JPH04121915A - Forming of insulating coat for aluminum wire rod - Google Patents

Abstract

PURPOSE:To ensure excellent adhesion, bending work and the like and further high withstanding voltage and reliable insulating characteristic by performing anode oxidation processing on an aluminum wire rod in a caustic soda bath, and forming a coat on this anode oxidation thin film foundation by cationic electrodeposition coating processing so as to form an insulating coat, on the aluminum with rod. CONSTITUTION:(A) Anode oxidation processing condition: (1) bath composition - 0.1-10 percent by weight of caustic soda aqueous solution (2) current density - DC 1-10A/dm<2> (3) bath temperature - 0-50 deg.C (4) processing time - 1 minute-1 hour, then, an anode oxidation thin film is set to 0.1-5mum, preferably 1-3mum is desirable. If it is less than 0.1mum, a problem on the point of strength remains. On the other hand if its thickness exceeds 5mum, the coat is easily broken by bending work, and its withstanding voltage is reduced after the bending work. (B) Cationic electrodeposition coating processing condition: any of cationic electrodeposition paint usually sold on the market is acceptable and either one of clear paint and paint containing pigment is also applicable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for forming an insulating film on an aluminum wire, and more particularly to a method for forming an insulating film by a base treatment by anodizing treatment and an electrodeposition coating process.

[Prior Art] Aluminum wires or strips (hereinafter referred to as "aluminum wires J") are widely used as electrical conductors used in various facilities and devices.

In addition, in practical use, an electrical insulating layer is often formed on the aluminum wire.

Conventionally, methods for forming such an electrically insulating layer include winding an insulating tape, applying enamel, forming an anodized film, and forming an insulating film by electrodeposition. Is it common?

That is, the method of winding the insulating tape is, for example, using glass fiber impregnated with polyester resin or the like to a thickness of 0.5'i.
This is a method of winding a tape of approximately nm size around an aluminum wire. Moreover, the enamel application method is a method of applying enamel in layers. The anodizing method involves forming a so-called insulating anodic oxide film while applying electricity to the wire in an acidic environment using the wire as an anode. Furthermore, the coating film forming method is mainly to form a coating film by electrodeposition coating using an anionic resin paint.

Here, for example, insulated coils for transformers, linear motors, etc.
When used in insulated electromagnetic coils for cars, etc., the tape winding method not only requires a great deal of labor and time for the winding operation, but also increases the thickness of the insulating layer, resulting in increased size and cost. In particular, when it is used to make ground coils (for levitation and propulsion) for multiple linear motor cars that are arranged over the entire section where the floating object travels, it is cost-effective. It is no exaggeration to say that it is impractical in terms of space factor, and with the enamel application method,
For flat wires like the above-mentioned ground coils, which have sharp corners, it is difficult to coat the corners with a uniform thickness, and a considerable number of coats are required to obtain sufficient insulation. Very expensive. Therefore, like the tape winding method described above, this method is inferior in practicality.

[Problems to be Solved by the Invention] However, both of these methods have the following problems.

■ With the usual method of anodizing using an acid bath (for example, the method disclosed in Japanese Patent Application Laid-Open No. 63-90105), cracks occur in the anodic oxide film when winding the aluminum wire into an electromagnetic coil, resulting in insulation. Sexuality decreases. However, the problem is that the thicker the anodized film on the head, the more likely it is to occur. It also avoids a significant increase in costs.

■ Electrodeposition coating treatment methods for aluminum materials are commonly used, such as electrodeposition using an anionic resin paint as described above, or forming a thick film of 30 μm or more, and the voltage characteristics obtained. The disadvantage is that it has some limitations. Also, during use, moisture may permeate through the resin coating and the coating may be corroded.

Furthermore, if the aluminum wire itself is dissolved to some extent and mixed into the paint, there is a problem in that the paint film is likely to peel off when bending the wire apart after forming the paint film.

By the way, in order to prevent aluminum ions from being brought into the anionic electrodeposition coating treatment tank, the thickness of the anodic oxide film base must be 3 μm or more.On the other hand, if this thickness is 3 μm or more, it will cause damage after the paint film is formed. Due to the contradictory phenomenon that cracks occur during bending and the withstand voltage decreases significantly, wire rods cannot be used for applications such as ground coils for linear motors and cars, transformer coils, etc., which require severe bending.

In addition, in cationic electrodeposition coating treatment, if the base anodic oxide film is thick, it will peel off during the electrodeposition coating treatment, so it is not widely used on aluminum materials.6 On the other hand, linear In the case of a coil for a motor car, the entire coil is wound and processed and finally sealed with resin, as shown in, for example, Japanese Patent Application Laid-Open No. 57-134915. Therefore, heat resistance during resin sealing and heat resistance against temperature rise during use are required. Here, heat resistance can be expressed in terms of softening resistance, but it is desirable that it be as stable as possible.

The present invention was developed in view of the above circumstances, and its purpose is to provide a film with excellent uniformity, corrosion resistance, and workability, and to ensure stable softening resistance as well as reliable insulation with high withstand voltage, at a low cost, and with adaptability. An object of the present invention is to provide a method for forming an insulating film on a wide range of aluminum wires.

[Means for Solving the Problems] The present invention was created based on numerous tests and studies conducted in order to establish a new and useful method for forming an insulating film by combining the above-mentioned anodic oxidation treatment and electrodeposition coating treatment. With something that
Breaking away from the conventional perception that the anodized film produced by anodizing peels off during electrodeposition coating treatment using a cationic electrodeposition resin paint (hereinafter simply referred to as "cationic electrodeposition coating treatment"), the anodization treatment is performed using a caustic soda aqueous solution. This is a method in which an insulating film is formed by performing a cationic electrodeposition coating treatment afterward.

That is, when focusing on cationic electrodeposition coating treatment, the interface between the aluminum wire and the electrodeposition coating film becomes alkaline during electrodeposition coating. The degree of alkalinity increases as the coating becomes thicker, that is, as the coating current increases or the current application time increases.

On the other hand, anodizing baths can be broadly classified into oxidation baths.

Neutral bath 7 Alkaline bath 6 Neutral bath has a very thin film (100 to 50 mm) called a barrier type film.
input) is generated. In addition, in acidic baths and alkaline conditions,
Thick porous film (0.1-50μm)
or generated.

Here, when these films come into contact with the above-mentioned interfacial alkali during electrocoating, the barrier type film is thin and easily melts, so the surface of the aluminum (subject to be coated) is eluted and mixed into the paint film. As a result, the electrical resistance, flexibility and adhesion of the coating film decrease.

This film dissolution is also evident from the fact that, in a softening resistance test, an electrical short circuit occurs between the load (such as a steel ball) and the aluminum material when the film softens as the temperature rises.

Furthermore, since the porous type film formed in an acidic bath is easily dissolved in an alkaline atmosphere, it can be said that it has the same defects as the barrier type film described above.

On the other hand, the film formed in alkaline water is highly resistant to alkali and therefore suffers from the above-mentioned defects.

When using various alkali baths, especially caustic soda baths, a high-quality coating with strong alkali resistance can be obtained at low cost. The reason for this is thought to be that anions (eg 804'-, po, '-) are not contained in the film.

Based on the above analysis, a caustic soda bath is used as the anodizing bath, and the thickness of the coating is formed to be larger depending on the required withstand voltage than with anionic electrodeposition coating. They have discovered that an insulating film with excellent voltage resistance, adhesion, etc. can be formed by applying a cationic electrodeposition coating treatment, which has advantages such as high voltage resistance and adhesion.

The processing conditions of the present invention are as follows.

(A) Anodizing treatment conditions: ■ Bath composition - 0.1 to 10% by weight caustic soda aqueous solution ■ Current density - DC 1 to IOA/dr / ■ Bath temperature - 0 to 50°C ■ Processing time - 1 minute to 1 hour The thickness of the anodized thin film (film) is preferably 0.1 to 5 μm, preferably 1 to 3 μm.

If the thickness is less than 0.1 μm, the film is too thin and there remains a problem in terms of strength, for example, as it may be broken by a loaded steel ball during a softening resistance test. On the other hand, if the thickness exceeds 5 μm, the film is likely to be destroyed by bending, and the withstand voltage after bending will decrease.

(B) Cationic electrodeposition coating treatment conditions: Any commercially available cationic electrodeposition coating may be used, and either a clear coating or a pigment-containing coating may be used.

Generally, resin paints whose main components are epoxy resins, aminoepoxy isocyanate resins, amine epoxy resins, epoxy aminoacrylic resins, etc., which are widely used as cationic electrodeposited resin paints, are used.

・Here, the voltage, flow density, bath temperature, processing time, etc. are determined as appropriate depending on the selected paint and the coating film thickness to be produced. 1
Baking is performed for 0 to 40 minutes.

Here, the present invention is characterized in that an anodizing treatment is performed in a caustic soda bath to form an anodized thin film base on the aluminum wire, and then an electrodeposition coating treatment using a cationic resin paint is performed.

[Function] According to the present invention, an anodic oxidation treatment is performed in caustic soda to form an anodized thin film base on the aluminum wire. This anodic oxidation thin film <tt film) has strong alkali resistance.

Thereafter, a cationic electrodeposition coating process is performed to form a coating film on the anodized thin film base.

Then, because of its strong alkali resistance, the anodic oxide film will not dissolve or peel, and aluminum ions will not be eluted, so a high-quality coating film can be produced efficiently.

Therefore, an insulating film consisting of an anodic oxide film and a coating film with excellent voltage resistance, adhesion, etc. can be formed on the aluminum wire.

[Example] The present invention will be explained in detail below.

(First example) Made of aluminum with a purity of 99.8% by weight, the cross section is 3.8m
The ground coil for a linear motor car with a length of 30 cm, which has an arc shape with a radius of 0.5n+n and a part of the corner of the + An oxide film and a coating film of 40 μm were formed to form an insulating film.

Degreasing treatment: 5% by weight caustic sorta (NaOH) solution, 5
0°C x 30 minutes.

Water washing Medium sum: 3vol 1% nitric acid, room temperature x 30 seconds.

Water Washing 4iii oxidation: 5g/, 1l caustic soda solution, 17
~20℃.

DC 4A/da&X energized for 5 minutes.

Water washing Electrodeposition coating: 10% by weight solution of epoxy resin cationic electrodeposition paint Power Top U-100 (manufactured by Nippon Paint), 27℃, O, IA/dcdX 2 minutes, final electric month 320cm, Baking: 170°C for 30 minutes.

As shown in Table 1, this insulating film was compared to the insulating film of Comparative Example 1 (in the first example, the anodic oxidation process was omitted and the electrolyte painting process was performed under the same conditions). In addition, since the adhesion of the coating film is excellent, the withstand voltage (V) after bending and stretching can be maintained at a significantly high level. It can also be seen that the softening resistance and the corrosion resistance of the base film due to the caustic soda bath are excellent (Example 2). Instead, this is a case where a 50 μm coating film is formed on a 2 to 3 μm anodic oxide film.

That is, a coating film was formed by applying current to a 20% by weight solution at a bath temperature of 29° C. for 180 seconds at a current density of 0.1 A/d−.

As shown in Table 1, this insulating film has less or less variation compared to Comparative Example 2 (in the second example, the coating film was formed by omitting the anodizing treatment in the caustic soda bath). It is clearly understood that stable voltage resistance, softening resistance and corrosion resistance can be obtained.

In contrast to the first embodiment, if a cationic electrodeposition coating treatment is applied to the anodic oxide thin film substrate that does not form during caustic soda, the corrosion resistance and coating adhesion of the substrate are the same. Therefore, it is understood that the withstand voltage increases in proportion to the coating thickness.

Note that the data shown in Table 1 is based on the following measurement method.

The bending process was performed in accordance with the JI 5H6864 standard (deformation cracking resistance test) and the JISC3003 standard, with bending angles of 10, 15° 2'0 and 25°, respectively, along the thickness direction of the wire.
A 180° bend was made at R. The extension test is JISC3
003, elongation was performed by 1°3.5 and 10%, respectively. Withstand voltage measurement is based on JISC2110 standard and J
According to the withstand voltage measurement method of the ISC3003 standard, the width is approximately 10
A knotted AJI foil was wrapped around a straight section or a bent section, and the withstand voltage was measured using a withstand voltage measuring device. Surface hardness is J I 5K
The hardness was measured based on the pencil hardness measuring method according to the 5400 standard and the J I 5C3003 standard. Softening resistance is JISC30
According to the 03 standard steel ball method, the temperature was measured when the steel ball came into contact with the aluminum sample when the temperature was raised. Also,
For the corrosion resistance test, the following test was conducted on the sample before cationic electrodeposition coating. Humidity test, humidity at 50℃ 9
The test was carried out by leaving it for 50 hours in an atmosphere of 8 to 100%.

(The following is a blank space) [Effects of the Invention] As is clear from the above explanation, according to the present invention, caustic soda Rakuchu positive lI! This method forms an insulating film on the aluminum wire by performing oxidation treatment and then forming a coating film on the cationic oxide thin film base by cationic electrodeposition coating, so it has excellent adhesion, bending, etc., and voltage resistance. Can guarantee high and reliable insulation properties. Therefore, it is possible to provide an insulated aluminum wire with wide applicability, such as making it possible to produce ground coils for linear motors and cars, transformer coils, etc. at a significantly reduced size and weight and at low cost.

Claims (1)

[Claims] (1) It is characterized by performing anodization treatment in a caustic soda bath to form an anodized thin film base on the aluminum wire, and then performing electrodeposition coating treatment using a cationic resin paint to form an insulating film. Method for forming an insulating film on aluminum wire.