Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR ADDING HIGH VTSCOSITY COMPOUND TO A MI~~ER AND AN
INTEGRATED PROCESS FOR COMPOUNDING SAME
S [0001) The present invention relates to a method for adding a high
consistency
compound, such as a high viscosity polydiorganosiloxane, to a mixer and an
integrated
process for producing catalyst containing silicone rubber compositions using
the method.
[0002) It is to be understood that the terms high consistency and high
viscosity when
1 U used herein with respect to a compound are intended to mean a compound
which does not or
substantially does not flow under its own weight, an example being a high
consistency
polydiorganosiloxane gum.
[0003) Traditionally high viscosity materials, such as siloxane gums, have
been fed
15 intobatch processes by such methods as pumping or simple dumping. Batch
processes tend
to have requirements for very high instantaneous feed rates for brief periods
of time and for a
variety of materials. Pump systems are available that can accommodate
materials such as
polydiorganosiloxane gums at the required rates but they are expensive to
purchase, install,
and maintain and if a variety of different gums are needed, these systems are
difficult to
20 changeover without cross-contamination. Simple dumping of high viscosity
materials is
inexpensive and very accurate and flexible, but not very controlled and can be
slow if
multiple containers are required. In addition, some mixers are not physically
constructed to
accommodate uncontrolled dumping. The present method is intended to retain the
flexibility
and low cost of the dumping technique while adding control to it.
[0004) EP 0524443 describes a method of dumping the entire contents of a
container at a
dumping station using a rigid container having an open upper end and at least
one hole in the
bottom of the container which has a flexible liner and which holds the
contents of the
container. When the container is inverted compressed gas is forced through the
hole in the
30 bottom forcing the flexible liner to evert and causing the contents of the
container to be
dumped at the dumping station. US 3824208 describes a process for forming a
free-flowing
particulate polymer mixture from a viscous tacky polymer.
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[0005] The present method is especially useful when incorporated into an
integrated
process for producing catalyst containing silicone rubber compositions,
resulting in
substantially reduced processing time and labour input compared to standard
methods for
producing such compositions as described in the applicants co-pending
application WO
02/096981 which was published after the International filing date of the
present application.
The integrated process using, for example, an organoperoxide catalyst,
involves forming a
powdered silicone rubber composition comprising a polydiorganosiloxane gum and
a
reinforcing filler, treating the reinforcing filler with a treating agent at a
temperature greater
than about 80oC, cooling the powdered silicone rubber composition by means of
a bulk solid
cooling apparatus, and admixing the cooled powdered silicone rubber with the
organoperoxide catalyst either before, during, or after a massing step.
[0006] In the past to prepare, for example, organoperoxide curing silicone
rubber
compositions it was common to prepare a polydiorganosiloxane gum having a
viscosity of
from 1 x 106 to 2 x 108 mPa.s at 25°C which was the basic ingredient of
the organoperoxide
curing silicone rubber composition. The gum was then transported to a dough-
mixer. Then,
there was added to the gum in the dough-mixer the requisite amount of
reinforcing fillers or
extending fillers, heat stabilizers, flame retardant additives, processing
aids, and other types
of ingredients that are normally associated or present in silicone rubber
compositions.
[0007] The dough-mixer comprises a large tank with two large mixing blades
therein
which agitate and mix the gum and the other ingredients into a uniform
mixture. Normally, it
takes a dough-mixer from a minimum of 3 hours to a maximum of 48 hours to form
a
-uniform homogeneous mass of diorganopolysiloxane gum, filler, and other
ingredients. After
dough mixing has been completed, the composition is cooled for several hours
either in the
dough-mixer or after removal from the dough-mixer. The resulting mass is then
dumped into
a cart, cut into pieces, passed through an extruder to screen out particles
and is then formed
into packageable slabs, for example 50 pound (22.7kg) slabs. The resulting
slabs are
packaged and shipped, or alternatively may be processed through other
extruding and forming
machines before they are shipped. In addition, in some cases, the 50 pound
(22.7kg) slabs are
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processed on a mill at which point a curing catalyst may be added and the
resulting milled
mass may then be extruded into the desired shape and shipped as such.
Alternatively, the
unanalysed mass may be shipped to the customer for subsequent addition of the
catalyst.
[0008] The above described method is both tune c°nsuming and labour
intensive and
requires multiple manual handling of the silicone rubber compositions during
compounding
and forming into a shippable form. The present process significantly shortens
the time
required to form the catalyst curable silicone rubber compositions and
eliminates the manual
handling of the silicone rubber compositions during compounding and forming
into a
shippable product. This reduction in time and elimination of manual handling
is achieved by
an integrated process comprising first forming a free-flowing particulate
polymer mixture
comprising in situ treated fumed silica and a high consistency
polydiorganosiloxane gum,
rapidly cooling the free-flowing po~~der by means of a bulk solids cooling
apparatus, and then
extruding the cooled free-flowing powder to effect massing, screening, and
shaping of the
silicone rubber composition into a form suitable for its intended use. The
catalyst may be
added to the silicone rubber composition at any stage after the cooling step,
that is to the free-
flowing powder, during the massing of the free-flowing powder, or as a
separate mixing step,
by for example, an in-line distributive mixer attached to the exit of the
extruder.
[0009] Link et al., U.S. Pat. No. 3,824,208, teach a process for producing a
free-
flowing particulate polymer mixture comprising a filler and a polymer having a
viscosity
from 1 x 103 to 2 x 108 centipoise at 25oC.
[0010] Bilgrien et al., U.S. Pat. No. 5,153,238, teach storage stable and gel-
free
_ organosiloxane compositions in the form of flowable powders prepared by
blending a high
polydiorganosiloxane into a quantity of fluidised reinforcing filler that is
heated to a
temperature of from 100oC to 200oC prior to or immediately following
introduction of the
polydiorganosiloxane. The silica filler is typically treated with an anti-
creping agent either
prior to or during this blending process. The resultant mixture is heated
while being
subjected to shearing forces that reduce its average particle size to achieve
a flowable powder.
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[0011] Mueller, U.S. Pat. No. 5,167,274, teaches a bulk solid cooling
apparatus
suitable for cooling free-flowing solid particulates.
[0012) Saxton, U.S. Pat. No. 3,006,029; Gale, U.S. Pat. No. 4,419,014; and
Fukumizu
et' al., U.S. Pat. No. 4,695,165; all described mixing/extruding devices which
may have use in
the present integrated process.
[0013] In a first embodiment of the invention there is provided a method for
adding~a
high viscosity compound into a mixer comprising inverting a container having a
flexible inner
liner bag, secured at an open end of the container and containing a high
viscosity compound,
over a delivery device positioned to deliver the high viscosity compound into
a mixer thereby
causing the high viscosity compound to transfer from the bag through the
delivery device into
the .=~:-ixer.
[0014] The method for adding the high consistency compound, which may for
example be a high viscosity polydiorganosiloxane goon, to a mixer comprises
inverting a
container having a flexible inner liner bag secured at an open top end of the
container and
containing a high consistency polydiorganosiloxane gum over a delivery device
positioned to
deliver said high consistency polydiorganosiloxane gum into a mixer thereby
causing the high
consistency polydiorganosiloxane gum to transfer from the bag through the
delivery device
into the mixer. In a preferred method the tapered delivery device contains one
or more
control rods positioned therein to control the rate of transfer of the high
consistency
polydiorganosiloxane gum into the mixer.
[0015] _ . It is a major problem when working with high consistency compounds
that
they do not flow and as such they may be difficult and bulky to transport and
transfer from
one container to another. One of the main advantages of the present invention
is that a high
consistency compound can be introduced into a mixer solely relying upon
gravity for energy
as no additional force is required.
(0016] The container containing the inner liner may be any of those containers
typically used for holding high consistency polydiorganosiloxane gum. The
container may be
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for example, a plastic drum, a metal drum, or fiber pack. It is preferred that
the container be
straight walled with a full cross-sectional opening, such as an open type drum
or fiber pack.
The container is fitted with a flexible bag-shaped inner liner. The liner can
be formed from
any, sufficiently strong impermeable material, such as polyethylene or a
flexible plastic or
rubber coated fabric liner. A rubber coated fabric liner is preferred. The
liner is attached at
the upper rim of the container only i.e, on the rim adjacent to the full cross-
sectional opening,
so that it is free to extend out of the inverted container when in use with
said bag everting as
it is drawn out of the container by the polydiorganosiloxane. As the liner is
drawn out a
peeling action occurs between the liner and the polydiorganosiloxane so that
the entire load of
the drum drops cleanly away from the liner under,gravity as the bag everts. If
the high
consistency polydiorganosiloxane gum were placed in the container without the
inner liner,
inverting the container would result in the high consistency
polydiorganosiloxane gum
floyving out ~n the form of a viscous liquid which would take either a very
long lime or would
require substantial expensive mechanical force, thereby substantially
increasing the cost of
introducing this component into the mixer. The liner can be attached to the
top of the drum
by standard methods such as a strap or drum lid clamp.
[0017] It is preferred that the container be vented on the bottom to prevent
formation
of a vacuum when the container is inverted. In the absence of a vent a vacuum
is formed in
the space between the liner and the container as the gum and liner move out of
the container
and no means of introducing air into the space between liner and container is
otherwise
available. Given the typically large cross-sectional area of the containers
used such a vacuum
may hinder the release of the gum from the container when inverted. However in
the present
invention the intention is to transfer the gum relatively quickly into a mixer
and as such a
sufficiently large vent hole is usually provided in.order to ensure that no or
substantially no
vacuum is created, whilst the gum is being transferred into the mixer, in
order so that the gum
and liner can freely slide out of the container when the container is
inverted. The flow of air
to this vent may be regulated to help control the rate at which the load of
high consistency
polydiorganosiloxane gum will drop from the container. The vent serves a
second purpose in
the present invention in that it provides a simple means of retracting the
liner back into the
container once the gum has been introduced into the mixer by sucking the liner
back into the
container by applying, for example, a suction cup to the vent hole and
extracting the air
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between the liner and the container with a vacuum. In the absence of this
process the mere
return of the liner into the container to its starting position requires
mechanical or manual
reinserted of the liner back into the container prior to its being loaded with
gum.
[0018] Preferably the delivery device is tapered. Most preferably the tapered
delivery
device is conically shaped with the diameter of the inlet being greater than
the diameter of the
outlet. The tapered delivery device can be constructed of standard materials
such as steel,
stainless steel, plastics, and the like. The tapered delivery device may be
lined with a non-
contaminating material such as polyethylene. Furthermore, the inside surface
of the tapered
delivery device or lining therein may be treated with a low viscosity fluid to
provide a low
friction surface for the high consistency polydiorganosiloxane gum to slide on
rather than
flowing. A preferred low viscosity fluid is a polydiorganosiloxane having a
viscosity of from
1 to 1 OU00 mpa.s. T;;e size o: the tapered delivery device wili depend upon
the required
delivery rate to the mixer into which the siloxane gum is to be delivered.
General guidance as
to useful size and shape is provided in the example provided herein. The
choice of a conical
delivery device provides a relatively large opening into which the gum is
supplied from the
container and provides a smaller more precisely located opening into the
mixer. The
reduction in diameter of the gum transferred into the delivery device acts as
a means of flow
control of the gum. It takes work to deform the gum in a conical delivery
device from for
example an initial 75cm diameter opening to a 45 cm diameter exit. In the
present invention
this work is provided at least substantially by gravity.
[0019] The degree of control required for the addition of the high consistency
compound can dictate to a large extent, the geometry of the required delivery
device. Totally
different results are obtained using tapered delivery devices of differing
geometries. These
differences are generally achieved depending on the difference in diameter
between the
delivery device opening and exits. In cases where the exit of the delivery
device had the same
or only a slightly smaller diameter (d2) than the diameter of the opening of
the delivery device
(d,) (e.g. where dz is >80% of d,) gum substantially slides through the
delivery device quickly
with only minor deformation and enters the mixer as a slightly elongated lump.
It was found
that unless the addition of all the gum in a single lump were required this
method was
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typically not desirable as the mixer into which the gum was being introduced
was typically
overwhelmed by the rapid introduction of such a large volume.
(0020] In cases where d2 was in the region of 50 to 70% of d~ the gum had to
deform
substantially which caused the flow rate of the gum a ntering in to the mixer
to be slowed to a
more desirable rate. Lubrication of the inner walls of the delivery device
meant that the gum
still~slid along the wall rather than sticking, allowing for the complete
emptying of the
delivery device. In this instance at first there is a large mass of gum
pushing (gravity) from
top to cause the gum in the delivery device to deform whilst traveling through
the delivery
device. However as the gum travels through the delivery device, the mass is
reduced and the
rate will tend to slow. By locating the delivery device opening well above the
mixer opening,
the material that has passed through the delivery device opening will
typically hang above the
mixer oper~ng still attached to the material in Lhe delivery-device and
actnallyserves to arag
that material.through the delivery device opening faster than it would
otherwise move, thus
enabling the rate of flow of the gum to remain more constant than it otherwise
would. The
strand of material hanging from the delivery device opening tends to stretch
and flow at a
relatively continuous rate into the mixer. However, as the last of the
material passes through
the delivery device opening, the suspended strand falls all at once into the
mixer resulting in a
sudden increase in the rate of introduction into the mixer which is a
potential problem-.
(0021] In cases where the exit is substantially smaller than the opening (e.g.
where, d2
was < 40% of dl this results in a further reduction in diameter of the
suspended strand of
material and thereby reduces the size of the final strand of material that
falls into the mixer
but importantly using a very small exit results in the overall flow rate being
slower than
, desired.unless some form of, mechanized force is provided._ Preferably d2 is
between S0 and
70% of d, .
[0022] In a preferred method the delivery device contains one or more control
rods
positioned therein as a means of enhancing flow control of the gum. The
control rods may be
formed from standard materials, such as those used to construct the tapered
delivery device.
The number of control rods and their size and placement in the tapered
delivery device is
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selected to control the flaw of the high consistency polydiorganosiloxane gum
from the
tapered delivery device at a desired rate.
[0023] The rods are preferably utilised when a relatively even distribution of
gum is
needed to be added into a mixer because whilst for some applications it is
acceptable to
merely dump the material as a single large lump into a mixer, for others it is
or may be
important to precisely control the rate of addition. 1n relation to high
consistency
polydiorganosiloxane gum the applicants may use a fairly wide range of
acceptable flow rates
that are substantially less than would be needed to transfer a single lump but
not precise
I O enough as to require expensive mechanical metering equipment (i.e.
positive displacement
pumps). Furthermore, it is also very important in a flexible batch based
system to be able to
change from one gum to another without a time consuming cleanout or material
wasting
pur -ge.and different components n~ t_o bE added with a_ltPrn~ti~re flew
rates.
[0024] The addition of the control rods as hereinbefore described provides. an
easy
means of changing the flow rate of the gum through the delivery device.
Changing the
size/diameter of the delivery device opening would normally require the
physical replacement
of the delivery device with an alternative having a different opening and/or
exit diameter.
However, by relying on the size and number of rods to change the flow
characteristics of the
gum the need for swapping the delivery device dependent on the product being
introduced
into the mixer negates the need for replacing the delivery device but merely
requires a change
in the size I number of rods. The control rods were also found to offer some
other
advantages. Since the gum actually has to flow around them, they provide
substantial drag
and yet they have limited surface area to accumulate gum and so after the gum
has passed
_.__.____ 25, -,-through the delivery device very little_residue remains on
the_control rods.- For a given,, _ _ .__ . _ _ ~__,_
moderate opening size various combinations of rod size and quantities were
evaluated.
Typically a single large diameter rod which is suitable to slow the gurn to a
desired rate was
found to have enough residue on it as to be undesirable. A single rod small
enough to have
minimal residue did not adequately control the flow. Multiple small rods
provided adequate
control while still not accumulating significant residue. The rods tended to
provide enough
extra drag so that as the last of the material passed through the delivery
device, it tended to
continue to elongate until when it finally broke free and dropped, there was
not sudden
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increase in flow rate to the mixer. By varying the diameter, number, and
orientation of the
rods we were able to adjust how the material flowed into the mixer and balance
the average
flow rate, with the residue and the suddenness of any initial or final slug of
material being
added. Typically it was found that the optimum diameter of each rod was in the
region of 1 to
2% of the diameter of t hz exit when introducing a high consistency
polydiorganosiloxane
gum into the mixer.
[0025] General guidance as to the number of control rods and their size and
placement
are provided in the example herein. The control rods may be formed, for
example, from rigid
or cable type materials. The control rods rnay be, for example, round, oval,
or polygonal in
cross-sectional shape.
[002C] T he present mzthod is especially useful when incorporated into an
integrates
process for producing catalyst containing silicone rubber compositions,
resulting in
substantially reduced processing time and labour input compared to standard
methods for
producing such compositions.
[0027] Hence, in a further embodiment of the invention there is provided an
integrated process for forming a catalyst containing silicone rubber
composition comprising
the steps of
(A) adding a high consistency polydiorganosiloxane gum to a mixer by
inverting a container having a flexible inner liner bag secured at an
open top end of the container and containing a high consistency
polydiorganosiloxane gum over a delivery device positioned to deliver
_ . _. _ the high consistency polydiorganosiloxane guru into the mixer thereby
-.
causing the high consistency polydiorganosiloxane gum to transfer
from the bag through the delivery device into the mixer,
(B) blending a composition comprising:
i) 100 parts by weight of the high consistency
polydiorganosiloxane gum,
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ii) about 10 to 80 parts by weight of a treated or untreated
reinforcing silica filler,
and when said reinforcing filler is untreated
5
iii) about 10 to 45 weight percent, based on the weight of the
reinforcing silica filler, of a treating agent for the reinforcing
silica filler
10 by introducing the filler into a mixer (1) and maintaining said filler in a
highly turbulent,
fluidized state at a temperature of from 80oC to about 350oC, maintaining the
temperature
and the filler in the highly turbulent fluidised state while introducing the
high consistency
polydiorgamosiioxane gum and subjecting the resulting mixture to a shearing
force sufficient
to achieve an average particle size of from 1 to 1000 microns thereby forming
a flowable
organopolysiloxane powder composition, and when required, introducing said
treating agent
into the mixer prior to, during, or after addition of the high consistency
polydiorgamosiloxane gum,
(C) directly transfernng the flowable organopolysiloxane powder
composition to a bulk solids cooling device and facilitating accelerated
bulk cooling thereof to a temperature below the decomposition and/or
activation temperature. of a catalyst added in step (D),
(D) feeding the bulk cooled flowable organopolysiloxane powder
composition to a massing apparatus and massing the
_. _ . organopolysiloxane composition therein at a temperature below the-
decomposition and/or activation temperature of a catalyst added in step
(E) adding a catalytic amount of a catalyst to the organopolysiloxane
composition either prior to, during, or after step (C) at a temperature
below the decomposition and/or activation temperature of the catalyst.
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[0028] It is to be understood that a massing step as referred to in the
present invention
comprises the conversion of a divided solid or powder into a single piece, or
mass, by
compression and mastication%kneading.
[0029] The resulting composition may then be recovered as a catalyst
containing
silicone rubber composition mass by any appropriate means. The present process
is an
integrated process. By "integrated" it is meant that steps subsequent to the
batch formation of
the powdered organopolysiloxane composition in step (B) are conducted in a
continuous
mode without manual handling of the organopolysiloxane composition until after
massing
and preferably after addition of a catalyst and massing.
[0030] Step (B) of the present process is conducted by adding at least a
portion of the
reinforcing silica filler to a high shear mixer and maintaining the fiiier in
a highly turbulent
fluidised state at a temperature of from 80oC to about 350oC. It is important
that the
temperature of the fluidised silica be maintained at..a temperature-of
80°C.or greater during
step (B) both to facilitate treatment of the filler with the treating agent
and to reduce the
formation of gels. Preferred is when the temperature within the mixer is
maintained within a
range of from about 90oC to 180oC. _
[0031] Any mixing apparatus capable of maintaining the reinforcing filler in a
fluidised state while blending the filler with the high consistency
polydiorganosiloxane gum
and applying sufficient shear to reduce the size of the resultant filler-
coated polymer particles
to a uniform powder may be used. Suitable mixers include but are not limited
to Waring~
blenders containing a high speed shearing blade at the bottom of a vertically
oriented conical
- chamber, mixers manufactured by Rheinstahl Henschel~AG, Kassel, Germany, and
mixer/granulators manufactured by Littieford Bros. Inc. Florence KY. Preferred
mixers for
use in the present process are the mixerlgranulators manufactured by
Littleford Bros. Inc.
Such mixers and their use to form powdered silicone compositions are
described, for
example, in Link et al., U.S. Pat. No. 3,824,208 and Bilgrien et al., U.S.
Pat. No. 5,153,238
which are hereby incorporated by reference for their teachings regarding such
use. These
mixers are referred to as "plough" or "ploughshare" mixers due to the presence
of at least one
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triangular or "T" shaped "plough" blade located in a horizontally oriented
cylindrical mixing
chamber. The plough blade rotates on the horizontal axis of the chamber with
the edge of the
blade close to the perimeter of the chamber. In addition to maintaining the
silica in a
fluidised state and uniformly dispersing the polymer particles throughout the
silica to achieve
a homogeneous blend, the plough blade is also believed to agglomerate the
particles produced
by the high speed shearing blade(s), also referred to as chopper blades,
present in the chamber
to achieve the desired final particle size.
[0032] The speed of the plough blade required to maintain the silica in a
fluidised
form is typically from about 30 to about 200 revolutions per minute (rpm) and
is dependent
upon the capacity of the mixing chamber and the particle size range desired
for the final
powder. A speed of from 80 to 180 rpm is preferred using a 130 litre capacity
mixing
chauwber. The speed would be proportionately slower for a larger capacity
mixer.
[0033] The mixing chamber also contains at least one high speed chopping blade
to
provide the shearing force required to reduce the particle size of the high
consistency
polydiorganosiloxane gum to a fine powder. In one preferred embodiment the
mixing
chamber preferably contains at least one conical array of five blades rotating
on a single shaft,
said blades ranging in diameter from 1 S to 23 cm, the smallest diameter blade
being located
closest to the mixer wall.
[0034] Preferably the speed of the chopping blades) should be from about 2000
to
about 4000 rpm to prepare the powdered silicone rubber composition of step
(B), with a
processing time of up to 30 minutes. The processing time period will vary
depending upon
25_ . the radius of the blades) and the volume of material in the mixer.
Smaller diameter blades
typically must rotate at a higher speed to impart the same level of shear to
the mixture present
in the mixer. To minimize processing time it is preferable to use the longest
chopper blades
that will not interfere with rotation of the plough blades located on either
side of the chopper
blades
[0.035] In a preferred embodiment of the present process, to reduce the
capacity of the
mixing chamber required to prepare a given amount of the blend, only a portion
of the filler is
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added initially, due to the large increase in filler volume during
fluidisation. This volume
decreases substantially as the silica densifies and coats the high consistency
polydiorganosiloxane gum in the mixing chamber. The remaining filler is
initially placed in a
hopper or other suitable dispensing container and allowed to drop into the
chamber as the
volume of silica initially present in the mixer decreases due to coating of
high consistency
polydiorganosiloxane gum particles.
[0036] The high consistency polydiorganosiloxane gum is added to the mixer,
after at
least a portion of the reinforcing silica filler has been added to the mixer
and fluidised and the
required temperature of the fluidised silica has been established, by means of
the method for
adding high consistency polydiorganosiloxane gum described above. The high
consistency
polydiorganosiloxane gum is added to the mixer as a single shot of one or more
masses
w~ghing ~sp to about 100 kg each, with the rate of addition and size of mass
entering the
mixer being primarily controlled by the tapered delivery device and any
control rods
positioned therein. The mass of high consistency polydiorganosiloxane gum
added to the
mixer is rapidly reduced by the shearing action of the mixer, which in the
case of the
Littleford-type mixer is provided by the chopper blades. The blending of the
reinforcing
silica filler with the high consistency polydiorganosiloxane gum is continued
until the
shearing force is sufficient to achieve an average particle size of from about
1 to 1000
microns thereby forming an organosiloxane composition in the form of a
flowable powder.
The length of time required to achieve such a particle size can vary from
about 2 minutes to
about 50 minute after addition of the high consistency polydiorganosiloxane
gum, depending
at least in part on the capacity of the mixer chamber and the shear force
provided by the
mixer.
_ .. _ _ _ _ . _ .. ._ _ . .
[0037) In the preferred process using a Littleford-type mixer the reduction
and
subsequent increase in the particle size of the high consistency
polydiorganosiloxane gum that
occurs during step (B) may be monitored by plotting the amount of electrical
power
consumed by the motors) driving the chopper blades as a function of time. This
method of
assessing the particle size of the high consistency polydiorganosiloxane gum
is described in
Bilgrien et al., U.S. 5,153,238 which is hereby incorporated by reference.
"~~'' ~''k~'' ~f N'~ ~ CA 02468070 2004-05-19 ~v
F RI%F~~~~~~.'i ~~~Sh YES tip ~ F 6
[0038] In step (B) after the reinforcing silica filler is fluidised and the
required
temperature established the treating agent may be added prior to, during, or
after addition of
the high consistency polydiorganosiloxane gum. Preferably when the treating
agent is added
during blending of the high consistency polydiorganosiloxane gum with the
fluidized
S reinforcing silica filler.
[0039] In the present integrated process when the desired particle size has
been
achieved, as indicated from the power consumption curve or by visual
examination of the
product, the powdered organopolysiloxane composition at a temperature of 80oC
or higher is
directly transferred to a bulk solids cooling device to facilitate accelerated
cooling of the
powdered organopolysiloxane composition to a temperature below the
decomposition and/or
activation of a subsequently to be added catalyst. The bulk solids cooling
device may be any
of those known in the art capable of facilitating the cooling of the powdered
organopolysiloxane composition. The term "facilitate" is used to distinguish
step B of the
1 S integrated process according to the present invention from those
situations where the bulk
powder of high consistency polydiorganosiloxane gum is allowed to cool
relatively
undisturbed under ambient conditions. Typically, although the powdered
organopolysiloxane
composition is free-flowing at this point it is somewhat sticky and easily
massed if significant
compaction occurs. Therefore, in choosing a bulk cooling device to facilitate
cooling of the
powdered organopolysiloxane compositions it is important to consider these
characteristics of
the powder. Suitable bulk cooling devices include, for example, belt coolers,
jacketed mixers
such as the above described Littleford-type mixer, fluidised mixers through
which cooling air
may be blown, and flow-through apparatus having one or more coating elements
positioned
therein. A preferred bulk solids cooling device is that described in Mueller,
U. S. Pat.
2S 5,167,274 which is hereby incorporated by reference.
[0040] Optionally, a means adapted to eliminate or reduce Lumps, large
particles
andlor agglomerates which could clog or otherwise compromise the capacity of
the bulk
solids cooling device may be positioned in the flow path between the mixer of
step (B) and
the bulk solids cooling device. Said means may be of any appropriate design,
for example a
powder mill, chopper or the like. One example of such a means useful in the
present process
Allf~ll~J~ECl SHEET:
~H,r~y~~~r ~~"~I:
k ~;~ r,.
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N
is described in Lynch et al, U.S. Pat. No..4,768,722 which is hereby
incorporated by
reference.
[0041] After the powder of high consistency polydiorganosiloxane gum has been
cooled to a temperature below the decomposition and/or activation temperature
of the catalyst
to be .added in subsequent steps, the powder is fed directly to a massing
apparatus suitable for
forming the powder into a coherent mass. Preferably the massing apparatus is a
single or
twin screw extruder capable of massing the powdered high consistency
polydiorganosiloxane
gum composition without generating significant heat. Most preferred are those
single screw
1 U extruders typically referred to as "cold feed" silicone rubber extruders
such as manufactured
by National Feed Screw {Massilon, OH) and Davis Standard (Mystic, CT). In a
preferred
process the exit end of such an extruder is fitted with a screen to strain out
particulates that
may >3e present i : the massed silicone rubber composition.
[0042] The catalyst may be added to the process anytime after the cooling step
(C);
that is, after step (C) and before step (D), during step (D), or after step
(D). The catalyst may
be proportioned between two or more of the above described addition points.
Because the
preferred extruders for use in step (D) typically have poor mixing
capabilities, it is preferred
that the catalyst be added in a mixing step conducted after step (D). In the
preferred
integrated process, a mixing device is coupled directly to the exit end of the
barrel of the
extruder of step (D). Any Iow temperature distributive-type mixing devices
known in the art
may be used for this mixing step. Such mixing devices are described, for
example, in
M.IxING IN POLYMER PROCESSING, Ed. By Rauwendaal, Marcel-Dekker, Inc., NY,
1991, pp. 164-187, in Gale U.S. Pat. No. 4,419,014, and in Saxton U.S. Pat.
No. 3,006,029.
_. 25 A preferred mixer for use in the present process is a cavity transfer
type mixer as described in.
the above citations which are hereby incorporated by reference. In the
preferred process the
catalysed silicone rubber composition is shaped into a suitable form for
shipping and handling
by means of a die positioned at the exit end of the extruder or when a
separate mixer is used
at the exit end of the mixer.
[0043] A catalyst containing silicone rubber composition mass is obtained from
the
present process. In the preferred process the massed silicone rubber
composition is extruded
~lMiwN,Q~f~~=a~~~Tj
_.,_... _...._-~ > ... ~~~.,~,,~
CA 02468070 2004-05-19 ~wur ~ ~,..'. ~~
16
',_
from the mixer into a size and configuration suitable for further processing
in moulding and
extruding applications. The final size and configuration of the material
produced by the
present process is not critical and will be generally dictated by the
requirements of the final
use of the composition.
S
[0044) Step (B) of the present process involves adding about 10 to 80 parts by
weight
of a reinforcing silica filler for each 100 parts by weight of the high
consistency
polydiorganosiloxane gum introduced in Step (A). Such reinforcing silica
fillers are well
known in the art and may be any of those finely divided silicas having a
surface area greater
than about 50 m2/g and include fumed silica, precipitated silica, and silica
gels. The
preferred silica is a fumed silica having a surface area within a range of
from about 75 m2/g
to 1000 m2lg. Preferred is when about 20 to 50 parts by weight of the
reinforcing silica filler
per 100 parts by weight of the high consistency polydiorganosiloxane guru is
addedyto the
present~process in step (A). Preferably the reinforcing silica filler is
introduced into the mixer
__in an untreated form .but..it may alternativel-y have.been pretreated -using
treating agents as
described below prior to introduction into the mixer.
[0045] Preferably the high consistency polydiorganosiloxane gum, which is the
major
component of the silicone rubber composition formed by the present process has
a viscosity
in a range of from about 6 x 104 to 1 x 108 mPa.s at 25oC. More preferably the
high
consistency polydiorganosiloxane gum has a viscosity in a range of from about
1 x 106 to 1 x
10~ mPa.s at 25°C.
[0046] _ The high consistency polydiorganosiloxane gum may be represented.by
the
general formula R3(RlR2Si0)nR3 where R1, R2, and R3 are each independently
selected
monovalent substituted or unsubstituted hydrocarbon groups and n, the average
number of
repeating units in the polymer, is selected to provide a viscosity within the
ranges described
above. The monovalent hydrocarbon groups represented by R1, R2, and R3 include
alkyl and
substituted alkyl groups containing from 1 to about 20 carbon atoms, alkenyl
groups such as
vinyl and 5-hexenyl, cycloalkyl groups such as cyclopentyl and cyclohexyl, and
aromatic
,~~'" -"' '~ r" ~ ' CA 02468070 2004-05-19
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hydrocarbon groups such as phenyl, benzyl and tolyl. R1, R2, and R3 may be
independently
substituted with, for example, substituents such as halogens, alkoxy groups,
and cyano
groups. Preferred monovalent hydrocarbon radicals are selected from the group
consisting of
alkyl groups comprising from 1 to 4 carbon atoms, alkenyl, phenyl, and 3,3,3-
trifluoropropyl.
Most preferably each R1 is independently selected from the group consisting of
methyl and
alkenyl groups comprising from 1 to S carbon atoms, R2 is methyl, and R3 is
selected from
the group consisting of methyl and alkenyl groups comprising from l to 5
carbon atoms. The
high consistency polydiorganosiloxane gum may be a homopolymer, a copolymer or
a
mixture containing two or more different homopolymers andlor copolymers. The
high
consistency polydiorganosiloxane gum may be, for example, trimethylsiloxy end-
capped
polydimethylsiloxane, vinyldimethylsiloxy end-capped polydimethylsiloxane,
vinyldimethylsiloxy end-capped polydimethyl/vinylmethylsiloxane copolymer, and
trimethylsiloxy end-capped polydimethyl/vinylmethylsiloxane copolymer.
_ 15 .(0047] Providing.-the reinforcing silica filler has not been pretreated,-
step-(B) also
requires the addition of a treating agent for the reinforcing silica filler.
The treating agent
may be any of those typically used to treated reinforcing silica fillers to
make them more
hydrophobic and to reduce or prevent a phenomena typically referred to as
"creping" or
"crepe hardening" that often occurs when mixture of such fillers and
polydiorganosiloxanes
are stored for any appreciable period of time. Creping is characterized by a
gradual increase
in the viscosity or decrease in the plasticity of such polydiorganosiloxane
compositions.
Although such crepe hardening may often be reversed by subjecting the
composition to
shearing forces using a rubber mill or sigma blade mixer, this adds an
additional process step
in the use of the composition and such step is preferably avoided.
[0048) Compounds which may be used as treating agents for the reinforcing
silica
fillers include, for example, liquid low-molecular weight silanol or alkoxy-
terminated
polydiorganosiloxanes, hexaorganodisiloxanes, hexaorganodisilazanes, cyclic
diorganosiloxanes, and partial hydrolyzates of such compounds. Preferred
treating agents for
use in the present process are a low molecular weight hydroxy end-blocked
polydimethylsiloxane fluid or a reaction product of a low molecular weight
(LMW) hydroxy
CA 02468070 2004-05-19
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end-blocked polydimethylsiloxane fluid and/or a LMW hydroxy end-blocked
phenylinethylsiloxane fluid and/or a LMW hydroxy end-blocked
methylvinylsiloxane fluid
which reaction may be catalysed using ammonium hydroxide or ammonium
carbonate.
[0049] The treating agent may be utilized in any appropriate amount that
reduces or
prevents crepe hardening of the silicone rubber composition prepared by the
present method.
Generally, a useful amount of treating agent is about 10 to 45 weight percent
based on the
weight of the reinforcing silica filler. Preferred is when about 15 to 35
weight percent of the
treating agent is added in step (B) of the present process, based on the
weight of the
reinforcing silica filler.
[0050] In addition to the above described components (B)(i-iii), optional
components
ma_y i3P. added .d,;~~;u g step ~) depe~~ding upon the properties desired in
the cured silicone
elastomer prepared from the process. Such optional components include
extending fillers
such as treated andlor untreated quartz, calcium carbonate, hydrated alumina
and
diatomaceous earth; pigments such as iron oxide and titanium oxide;
electrically conducting
fillers such as carbon black and finely divided metals; heat stabilizers such
as hydrated cerric
oxide; flame retardants such as antimony compounds, hydrated aluminium oxide;
magnesium
compounds and halogenated hydrocarbons; adhesion promoters; internal mould
release agents
such as zinc stearate and resinous organosiloxane copolymers as reinforcing
agents. The
treated extending fillers are typically treated with the agents described for
the treatment of the
reinforcing fillers.
[0051] The catalyst added to the present process is preferably either an
25_ organoperoxide type catalyst or a hydrosilylation catalyst, but is most
preferably an
organoperoxide catalyst.
(0052] Any suitable organoperoxide which is effective as a catalyst for the
curing of
silicone compositions may be used. The organoperoxide catalyst may be vinyl
specific and
require the presence of vinyl or other alkenyl groups substituted on the
polydiorganosiloxane
polymers. The organoperoxide may be non-vinyl specific, and react with
hydrocarbon groups
bonded to silicon atoms of the high consistency polydiorganosiloxane gum to
generate a free
;~.~r .t,~ ~r.~1 '~n ; ~ ~ g:~ ~T
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radical at which cross-linking may be effected_ The organoperoxide catalyst
may include di-
tertiary butyl peroxide, tertiary-butyl-triethylmethyl peroxide, tertiary-
butyl-tertiary-butyl-
tertiary-triphenyl peroxide, t-butyl perbenzoate and di-tertiary alkyl
peroxides such as
dicumyl peroxide and 2,5-bis(tert-butyl peroxy)-2,5-dimethylhexane. Other
suitable
organoperoxide catalyst which effect curing through sa~~;rated as well as
unsaturated
hydrocarbon groups on the siloxane chains are aryl peroxides such as tertiary-
butyl
perbenzoate, chloroalkyl peroxides such as 1,3-dichlorobenzoyl peroxide, 2,4-
dichlorobenzoyl peroxide, monochlorobenzoyl peroxide, benzoyl peroxide,
bis(ortho-
methylbenzoyl) peroxide, bis(meta-methylbenzoyl) peroxide, bis(para-
methylbenzoyl)
peroxide, or a similar monomethylbenzoyl peroxide, bis(2,4-dimethylbenzoyl)
peroxide, or a
similar dimethylbenzoyl peroxide, bis(2,4,6-trimethylbenzoyl) peroxide, or a
similar
trimethylbenzoyl peroxide. A preferred organoperoxide catalyst is selected
from the group
consisting of 2,4-dichlorobe:.zoyl peroxide an3 2,5-bis(tertiarybutyl peroxy)-
2,5-dimeihy't
hexane.
[0053] In the case of an organoperoxide catalyst, the catalytic amount of the
organoperoxide catalyst is that sufficient to effect cure of the
organopolysiloxane composition
when heated above the decomposition temperature of the organoperoxide.
Generally, about
0.1 to 10 weight percent of the organoperoxide may be added to the
organopolysiloxane
composition, based upon the weight of the organopolysiloxane composition.
[0054] Alternatively, providing the high consistency polydiorganosiloxane gum
contains two or more alkenyl groups per molecule, for example, vinyl groups,
curing of the
composition made in accordance with the process of the invention may be
carried out via an
., addition curing reaction using a catalyst comprising a platinum catalyst in
combination with a
polyorganosiloxane having at least two silicon-bonded hydrogen atoms per
molecule. The
platinum catalyst may be exemplified by the following: a fine-powdered
platinum,
chloroplatinic acid, alcohol-modified products of chloroplatinic acid,
platinum chelates, a
complex of platinum and diketone, coordination compounds of a chloroplatinic
acid and
olefins, a complex of a chloroplatinic acid and an alkenylsiloxane, The
platinum catalysts
may optionally be on an appropriate carrier such as alumina, silica, carbon
black or may be
encapsulated within at least one layer of a thermoplastic polymer selected
from the group
4~ ~~~ ref ~~~~;E% t
~~e ~~ ~~ CA 02468070 2004-05-19
consisting of organic polymers and polyorganosiloxanes. The most preferred
platinum
catalyst is a complex of a chloroplatinic acid and an alkenyl siloxane having
a very high
catalytic activity in a hydrosilylation reaction such as the platinum-
alkenylsiloxane complex
disclosed US 3419593 or a spherical fine-powdered catalyst composed of a
thermoplastic
resin that contains more than 0.01 wt.% of metal platinum atoms. The platinum
catalyst is
preferably used in an amount of 0.01 to 500 and more preferably 0.1 to 100
parts by weight
based on 106 parts by weight of the component A.
[0055] Polyorganosiloxanes having at least two silicon-bonded hydrogen atoms
per
molecule may be exemplified by the following compounds: trimethylsiloxy
terminated
polymethylhydrogensiloxane, a trimethylsiloxy terminated copolymer of
methylhydrogensiloxane and dimethylsiloxane, a copolymer of a
dimethylhydrogensiloxy
ter!tinated rzetl:~~;s?:y3.~oge~~siloxane ar~d dimethylsiloxane, a copolymer
of a
methylhydrogensiloxane and a cyclic dimethylsiloxane, an organopolysiloxane
composed of
siloxane units expressed by the formula (CH3)3HSiOliz, together with siloxane
units, of the
formula Si04i2 or CH3Si03,z and optionally units of the formula (CH3}ZSiO2n; a
dimethylhydrogensiloxy terminated polydiorganosiloxane, a
dimethylhydrogensiloxy
terminated copolymer of methylphenylsiloxane and a dimethylsiloxane, a
dimethylhydrogensiloxy terminated copolymer of methyl (3,3,3-trifluoropropyl)
siloxane and
dimethylsiloxane, or combinations of two or more of the above_ It is preferred
that the
viscosity of the polyorganosiloxane having at least two silicon-bonded
hydrogen atoms per
molecule at 25°C is within a range of 2 to 100,000 rnPa.s. Preferably
the polyorganosiloxane
having at least two silicon-bonded hydrogen atoms per molecule is added in
amount such that
the ratio of the total mole number of silicon-bonded hydrogen atoms to the
total mole number
25_ of alkenyl groups in the component A is in the range of from 0.5:1 to
20:1. -The-
polyorganosiloxanes having at least two silicon-bonded hydrogen atoms per
molecule may be
introduced into the composition during step B prior to, during, or after
addition of the high
consistency polydiorganosiloxane gum, or any time after the completion of step
C.
[0056] In the case where the catalyst is a platinum catalyst the composition
preferably
also includes one or more cure retarders which are preferably introduced into
the composition
before and/or simultaneously with the addition of the platinum catalyst.
Examples of suitable
~ ~ .~ f ~E , e;f j>ML '~ .Yt
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cure retarders include alkvne alcohols such as 3-methyl-1-butyn-3-vl, 3,S-
dimethyl-1-hexyn
3-0l, and 3-phenyl-1-butyn-3-ol; ene-yne compounds such as 3-methyl-3-penten-1-
yne and
3,5-dimethyl-3-hexen-1-yne; tetramethyltetrahexenylcyclotetrasiloxane, and
benzotriazole.
[0057] In a further embodiment of the invention there is provided a means for
adding
a high viscosity compound into a mixer comprising:-
a container having a closed end and an open end, a flexible inner liner bag
secured at the open
end of the container, which bag is adapted to receive an amount of a high
viscosity compound
and a delivery device, having an inlet and an outlet, wherein the delivery
device is adapted to
1 U receive high viscosity compound from the bag when the open end of said
container is placed
in communication with the inlet of the delivery device and deliver said high
viscosity
compound into a mixer.
[0058] In a still further embodiment of the invention there is provided an
apparatus
suitable for use in the integrated process as hereinbefore described. The
apparatus comprising
a means for adding a high viscosity compound into a mixer comprising:-
i) a container having a closed end and an open end, a flexible inner liner bag
secured at the open end of the container, which bag is adapted to receive an
amount of a high viscosity polymer and a delivery device having an inlet
and an outlet, wherein the delivery device is adapted to receive high
viscosity polymer from the bag when the open end of said container is
placed in communication with the inlet of the delivery device and deliver
said high viscosity polymer into a high-shear mixer,
25.. _ . _ ... a. _ a high.-shear mixer, . . _ _ _ _ _
b. a bulk solids cooling device and
c. a massing apparatus,
said mixer having a plurality of inlets, an outlet, a motor and one or more
high shear blades,
said motor being adapted to provide rotational energy to said high shear
blades contained
therein, and thereby fluidise powder introduced into the mixer through one or
more of said
inlets, the mixer is additionally adapted to receive high viscosity polymer
through a polymer
n;! ~E ~v~~ ; a~
CA 02468070 2004-05-19
"~ a I~W,..* ,F n 1~
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feed port from the container by way of the delivery device, for mixing with
said fluidised
powder to form a flowable powder, and a treating agent through one or more of
said inlets,
said bulk solids cooling device has an inlet and an outlet, the bulk solids
cooling device inlet
is adapted to receive flowable powder from said mixer, which powder is cooled
in the cooler
and subsequently transported from said bulk powder cooler exit to said massing
apparatus
which is adapted to mass any powder which has been cooled in said bulk solids
cooling
device, said apparatus being adapted to enable the introduction of one or more
additives into
free flowing powder prepared in mixer before, during or after cooling.
[0059) The invention will now be described by way of example and with
reference to
the Figures in which:-
Figure 1 is a schematic representation of an equipment configuration suitable
for delivering a
high viscosity poly:::er into a mixer; as~d
Figure 2 is a schematic representation of an equipment configuration suitable
for practising
the integrated process of the present invention utilizing the described high
consistency
polydiorganosiloxane gum delivery method.
[0060] With reference to Figure 1, there is provided a container in the form
of drum
10 which has a vent hole 11 and an inner liner bag 12. Imer liner bag 12 is
adapted to receive
an amount of high viscosity organopolysiloxane and is attached to the top of
drum 10 by
securing band 14. There is also provided a tapered delivery device 1 S having
an inlet 20 and
an outlet 21. The tapered delivery device 15 is comically shaped with the
diameter of the inlet
being greater than that of the outlet. Positioned in tapered delivery device 1
S are two control
rods 16 which are both perpendicular to each other and perpendicular to the
vertical axis of
tapered deliver device 1S. _ _ _ _ _ .-
[0061] In use high consistency organopolysiloxane in drum 10 is retained in
inner
liner bag 12, such that none of the high consistency polydiorganosiloxane gum
is in contact
with the drum 10 during storage. When the aforementioned high consistency
polydiorganosiloxane gum is required to be added into a mixer, such as mixer 1
in Figure 2,
drum 10 is upturned and placed over or in communication with inlet 20 of
tapered delivery
device 15. The high consistency polydiorganosiloxane gum leaves the drum and
passes
""' y~ '~ ~ CA 02468070 2004-05-19
23
,f,c ,
«r
through inlet 20 of delivery device 15. As the high consistency
polydiorganosiloxane gum
exits from drum 10 it draws liner 12 out from the interior of drum 10 causing
the liner to
event, as depicted in Figure 1. The high consistency polydiorganosiloxane gum
subsequently
passes through delivery device 15 and out through exit 21 and into a mixer
passing control
rods 16.
[0062] In Figure 1, liner 12 is illustrated exiting drum 10 and peeling away
from high
consistency polydiorganosiloxane gum 13 thereby effecting delivery of high
consistency
polydiorganosiloxane gum 13 to tapered delivery device 15.
[0063] The present method is especially useful when incorporated into an
integrated
process as depicted in Figure 2 for producing catalyst containing silicone
rubber
compositions, resulting in substantially reduced processing time and labor
input compared to
standard methods for producing such compositions. Referring to Figure 2 there
is provided a
preferred equipment configuration suitable for practising the present
integrated process for
manufacturing a catalyst containing silicone rubber composition, in this case
an
organoperoxide catalyst containing silicone rubber composition comprising the
apparatus for
adding high consistency polydiorganosiloxane gum to a high shear mixer 1. High-
shear
mixer 1 has attached thereto motor 2 for providing rotational energy to high
shear blades
contained therein (not shown), silica hopper 3, polydimethylsiloxane feed port
4 to which is
fitted delivery device 15 and feed port 5 for feeding the treating agent for
the silica filler and
optional ingredients as described herein. In the bottom of high-shear mixer 1
is an exit port
connected to powder mill 6. Powder mill 6 empties into bulk solids cooling
device 7. Bulk
solids cooling device 7 feeds into extruder 8 which has attached at its exit
end mixer 9. In use
Mixer 1 is initially heated to a temperature of above 80°C subsequent
to which silica is fed
into mixer 1 from hopper 3 and, when required, extending filler is introduced
into mixer 1
from feed port 5 and the fillers) is/are fluidised by means of the high shear
blades driven by
motor 2. After a short heating and fluidising period the high consistency
polydimethylsiloxane is introduced into mixer 1 through feed port 4 by way of
delivery
device 15 and treating agent is introduced into mixer 1 through feed port S.
After a further
predetermined period of time the pressure in mixer 1 was reduced in order to
extract any
remaining volatile species. Once the volatile species had been drawn off the
resulting
CA 02468070 2004-05-19
24
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c~.
powdered rubber base «~as passed through powder mill 6 to remove large
aggregates and into
bulk solids cooling device 7 in order to cool the powdered rubber base. Cooled
silicone
rubber base, upon exiting cooling device 7 was transferred into silicone
rubber extruder 8 and
the cooled silicone rubber base was massed and subsequently discharged through
exit 9, with
organoperoxide catalyst having been introduced therein through an entry port,
(not shown) in
extruder 8.
[0064] A 325 liter fiber pack drum fitted with a rubber coated fabric liner
was filled
with a vinyl-functional polydimethylsiloxane having a viscosity within a range
of 1 x 106 to 1
x 107 mPa.s at 25°C. The weight of polydimethylsiloxane placed in the
drum is reported in
Table 1. The drum was inverted over a tapered delivery device. The tapered
delivery device
was formed from sheet metal and was approximately 152 cm tall, 101 cm in
diameter at the
top, and 43 cm diameter at the boiiom. T he wail of the Tapered delivery
device was lI
degrees from vertical forming a 22 degree included angle. For some of the runs
reported in
. 15 Table 1 the tapered delivery device was fitted with an. extension that
extended the length by
28 cm, resulting in a 33 cm bottom opening. The tapered delivery device was
lined with
polyethylene sheets. The surface of the polyethylene sheets was sprayed with
polydimethylsiloxane fluid having a viscosity of 40 mPa.s at 25°C to
provide a low friction
surface. Holes were placed near the bottom opening of the tapered delivery
device to allow
control rods to be inserted across the opening to alter the flow of the
polydimethylsiloxane
therethrough. The bottom of the tapered delivery device was positioned about 2
meters above
a receiving container. Results using various delivery device openings, rod
sizes and
configurations, and polydimethylsiloxane loadings are given in Table 1.
Initial time is the
elapsed time from when the polydimethylsiloxane was added to the tapered
delivery device
--___ _ 25- _-until-it.began to enter. the receiver container.-Final-time is
the elapsed time from when the-- ----- -------
polydimethylsiloxane was added to the tapered delivery device until delivery
to the receiver
container was essentially complete. The Rate of delivery to the receiver
container is given in
Kg/h. Residual is the amount of added polydimethylsiloxane retained in the
drum and tapered
delivery device. Also given in Table 1 are control rod diameters and numbers
and their
positioning relative to each other (p = parallel, c=crossed).
~F r '~~ ~~ ~~f;w s
CA 02468070 2004-05-19
4.
Table 1
Opening PDMS Rod Rod Rod Initial Final Rate Residual
Size Wt. Dia. Quart. Config. Tirne Time (kg/hr.) (kg)
(cm) (kg) {mm) (sec) (sec)
33 182 6.35 2 p 40 106 165 0.09
33 182 9.52 1 - 34 66 340 0
43 182 9.52 Z c 27 62 311 0.34
43 I82 6.35 2 c 25 36 990 0.03
43 182 9.52 1 - 15 17 5498 0.03
43 304 3.17 2 p 30 83 344 0.45
9.52 1 c
43 304 6.35 2 p 30 127 188 1.91
9.52 1 c
43 _ 304 3.17 3_ .p _ 30 ._ 116 21.2 -0:02
1 c _ .
