JP3869433B2 - Method for producing blackened surface-treated copper foil for electromagnetic wave shielding - Google Patents

Description

  The present invention relates to a method for producing a blackened surface-treated copper foil for shielding electromagnetic waves and having a uniform appearance with low reflectance, uniform appearance and almost no residue, and the surface-treated copper foil.

Since a plasma display panel (PDP) emits a strong electromagnetic wave harmful to the human body from the image display surface, it is necessary to provide an electromagnetic wave shielding body to prevent the electromagnetic wave from being emitted. As the electromagnetic wave shielding body, a composite material manufactured by laminating a copper circuit on an insulating transparent base material such as PET is used. However, the composite material has excellent ability to prevent electromagnetic radiation and light transmittance. There are advantages. Specifically, the composite material is formed by laminating a copper foil having a predetermined surface roughness on the transparent substrate, and removing unnecessary copper foil by etching to form a desired copper circuit. Manufactured. The line width and pattern of the copper circuit are selected based on the required electromagnetic wave radiation ability and light transmittance.
However, if the copper circuit reflects external light, there is a problem of reducing the brightness of the display screen. Therefore, as an electromagnetic shielding copper foil, a copper foil that is surface-treated so as to be close to black and has a low reflectance is preferred.

However, the closer the surface of the surface-treated copper foil is to black, the more easily the appearance becomes uneven or the residue tends to be generated, such as powder sticking to the surface. The unevenness of the copper foil surface reduces the image quality of the PDP, and the residue is etched and falls on the portion where the transparent base material should appear, thereby reducing the light transmittance, so that the PDP resolution is generally lowered.
For this reason, research has been mainly conducted in the direction of surface treatment so that the surface of the copper foil is not completely black but has a chocolate color or dark metal color close to black. However, since the surface of the copper foil manufactured by the method as described above is not completely black, there is a limit to improving the reflectance as an electromagnetic shielding copper foil.

An object of the present invention is to provide a blackened surface-treated copper foil for shielding electromagnetic waves having a black appearance and a low reflectance, and a method for producing the same.
Another object of the present invention is to provide a blackened surface-treated copper foil for electromagnetic wave shielding and a method for producing the same, having a uniform appearance with almost no unevenness and residue while having a black appearance.
Still another object of the present invention is to provide a blackened surface-treated copper foil for electromagnetic wave shielding excellent in peel strength and a method for producing the same.

In order to achieve the above object, a method for producing a blackened surface-treated copper foil for shielding electromagnetic waves according to the present invention,
Forming a blackened plating layer containing Co on the surface of the copper foil by plating with Co or a binary electrolytic plating bath containing Co or more;
And oxidizing the surface of the blackened plating layer by disposing the copper foil on the anode and electrolyzing in a basic electrolytic bath.

It is preferable to further include a step of forming a fine copper particle layer on the surface of the copper foil before forming the blackened plating layer.
Furthermore, it is preferable to further include a step of forming an electrolytic chromate layer on the surface of the oxidized blackened plating layer.
On the other hand, it is preferable to further include a step of forming a plating film layer made of Zn or a Zn alloy on the back surface of the front surface on which the blackened plating layer is formed.
The pH of the basic electrolytic bath is preferably 10 or more.

Hereinafter, the present invention will be described in detail.
The electromagnetic shielding copper foil that is the subject of the present invention is an electrolytic copper foil capable of wide production, and the thickness of the copper foil is 1 to 35 μm, preferably 6 to 18 μm. The surface roughness (Rz: DIN) is 0.1 to 2.0 μm, preferably 0.5 to 1.5 μm. If the surface roughness is less than 0.1 μm, the adhesion to the transparent substrate will be insufficient, and the reliability of the electromagnetic wave shield will be reduced. If the surface roughness is greater than 2.0 μm, the copper foil will be formed after forming the circuit by etching. The unevenness of the surface of the transparent base material to which the is adhered becomes large, and the fogging of the display screen becomes large due to this, which is not preferable.

The main feature of the present invention is a blackened surface with a uniform appearance that does not generate unevenness or residue while blackening the surface of the copper foil by oxidizing the copper foil treated with a black surface in a basic electrolytic bath. The treatment copper foil can be obtained.
The blackening treatment of the copper foil is performed by placing the copper foil on the cathode in an electrolytic plating bath containing a metal that induces blackness, and depositing the metal plating layer on the surface of the copper foil of the cathode. Metals known to induce blackness include Cu, Cr, Al, Co, etc., but Cu can derive a perfect black color, but later on the copper foil circuit side when forming the copper foil circuit pattern There is a problem that it penetrates and damages the circuit pattern, and Cr causes a problem in the etching property at the time of forming the copper foil circuit, so that it is difficult to apply to the present invention. Moreover, Al cannot be anodized as described later due to its metal characteristics. Therefore, Co is the most suitable metal in consideration of product damage prevention, manufacturing process problems, anodizing efficiency, and the like.

Co blackening plating is performed, for example, by using an Ir electrode as the anode and plating the cathode with copper foil at a current exceeding the limit current density, and a Co blackening plating layer formed on the copper foil surface. Is in the form of an oxide such as Co ₃ O ₄ , CoO (OH), or CoO.
The concentration of Co contained in the electrolytic plating bath can be selected from 1 to 80 g / l, but the concentration at which the blackened plating layer can be formed most efficiently is 10 to 30 g / l. Current density industrially economical plating baths are 0.1~60A / dm ^2, in particular, a current density of 5~25A / dm ² is preferred. The plating time can be in the range of 1 to 20 seconds, but other than the above range is possible in consideration of the current density, the electrolyte concentration, and the like.

On the other hand, metal components other than Co can also be included in the electrolytic bath in order to improve the peel strength of the copper foil and to add the characteristics of the copper foil. Ni and Fe are suitable as elements for improving the peel strength without impairing the properties of the copper foil. The metal component concentration in the electrolytic solution in which the metal component and Co are combined is preferably in the range of 1 to 80 g / l in terms of plating efficiency.
The copper foil on which the blackened plating layer is formed is in a state where a plating particle layer is deposited in a nodule shape on the surface. However, the surface roughness of the copper foil on which the plated particle layer is formed is generally within the range that can be used for the copper foil for electromagnetic wave shielding. Depending on the conditions or plating conditions, the size and number of nodule particles deposited on the surface of the copper foil are partially different. In addition, hydrogen is generated at the cathode by the deposition reaction, and the thickness of the plating in the portion where such hydrogen is generated shows a fine difference from the thickness of the remaining portion.

For this reason, when the whole copper foil surface is looked at, the part from which a particle size and the number of particle | grains are relatively large compared with the surrounding part, or a hydrogen generation aspect differs will become uneven. In the case of very fine particles, the copper foil is dropped from the surface during the production process of the copper foil and becomes a residue, which degrades the copper foil quality.
In order to solve such a problem, the present invention places a copper foil with a blackened plating layer on the anode in a basic electrolytic bath, oxidizes (corrodes) the surface of the blackened plated layer, and to a certain extent. By flattening, the generation of unevenness and residue is reduced as much as possible.
The advantage of anodizing the blackened plating layer is that the surface of the blackened plating layer is uniformly corroded while the electrolyte flows in a uniform flow in the front-rear and left-right directions. .

The anodic oxidation bath is for basic electrolysis composed of a basic solution such as NaOH, KOH, etc., and the preferred current density during anodization is 1 to 30 A / dm ² , and the time is from 1 to 20 seconds. You can choose. The current density and time may vary according to the type, composition and temperature of the electrolyte. Anodization is performed, for example, by using stainless steel as a cathode and placing a blackened surface-treated copper foil on the anode.
An important point in the anodizing treatment is the pH adjustment of the basic electrolytic bath. In order to remove the residue effectively, the pH of the electrolytic bath must be at least 10 or more, and according to the experiment results of the present applicant, the most preferable result was shown at pH 13.

On the other hand, a fine copper particle layer can be deposited on the surface of the copper foil before blackening plating in order to reduce the reflectivity and improve the adhesion to the transparent substrate. The deposited copper particles act as an anchor, and when the copper foil is laminated on the transparent substrate, the peel strength is increased to improve the adhesion, and the appearance is irregularly reflected to reduce the reflectance.
Formation of a fine copper particle layer can be performed using the roughening process used for the copper foil for printed wiring boards. Roughening treatment is usually carried out in a copper sulfate plating bath, copper particles deposited amount when the roughening treatment is preferably in the range of 0.1 to 10 g / m ^2. Below the above range (decrease in roughness), the reflectivity decreases, but the peel strength (adhesiveness) decreases, and when above the range (increased roughness), the peel strength increases conversely. This is because the reflectance increases.

The surface roughness must be maintained within 0.1 to 2.0 μm in Rz (DIN standard) over the three steps of fine copper particle layer formation, blackening plating layer formation and anodizing treatment. The reason is as described above. When the surface treatment is performed within the above-described blackening plating conditions and anodizing conditions, the surface roughness can be maintained within the above ranges.
On the other hand, the copper foil of the present invention can be subjected to rust prevention treatment such as electrolytic chromate treatment. Further, when a plating film made of Zn or a Zn alloy is formed on the surface that has not been subjected to blackening plating, heating discoloration can be prevented in the heating step for manufacturing the electromagnetic wave shielding body.

  Hereinafter, the present invention will be specifically described by way of examples. However, the following examples are only for explaining the present invention, and those having ordinary knowledge in the art that the scope of the present invention is not limited to the following examples by the gist of the present invention. It is self-evident.

An electrolytic copper foil with a surface roughness (Rz) of 2 μm or less and a thickness of 10 μm is immersed in 100 g / l sulfuric acid for 5 seconds, pickled, washed with pure water, and then blackened under the following conditions And anodizing.
Blackening plating conditions: Co metal ion concentration of electrolytic bath 18g / l (Co is added to the plating bath in the form of cobalt sulfate), buffer solution (H ₃ BO ₃ ) concentration 30g / l, pH 3.5, electrolyte Temperature 30 ° C, current density 20A / dm ² , plating time 4 seconds.
Anodizing conditions: pH of NaOH anodizing bath: 13, anodizing bath temperature: 70 ° C., current density: 15 A / dm ² , oxidation treatment time: 4 seconds.

A fine copper particle layer was formed with a copper adhesion amount of 1.5 g / m ² , and blackening plating treatment and anodizing treatment were performed under the same conditions as in Example 1.

After pre-treating the surface of the copper foil under the same conditions as in Example 1, blackening plating treatment and anodizing treatment were performed under the following conditions.
Blacking plating conditions: Co metal ion concentration 10 g / l, Ni metal ion concentration 8 g / l, (Ni is added to the plating bath in the form of nickel sulfate), buffer solution (H ₃ BO ₃ ) concentration 30 g / l , PH 3.5, electrolyte temperature 30 ° C, current density 20A / dm ² , plating time 4 seconds.
Anodizing conditions: NaOH pH of anodizing bath: 13, anodizing bath temperature: 70 ° C., current density: 15 A / dm ² , oxidation treatment time 4 seconds.

  After forming a fine copper particle layer under the same conditions as in Example 2, blackening plating and anodizing were performed under the same conditions as in Example 3.

After pre-treating the surface of the copper foil under the same conditions as in Example 1, blackening plating treatment and anodizing treatment were performed under the following conditions.
Blacking plating conditions: Co metal ion concentration 10 g / l, Fe metal ion concentration 5 g / l (Fe is added to the plating bath in the form of iron sulfate), buffer solution (H ₃ BO ₃ ) concentration 30 g / l ,
pH 3.5, electrolyte temperature 30 ° C, current density 20A / dm ² , plating time 4 seconds.
Anodizing conditions: NaOH pH of anodizing bath: 12, anodizing bath temperature: 70 ° C., current density: 15 A / dm ² , oxidation treatment time: 4 seconds.

  After forming a fine copper particle layer under the same conditions as in Example 2, blackening plating and anodizing were performed under the same conditions as in Example 5.

Comparative Example 1
After pre-treating the surface of the electrolytic copper foil under the same conditions as in the above examples, blackening treatment plating was performed under the following conditions.
Co metal ion concentration 20g / l, pH 3.5, electrolyte temperature 30 ° C, current density 20A / dm ² , plating time 4 seconds.
Table 1 below shows the results of measuring the presence / absence of unevenness of the surface-treated copper foil according to the above examples and comparative examples, the presence / absence of residue generation (dusting) by rubbing, and the peel strength.

Unevenness: △: Slightly present, ▲: No residue generated (powder by rubbing): ○: Trace, ×: None

As shown in Table 1, in Comparative Example 1 in which only the blackening plating process was performed, unevenness and residue were generated on the surface. However, it can be seen that in Examples 1 to 6, which were anodized after the blackening plating process, unevenness and residue were not generated.
Further, Examples 2, 4, and 6 in which the fine copper particle layer was formed before the blackening plating treatment had a peel strength compared to Examples 1, 3, and 5 of the corresponding conditions in which the fine copper particle layer was not formed. You can see that it has risen. Further, it can be seen that Example 3 and Example 5 in which Ni and Fe are additionally included in the blackened plating layer have higher peel strength than Example 1 in which the above components and the like are not included.
If the electromagnetic wave shielding body is made of a composite material produced by laminating the surface-treated copper foil of the present invention having a uniform appearance as described above on an insulating transparent substrate such as PET, the resolution of the display screen is excellent. In addition, a plasma display panel can be manufactured, and the defect rate can be significantly reduced.

As described above, according to the manufacturing method of the present invention, the manufactured surface-treated copper foil has a black appearance with low reflectivity, and therefore has an advantage of not reducing the brightness of the PDP display screen.
In addition, the surface-treated copper foil according to the present invention has a uniform appearance with almost no unevenness and residue while having a black appearance, so the defect rate of the electromagnetic shielding composite material produced using this is remarkable. And the appearance of the PDP display screen manufactured using the composite material is excellent.

Claims (7)

Plating with Co or a binary electrolytic plating bath containing Co to form a blackened plating layer containing Co on the surface of the copper foil, and placing the copper foil on the anode in the basic electrolytic bath; And a step of oxidizing the surface of the blackened plating layer by electrolysis, and a method for producing a blackened surface-treated copper foil for shielding electromagnetic waves. The method according to claim 1, further comprising the step of depositing a fine copper particle layer on the surface of the copper foil before forming the blackened plating layer. The method according to claim 1, further comprising a step of forming an electrolytic chromate layer on the surface of the oxidized blackened plating layer. The manufacturing method according to any one of claims 1 to 3, further comprising a step of forming a plating film layer made of Zn or a Zn alloy on the back surface of the surface on which the blackening plating layer is formed. Method. The manufacturing method according to claim 1, wherein the pH of the basic electrolytic bath is 10 or more. The blackened surface-treated copper foil for electromagnetic wave shielding manufactured by the method as described in any one of Claims 1-5. An electromagnetic wave shielding composite material produced by laminating the blackened surface-treated copper foil according to claim 6 on an insulating transparent substrate.