PPTC heating element with different power densities

Abstract

A pPTC heating device having regions of different power density distributed across the surface of the device. The device is constructed using a base layer formed of pPTC material having segmented conductive plate layers disposed above and below the pPTC layer to control the current path through the device and thereby control the resistance of the device and the power density of the device.

Description

Background Technology

[0001] Positive temperature coefficient (PTC) materials are materials that exhibit a positive temperature coefficient, meaning that their resistance increases proportionally with increasing temperature. Typically, current can pass through a device made of PTC material until the material reaches a specific design temperature, at which point the resistance rises rapidly, effectively cutting off the current.

[0002] A polymer PTC (pPTC) is a PTC device composed of a non-conductive crystalline polymer incorporating carbon particles. Below a design temperature, the polymer is in a crystalline state, and the carbon particles form a conductive path through the polymer. If the current is too high, the device heats up, and the polymer becomes amorphous, thus separating the carbon particles and breaking the current path. Once the device cools down, the polymer returns to a crystalline state, thereby re-establishing the current path generated by the carbon particles.

[0003] pPTC is best known for its use in resettable fuses, where it stops current flow once the device reaches its design temperature and allows current flow again when the device cools down below its design temperature. Self-resetting fuses composed of pPTC are well-known in the art.

[0004] Another common application of pPTC is as a heating element. These devices have advantages over resistance heaters that use current through metal wires because, due to the properties of pPTC, pPTC heaters do not overheat and are self-limiting. Furthermore, PTC heating elements have high power density, thus generating heat very efficiently even in confined spaces.

[0005] pPTC heaters have numerous applications. For example, they can be used in water tank heating applications, such as water tanks or urea tanks; for comfort heating, such as car seat and steering wheel heaters; as lens defoggers and battery heaters, to name just a few. Typically, the device may comprise a flexible sheet of pPTC material with flexible conductive plates laminated on opposite sides of the pPTC material. In such applications, it may be desirable to be able to vary the power density over different surface areas of the device, for example, allowing for different heating temperatures in different surface areas of the device.

[0006] Power density depends on the voltage applied to the resistive and heating elements, which determines the current flowing through the device. In most cases, changing the power supply voltage requires additional components, thus increasing production costs.

[0007] Different power densities can also be achieved by using multiple sheets of PPTC material on the surface area of ​​the heater, each sheet having a different substrate concentration and therefore a different resistivity. However, changing the formulation of the PPTC material to obtain different resistivities is a challenge, requiring very precise control of substrate concentration and uniformity, which increases manufacturing costs.

[0008] Figures 1A and 1B show examples of two prior art pPTC heaters. The device includes two conductive plates 102 and 104 with layers of pPTC material 106 (a, b) disposed between the conductive plates. Figure 1A shows a device using low-resistivity pPTC material 106a, allowing a high current 100a between conductive plates 102 and 104. Figure 1B shows another version of the device where pPTC material 106b is a high-resistivity material, allowing a smaller current 100b to pass between conductive plates 102 and 104. Therefore, the devices in Figures 1A and 1B have different power densities; however, achieving different power densities requires reformatting the pPTC material 106 (A, B) between conductive plates 102 and 104 to change the resistivity. Summary of the Invention

[0009] To alleviate the aforementioned challenges, this paper discloses a novel method for controlling power density in pPTC heating devices. The invention describes a device with different power densities over a surface region. The method involves using a single pPTC substrate with a constant resistivity. Power density over the surface region is controlled by dividing the upper and lower conductive layers into multiple segments, thereby controlling the current path through the device and thus controlling the overall resistivity of the device. By varying the size and number of the segmented portions of the conductive layers on the surface region, different resistivity regions can be achieved within a single device, and thus different power densities can be achieved.

[0010] The segmented sections are used as resistors connected in series. Each segment will be smaller, and because multiple segments will be connected in series, each segment will be exposed to a lower voltage. Power dissipation can be adjusted without changing the size of the substrate or heater by varying the segmented sections and how they overlap between the top and bottom layers.

[0011] Another advantage of this segmentation strategy is that the heater can be divided into multiple zones, each with a different number of segments, resulting in varying power densities per square unit of the device's surface area. In zones with smaller segments, the greater number of segments leads to higher resistance, thus providing lower power output per square unit area, and the segments act as resistors connected in series. Conversely, in zones with larger segments, fewer segments are used. Therefore, these zones have lower resistance and higher power density per square unit area. This allows for flexible power density control across the entire surface of the heater, with different zones of the device exhibiting different power densities. Attached Figure Description

[0012] Figures 1A and 1B show schematic diagrams of a high-current prior art device and a low-current prior art device, both of which have a constant power density across the entire surface of the device.

[0013] Figure 2A , Figure 2B Two exemplary devices according to the present invention are shown, each with a different power density based on the size of the segmented portion in each conductive layer.

[0014] Figure 3 yes Figure 2A , Figure 2B A perspective view of the device, showing the positioning of the segmented sections in the top and bottom layers relative to each other.

[0015] Figure 4A , Figure 4B An embodiment of a pPTC heater with two different power density regions in a single device according to the present invention is shown.

[0016] Figure 5A , Figure 5B A second embodiment of the pPTC heater according to the invention is shown, having two different power density regions in a single device, one of which is a segmented section of different sizes.

[0017] Figure 6A , Figure 6B , Figure 6C Infrared images are shown, illustrating the various stages before and after voltage is applied to the device. Figure 4A , Figure 4B The heat is provided to different areas on the surface of the device.

[0018] Figure 7 This illustrates how the power density of a segment depends on the voltage, the resistivity of the PTC material, and the thickness of the PTC material.

[0019] Figure 8This demonstrates that the power dissipated by the entire device can be changed by altering the quantity of certain components. Detailed Implementation

[0020] Figure 2A , Figure 2B A schematic side view of two exemplary proof-of-concept embodiments of the device according to the present invention is shown. Figure 2A As shown, the upper conductive layer 202 and the lower conductive layer 204 are divided into several portions. In this embodiment, these portions are positioned to force the current to oscillate between the upper layer 202 and the lower layer 204 when current passes through the device. The path of the current through the device from left to right is shown by arrows, indicating that the current oscillates between the upper layer 202 and the lower layer 204 through the pPTC layer 206. As the current passes through the device, the current passes through the resistive layer 206 multiple times, acting as a series of resistors, with each transition through the pPTC layer 206 having a proportional voltage drop.

[0021] In a preferred embodiment of the invention, the segmented portions of the upper layer 202 and the lower layer 204 are offset from each other, such that the gaps between the portions of the upper layer 202 and the lower layer 204 are misaligned. The size of the gaps between the segmented portions in layers 202 and 204 forces current through the pPTC material 206 layer to reach the segmented portions of the opposite layer with a shorter path. In a preferred embodiment of the invention, the gap between any two segmented portions of layer 202 or 204 will be aligned with the midpoint of the segmented portion in the opposite layer.

[0022] Furthermore, for the device to function as intended, the gaps between the segments in each layer must be wide enough to force current through the pPTC layer 206 and into the segments of the opposite layer, rather than skipping the gaps between segments within the same layer. In a preferred embodiment of the invention, the gap between the segments of each layer is at least twice the thickness of the pPTC layer 206.

[0023] It should be noted that, Figure 2A In the device, conductive layers 202 and 204 have been divided into smaller segments. Figure 2B The smaller portions of conductive layers 210 and 212 of the device. Because the segmented portions in layers 202, 210 and 204, 212 act as low-resistance resistors connected in series. Figure 2A The device will have more Figure 2B The device has higher resistance, thus allowing a smaller current to pass through. Figure 2A The device instead of passing through Figure 2B The device. Therefore, Figure 2A , Figure 2B The pPTC layers 206 and 214 in the device can have the same formulation and the same resistivity, but the power density of the device, and therefore the heat generated by each device, will be different.

[0024] Figure 3 It shows Figure 2B A perspective view of the device shows the relative arrangement of segmented portions 302 in the upper layer and 304 in the lower layer, offset relative to each other. It should be noted that, in this embodiment, according to a preferred embodiment of the invention, the segmented portions are offset such that the gap between the segmented portions in each layer is aligned with the midpoint of the segmented portions in the opposing layer. In other embodiments, this alignment need not be precise for the device to operate as intended. The device can operate as intended as long as the gap between the segmented portions in one layer is not aligned with the gap between the segmented portions in the opposing layer. Furthermore, it should be noted that the device includes half-size segmented portions 302a and 304a located at the ends of the device to avoid wasting the surface area of ​​the pPTC layer 306.

[0025] It should be noted that, Figure 2A , Figure 2B and Figure 3 In the device, the entire surface area of ​​the device is composed of segmented sections of the same size. Figure 3 (Except for halves 302a and 304a shown). Therefore, the power density differs between devices, but remains constant over the entire surface area of ​​a single device. In other embodiments of the invention, different regions of the device surface may have segments of different sizes and different numbers of segments, thereby creating regions with different power densities on a single device.

[0026] The power density of a single segment can be referenced. Figure 7 Calculate the resistance. This can be given by the following equation:

[0027] (1)

[0029] in:

[0030] It is the thickness of the resistive PTC material in the current path;

[0031] The resistivity of PTC material; and

[0032] It is the conductive area through which electric current flows.

[0033] Note that in Figure 7 In the figure, an exemplary conductive region through which current flows is a rectangular region, the dimensions of which are shown as follows: It should be noted that, in various embodiments, the conductive region can be of any shape.

[0034] The power is given by the following formula:

[0035] (2)

[0036] in:

[0037] It is the voltage across the conductive region; and

[0038] It is the current passing through the conductive region.

[0039] because Equation (2) becomes:

[0040] (3)

[0041] Power density is the power per unit area. Therefore:

[0042] (4)

[0043] Substituting equation (1) for the resistance in equation (4) yields:

[0044] (5)

[0045] This equation clearly shows the power density of a portion of the device. It is a function of three variables: voltage, resistivity of the PTC material, and thickness of the PTC material. According to the present invention, various devices may have the same size, shape, and rated power (power dissipation under certain conditions), but one device may have a constant rated power (i.e., constant power density) on all surfaces, while another device may have a higher power region and a smaller power region (i.e., different power densities).

[0046] Figure 4A One embodiment is shown in which the device has two independent regions with different power densities. Figure 4A The top conductive layer 402 and bottom conductive layer 404 of the device are shown, both divided into segments of different sizes to create low-power-density and high-power-density regions, as illustrated. It should be noted that when the top layer is positioned above the bottom layer with the pPTC layer in between, the gaps between the segments in the top layer are aligned with the midpoints of the segments on the bottom layer, and vice versa. It should also be noted that a voltage source is connected between boards 408 and 406, which are configured in parallel to connect the low-power-density and high-power-density regions.

[0047] Besides the common boards 406 and 408 Figure 4AThe low-power-density and high-power-density regions of the device are electrically isolated from each other. Therefore, the gap between the low-power-density and high-power-density regions must be large enough to prevent current from jumping between the regions. In a preferred embodiment, the gap 410 between the low-power-density and high-power-density regions will need to be larger than the gap between the segmented portions of each respective region.

[0048] Figure 4B Showing Figure 4A Schematic diagram of the device. Segmented section of the low power density region Sa. It is connected in series to the power supply. Similarly, the segmented portion of Sb in the high power density region... Connected in parallel configuration to the segmented section On the same power supply. All segments of region Sa. The dimensions are equal. As long as the segmented portions of each region are of equal size, the power density will be uniformly distributed. This also applies to the segmented portions of region Sb. However, due to the segmented parts Larger than segmented part Segmented sections This will exhibit lower resistance, resulting in higher current. Simultaneously, the fewer segmented sections in region Sb lead to higher voltages applied to each individual section. Consequently, higher current and greater power dissipation occur in region Sb.

[0049] Figure 5A Another variation according to an embodiment of the invention is shown. Figure 5A The illustrated embodiments and Figure 4A The difference in the illustrated embodiment is that, Figure 5A The high-density regions are relatively small and surrounded by low-density regions. The top and bottom layers of the device are... Figure 5A These are shown as 502 and 504 respectively. Furthermore, as in the embodiment shown in Figure 4(A), a voltage source is connected to portions 506 and 508 of the top layer 502.

[0050] like Figure 5B As shown, the segmented portion of region Sa This forms low-power-density regions that are connected in series. The segmented portion of region Sb. This forms a second low power density region. The segmented portion of region Sc. A high power density region is formed, and its size is smaller than the segmented portions in regions Sa and Sb. In this embodiment, the segmented portions... and segmented parts Connected in series to the power supply. Figure 5A and Figure 4AThe difference between the embodiments lies in the fact that the bottom of the heater has a larger segmented section (and therefore a lower resistance per segment), which will result in a higher current flow, thus increasing the power density. To mitigate this, region Sb is segmented, and region Sc has been inserted between the segmented sections of region Sb. Region Sc will have a higher resistance. From the segmented section To the segmented section Then, in the segmented section... Then, in the segmented section... The total number of transitions in region Sb (all connected in series with the power source, therefore having the same current flowing through them) is less than the total number of transitions in region Sa. To maintain the same power density in region Sb as in region Sa, the current must be reduced. This reduction in current is achieved by replacing some segments of area Sb with segments that include area Sc. Region Sc will have higher resistance and a higher voltage drop. The higher voltage drop in region Sc will reduce the voltage drop in region Sb, thus reducing the power density. By changing the segments in each region, a balance can be achieved where region Sa will have the same power density as region Sb, while region Sc will have a higher power density.

[0051] Figure 6A , Figure 6B , Figure 6C Infrared images of a resistance heater with two different power density regions according to the present invention are shown. The images shown are for... Figure 5A , Figure 5B The embodiments of the present invention are shown. Figure 6A An image of the device before voltage is applied is shown. Figure 6B This represents the image after power is applied. Figure 6C The image shows the temperature after stabilization. It can be seen that the heater with higher power density heats up faster at the bottom and reaches a higher temperature, with the highest temperature occurring in the high power density region Sc.

[0052] In a preferred embodiment, the base resistive layer of the device is composed of pPTC. In one embodiment, the pPTC may be composed of polyethylene infused with carbon particles; however, any known pPTC formulation may be used. Furthermore, in a preferred embodiment, a monolithic PTC material with a constant resistivity will be used regardless of how many different power density sections are formed on the device surface. It will be appreciated that any number of different power density regions can be formed on the device surface by varying the size and number of segmented portions in each region of the conductive layer, and by providing the desired spacing between the segmented portions and regions to force the current path to oscillate between the upper and lower layers in each region. The overall size of the device, as well as the actual number of different power density regions and the size of the segmented portions of each power density region in any particular embodiment, will be driven by the desired application. Furthermore, in various embodiments, the conductive layer may be any conductive material, but in a preferred embodiment it will be copper or gold. In other embodiments, the pPTC material may also be segmented.

[0053] In some embodiments of the present invention, the segmented portions may have the same size, such as Figure 8 As shown. Therefore, the resistance of each segment is the same and is given by equation (1). Since all parts are connected in series, the total resistance of the device is given by the following equation:

[0054] (6)

[0055] in:

[0056] This is the total number of segments in the device. Equation (3) becomes:

[0057] (7)

[0058] To achieve different power density regions on the same device, the number of segments in different regions can be different. Substituting the resistor in equation (6) for equation (1) yields:

[0059] (8)

[0060] The dissipated power becomes:

[0061] (9)

[0062] The dimensions of a segment can be expressed by dividing the device by the number of segments:

[0063] (10)

[0064] in:

[0065] yes Figure 8 The total length of the device shown; and

[0066] yes Figure 8 The total width of the device shown.

[0067] Substituting equation (10) into equation (9), we get:

[0068] (11)

[0069] It can be clearly seen from equation (11) that by changing the number of segments, the same device can have regions with different power densities.

[0070] In other embodiments of the invention, another way to introduce higher power density is to provide smaller series segments. Therefore, if the segments are larger, the power density will be lower. According to Ohm's law, current is directly proportional to the applied voltage and inversely proportional to resistance. If one of the segments has different dimensions, the difference in power dissipation can be demonstrated by the current flow. Since all segments are connected in series, the current in all segments is equal, but the resistance depends on the thickness of the resistive PTC material. The resistivity of PTC materials and area Since resistance is inversely proportional to area, the smaller the area, the higher the resistivity.

[0071] The invention has been explained with reference to various embodiments, which are to be considered exemplary in nature and not to limit the scope of the invention, the scope of which is described in the following claims. Specifically, various embodiments of the apparatus of the invention may include materials of different resistivity, devices of different thicknesses, and combinations of removing portions of the conductive layer to disable small portions of the heater.

Claims

1. A device with different power densities, comprising: pPTC layer; A top layer of segmented conductive portions disposed on one side of the pPTC layer, the top layer having gaps between the segmented portions; and A bottom layer of segmented conductive portions disposed on opposite sides of the pPTC layer, the bottom layer having gaps between the segmented portions; The segmented conductive portions are arranged such that the gaps between the segmented portions in the top layer and the gaps between the segmented portions in the bottom layer are misaligned to form a current path through the device, the current path oscillating between the segmented portions in the top layer and the segmented portions in the bottom layer through the pPTC layer; The device has multiple segmented regions in the top and bottom layers, each segmented region having a different power density when a voltage is applied to the device.

2. The apparatus of claim 1, wherein the segmented portions of the top layer are spaced apart from each other, and the segmented portions of the bottom layer are spaced apart from each other, wherein the spacing is at least twice the thickness of the pPTC layer.

3. The apparatus of claim 1, wherein the segmented portions of the top layer and the bottom layer have constant dimensions.

4. The apparatus of claim 3, wherein the apparatus has a constant power density over its surface area.

5. The apparatus according to claim 1: The segmented portions are arranged such that the gaps between the segmented portions in the top layer are aligned with the midpoints of the segmented portions in the bottom layer; and The gaps between the segments in the bottom layer are aligned with the midpoints of the segments in the top layer.

6. The apparatus of claim 1, wherein the segmented portions in the top layer and the bottom layer serve as a series of resistive devices.

7. The apparatus of claim 1, wherein the apparatus has a plurality of segmented portion regions in the top layer and the bottom layer, the size of the segmented portion in each segmented portion region being different from the size of the segmented portions in the other regions.

8. The apparatus of claim 7, wherein the plurality of segmented portion regions in the top layer and the bottom layer are separated from each other by gaps that prevent current from passing between the segmented portion regions.

9. The apparatus of claim 7, wherein the segmented portions in each region have the same dimensions.

10. The apparatus of claim 7, wherein each of the plurality of regions is electrically connected in parallel.

11. The apparatus of claim 1, wherein the apparatus is a heater, and wherein each segmental portion provides a different temperature when a voltage is applied to the apparatus.

12. A heating element with different power densities, comprising: pPTC layer; The top layer of multiple segmented conductive regions is disposed on one side of the pPTC layer; and The bottom layer of multiple segmented conductive portion regions disposed on opposite sides of the pPTC layer; In each region, the top and bottom segments are spaced apart to have a gap therebetween, and the gaps in the top and bottom layers are misaligned to form a current path through the heating element, such that the current path oscillates between the top and bottom segments of the pPTC layer in each region. When a voltage is applied to the heating element, each segmented region has a different power density.

13. The heating element of claim 12, wherein the plurality of segmented portions in each layer are spaced apart to prevent current from flowing from one region to another.

14. The heating element according to claim 12: The segments of each region are spaced apart such that the gaps between the segments in the top layer of the region are aligned with the midpoints of the segments in the bottom layer of the region; and The segments of each region are spaced apart such that the gaps between the segments in the bottom layer of the region are aligned with the midpoints of the segments in the top layer of the region.

15. The heating element of claim 12, wherein each of the plurality of regions is electrically connected in parallel.

16. The heating element of claim 12, wherein the pPTC layer has a constant resistivity for each region.

17. The heating element of claim 16, wherein each segmented portion provides a different temperature when a voltage is applied to the heating element.

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