the reactivity of the plated layer is increased by the electrical difference between copper and the alloy plated layer, so that even after a short time treatment in a phosphate treatment solution for galvanized steel sheet, an excellent phosphate film can be obtained.

The reasons for limiting the deposition amount of copper are as follows.

When a small amount of copper attached to the surface of the plated steel is 0.2mg / m ² or less, the amount of copper adhesion is too small, the electrical difference between the copper and the plated layer is too small to show a large effect. In addition, when 10-20 mg / m ^{2 of} copper is attached, the phosphate treatment is excellent, but the excessive amount of zinc eluted into the phosphate solution due to excessive activation of the surface promotes solution degradation.

In the case where more than 20 mg / m ^{2 of} copper is deposited, the surface of the plating layer is completely covered, so that electrical non-uniformity on the surface of the steel sheet is not formed, so that the effect of improving the phosphate treatment property does not occur. Therefore, the deposition amount of copper is a good condition that can cause electrical irregularity due to the proper distribution of copper and iron on the surface of the steel sheet. That is, the copper adhesion amount which produces the improvement effect of a phosphate treatability is 0.2-10 mg / m <^2> .

As the copper deposition method, electroplating, vacuum deposition plating, electroless plating using a reducing agent, substitution plating, etc. are all possible, and the same effect can be obtained, but the electrochemical ionization tendency between copper and zinc-based alloy plating layers is large. It is the most suitable for the substitution plating method which is easy to install in the facility and easy to manage.

Hereinafter, the present invention will be described in more detail with reference to the following examples.

(Example)

With respect to the nickel alloy-plated steel sheet-coating weight of zinc in the 20g / m ² coated steel sheet, coating weight 20g / m ^2, an iron content of 17wt% of zinc-iron alloy plated steel sheet and the coating weight 20g / m ^2, the nickel content of 11wt% of zinc After copper plating, phosphate treatment and cationic electrodeposition plating by the following method, the phosphate treatment, post-coating corrosion resistance and water tightness were measured. As a result of the measurement, the galvanized steel sheet is shown in Table 1 below. The plated steel sheet is shown in Table 2 below, and the zinc-nickel alloy plated steel sheet is shown in Table 3 below.

On the other hand, in Comparative Example (15) and Inventive Example (27) of Table 2 below, the enlarged structure of the phosphate structure of the plated steel sheet was observed, and the result of Comparative Example (15) is shown in FIG. Honor 27 is shown in Figure 1 (b).

end. Copper plating

Plating bath condition: Cu ⁺² : 0.1∼1.0g / l , pH1.5, room temperature

Plating Method: Substitution Plating

Plating time: 0.5 to 5 seconds

I. Phosphate Treatment

1) Surface adjustment

Solution: PREPALENE-ZJ (Nippon Parkerizing)

Method: spray for 2 seconds in a 40 ° C solution

2): Phosphate Treatment

Solution: PALBOND 3312J (Nippon Parkerizing Co., Ltd.)

Method: Soak for 8 seconds in 60 ℃ solution

3) flushing: spraying tap water for 2 seconds at room temperature

4) Cr-treated

Solution: PALENE 62J (NipponParkerizing)

Method: spray for 1 second in 45 ℃ solution

5) Water washing: spray for 2 seconds at room temperature

All. Cationic electrodeposition coating work

1) Electrodeposition coating: paint DE1700 (Korea Chemical Co., Ltd. product)

Electrodeposition voltage 300V, electrodeposition time 3 minutes

2) Firing: 180 ℃ 30 minutes

hemp. Corrosion Resistance Test after Painting

After coating the electrodeposited specimens with X-type coating, conduct salt spray test for 800 hours in accordance with JIS 223721 to measure the coating film swelling width at one side of the cut.

Bar: Coating Film Adhesiveness Test

Cut the coating film into a checkerboard consisting of 100 squares of 1mm in length and 1mm in electrodeposited coated specimens, and measure the peeling amount of the film by immersion in distilled water at 98 ± 2 ℃ for 2 hours.

Table 1

*: 1 (good) ← evaluation criteria → 5 (bad)

TABLE 2

*: 1 (good) ← evaluation criteria → 5 (bad)

TABLE 3

*: 1 (good) ← evaluation criteria → 5 (bad)

As shown in Tables 1 to 3 and FIG. 1, when the copper plating is not performed or the deposition amount is too small (Comparative Examples (1-3, 15 to 17, 29 to 31)), the phosphate crystal size is coarse and uneven. , After corrosion, the corrosion resistance and water-resistant adhesion of the film is inferior, and if the amount of copper adhesion is too large [Comparative Examples (7-9, 21-23, 35-37)], the electrical non-uniformity of the surface of the steel sheet is reduced, It can be seen that corrosion resistance and coating film water adhesion resistance deteriorate after coating.

In Comparative Examples 4-6, 18-20, and 32-34, the phosphate treatability and paintability were excellent, but the substitution plating reaction was so great that the aging degree of the phosphate treatment solution was severe. However, in the case of copper deposition amount of 0.2 to 10 mg / m ² (Invention Examples (10-14, 24 to 28, 38 to 42)), phosphate crystal size is increased due to the increase of salt nucleation due to surface activation by electrical non-uniformity of the steel sheet surface. It becomes fine and uniform, and it is understood that not only the characteristics after coating are good, but also the degree of aging of the phosphate treatment solution is low.

As described above, the present invention not only improves the phosphate treatment property by attaching a small amount of copper to the surface of zinc and zinc-based alloy plated steel sheets, but also forms a uniform phosphate coating even during phosphate treatment in a continuous plating line. By doing so, there is an effect that can improve the productivity and paintability of the phosphate plated steel sheet.

Claims (2)

A zinc or zinc-based alloy plated steel sheet having excellent phosphate treatability, wherein the surface of the zinc or zinc-based alloy plated steel sheet is partially coated with a coating amount of 0.2 to 10 mg / m ² of copper. The zinc and zinc-based alloy plated steel sheet excellent in phosphate treatment property of Claim 1 whose copper partial coating layer is a substitution plating layer.