U.S. patent number 3,808,403 [Application Number 05/271,518] was granted by the patent office on 1974-04-30 for waterproof electrical heating unit sheet.
This patent grant is currently assigned to Kohkoku Chemical Industry Co., Ltd.. Invention is credited to Kanae Azuma, Toru Iizuka, Yoshinosuke Kanaya, Torahiko Saitoh, Katsuo Tonooka, Isao Yasuda.
United States Patent |
3,808,403 |
Kanaya , et al. |
April 30, 1974 |
WATERPROOF ELECTRICAL HEATING UNIT SHEET
Abstract
A heating unit sheet composed of an electroconductive high
molecular material and having a high degree of safety and excellent
flexibility and which is useful in many various applications,
equipped with electrodes and coated with insulating materials.
Inventors: |
Kanaya; Yoshinosuke (Gunma,
JA), Azuma; Kanae (Tochigi, JA), Tonooka;
Katsuo (Tochigi, JA), Yasuda; Isao (Tochigi,
JA), Iizuka; Toru (Tochigi, JA), Saitoh;
Torahiko (Tokyo, JA) |
Assignee: |
Kohkoku Chemical Industry Co.,
Ltd. (Tokyo, JA)
|
Family
ID: |
27298190 |
Appl.
No.: |
05/271,518 |
Filed: |
July 13, 1972 |
Foreign Application Priority Data
|
|
|
|
|
Jul 20, 1971 [JA] |
|
|
46-63483 |
Nov 5, 1971 [JA] |
|
|
46-88082 |
Dec 22, 1971 [JA] |
|
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46-120681 |
|
Current U.S.
Class: |
219/528; 219/543;
252/500; 219/212; 219/549; 338/211 |
Current CPC
Class: |
H05B
3/06 (20130101); H05B 3/26 (20130101); H05B
3/342 (20130101); B63C 11/28 (20130101); H05B
2203/011 (20130101); H05B 2203/017 (20130101); H05B
2203/029 (20130101); H05B 2203/026 (20130101); H05B
2203/036 (20130101); H05B 2203/013 (20130101); H05B
2203/016 (20130101); H05B 2203/021 (20130101) |
Current International
Class: |
B63C
11/02 (20060101); B63C 11/28 (20060101); H05B
3/34 (20060101); H05B 3/06 (20060101); H05B
3/22 (20060101); H05B 3/26 (20060101); H05b
003/36 () |
Field of
Search: |
;219/211,212,464,528,529,543,545,549 ;338/211,212,214 ;252/500 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Mayewsky; Volodymyr Y.
Attorney, Agent or Firm: Toren, McGeady & Stanger
Claims
1. A waterproof heating sheet comprising a laminate of:
a. an inner layer of woven fabric composed of flexible
heat-resistant synthetic fibers having a coating of an
electro-conductive high molecular weight cross-linked paint
composed of a graft polymer of a vinyl monomer grafted onto carbon
black, wherein said vinyl monomer possesses a functional group
selected from the group consisting of -OH, -COOH, -NH.sub.2, =NH,
-CONH, ##SPC11## SONH.sub.2, and is cross-linked with a
cross-linking agent selected from the group consisting of compounds
having the formula: ##SPC12##
wherein R is an aliphatic, aromatic or alicylic group and n is 2 or
4;
b. upper and lower waterproof insulating layers completely
surrounding said inner layer;
c. said inner layer having spaced-apart, flexible electrodes
conductively attached thereto; and
d. electrical leads connected to said electrodes, said leads
extending from
2. The heating sheet of claim 1 wherein the woven fabric has a
porosity of 20 to 65 percent by volume and consists of synthetic
fiber filaments having a melting point and thermal decomposition
temperature above 250.degree. C.
Description
The present invention relates to a heating sheet on which a
flexible high-molecular paint having electroconductive property is
applied.
Heating sheets conventionally used include metal foils having a
high electrical resistance and glass textures or asbestos paper on
which an electroconductive paint, containing powders of carbon or
metal, is applied and equipped with electrodes. Since these
materials lack pliability and flexibility, they are likely to form
cracks and be broken while in use.
Heating sheets may be incorporated in various materials used in
applications, such as, walls, floors and ceilings; furniture, such
as, stools and chairs; cars and trucks; live-stock breeding, such
as, hog-raising and poultry farming; the marine industry such as,
fish-raising in marshes, ponds and inland sea; agriculture, such
as, for heating hot-beds and nursery beds; civil engineering works,
such as, snow- and ice-melting of roads, runways, bridges, etc.;
heat insulation for water supply pipes and other pipe lines and
oven panels etc.; for warming clothing, such as, water-cloths,
overcoats, jumpers, trousers and other personal effects, such as,
gloves, shoes, slippers, and hosiery and many others.
However, the conventional heating sheets cannot be incorporated in
many materials because of the poor flexibility of the heating
sheets and furthermore, if cracks or defects are formed on the
heating sheet, an abnormally large current may flow at the sites
and evolve sufficient heat to cause a fire. Therefore, these
heating sheets could not be used for incorporation in those
materials which require flexibility, such as, clothes and small
articles.
Particularly, when the heating sheet is incorporated in an
aqualung, the working time in the water in connection with ocean-
and lake-raisings can be remarkably lengthened and thus the heating
sheet is very advantageous for future ocean developments and cold
district developments where snowfalls and icing cause
difficulties.
One of the objects of the present invention is to provide a heating
sheet which is accident-free and superior in pliability and
flexibility by equipping it with electrodes and wrapping the whole
with an insulating materials which are superior in pliability and
flexibility.
A further object is to provide a heating sheet which is
accident-free and superior in pliability and flexibility.
Another object of this invention is to provide an electroconductive
high molecular material for use as elements in a highly flexible
and accident-free heating sheet.
The definitions of the terms "heating sheet" and "heating unit
sheet" used in the present invention are; "heating sheet" means a
sheet which evolves heat all over the surface in contrast to a
linear heater such as nichrome wire, and not yet equipped with an
electrode, and "heating unit sheet" means "a heating sheet" which
is equipped with an electrode and further is electrically
insulated.
The important points on which the present invention differs from
the conventional heating sheets are:
1. High structure carbon is said to have good electroconductivity
but it is so coagulative that the structure of carbon is likely to
be nonuniform after application. This may cause the heating sheet
to deteriorate due to the heat evolution locally induced on the
surface. In this invention, high-dispersion grafted carbon which is
produced by grafting a vinyl resin to oil furnace black is
used.
2. The most important component of a flexible heating sheet is the
base material for applying paint thereon. The base material is
required to be thin enough and to have strength and resistance
against bending to maintain flexibility. The surface must be
uniformly uneven to assure uniform application of paint and hold an
appropriate porositing of volume to connect both side surfaces of
the material. Further, the fibers themselves must be heat-resistant
with high softening and decomposition temperatures and the product
must be free from shrinkage and elongation. For these reason,
high-melting synthetic fibers and the texture as referred to later
are employed in the present invention.
3. In conventional heating sheet, most vehicles for paint have only
poor ability to bind the carbon particles to each other and the
carbon particles to the base material and poor thermal resistance.
In this invention, however, use of cross-linking agent has led to
success in forming a strong combination between grafted carbon
particles.
4. The aging process of the coated film was necessary to make the
electrical properties stable, but a long endured heating may often
induce deterioration of the synthetic fibers which form the base
material. An appropriated condition has been found in this
invention, under which the treatment is completed in a shorter
period at a high temperature and thus constant properties can be
maintained for a long time.
5. A conventional flexible and highly resistant heating sheet can
is difficult to combine with wires which lead electricity without
introducing various mechanical and electrical problems. They have
been solved in this invention particularly by the application of
the thin electrodes.
As for the electrode of a conventional heating sheet, a thin metal
strip or foil has been used and closely attached to the heating
sheet by bonding, etc. Therefore, when the heating sheet with
electrode is bent, the electrode cannot follow the bending and
peeling-off or cracking of the electrode results which damages the
electrical contact and excessive current flows through the portion,
which portion is subjected to extraordinarily high temperatures as
compared with other normal portions and is very often damaged.
According to the present invention, the electrode is of a soft and
flexible structure and much less susceptible to damage by bending,
and even when it is damaged, the extraordinarily high temperature
melts the fibers and cuts off the circuit so that a high degree of
safety is assured.
The heating sheet of this invention can be prepared by the
following method.
An electroconductive high molecular paint which is prepared by
dissolving in a solvent an electroconductive high molecular
material superior in flexibility is applied in a thin layer onto
the surface of a sheet that is superior in pliability and
flexibility such as, for example, textures prepared of various
kinds of high temperature-resistant synthetic fibers, such as nylon
and Tetron fibers, and the resulting product is dried to form a
thin film of the electroconductive high molecular material on one
or both sides of the sheet. The application of the coating material
referred to above may be carried out in any selected way of coating
such as roll coater, doctor coater, dip coater and spraying coater.
The thin film of the electroconductive high molecular paint formed
on the sheet is then heated to accomplish the cross-linkage of the
electroconductive high molecular paint and to obtain the
electroconductive heating sheet. This heating sheet may be further
heated at high temperatures to stabilize the electrical properties.
Electrodes are fixed to the heating sheet being cut into appriciate
size and the process to prepare a heating sheet with electrodes is
completed. The heating sheet with electrodes can evolve heat when
the electrodes are connected by lead wires to a power source. For
the sake of safety in handling, the heating sheet with electrodes
should be wrapped on both sides with an insulating sheet prepared
from rubber or a flexible synthetic resin to obtain a heating unit
sheet.
The method of synthesizing the electroconductive flexible high
molecular material of the heating sheet will be explained as
follows.
Vinyl monomers are heated in the presence of carbon black to carry
out graft polymerization by the free radical initiation and
polymerization of the vinyl monomers to each other, and vinyl
polymers of relatively short chain lengths are chemically combined
on active spots on the surface of the carbon black in a radial
shape. As a result of the polymerization reaction, surface chemical
properties of the carbon black particles are changed because of the
plurality of vinyl polymer chains combined with the surface, and
the particles acquire better dispersivility in organic solvents.
Variation in the of vinyl monomer used makes possible different
miscibility in the solvent. In addition, the high molecular
substance can be made reactive by introducing certain functional
groups into the vinyl monomers.
The vinyl monomers described above are expressed by the following
formula of the general type: ##SPC1##
where R and R' mean a hydrogen atom and various substituents such
as alkyl group, and the monomers include those which contain
functional group such as acrylic and methacrylic acids, maleic acid
anhydride, acrylamide, and those having no functional group such as
esters of acrylic and methacrylic acids and maleic acid anhydride,
acrylamide, methacrylamide, acrylonitrile, methacrylnitrile, vinyl
acetate, styrene and derivatives thereof, vinyl ethers and vinyl
pyridines.
The cross-linking agents which react with the abovementioned
functional groups include high molecular compounds having epoxy
groups, metal organic compounds expressed by a general formula,
Me(OR).sub.n, where R is an alkyl group having 1 - 16 carbon atoms,
n is an integer of 2 - 4, and Me is a metal atom selected from the
group consisting of Ti, Zn, Mg, Pb, Cu, Al and Cd, amine compounds
and polyvalent alcohols. By combining the functional groups
introduced into the vinyl polymers mentioned above with the
cross-linking agents such as the high molecular compounds and the
organometallic compounds referred to above, vinyl polymers
polymerized on the surface of the grafted carbon particles can be
cross-linked, and therefore the carbon black particles can be
firmly combined both physically and chemically. Consequently, if
electricity is passed through for long time the carbon black
combined with vinyl polymers (electroconductive high molecular
paint), shift of carbon black toward the electrode can be
prevented. It is desirable to age the material at a temperature
above the service temperature in order to obtain a film having
better electrical stability.
It is possible that the heat treatment can be completed in a
shorter time and the cross-linking reaction can also be completed
to a necessary extent, even when a base texture sheet of synthetic
fiber is used, under a heating condition in which the base texture
is not thermally deteriorated, when the following electroconductive
polymer compositions are used. These compositions comprise polymers
having functional groups such as -OH, -COOH, -NH.sub.2, =NH, -CONH,
##SPC2## , and -SONH.sub.2 and the compounds used as cross-linking
agents are expressed by the following general formula, ##SPC3##
where R is an aliphatic, aromatic or alicyclic compound and n is an
integer from 2 to 4.
Reactive compounds expressed by the general formula ##SPC4##
and having 2 to 4 terminal aziridine rings, which are employed as
cross-linking agents in the present invention, include
N,N'-tetramethylene-bis-ethyleneurea,
N,N'-pentamethylene-bis-ethyleneurea,
N,N'-hexamethylene-bis-ethyleneurea,
N,N'-heptamethylene-bis-ethyleneurea, N,N'-octamethyleneurea,
p-phenylene-bis-ethyleneurea, m-phenylene-bis-ethyleneurea,
m-toluilene-bis-ethyleneurea,
l-chloro-m-phenylene-bis-ethyleneurea,
diphenyl-4,4'-bis-ethyleneurea,
3,3'-dimethyldiphenyl-4,4'-bis-ethyleneurea,
3,3'-dimethoxydiphenyl-4,4'-bis-ethyleneurea,
diphenylmethane-p,p'-bis-ethyleneurea,
tetramethylene-bis-ethyleneurethane,
hexamethylene-bis-ethyleneurethane,
nonamethylene-bis-ethyleneurethane,
decamethylene-bis-ethyleneurethane,
bis-phenyl-4,4'-bis-ethyleneurethane,
p-phenyl-4,4'-bis-ethyleneurethane,
p-phenyl-4,4'-bis-ethyleneurethane, p-cyclohexylethyleneurethane,
lysine-bis-ethyleneurea, tetraaziridinyl-m-xylenediamine,
tetraaziridinylmethyl-p-xylenediamine,
diaziridinylmethyl-m-xylenediamine,
diphenylmethane-4,4'-tetraaziridinylmethylenediamine,
bis-phenyl-4,4'-tetraaziridinylmethylenediamine.
The above mentioned compounds expressed by the general formula,
##SPC5##
are readily subject to cleavage of the aziridine rings on heating
and to react with functional groups such as -OH, -COOH, -NH.sub.2,
=NH, -CONH, ##SPC6## and -SONH.sub.2. Since the compounds expressed
by the general formula, ##SPC7##
used as cross-linking agent and the polymers having functional
groups such as -OH, -COOH, -NH.sub.2, =NH, -CONH, ##SPC8## , and
-SONH.sub.2 are contained together in the electroconductive polymer
compositions of the present invention, reactions of the former
compounds with the latter polymers can be most readily
accomplished.
The polymers to be employed in the present invention as having
those functional groups which react with the compounds expressed by
the general formula ##SPC9##
include following compositions, for example, graft carbon polymer
composition having the functional groups mentioned above prepared
by graft polymerization of carbon with vinyl monomers, mixture
compositions prepared by mixing polymers having the functional
groups above with carbon powder and compositions prepared by
combined use of the graft carbon polymer composition.
It is also an object of the present invention to provide flexible
heating sheets which can be used for more than 2,000 hours at
120.degree. C, and it is desirable to use a texture fabric of,
synthetic multifilament fibers with a thermal decomposition or
softening temperature higher than 250.degree. C Spun threads are
not uniform in thickness and do not possess a smooth surface or
elongation resistance). The texture should be plain woven, 0.10 to
0.15 mm thick, and carry 20 to 65 percent, preferably 40 to 60
percent, by volume of porosity, and a tensile strength of texture
greater than 10 kg/cm.
If the volume of porosity exceeds 65 percent, the applied carbon is
apt to fall out and in addition, a serious change of resistance
occurs. On the contrary, for the volume of porosity less than 20
percent the applied carbon is likely come off and, irrespective of
the of smoothness, plain weaving is difficult to perform. In
conclusion, therefore, the permissive range is 20 to 65 percent,
preferably 40 to 60 percent.
Appropriate choice of the volume of porosity permits better
adhesion of the coated film of grafted carbon paint since a portion
of the pain penetrates through the pore to the other side.
For example, 75 denier multifilament threads of polyester fibers
having a strength of 5 g per unit denier are woven in 110 and 98
threads per inch in the longitudinal and lateral direction,
respectively. The volume of porosity of this texture is about 50
percent. Less number of threads in the lateral direction by 10
percent is used because 10 percent shrinkage occurs during the
processing. Though polyester fibers are the most suitable, any
other heat resistant fibers may be used if the above requirements,
are met. Regarding the structure of the textures, any weaving
method can be used if the obtained volume of porosity, thickness
and smoothness satisfy the required conditions. The above texture
is required before use to be subjected to heat setting for 30 to 60
sec. at a temperature by 5.degree. to 10.degree. C below the
softening temperature of the fibers to assure the dimensional
stability of the fibers. For example, they are set for 45 sec. by
introducing them into an oven at 225.degree. C. Furthermore, it is
necessary before the grafted carbon paint is applied that the said
texture should be dipped in a suitable organic solvent (preferably
the same solvent as used for the paint) to remove bubbles inside
the texture.
The present invention also provides a new idea for placing
electrodes on the heating sheet. As a preferred embodiment, 34
copper wires of 0.01 mm.sup.2 cross-sectional area knitted in a
flat ribbon of 6 mm broadness are used. Plating the copper wires
with tin is more useful. At first, electroconductive silver paint
is applied in the shape of 1 cm broad band at the ends of the
heating sheet, dried by heating and the ribbon electrodes mentioned
above are placed on the portions and attached by sewing in zigzag
with electroconductive thin threads and then pressed with rollers.
The ribbon electrodes from the heating sheet are combined and
connected with external leads. The electrodes thus formed are
extremely thin (about 0.1 mm) and so flexible as not to affect
bending. Cracks and breaking do not cause any trouble owing to the
flexible structure.
The capacity for current of the ribbon-shaped knitted electrodes
above is 3.4A. When a larger capacity is required, the thickness
and number of the wire and width of the ribbon should be increased
to meet the requirement. Electroconductive thin wires refer to very
thin wires of copper, silver and others and tape-shaped thin copper
foils wrapping a cotton thread, which serve to pass the electric
current to the other side.
The heating sheet with electrode may be covered not only with a
flexible insulating material to make a flexible heater but also
with a rigid insulating material to use as a flat plate heater.
As the insulation materials, rubber sheets, rubber coated sheets
and synthetic resin sheets such as vinyl chloride sheets,
polyethylene sheets, polypropylene sheets, polyurethane sheets,
polyamide sheets, polyethylene telephtalate and
ethylene-vinylacetate copolymer sheets may be used, and also liquid
rubber and soft casting resins such as methane, and silicone-rubber
may be used.
A preferred embodiment of the present invention is described with
reference to the examples illustrated in the attached drawings in
which:
FIG. 1 is a fragmented plan view of the heating sheet with
electrodes of the present invention;
FIG. 2 is a sectional view of the heating sheet with electrodes
taken along lines 2--2 of FIG. 1.
FIG. 3 is a fragmented plan view showing the heating element;
FIG. 4 is a sectional view showing the electrodes and the structure
of the heating sheet taken along lines 4--4 of FIG. 3;
FIG. 5 is a sectional view similar to FIG. 4;
FIGS. 6 and 7 are fragmented plan views showing a further heating
sheet with electrodes;
FIGS. 8 and 9 are sectional views showing the electrodes and the
structure of the heating sheet with FIG. 8 taken along lines 8--8
of FIG. 7 and FIG. 9 depicting an assembled sheet;
FIGS. 10 and 11 are fragmented plan views showing a still further
heating sheet;
FIG. 12 is a plan view of a further heating sheet with
electrodes;
FIG. 13 is a sectional view taken along lines 13--13 of FIG. 12
showing its structure along lines 13--13
FIG. 14 is a plan view in perspective of a still further embodiment
of a heating sheet with electrodes; and
FIG. 15 is a sectional view taken along the lines 14--14; of FIG.
14 taken along lines 15--15
EXAMPLE 1
Oil furnace black -- 328 g
Acrylic acid -- 72 g
Butyl acrylate -- 256 g
.alpha.,.beta.-azo-bis-isobutylnitrile (initiator) -- 30 g
Methylisobutylketone -- 1,000 g
The above ingredients were placed in a three neck flask and
polymerized by agitating for 8 hours at 80.degree. C in a nitrogen
atmosphere. A polymerized liquid of 80 cps viscosity was obtained
with a yield of 97 percent. Then a solution of cross-linking agent
prepared as shown below was added to the polymerized liquid under
stirring.
Epoxy resin (cross-linking agent) -- 76 g
Methylisobutylketone (solvent) -- 200 g
Polymerized liquid mentioned above -- 1,656 g
As epoxy resin, ARALDITE (supplied from Shell Chemical Co.) of the
epoxy equivalent 76 was used. The same resin was used for the
cross-linking agent in all examples that follow.
Referring to FIGS. 1 and 2, the mixed solution (2) thus formed was
applied onto a texture or fabric (1) made of polyester fibers (No.
3311 Tetron from Teizin Co.) wet pick up of 115 g/m.sup.2 with a
dip coating machine at the speed of 3.4 m/min. and dried with hot
air at 150.degree. C (see FIG. 2). This was further heated for 16
hours at 220.degree. C to complete cross-linking and the aging
treatment. The resulting heating sheet element (3) had an area
resistance of 100.OMEGA..quadrature.(square).
On the other hand, a comparison specimen of a heating sheet element
was prepared by applying a mixed paint composed of 328 g of oil
furnace black, 328 g of acrylic resin and methylisobutylketone on a
texture of glass fibers, where carbon was neither polymerized nor
cross-linked. The pliability and flexibility of heating sheet
element (3) obtained in this example was compared with those of the
above product for comparison, as shown in Table 1.
Tests were conducted by JIS L-1079 using Scott's flexing tester and
by using Olsen's bending tester.
TABLE 1
Scott's flexing tester Olsen's bending (1 kg/1.5 cm load) tester (1
kg/1,5 cm load)
__________________________________________________________________________
Specimen for Cut at 28 Cut at 8 comparison repetitions repetitions
Product of this Nothing wrong at 1000 Nothing wrong at example
repetitions 2000 repetitions
As shown in Table 1, the heating sheet of this example proved to be
superior in pliability and flexibility. Then the heating sheet was
cut to appropriate dimensions, and an electroconductive paint (8)
of silver was applied to the areas (4) at which electrodes were to
be fixed, where ribbon wires (12) (4 mm wide, 0.2 mm thick and of
electrical capacity 5A) made of 16 co-axial cables were fixed by
sewing with copper threads (7) to compose electrodes for the
heating sheet (6).
The electrodes were so flexible that the whole body of the heating
sheet (6) was also very flexible and held good performance for a
long term.
The heating sheet obtained above was covered on both sides with
polyvinyl chloride sheets (5) (0.4 mm thick) (see FIGS. 1 and 2).
When the interval and length of the electrodes (10) were made to be
420 mm and 900 mm, respectively, and electric current was passed at
100 V and 570 W/m.sup.2, a temperature higher by 30.degree. C above
room temperature (20.degree. C) was obtained on the surface of
polyvinyl chloride sheet.
EXAMPLE 2
Oil furnace black -- 220 g
Acrylic acid -- 115 g
Acrilonitrile -- 85 g
Azo-bis-isobutylnitrile -- 20 g
Cyclohexanon -- 680 g
The above ingredients were mixed by agitation for 6 hours while
they were heated at 90.degree. C in the same manner as in Example
1. As a result, a solution of polymerized substance having
viscosity 95 cps was obtained with a yield of 98.5 percent.
Subsequently, a cross-linking agent dissolved in a solvent in the
proportion as shown below was added under stirring to the solution
of polymerized substance mentioned above.
Epoxy resin (cross-linking agent) -- 65 g
Cyclohexane (solvent) -- 170 g
Above solution of polymerized substance -- 1,220 g
The mixed solution (2) thus formed was applied onto a texture (1)
of polyamide fibers wet pickup of 140 g/m.sup.2 with a dip coating
machine at the rate of 1 m/min. and dried by a 150.degree. C hot
air. This was further heated for 30 hours at 200.degree. C to
complete cross-linking and aging treatment. The heating sheet
element (3) obtained had an area resistance of
50.OMEGA..quadrature.(square).
The pliability and flexibility of the heating sheet (3) obtained in
this example proved excellent as seen in the following table.
TABLE 2
Scott's flexible tester Olsen's bending (1 kg/1.5 cm load) tester
(1 kg/1.5 cm load)
__________________________________________________________________________
Product of this Nothing wrong at 1000 Nothing wrong at example
repetitions 2000 repetitions
A silver paint as electroconductive paint was applied to the
heating sheet element (3) and a ribbon wire (12) made of thin
copper wires was fixed in a zigzag line by sewing at the site with
thin copper wires (7) to form an electrode as shown in FIG. 6, and
a further amount of the silver paint (8') and (8") was applied on
the opposite side to cover the fixing wires (7) of the heating
element as shown in FIG. 5.
Since the electrodes (4) shown in FIGS. 6 and 7 were very flexible,
the heating sheet (6) of this invention was also very flexible as a
whole.
The above heating sheet (6) was covered on both sides with
polyvinyl chloride sheets (5) and (5') (0.4 mm thick). With the
interval and the length of electrodes (4) of 420 mm and 900 mm,
respectively, and the electricity of 100 V and 270 W/m.sup.2, a
temperature higher by 14.degree. C than room temperature
(20.degree. C) was obtained on the surface of the polyvinyl
chloride sheet.
EXAMPLE 3
Oil furnace black -- 184 g
Vinyl acetate -- 172 g
Maleic acid anhydride -- 196 g
Azo-bis-isobutylnitrile -- 32 g
Octyl alcohol -- 12 g
Cyclohexane -- 830 g
Above ingredients were agitated while being heated under the same
condition as in Example 2. A solution of polymerized substance of
viscosity 87 cps was obtained with a yield of 98.3 percent.
In the next step, a cross-linking agent dissolved in a solvent in a
proportion described below was added to the above solution under
stirring.
Epoxy resin -- 85 g
Cyclohexane -- 225 g
Above solution of polymerized substance -- 1,394 g
The mixed solution (2) thus formed was applied onto a texture (1)
made of polyester fibers with a dip coater under the same condition
as in Example 1, dried and thermally treated to obtain heating
sheet elements (3). The area resistance of the heating sheet
elements (3) was 200.OMEGA..quadrature.(square).
The pliability and flexibility of the heating sheet element (3) in
this example proved to be excellent as shown in the following
table.
TABLE 3
Scott's flexing tester Olsen's bending tester (1 kg/1.5 cm load) (1
kg/1.5 cm load)
__________________________________________________________________________
Product of this Nothing wrong at Nothing wrong at example 1000
repetitions 2000 repetitions
At the opposite ends on one side of the heating sheet element was
applied a silver paint (8) and two streaks of thin copper wires (7)
were fixed as electrode by sewing each at an end and parallel to
each other in a zigzag line. These electrodes were so flexible that
the heating sheet (6) of this example was as a whole very
flexible.
Meanwhile, the electrodes of (A) the heating sheet coated with
silver paint equipped with electrodes formed by pasting a 0.15 mm
thick copper foil thereon; (B) the heating sheet coated with silver
paint equipped with electrodes formed by sewing thereon, two
parallel fine copper wires in a straight line; and (C) the heating
sheet coated with silver paint equipped with electrodes formed by
sewing thereon fine copper wire in a zigzag form were subjected to
stamping tests to determine their resistance value variations. The
results are shown in Table 4.
TABLE 4
Results of Electrode Stamping Tests After 200 Stampings Resistance
Variation Rate After 10,000 Stampings
__________________________________________________________________________
Electrode of Heating Sheet A Damaged -- Electrode of Heating Sheet
B No Damage 13.7 % Electrode of Heating Sheet C No Damage 1.5 %
The above stamping tests were conducted as under.
The electrode portions are repeatedly stamped 20 times per minute
with a stamping total load of 50 kg whole current of 100 V is
passed. ##SPC10##
As seen from the above results, in case of the heating sheet (A) in
which the copper foil is pasted, the durability of the electrode is
very poor, while in case of the heating sheet (C) in which the fine
copper wire is sewn in a zigzag form, the electrode is very
flexible and electrically stable.
In this example, as the fine copper wire No. 40 copper thread was
used and the sewing span was 5 mm.
EXAMPLE 4
Oil furnace black -- 330 g
Acrylamide -- 137 g
Vinyl acetate -- 163 g
Azo-bis-isobutylnitrile initiator -- 35 g
Cyclohexanone -- 1,500 g
Above ingredients were stirred while being heated under the same
condition as in Example 2. A solution of polymerized substance of
viscosity 93 cps was obtained with a yield of 98.8 percent.
Subsequently, a cross-linking agent dissolved in a solvent was
added to the solution of polymerized substance in the proportion
described below while being stirred.
Tetrapropyl titanate (cross-linking agent) -- 84 g
Cyclohexane (solvent) -- 380 g
Above solution of polymerized substance -- 2,139 g
The mixed solution (2) thus formed was applied onto a texture (1)
made of polyamid fibers with a dip coating machine to wet pickup of
140 g/m.sup.2 at the rate of 1 m/min., and then dried with a hot
air of 150.degree. C. Further heating was continued for 30 hours at
200.degree. C to complete cross-linking and aging treatment. The
area resistance of the heating sheet element (3) obtained was
50.OMEGA..quadrature.(square).
The pliability and flexibility of the heating sheet produced in
this example proved excellent as shown in the table below.
TABLE 5
Scott's flexing tester Nothing wrong at (1 kg/1.5 cm load) (1
kg/1.5 cm load)
__________________________________________________________________________
Product of Nothing wrong at Nothing wrong at this example 1000
repetitions 2000 repetitions
As shown in FIG. 7 a silver paint (8) was applied onto the heating
sheet element (3) at the two areas (4) and two streaks of thin
copper wires (7) were fixed by sewing at each area almost in
parallel to each other, and the silver paint (8) placed on areas
(4) on the heating sheet. These electrodes were very flexible. The
whole body of the said heating sheet (6) was covered with films (5)
and (5') (0.5 mm thick) of polyvinyl chloride for insulation. The
films of polyvinyl chloride was so flexible that they did not
interfere with the flexibility of the heating sheet.
EXAMPLE 5
Mixture composition A
Oil furnace black -- 24.0 kg
Acrylic acid -- 4.4 kg
Butyl acrylate -- 15.6 kg
Azo-bis-isobutylnitrile -- 0.64 kg
Cyclohexanone -- 110.0 kg
Cyclohexanone and then other constituents, were placed in a 200l
reaction vessel provided with a reflux condenser and the reaction
was continued for 5 hours at 90.degree. C while nitrogen was being
introduced at the rate of 10l per minute. When the reaction was
completed, a dispersion of non-precipitative grafted carbon, of
which the viscosity was 18.5 cps at 20.degree. C and containing
28.9 percent of solid matter, was obtained.
To the 25 kg of mixed solution obtained, the solution of
cross-linking agent shown as the mixture composition B was added
and the whole mixture was made uniform with a stirrer. The paint
had a viscosity of 12.5 cps at 20.degree. C and contained 24.4
percent of solid matter.
Mixture composition B
Tetrapropyl titanate -- 0.897 kg
Cyclohexanone -- 6.36 kg
A portion of the above paint was applied onto a glass plate, dried
at 150.degree. C for an hour and heated at 225.degree. C for 5
hours and then the volume resistibity was 0.26 ohm/cm.
The original base material used was a texture having 50 percent by
volume of porosity which was prepared by weaving 75 denier
multifilament polyester fibers in 110 and 98 threads per inch in
the longitudinal and lateral directions, respectively. This texture
was introduced to pass into a vat of cyclohexanone solvent to
remove bubbles between the fibers. Subsequently the texture was
introduced five times into a paint bath at the rate of 1 m per
minute and then dried, taking 4 minutes at the drying temperature
150 to 160.degree. C. The amount of solid substance attached to the
texture amounted approximately to 9 g/m for a single dipping, and
to 41 g/m.sup.2 for five times of dipping.
The base material texture to which application of paint has been
done was heated at 180.degree. C in an oven for 2 hours to complete
the cross-linkage. Then, this was heated for additional 8 hours in
an oven at 225.degree. C for aging. The electrical resistance of
the product was 49 ohm per cm.sup.2 and was uniform everywhere on
the texture. Physical properties of the flexible heating sheet
obtained were as follows:
Tensile strength 26 kg/3 cm (longitudinal) 19.5 kg/3 cm (lateral)
Tear strength (test method JIS K6772) 160 g Bending test (Orsen) at
1 kg load applied No change occurred at 4000 bendings Flexing test
(Scott) at 1 kg load applied No change occurred at 2000 flexing
Electrodes were settled on the heating sheet of this invention at a
distance 50 cm .times. 50 cm, and an ac voltage 100V was applied
between them. A current of 2.0 A flew which remained constant for
500 hours and a uniform temperature between 62.degree. to
64.degree. C was maintained when the room temperature was
22.degree. C. The numerical values mentioned above show
satisfactory performance of the flexible heating sheet.
The heating sheet of the present invention showed excellent
flexibility in the direction perpendicular to the sheet so that
conductivity did not change even for bending up to 180.degree. and
no carbon was scraped off at the Gakushin-type friction strength
test.
EXAMPLE 6
A mixture consisting of 60 g of oil furnace black, 11 g of acrylic
acid, 39 g of butyl acrylate, 16 g of azo-bis-isobutylnitrile, and
1,100 g of cyclohexanone was treated to react for 5 hours in at
about 90.degree. C just as in Example 5 to obtain a liquid (A) of
graft carbon polymer in which acrylic acid and butyl acrylate were
grafted on the surface of carbon black. The product contained 28.8
percent of 18.5 cps solid. Then a mixed liquid as under was
prepared and mixed by a high-speed mixer.
Graft carbon polymer liquid (A liquid) -- 100 parts
Diaziridinyl-m-xylene diamine -- 6 parts
Cyclohexanone -- 4.5 parts
Thus obtained liquid (B) was applied to the texture uniformly in an
amount of 30 g/m.sup.2 in solid resin in a similar way as in
Example 5. Then the obtained heating sheet was heat treated at
220.degree. C for 3 hours and the integrated resistance was
128.OMEGA..quadrature.. The physical properties of this heating
sheet are as under which indicates excellent strength with good
flexibility.
Tensile strength (JIS L-1068) -- 35.2 kg/3 cm
Tear strength (JIS K-6772) -- 430 g
Bending test (Orsen) at 1 kg load
No change occurred at 10,000 bending Flexing test (JIS
L-1079)(Scott) at 1 kg load
No change occurred at 10,000 flexing
This heating sheet cut into a 50 cm length and 32 cm width sheet,
and a high conductivity paint with silver powder therein was
applied on the heating sheet at two sides in a width of 1 cm and a
length of 50 cm in the lateral direction of the heat to form the
electrode portions. Then the sheet was heat treated in a heating
oven at 150.degree. C for 10 minutes to make up fully the
conductivity the silver electrode. The resistances of the
electrodes of 50 cm length were 1.2.OMEGA. and 1.5.OMEGA.
respectively. On the silver electrode, a flat ribbon of 6 mm width
made of 34 copper wires each of 0.01 mm.sup.2 cross section was
placed and sewed with fine copper thread of No. 40 in a zigzag line
by a sewing machine. The resistance of this heating sheet was
76.3.OMEGA.. Then the heating sheet with the electrodes was covered
on both side with two sheets (0.8 mm thickness) of soft vinyl
chloride prepared by mixing 50 parts of plasticizer DOP
(di-2-ethylhexylphtalate) to polyvinyl chloride having average
polymerization degree of 1,200, and the sheet was insulated by a
hydraulic press at 150.degree. C for 5 minutes. The resistance
after the insulation treatment was 76.5.OMEGA. and showed no
substantial change. This indicates a stable insulation resistance
was obtained, and thus a heating unit sheet having excellent
flexibility was obtained. Then the heating unit sheet was subjected
to a durability test by giving the sheet an alternative current of
100V for 1 hour and stopping the current for 30 minutes and
repeating this cycle in a chamber maintained at 20.degree. C. The
surface temperature of the heating unit sheet during the current
passage was 70.degree. C in average. After 2,000 times of the above
current passages, the resistance of the heating unit sheet showed
75.2.OMEGA.. Thus it was confirmed that no substantial change of
resistance takes place and the sheet is an electrically stable
resistor.
The following examples show the modes of electrode setting on the
heating sheet.
EXAMPLE 7
As shown in FIG. 10 the parts of the heating sheet (3) obtained in
Example 1 which will compose electrodes were coated with a silver
paint (8), then covered with small pieces (13) of copper foil (6
mm.sup.2) at 3 cm intervals, ribbon wires (12) made of thin copper
wires were placed upon them, as shown in FIG. 11, and the whole was
fixed by sewing with thin copper (7) wires to form electrodes for
heating sheet.
The electrodes (4) of the heating sheet (6) of this example do not
lack flexibility since the copper pieces (13) are fixed at
intervals. Further, in this example terminals were fixed to the
copper pieces (13) and lead wires (9) were connected to the
terminals (11).
EXAMPLE 8
As shown in FIG. 10 the parts of the heating sheet element (3)
obtained in Example 2 which will compose electrodes were coated
with a silver paint (8) then covered with small pieces (13) of
copper foil (4 mm.sup.2) at 2 cm intervals, ribbon wires (12) were
placed upon them, as shown in FIG. 11 and the whole was fixed by
sewing with thin copper wires (7). Further, the same silver paint
(8) was applied on the other side to cover the fixing wires on the
heating sheet eleement (3) and the copper foils (13) and to reduce
the contact resistance to be used as electrode (4) of the heating
sheet (6).
The electrode part (4) of the heating sheet (6) of this example is
flexible enough because small pieces of copper foil (13) are fixed
at intervals.
EXAMPLE 9
The parts of the heating sheet element (3) obtained in Example 3
which will compose electrodes (4) were coated with a silver paint
(8), then covered with small pieces (13) of copper foil (13) (5
mm.sup.2) at 4 cm intervals and two streaks of thin copper wires
(7) were fixed by sewing together with the copper pieces to form
electrodes of the heating sheet (6).
Since the small pieces (13) of copper composing electrodes (4) are
fixed at intervals, the heating sheet (6) of this example is
sufficiently flexible.
EXAMPLE 10
The parts of the heating sheet element (3) obtained in Example 4
which will compose electrodes (4) were coated with a silver paint
(8), then covered with small pieces (13) of copper foil (4
mm.sup.2) at 5 cm intervals and three streaks of thin copper wires
(7) were fixed by sewing together with the copper pieces and again
the silver paint was applied from outside onto the fixing wires on
the heating sheet and the copper pieces to reduce the contact
resistance of electrodes. Thus, a heating sheet was composed.
Since the electrode parts (4) of the heating sheet (6) of this
example were made of small pieces of copper foil fixed at
intervals, they were very flexible.
EXAMPLE 11
The parts of the heating sheet element (3) obtained in Example 1
which will compose electrodes (4) were covered with small pieces
(13) of copper foil (4 mm.sup.2) at 2 cm intervals, ribbon wires
(12) were fixed on the parts with thin copper wires, and the silver
paint (8) was applied from outside onto the fixing wires on a
heating sheet and the small pieces of copper foil to reduce the
contact resistance of electrodes. Thus, a heating sheet (6) was
composed.
Since the electrode parts of the heating sheet of this example were
made of small pieces of copper foil fixed at intervals, they were
sufficiently flexible.
EXAMPLE 12
The parts of the heating sheet element (3) obtained in Example 2
which will compose electrodes (4) were covered with ribbon wires
which were fixed by sewing with thin copper wires (7) and as shown
in FIG. 5, the silver paint (8) was applied from inside onto the
fixing wires on the heating sheet element to reduce the contact
resistance of electrodes. Thus, a heating sheet was formed.
Since the electrodes of the product of this example were good in
flexibility, the heating sheet of this example as a whole was very
flexible.
EXAMPLE 13
The parts of the heating sheet (3) obtained in Example 3 which will
compose electrodes (4) were covered with small pieces (13) of
copper foil (3 mm.sup.2) at 3 cm.sup.2 intervals, ribbon wires (12)
were placed upon the areas and they were fixed by sewing all
together to form electrodes of a heating sheet.
Since the electrode parts (4) of the heating sheet (6) of this
example were covered with small pieces of copper foil (13) fixed at
intervals, they were sufficiently flexible.
EXAMPLE 14
At the parts of the heating sheet element (3) obtained in Example 4
which will be electrodes (4) were fixed by sewing four streaks of
thin copper wires (7) in parallel to each other, where the silver
paint (8) was applied from outside to cover the fixing wires on the
heating sheet to reduce the contact resistance of electrodes. Thus,
a heating sheet (6) was formed.
Since the electrode parts (4) of the product of this example were
very flexible, the heating sheet of this example as a whole was
sufficiently flexible.
EXAMPLE 15
At the parts of the heating sheet (3) obtained in Example 1 which
will compose electrodes, small pieces (13) of copper foil were
placed at 3 cm intervals, four streaks of thin copper wires (7)
were fixed by sewing in parallel at the areas, and the silver paint
(8) and (8') was applied from both sides, as shown in FIG. 9, to
cover the fixing wires on the heating sheet element (3) to reduce
the contact resistance of electrodes. Thus, a heating sheet (6) was
formed.
Since the electrode parts of the heating sheet of this example were
composed of small pieces of copper foil fixed at intervals, they
were sufficiently flexible.
EXAMPLE 16
In FIG. 12 and FIG. 13, (21) is a heating sheet, (23) is a ribbon
made by knitting fine metal wires which is sewed in a zigzag form
onto the heating sheet (21). The seams (25) formed on the heating
sheet (21) may be filled with a paint (26) having good electric
conductivity so as to reduce the contact resistance between the
conductive wire (24) and the heating sheet (21). As for the paint
(26) having good electric conductivity, and that used for the
portion (22) it may be prepared by dispersing powder such as silver
powder dispersed in synthetic resins.
The electrode in this example is prepared by sewing the ribbon (23)
of metal wires onto the portion (22) coated with paint having good
conductivity in a zigzag form using the fine wire (24).
EXAMPLE 17
In FIG. 14 and FIG. 15, the heating sheet (31) schematically shown
is covered on both sides by an insulating material (32) (32') and
on one side of thus obtained sheet (33) flexible insulating
material (34) is laminated to form a laminated layer (35) and the
sheet (33) and the laminated layer (35) are covered by a surface
protecting material (36). Thin electrode plates (37), (37') are
provided on the heating sheet (31) and lead wires (38), (38') are
connected to the electrode plates.
The insulating material (32), (32') may be a flexible thin
insulating sheet made of various synthetic sheets and rubber sheet.
The flexible insulating material (34) may be made of flexible
urethane, foamed rubber, foamed polyethylene etc., and laminated on
one side of the heating sheet (33) using a bonding agent. The
surface protecting material (36) may be rubber sheet, synthetic
resin sheet, synthetic resin leather, etc.
EXAMPLE 18
This example shows a water-proof heating unit sheet according to
the present invention. In FIG. 1, the heating sheet with electrodes
(4) is connected with a lead wire (15) and covered from both sides
with water-proof insulating sheets (5) and (5') and sealed by using
a bonding agent having high heat-resistance or by heat fusion.
The lead wire (15) penetrates the water-proof sealer (16) closely
adhering the water-proof insulating sheets (5) and (5'). The sealer
(16) is positioned at the inner portion of the water-proof
insulating sheets (5) and (5'). In this example, the opening for
the lead wire (15) is equipped with a conventional water-proof
device. As the water-proof sealer (16) is positioned at the inner
portion of the water-proof insulating sheets (5) (5'), and not at
the outer edge portion which is subjected impact, this sealer (16)
is free from damage. And as the sealer (16) is closely fixed to the
inner portion of and completely heated by (5) and (5') there is no
danger of water leakage even when the sealer (16) is damaged, due
to the close adhesion of the sheets (5) and (5').
* * * * *