EP0469628A1 - Elément de chauffage à conduction électrique - Google Patents

Elément de chauffage à conduction électrique Download PDF

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Publication number
EP0469628A1
EP0469628A1 EP91113044A EP91113044A EP0469628A1 EP 0469628 A1 EP0469628 A1 EP 0469628A1 EP 91113044 A EP91113044 A EP 91113044A EP 91113044 A EP91113044 A EP 91113044A EP 0469628 A1 EP0469628 A1 EP 0469628A1
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Prior art keywords
heating element
graphite particles
electrically
matrix
fine graphite
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German (de)
English (en)
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Kouji c/o Mitsui Mining Co. Ltd. Sakawaki
Yukinobu c/o Mitsui Mining Co. Ltd. Watanabe
Yutaka c/o Mitsui Mining Co. Ltd. Yamashita
Keiichiro c/o Mitsui Mining Co. Ltd. Koba
Hirokatsu c/o Mitsui Mining Co. Ltd. Kanda
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Mitsui Mining Co Ltd
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Mitsui Mining Co Ltd
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Publication of EP0469628A1 publication Critical patent/EP0469628A1/fr
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B3/00—Ohmic-resistance heating
    • H05B3/10—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
    • H05B3/12—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material
    • H05B3/14—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material the material being non-metallic
    • H05B3/141—Conductive ceramics, e.g. metal oxides, metal carbides, barium titanate, ferrites, zirconia, vitrous compounds

Definitions

  • the present invention relates to an electrically-conductive heating element suitable for use in a ceramic heater.
  • the heating element can produce heat by direct energization, and is usable in a wide range of industrial and civil fields.
  • Ceramic heaters employed these days are of the type that electricity is fed to a metallic resistance heating element embedded in a matrix made of a ceramic to obtain thermal energy by resistance heating.
  • Such ceramic heaters are known to include those having a metallic resistance heating member of tungsten or molybdenum embedded in a matrix composed principally of alumina, those containing a metallic resistance heating element such as palladium or platinum embedded in a matrix composed principally of cordierite, those having a metallic resistance heating element made of copper and embedded in a matrix composed principally of a borosilicate glass and alumina (Japanese Patent Application No. 20678/1987), etc.
  • a certain measure is taken to achieve a uniform heating temperature distribution, for example, by forming a heating resistance element, which is in the form of a wire, strip or the like, into a wavy, spiral or tortuous shape and then arranging it uniformly. Heat is however produced intensively near the heating resistance element only, so that they are still insufficient to provide a uniform heating temperature distribution.
  • These heaters also have unsolved problems such as the fact that their heating response is slow because heat must be conducted through a thick matrix and, in addition, high- temperature firing and adjustment of the firing atmosphere are needed upon production of ceramic heaters. It is therefore recently attempted to obtain a heating element, which permits production of uniform heat therethroughout, by adding an electrically-conductive material such as carbon to a heat-resistant ceramic.
  • a carbon material such as graphite powder is generally used as an electrically-conductive material.
  • Graphite powder which has conventionally been employed as an electrically-conductive material, can be obtained by mechanically comminuting natural or synthetic graphite or by subjecting carbon black to graphitization. It is, however, difficult to uniformly disperse such a carbon material in a raw ceramic batch, resulting in serious problems such that substantial variations may occur in electrical conductivity among materials to be obtained and the electrical conductivity may not be uniform throughout the product to be formed.
  • An object of the present invention is to overcome the above-described problems, and hence to provide a heating element - which features the possibility of production of heat by direct energization, quick response to energization, excellent thermal shock resistance and production of uniform heat and requires only an easy production process - and an electrically-conductive heating element having an electrical insulating layer integrated with the heating element and suited for use as a ceramic heater.
  • a formed ceramic body having uniform electrical conductivity can be obtained by adding, as an electrically-conductive material, foliated fine graphite particles having a high aspect ratio to a ceramic, an inherent electrical insulator, or the like, and, subsequent to formation of the resultant mass into a green body, sintering the green body, leading to the completion of the present invention.
  • the present invention therefore provides an electrically-conductive heating element, which comprises:
  • the foliated fine graphite particles which have high crystallinity and are highly effective in imparting electrical conductivity are dispersed uniformly in the matrix.
  • the electrically-conductive heating element according to the present invention is therefore an electrically-conducting heating element of the direct energization type, which has high electrical conductivity, can quickly respond to energization and is excellent in the temperature-raising characteristic, can produce uniform heat upon application of a low voltage, and has excellent heat resistance. It can be formed into an electrically-conductive heating element of a desired shape. It is therefore possible to meet the demands for heaters, such as a reduction in both dimensions and weight.
  • the electrically-conductive heating element is useful as a heater element for various electrical heaters and the like.
  • the optional formation of the insulating layer on the electrically-conductive heating element can provide electrical insulation and, moreover, can prevent oxidation of the foliated fine graphite particles and can improve the moisture resistance.
  • the insulating layer is therefore effective in prolonging the service life of the electrically-conductive heating element as a heater. Since the insulating layer uses the same batch as the matrix, which is a base member of a main body of the heating element, the main body of the heating element and the insulating layer are not separated due to any difference in thermal expansion coefficient when used as a heater.
  • the electrically-conductive heating element can be easily formed into a heater by mounting electrodes, for example, by baking an electrically-conductive paste or conducting metallization. It is therefore possible to provide a simplified process for the production of a heater.
  • Examples of the ceramic which makes up the matrix of the electrically-conductive heating element according to the present invention include oxide ceramics such as alumina, silica-alumina, cordierite, mullite, petalite, titania and zirconia; non-oxide ceramics such as silicon nitride and silicon carbide; and mixtures thereof. Depending on properties and performance desired for each product such as radiation property and thermal shock resistance, an appropriate ceramic can be selected from these ceramics.
  • examples of the glass include silicate glasses such as borosilicate glass, aluminosilicate glass and soda line glass; and oxynitride glasses.
  • the addition of a glass to a ceramic is advantageous in view of the production process because their combined use makes it possible to lower the sintering temperature.
  • the addition of such a glass component results in an electrically-conductive heating element having a lower withstandable maximum temperature. It is therefore necessary to suitably determine the proportion of a glass, which is to be added, in view of the application purpose and production conditions.
  • the foliated fine graphite particles added as an electrical-conductivity-imparting material are graphite particles having the very special shape that they have a particle size of 1-100 ⁇ m, a thickness not greater than 1 ⁇ m and an aspect ratio of 10-5,000. More preferably, the particle size, thickness and aspect ratio is 1-50 ⁇ m, not greater than 1 ⁇ m and 200-3,000, respectively, and the average particle size ranges from 10 ⁇ m to 30 ⁇ m or so. If the particle size of the foliated fine graphite particles becomes greater than 100 ⁇ m, it will be difficult to uniformly disperse the foliated fine graphite particles in the matrix-forming raw material powder.
  • Such foliated fine graphite particles can be prepared, for example, by dispersing expanded graphite particles - which have been obtained by causing natural graphite to expand in accordance with acid treatment, heat treatment or the like - in an aqueous solvent and then applying ultrasonic waves to the expanded graphite particles to break them up (see Japanese Patent Laid-Open No. 153810/1990).
  • foliated fine graphite particles have been formed into powder in such a state as being separated between layers while maintaining the crystalline form of the starting graphite such as natural graphite, and have the special shape and high crystallinity as described above.
  • foliated fine graphite particles useful in the practice of the present invention have the characteristic property that they are resistant to oxidation even in an oxidizing atmosphere.
  • foliated fine graphite particles obtained from natural graphite mined in China have high crystallinity of developed hexagonal graphite such that the lattice constant is about 0.67 nm, the crystallite thickness is approximately 70 nm and the crystallite size is about 100 nm.
  • graphite particles are available on the market. They can be classified in particle size, for example, to 1-30 ⁇ m (15 ⁇ m and smaller: 95%), 2-70 ⁇ m (44 / .Lm and smaller: 95%) and 2-100 ⁇ m (75 ⁇ m and smaller: 95%). They have a thickness substantially equal to or about a half of the particle size, so that they look as if they have a block-like shape. When graphite particles of such a block-like shape are used, it is difficult to form electrically-conductive paths by using them in a small amount. Use of such graphite particles in an increased amount to form electrically-conductive paths, however, leads to problems such that a dense, sintered body can hardly be obtained. On the other hand, foliated fine graphite particles usable in the present invention have a very thin thickness so that adjacent graphite particles tend to overlap, thereby making it possible to form electrically-conductive paths even at a low concentration.
  • the electrically-conductive heating element according to the present invention can be produced, for example, as will be described next.
  • a glass powder or a ceramic-glass mixture which will hereinafter be collectively called a "matrix-forming raw material powder" which had been ground and sifted for particle size adjustment in advance
  • foliated fine graphite particles having the above-described shape were added as an electrically-conductive material in an amount of 0.5-10 parts by weight, preferably 1-5 parts by weight. They were then mixed using a conventional powder mixer such as a kneader, a Henschel mixer, or a double-cone or twin-cylinder blender.
  • the foliated fine graphite particles are somewhat damaged and shortened in the lengthwise direction in the course of the mixing, but most of the foliated fine graphite particles remain within the range of 1-100 /.Lm. In the thicknesswise direction, they are not damaged practically.
  • the matrix-forming raw material powder preferably has a particle size not greater than about 100 ⁇ m from the standpoint of mixing readiness with the foliated fine graphite particles, no particular limitation is imposed on the particle size of the matrix-forming raw material powder. It is only necessary to use a matrix-forming raw material powder of a suitable particle size in accordance with the mixing and forming methods to be used and properties sought for the heating element to be produced. If foliated fine graphite particles are added in an amount smaller than 0.5 part by weight, they cannot exhibit sufficient electrical-conductivity-imparting effect because of discontinuation of electrically-conductive paths. On the other hand, amounts greater than 10 parts by weight impair the density of a heating element to be formed because of a reduction in the number of points of contact with the particles of the matrix-forming raw material powder.
  • the foliated fine graphite powder employed as a raw material for the electrically-conductive heating element according to the present invention are in a foliated form having a high aspect ratio.
  • the foliated fine graphite particles When mixed with the matrix-forming raw material powder, the foliated fine graphite particles are free from such a phenomenon that the graphite particles alone would be separated or would be concentrated locally.
  • the foliated fine graphite particles therefore permit uniform dispersion so that a uniform, distributed sate can be maintained not only in the green body but also in the sintered body. Further, water or an organic or inorganic binder may also be added, as needed, as a forming aid upon mixing.
  • the resultant mixture of the matrix-forming raw material powder and the foliated fine graphite particles are next formed into desired shape and dimensions by a forming method, for example, by a powder pressure forming method such as uniaxial pressure forming or cold isostatic pressing, by a forming method in which green sheets formed by the doctor blade method or calender roll method are stacked together, by slip casting, or by extrusion.
  • a powder pressure forming method such as uniaxial pressure forming or cold isostatic pressing
  • a forming method in which green sheets formed by the doctor blade method or calender roll method are stacked together by slip casting, or by extrusion.
  • the forming pressure can be preferably 2.9-98.1 MPa, especially 9.8-49.0 MPa or so.
  • green sheets are stacked together to conduct the forming, the mixture of the foliated fine graphite particles and the matrix-forming raw material powder are kneaded with an organic vehicle.
  • the above-prepared mass is then formed by the doctor blade method or the calender roll method into a green sheet in which the foliated fine graphite particles as one of the raw materials are uniformly dispersed in the matrix-forming raw material powder.
  • a plurality of such green sheets, the number of said green sheets depending on the specification of each product to be fabricated, are stacked together and pressure-bonded under heat to laminate them.
  • the foliated fine graphite particles are somewhat damaged or broken in the course of the formation. Even when the foliated fine graphite particles are broken in this stage, electrically-conductive paths to be formed will not be in a disconnected form. Practically, no problem therefore arises. This applies equally to a sintering step which will be described next.
  • the preformed green body is adjusted in shape and dimensions by cutting, grinding or the like as needed. Subsequent to degreasing at a temperature of 400 C or lower, the preformed green body is sintered at a temperature of 450- 1,500 ⁇ C.
  • the degreasing temperature and sintering conditions can be set suitably in accordance with the kinds of the binder and matrix-forming raw material powder used, the shape of the preformed green body, etc.
  • the matrix-forming raw material powder is a silica-alumina ceramic for example, it is necessary to set the sintering conditions at 1,100-1500 C for 0.5-5 hours and, where the glass component is contained in a large proportion, at 450-900 C for 10 minutes to 1 hour.
  • sintering in air is feasible where the proportion of the glass component in the matrix-forming raw material powder becomes 50 wt.% or higher because sintering at 900 C or lower is feasible so that there is no potential danger of oxidation of the mixed, foliated fine graphite particles.
  • the density of the preformed green body after the sintering namely, the density of the electrically-conductive heating element may be 1.85-2.20 g/cm 3 or so.
  • the electrically-conductive heating element is generally used in a form with an insulating layer formed on a surface thereof in order to improve its electrical insulation, moisture resistance, etc.
  • This insulating layer can be formed, for example, by baking a glaze or a low-melting glass on the surface of the electrically-conductive heating element obtained by the sintering.
  • the electrically-conductive heating element of the present invention can be obtained more efficiently in the form of an insulated, electrically-conductive heating element, in which a main body of the heating element and an insulating layer are firmly united together into an integral body, by covering a surface of the preformed green body with a layer composed of an organic vehicle component and the matrix-forming raw material powder - which has not been added with the foliated fine graphite powder as a conductivity-imparting material - before the sintering of the preformed green body and then sintering the thus-covered green body.
  • an insulated, electrically-conductive heating element will also be referred to simply as an "electrically-conductive heating element". This process is also effective in preventing oxidation of the foliated fine graphite particles during sintering.
  • the insulating layer can also be formed in the following manner. For example, a mixture of the foliated fine graphite particles and the matrix-forming raw material powder is kneaded with an organic vehicle. The resulting mass is formed by the doctor blade method, the calender roll method or the like into a heating-layer-forming green sheet in which the foliated fine graphite particles are uniformly distributed in the matrix-forming raw material powder. A plurality of such green sheets, the number of said green sheets being dependent on the specification of a product to be formed, are stacked together to provide a preformed green body.
  • the preformed green body is then sandwiched between insulating-layer-forming green sheets which have been prepared in a similar manner and which are composed of an organic vehicle component and the matrix-forming raw material powder not added with the foliated fine graphite powder as a conductivity-imparting material.
  • the resultant assembly is pressure-bonded under heat, whereby the preformed green body and the green sheets are laminated together.
  • Insulating paste layers composed of the matrix-forming raw material power and the organic vehicle are formed by a method such as screen printing on end and side surfaces of the preformed green body at areas where the surfaces are not used as electrode terminal attachment portions.
  • the preformed green body with the insulating paste layers is then sintered.
  • a slurry of the matrix-forming raw material powder which has not been added with the foliated fine graphite particles as a conductivity-imparting material is prepared with an adjusted viscosity.
  • the slurry is coated on an electrically-conductive heating element, which has been obtained in advance by sintering, or an unsintered green body, for example, by spraying the slurry onto the electrically-conductive heating element or the unsintered green body or by dipping the electrically-conductive heating element or the unsintered green body in the slurry, so that an insulating layer is formed.
  • the insulating layer is dried and then sintered.
  • the unsintered green body is also sintered concurrently with the sintering of the insulating layer.
  • the thickness of the insulating layer varies depending on the voltage applied when the heating element is used as a heater. For example, for voltages up to about 100 V, 0.2 mm or so is sufficient as the thickness of the insulating layer.
  • the formed body has uniform conductivity therethroughout and its volume resistivity is in the range of from 10- 1 ⁇ cm to 10 3 ⁇ cm.
  • the volume resistivity can be adjusted as desired within the above range.
  • Use of foliated fine graphite particles as an electrical-conductivity-imparting material permits the formation of many current flow paths despite the small volume occupied by them and hence facilitates to develop electrical conductivity, because the foliated fine graphite particles have a high aspect ratio. High conductivity can therefore be obtained by adding the foliated fine graphite particles in a small amount, thereby bringing about the advantage that the characteristic features of the matrix-forming raw material powder are not impaired.
  • the composition of the insulating layer is the same as that of the matrix-forming raw material powder employed as a base material for the heating element. While employed as a heater, the main body of the heating element and the insulating layer therefore remain free from separation which would take place if there were any substantial difference in thermal expansion coefficient between the main body of the heating element and the insulating layer. Further, the electrically-conductive heating element with the insulating layer formed thereon can be used easily as a heater by mounting electrodes thereon, for example, by baking an electrically conductive paste or by metallization.
  • the present invention does not require the step that an insulating layer made, for example, of alumina is provided around a heating element.
  • the present invention therefore makes it possible not only to simplify the production process for heaters but also to meet the demand for reductions in the dimensions and weight of heaters.
  • the heating element according to the present invention can be easily energized by applying a voltage thereacross, and uniformly produces heat therethroughout. Moreover, it is possible to choose the shape, dimensions and volume resistivity as desired and, by adjusting the level of electricity to be supplied, to control the heating temperature as desired. Specifically, the heating element can be heated from room temperature to 600 C or so in 10 minutes after the initiation of its energization at a voltage of from about several volts to about 100 V, and can be maintained in a stably heated state.
  • those having a low volume resistivity on the order of from 10- 1 Q'cm to 10 Q'cm can produce heat at a low voltage of from about several volts to about 40 V, so that they can be used as small, low-power, heating elements. Owing to the use of a low voltage, there is a smaller potential danger of electrification so that they are also advantageous from the standpoint of safety.
  • the electrically-conductive heating element according to the present invention can be easily formed into a heater element by mounting electrode thereon, for example, by baking an electrically conductive paste or by metallization.
  • Electrically-conductive heating elements according to the present invention are useful as warming, cooking or drying heating elements or as heating elements for fuel vaporizers.
  • the electrically-conductive heating elements of the present invention feature the use of the particular foliated fine graphite particles. It is, however, not fully clear how much the initial shape of the foliated fine graphite particles is retained in the heating elements. It may, however, be possible to estimate it by measuring the characteristic electrical conductivity, which has been achieved for the first time by the use of the foliated fine graphite particles, in relation to the content of the graphite particles.
  • Examples in which a matrix-forming ceramic was used as a matrix-forming raw material powder will be described as Examples 1-5 and Comparative Examples 1-2.
  • examples in which a glass or a glass-ceramic mixture was used as a matrix-forming raw material powder will be given as Examples 6-16 and Comparative Examples 3-7.
  • the foliated fine graphite particles employed in Examples 1-16 and Comparative Examples 3-7 were prepared in the following manner.
  • the preformed green body was fired further for 1 hour at 1,300 C, it was cooled to 500° C at a rate of 3° C per minute. The thus-fired body was then allowed to cool down to room temperature.
  • the resultant, electrically-conductive heating element had a density of 1.9 g /cm 3 and had been fully sintered. From the heating element, a rectangular parallelopipedal sample of 25 x 38 x 4.5 mm was cut out. A sinterable Ag paste was coated on both longitudinal end surfaces and then dried at 150°C, so that electrode-bearing surfaces were formed. The volume resistivity of the sample as measured by the four-terminal method was 1.3 ⁇ cm.
  • Electrically-conductive heating elements were produced in a similar manner to Example 1 except that the amount of the foliated fine graphite particles added was changed and the forming pressure was raised to 9.8 MPa.
  • the volume resistivities of the heating elements so obtained were as follows:
  • a batch (300 g) proportioned and kneaded under the same conditions as in Example 1 was filled in a square cylindrical mold of 130 x 130 x 12 mm and pressure formed under the pressure of 9.8 MPa.
  • the preformed green body was fired under the same conditions as in Example 1, whereby an electrically-conductive heating element was obtained.
  • the density and volume resistivity of the heating element were 2.2 g/cm 3 and 0.8 ⁇ cm, respectively.
  • the heating element was cut and polished into a sample of 113 x 120 x 10 mm.
  • a voltage of 13 V was applied at an inter-electrode distance of 113 mm so that a current of about 10 A was allowed to pass across the sample.
  • the sample was then heated to 220 C in about 10 minutes and was stably maintained at the same temperature. Further, the surface temperature of the sample was measured in equally-divided nine regions. The surface temperature was approximately 220 C in all the nine regions, whereby the sample showed a uniform temperature distribution.
  • Example 3 Against the surface of an electrically-conductive heating element produced under the same conditions as in Example 3, a glaze formed of 60 g of a frit adjusted to 149 ⁇ m or smaller [trade name: "3127", product of Ferro Enamels (Japan) Limited] and 40 g of water was sprayed. After the glaze was dried, the glazed heating element was heated at 1,100°C in a nitrogen gas atmosphere to bake the glaze onto the heating element. The resultant, surface-coated, electrically-conductive heating element was insulated at the surface thereof, but the volume resistivity of the energization characteristics of the whole heating element were exactly the same as those of the sample produced in Example 3.
  • This sample was divided substantially equally into nine pieces, each of 39 x 39 x 10 mm.
  • An electrically-conductive Ag paste was baked on each of the pieces. Terminals are attached to each piece (at an inter-terminal distance of 39 mm), followed by the measurement of its volume resistivity by the two- terminal method. All the pieces had a resistivity of 0.8 ⁇ cm.
  • a voltage of 7 V was applied to each piece to energize it at a current of 10 A, each piece was heated to 410° C in about 5 minutes. Each piece was successfully and stably maintained at the same temperature for 30 minutes or longer.
  • An electrically-conductive heating element was obtained in a similar manner to Example 1 except that "Cordierite N-53" (trade name; product of Nishimura Togyo K.K.) was used in place of "petalite N-10" and the firing temperature was lowered to 1,100°C.
  • the density and volume resistivity of the heating element were 1.7 g/cm 3 and 2.9 O . cm, respectively.
  • An energization test was also conducted under the same conditions as in Example 1. As a result, the current level and heating temperature were 1.2 A and 225 C, respectively, when a voltage of 12 V was applied.
  • a sintered body was obtained under the same conditions as in Example 3 except for the use of commercial graphite powder (particle size: 1-5 ⁇ m, thickness: 0.2-0.6 ⁇ m, aspect ratio: 2-8) in place of the foliated fine graphite particles.
  • the volume resistivity of a sample of 120 x 120 x 10 mm was as high as 1.2 x 10 3 ⁇ cm.
  • the volume resistivities of pieces obtained by dividing the sample into 9 equal sections of 39 x 39 x 10 mm varied within a range of from 0.7 x 10 3 ⁇ cm to 1.5 x 10 3 ⁇ cm.
  • a borosilicate glass powder having properties of a softening point of 800 C and a thermal expansion coefficient of 30 x 10- 7 /°C and adjusted in particle size to an average particle size of 3 ⁇ m; foliated fine graphite particles adjusted in particle size to an average particle size of 20 ⁇ m (particle size: 1-100 ⁇ m, thickness: not greater than 1 ⁇ m, aspect ratio: 10-5,000, average particle size: 20 ⁇ m); and, as ceramic powders, alumina, mullite and cordierite powders all adjusted in particle size to an average particle size of 2 ⁇ m.
  • the matrix-forming raw material powder was added with an organic vehicle which had been prepared by dissolving ethylcellulose as a binder in a-terpinol.
  • the resultant mixture was kneaded by a three-roll mill, followed by adjustment to a suitable viscosity.
  • the mixture so prepared was employed as an insulating paste.
  • the foliated fine graphite particles were added in the corresponding proportion shown as an outer percentage in Table 1 to form a homogeneous mixture.
  • Added next to 100 parts by weight of the mixture were 16 parts by weight of an acrylic resin, 3 parts by weight of dibutyl phthalate, 22 parts by weight of toluene and 48 parts by weight of ethanol.
  • the resulting mixture was mixed for 24 hours in a polyethylene-made pot mill with alumina-made balls filled therein, whereby a homogeneous slurry was prepared.
  • a green sheet of 0.3 mm in thickness was formed as a heating-layer-forming sheet from the slurry.
  • a green sheet of the matrix-forming raw material powder was also formed as an insulating-layer-forming sheet.
  • FIG. 1 As is illustrated in FIG. 1, three heating-layer-forming sheets 1 were stacked, and one insulating-layer-forming sheet 2 was superposed on each of the top and bottom of the stacked heating-layer-forming sheets 1.
  • the stacked layers were bonded together under pressure into a preformed green body of 100 x 50 mm.
  • An insulating paste layer 3 was formed on each side wall of the preformed green body. The assembly so formed was degreased and sintered in the environmental atmosphere in accordance with the exemplary degreasing and firing temperature pattern depicted in FIG. 2.
  • Electrode-bearing surfaces were formed on both end surfaces of the thus-obtained ceramic heating element, whereby a heater was formed. A voltage of 50 V was applied to the heater so that the heater was energized and heated. The electrical resistance at that time and the temperature of the surface of the heating element at the time of energization and heat production were measured by means of a non-contact type radiation thermometer. The results are shown in Table 1.
  • a heating element produced in a similar manner by using the heating-layer-forming sheets alone showed substantially the same characteristics as the heating element with the insulating layer formed thereon.
  • Electrode-bearing surfaces were also formed on both end surfaces of the electrically-conductive heating element having the insulating layer thereon, so that a heater was produced.
  • the heater was energized across both terminals.
  • an insulation resistance test was conducted. As a result, the insulation resistance was at least 800 M ⁇ at 300 C and at least 3 M ⁇ at 500 C so that the heater had sufficient insulation.
  • Example 6-16 In each comparative example, the same raw materials as in Comparative Examples 6-16 was used. The foliated fine graphite particles were added in the corresponding proportion indicated as an outer percentage in Table 1. Then, the procedures of Example 6-16 were followed to produce a formed product. Measurement results of its characteristics are shown in Table 1.
  • Example 6-16 the temperature became constant in about 30 seconds when the voltage of 50 V was applied.
  • the samples of these examples therefore showed sufficient characteristics as heaters.
  • the samples of Comparative Examples 3 and 5 did not permit energization because of the low contents of the foliated fine graphite particles as an electrically conductive material.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
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EP91113044A 1990-08-03 1991-08-02 Elément de chauffage à conduction électrique Withdrawn EP0469628A1 (fr)

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JP205111/90 1990-08-03

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EP1818639A1 (fr) * 2004-08-04 2007-08-15 Ibiden Co., Ltd. Four de cuisson et procédé de fabrication d'un article cuit céramique poreux utilisant le four de cuisson

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TWI395043B (zh) 2009-07-15 2013-05-01 Au Optronics Corp 電泳顯示薄膜、電泳顯示面板及其製造方法
TWI508610B (zh) * 2013-06-10 2015-11-11 Univ Far East 具有遠紅外線之介電發熱體及其製造方法

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Publication number Priority date Publication date Assignee Title
DE2000987A1 (de) * 1970-01-10 1971-07-15 Siemens Elektrogeraete Gmbh Elektrische Heizeinrichtung

Patent Citations (1)

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Publication number Priority date Publication date Assignee Title
DE2000987A1 (de) * 1970-01-10 1971-07-15 Siemens Elektrogeraete Gmbh Elektrische Heizeinrichtung

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1818639A1 (fr) * 2004-08-04 2007-08-15 Ibiden Co., Ltd. Four de cuisson et procédé de fabrication d'un article cuit céramique poreux utilisant le four de cuisson
EP1818639A4 (fr) * 2004-08-04 2007-08-29 Ibiden Co Ltd Four de cuisson et procédé de fabrication d'un article cuit céramique poreux utilisant le four de cuisson

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TW223729B (fr) 1994-05-11

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