Film Heater

Abstract

The film heater (10) comprises 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 provide a heat insulating function, and at least one hole (7) provided in each of the protrusions (6).

Description

[Technical field]

[0001] The present invention relates to an infrared radiation type film heater. [Background technology]

[0002] For example, indirect heating type foot heaters are sometimes used for heating electric vehicles in cold regions. For such heaters, film heaters that are structurally strong, lightweight, and have a small heat capacity are sometimes used. An example of a film heater is disclosed in, for example, Patent Document 1.

[0003] Furthermore, a film heater having an infrared radiation film with better quick heating performance is known. An example of the cross-sectional structure of such an infrared radiation type film heater 50 is shown in FIG. 2. This infrared radiation type film heater 50 is manufactured, for example, as follows. That is, for this infrared radiation type film heater 50, a so-called flexible printed circuit board is used, in which copper foil 52 laminated with polyimide resin 51 is etched into a lattice pattern. A polyimide adhesive 54 is selectively applied to the area other than the copper foil 52 on this flexible printed circuit board, and a drying process is performed. An infrared radiation paint containing carbon nanotubes and the like is applied thereon, and a drying process is performed to form a black film 55. Further, a polyimide cover film 59 with an adhesive layer is placed thereon. These are heat-sealed by stepwise heating and pressure application to form the infrared radiation type film heater 50.

[0004] In this infrared radiation type film heater 50, copper foil 52, which has been given a relatively high electrical resistance by lattice-shaped etching, and black film 55 containing carbon nanotubes are electrically connected in parallel. The black film 55 has very high thermal conductivity in the planar direction. As a result, the non-uniformity of the in-plane resistance value of the black film 55 is mitigated by the lattice-shaped copper foil 52, and the temperature distribution within the heater surface is made uniform.

[0005] Such an infrared radiation type film heater 50 has excellent performance. However, while it is desirable to use the infrared radiation type film heater 50 at about 135°C to ensure fast heating, the infrared radiation type film heater 50 can only be used at about 100°C to 105°C by itself to prevent burns or the like when touching the heater directly, and may not be able to fully exhibit fast heating. In addition, materials such as carbon nanotubes contained in the black film 55 and polyimide paint for lamination used in the polyimide cover film 59 are expensive. In addition, the infrared radiation type film heater 50 has a laminated structure of 4 to 5 layers with different expansion coefficients. Therefore, even if the temperature is raised and lowered slowly and stepwise in the pressurized heat fusion process of its manufacture, the infrared radiation type film heater 50 is likely to bend and air bubbles are likely to be generated between each layer. In addition, the manufacturing process takes a long time, resulting in low production efficiency, and the infrared radiation type film heater 50 is likely to be expensive. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2004-14178 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide an excellent infrared radiation film heater which has a simple structure, is inexpensive, has a good finished shape without bending, and exhibits high rapid heating performance. [Means for solving the problem]

[0008] According to one aspect of the present invention, a film heater comprises a heat-resistant insulating film, a metal foil provided on the heat-resistant insulating film, and a black film provided on the metal foil, the black film having protrusions configured to provide a thermal insulation function and at least one hole provided in each of the protrusions. Effect of the Invention

[0009] According to the present invention, an excellent infrared radiation type film heater can be provided. [Brief description of the drawings]

[0010] [Figure 1A] FIG. 1A is a schematic plan view showing an outline of a configuration example of a film heater according to one embodiment, illustrating a surface on which a heater pattern is formed. [Figure 1B] FIG. 1B is a schematic cross-sectional view showing an outline of a configuration example of a film heater according to one embodiment, and is a schematic view showing an outline of a partial cross section taken along line IB-IB shown in FIG. 1A. [Diagram 2] FIG. 2 is a schematic diagram showing an example of a cross-sectional structure of an infrared radiation film heater according to a conventional technique. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An embodiment will be described with reference to the drawings. This embodiment relates to an infrared radiation type film heater. This film heater can be used for various purposes. For example, this film heater can be used as a foot heater for an electric vehicle.

[0012] Fig. 1A is a schematic plan view showing an example of the configuration of a film heater 10 according to the present embodiment, showing a surface on which a heater pattern is formed, and Fig. 1B is a schematic cross-sectional view showing an example of the configuration of a film heater 10 according to the present embodiment, showing a schematic partial cross-section taken along line IB-IB shown in Fig. 1A.

[0013] The film heater 10 has a heat-resistant insulating film 1 and a metal foil 2 provided on the heat-resistant insulating film 1. The metal foil 2 has a heater pattern. When the film heater 10 is used as a foot heater for an EV whose normal temperature exceeds 100°C, the heat-resistant insulating film 1 is formed of, for example, polyimide (PI) resin. The metal foil 2 is formed of, for example, stainless steel (SUS). The heat-resistant insulating film 1 may be made of polyethylene terephthalate (PET) resin, polyethylene naphthalate (PEN) resin, or the like. The metal foil 2 may be made of copper, nichrome, or the like. These materials may be selected according to, for example, the operating temperature range 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.

[0014] The heat-resistant insulating film 1 and the metal foil 2 can be produced in the same manner as a so-called flexible printed circuit board for electronic circuit wiring, which is excellent in stability and economy. That is, the heat-resistant insulating film 1 is formed by laminating, for example, a PI resin with a thickness of 25 μm on a thin SUS film with a thickness of, for example, 30 μm. Then, the metal foil 2 is formed by processing the thin SUS film to remove a part of it so that the thin SUS film has a predetermined resistance value and temperature distribution. For example, etching can be performed as a process for removing a part of the thin SUS film.

[0015] The thickness of the metal foil 2 is determined by the required electrical resistance value, shape, etc. In order to achieve a uniform temperature distribution within the surface, it is preferable that the pattern part of the metal foil 2 is formed so as to minimize empty space. Both ends of the pattern part of the metal foil 2 are provided with connection parts 2a to be connected to a power source in order to apply a voltage to the metal foil 2.

[0016] When a poorly adhesive PET film, PEN film, or the like is used as the heat-resistant insulating film 1, the heat-resistant insulating film 1 and the metal foil 2 may be produced, for example, as follows. That is, the surface of the metal foil 2 is laminated with a heat-sealable resin. In addition, the surface of the heat-resistant insulating film 1, such as a PET film or PEN film, is activated by a corona discharge treatment. The heat-resistant insulating film 1 and the laminated surface of the metal foil 2 are heat-sealed.

[0017] In cases where the heat-resistant insulating film 1 is insufficiently thick and has poor mechanical strength, for example, a PI film having different physical properties may be heat-sealed to the above-mentioned PI resin laminate layer.

[0018] In this embodiment, a so-called SUS etching heater can be used, which has a heat-resistant insulating film 1 made of PI resin and a metal foil 2 made of SUS foil, formed by laminating PI resin on SUS foil. Such a structure including the heat-resistant insulating film 1 and the metal foil 2 is referred to as a metal foil heater 3 here.

[0019] 1A, in this embodiment, a touch sensor electrode 8 constituting an electrode of a capacitance-type touch sensor is provided on the outer periphery of the metal foil 2 forming the heater pattern on the heat-resistant insulating film 1. The touch sensor electrode 8 is formed of, for example, the same SUS foil as the metal foil 2. The touch sensor electrode 8 has a linear pattern so as to go substantially around 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.

[0020] As shown in FIG. 1B, a resin layer 4 is provided on the metal foil heater 3. An adhesive may be used for the resin layer 4. This adhesive is preferably a thermosetting adhesive that has good adhesive strength and heat shrinkability even when thin, rather than a thermoplastic adhesive that expands and contracts greatly with heating and cooling cycles. The adhesive used for the resin layer 4 is preferably an epoxy adhesive that has high heat resistance among general-purpose thermosetting adhesives. Epoxy adhesives are less expensive than polyimide adhesives. Furthermore, epoxy adhesives require simple curing conditions and can be manufactured in a relatively short time.

[0021] The resin layer 4 provided on the surface of the metal foil heater 3 has a thickness of, for example, about 10 μm to 30 μm. In order to isolate the metal foil 2 from the outside and to ensure the insulation of the metal foil 2, the resin layer 4 preferably has a thickness of, for example, about 15 μm.

[0022] As shown in FIG. 1B, a black film 5 is disposed and adhered on the resin layer 4. The black film 5 is a blackened film that exhibits an infrared radiation function. The black film 5 is formed by adding carbon to a resin base material. For example, a PI resin having excellent heat resistance can be used for the black film 5. For the black film 5, a relatively inexpensive PET resin, PEN resin, or the like can be used. In the black film 5, carbon is responsible for infrared radiation and is not responsible for electrical conduction. Therefore, inexpensive carbon black can be used. There is no need to use carbon nanotubes, which are expensive and have strict safety standards. That is, the black film 5 is blackened by containing carbon black. Other materials, such as black ceramics, may be used instead of carbon. However, carbon black is a preferable material in terms of infrared radiation efficiency, material availability, price, and other conditions.

[0023] The black film 5 can be formed, for example, by mixing carbon black with resin powder and molding the mixture into a film using a twin-screw kneading extruder. Alternatively, the black film 5 can be formed, for example, by dispersing carbon black in a resin solution, curing the solution using a heating roller, and molding the resulting mixture into a film.

[0024] The thickness of the black film 5 is, for example, 25 μm to 100 μm. In consideration of shape processing, the thickness of the black film 5 is preferably, for example, about 75 μm. The volume resistivity of the black film 5 containing the PI resin and carbon black is set to 1×10 10 Ω cm~1×10 13 It is about Ω cm, preferably 1×10 11 It is about Ω·cm.

[0025] The black film 5 is embossed. The black film 5 is embossed before it is attached to the metal foil heater 3. For this embossing, a pair of dies including a male die with an embossed shape having needle-like projections at the top and a corresponding female die are used. In the embossing, the black film 5 to be processed is sandwiched between the pair of dies and hot pressed or the like. When a PI resin is used, the hot press is performed at a molding temperature of, for example, 300°C to 370°C and a pressure of 1 kg / cm. 2 ~5kg / cm 2 This is carried out under the conditions that:

[0026] The black film 5 has protrusions 6 formed by embossing. The protrusions 6 are uniformly arranged over 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 in the touch sensor electrode 8 portion.

[0027] The protrusions 6 are preferably, for example, cylindrical or truncated conical. If the shape of the protrusions 6 is a prismatic shape with corners, the black film 5 may be wrinkled or cracked when the male mold is pressed in. For this reason, the shape of the protrusions 6 is preferably a shape without corners. In addition, in order to facilitate smooth removal from the mold, the shape of the protrusions 6 is preferably, for example, a truncated conical shape with a taper angle.

[0028] When the shape of the protrusions 6 is a truncated cone, the diameter of the bottom is preferably 2 mm to 8 mm, and more preferably 3 mm to 6 mm. Even when the shape of the protrusions 6 is other than that, the size of the protrusions in the planar direction is preferably 2 mm to 8 mm, and more preferably 3 mm to 6 mm. The height of the protrusions 6 is preferably 1 mm to 5 mm, and more preferably 2 mm to 4 mm.

[0029] The density of the arrangement of the protrusions 6 on the black film 5 is preferably at least one per 20 mm square. Although it depends on the diameter of the base of the protrusions 6, the density of the arrangement of the protrusions 6 is more preferably at least one per 5 mm square to 10 mm square.

[0030] At least one hole 7 is provided at the top of each protrusion 6, which is formed by a needle-like protrusion at the top of the male mold used for embossing. The diameter of the hole 7 is preferably 1 μm to 150 μm, and more preferably 10 μm to 50 μm. The number of holes 7 provided in each protrusion 6 may be two or more.

[0031] The holes 7 serve to release the pressure of the air in the protrusions 6 expanded by heating, the expansion pressure of the fine air bubbles contained in the resin layer 4, and the expansion pressure of the residual air bubbles between the resin layer 4 and the black film 5. It is difficult to avoid the generation of residual air bubbles between the resin layer 4 and the black film 5 in the bonding process. On the other hand, since the film heater 10 of this embodiment has a relatively simple structure, the air bubbles remaining between the laminated layers of the film heater 10 are relatively small overall. The holes 7 also serve to promote ventilation between the inside of the protrusions 6 and the outside air, thereby lowering the temperature inside the protrusions 6. The holes 7 also prevent the protrusions 6 from being crushed by the air that contracts during cooling.

[0032] In the infrared radiation type film heater 10 of this embodiment, the convex portion 6 is formed on the surface of the black film 5, which is the outermost layer. Air exists inside the convex portion 6, and the convex portion 6 exhibits a heat insulating function. As a result, the temperature of the top of the convex portion 6 is difficult to rise. In addition, the heat capacity of the hollow convex portion 6 is small. Therefore, for example, when the metal foil 2 is about 135°C, the temperature of the top of the convex portion 6 is lower than about 135°C, and even if a person's skin should directly touch the top of the convex portion 6 on the surface of the black film 5, the person hardly feels the high heat and usually does not get burned. Since the temperature of the metal foil heater 3 can be raised to a relatively high temperature, for example, about 135°C, the temperature rise time of the heated object is relatively short.

[0033] The black film 5 including the protrusions 6 is heated by the heat generated in the metal foil 2 mainly via the flat portions 5a of the black film 5 that are in contact with the resin layer 4. Therefore, the size and density of the protrusions 6 affect the temperature rise time at the tops of the protrusions 6 and the temperature rise time of the heated body due to infrared radiation.

[0034] It is preferable to use a thermosetting resin such as an epoxy adhesive having high heat resistance for the resin layer 4, but generally, thermosetting resins tend to continue to shrink over a long period of time when heated. By curing the resin while applying pressure, the resin layer 4 can be made flat at the beginning of manufacture. However, as the film heater 10 continues to be used, the resin layer 4 may shrink over time. In contrast, in the film heater 10 of this embodiment, the black film 5 adhered to the resin layer 4 has a protrusion 6 that is not in contact with the resin layer 4. This protrusion 6 serves to reduce the shrinkage force that the black film 5 receives from the resin layer 4. As a result, the curvature of the entire film heater 10 can be suppressed.

[0035] The film heater 10 of this embodiment has a relatively simple structure. Therefore, the film heater 10 is lightweight, resistant to vibration and impact, and has high robustness. In addition, by utilizing infrared radiation from the black film 5, the film heater 10 has relatively fast heating and consumes relatively little power. The manufacturing process of the film heater 10 is also relatively simple, and the time required for manufacturing is relatively short. The film heater 10 can be manufactured using relatively inexpensive general-purpose materials. For example, the film heater 10 can use relatively inexpensive materials such as a SUS etching heater that has been conventionally reliable and a PI film to which carbon black has been added. Therefore, the film heater 10 can be manufactured relatively inexpensively.

[0036] As described above, the film heater 10 of the present embodiment has excellent fast heating properties, energy saving properties, shape stability, cost efficiency, etc. The film heater 10 has a wide variety of applications, and has high performance, for example, as a heater for an electric vehicle.

[0037] In the above embodiment, an example in which the inside of the protrusion 6 is air has been described. However, this is not limited to this. In order to improve durability against crushing of the protrusion 6 due to the effect of repeated heating and cooling compared to when the inside of the protrusion 6 is air, a foam having open cells corresponding to the shape of the protrusion 6 may be disposed inside the protrusion 6. As the open cell foam, a heat-resistant polymer foam having a specific heat larger than that of ceramics may be used. For example, a silicone rubber sponge, a fluororubber sponge, or the like may be used. EXAMPLES

[0038] The film heater 10 according to the above-described embodiment was manufactured, and various characteristics were measured and evaluated.

[0039] [Sample preparation] As a sample of an infrared radiation type film heater, a film heater 10 was produced in consideration of use where the metal foil 2 is about 135°C. To produce the metal foil heater 3, a film in which a commercially available SUS foil was laminated with PI resin was used. The film used was a SUS foil with a thickness of 25 μm, with a PI resin with a thickness of 35 μm laminated on one side. Such films are widely available commercially for use as film heaters. In this example, a film with a size of 150 mm x 210 mm was used. Using such a film, a metal foil heater 3 was produced in which a heat-resistant insulating film 1 made of PI resin with a thickness of 35 μm was used as a base, and a metal foil 2 made of SUS foil with a thickness of 25 μm was provided on top of it.

[0040] The pattern of the metal foil 2 of the metal foil heater 3 was formed by a well-known etching method. That is, a predetermined pattern was formed on the surface of the SUS foil with a resist film, and unnecessary SUS foil was removed by immersion in an etching solution. In this embodiment, the heater pattern had as little open space as possible. The resistance value of the heater pattern was set to 4.5Ω. Connection parts 2a to be connected to a power source are provided at both ends of the heater pattern.

[0041] Further, a touch sensor electrode 8 for sensing a capacitive touch sensor was formed on the outer periphery of the heater pattern. The width of the touch sensor electrode 8 was 5 mm.

[0042] A commercially available general-purpose black PI film having excellent heat resistance was used as the black film 5. The black film 5 was colored black with carbon black.

[0043] The black film 5 was set in a mold of a hot press machine for embossing to form a convex portion 6. The hot press conditions were a temperature of 350° C., a time of 3 minutes, and a pressure of 3 kg / cm. 2 It was decided.

[0044] A plurality of samples with different bottom diameters, heights, and densities of the protrusions 6 were prepared. The diameters of the bottoms of the protrusions 6 were three types, 3 mm, 6 mm, and 10 mm. The heights of the protrusions 6 were four types, 2.5 mm, 3 mm, 4 mm, and 6 mm. The arrangement densities of the protrusions 6 were three types, one per 6 mm square, one per 10 mm square, and one per 18 mm square. In addition, a plurality of samples with different diameters of the holes 7 provided at the tops of the protrusions 6 were prepared. The diameters of the holes 7 were three types, 50 μm, 100 μm, and 200 μm. Six types of samples, Examples 1 to 6, were produced according to these combinations. The combinations of the dimensions of each part are shown in Table 1.

[0045] [Table 1]

[0046] In Examples 1 and 2, the density of the projections 6 was one per 6 mm square, the bottom diameter of the projections 6 was 3 mm, and the height was 2.5 mm. In Example 1, the diameter of the holes 7 was 50 μm, and in Example 2, the diameter of the holes 7 was 100 μm. The specifications of Examples 1 and 2 are expected to be the most practical in terms of safety and thermal efficiency.

[0047] In Examples 3 and 4, the density of the projections 6 was one per 10 mm square, the diameter of the bottom of the projections 6 was 6 mm, and the height was 3 mm. In Example 3, the diameter of the holes 7 was 50 μm, and in Example 4, the diameter of the holes 7 was 100 μm. Examples 3 and 4 were conducted to confirm whether the temperature at the top of the projections 6 could be further reduced by increasing the diameter of the projections 6.

[0048] In Example 5, the density of the projections 6 was one per 18 mm square, and the diameter of the bottom of the projections 6 was 10 mm. In Example 5, the height of the projections 6 was 4 mm, a silicone rubber sponge of approximately the same shape as the projections 6 was placed inside the projections 6, and the diameter of the holes 7 was 200 μm. The specifications of Example 5 were intended to confirm whether the temperature of the tops of the projections 6 could be lowered by increasing the diameter of the bottoms of the projections 6, even if the number of projections 6 was reduced and fingertips were more likely to come into contact with the high-temperature flat portion 5a of the black film 5. Example 5 was also intended to confirm whether the silicone rubber sponge placed inside the projections 6 could prevent the tops of the projections 6 from becoming indented.

[0049] In Example 6, similar to Example 5, the density of the arrangement of the protrusions 6 was one per 18 mm square, and the diameter of the bottom of the protrusions 6 was 10 mm. In Example 6, the height of the protrusions 6 was 6 mm, and no holes 7 were provided. The specifications of Example 6 were intended to confirm whether the temperature at the top of the protrusions 6 could be lowered without holes 7 if the internal space of the protrusions 6 was large, even if the number of protrusions 6 was reduced and fingertips were more likely to come into contact with the high-temperature flat portion 5a of the black film 5.

[0050] As described above, each black film 5 with different specifications of the convex portion 6 was adhered to the surface of the metal foil heater 3. A one-liquid epoxy adhesive (RO-8699, manufactured by Sanyu Rec Co., Ltd.) was used as the adhesive. The metal foil heater 3 was placed with the side on which the metal foil 2 was formed facing up, and about 20 μm of adhesive was applied to the upper surface of the metal foil heater 3. The black film 5 of each example was placed on top of it with its convex portion 6 facing up, and dried and cured at 150° C. for 1 hour. However, in the case of Example 5, the black film 5 was placed on the lower side and the metal foil heater 3 was placed on the upper side for adhesion. At this time, the penetration of the adhesive into the convex portion 6 was slight, and the voids of the silicone sponge inside the convex portion 6 were sufficiently secured.

[0051] The samples of Comparative Examples 1 and 2 have a flat black film 5 without a protrusion 6 bonded to a metal foil heater 3. This structure is such that when the metal foil 2 is heated to 135°C, touching the black film 5 may cause burns. The metal foil heater 3 and the black film 5 were bonded in the same manner as in the above-mentioned Examples. In Comparative Example 1, the operating conditions of the sample, such as the voltage applied to the metal foil 2, were the same as in Examples 1 to 6, and various measurements were performed. In Comparative Example 2, various measurements were performed under operating conditions in which the voltage applied to the metal foil 2 was lower than in Examples 1 to 6.

[0052] [Measurement method] For each sample shown in Table 1, the following measurements were carried out.

[0053] <Evaluation of fingertip contact with flat surface> An evaluation was made as to whether or not a fingertip could touch the flat portion 5a of the black film 5 on the metal foil heater 3, which may become hot during use of the film heater 10. The above-mentioned samples were used. The tip of an index finger was placed in contact with the black film 5 of each sample in a non-energized state, and it was confirmed whether or not the tip of the index finger could touch the flat portion 5a between the convex portions 6 of the black film 5 with a planar width.

[0054] <Surface temperature measurement> The surface temperature of each of the above-mentioned samples, the film heater 10, was measured. The film heater 10 was hung in the air at 25° C. in a windless environment.

[0055] A DC voltage of 12.5 V was applied to both ends of the metal foil 2, which is the heating element of the film heater 10, via a temperature regulator. A small thermocouple was adhesively fixed to the center of the back surface of the film heater 10, and the lead wire of the thermocouple was connected to the temperature regulator. The temperature of the film heater 10 was automatically controlled by the temperature regulator based on the temperature measured by the thermocouple. The temperature control was performed by time proportional temperature control by the temperature regulator so as to suppress overshoot. The control set temperature was 135°C. For Comparative Example 2, the applied voltage was 11.0 V. Since the power is about 22% lower than in the other examples, the control set temperature for Comparative Example 2 was accordingly set to 105°C.

[0056] The temperature was measured in five regions: a 50 mm square region in the center of the black film 5 and four 50 mm square regions at the four corners of the black film 5. The flat portions 5a between the protrusions 6 in each region and the tops of the protrusions 6 were used as measurement points. A tiny thermocouple was used as the temperature measuring element, and the temperature was measured using a digital thermometer after the temperature measuring element was brought into contact with each measurement point. The average value of the temperatures measured in the five regions was evaluated.

[0057] (Measurement of temperature rise of heated object due to infrared radiation) The temperature rise of the heated object due to infrared radiation from the film heater 10 was measured. The operation of the film heater 10 was controlled using the same temperature control system and control method as in the above-mentioned surface temperature measurement. A black cloth slightly larger than the film heater 10 was stretched in the air 15 cm away from the surface of the film heater 10, and this black cloth was used as the heated object. The surface temperature of the black cloth corresponding to the center of the film heater 10 was measured using far-infrared thermography. The temperature measurement of the black cloth surface was performed at 1-second intervals. The measured temperature was recorded from the start of power supply to the film heater 10 until the temperature was saturated. The time from the start of power supply until the temperature reached 90% of the saturation temperature was defined as the rise time. For Comparative Example 2, the applied voltage was 11.0 V and the control set temperature was 105°C.

[0058] <Measurement of reduction in height of convex parts and curvature of film heater> First, for the unused film heater 10 samples of each Example, the height of the top of the protrusions 6 was measured using a microscope and recorded. The protrusions 6 to be measured were the protrusions 6 within five 50 mm square regions at the center of the black film 5 and at each of the four corners of the black film 5, in the same manner as in the measurement of the surface temperature described above.

[0059] Next, for each sample, in the same manner as in the above-mentioned measurement of the surface temperature, the film heater 10 was hung in the air at 25°C in the absence of wind, and a voltage of 12.5 V DC was applied to the metal foil 2 via a temperature regulator. The controlled temperature set by the temperature regulator was set to 135°C, and an on-off cycle of one hour of current application followed by one hour of no current application was repeated 100 times. Similarly, 100 cycles of current application were repeated for the film heater according to the comparative example.

[0060] After the repeated current application, each sample was moved from the suspended state to a flat state, and the height of the top of the protrusion 6 was measured and recorded using a microscope, which was the same as the initial measurement. The difference between the initial measurement and the measurement after the repeated current application was calculated. The average of the differences obtained in the five regions was used as the evaluation subject.

[0061] In addition, for each sample after the repeated application of current, a microscope was used to measure the height of the point at which the curvature from the flat surface was greatest. Here, the samples were arranged so that the maximum curvature of the periphery was facing upward, regardless of whether it was on the front or back.

[0062] <Moisture resistance test and voltage resistance test for film heaters> Each sample was placed in a thermo-hygrostat chamber at 40°C and 95% RH without current flow and left for 8 hours. Then, each sample was removed from the thermo-hygrostat chamber, condensation was wiped off, and the sample was left for 1 hour at room temperature and humidity. Then, a voltage resistance test was performed on each sample. In the voltage resistance 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 film heater 10 was tested for the presence or absence of dielectric breakdown after the AC voltage was applied.

[0063] [Measurement results and evaluation] The results of each measurement are shown in Table 2.

[0064] [Table 2]

[0065] <Evaluation of fingertip contact with flat surface> In Examples 1 to 4 in which the interval between the convex portions 6 is 4 mm or less, the fingertips did not touch the flat portion 5a of the black film 5, even though the height of the convex portions 6 was 2.5 mm or 3 mm. On the other hand, in Examples 5 to 6 in which the interval between the convex portions 6 is 8 mm, the fingertips touched the flat portion 5a of the black film 5, even though the height of the convex portions 6 was 4 mm or 6 mm. From these results, it was considered that if the interval between the convex portions 6 is narrower than about 5 mm, the fingertips are unlikely to touch the flat portion 5a of the black film 5. It became clear that design criteria such as the distribution of the convex portions 6 that take safety into consideration can be set, such as setting the interval between the convex portions 6 to 5 mm or less so that parts of the body, including the fingertips, do not touch the flat portion 5a of the black film 5, which becomes hot.

[0066] <Surface temperature> The temperature of the flat portion 5a between the protrusions 6 was a temperature corresponding to the control set temperature of 135° C., that is, about 136° C.±1° C. However, in Comparative Example 2, the control set temperature was set to 105° C., and therefore the temperature of the flat portion 5a was 106.6° C.

[0067] In the film heaters 10 of Examples 1 to 4, the temperature at the top of the protrusions 6 was approximately 110° C. to 113° C. That is, the temperature at the top of the protrusions 6 was 21° C. to 26° C. lower than that of the flat portion 5a. Although there was a slight tendency for this temperature drop to be greater when the holes 7 were larger, no significant relationship was observed between the temperature drop and the diameter of the holes 7.

[0068] In the film heater 10 of Example 5, a silicone rubber sponge was disposed inside the protrusions 6. This increased heat conduction to the surfaces of the protrusions 6, and the temperature at the tops of the protrusions 6 was 116°C. In other words, the temperature at the tops of the protrusions 6 in Example 5 was slightly higher than the temperatures at the tops of the protrusions 6 in Examples 1 to 4. The temperature difference with the flat portions 5a was also 19°C, slightly smaller than in Examples 1 to 4.

[0069] In the film heater 10 of Example 6 in which no holes 7 were provided, the temperature difference between the tops of the protrusions 6 and the flat portion 5a was about 10°C, which was significantly smaller than in Examples 1 to 4. That is, it became clear that ventilation between the inside of the protrusions 6 and the outside air by providing the holes 7 is important in lowering the temperature at the tops of the protrusions 6.

[0070] As described above, it has become clear that the structure of the film heater 10 having the protrusions 6 with the holes 7 is effective in significantly lowering the surface temperature of the film heater 10. By arranging the protrusions 6 and shaping the protrusions 6 so that the flat portions 5a between the protrusions 6 described above are not brought into contact with fingertips or the like, it is possible to keep the temperature of the parts that a person may touch low, even if the metal foil 2 is heated to a high temperature. Therefore, it has been shown that the structure of this film heater 10 makes it possible to safely heat the metal foil 2 to a high temperature.

[0071] <Temperature rise of heated objects due to infrared radiation> As a result of measuring the temperature rise of the heated object due to infrared radiation from the black film 5 of the film heater 10, the saturation temperature of the surface of the black cloth to be heated was approximately 47.5°C ± 1°C. This saturation temperature was unrelated to the presence or absence, shape, and structure of the protrusions 6 and holes 7. It was shown that the provision of the black film 5 provided the effect of stable heating by infrared radiation from the black film 5.

[0072] The black fabric surface temperature rise time in Examples 1 to 4 was 65 to 69 seconds. In contrast, the black fabric surface temperature rise time in Comparative Example 1, in which the protrusions 6 were not provided, was 45 seconds. The black fabric surface temperature rise time in Examples 1 to 4 was about 1.5 times longer than the black fabric surface temperature rise time in Comparative Example 1. On the other hand, such an increase in the rise time is considered to be no problem in practical use.

[0073] The rise time of the black cloth surface temperature in Example 5 was 85 seconds. The reason for the long rise time in Example 5 was thought to be that the silicone sponge was placed inside the protrusions 6, which increased the heat capacity of these parts.

[0074] The rise time of the black fabric surface temperature in Example 6 was 54 seconds. The reason why the rise time in Example 6 was relatively short is considered to be that the area of ​​the flat portion 5a was relatively large and the hole 7 was not provided, so that the temperature rise of the black film 5 was relatively fast.

[0075] In Comparative Example 2, the power supply voltage was lowered to lower the surface temperature of black film 5 to about 107° C., so the rise time was significantly longer than in the other examples.

[0076] As described above, by providing the convex portion 6 and the hole 7, it is possible to make the temperature of the heated body by infrared radiation relatively fast by making the temperature of the flat portion 5a of the black film 5 relatively high at 135°C while keeping the temperature of the top of the convex portion 6 relatively low without lowering the power supply voltage.

[0077] Also, it was confirmed that, as in each example, even if relatively inexpensive general-purpose carbon black is used instead of an expensive material such as carbon nanotubes, a sufficient heating effect of the heated object by infrared radiation can be obtained. In other words, it became clear that the film heater 10 using general-purpose carbon black is highly economical.

[0078] <Regarding the reduction in height of the convex parts and the curvature of the film heater> As the results are shown in Table 2, in Examples 1 to 4 and 6, there was a tendency that the smaller the bottom diameter and the shorter the height of the protrusions 6, the smaller the reduction in the height of the protrusions 6 after repeated energization. Moreover, in Example 5, in which a silicone rubber sponge was placed inside the protrusions 6, it was found that the reduction in the height of the protrusions 6 could be significantly suppressed.

[0079] Moreover, the amount of bending of the film heater 10 after repeated energization is shown in Table 2. It became clear that the structure provided with a large number of small protrusions 6 had a smaller amount of bending after repeated energization.

[0080] It has become clear that the dimensions, shape, structure, etc. of the protrusions 6 can be designed while taking into consideration other characteristics such as prevention of fingertip contact with the flat portions 5a between the protrusions 6 and shape stability.

[0081] <Moisture resistance and voltage resistance of film heaters> None of the samples experienced dielectric breakdown. This is believed to be because, despite the holes 7 being provided at the tops of the protrusions 6 of the black film 5, the diameter of the holes 7 is suitable for suppressing the exchange between the air, which has small molecules inside the protrusions 6, and the moisture, which has large molecules outside the protrusions 6. It is also believed that moisture that penetrated into the inside of the protrusions 6 was blocked by the resin layer 4. From these facts, it is believed that the dielectric strength voltage of the film heater 10 was maintained. Thus, it has become clear that the holes 7 at the tops of the protrusions 6 do not practically cause problems resulting from moisture absorption.

[0082] Although the present invention has been described above by showing preferred embodiments, it goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention.

Claims

1. Heat-resistant insulating film, A metal foil provided on the heat-resistant insulating film, which functions as a heater pattern when a voltage is applied, wherein the heater pattern consists of a metal foil portion that is larger than the empty portion, A black film provided on the aforementioned metal foil and Equipped with, The black film has a plurality of protrusions provided by the sheet-like shape of the black film, flat portions other than the protrusions, and at least one hole provided in each of the protrusions, the flat portions are in contact with the member to which the metal foil is attached, and the protrusions are separated from the member to which the metal foil is attached, and the protrusions are configured to exhibit a heat insulating function. Infrared radiation type film heater.

2. The film heater according to claim 1, wherein the black film is configured to exhibit the heat insulation function by having air inside the protrusions.

3. The film heater according to claim 1, wherein the black film is configured to exhibit the heat insulation function by having a foam having open cells arranged inside the protrusions.

4. The black film is blackened by containing carbon black, as described in any one of claims 1 to 3.

5. The film heater according to any one of claims 1 to 3, wherein the black film has a shape such that a fingertip does not come into contact with the flat portion between the protrusions over a wide area.

6. The size of each of the protrusions in the planar direction is 2 mm or more and 8 mm or less, and the density of the arrangement of the protrusions is one or more per 20 mm square, according to any one of claims 1 to 3.

7. The film heater according to any one of claims 1 to 3, wherein the height of the protrusion is 1 mm or more and 5 mm or less.

8. The film heater according to any one of claims 1 to 3, wherein the size of the hole provided in the protrusion is 1 μm or more and 150 μm or less.

9. The film heater according to any one of claims 1 to 3, further comprising a heat-resistant and insulating resin layer provided on top of the metal foil heater formed by the heat-resistant insulating film and the metal foil, and below the black film.

10. The film heater according to claim 9, wherein the metal foil heater and the black film are bonded together by a heat-resistant adhesive that forms the resin layer.

11. The film heater according to any one of claims 1 to 3, wherein the metal foil has a shape formed by processing to remove it such that it has an electrical resistance value that generates a predetermined amount of heat when a voltage is applied.

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