U.S. patent application number 09/790822 was filed with the patent office on 2001-07-05 for graphite foam material and method of making same.
Invention is credited to Hayward, Tommie P..
Application Number | 20010006263 09/790822 |
Document ID | / |
Family ID | 23033308 |
Filed Date | 2001-07-05 |
United States Patent
Application |
20010006263 |
Kind Code |
A1 |
Hayward, Tommie P. |
July 5, 2001 |
Graphite foam material and method of making same
Abstract
Methods of making a graphite material are provided. A flexible
graphite is ground into a powder. The graphite powder is mixed with
a resin and the mixture is hot pressed. A second method of making a
graphite material is provided where the graphite is ground into a
powder; the graphite powder is soaked in a cryogenic liquid; the
soaked graphite powder is then expanded; the expanded soaked
graphite powder is mixed with a graphite powder; and the graphite
powder mixed with a resin are hot pressed. According to a third
method, the flexible graphite is ground into a powder; the graphite
powder is soaked into a cryogenic liquid, the soaked graphite
powder is expanded; and the expanded soaked graphic powder is
ground into a fine powder. The resulting graphite powder is mixed
with a resin. The graphite powder mixed with the resin is hot
pressed. According to a fourth method, graphite flakes are soaked
into an acid; the soaked graphite flakes are expanded; and the
expanded soaked graphite flakes are precompacted. The precompacted
soaked graphite flakes are ground into a powder. The ground
precompacted expanded soaked graphite powder is then mixed with a
resin. The graphite powder with the resin is hot pressed.
Inventors: |
Hayward, Tommie P.; (Saugus,
CA) |
Correspondence
Address: |
BLAKELY SOKOLOFF TAYLOR & ZAFMAN
12400 WILSHIRE BOULEVARD, SEVENTH FLOOR
LOS ANGELES
CA
90025
US
|
Family ID: |
23033308 |
Appl. No.: |
09/790822 |
Filed: |
February 21, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09790822 |
Feb 21, 2001 |
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09270900 |
Mar 15, 1999 |
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6217800 |
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09270900 |
Mar 15, 1999 |
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08724177 |
Sep 30, 1996 |
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5882570 |
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08724177 |
Sep 30, 1996 |
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08591363 |
Jan 25, 1996 |
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5582781 |
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Current U.S.
Class: |
264/29.1 ;
264/28; 423/448; 423/449.3; 524/495; 524/609 |
Current CPC
Class: |
B29C 43/003 20130101;
B29C 43/006 20130101; C04B 40/0071 20130101; C04B 40/0082 20130101;
C04B 20/002 20130101; Y02P 20/582 20151101; C04B 14/024 20130101;
C04B 26/02 20130101; C04B 14/022 20130101; C04B 38/0022 20130101;
C04B 14/024 20130101; C04B 14/024 20130101; B29K 2303/06 20130101;
C04B 35/536 20130101; C04B 26/02 20130101 |
Class at
Publication: |
264/29.1 ;
264/28; 423/448; 423/449.3; 524/495; 524/609 |
International
Class: |
C01D 003/00; C08L
001/00; C08J 003/00; C08K 003/04 |
Claims
What is claimed is:
1. A method of making a graphite material comprising the steps of:
a) grinding flexible graphite into a powder having a particle size
in a range of 25 to 80 mesh; b) mixing the graphite powder in an
amount ranging between approximately 10% - 90% by weight, with a
resin, in an amount ranging between approximately 10% - 90% by
weight; and c) hot pressing said graphite powder mixed with said
resin.
2. The method of claim 1 wherein before hot pressing, said graphite
powder mixed with said resin is introduced into a first mold.
3. The method of claim 2, said hot pressing is performed at a
pressure that is less than 1 pounds per square inch (psi) and at a
temperature of approximately 230.degree. Fahrenheit.
4. The method of claim 3 wherein hot pressing further including,
removing from said first mold said graphite powder mixed with the
resin, placing said graphite powder mixed with the resin into a
second mold, and hot-pressing said graphite powder mixed with the
resin at approximately 2000 pound per square inch (psi) and
approximately 350.degree. F. for approximately 30 minutes.
5. The method of claim 1 wherein said graphite material has a
density of approximately 1.5 grams/centimeter cube (g/cc).
6. The method of claim 1 wherein said resin includes phenolic
resin.
7. The method of claim 1 wherein said flexible graphite includes
recycled graphite foil.
8. The method of claim 3 wherein hot-pressing the graphite powder
mixed with the resin at a pressure that is less than 1 pound per
square inch (psi) and at a temperature of 230.degree. F. is
performed for approximately 30 minutes.
9. A method of making a graphite material, the method comprising:
a) grinding flexible graphite into a powder having a particle size
in a range of approximately 25 to 80 mesh; b) soaking the graphite
powder in a cryogenic liquid; c) expanding the soaked graphite
powder; d) mixing the graphite powder in an amount ranging between
approximately 10% - 90% by weight, with a resin, in an amount
ranging between approximately 10% - 90% by weight; and e) hot
pressing said graphite powder mixed with said resin.
10. The method of claim 9 wherein before hot pressing, said
graphite powder mixed with said resin is introduced into a first
mold.
11. The method of claim 10, said hot pressing is performed a
pressure that is less than 1 pound per square inch (psi) and at a
temperature of approximately 230.degree. Fahrenheit.
12. The method of claim 11 wherein said hot pressing further
including, removing from said first mold said expanded soaked
graphite powder mixed with the resin, introducing said expanded
soaked graphite powder mixed with the resin into a second mold, and
hot-pressing said expanded soaked graphite powder mixed with the
resin at approximately 2000 pounds per square inch (psi)
approximately 350.degree. Fahrenheit for approximately 30
minutes.
13. The method of claim 9 wherein said graphite material has a
density of approximately 1.5 grams/centimeter cube (g/cc).
14. The method of claim 9 wherein said resin includes phenolic
resin.
15. The method of claim 9 wherein said flexible graphite includes
recycled graphite foil.
16. The method of claim 11 wherein hot-pressing the graphite powder
mixed with the resin at a pressure that is less than 1 pound per
square inch (psi) and at a temperature of approximately 230.degree.
Fahrenheit is performed for approximately 30 minutes.
17. The method of claim 9, wherein expanding the soaked graphite
powder is performed by heating the expanded graphite powder to a
temperature of approximately 650.degree. Fahrenheit (F.).
18. A method of making a graphite material, the method comprising:
a) grinding flexible graphite into a powder having a particle size
in a range of approximately 25 to 80 mesh; b) soaking the graphite
powder in a cryogenic liquid; c) expanding the soaked graphite
powder; d) grinding the expanded soaked graphite powder into a
powder having a particle size in a range of approximately 48 to 100
mesh; e) mixing the graphite powder in an amount ranging between
approximately 10% - 90% by weight, with a resin, in an amount
ranging between approximately 10% - 90% by weight; and f) hot
pressing said graphite powder mixed with said resin.
19. The method of claim 18 wherein before hot pressing, said
graphite powder mixed with said resin is introduced into a first
mold.
20. The method of claim 19, said hot pressing is performed at a
pressure that is less than 1 pound per square inch (psi) and at a
temperature of approximately 230.degree. Fahrenheit.
21. The method of claim 20 wherein said hot pressing further
including, removing from said first mold said graphite powder mixed
with the resin, introducing said graphite powder mixed with the
resin into a second mold; and hot-pressing said graphite powder
mixed with the resin at approximately 2000 pound per square inch
(psi) and approximately 350.degree. Fahrenheit for approximately 30
minutes.
22. The method of claim 18 wherein said graphite material has a
density of approximately 1.5 grams/centimeter cube (g/cc).
23. The method of claim 18 wherein said resin includes phenolic
resin.
24. The method of claim 18 wherein said flexible graphite includes
recycled graphite foil.
25. The method of claim 20 wherein hot-pressing the graphite powder
mixed with the resin at a pressure that is less than 1 pound per
square inch (psi) and at a temperature of approximately 230.degree.
Fahrenheit is performed for approximately 30 minutes.
26. The method of claim 18, wherein expanding the soaked graphite
powder is performed by heating the expanded graphite powder to a
temperature of approximately 650.degree. Fahrenheit (F.).
27. A method of making a graphite material, the method comprising:
a) soaking graphite flakes into an acid; b) expanding the soaked
graphite flakes; c) precompacting the expanded soaked graphite
flakes; d) grinding the precompacted expanded soaked graphite
flakes into a powder having a particle size in a range of
approximately 25 to 80 mesh; e) mixing the ground, precompacted
expanded soaked graphite powder in an amount ranging between
approximately 10% - 90% by weight, with a resin, in an amount
ranging between approximately 10% - 90% by weight; and f) hot
pressing said ground, precompacted expanded graphite powder mixed
with said resin.
28. The method of claim 27, wherein before hot pressing, said
graphite powder mixed with said resin is introduced into a first
mold.
29. The method of claim 28, said hot pressing is performed at a
pressure that is less than 1 pound per square inch (psi) and at a
temperature of approximately 230.degree. Fahrenheit.
30. The method of claim 29 wherein said hot pressing further
including, removing from said first mold said graphite powder mixed
with the resin, placing said expanded soaked graphite powder mixed
with the resin into a second mold; and hot-pressing said graphite
powder mixed with the resin at approximately 2000 pounds per square
inch (psi) and approximately 350.degree. Fahrenheit for
approximately 30 minutes.
31. The method of claim 27 wherein said graphite material has a
density of approximately 1.5 grams/centimeter cube (g/cc).
32. The method of claim 27 wherein said resin includes phenolic
resin.
33. The method of claim 29 wherein hot-pressing the graphite powder
mixed with the resin at less than 1 pound per square inch (psi) and
at approximately 250.degree. F. is performed for approximately 30
minutes.
34. The method of claim 27, said acid includes sulfuric acid.
35. The method of claim 27, said acid includes nitric acid.
36. The method of claim 29 wherein hot-pressing the graphite powder
mixed with the resin at a pressure that is less than 1 pound per
square inch (psi) and at a temperature of approximately 230.degree.
Fahrenheit is performed for approximately 30 minutes.
37. A graphite material made by a process comprising: a) grinding
flexible graphite into a powder having a particle size in a range
of 25 to 80 mesh; b) mixing the graphite powder in an amount
ranging between approximately 10% - 90% by weight, with a resin, in
an amount ranging between approximately 10% - 90% by weight; and c)
hot pressing said graphite powder mixed with said resin.
38. The graphite material of claim 37 wherein before hot pressing,
said graphite powder mixed with said resin is introduced into a
first mold.
39. The graphite material of claim 38, said hot pressing is
performed at a pressure that is less than 1 pound per square inch
(psi) and at a temperature of approximately 230.degree.
Fahrenheit.
40. The graphite material of claim 39 wherein said hot pressing
further including, removing from said first mold said graphite
powder mixed with the resin, placing said graphite powder mixed
with the resin into a second mold, and hot-pressing said graphite
powder mixed with the resin at approximately 2000 pounds per square
inch (psi) and approximately 350.degree. Fahrenheit for
approximately 30 minutes.
41. The graphite material of claim 37 wherein said graphite
material has a density of approximately 1.5 grams/centimeter cube
(g/cc).
42. The graphite material of claim 37 wherein said resin includes
phenolic resin.
43. The graphite material of claim 37 wherein said flexible
graphite includes recycled graphite foil.
44. The graphite material of claim 39 wherein hot-pressing the
graphite powder mixed with the resin at a pressure that is less
than 1 pound per square inch (psi) and at a temperature of
approximately 230.degree. Fahrenheit is performed for approximately
30 minutes.
45. A graphite material made by a process comprising: a) grinding
flexible graphite into a powder having a particle size in a range
of 25 to 80 mesh; b) soaking the graphite powder in a cryogenic
liquid; c) expanding the soaked graphite powder; d) mixing the
expanded soaked graphite powder in an amount ranging between
approximately 10% - 90% by weight, with a resin, in an amount
ranging between approximately 10% - 90% by weight; and e) hot
pressing said expanded soaked graphite powder mixed with said
resin.
46. The graphite material of claim 45 wherein before hot pressing,
said expanded soaked graphite powder mixed with said resin is
introduced into a first mold.
47. The graphite material of claim 46, said hot pressing is
performed at a pressure that is less than 1 pound per square inch
(psi) and at a temperature of approximately 230.degree.
Fahrenheit.
48. The graphite material of claim 47 wherein said hot pressing
further including, removing from said first mold said expanded
soaked graphite powder mixed with the resin, placing said expanded
soaked graphite powder mixed with the resin into a second mold, and
hot-pressing said expanded soaked graphite powder mixed with the
resin at approximately 2000 pounds per square inch (psi), and
approximately 350.degree. Fahrenheit, for approximately 30
minutes.
49. The graphite material of claim 45 wherein said graphite
material has a density of approximately 1.5 grams/centimeter cube
(g/cc).
50. The graphite material of claim 45 wherein said resin includes
phenolic resin.
51. The graphite material of claim 45 wherein said flexible
graphite includes recycled graphite foil.
52. The graphite material of claim 47 wherein hot-pressing the
graphite powder mixed with the resin at a pressure that is less
than 1 pound per square inch (psi) and at a temperature of
approximately 230.degree. Fahrenheit is performed for approximately
30 minutes.
53. The graphite material of claim 45, wherein expanding the soaked
graphite powder is performed by heating the soaked graphite powder
to a temperature of approximately 650.degree. Fahrenheit (F.).
54. A graphite material made by a process comprising: a) grinding
flexible graphite into a powder having a particle size in a range
of 25 to 80 mesh; b) soaking the graphite powder in a cryogenic
liquid; c) expanding the soaked graphite powder; d) grinding the
expanded soaked graphite powder into a powder having a particle
size in a range of approximately 48 to 100 mesh; e) mixing the
graphite powder in an amount ranging between approximately 10% -
90% by weight, with a resin, in an amount ranging between
approximately 10% - 90% by weight; and f) hot pressing said
graphite powder mixed with said resin.
55. The graphite material of claim 54 wherein before hot pressing,
said graphite powder mixed with said resin is introduced into a
first mold.
56. The graphite material of claim 55, said hot pressing is
performed at less than 1 pound per square inch (psi) and at
approximately 250.degree. F.
57. The graphite material of claim 56 wherein hot-pressing the
graphite powder mixed with the resin at a pressure that is less
than 1 pound per square inch (psi) and at a temperature of
approximately 230.degree. Fahrenheit is performed for approximately
30 minutes.
58. The graphite material of claim 57 wherein said hot pressing
further including, removing from said first mold said graphite
powder mixed with the resin, placing said graphite powder mixed
with the resin into a second mold, and hot-pressing said graphite
powder mixed with the resin at approximately 2000 pounds per square
inch (psi) and approximately 350.degree. Fahrenheit for
approximately 30 minutes.
59. The graphite material of claim 54, wherein expanding the soaked
graphite powder is performed by heating the expanded graphite
powder to a temperature of approximately 650.degree. Fahrenheit
(F.).
60. A graphite material made by a process comprising: a) soaking
graphite flakes into an acid; b) expanding the soaked graphite
flakes; c) precompacting the expanded soaked graphite flakes; d)
grinding the precompacted expanded soaked graphite into a powder
having a particle size in an approximate range of 25 to 80 mesh; e)
mixing the expanded soaked graphite powder in an amount ranging
between approximately 10% - 90% by weight, with a resin, in an
amount ranging between approximately 10% - 90% by weight; and f)
hot pressing said graphite powder mixed with said resin.
61. The graphite material of claim 60 wherein before hot pressing,
said graphite powder mixed with said resin is introduced into a
first mold.
62. The graphite material of claim 61, said hot pressing is
performed at a pressure that is less than 1 pound per square inch
(psi) and at a temperature of approximately 230.degree.
Fahrenheit.
63. The graphite material of claim 62 wherein said hot pressing
further including, removing from said first mold said graphite
powder mixed with the resin, placing said graphite powder mixed
with the resin into a second mold, and hot-pressing said graphite
powder mixed with the resin at approximately 2000 pounds per square
inch (psi) and approximately 350.degree. Fahrenheit for
approximately 30 minutes.
64. The graphite material of claim 62 wherein hot-pressing the
graphite powder mixed with the resin at a pressure that is less
than 1 pound per square inch (psi) and at a temperature of
approximately 230.degree. Fahrenheit is performed for approximately
30 minutes.
65. The graphite material of claim 60 wherein expanded soaked
graphite flakes are precompacted to a density of approximately 0.1
g/cc.
66. A graphite material made by a process comprising: a) grinding
flexible graphite into a powder; b) mixing the graphite powder with
a thermoplastic material; and c) injecting into a mold the graphite
powder mixed with the thermoplastic material.
67. The graphite material of claim 66 wherein said plastic material
formed has a density of approximately 1.7 grams/centimeter
cube.
68. The process of claim 66 wherein said thermoplastic material is
Poly Phelene Sulfide.
69. A bipolar plate made of the graphite material of claim 67.
70. A gasket made by the graphite material of claim 67.
71. A graphite material made by a process comprising: a) grinding
flexible graphite into a graphite powder; b) soaking said graphite
powder into a cryogenic liquid; c) expanding the soaked braphite
powder; d) mixing the expanded graphite with a thermoset resin, and
e) heating the graphite resin mixture under pressure. f) heat
treating the product of step e.
72. The graphite material of claim 71 wherein expanding the soaked
graphite powder is performed by heating the soaked graphite
material.
73. The graphite material of claim 71 wherein said graphite of step
a is flexible graphite foil.
74. The graphite material of claim 71 wherein said graphite foil is
recycled graphite foil.
Description
[0001] This is a continuation of U.S. patent application Ser. No.
08/724,177 filed Sep. 30, 1996, which is a continuation of U.S.
patent application Ser. No. 08/591,363 filed Jan. 25, 1996.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to graphite foam material, of the type
used for high temperature insulation and the like, and to a method
of making the same. The invention also relates to a graphite
material that may be used and added to provide protection from
electrostatic discharge (ESD) or shielding from electromagnetic and
radio interference (EMI/RFI).
[0004] 2. Art Background
[0005] In the prior art, various forms of graphite material have
been used as insulating materials in high temperature applications
including industrial ovens and furnaces, vacuum furnaces and
controlled atmosphere heating apparatus and the like.
[0006] One of the first such graphite insulating materials was
powdered carbon black which had an appropriate amount of insulating
capacity, but was very difficult to handle, relatively heavy, and
extremely time consuming to replace. As a result with the advent of
foam and resin chemistry, a number of newer materials were
developed which were lighter and easier to handle, but which had
the requisite insulating capacity. One such material is a carbon
fiber insulating material made of a carbon fiber held in a matrix
by a phenolic resin material, and formed into a board or block.
[0007] Static electricity and electrostatic discharge (ESD) are
naturally occurring phenomena. Simply stated, static electricity is
electrical energy at rest on a surface. It is generally created by
the rubbing together and separating of two materials, one of which
is usually non-conductive. Typically, one material gives up
electrons and becomes positively charged; the other takes on the
electrons and becomes negatively charged. ESD may be defined as the
sudden discharge of an electrostatic potential from one body to
another. A good example may be the shock one receives when touching
a metal door knob after walking across a carpeted floor.
[0008] In many environments, ESD may damage or destroy sensitive
electronic components, erase or alter magnetic media, or set off
explosions or fires in flammable environments. These discharges may
be caused by a variety of sources, most commonly there is a direct
discharge from a person or equipment into a sensitive object.
[0009] One way of preventing ESD is to reduce the generation of
charges in the first place. A second way of preventing ESD is to
provide a ground path for the safe dissipation of accumulated
charges to ground. A third method is to provide shielding or
protection of devices and equipment from discharge through
packaging. ESD may also be controlled with materials, such as
conductive plastics, that do not generate high levels of charge,
that dissipate charges before they accumulate to dangerous levels,
or that provide electrostatic shielding to prevent charges from
reaching the sensitive product.
[0010] Electromagnetic Interference (EMI) is electrical energy,
either electromagnetic or in the radio frequency (RF) range in the
case of radio frequency interference (RFI) that is radiated by
specific sources. Some of these sources include computer circuits,
radio transmitters, fluorescent lamps, color TV oscillators,
electric motors, automotive ignition coils, overhead power lines,
lightning, TV games, and many other resources. EMI/RFI may
interfere with the operation of simple household appliances such as
causing the unwanted operation of garage door openers. On another
level, EMI/RFI may corrupt data in large scale computer systems,
cause inaccurate readings and output in aircraft guidance systems,
and interrupt the functioning of medical devices, such as
pacemakers.
[0011] Proper shielding may prevent products from emitting
electromagnetic or radio frequency energy to other susceptible
equipment. Shielding may also protect susceptible equipment from
the effects of externally radiated EMI/RFI as the shielding absorbs
the energy emitted, converting it to thermal energy.
[0012] EMI thermoplastic composites are used primarily for
shielding against emission or reception of EMI and RFI.
Traditionally, shielding has been accomplished by encasing
sensitive electronic parts in metal housings or by using metallic
coatings on the inside of plastic housings. Thermoplastic compounds
with appropriate shielding additives are cost effective
alternatives in many applications due to their ability to take on
complex shapes and maintain tight tolerances.
[0013] It is desirable to provide, at relatively low cost, a
compound/s that may dissipate charges before they accumulate to
dangerous levels, that provide electrostatic shielding to prevent
charges from reaching the sensitive product. Moreover, it is
desirable to provide, at relatively low cost, a material for
shielding against emission or re-emission of electrostatic.
SUMMARY OF THE INVENTION
[0014] The present invention is a composition of matter, and
specifically, a material comprising cryogenically treated graphite
or carbon particles which are then expanded by thermal shock/gas
expansion. The expanded particles are then combined with a phenolic
resin, or the like, and then thermoset under pressure at an
elevated temperature to form a hardened sheet or plate. The carbon
or graphite particles can be obtained from previously expanded
graphite which has been made into flexible graphite foil, and
therefore, the present invention permits the recycling of graphite
foil which is not otherwise commercially distributed. The method of
making said material is also described and claimed.
[0015] The material has generally the same insulating and other
physical characteristic as the prior art carbon fiber insulation
materials, and it is less expensive than prior art materials.
[0016] Another advantage of the present invention is that it can
utilize, without any drawbacks, recycled flexible graphite
material, as a starting material. Such recycled flexible graphite
material is currently typically being landfilled. Thus, the present
invention is particularly advantageous as a benefit to the
environment. Additionally, the advantageous method of making the
material and the quality of the material made in accordance with
the present invention provide additional benefits.
[0017] Another advantage is the reduced weight loss due to
oxidation, resulting in longer furnace life between successive
rebuilding of the furnace.
[0018] According to the present invention, one may use finished low
density blocks, boards, billets, etc. to make higher density parts
by cutting (i.e., using, for example, a cork bore or saw) to shape
or mold the material into a desired shape and pressing using
different pressures to the obtain desired density. For example, die
formed rings can be made using the present invention. The
compressive strength of the die formed rings was greater than or
equal to the strength of some monolithic graphites of the prior
art.
[0019] The present invention also includes a graphite material and
a method for making the graphite material by using a thermoplastic
material mixed with re-expanded graphite. The compound of thermo
plastic material and re-expanded graphite is fed into an injection
molding system at a relatively high temperature and injected into a
mold where a plastic material is formed. The plastic material is
then removed from the mold when the material is still very hot but
hard set.
[0020] The present invention further includes in one embodiment
thereof a method of making a graphite material. Flexible graphite
is ground into a powder having a particle size in the approximate
range of 25 to 80 mesh. The graphite powder is mixed in an amount
ranging between approximately 10% - 90% graphite powder by weight,
with a resin, in an amount ranging between approximately 10% - 90%
by weight. The graphite powder, mixed with the resin is hot
pressed.
[0021] The present invention also provides in another embodiment
thereof a method of making a graphite material. A flexible graphite
is ground into a powder having a particle size in an approximate
range of 25 - 80 mesh. The graphite powder is soaked in a cryogenic
liquid. The soaked graphite powder is expanded. The resulting
graphite powder is mixed in an amount ranging between approximately
10% - 90% by weight with a resin, in an amount ranging between
approximately 10% - 90% by weight. The expanded soaked graphite
powder that has been mixed with the resin is then hot pressed.
[0022] The present invention further provides in another embodiment
thereof a method of making a graphite material. A flexible graphite
is ground into a powder having a particle size in an approximate
range of 25 - 80 mesh. The graphite powder is then soaked in a
cryogenic liquid. The soaked graphite powder is then expanded. The
expanded soaked graphite powder is ground into a powder having a
particle size in an approximate range of 48 to 100 mesh. The
resulting graphite powder is mixed, in an amount ranging between
approximately 10% - 90% by weight with a resin in an amount ranging
between approximately 10% - 90% by weight. The graphite powder
mixed with the resin is then hot pressed.
[0023] The present invention provides in another embodiment thereof
a method of making a graphite material. Initially, graphite flakes
are soaked in an acid. The soaked graphite flakes are then
expanded. The soaked expanded graphite flakes are precompacted. The
precompacted expanded soaked graphite is then ground into a powder
that has a particle size in a range of approximately 25 to 80 mesh.
The graphite powder is mixed an amount ranging between
approximately 10% - 90% by weight with a resin in an amount ranging
between approximately 10% - 90% by weight. The graphite powder that
has been mixed with the resin is then hot pressed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The objects, features and advantages of the present
invention will become apparent to one skilled in the art from
reading the following detailed description in which:
[0025] FIG. 1 is a flow chart showing on embodiment of process of
the present invention;
[0026] FIG. 2 is a schematic drawing of the heat shock apparatus
used in one method of the present invention;
[0027] FIG. 3 is a graph showing the oxidation weight loss of prior
art rigid felt as compared with the material of the present
invention, which is the invented material at 670.degree. C. over
time;
[0028] FIG. 4 is a graph showing the final density of the invented
material as a result of the compressive force applied to it;
[0029] FIG. 5 is a graph showing steps of a second embodiment of a
method according to the present invention;
[0030] FIG. 6 is a flow chart diagram illustrating a third
embodiment of a process of making a graphite material according to
the present invention;
[0031] FIG. 7 is a flow chart diagram illustrating a fourth
embodiment of a process of making a graphite material according to
the present invention;
[0032] FIG. 8 is a flow chart diagram illustrating a fifth
embodiment of a process of making a graphite material according to
the present invention;
[0033] FIG. 9 is a flow chart diagram illustrating a sixth
embodiment of a process of making a graphite material according to
the present invention; and
[0034] FIG. 10 illustrates a graph in connection with the
resistivity per meter square of the graphite material produced by
way of the third, fourth, fifth and sixth embodiments of the method
of making a graphite material according to the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0035] In the following description, numerous specific details are
set forth to provide a thorough understanding of the present
invention. However, one having ordinary skill in the art should
recognize that the invention may be practiced without these
specific details. In some instances, well-known circuits,
structures, and techniques have not been shown in detail to avoid
obscuring the present invention.
[0036] The present invention relates to a material and methods of
making materials, with different densities, the materials having
superior heat insulation capacity for use in furnaces and other
apparatus. The method of making the present invention is shown in
the flow chart in FIG. 1.
[0037] The starting material is preferably recycled flexible
graphite, such as the type which may be obtained as a byproduct
from the manufacture of flexible graphite rolls.
[0038] The flexible graphite material is sometimes referred to as
vermiculated graphite. It is a graphite material which has already
been subjected to an expansion process, typically an acid treatment
of graphite followed by a heat shock treatment. The starting
material can be in the form of chunks, bricks, strips, or any other
form which may be obtained.
[0039] The flexible graphite is first ground to a very fine powder
having a particle size in the range of 35 to 80 mesh and a tap
density of approximately 0.177 - 0.230 g/cc. Somewhat smaller or
larger mesh can be used as well, but the particle size is
preferably within the range of 35 to 80 mesh as specified. The
flexible graphite can be ground in a cone mill grinder or hammer
mill grinder or other grinder known in the art.
[0040] In the next step, the powdered carbon particles are poured
into a container of liquid nitrogen, and permitted to absorb
sufficient liquid nitrogen so that they sink in the container below
the surface of the liquid nitrogen. It is believed that other
cryogenic liquids may also work, and are deemed to be within the
scope of the present invention. The sinking of the particles, while
not deemed critical to the subject process, appears to be an
adequate indicator of sufficient absorption of the liquid nitrogen
into the particles, which is important in the following expansion
step.
[0041] Alternatively, one may treat ground flexible graphite with
acid such as fuming nitric acid, sulfuric acid, etc., and then heat
the compound, of the respective acid and ground flexible graphite,
thereby causing graphite to expand. For example, an experiment was
conducted using 4 grams of ground flexible graphite and 6
centimeters cube (cc) of fuming nitric acid. The compound was then
heated to 1100.degree. Celsius (C.). The expansion ratio obtained
was 8 to 10 times.
[0042] The liquid nitrogen soaked carbon particles or the ground
flexible graphite particles treated with one of the above-mentioned
acids are next injected into a hot air burner in an oven with an
air stream flowing therethrough, the oven temperature being
approximately 650.degree. Fahrenheit (F.). One such acceptable hot
air burner is a propane burner such as a Universal.RTM. 40,000 BTU
per hour propane heater. One possible arrangement is shown in FIG.
2. As shown the heat shock/gas expansion apparatus comprises a
propane heater 20, with the heated air flow direction shown by
arrow A, coupled through a conduit 22 to a receiving means 24 which
receives the liquid nitrogen soaked particles through the top inlet
26 (which are added in the direction shown by arrow B. The
receiving means 24 is coupled through conduit 26 to heat treated
particles receiving means 28, which has a screen 30 to prevent the
particles, which are now very light, from becoming excessively
airborne.
[0043] If the recycled graphite particles are used, this heat
treatment or thermal shock/gas expansion expands the particles to
about 4 to 8 times their original size, and the density of the
particles is in the range of 0.080 to 0.030 grams per cubic
centimeter. The expanded particles may be compressed and molded to
the desired size, shape and density without using the next
steps.
[0044] The expanded, thermally-shocked, carbon material is then
mixed with a resin, and preferably a phenolic resin, and most
preferably a phenolic resin such as Borden Durite RD-2414 in a
preferred ratio of about 60% carbon to 40% resin by weight. Other
ratios may be used, and the selection of a ratio is within the
skill of persons of ordinary skill in the art.
[0045] The mixture is then thermoset at a temperature of
350.degree. F. and a pressure dependent upon the density required
for about 1 hour. The shape of the product can be any shape and
size as required for the intended purpose.
[0046] The thermoset product is then heat treated in a furnace. The
temperature of the heat treatment is preferably about 2000.degree.
F., but may vary from 1000 - 5000.degree. F. depending upon final
usage.
[0047] The density may be in the range from less than 0.1 g/cc to
approximately theoretical density.
[0048] FIG. 3 shows a comparison of prior art material to the
material of the present invention, and particularly shows that
there is substantially more weight loss from the prior art material
being exposed to elevated temperature over time which is considered
disadvantageous to those skilled in the art.
[0049] FIG. 4 illustrates the density of the material as a result
of the pressure applied to it during its manufacture.
[0050] In another embodiment of the present invention, a method for
making a substantially high density graphite material with plastic
characteristics (graphite-plastic) is provided. The main steps of
this method are shown in FIG. 5. According to this method, a
thermoplastic material, such Polyphelene Sulfide (PPS) may be mixed
with re-expanded graphite thereby producing graphite pellets. The
pellets may then be expanded by using the expansion process
described in the foregoing. In this respect, the description of the
expansion process presented in the foregoing is herein incorporated
by reference. Note that while the expansion process is not
necessary to the method described herein, this process is, however,
preferable.
[0051] In the embodiment, of the method according to the present
invention, described herein, the compound material, i.e., pellets,
include a thermoplastic material mixed with 45-60% re-expanded
graphite, but the present invention is not limited in scope in this
respect. The compound material is then injected into a mold at a
temperature of approximately 650.degree. F. The mold may have an
approximate dimension of 6".times.9".times.0.125", but the present
invention is not limited in scope in this respect. The injection of
the compound may be performed for approximately 1 minute. Graphite
material with plastic characteristics is then formed into plates,
or other type of shapes in the mold at a temperature of 250.degree.
Fahrenheit and removed therefrom when the material is still hot,
but hard set.
[0052] The resulting graphite material with plastic characteristics
produced may be formed into different geometry's due to its high
density of the produced which allows the graphite-plastic materials
produced to be shaped better. The graphite-plastic plates obtained
have a density of approximately 1.5 grams per cc. It is believed
that any thermoplastic material may be used in this process instead
of the PPS.
[0053] A graphite-plastic material according to the present
invention may also be obtained by using a thermosetting plastic
such as phenolic resin, epoxy resin, and mixing it with graphite
powder. The compound of thermoset material and the graphite powder
may then be heated to a temperature that is below the thermosetting
temperature (350.degree. F.) for approximately an hour and then
introduced in a mold by using a process of hot pressing which is
well-known by one skilled in the art. It will be noted that instead
of graphite powder, re-expanded graphite may be used in this
process.
[0054] The present invention also provides a method for making an
electrically conductive plastic that has a relatively low
resistivity. According to this process, a PPS material or a liquid
crystal polymer (LCP) resin is mixed with re-expanded graphite to
make pellets as explained above. The pellets are then mixed in a
tumbler with 20% by weight nickel coated carbon fibers. The nickel
coated carbon fibers may be a mixture of 50% carbon particles and
50% nickel in various concentrations. The addition of nickel coated
carbon fibers to the pellets causes a decrease the bulk resistance
of the pellets from approximately 0.100 ohm inches to 0.00085 ohm
inches. Then this compound is subject to an injection molding
process as explained in the foregoing. The material produced has
both a low electrical resistivity and a high corrosion resistance.
Moreover, the material produced may be used for bipolar plates in
photon exchange membrane (PEM) type fuel cells, gaskets such as
intake manifold, flange gaskets, etc. for automotive devices.
[0055] FIG. 6 illustrates a flow chart diagram for a third
embodiment of a process of making a graphite material according to
the present invention. The process starts at step 602 where
flexible graphite is ground into a very fine powder having a
particle size in an approximate range of 25 - 80 mesh and a tap
density in a range of approximately 0.177 - 0.230 grams/centimeter
cube (g/cc). However, the present invention may be practiced in
connection with other particle sizes and tap densities. The
flexible graphite may be ground in a cone mill grinder or hammer
mill grinder or other grinder known in the art. In one embodiment,
the starting material may be recycled flexible graphite, of a type
which may be obtained as a byproduct from the manufacture of
flexible graphite rolls. The starting material may be in the form
of chunks, bricks, strips, or any other form. The flexible graphite
material is sometimes referred to as vermiculated graphite.
Vermiculated graphite material is a material that has already been
subjected to an expansion process where typically the graphite
material is treated with an acid and then subjected to a heat shock
treatment.
[0056] The process then flows to block 604 where the graphite
powder obtained from grinding the flexible graphite is then mixed
with a resin. In one embodiment according to the present invention,
the resin includes a phenolic resin that may be Borden Durite RD
2414, but the present invention may be equally practiced in
connection with other resins. The graphite powder is mixed in an
amount ranging between approximately 10% - 90% by weight with
phenolic resin in an amount ranging between 10% - 90% by weight
such that the sum of the x% graphite and y% phenolic resin, of the
combination, equals 100%. Table 1 shows possible mixture ratios
between graphite and resin and the corresponding resistivities of
the mixtures in microhms per meter square.
1 TABLE 1 Graphite Resin Resistivity 90% 10% 17.8 Microhms/meter
square 80% 20% 26.5 Microhms/meter square 70% 30% 33.0
Microhms/meter square 60% 40% 61.1 Microhms/meter square 50% 50%
90.2 Microhms/meter square 40% 60% 166.0 Microhms/meter square 30%
70% 328.0 Microhms/meter square 20% 80% 2294.0 Microhms/meter
square 10% 90% N/A
[0057] Next, at block 608 the graphite powder mixed with the
phenolic resin (mixture) is hot pressed. Before hot pressing, the
combination of graphite powder with phenolic resin is introduced
into a first mold. The mold may have an approximate dimension of
6".times.9".times.0.125", but the embodiment of the process
described herein may be equally practiced in connection with molds
having higher or lower dimensions. The mixture combination is
introduced into the first mold by pouring graphite powder and the
phenolic resin into the first mold. The mixture is hot-pressed at a
pressure less than 1 pound per square inch (psi) at approximately
250.degree. F. for approximately 30 minutes. As a result of
subjecting the mixture to hot pressing, the particles of the
graphite powder and the phenolic resin bind together at a density
of approximately 0.1 g/cc. However, this density may be different
than 0.1 g/cc. The mixture is then removed from the first mold and
is placed into a second mold and hot-pressed at approximately
350.degree. F. at 2000 psi, for approximately 30 minutes.
[0058] The resulting graphite material obtained by way of the
process described above has a density of approximately 1.5
g/cm.sup.3. As one may see from Table 1, the more graphite the
mixture has, the resulting graphite material's resistivity is
lower, reaching 17.8 microhm per meter square for 90% graphite and
10% resin.
[0059] FIG. 7 illustrates a flow chart diagram in connection with a
fourth embodiment of a process of making a graphite material
according to the present invention. Initially, at block 702,
flexible graphite is ground into a powder that has a particle size
in a range of approximately 25 to 80 mesh. More details related to
this process step were provided above in the description connected
to the previous embodiment illustrated in FIG. 6. Next the process
flows to step 704 where the graphite powder is soaked in a
cryogenic liquid. More detail with respect to this step may be
found above in the description connected to FIG. 1.
[0060] Next, at block 706 the soaked graphite is expanded. In one
embodiment according to the present invention, the soaked graphite
compound may be expanded by heating the soaked graphite compound to
a temperature of approximately 650.degree. F. One way to perform
this expansion is by heating the soaked graphite as explained above
in the description connected to FIGS. 1 and 2.
[0061] Next at step 708 the expanded graphite compound is mixed in
an amount ranging between approximately 10% - 90% by weight with
phenolic resin in an amount ranging between 10% -90% by weight.
Table 2 below illustrates possible mixtures of graphite with the
resin and their respective resistivities.
2 TABLE 2 Graphite Resin Resistivity 90% 10% 10.0 Microhms/meter
square 80% 20% 17.0 Microhms/meter square 70% 30% 33.0
Microhms/meter square 60% 40% 38.7 Microhms/meter square 50% 50%
60.9 Microhms/meter square 40% 60% 84.5 Microhms/meter square 30%
70% 134.0 Microhms/meter square 20% 80% 248.0 Microhms/meter square
10% 90% 736.0 Microhms/meter square
[0062] Next the graphite mixture is hot pressed after initially
introducing the graphite mixture into a first mold. Hot pressing is
performed in a manner as explained above in the description in
connection with the embodiment of the process illustrated in FIG.
6.
[0063] FIG. 8 illustrates a flow chart in connection with an
embodiment of a fifth process of making a graphite material
according to the present invention. The embodiment of this process
starts at block 802 where flexible graphite is ground into a powder
that has a particle size in a range of approximately 25 - 80 mesh.
Next the process flows to block 804 where the graphite powder is
soaked in a cryogenic liquid. The process then flows to block 806
where the soaked graphite powder is expanded by heating to a
temperature at which the soaked graphite powder expands. In one
embodiment this temperature is approximately 650.degree. F., but
the present invention equally applies in connection with heating at
other temperatures that cause expansion of the soaked graphite
flakes. Next at block 808, the expanded graphite powder is ground
into a finer graphite powder that has a particle size in a range of
approximately 48 - 100 mesh but the present invention is not
limited in scope to this particle size range. At block 810, the
finer graphite powder is mixed in an amount ranging between
approximately 10% - 90% graphite powder by weight with phenolic
resin in amount ranging between 10% - 90% by weight. Next at block
812, the graphite mixture is hot pressed as explained above in the
description of the embodiments of the processes illustrated in
FIGS. 6 and 7.
[0064] Table 3 illustrates possible mixture ratios between graphite
and resin and the corresponding resistivities of the resulting
graphite materials.
3 TABLE 3 Graphite Resin Resistivity 90% 10% 15.0 Microhms/meter
square 80% 20% 23.6 Microhms/meter square 70% 30% 25.8
Microhms/meter square 60% 40% 46.1 Microhms/meter square 50% 50%
116.9 Microhms/meter square 40% 60% 161.8 Microhms/meter square 30%
70% 186.8 Microhms/meter square 20% 80% 1219.9 Microhms/meter
square 10% 90% N/A
[0065] FIG. 9 illustrates a sixth embodiment of a process of making
a graphite material according to the present invention. At block
902 natural graphite flakes are soaked in an acid. In one
embodiment the acid may be nitric acid or sulfuric acid. Next the
process flows to block 904 where the soaked natural graphite flakes
are expanded. The expansion is performed by heating the soaked
natural graphite flakes at a temperature of approximately
1200.degree. F. to expand in a range of 200 - 400 times depending
on the graphite. Next, at block 906, the expanded soaked natural
graphite flakes are precompacted to a density of approximately 0.1
g/cm.sup.3. Next, at step 908 the expanded precompacted soaked
natural graphite flakes are ground to a particle size in an
approximate range of 25 - 80 mesh. At block 910, the graphite
powder is mixed in a ratio ranging between approximately 10% - 90%
graphite powder by weight with a phenolic resin in an amount
ranging between 10% - 90% by weight. Next at block 912, the mixture
is hot pressed. The steps performed during the hot press stage are
similar to the steps described above in connection with hot
pressing.
[0066] Table 4 illustrates possible combination ratios between
graphite and resin, and the corresponding resistivity of the
resulting graphite materials.
4 TABLE 4 Graphite Resin Resistivity 90% 10% 18.05 Microhms/meter
square 80% 20% 21.3 Microhms/meter square 70% 30% 32.2
Microhms/meter square 60% 40% 73.0 Microhms/meter square 50% 50%
83.0 Microhms/meter square 40% 60% 119.0 Microhms/meter square 30%
70% 4136.0 Microhms/meter square 20% 80% N/A 10% 90% N/A
[0067] FIG. 10 illustrates four graphs in connection with the
resistivity of the graphite materials obtained by way of the four
processes explained in connection with FIGS. 6 - 9. The Y-axis
indicates the resistivity in microhms per meter square. The X-axis
indicates the ratio of graphite to resin utilized. The four
different graphs illustrated in the figure are distinguished from
one another by the symbols shown in the legend. For example, the
graph designated by the symbol "X" is in connection with the
embodiment of the process explained in connection with FIG. 7. For
this process, the resulting graphite material has a resisitivity of
approximately 10 microhms per meter square for a combination of 90%
graphite and 10% phenolic resin.
[0068] The graph designated by the symbol ".box-solid." is in
connection with the embodiment of the process explained in
connection with FIG. 8. The resulting graphite material obtained by
way of this process has a resistivity of approximately 16 microns
per meter square, for a ratio of 90% graphite and 10% phenolic
resin. Note that for combinations in the ranges of approximately
90%/10% - 75%/25% and 65%/35% - 40%/60% of graphite-to-phenolic
resin, the graphite material obtained by way of the process
represented by graph X has the lowest resistivity, compared with
the resistivities of the other graphite materials, obtained by way
of the other three processes.
[0069] In the foregoing specification, the invention has been
described with reference to specific embodiments thereof. It will
however be evident that various modifications and changes can be
made thereto without departing from the broader spirit and scope of
the invention as set forth in the appended claims. The
specification and drawings are, accordingly, to be regarded in an
illustrative rather than a restrictive sense.
* * * * *