Note: Descriptions are shown in the official language in which they were submitted.
43-4~0A
~L~)8~93~
TITLE: ELECTRICAL DEVICES CONTAINING READILY
BIODEGRADABLE DIELECTRIC FLUIDS
INVENTORS: RAI.P~ H. MUNC~I
QUENTIN E. THOMPSON
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to electrical devices
` containing readily biodegradable dielectric fluids. More
particularly, the invention relates to certain chlorinated
aromatic compounds having superior fire resistance and bio-
degradability, and which are especially useful as dielectric
fluids or impregnants in electrical capacitors and transformers.
Description of the Prior Art ~
A modern dielectric fluid must possess a uni~ue - -
combination of electrical characteristics and physical proper-
ties while minimizing adverse environmental effects. Fire
resistance is a very desirable property in order to avoid
secondary damage should failure of the electrical device -
cause electrical sparks or excessive heat.
Chlorinated aromatic compounds have long been known
and preferred as dielectric fluids for electrical apparatus.
The most familiar fluids in this class are known as "Askarels"*.
Askarel dielectric fluids are fire resistant, have a relatively
high dielectric constant, and are by far the most widely ac-
cepted fluid for use today in electrical capacitors and trans-
*Trademark ^~
.
.
: .
: .
.
43-4280A
~08~937
formers. Askarel fluids are formulations composed primarily
of polychlorinated biphenyls which are sometimes mixed with
chlorobenzenesto give particular viscosity characteristics.
Certain of the polychlorinated biphenyls, however,
have been discovered to be resistant to natural degradation
and, when released into the environment, these materials may
enter the life cycle and be potentially harmful to ecology.
Even though capacitors and transformers are customarily sealed
units and escape of the dielectric fluid (or impregnant) into
the environment can be prevented to a large degree, it has
nevertheless become desirable to provide an alternate fluid
which does not contain a major component having environmental ~;~
persistence.
Halogenated aromatic compounds other than polychlorin-
ated biphenyls have been heretofore disclosed as dielectric
fluids for electrical apparatus. U. S. Patent No. 2,617,770,
issued November 11, 1952, broadly discloses "halogenated com-
pounds of naphthalene, toluene, benzene, nitro-diphenyl, di-
phenyl oxide, diphenyl ketone, diphenyl methane, diphenyl
ethane, terphenyls and quaterphenyls". Similarly, U. S. Pat-
ent No. 2,410,714, issued November 5, 1946, discloses "chlor-
inated benzene, chlorinated diphenyl oxide, chlorinated diphenyl
methane, chlorinated diphenyl benzene and alkyl derivatives
thereOf"-
- Notwithstanding the early patent disclosures referred
to above, wide commercial acceptance of halogenated aromatic
compounds as dielectric fluids has been confined through the
years to polychlorinated biphenyls. The other known halogenated
aromatic~ having poss~ble utility as dielectric fluids never
achieved commercial significance for one or more technical or
~ .
-- 3 --
43-4280A
lQ81937
economic reasons. Thus, recently published efforts to pro-
vide alternate dielectric fluids for capacitors and trans-
formers have, for the most part, been directed away from
halogenated aromatic compounds because of the environmental
persistence incurred with certain of the polychlorinated bi-
phenyls.
It is an object of the present invention to provide
electrical devices containing readily biodegradable dielectric
fluids. It is a further object of this invention to provide
improved electrical capacitors and transformers containing
fire resistant, yet readily biodegradable, dielectric fluids.
Still another object of the present invention is to provide
fire resistant, readily biodegradable dielectric fluids having
outstanding viscosity properties for use in capacitors and
transformers. Other objects of this invention will become
apparent from the following description and claims.
5UMMARY OF THE INVENTION
It has now been discovered that certain halogenated
diphenylmethanes are superior dielectric fluids for electrical
apparatus because they combine the necessary electrical and
physizal properties with excellent biodegradability and fire
resistance. The dielectric fluids of this invention comprise
at least one halogenated diphenylmethane compound represented
by the structure
(X)n (R)m
~C~12 ~
43-4280A
37
where each X is individually chlorine, bromine or fluorine;
n is a whole number from 1 to 4; each R is individually an
alkyl group having from 1 to 5 carbon atoms; and m is zero
or a whole number from 1 to 3.
Surprisingly, only those halogenated diphenvlmethanes
having one unsubstituted phenyl group were found to be readily
biodegradable. Those diphenylmethanes with halogen substitution
on both phenyl groups, or with halogen on one phenyl and alkyl
substitution on the other phenyl, were found to resist microbial
degradation. This result was unexpected and the reasons there-
for are still not fully understood. The halogenated diphenyl-
methanes disclosed herein, i.e., those having one unsubstituted
phenyl ring, are particularly useful as capacitor impregnants
and as dielectric fluids for transformers. In such applications
; it has been found desirable to employ certain additives such as
stabilizers, e.g., epoxide stabilizers. The fluids are also
useful in power transmission cables, rectifiers, electromagnets,
circuit breakers and the like.
Electrical capacitors containing the halogenated di-
phenylmethanes of this invention may be constructed and impreg-
nated according to standard procadures. Such capacitors are
charac~erized by a low dissipation factor, high dielectric con-
stant, good low temperature performance, fire resis~ance and
excellent biodegradability of the impregnant itself.
DESCRIPTION OF DRAWING
FIGURE 1 is a perspective view of a partially un-
coiled convolutely wound capacitox in which the present inven-
tion may be embodied.
FIGURE 2 is a perspective view of a fully assembled
_ 5 _
43-4280A
~08~937
!
capacitor which contains the convolutely wound capacitance
section of the type shown in FIGURE 1 together with a dielec-
tric liquid impregnant.
DESCRIPTION OF PREFERRED EMBODIMENTS
The halogenated diphenylmethanes of this invention
are characterized by halogen substitution in only one aromatic
ring. Although alkyl substitution is permissible in the mole-
cule, it must occur in the same ring where the halogen ~ubsti-
tution took place. The other phenyl ring must be unsubstituted.
While not to be construed in a limiting sense, exemplary com-
pounds having the desired biodegradability coupled with fire
resistance and good electrical and physical properties, are
o-chlorodiphenylmethane; ~-chlorodiphenylmethane; 3,4-dichloro-
diphenylmethane; 2,4-dichlorodiphenylmethane; a dichlorodi-
phenylmethane mixture of the 2,4 and 3,4 isomers; and a tri-
chlorodiphenylmethane mixture of the 2,4,5 and 2,5,6 isomers.
Chlorine is the preferred halogen because of its lower cost
compared to bromine or fluorine. Tetrahalogenated diphenyl-
methanes having all halogens within one aromatic ring are also
within the present scope. Up to three alkyl groups of l to 5
carbon atoms, alike or unlike, may be present in the halogenated
ring. Exemplary alkyl-substituted halogenated diphenylmethanes
- are o-chlorotolylphenylmethane and p-chlorotolylphenylmethane.
Capacitor device3 employing the present invention
may have the general structure and configuration illustrated
in FIGURE 1 which is a convolutely wound capacitor 10 com-
prising separate electrode foils or armatures ll and 12 and
intermediate dielectric spacers 13 and 14. Terminal connectors
43-4280A
1~8193'7
15 and 16 have enlarged surfaces (not shown) in contact with
electrode foils 11 and 12. Electrode foils 11 and 12 may
comprise one or more o a number of different materials,
generally metallic and including for example aluminum, cop-
per and stainless steel. Dielectric spacers 13 and 14 gener-
ally comprise paper and/or polymeric film. ~hus, the dielec-
tric spacer 13 and the metallic electrode foils 11 and 12,
taken together, comprise a capacitor element structure. The
dielectric spacer materials, and ~he voids within and between
the materials and the electrode foils are impregnated with a
dielectric fluid.
With continued reference to FIGURE l of ~he draw-
ing, dielectric spacers 13 and 14 may be comprised of a solid
flexible porous material such as highly refined cellulose
paper, or of a substantially nonporous polymeric film mater-
ial such as a polyolefin, or of a combination of paper and
polymeric film. In a preferred embodiment, the paper material
is preferably two or more sheets of Kraft capacitor paper hav-
ing an individual sheet thickness not greater than about 1.0
miI and preferably about 0.3 mil and a total combined thick-
ness suitable for the design voltage of the capacitor. Such
paper has a dielectric strength which is relatively good as
compared to other dielectric strength which is relatively
good as compared to other dielectrics and has a relatively
high dielectxic con~tant. The polymeric material is prefer-
ably biaxially oriented polypropylene film although other
members of the polyolefin family, particularly polyethylene
and 4-methylpentene-1 have found some use in capacitor appli-
cations. Other useful polymeric materials include polyesters,
polycarbonates, polyvinylidene fluoride, and polysulfone.
43-4280A
~08193~
Although either paper or polymeric film may be used alone,
combinations of both are often employed. The paper is
positioned adjacent to the polymeric film to function as
a wick to pass the dielectric liquid impregnant into the
area coextensive with the area of contact between the
porous paper and the substantially nonporous polymeric
material.
Referring now to FIGURE 2, there is shown an
assembled capacitor unit 18 in which is encased a convo-
; 10 lutely wound capacitor of the type illustrated in FIGURE 1.
The assembled unit includes a container 19, a hermetically
; sealed cover 20 which includes a small dielectric fluid
fill hole 21, and a pair of terminals 22 and 23 projecting
through cover 20 and insulated therefrom. Terminals 22 and
23 are connected within container 19 to terminal connectors
15 and 16 shown in FIGURE 1. Although not illustrated, the
unit 18 shown in FIGURE 2 further includes the dielectric
fluid composition which occupies the remaining space in
container 19 not occupied by the capacitor element and which
also impregnates dielectric spaeers 13 and 14.
Impregnation of the capacitor is accomplishedwith conventional procedures. For example, in one general
impregnation method, capacitor units encased in assemblies
such as capacitor 18 of FIGURE 2 are dried under vacuum to
remove residual moisture. The drying temperature will vary
depending upon the length of the drying cycle ~ut u~ually
ranges from about 60 to 150C. With too low a temperature
the drying period is excessively long while too high a tem-
perature may cause decomposition of the paper or shrinkage
of the polymeric film utilized as the dielectric spacer.
-- 8 --
:,
43-4280A
937
~012 21 permits moisture and gases to vent from the interior
of container 19 during the drying process.
The impregnating dielectric liquid is admitted to
the capacitor assembly through hole 21 preferably while the
dried assembly is still under vacuum in a suitable evacuated
enclosure. The capacitor element within the container must
be submerged by the impregnating liquid and usually enough
of the impregnating liquid is introduced to completely flood
the container and displace all the air therein. The pressure
of the enclosure is then raised to atmospheric pressure and ~
the assembly is permitted to stand or soak for a number of -,
hours for thorough penetration of the liquid impregnant.
After impregnation the capacitor unit may be sealed by apply-
ing a quantity of a suitable solder to hole 21 or by other
sealing means. The capacitor assembly may 'chereafter be
subjected to an elevated temperature to increase pressure
within the capacitor assembly and aid the impregnation pro-
cess. Heat and pressure may enhance impregnability by chang-
ing the relative wettability, viscosity and solubility of
materials. In addition, expansion and contraction of indi-
vidual components of the system which may be the result of
heat and pressure may act as a driving force to induce migra-
tion of the liquid into the interstices of the dielectric
spacer material.
In addition to the pre3ence of one or more halo-
genated diphenylmethane compounds, the dielectric fluids of
this invention may contain minor amounts of numerous other
components. In particular, it is often desirable to include
a component to act as a stabilizer in the impregnated dielec-
tric system. The presence of a stabilizer is intended toneutralize certain ionizable contaminants or extraneous materials
_ g _
4~-4280A ~`
~ I
~IL081937
which may be pre~ent or which may be formed in the system.
Such contaminants may include residual catalyst or catalyst
activators which remain from resin forming reactions. Con-
taminants may also include degradation products caused by
environmental or voltage induced chemical reactions in the
system. In certain cases the stab.ilizer may act as a scavenger
for any hydrogen chloride evolved from the dielectric liquid
as a result, for example, of arcing conditions during opera-
tion. These undesirable contaminants and extraneous products
have an adverse effect on the dissipation factor or power
factor of the impregnated dielectric system, and stabilizing
agents have been found to be highly effective in maintaining
a low power factor in impregnated dielectric systems.
The particular stabili2ing agent is dependent in
part upon whether the electrical device, for example, the
capacitor, is to be employed in alternating current (A.C.) or
direct current (D.C.) service. Anthraquinone has exhibited
superior results for D.C. service. Particularly preferred
stabilizing agents for A.C. applications are epoxides generally
characterized by the group
-CH ---- CH-
" \ /'
O
examples of which are glycidyl ethers and derivatives of
ethylene oxide. Other examples are l-epoxyethyl-3,4-epoxy-
cyclohexane, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane
carboxylate, 3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-
methylcyclohexane carboxylate, and the like. These stabilizers
are preferably employed in the dielectric fluid compositions
of this invention in amounts in the general range of from
-- 10 --
43-4280~
~L08~93'7
0.001 to about 8 percent by weight, and more preferably from
about 0.1 to 3.0 perc0nt by weight.
The following Examples illustrate the superiority
of electrical apparatus containing dielectric fluids of the
present invention wherein all parts and percentages are ex-
pressed by weight unless otherwise specified.
" - ':
EXAMPLE 1
Numerous electrical capacitors of the type illus-
trated in FIGURES 1 and 2 of the drawing were constructed of
aluminum foil and paper separators and were impregnated ac-
cording to the foregoing description with a dielectric fluid
composition comprising 99.7 percent 3,4-dichlorodiphenylmethane
and 0.3 percent 3,4-epoxycyclohexylmathyl-3,4~epoxycyclohexane
carboxylate. A group of eight of these capacitors, designated
"Test Capacitors", were subjected to service and life tests in
a laboratory environment. The results of these tests were
compared to those obtained with a like group of identical
capacitors impregnated in a like manner with an electrical
grade polychlorinated biphenyl containing about 42 percent
chlorine, designated as "Control Capacitors". The impregnant
fox the Control Capacitors contained 0.3 percent 3,4-epoxy-
~; cyclohexylmethyl-3,4-epoxycyclohexane carboxylate. Test
results are presented in the following TABLE I.
.
-- 11 --
43 4280A
~L0~1937
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43-4280A
93'7
The data in TABLE I illustrate the excellent
electrical performance and reliability of capacitors impreg-
nated with a dielectric fluid composition of this invention
as compared to like capacitors of the prior art. In par-
ticular, TABLE I shows that there were no failures of the
test capacitors even though they were subjected to the ex-
treme test conditions of 100C. and 1,000 volts. The control
capacitors, on the other hand, although surviving up to the
final test conditions, suffered 87 percent failure at these
conditions. That is, 7 of the 8 capacitors in the control
group failed while the test capacitors were all still opera-
tive.
Halogenated diphenylmethanes of this invention,
i.e., those having halogen substitution (and op~ional alkyl
substitution) in only one phenyl ring, are useful as the
dielectric fluid for electrical ~ransformers for cooling
and insulating purposes. These compounds have the advantage
over mineral oil dielectrics because of ire resistance.
The additional advantages of excellent biodegradability and
20 outstanding viscosity properties make these halogenated di-
phenylmethanes attractive in transformer applications.
A typical electrical transformer in which the present
invehtion may be embodied is illustrated in U. S. Patent No.
-~ 3,362,908 issued January 9, 1968. Advantageously, an epoxide
~ stabilizer may be employed in conjunction with the halo~enated
.~ .
- 13 -
, ' ' ' ' ,
43-4280A
~081937
diphenylmethane for transformer service.
Although halogenated diphenylmethanes were long
ago disclosed broadly in the literature as dielectric or in-
sulating ~luids for electrical apparatus, there is found
little, if any, evidence of their industrial usage or accept-
ance. Polychlorinated biphenyls assumed through the years the
dominant role for halogenated aromatics having fire resistance
coupled with outstanding electrical properties. Thus, no
understanding was achieved in the art for the good or bad in
dustrial potential of halogenated diphenylmethanes because -
they were entirely overshadowed by the widespread acceptance
of polychlorinated biphenyls. Upon discovery of biodegradabil-
ity problems associated with certain of the polychlorinated
biphenyls, those skilled in the art of dielectric fluids im-
mediately sought alternate fluids other than those in the family
; of halogenated aromatic compounds.
Despite this discouraging atmosphere, it has sur-
prisingly been discovered that halogenated diphenylmethanes
can be superior dielectric fluids for use in electrical appara- ~ -
tus depending upon whether the halogen substitution (and optional
alkyl substitution) occurs in ~ne or in both phenyl rings.
This discovery was entirely unexpected and was not predictable
from prior art teachings. For ex~nple, it was entirely unpre- ;~
dictable that a mixture of 2,4 and 3,4-dichlorodiphenylmethane
would be highly biodegradable whereas a mixture of 2,4' and
4,4'-dichlorodiphenylmethane would be highly resistant to bio-
degradation.
Biodegradability has been established as a key factor
in determining the environmental persistence of organic compounds
or mixtures thereof. Biodegradability is the susceptibility of
- 14 -
1~8~93~
; a compound to degradation by a mixed bacterial population in
the presence of a natural energy source, e.g., waste water.
To illustrate the dramatic difference in biodegrad-
ability between single ring and double ring substitution in
halogenated diphenylmethane compounds, biodegradability testing
was conducted on a series of such compounds. Biodegradability
testing was carried out using a semi-continuous activated sludge
test which was patterned after the test methods for-surfa'ctants
set forth by the Subcommittee on Biodegradation Test Methods of
the Soap and Detergent Association ~Jour. Amer. Oil Chemists Soc.,
42, 986 ~1965)~.
In the semi-continuous activated sludge test, biode-
gradabi1ity is measured using activated sludge from a sewage
treatment plant as the source of microorganisms. A given level
of test compound and a synthetic sewage as an energy source are
fed on a periodic basis to the activated sludge contained in a
stirred aeration chamber. Aeration of the mixed liquor- (activ-
ated sludge and liquor) is carried out for "n-l" hours of a "n"
hours cycle. Cycle times generally employed are 24, 48 or 72
hours. Representative samples of the mixed liquor are taken
shortly after feeding and near the end of the aeration period
to determine the disappearance rate of the test compound
during the cycle. The cycle is repeated for as long as
necessary to obtain consistent biodegradation rate data.
The semi-continuous activated sludge test simulates
a secondary sewage treatment facility. The following
Example 2 describes details of the biodegradability tests
conducted on halogenated diphenylmethanes having single
ring substitution and double ring substitution, respectively.
- 15 -
~.3-~2~0~
37
EXA~IPLE 2
Activated sludge obtained from a typical treatment
plant of the ~Ietropolitan Sewer District of St. Louis, Mis-
souri was used in this Example. lhe mixed liquor as obtained
from the sewage treatment plant was filtered through a 20-mesh
stainless steel screen to remove any extraneous particulate
! matter. After adjustment with tap water to a suspended solids
content of 2,500 milligrams per liter, 1,500 milliliters of
the mixed liquor was charged to an aeration chamber. The aera-
tion chamber was then connected to a compressed air source and
the mixture aerated at a 0.1 cubic foot per hour ~SCFH) flow
rate (.0028 cubic meters per hour). During the aeration, agita-
tion of the mixed liquor using a magnetic stirrer was also pro-
vided. The compound to be tested in the form of either an
absolute ethanol or aqueous solution and 10 milliliters of a
synthetic sewage used as an energy source for the sludge micxo-
organisms were fed to the chamber at the beginning of each cycle.
For materials which have an appreciable disappearance rate, a
24 hour cycle was employed together with a 72 hour cycle on
weekends. For the more refractory materials, a basic 48 hour
cycle was ernployed. At the end of the aeration period or cycle,
the sludge was allowed to settle and 1 liter of supernatant liquid
was removed. The unit was re-fed, the mixed liquor vol~ne adjusted
to 1,500 milliliters with tap water, and the aeration cycle re-
peated. Samples of mixed liquor (e.g., 20 milliliters) were taken
through a side-arrn stopcock with 25 milliliter graduated cylinders
1 hour after feeding and at the end of the aeration cycle and
analyzed for the compound or compound~ of interest.
The initial feed rate for the chlorinated diphenyl-
methanes was 1 milligram per 24 hour cycle. The rate was in-
~ - 16 -
~3-42~0,~
337
,
creased to 3 mi].licJrams th~ second week and to 5 milligrams
the third week. The level was then maintained at 5 milligrams
until consistent disappearance rate data were obtained. For
those chlorinated diphenylmethanes which degraded rapidly at
the 5 milligram level, the feed rate was subsequently increased
to 20 milligrams and addit~onal data obtained.
The phrase "disappearance rate" as used herein is
synonymous with biodegradation rate or biodegradability. The
sampling and analytical procedures employed in the biodegrada-
tion rate determinations were as follows. 50 milliliter samplesof the mixed liquors were withdrawn after feeding and at the
end of the aeration cycle. The~amount of chlorinated diphenyl-
methane in the concentrated extracts was determined using flame-
ionization gas chromatography. From the analytical data, the
percentage biodegradation was calculated by the equation:
, ~ Biodegration = Cc Cn x lO0
where CO = milligrams of test material in
unit at beginning of aeration cycle
after feeding of test material
~ Cn = milligrams of test material in unit
at end of aeration cycle
Biodegradation data for 15 halogenated diphenylmethane compounds
of Example 2 are presented in the following TABLE II. It can
be observed that those halogenated diphenylmethanes having l un-
substituted phenyl ring are highly biodegradable, viz. Compounds
l through 8. In contrast, Compounds 9 through 15 which have
halogen or alkyl substitution in both phenyl rings are resistant
to biodegradation.
Surprisingly, it does not appear to be the mere pres-
ence of halogen in the second phenyl group which inhibits bio-
degradation. An alkyl group alolle can cause the same effect.
- 17 -
~
43-428OA
1~31937
See Compounds 14 and 15 which are, respectively, o-chloro-
benzylethylbenzene and ~-chlorobenzylethylbenzene. Presence
of an ethyl group in the second ring has inhibited biodegrada-
tion compared, for example, with Compounds 7 and 8 where the
halogen and the alkyl are in one ring, the second ring being
unsubstituteù.
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43-4280A
1~8~L937
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In the course of the present invention it was fur-
ther discovered that good biodegradability is not necessarily
associated with an unsubstituted phenyl ring in a diaryl com-
pound. For example, pentachlorodiphenyl sulfide, identified
herein as Compound No. 17 and having chlorine substitution in
both phenyl rings, was found to resist biodegradation but this
alone was not considered surprising. Another diphenyl sulfide,
however, which was 2,4,5-trichlorodiphenyl sulfide having single
ring substitution and identified herein as Compound l~o. 18, was
found to be equally resistant to biodegradation as Compound 17.
~;~ It was further discovered that halogen substitution
on a phenyl group in a mono-aryl compound does not automatically
render that group highly resistant to biodegradation. For ex-
.:-: ~. .
ample, two different dichlorobenzene compounds, identified
; herein as Compounds 21 and 22 respectively, exhibited excellent
biodegradability.
` EXAMPLE 3
To illustrate the unpredictability of biodegradation
rate among various aromatic structures having 1 to 3 aromatic
rings and dif~ering configurations of substitution, 7 compounds
other than halogenated diphenylmethanes were tested according
to the procedure of EXAMPLE 2. These compounds are identified
as Compounds 16 through 22 and their biodegradation results are
set forth in TABLE III below.
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43-4280A
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-- 25 --
43-4280A
L937
The outstanding electrical and biodegradation
properties of the single-ring substituted halogenated diphenyl-
m~thanes of this invention are evident in TABLES I and II re-
spectively. The following TABLE IV presents flammability data
on several compounds within the present invention as compared
to an electrical grade polychlorinated biphenyl containing
about 42 percent chlorine, designated as "Con~rDl". It can be
seen that certain o the halogenated diphenylmethanes of this
invention have a higher flash point than the Control.
TABLE IV
FLAMMABILITY PROPERTIES
.: '.
Compound Flash Fire A.I.T.
No. Pt.(C) Pt.~C) (C)
1 149 193 546
3 171-185 332 559
4 185 260 581
6 213 349 597
Control 180 None - ~-
It is to be understood that the halogenated diphenyl-
methane dielectric fluid compositions of this invention may
incorporate certain compounds i~ addition to the aforementioned
stabilizers in admixture therewith. For example,in order to
;~ achieve a particular desired dielectric constant or some other
desired property, it may be advisable to add a minor amount
of a diaryl sulfone, alkyl benzene, alkyl naphthalen~, alkyl
biphenyl, alkyl polyphenyl, alkyl aryl ether, diaryl alkane,
diaryl ether ester of a carboxylic acld, etc. Thus, the pre-
_ 26 -
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43-4280A
~8~93~7
ceding ex~mples and tables serve to illustrate preferred em-
bodiments of the present invention but the invention is not
to be limited to the compounds, compositions, electrical ap-
paratus or capacitors defined in these examples.
Because of their outstanding physical properties
and fire resistance coupled with excellent biodegradability,
the halogenated diphenylmethanes of this invention are useful and
valuable in numerous non-electrical applications. For exam-
ple, the excellent stability and viscosity properties of these
halogenated diphenylmethanes make them valuable and useful as
fire resistant hydraulic fluids and as heat transfer fluids.
In addition, there are certain plasticizer applica-
tions where fire retarding properties are desirable. These
readily-biodegradable halogenated diphenylmethanes could there-
fore be employed either as primary plasticizers or as additives
for plasticizers.
The fire resistant characteristics of these halogenated
diphenylmethanes are not important in all instances. For exam-
ple, these compounds are useful as dye solvents for pressure-
sensitive recording systems wherein a chromogenic substance mustbe dissolved within a microcapsule. Good biodegradability is
essential in such applications.
The single ring substituted halogenated diphenyl-
methanes of this inv~ntion can be prepared according to published
procedures well-known to those skilled in the art. For example,
a desired chlorinated diphenylmethane compound may be prepared
by the reaction of benæene with the corresponding chlorinated
benzyl chloride.
- 27 ~
