JP2025035507A - Thin, flexible electric heating device - Google Patents

Abstract

To provide a thin-film electric heating device that achieves a desired temperature at a low voltage (12 V or lower), even with a thin ink film thickness that exhibits excellent flexibility and can attain a high bending resistance with a bending radius of 0.5 mm or less.SOLUTION: The thin-film electric heating device includes: a base material formed of an electric insulative material; a heater area having a thin-film heater electric line formed of conductive ink, on the base material; and a connection area formed of a conductive material along two sides facing each other on both ends of the heater area, a connection terminal part connected to an external power source being set in the connection area. The electrical resistance of the connection area is lower than the electrical resistance of the heater area.SELECTED DRAWING: Figure 3

Description

Application for application of Article 30, Paragraph 2 of the Patent Act has been filed. Website address: https://unified. jcdbizmatch. jp/nanotech2023/Exhibitor/jp Posting date: December 1, 2022 [Publications, etc.] Exhibition name: J-FLEX2023 Venue: Tokyo Big Sight Date: February 1, 2023

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

So far, various thin heaters have been proposed in which a heating wire is formed on a substrate by printing with conductive ink. For example, 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) is known.

Special table 2018-513544 publication

In many of these conventional thin electric heating devices, the heater wire is formed by screen printing. In this case, due to the characteristics of the printing method, the thickness of the ink layer forming the heating wire is at least 5 μm or more. An ink layer of this thickness has poor flexibility and is difficult to bend, and it is particularly difficult to achieve an excellent bending radius of 0.5 mm or less. For this reason, many conventional thin electric heating devices are limited to use in a spread-out sheet-like state. However, if a heater with a curved or cylindrical shape that matches the shape of the object to be heated by the heater can be realized, not only will it be possible to efficiently heat the object, but it is expected that the range of uses for the heater will also expand. In addition, if it is easy to bend or roll, it is expected that the portability of the heater will also improve.

Generally, the thinner the conductor, the higher the resistance of the conductor layer. Therefore, in order to obtain the desired heater temperature with a thin conductor layer, it is necessary to increase the supply voltage, but this leads to increased power consumption. It is possible to reduce the supply voltage by increasing the thickness of the conductor, but this not only leads to increased manufacturing costs and reduced productivity, but also contradicts the above-mentioned demand for flexibility. Taking the above into consideration, in conventional heaters in which the heating wire is formed by screen printing, the ink film thickness is often set to 10 to 20 μm, and a single heating wire is made to fold back and forth multiple times within the heater heat generation area, thereby lengthening the distance of the heating wire. In this way, when the distance of the heating wire is extended, the resistance increases, and power consumption tends to increase. In particular, when considering a large area heater such as A3 size or larger, a film thickness of 30 μm or more is required in reality in order to keep power consumption as low as possible. In particular, when using a pattern in which the heating wire moves back and forth in small increments so as not to leave 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 for the ink film thickness forming the heating wire to be 200 μm or more in order to keep resistance as low as possible and reduce power consumption.

The above-mentioned Patent Document 1 discloses an electric heating device that can achieve a desired temperature at a low voltage (12 V or less), for example, by printing a silver paste pattern on graphene using screen printing, but 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 the screen printing method that has been used conventionally.

Here, when the heating wire is formed using flexographic printing or inkjet printing, the ink film thickness can be made 5 μm or less, so that flexibility can be imparted to the thin electric heating device. However, as described above, when the film thickness is made thin, the resistance of the conductor layer increases, so that it is not possible to create an electric heating device that can obtain the desired heating temperature at a low voltage by only thinking of making a pattern in which a single heating wire goes back and forth many times, as in the case of conventional screen-printed heating wires. Specifically, there is a demand for an electric heating device that has a flexible heating wire with a film thickness of 5 μm or less and can obtain the desired temperature at a low voltage (12 V or less). In particular, to obtain excellent flexibility with a bending radius of 0.5 mm or less, it is desirable to obtain the 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.

After extensive research, the inventors 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 create a heater that can obtain the desired temperature at a low voltage even with a film thickness of 5 μm or less, and thus completed the present invention.

Here, electrical resistance does not only mean resistance as a so-called physical value, but also means a concept of comprehensively evaluating the ease (difficulty) of electric current flow in the target area based on the shape of the heating wire pattern that constitutes the target area, the thickness (line width) of the heating wire, the spacing between the heating wires, the conductive material that forms the heating wire, etc. That is, for example, the thicker the heating wire is, and the more linear the heating wire is, the easier it is for the current to flow. Such ease of electric current flow is evaluated as low electrical resistance. Conversely, when the heating wire is thin and the pattern changes the direction of the heating wire extension multiple times as the heating wires cross and branch with each other, the more changes there are, the more difficult it is for the current to flow. Such difficulty of electric current flow is evaluated as high electrical resistance. This is a concept of deriving the level of electric resistance in the target area by comprehensively evaluating factors that affect the ease (difficulty) of electric current flow for the entire target area.

In order to solve the above problems, the thin electric heating device of the present invention comprises a substrate made of an electrically insulating material, a heater area having a thin-film heater electric heating wire formed on the substrate by conductive ink, and a connection area having connection terminals formed on both ends of the heater area by conductive material, each of which is connected to an external power source, and is characterized in that the electrical resistance of the connection area is lower than the electrical resistance of the heater area. With this configuration, even if the heater electric heating wire is formed by flexographic printing or inkjet printing that can achieve an ink film thickness of 5 μm or less with excellent flexibility, heat generation at a desired temperature can be obtained at a low voltage (12 V or less). Here, the conductive material forming the connection area may literally be a material that has conductivity, and may be, for example, the conductive ink forming the heater area. In other words, the connection area may be formed by printing a conductive ink like the heater area. Of course, the connection area may be formed of a separate conductive material different from the conductive ink used to form the heater area, for example, a metal material such as copper.

In another embodiment of the thin electric heating device of the present invention, the heater wire is a thin conductive ink film formed on the entire heater area on the substrate by flexographic printing, inkjet printing, or coating with an electric 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 on the entire heater area means placing conductive ink on the entire heater area by printing, that is, performing so-called solid fill printing on the entire area. As a printing method, flexographic printing or inkjet printing can be preferably used. Also, a thin conductive ink film can be formed by a method of coating a substrate with a conductive ink using a coater or the like, without using printing. When the electric heating wire of the heater area is such a solid fill pattern, the connection area is formed with a conductive material different from the conductive ink forming the heater wire, and a connection terminal part to be connected to an external power source is set at an appropriate point of the connection area. With this configuration, even if the heating wire is formed in a so-called solid filled pattern, it is possible to obtain a uniform heating effect with little temperature unevenness across the entire heater area.

In another embodiment of the thin electric heating device of the present invention, the heater wire is a thin-film heater wire formed by flexographic printing or inkjet printing of 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. In this embodiment, the heating wire pattern is a pattern in which the direction of current flow from one side of the connection terminal to the other changes multiple times. That is, the current flow path is not a pattern in which the current flows in a straight line from one side of the connection terminal to the other, but a pattern in which the direction of current flow changes multiple times between the path from one side of the connection terminal to the other, for example, a pattern in which the current flows in a zigzag shape. With this configuration, the electrical resistance of the heating wire can be increased, so that the heating wire can be heated at a higher temperature when compared with the same applied voltage.

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 in which the current flows becomes wider the further away from the point where the connection terminal is set in the direction perpendicular to the direction in which the current flows. This configuration makes it easier for the current to flow uniformly throughout the connection area, which in turn makes it easier for the current to flow more uniformly throughout the heater area, making it easier to obtain more uniform heat generation throughout the heater area. It also makes it possible to prevent overheating of the connection terminal and suppress deterioration of the connection area.

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

Another embodiment of the electric heating device of the present invention is characterized in that the heater areas are formed into a multi-layered shape by folding or bending the substrate in the electric heating device described above. With this configuration, it is possible to enhance the heat retention effect by stacking the heater areas in layers, so that the heater can generate a higher heat 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.

According to the present invention, it is possible to obtain a thin electric heating device that has excellent flexibility and can achieve bending resistance with a bending radius of 0.5 mm or less, and can obtain the 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, it is possible to obtain a more uniform heating temperature across the entire heater area with less power consumption.

FIG. 1 is a comparison of two embodiments (a) and (b) of a thin electric thermal device of the present invention, in which (a-1) and (b-1) show an outline 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. 3A to 3C are schematic diagrams showing examples of heating wire patterns in a heater area in a thin electric heating device of the present invention. FIG. 2 is a schematic diagram showing the relationship between the line width and spacing of heating wires in an example of a heating wire pattern in a thin electric heating device of the present invention. FIG. 2 is a schematic diagram showing a state in which a slit is made in one embodiment of a thin electric thermal device of the present invention. FIG. 2 is a schematic diagram showing an example of a connection area for one embodiment of a thin electric thermal device of the present invention. FIG. 1A is a table showing the relationship between the size and angle of a connection area in one embodiment of a thin electric thermal device of the present invention, FIG. 1B is a graph of the relationship obtained from table (a), and FIG. 1C is a schematic diagram showing an example of the position at which a connection terminal portion is set in the connection area. FIG. 1 is a schematic diagram showing one embodiment of a thin electric heating device of the present invention. 1 is a thermography image showing the heat generation state of a heater area in one embodiment of a thin electric thermal device of the present invention. 1 is a thermography image comparing the uniformity of heat generation in the heater area for one embodiment of a thin electric heating device of the present invention. 1 is a thermography image comparing the heat generation state when different electric thermal patterns are mixed in one embodiment of a thin electric thermal device of the present invention. FIG. 2 is a schematic diagram showing an example of how to fold the film device when it is used in a folded state, in one embodiment of the thin electric thermal device of the present invention.

Hereinafter, the thin electric thermal device of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing an outline of a thin electric heating device according to the present invention. The left column (a) shows a first embodiment in which the electric heating wire in the heater region is formed by printing or coating a solid pattern with conductive ink, and the right column (b) shows a second embodiment in which the electric heating wire in the heater region is formed by printing a pattern such as a grid pattern with conductive ink. In FIG. 1, (a-1) and (b-1) are schematic diagrams showing an outline of a thin electric heating device according to each embodiment, and (a-2) and (b-2) are schematic diagrams showing the positional relationship of each region of the heater area and the connection area. And (a-3) and (b-3) are schematic diagrams showing the flow of current assumed in each embodiment.

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 heating wire 21 (conductive ink thin film layer 2) formed by printing or the like on a substrate using a conductive ink. As shown in (a-2) and (b-2) of FIG. 1, the area having this heater heating wire 21 becomes the heater area HA. Then, along the two opposing sides (M, M) at both ends of the heater area HA, each connection area CA is formed by a conductive material. Here, the conductive material forming the connection area may literally be a material that has conductivity, and may be, for example, a conductive ink forming the heating wire 21 of the heater area. That is, the connection area may also be formed by printing the conductive ink by flexographic printing or inkjet printing, like the heater area. Of course, the connection area may be formed by a separate conductive material different from the conductive ink used to form the heater area, for example, a metal material such as copper.

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) that connects to an external power source to both poles (3a, ab). For convenience in illustrating the figure, this connection terminal 3 is indicated by a open circle, but in reality it is made of the same conductive material as the other areas of the connection area CA, and the point that connects to the external power source as the application point is simply referred to as the connection terminal 3 for convenience. In other words, when connecting to an external power source, a cord or the like that connects to the external power source is connected at an appropriate point within the connection area, and this connection point becomes the connection terminal 3.

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 printed with a so-called solid pattern over the entire heater area. That is, in this first embodiment, the heater wire 21 is a thin-film layer 2 made of conductive ink formed on a substrate over the entire heater area HA. Here, a general metal-containing ink can be used as the conductive ink. There is no particular limit to the size of the heater area.

In the first embodiment, the connection area CA formed along the two opposing sides (M, M) at both ends of the heater area HA is formed of a conductive material different from the conductive ink forming the heater electric heating wire 21. Here, a different conductive material means a material different from the ink forming the heater electric heating wire, and a metal foil of copper or aluminum or a conductive tape 4 can be preferably used. There is no problem if the metal contained in the conductive ink is the same as the metal that is the material of the conductive tape, for example, but since it is necessary that the electrical resistance of the connection area is lower than the electrical resistance of the heater area, it is desirable that the metal material forming the connection material has a higher conductivity than the heating wire of the heater area. This is not limited to the selection of the metal material, but also takes into consideration the relationship between the thickness of the heating wire of the heater area and the width of the connection area, and it is particularly preferable that the conductivity of the heater area is 10 times or more than the conductivity of the heating wire of the heater area, because this makes it easier for current to flow uniformly in the heater area. As an example of a specific method for forming the connection area, a thin film layer of conductive ink is formed in advance on the outer sides of both ends of the heater area, i.e., on the parts that will form the connection area, by printing in the same manner as the heater area. In this case, it is desirable for the parts that will become the connection area to be a so-called solid filled pattern. Then, the connection area can be formed by attaching conductive tape 5 to the parts where the solid pattern is printed. Alternatively, as a simpler method, the connection area can be formed by attaching conductive tape so that it partially overlaps both ends of the heater area, without bothering to form a thin film layer of conductive ink on the connection area part, so that the conductive tape extends beyond the heater area and the base material.

The connection terminal 3 is set in the connection area CA thus formed, and an electric current is passed through the heating wire formed in the heater area HA by connecting it to an external power source, so that the heater area heats up, and the thin electric heating device of the present invention can be used as a heater. The connection terminal may be set as a terminal from the design stage, but if an electrical connection is made at any point in the connection area, that point can be the connection terminal 3. For example, a simple method may be used in which a conductor with an alligator clip at the end is used to electrically connect the connection by clipping an appropriate point in the connection area with the clip. In this case, the point clipped by the alligator clip is set as the connection terminal. The position at which the connection terminal is set is preferably approximately the center of the connection area, as shown in FIG. 1. By setting the connection terminal at the center, the current is more likely to flow evenly in the vertical direction (Y-axis direction) of the connection area in FIG. 1, making it easier to generate heat more evenly throughout the entire heater area. It is also desirable to suppress overheating of the connection terminal and prevent deterioration of the connection terminal.

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 the connection area are connected). In addition, it is preferable that the length in the X-axis direction in FIG. 1 (the so-called width of the conductive tape) Lx is 10 mm or more. By setting the size of the connection area in this way, it becomes easier for current to flow more uniformly throughout the entire heater area, and the entire heater area can be heated more uniformly.

Next, the second embodiment shown in FIG. 1 (b) will be described. In the second embodiment, the heater area HA is formed with a heating wire 21 having a pattern such as a lattice. In the following description, the parts common to the first embodiment will be omitted, and the different parts will be mainly described. An example of a pattern of the heater area HA in the second embodiment is shown in FIG. 2. Each pattern shows a part of a repeated pattern. In addition, in this figure, the connection terminal part 3 (application point) is illustrated as being set on the outside of both the left and right ends of each pattern diagram. In other words, it is assumed that the direction of current flow is from left to right in the X-axis direction in FIG. 2. It is desirable that the pattern of the heating wire in the second embodiment is a pattern in which the direction of current flow from one connection terminal to the other connection terminal 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 entire heater area compared to the case of a pattern in which the current can flow in a straight line from one application point to the other application point without changing direction. The pattern in FIG. 2 (P-1) is a pattern in which the current flows in a zigzag pattern, while the patterns in FIG. 2 (P-2) to (P-4) are patterns in which straight lines in different directions intersect with each other. The intersecting patterns in FIG. 2 (P-2) to (P-4) do not form a straight path in the X-axis direction from connection terminal 3a to 3b, 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 be combinations of curved lines such as in FIG. 2 (P-5) or a houndstooth pattern with cutouts such as in FIG. 2 (P-6).

This is because, in a pattern in which the current can proceed in a straight line without changing direction, the current flows concentratedly along the route with the shortest distance, but when the direction of the current is forcibly changed multiple times by using a pattern in which the current is prohibited from proceeding in a straight line, as in the pattern shown in FIG. 2, the electrical resistance of the heating wire increases, and the current flows along routes other than the shortest route, which is thought to make it easier for the current to flow uniformly throughout the entire heater area. For this reason, by using a heating wire pattern in which the direction of the current changes multiple times, as in the pattern shown in FIG. 2, the entire heater area is more likely to generate heat uniformly without unevenness. By forming the heating wire pattern of the heater area in such a pattern, the electrical resistance of the heating wire is higher than in the case of the heating wire in which the entire area is filled with a solid color as in the first embodiment. The higher the electrical resistance, the easier it is to generate heat at a higher temperature with the same applied voltage, and this has the advantage of making it easier to efficiently obtain the desired heating temperature while reducing power consumption. Also, as mentioned above, by considering the pattern, it is possible to mix areas that heat up easily with areas that heat up less easily, so it is possible to design heaters to meet requests such as focusing on heating only a specific area or an extremely narrow area.

Among the examples of the heating wire patterns shown in FIG. 2, the more preferable ones are patterns in which a shape having a branch point formed by lines extending in different directions crossing each other is repeated multiple times, as shown in (p-2), (p-3), (p-4), and (p-5). Here, the crossing is not limited to a crossing but also includes a T-shaped crossing, and it is sufficient if there are multiple options for the next route at the crossing point. Also, particularly preferable are patterns that combine relatively long lines and relatively short lines, as shown in (p-3) and (p-4). Such patterns are preferable in that there is no option to proceed linearly without changing the route direction in the X-axis direction (direction of current flow) in the figure, so the current is forced to change direction as it proceeds, making it easier to obtain uniform heat generation throughout the heater area. In this way, (p-3) and (p-4) can be said to be patterns with high electrical resistance, and are also preferable in that they make it easier to obtain the desired heat generation temperature while suppressing power consumption. It goes without saying that FIG. 2 merely illustrates some preferred patterns, and the patterns that can be suitably used in the present invention are not limited to these.

Next, we will explain the case of mixing patterns. In order to obtain uniform heat generation throughout the entire heater area, it is desirable to configure the heating wire pattern by repeating the same pattern throughout the entire heater area. However, it is also possible to combine different patterns, and since different patterns result in different electrical resistance, it is possible to mix areas with different heat generation efficiency within the heater area. This can be used in applications where you want to heat only specific areas.

The pattern of the heating wire in the heater area is not only considered in terms of the difference in the pattern shape described above, but also in terms of the line width of the heating wire and the space between the heating wires (width) shown in FIG. 3. These can be considered in terms of the line width and the width in the X-axis direction and the Y-axis direction, respectively, as shown in FIG. 3. There are no particular restrictions on the line width, either 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), but generally, the wider the line width, the easier it is for current to flow, so the lower the electrical resistance, and the narrower the line width, the higher the electrical resistance. Considering that it can be formed without being crushed by printing and that it is easy to obtain a resistance value that is easy to design the pattern, it is easy to handle if the line width is 5 mm or more. There are no particular restrictions on the space between the lines, but for example, when the film thickness of the conductive ink is 0.8 μm, if the space between the lines is 0.5 mm, the mesh will be easily crushed when flexographically printed. For this reason, it is preferable that the space between the lines is at least 1 mm for both the space between the lines X and the space between the lines Y. The general trend in designing line width and spacing is as follows: If the line width and spacing are made finer, 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, the electrical resistance increases, and the pattern is more likely to generate heat with the same power consumption.

The design of the heating wire pattern can be simplified by determining a basic pattern and then cutting a portion of the substrate with a cutter or other blade to increase the spacing between the heating wires. For example, the basic pattern of FIG. 4(a) can be prepared with cuts as shown by hatching in (b) and (c), and the heating temperature can be compared by applying voltage under the same conditions. For example, when the heating temperature was 38°C in FIG. 4(a), the heating temperature rose to 44°C when a cut Sy was made vertically in the figure as in (b). However, in (c), where a cut Sx was made horizontally in the figure, the heating temperature was 38°C, the same as in FIG. 4(a) which was the basic pattern, and no increase in the heating temperature due to the addition of the cut Sx was observed. The test was conducted in a test room at a room temperature of about 25°C. These results show that (b), in which vertical cuts (Y-axis direction) are made to block the flow of current in the X-axis direction of the figure, generates more heat, whereas adding only horizontal cuts (X-axis direction), which is thought to barely block the flow of current, makes it difficult for the generated temperature to change.

The connection area CA in the second embodiment can be formed by printing the entire connection area with a conductive ink in a solid fill. As in the first embodiment, it can also be formed using different conductive materials, but in the second embodiment in which the heating wire of the heater area HA is formed in a pattern, if a solid filled print area having a certain width (length in the X-axis direction) is formed on both sides of the heater area, this area has a lower electrical resistance than the heater area, and can be easily used as the connection area CA. The width of the connection area CA in the second embodiment (length in the direction shown as the X-axis in Figure 1) is preferably wider than the width of the heating wire of the heater area. More preferably, it is three times or more wider than the width of the heating wire of the heater area. By making it wider, overheating of the connection terminal part, which is the application point, can be suppressed, and deterioration of the connection area can be prevented.

The connection area may be rectangular as shown in FIG. 1(a-1) as the first embodiment, but as shown in FIG. 1(b), it is preferable to make one side in contact with the heater area inclined in the Y-axis +- direction of FIG. 1 so that the width of the connection area (width in the X-axis direction) increases as it moves away from the point where the connection terminal is set, making it a dogleg shape (or an inverted dogleg shape). By making it in this shape, it becomes easier for the current to flow to a point away from the connection terminal as shown in FIG. 1(b-3), making it easier to heat the entire heater area uniformly. It also has the effect of preventing overheating of the connection terminal, preventing deterioration of the heater, and extending the service life. A preferred specific shape will be described with reference to FIG. 5. The inclination of the dogleg shape is preferably θ165° or less, and more preferably θ120° or less. The shapes at each inclination angle are shown in FIG. 5. (a) is the case where θ1 = 165°, and (b) is the case where θ2 = 120°. Furthermore, it is desirable that the connection terminal portion be located at the center of the section X2 in Figure (e), which is the narrowest part of the connection area. With this shape, the shortest route along which current flows from the connection terminal portion will immediately encounter the heater area, which has high electrical resistance. In contrast, if the shape of the connection area becomes wider as it moves away from the connection terminal portion, the wider the area, the lower the electrical resistance will be, and the easier it will be for current to flow. This means that current will also flow in the vertical direction in the figure, away from the connection terminal portion, making it easier for current to flow uniformly throughout the entire connection area.

The size of each part when the shape of the connection area is made to have one side "L-shaped" will be described with reference to (c) to (e) of FIG. 5. In order to facilitate the flow of current over the entire surface of the heater area, it is preferable that the resistance value of the section indicated by R in FIG. 5(c) is 2Ω or less, more preferably 1Ω or less, and even more preferably 0.2Ω or less. In order to obtain such a resistance value, it is preferable that the length of the part where the width (length in the X-axis direction) of the connection area is the shortest, indicated as X2 in FIG. 5(e), is 15mm or more. Also, it is preferable that the length of the part where the width of the connection area is the longest, indicated as X1 in FIG. 5(d), is 30mm or more. Here, when X1 is 30mm and X2 is 15mm, the inclination angle θ of the L-shaped shape changes depending on the length of Y1 of the connection area, as shown in the table of FIG. 6(a). Thus, for example, when X1=30mm and X2=15mm, the inclination angle θ can be calculated from the length of Y1 by the following formula (see also the graph shown in FIG. 6(b)).
y=-0.00000000X ⁶ +0.00000000X ⁵ -0.00000084X ⁴ +0.00022625X ³ -0.03511014X ² +3.15746757X+24.48872692
The shape of the connection area can be determined simply based on the above-mentioned concept.

In a film device having a connection area designed in this way, for example, when the length of Y1 in FIG. 5(d) is 300 mm and the heating wire (connection area) is formed with a thickness of 0.8 μm using silver-containing ink, the resistance value of section R is about 0.8 Ω. In a device in which the length of Y1 in FIG. 5(d) is 90 mm and the film thickness is 0.4 μm, the resistance value of section R is about 0.8 Ω. Note that when the connection area is formed with copper conductive tape as in the first embodiment, the resistance value of section R is less than 0.2 Ω in a device in which the length of Y1 in FIG. 5(d) is 300 mm.

If the heating wire pattern of the heater area and the shape of the connection area are as described above, the shape of the connection area can be determined simply as described above. However, if the heating wire pattern of the heater area is special or if the size of the thin electric heating device is to be A3 size or larger, the shape of the connection area can be determined according to the following concept. Specifically, after determining the heating wire pattern of the heater area and the size of the heater area, the resistance values of 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 Figure 6 (c), and the resistance value RXw between Rxw1 and Rxw2, which are the two points between which the width of the heater area in the X-axis direction is the widest, are actually measured, and RXw/RY is preferably 1.5 times or more, more preferably 2 times or more, which is preferable in that it provides uniformity in the surface of the heat generation of the heater area. In addition, the resistance value RXw between Rxw1 and Rxw2, which are the two points where the heater area has the widest width in the X-axis direction, and the resistance value RXn between Rxn1 and Rxn2, which are the two points where the heater area has the narrowest width in the X-axis direction, as shown in FIG. 6(c), are actually measured, and it is preferable to set RXn/RXw to 1.5 to 0.6, and more preferably 1.2 to 0.8, in order to obtain uniformity in the heat generation properties of the heater area within the surface.

Next, the matters common to the first and second embodiments will be described. The heating wire in the present invention is formed of conductive ink by flexographic printing or inkjet printing. In the first embodiment in which the heater area is solidly painted, a conductive ink film may be formed by coating. In order to obtain excellent flexibility, the thickness of the conductive ink is preferably 0.2 to 5 μm. If the film thickness is too thick, the flexibility will be poor, and if the film thickness is too thin, the electrical resistance of the heating wire will be too high, making it difficult to design the heater and undesirable in terms of the life of the heating wire. To achieve better flexibility, the film thickness is more preferably 1 μm or less. Furthermore, by setting the film thickness to 0.4 μm or more, the heater can be made to obtain the desired heating temperature at a lower voltage. And, the more preferable film thickness is 0.8 μm or more. With this film thickness, by selecting the heating wire pattern, it is easy to design a heater that can obtain the desired temperature at a low voltage (12 V or less), and it is also relatively easy to make the heater larger in area (A3 size or more).

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

In addition, in inkjet printing, a single application generally results in a film thickness of approximately 1 μm, but in high-definition printing inkjet printing, the film thickness may be as high as 0.1 μm. In either case, the film thickness can be adjusted by applying the film multiple times. The film thickness can also be adjusted by enlarging the nozzle of the inkjet printer and increasing the amount of each droplet. Furthermore, in the inkjet method, a pattern is formed using a silver-containing ink, and the pattern is plated with copper to increase the film thickness and reduce the resistance value. By utilizing these known techniques, a conductive ink layer of the desired thickness can be obtained.

In addition, if the pattern is a solid fill pattern, the conductive ink layer may be formed by coating. Any known coating technique can be used as long as it is a method that 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 preferably used. These coaters can form a thin film of conductive ink of about 1 μm, so that the flexibility of the electric heating device of the present invention is not impaired. In addition, coating in the present invention means forming a thin film layer of conductive ink over the entire surface of a specified area on one side of the substrate, and is not limited to coaters, and any widely known coating technique can be used.

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.

The substrate used in the thin electric heating device of the present invention may be an insulating material having heat resistance that can withstand the heating temperature of the heater, and for example, a polymer material film can be suitably used. 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, polystyrene, etc. In addition, the substrate is not limited to polymer materials, and paper, etc. can also be used. For example, high-quality paper can be used as long as it has heat resistance. There is no particular limit to the thickness of the substrate. Since the electric heating wire formed with conductive ink can be used without problems even in a folded state, the thickness of the substrate can be selected according to the purpose and use. In order to demonstrate 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. In addition, the shape of the substrate and the shape of the thin electric heating device created by printing, etc. may be in the form of a sheet or roll.

The thin electric heating device of the present invention configured as described above is, for example, made into a sheet 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 a surface. As explained above, various heating wire patterns can be easily created by printing, making it possible to design and create various heaters depending on the intended use. Furthermore, since the thin electric heating device of the present invention has excellent flexibility and can be bent or folded when used, it can be used in any shape depending on the shape of the object to be heated by the heater.

Furthermore, the thin electric heating device of the present invention takes advantage of this excellent flexibility and can increase the heating temperature of the heater area by stacking the heater areas. This is thought to be due to the fact that the heater areas are stacked in layers, which increases the heat retention effect, and the area of contact with the outside air is reduced, thereby suppressing 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 heating temperature of the heater while maintaining a low applied voltage, i.e., while keeping power consumption low.

The following describes the embodiments of the present invention in detail based on several examples, but the present invention is not limited to these.

Heating wires were formed in the following patterns using silver-containing ink by flexographic printing with an anilox roll of 700 lines on a substrate (A4630: polyester) of approximately A3 size (300 x 420 mm), and samples were prepared.
Comparative Example Sample
[Sample 01]:
The heater area was a pattern filled with solid black, no connection area was provided, and the heater area was connected to an external power source near the center of both ends.
Example sample
[Sample 02]:
The heater area was a pattern filled with solid black, similar to sample 01, and a 15 mm wide conductive tape (made of copper) was attached to both ends of the heater area to form a connection area. The connection terminal was set in the center of the connection area, similar to sample 01, and was connected to an external power source.
[Sample 03]:
The heater area and the connection area were patterned and shaped as shown in FIG. 7. The connection terminal was set in the center of the connection area as in sample 01 and connected to an external power source. The connection area was left as an ink thin film layer, and no conductive material was added. The details of the heater area pattern are shown in FIG. 3. The line width was 5 mm in both the X-axis direction and the Y-axis direction, and the line spacing was 1.5 mm in the X-axis direction and 15 mm in the Y-axis direction. The details of the connection area are shown in (d) and (e) of FIG. 5. In this embodiment, the longest part X1 of the X-axis width of the connection area was 32.5 mm, and the shortest part X2 was 15 mm. Y1 was 300 mm. At this time, the inclination angle θ3 of the connection area was 165°, and X3 was 17.5 mm.
[Sample 04]:
A 15 mm wide conductive tape (made of copper) was attached onto the connection area of Sample 03 in the same manner as Sample 02 to form a connection area of Sample 04. The connection terminal was set in the center of the connection area in the same manner as Sample 01, and was connected to an external power source.

A current was applied to each sample using an external power source (a stabilized DC power source), and the heat generation temperature in 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 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 value and voltage value displayed on the device.
The equipment used is 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.)

Sample 01, which is a comparative example, was not measurable because no current flowed and no heat was observed. For the other samples, the current values shown in Table 1 were 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 performed in a test room with a room temperature of about 25°C. As a result of measuring the heat generation temperature, Sample 01, which is a comparative example, did not generate any heat, whereas Samples 02 to 04 generated heat. 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 of all of Samples 02 to 04 were around 30°C, with no significant difference. However, as can be seen from the thermography images, Samples 03 and 04, which have a grid pattern, have better uniformity of heat generation temperature within the heater area than Sample 02, which has a solid black pattern of heating wires.

Using samples 02 to 04 used in Example 1, the difference in the uniformity of the heating temperature within the heater area of each sample was measured. As shown in Figure 9 (a), the heater area of each sample was divided into three areas 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. From the results in Table 2, it was confirmed that samples 03 and 04 actually have better uniformity of heating temperature in the heater area than sample 02. However, at a heating temperature of around 33°C in this test, even sample 02 had heating temperatures in each area within the range of about 33°C ± 2°C, so it can be said that the difference in heating is not a problem if it is used for normal insulation purposes.

Next, we confirmed the case where different patterns were mixed in the heater area. Specifically, we confirmed the difference in heat generation between the case where the entire heater area was configured with the same heating wire pattern and the case where the heater area was divided into arbitrary small areas and each small area was configured with a different heating pattern. Samples 05 to 08 with the heating pattern shown in the top row of Figure 10 were prepared, and the heat generation temperature in each small area was measured. In the heating pattern shown in the top row of Figure 10, the black parts are the parts without silver ink (non-heating wire), and the gray parts are the heating wire parts formed with silver-containing ink. The measurement results are shown in Table 3, and the thermographic images of each are shown in the middle row of Figure 9. The bottom row of Figure 9 shows the position of the small area where the heat generation temperature of each sample was measured, and each corresponds to the small area number in Table 3. The test was performed when the voltage was 5.0 V and the current value was adjusted so that the power consumption was 22.7 W and the same, as shown in Table 3. The results are shown in Table 3 and the thermography images (at the same voltage) shown in the middle of FIG. 10. As is obvious from the thermography images, in sample 05, in which the entire heater area is composed of the same pattern repeated, the heat generation in the heater area is almost uniform, whereas in samples 06 to 08, in which different patterns are mixed in the heater area, the heat generation temperature differs for each small area according to the electrical resistance of the pattern. This was also the case for the actual measured temperature values shown in Table 3. Specifically, in sample 06, small area 1 showed a higher heat generation temperature than small area 2. This is thought to be due to the fact that small area 1 has a pattern in which the path of the current changes more significantly, that is, a pattern in which it is difficult for the current to flow in the X-axis direction, and therefore the current has to zigzag more significantly and therefore has a higher electrical resistance, whereas the pattern in small area 2 has a smaller rate of change in the direction of the current flow and therefore has a smaller electrical resistance. This tendency is also seen in samples 07 and 08. In this way, with the present invention, by combining patterns with different electrical resistance, it is possible to change the degree of heat generation for each small partitioned area. This makes it relatively easy to design the heater's heat generating location according to the intended use, etc.

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 for use.
(Test 4-1): Used as a cylinder A heating wire was formed in a solid black pattern on a long substrate of 780 mm x 90 mm, and a conductive tape (copper) with a width of 15 mm was attached to the short sides at both ends to form a connection area. Then, a current was passed through the substrate in a cylindrical shape with one short side rolled inward to confirm the heat generation temperature. In this state, one of the connection areas is on the inner circumference side of the cylinder, and the other is on the outer circumference side of the cylinder. The size of the cylinder was determined by winding the film device so that the outer circumference of each cylinder had a predetermined diameter, and the length direction of the film device was 780 mm / cylinder outer circumference length mm = number of windings. The results are shown in Table 4. From this result, it was confirmed that the more the number of windings, that is, the more the overlap of the film device, the higher the heat generation temperature. When the sheet (long) was used in a flat state without being made into a cylindrical shape, the average heat generation temperature was 46.2 ° C., whereas when the sheet was used in a cylindrical shape with 15.6 windings, the average heat generation temperature rose to 107.8 ° C. It was also confirmed that the power consumption is almost the same when the device is placed flat and when it is placed cylindrically. This result 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 a stacked state. This shows that the device can be applied to cases where the object to be kept warm is cylindrical, that is, not only can it be adapted to the shape of the object to be kept warm, but it can also be used to save power while keeping the object warm at a higher temperature.

(Test 4-2): Use in Folding 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 folding was performed by folding inward from one short side of the film device at a length calculated by 780 mm in the length direction/number of folds. That is, in the case of folding two times to make three layers, as shown in FIG. 11(a), for example, the R side is folded inward as a valley fold at line F1, and then F2 is folded further inward as a valley fold to produce sample 13. In (a), it is the same as the so-called state where a sheet is folded in three. Similarly, if it is folded four times as shown in FIG. 11(b), it becomes sample 14 with five layers, and if it is folded six times as shown in FIG. 11(c), it becomes sample 15 with seven layers. In this folded state, as in the case of making it cylindrical in Test 4-1, one of the connection areas is on the inside of the fold, and the other is on the outside surface of the fold. The results are shown in Table 5. As in Test 4-1, it can be seen that the heating temperature increases as the number of folds increases and the overlap of the heater area increases. And, as in Test 4-1, the power consumption remains almost flat even when the temperature increases. Also, when comparing the heating temperatures of Sample 11 (7.8 turns) in Test 4-1 and Sample 15 (6 turns, 7 layers) in Test 4-2, it can be seen that they are almost the same at 90.4°C and 87.2°C. That is, it can be seen that the heating temperature can be increased as the overlap of the heater area increases. When folding, there is a limit to the number of folds due to the elasticity of the base material, but it is generally easier to roll it into a cylindrical shape. In any case, such a method of use is possible due to the excellent flexibility of the film device of the present invention, and it can be said that the film device of the present invention can be applied to various shapes according to the purpose of use and the desired heating temperature.

1 Thin electric heating device 2 Conductive ink thin film layer
21 Heater heating wire 3 Connection terminal portion 4 Conductive tape HA Heater area CA Connection area

Claims (6)

A substrate made of an electrically insulating material;
a heater area having a thin-film heater wire formed on the base material using conductive ink;
a connection area formed of a conductive material along two opposing sides at both ends of the heater area, the connection area having connection terminals to be connected to an external power source,
A thin electric heating device, characterized in that the electrical resistance of the connection area is lower than the electrical resistance of the heater area. 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 of a conductive ink,
The connection area is
Along the two opposing sides,
2. The thin electric heating device according to claim 1, wherein the thin electric heating device is made of a conductive material different from the conductive ink that forms the heater wire. The heater wire is a thin-film heater wire formed by flexographic printing or inkjet printing of a conductive ink,
A pattern is formed in which the direction of current flow from one of the connection terminals to the other changes multiple times,
The thin electric heating device according to claim 1 , wherein the width of the connection area in the direction of current flow is wider than the line width of the heater electric wire. The thin electric heating device according to 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 the direction perpendicular to the direction of current flow. 5. The thin electric thermal device according to claim 3, wherein the pattern is a pattern in which a shape having a branch point formed by the intersection of lines extending in different directions is repeated a plurality of times. 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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