Film heater

Abstract

A film heater (10) is provided with a heat-resistant insulating film (1), a metal foil (2) provided on the heat-resistant insulating film (1), and a black film (5) provided on the metal foil (2). The black film (5) has protrusions (6) configured to exhibit a heat-insulating function, and at least one hole (7) provided in each of the protrusions (6).

Description

Technical Field

[0001] This invention relates to an infrared radiating thin-film heater. Background Technology

[0002] For example, in the heating of electric vehicles used in cold regions, indirect heating type foot heaters are sometimes used. Such heaters sometimes use thin-film heaters that are structurally robust, lightweight, and have a small heat capacity. For example, an example of a thin-film heater is disclosed in Patent Document 1.

[0003] Furthermore, thin-film heaters with infrared radiating films that offer better rapid heating performance are known. An example of the cross-sectional structure of such an infrared radiating thin-film heater 50 is shown below. Figure 2 The infrared radiating thin-film heater 50 is manufactured, for example, as described below. Specifically, the infrared radiating thin-film heater 50 uses a so-called flexible printed circuit board (FPCB) on which a copper foil 52 laminated with polyimide resin 51 is etched into a grid pattern. Polyimide adhesive 54 is selectively coated onto areas of the FPCB other than the copper foil 52, and then dried. An infrared radiating coating containing carbon nanotubes or the like is coated onto these areas, and then dried to form a black thin film 55. Furthermore, a polyimide cover film 59 with an adhesive layer is disposed thereon. These are thermally fused together by staged heating and pressurization to form the infrared radiating thin-film heater 50.

[0004] In this infrared radiation type thin-film heater 50, a copper foil 52, which has become somewhat high-resistivity through lattice etching, is electrically connected in parallel with a black thin film 55 containing carbon nanotubes. The black thin film 55 has very high thermal conductivity in the planar direction. As a result, the non-uniformity of the in-plane resistivity of the black thin film 55 is mitigated by the lattice-shaped copper foil 52, and the temperature distribution within the heater surface is homogenized.

[0005] This infrared radiating thin-film heater 50 exhibits excellent performance. However, while it is intended to operate at around 135°C to ensure rapid heating, individual components can only operate at around 100°C to 105°C to prevent burns from direct contact with the heater, sometimes failing to fully realize its rapid heating potential. Furthermore, materials such as the carbon nanotubes contained in the black film 55 and the polyimide coating used for lamination in the polyimide covering film 59 are expensive. Additionally, the infrared radiating thin-film heater 50 has a 4-5 layered structure with varying coefficients of thermal expansion. Therefore, during the pressurized heat-welding process in its manufacturing, even with slow, phased heating and cooling, the infrared radiating thin-film heater 50 is prone to bending, and air bubbles easily form between the layers. Moreover, the manufacturing process is time-consuming and inefficient, making the infrared radiating thin-film heater 50 expensive.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2004-14178 Summary of the Invention

[0009] The technical problem that the invention aims to solve

[0010] The purpose of this invention is to provide an excellent infrared radiation type thin film heater, which has a simple and inexpensive structure, and has a good finished shape without bending, and exhibits high rapid heating performance.

[0011] Technical means to solve the problem

[0012] According to one aspect of the present invention, a thin-film heater includes: a heat-resistant insulating film; a metal foil disposed on the heat-resistant insulating film; and a black film disposed on the metal foil, the black film having: protrusions configured to perform heat insulation function; and at least one hole disposed in each of the protrusions.

[0013] The effects of the invention

[0014] According to the present invention, an excellent infrared-emitting thin-film heater can be provided. Attached Figure Description

[0015] Figure 1A This is a schematic top view showing a structural example of a thin-film heater according to one embodiment, and a view showing the surface on which the heater pattern is formed.

[0016] Figure 1B This is a schematic cross-sectional view showing a structural example of a thin-film heater according to one embodiment, schematically illustrating the structure along... Figure 1A A schematic diagram of a partial cross-section of the IB-IB line is shown.

[0017] Figure 2 This is a schematic diagram illustrating an example of the cross-sectional structure of a prior art infrared radiating thin-film heater. Detailed Implementation

[0018] Referring to the accompanying drawings, one embodiment will be described. This embodiment relates to an infrared-emitting thin-film heater. This thin-film heater can be used for various applications. For example, it can be used as a foot warmer for electric vehicles.

[0019] Figure 1A This is a schematic top view showing a structural example of the thin-film heater 10 of this embodiment, and a view showing the surface on which the heater pattern is formed. Figure 1B This is a schematic cross-sectional view showing a general example of the structure of the thin-film heater 10 of this embodiment, schematically showing along... Figure 1A A schematic diagram of a partial cross-section of the IB-IB line is shown.

[0020] The thin-film heater 10 has a heat-resistant insulating film 1 and a metal foil 2 disposed on the heat-resistant insulating film 1. The metal foil 2 has a heater pattern. When the thin-film heater 10 is used as a foot heater for EVs that commonly operate at temperatures exceeding 100°C, the heat-resistant insulating film 1 is formed, for example, using polyimide (PI) resin. The metal foil 2 is formed, for example, using stainless steel (SUS). The heat-resistant insulating film 1 can also be made of polyethylene terephthalate (PET) resin, polyethylene naphthalate (PEN) resin, etc. The metal foil 2 can also be made of copper, nickel-chromium alloy, etc. These materials can be selected, for example, depending on the operating temperature of the heater. For example, the thickness of the heat-resistant insulating film 1 is about 25 μm, and the thickness of the metal foil 2 is about 30 μm.

[0021] The heat-resistant insulating film 1 and the metal foil 2 can be fabricated in the same manner as so-called flexible printed circuit boards used for electronic circuit wiring, which offer excellent stability and cost-effectiveness. Specifically, the heat-resistant insulating film 1 is formed by laminating a 30 μm thick SUS film with a 25 μm thick PI resin. Subsequently, a process is performed to remove a portion of the SUS film to achieve a specified resistance value and temperature distribution, thereby forming the metal foil 2. As a process for removing a portion of the SUS film, etching may be performed, for example.

[0022] Furthermore, the thickness of the metal foil 2 is determined according to the required resistance value and shape. In order to ensure uniform temperature distribution within the surface, the patterned portion of the metal foil 2 is preferably formed in a manner that minimizes blank areas. Connection portions 2a for connecting to a power source to apply voltage to the metal foil 2 are provided at both ends of the patterned portion of the metal foil 2.

[0023] When using difficult-to-bond PET film, PEN film, etc., as the heat-resistant insulating film 1, the heat-resistant insulating film 1 and the metal foil 2 can be manufactured, for example, as described below. That is, the surface of the metal foil 2 is laminated with a heat-melting resin. Furthermore, the surface of the heat-resistant insulating film 1, such as the PET film or PEN film, is activated by corona discharge treatment. The laminated surfaces of the heat-resistant insulating film 1 and the metal foil 2 are then heat-fused together.

[0024] In cases where the thickness of the heat-resistant insulating film 1 is insufficient and the mechanical strength is weak, for example, a PI film with different physical properties can be further heat-fused onto the above-mentioned PI resin laminate.

[0025] In this embodiment, a so-called SUS etching heater can be used, which is formed by laminating PI resin with SUS foil to form a heat-resistant insulating film 1 of PI resin and a metal foil 2 of SUS foil. Here, the structure comprising such a heat-resistant insulating film 1 and metal foil 2 is referred to as a metal foil heater 3.

[0026] In addition, in this embodiment, such as Figure 1A As shown, a touch sensor electrode 8, constituting the electrode of a capacitive touch sensor, is provided on the outer periphery of a metal foil 2 on a heat-resistant insulating film 1, which forms a heater pattern. The touch sensor electrode 8 is formed from SUS foil, for example, the same as the metal foil 2. The touch sensor electrode 8 has a linear pattern that roughly surrounds the metal foil 2. The heater pattern of the metal foil 2 and the touch sensor electrode 8 can be formed simultaneously from the same metal foil.

[0027] like Figure 1B As shown, a resin layer 4 is disposed above the metal foil heater 3. The resin layer 4 can be made of an adhesive. Compared to thermoplastic adhesives with large expansion / contraction relative to heating / cooling cycles, a thermosetting adhesive that has adhesive strength even when thin and exhibits heat shrinkage is preferred. The adhesive used in the resin layer 4 is preferably an epoxy-based adhesive with high heat resistance among commonly used thermosetting adhesives. Epoxy-based adhesives are less expensive than polyimide-based adhesives. Furthermore, epoxy-based adhesives have simpler curing conditions and shorter manufacturing time.

[0028] The resin layer 4 disposed on the surface of the metal foil heater 3 has a thickness of approximately 10 μm to 30 μm. In order to isolate the metal foil 2 from the outside, and in order to ensure the insulation of the metal foil 2, the thickness of the resin layer 4 is preferably approximately 15 μm.

[0029] like Figure 1B As shown, a black film 5 is disposed and bonded on the resin layer 4. The black film 5 is a blackened film that performs infrared radiation. The black film 5 is formed from a material in which carbon is added to a resin substrate. For example, PI resin with excellent heat resistance can be used for the black film 5. The black film 5 can also use relatively inexpensive PET resin, PEN resin, etc. In the black film 5, carbon undertakes infrared radiation but does not undertake electrical conduction. Therefore, inexpensive carbon black can be used. Expensive and safety-critical carbon nanotubes are not required. That is, the black film 5 is blackened by containing carbon black. Other materials, such as black ceramics, can also be used instead of carbon. However, carbon black is the preferred material in terms of infrared radiation efficiency, material availability, and price.

[0030] The black film 5 can be formed, for example, by mixing carbon black into resin powder and forming it into a film using a twin-screw compounding extruder. Alternatively, the black film 5 can be formed, for example, by dispersing carbon black in a resin solution, curing it using heated rollers, and forming it into a film.

[0031] The thickness of the black film 5 is, for example, 25 μm to 100 μm. Considering shape processing, the thickness of the black film 5 is preferably, for example, around 75 μm. Taking into account the balance between infrared radiation performance and insulation resistance, the volume resistivity of the black film 5 containing PI resin and carbon black is 1 × 10⁻⁶. 10 Ω·cm~1×10 13 Approximately Ω·cm, preferably 1×10⁻⁶. 11 Approximately Ω·cm.

[0032] Embossing is performed on the black film 5. Embossing of the black film 5 is performed before bonding to the metal foil heater 3. In this embossing process, a pair of molds is used, including a male mold with an embossed shape having needle-like protrusions on the top and a corresponding female mold. During embossing, the black film 5 to be embossed is sandwiched between the pair of molds and subjected to hot pressing, etc. When using PI resin, hot pressing is performed at a molding temperature of, for example, 300°C to 370°C and a pressure of 1 kg / cm². 2 ~5kg / cm 2 Under these conditions, it will be carried out.

[0033] The black film 5 has protrusions 6 formed by embossing. These protrusions 6 are evenly distributed across the entire surface of the black film 5. However, in order to maintain the contact sensitivity of the touch sensor, the protrusions 6 are not provided on the touch sensor electrode 8 portion.

[0034] The protrusion 6 is preferably cylindrical or frustum-shaped. If the protrusion 6 is a prismatic shape with angles, wrinkles or cracks may occur in the black film 5 due to the pressing of the male mold. Therefore, the protrusion 6 is preferably without angles. Furthermore, to ensure smooth mold removal, the protrusion 6 is preferably frustum-shaped, for example, with a tapered angle.

[0035] When the protrusion 6 is truncated cone-shaped, the diameter of the bottom is preferably 2mm to 8mm, more preferably 3mm to 6mm. Even if the protrusion 6 has other shapes, the size of the protrusion in the surface direction is preferably 2mm to 8mm, more preferably 3mm to 6mm. The height of the protrusion 6 is preferably 1mm to 5mm, more preferably 2mm to 4mm.

[0036] The density of the protrusions 6 on the black film 5 is preferably one or more in a 20 mm square. Although it also depends on the diameter of the bottom of the protrusion 6, the density of the protrusions 6 is further preferably one or more in a 5 mm square to 10 mm square.

[0037] In addition, at least one hole 7 is provided on the top of each protrusion 6, formed by a needle-like protrusion on the top of the male die used for embossing. The diameter of the hole 7 is preferably 1 μm to 150 μm, more preferably 10 μm to 50 μm. The number of holes 7 provided in each of the protrusions 6 may also be two or more.

[0038] The hole 7 serves to release the pressure of air within the protrusion 6 that expands due to heating, the expansion pressure of tiny air bubbles contained in the resin layer 4, and the expansion pressure of residual air bubbles between the resin layer 4 and the black film 5. The generation of residual air bubbles between the resin layer 4 and the black film 5 is difficult to avoid during the bonding process. On the other hand, the film heater 10 of this embodiment has a relatively simple structure, therefore, the number of air bubbles remaining between the layers of the film heater 10 is generally smaller. Furthermore, the hole 7 promotes air exchange between the protrusion 6 and the outside air, reducing the temperature inside the protrusion 6. Additionally, the hole 7 prevents the protrusion 6 from being flattened by the contracting air during cooling.

[0039] In the infrared radiation type thin-film heater 10 of this embodiment, protrusions 6 are formed on the surface of the outermost black thin film 5. Air is present inside the protrusions 6, which function as heat insulation. As a result, the temperature at the top of the protrusions 6 is difficult to rise. Furthermore, the hollow protrusions 6 have a small heat capacity. Therefore, for example, when the metal foil 2 is at approximately 135°C, the temperature at the top of the protrusions 6 is lower than approximately 135°C. Even if a person's skin comes into direct contact with the top of the protrusions 6 on the surface of the black thin film 5, the person will hardly feel the heat and will generally not be burned. Since the temperature of the metal foil heater 3 can be raised to a relatively high temperature, such as approximately 135°C, the temperature rise time of the heated object is relatively short.

[0040] Furthermore, the black film 5, including the protrusion 6, is heated by the heat generated in the metal foil 2, through the flat portion 5a of the black film 5, which is mainly in contact with the resin layer 4. Therefore, the size and density of the protrusion 6 affect the temperature rise time of the top of the protrusion 6 and the temperature rise time of the heated body caused by infrared radiation.

[0041] The resin layer 4 is preferably made of a thermosetting resin such as an epoxy-based adhesive with high heat resistance. Generally, thermosetting resins tend to shrink with heating over a long period of time. By applying pressure while curing the resin, the resin layer 4 can be made planar in the early stages of manufacturing. However, if the thin-film heater 10 is used continuously, the resin layer 4 will shrink over time. In the thin-film heater 10 of this embodiment, the black film 5 bonded to the resin layer 4 has a protrusion 6 that does not contact the resin layer 4. This protrusion 6 functions to mitigate the shrinkage force on the black film 5 from the resin layer 4. As a result, bending of the thin-film heater 10 as a whole can be suppressed.

[0042] The thin-film heater 10 of this embodiment has a relatively simple structure. Therefore, the thin-film heater 10 is lightweight, highly resistant to vibration / shock, and has high robustness. Furthermore, by utilizing infrared radiation based on the black thin film 5, it exhibits good rapid heating performance and low power consumption. Additionally, the manufacturing process of the thin-film heater 10 is relatively simple, and the manufacturing time is short. Moreover, the thin-film heater 10 can be manufactured using relatively inexpensive and common materials. For example, relatively inexpensive materials such as the conventionally reliable SUS etching heater and the PI film with added carbon black can be used in the thin-film heater 10. Thus, the thin-film heater 10 can be manufactured relatively inexpensively.

[0043] As described above, the thin-film heater 10 of this embodiment exhibits excellent rapid heating performance, energy efficiency, shape stability, and economy. Although the thin-film heater 10 has a wide range of applications, it also performs well, for example, as a heater for electric vehicles.

[0044] Furthermore, in the above-described embodiment, an example was described where the interior of the protrusion 6 is filled with air. However, this is not a limitation. To improve the durability of the protrusion 6 against flattening caused by repeated heating and cooling compared to when the interior of the protrusion 6 is filled with air, a foam having continuous air bubbles corresponding to the shape of the protrusion 6 can also be disposed inside the protrusion 6. As the continuous air bubble foam, a polymer foam with a higher specific heat than ceramic can be used. For example, silicone rubber foam, fluororubber foam, etc., can be used.

[0045] Example

[0046] The thin-film heater 10 of the above embodiment was manufactured, and various characteristics were measured and evaluated.

[0047] [Sample Preparation]

[0048] As a sample of an infrared radiating thin-film heater, a thin-film heater 10 was fabricated with the metal foil 2 intended for use at approximately 135°C. To fabricate the metal foil heater 3, a commercially available film of SUS foil laminated with PI resin was used. The film used consisted of a 25 μm thick SUS foil laminated with a 35 μm thick PI resin film on one side. Such films are widely available commercially as thin-film heaters. In this embodiment, a film measuring 150 mm × 210 mm was used. Using this film, and with a 35 μm thick PI resin heat-resistant insulating film 1 as a substrate, a metal foil heater 3 with a 25 μm thick SUS foil disposed thereon was fabricated.

[0049] The pattern of the metal foil 2 in the metal foil heater 3 is formed using a known etching method. That is, a predetermined pattern is formed on the surface of the SUS foil using a resist film, and unwanted SUS foil is removed by immersion in an etching solution. In this embodiment, the heater pattern is designed with as few blank areas as possible. The resistance of the heater pattern is 4.5Ω. Connection portions 2a for power supply are provided at both ends of the heater pattern.

[0050] Additionally, a touch sensor electrode 8 for sensing a capacitive touch sensor is formed on the outer periphery of the heater pattern. The touch sensor electrode 8 has a width of 5 mm.

[0051] Black film 5 uses a commercially available, high-heat-resistant, general-purpose black PI film. Black film 5 is blackened by carbon black.

[0052] A black film 5 was placed on the mold of a hot press for embossing, forming a protrusion 6. The hot pressing conditions were set as follows: temperature 350℃, time 3 minutes, and pressure 3 kg / cm². 2 .

[0053] Multiple samples with different bottom diameters, heights, and densities of the protrusions 6 were prepared. The bottom diameters of the protrusions 6 were 3 mm, 6 mm, and 10 mm. The heights of the protrusions 6 were 2.5 mm, 3 mm, 4 mm, and 6 mm. The densities of the protrusions 6 were one 6 mm square, one 10 mm square, and one 18 mm square. Additionally, multiple samples with different diameters of the holes 7 located on the top of the protrusions 6 were prepared. The diameters of the holes 7 were 50 μm, 100 μm, and 200 μm. Six samples corresponding to these combinations from Examples 1 to 6 were fabricated. The combinations of dimensions, etc., of each part are shown in Table 1.

[0054] [Table 1]

[0055]

[0056] In Examples 1 and 2, the density of the protrusions 6 is one 6mm square, the bottom diameter of the protrusion 6 is 3mm, and the height is 2.5mm. In Example 1, the diameter of the hole 7 is 50μm, and in Example 2, the diameter of the hole 7 is 100μm. Furthermore, the specifications of Examples 1 and 2 represent the most practical specifications in terms of safety and thermal efficiency.

[0057] In Examples 3 and 4, the density of the protrusions 6 is one per 10 mm square, the bottom diameter of the protrusion 6 is 6 mm, and the height is 3 mm. In Example 3, the diameter of the hole 7 is 50 μm, and in Example 4, the diameter of the hole 7 is 100 μm. Furthermore, Examples 3 and 4 are used to confirm whether increasing the diameter of the protrusion 6 does not further reduce the temperature of the top of the protrusion 6.

[0058] In Example 5, the density of the protrusions 6 is one at 18 mm², and the bottom diameter of the protrusion 6 is 10 mm. In Example 5, the height of the protrusion 6 is 4 mm, and a silicone rubber sponge of approximately the same shape as the protrusion 6 is disposed inside the protrusion 6. The diameter of the hole 7 is 200 μm. The specifications of Example 5 are used to confirm whether, even if the number of protrusions 6 is reduced, which easily leads to contact between the fingertip and the high temperature of the flat portion 5a of the black film 5, the temperature of the top of the protrusion 6 cannot be reduced by increasing the bottom diameter of the protrusion 6. Furthermore, Example 5 is used to confirm whether the silicone rubber sponge disposed inside the protrusion 6 can suppress the depression of the top of the protrusion 6.

[0059] Similar to Example 5, in Example 6, the density of the protrusions 6 is one at 18 mm², and the bottom diameter of the protrusion 6 is 10 mm. In Example 6, the height of the protrusion 6 is 6 mm, and no hole 7 is provided. The specifications of Example 6 are used to confirm whether even if the number of protrusions 6 is reduced, it is easy to generate contact between the fingertip and the high temperature of the flat portion 5a of the black film 5. As long as the internal space of the protrusion 6 is large, even without the hole 7, it is impossible to reduce the temperature of the top of the protrusion 6.

[0060] As described above, black films 5 of different specifications for the protrusions 6 are bonded to the surface of the metal foil heater 3. A single-component epoxy adhesive (Sanyurec, RO-8699) is used as the adhesive. The metal foil heater 3 is positioned with the surface where the metal foil 2 is formed facing upwards. An adhesive layer of approximately 20 μm is applied to the upper surface of the metal foil heater 3, and the black films 5 of each embodiment are then positioned thereon with their protrusions 6 facing upwards. The mixture is dried and cured at 150°C for 1 hour. In Example 5, the black films 5 are positioned on the lower side and the metal foil heater 3 on the upper side for bonding. In this case, the adhesive penetration into the protrusions 6 is minimal, ensuring sufficient clearance within the silicone sponge of the protrusions 6.

[0061] The samples in Comparative Examples 1 and 2 were obtained by bonding a flat black film 5 without protrusions 6 to a metal foil heater 3. This structure is such that if the metal foil 2 comes into contact with the black film 5 when heated to 135°C, it could potentially cause burns. The bonding between the metal foil heater 3 and the black film 5 is the same as in the examples described above. In Comparative Example 1, the operating conditions of the sample, such as the applied voltage to the metal foil 2, were set to the same conditions as in Examples 1 to 6, and various measurements were performed. In Comparative Example 2, various measurements were performed under operating conditions where the applied voltage to the metal foil 2 was reduced compared to Examples 1 to 6.

[0062] [Measurement Method]

[0063] The following measurements were performed on each of the samples shown in Table 1.

[0064] <Evaluation of fingertip contact with the flat surface>

[0065] The evaluation focused on whether the fingertip contacted the flat portion 5a of the black film 5 on the metal foil heater 3, which could become a high-temperature component in the thin-film heater 10. The aforementioned samples were used. The tip of the index finger was brought into contact with the black film 5 of each sample in its unpowered state to confirm whether the tip of the index finger made contact with the protrusion 6 of the black film 5 and the flat portion 5a between the protrusions 6 with a surface-like width.

[0066] <Surface Temperature Measurement>

[0067] The surface temperature of the thin-film heater 10 used as each of the above samples was measured. The thin-film heater 10 was suspended in the air at 25°C in a windless environment.

[0068] A DC voltage of 12.5V was applied to both ends of the metal foil 2, which serves as the heating element of the thin-film heater 10, via a temperature regulator. A tiny thermocouple was attached and fixed to the center of the back of the thin-film heater 10, and the leads of the thermocouple were connected to the temperature regulator. The temperature of the thin-film heater 10 was automatically controlled by the temperature regulator based on the temperature measured by the thermocouple. Temperature control was performed to suppress overshoot using time-proportional temperature control via the temperature regulator. The control set temperature was set to 135°C. For Comparative Example 2, the applied voltage was set to 11.0V. This is approximately 22% lower than other examples; therefore, for Comparative Example 2, the control set temperature was set to 105°C.

[0069] The temperature measurement area was defined as five regions: a 50mm square area in the center of the black film 5 and four 50mm square areas at the four corners of the black film 5. The flat portion 5a between the protrusions 6 and the top of the protrusions 6 in each region were used as measurement points. Using tiny thermocouples as temperature sensors, the thermocouples were brought into contact with each measurement point, and temperature measurements were taken using a digital thermometer. The average temperature measured in the five regions was used as the evaluation metric.

[0070] Measurement of temperature rise of heated body caused by infrared radiation

[0071] The temperature rise of the heated object caused by infrared radiation from the thin-film heater 10 was measured. The operation of the thin-film heater 10 was controlled using the same temperature control system and method as described above for surface temperature measurement. A black cloth slightly larger than the thin-film heater 10 was suspended 15 cm above the surface of the thin-film heater 10, and this black cloth was used as the heated object. The surface temperature of the black cloth, corresponding to the central portion of the thin-film heater 10, was measured using a far-infrared thermal imager. The temperature of the black cloth surface was measured at 1-second intervals. The measured temperature from the start of power supply to the thin-film heater 10 until temperature saturation was recorded. The time from the start of power supply to reaching 90% of the saturation temperature was taken as the rise time. For Comparative Example 2, the applied voltage was set to 11.0V, and the control set temperature was set to 105°C.

[0072] <Measurement of the reduction in height of the protrusion and the bending of the thin-film heater>

[0073] First, for the unused thin-film heater 10 samples of each embodiment, the height of the top of the protrusion 6 was measured using a microscope and recorded. The protrusion 6 being measured was the same as that used for the surface temperature measurement described above, consisting of five 50mm square areas of the protrusion 6 in the central portion and the four corner portions of the black thin film 5.

[0074] Next, for each sample, similar to the surface temperature measurement described above, the thin-film heater 10 was suspended in the air at 25°C in a windless environment, and a DC voltage of 12.5V was applied to the metal foil 2 via a temperature regulator. The control setting temperature of the temperature regulator was set to 135°C, and the on-off cycle of 1 hour followed by 1 hour of no-on time was repeated 100 times. The thin-film heater of the comparative example was also subjected to 100 cycles of repeated energizing.

[0075] After repeated energizing, each sample was moved from the suspended state to a flat state, and the height of the top of protrusion 6 was measured and recorded using a microscope, in the same manner as the initial measurement. The difference between the initial measurement and the measurement after repeated energizing was calculated. The average of the differences obtained in the five regions was used as the evaluation object.

[0076] In addition, for each sample after repeated energizing, the height of the part with the greatest curvature from the plane was measured using a microscope. Here, regardless of whether it was inside or outside, the sample was arranged so that the part with the greatest curvature at the periphery faced upwards, and the measurement was performed.

[0077] <Moisture Resistance and Voltage Resistance Tests for Thin Film Heaters>

[0078] Each sample was placed in a constant temperature and humidity bath at 40°C and 95% RH for 8 hours without power. Then, each sample was removed from the bath, wiped clean of condensation, and placed at room temperature and humidity for 1 hour. Next, a withstand voltage test was performed on each sample. In the withstand voltage test, an AC voltage of 1500V was applied between the surface of the black film 5 and the metal foil 2 for 1 minute. The insulation of the film heater 10 was tested for damage after the AC voltage was applied.

[0079] [Measurement Results and Evaluation]

[0080] The results of each measurement are shown in Table 2.

[0081] [Table 2]

[0082]

[0083]

[0084] Evaluation of the contact between the fingertips and the flat surface

[0085] In embodiments 1 to 4, where the spacing of the protrusions 6 is 4 mm or less, the fingertip does not contact the flat portion 5a of the black film 5 even though the height of the protrusions 6 is 2.5 mm or 3 mm. On the other hand, in embodiments 5 to 6, where the spacing of the protrusions 6 is 8 mm, the fingertip contacts the flat portion 5a of the black film 5 even though the height of the protrusions 6 is 4 mm or 6 mm. Based on these results, it is believed that if the spacing of the protrusions 6 is narrower than about 5 mm, the possibility of the fingertip contacting the flat portion 5a of the black film 5 is low. It has been clarified that design criteria such as setting the distribution of the protrusions 6 with safety considerations, for example, setting the spacing of the protrusions 6 to 5 mm or less, can be set so that a part of the body including the fingertip does not come into contact with the flat portion 5a of the black film 5, which becomes hot.

[0086] <Regarding surface temperature>

[0087] The temperature of the flat portion 5a between the protrusions 6 is approximately 136°C ± 1°C, which corresponds to the control set temperature of 135°C. However, in Comparative Example 2, since the control set temperature is set to 105°C, the temperature of the flat portion 5a is 106.6°C accordingly.

[0088] In the thin-film heater 10 of Examples 1-4, the temperature at the top of the protrusion 6 is approximately 110°C to 113°C. That is, the temperature at the top of the protrusion 6 is 21°C to 26°C lower than that of the flat portion 5a. Regarding this temperature reduction, although a tendency has been observed that the larger the hole 7 is, the greater the temperature reduction, no significant relationship has been found between the temperature reduction and the diameter of the hole 7.

[0089] In the thin-film heater 10 of Example 5, a silicone rubber sponge is disposed inside the protrusion 6. Therefore, heat conduction to the surface of the protrusion 6 is increased, and the temperature at the top of the protrusion 6 is 116°C. That is, the temperature at the top of the protrusion 6 in Example 5 is slightly higher than the temperature at the top of the protrusion 6 in Examples 1-4. The temperature difference with the flat portion 5a is also 19°C, which is slightly smaller than in Examples 1-4.

[0090] Furthermore, in the thin-film heater 10 of Embodiment 6 without the hole 7, the temperature difference between the top of the protrusion 6 and the flat portion 5a is about 10°C, which is significantly smaller compared to the cases of Embodiments 1 to 4. That is, it is clear that the gas exchange between the inside and outside of the protrusion 6 through the hole 7 is important for reducing the temperature of the top of the protrusion 6.

[0091] As described above, it is clear that the structure of the thin-film heater 10 with the protrusion 6 having the hole 7 significantly reduces the surface temperature of the thin-film heater 10. By configuring and shaping the protrusion 6 in a way that prevents fingertips or the like from contacting the flat portion 5a between the protrusions 6, the temperature of the portion that may come into contact with a person can be kept low, for example, even if the metal foil 2 is at a high temperature. Therefore, it is shown that, according to the structure of this thin-film heater 10, the metal foil 2 can be safely heated to a high temperature.

[0092] <Regarding the temperature rise of the heated body caused by infrared radiation>

[0093] The temperature rise of the heated body caused by infrared radiation from the black thin film 5 based on the thin film heater 10 was measured. The result showed that the saturation temperature of the surface of the black cloth, which is the heated body, was approximately 47.5°C ± 1°C. This saturation temperature is independent of the presence, shape, or structure of the protrusions 6 and the holes 7. This demonstrates that by setting the black thin film 5, a stable heating effect caused by infrared radiation from the black thin film 5 can be obtained.

[0094] Furthermore, the surface temperature rise time of the black fabric in Examples 1-4 was 65-69 seconds. In contrast, the surface temperature rise time of the black fabric in Comparative Example 1, which did not have the protrusion 6, was 45 seconds. The surface temperature rise time of the black fabric in Examples 1-4 was approximately 1.5 times longer than that of Comparative Example 1. On the other hand, it is considered that such a long rise time is not a problem in practical application.

[0095] Furthermore, the temperature rise time of the black cloth surface in Example 5 was 85 seconds. It is believed that the long rise time in Example 5 is due to the presence of silicone sponge inside the protrusion 6, thus increasing the heat capacity of these parts.

[0096] Furthermore, the temperature rise time of the black cloth surface in Example 6 was 54 seconds. It is believed that the rise time in Example 6 was relatively short because the area of ​​the flat portion 5a was relatively large and no holes 7 were provided, thus the temperature of the black film 5 rose relatively quickly.

[0097] In Comparative Example 2, the surface temperature of the black film 5 was reduced to about 107°C due to the reduction of the power supply voltage, resulting in a significantly longer rise time compared to other examples.

[0098] As described above, by providing the protrusion 6 and the hole 7, the temperature of the top of the protrusion 6 is kept low, and the temperature of the flat portion 5a of the black film 5 is kept high at 135°C without reducing the power supply voltage, thereby enabling the temperature of the heated body caused by infrared radiation to rise faster.

[0099] Furthermore, it was confirmed that, as in the embodiments, even without using expensive materials such as carbon nanotubes, and instead using relatively inexpensive, universally available carbon black, sufficient heating effect on the heated object based on infrared radiation can be obtained. That is, it was demonstrated that the thin-film heater 10 using universally available carbon black achieves high economic efficiency.

[0100] <Regarding the reduction in height of the protrusion and the bending of the thin-film heater>

[0101] As shown in Table 2, in Examples 1-4 and Example 6, the following trend was observed: the smaller the bottom diameter of the protrusion 6 and the lower its height, the smaller the reduction in height of the protrusion 6 after repeated energization. Furthermore, in Example 5, where a silicone rubber sponge was provided inside the protrusion 6, it was confirmed that the reduction in height of the protrusion 6 could be significantly suppressed.

[0102] Furthermore, the results of the bending amount of the thin-film heater 10 after repeated energizing are shown in Table 2. It is clear that the bending of the structure with multiple small protrusions 6 decreases after repeated energizing.

[0103] It was clarified that the size, shape, and structure of the protrusion 6 could be designed while taking into account other characteristics such as preventing the fingertip from contacting the flat portion 5a between the protrusion 6 and the protrusion 6, and shape stability.

[0104] <Regarding the moisture resistance and voltage resistance of thin-film heaters>

[0105] None of the samples experienced insulation failure. This is believed to be because, although a hole 7 is provided at the top of the protrusion 6 of the black film 5, the diameter of the hole 7 is suitable for suppressing the exchange between the small air molecules inside the protrusion 6 and the large moisture molecules outside the protrusion 6. Furthermore, it is believed that moisture penetrating into the protrusion 6 is also blocked by the resin layer 4. Therefore, it is believed that the insulation withstand voltage of the thin-film heater 10 is maintained. Thus, it is clear that the hole 7 at the top of the protrusion 6 will not cause problems due to moisture absorption in practical applications.

[0106] The present invention has been described above with reference to preferred embodiments, but the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the present invention.

Claims

1. A thin film heater characterized by comprising: a heat resistant insulating thin film; a metal foil provided on the heat resistant insulating thin film; and a black thin film provided on the metal foil, the black thin film having protrusions configured to function as heat insulators, and at least one hole provided in each of the protrusions.

2. The thin film heater according to claim 1, wherein the black thin film is configured to function as the heat insulators by the presence of air inside the protrusions.

3. The thin film heater according to claim 1 or 2, wherein the black thin film is blackened by containing carbon black.

4. The thin film heater according to claim 1 or 2, wherein a size of each of the protrusions in a surface direction is 2 mm or more and 8 mm or less, and a density of arrangement of the protrusions is 1 or more per 20 mm square.

5. The thin film heater according to claim 1 or 2, wherein a height of the protrusions is 1 mm or more and 5 mm or less.

6. The thin film heater according to claim 1 or 2, wherein a size of the hole provided in the protrusions is 1 μm or more and 150 μm or less.

7. The thin film heater according to claim 1 or 2, further comprising: a resin layer provided on a metal foil heater formed by the heat resistant insulating thin film and the metal foil and under the black thin film, having heat resistance and having insulating properties.

8. The thin film heater according to claim 7, wherein the metal foil heater and the black thin film are bonded by an adhesive forming the heat resistance of the resin layer.

9. The thin film heater according to claim 1 or 2, wherein the metal foil has a shape formed by processing to have a resistance value to obtain a prescribed heat generation when a voltage is applied. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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