JPH11339933A - Expansion graphite flat heating element and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flexible and lightweight heating element having no concentrated heated portion, capable of constantly heating a wide face and excellent in heat diffusion efficiency by using a specific quantity of expansion graphite powder and/or pulverized material and a specific quantity of a binder. SOLUTION: A binder 0.5 pts.wt. or above is added to expansion graphite powder and/or expansion graphite pulverized material 100 pts.wt. so that the binder is sprinkled over only the portion kept in point contact with the wall face of the expansion graphite having a micro cell structure, and the mixture is uniformly mixed and dispersed to obtain a molding composition. Not only the expansion graphite obtained from natural graphite or artificial graphite but also the expansion graphite refined with expansion graphite wastes can be used. Various synthetic resins, natural resins, coal, petroleum pich or tar can be used for the binder, and a material having a high residual carbon ratio after it is burned is desirous. The obtained expansion graphite composition is molded and/or baked at the prescribed temperature and pressure to form a heating element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating element for heating various kinds of floors, walls, panels and the like, and a method for producing the same.

[0002]

2. Description of the Related Art As a heating element for heating a floor and / or a wall, a method of boiling hot water with a gas or the like and circulating the same through a pipe is conventionally known and used. However, this method has a problem in terms of thermal efficiency due to boiling of hot water, and additionally requires new energy for circulating the hot water, which is economically expensive.

[0003] Nichrome wires are most commonly used as electric heaters, but disconnection is inevitable in long-term use.

Although carbon fibers having a light and moderate electric resistance value are excellent as an electric heating element, a potential difference, a thermal gradient and static electricity are generated between the monofilaments at the time of energization, which causes fluffing and disconnection. .

[0005] Such a linear heating element is attached to an insulating panel and is energized to be used as a sheet heating element. In this case, the planar heating element has a problem in terms of heat diffusion because the heating portion is concentrated on the line portion. That is, only the portion near the line has a high temperature. For this reason, various attempts have been made to increase the heat diffusion efficiency, but they have not yet reached a satisfactory stage. In order to improve the heat diffusion efficiency, there is a method of making a heating plate by making slits (cuts) in the carbon plate or nichrome plate to increase the area and increase the heat diffusion efficiency. However, most of these are brittle materials, At present, it is heavy and difficult to use. Further, in the case of a nichrome plate, the electric resistance value is low, and it is necessary to lengthen the distance in order to use it as a heating element, which limits the use. In addition, since many carbon plates used as heating elements are obtained by cutting from a mass of graphite, it is difficult to produce a large-area carbon plate. Therefore, there is a method in which graphite particles are kneaded with a binder such as tar or pitch and formed and fired to produce a carbon plate. In this case, the one-dimensional shrinkage rate is about 20%, and the volume shrinkage rate is 50%. In this case, dimensional stability cannot be obtained, so that secondary processing is required, and there is a problem that the cost is increased from an economical viewpoint.

[0006]

SUMMARY OF THE INVENTION The present invention solves or greatly reduces the above-mentioned problems of the prior art.
A main object of the present invention is to provide a technology capable of performing constant heating on a wide surface without a centralized heating portion because the entire surface is a heating element.

Another object of the present invention is to provide a technique for obtaining a heating element having excellent heat diffusion efficiency.

Another object of the present invention is to provide a technology for a heating element that is more flexible and lighter than a conventional graphite plate.

Still another object of the present invention is to provide a technology of a heating element which is more economical than a conventional heating element.

[0010]

In order to solve the above problems, the present inventor can achieve the object by using expanded graphite powder and / or pulverized material as a lightweight carbon material. I found that.

According to the conventional technology for manufacturing an expanded graphite plate, the thickness is 1 mm.
The above cannot be manufactured. A conventional expanded graphite plate of 1 mm or less has low strength and its use is limited. In the present invention, a binder is used in order to have a thickness of 1 mm or more. In this case, about 0.1% of the mixture is used so that the binder is present only at a point contact with the wall surface of the expanded graphite having a microcell structure.
Molding is performed using a binder of 5% or more (“%” and “parts” in the following description of the specification mean “% by weight” and “parts by weight”, respectively). (The thus-prepared product is referred to as a molded product or a plate in the following description.)

When this is fired, a carbon-carbon composite material having a small shrinkage due to firing (eg, a shrinkage of a product fired at 1000 ° C. at a binder amount of 10% of 0.42%) and high dimensional accuracy can be obtained. (The thus-prepared product is referred to as a fired body or a fired plate in the following description.) By slitting the formed body and / or the fired body, the path through which electricity flows is changed, and the directionality is determined. . That is, the electric resistance value is changed by inserting the slit.

It has been known in the art that a heating element can be formed from a carbon-carbon composite material which can form an expanded graphite plate into an arbitrary shape with such a small amount of binder and has a very small shrinkage after firing. However, it is difficult to predict from the method of manufacturing the carbon heating element by the cutting method.

That is, the present invention provides a molded article from the following expanded graphite-based composition, and a sheet heating element from a fired article obtained by firing the same, and a method for producing the same. Expanded graphite powder and / or pulverized expanded graphite 100
A sheet heating element comprising an expanded graphite-based composition, comprising at least one part by weight and at least 0.5 part by weight of a binder. 2. Expanded graphite powder and / or pulverized expanded graphite 100
An expanded graphite-based sheet heating element comprising at least 0.5 parts by weight of a binder and 0.5 parts by weight of a binder. 3. Expanded graphite powder and / or pulverized expanded graphite 100
3. The method for producing an expanded graphite-based sheet heating element according to claim 2, wherein the mixture is obtained by uniformly mixing parts by weight and 0.5 parts by weight or more of a binder, and then molding the mixture. 4. Expanded graphite powder and / or pulverized expanded graphite 100
An expanded graphite-based sheet heating element obtained by firing an expanded graphite-based molded article, comprising at least one part by weight and at least 0.5 part by weight of a binder. 5. Expanded graphite powder and / or pulverized expanded graphite 100
5. The method for producing an expanded graphite-based sheet heating element according to claim 4, wherein after uniformly mixing parts by weight and 0.5 parts by weight or more of the binder, the mixture is molded and fired. 6. 6. A heating element for wall heating, comprising the expanded graphite-based heating element according to claim 2 or 4. A method for manufacturing a heating element for wall heating, comprising the expanded graphite-based heating element according to claim 2 or 4. 8. 8. A heating element for floor heating, comprising the expanded graphite heating element according to claim 2 or 4. A method for manufacturing a heating element for floor heating, comprising the expanded graphite-based heating element according to claim 2. 10. 10. A heating element for panel heating, comprising the expanded graphite-based heating element according to claim 2 or 4. A method for manufacturing a heating element for panel heating, comprising the expanded graphite-based heating element according to claim 2.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, 100 parts of expanded graphite powder and / or pulverized expanded graphite are mixed with 0.5% of a resin having a molecular structure mainly composed of tar, pitch and aromatic ring as a binder. -20 parts are added, and the mixture is uniformly mixed and dispersed to obtain a molding composition.

In the present invention, a graphite intercalation compound is synthesized by treating concentrated graphite, concentrated nitric acid, etc. between layers of graphite having a crystal structure such as natural graphite, quiche graphite, scale graphite, artificial graphite, etc., as expanded graphite. Not only expanded graphite obtained by a known technique of washing with water and heating to produce the same but also, for example, refined expanded graphite waste generated during the production of an engine gasket for an automobile can be used. In the present specification, expanded graphite means that at least one of these materials and / or a combination thereof is used.

The properties of the expanded graphite used in the present invention are not particularly limited, and usually have a bulk density of 0.004 to 0.30.
g / cm ³ , the larger the bulk density and the smaller the particle size, the higher the density of the resulting expanded graphite plate.
Conversely, the smaller the bulk density and the larger the particle size, the lower the density of the expanded graphite plate formed and the lighter the weight.

The binder used in the present invention is not particularly limited. For example, various kinds of synthetic resins (for example, phenol resin, furan resin, polyimide resin, etc.), natural resins (for example, pine resin), Coal / petroleum pitch, tar and the like are exemplified, and those having a high residual coal ratio after firing are desirable.

As the binder, either powdery or liquid can be used. It is desirable that the binder is uniformly mixed and dispersed in the expanded graphite, and exhibits good fluidity under heat and pressure during molding of the obtained composition. It is also possible to disperse and mix the binder used in the expanded graphite in a state of being dissolved, diluted or dispersed in an organic solvent. Such a use method promotes uniform mixing and improves compatibility between the two.

The heating element made of the expanded graphite composition according to the present invention is produced by molding the above-mentioned composition for molding expanded graphite at a predetermined temperature and pressure and / or firing it. (When referred to as a heating element in this specification, it indicates an expanded graphite molded article or a fired article obtained by firing the same.) The molding conditions include the properties of the expanded graphite and the binder in the composition, the mixing ratio, the mixing state, and the heating element. It is not particularly limited because it varies depending on the specific application of the normal temperature, but usually the temperature is 80 to
The temperature is about 200 ° C., more preferably 140 to 170 ° C., and the pressure is about 2 to 20 MPa, more preferably about 8 to 15 MPa.

The expanded graphite sheet heating element according to the present invention is not particularly limited. However, if the heating element surface temperature is 250 ° C. or less, the expanded graphite molded article can be used as it is without firing. When the surface temperature of the heating element is 250 ° C. or higher, it is preferable to use a fired one, and it is desirable to heat-treat or bake in advance to a temperature higher than the use temperature.

The heating element made of the expanded graphite composition according to the present invention may be provided with a slit after molding as a path through which electricity flows, or may be formed into a shape with a slit at the time of molding.

The heating element made of the expanded graphite molded article according to the present invention has a specific resistance at room temperature of 2.84 to 4.14 × 10 ⁻⁵ Ωm with a binder amount of 0.5 to 20%, which is not oxidized. 0.9 to 1000 ° C fired in an atmosphere
1.1 × 10 ⁻⁵ Ωm.

The specific resistance of nichrome, which is generally used as a heating element, is 0.95 to 1 × 10 ⁻⁶ Ωm. It has a specific resistance of 10 to 50 times.

In the case of producing a sheet heating element from the expanded graphite plate according to the present invention, it is possible to change the resistance value by changing the slits and the thickness of the plate. That is, when a small-sized planar heating element having a high resistance value is obtained, the width between the slits may be reduced, the length of the current flow path may be increased, and the thickness of the plate may be reduced. Conversely, when obtaining a large planar heating element with a low resistance value, the width between the slits should be wide, and the current path should be short.
Increase the thickness of the board.

When designing a wall heating element from the expanded graphite based sheet heating element according to the present invention, a large number of expanded graphite plates are used. The number is reduced and the total resistance value is set to a predetermined value. When the expanded graphite plates are used in parallel in an electric circuit, the number of slits of one expanded graphite plate may be adjusted to a predetermined resistance value. Heating elements for floors and panels can be designed in a similar way. In this case, by using a heat insulating material or a reflector on one side of the expanded graphite heating element, heating and economic efficiency can be improved.

The expanded graphite-based sheet heating element according to the present invention can be used as it is, but is not limited thereto, but may be put in a bag of heat-resistant cloth (for example, a glass fiber cloth) or heat-resistant. It is also possible to coat with a film.
In the case of a heating element used at a low temperature, for example, when used at a heating element surface temperature of 200 ° C. or lower, a heating element inserted in a molding resin can be used. When the electric circuit is short-circuited due to dust or the like between the slits of these heating elements, a short circuit can be prevented by inserting a heat-resistant insulator between the slits.

[0028]

The following examples are provided to further clarify the features of the present invention. Example 1 To 100 parts of pulverized expanded graphite (18 mesh under), 1 part of 200 mesh under novolak type phenol resin (flow 30 mm, gel time 55 seconds, ortho / para orientation ratio = 55/45) was added, and the mixture was homogenized. To obtain an expanded graphite composition.

Next, the obtained expanded graphite composition was molded using a hot press at 160 ° C. and 10 MPa for 2 minutes, and the total porosity was calculated from the bulk density and true density of the molded product. In addition, 400 mm x 300 mm x
A 2 mm plate is produced (hereinafter referred to as an expanded graphite molded plate) 40
The 0 mm side is set to be horizontal, the 300 mm side is set to be vertical, and slits having a length of 290 mm and a width of 3 mm are vertically and alternately formed so that the expanded graphite molded plate has a width of 10 mm. A copper electrode was sandwiched between the ends of the expanded graphite molded plate having the slits as described above to form an electrode. A temperature controller (FT-1000, manufactured by Fultech) was connected to the electrode, and the center of the heating element made of the expanded graphite molded plate was maintained at a predetermined temperature while being measured with an infrared thermocouple. At this time, the temperature dispersion of the entire surface of the heating element surface was measured using a thermoview (manufactured by NEC Corporation,
6T62, measurement temperature: -40 to 2000 ° C, sensor:
Temperature variations were observed for Hg, Cd, Te types, wavelength: 8 to 13 μm). The apparent electric resistance value of the heating element was measured with a tester.

The bending test was performed with a size of 20 mm × 10 mm × 4 mm
Is prepared, the bending span is 10 mm, and the test speed is 2 m.
m / min. The results obtained by this example, the following examples and comparative examples are shown in Tables 1 and 2 below.

Example 2 A composition was prepared and various tests were carried out in the same manner as in Example 1 except that the amount of the novolak type phenol resin was changed to 3 parts.

Example 3 A composition was prepared and various tests were conducted in the same manner as in Example 1 except that the amount of the novolak type phenol resin was changed to 5 parts.

Example 4 A composition was prepared and various tests were carried out in the same manner as in Example 1 except that the amount of the novolak type phenol resin was changed to 7 parts.

Example 5 A composition was prepared and various tests were carried out in the same manner as in Example 1 except that the amount of the novolak type phenol resin used was changed to 10 parts.

Example 6 A molded body obtained in the same manner as in Example 1 was fired from room temperature to 1000 ° C. for 24 hours in an argon gas atmosphere to obtain a fired body. About the obtained fired body, Example 1
Various tests were performed in the same manner as described above.

Example 7 A sinter was performed in the same manner as in Example 6 except that a molded article obtained in the same manner as in Example 2 was used, and various tests were performed.

Example 8 The same procedure as in Example 6 was repeated except that the molded product obtained in Example 3 was used, and firing was performed, and various tests were performed.

Example 9 A sinter was performed in the same manner as in Example 6 except that the molded body obtained in the same manner as in Example 4 was used, and various tests were performed.

Example 10 Except for using the molded body obtained in the same manner as in Example 5, firing was performed in the same manner as in Example 6, and various tests were performed.

Example 11 An expanded graphite molded plate having the same composition as in Example 5 was 1035 mm × 1
035 mm x 2 mm, and the expanded graphite molded plate has a width of 1
Slits having a length of 910 mm and a width of 5 mm were alternately inserted up and down so as to be 25 mm, and eight plates were prepared. Prepare a 3m × 3m × 2m high room surrounded by an 8mm thick veneer plate, fix the expanded graphite molded plate as a set of two at the center of the inside of one wall, and apply the same method to the four walls 8 in total
Expanded graphite molded plates having slits were arranged. The ends of the expanded graphite molded plates each having a slit were sandwiched between copper electrodes and electrically connected in series. A temperature controller (FT-1000 manufactured by Fultech) and a power supply were connected, and the center of an expanded graphite molded plate (expanded graphite heating element) having a slit on one wall was measured with an infrared thermocouple, and measured at 1 ° C. per minute. The temperature was raised to 60 ° C. at the temperature rising rate, and this temperature was maintained. Attach K thermocouples to the four corners of the 1m square in the center of the floor of the room and the four corners of the 1m square in the center of the room so as to be perpendicular to the veneer board by 100mm.
When the temperature reached 40 ° C. for the first time, the temperature difference between the lowest temperature portion of the other three temperatures and 40 ° C. was measured at the floor and the ceiling, respectively. The first room temperature was 15 ° C
Met.

Example 12 The same heating element as that of Example 11 and an extruded graphite molded plate were produced, and four sheets were placed on the floor and insulated with a glass cloth so as not to contact with each other, and were laid all over the center of the floor. As in Example 11, they were electrically connected in series, and a temperature controller was connected. A 4 mm-thick veneer plate was spread on this. The infrared thermocouple was measured at the center of the heating element from above a 4 mm veneer plate, and the surface temperature was maintained at 60 ° C. As in the case of Example 11, K thermocouples were vertically mounted at 100 mm at four corners of a 1 m square at the center of the floor of the room.
When the temperature reached ° C, the temperature difference of the lowest temperature portion from the other three points with respect to 40 ° C was measured. Other conditions were the same as in Example 11.

Example 13 An expanded graphite fired plate 400 mm × 3 having the same composition as in Example 10
00mm x 2mm, 400mm side horizontal, 3mm
The heat generating element was formed by vertically and alternately vertically inserting slits having a length of 280 mm and a width of 5 mm so that the 00 mm side was vertical and the expanded graphite fired plate had a width of 20 mm. A temperature controller and an infrared thermocouple were connected in the same manner as in Example 1, and the center of the heating element was kept at 400 ° C. 500mm × 500mm × 10 at a place 500mm away from this panel heating element
mm kao wool plates are set up in parallel to each other, and K thermocouples are attached to the four ends thereof.
The temperature difference of the lowest temperature portion at 100 ° C. was measured.

COMPARATIVE EXAMPLE 1 A nichrome wire having a diameter of about 1 mm was immersed in about 12 m to 400 mm × 30 so as to be close to the apparent electric resistance of Examples 1 to 10.
It is stuck on a mica board of 0 mm x 1 mm in a length of 30 cm and meandering in 40 rows, the interval between rows is 1 cm, a temperature controller is connected in the same manner as in Example 1, and the infrared thermocouple is placed at the center of the board. The Nichrome portion was measured and the temperature variation of the entire surface when the temperature reached a predetermined temperature was examined and calculated as the maximum temperature difference.

Comparative Example 2 A mica plate of 1035 mm × 1035 mm × 2 mm was 4 mm thick.
Example 1 A sheet-like heating element was formed by sticking a 8 mm × 2 mm × 1 mm nichrome plate meandering at an interval of 125 mm.
Eight sheets were prepared in the same manner as 1 and evaluated in the same manner. However, the surface temperature was measured using an infrared thermocouple on the nichrome plate at the center of the wall surface as a measurement point.

Comparative Example 3 Example 1 was repeated except that the mica plate surface heating element used in Comparative Example 2 was used.
Performed similarly to 2.

Comparative Example 4 About 6 m of a nichrome wire having a diameter of about 1 mm was
A mica plate of 0 mm × 1 mm was attached in a meandering manner in 20 rows with a length of 30 cm, and the procedure was the same as in Example 13 except that the spacing between the rows was 2 cm.

Comparative Example 5 50 parts of graphite particles having an average particle diameter of 40 μm were mixed well with 50 parts of granular coal tar pitch, and then mixed with a kneader.
Heat was mixed at 00 ° C. This was formed into a size of 100 mm × 100 mm × 6 mm using a hot press at 80 ° C. Then, it was fired in an argon gas atmosphere to 1000 ° C. over 240 hours. A test piece was cut and subjected to a bending test under the same conditions as in Example 1.

[0048]

[Table 1]

[0049]

[Table 2]

Note: The data of Example 13 and Comparative Example 4 in Table 2 were measured at four points, and when one point reached 100 ° C., the minimum temperature was 87 ° C. (Example 13) and 68 ° C.
(Comparative Example 4).

[0051]

The expanded graphite sheet heating element according to the present invention comprises:
Molding is possible even with a small amount of binder, and the formed body and its fired body are lighter than conventional carbon materials because of the porous body having many open pores and closed pores. The planar heating element obtained by sintering the expanded graphite-based molded article according to the present invention has a smaller sintering shrinkage ratio than a conventional carbon material and has excellent dimensional stability. Therefore, secondary processing is almost unnecessary.

The sheet heating element made of the expanded graphite molded article and / or fired article according to the present invention has a flexibility of 5% or more compared to 1% or less of the conventional carbon material, and is excellent in flexibility.

In the case of a conventional planar heating element in which a linear heating element such as a nichrome wire is adhered to an insulating plate, the heating element itself has a very high temperature, and the temperature difference from portions other than the heating element is large.
Although it becomes local heating, the expanded graphite-based sheet heating element according to the present invention is excellent in temperature dispersibility because the entire surface is a heating element,
Sufficient heating efficiency can be obtained at a lower temperature than conventional products. In the expanded graphite-based sheet heating element according to the present invention, an organic plate such as a wooden board in contact with the sheet is not browned at a temperature of 150 ° C. or less, but a sheet heating element made of a linear heating element such as a conventional nichrome wire. Even when the entire surface of the body was 60 ° C. or less, scorching was observed on an organic material plate such as a wooden plate in contact therewith.

In summary, the expanded graphite-based sheet heating element obtained by the present invention is a sheet heating element obtained by attaching a conventional line heating element such as a nichrome wire or carbon fiber to an insulating plate. Compared with conventional products, the heat diffusion efficiency is high, and there is no danger of fire or the like because local heating is not involved.

Continuation of the front page (72) Inventor Kawakami Shin-Shiya 3-3-32 Hirano Honcho, Hirano-ku, Osaka-shi, Japan Inside Nippon Cal Co., Ltd. (72) Inventor Takeshi Ken Hirohata Mikadai, Kawachinagano-shi, Osaka 1-35- 3 (72) Inventor Sadataka Tamura 3-6-13-305 Minamisakurazuka, Toyonaka City, Osaka (72) Inventor Taichi Nishiura 3-32, Hirano Honcho, Hirano-ku, Osaka, Japan Inside Nippon Cal Co., Ltd.

Claims (11)

[Claims] 1. A sheet heating element comprising an expanded graphite composition, comprising 100 parts by weight of an expanded graphite powder and / or a pulverized expanded graphite and 0.5 parts by weight or more of a binder. 2. An expanded graphite-based sheet heating element comprising 100 parts by weight of an expanded graphite powder and / or pulverized expanded graphite and 0.5 parts by weight or more of a binder. 3. The method according to claim 2, wherein 100 parts by weight of the expanded graphite powder and / or the pulverized expanded graphite and 0.5 parts by weight or more of the binder are uniformly mixed, and then the mixture is molded. A method for producing the expanded graphite-based sheet heating element according to the above. 4. An expanded graphite surface obtained by firing an expanded graphite molded body comprising 100 parts by weight of an expanded graphite powder and / or pulverized expanded graphite and 0.5 parts by weight or more of a binder. Heating element. 5. The method according to claim 4, wherein 100 parts by weight of the expanded graphite powder and / or pulverized expanded graphite and 0.5 parts by weight or more of the binder are uniformly mixed, and then the mixture is molded and fired. 3. The method for producing an expanded graphite-based sheet heating element according to item 1. 6. A heating element for wall heating, comprising the expanded graphite-based heating element according to claim 2 or 4. 7. A method of manufacturing a heating element for wall heating, comprising the expanded graphite heating element according to claim 2 or 4. 8. A heating element for floor heating, comprising the expanded graphite heating element according to claim 2 or 4. 9. A method for manufacturing a heating element for floor heating, comprising the expanded graphite heating element according to claim 2 or 4. 10. A heating element for panel heating, comprising: the expanded graphite-based heating element according to claim 2 or 4. 11. A method for manufacturing a heating element for panel heating, comprising the expanded graphite-based heating element according to claim 2 or 4.