JP2712661B2 - How to adjust the electroplating bath - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a method for adjusting an electroplating bath for accurately controlling the concentration of sodium sulfate in a plating bath used for sulfate electroplating.

[Conventional technology]

In a plating bath of sulfuric acid electroplating represented by electrogalvanizing, sodium sulfate is supplied as an electrolytic supporting salt in order to save power when plating is conducted. Other examples of the electrolytic supporting salt include sodium acetate, ammonium sulfate, and the like. However, sodium sulfate is generally used due to problems in operating environment and waste liquid treatment.

The sodium sulfate put into the plating bath does not directly participate in the plating reaction, reduces the electric resistance between the cathode and the anode, contributes to power saving, and is consumed as the plating operation proceeds. Therefore, in order to maintain the power saving effect, it is necessary to keep replenishing sodium sulfate and maintain the concentration of sodium sulfate in the plating bath at an appropriate value. That is, if the concentration of sodium sulfate in the plating bath is too high, burning of the plating surface occurs, and if the concentration is too low, a sufficient power saving effect cannot be obtained.

Conventionally, methods for maintaining and controlling the concentration of sodium sulfate in a plating bath include a method of adjusting the amount of sodium sulfate to be added based on the electric conductivity of a plating solution (Japanese Patent Laid-Open No. 57-63699) and a method using fluorescent X-rays. A method based on the amount of Na ions obtained by instrumental analysis such as analysis has been mainly employed.

[Problems to be solved by the invention]

However, in the former method using the electric conductivity method, the measured electric conductivity is easily affected by the pH, temperature, and plating metal ion concentration of the plating bath. There is a problem with difficulty. However, the device itself is simple and inexpensive.

Also, the latter method of measuring Na ions by fluorescent X-ray analysis has a problem in that measurement accuracy is difficult to obtain because Na is in the light element measurement limit region. Further, the sampling system which receives the plating solution on the filter paper has a problem that the sampling mechanism is complicated and easily broken, and the cost is high.

An object of the present invention is to solve these problems and to provide a plating bath adjustment method capable of maintaining the concentration of sodium sulfate in a plating bath with high accuracy and economical efficiency.

[Means for solving the problem]

The method for adjusting the electroplating bath of the present invention comprises measuring a plating metal ion concentration, a Fe ion concentration, a sulfate ion concentration, a pH and a temperature of a sulfate plating bath used for electroplating, and measuring these values in the plating bath. The sodium ion concentration dependent on sodium sulfate is determined by the following equation, and the amount of sodium sulfate supplied is controlled based on the sodium sulfate concentration obtained from the determined sodium ion concentration.

[Action]

The present invention is to directly measure the Na ion concentration or the sodium sulfate concentration in order to prevent the required concentration of sodium sulfate in the plating bath from being inaccurate as in a conventional electric conduction method or X-ray fluorescence analysis. Instead, the concentration of sodium sulfate is accurately obtained by calculation regardless of the input of sodium sulfate.

That is, according to the study of the present inventors, the Na ion concentration depending on sodium sulfate in the plating bath, the hydrogen ion concentration (pH) contained in the plating bath, the plating bath temperature affecting the pH value, SO ₄ ^2- ion, Z present in the plating bath
n ion, Ni ion, Fe ^T ion (total Fe ion −Fe ²⁺ + Fe
³⁺ ) and the concentration of plating metal ions such as Fe ³⁺ (or Fe ²⁺ ) ions can be accurately calculated according to the following equation (1).

[Na] (g / l) = K ₁ × 46.0 (atomic weight of Na × 2) × A (mol
/ l) + K ₂ …… (1) [SO ₄ ], [Zn], [Ni], [Fe ^T ], [Fe ³⁺ ] Each ion concentration of SO ₄ ion, Zn ion, Ni ion, Fe ^T ion and Fe ³⁺ ion γ (T) = Activity coefficient (function of plating solution temperature T) K ₁ , K ₂ = correction coefficient (basically, tuning is performed in correspondence of the actually measured value and the estimated value with K ₁ = 1, K ₂ = 0) SO ₄ ion, Zn ion, Ni ion, total Fe ion, Fe ³⁺ ion plating metal ion concentration, sulfate ion concentration and
The pH can be easily and accurately measured online. Therefore, from these, the Na ion concentration depending on sodium sulfate in the plating bath was calculated, and this calculated
By controlling the amount of sodium sulfate supplied to the plating bath according to the amount of sodium sulfate based on the Na ion concentration, the amount of sodium sulfate in the plating bath can be easily and accurately maintained at an appropriate value.

Japanese Patent Application Laid-Open No. 60-164239 does not describe a method of controlling the replenishment amount of sodium sulfate as in the present invention. However, when quantifying the plating metal ion concentration of the plating bath by fluorescent X-ray analysis, sodium sulfate is used. In order to correct the matrix effect caused by the absorption of fluorescent X-rays by Na ions from the surface, a technique for estimating the sodium sulfate concentration by calculation from the measured values of the plating metal ion concentration and the sulfate ion concentration in the plating bath is described. However, since the concentration of Fe ions as impurities, the pH value, and the activity coefficient that is a function of the temperature of the plating bath are not taken into account, a method for controlling the replenishment amount of sodium sulfate as in the present invention is assumed. Applied to
No high-precision control is performed.

〔Example〕

 Hereinafter, embodiments of the present invention will be described.

FIG. 1 shows an on-line measurement system used in the method of the present invention. The pH of the sulfuric acid plating bath 1 in the tank is
Through a pH meter. The measured pH is corrected based on the plating bath temperature measured by the thermometer through the system 3. In addition, fluorescent X
The ion concentration of Ni, Zn, and Fe ^{T in} the plating bath 1 and the sulfate ion concentration of the plating bath 1 are measured by a line analyzer, and the Fe ³⁺ ion concentration of the system 5 is measured by an absorptiometer.

The pH meter used for pH measurement is, for example, a glass electrode type for low pH, and the plating bath temperature used for correcting the measured value may be based on the measured value of the plating bath management thermometer,
It may be based on the measurement value of a thermometer with a built-in pH meter.

In addition, in a normal plating bath, the Fe ³⁺ ion concentration may be very small.In such a case, the Fe ³⁺ ion concentration may be ignored, and when other metal ions are 0.1 g / l or less, You can ignore it.

The pH corrected by the measured plating metal ion concentration, sulfate ion concentration, and temperature is substituted into the above equation (1) by a separately installed computer. From the Na ion concentration of the plating bath 1 thus obtained, the amount of sodium sulfate in the plating bath 1 is determined in order to properly control the sodium sulfate concentration of the plating bath 1. This calculation is also performed in the computer, and the method will be described below with reference to the flowchart of FIG.

Control upper limit of Na concentration in plating bath: NaMAX, lower limit: N
aMIN. When each metal ion concentration, sulfate ion concentration and pH value of the plating bath are measured, and the calculated Na value obtained by using the equation (1) exceeds the upper limit from each of the measured values (Na> NaMAX is Y
If es), dilute the plating bath by injecting water (guess xl / h) into the plating bath. Compare the Na operation value with the upper and lower limits, and if less than the upper limit (Na> NaMAX is No), water is not injected. N
aWhen the calculated value is less than the upper limit and less than the lower limit (Na <NaMIN
If Yes, add a fixed amount of sodium sulfate powder or a concentrated aqueous solution of sodium sulfate for a fixed time (T ₁ h). When the Na operation value is less than the upper limit and less than the lower limit (Na <NaMI
If N is No), the current status is maintained. By repeating this flow, sodium sulfate is effectively introduced into the plating bath, and its concentration is maintained within an appropriate range.

The method of the present invention can be applied to, for example, pure zinc electroplating, Ni-Zn alloy electroplating, and Fe-Zn alloy electroplating.

FIG. 3 shows the result when the concentration of sodium sulfate was actually controlled in pure zinc electroplating. Third
The figure shows the case of the conventional electric conductivity method and the fluorescent X-ray method together with the method of the present invention. The results are shown by the correspondence between the online Na analysis value in each method and the amount of Na by the atomic absorption method (standard method). As is clear from the figure, compared with the conventional electric conductivity method and the fluorescent X-ray method, the Na analysis value according to the method of the present invention is a high level result which is in good agreement with the atomic absorption method.

〔The invention's effect〕

The plating bath adjusting method of the present invention can accurately control the concentration of sodium sulfate online. Therefore,
It reduces the power consumption in the plating operation and contributes to the reduction of the electroplating cost. Moreover, since the measurement system is simplified, the durability of the system is excellent.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an on-line measuring system used in the plating bath adjusting method of the present invention, FIG. 2 is a flowchart showing an operation for automatically feeding sodium sulfate, and FIG.
FIG. 3 is a diagram showing the relationship between the Na analysis value and the Na value by the atomic absorption method for the method of the present invention and the conventional method.

Claims (1)

(57) [Claims] 1. A plating metal ion concentration, a Fe ion concentration, a sulfate ion concentration of a sulfate plating bath used for electroplating.
The pH and temperature were measured, and the Na ion concentration depending on the sodium sulfate concentration of the plating bath was determined from the measured values according to the following formula.The replenishment amount of sodium sulfate was determined based on the sodium sulfate concentration obtained from the determined Na ion concentration. And controlling the electroplating bath. (Na) _{(g / l) = K 1} × 46.0 × A (g / mol) + K 2 where (Na) = Na ion concentration K _1, K ₂ = correction coefficient A = [SO _4] / B ₁ -10 ^{- pH} / ^2γ (T) - [Zn] / B ₂ - [Ni] / B ₃ - ([Fe ^T] + 0.5 [Fe ^3+]) / B ₄ [SO _4], [Zn], [Ni] , [Fe ^T ], [Fe ³⁺ ] = SO ₄ ion, Zn ion, Ni ion, Fe ^T ion, Fe ³⁺ ion concentration (g / l) γ (T) = activity coefficient (plating bath B ₁ , B ₂ , B ₃ , B ₄ = constant (g / mol)