Film heater

Abstract

A 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) includes protruding portions (6) formed so as to exhibit a heat-insulating function, and at least one hole (7) provided in each of the protruding portions (6).

Description

Film Heater

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

[0002] For example, indirect heating foot heaters are sometimes used to heat electric vehicles in cold climates. These heaters often use film heaters, which are structurally strong, lightweight, and have a small heat capacity. 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 rapid heating performance is known. An example of the cross-sectional structure of such an infrared radiation film heater 50 is shown in FIG. 2 . This infrared radiation film heater 50 is manufactured, for example, as follows. That is, this infrared radiation film heater 50 uses a so-called flexible printed circuit board, in which copper foil 52 laminated with polyimide resin 51 is etched into a grid pattern. A polyimide adhesive 54 is selectively applied to the area of ​​this flexible printed circuit board other than the copper foil 52, and a drying process is performed. An infrared radiation paint containing carbon nanotubes or the like is applied thereon, and a drying process is performed thereon to form a black film 55. A polyimide cover film 59 with an adhesive layer is further placed thereon. These are thermally fused together by stepwise heating and pressure to form the infrared radiation film heater 50.

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

[0005] Such an infrared radiation film heater 50 has excellent performance. However, while it is desirable to use the infrared radiation film heater 50 at approximately 135°C to ensure rapid heating, it can only be used at approximately 100°C to 105°C by itself to prevent burns or other injuries if the heater is directly touched, and this may prevent the heater from fully achieving its rapid heating performance. Furthermore, materials such as the carbon nanotubes contained in the black film 55 and the polyimide coating material for lamination used in the polyimide cover film 59 are expensive. Furthermore, the infrared radiation film heater 50 has a laminated structure of four to five layers with different expansion coefficients. Therefore, even if the temperature is slowly increased and decreased in stages during the pressure heat fusion process of its manufacture, the infrared radiation film heater 50 is prone to bending and air bubbles are likely to form between the layers. Furthermore, the manufacturing process takes a long time, resulting in low production efficiency, and the infrared radiation film heater 50 tends to be expensive.

[0006] Japanese Patent Application Publication No. 2004-14178

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

[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 exhibit a heat insulating function and at least one hole provided in each of the protrusions.

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

[0010] Fig. 1A is a schematic plan view showing an outline of an example of the configuration of a film heater according to one embodiment, showing a surface on which a heater pattern is formed. Fig. 1B is a schematic cross-sectional view showing an outline of an example of the configuration of a film heater according to one embodiment, showing a schematic outline of a partial cross-section taken along line IB-IB shown in Fig. 1A. Fig. 2 is a diagram showing an outline of an example of the cross-sectional structure of an infrared radiation film heater according to prior art.

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

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

[0013] The film heater 10 includes 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 film heater 10 is used as a foot heater for an electric vehicle (EV) whose normal operating temperature exceeds 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 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 can be selected depending on, for example, the operating temperature range of the heater. For example, the thickness of the heat-resistant insulating film 1 is approximately 25 μm, and the thickness of the metal foil 2 is approximately 30 μm.

[0014] The heat-resistant insulating film 1 and metal foil 2 can be fabricated in the same manner as so-called flexible printed circuit boards for electronic circuit wiring, which are highly stable and economical. That is, the heat-resistant insulating film 1 is formed by laminating, for example, a 25 μm thick PI resin onto a thin SUS film, for example, a 30 μm thick. Then, the metal foil 2 is formed by removing a portion of the thin SUS film so that the thin SUS film has a predetermined resistance value and temperature distribution. For example, etching can be used to remove a portion 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 portion of the metal foil 2 is formed so as to minimize empty spaces. Connection portions 2a are provided at both ends of the pattern portion of the metal foil 2 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: The surface of the metal foil 2 is laminated with a heat-sealable resin. 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] When the heat-resistant insulating film 1 is not thick enough to have low mechanical strength, for example, a PI film having different physical properties may be heat-sealed to the laminate layer of the PI resin described above.

[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 onto SUS foil. A structure including such a heat-resistant insulating film 1 and metal foil 2 will be referred to as a metal foil heater 3 here.

[0019] 1A, in this embodiment, a touch sensor electrode 8 that constitutes an electrode of a capacitance-type touch sensor is provided on the outer periphery of the metal foil 2 that forms the heater pattern on the heat-resistant insulating film 1. The touch sensor electrode 8 is formed, for example, from the same SUS foil as the metal foil 2. The touch sensor electrode 8 has a linear pattern that extends approximately 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, which has adhesive strength and heat shrinkability even when thin, rather than a thermoplastic adhesive, which expands and contracts significantly with heating and cooling cycles. Of the general-purpose thermosetting adhesives, an epoxy-based adhesive, which has high heat resistance, is preferred for the adhesive used for the resin layer 4. Epoxy-based adhesives are less expensive than polyimide-based adhesives. Epoxy-based adhesives also require simple curing conditions and require a relatively short manufacturing time.

[0021] The thickness of the resin layer 4 provided on the surface of the metal foil heater 3 is, 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 thickness of the resin layer 4 is preferably, 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 infrared radiation function. The black film 5 is formed by adding carbon to a resin base material. For example, PI resin, which has excellent heat resistance, can be used for the black film 5. Relatively inexpensive PET resin, PEN resin, etc. may also be used for the black film 5. The carbon in the black film 5 is responsible for infrared radiation but not electrical conductivity. Therefore, inexpensive carbon black can be used. Carbon nanotubes, which are expensive and subject to strict safety standards, do not need to be used. In other words, the black film 5 is blackened by containing carbon black. Instead of carbon, other materials, such as black ceramic, may be used. However, carbon black is a preferred material in terms of infrared radiation efficiency, material availability, price, etc.

[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 with a heated roller, and molding the solution 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 PI resin and carbon black is set to 1×10 in consideration of the balance between infrared radiation performance and insulation resistance. １０ Ω cm to 1 x 10 １３ 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 bonded to the metal foil heater 3. For this embossing, a pair of dies is used, including a male die with an embossed shape having needle-like protrusions at the top and a corresponding female die. In the embossing, the black film 5 to be processed is sandwiched between the pair of dies and subjected to hot pressing or the like. When a PI resin is used, the hot pressing is performed at a molding temperature of, for example, 300°C to 370°C and a pressure of 1 kg / cm. ２ ~5 kg / cm ２ This is done under the condition 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 cylindrical or truncated conical, for example. If the protrusions 6 are prismatic with corners, there is a risk that wrinkles or cracks will occur in the black film 5 when the male mold is pressed in. For this reason, the shape of the protrusions 6 is preferably a shape without corners. Furthermore, in order to allow the protrusions 6 to be smoothly removed from the mold, the shape of the protrusions 6 is preferably a truncated conical shape with a tapered angle, for example.

[0028] When the shape of the protrusions 6 is a truncated cone, the diameter of the bottom is preferably 2 mm to 8 mm, 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, more preferably 3 mm to 6 mm. The height of the protrusions 6 is preferably 1 mm to 5 mm, more preferably 2 mm to 4 mm.

[0029] The density of the arrangement of the protrusions 6 on the black film 5 is preferably one or more 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 one or more per 5 mm square to 10 mm square.

[0030] At least one hole 7 is provided at the top of each protrusion 6, 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 inside the protrusions 6 that expand due to heating, the expansion pressure of fine air bubbles contained in the resin layer 4, and the expansion pressure of air bubbles remaining 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 during the bonding process. On the other hand, because the film heater 10 of this embodiment has a relatively simple structure, the amount of air bubbles remaining between the laminated layers of the film heater 10 is relatively small overall. The holes 7 also 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 air that contracts during cooling.

[0032] In the infrared radiation film heater 10 of this embodiment, protrusions 6 are formed on the surface of the outermost black film 5. Air exists inside the protrusions 6, providing heat insulation. As a result, the temperature at the top of the protrusions 6 is less likely 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 were to come into direct contact with the top of the protrusions 6 on the surface of the black film 5, the person would barely feel the heat and would not normally be burned. Because 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.

[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-based adhesive, which has high heat resistance, for the resin layer 4. However, thermosetting resins generally tend to shrink over time when heated. By curing the resin while applying pressure, the resin layer 4 can be made flat at the initial stage 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 convex portions 6 that are not in contact with the resin layer 4. These convex portions 6 function to mitigate the shrinkage force that the black film 5 receives from the resin layer 4. As a result, 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 highly robust. Furthermore, by utilizing infrared radiation from the black film 5, the film heater 10 heats up relatively quickly and consumes relatively little power. The manufacturing process for the film heater 10 is also relatively simple, and the manufacturing time is relatively short. Furthermore, 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 and a PI film containing carbon black, which have a long history of reliability. Therefore, the film heater 10 can be manufactured relatively inexpensively.

[0036] As described above, the film heater 10 of this embodiment has excellent properties such as quick heating, energy saving, shape stability, and economy. The film heater 10 has a wide range of applications, and the film heater 10 also has high performance as a heater for electric vehicles, for example.

[0037] In the above-described embodiment, the inside of the protrusion 6 is filled with air. However, this is not limited to this. To improve durability of the protrusion 6 against crushing due to repeated heating and cooling compared to when the inside of the protrusion 6 is filled with 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 higher specific heat than ceramic may be used. For example, a silicone rubber sponge, a fluororubber sponge, or the like may be used.

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

[0039] [Sample Preparation] As a sample of an infrared radiation film heater, a film heater 10 was prepared, taking into consideration use where the metal foil 2 would reach approximately 135°C. To prepare the metal foil heater 3, a commercially available film in which PI resin was laminated to SUS foil was used. The film used was a 25 μm-thick SUS foil with a 35 μm-thick PI resin laminated on one side. Such films are widely available commercially for use in film heaters. In this example, a film measuring 150 mm x 210 mm was used. Using this film, a metal foil heater 3 was prepared, in which a 35 μm-thick heat-resistant insulating film 1 made of PI resin was used as a base, and a 25 μm-thick SUS foil metal foil 2 was provided on top of it.

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

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

[0042] A commercially available general-purpose black PI film with 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 convex portions 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] Multiple samples were prepared with different bottom diameters, heights, and densities of the protrusions 6. The bottom diameters 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 density of the arrangement of the protrusions 6 was three types: one per 6 mm square, one per 10 mm square, and one per 18 mm square. Additionally, multiple samples were prepared with different diameters of the holes 7 provided at the tops of the protrusions 6. 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 based on these combinations. The combinations of dimensions and other parameters of each part are shown in Table 1.

[0045]

[0046] In Examples 1 and 2, the density of the projections 6 was one per 6 mm square, and 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, and 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 protrusions 6 were arranged at a density of one per 18 mm square, and the diameter of the bottom of the protrusions 6 was 10 mm. In Example 5, the height of the protrusions 6 was 4 mm, silicone rubber sponges of approximately the same shape as the protrusions 6 were installed inside the protrusions 6, and the diameter of the holes 7 was 200 μm. The specifications of Example 5 were intended to confirm whether the temperature at the top of the protrusions 6 could be reduced by increasing the diameter of the bottom of the protrusions 6, even if the number of protrusions 6 was reduced and fingertips were more likely to come into contact with the high-temperature flat portions 5 a of the black film 5. Furthermore, Example 5 was intended to confirm whether the silicone rubber sponges installed inside the protrusions 6 could prevent depressions at the top of the protrusions 6.

[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 even without the holes 7 if the internal space of the protrusions 6 was large, even if the number of protrusions 6 was reduced, making it easier for fingertips to come into contact with the high-temperature flat portions 5 a of the black film 5.

[0050] As described above, each black film 5 with different specifications for the protrusions 6 was adhered to the surface of the metal foil heater 3. A one-component 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 approximately 20 μm of adhesive was applied to the top surface of the metal foil heater 3. The black film 5 of each example was then placed on top with its protrusions 6 facing upward, and dried and cured at 150°C for 1 hour. However, in Example 5, the black film 5 was placed on the bottom and the metal foil heater 3 on the top for adhesion. At this time, only a small amount of adhesive penetrated into the protrusions 6, and sufficient voids in the silicone sponge inside the protrusions 6 were secured.

[0051] The samples of Comparative Examples 1 and 2 had a flat black film 5 without any protrusions 6 adhered to the 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 adhesion between the metal foil heater 3 and the black film 5 was the same as in the above-mentioned Examples. In Comparative Example 1, various measurements were performed under the same operating conditions as in Examples 1 to 6, such as the voltage applied to the metal foil 2. 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] The following measurements were carried out for each sample shown in Table 1.

[0053] <Evaluation of Fingertip Contact with Flat Portion> An evaluation was made to see whether or not a fingertip could touch the flat portion 5a of the black film 5 on the metal foil heater 3, which can become hot during use of the film heater 10. Each of the above-described samples was used. The tip of the index finger was placed in contact with the black film 5 of each sample in the 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 over a wide area.

[0054] <Measurement of Surface Temperature> The surface temperature of each of the above-described samples, that is, 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 wires of the thermocouple were 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 using the temperature regulator to suppress overshoot. The control temperature setting was 135°C. For Comparative Example 2, the applied voltage was 11.0 V. Since the power was approximately 22% lower than in the other examples, the control temperature setting 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 small 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 used as the evaluation target.

[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 used for measuring the surface temperature described above. A black cloth slightly larger than the film heater 10 was placed in the air 15 cm away from the surface of the film heater 10, and this black cloth served 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 reached saturation. The rise time was the time from the start of power supply until the temperature reached 90% of the saturation temperature. For Comparative Example 2, the applied voltage was 11.0 V and the control temperature setting was 105°C.

[0058] <Measurement of reduction in height of protrusions and curvature of film heater> First, for the unused sample of film heater 10 of each example, the height of the top of the protrusions 6 was measured using a microscope and recorded. As in the measurement of the surface temperature described above, 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.

[0059] Next, for each sample, in the same manner as in the measurement of the surface temperature described above, the film heater 10 was suspended in windless air at 25°C, and a DC voltage of 12.5 V was applied to the metal foil 2 via a temperature regulator. The controlled temperature set by the temperature regulator was 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. The film heater according to the comparative example was also subjected to 100 repeated cycles of current application in the same manner.

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

[0061] After the repeated application of current, the height of the point where the curvature from the flat surface was greatest was measured using a microscope. The samples were placed so that the maximum curvature of the periphery was facing upward, regardless of whether they were on the front or back.

[0062] <Moisture Resistance Test and Voltage Withstand Test of Film Heater> 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 at room temperature and humidity for 1 hour. Then, a voltage withstand test was performed on each sample. In the voltage withstand test, an AC voltage of 1500 V 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 dielectric breakdown after the AC voltage application.

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

[0064]

[0065] <Evaluation of Fingertip Contact with Flat Portion> In Examples 1 to 4, in which the spacing between the protrusions 6 was 4 mm or less, the fingertips did not touch the flat portion 5 a of the black film 5, even though the height of the protrusions 6 was 2.5 mm or 3 mm. On the other hand, in Examples 5 and 6, in which the spacing between the protrusions 6 was 8 mm, the fingertips touched the flat portion 5 a of the black film 5, even though the height of the protrusions 6 was 4 mm or 6 mm. From these results, it was considered that if the spacing between the protrusions 6 is narrower than about 5 mm, the possibility of the fingertips touching the flat portion 5 a of the black film 5 is low. It became clear that design criteria such as the distribution of the protrusions 6 can be established with safety in mind, such as setting the spacing between the protrusions 6 to 5 mm or less so that parts of the body, including the fingertips, do not come into contact with the flat portion 5 a of the black film 5, which becomes hot.

[0066] <Regarding 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 portions 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. That is, 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 addition, 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. In other words, it became clear that the ventilation between the inside of the protrusions 6 and the outside air, which is achieved by providing the holes 7, is important in lowering the temperature at the tops of the protrusions 6.

[0070] As described above, it has been demonstrated that the structure of the film heater 10 having the protrusions 6 with holes 7 is effective in significantly reducing the surface temperature of the film heater 10. The arrangement and shape of the protrusions 6, which are designed so that the flat portions 5a between the protrusions 6 do not come into contact with fingertips or the like, can keep the temperature of areas that may be touched by a person low, even if the metal foil 2 is heated to a high temperature. Therefore, it has been demonstrated that the structure of this film heater 10 can safely heat the metal foil 2 to a high temperature.

[0071] <Regarding the temperature rise of the heated object due to infrared radiation> Measurements of the temperature rise of the heated object due to infrared radiation from the black film 5 of the film heater 10 revealed that the saturation temperature of the surface of the black cloth, which was the heated object, was approximately 47.5°C ± 1°C. This saturation temperature was unrelated to the presence or absence, shape, and structure of the convex portions 6 and holes 7. This showed that the provision of the black film 5 provided a stable heating effect due to infrared radiation from the black film 5.

[0072] Furthermore, the rise time of the black fabric surface temperature in Examples 1 to 4 was 65 to 69 seconds. In contrast, the rise time of the black fabric surface temperature in Comparative Example 1, which was not provided with the convex portions 6, was 45 seconds. The rise time of the black fabric surface temperature in Examples 1 to 4 was about 1.5 times longer than the rise time of the black fabric surface temperature in Comparative Example 1. However, such a long rise time is considered to pose no practical problem.

[0073] The rise time of the surface temperature of the black fabric 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 surface temperature of the black fabric in Example 6 was 54 seconds. The reason why the rise time of Example 6 was relatively short is thought to be that the area of ​​the flat portion 5 a was relatively large and no holes 7 were provided, so the temperature of the black film 5 rose relatively quickly.

[0075] In Comparative Example 2, the power supply voltage was lowered to lower the surface temperature of the 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] Furthermore, it was confirmed that a sufficient heating effect of the heated object by infrared radiation could be obtained even when using relatively inexpensive general-purpose carbon black instead of an expensive material such as carbon nanotubes, as in each example. In other words, it was made clear that the film heater 10 using general-purpose carbon black is highly economical.

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

[0079] The amount of bending of the film heater 10 after repeated energization is shown in Table 2. It was found that the structure provided with a large number of small protrusions 6 resulted in less 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 preventing fingertip contact with the flat portions 5a between the protrusions 6 and shape stability.

[0081] <Moisture Resistance and Voltage Withstand Performance of the Film Heater> None of the samples experienced dielectric breakdown. This is thought 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 was suitable for suppressing the exchange between the air with small molecules inside the protrusions 6 and the moisture with large molecules outside the protrusions 6. It is also thought that moisture that penetrated inside the protrusions 6 was blocked by the resin layer 4. From these factors, it is thought that the dielectric withstand voltage of the film heater 10 was maintained. As such, it has been revealed that the holes 7 at the tops of the protrusions 6 do not cause problems due to moisture absorption in practical use.

[0082] The present invention has been described above by showing preferred embodiments, but 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. A film heater comprising: a heat-resistant insulating film; a metal foil provided on the heat-resistant insulating film; and a black film provided on the metal foil, wherein the black film has protrusions configured to exhibit a heat insulating function, and at least one hole provided in each of the protrusions.

2. The film heater according to claim 1, wherein the black film is configured to exhibit the heat insulating function when air is present inside the protrusions.

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

4. A film heater according to claim 1 or 2, wherein the size of each of said projections in the planar direction is 2 mm or more and 8 mm or less, and said projections are arranged at a density of at least one projection per 20 mm square.

5. A film heater according to claim 1 or 2, wherein the height of the convex portion is 1 mm or more and 5 mm or less.

6. A film heater according to claim 1 or 2, wherein the size of the holes provided in the convex portions is 1 μm or more and 150 μm or less.

7. A film heater according to claim 1 or 2, further comprising a heat-resistant and insulating resin layer provided above the metal foil heater formed by the heat-resistant insulating film and the metal foil and below the black film.

8. A film heater according to claim 7, wherein the metal foil heater and the black film are bonded together by a heat-resistant adhesive that forms the resin layer.

9. A film heater according to claim 1 or 2, wherein the metal foil has a shape formed by removal processing so as to have an electrical resistance value that generates a predetermined amount of heat when a voltage is applied.

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