U.S. patent application number 09/833458 was filed with the patent office on 2002-10-17 for conductive polymers and methods of use.
Invention is credited to Hayward, Tommie P., Roemmler, Mike G..
Application Number | 20020149004 09/833458 |
Document ID | / |
Family ID | 25264475 |
Filed Date | 2002-10-17 |
United States Patent
Application |
20020149004 |
Kind Code |
A1 |
Hayward, Tommie P. ; et
al. |
October 17, 2002 |
Conductive polymers and methods of use
Abstract
A method and apparatus comprising expanded, or flexible,
graphite mixed into a polymer material is disclosed. A method for
using expanded graphite that has been pre-compressed prior to
milling to enable a polymer material to accept an electrostatic
modification to the surface or to dissipate electrostatic
discharges. Other embodiments relate to methods of making polymer
materials, methods of making molded polymer articles or objects,
and methods of electrostatically modifying molded conductive
polymer materials.
Inventors: |
Hayward, Tommie P.; (Saugus,
CA) ; Roemmler, Mike G.; (Los Angeles, CA) |
Correspondence
Address: |
BLAKELY SOKOLOFF TAYLOR & ZAFMAN
12400 WILSHIRE BOULEVARD, SEVENTH FLOOR
LOS ANGELES
CA
90025
US
|
Family ID: |
25264475 |
Appl. No.: |
09/833458 |
Filed: |
April 11, 2001 |
Current U.S.
Class: |
252/500 |
Current CPC
Class: |
C08K 3/04 20130101; B29K
2303/06 20130101; B29C 43/006 20130101; B29C 43/003 20130101 |
Class at
Publication: |
252/500 |
International
Class: |
H01B 001/00 |
Claims
What is claimed is:
1. A method comprising: combining a polymer and one to 20 percent
expanded graphite; and pelletizing the combination.
2. The method of claim 1, wherein; pelletizing comprises
extruding.
3. The method of claim 1, further comprising; prior to pelletizing
combining the expanded graphite with a filler of at least one of
carbon black, carbon fibers, mineral filler, re-expanded graphite,
and recycled expanded graphite.
4. The method of claim 3, wherein; the carbon fibers are at least
one of polyacrylnitrile fibers, pitch carbon fibers and rayon-based
carbon fibers.
5. The method of claim 1, wherein said polymer material is one of a
thermoset material and a thermoplastic material.
6. A method comprising: pelletizing a moldable polymer with one to
20 percent expanded graphite; and introducing the pellets into a
mold.
7. The method of claim 6, wherein said polymer material is one of a
thermoset material and a thermoplastic material.
8. The method of claim 6, wherein introducing the pellets into the
mold is achieved by injection molding.
9. The method of claim 6, wherein introducing the pellets into the
mold further comprises forming an object.
10. The method of claim 9, wherein the amount of graphite is
sufficient to conduct, the method further comprising after coupling
the molded object to a conductive path, electrostatically modifying
the surface of the molded material.
11. The method of claim 10, wherein the modifying comprises
painting.
12. The method of claim 11, wherein the painting comprises
primerless painting adherence to the object.
13. The method of claim 6, further comprising; prior to pelletizing
combining the expanded graphite with a filler of at least one of
carbon black, carbon fibers, mineral filler, glass, re-expanded
graphite, and recycled expanded graphite.
14. The method of claim 6, wherein; the carbon fibers are at least
one of polyacrylnitrile fibers, pitch carbon fibers and rayon-based
carbon fibers.
15. The method of claim 6, wherein the polymer material is combined
with five to 10 percent expanded graphite.
16. The method of claim 6, wherein the polymer material is combined
with seven to 10 percent expanded graphite.
17. A method comprising: providing a molded polymer comprising one
to 20 percent expanded graphite; and coupling said molded polymer
to a conductive path.
18. The method of claim 17, wherein said polymer material is one of
a thermoset material and a thermoplastic material.
19. The method of claim 17, further comprising after coupling the
molded polymer material to the conductive path, electrostatically
modifying the surface of the polymer material.
20. The method of claim 19, wherein the modifying comprises
painting.
21. The method of claim 20, wherein painting comprises primerless
painting adherence to the polymer.
22. The method of claim 17, wherein the polymer material is
combined with one to 10 percent expanded graphite.
23. The method of claim 17, wherein the polymer material is
combined with six to 10 percent expanded graphite.
24. A method comprising: pre-compressing expanded graphite; milling
the pre-compressed expanded graphite; combining the milled expanded
graphite in an amount of one to 20 percent with a polymer; and
pelletizing the combination.
25. The method of claim 24, further comprising; forming an object
of the combined graphite and polymer.
26. The method of claim 24, further comprising; coupling the object
to a conductive path as part of an electrostatic operation.
27. The method of claim 24, wherein said polymer material is one of
a thermoset material and a thermoplastic material.
28. The method of claim 24, further comprising after coupling the
molded polymer material to the conductive path, electrostatically
modifying the surface of the polymer material.
29. The method of claim 28, wherein the modifying comprises
painting.
30. The method of claim 28, wherein painting comprises primerless
painting adherence to the polymer.
31. The method of claim 24, wherein the polymer material is
combined with one to 10 percent expanded graphite.
32. The method of claim 24, wherein the polymer material is
combined with six to 10 percent expanded graphite.
33. The method of claim 24, further comprising; prior to combining
the expanded graphite and the polymer, the expanded graphite is
combined with a filler of at least one of carbon black, carbon
fibers, mineral filler, glass, re-expanded graphite and recycled
expanded graphite.
34. The method of claim 24, wherein; the carbon fibers are at least
one of polyacrylnitrile fibers, pitch carbon fibers and rayon-based
carbon fibers.
35. An apparatus comprising: an injection molded polymer material
comprising one to 20 percent expanded graphite that is connectable
to a conductive path.
36. The apparatus of claim 35, wherein said polymer material is one
of moldable thermoset material and moldable thermoplastic
material.
37. The apparatus of claim 35, wherein the polymer material
comprises five to 10 percent expanded graphite.
38. The apparatus of claim 35, wherein the polymer material
comprises seven to 10 percent expanded graphite.
Description
BACKGROUND
[0001] 1. Field of the Invention
[0002] Graphite containing polymer material.
[0003] 2. Related Art
[0004] In the prior art various forms of graphite material have
been used to enable polymer material to conduct or dissipate
electrostatic charge. One of the first such graphite containing
materials added to polymers was carbon black which has an
appropriate amount of electrostatic dissipative capacity, but is
difficult to handle, relatively light and extremely time consuming
to put in place.
[0005] 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 material takes
on electrons and becomes negatively charged. ESD may be
characterized as the sudden discharge of electrostatic potential
from one body to another. A good example may be the shock one may
receive when touching a metal door after walking across a carpeted
floor.
[0006] 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.
[0007] 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 before they can build up to a level that is
harmful to sensitive equipment. 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,
dissipate charges before they can accumulate at dangerous levels,
or that provide electrostatic shielding to prevent charges from
reaching the sensitive device.
[0008] Floors of clean rooms that need to have low electrostatic
discharge potential for, as an example, manufacturing semiconductor
devices, need to be conductive and lightweight. These floors
require lightweight floor panels, because they tend to be suspended
on vibration dampening mechanisms. A lightweight, conductive
polymer that dissipates electrostatic charges before they build up
to dangerous levels would be useful.
[0009] Other applications for ESD polymer materials are as computer
covers and chip trays. Computer covers that offer ESD protection
will protect delicate computer components on the inside from
harmful electrostatic discharges. Chip trays are used to move and
store semiconductor circuits during dicing, testing and packaging
operations. These operations are generally when sensitive
integrated circuits are most vulnerable to ESD. An electrostatic
dissipative chip tray allows electrostatic charges to bleed off
before they build up to dangerous levels that could harm an
isolated integrated circuit chip.
[0010] U.S. Pat. No. 5,582,781 discloses, inter alia, a method of
making graphite foam material. Expanded graphite is made from
flexible graphite foil. The expanded graphite is then compounded
into sheets to make insulation material.
[0011] U.S. Pat. No. 5,882,570 discloses, inter alia, a method of
injection molding graphite and a thermoplastic material. This
method also uses 45 to 60 percent by weight expanded graphite. The
compound of thermoplastic material and re-expanded graphite is fed
into a molding system (e.g. injection molding system) at relatively
high temperature and injected into a mold where a plastic material
is formed. The material is valuable for its heat conducting
capacity for use in for example, thermal management.
[0012] Many parts of automobiles are painted using an electrostatic
painting scheme. Electrostatic painting increases the uniformity
with which the applied paint covers the part that is painted
compared with plain spray painting. Paint in the form of small
droplets or a fine powder is given an electrical charge, while the
part to be painted is given the opposite charge. The charge
differential impels the paint toward the part to be painted. When
the paint touches the part the charge differential is neutralized
allowing the paint to adhere to the part.
[0013] For this electrostatic paint scheme to work the part to be
painted must be able to hold or dissipate a charge. When the part
is a non-conductive polymer, a conductive primer must be coated
over the part to enable the paint to uniformly cover the part. This
primer generally contains a Volatile Organic Compound (VOC).
[0014] Emissions of VOCs have been curtailed by local, state and
federal regulations. A limit on VOC emissions either eliminates the
option of electrostatic painting of polymer parts, or is a limiting
factor in the capacity of a painting operation that uses VOCs to
paint polymers. A method that reduces or eliminates VOCs from the
electrostatic paint scheme would increase the number of parts an
operation could paint in a given time.
[0015] It is desirable to provide, at relatively low cost,
compounds that may dissipate charges before they accumulate to
dangerous levels, or allow themselves to be electrostatically
modified.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The invention is illustrated by way of example, and not
limitation, in the figures of the accompany drawings, in which:
[0017] FIG. 1 is a flow diagram representing one method of forming
ground expanded graphite.
[0018] FIG. 2 is a flow diagram representing an optional method of
re-expanding ground graphite.
[0019] FIG. 3 is a flow diagram representing one method of
combining the expanded graphite with a polymer and pelletizing the
combination.
[0020] FIG. 4 is a flow diagram representing an alternate method of
combining the expanded graphite with a polymer.
[0021] FIG. 5 is a flow diagram representing one method of forming
polymer objects from graphite polymer pellets.
[0022] FIG. 6 is an illustration of one method of providing a floor
with an electrostatic dissipative ability.
[0023] FIG. 7 is a flow diagram of one method of forming and
electrostatically modifying a conductive polymer.
DETAILED DESCRIPTION
[0024] A method for combining expanded graphite and polymer
materials as polymer articles, and a method of making polymer
articles is disclosed. According to one embodiment, the expanded
graphite in the molded polymer material enables an electrostatic
change to be made to the surface of the polymer material. In
another embodiment, the expanded graphite combined with the polymer
material allows the polymer material to act as an electrostatic
discharge material.
[0025] Reference will now be made to drawings wherein like
structures will be provided with like reference designations. In
order to show the structures and techniques most clearly, the
drawings included herein are diagrammatic representations of the
indicated structures and techniques. Thus, the actual appearance of
the fabricated structures, for example in a photograph, may appear
different while still incorporating the essential structures and
techniques described herein. Moreover, the drawings show only the
structures and techniques necessary to understand what is claimed.
Additional structures known in the art have not been included to
maintain the clarity of the drawings.
[0026] Graphite containing polymers can be made from newly
manufactured natural or synthetic expanded graphite material,
flexible graphite material or, without major detriment, recycled
expanded or flexible graphite material as a starting material. FIG.
1 is a flow diagram representing one method of forming ground
expanded graphite. In this example, graphite at block 101 is mined
from the earth. The graphite can be 30 to 400 mesh, preferably 50
to 100 mesh, and more preferably 50 to 80 mesh.
[0027] Expanded graphite is generally produced by combining
graphite with an intercalation agent. The most common intercalation
agent is concentrated sulfuric acid often mixed with a strong
oxidizer like nitric acid or hydrogen peroxide. The quantity of
acid should be just enough to wet the graphite, but not enough to
make graphitic acid.
[0028] In addition to the acid treatment, expanded natural graphite
(also described as graphite vermiculite or graphite worms) is
generally obtained by the exposure of soaked graphite to heat of
more than 200.degree. C. as seen in block 103. Common graphite
expansion operations work at temperature levels of 800-1100.degree.
C. Graphite typically expands at these temperature levels 100-150
times from a bulk density on the order of 0.5 grams per cubic
centimeters (g/cc) to a bulk density on the order of 0.003-0.005
g/cc. Expanded graphite is a flaky, high crystalline form of
graphite.
[0029] Utilizing expanded graphite presents challenges in that, in
its expanded state, the extremely low bulk density makes the
material difficult to process into articles and difficult to
transport. Accordingly, the expanded graphite flakes are generally
compressed or compacted prior to use. The compacted expanded
graphite is generally referred to as "flexible" graphite as shown
in block 105A of FIG. 1. Alternately, the compacting operation may
be skipped and the process proceeds as described below with
grinding/milling.
[0030] Recycled flexible graphite can also be used alone or in
combination with newly processed or virgin graphite. Recycled
flexible graphite includes flexible graphite that had been produced
for some other purpose, or used in some other process, that at the
point of use as described herein may otherwise be considered waste.
It may exist in a flexible (e.g. compacted) form or as expanded
recycled graphite that may be compressed. Block 105B of FIG. 1
describes the inclusion of recycled graphite in the operation
described in FIG. 1.
[0031] As shown in FIG. 1, the virgin flexible graphite of block
105A or the recycled flexible graphite of block 105B is
ground/milled as shown in block 106. According to one embodiment,
following compacting, as shown in block 105A, the flexible graphite
is ground and/or milled to a fine powder having a particle size on
the order of about one to 1000 microns, and a tap density of
approximately 0.05 to 0.20 grams per cubic centimeters (g/cc) as
shown in block 106, preferably within the range of five to 500
micron with a tap density of 0.05 to 0.15 g/cc. Somewhat smaller or
larger particle size can be used as well. Where recycled flexible
graphite is used, the recycled graphite may be ground or milled to
a particle size on the order of about 200 to 700 microns, and a tap
density of approximately 0.1 to 0.3 g/cc. The virgin or recycled
flexible graphite can be ground in a cone mill grinder or hammer
mill grinder or other grinder known in the art. The following
paragraphs describe one suitable grinding and milling
operation.
[0032] If after grind/mill, the graphite is to be re-expanded, the
process proceeds at FIG. 2. It is possible however, to proceed
directly to pelletizing at FIG. 3.
[0033] Virgin or recycled flexible graphite in sheets of, for
example, approximately one foot (about 30 centimeters) on a side
are placed into a shredder. An example of a suitable shredder
includes a Jabed Tech. shredder. This shredder has a series of
gears and teeth that reduce the graphite sheets to a size of about
one inch (about 2.5 centimeters) square.
[0034] Once through the shredder, the graphite is put into a rotary
grinder. An example of a suitable rotary grinder is a 1831K
commercially available from Rapid Granulator of Rockford, Ill. This
rotary grinder has a cylinder lying on its side. Inside the
cylinder is a tri-vaned impeller or rotor. The rotor moves the
graphite pieces along the wall of the cylinder where they come in
contact with knives set in the sides of the cylinder. The
combination of the vanes and the knives cut the graphite into
pieces of about 1/4 to 1/8 inch (about 0.6 to 0.3 centimeters). A
screen at the bottom of the cylinder retains the graphite within
the cylinder while the pieces are greater than 1/4 inch in size.
Once the pieces are cut down to less than 1/4 inch, they pass
through the screen and out of the rotary grinder.
[0035] After the graphite pieces leave the rotary grinder, they are
sent to the pin mill. An example of a suitable pin mill is a KEK34
commercially available from Kemtech of Cheshire, Canada. This pin
mill is a drum containing a set of rotating pins arranged along the
circumference of a circle with a smaller diameter than that of the
drum. The position and size of the pins along with their rotation
speed break the graphite into particles in the size range of 300 to
1000 microns.
[0036] From the pin mill, the graphite particles enter an air mill.
An example of a suitable air mill is a MICROFET MT24 commercially
available from ALTET of Pennsylvania. This air mill is a vertical
chamber into which the graphite particles are placed. Jets
introduce air at about 120 pounds per square inch into the bottom
of the mill with velocities of approximately 500 cubic feet per
minute. These air jets keep the graphite particles suspended in the
chamber where collisions with other particles finally mill the
graphite down to a size of about 10 microns. A sifter wheel at the
top of the chamber, spinning at about 5000 revolutions per minute,
allows the approximately 10 micron graphite particles to exit the
mill.
[0037] FIG. 2 is a flow diagram representing an optional method of
re-expanding ground/milled graphite according to one embodiment.
The re-expansion can be effected by acid treatment or liquid soak.
An acid treatment decision made at block 201 will result in an acid
treatment at block 203A. The acid is an intercalation agent. The
most common intercalation agent is concentrated sulfuric acid often
mixed with an oxidizer like nitric acid or hydrogen peroxide.
[0038] After the acid treatment, expanded graphite is generally
obtained by the exposure of soaked graphite to heat of more than
200.degree. C. as seen in block 203B, typically temperature levels
of 800-1100.degree. C.
[0039] A liquid soak decision made at block 201 in FIG. 2 results
in the graphite soaking in a wetting agent in block 202. In one
embodiment the wetting agent can be a cryogenic liquid. One
commonly used cryogenic liquid is liquid nitrogen. In another
embodiment, the soaking agent can be water.
[0040] When water is used as the soaking agent, the powdered
graphite particles are metered through a feeder into a high speed
continuous blender. Simultaneously, water possibly containing at
least a surfactant is metered into the high speed continuous
blender allowing the graphite particles to absorb the moisture
needed for thermal expansion at block 202.
[0041] The liquid soak and acid treatment paths remerge at block
204, air expansion. Generally, the graphite is introduced to hot
air that causes expansion of the graphite. The air is generally
above 200.degree. C. One example is a 540,000 British Thermal Units
(BTU) gas fired tube furnace with an operating temperature above
500.degree. C., and preferably between 800.degree. C. and
1100.degree. C., as shown in block 204. Graphite typically expands
at these temperatures 100-150 times.
[0042] According to one embodiment, following air expansion, as
shown in block 204 of FIG. 2, the expanded graphite is ground or
milled to a fine powder having a particle size on the order of
about 1 to 1000 microns, and a tap density of approximately 0.05 to
0.20 g/cc. preferably within the range of 5 to 500 micron with a
tap density of 0.1 to 0.15 g/cc as shown in block 206. If desired,
the expanded graphite can be ground in a cone mill grinder or
hammer mill grinder or other grinder known in the art, as described
herein above.
[0043] Following grinding and/or milling, the expanded graphite
(including the optionally re-expanded graphite material) is
introduced to a moldable polymer and combined to make a moldable
polymer material, as referenced in block 301 of FIG. 3. Suitable
polymers include thermoplastic and thermoset polymers. In this
regard, the polymer material comprises expanded graphite and
polymer as a polymerized product, a combination or a mixture. The
introduction takes place for example, in a heated mixing chamber
that has a screw impeller to force the two materials into contact
with each other while heating them to allow mixing of the expanded
graphite and the moldable polymer into a moldable polymer material.
In this example, the moldable polymer material is then pushed
through an extruder, that pelletizes the material, as shown in
block 302, by the screw impeller. The expanded graphite and the
polymer can be combined by mixing together in a tubular mixer and
heating the mixer while a large screw impeller, such as a KMD 90-26
extruder commercially available from Mannesmann-Demag-Krauss-Maffei
of Munich, Germany, mixes the combination and extrudes the combined
material through a pelletizer.
[0044] Suitable polymers for the operation described with reference
to FIG. 3 include, but are not limited to, thermoplastic resins.
The thermoplastics include but are not limited to polyphenylene
sulfide (PPS), nylon (e.g. nylon66), polycarbonate (PC),
polyphenylene oxide (PPO), acrylonitrile butadiene styrene (ABS),
polypropylene (PP), high density polyethylene (HDPE) and
thermoplastic olefin (TPO). Suitable polymers also include the
thermoset type, such as phenolic resin (e.g. resol-type or
Novolac-type resin).
[0045] Graphite combines well with polymer materials. Combinations
of graphite and polymer can run the full spectrum of weight ratios
from one percent graphite to 99 percent graphite. Of particular
interest are those graphite polymer weight ratios yielding one to
20 percent graphite.
[0046] Prior to pelletizing to combine expanded graphite with
polymer in FIG. 3, expanded graphite, or a mixture of expanded
graphite and polymer, can be combined with a filler. Suitable
fillers include, but are not limited to at least one of the
following: carbon black, carbon fibers, mineral fillers including,
but not limited to talc, re-expanded graphite, recycled expanded
graphite, glass, carbon nanotubes, clay, synthetic graphite,
stainless steel fibers and aluminum or copper flake. The carbon
fibers used as a filler with expanded graphite include but are not
limited to polyacrylnitrile (PAN) fibers, pitch carbon fibers and
rayon-based carbon fibers.
[0047] FIG. 4 illustrates an alternative pelletizing embodiment.
Expanded graphite at block 401A is combined with a polymer and/or
filler, as mentioned above, from block 401B. The pellets (premix)
produced at block 402, in one embodiment, can be 30 percent
expanded graphite and 70 percent polymer. Premixing the expanded
graphite in a polymer, filler mix reduces the dust generated by
handling expanded graphite. For example, a manufacturer of polymer
pellets (e.g. a compactor) or a manufacturer of polymer components
may desire to receive expanded graphite from a graphite supplier in
a form that is generally free of graphite dust, such as a premix of
polymer and expanded graphite. Additional polymer or filler at
block 403 can be combined with the pelletized expanded graphite
polymer/filler mix from block 402. The pellets derived from block
404, in one embodiment can be approximately one to 20 percent (e.g.
10 percent) expanded graphite, and ready for molding.
[0048] FIG. 5 is a flow diagram representing one method of forming
polymer material articles or objects from polymer material pellets
formed according to the techniques described above. The basic
methods of molding a polymer into an article or object are
injection molding, blow molding and compression molding. Injection
molding is typically used for forming thermoplastic polymers into
solid objects. Blow molding is typically used to form hollow
objects out of thermoplastic materials. Compression molding is
typically used to form solid objects out of thermoset polymers.
Other suitable molding techniques include, but are not limited to,
injection compression molding, roto-molding and sheet molding.
[0049] Injection molding begins by placing a polymer (e.g., a
thermoplastic polymer material including expanded graphite) in a
chamber that can be heated and compressed, as shown in block 502.
As the polymer material is heated until it softens and turns
liquid, the chamber is compressed so the polymer material is forced
to enter a mold held adjacent to the chamber. Compression is
applied to the heated chamber until the liquid polymer material
fills the mold, as shown in block 503. When the polymer material
cools, the mold is opened and the solid polymer material object is
removed from the mold.
[0050] Blow molding begins with a molten tube of polymer material,
derived for example from the polymer material pellets described
above, that is placed in a mold, as shown in block 502. Compressed
air is introduced into the tube of polymer material, causing the
tube to expand until it fills the confines of a blow mold, as shown
in block 503. When the polymer cools, the blow mold is opened and
the hollow polymer material object is removed.
[0051] Compression molding begins with an open mold and an amount
of polymer material, derived for example from the polymer material
pellets described above, placed in the mold. The mold is closed
confining the polymer material within the mold, as shown in block
502. The mold compresses the polymer material forcing it to fill
the contours of the mold. While the mold is closed, it is heated
causing the polymer material to undergo a chemical change that
permanently hardens the polymer material into the shape of the
mold, as shown in block 503. When the polymer material cools, the
mold is opened and the polymer material object is removed.
[0052] Alternative molding techniques include extruding the polymer
material into the desired object. Examples of this technique
include, but are not limited to, pipes and plates.
[0053] Following molding, a conductive polymer material object can
have its surface electrostatically modified, because it can carry
current away or hold a charge, as shown in block 504a of FIG. 5. In
one example, a conductive polymer material object can have its
surface painted electrostatically. A voltage element can give a
conductive polymer object a charge. A painting element can give
paint an opposite charge. The differences in charge will impel the
paint to come in contact with the object, where the paint adheres
to the object surface, coating the object in paint.
[0054] FIG. 6 illustrates an electrostatic painting operation to
alter the surface of a polymer material. The surface altering
operation, taking place on the surface of the polymer material, is
that of painting. Molded polymer material object 20 that is mixed
with expanded graphite in the illustrated example is a mirror
shroud for an automobile. Molded polymer material object 20 is
attached to conductive path 10. Conductive path 10 is coupled to
voltage source 40 which allows a charge to build up on the surface
of molded polymer material object 20. Molded polymer material
object 20 made of a conductive polymer allows the object to conduct
electricity.
[0055] In an electrostatic painting environment such as shown in
FIG. 6, electrostatic paint sprayer 30 impels small droplets of
paint, or small amounts of electrostatically charged powdered
paint, toward oppositely charged molded polymer material object 20.
In this electrostatic environment the paint strikes the surface of
the polymer object and adheres thereto.
[0056] The attraction of the paint particles in the electrostatic
painting operation in FIG. 6 to the surface of molded polymer
material object 20, allows a uniform distribution of paint on the
surface of molded polymer material object 20. Molded polymer
material comprising at least five percent expanded graphite is
sufficiently conductive to accomplish an electrostatic painting
process according to current technologies. Acceptable results were
achieved with polymer material objects comprising at least five
percent expanded graphite. Additionally, the electrostatic painting
operation allows a reduction of the quantity of paint used to
achieve a given thickness of paint uniformly distributed on molded
polymer material object 20.
[0057] For example in FIG. 6, a typical electrostatic painting
operation for a nonconductive polymer object employs a conductive
primer over the molded polymer object. This operation typically
requires one primer coat, two base coats and two clear coats to
cover a nonconductive polymer object. Experimental studies indicate
that the primer coat, to electrostatically paint an object of a
conductive polymer material as described herein, can be reduced by
20 to 25 percent in most instances, and in some cases the primer
can be eliminated altogether. Additionally these studies show,
consumption of paint in the base and clear coats is reduced by 20
to 25 percent with such conductive polymer objects as well.
[0058] A third benefit of the conductive polymer material object
described in FIG. 6 is the electrostatic lines of force developed
within the electrostatic painting operation between the paint gun
and the conductive polymer material object to be painted, permit
elements of paint to avoid striking the forward surface of molded
polymer material object and wrap around a far edge to strike a
non-obvious, and even shadowed, area of the surface enabling a more
uniform coverage of paint on the conductive polymer material object
then can be achieved with a non-conducting surface. In the example
of the mirror shroud shown in FIG. 6, a portion of the paint
directed by the paint gun at the exterior of the shroud will wrap
around the exterior and adhere to the inner walls. For mirror
shrouds housing a recessed mirror, where a conductive polymer
material object is painted the ability to pain the inner walls
offers an attractive benefit.
[0059] FIG. 7 illustrates another embodiment of the described
conductive polymer material. This embodiment is an electrostatic
dissipative clean room floor. For example, multiple integrated
circuit chips can be contained in chip tray 50. Chip tray 50 rests
on an example of a typical clean room bench 55. Typical clean room
bench 55 is constructed of conductive elements, so it can bleed off
electrostatic charge. A conductive path is made between chip tray
50 and typical clean room bench 55, merely by placing chip tray 50
on clean room bench 55. Typical clean room bench 55 is placed on
clean room floor 60 extending the conductive path from chip tray 50
to clean room floor 60.
[0060] In FIG. 7 clean room floor 60, in this example, comprises
conductive polymer material floor panels 65, and conductive frame
70. Conductive polymer material floor panels 65 fit into conductive
frame 70, and conductive frame 70 supports conductive polymer
material floor panels 65. In this example, electrostatic energy
travels from one conductive floor panel to another through the
conductive frame. Clean room floor 60 is coupled to ground 75, thus
allowing the electrostatic charge to travel from chip tray 50 to
ground 75 through a path made of typical clean room bench 55 to
clean room floor 60 through successive conductive floor panels
70.
[0061] In FIG. 7 human 80 is provided to show scale. Human 80 is
connected to the ground path by way of conductive booties 85.
Suitable conductive polymer material floor panels include at least
five percent graphite material.
[0062] In the preceding detailed description, the invention is
described with reference to specific embodiments thereof. It will,
however, be evident that various modifications and changes may be
made thereto without departing from the broader spirit and scope of
the invention as set forth in the claims. The specification and
drawings are, accordingly, to be regarded in an illustrative rather
than a restrictive sense.
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