Patent Application
20080081178
Hereinafter, preferred embodiments of the present invention are described with reference to the drawings. Incidentally, a redundant description is avoided as for elements each having substantially the same functional constitution are respectively identified by the same reference numerals in the present specification and the drawings.
A manufacture of a transparent conducting film is started.
Fluid material containing transparent conducting particles is prepared. In the present embodiment, dispersion liquid as the fluid material is prepared by dispersing indium oxide containing Sn (tin) (In2O3 (called also as ITO)) into an alcoholic solvent as the transparent conducting particles. Incidentally, it is preferable that a particle size of the transparent conducting particle is 100 nm or less.
For example, In2O3 containing Zn (IZO), In2O3 containing F (FTO), SnO2 containing Sb (ATO), ZnO, ZnO containing Al (AZO), ZnO containing Ga (GZO), CdSnO3, Cd2SnO4, TiO2, CdO, and so on may be used as the transparent conducting particles other than In2O3 containing Sn (ITO). Besides, they may be used independently, or two or more kinds may be combined arbitrary. It is preferable to use metal oxide of which main constituent is In or Sn among them to consist with conductivity and transparency.
When the transparent conducting fine particles are composed of In and Sn, it is preferable that a content of Sn is made to be 20 wt % or less. This is because resistance deteriorates caused by a scattering of a carrier if an amount of Sn included in the transparent conducting fine particles becomes large. Besides, it is more preferable that the content of Sn is from 5 wt % to 15 wt %. This is because the resistance deteriorates caused by decreased carrier density if the amount of Sn included in the transparent conducting fine particles is too small.
Besides, it is preferable that weight ratio of the transparent conducting fine particles relative to the fluid material is set to 5 wt % to 50 wt %. It is more preferable to be set to 10 wt % to 40 wt %. This is because there is a possibility that film thickness of a coating film becomes nonuniform when the fluid material is coated on the substrate at a later-described step 2 because viscosity of the fluid material becomes too small if the weight ratio of the transparent conducting fine particles relative to the fluid material is too small. Besides, if the weight ratio of the transparent conducting fine particles relative to the fluid material becomes too large, there is a possibility that a dispersion stability of the fine particles deteriorates to thereby lower the film density after the film is coated.
The fluid material prepared in the above-stated step 1 is coated on the substrate. In the present embodiment, the dispersion liquid as the fluid material is coated on a polymer film as an example of a transparent substrate. As the transparent substrate, for example, cellulose triacetate, cellulose diacetate, nitrocellulose, polystyrene, polyethylene terephthalate, polyethylene naphthalate, polyimide, and so on can be used as the material. It is preferable to use polyethylene terephthalate which is superior in transparency and cheep among them.
In the present embodiment, the film coating is performed by coating the ITO dispersion liquid as the fluid material on the polymer film by using an applicator of 3 μm. As a method of coating the fluid material on the substrate, a publicly known method such as, for example, a roll coat, screen printing, spray coat, dip coat, and spin coat can be used in addition to the method using the applicator.
The coating film coated on the substrate is dried. As dry temperature, it is preferable to set to a softening point or less of the polymer film used as the substrate. Concretely speaking, for example, it is preferable that the dry temperature is set at 80° C. or less when polyethylene terephthalate (PET) is used as the film.
Pressure is added to the coating film. In the present embodiment, the pressure is added to a surface of a coating film 2 so that density of the coating film 2 is to be 3.0 g/cm3 or more by using a roll press 1 of which schematic side view is shown in
In the present embodiment, a line pressure of the roll press 1 is set to be 200 kg/cm or more. Accordingly, the pressure is added to the coating film 2 by using the roll press 1, and it becomes possible such that the density of the coating film 2 is to be 3.0 g/cm3 or more. As stated above, the roll press 1 is applied to the coating film 2, and thereby, a contact between particles becomes good and the film density increases. At the same time, a coating film surface becomes smooth, and thereby, the visible light transmittance and visual transparency of the manufactured transparent conducting film improve spectacularly. Incidentally, as a method adding the pressure to the coating film 2, a publicly known pressure means such as, for example, a sheet press may be used in addition to the method using the roll press 1 as stated above.
An electromagnetic wave is irradiated to the coating film, and the transparent conducting fine particles of the coating film are sintered, to thereby form the transparent conducting film. In the present embodiment, for example, a microwave is used as the electromagnetic wave. In this case, it is possible to make the resistance after the microwave burning small if the density of the coating film is set to a large value, because the contacts between the transparent conducting fine particles with each other become frequent and the sintering is accelerated. For example, the density of the coating film is set to be 3.0 g/cm3 or more to make the resistance after the microwave burning to be less than 102Ω/□ (sheet resistance).
In the present embodiment, the microwave with a frequency of 2.45 GHz is irradiated to the coating film at 1000 W for 10 minutes as the electromagnetic wave. In this case, dielectric loss of the polymer film used as the substrate is small, and therefore, an absorption does not occur even if the microwave is irradiated, and the polymer film is not heated. On the contrary, dielectric loss of the coating film of oxide applied on the polymer film is large, and therefore, the heat is generated by irradiating the microwave. It is possible to selectively heat only the coating film on the polymer film by using the above. Besides, the oxide coating film has a microwave high-speed responsiveness, and therefore, it is possible to easily control arrival time to required temperature by means of heating time and output adjustment.
In the present embodiment, the polymer film 10 on which the coating film 2 is applied is mounted on a conductive foamed sheet 11 such as, for example, a foamed Ni sheet, as shown in
A manufacture of the transparent conducting film on the polymer film being the substrate is completed by the above-stated steps 1 to 5.
According to the embodiment as stated above, a coating film is formed by coating fluid material containing transparent conducting fine particles on a substrate, an electromagnetic wave is irradiated to this coating film after pressure is added, when the transparent conducting film is manufactured, and thereby, a sintering between the transparent conducting fine particles constituting the coating film can be accelerated. Consequently, it becomes possible to manufacture a transparent conducting film having lower resistance and good visible light transmittance and visual transparency compared to a transparent conducting film manufactured by a conventional publicly known manufacturing art of the transparent conducting film coating fluid material containing transparent conducting fine particles on a substrate. In particular, when the coating film is pressurized so that the film density of the coating film becomes 3.0 g/cm3 or more, the low resistance is more accelerated, and it becomes possible to make the resistance very low. Accordingly, it becomes possible to manufacture the transparent conducting film having a characteristic equivalent or more than the transparent conducting film manufactured by using the physical method such as the spattering method at a low price by using the manufacturing method of the transparent conducting film according to the procedure coating the fluid material containing the transparent conducting fine particles on the substrate.
In particular, when indium oxide containing tin of which particle size is 100 nm or less is used as the transparent conducting fine particles, it becomes possible to manufacture the transparent conducting film having a very high visual transparency without generating a scattering of light inside of the coating film. Besides, the particle size is made small, and thereby, it becomes possible to fully enlarge the film density when the pressure is added to the coating film by using, for example, a roll press, the sintering between particles is appropriately accelerated when the microwave is irradiated. Accordingly, it becomes possible to further lower the resistance of the manufactured transparent conducting film.
Further, when the roll press 1 shown in
Besides, the conductive foamed sheet is grounded to the transparent conducting fine particle film when the microwave is irradiated to the coating film, and thereby, it is possible to suppress discharge, and to avoid a damage such that the substrate being, for example, the polymer film and so on is melted, or the like. Further, there also is an effect to prevent a damage of the substrate because the coating film and the substrate become locally high temperature.
The preferred embodiment of the present invention is described with reference to the attached drawings hereinabove, but the present invention is not limited to the above-stated example. It is obvious that those in the art may reach various modified examples or adjusted examples within a category of a technical idea described in claims, and it should be understood that those examples also obviously belong to the technical range of the present invention.
In the above-stated embodiment, a case when the fluid material containing the transparent conducting particles is the dispersion liquid is described, but the fluid material containing the transparent conducting particles may be, for example, semi-liquid, paste, melt, solution, dispersion liquid, suspension, granular material, or the like. Besides, as a method to make the fluid material into a coating medium, methods such as a boll mill, beads mill, sand grinder, and paint shaker can be used. As a solvent to which the transparent conducting particles are mixed when the fluid material is prepared, for example, solvents such as water, alcohol, ketone, ether, and ester can be used. Besides, a surface active agent, binder, and so on may be added in some cases.
In the above-stated embodiment, a case is described when the transparent substrate to which the fluid material is coated is a polymer film in which, for example, cellulose triacetate, cellulose diacetate, nitrocellulose, polystyrene, polyethylene terephthalate, polyethylene naphthalate, polyimide, and so on are used as the material. However, the transparent substrate to which the fluid material is coated may be a polymer film of which material is other than the above, and it may be the one other than a polymer film. Besides, the substrate to which the fluid material is coated is not necessarily be transparent.
In the above-stated embodiment, a case is described when the microwave of 2.45 GHz is irradiated at 1000 W for ten minutes as the electromagnetic wave, but the frequency of the electromagnetic wave to be irradiated may be 1 GHz to 1 THz. Besides, irradiation input power of the microwave may be other values such as, for example, 500 W to 1000 W. Irradiation time of the microwave is preferable to be, for example, 1 minute to 10 minutes because it may cause a damage on the substrate resulting from the heat transmitted thereto if the irradiation time becomes long.
In the above-stated embodiment, a case is described when the foamed Ni sheet is used as the conductive foamed sheet 11. However, a sheet constituted by arbitrary material having good electronic conductivity, and heat release performance may be used as the conductive foamed sheet 11.
In the above-stated embodiment, a case is described when the irradiation of the electromagnetic wave to the coating film 2 shown in
The present invention is described by using examples and comparative examples.
In a Table 1 shown in
The characteristics of the respective data shown in the Table 1 are measured as stated below.
BET particle size (nm)=6/(ρ×specific surface area)×109
(film density)={(substrate weight to which the coating film is applied)−(substrate weight)}/{(area of coating film)×(film thickness of coating film)}
Next, respective conditions when the transparent conducting film is manufactured are described as for the respective data (examples 1 to 6 and comparative examples 1 to 4) shown in the above-stated Table 1.
The data of the example 1 show the respective characteristics of the transparent conducting film manufactured by the following procedure by using the manufacturing method of the present invention. At first, ITO powder (BET particle size of 30 nm) 7.5 g containing SnO2 15 wt % as the transparent conducting particles is mixed with alcoholic solvent 17.5 g and an anionic surface active agent 0.225 g, then they are rotated for 30 minutes at 300 rpm by a planetary ball mill (P-5 type, manufactured by Friche, container capacity of 80 ml, beads PSZ 0.3 mm), to thereby prepare dispersion liquid as the fluid material. The ITO dispersion liquid with ITO content of 30 wt % obtained as stated above is coated on a PET film (Lumirror 100T, manufactured by Toray Co., Ltd., haze of 1.5%, total light transmittance of 89%) as the substrate by an applicator (film transportation speed of 5 m/min), and it is dried at the temperature of 80° C. After that, this PET film is pressurized with the line pressure of 200 kg/cm by using the roll press (film transportation speed of 2.5 m/min) shown in
The data of the example 2 show the respective characteristics of the transparent conducting film manufactured by a similar procedure to the case of the data of the example 1 except that the microwave irradiation is performed at 500 W.
The data of the example 3 show the respective characteristics of the transparent conducting film manufactured by the similar procedure to the example 1 except that the time of the microwave irradiation is for 5 minutes.
The data of the example 4 show the respective characteristics of the transparent conducting film manufactured by a similar procedure to the example 2 except that the time of the microwave irradiation is for 5 minutes.
The data of the example 5 show the respective characteristics of the transparent conducting film manufactured by the similar procedure to the example 1 except that the line pressure of the roll press is set to 300 kg/cm.
The data of the example 6 show the respective characteristics of the transparent conducting film manufactured by the similar procedure to the example 2 except that the line pressure of the roll press is set to 300 kg/cm.
The data of the comparative example 1 show the respective characteristics of the transparent conducting film manufactured by the following procedure by using the conventional publicly known manufacturing method. Namely, the transparent conducting film of the comparative example 1 is a film in which the dispersion liquid prepared by the similar procedure to the example 1 is coated on the substrate by the applicator, and it is dried at 80° C. The film is manufactured without performing neither the roll press nor the microwave burning after that. Incidentally, the film density of this transparent conducting film is 2.6 g/cm3.
The data of the comparative example 2 show the respective characteristics of the transparent conducting film manufactured by the following procedure by using the conventional publicly known manufacturing method. Namely, the transparent conducting film of the comparative example 2 is manufactured by coating the dispersion liquid prepared as same as the case of the example 1 on the substrate by the applicator, drying at 80° C., and performing the roll press after that, but without performing a microwave process.
The data of the comparative example 3 show the respective characteristics of the transparent conducting film manufactured by the following procedure by using the conventional publicly known manufacturing method. Namely, the transparent conducting film of the comparative example 3 is manufactured by coating the dispersion liquid prepared as same as the case of the example 1 on the substrate by the applicator, drying at 80° C., and after that, irradiating the microwave at 1000 W for 10 minutes without performing the roll press.
The data of the comparative example 4 show the respective characteristics of the transparent conducting film manufactured by the following procedure by using the conventional publicly known manufacturing method. Namely, the transparent conducting film of the comparative example 4 is manufactured by coating the dispersion liquid prepared as same as the case of the example 1 on the substrate by the applicator, drying at 80° C., after that, performing the roll press, and heating at 100° C. in an electric furnace under the nitride atmosphere.
As shown in the data of the examples 1 to 6 in the above-stated Table 1, in case of the transparent conducting film manufactured by using the manufacturing method of the present invention, the coating film is formed by coating the fluid material containing the transparent conducting particles on the substrate, the pressure is added to the coating film by using the roll press, and thereafter, the sintering of the transparent conducting particles is accelerated by irradiating the microwave. As a result, it can be seen that the surface resistance of less than 100Ω/□ is realized, which is drastically lower than the values of the surface resistances of from 650Ω/□ to 20000Ω/□ of the transparent conducting films manufactured by using the conventional publicly known manufacturing method as shown by the data of the comparative examples 1 to 4 in the above-stated Table 1. Incidentally, as shown by the data of the comparative examples 1 and 3, it can be seen that the film density of the transparent conducting film is very small to be 2.6 (g/cm3), and thereby, the surface resistance of the manufactured transparent conducting film becomes very large when the pressure is not added to the coating film at the time of manufacturing.
Incidentally, in the examples 1 to 6 of the above-stated Table 1, the burning is performed by using the foamed Ni sheet, and therefore, the discharge is prevented and the burning can be performed without damaging the film. On the contrary, when the microwave irradiation is performed without spreading the foamed Ni sheet, there is a possibility that the coating film becomes locally high temperature and disappeared caused by the discharge. Accordingly, it is preferable that a conductive foamed sheet such as the foamed Ni sheet is to be spread when the microwave irradiation is performed.
Further, as shown by the data of the examples 1 to 6 of the above-stated Table 1, the total light transmittances of the manufactured transparent conducting films become 85% or more, and these values are the same as or more than the total light transmittances of 74.7% to 86.4% of the transparent conducting films manufactured by using the conventional publicly known manufacturing method shown by the data of the comparative examples 1 to 4, and it can be seen that the transparent conducting film manufactured by the manufacturing method of the present invention is superior in the visible light transmittance. Besides, as shown by the data of the examples 1 to 6 of the above-stated Table 1, the haze of the manufactured transparent conducting films are 1.5% to 1.8%, and these values are the same as or less than the haze of the transparent conducting films of 1.7% to 12.5% manufactured by the conventional publicly known manufacturing method shown by the data of the comparative examples 1 to 4, and it can be seen that the transparent conducting film manufactured by the manufacturing method of the present invention keeps a high visual transparency.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-268908 | Sep 2006 | JP | national |
