JPH044588A - Surface form heat emitting element - Google Patents

Abstract

PURPOSE:To accomplish a stable heat emission characteristics with less dispersion of electric resistance by using a heat emitting base material consisting of a carbon film, and covering this film with electrical insulative resin. CONSTITUTION:A surface form heat-emitting element 1 comprises a carbon film 2 and an electrical insulative resin 3 covering the whole of this film 2. A lead 4 consisting of carbon film 2 extends from this surface form heat- emitting element 1. The carbon film 2 is made of a starting material capable of being carbide or graphitized, which is subjected to the extrusion shaping process, etc., to turn into film shape, followed by carbiding or graphitizing process. Favorable example of the insulative resin is a thermoplastic resin such as polyethylene and polypropylene. Thereby a stable heat emission characteristic is obtained, which includes less dispersion of the electric resistance.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a sheet heating element that exhibits stable heating characteristics.

[Prior Art and Problems to be Solved by the Invention] A planar heating element is usually composed of a heat generating base material and an electrically insulating resin covering the heat generating base material.

Conventionally, as the above-mentioned heat generating base material, mixed paper made by mixing carbon fibers and valves (Japanese Patent Publication No. 51-3099), web made by mixing carbon fibers and synthetic fibers (Japanese Patent Publication No. 51-3099),
(Japanese Patent Application Laid-Open No. 63-24582), carbon fiber string-like material
(No. Publication) has been proposed. The electrical resistance of the carbon fiber itself in these heat generating base materials can be adjusted by the type of fiber material, the heat treatment temperature for carbonization or graphitization, and the like. Therefore, the electrical resistance value of the heat generating base material can be controlled by adjusting the content of carbon fibers in the case of mixed paper or webs, and by adjusting the number of carbon fibers in the case of string-like materials.

However, with these heat generating base materials, the electric resistance fluctuates, so the heat generating properties are not stabilized. That is, the electrical resistance of a heat-generating base material made of mixed paper, a web, or a string-like material depends on the dispersibility of carbon fibers and the contact nature of the carbon fibers with each other. On the other hand, when using carbon fibers, it is difficult to uniformly disperse a large number of fibers. Moreover, the fiber lengths of the carbon fibers contained in these heat generating base materials generally differ. Therefore, when using the carbon fibers, the electrical resistance of the heat generating base material also changes based on changes in the dispersibility of the carbon fibers and the contact between the fibers. In particular, in the case of mixed papermaking, especially mixed papermaking using valves, volatile matter, especially water, generated with heat generation causes
Electrical resistance tends to fluctuate significantly. For this reason, the above-mentioned special public
Publication No. 1-3099 discloses that the variation in the electrical resistance value of the planar heating element is improved by heating a mixed paper made of carbon fibers and bulbs to remove volatile matter immediately before coating with a thermoplastic resin. Width from 10Ω to 4Ω, variation % or 14.
It is described that it decreases from 8% to 3.9%.

However, even with this method, variations in the electrical resistance values of the sheet heating elements are still large.

Therefore, an object of the present invention is to provide a planar heating element that exhibits stable heating characteristics with little variation in electrical resistance.

Structure of the Invention In order to achieve the above object, the inventors of the present invention have conducted intensive studies and found that when using a carbon film as a heat generating base material, a planar heat generating system that exhibits stable electrical resistance with almost no variation is possible. The present invention was completed based on the discovery that the present invention can be obtained using the following methods. That is, the present invention provides a planar heating element in which a carbon film is coated with an electrically insulating resin.

The carbon film used in the planar heating element of the present invention may be any carbon film starting from polyacrylonitrile, rayon, phenol resin, cellulose, pi-soti, or the like.

The carbon film can be produced by forming the starting material that can be carbonized or graphitized into a film shape using an extrusion method or the like, and then subjecting it to carbonization or graphitization treatment. In addition, when pitch is used as a raw material, it is preferable to manufacture a carbon film by the method previously proposed by the present applicant (Japanese Patent Application No. 1-227740).

This method involves the production of a tape-shaped pitch-based carbon film by extruding pitch for spinning from a slit-type nostle, pulling the extruded planar pitch into a winding device, winding it up, infusibleizing the pitch, and carbonizing it. In the method, the surface is placed near both end surfaces in the width direction of the planar pitch whose width is decreasing due to traction, and in a direction symmetrical to an imaginary plane perpendicular to the plane in the longitudinal direction of the slit passing through the center point of the slit. A method for producing a tape-shaped pitch film by blowing an air stream having an outward component and a downward component before the pitch is sufficiently solidified, and then infusible and carbonizing the tape-shaped pitch film. ”.

More specifically, extruding mesophase or mesophase pitch including isotropic pitch from a slit-shaped nozzle,
The extruded planar pitch is pulled to a winding device and wound up.

At this time, in order to prevent necking down of the planar pitch, before the planar pitch is sufficiently solidified, an air stream such as air or nitrogen is introduced near both end faces in the width direction of the planar pitch whose width is decreasing due to traction. is sprayed at a speed of, for example, about 50 to 100 m/sec in a direction that increases the width of the planar pitch to produce a pitch film. Then, the obtained pitch film is
In accordance with the conventional method adopted when manufacturing carbon fiber,
It is infusible and carbonized to form a tape-like pitch-based film. Infusibility is achieved, for example, at 280 to 340°C in an oxygen atmosphere.
It is carried out at a certain temperature. The thinner the sheet-like pitch is, the shorter the time required for infusibility to be completed.

The infusible material thus obtained can be fired at a temperature corresponding to the desired electrical resistance of the carbon film. That is, as the firing temperature increases, the degree of carbonization and graphitization increase, resulting in a carbon film with low electrical resistance. Carbonization of infusible substances involves nitrogen, carbon dioxide,
1000-2000 in an atmosphere such as argon. It is carried out at a temperature of about 'C. Graphitization of the infusible material is carried out at a temperature of about 2,000 to 3,000°C in an atmosphere of argon or the like.

The electrical resistance value of the carbon film can be determined depending on the desired heat generation properties, and is, for example, 10-4 to 10-1Ω·c11.
A carbon film of about 100 liters can be used.

The thickness of the carbon film is, for example, about 5 to 100 μm,
Preferably it is about 10 to 40 μm.

Further, the width of the carbon film can be set according to the size of the planar heating element, for example, 0.5 to 50 mm, preferably 2 mm.
It is about 45 mm.

In the present invention, there are no particular limitations on the starting materials, manufacturing method, etc. of the carbon film used, and carbon films obtained by other methods can also be used.

As mentioned above, the specific resistance of the carbon film, which can be controlled by the firing temperature, varies depending on the shape of the carbon film, that is, the aspect ratio and length, but since it is film-like, the cross-sectional shape of the carbon film is approximately constant. . Furthermore, since the carbon film is fired at a high temperature as described above, unlike conventional mixed paper, no volatile matter is generated and there is almost no change in electrical resistance. Therefore, when a carbon film is used as a heat generating base material, the variation in electrical resistance is significantly smaller than when carbon fiber is used.

Examples of electrically insulating resins include thermoplastic resins such as polyethylene, polypropylene, ethylene-propylene copolymer, polyvinyl chloride, acrylic resin, styrene resin, polyester, nylon, polycarbonate, and fluororesin; silicone resin, and epoxy resin. Examples include thermosetting resins such as phenol resin, diallyl phthalate resin, polyimide, and polyurethane. A preferred electrically insulating resin is a thermoplastic resin. At least one of these resins can be used.

In the planar heating element of the present invention, the carbon film may be coated with an electrically insulating resin.

FIG. 1 is a perspective view showing an example of a sheet heating element of the present invention. The planar heating element (1) is composed of a carbon film (2) and an electrically insulating resin (3) covering the entire carbon film (2). Further, a lead (4) made of the carbon film (2) extends from the planar heating element (1).

In such a planar heating element (1), the heating base material is composed of a planar carbon film (2) that is baked at a high temperature and integrated, so it is different from the conventional heating base material made of mixed paper. In contrast, the electrical resistance hardly changes and it exhibits stable heat generation characteristics.

Moreover, since the lead (4) extends integrally with the carbon film (2), which is the heat generating base material, not only is there no need to connect the lead separately, but also breakage due to the lead (4) falling off is prevented. possible and highly reliable.

Note that an electrode made of a conductive metal may be attached to the carbon film.

FIG. 2 is a perspective view showing another example of the sheet heating element of the present invention. Note that the same elements as those of the planar heating element shown in FIG. 1 will be described with the same reference numerals. The planar heating element (11) of this example includes a carbon film (2) and a conductive adhesive (not shown) on both ends of the carbon film (2) in the width direction.
Metal wire (14a) as an electrode attached to
14b), the carbon film (2) and the metal wire (1
4a) (14b) is composed of an electrically insulating resin (3) covering the entirety thereof.

FIG. 3 is a perspective view showing still another example of the sheet heating element of the present invention. The planar heating element (21) of this example includes a carbon film (2) and a metal film (24a) as an electrode, which is narrower than the carbon film (2) and laminated on the upper and lower surfaces of the carbon film (2). (24b), and an electrically insulating resin (3) that entirely covers the carbon film (2) and metal films (24a) (24b).

Note that the planar heating element only needs to have at least one carbon film coated with an electrically insulating resin.

Alternatively, it may have a laminated structure in which a plurality of carbon films are alternately laminated using the electrically insulating resin and the entire structure is covered with the electrically insulating resin. In this case, a plurality of laminated carbon films are converged from the end face of the planar heating element.
It may be extended as one lead. Furthermore, the leads may be separately connected to the carbon film as shown in FIGS. 2 and 3.

The planar heating element of the present invention can be produced by, for example, bonding an electrically insulating resin film on both sides of a carbon film by thermocompression, cooling the heating element to solidify it, and cutting it into a predetermined length. Can be manufactured.

FIG. 4 is a schematic diagram showing an apparatus for manufacturing a planar heating element according to the present invention.

In this example, the carbon film (31) serving as the heat generating base material is
It is supplied between a pair of heating pressure rollers (33a) and (33b) via a pair of rollers (32a) and (32b). In addition, each heating pressure roller (33a) (33b),
Electrically insulating thermoplastic resin film (34a) (34b
) is continuously supplied, and a pair of heated pressure rollers (33a)
(33b), both sides of the carbon film (31) are continuously thermocompressed with thermoplastic resin films (34a) and (34b). Note that the thermoplastic resin film (
The width of 34a) (34b) is greater than the width of the carbon film (31).

Next, a pair of cooling rollers (35a) (35b) +
, : , Thermoplastic film (34a) bonded with heat and pressure
(34b) is cooled and solidified to a certain thickness, and then cut into a predetermined length by a cutter (36). By exposing the carbon film (31) from both ends of the heating element obtained by cutting, the planar heating element shown in FIG. 1 is obtained.

In such a manufacturing method, a carbon film (31) and an electrically insulating thermoplastic resin film (34a) (34b)
Since this method is used, planar heating elements can be manufactured continuously.

In addition, the sheet heating element can be manufactured not only by the method described above, but also by a method of coating the entire carbon film with an electrically insulating resin, such as hot melt coating, dipping in molten resin or resin liquid, etc. can.

[Effects of the Invention] Since the planar heating element of the present invention uses a carbon film as a heating base material, it exhibits stable heating characteristics with little variation in electrical resistance.

[Examples] The present invention will be described in more detail below based on Examples.

Example: Coal-based mesoface pitch was melted, 15 mm x 0.1
A pitch film was produced by extruding from a nozzle having a 5 mm slit and rapidly cooling.

Next, the pitch film was heated in air at about 300°C to make it infusible, and then carbonized at 1500°C in a nitrogen gas atmosphere to obtain a carbon film with a thickness of 38 μm and a width of 7°5 mm. The electrical specific resistance of the carbon film is 3.0XI
It was O''Ω・cm.

A planar heating element was produced using the obtained carbon film and a polypropylene film having a thickness of 100 μm using the apparatus shown in FIG. That is, a polypropylene film with a thickness of 100 μm is supplied on both sides of a running carbon film, and after being thermocompressed using a heating pressure roller at a temperature of 150°C, it is cooled using a cooling roller at a temperature of 30°C to solidify to a constant thickness. A large number of planar heating elements were produced by cutting the sheet into lengths of 100c+n using a cutter.

Then, the electrical resistance of the obtained planar heating element was measured, and the average value, variation width, and variation % were determined. The results are shown in the table below.

As is clear from the table, there is almost no variation in electrical resistance in the planar heating element using carbon film.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of the sheet heating element of the present invention, FIG. 2 is a perspective view showing another example of the sheet heating element of the invention, and FIG. 3 is a perspective view of the sheet heating element of the invention. FIG. 4 is a perspective view showing still another example. FIG. 4 is a schematic diagram showing an apparatus for manufacturing a sheet heating element of the present invention. (1) (I 1) (21) ... Planar heating element, (2
)...Carbon film, (3)...Electrical insulating resin, (31)...Carbon film,

Claims (1)

[Claims] A planar heating element in which a carbon film is covered with an electrically insulating resin.