JPH04349387A - Conductive heating element - Google Patents

Abstract

PURPOSE:To provide conductive heating element for a ceramic heater having uniform conductivity by adding thin piece graphite which has a high aspect ratio as conductive material to a ceramic, etc., of an originally electric insulator and molding and then, sintering it. CONSTITUTION:Thin piece graphite with a grain size of 1-100mum, a thickness of 1mum or less and an aspect ratio of 10-5000 is used as conductivity endowing material, 0.5-10 parts by weight of the graphite are uniformly dispersed in 100 parts by weight of matrix made up of ceramic, glass or a mixture of glass and ceramic. Insulation sheets are piled up on and under that green sheet 1, and an insulation paste layer 3 is formed at the side of the green sheet 1 and they are degreased at a temperature of 400 deg.C or less, and thereafter, sintered at a temperature of 450-1500 deg.C. A direct current-flow type conductive heating element with high conductivity, speedily answering to a current flow, good in temperature-up characteristic, uniformly heating by applying a low voltage and good in heat resistance.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive heating element for a ceramic heater, which can be used in a wide range of industrial and consumer fields and can generate heat by direct energization to the heating element.

0002

BACKGROUND OF THE INVENTION Most of the ceramic heaters currently in use conduct electricity through a metal resistance heating element embedded in a ceramic matrix, and obtain thermal energy by the resistance heating. Such ceramic heaters include those in which a metal resistance heating element such as tungsten or molybdenum is embedded in a matrix whose main component is alumina, or one in which a metal resistance heating element such as palladium or platinum is embedded in a matrix whose main component is cordierite. There are known methods in which a metal resistance heating element made of copper is embedded in a matrix mainly composed of borosilicate glass and alumina (Japanese Patent Application Laid-Open No. 62-20678).

However, in such ceramic heaters, in order to make the heat generation temperature distribution uniform, the heat generating resistor, which is a filament, is processed into a shape such as wavy, spiral, meandering, etc., and arranged uniformly. However, only the area near the heating resistor generates strong heat, and it is still not sufficient to make the heat generation temperature distribution uniform.The response of heat generation is slow due to heat conduction through a thick matrix. Issues such as the need for high-temperature firing and the need to adjust the firing atmosphere during the manufacture of ceramic heaters remained. For this reason, attempts have recently been made to add conductive materials such as carbon to heat-resistant ceramics to create a heating element that can generate heat uniformly throughout. However, carbon materials such as graphite powder, which are obtained by mechanically crushing natural graphite or artificial graphite or graphitizing carbon black, which are conventionally used as conductive materials, are difficult to uniformly disperse in ceramic raw materials. There were major problems such as large variations in the conductivity of the resulting material and non-uniform conductivity of the entire molded body.

[0004] In order to solve these problems and obtain ceramic materials with uniform conductivity, various methods have been tried. A method of kneading, molding and sintering this as a pre-treated raw material (Japanese Unexamined Patent Publication No. 59-217668)
Japanese Patent Application Laid-open No. 19505/1983 discloses a method of nitriding ceramic while sintering it in order to tightly fill a ceramic molded body with a carbon material. However, these methods still have problems such as complicating the ceramic heater manufacturing process and being limited to specific ceramic materials.

[0005]

[Problems to be Solved by the Invention] The present invention solves the above problems, allows direct energization to generate heat, has a fast energization response, and
To provide a heating element that has excellent thermal shock resistance, uniform heat generation, and is easy to manufacture, and a conductive heating element for a ceramic heater having an electrical insulating layer integrated with the heating element. The purpose is to

[0006]

[Means for Solving the Problems] As a result of intensive studies to solve the above-mentioned problems, the present inventors have developed flaky graphite with a high aspect ratio as a conductive material for ceramics, etc., which are originally electrical insulators. It was discovered that a ceramic shaped body with uniform conductivity could be obtained by adding it and sintering it after molding, leading to the completion of the present invention.

That is, in the present invention, flaky graphite having a particle diameter of 1 to 100 μm, a thickness of 1 μm or less, and an aspect ratio of 10 to 5,000 is used as the conductivity imparting material. The weight part is a matrix made of ceramic, glass, or a mixture of glass and ceramic.
00 parts by weight, or having an insulating layer made of the matrix material integrated with the conductive heating element on the surface of the conductive heating element. It is a conductive heating element.

Examples of ceramics constituting the matrix of the conductive heating element of the present invention include oxide ceramics such as alumina, silica alumina, cordierite, mullite, petalite, titania, and zirconia, silicon nitride, silicon carbide, etc. Examples include non-oxide ceramics and mixtures thereof, and an appropriate ceramic can be selected from among these ceramics depending on the properties and functions desired for the product, such as radiation characteristics and thermal shock resistance. Examples of glass include borosilicate glass, aluminosilicate glass, silicate glass such as soda lime glass, and oxynitride glass. A glass having a composition that softens at a temperature of approximately 50 to 500° C. and does not cause shape deformation may be selected and used. In order to prevent destruction due to thermal shock, these raw materials preferably have a coefficient of thermal expansion of approximately 40×10 −7 (1/° C.) or less.

Both ceramic and glass can be used alone, but adding glass to ceramic can lower the sintering temperature, which is beneficial in terms of the manufacturing process. On the other hand, since the addition of the glass component lowers the heat resistance temperature of the resulting conductive heating element, the proportion of glass to be added may be appropriately determined in consideration of the purpose of use and manufacturing conditions.

In the conductive heating element of the present invention, the flaky graphite added as the conductivity imparting material has a particle size of 1 to 1
00μm, thickness is 1μm or less, aspect ratio is 10-5
,000, which has a very special shape. More preferably, the particle size is 1 to 50 μm, the thickness is 1 μm or less, and the aspect ratio is 200 to 3,000, and the average particle size is about 10 to 30 μm. Here, if the particle size of the flaky graphite powder is larger than 100 μm, it will be difficult to uniformly disperse the flaky graphite powder in the raw material matrix, and if it is smaller than 1 μm, it will be difficult to form a conductive path. Alternatively, in order to form conductive paths, the amount of flaky graphite powder used must be increased, making it difficult to obtain a dense sintered body. Such flaky graphite can be produced, for example, by dispersing expanded graphite obtained by expanding natural graphite through acid treatment, heat treatment, etc. in an aqueous solvent and crushing it by applying ultrasonic waves. (Japanese Unexamined Patent Publication No. 2-153810, etc.). This flaky graphite is made by powdering raw material graphite such as natural graphite in a state where the layers are exfoliated while retaining its crystalline form, and exhibits the special shape and high crystallinity described above. It is. Because of this high crystallinity, the flaky graphite powder used in the present invention has the characteristic that it is difficult to be oxidized even in an oxidizing atmosphere. For example, flaky graphite obtained from natural graphite produced in China is a highly crystalline flaky graphite with developed hexagonal graphite, a lattice constant of 0.67 nm, a crystallite thickness of 70 nm, and a crystal spread of about 100 nm. It is. There are various graphite powders on the market, for example,
Particle size 1-30 μm (95% below 15 μm), 2-70
μm (44μm or less 95%), 2-100μm (75μm or less)
It has a block-like shape with a thickness that is approximately equal to or approximately 1/2 the size of the particle size. When using block-shaped graphite powder like this, it is difficult to form a conductive path with a small amount of use, and if the amount used is increased to form a conductive path, a dense sintered body can be obtained. There are problems such as difficulty in being exposed. On the other hand, the flaky graphite powder used in the present invention is
Since the thickness is very thin, adjacent graphite powders tend to overlap, and a conductive path can be formed with a small amount of usage.

The conductive heating element of the present invention can be manufactured, for example, by the following method. First, 100 parts by weight of a ceramic powder, glass powder, or a mixture of ceramic and glass (hereinafter collectively referred to as raw material matrix powder) that has been crushed in advance and whose particle size has been adjusted is added to
Adding 0.5 to 10 parts by weight, preferably 1 to 5 parts by weight of flaky graphite powder having the above shape as a conductive material,
Mix using a conventional powder mixer such as a kneader, Henschel mixer, double cone type or V type blender. Here, the flaky graphite powder is somewhat broken and shortened in the length direction during the mixing process, but most of it is 1 to 1
The thickness is within 0.00 μm, and there is almost no breakage in the thickness direction.

The raw material matrix powder to be used preferably has a particle size of about 100 μm or less in view of ease of mixing with the flaky graphite powder, but is not particularly limited, and depends on the mixing and molding methods used and the characteristics of the heating element desired. Depending on the particle size, it is sufficient to use one with an appropriate particle size. Added amount of flaky graphite is 0
．． If it is less than 5 parts by weight, the conductive path becomes discontinuous and the effect of imparting conductivity is small, and if it exceeds 10 parts by weight, the contact points between the raw material matrix powder particles are reduced, etc.
This is not preferable because the compactness of the heating element is impaired.

The flaky graphite powder used as a raw material for the conductive heating element of the present invention has a flaky shape with a high aspect ratio, so when mixed with the raw material matrix powder, only the graphite powder may separate. , uneven distribution, etc., and can be uniformly dispersed, so that a uniformly dispersed state is maintained even in molded bodies and sintered bodies. If necessary, water or an organic or inorganic binder may be added as a forming aid during mixing.

Next, a mixture of raw material matrix powder and flaky graphite powder was produced by a powder pressure molding method such as uniaxial pressure molding or cold isostatic compression molding, a doctor blade method, a calendar roll method, etc. It is molded into a desired shape and size using a molding method such as a method in which green sheets are laminated and molded, a slip cast molding method, an extrusion molding method, or the like.

For example, when using a powder pressure molding method, the molding pressure is 2.9 to 98.1 MPa, particularly 9.8 to 4 MPa.
Approximately 9.0 MPa is preferable. In addition, when using a method of laminating and forming green sheets, a mixture of flaky graphite powder and raw material matrix powder is kneaded with an organic vehicle, and the raw material flaky graphite powder is mixed using a doctor blade method, a calendar roll method, etc. A green sheet uniformly dispersed in a raw material matrix powder is prepared as a heat generating layer of a conductive heat generating element, and a plurality of green sheets are laminated according to the product specifications and formed by laminating by heat compression bonding or the like.

[0016] Although the flaky graphite powder may be broken to some extent during the molding process due to the forming method, even if it is broken at this stage, the conductive path constructed by the flaky graphite will not become discontinuous, so it is practically no problem. Not. This also applies to the sintering process described below.

After molding, the shape and dimensions are adjusted by cutting, processing, etc. as necessary, and then degreased at a temperature of 400°C or less, and then sintered at a temperature of 450 to 1,500°C. The degreasing temperature and sintering conditions may be set appropriately depending on the binder used, the type of raw material matrix powder, the shape of the molded body, etc. For example, when the raw material matrix powder is a silica-alumina ceramic, the 0 at temperature in °C
．． 5 to 5 hours, if there is a lot of glass component, 450 to 90
The heating time may be 10 minutes to 1 hour at 0°C. In addition, it is preferable to perform sintering in an inert gas atmosphere, but if the amount of glass components in the raw material matrix exceeds 50% by weight, sintering is performed at 900°C.
Sintering in air is possible because there is no risk of oxidation of mixed flaky graphite. The density of the molded body after sintering (conductive heating element) is 1.85 to 2.
．． Approximately 20 g/cm3 is sufficient.

The conductive heating element is usually used with an insulating layer formed on its surface in order to improve electrical insulation and moisture resistance. This insulating layer can be formed on the surface of the conductive heating element obtained by sintering by a method such as powder baking or low melting point glass baking. At the time of sintering, the heating element body and the insulating layer are tightly integrated by covering the surface with a layer consisting of raw material matrix powder and organic vehicle component without adding flaky graphite, which is a conductive material, and sintering. A conductive heating element with an insulating layer can be obtained (hereinafter, this is also simply referred to as a conductive heating element). Furthermore, this method has the effect of preventing oxidation of flaky graphite during sintering.

The shape of the insulating layer can be determined, for example, by kneading a mixture of flaky graphite powder and raw material matrix powder with an organic vehicle, and then uniformly distributing the flaky graphite powder into the raw material matrix powder by a doctor blade method, a calendar roll method, etc. A molded body made by laminating multiple green sheets for the heat generating layer dispersed in the green sheet according to the product specifications is used as a raw material matrix powder that does not contain flaky graphite powder, which is a conductivity-imparting material, made by the same method. and an insulating layer green sheet made of an organic vehicle component, and then laminated by heat and pressure bonding, and then an insulating layer made of a raw material matrix powder and an organic vehicle is applied to the ends and sides of the molded body in areas that are not used as electrode terminal attachment parts. This can be done by forming a paste layer using a method such as screen printing and then sintering it. In addition, a slurry of raw material matrix powder without the addition of flaky graphite, which is a conductivity-imparting material whose viscosity has been adjusted, is prepared, and this slurry is sprayed onto a conductive heating element obtained by pre-sintering or a molded object before sintering. Using a method such as dipping the conductive heating element or the molded article before sintering into the slurry, the slurry is applied to the conductive heating element or the molded article before sintering to form an insulating layer, and then sintered after drying. It can also be carried out using a method or the like. The thickness of the insulating layer can be adjusted depending on the voltage used when used as a heater, but for example, in the case of a voltage up to about 100 V, an insulating layer thickness of about 0.2 mm is sufficient.

[0020] In the conductive heating element of the present invention, since flaky graphite, which is a conductive material, is uniformly dispersed, the entire molded body has uniform conductivity and has a volume resistivity of 10-1 to 103.
The volume resistivity is in the range of Ω·cm, and the volume resistivity can be arbitrarily adjusted within this range by changing the amount of flaky graphite added. When flaky graphite powder is used as the conductivity imparting material, since the graphite aspect ratio is large, a large number of current flow paths can be formed despite the small volume occupancy.
Easily exhibits conductivity. Therefore, high conductivity can be obtained with a small amount of addition, so there is an advantage that the characteristics of the raw material matrix are not impaired.

[0021] Furthermore, since the conductive heating element having the insulating layer formed from the raw material matrix has the same composition of the raw material matrix powder of the heating element base material and the component composition of the insulating layer, when used as a heater, the heating element The main body and the insulating layer do not separate due to differences in thermal expansion coefficients, and can be easily used as a heater by attaching electrodes by baking conductive paste or metal spraying. Unlike the heater manufacturing method, there is no need for the step of providing an insulating layer such as alumina around the heating element, and the method not only simplifies the heater manufacturing method, but also meets the demands for miniaturization and weight reduction of the heater.

[0022] This heating element can be easily energized by applying a voltage, and the entire molded body generates heat uniformly. Moreover, the shape, dimensions and volume resistivity can be selected arbitrarily, and
By adjusting the amount of electricity, it is possible to arbitrarily control the heat generation temperature. That is, several V~100
With a voltage load of about V, heat can be generated from room temperature to about 600° C. within 10 minutes from the start of electricity supply, and a stable heat generation state can be maintained. Especially 10-1~10Ω・cm
Those with low volume resistance can generate heat at a low voltage of a few V to 40 V, and can be used as a small, low-power heating element. Also, because of the low voltage, there is no risk of electric shock. It is small and has an advantage in terms of safety. This conductive heating element can be easily made into a heater element by attaching electrodes to it by baking a conductive paste, metal spraying, or the like.

The conductive heating element of the present invention is useful as a heating member for heating, cooking, drying, fuel vaporizers, and the like.

As mentioned above, the conductive heating element of the present invention is characterized by using a specific flaky graphite powder. It is not necessarily clear to what extent this is maintained. However, it is possible to know the excellent conductive properties achieved for the first time by using the flaky graphite powder by measuring the relationship with the graphite content.

[0025]

[Examples] The present invention will be explained in more detail with reference to Examples below.

Examples 1 to 5 and Comparative Examples 1 to 2 use ceramic matrix as the raw material matrix powder.
Examples 6 to 16 and Comparative Examples 3 to 7 show examples using glass or a mixture matrix of glass and ceramic.

The flaky graphite powder used in Examples 1 to 16 and Comparative Examples 3 to 7 was produced in the following manner.

Natural flaky graphite powder produced in China was treated with a mixed acid of sulfuric acid and nitric acid (sulfuric acid: nitric acid = 11:1 by weight) to form a graphite intercalation compound, washed with water, dried, and then treated in a nitrogen gas atmosphere. The mixture was rapidly heated to 800°C and maintained for 30 minutes to obtain expanded graphite powder. Next, this expanded graphite powder was dispersed in water and pulverized by applying ultrasonic waves at a frequency of 50 Hz to obtain flaky graphite powder.

(Example 1) Particle size 1 was added to 100 g of Petalite N-10 (manufactured by Nishimura Pottery) whose particle size was adjusted to 250 μm or less.
0 to 50 μm (average particle size 20 μm), thickness approximately 0.1 μm
, flaky graphite powder with an aspect ratio of 100 to 500 2.5
g was added thereto, and the mixture was stirred and mixed in a kneader for 5 minutes. 50g of the obtained mixture was placed in a 48mmφ cylindrical mold for 4.9
Pressure molding was performed at a pressure of MPa to obtain a preform. This preform was heated in an electric furnace under a nitrogen atmosphere from room temperature to
The temperature is raised to 300℃ at a rate of 3℃ per minute, and then
After firing at 00℃ for 1 hour, 500℃ was fired at a rate of 3℃ per minute.
The temperature dropped to ℃. The conductive heating element obtained by further cooling to room temperature had a density of 1.9 g/cm 3 and was sufficiently sintered. A rectangular parallelepiped sample measuring 25 x 38 x 4.5 mm was cut out from this heating element, and a sintered Ag paste was applied to the longitudinal end face and dried at 150°C to form an electrode extraction surface. The volume resistivity of this sample measured by the four-terminal method was 1.3 Ω·cm. In addition, when the same sample was loaded with a voltage of 12V and 18V at room temperature and a current of 2.7A and 4.6A was applied, the entire sample was completely removed in about 5 minutes and about 2 minutes. The temperature rose to approximately 400°C and 500°C, and by continuing to supply electricity, the temperature could be maintained at the same temperature in a stable state.

(Example 2) A conductive heating element was produced in the same manner as in Example 1, except that the amount of flaky graphite powder added was changed and the molding pressure was 9.8 MPa. The volume resistivity of the heating element obtained was as follows.

Addition amount (g) 1.3 1.
5 1.8 2.0 2.3 Volume resistivity (Ω・c
m) 18 7.4 3.0 1.7
0.9 (Example 3) Mixed raw material 3 prepared under the same conditions as Example 1
00g was filled into a 130mm square prismatic mold, and 9.8
Compression molded at a pressure of MPa, 130 x 130 x 12 mm
A preformed body was obtained. This molded body was fired under the same conditions as in Example 1 to obtain a conductive heating element. The density of this heating element is 2.2g/cm3, and the volume resistivity is 0.8Ω・
It was cm. This was cut and polished to a size of 113 x 120 x
When a 10 mm sample was used and a voltage of 13 V was applied with a terminal spacing of 113 mm and a current of about 10 A was applied, the temperature rose to 220° C. in about 10 minutes and was able to maintain a stable state. In addition, when the surface temperature of this sample was measured in 9 equally divided areas, it was found that all 9 areas were approximately 220 degrees Celsius.
, indicating a uniform temperature distribution.

(Example 4) On the surface of the conductive heating element produced under the same conditions as in Example 3, a frit prepared with 60 g of frit (trade name 3127, manufactured by Nippon Ferro Co., Ltd.) adjusted to 149 μm or less and 40 g of water was applied. After spraying the chemical and drying, baking was performed by heating at 1,100° C. in a nitrogen atmosphere. Although the surface of the obtained surface-coated conductive heating element was insulated, the volume resistivity and current conduction characteristics of the heating element as a whole were exactly the same as those of the sample of Example 3.

This sample was divided into approximately 9 equal parts, 39×39×
Divided into 10 mm pieces, baked with Ag conductive paste and attached terminals to each piece (distance between terminals: 39 mm), and measured the volume ratio using the two-terminal method. Both were 0.8 Ω.
・It was cm. Furthermore, when a current of 10 A was applied to each sample at a voltage of 7 V, each sample lost 410 volts in about 5 minutes.
℃ and could be stably maintained at that temperature for more than 30 minutes.

(Example 5) The same procedure as in Example 1 was conducted except that Cordierite N-53 (manufactured by Nishimura Ceramics) was used instead of Petalite N-10 and the firing temperature was changed to 1,100°C. A sex heating element was obtained. The density of this heating element is 1.7
g/cm3, and the volume resistivity was 2.9Ω·cm. In addition, the results of conducting a current test using the same method as in Example 1 showed that the current amount was 1.2A under a voltage load of 12V, and the heat generation temperature was 2.
The temperature was 25°C.

(Comparative Example 1) Commercially available graphite powder (particle size 1 to 5 μm, thickness 0.2 to 0.6 μm) was used instead of flaky graphite powder.
A sintered body was obtained by operating under the same conditions as in Example 3, except that a sintered body with an aspect ratio of 2 to 8) was used. 120×120×10m
The volume resistivity of the sample of m is as large as 1.2×103 Ω・cm, and the volume resistivity of the sample divided into 9 pieces of 39×39×10 mm is 0.7×103 to 1.5×103 Ω・
It varied between cm.

(Comparative Example 2) The amount of graphite powder used was 3.5g.
Two sintered bodies were produced in the same manner as in Comparative Example 1 except for the following. The volume resistivity of each is 5.2 and 6.7 respectively
Ω·cm, and it can be seen that even if they are manufactured under the same conditions, there are variations in their properties.

(Examples 6 to 16) As raw materials, softening point 8
00℃, thermal expansion coefficient of 30 x 10-7/℃, borosilicate glass powder whose particle size is adjusted to an average particle size of 3 μm, flaky graphite powder whose particle size is adjusted to an average particle size of 20 μm (particle size is 1 to 100 μm, thickness of 1 μm or less, aspect ratio of 10 to 5,000, average particle size of 20 μm), and alumina, mullite, and cordierite powder each adjusted to an average particle size of 2 μm as ceramic powder. In addition, an insulating paste was used by adding an organic vehicle in which ethyl cellulose as a binder was dissolved in α-terpineol to the raw material matrix powder and kneading the mixture using a three-roll mill to obtain an appropriate viscosity.

[0038] To the raw material matrix powder, flaky graphite powder was added in proportions as shown in Table 1 to form a homogeneous mixture. To 100 parts by weight of this mixture, 16 parts by weight of acrylic resin, 3 parts by weight of dibutyl phthalate, 22 parts by weight of toluene, and 48 parts by weight of ethanol were added using a polyethylene pot mill equipped with alumina balls. A homogeneous slurry was prepared by mixing for 24 hours.

Next, a green sheet with a thickness of 0.3 mm was produced from the slurry using a doctor blade method, and was used as a sheet for a heat generating layer. Further, in the same manner, a green sheet containing only the raw material matrix powder was produced and used as a sheet for an insulating layer.

Next, as shown in the example of FIG. 1, three sheets 1 for the heat generating layer are stacked and one sheet 2 for the insulating layer is stacked on top and bottom of the sheets 2, respectively.
A molded product with a thickness of 0 mm and an insulating paste layer 3 formed on the side surface of the molded product was degreased and degreased as shown in FIG. 2 in an air atmosphere.
Degreasing and sintering were performed using an example firing temperature pattern.

An electrode extraction surface was formed on the end face of the obtained ceramic heating element to serve as a heater, and a voltage of 50 V was applied to generate electricity. Table 1 shows the results of measuring the electrical resistance value at this time and the temperature of the surface of the heating element during energization and heating using a non-contact radiation thermometer.

[0042] Furthermore, the properties of a heat generating element produced in the same manner using only the sheet for the heat generating layer were almost the same as those of the heat generating element on which an insulating layer was formed.

[0043] Also, an electrode extraction surface is formed on the end face of the conductive heating element on which an insulating layer has been formed, and electricity is applied between both terminals of the heater. When a predetermined temperature is reached and the temperature is stabilized, an insulation resistance test is carried out. As a result of measurement, insulation resistance was 300℃
The resistance is 800MΩ or more at temperature, and 3MΩ or more at 500°C, and has sufficient insulation properties.

[0044]

[Table 1] (Comparative Examples 3 to 6) Using the same raw materials as Examples 6 to 16,
The flaky graphite powder was added in portions at the compounding ratio shown in Table 1, and the subsequent operations were the same as in Examples 6 to 16 to produce a molded body, and the properties were measured. The results are shown in Table 1. Shown below.

In Examples 6 to 16, when a voltage of 50 V is applied, the temperature reaches a constant temperature in about 30 seconds, and exhibits sufficient characteristics as a heater, whereas in Comparative Examples 3 and 5, the conductive Because the content of flaky graphite powder, which is a conductive substance, is too low in content, electricity cannot be applied.On the other hand, in Comparative Examples 4 and 6, the content of flaky graphite powder, which is a conductive substance, is too high, resulting in a dense sintered body. was not obtained.

[0046]

[Effect of the invention] The conductive heating element of the present invention has high crystallinity,
The flaky graphite powder, which has a large effect of imparting conductivity, is uniformly dispersed in the raw material matrix powder, so it has high conductivity, has a fast response to electricity, has excellent temperature rise characteristics, and generates heat evenly with low voltage application. , is a direct current type conductive heating element with excellent heat resistance, and can be made into a desired shape, so it can meet the demands for smaller and lighter heaters, and can be used in various electric heating devices. It is a material useful as a heater element such as.

Furthermore, by forming an insulating layer on the conductive heating element, in addition to providing electrical insulation, oxidation of the flaky graphite powder can be prevented and moisture resistance is improved, which has the effect of extending the life of the heater. Since the composition of the raw material matrix powder, which is the base material of the heating element body, and the composition of the insulating layer are the same, when used as a heater, the heating element body and the insulation layer may separate due to the difference in coefficient of thermal expansion. Moreover, the heater can be easily manufactured by attaching electrodes by baking a conductive paste or metal spraying, which simplifies the manufacturing method of the heater.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing an example of laminating green sheets for a heat generating layer and an insulating layer and forming an insulating paste layer when manufacturing a heat generating element on which an insulating layer is formed.

FIG. 2 is a graph showing an example of a temperature pattern for degreasing and sintering when a heating element is manufactured by producing green sheets, laminating and sintering them.

[Explanation of symbols]

1 Sheet for heat generating layer 2 Insulating layer sheet 3 Insulating paste layer

Claims (2)

[Claims] [Claim 1] The conductivity-imparting material has a particle size of 1 to 1.
100μm, thickness 1μm or less, aspect ratio 10~
5,000 flake graphite is used, and 0.5 to 10 parts by weight of the graphite is uniformly dispersed in 100 parts by weight of a matrix made of ceramic, glass, or a mixture of glass and ceramic. Conductive heating element. 2. A conductive heating element, comprising an insulating layer made of the matrix material and integrated with the conductive heating element, on a surface of the conductive heating element according to claim 1.