JPH1018053A - Production of zn-ni alloy plated steel sheet excellent in water resisting secondary adhesion and bare corrosion ersistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a Zn-Ni alloy plated steel sheet stably producing a Zn-Ni alloy plated steel sheet improved in water resisting secondary adhesion and furthermore excellent in bare corrosion resistance without being influenced by the line speed. SOLUTION: At least one side of a steel sheet is subjected to Zn-Ni alloy plating treatment, and a post-treating soln. of 2.5 to 4.5pH contg. one or more kinds selected from H2 PO4 <-> , HPO4 <2-> and H3 PO4 by 15 to 170g/l as the P concn. and contg. Co by 0.3 to 10g/l, and in which the liq. soln. is preferably regulated at 40 to 70 deg.C is brought into contact with the above formed Zn-Ni alloy coating.

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 plated steel sheet having excellent water-resistant secondary adhesion and bare corrosion resistance of a plated surface, and is effective for improving the adhesion between a plated steel sheet and a coating film. Zn- with excellent bare corrosion resistance in the unpainted state
It relates to the post-processing technology after Ni 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, plating adhesion, and coating film adhesion. In particular, regarding corrosion resistance,
Strict rust prevention standards such as 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 parts), demand for steel plates with high corrosion resistance Have been.

[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 coating film adhesion and corrosion resistance of a Zn-Ni plated steel sheet after coating are affected by the surface condition of the plated film after the Zn-Ni plating treatment. Improvements have been made by post-processing after plating. 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. 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 is performed by performing a cathode treatment or an anode treatment with a Zn-Ni plating solution or sulfuric acid in the last cell of the plating treatment.
A method has been proposed in which Zn on a plating film surface of a plated steel sheet is preferentially dissolved to improve water-resistant secondary adhesion and craterability during cationic electrodeposition coating. Japanese Patent Publication No. Hei 4-2674 discloses that after Zn-Ni plating, Zn-
There has been proposed a method of improving the chemical conversion treatment property of a Zn-Ni plated steel sheet and improving the coating film adhesion by performing an etching treatment of 0.01 to 1 g / m ^{2 with} a Ni plating solution or diluted sulfuric acid or diluted hydrochloric acid.

[0006] JP-A-6-293973 discloses that Ni, Co, Fe
One or more heavy metal ions, 1.5-40 g / l, phosphate ion
0.5 to 10 g / l, 1 to 250 g / l of sulfate ion and 1 to 20 g / l of organic acid, and treatment of the Zn-based plated steel sheet with an acidic displacement plating solution having a pH of 2 to 4.5 makes sludge. A method is disclosed in which a heavy metal such as Ni is efficiently deposited without causing the occurrence of coating, thereby eliminating poor coating film adhesion and improving blackening resistance of an uncoated plate.

[0007] As described in the prior art, poor water-resistant secondary adhesion of a Zn-Ni plated steel sheet is caused by the presence of Zn or a large amount of oxides or hydroxides of Zn on the surface of the plating film. It is caused by being. In this regard, according to the techniques described in Japanese Patent Publication No. 2-56437 and Japanese Patent Publication No. 4-2674, the Zn-Ni plating
Zn on the plating film surface can be dissolved by a 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 the above-mentioned Japanese Patent Application Laid-Open No. 6-293973, the water-resistant secondary adhesion and the bare corrosion resistance are inferior as described later, and the waste liquid treatment is complicated because an organic substance is added to the liquid. There was a problem of becoming.

[0014]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned various problems of the prior art, and the main object of the present invention is to improve the secondary adhesion of water and to improve the bare Zn corrosion resistance. 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 −Ni alloy 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 Co on the plating film surface.
The immersion treatment with an aqueous solution of Co or Co chloride was examined, but not only could not obtain sufficient performance, but also the plated steel sheet had uneven appearance. In addition, Co flash plating by electrolytic treatment after plating treatment was examined, but new equipment for Co deposition is required, the process becomes complicated, and it is uneconomical.

Further, the electroless Co plating was examined.
For example, when hypophosphite ion, which is a Co ion reducing agent, is consumed in electroless Co-P plating, the chemical must be frequently added or the solution needs to be exchanged, 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 Co to a phosphoric acid-based solution, the stable etching effect by the phosphoric acid-based solution and the replacement of Co on the surface of the plating film can be obtained. It was newly found that the Zn-rich state on the plating film surface can be eliminated by the precipitation effect. further,
Co stabilizes Zn hydroxide, which has low electrical conductivity, in the corrosion of Zn-plated steel sheets.
The effect of improving corrosion resistance was expected by the inclusion of Co.

Further, based on this finding, the present inventors examined 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 and the Co content in the processing solution, the pH, and the liquid temperature are in appropriate ranges, without causing various problems in the prior art,
It has been found that the water-resistant secondary adhesion can be improved.

Further, it has been found that the presence of the Co-rich layer on the outermost surface of the Zn—Ni plating film improves the bare corrosion resistance, and the present invention has been reached. That is,
The present invention performs a Zn-Ni alloy plating process on at least one surface of the steel ^{_{plate, H 2 PO 4 -, 15~170g}} / l as P concentration of 1 or more of selected from the HPO ₄ ^2-and H ₃ PO ₄ Contains and 0.
A post-treatment liquid containing 3 to 10 g / l of Co and adjusted to a pH of 2.5 to 4.5 is brought into contact with the Zn-Ni alloy film formed as described above, whereby water-resistant secondary adhesion and bare corrosion resistance are obtained. This is a method for producing an excellent Zn-Ni alloy plated steel sheet.

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

[0023]

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 Co ions is used as a post-treatment of the Zn-Ni alloy plating treatment. According to this method, the post-treatment can be performed in a short time. In addition, when the treatment time is prolonged, the exposed portion of Zn to be dissolved is reduced due to the deposition of Co on the plating surface layer, and the Zn dissolution rate is reduced. Is less dependent on the line speed.

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 bare corrosion resistance can be produced without being affected by the line speed without causing the problems of the prior art. It can be manufactured stably. In addition,
The effect of improving water-resistant secondary adhesion and bare corrosion resistance varies greatly depending on the post-treatment conditions.

That is, when the post-treatment of the Zn—Ni alloy plating is performed under conditions that deviate from the conditions specified in the present invention,
The effect of improving water-resistant secondary adhesion and bare corrosion resistance cannot be obtained, and furthermore, problems such as formation of precipitates composed of Co and phosphate and occurrence of uneven appearance occur, which are preferable in terms of product quality and operation. Absent. 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% by weight, more preferably 10 to 14% by weight. The reason is that if the Ni content is less than 7 wt%, bare corrosion resistance expected from Zn-Ni plating cannot be obtained, and if the Ni content exceeds 15 wt%, not only good bare corrosion resistance cannot be obtained, This is because plating adhesion to processing becomes unstable, and problems such as powdering occur during processing of plated steel sheets such as press working, and fatal defects occur as treated steel sheets.

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 water-resistant secondary adhesion is small. 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.

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 Co is added and contained are not particularly limited. In the production method of the present invention, the Co content in the post-treatment liquid is 0.3 to 10 g / l, more preferably 1 to 5 g.
g / l.

When the amount of Co added is less than 0.3 g / l, the effect of improving post-treatment water secondary adhesion and bare corrosion resistance is small. Conversely, when the amount of Co exceeds 10 g / l, The appearance unevenness may occur in the plating film. It is considered that the above-described effect of improving the bare corrosion resistance of Co in the present invention is because Co forms a corrosion product having excellent corrosion resistance.

Further, according to the present invention, H ₂ P
By setting at least one selected from O ₄ ⁻ , HPO ₄ ²⁻ and H ₃ PO ₄ to 15 g / l or more in terms of P concentration, as described in Examples below, the aforementioned water-resistant secondary adhesion In addition to improved properties, excellent bare corrosion resistance has become achievable. this is,
By increasing the concentration of H ₂ PO ₄ ⁻ , HPO ₄ ²⁻ , and H ₃ PO _{4 in} the post-treatment solution, Co in the post-treatment solution is incorporated into the plating film together with P, and the plating film, which controls bare corrosion resistance, Co on top
This is considered to form a rich layer.

The Co source may be any as long as it can dissociate Co into Co ions in the treatment solution.
Or Co hydrochloric acid, Co acetate, Co carbonate, or the like.
In 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 the pH of the post-treatment solution.
If the value is less than 2.5, the etching effect of Zn by post-processing becomes too large, and if the line speed is low, the processing time is prolonged, resulting in over-etching, which may cause discoloration and uneven appearance of the plated steel sheet. PH of the post-treatment solution
If it exceeds 4.5, most of the added Co becomes a precipitate in the processing solution, which causes clogging of piping and the like.

Therefore, 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 the post-treatment on the improvement of the secondary adhesion to water and bare corrosion resistance is small, and if the liquid temperature exceeds 70 ° C., the phosphorus containing Co This is because a precipitate composed of Co and a phosphate is generated in the acid-based treatment liquid.

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 of bringing the post-treatment liquid into contact with the Zn—Ni alloy-plated steel sheet, any of an immersion treatment, a spray treatment, or 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 bare corrosion resistance with the same coating weight, the Zn-Ni alloy coated steel sheet was adjusted to 30 g / m ² per one side of the steel sheet in order to investigate the bare corrosion resistance at 19 wt%.

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.

Co in the post-treatment solution was added in the form of Co sulfate, Co chloride or Co carbonate, and the Co content in the post-treatment solution was adjusted to a range of 0 to 15 g / l in terms of Co. The temperature of the post-treatment liquid is
It was varied in the range of 20-80 ° C. The various post-treatment Zn-Ni alloy coated steel sheets were evaluated for the secondary water resistance and bare corrosion resistance as well as the plating adhesion necessary for Zn-Ni alloy coated steel sheets by the methods described below. did.

[Water Resistance Secondary Adhesion:] The post-treatment Zn-Ni alloy plated steel sheet was subjected to a chemical conversion treatment using a phosphating solution (trade name: Surfdyne SD2500MZL, manufactured by Nippon Paint Co., Ltd.). Later, cationic electrodeposition coating (paint: trade name; U26
02, Nippon Paint Co., Ltd., coating thickness: 20 μm), intermediate coating (paint: OTO4830, Nippon Paint Co., coating thickness: 35 μm), top coating (paint:
Product name: OTO640, manufactured by Nippon Paint Co., Ltd., coating thickness:
35μm) and apply the coated sample to 50 ° C pure hot water for 10 minutes.
After immersing for days, make a scratch on the paint film to reach the base iron in the shape of a base with a cutter knife at intervals of 2 mm, and visually observe the peeling area ratio of the paint film when the tape was peeled off. evaluated.

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 peeling area ratio of the film of not less than 20%, less than 50% 1: peeling area ratio of the coating film is 50% or more [bare corrosion resistance:] coating weight 30 g / m ² postprocessed Zn-Ni
The alloy-coated steel sheet was subjected to a salt spray test (JIS Z-2371) for 25 days without painting, to examine the area ratio of red rust occurrence, and to evaluate bare corrosion resistance according to the following criteria.

◎: Red rust generation area ratio is less than 5% ○: Red rust generation area rate is 5% or more and less than 10% △: Red rust generation area rate is 10% or more and less than 30% ×: Red rust generation area rate is 30% [Plating Adhesion:] After treatment of Zn-Ni alloy plated steel sheet
A zero-t bending adhesion test was performed in which the tape was bent 180 degrees and the tape processed part was peeled off with a cellophane tape, and the amount of plating peeling on the tape after peeling was visually observed, and evaluated according to the following criteria.

5: No peeling 4: Slight peeling 3: Small peeling 2: Large peeling 1: Peeling without processing The evaluation results obtained above are shown in Table 1 together with the production conditions described above. .

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 secondary water resistance and the bare corrosion resistance aimed at by the present invention. Obtained. Further, at the time of the post-treatment described above, as a result of visually observing the state of formation of the precipitate in the processing solution, under the production conditions of the present invention, no formation of a precipitate was 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.

[0043]

[Table 1]

[0044]

[Table 2]

[0045]

[Table 3]

[0046]

The production method of the present invention is extremely effective in improving the adhesion between a plated steel sheet and a coating film, and furthermore, by establishing a post-treatment technique of Zn-Ni plating which is excellent in bare corrosion resistance, provides a secondary adhesion to water resistance. It has made it possible to stably produce Zn-Ni alloy-coated steel sheets with excellent resistance and bare corrosion resistance without being affected by line speed and without causing operational problems.

Claims (2)

[Claims] At least one side of a steel sheet has a Zn-Ni alloy coating.
H processing_TwoPO _Four ^-, HPO_Four ^2-And H_ThreePO_Four From within
Containing 15 to 170 g / l as a P concentration of at least one selected material,
PH 0.3 to 4.5 containing 0.3 to 10 g / l Co
The post-treatment liquid was brought into contact with the Zn-Ni alloy film formed above.
Water resistant secondary adhesion and bare corrosion resistance
Manufacturing method of excellent Zn-Ni alloy plated steel sheet. 2. The method according to claim 1, wherein the temperature of the post-treatment liquid is adjusted to 40 to 70 ° C. .