JPH0361392A - Electroaluminum plating method using low melting point composition and bath thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a novel low melting point composition containing aluminum and a method for efficiently electroplating aluminum using this composition.

(Prior art) Aluminum electroplating requires water l8 because aluminum has a large affinity for oxygen and its potential is lower than that of hydrogen.
It is difficult to perform this process using a liquid plating bath. For this reason, non-aqueous plating baths, particularly organic solvent-based plating baths, have been studied for electroplating aluminum.

For this organic solvent-based plating bath, aluminum chloride and LiAj2H- or LiH are dissolved in ether: l Dissolve L Tamo (1) Ya, A, eC! 2. and I-i A
12 H4 dissolved in tetrahydrofuran is a typical example (for example, D, E, COL
I Ch et al., J. Electrochem, vol. 99 (
6), p. 234). However, all of these plating baths contain highly active LiAj2H4 or LiH, so if oxygen or moisture is present, they will react with them and decompose, reducing current efficiency and shortening the life of the bath. It had the disadvantage that it became shorter. Furthermore, the boiling point of the organic solvent used is low and there is a high risk of explosion or combustion.

Furthermore, as another example, triethylaluminum and N
A method of dissolving aF in tonorenine has also been proposed (R, 5uchentrunk).

Z, Werkstofftech,, vol. 12.

(p. 190) However, in this case as well, the handling of highly dangerous triethylaluminum is extremely problematic.
It is thought that practical application will be difficult.

(Problem to be solved by the invention) Although the above-mentioned conventional technology has succeeded in plating aluminum, it is difficult to handle the chemical substances used, so it cannot be widely used as a practical technology. It's hard to call it a thing.

The present invention provides a new electrolytic aluminum plating bath that is easy to handle and can efficiently plate aluminum, and a plating method using the bath.

(Means for Solving the Problems) The present invention is a novel low melting point composition formed by mixing an aluminum halide and a 1,3-dialkylbenzimidazolium halide, and further comprises a mixture of this new composition. This is an electrolytic aluminum plating method used as a plating bath.

One of the characteristics of the novel composition according to the present invention is that the two compounds form a low melting point compound in a wide composition range and become a liquid that is easy to handle even at room temperature.
A second feature is that the new composition has a fairly high ionic conductivity in the molten state.

In other words, these characteristics are important basic characteristics of an excellent plating bath, and it can be said that the new composition has very excellent characteristics as an electrolytic aluminum plating bath.

The 1,3-dialkylbenzimidazolium halide described here is a compound represented by the following general formula.

(In the formula, R' and R2 each represent a carbon IJ [1 to 6 alkyl group, and X- represents an anion.) Specific examples of 1.3-dialkylbenzimidazolium halides include 1. 3-dimethylbenzimidazolium bromide, 1,3-dimethylbenzimidazolium iodide, l-methyl-3-ethylbenzimidazolium bromide, l-methyl-3-ethylbenzimidazolium chloride, 1-methyl-3-butyl Examples include benzimidazolium fluoride and l-ethyl-3-propylbenzimidazolium bromide.

In addition, aluminum halides include A42X, (X
represents a halogen atom), specifically A I F s , A Q CQ 3, A Q B
Mention may be made of r 3 and /II3.

The novel composition containing aluminum according to the invention comprises:
It is produced by mixing and melting an aluminum halide and a 1,3-dialkylbenzimidazolium halide. In this case, a low melting point composition can be obtained by mixing 20 to 80 mol% of aluminum halide and 80 to 20 mol% of 1,3-dialkylbenzimidazolium halide. For example, a composition of aluminum chloride and 1-methyl-3-ethylbenzimidazolium bromide is liquid at room temperature and has a fairly low viscosity in the aluminum chloride concentration range of 55 to 80 mol%.

In order to efficiently carry out electrolytic aluminum plating using the above composition as a plating bath, the preferred composition ratio is 50 to 75 mol% of aluminum halide and 1.3% by mole of aluminum halide.
- dialkylbenzimidazolium halide is 25
~50 mol%, more preferably 55-70 mol% aluminum halide and 30-45 mol% 13-dialkylbenzimidazolium halide. In a system with too little aluminum halide, a reaction that appears to be decomposition of the 1,3-dialkylbenzimidazolium cation occurs, and in a system with too much aluminum halide, the viscosity of the plating bath tends to increase.
Not preferred).

The preparation of the novel compositions can generally be carried out by the two-step process described below.

As the first step, the alkyl halide and 1-alkylbenzimidazole are charged into an autoclave equipped with a stirrer together with a reaction solvent, and heated to 30 to 200°C, preferably 50°C.
After the reaction is carried out at 150° C. and quaternized, the solvent and unreacted substances are removed to obtain 1,3-dialkylbenzimidazolium halide. As the reaction solvent in this case, hydrocarbon solvents such as benzene, toluene, and hexane, polar solvents such as water, methanol, ethanol, tetrahydrofuran, dimethylformamide, and dimethyl sulfoxide, etc. can be used.

In the second step, a predetermined amount of the 1,3-dialkylbenzimidazolium halide and aluminum halide produced in the first step are mixed, and the mixture is heated in an inert gas atmosphere or suspended in an appropriate solvent. After heating and mixing in a cloudy state, the desired electrolytic aluminum plating bath can be manufactured by removing the solvent. In either case, considerable heat is generated during mixing, so care must be taken to prevent the reaction temperature from running out of control.

Electroaluminum plating is performed in a dry oxygen-free atmosphere in ff1Q from the viewpoint of maintaining the stability of the plating bath and the plating properties. Plating conditions include bath temperature 0~300℃ and current density 0.0 using direct current or pulse current.
When carried out at 1 to 50 A/dm2, uniform plating can be achieved with good current efficiency. If the bath temperature is too low, uniform plating will not be achieved, and if the bath temperature is too high or the current density is too high, the 1,3-dialkylbenzimidazolium cation will decompose, the plating layer will become non-uniform, and current efficiency will deteriorate. This is undesirable as it causes a decrease in

When uniformly and continuously plating strips, etc., it is necessary to replenish the plating bath with β ions to keep the concentration of AI2 ions in the plating bath within a certain range. AJ2 ions are automatically replenished according to the amount, and the Aff ion concentration can be maintained within a certain range even without replenishment of aluminum halide.

When plating efficiently at low temperatures, it is effective to add an organic solvent to the plating bath in order to reduce the viscosity of the plating bath. In this case, the organic solvent is preferably an inert solvent such as benzene, toluene, xylene, or chlorobenzene, and is usually used in an amount of 5 to 100 Vol.

Furthermore, in order to increase the conductivity of the plating bath or to make the aluminum plating layer uniform, it is also effective to add an alkali metal or alkaline earth metal halide. This place Δ A L-hII whole box master t-L
As an example of a halide of earth alkali class 10 total pressure, LiC
ff, NaCl2, NaF, CaCffz, etc., and these compounds are usually added to the plating bath at a concentration of 0.1~
It is used by adding 30 mol%.

(Example 1) 1.0 mol of l-methylbenzimidazole (132,2
g), 1.1 mol (tt 9.9 g) of ethyl bromide, and 100 g of methanol as a solvent were charged into a stainless steel autoclave, and reacted at 90° C. for 5 hours with stirring.

The solvent and unreacted substances were distilled off from the reaction product using a rotary evaporator to obtain 236.7 g of a solid.

This solid substance was 1-methyl-3-ethylbenzimidazolium bromide, and the reaction yield based on 1-methylbenzimidazole was 98 mol%.

Next, 24.1 g (0.10 mol) of the obtained l-methyl-3-ethylbenzimidazolium bromide was placed in a glass reactor in a nitrogen atmosphere, and aluminum chloride 2
6.6 g ((L 20 mol)) were gradually mixed. By introducing aluminum chloride, a reaction occurred at the solid interface with 1-methyl-3-ethylbenzimidazolium bromide, and liquefaction gradually proceeded. Since this reaction is accompanied by heat generation, the entire amount of aluminum chloride was added while being careful not to let the reaction temperature exceed 80°C.This mixture is a liquid at room temperature, and the conductive dust is 2.6 mS/c at 25°C.
In addition, in this system, when the molar ratio of aluminum chloride and 1-methyl-3-ethylbenzimidazolium bromide was changed from 1 to 2, the relationship between temperature and conductive dust was as shown in Table 1. Since it is in a solution state at room temperature in the entire molar ratio range and exhibits high conductive dust, it is considered as a trough in electrolytic aluminum plating.

Table 1 Relationship between molar ratio and conductive dust Molar ratio 1.0 1.5 2.0 Temperature 25 (°C) 1.0 1.7 2.
630 1.4 2.0
3.140 2.6 3.6
4.650 4.3
5.5 6.460 6.1
7.5 8.5 (Examples 2.3 and 4) By the same reaction method as in Example 1, l-methyl-3-ethylbenzimidazolium chloride (Example 2), from l-isopropylbenzimidazole and ethyl bromide
-Isopropyl-3-ethylbenzimidazolium bromide (Example 3) was synthesized.

These quaternary salts were mixed with aluminum chloride in the same manner as in Example 1 to prepare a composition in which the molar ratio of aluminum chloride to quaternary salt was 2.0. Table 2 shows the results of measuring conductive dust in these compositions.

Furthermore, a composition in which the molar ratio of aluminum bromide and l-methyl-3-ethylbenzimidazolium bromide synthesized in Example 1 was 2.0 was prepared (Example 4), and the results of measuring conductive dust are shown in Table 2. It was shown to.

Table 2 Conductive dust of various compositions (Example 5) A cold-rolled steel plate with a thickness of 0.5 mm was washed with solvent vapor by a conventional method.
Immediately after drying the product which had been subjected to alkaline degreasing and pickling, it was immersed in an electrolytic aluminum plating bath using the composition shown in the above example, which had been previously kept in a nitrogen atmosphere.

After that, a cold-rolled steel plate was used as a cathode, and an aluminum plate (purity 99.
99%, plate thickness 1. On+n+) was used as an anode to perform aluminum plating on a cold-rolled steel plate by direct current.

The plating bath of Example 1 with a composition in which the molar ratio of aluminum chloride and l-methyl-3-ethylbenzimidazolium bromide was 2.0 was used as the plating bath, and the electrolytic conditions were a bath temperature of 25°C and a current density of LA/dm. When plating was performed for 30 minutes, a dense aluminum plating with a plating layer thickness of 6 microns was obtained with a current efficiency of 95% or more.

(Example 6) Hoborei 1″) 17ri-Seido 1e P A 1 Shi 5 Nika 8 P1
Example 5 Using a plating bath with a composition in which the molar ratio of -1 sheep-3-ethylbenzimidazolium chloride was 2.0,
Aluminum plating was applied to a cold rolled steel sheet in the same manner as above.

The electrolytic conditions were a bath temperature of 50°C and a current density of 4A/dm2. When plating was performed for an electrolysis time of 10 minutes, a dense aluminum plating with a plating layer thickness of 8 microns was obtained with a current efficiency of 95% or more.

(Example 7) A composition having a molar ratio of aluminum chloride and 1-isopropyl-3-ethylbenzimidazolium bromide of 2.0 described in Example 3 and toluene as an organic solvent were used at 1:1.
(volume ratio) was mixed to prepare a matting bath. This plating bath was heated to 8.5°C at 25°C. It exhibited an electrical conductivity of 1 ms/cm, which was more than twice as high as that of one without toluene.

Aluminum plating was performed using this plating bath in the same manner as in Example 5.

The electrolytic conditions were a bath temperature of 25°C, a current density of LA/dm", and an electrolytic time of 30 minutes. A dense and glossy aluminum plating with a plating layer thickness of 6 microns was obtained with a current efficiency of 95% or more. It was done.

(Effects of the Invention) According to the present invention, aluminum plating can be performed with high current efficiency and high current density with good productivity.

Furthermore, in the electroaluminum plating bath of the present invention and the plating method using the bath, when aluminum is used for the anode, Aβ ions consumed by plating are automatically replenished by Aff dissolution from the anode, making bath management easy. In this respect as well, the workability is superior to other methods.

Claims (2)

[Claims] (1) Aluminum halide and the following formula ▲ Numerical formula, chemical formula, table, etc. ▼ (In the formula, R^1 and R^2 each represent an alkyl group with 1 to 6 carbon atoms, and X^- is an anion A low melting point composition obtained by mixing a 1,3-dialkylbenzimidazolium halide represented by the following formula. (2) An electrolytic aluminum plating method using the low melting point composition according to claim 1 as a plating bath.