U.S. patent number RE42,099 [Application Number 12/592,418] was granted by the patent office on 2011-02-01 for methods and apparatus for producing and treating novel elastomer composites.
This patent grant is currently assigned to Cabot Corporation. Invention is credited to Bin Chung, Joseph Cianciolo, Susan W. Green, Ivan Z. Podobnik.
United States Patent |
RE42,099 |
Chung , et al. |
February 1, 2011 |
Methods and apparatus for producing and treating novel elastomer
composites
Abstract
Elastomer masterbatch is processed in a continuous compounder
having multiple parallel elongate rotors axially oriented in an
elongate processing chamber. Optionally, additional materials are
compounded into the masterbatch, e.g., additives, other elastomeric
compositions, etc. Preferably, the masterbatch then is further
processed in an open mill. Excellent control of Mooney Viscosity is
achieved. In certain preferred embodiments, elastomer composites
are produced by novel continuous flow methods and apparatus in
which fluid streams of particulate filler and elastomer latex are
fed to the mixing zone of a coagulum reactor to form a coagulated
mixture in semi-confined flow continuously from the mixing zone
through a coagulum zone to a discharge end of the reactor. The
particulate filler fluid is fed under high pressure to the mixing
zone, such as to form a jet stream to entrain elastomer latex fluid
sufficiently energetically to substantially completely coagulate
the elastomer with the particulate filler prior to the discharge
end without need of adding acid or salt solution or other
coagulation step. The coagulated elastomer and particulate filler
composite is fed into the aforesaid continuous compounder for
processing and control of its moisture level and Mooney Viscosity.
Novel elastomer composites are produced. Such novel elastomer
composites combine material properties and characteristics, such as
choice of filler, elastomer, level of filler loading, moisture
level, Mooney Viscosity, balance between molecular weight and
amount of bound rubber, and macro-dispersion not previously
achieved.
Inventors: |
Chung; Bin (Nashua, NH),
Green; Susan W. (Boxboro, MA), Podobnik; Ivan Z. (Mason,
NH), Cianciolo; Joseph (Methuen, MA) |
Assignee: |
Cabot Corporation (Boston,
MA)
|
Family
ID: |
22441622 |
Appl.
No.: |
12/592,418 |
Filed: |
November 24, 2009 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
10051357 |
Jan 18, 2002 |
6929783 |
|
|
|
09549051 |
Apr 13, 2000 |
6372822 |
|
|
|
60129791 |
Apr 16, 1999 |
|
|
|
Reissue of: |
11203568 |
Aug 12, 2005 |
07582689 |
Sep 1, 2009 |
|
|
Current U.S.
Class: |
523/333; 523/334;
523/351; 422/224; 422/225; 422/187; 524/495 |
Current CPC
Class: |
B29B
7/46 (20130101); C08J 3/22 (20130101); B29B
7/60 (20130101); B29B 7/72 (20130101); B29B
15/04 (20130101); B29B 7/002 (20130101); B29B
7/007 (20130101); B29B 7/7495 (20130101); B29B
7/465 (20130101); B29C 48/761 (20190201) |
Current International
Class: |
C09B
67/00 (20060101) |
Field of
Search: |
;523/333,334,351
;422/187,224,225 ;524/495 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
581493 |
|
Nov 1976 |
|
CH |
|
909255 |
|
Apr 1954 |
|
DE |
|
1063364 |
|
Aug 1959 |
|
DE |
|
1620918 |
|
Mar 1972 |
|
DE |
|
3916981 |
|
Jul 1989 |
|
DE |
|
051450 |
|
May 1982 |
|
EP |
|
0278743 |
|
Aug 1988 |
|
EP |
|
0287138 |
|
Oct 1988 |
|
EP |
|
0287392 |
|
Oct 1988 |
|
EP |
|
0423759 |
|
Apr 1991 |
|
EP |
|
0570715 |
|
Nov 1993 |
|
EP |
|
0620250 |
|
Mar 1994 |
|
EP |
|
0763558 |
|
Mar 1997 |
|
EP |
|
705334 |
|
Mar 1954 |
|
GB |
|
1421011 |
|
Jan 1976 |
|
GB |
|
2098972 |
|
Dec 1981 |
|
GB |
|
2196547 |
|
May 1988 |
|
GB |
|
57 053340 |
|
Mar 1982 |
|
JP |
|
60-015110 |
|
Jan 1985 |
|
JP |
|
WO 96/37547 |
|
Nov 1996 |
|
WO |
|
WO 97/36724 |
|
Oct 1997 |
|
WO |
|
WO 99/16600 |
|
Apr 1999 |
|
WO |
|
Other References
PCT/US00/09925 May 17, 2001 Written Opinion. cited by examiner
.
PCT/US97/05276 Internation Search Report Patent Family Annex. cited
by examiner .
PCT/US97/05276 Jan. 13, 1998 Written Opinion. cited by examiner
.
PCT/US98/20279 Nov. 2, 1999 Internation Search Report. cited by
examiner .
Wahab, Shukri Bin Abdul et al., Natural Rubber Carbon Black
Masterbatches from Field Latex, pp. 29-41, Proceedings of NR
Technology Seminar, Rubber Research Institute of Malaysia, Kuala
Lumpur, Malaysia, Dec. 1978. cited by examiner .
Database WPI, week 8345, Derwent Publications Ltd., London, GB, AN
93-357278, XP002036310 & JP 05 262 918A (Yokohama Rubber Co.,
Ltd.), Oct. 12, 1993. cited by examiner .
"Continuous Mixers for the Polymer Industry" Farrel Corporation
Bulliten No. 234-B 1993. cited by examiner .
Functionalization of Elastomer by Reactive Mixing by the Malaysian
Rubber Producers Research Associate, the Common Fund for
Commodities, pp. 308-312, Research Disclosure, Jun. 1994. cited by
examiner .
"CP Series II Compact Processor" Farrel Corporation Bulletin No.
262-C 1995. cited by examiner .
*PCT/US00/09925 May 17, 2001 Written Opinion. cited by other .
*PCT/US97/05276 International Search Report Patent Family Annex.
cited by other .
*PCT.US97/05276 Jan. 13, 1998 Written Opinion. cited by other .
*PCT/US98/20279 Nov. 2, 1999 International Search Report. cited by
other .
*Wahab, Shukri Bin Abdul et al., Natural Rubber Carbon Black
Masterbatches from Field Latex, pp. 29-41, Proceedings of NR
Technology Seminar, Rubber Research Institute of Malaysia, Kuala
Lumpur, Malaysia, Dec., 1978. cited by other .
*Database WPI, week 9345, Derwnt publications Ltd., London, GB, AN
93-357278, XP002036310 & JP 05 262 918A (Yokohama Rubber Co.,
Ltd.), Oct. 12, 1993. cited by other .
*"Continuous Mixers for the Polymer Industry" Farrel Corporation
Bulletin No. 234-B 1993. cited by other .
*Functionalization of Elastomer by Reactive Mixing by the Malaysian
Rubber Producers Research Associate, the Common Fund for
Commodities, pp. 308-312, Research Disclosure, Jun. 1994. cited by
other .
*"CP -- Series II Compact Processor" Farrel Corporation Bulletin
No. 262-C 1995. cited by other.
|
Primary Examiner: Cain; Edward J
Parent Case Text
.Iadd.This application is a reissue of U.S. patent application Ser.
No. 11/203,568, filed Aug. 12, 2005, now U.S. Pat. No. 7,582,689
which is a continuation of and claims the priority of U.S. patent
application Ser. No. 10/051,357, filed Jan. 18, 2002, now U.S. Pat.
No. 6,929,783 which claims priority as a divisional application of
U.S. application Ser. No. 09/549,051, filed Apr. 13, 2000, now U.S.
Pat. No. 6,372,822, which claims priority from U.S. Provisional
Application No. 60/129,791, filed Apr. 16, 1999..Iaddend.
Claims
We claim:
1. An elastomer composite comprising substantially coagulated
elastomer in which particulate filler has been dispersed by:
feeding a continuous flow of first fluid comprising elastomer latex
to a mixing zone of a coagulum reactor defining an elongate
coagulum zone extending from the mixing zone to a discharge end;
feeding a continuous flow of second fluid comprising particulate
filler under pressure to the mixing zone of the coagulum reactor to
form a mixture with the elastomer latex, the mixture passing as a
continuous flow to the discharge end, and the particulate filler
being effective to coagulate the elastomer latex, wherein mixing of
the first fluid and the second fluid within the mixing zone is
sufficiently energetic to substantially completely coagulate the
elastomer latex with the particulate filler prior to the discharge
end; discharging a substantially continuous flow of elastomer
composite from the discharge end of the coagulum reactor; feeding
the elastomer composite from the discharge end of the coagulum
reactor to a continuous compounder having multiple parallel
elongate rotors axially oriented in an elongate processing chamber;
processing the elastomer composite through the processing chamber
of the continuous compounder by controlled operation of the rotors;
and discharging the elastomer composite from a discharge orifice of
the continuous compounder.
Description
FIELD OF THE INVENTION
The present invention is directed to novel methods and apparatus
for producing and treating elastomer composites, and to novel
elastomer composites produced using such methods and apparatus.
More particularly, the invention is directed to continuous flow
methods and apparatus for producing and treating elastomer
masterbatch of particulate filler finely dispersed in elastomer,
for example, elastomer composites of carbon black particulate
filler finely dispersed in natural rubber, and rubber materials and
products formed of such masterbatch compositions.
BACKGROUND
Numerous products of commercial significance are formed of
elastomeric compositions wherein particulate filler is dispersed in
any of various synthetic elastomers, natural rubber or elastomer
blends. Carbon black, for example, is widely used as a reinforcing
agent in natural rubber and other elastomers. It is common to
produce a masterbatch, that is, elastomer coagulated with carbon
black or other filler and optionally containing various additives,
such as extender oil. Carbon black masterbatch can be prepared with
different grades of carbon black, that is, carbon blacks which vary
both in surface area per unit weight and in "structure."
While a wide range of performance characteristics can be achieved
employing currently available materials and manufacturing
techniques, there has been a longstanding need in the industry to
develop elastomeric compositions having improved properties and to
reduce the cost and complexity of current manufacturing techniques.
In particular, it is known for example that macro-dispersion level,
that is, the uniformity of dispersion of the carbon black or other
filler within the elastomer, can significantly impact performance
characteristics. For elastomeric compositions prepared by
intensively mixing the carbon black or other filler with natural
rubber or other elastomer (such as in a Banbury mixer or the like),
any increase in macro-dispersion requires longer or more intensive
mixing, with the consequent disadvantages of increased energy
costs, manufacturing time, and similar concerns. For carbon black
fillers of certain surface area and structure characteristics,
dispersion beyond a certain degree has not been possible or
commercially practicable using known mixing apparatus and
techniques. In addition, such prolonged or more intensive mixing
degrades the natural rubber or other elastomer by reducing its
molecular weight, rendering the finished elastomeric compound
undesirable for certain applications.
In addition to dry mixing techniques, it is known to continuously
feed latex and a carbon black slurry to an agitated coagulation
tank. Such "wet" techniques are used commonly with synthetic
elastomer, such as styrene-butadiene rubber (SBR). The coagulation
tank contains a coagulant such as salt solution or an aqueous acid
solution typically having a pH of about 2.5 to 4. The latex and
carbon black slurry are mixed and then coagulated in the
coagulation tank into small beads (typically a few millimeters in
diameter) referred to as wet crumb. The crumb and acid (or saline)
effluent are separated, typically by means of a vibrating shaker
screen or the like. The crumb is then dumped into a second agitated
tank where it is washed to achieve a neutral or near neutral pH.
Thereafter the crumb is subjected to additional vibrating screen
and drying steps and the like. Variations on this method have been
suggested for the coagulation of natural and synthetic elastomers.
In U.S. Pat. No. 4,029,633 to Hagopian et al, which like the
present invention is assigned to Cabot Corporation, a continuous
process for the preparation of elastomer masterbatch is described.
An aqueous slurry of carbon black is prepared and mixed with a
natural or synthetic elastomer latex. This mixture undergoes a
so-called creaming operation, optionally using any of various known
creaming agents. Following the creaming of the carbon black/latex
mixture, it is subjected to a coagulation step. Specifically, the
creamed carbon black/latex mixture is introduced as a single
coherent stream into the core of a stream of coagulating liquor.
The solid stream of creamed carbon black/latex mixture is said to
undergo shearing and atomizing by the stream of coagulating liquor
prior to coagulation, being then passed to a suitable reaction zone
for completion of the coagulation. Following such coagulation step,
the remainder of the process is substantially conventional,
involving separation of the crumb from the waste product "serum"
and washing and drying of the crumb. A somewhat similar process is
described in U.S. Pat. No. 3,048,559 to Heller et al. An aqueous
slurry of carbon black is continuously blended with a stream of
natural or synthetic elastomer latex. The two streams are mixed
under conditions described as involving violent hydraulic
turbulence and impact. As in the case of the Hagopian et al. patent
mentioned above, the combined stream of carbon black slurry and
elastomer latex is subsequently coagulated by the addition of an
acid or salt coagulant solution.
Since good dispersion of a coagulating filler in the elastomer has
been recognized for some time as being important for achieving good
quality and consistent product performance, considerable effort has
been devoted to the development of procedures for assessing
dispersion quality in rubber. Methods developed include, e.g. the
Cabot Dispersion Chart and various image analysis procedures.
Dispersion quality can be defined as the state of mixing achieved.
An ideal dispersion of carbon black is the state in which the
carbon black agglomerates (or pellets) are broken down into
aggregates (accomplished by dispersive mixing) uniformly separated
from each other in the elastomer (accomplished by distributive
mixing), with the surfaces of all the carbon black aggregates
completely wetted by the rubber matrix (usually referred to as
incorporation).
Macro-dispersion of carbon black or other filler in uncured natural
rubber or other suitable elastomer can be assessed using image
analysis of cut surface samples. Typically, five to ten arbitrarily
selected optical images are taken of the cut surface for image
analysis. Knife marks and the like preferably are removed using a
numerical filtering technique. Cut surface image analysis thus
provides information regarding the carbon black dispersion quality
inside a natural rubber compound. Specifically, percent undispersed
area D(%) indicates carbon black macro-dispersion quality. As
macro-dispersion quality is degraded, percent undispersed area
increases. Dispersion quality can be improved, therefore, by
reducing the percent undispersed area.
A commercial image analyzer such as the IBAS Compact model image
analyzer available from Kontron Electronik GmbH (Munich, Germany)
can be used to measure macro-dispersion of carbon black or other
filler. Typically, in quantitative macro-dispersion tests used in
the rubber industry, the critical cut-off size is 10 microns.
Defects larger than about 10 microns in size typically consist of
undispersed carbon black or other filler, as well as any grit or
other contaminants, which can affect both visual and functional
performance. Thus, measuring macro-dispersion involves measuring
defects on a surface (generated by microtoming, extrusion or
cutting) greater than 10 microns in size, by total area of such
defects per unit area examined, using an image analysis procedure.
Macro-dispersion D(%) is calculated as follows: .times.
.times..function..times..times. .times..times..PI..times. .times.
##EQU00001## where A.sub.m=Total sample surface area examined
N.sub.i=Number of defects with size D.sub.i D.sub.i=Diameter of
circle having the same area as that of the defect (equivalent
circle diameter) m=number of images
There has long been a need in various industries for elastomeric
compounds of particulate filler dispersed in suitable elastomer,
especially, for example, carbon black dispersed in natural rubber,
having improved macro-dispersion. As discussed above, improved
macro-dispersion can provide correspondingly improved aesthetic and
functional characteristics. Especially desirable are new
elastomeric compounds of carbon black in natural rubber wherein
improved macro-dispersion is achieved together with controlled
Mooney Viscosity, higher molecular weight of the natural rubber,
and higher amount of bound rubber.
It is an object of the present invention to meet some or all of
these long felt needs.
SUMMARY OF THE INVENTION
In accordance with a first aspect, a method of treating a
substantially coagulated masterbatch having a particulate filler
and an elastomer includes the steps of feeding the masterbatch to a
feed port of a continuous compounder having multiple rotors axially
oriented in an elongate processing chamber; processing the
masterbatch through the processing chamber of the continuous
compounder by controlled operation of the rotors; and discharging
the masterbatch from a discharge orifice of the continuous
compounder. In certain preferred embodiments, the method may also
include the step of passing the masterbatch from the discharge
orifice of the continuous compounder through an open mill and/or
the step of compounding additional material into the masterbatch in
the continuous compounder. In certain preferred embodiments, the
additional material may be selected from additional filler,
additional elastomer, a second masterbatch, oil and other
additives. In certain preferred embodiments, the continuous
compounder dries the masterbatch. In certain preferred embodiments,
the continuous compounder controls the Mooney Viscosity of the
masterbatch.
In accordance with another aspect, a continuous flow method of
producing elastomer composite includes the steps of feeding a
continuous flow of first fluid including elastomer latex to a
mixing zone of a coagulum reactor defining an elongate coagulum
zone extending from the mixing zone to a discharge end; feeding a
continuous flow of second fluid having particulate filler under
pressure to the mixing zone of the coagulum reactor to form a
mixture with the elastomer latex, the mixture passing as a
continuous flow to the discharge end and the particulate filler
being effective to coagulate the elastomer latex, wherein mixing of
the first fluid and the second fluid within the mixing zone is
sufficiently energetic to substantially completely coagulate the
elastomer latex with the particulate filler prior to the discharge
end; discharging a substantially continuous flow of elastomer
composite from the discharge end of the coagulum reactor; feeding
the substantially continuous flow of elastomer composite to a feed
port of a continuous compounder having multiple parallel rotors
axially oriented in an elongate processing chamber; processing the
elastomer composite through the processing chamber of the
continuous compounder by controlled operation of the rotors; and
discharging the elastomer composite from a discharge orifice of the
continuous compounder. In certain preferred embodiments, the method
also includes the step of processing the elastomer composite from
the discharge orifice of the continuous compounder through an open
mill.
In accordance with another aspect, an apparatus for producing
elastomer composite of particulate filler dispersed in elastomer
has a coagulum reactor defining a mixing zone and an elongate
coagulum zone extending from the mixing zone to a discharge end;
latex feed means for feeding elastomer latex fluid continuously to
the mixing zone; filler feed means for feeding particulate filler
fluid as a continuous jet into the mixing zone to form a mixture
with the elastomer latex fluid traveling from the mixing zone to
the discharge end of the coagulum zone, wherein the distance
between the mixing zone and the discharge end is sufficient to
permit substantially complete coagulation of the elastomer latex
prior to the discharge end; and a continuous compounder having a
feed port operatively connected to the discharge end of the
coagulum zone for receiving the coagulated mixture of elastomer
latex and particulate filler, a discharge orifice, an elongate
processing chamber, and a plurality of rotors axially oriented
within the processing chamber. In certain preferred embodiments,
the apparatus further has conveying means for conveying a
substantially continuous flow of elastomer composite from the
discharge end of the coagulum zone to the feed port of the
continuous compounder.
In accordance with another aspect, an elastomer composite has
substantially coagulated elastomer in which particulate filler has
been dispersed by feeding a continuous flow of first fluid having
elastomer latex to a mixing zone of a coagulum reactor defining an
elongate coagulum zone extending from the mixing zone to a
discharge end; feeding a continuous flow of second fluid having
particulate filler under pressure to the mixing zone of the
coagulum reactor to form a mixture with the elastomer latex, the
mixture passing as a continuous flow to the discharge end, and the
particulate filler being effective to coagulate the elastomer
latex, wherein mixing of the first fluid and the second fluid
within the mixing zone is sufficiently energetic to substantially
completely coagulate the elastomer latex with the particulate
filler prior to the discharge end; discharging a substantially
continuous flow of elastomer composite from the discharge end of
the coagulum reactor; feeding the elastomer composite from the
discharge end of the coagulum reactor to a continuous compounder
having multiple parallel elongate rotors axially oriented in an
elongate processing chamber; processing the masterbatch through the
processing chamber of the continuous compounder by controlled
operation of the rotors; and discharging the masterbatch from a
discharge orifice of the continuous compounder.
In accordance with another aspect, masterbatch is processed in a
continuous compounder as described above along with the addition of
other materials. Specifically, the additional materials may be
additional filler; additional elastomers; additional masterbatch,
comprising elastomer composite and carbon black or other filler;
any of various known additives used in elastomer composites, such
as antioxidants, antiozonants, plasticizers, processing aids (e.g.,
liquid polymers, oils and the like), resins, flame-retardants,
extender oils, lubricants, and a mixture of any of them; and a
vulcanization system, or a mixture of any of these.
In accordance with another aspect, a method for preparing elastomer
masterbatch comprises feeding simultaneously a particulate filler
fluid and an elastomer latex fluid to a mixing zone of a coagulum
reactor, followed by further processing in a de-watering extruder
and continuous compounder, as disclosed above. Most preferably the
coagulum reactor, de-watering extruder and the continuous
compounder operate together in a continuous flow production line. A
coagulum zone of the coagulum reactor extends from the mixing zone,
preferably progressively increasing in cross-sectional area in the
downstream direction from an entry end to a discharge end. The
elastomer latex may be either natural or synthetic and the
particulate filler fluid comprises carbon black or other
particulate filler effective to coagulate the latex. The
particulate filler fluid is fed to the mixing zone preferably as a
continuous, high velocity jet of injected fluid, while the latex
fluid is fed at low velocity. The velocity, flow rate and
particulate concentration of the particulate filler fluid are
sufficient to cause high shear mixing with the latex fluid and flow
turbulence of the mixture within at least an upstream portion of
the coagulum zone, so as to substantially completely coagulate the
elastomer latex with the particulate filler prior to the discharge
end. Substantially complete coagulation is thus achieved, in
accordance with preferred embodiments, without the need of
employing an acid or salt coagulation agent. The coagulum reactor
is discussed in detail in commonly owned and copending U.S.
application Ser. No. 08/823,411 and in Published PCT Application
Serial Number PCT/US97/05276, both of which are incorporated herein
by reference. The masterbatch from the coagulum reactor is fed
through a de-watering extruder to remove the bulk of the water from
the masterbatch and then into a feed port of the continuous
compounder disclosed above, preferably in a continuous flow stream
from the coagulum reactor. The continuous compounder dries the
elastomer masterbatch, provides control over the Mooney Viscosity
of the elastomer masterbatch and, in certain preferred embodiments,
control over other characteristics and performance properties of
the masterbatch via manipulation of continuous compounder operating
parameters, including rotor speed, throughput rate, discharge
orifice opening size, discharge orifice temperature and processing
chamber temperature. The masterbatch may, in accordance with
certain preferred embodiments, optionally be further processed
after the continuous compounder by an open mill to further control
the Mooney Viscosity of the masterbatch. This is especially
advantageous, since the elastomer masterbatch produced by the
coagulum reactor may have a Mooney Viscosity which is too high for
use in certain applications. Further processing of the masterbatch
by the continuous compounder and the open mill is now found to
provide excellent product control to achieve a desired Mooney
Viscosity and moisture level.
In especially preferred embodiments, the above disclosed
de-watering extruder is connected to the coagulum reactor by a
conveyor or conduit for carrying masterbatch from the coagulum
reactor to the de-watering extruder, and the continuous compounder
is directly downstream of the de-watering extruder, such that the
masterbatch is produced and treated in a continuous flow process.
Thus, a continuous process line is created for the formation and
treatment of elastomer masterbatch, which provides for
significantly enhanced economies of production. Use of the
continuous compounder with a de-watering extruder and coagulum
reactor in a continuous process line can facilitate controlling and
changing operating parameters of the masterbatch production and
treatment line without interrupting the continuous process
line.
In accordance with an apparatus aspect, a coagulum reactor,
de-watering extruder and continuous compounder described above are
coupled in a masterbatch production and treatment line. In
accordance with certain preferred embodiments, an open mill is
provided to cool the elastomer masterbatch and further control its
Mooney Viscosity after it passes through the continuous
compounder.
In accordance with another apparatus aspect, means are provided for
feeding elastomer latex fluid to the mixing zone of the aforesaid
coagulum reactor, preferably under low pressure, substantially
laminar type flow conditions, and means are provided for
simultaneously feeding particulate filler fluid to the mixing zone
under pressure sufficient to create a jet of adequate velocity or
kinetic energy to entrain the elastomer latex, as described above,
and achieve coagulation before the product flowing downstream from
the mixing zone reaches the discharge end of the coagulum reactor.
In accordance with certain preferred embodiments described in
detail below, means for feeding the elastomer latex fluid and
separate means for feeding the particulate filler fluid each may
comprise a feed channel in a mixing head integral with a
substantially tubular member defining the coagulum zone. The mixing
zone may be provided at the junction of such feed channels within
the mixing head. In accordance with certain preferred embodiments,
the mixing zone is simply a coaxial extension of the coagulum zone.
Progressive increase in the cross-sectional area of the coagulum
reactor is continuous in certain preferred embodiments and is
step-wise in other preferred embodiments. A de-watering extruder
and continuous compounder are positioned downstream of the coagulum
reactor to further process the elastomer masterbatch, providing
drying and control of the Mooney Viscosity and other physical
properties and performance characteristics of the elastomer
masterbatch. In certain preferred embodiments, an open mill may be
coupled to the discharge orifice of the continuous compounder,
either directly or via a conveyor or other conduit, to provide yet
further treatment of the elastomer masterbatch. Additional optional
and preferred features of the apparatus disclosed here for
continuous flow production of elastomer masterbatch are discussed
in the detailed description below.
In accordance with yet another aspect, elastomer composites are
provided as a product of the process or apparatus disclosed above.
In accordance with preferred embodiments, novel elastomer
composites are provided having macro-dispersion level of the
particulate filler, molecular weight of the elastomer, particulate
loading level, choice of particulate filler (including, for
example, carbon black fillers of exceptionally high surface area
and low structure), controlled Mooney Viscosity and/or other
physical properties or performance characteristics not previously
achieved. Additionally, a suitable balance can be obtained between
the molecular weight and bound rubber of the masterbatch for a
given Mooney Viscosity. In that regard, the methods and apparatus
disclosed here can achieve excellent macro-dispersion, even of
certain fillers, such as carbon blacks having a structure to
surface area ratio DBP:CTAB less than 1.2 and even less than 1, in
elastomers such as natural rubber, while minimizing degradation of
the molecular weight of the elastomer and highly controlled Mooney
Viscosity. In accordance with yet other aspects of the invention,
intermediate products are provided as well as final products which
are formed of the elastomer composites produced by the method or
apparatus disclosed here, e.g., tires and tire components. Further
examples of such final products are listed below.
These and other aspects and advantages of various embodiments of
the invention will be further understood in view of the following
detailed discussion of certain preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
The following discussion of certain preferred embodiments will make
reference to the appended drawings wherein:
FIG. 1 is a schematic flow chart illustration of the apparatus and
method for preparing elastomer masterbatch in accordance with
certain preferred embodiments of the present invention;
FIG. 2 is an elevation view, partly schematic, of a preferred
embodiment consistent with the schematic flow chart illustration of
FIG. 1;
FIG. 3 is an elevation view, partially schematic, of an alternative
preferred embodiment consistent with the schematic flow chart
illustration of FIG. 1;
FIG. 4 is an elevation view, partially in section, of the mixing
head/coagulum reactor assembly of the embodiment of FIG. 3;
FIG. 5 is an elevation view, partially in section, corresponding to
the view of FIG. 4, illustrating an alternative preferred
embodiment;
FIG. 6 is a section view taken through line 6-6 of FIG. 5;
FIG. 7 is a section view of a mixing head suitable for use in an
alternative preferred embodiment;
FIG. 8 is a schematic flowchart of a portion of an alternative
embodiment of the masterbatch production line of FIG. 1 showing the
continuous compounder of FIG. 1 in section; and
FIG. 9 is a schematic flowchart of a portion of an alternative
embodiment of the apparatus and method of FIG. 1.
It should be understood that the appended drawings are not
necessarily precisely to scale. Certain features may have been
enlarged or reduced for convenience or clarity of illustration.
Directional references used in the following discussion are based
on the orientation of components illustrated in the drawings unless
otherwise stated or otherwise clear from the context. In general,
apparatus in accordance with different embodiments of the invention
can be employed in various arrangements. It will be within the
ability of those skilled in the art, given the benefit of the
present disclosure, to determine appropriate dimensions and
orientations for apparatus of the invention employing routine
technical skills and taking into account well-known factors
particular to the intended application, such as desired production
volumes, material selection, duty cycle, and the like. Reference
numbers used in one drawing may be used in other drawings for the
same feature or element.
DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS
The following is a detailed description of certain preferred
embodiments of the present invention and is not intended to limit
the present invention to the embodiments described below.
By virtue of the method and apparatus disclosed here, wet elastomer
masterbatch can be processed to remove moisture, reduce its Mooney
Viscosity, and/or to compound it with other materials. Preferably
the masterbatch is produced in a continuous flow process involving
mixture of elastomer latex and particulate filler fluids at
turbulence levels and flow control conditions sufficient to achieve
coagulation even without use of traditional coagulating agents. In
fact, it will be immediately recognized to be of great commercial
benefit that elastomer masterbatch crumb is achieved, that is,
coagulated latex is achieved, without the need for either intensive
dry mastication of elastomer with filler or exposing a liquid
latex/particulate composition to a stream or tank of coagulant.
Thus, in routine commercial implementation the cost and complexity
of employing acid coagulation solutions can be avoided. Prior
techniques involving premixing of latex and particulate, such as in
the above-mentioned Heller et al. patent and Hagopian et al. patent
do not even recognize the possibility of achieving coagulation
without exposing the latex/particulate mixture to the usual
coagulant solution with its attendant cost and waste disposal
disadvantages. Elastomer masterbatch produced by this continuous
flow process may have a Mooney Viscosity and moisture level which
are too high for certain applications. The use of a de-watering
extruder and continuous compounder, described in greater detail
below, dries the elastomer masterbatch and controls its Mooney
Viscosity, while optimizing molecular weight and bound rubber.
Feed rates of latex fluid and particulate filler fluid to the
mixing zone of the coagulum reactor can be precisely metered to
achieve high yield rates, with little free latex and little
undispersed filler in the product crumb at the discharge end of the
coagulum reactor. Without wishing to be bound by theory, it
presently is understood that a quasi-mono-phase system is
established in the mixing zone except that coagulum solids are
being formed there and/or downstream thereof in the coagulum zone.
Extremely high feed velocity of the particulate filler fluid into
the mixing zone of the coagulum reactor and velocity differential
relative the latex fluid feed are believed to be significant in
achieving sufficient turbulence, i.e., sufficiently energetic shear
of the latex by the impact of the particulate filler fluid jet for
thorough mixing and dispersion of the particulate into the latex
fluid and coagulation. High mixing energies yield product
masterbatch crumb with excellent dispersion, together with
controlled product delivery. The coagulum is created and then
formed into a desirable extrudate.
Certain preferred embodiments are discussed below, of methods and
apparatus for producing the novel elastomer composites disclosed
here. While various preferred embodiments of the invention can
employ a variety of different fillers and elastomers, certain
portions of the following detailed description of method and
apparatus aspects of the invention will, for convenience, describe
their use primarily in producing masterbatch comprising natural
rubber and carbon black. It will be within the ability of those
skilled in the art, given the benefit of this disclosure, to employ
the method and apparatus disclosed here in accordance with the
principles of operation discussed below to produce masterbatch
comprising a number of alternative or additional elastomers,
fillers and other materials. In brief, such methods for preparing
elastomer masterbatch involve feeding simultaneously a slurry of
carbon black or other filler and a natural rubber latex fluid or
other suitable elastomer fluid to a mixing zone of a coagulum
reactor. A coagulum zone extends from the mixing zone, preferably
progressively increasing in cross-sectional area in the downstream
direction from an entry end to a discharge end. The slurry is fed
to the mixing zone preferably as a continuous, high velocity jet of
injected fluid, while the natural rubber latex fluid is fed at
relatively low velocity. The high velocity, flow rate and
particulate concentration of the filler slurry are sufficient to
cause mixture and high shear of the latex fluid, flow turbulence of
the mixture within at least an upstream portion of the coagulum
zone, and substantially completely coagulate the elastomer latex
prior to the discharge end. Substantially complete coagulation can
thus be achieved, in accordance with preferred embodiments, without
the need of employing an acid or salt coagulation agent. The
preferred continuous flow method of producing the elastomer
composites comprises the continuous and simultaneous feeding of the
latex fluid and filler slurry to the mixing zone of the coagulum
reactor, establishing a continuous, semi-confined flow of a mixture
of the latex and filler slurry in the coagulum zone. Elastomer
composite crumb in the form of "worms" or globules are discharged
from the discharge end of the coagulum reactor as a substantially
constant flow concurrently with the on-going feeding of the latex
and carbon black slurry streams into the mixing zone of the
coagulum reactor. Notably, the plug-type flow and atmospheric or
near atmospheric pressure conditions at the discharge end of the
coagulum reactor are highly advantageous in facilitating control
and collection of the elastomer composite product, such as for
immediate or subsequent further processing steps. Feed rates of the
natural rubber latex fluid and carbon black slurry to the mixing
zone of the coagulum reactor can be precisely metered to achieve
high yield rates, with little free latex and little undispersed
carbon black in the product crumb at the discharge end of the
coagulum reactor. Without wishing to be bound by theory, it
presently is understood that a quasi-mono-phase system is
established in the mixing zone except that coagulum solids are
being formed there and/or downstream thereof in the coagulum zone.
Extremely high feed velocity of the carbon black slurry into the
mixing zone of the coagulum reactor and velocity differential
relative the natural rubber latex fluid feed are believed to be
significant in achieving sufficient turbulence, i.e., sufficiently
energetic shear of the latex by the impact of the particulate
filler fluid jet, for thorough mixing and dispersion of the
particulate into the latex fluid and coagulation. High mixing
energies yield the novel product with excellent macro-dispersion,
together with controlled product delivery. The coagulum is created
and then formed into a desirable extrudate. The bulk of the water
in the extrudate is then preferably removed by a de-watering
extruder (e.g., from approximately 80% water content to
approximately 15% to 25% water content) and further processed by a
continuous compounder to dry the elastomer masterbatch to a desired
level (e.g., below approximately 1% water content) and control its
Mooney Viscosity. In certain preferred embodiments, the masterbatch
is then processed by an open mill to further control the Mooney
Viscosity of the elastomer masterbatch.
The aforesaid preferred apparatus and techniques for producing the
elastomer composites disclosed here are discussed in conjunction
with the appended drawings, wherein a continuous flow method of
producing elastomer masterbatch employs a continuous, semi-confined
flow of elastomer latex, for example, natural rubber latex (field
latex or concentrate) mixed with a filler slurry, for example, an
aqueous slurry of carbon black, in a coagulum reactor forming an
elongate coagulum zone which extends, preferably with progressively
increasing cross-sectional area, from an entry end to a discharge
end. The term "semi-confined" flow refers to a highly advantageous
feature. As used here the term is intended to mean that the flow
path followed by the mixed latex fluid and filler slurry within the
coagulum reactor is closed or substantially closed upstream of the
mixing zone and is open at the opposite, downstream end of the
coagulum reactor, that is, at the discharge end of the coagulum
reactor. Turbulence conditions in the upstream portion of the
coagulum zone are maintained in on-going, at least quasi-steady
state fashion concurrently with substantially plug flow-type
conditions at the open discharge end of the coagulum reactor. The
discharge end is "open" at least in the sense that it permits
discharge of coagulum, generally at or near atmospheric pressure
and, typically, by simple gravity drop (optionally within a
shrouded or screened flow path) into suitable collection means,
such as a hopper connected to a de-watering extruder. Thus, the
semi-confined flow results in a turbulence gradient extending
axially or longitudinally within at least a portion of the coagulum
reactor. Without wishing to be bound by theory, it presently is
understood that the coagulum zone is significant in permitting high
turbulence mixing and coagulation in an upstream portion of the
coagulum reactor, together with substantially plug-type discharge
flow of a solid product at the discharge end. Injection of the
carbon black or other filler slurry as a continuous jet into the
mixing zone occurs in on-going fashion simultaneously with ease of
collection of the elastomer masterbatch crumb discharged under
substantially plug-type flow conditions and generally ambient
pressure at the discharge end of the coagulum reactor. Similarly,
axial velocities of the slurry through the slurry nozzle into the
mixing zone and, typically, at the upstream end of the coagulum
zone are substantially higher than at the discharge end. Axial
velocity of the slurry will typically be several hundred feet per
second as it enters the mixing zone, preferably from a small bore,
axially oriented feed tube in accordance with preferred embodiments
discussed below. The axial velocity of the resultant flow at the
entry end of a coagulum reactor with expanding cross-sectional area
in a typical application may be, for example, 5 to 20 feet per
second, and more usually 7 to 15 feet per second. At the discharge
end, in contrast again, axial velocity of the masterbatch crumb
product being discharged there will in a typical application be
approximately 1 to 10 feet per second, and more generally 2 to 5
feet per second. Thus, the aforesaid semi-confined turbulent flow
achieves the highly significant advantage that natural rubber or
other elastomer latex is coagulated by mixture with carbon black or
other filler even in the absence of subsequent treatment in a
stream or tank of acid, salt or other coagulant solution, with
controlled, preferably quasi-molded product delivery from the
coagulum reactor for subsequent processing.
It should also be recognized in this regard that the turbulence of
the flow lessens along the coagulum reactor toward the discharge
end. Substantial plug flow of a solid product is achieved prior to
the discharge end, dependent upon such factors as percent of
capacity utilization, selection of materials and the like.
Reference here to the flow being substantially plug flow at or
before the discharge end of the coagulum reactor should be
understood in light of the fact that the flow at the discharge end
is composed primarily or entirely of masterbatch crumb, that is,
globules or "worms" of coagulated elastomer masterbatch. The crumb
is typically quasi-molded to the inside shape of the coagulum zone
at the point along the coagulum zone at which flow became
substantially plug flow. The ever-advancing mass of "worms" or
globules advantageously have plug-type flow in the sense that they
are traveling generally or primarily axially toward the discharge
end and at any point in time in a given cross-section of the
coagulum zone near the discharge end have a fairly uniform
velocity, such that they are readily collected and controlled for
further processing. Thus, the fluid phase mixing aspect disclosed
here can advantageously be carried out at steady state or
quasi-steady state conditions, resulting in high levels of product
uniformity.
A preferred embodiment of the method and apparatus disclosed here
is illustrated schematically in FIG. 1. Those skilled in the art
will recognize that the various aspects of system configuration,
component selection and the like will depend to some extent on the
particular characteristics of the intended application. Thus, for
example, such factors as maximum system through-put capacity and
material selection flexibility will influence the size and layout
of system components. In general, such considerations will be well
within the ability of those skilled in the art given the benefit of
the present disclosure. The system illustrated in FIG. 1 is seen to
include means for feeding natural rubber latex or other elastomer
latex fluid at low pressure and low velocity continuously to a
mixing zone of a coagulum reactor. More particularly, a latex
pressure tank 10 is shown, to hold the feed supply of latex under
pressure. Alternatively, a latex storage tank can be used, equipped
with a peristaltic pump or series of pumps or other suitable feed
means adapted to hold elastomer latex fluid to be fed via feed line
12 to a mixing zone of a coagulum reactor 14. Latex fluid in tank
10 may be held under air or nitrogen pressure or the like, such
that the latex fluid is fed to the mixing zone at a line pressure
of preferably less than 10 psig, more preferably about 2-8 psig,
and typically about 5 psig. The latex feed pressure and the flow
lines, connections, etc., of the latex feed means should be
arranged to maintain shear in the flowing latex fluid as low as
reasonably possible. Preferably all flow lines, for example, are
smooth, with only large radius turns, if any, and smooth or flared
line-to-line interconnections. The pressure is selected to yield
the desired flow velocity into the mixing zone; an example of a
useful flow velocity is no more than about 12 feet per second.
Suitable elastomer latex fluids include both natural and synthetic
elastomer latices and latex blends. The latex must, of course, be
suitable for coagulation by the selected particulate filler and
must be suitable for the intended purpose or application of the
final rubber product. It will be within the ability of those
skilled in the art to select suitable elastomer latex or a suitable
blend of elastomer latices for use in the methods and apparatus
disclosed here, given the benefit of this disclosure. Exemplary
elastomers include, but are not limited to, rubbers, polymers
(e.g., homopolymers, copolymers and/or terpolymers) of
1,3-butadiene, styrene, isoprene, isobutylene,
2,3-dimethyl-1,3-butadiene, acrylonitrile, ethylene, and propylene
and the like. The elastomer may have a glass transition temperature
(Tg) as measured by differential scanning calorimetry (DSC) ranging
from about -120.degree. C. to about 0.degree. C. Examples include,
but are not limited to, styrene-butadiene rubber (SBR), natural
rubber and its derivatives such as chlorinated rubber,
polybutadiene, polyisoprene, poly (stryene-co-butadiene) and the
oil extended derivatives of any of them. Blends of any of the
foregoing may also be used. The latex may be in an aqueous carrier
liquid. Alternatively, the liquid carrier may be a hydrocarbon
solvent. In any event, the elastomer latex fluid must be suitable
for controlled continuous feed at appropriate velocity, pressure
and concentration into the mixing zone. Particular suitable
synthetic rubbers include: copolymers of from about 10 to about 70
percent by weight of styrene and from about 90 to about 30 percent
by weight of butadiene such as copolymer of 19 parts styrene and 81
parts butadiene, a copolymer of 30 parts styrene and 70 parts
butadiene, a copolymer of 43 parts styrene and 57 parts butadiene
and a copolymer of 50 parts styrene and 50 parts butadiene;
polymers and copolymers of conjugated dienes such as polybutadiene,
polyisoprene, polychloroprene, and the like, and copolymers of such
conjugated dienes with an ethylenic group-containing monomer
copolymerizable therewith such as styrene, methyl styrene,
chlorostyrene, acrylonitrile, 2-vinyl-pyridine,
5-methyl-2-vinylpyridine, 5-ethyl-2-vinylpyridine,
2-methyl-5-vinylpyridine, alkyl-substituted acrylates, vinyl
ketone, methyl isopropenyl ketone, methyl vinyl either,
alphamethylene carboxylic acids and the esters and amides thereof
such as acrylic acid and dialkylacrylic acid amide. Also suitable
for use herein are copolymers of ethylene and other high alpha
olefins such as propylene, butene-1 and pentene-1. As noted further
below, the rubber compositions of the present invention can
contain, in addition to the elastomer and filler, a coupling agent,
and optionally, various processing aids, oil extenders and
antidegradents.
In that regard, it should be understood that the elastomer
composites disclosed here include vulcanized compositions (VR),
thermoplastic vulcanizates (TPV), thermoplastic elastomers (TPE)
and thermoplastic polyolefins (TPO). TPV, TPE, and TPO materials
are further classified by their ability to be extruded and molded
several times without loss of performance characteristics.
Where the elastomer latex comprises natural rubber latex, the
natural rubber latex can comprise field latex or latex concentrate
(produced, for example, by evaporation, centrifugation or
creaming). The natural rubber latex must, of course, be suitable
for coagulation by the carbon black. The latex is provided
typically in an aqueous carrier liquid. Alternatively, the liquid
carrier may be a hydrocarbon solvent. In any event, the natural
rubber latex fluid must be suitable for controlled continuous feed
at appropriate velocity, pressure and concentration into the mixing
zone. The well known instability of natural rubber latex is
advantageously accommodated, in that it is subjected to relatively
low pressure and low shear throughout the system until it is
entrained into the aforesaid semi-confined turbulent flow upon
encountering the extraordinarily high velocity and kinetic energy
of the carbon black slurry in the mixing zone. In certain preferred
embodiments, for example, the natural rubber is fed to the mixing
zone at a pressure of about 5 psig, at a feed velocity in the range
of about 3-12 ft. per second, more preferably about 4-6 ft. per
second. Selection of a suitable latex or blend of latices will be
well within the ability of those skilled in the art given the
benefit of the present disclosure and the knowledge of selection
criteria generally well recognized in the industry.
The particulate filler fluid, for example, carbon black slurry, is
fed to the mixing zone at the entry end of coagulum reactor 14 via
feed line 16. The slurry may comprise any suitable filler in a
suitable carrier fluid. Selection of the carrier fluid will depend
largely upon the choice of particulate filler and upon system
parameters. Both aqueous and non-aqueous liquids may be used, with
water being preferred in many embodiments in view of its cost,
availability and suitability of use in the production of carbon
black and certain other filler slurries.
When a carbon black filler is used, selection of the carbon black
will depend largely upon the intended use of the elastomer
masterbatch product. Optionally, the carbon black filler can
include also any material which can be slurried and fed to the
mixing zone in accordance with the principles disclosed here. Other
suitable particulate fillers include, for example, conductive
fillers, reinforcing fillers, fillers comprising short fibers
(typically having an L/D aspect ratio less than 40), flakes, etc.
Thus, exemplary particulate fillers which can be employed in
producing elastomer masterbatch in accordance with the methods and
apparatus disclosed here, are carbon black, fumed silica,
precipitated silica, coated carbon black, chemically functionalized
carbon blacks, such as those having attached organic groups, and
silicon-treated carbon black, either alone or in combination with
each other. Suitable chemically functionalized carbon blacks
include those disclosed in International Application No.
PCT/US95/16194 (WO 9618688), the disclosure of which is hereby
incorporated by reference. In silicon-treated carbon black, a
silicon containing species such as an oxide or carbide of silicon,
is distributed through at least a portion of the carbon black
aggregate as an intrinsic part of the carbon black. Conventional
carbon blacks exist in the form of aggregates, with each aggregate
consisting of a single phase, which is carbon. This phase may exist
in the form of a graphitic crystallite and/or amorphous carbon, and
is usually a mixture of the two forms. As discussed elsewhere
herein, carbon black aggregates may be modified by depositing
silicon-containing species, such as silica, on at least a portion
of the surface of the carbon black aggregates. The result may be
described as silicon-coated carbon blacks. The materials described
herein as silicon-treated carbon blacks are not carbon black
aggregates which have been coated or otherwise modified, but
actually represent a different kind of aggregate. In the
silicon-treated carbon blacks, the aggregates contain two phases.
One phase is carbon, which will still be present as graphitic
crystallite and/or amorphous carbon, while the second phase is
silica (and possibly other silicon-containing species). Thus, the
silicon-containing species phase of the silicon-treated carbon
black is an intrinsic part of the aggregate; it is distributed
throughout at least a portion of the aggregate. It will be
appreciated that the multiphase aggregates are quite different from
the silica-coated carbon blacks mentioned above, which consist of
pre-formed, single phase carbon black aggregates having
silicon-containing species deposited on their surface. Such carbon
blacks may be surface-treated in order to place a silica
functionality on the surface of the carbon black aggregate. In this
process, an existing aggregate is treated so as to deposit or coat
silica (as well as possibly other silicon-containing species) on at
least a portion of the surface of the aggregate. For example, an
aqueous sodium silicate solution may be used to deposit amorphous
silica on the surface of carbon black aggregates in an aqueous
slurry at high pH, such as 6 or higher, as discussed in Japanese
Unexamined Laid-Open (Kokai) Publication No. 63-63755. More
specifically, carbon black may be dispersed in water to obtain an
aqueous slurry consisting, for example, of about 5% by weight
carbon black and 95% by weight water. The slurry is heated to above
about 70.degree. C., such as to 85-95.degree. C., and the pH
adjusted to above 6, such as to a range of 10-11, with an alkali
solution. A separate preparation is made of sodium silicate
solution, containing the amount of silica which is desired to be
deposited on the carbon black, and an acid solution to bring the
sodium silicate solution to a neutral pH. The sodium silicate and
acid solutions are added dropwise to the slurry, which is
maintained at its starting pH value with acid or alkali solution as
appropriate. The temperature of the solution is also maintained. A
suggested rate for addition of the sodium silicate solution is to
calibrate the dropwise addition to add about 3 weight percent
silicic acid, with respect to the total amount of carbon black, per
hour. The slurry should be stirred during the addition, and after
its completion for from several minutes (such as 30) to a few hours
(i.e., 2-3). In contrast, silicon-treated carbon blacks may be
obtained by manufacturing carbon black in the presence of
volatizable silicon-containing compounds. Such carbon blacks are
preferably produced in a modular or "staged" furnace carbon black
reactor having a combustion zone followed by a zone of converging
diameter, a feed stock injection zone with restricted diameter, and
a reaction zone. A quench zone is located downstream of the
reaction zone. Typically, a quenching fluid, generally water, is
sprayed into the stream of newly formed carbon black particles
flowing from the reaction zone. In producing silicon-treated carbon
black, the aforesaid volatizable silicon-containing compound is
introduced into the carbon black reactor at a point upstream of the
quench zone. Useful compounds are volatizable compounds at carbon
black reactor temperatures. Examples include, but are not limited
to, silicates such as tetraethoxy orthosilicate (TEDS) and
tetramethoxy orthosilicate, silanes such as, tetrachloro silane,
and trichloro methylsilane; and volatile silicone polymers such as
octamethylcyclotetrasiloxane (OMTS). The flow rate of the
volatilizable compound will determine the weight percent of silicon
in the treated carbon black. The weight percent of silicon in the
treated carbon black typically ranges from about 0.1 percent to 25
percent, preferably about 0.5 percent to about 10 percent, and more
preferably about 2 percent to about 6 percent. The volatizable
compound may be pre-mixed with the carbon black-forming feed stock
and introduced with the feed stock into the reaction zone.
Alternatively, the volatizable compound may be introduced to the
reaction zone separately, either upstream or downstream from the
feed stock injection point.
As noted above, additives may be used, and in this regard coupling
agents useful for coupling silica or carbon black should be
expected to be useful with the silicon-treated carbon blacks.
Carbon blacks and numerous other suitable particulate fillers are
commercially available and are known to those skilled in the
art.
Selection of the particulate filler or mixture of particulate
fillers will depend largely upon the intended use of the elastomer
masterbatch product. As used here, particulate filler can include
any material which can be slurried and fed to the mixing zone in
accordance with the principles disclosed here. Suitable particulate
fillers include, for example, conductive fillers, reinforcing
fillers, fillers comprising short fibers (typically having an L/D
aspect ratio less than 40), flakes, etc. In addition to the carbon
black and silica-type fillers mentioned above, fillers can be
formed of clay, glass, polymer, such as aramid fiber, etc. It will
be within the ability of those skilled in the art to select
suitable particulate fillers for use in the method and apparatus
disclosed here given the benefit of the present disclosure, and it
is expected that any filler suitable for use in elastomer
compositions may be incorporated into the elastomer composites
using the teachings of the present disclosure. Of course, blends of
the various particulate fillers discussed herein may also be
used.
Preferred embodiments of the invention consistent with FIG. 1 are
especially well adapted to preparation of particulate filler fluid
comprising aqueous slurries of carbon black. In accordance with
known principles, it will be understood that carbon blacks having
lower surface area per unit weight must be used in higher
concentration in the particulate slurry to achieve the same
coagulation efficacy as lower concentrations of carbon black having
higher surface area per unit weight. Agitated mixing tank 18
receives water and carbon black, e.g., optionally pelletized carbon
black, to prepare an initial mixture fluid. Such mixture fluid
passes through discharge orifice 20 into fluid line 22 equipped
with pumping means 24, such as a diaphragm pump or the like. Line
28 passes the mixture fluid to colloid mill 32, or alternatively a
pipeline grinder or the like, through intake port 30. The carbon
black is dispersed in the aqueous carrier liquid to form a
dispersion fluid which is passed through outlet port 31 and fluid
line 33 to a homogenizer 34. Pumping means 36, preferably
comprising a progressing cavity pump or the like is provided in
line 33. Homogenizer 34 more finely disperses the carbon black in
the carrier liquid to form the carbon black slurry which is fed to
the mixing zone of the coagulum reactor 14. It has an inlet port 37
in fluid communication with line 33 from the colloid mill 32. The
homogenizer 34 may preferably comprise, for example, a
Microfluidizer.RTM. system commercially available from
Microfluidics International Corporation (Newton, Mass., USA). Also
suitable are homogenizers such as models MS18, MS45 and MC120
Series homogenizers available from the APV Homogenizer Division of
APV Gaulin, Inc. (Wilmington, Mass., USA). Other suitable
homogenizers are commercially available and will be apparent to
those skilled in the art given the benefit of the present
disclosure. Typically, carbon black in water prepared in accordance
with the above described system will have at least about 90%
agglomerates less than about 30 microns, more preferably at least
about 90% agglomerates less than about 20 microns in size.
Preferably, the carbon black is broken down to an average size of
5-15 microns, e.g., about 9 microns. Exit port 38 passes the carbon
black slurry from the homogenizer to the mixing zone through feed
line 16. The slurry may reach 10,000 to 15,000 psi in the
homogenizer step and exit the homogenizer at about 600 psi or more.
Preferably, a high carbon black content is used to reduce the task
of removing excess water or other carrier. Typically, about 10 to
30 weight percent carbon black is preferred. Those skilled in the
art will recognize, given the benefit of this disclosure, that the
carbon black content (in weight percent) of the slurry and the
slurry flow rate to the mixing zone should be coordinated with the
natural rubber latex flow rate to the mixing zone to achieve a
desired carbon black content (in phr) in the masterbatch. The
carbon black content will be selected in accordance with known
principles to achieve material characteristics and performance
properties suited to the intended application of the product.
Typically, for example, carbon blacks of CTAB value 10 or more are
used in sufficient amount to achieve carbon black content in the
masterbatch of at least about 30 phr.
The slurry preferably is used in masterbatch production immediately
upon being prepared. Fluid conduits carrying the slurry and any
optional holding tanks and the like, should establish or maintain
conditions which substantially preserve the dispersion of the
carbon black in the slurry. That is, substantial reaglomeration or
settling out of the particulate filler in the slurry should be
prevented or reduced to the extent reasonably practical. Preferably
all flow lines, for example, are smooth, with smooth line-to-line
interconnections. Optionally, an accumulator is used between the
homogenizer and the mixing zone to reduce fluctuations in pressure
or velocity of the slurry at the slurry nozzle tip in the mixing
zone.
Natural rubber latex fluid or other elastomer latex fluid passed to
the mixing zone via feed line 12 and carbon black slurry fed to the
mixing zone via feed line 16 under proper process parameters as
discussed above, can produce a novel elastomer composite,
specifically, elastomer masterbatch crumb. Means may also be
provided for incorporating various additives into the elastomer
masterbatch. An additive fluid comprising one or more additives may
be fed to the mixing zone as a separate feed stream. One or more
additives also may be pre-mixed, if suitable, with the carbon black
slurry or, more typically, with the elastomer latex fluid.
Additives also can be mixed into the masterbatch subsequently,
e.g., by dry mixing techniques. Numerous additives are well known
to those skilled in the art and include, for example, antioxidants,
antiozonants, plasticizers, processing aids (e.g., liquid polymers,
oils and the like), resins, flame-retardants, extender oils,
lubricants, and a mixture of any of them. The general use and
selection of such additives is well known to those skilled in the
art. Their use in the system disclosed here will be readily
understood with the benefit of the present disclosure.
The mixing zone/coagulum zone assembly is discussed in more detail
below. The elastomer masterbatch crumb is passed from the discharge
end of coagulum reactor 14 to suitable drying and compounding
apparatus. In the preferred embodiment of FIG. 1, the masterbatch
crumb is passed first via conveying means 41 to a de-watering
extruder 40. In routine preferred embodiments consistent with that
illustrated in FIG. 1 producing natural rubber masterbatch with
carbon black filler, the de-watering operation will typically
reduce water content from about 70-80 weight percent, to about
15-25 weight percent. Water is discharged from de-watering extruder
40 via effluent stream 43. Suitable de-watering extruders are well
known and commercially available from, for example, the French Oil
Machinery Co. (Piqua, Ohio, USA).
The masterbatch is passed from de-watering extruder 40 via conveyor
or simple gravity drop or other suitable means 101 to a continuous
compounder 100 and then to an open mill 120. In routine preferred
embodiments consistent with that illustrated in FIG. 1 producing
natural rubber masterbatch with carbon black filler, the
compounding and milling operation will typically reduce water
content from about 15-25 weight percent, to less than 1 weight
percent. In certain preferred embodiments, additives can be
combined with the masterbatch in continuous compounder 100.
Specifically, additives such as antioxidants, antiozonants,
plasticizers, processing aids (e.g., liquid polymers, oils and the
like), resins, flame-retardants, extender oils, lubricants, and a
mixture of any of them, can be added in continuous compounder 100.
In certain other preferred embodiments, additional elastomers can
be combined with the masterbatch in continuous compounder 100 to
produce elastomer blends. Exemplary elastomers include, but are not
limited to, rubbers, polymers (e.g., homopolymers, copolymers
and/or terpolymers) of 1,3-butadiene, styrene, isoprene,
isobutylene, 2,3-dimethyl-1,3-butadiene, acrylonitrile, ethylene,
and propylene and the like. Continuous compounder 100 dries the
masterbatch, masticates the masterbatch, provides control of its
Mooney Viscosity and molecular weight, and minimizes the reduction
of bound rubber. Suitable continuous compounders are well known and
commercially available, including for example, the Unimix
Continuous Mixer from Farrel Corporation of Ansonia, Conn.
As seen in FIGS. 1 and 8, the elastomer masterbatch is fed from
coagulum reactor 14 to de-watering extruder 40 and then into feed
port 102 formed in an elongate processing chamber 104 of continuous
compounder 100. In certain preferred embodiments, feed port 102 is
a hopper which facilitates a gravity drop of the elastomer
masterbatch from de-watering extruder 40. Feed port 102 may also be
fed via conveyor means such as a conveyor belt, conduit, pipe, or
any other suitable means for transporting elastomer masterbatch.
Processing chamber 104 is contained within housing 105 of
continuous compounder 100. Elongate rotors 106 are seen to be
parallel to each other and axially oriented in processing chamber
104. Rotors 106 are driven by motor 108 via gear reducer 110 and
bearings 112. Rotors 106 are adapted in accordance with known
designs for processing material axially through elongate processing
chamber 104. As seen in FIG. 8, multiple rotors 106 are axially
oriented in processing chamber 104. Rotors 106 preferably are
segmented, with different segments optionally having different
thread or screw configurations. In a preferred embodiment,
processing chamber 104 houses two rotors 106 having different
profiles. Suitable rotors 106 having different profiles include,
for example, rotor model numbers 7 and 15 from Farrel Corporation
of Ansonia Conn. In a preferred embodiment, rotors 106 contain a
fluid which can be temperature controlled to provide heating and/or
cooling to the elastomer masterbatch.
As seen in the embodiment illustrated in FIG. 8, each rotor 106 has
a first segment 116 and a second segment 118. As the elastomer
masterbatch passes through processing chamber 104, the rotors
masticate the material, thereby mixing and drying the elastomer
masterbatch. Port 109 is provided in processing chamber 104 for the
addition of liquid additives. Dry materials can be added to the
elastomer masterbatch via feed port 102. Vent 111 is provided in
processing chamber 104 to allow moisture to vent as the elastomer
masterbatch dries. The elastomer masterbatch exits processing
chamber 104 via discharge orifice 114. A first temperature control
device 115 provides heating and/or cooling to continuous compounder
100, typically with heated water. A second temperature control
device 117 provides heating and/or cooling to discharge orifice
114, typically with chilled water. During a typical process, heat
is added during startup, and then, once the process is fully
underway, heating is discontinued and cooling is applied. During
startup, heat is typically applied specifically to processing
chamber 104 and discharge orifice 114, and during operation,
cooling is applied specifically to feed port 102, processing
chamber 104 and rotors 106. In a typical application, with a
nominal throughput of 1000 lbs/hour of elastomer masterbatch,
approximately 250,000-500,000 BTU/hr may be removed by cooling. As
noted above, preferred embodiments of continuous compounder 100 dry
the masterbatch as well as controlling its Mooney Viscosity and
molecular weight, while not excessively reducing bound rubber.
Certain preferred embodiments of continuous compounder 100 can
reduce water content of the elastomer masterbatch from up to
approximately 25 weight percent, to less than approximately 1
weight percent.
Control of the operating parameters of continuous compounder 100
allows control of the Mooney Viscosity, moisture content, molecular
weight and bound rubber of the elastomer masterbatch. Such
operating parameters include throughput rate of the continuous
compounder, rotor speed, discharge orifice size and temperature,
and processing chamber temperature.
In certain preferred embodiments, the elastomer masterbatch
discharged from continuous compounder 100 is fed to open mill 120.
The elastomer masterbatch is discharged as a length of extrudate
and may be cut into smaller lengths prior to entering open mill
120. The elastomer masterbatch may optionally be fed to open mill
120 via conveyor 119. Conveyor 119 may be a conveyor belt, conduit,
pipe, or other suitable means for transporting the elastomer
masterbatch from continuous compounder 100 to open mill 120. Open
mill 120 comprises a pair of rollers 122 which further control the
Mooney Viscosity of the elastomer masterbatch. Rollers 122 may
optionally be heated or cooled to provide enhanced operation of
open mill 120. In certain embodiments, open mill 120 may reduce the
temperature of the elastomer masterbatch approximately 100.degree.
C.
After exiting open mill 120, the elastomer masterbatch optionally
may be fed by conveyor 200 to cooling system 202, as seen in FIG.
9. Cooling system 202 may include a cooling water spray 204, with
its water being fed from cooling water tank 206 or other water
source. The water from cooling water spray 204 may be sprayed
directly onto the elastomer masterbatch. In certain embodiments, an
antistick agent, e.g., Promol, manufactured by Hans W. Barbe, of
Germany, and containing silicates and calcium stearate, may be
added to the water spray or used in place of the water spray.
Optionally, the elastomer masterbatch can then be fed by conveyor
208 to granulator 210. If cooling water spray 204 has been used,
optionally an air knife 212 or other high pressure air blower or
other suitable means can be used to remove any cooling water that
did not evaporate from the elastomer masterbatch. The elastomer
masterbatch can then optionally be fed by conveyor 214 to a baler
216, where the elastomer masterbatch can be baled more or less
tightly or densely by varying the dwell time, that is, the pressure
and time in baler 216, depending on its intended use. For example,
a looser bale may be preferred for use in a Banbury mixer or the
like. As indicated above, the continuous compounder embodying the
method and apparatus of the present invention is controllable so as
to control the change in Mooney Viscosity, molecular weight, bound
rubber, and drying of the masterbatch processed in the continuous
compounder. The degree of change and final value of the these
parameters will be selected in accordance with the intended use
application of the resultant masterbatch. It will be within the
ability of those skilled in the art, given the benefit of this
disclosure, to select suitable rotor designs, and rotor operating
conditions and parameters, to control the Mooney Viscosity,
molecular weight, bound rubber and drying of the elastomer
masterbatch processed in the continuous compounder. Typically, the
Mooney Viscosity of masterbatch produced in the coagulum reactor is
higher than desired for certain end use applications. The
continuous compounder can advantageously reduce the Mooney
Viscosity of the masterbatch to a selected lower value.
FIG. 8 schematically illustrates a subsystem 58 for introducing dry
additives via conduit 171 and feed port 102 into continuous
compounder 100. Also schematically illustrated in FIG. 8 is
subsystem 59 for introducing liquid additives via conduit 172 and
feed port 102 into continuous compounder 100. Conduits 171, 172,
173 may be, for example, pipes, conveyor belts, or other suitable
means for transporting material from the respective subsystem to
continuous compounder 100. Exemplary additives include, for
example, filler (which may be the same as, or different from, the
filler used in the coagulum reactor; exemplary fillers including
silica and zinc oxide, with zinc oxide also acting as a curing
agent), other elastomers, other or additional masterbatch,
antioxidants, antiozonants, plasticizers, processing aids (e.g.,
stearic acid, which can also be used as a curing agent, liquid
polymers, oils, waxes, and the like), resins, flame-retardants,
extender oils, lubricants, and a mixture of any of them. The
addition of elastomers can produce elastomer blends via continuous
compounder 100. Exemplary elastomers include, but are not limited
to, rubbers, polymers (e.g., homopolymers, copolymers and/or
terpolymers) of 1,3-butadiene, styrene, isoprene, isobutylene,
2,3-dimethyl-1,3-butadiene, acrylonitrile, ethylene, and propylene
and the like. It is to be appreciated that any combination of
elastomers, additives and second masterbatch may be added in
continuous compounder 100 to the elastomer masterbatch produced in
the coagulum reactor 14.
The dimensions and particular design features of the coagulum
reactor 14, including the mixing zone/coagulum zone assembly,
suitable for an embodiment in accordance with FIG. 1, will depend
in part on such design factors as the desired throughput capacity,
the selection of materials to be processed, etc. One preferred
embodiment is illustrated in FIG. 2 wherein a coagulum reactor 48
has a mixing head 50 attached to a coagulum zone 52 with a
fluid-tight seal at joint 54. FIG. 2 schematically illustrates a
first subsystem 56 for feeding elastomer latex to the mixing zone,
subsystem 57 for feeding carbon black slurry or other particulate
filler fluid to the mixing zone, and subsystem 58 for feeding an
optional additive fluid, pressurized air, etc. to the mixing zone.
The mixing head 50 is seen to have three feed channels 60, 61, 62.
Feed channel 60 is provided for the natural rubber latex fluid and
feed channel 62 is provided for direct feed of gas and/or additive
fluid. In connection with preferred embodiments employing direct
injection of additives, significant advantage is achieved in
connection with hydrocarbon additives or, more generally, non-water
miscible additives. While it is well known to employ emulsion
intermediates to create additive emulsions suitable for
pre-blending with an elastomer latex, preferred embodiments in
accordance with the present disclosure employing direct injection
of additives can eliminate not only the need for emulsion
intermediates, but also the equipment such as tanks, dispersing
equipment, etc. previously used in forming the emulsions.
Reductions in manufacturing cost and complexity can, therefore, be
achieved. As discussed further below, the feed channel 61 through
which slurry is fed to the mixing zone is preferably coaxial with
the mixing zone and the coagulum zone of the coagulum reactor.
While only a single feed channel is shown to receive the elastomer
latex fluid, any suitable number of feed channels may be arranged
around the central feed channel through which the slurry is fed to
the mixing zone. Thus, for example, in the embodiment of FIG. 2 a
fourth feed channel could be provided through which ambient air or
high pressure air or other gas is fed to the mixing zone.
Pressurized air may be injected likewise with the slurry through
the central axial feed channel 61. Auxiliary feed channels can be
temporarily or permanently sealed when not in use.
The coagulum zone 52 of the coagulum reactor 48 is seen to have a
first portion 64 having an axial length which may be selected
depending upon design objectives for the particular application
intended. Optionally, the coagulum zone may have a constant
cross-sectional area over all or substantially all of its axial
length. Thus, for example, the coagulum reactor may define a
simple, straight tubular flow channel from the mixing zone to the
discharge end. Preferably, however, for reasons discussed above,
and as seen in the preferred embodiment illustrated in the
drawings, the cross-sectional area of the coagulum zone 52
increases progressively from the entry end 66 to discharge end 68.
More specifically, the cross-sectional area increases in the
longitudinal direction from the entry end to the discharge end. In
the embodiment of FIG. 2, the coagulum zone increases in
cross-sectional area progressively in the sense that it increases
continuously following constant cross-sectional portion 64.
References to the diameter and cross-sectional area of the coagulum
reactor (or, more properly, the coagulum zone defined within the
coagulum reactor) and other components, unless stated otherwise,
are intended to mean the cross-sectional area of the open flow
passageway and the inside diameter of such flow passageway.
Elastomer composite, specifically, coagulated elastomer latex in
the form of masterbatch crumb 72, is seen being discharged from the
coagulum reactor 48 through a diverter 70. Diverter 70 is an
adjustable conduit attached to the coagulum reactor at discharge
end 68. It is adjustable so as to selectively pass the elastomer
masterbatch crumb 72 to any of various different receiving sites.
This feature advantageously facilitates removal of masterbatch
crumb from the product stream, for example, for testing or at the
beginning of a production run when initial process instability may
result temporarily in inferior product. In addition, the diverter
provides design flexibility to direct product from the coagulum
reactor to different post-processing paths. In accordance with the
preferred embodiment of FIG. 1, the masterbatch crumb 72 being
discharged from coagulum reactor 48 through diverter 70 is seen to
be received by de-watering extruder 40 and from there fed into
continuous compounder 100 via feed port 102.
The cross-sectional dimension of coagulum reactor 48 is seen to
increase at an overall angle .alpha. between entry end 66 and
discharge end 68. Angle .alpha. is greater than 0.degree. and in
preferred embodiments is less than 45.degree., more preferably less
than 15.degree., most preferably from 0.5.degree. to 5.degree.. The
angle .alpha. is seen to be a half angle, in that it is measured
from the central longitudinal axis of the coagulum zone to a point
A at the outer circumference of the coagulum zone at the end of the
coagulum reactor. In this regard, it should be understood that the
cross-sectional area of the upstream portion of the coagulum
reactor, that is, the portion near the entry end 66, preferably
increases sufficiently slowly to achieve quasi-molding of the
coagulum in accordance with the principles discussed above. Too
large an angle of expansion of the coagulum zone may result in the
elastomer masterbatch not being produced in desirable crumb form of
globules or worms and simply spraying through the coagulum reactor.
Increasing the bore of the coagulum reactor too slowly can result,
in certain embodiments, in backup or clogging of the feeds and
reaction product into the mixing head. In a downstream portion of
the coagulum zone, wherein the latex has been substantially
coagulated and flow has become essentially plug flow, the coagulum
zone may extend either with or without increase in cross-sectional
area. Thus, reference here to the coagulum zone in preferred
embodiments having a progressively increasing cross-sectional area
should be understood to refer primarily to that portion of the
coagulum zone wherein flow is not substantially plug flow.
The cross-sectional area of the coagulum zone (that is, at least
the upstream portion thereof, as discussed immediately above) may
increase in step-wise fashion, rather than in the continuous
fashion illustrated in the embodiment of FIG. 2. In the embodiment
illustrated in FIG. 3, a continuous flow system for production of
elastomer masterbatch in accordance with the method and apparatus
disclosed here, is seen to include a mixing head/coagulum zone
assembly wherein the cross-sectional area of the coagulum zone
increases in stepwise fashion. Preferably, the individual sections
of the coagulum zone in such a step-wise embodiment have a flared
connection to adjacent sections. That is, they combine to form a
smooth and generally continuous coagulum zone surface, as opposed,
for example, to a sharp or instantaneous increase in diameter from
one section to the next. The coagulum zone of FIG. 3 increases in
three steps, such that there are four different sections or
sub-zones 74-77. Consistent with the design principles discussed
immediately above, the cross-sectional area of coagulum zone 53
increases from the entry end 66 to point A at the discharge end 68
at an overall angle which achieves the necessary flow control in
the upstream portion of the coagulum reactor. The first section 74
can be taken as including (a) the constant diameter portion of the
mixing head 50 immediately downstream of the mixing zone, and (b)
the same or similar diameter portion connected thereto at joint 54
at the entry end 66. This first section has a constant
cross-sectional diameter D.sub.1 and an axial dimension or length
L.sub.1. In this first section 74 the length L.sub.1 should be
greater than three times the diameter D.sub.1, more preferably
greater than five times D.sub.1, and most preferably from about 12
to 18 times D.sub.1. Typically, this section will have a length of
about fifteen times D.sub.1. Each subsequent section preferably has
a constant cross-sectional dimension and cross-sectional area
approximately double that of the preceding (i.e., upstream)
section. Thus, for example, section 75 has a constant
cross-sectional dimension and a cross-sectional area which is twice
that of section 74. Similarly, the cross-sectional area of section
76 is double that of section 75, and the cross-sectional area of
section 77 is double that of section 76. In each of sections 75-77,
the length is preferably greater than three times its diameter,
more preferably about three to seven times its diameter and
generally about five times its diameter. Thus, for example, in
section 76 longitudinal dimension L.sub.3 is preferably about five
times its diameter D.sub.3.
A mixing head and coagulum zone assembly corresponding to the
embodiment of FIG. 3 is shown in FIG. 4 partially in section view.
Mixing head 50 is integral with coagulum zone extender 53 via joint
54. It defines a mixing zone wherein multiple feed channels 60, 61,
62 form a junction, with an elongate, substantially cylindrical
channel 80 substantially coaxial with the coagulum zone portion
within extender 53. It will be recognized that it is not essential
to the operability of the method and apparatus disclosed here, to
precisely define the boundaries of the mixing zone and/or coagulum
zone. Numerous variations are possible in the design of the flow
channels junction area, as will be apparent to those skilled in the
art given the benefit of the present disclosure. In that regard, as
a generally preferred guideline, in embodiments of the type
illustrated in FIG. 4, for example, the slurry tip 67 generally is
upstream of the beginning of cylindrical portion 80, being
approximately centered longitudinally in the junction of the feed
channels. In such embodiments, preferably, the minimum
cross-sectional area defined by the imaginary cone from the slurry
tip 67 to the circumferential perimeter at the beginning of the
cylindrical portion 80 is advantageously greater than, or at least
equal to, the cross-sectional area of the latex feed channel 60.
Preferably, both channel 80 and at least the upstream portion of
the coagulum zone wherein flow turbulence exists prior to
substantially complete coagulation of the elastomer latex, have a
circular cross-section.
The means for feeding carbon black slurry or other particulate
filler fluid is seen to comprise a feed tube 82 extending
substantially coaxially with the mixing chamber to an opening or
slurry nozzle tip 67 which is open toward the coagulum zone. This
is a highly advantageous feature of the preferred embodiments
discussed here. The carbon black slurry, as noted above, is fed to
the mixing zone at very high velocity relative the feed velocity of
the latex, and the axial arrangement of narrow bore feed tube 82
results in excellent development of flow turbulence. The diameter
D.sub.m of the channel 80 (which, as noted above, is preferably
substantially equal to the diameter D.sub.1 of immediately
following portion of section 74 of the coagulum zone) preferably is
at least twice the inside diameter of slurry feed tube 82, more
preferably about four to eight times the diameter of feed tube 82,
typically about seven to eight times that diameter. Feed tube 82 is
seen to form a fluid-tight seal with the entry port 83 at the
upstream end of feed channel 61 of mixing head 50. The diameter of
the axial feed tube 82 is determined largely by the required
volumetric flow rate and axial velocity of the slurry as it passes
through the slurry nozzle tip 67 into the mixing chamber. The
correct or required volume and velocity can be readily determined
by those skilled in the art given the benefit of this disclosure,
and will be a function, in part, of the concentration and choice of
materials. Embodiments such as that illustrated and disclosed here,
wherein the feed tube for the carbon black slurry is removable,
provide desirable flexibility in manufacturing different
masterbatch compositions at different times. The feed tube used in
one production run can be removed and replaced by a larger or
smaller bore tube appropriate to a subsequent production. In view
of the pressure and velocity at which the slurry exits the feed
tube, it may be referred to as a spray or jet into the mixing zone.
This should be understood to mean in at least certain embodiments,
high speed injection of the slurry into an area already
substantially filled with fluid. Thus, it is a spray in the sense
of its immediate distribution as it passes through the slurry
nozzle tip, and not necessarily in the sense of free-flying
material droplets in a simple spreading trajectory.
The additional feed channels 60 and 62 are seen to form a junction
84, 85, respectively, with feed channel 60 and downstream channel
80 at an angle .beta.. The angle .beta. may in many embodiments
have a value from greater than 0.degree. to less than 180.degree..
Typically, .beta. may be, for example, from 30.degree.-90.degree..
It is desirable to avoid a negative pressure, that is, cavitation
of the latex fluid as it is entrained by the high velocity slurry
exiting at slurry nozzle tip 67, since this may disadvantageously
cause inconsistent mixing leading to inconsistent masterbatch
product. Air or other gas can be injected or otherwise fed to the
mixing zone to assist in breaking any such vacuum. In addition, an
expanded feed line for the natural rubber latex leading to the
entry port 86 of feed channel 60 is desirable to act as a latex
fluid reservoir. In the preferred embodiment of FIG. 4, latex feed
channel 60 intersects the mixing zone adjacent slurry nozzle tip
67. Alternatively, however, the latex feed channel can intersect
the mixing channel upstream or downstream of the slurry nozzle tip
67.
The carbon black slurry or other particulate filler fluid typically
is supplied to feed tube 82 at a pressure above about 300 psig,
such as about 500 to 5000 psig, e.g. about 1000 psig. Preferably
the liquid slurry is fed into the mixing zone through the slurry
nozzle tip 67 at a velocity above 100 ft. per second, preferably
about 100 to about 800 ft. per second, more preferably about 200 to
500 ft. per second, for example, about 350 feet per second. Arrows
51 in FIG. 4 represent the general direction of flow of the
elastomer latex and auxiliary feed materials through feed channels
60 and 62 into the channel 80 below slurry nozzle tip 67. Thus, the
slurry and latex fluids are fed to the mixing zones at greatly
different feed stream velocities, in accordance with the numbers
set forth above. While not wishing to be bound by theory, it
presently is understood that the differential feed achieves latex
shear conditions in the mixing zone leading to good
macro-dispersion and coagulation.
An alternative preferred embodiment is illustrated in FIGS. 5 and 6
wherein the single axial feed tube 82 in the embodiment of FIG. 4
is replaced by multiple axially extending feed tubes 90-92. Even
greater numbers of feed tubes may be employed, for example, up to
about 6 or 8 axially-extending feed tubes. Advantageously,
production flexibility is achieved by using different feed tubes of
different diameter for production of different formulations. Also,
multiple feed tubes can be used simultaneously to achieve good flow
turbulence within the mixing zone and coagulum zone of the coagulum
reactor.
An alternative embodiment of the mixing head is illustrated in FIG.
7. Mixing head 150 is seen to define a mixing zone 179. An axial
feed channel 161 receives a feed tube 182 adapted to feed carbon
black slurry or other particulate filler fluid at high velocity
into the mixing chamber 179. It can be seen that the central bore
in feed tube 182 terminates at slurry nozzle tip 167. A constant
diameter nozzle land 168 is immediately upstream of slurry nozzle
tip 167, leading to a larger bore area 169. Preferably the axial
dimension of land 168 is about 2 to 6, e.g. about 5, times its
diameter. A second feed channel 160 forms a junction 184 with the
mixing zone 179 at a 90.degree. angle for feeding elastomer latex
fluid to the mixing zone. The cross-sectional diameter of the latex
fluid feed channel 160 is substantially larger than the
cross-sectional diameter of the slurry nozzle tip 167 and land 168.
Without wishing to be bound by theory, the axial elongation of
nozzle land 168, coupled with the expanded diameter bore section
upstream of the nozzle land, is believed to provide advantageous
stability in the flow of slurry through feed tube 182 into the
mixing zone 179. The bore of feed tube 182 is found to function
well with a 20.degree. chamfer, that is, conical area 169 which
expands in the upstream direction at about a 20.degree. angle.
Downstream of mixing zone 179 is an elongate coagulum zone.
Consistent with the principles discussed above, such coagulum zone
need be only marginally elongate. That is, its axial dimension need
be only marginally longer than its diameter. Preferably, however, a
progressively enlarged coagulum zone is used.
As discussed above, coagulation of the elastomer masterbatch is
substantially complete at or before the end of the coagulum
reactor. That is, coagulation occurs within the coagulum zone of
the coagulum reactor without the necessity of adding a stream of
coagulant solution or the like. This does not exclude the
possibility that some initial coagulation occurs in the mixing
zone. The mixing zone may be considered an extended portion of the
coagulum zone for this purpose. Also, reference to substantially
complete coagulation prior to the elastomer masterbatch exiting the
coagulum reactor is not meant to exclude the possibility of
subsequent processing and follow-on treatment steps, for any of
various purposes appropriate to the intended use of the final
product. In that regard, substantially complete coagulation in
preferred embodiments of the novel method disclosed here employing
natural rubber latex means that at least about 95 weight percent of
the rubber hydrocarbon of the latex is coagulated, more preferably
at least about 97 weight percent, and most preferably at least
about 99 weight percent is coagulated.
The method and apparatus disclosed and described here produce
elastomer composites having excellent physical properties and
performance characteristics. Novel elastomer composites of the
present invention include masterbatch compositions produced by the
above-disclosed method and apparatus, as well as intermediate
compounds and finished products made from such masterbatch
compositions. Notably, elastomer masterbatch can be produced using
natural rubber latex (latex concentrate or field latex), along with
various grades of carbon black filler, having excellent physical
properties and performance characteristics. Carbon blacks presently
in broad commercial use for such application as tire tread have
been used successfully, as well as carbon blacks heretofore
considered unsuitable for commercial use in known production
apparatus and methods. Those unsuitable because their high surface
area and low structure rendered them impractical to achieve
acceptable levels of macro-dispersion at routine commercial loading
levels for the carbon black and/or to preserve the molecular weight
of the elastomer are highly preferred for the novel elastomeric
masterbatch compositions disclosed here. Such elastomer composites
are found to have excellent dispersion of the carbon black in the
natural rubber, controlled Mooney Viscosity and moisture level,
together with good preservation of the molecular weight of the
natural rubber. Moreover, these advantageous results were achieved
without the need for a coagulation step involving a treatment tank
or stream of acid solution or other coagulant. Thus, not only can
the cost and complexity of such coagulant treatments be avoided, so
too the need to handle effluent streams from such operations.
Prior known dry mastication techniques could not achieve equal
dispersion of such fillers without significant molecular weight
degradation, nor was the Mooney Viscosity of the masterbatch
controlled to a desired level and, therefore, could not produce the
novel natural rubber masterbatch compositions made in accordance
with certain preferred embodiments of the present invention. In
that regard, novel elastomer composites are disclosed having
excellent macro-dispersion of the carbon black in the natural
rubber and controlled Mooney Viscosity and moisture level, even of
carbon blacks having a structure to surface area ratio DBPA:CTAB
less than 1.2 and even less than 1.0, with high molecular weight of
the natural rubber. Known mixing techniques in the past did not
achieve such excellent macro-dispersion of carbon black without
significant molecular weight degradation of the natural rubber and,
therefore, did not produce the novel masterbatch compositions and
other elastomer composites of the present invention. Preferred
novel elastomer masterbatch compositions in accordance with this
disclosure, having carbon black macro-distribution levels and
controlled Mooney Viscosity levels not heretofore achieved, can be
used in place of prior known masterbatch having poorer
macro-dispersion. Thus, masterbatch disclosed here can be
incorporated into cured compounds in accordance with known
techniques. Such novel cured compounds are found in preferred
embodiments to have physical characteristics and performance
properties generally comparable to, and in some instances
significantly better than, those of otherwise comparable cured
compounds comprising masterbatch of poorer macro-dispersion.
Masterbatch can be produced in accordance with the present
invention, however, with reduced mixing time, reduced energy input,
and/or other cost savings.
Particularly with respect to certain preferred embodiments, natural
rubber latex and carbon black filler masterbatch can be produced
having excellent physical characteristics and performance
properties. Excellent macro-dispersion of the carbon black is
achieved, even using carbon blacks of exceptionally high surface
area and low structure, without the degree of degradation of the
natural rubber which would be caused by dry mastication for
sufficient time and at sufficient intensity levels to achieve the
same degree of carbon black dispersion. Especially advantageous in
this regard are novel natural rubber masterbatch compositions
wherein a high degree of dispersion is achieved, using carbon
blacks having structure to surface area ratio, DBPA:CTAB of less
than 1.2 and even less than 1.0. As used here, the carbon black
structure can be measured as the dibutyl phthalate adsorption
(DBPA) value, expressed as cubic centimeters of DBPA per 100 grams
carbon black, according to the procedure set forth in ASTM D2414.
The carbon black surface area can be measured as CTAB expressed as
square meters per gram of carbon black, according to the procedure
set forth in ASTM D3765-85. Novel natural rubber masterbatch is
achieved, therefore, having heretofore unachievable combinations of
physical characteristics such as molecular weight distribution and
filler dispersion levels, and/or incorporating heretofore
unsuitable fillers such as carbon black of extraordinarily high
surface area and low structure. The dispersion quality of natural
rubber masterbatch produced in accordance with the methods and
apparatus disclosed here can be demonstrated with reference to the
well known characteristics of MW.sub.sol (weight average) and
macro-dispersion. Specifically, the macro-dispersion level in
masterbatch produced in accordance with preferred embodiments is
significantly better than that in masterbatch of approximately
equal MW.sub.sol produced using dry mastication. Most notably, the
dispersion quality of these preferred embodiments does not depend
significantly on the morphology of the carbon black filler. It will
be recognized that other factors affecting the level of dispersion
achievable using the method and apparatus disclosed here, include
the concentration of the carbon black in the slurry, total energy
input into the slurry and energy input during mixing of the fluid
streams, etc.
The macro-dispersion quality of carbon black in natural rubber
masterbatch disclosed here is significantly better than that in
previously known masterbatch of approximately equal MW.sub.sol
(weight average). In some preferred embodiments of novel elastomer
composites, excellent carbon black distribution is achieved with
MW.sub.sol approximately that of natural rubber in the field latex
state, (e.g., approximately 1,000,000) a condition not previously
achieved. The dispersion quality advantage is especially
significant in the above mentioned preferred embodiments using
carbon black with low structure and high surface area, e.g., DBPA
less than 110 cc/100 g, CTAB greater than 45 to 65 m.sup.2/g, and
DBPA:CTAB less than 1.2 and preferably less than 1.0.
The methods and apparatus of the present invention provide
elastomer masterbatch improved commercial value of the masterbatch.
Controlling the Mooney Viscosity and moisture level of the
elastomer masterbatch provides a product which is better suited for
certain preferred end use applications. Employing the continuous
compounder reduces or even eliminates the need for further
mastication in downstream processes at end user facilities.
Providing additional elastomers, additives and masterbatch within
the continuous compounder eliminates additional processing steps at
end user facilities where the masterbatch is used to produce end
products.
The methods and apparatus of the present invention can be used to
form products which include, but are not limited to tires, tire
treads, tire sidewalls, wire-skim for tires, cushion gum for
retread tires, rubber components of engine mounts, tank tracks,
mining belts, rubber components of hydro-mounts, bridge bearings,
and seismic isolators.
Results of experiments using the invention disclosed herein follow,
wherein "FCM" represents the continuous compounder, or Farrel
Unimix Continuous Mixer, and "OM" represents the open mill:
Trial #1 Data
This trial was conducted to test the drying capability of the
continuous compounder (FCM). This trial was also designed to test
the capability to add and incorporate a stream of oil. This wet
sample was made from natural rubber latex concentrate and N351 type
carbon black. The masterbatch was fed into the continuous
compounder with a moisture level of approximately 20 weight
percent.
TABLE-US-00001 CB Oil Rate Loading Loading (lb/hr Orifice Product
Moisture Bound Sample (phr) (phr) dry) RPM (%) Temp (F.) (%) MV MW
Rubber Bin #1 initial 35 -- -- -- -- -- .sup.-20 112.5 762K 49.77
product Bin #2 initial 35 -- -- -- -- -- .sup.-20 110.1 740K 44.94
product #1 34 17 465 500 33 275 1.32 68.7 681K 31.55 #2 35 18 372
500 23 300 0.70 68.6 692K 33.64 #3 34 18 372 510 17 315 0.14 68.2
687K 37.28 #4 -- 17 372 510 17 330 0.40 66.2 672K 32.63 #5 34 20
419 450 32 306 0.39 65.6 702K 34.68
Trial #2 Data
This trial was conducted to test the drying capability of the
continuous compounder (FCM). This trial was also designed to test
the capability to add and incorporate a stream of oil. This wet
sample was made from natural rubber field latex and N220 type
carbon black. The masterbatch was fed into the continuous
compounder with a moisture level of approximately 25 weight
percent.
TABLE-US-00002 CB Oil Rate Product Loading Loading (lb/hr Orifice
Temp (F.) Moisture Bound Sample (phr) (phr) dry) RPM (%) max (%) MV
MW Rubber Bin #1 initial 54 -- -- -- -- -- .sup.-25 196.0 707K
76.63 product Bin #2 initial -- -- -- -- -- -- .sup.-25 160.9 723K
75.84 product #12 54 4 400 425 35 325 0.25 135.4 537K 72.79 #13 54
3 336 375 38 340 0.08 135.9 510K 70.11
Trial #3 Data
This trial was conducted to test the drying capability of the
continuous compounder (FCM). The open mill (OM) was also
incorporated into this trial. This trial was also designed to test
the capability to add and incorporate streams of oil, stearic acid
(SA), and an antioxidant (Santoflex 6PPD). This wet sample was made
from natural rubber field latex and Cabot experimental carbon black
A. The masterbatch was fed into the continuous compounder with a
moisture level of approximately 22 weight percent.
TABLE-US-00003 SA/ Maximum CB Oil 6PPD Rate Product Loading Loading
Loading (lb/hr Orifice Temp (F.) Moisture Sample (phr) (phr) (phr)
dry) RPM (%) max (%) initial product 50 -- -- -- -- -- -- .sup.-22
6A OM 49 -- -- -- -- -- -- -- 7A FCM 49 -- 2/1 302 260 42 350 0.25
7A OM -- -- 7 217 -- -- 190 0.35 8A FCM 46 5 2/1 312 265 41 320
0.58 8A OM -- 5 2/1 200 -- -- -- 0.61 Sample MV MW Bound Rubber
Macro-Dispersion initial product 194 609K 77.81 A-4/0.30 6A OM 171
332K 69.30 A-4/0.06 7A FCM 157 517K 74.66 A-4/0.13 7A OM 135 386K
66.84 -- 8A FCM 138 496K 70.83 A-4/0.10 8A OM 118 440K 56.82 --
Trial #4 Data
This trial was conducted to test the drying capability of the
continuous compounder (FCM). The open mill (OM) was also
incorporated into this trial. This trial was also designed to test
the capability to add and incorporate streams of oil, stearic acid
(SA), silica, and an antioxidant (Santoflex 6PPD). This wet sample
was made from natural rubber field latex and N220 type carbon
black. The masterbatch was fed into the continuous compounder with
a moisture level of approximately 25 weight percent.
TABLE-US-00004 SA/ CB Oil Silica 6PPD Rate Maximum Loading Loading
Loading Loading (lb/hr Orifice Product Moisture Sample (phr) (phr)
(phr) (phr) dry) RPM (%) Temp (F.) (%) initial product 53 -- -- --
-- -- -- -- .sup.-25 1A FCM 53 -- -- -- 500 450 42 -- 1.27 1A OM --
-- -- -- 240 -- -- 200 0.23 2C FCM 53 8.5 -- -- 453 485 35 320 0.39
2C OM 55 8.5 -- -- 380 -- -- 240 0.22 3A FCM 52 8.5 -- 3.1/3.1 487
500 40 340 0.06 3A OM 51 8.5 -- 3.1/3.1 540 -- -- 210 0.25 5A FCM
52 8.5 8 3.1/3.1 470 490 41 330 0.24 5A OM 51 8.5 8 3.1/3.1 540 --
-- 210 0.34 Sample MV MW Bound Rubber % Macro-Dispersion initial
product 154 688K 55.79 B-5/0.40 1A FCM 148 536K 69.33 A-4/0.07 1A
OM 134 493K 69.44 -- 2C FCM 98 557K 60.62 A-3/0.03 2C OM 108 494K
66.91 A-3/0.09 3A FCM 90 610K 36.31 A-3/0.02 3A OM 90 636K 42.61
A-4/0.11 5A FCM 103 573K 51.70 B-4/0.33 5A OM 90 552K 48.67
A-4/0.20
Trial #5 Data
This trial was conducted to test the drying capability of the
continuous compounder (FCM). The open mill (OM) was also
incorporated into this trial. This wet sample was made from natural
rubber field latex and N234 type carbon black. The masterbatch was
fed into the continuous compounder with a moisture level of
approximately 24 weight percent.
TABLE-US-00005 CB Rate Maximum Loading (lb/hr Orifice Product
Moisture Sample (phr) dry) RPM (%) Temp (F.) (%) initial product 51
-- -- -- -- .sup.-24 FC1 FCM 52 300 250 44 340 0.50 FC1 OM 52 -- --
-- -- 0.15 Sample MV MW Bound Rubber % Macro-Dispersion initial
product 218 688K 72.21 A-4/0.18 FC1 FCM 160 645K 69.36 A-3/0.03 FC1
OM 141 335K 63.55 A-4/0.12
Trial #6 Data
This trial was conducted to test the drying capability of the
continuous compounder (FCM). The open mill (OM) was also
incorporated into this trial. This trial was also designed to test
the capability to add and incorporate streams of oil, stearic acid
(SA), zinc oxide (ZnO), silica, and an antioxidant (Santoflex
6PPD). The feasibility of adding butadiene rubber was also
investigated for sample FA4 during this trial. This wet sample was
made from natural rubber field latex and N220 type carbon black.
The masterbatch was fed into the continuous compounder with a
moisture level of approximately 20 weight percent.
TABLE-US-00006 SA/ CB Oil Silica 6PPD/ZnO Rate Maximum Loading
Loading Loading Loading (lb/hr Orifice Product Moisture Sample
(phr) (phr) (phr) (phr) dry) RPM (%) Temp (F.) (%) initial product
74 -- -- -- -- -- -- -- .sup.-20 FA3 FCM -- 7.9 7.1 2.9/2.9/5.0 400
300 59 335 0.37 FA3 OM 73 7.9 7.1 2.9/2.9/5.0 -- -- -- -- 0.14 FA4
FCM -- 5.5 5.0 2.0/2.0/3.5 400 300 48 330 0.63 FA4 OM 55 5.5 5.0
2.0/2.0/3.5 -- -- -- -- 0.19 Sample MV MW Bound Rubber %
Macro-Dispersion initial product >200 611K 70.74 A-3/0.10 FA3
FCM 154 483K 70.71 A-3/0.10 FA3 OM 133 362K 54.58 A-4/0.17 FA4 FCM
125 370K 44.08 -- FA4 OM 113 376K 43.68 C-6/1.36
Trial #7 Data
This trial was conducted to test the drying capability of the
continuous compounder (FCM). The open mill (OM) was also
incorporated into this trial. This trial was also designed to test
the capability to add and incorporate streams of oil, stearic acid
(SA), zinc oxide (ZnO), silica, and an antioxidant (Santoflex
6PPD). This wet sample was made from natural rubber field latex and
N220 type carbon black. The masterbatch was fed into the continuous
compounder with a moisture level of approximately 24 weight
percent.
TABLE-US-00007 SA/ CB Oil Silica 6PPD/ZnO Rate Max Loading Loading
Loading Loading (lb/hr Orifice Product Moisture Sample (phr) (phr)
(phr) (phr) dry) RPM (%) Temp (F.) (%) initial product 53 -- -- --
-- -- -- -- .sup.-24 FB1 FCM 53 8.5 -- 3.1/3.1 400 410 39 339 0.45
FB1 OM 54 8.5 -- 3.1/3.1 -- -- -- -- 0.31 FB2 FCM 53 8.5 7.7
3.1/3.1/5.4 400 330 49 342 0.44 FB2 OM 53 8.5 7.7 3.1/3.1/5.4 -- --
-- -- 0.26 Sample MV MW Bound Rubber % Macro-Dispersion initial
product 189 751K 63.42 A-3/0.09 FB1 FCM 84 483K 41.04 A-3/0.07 FB1
OM 86 362K 43.91 A-4/0.06 FB2 FCM 78 370K 49.85 A-4/0.14 FB2 OM 80
376K 49.34 A-4/0.17
In view of the foregoing disclosure, it will be apparent to those
skilled in the art that various additions, modifications, etc. can
be made without departing from the true scope and spirit of the
invention. All such additions and modifications are intended to be
covered by the following claims.
* * * * *