JPH02305988A - Composition having low melting point and aluminum electroplating method with bath of this composition - Google Patents

Abstract

PURPOSE:To obtain an easily handleable bath enabling efficient plating by using a mixture of Al halide with trialkylimidazolium halide represented by a specified general formula as an org. solvent-contg. Al electroplating bath. CONSTITUTION:1,2,3-Trialkylimidazolium halide represented by the formula (where each of R<1> to R<3> is 1-6C alkyl and X is an anion) is mixed with AC halide in (80-20):(20-80) molar ratio. This mixing is slowly carried out under heating in an inert gaseous atmosphere while paying attention to the generation of heat. The resulting mixture is an easily handleable liq. at ordinary temp. and has high electrical conductivity. By using the mixture as a plating bath, Al plating can be carried out at high current density with high current efficiency and satisfactory productivity.

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) Electroplating of aluminum is difficult to perform in an aqueous plating bath because aluminum has a large affinity for oxygen and has a lower potential than hydrogen. For this reason, non-aqueous plating baths, particularly organic solvent-based plating baths, have been studied for electroplating aluminum.

Typical examples of this organic solvent-based plating bath include those in which aluminum chloride and LiAl2H or LiH are dissolved in ether, and those in which A 12 C12s and LiA flood H4 are dissolved in tetrahydrofuran (for example, D., E., Couch et al., J., Electroch.
Em, Vol. 99 (6), p. 234), these plating baths all contain highly active LiAlH4 or LiH, so if oxygen or moisture is present, they will react with them. This has the disadvantage that the current efficiency decreases and the life of the bath is shortened. 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 plating bath in which aF is dissolved in toluene 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 problems) The present invention relates to an aluminum halide.

1.2.3-1-Realkylimidazolium halide and an electrolytic aluminum plating method using this new composition 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 narrow 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.

That is, these characteristics are important basic characteristics of an excellent plating bath, and it can be said that the new composition has extremely excellent characteristics as an electrolytic aluminum plating bath.

The 1,2,3-trialkylimidazolium halide described here is a compound represented by the following general formula.

(In the formula, R', R'' and R3 each have 1 to 6 carbon atoms.
(X represents an anion) Specific examples of 1.2.3-trialkylimidazolium halides include 1,2.3-trimethylimidazolium bromide, 1,2.3- Trimethylimidazolium iodide, 1,2-dimethyl-3-ethylimidazolium bromide, 1,2-dimethyl-3-ethylimidazolium bromide, 1,2-dimethyl-3-
Examples include butylimidazolium fluoride.

Also, aluminum halide is /'12X, (
X represents a halogen atom), specifically A9F, /12cg, A I2B r s
J5 and Al2I3 may be mentioned.

The novel composition containing aluminum according to the invention comprises:
It is produced by mixing and melting aluminum halide and 1.2°3-trialkylimidazolium halide. In this case, 20-80 mol% aluminum halide and 80-20 mol% 1.2.3
- A low melting point composition can be obtained by mixing a trialkylimidazolium halide. For example, in a composition of aluminum chloride and 1,2-dimethyl-3-ethylimidazolium bromide, the concentration of aluminum chloride is 55 to 80 mol% at 50°C.
It is a liquid and has a fairly low viscosity.

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 1,2% of aluminum halide.
．． 3-trialkylimidazolium halide is 25
~50 mol%, more preferably 55-70 mol% aluminum halide and 30-45 mol% l,2.3-)-realkylimidazolium halide. In systems with too little aluminum halide, l,2
．． 3-) A reaction that appears to be decomposition of the realkylimidazolium cation occurs, and a system containing too much aluminum halide tends to increase the viscosity of the plating bath, so A is 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 1,2-dialkylimidazole are charged into an autoclave equipped with a stirrer together with a reaction solvent, and heated to a temperature of 30 to 200°C, preferably 50 to 50°C.
After six reactions in which the mixture is reacted at 150° C. and quaternized, the solvent and unreacted substances are removed to obtain a 1,2,3-trialkylimidazolium 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 1,2,3-trialkylimidazolium halide and aluminum halide produced in the first step are mixed and heated in an inert gas atmosphere, or both are mixed in an appropriate solvent. The desired electrolytic aluminum plating bath can be manufactured by heating and mixing in a suspended state and then 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 generally performed in a dry, oxygen-free atmosphere from the viewpoint of maintaining the stability of the plating bath and the plating properties. The plating conditions include bath temperature of 0 to 300°C, current density of 0, Ol
When carried out at ~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 1.2.3-trialkylimidazolium cation will decompose, the plating layer will become uneven, and is undesirable because it causes a decrease in current efficiency.

When uniformly and continuously plating strips, etc., it is necessary to replenish the plating bath with β ions to maintain the A2 ion concentration within a certain range. AI2 ions are automatically replenished accordingly, and the AI2 ion concentration can be maintained within a constant range even without replenishing 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 Vo1%.

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. In this case, examples of alkali metal or alkaline earth metal halides include LiCl2, N
Examples include aCρ, NaF, CaCl22, etc. 1 Usually, 0.1 to 30 mol% of these compounds are added to the plating bath.
It is used by adding it.

(Example 1) 1.0 mol of 1.2-dimethylimidazole (96, Ig
), 1.1 mol (119.9 g) of ethyl bromide, and 50 g of methanol as a solvent were charged into a stainless steel autoclave, and the mixture was 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 201.5 g of a solid. This solid substance was 1,2-dimethyl-3-ethylimidazolium bromide, and the reaction yield based on 1,2-dimethylimidazole was 98 mol%.

Next, 20.5 g of the obtained 1,2-dimethyl-3-ethylimidazolium bromide (0.10 g) was placed in a glass reactor in a nitrogen atmosphere, and 20.5 g of aluminum chloride
6.6 g (0.20 mol) were gradually mixed. 1. By adding aluminum chloride and heating to 80°C.
A reaction occurs at the solid interface with 2-dimethyl-3-ethylimidazolium bromide, and liquefaction gradually progresses, but this reaction is accompanied by heat generation, so aluminum chloride is added while being careful not to let the reaction temperature exceed 90°C. I put in the whole amount.

This mixture is liquid at room temperature and has an electrical conductivity of 6.5 at 25°C.
It showed 5mS/cm. In addition, in this system, the relationship between temperature and conductivity when changing the molar ratio of aluminum chloride and 1,2-dimethyl-3-ethylimidazolium bromide from 1.2 to 2 is shown in Table 1. , is in a solution state at 50° C. within the total molar ratio range and exhibits high conductivity, making it excellent as an electrolytic aluminum plating bath.

Table 1 Relationship between molar ratio and conductivity Temperature 25 ('C) 6.530
7,540
! 0.2 10.05 (113,513,41
3,2 6017,61? , 0 16.6 (Examples 2, 3.4 and 5) Using the same reaction method as in Example I, 1,2-dimethyl-3-ethylimidazolium chloride (Ex. Example 2), 1.2-
1.2- from dimethylimidazole and butyl chloride
1.2° 3-trimethylimidazolium bromide (Example 4) was prepared from dimethyl-3-butylimidazolium chloride (Example 3), 1,2-dimethylimidazole and methyl bromide.

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 the electrical conductivity of these compositions.

Furthermore, aluminum bromide and 1, 2 produced in Example 2
A composition having a molar ratio of -dimethyl-3-ethylimidazolium chloride of 2.0 was prepared (Example 5), and the conductivity was measured. Table 2 shows the results.

Table 2 Electrical conductivity of various compositions 2 25 6, 8 50 12.6 3254・8 50 10, 2 4 25 4, 6 50 10.1 (Example 6) Conventional method applied to cold rolled steel plate with a thickness of 0.5 mm by solvent vapor cleaning,
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 1.0 mm) was used as an anode, and aluminum plating was performed on a cold rolled steel plate by direct current.

As a plating bath, aluminum chloride of Example 1 and 1.2-
When plating was performed using a plating bath with a composition in which the molar ratio of dimethyl-3-ethylimidazolium bromide was 2.0, the electrolytic conditions were a bath temperature of 25 ° C., a current density IA / d, and an electrolytic time of 30 minutes. Dense aluminum plating with a plating layer thickness of 6 microns was obtained with a current efficiency of 95% or more.

(Example 7) The molar ratio of aluminum chloride and 1,2-dimethyl-3-ethylimidazolium chloride described in Example 2 was 2.
Aluminum plating was performed on a cold rolled steel sheet in the same manner as in Example 6 using a plating bath having a composition of No. 0.

When plating was carried out under the electrolytic conditions of a bath temperature of 50° C., a current density of 4 A/dm'', and an electrolytic time of 10 minutes, dense aluminum plating with a plating layer thickness of 8 microns was obtained with a current efficiency of 95% or more.

(Example 8) The molar ratio of aluminum chloride and 1,2-dimethyl-3-ethylimidazolium chloride described in Example 2 was 2.
A plating bath was prepared by mixing the composition of No. 0 and toluene as an organic solvent at a ratio of 1:1 (volume ratio). This plating bath is 2
16. at 5°C. It exhibited an electrical conductivity of 3 mS/cm, which was more than twice as high as that without toluene.

Aluminum plating was performed using this plating bath in the same manner as in Example 6.

The electrolytic conditions were a bath temperature of 25°C and a current density of IA/dm2. When plating was performed for 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.

(Example 9) The molar ratio of aluminum chloride and 1,2-dimethyl-3-butylimidazolium chloride described in Example 3 was 2.
Aluminum plating was performed on a steel plate (thickness: 0.5 mm) in the same manner as in Example 6 using a plating bath having a composition of 0.

When plating was carried out under the electrolytic conditions of a bath temperature of 50° C., a current density of 4 A/dm'', and an electrolytic time of 10 minutes, dense aluminum plating with a plating layer thickness of 8 microns was obtained with a current efficiency of 95% or more.

(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 electrolytic aluminum plating bath of the present invention and the plating method using the bath, when aluminum is used for the anode, the he2 ions consumed during plating are automatically replenished by /l dissolution from the anode, so bath management is possible. is simple, and in this respect also has better workability than other methods.

Claims (2)

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