Transparent Planar Heater

Abstract

To provides a transparent planar heater with a high heat generation rate and a high maximum temperature.SOLUTION: A transparent planar heater 10 includes a transparent substrate 11, a heat generating layer 20 in which a first transparent conductive oxide layer 12, a metal layer 13, and a second transparent conductive oxide layer 14 are laminated in this order on the transparent substrate 11 from the transparent substrate 11 side, and a pair of electrodes 15 provided at both ends on the transparent substrate so as to sandwich the heat generating layer 20, and the specific resistance of the first transparent conductive oxide layer 12 and the second transparent conductive oxide layer 14 is 3.0×10-4 Ω cm or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a transparent planar heater. [Background technology]

[0002] Conventionally, defrosters using transparent conductive films have been used to prevent fogging and condensation on automobile windows, etc., and consideration has been given to providing transparent planar heaters to prevent a decrease in illuminance due to snow accumulation, freezing, and water droplets on the front cover of the light, etc. Also, in cold regions, there is an increasing need to use transparent planar heaters to melt snow and prevent freezing in order to prevent a decrease in visibility of road signs and traffic lights due to snow accumulation and freezing on the road signs and traffic lights. Furthermore, there is an increasing need to provide transparent planar heaters for temperature control to prevent liquid crystal malfunction and assist startup of liquid crystal display elements used in low-temperature environments in cold regions.

[0003] As an example of such a transparent planar heater, Patent Document 1 discloses a transparent sheet heater that uses a transparent conductive plastic film as a heating element and has a pair of metal electrodes that do not contain resin components formed directly on the film at a predetermined distance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 7-153559 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the transparent sheet heater described in Patent Document 1 has a slow heat generation rate and a low maximum temperature, and therefore has a problem of low water droplet removal performance.

[0006] SUMMARY OF THE PRESENT EMBODIMENTS An object of the present invention is to provide a transparent planar heater that has a fast heat generation rate and a high maximum temperature. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above problems, and as a result have found that the above problems can be solved by a transparent planar heater having a specific laminated structure, thereby completing the present invention. Effect of the Invention

[0008] According to the present invention, there is provided a transparent planar heater which has a high heat generation rate and a high maximum temperature. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view showing a structure of a transparent planar heater according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing X-ray diffraction spectra of the transparent planar heaters obtained in Comparative Example 2 and Example 1 of the present application. [Diagram 3] 1(a) is a TEM image of the transparent conductive oxide layer of Comparative Example 2, and FIG. 1(b) is a TEM image of the transparent conductive oxide layer of Example 1, respectively. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] A transparent planar heater according to one embodiment of the present invention will be described below with reference to the drawings as appropriate. However, the technical scope of the present invention should be determined based on the description of the claims, and is not limited to the following embodiments. In the description of the drawings, the same elements are given the same reference numerals, and duplicated descriptions are omitted. Also, the dimensional ratios in the drawings are exaggerated for the convenience of explanation, and may differ from the actual ratios.

[0011] Fig. 1 is a cross-sectional schematic diagram showing a structure of a transparent sheet heater according to one embodiment of the present invention. As shown in Fig. 1, a transparent sheet heater 10 of this embodiment includes a heat generating layer 20 on one surface of a transparent substrate 11. The heat generating layer 20 has a laminated structure in which a first transparent conductive oxide layer 12, a metal layer 13, and a second transparent conductive oxide layer 14 are laminated in this order from the transparent substrate 11 side. In addition, a pair of electrodes 15 is provided on both ends of the transparent substrate 11 so as to sandwich the heat generating layer 20 in order to pass electricity through the heat generating layer 20.

[0012] In the transparent planar heater of this embodiment, the heat generating layer 20 has the laminated structure as described above. If a desired high heat generation rate (temperature rise rate) is to be obtained using only the transparent conductive oxide layer, the film thickness must be increased, resulting in reduced productivity and increased costs. Furthermore, a thick transparent conductive oxide layer will have increased light scattering, resulting in reduced transparency. Similarly, if a desired high heat generation rate is to be obtained using only the metal layer, the film thickness must also be increased, resulting in reduced transparency.

[0013] As described above, the heat generating layer of this embodiment has a laminated structure in which a first transparent conductive oxide layer, a metal layer, and a second transparent conductive oxide layer are laminated in this order from the transparent substrate side. By using such a laminated structure, a transparent planar heater is obtained that has a high heat generation rate and a high maximum temperature while maintaining transparency. As a result, the transparent planar heater of this embodiment has excellent water droplet removal performance. Furthermore, since the structure sandwiches the metal layer between two transparent conductive oxide layers, deterioration of the metal layer can be suppressed, resulting in excellent durability.

[0014] The first transparent conductive oxide layer 12 and the second transparent conductive oxide layer 14 have a specific resistance of 3.0×10 -4 The transparent conductive oxide layer of the present embodiment has such a low resistivity that it can realize a high heat generation rate and a high maximum temperature of the transparent planar heater.

[0015] Furthermore, the transparent planar heater of this embodiment has a very thin protective layer on the outermost surface or does not have a protective layer, which results in a transparent planar heater with excellent heat transfer from the outermost surface.

[0016] In this specification, "transparent" means that visible light is transmitted, and light may be scattered to a certain extent. The level of light scattering required varies depending on the application of the transparent planar heater. According to one embodiment, the visible light transmittance of the transparent planar heater is preferably 70% or more, and more preferably 80% or more. In this specification, the visible light transmittance means the transmittance of light at a wavelength of 550 nm measured by the method described in the examples.

[0017] The main components of the transparent planar heater of this embodiment will be described in more detail below.

[0018] [Transparent base material] The transparent substrate may have a single layer structure or a multi-layer structure having two or more layers. In addition, the transparent substrate may be a commercially available product or a synthetic product.

[0019] The transparent substrate may be made of one material alone or in combination of two or more materials. From the viewpoints of heat resistance, transparency, etc., the transparent substrate is preferably made of glass substrates such as white plate glass, blue plate glass, quartz glass, alkali-free glass, and sapphire glass. In addition to the glass substrate, a transparent plastic substrate such as polyamide, polyacetal, polyethylene terephthalate, polybutylene terephthalate, and polycarbonate may be used.

[0020] The thickness of the transparent substrate (the total thickness in the case of a multi-layer structure) is preferably 0.1 mm or more, and from the viewpoints of handleability and mechanical strength, is preferably 0.2 to 2 mm.

[0021] [Heat generation layer] The heat generating layer according to this embodiment has a laminated structure in which a first transparent conductive oxide layer, a metal layer, and a second transparent conductive oxide layer are laminated in this order from the transparent substrate side. In this specification, the first transparent conductive oxide layer and the second transparent conductive oxide layer are also collectively referred to as "transparent conductive oxide layers".

[0022] <Transparent conductive oxide layer> Examples of materials constituting the transparent conductive oxide layer include indium-tin oxide (ITO), indium-zinc oxide (IZO (registered trademark)), zinc-tin oxide (ZTO), indium-gallium oxide (IGO), indium-zinc-tin oxide (IZTO (registered trademark)), indium-gallium-zinc oxide (IGZO), aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO), antimony-doped tin oxide (ATO), fluorine-doped tin oxide (FTO), niobium-doped titanium oxide (NTO), tantalum-doped titanium oxide (TTO), vanadium-doped titanium oxide (VTO), tin oxide, indium oxide, and halogen-containing tin oxide. These may be used alone or in combination of two or more.

[0023] Among these, indium-tin oxide (ITO), niobium-doped titanium oxide (NTO), and tin oxide are preferable from the viewpoint of durability.

[0024] The first transparent conductive oxide layer and the second transparent conductive oxide layer may each have a single layer structure or a multi-layer structure of two or more layers. The first transparent conductive oxide layer and the second transparent conductive oxide layer may be made of the same material or different materials. They are preferably made of the same material.

[0025] The transparent conductive oxide layer is preferably formed by a dry process in which a film is formed in a non-solution. Examples of dry processes include physical vapor deposition methods such as vacuum deposition, molecular beam epitaxy, ion plating, ion beam deposition, conventional sputtering, magnetron sputtering, and ion beam sputtering; and chemical vapor deposition methods such as thermal CVD, photo-CVD, plasma CVD, epitaxial CVD, atomic layer deposition, and MO-CVD. The transparent conductive oxide layer and the metal layer can be formed by successive film formation.

[0026] The thickness of each of the first transparent conductive oxide layer and the second transparent conductive oxide layer (the total thickness in the case of a multi-layer structure) is preferably 5 to 300 nm, more preferably 10 to 200 nm, and further preferably 10 to 50 nm.

[0027] The transparent conductive oxide layer of this embodiment has a specific resistance of 3.0×10 -4 Ω·cm or less. Resistivity is 3.0×10 -4 If the resistivity exceeds Ω·cm, the heat generation rate will be slow and the maximum temperature will be low. -4 Ω cm or less, more preferably 1.0×10 -4 The resistivity is Ω·cm or less. There is no particular limit to the lower limit of the resistivity, and the lower the value, the more preferable. The resistivity of the transparent conductive oxide layer can be measured by the method described in the Examples.

[0028] As a means for achieving such a specific resistance, a heat-generating layer including a transparent conductive oxide layer and a metal layer may be formed and then subjected to a heat treatment, as will be described later.

[0029] <Metal layer> Examples of materials constituting the metal layer include simple metals such as gold, silver, copper, palladium, nickel, aluminum, and chromium, and alloys containing these metals. These materials may be used alone or in combination of two or more. The metal layer may have a single layer structure or a multi-layer structure of two or more layers.

[0030] From the viewpoint of durability, the material is preferably simple silver, an alloy containing silver, or copper, more preferably simple silver or an alloy containing silver, and even more preferably an alloy containing silver. The content of metals other than silver contained in the silver-containing alloy is preferably 1 mass % or more from the viewpoint of preventing deterioration.

[0031] Examples of metals other than silver contained in the silver-containing alloy include gold, copper, palladium, platinum, tungsten, titanium, cobalt, chromium, nickel, tin, indium, IT (indium-tin), zinc, etc. Specific examples of the silver-containing alloy include AgPd, AgCu, AgPdCu, AgNdCu, AgInSn, AgSnSb, etc. Among these, AgPd and AgPdCu are preferred from the viewpoint of further improving durability.

[0032] The metal layer may have a single-layer structure or a multi-layer structure of two or more layers.

[0033] The thickness of the metal layer (the total thickness in the case of a multi-layer structure) is preferably 1 to 100 nm, more preferably 5 to 50 nm, and further preferably 10 to 30 nm.

[0034] The metal layer is preferably formed by the dry process described above in the transparent conductive oxide layer section. The specific example of the dry process is the same as above, so the description is omitted here. The first transparent conductive oxide layer, the metal layer, and the second transparent conductive oxide layer can be formed by successive film formation to form the heat generating layer.

[0035] When forming a transparent conductive oxide layer and a metal layer, the film formation temperature must be 100°C or lower. By setting the film formation temperature to 100°C or lower, the material contained in the metal layer in particular becomes a continuous film, the resistance of the entire transparent planar heater decreases, the heat generation rate increases, and the maximum temperature reaches a high level. If the film formation temperature exceeds 100°C, the material contained in the metal layer (particularly the silver alloy) will exist in an island shape due to surface diffusion, and the resistance of the entire transparent planar heater will increase. As a result, the heat generation rate will slow down and the maximum temperature will also decrease. The upper limit of the film formation temperature is preferably 60°C or lower, more preferably 40°C or lower. The lower limit of the film formation temperature is usually 0°C or higher.

[0036] An adhesive layer may be provided between the first transparent conductive oxide layer and the metal layer, and between the second transparent conductive oxide layer and the metal layer, in order to enhance adhesion between the layers. The material for forming the adhesive layer is not particularly limited as long as it can ensure adhesion. Specific examples include silicon oxide (SiO2), aluminum oxide (Al2O3), titanium oxide (TiO2), chromium, titanium, etc. The thickness of the adhesive layer is not particularly limited, but is usually about 1 to 20 nm.

[0037] <Electrode> The transparent planar heater of this embodiment includes a pair of electrodes for passing electricity through the heat generating layer.

[0038] Any material that is conductive can be used as the material for the electrode. Examples of preferred electrodes include metal paste, conductive resin, metal foil, metal tape, and metal plating layer, which can be used alone or as a laminate, multilayer, or mixed layer. From the viewpoint of contact resistance, it is preferable to use an electrode with a lower resistance value. Specifically, the electrode preferably contains at least one selected from the group consisting of gold, silver, copper, and aluminum, and more preferably contains silver.

[0039] The thickness of the electrodes should be sufficient to allow the current flow necessary for the heat generating layer of this embodiment to function, and is usually 0.1 μm or more, preferably 0.5 μm to 100 μm, more preferably 1 to 50 μm, and even more preferably 5 to 20 μm.

[0040] The method for forming the electrode is not particularly limited, and examples thereof include dry processes such as physical vapor deposition methods such as vacuum deposition, sputtering, and ion plating; chemical vapor deposition methods such as thermal CVD and atomic layer deposition; and the like. In addition, wet processes such as various coating methods and electrodeposition methods such as dip coating, spin coating, spray coating, gravure coating, die coating, and doctor blade methods can also be used. In addition, examples include silver salt methods, electrolytic plating, electroless plating, and lamination of metal foils, and are appropriately selected depending on the material of the electrode.

[0041] <Protective layer> The transparent planar heater of this embodiment may have a protective layer on the surface of the second transparent conductive oxide layer opposite to the metal layer. The protective layer can improve the durability of the transparent planar heater. Examples of materials for the protective layer include silica, alumina, and titania. Also usable are those obtained by coating and curing a known UV-curable resin, coating and curing an electron beam-curable resin, coating and curing a thermosetting resin, and the like.

[0042] When a protective layer is provided, the thickness of the protective layer is usually 1 μm or less, and preferably 500 nm or less. However, the transparent planar heater of this embodiment is excellent in durability even without a protective layer, and the transparent planar heater has excellent heat transfer from its outermost surface when it does not have a protective layer. From this viewpoint, the transparent planar heater according to a preferred embodiment does not have a protective layer.

[0043] [Manufacturing method of transparent sheet heater] A method for manufacturing a transparent planar heater according to a preferred embodiment includes the steps of sequentially depositing a first transparent conductive oxide layer, a metal layer, and a second transparent conductive oxide layer on a transparent substrate at a deposition temperature of 100°C or lower to form a heat-generating layer, forming electrodes, and heat-treating the heat-generating layer at a temperature of 150°C or higher.

[0044] The method for forming the transparent conductive oxide layer and metal layer for forming the heat generating layer and the step of forming the electrodes are as described above, so in this section, the step of heat treating the heat generating layer will be described. The step of forming the electrodes may be performed before or after the heat treating step described below. In the heat treating step, passing electricity through the heat generating layer is a preferred method, so it is preferable to form the electrodes before the heat treating step.

[0045] <Process for heat treatment of the heating layer> In this step, the heat generating layer is heat-treated. This heat treatment crystallizes the transparent conductive oxide contained in the transparent conductive oxide layer, and the resistivity of the transparent conductive oxide layer can be reduced. In other words, this step can be said to be a step of performing a crystallization treatment on the transparent conductive oxide.

[0046] The heat treatment method is not particularly limited, and examples thereof include a method of heating using a hot plate, a laser, infrared rays (microwaves), a halogen lamp, hot air, etc., or a method of passing electricity using electrodes, etc. These methods may be used alone or in combination of two or more.

[0047] Among these, the method of passing electricity through the heat generating layer using electrodes is preferred from the viewpoints of being a simpler method, ease of controlling the heat treatment temperature, etc. As an example, the voltage applied during passing electricity is preferably 1 to 10 V.

[0048] The heat treatment temperature in this step is preferably 150 to 300° C., more preferably 170 to 280° C. The heat treatment time is preferably 60 to 300 seconds, more preferably 100 to 250 seconds.

[0049] The resistivity of the transparent conductive oxide layer thus obtained is 3.0×10 -4 Ω·cm or less.

[0050] The heat treatment in this step crystallizes the transparent conductive oxide, and the presence or absence of this crystallization can be confirmed by X-ray diffraction (XRD) of the transparent conductive oxide layer. As an example, FIG. 2 shows the X-ray diffraction spectrum of the transparent planar heater of Comparative Example 2 of the present application, which was not subjected to the above heat treatment step, and the transparent planar heater of Example 1 of the present application, which was subjected to the above heat treatment step. Arrow 1 in the spectrum indicates a peak derived from the (111) plane of silver (Ag) contained in the metal layer, arrow 2 indicates a peak derived from the (400) plane of ITO, and arrow 3 indicates a peak derived from the (222) plane of ITO. As can be seen from FIG. 2, no peak derived from ITO crystals is seen in the XRD spectrum of Comparative Example 2, which was not subjected to the heat treatment step. On the other hand, a peak derived from ITO crystals is seen in the XRD spectrum of Example 1, which was subjected to the heat treatment step, and it can be seen that the crystallization of ITO has progressed by the heat treatment. The XRD spectrum can be measured by the method described in the Examples.

[0051] The crystal morphology of the transparent conductive oxide layer can also be confirmed by observation with a transmission electron microscope (TEM). FIG. 3 shows TEM images of the transparent conductive oxide layer, where (a) shows a TEM image of the transparent conductive oxide layer of Comparative Example 2, and (b) shows a TEM image of the transparent conductive oxide layer of Example 1. In the TEM image of Comparative Example 2 in FIG. 3(a), a mixture of crystal stripes specific to crystals and irregular structures specific to amorphous structures can be observed, but the size of the crystal stripes is small. On the other hand, in the TEM image of Example 1 in FIG. 3(b), large and regular crystal stripes can be seen, and it can be confirmed that the crystallization of ITO contained in the transparent conductive oxide layer is progressing.

[0052] From such a TEM image, the average crystallite size of the transparent conductive oxide can be measured. For example, the average crystallite size of the transparent conductive oxide contained in the transparent conductive oxide layer is preferably 10 nm or more. With such a crystallite size, the resistivity of the transparent conductive oxide layer can be further reduced, and the transparent planar heater has excellent heat generation speed and maximum temperature.

[0053] Moreover, the crystallinity of the transparent conductive oxide can be calculated from such a TEM image. For example, the crystallinity of the transparent conductive oxide contained in the transparent conductive oxide layer is preferably 70% or more, more preferably 90% or more. With such a crystallinity, the resistivity of the transparent conductive oxide layer can be further reduced, and the transparent planar heater has excellent heat generation speed and maximum temperature.

[0054] The TEM observation, the measurement of the average crystallite size, and the calculation of the crystallinity can be carried out by the methods described in the Examples.

[0055] [Application] The transparent planar heater of the present embodiment can be used, for example, to remove water droplets from vehicle members. Examples of vehicle members include exterior members for automobiles, industrial vehicles, personal vehicles, self-propelled vehicle bodies, railway vehicles, etc., and plastic vehicle windows.

[0056] Examples of the exterior parts for vehicles include door mirrors, turn signal lenses, headlamp covers, etc. Examples of the plastic windows for vehicles include sunroofs, front glass, side glass, rear glass, rear quarter glass, rear door quarter glass, etc.

[0057] It can also be used to remove water droplets from camera lenses used in around-view monitor systems, rearview monitor systems, and the like. EXAMPLES

[0058] The present invention will now be described in further detail with reference to examples.

[0059] In each of the following Examples and Comparative Examples, a 1 mm thick alkali-free glass substrate (manufactured by Shimadzu East Japan Science Co., Ltd.) was used as the transparent base material. The transparent conductive oxide layer and metal layer in each of the Examples and Comparative Examples were formed by the following method. The substrate temperature was room temperature (25°C), and the target-substrate distance was 55 mm.

[0060] The transparent conductive oxide layer was formed by RF (radio frequency) magnetron sputtering using an ITO (SnO2: 10% by mass) target and a sputtering device (Canon Anelva Corporation, L-332SRF). The film formation conditions were Ar gas (purity 99.9999%): 10 sccm, film formation pressure: 0.5 Pa, and input power: 100 W.

[0061] The metal layer was formed by RF magnetron sputtering using a sputtering device similar to that described above, using an AgPd (Ag:Pd:=99.0:1.0 (mass ratio)) target. The deposition conditions were Ar gas: 10 sccm, deposition pressure: 0.5 Pa, and input power: 15 W.

[0062] The thickness of each layer was controlled according to a previously measured sputtering rate.

[0063] Example 1 A first transparent conductive oxide layer (thickness: 20 nm), a metal layer (thickness: 10 nm), and a second transparent conductive oxide layer (thickness: 20 nm) were successively deposited on the surface of alkali-free glass by film formation in this order to form a heat generating layer and obtain a laminate.

[0064] Silver paste (Dotite (registered trademark), manufactured by Fujikura Kasei Co., Ltd.) was applied to the obtained laminate to form electrodes so that the electrode distance was 10 mm and the electrode width was 10 mm. Then, a direct current voltage of 4 V was applied using the formed electrodes, and the temperature was maintained at 180°C for 150 seconds to crystallize the ITO (heat treatment process), thereby producing a transparent planar heater.

[0065] Example 2 A first transparent conductive oxide layer (thickness 200 nm), a metal layer (thickness 10 nm), and a second transparent conductive oxide layer (thickness 200 nm) were laminated in this order on the surface of the alkali-free glass by continuous film formation to form a heat generating layer. A transparent flat heater was produced in the same manner as in Example 1 except for this.

[0066] Comparative Example 1 A transparent planar heater was produced in the same manner as in Example 1, except that only a transparent conductive oxide layer (film thickness 300 nm) was formed on the surface of the alkali-free glass and no heat treatment step was performed.

[0067] Comparative Example 2 A transparent planar heater was produced in the same manner as in Example 1, except that the heat treatment step was not carried out.

[0068] [evaluation] (sheet resistance, resistivity) The sheet resistance of the entire transparent planar heater and the resistivity of the transparent conductive oxide layer were measured using a Hall effect measuring device (ResiTest8400, manufactured by Toyo Corporation). When there were two transparent conductive oxide layers, the resistivity showed the same value.

[0069] (heat release rate) A voltage of 6 V was applied using the electrodes of the transparent planar heaters of each of the Examples and Comparative Examples prepared above. The heat generation rate was calculated from the temperature change from the start of voltage application until 7 seconds later.

[0070] (Maximum temperature reached) After the voltage application was started, the device was left for a certain period of time, and the maximum temperature reached was measured.

[0071] (Transmittance of light with a wavelength of 550 nm (visible light transmittance)) The transmission and reflection spectra of the transparent sheet heater at a wavelength of 550 nm were measured using a spectrophotometer (Shimadzu Corporation, ultraviolet-visible-near infrared spectrophotometer, UV-3150) and calculated.

[0072] The evaluation results are shown in Table 1 below.

[0073] [Table 1]

[0074] (X-ray diffraction of a transparent flat heater) X-ray diffraction analysis was performed on the transparent planar heaters obtained in Comparative Example 2 and Example 1. The device used was an XRD-6100 manufactured by Shimadzu Corporation, and measurements were performed using the θ-2θ method. The results are shown in FIG.

[0075] As is clear from Fig. 2, no ITO peak was observed in the transparent planar heater of Comparative Example 2. However, a peak (arrow 2) derived from the (222) plane of ITO and a peak (arrow 3) derived from the (400) plane were observed in the transparent planar heater of Example 1. From this result, it was found that the ITO contained in the heat-treated transparent planar heater of Example 1 has crystallinity.

[0076] (Average crystallite size and crystallinity of ITO) For the transparent planar heater obtained in Example 1, the average crystallite size of the ITO contained in the transparent conductive oxide layer was measured and the degree of crystallinity was calculated from the TEM observation images.

[0077] The transparent conductive oxide layer of the transparent flat heater obtained in Example 1 was sliced ​​by a macrosampling method using a high-performance focused ion beam device (MI4050, Hitachi High-Tech Corporation). After that, the damaged layer was removed using an ion milling device (IM4000PLUS, Hitachi High-Tech Corporation), and the crystal structure was observed using a transmission electron microscope (TEM, JEM-4010, JEOL Ltd.). The average of the major axes of the regular crystal stripes seen in the observation field was calculated to be the average crystallite size of ITO. As a result, the average crystallite size of ITO in Example 1 was calculated to be 10 nm. In addition, the area ratio of the area of ​​the regular crystal stripes seen in the observation field to the entire observation field was used as the crystallinity. As a result, the crystallinity of ITO in Example 1 was calculated to be 90%. The same was performed for Comparative Example 2, and the crystallinity of ITO in Comparative Example 2 was calculated to be 50%. [Explanation of symbols]

[0078] 10 Transparent surface heater, 11 Transparent base material, 12 first transparent conductive oxide layer, 13 metal layer, 14 second transparent conductive oxide layer, 15 electrodes, 20 Heat generating layer.

Claims

1. A glass substrate; a heat generating layer including a first transparent conductive oxide layer, a metal layer, and a second transparent conductive oxide layer laminated in this order on the glass substrate; A pair of electrodes are provided on both ends of the glass substrate so as to sandwich the heat generating layer; having The first transparent conductive oxide layer and the second transparent conductive oxide layer have a specific resistance of 3.0×10 －４ A transparent planar heater having a resistivity of Ω·cm or less (excluding those having a colored coating layer disposed between the glass substrate and the electrodes).

2. A glass substrate; a heat generating layer including a first transparent conductive oxide layer, a metal layer, and a second transparent conductive oxide layer laminated in this order on the glass substrate; A pair of electrodes are provided on both ends of the glass substrate so as to sandwich the heat generating layer; having The first transparent conductive oxide layer and the second transparent conductive oxide layer have a specific resistance of 3.0×10 －４ Ω cm or less, A transparent planar heater, wherein the entire surface of the first transparent conductive oxide layer on the glass substrate side is adhered to the glass substrate.

3. 3. The transparent planar heater according to claim 1, wherein the first transparent conductive oxide layer and the second transparent conductive oxide layer contain indium-tin oxide.

4. 4. The transparent planar heater according to claim 1, wherein the metal layer contains silver or an alloy containing silver.

5. 5. The transparent sheet heater according to claim 1, which has a visible light transmittance of 70% or more.

6. The transparent sheet heater according to any one of claims 1 to 5, wherein the average crystallite size of the transparent conductive oxide contained in the first transparent conductive oxide layer and the second transparent conductive oxide layer is 10 nm or more.

7. A transparent sheet heater described in any one of claims 1 to 6, wherein the crystallinity of the transparent conductive oxide contained in the first transparent conductive oxide layer and the second transparent conductive oxide layer is 70% or more.

8. A process for forming a heat generating layer by sequentially depositing a first transparent conductive oxide layer, a metal layer, and a second transparent conductive oxide layer on a glass substrate at a deposition temperature of 100°C or less; forming an electrode; A step of heat-treating the heat generating layer at a temperature of 150° C. or more; A method for producing a transparent planar heater (excluding those having a colored coating layer disposed between the glass substrate and the electrodes), comprising:

9. A process for forming a heat generating layer by sequentially depositing a first transparent conductive oxide layer, a metal layer, and a second transparent conductive oxide layer on a glass substrate at a deposition temperature of 100°C or less; forming an electrode; A step of heat-treating the heat generating layer at a temperature of 150° C. or more; Including, A method for manufacturing a transparent planar heater, wherein the entire surface of the first transparent conductive oxide layer on the glass substrate side is adhered to the glass substrate.

10. The method according to claim 8 or 9, wherein the heat treatment step includes passing a current through the heat generating layer.

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