U.S. patent application number 11/609147 was filed with the patent office on 2008-06-12 for intrinsically conductive thermoplastic composition and compounding processing for making conductive fiber.
Invention is credited to Jayantha Amarasekera, Bo Liu, Lowrence D. Lucco.
Application Number | 20080139065 11/609147 |
Document ID | / |
Family ID | 39498635 |
Filed Date | 2008-06-12 |
United States Patent
Application |
20080139065 |
Kind Code |
A1 |
Amarasekera; Jayantha ; et
al. |
June 12, 2008 |
INTRINSICALLY CONDUCTIVE THERMOPLASTIC COMPOSITION AND COMPOUNDING
PROCESSING FOR MAKING CONDUCTIVE FIBER
Abstract
A conductive thermoplastic composition capable of forming
conductive fibers including monofilaments, methods of making these
compositions, and fibers including these compositions. The
conductive thermoplastic compositions may be formed using any
method capable of forming the compositions into fibers. The fibers
are substantially smooth and/or are capable of being woven into
fabrics or other articles to provide conductive properties to the
fabric or article. These fibers provide effective static charge
dissipation that may be imparted into applications such conveying
belts or protective clothing for clean room operation.
Inventors: |
Amarasekera; Jayantha;
(Exton, PA) ; Liu; Bo; (Cootesville, PA) ;
Lucco; Lowrence D.; (Parkesburg, PA) |
Correspondence
Address: |
SABIC - LNP-CE 08CE;SABIC Innovative Plastics - IP LEGAL
ONE PLASTICS AVENUE
PITTSFIELD
MA
01201-3697
US
|
Family ID: |
39498635 |
Appl. No.: |
11/609147 |
Filed: |
December 11, 2006 |
Current U.S.
Class: |
442/189 ;
252/500; 252/503; 252/601; 252/8.84; 264/172.11; 264/172.16;
428/367 |
Current CPC
Class: |
D01F 6/62 20130101; Y10T
428/2918 20150115; Y10T 428/298 20150115; D01F 6/92 20130101; Y10T
442/696 20150401; D01F 1/09 20130101; C08L 67/02 20130101; Y10T
442/3065 20150401; C08L 2666/20 20130101; C08L 77/00 20130101; C08L
67/02 20130101 |
Class at
Publication: |
442/189 ;
252/500; 252/503; 252/601; 252/8.84; 264/172.11; 264/172.16;
428/367 |
International
Class: |
D03D 15/00 20060101
D03D015/00 |
Claims
1. A thermoplastic composition, comprising: from 60 to 99% by
weight of an organic polymer; and from 0.5 to 40% by weight of a
conductive filler; wherein the thermoplastic composition is capable
of forming a fiber having an average diameter with a standard
deviation of 0.02 mm or less along a length of the fiber.
2. The thermoplastic composition of claim 1, wherein the organic
polymer is an amorphous polymer selected from polycarbonates,
polyethersulfones, polysulfonates, polyetherimides,
poly(p-phenylene oxide); polyamideimides, atactic polystyrene,
polyarylsulfones, polyvinyl chlorides, or a combination comprising
at least one of the foregoing amorphous polymers.
3. The thermoplastic composition of claim 1, wherein the organic
polymer is a semi-crystalline polymer selected from polyesters,
polyamides, polyphthalamide; polyphenylene sulfides; polyether
etherketones; polyetherketones; polyether ketone ketones, liquid
crystal polymers, polyimides, polyacetals, syndiotactic
polystyrene, polyacrylics, polyarylates, polytetrafluoroethylenes;
polysulfonates; polyvinyl alcohols, polysulfonamides,
polysilazanes, polyphosphazenes, polyureas, or a combination
comprising at least one of the foregoing semi-crystalline
polymers.
4. The thermoplastic composition of claim 1, wherein the organic
polymer is selected from polyetherimide, polybutylene
terephthalate, and an permanent anti-static agent, such as
polyamide/polyetheramide copolymer, or a combination comprising at
least one of the foregoing organic polymers.
5. The thermoplastic composition of claim 4, wherein the organic
polymer comprises a mixture of polybutylene terephthalate and a
permanent anti-static agent and wherein the permanent anti-static
agent is present in an amount from 1 to 40% by weight of the total
weight of the thermoplastic composition.
6. The thermoplastic composition of claim 5, wherein the permanent
anti-static agent comprises a polyamide/polyetheramide
copolymer.
7. The thermoplastic composition of claim 5, wherein the permanent
anti-static agent is present in an amount from 10 to 35% by weight
of the total weight of the thermoplastic composition.
8. The thermoplastic composition of claim 1, wherein the conductive
filler is selected from low-structure carbon black, single-wall
carbon nanotubes, multi-wall nanotubes, vapor-grown carbon fibers,
metal coated small carbon fibers, metal coated mineral particles
with an average particle size smaller than 2 microns or a
combination comprising at least one of the foregoing conductive
fillers.
9. The thermoplastic composition of claim 8, wherein the conductive
filler comprises low-structure carbon black having a surface area
less than 300 m.sup.2/g.
10. The thermoplastic composition of claim 1, wherein the
conductive filler is present in an amount of from 2 to 20% by
weight of the total weight of the thermoplastic composition.
11. The thermoplastic composition of claim 1, further comprising an
additive selected from a flame retardant agent, an antidrip agent,
a heat stabilizer, a light stabilizer, an antioxidant, a
plasticizer, an antistat agent, a mold release agent, a UV
absorber, a lubricant, a pigment, a dye, a colorant, or
combinations including one or more of the foregoing additives.
12-32. (canceled)
Description
FIELD OF THE INVENTION
[0001] The present invention relates to thermoplastic compositions,
and in particular to conductive thermoplastic compositions useful
for forming conductive fibers.
BACKGROUND OF THE INVENTION
[0002] Electrostatic charge is the result of a transfer of
electrons that occurs due to the sliding, rubbing, or separation of
material, which is a typical generator of electrostatic voltages.
Under the right conditions, this induced charge can build to 30,000
to 40,000 volts. When this happens to an insulating material, the
built-up charge tends to remain in the localized area of contact.
The electrostatic voltage then can discharge through an arc or
spark when the material comes in contact with a body of a
sufficiently different potential, such as a human being or an
electronic part. Those arcs or sparks can be very dangerous. For
example, there is a potential fire hazard related to static
sparking for an industrial conveying belts used in paper making
industries. There is also a potential hazard of damaging electronic
parts during handling due to electrostatic discharge (ESD). If
electrostatic discharge occurs to a person, the results can range
anywhere from a mild to a painful shock. In extreme cases, ESD
could even result in loss of life. Therefore, it is important to
effectively manage ESD. For example, at an operation where electric
shock is subject to happen due to static electricity, protective
clothing is necessary for operator's safety.
[0003] The surface resistivity spectrum is divided into four
different classifications of material conductivity: anti-static
materials with a surface resistivity in the range of 10 9 to 10 12
ohm/sq.; statically dissipative materials with a surface
resistivity in the range of 10 6 to 10 9 ohm/sq.; conductive
materials with a surface resistivity in the range of 10 2 to 10 5
ohm/sq.; and electrostatic shielding materials with a surface
resistivity in the range of 10 0 to 10 2 ohm/sq. Anti-static
materials can suppress initial charges and minimize the occurrence
of tribocharging. They provide insulation against moderate to high
leakage currents. Dissipative materials can prevent electrostatic
discharge to/from human contact and provide insulation against high
leakage currents. Conductive materials can dissipate tribocharging
from high-speed motion and provide a grounding path for charge
bleed-off. Electrostatic shielding materials can shield
electromagnetic interference/radio frequency interference and block
high electrostatic discharge voltages.
[0004] Polymers are typically electrically insulating materials
with high surface resistivities in the range of 10 14 to 10 16
ohms/sq. It is known that polymers may be made conductive using
electrically conductive fillers/additives such as carbon black,
carbon fibers and metal powder. In one embodiment, metal powder has
been used. Unfortunately, when using metal powder, a large quantity
of the powder is necessary, which may adversely affect the
properties of the composition since less polymer material is
utilized. In addition, since metal powders are expensive, the costs
associated with using metal powders make this solution less
economically feasible.
[0005] In another proposed prior art solution, carbon fibers have
been added to make the resulting compositions conductive. The
addition of carbon fibers, however, leads to stiffening and to a
reduction of impact strength and elongation at break, which is
particularly disadvantageous if tubes or fibers are to be made from
the conductive composition.
[0006] In addition, other prior art methods have involved the use
of conductive coatings. However, these methods of treating plastics
filaments or fibers with conductive coatings have many drawbacks
including the decrease or even loss of electrical static
dissipation properties due to wear-off of the coatings, as well as
limited heat and hydrolytic stability of the coatings.
[0007] Accordingly, it would be beneficial to provide a
thermoplastic composition capable of forming conductive fiber. It
would also be beneficial to provide a method of making conductive
materials capable of forming fibers including monofilaments. It
would also be beneficial to provide conductive fibers and/or
monofilaments capable of being woven to form fabrics and/or other
articles having conductive properties.
BRIEF SUMMARY OF THE INVENTION
[0008] The present invention provides a thermoplastic composition
capable of forming conductive fiber, methods of making these
compositions, and fibers including these compositions. The
conductive thermoplastic resin of the present invention may be
formed using a method, such as through melt spinning, into fibers
that may then be woven into fabrics. The fibers formed using the
compositions are substantially smooth and are capable of being
woven into fabrics and/or other articles. These fibers provide
effective static charge dissipation that may be imparted into
applications such conveying belts or protective clothing for clean
room operation. Those fibers including monofilaments or
multifilament, as well as fabrics including the filaments or
fibers, are conductive and may be used in any material handling
process wherein safe dissipation of charge into the atmosphere is
beneficial.
[0009] Accordingly, in one aspect, the present invention provides a
thermoplastic composition that includes from 60 to 99% by weight of
an organic polymer and from 0.5 to 40% by weight of a conductive
filler; wherein the thermoplastic composition is capable of forming
fibers.
[0010] In another aspect, the present invention provides fibers
that include a thermoplastic composition that includes from 60 to
99% by weight of an organic polymer and from 0.5 to 40% by weight
of a conductive filler and a conductive article that includes one
or more of these fibers.
[0011] In still another aspect, the present invention provides
method of forming a thermoplastic composition including the steps
of dispersing 0.5 to 40% by weight of a conductive filler into 60
to 99% by weight of an organic polymer; wherein the thermoplastic
composition is capable of forming fibers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a representative appearance of monofilaments made
using compositions of the present invention compared to prior art
compositions observed using optical microscopy.
DETAILED DESCRIPTION OF THE INVENTION
[0013] The present invention is more particularly described in the
following description and examples that are intended to be
illustrative only since numerous modifications and variations
therein will be apparent to those skilled in the art. As used in
the specification and in the claims, the term "comprising" may
include the embodiments "consisting of" and "consisting essentially
of." All ranges disclosed herein are inclusive of the endpoints and
are independently combinable. The endpoints of the ranges and any
values disclosed herein are not limited to the precise range or
value; they are sufficiently imprecise to include values
approximating these ranges and/or values.
[0014] As used herein, approximating language may be applied to
modify any quantitative representation that may vary without
resulting in a change in the basic function to which it is related.
Accordingly, a value modified by a term or terms, such as "about"
and "substantially," may not be limited to the precise value
specified, in some cases. In at least some instances, the
approximating language may correspond to the precision of an
instrument for measuring the value.
[0015] The present invention provides a conductive thermoplastic
composition capable of forming conductive fiber, methods of making
these compositions, and fibers made from these compositions. The
plastic fibers or filaments are substantially smooth and capable of
being woven into fabrics or other articles. The fibers provide
effective electrical static dissipation to articles containing
fibers or filaments. The intrinsically conductive thermoplastic
fibers or filaments have long-lasting electrical static dissipation
effects and/or excellent environmental stability while also
providing excellent physical properties as compared to prior art
materials.
[0016] It is known that anti-static agent can be added to injection
moldable polymer compounds to impart anti-static performance in the
injection molded parts. Unfortunately, the same approach has not
been successfully used for fiber application because of extremely
high loading of anti-static agents that is often required. Since
those anti-static agents are typically of low molecular weight
small molecules or oligomer, fiber strength decreases quickly with
the addition of a large amount of anti-static agents, which makes
it not suitable for a fabric weaving process or other processes for
integrating fibers into an article. The present invention shows a
new approach of using a combination of permanent anti-static agent
with conductive filler can be useful for making thermoplastic
compositions that are capable of being formed into fibers including
monofilaments that can then be used in the formation of fabrics or
other articles having conductive properties.
[0017] The conductive thermoplastic compositions include an organic
polymer capable of being extruded and a conductive filler. The
conductive filler provides decreased resistances to the
thermoplastic composition such that fibers or filaments made from
the thermoplastic composition exhibit conductive properties. The
thermoplastic compositions achieve the reduced resistances through
the use of lesser amounts of conductive filler than prior art
materials that enables the thermoplastic composition to have
reduced resistances while also maintaining all or substantially all
of the physical properties of the organic polymer. Therefore,
unlike prior art conductive materials, the thermoplastic
compositions of the present invention are capable of being formed
into fibers including monofilaments that can then be used in the
formation of fabrics or other articles having conductive
properties.
[0018] As used herein, the term "capable of being formed into
fibers" refers to a composition that forms a substantially smooth
fiber as compared to compositions that form uneven fibers. Uneven
fibers have thinner areas that are more susceptible to breakage
when attempting to use these fibers to form articles. The "fibers"
formed using the compositions of the present invention have a
thickness that enables them to be capable of being woven or
otherwise formed into an article, while not being too thin such
that break easily during formation of the articles having
conductive properties. In addition, these fibers have an average
diameter that varies little along the length of the fiber.
Accordingly, in one embodiment, the fibers of the present invention
include single filaments that individually have a diameter between
0.05 mm and 0.8 mm. In an alternative embodiment, the fibers
include single fibers or filaments that individually have a
diameter between 0.08 mm and 0.5 mm. In yet another alternative
embodiment, the fibers include single filaments that individually
have a diameter between 0.1 mm and 0.3 mm. Additionally, in one
embodiment, the fibers have an average diameter with a standard
deviation of less than about 0.02 mm along the length of the fiber.
In an alternative embodiment, the fibers have an average diameter
with a standard deviation of less than about 0.015 mm along the
length of the fiber. In still another embodiment, the fibers have
an average diameter with a standard deviation of less than about
0.01 mm along the length of the fiber.
[0019] Compositions that are capable of being formed into fibers
also refers to compositions that form fibers with sufficient
flexibility to be woven or otherwise formed into an article without
substantial breakage of the fibers during formation of the article,
as well as having sufficient flexibility such that the fibers do
not suffer substantial breakage when the article is used in normal
operation. While it may be possible to form a fiber with some prior
art compositions, these compositions form fibers that are uneven
and/or that break during formation of conductive articles and/or
use of the conductive articles. The compositions of the present
invention, since they are capable of being formed into fibers, do
not suffer the same drawbacks. As such, the fibers of the present
invention are less brittle, have greater impact strength and/or
better elongation at break properties as compared to fibers made
from prior art materials.
[0020] In addition to being capable of being formed into fibers,
the thermoplastic compositions also provide conductive properties
to fibers formed from the compositions and articles that include
these fibers. In order to provide conductive properties to the
fiber, the compositions are sufficiently conductive such that the
resulting fibers have, in one embodiment, a resistance equal to or
less than 10.sup.10 ohms. In an alternative embodiment, the fibers
have a resistance equal to or less than 10.sup.8 ohms. In still
another embodiment, the fibers have a resistance equal to or less
than 10.sup.6 ohms. In another aspect, the fibers have a specific
resistance, in one embodiment, equal to or less than 10.sup.6
ohms-cm. In an alternative embodiment, the fibers have a specific
resistance equal to or less than 10.sup.4 ohms-cm. In still another
embodiment, the fibers have a specific resistance equal to or less
than 10.sup.3 ohms-cm. As used herein, "specific resistance" refers
to the electrical resistance offered by a material to the flow of
current, times the cross-sectional area of current flow and per
unit length of current path, whereas the "resistance" refers to the
composition's opposition to the flow of electric current.
[0021] Accordingly, in one aspect, the present invention includes a
thermoplastic composition having an organic polymer. The organic
polymer serves as the base material for the thermoplastic
composition. The organic polymer may be a crystalline polymer or an
amorphous polymer. The organic polymer used in the conductive
compositions may be selected from a wide variety of thermoplastic
resins or blends of thermoplastic resins. The organic polymer may
also be a blend of polymers, copolymers, terpolymers, or
combinations including at least one of the foregoing organic
polymers. Examples of the organic polymer include, but are not
limited to, polyacetals, polyacrylics, polycarbonates,
polystyrenes, polyesters, polyamides, polyamideimides,
polyarylates, polyarylsulfones, polyethersulfones, polyphenylene
sulfides, polyvinyl chlorides, polysulfones, polyimides,
polyetherimides, polytetrafluoroethylenes, polyetherketones,
polyether etherketones, polyether ketone ketones, polybenzoxazoles,
polyoxadiazoles, polybenzothiazinophenothiazines,
polybenzothiazoles, polypyrazinoquinoxalines, polypyromellitimides,
polyquinoxalines, polybenzimidazoles, polyoxindoles,
polyoxoisoindolines, polydioxoisoindolines, polytriazines,
polypyridazines, polypiperazines, polypyridines, polypiperidines,
polytriazoles, polypyrazoles, polypyrrolidines, polycarboranes,
polyoxabicyclononanes, polydibenzofurans, polyphthalides,
polyacetals, polyanhydrides, polyvinyl ethers, polyvinyl
thioethers, polyvinyl alcohols, polyvinyl ketones, polyvinyl
halides, polyvinyl nitriles, polyvinyl esters, polysulfonates,
polysulfides, polythioesters, polysulfones, polysulfonamides,
polyureas, polyphosphazenes, polysilazanes, or the like, or a
combination including at least one of the foregoing organic
polymers.
[0022] In one embodiment, polyimides may be used as the organic
polymers in the thermoplastic compositions. Useful thermoplastic
polyimides have the general formula (I)
##STR00001##
wherein a is, in one embodiment, greater than or equal to 10, and
in another embodiment greater than or equal to 1000; and wherein V
is a tetravalent linker without limitation, as long as the linker
does not impede synthesis or use of the polyimide. Suitable linkers
include (a) substituted or unsubstituted, saturated, unsaturated or
aromatic monocyclic and polycyclic groups having 5 to 50 carbon
atoms, (b) substituted or unsubstituted, linear or branched,
saturated or unsaturated alkyl groups having 1 to 30 carbon atoms;
or combinations thereof. Suitable substitutions and/or linkers
include, but are not limited to, ethers, epoxides, amides, esters,
and combinations thereof. Exemplary linkers include, but are not
limited to, tetravalent aromatic radicals of formula (II), such
as
##STR00002##
wherein W is a divalent moiety selected from --O--, --S--,
--C(O)--, --SO.sub.2--, --SO--, --C.sub.yH.sub.2y-- (y being an
integer from 1 to 5), and halogenated derivatives thereof,
including perfluoroalkylene groups, or a group of the formula
--O-Z-O-- wherein the divalent bonds of the --O-- or the --O-Z-O--
group are in the 3,3', 3,4', 4,3', or the 4,4' positions, and
wherein Z includes, but is not limited, to divalent radicals of
formula (III).
##STR00003##
R in formula (I) includes substituted or unsubstituted divalent
organic radicals such as (a) aromatic hydrocarbon radicals having 6
to 20 carbon atoms and halogenated derivatives thereof, (b)
straight or branched chain alkylene radicals having 2 to 20 carbon
atoms; (c) cycloalkylene radicals having 3 to 20 carbon atoms, or
(d) divalent radicals of the general formula (IV)
##STR00004##
wherein Q includes a divalent moiety selected from --O--, --S--,
--C(O)--, --SO.sub.2--, --SO--, --C.sub.yH.sub.2y-- (y being an
integer from 1 to 5), and halogenated derivatives thereof,
including perfluoroalkylene groups.
[0023] Exemplary classes of polyimides that may be used in the
thermoplastic compositions include polyamidimides and
polyetherimides, particularly those polyetherimides that are melt
processable.
[0024] Beneficial polyetherimide polymers include in one embodiment
more than 1, in another embodiment 10 to 1000 or more, and in still
another embodiment 10 to 500 structural units, of the formula
(V)
##STR00005##
wherein T is --O-- or a group of the formula --O-Z-O-- wherein the
divalent bonds of the --O-- or the --O-Z-O-- group are in the 3,3',
3,4', 4,3', or the 4,4' positions, and wherein Z includes, but is
not limited, to divalent radicals of formula (III) as defined
above.
[0025] In one embodiment, the polyetherimide may be a copolymer,
which, in addition to the etherimide units described above, further
contains polyimide structural units of the formula (VI)
##STR00006##
wherein R is as previously defined for formula (I) and M includes,
but is not limited to, radicals of formula (VII).
##STR00007##
[0026] The polyetherimide may be prepared by any of the methods
including the reaction of an aromatic bis(ether anhydride) of the
formula (VIII)
##STR00008##
with an organic diamine of the formula (IX)
H.sub.2N--R--NH.sub.2 (IX)
wherein T and R are defined as described above in formulas (I) and
(IV).
[0027] Illustrative examples of aromatic bis(ether anhydride)s of
formula (VIII) include
2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride;
4,4'-bis(3,4-dicarboxyphenoxy)diphenyl ether dianhydride;
4,4'-bis(3,4-dicarboxyphenoxy)diphenyl sulfide dianhydride;
4,4'-bis(3,4-dicarboxyphenoxy)benzophenone dianhydride;
4,4'-bis(3,4-dicarboxyphenoxy)diphenyl sulfone dianhydride;
2,2-bis[4-(2,3-dicarboxyphenoxy)phenyl]propane dianhydride;
4,4'-bis(2,3-dicarboxyphenoxy)diphenyl ether dianhydride;
4,4'-bis(2,3-dicarboxyphenoxy)diphenyl sulfide dianhydride;
4,4'-bis(2,3-dicarboxyphenoxy)benzophenone dianhydride;
4,4'-bis(2,3-dicarboxyphenoxy)diphenyl sulfone dianhydride;
4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)diphenyl-2,2-propane
dianhydride;
4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)diphenyl ether
dianhydride;
4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)diphenyl sulfide
dianhydride;
4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)benzophenone
dianhydride and
4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)diphenyl sulfone
dianhydride, as well as various mixtures thereof.
[0028] The bis(ether anhydride)s may be prepared by the hydrolysis,
followed by dehydration, of the reaction product of a nitro
substituted phenyl dinitrile with a metal salt of dihydric phenol
compound in the presence of a dipolar, aprotic solvent. A
beneficial class of aromatic bis(ether anhydride)s included by
formula (VIII) above includes, but is not limited to, compounds
wherein T is of the formula (X)
##STR00009##
and the ether linkages, for example, are beneficially in the 3,3',
3,4', 4,3', or 4,4' positions, and mixtures thereof, and where Q is
as defined above.
[0029] Any diamino compound may be employed in the preparation of
the polyimides and/or polyetherimides. Examples of suitable
compounds are ethylenediamine, propylenediamine,
trimethylenediamine, diethylenetriamine, triethylenetertramine,
hexamethylenediamine, heptamethylenediamine, octamethylenediamine,
nonamethylenediamine, decamethylenediamine, 1,12-dodecanediamine,
1,18-octadecanediamine, 3-methylheptamethylenediamine,
4,4-dimethylheptamethylenediamine, 4-methylnonamethylenediamine,
5-methylnonamethylenediamine, 2,5-dimethylhexamethylenediamine,
2,5-dimethylheptamethylenediamine, 2,2-dimethylpropylenediamine,
N-methyl-bis(3-aminopropyl)amine, 3-methoxyhexamethylenediamine,
1,2-bis(3-aminopropoxy)ethane, bis(3-aminopropyl)sulfide,
1,4-cyclohexanediamine, bis-(4-aminocyclohexyl)methane,
m-phenylenediamine, p-phenylenediamine, 2,4-diaminotoluene,
2,6-diaminotoluene, m-xylylenediamine, p-xylylenediamine,
2-methyl-4,6-diethyl-1,3-phenylene-diamine,
5-methyl-4,6-diethyl-1,3-phenylene-diamine, benzidine,
3,3'-dimethylbenzidine, 3,3'-dimethoxybenzidine,
1,5-diaminonaphthalene, bis(4-aminophenyl) methane,
bis(2-chloro-4-amino-3,5-diethylphenyl)methane,
bis(4-aminophenyl)propane, 2,4-bis(b-amino-t-butyl)toluene,
bis(p-b-amino-t-butylphenyl)ether,
bis(p-b-methyl-o-aminophenyl)benzene, bis(p-b-methyl-o-aminopentyl)
benzene, 1,3-diamino-4-isopropylbenzene, bis(4-aminophenyl)sulfide,
bis(4-aminophenyl)sulfone, bis(4-aminophenyl)ether and
1,3-bis(3-aminopropyl)tetramethyldisiloxane. Mixtures of these
compounds may also be present. In one embodiment, the diamino
compounds are aromatic diamines, especially m- and
p-phenylenediamine and mixtures thereof.
[0030] In an exemplary embodiment, the polyetherimide resin
includes structural units according to formula (V) wherein each R
is independently p-phenylene or m-phenylene or a mixture thereof
and T is a divalent radical of the formula (XI)
##STR00010##
[0031] Generally, useful polyetherimides have a melt index of 0.1
to 10 grams per minute (g/min), as measured by Amerimay Society for
Testing Materials (ASTM) D1238 at 295.degree. C., using a 6.6
kilogram (kg) weight. In one embodiment, the polyetherimide resin
has a weight average molecular weight (Mw) of 10,000 to 150,000
grams per mole (g/mole), as measured by gel permeation
chromatography, using a polystyrene standard. Such polyetherimide
polymers typically have an intrinsic viscosity greater than 0.2
deciliters per gram (dl/g), beneficially 0.35 to 0.7 dl/g measured
in m-cresol at 25.degree. C.
[0032] In another embodiment, the organic polymers include
polyesters. The high molecular weight polyesters used in the
practice of the present invention are polymeric glycol esters of
terephthalic acid and isophthalic acid. They are widely available
commercially. Otherwise they can be readily prepared by known
techniques, such as by the alcoholysis of esters of terephthalic
and/or isophthalic acid with a glycol and subsequent
polymerization, by heating glycols with free acids or with halide
derivatives thereof, and similar processes.
[0033] Although the glycol portion of the polyester can contain
from 2 to 10 atoms in one embodiment, the glycol portion, in
another embodiments, can contain from 2 to 4 carbon atoms in the
form of linear methylene chains.
[0034] Exemplary polyesters will be of the family including high
molecular weight polymeric glycol terephthalates or isophthalates
having repeating units of the general formula (XII)
##STR00011##
wherein n is a whole number of from 2 to 4, and mixtures of such
esters, including copolyesters of terephthalic and isophthalic
acids of up to 30 mole percent isophthalic units.
[0035] Especially beneficial polyesters are poly(ethylene
terephthalate) and poly(1,4-butylene terephthalate). Special
mention is made of the latter because it crystallizes at such a
good rate without the need for nucleating agents or long cycles, as
is sometimes necessary with poly(ethylene terephthalate).
[0036] Illustratively, high molecular weight polyesters, such as
poly(1,4-butylene terephthalate), will have an intrinsic viscosity
of at least about 0.7 deciliters/gram and, in alternative
embodiments, at least 0.8 deciliters/gram as measured in a 60:40
phenol tetrachloroethane mixture at 30.degree. C. At intrinsic
viscosities of at least about 1.0 deciliters/gram, there is further
enhancement of toughness of the present compositions.
[0037] As will be understood by those skilled in the art, the
poly(1,4-butylene terephthalate) block can be straight chain or
branched, e.g., by use of a branching component which contains at
least 3 ester-forming groups. This can be a polyol, e.g.,
pentaerythritol, trimethylolpropane, and the like, or a polybasic
acid compound, e.g., trimethyl trimesitate, and the like.
[0038] In addition to the organic polymer, the thermoplastic
compositions of the present invention include at least one
conductive filler. The conductive filler is chosen such that the
resulting thermoplastic composition is capable of being formed into
fibers. As such, not all conductive fillers can be used in the
present invention, only those that permit the resulting
thermoplastic composition to be capable of being formed into
fibers. In one embodiment, the conductive filler is a low-structure
carbon black. A "low-structure carbon black is one that has a lower
surface area. In one embodiment, the low-structure carbon black has
a surface area less than 300 m.sup.2/g. In another embodiment, the
low-structure carbon black has a surface area less than 200
m.sup.2/g. In still another embodiment, the low-structure carbon
black has a surface area less than 150 m.sup.2/g.
[0039] In an alternative embodiment, either alone or in conjunction
with a low-structure carbon black, the conductive filler may
include carbon nanotubes. In one embodiment, the carbon nanotubes
are single-wall nanotubes while in an alternative embodiment; the
carbon nanotubes are multi-wall nanotubes. Other conductive fillers
that may be used in the present invention include, but are not
limited to, metal coated mineral particles, small metal particles,
vapor grown carbon tubes, and/or any other conductive filler that
permits the resulting thermoplastic composition to be capable of
being formed into fibers.
[0040] The amount of filler used in the thermoplastic composition
is dependent on one more factors including, but not limited to, the
organic polymer used, the type of conductive filler used, the
presence of additional polymers, the size of the fibers to be
formed, the application in which the fibers will be used, and/or
the presence of any other additives or fillers. In one embodiment,
the amount of conductive filler added is from 0.5 to 40% by weight
of the thermoplastic composition. In another embodiment, the amount
of conductive filler added is from 1 to 35% by weight of the
thermoplastic composition. In still another embodiment, the amount
of conductive filler added is from 2 to 30% by weight of the
thermoplastic composition.
[0041] In alternative embodiments of the present invention, other
polymers can be included depending on the selected properties of
the thermoplastic compositions and/or the fibers made from the
thermoplastic composition. In one embodiment, the thermoplastic
compositions include a polyamide/polyetheramide copolymer as part
of the thermoplastic composition. In one embodiment, the
polyamide/polyetheramide copolymer is included in an amount from 1
to 40% by weight of the total weight of the thermoplastic
composition. In another embodiment, the polyamide/polyetheramide
copolymer is included in an amount from 10 to 35% by weight of the
total weight of the thermoplastic composition. In still another
embodiment, the polyamide/polyetheramide copolymer is included in
an amount from 15 to 35% by weight of the total weight of the
thermoplastic composition.
[0042] The thermoplastic compositions of the present invention may
be formed using any known method of dispersing a conductive filler
in an organic polymer. In one embodiment, the organic polymer has a
sufficient molecular weight to enable the filler to be dispersed in
the organic polymer using an extrusion process. When an extrusion
process is used, it has been discovered that higher process speeds
provide generally better dispersion of the conductive filler in the
organic polymer. In one embodiment, the extruder has a screw speed
operating at 250 RPM or above. In another embodiment, the extruder
has a screw speed operating at 300 RPM or above. In still another
embodiment, the extruder has a screw speed operating at 375 RPM or
above. The method of determining the method of dispersing the
filler and/or the operating parameters of the method may be based
upon one or more factors including, but not limited to, the type
and/or amount of conductive filler, the type and/or amount of the
organic polymer, the selected resistivity of the fibers, the
presence of other additives, the screw deign (for extruders),
and/or the application in which the fibers will be used.
[0043] The fibers may be formed using any known method capable of
forming a fiber using a thermoplastic composition. Examples
include, but are not limited to, wet spinning, dry spinning, melt
spinning, gel spinning, or a combination including one or more of
the foregoing methods. The method used may be based on one or more
factors including, but not limited to, the type of organic polymer
used, the type of conductive polymer use, and/or the thickness of
the fibers to be formed.
[0044] The compositions of the present invention may include one or
more additional additives provided the resulting thermoplastic
compositions are still capable of forming fibers. Examples of
additional additives include, but are not limited to,
flame-retardant agents, antidrip agents, heat stabilizers, light
stabilizers, antioxidants, plasticizers, antistat agents, mold
release agents, UV absorbers, lubricants, pigments, dyes,
colorants, or combinations including one or more of the foregoing.
When used, these additives total from 0.1 to 10% by weight of the
total weight of the thermoplastic composition.
[0045] The present invention is further illustrated by the
following non-limiting examples.
EXAMPLES
[0046] A first set of experiments was performed to evaluate
multiple conductive thermoplastic compositions to determine whether
they provided adequate conductive characteristics and to determine
whether they were capable of being formed into fibers including
monofilaments that could then be used in one or more subsequent
applications.
[0047] For each of these samples, the conductive thermoplastic
compositions were formed using an extrusion process. A 25 mm 10
barrel Werner & Pfleiderer twin-screw extruder with a screw
designed for improving distributive dispersion was used to make the
samples. The zone temperatures were set in the range of 237 to
249.degree. C. for PBT based materials, while for PEI based
material, the zone temperatures were set at 369 to 372.degree.
C.
[0048] Pellets were dried using a MaGuire low pressure vacuum dryer
for 1 hour before injection molding into testing specimens using a
220-ton Cincinnati injection-molding machine. Melt temperatures
were 490.degree. F. and 700.degree. F. for PBT and PEI,
respectively. Mold temperatures were 200.degree. F. and 300.degree.
F. for PBT and PEI, respectively.
[0049] Molten strands were generated from a capillary rheometer
with a die of 1 mm in diameter. The barrel setting temperature
varied with the materials under evaluation. The molten strands then
went over a deflection wheel in the air before they were attached
to a torque winder for drawing down into fiber. Torque winder speed
was set at 99 ft/min.
[0050] Both surface resistivity and volume resistivity were
measured on molded 3''.times.5''.times.0.125'' plaques using Dr.
Thiedig MILLI-TO 2 resistance meter if the reading is below 10 7
and Hewlett Packard high resistance meter for any readings above 10
7 per ASTM standard D 4496 & D257. Resistance of the fiber
specimens were measured using PRS-801 Resistance Test System with
an applied voltage of 10V. The specific resistance of the fiber was
calculated as:
Specific Resistance=R*A/L [0051] R is resistance [0052] A is the
cross-section area of the filament [0053] L is the length of the
filament measured The materials used in the experiments were as
follows: [0054] PBT: VALOX.TM. 315: IV is 1.2 dg/l and acid number
is 33 to 43 meq/kg. Mw=110000 [0055] PEI: ULTEM.TM. 1010: Tg=217 C,
Melt Flow Rate=17.8 g/10 min at 337 C and 6.6 kgf [0056]
Low-structure conductive carbon black-1 (LCB-1): Erachem Ensaco
250, surface area 65 m.sup.2/g, sulphur content: <0.05% [0057]
Low-structure conductive carbon black-2 (LCB-2): Cabot Vulcan XC72:
surface area 254 m.sup.2/g, sulphur content: 0.6% [0058]
High-structure conductive carbon black-1(HCB-1): Akzo Ketjen
EC-300J, surface area 795 m.sup.2/g [0059] High-structure
conductive carbon black-2(HCB-2): Akzo Ketjen EC-600JD, surface
area 1250-1353 m.sup.2/g [0060] Chopped carbon fiber: Toho F202, 7
micron in diameter, 1/8'' in length [0061] Multi-wall carbon nano
tube masterbatch: Hyperion MB5015-00, 15% in PBT [0062] PA/PEA
copolymer: Polyamide/polyether amide copolymer, Ciba IRGASTAT.TM. P
20
[0063] Both semi-crystalline thermoplastic polymer such
polybutylene terephthalate ("PBT") and amorphorous thermoplastic
polymer such as polyetherimide ("PEI") were evaluated in this
invention.
[0064] The fiber properties of PBT with various conductive fillers
are shown in Table 1. Formulation 1 is polybutylene terephthalate
("PBT") with low-structure carbon black LCB-1. Formulations 2 and 3
are PBT with two high-structure carbon blacks. High Structure HCB-2
has higher surface area than High Structure HCB-1. As shown,
although both low-structure and high structure carbon blacks result
in fiber resistance in a range of 10 5 ohm to 10 6 ohm and specific
resistance in a range of 10 2 to 10 3 ohm-cm, only low-structure
carbon black in Formulation 1 yields good fiber. With
high-structure carbon blacks, no fibers with acceptable appearance
and integrity could be made. Low-structure carbon black has
surprisingly good effects on making fibers that are conductive and
capable of electric charge dissipation.
[0065] A loading range from 17 to 1% was examined with Formulations
4 to 7 using low-structure carbon black LCB-1 in PBT. Higher
loadings up to 25% were examined and the data are shown with
Formulations 12 to 13 in Table 2. An increase in the loading of
low-structure carbon black LCB-1 would reduce both fiber resistance
and specific resistance. PA/PEA copolymer was incorporated to
further reduce the resistance in fibers. Fiber resistance of 10 10
ohm or less may be achieved from those formulations. The specific
resistance of 10 6 ohm-cm or less may be obtained as well.
[0066] From the Table 1, we can see that combination of a permanent
anti-static agent, such as PA/PEA copolymer with low-structure
carbon black, such as LCB-1 in Formulation 4 provides a lower
resistance and specific resistance than both using low-structure
carbon black alone (in Formulation 1) or using predominately PA/PEA
copolymer (in Formulation 7). There is a synergistic effect of
combining permanent anti-static agent with low-structure carbon
black.
[0067] A similar study was carried out to evaluate the effect of
loading using high-structure carbon blacks in PBT. As shown by
Formulation 9 to 11, an increase in the loading of high-structure
carbon black HCB-2 would reduce both fiber resistance and specific
resistance. PA/PEA copolymer was also incorporated to reduce the
resistance in fibers. At the same loading of 10% high-structure
carbon black HCB-1, 25% PA/PEA copolymer lowers the fiber
resistance from 10 6 ohm to 10 5 ohm when comparing Formulation 8
with Formulation 2. As may be seen from the results, although
high-structure carbon black at those loadings may impart fiber
resistance sufficient for electrical charge dissipation, they are
not able to result in good fibers.
[0068] FIG. 1 is a representative appearance of the fibers observed
using optical microscopy. The top fiber shown in the picture is
made of low-structure carbon black, such as Formulation #1 and it
is smooth and uniform. In contrast, the bottom fiber made of
high-structure carbon black, such as Formulation #2 is rough and
uneven. The uneven filaments are not acceptable, as they tend to
break during a fabric weaving process.
TABLE-US-00001 TABLE 1 Compositions And Properties of PBT Filled
With Conductive Carbon Blacks And The Fibers Made Of Those
Compositions Formulation 1 2 3 4 5 6 7 8 9 10 11 PBT 82.50 89.50
91.50 57.50 60.50 63.50 73.50 64.50 66.50 68.50 70.50 PA/PEA 25.00
25.00 25.00 25.00 25.00 25.00 25.00 25.00 copolymer Low-structure
17.00 17.00 14.00 11.00 1.00 LCB-1 High-structure 10.00 10.00 HCB-1
High-structure 8.00 8.00 6.00 4.00 HCB-2 Heat Stabilizer 0.50 0.50
0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 Fiber Appearance
SMOOTH UNEVEN UNEVEN SMOOTH SMOOTH SMOOTH SMOOTH UNEVEN UNEVEN
UNEVEN UNEVEN GOOD BAD BAD GOOD GOOD GOOD GOOD BAD BAD BAD BAD
Electrical Properties of Fiber Length, mm 50 50 50 60 60 60 50 50
50 50 50 Resistance, ohm 3.2E+05 1.3E+06 3.2E+05 8.6E+04 3.2E+06
8.9E+10 1.6E+11 3.1E+05 3.4E+05 4.8E+05 1.3E+07 Specific 22 132 18
5 95 3.E+06 1.E+07 18 19 27 720 Resistance, ohm-cm Mechanical
Properties Tensile Modulus, 0.518 0.472 0.458 0.32 0.319 0.309
0.279 0.29 0.271 0.269 0.268 msi Notched Izod 0.68 0.59 0.63 1.1
1.29 1.38 1.9 1.08 1.01 1.21 1.32 Impact, ft-lb/in Electrical
Properties of Molded Plaques Surface 5.5E+01 1.6E+02 1.8E+02
3.1E+01 1.3E+02 4.5E+09 7.9E+10 6.6E+01 1.6E+02 3.0E+02 1.3E+06
Resistivity, ohm/sq Volume 6.0E+01 2.4E+02 1.4E+02 8.7E+01 5.2E+02
5.6E+09 4.2E+11 1.3E+02 9.7E+01 3.0E+02 1.1E+07 Resisitivity,
ohm-cm Fiber Processing Information Temperature, C. 255 255 255 235
235 235 235 235 235 235 235 Average 0.210 0.252 0.196 0.219 0.151
0.158 0.218 0.190 0.212 0.201 0.192 Diameter, mm Std. Deviation
0.007 0.084 0.067 0.008 0.006 0.007 0.005 0.069 0.079 0.052 0.031
Diameter, mm
[0069] As may be seen from these examples, not all conductive
fillers could be used to form thermoplastic compositions capable of
being formed into fibers. Regardless of the organic polymer or
combination of organic polymers or the amount of conductive filler
used, those fibers formed using high structure carbon black had an
uneven appearance and an average fiber diameter that varied widely
(i.e. having a standard deviation of at least 0.03 mm) whereas
fibers formed using the low-structure carbon black all had a
substantially smooth appearance and an average fiber diameter that
varied little (i.e. having a standard deviation of 0.02 mm or
less).
[0070] As shown in Table 2, although sulfur content of
low-structure carbon black LCB-2 is higher than low-structure
carbon black LCB-1, PBT filled with either of those low-structure
carbon blacks can be made into fibers with smooth appearance and an
average fiber diameter that varied little (i.e. having a standard
deviation of less than 0.02 mm). A loading range from 20 to 25% was
examined with Formulations 12-13 for LCB-1 and Formulation 14-15
for LCB-2. Fiber resistance of 10 5 ohm or less may be achieved
from those formulations. The specific resistance of 10 1 ohm-cm or
less may be obtained as well.
TABLE-US-00002 TABLE 2 Compositions And Properties Of PBT Filled
With Low-Structure Conductive Carbon Blacks And The Fibers Made Of
Those Compositions Formulation 12 13 14 15 PBT 79.50 90.00 79.50
90.00 Low-structure LCB-1 20.00 25.00 Low-structure LCB-2 20.00
25.00 Heat Stabilizer 0.50 0.50 0.50 0.50 Monofilament Appearance
SMOOTH SMOOTH SMOOTH SMOOTH GOOD GOOD GOOD GOOD Electrical
Properties of Monofilament Length, mm 50 50 50 50 Resistance, ohm
9.1E+04 4.6E+04 9.1E+04 5.0E+04 Specific Resistance, ohm-cm 5 2 5 2
Mechanical Properties Tensile Modulus, msi 0.53 0.58 0.54 0.60
Electrical Properties of Molded Plaques Surface Resistivity, ohm/sq
20 9 20 9 Volume Resisitivity, ohm-cm 71 62 71 62 Monofilament
Processing Information Temperature, C. 250 250 250 250 Average
Diameter, mm 0.195 0.160 0.195 0.140 Std. Deviation, mm 0.009 0.011
0.010 0.012
[0071] In the next set of formulations, polyetherimide ("PEI") was
used as the thermoplastic substrate instead of PBT. Table 3 lists
the fiber properties of PEI with carbon blacks. Formulations 16 and
17 are PEI with low-structure carbon black LCB-1 and high-structure
carbon black HCB-1, respectively. Similar to PBT, only
low-structure carbon black was capable of yielding satisfactory
fibers that were also electrically conductive. No uniform and
smooth fibers could be made with PEI filled with high-structure
carbon black and those fibers formed using high structure carbon
black had an average fiber diameter that varied widely whereas
fibers formed using the low-structure carbon black had an average
fiber diameter that varied little.
TABLE-US-00003 TABLE 3 Compositions And Properties of PEI Filled
With Conductive Carbon Blacks And The Fibers Made Of Those
Compositions Formulation 16 17 PEI 83.00 90.00 Low-structure LCB-1
17.00 High-structure HCB-1 10.00 Fiber Appearance SMOOTH UNEVEN
GOOD BAD Electrical Properties of Fiber Length, mm 50 50
Resistance, ohm 2.5E+06 6.5E+06 Specific Resistance, ohm-cm 153 401
Mechanical Properties Tensile Modulus, msi 0.618 0.584 Notched Izod
Impact, ft-lb/in 0.57 0.54 Electrical Properties of Molded Plaques
Surface Resistivity, ohm/sq 1.5E+03 4.9E+03 Volume Resisitivity,
ohm-cm 1.5E+03 7.3E+03 Fiber Processing Information Temperature, C.
370 370 Average Diameter, mm 0.199 0.198 Std. Deviation Diameter,
mm 0.005 0.035
[0072] In the next formulations, the use of carbon nanotubes and
carbon fibers were investigated as alternative conductive fillers.
As shown in Table 4, multi-wall carbon nanotubes (MWNT) of low
concentration (such as 3% in Formulation 18 and 4.95% in
Formulation 19) may impart high conductivity in PBT fibers. At
those loadings, fiber resistance of 10 8 ohm and the specific
resistance of 10 4 ohm-cm can be obtained. On the contrary, chopped
carbon fibers (in Formulation 20 and Formulation 21) could not
impart conductivity in fibers, even at a loading as high as
17%.
TABLE-US-00004 TABLE 4 Compositions And Properties of PBT Filled
With Chopped Carbon Fibers And Multi-Wall Nano-Tubes And The Fibers
Made Of Those Compositions Formulation 18 19 20 21 PBT 71.50 94.55
57.50 82.50 PA/PEA copolymer 25.00 25.00 Chopped CF 17.00 17.00
MWNT 3.00 4.95 Heat Stabilizer 0.50 0.50 0.50 0.50 Fiber Appearance
SMOOTH SMOOTH LOTS OF LOTS OF GOOD GOOD BREAKAGE, BREAKAGE, UNEVEN
UNEVEN BAD BAD Electrical Properties of Fiber Length, mm 50 50 50
50 Resistance, ohm 6.6E+08 1.9E+08 6.5E+12 1.7E+13 Specific
Resistance, ohm-cm 3.8E+04 1.1E+04 6.E+05 3.E+09 Mechanical
Properties Tensile Modulus, msi 0.291 0.469 0.916 1.31 Notched Izod
Impact, ft-lb/in 1.5 0.9 1.25 0.88 Electrical Properties of Molded
Plaques Surface Resistivity, ohm/sq 8.1E+07 1.4E+05 2.7E+02 2.0E+04
Volume Resisitivity, ohm-cm 1.8E+08 9.2E+05 5.6E+02 2.0E+05 Fiber
Processing Information Temperature, C. 235 245 235 255 Average
Diameter, mm 0.19 0.195 0.244 0.351 Std. Deviation Diameter, mm
0.018 0.013 0.107 0.113
[0073] As with the compositions using high-structure carbon black,
regardless of the organic polymer or combination of organic
polymers or the amount of conductive filler used, those fibers
formed using chopped carbon fiber as the conductive filler had an
uneven appearance and an average fiber diameter that varied widely
whereas fibers formed using the multi-wall carbon nanotubes all had
a substantially smooth appearance and an average fiber diameter
that varied little.
[0074] Lastly, the effects of processing parameters were
investigated to determine the effect of these processing parameters
on the final properties of the fibers. An extrusion processing
experiment was conducted using Formulation #1 to evaluate the
effects of processing parameters. As shown in Table 5, a screw
speed higher than 250 was beneficial, while a screw speed higher
than 375 even more beneficial in order to obtain better dispersion
of the fillers and achieve a resistance lower than 10E+09 ohm in a
resulting fiber.
TABLE-US-00005 TABLE 5 Effects Of Compounding Screw Speed On
Electrical Properties Of Fibers Made Of PBT Filled With
Low-Structure Carbon Black LCB-1 Extrusion Processing Condition
Rate 30 30 30 30 Screw Speed 250 375 450 575 Electrical Properties
of Fiber Resistance, ohm 1.90E+09 3.3E+06 3.2E+05 1.26E+05 Specific
resistance SR, 109387 98 22 7 ohm-cm
[0075] The compositions of the present invention are especially
useful in any applications wherein conductive properties are
beneficial. Due to the low specific resistance of fibers formed
using these thermoplastic compositions, fabrics or other articles
that include these fibers are capable of dissipating any electric
or static charge that might build up during use of the article. As
such, the risk of shock or fire due to sudden discharge of this
charge is substantially reduced. Examples of such applications
include, but are not limited to, conveyor belts, electronic parts
handling applications, protective clothing, and the like.
[0076] As set forth herein, compounds are described using standard
nomenclature. For example, any position not substituted by any
indicated group is understood to have its valency filled by a bond
as indicated, or a hydrogen atom. A dash ("-") that is not between
two letters or symbols is used to indicate a point of attachment
for a substitute. For example, --CHO is attached through carbon of
the carbonyl group. Unless defined otherwise, technical and
scientific terms used herein have the same meaning as is commonly
understood by one of skill in the art to which this invention
belongs. Where a measurement is followed by the notation
"(.+-.10%)" or "(.+-.3%)", the measurement may vary within the
indicated percentage either positively or negatively. This variance
may be manifested in the sample as a whole (e.g., a sample that has
a uniform width that is within the indicated percentage of the
stated value), or by variation(s) within the sample (e.g., a sample
having a variable width, all such variations being within the
indicated percentage of the stated value).
[0077] While typical embodiments have been set forth for the
purpose of illustration, the foregoing descriptions should not be
deemed to be a limitation on the scope of the invention.
Accordingly, various modifications, adaptations, and alternatives
may occur to one skilled in the art without departing from the
spirit and scope of the present invention.
* * * * *