JPH11354257A - Carbon heating element and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a heating element suitable for a cooking appliance for domestic use and a space heater by uniformly mixing graphite carbon, a resin material with high carbon remainder yield after baking and ceramics whose specific resistance is a specified value or more and molding and working the mixture into a hollow body shape. SOLUTION: Graphite powder is used, and as binder, thermosetting resin monomer in which carbon remainder yield after baking is almost 100% and a coefficient of contraction at the time of baking is small or initial polymer is used. As ceramics, it is desirable that boron nitride which is excellent in moldability by uniformly mixing graphite and binder, is excellent in mold release property and has high specific resistance of 10<14> to 10<15> μΩ.cm up to the vicinity of 2200 deg.C in inactive atmosphere is used. It is desirable that binder is blended by 45 to 50 pts.wt. for 5 to 50 pts.wt. of graphite powder and boron nitride is blended by 25 to 50 pts.wt. for 50 pts.wt. of graphite powder. After sufficient drying is performed after the mixing and extrusion molding, a precursor treatment is performed at 800 deg.C or more in inactive gas and a carbonizing baking treatment is performed at 1200 deg.C or more in vacuum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a structure and a method for manufacturing a carbon heating element.

[0002]

2. Description of the Related Art Carbon materials are excellent in heat resistance, thermal shock resistance and corrosion resistance, and have the highest heat emissivity among all materials.
Further, since it has a very high melting point of 3800 ° C., it is very suitable for a heating element. Therefore, it is particularly used as a heating element for a high-temperature electric furnace of a semiconductor manufacturing apparatus.

[0003]

The heating element of the above-mentioned conventional construction has a problem that it is difficult to use it as a heating element for home cooking appliances or a heating element for a heater.

That is, the specific resistance is 1500 to 2000 μm.
Since it is as small as Ω · cm, the heating element must be thick and long in order to obtain a required heat generation amount. That is, the power consumption of the heating element for a high-temperature electric furnace for manufacturing a semiconductor is about 50 kW, and the heating element used for the heating element is 100 V suitable for a heating element for a home cooking appliance and a heating element for a heater. When applied to a device of about 30 cm at -500 W, the wire diameter becomes about 0.6 mm. In this case, the watt density is as large as 86 W / cm ^2, and the temperature of the heating element reaches about 1730 ° C.
That is, it exceeds the firing temperature. For this reason, it is very easy to disconnect and becomes unsuitable for practical use. Also, even when the temperature does not reach such a level as to cause the disconnection, the specific resistance is greatly reduced and the power consumption is increased.

[0005]

SUMMARY OF THE INVENTION The present invention provides a hollow carbon heating element having a reduced cross-sectional area and a high electrical resistance, and suitable for household cooking appliances and heaters. Things.

[0006]

DETAILED DESCRIPTION OF THE INVENTION According to the first aspect of the present invention, there is provided a carbon heating element having a hollow body, which can reduce the cross-sectional area and increase the electric resistance, and is suitable for household cooking appliances and heaters. It is a heating element.

[0007] The invention described in claim 2 is characterized in that graphite carbon,
A resin material having a carbon residue yield of about 100% after firing and a ceramic material having a specific resistance of 10 ¹³ μΩ · cm or more are uniformly kneaded and formed into a hollow body to increase the electric resistance. And a carbon heating element suitable for home cooking appliances and heaters.

[0008] The invention described in claim 3 is characterized in that graphite carbon,
A resin material having a carbon residue yield of about 100% after firing and a ceramic having a specific resistance of 10 ¹³ μΩ · cm or more are uniformly kneaded and formed into a hollow body. Precursor processing is performed in which the temperature is increased and heated in an inert gas atmosphere, and then carbonized and baked in vacuum at a temperature higher than the processing temperature of the precursor, whereby the resin material changes to glassy carbon exhibiting high resistivity. In addition, the method can produce a carbon heating element suitable for household cooking appliances and heaters because the electric resistance can be increased as a whole.

According to a fourth aspect of the present invention, the resin material is
The carbon heating element is selected from a compound group consisting of a polymerizable thermosetting resin monomer or a low polymer and has a high electric resistance and is suitable for household cooking appliances and heaters.

According to a fifth aspect of the present invention, the resin material is
By selecting from the group of compounds consisting of monomers or low polymers of polymerizable thermosetting resins, it has good compatibility with graphite, uniform dispersion of the material, high electric resistance, and can be used for household cooking appliances and This is a method for producing a carbon heating element suitable for a heater.

[0011] The invention described in claim 6 is a method for molding a hollow material into a monomer or prepolymer selected from the group consisting of a furan-based resin, a phenol-based resin, and a thermosetting resin as a resin material. And a carbon heating element that is easy to manufacture.

[0012] The invention as set forth in claim 7 is characterized in that, as the resin material, a monomer selected from a group of compounds of a furan-based resin, a phenol-based resin or a thermosetting resin or an initial polymerized product is formed into a hollow body. And a method of manufacturing a carbon heating element which is easy to manufacture.

[0013] The invention described in claim 8 is a carbon heating element which has good moldability when molding into a hollow body using boron nitride as a resin material, has an easy resistance value adjustment, and is easy to manufacture. I have.

According to a ninth aspect of the present invention, there is provided a carbon heating element having good moldability when molding into a hollow body using boron nitride as a resin material, easy adjustment of a resistance value, and easy production. Manufacturing method.

According to a tenth aspect of the present invention, after the treatment of the precursor, the carbonization firing is performed in a vacuum at a temperature at least equal to the processing temperature of the precursor and at a temperature equal to or higher than the exothermic temperature of the heating element. By implementing the method, a method of manufacturing a carbon heating element capable of removing impurities and having less deterioration in characteristics even after long-term use is provided.

According to the eleventh aspect of the present invention, the treatment of the precursor is performed in an inert gas atmosphere at a temperature of at least 800 ° C., so that the moldability is good and the specific resistance can be increased. And a method for producing a carbon heating element suitable for cooking appliances and heaters.

The invention described in claim 12 is a method for producing a carbon heating element in which the carbonization firing temperature is set to 1200 ° C. or higher and the electric characteristics are stable even after long-term use.

[0018]

Embodiments of the present invention will be described below. In general, it is known that carbon has an intermediate structure in a wide range from a glassy amorphous structure to a hexagonal crystal structure. As a matter of course, the electrical resistivity is higher for a glassy compound, and is lower for higher crystallinity.

In this embodiment, graphite powder is used as graphite carbon as a main component, and as a binder for binding graphite carbon, the yield of carbon residue after firing is almost 100%. A thermosetting resin with a small shrinkage is used. Graphite is structurally stable up to about 3800 ° C., and is stable to the temperature during firing and the temperature during use. As the binder, as a result of various studies by the inventors, furfuryl alcohol resins, furfuryl alcohol / furfural copolymer resins, furfural resins such as furfural / phenol copolymer resins, phenols such as resol type and novolak, etc. It has been found that monomers or prepolymers selected from the group of thermosetting resin compounds such as resin series, xylene resin and toluene resin are suitable. That is, the resin group has very good compatibility with graphite, and the graphite is sufficiently dispersed uniformly in the molded body during molding. The mixing ratio at this time is 99 to 99 parts by weight of the graphite powder with respect to 1 to 80 parts by weight of the binder.
20 parts by weight, preferably 5 to 50 parts by weight of graphite powder and 95 to 50 parts by weight of binder. With the above configuration, the carbon powder and the binder are firmly bonded to each other, and exhibit high mechanical strength after carbonization and firing.

Hereinafter, a method of manufacturing the heating element according to the present embodiment will be described. The graphite powder and the binder are kneaded and uniformly dispersed using a mixer or the like, and a shearing force is applied using a three-roll mill or the like to sufficiently dissolve and bind them, thereby obtaining graphite. An organic substance is physicochemically bonded to the surface of the primary particles of the powder. Using this as a starting material, heat treatment is performed after molding to form a heating element.

However, in this state, the obtained resistor has a low electric resistivity and has extremely poor releasability during extrusion molding with a plunger or the like. For this reason, a carbon rod having a predetermined shape cannot be obtained.

Therefore, as a result of various studies, the present inventors have found that, when ceramics are added to the starting material, a resistor having a predetermined resistivity and good moldability can be molded. As the ceramics,
Mixes evenly with graphite and binder and has good moldability.
Low frictional resistance during extrusion molding, excellent mold release properties, and 10 ° C up to around 2200 ° C in an inert atmosphere.
Boron nitride, which has a high specific resistance of ¹⁴ to 10 ¹⁵ μΩ · cm, is the most suitable.

The thermal conductivity of boron nitride is 20 to 30 W / (m · K) which is almost equal to that of stainless steel. Boron nitride is a substance whose structure is very similar to graphite. Graphite belongs to the hexagonal system, and the lattice constant of the crystal is a =
2.4704 ° and c = 6.7244 °. On the other hand, boron nitride belongs to the same hexagonal system, a = 2.5044 °, c
= 6.6562 °. The lattice constant mismatch Δa with respect to graphite is 0.034 °, which is only 1.4%. Similarly, the mismatch Δc is −0.068.
2%, which is only -1.0%. That is, at the time of molding, it can be regarded as equivalent to graphite. Molybdenum disulfide, which is a typical substance generally used as a mold release agent, is easily oxidized and decomposed at 600 ° C. or higher, and cannot be used in this embodiment. That is, the coefficient of friction rapidly increases. On the other hand, boron nitride has a constant frictional resistance around 0.2 up to around 1000 ° C., and is rich in shape-forming properties and releasability.

An extremely important specific resistance as a resistor is 1500 to 2000 μΩ · cm for graphite alone.
It has a property closer to a conductor than a heating element. On the other hand, boron nitride has a high specific resistance of 10 ¹⁴ to 10 ¹⁵ μΩ · cm up to around 2200 ° C. in an inert atmosphere and belongs to the category of insulator. As a result of various studies by the inventors, the thickness of the heating element was set to about 1 mm in diameter, the total length of the heating element was set to 290 mm, and the specific resistance was 10,000 to 18000 μm.
It has been found that a material of Ω · cm can be formed by setting graphite to 100 parts by weight and boron nitride to 50 to 100 parts by weight.

As the heating element, a material having a high thermal conductivity that quickly rises and uniformly generates heat is desired. However, as described above, boron nitride is 20 to 30 W / cm, which is almost the same as stainless steel, which is unusual for ceramics. It has a thermal conductivity of (m · K) and is an ideal compounding material.

In summary, by using boron nitride as a raw material of the present heating element, a desired high electric resistivity can be freely designed only by changing the compounding ratio, and the same behavior as graphite at the time of material kneading can be obtained. The releasability is extremely improved.

As described above, in the carbon heating element of this embodiment, 99 to 20 parts by weight of a binder and preferably 5 to 50 parts by weight of a binder,
The binder is 45 to 50 parts by weight based on parts by weight. Further, boron nitride is used in an amount of 2.5 to 5 parts by weight with respect to 5 parts by weight of graphite powder, and 25 to 50 parts by weight with respect to 50 parts by weight of graphite powder.
At this time, the electrical resistance can be increased by increasing the compounding amount of boron nitride.

Examples of the binder include furfuryl alcohol resins, furfuryl alcohol / furfural copolymer resins, furan resins such as furfural / phenol copolymer resins, phenol resins such as resole and novolak, xylene resins, and toluene. A compound containing at least one or more monomers or prepolymers selected from a thermosetting resin compound group such as a resin is used. These are sufficiently kneaded by a mixer, and the obtained kneaded material is subjected to physicochemical bonding between graphite, boron nitride and an organic substance while applying a shearing force using a roll mill. Next, after forming into a sheet shape, it is extruded into a hollow body by a plunger. In this embodiment, the diameter is 0.8.
Extruded into a pipe shape of ~ 2mm. At this time, the added graphite and boron nitride act as a release agent, and can accurately form a predetermined hollow carbon rod. Note that the thickness of the hollow body can be appropriately adjusted, and a resistor having a desired electric resistivity can be obtained.

After the hollow molded body thus obtained was cut into a suitable length, it was kept at 180 ° C. for 1 hour while being slowly dried at a rate of 5 to 10 ° C./hour in an air oven. Allow the liquid to dry completely. Then, the temperature is raised to 300 ° C. at a rate of 5 ° C./hour in an inert gas atmosphere such as nitrogen or argon by a horizontal tubular furnace. Thereafter, the temperature is raised at a rate of 20 ° C./hour until the temperature reaches 800 ° C. or more, preferably 1000 ° C., and the temperature is kept for 3 hours in this state. That is, the precursor is cooled at a temperature equal to or higher than the processing temperature of the precursor and thereafter in a furnace to complete the calcination, that is, the precursor processing.

Thus, the completed precursor is fully fired.
The purpose of the main firing is roughly divided into two. The first is
It is to remove impurities. Second, by performing heat treatment at a temperature higher than the actual use temperature of the heating element, structural changes do not occur even after long-term actual use, and a constant resistance value, that is, a constant power consumption, is maintained. Is to be able to do it.

According to the investigation by the inventors, when graphite, particularly natural graphite, is used as a material, a greater or lesser amount of a mineral component is mixed. These impurities include:
There are Si, Fe, Ca, Al, K and the like. When these are contained, the oxidation start temperature of carbon is lowered by about 100 ° C. as compared with fully purified graphite, and the carbon becomes active, and is extremely unsuitable as a carbon heating element. When such a heating element is sealed in a quartz tube, the temperature of the heating element is 1000 ° C.
When the temperature reaches the above, K causes devitrification of the glass and significantly impairs the mechanical strength of the quartz tube.

For the reasons described above, the impurities need to be thoroughly removed. For this reason, in this embodiment, the carbonization firing conditions are performed at a temperature higher than the processing temperature of the precursor, at a temperature higher than the heat generation temperature of the carbon rod when actually used as a heating element, and under reduced pressure vacuum. That's what we do. Specifically, the temperature is 1200 ° C. or higher. Therefore, impurities can be removed.

By setting the firing temperature, the characteristics when used as a heating element are very stable. That is, it is possible to prevent the glassy carbon generated by the precursor treatment from gradually changing its structure into a crystal. FIG. 1 is a characteristic diagram showing the relationship between the carbonization firing temperature and the volume resistivity. As can be seen from this figure, when the carbonization firing temperature is higher than the processing temperature of the precursor and higher than the actual use temperature, the change in the volume resistivity is very small.

When the carbonization firing temperature is set to 1500 to 1600 ° C. and the carbonization firing is performed under reduced pressure vacuum (10 ⁻³ Torr), the specific resistance suitable for the heating element is 100%.
A heating element of 00 to 18000 μΩ · cm was obtained.

Table 1 shows that the heat treatment was carried out at 1600 ° C. in an inert gas atmosphere and that the heat treatment was carried out at 1600 ° C. under vacuum (10 ⁻³ Torr).
The result of the composition analysis of the carbon heating element when the heat treatment is performed in r) is shown. All are kept at the same temperature for 3 hours. As can be seen from the analysis data, it can be proved that the excess impurities are almost completely removed under reduced pressure vacuum.

[0036]

[Table 1]

Table 2 shows a comparison of the electrical resistivity between the round bar and the hollow molded body when the specific resistance is 18000 μΩ · cm, the diameter of the heating element is 1 mm, and the total length of the heating element is 290 mm. At this time, the thickness of the hollow molded body was 0.1 mm and 0.1 mm.
It is set to 2mm.

[0038]

[Table 2]

The electric resistivity in this case can be calculated by the following equation (1). Electric resistivity (Ω) = specific resistance × total length of heating element / cross-sectional area (Equation 1) For example, when the wall thickness is 0.1 mm, the electric resistivity is 2.8 times larger than a round bar. Can be. Also, it is obvious that by further reducing the wall thickness,
The electric resistivity can be further increased. Thus, a heating element having an arbitrary electric resistivity can be manufactured by adjusting the thickness of the hollow molded article.

Next, the results of checking the characteristics as a heating element of a hollow molded article manufactured according to the present embodiment as a carbon heating element will be described. The sample used in the experiment was placed in a quartz tube having an appropriate thickness, evacuated to vacuum, and then instantaneously 1400
C. to remove impurities adhering during the storage, followed by filling with argon gas at 600 Torr. The characteristic of this heating element is that the specific resistance is 18000 μΩ
cm, the diameter of the heating element is 1.2 mm, the wall thickness is 0.1 mm, the heating length is 280 mm, and the heating temperature is 100 V-380 W.
200 ° C. 2 at 100V for this sample
When a cycle test was carried out with a two-minute rest and a two minute pause, there was no disconnection in 8760 hours (equivalent to one year) in the conduction time,
In addition, a heating element having high durability with a change in power consumption of 10% or less as compared with the initial stage could be obtained.

Further, since the carbon heating element has a large emissivity of 0.8, it is suitable for a heating element of a cooking device having a large interior such as a microwave oven. For example, when the present heating element is incorporated in a microwave oven, and when toasting is baked with the same power consumption, it can be cooked in half 3 minutes instead of 6 minutes in the past. For this reason, when the carbon heating element of this embodiment is used, significant energy savings can be achieved. Further, when used as a heating element of an electric heater, in order to raise a place 10 cm away from the heating element by 35 ° C. as compared with room temperature, the power consumption of the heating element is 167 W, whereas the power consumption of the conventional heating element is 167 W. 186 W for a heater such as a quartz tube heater using Ni-Cr as a heating element
Needed. That is, when the heating element of this embodiment is used, power consumption can be reduced by about 10%.

[0042]

According to the first aspect of the present invention, there is provided a carbon heating element which can be formed into a hollow shape and has a small cross-sectional area and a high electric resistance, and is suitable for household cooking appliances and heaters. It can be realized.

The invention according to claim 2 is characterized in that graphite carbon and
The electric resistance can be increased as a hollow configuration made of a resin material with a carbon residue yield of about 100% after firing and a ceramic with a specific resistance of 10 ¹³ μΩ · cm or more. It is possible to realize a carbon heating element suitable for a heater or a heater.

[0044] The invention described in claim 3 is characterized in that graphite carbon,
A resin material having a carbon residue yield of about 100% after firing and a ceramic having a specific resistance of 10 ¹³ μΩ · cm or more are uniformly kneaded and formed into a hollow body. Perform a precursor treatment of heating and heating in an inert gas atmosphere, and then perform carbonization and firing in vacuum at a temperature higher than the temperature of the precursor treatment, so that the resin material becomes glassy carbon having a high resistivity. Accordingly, the present invention realizes a method for manufacturing a carbon heating element suitable for household cooking appliances and heaters, which can change the electric resistance as a whole.

According to a fourth aspect of the present invention, the resin material comprises:
As a configuration selected from a compound group consisting of a monomer or a low polymer of a polymerizable thermosetting resin, a carbon heating element having high electric resistance and suitable for home cooking appliances and heaters is realized.

According to a fifth aspect of the present invention, the resin material comprises:
By selecting from a group of compounds consisting of a polymerizable thermosetting resin monomer or a low polymer, a method for producing a carbon heating element suitable for home cooking appliances and heaters is realized.

According to a sixth aspect of the present invention, the resin material comprises:
As a composition of monomers or prepolymers selected from the compound group of furan-based resin, phenol-based resin, or thermosetting resin, it has good moldability when molded into a hollow body, and realizes an easy-to-manufacture carbon heating element. Things.

According to a seventh aspect of the present invention, the resin material comprises:
As a monomer or prepolymer selected from a group of compounds of a furan-based resin, a phenol-based resin, or a thermosetting resin, the moldability when molding into a hollow body is good, and a method for manufacturing a carbon heating element that is easy to produce is realized. Things.

The carbon heating element according to the eighth aspect of the present invention has a structure in which boron nitride is used as the resin material, has good moldability when molded into a hollow body, easily adjusts the resistance value, and is easy to manufacture. Is realized.

According to the ninth aspect of the present invention, there is provided a carbon heat generating apparatus which uses boron nitride as a resin material, has good moldability when molded into a hollow body, easily adjusts a resistance value, and is easily manufactured. It is intended to realize a body manufacturing method.

According to a tenth aspect of the present invention, after the treatment of the precursor, carbonization and firing are performed at a temperature at least equal to or higher than the processing temperature of the precursor and at a temperature equal to or higher than the exothermic temperature of the heating element. Thus, a method of manufacturing a carbon heating element capable of removing impurities and having less deterioration in characteristics even after long-term use is realized.

According to the eleventh aspect of the present invention, the treatment of the precursor is carried out in an inert gas atmosphere at a temperature of at least 800 ° C., so that the moldability is good and the specific resistance can be increased. And a method for producing a carbon heating element suitable for a cooking appliance or a heater.

The twelfth aspect of the present invention realizes a method for producing a carbon heating element having stable electric characteristics even after long-term use by setting the carbonization firing temperature to 1200 ° C. or higher.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing a relationship between temperature and resistance of a carbon heating element according to an embodiment of the present invention.

[Procedure amendment]

[Submission date] August 2, 1999

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction contents]

[Document Name] Statement

Patent application title: Carbon heating element and method for producing the same

[Claims]

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a structure and a method for manufacturing a carbon heating element.

[0002]

2. Description of the Related Art Carbon materials are excellent in heat resistance, thermal shock resistance and corrosion resistance, and have the highest heat emissivity among all materials.
Further, since it has a very high melting point of 3800 ° C., it is very suitable for a heating element. Therefore, it is particularly used as a heating element for a high-temperature electric furnace of a semiconductor manufacturing apparatus.

[0003]

The heating element of the above-mentioned conventional construction has a problem that it is difficult to use it as a heating element for home cooking appliances or a heating element for a heater.

That is, the specific resistance is 1500 to 2000 μm.
Since it is as small as Ω · cm, the heating element must be thick and long in order to obtain a required heat generation amount. That is, the power consumption of the heating element for a high-temperature electric furnace for manufacturing a semiconductor is about 50 kW, and the heating element used for the heating element is 100 V suitable for a heating element for a home cooking appliance and a heating element for a heater. When applied to a device of about 30 cm at -500 W, the wire diameter becomes about 0.6 mm. In this case, the watt density is as large as 86 W / cm 2, and the temperature of the heating element reaches about 1730 ° C.
That is, it exceeds the firing temperature. For this reason, it is very easy to disconnect and becomes unsuitable for practical use. Also, even when the temperature does not reach such a level as to cause the disconnection, the specific resistance is greatly reduced and the power consumption is increased.

[0005]

SUMMARY OF THE INVENTION The present invention provides a hollow carbon heating element having a reduced cross-sectional area and a high electrical resistance, and suitable for household cooking appliances and heaters. Things.

[0006]

DETAILED DESCRIPTION OF THE INVENTION According to the first aspect of the present invention, there is provided a carbon heating element having a hollow body, which can reduce the cross-sectional area and increase the electric resistance, and is suitable for household cooking appliances and heaters. It is a heating element.

[0007] The invention described in claim 2 is characterized in that graphite carbon,
A resin material having a carbon residue yield of about 100% after firing and a ceramic material having a specific resistance of 1013 μΩ · cm or more are uniformly kneaded and formed into a hollow body to increase the electrical resistance. It is a carbon heating element suitable for cooking equipment and heaters.

[0008] The invention described in claim 3 is characterized in that graphite carbon,
A resin material having a carbon residue yield of about 100% after firing and a ceramic having a specific resistance of 1013 μΩ · cm or more are uniformly kneaded and formed into a hollow body, and the obtained formed body is inertized. Precursor processing of heating and heating in a gas atmosphere is performed, and then carbonized and fired in vacuum at a temperature higher than the processing temperature of the precursor, and the resin material changes to glassy carbon exhibiting high resistivity, It is a method of manufacturing a carbon heating element that can increase the electric resistance as a whole and is suitable for household cooking appliances and heaters.

According to a fourth aspect of the present invention, the resin material is
The carbon heating element is selected from a compound group consisting of a polymerizable thermosetting resin monomer or a low polymer and has a high electric resistance and is suitable for household cooking appliances and heaters.

According to a fifth aspect of the present invention, the resin material is
By selecting from the group of compounds consisting of monomers or low polymers of polymerizable thermosetting resins, it has good compatibility with graphite, uniform dispersion of the material, high electric resistance, and can be used for household cooking appliances and This is a method for producing a carbon heating element suitable for a heater.

[0011] The invention described in claim 6 is a method for molding a hollow material into a monomer or prepolymer selected from the group consisting of a furan-based resin, a phenol-based resin, and a thermosetting resin as a resin material. And a carbon heating element that is easy to manufacture.

[0012] The invention as set forth in claim 7 is characterized in that, as the resin material, a monomer selected from a group of compounds of a furan-based resin, a phenol-based resin or a thermosetting resin or an initial polymerized product is formed into a hollow body. And a method of manufacturing a carbon heating element which is easy to manufacture.

[0013] The invention described in claim 8 is characterized in that carbon nitride, which is easy to produce, has good moldability when formed into a hollow body by using boron nitride as a ceramic, is easy to adjust the resistance value, and is easy to produce. It is a heating element.

According to a ninth aspect of the present invention, there is provided a carbon material which has good moldability when formed into a hollow body using boron nitride as the ceramics, has an easy resistance value adjustment, and is easy to manufacture. It is a method of manufacturing a heating element.

According to a tenth aspect of the present invention, after the treatment of the precursor, the carbonization firing is performed in a vacuum at a temperature at least equal to the processing temperature of the precursor and at a temperature equal to or higher than the exothermic temperature of the heating element. By implementing the method, a method of manufacturing a carbon heating element capable of removing impurities and having less deterioration in characteristics even after long-term use is provided.

According to the eleventh aspect of the present invention, the treatment of the precursor is performed in an inert gas atmosphere at a temperature of at least 800 ° C., so that the moldability is good and the specific resistance can be increased. And a method for producing a carbon heating element suitable for cooking appliances and heaters.

The invention described in claim 12 is a method for producing a carbon heating element in which the carbonization firing temperature is set to 1200 ° C. or higher and the electric characteristics are stable even after long-term use.

[0018]

Embodiments of the present invention will be described below. In general, it is known that carbon has an intermediate structure in a wide range from a glassy amorphous structure to a hexagonal crystal structure. As a matter of course, the electrical resistivity is higher for a glassy compound, and is lower for higher crystallinity.

In this embodiment, graphite powder is used as graphite carbon as a main component, and as a binder for binding graphite carbon, the yield of carbon residue after firing is almost 100%. A thermosetting resin with a small shrinkage is used. Graphite is structurally stable up to about 3800 ° C., and is stable to the temperature during firing and the temperature during use. As the binder, as a result of various studies by the inventors, furfuryl alcohol resins, furfuryl alcohol / furfural copolymer resins, furfural resins such as furfural / phenol copolymer resins, phenols such as resol type and novolak, etc. It has been found that monomers or prepolymers selected from the group of thermosetting resin compounds such as resin series, xylene resin and toluene resin are suitable. That is, the resin group has very good compatibility with graphite, and the graphite is sufficiently dispersed uniformly in the molded body during molding. The mixing ratio at this time is 99 to 99 parts by weight of the graphite powder with respect to 1 to 80 parts by weight of the binder.
20 parts by weight, preferably 5 to 50 parts by weight of graphite powder and 95 to 50 parts by weight of binder. With the above configuration, the carbon powder and the binder are firmly bonded to each other, and exhibit high mechanical strength after carbonization and firing.

Hereinafter, a method of manufacturing the heating element according to the present embodiment will be described. The graphite powder and the binder are kneaded and uniformly dispersed using a mixer or the like, and a shearing force is applied using a three-roll mill or the like to sufficiently dissolve and bind them, thereby obtaining graphite. An organic substance is physicochemically bonded to the surface of the primary particles of the powder. Using this as a starting material, heat treatment is performed after molding to form a heating element.

However, in this state, the obtained resistor has a low electric resistivity and has extremely poor releasability during extrusion molding with a plunger or the like. For this reason, a carbon rod having a predetermined shape cannot be obtained.

Therefore, as a result of various studies, the present inventors have found that, when ceramics are added to the starting material, a resistor having a predetermined resistivity and good moldability can be molded. As the ceramics,
Mixes evenly with graphite and binder and has good moldability.
Low frictional resistance during extrusion molding, excellent mold release properties, and 10 ° C up to around 2200 ° C in an inert atmosphere.
Boron nitride, which has a high specific resistance of 14 to 1015 μΩ · cm, is the most suitable.

The thermal conductivity of boron nitride is 20 to 30 W / (m · K) which is almost equal to that of stainless steel. Boron nitride is a substance whose structure is very similar to graphite. Graphite belongs to the hexagonal system, and the lattice constant of the crystal is a =
2.4704 ° and c = 6.7244 °. On the other hand, boron nitride belongs to the same hexagonal system, a = 2.5044 °, c
= 6.6562 °. The lattice constant mismatch Δa with respect to graphite is 0.034 °, which is only 1.4%. Similarly, the mismatch Δc is −0.068.
2%, which is only -1.0%. That is, at the time of molding, it can be regarded as equivalent to graphite. Molybdenum disulfide, which is a typical substance generally used as a mold release agent, is easily oxidized and decomposed at 600 ° C. or higher, and cannot be used in this embodiment. That is, the coefficient of friction rapidly increases. On the other hand, boron nitride has a constant frictional resistance around 0.2 up to around 1000 ° C., and is rich in shape-forming properties and releasability.

An extremely important specific resistance as a resistor is 1500 to 2000 μΩ · cm for graphite alone.
It has a property closer to a conductor than a heating element. On the other hand, boron nitride has a high specific resistance of 10 14 to 10 15 μΩ · cm up to around 2200 ° C. in an inert atmosphere and belongs to the category of insulator. As a result of various studies by the inventors, the thickness of the heating element was set to about 1 mm in diameter, the total length of the heating element was set to 290 mm, and the specific resistance was 10,000 to 18000 μm.
It has been found that a material of Ω · cm can be formed by setting graphite to 100 parts by weight and boron nitride to 50 to 100 parts by weight.

As the heating element, a material having a high thermal conductivity that quickly rises and uniformly generates heat is desired. However, as described above, boron nitride is 20 to 30 W / cm, which is almost the same as stainless steel, which is unusual for ceramics. It has a thermal conductivity of (m · K) and is an ideal compounding material.

In summary, by using boron nitride as a raw material of the present heating element, a desired high electric resistivity can be freely designed only by changing the compounding ratio, and the same behavior as graphite at the time of material kneading can be obtained. The releasability is extremely improved.

As described above, in the carbon heating element of this embodiment, 99 to 20 parts by weight of a binder and preferably 5 to 50 parts by weight of a binder,
The binder is 45 to 50 parts by weight based on parts by weight. Further, boron nitride is used in an amount of 2.5 to 5 parts by weight with respect to 5 parts by weight of graphite powder, and 25 to 50 parts by weight with respect to 50 parts by weight of graphite powder.
At this time, the electrical resistance can be increased by increasing the compounding amount of boron nitride.

Examples of the binder include furfuryl alcohol resins, furfuryl alcohol / furfural copolymer resins, furan resins such as furfural / phenol copolymer resins, phenol resins such as resole and novolak, xylene resins, and toluene. A compound containing at least one or more monomers or prepolymers selected from a thermosetting resin compound group such as a resin is used. These are sufficiently kneaded by a mixer, and the obtained kneaded material is subjected to physicochemical bonding between graphite, boron nitride and an organic substance while applying a shearing force using a roll mill. Next, after forming into a sheet shape, it is extruded into a hollow body by a plunger. In this embodiment, the diameter is 0.8.
Extruded into a pipe shape of ~ 2mm. At this time, the added graphite and boron nitride act as a release agent, and can accurately form a predetermined hollow carbon rod. Note that the thickness of the hollow body can be appropriately adjusted, and a resistor having a desired electric resistivity can be obtained.

After the hollow molded body thus obtained was cut into a suitable length, it was kept at 180 ° C. for 1 hour while being slowly dried at a rate of 5 to 10 ° C./hour in an air oven. Allow the liquid to dry completely. Then, the temperature is raised to 300 ° C. at a rate of 5 ° C./hour in an inert gas atmosphere such as nitrogen or argon by a horizontal tubular furnace. Thereafter, the temperature is raised at a rate of 20 ° C./hour until the temperature reaches 800 ° C. or more, preferably 1000 ° C., and the temperature is kept for 3 hours in this state. That is, the precursor is cooled at a temperature equal to or higher than the processing temperature of the precursor and thereafter in a furnace to complete the calcination, that is, the precursor processing.

Thus, the completed precursor is fully fired.
The purpose of the main firing is roughly divided into two. The first is
It is to remove impurities. Second, by performing heat treatment at a temperature higher than the actual use temperature of the heating element, structural changes do not occur even after long-term actual use, and a constant resistance value, that is, a constant power consumption, is maintained. Is to be able to do it.

According to the investigation by the inventors, when graphite, particularly natural graphite, is used as a material, a greater or lesser amount of a mineral component is mixed. These impurities include:
There are Si, Fe, Ca, Al, K and the like. When these are contained, the oxidation start temperature of carbon is lowered by about 100 ° C. as compared with fully purified graphite, and the carbon becomes active, and is extremely unsuitable as a carbon heating element. When such a heating element is sealed in a quartz tube, the temperature of the heating element is 1000 ° C.
When the temperature reaches the above, K causes devitrification of the glass and significantly impairs the mechanical strength of the quartz tube.

For the reasons described above, the impurities need to be thoroughly removed. For this reason, in this embodiment, the carbonization firing conditions are performed at a temperature higher than the processing temperature of the precursor, at a temperature higher than the heat generation temperature of the carbon rod when actually used as a heating element, and under reduced pressure vacuum. That's what we do. Specifically, the temperature is 1200 ° C. or higher. Therefore, impurities can be removed.

By setting the firing temperature, the characteristics when used as a heating element are very stable. That is, it is possible to prevent the glassy carbon generated by the precursor treatment from gradually changing its structure into a crystal. FIG. 1 is a characteristic diagram showing the relationship between the carbonization firing temperature and the volume resistivity. As can be seen from this figure, when the carbonization firing temperature is higher than the processing temperature of the precursor and higher than the actual use temperature, the change in the volume resistivity is very small.

When the carbonization firing temperature is set to 1500 to 1600 ° C. and the carbonization firing is performed under reduced pressure vacuum (10 −3 Torr), the specific resistance suitable for the heating element is 100.
A heating element of 00 to 18000 μΩ · cm was obtained.

Table 1 shows that the heat treatment was carried out at 1600 ° C. in an inert gas atmosphere and that the heat treatment was carried out at 1600 ° C. under vacuum (10 −3 Torr).
The result of the composition analysis of the carbon heating element when the heat treatment is performed in r) is shown. All are kept at the same temperature for 3 hours. As can be seen from the analysis data, it can be proved that the excess impurities are almost completely removed under reduced pressure vacuum.

[0036]

[Table 1]

Table 2 shows a comparison of the electrical resistivity between the round bar and the hollow molded body when the specific resistance is 18000 μΩ · cm, the diameter of the heating element is 1 mm, and the total length of the heating element is 290 mm. At this time, the thickness of the hollow molded body was 0.1 mm and 0.1 mm.
It is set to 2mm.

[0038]

[Table 2]

The electric resistivity in this case can be calculated by the following equation (1). Electric resistivity (Ω) = specific resistance × total length of heating element / cross-sectional area (Equation 1) For example, when the wall thickness is 0.1 mm, the electric resistivity is 2.8 times larger than a round bar. Can be. Also, it is obvious that by further reducing the wall thickness,
The electric resistivity can be further increased. Thus, a heating element having an arbitrary electric resistivity can be manufactured by adjusting the thickness of the hollow molded article.

Next, the results of checking the characteristics as a heating element of a hollow molded article manufactured according to the present embodiment as a carbon heating element will be described. The sample used in the experiment was placed in a quartz tube having an appropriate thickness, evacuated to vacuum, and then instantaneously 1400
C. to remove impurities adhering during the storage, followed by filling with argon gas at 600 Torr. The characteristic of this heating element is that the specific resistance is 18000 μΩ
cm, the diameter of the heating element is 1.2 mm, the wall thickness is 0.1 mm, the heating length is 280 mm, and the heating temperature is 100 V-380 W.
200 ° C. 2 at 100V for this sample
When a cycle test was carried out with a two-minute rest and a two minute pause, there was no disconnection in 8760 hours (equivalent to one year) in the conduction time,
In addition, a heating element having high durability with a change in power consumption of 10% or less as compared with the initial stage could be obtained.

Further, since the carbon heating element has a large emissivity of 0.8, it is suitable for a heating element of a cooking device having a large interior such as a microwave oven. For example, when the present heating element is incorporated in a microwave oven, and when toasting is baked with the same power consumption, it can be cooked in half 3 minutes instead of 6 minutes in the past. For this reason, when the carbon heating element of this embodiment is used, significant energy savings can be achieved. Further, when used as a heating element of an electric heater, in order to raise a place 10 cm away from the heating element by 35 ° C. as compared with room temperature, the power consumption of the heating element is 167 W, whereas the power consumption of the conventional heating element is 167 W. 186 W for a heater such as a quartz tube heater using Ni-Cr as a heating element
Needed. That is, when the heating element of this embodiment is used, power consumption can be reduced by about 10%.

[0042]

According to the first aspect of the present invention, there is provided a carbon heating element which can be formed into a hollow shape and has a small cross-sectional area and a high electric resistance, and is suitable for household cooking appliances and heaters. It can be realized.

The invention according to claim 2 is characterized in that graphite carbon and
The electrical resistance can be increased as a hollow structure composed of a resin material with a carbon residue yield of about 100% after firing and a ceramic material with a specific resistance of 1013 μΩ · cm or more. It is possible to realize a carbon heating element suitable for a heater.

[0044] The invention described in claim 3 is characterized in that graphite carbon,
A resin material having a carbon residue yield of about 100% after firing and a ceramic having a specific resistance of 1013 μΩ · cm or more are uniformly kneaded and formed into a hollow body, and the obtained formed body is inertized. Precursor processing of heating and heating in a gas atmosphere is performed, and then carbonization and firing in vacuum at a higher temperature than the precursor processing temperature, the resin material changes to glassy carbon exhibiting high resistivity. Accordingly, it is possible to increase the electric resistance as a whole, and to realize a method of manufacturing a carbon heating element suitable for home cooking appliances and heaters.

According to a fourth aspect of the present invention, the resin material comprises:
As a structure selected from a compound group consisting of a monomer or a low polymer of a polymerizable thermosetting resin, a carbon heating element having high electric resistance and suitable for home cooking appliances and heaters is realized.

According to a fifth aspect of the present invention, the resin material comprises:
By selecting from a group of compounds consisting of a polymerizable thermosetting resin monomer or a low polymer, a method for producing a carbon heating element suitable for home cooking appliances and heaters is realized.

According to a sixth aspect of the present invention, the resin material comprises:
As a composition of monomers or prepolymers selected from the compound group of furan-based resin, phenol-based resin, or thermosetting resin, it has good moldability when molded into a hollow body, and realizes an easy-to-manufacture carbon heating element. Things.

According to a seventh aspect of the present invention, the resin material comprises:
As a monomer or prepolymer selected from a group of compounds of a furan-based resin, a phenol-based resin, or a thermosetting resin, the moldability when molding into a hollow body is good, and a method for manufacturing a carbon heating element that is easy to produce is realized. Things.

According to the eighth aspect of the present invention, the configuration using boron nitride as the ceramic has good moldability when molded into a hollow body, easy adjustment of the resistance value, and easy production. This realizes a carbon heating element.

According to the ninth aspect of the present invention, when the boron nitride is used as the ceramic , the moldability when forming into a hollow body is good, the resistance value is easily adjusted, and the production is easy. The present invention realizes a method for manufacturing a carbon heating element.

According to a tenth aspect of the present invention, after the treatment of the precursor, carbonization and firing are performed at a temperature at least equal to or higher than the processing temperature of the precursor and at a temperature equal to or higher than the exothermic temperature of the heating element. Thus, a method of manufacturing a carbon heating element capable of removing impurities and having less deterioration in characteristics even after long-term use is realized.

According to the eleventh aspect of the present invention, the treatment of the precursor is carried out in an inert gas atmosphere at a temperature of at least 800 ° C., so that the moldability is good and the specific resistance can be increased. And a method for producing a carbon heating element suitable for a cooking appliance or a heater.

The twelfth aspect of the present invention realizes a method for producing a carbon heating element having stable electric characteristics even after long-term use by setting the carbonization firing temperature to 1200 ° C. or higher.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing a relationship between temperature and resistance of a carbon heating element according to an embodiment of the present invention.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Yasunori Kaneko 1006 Kazuma Kadoma, Osaka Pref.Matsushita Electric Industrial Co., Ltd.

Claims (12)

[Claims] 1. A carbon heating element molded into a hollow shape. 2. Graphite carbon, a resin material having a carbon residue yield of about 100% after firing, and a specific resistance of 10 ¹³ μΩ ·
A carbon heating element made of a ceramic with a diameter of at least 1 cm. 3. Graphite carbon, a resin material having a carbon residue yield of about 100% after firing, and a specific resistance of 10 ¹³ μΩ ·
cm or more of ceramics are uniformly kneaded, molded into a hollow body, and the obtained molded body is subjected to a precursor treatment of heating and heating in an inert gas atmosphere. A method for producing a carbon heating element that is carbonized and fired in a vacuum at an even higher temperature. 4. The carbon heating element according to claim 1, wherein the resin material is selected from a compound group consisting of a monomer of a polymerizable thermosetting resin or a low polymer. 5. The method for producing a carbon heating element according to claim 3, wherein the resin material is selected from a compound group consisting of a monomer of a polymerizable thermosetting resin or a low polymer. 6. The carbon heating element according to claim 1, wherein the resin material is a monomer or prepolymer selected from the group consisting of a furan-based resin, a phenol-based resin, and a thermosetting resin. 7. The method for producing a carbon heating element according to claim 5, wherein the resin material is a monomer or prepolymer selected from the group consisting of a furan-based resin, a phenol-based resin, and a thermosetting resin. 8. The carbon heating element according to claim 4, wherein boron nitride is used as the resin material. 9. The method for producing a carbon heating element according to claim 5, wherein boron nitride is used as the resin material. 10. After the treatment of the precursor, carbonization and calcination are performed at a temperature at least equal to or higher than the processing temperature of the precursor and at a temperature equal to or higher than the heat generation temperature of the heating element.
3. The method for producing a carbon heating element described in 1. above. 11. The method for producing a carbon heating element according to claim 3, wherein the treatment of the precursor is performed at a temperature of at least 800 ° C. in an inert gas atmosphere. 12. The method for producing a carbon heating element according to claim 3, wherein the carbonization firing temperature is 1200 ° C. or higher.