JP5306620B2 - Copper foil for ultrasonic welding and surface treatment method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide copper foil which has excellent ultrasonic weldability and can be joined with other copper foil or with other metal, and to provide a surface treatment method for the copper foil. <P>SOLUTION: The copper foil is provided in which at least one surface is coated with a hydrated chromium oxide layer and the coating amount of the hydrated chromium oxide layer to the surface of the copper foil is controlled to 0.5 to 70 &mu;g-Cr/dm<SP>2</SP>. The surface treatment method for copper foil having excellent ultrasonic weldability is provided in which the copper foil is immersed into a chromic acid aqueous solution obtained by dissolving at least one selected from hexavalent chromium compounds into water, and thus the surface of the copper foil is coated with a hydrated chromium oxide layer. Alternatively, the surface treatment method for copper foil having excellent ultrasonic weldability is also provided in which copper foil is subjected to electrolytic treatment with a chromic acid aqueous electrolytic solution obtained by dissolving at least one selected from hexavalent chromium compounds into water, and thus the surface of the copper foil is coated with a hydrated chromium oxide layer. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a copper foil excellent in ultrasonic weldability, and a surface treatment method thereof, in which copper foils are welded to each other or from a copper foil and another metal material by an ultrasonic welding method.

  Conventionally, ultrasonic welding has been performed as one method for joining metal parts such as copper foil. As shown in FIG. 1, a general ultrasonic welding apparatus is provided with a welding head 12 at the front end of a horn 1 projecting forward of an ultrasonic vibration unit U, and the front end of which is a welding tip ( (Sound pole) 11. An anvil 2 is provided so as to face the welding tip 11 and pressurization is performed with an object to be welded (for example, a copper foil) 13 sandwiched between the welding tip 11 and the anvil 2, and the welding tip 11 is ultrasonically applied. Vibrating energy is applied to vibrate, and welding is performed by vibrational heat (frictional heat) generated between the welding tip 11 and the workpiece (copper foil) 13 at that time. Since this ultrasonic welding has a lower joining temperature than resistance welding, it is difficult to damage the base material. In particular, when joining dissimilar metals, there is an advantage that no brittle product is seen at the joint and the cost is low.

  Ultrasonic welding has the advantages as described above, and is often used for assembling various electronic components in order to take advantage of the advantages. In the case of electronic parts used in automobiles and the like, with the recent increase in density, electrical connection parts are required to be more reliable, especially for joints between dissimilar metals such as terminals and copper foil, There is a demand for more reliable joining.

  Moreover, the copper foils of the negative electrode current collector of the lithium ion battery, or the connection between the copper foil and the tab terminal is performed by ultrasonic welding, and a strong bonding strength is required.

  In ultrasonic welding, when ultrasonic vibration is applied with a constant pressure applied to the joint surface, the joint surface is rubbed, the oxide film and impurities are mechanically cleaned, and atomic diffusion is induced, causing mutual interaction. To be joined.

  When performing ultrasonic welding of copper foil, the present inventors have a great influence on ultrasonic weldability (bonding strength) due to the thickness of the anticorrosive treatment layer provided on the surface of the copper foil and the surface roughness of the copper foil. As a result, the present invention has been completed.

  In the case of copper foil, the weldability is better when the rust preventive treatment is not applied. However, it is not suitable for practical use because it easily oxidizes in the atmosphere without rust prevention treatment. In order to prevent this, it is common to perform a chromate treatment in an acidic bath (pH 1-2) to form a chromium hydrated oxide film called a chromate film. The reason why the chromium hydrated oxide film is chromated with an acidic bath is that the rust preventive layer is deposited relatively thick to sufficiently exhibit the rust preventive effect.

  The copper foil coated with the chromate film is not easily discolored in the air, but on the other hand, when the thickness of the chromate film is thick, there are cases where the bonding strength by ultrasonic welding is not sufficient.

  This is because the surface of the copper foil covers the surface of the copper foil, so even if ultrasonic vibration is applied, the surface is difficult to clean, and pure copper does not come out on the surface. It is thought that this is because

  Moreover, it became clear by experiment of this inventor that the roughness of the surface of copper foil has a big influence on the joining force by ultrasonic welding of copper foil. That is, when ultrasonic vibration is applied to a copper foil having a rough surface to bond the copper foils to each other, the copper foil having a rough surface has a low bonding strength. This is presumed that since the roughness is rough, the contact at the time of bonding becomes local, and bonding occurs in the convex and concave portions, but bonding does not occur in the concave portions and the bonding strength decreases.

  In order to solve the above-described problems, the present invention provides a copper foil excellent in ultrasonic weldability and a surface treatment of the copper foil when joining copper foils or a copper foil and another metal by ultrasonic welding. And a method.

The copper foil for ultrasonic welding of the present invention is a copper foil coated with a chromium hydrated oxide layer on at least one surface, and Rz (JISB0601-1994) on the surface coated with the chromium hydrated oxide layer. 10 point average roughness) is 2.0 μm or less, and the coating amount of the chromium hydrated oxide layer on the surface of the copper foil is 0.5 to 70 μg-Cr / dm ^2. .

The surface treatment method of the copper foil for ultrasonic welding of the present invention is a chromic acid aqueous solution in which at least one of hexavalent chromium compounds is dissolved in water with a copper foil having a surface Rz of 2.0 μm or less. It is a surface treatment method in which the surface of the copper foil is immersed and a hydrated chromium layer having a coating amount of 0.5 to 70 μg-Cr / dm ² is coated.

The surface treatment method of the second copper foil for ultrasonic welding according to the present invention comprises a copper foil having a surface Rz of 2.0 μm or less and a chromic acid aqueous solution in which at least one of hexavalent chromium compounds is dissolved in water. In this surface treatment method, the surface of the copper foil is electrolytically coated with a chromium hydrated oxide layer having a coating amount of 0.5 to 70 μg-Cr / dm ² .

By this invention, the copper foil for ultrasonic welding excellent in the weldability of the copper foils by ultrasonic welding or the copper foil and another metal can be provided.
Moreover, the surface treatment method of the copper foil for ultrasonic welding of this invention easily manufactures the copper foil for ultrasonic welding excellent in the weldability of the copper foils by ultrasonic welding, or copper foil and another metal. be able to.

The present invention will be described in detail below. In addition, in this invention, when it is not necessary to express chromic anhydride, chromate, and dichromate separately, these are generically expressed as a hexavalent chromium compound.
Moreover, in this invention, when it is not necessary to express an electrolytic copper foil and a rolled copper foil separately, these are generically expressed as a copper foil.

In the copper foil of the present invention, the coating amount of the chromium hydrated oxide on at least one surface of the copper foil is 0.5 to 70 μg-Cr / dm ² .
Moreover, the copper foil of this invention is a copper foil whose surface roughness is 2.0 micrometers or less by 10-point average roughness (Rz) prescribed | regulated by JISB0601-1994.

Why hydrated chromium oxide coated amount of the chromium coating is a 0.5~70μg-Cr / dm ² is below the 0.5μg-Cr / dm ^2, the bonding strength is good, the surface of the copper foil Is oxidatively discolored and is not practical. Further, if it exceeds 70 μg-Cr / dm ² , discoloration is difficult, but the bonding strength is lowered.

  The reason why the amount of chromium hydrated oxide coating affects weldability is that, as described above, the chromium hydrated oxide coating covers the copper foil surface, so when the coating thickness is thick, ultrasonic vibration is applied. Even so, the surface is difficult to clean and pure copper does not come out on the surface, so that it is difficult for atomic diffusion to occur and the bonding force is considered weak.

Also, the surface roughness of the copper foil affects the bonding force. When ultrasonic vibration is applied to a copper foil having a 10-point average roughness (Rz) specified by JISB0601-1994 exceeding 2.0 μm, the bonding strength is reduced.
When the copper foils having an Rz of more than 2.0 μm are ultrasonically bonded and the cross section of the copper foil is observed, voids are often generated. This is because the contact at the time of joining becomes local because of the roughness, and joining occurs at the convex and concave portions of the unevenness, but joining does not occur at the concave portions, and the portion becomes a void and the joining strength is reduced. It is done.

  In the case of the electrolytic copper foil, the method for producing the chromium hydrated oxide coating layer does not particularly perform any pretreatment when the surface is not oxidized. If the surface is oxidized, pickle, wash with water, or wash and dry. Thereafter, the copper foil is immersed in an aqueous chromic acid solution in which at least one selected from the group of chromium trioxide, chromate, and dichromate is dissolved in water, and a chromium hydrated oxide layer is deposited. .

  In the case of rolled copper foil, degrease the rolling oil remaining on the surface, wash the degreased copper foil with water, or wash with water and dry, and remove the degreased copper foil with chromium trioxide, chromate, dichromic acid. A chromium hydrated oxide layer is deposited by immersing in a chromic acid aqueous solution prepared by dissolving at least one selected from the group of salts in water.

  Another method for producing the chromium hydrated oxide layer is that the copper foil is pickled if necessary, degreased, washed with water, or washed with water and dried, and the copper foil is treated with chromium trioxide, chromate, dichromate. An aqueous chromic acid solution prepared by dissolving at least one selected from the group of the above in water is used as an electrolytic solution, and a chromium hydrated oxide layer is deposited.

As a treatment method prior to the surface treatment of the copper foil with an aqueous chromic acid solution, pickling is effective by immersing in dilute sulfuric acid at H ₂ SO ₄ = 5 to 200 g / l and temperature = 10 ° C. to 80 ° C. is there.
In the case of degreasing, the cathode or / and the anode in an aqueous solution of NaOH = 5-200 g / l, temperature = 10 ° C.-80 ° C., current density = 1-10 A / dm ² , 0.1 min-5 min It is effective to perform electrolytic degreasing.

  As the chromic acid aqueous solution, 1 to 10 g / l of hexavalent chromium (any one of chromic anhydride, chromate or dichromate), 10 to 50 g / l of sodium hydroxide, and pH of about 13 The copper hydrated oxide layer is coated by immersing the degreased copper foil in the (alkaline) chromic acid aqueous solution. The coating thickness can be controlled by adjusting the immersion time.

In the electrolytic surface treatment method of the copper foil with the chromic acid electrolytic solution, the copper foil is first pickled and degreased as necessary. The pickling and degreasing treatment methods are the same as described above.
Next, the pretreated copper foil is subjected to cathodic electrolysis with a chromic acid electrolyte obtained by dissolving a hexavalent chromium compound in water. Electrolysis conditions, to be treated copper foil on the cathode, anode iridium oxide coated titanium plate, the cathode electrolysis current density and 0.1 to 10 A / dm ^2.
As chromic acid electrolyte, 1-10 g / l of hexavalent chromium compound (any one of chromic anhydride, chromate, or dichromate), 10-50 g / l of sodium hydroxide, pH The chromium hydrated oxide layer is coated with a copper foil that is adjusted to about 13 and pretreated with the (alkaline) chromic acid electrolyte as necessary. The coating thickness can be controlled by adjusting the electrolysis time.

  Hereinafter, the present invention will be described with reference to specific examples (examples).

<Example 1>
Electrolytic copper foil: thickness = 10 μm; WS foil gloss side (cathode drum side) surface roughness manufactured by Furukawa Circuit Foil Co., Ltd .: Rz = 1.43 μm
Rough surface side (electrolytic bath side) surface roughness: Rz = 1.69 μm

After immersing the electrolytic copper foil in an aqueous chromic acid solution consisting of an alkaline solution of chromic anhydride (chromic anhydride: 5 g / l; sodium hydroxide: 30 g / l; pH: 13.0; bath temperature: 25 ° C.) for 10 seconds Then, it was washed with water and dried to form a chromium hydrated oxide layer on both sides of the copper foil. The thickness of the hydrated chromium oxide layer is shiny side (cathode drum side) 35μg-Cr / dm ^2, the matte side (electrolytic bath side) was 29μg-Cr / dm ^2. The thickness of the chromium hydrated oxide layer was measured with a fluorescent X-ray analyzer. The copper foil on which the film was formed was evaluated for the following items. The results are shown in Table 1.

<Example 2>
Cathodic electrolytic treatment (cathode: copper foil to be treated, anode (counter electrode): iridium oxide-coated titanium plate, cathode electrolysis using the electrolytic copper foil shown in Example 1 and an aqueous chromic acid solution having the same composition as in Example 1 as the electrolyte. Current density: 0.5 A / dm ² , treatment time: 5 seconds). The treated copper foil was washed with water and dried to form a chromium hydrated oxide layer on both sides of the copper foil. The characteristic evaluation similar to Example 1 was performed about the copper foil in which the membrane | film | coat was formed. The results are shown in Table 1. The thickness of the resulting coating, shiny side (cathode drum side) 62mg-Cr / dm ^2, the matte side (electrolytic bath side) was 50mg-Cr / dm ^2.

<Example 3>
Electrolytic copper foil: thickness = 10 μm; WS foil gloss surface side (cathode drum side) manufactured by Furukawa Circuit Foil Co., Ltd. surface roughness: Rz = 0.57 μm
Rough surface side (electrolytic bath side) surface roughness: Rz = 0.78 μm

After immersing in an alkaline solution of chromic anhydride (chromic anhydride: 5 g / l; sodium hydroxide: 30 / l; pH: 13.0; bath temperature: 25 ° C.) for 10 seconds, washing with water and drying, Chromium hydrated oxide layers were formed on both sides. The thickness of the hydrated chromium oxide layer is shiny side (cathode drum side) 20μg-Cr / dm ^2, the matte side (electrolytic bath side) was 18μg-Cr / dm ^2. The copper foil was evaluated for the same characteristics as in Example 1. The results are shown in Table 1.

<Example 4>
Rolled copper foil thickness: 10 μm
A surface roughness: Rz = 0.65 μm
B surface roughness: Rz = 0.72 μm
The outer surface of the copper foil coil is the A surface, and the inner surface is the B surface.

After immersing in an alkaline solution of chromic anhydride (chromic anhydride: 5 g / l; sodium hydroxide: 30 g / l; pH: 13.0; bath temperature: 25 ° C.) for 10 seconds, washing with water and drying, Chromium hydrated oxide layers were formed on both sides. The thickness of the hydrated chromium oxide layer, A side is 20μg-Cr / ^dm 2, B side was 21μg-Cr / dm ^2. The copper foil was evaluated for the same characteristics as in Example 1. The results are shown in Table 1.

< Reference Example 1 >
Electrolytic copper foil: thickness = 10 μm; MPL foil manufactured by Furukawa Circuit Foil Co., Ltd. Glossy surface side (cathode drum side) Surface roughness: Rz = 2.10 μm
Rough surface side (electrolytic bath side) surface roughness: Rz = 2.54 μm
After immersing in the same chromic anhydride alkaline solution (chromic acid aqueous solution) as in Example 1 for 10 seconds, it was washed with water and dried to form a chromium hydrated oxide layer on both sides of the copper foil. The thickness of the hydrated chromium oxide layer is shiny side (cathode drum side) 38μg-Cr / dm ^2, the matte side (electrolytic bath side) was 57μg-Cr / dm ^2. The copper foil was evaluated for the same characteristics as in Example 1. The results are shown in Table 1.

<Comparative Example 1>
The same electrolytic copper foil as that shown in Example 1 was used, and the chromate treatment bath was an acid bath (chromic anhydride: 5 g / l; pH: 1.5; bath temperature: 25 ° C.). Electrolytic treatment (cathode: copper foil to be treated, counter electrode: iridium oxide-coated titanium plate, cathode electrolytic current density: 0.5 A / dm ² , treatment time: 5 seconds) was performed. The copper foil after the treatment was washed with water and dried to prepare a chromate antirust treatment, and the same characteristics evaluation as in Example 1 was performed. The results are shown in Table 1. The thickness of the resulting coating, shiny side (cathode drum side) 82mg-Cr / dm ^2, the matte side (electrolytic bath side) was 74mg-Cr / dm ^2.

<Comparative example 2>
The same electrolytic copper foil as the electrolytic copper foil shown in Example 1 was used, and immersion was performed for 10 seconds in a treatment solution obtained by further diluting the same chloric acid aqueous solution as in Example 1 10 times. The treated copper foil was washed with water and dried, and the same characteristic evaluation as in Example 1 was performed. The results are shown in Table 1. The thickness of the resulting coating, shiny side (cathode drum side) 0.4μg-Cr / dm ^2, the matte side (electrolytic bath side) was 0.3 μg-Cr / dm ^2.

  The characteristics of the copper foils surface-treated in the above Examples and Comparative Examples were measured and evaluated for the following items.

(1) Rust prevention power: The copper foil was placed in a constant temperature and humidity chamber (temperature: 40 ° C .; relative humidity: set to 90%) for 72 hours, and changes with time in the degree of oxidation discoloration and rust generation were visually observed. The evaluation was evaluated as A, which is the best one with no discoloration, in the order of A> B> C (with oxidation discoloration) according to the degree of oxidation discoloration (no oxidation discoloration).

(2) Weldability 1: Ten copper foils were stacked and welded by an ultrasonic welding machine manufactured by Branson Co., Ltd. The weld strength was evaluated by measuring the joint strength. The bonding strength was evaluated in the order of (strong) A>B> C (weak).
(3) Weldability 2: Using a Branson Co., Ltd. ultrasonic welder, the copper foil and the tab terminal of the negative electrode current collector of the lithium ion battery were overlapped and welded. The weldability was evaluated in the order of (strong) A>B> C (weak) by measuring the joint strength and measuring the strength in the same manner as described above.

In Table 1, “weldability” is shown as a comprehensive evaluation because the characteristics of weldability 1 and 2 have the same tendency.
Moreover, the column of “Comprehensive evaluation” was ranked by comprehensively evaluating rust prevention power and weldability.
As is apparent from Table 1, the surface-treated copper foil of each example is excellent in weldability in ultrasonic welding and exhibits a rust prevention function. In addition, although the weldability of Example 2 was evaluated as B, it is a little inferior compared with Example 1 .
In Reference Example 1, since the surface roughness of the untreated copper foil is rough, the adhesive strength is slightly inferior. However, depending on the importance of the welding strength, it was evaluated as B because it showed practical strength.
On the other hand, although the surface-treated copper foil of Comparative Example 1 seems to be due to the thick rust preventive layer, the weldability is inferior.
Moreover, since the thickness of a rust prevention layer is thin, the surface treatment copper foil of the comparative example 2 is excellent in weldability, but is inferior in the rust prevention function.

As described above in detail, the copper foil excellent in ultrasonic weldability of the present invention is a copper foil excellent in weldability between copper foils by ultrasonic welding or between the copper foil and another metal.
Moreover, the surface treatment method of the copper foil excellent in ultrasonic weldability of the present invention is to easily produce copper foils excellent in weldability between copper foils by ultrasonic welding or between copper foil and other metals. Can do.

It is explanatory drawing which shows the principal part of an ultrasonic welding apparatus.

Explanation of symbols

U ultrasonic vibration unit 1 horn 2 anvil 11 welding tip 12 welding head 13 copper foil

Claims (3)

The copper foil is coated with a chromium hydrated oxide layer on at least one surface, and the surface coated with the chromium hydrated oxide layer has an Rz (10-point average roughness defined by JISB0601-1994) of 2 The copper foil for ultrasonic welding which is 0.0 micrometer or less and the coating amount to the said copper foil surface of the said chromium hydrated oxide layer is 0.5-70 microgram-Cr / dm < ² >. A copper foil having a surface Rz (10-point average roughness specified by JISB0601-1994) of 2.0 μm or less is immersed in an aqueous chromic acid solution in which at least one of hexavalent chromium compounds is dissolved in water, and the copper foil The surface treatment method of the copper foil for ultrasonic welding which coat | covers the chromium hydrated oxide layer whose coating amount is 0.5-70 microgram-Cr / dm < ² > on the surface of this. A copper foil having a surface Rz (10-point average roughness specified by JISB0601-1994) of 2.0 μm or less is electrolytically treated with a chromic acid aqueous solution in which at least one hexavalent chromium compound is dissolved in water, wherein the surface of the copper foil, the surface treatment method of ultrasonic welding for copper foil coating amount to coat the hydrated chromium oxide layer of 0.5~70μg-Cr / dm ^2.

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