METHOD FOR MANUFACTURING BLACK SURFACE-

TREATED COPPER FOIL FOR EMI SHIELD AND COPPER

FOIL THE SAME AND THE COMPOSITE MATERIAL USING

IT Technical Field [1] The present invention relates to a method for preparing a black surface-treated copper foil for electromagnetic radiation shielding and a copper foil produced by the method, which has low light reflectance and no stain, and hardly has residues, thereby having a uniform and consistent appearance. Background Art [2] Plasma display panel shows strong electromagnetic radiation which may be un¬ desirable to the health of human, from the display screen, therefore it is required to prevent such electromagnetic radiation by forming an electromagnetic radiation shield. As a conventional electromagnetic radiation shield, a composite material, which is produced by laminating a copper circuit to an insulating transparent base layer such as PET and the like has been used, wherein the composite material has advantages of an excellent electromagnetic shielding effect and light transmission. Particularly, the composite material is produced by laminating a copper foil having a certain surface roughness onto the transparent base layer, and removing unnecessary parts of the copper foil by etching so as to form a copper circuit with a desired pattern. Appropriate circuit line width and pattern of the copper circuit are selected based on the required level of electromagnetic shielding capability and light transmission. [3] On the other hand, there is a problem that the brightness of the display screen is degraded when the copper circuit reflects external light. Therefore, as a copper foil for electromagnetic radiation shielding, a copper foil which is surface-treated to have a color close to black and thus has low reflectance is favored. Disclosure of Invention Technical Problem [4] However, when the surface of the surface-treated copper is closer to black color, more stains on the appearance are likely to be occurred, or more residues tend to be generated on the surface with a recognizable amount by rubbing. Such stains on the surface of the copper foil degrade the image quality of PDP, and the residues come off from a part where the transparent substrate should be exposed by etching and thus lower the light transmission. Therefore, above problems lower the resolution of PDP overall. [5] Under the circumstance as above, the main stream of researches, which have been made conventionally, is to develop colors close to black color such as chocolate or dark metal color, instead of complete black, on the surface of the copper foil by surface treatment. However, since the surface of the copper foil obtained by those conventional methods is not completely black, there have been limitations on the improvement of re¬ flectance of such copper foil for electromagnetic radiation shielding. Technical Solution [6] The object of the present invention is to provide a surface-blackened copper foil for electromagnetic radiation shielding, which has low reflectance owing to its black- colored surface. [7] Further, another object of the present invention is to provide a surface-blackened copper foil which has a uniform appearance hardly having stains or residues, even though the copper foil has a black-colored surface, and exhibits excellent etching property and chemical resistance, and further a method for manufacturing the same. [8] Detailed description of the invention [9] In order to achieve said objects of the present invention, provided is a method for producing a surface-blackened copper foil for electromagnetic radiation shielding, specifically a method for producing a surface-treated copper foil for electromagnetic radiation shielding which comprises placing a copper foil as a cathode in an elec¬ troplating bath and forming a black plated layer on the surface of the copper foil, which is characterized by using an electroplating bath, which comprises Co, Ni, an ammonium compound and a chelating agent to form a black plated layer comprising Co and Ni on the surface of said copper foil. [10] The electroplating bath may further additionally comprise any one or more of Fe, Cu, Zn, Cr, Mo, W, V, Mn, Ti and Sn, thereby preferably forming a black plated layer which comprises essentially Co and Ni, and optionally any one or more of Fe, Cu, Zn, Cr, Mo, W, V, Mn, Ti and Sn. [11] The ammonium compound may include ammonium salts and ammonium complex. [12] The chelating agent may be at least one selected from glycine, citrates and py¬ rophosphates. [13] It is preferred that, for the concentration of the metal components, Co is 1-20 g/1 and Ni is 1-20 g/1, the concentration of the ammonium compound is 50 g/1 or less; and the concentration of the chelating agent is 100 g/1 or less. [14] It is preferred that the method according to the present invention further comprises a step of forming a deposited layer of fine copper particles on the surface of the copper foil, before forming said black plated layer comprising Co and Ni. [15] Further, it is preferred that the method according to the present invention comprises an additional step of forming a layer of electrolytic chromate on said black plated layer comprising Co and Ni. [16] Still further, it is preferred that the method according to the present invention comprises an additional step of forming a plated layer comprised of Zn or Zn-alloy on the other side of the surface of the copper foil where said plated layer is formed. [17] Hereinafter, the present invention is further described in detail. [18] The copper foil for electromagnetic radiation shielding, the subject of the present invention, is an electrolytic copper foil which may be available for the production with wide width, wherein the thickness of said copper foil is 1-35D, and preferably 6-18D, and the surface roughness (Rz: DIN) of said copper foil is 0.1-2.0 D, and preferably 0.5-1.5 D. When the surface roughness is less than 0.1 D, it will result in insufficient adhesion with the transparent substrate thereby decreasing the reliability of the elec¬ tromagnetic radiation shield. When the surface roughness is more than 2.0 D, the surface unevenness of the transparent substrate having copper foil adhered thereto becomes greater after forming a circuit by etching, and this will further cause de¬ terioration in display sharpness, undesirably. [19] The surface treatment of the copper foil for blackening is carried out by placing a copper foil as a cathode in an electroplating bath, which contains metal that develops black color, and depositing the metal layer onto the surface of said copper foil cathode. As for the black color-developing metals, Cu, Cr, Co, Ni and the like are known in this field of art. However, though Cu may develop complete black color, it causes a problem of damaging a copper foil circuit pattern by permeating into the copper foil circuit during the formation of the circuit pattern, and Cr adversely affects to the etching performance in the formation of a copper foil circuit, thus theses are not suitably applicable to the present invention. In viewing the aspects of preventing damages in products, problems in the manufacturing process and the like, Co and Ni are the most suitably applicable metal in the present invention. [20] For developing black color in the plated layer of Co and Ni, these should be deposited on the surface of the copper foil in the form of oxides such as Co O , CoO(OH) or CoO, and NiO, Ni 2O or Ni(OH) by electroplating with a current close to a limiting current density. [21] The present invention provides a black-surface treated copper foil comprising a black plated layer having uniform and consistent appearance, by forming a black plated layer on a copper foil through a method so-called a complex-ion plating process, which comprises adding an ammonium compound to a Co- and Ni-containing elec¬ troplating bath, and forming a complex compound by chemically binding ammonium, as a ligand, to the central metal ions, Co and Ni. Though the detailed reaction mechanism is not fully understood, owing to the complicated reaction procedures starting from the addition of starting materials to the production of final products, it is believed that the plating of Co and Ni to the copper foil through the complex-ion plating process makes the plating process comprising Co and Ni totally different from the conventional plating process where ammonium compounds are not introduced, and thus non-uniform plating as occurred in conventional methods can be successfully prevented. [22] Further, the black plated layer comprising Co and Ni formed by said process has advantages of excellent etching property and chemical resistance in later etching process for the formation of copper circuit patterns. [23] Specifically, the plating process may be carried out by using an Ir electrode as an anode and a copper foil as a cathode. The detailed composition of the electroplating bath is described below. [24] When each concentration of Co and Ni in the electroplating bath is less than 1 g/1, the plated layer does not develop complete black color, on the other hand, when it is more than 20 g/1, residues may be generated disadvantageously by being smeared. Therefore, each concentration of Co and Ni contained in the electroplating bath is preferably in the range of 1-20 g/1, respectively. [25] To the plating bath of the present invention, it is possible to further add any one or more of Fe, Cu, Zn, Cr, Mo, W, V, Mn, Ti and Sn other than said Co and Ni components, for the purposes of imparting further necessary physical or mechanical properties such as improved etching property and chemical resistance to the copper foil, or improving peeling strength between the transparent substrate and the copper foil and the like. When Fe is added to the black plated layer, for example, it has an advantage that the reaction rate in later etching process for the formation of copper foil circuit patterns becomes significantly rapid. When Zn is added to the black plated layer, adhesion, i.e. peeling strength, with the PET substrate becomes greatly improved. For obtaining optional effects from additional metal components, those additional components should be contained in the plating bath at least 1 g/1 or more. However, when the additional components are excessively introduced to the plating bath, the plated layer may not develop complete black color, therefore the upper limit of the additional components is preferably 1-10 g/1. [26] As for the ammonium compound being used as a ligand, ammonium salts such as ammonium sulfate, ammonium chloride, ammonium acetate and the like may be used, and ammonium compounds in the form of ammonium complex compound may also be used. When the concentration of the ammonium compounds in the plating bath is more than 50 g/1, the plated layer may not have complete black color, therefore it is preferably 50 g/1 or less. On the other hand, when the concentration of the ammonium compounds is less than 1 g/1, the dissolution resistance of the plating bath is uneco- nomically increased. Therefore, the concentration of the ammonium compounds is more preferably 1-50 g/1. [27] As for the chelating agent for binding ammonium with central metal ions, glycine, citrates, pyrophosphates and the like may be suitably used. When the concentration of the chelating agent is more than 100 g/1, complete black color may not be developed and stains may be occurred on the surface of the copper foil, therefore it is preferably 100 g/1 or less. Further, in order to promote the reaction between the ammonium compound and the central metal ions, the concentration of the chelating agent is desirably 5 g/1 or more. Therefore, the concentration of the chelating agent is more preferably 5-100 g/1. [28] From the aspect of industrial economy, current density is in the range of 0.1-60 A/ dm , and preferably in the range of 5-45 A/dm . When the current density is less than 0.1 A/dm , the desired black plated layer cannot be obtained and when the current density is not less than 60 A/dm , plating is achieved so excessively that residues tends to come off easily and stained. The pH value of a plating bath is preferably in the range of 2.5-6.0, and more preferably 4.0-5.8. When the pH value is less than 2.5, the black plated layer becomes melted out. In the meantime, when the pH value is not less than 6.0, the other surface (backside) which is not black surface-treated, becomes discolored, and the electrolytic liquid becomes precipitated, thereby deteriorating the stability of the electrolytic liquid. [29] The plating time may be in the range of 1-40 seconds, but the plating time out of said range is also possible, depending on the current density, the concentration of electrolytic liquid and the like. [30] On the other hand, in order to reduce the reflectance as well as to improve the adhesion with a transparent substrate, a layer of fine copper particles may be deposited onto the surface of the copper foil before carrying out plating for blackening. The deposited copper particles are served as an anchor so that the adhesiveness may become improved by increased peel strength in layering the copper foil onto the transparent substrate, and reduce the reflectance by diffused reflection of external light. [31] The fine copper particles may be formed by a treatment for roughing, which is applied to a copper foil for a printed circuit board(PCB). Such treatment for roughing is typically carried out in a plating bath of copper sulfate, and the amount of copper particles attached during the roughing process is preferably in the range of 0.1-10 g/D, and more preferably in the range of 0.5-8 g/D. Throughout the surface treating processes including the formation of fine copper particles and black plated layer, the surface roughness should be maintained in the range of 0.1 -2.0D in Rz (DIN standard) as described above. When carrying out the surface treatment under the conditions for the formation of fine copper particle and the plating process for blackening as described above, the surface roughness may be naturally maintained in said range. [32] Further, an anticorrosive treatment may be made to the copper foil according to the present invention, for example electrolytic chromate treatment and the like. Ad¬ ditionally, when plating Zn or Zn-alloy on the surface of the copper foil where the black plated layer is not formed, it is possible to prevent discoloration during a heating process in manufacturing an electromagnetic radiation shield. [33] Mode for the Invention [34] Hereinafter, the present invention is described further in detail through preferred embodiments of the present invention. However, it will be apparent to those ordinarily skilled in the art that those embodiments given below are only for the purpose of il¬ lustrating the present invention, by no means restricting the scope of the invention in context of the invention. [35] [36] Example [37] Example 1 [38] An electrolytic copper foil having a surface roughness(Rz) of 2D or less and a thickness of 1OD was immersed into 100 g/1 of sulfuric acid for 5 seconds, and washed with acid and then with pure water. Then, a surface conventionally called as a shiny side of the copper foil was subjected to a plating process for blackening under the conditions given below. After the plating process for blackening, the blackened surface was subjected to an anticorrosive treatment by using Cr. [39] - composition of the electrolytic bath (concentration): 4 g/1 of Co ion (CoSO D7HO), 5 g/1 of Ni ion (NiSO 4 D6H 2O), 15 g/1 of ammonium sulfate ((NH 4 ) 2 SO 4 ), and 25 g/1 of sodium citrate (C 6 H 5 Na 3 O 7 D2H 2O), [40] - pH value of the electrolytic liquid: 5.4, [41] - temperature of the electrolytic liquid: 25 °C, [42] - current density: 20 A/dm , and [43] - plating time: 8 seconds. [44] Example 2 [45] A layer of fine copper particles was formed with an amount of copper attached thereto of 1.5 g/m2, and then a plating process for blackening and anticorrosive treatment were carried out under the same conditions as in Example 1. [46] Example 3 [47] The surface of a copper foil was pretreated under the same conditions as in Example 1, and then the surface conventionally called as a shiny side of the copper foil was subjected to a plating process for blackening under the conditions given below. After the plating process for blackening, the blackened surface was subjected to an an- ticorrosive treatment by using Cr. [48] - composition of the electrolytic bath (concentration): 5 g/1 of Co ion (CoSO D7H0), 3 g/1 of Ni ion (NiSO D6HO), 30 g/1 of a buffer solution (H BO ), 15 g/1 of ammonium sulfate ((NH 4 ) 2 SO 4 ), and 25 g **/1 of sodium citrate (C 6 H 5 Na 3 O 7 D2H 2O), [49] - pH value of the electrolytic liquid: 5.4, [50] - temperature of the electrolytic liquid: 25 °C, [51] - current density: 20 A/dm and [52] - plating time: 10 seconds. [53] Example 4 [54] The surface of a copper foil was pretreated under the same conditions as in Example 1, and then the surface conventionally called as a matte side of the copper foil was subjected to a plating process for blackening under the conditions as in Example 3. After the plating process for blackening, the blackened surface was subjected to an an- ticorrosive treatment by using Cr. [55] Example 5 [56] An electrolytic copper foil having a surface roughness(Rz) of 2D or less and a thickness of 18D was immersed into 100 g/1 of sulfuric acid for 5 seconds, and washed with acid and then with pure water. Then, a surface conventionally called as a shiny side of the copper foil was subjected to a plating process for blackening under the conditions given below. After the plating process for blackening, the blackened surface was subjected to an anticorrosive treatment by using Cr. [57] - composition of the electrolytic bath (concentration): 4 g/1 of Co ion (CoSO D7HO), 5 g/1 of Ni ion (NiSO D6HO), 30 g/1 of a buffer solution (H BO ), 15 g/1 of ammonium acetate (CH 3 CO2 NH 4 ), and 25 g ^/1 of sodium citrate (C 6 H5 Na3 O7 D2H2O), [58] - pH value of the electrolytic liquid: 5.8, [59] - temperature of the electrolytic liquid: 25 °C, [60] - current density: 25 A/dm and [61] - plating time: 10 seconds. [62] Example 6 [63] An electrolytic copper foil having a surface roughness(Rz) of 2D or less and a thickness of 18D was immersed into 100 g/1 of sulfuric acid for 5 seconds, and washed with acid and then with pure water. Then, a surface conventionally called as a shiny side of the copper foil was subjected to a plating process for blackening under the conditions given below. After the plating process for blackening, the blackened surface was subjected to an anticorrosive treatment by using Cr. [64] - composition of the electrolytic bath (concentration): 4 g/1 of Co ion (CoSO D7HO), 5 g/1 of Ni ion (NiSO D6HO), 30 g/1 of a buffer solution (H BO ), 10 g/1 of ammonium chloride (NH Cl), and 25 g/1 of sodium citrate (C H Na O D2HO), [65] - pH value of the electrolytic liquid: 5.2, [66] - temperature of the electrolytic liquid: 25 °C, [67] - current density: 20 A/dm and [68] - plating time: 10 seconds. [69] Example 7 [70] The surface of a copper foil was pretreated under the same conditions as in Example 1, and then the surface conventionally called as a shiny side of the copper foil was subjected to a plating process for blackening under the conditions given below. After the plating process for blackening, the blackened surface was subjected to an an- ticorrosive treatment by using Cr. [71] - composition of the electrolytic bath (concentration): 4 g/1 of Co ion (CoSO D7HO), 5 g/1 of Ni ion (NiSO4DoHO), 1 g/1 of Fe ion (FeSO4D7HO), 30 g/1 of a buffer solution (H BO ), 15 g/1 of ammonium sulfate ((NH ) SO ), and 25 g/1 of sodium citrate (C H

[72] - pH value of the electrolytic liquid: 5.4, [73] - temperature of the electrolytic liquid: 25°C, [74] - current density: 20 A/dm and [75] - plating time: 8 seconds. [76] Example 8 [77] An electrolytic copper foil having a surface roughness(Rz) of 2D or less and a thickness of 18D was immersed into 100 g/1 of sulfuric acid for 5 seconds, and washed with acid and then with pure water. Then, a surface conventionally called as a shiny side of the copper foil was subjected to a plating process for blackening under the conditions given below. After the plating process for blackening, the blackened surface was subjected to an anticorrosive treatment by using Cr. [78] - composition of the electrolytic bath (concentration): 5 g/1 of Co ion (CoSO D7HO), 4 g/1 of Ni ion (NiSO D6HO), 2 g/1 of Zn ion (ZnSO DHO), 30 g/1 of a buffer solution (H BO ), 15 g/1 of ammonium sulfate ((NH ) SO ), and 25 g/1 of sodium citrate (C H 3 3 4 2 4 6 5 Na O D2HO), 3 7 2 [79] - pH value of the electrolytic liquid: 5.4, [80] - temperature of the electrolytic liquid: 25 °C, [81] - current density: 20 A/dm and [82] - plating time: 10 seconds. [83] Example 8 [84] An electrolytic copper foil having a surface roughness(Rz) of 2D or less and a thickness of 18D was immersed into 100 g/1 of sulfuric acid for 5 seconds, and washed with acid and then with pure water. Then, a surface conventionally called as a shiny side of the copper foil was subjected to a plating process for blackening under the conditions given below. After the plating process for blackening, the blackened surface was subjected to an anticorrosive treatment by using Cr. [85] - composition of the electrolytic bath (concentration): 5 g/1 of Co ion (CoSO D7H0), 4 g/1 of Ni ion (NiSO D6HO), 1 g/1 of Fe ion (FeSO D7HO), 2 g/1 of Zn ion (ZnSO DH O), 30 g/1 of a buffer solution (H BO ), 15 g/1 of ammonium sulfate ((NH ) SO ), and 25 g **/1 of sodium citrate (C 6 H5 Na3 O7 D2H20), [86] - pH value of the electrolytic liquid: 5.4, [87] - temperature of the electrolytic liquid: 25°C, [88] - current density: 20 A/dm and [89] - plating time: 10 seconds. [90] Comparative example 1 [91] Electroplating was carried out under the same conditions as in Example 1, except that ammonium sulfate was not used. [92] Comparative example 2 [93] Electroplating was carried out under the same conditions as in Example 1, except that the concentration of (NH ) SO was 60 g/1. [94] Comparative example 3 [95] Electroplating was carried out under the same conditions as in Example 1, except that sodium citrate was not used. [96] Comparative example 4 [97] Electroplating was carried out under the same conditions as in Example 1, except that the concentration of sodium citrate was 120 g/1. [98] Comparative example 5 [99] Electroplating was carried out under the same conditions as in Example 1, except that the concentration of Co ion (CoSO D7HO) was 25 g/1. [100] Comparative example 6 [101] Electroplating was carried out under the same conditions as in Example 1, except that the concentration of Ni ion (NiSO D6HO) was 25 g/1. [102] With the surface-treated copper foil obtained from the examples and comparative examples, the generation of stains and smudging when rubbing, etching property and chemical resistance were tested, and the results are given in the following table. [103] Stains were observed by naked eyes. Etching property was determined by the presence of etching residues after a step comprised of laminating the blackened surface of the copper foil to FR-4 resin and immersing the laminated resin into a ferric chloride etching solution at 50°C for 15 minutes. Chemical resistance was determined by a method comprised of laminating the blackened surface of the copper foil to FR-4 resin, forming a circuit having the width of 400D on the blackened surface with ink, etching the resulted circuit under the same conditions as in the estimation of etching property, removing ink with IN NaOH at 50°C, and determining the degree of permeation of the etching solution to the comer of the circuit pattern remained after the above etching step by using a polarized microscope. [104] Table 1

[105] Stain: Δ - little present, A - no stain [106] Residuesfsmudged by rubbing*): x- great amount, O - small amount, • - no smudging [107] Etching property: O no residue after etching, x - residues occurred after etching [108] Chemical resistance: O less than 0.1 D of permeation, x - not less than 0.1 D of permeation [109] As seen from the above table, the examples according to the present invention provide a uniform and consistent black-colored appearance without stains or residues smudged by rubbing, and good etching property, chemical resistance and the like, all of which are characteristics required to a copper foil for EMI shield. Therefore, when applying the surface-treated copper foil obtained by the method of the present invention to manufacture of an electromagnetic radiation shield by layering the copper foil to an insulating transparent base layer such as PET, it is possible to obtain a PDP having excellent resolution of the screen, and the defective rates in production of such PDP becomes significantly lowered. [110] Particularly, Example 7 where Fe was additionally used, showed significantly rapid reaction rate in the etching step as compared to other examples 1-6 and no generation of etching residues, and Example 8 which Zn was additionally used, showed excellent peel strength. Further, Example 2 where fine copper particles were plated before elec¬ troplating for blackening, and Example 4 where electroplating was carried out on the matte side showed high peel strength. [Ill] Industrial Applicability [112] As described so far, the surface-treated copper foil produced by the method of the present invention has black-colored appearance which has low reflectance, therefore providing an advantage that it does not degrade the brightness of the PDP screen. [113] Further, since the surface-treated copper foil produced by the present invention has a uniform appearance without stains or residues even though it has black-colored appearance, and excellent etching property and chemical resistance, a composite material for an electromagnetic radiation shield using the same may be produced with a significantly lowered defective rate, and the screen of a PDP manufactured by using said composite material will have excellent appearance.