Patent Application
20150152567
The present application is based on Japanese patent application No. 2013-248021 filed on Nov. 29, 2013, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The invention relates to a copper foil and a method of manufacturing the copper foil.
2. Description of the Related Art
In case of bare copper foils, the surface is subjected to a reddish brown to black discoloration over time due to oxidation, whereby the appearance deteriorates. In case of copper foils of Sn-plated copper, the surface is grey in color and therefore the appearance is not good.
Thus, an oxidation-resistant copper foil is needed which can maintain the excellent appearance or color of copper-based metal materials.
A method for improving the corrosion resistance of copper or copper alloy members is known in which zinc (Zn) is plated on a surface of copper material and is subsequently diffused by heat treatment to form a copper-zinc (Cu—Zn) layer with a zinc (Zn) concentration of 10 to 40% (see JP-A-S62-040361).
Another method is known in which a layer of nickel (Ni), etc., is formed on a surface of a copper-based member by plating.
In recent years, it was reported that amorphous alloys exhibit excellent corrosion resistance due to the structure in which atoms are densely packed (see WO2007/108496, JP-A-2008-045203, JP-A-2004-176082, JP-A-2001-059198 and JP-A-2010-163641).
The researches by the present inventors prove that even the copper-based member disclosed in JP-A-S62-040361 does not sufficiently exhibit satisfactory required performance of products, i.e., oxidation resistance in a long-term use at high temperature when used as, e.g., power and signal transmission cable conductors for automobiles and vehicles in which ambient temperature or the combination of ambient temperature and operating temperature reaches 100° C. or more.
When the layer of nickel (Ni) etc. is formed on the surface of the copper foil, the copper foil becomes thick and hard and this results in a decrease in flexibility and poor handling properties.
The amorphous alloys disclosed in WO2007/108496, JP-A-2008-045203, JP-A-2004-176082, JP-A-2001-059198 and JP-A-2010-163641 are disadvantageous in that the manufacturing process is complicated since it is necessary to use a material formed by alloying plural metal elements, and a technique of forming an amorphous layer using a non-alloyed zinc element has not been sufficiently researched yet.
It is an object of the invention to provide a copper foil that is excellent in oxidation resistance, can maintain the excellent appearance or color of copper-based metal materials and is excellent in handling properties, as well as a method of manufacturing the copper foil.
(1) According to one embodiment of the invention, a copper foil comprises:
a copper-based metal sheet comprising mainly a copper; and
a surface-treated layer that is provided on the copper-based metal sheet and comprises an amorphous layer comprising oxygen and a metal with a higher oxygen affinity than a copper,
wherein a total thickness of the copper-based metal sheet and the surface-treated layer is less than 0.55 mm.
In the above embodiment (1) of the invention, the following modifications and changes can be made.
(i) The surface-treated layer is provided on one side or both sides of the copper-based metal sheet.
(ii) The amorphous layer further comprises a copper diffused from the copper-based metal sheet.
(iii) The surface-treated layer further comprises a diffusion layer under the amorphous layer, and wherein the diffusion layer comprises a copper and a metal with a higher oxygen affinity than the copper, or oxygen, copper and a metal with a higher oxygen affinity than a copper.
(iv) The metal with a higher oxygen affinity than copper comprises zinc.
forming a layer comprising a metal with a higher oxygen affinity than a copper on a surface of a copper-based metal sheet comprising mainly a copper; and
subsequently heat-treating the formed layer at a temperature of not less than 30° C. and not more than 300° C. for not less than 5 seconds and not more than 60 minutes so as to have a surface-treated layer.
In the above embodiment (2) of the invention, the following modifications and changes can be made.
(vi) The metal with a higher oxygen affinity than copper comprises zinc.
(vii) The surface-treated layer has a thickness of not less than 3 nm and not more than 300 nm.
According to one embodiment of the invention, a copper foil can be provided that is excellent in oxidation resistance, can maintain the excellent appearance and color of copper-based metal materials and is excellent in handling properties, as well as a method of manufacturing the copper foil.
Next, the present invention will be explained in more detail in conjunction with appended drawings, wherein:
Copper foils in the embodiments of the invention are each provided with a copper-based metal sheet including mainly a copper; and a surface-treated layer which is provided on the copper-based metal sheet and has an amorphous layer containing oxygen and a metal with a higher oxygen affinity than copper; wherein the total thickness of the copper-based metal sheet and the surface-treated layer is less than 0.55 mm. The surface-treated layer(s) is provided on one or both sides of the copper-based metal sheet. The copper foils of the invention include copper alloy foils.
A copper foil 10 shown in
The Cu sheet 1 includes mainly Cu which is preferably contained in an amount of not less than 90 mass %. That is, Cu alone or a Cu alloy containing not more than 10 mass % of impurities is preferable. It is possible to use, e.g., pure copper such as oxygen-free copper or tough pitch copper, or dilute-copper alloys containing 3 to 15 mass ppm of sulfur, 2 to 30 mass ppm of oxygen and 5 to 55 mass ppm of Ti.
The thickness of the Cu sheet 1 is preferably from 10 μm to 500 μm, more preferably from 10 μm to 400 μm, and further preferably from 10 μm to 300 μm. When too thin, creases, etc., are likely to be formed on the copper sheet and handling properties become poor. On the other hand, when too thick, it is difficult to freely process into various shapes.
The surface-treated layer 2 has an amorphous layer containing oxygen and a metal with a higher oxygen affinity than copper. Alternatively, the surface-treated layer 2 may have an amorphous layer containing oxygen, a metal with a higher oxygen affinity than copper and copper diffused from the Cu sheet 1.
The surface-treated layer may be a surface-treated layer 3 having an amorphous layer 5 and a diffusion layer 4 which is formed thereunder and contains copper and a metal with a higher oxygen affinity than copper, or preferably oxygen, copper and a metal with a higher oxygen affinity than copper, as is the second embodiment (a copper foil 20) shown in
The metal with a higher oxygen affinity than copper, which constitutes the surface-treated layer 2 (amorphous layer) and the amorphous layer 5, is preferably zinc. Besides zinc, it is possible to use, e.g., Ti, Mg, Zr, Al, Fe, Sn and Mn, etc. Ti, Mg and Zr, which are easily oxidized and removed at the time of manufacturing copper, are particularly preferable from the viewpoint of recycling. The same applies to the metal with a higher oxygen affinity than copper, which constitutes the diffusion layer 4, and it is preferable to use the same metal as the metal with a higher oxygen affinity than copper, which constitutes the amorphous layer.
The amorphous layer with randomly-arranged elements is considered to have a denser structure than a crystalline layer with regularly-arranged elements. Therefore, copper diffusion to the surface of the surface-treated layer and oxygen ingress into a copper raw material, which cause oxidation of the copper raw material, are suppressed or reduced by the amorphous layer. It is believed that the amorphous layer thereby serves as a barrier layer which inhibits bonding between copper and oxygen.
Oxygen needs to preferentially bond to a metal other than copper so that the amorphous layer is formed. Then, in order to accelerate the formation of the amorphous layer, it is preferable that a metal with a higher oxygen affinity than copper (e.g., zinc) be arranged on the surface of the Cu sheet 1.
Different types of elements are in contact with each other at an interface between the surface-treated layers 2 and 3 and another layer and a gradual concentration change is generally seen at such an interface, which makes difficult to define the thickness of the surface-treated layer. Therefore, the thickness of the surface-treated layer in the invention is defined as “a thickness of a layer which contains oxygen, a metal with a higher oxygen affinity than copper and, in some cases, copper, and in which each of the constituent elements is contained in the amount of not less than 2 at % in terms of atomic concentration (at %) as an elemental content ratio”.
The thickness of the surface-treated layer 2 is preferably not less than 3 nm and not more than 300 nm depending on the heat treatment conditions, more preferably not less than 5 nm and not more than 200 nm, and further preferably not less than 6 nm and not more than 150 nm. Meanwhile, the thickness of the surface-treated layer 3 is preferably not less than 6 nm and not more than 300 nm as the total of the thickness of the diffusion layer 4 and the thickness of the amorphous layer 5.
When the diffusion layer 4 is provided, the lower limit of the thickness thereof is not specifically limited as long as the Cu sheet 1 is covered, and the lower limit of coating thickness is preferably about 3 nm in effect. In addition, the upper limit of the thickness of the diffusion layer 4 is preferably not more than 0.1 μm. When the diffusion layer 4 is more than 0.1 μm, the amorphous layer 5 contributing to develop high oxidation resistance may be stabilized and become less likely to be formed. The thickness of the amorphous layer 5 is not specifically limited but is preferably not less than 3 nm.
The total thickness of the Cu sheet 1 and the surface-treated layer 2 or 3 is less than 0.55 mm, preferably not less than 0.015 mm and not more than 0.4 mm, and more preferably not less than 0.015 mm and not more than 0.3 mm. When too thin, creases, etc., are likely to be formed on the copper sheet and handling properties become poor. On the other hand, when too thick, it is difficult to freely process into various shapes.
Method of Manufacturing Copper Foil
Next, a method of manufacturing the copper foils in the present embodiments will be described.
In case that a metal with a higher oxygen affinity than copper is, e.g., zinc, Zn layers are formed on the surfaces of the Cu sheet 1 by electrolytic plating in size and shape of the finished product. By subsequent heating in the ambient air at a temperature of not less than 30° C. and not more than 300° C. for not less than 5 seconds and not more than 60 minutes, the surface-treated layers 2 (amorphous layers) are formed. The thickness of the Zn layer is preferably not less than 3 nm and not more than 300 nm, more preferably not less than 5 nm and not more than 200 nm, and further preferably not less than 6 nm and not more than 150 nm. A copper foil provided with the surface-treated layers 2 having the amorphous layer containing at least zinc and oxygen is thus obtained. In other words, it is possible to form the surface-treated layer 2 (amorphous layer) on the surface of the Cu sheet 1 by a simple method in which a zinc cover layer is simply provided and heat-treated under the predetermined conditions.
In the present embodiments, the cover layer is heat-treated preferably at a temperature of not less than 30° C. and not more than 300° C. for not less than 5 seconds and not more than 60 minutes as described above, more preferably at a temperature of not less than 40° C. and not more than 150° C. for not less than 20 seconds and not more than 30 minutes, and further preferably at a temperature of not less than 50° C. and not more than 100° C. for not less than 30 seconds and not more than 15 minutes. In addition, a plating process can be suitably used for forming the Zn layer. In addition to the plating process, it is possible to use a sputtering method, a vacuum deposition method and a cladding process, etc.
Alternatively, as a manufacturing method in another embodiment, the surface-treated layer 2 (amorphous layer) may be formed by preliminarily plating zinc before processing into the size and shape of the finished product and heat-treating after processing into the size and shape of the finished product.
Meanwhile, the diffusion layer 4 can be formed by, e.g., covering the surface of the Cu sheet 1 with zinc before forming the amorphous layer 5 of the surface-treated layer 3 and then heating in the ambient air or holding in an oil bath or salt bath at a temperature of not less than 50° C. Alternatively, the diffusion layer 4 may be manufactured using electric resistance heat. After that, the amorphous layer 5 is formed on the surface of the diffusion layer 4 by the same method as that used for forming the surface-treated layer 2 (amorphous layer).
Intended Use
The copper foils in the embodiments of the invention are applicable to objects having various structures and also complicated structures. It is possible to suitably use for surface treatment of, e.g., roofs, etc., of buildings, Buddha statues and radiators in heat-treating furnace, etc. In addition, since the form of foil only requires a sticking process, it is possible to apply to materials difficult to process by plating, such as ceramics, Al and Ti. Furthermore, it is possible to use as copper foils for printed circuit board, etc.
In the embodiments of the invention, it is possible to suppress oxidation of the copper-based metal sheet and to maintain color equivalent to the copper-based metal material since the surface-treated layer 2 or 3, which serves as a barrier layer for suppressing or reducing copper diffusion to the surface of the surface-treated layer and oxygen ingress into the copper-based metal sheet, is formed on the surface of the copper-based metal sheet.
In addition, in the embodiments of the invention, the thickness of copper foil including the surface-treated layer is less than 0.55 mm and, in addition to this, it is not necessary to plate Ni, etc. Therefore, flexibility (handling properties) is excellent and it is possible to freely process into various shapes and to attach to objects formed of any material with any size. Thus, when attached to, e.g., ceramics, resin or Fe-based structure material, excellent appearance and color of copper or copper alloy can be maintained without degradation over time. In addition, strength and heat resistance of surface which are possessed by metal can be added to non-metal (resin, etc.) by attaching the copper foil of the invention.
The following examples further illustrate the invention but the invention is not limited thereto.
Table 1 shows the configurations of the samples in Examples 1 to 6 and Comparative Examples 1 to 5. Table 1 also shows the evaluation results of the evaluation items described later.
The samples in Examples 1 to 6 shown in Table 1 were generally made as follows: a cover layer formed of zinc plating with various thickness (0.002 to 0.27 μm) was formed on a flat sheet formed of tough pitch copper by electrolytic plating and annealing was then performed in the ambient air. The details of Examples 1 to 6 and Comparative Examples 1 to 5 will be described later.
Meanwhile, in Comparative Example 1 for evaluating influence of the thickness of the zinc layer on the characteristics of the Cu-based metal sheet (Cu sheet), a zinc layer with a different thickness was formed and heat treatment was then performed in the same manner as Example 1. In Comparative Examples 2 and 3 for evaluating influence of the heat treatment conditions on the characteristics of the Cu-based metal sheet (Cu sheet), the sample was made under a different heat treatment condition (Comparative Example 2) or was made without heat treatment (Comparative Example 3).
Furthermore, as the samples of Comparative Examples 4 and 5, tough pitch copper (Comparative Example 4) and a Cu-30 mass % Zn alloy (Comparative Example 5) were prepared.
Presence of the amorphous layer shown in Table 1 was confirmed by RHEED analysis (Reflection High Energy Electron Diffraction). The samples showing a halo pattern indicating presence of the amorphous layer are indicated by “Present”, and the samples showing electron diffraction spots indicating a crystalline structure are indicated by “Not present”.
Here, appearance evaluation, corrosion resistance evaluation and overall evaluation of the obtained samples shown in Table 1 were performed as follows.
For evaluating “appearance”, a constant temperature test to hold samples in the ambient air in a constant-temperature oven set at 100° C. for up to 1000 hours and a 100-hour holding test in a test chamber at a temperature of 85° C. and humidity of 85% were conducted. Using change in color and gloss before and after the tests as criteria for judgment, the samples with the least change were evaluated as “⊚ (excellent)”, the samples with the most significant change and with associated deterioration in appearance were evaluated as “X (bad)”, and the samples with the change in-between were evaluated as either “◯ (acceptable)” or “Δ (unacceptable)”.
For evaluating “oxidation resistance”, each sample was kept in the ambient air in a constant-temperature oven set at 100° C. for up to 1000 hours and an increase in oxide film was measured after the test. Based on comparison with the initial thickness (before the test) of the oxide film, the samples with the least change were evaluated as “⊚ (excellent)”, the samples with the most significant change and with associated deterioration were evaluated as “X (bad)”, and the samples with the change in-between were evaluated as either “◯ (acceptable)” or “Δ (unacceptable)” depending on the extent of the change. Using comparison results with the initial thickness (before the test) of the oxide film as quantitative criteria, the samples of which oxide film after 1000 hours has a thickness three times or more were all evaluated as “X” regardless of the change in appearance.
For “overall evaluation”, the results of the above items were comprehensively assessed, and ⊚ and ◯ are judged as “passed the test” and Δ and x were judged as “failed the test”.
The details of Examples 1 to 6 and Comparative Examples 1 to 5 are described below.
A 0.5 mm-thick flat sheet formed of pure Cu (tough pitch copper; hereinafter, described as “TPC”) was prepared, a 0.002 um-thick cover layer formed of zinc was then formed on a surface of the flat sheet by electrolytic plating and heat treatment was subsequently performed in the ambient air at a temperature of 50° C. for 10 minutes, thereby obtaining a sample provided with a surface-treated layer. Based on Auger analysis performed on the obtained sample from the surface in a depth direction, it was confirmed that a 0.003 μm-thick surface-treated layer composed of zinc (Zn), oxygen (O) and copper (Cu) was formed.
In Example 2, a 0.5 mm-thick flat sheet formed of TPC was prepared, a 0.005 μm-thick Zn layer was then formed on a surface of the flat sheet by electrolytic plating and heat treatment was subsequently performed in the ambient air at a temperature of 50° C. for 1 hour, thereby obtaining a sample. Based on Auger analysis performed on the obtained sample from the surface in a depth direction, it was confirmed that a 0.006 μm-thick surface-treated layer composed of zinc (Zn), oxygen (O) and copper (Cu) was formed.
In Example 3, a 0.5 mm-thick flat sheet formed of TPC was prepared, a 0.008 μm-thick Zn layer was then formed on a surface of the flat sheet by electrolytic plating and heat treatment was subsequently performed in the ambient air at a temperature of 100° C. for 5 minutes, thereby obtaining a sample. Based on Auger analysis performed on the obtained sample from the surface in a depth direction, it was confirmed that a 0.01 μm-thick surface-treated layer composed of zinc (Zn), oxygen (O) and copper (Cu) was formed.
In Example 4, a 0.5 mm-thick flat sheet formed of TPC was prepared, a 0.04 μm-thick Zn layer was then formed on a surface of the flat sheet by electrolytic plating and heat treatment was subsequently performed in the ambient air at a temperature of 120° C. for 10 minutes, thereby obtaining a sample. Based on Auger analysis performed on the obtained sample from the surface in a depth direction, it was confirmed that a 0.05 μm-thick surface-treated layer composed of zinc (Zn), oxygen (O) and copper (Cu) was formed.
In Example 5, a 0.5 mm-thick flat sheet formed of TPC was prepared, a 0.08 μm-thick Zn layer was then formed on a surface of the flat sheet by electrolytic plating and heat treatment was subsequently performed in the ambient air at a temperature of 300° C. for 5 seconds, thereby obtaining a sample. Based on Auger analysis performed on the obtained sample from the surface in a depth direction, it was confirmed that a 0.1 μm-thick surface-treated layer composed of zinc (Zn), oxygen (O) and copper (Cu) was formed.
In Example 6, a 0.5 mm-thick flat sheet formed of TPC was prepared, a 0.27 μm-thick Zn layer was then formed on a surface of the flat sheet by electrolytic plating and heat treatment was subsequently performed in the ambient air at a temperature of 150° C. for 30 seconds, thereby obtaining a sample. Based on Auger analysis performed on the obtained sample from the surface in a depth direction, it was confirmed that a 0.3 μm-thick surface-treated layer composed of zinc (Zn), oxygen (O) and copper (Cu) was formed.
In Comparative Example 1, a 0.5 mm-thick flat sheet formed of TPC was prepared, a 0.95 μm-thick Zn layer was then formed on a surface of the flat sheet by electrolytic plating and heat treatment was subsequently performed in the ambient air at a temperature of 100° C. for 5 minutes, thereby obtaining a sample. Based on Auger analysis performed on the obtained sample from the surface in a depth direction, it was confirmed that a 1 μm-thick surface-treated layer composed of zinc (Zn) and oxygen (O) was formed.
In Comparative Example 2, a 0.5 mm-thick flat sheet formed of TPC was prepared, a 0.01 μm-thick Zn layer was then formed on a surface of the flat sheet by electrolytic plating and heat treatment was subsequently performed in the ambient air at a temperature of 400° C. for 60 seconds, thereby obtaining a sample. Based on Auger analysis performed on the obtained sample from the surface in a depth direction, it was confirmed that a 0.02 μm-thick surface-treated layer composed of zinc (Zn), oxygen (O) and copper (Cu) was formed.
In Comparative Example 3, a 0.5 mm-thick flat sheet formed of TPC was prepared and a 0.02 μm-thick Zn layer was then formed on a surface of the flat sheet by electrolytic plating, thereby obtaining a sample.
In Comparative Example 4, a 0.5 mm-thick flat sheet formed of TPC was used as an evaluation sample.
In Comparative Example 5, a 0.5 mm-thick flat sheet formed of Cu-30 mass % Zn alloy (brass) was used as an evaluation sample.
In addition, based on the results including other Examples, it was found that the average elemental content of zinc (Zn) was in a range of 35 to 68 at %, that of oxygen (O) in a range of 30 to 60 at % and that of copper (Cu) in a range of 0 to 15 at %.
On the other hand, the sample in Comparative Example 1 contained 33 at % of zinc (Zn), 41 at % of oxygen (O) and 26 at % of copper (Cu), and the sample in Comparative Example 5 contained 5 at % of zinc (Zn), 46 at % of oxygen (O) and 49 at % of copper (Cu).
In Example 3, as shown in
Meanwhile, as shown in
In addition, according to Table 1, in Examples 1 to 6 in which surface-treated layers with various thicknesses of 0.003 to 0.3 μm are respectively provided and each have an amorphous structure, good results were obtained from the evaluations of appearance and oxidation resistance. Excellent characteristics were exhibited especially when the thickness of the surface-treated layer was 0.006 to 0.05 μm.
From the above results, it was confirmed that, in the structures of Examples 1 to 6, the process of oxidation does not occur and a stable surface condition is maintained even in the constant temperature test at 100° C. for 1000 hours and also under the environment of 85° C.×85%.
On the other hand, satisfactory characteristics were not obtained in some cases in Comparative Examples 1 to 3 even though a Zn-based surface-treated layer is provided in the same manner. The evaluation result of oxidation resistance is “Fail” for all of the samples in which an amorphous surface layer was not formed, such as Comparative Example 1 with thick zinc, Comparative Example 2 with excessive heat treatment after plating and Comparative Example 3 with no heat treatment after plating.
As for the cost performance (economic performance), Examples 1 to 6 do not require, e.g., coating of noble metal excellent in oxidation resistance of material per se but expensive, uses cheap Zn with very small thickness, and are thus extremely excellent in productivity and economic performance.
It should be noted that the invention is not intended to be limited to the embodiments and the examples, and various kinds of modifications can be implemented.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-248021 | Nov 2013 | JP | national |
