Thin electric heating device having excellent bending resistance

Abstract

The purpose of the present invention is to provide a thin electric heating device which has excellent flexibility, which can achieve bending resistance with a bending radius of not more than 0.5 mm, and with which a desired temperature can be obtained at a low voltage (12 V or less) even when the thin electric heating device is thin-film shaped having an ink film thickness. A thin electric heating device 1 has a configuration characterized by comprising: a base substrate that is made of an electric insulating material; a heater area that has a thin-film heater electric heating wire which is formed of a conductive ink on the substrate; and a connection area in which connection terminal parts, which are formed of a conductive material along respective two opposing sides at both ends of the heater area and which are each connected to an external power source, are set, wherein the electric resistance of the connection area is lower than the electric resistance of the heater area.

Description

Thin electrothermal device with excellent flexibility

[0001] The present invention relates to a thin electric heating device having a heater wire formed by printing or the like on a substrate using conductive ink, and in particular to a thin electric heating device in which the heater wire can be formed into a thin film and which has excellent bending resistance.

[0002] Various thin heaters have been proposed in which a heating wire is formed on a substrate by printing with conductive ink, such as a thin electric heating device in which a silver paste pattern is printed on a substrate by screen printing (see, for example, Patent Document 1).

[0003] Special table 2018-513544 publication

[0004] Many of these conventional thin electric heating devices have heater wires formed by screen printing. In this case, due to the characteristics of this printing method, the ink layer forming the heating wire must be at least 5 μm thick. An ink layer of this thickness lacks flexibility and is therefore difficult to bend, particularly to achieve an excellent bending radius of 0.5 mm or less. For this reason, many conventional thin electric heating devices have been limited to use in a spread-out sheet state. However, if heaters with curved or cylindrical shapes could be created to match the shape of the object to be heated, not only would they be able to heat the object efficiently, but the range of heater applications would also be expanded. Furthermore, if heaters could be easily bent or rolled, their portability would also be improved.

[0005] Generally, the thinner the conductor, the higher the resistance of the conductor layer. Therefore, to achieve the desired heater temperature with a thin conductor layer, a higher supply voltage is required, which leads to increased power consumption. While it is possible to lower the supply voltage by increasing the conductor thickness, this not only increases manufacturing costs and reduces productivity, but also contradicts the aforementioned requirement for flexibility. Taking all of these factors into consideration, conventional heaters with heating wires formed by screen printing often have ink film thicknesses of 10 to 20 μm and a pattern in which a single heating wire is folded back and forth multiple times within the heater's heat-generating area, thereby increasing the distance of the heating wire. Increasing the distance of the heating wire thus increases resistance and therefore power consumption. In particular, when considering large-area heaters, such as those for A3 size or larger, a film thickness of 30 μm or more is realistically required to minimize power consumption. In particular, when a pattern of fine back-and-forth movement is adopted to prevent gaps between the heating wires throughout the entire area in order to eliminate unevenness in the heating temperature within the heater heating area, it is desirable that the ink film thickness forming the heating wire be 200 μm or more in order to reduce resistance as much as possible and suppress power consumption.

[0006] The aforementioned Patent Document 1 discloses an electric heating device that can achieve a desired temperature at a low voltage (12 V or less), in which a silver paste pattern is printed on graphene using, for example, screen printing. However, the thickness of the silver paste is 25 μm. Thus, it has been difficult to manufacture a practical thin electric heating device with excellent flexibility using conventional screen printing.

[0007] Here, when a heating wire is formed using flexographic printing or inkjet printing, the ink film thickness can be reduced to 5 μm or less, thereby imparting flexibility to a thin electric heating device. However, as described above, a thinner film thickness increases the resistance of the conductor layer. Therefore, it has not been possible to create an electric heating device that can generate a desired temperature at a low voltage simply by using a single heating wire that is repeatedly reciprocated, as in the case of conventional screen-printed heating wires. Specifically, there is a demand for a flexible electric heating wire with a film thickness of 5 μm or less that can generate a desired temperature at a low voltage (12 V or less). In particular, to achieve excellent flexibility with a bending radius of 0.5 mm or less, it is desirable to be able to generate a desired temperature at a low voltage (12 V or less) even with an electric heating wire with a film thickness of 1 μm or less.

[0008] As a result of extensive research, the inventors have discovered that for a heater having a thin-film electric heating wire formed by flexographic printing, inkjet printing, or coating, by focusing on the electrical resistance of the area having the electric heating wire and the area having terminals connected to an external power source, it is possible to produce a heater that can obtain a desired temperature at a low voltage even if the film thickness is 5 μm or less, and have completed the present invention.

[0009] Here, electrical resistance does not refer solely to the resistance value as a so-called physical value, but rather refers to a concept that comprehensively evaluates the ease (difficulty) of current flow in a target area based on differences in the shape of the heating wire pattern that constitutes the target area, the thickness (wire width) of the heating wires, the spacing between the heating wires, the conductive material that forms the heating wires, etc. In other words, for example, the thicker the thickness (wire width) of the heating wires and the more linear the heating wires, the easier the current will flow. Such ease of current flow is evaluated as low electrical resistance. Conversely, when the heating wires are thin or the pattern changes direction multiple times due to the heating wires crossing and branching, the more changes there are, the more difficult the current will flow. Such difficulty of current flow is evaluated as high electrical resistance. This concept derives the level of electrical resistance in a target area by comprehensively evaluating factors that affect the ease (difficulty) of current flow for the entire target area.

[0010] To solve the above problems, the present invention provides a thin electric heating device comprising a substrate made of an electrically insulating material, a heater area having a thin-film heater wire formed on the substrate using a conductive ink, and connection areas formed along two opposing edges of the heater area using a conductive material, each of which has a connection terminal for connection to an external power source. The connection areas have a lower electrical resistance than the heater area. This configuration allows for the heater wire to be formed by flexographic printing or inkjet printing, which allows for a highly flexible ink film thickness of 5 μm or less, and allows for heat generation at a desired temperature at a low voltage (12 V or less). The conductive material forming the connection area may literally be any material that is electrically conductive, and may be, for example, the conductive ink used to form the heater area. That is, the connection area may also be formed by printing a conductive ink, similar to the heater area. Of course, the connection area may also be formed from a different conductive material than the conductive ink used to form the heater area, such as a metal material such as copper.

[0011] Another embodiment of the thin electric heating device of the present invention is characterized in that the heater wire is a thin conductive ink film formed over the entire heater area on the substrate by flexographic printing, inkjet printing, or coating with a conductive ink, and the connection area is formed along the two opposing sides with a conductive material different from the conductive ink forming the heater wire. Here, forming a thin conductive ink film over the entire heater area means applying conductive ink over the entire heater area by printing, i.e., performing so-called solid fill printing over the entire area. Flexographic printing or inkjet printing is preferably used as the printing method. Alternatively, a thin conductive ink film can be formed by coating the substrate with conductive ink using a coater or the like, instead of printing. When the heater area heating wire has such a solid fill pattern, the connection area is formed with a conductive material different from the conductive ink forming the heater wire, and connection terminals for connection to an external power source are provided at appropriate locations in the connection area. With this configuration, even if the heating wire is formed in a so-called solid pattern, it is possible to obtain a uniform heating effect with little temperature unevenness across the entire heater area.

[0012] Another embodiment of the thin electric heating device of the present invention is characterized in that the heating wire is a thin-film heating wire formed by flexographic printing or inkjet printing of a conductive ink, forming a pattern in which the direction of current flow from one of the connection terminals to the other changes multiple times, and the width of the connection area in the direction of current flow is wider than the line width of the heating wire. In this embodiment, the heating wire pattern changes the direction of current flow multiple times from one of the connection terminals to the other. That is, the current flow path does not proceed in a straight line from one of the connection terminals to the other, but rather changes the direction of current flow multiple times between the connection terminals, for example, in a zigzag pattern. This configuration increases the electrical resistance of the heating wire, allowing the heating wire to generate heat at a higher temperature when the same applied voltage is used.

[0013] Another aspect of the thin electric heating device of the present invention is characterized in that the width of the connection area in the direction of current flow increases as the distance from the location of the connection terminal in the direction perpendicular to the direction of current flow increases. This configuration facilitates a uniform current flow throughout the connection area, which in turn facilitates a more uniform current flow throughout the heater area, making it easier to achieve more uniform heat generation throughout the heater area. It also prevents overheating of the connection terminal and suppresses deterioration of the connection area.

[0014] In another embodiment of the thin electric heating device of the present invention, the pattern is a pattern in which a shape having branch points formed by lines extending in different directions intersecting is repeated multiple times. With this configuration, the heating wires in the heater area can be designed as a pattern with excellent heating efficiency that can obtain a higher heating temperature at a low voltage, resulting in a thin electric heating device that generates heat efficiently while reducing power consumption.

[0015] Another embodiment of the electric heating device of the present invention is characterized in that, in the electric heating device described above, the base material is folded or bent to form a shape in which the heater areas are stacked in multiple layers. With this configuration, it is possible to enhance the heat retention effect by stacking the heater areas in multiple layers, so that the heater can generate heat at a higher temperature while maintaining a low voltage, i.e., while keeping power consumption low, resulting in a thin electric heating device with extremely excellent heat generation efficiency.

[0016] According to the present invention, a thin electric heating device can be obtained that is highly flexible and can achieve bending resistance with a bending radius of 0.5 mm or less, and that can obtain a desired temperature at a low voltage (12 V or less) even with a thin ink film thickness. In particular, even when enlarged to A3 size or larger, a more uniform heating temperature can be obtained across the entire heater area with less power consumption.

[0017] 1A and 1B are diagrams comparing two embodiments of a thin electric heating device of the present invention, where (a-1) and (b-1) show an overview of the entire device, (a-2) and (b-2) show the positional relationship of each area of ​​the device, and (a-3) and (b-3) are schematic diagrams showing the expected current flow in each embodiment.

[0034] A schematic diagram showing an example of a heating wire pattern in the heater area of ​​a thin electric heating device of the present invention. A schematic diagram showing the relationship between the heating wire line width and the spacing between wires for an example of a heating wire pattern in a thin electric heating device of the present invention. A schematic diagram showing a state in which a slit has been made in an embodiment of a thin electric heating device of the present invention. A schematic diagram showing an example of a connection area for an embodiment of a thin electric heating device of the present invention. (a) is a table showing the relationship between the size and angle of the connection area for an embodiment of a thin electric heating device of the present invention, (b) is a graph of the relationship obtained from the table in (a), and (c) is a schematic diagram showing an example of the position of the connection terminal in the connection area. A schematic diagram showing an embodiment of a thin electric heating device of the present invention. FIG. 1 is a thermographic image showing the heat generation state of the heater area for one embodiment of the thin electric thermal device of the present invention. FIG. 2 is a thermographic image comparing the uniformity of heat generation in the heater area for one embodiment of the thin electric thermal device of the present invention. FIG. 3 is a thermographic image comparing the heat generation state when different electric thermal patterns are mixed for one embodiment of the thin electric thermal device of the present invention. FIG. 4 is a schematic diagram showing an example of how to fold the film device for use in a folded state for one embodiment of the thin electric thermal device of the present invention.

[0018] The thin electric heating device of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a diagram illustrating an outline of a thin electric heating device according to the present invention. The left-hand column (a) shows a first embodiment in which the heating wire in the heater region is formed by printing or coating a solid pattern with conductive ink. The right-hand column (b) shows a second embodiment in which the heating wire in the heater region is formed by printing a grid-like or other pattern with conductive ink. In FIG. 1, (a-1) and (b-1) are schematic diagrams illustrating the outline of the thin electric heating device according to each embodiment, and (a-2) and (b-2) are schematic diagrams illustrating the positional relationship between the heater area and the connection area. Finally, (a-3) and (b-3) are schematic diagrams illustrating the expected current flow in each embodiment.

[0019] As shown in (a-1) and (b-1) of FIG. 1, the thin electric heating device 1 of the present invention has a thin-film heater wire 21 (conductive ink thin film layer 2) formed on a substrate by printing or the like using a conductive ink. As shown in (a-2) and (b-2) of FIG. 1, the area containing this heater wire 21 is the heater area HA. ​​Then, along two opposing sides (M, M) at both ends of the heater area HA, respective connection areas CA are formed using a conductive material. Here, the conductive material forming the connection area may literally be a material that is conductive, and may be, for example, the conductive ink used to form the heater area's heating wire 21. That is, like the heater area, the connection area may also be formed by printing using a conductive ink using a flexographic printing method, inkjet printing, or the like. Of course, the connection area may also be formed using a conductive material different from the conductive ink used to form the heater area, such as a metal material such as copper.

[0020] Within this connection area CA, for example, at the position indicated by the open circle in FIG. 1 , the connection terminal 3 is set. This connection terminal 3 is a so-called application point where a voltage is applied to the heater area HA by connecting a cord or the like (neither of which is shown) connected to an external power source to both poles (3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h, 3i, 3j, 3j, 3k, 3k, 3m ...

[0021] Next, each of the embodiments shown in (a) and (b) in FIG. 1 will be described. As a first embodiment, the thin electric heating device 1(a) shown in (a-1) in FIG. 1 has a thin-film heater wire 21 formed in the heater area HA, which is formed by printing a so-called solid pattern over the entire heater area. That is, in this first embodiment, the electric heating wire 21 is formed by forming a thin-film layer 2 made of conductive ink on a substrate over the entire heater area HA. ​​Here, a general metal-containing ink can be used as the conductive ink. Furthermore, there is no particular limitation on the size of the heater area.

[0022] In the first embodiment, the connection area CA formed along the two opposing sides (M, M) of the heater area HA is formed of a conductive material different from the conductive ink forming the heater wire 21. Here, "different conductive material" means a material different from the ink forming the heater wire, and copper or aluminum foil or conductive tape 4 can be suitably used. While the metal contained in the conductive ink may be the same as, for example, the metal used in the conductive tape, it is desirable that the metal material forming the connection material be more conductive than the heater wire, since the electrical resistance of the connection area must be lower than that of the heater area. This consideration is not limited to the selection of the metal material, but also takes into account the relationship between the thickness of the heater wire and the width of the connection area. It is particularly preferable for the conductivity of the heater area to be 10 times or more that of the heater wire, as this facilitates uniform current flow through the heater area. One example of a specific method for forming the connection area is to form a thin film layer of conductive ink on the outer sides of both ends of the heater area, i.e., on the portions forming the connection area, by printing in the same manner as the heater area. In this case, it is desirable that the connection area be a so-called solid filled pattern. The connection area can then be formed by applying conductive tape 5 to the area where the solid pattern is printed. Alternatively, as a simpler method, the connection area can be formed by applying conductive tape so that it partially overlaps both ends of the heater area, without bothering to form a thin film layer of conductive ink in the connection area, so that the conductive tape extends beyond the heater area and substrate.

[0023] By setting the connection terminal 3 within the connection area CA thus formed and connecting it to an external power source to pass current through the heating wire formed in the heater area HA, the heater area can be heated, allowing the thin electric heating device of the present invention to be used as a heater. The connection terminal may be formed as a terminal from the design stage, or any location within the connection area can be used as the connection terminal 3 if an electrical connection is made. For example, a simpler method would be to use a conductor with an alligator clip at the end and clip the appropriate location within the connection area. In this case, the location clipped by the alligator clip would be set as the connection terminal. The connection terminal is preferably located approximately in the center of the connection area, as shown in Figure 1. Setting it in the center facilitates even current flow in the vertical direction (Y-axis direction) of the connection area in Figure 1, facilitating more uniform heating throughout the heater area. This is also desirable in terms of suppressing overheating of the connection terminal and preventing its deterioration.

[0024] Regarding the size of the connection area, it is preferable that the length in the Y-axis direction in FIG. 1 roughly matches the length in the Y-axis direction of the heater area (the length of the two opposing sides at both ends of the heater area, i.e., the length of one side (M) where the heater area and connection area are connected). Furthermore, the length in the X-axis direction in FIG. 1 (the so-called width of the conductive tape) Lx is preferably 10 mm or more. Setting the size of the connection area in this way makes it easier for current to flow more uniformly throughout the heater area, allowing the entire heater area to generate heat more uniformly.

[0025] Next, we will explain the second embodiment shown in FIG. 1 (b). In this second embodiment, the heater area HA is formed with heating wires 21 having a grid-like pattern or the like. In the following explanation, we will omit the parts common to the first embodiment and mainly discuss the differences. An example of a pattern for the heater area HA in the second embodiment is shown in FIG. 2. Each pattern shows a portion of a repeating pattern. Furthermore, in this figure, the connection terminals 3 (application points) are illustrated as being located on the outer sides of both the left and right ends of each pattern. That is, the figure assumes that the current flows from left to right along the X-axis in FIG. 2. It is desirable that the heating wire pattern in the second embodiment be a pattern in which the direction of current flow from one connection terminal to the other changes multiple times, as in the example shown in FIG. 2. By changing the direction of current flow multiple times in this way, it becomes easier for the current to flow uniformly throughout the heater area compared to a pattern in which the current flows in a straight line from one application point to the other without changing direction. The pattern in Figure 2 (P-1) is a pattern in which the current flows in a zigzag pattern, while the patterns in Figure 2 (P-2) to (P-4) are patterns in which straight lines in different directions intersect with each other. The intersecting patterns in Figure 2 (P-2) to (P-4) do not form a straight path in the X-axis direction from connection terminal 3a to 3b in Figure 2, and are patterns in which the direction of current flow is always forcibly changed at the intersection. Such patterns are not limited to combinations of straight lines, but may also include combinations of curved lines as in Figure 2 (P-5) or a houndstooth pattern (punched metal) with cutouts as in Figure 2 (P-6).

[0026] This is thought to be because, in a pattern where the current can flow in a straight line without changing direction, the current tends to flow along the shortest route. However, when a pattern like the one shown in Figure 2 is used, which prohibits the current from flowing in a straight line and forces the current to change direction multiple times, the electrical resistance of the heating wire increases, causing the current to flow along routes other than the shortest route, making it easier for the current to flow uniformly throughout the heater area. Therefore, by using a heating wire pattern that changes the current direction multiple times, as shown in Figure 2, the entire heater area tends to generate heat more uniformly and without unevenness. Furthermore, forming a heating wire pattern in this type of heater area increases the electrical resistance of the heating wire compared to a heating wire in which the entire area is solidly filled, as in the first embodiment. Higher electrical resistance means that the current tends to heat up at a higher temperature with the same applied voltage, which has the advantage of reducing power consumption and making it easier to efficiently obtain the desired heating temperature. Furthermore, as mentioned above, by considering the pattern, it is possible to mix areas that generate heat easily with areas that do not generate heat easily, making it possible to design a heater that meets the needs of those who want to heat only a specific area or only an extremely narrow area in a focused manner.

[0027] Among the heating wire pattern examples shown in FIG. 2, more preferred are patterns such as those shown in (p-2), (p-3), (p-4), and (p-5), which have a repeated pattern of multiple branches formed by lines extending in different directions crossing each other. Here, "crossing" refers not only to crossings but also to T-shaped crossings, as long as there are multiple options for the next path at the crossing point. Particularly preferred are patterns such as those shown in (p-3) and (p-4), which combine relatively long and relatively short lines. Such patterns are preferred because they do not allow for a linear path along the X-axis (current direction) in the figure without changing direction, forcing the current to change direction as it moves, making it easier to achieve uniform heat generation throughout the heater area. As such, (p-3) and (p-4) can be said to have high electrical resistance, making them preferable because they reduce power consumption and facilitate achieving the desired heating temperature. It should be noted that FIG. 2 merely shows some preferred patterns as examples, and it goes without saying that the patterns that can be suitably used in the present invention are not limited to these.

[0028] Next, we will explain the case where patterns are mixed. In order to obtain uniform heat generation throughout the entire heater area, it is desirable to configure the heating wire pattern so that the same pattern is repeated throughout the entire heater area. However, it is also possible to combine different patterns, and since different patterns result in different electrical resistances, it is possible to mix areas with different heat generation efficiencies within the heater area. This can be used in applications where you want to heat only specific areas.

[0029] The heating wire pattern in the heater area is determined not only by the differences in pattern shape described above, but also by the line width of the heating wires and the spacing between the heating wires (width) shown in Figure 3. These can be considered in terms of the line width and the width of the spacing between the heating wires in the X-axis direction and the Y-axis direction, respectively, as shown in Figure 3. There are no particular restrictions on the line width, either for the width of the heating wire extending in the Y-axis direction (line width X) or the width of the heating wire extending in the X-axis direction (line width Y). However, generally, a wider line width allows for easier current flow and therefore lowers electrical resistance, while a narrower line width increases electrical resistance. Considering that the pattern can be formed without being crushed by printing and that it is easy to obtain a resistance value that facilitates pattern design, a line width of 5 mm or more is easy to handle. There are also no particular restrictions on the spacing between the lines. However, for example, if the conductive ink film thickness is 0.8 μm, a spacing of 0.5 mm will result in the mesh being easily crushed during flexographic printing. For this reason, it is preferable that the spacing between the lines be at least 1 mm for both the line spacing X and the line spacing Y. The general trend in designing the wire width and spacing is as follows: If the wire width and spacing are made smaller, the number of heating wires per given heater area increases, resulting in a finer mesh. In this case, the direction of current flow changes minutely, increasing electrical resistance and resulting in a pattern that is more likely to generate heat with the same power consumption.

[0030] The heating wire pattern can be designed by first determining a basic pattern and then cutting a portion of the substrate with a cutter or other blade to easily increase the spacing between the heating wires. For example, the basic pattern in Figure 4(a) can be prepared with cuts made as shown by the hatching in (b) and (c), and the heat generation temperature can be compared by applying a voltage under the same conditions. The heat generation properties of each pattern can be easily evaluated. For example, when the heat generation temperature was 38°C in Figure 4(a), making a cut Sy in the vertical direction as in (b) increased the heat generation temperature to 44°C. However, when a cut Sx was made in the horizontal direction as in (c), the heat generation temperature was the same as in Figure 4(a), at 38°C, and no increase in the heat generation temperature due to the addition of the cut Sx was observed. This test was conducted in a test room at a room temperature of approximately 25°C. These results show that (b), in which vertical cuts (Y-axis direction) are made to obstruct the flow of current in the X-axis direction in the figure, generates more heat, whereas adding only horizontal cuts (X-axis direction), which is thought to hardly obstruct the flow of current, makes it difficult for the heat generation temperature to change.

[0031] In the second embodiment, the connection area CA can be formed using a conductive ink printed in a solid fill across the entire connection area. As in the first embodiment, it can also be formed using a different conductive material. However, in the second embodiment, in which the heating wire of the heater area HA is formed in a pattern, forming a solid-printed area of ​​a certain width (length in the X-axis direction) on both sides of the heater area makes this area have lower electrical resistance than the heater area, and can therefore be easily used as the connection area CA. In the second embodiment, the width of the connection area CA (length in the direction indicated by the X-axis in FIG. 1 ) is preferably wider than the width of the heating wire in the heater area. More preferably, it is at least three times the width of the heating wire in the heater area. By making the width wider, overheating of the connection terminal, which serves as the application point, can be suppressed, preventing deterioration of the connection area.

[0032] The connection area may be rectangular, as shown in FIG. 1(a-1) as a first embodiment. However, as shown in FIG. 1(b), it is preferable to tilt one side of the connection area in contact with the heater area in the +- direction of the Y axis in FIG. 1, forming a "<" shape (or ">" shape) so that the width of the connection area (width in the X-axis direction) increases with increasing distance from the location where the connection terminal is set. This shape facilitates current flow even to areas farther from the connection terminal, as shown in FIG. 1(b-3), making it easier to generate heat uniformly throughout the heater area. It also has the effect of preventing overheating of the connection terminal and deterioration of the heater, thereby extending its service life. A specific preferred shape will be described with reference to FIG. 5. The tilt of the "<" shape is preferably θ1 = 165° or less, more preferably θ120° or less. The shapes at various tilt angles are shown in FIG. 5. (a) shows the case where θ1 = 165°, and (b) shows the case where θ2 = 120°. It is desirable that the connection terminal be located at the center of the section X2 in Figure (e), which is the narrowest part of the connection area. This shape ensures that the shortest route for current flow from the connection terminal will immediately encounter the heater area, which has high electrical resistance. On the other hand, if the connection area is shaped to become wider as it moves away from the connection terminal, the electrical resistance decreases and current flows more easily. This allows current to flow in the vertical direction in the figure, away from the connection terminal, making it easier for current to flow uniformly throughout the connection area.

[0033] The dimensions of each part of the connection area when one side is "<" shaped will be described with reference to FIGS. 5(c) to 5(e). To facilitate current flow across the entire heater area, the resistance value of the section indicated by R in FIG. 5(c) is preferably 2 Ω or less, more preferably 1 Ω or less, and even more preferably 0.2 Ω or less. To achieve such a resistance value, the length of the portion where the width (length in the X-axis direction) of the connection area is shortest, indicated as X2 in FIG. 5(e), is preferably 15 mm or more. Furthermore, the length of the portion where the width of the connection area is longest, indicated as X1 in FIG. 5(d), is preferably 30 mm or more. Here, when X1 is 30 mm and X2 is 15 mm, the inclination angle θ of the dogleg shape changes depending on the length Y1 of the connection area, as shown in the table in FIG. 6(a). Thus, for example, when X1 = 30 mm and X2 = 15 mm, the inclination angle θ can be calculated from the length Y1 using the following formula (see also the graph in FIG. 6(b)). The shape of the connection area can be simply determined based on the above-mentioned concept.

[0034]

[0035] In a film device having a connection area designed in this manner, for example, when the length of Y1 in Figure 5(d) was 300 mm and the heating wire (connection area) was formed using a silver-containing ink with a film thickness of 0.8 μm, the resistance value of section R was approximately 0.8 Ω. Furthermore, in a device where the length of Y1 in Figure 5(d) was 90 mm and the film thickness was 0.4 μm, the resistance value of section R was approximately 0.8 Ω. Furthermore, when the connection area was formed using copper conductive tape as in the first embodiment, the resistance value of section R was less than 0.2 Ω in a device where the length of Y1 in Figure 5(d) was 300 mm.

[0036] As described above, the shape of the connection area can be determined simply for the heater area heating wire pattern and connection area shapes. However, if the heater area heating wire pattern is special or if the thin electric heating device is to be A3 size or larger, the shape of the connection area can also be determined based on the following concept. Specifically, after determining the heater area heating wire pattern and heater area size, the resistance values ​​in the following sections can be measured and adjusted. The resistance value RY between two points Ry1 and Ry2 in the Y-axis direction in the diagram shown in FIG. 6( c) and the resistance value RXw between Rxw1 and Rxw2, which are the two points where the heater area width in the X-axis direction is widest, are measured. Setting RXw / RY to preferably 1.5 times or more, more preferably 2 times or more, is preferred because it ensures in-plane uniformity in the heat generation of the heater area. Furthermore, the resistance value RXw between Rxw1 and Rxw2, which are the two points where the width of the heater area in the X-axis direction is the widest, and the resistance value RXn between Rxn1 and Rxn2, which are the two points where the width of the heater area in the X-axis direction is the narrowest, as shown in Figure 6(c), are actually measured, and it is preferable to set RXn / RXw to be 1.5 to 0.6, and more preferably 1.2 to 0.8, since this will ensure in-plane uniformity in the heat generation of the heater area.

[0037] Next, we will explain the commonalities between the first and second embodiments. The heating wire in the present invention is formed using conductive ink by flexographic printing or inkjet printing. Furthermore, in the first embodiment, in which the heater area is solidly filled, a conductive ink film may be formed by coating. To achieve excellent flexibility, the conductive ink film thickness is preferably 0.2 to 5 μm. A thick film thickness results in poor flexibility, while a thin film thickness results in excessively high electrical resistance of the heating wire, making heater design difficult and undesirable in terms of the heating wire's lifespan. To achieve even better flexibility, a film thickness of 1 μm or less is more preferable. Furthermore, a film thickness of 0.4 μm or more allows the heater to achieve the desired heating temperature at a lower voltage. An even more preferable film thickness is 0.8 μm or more. This film thickness allows for easy design of a heater that can achieve the desired temperature at a low voltage (12 V or less) by selecting the heating wire pattern, and also makes it relatively easy to increase the heater area (A3 size or larger).

[0038] To obtain a conductive ink layer of this thickness, it is preferable to use flexographic printing. A conductive ink layer (heating wire) of the desired thickness can be formed by selecting the number of lines in the anilox roll used in flexographic printing. For example, with an anilox roll of 1200 lines, there are 1200 cells per inch, so 25.4 mm / 1200 = 21 μm (cell width), resulting in a film thickness of 0.4 μm. With a 700 line anilox roll, 25.4 mm / 700 = 36 μm (cell width), resulting in a film thickness of 0.8 μm.

[0039] Inkjet printing generally produces a film thickness of approximately 1 μm per coating, but high-resolution inkjet printing can produce a film thickness of approximately 0.1 μm. In either case, the film thickness can be adjusted by applying multiple coatings. The film thickness can also be adjusted by enlarging the inkjet printer's nozzle and increasing the volume of each droplet. Furthermore, inkjet printing employs a technique in which a pattern is formed using a silver-containing ink and copper plating is applied to the printed pattern to increase the film thickness and lower the resistance. By utilizing these known techniques, a conductive ink layer of the desired thickness can be obtained.

[0040] Furthermore, if a solid fill pattern is desired, the conductive ink layer may be formed by coating. Any known coating technique can be used as long as it can coat one side of the substrate with a thin film of conductive ink. For example, a roll coater or a slit coater can be suitably used. These coaters can also form thin films of conductive ink about 1 μm thick, so the flexibility of the electric heating device of the present invention is not impaired. Furthermore, coating in the present invention refers to forming a thin film layer of conductive ink over the entire surface of a predetermined area on one side of the substrate, and is not limited to coaters; a wide range of known coating techniques can be used.

[0041] The conductive ink used to form the heating wire of the thin electric heating device of the present invention can be any commercially available conductive ink suitable for the printing method used. In general, inks containing metals such as Ag, Cu, and Pd are preferably used.

[0042] The substrate used in the thin electric heating device of the present invention may be any insulating material with heat resistance sufficient to withstand the heating temperature of the heater, and for example, a polymeric material film is suitable. Examples include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyamide, polyether, polysulfone, polyethersulfone (PES), polycarbonate (PC), polyarylate, polyetherimide, polyetheretherketone (PEEK), polyimide, polymethyl methacrylate (PMMA), polyacetate, phenoxy resin, and polystyrene. Furthermore, the substrate is not limited to polymeric materials, and can also be made of paper or other materials. For example, high-quality paper can be used as long as it is heat-resistant. There are no particular limitations on the thickness of the substrate. Because the heating wire formed with conductive ink can be used without problems even when folded, the thickness of the substrate can be selected according to the intended use and application. To take advantage of the advantages of a thin device, such as excellent flexibility and ease of handling, the thickness of the substrate is preferably 5 μm to 1 mm. The shape of the substrate and the thin electric thermal device produced by printing or the like may be in the form of a sheet or a roll.

[0043] The thin electric heating device of the present invention configured as described above can be produced, for example, in a sheet form of a desired size depending on the intended use. When in use, the sheet-like film device is unfolded, connected to an external power source, and energized, allowing it to be used as a thin film heater in which the heater area generates heat on its surface. As explained above, various heating wire patterns can be easily produced by printing, making it possible to design and produce a variety of heaters depending on the intended use. Furthermore, the thin electric heating device of the present invention has excellent flexibility and can be bent or folded for use, allowing it to be used in any shape depending on the shape of the object to be heated.

[0044] Furthermore, the thin electric heating device of the present invention takes advantage of its excellent flexibility by stacking heater areas, allowing the heater areas to generate higher temperatures. This is thought to be due to the fact that the layered heater areas enhance the heat retention effect and the reduced surface area in contact with the outside air suppresses cooling by the outside air. This type of use is made possible by the thin electric heating device of the present invention, which can achieve excellent bending with a bending radius of 0.5 mm or less, and has the advantage of being able to increase the heater's generating temperature while maintaining a low applied voltage, i.e., keeping power consumption low.

[0045] Hereinafter, the present invention will be described in detail based on several examples, but the present invention is not limited to these examples.

[0046] The following patterns of heating wires were formed on a substrate (A4630: polyester) approximately A3 size (300 x 420 mm) using silver-containing ink by flexographic printing with an anilox roll 700 lines. Each sample was prepared. <Comparative Sample> (Sample 01): The heater area was a solid black pattern, with no specific connection area. The heater area was connected to an external power supply near the center of both ends of the heater area. <Example Sample> (Sample 02): The heater area was a solid black pattern, similar to Sample 01, with 15 mm-wide conductive tape (made of copper) attached to both ends of the heater area to form connection areas. The connection terminal was located in the center of the connection area, similar to Sample 01, and connected to an external power supply. (Sample 03): The heater area and connection area were patterned and shaped as shown in Figure 7. The connection terminal was located in the center of the connection area, similar to Sample 01, and connected to an external power supply. The connection area remained a thin ink layer, with no additional conductive material added. The heater area pattern is shown in detail in Figure 3. The line width is 5 mm in both the X-axis and Y-axis directions, with the line spacing being 1.5 mm in the X-axis direction and 15 mm in the Y-axis direction. The connection area is shown in Figures 5(d) and 5(e). In this example, the longest portion of the connection area in the X-axis direction, X1, was 32.5 mm, and the shortest portion, X2, was 15 mm. Y1 was 300 mm. The inclination angle of the connection area was θ3 = 165°, and X3 = 17.5 mm. (Sample 04): Similar to Sample 02, a 15 mm-wide conductive tape (made of copper) was attached to the connection area of ​​Sample 03 to form the connection area for Sample 04. The connection terminal was located in the center of the connection area, similar to Sample 01, and connected to an external power source.

[0047] An external power supply (DC stabilized power supply) was used to pass a current through each sample, and the heating temperature of the heater area was measured after 10 minutes. The DC stabilized power supply was connected to the sample device by clamping it with an alligator clip at the position of the above-mentioned connection terminal of each device. The amount of current was adjusted with the power supply knob, and the resistance value was calculated from the current and voltage values ​​displayed on the device. The equipment used was as follows. External power supply: DC stabilized power supply AD-8722D (manufactured by A&D Co., Ltd.) Temperature measuring device: Compact thermography camera FLIR C3-X (manufactured by A&D Co., Ltd.)

[0048] For Sample 01, a comparative example, no current flowed and no heat generation was observed, resulting in measurement being impossible. For the other samples, a current of the value listed in Table 1 was passed so that the power consumption was 13.4 W. The measured heat generation temperatures are shown in Table 1, and thermography images of each sample are shown in Figure 8. The test was conducted in a test room at a room temperature of approximately 25°C. The heat generation temperature measurement revealed that Sample 01, a comparative example, did not generate any heat at all, while Samples 02 to 04 did. This confirmed that all of Samples 02 to 04, which are examples, function as film heaters (thin electric heating devices). At a power consumption of 13.4 W in this test, the heat generation temperatures for all of Samples 02 to 04 were around 30°C, with no significant difference observed. However, as can be seen from the thermography images, Samples 03 and 04, which have a grid-like pattern for the heating wire, exhibit superior heat generation temperature uniformity within the heater area compared to Sample 02, which has a solid black pattern.

[0049]

[0050] Using Samples 02 to 04 used in Example 1, we measured the differences in the uniformity of the heating temperature within the heater area for each sample. As shown in Figure 9(a), the heater area of ​​each sample was divided into three sections, vertically and horizontally, for a total of nine areas, and the actual heating temperature was measured for each area. The measurement results are shown in Table 2, and the respective thermographic images are shown in the lower part of Figure 9. The results in Table 2 confirm that Samples 03 and 04 actually have better uniformity of the heating temperature within the heater area than Sample 02. However, at a heating temperature of around 33°C in this test, even Sample 02's heating temperature in each area was within a range of approximately 33°C ± 2°C. Therefore, when used for normal heat retention purposes, it can be said that the difference in heating non-uniformity is not a problem.

[0051]

[0052] Next, we investigated the effect of different patterns mixed within the heater area. Specifically, we compared the difference in heat generation between a case where the entire heater area was constructed with the same heating wire pattern and a case where the heater area was divided into arbitrary small areas with different heating wire patterns. Samples 05 to 08 with the heating patterns shown in the top row of Figure 10 were prepared, and the heat generation temperature in each small area was measured. Note that in the heating pattern shown in the top row of Figure 10, the black areas represent areas without silver ink (non-heating wire), and the gray areas represent heating wire areas formed with silver-containing ink. The measurement results are shown in Table 3, and the respective thermographic images are shown in the middle row of Figure 9. The bottom row of Figure 9 shows the location of the small areas where the heat generation temperature of each sample was measured, corresponding to the small area numbers in Table 3. As shown in Table 3, the test was conducted with measurements at the same voltage of 5.0 V and with the current value adjusted to achieve the same power consumption of 22.7 W. The results are shown in Table 3 and the thermography images (at the same voltage) in the middle of Figure 10. As is clear from the thermography images, Sample 05, in which the entire heater area is composed of the same repeated pattern, generated heat almost uniformly within the heater area. In contrast, Samples 06-08, in which different patterns were mixed within the heater area, generated different heat temperatures in each small area depending on the electrical resistance of the pattern. This was also evident in the actual temperature measurements shown in Table 3. Specifically, in Sample 06, Small Area 1 exhibited a higher heat temperature than Small Area 2. This is thought to be due to the fact that Small Area 1 exhibits a pattern in which the current flow path changes more significantly, i.e., the pattern makes it difficult for the current to flow in the X-axis direction. Therefore, the current is forced to flow in a larger zigzag pattern, resulting in higher electrical resistance. In contrast, the pattern in Small Area 2 exhibits a smaller change in the direction of current flow, resulting in lower electrical resistance. This same trend is observed in Samples 07 and 08. In this way, in the present invention, by combining patterns with different electrical resistances, it is possible to vary the degree of heat generation for each small partitioned area.Therefore, it is relatively easy to design the heating location of the heater according to the intended use, etc.

[0053]

[0054] Taking advantage of the excellent flexibility of the thin electric heating device of the present invention, the heat generation temperature was confirmed when the film device was rolled into a cylindrical shape and when it was folded. (Test 4-1): Used in a Cylindrical Form A heating wire was formed in a solid black pattern on a long substrate measuring 780 mm x 90 mm, and 15 mm-wide conductive tape (copper) was attached to both short edges to form connection areas. The device was then rolled into a cylindrical shape with one short edge folded inward, and the heat generation temperature was confirmed by passing an electric current through it. In this state, one of the connection areas was located on the inner circumference of the cylinder, and the other on the outer circumference of the cylinder. The size of the cylinder was determined by wrapping the film device so that the outer circumference of each cylinder had a predetermined diameter, with the film device being wrapped around the length of the film device (780 mm) / outer circumference length of the cylinder (mm) = number of windings. The results are shown in Table 4. These results confirm that the heat generation temperature increased with an increase in the number of windings, i.e., the greater the number of overlaps of the film device. When the sheet (long length) was used flat without being cylindrical, the average heating temperature was 46.2°C. However, when the sheet was wrapped 15.6 times to form a cylindrical shape, the average heating temperature rose to 107.8°C. It was also confirmed that the power consumption was almost the same when the sheet was used flat and when it was used in a cylindrical shape. These results confirmed that the thin electric heating device of the present invention can increase the heating temperature without changing the power consumption by using the heater areas in an overlapping state. This indicates that the device can be used when the object to be kept warm is cylindrical, i.e., it can be adapted to the shape of the object to be kept warm, and can be used to keep the temperature higher while saving power.

[0055]

[0056] (Test 4-2): Use in Folded State The thin electric heating device used in Test 4-1 was used in a folded state instead of being rolled into a cylindrical shape, and the heat generation temperature was confirmed. The film device was folded inward from one short edge to a length calculated by the longitudinal direction (780 mm / fold count). That is, when folding two times to form a three-layer film, as shown in FIG. 11(a), the R-side was folded inward along line F1, and then the same valley fold was continued along line F2, resulting in Sample 13. (a) is equivalent to a sheet folded in three. Similarly, folding four times as shown in FIG. 11(b) results in Sample 14, which is five layers long, and folding six times as shown in FIG. 11(c) results in Sample 15, which is seven layers long. In this folded state, one of the connection areas is on the inside of the fold, and the other is on the outside of the fold, as in the cylindrical form in Test 4-1. The results are shown in Table 5. As in Test 4-1, it can be seen that the heat generation temperature increases as the number of folds and the overlap of the heater areas increase. Also, as in Test 4-1, power consumption remains roughly flat even as the temperature increases. Furthermore, comparing the heat generation temperatures of Sample 11 (7.8 folds) in Test 4-1 and Sample 15 (6 folds, 7 layers) in Test 4-2, it can be seen that they are almost identical at 90.4°C and 87.2°C. This indicates that the heat generation temperature can be increased as the heater area overlaps. While there is a limit to the number of folds possible when folding due to factors such as the elasticity of the substrate, it is generally easier to roll the film into a cylindrical shape. In any case, the excellent flexibility of the film device of the present invention makes such usage possible, and it can be said that the film device of the present invention can be applied to various shapes depending on the purpose of use and the desired heat generation temperature.

[0057]

[0058] REFERENCE SIGNS LIST 1 Thin electric heating device 2 Conductive ink thin film layer 21 Heater heating wire 3 Connection terminal 4 Conductive tape HA Heater area CA Connection area

Claims

1. A thin electric heating device comprising: a substrate made of an electrically insulating material; a heater area having a thin-film heater wire formed on the substrate using conductive ink; and connection areas formed of a conductive material along two opposing sides at both ends of the heater area, the connection areas having connection terminals to be connected to an external power source, the connection areas having a lower electrical resistance than the heater area.

2. The thin electric heating device according to claim 1, characterized in that the heater heating wire is a thin conductive ink film formed over the entire heater area on the substrate by flexographic printing, inkjet printing or coating with a conductive ink, and the connection area is formed along the two opposing sides with a conductive material different from the conductive ink that forms the heater heating wire.

3. The thin-type electric heating device according to claim 1, characterized in that the heater wire is a thin-film heater wire formed by flexographic printing or inkjet printing of a conductive ink, forming a pattern in which the direction of current flow from one side of the connection terminal to the other changes multiple times, and the width of the connection area in the direction of current flow is wider than the line width of the heater wire.

4. A thin electric thermal device as described in claim 3, characterized in that the width of the connection area in the direction of current flow becomes wider the further away from the point where the connection terminal portion is set in a direction perpendicular to the direction of current flow.

5. The thin electric heating device according to claim 3 or 4, characterized in that the pattern is a pattern in which a shape having branch points formed by the intersection of lines extending in different directions is repeated multiple times.

6. The thin electric heating device according to claim 1, characterized in that the heater area is formed into a multi-layered shape by folding or bending the base material.

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