Note: Descriptions are shown in the official language in which they were submitted.
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INSULATED CONDUCTOR HAVING
ADHESIVE OVERCOAT
BACKGROUND OF THE INVENTION
Electrical failure of transformer coils, trays-
posed cables, and other electrical equipment can occur
when short circuit forces or mechanical abuse damage
insulation. The mechanical strength of insulated coils
and cables can be increased by bonding the individual
insulated electrical conductor together into a single
mass. This has been accomplished by placing adhesive
coated paper in between the layers of conductors. How-
ever, while this increases strength and reduces insulation damage, it also increases the cellulosic content of the
electrical apparatus. Cellulose is undesirable if certain
dielectric fluids are present because they react with
cellulose to produce compounds which increase the conduct
lo tivity of the fluid. Another technique for forming single mass out of multiple conductors is to cover the
conductors with an adhesive either before or after the
conductors have been juxtaposed. While this technique has
also worked, it involves an additional step, and difficult
ties may be encountered in obtaining good adhesion between the insulation and the adhesive.
SUMMARY OF THE INVENTION
We have discovered a method of preparing an
adhesively coated insulated conductor which can be bonded
I to itself to form a solid mass which is resistant to
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electrical stress and mechanical abuse. The adhesively
coated conductor according to this invention can be made
in a single pass in a manufacturing process that requires
very little space. The adhesive overcoat can be rapidly
cured to the B-stage with ultraviolet light ( W ) which
requires less energy than a thermal cure. It can then be
easily thermally cured to C-stage (i.e., completely cured)
once the conductors have been formed into a coil or cable.
Since the overcoat is 100% solids no solvent is evolved
during curing and thus problems of air pollution and the
collection and containment of vaporized solvent are
avoided. The adhesive coated conductor has an excellent
shelf life and can be stored for long periods of time
prior to use. The overcoat does not flake and adds to the
insulating qualities of the undercoat.
While ultraviolet curable compositions are not
meant to be cured by heat, we have found that such combo-
sessions can be very usefully adapted to producing adhesive
coatings by only partially curing them with ultraviolet
light and later completing the cure with heat. In spite
of this unusual us ox W compositions, we have obtained
excellent adherence between bonded conductors, and no
adverse reactions have been observed that have lowered
electrical or mechanical properties.
US Surprisingly, we have discovered that the over-
coat has a synergistic interaction with a powder coated
undercoat in that the dielectric strength of the overcoat
on top of the undercoat is greater than the sum of the
dielectric strengths of the two coatings by themselves.
RELEVANT ART
US. Patent 3,619,259 and 3,911,202 disclose W
polymerization of continuous films which may be used for
the purpose of electrical insulation.
US. Patents 4,184,001 and 4,268,659 disclose US
curable compositions specifically for use as insulation of
electric wires.
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US. Patent 4,317,858 discloses a W curable
adhesive.
US. Patents 4,032,673 and 4,239,077 disclose US
curable resins for use in transformer coils.
DESCRIPTION OF THE INVENTION
The accompanying drawing is an isometric view in
section of a certain presently preferred embodiment of an
insulated conductor having an adhesive overcoat according
to this invention.
In the drawing, conductors 1 are covered with a
powder-coated insulation 2 over which has been applied a
liquid resin 3 which has been B-staged with ultraviolet
light at 4. At 5, the B-staged resin on adjacent strands
of the conductor has been C-staged forming a solid mass 6.
The conductor used in this invention may be of
any material, though it is typically a metal such as
copper or aluminum. The conductor may be round or recta-
galore wire or strip.
An insulating coating is applied over the con-
doctor. The coating can be of almost any resin including
epoxies, polyamides, polysulfones, polyester asides, and
other resins. The coating is preferably an epoxy because
those resins have the best combination of electrical,
chemical, and mechanical properties for use in trays-
former. (See, for example, US. Patents 4,D~8,809 and
4,241,101.) The coating must be applied by a powder
coating technique such as a fluidized bed, an electron
static fluidized bed, or an electrostatic spray gun.
After the coating has been applied to the conductor, it is
fully cured. The coating may be of any thickness but it
is typically about 3 to about 8 miss. A description of a
suitable powder coating process can be found in US.
Patent 4,127,695. Since the powder coating is typically
cured by heat, it may be desirable to cool the coating in
water or air prior to coating with the W adhesive.
Cooling may be desirable if the wire is to be wound on a
spool before the US adhesive
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is applied, but if the US adhesive is to be applied rimmed-
lately, it may be desirable to have the powder coated wire
warm so as to aid in the flow of the viscous W adhesive.
However, the powder coated wire should not be so hot that
it cures the US adhesive to the C-stage. It is, of course,
preferable to coat the powder coated wire with the W adhesive
immediately in order to avoid the extra steps ox winding and
unwinding the conductor.
The adhesive overcoat may be of any liquid resin
which can be B-staged with ultraviolet light and thermally
cured to the C-stage. This can be accomplished with an ultra-
violet curable resin by only partially curing it to the B-stage
and then completing the cure to the Stag using heat. However,
it is more desirable to use a specially prepared resin which
has two components W curable component and a heat-sensitive
component. A two-component resin is easier to work with because
the ultraviolet light can only cure it to the B-stage and thus
it is not necessary to carefully control the exposure to ultra-
violet light as it would be if the ultraviolet light could
cure the resin all the way to the C-stage. An example of a
two-component resin is given in Example 1, Composition A.
another suitable ultraviolet curable adhesive is described by
F. I. Settler in US. Patent 4,317,858.
The adhesive overcoat must be a liquid, and it is
preferably 100% solids to reduce air pollution and the cost
of recover no solvents. Suitable resins include acrylated
epoxies, cat ionic photo-initiated epoxies, ~hiol-polyene systems,
and acrylo~urethanes. Acrylated epoxies are preferred as they
have the best properties. A resin can be applied by reverse
roller coating, by dipping and passing through a die or a wiper
of leather or felt, or other technique. Reverse roller coating
is preferred as it produces a thinner and more easily controlled
coating.
After the adhesive overcoat has been applied, it
is cured to the B-stage. The B-stage is the point at
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which the coating becomes dry, tack free, and non-
blocking. This occurs when the resin is cured past its
gelatin point. The cure to the B-stage is accomplished
using ultraviolet light of a frequency and intensity which
depend upon the particular composition used and the speed
with which the conductor passes under the light. After
the adhesive overcoat has been cured to the B-stage, the
conductor can be wound onto reels or it can be used mime-
doughtily. The stooged coating can be ox any thickness,
but it is preferably about 0.25 to about I miss as a
thinner coating has a poor bond strength and a thicker
coating uses too much space.
In the next step of this invention strands of
the conductor are placed side-by-side. The conductors
with the adhesive overcoat may be used to form transformer
coils, motor coils ! transposed cables, or other structures
where the fusion of adjacent conductors into a solid mass
would be desirable.
In the final step of this invention the adhesive
overcoat is heated to complete its cure to the C-stage.
The temperature and time required to complete the cure
will depend upon the particular adhesive overcoat compost-
lion that is used.
The following examples further illustrate this
invention.
EXAMPLE 1
A 0.114 x 0.289 inch rectangular aluminum wire
was powder coated with an epoxy powder coating resin
described in the example of US. Patents 4,241,101 or
4,088,809. The powder coating was cured in a wire tower
at a speed of 10-53 ft/min and a tower temperature of
300-450C and had a thickness of 3 to 8 miss. After the
powder coated wire had been fused and cured, short lengths
of the powder coated wire were cut and an adhesive over-
coat was brushed onto the wire by hand and cured to the
B-stage under ultraviolet radiation. The following
ultraviolet curable overcoats were used.
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Composition
(parts by weight)
Ingredients _ A By C
Solid diglycidyl ether of bisphenol A
sold by Dow Chemical Co. as "DYER 662"55.356.4 55.7
Tetraethylene glycol diacrylate33.033.7 33.6
Triethanolamine borate in phenoxyethyl
acrylate sold by Westinghouse as "WHITE" 8.3 8.4 8.2
Isopropyl Bunsen ether sold by
Stouffer as "V-10" photoinitiator1.31.4 --
Isobutyl Bunsen ether sold by
Stouffer as "V_30't photo initiator 1.4
Fluorinated alkyd ester sold by 3~1
as "FC-430" Surfactant 2.1 -- 1.1
15 Picnic acid -- -- 0.01
Three pieces of the adhesive coated wire were clamped
together overlapping about inch and were heated to 130~
for six hours in either air or in kerosene. After cooling
the bonded sample were subjected to tensile shear testing
I (double lap shear testing) at temperatures from 25 to
175C. The results era given in the following table.
Overcoat
Test Composition Composition Composition C
Temp. (C) Bid. 3.0-4.0 old. 3.0-h.OBld. 2.5-4.0
Cured in Kerosene
2663
Cured in Air
1276 1757 2000~ 2708
loo 2486
30 125 2351
150 1537
175 638
This example shows that US sensitive adhesives
can be formulated and applied to powder coated conductors
with good tensile shear strengths at temperatures as high
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as 175C. It also shows that bonding in kerosene does not
adversely affect the bond strength of these adhesives.
EXAMPLE II
Rectangular aluminum wire (0.114 x 0.289 in) was
coated with the powder disclosed in US. Patent 4,241,101
in a wire tower, then cured and spooled. Short lengths
~v12 in) were cut and straightened, then coated manually
with two different US sensitive adhesives.
Composition A
"DYER 66~" epoxy resin 47.1 pow
Limonene dioxide 31.3 pow
Methyl tetrahydrophthalic android 15.7 pow
~liphatic triglycidyl ether sold by
Sullenness as "5044" epoxy Rosen pow
triaryl sulfonium hexafluoro phosphate
sold by EM as "FC-S08" photo initiator 5.1 pow
Chromium acetylacetonate 0.04 pow
Composition B
"DYER 662" epoxy resin 45.5 pow
1,6-hexanediol diacrylate 6.9 pow
2-ethoxyethyl acrylate 9.2 pow
Bottle glycidyl ether sold by Cuba
Geigy as "RD-l" delineate 5.0 pow
Diglycidyl ether of neopentyl glycol 5.0 pow
Methyl tetrahydrophthalic android 15.0 pow
"V-30" photo initiator 0.64 pow
Chromium acetylacetonate 0.04 pow
Wires overreacted with the above composition and
B-staged were overlapped in pairs by a distance of 1 in.
along their long axes and subjected to a pressure of 50
- psi. The pairs were placed in a laboratory air circulate
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in oven for 6 hours at 130C to C-stage the adhesive
overcoats. After cooling, the bond pairs were tested for
lap shear strength at 150C. The results were as follows
(average of 5 samples):
Overcoat Lap Shear Strength (Pi )
Composition A 58
Composition B 154
After the adhesive had been Staged some samples were
shelf aged for a period of 3 months.
The tensile shear test as described in Example I
was repeated. The results were as follows (average of 5
samples):
Overcoat Lap Shear Strength (psi)
Composition A 51
Composition B 150
These results show that the W adhesives of this
invention can be applied to powder coated conductors and
can retain their tensile shear strength (single lap shear
test) after shelf aging for periods of at least 3 months.
EXAMPLE III
Samples of 0.064 x .258 inch copper wire were
coated with 4 miss of epoxy powder coating as in Example
I. The samples were then coated with various adhesive
overcoats including the same epoxy powder coating, Formvar
and a W composition which consisted of
Acrylated epoxy - 55.5% (50% phenoxyethyl acrylate);
W catalyst - 2.5%;
Hexamethoxymethyl mailmen (sold by American Cyanamid
as "Camel 303"~ - 6.4%;
Rhenoxyethyl acrylate - 6.4%;
Vinyl acetate - 8.4%;
Epoxy novolac - 6.4%;
"WHITE" - 6.0%;
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Benzodimethyl melamines - 0.18% and blocked
acrylated urethane - 6~2%;
Tetraethylene glycol diacrylate - 1.8%;
Catalyst Lowe (manufactured by American
Cyanamid) - 0.03%;
Iron or chromium acetylacetonates - 0.03%
The ultraviolet adhesive overcoat was prepared
in the following manner:
Three six inch samples were overlapped one inch
lo and clamped together under a pressure of 10 psi. Beam
tests were also performed on the samples. In a beam test,
two beams 5 inches apart are placed under a stack of 5
wires bonded together and a third beam is pressed downward
between the other two beams. The psi required to produce
a failure are measured. The following. table shows the
results.
Test Temperature
Adhesive. T. 120C
Powder Coated Epoxy 480 650
Eormvar* 830 430
W 872 736
*a wire enamel which contains polyvinyl formal as
a base resin. Other resins such as phenols, blocked
.isocyanates, and mailmen formaldehyde are added,
I depending on the supplier.
These results show that correctly formulated US
adhesives have beam shear strengths comparable to those of
either powdered or solvent based adhesives when applied
over powder coated conductors.
EXAMPLE V
A further benefit of using US sensitive over
coats is a marked improvement in electric strength. A
spool of 0.064 x 0.258 copper rectangular wire was coated
with powder manufactured by HAZEL and finely ground.
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Example I was repeated and the dielectric
strength of samples with and without W overcoat were
tested. The following table gives the results on 0.064 by
0.258 inch rectangular copper wire.
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EXAMPLE VI
Three samples of rectangular aluminum wire
coated with the same powder used in Example I were dipped
into a W sensitive resin comprised of:
"DYER 662" epoxy resin 502.5 g
"WHITE" 75.0
Tetraethylene glycol diacrylate200.0
Ethyl Huxley acrylate 150.0
2-hydroxy ethyl acrylate 37.5
lo "V-10" photo initiator 3.75
Tert-butyl perbenzoate 3.75
Excess resin was wiped off and the coating was irradiated
for 8 minutes under a source of ultraviolet light.
After the irradiation, the coating was dry to
the touch and measured 3.5 mix (addition to the thick-
Nazi.
The three samples were pressed together under
nominal spring pressure (from a bulldog clip) at 150C for
I hours.
AYE double lap-shear test gave a test value ox 184
lobs. on the two adhered areas of 0.350 x 0.258 in., equip-
alert to Lowe psi.
