Note: Descriptions are shown in the official language in which they were submitted.
20~77~
PATENTS
60SI-1490
IMPROVED ~EAT CU ~ LE 5ILICONE
R~BBER CO~POSITIONS EMPLOYING VINYL
~Q RESIN AMD A SIN~LE VINYL CHAIN STOPPED POLYMER
~A~R~ROUND~5~F TH~ INVENTI~N . .
~ he pres~nt invention relate3 to hast cur~hle
silicone rubber ~ompo~itions. More partlcularly, the
invention r~lates to hest cuxable ~ilicone rubber
comp~ition~ whi~h ~re ~ubst~ntially free o~ vinyl
containing organo~iloxan~ oLls and have lmproved tear
and ten~ile strength, and compres3ion set propertie~.
- He~t curable silicone rubber compo~itions are
k~own in the art. Such composition~ are known for
their ability to r~sist oh~nge at elevated t0mperature
and exposure to adver~e conditions over extended
period~ of time. In general, m~terials are needed
which have no~ only ~he ou~tandin~ properties of
organopoly8iloxane elastomer~ but al80 have a hi~h
dsgrea of tear and tensile strength. In particular
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20~77~1
_~_ P~TE~S
application~, æuch a~ gasketing applications, a~ati~factory degree o~ r~ n~y a~ mea ured by
compre~sion 8et i8 al~o required.
Efforts have been mad~ in the pa~t t~ produce heat
5 curable silicone 21astomer compositions haYing
increasad tear strength and reduced compre~sion set
propertias.
U.5. Paterlt No. 4,539,357 (~obe~r '357) disclo~es
an exemplary he~t-cur~bl~ one composition
10 comprising a vinyl-terminated line~r
diorganopoly~iloxane gum h~ving a vi~co~ity in the
range of lx106 to 20x107 cen~lpoi~e at 25C, a vinyl-
con~aining diorg~nopoly~ilo~ano ~um having a vi8c081ty
varying from lx106 to 20x107 centlpoise a~ 25C, a
fill0r, ~ hydride-containing polysiloxane, and an
org~nic peroxid~ or organic hydroperoxide curing agent.
The compo~ition may furthex compri e a vinyl-containing
or~anopolysiloxane r~sin copoly~er. It i~ ~tated in
3 2 0 ~ 7 7~.1PATENTS
~Q~so
Bobear ~357 at column 6, lines 22-29 that ~here ~hould
be no vinyl-containing fluid in the composition since
it has been found that composit~ons containing vinyl-
containing fluids of a viscosity of 500,000 centipoise
S or less rQsult in elastomer with good tear strength
initially, but after the composition ha~ been ~ubjected
to po~t-cur~, it~ tear strength properties degrade
dramatically. After post-cure baking, the Bobear '357
composition ha~ a tear strength of above 200 pi.
U.S. Patent No. 3,6S~,475 to Wada et al. (Wada
'475) di~clo~e~ heat curabl elastomeric silicone
compositions report~dly having high tear strength,
excellent compression set and resiliency, comprising
two vinyl-unsaturated polydiorganopoly~iloxanes each
having a degree of pol~mexization of at lea~t 3000; a
vinyl-un~aturated polydiorganopolysiloxane having a
degree of polymerization of from 10 to 1000; a ~ilica
filler; and an organic peroxide catalyst. The sample~
prepared in the Wada '475 examplaæ had tear strength
values of about 40 kg/cm, i.e., about 225 pi.
U.S. Patent No. 3,671,480 to Wada et ~ Wada
'480) disclo~e~ a heat curable elastomeric ~ilicone
compositîon having Lmproved tear ~trength and ~uperior
compre~sion set, comprising a mixtuxe of two vinyl-
unsaturated polydi.organopolysiloxanes, one o~ whichappear~ to have a hi~h molecular weight and the other
o~ which appears to have a low molecular weight; a
polyorganohydrogensiloxane; ~ilica fill~r; and a
platinum co~pound. The examples in Wada ~4B0 report
tear strength values of about S0 kgJcm, i.e.~ about ~80
pi. Compre~sion 8et value~ are not givsn.
U.S. Patent No. ~,061,609 to Rob~ar (Bobear '609)
di~cusces a platinum catalyzed silicone rubber
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~ P~EN~
Ç~a~Q
composition comprising a vinyl-containing polysiloxane
or a blend of such polysiloxanes; platinum; and ~
hydrogen-containing polysiloxane. Preferably, the
vinyl-containing polysiloxane has a vi~cosity in the
range of 1000 to 300,000,000. A low viscosity vinyl-
containing polysiloxane may be added to the basic
composition a~ a rein~orcing agent to give the final
composition good physical strength. ClaLm 4 in Bobear
'609 recites a first polysiloxane having a viscosity of
l,000,000 to 200,000,900 centipoise at 25C and a
second polysiloxane having a viscosity of 50,000 ~o
500,000 centipoise at 25C. The Bobear patent is
directed to Lmproving the work life of silicone rubber
co~positions, rather than tear strQngth. In the
examples, tear strength value~ of greater than 200 pi
were obtained, but the compositions having these values
contained two high viscosity vinylpolysilo~anes rather
than one high ~i~co~ity vinylpolysiloxane and one low
viscosity vinylpolysiloxane.
U.S. Patent No. 3,660,345 to Bobear (Bobear '345)
disclose~ oganopolysiloxane compositions which are
convertlble to elastomers having high tear strength and
resiliency, compri3ing a two component blend of vinyl-
contalning orgar.opolysiloxan~s; ~ilica ~iller, and a
~5 process aid which can be, for example, a methoxy-
termin~ted polysiloxane, a ~ilanol-terminated
polydLmethyl~iloxane, or hexamethyldisilazane. A
peroxide is used a~ the cataly~t. The visco~i~y of one
of the two vinyl-containing organopolysiloxanes can be
in the range of 1 to 1 billion centipoise at 25C,
while the viscosity o~ the other can be between lOO,OOD
to 2,000,000,000 centipoise at 25C. The examples in
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2~77~3~
_ S ~ PMENTS
60S~-149Q
E~obear '345 report tear ~trength ~ralue8 of greater than
200 pi.
11.S. Patent No. 3,696,068 to Creamer disclose~
heat-curable silicone gumstock composition~ ha~ing high
"B" tear strength ~s well as low compression set
values, comprising a vinyl-containing
diorg~nopolysiloxane gum and a linear vinyl-containing
fluid having a vi5c08ity of from 10 to 150,000
centistokes at 25C. The cross-linkable vinyl siloxane
gum has a viscosity in exce~s of 200,000 centistoke~ at
25C. The Creamer composition i~ cured by a peroxide
ca~alyst. Some of the samples prepared in Creamer had
tear strength values in exc2ss of 150 pi. Tear
strength after post cure was not mea~ured in any of the
examples, which i~ significant since, as pointed out
pre~i.ously herein, it has been found that, in
composition~ containing low ~isc08ity vinyl-containing
fluids, tear strength drop~ dr~matically after po8t
cure.
~O U.S. Patent No. 3,884,866 to Jeram et al.
di~closes a high 3trength or~anopoly~iloxane
compo~ition suited for low pre0~ure in~ec~ion molding,
comprising ~A) a first oomponen~ containin~ (i) a
vinyl-containing high vi8c08ity oxgsnopolysilo~ane
having a vi~c08ity of 5000 to 1,000,000 centipoise at
25C; and (ii) a low visco~ity o~ 50 to 5000 centipoise
at 25~C; (iii) a ~iller; and (iv) a platinum catalyst;
and (B) a hydrogen ~ilicone composition. The highest
t~ar strength reported in the example~ was 250 pi.
~lthough heat curable silicone rubber compositions
having good tear and ten~ile strength, and low
compression set properties are known in the art, it is
de~irable to provide heat curable silicone rubber
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2~75~
-6- PAT~NTS
compo~ition~ which have good Rtrength and compre~sion
set properties rQsulting from formulations which are
more ea~ily proces~ed, have more repeatable and
con~istent results, and have stable properties.
It is therefore an ob~ect of the inv~ntion to
provide a heat curable silicone rubber composition
having good tear and tensile strength and low
compre~sion set employing more ea~ily proc~ssed
components.
SUMMARY OF THE I~e~lrg~
rhe present invention is based upon the discovery
that an oil-fre~ combination of a vinyl containing
diorganopoly~iloxane gum and a vinyl containing
organosiloxane resin will cure in the pr~ence of a
catalyst and a cross-linking agent to fonm a heat cured
silicone elastomer having high tear and ten~ile
strength and low compression 80t.
In contrast to some pre~ious compositions, the
pr~ent invention utilizes a single lower molecular
weight gum inste~d of a higher weight gum and a vinyl-
containing oil. A high cxoss~link density in the final
cured polymer i~ khu~ achieved which exhibits a mono~
modal molecular weight distribution o the ~inyl cha~n-
~opped PO1YmQr~
In a particular embodiment, the invention
comprises (A) 100 parts by woight of a vinyl oontaining
organopoly~iloxane or blend ha~ing a vi8c08ity of about
3,000,000 to about 100,000,000 centipoi~e at 25C and
being ~ub~tantially free of vinyl containing
organo~iloxane oil; and (B) from abou~ 1 to about 30
par~s by weight, based upon Component (A), of an
organopoly~iloxane resin or resins having ~Q or NDQ
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20877~
_,_ PATENTS
units where each M unit can represent M or M' e.g. M-
vinyl units and where each D unit can repres2nt D or D'
e.g. D-vinyl units, and up to about 10 weight percent ~ -
vinyl groups. The composi~ion al80 include~ (C~ up to
5 about 200 part~ by waight, ba~ed upon Component (A), of
a filler, and (D) up to about 29 p~rts by weight, based
upon Component (A), of an organohydrogensiloxane cro8s-
linking agent having a hydrogen content ranging from
about 0.05 to about 2 weight percent and a viscosity
from about 5 to about 500 centipoise at 25C. The
composition may further include a processing aid~ a
~urface treat~ent for the filler, a coupling agent,
catalyst, an acid ~cceptor, ~nd a heat age additive.
The heat curable composition~ of the invention
have good tensile and tear ~trength and low compres~ion
set properties without sacrificing other beneficial
properties including oil resistance, hardness and
elongationO
DESCRIPTION OF TEE IN~VENTIQN: ,
The present in~ontion is directed ~o a heat
cursble silicone composition having improved
compre~sion ~et and toar ~tren~th propertie~,
containing (A) a vinyl con~aining diorganopolysiloxane
gum or blands of vinyl containing diorganopolysiloxane
gum8 having a visco~ity fro~ about 3,000,000 to about
100,000,000 centipoise (Cp8) at 25C, (B) an
organopolysiloxane re8in copolymer, (c) a fill~r, and
(D) a cross linking agen~ curable in the presence of a
catalyst.
Component (A) is a vinyl containing
dio~ganosilosane gum or blend of such gums ha~ing a
visco~ity fro~ about 3,000,000 to ~bout 100,000,000 Cp8
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~77~1
: -8~ P~ENTS
60~-14~Q
at 25C. Preferably, the gum has a visco~ity of
between about 3,000,000 and 85~ noo, ~oo cps, more
preferably, about 13,000,000 Cp8 at 25C~ The gum may
have a weight percent vinyl concentration of from about
5xlO-s to about 1. The gum preferably has a weight
percent vinyl concentration in the range from about
6.5xlO-s to about O.U3, more prefsrably from about 8x10-5
to about 1.5xlO-', and more preferably yet from about
8xlO-s to about 1.2x10-4. The organo groups in the
vinyl polymer or polym~rs of the gum should all be
monovalent hydrocarbon radicals.
The vinyl poly~er or polymers of Compon~nt (A) may
contain vinyl-on-chain groups and vinyl end-groups.
Preferably, the polymer i8 vinyl terminated. More
pr~ferably the polymer is free of vi~yl substitution
except at the chain ends. In other pxeferxed
embodLments, Component (A) ha~ the formula:
Vi5iORl2 (SiORl2)x(SiOR22)y SiRl2Vi
wherein Vi i~ vinyl; R1 is independently choMen
from monovalent hydrocarbon radicals, ree o~ ~liphatic
unsaturation, and containing 1 to about 8 carbon atom~;
RZ i8 independen~ly cho~en from monovalent hydrocarbon
radical~ containing 1 to about 8 carbon atoms; and x
and y are int~gers cho~en Ruch that Component ~A) has
a vi~c08ity which ranges from about 3,000,000 to about
85,000,000 Cp8 at 25C and a weight percent vinyl
concentra~ion in the range from about 5x10-5 ~o about
2xlO-', preferahly from about 8x10-5 to about 1.5x10-4,
and more pxeferably from about 8x10-5 to about 1.2x10-4.
The vinyl containing polymers of Component (A~ can
be made by a process well known in the art, or
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~77~:~
-~ 9 - PATE:Nq'S
example, by reacting cyclotetrasiloxanes in the
pr~sence of low molecular weight, linear vinyl chain
stoppers at high temperatures in the pre~ence of ba~ic
catalysts so as to yield a poly~er of the d~sired
S molecular weight. When the reaction is over, the
catalyst i~ neutralized and tho exces~ cyclics are
vented off to result in the desixed polymer. By
controlling the amount of chain stopper and the
temperature of the rea~tion, the molecular weight of
the des~red vinyl-containing polymer end product can be
controlled. For more detail~ of the process by which
~uch vinyl containing polymers are produced, reference
i8 made, for 2xample, to U.S. Patent No. 3,660,345,
which is incorporated herein by reference.
Component (A) pre~erably has a pen~tration of
about 1000. In Exampl~ V and VI below the gum u~ed
ha~ a penetration of 1600 as measured using Universal
Penetrometer by Precision Scientific Model No. 73510
with a sub~tantially air free sample. The sample
penetration is measured at 25C~lnC using ~ lO0 gm
weight and a 1/4" diameter by 3~16" needle ~oot with
rounded edge~. The needle is lowered until it, ~ust
touche~ the sur~ace o~ the polymer. Then, the ~ime to
achieve up to 300 mm penotration i8 detonmined or the
amount of penetxa~ion a~ex 60 3eC. Penetration gum is
de~ined as:
DeDth of Penetration X 60 s~c. at 25C
Time
Penetration may be controlled by controlling the
molecular weight and the vi~co~ity of the gum. In the
present invention, the molecular weight o f Component
(A) is preferably between about 300,000 and about
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-10- PATENTS
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850,000, and the vi8~08ity i8 preferably b~tween
3,000 t 000 and about 85,000,OD9 cps at 25C.
In accordance with the invention, the amount of
gum present in the final product may vary. However,
for purposes of explanation herein, it is assum~d that
100 part~ by waight of the g~m is combined with varying
amounts of the other components. In some example~, the
formulation has 80 part~ of Component (A). In each
cas~, the ~mount of other components in the final
product may be calculated or otherwise r~adily
inferred. In the example~ below Component ~Al) i~ a
vinyl-stopped polydiorganosiloxane of about 9000 D
units in length. CQmponent ~A2) is a vinyl-stopped
polydiorgano~iloxane of about 6000 D unit~ in length.
Component (B) is (1) an organopolysiloxane resin
copolymer. The re~in copol~mer may contain R3SiOl~2
monofunctional unit~ (~ units) and SiO2
quadrifunctio~al unit~ ~Q units), where each R is
independently selected from the ~roup consisting of
2G vinyl radicals and mono~alent hydrocarbon radiGals free
of aliphatic un~aturation. The ratio of M units to Q
units range~ from about 0.5:1 to about 1.5:1, wh~rein
the re~in copolymer contains about 0.5 to 10.0 weight
percent vinyl groups. Alternatively, Component (B) m~y
comprise (2) an organopolysiloxane resin copolrmer
con~aining M and Q uni~ as aforesaid and ~2SiO2~2
difunctional (D units) where each R i~ independently
selected from the group consisting of vinyl radical~
and monovalent hydrocarbon radical~ free of aliphatic
unsaturation. Each M unit may represent ~ or M' e.g.
M-vinyl units, and each D unit may repreYent D or D'
e.g. D-vinyl units. The ratio of M units ~o Q units is
from 0.5:1 to about 1.5:1 and the D units are present
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~77~1
PAT~TS
60SI~14~0
in an amount of rom about 1 to 70 mol percent based
upon the total number of mols of siloxy unit~ in the
copolymer. The resinous copolym~r contains from about
0.5 to about 10.0 weight percent vinyl groups. The
organopoly~iloxan~ r~sin copolymer of Component (B) may
contain mixtures of the MQ and the M D Q, ra~ins.
~ h~ organopoly~iloxane resin copolymer~ of
Component (B) in th~ pre~ent compo~ition and their
m~nufacture are well known in the art. Such resin~ are
usually produced by hydrolysi~ of chlorosilane~ in a
process de~cribed in U.SO Patent No~ 3,436,366 which i~
incorporated herein by reference.
Component ~B) i~ pre3ent in the compo~itio~ of the
present invention in an amount ranging ~rom about 1.0
to about 30, preferably from 1.0 to about 20 and more
preferably from about 4 to about 12 psrts by weight,
based upon Component (A).
Component tB) in ~he examples below compri~es (B2)
dispersed in xylene. ~uch of the xylene has been
vacuum stripped ~o it rQsults in a composition
~omprising 60% by weight solid~ and 40~ by weight
xylene. The process for m~nufacturing the compo~ition
include~ a cook and strip ~tep to ~acilitate the
remo~l o~ khe residual xylene from the ~ini~hed
compound.
Component (C) compri3e~ ~rom about 5 to about 200,
pr~erably from about 10 to abou~ 100 and more
pre~erably from about 20 to a~out 50 parts by weight,
bs~ed on Component ~A), of reinforcing filler~ su~h as
SiO2. The filler i8 needed in the compo~ition to
provide a high tear stren~th. Examples of r0inforcing
filler~ that may be used include fumed ~ilica and
precipitated silica, with fumed ~ilica being preferred.
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6QSI-1490
The filler preferably has a surface area of between
about 100 and about 30Q m2Jgm. More preferably, the
~urfac~ area is between 160 and 240 m2/gm The ~iller
may be treated with various a~ents 80 as to pre~ent the
compo~ition from ~tructuring, for example
cyclopolyGiloxanes as di~closed in U~S. Patent NQ .
2,938,009 to Luca~ and sila~anes a~ disclosed in U.S.
Patenk No. 3,635,743 to Smith, or both. The
cyclopolysiloxanes present may b~ for example, a
cyclotetramethyl siloxane present in the amount of
about 15 to 20 weight per~ent of the filler. In the
examples below, Component (C) i8 fum~d silica treated
as in Lucas above having a ~urf acs area~ in the
untreated state, of 240 mZ/gm or 160 m2/gm. A further
surface treatment with a linear vinyl contalning
silazane may be provided in ~itu.
In addition to the foregoing, Component (D) in the
form of a hydride cross-lînking agent may be employed.
In the preferred embodiment, Component (D) may be a
random copolymer formed of a polydimethylsiloxane
(PD~S) and a polymethylhydrogen~iloxane (PMHS) ha~ing
the fonm:
R3SiO(SiORH5iOR2~XSiR
wherein each R i5 independently chosen from a
hydrogen or monovalent hydrocarbon radical free of
aliphatic unsaturation containing 1 to about 8 carbon
atoms, and x ranges from about 2 to about 100. In the
pr~sent invention, the hydride iB present in an amount
of about .1 to 10 parts by weight based upon Component
(A3, pr~ferably 0.625 to 2.5 parts by weight based upon
Component (A). A~ mentioned above, when a hydride
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20;~
~ -13- PATENTS
Q~l~Q '
agent is employed, a platinum c~talyst may be
sub~tituted for the peroxide catalyst to cure the
co~position. In Component ~D), x may vary ~o that (D)
has a vi5c05ity ranging from about 5 to 500 cps,
preferably from about 10 to about 100 Cp8 and most
preferably from about 10 to 50 cp3 at 25C. In a
preferred embodLment, Component (D) has a hydrogen
content ranging from about .5 to ~bout 2 weight
percent. In the example~ below, Component tD) has a
0 vi~CQ. ity of ~bout 30 centi~tokes, a hydride content of
about 0.8 percent by weight, and a chain length of
about 100 units.
The linear hydrid~ descri~sd above can be made by
many procedures which are known in the art and
particularly by the hydrolysi~ c~ appropriate
chloro~ilane~. SQe for example, U.S. Patent No.
4,041,101 which is incorporated herein by reference.
Other components may al80 be employed as di3cussed
h~reinafter. For example, in order to allow for easier
incorporation o~ the filler in the gum, Component (E),
a processing aid or plasti~izQr, may be employed. In
the prefer~ed emhodiment, Component (E) i~ a low
vi8'08ity sLl~nol ~toppod ~iloxane fluid having a
vi8c08ity ranging from About 3-50 Cp8 and preferably 3
to 30 cp~ at 2SC. The ~iloxane fluid i3 an
equilibrium mix o~ low molecular weight oligomers of
from about 4 to about 10 but pr~ferably between 4 and
6 repeating units in length with a minimum ~mount of
cyclics in equilibrium with the oligcmer~. The
39 pro~e3~ing aid ~E) may have the fo~m:
Ho~R2sio)xH
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2~7~1
~14~ PATENT5
where each R is CH3 ~ and x i8 between 4 and 10,
preferably between 4 and 6, with re~ulting cyclics of
the same number of units in e~uilibrium.
In the present invention, the proeessing aid may
be pre~ent in amounts up to 20 parts by weight based
upon Component (A), And preferably is present in
~mounts between 2 and 10 parts by weight based upon
Component (A) and moxe preferably 3 parts by weight.
Up to about 5 weight percent of Component (E) is
preferred for many application~. It shoulcl be
underætood that typicslly the moxe filler th~t i used
the greater amount of processing aid is employed.
Another Compon~nt (F) may ~e vinyl ~topped linear
silazane such a3 tetramethyl-diYinyl ~ilazane. The
material may be added a~ a coupling agent in-~itu for
enhancing the bonding of filler to gum. Component tF)
i~ preferably pr~ent in an amount up to 2 percent by
weight, ba~ed upon the weight of Component (A). More
prefer~bly, Component ~F) i3 present in an amount of
only up to about .3 part~ by weight, based upon 100
parts by weight of Component ~A).
In order ~o form a hea~ curable rubber, an orgsnic
p~roxide free radical initiator or curing catalyst i~
providbd. The pre~erred peroxide curing ayent~ are
thormal decompo~i~ion organic peroxide~ conveniently
u~ed to cur~ ~ilicone elastomers. Exæmples of suitable
organic peroxide free radi~al initiators for u~e in the
present invention are di~clo~ed, for ex2mple, in U.S.
Patent No. 4,539,357 to ~obear which is incorporated
herein by reference. 5uitable peroxide ~ataly~ts
include dialkyl peroxide ~uch as di-ter~iary-butyl
peroxide, t~rtiary-butyl-triethylmethyl peraxide,
tertiary-butyl-tertiary-butyl tertLary-triphenyl
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60SI-~4_0
peroxide, t-butyl perbenzoate and a di-tertiary alkyl
peroxide such as dicumyl peroxide. Vnder certain
condition~ hereinafter de~cribed, such as when a
hydrid~ is used, a platinum catal~st may be employed
5 instead of an initiator. In the example~ below, the
preferred catalyst is a vinyl specific catalYst such
a~ 2,5 dimethyl-2,5-di(t-butyl peroxy) hexane e.g.,
~Lupersol ~101).
Other agent~ may also be added including an acid
acceptor, such a ~gO or ZnO. Acid would otherwise
cause cleavage of the product chains. The acid
acceptor may be present, in smalI amvunts of about 1 to
about 10 parts by weight, bas2d upon Component (A).
In addition to th~ foregoing, a he t aging
component such as fumed TiO2, iron octoate, CelOH)4, or
mixtures thereof, may be pre~ent in ralatively small
~ounts, e.g., up to 2 psrt by weight ba~ed upon
Component ~A). In the example~ below the heat aging
component consists of 33 weight percent TiOz, 5 weight
percent iron octoate tl2% iron in mineral spirits), 10
weight percent treated ~umed silica ~160 mZ/gm), and 50
weight percent of an 8~0 penetration vin~ opped,
vinyl-on-chain gum~
Copending U.S. patent application serial no.
07~587,876, filed 9/25/90, attorney docket no. 60SI-
1336, which is incorporated herein by ref~rence,
discloses heat curable silicone rubber compositions
containing blends of vinyl containing
organopolysiloxane gum8, a vinyl chain stopped PDMS,
oil, MQ and MDQ re~ins, filler and a process aid cured
with a peroxide initiator. The composition3 ar~
formulated for increa~ed tear strength and reduced
compression set properties. ~odified versions,
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-16- PAT~M~S
substantially free of vinyl-containing silicone oil, of
one or more compositions di~clo~ed therein are useful
materials for uæe in a heat curable silicone rubber of
the present invention.
~XAMPLES I YI
The tahle below lists a number of ~ormulations and
their respective properties illuætrative of the present
invention. Examples I and III contain a low m~lecular
weight vinyl chain stopped oil of the type di~closed in
Patent Application Attorney Dockat No: 60SI-1336. This
vinyl containing oil appears to positively affect
compression Bet but is detrLmental to other propertie~.
Examples II and IV do not have the low molecular weight
vinyl containin~ oil component. The oil contributes ~o
the overall ~inyl level in the formulation and thus
contributes to the cros~link den~ity, leading to the
positive effect on compression sat. However, it
produces a bi-modal molecular weight distrihution to
the vinyl chain-qtopped pol~ner. A similar ~inyl
level, and therefore cro3~1ink den~ity, can be achie~ed
with a lower vi c08ity polymer hs~ing an intermediate
molecular wei~ht, which give~ a mono-modal molecular
weight distribution in the vinyl chain stopped pol~ner.
According to the present inventio~, the ~inal gum
~5 pol~ner composition ~hould be substantially free o~
vinyl containing oil and have a mono-modal molecular
weight di~tribution. Examples V and VI illustrate
formulations r~sulting in surprisingly high ~ensile
strength with excellent compression set and tear
strength using a high penetration gum. In Ex~mples V
and VI, Component (A) has a molecular weight of about
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-17- PATENT5
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450, 000 and a vi8c03ity of about 13, 000, 000 Cp8 a~
25 ~C
TA~ILR
~)W{P1~ I II ~I~ IV V VI
S C~PO~NT
~A~ ~3 P~n-tr~tlan ~ 0 ~0 eo 8D
16 P~tnDt~tion ~ -- -- 95 0d
oll 15 -- 15 --- -- -- :
~B) R~ 301u~c10n ~0 10 ~0 10 10 12
0 ~} ~ Prot0l1~ Ald ~ ~ ~ 6 ~ 3 5
(D) Cro~J-Llnl~ing ~9 int 0 6 0 6 ~ 0 l a 1 ~ 1
Coupllng J~g~nt ~F~ 0 ~5 0 15 0 15 0 15 0 15 0 1
O --- 0.~ 0 1 ---- -- 0 1
(C) ~2~0 ~2~ 30 30 30 30 3C -_
~c1 ~160 ~2~gn~) - -- -- 30
~MgO) A~d A~ptor ~G~ -- -- -- 1 0
'c-A~o Add~tlv- __ __ __ __ __ 0 0
P~OP~
ll~ qtr-ngeh ( p-l ) t377 1537 16~2 1059 16~2 1953
2û ~long-tlon ~ 661 657 ~07 8~0 903 733
'r~r 9éronqth (pl) 1~ 1139 l~g 214 152 170
~-rd~ 55 31 ~ S0 50
Ca-pr,~-~lon 8-t 20.9 24.3 Z0.~ 25 5 20 6 20.7
Al~hough the pre~ent invention has been described
25 with reference to specific embodiments, it is to be
understood ~ha~ substitutiono, addi'cion~, deletion~ and
modi Fications wS thin the ~kill o~ an o~dinary ar~i~an
can be made without depsrting from the scope of the
invention a~ defined in the appended claim~.
Test data were ob~ained from the following ASTM methods and
procedures: Shore A - D-2240, Tensile, Elongation and modulus -
D-412 (Die D~9 Tear - D-624 (Die B); and Compression Set - D-395
(method B).
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