JP6597139B2 - Blackening plating solution, conductive substrate - Google Patents

Description

  The present invention relates to a blackening plating solution and a conductive substrate.

  The capacitive touch panel converts information on the position of an adjacent object on the panel surface into an electrical signal by detecting a change in electrostatic capacitance caused by the object adjacent to the panel surface. Since the conductive substrate used for the capacitive touch panel is installed on the surface of the display, the material of the conductive layer of the conductive substrate is required to have low reflectance and be difficult to be visually recognized.

  Therefore, as a material for the conductive layer used in the capacitive touch panel, a material having low reflectivity and hardly visible is used, and wiring is formed on a transparent substrate or a transparent film.

  For example, Patent Document 1 discloses a transparent conductive film including a polymer film and a transparent conductive film made of a metal oxide provided thereon by a vapor deposition method. The use of an indium oxide-tin oxide (ITO) film is disclosed.

  By the way, in recent years, the display screen including a touch panel has been increased in screen size. Correspondingly, a conductive substrate such as a transparent conductive film for a touch panel is required to have a large area. However, since ITO has a high electric resistance value, there is a problem that it cannot cope with an increase in the area of the conductive substrate.

  Therefore, it has been studied to use a metal such as copper in place of ITO as a material for the conductive layer. However, since the metal has a metallic luster, there is a problem that the visibility of the display decreases due to reflection. For this reason, a conductive substrate having been subjected to a blackening process in which a blackened layer made of a black material is formed on the surface of the conductive layer by a dry method has been studied.

  However, it took time to sufficiently blacken the conductive layer surface by the dry method, and the productivity was low.

  Therefore, the inventors of the present invention have studied the blackening treatment by the wet method because the vacuum environment as required by the dry method is not required, the equipment can be simplified, and the productivity is excellent. It was. Specifically, it has been studied to form a blackened layer by a wet method using a plating solution containing Ni and Zn as main components.

JP 2003-151358 A

  However, when a blackening treatment is performed by a wet plating method using a plating solution containing Ni and Zn as main components, the blackening layer formed by the blackening treatment is compared with the copper layer formed as a conductive layer. In some cases, the reactivity to the plating solution is high. And when producing a conductive substrate having a desired wiring pattern, after forming a copper layer as a conductive layer and a blackened layer, it will be patterned by etching, but a copper layer for the etchant, Due to the difference in reactivity with the blackened layer, it may be difficult to pattern the blackened layer into a desired shape.

  In view of the above-described problems of the prior art, an object of one aspect of the present invention is to provide a blackening plating solution capable of forming a blackening layer that can be patterned into a desired shape when etched together with a copper layer. And

In order to solve the above problems, in one aspect of the present invention,
A blackening plating solution for forming a blackened layer on the surface of the copper layer,
Blackening plating containing a nickel compound, a zinc compound, a tin compound, and amidosulfuric acid, wherein the tin compound is tin sulfate, and the concentration of the tin compound is 0.3 g / L or more and 0.9 g / L or less. Provide liquid.

  According to one aspect of the present invention, it is possible to provide a blackening plating solution capable of forming a blackening layer that can be patterned into a desired shape when etched together with a copper layer.

Sectional drawing of the electroconductive board | substrate which concerns on embodiment of this invention. Sectional drawing of the electroconductive board | substrate which concerns on embodiment of this invention. The top view of the electroconductive board | substrate provided with the mesh-shaped wiring which concerns on embodiment of this invention. Sectional drawing in the AA 'line of FIG.

Hereinafter, an embodiment of the blackening plating solution and the conductive substrate of the present invention will be described.
(Blackening plating solution)
The blackening plating solution of this embodiment contains a nickel compound, a zinc compound, a tin compound, and amidosulfuric acid, and the concentration of the tin compound is 0.3 g / L or more and 0.9 g / L or less. it can.

  The inventors of the present invention diligently studied a blackening plating solution capable of forming a blackening layer having a reactivity to the etching solution equal to or lower than that of the copper layer.

  Then, while proceeding with the study on the blackening plating solution, the inventors of the present invention made the blackening layer a layer containing nickel, zinc, and tin, thereby reacting the blackening layer with the etching solution. It was found that the desired shape can be obtained even when etching is performed simultaneously with the copper layer.

  For this reason, the blackening plating solution of this embodiment is preferably a plating solution that can form a layer containing nickel, zinc, and tin as metal components.

  Therefore, the blackening plating solution of the present embodiment can contain a nickel compound, a zinc compound, and a tin compound. Furthermore, by containing amidosulfuric acid that functions as a complexing agent, it is possible to suppress the occurrence of color unevenness in the formed blackened layer.

  However, according to the study by the inventors of the present invention, when the concentration of the tin compound in the blackening plating solution is less than 0.3 g / L, the effect of suppressing the reactivity to the etching solution may not be sufficient. It was. For this reason, it is preferable that the density | concentration of the tin compound in the blackening plating solution of this embodiment is 0.3 g / L or more. In particular, the concentration of the tin compound in the blackening plating solution of the present embodiment is more preferably 0.4 g / L or more.

  In addition, when the concentration of the tin compound in the blackening plating solution exceeds 0.9 g / L, the function of suppressing the reflection of light on the copper layer surface by the blackening layer formed by the blackening plating solution is reduced, and the conductivity is reduced. The reflectance of the conductive substrate may be high. For this reason, it is preferable that the density | concentration of the tin compound in the blackening plating solution of this embodiment is 0.9 g / L or less. In particular, the concentration of the tin compound in the blackening plating solution of the present embodiment is more preferably 0.8 g / L or less, and particularly preferably 0.7 g / L or less.

  About the nickel compound, zinc compound, and tin compound contained in the blackening plating solution of this embodiment, any metal component may be used as long as nickel, zinc, and tin are ionized in the plating solution. The type of each compound is not particularly limited. For the nickel compound, the zinc compound, and the tin compound, for example, any compound selected from a sulfuric acid compound, a hydrochloric acid compound, and a sulfamic acid compound can be used. The nickel compound, the zinc compound, and the tin compound may be the same type of compound, for example, nickel sulfate, zinc sulfate, tin sulfate, or the like, but may be different types of compounds.

  In particular, it is preferable that the nickel compound, the zinc compound, and the tin compound are nickel sulfate, zinc sulfate, and tin sulfate, respectively, because the pH of the plating solution can be easily adjusted. In this case, the blackening plating solution of this embodiment includes nickel sulfate, zinc sulfate, tin sulfate, and amidosulfuric acid, and the concentration of tin sulfate is 0.3 g / L or more and 0.9 g / L or less. Can do.

As described above, the blackening plating solution of the present embodiment can contain a nickel compound, a zinc compound, a tin compound, and amidosulfuric acid. The content of each component other than the tin compound in the blackening plating solution of the present embodiment is not particularly limited, and can be arbitrarily set according to the degree of suppression of reflectance required for the blackening layer to be formed. You can choose.
For example, when nickel sulfate is used as the nickel compound, nickel sulfate is considered to exist as nickel sulfate hexahydrate in the blackening plating solution, but the concentration of nickel sulfate hexahydrate in the blackening plating solution is 30 g. / L or more is preferable. This is because by setting the concentration of nickel sulfate hexahydrate to 30 g / L or more, sufficient nickel can be supplied into the blackened layer to be formed, and color unevenness can be prevented from occurring in the blackened layer. . The upper limit of the concentration of nickel sulfate hexahydrate in the blackening plating solution is not particularly limited, and for example, it can be added so as to be equal to or lower than the saturation concentration of nickel sulfate hexahydrate. In particular, from the viewpoint of suppressing the formation of precipitates or the like in the plating solution before forming the blackened layer using the blackening plating solution, it is preferably 100 g / L or less.

  When zinc sulfate is used as the zinc compound, zinc sulfate is considered to exist as zinc sulfate heptahydrate in the blackening plating solution, but the concentration of zinc sulfate heptahydrate in the blackening plating solution is 1 It is preferable that it is 0.5 g / L or more and 4.8 g / L or less. This is because the concentration of zinc sulfate heptahydrate in the blackening plating solution is 1.5 g / L or more, so that the blackened layer formed is more suitable for suppressing light reflection particularly on the copper layer surface. This is because the light reflectance of the conductive substrate can be particularly suppressed. Further, when the concentration of zinc sulfate heptahydrate is higher than 4.8 g / L, color unevenness or the like may occur in the blackened layer to be formed, so that it is preferably 4.8 g / L or less.

  In addition, the ratio of the content (content weight) of zinc as the metal component to the total content (content weight) of nickel and zinc as the metal components contained in the blackening plating solution is 2 wt% or more and 20 wt% or less. It is preferable that

  A blackening layer can be made into the color suitable for suppressing reflection of the light in a copper layer surface by containing nickel and zinc simultaneously. When the ratio of zinc as the metal component to the total weight of nickel and zinc as the metal component contained in the blackening plating solution is 2% by weight or more, reflection of light on the surface of the copper layer is suppressed. This is because the color can be particularly suitable for the above, and the reflectance of the conductive substrate can be suppressed.

  However, if the proportion of zinc becomes too high, color unevenness may occur in the formed blackened layer. For this reason, it is preferable that the ratio of zinc as the metal component to the total weight of nickel and zinc as the metal component contained in the blackening plating solution is 20% by weight or less.

  The concentration of amidosulfuric acid in the blackening plating solution is not particularly limited, but is preferably 10 g / L or more and 30 g / L or less, for example.

  In addition, the agent used for adjusting the pH of the blackening plating solution of the present embodiment is not particularly limited, but an alkali containing no metal component is used so as not to affect the blackening layer to be formed. It is preferable. For this reason, for example, the pH is preferably adjusted with aqueous ammonia. In addition, when the pH of the blackening plating solution of this embodiment is adjusted with ammonia water, the blackening plating solution of this embodiment can further contain ammonia water or a component derived from added ammonia water.

  The pH range of the blackening plating solution of the present embodiment is not particularly limited, but is preferably 2.0 or more and 4.0 or less, for example.

  This is because when the pH of the blackening plating solution is less than 2.0, the formed blackened layer may not have a color that can sufficiently suppress the reflection of light. Further, when the pH of the blackening plating solution exceeds 4.0, some components of the blackening plating solution may be deposited. When the blackening layer is formed using such a blackening plating solution, the blackening This is because color unevenness may occur in the layer.

  The blackening plating solution of this embodiment can contain arbitrary components other than the nickel compound, zinc compound, tin compound, and amidosulfuric acid. For example, a molybdenum (Mo) compound or the like can be added as an additive.

  According to the blackening plating solution of this embodiment described above, it is possible to form a blackening layer that is equivalent in reactivity to the copper layer as the conductive layer and the etching solution, or less reactive than the copper layer. For this reason, even when the copper layer and the blackened layer formed by the blackened plating solution of the present embodiment are simultaneously etched and patterned, a desired shape can be obtained.

Moreover, according to the blackening plating solution of this embodiment, it can be used suitably when forming the blackening layer which can fully suppress the reflection of the light in the copper layer surface of an electroconductive board | substrate. Furthermore, by using the blackening plating solution of the present embodiment, the blackened layer can be formed by a wet method such as an electrolytic plating method, so that it is compared with the blackened layer conventionally formed by a dry method. Thus, the blackened layer can be formed with high productivity.
(Conductive substrate)
Next, a configuration example of the conductive substrate of this embodiment will be described.

  The conductive substrate of the present embodiment includes a transparent substrate, a copper layer disposed on at least one surface of the transparent substrate, a blackened layer formed on the copper layer using a blackened plating solution, Can have.

  In addition, the conductive substrate in the present embodiment is a substrate having a copper layer and a blackened layer on the surface of the transparent base before patterning the copper layer and the like, and a substrate obtained by patterning the copper layer, that is, And a wiring board.

  First, each member included in the conductive substrate will be described below.

  The transparent substrate is not particularly limited, and a transparent substrate such as a resin substrate (resin film) that transmits visible light or a glass substrate can be preferably used.

  As a material for the resin substrate that transmits visible light, for example, a polyamide resin, a polyethylene terephthalate resin, a polyethylene naphthalate resin, a cycloolefin resin, a polyimide resin, a polycarbonate resin, or the like can be preferably used. In particular, PET (polyethylene terephthalate), COP (cycloolefin polymer), PEN (polyethylene naphthalate), polyimide, polycarbonate, and the like can be more preferably used as the material for the resin substrate that transmits visible light.

  It does not specifically limit about the thickness of a transparent base material, It can select arbitrarily according to the intensity | strength, electrostatic capacitance, light transmittance, etc. which are required when it is set as an electroconductive board | substrate. The thickness of the transparent substrate can be, for example, 10 μm or more and 200 μm or less. In particular, when used for touch panel applications, the thickness of the transparent substrate is preferably 20 μm or more and 120 μm or less, and more preferably 20 μm or more and 100 μm or less. In the case of use for touch panel applications, for example, particularly in applications where it is required to reduce the thickness of the entire display, the thickness of the transparent substrate is preferably 20 μm or more and 50 μm or less.

  The total light transmittance of the transparent substrate is preferably higher. For example, the total light transmittance is preferably 30% or more, and more preferably 60% or more. When the total light transmittance of the transparent substrate is in the above range, the visibility of the display can be sufficiently ensured when used for, for example, a touch panel.

  In addition, the total light transmittance of a transparent base material can be evaluated by the method prescribed | regulated to JISK7361-1.

  Next, the copper layer will be described.

  The method for forming the copper layer on the transparent substrate is not particularly limited, but it is preferable not to dispose an adhesive between the transparent substrate and the copper layer in order not to reduce the light transmittance. That is, the copper layer is preferably formed directly on at least one surface of the transparent substrate. In addition, when arrange | positioning an adhesion layer between a transparent base material and a copper layer as mentioned later, it is preferable that the copper layer is directly formed on the upper surface of the adhesion layer.

  In order to directly form the copper layer on the upper surface of the transparent substrate or the like, the copper layer preferably has a copper thin film layer. Moreover, the copper layer may have a copper thin film layer and a copper plating layer.

  For example, a copper thin film layer can be formed on a transparent substrate by a dry plating method, and the copper thin film layer can be used as a copper layer. Thereby, a copper layer can be directly formed on the transparent substrate without using an adhesive. As the dry plating method, for example, a sputtering method, a vapor deposition method, an ion plating method, or the like can be preferably used.

  In addition, when increasing the thickness of the copper layer, the copper thin film layer and the copper plating layer are formed by forming a copper plating layer by an electroplating method which is a kind of wet plating method using the copper thin film layer as a power feeding layer. It can also be set as the copper layer which has. Since the copper layer has the copper thin film layer and the copper plating layer, the copper layer can be directly formed on the transparent substrate without using an adhesive.

  The thickness of the copper layer is not particularly limited, and when the copper layer is used as a wiring, it can be arbitrarily selected according to the magnitude of the current supplied to the wiring, the wiring width, and the like.

  However, when the copper layer is thick, it takes time to perform etching to form a wiring pattern, so that side etching is likely to occur, and it may be difficult to form fine lines. For this reason, it is preferable that the thickness of a copper layer is 5 micrometers or less, and it is more preferable that it is 3 micrometers or less.

  In particular, from the viewpoint of reducing the resistance value of the conductive substrate so that sufficient current can be supplied, for example, the copper layer preferably has a thickness of 50 nm or more, more preferably 60 nm or more, and 150 nm. More preferably, it is the above.

  In addition, when a copper layer has a copper thin film layer and a copper plating layer as mentioned above, it is preferable that the sum total of the thickness of a copper thin film layer and the thickness of a copper plating layer is the said range.

  In any case where the copper layer is composed of a copper thin film layer or has a copper thin film layer and a copper plating layer, the thickness of the copper thin film layer is not particularly limited. The following is preferable.

  As described later, the copper layer can be used as a wiring by patterning it into a desired wiring pattern, for example. And since a copper layer can make an electrical resistance value lower than ITO conventionally used as a transparent conductive film, the electrical resistance value of an electroconductive board | substrate can be made small by providing a copper layer.

  Next, the blackening layer will be described.

  The blackening layer can be formed using the blackening plating solution described above. For this reason, for example, after forming the copper layer, it can be formed on the upper surface of the copper layer by a wet method such as an electrolytic plating method.

  Since the blackening plating solution has already been described, the description thereof is omitted here.

  Although the thickness of a blackening layer is not specifically limited, For example, it is preferable that it is 30 nm or more, and it is more preferable that it is 50 nm or more. This is because light reflection on the surface of the copper layer can be particularly suppressed by setting the thickness of the blackened layer to 30 nm or more.

  The upper limit of the thickness of the blackening layer is not particularly limited, but even if it is thicker than necessary, the time required for film formation and the time required for etching when forming the wiring are increased, resulting in an increase in cost. Will be invited. For this reason, the thickness of the blackened layer is preferably 120 nm or less, and more preferably 90 nm or less.

  When the blackening layer is formed with the blackening plating solution described above, the blackening layer can be a layer containing nickel, zinc, and tin.

  For this reason, the conductive substrate of the present embodiment has a transparent base material, a copper layer disposed on at least one surface of the transparent base material, and a blackening layer disposed on the copper layer, The blackening layer may be configured to include nickel, zinc, and tin.

  Further, the conductive substrate can be provided with any layer other than the above-described transparent base material, copper layer, and blackening layer. For example, an adhesion layer can be provided.

  A configuration example of the adhesion layer will be described.

  As described above, the copper layer can be formed on the transparent substrate, but when the copper layer is directly formed on the transparent substrate, the adhesion between the transparent substrate and the copper layer may not be sufficient. . For this reason, when forming a copper layer directly on the upper surface of a transparent base material, a copper layer may peel from a transparent base material at the time of a manufacture process or use.

  Therefore, in the conductive substrate of the present embodiment, an adhesion layer can be disposed on the transparent substrate in order to improve the adhesion between the transparent substrate and the copper layer.

  By arrange | positioning an adhesion layer between a transparent base material and a copper layer, the adhesiveness of a transparent base material and a copper layer can be improved, and it can suppress that a copper layer peels from a transparent base material.

  Further, the adhesion layer can function as a blackening layer. For this reason, it becomes possible to also suppress reflection of the light of a copper layer by the light from the lower surface side of a copper layer, ie, the transparent base material side.

  The material constituting the adhesion layer is not particularly limited. The adhesion between the transparent substrate and the copper layer, the degree of suppression of light reflection on the required copper layer surface, and a conductive substrate are used. It can be arbitrarily selected according to the degree of stability to the environment (for example, humidity and temperature).

  The adhesion layer preferably contains at least one metal selected from, for example, Ni, Zn, Mo, Ta, Ti, V, Cr, Fe, Co, W, Cu, Sn, and Mn. The adhesion layer may further contain one or more elements selected from carbon, oxygen, hydrogen, and nitrogen.

  The adhesion layer can also include a metal alloy including at least two kinds of metals selected from Ni, Zn, Mo, Ta, Ti, V, Cr, Fe, Co, W, Cu, Sn, and Mn. Also in this case, the adhesion layer can further include one or more elements selected from carbon, oxygen, hydrogen, and nitrogen. At this time, as a metal alloy containing at least two kinds of metals selected from Ni, Zn, Mo, Ta, Ti, V, Cr, Fe, Co, W, Cu, Sn, and Mn, a Cu—Ti—Fe alloy is used. Alternatively, a Cu—Ni—Fe alloy, Ni—Cu alloy, Ni—Zn alloy, Ni—Ti alloy, Ni—W alloy, Ni—Cr alloy, and Ni—Cu—Cr alloy can be preferably used.

  The method for forming the adhesion layer is not particularly limited, but it is preferable to form the film by a dry plating method. As the dry plating method, for example, a sputtering method, an ion plating method, a vapor deposition method, or the like can be preferably used. In the case where the adhesion layer is formed by a dry method, it is more preferable to use a sputtering method because the film thickness can be easily controlled. Note that, as described above, one or more elements selected from carbon, oxygen, hydrogen, and nitrogen can be added to the adhesion layer, and in this case, a reactive sputtering method can be more preferably used.

  When the adhesion layer contains one or more elements selected from carbon, oxygen, hydrogen, and nitrogen, one or more elements selected from carbon, oxygen, hydrogen, and nitrogen in the atmosphere when forming the adhesion layer Can be added to the adhesion layer. For example, when adding carbon to the adhesion layer, carbon monoxide gas and / or carbon dioxide gas, when adding oxygen, oxygen gas, when adding hydrogen, hydrogen gas and / or water, In the case of adding nitrogen, nitrogen gas can be added to the atmosphere when dry plating is performed.

  A gas containing one or more elements selected from carbon, oxygen, hydrogen, and nitrogen is preferably added to an inert gas and used as an atmosphere gas during dry plating. Although it does not specifically limit as an inert gas, For example, argon can be used preferably.

  By forming the adhesion layer by dry plating as described above, the adhesion between the transparent substrate and the adhesion layer can be enhanced. And since an adhesion layer can contain a metal as a main component, for example, its adhesiveness with a copper layer is also high. For this reason, peeling of a copper layer can be suppressed by arrange | positioning an adhesion layer between a transparent base material and a copper layer.

  The thickness of the adhesion layer is not particularly limited, but is preferably 3 nm to 50 nm, for example, more preferably 3 nm to 35 nm, and still more preferably 3 nm to 33 nm.

  When the adhesion layer also functions as a blackening layer, that is, when light reflection in the copper layer is suppressed, the thickness of the adhesion layer is preferably 3 nm or more as described above.

  The upper limit value of the thickness of the adhesion layer is not particularly limited, but even if it is thicker than necessary, the time required for film formation and the time required for etching when forming the wiring are increased, resulting in an increase in cost. Will be invited. For this reason, the thickness of the adhesion layer is preferably 50 nm or less as described above, more preferably 35 nm or less, and further preferably 33 nm or less.

  Next, a configuration example of the conductive substrate will be described.

  As described above, the conductive substrate of this embodiment can have a transparent base material, a copper layer, and a blackening layer. Further, a layer such as an adhesion layer can be optionally provided.

  A specific configuration example will be described below with reference to FIG. FIG. 1 shows an example of a cross-sectional view of the conductive substrate of the present embodiment on a plane parallel to the lamination direction of the transparent base material, the copper layer, and the blackening layer.

  The conductive substrate of the present embodiment can have a structure in which, for example, a copper layer and a blackened layer are laminated in that order from the transparent substrate side on at least one surface of the transparent substrate.

  Specifically, for example, as in the conductive substrate 10A shown in FIG. 1A, the copper layer 12 and the blackened layer 13 are laminated on the one surface 11a side of the transparent base material 11 one by one in that order. can do. Moreover, like the electroconductive board | substrate 10B shown in FIG.1 (b), copper layer 12A, 12B on the one surface 11a side of the transparent base material 11, and the other surface (other surface) 11b side, respectively. And the blackening layers 13A and 13B can be stacked one by one in that order.

  Furthermore, as an arbitrary layer, for example, a configuration in which an adhesion layer is provided may be employed. In this case, for example, a structure in which an adhesion layer, a copper layer, and a blackening layer are formed in that order from the transparent substrate side on at least one surface of the transparent substrate.

  Specifically, for example, as in the conductive substrate 20A shown in FIG. 2A, the adhesion layer 14, the copper layer 12, and the blackening layer 13 are formed on the one surface 11a side of the transparent substrate 11. They can be stacked in order.

  In this case as well, a configuration in which an adhesive layer, a copper layer, and a blackening layer are laminated on both surfaces of the transparent substrate 11 can be employed. Specifically, as in the conductive substrate 20B shown in FIG. 2B, the adhesion layers 14A and 14B and the copper layer are respectively formed on the one surface 11a side and the other surface 11b side of the transparent base material 11. 12A and 12B and blackening layers 13A and 13B can be stacked in that order.

  In FIG. 1B and FIG. 2B, when a copper layer, a blackened layer, etc. are laminated on both surfaces of the transparent substrate, the transparent substrate 11 is laminated on the upper and lower sides of the transparent substrate 11 with the symmetrical surface as the symmetrical surface. Although the example which arrange | positioned so that the layer which became symmetrical may be shown, it is not limited to the form which concerns. For example, in FIG. 2B, the configuration on the one surface 11a side of the transparent substrate 11 is similar to the configuration of FIG. 1B, without providing the adhesion layer 14A, the copper layer 12A, the blackening layer 13A, May be laminated in that order, and the layers laminated above and below the transparent substrate 11 may be asymmetrical.

  By the way, in the electroconductive board | substrate of this embodiment, by providing a copper layer and a blackening layer on a transparent base material, reflection of the light by a copper layer is suppressed and the reflectance of an electroconductive board | substrate is suppressed. Can do.

  The degree of reflectivity of the conductive substrate of the present embodiment is not particularly limited. For example, in order to increase the visibility of a display when used as a conductive substrate for a touch panel, the reflectivity is lower. Is good. For example, the average reflectance of light having a wavelength of 400 nm to 700 nm is preferably 20% or less, and more preferably 19% or less.

  The reflectance can be measured by irradiating the blackened layer of the conductive substrate with light. Specifically, for example, as shown in FIG. 1A, when the copper layer 12 and the blackened layer 13 are laminated in this order on the one surface 11a side of the transparent base material 11, the blackened layer 13 is irradiated with light. Measurement can be performed by irradiating the surface A of the chemical layer 13 with light. In the measurement, light having a wavelength of 400 nm or more and 700 nm or less is irradiated to the blackened layer 13 of the conductive substrate, for example, at a wavelength of 1 nm as described above, and the average value of the measured values is used as the reflectance of the conductive substrate. be able to.

  The conductive substrate of this embodiment can be preferably used as a conductive substrate for a touch panel. In this case, the conductive substrate can be configured to have mesh-like wiring.

  The conductive substrate provided with the mesh-like wiring can be obtained by etching the copper layer and the blackening layer of the conductive substrate of the present embodiment described so far.

  For example, a two-layer wiring can be used as a mesh wiring. A specific configuration example is shown in FIG. FIG. 3 shows a view of the conductive substrate 30 provided with mesh-like wiring as viewed from the upper surface side in the stacking direction of the copper layer or the like, and the transparent substrate and the copper layer are patterned so that the wiring pattern is easy to understand. The layers other than the wirings 31A and 31B formed in this manner are not shown. Moreover, the wiring 31B seen through the transparent base material 11 is also shown.

  The conductive substrate 30 shown in FIG. 3 has a transparent base material 11, a plurality of wirings 31A parallel to the Y-axis direction in the drawing, and wirings 31B parallel to the X-axis direction. The wirings 31A and 31B are formed by etching a copper layer, and a blackening layer (not shown) is formed on the upper or lower surface of the wirings 31A and 31B. The blackened layer is etched in the same shape as the wirings 31A and 31B.

  The arrangement of the transparent substrate 11 and the wirings 31A and 31B is not particularly limited. An example of the arrangement of the transparent substrate 11 and the wiring is shown in FIGS. 4A and 4B correspond to cross-sectional views taken along line AA ′ of FIG.

  First, as shown to Fig.4 (a), wiring 31A, 31B may be arrange | positioned at the upper and lower surfaces of the transparent base material 11, respectively. In FIG. 4A, blackened layers 32A and 32B etched in the same shape as the wiring are disposed on the upper surface of the wiring 31A and the lower surface of 31B.

  Further, as shown in FIG. 4B, a pair of transparent base materials 11 is used, and wirings 31A and 31B are arranged on the upper and lower surfaces across one transparent base material 11, and one wiring 31B is You may arrange | position between the transparent base materials 11. Also in this case, blackened layers 32A and 32B etched in the same shape as the wiring are disposed on the upper surfaces of the wirings 31A and 31B. As described above, an adhesion layer can be provided in addition to the copper layer and the blackened layer. Therefore, in either case of FIGS. 4A and 4B, for example, an adhesion layer can be provided between the wiring 31 </ b> A and / or the wiring 31 </ b> B and the transparent substrate 11. When the adhesion layer is provided, it is preferable that the adhesion layer is also etched in the same shape as the wirings 31A and 31B.

  The conductive substrate having the mesh-like wiring shown in FIG. 3 and FIG. 4A is, for example, copper layers 12A and 12B, blackening layer 13A on both surfaces of the transparent base material 11 as shown in FIG. 13B and a conductive substrate provided with 13B.

  The case where it is formed using the conductive substrate of FIG. 1B will be described as an example. First, the copper layer 12A and the blackened layer 13A on the one surface 11a side of the transparent base material 11 are shown in FIG. Etching is performed so that a plurality of linear patterns parallel to the Y-axis direction are arranged at predetermined intervals along the X-axis direction. In addition, the X-axis direction in FIG.1 (b) means the direction parallel to the width direction of each layer. Further, the Y-axis direction in FIG. 1 (b) means a direction perpendicular to the paper surface in FIG. 1 (b).

  Then, the copper layer 12B and the blackened layer 13B on the other surface 11b side of the transparent substrate 11 are arranged in a Y-axis direction with a plurality of linear patterns parallel to the X-axis direction in FIG. Etching is performed so as to be disposed along the line.

  Through the above operation, the conductive substrate having the mesh-like wiring shown in FIGS. 3 and 4A can be formed. Note that the etching of both surfaces of the transparent substrate 11 can be performed simultaneously. That is, the etching of the copper layers 12A and 12B and the blackening layers 13A and 13B may be performed simultaneously. 4A, a conductive substrate having an adhesion layer patterned in the same shape as the wirings 31A and 31B between the wirings 31A and 31B and the transparent base material 11 is shown in FIG. It can be manufactured by performing etching in the same manner using the conductive substrate shown.

  The conductive substrate having the mesh-like wiring shown in FIG. 3 can also be formed by using two conductive substrates shown in FIG. 1 (a) or FIG. 2 (a). The case where two conductive substrates shown in FIG. 1A are used will be described as an example. For the two conductive substrates shown in FIG. 1A, a copper layer 12 and a blackened layer 13 are respectively formed as X Etching is performed so that a plurality of linear patterns parallel to the axial direction are arranged along the Y-axis direction at predetermined intervals. Then, the conductive substrate having mesh-like wiring is obtained by bonding the two conductive substrates so that the linear patterns formed on the respective conductive substrates cross each other by the etching process. be able to. The surface to be bonded when the two conductive substrates are bonded is not particularly limited. For example, the surface A in FIG. 1A on which the copper layer 12 or the like is laminated and the other surface 11b in FIG. 1A on which the copper layer 12 or the like is not laminated are bonded together, and FIG. It is also possible to have the structure shown in FIG.

  Further, for example, the other surface 11b in FIG. 1A in which the copper layer 12 or the like of the transparent substrate 11 is not laminated may be bonded so that the cross section has the structure shown in FIG. it can.

  4 (a) and 4 (b), a conductive substrate having an adhesion layer further patterned in the same shape as the wirings 31A and 31B between the wirings 31A and 31B and the transparent base material 11, It can be manufactured by using the conductive substrate shown in FIG. 2A instead of the conductive substrate shown in FIG.

  The wiring width and the distance between the wirings in the conductive substrate having the mesh-like wiring shown in FIGS. 3 and 4 are not particularly limited, and may be selected according to the amount of current flowing through the wiring, for example. Can do.

  3 and 4 show an example in which a mesh-like wiring (wiring pattern) is formed by combining linear wirings, but the present invention is not limited to such a configuration, and a wiring pattern is configured. The wiring can have any shape. For example, the shape of the wiring constituting the mesh-like wiring pattern can be changed to various shapes such as jagged lines (zigzag straight lines) so that moire (interference fringes) does not occur between the images on the display.

  Thus, a conductive substrate having a mesh-like wiring composed of two layers of wiring can be preferably used as a conductive substrate for a projected capacitive touch panel, for example.

  The conductive substrate according to the present embodiment has a structure in which the blackening layer is laminated on the copper layer formed on at least one surface of the transparent base material. And since the blackening layer is formed using the blackening plating solution as described above, the reactivity of the blackening layer to the etching solution is equal to or less than that of the copper layer. Therefore, as described above, when the copper layer and the blackened layer are patterned by etching, the blackened layer can be easily patterned into a desired shape.

  Moreover, the blackening layer contained in the conductive substrate of this embodiment can be a conductive substrate that sufficiently suppresses reflection of light on the surface of the copper layer and suppresses reflectance. Moreover, the visibility of a display can be improved when used for applications such as a touch panel.

Furthermore, since the blackening layer can be formed by the wet method using the blackening plating solution described above, the conductive substrate can be formed with higher productivity than the case of forming the blackening layer using the conventional dry method. Can be produced.
(Method for producing conductive substrate)
Next, a configuration example of the method for manufacturing the conductive substrate according to the present embodiment will be described.

The manufacturing method of the conductive substrate of this embodiment can have the following processes.
A copper layer forming step of forming a copper layer on at least one surface of the transparent substrate.
A blackened layer forming step of forming a blackened layer on the copper layer using a blackened plating solution.

  The blackening plating solution contains the above-described nickel compound, zinc compound, tin compound, and amidosulfuric acid, and the concentration of the tin compound is 0.3 g / L or more and 0.9 g / L or less. A plating solution can be used.

  The manufacturing method of the conductive substrate of this embodiment will be specifically described below.

  In addition, the above-mentioned electroconductive board | substrate can be suitably manufactured with the manufacturing method of the electroconductive board | substrate of this embodiment. For this reason, since it can be set as the structure similar to the case of the above-mentioned electroconductive board | substrate except the point demonstrated below, description is abbreviate | omitted partially.

  The transparent base material used for the copper layer forming step can be prepared in advance. Although the kind of transparent base material to be used is not particularly limited, a transparent base material such as a resin substrate (resin film) that transmits visible light or a glass substrate can be preferably used as described above. The transparent base material can be cut into an arbitrary size in advance if necessary.

  And as above-mentioned, it is preferable that a copper layer has a copper thin film layer. The copper layer can also have a copper thin film layer and a copper plating layer. For this reason, a copper layer formation process can have a process of forming a copper thin film layer, for example with a dry plating method. The copper layer forming step includes a step of forming a copper thin film layer by a dry plating method, a step of forming a copper plating layer by an electroplating method which is a kind of wet plating method, using the copper thin film layer as a power feeding layer, You may have.

  The dry plating method used in the step of forming the copper thin film layer is not particularly limited, and for example, a vapor deposition method, a sputtering method, an ion plating method, or the like can be used. In addition, as a vapor deposition method, a vacuum vapor deposition method can be used preferably. As the dry plating method used in the step of forming the copper thin film layer, it is more preferable to use the sputtering method because the film thickness is particularly easy to control.

  Next, the process of forming a copper plating layer will be described. The conditions in the step of forming the copper plating layer by the wet plating method, that is, the conditions for the electroplating treatment are not particularly limited, and various conditions according to ordinary methods may be adopted. For example, a copper plating layer can be formed by supplying a base material on which a copper thin film layer is formed in a plating tank containing a copper plating solution and controlling the current density and the conveyance speed of the base material.

  Next, the blackening layer forming process will be described.

  In the blackening layer forming step, blackening plating including the above-described nickel compound, zinc compound, tin compound, and amidosulfuric acid, and the concentration of the tin compound is 0.3 g / L or more and 0.9 g / L A blackened layer can be formed using the liquid.

  The blackening layer can be formed by a wet method. Specifically, for example, a blackened layer can be formed on the copper layer by an electrolytic plating method in a plating tank containing the blackened plating solution described above using a copper layer as a power feeding layer. In this way, by using the copper layer as a power feeding layer and forming the blackened layer by electrolytic plating, the blackened layer can be formed on the entire surface of the copper layer opposite to the surface facing the transparent substrate.

  Since the blackening plating solution has already been described, the description thereof is omitted.

  Note that a blackened layer containing nickel, zinc, and tin can be formed by the blackened layer forming step.

  In the method for manufacturing a conductive substrate according to the present embodiment, an arbitrary step can be further performed in addition to the above-described steps.

  For example, when forming an adhesion layer between a transparent substrate and a copper layer, an adhesion layer forming step of forming an adhesion layer on the surface of the transparent substrate on which the copper layer is formed can be performed. When carrying out the adhesion layer forming step, the copper layer forming step can be carried out after the adhesion layer forming step, and in the copper layer forming step, copper is applied to the substrate on which the adhesion layer is formed on the transparent substrate in this step. A thin film layer can be formed.

  In the adhesion layer forming step, the film formation method of the adhesion layer is not particularly limited, but it is preferable to form the film by a dry plating method. As the dry plating method, for example, a sputtering method, an ion plating method, a vapor deposition method, or the like can be preferably used. In the case where the adhesion layer is formed by a dry method, it is more preferable to use a sputtering method because the film thickness can be easily controlled. As described above, one or more elements selected from carbon, oxygen, hydrogen, and nitrogen can be added to the adhesion layer, and in this case, the reactive sputtering method can be more preferably used.

  The conductive substrate obtained by the method for manufacturing a conductive substrate of the present embodiment can be used for various applications such as a touch panel. And when using for various uses, it is preferable that the copper layer and blackening layer which are contained in the electroconductive board | substrate of this embodiment are patterned. In addition, when providing an adhesion layer, it is preferable that the adhesion layer is also patterned. The copper layer and the blackening layer, and in some cases, the adhesion layer can be patterned in accordance with a desired wiring pattern, for example. The copper layer and the blackening layer, and in some cases, the adhesion layer can be patterned in the same shape It is preferable that

  For this reason, the manufacturing method of the electroconductive board | substrate of this embodiment can have the patterning process of patterning a copper layer and a blackening layer. When the adhesion layer is formed, the patterning step can be a step of patterning the adhesion layer, the copper layer, and the blackening layer.

  The specific procedure of the patterning step is not particularly limited, and can be performed by an arbitrary procedure. For example, in the case of the conductive substrate 10A in which the copper layer 12 and the blackened layer 13 are laminated on the transparent substrate 11 as shown in FIG. 1A, first, a mask having a desired pattern on the surface A on the blackened layer 13. A mask placement step of placing the can be performed. Next, an etching step of supplying an etching solution to the surface A on the blackened layer 13, that is, the surface side where the mask is disposed can be performed.

  The etchant used in the etching step is not particularly limited. However, the blackened layer formed by the conductive substrate manufacturing method of the present embodiment exhibits almost the same reactivity to the etching solution as the copper layer. For this reason, the etching liquid used in an etching step is not specifically limited, The etching liquid generally used for the etching of a copper layer can be used preferably.

  As the etching solution, for example, a mixed aqueous solution containing at least one selected from sulfuric acid, hydrogen peroxide solution, hydrochloric acid, cupric chloride, and ferric chloride can be preferably used. The content of each component in the etching solution is not particularly limited.

  The etching solution can be used at room temperature, but it can also be used by heating in order to increase the reactivity.

  In addition, as shown in FIG. 1B, a patterning process for patterning a conductive substrate 10B in which copper layers 12A and 12B and blackening layers 13A and 13B are laminated on one surface 11a and the other surface 11b of the transparent substrate 11 is also performed. Can be implemented. In this case, for example, a mask placement step of placing a mask having a desired pattern on the surface A and the surface B on the blackening layers 13A and 13B can be performed. Next, an etching step of supplying an etching solution to the surface A and the surface B on the blackening layers 13A and 13B, that is, the surface side where the mask is disposed can be performed.

  The pattern formed in the etching step is not particularly limited, and can be an arbitrary shape. For example, in the case of the conductive substrate 10A shown in FIG. 1A, the pattern is formed so that the copper layer 12 and the blackened layer 13 include a plurality of straight lines or jagged lines (zigzag straight lines) as described above. Can be formed.

  In the case of the conductive substrate 10B shown in FIG. 1B, a pattern can be formed so that the copper layer 12A and the copper layer 12B form a mesh-like wiring. In this case, it is preferable to perform patterning so that the blackened layer 13A has the same shape as the copper layer 12A and the blackened layer 13B has the same shape as the copper layer 12B.

  Further, for example, after patterning the copper layer 12 and the like on the conductive substrate 10A described above in the patterning step, a lamination step of laminating two or more patterned conductive substrates can be performed. When laminating, for example, by laminating so that the pattern of the copper layer of each conductive substrate intersects, it is also possible to obtain a laminated conductive substrate provided with mesh-like wiring.

  The method for fixing two or more laminated conductive substrates is not particularly limited, but can be fixed by, for example, an adhesive.

  The conductive substrate obtained by the above-described method for manufacturing a conductive substrate according to this embodiment has a structure in which a blackening layer is stacked on a copper layer formed on at least one surface of a transparent base material. . And since the blackening layer is formed using the blackening plating solution as described above, the reactivity of the blackening layer to the etching solution is equal to or less than that of the copper layer. Therefore, as described above, when the copper layer and the blackened layer are patterned by etching, the blackened layer can be easily patterned into a desired shape.

  In addition, the blackening layer included in the conductive substrate obtained by the method for manufacturing the conductive substrate of the present embodiment is a conductive substrate that sufficiently suppresses reflection of light on the surface of the copper layer and suppresses reflectance. Can do. For this reason, when it uses for uses, such as a touch panel, for example, the visibility of a display can be improved.

  Furthermore, since the blackening layer can be formed by the wet method using the blackening plating solution described above, the conductive substrate can be formed with higher productivity than the case of forming the blackening layer using the conventional dry method. Can be produced.

Specific examples and comparative examples will be described below, but the present invention is not limited to these examples.
(Evaluation methods)
First, a method for evaluating the obtained conductive substrate will be described.
(1) Reflectance Measurement was performed by installing a reflectance measurement unit in an ultraviolet-visible spectrophotometer (Shimadzu Corporation model: UV-2600).

As will be described later, in each experimental example, a conductive substrate having the structure shown in FIG. For this reason, the reflectance measurement is performed with light having a wavelength of 400 nm or more and 700 nm or less with an incident angle of 5 ° and a light receiving angle of 5 ° with respect to the surface A of the blackened layer 13 of the conductive substrate 10A shown in FIG. Irradiation was performed at 1 nm intervals to measure regular reflectance, and the average value was defined as the reflectance (average reflectance) of the conductive substrate.
(2) Etching characteristics It was immersed in an etching solution of 40 g / L sulfuric acid and 20 mL of 35% hydrogen peroxide solution, and the solution temperature was 30 ° C., and the time until the blackened layer was dissolved and the copper layer was exposed was measured. .

In addition, the copper layer has confirmed beforehand that it will be 30 seconds after a copper layer is exposed until it melt | dissolves.
(3) Determination A conductive substrate having a reflectivity of 20% or less and an etching property evaluation result of 5 seconds or more was determined to be ◯.

A conductive substrate having a reflectivity of more than 20% and / or an evaluation result of etching characteristics of less than 5 seconds was judged as x.
(Sample preparation conditions)
In the following examples and comparative examples, conductive substrates were produced under the conditions described below and evaluated by the above-described evaluation method.
[Example 1]
(1) Blackening plating solution In Example 1, a blackening plating solution containing nickel sulfate as a nickel compound, zinc sulfate as a zinc compound, tin sulfate as a tin compound, and further containing amidosulfuric acid was prepared. . In the blackening plating solution, the concentration of nickel sulfate hexahydrate was 40 g / L, the concentration of zinc sulfate heptahydrate was 4.8 g / L, the concentration of tin sulfate was 0.3 g / L, Each component was added and prepared so that a density | concentration might be 11 g / L.

Ammonia water was added to the blackening plating solution to adjust the pH of the blackening plating solution to 3.
(2) Conductive substrate (copper layer forming process)
A copper layer was formed on one side of a long transparent substrate made of polyethylene terephthalate resin (PET) having a length of 100 m, a width of 500 mm, and a thickness of 100 μm. In addition, about the transparent base material made from the polyethylene terephthalate resin used as a transparent base material, when the total light transmittance was evaluated by the method prescribed | regulated to JISK7361-1, it was 97%.

  In the copper layer forming step, a copper thin film layer forming step and a copper plating layer forming step were performed.

  First, the copper thin film layer forming step will be described.

  In the copper thin film layer forming step, the above-mentioned transparent base material was used as a base material, and a copper thin film layer was formed on one surface of the transparent base material.

  In the copper thin film layer forming step, first, the above-mentioned transparent base material, which was previously heated to 60 ° C. to remove moisture, was placed in the chamber of the sputtering apparatus.

Next, after exhausting the inside of the chamber to 1 × 10 ⁻³ Pa, argon gas was introduced, and the pressure in the chamber was set to 1.3 Pa.

  Electric power was supplied to a copper target previously set on the cathode of the sputtering apparatus, and a copper thin film layer was formed on one surface of the transparent substrate so as to have a thickness of 0.2 μm.

  Next, a copper plating layer was formed in the copper plating layer forming step. The copper plating layer was formed by electroplating so that the thickness of the copper plating layer was 0.3 μm.

  By carrying out the above copper thin film layer forming step and the copper plating layer forming step, a copper layer having a thickness of 0.5 μm was formed as a copper layer.

The substrate formed in the copper layer forming step, on which the 0.5 μm thick copper layer was formed on the transparent base material, was immersed in 20 g / L sulfuric acid for 30 seconds and washed, and then the following blackened layer forming step was performed. .
(Blackening layer forming process)
In the blackening layer forming step, a blackening layer was formed on one surface of the copper layer by electrolytic plating using the blackening plating solution of the above-described embodiment. In the blackening layer forming step, the blackening layer was formed by performing electrolytic plating under the conditions that the temperature of the blackening plating solution was 40 ° C., the current density was 0.2 A / dm ² , and the plating time was 100 sec.

  The thickness of the formed blackened layer was 70 nm.

The conductive substrate obtained by the above steps was evaluated for the reflectance and etching characteristics described above. The results are shown in Table 1.
[Example 2 and Example 3]
When preparing the blackening plating solution, each example was the same as in Example 1 except that the concentration and pH of tin sulfate in the blackening plating solution were changed to the values shown in Table 1. A blackening plating solution was prepared.

  Moreover, except having used the blackening plating solution produced in each Example when forming a blackening layer, the electroconductive board | substrate was produced similarly to Example 1 and evaluated.

The results are shown in Table 1.
[Comparative Examples 1 to 3]
When preparing the blackening plating solution, each comparative example was the same as in Example 1 except that the concentration and pH of tin sulfate in the blackening plating solution were changed to the values shown in Table 1. A blackening plating solution was prepared. In Comparative Example 1, tin sulfate was not added.

  Moreover, except having used the blackening plating solution produced by each comparative example when forming a blackening layer, the electroconductive board | substrate was produced similarly to Example 1 and evaluated.

  The results are shown in Table 1.

表１に示した結果より、調製した黒化めっき液内のすず化合物である硫酸すずの濃度が０．３ｇ／Ｌ以上０．９ｇ／Ｌ以下である、実施例１〜実施例３については、エッチング特性の評価結果が５秒以上となっていた。すなわち、黒化層のエッチング液に対する反応性が銅層と同等以下になっていることを確認できた。

From the results shown in Table 1, etching was carried out for Examples 1 to 3 in which the concentration of tin sulfate, which was a tin compound in the prepared blackening plating solution, was 0.3 g / L or more and 0.9 g / L or less. The evaluation result of the characteristic was 5 seconds or more. That is, it was confirmed that the reactivity of the blackened layer to the etching solution was equal to or less than that of the copper layer.

  Moreover, about Example 1- Example 3, a reflectance was also 20% or less, and it has confirmed that the formed blackening layer could especially suppress reflection of the light in the copper layer surface.

  On the other hand, for Comparative Examples 1 and 2 in which the concentration of tin sulfate in the prepared blackening plating solution is less than 0.3 g / L, the evaluation result of the etching characteristics is 4 seconds, which is more than that of Examples 1 to 3. It was confirmed that it was significantly shortened. This is presumably because the amount of tin sulfate, which is a tin compound, was not sufficient, and the effect of suppressing the reactivity of the blackened layer to the etching solution was not sufficient.

  Moreover, about the comparative example 3, since the density | concentration of the tin sulfate in blackening plating solution was 1 g / L of 0.9 g / L or more, the formed blackening layer suppresses reflection of the light on the copper layer surface. The function was not sufficient, and the reflectance was a very high value of 57.7%.

10A, 10B, 20A, 20B, 30 Conductive substrate 11 Transparent base material 12, 12A, 12B Copper layer 13, 13A, 13B, 32A, 32B Blackening layer

Claims (6)

A blackening plating solution for forming a blackened layer on the surface of the copper layer,
Blackening plating containing a nickel compound, a zinc compound, a tin compound, and amidosulfuric acid, wherein the tin compound is tin sulfate, and the concentration of the tin compound is 0.3 g / L or more and 0.9 g / L or less. liquid. The blackening plating solution according to claim 1, wherein the nickel compound includes nickel sulfate and the zinc compound includes zinc sulfate. The blackening plating solution according to claim 2 , wherein the zinc sulfate is zinc sulfate heptahydrate, and the concentration of the zinc sulfate heptahydrate is 1.5 g / L or more and 4.8 g / L or less.   The blackening plating solution according to any one of claims 1 to 3, wherein the pH is adjusted with aqueous ammonia, and the pH is 2.0 or more and 4.0 or less. A transparent substrate;
A copper layer disposed on at least one surface of the transparent substrate;
A conductive substrate having a blackened layer formed by the blackened plating solution according to any one of claims 1 to 4 on the copper layer. A transparent substrate;
A copper layer disposed on at least one surface of the transparent substrate;
A blackening layer disposed on the copper layer,
The blackening layer is observed containing nickel, zinc, and tin,
When immersed in an etching solution composed of sulfuric acid and hydrogen peroxide solution at a liquid temperature of 30 ° C., the time until the blackened layer is dissolved and the copper layer is exposed is 5 seconds or longer, and A conductive substrate having an average reflectance of 20% or less of light having a wavelength of 400 nm to 700 nm on the surface of the blackened layer .

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