JPH1092556A - Thermally stable planar heating element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress local heat radiation and provide heat radiation uniform in the whole surface area by using a fiber sheet consisting of evenly mixed short fibrous pulp of a non-conductive fiber which is not thermally melted and short fibrous chops of carbon fiber. SOLUTION: This planer heating element is produced by combining short fiber pulp of non-conductive fibers, which is not thermally melted, with carbon fiber chops and impregnating the resultant mixture with resin. The obtained mixture is formed into paper, sheets, mats, nonwoven cloth, fabrics, etc. Besides carbon fibers, metal fibers are supposed to be usable but in the case metals are used, the electric resistance is varied during the use due to rust and oxidation and thus metals are not preferable. In the sheet, short fiber chops of carbon fiber are uniformly dispersed and fixed without being partly concentrated. Consequently, the electric resistance value can be set freely by changing the contact of the short fiber chops of the carbon fiber. That is, the electric resistance is lowered and the highest achievable temperature can be heightened by increasing the content. Furthermore, based on the performance demanded, the non- conductive fiber pulp is mixed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called sheet-like heating element of a sheet-like type which is uniformly heated over the entire surface by energization. The present invention relates to a planar heating element which is less likely to cause a short circuit in the conductive heating section even when used for a long time.

The planar heating element of the present invention has excellent long-term stability during heating, and is particularly suitable for buildings used continuously for a long period of time, and is useful for building inner walls, floors, roofs, desk chairs and the like. Used for furniture, etc. Conventionally, it is often carried out with a hot water pipe or the like, but it is suitable for providing a simple heat generation system without problems such as initial cost, repair, and loss of startup time during operation.

[0003]

2. Description of the Related Art Various types of sheet-like sheet heating elements have been known. For example, a nichrome wire is used as a heating element, a material laid on paper or a sheet, a pipe-shaped heating element is bent and processed into a planar shape, and a carbon is used as an electric heating element on a substrate such as a film or sheet. There were coated or printed materials such as paints and inks to which conductive particles such as black were added, and products uniformly dispersed in a thermoplastic resin or the like.

[0004] As such a planar heating element,
A combination of carbon fiber and pulp is disclosed in, for example,
Japanese Patent Application Laid-Open No. 50306 and Japanese Patent Application Laid-Open No. 8-17560 are described.

[0005]

However, these heating elements have various problems related to shape stability and contact points. That is, the pulp used in combination with the carbon fiber is not limited to any type.For example, when a pulp having a heat melting property such as polyethylene is used as the pulp, the carbon fiber and these polyethylene pulp are In some cases, heat welding may occur, causing inconvenience in contact points and conductivity.

[0006]

Means for Solving the Problems The present inventors have considered the above problem, and have no local heat generation, generate uniform heat over the entire surface,
Furthermore, the present inventors have conducted various studies with the aim of developing a planar heating element which does not cause an accident such as a short circuit even when used continuously for a long period of time in a building or the like, and reached the present invention.

That is, the present invention provides a conductive heating element in which a fiber containing carbon fiber as an essential component is impregnated with a resin and a sheet heating element which requires an electrode band pair as an essential component. The present invention provides a planar heating element comprising a short fiber pulp of a non-conductive fiber and a short fiber chop of a curved carbon fiber which are not thermally melted, and using a fiber sheet in which they are uniformly mixed. is there.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a detailed description will be given. The planar heating element that uniformly generates heat over the entire heating section by energization may have, for example, a conductive heating section and a pair of electrode strips in a state where a conductive substance is dispersed or impregnated in a resin. By selecting a specific configuration, either one having a PTC function or one having no PTC function as used in the present invention can be obtained.

The element of the present invention is preferably a "planar heating element having no PTC function", for example, using a conductive fiber chop as a conductive substance, and
It can also be obtained by combining short fiber pulp of non-conductive fibers having no heat melting property and selecting those impregnated with resin.

[0010] The planar heating element can be obtained, for example, as follows. The conductive heating portion of the heating element is generally made of a sheet mainly composed of carbon fiber short fiber chops. The sheet can be used irrespective of its form as long as it can generate heat when energized.For example, papers, sheets, mats, nonwoven fabrics, woven fabrics, etc. made of various materials including short carbon fiber chops Material is suitable. Here, as the conductive fibers contained in the conductive sheet, short fibers having an aspect ratio of 50 or more are preferable. The fiber diameter is usually 5 to 20 μm.

Specifically, so-called non-woven fabrics, mats, and so-called papers made by the papermaking method, and so-called non-woven fabrics, mats in which the contact portions of random fibers are physically entangled, or the fibers are bound together by needle punch without using a binder. Sheets or woven fabrics woven from yarns containing carbon fiber short fiber chop fibers, such as carbon fiber short fiber chops from 2 to 10
Those containing 0% by weight can be used.

The present inventors have found that the conductive fiber contained in the sheet is a carbon fiber chop (short fiber), and that the short fiber pulp of a non-conductive fiber which is not melted by heat is most suitable. Was found.

That is, metal fibers can be used as the conductive fibers other than carbon fibers. However, in the case of metal fibers, the electric resistance value is small, and when the temperature required for use in a building or the like is usually obtained. Although it depends on the fiber diameter, uniform dispersion is difficult due to the small amount used. In addition, the metal may change its electric resistance value during use due to factors such as rust and oxidation. For example, carbon fibers that do not change over time are more suitable.

Further, it has been found that a more suitable planar heating element can be produced by using a carbon fiber chop having a fiber length of 1 mm to 200 mm as a short-fiber chop of carbon fiber as a current-carrying heating part.

In the case of carbon fiber, if the fiber length is less than 1 mm, the PTC function tends to be exhibited as described above, and there is a danger of short circuit.
If the length is longer than 00 mm, the electric resistance value becomes too small, and similarly to metal fibers, the amount of use is small and the problem of uniform dispersion may occur.

Further, as described later, in the case of a curved carbon fiber, since the fiber may be entangled particularly when the resin is dispersed, the fiber length is preferably 200 mm or less.

As the curved fibers in the present invention, those having a specific volume of 9 cm ³ / g or more when converted into an aspect ratio of 500 are preferable. The specific volume is the reciprocal of the bulk density measured under a pressure of 150 g / cm ² after a fiber sample is placed in a 500 ml beaker so as to fill the volume of the beaker.

When straight fibers and curved fibers are compared, the curved fibers are superior in terms of the stability of the carbon fiber content and the electric resistance value. In other words, when the fiber shape is straight, the electric resistance value changes linearly with the change in the content, whereas in the case of a curved shape, the tendency is small, so even if the uniformity of the content is lost, The curved shape is preferable because the deflection is relatively small. If the same electrical resistance absolute value is obtained, the curved fiber can achieve the same with a smaller fiber usage amount than the straight fiber.

As this curved carbon fiber, generally, PA
Carbon fibers known as pitch-based, rather than N-based carbon fibers, are more suitable for their production. Among them, a production method called a blowing method is particularly suitable, and carbon fibers produced by this method are most suitable. However, similar effects can be expected with straight carbon fibers produced by other methods if they are later processed into a curved shape by heat treatment or the like.

In addition, a curved carbon fiber chop is indispensable, and a straight carbon fiber may be used together if necessary as long as the PTC function is not exhibited.

The sheet containing the chopped carbon fiber short fibers used in the present invention is one in which the chops are fixed in a state of being uniformly dispersed without bias, and a sheet or paper-like material in advance is more suitable. ing. In fact, it is possible to make a sheet by extrusion molding from a thermoplastic resin compound in which these fibers are kneaded into resin, but it is possible to cut the fibers during the kneading work to make it uniform,
The stability of the resistance value when the sheet heating element is used deteriorates, which is not preferable in terms of output setting.

In the present invention, the electric resistance value can be freely set by changing the content of the short fiber chop of the carbon fiber. For example, by increasing these contents per unit area, The resistance value can be reduced, the power consumption can be increased, and the maximum temperature can be increased. Further, an appropriate amount of the non-conductive fiber pulp that does not melt is mixed according to the required performance required.

As the non-conductive short fiber pulp that does not melt, any known and commonly used short fiber pulp can be used.
For example, wood pulp, bamboo pulp, straw pulp and the like can be mentioned, but cellulose pulp composed only of cellulose fiber is preferable. .

It is particularly preferred that the amount of short fiber pulp used is selected so that the content of carbon fiber short fiber chops in the obtained element exceeds 20% by weight.

If necessary, various other organic fibers and inorganic fibers such as glass fibers and ceramic fibers may be used in combination with the carbon fiber chop and the short fiber pulp.

In the present invention, a suitable conductive sheet can be obtained by impregnating a resin containing the short fiber chop of carbon fibers and the short fiber pulp with a resin. Alternatively, the resin may be impregnated with a liquid resin and dried, or alternatively, the solid non-conductive fiber may be directly heated to a temperature equal to or higher than its melting point to be impregnated into a liquid state and cooled.

Further, when thermoplastic organic fibers are used as the non-conductive fibers, when the melting temperature of the fibers is lower than the temperature at the time of molding as a sheet heating element, pressurization during molding operation, When heated, it melts and loses its fiber shape, but the original purpose of this material is to hold the conductive fibers until it is molded and fixed as a sheet heating element. It is not necessary to keep that shape after it has become. However, in selecting the non-conductive fiber, it is preferable to select the non-conductive fiber in consideration of the relationship between the non-conductive fiber and the short fiber pulp that does not melt.

When this thermoplastic fiber is used in a sufficient weight, the impregnating resin described later is unnecessary. However, when the thermoplastic fiber does not have adhesiveness when heated, it is necessary to secure insulation. In many cases, adhesion to the surface film to be used is difficult. In such a case, a pressure-sensitive adhesive such as a pressure-sensitive adhesive may be used.

When the fibers and the short fiber pulp are melted, the function as an obstacle that hinders the contact between the carbon fiber short fiber chops is lost, so that the electric resistance value is reduced. Of course, in this case, it is necessary to consider the composition design of the material of the conductive heat generating portion, such as fibers and resin, in advance of the change.

Further, depending on the required electric resistance value and other functions, a material other than a fibrous form can be added to the conductive heat generating portion as a component. When changing the conductivity and other properties as a planar heating element, and if necessary when processing into paper, sheet, mat, nonwoven fabric, woven fabric, etc.,
These materials can be added freely.

In order to further increase the conductivity of the sheet heating element,
For example, use of fine powder of metal powder or graphite powder together, add various pigments to add color to products, and various sizing for paper making and sheeting when stabilizing the shape of the conductive heating part Materials can be added.

As an example of the present invention, for example, when a short fiber chop and the short fiber pulp are made into conductive paper, various resins can be used to fix the fibers. In the present invention, in consideration of the electric resistance value of the heating element obtained when using this conductive paper,
What is necessary is just to design a resin kind and a composition ratio, and just to evaluate materials other than a conductive material collectively as a non-conductive material.

In this case, changing the weight per unit area has the same effect, but practically it is necessary to consider the stability of the resulting sheet or paper.

The chopped carbon fiber short fiber chop that can be used in the present invention is desirably 10 to 200 g per square meter in view of the desired performance of the sheet heating element. If it is less than 10 g, uniform dispersion of the fiber itself becomes difficult,
If the amount exceeds g, it becomes difficult to impregnate and immobilize the resin, and even if a carbon fiber larger than practical is used, there is no improvement in performance such as output, and this may simply be economically disadvantageous. Many.

The resin to be impregnated into the carbon fiber short fiber chop to obtain the conductive heating section of the present invention is, for example, 10
It melts at 0-200 ° C and is impregnated into the fiber at the same time as the molding pressure. After a certain period of time, the thermosetting resin or the resin cures at 100-200 ° C. The thermoplastic resin to be impregnated is exemplified.

Of course, both may be used in combination.
Further, both may be separated and processed stepwise.

Examples of resins that can be used for this purpose include phenol resins, urea resins, melamine resins, unsaturated polyester resins, polyurethane resins, alkyd resins,
Epoxy resin, silicone resin, and other thermosetting resins, various polyolefin resins, polyester resins,
Polycarbonate resin, polyterpene resin, petroleum resin,
And other thermoplastic resins can be used.

The thermosetting resin may be used in an uncured, uncured or semi-cured state, and is impregnated in a softened or molten state by heating, and then cured to fix the conductive material. Will be transformed.

Further, in order to change the conditions of impregnation and curing, these resins may be mixed or modified, and may be used as long as the above conditions are satisfied.

The maximum temperature of the heat generated by the planar heating element is determined by the heating area (or the distance between the electrode strips), the type, shape and content of the conductive fiber used, the softening point of the impregnating resin, and the applied voltage ( However, the heating area and applied voltage are naturally determined by the application site. Therefore, the short-fiber chop of the carbon fiber in the conductive heating section and the non-conductive non-conductive It can be determined by selecting the composition of the short fiber pulp of the fiber and the resin for impregnation.

The resin to be impregnated is preferably selected so as to satisfy the following equation.

[0042]

[Formula 4] Flow temperature of resin impregnated in element−steady maximum reached temperature of element> 30 ° C. (1)

These resins can be used in a single sheet or film, but can also be used in a state of being applied to a sheet or film used on the surface, and the latter is simpler and more suitable in the production process.

A conductive heat generating portion in which resin is impregnated with a carbon fiber short fiber chop having no PTC function and a non-conductive fiber short fiber pulp which is not thermally melted and dispersed is fixed, At least one electrode band is provided along each of two opposite edges of one surface, and the electrode band pair and the conductive heat generating portion are overlapped and closely contacted to form a planar heat generating element (A). Of course, the electrode strips need only be provided in parallel, and do not necessarily have to be along each of the two opposite edges of the surface. In the case of a constant voltage application, the element generates heat at a higher temperature as the distance between the electrodes is smaller. A high temperature exotherm is obtained.

The number of electrode strip pairs may be one or two or more.
Make them all parallel. For example, A, B, C,
The four electrode strips D are arranged in parallel in this order at an arbitrary interval.
By adjusting the distance between the electrodes with a switch, for example, between A, D, B, C, B, D, and C, the exothermic temperature and exothermic part can be adjusted.

When a voltage is applied between the pair of electrode strips, a current flows between the electrodes and the conductive portion generates heat.
The imprint voltage may be an AC voltage or a DC voltage.

When electrical insulation of the surface is required,
The closely-connected conductive heating portions of the electrode strip pairs are
Except for the partially exposed portion necessary for the wiring, the entirety of one surface, preferably both surfaces, on which the electrode band pairs are provided, may be covered with an insulating film.

The insulating film used in the sheet heating element is
Any material can be used regardless of its material as long as it can insulate the surface where current is generated and heated.

In the present invention, as the insulating layer (plastic layer), use is made of a film or sheet which does not melt at the ultimate temperature of heat generation of the finally obtained sheet heating element, the molding temperature and pressure. Is good.

A film that melts at the temperature and pressure during molding,
Although a sheet can be used, in such a case, the conductive sheet for generating heat is impregnated and the electric resistance value is lowered. However, in this case, unless the material has a sufficient thickness, electrical insulation on the surface cannot be ensured.

Films and sheets of polyvinylidene fluoride, heat-resistant polyvinyl chloride, various polyesters, polyurethanes and the like can be used as the surface insulating layer which does not melt at the temperature and pressure during molding.

As the type of melting at the temperature and pressure during molding, polyethylene, polypropylene, polyvinyl chloride, and various other polyolefin films and sheets having a lower melting temperature can be used. However, these classifications are based on a molding temperature of 130 to 140 ° C., and if the molding temperature changes, the classification will also change.

The films and sheets of these thermoplastic resins must be selected in consideration of the maximum temperature at which heat is actually generated. For example, when heat is generated at a maximum of 50 to 60 ° C., polyethylene, ethylene-vinyl acetate copolymer,
A thermoplastic resin film or sheet that can be melted and impregnated at a temperature of about 100 ° C., such as a low-melting polyester, can be used.

However, when the exothermic temperature rises to 100 ° C., a heat-resistant thermoplastic resin film or sheet must be used. For example, films and sheets of polyester, polyurethane and the like having a high heat melting temperature can be used.

In this case, the melt impregnation temperature is 140 to 15
It becomes 0 degreeC or more. Even when the heat generation temperature is further increased, a thermoplastic resin film or sheet having a melting temperature higher than the maximum use temperature may be used.

Among these films and sheets, the material whose melting temperature rises due to heat history is more suitable for the purpose. For example, films and sheets of thermoplastic polyurethane, etc., after forming a planar heating element, by actually repeating the heat generation, it has been found that the melting temperature increases, the thermoplastic resin film of the present invention, It is one of the most suitable as a sheet.

Various materials can be selected so as to satisfy the following temperature conditions, for example.

[0058]

[Formula 5] Flow temperature of resin impregnated in the element−steady maximum temperature of the element> 30 ° C. (1)

[0059]

[Equation 6] Insulating film coating temperature> Flow temperature of impregnated resin in element> Steady maximum temperature of element (2)

The sheet heating element thus obtained is provided with an appropriate surface in accordance with a use department and a use form in practical use, processed into a required shape, and installed.

The planar heating element produced by the present invention is characterized in that it can be obtained in the form of a thin sheet. That is, there is an advantage in that heat is uniformly generated from the entire surface in the form of a thin film, and further, in the present invention, a flexible planar heating element can be obtained.

The place where the immediate heating element is used is often the inside and outside walls of a building, roof, floor, indoor furniture, etc.
It is desirable to form a thin film or a thin plate. Therefore, the sheet heating element used in the present invention has a thickness of 1.5
mm and as thin as possible. When the thickness is 1.5 mm or more, usefulness such as flexibility tends to be weakened.

The present invention is implemented, for example, as follows.
First, determine the size and structure of the sheet heating elements and stack them accordingly. For example, in order from the upper layer, a polyester film to be an insulating layer / a thermoplastic resin (film) to be impregnated
/ Cutting a foil of a fixed width at both ends to serve as electrodes, stacking conductive sheet to generate heat, thermoplastic resin (film) to be impregnated / polyester film.

In this case, when a metal portion is further disposed on the surface, a film having a required thickness may be used instead of the polyester film, and a metal sheet or plate may be disposed outside the film.

After stacking, in one method, a sheet is heated and impregnated with a thermoplastic resin, and the upper and lower polyester films are simultaneously adhered and fixed to form a sheet heating element. In this case, the compression molding temperature must be higher than the melting temperature of the thermoplastic resin to be impregnated and lower than the melting temperature of the polyester film to be the upper and lower insulating layers. Further, the molding of the molded article is performed after at least the surface temperature of the molding machine becomes lower than the melting temperature of the thermoplastic resin.

Another method is to heat the above-mentioned stacked product in advance at a temperature not lower than the melting temperature of the thermoplastic resin, to melt the thermoplastic resin, and to cool at a temperature required for cooling, for example, 30 ° C. or less. Between rolls held at a temperature of
This is a method of cooling simultaneously with impregnation.

The method of impregnation through a roll is suitable for large-scale production, but good impregnation cannot be obtained unless the working conditions are precisely set. For this reason, in the case of a small amount, a method of compression molding to obtain a sheet heating element is convenient.

Of course, in this step, a polyester film to be a surface insulating layer is coated with a thermoplastic resin or a thermosetting resin to be impregnated in advance, or a film is laminated to integrate the surface layer and the impregnating resin. Can also be used, which is more preferable in terms of simplifying the molding process. In addition, the impregnating resin may be used by impregnating the conductive sheet in advance.

The sheet heating element of the present invention may be provided with a multiple safety mechanism. It consists of a thermocouple that opens and closes contacts (ON / OFF of energization) above and below a certain temperature, and a temperature fuse that melts when held at a certain current value for a certain period of time. It consists of attaching.

The excellent planar heating element according to the present invention comprises:
For example, it is suitable for heat insulation and heating of the interior and exterior walls and floors of buildings, furniture and the like.

[0071]

Embodiments will be described below in accordance with embodiments.

Example 1 Chop chopped carbon fiber [yarn length 3 mm, fiber diameter 13 μm
m, specific volume: 9 cm ³ / g or more] in a short fiber pulp of cellulose fiber, 30% by weight; 60 g / m ²
Of the conductive mixed paper in which the fibers are uniformly dispersed and fixed
cm × 43 cm, 140-150 cm on both sides
A thermoplastic film (polyurethane resin) that melts at ℃ is placed one by one, and copper foil with a width of 10 mm and a thickness of 50 μm is placed on both opposing ends of the mixed paper in direct contact with the mixed paper, and the outer layers are insulated. Therefore, a 30 μm thick polyethylene terephthalate (PET) film was provided.

This was press-molded at 160 ° C. and 5 kg / cm ² to obtain a sheet heating element. The electrical resistance of this product is 120Ω
Met. A voltage of 100 V was applied to the product. The surface temperature was 36 ° C after 3 minutes, 51 ° C after 5 minutes, and 65 ° C after 10 minutes.

[0074]

According to the present invention, since short fiber pulp of non-conductive fiber which is not heat-melted is used as pulp for short fiber chop of carbon fiber, there is a possibility that problems due to contact points and inconvenience in conductivity may occur. It has a particularly remarkable effect of being small. When the element of the present invention is used, when the sheet heating element is used for a building or the like and used stably for a long period of time, it is possible to provide a material having excellent stability without abnormal heat generation due to short circuit. Can be done.

Claims (7)

[Claims] 1. A sheet-like heating element in which a fiber containing carbon fibers as an essential component and a resin is impregnated with a resin, and a planar heating element which requires an electrode band pair as an essential component, have a non-heat-melting non-fusible material as its conductive heating portion. A sheet heating element comprising a short fiber pulp made of conductive fibers and a short fiber chop made of curved carbon fibers, and using a fiber sheet in which they are uniformly mixed. 2. The fiber sheet, when the total of short fiber pulp of non-conductive fiber and non-heat-fusible short fiber pulp and short fiber chop of curved carbon fiber is 100% by weight, the latter exceeds 20% by weight. Fiber sheet. 3. A sheet heating element in which a carbon fiber impregnated with a resin and a conductive sheet and a pair of electrode strips are indispensable.
A planar heating element characterized by using a conductive sheet containing a carbon fiber chop of 1 mm in a content of more than 20% by weight. 4. The element according to claim 1, wherein the carbon fiber chop contained in the element is 10 to 200 g / m ² . 5. The element according to claim 1, wherein a resin to be impregnated is selected so as to satisfy the following expression. Flow temperature of impregnated resin in element-Maximum steady-state temperature of element> 30 ° C (1) 6. The element according to claim 1, wherein the conductive heating portion and the electrode band pair are covered with an insulating film so that both of the electrode band pairs are partially exposed. 7. The method according to claim 5, wherein the selection is made so as to satisfy the following two expressions.
The described element. Flow temperature of impregnated resin in element-steady maximum temperature of element> 30 ° C (1) Insulating film coating temperature> flow temperature of impregnated resin in element> steady maximum temperature of element (2 )