U.S. patent application number 10/858842 was filed with the patent office on 2005-04-21 for chopped carbon fiber preform processing method using coal tar pitch binder.
Invention is credited to Golubic, Thomas A., Snyder, David R., Wombles, Robert H..
Application Number | 20050081752 10/858842 |
Document ID | / |
Family ID | 25315858 |
Filed Date | 2005-04-21 |
United States Patent
Application |
20050081752 |
Kind Code |
A1 |
Snyder, David R. ; et
al. |
April 21, 2005 |
Chopped carbon fiber preform processing method using coal tar pitch
binder
Abstract
A procedure for forming a chopped carbon fiber preform using a
coal tar pitch binder and the product thereof.
Inventors: |
Snyder, David R.; (Cuyahoga
Falls, OH) ; Wombles, Robert H.; (Gibsonia, PA)
; Golubic, Thomas A.; (Boardman, OH) |
Correspondence
Address: |
REED SMITH LLP
P.O. BOX 488
PITTSBURGH
PA
15230-0488
US
|
Family ID: |
25315858 |
Appl. No.: |
10/858842 |
Filed: |
June 1, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10858842 |
Jun 1, 2004 |
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10476017 |
Mar 25, 2004 |
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10476017 |
Mar 25, 2004 |
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PCT/US02/14816 |
May 9, 2002 |
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Current U.S.
Class: |
106/282 ;
106/284; 208/22; 208/39; 208/40; 208/41; 208/42; 208/44;
524/66 |
Current CPC
Class: |
B29C 48/92 20190201;
C04B 35/532 20130101; C10C 1/16 20130101; B29C 48/022 20190201;
B29C 2948/92704 20190201; C04B 2235/96 20130101; C04B 2235/614
20130101; C04B 2235/77 20130101; C08L 2555/54 20130101; C04B 35/522
20130101; C08L 95/00 20130101; C04B 2235/6021 20130101; C10C 3/06
20130101; C10L 1/322 20130101; B29C 48/03 20190201; C04B 35/83
20130101; C10C 3/002 20130101; C08J 3/201 20130101; C08J 2395/00
20130101; F16D 69/023 20130101 |
Class at
Publication: |
106/282 ;
208/022; 208/044; 208/039; 208/040; 208/041; 208/042; 524/066;
106/284 |
International
Class: |
C10C 001/00; C10C
003/02; C10C 001/20; C10C 001/04; C08J 003/00; C08L 001/00; C08L
095/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 11, 2001 |
US |
09853372 |
Claims
What is claimed is:
1. A method of making a carbonized preform: placing a removable
inside sleeve and a removable outside sleeve on a mold pan;
distributing chopped carbon throughout the mold pan and sleeves;
pressing the chopped fibers with a pressing plate; removing the
inside and outside sleeves; sealing a vacuum/pressure chamber to
the mold pan and applying a vacuum thereto; introducing liquid coal
tar pitch into the mold pan; pressurizing the vacuum/pressure
chamber with nitrogen; releasing the pressure and removing the
vacuum pressure chamber; allowing the mold pan to cool; and
removing the pressing plate and carbonized preform.
2. A carbonized preform made utilizing the steps of claim 1.
3. A method of making a carbonized preform: placing a removable
inside sleeve and a removable outside sleeve on a mold pan;
distributing a mixture including milled high softening point coal
tar pitch and chopped carbon fibers in the mold pan and sleeves;
pressing the chopped fibers with a pressing plate; removing the
inside and outside sleeves; baking the mixture in the pan mold;
allowing the mold pan to cool; and removing the pressing plate and
carbonized preform from the mold pan.
4. The method of claim 3 further comprising using a preform removal
fixture to remove the preform from the mold pan
5. A carbonized preform made utilizing the steps of claim 3.
Description
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 10/476,017 filed Oct. 23, 2003 and claims the
benefit under 35 USC 119(e) of U.S. Provisional Application Ser.
No. 60/475,107 filed May 30, 2003.
FIELD OF THE INVENTION
[0002] The present invention relates to friction material preforms
using a coal tar-pitch binder, and more specifically, a chopped
carbon fiber preform using a coal tar pitch binder and the method
of making thereof.
BACKGROUND OF THE INVENTION
[0003] Coal tar is a primary by-product material produced during
the destructive distillation or carbonization of coal into coke.
While the coke product is utilized as a fuel and reagent source in
the steel industry, the coal tar material is distilled into a
series of fractions, each of which are commercially viable products
in their own right. A significant portion of the distilled coal tar
material is the pitch residue. This material is utilized in the
production of anodes for aluminum smelting, as well as electrodes
for electric arc furnaces used in the steel industry. In evaluating
the qualitative characteristics of the pitch material, the prior
art has been primarily focused on the ability of the coal tar pitch
material to provide a suitable binder used in the anode and
electrode production processes. Various characteristics such as
softening point, specific gravity, percentage of material insoluble
in quinoline, also known as QI, and coking value have all served to
characterize coal tar pitches for applicability in these various
manufacturing processes and industries.
[0004] Softening point is the basic measurement utilized to
determine the distillation process end point in coal tar pitch
production and to establish the mixing, forming or impregnating
temperatures in carbon product production. All softening points
referred to herein are taken according to the Mettler method or
ASTM Standard D3104. Additional characteristics described herein
include QI, which is utilized to determine the quantity of solid
and high molecular weight material in the pitch. QI may also be
referred to as .alpha.-resin and the standard test methodology used
to determine the QI as a weight percentage include either ASTM
Standard D4746 or ASTM Standard D2318. Percentage of material
insoluble in toluene, or TI, will also be referred to herein, and
is determined through ASTM Standard D4072 or D4312.
[0005] Mirtchi and Noel, in a paper presented at Carbon '94 at
Granada, Spain, entitled "Polycyclic Aromatic Hydrocarbons in
Pitches Used in the Aluminum Industry," described and categorized
the PAH content of coal tar pitches. These materials were
classified according to their carcinogenic or mutagenic effect on
living organisms. The paper identified 14 PAH materials which are
considered by the United States Environmental Protection Agency to
be potentially harmful to public health. Each of the 14 materials
is assigned a relative ranking of carcinogenic potency which is
based on a standard arbitrary assignment of a factor of 1 to
benzo(a)pyrene or B(a)P. Estimations of potential toxicity of a
pitch material may be made by converting its total PAH content into
a B(a)P equivalent which eliminates the necessity of referring to
each of the 14 materials individually, providing a useful shorthand
for the evaluation of a material's toxicity.
[0006] A typical coal tar binder pitch is characterized as shown in
Table I.
1 TABLE I Softening Point, .degree. C. 111.3 Toluene Insolubles,
wt. % 28.1 Quinoline Insolubles, wt. % 11.9 Coking Value, Modified
Conradson, 55.7 wt. % Ash, wt. % 0.21 Specific Gravity,
25/25.degree. C. 1.33 Sulfur, wt. % 0.6 B(a)P Equivalent, ppm
35,000
[0007] Two shortcomings with respect to the use of coal tar pitch
in general, and more specifically in the aluminum industry, have
recently emerged. The first is a heightened sensitivity to the
environmental impact of this material and its utilization in
aluminum smelting anodes. The other is a declining supply of crude
coal tar from the coke-making process. Significant reductions in
coke consumption, based upon a variety of factors, has reduced the
availability of crude coal tar. This reduction in production of
these raw materials is expected to escalate in the near future and
alternative sources and substitute products have been sought for
some period. No commercially attractive substitute for coal tar
pitch in the aluminum industry has been developed, however.
[0008] There are two traditional methods of distilling coal tar,
continuous and batch. Continuous distillation involves a constant
feeding of the material to be distilled, i.e., coal tar, and the
constant removal of the product or residue, i.e., coal tar pitch.
Traditional continuous distillations are typically performed at
pressures of between 60 mmHg and 120 mmHg and at temperatures of
between 350.degree. C. and 400.degree. C. and are typically able to
produce a coal tar pitch having a maximum softening point of
approximately 140.degree. C. Batch distillation can be thought of
as taking place in a crucible, much like boiling water. High heat
levels are developed as a result of the longer residence time of
the coal tar in the crucible. Although higher softening points of
up to 170.degree. C. can be reached using batch distillation, the
combination of high heat and longer residence time can often lead
to decomposition of the coal tar pitch and the formation of
unwanted mesophase pitch. Processing times for the distillation of
coal tar using known continuous and batch distillation range from
several minutes to several hours depending upon the coal tar pitch
product to be produced.
[0009] High efficiency evaporative distillation processes are known
that subject a material to elevated temperatures, generally in the
range of 300.degree. C. to 450.degree. C., and reduced pressures
generally in the range of 5 Torr or less, in a distillation vessel
to evolve lower molecular weight, more volatile components from
higher molecular weight, less volatile components. Such high
efficiency evaporative distillation processes may be carried out
using conventional distillation equipment having enhanced vacuum
capabilities for operating at the above specified temperature and
pressure ranges. In addition, high efficiency evaporative
distillation processes may be carried out in an apparatus known as
a wiped film evaporator, or WFE, and thus such processes are
commonly referred to as WFE processes. Similarly, high efficiency
evaporative distillation processes may be carried out in an
apparatus known as a thin film evaporator, and thus such processes
are commonly referred to as thin film evaporator processes. WFE and
thin film evaporator processes are often used as efficient,
relatively quick ways to continuously distill a material.
Generally, WFE and thin film evaporator processes involve forming a
thin layer of a material on a heated surface, typically the
interior wall of a vessel or chamber, generally in the range of
300.degree. C. to 450.degree. C., while simultaneously providing a
reduced pressure, generally in the range of 5 Torr or less. In a
WFE process, the thin layer of material is formed by a rotor in
close proximity with the interior wall of the vessel. In contrast,
in a thin film evaporator process, the thin film evaporator
typically has a spinner configuration such that the thin layer of
material is formed on the interior wall of the vessel as a result
of centrifugal force. WFE and thin film evaporator processes are
continuous processes as they involve the continuous ingress of feed
material and egress of output material. Both wiped film evaporators
and thin film evaporators are well known in the prior art.
[0010] One prior art WFE apparatus is described in Baird, U.S. Pat.
No. 4,093,479. The apparatus described in Baird includes a
cylindrical processing chamber or vessel. The processing chamber is
surrounded by a temperature control jacket adapted to introduce a
heat exchange fluid. The processing chamber includes a feed inlet
at one end and a product outlet at the opposite end.
[0011] The processing chamber of the apparatus described in Baird
also includes a vapor chamber having a vapor outlet. A condenser
and a vacuum means may be placed in communication with the vapor
outlet to permit condensation of the generated vapor under
sub-atmospheric conditions. Extending from one end of the
processing chamber to the other end is a tube-like motor-driven
rotor. Extending axially outward from the rotor shaft are a
plurality of radial rotor blades which are non-symmetrically
twisted to extend radially from one end of the chamber to the other
between the feed inlet and the product outlet. The rotor blades
extend into a small but generally uniform closely spaced thin-film
relationship with respect to the interior wall of the processing
chamber so that, when the rotor rotates, the rotor blades provide a
thin, wiped or turbulent film of the processing material on the
interior wall of the processing chamber.
[0012] In operation, a material to be processed is introduced into
the feed inlet by a pump or by gravity. The material is permitted
to move downwardly and is formed into a thin-film on the interior
wall of the processing, chamber by the rotating rotor blades. A
heat-exchange fluid, such as steam, is introduced into the
temperature control jacket so that the interior wall of the
processing chamber is heated to a steady, pre-selected temperature
to effect the controlled evaporation of the relatively volatile
component of the processing material. A relatively non-volatile
material is withdrawn from the product outlet, and the vaporized
volatile material is withdrawn from the vapor chamber through the
vapor outlet.
[0013] One of the major uses of coal tar pitch is as a binder for
carbon/graphite products. These products range from anodes for the
production of aluminum to fine grain graphite products for use in
electric discharge machining. Carbon/graphite products contain two
major components petroleum coke and coal tar pitch. Coal tar pitch
is the binder that holds the structure together. The major steps in
production of the finished product are mixing, forming,
carbonization for carbon products, and carbonization followed by
graphitization for graphite products. The major problem experienced
with pitch in the process is evolution of volatiles during the
carbonization step. Volatiles evolution causes two major problems:
1) emissions of organic compounds, and 2) reduction of the density
of the finished baked product. Volatiles emissions are an
environmental concern which must be addressed by either capture or
destruction of the organic compounds generated. The reduction of
the density of the carbon/graphite product results in an inferior
product with reduced strength, increased reactivity, and increased
electrical resistivity. An advantage therefore exists for
carbon/graphite products having low yield of volatiles.
[0014] Automobile brakes are produced by binding a number of
inorganic and organic substituents with phenolic resin. The process
is in certain respects similar to the one discussed for the
production of carbon/graphite products above. One of the major
problems experienced with automobile brakes is a characteristic
called fade. Fade is a reduction of the friction characteristics of
the friction material when it becomes hot. Everyone who drives an
automobile has experienced fade when the brake is being applied on
a downhill grade. As the brake begins to get hot, the driver must
push harder on the brake pedal to achieve the same braking
capacity. It is believed that fade is caused by the heat
instability of the phenolic resin binder of the friction material.
As the brake gets hot the phenolic resin begins to decompose
resulting in production of a gas layer between the two sliding
components. This gas layer causes a loss of friction resulting in
the need to push harder on the brake pedal. An advantage therefore
exists for brake formulations resulting in a reduction of fade.
[0015] Aircraft brakes are produced by carbon impregnation of a
carbon fiber preform. The process used for carbon impregnation is
called chemical vapor infiltration. Chemical vapor infiltration is
performed by coking methane gas in the preform to result in a
carbon filled carbon fiber preform. The chemical vapor infiltration
process is very time consuming with about 600 hours of processing
time required to produce a finished product. An advantage therefore
exists for a carbon infiltration process having a reduced time.
[0016] Natural rubber is used to produce many of the products we
use each day. One rubber product which plays a great part in each
of our lives is tires. A tire is produced from a number of
different rubber formulations. Different formulations are used to
produce the tread, sidewalls, belt coating, and rim. One of the
most important characteristics of the different rubber formulations
used to produce a tire is the adhesive properties for each of the
rubber formulations for each other. An advantage therefore exists
for a rubber formulation having increased adhesive properties.
[0017] Mesophase pitch is a highly structured pitch which is used
in applications where strength or the ability to conduct heat or
electricity is important. Significant work has been performed to
produce mesophase pitch from coal tar pitch with limited success
because of the quinoline insolubles content of the pitch. It has
been shown that the quinoline insolubles particles in coal tar
pitch hinder coalescence of the mesophase spheres causing a poor
quality mesophase to be formed. Known methods of producing
mesophase from coal tar pitch involve a filtration or
centrifugation step for removing the quinoline insolubles. While
these processes work quite well and allow for production of a high
quality mesophase, they result in a very high cost of the mesophase
product. An advantage therefore exists for a lower cost production
of a high quality mesophase.
SUMMARY OF THE INVENTION
[0018] The present invention relates to a method of making a high
softening point coal tar pitch using high efficiency evaporative
distillation, as well as the uses and applications of such pitch.
According to the method, a feed coal tar pitch having a softening
point in the range of 70.degree. C. to 160.degree. C. is fed into a
processing vessel wherein the processing vessel is heated to a
temperature in the range of 300.degree. C. to 450.degree. C. and
wherein a pressure inside the processing vessel is in the range of
5 Torr or less. An output coal tar pitch is withdrawn from the
processing vessel. The output coal tar pitch has a softening point
in the range of 140.degree. C. to 300.degree. C. and has less than
5% mesophase. A mesophase content of greater than 5% in the output
coal tar pitch will degrade its performance as a binder for
carbon-carbon composites, and in the production of graphite
electrodes and anodes used for aluminum production. Preferable
ranges for the output coal tar pitch include a softening point in
the range of 150.degree. C. to 250.degree. C. and less than 1%
mesophase. Also, the output coal tar pitch preferably has a B(a)P
Equivalent less than or equal to 24,000 ppm. The feed coal tar
pitch may preferably have a softening point in the range of
110.degree. C. to 140.degree. C., and the processing vessel may
preferably be heated to a temperature in the range of 300.degree.
C. to 450.degree. C. The output coal tar pitch may also be combined
with a plasticizer such as a low viscosity, preferably between 2
and 5 centistokes at 210.degree. F., low B(a)P equivalent,
preferably no more than 5,000 ppm B(a)P, coal tar, or such a coal
tar in combination with a petroleum oil where the petroleum oil
constitutes 30% to 60% of the mixture.
[0019] The present invention also relates to a method of making a
mesophase coal tar pitch having 10% to 100% mesophase. According to
this method, a feed coal tar pitch having a softening point in the
range of 70.degree. C. to 160.degree. C. is fed into a processing
vessel, wherein the processing vessel is heated to a temperature in
the range of 300.degree. C. to 450.degree. C. and wherein a
pressure inside the processing vessel is in the range of 5 Torr or
less. A quinoline insoluble-free and ash-free distillate having a
softening point in the range of 25.degree. C. to 60.degree. C. is
obtained from the processing vessel. The distillate is heat treated
at a temperature in the range of 370.degree. C. to 595.degree. C.
for between three and eighty hours.
[0020] The present invention also relates to a method of making a
quinoline insoluble-free and ash-free coal tar pitch. The method
includes steps of feeding a feed coal tar pitch having a softening
point in the range of 70.degree. C. to 160.degree. C. into a first
processing vessel, wherein the first processing vessel is heated to
a temperature in the range of 300.degree. C. to 450.degree. C. and
wherein a pressure inside the first processing vessel is in the
range of 5 Torr or less, obtaining a quinoline insoluble-free and
ash-free distillate having a softening point in the range of
25.degree. C. to 60.degree. C. from the first processing vessel,
heat treating the distillate at a temperature in the range of
350.degree. C. to 595.degree. C. for between five minutes and forty
hours, distilling the heat treated distillate to obtain a pitch
having a desired softening point, feeding the pitch having a
desired softening point into a second processing vessel, wherein
the second processing vessel is heated to a temperature in the
range of 300.degree. C. to 450.degree. C., and withdrawing an
output coal tar pitch from the second processing vessel. The first
and second processing vessel may be the same vessel, or may be
different vessels.
[0021] Alternatively, a hydrocarbon mixture, such as a mixture of
coal tar pitch and petroleum pitch, may be used as a feed material
in place of the feed coal tar pitch in each of the methods of the
present invention. The hydrocarbon mixture preferably has a coal
tar pitch content of at least 50%.
[0022] Each of the methods of the present invention may be
performed using conventional distillation equipment, a wiped film
evaporator, or a thin film evaporator. Conventional distillation is
limited to a softening point pitch of 180.degree. C.
[0023] Generally, at least one presently preferred embodiment of
the present invention broadly contemplates output coal tar pitch
having a high softening point greater than 170.degree. C. used as a
"modifier" in the formation of carbon/graphite products. The
utilization of high softening point pitch product of the present
invention addresses the problems associated with evolution of
volatiles during production by yielding a lower number of
volatiles. The lower volatiles yield means there are fewer organic
compounds to capture or destroy, and the product produced has a
higher density with resulting superior properties of the finished
carbon/graphite product. Also, the high softening point coal tar
pitch portion of the resulting carbon/graphite product shrinks
thereby improving product density and strength. The resulting
product exhibits increased efficiency to conduct heat and
electricity.
[0024] Further, at least one presently preferred embodiment of the
present invention broadly contemplates high softening point coal
tar pitch used as a binder in the formation of automobile brakes.
The addition of the high softening point pitch product of this
invention to brake formulations results in a reduction of fade
because the pitch is very stable to high temperatures, therefor it
does not decompose and produce the gas bubble responsible for
fade.
[0025] Further, at least one presently preferred embodiment of the
present invention broadly contemplates high softening point coal
tar pitch used as a saturant in the formation of aircraft brakes.
The saturation of carbon fiber preforms can be performed with the
high softening point pitch of the present invention resulting in a
95% saturation of the carbon fiber preform in about one hour. This
preliminary quick saturation has the potential to reduce the time
necessary for complete carbon saturation of the preform by many
hours. Also, dynamometer testing results of the finished aircraft
brakes produced using high softening point pitch have shown
superior friction characteristics.
[0026] Additionally, at least one presently preferred embodiment of
the present invention broadly contemplates high softening point
coal tar pitch used in the production of rubber products. Rubber
formulations containing the pitch of this invention have exhibited
superior adhesive properties.
[0027] Further, at least one presently preferred embodiment of the
present invention broadly contemplates distillate used to make
mesophase pitch. The distillate product of this invention is a
quinoline insolubles free coal tar derived material which has been
shown to produce high quality mesophase. Also, the economics for
mesophase production of the present invention result in a product
with a much lower cost.
[0028] Additionally, at least one embodiment of the presently
preferred invention contemplates using high softening point coal
tar pitch as a means to uniformly distribute chopped carbon fibers
in a friction material preform without the use of phenolic resin.
Aircraft and automobile brake preforms are typically formed using
phenolic resin. In the present invention the phenolic resin used in
producing these preforms is replaced by high softening point
pitch.
DETAILED DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1a is a top view of preform mold pan;
[0030] FIG. 1b is a cross-sectional view through AA of FIG. 1 of a
preform mold pan with removable inside and outside sleeves
inserted;
[0031] FIG. 2a is a cross-sectional view of a preform mold pan with
perforated pressing plate;
[0032] FIG. 2b is a top view of perforated pressing plate;
[0033] FIG. 3 is a cross-sectional view of a preform mold pan with
removable inside and outside sleeves removed;
[0034] FIG. 4 is a cross-sectional view of a preform mold pan with
vacuum/pressure chamber;
[0035] FIG. 5 is a cross-sectional view of a preform mold pan
according to another example; and
[0036] FIG. 6 is a top view of a preform removal fixture.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0037] According to the present invention, a high softening point,
low volatility coal tar pitch is produced by processing a feed coal
tar pitch having a softening point in the range of 70.degree. C. to
160.degree. C., and preferably in the range of 110.degree. C. to
140.degree. C., using a high efficiency evaporative distillation
process carried out in a processing vessel operating at
temperatures of 300.degree. C. to 450.degree. C. and pressures of 5
Torr or less. This temperature range is important because operating
below the bottom temperature will not yield the desired softening
point in the output material and operating above the top
temperature will result in thermal cracking and thermal degradation
in the output material. Similarly, this pressure range is important
because if the pressure is higher than the specified top range
pressure, higher operating temperatures will be necessary to
achieve the desired softening point, which higher temperatures will
result in thermal cracking and thermal degradation in the output
material.
[0038] According to the present invention, the processing may be
performed using a WFE apparatus, and for purposes of illustration
and not limitation, the present invention will be described with
respect to processing using a WFE apparatus. It will be
appreciated, however, that conventional distillation equipment and
conventional thin film evaporators may be used so long as such
equipment and evaporators may be operated at the temperatures and
pressures described herein. In the case where a thin film
evaporator is used, the thin film evaporator preferably should form
a film on the interior wall thereof having a minimum thickness that
is no smaller than the thickness of the largest QI particle
contained in the feed material.
[0039] Any known WFE apparatus may be used as long as it is capable
of operating at temperatures of 300.degree. C. to 450.degree. C.
and pressures of 5 Torr or less. Preferably, the WFE apparatus
should be capable of processing a minimum film thickness of 1
millimeter, and operating with a wiper speed of 200 rpm to 3000
rpm. The processing chamber or vessel wall of the WFE is heated to
a temperature of between 300.degree. C. and 450.degree. C., and
preferably between 300.degree. C. to 400.degree. C. The appropriate
feed rate of the feed coal tar pitch into the WFE apparatus will
depend on the processing surface area of the vessel. The feed rate
should be between 10 and 100 pounds/square foot of surface
area/hour, and preferably between 35 and 50 pounds/square foot of
surface area/hour. If the feed coal tar pitch is fed into the WFE
apparatus at the rate of between 10 and 100 pounds/square foot of
surface area/hour, the residence time of the feed coal tar pitch in
the WFE apparatus will be approximately 1 to 60 seconds. If the
feed coal tar pitch is fed at the preferred rate of between 35 and
50 pounds/square foot/hour, the residence time of the feed coal tar
pitch in the WFE apparatus will be approximately 5 to 30 seconds.
The residue of the WFE will be an output coal tar pitch having a
softening point in the range of 140.degree. C. to 300.degree. C.,
preferably 150.degree. C. to 2500C, and having a minimal formation
of mesophase of 0% to 5%, preferably 0% to 1%. In the case where
conventional distillation equipment adapted to operate at the
specified temperatures and pressures is used, the output coal tar
pitch will have a softening point in the range of 140.degree. C. to
1800C. In order to achieve softening points in the output coal tar
pitch in excess of 180.degree. C. according to the present
invention, it is necessary to use a WFE or a thin film evaporator,
as the residence time required to produce softening points in the
output coal tar pitch in excess of 180.degree. C. using a
conventional distillation apparatus will yield unwanted results
such as the production of excess mesophase. Also, use of a high
efficiency evaporative distillation process such as a WFE process
facilitates the removal of high boiling point PAH's, particularly
benzo(a)pyrene, from the feed coal tar pitch, resulting in an
output coal tar pitch having a B(a)P equivalent of no more than
24,000 ppm. The yield of the output coal tar pitch at a given
vessel temperature depends on the softening point of the feed coal
tar pitch.
EXAMPLE 1
[0040] A feed coal tar pitch having, a softening point of
109.degree. C. is fed into a WFE apparatus having a 1.4 square foot
vessel operating at a temperature of 335.degree. C., 18.5 mmHg
absolute, and at a feed rate of 77 pounds/square foot of surface
area/hour. The output coal tar pitch of the WFE apparatus has a
pitch yield of 85%. A laboratory analysis of the output coal tar
pitch is summarized in the following Table II:
2 TABLE II Softening Point, .degree. C. 140.6 Toluene Insolubles,
wt. % 32.9 Quinoline Insolubles, wt. % 15.1 Coking Value, Modified
64.9 Conradson, wt. % Ash, wt. % 0.20 Specific Gravity,
25/25.degree. C. 1.35 Beta Resin, wt. % 17.8
EXAMPLE 2
[0041] A feed coal tar pitch having a softening point of
109.degree. C. is fed into a WFE apparatus having a 1.4 square foot
vessel operating at a temperature of 335.degree. C., 10.4 mmHg
absolute, and at a feed rate of 95 pounds/square foot/hour. The
output coal tar pitch of the WFE apparatus has a pitch yield of
73%. A laboratory analysis of the output coal tar pitch is
summarized in the following Table III:
3 TABLE III Softening Point, .degree. C. 163.0 Toluene Insolubles,
wt. % 37.7 Quinoline Insolubles, wt. % 17.0 Coking Value, Modified
71.6 Conradson, wt. % Ash, wt. % 0.22 Specific Gravity,
25/25.degree. C. 1.36 Beta Resin, wt. % 20.7
EXAMPLE 3
[0042] A feed coal tar pitch having a softening point of
109.degree. C. is fed a WFE apparatus having a 1.4 square foot
vessel operating at a temperature of 350.degree. C., 5.0 mmHg
absolute and at a feed rate of 65 pounds/square foot/hour. The
output coal tar pitch of the WFE apparatus has a pitch yield of
74.2%. A laboratory analysis of the output coal tar pitch is
summarized in the following Table IV:
4 TABLE IV Softening Point, .degree. C. 200.0 Toluene Insolubles,
wt. % 42.2 Quinoline Insolubles, wt. % 18.2 Coking Value, Modified
76.5 Conradson, wt. % Ash, wt. % 0.27 Specific Gravity,
25/25.degree. C. 1.378 Beta Resin, wt. % 24.1
EXAMPLE 4
[0043] A feed coal tar pitch having a softening point of
109.degree. C. is fed into a WFE apparatus having a 1.4 square foot
vessel operating at a temperature of 365.degree. C., 5.0 mmHg
absolute, and at a feed rate of 67 pounds/square foot/hour. The
output coal tar pitch of the WFE apparatus has a pitch yield of
67%. A laboratory analysis of the output coal tar pitch is
summarized in the following Table V:
5 TABLE V Softening Point, .degree. C. 225 Toluene Insolubles, wt.
% 48.9 Quinoline Insolubles, wt. % 23.3 Coking Value, Modified 81.2
Conradson, wt. % Ash, wt. % 0.24 Specific Gravity, 25/25.degree. C.
1.365 Beta Resin, wt. % 25.7
[0044] The output coal tar pitch having a softening point in the
range of 140.degree. C. to 300.degree. C., and preferably in the
range of 150.degree. C. to 250.degree. C., may be used as a binder
for carbon-carbon composites and friction materials, and in the
production of graphite electrodes and anodes used for aluminum
production. In addition, the output coal tar pitch having a
softening, point in the range of 140.degree. C. to 300.degree. C.,
and preferably in the range of 150.degree. C. to 250.degree. C.,
may be combined with a plasticizer to produce a pitch having a
110.degree. C. softening point suitable for use in aluminum anode
production, including Soderberg binder pitch, and any other
industrial application where very low PAH contents are required.
The plasticizer may be low viscosity, preferably between 2 and 5
centistokes at 210.degree. F., low B(a)P equivalent, preferably no
more than 5,000 ppm B(a)P, coal tar, or such a coal tar in
combination with a petroleum oil where the petroleum oil
constitutes 30% to 60% of the mixture. One suitable plasticizer is
the coal tar pitch blend described in McHenry et al., U.S. Pat. No.
5,746,906, the disclosure of which is incorporated herein by
reference.
[0045] Alternatively, according to an alternate embodiment of the
present invention, a hydrocarbon mixture, such as a mixture of coal
tar pitch and petroleum pitch, may be used as a feed material in
place of the feed coal tar pitch. The hydrocarbon mixture in this
embodiment preferably has a coal tar pitch content of at least 50%.
The distillate produced when using a hydrocarbon mixture as the
feed material may then be used in the methods described below.
[0046] The distillate evolved by processing the feed coal tar pitch
in the WFE apparatus will be quinoline insoluble-free, which as
used herein means it has a QI in the range of 0% to 0.5%, and
ash-free, which as used herein means it has an ash content in the
range of 0% to 0.1%. A quinoline insoluble-free, ash free
distillate is desirable for at least two reasons. First, the
distillate may be used to create materials that will be used as an
impregnating pitch to fill in porosity in carbon structures, and it
is known that QI and ash hinders the ability to fill in such
porosity. Second, the distillate may be used to create mesophase
pitch, and QI is known to hinder the coalescence of mesophase
spheres. The distillate will comprise a pitch having a softening
point in the range of 25.degree. C. to 60.degree. C.
[0047] The distillate may be used to produce a quinoline
insoluble-free and ash-free pitch of a desired higher softening
point by first heat treating the distillate at temperatures between
350.degree. C. and 595.degree. C. for between 5 minutes and 40
hours. The heat treating step may, for example, be performed by
placing the distillate in a flask containing a short distillation
column, and heating and stirring the distillate therein under a
slight vacuum of no more than 600 mmHg Absolute. The step of heat
treating the distillate will result in a pitch having a softening
point in the range of 60.degree. C. to 110.degree. C. The heat
treated distillate may then be distilled by known conventional
means to obtain a pitch residue of a desired softening point. The
resulting pitch may be used in the production of carbon fibers and
fuel cells. As an alternative, a narrow boiling range quinoline
insoluble-free pitch may be produced by further processing the
quinoline insoluble-free and ash-free pitch produced through heat
treating and distillation using a high efficiency evaporative
distillation process, such as a WFE or a thin film evaporator
process, at temperatures in the range of 300.degree. C. to
450.degree. C. and pressures no greater than 5 Torr, wherein the
narrow boiling range pitch is the residue of such processing.
EXAMPLE 5
[0048] A 25-30.degree. C. softening point distillate produced from
a feed coal tar pitch having a softening point of 110.degree. C. is
heat treated at 360.degree. C. for approximately 8 hours to produce
a pitch having a softening point of 60.degree. C. The 60.degree. C.
softening point pitch is distilled in a batch/pot distillation at
an overhead temperature of 400.degree. C. to produce a pitch having
a softening point of 98.9.degree. C. with a 70% yield. A laboratory
analysis of the resulting pitch is summarized in the following
Table VI:
6 TABLE VI Toluene Insolubles, wt. % 18.3 Quinoline Insolubles, wt.
% 0.5 Coking Value, Modified Conradson, 46 wt. % Ash, wt. % 0.04
Specific Gravity, 25/25.degree. C. 1.29 Beta Resin, wt. % 17.8
[0049] Alternatively, a mesophase pitch having mesophase content in
the range of 70% to 100%, and preferably in the range of 75% to
85%, may be produced from the distillate by heat treating the
distillate at temperatures between 370.degree. C. and 595.degree.
C. for between 3 and 40 hours. The yield of the mesophase pitch is
generally in the range of 70% and 100%. The mesophase pitch may be
used in carbon fibers, lithium-ion batteries and graphite foam.
[0050] Alternatively, according to an alternate embodiment of the
present invention, a hydrocarbon mixture, such as a mixture of coal
tar pitch and petroleum pitch, may be used as a feed material in
place of the feed coal tar pitch. The hydrocarbon mixture in this
embodiment preferably has a coal tar pitch content of at least
50%.
[0051] Carbon/Graphite Products
[0052] The present invention also relates to applications of the
output coal tar pitch having a high softening point. In a first
application, output coal tar pitch having a high softening point in
the preferred range of 150.degree. C.-250.degree. C., more
preferably in the range of 160.degree. C.-220.degree. C., and most
preferably in the range of 170.degree. C.-200.degree. C. is used as
a "modifier" in the formation of carbon/graphite products which are
traditionally formed from coke an 110.degree. C. softening point
coal tar pitch. One embodiment of the present invention involves
substituting the 110.degree. C. softening pint coal tar pitch with
160.degree. C. softening point coal tar pitch in the production of
the carbon/graphite products. In another embodiment, the output
coal tar pitch having a high softening point is used as a
substitute for a portion of the coke in the production of the
carbon/graphite products.
EXAMPLE 6
[0053] Pitch having a softening point of 160.degree. C. is used as
a replacement for 110.degree. C. pitch in the extrusion of
{fraction (5/16)}" diameter.times.12" long gouging rods. The pitch
is mixed with coke at a pitching level of approximately 60% by
weight and extruded to form the finished piece. The products are
baked and graphitized. The properties of these products are set
forth in Table VII.
7TABLE VII Graphite Properties - Extrusion Process 110.degree. C.
SP 160.degree. C. SP Pitch Pitch % Change Baked Density 1.57 1.64
+4.5 g/cc Baked Flex 5,042 6,562 +30 Strength psi Graphite 1.59
1.65 +3.8 Density g/cc Graphite Flex 3,937 5,901 +50 Strength psi
Graphite 0.00056 0.00048 -14.3 Resistivity ohm-ins. Scrap 4.2% 3.0%
-28.6
[0054] The carbon and graphite products produced had improved
density, strength, and resistivity properties using the 160.degree.
C. high softening point pitch over the typical 110.degree. C.
pitch. The density of the graphite improved 3.8%, the graphite
strength improved 14.3%.
[0055] The use of 180.degree. C. softening point pitch as a
replacement for coke flour in 15/8" diameter.times.24" long and
15/8" diameter.times.48" long graphite pieces. In the formulation,
10 wt. % of the coke flour is removed and 15 wt. % of 180.degree.
C. pitch is added as a milled solid to the mix. The products are
baked and graphitized. The properties of these products are set
forth in Table VIII.
8TABLE VIII Graphite Properties - Using 180.degree. C. Pitch to
replace coke 180.degree. C. SP Control Pitch % Change Density g/cc
1.71 1.79 +4.7 Resistivity 0.00045 0.00042 -6.7 ohm-ins.
[0056] The carbon and graphite products produced had improved
density, and resistivity properties using the 180.degree. C. high
softening point pitch over the typical coke The density of the
graphite improved 4.7%, the resistivity improved 6.7%.
[0057] Friction Materials
[0058] In a second application, the output coal tar pitch is used
in the formation of friction materials, in the brakes of various
kinds of vehicles such as aircraft and automobiles.
[0059] In the formation of semi-metallic automobile brakes, coal
tar pitch having a high softening point in the preferred range of
150.degree. C.-250.degree. C., more preferably in the range of
170.degree. C.-240.degree. C., and most preferably in the range of
180.degree. C.-230.degree. C. is used as a binder. It is preferred
to use a crosslinking additive to further increase the softening
point of the pitch during post cure with temperatures in the range
of 350.degree. F. to 450.degree. F.
EXAMPLE 7
[0060] The 180.degree. C. softening point coal tar pitch can be
used as a replacement for 3 wt. % of a total 8 wt. % phenolic resin
in a semi-metallic automobile brake pad.
9TABLE IX A typical (control) semi-metallic automobile brake pad
formulation as follows: 34 wt. % Steel Fiber 25 wt. % Sponge Iron
15 wt. % Graphite 5 wt. % Petroleum Coke 8 wt. % Phenolic Resin 6
wt. % Filler 3 wt. % Friction Polymer 3 wt. % Magnesium Oxide 1 wt.
% Alumina
[0061] Mixing
[0062] 3 wt. % of the 8 wt. % of phenolic resin is removed and 3
wt. % of 180.degree. C. softening point coal tar pitch that has
been milled to 50% through 200 mesh is added in its place and then
mixed at ambient temperature.
10TABLE X A semi-metallic automobile brake pad formulation
according to this example has the following composition: 34 wt. %
Steel Fiber 25 wt. % Sponge Iron 15 wt. % Graphite 5 wt. %
Petroleum Coke 5 wt. % Phenolic Resin 6 wt. % Filler 3 wt. %
Friction Polymer 3 wt. % Magnesium Oxide 1 wt. % Alumina 3 wt. %
180.degree. C. softening point coal tar pitch
[0063] The semi-metallic brake mixture is molded at 280.degree. F.
at a pressure of 3.5-4.0 tons/sq.in. The pressure is released at 45
sec., 90 sec., 135 sec., and 180 sec. to vent the mold. The total
time for the mold cycle is 5 minutes. The brake pad is then post
cured for 4 hours at 350.degree. F. The properties of the
composition are presented in Table XI.
11TABLE XI With 180.degree. C. Softening Point % Control Pitch
Change Wear Friction mm 1.27 1.19 315.degree. C. 0.24 0.28
425.degree. C. 1.26 0.51 TOTAL: 2.77 1.97 -29%.sup.1 grams 23 22
315.degree. C. 4 4 425.degree. C. 22 11 TOTAL 49 37 -24%.sup.2
Rotor mm -0.015 -0.011 -0.011 0.003 0.012 -0.033 TOTAL -0.014
-0.014 grams -2 -2 Rotor Surface Initial 1.21 1.6 Final 3.73 1.63
Increase 2.52 -0.03 Friction Overall Rated 0.196 0.203 Average Post
Burnish 0.225 0.222 Ramps Average All Rated 0.208 0.210 Ramps
Average +7.5%.sup.3 Fade Heating 0.160 0.172 Cycle Minimum All
Others 0.140 0.146 Minimum 315.degree. C. Wear- 0.185 0.199 Final
.mu. 425.degree. C. Wear- 0.140 0.205 Final .mu. EFFECTIVENESS Pre
Burnish Effectiveness 50 kph 0.249 0.241 average 100 kph 0.185
0.146 average Post Burnish Effectiveness 50 kph 0.223 0.208 average
100 kph 0.228 0.235 average Post Fade Stability Effectiveness 50
kph 0.199 0.200 average 100 kph 0.213 0.219 average 130 kph 0.213
0.226 average Post 425.degree. C. Effectiveness 50 kph 0.187 0.200
average 100 kph 0.183 0.213 average
[0064] As shown in Table XI, the results show improved wear,
especially high temperature wear (425.degree. C.), using coal tar
pitch (1), (2) Both as a thickness loss (mm) and weight loss
(grams), the wear is reduced by 29% and 24% in the present example
as compared to the control formulation (non-pitch containing). (3)
The Fade Heating Cycle Minimum is improved by 7.5% using the coal
tar pitch of the present invention. A more stable coefficient of
friction as the brake pad is tested over the range of energy
conditions results when coal tar pitch is used compared to the
control formulation. This is shown in the table under Effectiveness
with the values indicated.
[0065] In the formation of aircraft brakes coal tar pitch having a
high softening point in the preferred range of 160.degree.
C.-240.degree. C., more preferably in the range of 170.degree.
C.-220.degree. C., and most preferably in the range of 180.degree.
C.-200.degree. C. is used in the saturation of carbon fiber
preforms for aircraft brakes.
EXAMPLE 8
[0066] A low QI (Quinoline Insoluble) 180.degree. C. softening
point coal tar pitch can be used to saturate aircraft brake carbon
fiber preforms to reduce the porosity of the preform from 75 vol. %
to 5 vol. % in the following manner.
[0067] A carbon fiber preform with approximately 25 vol. % carbon
fibers is placed under vacuum (<10 mmHg) and heated to
325.degree. C. Low QI (<10 wt. %) 180.degree. C. softening point
coal tar pitch at 325.degree. C. is introduced into the carbon
fiber preform. The coal tar pitch saturated carbon fiber preform is
pressurized with nitrogen at 15 psig. The saturated carbon fiber
preform is cooled. The saturated carbon fiber preform is further
processed by the initiation of densification steps using Chemical
Vapor Infiltration (CVI).
[0068] By saturating the carbon fiber preform with coal tar pitch
to raise the initial density of the carbon fiber preform before
CVI, the hours of actual CVI required to reach density
specification is greatly reduced (by as much as 30%) as shown in
Table XII. This provides a significant cost benefit to the
processing of the carbon fiber preform to produce an aircraft brake
disk.
[0069] Rubber Products:
[0070] In an additional application of the present invention, coal
tar pitch having a high softening point in the preferred range of
100.degree. C.-200.degree. C., more preferably in the range of
120.degree. C.-180.degree. C., and most preferably in the range of
140.degree. C.-180.degree. C. is used in the production of rubber
products such as tire compounds with natural rubber in the
formulation.
EXAMPLE 9
[0071] The addition of 6 parts of 140.degree. C. softening point
coal tar pitch to a Wire Belt-Coat Compound formulation with 0.5
parts additional sulfur.
12TABLE XIII A typical Wire Belt-Coat Compound formulation (control
compound) consists of the following: 100 parts Natural Rubber 55
parts Carbon Black 15 parts Silica 4 parts Paraffinic Oil 2 parts
Stearic Acid 6 parts Zinc Oxide 1 part Antiox., TMQ 0.75 parts
Cobalt Napthenate 3 parts Resorcinol 2.5 parts HMMM 4.0 parts
Sulfur 0.9 parts TBSI
[0072] From the Wire Belt-Coat Compound formulation, the Resorcinol
and HMMM are removed and 6 parts of 140.degree. C. softening point
coal tar pitch that has been milled to 50% through 200 mesh and 0.5
parts of additional sulfur is added.
13TABLE XIV A Wire Belt-Coat Compound formulation according to the
present example (Coal Tar Pitch Compound) consists of the
following: 100 parts Natural Rubber 55 parts Carbon Black 15 parts
Silica 4 parts Paraffinic Oil 2 parts Stearic Acid 6 parts Zinc
Oxide 1 part Antiox., TMQ 0.75 parts Cobalt Napthenate 4.5 parts
Sulfur 0.9 parts TBSI 6 part 140.degree. C. softening point coal
tar pitch
[0073] The formulation was prepared as follows:
[0074] Stage 1
[0075] Starting Temperature, .degree. F.: 150-160 Rotor Speed, rpm:
70 Ram Pressure, psi: 50
14 Time, Minutes Ingredient or Procedure 0 1/2 Rubber, Silica, 1/2
Carbon Black, 1/2 Rubber 13/4 All except TBSI, Zinc Oxide, HMMM,
Sulfur 31/2 Sweep 5 Sweep 6 Dump
[0076] Set mill rolls temperature at 130.degree. F. Band Stage I
mix.
[0077] Cut three times each side, three end passes, sheet to
cool.
[0078] Stage II
[0079] Starting Temperature, .degree. F.: 100-110 Rotor Speed, rpm:
60 Ram Pressure, psi: 50
15 Time, Minutes Ingredient or Procedure 0 1/2 Stage I, TBSI,
Sulfur, HMMM, ZnO, 1/2 Stage I 1 Sweep 21/2 Dump
[0080] Set Mill rolls temperature at 130.degree. F. Band Stage II
mix.
[0081] Five cuts each side, five end passes, set grain for two
minutes, sheet to cool.
[0082] Compounds rested for 24 hours at 72.degree. F. before
testing and curing.
[0083] The properties of the Wire Belt-Coat Compound using the coal
tar pitch formulation is set forth in Table V.
16TABLE XV Coal Tar Pitch Test Control Compound Compound Rheometer
Data, ASTM D 2084-95 Max. Torque, M.sub.H, lbf-in. 125.0 82.6 Min.
Torque, M.sub.L, lbf-in. 22.4 23.1 Scorch Time, t.sub.s2, min. 2.3
2.9 Cure Time, t.sub.50, min. 7.3 7.2 Cure Time, t90, min. 19.1
13.0 Mooney Viscosity, ASTM D1646-98a Initial Viscosity, MU 135.0
131.7 Viscosity @ 4 min., MU 93.2 98.1 Cure/Mold Data, ASTM D
3182-94 Test Plaques 31 28 Rubber Adhesion 40 35 DeMattia Flex 40
35 Physical Properties, ASTM D 412-98a, D 2240-00- Shore A
Durometer, points 88 75 Tensile Strength, psi 2820 3050 Ultimate
Elongation, % 230 530 100% Modulus, psi 1200 440 300% Modulus, psi
-- 1550 Heat-Aged Properties ASTM D573-99 Shore A Durometer, points
89 79 Tensile Strength, psi 1710 2770 Ultimate Elongation % 120 420
100% Modulus, psi 1460 690 300% Modulus, psi -- 2120 Wire Adhesion,
ASTM D 2229-99 Unaged Adhesion, lbs./force 182 160 Rubber Coverage,
% 100 75 Aged Adhesion, lbs./force 106 118 Rubber Coverage, % 80 75
Demattia Flex, ASTM D 813- 1,000 cycles 10,000 cycles 95(00) (1)
Rubber to Rubber Adhesion, ASTM D 413 At Room Temp. Adhesion, 78
249 (2) ppi At 212.degree. F. .degree.Adhesions,
ppi.degree..degree. 63 291
[0084] The tests show the coal tar pitch containing compound to
have (1) improved Demattia Flexibility results, (2) improved Rubber
to Rubber Adhesion, and improved Heat Aged properties over the
properties of the non-pitch containing control compound.
[0085] Mesophase Pitch:
[0086] Further, another presently preferred embodiment of the
present invention broadly contemplates distillate used to make
mesophase pitch.
[0087] During the preparation of high softening point (SP) pitches
(140 to 240.degree. C. SP), a distillate fraction (overhead) is
also produced. The overhead contains <0.1 wt % quinoline
insolubles (QI) and <1 wt % toluene insolubles (TI). The
material contains mostly aromatic hydrocarbons boiling above
250.degree. C. (most boiling above 380.degree. C.). Because of its
aromatic nature and lack of solids (QI), overhead can be converted
to mesophase under the proper treatment conditions. Mesophase is
usually defined as an optically anisotropic liquid crystal
carbonaceous phase or pitch which forms from the overhead under
proper conditions. Mesophase pitch can be used in specialty
applications such as carbon/carbon composites, lithium batteries,
heat management devices, foams, and mesocarbon beads.
[0088] Mesophase can be prepared in concentrations of <1 vol %
to over 80 vol % by various thermal treatment methods.
EXAMPLE 10
[0089] Approximately 500 g of overhead was thermally treated at
400.degree. in a 500-ml glass reactor under a nitrogen atmosphere
sweep of 750 cc/min. After 40 hours, the mesophase content was 0.9
vol % and increased to 46.0 wt % after 68 hours.
EXAMPLE 11
[0090] In an apparatus similar to one used in Example 1, overhead
was treated at 440.degree. C. After 35 hours, the mesophase content
was 80.2 vol %.
EXAMPLE 12
[0091] The overhead was first distilled to a 107.degree. C. SP
pitch by vacuum distillation with some heat treatment during
distillation. The resultant pitch (1.1 vol % mesophase) was then
heat treated in a 20-ml covered crucible at 450.degree. C. for 2
hours. The mesophase content was 76.6 vol %. Treatment of the pitch
in the crucible at 430.degree. C. for 3 hours produced a mesophase
content of 15.8 vol %. These tests were conducted in an oven with
no nitrogen purge.
EXAMPLE 13
[0092] The overhead was treated in a 100-ml glass reactor at
430.degree. C. for 15, 17, and 19 hours; the mesophase content was
6.9, 35.3, and 81.8 vol %, respectively.
[0093] Nitrogen was swept over the material being treated at a rate
of 450 cc/min.
EXAMPLE 14
[0094] The overhead was vacuum distilled with no heat treatment to
a soft pitch (54.0.degree. C. SP). The soft pitch was then heat
treated in the 100-ml glass reactor with nitrogen purge. After 39
hours at 400.degree. C. the mesophase was 3.9 vol %. The soft pitch
was also heat treated for 31 hours at temperatures ranging from 430
to 455.degree. C. for a total of 31 hours; the mesophase content
was 82.4 vol %.
EXAMPLE 15
[0095] The overhead was heat treated at 440.degree. C. in the
100-ml glass reactor, however, 5% oxygen was added to the purge
gas. After 8 hours, the mesophase content was 19.8 vol %. The
nature of the mesophase was changed by the presence of oxygen; the
small mesophase spheres were prevented from coalescing to larger
spheres or mosaic structures. The 10-.mu.m spheres retained their
individuality.
EXAMPLE 16
[0096] A larger quantity (about 2 Kg) of mesophase material was
prepared in a 4-liter glass reactor with nitrogen purge. The
overhead was heat treated for 36 hours at temperatures ranging from
410 to 440.degree. C. The mesophase content of the product was 28.8
vol %.
[0097] Carbonized Preforms:
EXAMPLE 17
[0098] A procedure for forming a chopped carbon fiber carbonized
preform 10 using the following steps (FIGS. 1-4):
[0099] 1. Construct a mold pan 12 to the inside and outside
dimensions of the required finished preform size (allow for
machining to finished dimensions). The height of the mold pan 12
should be greater than the finished dimensions to allow for a
pressing plate 14 (FIG. 1b).
[0100] 2. Construct a removable inside sleeve 16 and outside sleeve
18 several times the height of the preform mold height. Place the
sleeves 16, 18 onto the mold pan 12 (FIG. 1b).
[0101] 3. Distribute chopped carbon fibers 20 throughout the mold
pan 12 and sleeves 16, 18 and to a specified depth to achieve the
needed final carbon fiber volume after compaction (FIG. 1b).
[0102] 4. Place the perforated pressing plate 14 onto the chopped
fibers 20 and press the chopped fibers 20 to the determined height
(FIGS. 2a and 2b).
[0103] 5. Lock the perforated plate 14 in place (FIG. 2a) with a
locking mechanism 22, for example, steel pins.
[0104] 6. Remove the inside and outside sleeves 16, 18 (FIG.
3).
[0105] 7. Place a vacuum/pressure chamber 24 over the mold pan 12
and seal the vacuum/pressure chamber 24 to the mold pan 12 (FIG.
4).
[0106] 8. Pull a vacuum on the vacuum/pressure chamber 24 and mold
pan 12 (FIG. 4).
[0107] 9. Introduce liquid coal tar pitch 26 having a softening
point greater than or equal to 140.degree. C. into the mold pan 12,
filling the chopped fiber volume with liquid coal tar pitch 26
(FIG. 4).
[0108] 10. Pressure the vacuum/pressure chamber 26 and mold pan 12
with nitrogen at a pressure greater than or equal to 30 psi to
achieve complete saturation of the chopped fibers.
[0109] 11. Release the pressure and remove the vacuum/pressure
chamber 24.
[0110] 12. Allow the mold pan 12 to cool and carbonize the preform
10 in the mold pan 12.
[0111] 13. Remove the perforated pressing plate 14 and carbonized
preform 10.
EXAMPLE 18
[0112] A procedure for forming a chopped carbon fiber preform using
a coal tar pitch binder having a high softening point by uniformly
distributing chopped carbon fibers in a preform mold and binding
(lock in place) the fibers without the use of phenolic resin using
the following steps (FIGS. 1-3, 5, 6):
[0113] Procedure:
[0114] 1. Construct a mold pan 12 to the inside and outside
dimensions of the required finished preform size (allow for
machining to finished dimensions). The height of the mold pan 12
should be greater than the finished dimensions to allow for a
pressing plate 14 (FIG. 1b).
[0115] 2. Construct a removable inside and outside sleeves 16, 18
several times the height of the preform mold height. Place the
sleeves 16, 18 onto the mold pan 12 (FIG. 1b).
[0116] 3. Mix quantities of chopped carbon fibers, milled
(powdered) high softening point coal tar pitch having a softening
point greater than or equal to 140.degree. C. and other friction
additives, for example, graphite and/or coke.
[0117] 4. Distribute the mix in 3. uniformly throughout the mold
pan 12 and sleeves 16, 18 (FIG. 1b).
[0118] 5. Place the perforated pressing plate 14 onto the mix and
press the mix to the determined preform height (FIG. 2a).
[0119] 6. Lock the perforated pressing plate 14 in place with a
locking mechanism 22 (FIG. 2a).
[0120] 7. Remove the inside and outside sleeves 16, 18 FIG. 3).
[0121] 8. Bake the perforated plate mold to 800.degree. C. to melt
and carbonize the high softening point pitch in the mold pan 12. 9.
Cool and remove the perforated pressing plate 14 and carbonized
preform. If it is difficult to remove the preform, the fixture 28
in FIGS. 5-6 may be used to help extract the preform.
[0122] Fixture 28 is a steel plate 30 with center sleeve 32. An
attachment mechanism 34 disposed on the center sleeve 32 may be
used for pulling the preform removal fixture 28. The preform may
further include a lip 36 (preferably 1/2") for locking down when
pulling the preform.
[0123] In the above procedures, steps may be combined or deleted
without substantially affecting the resulting product.
[0124] If not otherwise stated herein, it may be assumed that all
components and/or processes described heretofore may, if
appropriate, be considered to be interchangeable with similar
components and/or processes disclosed elsewhere in the
specification, unless an express indication is made to the
contrary.
[0125] If not otherwise stated herein, any and all patents, patent
publications, articles and other printed publications discussed or
mentioned herein are hereby incorporated by reference as if set
forth in their entirety herein.
[0126] Although the invention has been described in detail for the
purpose of illustration based on what is currently considered to be
the most practical and preferred embodiments, it is to be
understood that such detail is solely for that purpose and that the
invention is not limited to the disclosed embodiments, but, on the
contrary, is intended to cover modifications and equivalent
arrangements that are within the spirit and scope of the appended
claims.
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