JP3221897B2 - Purification method of electroaluminum plating solution and plating method - Google Patents

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 obtaining a stable plating appearance and a uniform film pressure with simple equipment in a non-aqueous electrolytic aluminum plating using a room temperature molten salt bath. It is.

[0002]

2. Description of the Related Art It is well known that aluminum metal materials have excellent corrosion resistance. However, aluminum has a high affinity for oxygen and has a potential lower than that of hydrogen, so that it is difficult to deposit aluminum from an aqueous solution. Therefore, aluminum electroplating has conventionally been performed in an organic solvent-based plating bath or a molten salt bath. As an organic solvent-based plating bath, AlCl ₃ —LiAlH ₄ or LiH ₂ dissolved in ether or tetrahydrofuran, NaF · 2Al (C ₂ H
₅ ) The toluene solution of ₃ is typical. However, these baths have the danger of explosion when in contact with air or water and are difficult to handle. Further, as a bath having no danger of explosion, a room-temperature molten salt bath such as an aluminum halide and an alkylpyridinium halide or an alkylimidazolium halide is also known.

[0003] Since electric aluminum plating using a room temperature molten salt bath uses an aluminum halide,
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 high-purity plating cannot be obtained, but also it is difficult to obtain a stable plating appearance. As a method of purifying a plating solution, it has been proposed to immerse metal aluminum and perform substitution purification (Japanese Patent Application Laid-Open No. 64-17889). However, it was difficult to always obtain a stable plating film. In addition, these molten salt baths use equipment (equipment) with good airtightness, and unless plating is performed in an inert dry oxygen-free atmosphere, oxygen, water and hydrogen chloride generated by moisture absorption will be present in the bath. In addition to dissolving and deteriorating the plating solution, there is a problem that the electrodeposition of aluminum is inhibited at the time of plating, so that dark gray coarse precipitation or non-uniform granular precipitation easily occurs.

[0004]

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

[0005]

SUMMARY OF THE INVENTION The present invention relates to a method of immersing metallic aluminum in a room temperature molten salt bath comprising (A) an aluminum halide and (B) a monoalkyl- or dialkyl-imidazolium halide, By bubbling a dry oxygen-free gas, it is possible to remove impure metals, oxygen, water and hydrogen chloride which hinder the electrodeposition of aluminum, and to obtain a plating solution capable of obtaining a stable and dense white aluminum plating film. It was based on the knowledge that it could be done. Further, using the 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, it prevents re-dissolution of oxygen, hydrogen chloride, etc., and has the effect of removing dissolved gas.
This is based on the finding that a uniform plating film can be obtained even in a facility having no airtightness.

That is, the present invention relates to (A) an aluminum halide and (B) a monoalkyl- or dialkyl-
An electric aluminum plating solution obtained by mixing and melting an imidazolium halide in a molar ratio of 1: 1 to 3: 1 by dipping metal aluminum and bubbling an inert dry oxygen-free gas. Provided is a method for purifying an aluminum plating solution. The present invention also uses a plating solution obtained by the refining method according to claim 1 and bubbling an inert dry oxygen-free gas into a plating bath at a bath temperature of 25 to 80 ° C and a current density of 0.2. 10 A / dm ² ,
Provided is an electric aluminum plating method characterized by plating by direct current or pulse 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.
It is adjusted by mixing and melting at a molar ratio of 3: 1. Optimally, the molar ratio of component (A) to component (B) is 2: 1. Here, if the amount of aluminum halide is less than 1: 1, a reaction considered to decompose the imidazolium cation occurs. If the amount is more than 3: 1, the viscosity of the plating bath increases, and the bath is deteriorated and plating is not preferable.
The aluminum halide of the component (A) is represented by AlX ₃ , wherein X is a halogen such as chlorine, bromine or iodine, and chlorine is preferred. As the monoalkyl- or dialkyl-imidazolium halide of the component (B), a 1-alkyl or 1,3-dialkylimidazolium halide represented by the general formula (2) is preferable.

[0008]

Embedded image

[Wherein 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 a halogen. As the 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 one or a mixture of two or more of these halogens, such as 3-butylimidazolinium chloride, in which halogen is replaced with bromine or iodine.

Next, the purification method of the present invention will be described. In the purification method, metallic aluminum is immersed in the molten salt bath while bubbling an inert dry oxygen-free gas. That is, inert dry oxygen-free gas is bubbled into 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. After cooling, it can be used as an aluminum plating solution, but it is better to use it after filtering as much as possible. Here, the purity of metal aluminum is 99.99%
The above are preferred. The surface area of the metal aluminum to be immersed is 20 to 50 dm ² per liter of plating solution.
It is desirable that The metal aluminum is preferably an aluminum wire or aluminum powder having a large surface area. 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. The purification time is 4
If the time is shorter than this, the substitution reaction is not sufficient, and it is difficult to obtain a stable plating film. Bubbling volume of inert dry oxygen-free gas is 0.5 liter / mi per liter
n is sufficient.

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

[0012]

Embedded image

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 a hydrogen or alkyl group having 1 to 2 carbon atoms, and A is another copolymer N is an integer of 2 or more and 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) reaches 80,000. The polymer represented by the formula (1) is added for uniformity, smoothness of the film and prevention of dendrite precipitation.
Styrene, α-methylstyrene, vinyl toluene, m-
Examples include styrene homopolymers such as methylstyrene, copolymers thereof, and copolymers of a styrene monomer and another polymerizable vinyl monomer. Examples of other vinyl monomers A in the case of a copolymer include maleic anhydride, maleic acid, acrylic acid, methacrylic acid, methyl methacrylate, glycidyl methacrylate, itaconic acid, acrylamide,
Acrylic nitrile, maleimide, vinyl pyridine, vinyl carbazole, acrylate, methacrylate, fumarate, vinyl ethyl ether, vinyl chloride and the like can be mentioned. Of these, those with 3 carbon atoms
Preferred is an α, β-unsaturated carboxylic acid of 10 to 10 or an alkyl (1 to 3 carbon atoms) ester thereof. Of these,
Polystyrene having a molecular weight of 300 to 5000, poly-α-methylstyrene and the like are preferred. The addition amount is 0.1 to 50 g /
1, preferably 1 to 10 g / 1, which is 0.1
If the amount is less than g / 1, the smoothness and the effect of preventing dendrids are small. In addition, as a brightener,
Nitrogen-containing heterocyclic compounds such as hydrazides, pyrimidines and 1,10-phenanthroline may be added.

The flow rate of the inert dry oxygen-free gas to be bubbled is preferably 0.3 to 1 liter / min per liter of bath. If less than 0.3 liter / min,
The degassing effect is small, and the effect does not change even if it exceeds 1 liter / min. Conversely, gas consumption is large and uneconomical.
As the inert dry oxygen-free gas used in the present invention, an inert gas such as dry N ₂ gas and Ar gas is selected. Dry N ₂ gas may be obtained by separation by a hollow fiber membrane, oxygen adsorption under high pressure, deoxidation by adding hydrogen gas, or dehydration by cooling and heating. Aluminum plating is performed by using aluminum as an anode and applying a direct current or pulse current to a bath temperature of 25 to 80 ° C, preferably 50 to 80 ° C.
60 ° C., current density 0.2 to 10 A / dm ^2, preferably 0.5 to
It is better to carry out at 6 A / dm ² . In the present invention, by using the bubbling of the inert dry oxygen-free gas and the swinging of the cathode in combination, the appearance becomes more uniform and the variation in the film thickness is reduced. The relationship between the bubbling flow rate, the cathode oscillation speed and the film thickness distribution is shown in FIGS.

According to the plating method of the present invention, plating in the air is possible. However, in order to improve the stability of the plating bath, an inert dry oxygen-free gas is purged into the plating tank after the plating is completed. It is desirable to keep it tightly 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. Because it can be made, it is advantageous for industrialization. Next, the present invention will be described with reference to examples.

[0017]

【Example】

Example 1 An aluminum wire (1 mmφ) having a purity of 99.99% per liter of a bath was prepared by mixing and melting AlCl ₃ and 1-methyl-3-propylimidazolium bromide in a molar ratio of 2: 1. ) 80 m, immersed in dry N ₂ gas
Bath temperature 80-90 while bubbling at liter / min
C. for 8 hours. Then, after cooling, suction filtration was performed with a glass fiber filter paper to remove a powdery black precipitate, and the resultant was used as an electroaluminum plating bath. When this plating solution was analyzed by an atomic absorption spectrophotometer, Fe detected at 16 ppm before purification was reduced to 4 ppm. Lead was not detected. Next, the copper plate (thickness: 0.3 mm) used as the cathode was subjected to alkali degreasing, electrolytic cleaning, and pickling as pretreatment, followed by water washing and drying. Plating was performed using the copper plate as a cathode and the aluminum plate (purity 99.99%) as an anode, immersed in the plating bath maintained at 40 ° C., and plated in a dry N ₂ gas atmosphere at a DC current of 2 A / dm ² for 15 minutes. Was performed. The plating bath was stirred with a stirrer. As a result, white dense aluminum plating having a current efficiency of 95% or more and a film thickness of 6 μm was obtained.

Example 2 A dry N ₂ gas was plated using a plating bath obtained by adding 4 g / 1 of polystyrene having a weight average molecular weight of 5,000 to a plating bath purified by the same method as in Example 1 by setting the atmosphere for plating to air. A copper plate treated in the same manner as in Example 1 was used as a cathode and an aluminum plate was used as a cathode while bubbling at a rate of 0.5 L / min per liter for 30 minutes at a bath temperature of 50 ° C. and 2 A / dm ^2. Plating was performed.
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 plating was performed in the atmosphere, and plating was performed while bubbling dry Ar gas at a flow rate of 1.0 liter / min per liter in a plating bath. Was performed. This results in a current efficiency of 95
A white, smooth aluminum plating having a% film thickness of 11.4 μm was obtained.

Example 4 AlCl_ThreeAnd 1-methyl-3-propylimidazolium bromide
Plating bath formed by mixing and melting a 2: 1 molar ratio with Mide
Is adjusted to 10 liters and 45 dm per liter^TwoNo
Luminium wire (99.99%) immersed in dry N_TwoGas
0.5 liter / min per liter bubbling
Then, the solution was heated to a temperature of 80 to 90 ° C. and purified for 12 hours.
After cooling this plating solution, suction filtration with glass fiber filter paper
To remove a black powdery precipitate, and to obtain a weight average molecular weight of 91.
Add 2.5g / 1 of polystyrene of No. 7 to make a plating solution
Was. Next, a steel plate (200 × 200 × 0.3 mm) is formed by a standard method.
Pre-treatment, and a 2 μm thick copper strike in a copper cyanide plating bath.
After being subjected to like plating, it was dried to obtain a cathode. Electricity
Luminium plating uses the copper plating plate as a cathode and aluminum plating.
Immersion in the plating bath maintained at 50 ° C.
Pickled and dried in air N _Two5 liters of gas in plating bath
1. While bubbling at a flow rate of
5A / dm^TwoFor 60 minutes. In addition, plating
The object was swung at a cathode swing speed of 6.8 m / min. This
Average thickness 5.6μ, standard deviation 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 in Example 1 except that
Of poly-α-methylstyrene having an average molecular weight of 664
Add 2.5 g / l, dry N_TwoOne liter of gas
0.5 liter / min per Torr
The copper plate which had been subjected to the same pretreatment as in Example 1 was used as a cathode and an aluminum plate.
2A / dm at a bath temperature of 50 ° C.^TwoAt 30
The plating was performed for minutes. As a result, the current efficiency is 94%,
White and smooth aluminum plating with a thickness of 11.1μ was obtained.
Was.

Comparative Example 1 An aluminum wire (99.99%) was added to a bath prepared by mixing and melting AlCl ₂ and 1-methyl-3-propylimidazolium bromide in a molar ratio of 2: 1 per 1 liter of the bath. 8
It was immersed in 0 m (1 mmφ) and left at a bath temperature of 80 to 90 ° C. for 8 hours. The copper plate was pretreated in the same manner as in Example 1 removed aluminum wire from the plating solution cathode, aluminum plate (99.99%) relates plating bath maintained at 50 ° C. as an anode, in a dry N ₂ gas atmosphere The plating was performed at a DC current of 1 A / dm ² for 30 minutes. The plating bath was stirred with a stirrer. The aluminum plating thus obtained had a non-uniform dark gray needle-like coarse sedimented coating. Comparative Example 2 Example 1 except that the plating atmosphere was air.
The plating was performed in the same manner as in the above. The aluminum plating thus obtained had a plating film of non-uniform granular precipitation with the base material exposed. Comparative Example 3 Plating was performed in the same manner as in Example 1 except that hydrogen chloride gas was bubbled into the plating bath. The aluminum plating thus obtained had a non-uniform, dark gray, poorly adhered plating film with an exposed substrate. Comparative Example 4 Plating was carried out in the same manner as in Example 1 except that oxygen gas was bubbled into the plating bath. In this method, the aluminum plating was not electrodeposited.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the injection amount of nitrogen gas in a mixed molten aluminum plating solution and the variation in plating film thickness.

FIG. 2 is a diagram showing a relationship between a cathode swing speed and a variation in plating film thickness in a mixed molten electric aluminum plating solution.

Continuation of the front page (56) References JP-A-3-28391 (JP, A) JP-A-3-61392 (JP, A) JP-A-63-100191 (JP, A) JP-A-1-104795 (JP) JP-A-62-70593 (JP, A) JP-A-63-183199 (JP, A) JP-A-3-72100 (JP, A) JP-A-4-254600 (JP, A) 3-19319 (JP, B2) JP 6-13758 (JP, B2) Patent 3034635 (JP, B2) Patent 2623486 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) C25D 3/66 C25D 21/14-21/18

Claims (6)

(57) [Claims] 1. An electroaluminum plating solution obtained 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 , 1 liter of plating solution
Immersed in a metal aluminum having a surface area of ²⁰ to 50 dm ² per metal and without energizing the metal aluminum,
(E) A method for purifying an electric aluminum plating solution, comprising bubbling an inert dry oxygen-free gas into the electric aluminum plating solution. 2. An aluminum halide (A), and (B) an aluminum halide.
Monoalkyl- or dialkyl-imidazolium halo
Mix and melt with a genoide in a molar ratio of 1: 1 to 3: 1.
Metal aluminum immersed in electric aluminum plating solution
(E) without energizing the metallic aluminum
Inert dry oxygen-free gas in electroaluminum plating solution
Using an electroplating solution obtained by a method for purifying an electroaluminum plating solution including bubbling a bath temperature of 25 to 80 ° C while bubbling an inert dry oxygen-free gas into a plating bath, A method for electroplating aluminum at a density of 0.2 to 10 A / dm ² by direct current or pulse current. 3. A plating solution containing the polymer of the general formula (1) in 0.1%.
3. The plating method according to claim 2, wherein a plating solution containing 1 to 50 g / 1 is used. Embedded image [Wherein R ^{1 to} R ³ are each hydrogen or a carbon number of 1 to 5;
R ⁴ and R ⁵ are each hydrogen or an alkyl group having 1 to 2 carbon atoms, A is another copolymerizable vinyl monomer, and n is an integer of 2 or more and m is an integer of 0 or more;
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 the air. 5. The plating method according to claim ₂ , wherein a dry N ₂ gas is used as the inert dry oxygen-free gas for bubbling. 6. The plating method according to claim 2, wherein the flow rate of the inert dry oxygen-free gas to be bubbled is 0.3 to 1.0 liter / min per liter of the plating solution, and the swing of the cathode is used together. .