Fibrous heating element

A fibrous heating element having an electrical resistance of 1 to 100 .OMEGA./m is prepared by coating a core fiber, preferably a yarn, with one or more electroconductive layers consisting of a polyurethane resin having carbon particles dispersed therein. The fibrous element is pliable and can be knit or woven into a fabric, and is particularly suitable for use in an electric heating blanket or in an industrial heating element.

BACKGROUND 
The present invention relates to a fibrous heating element which can be 
woven or knit into fabrics, such as fabric-forming yarns and can be 
attached to objects by sewing. The invention also relates to a method for 
the production of such a heating element, and a fabric heating element 
made with that fibrous heating element. 
As means of heating or keeping various instruments and devices warm, 
flexible heating wires comprising a fine metal wire have been 
conventionally used. Such heating wires are widely utilized in various 
products such as electric blankets and carpets. 
While Nichrome wires are conventionally used for the heating element in 
products which are required to be flexible, such as the above-mentioned 
household products, either a flexible core having a very fine resistance 
wire spirally would thereon or a fabric having carbon particles bonded 
thereon by a resin binder has been used as the heating element. 
For example, in Japanese patent publication No. 52-14449 there is disclosed 
a planar heating element which comprises an electroconductive cloth of a 
glass-fiber fabric having tinned copper wires woven therein and coated 
with silicone-type electric conductive paint. 
However, the known planar heating elements represented by the above example 
are poor in pliability, and they fail to meet required characteristics 
with respect to bend yield resistivity and friction or abrasion 
resistance. In addition they lack flexibility for apparel use or medical 
use. 
There have been several attempts to obtain fibrous heating elements which 
comprise a pliable yarn coated with carbonaceous particles. For example, 
Japanese patent application Kokai (=laying-open) publication No. 51-109321 
discloses an invention, according to which a conjugate filament having a 
sheath component of a low melting point is subjected to heating to have 
the sheath component swelled and to have carbonaceous particles attached 
to and/or contained in the filament. This heating element has a positive 
temperature coefficient of resistance and does not need temperature 
control means. However, according to the above method of having 
carbonaceous particles attached to filaments, particularly where the 
filaments have a large diameter, it is difficult to obtain a filament 
containing carbonaceous particles in a sufficient amount to provide the 
resistance value required for a heating element. According to an example 
recited in that publication, the filament obtained has an electric 
resistivity as high as 10.sup.7 .OMEGA./cm, which is not satisfactory for 
a heating element. 
Japanese patent publication No. 58-25086 discloses coating a fiber of a 
heat shrinkable polymer with an electric conductive layer and then 
heat-treating the fiber to obtain a product fiber having a low resistance 
value per unitary length. However, the invention of this publication is 
directed to an improvement in the electrostatic property of carpets, and 
the electric resistance value of the fiber obtained is only about 
3.3.times.10.sup.7 .OMEGA./cm, and the products according to this 
invention are not useful as a heating element. 
In Japanese utility model publication No. 38-1470, there is disclosed a 
pliable heating element which comprises a reinforcement fiber and a 
heating layer coated on the fiber, wherein the heating layer is an 
electric conductive rubber or plastic. However, the electric resistivity 
of the pliable heating element is only 50 to 100 .OMEGA./cm, and it is 
ineffective as a heating element. 
In Japanese utility model publication No. 40-15750, there is disclosed an 
electric conductive fiber which comprises an insulator fiber and electric 
conductive particles adhered to the insulator fiber. However, in this 
method, it is difficult to adhere carbon particles uniformly, and an 
electric conductive fiber having the required electric resistance value is 
difficult to obtain. 
Japanese patent publication No. 46-23357 discloses a method of producing an 
electric conductive fiber, which comprises adhering a paste like mixture 
of a polyurethane, a solvent and electric conductive particles on a 
synthetic filament, and forming electric conductive coating by removing 
the solvent. However, the electric conductive fiber is intended to be 
anti-electrostatic, and the electric conductive fiber is not suitable for 
uses as a heating element because of its low electric resistivity of less 
than 10.sup.9 .OMEGA./cm. 
A first object of the present invention is to provide a fibrous heating 
element which has an electric resistance value higher than that of metals 
but lower than that of anti-electrostatic fibers, excellent flexibility 
and resistant to breaking on bending and abrasion, and which can be 
processed by weaving and knitting, and is usable as a sewing yarn or 
thread. 
A second object of the invention is to provide a method for the production 
of such a fibrous heating element. 
A third object of the invention is to provide a fabric heating element 
produced by forming the above fibrous heating element into a form of a 
pliable fabric, which can be attached to textile products such as clothes, 
for example, by sewing. 
According to the present invention, the above objects have been attained by 
providing a fibrous heating element produced by coating a core fiber with 
at least one electric conductive layer of a polyurethane resin containing 
the carbonaceous particles dispersed therein. 
The electric conductive layer according to the invention comprises a 
polyurethane resin containing carbonaceous particles dispersed therein, 
and gives a resistance element having a resistivity value remarkably 
greater than comparable values of metal resistance elements but lower than 
those of anti-electrostatic fibers. The heating element comprising a core 
fiber coated with at least one conductive layer according to the invention 
is pliable and resistant to breakage when bent or abraded, so that the 
fabric heating element made of such a fibrous heating element exhibits 
pliability and processability similar to those of conventional fabrics.

DESCRIPTION OF THE INVENTION 
With reference to the accompanying drawings, the present invention will now 
be described in detail, and initially in connection with the fabric 
heating element made of the fibrous heating element of the present 
invention. 
FIG. 1 is a partial plan view, showing an example of fabric heating 
elements according to the invention. 
As shown in FIG. 1, the fabric heating element indicated at 1 consists of a 
woven fabric made of electrodes 2 in warps, which consist of a fine copper 
wire plated with tin, and nonconductive yarns 3 of, for example, a 
polyester fiber, and for the woofs fibrous heating elements 4 and 
nonconductive yarns 5 similar to the above yarns 3, the yarns 5 being 
incorporated in a proportion necessary for obtaining the desired amount of 
calories. This fabric can be produced by an ordinary loom. The electrode 2 
is for supplying power to the fibrous heating elements 4. 
The fabric heating element 1 can be formed on either one surface or both 
surfaces with a insulating layer (not shown) by coating a pliable 
insulating polymer, such as polyethylene, silicone resin or the like. 
An insulating layer can be formed by suitable coating means depending on 
the particular resin or polymer to be used. Alternatively, both surfaces 
of the fabric heating element can be covered with a film of a 
thermoplastic resin and then heat cured to form an insulating layer. The 
thickness of the insulating layer should be adjusted taking into 
consideration the voltage of the power source to be used. In this 
connection, it may be advantageous to supply an insulating resin in a 
molten condition through a nozzle slit of a melt extruder to at least a 
portion of wire electrode of the fabric heating element, then optionally 
cover the formed layer of the insulating resin with a film of a 
thermoplastic resin, and press with cooled rollers, whereby it is feasible 
to obtain a fabric heating element in which the contact portions of wire 
electrodes and fibrous heating elements can always maintain close contact 
with each other. With the so produced fabric heating element, even if an 
external force is applied to bend it, when electric current is being 
supplied, there is no danger of sparks being generated, and the heating 
element is extremely safe. 
The fabric heating element illustrated in FIG. 1 is very pliable, so that 
it is useful not only for electric heating blankets and carpets, clothes, 
medical auxiliary appliances, bedding, sofa material and so forth, but 
also for a heating source in a broad range of industrial materials, such 
as ones for deicing, de-frosting, de-dewing, drying and so forth. 
FIG. 2 illustrates the basic structure of fabric heating element 10 
produced by Russel knitting in which woofs are laid in stitch. This 
heating element 10 consists of an electrode part 11 and a heat generating 
part 12, each of which consists of loop yarns and reinforcing yarns. 
The electrode part 11 includes a reinforcing yarns 13, which comprises a 
single wire electrode or electrodes of, for example, a copper wire plated 
with tin and which is electrically connected to the fibrous heating 
elements 4 by loop yarns 14. The loop yarns should preferably also 
comprise electric conductive yarns. 
The heat generating part 12 is made of a reinforcing yarns 15, generally of 
nonconductive yarns, such as polyester multifilaments and loop yarns 16. 
Further, this knit fabric can be made a mesh-type fabric by mesh-knitting 
with a conventional warp knitting machine. The fabric heating element 
according to the present invention can be produced in any other knit form 
than the one illustrated in FIG. 2 by any of the known knitting methods. 
The fabric heating element according to the invention can be made in the 
form of a mesh knit fabric or a mesh woven fabric by any suitable means, 
and coated with an electrical material. The coating can be carried out by 
dipping the fabric in a molten resin or in a resin solution. A film of a 
thermoplastic resin may be applied on both surfaces of the fabric and the 
fabric heated to the melting point of the resin. By blowing air, or 
forming small holes by rolls provided with pins and then heating to the 
melting point, it is feasible to produce a coating having mesh openings. 
As described above with reference to FIG. 1 and 2, the fabric heating 
element of the invention comprises a fabric which can be produced by an 
ordinary loom or knitting machine, so that it characteristically is 
possessed of a much higher pliability than conventional planar heating 
elements produced by forming a conductive layer on a nonconductive base 
material. 
Moreover, where the fabric heating element of the invention is used for 
electric heating blankets or carpets, clothes or other similar goods, it 
can be combined with another material by sewing, as contrasted to 
conventional planar heating elements, so that it is highly advantageous 
from an industrial point of view. 
FIG. 3 shows a partly broken-away perspective view of a fibrous heating 
element of the invention in which a three folded yarn is used as core 
fiber. 
The fibrous heating element 4 comprises a core fiber 20a of three folded 
polyester yarn and electric conductive layers 21, 22 and 23 of a 
polyurethane polymer having carbonaceous particles dispersed therein, 
formed to cover the core fiber. 
The core fiber has thickness usually within the range of 0.1 to 0.5 
mm.phi., more preferably, in the range of 0.2 to 0.3 mm.phi., preferably 
in the form of a spun yarn, a double-structured yarn, or a textured yarn. 
Each of the above yarns has a large area for contact with the synthetic 
resin or polymer forming the electric conductive layer and adheres 
strongly to the resin. 
For the above-mentioned yarns, there is preferably used a multi-folded 
yarn, particularly a two folded yarn or a three folded yarn. Three folded 
yarns in particular exhibit little surface irregularity due to twisting, 
and provide a fibrous heating element of high quality. 
The above-mentioned double-structured yarn consists substantially of a 
non-twisted multi-filament as the core part and flock-like short fibers or 
a substantially non-twisted multi-filament as the sheath part wound on the 
surface of the core multi-filament. 
When the above-mentioned double structured yarn is made of multi-filaments, 
it is feasible to minimize the elongation of the core fiber and prevent a 
change in the electric resistance value from occurring when the core fiber 
undergoes elongation. If the multi-filament has a number of twists 
exceeding 100 T/m, then core fibers made thereof generally tend to undergo 
undesirably large elongation and change its calorific value. Accordingly, 
the twist number should preferably be below the above recited value, more 
preferably 60 T/m or below. However, if the core fiber fails to have a 
good bundling property, the average thickness of the yarn tends to become 
very irregular and adversely affect the evenness of the thickness of the 
heat generating part or layer. Accordingly, rather than be completely 
devoid of twist, the multifilament should be twisted at a degree whereby a 
certain degree of the bundling property can be exhibited, for example 10 
T/m. 
The fiber forming the outer layer of the core fiber should preferably be of 
a shape suitable for adhesion to an electric conductive layer. For 
example, the outer layer may be made by interlacing a fiber surrounding 
the core fiber with an air jet, double-structured by twisting, or formed 
with loops of a textured yarn or a crimp yarn. For the core fiber in the 
present invention, use may be made of a plurality of the above-mentioned 
fibrous heating elements which are twisted together, making it possible to 
lower the resistance value per unit length. 
While the fiber of the core fiber may be any natural fiber or synthetic 
fiber, the below mentioned fibers are preferred, depending on the intended 
use of the fibrous heating element. 
Thermoplastic synthetic fibers are advantageously useful for they not only 
are heat resistant, non-hygroscopic, chemical resistant and less liable to 
deterioration by heat, but they also are capable of breaking by melting 
when a local overheating has taken place and function as a thermostatic 
fuse. Preferably, the fiber should be a nylon type fiber, a polyester type 
fiber or a polyolefin type fiber having a definite melting point. 
Heat resistant fibers having an indefinite melting point, in contrast to 
the above-mentioned fibers, are desirable fibers in that they can provide 
a heating element for use in a high temperature range. Desirable fibers in 
this respect are, for example, polyfluoroethylene type fibers and wholly 
aromatic polyamide fibers. Particularly, the latter fibers can provide 
high tensile-strength fibrous heating element, and the heating element is 
suitable for industrial uses. 
For the fiber in the core fiber, in addition to a fiber having an ordinary 
round cross-section, fibers may be used having a modified cross-sectional 
shape to obtain improved adhesion between the fiber and the conductive 
layer. Particularly where a multi-filament fiber is used, it is preferable 
that the fiber has a modified cross-sectional shape, for example, a 
triangular shape, a Y-letter shape, a T-letter shape, a +shape, a star 
shape or a wedge shape, or a U-letter shape, C-letter shape, a flat shape 
or a flattened concavoconvex shape. Fibers having such cross-sectional 
shapes may be used to form a core fiber in the form of either a group 
having the same cross-sectional shape or a mixture or a fiber blend of 
different cross-sectional shapes. For purposes of the present invention, 
where a fiber of a modified cross-sectional shape is used, the 
cross-sectional shape should preferably be such that, supposing the width 
of an open space between adjacent projections to be W, the height of 
projections to be H, the largest radius to be OR, and the cross-sectional 
area to be A, H/W.gtoreq.0.6, H/R.gtoreq.0.7 and A/.pi.R.sup.2 
.gtoreq.0.5. Fibers meeting the above requirements can be preferably 
employed for the material for the core fiber according to the invention. 
If the distance of the open space between adjacent projections or branches 
W is sufficiently small relative to the height of the projections or 
branches (or the depth of concavities) H, the fibers have a higher 
anchoring property preventing the conductive layer from being stripped off 
the open space, and H/W should preferably be 0.6 or above or, more 
preferably, 0.8 or above. Fibers where the height of the projection or 
branch (or the depth of the concavities) is sufficiently great, and which 
have open spaces peripherally at many points, and where the longest radius 
in cross-section is R, H/R is preferably greater than 0.7. Furthermore, to 
let a small amount of the fiber occupy a large volume, it is preferable to 
set the cross-sectional area of the fiber, A, such that A/.pi.R.sup.2 is 
smaller than 0.5 inclusive or, particularly preferably 0.4 or below. 
Fibers having a modified cross-sectional shape as described above may be 
filaments, staple fibers or mixtures of them. 
When use is made of a fiber of a synthetic polymer which contains a 
functional group directly bonded to a base polymer, an improvement is 
obtained in the adhesion of the fibrous heating element to the conductive 
layer. The functional group may be a peroxide group, a carboxyl group, a 
carbonyl group, a sulfoxide group, a hydroxide group, an amino group, an 
amide group, or a quaternary amino group. Those functional groups may be 
formed by an oxidation treatment, a decomposition treatment and a plasma 
treatment which is advantageous from the standpoint of mechanical 
characteristics. 
The oxidation treatment involves oxidizing the fiber surface with an 
oxidizing agent and forming a functional group containing oxygen. Both 
conventional liquid-phase oxidation and gas-phase oxidation can be 
utilized. 
The decomposition treatment forms terminal functional groups by decomposing 
the polymer. The alkaline decomposition of a polyester is a representative 
treatment of this type. In each of the above treatments, preferably, only 
the fiber surface should be treated. 
For the plasma treatment, any of the methods usually employed in treating 
fibers can be used. When using the plasma treatment, the number of 
functional groups bonded to molecular chains on the surface (within 3000 
.ANG.) of a synthetic resin are increased. Using the appropriate ambient 
gas, it is possible to form carbonyl groups, carboxyl groups, hydroxyl 
groups, hydrooxyperoxide groups, amino groups, amide groups and so forth. 
It is not necessary that the core fibers be in a bundled form. The fibers 
may be dispersed in the electric conductive layer providing a large area 
of contact between the monofilament fibers or fiber groups forming the 
core fiber and the electric conductive layer. If a stress is generated in 
the fibrous heating element, the stress is shared by each individual 
monofilament fiber or individual group of fibers, thereby improving the 
mechanical strength of the fibrous heating element. 
To provide a fibrous heating element having structural features as 
described above, the core fiber may be made either of a yarn as spun and 
then drawn or of a yarn which has once been taken up on a bobbin and then 
unwound. 
The core fiber can be treated by an agent having an affinity for both the 
polyurethane resin and the core fiber. 
Any polyurethane resin can be used that retains stable electric resistance 
properties within the operating temperature range (20.degree. to 
100.degree. C.), and melts or softens above the upper limit of the 
operating temperature. A suitable polyurethane resin is of the polyester 
type, the reaction product of a diisocyanate and a polyester type polyol 
obtained by reacting an acid with a diol component. 
The above acid component comprises dicarboxylic acids such as adipic acid, 
sebacic acid and so forth, to which an aromatic dicarboxylic acid such as 
terephthalic acid, isophthalic acid and so forth may be added. The diol 
component is usually ethylene glycol, propylene glycol, 2,3-butanediol, 
caprolactonedio, polyethylene glycol, polypropylene glycol, polybutanediol 
and so forth. 
For the isocyanate component, use is normally made of hexamethylene 
diisocyanate, tolyenediisocyanate, xylenediisocyanate, bis-4-isocyanate 
phenylmethane, isophoronediisocyanate and so forth. 
Fine air bubbles formed in the electric conductive layer of the fibrous 
heating element of the invention improve its pliability. 
In the fibrous heating element according to the present invention, the 
polyurethane resin forming the electric conductive layer may be made of a 
cross-linked structure, whereby an improvement can be attained in 
mechanical strength characteristics, thermal resistivity and solvent 
resistivity. 
If cross-linking and depositing the resin on the core fiber are carried out 
simultaneously, viscosity increases through gelation as cross-linking 
proceeds. Thus, the cross-linking reaction should preferably be effected 
at the same time the electric conductive layer if formed, or after the 
electric conductive layer has been formed. 
The cross-linking reaction can be a radical reaction, a reaction by 
electron beams and a photo reaction. The polyurethane resin obtained from 
the above exemplified components can be cross-linked using a cross-linking 
agent which provides radicals by abstracting hydrogen atoms from a 
methylene group such as benzoyl peroxide, one in which the polymer chain 
or side chain of the polymer is cut and re-oriented by electron beams such 
as .tau. rays, one in which a polyurethane prepared from a diol having 
double bonds, such as 1,2- or 1,4-polybutadiendiol, is subjected to 
radiation, and so forth. 
By having the electric conductive layer cross-linked as above, it is 
possible to improve thermal resistivity, solvent resistivity, mechanical 
strength and so forth. 
The following solvents and mixtures of these solvents, 
N,N-dimethyl-formamide, N,N-dimethylacetamide, dimethylsulfoxide, 
tetrahydrofuran, dioxane are available for use with polyurethanes. To coat 
large amounts of the electroconductive resin uniformly, the weight of 
solvent should be 1 to 10 times, preferably 2 to 6 times the weight of 
electroconductive resin. 
Carbon black and/or graphite particles are used as the carbonaceous 
particles in the electroconductive resin. Suitable carbon blacks are, for 
example, acetylene black, channel black, furnace black and so forth. 
Mixture of these carbon blacks can also be used. The usual average 
particle diameter of carbon black(s) is within a range of 1 to 500 m.mu., 
preferably 5 to 300 m.mu., more preferably 10 to 200 m.mu., for good 
dispersion in the polyurethane resin. 
Suitable graphites are, for example, block graphite, scaly graphite, powder 
graphite, or artificial graphite. Mixture of these graphite particles can 
also be used. The usual average diameter of graphite particles is within a 
range of 0.1 to 100 .mu.m, preferably 0.2 to 50 .mu.m, more preferably 0.5 
to 20 .mu.m are used, for good dispersion in the polyurethane resin. 
The amount of the carbonaceous particles used is preferably 30 to 100 parts 
by weight or, more preferably, 40 to 60 parts by weight, to 100 parts by 
weight of polyurethane resin. With an amount less than 30 parts by weight, 
the resistivity of the fibrous heating element becomes too high and 
unsuitable for a heater. With an amount of more than 100 parts by weight, 
it is difficult to obtain a uniform resistivity, and properties such as 
bending resistivity and friction resistivity become low, because the 
amount of the polyurethane resin present is small. 
When both carbon black and graphite are used as the carbonaceous particles, 
the weight ratio (carbon black/graphite particles) is preferably 1 to 4, 
more preferably 1.5 to 2.5. Over or under that range, the resistance value 
of the fibrous heating element becomes too high, and the resistivity of 
the fibrous heating element is not uniform. 
While the fibrous heating element according to the present invention 
comprises one or more carbonaceous particle dispersion layer(s), 2 to 4 
layers should preferably be formed by coating. This compensates for any 
irregularity in fiber diameter, and any irregularity in resistivity can be 
minimized. The concentration of the carbonaceous particles dispersed in 
the synthetic polymer layer can be varied from layer to layer as required. 
The resistance value of the fibrous heating element of the invention can be 
set within a wide range by controlling the content of electric conductive 
particles in the synthetic polymer layer, and the number and the thickness 
of conductive layers coated. A practical range of the resistance value is 
on the order of 1 to 100 k.OMEGA./m, or, more preferably, 3 to 50 
k.OMEGA./m. When the resistance value is smaller than 1 k.OMEGA./m, 
heating power per unit length becomes too high, and when the resistance 
value is larger than 100 k.OMEGA./m, heating power per unit length becomes 
too low, and the fibrous heating element is not suitable for heater. 
To obtain the above resistance values and desired mechanical strength, the 
thickness of the electric conductive layer(s) is preferably 20 to 700 
.mu.m. 
The thickness of the fibrous heating element is determined from the desired 
thickness of electric conductive layer(s) and the preferred fibrous 
heating elements have a thickness which can be used as components of 
fabric, and the range of thickness is 0.3 to 1.5 mm.phi.. 
The above described fibrous heating element according to the invention can 
be produced by the following steps: 
Preparation of the core fiber: So that the core fiber can be prepared 
continuously, there is provided a yarn having no knots or like defects. 
Preparation of the resin solution having carbonaceous particles suspended 
therein (hereinafter referred to as suspension): The resin is dissolved in 
an appropriate solvent usually at a solution viscosity of 20 to 100 poise 
(measured by B type viscometer). Then, carbonaceous particles are 
suspended in the solution and stirred, and the resulting suspension is 
placed in a closed vessel in order to prevent the solvent from 
evaporating. The solution viscosity is selected to be within a range in 
which the carbonaceous particles do not settle during processing. 
The above prepared core fiber is coated by dipping in the suspension in the 
closed vessel while the suspension is stirred, taken out of the suspension 
and then passed through the die of an appropriate orifice diameter to 
control the amount of the suspension deposited. In order to enhance the 
mechanical strength of the heat generating layer, it is necessary that the 
individual fibers forming the core fiber to adequately wetted with the 
suspension, and the viscosity of the suspension and the orifice diameter 
of the die are adjusted accordingly. Industrially, it is preferable to 
employ a method in which the core fiber, taken up on a bobbin, is 
continuously withdrawn by a roller mechanism and dipped in the suspension. 
After it has been coated, the core fiber is continuously subjected to a 
solvent removing process, such as drying or coagulation. 
In the case of drying, the process is usually effected by a ventilation 
drying method, optionally heating the air to be supplied to promote 
drying. 
In the case of coagulation, because uniform and fine bubbles are formed in 
the electroconductive layer(s), a flexible fibrous heating element can be 
obtained. 
To compensate for any irregularity in the yarn diameter and/or in the 
resistance value and obtain fibrous heating elements of uniform 
characteristics, it is preferable to utilize plural electroconductive 
layers. To do this, the above described coating step including the solvent 
removing process is repeated. When the drying process is used to remove 
solvent, it is necessary that drying be sufficient so that the resin layer 
formed in a preceding step does not become dissolved in the suspension in 
a succeeding coating step. 
The fabric heating element according to the present invention can be 
produced from the above described fibrous heating element by forming it 
into a woven or knit fabric using conventional methods. And when doing 
this, the fibrous heating element is generally disposed in the woof 
portion and the wire electrodes are generally disposed in the warp 
portion. 
Fabric heating elements comprising a fabric made from the above described 
fibrous heating elements are generally structured such that a heat 
generating part comprising fibrous heating elements and nonconductive 
yarns is disposed between two electrodes. Thus, it is important to provide 
means for connecting the electrodes to an external power source. 
FIG. 5 illustrates an embodiment in which a binding yarn is used to fasten 
the wire electrodes 2 and the fibrous heating elements 4 together. The 
binding yarn 35 comprises a heat shrinkable yarn and is used at the 
portion in which the warp comprises the wire electrodes 2. Weaving is by 
letting the binding yarn 35 entwine all woofs which cross the electrode 
wires 2. The binding yarn 35 runs parallel with the fibrous heating 
element 4 and woofs 36 of nonconductive fiber stepping over the two wire 
electrodes 2 and being crossed with woofs and strongly pressing the wire 
electrodes 2 and woofs 36 against the warps. After weaving, heating will 
shrink the binding yarns and fasten the wire electrodes and the woofs. The 
above described manner of applying the binding yarn 35 can be applied also 
in the case of a knit fabric. 
With woven or knit fabric heating elements as described above, the yarns 
crossing the wire electrodes make it difficult to attach lead wire to the 
electrodes for connection to a power source. Means for solving this 
difficulty will be described below. 
One of the means consists in providing a fabric having the surfaces of the 
fibrous heating element and wire electrodes woven coated with an 
insulating material and applying a coating of a release agent or a 
covering of a protective layer at the predetermined locations between the 
wire electrodes and the insulating material. Generally the release agent 
is a silicone resin type agent or a fluorine resin type release agent. The 
covering may be made of a parting paper having a release agent coated on a 
rear face thereof. Use may also be made of a thin conductive foil or 
sheet, which may be double-folded and attached to the electrodes by any 
suitable means, for example, by soldering or by using a conductive bonding 
agent. When applying the covering, it may be desirable to partially expose 
the portion of the electrodes which is to be attached to the connection 
with the lead wires. 
In an alternative means for the connection of electrodes to lead wires, use 
is made of two terminal plates, at least one of which has projections on 
its surface applied to the faces of the electrode in a manner such that 
the projections penetrate the electrode and tightly fasten the two 
terminal plates to each other. According to this method, even if the 
electrodes are covered with a resin film or a covering sheet, the desired 
electrical connection can be attained without removing the film or cover 
sheet. 
Although the fibrous heating elements are usually arranged to form a 
parallel circuit as shown in FIG. 6, they may be run in a zigzag path 
between two electrodes along woofs so that they contact the electrodes 
intermittently to vary the amount of heat to be generated. 
In a modified arrangement, the fibrous heating element may be used in both 
the warp and the woof providing power-source terminals at appropriate 
locations. The heating element may be wound about the steering wheel or 
hand of an automobile or motor bicycle to form a warming or heating face. 
As an alternative means of providing the fibrous heating element in a 
fabric, the element may be used as a sewing yarn or thread and sewn into 
the fabric. 
A planar heating element comprising a fabric according to the present 
invention may be produced as a pattern of unitary heating elements in a 
fabric or in the form of having a repeating pattern, which may be cut to 
the desired length. It is possible to produce a fabric having strands of 
the electrode incorporated therein and cut this heating element along the 
warp direction into segments corresponding to the voltages desired. In 
this case, the number of patterns to be woven or knit can be reduced, and 
the cost of production can be lowered. Also in this case, those electrodes 
to which lead wires are not connected can be made functional to provide 
uniform electric current to the respective fibrous heating elements and to 
form bypath circuits in case of a local failure in electrical conduction. 
It is feasible to incorporate a temperature control device known per se 
into the fabric heating element according to the present invention. 
The characteristics of the fibrous heating element of the present invention 
will be described by means of the following examples: 
EXAMPLE 1 
Preparation of synthetic-polymer suspension 
100 parts by weight of polyester type polyurethane resin (product of 
Dainichiseika Color & Chemicals MFG.Co., LTD) was uniformly dissolved in 
540 parts by weight of a mixed solvent of methyl ethyl ketone, 
(hereinafter referred to as MEK) and dimethylformamide (hereinafter 
referred to DMF) (weight ratio of MEK/DMF:80/20). 50 parts by weight of 
carbon (black average particle diameter:40 m.mu.) and 30 parts by weight 
of graphite particle (average particle diameter:8.8 .mu.m) are added and 
dispersed in the polyurethane, which had a viscosity of 45 poise at 
30.degree. C. 
Coating conditions 
While the above prepared dipping solution was being stirred, a two folded 
polyester spun yarn of 20-count was dipped in and passed through the 
solution at a rate of 2 m/min at 20.degree. C., the amount of the solution 
deposited was adjusted through stainless steel dies having the orifice 
sizes shown in Table 1. Thereafter, the yarn was continuously passed 
through a hot air dryer maintained at 120.degree. C. to form an 
electroconductive layer containing carbonaceous particles dispersed 
therein around the core fiber. The appearance and various characteristics 
of the fiber samples obtained by the above-described 1st stage drying and 
solidification procedure are shown in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Orifice Diameter 
Electric 
Microscopic observation 
diameter 
Resin deposit 
of fibrous 
resistance 
Surface 
Sectional 
Sample 
(mm .phi.) 
amount (g/m) 
heating element 
(k.OMEGA./m) 
structure* 
structure 
__________________________________________________________________________ 
1 1.0 0.13 0.62 .+-. 0.15 
22.5 .+-. 1.8 
Considerable 
Rings of carbonaceous 
particles, observ- 
able on periphery 
2 0.8 0.12 0.55 .+-. 0.15 
24.9 .+-. 2.0 
Considerable 
Rings of carbonaceous 
particles, observ- 
able on periphery 
3 0.7 0.11 0.49 .+-. 0.11 
27.8 .+-. 2.4 
Considerable 
Rings of carbonaceous 
particles, observ- 
able on periphery 
4 0.5 0.085 0.43 .+-. 0.13 
31.1 .+-. 3.1 
Considerable 
Rings of carbonaceous 
particles, observ- 
able on periphery 
__________________________________________________________________________ 
*Concavoconvex irregularities. 
Repetitional coating conditions 
Samples Nos. 3 and 4 in Table 1 were subjected to a 2nd stage treatment 
using the same dipping solution and in the same manner as above, except 
that for Sample No. 3 a die of an orifice size of 0.8 mm was used, while 
for the Sample No. 4 use was made of a die of an orifice size of 0.7 mm. 
Sample No. 4 was subjected to a 3rd stage treatment in the same manners as 
in the lst and 2nd stage treatments, and in this 3rd stage, a die of an 
orifice size of 0.8 mm was used. The results are shown in Table 2. 
TABLE 2 
__________________________________________________________________________ 
Sample Orifice Diameter 
Electric 
Microscopic observation 
(Repeated 
diameter (mm .phi.) 
Resin deposit 
of fibrous 
resistance 
Surface Sectional 
coating times) 
(1st/2nd/3rd) 
amount (g/m) 
heating element 
(k.OMEGA./m) 
structure* 
structure 
__________________________________________________________________________ 
3 0.7/1.0 0.13 0.56 .+-. 0.09 
18.8 .+-. 1.2 
Not considerable 
Rings of carbonaceous 
(1) particles, observable 
both on outer 
periphery 
and in an inner layer 
4 0.5/0.7 0.11 0.49 .+-. 0.09 
25.7 .+-. 1.9 
Not considerable 
Rings of carbonaceous 
(1) particles, observable 
both on outer 
periphery 
and in an inner layer 
4 0.5/0.7/1.0 
0.13 0.55 .+-. 0.03 
13.8 .+-. 0.5 
Concavoconvex 
Rings of carbonaceous 
(2) irregularities, 
particles, observable 
both on outer 
periphery 
and in an inner 
__________________________________________________________________________ 
layer 
*Concavoconvex irregularities. 
On considering the data in Tables 1 and 2, the following desirable results 
of repeated coating were noted: 
(1) From a comparison of Sample No. 1 (coated one time only), Sample No. 3 
(coated twice) and Sample No. 4 (coated three times), each having 
essentially same amount of polymer deposited, it is seen that the urethane 
resin was more uniformly deposited in Sample No. 4 than in Sample No. 3, 
and that the deposit in Sample No. 3 was more uniform than in Sample No. 
1. The same order was observed with regard to the uniformity of the 
diameter of the fibrous heating elements and the electric resistance per 
unit length. 
(2) When a comparison was made of the electric resistance values of fibrous 
heating elements having the same amount of polymer deposited thereon, it 
was found that the electric resistance values were lower with those 
fibrous heating elements having the greater number of coating layers. 
(3) By using plural coatings, irregularities on the surface were reduced 
and the surface of the fibrous heating element was made smooth and had low 
coefficient of friction, so that the element was readily processable for 
weaving or knitting. 
Sample No. 2 was subjected to a 2nd stage coating with a solution having an 
8.3 wt % concentration of carbonaceous particles suspended in a solution 
containing 16.7 wt % of the polymer. The properties of the treated fibrous 
heating element are shown in Table 3. 
TABLE 3 
______________________________________ 
Sample Deposit 
(repeated 
amount of Electric 
coating resin resistance Surface structure 
times) (g/m) (.OMEGA./m) 
(Smoothness) 
______________________________________ 
2 0.14 17.5 .+-. 0.9 
Superior to 
(1) sample No. 2 (2 times) 
sample No. 4 (2 times) 
______________________________________ 
The bend strength and resistance to friction of Sample No. 3, Nichrome wire 
and a commercially obtained cord heater, were measured and the results are 
shown in Table 4. 
TABLE 4 
______________________________________ 
Times Times -Resistance of bending of abrasion 
value before before 
(.OMEGA./m) 
break break 
______________________________________ 
Nichrome wire 
(0.1 mm .phi.) 
154 2-3 2 
(0.32 mm .phi.) 
18 3 
Commercially obtained 
46-48 200-300 -- 
cord heater (2.1 mm .phi.) 
Fibrous heating 
13,000-14,000 
3,000-5,000 
122 
element (0.56 mm .phi.) 
______________________________________ 
From Table 4, it is seen that the fibrous heating element according to the 
present invention is exceptionally durable in comparison to a conventional 
wire heater. 
EXAMPLE 2 
Three different solutions having carbonaceous particles at concentrations 
of 12 wt %, 10 wt % and 5 wt % were prepared using the procedure of 
Example 1. The ratio, carbon black/graphite particles, was 2/1. 
A core fiber of three folded polyester spun yarn (30-count) was dipped in 
and passed through the suspension containing 12 wt % of carbonaceous 
particles maintained at 20.degree. C. at a rate of 2 m/min, then the 
amount of the dipping solution deposited on the core fiber was adjusted 
through a die, and the yarn was continuously dried in a drier having its 
temperature maintained at 120.degree. C., to obtain a fiber coated with a 
layer of polymer having carbonaceous particles dispersed therein. The 
procedure was repeated using the suspension containing 10 wt % of 
carbonaceous particles and then the suspension containing 5 wt % of 
carbonaceous particles, to obtain a fibrous heating element having three 
coating layers with carbonaceous particles dispersed therein. The fibrous 
heating element thus obtained was found to be high in pliability, 
remarkable in bending resistivity and friction resistivity, and have 12.8 
K.OMEGA./m as its electric resistance value. 
EXAMPLE 3 
A double-structured yarn (0.6 mm.phi.) consisting of polyester 
multi-filament (75D-25fil) as its core part and polyester staples (3d, 1.5 
inch) as its sheath part, wound on the surface of the multi-filament core, 
was used as a core fiber. Except for changing the core fiber, a fibrous 
heating element was prepared using the same process as Example 2. The 
fibrous heating element thus obtained was found to be high in pliability, 
remarkable in bending resistivity and friction resistivity, and having 
10.8 K.OMEGA./m for the electric resistance value. 
EXAMPLE 4 
A three folded polyester textured yarn whose cross-sectional shape is 8 
leafs' type (0.56 mm.phi.) was used as a core fiber. Except for changing 
the core fiber, a fibrous heating element was prepared using the same 
process as Example 2. The fibrous heating element thus obtained was found 
to be high in pliability, remarkable in bending resistivity and friction 
resistivity, and have 14.2 K.OMEGA./m for the electric resistance value. 
EXAMPLE 5 
A two folded wholly aromatic-polyamide spun yarn (20-count, 0.56 mm.phi.) 
was used as the core fiber. Except for changing the core fiber, a fibrous 
heating element was prepared using the same process as Example 2. The 
fibrous heating element thus obtained was found to be high in pliability, 
remarkable in bending resistivity and friction resistivity, and have 11.6 
K.OMEGA./m for the electric resistance value. 
EXAMPLE 6 
100 parts by weight of polyester type polyurethane resin (product of 
Dainichiseika Color & Chemicals (MFG.Co., LTD) was uniformly dissolved in 
500 parts by weight of mixed solvent of MEK and DMF (weight ratio of 
MEK/DMF: 10/90). 50 parts by weight of carbon black (average particle 
diameter: 40 m.mu.) and 30 parts by weight of graphite particle (average 
particle diameter: 8. .mu.m) were added and dispersed in the polyurethane 
solution. The solution had a viscosity of 80 poise at 30.degree. C., as 
measured with a B type viscometer. 
While the above prepared dipping solution was being stirred, a two folded 
polyester spun yarn of 20-count was dipped in and passed through the 
solution at a rate of 10 m/min at 20.degree. C., and the amount of the 
solution, deposited was adjusted by stainless steel dies of orifice size 
0.6 mm.phi.. The dispersion deposited on the yarn was coagulated by being 
continuously passed through a coagulation bath of DMF aqueous solution 
(weight ratio of DMF/water:2/98) maintained at 20.degree. C., and the 
solvent was removed by being passed through a solvent-removing bath of 
water. The thus treated yarn was dried using a Nelson type drying roller 
maintained at 120.degree. C. The fibrous heating element produced had a 
diameter of 0.5 mm.phi., and an electric resistance value of 16 
k.OMEGA./m. 
EXAMPLE 7 
Using Sample No. 4 prepared in Example 1 and a 4-count polyester spun yarn 
for woofs, and polyester filament (150D-50fil) and tin-plated copper wires 
(0.1 mm.phi.) for warps, a plain woven fabric was produced in the usual 
manner weaving the fibrous heating element in one in every three woofs of 
the count-4 polyester spun yarn. Also, tin-plated copper wires were 
disposed in twenty warps at each of the sides of the fabric, inside of 
edges of the warps, to form wire electrodes. The distance between the two 
electrodes was set to be 10 cm. 
To a portion of the wire electrodes of the woven fabric obtained above, 
molten polyethylene having a melt index of 3.7 g/10 min and a density of 
0.923 g/cm.sup.3 was supplied at 310.degree. C. through the nozzle slit of 
a melt extrusion laminator. At the same time, both faces of the fabric 
were covered with a polyester film of a thickness of 25 .mu.m, and then a 
pressure of 10 kg/cm was applied to the fabric by water cooled rollers 
maintained at 30.degree. C., to form an insulating film and to obtain a 
fabric heating element 20 cm in length and 11 cm in width. A heater was 
made by connecting lead wires to the above obtained fabric heating 
element. The fabric heating element had a resistance value of 14 .OMEGA. 
and was pliable and capable of being sewn like ordinary fabrics in 
general. 
As can be understood from considering the results of the above examples, 
the fibrous heating element described is useful as heat generating element 
in a variety of goods such as (1) winter clothes, outer-garments for 
riders, fishermen, divers and so forth, inner garments, work clothes, 
underwear and so forth; (2) in furniture and bedding, such as carpets, 
blankets, lap robes, seating material for railway passenger cars and 
automobiles; (3) in the medical field for medical-care supporters, belly 
bands, warming mats and sheets and so forth; (4) for household goods, such 
as gloves, shoes, socks, cushions and so forth; (5) in construction 
materials, such as flooring, wall, floor warmers and so forth; (6) in 
electric appliances, such as electrical instruments and appliances, 
heating members for meters and so forth; (7) in agriculture and civil 
engineering, such as bed warming sheets, maturing sheets and so forth.