JP2939343B2 - Method of forming ceramic film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a multilayer ceramic film on a surface of a metal substrate, and more particularly to a wiring method which requires heat resistance, fire resistance and corrosion resistance, and which can be used in an ultra-high vacuum and radiation exposure environment. The present invention relates to a method for forming electric wires for winding and other ceramic-coated metal materials.

[0002]

2. Description of the Related Art As a wire requiring heat resistance and corrosion resistance, a covered wire in which a conductor is coated with an organic substance is conventionally used. However, the organic coating did not have sufficient heat resistance, radiation resistance, and degassing properties in vacuum. Therefore, in order to impart heat resistance, fire resistance, radiation resistance, degassing properties in a vacuum, and the like, electric wires having a conductor coated with ceramics have been studied. As a method of forming ceramics, in the gas phase, a method of forming a film by CVD (chemical vapor deposition), PVD (physical vapor deposition), or thermal spraying, and in the liquid phase, immersion in an alkoxide solution, drying, and heat curing. Methods and methods for forming ceramics by electrolysis are known. Further, as a solid phase method, there is known a method in which a raw ceramic powder is made into a slurry with a melting aid, dried, heated and sintered after application.

[0003] In particular electrolytic process, there is uniform film is easily obtained, wherein, in an acidic solution, anodized to form an Al ₂ O ₃ film has been known by anodic electrolysis on aluminum. However, although alumite-coated electric wires using alumite for covering the conductor are excellent in heat resistance, they are gradually not used because of poor flexibility and degassing properties in vacuum. Instead, electric wires coated with a ceramic coating by the anodic spark discharge method have attracted attention because they are not only excellent in heat resistance but also excellent in porosity, degassing properties in vacuum, and corrosion resistance.

[0004] However, electric wires coated with a ceramic coating by the anodic spark discharge method have low surface hardness of the coating, so that they are susceptible to damage due to nicking and abrasion, easily deteriorate in insulation, and have slipperiness when winding a coil or the like. There was also a problem.
Further, there is a demand for an increase in dielectric breakdown voltage and an improvement in insulation properties when wound around a coil or the like.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for forming a ceramic film on a metal substrate having a high dielectric breakdown voltage and an excellent insulating property when wound around a coil or the like. I do.

[0006]

According to the present invention, a first film having excellent adhesion and flexibility is formed on a metal substrate by spark discharge, and then a dielectric breakdown voltage, hardness, abrasion resistance and the like are formed thereon. It has been made based on the finding that the above problem can be efficiently solved by forming a second film having excellent resistance.

That is, according to the present invention, an electric current is supplied to a metal substrate in an electrolytic bath by using the metal substrate as an anode.
Forming a first film by spark discharge in a first electrolytic bath containing a silicate and / or an oxyacid salt, and then suspending the ceramic fine particles in a suspended state. A method for forming a multilayer ceramic film on a surface of a metal substrate, comprising forming a second film by spark discharge in a contained second electrolytic bath.

The first-stage electrolytic bath used in the present invention includes water-soluble or colloidal silicate and / or tungstic acid, stannate, molybdic acid, borate, aluminate, phosphate and the like. An aqueous solution to which one or more oxyacid salts are added is used. Here, as the silicate,
General formula M ₂ O · nSiO ₂ (M represents an alkali metal, and n represents 0.
Various water-soluble compounds such as sodium silicate, potassium silicate,
Colloidal silica and the like can be mentioned as lithium silicate and water-dispersible ones. These silicates can be used alone or as a mixture of two or more. Further, one or more kinds of metal ions such as Ni, Co, Zn, Ca, Ba, Mg, Pb, and Cr can be added in the form of a soluble salt.

The silicate and / or the aqueous solution used for the electrolytic bath
Alternatively, the concentration of the oxyacid salt is preferably 5 g / l or more,
200 g / l is preferred. In particular, in the case of oxyacid salts, the film formation rate increases most when the concentration is close to saturation. However, a phenomenon in which the formed film becomes non-uniform as the concentration increases easily occurs. The pH of the aqueous solution is arbitrary, but is preferably 3 to 13.5.

In the second electrolytic bath of the present invention, a colloidal silicate and / or an oxyacid salt such as tungstic acid, stannate, molybdic acid, borate, aluminate or phosphate is used. A solution in which ceramic fine powder is dispersed in an aqueous solution containing at least two or more species is used (Japanese Patent Application No. 1-22863).
No. 9). Further, one or more kinds of metal ions such as Ni, Co, Zn, Ca, Ba, Mg, Pb, and Cr can be added in the form of a soluble salt.

The silicate and / or the aqueous solution used for the electrolytic bath
Alternatively, the concentration of the oxyacid salt, the type of the silicate, and the like are the same as those described for the first electrolytic bath.

As the ceramic fine particles to be added to the aqueous solution, various fine particles which are insoluble and dispersible in the aqueous solution can be used. For example, Al ₂ O ₃ , Al (OH) ₃ , SiO ₂ , 3Al
_{2 O 3 · 2SiO 2, TiO} 2, Cr 2 O 3, ZnO 2, partially stabilized zirconia, oxides such as stabilized zirconia-based ceramics or S
Non-oxide ceramics such as iC, SiN, ZnSi ₂ , TiSi ₂ , MoSi ₂ , WSi ₂ and BN can be added and mixed. These can be used alone or as a mixture of two or more.

The particle diameter of the ceramic fine particles is 0.03 μm.
A particle size of m to 100 μm is good, especially 0.03 μm
~ 20 µm is preferred. That is, as the particle diameter increases, the eutectoid becomes more difficult, and even when eutectoid, the coating becomes non-uniform. The amount of the ceramic fine particles to be added can be arbitrarily determined depending on the type of the electrolytic solution in which the fine particles are suspended and the amount of the fine particles to be precipitated. This is the most preferable in view of the above.

In the present invention, in addition to the above ceramic fine particles, fine particles having self-lubricating properties may be added. The fine particles having self-lubricating properties are as described above. Further, in the case of fine particles having poor solution dispersibility, it is preferable to add and disperse a cationic, nonionic, nonionic or anionic surfactant.

In the first-stage electrolysis according to the present invention, the metal substrate on which a film can be formed by spark discharge includes aluminum and its alloys, zirconium, titanium, niobium, and the like.
Magnesium and its alloys; Therefore, these metals themselves or plates, foils, wires or plated materials obtained by cladding this metal on steel, stainless steel or the like can be used as the metal substrate. As the plating method, vapor deposition, ion plating, CVD method,
Electroplating from a non-aqueous solvent may be used.
The shape of the metal substrate may be arbitrary, and examples thereof include a flat plate, a line, a rectangular parallelepiped, and a sphere.

Usually, when a composite film is formed on such a metal substrate by spark discharge, it is not particularly necessary to perform a pretreatment, but it is preferable to sufficiently clean the metal substrate by degreasing, etching, pickling or the like. In performing the anodic spark discharge of the present invention, a metal substrate on which a ceramic film is to be formed is used as an anode, and electrolysis is performed in an electrolytic bath using an insoluble electrode such as iron, stainless steel or nickel as a cathode. The thickness of the first-stage spark discharge film is preferably 0.1 μm to 20 μm, and more preferably 1 μm to 5 μm. At the time of electrolysis, the current density and the electrolysis time are conditions under which the above film thickness can be formed, and the current density is usually preferably 0.2 A / dm ^{2 to} 10 A / dm ^2, and the electrolysis time is 30 seconds or more. It is good to do.
In this case, the voltage at the time of film formation is set to 100 V or more. The bath temperature during this electrolysis is 5 to 90 ° C, preferably 15 to 60 ° C.

In the present invention, subsequent to the first-stage electrolysis, the second-stage electrolysis is performed using the metal substrate on which the spark discharge film is formed by the first-stage electrolysis as an anode. As the cathode, an insoluble electrode such as iron, stainless steel, and nickel is used. The thickness of the film formed by the second spark discharge is preferably 1 μm or more, and more preferably 5 μm to 30 μm.

It is preferable that the total thickness of the first and second spark discharge films is 1 μm to 50 μm.
Further, the ratio of the thickness of the first and second spark discharge films can be arbitrarily determined, but is preferably set to 1/2 to 1/20. At the time of electrolysis, the current density and the electrolysis time are conditions under which the above film thickness can be formed. The current density may be usually 0.2 A / dm ^{2 to} 10 A / dm ² , and the electrolysis time is usually 5 minutes or more. . The bath temperature during the electrolysis is 5 to 90C, preferably 15 to 60C. Spark discharge is performed while maintaining the suspended state of the ceramic fine particles in the second-stage electrolytic bath. Since the ceramic fine particles settle by their own weight, it is important to carry out the operation while maintaining a uniform suspension state by a conventional method. For example, it can be performed by stirring or circulation of the liquid.

The output of the power source used for the first and second electrolysis steps in performing the anode spark discharge in the present invention may be a DC having an arbitrary waveform, but may be a pulse waveform (rectangular waveform), a sawtooth waveform, or a single-phase half-wave. A wave shape is preferred.

[0020]

According to the present invention, the surface of a metal substrate has heat resistance, fire resistance and corrosion resistance, a high dielectric breakdown voltage,
It is possible to form a multilayer ceramic film having excellent insulating properties when wound around a coil or the like. Therefore, when a multilayer ceramic film is applied to an aluminum electric wire or an aluminum clad electric wire according to the method of the present invention, it is possible to obtain a ceramic-coated electric wire in which the dielectric breakdown voltage is further increased in addition to flexibility, and the film is hardly broken by marks or the like.

Furthermore, if the thus obtained ceramic-coated electric wire is wound around a coil, the insulation resistance and the breakdown voltage during winding are high. it can. or,
When a multilayer ceramic film is formed on an aluminum thin plate, it becomes an insulating ceramic thin plate, so that it can be used not only as an insulating foil but also as a flexible substrate for electronic circuits utilizing the high thermal conductivity of aluminum.
Further, the film according to the present invention has a high insulation resistance and a high breakdown voltage and is excellent in adhesion, so that it can be used for ordinary mechanical parts, electronic parts and the like.

Next, the present invention will be described by way of examples.

[0023]

【Example】

Example 1 An aluminum conductor having a diameter of 0.8 mmφ was cleaned by degreasing, alkali etching and acid activating treatment and then used as an anode, while a stainless steel plate was used as a cathode and Na ₂ O · nSiO ₂ 12 was used.
Electrolysis was performed with a 0 g / l aqueous solution at a bath temperature of 30 ° C., and a first ceramic film having a thickness of 3 μm was formed by anodic spark discharge.

Then, the aluminum conductor was used as an anode and the stainless steel plate was used as a cathode, and Na ₄ P ₂ O ₇ .10H ₂ O 70 g / l
Zirconia fine particles (trade name, TZ, manufactured by Tosoh Corporation)
(O, average particle size 0.4 μm) was suspended in a solution in which 50 g / l was suspended, and a second ceramic film having a thickness of 12 μm was formed by anodic spark discharge. As a result, a spark discharge film having a total of 15 μm of the two ceramic films could be formed.

Example 2 Using the same anode and cathode as in Example 1, Na ₂ B ₄ O ₇ .10H ₂ O
A 100 g / l aqueous solution was heated to a liquid temperature of 50 ° C. and electrolyzed, and a 3 μm-thick first ceramic film was formed by anodic spark discharge. Then, using this aluminum conductor as the anode and the stainless steel plate as the cathode, Na ₄ P ₂ O ₇ .10H ₂ O 70 g / l
Alumina fine particles (manufactured by Showa Denko KK, trade name, AL-
45) Electrolysis was performed in a solution in which 50 g / l was suspended, and a second ceramic film having a thickness of 10 μm was formed by anodic spark discharge. As a result, a spark discharge film having a total of 12 μm of the two ceramic films could be formed.

Example 3 A titanium wire having a diameter of 0.3 mφ was cleaned by degreasing and acid-activating treatment and then used as an anode, while a stainless steel plate was used as a cathode and an aqueous solution of 200 g / l of K ₂ O.nSiO ₂ was used. Electrolysis is performed at a liquid temperature of 30 ° C., and a 5 μm-thick first
Was formed.

Then, using this titanium wire as an anode and a stainless steel plate as a cathode, Na ₄ P ₂ O ₇ .10H ₂ O 70 g / l was used to prepare alumina fine particles (AL-4, trade name, manufactured by Showa Denko KK).
5) Electrolysis was performed in a solution in which 50 g / l was suspended, and a second ceramic film having a film thickness of 10 μm was formed by anodic spark discharge. As a result, the total of two ceramic films is 1
A 5 μm spark discharge film was formed.

Comparative Example 1 Using the same anode and cathode as in Example 1, electrolysis was performed with the same electrolytic solution as in the second stage of Example 1, and a single ceramic film having a thickness of 15 μm was formed by anode spark discharge. did.

Comparative Example 2 Using the same anode and cathode as in Example 3, electrolysis was performed using the same electrolytic solution as in the second stage of Example 3, and a single ceramic film having a thickness of 15 μm was formed by anode spark discharge. did.

Comparative Example 3 Using the same anode and cathode as in Example 1, electrolysis was performed using the same electrolytic solution as in the first stage of Example 1, and a single ceramic film having a thickness of 15 μm was formed by anodic spark discharge. .

The characteristics of the electric wire having the ceramic film thus obtained were measured by the following methods. The results are shown in Table 1. The dielectric breakdown voltage was measured in accordance with the “ Method for testing enameled copper wire and enameled aluminum wire”, and JIS C3003 11, (2) “From two pieces”.

Insulation resistance test method Five test pieces having a length of 30 cm were taken from the same winding frame, and the test piece was gently wound five times around a metal cylinder having a diameter of 3 mm and having a smooth surface. The insulation resistance between the metal cylinder and the conductor was measured while applying a tension of 0.2 kgf).
Further, the leak frequency is indicated by the number of times of conduction.

After the hardness test plate was dried at 110 ° C. for 1 hour and allowed to cool, the tip was sharpened flat, and a sharpened pencil was strongly pressed against the ceramic surface at an angle of 45 ° with respect to the ceramic surface to achieve a uniform speed. (3 cm / sec). The test was repeated five times, and the hardness was indicated by the hardness of the pencil when the ceramic surface was not scratched four or more times.

[0034]

[Table 1]

Claims (1)

(57) [Claims] 1. A method for forming a two-layer ceramic film on a metal substrate by spark discharge by applying a current to the metal substrate in an electrolytic bath as an anode, comprising a silicate and / or an oxyacid salt. After forming the first film by spark discharge in the first electrolytic bath, the second film is formed by spark discharge in the second electrolytic bath containing the ceramic fine particles in a suspended state. A method of forming a multilayer ceramic film on the surface of a metal substrate.