ORGANOPOLYSILOXANE LIQUID INJECTION MOLDING COMPOSITION

COMPOSITION DE MOULAGE PAR INJECTION LIQUIDE D'ORGANOPOLYSILOXANE

English Abstract

ORGANOPOLYSILOXANE LIQUID INJECTION MOLDING
COMPOSITION
Abstract of the Disclosure
There is provided a translucent, high strength liquid
injection molding composition cured through SiH addition
reactions with a controlled mixture of olefin containing
organopolysiloxanes. The instant cured elastomer exhibits
extremely good application rates, easy release, high hardness,
high tear, good tensile strength and good elongation.

Claims

- 17 - 60SI 886
The embodiments of the invention in which an
exclusive property or privilege is claimed are defined
as follows:
1. An organopolysiloxane composition
comprising:
(A) 100 parts by weight of a vinyl-containing
polyorganosiloxane component comprising:
(1) 60 to 75 parts by weight of a linear
high viscosity vinyl end-stopped
organopolysiloxane having no more than 25 mole
percent of phenyl radicals and having a
viscosity of from about 5,000 to about 40,000
centipoise at 25°C, and
(2) 25 to 40 parts by weight of a linear
low viscosity organopolysiloxane having at
least one terminal vinyl group per molecule
having a vinyl content that may vary from 0.01
mole percent vinyl to 60 mole percent vinyl,
having a viscosity that varies from about 50
to about 2,000 centipoise at 25°C and having
no more than 25 mole percent phenyl radicals;
(B) from about 5 to about 70 parts by weight of a
filler or combination of fillers;
(C) from about 0.1 to 50 parts per million of the
total organopolysiloxane composition of platinum
catalyst; and
(D) from about 0.5 to 25 parts by weight of a SiH
composition selected from the class consisting of
hydrogen containing silanes and hydrogen containing
organopolysiloxanes;
wherein the organopolysiloxane composition has
an application rate of at least about 100 gm/min.
2. The composition of claim 1 wherein said
high viscosity vinyl end-stopped organopolysiloxane is
represented by the general formula.

- 18 - 60SI 886
<IMG>
where Vi stands for vinyl, R is selected from the group
consisting of monovalent hydrocarbon radicals and
halogenated monovalent hydrocarbon radicals having up to
about 20 carbon atoms, and x may vary from about 100 to
about 10,000.
3. The composition of claim 1 wherein said
low viscosity organopolysiloxane is represented by the
general formula:
<IMG>
wherein R is selected fro the group consisting of
monovalent hydrocarbon radicals and halogenated
monovalent hydrocarbon radicals having up to about 20
carbon atoms, R1 is the same as R except that at least
one R1 must be vinyl, and y may vary from about 1 to
about 300.
4. The composition of claim 3 wherein only
one R1 is vinyl.
5. The composition of claim 1 wherein said
SiH composition is selected from the group consisting of
organopolysiloxanes having from about 0.5 to about 99.5
percent by number units the general formula:
Rf Hg SiO(4-f-g)/2

- 19 - 60SI 886
and from about 99.5 to about 0.5 percent by number units
of the formula:
Rc SiO (4-c)/2
where R is a saturated monovalent hydrocarbon radical
and a saturated halogenated hydrocarbon radical having
up to about 20 carbon atoms, c has a value of from 0 to
3.0, f has a value of from 0 to 2 and the sum of f and g
is equal to from 1.0 to 3Ø
6. An organopolysiloxane composition
comprising component 1 packaged separately from
component 2, either component comprising all of or part
of:
(A) 100 parts by weight of a vinyl-containing
polyorganosiloxane component comprising:
(1) 60 to 75 parts by weight of a linear
high viscosity vinyl end-stopped
organopolysiloxane having no more than 25 mole
percent of phenyl radicals and having a
viscosity of from about 5,000 to about 40,000
centipoise at 25°C, and
(2) 25 to 40 parts by weight of a linear
low viscosity organopolysiloxane having at
least one terminal vinyl group per molecule
having a vinyl content that may vary from 0. 01
mole percent vinyl to 60 mole percent vinyl,
having a viscosity that varies from about 5 0
to about 2, 000 centipoise at 25°C and having
no more than 25 mole percent phenyl radicals;
(B) a filler or combination of fillers;
(C) component 1 comprising the entire amount of
from 0.1 to 50 parts per million of the total
organopolysiloxane composition of a platinum catalyst;
and

- 20 - 60SI 886
(D) component 2 comprising the entire amount of
from about 0.5 to 25 parts by weight a SiH composition
selected from the class consisting of hydrogen
containing silanes and hydrogen containing
organopolysiloxanes where a total of about 5 to about 70
parts by weight said filler or combination of fillers is
present which may be divided between or wholly added to
either component;
wherein the organopolysiloxane composition has
an application rate of at least about 100 gm/min.
7. The composition of claim 6 wherein said
high viscosity vinyl end-stopped organopolysiloxane is
represented by the general formula:
<IMG>
where Vi stands for vinyl, R is selected from the group
consisting of monovalent hydrocarbon radicals and
halogenated monovalent hydrocarbon radicals having up to
about 20 carbon atoms, and x may vary from about 100 to
about 10,000.
8. The composition of claim 6 wherein said
low viscosity organopolysiloxane is represented by the
general formula:
<IMG>
wherein X is selected fro the group consisting of
monovalent hydrocarbon radicals and halogenated

- 21 - 60SI 886
monovalent hydrocarbon radicals having up to about 20
carbon atoms, R1 is the same as R except that at least
one R1 must be vinyl, and y may vary from about 1 to
about 300.
9. The composition of claim 8 wherein only
one R1 is vinyl.
10. The composition of claim 6 wherein said
SiH composition is selected from the group consisting of
organopolysiloxanes having from about 0.5 to about 95.5
percent by number units the general formula:
Rf Hg Sio(4-f-g)/2
and from about 99.5 to about 0.5 percent by number units
of the formula:
Rc SiO(4-c)/2
where R is a saturated monovalent hydrocarbon radical
and a saturated halogenated hydrocarbon radical having
up to about 20 carbon atoms, c has a value of from 0 to
3.0, f has a value of from 0 to 2 and the sum of f and g
is equal to from 1.0 to 3Ø

Description

1309~33 60SI 886
~RGANOPOLYSILOXANE LIQUID
INJECTION MOLDING COMPOSITION
, ~, . .. . ...
The present invention relates to translucent, high
strength, organopolysiloxane, liquid injection molding
compositions. More particularly, the present invention relates
to such compositions which are cured through SiH addition
reactions with a controlled mixture of olefin containing
organopolysiloxanes.
Back~round of the Invention
Liquid injection moldable (LIM) organopolysiloxane
compositions are known and used. A problem with all such
compositions is that the application rate, hardness, tensile
strength, elongation and tear are so interdependent within
themselves and with the viscosity of the uncured liquid, that
it is difficult to improve one property without suffering loss
in another. Particularly, it is desirable to improve hardness
and tear strength without reduction of other properties.
U.S. Pat. Nos. 3,884,866 and 3,957,7l3, Jeram, describe
high strength addition cured compositions suitable for low
pressure liquid injertion molding. These compositions comprise
a first component containing a high viscosity vinyl end-stopped
organopolysiloxane, a low viscosity vinyl containing
organopolysiloxane, filler, and platinum catalyst which is
cured by mixing with a second component containing a hydrogen
silicone composition. This composition is difficult to apply,
that is has low application rates, and moreover, attempts to
raise the application rate by lowering component viscosities
leads to adverse effects on other properties.

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U.S. Pat. No. 4,162,243, Lee9 et al., disclose compositions
similar to Jeram which contain, as the most important distinc-
tion, fumed silica treated with hexamethyldisilazane and
tetramethyldivinyldisilazane. The Lee, et al., compositions
cure to elastomers having high hardness with good retention of
other properties including strength, elongation, and tear in
addition ta having low viscosity in the uncured state.
U.S. Pat. No. 49427,801, Sweet, extends Lee, et al., by
incorporating a MMViQ resin in addition to the vinyl
I0 containing treated fumed silica. This produces elastomers
having even higher hardness and tear strengths but has the
disadvantage of higher compression set and lower Bashore
resilience.
It is an object of the present invention to produce a
liquid injection molding organopolysiloxane composition having
improved ease of application without adverse effects on other
physical properties.
It is another object of the present invention to produce
such liquid injection molding organopolysiloxane compositions
having exceptional application rates.
These and other objects will become apparent to those
skilled in the art upon considerat;on of the instant
specification, examples and claims.

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--3--
Detailed Description of the Invention
There is provided by the present invention a LIM
organopolysiloxane composition combining low viscosity, high
strength, good elongation, good hardness and tear strength,
with exceptionally high application rates comprising:
(A) lO0 parts by weight of a vinyl-containing
polyorganosiloxane component comprising:
(l) 55 to 80 parts by weight of a linear high
viscosity vinyl end stopped organopolysiloxane
having no more than 25 mole percent of phenyl
radicals and having a viscosity of from about
5,000 to about 40,00Q centipoise at 25C, and
(2) 20 to 45 parts by weight of a linear low
viscosity organopolysiloxane having at least one
terminal vinyl group per molecule, having a
vinyl content that may vary from O.Ol mole
percent vinyl to 60 mole percent vinyl, having a
viscosity that varies from about 50 to about
2,000 centipoise at 25C and having no more than
25 mole percent phenyl radicals;
(B) from about 5 to about 70 parts by weight of a filler
or combination of fillers;
(C) from about O.l to 50 parts per million of the total
organopolysiloxane composition of a platinum catalyst;

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(D) from about O.l to lO parts by weight a SiH composition
selected from the class consisting of hydrogen
containing silanes and hydrogen containing
B organopolysiloxanes~
This composition may either be cured to an elastomer at room
temperature for 16 hours or may be cured at elevated
temperatures~ such as, for example, 200C for lO seconds. In a
preferred embodiment, the above composition is a two-component
composition where the first component contains at least all of
ingredient (C), and the second component contains at least all
of ingredient (D).
The linear high viscosity vinyl end-stopped organopoly-
siloxane, A (l), of the present invention has no more than 25
mole percent of phenyl radicals and a viscosity of from about
5,000 to about 40,000 centipoise at 25C, preferably from about
lO,000 to about 25,000 centipoise at 25~C. These high
viscosity organopolysiloxanes may be represented by the general
formula:
R ~ R ~ R
(1) Vi- SitOSitOSi~i
R ~ R J x R
where ~i stands for vinyl, R is selected from the group
consisting of monovalent hydrocarbon radicals and halogenated
monovalent hydrocarbon radicals having up to about 20 carbon
atoms, and x may vary from about lO0 to about lOsO00,
preferably from 500 to 2,000.

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The linear low viscosity organopolysiloxane, A (2), of the
instant invention has at least one terminal vinyl group per
molecule, a vin~l content that may vary from about 0.01 mole
percent vinyl to about 60 mole percent vinyl, preferably .05 to
10 mole percent vinyl; a viscosity that varies from about 50 to
about 2,000 centipoise at 25C, preferably from about 50 to
about 1,000 centipoise at 25C; and no more than about 25 mole
percent phenyl radicals. These low viscosity organopolysilox-
anes may be represented by the general formula:
R ~ R ~ R
(2) R - Si ~ OSi t OSi -
R ~ R J y R
wherein R is defined above, wherein Rl is the same as R
except that at least one Rl must be vinyl, and y may vary
from about 1 to about 300. Suitable low viscosity organopoly-
siloxanes are disclosed in United States Patent
Number 3,884,866.
As stated above, R is selected from the group consisting of
monovalent hydrocarbon radicals and halogenated monovalent
hydrocarbon radicals having up to about 20 carbon atoms, that
is, radicals normally associated as substituent groups for
organopolysiloxanes. Thus, the radical R may be selected from
the class consisting of mononuclear and binuclear aryl radicals
such as, phenyl, tolyl, xylyl, naphthyl and etc.; halogenated
mononuclear and binuclear aryl radicals such as, chlorophenyl,
chloronaphthyl, and etc.; mononuclear aryl lower alkyl radicals
having from 1 to 8 carbon atoms per alkyl groups such as,

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benzyl, phenyl and etc.; lower alkyl radical having from l to 8
carbon atoms such as, methyl, ethyl, propyl, butyl, pentyl,
hexyl, octyl and etc.; lower alkenyl radicals having from 2 to
8 carbon atoms such as, vinyl, allyl and l-propenyl; halo lower
alkyl radicals having from l to 8 carbon atoms such as, chloro-
propyl, trifluoropropyl; and cycloalkyl radicals such as,
cyclobutyl, cyclopentyl and cyclohexyl. Though R may be any of
the above, persons skilled in the art will readily recognize
that not every R can be a high molecular weight radical and
that R should not be chosen so as to adversely affect the vinyl
group reactions. Preferably R is a lower alkyl radical of l to
8 carbon atoms, such as, methyl, ethyl and phenyl
trifluoropropyl. More particularly, R is at least about 70
percent by number methyl.
The essence of the present invention, and particularly the
way in which the present invention distinguishes from the
SiH/olefin addition silicone rubber compositions of the prior
art, is the presence in the composition of critical ratios of
low viscosity vinyl containing organopolysiloxanes to high
viscosity vinyl containing organopolysiloxanes. Within the
ratios, co~positions with high application rates may be
produced without adversely effecting other physical
properties. As above, these vinyl containing
organopolysiloxanes are the high viscosity organopolysiloxane,
A(l) and the low viscosity organopolysiloxane, A(2). For each
lO0 parts by weight vinyl containing organopolysiloxane there
should be from about 55 to about 80 parts by weight A(l), and
B from about 20 to about 45 parts by weight ~ 2). More
preferably, there should be from about 60 to about 75 parts by
- 3D weight (A)l and about 25 to about 40 parts by weight A(2).

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This mixture of vinyl containing organopolysiloxanes results in
a cured composition having exceptionally high application
rates, along with good hardness, high tear, high tensile
strength, and good elongation. The cured composition should
exhibit an application rate of at least lO0 gm/min as well as
have a tensile strength of about 900 psi or more, an
eleongation of about 500% or more, a tear strength of about 175
psi or more, and a Shore A hardness of 30 to 35 or more.
The SiH composition, (D), of the present invention serves
as a crosslinking agent and may be selected from the class
consisting of hydrogen containing silanes and hydrogen contain-
ing organopolysiloxanes. It is preferably a hydrogen contain-
ing organopolysiloxane. Thus hydrogen containing organopoly-
siloxanes of the present invention can be characterized as
copolymers containing at least one unit per molecule having the
formula:
(3) Rf Hg SiO (4 f_g)/2
with the remaining siloxane units in the organopolysiloxane
having the formula:
(4) c (4-c)/2
where R herein is defined above but should be saturated; c has
a value of from 0 to 3, inclusive; f has a value of from 0 to
2, inclusive; and the sum of f and 9 is equal to fro~ l.0 to
3.0 inclusive. The viscosity of the hydrogen containing
organopolysiloxane should range from about 5 to about lO00 and
preferably from about 5 to about lO0 centipoise at 25~C. The

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copolymer generally contains from 0.5 to 99.5 mole percent of
units of Formula (3) and from 0.5 to 99.5 mole percent of the
units of Formula 4.
Preferred among the hydrogen containing organopolysiloxanes
described above are MQ resins having units of, for example,
H(R)2SiOl/2 and SiO2. Also included therein are MDQ,
MTQ, MDT, etc. resins with hydrogen substitution. This
B copolymer generally contains from 0.5 to 99.5 mole percent of
the units of formula3~ and from 0.5 to 99.5 mole percent of the
units of formula 4.
Another suitable hydrogen containing organopolysiloxane is
the MQ resin organopolysiloxane polymer of the formula
R ~ R ~ ~ R ~ R
(7) R3 - Si ~ SiO ~ Si ~ Si~
R ~ R J h ~ Ji R
wherein R is defined above, excluding unsaturated compounds,
R3 is the same as R excluding unsaturated compounds and with
the addition of hydrogen, h varies from 1 to 200, and i varies
from 5 to 200. More preferably, h varies from 10 to 100 and
varies from 5 to 100.
The hydrogen containing organopolysiloxane, (D), is
utilized at a concentration of anywhere from about 0.5 to 25
parts by weight per 100 parts by weight (A), and preferably, at

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a concentration of from about 0.5 to 10 parts by weight per 100
parts by weight (A). It is desirable that in tne SiH material
there is at least one hydrogen atom for every vinyl group in
(A) and preferably from about 1.5 to about 2.5 hydrogen atoms
for every vinyl group.
Many types of platinum catalysts for this SiH olefin
addition reaction are known and such platinum catalysts may be
used also for the reaction of the present case. The preferred
platinum catalysts especially when optical clarity is required
are those platinum compound catalysts which are soluble in the
present reaction mixture. The platinum compound can be
selected from those having the formula (PtC1201efin)2 and
H(PtC1301efin) as described in U.S. Pat. No. 3,159,601,
Ashby. The olefin shown in the previous formulas can be almost
any type of olefin but is preferably an alkenylene having from
2 to 8 carbon atoms, a cycloalkenylene having from 5 to 7
carbon atoms or styrene. Specific olefins utilizable in the
above formulas are ethylene, propylene, the various isomers of
butylene, octylene, cyclopentene, cyclohexene, cycloheptene,
etc.
A further platinum containing material usable in the
composition of the present invention is the platinum chloride
cyclopropane complex (PtC12C3H6~2 described in U.S.
Pat. No. 3,159,662, Ashby.
Still, further, the platinum containing material can be a
complex formed from chloroplatinic acid with up to 2 moles per
gram of platinum of a member selected from the class consisting
of alcohols, ethers, aldehydes and mixtures of the above as
described in U.S. Pat. No. 3,220,972, Lamoreaux.

13 09~33
60SI 8~6
-- 10 --
The preferred platinum compound to be
used not only as a platinum catalyst but also
as a flame retardant additive is that disclosed
in French Pat. No. 1,548,776, Karstedt. Generally
speaking, this type of platinum complex is
formed by reacting chloroplatinic acid
containing 4 moles of water of hydration with
tetravinylcyclotetrasiloxane in the presence of sodium
bicarbonate in an ethanol solution.
Persons skilled in the art can easily
determine an effective amount of platinum catalyst.
Generally, an effective amount ranges from about 0.1
to 50 parts per million of the total organopolysiloxane
composition.
In order to get high tensile strength
in the compositions of the instant case and
particularly where compositions are formed to
thin coatings or films, it is desirable to
incorporate a filler, (B), into the composition.
Illustrative of the many fillers which can be
employed are titanium dioxide, lithopone, zinc
oxide, zirconium silicate, silica aeorgel, iron oxide,
diatomaceous earth, calcium carbonate, fumed silica,
silazane treated silica, precipitated silica, glass
fibers, magnesium oxide, chromic oxide, zirconium
oxide, aluminum oxide, alpha ~uartz, calcined clay,
asbestos, carbon, graphite, cork, cotton, synthetic
fibers and etc.
The preferred fillers that should
be utilized iII the composition of the
instant case are either a fumed silica or a

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precipitated silica that has been surf~ce treated. In one
method of surface treatment, the fumed silica or precipitated
silica is exposed to cyclic organopolysiloxanes under heat and
pressure. This method of surface treatment is disclosed in
United States Patent Number 2,938,009 - Lucas.
Another method ~or surface treating fillers is ~ne
in which silica is exposed to siloxanes or silanes in the
presence of an amine compound. ~his method is disclosed in
U.S. Pat. No. 3,024,l26
The preferred method of surface treating fillers employs
methyl silane silazane surface treating agents. Methylsilane
or silazane surface treated fumed or precipitated silica
fillers flow easily and do not undesirably increase the low
viscosity of the uncured composition. At the same time,
however, the silazane treated silica fillers increase the
physical properties of the cured elastomer, particularly, the
tear strength of the cured elastomer. Best properties are
obtained where the silazane treatment is applied to the filler
in situ, that is, where the filler has been combined with
composition (A). Silazane treated fumed silica or precipitated
silica are described in United States Patent Number
3,635,743 - Smith and United States Patent Number
3,847,848 - Beers.
The filler, (B), is generally utilized in a concentration
of 5 to 70 parts, preferably l5 to 50 parts filler for each lO0
parts by weight of (A). The preferred filler is silazane
treated fumed silica or mixtures of silazane treated fumed
silica with silazane treated precipitated silica. Such

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mixtures of silica should contain a weight ratio of fumed
silica to precipitated silica of about 25/1 to about 1/1 and
preferably from about 10/1 to about 5/1.
The ingredients present in composition (C), component 1,
are packaged separately from the ingredients present in
composition (D), component 2, until the time of cure.
B Compositions (A), (B), 1~ and additives may be divided between
either component or wholly added to one component. Premature
reactions are hindered in this manner during storage and
transport. When it is desired to form the cured silicone
rùbber composition, the two components are mixed into each
other and the composition is allowed to cure either for 16
hours at room temperature or at increasingly elevated
temperatures for increasingly lower cure times.
Mixed components 1 and 2 may be injection molded directly
or dissolved in solvents for application as a film or coating.
In injection molding, the mixing barrel and shot chamber must
be cool in order to prevent premature cure. The mold
temperature generally varies from about 150F to about 500F.
Solvents for coating films or coatings include the usual
organic solvents for the prior art SiH olefin addition
reactants. Such solvents are, for example, hexane, heptane,
pentane, octane, cyclohexane, toluene, xylene, acetone, and
others. Other ingredients may of course be added to achieve
various purposes. Pigments, thixotropic agents, thermal
stabilizers, and the like may be added according to the
teachings in the art. Particularly, it is desirable to add
inhibitors, such as the maleates, in order to obtain a
reasonable work life in the catalyzed material. Suitable
inhibitors are taught in U.S. Pat. No. 4,256,870 .

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-13-
Examples
Materials
A~l) High Viscosity Vinyl End-stopped Organopolysiloxane
HVO-82 - dimethylvinyl terminated polydimethylsiloxane
polymer having a viscosity of 82,000 centipoise
at 25C.
HYO-22 - dimethylvinyl terminated polydimethylsiloxane
polymer having a viscosity of 22,000 centipoise
at 25C.
HVO-10 dimethylvinyl terminated polydimethylsiloxane
polymer having a viscosity of 10,400 centipoise
at 25C.
A(2) Low Viscosity Vinyl Containing Organopolysiloxane
LVO-316 dimethylvinyl terminated polydimethylsiloxane
polymer having a viscosity of 316 centipoise at
25C.
LVO-530 dimethylvinyl-trimethyl terminated
polydimethylsiloxane polymer having a viscosity
of 530 centipoise at 25C.
(B) Silica filler
Fumed Silica - Hexamethyldisilazane treated

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~C) Catalyst
La~oreaux platinum catalyst, octanol complex
(D) SiH Crosslinking Agent
RHC - resin hydride crosslinker, represented by the
formula M2HQ, having a viscosity of 20
centipoise at 25C and approximately 0.9 percent
by weight H.
The following examples are presented for the purpose of
illustrating the present invention and are not meant in any way
1~ or manner to limit the scope of the present specification or claims.
Example l - 8
Liquid inJection molding compositions were prepared by
first mixing the high viscosity vinyl containing
organopolysiloxane with the treated fumed silica in three equal
additions. ~he resultant batch is well mixed and cooked for
three hours under full vacuum at 125C steam heat. The batch
is cooled and the other ingredients, excepting the hydride
crosslinker, are added and mixed until the composition is
homogeneous. The application rate of this composition without
hydride crosslinker is tested using a Semco tube at 90 psig and
a l/8 inch nozzle.

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-15-
To each liquid injection molding composition is added
hydride crosslinker in an amount of 0.75, 1.0, 1.25 and l.S
parts by weight. All four samples are cured for one hour at
lOO~C. Hardness, tensile strength, elongation and tear
strength were tested on each of the four samples. The sample
with maximum hardness is selected as representative of the
properties of that particular composition. This sample is
assumed to have a constant SiH/Vi ratio with other compositions
at maximum hardness. In this manner, SiH/Vi ratio is held
constant experimentally rather than through calculation based
upon vinyl content and hydride content assumptions.
.~
_ _ _ _ _ _ ~

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-16-
Tabl e
Exampl e 1 2 3 4 5 6 7 8
HY0-82 85 60
HV0-22 85
HV0-10 85 85 72 72 80
LV0-316 15 15 15 15 ~6 16 10 20
LV0-530 12 12 10 20
F i 11 er 35 35 35 35 35 35 35 35
Catalyst, ppm 10 10 10 10 10 10 10 10
RHC 1 1 1 1 1.51.25 1.25 1.5
Appl icdtion
Rate, g/m 3 36 60 70 136 kO 52 21.5
Cured Pr~perties 1 hr at 100C
Shore A 41 38 42 33 38 32 39 41
Tensile, psi1125 11501000 840 95D ~70970 1180
Elongation, X 660 770 520 650 500 590 570 560
Tear, pi 240 70 70 75 200 20080 175
.