JPH05148680A - Method for purifying aluminum electroplating bath and plating method - Google Patents

Abstract

PURPOSE:To always stably obtain a white dense Al plating film by immersing metallic Al in a molten salt bath consisting of specified components at ordinary temp. and blowing inert dry oxygen-free gas as bubbles. CONSTITUTION:An Al halide is mixed with a monoalkyl- or dialkylimidazolium halide in (1:1)-(3:1) molar ratio and this mixture is melted. Metallic Al is immersed in the resulting plating bath and plating is carried out at 25-80 deg.C temp. of the bath with DC or pulsating current at 0.2-10A/dm<2> current density while blowing inert dry oxygen-free gas into the bath as bubbles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refining method and a plating method for always obtaining stable plating appearance and uniform film pressure with simple equipment in non-aqueous solution aluminum electroplating in a room temperature molten salt bath. Is.

[0002]

2. Description of the Related Art It is well known that aluminum metal materials have excellent corrosion resistance. However, since aluminum has a high affinity for oxygen and its electric potential is baser than hydrogen, it is difficult to deposit aluminum from an aqueous solution. Therefore, aluminum electroplating has been conventionally performed in an organic solvent-based plating bath or a molten salt bath. As the organic solvent-based plating bath, AlCl ₃ -LiAlH ₄ or LiH dissolved in ether or tetrahydrofuran, NaF · 2Al (C ₂ H
₅ ) A toluene solution of ₃ is typical. However, these baths have a risk of exploding when they come into contact with air or water, and are difficult to handle. In addition, as a bath without danger of explosion, a room temperature molten salt bath of an aluminum halide and an alkylpyridinium halide or an alkylimidazolium halide is also known.

Electrolytic aluminum plating in a room temperature molten salt bath uses aluminum halides,
It contains impurities such as Fe, Pb, SO ₄ , and H ₂ O. Further, pyridinium halides and imidazolium halides have high hygroscopicity. Due to this cause, not only plating with high purity cannot be obtained, but also stable plating appearance is difficult to obtain. As a method of refining a plating solution, it has been proposed to immerse metallic aluminum and perform displacement purification (Japanese Patent Laid-Open No. 64-17889). However, according to the experiments conducted by the present inventors, it is possible to immerse metallic aluminum and leave it alone. However, it was difficult to always obtain a stable plating film. In addition, these molten salt baths use equipment (equipment) with good airtightness, and if plating is not performed in an inert dry and oxygen-free atmosphere, hydrogen chloride generated by oxygen, water and moisture absorption will occur in the bath. Not only does it dissolve and deteriorate the plating solution, but it also hinders the electrodeposition of aluminum during plating, which tends to cause dark gray coarse precipitation and uneven granular precipitation.

[0004]

DISCLOSURE OF THE INVENTION The present invention provides a plating solution which, when plating in a room temperature molten salt bath, can always obtain a stable and uniform plating film without using equipment with good airtightness. It is an object to provide a refining method and a plating method.

[0005]

According to the present invention, metallic aluminum is immersed in an ambient temperature molten salt bath composed of (A) aluminum halide and (B) monoalkyl- or dialkyl-imidazolium halide and is inert. By bubbling a dry oxygen-free gas, it is possible to remove impure metals, oxygen, water and hydrogen chloride that inhibit the electrodeposition of aluminum, and obtain a plating solution that is always stable and gives a white dense aluminum plating film. It was made based on the knowledge that it was possible. Furthermore, using the above-mentioned purified solution or a plating solution obtained by adding a specific polymer to the solution,
By performing plating while bubbling an inert dry oxygen-free gas in the bath, while preventing redissolution of oxygen, hydrogen chloride, etc., the effect of removing dissolved gas,
This was done based on the finding that a uniform plating film can be obtained even in equipment that does not have airtightness.

That is, the present invention relates to (A) an aluminum halide and (B) a monoalkyl- or dialkyl-
Electricity characterized by immersing metallic aluminum in an electric aluminum plating solution prepared by mixing and melting imidazolium halide with a molar ratio of 1: 1 to 3: 1 and bubbling an inert dry oxygen-free gas. A method for purifying an aluminum plating solution is provided. The present invention also uses the plating solution obtained by the refining method according to claim 1, while bubbling an inert dry oxygen-free gas into the plating bath at a bath temperature of 25 to 80 ° C. and a current density of 0.2. At ~ 10 A / dm ² ,
Provided is a method for electroplating aluminum, which comprises plating with direct current or pulsed current.

The plating bath used in the present invention comprises (A) an aluminum halide and (B) a monoalkyl- or dialkyl-imidazolium halide in a ratio of 1: 1 to 1.
It is prepared by mixing and melting at a molar ratio of 3: 1. The optimum ratio is 2: 1 for the component (A) and the component (B). If the amount of aluminum halide is less than 1: 1, a reaction that seems to be decomposition of the imidazolium cation occurs, and if it is more than 3: 1, the viscosity of the plating bath increases and the bath deteriorates and plating is unfavorable.
The aluminum halide as the component (A) is represented by AlX ₃ , where X is a halogen such as chlorine, bromine or iodine, and chlorine is preferable. As the monoalkyl- or dialkyl-imidazolium halide of the component (B), 1-alkyl or 1,3-dialkylimidazolium halide represented by the general formula (2) is preferable.

[0008]

[Chemical 2]

[In the formula, R ⁶ has 1 to ⁶ carbon atoms, preferably 1
To 3 alkyl groups, R ⁷ is an alkyl group having 1 to 12 carbon atoms, preferably 1 to 5 carbon atoms, and X is halogen. ] As the above-mentioned alkyl imidazolium halide, specifically, 1-methyl imidazolinium chloride, 1-ethyl imidazolinium chloride, 1-propyl imidazolinium chloride, 1-octyl imidazolinium chloride, 1-methyl- 3-ethylimidazolinium chloride, 1,3-dimethylimidazolinium chloride, 1,
3-diethylimidazolinium chloride, 1-methyl-
3-Propylimidazolinium chloride, 1-butyl-
Examples thereof include 3-butylimidazolinium chloride and the like, and one or a mixture of two or more of those in which these halogens are replaced by bromine or iodine.

Next, the purification method of the present invention will be described. In the refining method, metallic aluminum is immersed in the molten salt bath while bubbling an inert dry oxygen-free gas. That is, an inert dry oxygen-free gas is bubbled through the molten salt bath in the presence of metallic aluminum. The temperature at that time is preferably 80 to 100 ° C., and the time is preferably 4 hours or more. It can be used as an aluminum plating solution after cooling, but it is better to use it after filtering as much as possible. Here, the purity of metallic aluminum is 99.99%
The above is preferable. The surface area of the metallic aluminum to be dipped is 20 to 50 dm ² per liter of plating solution.
Is desirable. The metal aluminum is preferably an aluminum wire or aluminum powder having a large surface area. This is because if the temperature is lower than 80 ° C, the substitution reaction is slow, and if it exceeds 100 ° C, saturated vapor of aluminum chloride is generated, which is not preferable. Purification time is 4
This is because if it is less than the time, the substitution reaction is not sufficient, and it is difficult to obtain a stable plating film. Bubbling amount of inert dry oxygen-free gas is 0.5 liter / mi per liter.
n is enough.

For the plating, the plating solution purified by the above method, or the polymer represented by the general formula (1) is added to the solution.
It is preferable to use a plating solution added with 0.1 to 50 g / 1 while bubbling an inert dry oxygen-free gas into the plating solution.

[0012]

[Chemical 3]

[Wherein R ^{1 to} R ³ are each hydrogen or an alkyl group having 1 to 5 carbon atoms, R ⁴ and R ⁵ are each hydrogen or an alkyl group having 1 to 2 carbon atoms, and A is another copolymerization Is a vinyl monomer, n is an integer of 2 or more, m is an integer of 0 or more, and the sum of n + m is an arbitrary number until the weight average molecular weight of the polymer of the general formula (1) becomes 80,000. The polymer represented by the formula (1) is added for the purpose of film uniformity, smoothness and prevention of dendrite precipitation.
Styrene, α-methylstyrene, vinyltoluene, m-
Examples thereof include styrene homopolymers such as methylstyrene, copolymers thereof, and copolymers of styrene monomers and other polymerizable vinyl monomers. In addition, examples of other vinyl-based monomers A in the case of a copolymer include maleic anhydride, maleic acid, acrylic acid, methacrylic acid, methyl methacrylate, glycidyl methacrylate, itaconic acid, acrylamide,
Examples thereof include acrylonitrile, maleimide, vinyl pyridine, vinyl carbazole, acrylic acid ester, methacrylic acid ester, fumaric acid ester, vinyl ethyl ether and vinyl chloride. Of these, carbon number 3
An α, β-unsaturated carboxylic acid having 10 to 10 or an alkyl (C 1 to C 3) ester thereof is preferable. Of these,
Polystyrene having a molecular weight of 300 to 5,000, poly-α-methylstyrene and the like are preferable. The addition amount is 0.1 to 50 g /
1, preferably 1 to 10 g / 1, which is 0.1
If it is less than g / 1, the smoothness and dendrite-preventing effect are small, and if it exceeds 50 g / 1, black precipitates are generated, resulting in poor plating, which is not preferable. As a brightener,
Nitrogen-containing heterocyclic compounds such as hydrazides, pyrimidines and 1,10-phenanthroline may be added.

The flow rate of the bubbling inert dry oxygen-free gas is preferably 0.3 to 1 liter / min per liter of the bath. If less than 0.3 liter / min,
The deaeration effect is small and the effect does not change even if it exceeds 1 liter / min. On the contrary, the gas consumption is large and uneconomical.
The inert dry oxygen-free gas used in the present invention is selected from inert gases such as dry N ₂ gas and Ar gas. As the dry N ₂ gas, those obtained by separation by a hollow fiber membrane, oxygen adsorption method under high pressure, deoxidation treatment by hydrogen gas addition, dehydration treatment by cooling and heating may be used. Aluminum plating uses aluminum as an anode, and the bath temperature is 25 to 80 ° C., preferably 50 to 50 by direct current or pulse current.
60 ° C., current density 0.2 to 10 A / dm ² preferably 0.5 to
It is better to do it at 6 A / dm ² . In the present invention, the bubbling of the inert dry oxygen-free gas and the cathode oscillation are used in combination to further make the appearance uniform and reduce the variation in the film thickness. The relationship between the bubbling flow rate, the cathode oscillation speed, and the film thickness distribution is shown in FIGS. 1 and 2.

According to the plating method of the present invention, it is possible to perform plating in the atmosphere. However, in order to improve the stability of the plating bath, the plating bath is purged with an inert dry oxygen-free gas after the completion of plating. It is desirable to keep it closed and stored.

[0016]

According to the present invention, uniform and smooth aluminum plating can be obtained at room temperature or low temperature (40 to 60 ° C.) with simple equipment without using equipment and equipment having good airtightness. Since it is possible, it is advantageous for industrialization. Next, the present invention will be described with reference to examples.

[0017]

【Example】

Example 1 In a plating bath prepared by mixing and melting AlCl ₃ and 1-methyl-3-propylimidazolium bromide in a molar ratio of 2: 1, an aluminum wire (1 mmφ) having a purity of 99.99% per 1 liter of the bath was prepared. ) Immerse 80 m and dry N ₂ gas to 0.5
Bath temperature 80-90 while bubbling at l / min
It was left for 8 hours between ° C. Then, after cooling, suction filtration was performed with a glass fiber filter paper to remove the powdery black precipitate, and the electrolytic aluminum plating bath was obtained. When this plating solution was analyzed by an atomic absorption spectrophotometer, Fe detected at 16 ppm before purification was reduced to 4 ppm. No lead was detected. Next, a copper plate (plate thickness: 0.3 mm) used as a cathode was subjected to alkali degreasing, electrolytic cleaning, and pickling as pretreatments, followed by washing with water and drying. For the plating, the copper plate was used as a cathode and the aluminum plate (purity 99.99%) as an anode was immersed in the plating bath kept at 40 ° C. and plated at a direct current of 2 A / dm ² for 15 minutes in a dry N ₂ gas atmosphere. Was done. The plating bath was stirred with a stirrer. As a result, a white dense aluminum plating having a current efficiency of 95% or more and a film thickness of 6 μm was obtained.

Example 2 The atmosphere for plating was set to the air, and 4 g / 1 of polystyrene having a weight average molecular weight of 5000 was added to the plating bath purified by the same method as in Example 1 to dry N ₂ gas. While bubbling in the bath at 0.5 liter / min per liter, the copper plate pretreated in the same manner as in Example 1 was used as the cathode and the aluminum plate as the anode, and the bath temperature was 50 ° C. and 2 A / dm ² for 30 minutes. Plated.
As a result, white and smooth aluminum plating having a current efficiency of 95% and a film thickness of 11.4 μm was obtained. Example 3 Plating was performed in the same manner as in Example 2 except that the atmosphere for plating was atmospheric air and dry Ar gas was plated in the plating bath while bubbling at a flow rate of 1.0 liter / min per liter. Was done. As a result, the current efficiency is 95
%, White and smooth aluminum plating with a film thickness of 11.4 μm was obtained.

Example 4 AlCl₃And 1-methyl-3-propylimidazolium broth
Plating bath prepared by mixing and melting a mide with a molar ratio of 2: 1
Is adjusted to 10 liters and 45 dm per liter²A
Luminium wire (99.99%) is dipped and dried N₂Gas
Bubbling 0.5 liters / min per liter
, The bath temperature was heated to 80 to 90 ° C., and the mixture was purified for 12 hours.
After cooling this plating solution, suction filtration with glass fiber filter paper
The black powdery precipitate to remove the weight average molecular weight of 91
2.5g / 1 of 7 polystyrene was added to make a plating solution.
It was Next, a steel plate (200 x 200 x 0.3 mm) is prepared by a conventional method.
Pre-treated, and then a copper strike with a thickness of 2μ in a copper cyanide plating bath
After performing like plating, it was dried and used as a cathode. Electricity
Luminium plating uses the copper-plated plate as the cathode and aluminum.
Using the aluminum plate as the anode, dip it in the plating bath maintained at 50 ° C.
Pickled and dried in air N ₂5 liters of gas in the plating bath
While bubbling at a flow rate of 1 / min, direct current is 0.
5 A / dm²For 60 minutes. Incidentally, plating
The object rocked at a cathode rocking speed of 6.8 m / min. By this
With an average film thickness of 5.6μ and a standard deviation of 0.34
A dense and smooth white aluminum plating was obtained. Example 5 1-Methyl-3-propylimidazolium bu of Example 1
Place romide in 1-Butylimidazolium bromide
Purified by the same method as Example 1 except that the
Of poly-α-methylstyrene having an average molecular weight of 664 in the bath
Add 2.5 g / l and dry N₂1 liter of gas in the plating bath
While bubbling 0.5 liter / min per torr,
A copper plate that had been pretreated in the same manner as in Example 1 was used as the cathode and aluminum plate.
2A / dm at a bath temperature of 50 ° C with an aluminum plate as the anode²At 30
Plated for minutes. As a result, the current efficiency is 94%,
White and smooth aluminum plating with a film thickness of 11.1μ was obtained.
It was

Comparative Example 1 AlCl ₂ and 1-methyl-3-propylimidazolium bromide were mixed and melted at a molar ratio of 2: 1 and aluminum wire (99.99%) was added per 1 liter of the bath. 8
It was immersed in 0 m (1 mmφ) and left for 8 hours at a bath temperature of 80 to 90 ° C. With respect to a plating bath in which an aluminum wire was removed from this plating solution and a copper plate pretreated in the same manner as in Example 1 was used as a cathode and an aluminum plate (99.99%) was used as an anode at 50 ° C., a dry N ₂ gas atmosphere was used. Plating was performed at a direct current of 1 A / dm ² for 30 minutes. The plating bath was stirred with a stirrer. The aluminum plating obtained from this had a non-uniform dark gray needle-like coarse precipitation co-deposited film. Comparative Example 2 All of Example 1 except that the atmosphere for plating was atmospheric air.
Plating was performed in the same manner as in. The aluminum plating obtained in this manner had a plating film with an exposed non-uniform granular deposit. Comparative Example 3 Plating was performed in the same manner as in Example 1 except that hydrogen chloride gas was bubbled in the plating bath. The aluminum plating thus obtained had a non-uniform dark gray plating film with poor adhesion, in which the substrate was exposed. Comparative Example 4 Plating was performed in the same manner as in Example 1 except that bubbling of oxygen gas was performed in the plating bath. Aluminum plating was not electrodeposited by this method.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a jetting amount of nitrogen gas in a mixed molten electro-aluminum plating solution and variations in plating film thickness.

FIG. 2 is a diagram showing a relationship between a cathode oscillating speed in a mixed molten electro-aluminum plating solution and variations in plating film thickness.

Claims (6)

[Claims] 1. An electroaluminum plating solution prepared by mixing and melting (A) an aluminum halide and (B) a monoalkyl- or dialkyl-imidazolium halide in a molar ratio of 1: 1 to 3: 1. A method for purifying an aluminum electroplating solution, which comprises immersing aluminum and bubbling an inert dry oxygen-free gas. 2. The plating solution obtained by the purification method according to claim 1 is used, and a bath temperature of 25 to 80 ° C. and a current density of 0.2 while bubbling an inert dry oxygen-free gas into the plating bath. An aluminum electroplating method, characterized in that plating is performed by direct current or pulse current at 10 A / dm ² . 3. The plating solution obtained by the purification method according to claim 1 contains 0.1 to 50 g / polymer of the general formula (1).
The plating method according to claim 2, wherein a plating solution added with 1 is used. [Chemical 1] [Wherein R ^{1 to} R ³ are each hydrogen or 1 to 5 carbon atoms]
Alkyl group, R ⁴ and R ⁵ are each hydrogen or an alkyl group having a carbon number of 1 to 2, A is the other copolymerizable vinyl monomer, n is 2 or more, m is an integer of 0 or greater, n
The sum of + m is an arbitrary number until the weight average molecular weight of the polymer of the general formula (1) reaches 80,000. ] 4. The plating method according to claim 2, wherein the plating is performed in an open system in air. 5. The plating method according to claim ₂ , wherein dry N ₂ gas is used as the inert dry oxygen-free gas for bubbling. 6. The plating method according to claim 2 or 3, wherein the flow rate of the bubbling inert dry oxygen-free gas is 0.3 to 1.0 liter / min per liter of the plating solution, and cathode oscillation is also used. ..