JPH09263954A - Production of zinc-nickel galvannealed steel sheet excellent in chemical convertibility - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for stably producing Zn-Ni galvannealed steel sheet excellent in chemical convertibility without being affected by the line speed. SOLUTION: The Zn-Ni galvannealed steel sheet is produced by galvannealing a Zn-Ni on at least one surface of the steel sheet with a chlorate bath and allowing the formed Zn-Ni galvannealed film to contact with a post treating solution containing >=4g/1 to <70g/l one or more kinds selected from among H2 PO4 , HPO4 <2-> and H3 PO4 as the concentration of P and 0.1-5g/l Ni and adjusted to pH2.0-5.0.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a Zn--Ni plated steel sheet having excellent chemical conversion treatability, and in particular, unevenness such as a pattern does not occur after the chemical conversion treatment of the Zn--Ni plated steel sheet,
This is a proposal for a post-treatment technology after Zn-Ni plating treatment.

[0002]

2. Description of the Related Art Steel sheets for automobiles are required to have many properties such as press workability, corrosion resistance, paintability and adhesion.
In particular, regarding corrosion resistance, it is very strict as represented by so-called 10-5-2-1 (10 years without perforated rust, 5 years without surface rust, 2 years without engine room rust, 1 year without floor rust) There is a rust prevention standard, and steel plates with high corrosion resistance are required.
Therefore, a Zn-Ni plated steel sheet having a sacrificial corrosion resistance and exhibiting a corrosion resistance 5 to 10 times that of a Zn plated steel sheet is widely used as a steel sheet for automobiles which requires high corrosion resistance.

In order to use this Zn-Ni plated steel sheet advantageously as a steel sheet for automobiles, many proposals for improvement in various properties such as chemical conversion treatment, corrosion resistance, press workability, paintability and adhesion have been made. There is. Among the,
It is known that the chemical conversion treatment of Zn-Ni plated steel sheet and the adhesion after coating are influenced by the surface condition of the coating after Zn-Ni plating. Have been improved.

For example: According to Japanese Patent Publication No. 1-21234, the oxide present on the surface of the Zn-Ni-plated steel sheet is removed by performing a cathode treatment, an anode treatment and a dipping treatment in a phosphoric acid compound bath after the plating treatment. , A method for improving the corrosion resistance after coating and the water-resistant secondary adhesion is proposed. . In Japanese Patent Publication No. 2-56437, the Zn on the plating film surface of the Zn-Ni plated steel sheet is preferentially dissolved by performing cathode treatment or anode treatment with a Zn-Ni plating solution or sulfuric acid in the final cell of the plating treatment. However, there has been proposed a method of improving the water-resistant secondary adhesion and the cratering property during cationic electrodeposition coating. . Japanese Patent Publication No. 4-2674 discloses a Zn-Ni plating solution, or 0.01 to 0.01% with a dilute sulfuric acid or dilute hydrochloric acid.
There has been proposed a method of improving chemical conversion treatability of a Zn-Ni plated steel sheet and improving coating film adhesion by performing an etching treatment of 1 g / m ² . . JP-A-6-293973 discloses that one or more heavy metal ions of Ni, Co and Fe are 1.5 to 40 g / l and phosphate ions are 0.5 to 10 g / l.
By treating the Zn-based plated steel sheet with an acidic displacement plating solution containing 1, 2, to 250 g / l of sulfate ion and 1 to 20 g / l of organic acid and having a pH of 2 to 4.5, sludge is not generated, A method is disclosed in which a heavy metal such as Ni is efficiently deposited to eliminate defective coating film adhesion and improve black rust resistance of an uncoated plate. . In Japanese Patent Laid-Open No. 7-166366, after a Zn-Ni plating treatment, a solution containing H ₂ PO ₄ ⁻ ions and HPO ₄ ²⁻ ions and further containing citrate ions is added to a Zn—Ni plated steel sheet. There has been proposed a method of improving press moldability and chemical conversion treatability by contacting with each other.

[0005]

As described in the proposals relating to the prior art as described above, the poor chemical conversion treatment of the Zn-Ni plated steel sheet is caused by Zn or Zn oxide or hydroxide on the surface of the plated film. It is caused by the existence of many things. That is, the excessive Zn on the surface of the plating film is often in a non-uniform state, so that uneven chemical conversion treatment is likely to occur. Further, the oxides and hydroxides on the surface of the plating film hinder the chemical conversion treatment itself, so that uneven chemical conversion treatment tends to occur. Furthermore, in automobile manufacturers and other processors, the Zn-Ni plated steel sheet is pressed into a predetermined shape, then placed in a rack or the like with oil and temporarily stored, and after a certain time, chemical conversion treatment is performed. There is a case. In this case, excess Zn and oxides, hydroxide and oil are firmly bonded at the contact part between the plated surface of the Zn-Ni plated steel sheet and the rack, and these cause chemical conversion treatment failure and become a pattern on the appearance. Looks like This pattern is often left as a mark after painting, which is a defective product.

With respect to this point, according to the techniques described in Japanese Patent Publication No. 2-56437 and Japanese Patent Publication No. 4-2674,
After the Zn-Ni plating treatment, Zn on the surface of the plating film can be dissolved with a Zn-Ni plating solution or diluted sulfuric acid or diluted hydrochloric acid. However, when Zn is dissolved in a Zn-Ni plating solution, the pH of the plating film surface increases due to dissolution of Zn, and Zn ions in the plating solution become Zn hydroxide and adhere to the surface of the plated steel sheet. The amount of this deposited Zn hydroxide varies depending on the operating conditions such as the line speed, the pH of the plating solution, and the solution temperature.If the amount of deposit is small, it can be removed by normal washing or flushing, but if the amount of deposit is large, Has a problem that it remains and causes unevenness in the color tone of the plating film and uneven formation after the chemical conversion treatment. Furthermore, the pH of this Zn-Ni plating solution is as low as 2.5 or less, and the etching rate of Zn is high. Therefore, if the line speed is slowed, there is a problem that over-etching causes discoloration of the plating film. On the other hand, when Zn is dissolved with dilute sulfuric acid or dilute hydrochloric acid, a liquid composition containing Zn dissolved from the surface of the plating film over time is obtained. As a result, the dissolution rate of Zn due to the acid changes due to the change in the liquid composition, so that there is a problem that it is not possible to stably manufacture a Zn-Ni plated steel sheet having constant performance at various line speeds. Furthermore, when the concentration of Zn in the acid increases due to dissolution of Zn, the pH on the surface of the plating film rises and Zn hydroxide is generated, and uneven coloring may occur due to residual Zn hydroxide. Also, the cost of using acid as a disposable product increases.

Further, the proposal described in Japanese Patent Publication No. 1-21234 is a method of dissolving and removing oxides and hydroxides existing on the surface of a plating film by using a phosphoric acid-based solution. The proposal described in JP-A No. 7-166366 is also a method using a phosphoric acid-based solution. According to these methods, dissolved Zn reacts with phosphate ions and precipitates as a phosphate Zn compound.
There is no change in the liquid composition due to Zn ions, and the same etching performance can be maintained by supplying the reacted phosphate ions. However, due to the precipitation of the phosphoric acid Zn compound, there is a problem that the line piping is clogged and operation is hindered, or the precipitate adheres to the roll and is transferred to the plated steel sheet, resulting in uneven color tone. It was Furthermore, if electroless treatment such as immersion treatment is performed,
The dissolved amount of Zn had a great influence on the processing time (that is, the line speed), and at a high line speed, a constant good performance could not be obtained stably.

As a method for preventing the precipitation of the Zn phosphate compound, there is a proposal described in JP-A-6-293973. However, this proposal aims at improving the paint adhesion of Zn-containing plated steel sheets and preventing blackening of unpainted sheets,
The present invention relates to a pretreatment liquid for chromate treatment, and the proposed steel sheet has no posttreatment (chemical conversion treatment). Moreover, this pretreatment liquid has a low P concentration (PO
_The Zn etching ability is low because it is ₄ 10 g / l or less = P concentration 3.3 g / l or less). Therefore, this proposed technique does not have the effect of preventing the occurrence of unevenness such as patterns after chemical conversion treatment.

An object of the present invention is to solve various problems of the above-mentioned prior art, and the main object thereof is to stably produce a Zn-Ni plated steel sheet having excellent chemical conversion treatability without being affected by the line speed. It is to propose a manufacturing method. Another object of the present invention is to establish a post-treatment technique after the Zn-Ni plating treatment in which unevenness in the chemical treatment is not generated, particularly a pattern does not occur after the chemical treatment of the Zn-Ni plated steel sheet.

[0010]

[Means for Solving the Problems] The inventors of the present invention have made earnest studies in order to achieve the above-mentioned object while taking into consideration various problems in the prior art. As a result, the inventors first of all, in the above-mentioned conventional technology, as a treatment liquid without deterioration of the treatment capacity due to the post-treatment, dissolved Zn can be discharged out of the system, or the Zn concentration in the post-treatment liquid. Attention was paid to Zn plating solutions, Zn-Ni plating solutions, and phosphoric acid-based solutions, which have small fluctuations. Furthermore, Zn plating solution and Zn-Ni plating solution are
Since Zn hydroxide is generated and adheres to the surface of the plated steel sheet, it is not suitable as a treatment liquid with a small pH fluctuation on the surface of the plated film. In this respect, it has been found that the phosphoric acid-based solution has a pH buffering ability to prevent pH fluctuation and a stable Zn etching effect can be expected.

On the other hand, the inventors have found that the Zn on the surface of the plating film is
As a post-treatment method to eliminate the rich state, we considered depositing Ni on the plating film surface. With respect to this point, dipping treatment with an aqueous solution of Ni sulfate or Ni chloride was examined, but not only sufficient performance was not obtained, but also uneven appearance occurred on the plated steel sheet. In addition, we investigated Ni flash plating by electrolytic treatment after plating, but it is uneconomical because new equipment for Ni electrodeposition is required. Furthermore, although electroless Ni plating was studied, for example, when hypophosphorous acid, which is a reducing agent for Ni, is consumed in electroless Ni-P plating, it is necessary to frequently add it or perform liquid exchange. Not only is it awkward and operation is complicated, but it is uneconomical.

Therefore, the inventors have continued to make further studies based on the findings from the above-mentioned prior art and the results of the study of Ni precipitation. As a result, when the Zn-Ni plated steel sheet was post-treated with a treatment solution in which Ni was added to the phosphoric acid-based solution, the stable etching effect of the phosphoric acid-based solution and the substitution precipitation effect of Ni on the plating film surface were observed. It was newly discovered that the Zn rich state on the plating film surface can be eliminated in a short time.
Based on this finding, the inventors further investigated the relationship between the post-treatment conditions and the chemical conversion treatability of the Zn-Ni plated coating after the treatment. As a result, the phosphorus concentration and Ni
The effect of preventing pattern generation after chemical conversion treatment differs greatly depending on the processing conditions such as content, pH, and liquid temperature, and phosphate precipitates or Ni and phosphate precipitates occur, resulting in uneven appearance. It was found that there are unfavorable conditions in operation. In particular, when the proper post-treatment conditions for Zn-Ni plated steel sheet plated with a chloride bath are set, it is possible to significantly improve the chemical conversion treatability without causing various problems in the conventional technique, and conceived the present invention. It came to do.

That is, the present invention is excellent in chemical conversion treatability.
It is a method for producing a Zn-Ni plated steel sheet, and the essential constitution is that Zn-Ni plating is performed by using a chloride bath on at least one surface of the steel sheet.
Subjecting the alloy plating process, for that Zn-Ni plating film which forms ^{_{the, H 2 PO 4 -, 4g}} / l as P concentration of one or more one selected from among HPO ₄ ^2-and H ₃ PO ₄ 70g or more
PH less than 1 / l and containing 0.1-5 g / l Ni
It is characterized in that the post-treatment liquid is brought into contact with it after adjusting to 2.0 to 5.0.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION A method for producing a Zn-Ni plated steel sheet according to the present invention is a phosphoric acid-based treatment liquid containing Ni ions as a post-treatment for Zn-Ni alloy plating treatment using a chloride bath. It is characterized by using. According to such a method of the present invention, post-treatment in a short time is possible, and even when the treatment time is long, the dissolution rate of Zn is slow,
There is no overetching and the dependency of the treatment effect on the line speed is reduced. That is, according to the present invention, it is possible to stably manufacture a Zn-Ni plated steel sheet in which the unevenness such as a pattern does not occur in the chemical conversion treatment without being affected by the line speed, without causing the problems of the conventional technology.

The method of the present invention will be specifically described below. The method for producing a Zn-Ni plated steel sheet according to the present invention particularly relates to a post-treatment technique for a Zn-Ni alloy plating treatment using a chloride bath. In the present invention, the reason why the treatment bath for the Zn-Ni alloy plating treatment is limited to the chloride bath is that other treatment baths, for example, when a sulfuric acid bath is used, the Zn amount on the surface of the Zn-Ni plating film becomes excessive, This is because good chemical conversion treatability cannot be obtained under the above treatment conditions.

In the method of the present invention, the Ni content of the Zn-Ni plated steel sheet used as the treated steel sheet is 7 to 15%, more preferably 10 to 14%. The reason for this is that if the Ni content is less than 7%, not only the corrosion resistance required for Zn-Ni plating cannot be obtained, but also chemical conversion treatment unevenness may occur even when the treatment liquid of the present invention is used. On the other hand, when the Ni content exceeds 15%,
This is because the plating adhesion to processing becomes unstable, and problems such as powdering occur during processing of plated steel sheets such as press working, which is a fatal drawback as a treated steel sheet.

In the method of the present invention, the post-treatment liquid is H ₂ PO ₄
^- , Any one selected from HPO ₄ ^2- and H ₃ PO ₄ 1
A phosphoric acid-based liquid containing at least one species is used. The salt at this time is not related to the types of cations such as Na ⁺ , K ⁺ , Mg ²⁺ , NH ₄ ⁺ , and Al ³⁺ .

In the method of the present invention, H ₂ PO ₄ in the post-treatment liquid is used.
^- , The concentration of HPO ₄ ^2- or H ₃ PO ₄ is 4 g / P conversion.
1 or more and less than 70 g / l, preferably 5 to 50 g / l, more preferably 10 to 40 g / l. The reason for this is that if the P concentration in the treatment liquid is less than 4 g / l, the effect of etching the Zn by the treatment liquid is small and the effect of preventing chemical conversion treatment patterns is small. On the other hand, if the P concentration in the treatment liquid is 70 g / l or more,
This is because the etching amount of Zn becomes too large and the appearance becomes uneven.

The components in the treatment liquid include elements that inevitably enter during operation and elements that are inevitably mixed in from industrial chemicals, but the amounts thereof are not particularly limited. Further, the amount of sulfate ion, chlorine ion, acetate ion and the like mixed when pH is adjusted and Ni is added and contained as described later is not particularly limited.

In the method of the present invention, the Ni content in the post-treatment liquid is 0.1-5 g / l, preferably 0.2-4 g / l. The reason for this is that if the Ni content is less than 0.1 g / l, the effect of preventing the chemical conversion treatment pattern due to the post-treatment is small, while if the Ni content exceeds 5 g / l, the effect of Ni addition saturates, This is because not only the amount of Ni deposited by substitution will be excessive and the color tone will deteriorate, but also the cost of the post-treatment liquid due to addition will increase. Incidentally, the Ni source may be any as long as it dissociates Ni as Ni ions in the treatment liquid, for example, Ni sulfate or hydrochloric acid.
Ni, Ni carbonate, Ni acetate, etc. can be used.

In the method of the present invention, the temperature of the post-treatment liquid is
The temperature is preferably 30 to 70 ° C, more preferably 40 to 60 ° C. The reason for this is that when the temperature of the post-treatment liquid is lower than 30 ° C., the effect of preventing the chemical conversion pattern due to the post-treatment is small, it takes a long time to obtain sufficient performance, and the productivity is poor. That is, the higher the temperature of the post-treatment liquid, the greater the effect of preventing the chemical conversion treatment pattern. However, when the temperature of the post-treatment liquid exceeds 70 ° C., the etching amount of Zn becomes large, resulting in uneven appearance. Therefore, in the present invention, it is desirable that the liquid temperature of the post-treatment liquid be in the range of 30 to 70 ° C.

In the method of the present invention, the pH of the post-treatment liquid is
It is set to 2.0 to 5.0, preferably 2.5 to 4.0. The reason for this is that if the pH of the post-treatment liquid is less than 2.0, the etching amount of Zn due to the post-treatment becomes too large. Therefore, if the line speed becomes slow, the processing time becomes long, resulting in over-etching, which may cause discoloration or uneven appearance of the plated steel sheet. On the other hand, when the pH of the post-treatment liquid exceeds 5.0, it was added.
Most of Ni becomes a precipitate in the treatment liquid, which causes clogging of piping. Therefore, from the viewpoint of stable operation, the pH is
It is desirable to set it in the range of 2.0 to 5.0.

In the method of the present invention, the post-treatment time may be 0.5 seconds or longer. Further, as a method for bringing the post-treatment liquid into contact with the Zn-Ni plated steel sheet, any of dipping treatment, spraying treatment and a mixture treatment thereof may be used.
Since the spraying process is likely to cause unexpected troubles such as nozzle clogging, the immersion process, particularly the immersion process using liquid agitation such as counter flow together, is most suitable from the viewpoint of stable operation.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.
In this example, first, various Zn-Ni plated steel sheets adjusted to have a Ni content of 5 to 17% and a coating weight of 15 to 35 g / m ² by an electroplating method using a Zn-Ni plating solution in a chloride bath. And then using these post-treatment liquids adjusted to various conditions as shown in Table 1 for these Zn-Ni plated steel sheets,
Post-treatment was performed by a spray method or a dipping method. The post-treatment liquid was Na ₂ HPO ₄ , NaH ₂ PO ₄ , Na ₃ PO ₄ , K ₂ HP.
O _4, using _{KH 2 PO 4, K 3 PO} 4 or the like and bath preparation, 3 to 72 in P concentration
The range was adjusted to g / l. The pH of the post-treatment liquid is phosphoric acid,
PH 1.8-5.2 with sulfuric acid and sodium hydroxide
Adjusted to the range. The Ni content was adjusted in the range of 0.05 to 5.20 g / l in terms of Ni by adding it in the form of Ni sulfate, Ni chloride or Ni carbonate. The temperature of the post-treatment liquid was changed in the range of 25 to 75 ° C.

Various Zn—Ni thus post-treated
The chemical conversion treatability of the plated steel sheet was evaluated by the method described below. [Chemical conversion treatability] Applying cleaning oil after pressing to Zn-Ni plated steel sheet and pressing a sponge-like cushion material made of urethane resin against it, under wet conditions of 37 ° C and relative humidity of 90%.
Leave for 10 days. Next, the Zn-Ni plated steel sheet was subjected to alkaline degreasing for a short time and subjected to a chemical conversion treatment with Nippon Paint's chemical conversion solution (product name: PB3020), and then the presence or absence of a chemical conversion treatment pattern was visually determined. did. In addition to the pattern of cushion marks, the presence or absence of overall chemical conversion treatment unevenness and appearance unevenness was also evaluated in the same manner. Furthermore, the presence or absence of precipitate in the post-treatment liquid was evaluated by visual observation after the post-treatment liquid was bathed.

The results are shown in Table 1. As is clear from the results shown in Table 1, it was found that the post-treatment technique of the present invention can stably produce a Zn-Ni plated steel sheet in which unevenness such as a pattern does not occur in the chemical conversion treatment.

[0027]

[Table 1]

[0028]

As described above, according to the present invention, which has established the post-treatment technology after the Zn-Ni plating treatment, in which unevenness such as a pattern does not occur in the chemical conversion treatment of the Zn-Ni plated steel sheet, the chemical conversion treatability is The excellent Zn-Ni plated steel sheet can be stably manufactured without being affected by the line speed, and its industrial value is very large.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Chiaki Kato 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Inside the Technical Research Institute, Kawasaki Steel Co., Ltd. Kawasaki Steel Co., Ltd. Chiba Steel Works (72) Inventor Toshihiro Kikuchi 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Chiba Steel Works

Claims (1)

[Claims] 1. A Zn-Ni alloy obtained by subjecting at least one surface of a steel sheet to a Zn-Ni alloy plating treatment using a chloride bath, and forming the Zn-Ni alloy.
For the plating film, at least one selected from H ₂ PO ₄ ⁻ , HPO ₄ ^2−, and H ₃ PO ₄ is used as a P concentration of 4 g /
1 to 70 g / l and 0.1 to 5 g / l of Ni, and a post-treatment liquid adjusted to pH 2.0 to 5.0 is brought into contact with the Zn-Ni plated steel sheet having excellent chemical conversion treatability. Production method.