JPS6248352B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an electric heating element comprising a short fibrous conductive base material and an electrically insulating matrix.

Composite materials, which are made by filling and mixing an appropriate amount of conductive fine particles into an electrical insulator such as a synthetic resin, form an electrical circuit network through contact between the conductive particles and an extremely thin layer of matrix interposed between the particles. ,
When energized, so-called Joule heat is generated. Conventionally, as this type of heating element, there is a planar heating element formed by filling and mixing conductive particles, carbon black, into synthetic resin, and it has already been used in roof heating for snow melting, transport pipes for chemicals, and It is used to keep tanks warm or as a heater for greenhouse cultivation.

In this type of electric heating element, the resistance value is mainly determined by the filling ratio of the conductive filling material, and since the contact between the conductive filling materials is point contact with a spherical surface, it has a relatively high specific resistance. The material is obtained, but by sufficiently mixing the conductive filling material, the countless contact points between the materials are uniformly distributed within the heating element, and the heat generation at the materials and their contact points equalizes the overall heat generation amount. This is advantageous in that the temperature distribution is substantially constant.

On the other hand, an electric heating element in which carbon fiber cloth is mixed in a ceramic matrix or the like and fibrous carbon is used as a resistance element has already been proposed (see Japanese Patent Publication No. 10781/1983). However, in such an electric heating element, since the matrix is filled with bundles of carbon fibers in a focused state, the fiber bundles come into contact with each other, and therefore a relatively small number of contact parts are locally inside the resistor. As a result, not only the temperature distribution becomes uneven, but also the electrical resistance increases unless a large amount of carbon fiber is filled, and furthermore, the variation in the electrical resistance value increases.

The present invention improves the electrical and thermal properties of such an electrical heating element using carbon fibers, and while using a fibrous conductive filling material, it has the same electrical conductivity as when using fine particles such as carbon black. Numerous points of contact between the filling materials are uniformly distributed within the heating element, and the amount of heat generated from the filling materials and those contact points is equalized overall, resulting in a nearly constant temperature distribution. The present invention provides a method for easily manufacturing a heating element.

Further, the present invention exhibits an excellent reinforcing effect by uniformly dispersing the fibrous conductive filling material having the above-mentioned electrical properties, and provides an excellent mechanical effect that cannot be obtained with the previously proposed heating element. The present invention provides a manufacturing method capable of obtaining a composite heating element with high physical strength. Heating elements with such mechanical reinforcing properties can be used as structural surface heating elements in new fields of electrical heat generation, such as for use in wall and floor materials of houses, giving them the function of panel heaters. It enables the use of the body.

Since the method of the present invention for achieving the above-mentioned purpose uses short fiber-like conductive filler material, the distribution of the conductive filler material can be easily uniformized by kneading, etc., as in the case of using conventional conductive particles. Therefore, short fibers as a conductive filler material are continuously split using a flying device, and the separated single fibers are flown in the air. Continuously supplying an electrically insulating matrix to the passage and mixing it with flying short fibers,
By continuously collecting and fixing them on a collection zone, a short fiber composite heating element in which the short fiber conductive filler material is uniformly distributed within the matrix is obtained.

As the matrix of the short fiber composite heating element of the present invention, any organic or inorganic material can be used as long as it is an insulating material that can be molded as a composite material and has a relatively high heat distortion temperature. For example, Epoxy resin, glass, etc. can be used.

Further, as the conductive filling material, a conductive fibrous material such as carbon fiber, copper, or nichrome wire, that is, a linear material having a relatively large length relative to the diameter can be used. In order to obtain a particularly strong electric heating element, it is effective to use a conductive filling material with a large reinforcing effect such as carbon fiber, but it is also effective to use a non-conductive reinforcing fiber such as glass fiber as the conductive filling material. It can also be filled into the matrix together with the material in the required proportions. The mixing ratio of the conductive filling material and the non-conductive reinforcing fiber, and the composite ratio of these filling materials and the matrix are appropriately determined according to the required performance of specific resistance and mechanical strength necessary for the electric heating element. It will be done.

Furthermore, when non-conductive reinforcing fibers such as glass and vinylon are mixed and filled, the friction between the short fibers as the conductive filling material and the non-conductive fibers prevents the fibers from moving during molding. , it is possible to improve molding workability and uniformity of fiber distribution.

1 and 2 show an example of a short fiber composite heating element manufactured according to the present invention, in which a heating plate 1
is a short fibrous conductive filler material 2 such as carbon fiber,
Each of the fibers is defibrated and separated into single fibers, and filled in a matrix 3 made of synthetic resin or the like, with countless contact points between the single fibers uniformly distributed. Incidentally, conductive wires 4 for flowing current can be buried in both ends of the heat generating plate 1 as necessary.

The short fiber-shaped conductive filling material 2 can be unoriented, but by orienting it in a certain direction, the electrical properties in the plane of the heating plate can be given directionality.

In the heat generating plate described above, the distribution of the short fibers as the conductive filling material in the thickness direction needs to be uniform except for the surface layer portion where electrical insulation is required.

In addition, it is generally desirable that the distribution of the conductive short fibers in the plane direction be uniform, but for example, in order to suppress the amount of heat generated near the conductive wire 4, it is preferable to fill the portion close to the conductive wire 4 with a large amount. The distribution can be arbitrarily changed depending on the purpose, such as reducing the electrical resistance.

FIG. 3 shows an outline of an apparatus for carrying out the method of the present invention, in which conductive fibers 12 supplied to an inlet 13 of a flying device 11 are separated by a guiding roller 14 and a separating flying roller 15. The fibers are guided to the contact point, where they are simultaneously cut and split by the splitting flying roller 15 that rotates at high speed, and the fibers are continuously flown into the air flow in the state of being separated into single fibers. It is supplied through the moving path 16 from the discharge port 17 at the tip onto the belt-shaped collection band 18 and collected by the collection band 18 . If the discharge port 17 is formed into a slit shape having a gap sufficiently smaller than the length of the flying short fibers, the short fibers passing through the discharge port 17 can be oriented in the longitudinal direction of the slit and accumulated.

On the other hand, a supply device 20 for the matrix 19 made of synthetic resin or the like supplies the matrix 19 filled in a hopper 21 into the air flow of the flight passage 16 through a supply port 22 that opens at the starting end of the flight passage 16. By supplying the matrix to this flying path, short fibers and matrix are collected on the collection zone 18 in a uniformly mixed state to form a layered mixture 23, and as the collection zone 18 moves, the short fibers and the matrix are collected on the collection zone 18 in a uniformly mixed state. It also moves in the direction of the arrow.

Next, this layered mixture 23 is sent to a heating device 24 disposed along the collection body 18, where it is heated to a temperature higher than the softening point of the matrix 19 and fused, and is heated with a roller 25 or the like as necessary. Pressure is applied to form a band-shaped short fiber composite heating plate 26. When the layered mixture 23 is heated and pressurized, a sheet-like material is added to the upper and lower surfaces or either surface for surface protection, insulation improvement, or surface finishing when used as wall material or floor material. It is also possible to polymerize 27 in advance and integrate them into the short fiber composite heating plate 26 during the heating and pressurization described above.

In the above-mentioned apparatus, the supply port 22 of the matrix 19 may be opened just above the splitting flying roller of the flying device 11, and the short fibers and the matrix may be flown into the flying path 16 in a mixed state. Also,
If necessary, the number of flying devices can be increased and thicker ones can be manufactured.

Next, examples of the present invention will be shown.

Epoxy resin was used as the matrix and carbon fiber (thickness 10μ) was used as the conductive filling material.The average fiber length of the carbon fiber was
It was divided into 30 mm single fibers to create a non-oriented web. A matrix prepared by mixing 100 parts by weight of epoxy resin with 20 parts by weight of aromatic amine as a curing agent is impregnated into the above web, and after vacuum degassing, the pressure is 10 to 15%.
Kg/cm ² , pressed at a temperature of 150℃, thickness 1.2mm
A plate-shaped heating element was molded.

FIG. 4 shows the electric resistivity in the plane direction and the thickness direction of a plate-shaped composite heating element with a carbon fiber filling rate of 2.5 to 20% (Vo1.%).

In addition, Figures 5a and b show the relationship between the heat flow rate and current application time when the current amount is 1.5A and 3.0A, and when the carbon fiber filling rate is 5, 10, 15, and 20% (wt.%). It shows about.

As is clear from these experimental results, in composite heating elements with a carbon fiber filling rate in the range of 5% to 20%,
Its volume resistance value is 0.3 to 0.03Ω in the plane direction.
cm, and a thickness in the range of 10 ⁶ to ^{10 2} Ω·cm was obtained.

Further, these heating elements had a heat flow rate of 600 to 100 Kcal/m ² h under a current of 1.5 A, and a heat flow of 800 to 400 Kcal/m ² h under a current of 3.0 A.

As described above, the specific resistance of the short fiber composite plate-shaped heating element is much larger in the thickness direction than in the planar direction, indicating insulating properties. This brings about advantages such as easy prevention of electrical leakage from the heat generating surface during use.

Figures 6a and 6b show an experimental example of the reinforcing effect when carbon fiber as a conductive filler material is mixed with glass fiber as a non-conductive reinforcing fiber. Figure a shows the relationship between the carbon fiber filling rate, bending strength, and bending elastic modulus in the plate-shaped heating element described above, and figure b shows the relationship between the carbon fibers in the plate-shaped heating element and the matrix (epoxy resin). E glass fiber (thickness 10μ, average fiber length 30mm) until the total fiber amount is 20% (Vo1.%)
The graph shows the bending strength and elastic modulus when carbon fiber filling rate is 20% in Figure 6a.
The case corresponds to the case in which the proportion of carbon fiber is 100% in Figure b. As can be seen from Figure 5, the carbon fiber filling rate of the heating element is determined depending on the required heat flow rate, but the mechanical strength of the heating element in that case is as shown in Figure 6. From the relationship between a and b, it can be seen that it can be sufficiently increased by mixing reinforcing fibers. Therefore, it is possible to easily obtain a heating element in which both the heat flow rate and the mechanical strength maintain the set values.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway plan view showing an example of the structure of a short fiber composite heating element produced according to the present invention, FIG. 2 is a side sectional view thereof, and FIG. Configuration diagram showing an outline through a side cross section, No. 4
Figures 5a and 5b and 6a and 6b are graphs showing experimental results for the short fiber composite heating element of the present invention. 2... Conductive filling material, 3, 19... Matrix, 11... Flying device, 12... Conductive fiber,
16...Flight path, 18...Collector, 23...Layered mixture, 26...Short fiber composite heating element.

Claims (1)

[Claims] 1 A flying device continuously splits short fibers as a conductive filler material and flies them in the air in a defibrated and separated state into single fibers, and an electric current is applied to the flying path of the short fibers. A layered mixture in which an insulating matrix is continuously supplied and mixed with flying short fibers, and these are continuously collected on a collection zone that moves approximately horizontally, forming a layered mixture on the collection zone. 1. A method for producing a short fiber composite heating element, characterized in that the short fiber composite heating element is obtained by fixing the body by fusion of a matrix or the like to obtain a short fiber composite heating element in which numerous contact points between single fibers are uniformly distributed.