Patent Grant
10217386
The present invention relates to a light-transmitting substrate having a function of raising surface temperature thereof.
Signs having a snow-melting function for preventing degradation of visibility of the signs due to adhesion of snow are disclosed in Patent document 1, and so forth. The sign disclosed in Patent document 1 has a structure that a snow-melting unit is disposed on a surface of an LED display comprising a plurality of LEDs disposed in the form of matrix. The surface of the LED display is covered with an acrylic resin plate. The snow-melting unit has a configuration that two of acrylic resin plates other than that of the LED display are facingly disposed with a metal frame between them, and a heater in the form of cord is disposed in the internal space, and the sign has a configuration that this snow-melting unit is adhered to the acrylic resin plate on the surface of the LED display. When the heater is electrified, air in the internal space of the snow-melting unit is heated by the Joule heat generated by the heater and heat accompanying molecular motions caused by emitted far-infrared rays, and the acrylic resin plate is heated by the air. As a result, snow adhered to the acrylic resin plate can be melted.
The snow-melting unit disclosed in Patent document 1 has a configuration that an internal space is formed by facingly disposed two of acrylic resin plates, air in the internal space is heated with the heater, and the acrylic resin plate is heated with the air. However, since both air and acrylic resin plate have a low thermal conductivity (about 0.17 to 0.25 W/mK at ordinary temperature), and therefore they cannot efficiently conduct the heat generated by the heater to the surface of the acrylic resin plate. Therefore, it is difficult to obtain high thermal conduction efficiency with this unit, and electric power required for melting snow becomes large. In addition, since the internal space is formed by facingly disposed two of the acrylic resin plates with the frame between them, the sign requires members that do not directly relate to display of the sign, and thickness of the snow-melting unit becomes larger. Further, since it employs the structure that the internal space is formed, rigidity is required for the acrylic resin plates, and therefore even if it is desired to make the acrylic resin plates of the snow-melting unit thinner in order to improve the thermal conduction efficiency, and obtain a thinner unit, it is difficult to do so more than a certain extent. Furthermore, since the unit suffers from low thermal conduction efficiency, and requires much electric power for melting snow, it is necessary to use a heater having a diameter larger than a certain extent, and thus it becomes difficult to see the sign displayed on the LED display through the snow-melting unit.
An object of the present invention is to provide a thin light-transmitting substrate showing high thermal conduction efficiency, and having a function of raising temperature of the surface thereof.
In order to achieve the aforementioned object, the light-transmitting substrate of the present invention comprises a substrate that transmits at least a light of a predetermined wavelength, and a conductor pattern that is disposed on the substrate, and generates heat to raise temperature of the surface of the substrate when an electric current is supplied. The conductor pattern is directly disposed on the substrate without any adhesive layer.
According to the present invention, there can be obtained a light-transmitting substrate that can be made thin in spite of having the function of raising the surface temperature, and shows high thermal conduction efficiency.
Hereafter, embodiments of the present invention will be explained with reference to the drawings.
The light-transmitting substrate of the first embodiment will be explained. This light-transmitting substrate is disposed on such an article as a device that emits light from the inside to the outside of the device, transparent article in which light transmits at least the outermost surface layer thereof, and mirror, so that the substrate constitutes the outermost surface, and has a function of evaporating or melting moisture or snow adhering to the surface.
A sectional view of a light-transmitting substrate of this embodiment is shown as
An adhesive layer used for adhering a conductor pattern to a substrate, such as an adhesive layer made from epoxy resin or acrylic resin, generally contains air, and therefore shows low thermal conductivity. However, according to this embodiment, the conductor pattern 43 is directly disposed on the substrate 10 without any adhesive layer, and therefore heat generated by the conductor pattern 43 can be highly efficiently conducted to the substrate 10. Therefore, snow or moisture adhering to the substrate 10 can be melted or evaporated with reduced electric power to be supplied to the conductor pattern.
Such a conductor pattern 43 can be formed by, for example, sintering conductive particles. Specifically, it can be formed by sintering conductive particles placed on the substrate 10 with light. The conductor constituting the conductor pattern 43 can be thereby adhered to the substrate 10 at the interface of the conductor pattern 43 and the substrate 10. The sintering method is not limited to sintering with light, and any other sintering method may be used so long as a method that can sinter conductive particles and adhere them to the substrate 10 is chosen. For example, a method of irradiating electromagnetic waves, and a method of locally flowing an electric current can be used.
The conductor pattern 43 is desirably a porous member containing voids 40a in the inside thereof, as shown in
The substrate 10 may be made of any material, and for example, one made of a resin can be used.
The substrate 10 may also have a configuration that it contains a base material that transmits light of a predetermined wavelength, and a filler dispersed in the base material. In such a case, by using a material showing a thermal conductivity higher than that of the base material as the filler, thermal conductivity of the substrate can be improved. For example, a silicone resin can be used as the base material, and silica having a particle diameter of several nanometers to several tens of micrometers can be used as the filler.
As the shape of the conductor pattern 43, any desired shape such as line, grid, and circle can be used, as top views and sectional views of examples thereof are shown in
The conductor pattern 43 may also have a configuration that it has a region constituted with a conductor material different from that of another region. For example, if the conductor pattern 43 of a region of which temperature is desired to be made higher than that of the other region is formed with a conductor material having a larger electric resistance in the substrate 10, calorific value thereof can be made higher.
It is desirable that, for at least a part of the conductor pattern 43, the surface thereof not contacting with the substrate 10 is a curved surface. For example, a conductor pattern 43 having a section of semicircle shape, or a conductor pattern 43 having an R-shaped end can be used. By using a conductor pattern having such a curved surface, the area that does not contact with the substrate 10 can be reduced compared with, for example, the case of using a conductor pattern having a rectangular section, therefore heat radiation from the surface not contacting with the substrate 10 can be reduced, and a larger amount of heat can be conducted to the substrate 10. If adhesion of moisture is not good for the base material of the substrate, the surface to which snow or moisture adheres may be protected by providing a coating film or the like thereon.
The method for producing the light-transmitting substrate of the first embodiment will be explained with reference to
First, as shown in
Then, as shown in
As described above, temperature of the conductive particles in the region of the film 41 irradiated with the light flux 12 rises due to the irradiation of light. This heat is used for sintering of the conductive particles, and at the same time, it conducts to the surrounding portions of the film 41 and the substrate 10, and radiated. Therefore, temperature of only the region of the film 41 irradiated with the light flux 12, or only the region irradiated with the light flux 12 and adjacent regions thereof reaches the temperature at which the conductive particles are sintered, and temperature of the film 41 of a part outside the aforementioned region and temperature of the substrate 10 do not reach the temperature at which the materials constituting them are melted or denatured.
That is, according to this embodiment, only a part of the film 41 is irradiated with the light flux 12, therefore heat can be conducted to the substrate 10 and the surrounding part of the film 41, and radiated, and temperature rise of the substrate 10 can be suppressed. Accordingly, even if the substrate 10 consists of a material that is easily deformed by heat such as a thin and flexible resin material, deformation, distortion, and denaturation such as opacification of the substrate possibly caused by the light sintering can be prevented. In addition, when the substrate 10 is flexible, the flexibility can be maintained.
In the step of
In other words, when the sintering is performed in the film 41 with the light flux 12 of laser light, a porous conductor pattern 43 can be formed by adjusting irradiation intensity of the light flux 12 so that the film 41 should have an appropriate temperature. Specifically, by using a stretched polyethylene terephthalate (PET) film (melting point, about 250° C.; heatproof temperature, about 150° C.) as the substrate 10, and irradiating the substrate 10 with the light flux 12 of laser light from the back surface of the substrate 10 with adjusting the intensity of the light flux so that shape of the substrate is maintained to sinter the conductive particles in the film 41, the porous conductor pattern 43 can be formed.
If the conductor pattern 43 is porous, the conductor pattern 43 itself has shape-following property (flexibility) as described above. Therefore, even if the flexible substrate 10 is deformed, the conductor pattern 43 also deforms to follow the substrate, thus the conductor pattern 43 does not easily peel from the substrate 10, and cracks and so forth are not easily produced, either. As a result, there can be provided a flexible light-transmitting substrate that does not easily produce disconnection.
As for shape of the light flux 12 irradiated on the film 41 in the step shown in
By the steps explained above, the conductor pattern 43 can be formed on the substrate 10 through such easy steps as application and light irradiation.
In the step shown in
When there is a region of the film 41 that is not irradiated with the light, sintering does not occur in this region, and therefore the particles remain in a state of being not sintered. Such a portion of the film 41 in which the particles are not sintered may be removed in the following step. For example, such a portion of the film 41 can be removed by using an organic solvent or the like. For such a portion of the film 41, sintering can also be additionally performed by heating or the like.
The substrate 10 may consist of any material, so long as at least the surface thereof is insulating, it has such a translucency that irradiation of the light flux 12 through it is possible, and it can bear the temperature that the substrate 10 reaches at the time of irradiation of the light flux 12 on the film 41. There can be used, for example, organic materials such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), polystyrene (PS), polyimide, epoxy, silicone, glass/epoxy resin substrate, and paper/phenol resin substrate, and inorganic materials such as ceramics and glass. The substrate 10 may also consist of a flexible printed circuit board or a metal substrate of which surface is coated with an insulating layer, so long as at least a part of irradiated light can transmit through it. The substrate 10 in the form of a film can also be used.
As material of the conductive particles contained in the film 41, one or more kinds of conductive metals and conductive metal oxides of Au, Ag, Cu, Pd, Ni, ITO, Pt, Fe, and so forth can be used. As for particle size of the conductive particles, the conductive particles may consist only of nanoparticles having a particle size smaller than 1 μm, or a mixture of nanoparticles having a particle size smaller than 1 μm and microparticles having a particle size not smaller than 1 μm.
As the insulating material at least contained in the film 41, or the insulating material that coats the conductive particles contained in the film 41, there can be used one or more kinds of materials selected from organic materials such as styrene resin, epoxy resin, silicone resin, and acrylic resin, inorganic materials such as SiO2, Al2O3, and TiO2, and organic and inorganic hybrid materials. Thickness of the insulating material layer that coats the conductive particles in the film 41 is preferably about 1 nm to 10 μm. If the insulating material layer is unduly thin, the particles aggregate at the time of the application of ink, and therefore sintering temperature rises. If the insulating material layer is unduly thick, the electric conductivity of the conductor pattern 43 obtained after sintering by light irradiation is degraded, and thus resistance becomes higher.
The conductive particles and the insulating material, or the conductive particles coated with the insulating material layers are made into a dispersion to be applied in the step shown in
As for size of the conductor pattern 43, it can be formed to have, for example, a width of 1 μm or larger, and a thickness of about 1 nm to 10 μm. Electric resistivity of the conductor pattern 43 is desirably 10−4 Ω·cm or lower, particularly desirably such a low resistance as 10−6 Ω·cm order.
As the method for forming the film 41 in the step shown in
In the explanation of this embodiment described above, the film 41 on the substrate 10 is irradiated with the light flux 12 from above. However, if a substrate that can transmit the light flux 12 is used as the substrate 10, the light flux 12 may be transmitted through the substrate 10 and irradiated on the film 41.
In the above explanation of the first embodiment, the sintering of the particles in the film 41 is performed by irradiating the light flux. However, the same functions and effects can be obtained even by using a method other than light flux irradiation, if the method is a method that can supply energy to only a part of the film 41 to heat it. For example, a method of irradiating converged microwaves, or a method of contacting a needlelike probe with the film or bringing the same close to the film, and locally supplying electric current or electric power can be used.
According to this embodiment, there can be obtained a light-transmitting substrate that is thin and shows high thermal conduction efficiency, because it comprises only one substrate, and has a function of raising surface temperature thereof.
The light-transmitting substrate of the second embodiment will be explained.
In the light-transmitting substrate of the second embodiment, a light-emitting element 30 is mounted on the surface of the substrate 10 on which the conductor pattern 43 of the first embodiment is disposed, as shown in
As shown in
In the second embodiment, the shape of the conductor pattern 43 and the disposition of the light-emitting element 30 may be desired shape and disposition, as examples of top view and side view thereof are shown in
Further, as shown in
The shapes and configurations of the conductor pattern 43 other than those explained above are the same as those of the first embodiment, and therefore explanations thereof are omitted.
The method for producing the light-transmitting substrate of the second embodiment will be explained with reference to
First, in the steps shown in
As shown in
As shown in
When the conductor pattern 43 is formed also on the back surface of the substrate 10 via the through-hole 43b, the steps of
By the steps explained above, the conductor pattern 43 can be formed on the upper and lower surfaces of the substrate 10 through such easy steps as application and light irradiation, and a light-transmitting substrate mounting a light-emitting element 30 can be produced.
As the light-emitting element 30, any kind of light-emitting element may be used, and for example, LED, LD, and display devices (liquid crystal display device, plasma display device, EL display device, etc.) can be used. As LED, InGaN type LED that emits, for example, blue light (wavelength 460 nm), InGaN type LED that emits, for example, green light (wavelength 520 nm), and AlGaInP type LED that emits, for example, red light (wavelength 620 nm) can be used. The light-emitting element is not limited to those of these wavelengths, and any light-emitting element that emits ultraviolet light, visible light, infrared light, or the like may be used. It is also possible to mount a light-receiving element instead of the light-emitting element 30 to constitute a light-receiving device.
In the explanation of this embodiment described above, the film 41 on the substrate 10 is irradiated with the light flux 12 from above. However, the light flux 12 may be transmitted through the substrate 10 and irradiated on the film 41. According to this method, the formation of the conductor pattern 43 and connection between the light-emitting element 30 and the conductor pattern 43 can be simultaneously or successively performed by irradiation of the light flux 12, and it is not necessary to use bumps or the like. The electrode 31 and the conductor pattern 43 may also be connected by sintering conductive particles between them using a dispersion in which the conductive particles and an insulating material are dispersed, or a dispersion in which the conductive particles coated with an insulating material layer are dispersed, as in the case of the film 41.
The light-transmitting substrates of the first and second embodiments can be disposed on a display device, signal device, or illumination device so that the substrate constitutes the outermost surface. Snow and moisture adhering to these devices can be thereby, for example, evaporated. In these devices, the light-transmitting substrate is preferably disposed so that the surface opposite to the surface on which the conductor pattern 43 is disposed faces the outside.
Further, by facingly disposing the light-transmitting substrate 101 of the first embodiment, and the light-transmitting substrate 102 of the second embodiment carrying the light-emitting element 30 so that the surfaces on which the conductor patterns 43 are formed face each other as shown in
In the above explanations of the second and fourth embodiments, examples in which the light-emitting element 30 is flip-chip mounted are explained. However, as shown in
When a space is formed between the two substrates 10 as shown in
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