JPH02305989A - 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 alkyl-aminopyridinium halide represented by a specified general formula as an org. solvent-contg. Al electroplating bath. CONSTITUTION:1-Alkyl-aminopyridinium halide represented by the formula (where R<1> is 1-12C alkyl or aralkyl, each of, R<2> and R<3> is H or 1-6C alkyl, R<2> and R<3> is 1-pyrrolidinyl or piperidino together with N to which R2 and R3 bond and x is an anion) is mixed with Al halide preferably in (25-50):(55-70) molar ratio. This mixing is slowly carried out in an inert 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 are those in which aluminum chloride and LiAβH4 or LiH are dissolved in ether, and those in which AβCβ and LiAβH4 are dissolved in tetrahydrofuran (for example, D,
E, Couch et al., J, Electrochem,, 9
(Vol. 9 (6), p. 234), both of these platings are highly active LiA QH4 or L
Since it contains iH, if oxygen or moisture is present, it reacts with them and decomposes, resulting in lower current efficiency and shorter bath life. 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 cooling 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 cannot be widely used as a practical technology due to the difficulty in handling the chemical substances used. It's hard to say.

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 an I-alkyl-aminopyridinium halide, and furthermore, this novel composition is mixed in a plating bath. This is an electrolytic aluminum plating method used as

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 it becomes a liquid that is easy to handle even at room temperature. The novel composition has a considerably 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-alkyl-aminopyridinium halide described here is a compound represented by the following general formula.

Chapter 9 (In the formula, R1 represents an alkyl group having 1 to 12 carbon atoms or an aralkyl group, R2 and R3 each represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, or R2 and R3 are bonded together. 1-pyrrolidinyl group or piperidino group together with the nitrogen atom, and X represents an anion) Specific examples of l-alkyl-amine pyridinium halides include l-methyl-4-dimethylaminopyridinium ioguide. , 1-ethyl-4-dimethylaminopyridinium bromide, 1-ethyl-4-dimethylaminopyridinium chlorite, l-ethyl-4-(N
-ethyl-N-methylamino)pyridinium chloride, 1-ethyl-4-aminopyridinium iodide,
1-n-butyl-4-dimethylaminopyridinium fluoride, l-benzyl-4-dimethylaminopyridinium chloride, 1-n-butyl-4-dimethylaminopyridinium chloride, l-ethyl-4-biperidinopyridinium Nium bromide% 1-ethyl-4-(
Examples thereof include 1-pyrrolidinyl)pyridinium chloride and -ethyl-4-(l-pyrrolidinyl)pyridinium bromide.

Further, the aluminum halide is a compound represented by AβX, (X represents a halogen atom), and specific examples include AβFJ, /lICβ3°A I2B r s, and AI2Im.

The novel composition containing aluminum according to the invention comprises:
It is produced by mixing and melting an aluminum halide and a 1-alkylaminopyridinium 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-alkyl aminopyridinium halide. and 1-ethyl-4-dimethylaminopyridinium bromide, the aluminum chloride concentration was 20
In the range of ~80 mol %, one is obtained which is liquid at 50° C. 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 25 to 50 mol % of l-alkyl-aminopyridinium halide.
mole %, more preferably aluminum halide is 5
5 to 70 mol% and 30 to 45 mol% of l-alkyl-aminopyridinium halide. A system with too little aluminum halide causes a reaction that appears to be decomposition of the 1-alkyl-aminopyridinium cation, and a system with too much aluminum halide tends to increase the viscosity of the plating bath, which is not preferred.

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

In the first step, the alkyl halide and aminopyridine are charged together with a reaction solvent into an autoclave equipped with a stirrer, and reacted at 30 to 200°C, preferably 50 to 150°C, to quaternize. After the reaction, the solvent and unreacted substances are removed to obtain l-alkyl-amino and lysinium 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, predetermined amounts of l-alkyl-aminopyridinium halide and aluminum halide produced in the first step are mixed and heated in an inert gas atmosphere, or both are suspended in an appropriate solvent. The desired electrolytic aluminum plating bath can be manufactured by heating and mixing in a state where the mixture is heated 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
~50 A/dm", current efficiency is good and uniform plating can be achieved. 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. This is undesirable because decomposition of the 1-alkyl-amino didinium cation, non-uniformity of the plating layer, and further reduction of current efficiency occur.

When uniformly and continuously plating strips, etc., it is necessary to replenish the plating bath with /l ions to keep the concentration of AI2 ions within a certain range.In this case, if the anode is an aluminum soluble electrode, the amount of current applied 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 LiCj2, N
Examples include aCl2, NaF, CaCβ2, etc., and usually 0.1 to 30 mol of these compounds are added to the plating bath.
It is used by adding %.

(Example 1) 4-dimethylaminopyridine 1.0 mol (122.2 g
), 1.1 mol (119.9 g) of ethyl bromide, and 120 g of ethanol as a solvent were placed in a stainless steel autoclave and reacted with stirring at 110°C for 9 hours.
The solvent and unreacted substances were distilled off from the reaction product using a rotary evaporator to obtain 229.1 g of a solid.

This solid substance was 1-ethyl-4-dimethylaminopyridinium bromide, and the reaction yield based on 4-dimethylaminopyridine was 99 mol%.

Next, 23.1 g (0.10 mol) of the obtained 1-ethyl-4-dimethylaminopyridinium chlorite was placed in a glass reactor in a nitrogen atmosphere, and aluminum chloride 1
3.3 g (0.10 mol) were gradually mixed. By introducing aluminum chloride, a reaction occurs at the solid interface with 1-ethyl-4-dimethylaminopyridinium bromide, and liquefaction gradually progresses, but this reaction is accompanied by considerable heat generation at the beginning, so that one repulsion part The entire amount of aluminum chloride was added while being careful not to exceed 70°C.

This mixture is liquid at room temperature and has an electrical conductivity of 8.0 at 25°C.
It showed 1ms/cm. Furthermore, in this system, the relationship between temperature and conductivity when the molar ratio of aluminum chloride and 1-ethyl-4-dimethylaminopyridinium chlorite is changed from 0.8 to 2 is shown in Table 1. It is in a solution state at room temperature within the total molar ratio range and exhibits high conductivity and strength, making it excellent as an electrolytic aluminum plating bath.

Table 1 Relationship between molar ratio and conductivity Temperature 25 ('C) 4.1 8.1 6.2 5
．． 430 4.8 9.6 7.4 6.540
6.3 13,2 10. OL850
9.4 17.2 13.2 11.660 1
2.7 21.4 16.8 14.5 (Example 2.3
and 4) 1-ethyl-4-dimethylaminopyridinium chlorite (Example 2), 4-(1
-pyrrolidinyl)pyridine and ethyl chloride to 1-
Ethyl-4-(1-pyrrolidinyl)pyridinium chloride (Example 3) was prepared.

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 1.0 and 2.0. Table 2 shows the results of measuring the electrical conductivity of these compositions.

Furthermore, a composition was prepared in which the molar ratio of aluminum bromide and l-ethyl-4-dimethylaminopyridinium chlorite produced in Example 2 was 1.0 and 2.0 (Example 4),
Table 2 shows the results of measuring the electrical conductivity.

Table 2 Electrical conductivity of various compositions 2 1.0 25 9.
850 10.5 2.0 25 6.4 50 13.1 3 1.0 25 4.750
10, t 2.0 25 3.1 4 1.0 50 14.72.0
50 10.2 (Example 5) A cold rolled steel plate with a thickness of 0.5 mm was subjected to solvent vapor cleaning by a conventional method.
Immediately after drying the product that 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. The cathode is 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.

The plating bath of Example 1 having a composition in which the molar ratio of aluminum chloride and 1-ethyl-4-dimethylaminopyridinium 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 1 A/dm. ”, electrolysis time 30
When plating was carried out in minutes, dense aluminum plating with a plating layer thickness of 6 microns was obtained with a current efficiency of 95% or more.

(Example 6) Aluminum chloride and 1-ethyl-4- described in Example 2
The molar ratio of dimethylaminopyridinium chloride is 2.
Aluminum plating was performed on a cold rolled steel sheet in the same manner as in Example 5 using a plating bath having a composition of 0.

Electrolysis conditions: bath temperature 50°C, current density 10A/dm”
, when plating was carried out with an electrolysis time of 10 minutes, the current efficiency was 9
At 5% or more, dense aluminum plating with a plating layer thickness of 20 microns was obtained.

(Example 7) Aluminum chloride and l-ethyl-4- described in Example 2
The molar ratio of dimethylaminopyridinium chloride is 2.
A tightening 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 25
It exhibited an electrical conductivity of 12.6 mS/cm at °C, which was more than twice as high as that without toluene.

Using this plating bath, aluminum plating was performed 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 8) Aluminum chloride and l-dithyl-4- described in Example 3
A steel plate (thickness: 0.5 mm) was plated with aluminum in the same manner as in Example 5 using a composition having a molar ratio of (l-pyrrolidinyl)pyridinium chloride of 2.0 as a plating bath.

The electrolytic conditions were a bath temperature of 50°C, a current density of 1OA/dm,
When plating was performed with an electrolysis time of 10 minutes, the current efficiency was 95
% or more, a dense aluminum plating with a plating layer thickness of 20 microns was obtained.

(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 and the plating method using the bath of the present invention, when aluminum is used for the anode, the β ions consumed during plating are automatically replenished by β 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 represents an alkyl group or aralkyl group having 1 to 12 carbon atoms, and R^2 and R^3 Each represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, or R^2 and R^3 together with the nitrogen atom to which they are bonded represent 1-
A low melting point composition obtained by mixing a 1-alkyl-aminopyridinium halide represented by a pyrrolidinyl group or a piperidino group, and X represents an anion. (2) An electrolytic aluminum plating method using the low melting point composition according to claim 1 as a plating bath.