JPH10204648A - Production of zinc-nickel alloy plated steel sheet excellent in secondary adhesion resistance to water and corrosion resistance after coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a Zn-Ni alloy plated steel sheet by which a Zn-Ni alloy plated steel sheet excellent in secondary adhesion resistance and corrosion resistance after coating to water can stably be produced without being influenced by a line velocity. SOLUTION: After Zn-Ni alloy plating film is formed on at least one side of a steel sheet by Zn-Ni alloy plating, a post-treating soln. of pH2.5 to 4.5 contg. one or more kinds selected from among H2 PO4 <-> , HPO4 <2-> and H3 PO4 by 15 to 170g/l as the concn. of P, furthermore contg. 1 to 50g/l Ni and 0.3 to 10g/l Co, and in which the soln. temp. is preferably regulated to 40 to 70 deg.C is brought into contact with the Zn-Ni alloy plating film.

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 alloy coated steel sheet having excellent chemical conversion properties, secondary water resistance and corrosion resistance after painting, and is effective for improving the adhesion between a coated steel sheet and a coating film. The present invention relates to a post-treatment technique after Zn-Ni plating, which has good corrosion resistance after painting.

[0002]

2. Description of the Related Art Steel sheets for automobiles are required to have many performances such as press workability, corrosion resistance, paintability, plating adhesion, and coating film adhesion. In particular, regarding corrosion resistance,
Very strong rust prevention standards represented by 2-1 (10 years without perforated rust, 5 years without surface rust, 2 years without rust in engine room, 1 year without rust on floor back), high corrosion resistant steel plate Is required.

[0003] 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, Zn-Ni alloy-plated steel sheets (hereinafter also referred to as Zn-Ni-plated steel sheets) have been used as automotive steel sheets in an advantageous manner, because of their chemical conversion properties, corrosion resistance, press workability, paintability, plating adhesion, and coating film. Many improvements have been made in various performances such as adhesion.

[0004] Among them, it is known that the chemical conversion property of a Zn-Ni plated steel sheet and the coating film adhesion after coating are affected by the surface condition of the plated film after the Zn-Ni plating treatment. Regarding this point, improvements have been made by post-processing after plating. For example, Japanese Patent Publication No. 1-21234 discloses that after a plating treatment, 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. There has been proposed a method of removing and improving the corrosion resistance after painting and the water-resistant secondary adhesion.

In Japanese Patent Publication No. 2-56437, a Zn-Ni plating solution or sulfuric acid is subjected to a cathodic treatment or an anodic treatment in the final cell of the plating treatment to thereby provide a Zn-Ni plating solution.
Preferentially dissolve Zn on the plating film surface of Ni plated steel sheet,
Methods have been proposed to improve the water-resistant secondary adhesion and the cratering property during cationic electrodeposition coating. In Japanese Patent Publication No. Hei 4-2674, after Zn-Ni plating, Zn
-0.01 to 1 g / m ^{2 with} Ni plating solution or diluted sulfuric acid or diluted hydrochloric acid
There has been proposed a method of improving the chemical conversion property of a Zn-Ni plated steel sheet and improving the adhesion of a coating film by performing an etching treatment.

[0006] JP-A-6-293973 discloses that Ni, Co,
One or more heavy metal ions of Fe 1.5 to 40 g / l, phosphate ions 0.5 to 10 g / l, sulfate ions 1 to 250 g / l, and organic acid 1
Treating Zn-based plated steel sheet with an acidic displacement plating solution containing up to 20 g / l and having a pH of 2 to 4.5 enables efficient deposition of heavy metals such as Ni without sludge generation and adhesion of the coating film. A method for eliminating poor quality and improving blackening resistance of an uncoated plate is disclosed.

[0007] As described in the above prior art, poor water-resistant secondary adhesion and poor corrosion resistance after painting of Zn-Ni plated steel sheets are caused by Zn or oxides or hydroxides of Zn on the plating film surface. Caused by the presence of many.
In this regard, Japanese Patent Publication No. 2-56437 and Japanese Patent Publication No. 4-26
According to the technique described in Japanese Patent No. 74, after Zn-Ni plating treatment
Zn on the plating film surface can be dissolved by a Zn-Ni plating solution or diluted sulfuric acid or diluted hydrochloric acid.

[0008] However, when Zn is dissolved with 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 steel sheet surface. The amount of Zn hydroxide attached 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 Zn hydroxide attached is small, it can be removed by ordinary washing or brushing. When the amount of adhesion is large, there is a problem that it remains and causes unevenness of color tone of the plating film and formation unevenness after the chemical conversion treatment.

Further, the pH of the Zn—Ni plating solution in this case is
Since the etching speed of Zn is as low as 2.5 or less and the etching speed of Zn is high, there is a problem that when the line speed is reduced, the plating film is discolored due to overetching. On the other hand, when Zn is dissolved with dilute sulfuric acid or dilute hydrochloric acid, the treatment liquid becomes a liquid composition containing Zn dissolved from the plating film surface over time.

As a result, due to the change in the liquid composition,
Since the dissolution rate of Zn changes, there has been a problem that Zn-Ni plated steel sheets having constant performance cannot be stably manufactured at various line speeds. Furthermore, when the Zn concentration in the acid solution 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.

Further, if the acid solution is disposable in order to cope with these problems, a problem of waste acid treatment occurs and it is not economical. Next, a proposal described in Japanese Patent Publication No. 1-21234 is a method for removing oxides and hydroxides present on the plating film surface using a phosphoric acid-based solution. According to this method, dissolved Zn binds to 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, and furthermore, the reaction does not occur. The same etching performance can be maintained by replenishing the prepared phosphate ions.

However, the above-mentioned precipitation of the phosphate compound blocks the line piping and hinders the operation, or the precipitate adheres to the roll for transporting the steel strip and is transferred to the plated steel sheet. Therefore, there is a problem that color tone unevenness occurs. Furthermore, when treated by an electroless method such as immersion treatment, the amount of dissolved Zn was greatly affected by the treatment time, that is, the line speed, and a product with good performance could not be obtained stably at a high line speed.

Further, in the case of the proposal described in Japanese Patent Application Laid-Open No. Hei 6-293973, the water-resistant secondary adhesion and corrosion resistance after coating, which are the objects of the present invention, are inferior. There was a problem that it became complicated.

[0014]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned various problems of the prior art, and a main object of the present invention is to provide a Zn—Ni alloy having excellent secondary adhesion to water and corrosion resistance after painting. An object of the present invention is to provide a method for producing a Zn—Ni alloy-plated steel sheet that can stably produce a plated steel sheet without being affected by the line speed.

[0015]

Means for Solving the Problems The present inventors have conducted intensive studies in order to realize the above-mentioned object while taking into account various problems in the prior art. As a result, the present inventors first, in the above-mentioned prior art, as a processing liquid without deterioration with time of the processing capacity in the post-processing, a processing liquid in which dissolved Zn can be discharged out of the system, or a Zn concentration in the processing liquid It is considered that a treatment solution with small fluctuation of the Zn is desirable, and a Zn plating solution, a Zn-Ni plating solution,
We focused on the phosphoric acid solution.

However, the treatment with a Zn plating solution or a Zn—Ni plating solution is not suitable because a hydroxide of Zn is generated and adheres to the surface of the plated steel sheet due to a pH fluctuation on the surface of the plating film. On the other hand, it has been found that the phosphoric acid-based solution has a pH buffering property for preventing pH fluctuation and a stable Zn etching effect can be expected.

On the other hand, the present inventors have proposed that the
As a post-treatment method to eliminate the Zn-rich state, consider depositing Ni and Co on the plating film surface.
The immersion treatment with aqueous solutions of Ni sulfate, Ni chloride and Co sulfate was studied, but not only did not obtain sufficient performance, but also the appearance of the plated steel sheet was uneven. In addition, although Ni flash plating and Co flash plating by electrolytic treatment after plating treatment were examined, new equipment for Ni and Co deposition is required, and the process becomes complicated and uneconomical.

Further, the electroless Ni plating was examined.
For example, when hypophosphite ion, which is a reducing agent for Ni ions, is consumed in electroless Ni-P plating, it is necessary to frequently add the chemical or perform a liquid exchange, which makes the operation complicated. Or uneconomical. Therefore, the present inventors have further studied diligently based on the above-mentioned examination results.

As a result, when the Zn-Ni plated steel sheet is post-treated using a treatment solution obtained by adding Ni and Co to a phosphoric acid-based solution, a stable etching effect by the phosphoric acid-based solution and the Ni-coating on the plating film surface can be obtained. It is newly found that the Zn-rich state on the plating film surface can be eliminated by the effect of substitutional precipitation of Co and Co. Further, based on the present findings, the present inventors have studied the relationship between the post-treatment conditions and the performance of the Zn—Ni plating film after the treatment.

As a result, when the processing conditions such as the phosphorus concentration, the Ni content, the Co content, the pH, and the liquid temperature in the processing solution are within appropriate ranges, the water-resistant secondary adhesion can be achieved without causing various problems in the prior art. It has been found that the properties and corrosion resistance after painting can be improved, and the present invention has been achieved. That is, the present invention is, after form the a Zn-Ni alloy plated film by at least one side Zn-Ni alloy plated steel ^{_{plate, H 2 PO 4 -, HPO}} 4 2- and H ₃ PO ₄
A post-treatment solution adjusted to pH 2.5-4.5, containing at least one selected from the group consisting of 15-170 g / l as a P concentration and containing 1-50 g / l Ni and 0.3-10 g / l Co. In contact with the Zn—Ni alloy plating film, which is a method for producing a Zn—Ni alloy plated steel sheet having excellent water-resistant secondary adhesion and corrosion resistance after painting.

In the present invention, the temperature of the post-treatment liquid is preferably adjusted to 40 to 70 ° C.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The method of the present invention is characterized in that a phosphoric acid-based treatment solution containing Ni ions and Co ions is used as a post-treatment of the Zn-Ni alloy plating treatment. If the treatment becomes possible and the treatment time becomes longer, the dissolution of Zn by post treatment and the plating surface layer
Since the precipitation amount of Ni and Co increases, the plating surface
The exposed portion of Zn decreases with time, and the dissolution rate of Zn decreases.

For this reason, discoloration due to over-etching is eliminated, and the line speed dependence of the processing effect is reduced. That is, according to the method of the present invention, a Zn-Ni alloy-plated steel sheet having both excellent water-resistant secondary adhesion and corrosion resistance after painting can be stably produced without being affected by the line speed, without causing the problems of the prior art. Can be manufactured.

The effect of improving the secondary adhesion to water and the corrosion resistance after painting greatly varies depending on the post-treatment conditions. That is, Zn under the conditions deviating from the conditions specified in the present invention.
-When post-treatment of Ni alloy plating is performed, the effect of improving the secondary adhesion to water and the corrosion resistance after painting cannot be obtained, and furthermore, precipitates composed of Ni and phosphate are generated and appearance unevenness occurs. This is undesirable in terms of product quality and operation.

Hereinafter, the production method of the present invention will be described more specifically. In the production method of the present invention, the Ni content in the plating film of the Zn—Ni alloy plated steel sheet used as the base material is 7 to 15 wt%, more preferably 10 to 14 wt%. The reason for this is that if the Ni content is less than 7 wt%, the corrosion resistance after painting expected for Zn-Ni plating cannot be obtained, and conversely, the Ni content is 15 wt%.
%, Not only good corrosion resistance after coating is not obtained, but also the plating adhesion to processing becomes unstable, causing problems such as powdering during processing of plated steel sheets such as press working, which is fatal as a treated steel sheet. This is because defects occur.

In the method of the present invention, the post-treatment liquid is H ₂ PO ₄
^-, used liquid phosphate as a main component at least one member selected from among HPO ₄ ^2-and H ₃ PO _4. In the phosphate used at this time, the type of cation such as Na ⁺ , K ⁺ , Mg ²⁺ , NH ₄ ⁺ , and Al ³⁺ is not limited. In the production method of the present invention, H ₂ PO ₄ in the post-treatment liquid ^-, HPO ₄ ^2- and
The concentration of one or more compounds selected from H ₃ PO ₄ is P
The concentration is preferably 15 to 170 g / l, more preferably 50 to 170 g / l.
130 g / l, and more preferably 70 to 110 g / l.

If the concentration in the post-treatment liquid is less than 15 g / l in terms of P concentration, the effect of the post-treatment liquid on etching Zn is small,
The effect of improving the secondary water resistance and the corrosion resistance after coating, which are the objects of the present invention, cannot be obtained. Conversely, if the concentration in the post-treatment liquid exceeds 170 g / l in terms of P concentration, phosphate-based crystals will crystallize out when the liquid temperature drops, causing clogging of the pipes, etc., hindering stable operation. You.

In the production method of the present invention, the
The Ni content is 1 to 50 g / l, more preferably 3 to 25 g / l. The Co content in the post-treatment liquid is 0.3 to 10 g / l, more preferably 1 to 5 g / l. When the Ni content is less than 1 g / l and when the Co content is less than 0.3 g / l, the effect of improving the water-resistant secondary adhesion by the post-treatment is small. On the other hand, when the Ni content is 50 g / l, If it exceeds, if the Co content exceeds 10 g / l, the corrosion resistance after painting may deteriorate.

The reason for the deterioration of the corrosion resistance is that the amount of Ni or Co deposited on the plating surface increases, and a potential difference occurs between the plating surface portion and the plating layer at the flaws provided for the purpose of examining the corrosion resistance after coating. It is estimated that the corrosion resistance after painting deteriorated in order to increase the consumption rate of plating during the test. Note that Ni is used as a Ni source and a Co source in the post-treatment solution.
As the Ni ion, any one capable of dissociating Co as a Co ion may be used. Examples of the Ni source include Ni sulfate, Ni chloride, and N acetate.
i, one or more selected from Ni carbonate and the like, and the Co source may be one or more selected from Co sulfate, Co hydrochloride, Co acetate, Co carbonate and the like.

The other components in the post-treatment liquid are not particularly limited in the amount of elements that are unavoidable in the operation. Further, the amounts of sulfate ions, chloride ions, acetate ions, and the like mixed when Ni and Co are added and contained are not particularly limited. Furthermore, in the production method of the present invention, the pH of the post-treatment liquid is 2.5 to 4.5, more preferably
3.0 to 4.0.

The reason for this is that if the pH of the post-treatment liquid is less than 2.5, the etching effect of Zn by the post-treatment is too large, and if the line speed is low, the processing time is prolonged, resulting in over-etching, discoloration and appearance of the plated steel sheet. Unevenness may occur.On the other hand, when the pH of the post-treatment solution exceeds 4.5, most of the added Ni becomes a precipitate in the treatment solution,
This is because it may cause blockage of piping and the like.

For this reason, from the viewpoint of stable operation, the pH is 2.5
Limited to the range of ~ 4.5. In the production method of the present invention, the temperature of the post-treatment liquid is 40 to 70 ° C, more preferably 50 to 70 ° C.
Desirably, it is set to 60 ° C. The reason for this is that if the temperature of the post-treatment liquid is lower than 40 ° C., the effect of preventing the non-uniformity of the chemical conversion treatment by the post-treatment and the effect of improving the secondary water resistance are small. That is,
In the present invention, the higher the temperature of the post-treatment liquid, the greater the effect of improving the water-resistant secondary adhesion, and the prevention of non-uniform chemical conversion treatment.

Conversely, if the solution temperature exceeds 70 ° C., precipitates composed of Ni and phosphate are generated in the phosphoric acid-based treatment solution containing Ni. Therefore, from the viewpoint of operation, the temperature of the post-treatment liquid is preferably in the range of 40 to 70 ° C. In the above-described manufacturing method of the present invention, the post-processing time may be 1 second or more.

As a method for bringing the post-treatment liquid into contact with the Zn—Ni alloy plated steel sheet, any of an immersion treatment, a spray treatment, and a treatment method combining these may be used.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. By an electroplating method using a Zn-Ni plating solution in a sulfuric acid bath or a chloride bath, the Ni content in the plating film is 5 to 5.
In order to investigate the corrosion resistance after coating with the same plating adhesion amount at 20 wt%, various Zn—Ni alloy plated steel plates were manufactured with the plating adhesion amount adjusted to 20 g / m ² per one surface of the steel plate, and used as test materials.

Next, the test material was subjected to a post-treatment for 1 to 20 seconds by a spray method or an immersion method using the post-treatment liquid adjusted to various conditions shown in Table 1. In addition, the post-treatment liquid was prepared using sodium phosphate monobasic, sodium phosphate dibasic, and phosphoric acid, and adjusted to a P concentration of 10 to 200 g / l. The pH of the post-treatment solution was adjusted to a range of 2.0 to 5.0 using phosphoric acid and sodium hydroxide.

Ni in the post-treatment solution was added in the form of Ni sulfate, Ni chloride or Ni carbonate, and the Ni content in the post-treatment solution was adjusted to a range of 0 to 60 g / l in terms of Ni. Co in the post-treatment solution is added in the form of Co sulfate, Co chloride or Co carbonate,
The Co content was adjusted to a range of 0 to 15 g / l in terms of Co. 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
Regarding the alloy-plated steel sheet, the water-resistant secondary adhesion and the corrosion resistance after painting were evaluated by the methods described below (Examples 1 to 34,
Comparative Examples 1 to 13). Further, the steel sheet subjected to the post-treatment was evaluated for the adhesion between the steel sheet and the plating layer, which is indispensable for the Zn—Ni alloy-plated steel sheet, by the method described below (Example 1).
To 34, Comparative Examples 1 to 13).

For comparison, Zn not subjected to post-processing was used.
-Performance was also evaluated for Ni alloy plated steel sheets (Comparative Example
14). [Water resistant secondary adhesion] Chemical conversion treatment solution (Phosphate treatment solution, trade name; Surfdyne SD2500MZL) for Zn-Ni alloy plated steel sheet
, Nippon Paint Co., Ltd.), followed by cationic electrodeposition coating (paint: U2602, Nippon Paint Co., Ltd., coating thickness: 20 μm), intermediate coating (paint: Product name: OTO4830, manufactured by Nippon Paint Co., Ltd.
Coating thickness: 35μm), top coat (paint: trade name: OTO6)
40, manufactured by Nippon Paint Co., Ltd., coating thickness: 35 μm), and the coated sample was immersed in pure hot water at 55 ° C. for 10 days. The wound area reaching the iron was cut, and the peeled area ratio of the coating film when the tape was peeled off was visually observed and evaluated according to the following criteria.

5: Peeling area ratio of coating film is less than 1% 4: Peeling area ratio of coating film is 1% or more and less than 5% 3: Peeling area ratio of coating film is 5% or more and less than 20% 2: Coating The peeling area ratio of the film is 20% or more and less than 50% 1: The peeling area ratio of the coating film is 50% or more [Corrosion resistance after coating] A chemical conversion treatment solution (phosphate treatment solution, trade name) ; Surfdyne SD2500MZL,
Nippon Paint Co., Ltd.)
Cationic electrodeposition coating (paint: trade name: U2602, manufactured by Nippon Paint Co., Ltd., coating thickness: 20 μm) was performed, a scratch reaching the base iron was made with a cutter knife, and the following combined cycle test was performed for 30 days. Thereafter, the swollen width of the coating film from the scratch was measured, and the corrosion resistance after coating was evaluated according to the following criteria.

：: Maximum coating swelling width less than 2 mm ○: Maximum coating swelling width of 2 mm or more and less than 5 mm △: Maximum coating swelling width of 5 mm or more, less than 10 mm ×: Maximum coating swelling width of 10 mm or more Conditions for cycle test (1 cycle / day): Salt spray (36 ° C, 6 hours) → dry (50 ° C, 3 hours) → wet (60 ° C, RH: 95%, 15 hours) [Plating adhesion] Zn- After cutting the Ni alloy-plated steel sheet to a width of 25 mm, bending the test piece by 180 degrees, attaching a cellophane tape to the outer surface side of the steel sheet bent at 180 degrees,
After adhering the cellophane tape and the processing part in the processing part, peel off the cellophane tape, peel off to the cellophane tape,
The amount of the adhered plating was visually observed and evaluated according to the following criteria.

In the case where the peeling amount is large in the plating adhesion test, a cellophane tape is applied in a state where the cell is not bent (flat plate), and the cellophane tape and the steel sheet are brought into close contact with each other. The amount of plating peeled and adhered to the tape was visually observed. 5: 180 degree bending processing, no plating peeling 4: 180 degree bending processing, slight plating peeling 3: 180 degree bending processing, small amount of plating peeling 2: 180 degree bending processing, large amount of plating peeling 1: 180 degree Plating delamination occurs even without bending. The evaluation results obtained above are shown in Table 1 together with the manufacturing conditions described above.

[0043]

[Table 1]

[0044]

[Table 2]

[0045]

[Table 3]

As shown in Table 1, the Zn—Ni alloy-plated steel sheet obtained by the production method of the present invention has excellent performance in both the water-resistant secondary adhesion and the post-paint corrosion resistance aimed at by the present invention. was gotten. Further, at the time of the post-treatment, as a result of visually observing the state of formation of the precipitate in the treatment liquid, under the production conditions of the present invention, the formation of a precipitate was not observed, and according to the production method of the present invention, High quality of the above
It has been found that the Zn-Ni alloy coated steel sheet can be manufactured without operational problems.

[0047]

As described above, according to the present invention, the post-treatment technique after the Zn-Ni alloy plating treatment is effective in improving the adhesion between the plated steel sheet and the coating film without causing unevenness during the chemical conversion treatment. Has been established, and it is possible to manufacture Zn-Ni alloy plated steel sheets excellent in both water resistance secondary adhesion and post-paint corrosion resistance stably without being affected by line speed and without causing operational problems. it can.

Claims (2)

[Claims] After a Zn—Ni alloy plating film is formed on at least one surface of a steel sheet by a Zn—Ni alloy plating process, H ₂ P
One or more selected from O ₄ ⁻ , HPO ₄ ²⁻ and H ₃ PO ₄ are contained in a P concentration of 15 to 170 g / l and 1 to 50 g / l of Ni.
The post-treatment solution containing 0.3 to 10 g / l of Co and adjusted to pH 2.5 to 4.5 is brought into contact with the Zn-Ni alloy plating film, and has excellent secondary water resistance and corrosion resistance after painting. Manufacturing method of Zn-Ni alloy plated steel sheet. 2. The production of a Zn—Ni alloy plated steel sheet having excellent water-resistant secondary adhesion and corrosion resistance after painting according to claim 1, wherein the temperature of the post-treatment liquid is adjusted to 40 to 70 ° C. Method.