JP2000290794A - High efficiency electroplating method for iron group metals - Google Patents

Abstract

PROBLEM TO BE SOLVED: To continuously execute electroplating of nickel or the like having high quality at a high speed by adding acid of a pH lower than that of boric acid having buffering action, into a plating bath contg. the sulfate of iron-group metals such as nickel and boric acid and passing the material to be plated therethrough at a specified current density. SOLUTION: The material to be plated such as a galvanizing material, a galvannealing material and a nonplating material is passed through a plating bath contg. the sulfate of iron-family metals such as Fe, Ni and Co of about 1 to 2 mol/l and boric acid of about 0.1 to 1.0 mol/l, and iron-family metal electroplating is continuously executed. At this time, this plating bath is added with acid of a pH lower than that of boric acid having buffering action. As this acid, sulfuric acid or hydrogen sulfate is preferable, and its concn. is preferably controlled to 0.025 to 0.15 mol/l. The buffering capacity of boric acid is superposed on the pH buffering capacity of the acid to suppress the generation of plating burning, by which high efficiency electroplating of iron-group metals with 50 to 200 A/dm2 high current density and high productivity is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for electroplating iron group metals.

[0002]

2. Description of the Related Art Iron group metals are widely used in machine parts such as screws, automobiles, home appliances, and building materials with a coating weight of about several tens to several hundreds mg / m ² for the purpose of decoration, improvement of paintability, and the like. . There are a wide variety of deposition methods, such as an electroplating method using a Watts bath and a chloride bath, and an electroless plating method using hypophosphorous acid as a reducing agent.

When such an iron-group metal plating is used as a long-life rust preventive material for automobiles, home appliances, and building materials, it is different from decorative ones, and is several g / m ² to several tens g / m ^2.
A certain amount of adhesion is required. Until now, iron group plating was mainly used only in fields with a small amount of adhesion, such as corrosion protection and decoration of machine parts. It is too big.

[0004] Taking nickel as an example, in the practical plating (I) (edited by the Japan Plating Association), the current density of electro-nickel plating is described as a maximum of about 10 A / dm ² , and several g / g Obviously, it takes a long time to obtain a nickel deposition amount of m ² to several tens g / m ^2, which indicates that productivity is extremely low.

To solve the above problem, Japanese Patent Publication No. Hei 4-25356
In the publication, nickel plating consisting of a sulfate-based supporting electrolyte is described.
High-speed nickel plating from a bath
However, also in this case, the current density is 20 to 50 A / dm.^TwoAnd small
G, several g / m^TwoTo several tens g / m ^TwoAbout nickel adhesion
To achieve this, the threading speed must be significantly reduced,
And poor productivity. Also, JP-A-9-111
No. 491 discloses a sulfate-based supporting electrode without adding boric acid.
Inexpensive nickel plating from nickel plating bath
But also here at high current density
Plating is impossible, for example, a current density of 100 A / d
m^TwoWhen plating with a degree of plating
Blackening may occur, making it unusable in appearance.
I understood.

As a general means for preventing plating burnout, it is conceivable to lower the pH of the bath. In Japanese Patent Publication No. 25356/1992, the hydrogen ion activity is controlled to adjust the pH to 1.3 to 1.
It is known that nickel plating is likely to appear when the plating rate exceeds 50 A / dm ^2. Turns out to be impossible.

[0007] In comparison with commonly used electrogalvanizing, the current density is usually 50 to 200 A / dm ^2.
, And produces a wide range of coating weights from tens of mg / m ² to tens of g / m ² at high speed. Therefore, in order to obtain a coating weight of about several tens of g / m ² even in the plating of an iron group metal, a technique capable of producing in the above-mentioned current density range is necessary. Absent.

[0008] The beautiful appearance and corrosion resistance of nickel and cobalt and the good paintability of iron can be utilized by plating further on zinc plating or zinc alloy plating provided for corrosion resistance. However, when an iron group metal is plated using zinc plating or zinc alloy plating as an original plate, pits are likely to be generated, and in order to prevent this, it is necessary to add an organic additive such as sodium lauryl sulfate. However, under a high current density exceeding 50 A / dm ² , the decomposition of the organic additives proceeds, and the decomposed organic impurities cause poor appearance such as plating burnout and poor plating adhesion. You have to sacrifice productivity.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of electroplating iron group metals with high efficiency in view of the above problems.

[0010]

Means for Solving the Problems The present inventors have investigated the occurrence of plating and burn under high current density using nickel as the iron group metal. At the cathode, hydrogen is generated by electrolysis of water along with the electrodeposition of nickel, and alkali (hydroxide ion) is generated, and an alkaline atmosphere is formed near the cathode. Under alkaline conditions, nickel precipitates as nickel hydroxide and should cause plating burns.However, since the bath contains boric acid with pH buffering ability, it does not reach the alkaline atmosphere under low current density. As a result, good nickel plating is deposited. However, at high current densities, the alkali (hydroxide ions) generated by the electrolysis of water far exceeds the pH buffering capacity of boric acid, and the pH near the cathode rises sharply, resulting in plating. Found burns. As a result of examining a means for lowering the pH of the bath to prevent this, while plating can be prevented from being burnt, the phenomenon that the electrodeposition efficiency of plating has been remarkably reduced and the amount of applied plating cannot be obtained has occurred. Next, when the relationship between the pH and the electrodeposition efficiency of plating was investigated, it was clear that the electrodeposition efficiency tended to decrease as the pH decreased. In order to achieve both the suppression and the electrodeposition efficiency of plating, it has been found that it is extremely difficult to control simply by lowering the pH of the bath.

Therefore, the present inventors have paid attention to the fact that a good plating can be produced with the buffering ability of boric acid at a low current density, and studied an acid having a buffering ability at a low pH. Sulfuric acid was used as an acid having a buffer action at a lower pH than boric acid. Although sulfuric acid is a strong acid, the second dissociation of protons is incomplete, so that a buffer system of sulfuric acid and nickel sulfate is established, and exhibits a pH buffering ability at a lower pH than boric acid. First, when boric acid was not added and only sulfuric acid was present,
With a small amount of sulfuric acid of about 0.05 mol / l, plating burn and plating unevenness occurred. This is presumed to be because the buffering capacity of sulfuric acid was so small that it was not possible to buffer the alkaline atmosphere at the interface of the material to be plated, which was generated by high current density electrolysis. On the other hand, when about 0.1 mol is added, plating burns can be suppressed, but plating unevenness occurs. Next, it has been found that when boric acid and sulfuric acid coexist, both good appearance and high efficiency can be achieved. This is because the pH buffering capacity of boric acid is superimposed on the pH buffering capacity of sulfuric acid, and the alkali atmosphere at the interface of the material to be plated, which should occur during electrolysis, is suppressed to the extent that plating and burns do not occur. It is presumed to be due to both the effect of suppressing plating unevenness.

The present invention has been made on the basis of these findings. The gist of the invention is as follows: (1) A material to be plated is passed through to continuously form an iron group metal (Fe, Ni, Co).
In the method for producing electroplating, an acid having a buffer action at a lower pH than boric acid is added to a plating bath containing a sulfate of iron group metal and boric acid, and a current density of 50 to 200 A /
High efficiency electroplating method of an iron group metal, characterized in that plated with dm ^2, a (2) acid or sulfuric bisulfate having a buffering action at lower pH than boric acid, its concentration is 0.025 to 0 (1) The method for highly efficient electroplating of an iron group metal according to the above (1), wherein (3) the iron group metal is nickel and the sulfate is nickel sulfate. The high-efficiency electroplating method for an iron group metal according to the above (1) or (2),
(4) The above (1) or (2), wherein the material to be plated is a galvanized material or a zinc alloy plated material.
Or (5) the method for high-efficiency electroplating of an iron group metal according to (3), wherein (5) the material to be plated is a non-plated material. A high-efficiency electroplating method for the iron group metal described in the above.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. First, examples of acids having a buffering action at a lower pH side than boric acid include phosphoric acid, phosphate, sulfuric acid, hydrogen sulfate and the like. However, a phosphoric acid is not preferable because it forms a precipitate with the iron group. Therefore, as the acid having a buffer action at a lower pH side than boric acid in the present invention, sulfuric acid or hydrogen sulfate is used. When the concentration of the sulfuric acid or hydrogen sulfate is less than 0.025 mol / l, the buffer action is weak, Because burns occur at high current density,
More than this. Further, if it exceeds 0.15 mol / l, no burn occurs, but the efficiency is remarkably reduced and the productivity is affected. In addition, hydrogen hydrogen sulfate is, for example, ammonium hydrogen sulfate, sodium hydrogen sulfate,
Any salt having one proton as a cation, such as potassium hydrogen sulfate, may be used.

It is of course possible to operate at a current density of less than 50 A / dm ² , but in order to secure a basis weight of several g / m ² or more, the operation is further increased in consideration of productivity. 200A
Beyond / dm ^2, because it may burn occurs,
It shall be less than this.

The iron group metal is introduced as iron sulfate, nickel sulfate or cobalt sulfate in consideration of the buffering action with sulfuric acid or hydrogen sulfate. If the sulfate concentration of the iron group metal is too low, the metal ion activity in the vicinity of the electrode becomes insufficient and burns occur,
If the amount is too large, the metal will flow out due to the removal of the plating solution by the plate, which is disadvantageous in terms of cost and there is a possibility of sedimentation. Therefore, considering the above points, 1 mol / l to 2 mol.
/ L is preferred. If the amount of boric acid is too small, the buffer capacity is reduced, and plating and burn easily occur. If the amount is too large, problems such as precipitation occur. Considering the above, 0.1 mol
/ L to 1.0 mol / l is preferred.

If the bath temperature of plating is too low, plating burns are liable to occur, and if it is too high, problems occur in cost and safety.

In order to increase the electric conductivity of the plating bath of the present invention, NH ₄ ⁺ ion, Na ⁺ ion, K ⁺ ion, Li
⁺ Ions can be added as sulfates, which can reduce electricity costs. However, since excessive addition may cause precipitation or burn, the upper limit is set to 0.5 mol / l or less in terms of cation concentration.

Further, Cr and C are inevitably contained in the plating bath.
o, Fe, Ni, Cu, Mn, P, Pb, Sn, Sb,
There is no problem in the present invention even if Cd, Si, Zn, Mo, V, Nb, Ti and the like are included.

When the material to be plated is a galvanized material or a zinc alloy-plated material, the composition of the material is not limited. As zinc alloys, zinc-iron, zinc-nickel, zinc-
As long as it is an alloy plating mainly composed of zinc, such as chromium, zinc-tin, and zinc-nickel-chromium, the kind of metal contained in the alloy is not particularly limited, and a multi-element alloy may be used.
Further, it does not matter whether the plating material is a hot-dip plating material or an electroplating material.

When a non-plated material is used as the material to be plated, a low-carbon aluminum-killed steel, a very low-carbon steel, a low-alloy steel,
High alloy steel or the like can be selected, and the material may be a cold rolled material or a hot rolled material.

For cleaning the plating material, a conventionally used method can be applied. For example, any one of alkali degreasing, electrolytic degreasing, and pickling, or a combination thereof can be applied.

Further, for the purpose of improving paintability, weldability, lubricity, corrosion resistance, etc. on the surface of the iron group metal plating thus obtained, if necessary, electroplating, chromate treatment, phosphoric acid treatment, etc. Salt treatment, lubricity improvement treatment, resin coating treatment, weldability improvement treatment, and the like can be performed.

[0023]

Next, examples of the present invention will be described together with comparative examples. Plating was performed under the plating solution components and plating conditions shown in Tables 1 and 2. A 0.7 mm-thick cold-rolled steel sheet or a hot-rolled steel sheet subjected to alkaline electrolytic degreasing and pickling, or various 0.7 mm-thick galvanized steel sheets subjected to alkaline electrolytic degreasing were used as the original sheets. Under the above conditions, iron or nickel or cobalt plating with an adhesion amount of 10 g / m ² was performed, and the electrodeposition efficiency, plating adhesion, plating appearance, and productivity of the plating were evaluated. The adhesion amount of the iron group metal was measured by dissolving the plating and using an atomic absorption method. The electrodeposition efficiency of the plating was evaluated from the ratio between the amount of adhesion and the amount of electricity determined above. The plating adhesion was evaluated from the state of peeling of the plating at the contact bending portion after the contact bending, and was evaluated as follows: ○ (no plating peeling or slight peeling that is practically acceptable), × (peeling off or practically unusable) Large peeling). The plating appearance was visually evaluated as ○ for uniform appearance without burnt, and x for unburned or uneven appearance due to burnt appearance. The productivity is as follows: Ni plating at a current density of 100 A / dm ² on an electroplating line with a cell length of 1 m × 5 cells.
Was evaluated at the maximum line speed at the time of plating at 10 g / m ² , and ○ was given when 50 m / min or more, and × was given when less than 50 m / min.

In Examples 1 to 16, which are the present invention, the electrodeposition efficiency of plating was as high as 60% or more, the plating adhesion and appearance were good, and the productivity was good. On the other hand, in Comparative Examples, in Comparative Examples 1 and 2, the amount of hydrogen sulfate in the bath was too small or absent, so that plating and burn occurred under high current density, and the plating adhesion was deteriorated. In Comparative Examples 3 and 4, the concentrations of hydrogen sulfate and sulfuric acid were too high, so that the electrodeposition efficiency of plating was low and the productivity was poor. In Comparative Examples 5 and 6, the current density was too high, so that plating burns occurred and the plating adhesion was poor. In Comparative Example 7, plating unevenness occurred because boric acid was not present. In Comparative Example 8, another inorganic acid was used instead of sulfuric acid, but plating and burn occurred, and the plating adhesion was poor. In addition, in a bath using hydrochloric acid, chlorine was generated from the anode, causing a problem in safety.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

[0028]

As described above, the present invention makes it possible to provide an electroplating method for an iron group metal with high efficiency at a high current density and greatly contributes to industrial development. .

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masahiro Yui 5-3 Tokai-cho, Tokai-shi, Aichi F-term in Nippon Steel Corporation Nagoya Works (reference) 4K023 AA12 AA13 AA14 BA06 CA01 CA09 DA02 DA07 4K024 AA03 AA04 AA05 AA17 AB01 AB02 BA03 BC01 CA01 CA03 CA06 DA02 DA04 GA01 GA02

Claims (5)

[Claims] In a method for continuously producing an iron group metal electroplating by passing a material to be plated, a buffering action at a pH lower than that of boric acid is applied to a plating bath containing a sulfate of iron group metal and boric acid. Having an electric current density of 50 to 200 A
A high-efficiency electroplating method for iron group metals, characterized by plating at / dm ² . 2. The acid having a buffering action at a lower pH than boric acid is sulfuric acid or hydrogen sulfate, and the concentration thereof is 0.025.
2. The composition according to claim 1, wherein the amount is 0.15 mol / l.
2. A highly efficient electroplating method for an iron group metal according to claim 1. 3. The iron group metal is nickel, and the sulfate is
3. The method according to claim 1, wherein the material is nickel sulfate.
2. A highly efficient electroplating method for an iron group metal according to claim 1. 4. The method according to claim 1, wherein the material to be plated is a galvanized material or a zinc alloy plated material. 5. The highly efficient electroplating method for an iron group metal according to claim 1, wherein the material to be plated is a non-plated material.