JP2854864B2 - Surface heating element made of carbon fiber / carbon composite - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a carbon fiber / carbon composite surface heating element that generates heat by Joule heat.

(Conventional technology and its problems) In technical fields such as formation of various functional thin films on the surface of a base material, diffusion of impurities into the base material, heating and melting of a substance contained in a crucible, in a predetermined atmosphere, Heating an object to be heated, such as a substrate, is performed under a predetermined temperature condition. In this case, a resistance heating element that generates Joule heat is generally used as the heating means.

At the time of this heat treatment, the surface temperature distribution of the base material and the like are important control targets, for example, in relation to the characteristics required for the formed thin film, the film forming speed, and the like.

For this reason, the heating element is required to have a wide variety of materials and shapes, and the conditions for supplying power to the heating element are appropriately selected.

As a constituent material of the heating element, a refractory metal such as tungsten or molybdenum or graphite is employed. Also,
The shape of the heating element is also designed in an appropriate shape, for example, a plate shape, a tubular shape, or the like in relation to a required temperature condition.

However, in the case of the high-melting-point metal heating element, it tends to be thermally deformed and lacks dimensional stability at high temperatures, and thus its shape changes from its initial shape in the process of repeated use. As a result, the aspect of heating changes, and there arises a problem that the temperature of the substrate or the like cannot be maintained at a predetermined value.

On the other hand, a heating element made of graphite (or carbon) does not cause the above-described thermal deformation and has an advantage of excellent corrosion resistance, but has a problem of low mechanical strength. In addition, there is a problem that it is difficult to process into a desired heating element shape at the time of manufacturing because of brittleness.

In general, a heating element that generates resistive heat has a small cross-sectional area for current conduction. For example, the overall shape is thin (in the case of a plate-shaped heating element).
In this case, the resistance can be increased and the compactness can be achieved.However, when the graphite heating element is made thinner, the mechanical strength of the graphite is small. It may be damaged during mounting. Therefore, in the case of a graphite heating element, its thickness is usually 10 to 20 mm.
It has to be to the extent.

As described above, graphite is useful as a material for a heating element because of its excellent heat resistance and corrosion resistance. However, it should be a thin heating element because of its low mechanical strength and brittleness. There is a problem that can not be.

On the other hand, a carbon fiber / carbon composite (hereinafter, referred to as “C / C composite”), which is a composite in which a matrix is carbon (or graphite) and a reinforcing material is made of carbon fiber (or graphite fiber), is known. Since this C / C composite has light weight, high heat resistance, and excellent mechanical strength, attempts have been made to use it as a heating element.For example, in JP-A-56-134565, It is disclosed that a laminated cured body of a thermosetting resin and a cellulose sheet is graphitized to form a highly anisotropic carbon block, which is used as a heating element.

In Japanese Patent Application Laid-Open No. 58-110411, a mixture of a thermosetting resin and a carbon fiber is fired in a thin ceramic pipe to form an anisotropic C / C composite, which is used as a heating element. Further, Japanese Patent Application Laid-Open No. 58-126510 discloses the use of a C / C composite filament as a resistance heating element used for reinforcing an optical fiber connection portion. Each of the heating elements disclosed herein has a higher mechanical strength than those made of graphite, but is a rod or a striated body and is not formed as a plane or as a whole as a plane. is not.

The present invention solves the above-mentioned problems of the conventional heating element, has a small variation in the amount of heat generated on the heating surface, has a large mechanical strength and is less likely to be damaged, and has a small size that is precise and complicated in manufacturing. It is intended to provide a C / C composite surface heating element that can be processed.

(Means for Solving the Problems) In order to achieve the above object, the C / C composite surface heating element of the present invention has a configuration in which the configuration is formed in a plane or as a whole as a plane, and Regardless of the location, the carbon fibers are arranged uniformly and the electric resistance is substantially the same.

 The heating element of the present invention is made of a C / C composite.

The heating element of the present invention is formed in a plane or as a plane as a whole. The surface shape is a flat surface or a curved surface. Here, examples of the curved surface include a cylindrical curved surface, a hemispherical curved surface, a parabolic curved surface, and a truncated conical curved surface. The overall shape of the heating element, that is, the shape of the heating surface, is determined according to the purpose of use of the heating element.

However, in the heating element of the present invention, it is necessary that the carbon fibers are uniformly arranged and the electric resistance is substantially the same regardless of the shape of the heating surface.

In the present invention, the portion in the heat generating surface refers to a portion having a certain extent in the heat generating surface and having such a size as to be visually recognized in a certain size visual field.
For example, it does not mean a point-like minute portion. Also,
When a circular woven fabric or a helical circular woven fabric described later is used as the carbon fiber, the woven density is dense on the inside and coarse on the outside, but the state of the coarse and dense is not so remarkable. In such a case, the arrangement pattern of the carbon fibers is assumed to be substantially the same.

If the arrangement pattern does not satisfy the above condition, that is, if the arrangement pattern of the carbon fibers is different between the portions on the heating surface, the electric resistance between the portions will not be the same, and as a result, Joule fever is different. Therefore, if the influence of heat radiation is not taken into consideration, temperature unevenness occurs on the heat generating surface.

In order to make the arrangement pattern of the carbon fibers the same or substantially the same between the respective portions in the heating surface, the carbon fibers may be arranged in the matrix carbon by a method described later during the production of the heating element. .

That is, the heating element of the present invention can be manufactured by the following method.

The first method is a prepreg method. In this method, first, a prepreg in which a carbon fiber to be described later is impregnated with a thermosetting resin such as a phenol resin or a furan resin of a B stage or a carbonizable substance such as a pitch is used. It is laminated or wound as many times as necessary to shape it into a desired heating element shape.

Next, the obtained shaped body is fired in a temperature range of 600 to 3000 ° C. under an inert gas atmosphere, and the carbonizable substance in the prepreg is pyrolyzed to be carbonized or graphitized, and C / C
A heating element is obtained as a composite. However, since the obtained heating element is porous and has a low density, it is impregnated with the carbonizable substance again, and the operation of firing is repeated a plurality of times to increase the density to a predetermined density. preferable.

The second method is a resin impregnation method. This method is a method of laminating or winding a raw carbon fiber itself to shape it into a heating element, impregnating it with the above-mentioned carbonizable substance, and firing it. As in the case of the prepreg method, it is preferable to repeat the impregnation and firing as necessary times to increase the density.

The third method is a CVD method. In this method, the raw carbon fiber is shaped into a heating element shape in the same manner as in the resin impregnation method, and this is heat-treated in a stream containing hydrocarbons such as methane and propane at a high temperature of 1000 to 2000 ° C. In this method, a required amount of pyrolytic carbon (or graphite) is deposited on the surface of the carbon fiber to form a C / C composite, which is used as a heating element.

The fourth method is a method that can be called a blend method applicable to short fibers having a single yarn diameter of about 3 to 15 μm and an aspect ratio of several hundred. In this method, various molding methods are applied to the mixture of the short fibers and the carbonizable substance,
After being formed into a heating element, it is fired.

In the first to fourth methods described above, the preliminarily shaped heating element is fired, but after the firing, machining such as cutting may be performed to obtain a desired heating element shape.

The carbon fibers used in these methods include the following forms.

First is the woven fabric. The woven fabric may be any of a plain woven fabric, a twill woven fabric, and a satin woven fabric. Also, JP-A-51-58568,
The circular woven fabric or spiral circular woven fabric disclosed in JP-B-59-32291 can be used. The above-mentioned woven fabric is shown in FIG. 13 which is a plan view of the whole, FIG. 14 and FIG. 15 which are partially enlarged views, and as shown in FIG. The continuous warp and the weft constitute a plain weave design or a ridge weave design, and a plurality of warps are arranged in the circumferential direction.
In the portion where the warp intersects, it intersects the warp at a substantially right angle, is generally arranged in the radial direction of the circle drawn by the warp, and the portion of one or more circumferences is a continuous layer of the same circle. It is characterized by being formed in.

What kind of structure and what kind of fabric to use may be determined according to the shape of the heating element, required characteristics, and the like. For example, in the case of a heating element having a relatively complicated shape, it is preferable to use a satin woven fabric having excellent drapability. One of these fabrics may be used, or a plurality of these may be laminated. In the case of laminating, if the warp or weft direction is slightly shifted between adjacent fabrics (for example, 15 ° or 30 ° each), the anisotropy is improved and the resistance value is reduced. It becomes pseudo-isotropic inside. However, the woven fabric can be used by laminating the warp or the weft in the same direction.

Second is a defibrated mat. This is one in which each short carbon fiber is randomly oriented, and originally has pseudo-isotropic properties.

Third is a chopped strand mat. this is,
This is a mat formed by cutting a bundle of carbon fibers into a predetermined length and randomly orienting each cut bundle, and also has a pseudo-isotropic property.

Fourth is a swirl mat. This is not a short fiber but a fiber that has been fibrillated or has not been fibrillated, or a continuous fiber (or a continuous fiber bundle) that is randomly oriented.

Fifth is a tubular braid. It is rich in its elasticity in the radial and longitudinal directions. It can be used as it is, or it can be used by crushing it flat.

The sixth is a unidirectionally aligned continuous fiber body which is aligned in one direction in parallel with each other and in a tape or sheet shape. This usually includes B to maintain the alignment.
The stage is impregnated with a thermosetting resin such as a phenol resin or a pitch. Separately, it is called a unidirectional prepreg.

A seventh aspect is a short fiber having a small aspect ratio,
It is used at the time of producing the heating element by the above-mentioned blending method.

The defibrated mat, chopped land mat,
The swirl mat, the tubular braid, and the one-way aligned body may also be used alone, or may be used by lamination or winding. When the one-way aligned body is used by laminating or winding, it is preferable that the unidirectional aligned body be pseudo-isotropic as in the case of the woven fabric.

In the case where the carbon fibers of the above-described first to sixth embodiments are laminated and used, if the stitches are integrally stitched by using, for example, single-ring stitching using a thread of the carbon layer fiber, the delamination strength and the interlaminar shear of the heating element are obtained. It is preferable because strength and impact strength are improved.

In the present invention, when carbon fibers are used by laminating or winding, the same types and forms of carbon fibers are used.

Electric resistance of the heating element of the present invention, the type of carbon fiber used, the form, the manner of arrangement, the content, the firing temperature when making the carbon fiber, the type of matrix carbon, the bulk density of the heating element, C It changes depending on the firing temperature when forming the / C composite.

(Example) Hereinafter, the heating element of the present invention will be described in more detail with reference to the attached drawings.

1 to 4 exemplify a heating element having a planar shape as a whole. FIG. 1 shows an energization path, that is, a non-inductively wound disk-shaped heating element in which the heat generating portions are arranged symmetrically to the left and right, and FIG. 2 shows a disk in which the energizing path (heat generating portion) is arranged in a spiral shape. Heating element. FIG. 3 shows a square plate-shaped heating element in which the energizing path (heating portion) is bent in a zigzag manner, and FIG. 4 shows the area of the energizing path (heating portion) in FIGS.
A square plate-shaped heating element larger than that of the heating element illustrated in the figure is shown. In these heating elements, the surface of the current path functions as a heating surface. The plate-shaped heating element shown in FIGS.
For example, it can be manufactured as follows. In other words, the carbon fiber woven fabric, unidirectionally aligned body, and carbon fiber defibrated mat, chopped strand mat, swirl mat, and carbon fiber short fiber described above which are laminated so as to have a similar isotropic shape are used. In any of the methods, a thin C / C composite plate may be manufactured, and the thin C / C composite plate may be cut using a saw, for example, to cut off portions other than the energized path. For example, in the case of the heating element 1 shown in FIG.
Manufactures a C composite disc and passes it with a thread saw.
a, It is manufactured by cutting off other parts except for the terminals 1b and 1b. In the production of the disc-shaped heating element as shown in FIGS. 1 and 2, the above-mentioned circular fabric or spiral circular fabric can be used as the carbon fiber.

In the case of a heating element having a narrow energizing path as shown in FIGS. 1 to 3, a pattern corresponding to the energizing path is formed by using a tape-shaped one-way aligning body, and the pattern is fired. May be.

In these heating elements, the carbon fibers form the same or substantially the same arrangement pattern at any position when viewed through a direction perpendicular to the heating surface.

Therefore, since the electrical resistance is the same or substantially the same in any part, the generated Joule heat is the same or substantially the same in any part,
As a result, if the influence of heat radiation is not taken into consideration, the temperature unevenness in the heat generating surface is eliminated or the variation is reduced.

Further, since this heating element is a C / C composite, its mechanical strength is large, and it can be processed into a thin and long shape.

The heating element as shown in FIG. 1 to FIG.
It can be used when a superconducting thin film is formed on a substrate surface by a CVD method. That is, when a thin film of a superconducting material having various compositions is formed on a substrate surface by the CVD method, the surface temperature of the substrate is set to about 800 to 1000 ° C., and the surface temperature varies depending on the composition of the material to be formed. An operation of controlling the in-plane variation of the temperature to within ± 5 ° C. is performed. At this time, in order to set the surface temperature of the base material within the above range, it is necessary that the heating element to be used is to generate resistance heat to a temperature of up to about 1200 ° C., and furthermore, the reactive gas used is a CVD method. It is necessary to have resistance to erosion.

FIGS. 5 to 7 exemplify a heating element which is effective as a heating means for a tubular furnace, in which the heating surface has a cylindrical curved surface or a cylindrical curved surface as a whole. FIG. 5 is a cylindrical heating element itself, and FIG. 6 is a heating element having a separation slit formed in the longitudinal direction of the cylinder and having an energizing path extending in the longitudinal direction while making a U-turn at this slit position. The seventh
The figure shows a helical heating element in which the energization path extends helically in the longitudinal direction.

In the production of these heating elements, the woven fabric of carbon fiber, a one-way aligned body, a defibrated mat of carbon fiber,
A cylindrical C / C composite is manufactured using a chopped strand mat, a swirl mat wound, or a carbon fiber braid. In the case of the heating element shown in FIGS. 6 and 7, the C / C composite is used. A cutting process is performed to form a target energization path. The mixture of the carbon fiber and the carbonizable substance may be formed into a cylindrical shape, cut into a C / C composite, and then subjected to cutting. In the production of a cylindrical heating element, a filament winding method can be applied at the time of molding the cylinder. Further, in the case of the spiral heating element shown in FIG. 7, the spiral heating element can be manufactured by forming a spiral with a tape-shaped unidirectionally aligned body and firing the spiral.

Also in this case, as in the case of the heating element shown in FIGS. 1 to 4, the carbon fibers are uniformly arranged on any part of the heating surface. Therefore, since the electrical resistance is the same or substantially the same in any of the portions, the generated Joule heat is the same or substantially the same in any of the portions. As a result, the influence of heat dissipation must be taken into account. In this case, the temperature unevenness in the heat generating surface is eliminated or the variation is reduced.

FIG. 8 to FIG. 10 exemplify a heating element whose heating surface is a truncated conical curved surface and which is effective for changing the degree of heating of the object to be heated in the vertical direction. FIG. 8 shows a heating surface on the entire surface, FIG. 9 shows a heating element in which slits are alternately formed in the vertical direction from upper and lower ends, and a current path is a heating element which is bent zigzag up and down. FIG. The heating element is a heating element in which slits in the circumferential direction alternately enter and sandwich the energization path along the circumferential curved surface.

The heating element in FIG. 8 is obtained by drawing and shaping a carbon fiber woven fabric, a woven fabric cut into a shape corresponding to a planar development view of the heating element, a defibrated mat, a chopped strand, a swirl mat, a one-way aligned body, a short It can be produced using a mixture of fibers and a carbonizable substance (by a blending method) or a laminate in which they are appropriately combined. As a woven fabric used for drawing and shaping, a satin woven fabric is preferable because of its good drapability. The above-mentioned circular woven fabric or spiral circular woven fabric is suitable as a fiber material of the heating element.

9 and 10 may be manufactured by cutting the heating element of FIG. Further, it can also be manufactured by forming a green molded body having a path corresponding to an energizing path pattern using a tape-shaped one-way aligned body and firing the green molded body.

FIG. 11 exemplifies a half of a heating element that can be incorporated in a spherical furnace, and its heating surface is a hemispherical curved surface. Twelfth
The figure exemplifies a heating element for a calibration furnace at the time of infrared temperature measurement, and its heating surface forms a parabolic curved surface.

These heating elements can be manufactured in the same manner as in the case of the heating element having a truncated conical surface shown in FIGS. 8 to 10.

Note that the present invention is not limited to the above embodiment,
Various modifications are possible. That is, the C / C composite can change not only the electrical resistance but also the thermal conductivity by changing the arrangement pattern of the carbon fibers,
Also in the case of the heating element of the present invention, by setting the carbon fibers to have a predetermined arrangement pattern, it is possible to adjust the amount of Joule heat generated from the heating element and to adjust the heat conduction amount of the heating element. Become.

(Effects of the Invention) As is apparent from the above description, the surface heating element made of carbon fiber / carbon composite of the present invention has a configuration in which the surface or the entire surface is formed in a planar shape, and any part in the heating surface. Taking into account, the carbon fibers are arranged uniformly, so that the current path, that is, the electric resistance on the heat generating surface is the same or substantially the same at any part, and the generated Joule heat is also between the parts. The same or substantially the same.

Also, C / C composites have high mechanical strength,
Further, since it is not as brittle as graphite, processing is easy, and the heating element can be made thin. In addition, there is little fear of damage or the like. As a result, the total resistance of the heating element can be increased, so that even if the energization load is small, it can be heated to a required high temperature. And since the current-carrying load is small, not only the heating element itself, but also the power supply system, electrode system,
The control system can be made compact.

Furthermore, even when the shape of the object to be heated is complicated, it can be shaped into a heating element at a stage before firing, that is, at a stage where the carbon fiber and the matrix have flexibility, and
Even after being made into a C / C composite, it can be processed precisely without fear of breakage because of its high mechanical strength and not so brittle.

Furthermore, since the heat conductivity of the C / C composite is higher than that of graphite, the heating element of the present invention can start operation at a high temperature rising rate, that is, at a high temperature when used.

[Brief description of the drawings]

1A, 2 to 4 are plan views showing the heating element of the present invention, and FIG. 1B is a plan view of each part (A to E) of FIG. 1A when a carbon fiber fabric is used. )), A partially enlarged view showing a state in which the carbon fibers are uniformly arranged, FIGS.
12 is a perspective view showing still another heating element of the present invention, FIG. 13 is a plan view of the entire spiral circular fabric, FIGS. 14 and 15 are partially enlarged views thereof, and FIG. It is a sketch which shows the state extended. 1 ... heating element, 1a ... energizing path, 1b ... terminal.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takashi Nakajima 3-19-14 Chuo, Ota-ku, Tokyo Inside Hanawa Thermoelectric Metal Co., Ltd. (72) Inventor Shigeru Kaito 1-1-1 Sonoyama, Otsu City, Shiga Prefecture Toray Shiga Works Co., Ltd. (72) Atsushi Kitamura 1-1-1, Sonoyama, Otsu City, Shiga Prefecture Toray Shiga Works Co., Ltd. (72) Inventor Jun Haneda 2-2-1 Nihonbashi Muromachi, Chuo-ku, Tokyo Toray (56) References JP-A-63-24582 (JP, A) JP-A-58-110411 (JP, A) JP-A-56-134565 (JP, A) (58) Fields surveyed ( Int.Cl. ⁶ , DB name) H05B 3/20 373

Claims (2)

(57) [Claims] The present invention is characterized in that carbon fibers are uniformly arranged and the electric resistance is substantially the same regardless of which part is taken in the heating surface. Surface heating element made of carbon fiber / carbon composite. 2. The carbon fiber according to claim 1, wherein said carbon fiber is in the form of a woven fabric, a defibrated mat, a chopped strand mat, a swirl mat, a tubular braid, or a one-way aligned body. Surface heating element made of carbon fiber / carbon composite.