Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ROOM TEMPERATURE CURABLE SILICONE SEALANT
FIELD OF THE INVENTION
The invention relates to one part room temperature vulcanizable ("RTV")
silicone sealants, more particularly to one part RTV silicone sealants that
exhibit a
reduced tendency to stain porous substrates.
BRIEF DESCRIPTION OF THE RELATED ART
Silicone compositions which cure to produce elastomers are widely used as
sealants and caulks in building and construction applications. Known silicone
sealant compositions may stain substrates to which they are applied,
particularly
porous substrates, such as for example, marble, concrete, granite, sandstone,
and
limestone. Furthermore, the exposed surfaces of cured sealants tend to attract
dirt,
dust, grime and other forms of pollution.
Many attempts have been made to alleviate the staining an dirt pick-up
problems. For example, Mikami et al (US 5,432,218 ) discloses a room
temperature curable polysiloxane with paintability and improved resistance to
stain
due to a component containing an unsaturated fatty acid, such as soy oil fatty
acids,
linseed oil fatty acids, and tung oil fatty acids. Similarly, a combing :ion
of a drying
oil and zinc oxide which increases the longevity of the drying oil has been
claimed
as the responsible component for lengthening the nonstain and dirt pickup
effects of
a two part silicone polymer sealant (US 5,733,960). Kinami et. al. (US
5,326,816)
discloses organopolysilethylenesiloxane sealants that exhibit reduced
staining.
SUMMARY OF THE INVENTION
In a first embodiment, the present invention is directed to a one part,
temperature vulcanizable silicone sealant composition comprising a moisture
curable
polyorganosiloxane polymer and a filler wherein the sealant composition, when
cured, exhibits a tensile modulus at 50 % elongation of from about 30 pounds
per
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square inch to about 100 pounds per square inch and exhibits a reduced
tendency to
stain substrates in contact with the cured sealant.
In a second embodiment, the present invention is directed to a silicone
sealant, comprising:
(a) a moisture curable organopolysiloxane component, comprising a
mixture or reaction product of:
(i) an organopolysiloxane polymer comprising, on average, from
greater than 1 to less than 2 reactive sites per molecule,
wherein greater than about 90 parts by weight per 100 parts
by weight of organopolysiloxane polymer has at least one
reactive site per molecule, and
(ii) a polyfunctional organosilicon compound comprising one or
hydrolyzable groups per molecule and at least one functional
group that is capable of reacting with the reactive sites of the
organopolysiloxane polymer,
(b) a condensation cure catalyst, and
(c) a filler.
In a third embodiment, the present invention is directed to a silicone sealant
comprises a moisture curable organopolysiloxane component, comprising a
mixture
or reaction product of:
(i) a mixture of one or more linear organopolysiloxane polymers having
one hydrolyzable silyl end group and one non-hydrolyzable silyl end
group per molecule and a linear organopolysiloxane polymer having
two hydrolyzable silyl end groups per molecule, wherein the mixture
comprises, on average, from greater than 1 to less than 2
hydrolyzable silyl end group per molecule, and
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(ii) a polyfunctional organosilicon compound comprising two or more
hydrolyzable groups per molecule.
The composition of the present invention, when cured, exhibits a reduced
tendency to stain or bleed into substrates and a reduced tendency to pick-up
dirt on
the surface of the sealant.
DETAILED DESCRIPTION OF THE INVENTION
In a preferred embodiment the composition of the present invention contains,
based on 100 parts by weight ("pbw"), of the composition, no more than 10 pbw
more preferably, no more than 5 pbw, still more preferably no more than 2 pbw
non-curable plasticizers. Most preferably, the composition of the present
invention
contains no or substantially no conventional non-curable plasticizers. Non-
curable
plasticizers are compounds that are useful to reduce the tensile modulus of
the cured
sealant composition and that are substantially chemically inert components of
the
sealant composition, i.e., that have no functional groups that are capable of
reacting
with the moisture curable organopolysiloxane polymer under moisture cure
conditions. Suitable non-curable plasticizers include, for example,
polyorganosiloxane plasticizers, such as, for example, trimethylsilyl-
terminated
polydimethylsiloxane polymers, and organic plasticizer compounds, such as, for
example, dioctyl phthalate.
In a preferred embodiment, the sealant of the present invention, when cured,
exhibits a tensile modulus at 50% elongation, determined according to ASTM
D412, of from about 30 pounds per square inch ("psi") to about 100 psi, more
preferably, from about 45 pounds per square inch ("psi") to about 65 psi, and
still
more preferably from about 45 psi to about 55 psi.
In a preferred embodiment, the silicone sealant of the present invention
comprises, based on 100 parts by weight of the sealant composition, from 20
pbw to
90 pbw, more preferably from 30 pbw to 75 pbw, even more preferably from 40
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pbw to 60 pbw, of the moisture curable organopolysiloxane polymer, from 0.1
pbw
to 10 pbw, more preferably from 1 pbw to 7 pbw, even more preferably from 3
pbw to 5 pbw, of the catalyst and from 1 pbw to 80 pbw, more preferably from 2
pbw to 78 pbw, even more preferably from 3 pbw to 65 pbw, of the tiller.
The organopolysiloxane polymer may be any organopolysiloxane polymer
having, on average, from greater than 1 to less than 2, more preferably from
1.1 to
1.9 and even more preferably from 1.3 to 1.7, reactive sites per molecule. In
a
preferred embodiment, based on 100 pbw of the organopolysiloxane polymer,
greater than or equal to about 95 pbw, more preferably greater than or equal
to
about 98 pbw, even more preferably greater than or equal to about 99 pbw and
most
preferably, substantially all, of the organopolysiloxane polymer has at least
one
reactive site per molecule. Suitable reactive sites are silicon-bonded
substituents,
such as for example, hydrogen atoms, alkenyl groups and hydrolyzable groups
which are reactive with the primary functional groups of the polyfunctional
organosilicon component of the present invention, as further described below,
under
selected reaction conditions or under processing conditions anticipated during
compounding of the composition of the present invention or under moisture cure
conditions. Suitable hydrolyzable groups, include, for example, hydroxy,
alkoxy,
oximo, amino, aminoxy and acyloxy groups.
In a first preferred embodiment, the organopolysiloxane polymer comprises
a mixture of an organopolysiloxane polymer having two reactive sites per
molecule
and an organopolysiloxane polymer having one reactive site per molecule. In a
second preferred embodiment, the organopolysiloxane consists essentially of a
mixture of an organopolysiloxane polymer having two reactive sites per
molecule
and an organopolysiloxane polymer having one reactive site per molecule. In a
third preferred embodiment, the organopolysiloxane polymer consists of a
mixture
of an organopolysiloxane polymer having two reactive sites per molecule and an
organopolysiloxane polymer having one reactive site per molecule.
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In a first preferred embodiment, the organopolysiloxane mixture comprises
one or more linear organopolysiloxane polymers having two reactive sites per
molecule and one or more linear organopolysiloxane polymers having one
reactive
site per molecule. In a second preferred embodiment, the organopolysiloxane
mixture consists essentially of one or more linear organopolysiloxane polymers
having two reactive sites per molecule and one or more linear
organopolysiloxane
polymers having one reactive site per molecule. In a third preferred
embodiment,
the organopolysiloxane mixture consists of one or more linear
organopolysiloxane
polymers having two reactive sites per molecule and one or more linear
organopolysiloxane polymers having one reactive site per molecule.
In the case of mixtures of linear organopolysiloxane polymers having two
reactive sites per molecule and one or more linear organopolysiloxane polymers
having one reactive site per molecule, the relative amount of reactive sites
can be
expressed in an alternative way, that is, it is preferred that from 50 % to 99
% , more
preferably from 60% to 95%, still more preferably from 70% to 90% of the
terminal silicon atoms of the linear organopolysiloxane polymers are
substituted
with reactive substituent groups, such as, for example, a hydrolyzable group,
and
from 1 % to 50%, more preferably from 20 to 40%, still more preferably from
10%
to 30% of the of the linear organopolysiloxane polymers are substituted with
non-
reactive substituent groups, such as for example, alkyl groups.
Suitable organopolysiloxane polymers are made by conventional
polymerization techniques, wherein the relative amount of reactants are
controlled
to provide an organopolysiloxane polymer having a selected amount of reactive
sites
per molecule.
In a preferred embodiment, a silicon bonded hydroxy, that is, silanol,
functional organopolysiloxane polymer is made by a base catalyzed
equilibration/chain extension polymerization reaction of a cyclic
polysiloxane, such
as, for example, octamethylcyclotetrasiloxane, and a trialkyl-stopped
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polydialkylsiloxane polymer, such as, for example, trimethyl-stopped
polydimethylsiloxane, wherein a stoichiometric amount of water is added to the
reaction mixture to arrive at a selected average silanol content. The product
of the
polymerization reaction is then neutralized with phosphoric acid.
In a preferred embodiment, the organopolysiloxane polymer exhibits a
viscosity of from 5,000 to 500,000 centiPoise ('' cp" ), preferably from
20,000 to
150,000 cp, and more preferably from 40,000 to 80,000 cp, at 25 °C.
In a preferred embodiment, the organopolysiloxane polymer comprises a
mixture of two or more silicone polymers or copolymers having structural units
according to structural formula (I):
RuSi04_~,z
wherein each R is independently H, hydroxyl or a monovalent hydrocarbon
radical hydroxyl, wherein 0 <_ a <_ 4, provided that at least one R group per
molecule of the organopolysiloxane polymer is H, hydroxyl or alkenyl and, on
average, more than l and less than 2 R groups per molecule of the
organopolysiloxane polymer are each H, hydroxyl or alkenyl.
Suitable monovalent hydrocarbon radicals include monovalent acyclic
hydrocarbon radicals, monovalent alicyclic hydrocarbon radicals and monovalent
aromatic hydrocarbon radicals.
As used herein, the terminology " monovalent acyclic hydrocarbon radical"
means a monovalent straight chain or branched hydrocarbon radical, preferably
containing from 1 to 20 carbon atoms per radical, which may be saturated or
unsaturated and which may, optionally, be substituted, for example with one or
more halo groups. Suitable monovalent acyclic hydrocarbon radicals include,
for
example, alkyl radicals, such as, for example, methyl, ethyl, sec-butyl, tert-
butyl,
octyl, dodecyl, stearyl and eicosyl, haloalkyl, such as tritluoropropyl,
alkenyl
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radicals, such as, for example, ethenyl and propenyl, and alkynyl radicals,
such as,
for example, propynyl and butynyl.
As used herein, the terminology '' alicyclic hydrocarbon radical" means a
radical containing one or more saturated hydrocarbon rings, preferably
containing
from 6 to 10 carbon atoms per ring, per radical which may optionally be
substituted
on one or more of the rings with one or more alkyl groups, each preferably
containing from 2 to 6 carbon atoms per group and which, in the case of two or
more rings, may be fused rings. Suitable monovalent alicyclic hydrocarbon
radicals
include, for example, cyclohexyl and cyclooctyl.
As used herein, the terminology '' monocyclic aromatic hydrocarbon radical"
means a hydrocarbon radical containing one aromatic ring per radical, which
may
optionally be substituted on the aromatic ring with one or more alkyl groups,
each
preferably containing from 2 to 6 carbon atoms per group. Suitable monovalent
aromatic hydrocarbon radicals include, for example, phenyl, tolyl, xylyl,
2,4,6-
trimethylphenyl and naphthyl.
In a highly preferred embodiment, the organopolysiloxane polymer
comprises a mixture of two or more linear polymers or copolymers of the
structural
formula (II):
1 R~4 R6 ~8
R2 Si p ~ Si 0 ~ Si O ~ Si R10
Y
R3 R~ R7 R9
(II)
wherein:
each R', R', R3, R~, R5, R6, R', R~, Ry and R'° is independently H,
hydoxyl or a monovalent hydrocarbon radical, provided that at least
one of R', R2, R3, R4, R5, R6, R', Rg, R9 and R'° per molecule is H,
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hydroxyl or alkenyl and, on average based on all molecules of the
mixture, more than 1 and less than 2 of R', R2, R3, R4, R'S, R~, R',
Rg, Ry and R'° per molecule are each H, hydroxyl or alkenyl, and
m is selected to provide a polymer that exhibits a viscosity of from
5,000 to 500,000 cp at 25 °C.
In a preferred embodiment, each R', R3, R~, R5, R6, R', Rg and R9 is
independently (C,-C~)alkyl, fluoroalkyl or phenyl and each RZ and R'°
is hydroxyl,
(C,-CR)alkyl, tluoroalkyl or phenyl.
In a preferred embodiment, each R', R3, R', R5, R6, R', Ra and R9 is
independently (C,-C~)alkyl, fluoroalkyl or phenyl and each RZ and R'°
is H, alkenyl,
(C,-C~)alkyl, fluoroalkyl or phenyl.
Suitable polyfunctional organosilicon compounds are those that contain a
primary functional group such, as for example, an H, alkoxy or alkenyl group,
that
capable of reacting with the reactive sites of the organopolysiloxane polymer
under
selected reaction conditions or under processing conditions anticipated during
compounding of the composition of the present invention or under moisture cure
conditions, and that contain one or more secondary functional groups per
molecule,
preferal ~y hydrolyzable groups, such as, for example, alkoxy, oximo, amino,
aminoxy or acyloxy groups, each of which is reactive under room temperature
vulcanization conditions to thereby allow moisture curing of the sealant
composition. The polyfunctional organosilicon compounds can be silanes of
partially hyurolyzed products of silanes.
Suitable polyfunctional organosilicon compound include, for example,
vinyltrimethoxysilane, tetramethoxysilane, methyltriethoxysilane,
tetraethoxysilane,
methyltrimethoxysilane, methylphenyldiethoxysilane, 3,3,3-
tritluoroprpoyltrimethoxysilane, methyl(tri(methylethylketoximo)silane,
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ethyl(tri(N,N-diethylamino)silane, methyltri(N-methylacetamido)silane, n-
propylorthosilicate and ethylpolysilicate.
In a preferred embodiment, the polyfunctional organosilicon compound is
one according to the structural formula (III):
R"4Si (III)
wherein:
each R" is independently H, alkoxy, alkenyl, oximo, amino, aminoxy,
acyloxy or a monovalent hydrocarbon radical, provided that at least one R"
is H, alkoxy or alkenyl and that at least one other R" is alkoxy, oximo,
amino, aminoxy or acyloxy.
In a first preferred embodiment, at least three R" substituents are each
alkoxy, more preferably (C,-C~)alkoxy, even more preferably, methoxy or
ethoxy,
and the remaining R" substituent, if any, is (C,-C~)alkyl, (CZ-Cx)alkenyl,
aryl or
fluoroalkyl. Preferred polyfunctional organosilicon compounds include, for
example, v~nyltrimethoxysilane, tetramethoxysilane, methyltriethoxysilane,
tetraethoxysilane, methyltrimethoxysilane. Most preferably, polyfunctional
organosilicon compound comprises methyltrimethoxysilane.
In a second preferred embodiment, one R" is H or alkenyl, at lea:;: two R"
substituents are each alkoxy, more preferably (C,-Cn)alkoxy, even more
preferably,
methoxy or ethoxy, and the remaining R" substituent, if any, is (C,-C~)alkyl,
aryl
or fluoroalkyl. Preferred polyfunctional organosilicon compounds include, for
example, vinyltrimethoxysilane, vinyltriethoxysilane .
In a preferred embodiment, the moisture curable organopolysiloxane
polymer is made by reaction of 100 pbw of a functional organopolysiloxane
polymer with from about 1.0 to about 30 pbw, more preferably from about 2.0 to
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about 15 pbw, and most preferably from about 3.0 to about 10 pbw of the
polyfunctional organosilicon compound.
In a preferred embodiment, a suitable moisture curable organopolysiloxane
polymer is formed during compounding of the composition of the present
invention
by an in situ condensation reaction of a silanol, that is, silicon bonded
hydroxy,
organopolysiloxane polymer with a polyfunctional organosilicon compound having
alkoxy primary functional groups.
Alternatively, a suitable moisture curable organopolysiloxane polymer is
formed by reacting the organopolysiloxane polymer with the polyfunctional
organosilicon compound prior to addition to the composition of the present
invention. In a first embodiment, the moisture curable organopolysiloxane
polymer
is formed by a condensation reaction of a hydroxy functional
organopolysiloxane
polymer with a polyfunctional organosilicon compound having alkoxy primary
functional groups in the presence of a condensation cure catalyst, such as for
example a condensaticn cure catalyst as described in more detail below. In a
second
embodiment, the moisture curable organopolysiloxane polymer is formed by an
addition reaction of (i) m alkenyl functional organopolysiloxane polymer with
a
polyfunctional organosilicon compound having hydride primary functional groups
or
(ii) a hydride functional organo~olysiloxane polymer with a polyfunctional
organosilicon compound having ..lkenyl primary functional groups under
hydrosilylation conditions in the presence of a suitable hydrosilylation
catalyst, such
as, for example a platinum or rhodium-containing hydrosilylation catalyst.
The condensation cure catalyst of the composition of the present invention
are those that, in the presence of moisture, catalyze the room temperature
crosslinking of the crosslinkable organopolysiloxane polymer. Suitable
condensation cure catalysts include, for example, dialkyltincarboxylates, such
as,
for example, dibutyl tin dilaurate, dibutyl tin diacetate, and tin-2-
ethylhexanoate,
alkyl titanates, such as for example, tetrabutyl tin titanate, tetra-n-propyl
titanate,
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and organosiloxy titanium compounds. Various other condensation catalysts are
known in the art.
In a preferred embodiment, the condensation cure catalyst comprises a
compound according to structural formula (IV):
/R14 / OR17
,. O C /~ .. O C
~R18
R1 \ ~ ~CR15
O 'O C~. ~O C
R16
s R19
(IV)
wherein:
X is titanium, lead, tin, zirconium, antimony, iron, cadmium, barium,
manganese, zinc, chromium, cobalt, nickel, aluminum, gallium or
germanium;
R" is a divalent, optionally substituted, hydrocarbon radical;
R'4, R'° and R'y are each independently a monovalent hydrocarbon
radical;
R'S and R'8 are each independently H or a monovalent hydrocarbon radical;
R" is a monovalent hydrocarbon radical, amino, ether, or a polyether group
of the formula (CqH,qO)~R'-°
RZ° is a monovalent hydrocarbon radical;
q and v are each integers, wherein 2 <_ q<_ 4 and 1 <_ v <_ 20; and
s and t are each numbers, wherein 0.7 <_ s _< 1.3; and 0.8 <_ t _< 1.2.
In a preferred embodiment, X is titanium.
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In a preferred embodiment, s and t ar., each 1.
In a highly preferred embodiment, R" is a divalent hydrocarbon radical of 2
to 20 carbon atoms, more preferably 2-10 carbon atoms, per group, optionally
substituted with halo, cyano, vitro, carboxyl, carboxy ester, acyl
halohydrocarbon
or hydrocarbon substituent groups of up to 8 carbon atoms per group.
In preferred embodiment, X is titanium, R'3 is propyl, R'5 and R'~ are each
H, R" R'fi and R'9 are each methyl and R" is ethyl.
The preparation of compounds according to structural formula (III) is
described in U.S. Patent Nos. 3,689,454 and 3,779,986.
In a preferred embodiment, the composition of the present invention
comprises from 0.1 to 10 pbw, preferably from 1 to 7 pbw, and most preferably
from 3 to 5 pbw of the condensation cure catalyst.
The filler component of the composition of the present invention comprises a
reinforcing filler, a semi-reinforcing tiller, a non-reinforcing filler or a
mixture
thereof.
In a preferred embodiment, the filler of the present invention compnses a
reinforcing tiller. Suitable reinforcing tillers include, fc ~ example, fumed
silica,
surface-treated, for example, hydrophobicized, fumed sii.ca, carbon black,
titanium
dioxide, ferric oxide, aluminum oxide, as well as other metal oxides and are
commercially available from a number of sources. In a preferred embodiment,
the
reinforcing filler comprises fumed silica.
In a preferred embodiment, the silicone sealant of the present invention
comprises, based on 100 parts by weight of the sealant composition, from 1 pbw
to
10 pbw, more preferably from 2 pbw to 8 pbw, even more preferably from 3 pbw
to 5 pbw, of a reinforcing filler.
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The filler may, optionally, comprise a semi-reinforcing or non-reinforcing
filler. Suitable semi-reinforcing or non-reinforcing tillers include, for
example,
quartz, precipitated silica, hydrophobicized precipitated silica, calcium
carbonate
and are commercially available from a number of sources. In a preferred
embodiment, the semi-reinforcing or non-reinforcing tiller comprises calcium
carbonate.
In a preferred embodiment, the silicone sealant of the present invention
comprises, based on 100 parts by weight of the sealant composition, from 0 pbw
to
70 pbw, more preferably from 30 pbw to 60 pbw, even more preferably from 40
pbw to 60 pbw, of a semi-reinforcing or non-reinforcing filler.
The composition of the present invention may, optionally, further comprise a
hydrocarbon fluid to adjust the viscosity of the composition. The hydrocarbon
fluid
may be any (CS-C24)hydrocarbon fluid, including aliphatic, alicyclic and
aromatic
(CS-C~4)hydrocarbon fluids, such as for example, heptane, eicosane,
cyclohexane,
cyclooctane, benzene and toluene or a mixture of such fluids. In a preferred
embodiment, the hydrocarbon fluid comprises one or more linear or branched (CS-
Cz4)alkanes, more preferably one or more linear (C",-C,ri)alk~nes. Suitable
hydrocarbon fluids include, for example, heptane, hexane, octane, nonane,
decane,
undecane, dodecane, heptadecane, octadecane, eicosane. In a preferred
embodiment, the composition of the present invention comprises from 1 pbw to
40
pbw, more preferably from 2 pbw to 20 pbw, even more preferably from 3 pbw to
10 pbw, of the hydrocarbon fluid.
The silicone sealant composition of the present invention may, optionally,
further comprise other known components, such as, for example, dyes, pigments
anti-oxidants, UV stabilizers, adhesion-enhancing agents, thermal stabilizing
agents,
biocides, non-silicone polymers, can be used in this composition, as long as
they do
not interfere with the non staining, dirt pickup or other properties of the
silicone
sealant composition.
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The composition of the present invention is made by combining and mixing
the components of the composition. The mixing may be conducted as a batch
process or as a continuous process and any convenient mixing apparatus, such
as for
example, a planetary mixer, may be used to mix the components. In a preferred
embodiment, the composition of the present invention is made by continuously
compounding the composition in an extruder, preferably a twin screw extruder.
The composition of the present invention is used by exposing the
composition to ambient moisture and allowing the composition to cure.
Preferably,
the composition is maintained in moisture-impervious packaging up until the
time of
use. In a preferred embodiment, the composition is used to seal a gap between
a
tirst substrate and a second substrate, wherein the second substrate is spaced
apart
from the first substrate to form a gap, by applying an amount of the
composition
effective to bridge the gap and allowing the composition to cure in place to
form an
elastomeric seal between the substrates.
An assembly, comprising a first substrate, a second substrate, spaced apart
from the first substrate, and a cured silicone sealant composition of the
present
invention disposed between the first and second substrates and bonded to each
of the
substrates, wherein the assembly exhibits an improved resistance to staining
and dirt
pick up.
In a preferred embodiment, at least one of the tirst and second substrates i:
a
porous substrate, such as, for example, a marble, concrete, granite,
sandstone, or
limestone substrate.
Example l and ComQarative Examples C 1 - C6
The composition of Example 1 was made by combining, based on 100 pbw
total sealant composition, the following components in a Werner-Ptleiderer
twin
screw extruder:
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(a) 44.4 pbw of an organopolysiloxane polymer (a hydroxy-terminated
dimethylsiloxane polymer containing, based on the total weight of
endgroups, 18.6 wt% trimethylsilyl endgroups and 81.4 wt %
dimethylsilanol endgroups (about 1.63 silicone-bonded hydroxy
groups per molecule) groups and exhibiting a viscosity of a 54,000
centiPoise);
(b) 5.0 pbw of a reinforcing filler (octamethylcyclotetrasiloxane-treated
fumed silica);
(c) 43.0 pbw of a non-reinforcing filler (stearic acid treated calcium
carbonate tiller, Hi-Ptlex 100 from Specialty Minerals Inc),
(d) 5.0 pbw of a mixture of linear, aliphatic (C,~-C,5) hydrocarbons
(Conosol D-200, Conoco) ; and
(e) 2.60 pbw of a liquid blend consisting, based on total weight of the
blend, of:
(i) 57 wt% of a polyfunctional silicon compound
(methyltrimethoxysilane),
(ii) 11 wt% of an adhesion promoter (tris-[3-
(trimethoxysilyl)propyl] isocyanurate), and
(iii) 32 wt% of a curing catalyst (1,3-propanedioxytitanium
(ethylacetoacetate-acetylacetonate).
The organopolysiloxane polymer, tamed silica and calcium carbonate were
continuously fed into barrel I of the extruder. The hydrocarbon fluid and
liquid
blend were added further downstream. A vacuum was applied at barrel 12. The
extruder processing temperature was maintained at 75°C from barrel 1 to
barrel 11.
Barrels 12-14 were cooled such that the RTV sealant exited the extruder at
between
25-35 ° C.
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After standing for 4 days at room temperature, the sealant composition of
Example 1 was tested for a variety of rheological and cured physical
properties. The
ASTM test methods used and test results are listed in TABLE I below.
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TABLE I
Property ASTM Test Ex 1
Method
Specific Gravity - .. - .... C97 1.36
Application Rate (g/min) C 1183 279
Tack Free Time (hr) C679 6
1/8 inch cure through time (hr) -- 24
Boeing Flow (in) D2202 0.10
Properties for 7 Day RT Cured Sheet
Durometer, Shore A C661 24
Tensile Strength (psi) D412 251
Elongation (%) D412 649
Modulus ~ 50% elongation (psi) D412 56
Peel Adhesion after 14 day cure (ppi/ C794
% cohesive failure)
- on concrete 32/50
- on polished granite 37/ 100
on marble 32/ 100
- on anodized aluminum - 28/ 100
- on glass 29/ 100
- on Duranar~'~' coated aluminum 34/ 100
- on polyacrylate 27/ 100
on polycarbonate 30/ 100
Stain Testine
The compositions of Example 1 and Comparative Examples C 1 - C6 below
were subjected to stain testing according to ASTM C-1248 and according to an
extended stain test wherein H-specimens were placed outdoors at a 75°
angle, facing
upward for an extended period of time.
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Ex# Sealant Approximate Modulus ~a
50 % elongation (psi)
C 1 Silicone sealant containing polyorganosiloxane
plasticizes (trimethylsilyl-terminated 56
polydimethylsiloxane)
C2 Silicone sealant containing polyorganosiloxane
plasticizes (trimethylsilyl-terminated 50
polydimethylsiloxane)
C3 Silicone Sealant (Dow Corning 790) 25
C4 Silicone Sealant (Dow Corning 795) 65
C5 Siliconized polyether sealant containing organic 35
plasticizes (dioctyl phthalate)
C6 Siliconized polyether sealant containing organic 25
plasticizes (dioctyl phthalate)
TABLE II below shows the stain and dirt pickup properties for the
composition of Example 1 and the compositions of Comparative Examples C1- C6.
The following notation is used in the TABLE II: No Staining Detected (+++),
Stain Barely Detected (++), Very Little Stain (+), Stain Noticeable (-), Stain
Very
Apparent (--), Unacceptable Stain (---).
TABLE II
ASTM C-1248 Results Extended
Stain
Test
Results
Ex Initial1 Month 2 Month 4 Month
#
1 no stain +++ +++ +++ +++
C significant stain + + - - --
1 +
C2 significant stain + + - - ---
+
C3 significant stain +++ ++ + +
C4 significant stain + + + + + +
+
C5 significant stain + + - - --
+
C6 significant stain + + + + + +
+
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CA 02393051 2002-05-30
WO 01/42365 PCT/US00/31577
The composition of the present invention exhibits a reduced tendency to stain
or bleed into substrates and a reduced tendency to pick-up dirt on the surface
of the
sealant. Sealant compositions that a exhibit tensile modulus of less than or
equal to
100 psi typically include non-curable plasticizers to adj ust the tensile
modulus of
such compositions. However, the non-curable plasticizers tend to promote
staining,
bleeding and dirt pick-up. The sealant composition of the present invention
exhibits
a tensile modulus of less than or equal to 100 psi and, compared to
conventional
compositions which contain non-curable plasticizers, exhibits a reduced
tendency to
stain or bleed into substrates and a reduced tendency to pick-up dirt on the
surface
of the sealant.
Since the composition of the present invention contains only a small to
negligible amount of organopolysiloxane polymer lacking reactive sites, the
cured
sealant compositions contains only a small to negligible amount of free
organopolysiloxane polymer, that is, substantially all of the
organopolysiloxane
polymer becomes chemically bound into a crosslinked organopolysiloxane network
of cured sealant composition. The use of a selected amount organopolysiloane
polymer having one reactive site per molecule allows control of the crosslink
density of the network and tensile modulus of the cured sealant, without
requiring
the use of the non-curable plasticizers. The cured sealant composition
contains
substantially no free non-curable plasticizers or organopolysiloxane polymer
species
that can then bleed from the sealant and into the substrate and stain the
substrate. It
is believed that the substantial absence of non-curable plasticizers and free
organopolysiloxane polymer species increases the surface tension of exposed
surfaces of the cured sealant composition and thereby reduces its affinity for
dirt,
grime, carbon and other pollutants.
19
