Note: Descriptions are shown in the official language in which they were submitted.
CA 0223~604 1998-04-22
W O 97/15934 PCT/JP96/03051
ELECTRICALLY CONDUCTIVE POLYMER COMPOSITION
Technical Field
This invention relates to an electrically conductive
polymer composition and particularly to a white or colored
conductive polymer composition which can be used to form
electrically conductive filaments (including conjugate fibers
containing such filaments), films, sheets, three dimensional
articles, and similar products. A conductive shaped product
obtained from the composition according to this invention can
be employed in antistatic mats, materials for shielding
electromagnetic waves, IC trays, in construction materials such
as floor and ceiling materials for clean rooms, sealing
materials, tiles, and carpets, in packaging for film, dust-free
clothing, and conductive parts of office equipment (rollers,
gears, connectors, etc.).
Background Art
It is well known to disperse an electrically conductive
material in an electrically insulating polymer to prevent
static charge or other purposes and obtain an electrically
conductive polymer (see, for example, Japanese Patent
Publication (Kokoku) No. 58-39175). As electrically conductive
materials which are admixed with polymers, ionic or nonionic
organic surfactants, metal powders, electrically conductive
metal oxide powders, carbon black, carbon fibers, and the like
are generally used. There are dispersed in a polymer by
melting and kneading to form an electrically conductive polymer
composition, which is shaped to obtain an electrically
conductive article having a volume resistivity of 10 - 10
Q cm.
It is also known that use of a material having a large
aspect ratio such as flakes or whiskers as the conductive
material can provide a polymer with electrical conductivity
using a relatively small amount. This is because a conductive
material having a large aspect ratio increases the number of
contact points between the material for the same unit weight,
so it is possible to obtain electrlcal conductivity using a
smaller amount.
CA 0223~604 l998-04-22
W O 97/15934 PCT/JP96/03051
However, a conventional electrically conductive polymer
composition has problems with respect to stability at high
temperatures (heat resistance and dimensional stability),
moldability, and color.
For example, when an organic surfactant is used as the
conductive material, the heat resistance is poor, and the
electrical conductivity is easily influenced by humidity. An
inorganic conductlve material is usually in the form of
spherical particles, so it is necessary to mix a large quantity
exceeding 50 wt% based on the total weight of the composition,
so the physical properties of the polymer worsen, and its
moldability into filaments or films is decreased.
Even with flake-shaped or whisker-shaped conductive
materials having a large aspect ratio, it has been
conventionally necessary to use them in an amount exceeding 40
wt~ based on the total weight of the composition. When such a
large amount of an electrically conductive material is mixed in
a polymer, a directionality (anisotropy) develops at the time
of shaping, and the moldability and electrical conductivity are
worsened.
In the case of carbon black, if the amount required to
impart electrical conductivity (generally at least 10 wt% based
on the total weight of the composition) is used, the
composition becomes black, and a white or colored formed
product can not be obtained.
Carbon fibers, and particularly graphitized carbon fibers,
have good electrical conductivity, and it has been attempted to
disperse carbon fibers into a polymer as a conductive material.
In particular, carbon fibers formed by vapor phase growth
method ~pyrolysis method) and graphitized, if necessary, by
heat treatment, and which are hollow or solid with a fiber
diameter of from 0.1 ~m to several ~m have high electrical
conductivity and have attracted attention as a conductive
material. However, even with such carbon fibers, when they are
admixed in an amount sufficient to impart electrical
conductivity, the polymer composition ends up becoming black.
Recently, carbon microfibers with a far smaller fiber
diameter than carbon fibers formed by the vapor phase growth
CA 0223S604 1998-04-22
W O 97/15934 PCT/JP96/03051
method (referred to below as hollow carbon microfibers~ have
been developed. See, for example, Japanese Patent Publications
(Kokoku) Nos. 3-64606 and 3-77288, ~apanese Patent Laid-Open
(Kokai) Applications Nos. 3-287821 and 5-125619, and U.S.
Patent No. 4,663,220. These microfibers have an outer diameter
of less than 0.1 ~m, and normally on the order of several
nanometers to several tens of nanometers. As they have a
slenderness of the nanometer order, they are also referred to
as nanotubes or carbon fibrils. They are usually extremely
10 fine hollow carbon fibers having a tubular wall formed by
stacking of layers of graphitized carbon atoms in a regular
arrangement. These hollow carbon microfibers are used as a
reinforcing material in the manufacture of composite materials,
and it has been proposed to mix them into various types of
15 resins and rubber as a conductive material. (See, for example,
Japanese Patent Laid-Open (Kokai) Applications Nos. 2-232244,
2-235945, 2-276839, and 3-55709).
In Japanese Patent Laid-Open (Kokai) Application No. 3-
74465, a resin composition is disclosed which is imparted
20 electrical conductivity and/or a jet black color and which is
formed from 0.1 - 50 parts by weight of carbon fibrils (hollow
carbon microfibers) in which at least 50 wt% of the fibers are
intertwined to form an aggregate, and 99.9 - 50 parts by weight
of a synthetic resin. In that application, it is described
25 that it is preferred to use at least 2 parts by wight of hollow
carbon microfibers to impart electrical conductivity, and when
imparting only a jet black color, the amount used is preferably
0.1 - 5 parts by weight.
As described above, carbonaceous conductive materials have
30 excellent heat stability and can impart electrical conductivity
to a polymer by using in a relatively small amount, but they
have the drawback that they end up blackening the polymer.
Uses for conductive polymers include antistatic mats,
0 electromagnetic wave shield materials, IC trays, building
35 materials, and packaging for film, and in each of these uses,
there is a strong need to be able to freely perform coloring,
either for reasons of visual design or to permit
differentiation of products (such as in the case of IC trays).
CA 0223~604 1998-04-22
W O 97/15934 PCT/JP96/03051
An object of the present invention is to provide an
electrically conductive polymer composition which has excellent
electrical conductivity, heat resistance, and moldability, and
which can be used to form a white or colored product by any
melt-molding methods including melt spinning, melt extrusion,
and injection molding.
A more specific object of the present invention is to
provide a white or freely colored electrically conductive
polymer composition which uses a carbonaceous conductive
material and which can be used to form a product of a desired
color.
Disclosure of Invention
As stated above, when a carbonaceous conductive material
~carbon black, carbon fibers, etc.) is blended with a polymer,
the composition as a whole ends up black, so until now, it has
been thought that it would be difficult to use a carbonaceous
conductive material to form a white or colored (with a color
other than black) conductive product, and it was never
attempted to make one.
The present inventors investigated the characteristics of
the above-described hollow carbon microfibers as an
electrically conductive material. It was found that because
microfibers are extremely slender, they can impart electrical
conductivity to a polymer when mixed in an amount of at least
0.01 wt% which is far less than the amount used of conventional
carbon fibers. Furthermore, it was found that when the content
is less than 2 wt%, the amount of blackening of the polymer by
the carbon fibers decreases and can be substantially entirely
hidden by the simultaneous presence in the polymer of a white
powder to obtain a white conductive formable composition.
Furthermore, it was found that by mixing a coloring agent in
the white composition, a desired color can be obtained, thereby
attaining the present invention.
Accordingly, the present invention resides in a white
electrically conductive polymer composition comprising hollow
carbon microfibers and an electrically conductive white powder
dispersed in a moldable organic polymer. In general, it
contains, with respect to the total weight of the composition,
CA 0223~604 1998-04-22
W O 97tl5934 PCT/JP96/03051
at least 0.01 wt~ and less than 2 wt% of hollow carbon
microfibers and 2.5 - 40 wt% of an electrically conductive
white powder.
By further admixing a coloring agent (colored pigment,
paint, etc.) with the white conductive polymer composition, an
electrically conductive polymer composition having a desired
color can be obtained.
In the present invention, two types of electrically
conductive materials, (A) hollow carbon microfibers, which are
conductive fibers, and (B) a conductive white powder, are
dispersed in a moldable polymer. The use of the hollow carbon
microfibers is expected to blacken the polymer, but when the
amount is less than 2 wt%, by the simultaneous presence of the
white powder, the blackening is counteracted, and a visually
white composition can be obtained. As a result of imparting
electrical conductivity by means of the hollow carbon
microfibers, the amount of the electrically conductive white
powder can be limited to a relatively small amount of 2.5 - 40
wt% necessary for whitening (hiding of the black color). If
whitening is performed in this manner, and if a coloring agent
is further added, coloring can be freely performed.
Best Mode for Carrying Out the Invention
The hollow carbon microfibers used in the present
invention as conductive fibers are extremely fine, hollow
carbon fibers obtained by the vapor phase deposition method ~a
method in which a carbon-containing gas such as Co or a
hydrocarbon is catalytically pyrolyzed in the presence of a
transition metal-containing particles whereby the carbon formed
by pyrolysis grows on the particles as starting points of
growth to form fibers). In general, the outer diameter of the
hollow carbon microfibers is less than 0.1 ~m (100 nm), and
preferably they have an outer diameter of 3.5 - 70 nm and an
aspect ratio of at least 5. Preferred hollow carbon
microfibers are carbon fibrils described in U.S Patent No.
4,663,230 or Japanese Patent Publications (Kokoku) Nos. 3-64606
and 3-77288, or hollow graphite fibers described in Japanese
Patent Laid-Open (Kokai) Application No. 5-125619.
Particularly preferred hollow carbon microfibers for use
CA 0223~604 1998-04-22
W O 97/15934 PCT/JP96/03051
in the present invention are those commercially available from
Hyperion Catalysis International, Inc. (USA) under the
trademark Graphite Fibril. These are graphitic hollow
microfibers with an outer diameter of 10 - 20 nm (0.01 - 0.02
5 ~m), an inner diameter of at most 5 nm (0.005 ~m), and a length
of 100 - 20,000 nm (0.1 - 20 ~m).
These hollow carbon microfibers have less ability to
produce black coloration or to conceal than normal carbon
black, and due to their extremely large aspect ratio of 5 -
10 1000, they can be bent. Preferably, the hollow carbon
microfibers have a volume resistivity in bulk of at most 10
Q-cm (measured under a pressure of 100 kg/cm2), and more
preferably at most 1 Q-cm.
The electrically conductive white powder used in this
15 invention performs the two functions of imparting electrical
conductivity and whiteness to the polymer. However, for
electrical conductivity, the hollow carbon microfibers are also
present, so the amount of powder which is added can be limited
to the amount necessary to produce whitening. The conductive
20 white powder preferably has a volume resistivity of at most 10
Q-cm (measured under a pressure of 100 kg/cm~) and a whiteness
of at lease 70, and more preferably it has a volume resistivity
of at most 103 Q-cm and a whiteness of at least 80.
Here, the whiteness refers to the value W(Lab) calculated
25 using the following equation from the values of L, a, and b
measured by the Hunter Lab colorimetric system:
W(Lab)= 100 - [(100 - L) + a + b]
The shape of the conductive white powder is not critical.
For example, it can be from completely spherical to roughly
30 spherical powder (collectively referred to below as roughly
spherical powder), or it can be flake-shaped or whisker-shaped
powder having a large aspect ratio (collectively referred to t
below as high aspect ratio powder). However, spherical white
powder generally has a greater ability to conceal, so
35 preferably at least a portion of the conductive white powder is
roughly spherical powder.
The average particle size of the conductive white powder
(the corresponding diameter in the case of roughly spherical
CA 0223~604 1998-04-22
W O 97/15934 PCT/JP96/03051
powder, and the average value of the largest dimension in the
case of flake-shaped or whisker-shaped high aspect ratio
powder) is preferably 0.05 - 10 ~m and more preferably 0.08 - 5
~m. More specifically, for a roughly spherical white powder,
the average particle diameter is preferably at most l ~m, and
more preferably at most 0.5 ~m. For a flake-shaped or whisker-
shaped white powder with an aspect ratio of 10 - 200, the
average particle diameter can be up to 10 ~m or more, and
preferably it is at most 5 ~m.
If the average particle diameter of the electrically
conductive white powder is less than 0.05 ~m, the powder
becomes transparent and the whiteness decreases, and in the
case of the below-described surface coating-type electrically
conductive white powder, the amount of surface coating
increases, and this may lead to a decrease in whiteness. On
the other hand, if the average particle diameter exceeds l ~m
for roughly spherical powder and exceeds 10 ~m for high aspect
ratio powder, particularly when the product which is formed is
a film or filaments, the thickness or diameter of which is
generally several ~m to several hundred ~m, the smoothness of
the film tends to decrease or breakage during melt spinning
tends to occur.
When the electrically conductive white powder has an
average particle diameter within the above-described range, the
relative surface area thereof is generally in the range of
0.5 - 50 mZ/g and preferably 3 - 30 mZ/g for roughly spherical
powder and is 0.1 - 10 m2/g and preferably l - 10 mZ/g for high
aspect ratio powder.
The electrically conductive white powder used in this
invention can be (1) a white powder which itself is
electrically conductive, or (2) a non-conductive white powder
the surface of which is coated with a transparent or white
electrically conductive metal oxide (referred to below as a
surface coated conductive white powder).
An example of (1) is a white metal oxide powder, the
electrical conductivity of which is increased by doping with
another element. specific examples include aluminum-doped zinc
oxide (abbreviated as AZO), antimony-doped tin oxide
CA 0223~604 1998-04-22
WO 97/15934 PCT/JP96/03051
(abbreviated as ATO), and tin-doped indium oxide ~abbreviated
as ITO). The white powder having electrical conductivity by
itself preferably has a such a particle diameter that the
whiteness is at least 70. For example, when the pa7-ticle
diameter of ATO or ITO becomes small, the particles become
transparent and the whiteness tends to decreases. For this
reason, a preferred conductive white powder is AZO having a
high whiteness.
Examples of a surface-coated conductive white powder (2)
are nonconductive white powders such as titanium oxide, zinc
oxide, silica, aluminum oxide, magnesium oxide, zirconium
oxide, a titanate of an alkali metal (such as potassium
titanate), aluminum borate, barium sulfate, and synthetic
fluoromica with the surface thereof coated with a transparent
or white electrically conductive metal oxide such as ATO, AZO,
or ITO. Titanium oxide is most preferred as the nonconducti~e
white powder because its coloring ability is greatest, but
others can be used alone or in combination with titanium oxide.
ATO and AZ0 are preferred as the conductive metal oxide for
surface coating because they have good co~ering properties.
As a method of surface coating, a dry method (such as a
method in which a conductive metal oxide is deposited by plasma
pyrolysis onto a nonconductive white powder in a fluidized bed)
is possible, but at present, a wet method is more suitable from
an industrial viewpoint. Surface coating by a wet method can
be carried out in accordance with the method described in
Japanese Patent Publication (Kokoku) No. 60-49136 and U.S.
Patent No. 4,452,830, for example. This method will be
explained for surface coating with ATO. An alcoholic solution
containing hydrolyzable water-soluble salts of antimony and tin
(such as antimony chloride and tin chloride) in predetermined
proportions is gradually added to a dispersion of a
nonconductive white powder (such as titanium oxide powder) in
water. The chloride salts are hydrolyzed and the hydrolyzates
(precursor of ATO in the form of hydroxides) are co-deposited
on the titanium oxide powder so as to coat the powder. After
the white powder on which the ATO precursor is deposited is
collected and calcined, a white powder coated on its surface
CA 0223~604 1998-04-22
W O 97/15934 PCTIJP96/03051
with ATO is obtained.
The amount of surface coating of the nonconductive white
powder with the transparent or white conductive metal oxide is
preferably such that the volume resistivity (measured at 100
kg/cm) of the white powder after surface coating is reduced to
10 Q.cm or less. The amount of coating is generally 5 - 40 wt~
relative to the nonconductive white powder and preferably in
the range of 10 - 30 wt%.
The amount of conductive materials used in the conductive
polymer composition of this invention, in wt~ based on the
total weight of the composition, is at least 0.01~ and less
than 2%, preferably 0.05 - 1.5%, and more preferably 0.1 - 1%
for the hollow carbon microfibers, and is 2.5 - 40%, preferably
5 - 35%, and more preferably 7.5 - 30~ for the electrically
conductive white powder. The larger the amount of the hollow
carbon microfibers, it is preferable to also increase the
amount of the electrically conductive white powder in order to
counteract blackening. As a result, the electrical
conductivity of the composition becomes high. Therefore, the
amount of the hollow carbon microfibers can be selected in
accordance with the electrical conductivity required for the
use.
If the amount of the hollow carbon microfibers is less
than 0.01%, it becomes difficult to impart sufficient
electrical conductivity to the polymer, even if a conductive
white powder is also added. On the other hand, if the amount
is 2~ or more, the blackening of the polymer composition
becomes noticeable, and it becomes difficult to produce
whitening or coloration even if a conductive white powder is
present. If the amount of the conductive white powder is less
than 2.5%, whitening or coloration becomes difficult, and the
electrical conductivity also decreases. If the amount exceeds
40~, the amount of powder is too great, and the moldability of
the polymer and the properties, particularly mechanical
properties, of the molded product deteriorate.
When the conductive white powder contains a high aspect
ratio powder (whether it consists solely of the high aspect
ratio powder or is a mixture of that powder with a roughly
CA 0223~604 1998-04-22
WO 97/lS934 PCT/JP96/03051
spherical powder), the high aspect ratio powder has a tendency
to impart directionality to the polymer. In order to avoid
excessive directionality, the amount of high aspect ratio
powder is preferably at most 35% and particularly at most 25~.
When only a conductive white powder is mixed with a
polymer to impart electrical conductivity according to a
conventional manner, it is necessary to use a large amount of
the conductive white powder, i.e., at least 50% of the
composition and preferably at least 60% in order to obtain
sufficient electrical conductivity. In the present inven~iorl,
by simultaneously using hollow carbon microfibers in a small
amount of less than 2%, electrical conductivity is imparted
primarily by the carbon fibers, so the amount of the conductive
white powder can be reduced to the amount necessary for
whitening. As a result of greatly reducing the amount of this
pigment, it is possible to impro~e the polymer properties.
Furthermore, even when the white powder has a high aspect
ratio, a high directionality can be prevented, and good
moldability can be maintained.
The reason that the electrical conductivity of the polymer
can be increased by as little as less than 2~ of carbon fibers
is because hollow carbon microfibers are, as described above,
extremely slender and hollow. Electrical conduction occurs
along the contact points between the electrically conductive
materials. Therefore, the more slender and the lower the bulk
specific gravity (hollowness contributes to a low bulk specific
gravity), the more contact points between fibers per unit
weight. In other words, electrical conductivity can be
imparted with a smaller amount of electrically conductive
fibers. The hollow carbon microfibers used in this invention
are extremely fine with a fiber outer diameter of at most 0.07
~m (70 nm), and normally at most several tens of nanometers,
and they have a low specific gravity due to being hollow, so
the number of contact points between fibers per unit weight
increases, and they can impart electrical conductivity in as
small an amount as less than 2~.
Furthermore, the hollow carbon microfibers aGt as
conducting wires linking the electrically conductive white
CA 0223~604 l998-04-22
W O 97/15934 PCT/JP96/03051
11
powder. Namely, even if particles of the white powder are not
directly contacting, electrical contact is maintained by the
hollow carbon microfibers, and this is thought to further
contribute to electrical conductivity.
The hollow carbon microfibers used in the present
invention have an outer diameter of at most 70 nm, which is
shorter than the shortest wavelength of visible light.
Therefore, visible light is not absorbed and passes through
them, so it is thought that when present in a small amount of
less than 2%, the presence of the carbon fiber~ does no~
substantially affect the whiteness. Furthermore, as stated
above, the amount of the carbon fibers is not large enough to
produce directionality of the polymer, so the moldability is
not impeded.
In Japanese Patent Laid-Open (Kokai) Application No. 3-
74465, a polymer composition is made jet black by using 0.1 - 5
wt%, based on the weight of the composition, of hollow carbon
microfibers (carbon fibrils), and it is written that mixing of
at least 2 wt~ is desirable to impart electrical conductivity.
In contrast, in the present invention, when less than 2 wt% is
used, the color does not become jet black, and electrical
conductivity can be imparted. The cause of the difference is
thought to be that in the composition of the above-mentioned
Japanese Kokai application, at least 50 wt% of the hollow
microfibers are present in the form of aggregated fibers
forming an aggregate of 0.10 - 0.25 mm, so a large amount of
fibers is necessary to obtain electrical conductivity, and even
a small amount strongly blackens the polymer, In contrast, in
the present invention, the hollow carbon microfibers are
dispersed throughout the entire polymer, It is conjectured
that due to the dispersion of the fibers and the presence of
the electrically conductive white powder, when the hollow
carbon microfibers are present in an amount of less than 2 wt~,
blackening of the polymer composition is counteracted by the
action of the white powder, and a high electrical conductivity
is imparted.
The polymer used in the moldable composition according to
this invention is not critical as long as it is a moldable
CA 0223~604 1998-04-22
W O 97/15934 PCT/JP96/03051
12
resin, and it can be a thermoplastic resin or a thermosetting
resin. Examples of suitable thermoplastic resins are
polyolefins such as polyethylene and polypropylene, polyamides
such as Nylon 6, Nylon 11, ~ylon 66, and ~ylon 6,10, polyesters
such as polyethylene terephthalate and polybutylene
terephthalate, and silicones. In addition, acrylonitrile,
styrene, and acrylate resins, polyvinyl chloride,
polyvinylidene chloride, polyvinyl acetate, polyketones,
polyimides, polysulfones, polycarbonates, polyacetals,
fluoroplastics, etc. can be used.
Examples of thermosetting resins which can be used in the
composition of the present invention are phenolic resins, urea
resins, melamine resins, epoxy resins, and polyurethane resins.
Mixing of the conductive materials (fiber and powder~ with
the polymer can be performed using a conventional mixing
machine such as a heated roll mill, an extruder, or a melt
blender which can disperse the conductive materials in the
polymer in a melt or softened state. The hollow carbon
microfibers and the electrically conductive white powder as the
conductive materials can each be a mixture of two or more
classes. The composition obtained by mixing can be shaped into
a suitable formed such as pellets or particles, or it can be
immediately used for molding as is.
In addition to the above-described components, the
conductive polymer composition of this invention may contain
one or more conventional additives such as dispersing agents,
coloring agents (white powder, colored pigments, dyes, etc.),
charge adjusting agents, lubricants, and anti-oxidizing agents.
There are no particular restrictions on the types and amounts
of such additives.
Addition of white powder as a coloring agent increases the
whiteness of the composition. Addition of one or more colored
pigments and/or dyes makes it possible to impart any desired
color to the polymer composition of this invention.
There are no particular restrictions on the molding method
for the conductive polymer composition according to the present
invention or on the shape of the formed product. Molding can
be performed by any suitable method including melt spinning,
CA 0223~604 1998-04-22
W O 97/15934 PCT/JP96/03051
13
extrusion, injection molding, and compression molding, which
can be appropriately selected depending on the shape of the
article and the type of the resin. A melt molding method is
preferred, but solution molding method is also possible in some
cases. The shape of the articles can be filaments, films,
sheets, rods, tubes, and three-dimensional moldings.
When the conductive polymer composition of the present
invention does not contain a coloring agent, a formed product
having a whiteness of at least 40 and preferably at least 50
can be obtained. If the whiteness is at least 40, coloring to
a desired color with good color development can be performed by
adding a coloring agent.
The product formed using a conductive polymer composition
according to this invention in general has a volume resistivity
of 10~ - 101~ Q-cm and preferably 10~ - 108 Q cm and a surface
resistance of at most 10'~ Q~ and preferably 102 - 10 Q~ . In
the case of filaments, it has an excellent electrical
conductivity of at most 101C Q per centimeter of filament.
Due to this excellent electrical conductivity, a
20 conductive polymer composition according to this invention can
be used in any application in which antistatic or
electromagnetic wave-shielding properties are necessary. ~or
example, the composition of this invention can be used to
manufacture IC trays which are differentiated by color
25 according to the type of product. Furthermore, in the
manufacture of antistatic mats, building materials for clean
rooms and the like, packaging materials for film,
electromagnetic wave shielding materials, dust-free clothing,
electrically conductive members, etc., aesthetically attractive
30 products can be manufactured by coloring them to any desired
color.
By combining the conductive polymer composition of this
invention with a nonconductive polymer, a composite shaped
J product can be manufactured. For example, as described in
Japanese Patent Laid-Open (Kokai) Application No. 57-6762, a
conductive polymer composition according to this invention and
a common nonconductive polymer can be melt-spun together
through a conjugate fiber spinneret having at least two
-
CA 0223~604 1998-04-22
W O 97/15934 PCT/JP96/03051
14
orifices, and a conjugate filament having a conductive part and
a nonconductive part in its cross section can be spun. Using
such conjugated filaments, an antistatic fiber product (such as
an antistatic mat, dust-free clothing, and carpets) having a
drape better than those formed of conductive filaments which
are entirely composed of a conductive polymer composition can
be manufactured. In the case of films and sheets, the
composition can be laminated with a nonconductive polymer.
Examples
The following examples are presented to further illustrate
the present invention. These examples are to be considered in
all respects as illustrative and not restrictive. In the
example, all parts and % are by weight unless otherwise
specified.
The electrically conductive materials used in the examples
were as follows.
1. hollow carbon microfibers - Graphite Fibril BN and CC
(tradenames of Hyperion Catalysis International, Inc.).
Graphite Fibril BN is a hollow fiber with an outer diameter of
0.015 ~m (15 nm), an inner diameter of 0.005 ~m (5 nm), a
length of 0.1 - 10 ~m ~100 - 10,000 nm), and a volume
resistivity in bulk (measured under a pressure of 100 kg/cm~) of
0.2 Q-cm. &raphite fibril CC is a hollow fiber with an outer
diameter of 0.015 ~m (15 nm), an inner diameter of 0.005 ~m (5
nm), a length of 0.2 - 20 ~m (200 - 20,000 nm), and a volume
resistivity in bulk of 0.1 Q-cm.
2. ATO-coated titanium dioxide powder: Spherical titanium
oxide powder (W-P made by Mitsubishi Materials, average
particle diameter of 0.2 ~m and a specific surface area of 10
m~/g) coated with 15% ATO. It had a volume resistivity of 1.8
Q-cm at a pressure of 100 kg/cm2 and a whiteness of 82.
3. ATO-coated fluoromica powder: Synthetic fluoromica
powder (W-MF made by Mitsubishi Materials, average particle
diameter of 2 ~m, aspect ratio of 30, specific surface area of
3.8 mZ/g) coated with 25% ATO. It had a volume resistivity of
20 Q-cm at a pressure of 100 kg/cm2 and a whiteness of 81.
4. AZ0 powder: Spherical Al-doped zinc oxide powder (23-K
made by Hakusui Chemical, average particle diameter of 0.25 ~m,
CA 0223~604 1998-04-22
W O 97/15934 PCT/JP96/03051
volume resistivity of 10~ Q-cm at a pressure of 100 kg/cm2, and
a whiteness of 75).
5. Electrically conductive carbon black (abbreviated CB)
(#3250 made by Mitsubishi Chemical, average particle diameter
of 28 nm), which was used as a comparative carbonaceous
electrically conductive material.
The following materials were used as a polymer.
1. Low-density polyethylene resin (Showlex F171 made by
Showa Denko).
2. Nylon 6 (Novamide 1030 made by Mitsubishi Chemical).
3. Silicone rubber (X-31 made by Shin-Etsu Chemical).
The surface resistance in the examples was the value
measured with an insulation-resistance tester (Model SM 8210
made by Toa Denpa). The volume resistivity was the value
measured with a digital multimeter (Model 7561 made by Yokogawa
Electric). Whiteness was measured using a colorimeter (Color
Computer SM7 made by Suga Testing Instruments).
Example 1
1 part of hollow carbon microfibers (Graphite Fibril BN),
29 parts of ATO--coated titanium dioxide powder, and 70 parts of
polyester resin were melt-blended in a roll mill at 175~C so as
to distribute the fibers and the powder uniformly in the resin.
The resulting conductive polymer composition was pelletized,
and the pellets were melt-extruded into a 75 ~m-thick film.
The resulting white conductive film had a surface resistance of
2 x 105 Q~ and a whiteness of 49.
The above procedure was repeated to form a conductive
white film while varying the amount of the conductive materials
or by omitting the hollow carbon microfibers or by using
conductive carbon black instead. The results and the
composition are shown in Table 1.
The results of another series of test runs in which
Graphite Fibril CC was used as the hollow carbon microfibers
are shown in Table 2.
As can be seen from the above tables, when hollow carbon
microfibers were not employed, the film had a high whiteness,
but electrical conductivity could not be developed. In
contrast, by adding but a minute quantity of 0.5 - 1.5% of
CA 0223~604 1998-04-22
W O 97/15934 PCT/JP96/03051
16
hollow carbon microfibers, the film had a sufficient electrical
conductivity while a whiteness of at least 40 was maintained.
On the other hand, when the same amount of carbon black was
added instead of hollow carbon microfibers, electrical
conductivity was not attained, and the film was essentially
black.
T a b I e
Run Composition (wtX) Surface White-
NQ Resist. n~ss
Resin G F C B A T O Q / ~]
1 70 0.5 - 29.5 3 xlO' 53 Tl
2 70 1.0 - 29.0 2 XlOs 49 Ti
3 70 1.5 - 28.5 9 X103 44 Tl
4 70 - - 30 >1012 71 C0
- 1 29.0 >lol2 21 CO
Resin : Polyethylene, GF = Graphite Fibril BN
CB = Carbon Black, ATO = ATO-coated titanium oxide powder
Tl = This Invention, C0 = Comparative
T a b I e 2
Run Composition (wt%) Surface White-
NQ Resist. ness
Resin G F A T O Mica Q / [~
1 70 0.5 29.5 - 1 xlO6 55 Tl
2 70 1.0 29.0 - 6 X103 51 Tl
3 70 1.5 28.5 - 7 xlo2 44 Tl
4 65 0.5 24.5 10 5 XlOs 54 Tl
Resin : Polyethylene, GF = Graphite Fibril CC
AT0 = ATO-coated titanium oxide powder
Mica = ATO-coated synthetic fluoromica
Tl = This Invention
Example 2
0.5 parts of hollow carbon microfibers (Graphite Fibril
CC), 24.5 parts of ATO-coated titanium dioxide powder, and 75
parts of Nylon 6 resin were melt-blended at 250~C in a twin-
screw extruder. The resulting conductive polymer composition
CA 0223~604 1998-04-22
W O 97/15934 PCT/JP96/03051
17
was pelletized, and the pellets were melt-spun through a melt
spinning machine to form 12.5 denier Nylon filaments. The
resulting filaments had an electrical resistance of 4 x 10' Q
per cm of filament and a whiteness of 52.
The above process was repeated while varying the amount of
the conductive materials or by substituting carbon black for
hollow carbon microfibers. The results and the blend
compositions are shown in Table 3.
T a b I e 3
Run Composition (wt%) Electric White-
N~ Resist. ness
Resin G F C B A T O Q / cm
1 75 0.5 - 24.5 4 X108 52 Tl
2 70 1.0 - 29.0 5 X106 44 Tl
3 70 - 1.0 29.0 >1012 28 C0
4 40 - 1.0 59.0 7 xlo'~ 35~ C0
Resin : 6 Nylon. GF = Graphite Fibril CC
CB = Carbon Black. AT0 = AT0-coated titanium oxide powder
Tl = This Invention. C0 = Comparative
~ Breakage of filaments occurred during spinning
By comparing Tests Nos. 2 and 3, it can be seen that
electrical conductivity was not obtained when hollow carbon
microfibers were replaced by the same amount of carbon black.
On the other hand, as shown in Run No. 4, if the amount of
electrically conductive white powder was increased to 50~ or
more, electrical conductivity was exhibited, but the electrical
conductivity was lower than for the present invention.
Moreover, due to blending a large amount of powder, breakage of
filaments occurred during melt spinning, and the moldability
was greatly decreased.
Example 3
0.075 parts of hollow carbon microfibers (Graphite Fibril
CC), 19.925 parts of ATO-coated titanium oxide powder, and 80
parts of silicone rubber were uniformly mixed in a roll mill to
obtain a semi-fluid conductive polymer composition which is
suitable as a conductive sealant, for example. The volume
CA 0223~604 1998-04-22
W o 97/15934 PCT/JP96103051
18
resistivity of this rubbery composition was 9 x 10 Q cm and it
had a whiteness of 69.
The above process was repeated while varying the amount of
the electrically conductive materials or by also including ATO-
coated fluoromica powder in the electrically conductivematerials to obtain a conductive polymer composition. The
results and the composition of the blend are shown in Table 4.
Electrical conductivity was obtained using only 0.075~ of
hollow carbon microfibers. It can also be seen that
simultaneous use of flake-shaped electrically conductive whi~e
powder is effective.
T a b i e 4
Run Composition (wt%) ~olume White-
NQ Resist. ness
Resin G F ATO Mica Q ~ cm
1 80 0.07519.925 - 9 X105 69 Tl
2 80 0.3 19.7 - 3 xlO6 51 Tl
3 80 1.0 19.0 - 7 X102 42 Tl
4 65 1.8 33.2 - 7 x10~ 41 Tl
0.3 9.7 -- 8 X106 46 Tl
6 70 0.3 9.7 20 3 XlOs 58 Tl
Resin : Sillicone rubber, GF = Graphite Fibril CC
ATO = ATO-coated titanium oxide powder
Mica = AT0-coa ted synthetic fluoromi ca
Tl = This Invention
Example 4
0.3 parts of Graphite Fibril CC, 34.7 parts of AZO powder,
and 65 parts of silicone rubber were uniformly mixed in a roll
mill to obtain a semi-fluid conductive polymer composition
similar to that of Example 3. This rubbery composition had a
volume resistivity of 8 x 106 Q-cm and a whiteness of 55.
The above process was repeated while varying the amount of
the electrically conductive materials to prepare a conductive
polymer composition. The results and the blend composition are
shown in Table 5. Even when the white powder was AZO powder
which itself is electrically conductive, a high whiteness and
electrical conductivity could be obtained.
CA 0223~604 1998-04-22
W O 97/15934 PCT/JP96/03051
19
T a b I e 5
Run Composition (wt~/~) Volume ~hite-
N~Resist. ness
Resin G F A Z O Q ~cm
165 0.3 34.7 8 X106 55 Tl
265 1.0 34.0 1 X103 43 Tl
Resin : Sillicone rubber. GF = Graphite Fibril CC
AZO = Al-doped zinc oxide powder
Tl = This Invention
Industrial Applicability
Even though an electrically conductive polymer composition
of this invention contains hollow carbon microfibers which are
a class of carbon fibers, the amount thereof is limited to less
than 2 wt%, and by the concurrent presence of an electrically
conductive white powder, blackening due to the carbon fibers is
suppressed, and it can form molded products having a white
outer appearance and excellent electrical conductivity. The
conductive polymer composition can be white or can be freely
colored to a desired color by use of a coloring agent to give
aesthetically attractive conductive products.
Furthermore, by including hollow carbon microfibers which
impart high electrical conductivity, the amount of electrically
conductive white powder can be decreased, and a deterioration
in the physical properties of molded product due to a large
amount of conductive powder can be avoided. Since the amount
of carbon fibers is small, a decrease in moldability can also
be avoided. In addition, the conductive materials produces a
reinforcing and packing effect, and the resulting molded
product has excellent mechanical properties such as dimensional
stability and tensile strength.
Thus, the conductive polymer composition can be used to
manufacture various products having antistatic or
electromagnetic wave-shielding functions, and it can be used to
manufacture products which have an attractive appearance or
which can be differentiated by color.
