Patent Application
20150232342
The present invention relates to a copper foil for producing graphene, and a method of producing graphene using the same.
Graphite has a layered structure where a plurality of layers of carbon six-membered rings planarly arranged is laminated. The graphite having a mono atomic layer or around several atomic layers is called as graphene or a graphene sheet. The graphene sheet has own electrical, optical and mechanical properties, and in particularly has a high carrier mobility speed. Therefore, the graphene sheet has expected to be applied in various industries as a fuel cell separator, a transparent electrode, a conductive thin film for a display device, a “mercury-free” fluorescent lamp, a composite material, a carrier for Drug Delivery System (DDS) etc.
As a method of producing the graphene sheet, it is known that graphite is peeled with an adhesion tape. However, there are problems in that the number of the layer(s) of the graphene sheet obtained is not uniform, a wide area graphene sheet is difficult to be provided, and it is not suitable for mass production.
A technology has been developed that a sheet-like monocrystal graphitized metal catalyst is contacted with a carboneous substance and then is heat treated to grow the graphene sheet (Chemical Vapor Deposition (CVD) method) (Patent Literature 1). As the monocrystal graphitized metal catalyst, there is described a metal substrate made of Ni, Cu or W, for example.
Similarly, a technology has been reported that a graphene film is formed by the chemical vapor deposition method on a copper layer formed on an Ni or Cu metal foil or an Si substrate. The graphene film is formed at about 1000° C. (Non-Patent Literature 1).
However, it is not easy and spends high costs to produce the monocrystal metal substrate, a wide area substrate is difficult to be provided, and a wide area graphene sheet is thus difficult to be provided, as described in Patent Document 1. On the other hand, Non-Patent Document 1 describes that Cu is used as the substrate. Graphene is not grown on a copper foil in a plane direction within a short time. A Cu layer formed on an Si substrate is annealed to provide coarse grains, thereby providing a substrate. This may because unevenness exists on the copper foil to inhibit graphene from growing. When a Cu layer is formed on the Si substrate, the size of graphene is limited to the size of the Si substrate and the production costs are high. On the other hand, the monocrystal copper foil has less grain boundaries, but undesirably the costs are high and the size is limited.
Specifically, an object of the present invention is to provide a rolled copper foil for producing graphene being capable of producing graphene having a large area with low costs, and a method of producing graphene using the same.
A first aspect of the present invention provides a rolled copper foil for producing graphene, wherein a ratio (IC/IA) of a maximum value of a detected intensity (IC) at α=15 degrees and β=90 degrees±2 degrees and a maximum value of a detected intensity (IA) at α=70 degrees and β=0 degree±2 degrees is less than 1, and a ratio (ID/IB) of a maximum value of a detected intensity (ID) at α=15 degrees and β=270 degrees±2 degrees and a maximum value of a detected intensity (IB) at α=70 degrees and β=180 degrees±2 degrees is less than 1, shown in {111} pole figure.
Preferably, the IA is 1 or more.
Preferably, the IB is 1 or more.
Preferably, The rolled copper foil for producing graphene consists of tough pitch copper in accordance with JIS-H3100, or consists of oxygen free copper in accordance with JIS-H3100 or JIS-H3510, or contains 0.0001% by mass to 0.05% by mass of one or more of elements selected from the group consisting of Sn and Ag to the tough pitch copper or the oxygen free copper.
Preferably, 60 degree gloss of the surface is 130% or more both in a rolling direction and a transversal direction, and a surface roughness Ra is 0.20 μm or less in a rolling direction and a transversal direction.
Further, the present invention provides a method of producing graphene using the rolled copper foil for producing graphene, comprising the steps of: providing a hydrogen gas and a carbon-containing gas while placing the heated rolled copper foil for producing graphene in a predetermined chamber to form graphene on a surface of a copper plated layer of the rolled copper foil for producing graphene; and laminating a transfer sheet on the surface of the graphene, and etching and removing the copper foil for producing graphene while transferring the graphene to the transfer sheet.
According to the present invention, there can be provided a rolled copper foil being capable of producing graphene having a large area with low costs.
Hereinafter, a rolled copper foil for producing graphene according to an embodiment of the present invention will be described. The symbol “%” herein refers to % by mass, unless otherwise specified.
As the rolled copper foil, tough pitch copper (TPC) in accordance with JIS-H3100 (alloy number: C1100) or oxygen free copper (OFC) in accordance with JIS-H3510(alloy number: C1011) or JIS-H3100(alloy number: C1020) can be used. By using the TPC or OFC, the copper foil has a relatively high purity and is likely to have a predetermined crystal orientation as described later.
When the copper foil has a high purity of exceeding 99.999%, the copper foil is softened at normal temperature, has a rolling texture to be controlled with difficulty and is unlikely to have a predetermined crystal orientation as described later.
In addition, to the tough pitch copper or the oxygen free copper, a composition containing 0.050% by mass or less of one or more of elements selected from the group consisting of Sn and Ag can be used. When the above-described elements are contained, the copper foil can have improved strength and adequate elongation, and the grain size can be increased. If a content percentage of the above-described elements exceeds 0.050% by mass, the strength may be further increased, but the elongation may be decreased to degrade workability and the crystal orientation may be inadequate. More preferably, the content percentage of the above-described elements is 0.04% by mass or less. Further preferably, the content percentage of the above-described elements is 0.03% by mass or less. Most preferably, the content percentage of the above-described elements is 0.02% by mass or less.
Although a lower limit of the content percentage of the above-described elements is not especially limited, the lower limit may be 0.0001% by mass, for example. If the content percentage of the above-described elements is less than 0.0001% by mass, the content percentage may be difficult to be controlled. Preferably, the lower limit of the element content percentage is 0.0010% by mass or more, more preferably 0.003% by mass or more, further preferably 0.004% by mass or more, and most preferably 0.005% by mass or more. One or more elements selected from the group consisting of Ag, Sn, Ni, Si, P, Mg, Zr, Cr, Mn, Co, Zn, Ti, B and V may be added so long as the crystal orientation is not significantly affected (for example, 0.05% by mass or less). However, the elements added are not limited thereto.
The thickness of the copper foil is not especially limited, but is generally 5 to 150 μm. Preferably, the thickness of the copper foil base is 12 to 50 μm for ease of etching and removal as described later while assuring handleability. If the thickness of the copper foil base is less than 12 μm, it may be easily broken and have less handleability. If the thickness exceeds 50 μm, etching and removal may be difficult.
As shown in
When the thickness of the copper foil and the oil film equivalent satisfy the above-described relational expression, the rolled copper foil will have the predetermined crystal orientation as described below.
The present inventors have reviewed a factor to uniformly grow graphene on the rolled copper foil and have found that controlling the rolling texture is important.
In other words, in the rolled copper foil for producing graphene of the present invention, a ratio (IC/IA) of a maximum value of a detected intensity (IC) at α=15 degrees and β=90 degrees±2 degrees and a maximum value of a detected intensity (IA) at α=70 degrees and β=0 degree±2 degrees is less than 1, and a ratio (ID/IB) of a maximum value of a detected intensity (ID) at α=15 degrees and β=270 degrees±2 degrees and a maximum value of a detected intensity (IB) at α=70 degrees and β=180 degrees±2 degrees is less than 1, shown in the {111} pole figure.
The (IC/IA) and (ID/IB) are each preferably 0.99 or less, more preferably 0.98 or less, further preferably 0.95 or less, still preferably 0.90 or less, and most preferably 0.85 or less.
The lower limit of the (IC/IA) is not especially limited, but is 0.001 or more, 0.01 or more, 0.05 or more, 0.1 or more or 0.2 or more. Also, the lower limit of the (ID/IB) is not especially limited, but is 0.001 or more, 0.01 or more, 0.05 or more, 0.1 or more or 0.2 or more.
In view of the above, in the rolled copper foil for producing graphene according to the present invention, the values of the IC and ID that are generally highest intensities are lower than the values of the IA and IB that are lowest intensities. In this manner, the detected intensity can be close to the uniform value irrespective of α or β and does not have a peak at the specific α or β and the specific crystal orientation of the copper foil that inhibits graphene from growing can be decreased.
Furthermore, the above-described IA is preferably 1 or more and the above-described IB is preferably 1 or more. In the {111} pole figure of the rolled copper foil, by controlling the values of the IA and IB, which generally have the lowest intensity, to 1 or more, the detected intensity will be closer to a uniform value irrespective of α or β and does not have a peak at the specific α or β. It is thus contemplated that an atomic arrangement on the surface of the copper foil becomes optimum for growing graphene.
The IA is preferably 1.5 to 7.3, more preferably 2.5 to 7.0, further preferably 2.7 to 6.5 and most preferably 2.7 to 6.0. When the value of the IA is within the aforementioned preferable range, graphene tends to have a low sheet resistance.
The IB is preferably 1.5 to 8.0, more preferably 2.0 to 7.9, further preferably 2.5 to 7.8 and most preferably 3.0 to 7.8. When the value of the IB is within the aforementioned preferable range, graphene tends to have a low sheet resistance.
The {111} pole figure is measured for the surface of the copper foil by a reflection method using an X ray diffractometer. If an incident angle of X rays is shallow to a sample surface, it is difficult to measure in the reflection method. In fact, a measurable angle range is 0°<=α<=75°, 0°<=β<=360° (where α: an axis perpendicular to a rotational axis of a diffraction goniometer specified in the Schultz method, β: an axis parallel to the rotational axis) on the pole figure.
By defining the state having no texture (i.e., the crystal orientation is random) as 1, the intensity of the texture on the pole figure is standardized. By defining the crystal orientation is random, the {111} pole figure of a copper powder sample is measured and is defined as 1.
60 degree gloss (JIS Z8741) of the copper foil surface is 130% or more both in a rolling direction and a transversal direction.
As described later, after graphene is produced using the rolled copper foil for producing graphene according to the present invention, the graphene is needed to be transferred from the copper foil to the transfer sheet. It is found that when a surface of the copper foil is rough, it is difficult to transfer the graphene, and the graphene is broken. It is preferable that the surface irregularity of the copper foil is smooth.
An upper limit of the 60 degree gloss in a rolling direction or a transversal direction is not especially limited. When it is less than 500%, the production conditions such as rolling reduction ratio may not strictly specified upon the production of the copper foil substrate, which is preferable in that degree of freedom in the production is high. Practically, the upper limit of the 60 degree gloss in a rolling direction and a transversal direction is about 800%.
In addition, in order to ease the transfer of the graphene to the transfer sheet, the surface of the copper foil in the rolling direction has an arithmetic mean roughness Ra of preferably 0.20 μm or less.
Using the rolled copper foil for producing graphene as specified above, the large-area graphene can be produced at low costs and a high yield.
<Production of Rolled Copper Foil for producing Graphene>
The rolled copper foil for producing graphene according to the embodiment of the present invention can be produced as follows, for example: Firstly, a copper ingot having a predetermined composition is produced, is hot rolled and cold rolled, and is then annealed and cold rolled repeatedly to provide a rolled sheet. The rolled sheet is annealed to be re-crystallized, and finally cold rolled to the predetermined thickness, thereby providing a copper foil substrate.
Here, in the final cold rolling, the oil film equivalent at the final pass and the oil film equivalent at the previous pass before the final pass satisfy the above-described relationship against the thickness of the final rolled copper foil (see
When the rolled copper foil has the predetermined crystal orientation, it is contemplated that graphene growth is promoted on the surface of the rolled copper foil.
The oil film equivalent is represented by the following equation:
Oil film equivalent={(rolling oil viscosity,kinetic viscosity at 40° C. [cSt])×(rolling speed [mpm]+roll circumferential speed [mpm])}/{(roll angle of bite [rad])×(yield stress of material [kg/mm2])}.
In order to lower the oil film equivalent, known methods may be used, e.g., rolling oil having low viscosity is used, or the rolling speed is decreased.
Next, referring to
First, the above-described rolled copper foil 10 for producing graphene of the present invention is placed in a chamber (such as a vacuum chamber) 100 and is heated by a heater 104. At the same time, the pressure in the chamber 100 is reduced or the chamber 100 is vacuum-evacuated. Then, a carbon-containing gas G and a hydrogen gas are fed to the chamber 100 through a gas supply inlet 102 (
Then, the rolled copper foil 10 for producing graphene is cooled to normal temperature, a transfer sheet 30 is laminated on the surface of the graphene 20, and the graphene 20 is transferred to the transfer sheet 30. Next, the laminate is continuously immersed into an etching tank 110 via a sink roll 120, and the rolled copper foil 10 for producing graphene is removed by etching (
In addition, the laminate from which the rolled copper foil 10 for producing graphene is removed is pulled up, and a substrate 40 is laminated on the graphene 20. While the graphene 20 is transferred to the substrate 40, the transfer sheet 30 is removed, whereby the graphene 20 laminated on the substrate 40 can be produced.
As the transfer sheet 30, a variety of resin sheets (a polymer sheet such as polyethylene, polyurethane etc.) can be used. As an etching liquid for etching and removing the rolled copper foil 10 for producing graphene, a sulfuric acid solution, a sodium persulfate solution, a hydrogen peroxide and sodium persulfate solution, or a solution where sulfuric acid is added to hydrogen peroxide can be, for example, used. As the substrate 40, an Si, SiC, Ni or Ni alloy can be, for example, used.
Each cooper ingot having a composition shown in Table 1 was prepared, was hot rolled, was cold rolled, and was annealed in an annealing furnace set at the temperature of 300 to 800° C. and cold rolled repeatedly to provide a rolled sheet having a thickness of 1 to 2 mm. The rolled sheet was annealed and re-crystallized in the annealing furnace set at the temperature of 300 to 800° C., and was finally cold rolled to a thickness shown in Table 1 to provide a copper foil.
Here, the oil film equivalents were adjusted to the values shown in Table 1 both at a final pass of the final cold rolling and a previous pass before the final pass of the final cold rolling.
The oil film equivalent is represented by the following equation:
(Oil film equivalent amount)={(rolling oil viscosity, kinetic viscosity at 40° C., cSt)×(rolling speed; m/min)}/{(yield stress of material; kg/mm2)×(roll angle of bite; rad)}
The 60 degree gross of each copper foil surface after the final cold rolling in Examples and Comparative Examples was measured. The 60 degree gross were measured using a gloss meter in accordance with JIS-Z8741 (trade name “PG-1 M” manufactured by Nippon Denshoku Industries Co., Ltd.) In Table, G60RD and G60TD represent 60 degree gloss in a rolling direction and a transversal direction, respectively.
The surface roughness Ra of each copper foil in Examples and Comparative Examples after the final cold rolling was measured.
The surface roughness Ra was measured as an arithmetic mean roughness (Ra; μm) in accordance with JIS-B0601 using a contact roughness meter (trade name “SE-3400” manufactured by Kosaka Laboratory Ltd.). Under the conditions of a measurement sampling length of 0.8 mm, an evaluation length of 4 mm, a cut off value of 0.8 mm and a feed rate of 0.1 mm/sec, ten measurements were done in parallel with a rolling direction at different measurement positions, and values for ten measurements were averaged.
The {111} pole figure was measured for the surface of each copper foil in Examples and Comparative Examples after the final cold rolling by a reflection method using an X ray diffractometer (RINT 2500 manufactured by Rigaku Corporation). If an incident angle of X rays is shallow to a sample surface, it is difficult to measure in the reflection method. In fact, a measurable angle range is 0°<=α<=75°, 0°<=β<=360° (where α: an axis perpendicular to a rotational axis of a diffraction goniometer specified in the Schultz method, β: an axis parallel to the rotational axis) on the pole figure.
By defining the state having no texture (i.e., the crystal orientation is random) as 1, the intensity of the texture on the pole figure was standardized. By defining the crystal orientation was random, the {111} pole figure of a copper powder sample was measured and was defined as 1.
As the X-ray irradiation conditions, a Cu tube was used, a tube voltage was 40 kV and a tube current was 100 mA. By the Schultz reflection method, the {111} pole figure was measured.
The rolled copper foil for producing graphene (horizontal and vertical 100×100 mm) in each Example was placed in a vacuum chamber, and heated at 1000° C. Under vacuum (pressure: 0.2 Torr), hydrogen gas and methane gas were fed into the vacuum chamber (fed gas flow rate: 10 to 100 cc/min), the copper foil was heated to 1000° C. for 30 minutes and held for 1 hour to grow graphene on the surface of the copper foil.
In each Example, graphene was tried to be produced ten times under the above-described conditions, a sheet resistance of graphene was measured and a manufacturing yield of graphene was evaluated.
The resistance value (sheet resistance: Ω/sq) of graphene was measured by a four terminal method after transferring graphene on the surface of the copper foil in the above-described ten samples to a PET film and the average value was determined. When the resistance value of graphene is 600 Ω/sq or less, there is no practical problem.
The manufacturing yield of graphene was evaluated by observing graphene on the surface of the copper foil in the above-described ten samples by the atomic force microscope (AFM). When scale-like irregularities were observed on the whole surface by the AFM, graphene might be produced. Based on the number of times of the graphene production when graphene was tried to be produced ten times, a yield was evaluated by the following rating: The rating “Good” may not have practical problems.
Good: Graphene was produced four times or more, when graphene was tried to be produced ten times
Bad: Graphene was produced three times or less, when graphene was tried to be produced ten times
Table 1 shows the obtained result.
As apparent from Table 1, in each of Examples where the (IC/IA) and (ID/IB) were less than 1, the sheet resistance of graphene was low and the manufacturing yield of graphene was excellent. In addition, in each of Examples, the detection intensities IA and IB were 1 or more.
On the other hand, in each of Comparative Examples where the oil film equivalent and the thickness at the final cold rolling were outside of the range in the above-described relational expression, the (IC/IA) and (ID/IB) was 1 or more, the sheet resistance of graphene was high and the manufacturing yield of graphene was poor.
In Comparative Example 1, the IA and IB were less than 1. The reason is unclear, but it is presumed that the oil film equivalent is extremely low and the thickness of the copper foil is relatively thin, so that the crystal orientation that inhibits the growth of graphene is significantly grown.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-180590 | Aug 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/068636 | 7/8/2013 | WO | 00 |
