Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE I~VEN~I ~N
Electric Wire
BACKGROUND OF THE IN~7ENTION
Field of the.Invention
The prcsent invention relates to an electric wire,
and more particularly, it relates to an electric wire
which is applied to an electric.wire requiring.fire
resistance and heat resistance such as a magnet wire or a
wire employed in the vicinity of-a nuclear.reactor, or a
special wire or cable requiring corrosion resistance.
Description of the-Prior Art
The aforementioned electric wire requiring.heat
resistance or corrosion resistance..is-generally prepa.r.ed
by a covered conductor, which is coated with organic
material. However, an organic coa.ting film is
insufficient in long-term stability, heat resistance.,
chemical durability and the like.
Thus, there has been provided a conductor coated with
a compound of metal or metalloid, which.is different from
the material for the conductor, in order to attain heat
resistance and corrosion resistance. For example,
National Patent Publication Gazette No. 501783/1985 in the
name.of Raychem Inc., published in Japan on Octo~er 17,
1985, discloses a conductor which is coated with an oxide
or a nitride by vacuum deposition, in order to provide
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heat resistance to an elec~ric wire to be utilized under a
high temperature. A compound for forming such coating is
prepared by an oxide or a nitride of aluminum, silicon
e~c. Since such oxide is excellent in heat resistance and
corrosion resistance, an electric wire coated with the
oxide can be provided with high heat resistance and
corrosion resistance.
The aforementioned electric wire which is covered
with a ceramic film has been studied for improving these
characteristics. Such a ceramic film is formed by:
(a) a method of forming a film from a vapor phase
(vapor phase thin film growth method), such-as CVD
(chemical vapor deposition), PVD (physical vapor
deposition) or flame coating;
(b) an electrochemical method of forming a film in a
solution, such as plating;
(c) a sol-gel method of forming a film from a li~uid
phase by chemical reaction of reacting alkoxide; or
Id) a method of forming a film by dipping in a melt.
As hereinabove described, it i5 well known that an
oxide of ceramics such as A1203 or SiO2 is excellent in
heat resistance and corrosion resistance. However, such
an oxide formed by vacuum deposition is rather
insufficient in adhesion to the material, such as copper,
for a conductor. Therefore, when an electric wire coated
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with an oxide is used under corrosive environment over a
long period of time, for example, the oxide film may
partially peel off from the copper surface., to result in
corrosion from the exposed portion.
The vapor phase thin film grow~h method such as
vacuum deposition is employed as a method of forming.an
oxide film on the surface of a conductor. However, a film
obtained by vacuum deposition or the like may be inferior
in flexibility. Therefore., when a wire coated with an
oxide by vacuum deposition is used in a bended state, for
example, the oxide film may be broken by stress applied to
the surface of the conductor, to result in corrosion from
the broken portion.
SUMMAR~ OF THE INVENTION
Accordingly, an object of the present invention is to
provide an electric wire which effectuates excellent-heat
resistance and corrosion resistance over a long period of
time, by forming a film having excellent adhesion.and
flexibility. Another object of the present invention is
to provide an electric wire which can be industrially
obtained by simple means.in a step of coating an elonga.ted
wire conductor.
An electric wire in accordance with the present
invention comprisRs a conductor and a gel film formed by
applying a solution ob.tained by hydrolyzing and
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deh~drating/condensillg alkoxide on.o an ou~er ~art of the
conductor and leaving the same.
The gel film contributing to heat resistance, which
is formed by-a sol-gel method in the present inventionj is
excellent in flexibility and adhesion since the same-is
left not to be completely changed-into a ceramic state but
to remain in a gel state This gel film is changed into a
ceramic state by heating, to be improved in heat
resistance. However, it has been recogni~ed that its
flexibility is reduced as much as it is changed into a
ceramic state. On the basis of such a viewpoint of the
inventors, the gel film is formed as a main heat resisting
layer in the present invention. The conductor is
preferably left in an atmosphere-being at a temperature
not less than 25C, not more than 400C, in order to form
the gel film as a main heat resisting layer.
When the outer surface of a conductor coated with the
solution obtained by hydrolyzing and
dehydrating/condensing alkoxide and left is oxidized by
heat, an oxide thus produced is so fragile that adhesion
between the gel film and the conductor surface is lost to
cause peeling of the film. In order to prevent this, the
conductor surface is preferably plated with Ni or Cr for
attaining oxidation resistance, before the same is coated
with the solution and left in the aforementioned manner.
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Upon heating, the gel film is considerably shrunk to
be reduced in thickness. Such shrinkage of the film may
result in inferior durability of insulation. While a
conductor subjected to low voltage may be simply coated
with a gel film alone, a problem is caused in durability
of insulation when such a simple coa.ted wire is applied-to
a power cable. Therefore, particulates of a metal oxide.,
a metal nitride or a metal boride are preferably
dispersed/mixed-in the.gel film as ceramic filler for
suppressing shrinkage.of the gel film.
Although the gel film is considerably flexible in a
natural state, such flexibility may be lost when the gel
film is heated to be changed into a ceramic state. Even
if the electric wire is utilized in a portion-exposed to
strong vibration, the film changed into a ceramic state
must not peel off from the conductor by cracking.caused.by
the strong vibration. Thus, particularly strong adhesion
may be required between the gel film and the conductor.
In this case, an adhesion layer may be provided between
the gel film and the conductor, or between the gel film
and a plating layer formed on the surface of the
conductor. The adhesion layer may be prepared by a film
completely changed into a ceramic state by applying a
solution obtained by hydrolyzing and
dehydrating/condensing alkoxide and thereafter heating the
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same. Alternatively, the adhesion layer may be prepared
by a ceramic layer formed by CVD, on the basis of such a
viewpoint of the inve~tors that a layer formed by CVD is
larger in adhesion to a substrate than a gel film.
The inventive wire may be provided with an outermost
layer of organic material, in order to improve
slipperiness in winding and durability of insulation under
the room temperature. In this case-, the particulates of a
metal oxide etc. may be~dispersed~mixed in the organic
material layer to improve durability of insulation.
Further, the organic material layer may be formed from a
solution of organic material, added to which is a solution
obtained b~ hydrolyzing and dehydrating/condensing
alkoxide with addition of tetraalkylammonium halide to be
mixable into the solution of organic material, in order to
improve heat resistance.
A gel film in accordance with the present invention
may be formed as a multilayer film having two or more
layers, in order to improve-heat resistance, corrosion
resistance and durability of insulation. In the process
of forming the gel film in accordance with the present
invention, alkoxide may be hydrolyzed ~y moisture
contained in the atmospheric air, without directly adding
water to an alkoxide solution.
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These and ot'ner objects, features, aspects and
advantages of the present invention will become more
apparent from the following detailed description of the
present-invention when taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION ~F THE DRAWINGS
Figs. lA, lB, lC and lD are sectional views showing
electric wires in accordance with the present invention;
and
Fig. 2 illustrates an apparatus for performing a heat
resistance test on samples of the electric wires in
accordance with the present invention.
DESCRIPTION OF THE PREFERRED E~BODIMENTS
Figs, lA to lD are sectional views showing electric
wires in accordance with the prese~t invention.
Fig, lA shows an electric wire, which-comprises a
conductor 1 of~copper etc, coated with a gel film 2 of one
or more layers,- Fig, lB shows an electric wire which
comprises a conductor 1, a plating layer 3 of Ni or Cr
formed on the suxface thereof, a gel film 2 covering the
plating layer 3 and a covering layer 6 of organic
material, Fig, lC shows an electric wire which has a gel
film 2 and a ceramic film 4 formed under the gel film 2 by
CVD to serve as an adhesion layer. Fig. lD shows an
electric wire which has a ceramic film 5 formed by a
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starting raw material of alkoxide, to serve as an adhesion
layer. This ceramic film 5 is formed by applying a
solution obtained by hydrolyzing and
dehydratinglcondensing metal alkoxide and thereafter
heating the same.
Samples for a heat resistance test of the
aforementioned electric wires embodying the present
invention were prepared as follows.: Each of coating
solutions-1 to 6, being prepared by the following methods,
was applied onto a copper wire of 2.0 mm~ in diameter by a
dipping method at a lift-up speed of 1.0 m/min., to form a
multilayer film on.the.copper.wire.
Coatinq Solution 1
Tetrabutylorthosilicate ISi(OC4Hg)4], iso~ropyl
alcohol ~C3H70H] and water ~H2O] were mixed.in the mole
ratio 10:50:40 to obtain.a solution, to which nitric acid
was added by 1/100 mol of tetrabutylorthosilicate. Then
the solution was stirred at a temperature of 80C for 100
minutes, and thereafter returned to the room temperature.
oatinq Solution 2
Tetraethylorthosilicate [SitOC2H5)4], ethyl alcohol
IC2H5OH] and water.lH2O] were mixed.in the mole ratio
3:60:37 to obtain a solution, to which nitric acid was
added by 1l100 mol of tetraethylorthosilicate. Then the
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solution was stirred at a temperature o~ 70C for 100
minutes, and thereafter returned to the room temperature~
Coatinq Solution 3
Tetrabutylorthosilicate ISi(OC4Hg)4~, isopropyl
alcohol IC3H7OH) and water ~H2O] were mixed in the mole
ratio 20:60:20 to obtain a solutionj to which nitric acid
was added by 1/100 mol of tetrabutylorthosilicate. Then
the solution was stirred at a temperature o~ 80C for 200
minutes, and thereafter returned to the room temperature.
Coating Solution 4
Tetrabutylorthosilicate [Si(OC4H9)4~, isopropyl
alcohol IC3H70H] and water IH2O] were mixed in the mole
ratio 10:50:40 to obtain a solution of 100 g, to which
silicagel by Wako Junyaku (WAXOGEL, C-100) of 30 g was
previously added. Then nitric acid was added by 1/100 mol
of tetrabutylorthosilicate, and the solution was stirred
at a temperature of 80C for 100 minutes, and therea~ter
returned to the room temperature.
Coatinq Solution 5
p-xylene 30~ solution of polyimide
Coatinq Solution 6
Tetrabutylorthosilicate ISi(OC4Hg)4], isopropyl
alcohol [C3H70H] and water ~H2O~ were mixed in the mole
ratio 10:50:40 to obtain a solution, to which nitric acid
was added by l/100 mol of tetrabutylorthosilicate. Then
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the solution was stirred at a temperature of 80C for 100
minutes and.thereafter returned to the room.temperature.
Tetrabutylammonium bromide l(C4H9)4N Br ~ of 20 g was
added to the solution of 100 g and stirred with addition
of chloroform ICHCl3], to perform extraction.
This extract was decompressed/dried by an evaporator
to remove the solvent, thereby to obtain a pale yellow
consistent solution lSiO2 polymer]. This SiO2 polymer was
mixed into 10 ml of a p-xylene 30% solution of polyimide,
which was then stirred under the room temperature.
Each of the coating solutions 1 to 6 was employed for
coating, to form a film by the following treatment. Thus,
samples A, B, C, D, E and F were obtained by copper.wires
having multilayer coating films at least including gel
~ilms, as shown in Tables 1 to 6.
Table 1 (Sample A)
1st Laver 1 2nd Layer 3rd LaYer. 4th Layer
SubstanceNi PlatinqGel Gel Gel
Coating __
Solution Solution 1 Solution 2 Solution 2
HeaOed at HeaOed at Left at 25C
Treatment__ 280 C for 220 C for for 6 h.
Film 15 min. 15 min.
Thickness 3 2 2.6 20.0
(~m) .
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Table 2 (Sample B)
_ 1st LaYer 2nd Layer 3rd Layer 4th LaYer-
Substance Gel Gel Gel Resin
Coating Solution 1 Solution:2 Solution 2 Solution 5
HeaOed atHeaOed at HeaOed at HeaOed at
Treatment 280 C for220 C for 170 C for 200 C for
15 min.15 min. 15 min. 30 min.
Film
Thickness 2 2.6 11.5 7
(~m)
Table 3 (Sample C)
.
1st Layer 2nd LaYer 3rd Layer
Substance~ Ni Plating Gel Resin
Coating
Solution __ Solution 1 Solution 5
HeatOed at Hea~ed at
Treatment __. 200 C for 200 C for
15 min. 30 min.
Film
Thickness 3 5.2 7
(~m)
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Table 4 (Sample C)
; 1st Layer2nd Layer 3rd Laver
SubstanceNi PlatingGel Resin
Coating
Solution __Solution 4 Solution 5
HeaOed at HeaOed at
Treatment__300 C for 200 C for
Film 15 min. 30 min.
(~m) 15
Table 5 (Sample E)
1st LaYer 2nd LaYer 3rd Layer
SubstanceNi Platin~ Gel Resin
Coating
Solution _Solution 4 Solution 6
HeaOed at HeaOed at
Treatment__ 300 C for 200 C for
Film 15 min. 30 min.
(~m) 15 7
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Table 6 (Sample F)
1st Layer 2nd Laver 3rd Layer 4th LaYer
Substance Ni Platin Ceramics Gel Resin
g
Coating
Solution __ Solution 3 Solution 1 Solution 6
~eaOed at HeaOed at Heated at
Treatment __ 500 C for 200 C for 200C for
Film 15 min. 15 min. 30 min.
Thickness ~.3 5.1
Each sample thus obtained was subjected to a heat
resistance test as follows:
Heat Resistance Test
Insulation Test: As shown in Fig. 2, two samples 7a
and 7b were brought into contact with each other to be
heated by a heater 12 at à prescribed temperature for 30
minutes with application of voltage of 50 V, thereby to
confirm insulating performance.
~ ibration Test: In the insulation test, a motor 15
as shown in Fig. 2 was rotated with a dead weight 16 of 5
g, to apply vibration.
Referring to Fig. 2, numerals 7a and 7b indicate the
samples, numeral 8 indicates a quartz plate on which the
samples 7a and 7b are placed to be in contact with each
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other, and numeral 9 indicates a quartz pipe for storing
the samples 7a and 7b placed on the quartz plate 8, having
an end sealed by a closure 10 of silicon rubber and
another end blocked by a glass wool member ll. A heater
12 prepared by a tube furnace is provided around the
quartz pipe 9, in order to heat the samples 7a and 7b. A
thermocouple 13 is inserted into the quartz pipe 9 through
the closure 10, in order to measure the temperatures of
the samples 7a and 7b. Numerals 14a and 14b indicate lead
wires, which are connected to the-samples 7a and 7b
respectively, to be linked to electrodes for the
insulation test. The motor 15 is provided on an end of
the quartz plate 8 outwardly extending from the quartz
pipe 9 through the glass 9 wool member 11, in order to
apply vibration to the samples 7a and 7b. The dead weight
16 of 5 g is mounted on the shaft of the motor 15, which
is rotated to vibrate the quartz plate 8, thereby to
transfer the vibration to the samples 7a and 7b. A
support 17 is provided in order to support the quartz
plate 8.
Table 7 shows the results of such a heat resistance
test with characteristics of the respective samples under
the room temperature. Referring to Table 7, "x mmd`' shows
the value of a diameter which caused no abnormality in the
coated layer when the copper wire of each sample was wound
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on a rod of x mm in diameter in a bending test. Table 7
also shows voltage resistance (V). Table 7 further shows
results of insulation-sustainable temperature (C) and
vibration-proof temperature ~C). The
"insulation-sustainable temperature" indicates.the.maximum
temperature capable of sustaining insulating performance
and the `'vibration-proof temperature" indicates the
maximum temperature capable of sustaining insu~ating
performance against the vibration applied in the
aforementioned manner.
It is understood from the result of the insulation
test that the electric wire in accordance with the present
invention is excellent in flexibility and its insulating
performance can be maintained under a high temperature.
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Table 7
Sample ¦ Characteristics under Heat Resis' :ance Test
Room TemPera :ure Insulation- Vibration-
Bending Test Voltage Sustainable O Prof o
Resistance (V) Temperature ( C) Temperature ( C)
A 5 mmd200 550 380
B 2 mmd900 700 500
C 2 mmd600 600 550
D 2 mmd>1000 >800 720
E 2 mmd>1000 >800 650
F 2 mmd700 >800 >800
Although the present invention has been:described and
illustrated.in detail, it is clearly understood!that the
same is by way of illustration.and example only and is not
to be taken by way of limitation, the spirit and scope of
the present invention being limited only by the terms of
the appended claims.
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