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BACKGROUND OF THE INVENTION
1. Field Of The Invention
This invention relates to filled organic elastomeric matrixes and to
coupling compositions added to the filler-organic elastomeric matrix for
conserving or enhancing the physical and electrical properties of the
filled organic elastomeric matrix. The invention more particularly relates
to novel coupling compositions for addition to filler-organic elastomer
blends for providing curable compositions having special application as
insulation coatings for electrical cables upon curing with organic
peroxides. The invention also relates to curable compositions containing
the filler, organic elastomer, peroxide and coupling composition and to
cured compositions resulting therefrom. The invention also relates to
electrical cables provided with such cured compositions and methods for
making same.
2. Description Of The Prior Art
A substantial amount of research has been performed heretofore in
connection with the treatment of fillers or reinforcing agents for the
purpose of improving physical or mechanical properties of plastics, resins
or rubbers reinforced with the filler. Much of this research has centered
on the pretreatment of glass fiber reinforcement materials for resins and
rubbers. For example, U.S. Pat. No. 3,702,783 describes the application as
a size to glass fibers of a blend of 3-glycidoxypropyltrimethoxysilane and
methyltrimethoxysilane. U.S. Pat. No. 3,816,235 discloses a size
composition for the treatment of glass fibers wherein the size composition
contains a blend of aminoalkyltriethoxysilane and methyltriethoxysilane.
U.S. Pat. No. 3,944,707 discloses the use as a size for glass fiber
reinforcement for plastics, blends of vinyl silane or vinyl siloxanes and
a beta-haloalkoxysilane. Similarly, U.S. Pat. No. 3,993,837 discloses
glass fiber size compositions containing blends of epoxyalkylsilane or
siloxane and a beta-haloalkoxysilane.
U.S. Pat. No. 4,049,865 discloses glass fiber size compositions containing
a blend of an aminoalkylsilane and a vinyl silane. U.S. Pat. No. 4,130,677
discloses the sizing of glass bottle surfaces with am aminoalkylsilane.
None of these patents disclose or remotely suggest the use of blends of an
ethylenically unsaturated silane having at least 1 silicon bonded hydroxy
or alkoxy group and an organosiloxane oligomer having at least one silicon
bonded hydroxy or alkoxy group reactive with the inorganic substrate as an
integral coupling composition for improving mechanical and electrical
properties by mixing with an organic elastomer, a filler and peroxide
followed by curing.
Martens et al U.S. Pat. No. 3,148,169 discloses the pretreatment of clay
filler with a silicone fluid to coat the clay particles to impart a
hydrophobic character to the clay and to mask the acidic nature of the
clay so that peroxides later used as crosslinking agents are not
deactivated.
Rykowski U.S. Pat. No. 4,179,537 discloses blends of an organofunctional
silane, e.g., vinyltrialkoxysilanes, methacryloxyalkyltrialkoxysilanes,
vinyltrihalosilanes and the like with a non-organofunctional silane, e.g.,
alkyltrialkoxysilanes, and the incorporation of such blends into organic
resins, e.g., EPDM rubber for improving the adhesion between inorganic
substrates such as clay fillers and the resin. This patent fails to
disclose, teach or suggest the incorporation of siloxane oligomers in the
coupling composition and suggests that the presence of siloxane oligomers
in the resin-filler system could have a detrimental effect on coupling
efficiency (col. 4, lines 54-63).
The Rykowski patent teaches the use of blends containing silanes having
silicon-bonded 2-methoxyethoxy groups, e.g.,
vinyl-tris(2-methoxyethoxy)silane (Col. 2, lines 44-47), which releases
2-methoxyethanol as a hydrolysis by-product during use. The possible
teratogenic properties of 2-methoxyethanol are currently under study
indicating a potentially unacceptable risk in using
vinyl-tris(2-methoxyethoxy)silane or similar materials as coupling agents
or as components of coupling compositions.
Vinyl-tris(2-methoxyethoxy)silane, has been used industrially for many
years as a coupling additive in mineral-filled EPM and EPDM wire and cable
insulations. EPM is an ASTM designation for copolymers or ethylene and
propylene; EPDM is a terpolymer of ethylene, propylene and a diene monomer
such as ethylidene nor-bornene or 1,4 hexadiene.
Vinyl-tris(2-methoxyethoxy)silane has been extensively used heretofore
because it provides a unique balance of elastomer reinforcement and the
degree of wet electrical stability required. It releases 2-methoxyethanol
as a hydrolysis by-product when it is used and, unfortunately, 2-methoxy
ethanol is now being studied as a suspected teratogen.
Vinyl-tris(2-methoxyethoxy)silane provided such a unique combination of
high elastomer reinforcement, i.e., high degree or mechanical properties,
and high degree of wet electrical stability, that it became the industry
standard. No other single polymerizable, hydrolyzable silane has been
found that can provide comparable performance on a one for one replacement
basis. Many such other silanes provide acceptable electrical stability but
fail to provide mechanical properties that are acceptable in every
respect; notably as judged by 300% modulus which varies significantly with
the other silanes.
None of the prior art references identified above discusses or suggests any
compositions containing a blend comprising an organofunctional silane
polymerizable with an organic elastomeric matrix and reactive with an
inorganic substrate filler and an organosiloxane oligomer reactive with
the inorganic substrate filler that is capable of providing mechanical
properties and wet electrical stability properties comparable to the
heretofore industry standard, vinyl-tris(2-methoxyethoxy)silanes.
3. Summary Of The Invention
The present invention is based on the discovery that coupling compositions
containing an ethylenically unsaturated silane having hydroxy or alkoxy
groups reactive with an inorganic substrate and an ethylenically
unsaturated group polymerizable with an organic elastomeric matrix and an
organosiloxane oligomer containing hydroxyl or alkoxy groups reactive with
the inorganic substrate can be substituted on a one for one weight basis
for the industry standard coupling agent vinyl-tris(2-methoxyethoxy)silane
to provide comparable mechanical and electrical properties in the cured
state of the organic elastomeric matrix without releasing the suspected
teratogen, 2-methoxyethanol. It is also based on the further unexpected
discovery that a higher ultimate elongation at equivalent modulus are
provided by certain coupling compositions of the present invention as
compared to the industry standard, vinyl-tris(2-methoxyethoxy)silane. As a
result, wires and cables insulated with cured elastomeric matrixes
containing our novel coupling compositions can survive more severe bending
without harming the insulation and thus can be more easily threaded
through intricate conduits or passageways during installation, a
characteristic that is particularly advantageous under cold or adverse
weather conditions.
The present invention also includes novel curable organic elastomeric
compositions containing the novel coupling compositions compounded with an
organic elastomer, an inorganic filler, and a peroxide crosslinking agent
as well as other optional ingredients such as antioxidants, stabilizers,
and the like conventionally used in compounding elastomeric compositions.
In addition, the present invention includes novel cured elastomeric
compositions obtained by heating the curable compositions of this
invention to a temperature high enough to decompose the peroxide and thus
initiate crosslinking. Furthermore, this invention includes wire and cable
comprising a conductor coated with the novel cured composition as
electrical insulation.
4. Detailed Description Of The Invention
In accordance with this invention, the novel coupling compositions are
prepared by simply mixing from 5 to 95 wt. % of the ethylenically
unsaturated silane and from 95 to 5 wt. % of an organosiloxane oligomer
having at least one silicon-bonded hydroxyl or alkoxy group, based on the
combined weight of the two components. Preferred ratios include 25 to 85
wt. % of the ethylenically unsaturated silane and 75 to 15 wt. % of the
organosiloxane oligomers, based on the weight of the two components.
Suitable ethylenically unsaturated silanes contain at least one
silicon-bonded ethylenically unsaturated group, preferably containing
carbon and hydrogen or carbon, hydrogen and and oxygen, for example,
vinyl, allyl, methacryloxypropyl, acryloxybutyl and the like, and at least
one, preferably three, silicon-bonded hydroxy and/or alkoxy groups having
1 to 4 carbon atoms each, methoxy, ethoxy, isopropoxy and the like. Any
valences of silicon of the silanes not filled by ethylenically unsaturated
groups and hydroxyl or alkoxy groups are satisfied by monovalent
hydrocarbon groups having 1 to 6 carbon atoms, such as methyl, ethyl,
propyl, phenyl and the like. The silicon-bonded ethylenic groups of the
silane are polymerizable with the ethylenically unsaturated groups
contained in the organic elastomer; the hydroxy and/or alkoxy groups are
reactive with the inorganic filler. Examples of suitable ethylenically
unsaturated silanes are vinyltriethoxysilane, vinyltrimethoxysilane,
allyltriethoxysilane, allyl triisopropoxysilane,
gamma-methacryloxypropyltrimethoxysilane,
gamma-acryloxypropyltriethoxysilane,
beta-triacryloxyethoxytrimethoxysilane, and the like. Ethylenically
unsaturated silanes that can be used in the composition of this invention
include those represented by the formula:
R.sub.a SiX.sub.b Y.sub.c
wherein R is a silicon-bonded monovalent hydrocarbon group free of
ethylenic unsaturation and having 1 to 6 carbon atoms, such as methyl,
ethyl, butyl, isobutyl, phenyl and the like, X is a silicon-bonded
hydroxyl or alkoxy group having 1 to 4 carbon atoms, such as, methoxy,
ethoxy, isopropoxy and the like, Y is a silicon-bonded ethylenically
unsaturated monovalent organic group composed of carbon and hydrogen or
carbon, hydrogen and oxygen, such as vinyl, allyl, methacryloxypropyl,
acryloxybutyl and the like, a is an integer of 0 to 2, preferably 0, b is
an integer of 1 to 3, preferably 3, c is an integer of 1 to 3, preferably
1, and a+b+c is equal to 4.
The organosiloxane oligomers used in the coupling compositions of this
invention have an average of no more than 20, preferably 2 to 10, siloxy
units per molecule, it being understood that such oligomers are, in fact,
mixtures of siloxane molecules having different numbers of siloxy units to
the molecule. Suitable organosiloxane oligomers include linear, branched
and cyclic polysiloxanes and mixtures of any two or more of the linear,
branched and cyclic polysiloxanes. Such oligomers contain at least one
silicon-bonded hydroxyl or alkoxy group per molecule and preferably at
least one hydroxyl or alkoxy group per siloxy unit. Any valences of
silicon not satisfied by a divalent oxygen atom in a .tbd.SiOSi.tbd.
linkage or by a hydroxy or alkoxy group is satisfied by a monovalent
hydrocarbon group free of ethylenic unsaturation and having 1 to 6 carbon
atoms, preferably alkyl. Organosiloxane oligomers useful in the
compositions of this invention include those linear, branched and cyclic
oligomers represented by the formula:
D.sub.g [R.sub.d X.sub.2-d SiO].sub.e [R.sub.2 SiO].sub.f Z.sub.g
wherein R and X are as defined above and may be the same or different
throughout the molecule, D is X or OSIR.sub.3, Z is R or SiR.sub.3, d is
an integer of 0 or 1, preferably 1, e is an integer having an average
value of 1 to about 10, f is an integer having an average value of 0 to
about 9, g is an integer of 0 or 1, e+f is equal to 3 to about 10 when g
is 0, e+f is equal to 1 to about 9 when g is 1, and e+f+g is equal to 2 to
about 10. Preferred organosiloxane oligomers are represented by the
formula
RO[R'(RO)SiO].sub.x R
wherein R is as defined above, preferably alkyl such as ethyl, R' is alkyl,
preferably methyl, and x is an integer having an average value of 2 to
about 10.
When vinyltriethoxysilane is used in the coupling compositions, it is
present in the preferred amount of 55 to 85 wt. %, most preferably 65 to
75 wt. %, and organosiloxane oligomer is present in the preferred amount
of 45 to 15 wt. %, most preferably 35 to 25 wt. %, based on the combined
weights of these two components. In the case of using
vinyltrimethoxysilane in the coupling composition, it is present in the
preferred amount of 40 to 80 wt. %, most preferably, 60 to 70 wt. %, and
the organosiloxane oligomer is present in the preferred amount of 60 to 20
wt. %, most preferably 40 to 30 wt. %, based on the combined weights of
the two components. When using gamma-methacryloxypropyl trimethoxysilane
in the coupling compositions, it is present in the preferred amount of 25
to 65 wt. %, most preferably 45 to 55 wt. %, and the organosiloxane
oligomer is present in the preferred amount of 75 to 35 wt. %, most
preferably 55 to 45 wt. %, based on the combined weight of the two
components.
Optionally, the coupling compositions of this invention can contain a third
component which is ethylenically unsaturated organosiloxane oligomer
having per molecule no more than 100 siloxy units and having per molecule
at least one silicon-bonded ethylenically unsaturated group polymerizable
with the organic elastomeric matrix. The third component can be used, if
desired, to replace a portion of the ethylenically unsaturated silane for
the purpose of reducing volatitity and improve somewhat the electrical
properties. The third component can be present in the coupling composition
in amounts up to 10 wt. %, preferably up to 5 wt. %, based on the combined
weights of the three components and the proportion of ethylenically
unsaturated silane is decreased by a corresponding amount. Suitable
ethylenically unsaturated organosiloxane oligomers include linear,
branched and cyclic oligomers or mixtures of two or more of the linear,
branched and cyclic oligomers. Such oligomers contain at least one
silicon-bonded monovalent ethylenically unsaturated group, such as vinyl,
allyl, methacryloxypropyl, acryloxybutyl and the like, and preferably at
least one such ethylenically unsaturated group per siloxy unit in the
molecule, any valence of silicon not satisfied by a divalent oxygen atom
in a .tbd.SiOSi.tbd. linkage or by an ethylenically unsaturated group is
satisfied by a monovalent hydrocarbon or hydrocarbonoxy group free of
ethylenic unsaturation, preferably an alkyl or alkoxy group having 1 to 12
carbon atoms. Ethylenically unsaturated organosiloxane oligomers useful in
this invention include those linear, branched or cyclic oligomers
represented by the formula:
R".sub.p [R.sub.d Y.sub.2-d SiO].sub.m [R.sub.2 SiO].sub.n [SiR".sub.3
].sub.p
wherein d, R and Y are as described above and need not be the same through
the molecule, R" is a monovalent hydrocarbon group preferably alkyl, or a
hydrocarbonoxy group, preferably alkoxy, having 1 to 18 carbon atoms and
being free of ethylenic unsaturation and need not be the same throughout
the molecule, m is an integer of 1 to about 100, n is an integer of 0 to
about 99, and p is an integer of 0 or 1, m+n is equal to 1 to about 98
when p is 1, m+n is equal to 3 to about 100 when p is 0, and m+n+p is
equal to 2 to about 100. Preferred ethylenically unsaturated
organosiloxane oligomers are represented by the formula:
R"[RYSiO].sub.z SiYR"R
wherein R, R" and Y are as defined above and preferably R" is alkoxy having
1 to 18 carbon atoms and R is alkyl having 1 to 4 carbon atoms and y is 4
to 100, preferably 4 to 16. Y is preferably vinyl but can be any
ethylenically unsaturated group polymerizable with the organic elastomeric
matrix.
The curable compositions of the present invention comprise, (1) an organic
elastomer, (2) an inorganic filler, (3) a coupling composition as
described above, and (4) a peroxide capable of crosslinking the organic
elastomer. Typical organic elastomers to which the present invention
applies include any of the synthetic or natural rubbers with which fillers
are conventionally employed including natural rubber, synthetic rubbers
such as styrene-butadiene rubber, ethylene-propylene copolymers,
ethylene-propylene terpolymer rubbers in which the third monomeric
component is ethylidene norbornene or 1,4-hexadiene, urethane rubbers,
polyisobutadiene rubbers, and any other vulcanizable or crosslinkable
elastomeric material.
The organic fillers used in the curable compositions are known to those
skilled in the art and include any suitable finely divided or particulate
inorganic substance. At the time of incorporation into the curable
composition most fillers may be in the form of finely divided particles.
They may be approximately isometric, having a maximum diameter, i.e., a
maximum linear dimension of ten microns, preferably five microns; or they
may be in the form of plates or needles (fibers) having a thickness or
diameter of ten microns or less, preferably five microns or less.
Compositions containing larger particles tend to be highly abrasive to
processing equipment and may be undesirable or less preferred for this
reason. The minimum size of the filler particles is not critical, any of
the conventionally used fillers being suitable in this respect. Among the
specific fillers which may be used in the present invention are asbestos,
ground glass, kaolin and other clay minerals, silica, calcium silicate,
calcium carbonate (whiting), magnesium oxide, barium carbonate, barium
sulfate (barytes), metal fibers and powders, glass fibers, refractory
fibers, non-reinforcing carbon blacks, titanium dioxide, mica, talc,
chopped glass, alumina, aluminatrihydrate, quartz, wollastonite (calcium
silicate), and inorganic coloring pigments. Kaolin clay is a filler of
choice in the wire and cable industry and therefore is preferred.
Suitable peroxides are also well known to those skilled in this art. Any
peroxide that is capable of crosslinking the organic elastomer can be
used. For example, any of the peroxides described or listed in Martens'
U.S. Pat. No. 3,148,169 can be employed and said Martens' disclosure is
incorporated herein by reference. The peroxide is heat decomposable, that
is, is heat activated so that when a mixture of the organic elastomer and
peroxide is heated to a given temperature or temperature range peroxide
decomposes and the crosslinking reaction takes place.
Any other additives to the curable composition can be used. For example,
stabilizers and antioxidants can be added. Additional pigmentation can be
provided and any other additive for providing other properties can be
used.
The proportions of components in the curable composition are not narrowly
critical and conventionally are based on weight parts per 100 wt. parts of
organic elastomer. On this basis the inorganic filler can be varied from
25 to 200, preferably 50 to 150, wt. parts per 100 wt. parts of elastomer.
The coupling composition can be present in an amount ranging from 0.1 to
10, preferably from 0.5 to 3 weight parts per 100 wt. parts of filler and
the peroxide can be used in amounts of 0.5 to 10 wt. parts, preferably 2
to 5 wt. parts per 100 wt. parts of elastomer.
The curable compositions except for the peroxide component are
conventionally prepared in a Banbury mixer or any other intensive mixer.
Accepted rubber industry techniques were used. Then the resulting compound
is transferred to a roll mill wherein it is rolled and the peroxide is
added and mixed into the compound to result in a curable composition which
then can be used to coat electrical conductors for the purpose of
insulating same after curing. These compositions can be used for a variety
of other electrical insulation purposes including encapsulating of
electrical components and other applications.
In order to cure the curable compositions it is only necessary to apply
heat above the temperature at which the peroxide decomposes and thus
becomes activated. Preferably a peroxide is chosen for use having a
decomposition temperature in excess of 200.degree. F., preferably in
excess of 250.degree. F. In producing wire and cable the curable
composition in heated, readily deformable condition (but below the
decomposition temperature of the peroxide) is applied through an extruder
to a conductor to form an insulating coating around the conductor. After
extrusion onto the conductor the combined conductor and coating of curable
composition is passed into an oven or autoclave where the temperature is
raised to a point above the decomposition temperature of the peroxide upon
which the curable composition cross links or cures to form a tough
thermoset insulating coating around the conductor.
The following Examples are presented. The numbered Examples represent the
present invention; the lettered Examples do not represent this invention
but are presented for comparison purposes. Temperatures given are in
.degree.F. and parts and percentages are on a weight basis unless
otherwise stated. The following designations used in the Examples and
elsewhere herein have the following meanings.
______________________________________
Me: methyl
Et: ethyl
Vi: vinyl
psi: pounds per square inch
%: percent by weight unless otherwise stated
g: grams
wt: weight
pts: parts by weight unless otherwise stated
Hardness, Shore A ASTM D-2240-81
Ultimate elongation, %
300% Modulus, psi ASTM D-412-80
Tensile, psi
Dielectric Constant at 1kc
as cured
7 days in 75.degree. C. water
Dissipation Factor at 1kc
ASTM D-150-81
as cured
7 days in 75.degree. C. water
Volume Resistivity, ohm-cm.about.
ASTM D-991-82
Oscillating Disc Rheometer.about.
ASTM D-2084-81
______________________________________
In the Tables, the values given for each component or ingredient of the
compositions defined therein are on a weight basis per 100 weight parts of
elastomer, i.e., ethylene-propylene copolymer.
EXAMPLES 1-5
Eight rubber formulations (Examples 1-5 and Comparisons A, B and C) were
prepared from 100 wt. parts of an ethylene-propylene copolymer (Vistalon
404 sold by Exxon), 110 wt. parts of calcined clay (Whitetex sold by
Freeport Kaolin), 5 wt. parts of zinc oxide, 1.5 wt. parts of antioxidant
(Agerite Resin D sold by R. T. Vanderbilt), 5 wt. parts of carbon black
and 2 wt. parts of a peroxide identified in Table 1 and 1.1 wt. parts of a
silane or a blend of a silane and a siloxane oligomer as identified in
Table 1. In each instance the formulations were prepared in a "B" Banbury
mixer using the following mixing procedure and also using full cooling
water in the mixing machine. Initially the copolymer and antioxidant were
placed in the mixer and mixed for 30 seconds at #2 speed after the ram was
completely down. Thereafter, one-half of the clay was added and mixed for
30 seconds at #2 speed after the ram was completely down following which
the second half of the clay and all of the carbon black were added and
mixed for 30 seconds at #2 speed after ram down. In Examples 1-3 the
silane-siloxane blend was added with the second half of the clay and in
Examples 4 and 5 and Comparisons A-C the silane or silane-siloxane blend
was added with the first half of the clay. Then in all instances all of
the zinc oxide was added and the formulation mixed again at #2 speed for
30 seconds with the ram fully down. Thereafter, any materials on the
exterior surfaces on the ram or mixer were swept into the mixture and the
ram run down after which mixing was continued for 30 seconds at #2 speed.
The exterior surfaces of the ram and mixture were swept to move any of the
above-mentioned ingredients into the mixture after which the contents were
again mixed at #3 speed for 15 seconds. Thereafter, the contents of the
mixer were dumped and sheeted off on a 6.times.12 roll mill using a roll
temperature of 120.degree. to 130.degree. F.
The resulting rubber compounds were catalyzed with the above-identified
peroxide on the 6.times.12 roll mill at a roll temperature of 120.degree.
to 130.degree. F. Test plaques were made from each rubber compound and
cured for 25 minutes at 340.degree. F. The test plaques for each compound
were tested for mechanical properties and electrical properties as set
forth in Table 1. The results are likewise given in Table 1.
Comparison A illustrates the poor results in mechanical properties,
especially modulus and the electrical properties including poor dielectric
constant under wet conditions and poor dissipation factor under wet
conditions. Comparison B illustrates a highly acceptable formulation
commercially used heretofore but which used a silane that gives off a
by-product that is suspected of being teratogenic. Examples 1-5 illustrate
the improvements in elongation while maintaining acceptable modulus,
hardness and tensile strength by using the blends of this invention which
are not troubled by teratogenic or other toxic side effects from
by-products. In addition, in some instances, for example as shown in
Examples 3 and 4, the mechanical properties are superior to those obtained
with the best available commercial formulation. These Examples demonstrate
the achievements of providing a safer formulation in use and providing in
some instances better properties than the best commercial formulation. The
electrical properties as shown for Examples 1-5 in Table 1 are not
deteriorated. Moreover, Table 1 illustrates the control available to the
compounder through the use of the present invention for controlling
mechanical properties of the ultimate compound. In addition, the
replacement of a portion of the vinyltrimethoxysilane with an equivalent
weight amount of methylvinylsiloxane as illustrated by Examples 2 and 5 do
not alter the performance of the blend. The results given in Table 1 for
formulations 1-5 also illustrate that the wet electrical properties for
Examples 1-5 and Comparisons B and C are stable. The best mechanical
properties, i.e., elongation, modulus and tensile strength were achieved
by the compound of Example 4 of the present invention.
TABLE 1
__________________________________________________________________________
EXAMPLE A B C 1 2 3 4 5
__________________________________________________________________________
Ethylene-propylene copolymer
100
Calcined clay 110
Zinc oxide 5
Antioxidant.sup.(1)
1.5
Carbon black 5
Peroxide.sup.(2)
2.0
Vinyl-tris(2-methoxyethoxy)
-- 1.1
-- -- -- -- -- --
silane
Vinyltrimethoxysilane
-- -- -- .55
.495
.66
.77
.715
Methylethoxysiloxane
-- -- 1.1
.55
.55
.44
.33
.33
oligomer.sup.(3)
Methylvinylsiloxane.sup.(4)
-- -- -- -- .055
-- -- .055
Mechanical Properties, cured 25 minutes at 340.degree. F.
Hardness, Shore A
62 63 61 63 63 63 62 62
Ultimate elongation, %
960
350
980
440
450
420
370
410
300% Modulus, psi
370
1030
410
930
930
1000
1040
990
Tensile, psi 860
1100
880
1030
1020
1090
1110
1070
Set at break, %
120
15 115
20 25 20 10 15
Electrical Properties
Dielectric Constant at 1kc
as cured 3.07
2.99
2.96
3.07
3.09
3.04
3.02
2.96
7 days in 75.degree. C. water
4.21
2.97
2.89
3.07
3.09
3.00
2.90
2.90
Dissipation Factor at 1kc
as cured .003
.003
.003
.003
.004
.003
.003
.004
7 days in 75.degree. C. water
.072
.003
.003
.002
.003
.003
.003
.003
Volume Resistivity .times. 10.sup.15(5)
as cured 24 61 54 12 18 16 63 60
7 days in 75.degree. C. water
.01
8.5
7.8
7.7
11 7.4
8.7
9.1
__________________________________________________________________________
FOOTNOTES TO TABLE 1
.sup.(1) poly2,2,4-trimethyl-1,2-dihydroquinoline
.sup.(2) .alpha.,.alpha.bis(t-butylperoxy)diisopropylbenzene
.sup.(3) A mixture of linear, branched and cyclic oligomers made by
reacting MeSiCl3, water and ethanol and having an average molecular weigh
of about 500 and an ethoxy content of about 35 to 55 wt. %. The mixture
can be represented, on a linear basis, by the formula:
EtO[(Me)(EtO)SiO].sub.x Et; x = 2,3,4,5 and higher.
.sup.(4) A mixture of fatty alcohol, mostly dodecoxy endblocked
methylvinylsiloxane fluid having the formula C.sub.n H.sub.2n+1
O[(Me)(Vi)SiO].sub.x C.sub.n H.sub.2n+ 1 in which n = 10 to 18, preferabl
12 to 16 and x = 4 through 100, preferably 4 through 16.
.sup.(5) ohmcm
EXAMPLES 6-10
Five rubber formulations (Examples 6-10) were prepared using the types and
amounts of components set forth in Table 2 below. In the cases of Examples
6-8 the procedure used was the same as those described for Examples 1-3.
In Examples 9 and 10 the procedure used was the same as that described in
Examples 4 and 5. The resulting rubber compounds were catalyzed and test
plaques were cured from each rubber compound and tested in the manner
described for Examples 1-5. The test results are given in Table 2 below.
In Table 2 the results for Examples 6-10 are compared against rubber
compound containing no silane or siloxane coupling agent (Comparison A),
against one of the better known commercial rubber compounds containing one
of the better silane coupling agents (Comparison B), and rubber compounds
containing the siloxane oligomer or fluid (Comparison C). The problem with
the silane used in Comparison B is that it gives off a by-product which is
suspected of being teratogenic. None of the silane-siloxane blends used in
Examples 6-10 are suspected of being or emitting teratogens, therefore
providing this further advantage to the compositions made pursuant to this
invention. Furthermore, the mechanical properties of rubber compounds of
at least some of the Examples of this invention are better than those of
the commercial compound of Comparison B, specifically the rubber compound
of Example 8 provides a substantial high tensile strength and modulus and
a substantial higher ultimate elongation. Example 9 provides higher
modulus and tensile strength. The wet electrical properties of all
compositions containing silane or silane-siloxane blends are stable
according to the data given in Table 2.
TABLE 2
__________________________________________________________________________
EXAMPLE A B C 6 7 8 9 10
__________________________________________________________________________
Ethylene-propylene copolymer
100
Calcined clay 110
Zinc oxide 5
Antioxidant.sup.(1)
1.5
Carbon black 5
Peroxide.sup.(2)
2.0
Vinyl-tris(2-methoxyethoxy)
-- 1.1
-- -- -- -- -- --
silane
Vinyltriethoxysilane
-- -- -- .605
.715
.66
.825
.77
Methylethoxysiloxane
-- -- 1.1
.495
.385
.385
.275
.275
oligomer.sup.(3)
Methylvinylsiloxane.sup.(4)
-- -- -- -- -- .055
-- .055
Mechanical Properties, cured 25 minutes at 340.degree. F.
Hardness, Shore A
62 63 61 63 63 64 63 62
Ultimate elongation, %
960
350
980
440
410
410
350
380
300% Modulus, psi
370
1030
410
950
960
1010
1040
1050
Tensile, psi 860
1100
880
1030
1060
1090
1110
1020
Set at Break, %
120
15 115
20 20 20 15 15
Electrical Properties
Dielectric Constant at 1kc
as cured 3.07
2.99
2.96
3.02
3.05
3.07
3.04
3.08
7 days in 75.degree. C. water
4.21
2.97
2.89
3.03
3.05
3.06
2.92
3.10
Dissipation Factor at 1kc
as cured .003
.003
.003
.003
.004
.004
.003
.004
7 days in 75.degree. C. water
.072
.003
.003
.002
.002
.003
.003
.003
Volume Resistivity .times. 10.sup.15(5)
as cured 24 61 54 62 9.7
24 54 34
7 days in 75.degree. C. water
.01
8.5
7.8
5.1
6.7
6.9
7.1
5.7
__________________________________________________________________________
.sup.(1) through .sup.(5) same as footnotes .sup.(1)-(5) respectively of
Table 1.
EXAMPLES 11-14
Four rubber formulations (Examples 11-14) were prepared from components
substantially the same as those described for Examples 1-10 except that
the silanes and siloxanes and the amounts thereof as set forth in Table 3
below were used. The procedures used in Examples 11 and 12 were the same
as procedures as described in Examples 1-3. Examples 13 and 14 used the
same procedures as are described for Examples 4 and 5. The resulting
rubber compounds were catalyzed and test plaques were made and cured and
tested in the manner described for Examples 1-10 for mechanical properties
and electrical properties. The results are set forth in Table 3.
None of the rubber compounds produced according to this invention in
Examples 11-14 utilize a silane which produces a by-product which is
suspected of being teratogenic and however provides equivalent or better
mechanical and electrical properties than one of the best known commercial
compounds such as that described for Comparison B. For example, the
modulus for Example 13 is somewhat improved with little sacrifice of
tensile strength. The results of Table 3 clearly illustrate the control
provided to the compounder of mechanical and electrical properties by
means of manipulation of the relative proportions of siloxane and silane
coupling agents used in the blends of the present invention.
TABLE 3
__________________________________________________________________________
EXAMPLE A B C 11 12 13 14
__________________________________________________________________________
Ethylene-propylene copolymer
100
Calcined clay 110
Zinc oxide 5
Antioxidant.sup.(1)
1.5
Carbon black 5
Peroxide.sup.(2) 2.0
Vinyl-tris(2-methoxyethoxy)silane-
-- 1.1
-- -- -- -- --
methacryloxypropyltrimethoxysilane
-- -- -- .385
.495
.44
.715
Methylethoxysiloxane
-- -- 1.1
.715
.605
.605
.385
oligomer.sup.(3)
Methylvinylsiloxane.sup.(4)
-- -- -- -- -- .055
--
Mechanical Properties, cured 25 minutes at 340.degree. F.
Hardness, Shore A 62 63 63 64 63 63 64
Ultimate elongation, %
960
350
980
420
400
350
370
300% Modulus, psi 370
1030
410
970
990
1040
1010
Tensile, psi 860
1100
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