Ceramic heater

Abstract

To provide a ceramic heater capable of suppressing breakage of a heater due to thermal shock.SOLUTION: A ceramic heater 100 includes a ceramic body 10 having a heat generating resistor 13; and a coating layer 20 mainly made of glass and configured to cover at least regions having corner parts 11E and 12E and the heat generating resistor on a surface of the ceramic body. A ceramic particle 21 is attached to at least a part of a portion of the surface of the coating layer covering the ceramic body.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a ceramic heater used, for example, for air conditioning of electric vehicles or for heating and keeping batteries warm. [Background technology]

[0002] Systems that use ceramic heaters to heat coolant or other fluids are being considered for air conditioning or battery heating and insulation in electric vehicles. Battery performance declines in cold regions, making battery heating and insulation particularly important.

[0003] This ceramic heater has a structure in which a ceramic layer is wound around the outer periphery of a cylindrical or columnar ceramic tube that serves as a core material, and a heater pattern is formed on the ceramic layer (see Patent Document 1). When the heater pattern is energized and heated, the ceramic heater generates heat.

[0004] However, ceramic heaters are susceptible to thermal shock, and if a ceramic heater that has been heated to a high temperature is suddenly cooled, cracks or the like may occur, potentially damaging the heater. In particular, when a ceramic heater is used to heat a medium (fluid) such as a coolant liquid, if droplets fall on the ceramic heater when it is in an empty-heating state (heated in air), the thermal shock becomes large. On the other hand, as a conventional method for protecting ceramic members, coating the surface with glass (glaze) as in the technique of Patent Document 1 above has been known. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-92880 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the glaze is fired at high temperatures, the viscosity of the glass material in the glaze decreases, and the glaze thickness tends to become thin, especially at the corners of the object, which may reduce the protection of the corners of the ceramic heater and ultimately the thermal shock resistance. To address this issue, it is possible to ensure the thickness of the glaze at the corners by applying the glaze in multiple steps, but this is not practical as it increases the number of steps and costs. SUMMARY OF THE INVENTION An object of the present invention is to provide a ceramic heater that can prevent damage to the heater due to thermal shock. [Means for solving the problem]

[0007] In order to solve the above problems, the ceramic heater of the present invention is a ceramic heater comprising a ceramic body having a heating resistor, and a coating layer made mainly of glass and configured to cover at least the corners and the area of ​​the surface of the ceramic body having the heating resistor, and is characterized in that ceramic particles adhere to at least a portion of the surface of the coating layer that covers the ceramic body.

[0008] If the coating layer does not contain ceramic particles, the viscosity of the glass material decreases when the coating layer is fired at a high temperature, and the thickness of at least a portion (corner, etc.) of the ceramic body becomes thin. Therefore, if ceramic particles are attached to the thinner portions of the surface of the coating layer, the thinner portions of the coating layer are protected by the ceramic particles. This reduces the thermal shock in the areas where the coating layer is thin, and prevents the heater from being damaged by the thermal shock.

[0009] In the ceramic heater of the present invention, the ceramic body may contain alumina as a main component, and the ceramic particles may be alumina particles. In this ceramic heater, the ceramic body and the ceramic particles have similar components, so the difference in thermal expansion coefficient between the ceramic body and the ceramic particles can be reduced, and the thermal shock to the coating layer can be reduced.

[0010] In the ceramic heater of the present invention, the ceramic particles may be attached to a portion of the surface of the coating layer that further covers the outer peripheral surface of the ceramic body. According to this ceramic heater, the ceramic particles cover the heating resistor and protect the portion of the ceramic body that becomes hot, so that thermal shock in this portion can be alleviated.

[0011] In the ceramic heater of the present invention, the ceramic body may be cylindrical and have an inner hole, the coating layer may cover at least a part of the surface of the inner hole, and the ceramic particles may be attached to the surface of the coating layer that covers the surface of the inner hole. According to this ceramic heater, the ceramic particles also protect the inner hole side of the ceramic body, so that thermal shock in this area can be alleviated.

[0012] In the ceramic heater of the present invention, the coverage of the coating layer with the ceramic particles may be 88.5% or more. In this ceramic heater, the ceramic particles cover most of the coating layer, and therefore most of the corners and the region of the ceramic body having the heating resistor 13, so that thermal shock can be further alleviated. [Effects of the Invention]

[0013] According to the present invention, a ceramic heater can be obtained that can suppress damage to the heater due to thermal shock. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a front view showing a ceramic heater according to an embodiment of the present invention. [Figure 2] FIG. 2 is a perspective view showing the configuration of a ceramic body. [Figure 3] FIG. 10 is a partially enlarged cross-sectional view showing a coating layer containing no ceramic particles. [Figure 4] FIG. 2 is a partially enlarged cross-sectional view showing a coating layer to which ceramic particles are attached. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a front view showing a ceramic heater 100 according to an embodiment of the present invention, FIG. 2 is a perspective view showing the configuration of a ceramic body 10, FIG. 3 is a partially enlarged cross-sectional view showing a coating layer 20 that does not contain ceramic particles, and FIG. 4 is a partially enlarged cross-sectional view showing a coating layer 20 to which ceramic particles 21 are attached. The ceramic heater 100 according to the embodiment of the present invention can be used, for example, for air conditioning of electric vehicles or for heating and keeping batteries warm, etc. The ceramic heater 100 of this example is for heating liquid, and heats a liquid such as a coolant liquid, thereby heating an object to be heated via the liquid.

[0016] As shown in FIG. 1, the ceramic heater 100 includes a cylindrical ceramic body 10 extending in the direction of an axis O, and a coating layer 20 made mainly of glass and covering the surface of the ceramic body 10. A heating resistor 13 is embedded inside the ceramic body 10 (FIG. 2). The coating layer 20 is configured to cover at least a portion of the surface of the ceramic body 10 (the corners 11E and 12E (see FIG. 3) and the region having the heating resistor 13). Here, the term "cylinder" includes a "cylinder." Furthermore, the term "main body" refers to more than 50 mass % of the coating layer 20.

[0017] In the example of Figure 1, the heating resistor 13 is formed from the tip of the ceramic body 10 to a position slightly rearward of the axis O, so the coating layer 20 covers the ceramic body 10 from the tip to the rearward of the heating resistor 13 along the axis O. As a result, the coating layer 20 protects the ceramic body 10 near the heating resistor 13, which becomes hot when heated, and reduces thermal shock. The reduction of thermal shock at the corners 11E and 12E will be described later.

[0018] A pair of external terminals 17 for applying electrical current to heat the heating resistor 13 are exposed on the outer surface of one end (rear end) of the ceramic body 10. Furthermore, a donut-shaped ceramic flange portion 15 for attaching the ceramic heater 100 to an object to be attached (such as an electric vehicle) is fitted onto the ceramic body 10 slightly distal to the external terminal 17 and fixed in place with glass or the like. The coating layer 20 covers the outer surface of the ceramic body 10 on the tip side of the flange portion 15 .

[0019] The ceramic body 10 includes a ceramic tube 11 and a ceramic layer (ceramic sheet) 12 that covers almost the entire outer periphery of the ceramic tube 11. Since the ceramic layer 12 does not completely cover the outer periphery of the ceramic tube 11, slits 12v extending in the axial direction (parallel to the direction in which the axis L extends) are formed on the outer periphery of the ceramic body 10.

[0020] In this example, the ceramic body 10 has a cylindrical shape with a through-hole (inner hole) 10h at the center (FIG. 2). The liquid flowing inside the through-hole 10h is heated by the ceramic heater 100, and the liquid on the outer periphery of the ceramic heater 100 is also heated by the ceramic heater 100.

[0021] 2, a heating resistor 13 having a serpentine pattern and a pair of internal terminals 26 are formed on the inner peripheral surface (the surface on the ceramic tube 11 side) or inside the ceramic layer 12. These internal terminals 26 are electrically connected to external terminals 17 at the end of the outer peripheral surface of the ceramic layer 12 through via conductors or the like (not shown). The heating resistor 13 is disposed near the front end of the ceramic body 10 , and the external terminal 17 is disposed near the rear end of the ceramic body 10 . The ceramic tube 11 and ceramic layer 12 may be made of alumina, for example.

[0022] 3 and 4, the mitigation of thermal shock at corners 11E and 12E by ceramic particles 21 will be described. In this example, corners 11E and 12E are exemplified as "at least a portion of the portion covering ceramic body 10," but the covered portion is not limited thereto. 3 and 4 are partially enlarged cross-sectional views along the axis O of the tip portion (region A in FIG. 1) of the ceramic body 10. Specifically, FIGS. 3 and 4 show cross sections of a region on one side (left side) of the tip portion of the ceramic tube 11 across the through-hole 10h, and the ceramic layer 12 covering the outer surface of the ceramic tube 11.

[0023] As shown in FIG. 3, the coating layer 20 covers at least the area of ​​the surface of the ceramic body 10 where the heating resistor 13 is located and the corners 11E and 12E. In this example, the ceramic body 10 is configured such that the ceramic layer 12 wraps around the outer periphery of the ceramic tube 11. Therefore, not only the corner 11E at the tip of the ceramic tube 11 but also the corner 12E at the tip of the ceramic layer 12 are exposed. Moreover, a "corner" is a convex edge (end). In this example, since the corners 11E are chamfered, the number of corners 11E is usually four, or five when the ceramic layer 12 covers the outer periphery of the ceramic tube 11 as shown in Figure 3 (when the corner 12E overlaps with one of the corners 11E in the direction of the axis O, the corner of the overlapping portion is represented by 13E).

[0024] As shown in FIG. 3, if no ceramic particles are included, the viscosity of the glass material decreases when coating layer (glaze) 20 is fired at a high temperature, and the thickness of corners 11E and 12E becomes thin. Therefore, as shown in Figure 4, when ceramic particles 21 are attached to the surface of coating layer 20 in areas that cover at least a portion of corners 11E and 12E, ceramic particles 21 protect corners 11E and 12E where coating layer 20 is thin. This reduces the thermal shock at the corners 11E and 12E, and prevents the heater from being damaged by the thermal shock.

[0025] The ceramic particles 21 are mixed and dispersed in a coating liquid that will become the coating layer 20. The coating liquid containing the ceramic particles 21 is applied to the ceramic body 10 and then fired, thereby forming the coating layer 20 and causing the ceramic particles 21 to adhere (adhere) to the surface of the coating layer 20. Furthermore, the heat generated during firing causes some of the adjacent ceramic particles 21 to bond together. Furthermore, as in this example, when the ceramic body 10 is composed of multiple components (ceramic tube 11 and ceramic layer 12) and each component has a corner, at least a portion of each of the corners must be covered with the coating layer 20 and have ceramic particles attached thereto.

[0026] Examples of ceramic particles 21 include, but are not limited to, alumina-based ceramics, yttria-based ceramics, aluminum nitride, silicon nitride, and silicon carbide. However, if the ceramic body 10 is mainly composed of alumina and the ceramic particles 21 are alumina particles, the components of the ceramic body and the ceramic particles are similar, so the difference in thermal expansion coefficient between the ceramic body and the ceramic particles can be reduced, and the thermal shock to the coating layer can be reduced. The average particle size (D50) of the ceramic particles 21 can be set to, for example, 1 to 100 μm, and is preferably 20 μm or more.

[0027] Ceramic particles 21 may be attached to the surface of the coating layer 20 at a portion that covers the outer peripheral surface of the ceramic body 10 . In this way, the ceramic particles 21 protect the portion of the ceramic body 10 that covers the heating resistor 13 and becomes hot, thereby mitigating the thermal shock of this portion.

[0028] Alternatively, the ceramic body 10 may be cylindrical and have an inner hole 10h, the coating layer 20 may cover at least a part of the surface of the inner hole 10h, and the ceramic particles 21 may be attached to the surface of the coating layer 20 covering the inner hole 10h. In this way, the ceramic particles 21 also protect the inner hole 10h side of the ceramic body 10, so that the thermal shock in this portion can be alleviated.

[0029] The coverage of the coating layer 20 with the ceramic particles 21 may be 88.5% or more. In this way, the ceramic particles 21 cover most of the coating layer 20, and therefore most of the area of ​​the ceramic body 10 having the corners 11E, 12E and the heating resistor 13, thereby further reducing thermal shock.

[0030] Here, the coverage is calculated as follows. First, an elemental mapping image of Si is obtained by EDS (energy dispersive X-ray analysis: acceleration voltage 15 Kev) on the surface of the coating layer 20 at the corner of the ceramic body 10. Then, this image is binarized and image analysis is performed to determine the area ratio of the region of components other than Si (e.g., Al) derived only from the ceramic particles 21, which is regarded as the coverage ratio. This is because the coating layer 20 is a glaze mainly composed of glass and contains SiO2 and B2O3, whereas if the ceramic particles 21 are alumina (Al2O3), they do not contain Si, and therefore the area ratio of the region other than Si is the area ratio of the portion where the ceramic particles 21 cover the coating layer 20.

[0031] Therefore, if a mapping image of elements contained only in either the coating layer 20 or the ceramic particles 21 is obtained, the coverage can be calculated. The surface of the coating layer 20 is measured by EDS at three locations, and the average value is used as the coverage rate.

[0032] It goes without saying that the present invention is not limited to the above-described embodiments, but covers various modifications and equivalents that fall within the spirit and scope of the present invention. The coating layer may cover at least a portion of the ceramic body, for example, at least a portion of the corners (there may be areas of the corners where the coating layer is not formed). The ceramic particles may be layered completely over the coating layer. The ceramic heater (ceramic body) is not limited to a cylindrical shape, but may be plate-shaped. In the case of a plate-shaped heater, in addition to the four corners at the tip, there are four corners that form ridges and extend in the axial direction, so the entire heater from the heat-generating part to the rear end must be coated. [Explanation of symbols]

[0033] 10 ceramic body 10h Through hole (inner hole) 11E, 12E, 13E: Areas where the ceramic body is covered (corners) 13 Heating resistor 20 Coating Layer 21 Ceramic particles 100 Ceramic heater O axis

Claims

1. a ceramic body having a heating resistor; a coating layer mainly made of glass and configured to cover at least the corners and the region of the surface of the ceramic body having the heating resistor; A ceramic heater comprising: A ceramic heater characterized in that ceramic particles are adhered to at least a portion of the surface of the coating layer that covers the ceramic body.

2. 2. The ceramic heater according to claim 1, wherein the ceramic body is mainly composed of alumina, and the ceramic particles are alumina particles.

3. 3. The ceramic heater according to claim 1, wherein the ceramic particles are attached to a portion of the surface of the coating layer that further covers the outer circumferential surface of the ceramic body.

4. the ceramic body has a cylindrical shape with an internal bore; The coating layer covers at least a part of the surface of the inner hole, 3. The ceramic heater according to claim 1, wherein the ceramic particles are attached to the surface of the coating layer that covers the surface of the inner hole.

5. 3. The ceramic heater according to claim 1, wherein the coverage of the coating layer with the ceramic particles is 88.5% or more.

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