Note: Descriptions are shown in the official language in which they were submitted.
213665~
F~FRn OF T~F, TNVFNTION
The present invention relates to a process to convert a stable
particulated syrup comprising a continuous resin phase and a
discontinuous rubber-like composite phase to a (post inversion) metastable
syrup typically comprising co-continuous resin- and rubber-like composite
phases.
Still later in the process the metastable co-continuous resin and
rubber-like composite phase may be particulated to form a stable dispersed
rubber-like composite phase in a syrup comprising a continuous resin
phase.
RA(~K(~R()IJN~) OF T~ ~NV~,NTI()N
The field of the manufacture of impact modified plastics is
relatively old and the current industrial processes for their manufacture
are fairly well known. According to conventional technology typically a
solution of rubber, typically comprising 1 to about 20, preferably from 3
to 12 weight %, most preferably 4 to 10 weight ~ of rubber dissolved in
one or more monomers is polymerized in a first stage reactor under
3 mechanical agitation. Whether the polymerization occurs in a batch,
stirred plug flow or continuous stirred tank reactors, almost all prior art
and disclosures clearly teach that the particle size, particle size distribution
2136655
and morphology of the dispersed rubber-like composite phase of the final
product is largely determined during particulation in the early part of the
process.
Particulation is the generic term used to describe the formation of
the dispersed rubber-like composite phase regardless of its mechanism.
In the production of high impact polystyrene in a batch process or
in a stirred plug flow reactor, the rubber-like composite phase is the
continuous phase and the resin phase (monomer/resulting polymer phase)
is dispersed. Typically, in conventional processes, as the polymerization
proceeds in time with a batch reactor or in space with a stirred plug flow
reactor, at some point between S and 20 ~ conversion the system
undergoes particulation by phase inversion under the application of a shear
field generated by mechanical agitation. That is the rubber-like composite
phase becomes the dispersed phase and the resin phase becomes the
continuous phase. This does not happen instantaneously but occurs over a
considerable period of time or space, typically from 20 to 50 minutes or
reactor space which produces 2 to 8 ~ conversion. That is the rubber-
like composite phase and resin phase become co-continuous for a period
of time or space before the particulation process is complete.
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The ternary phase diagram of the styrene-polystyrene-polybutadiene
system has been well studied and is well known. For example, the phase
diagram and what happens during the polymerization of high impact
polystyrene is discussed in Kirk-Othmer, Encyclopedia of Chemical
Technology, published in 1983, Volume 21, pages 823 through 826.
In the production of high impact polystyrene in a continuous stirred
tank reactor (CSTR) the rubber phase is particulated by the mechanism of
dispersion. That is the rubber or rubber-like composite phase is dispersed
in a CSTR that is operated with a continuous resin phase.
The distinction between rubber phase and rubber-like composite
phase used in this document is as follows: The rubber phase is simply
2 o rubber dissolved in one or more monomers, while the rubber-like
composite phase refers to rubber that has been modified by reaction with
one or more monomers during polymerization. That is during
polymerization polymer chains containing one or more monomers is
grafted to the rubber molecules. In addition to graft copolymer, the
rubber-like composite phase may contain occluded polymer. Occluded
3 polymer is not grafted to the rubber molecules and resides within the
rubber-like composite phase.
21~665~
According to conventional wisdom the polymer chemist has a
limited degree of freedom concerning the process of particulation in the
manufacture of impact modified thermoplastic resins. That is
particulation is limited to the region of phase inversion in a batch process
and stirred plug flow reactors or at the point of dispersion in CSTR's. It
is impossible to precisely control particulation in batch or plug flow
reactors since it occurs over a period of time or a region of reactor space.
In a CSTR particulation by dispersion occurs almost instantaneously, but
due to the dynamics of the system the time the particles spend in the
reactor is described by an exponential distribution. That is some particles
exit the reactor shortly after forming while others may reside much
2 o longer. Furthermore, in a CSTR it is difficult, if not impossible to ensure
that each unit volume of the reactants under goes the same or comparable
shear history. As a result the particle size distribution of the dispersed
rubber-like composite phase is typically broadest when formed in a CSTR.
Particle size, particle size distribution and morphology contribute to
a number of properties of the product including impact resistance, gloss
3 and translucency. Unfortunately, generally to maximize one property
tends to reduce one or more of the other properties of the final polymer.
There have been some attempts to overcome these deficiencies by
2136655
blending resins having different particle sizes. Such an approach is
expensive as it requires passing a melt blend of the resins through an
extruder. Additionally, the properties of a blend may be lower than that
expected from the weighted numerical average of the properties of each of
the components in the blend.
The following is representative of the state of the art in the
polymerization of impact modified thermoplastics. Almost all techniques
largely determine the final particle size of the rubber-like composite phase
at the point of phase inversion or dispersion.
United States Patent 2,694,692 issued November 16, 1954,
assigned to The Dow Chemical Company discloses the desirability and
2 o criticality of agitation during the early stages of polymerization of impact
modified thermoplastic polymers.
United States patent 3,658,946 issued April 25, 1972, assigned to
Badische Aniline-& Soda-Fabrik Aktiengesellschaft (BASF) discloses
particle size and distribution of impact modified thermoplastics may be
controlled by varying the stirrer speed or shear during the early part of the
reaction-
United States patent 3,660,535 issued May 2, 1972 assigned to the
Dow Chemical Company discloses stirring or mechanical agitation during
_ 2l366~
the initial stages of polymerization to create the required particle size
distribution in the polymerization of an impact modified thermoplastic.
United States patent 3,903,202 issued September 2, 1975 assigned
to Monsanto Company teaches dispersing under mechanical agitation a
monomer syrup containing rubber into a partially polymerized monomer,
during the early stages of polymerization to create the required dispersion
of impact modifier throughout the resin phase.
United States patents 4,857,587 and 4,861,827 issued August 15
and 29, 1989 respectively, assigned to Fina Technology Inc. discloses the
use of mechanical agitation during the early stages of the polymerization
of an impact modified thermoplastic to create the required dispersion of
rubber throughout the continuous resin phase.
There are three patents which Applicants are aware of which state
the control of shear is important in the process.
Canadian Patent 832,523 issued January 20, 1970 to Shell
Internationale Research Maatschappij N.V., teaches HIPS containing a
bimodal particle size distribution. The HIPS comprises from 70 to 99
weight % of polystyrene and from 1 to 30 weight % of a dispersed rubber
phase having a particle size distribution so that from 70 to 97 % of the
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particles have a diameter from 1 to 3 microns and from 30 to 3 % of the
particles have a diameter from 5 to 25 microns.
The Shell patent teaches controlling agitation or shear during the
early stages of polymerization to obtain the required particle distribution.
The Shell patent teaches using the shear of a conventional process.
It is interesting to note that while the Shell patent also clearly
contemplates blending impact modified polystyrenes (page 4, lines 10-15)
and interpolymerizing styrene monomer containing two distinct types of
rubber to obtain the required particle size distribution, it does not teach or
disclose blending syrups having different particle size distributions and
completing the polymerization to directly yield a product having a bi-
2 o modal particle size distribution.
U.S. patent 4,007,234, assigned to Hoechst A.G., issued February
8, 1977 discloses a process for controlling the particle size distribution in
high impact styrene copolymers modified with ethylene-propylene
rubbers. The polymer is prepared using a mass/mass or mass/suspension
process with high shear in the prepolymerizer. The resulting polymer is
3 then subjected to a two stage shearing action. A catalyst is introduced into
the polymer prior to or during the second shearing to crosslink the rubber
particles and to maintain particle size. While the Hoechst patent teaches
2136655
shearing the polymer, it does not disclose shearing the syrup as required
in the present invention. Additionally, the rubber used in the Hoechst
process is EPDM which is not used in the present invention.
United States Patent 5,210,132 assigned to the Mitsui Toatsu
Chemicals, Inc. issued May 11, 1993 discloses a process which forms a
dispersed rubber-like composite phase in a continuous resin phase. The
particulated syrup is then subjected to shear in a device having at least
three shearing blades or rotors. The shearing rotors and stators are
coaxial and have comb like cuts at interposing ends or sections to form a
multilayer structure. The result is that the Mitsui patent teaches shearing
a particulated syrup using a multi-zone shear field having at least three
different shear rates. It is an essential feature of the Mitsui patent that the
syrup be particulated prior to subjecting it to shear. The Mitsui patent
teaches against the subject matter of the present invention in that the
present invention relates to the departiculation of a stable particulated
syrup to a post inversion metastable syrup and particulating the said post
inversion metastable syrup to a stable state. A number of essential
features of the Mitsui patent teaches away from the subject matter of the
present invention.
2136655
None of the above art suggests a process to form a post inversion
metastable syrup from a stable particulated one. Metastable syrups have
been studied from an academic perspective. In Rubber-Toughened
Plastics, edited by C. Keith Riew, published by The American Chemical
Society in 1989, on page 25 of a review article, mentions some earlier
work in which bulk ABS was produced under high shear and
reagglomeration was noted.
Accordingly, the present invention seeks to provide for the
industrial production of a post inversion metastable syrup consisting of co-
continuous resin and rubber-like composite phases to provide additional
degrees of freedom to control or manipulate the particle size distribution
2 o in impact modified thermoplastics.
As used in this specification the following terms have the following
meanings:
"Dispersion" means a system of two or more phases in which one
phase forms a continuous phase and the other phases are dispersed as
small droplets or particles through the continuous phase;
"Resin phase" means a solution of polymer resin dissolved in one
or more monomers or the polymer itself;
- 10-
213665~
-
"Rubber phase" means an uncrosslinked rubber dissolved in one or
more monomers, or the rubber itself;
"Rubber-like composite phase" means a composite of a rubber
phase as defined above and one or more resin phases as defined above
said composite may contain resin polymers occluded by or grafted onto
the rubber polymers;
"Dispersed rubber-like composite phase" means a rubber-like
composite phase dispersed throughout a continuous resin phase;
"Post inversion metastable syrup" or "metastable syrup" means a
syrup polymerized under low shear conditions past the normal phase
inversion region described earlier for batch processes and plug flow
reactors and consists of a rubber-like composite phase that is continuous
or co-continuous with resin phase in a metastable free energy state [e.g.
Gibbs or Helmholtz]. Post inversion metastable syrups may also be
generated by departiculation or reverse inversion of particulated stable
syrups;
"Particulation" a term used to describe the formation of a dispersed
rubber-like composite phase regardless of its mechanism;
"Dispersing" or "phase dispersion" or "particulation by dispersion"
means the formation of a dispersed rubber-like composite phase in a
21366~
continuous resin phase by dispersing with mechanical agitation a rubber
phase or continuous rubber-like composite phase into a tank which has a
continuous resin phase. Typically, this process occurs in a continuous
stirred tank reactor (CSTR);
"Inverting", or "inversion", or "phase inversion" or "particulation
by inversion" means the formation of a dispersed rubber-like composite
phase in a continuous resin phase from a syrup which has a continuous or
co-continuous rubber-like composite phase;
"Rapid phase inversion" or "step like phase inversion" (as opposed
to "inverting", or "inversion", "phase inversion", or "particulation by
inversion") means the particulation of a post inversion metastable syrup in
2 o a relatively short time or small reactor volume to a stable syrup consisting
of a dispersed rubber-like composite phase and a continuous resin phase;
"Departiculation" or "Reverse Inversion" means subjecting a stable
syrup consisting of a dispersed rubber-like composite phase and a
continuous resin phase, to conditions which causes the dispersed rubber-
like composite phase and the continuous resin phase to become co-
continuous. The resulting syrup is in a post inversion metastable state;
and
- 12-
2136655
-
"Low shear" means a shear field which is not sufficient to invert a
metastable syrup. Low shear fields occur in static mixer reactors or during
mechanical agitation of anchor or turbine agitators or other agitators
operated at low rates of rotation. Typically with driven agitators the rates
of rotations are less than 15, preferably less than 10 RPM's most
preferably as low as possible. Of course one skilled in the art will be
aware that the degree of agitation will depend on reactor configuration and
a~propriate speeds can be determined by routine experimentation after
reading this specification.
.~TJl\/Il~ARY OF T~, ~NVFNTI()N
According to the broadest aspect of the present invention there is
provided a process comprising subjecting at least a portion of a stable
syrup comprising a continuous resin phase and a discontinuous rubber-like
composite phase to high shear and pressure to form a metastable syrup
comprising a continuous or co-continuous rubber-like composite like
phase and a discontinuous or co-continuous resin phase, respectively.
A further embodiment of the present invention provides, a process
3 for the production of a stable syrup comprising a continuous resin phase
and a dispersed rubber-like composite phase and exposing said stable
syrup to a controlled high shear and pressure field to produce a post
- 13 -
2t366~
inversion metastable syrup consisting of co-continuous resin and rubber-
like composite phases and further exposing said metastable syrup to a
lower controlled relatively uniform shear field to particulate it to a stable
state. This process provides additional degrees of freedom to control or
manipulate the particle size distribution in impact modified thermoplastics.
There are a number of advantages of the process of the present
invention. The invention permits a high degree of control over the
particle size, narrowing of the particle size distribution and the process is
easily modified by stream splitting and the application of multiple uniform
shear field generating devices to produce bi- or multimodal particle size
distributions all of which will lead to a better or better balance of
2 o properties .
RRTF,F nF,~(~RTPTT()N OF TT~F, T)R~VVTN(~
Figure 1 is a transmission electron micrograph (7,500 X) of an
advanced and devolatilized stable particulated syrup obtained from the
stirred tank reactor of example 2 at 32.90 ~ solids, prior to
departiculation under shear and pressure.
Figure 2 is a transmission electron micrograph (7,500 X) of an
advanced and devolatilized post inversion metastable syrup in which the
rubber-like composite and resin phases are co-continuous. The post
- 14-
213665~
inversion metastable syrup was prepared from the stable particulated syrup
shown in Figure 1 by flowing it through a gear pump at 90 RPM with a
restricted discharge port at 32.88 % solids. This inputed high shear and
pressure into the stable particulated syrup and caused it to departiculate to
a metastable state.
Figure 3 is a transmission electron micrograph (7500 X) of an
advanced and devolatilized stable particulated syrup that was plepared
from the metastable syrup shown in Figure 2 by the application of a
uniform shear field, which caused a rapid or step-like phase inversion.
nF,TA~,F,n nF,~ ,R~PTl()N
The process of the present invention is extremely broad in its
application. For example the at least a portion of the syrup could
comprise the entire syrup. The resulting departiculated metastable syrup
could then be divided into two or more streams each of which are further
separately treated to form different particle size distributions which are
further recombined to form a bi- or multimodal dispersed rubber-like
composite phase. On the other hand the stable particulated syrup could be
divided into two or more portions each of which are separately subjected
to a controlled high shear and pressure to cause departiculation. The
resulting post inversion metastable syrups may then be separately further
2136655
-
treated to form different particle size distributions and are further
combined to form a bi- or multimodal dispersed rubber-like composite
phase.
The syrups which may be treated in accordance with the present
invention typically are syrups which would be polymerized to form impact
modified polymers including high impact polystyrene (HIPS), acrylonitrile
butadiene styrene polymers (ABS) and methyl methacrylate butadiene
styrene polymers (MBS).
The monomers useful in the syrups which may be treated in
accordance with the present invention may be selected from the group
consisting of C8 ,2 vinyl aromatic monomers which are unsubstituted or
substituted by a C, 4 alkyl radical, Cl 8 alkyl esters of acrylic or
methacrylic acids, maleic anhydride, and acrylonitrile and
methacrylonitrile .
Suitable C8 l2 vinyl aromatic monomers which are unsubstituted or
substituted by a C, 4 alkyl radical include styrene, ~-methyl styrene, p-
methyl styrene, and p-t-butyl styrene. Useful C, 8 alkyl esters of acrylic
and methacrylic acids include methyl methacrylate, ethyl methacrylate,
methyl acrylate, ethyl acrylate, and ethylhexyl acrylate.
- 16-
213665S
The resin component in the syrup may comprise a co- or homo-
polymer or resin of one or more C8 l2 vinyl aromatic monomers which are
unsubstituted or substituted by a C, 4 alkyl radical. A suitable resin
includes polystyrene. However, the resin may be a copolymer comprising
from 5 to 95, preferably from 50 to 90 weight ~ of one or more C~l2
vinyl aromatic monomers and from 95 to 5, preferably from 50 to 10
weight ~ of one or more monomers selected from the group consisting of
C1-8 alkyl esters of acrylic and methacrylic acids, maleic anhydride and
acrylonitrile and methacrylonitrile. Typically such polymers are
copolymers of styrene and one or more monomers selected from the group
consisting of acrylonitrile, methacrylonitrile, methyl acrylate, ethyl
acrylate, methyl methacrylate, ethyl methacrylate, butyl acrylate, butyl
methacrylate, ethylhexyl acrylate, and maleic anhydride.
When finally finished the resin polymers should have a number
average molecular weight (Mn) greater than 65,000 preferably greater
than 70,000 for the styrene containing polymers and a number average
molecular weight of greater than 30,000 for the predominantly ester
3 polymers .
The rubbers which may be used as impact modifiers in the present
invention will typically have a (weight average) molecular weight (Mw) of
213665~
greater than about 100,000, preferably greater than 200,000. Block
rubber copolymers have significantly lower molecular weight, typically
greater than 50,000 (Mw). The rubbers may be selected from the group
consisting of:
(i) co- or homopolymers of C4 6 conjugated diolefins which are
unsubstituted or substituted by a halogen atom, preferably a
0
chlorine or bromine atom;
(ii) random, block, linear, star and tapered copolymers comprising
from 10 to 80 weight ~ of one or more C8 l2 vinyl aromatic
monomers which are unsubstituted or substituted by a C, 4 alkyl
radical, from 20 to 90 weight % of one or more C4 6 conjugated
diolefins; and
(iii) copolymers comprising from 1 to 50 weight % of acrylonitrile or
methacrylonitrile and from 50 to 99 weight % of one or more C4 6
conjugated diolefins.
Suitable polymers which are co or homopolymers of C4 6
conjugated diolefins include homopolymers of butadiene and copolymers
3 of butadiene and isoprene. Preferably the polymer will be a homopolymer
of butadiene. Generally the polymers have a level of stereospecificity. The
selection of the degree of stereospecificity will depend to some extent
- 18 -
2136655
upon the properties required in the final product. Some polybutadienes
contain over 90, most preferably over 95 weight % of monomer in the cis
configuration. Such a type of rubber is commercially available from
Polysar Rubber Corporation under the trademark TAKTENE~ 1202. The
polybutadiene may contain a lower amount, typically from 50 to 65, most
preferably about 50 to 60 weight % of monomer in the cis configuration
such as rubbers which are available from Firestone under the trademark
DIENEa~55 or from the Polysar Rubber Corporation under the trademark
TAKTENE~ 550.
Suitable rubbery polymers may comprise: from 10 to 80,
preferably from 20 to 50 weight % of one or more C8 ,2 vinyl aromatic
monomers which are unsubstituted or substituted by a Cl 4 alkyl radical,
from 20 to 90, preferably from 80 to 50, weight % of one or more C4 6
conjugated diolefins. Such rubber polymers may be random or block such
as linear block, star block or tapered block polymers.
Random copolymers having the above composition are the
commercially available styrene butadiene rubbers (SBR). A number of
block copolymers are available from Shell under the trademark
KRATON~.
- 19-
2136655
-
The rubbery polymer may comprise from 1 to 50, preferably from
5 to 35 weight % of acrylonitrile or methacrylonitrile and from 50 to 99,
preferably from 95 to 65 weight 5~ of one or more C4 6 conjugated
diolefins.
The above polymers are the commercially available nitrile rubbers
available from Polysar Rubber Corporation under the trademark
KRYNAC~ and from Bayer AG under the trademark PERBUNAN~.
It should be kept in mind that the rubber should be soluble in one
or more of the monomers of the syrup or the diluent or solvent for the
monomers. The solubility of the above rubbers in various monomers
and/or diluents or solvents may be easily determined by non-inventive
routine testing.
Typically, from about 1 to 20, preferably from about 3 to 12, most
preferably from 4 to 10 weight % of the rubber is dissolved in the
monomer or a mixture of monomers to form a syrup.
In a typical batch or plug flow reactor system the syrup is subjected
to the usual polymerization process under agitation. At some point
3 between 5 and 20 % conversion the system undergoes particulation by
phase inversion under the application of a shear field generated by
mechanical agitation. That is the rubber-like composite phase becomes
- 20 -
21~6655
the dispersed phase and the resin phase becomes the continuous phase.
This does not happen instantaneously but occurs over a considerable
period of time or space, typically from 20 to 50 minutes or reactor space
which produces 2 to 8 % conversion. As a result there tends to be a
particle size distribution within the inverted syrup. In accordance with the
present invention it is possible to departiculate such a syrup to a
metastable state and in a further embodiment in a separate step particulate
the metastable syrup in a rapid or step-like phase inversion.
In a preferred embodiment of the present invention the initial syrup
is polymerized in a batch or plug flow process either thermally or in the
presence of one or more initiators. Typical polymerization temperatures
(in the reactors) range from 80 to 180, more typically 90 to 170C.
Under these conditions the syrup undergoes phase inversion. The
resulting particulated syrup is then treated in accordance with the present
invention to produce a post inversion metastable syrup. In accordance
with this aspect of the invention, the particulated syrup is polymerized to a
conversion between 1 % above the point at which the syrup has inverted
and the point at which the rubber has become crosslinked to form a
network. Preferably the degree of conversion is between S and 75 %
before the syrup is treated in accordance with the present invention.
2136655
In a particularly preferred embodiment the post inversion
metastable syrup may be handled using low shear methods such as low
shear pumps, gravity feeds or vacuum and pressure techniques.
A reactor or a chain of reactors such as a plug flow reactor may be
used to produce such a syrup. Upon inversion or dispersion the rubber-
like composite phase will be distributed throughout the continuous resin
phase. The plug flow reactors should have a length to diameter ratio of
greater than about 3:1, preferably from about 5:1 to 15:1, most preferably
about 9:1. The reactors may contain an agitator to provide for movement
of the syrup for heat transfer requirements.
Another way of producing a particulated syrup is to feed a rubber
2 o solution or partially polymerized syrup below its inversion point to a
continuous stirred tank reactor (CSTR) operated at an equilibrium
conversion sufficiently high so that the said rubber solution or rubber-like
composite phase is dispersed as discrete particles in a continuous resin
phase. The resulting syrup may then be treated in accordance with the
present invention.
If a stable particulated syrup having a dispersed rubber-like
composite phase is subjected to high shear preferably under pressure
greater than about 200 psi, prior to the rubber phase becoming crosslinked
21366~5
it will departiculate to a post inversion metastable syrup in which the
rubber-like composite phase is co-continuous with the resin phase.
One way to generate a post inversion metastable syrup is to pump a
stable particulated syrup through a restricted orifice using a gear pump.
The pressure should be greater than 200 psi, preferably between 250 to
500 psi.
The shear/pressure requirements for the departiculation of a stable
particulated syrup will depend on a number of factors including the type
and configuration of equipment used, the degree of polymerization of the
syrup and the viscosity of the syrup. While it is difficult to scale up from
laboratory equipment to plant scale equipment the relative magnitudes of
the shear on each side of the crossover point may be examined using a
device capable of delivering high shear and pressure. Syrup samples may
be placed in such a device and each subjected to different shear rates and
pressures. The resulting sample is then polymerized in a glass tube to
completion and the product can be analyzed by the Test for Particulation
and Transmission Electron Microscopy described in the Specific
Embodiments. By observing the morphology of the sample and
correlating it to shear rate and pressure, it is possible to define the
conditions where the syrup will undergo departiculation (forming a post
- 23 -
2136655
inversion metastable syrup in which the rubber phase is continuous or co-
continuous with the resin phase). Generally the shear rates and pressure
to cause a stable syrup to departiculate to a post inversion metastable
syrup are quite high.
It is also believed that a stable particulated syrup may be
departiculated by pumping under pressure through a controlled shear
device consisting of a stator and a rotor, which is described in detail in
copending US application serial number 094,309, filed July 19, 1993.
A useful indication of particle size is reflected by the volume
average particle diameter. The volume average particle diameter is given
by the ratio of the fourth moment of the particle size distribution to the
2 o third moment of the particle size distribution.
Volume Average diameter - ~ 3
wherein nj is the number of all particles having diameter dj summed over
all particles.
Often, but not invariably, the dispersed particles have a log normal
distribution and the particle size density distribution is given by:
p(x) 1 exp( o 5( lnx -
- 24 -
2136655
-
where p(x) is the particle density at diameter x, ~ is a parameter indicating
the location of the distribution, and a is a parameter indicating the spread
or breadth of the distribution. In cases where the particle size distribution
is log normal these two parameters, ,u and a, uniquely determine the
distribution.
A typical particle size distribution may be characterized as a particle size
distribution having a volume average particle diameter from 0.1 to 30,
preferably from 0.5 to 10, most preferably from 0.5 to 5, micrometers.
Preferably for high impact polystyrene type systems the volume average
particle diameter will be from 0.5 to 15 micrometers. Preferably for the
ABS, MBS and the ester (e.g. acrylate and methacrylate) resin type
systems the volume average particle diameter will be from 0.05 to 5
micrometers. As noted above there are a number of bi- and poly- modal
particle size distributions which give useful properties. Generally useful
bi- or poly- modal particle size distribution comprises from 100 to about
40 % of small particles from about 0 to about 60 % of medium sized
particles and from 0 to 20 weight ~ of particles outside the specified sizes
3 for small and medium particles. The ratio of diameters of small to
medium particles may range from 1:1.15 to 1:20 preferably from 1:1.3 to
1:6.
2136655
Useful uniform shear devices are described in the above noted
patent application.
The device may comprise a stator and a rotor, most preferably with
an adjustable gap there between, and a controlled or determined path
length through which the syrup must flow.
The device may comprise a tubular stator member, such as a
straight or tapered pipe. Inside the tubular member is a closed cylinder or
cone which is the rotor. Preferably the rotor is movable within the stator
to control either or both the clearance between the rotor and stator and the
path length over which the fluid is subjected to shear. More particularly
the device may be a Couette fluid shear field generator comprising:
(i) a chamber having a circular cross section perpendicular to its
longitudinal axis and at least one input port and at least one output
port;
(ii) a cylinder within said chamber, said cylinder having a circular
cross section perpendicular to its longitudinal axis, a surface closely
conforming to the internal surface of said chamber and occupying
3 substantially all the space within said chamber except for a closely
controlled clearance between the internal surface of the chamber
and the external surface of the cylinder; and
- 26 -
21366S~
(iii) means for rotating at least one of said chamber and cylinder
relative to each other.
Preferably the cylinder is a rotor and the chamber is closed and a stator.
Preferably a drive means passes through one end of said chamber and to
rotate the cylinder relative to the chamber.
The internal shape of the chamber and the external shape of the
rotor conform. Suitable shapes for the chamber and rotor include
cylindrical, frustro-conical (tapered cylindrical), and conical. Spherical,
hemi-spherical and parabolic shapes would likely be useful but may be
more difficult to use in plant operations. A special shape would be a plate
shaped stator or chamber and a plate shaped rotor. A further special
configuration is a plate shaped stator with a conical shaped rotor or
conical stator with plate shaped rotor.
Suitable ratios of dimensions for the shear field generator will
depend upon the required residence time, the diameter of the rotor and the
chamber and the speed of rotation. Clearance between the chamber wall
and the surface of the rotor for a cylindrical chamber and rotor may be
defined in terms of the ratio of the radius of the rotor (rr) to the radius of
the chamber (rc). Typical ratios range from 0.999 to 0.750, preferably
from 0.993 to 0.875. The ratio of the length to the diameter of the
- 27 -
2136655
chamber (L/D ratio) should be greater than 0.25:1, preferably between
0.5:1 to 10:1 and most preferably between 0.5:1 to 3:1. The input and
output ports should be preferably located at each end of the chamber.
A relatively uniform controlled shear field may also be provided by
flowing said syrup through a device comprising a closed chamber having a
circular cross section perpendicular to its longitudinal axis, a continuous
side wall and a conical projection along its longitudinal axis, said conical
projection having a low apical angle, a planar end perpendicular to the
longitudinal axis of said chamber and placed adjacent the apex of said
conical projection and means for rotating said conical projection and said
plate relative to each other. The apical angle is less than, 7 preferably less
than 4, most preferably less than 2. The gap between the tip of the cone
and the plate should be minimal.
The free volume within the device should be less than 10%,
preferably less than 5 %, most preferably less than 3 % of the volume of
the reactors upstream of the device. As a result residence time of the
syrup as it flows through the device should be low. Typically the
residence time should be less than 10 minutes, preferably less than 5
minutes most preferably less than 3 minutes. Of course, the residence
time will depend on the free volume within the chamber and the flow rate
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through the controlled shear (field) device. Typically the conversion of
the monomers will be less than 5 %, preferably less than 2%, most
preferably less than 1% within the controlled shear field device.
l;,XAl~P~ '.S
The present invention will be illustrated by the following examples
which are not intended to limit the invention. In the examples, unless
otherwise indicated parts means parts by weight and % means weight %.
(~ontim~ Stirre(l T~nk Re~ctor ((~STR):
The CSTR was a glass 1.0 L vessel equipped with a bottom outlet
port. The reactor has a external heating jacket with ports to flow hot oil
through and was connected to a heating circulating oil bath to provide
2 o temperature control. The top of the reactor was removable and equipped
for mechanical agitation. A drive shaft passed through a seal in the top of
the reactor. One end of the drive shaft was attachable to an electric motor
and the other end was attachable to an agitator. Batch (syrup) temperature
was measured in the middle of the reactor and recorded. The temperature
in all transfer lines were controlled.
Polymeri7~tion Apl?ar~tll~ (Type T):
One litre of feed solution was fed from the dissolving tank to a gear
pump which delivered it to the stirred tank reactor. The polymerization
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was operated in batch mode and was sampled for solids content. When
the desired solids content was reached the bottom outlet valve was opened
and the syrup was pumped through a gear pump. The gear pump was
operated at various RPM's under low and high pressure. Pressure was
generated by partially closing a valve that was downstream from the gear
pump. The gear pump was capable of generating 750 psi and was
protected by a pressure relief valve, which opened at about 350 psi.
Polymeri7~tion App~r~tll~ (Type TT):
Feed solution was fed from the dissolving tank to a gear pump
which delivered it to the continuous stirred tank reactor. The syrup exited
the reactor through the bottom outlet port using a three way valve. Level
control was maintained by manually adjusting the three way valve. When
equilibrium solids were achieved the feed pump was turned off, the three
way bottom outlet valve was switched and the syrup was pumped through
a gear pump. The gear pump was operated at various RPM' s under low
and high pressure. Pressure was generated by partially closing a valve
that was downstream from the gear pump. The gear pump was capable of
generating 750 psi and was protected by a pressure relief valve, which
opened at about 350 psi.
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Polymeri7,~tion~:
Using one of the above apparatuses a series of experiments were
carried out. Styrene containing 8 weight % of a medium cis rubber was
polymerized by thermal or 0.028 % t-butylperoxyacetate initiation under
mechanical agitation. Samples of the resulting syrup were taken from the
reactor and after treatment in the gear pump. The syrup samples were
advanced at 140C for 24 hours and then devolatilized at 220C for 30
minutes in a vacuum oven under reduced pressure (~ S mm Hg). The
resulting samples of rubber modified polystyrene then subjected to
analysis.
Test For Particlllation:
Three tenths of a gram of a devol~tili7ed HIPS resin is shaken in 15
mL of 2-butanone (MEK) and inspected for visible gel particles. A well
particulated HIPS resin will appear as a milk like suspension, while a non-
particulated HIPS resin (one with a co- or continuous rubber phase) will
appear as a single gel particle in a clear solution. "Partially particulated"
HIPS resins are ones that fall between these two extremes.
M~ rement of ~welling In~1~,x an~ el ~ont~,nt:
Approximately one gram of polymer is accurately weighed and
dissolved in 40 mL of toluene and centrifuged at 17,000 RPM, at -7 C,
213665~
for two hours. The supernatant liquid is decanted, 40 mL of fresh toluene
is added to the precipitated gel, and the mixture treated in an ultrasonic
bath for two hours. The sample is then centrifuged at 17,000 RPM and -
7C for two hours. The supernatant liquid is decanted. The wet gel is
weighed and then dried and weighed again. The swelling index is
calculated by dividing the wet gel weight by the dry gel weight, and the
gel level is calculated by dividing the dry gel level by the initial sample
weight.
P~rticle ~i7.~ M~ Urement:
An Horiba photosedimentometer was used for particle size analysis.
A typical procedure involves dispersing enough HIPS resin such that the
starting absorbency of the instrument lies between 0.75 and 0.85 in 10 mL
of MEK. The sample is inspected for complete dispersion and is
measured immediately in centrifugal mode. The machine reports area
median. The output was fitted to a log normal distribution, where
appropriate, to calculate the appropl;ate values for the characterization of
the particle size distribution.
Tr~n~mi~sion Flectron Microscopy (TFM):
TEM' s were taken of selected samples using routine methods.
21366SS
Synlp ~Soli(1c:
Syrup solids were determined using gravimetric analysis by
devol~tili7ing the sample at high temperature (220C) and reduced
pressure (5 mm Hg).
Fx~mple 1:
The feed syrup comprised 8 % medium cis polybutadiene and
0.028 ~ t-butylperoxyacetate in styrene. The polymerization was
operated in batch mode using the type I apparatus. A turbine agitator was
operated at 60 RPM. When the syrup solids reached about 27.5 ~ it was
discharged through the gear pump at different shear rages (e.g. RPM)
under pressure. A syrup sample taken from the reactor prior to the gear
pump was advanced, devolatilized and found to be particulated; volume
average diameter = 2.48 ,uM. The remaining samples were discharged
through the gear pump under shear and pressure. The other samples were
tested for departiculation (the absence of particles) using the test for
particulation.
The results of the experiment are set forth in Table I.
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TABLE I
RESULTS OF EXAMPLE I
Gear Pump RPM Test for Particulation
4 Gel and Turbidity
Gel and Turbidity
Gel and Turbidity
0 90 Gel, Little Turbidity
110 Gel, Little Turbidity
The "gel" from the particulation test shows departiculation and the
declining turbidity shows increasing departiculation (e.g. less particles)
with increasing shear (and likely pressure).
Fx~mple ~:
The feed syrup comprised 8 % medium cis polybutadiene and
0.028 % t-butylperoxyacetate in styrene. The polymerization was
operated in batch mode using the Type I apparatus. A turbine agitator
was operated at 60 RPM. When the syrup solids reached about 30 % it
was discharged through the gear pump under low (up to at most 30 psi)
and high pressure (above 200 psi) at different shear rates (gear pump
RPM). A syrup sample taken from the reactor before the gear pump was
advanced, devolatilized and found to be particulated; volume average
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diameter = 2.62 ,uM. The other samples were tested for departiculation
(the absence of particles) using the test for particulation.
The results of the experiment are set forth in Table II.
TABLE II
RESULTS OF EXAMPLE 2
0 Gear Pump RPM Pressure Test for Particulation
Low Particulated, Volume Average
Diameter = 2.34,uM
High Gel and Turbidity
High Gel, Little Turbidity
High Gel, Little Turbidity
The "gel" from the particulation test shows departiculation and the
declining turbidity shows increasing departiculation (e.g. less particles)
with increasing shear (and likely pressure).
The above example shows under the conditions tested both high
pressure and shear are needed to change a stable particulated syrup into a
post inversion metastable syrup.
3 0 The post inversion metastable syrups obtained from the gear pump
under high shear and pressure were then treated to a lower controlled
shear field for 2 minutes at 115 C, in batch mode (shear rate = 6.8
sec~l).
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The results of the treatment are set forth in Table III.
TABLE III
PARTICULATION OF POST INVERSION METASTABLE SYRUPS
Metastable Syrup Sample Particulated Volume Average Diameter
After Treatment (,.4M)
0 Gear Pump = 10 RPM Yes 2.28
Gear Pump = 45 RPM Yes 1.80
Gear Pump = 90 RPM Yes 1.60
The above example shows it is possible to convert a stable
particulated syrup to a post inversion metastable syrup and further to
convert the post inversion metastable syrup back to a stable particulated
syrup with a different particle size.
Figure 1 is an electron micrograph (7,500 X) of the sample of
syrup taken from the reactor prior to the gear pump and advanced to
completion and devolatilized. The figure clearly shows a large particle
size particulated syrup.
Figure 2 is an electron micrograph (7,500 X) of a sample of syrup
which had passed through the gear pump at 90 RPM and under high
pressure. The sample was then advanced and devolatilized. The figure
shows a co-continuous resin and rubber-like.
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-
Figure 3 is an electron micrograph (7,500 X) of a sample of the
syrup passed through the gear pump at 90 RPM and under high pressure
and treated in a uniform shear field. The sample was advanced and
devolatilized. The figure shows a relatively smaller particle size
distribution than that in Figure 1.
Fx~mple ~:
The feed syrup comprised 8 % medium cis polybutadiene in
styrene. The polymerization was operated in batch mode using the type I
apparatus and was thermally initiated. A turbine agitator was operated at
60 RPM. When the syrup solids reached about 43 % it was discharged
through the gear pump at different shear rates (e.g. RPM) under low and
high pressure. A syrup sample taken from the reactor prior to the gear
pump was advanced, devolatilized and found to be particulated; volume
average diameter = 1.94 ~M. The other samples were tested for
departiculation (the absence of particles) using the test for particulation.
The results of the experiment are set forth in Table IV.
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21366SS
_
TABLE IV
RESULTS OF EXAl\~PLE 3
Gear Pump RPM Pressure Test for Particulation
Low Particulated, Volume Average
Diameter = 1.99 ,uM
High Gel and Turbidity
High Gel and Turbidity
High Gel and Turbidity
The "gel" from the particulation test shows departiculation and the
declining turbidity shows increasing departiculation (e.g. less particles)
with increasing shear (and likely pressure).
Fx~mple 4:
The feed syrup comprised 8 ~ medium cis polybutadiene and
0.028 ~ t-butylperoxyacetate in styrene. The polymerization was
operated in continuous mode using the type II apparatus. The feed
solution was fed at 435 mL/hr. A turbine agitator was operated at 100
RPM. When the equilibrium syrup solids of 27 ~ was reached the feed
3 pump was turned off, the bottom outlet three way valve was switched and
the syrup was discharged through the gear pump under different shear
(e.g. RPM) and under low (less than 30 psi) and high pressure (greater
than 200 psi). A syrup sample from the reactor before the gear pump was
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213665à
advanced, devolatilized and found to be particulated; volume average
diameter = 2.60 ,uM. The other samples were tested for departiculation
(the absence of particles) using the test for particulation.
The results of the experiment are set forth in Table V.
TABLE V
RESULTS OF EXAMPLE 4
Gear Pump RPM Pressure Test for Particulation
Low Particulated, Volume Average
Diameter = 2.89 ,uM
High Gel and Turbidity
High Gel and Turbidity
High Gel and Turbidity
The "gel" from the particulation test shows departiculation and the
declining turbidity shows increasing departiculation (e.g. less particles)
with increasing shear (and likely pressure).
F,x~mple 5:
The feed syrup comprised 8 % medium cis polybutadiene and
0.028 % t-butylperoxyacetate in styrene. The polymerization was
operated in continuous mode using the type II apparatus. The feed
solution was fed at 435 mL/hr. A turbine agitator was operated at 60
RPM. When the equilibrium syrup solids of 28 % was reached the feed
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pump was turned off, the bottom outlet three way valve was switched and
the syrup was discharged through the gear pump under low and high
pressure. A syrup sample from the reactor before the gear pump was
advanced, devol~tili7ecl and found to be particulated; volume average
diameter = 2.52 ,.4M. The other samples were tested for departiculation
(the absence of particles) using the test for particulation.
The results of the experiment are set forth in Table VI.
TABLE VI
RESULTS OF EXAMPLE S
Gear Pump RPM Pressure Test for Particulation
Low Particulated, Volume Average
Diameter = 2.59,uM
High Gel and Turbidity
High Gel, Little Turbidity
High Gel, LittleTurbidity
The "gel" from the particulation test shows departiculation and the
declining turbidity shows increasing departiculation (e.g. less particles)
with increasing shear (and likely pressure).
The above examples show it is possible to departiculate stable
particulated syrups formed in batch or continuous polymerizations with
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thermal or t-butylperoxyacetate initiation to post inversion metastable
syrups.
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