JP3072262B2 - Method for producing Zn-Ni plated steel sheet excellent in chemical conversion property and water-resistant secondary adhesion - Google Patents

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 a Zn-Ni plated steel sheet having excellent chemical treatment properties and water-resistant secondary adhesion. Zn-Ni effective for improving adhesion between steel sheet and coating film
This is a proposal for a post-processing technique after plating.

[0002]

2. Description of the Related Art Steel sheets for automobiles are required to have many performances such as press workability, corrosion resistance, paintability and adhesion.
In particular, the corrosion resistance is extremely severe 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 are rust prevention standards, and steel plates with high corrosion resistance are required.
Therefore, Zn-Ni plated steel sheets having sacrificial corrosion resistance and exhibiting 5 to 10 times the corrosion resistance of Zn plated steel sheets are widely used as automotive steel sheets requiring high corrosion resistance.

Conventionally, in order to use this Zn-Ni plated steel sheet advantageously as a steel sheet for automobiles, various improvements such as chemical conversion treatment, corrosion resistance, press workability, paintability and adhesion have been made. . Among them, Zn-
It is known that the chemical conversion property and adhesion after painting of Ni-plated steel sheets are affected by the surface condition of the film after Zn-Ni plating, and this is improved by post-treatment after plating. Has been done.

For example,. In Japanese Patent Publication No. 1-21234, after plating, a cathode treatment, an anodic treatment, and an immersion treatment with a phosphate compound bath are performed to remove oxides present on the plating film surface of the Zn-Ni plated steel sheet. Methods have been proposed for improving the corrosion resistance after painting and the secondary adhesion to water. . In Japanese Patent Publication No. 2-56437, in the last cell of the plating treatment, Zn on the plating film surface of the Zn-Ni plated steel sheet is preferentially dissolved by performing a cathode treatment or an anode treatment with a Zn-Ni plating solution or sulfuric acid. However, there has been proposed a method for improving water-resistant secondary adhesion and cratering property during cationic electrodeposition coating. . In Japanese Patent Publication No. Hei 4-2674, after the Zn-Ni plating treatment, a Zn-Ni plating solution or diluted sulfuric acid, 0.01 to
A method has been proposed in which a 1 g / m ² etching treatment is performed to improve the chemical conversion treatment property of a Zn—Ni plated steel sheet and to improve the coating film adhesion. . In JP-A-6-293973, one or more heavy metal ions of Ni, Co, Fe are 1.5 to 40 g / l, and phosphate ions are 0.5 to 10 g / l.
l, containing zinc ion 1 to 250 g / l and organic acid 1 to 20 g / l, and treating the Zn-based plated steel sheet with an acidic displacement plating solution having a pH of 2 to 4.5 without generating sludge. There is disclosed a method of efficiently depositing heavy metals such as Ni to eliminate poor coating film adhesion and improve black rust resistance of an uncoated plate. . In JP-A 7-166366 and JP after Zn-Ni plated, H ₂ PO ₄ ^- comprising ions and HPO ₄ ^2-ions, the more solution pH3~4 containing citrate ions, Zn-Ni plated steel sheet There has been proposed a method of improving press formability and chemical conversion treatment properties by contacting the same.

[0005]

As described in the proposals according to the prior art, poor chemical conversion treatment and poor water-resistant secondary adhesion of a Zn—Ni plated steel sheet may cause Zn or Ni on the surface of the plating film. This is caused by the presence of a large amount of oxides and hydroxides of Zn.

In this regard, 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 plating film surface 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 the 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 Zn hydroxide varies depending on operating conditions such as the line speed, the pH of the plating solution, and the temperature of the plating solution. When the amount of adhesion is small, it can be removed by ordinary washing or flushing, but when the amount of adhesion is large, Has a problem in that it remains and causes color tone unevenness of the plating film and chemical conversion unevenness after the chemical conversion treatment. Further, since the pH of the Zn-Ni plating solution is as low as 2.5 or less and the etching rate of Zn is high, there is a problem that when the line speed is reduced, the plating film is over-etched and discolored. On the other hand, when Zn is dissolved with dilute sulfuric acid or dilute hydrochloric acid, a solution composition containing Zn dissolved from the plating film surface with time is obtained. As a result, the dissolution rate of Zn by an acid changes due to a change in the liquid composition, and thus there has been a problem that, at various line speeds, an operation for stably producing a Zn—Ni-plated steel sheet having constant performance cannot be performed. Furthermore, when the Zn concentration in the acid increases due to the dissolution of Zn, the pH on the surface of the plating film increases, and Zn hydroxide is generated, and color tone unevenness may occur due to residual Zn hydroxide. In addition, disposable acids increase costs.

Next, the proposal described in Japanese Patent Publication No. 1-22344 is a method of removing oxides and hydroxides present on the surface of a plating film using a phosphoric acid-based solution. The proposal described in JP-A-7-166366 is a method using a phosphoric acid-based solution. According to these methods, the dissolved Zn reacts with phosphate ions and precipitates as a phosphate compound.Therefore, there is no change in the liquid composition due to Zn ions as in the case of dilute sulfuric acid or dilute hydrochloric acid. The same etching performance can be maintained by supplying the added phosphate ions. However, due to the precipitation of the phosphate compound, the line piping is clogged and hinders the operation,
Alternatively, there is a problem in that the precipitate adheres to the roll and is transferred to the plated steel sheet, thereby causing color tone unevenness. Furthermore, when electroless treatment such as immersion treatment, the amount of dissolved Zn greatly affects the treatment time (that is, line speed),
At high line speeds, certain good performance was not stably obtained.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned various problems of the prior art. The main object of the present invention is to produce a Zn-Ni plated steel sheet having excellent chemical conversion properties and water-resistant secondary adhesion by the line speed. An object of the present invention is to propose a method of manufacturing stably without any problem. Another object of the present invention is to establish a post-treatment technique after the Zn-Ni plating treatment, which does not cause unevenness during the chemical conversion treatment of the Zn-Ni plated steel sheet and improves the adhesion between the plated steel sheet and the coating film. It is in.

[0009]

Means for Solving the Problems In order to realize the above object, the present inventors have conducted intensive studies while considering various problems in the prior art. As a result, the inventors first found that, in the above-mentioned prior art, as a processing solution without deterioration with time of the processing ability due to post-processing, a processing solution in which dissolved Zn can be discharged out of the system, or a Zn concentration in the post-processing solution We focused on a Zn plating solution, a Zn-Ni plating solution, and a phosphoric acid-based solution, which have small fluctuations. Furthermore, Zn plating solution and Zn-Ni plating solution
Since a hydroxide of Zn is generated and adheres to the surface of the plated steel sheet, it is not suitable as a treatment liquid having small pH fluctuation on the surface of the plated film. In this regard, it has been found that the phosphoric acid-based liquid has a pH buffering ability for preventing pH fluctuation, and a stable Zn etching effect can be expected.

[0010] On the other hand, the inventors have proposed that Zn
As a post-treatment method for eliminating the rich state, it was considered to deposit Ni on the coating film surface. In this regard, immersion treatment with an aqueous solution of Ni sulfate or Ni chloride was examined, but not only did not obtain sufficient performance, but also appearance unevenness occurred in the plated steel sheet. In addition, Ni flash plating by electrolytic treatment after plating treatment was examined, but new equipment for Ni deposition is required, which is uneconomical. Furthermore, we studied electroless Ni plating.For example, when hypophosphorous acid, which is a reducing agent for Ni, is consumed in electroless Ni-P plating, it is necessary to add it frequently or perform liquid exchange. As a result, the operation becomes complicated and uneconomical.

Therefore, the present inventors have further studied intensively based on the knowledge from the above-mentioned prior art and the above-mentioned study results of Ni precipitation. As a result, when the Zn-Ni-plated steel sheet is post-treated using a treatment solution obtained by adding Ni to a phosphoric acid-based solution, the stable etching effect of the phosphoric acid-based solution and the effect of Ni substitution precipitation on the plating film surface are obtained. It was newly found that the Zn-rich state on the plating film surface can be eliminated in a short time.
Further, based on this finding, the inventors studied the relationship between the post-treatment conditions and the performance of the Zn—Ni plating film after the treatment. As a result, if the processing conditions such as phosphorus concentration and Ni content in the processing solution, pH,
The present inventors have found that the chemical conversion property and the water-resistant secondary adhesion can be greatly improved without causing various problems in the conventional technology, and have arrived at the present invention.

That is, the present invention provides a chemical conversion treatment and water resistance 2
This is a method for producing a Zn-Ni-plated steel sheet having excellent secondary adhesion, the gist of which is that at least one side of the steel sheet has a Zn-Ni
The Zn-Ni plating film formed by performing the alloy plating process is coated with at least one selected from H ₂ PO ₄ ⁻ , HPO ₄ ²⁻ and H ₃ PO ₄ as a P concentration of 15 to 170. g / l and containing 1-50 g / l Ni, pH 2.5
The treatment liquid is brought into contact with the mixture after adjusting to 4.5.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The method for producing a Zn-Ni plated steel sheet according to the present invention is characterized in that a phosphoric acid-based treatment solution containing Ni ions is used as a post-treatment of a Zn-Ni alloy plating treatment. is there. According to such a method of the present invention, post-processing can be performed in a short time, and even when the processing time is long, the dissolution rate of Zn is low, so there is no over-etching, and the processing effect depends on the line speed. Is less effective. That is,
ADVANTAGE OF THE INVENTION According to this invention, Zn which is excellent in water-resistant secondary adhesion without generating chemical conversion treatment unevenness, without causing the problem which the prior art has.
-Ni-plated steel sheets can be stably manufactured without being affected by the line speed. Further, according to the method of the present invention, it is possible to reduce the amount of a precipitate composed of a phosphate compound containing Zn that dissolves from the plating film during the post-treatment, and the maintenance work of the post-treatment equipment in the line operation is reduced. . Regarding this point, by adding and including Ni in the post-treatment solution, the amount of dissolved Zn can be 1 to 3 in addition to the precipitation of Ni.
It is thought that this is due to the fact that it decreases as a percentage.

The effects of improving the chemical conversion property and the secondary adhesion to water are greatly different depending on the post-treatment conditions. That is, when a post-treatment of Zn-Ni alloy plating is performed under conditions that deviate from the present invention, a precipitate of phosphate or a precipitate composed of Ni and phosphate is generated, resulting in uneven appearance or water resistance. Many problems occur, such as no improvement effect of the secondary adhesion, which is not preferable in operation. For example, the processing method described in Japanese Patent Publication No. Hei 6-293973 has a lower P concentration in the processing solution and a lower Zn etching ability as compared with the method of the present invention. The effect of improvement was insufficient.

The method of the present invention will be specifically described below. In the method of the present invention, Zn-Ni used as a treated steel sheet
The Ni content of the plated steel sheet is 7 to 15%, more preferably 10%.
~ 14%. The reason is that if the Ni content is less than 7%,
Not only is the corrosion resistance required for Zn-Ni plating not obtained, but also chemical conversion treatment unevenness may occur. On the other hand, the Ni content
If it exceeds 15%, plating adhesion to processing becomes unstable, problems such as powdering occur at the time of plating steel sheet processing such as press working, and there is a fatal defect as a treated steel sheet.

In the method of the present invention, the Zn-Ni alloy plating method is not particularly limited, and a conventionally known method such as an electroplating method, a vapor-phase plating method, and a hot-dip plating method can be used. In the case of electroplating, a sulfuric acid bath, chloride
You may use other baths or mixed bath except bath.

In the method of the present invention, the post-treatment liquid is H ₂ PO ₄
^-, any one selected from among HPO ₄ ^2-and H ₃ PO ₄ 1
A phosphoric acid-based liquid containing at least a seed as a main component is used. The salt at this time has nothing to do with the type of cation such as Na ⁺ , K ⁺ , Mg ²⁺ , NH ₄ ⁺ , and Al ³⁺ .

In the method of the present invention, the H ₂ PO ₄
^- the concentration of HPO ₄ ^2-or H ₃ PO ₄ is a P concentration terms 15-17
0 g / l, preferably 50-130 g / l, more preferably
The range is 70 to 110 g / l. The reason for this is that when the P concentration in the treatment liquid is less than 15 g / l, the effect of etching the Zn by the treatment liquid is small, and the effect of improving the non-uniformity of the chemical conversion treatment and the secondary adhesion to water is small. On the other hand, if the P concentration in the processing liquid exceeds 170 g / l, when the liquid temperature is lowered, phosphoric acid-based crystals are crystallized, resulting in clogging of the pipe and the like, which is not suitable for stable operation.

The components in the treatment liquid include elements that are unavoidable in the operation and elements that are unavoidably mixed from industrial chemicals, but their amounts are not particularly limited. In addition, the amounts of sulfate ions, chloride ions, acetate ions, and the like mixed when adjusting pH and adding and containing Ni described below are not particularly limited.

In the method of the present invention, the Ni content in the post-treatment solution is 1 to 50 g / l, preferably 3 to 25 g / l.
The reason for this is that if the Ni content is less than 1 g / l, the effect of improving the water-resistant secondary adhesion by post-treatment is small, while if the Ni content exceeds 50 g / l, the effect of adding Ni is saturated. This is because the cost of the post-treatment liquid due to the addition of Ni increases. Note that the Ni source may be any source that dissociates Ni as Ni ions in the processing solution, such as Ni sulfate or N hydrochloric acid.
i, Ni carbonate, Ni acetate and the like can be used.

In the method of the present invention, the temperature of the post-treatment liquid is
It is desirable that the temperature be 40 to 70 ° C, more preferably 50 to 60 ° C. The reason for this is that if the temperature of the post-treatment liquid is less than 40 ° C., the effect of improving post-treatment non-uniformity in chemical conversion treatment and water-resistant secondary adhesion is small. In other words, the higher the temperature of the post-treatment liquid, the greater the effect of improving the non-uniformity of the chemical conversion treatment and the secondary water resistance. However, when the temperature of the post-treatment liquid exceeds 70 ° C., precipitates composed of Ni and phosphate are generated in the phosphoric acid-based treatment liquid containing Ni. Therefore, it is desirable that the temperature of the post-treatment liquid be in the range of 40 to 70 ° C. from the viewpoint of stable operation.

In the method of the present invention, the pH of the post-treatment solution is
2.5 to 4.5, more preferably 3.2 to 4.0. The reason for this is that if the pH of the post-treatment solution is less than 2.5, Zn
Etching effect becomes too large. Therefore, when the line speed is reduced, the processing time becomes longer, resulting in over-etching, which may cause discoloration and uneven appearance of the plated steel sheet. On the other hand, when the pH of the post-treatment liquid exceeds 4.5, most of the added Ni becomes a precipitate in the treatment liquid, causing clogging of pipes and the like. Therefore, from the viewpoint of stable operation, pH is
It is desirable to be in the range of 2.5 to 4.5.

In the method of the present invention, the post-processing time may be 1 second or more. As a method of bringing the post-treatment liquid into contact with the Zn—Ni plated steel sheet, any of immersion treatment, spray treatment, and a mixture thereof may be used.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.
In this embodiment, the sulfuric acid Yokua Rui by electroplating method using Zn-Ni plating solution comprising a mixed bath of chloride baths and sulfuric acid bath, Ni content: 5-20%, coating weight 10 to 40 g / m ² Each of the Zn-Ni plated steel sheets adjusted to the above conditions was manufactured, and post-treatment was performed for 1 to 20 seconds by a spray method or an immersion method using a post-treatment liquid adjusted to various conditions as shown in Table 1. The post-treatment solution is prepared by using sodium phosphate (1), sodium phosphate (2) and phosphoric acid, and has a P concentration of 10 to 200 g / g.
1 range. The pH of the post-treatment solution was adjusted to pH 2.0 to 5.0 using phosphoric acid, sulfuric acid and sodium hydroxide. Ni content is Ni sulfate, Ni chloride or Carbonate
It was added in the form of Ni and adjusted to a range of 0 to 60 g / l in terms of Ni. The temperature of the post-treatment liquid was changed in the range of 20 to 75 ° C.

Various types of Zn-Ni thus post-treated
For the plated steel sheet, the chemical conversion property and the water-resistant secondary adhesion were evaluated by the methods described below. [Chemical conversion treatment] Zn-Ni plated steel sheet is treated with Nippon Paint's chemical conversion treatment solution (phosphate treatment solution: Surfdyne SD2500MZL)
After the chemical conversion treatment according to (1), the chemical conversion treatment unevenness was visually observed and evaluated. The evaluation criteria were 1 when there was chemical conversion unevenness on the entire surface, 2 when there was much unevenness, 3 when there was little unevenness, 4 when there was slight unevenness, and 5 when there was no unevenness. [Waterproof secondary adhesion] Nippon Paint's chemical conversion treatment solution (Phosphate treatment solution: Surfdyne SD2500)
MZL), cationic electrodeposition coating (U2602: 20 μm), intermediate coating (OTO4830: 35 μm)
m), top-coating (OTO640: 35 μm), immersing the coated sample in pure hot water at 50 ° C for 10 days,
Scratches reaching the ground iron were cut in a grid pattern at intervals of mm with a cutter knife, and the peeled area ratio of the coating film when the tape was peeled off was evaluated by visual observation. The evaluation criteria are 1 when the peeling area ratio of the coating film is 50 to 100% and 1 when the peeling area ratio of the coating film is 20 to 100%.
The case of 50% was 2; the case where the peeling area ratio of the coating film was 5 to 20% was 3; the case where the peeling area ratio of the coating film was less than 5% was 4;

Furthermore, the corrosion resistance and plating adhesion essential for the Zn—Ni plated steel sheet were evaluated by the methods described below. [Corrosion resistance] A sample having a coating weight of 20 g / m ² was subjected to a salt spray test (JIS Z-2371) for 14 days without coating, and evaluated by the area ratio of red rust occurrence. The evaluation criteria are 1 when the area ratio of red rust is 80-100%, 2 when the area ratio is 50-80%,
The case of 20 to 50% was 3, the case of 5 to 20% was 4, and the case of 0 to 5% was 5. [Plating Adhesion] A Zn-Ni plated steel sheet was bent at 180 ° C., and the tape processed part was subjected to a zero-T bending adhesion test in which the tape-processed part was peeled off with a cellophane tape. . The evaluation criteria were 1 when peeling was performed without processing, 2 when the peeling amount was large, 3 when the peeling amount was small, 4 when slightly peeled, and 5 when not peeling.

The results are shown in Tables 1 and 2. As is clear from the results shown in these tables,. It can be seen that the proper Ni content of the Zn-Ni plated steel sheet is 7 to 15% (see Examples 1 to 5 and Comparative Examples 1 and 2). . It can be seen that the appropriate P concentration of the post-treatment solution is 15 to 170 g / l (see Examples 6 to 10 and Comparative Examples 3 and 4). . It can be seen that the appropriate amount of Ni added to the post-treatment solution is 1 to 50 g / l (see Examples 11 to 16 and Comparative Examples 5 to 6). . Proper pH of the post-treatment liquid is found to be 2.5 to 4.5 (see Examples 17-21 and Comparative Examples 7-8). . It can be seen that the appropriate temperature of the post-treatment liquid is 40 to 70 (see Examples 22 to 25 and Comparative Examples 9 to 10). . Zn-Ni with good performance in both spraying and dipping
It can be seen that a plated steel sheet can be manufactured (see Examples 26 to 29 ). . It can be seen that a Zn-Ni plated steel sheet having good performance can be manufactured with a processing time of 1 second or more (see Examples 30 to 34 ).

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

As described above, the post-treatment technique after the Zn-Ni plating treatment is effective in improving the adhesion between the plated steel sheet and the coating film without generating unevenness during the chemical conversion treatment of the Zn-Ni plated steel sheet. According to the established invention, it is possible to stably produce a Zn—Ni-plated steel sheet excellent in chemical conversion treatment and water-resistant secondary adhesion without being affected by the line speed.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-64-28389 (JP, A) JP-A-2-29079 (JP, A) JP-A-6-101089 (JP, A) JP-A 53-28 115624 (JP, A) JP-A-6-293973 (JP, A) JP-A-59-193279 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 22/00-22 / 86 C23C 28/00 C25D 5 / 26,5 / 48,3 / 56

Claims (3)

(57) [Claims] On at least one surface according to claim 1 steel sheet, subjected to Zn-Ni alloy plating process, for that Zn-Ni plating film which forms the, H ₂ PO ₄ ^-, from among HPO ₄ ^2-and H ₃ PO ₄ PH 2.5 to 4. containing any one or more selected as a P concentration in the range of 15 to 170 g / l and containing 1 to 50 g / l of Ni.
5. A method for producing a Zn-Ni plated steel sheet having excellent chemical conversion property and water-resistant secondary adhesion, characterized by contacting a post-treatment liquid adjusted to 5. 2. The method according to claim 1, wherein the temperature of the post-treatment liquid is adjusted to 40 to 70 ° C. Wherein said Zn-Ni alloy plating process, bath sulfate or
The method according to claim 1, wherein the method is performed using a mixed bath of a sulfuric acid bath and a chloride bath .