Note: Descriptions are shown in the official language in which they were submitted.
2~87r~77
P~TENTS
60SI~14
IMPROVED HEAT CURBD ~LASTOMER COMPOSITIONS BASED ON A
VINYL FUNCTIONAL RESIN, A SINGLE VINYL CHAIN-STOPPED
POLY~ER, AND VINYL-ON-CHAIN POLYNERS
FIELD OF_THE INV~NTION
The present invention relates to heat cured
~ilicone elastomer compositions. ~ore particularly,
the invention relates to heat cured silicone elastomer
compositions haring the proper~ies of high tear
strength, good tensile ~trength, low compra~sion set,
good oil resistance, and good heat age resistance.
~he invention further relates to gaskets comprising the
heat cured silicone elastomer compositions.
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~8777~
- 2 - PATENq~S
6Qg~I-1489
~ACRGROVND OF THE INVENT~ON
Heat curable silicone rubber compo~ition~ are
known in the art. Such ~ompo~ition8 are known for
their ability to resi~t change at elevated temperature
and exposur~ to adver~e conditions over ext~nded
period~ of time. As a result, thesQ composition~ have
become attractivo for gasketing appl~cations. Efforts
in the past have been made to produce he~t cured
silicone elastomer compositions having good tear and
tensile strength and reduced compres~ion set
properti~s. A problem with such efforts, however, has
bsen the sacrifice of satisfactory tear strength and
- elongation characteristics while attemp~ing to improve
compression set, oil and heat age rQsistance charac-
teri~tics, and vice versa. A balance of these
propsrties i8 necessary to provide a composition for
gasketing applications in internal combustion engines.
U.S. Patent No. 3,671,480 to Wada et al. (Wada)
discloses a heat curable ela~tomeric silicone
composition having improved tear strQngth comprising a
mixture of two vinyl-unsaturated polydiorgano-
polysiloxanes, one of which appears to have a high
molecular weight and the other o~ which appears ~o have
~:
3 2~7 7 7 7 60SI-I489
a low molecular weight. The -composition further
comprises a polyorganohydrogensiloxane, a silica filler
and a platinum compound. The examples in Wada report
te~r strength values of about 50 kg~cm, i.e., about 2~0
pi. Compre~sion set values are not given.
U.S. Patent No. 3,652,475 to Wada et al. (Wada)
disclose~ heat curable elastomeric silicone compo-
sitions reportedly having high tear strength, good
compre~sion set and resiliency. The compo~itions
compri~e two vinyl-unsaturated polydiorgano-
polysiloxane~ each having a degree of polymerization of
at least 3000, a vinyl-unsaturated polydiorgano-
~ polysiloxane having a degree o polymerization of from
10 to 1000, a silica filler, and an organic p~roxide
catalyst. The samples prepared in the Wada exampleshad tear strength ~alues of about 40 kg/cm, i.e., about
225 pi.
U.S. Patent No. 4,539,357 ~obear '3573 discloses
a heat-curable silicone composition comprising a vinyl-
terminated linear diorganopolysiloxane gum having aviacosity in the range of ls106 to 20xlO' centipoise at
25C, a vinyl-containing diorganopolysiloxane gum
having a viscosity of lxlOs to 20xlO' centipoise at
25C, a filler, a hydride-containing polysiloxane, and
an organic peroxide or organic hydroperoxide curing
agent. The composition ~ay further compri~e a ~inyl-
containing organopolysiloxane resin copolymer. It i~
stated in Bobear '357 at column 6, l~ne~ 22-29 that
there should be no vinyl-containing fluid in the
compo~ition since it has been found that composition~
containing vinyl-containing fluid3 of a vi3cosi~y of
500,000 centipoi~Q or 1Q~8 r~ult in elastomers with
good taar strength initially, but after the com~position
_ 4 _ ~ PATENTS
~a~ i . 60sI l489
ha~ been sub~ected to po~t-cure, its tear ~trength
propertie~ degrade dramatically. After post-cure, the
Bobear '357 compo~ition ha~ a tear ~trength of above
200 pi.
~.S. Patent No. 4,061,609 to ~obear disclo~es a
platinum catalyzed silicone rubber composition com-
pri~ing a vinyl-containing polysiloxane or a blend of
~uch poly~iloxanes, platinum, and a hydrogen-containing
polysiloxane. Preferably, the ~inyl-containing poly-
siloxane has a visco~ity in the range of 1,000 to
300,000,000. A low vi~cosity vinyl-containing
poly~iloxane may be added to the basic composition as
_ a reinforcing agent to give the inal composition good~
phy~ical ~trength. Claim 4 in ~obear recite~ a first
polysiloxane having a viscosity of l,000,000 to
200,000,000 centipoi~e at 25C and a second poly-
~iloxane having a viscosity of S0,000 to 500,000
centipoi~e at 25C. The Bobear patent i~ directed to
improving the work life of ~ one rubber compo-
~itions. In the example~, tear strength value~ of
greater than 200 pi were obtained, but the compo3itions
having these values contained two high viscosity vinyl-
cont~ining polysiloxa~ss ~ather than one high visco~ity
vinyl-containing polysiloxane and one low visco~ity
~inyl-containing polysiloxane.
l~.S. Patent No. 3,660,345 to Bo~ear disclose~
organopolysiloxane compositions which are convertib}e
to elastomers ha~ing high tear 3trength and resiliency.
The compo~ition~ comprise a two component bland of
vinyl-containing organopoly~iloxane~, ~ilica filler,
and a proceq~ aid which can be a methoxy-~erminated
polysiloxane, a ~ilanol-terminated polydimethyl-
siloxane, or h~xamethyldi~ilazane, for example. A
2 a 87 7 7 6PATE~TS
peroxide is used as the catalyst. The vi3c08ity of one
of the two vinyl-containing organopoly~iloxane~ can be
in the range of 1 to 1 billion centipoise at 25C,
while the viscosity of the other can bo between 100,000
to 2,000,000,000 centipoise at 25C. The ~xamples in
Bobear report tear ~trength values of greater than 200
pi .
~ .5. Patent No. 3,~96,068 to Creamer discloses
heat-curable silicone gumstock composition~ having hi`qh
die "B" tear strength as well a~ low compres~ion ~et
values. The compositions comprisQ a vinyl-containing
diorganopolysiloxane gum and a linear ~inyl-containing
1uid having a vi8cosity of from 10 to 150,000-
centistokes at 25C. The cros~-linkable vinyl siloxane
gum has a viscosity in Qxcess of 200,000 cQntistokes at
~5C. The Creamer composition is cured by a peroxide
catalyst. Some of the ~amples prepared in Crezmer had
tear strength valuRs in excess of 150 pi. Tear
strength after post cure was not measured in any of the
e~amples, which i8 significant since, as pointed out
previously herein, it ha~ ~een found that tear ~trength
drops dramatically after post cure in compositions
containiny low viscosity vinyl-containing fluids.
U.S. Patent No. 3,884,866 to Jeram et al. (Jeram)
discloses a high strength organopolysiloxane compo-
sition ~uited for low pressure in~ection molding,
comprising: (A) a component containing (i3 a vinyl-
containing high viscos~ty organopolysiloxane having a
viscosity of 5000 to 1,000,000 centipoise at 25C, (ii)
a vinyl-containing }ow viscosity organopolysiloxane
having a viscosity of S0 to 5000 centipoi~e at 25C,
(iii) a filler, and (iv3 a pla~inum catalyst; and (~)
- 6 - PArEN~S
æ~ g~ ~7 ~ 60S~ 9
a hydrogen siloxane co~position. Th~ highQst tear
strength reported in the examples was 250 pi.
Although heat curable silicone rubber compositions
having tear strength of greater than 250, reasonably
good tensllQ strQngth and low compression ~e~
propQrties are known in the art, compositions ~or use
in gasketing applications in combustion engines must
also exhibit excellent heat age rQsistance and oil
resistance over time. Compositions are also desired
which are more easily processed, have more repe~table
and consist~nt resultR, and have ~table propQrties.
These properties are also desirable in compositions
uned for sQaling and vibration dampening. Thus, it i8
desirable to provide heat cured silicone Qlastomer
compositions having the properties and durability that
~nable their use in gasketing, sealing and vibration
dampening appl}cations.
SUMMARY OF THE INVENTION
The present invention is bas~d upon the discovery
that a balance of propertie~ necessary for a compo-
sition used in gasketing, sealing and vibration
dampening applications can be achieved by adding a
vinyl-stopped, vinyl-on-chain siloxane gum to a heat-
curable gum/resin silicone ela~tomer.
According to the present invention, compositions
can be produced which, upon heat-curing, exhibit a tear
3trength of between about 200 and about 300, a compres-
~ion set of les~ than 20, good tensile strength, and
good hsat-age and oil resistance propertiQs. The
compositions are also easily proce~ed and produce
repeatable and consistent results. A vinyl-on-chain
siloxane gum, componen~ (D~, i8 added to a blend
~t~
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- 7 - P~TENTS
2 ~ 87 7 7 7 6pSI-1489
comp~ising (A) a vinyl-stopped organopolysiloxane gum,
(B) an MQ or M D-vinyl Q resin or blends thereof, (C)
a silica filler, and (G) an organohydrogensiloxane
cross-linking agent. The mixture produces a silicone
elastomer which is heat curable in the presQnce o~ a
catalyst.
In one group of compositions, blends are
formulated which comprise, by weight:
(A) 100 parts by weight of ~inyl-stopped
diorganopolysiloxanQ having a viscosity of about 3
million to about 100 million CQntipoi8e (Cp8) at 25~C;
(B) up to 30 parts by weight based on Component
(A) of (1) an organopolysiloxanQ resin copolymer. Tho
rQsin copolymQr may contain R3SiO1~l monofunctiona~
llnit~ (M units) and SiO2 quadri-~unctional units ~Q
units), where each R is indepQndently selected ~rom the
group consisting of vinyl radicals and mono~alent
hydrocarbon radicals free of aliphatic unsaturation.
The ratio of M units to Q units ranges from about 0.5:1
to about 1.5:1, wherein the resin copolymer contains
about 0.5 to 10.0 weight ~ vinyl
groups. Alternatively, Component (B) may comprise (2)
an organopolysiloxane re~in copolymer contain~ng ~ and
Q units as a~oresaid and R2SiO2,2 difunctional (D units)
where each R is independently ~elected from the group
consisting of vinyl radicals and monovalent hydrocarbon
radicals free of aiiphatic unsaturation. Each M unit
may represent ~ or M' e.g. M-vinyl units, and each D
unit may represent D or D' e.g. D-~inyl units. The
ratio of ~ units to Q units is from 0.5:1 to about
1.5:1 and the D unit are present in an amount of from
about 1 to 70 mol percent based upon the total number
of mols of siloxy units in the copolymer. The resinous
~ ~ ~ 7 7 7 7 PllTEl TS
copolymer contains from about 0.5 to about 10.0 weight
p2rcent vinyl groups. The organopolysiloxane resin
copolymer of Component (B) may contain mixture~ o~ the
MQ and the M D-vinyl Q, resins.
(CJ up to about 200 parts based upon Component (A)
of a finely divided silica filler;
(D) up to about 100 parts based upon Component (A)
of a vinyl-~topped, vinyl-on-chain polymer having ~rom
about 5xl o-5 to about 5 weight percent vinyl; and
(G) a random copolymer ~ormed of a polydimethyl
siloxanQ (PDMS) and a polymethyl hydrogan siloxanQ
(PMHS) having the form:
R3SiO(SiORHSiOR2)XSiR3
wherein each R is 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 present
invention, the hydride is present in an amount ranging
from about 0.1 to 10 weigh~ percent of Component ~A),
preferably 0.5 to 8, and more preferably 0.8 to 2.5
parts by weight. When a hydride agent is employed, a
platinum catalyst may be substituted ~or the peroxide
catalyst to cura the composition. In Component (G~ x
may vary 80 that (G) has a viscosity ranging from about
5 to 500 cps, preferably from about 10 to about 100 cps
and more preferably from about 10 to 50 cps at 25C.
In order to improve propertie3 or processing, the
composition may also contain:
(E) up to about 2 parts by waight of a
tetramethyl-divinyl silazane based upon 100 parts by
weight of Component (A); and
2 9 8 7 ~ ~ 7 6 os I I 4 8 9
(F) up to abou~ 10 parts of a processing aid
comprising low viscosity silanol stopped siloxane fluid
of a about 3 to 500 centipoise at 2SC, or a dim~thyl
trimethoxy siloxane polymer, or similar COmpQ~itions
such as silanol or methoxy ~luids of other vi8co8itie8.
From 15 to 20 parcent of a cyclic methyl tetramer
may be used to treat the filler prior to compounding.
A Rmall amount of water may also be added to
incrQase the processibility of the blend. I~ used,
only up to about 0.1 partR by weight water based on
Component ~A) is usually employed.
In addition to the foregoing, a heat aging
component such a~ fumed TiO2, iron octoate, Ce(OH)4, or-
mixtures thQreof, may be presQnt in relatively small
amounts, e.g., up to 2 part~ by weight based upon
Component (A). In the examples below the heat aging
component consists of 33 weight percent TiO2, 5 weight
percent iron octoate solution (which comprises about 12
weight percent iron in mineral spirits), 1~ weight
percent treated fumed silica (160 m2/gm), and 50 weight
percent of an 800 penetration vinyl-stopped, vinyl-on-
chain gum.
An acid acceptor, Component (I), may also be added
to soak up acid. This acid could otherwise cause
cleavage of th~ product matrix. In one embodLment, (I)
comprises a masterbatch of about 25% MgO in a vinyl
siloxane polymer.
The heat-curable compositions of the present
invention provide heat cured silicone elastomers having
high tear strength, good tensilQ strength, low
compression set, and good heat-age and oil resistance.
This exc~llent balance of properties is exhibited
- 10 - P~TENTS
2 0 ~ ~ 7 ~ 7 60SI-1489
throughout extended periods of use at high temperatures
making these compositions extremely attractive for
ga~keting, sealing and vibration dampening applications
DES~RIPTION 5~rHE INVENTION
5The compositions of the present invention contain
(A) a vinyl-stopped diorganosiloxane gum or gums having
a viscosity of about 3 million to 100 million cps at
25C; (B) an oryanopolysiloxane resin of the MQ or N D-
vinyl Q types: (C) a finely divided silica filler; (D)
a vinyl-on-chain siloxane gum; and (G) an
organohydrogensiloxane cross-linking agent.
Combinations of various other COmpOnQnts as dQscribad-
horQin may also be added.
The vinyl-on-chain siloxane gum i8 add~d in an
amount of up to about 100 parts by weight based on
Component (A). The actual amount of Component (D) to
be added varies depending upon the vinyl content in
Component (D) and the amount of cross-linking dasired.
The amount of cros6-linking can closely control the
properties exhibited by the cured product.
According to an embodLment of the present
invention, the vinyl-on-chain polym~r is a
diorganosiloxane gum h~ving a vinyl content of about 3
weight percent vinyl, or higher. Herein, thi~ typP of
gum is referred to as a "very high vinyl-on-chain~' gum.
When using a very high vinyl-on-chain gum, about 0.1 to
about 10 parts, preferably up to 4 parts by weight i8
added ba~ed on Component (A). One Example of a Yery
high vinyl-on-chain gum is a siloxane g~m having 4.08
weight percent vinyl and being about 2500-3500 D units
in length, herein designated Component (Dl).
- ll - PATENTS
20 8~ 7 7 ~ 60SI-148g
In another embodiment, a vinyl-on-chain gum is
added which has a vinyl content of between about 0.1
and about 3 weight percent vinyl, herein ~eferred to as
a "high vinyl-on-chain" gum. When using a high vinyl-
on-chain gum, about 0.1 to about 10 parts by weight are
added ba~ed upon Component (A). In the Examples below,
Component (D2) i8 a high vinyl-on-chain gum having a
vinyl content of about 0.6 weight percent.
In yet another embodLment, a "moderate vinyl-on-
chain", vinyl-stopped gum is used, defined herein as
containing from about 5x10-5 up to about l.0 weight
percent vinyl. Nhen using a moderate vinyl-on-chain,
-. vinyl chain-stoppQd gum, about 0.1 to about 100 parts~
by weight are added based on Component (A). In the
Examples below, Component (D3) has a vinyl content of
approximately 0.0~ weight percent.
The vinyl polymer or polymers of Component (D)
contain vinyl-on-chain groups and vinyl and-groups. In
preferred embodiments, Component (D) has the formula:
ViSiOR12 (SiORlRVl)~(SiOR22)y SiR12Vi
Wherein Vi is vinyl, RVl i~ a vinyl radical having
from 2 to about 10 carbon atoms, each R1 is indepen-
dently chosen ~rom a vinyl radical having from 2 to
about 10 carbon atoms, and a monovalent hydrocarbon
free radical free of aliphatic unsaturation and
containing 1 to about 8 carbon atoms, each R2 i8
independently chosen from a vinyl radical having from
2 to about lO carbon atoms, and a monovalent hydro-
carbon free radical free of aliphatic unsaturation and
containing 1 to about 8 carbon atoms, and x and y are
integers, wherein x, y, RV~, R1 and R2 are chosen such
- 12 - r PATEN~S
2~87 ~7 60SI-1489
that Component (D) has a weight percent vinyl concen-
tration in the range from about 5x10-5 to about 5
weight percent, preferably from about 0.01 to about 4,
and more preferably from about 0.05 to about 4. The
S amount of Component (D) added to the blend may be
increased whon the vinyl concentration of Component (D)
i8 low, and a les~er amount of Component (D) may be
added when its vinyl concentration i8 high. For
example, when u~ing a vinyl-on-chain gum having a vinyl
content of about 4 weight percent, only about 0.5 parts
by weight based on Component (A) is added. When using
a gum having a vinyl content of only about 0.6 weight
percent, however, 5 part~ by weight are added based on
Component (A).
The vinyl-on-chain units of Component (D) provide
increasod cross-linking of the cured rubber and enhance
those properties necessary for u3e in gasketing,
sealing and vibration dampening applications.
The vinyl containing polymers of Component (D) can
be made by a process well known in the art, for
example, by reacting cyclotetrasiloxanes in the
presence of low molecular weight, linear vinyl chain
stopper3 at high temperatures in the presence of basic
cataly~ts so as to yield a polymer of the de~ired
molecular weight. When the reaction i~ over, the
catalyst is neutralized and the excess cyclics are
vented off to result in the desired polymer. By
controll-ing the amount of chain stopper and the
temperature of the reaction, the molecular weight of
the desired vinyl-containing polymer end product can be
controlled. For more d~tail~ of the process by which
such vinyl containing polymers are produced, reference
i8 made, for example, to U.S. Patent No. 3,660,345,
- 13 ~ 2 PATENTS
0 7 7 7 60SI-1489
which is incorRorated herein by reference. Component
(D) i~ preferably a vinyl-on-chain diorganopolysiloxane
or vinyl-on-chain diorganosiloxane blend.
Component (A) is a vinyl containing diorgano
siloxanQ gum or blend of such gum5 having a viscosity
from about 3,000,000 to about 100,000,000 cps at 25Co
Preferably, the gum has a ~i8c08ity of betweQn about
7,000,000 and 84,000,000 cps, more preferably, about
13,000,000 cps at 25C. The gum i~ preferably vinyl-
stopped and has substantially no vinyl-on-chain. The
organo groups in the gum should all be monovalent
hydrocarbon radicals. The gum may have a weight
percent vinyl cQncQntration of from about sx10-5 to-
about 1. The gum preferably has a weight percent vinyi
concentration in the range from about 6.5x10-5 to about
0.03, more preferably from about 8x10-5 to about 1.5x10-
~and more preferably yet from about 8x10-5 to about
1.2x10-'. The organo groups in the viny~ polymer or
polymers of the gum should all be monovalent
hydrocarbon radicals.
In a preferred embodiment, Component (A) has the
structure:
ViSiORl2 ~ SiORl2 ) X ( SiOR22 ) y SiRl2Vi;
wherein Vi is vinyl and each Rl i8 independently chosen
from monovalent hydrocarbon free radicals free of
aliphatic unsaturation and containing 1 to about 8
carbon atom~; each R2 is independently chosen from
monov~lent hydrocarbon radicals containing 1 to about
8 carbon atoms; and x and y are integers chG~en ~uch
that the viscosity is about 3,000,000 to about
100,000,000 cps at 25. In other preferred
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- 14 - PATENTS
2 ~ ~7 ~ ~ ~ 60SI-1489
embodiments, x and y are integers chosen such that
Component (A) ha~ a vi~cosity which ranges from about
3,000,000 to about 85,000,000 cps at 25C and a weight
percent vinyl concentration in the range from about
5x10-5 to about 2xlO-~, preferably from about 8x10-5 to
about l.5xlO-~ and more preferably from about 8.0xlO-s
to about 1.2xlO-'.
In accordance with tha invention, the amount of
Component (A~ present in the ~inal product may vary.
However, for purposes of explanation herQin, it i8
a~sumed that 100 part3 by weight of the gum is combined
with varying amounts of the other component~, and the
amount of gum in the final product may thereby be
inferred. In the Examples b~low, Component ~A) is a
vinyl-stoppQd gum of about 6000 D units in length and
has substantially no vinyl-on-chain.
Component (B) may be (1) an organopolysiloxane
resin copoly~er in an appropriate ~olvent (e.g.
xylene). The resin copolymer may contain R3SiO1~2
monofunctional units (M units) and SiO2 quadri-
functional units (Q units), where each R is indepen-
dently selected from the group consisting of vinyl
radicals and monovalent hydroc~rbon radicals free of
aliphatic unsaturation. The ratio of M units to Q
units ranges from about 0.5:1 to about 1.5:1, wherein
about 0.5 to 10.0 weight percent are vinyl groups.
Alternatively, Component (B) may co~p~ise (~) an
organopolysiloxane resin copolymer containing M and Q
units as aforesaid and R2SiO2/2 difunctional (D or D
vinyl units), in an appropriate solvent, where each R
is independQntly selectQd from the group consisting of
vinyl radicals and monovalent hydrocarbon radicals free
of aliphatic un~aturation. The ratio of ~ units to Q
`. .
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~ , ,.
2 O 8 6 OS I -14 8 9
units is from 0.5:1 to about 1.5:1 and the D or D vinyl
units are present in an amount of from about 1 to 70
mol percent based upon the total number of mols of
siloxy units in the copolymer. The resinous copolymer
contains from about 0.5 to about 10.0 weight percent
~inyl groups. The organopolysiloxanQ resin copolymer
of Component (B) may contain mixtures of the MQ and the
M-D vinyl-Q, resins.
The organopolysiloxane rQsin copolymers of
Component (~) in the present composition and their
manufacture are well known in the art. Such rQsin~ are
usually produced by hydrolysi~ o chlorosilanes in a
- process dQscribQd in U.S. Patent No. 3,436,366 which is~
incorporated herQin by rQferQncQ.
Component (B) is presQnt in the composition of the
present invention in an amount ranging from about 1.0
to about 30, preferably from 1.0 to 20 and more prefer-
~bly from 4 to about 12 par~s by weight basQd on
Component (A). Component (B) in the Examples below
comprises (B2) dispersed in xylene. Much of the ~ylene
has been vacuum stripped 80 as to result in a co~po-
sition comprising 60% by waight solids and 40% by
weight xylene.
The process for manufacturing the compositio~
includes a cook and strip step to facilitate the
removal of the residual xylene from the finished
compound.
Component (C) comprise~ from about 5 to about 200,
preferably from about 10 to about 100 and more
preferably from about 20 to about 50 parts by weight of
reinforcing fillers such as SiO2 based on Component
(A~. Examples of reinforcing fillers that may be used
include fumed silica and precipitated silica, with
- 16 - ~ PATENTS
~ 7 ~ ~ ~ 60SI-1489
fumed silica being preferred. The filler may be pre-
treated or treated in-situ with various agents, for
example cyclopolysiloxanes as disclosed in U.S. Patent
No. 2,938,009 to Lucas and silazanes as disclosed in
U.S. Patent No. 3,635,743 to Smith. The cyclopoly-
siloxanes may be, for example, a cyclotetramethyl
s~loxane present in the amount of about 15 to 20 weight
percent of the filler. Preferred fumed silica fillers
may have a ~urface area of ab~ut 100 m2/gm to about 300
m2/gm and pre~erably about 160 m2Jgm to about 240 m2/gm~
The higher surfacQ area ~iller~ tend to result in
better properties, however, they are more expensiva
than the lower surface area fillQrs and require surface`
trea~ments ox more processing aid to incorporate them
into the gum. In the Examples below, the filler
Component (C) comprises a fumed silica filler having a
surface area of about 160 m2/gm and which has been
pretreated with octamethyl cyclotetrasiloxane. Where
Component (Cl) is used, the filler has a surface area
of about 240 mZ/gm and has been pretreated with
octamathyl cyclotetrasilo~ane.
Component (~) is a vinyl terminated silazane
coupling agent and surface treatment for the filler
which may take the form:
ViSiR2NHSiR2~i
wherein R i8 an organic such as CH3. The coupling
agent promotes bonding between Component~ tA) and (C)
and between components (B~ and (C)~ and may be applied
to the filler, Component (C), prior to mixing with the
other components.
- 17 ~ 2 ~ 3 7 7 7 7 PATENTS
Component (E) may be ~inyl stopped linear silazane
such as tetramethyl-divinyl silazane. The material is
added for enhancing the bonding of filler to polymer.
In the present inventionr the silazane also acts as a
filler treatment in-situ.
Component (E) i~ preferably prQsent in an amount
of up to about 2 percent, more preferably up to about
0.3 percent by weight based on the weight of Component
(A). Component (E3 may be present in an amount of only
10 about 0.03 parts by weight based on 100 part~ of
Component (A), however, ~lightly higher amounts are
preferred.
- In addition to, in con~unction with, or in place
of Component (E), small amounts o~ hexamethyl
disilazane may be used to treat fumed silica filler
prior to mixing the filler with the other components,
or in-situ. If used, up to about 20 parts by weight of
hexamethyl disilazane i8 added based on 100 parts
filler.
Other components may also ba employed as di~cussed
hereinafter. For example, in order to allow for easier
incorporation of the filler in the gum, Component (F),
a processing aid or plasticizer is employed. In the
preferred embodiment, Component (F) is a low vi3c08ity
silanol stopped siloxane fluid ha~ing a viscosity
ranging from about 3-500 cps and preferably 3 to 50 Cp8
at 25C. The siloxane fluid i8 an equilibri~m mix of
low molecular weight oligomers of about 4 to about 10
D units, preferably between 4 and 6 repeating units in
length with a minimum amount of cyclics in equilibrium
with the oligomer6. The procQssing aid ~F) may have
the ~orm o~ ~R~SiOl,2)XOH where each R i~ CH3 and x i8
between 4 and 10, preferably between 4 and 6, with
.. . . -
- 18 - PATENTS
~ 87 177 60 I-1482
resulting cyclics of the same number of ~nits in
eguilibrium. Alkoxy terminated siloxanes such as
trimethyoxy siloxane may also be used as process aids.
In the present invention, the proces~ing aid i8 present
in amountQ between 2 and 10 weigh~ percent of Component
(A) preferably between 2.5 and 5.0 parts by waight and
most preferably about 3.5 parts by weight based on
Component (A). It should be understood that typically
the more filler that i8 used the greater amount of
processing aid is employed. In the Examples below,
Component (F) has a silanol content of about 7.5 ~ by
weight although a silanol content of about 5 to about
10 weight percent i8 expected to provide good re~ult~.
In addition to the foregoing, Component (G) in the
form of a hydride cross-linking agent may be employed.
In a preferred embodiment, Component (G3 may be a
random copolymer formed of a polydimethyl siloxane
(PDMS) and a polymethyl hydrogen siloxane (PMHS) having
the form:
R3SiO(SiORHSiOR2)XSiR3
wherein Pach R is independently chosen from a hydrogen
or monovalent hydrocarbon radical free of aliphatic
unsaturation containing 1 to about B carbon atoms, and
~ ranges from about 2 to about 100. In the present
invention, component (G) i8 pre~ent in an amount
ranging from about 0.1 to 10 weight percent of
Component (A), preferably 0.5 to 8, and more preferably
0.8 to 2.5 parts by weight. When a hydride agent is
employed, a platinum catalyst may be substituted for
the peroxide catalyst to cure the composition. In
Component ~G~ x may vary so that (G) has a viscosity
9 ~ 7 PATENTS
208 7 7 1 60SI-1489
ranging from about 5 to 500 Cp8, preferabl~ from about
10 to about 100 Cp8 and more preferably ~rom about 10
to 50 cps at 25C.
~he linear hydride described above can be made by
many procedures which are known in the art and particu-
larly by the hydrolysis of appropriate chlorosilanes.
See ~or example, U.S. Patent No. 4,041,101 which is
incorporated herein by reference. In the Examples
below, Component (G) has a viscosity of about 30
centistokes, a hydride content of about 0.8 percent by
weight, and a chain length of about 100 units.
A small amount of water may also be added to
- increase tha processibility of the blend. If used,
only up to about 0.1 parts by weight water based on
Component (A) is usually employed.
To improve the heat-age resistance of the cured
compositions of the present invention, Component (H~,
a heat-age additive, may be employed. The heat aging
component such as fumed TiO2, iron octoate, Ce(OH)4, or
mixtures thereof, may be present in relatively small
amounts, e.g., up to 2 parts by weight based upon
Component (A). In the examples below the heat aging
component consists of 33 weight percent TiO2, 5 weight
percent iron octoate (12% iron in mineral spirits~, 10
weight percent treated fumed silica (160 m2/gm), and 50
weight percent of an 800 penetration vinyl-stopped,
vinyl-on-chain gum.
Only up to about two parts by weight Component (H)
i~ needed based on Component (~) to Lmprove the heat-
age characteristics of the compo~ition. In theExamples below, 0.8 parts by weight of Component (H) is
used based on Component (A).
~.~
- 20 - 7 ~ ~ PATENTS
2 ~
Penetration i8 measured using Vniversal
Penetrometer by Precision Scientific Model No. 73510
with a Yub~tantially air free sample. The sample
penetration i8 measured at 25C~1C using a 100 gr
weight and a 1/4" diameter by 3/16" needle foot with
rounded edges. The needle is lowered until it ~ust
touches the surface of the polymer. Then, the tLme to
achieve up to 300 mm penetration is determined or the
amount of penetration after 60 sec. Penetration gum i8
defined as:
D ~ trati~ X 60 sec. at 25C
Time
Penetration may be controlled by controlling the
molecular weight and th~ viscosity of the gum.
An acid acceptor, such as MgO or ZnO, Component
(I), may also be added in amounts from 0.5 to about 10
parts by weight based on ~omponent A. This acid could
otherwise causQ cleava~e of the product matrix. In the
Examples below, 1.0 parts by weight of MgO masterbatch
which comprises about 25% MgO in a methyl vinyl poly-
siloxane is used for Component (I) based on Component
(A).
Other components which may be added to the blends
of the present invention include, but are not limited
tos
(~) a heat age additive comprising cexium
hydroxide, preferably about 75% by weight~ master-
batched in polydimethylsiloxane fluid having a
viscosity of about 30,000 Cp8 at 25C.
In order to form a heat curable rubber, an organic
peroxide, free radical initiator or curing catalyst is
provided. The preferred peroxide curing agents are
~ ~
2 ~ 8 7 7 ~ ~ PATE~TS
60SI-1489
thermal decomposition organic peroxides conveniently
used to cure silicone elastomers. Examples of suitable
organic peroxide free radical initiator8 for usa in the
pre~ent invention are disclosed, for example, in U.S.
Patent No. 4,539,357 to ~obear which i~ incorporated
herein by refQrence. Suitable peroxide catalysts
include dialkyl peroxide such as di-tertiary-butyl
peroxide, tertiary-butyl-triethylmethyl peroxide, di-
tertiary-butyl-tertiary-triphenyl peroxide, k-butyl
perbenzoate and a di-tertiary alkyl peroxide such a-q
dicumyl peroxide. Under cQrtain conditions hereinaftQr
dc~cribed, such a~ when a hydride is used, a platinum
catalyst may be Qmployed in~tead as an initiator. In
the examplQA below, tha preferred catalyst is a vinyl
sp~cific catalyst such as 2,5 dimethyl-2,5-di(t-butyl
peroxy) hexane Q.g., (Luper801 ~lOl).
Frequently used thermal decomposition catalysts
activate within a temperature range of about 330F to
about 390F.
Copending U.S. patent application serial no.
07/587,876, filed September 25, l990, attorney docket
no. 60SI-1336, incorporated herein by reference,
discloses heat curable silicone rubber compositions
containing blends o~ vinyl containing organopoly-
siloxane gums and oils, MQ and M-D vinyl-Q resins,
filler and a proce~s aid axe cured with a peroxide
initiator. The compositions are formulated for
increased tear strength and reduced compressîon sat
properties.
~ ' - '
.
- 22 - ~ 7 ~ PATENTS
60SI-1489
EXAMPLES
The ~ollowing Exa~.ples ~hown below u~ed components
mixed in variou~ proportion~ to produce heat curable
siliconQ rubber compositions:
EXAMPLES I - Iy
The Components (A) - (I) were mixed in various
proportions to produce the compositions of Examples I-
IV li~ted below in Table I. In each Example,
Component~ A-G were mixed prior to adding Component~ H
and I. The component~ are expressed in parts by
weight .
T~BLE I
Example
Component I II III IV
A 88 88 85 89.5
B 12 10 10 10
C 30 30 30 30
Dl - - - 0.5
D2 - - 5
20 D3 - 2 - -
E 0.14 0.14 d.l4 0.14
F 3.5 3.5 3.5 3.5
G 1.4 1.4 1.4 1.4
Nater 0.1 0.1 0.1 0.1
H 0.8 0.8 0.8 0.8
I 1.0 1.0 1.0 1.0
- 2~7`~
Table~ IIa IIc bQ7 ow show thQ propertiE~EI of the
cQmposit~on~ of Examples I-I~ aftQr f~r~t (Ila~, s~cond
~IIb) and third (IIc) cure~. All c~ condltion~ e
with a peroxide catalyst . q~he camposi~t Qns of th~
5 E~mple~ were molded at 350 for 15 m~nu~e~ after a
compound w~3t-in or aqing period of 3 days, 7 days and
23 days. The propertiQs of the composition~ a~ter 3
d~y8 are 3ho~m in Tabla IIa. T~e proper~3s aftE~r 7
dayu and 23 days are ~hown in Table~ IIb and IIC,
10 respectiYe7 y.
Test data were obtaine~ from the following ASTM methods and
procedures: Shore A - 0-2240; Tensile, Elongation and modulus -
D-412 (Die C); Tear - D-624 (D~e 3); and Compression Set - 0-3gS
(method B ) .
~ ~L
E~ample
p~:~perty
Shore A 50 49 51 50
Tensile, p~i 1953 2046 1285 ~545
2G Elon~ation, % 733 749 7g?
B, ppi 170 150 2S0 271~
Comp. Set, ~ 20 . 7 18 . 8 17 . 9 1~.6
~antple
25 P~P~rty I r~ T~
Shore Sl 49 50 51
Tensile, p~i 1460 131U 1440 14~5
Elongation, ~ 796 789 8 01 B17
Te~r-B, ppi 276 276 249 270
30 Comp. Se~ % _ 17.7 17.9 17.4
~-`
2 0 ~ ~ ~ 7 ~ P~TENT~
60SI-1489
TABLE IIc
Example
ProPerty I II III IV
Shore - 48 49 51
Tensile, psi - 1401 1501 1~5
Elongation, % - 806 810 792
Tear-B, ppi - 255 257 297
Comp. Set, ~
Table IId below shows the change in the values of
the properties of the compositions of Examples I-IV
after heat-aging for 168 hours at 350F per ASTM D573.
Repeated tQst re~ults appear in parenthesis ( ).
TABLE IId
Example
15 Property I II III IV
Shore A ~5 +4 ~6 +6
(+5) (l6) (~6)
Tensiler % -23.2 -10.7 -18.9 -26.9
(-4.2) (-20.9) ( 7.5)
Elongation,% -15.1 -10.6 -16.4 -19.5
(-12.5~ ~-14.3) ~-10.7)
~ able IIe below shows the change in the ~alues of
the properties of the compositions of Example I-IV
after immersion in AS~M #1 oil for 168 hour~ at 300F
per A3TM D471. Repeated test results appear in
parQnthesis ~ ).
~77~
- 25 - PATENTS
60SI-1489
TABLE IIe
Exam~le
Property I II III IV
Shore A -3 -4 _3 _3
(-5) (-4) (-4)
Tensile, ~ -28.3 -12.9 -23 -38
(-26.8) (-35.8) (-20j
Elongation,% -14. 4 -6. 3 -14.2 -22
(-lg.l) (-28.5) (-14.8)
Volume, ~ 4.5 4.8 4.9 ~.9
(4.9) (4.5) (5.4)
Tablo IIf below shows the change in the value o~
properties of the composition of ExamplQs I-IV after
immer~ion in ASTM #2 oil for 168 hours at 300F per
15 ASTM D471.
~A~LE I.If
Exam~le
Property I II III IV
Shore A -7 -8 -7 -6
Tensile, % -34.6 -22.1 -26.7 -17.0
Elongation,% -20.7 -16. 6 -20.5 -9.3
Volume, ~ 10.4 10.2 10.3 10.6
Table IIg below show~ the data obtained from
individual test specimens for tear strength property,
~5 of the compo~itions of Examples I-IV, when tested per
ASTM D624 B.
2~87777
- 26 - PATE~TS
60SI-1489
TABLE IIq
Property Example
Tear B (ppi) I II III IV
Specimen 1 167 139 262 314
Specimen 2 170 147 240 ~76
Specimen 3 254 256 260 264
Specimen 4 2B7 274 249 254
Specimen 5 276 282 270 270
Specimen 6 252 276 242 281
Specimen 7 -- 298 257 297
Specimen 8 -- 253 212 296
Specimen 9 -- 256 265 307
The compositions of Examples II-IV exhibit
enhanced properties which make them useful for many
ga~keting and sealing applications. Although it may
not be immediately apparent, due to the wide variation
in data a~sociated with elastomer testing (particularly
where ~ change in property tested i8 involved), the
observed trend is an Lmprovement in compression 8et,
tear strength consistency, heat age and oil im~ersion
resi~tance when cross link density is increased by
inclusion of Component ~D).
EXAMPLE~ V-XII
The Components ~A) - (I) were mixed in various
proportions to produce the compositions of Examples V-
XII listed below in Table III. The component~ are
expressed in parts by weight. Componsnt (Cl) i8 a
2~7 7 ~ ~
- 27 - PATENTS
60SI-1489
tetramer treated fumed 6ilica filler similar to
Component (C~ but has a surface area of 240 m2/gm.
TA9LB III
co~Ronont ~aoDlo
v VI vsI v~Ir IX X XI XII
A 85 BS 85 35 35 35 35 as
8 10 10 10 10 10 10 10 10
c 29 - 29 - 29 - 29
Cl -29 - 29 - 29 - 29
0 02 5 5 5 5 5 5 5 5
F 3 3 3 3 3 3 3 3
~tor .1 .1 .1 .1 .1 .1 .1 .1
15 ~ .8 .n .B .8 .8 .3 .8 .8
I 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
Examples V-VIII were mixed in a tangential blade
doughmixer whereas Examples IX-XII were mixed in an
overlapping, sigma blade doughmixer. ExEmples V, VI,
IX and X were cooked for a period of one hour at 360F.
Examples VII, VIII, XI and XII were cooked for a period
of four hours at 360F. Tables IVa and IVb below Qhow
the median values of the properties of the compositions
of Examples V-XII.
;2 5 DU~ IVa
ProPorty ~x~Dlo
V VI VII Vlll
Ag~ in days 7 ~ 3 2
9boro A 51 51 52 53
Tsn~llo, p-i 1360 1~7 lU8 1~05
Uong~tlon, t 721 785 721 698
To~r-~3, ppi 23- 239 262 210
1000 ~oduluD, p~i 219 19~ 22~ 237
200- ~odulu, p~i 35~ 321 37~ 392
3001~ duluD, pDi 509 4~1 51~3 5~5
- 28 ~ 7 7 7 7 P~TENTS
60SI-1~489
TA~g IVb
ProDortY ~xa~Pln
IX X X~ XrI
Ago ln day- 7 ~ 3 2
9~ore A 51 52 52 52
T D - 11e~ P-1 1155 1603 1407 1552
Rlo~gntlon, t 803 010 725 792
T ~r-a, PP1 202 209 20~ 219
100~ ~OdU1U-, P-1 201 20a 22~ 216
1 0 200- ~cdUlu-~ p-l 333 3-0 372 352
300~ ~odulu-, p-l 459 ~65 50a ~a1
Tables Va and Vb below ~how the average ~alu~s of
the properties o the compositions of Examples V-XII.
.. ~
15 PrO~rtY l~xanpl~
V V1 Vl~ y~I~
Ag- ln day- 7 ~ 3 2
abor~ A 51 51 52 53
S-n-llo, p-l 1359 1~3~ 1377 1396
2 0 Rlong-tlon, ~ 721 707 71- 631
T Ur-a, ppl 220 241 25~ 213
lOOt dulu-, p-l 219 193 219 237
200t dulu-, p-l 366 320 376 393
300~ Iodulu-, p~l 50a ~ 521 5~7
_~g.~
PropsrtY ~a~le
IX X Xl XlY
Ag~ in d~y 7 3 2
8bOre A 51 52 52 52
Tenollo, p-l 14~3 1594 1419 1502
~longatlon, ~ 793 815 7~D 795
Tbar-13, ppl 194 210 203 220
100~ ~odulue, p~l tOl 209 223 217
200~ ~odulu~, p~l 333 341 370 353
300~ loodulu-, pDl ~59 ~65 507 ~03
~087~7
- 29 - PATENTS
6OSI-1489
Tables VIa and YIb below show the change in the
~alues of the properties of the compositions of
Example~ V-XII after heat aging for 168 hour~ at 350F
per ASTM D573.
~ABLE VIa
Property Example
V VI VII VIII
Shore A +5 ~5 +4 ~5
TQnsile -11.4 -10.0 -11.8 -4.2
% change
Elongation -13.0 -13.4 -9.6 -9.5
% change
TABLE VI~
ProPerty Example
IX X XI XII
Shore A +5 +5 +4 +5
Tensile -17.2 -17.2 -17.4 -13.7
% change
210ngation -16.7 -15.0 -13.9 -13.6
% change
Tables VIIa and VIIb below show the change in the
values of the properties of the compositions of
Examples V-XII after exposure to ASTM reference oil #l
for 168 hour~ at 300~F per ASTM D47~.
3 o ~ 7 PATENTS
60SI--1489
TABLE VIIa
Property Example
V VI VII VIII
Shore A -4 -4 -5 -3
Tensile -24.7 -16.4 -18.2 -19.2
~ change
Elongation -24.2 -19.2 -16.5 -24.3
~ change
Volume 4.8 5.1 4.9 5.2
% change
TABLE VIIb
Property Example
IX X ~I XII
Shore A -5 4 -4 -4
Tensile -23.0 -20.2 -23.3 -21.0
% change
Elongation -19.4 -15.8 -16.4 -16.7
~ change
Volume 4.6 4.8 5.0 4.9
~ change
rables VIIIa and VIIIb balow show the change in
the values of the properties of the compositions of
Ex~mples V-XII after expo~ure to ASTM reference oil #2
for 168 hours at 300nF per AST~ D471.
31 2~777 PATENTS
- 60SI-1489
TABLE VIIIa
Pro~erty Example
V VI VII VIII
5hore A -7 -7 -7 -6
TensilQ -10.6 -8.8 -17.2 -11.4
~ change
Elongation -12.1 -I4.4 -13.6 -14.6
% change
Volume 10.4 10.3 10.7 10.4
% change
. .
TA~LE VIIIb
Pro~erty Example
IX X XI XII
Shore A -7 -7 -8 -7
15 Tensile -16~5 -17.2 -31.3 -11.3
% change
Elongation -17.2 -14.5 -24.3 -12.2
% change
~olume 10.4 10.5 10.7 10.4
% change
EXAMPLES XIII - XIV
The Components lA) ~ were mixed in ~arious
proportions to produce the compositions of Examples
XIII and XIV lis~ed below in Table IX~ In each
:
2~8~
- 32 -- PATENTS
60SI-1489
Example, Components A-G were mixed prior to adding
Components H, I and ~. The components ar~ expressed in
parts by weight.
TA~L~ IX
Example
Component XIII XIV
A 87.0 89.5
B 10.0 10
C1 28 28
10 Dl -- 0.5
D3 3.0 --
E 0.14 0.14
F 3.5 3.5
G 1.4 1.4
15 ~ater C.l 0.1
O.S 0.5
I 1.0 1.0
0.5 0.5
Table X below shows the properties of the
compo~ition3 of Example~ XIII and XIV.
, '
- 2~7~
3 3 _ PATENTS
60SI-1489
TABLE X
Ex~mpl~
Property XIII XIV
Shore A 47 50
Tensile, psi 1677 1512
~longation, % 892 787
Tear-B, ppi 183 145
Comp. Set t % 24.5 20.2
100~ modulu~, p8i 153 179
Specific Gravity 1.116 1.116
After 168 hour heat-aqe at 350~F
Shore A 53 56
Tensile, p8i 1417 1413
Elongation, ~ 816 748
Although the present invention has been described
in connection with preferred embodiment~ J it will be
appreciated by those skilled in the art that additions,
modifications, ~ubstituents and deletion~ not
specifically dQscribed may be made without departing
from the spirit and scope of the invention defined in
the appended claims.
