Note: Descriptions are shown in the official language in which they were submitted.
~3~
SPECIFICATION
TITLE OF THE INVENTION
~IGH THERMAL CON~UCTIVITY PITCH-BASED CARBON FIBER
AND METHOD OF PRODUCING THE SAME
BACKGROUND OF THE INVENTION
Field of the Invention:
The present invention generally relates to a carbon
fiber. More specifically, the present invention relates to
a high thermal conductivity pitch-based carbon fiber having
a higher thermal conductivity, a larger compressive strength
and excellent yarn handleability and being applicable widely
as the carbon fiber reinforced composite materials for
printing substrates, IC substrates and heat sinks for
electronic devices. The present invention also relates to
a method of producing the same.
Description of the Related Art:
A variety of fiber reinforced composite materials
have been proposed recently as the materials of printing
substrates, IC substrates and heat sinks. High thermal
cGnductivity is particularly indispensable for the fibers
to be used in such fiber reinforced composite materials.
PAN-based and pikch-based carbon fibers have
conventionally been produced and used widely as the carbon
fiber. The mechanical properties of PAN-based carbon fibers
3~
are excellent, but the thermal conductivity thereof is
distinctively low, generally as low as 10 W/m/K or less~
It has not been known any PAN-based carbon fiber with a
thermal conductivity of 7S W/m/K or more. I'here is no
expectation of the improvement of the thermal conductivity.
PAN-based carbon fibers therefore cannot be used favorably
in the carbon fiber reinforced composite materials described
hereinabove.
Alternatively, it has not been known any pitch~based
carbon fiber with satisfactorily high and balanced mechanical
properties, in particular compressive strength and yarn
handleability in producing fiber reinforced composite materials.
Enhanced mechanical properties, in particular such
as enhanced compressive strength as well as high thermal
conductivity, have been demanded for the carbon fiber to
be used in the carbon fiber reinforced composite materials
for printing substrates and the like mentioned hereinabove.
Carbon fiber may be impregnated with metallic
materials in producing thermally conductive members for
printing substrates or carbon fiber reinforced composite
materials for heat sinks. Particularly in such cases,
less fiber agglutination, namely excellent yarn handleability,
lS reqUlred.
During the process of investigating the relation
between the thermal conductivity and the mechanical strength
-- 2
2 ~
with respect to the crystalline structure of a pi.tch-based
carbon fiber, the present inventors have found that an excellent
pitch-based carbon fiber of high thermal conductivity can
be obtained which is provided with tensile strength and
tensile elastic modulus, each above a preset level and has
remarkably increased thermal conductivity and compressive
strength, by controlling the crystalline structure of the
carbon fiber, in particular the stack height (Lc 002),
within a specific range, more specifically by controlling
the ratio of the stack height (Lc 002)/ the density (p~
within a specific range, and that the carbon fiber can
acquire excellent yarn handleability in producing composite
materials to be able to produce superior carbon fiber
reinforced composite materials, by the regulation of the
degree of agglutination of such carbon fiber at 30~ or less.
The present invention has been achieved on such novel
findings.
SUMMARY OF THE INVENTION
___
It is an object of the present invention ko provide
a pitch-based carbon fiber of high thermal conductivity
and a method of producing the same, the high thermal conductivity
pitch-based carbon fiber having a higher thermal conductivity
and a greater compressive strength with no deterioration
of tensile strength and tensile elastic modulus, along with
-- 3 --
~3J3~
excellent yarn handleability.
The object mentioned above can be achieved by a
high thermal conductivity pitch-based carbon fiber according
to the present invention. The present invention is summarized
as a pitch-based carbon fiber of high thermal conductivity,
characterized by having a thermal conductivity in the axial
direction of fi~er of 300 to 1,500 W/m/K, a ratio of stack
height (Lc 002)/density (p) of 70 to 500, a degree of fiber
agglutination of 0 to 30~, and a compressive strength of
0.2 to 0.5 GPa.
The present inventors have found during the process
of investigation and development to obtain a pitch-based
carbon fiber with excellent thermal conductivity by using
pitch as the raw material, that the promotion of crystal-
lization of the fiber is required in order to increase the
thermal conductivity in the axial direction of the fiber
but the crystallization facilitated too far distinctively
reduces the mechanical properties of the fiber, in particular
the compressive strength.
The present inventors have thus found that the
crystalline structure of a carbon fiber, in particular the
stack height (Lc 002) thereof, should be within a specific
range; in other words, the ratio of stack height (Lc 002)/-
density (p) should be in the range of 70 or more to 500
or less, in order to obtain a pitch-based carbon fiber of
-- 4 --
high thermal conductivity, having balanced mechanical
properties with a thermal conductivity of 300 to 1500 W/m/K
and a compressive strength of 0.2 to 0.5 GPa, as well as
a tensile strength of 2.5 to 4.5 GPa and a tensile elastic
modulus of 700 to 950 GPa. If the ratio of stack height
~Lc 002)/density (p) is less than 70, the thermal conductivity
will not reach 300 W/m/K; if the ratio is above 500 W/m/K,
the compressive strength gets smaller than 0.2 GPa, and
mechanical properties balanced with tensile strength and
tensile elastic modulus cannot be obtained.
More explanation of the high thermal conductivity
pitch-based carbon fiber in accordance with the present
invention will now follow. In the high thermal conductivity
pitch-based carbon fiber in accordance with the present
invention, the stack height (Lc 002) is important among
the factors defining the crystalline structure. In accordance
with the present invention, the stack height (Lc Q02) is
generally 160 to 1,000 A while the layer si~e (La 110) is
200 to 1,000 A and the interlayer spacing (doo2~ is 3.36
to 3.40 A. The density (p) of the fiber of the present
invention is generally 2.16 to 2.24 g/cm3.
By controlling the degree of agglutination at 30%
or less, the yarn handleability of the pitch-based carbon
fiber of the present invention in producing a composite
material can be improved, whereby an excellent carbon fiber
~3~
reinforced eomposite material can be produced. If the
degree of agglutination exceeds 30~, the yarn handleability
is remarkably reduced; in case that carbon fibers are
impregnated with metal such as aluminium to produce a
carbon fiber reinforced composite material, for example,
each carbon fiber generally comprising 100 to 10,000
filaments is not uniformly impregnated with melted metal,
so a carbon fiber reinforced composite material with
desirable properties cannot be produced.
Further explanation of the pitch-based carbon fiber
in accordance with the present invention will now follow.
According to the present invention, there can be obtained
a high thermal conductivity pitch-based carbon fiber having
a thermal conductivity as high as 300 to 500 W/m/K, and
balanced mechanical properties such as a compressive
strength of 0.3 to 0.5 GPa, as well as a tensile strength
of 2.5 to 4.0 GPa, and a tensile elastic modulus of 700
to 900 GPa; and a high thermal eonductivity pitch-type
carbon fiber having a thermal conductivity of 500 W/m/K or
more, namely 500 to 1500 W/m/K, and balaneed mechanieal
properties such as a compressive strength of 0.2 to 0.4
GP~, as well as a tensile strength o~ 2.5 to 4.5 GPa, and
a tensile elastic modulus of 700 to 950 GPa.
In order to obtain a high thermal conductivity
pitch-based carbon fiber having a thermal conductivity as
~53~
high as 300 to 500 W/m/K, the crystalline structure of the
carbon fiber, particularly with respect to stack height
(Lc 002), should be within a specific range; more specifically~
the ratio of stack height (Lc 002)/density (p) should be
within the range of 70 or more to 180 or less. In case
that the ratio of stac~ height (Lc 002)/density (p) is less
than 70, the thermal conductivity will not reach 30~ W/m/K;
in case that the ratio exceeds 180, the compressive strength
gets smaller than 0.3 GPa, and the mechanical properties
balanced with tensile strength and tensile elastic modulus
cannot be obtained.
For further explanation of the present invention,
the stack height (Lc 002) is generally 160 to 400 A, while
the layer size (La 110) is 200 to 500 A, and the interlayer
spacing (doo 2 ) iS 3~37 to 3.40 A. The density (p) of such
fiber is generally 2.16 to 2.22 g/cm3.
By controlling the degree of agglutination at 20~
or less, the yarn handleability of such pitch-based carbon
fiber in producing a composite material can be improved,
whereby an excellent carbon fiber reinforced composite
material can be produced.
In order to obtain a high thermal conductivity
pitch-based carbon fiber having a thermal conductivity of
500 to 1,500 W/m/K or a super-high thermal conductivity
pitch-based carbon fiber, the crystalline structure of the
-- 7 --
~ 2~3~
carbon fiber, in particular the stack height (Lc 002), should
be within a specific range; more specifically, the ratio
of stack height ~Lc 002)/density (p3 should be within the
range of 120 or more to 500 or less. In case that the
ratio of stack height (Lc 002)/density ~p) is less than
120, the thermal conductivity will not reach 500 W/mlK;
in case that the ratio exceeds 500, the compressive
strength gets smaller than 0.2 GPa, and the mechanical
properties balanced with tensile strength and tensile
elastic modulus cannot be obtained.
For furthermore explanation of the super-high
thermal conductivity pitch-based carbon fiber of the present
invention, the stack height (Lc 0023 is generally 260 to
1,000 A, the layer size (La 110) is 300 to 1,000 A, and
the interlayer spacing (doo 2 ) iS 3.36 to 3.39 A.
The density (p) of such fiber is generally 2.18 to 2.24
g/cm3.
By controlling the degree of agglutination of such
pitch based carbon fiber at 30~ or less, the yarn handle~
ability thereof in producing a composite material can be
improved, whereby an excellent carbon fiber reinforced
composite material can be produced.
It has been found tha* the high thermal conductivity
pitch-based carbon fiber of the present invention can be
preferably produced, by infusibilizing the pitch fiber
-- 8 --
2 ~
obtained by spinning carbonaceous pitch by routine methods,
passing the i.nfusibilized fiber through an oxygen containing
atmosphere at a temperature of 300 to 500C, preferably
350 to 480C, for an extremely short period of time, to
effect a thermal treatment while stretching the fiber at
a ratio of 5 to 100%, subsequently passing the fiber through
an oxygen containing atmosphere the maximum temperature
of which is 500 to 700 C, preferably 550 to 650 C, for
a short period of time, to effect pre-carbonization
treatment while stretching the fiber at a ratio of 5 to
100%, and subsequently carbonizing the fiber in an inert-gas
atmosphere the maximum temperature of which is 2,300 to
3,200 C, while effecting the stretching process of 1 to
30% if necessary.
According to the production method of the present
invention, infusibilized and fragile fiber which has been
rendered infusible by heating up to 150 to 350C, in an
oxidative atmosphere following routine methods, is processed,
prior to pre-carbonization, in an oxygen-containing
atmosphere for a short period of time at a high temperature
of 300 to 500 C. Therefore, the fiber surface is selectively
oxidized while the inside of the fiber is progressively
polymeriæed thermally or carbonized at the high-temperature.
Consequently, the infusibilized fiber is strengthened,
which enables further stretching process of the infusiblized
_ g _
2 ~
fiber in a furnace for pre-carbonization. Thus, the degree
of agglutination of the pre-carbonized fiber is possibly
reduced.
It has been found that the carrying out the process
of stretching ana thermal treatment of the fiber in two
stages, namely after the process of infusibilization and
during the process of pre-carbonization, the orientation
prop~rties of the fiber are improved, and the thermal
conductivity thereof is particularly increased, so that
the fiber with a higher thermal conductivity can be obtained.
The process of stretching and thermal treatment in either
one of the stages, namely one-stage process of stretching
and thermal treatment, cannot produce a high thermal
conductivity pitch-based carbon fiber constructed in
accordance with the present invention.
It has been found that in order to obtain a super-
hlgh thermal conductivity pitch-based carbon fiber having
a thermal conductivity of 500 W/m/K or more. the process
of stretching and thermal treatment is necessarily carried
out in three stages, namely after infusibilization process,
during pre-carbonization process, and during carbonization
process. The process of stretching and thermal treatment
in one stage or two stages cannot produce a pitch-based
carbon fiber of super-high thermal conductivity in the above
structure.
-- 10 --
~33~
During the process of stretching and thermal treatment
in the first stage after infusibilization process, it is
preferable that the o~ygen concentration in the oxygen-
containing atmosphere is 5 to 80 ~; the retention time in
a furnace is 1 to 200 seconds (preferably 10 to 100 seconds);
and the tension per filament is 0.003 to 0.17 g. During
the process of stretching and thermal treatment in the
second stage in the process of pre-carbonization after
infusibilization, it is preferable that the oxygen concen-
tration in the oxygen-containing atmosphere is 0.01 to 30%;
the retention time in a furnace is 20 to 300 seconds
(preferably 50 to 200 seconds); and the tension per filament
is 0.006 to 0.33 g.
In case that the process o~ stretching and thermal
treatment is required in the third stage of the carbonizing
process, the retention time in a furnace during the process
of stretching and thermal treatment in the third stage is
1 to 100 minutes (preferably 2 to 60 minutes); and the
tension per filament is 0.05 to 20 g.
DESCRIPTION OF THE PREFERR_D EMBODIMENTS
The method of producing the pitch-based carbon fiber
of the present invention will now be explained in more
details.
Carbonaceous pitch can be spun by methods well known
-- 11 --
to those skilled in the art. Carbonaceous pitch suitable
for the production of a pitch-based carbon fiber employing
pitch and the like such as petroleum pitch, coal pitch and
aromatic hydrocarbons as raw ma~erials, is heated and melted
to spin filaments of 1 to 2,000, preferably 50 to 1,000.
Treatment oil is given to the individual filaments by using
an oiling roller in routine use, whereby a great number
of the filaments are bundled, and the filaments in a bundle
are then wound as one thread onto a bobbin.
As the treatment oil, there can be used water; alcohols
such as ethyl alcohol, isopropyl alcohol, n-propyl alcohol,
butyl alcohol, etc.; or dimethyl polysiloxane, alkylphenyl
polysiloxane, etc. with a viscosity of 5 to 1,000 cst
(at 25 C), which are diluted with a solvent of a lower
boiling point such as silicone oil (polysiloxane) or paraffin
oil or are dispersed in water by the addition of emulsifiers;
graphite or polyethylene glycol and hindered esters,
similarly dispersed; surfactants diluted with water; and
other various kinds of treatment oils which are used in
common fibers for example polyester fiber and which do not
deteriorate pitch fibers.
The amount of treatment oil to be added to a pitch
fiber is generally 0.01 to 10 % by weight, and it is
specifically 0.05 to 5% by weight preferably.
By simultaneous release of plural bobbins, for example
- 12 -
2 to 50, or the multiple repetition of release and bundling
such as step-wise release of the bobbins, for example 2 to
10 at a first time and the remaining portions at next time,
the threads of 2 to 50, each composed of a great number
of filaments once wound onto one bobbin as has been described
above, are bundled (subjected to yarn doubling~ to produce
a pitch fiber bundle (referred to as "pitch fiber" hereinafter)
from 100 to 100,000 filaments, preferably from 500 to 10,000
filaments. The resulting pitch fiber is then wound onto
another bobbin.
On considering the infuxibilizing process and pre-
carbonization, a heat-resistant treatment oil is put into
the pitch fiber during such bundling. The heat resistant
treatment oil is preferably alkylphenyl polysiloxane
containing 5 to 80% of phenyl group, more preferably alkyl-
phenyl polysiloxane containing 10 to 50 % of phenyl group.
The alkyl group is preferably methyl group, ethyl group
and propyl group. Also, two or more species of alkyl
groups may be contained in one molecule. There are used
those with a viscosity of 10 to 100 cst at 25C.
Antioxidant described hereinbelow may also be added.
As other preferable treatment oils, there may be
used dimethyl polysiloxane with an antioxidant added and
preferably with a viscosity of 5 to 1,000 cst at 25C.
As the antioxidant, there may be included amines, organic
selenium compounds, phenols and the like, such as phenyl-~-
naphthylamine, dilauryl selenide, phenothiazine, and ferric
octoate. These antioxidants may possibly be added to the
alkylphenyl polysiloxane described above, for the objective
to enhance heat resistance.
As preferable treatment oils, there may further be
included the individual treatment oils emulsified with
surfactants of a boiling point o~ 600 C or less. As the
surfactants, there may be used polyoxyethylene alkylether,
polyoxyethylene alkylester, polyoxyethylene modified silicon,
polyoxyalkylene modified silicone and the like.
These treatment oils are added to a pitch fiber at
a ratio of 0.01 to 10~ by weight, preferably 0.05 to 5
by weight, by means of roller contact, spray coating,
foam coating and the like.
By adding a heat resistant treatment oil to the
bundled pitch fiber as has been described above, the pitch
fiber can acquire remarkably increased strength and
distinctively improved yarn handleability.
The pitch fiber thus produced is released from the
bobbin and is transferred and fed to an infusibilizing
furnace.
The inside of an infusiblizing furnace can be set
at a certain predetermined temperature in the range of
150 to 350 C. It can be set so as to have the temperature
- 14 -
s~
gradually elevating from 150C to 350C.
The inside of an infusibilizing furnace should be
in an oxidative atmosphere. Oxidative gas such as air,
oxygen, a mixed gas of air and oxygen~ or a mixed gas of
air and nitrogen, is fed into an infusibilizing furnace.
Oxygen rich gas of an oxygen concentration of 30 to 90%
is preferably used as preferable gas.
According to the present invention, no tension is
loaded onto a pitch fiber during the infusibilizing process.
However, it is preferable to effect the infusibilizing
process under the tension of 0.001 to 0.2 g per filament,
in order to prevent the occurrence of dragging flaw caused
by the dragging of the fiber on the bottom and wall of a
furnace due to the deflection of the fiber inside the
infusibilizing furnace, and in order to improve the
properties of a carbon fiber, such as appearance, tensile
strength and tensile elastic modulus.
The infusibilizing process is effected in such
fashion that the oxygen concentration in the infusibilized
fiber is 7 to 12% by weight.
According to the present invention, the fiber thus
infusibilized and containing oxygen of a concentration of
7 to 12% by weight is subjected to a first-stage process
of stretching and thermal treatment in an oxygen-containing
atmosphere, prior to the process of pre-carbonization in
~3~
a pre-carbonizing furnace.
The temperature inside of the furnace for the process
of stretching and thermal treatment is preferably higher
by 100 to 200 C than the infusibilizing temperature, and
generally i6 a certain fixed temperature in the range of
300 to 500 C, for example 450 C. The inside of the
furnace may also be set to have the temperature gradient
gradually elevating at the inlet to the outlet of the
furnace, with the provision that the maximum temperature
in such case should not exceed 300 to 500C. It can possibly
be set such that the temperature at the furnace inlet is
350 C while the temperature at the furnace outlet is 500 C.
If the temperature for the thermal treatment exceeds 500 C,
the infusibilized fiber is unfavorably oxidized too far;
if the temperature is less than 300C, the period of time
for thermal treatment is prolonged, or the surface oxidation
of the infusibilized fiber gets unsatisfactory. Thus,
expected effects can hardly be obtained.
The inside of the furnace for thermal treatment
should be in an oxygen-containing atmosphere. Oxidative
gas such as air, a mixed gas of air and oxygen, a mixed
gas of air and nitrogen, or a mixed gas of nitrogen and
oxygen is fed into an infusibilizing furnace.
The oxygen concentration is 5 to 80 ~, preferably 10 to
50 %. Generally, air is preferably used. In some case,
- 16 -
2 ~
a mixed gas of NOx, SOx, Cl2 and the like contained in air
may be used.
According to the present invention, the retention
time of the infusibilized fiber inside the furnace of
thermal treatment is 1 to 200 seconds, preferably 10 to
100 seconds. The retention time may be determined, depending
on the temperature of thermal treatment. ~hen the retention
time exceeds 200 seconds, the infusibilized fiber is
unfavorably oxidized too much even if the temperature of
thermal treatment is set at 300C; when the retention time
is less than one second, the infusibilized fiber is not
oxidized satisfactorily if the temperature of thermal
treatment is set at 500C. Thus, expected effects can
hardl~ be obtained.
According to the present invention, tension is also
loaded on the infusibilized fiber during the process of
thermal treatment, to effect the stretching treatment of
5 to 100 ~. Hence, the tension loaded onto the infusibilized
fiber usually is lO to 500 g per 3,000 filaments, namely
0.003 to 0.17 g per filament.
The stretching may be adjusted by the adjustment
of the dimension of tension or by the differential movement
of two or more rolls.
According to the process configuration hereinabove
mentioned, the infusibilized fiber is oxidized selectively
~3 ~ 3~
only on the surface thereof, while thermal polymerization
of the inside of the fiber by high-temperature is furthermore
facilitated, so that the infusibilized fiber composed of
a great number of filamments can acquire increased strength.
For that reason, the infusibilized fiber is oxidized prior
to the pre-carbonization only on the surface of the fiber.
Thus, the properties of the carbon fiber as a product are
not deteriorated.
According to the present invention, the degree of
agglutination of the infusibilized fiber on the surface
in a furnace of pre-carbonization is also decreased due
to the oxidization of the surface of the infusibilized
fiber.
According to the present invention, furthermore,
the infusibilized fiber is oxidized selectively only on
the surace thereof, while thermal polymerization of the
inside of the fiber by high-temperature is facilitated,
so that the infusibilized fiber can acquire increased
strength. The orientation property of the fiber is further
improved by the stretching process of the infusibilized
fiber, so the properties of the carbon fiber thus obtained
are improved.
The infusibilized fiber thus subjected to the process
of thermal treatment and stretching is transferred and fed
to a furnace for pre-carbonization, where the process of
- 18 -
pre-carbonization, namely a second-stage process of
stretching and thermal treatment, is effected in an oxygen-
containing atmosphere.
The temperature inside the furnace of pre-carbonization
is set so that the maximum temperature should he in the
range of 500 to 700 C. It may be set so as to have the
temperature environment elevating step wise from 400C,
500C to 600C, at the inlet to the outlet, the maximum
temperature reaching a temperature in the range of 500 to
700C. If the temperature for thermal treatment is above
700C, the oxidization of the pre-carbonized fiber progresses
too far, unfavorably; if the maximum temperature is less
than 500 C, the period of time for thermal treatment is
prolonged or the surface of the pre-carbonized fiber is
not satisfactorily oxidized. Thus, expected effects can
hardly be obtained.
The inside of the furnace of thermal treatment is
maintained in an atmosphere containing oxygen or a lower
concentration, by feeding, into the furnace of thermal
treatment, inert gas mixed with a small amount of oxygen
or air. The concentration of oxygen is 0.01 to 30 %,
preferably 0.05 to 10 %. As the inert gas, nitrogen gas
or argon gas can be used. Nox, SOx, water vapor,
carbonate gas, halogen gas, and the vapor of strong acids
may be used as well.
-- 19 --
---` 2~3~6~
According to the present invention, the retention
time of the fiber inside the furnace of pre-carbonization
is 20 to 300 seconds, preferably 50 to 200 seconds.
The retention time may be determined, depending on the
relation between the temperature of the thermal treatment
and the oxygen concentration.
If the oxygen content in the atmosphere containing
oxygen of a lower concentration is too less such as less
than 0.01 %, the surface of the infusibilized fiber cannot
effectively be oxidized by heating for a short period of
time during the pre-carbonization; if the content exceeds
30 % inversely, it is too much to effect selective oxidation
of the surface of the infusibilized fiber even by the thermal
treatment for a short period of time, which is disadvantageous
in that the inside of the fiber is also oxidized.
When the period of time for the thermal treatment
of the infusibilized fiber in the atmosphere containing
a lower concentration of oxygen is less than 20 seconds,
it is too short to effectively oxidize the surface of the
infusibilized fiber even if the oxygen content in the
atmosphere is increased; when it exceeds 300 seconds,
the period is too long to prevent the oxidation of the
inside of the infusibilized fiber even if the oxygen content
in the atmosphere is decreased.
According to the present invention, furthermore,
- 20 -
~3~
tension is loaded onto the fiber to effect the stretching
process of 5 to 100 %, concurrently with the therrnal
treatment. Therefore, the tension generally loaded onto
the infusibilized fiber is 20 to 1,000 g per 3,000 filaments,
namely 0.006 to 0.33 g per filament. The stretching
condition may be set by means of the adjustment of the
dimension of the tension or by means of the adjustment of
differential movement of two or more rolls.
According to the present invention, the infusibilized
fiber is heated and oxidized in the atmosphere containing
oxygen of a low concentration in the furnace of pre-carbonization
for a short period of time, whereby only the surface of
the fiber is selectively oxidized for the strengthening
of the surface while the fiber is concurrently carbonized
preliminarily, to enable further stretching process of the
infusibilized fiber in the furnace of pre-carbonization.
Thus, the degree of agglutination of the pre-carbonized
fiber is possibly reduced.
As has been mentioned insofar, the process of
stretching and thermal treatment carried out in two stages,
namely after the infusibilizing process and during the pre-
carbonizing process, can reduce the degree of agglutination
of the carbon fiber down to 30 ~, preferably down to 20%
or less. The orientation property of the fiber is simul-
taneously improved, particularly the thermal conductivity
- 21 -
2~3~
is increased, whereby the fiber of high thermal conductivity
is obtained~ The process of stretching and thermal treatment
in either one of the stages, namely one-stage process of
stretching and thermal treatment, cannot produce a pitch-
based carbon fiber of high thermal conductivity constructed
in accordance with the present inventionO
The fiber pre-carbonized in such manner is then
transferred and fed to a furnace of carbonization, where
the fiber is carbonized in the atmosphere of inert gas
the maximum temperature of which is 2,300 to 3,000 C.
According to the production method described above,
there can be obtained a high thermal conductivity pitch-
based carbon fiber having a thermal conductivity in the
axial direction of fiber of 300 to 500 W/m/K, a ratio of
stack height (Lc 002) of the crystalline structure of the
fiber/density (p) of the fiber of 70 to 180, a degree of
agglutination of 0 ~o 20 %, and a compressive strength of
0.3 to 0-5 GPa, as well as a tensile strength of 2.5 ~o
4.0 GPa and a tensile elastic modulus of 700 to 900 GPa.
~ ccording to another embodiment of the present
invention, there can be further obtained a super-high
thermal conductivity pitch-based carbon fibers having a
higher thermal conductivity. In order to obtain such
pitch carbon fiber of super-high thermal conductivity, the
pre-carbonized fiber produced in the above described manner
~ 22 -
~3~
is transferred and fed to a furnace of carbonization, where
the fiber is carbonized while being subjected to the stretching
process in the atmosphere of inert gas the ma~imum temperature
of which is 2,600 to 3,200 C.
For further explanation, the retention time of the
fiber in a furnace of carbonization should be 1 to 100
minutes, preferably 2 to 60 minu-tes. The retention time
is determined, depending on the temperature of the thermal
treatment.
According to the present embodiment, tension is
loaded onto the fiber simultaneously during the carbonization
process thereby effecting the stretching process of 1 to
30 %. Thus, the tension loaded onto the fiber is generally
150 to 60,000 g per 3,000 filaments, namely 0.05 to 20 g
per filament.
The present embodiment, as the process of
stretching and thermal treatment is carried out in three
stages, namely after the infusibilizing process, during
the pre-carbonizing process, and the stretching process
during the carbonization process, it can remarkably improve
the orientation property of the fiber, and specifically
increase the thermal conductivity distinctively, whereby
the fiber of super-high thermal conductivity is obtained.
The super-high thermal conductivity pitch-based carbon
fiber in the above configuration in accordance with the
present invention, cannot be produced by the process of stretching
- 23 -
2~3~
and thermal treatment in one or two stages.
According to *he present production method described
above, there can be obtained a super-high thermal conductivity
pitch-based carbon fiber having a thermal conductivity in
the axial direction of fiber of 500 to 1,500 W/m/K, a ratio
of stack height (Lc 002) of the crystalline structure of
the fiber/densit~ (p)of the fiber of 120 to 500, a degree
of agglutination of 0 to 30 ~, and a compressive strength
of 0~2 to 0.4 GPa, as well as a tensile strength of 2.5
to 4.5 GP a and a tensile elastic modulus of 700 to 950 GPa.
In the present Description, the properties of the
carbon fibers are determined by employing the following
measuring methods.
* Thermal conductivity
Thermal conductivity of a carbon fiber was measured
by means of laser flash method, by using as a sample the
carbon fiber bundle impregnated with epoxy resin.
* X-ray structural parameters
Parameters such as stack height (Lc 002), layer size
(La 110), and interlayer spacing (doo2), representing the
micro structure of a carbon fiber, were determined by X-ray
diffraction method.
The stack height (hc 002) represents the apparent
stack height of (002) planes in a crystal of carbon fiber.
A larger stack height (Lc 002) is generally regarded as
- 24 -
~3~
an indication of better crystallinity. ~he layer size
(La 110) represents the apparent layer size in a crystal
of carbon fiber. A larger layer size (La 110) is generally
regarded as an indication of better crystallinity.
Alternatively, the interlayer spacing (doo 2 ) represents
a interlayer spacing of (002) plane in a crystal of carbor.
fiber. A smaller interlayer spacing (doo 2 ) iS generally
regarded as an indication of better crystallinity.
After the carbon fibers were ground in a mortar,
the stack ~eight (Lc 002), layer size (La llO), and
interlayer spacing (doo 2 ) of the powdery carbon fibers
thus obtained were measured and analyzed according to
Gakushinho "Measuring Method for Lattice Constant and
Crystalline Size of Artificial Graphite". Based on the
following formulas, those parameters were calculated;
Lc 002 = K~/~cos~
La llO = K~/~'cos~'
do 0 2 = ~/2 sin~
wherein
K = l.0, ~ = 1.5418 A
~ : calGulated from (002) diffraction angle 2~
0' : calculated from (110) diffraction angle 2a
: FWHM of (002) diffraction pattern calculated with
correction;
~' : FWHM of (110) diffraction pattern calculated with
correction.
~ ~ ~ c~
* Density (p)
Density (p) was measured with a density gradient
tube.
* Degree of agglutination
Carbon fiber composed of 3,000 filaments was cut in
1.5 mm-wide sections, which were then immersed in ethanol
followed by air spraying for 30 seconds. The total number
(N) of the filaments in agglutination was counted under
microscopic observation of 20 magnification. Then, the
degree of agglutination was determined based on the following
formula;
Degree of agglutination = ~N/3,000) x 100 (~)
* Compressive strength
A sample of carbon fiber impregnated with epoxy
resin was measured according to ASTM D3410.
The method of producing a high thermal conductivity pitch-based
carbon fiber in accordance with the present invention will
now be explained in examples hereinafter.
Example 1
~ `or producing pitch fiber, carbonaceous pi~ch
containing optically anisotropic phase at the ratio of 45 ~
and having a softening point of 226 C, was used as precursor
pitch. The precursor pitch was continuously separated into
the pitch with more contents of the optically anisotropic
phase and the pitch with more contents of optically
- 26 -
-
2 ~
isotropic phase, which were then individually drawn.
The obtained pitch containing the optically anisotropic
phase more, contains 100 % of the optically anisotropic
phase. Its softening point was 270 C and the insoluble
part in quinoline was 28.0 % by weight. The pitch for
carbon fiber was passed through a melt spinning machine
with a spinning no~le having 500 pores Ithe pore size of
the nozzle, 0.3 mm in diameter), and was spun at 335 C.
The 500 filaments thus spun were nearly bundled with
an air sucker and was then introduced to an oiling roller.
By feeding a treatment oil to the filaments at a ratio of
about 0.2 % by weight, a pitch fiber composed of 500 filaments
was formed. As the treatment oil, methylphenyl polysiloxane
of a ~-iscosity of 14 cst at 25 C was used.
The pitch fiber was wound onto a stainless-steel
bobbin of a 210 mm diameter and a 200 mm width, and was
spun at a winding velocity of about 500 m/min for 10 minutes.
The traverse pitch per one rotation of the bobbin was 10 mm.
No break of fiber occurred during the spinning.
Six of the bobbins wound with the pitch fiber were
then unwound, and were then bundled while adding a heat-
resistance treatment oil by using an oiling roller, to form
the pitch fiber composed of 3,000 filaments. Then, the
formed fiber was wound onto another stainless bobbin.
As the treatment oil during the bundling, methylphenyl
- 27 -
~3~
polysiloxane of 40 cst at 25 C (the content of phenyl group
is 45 mol ~) was used. The added amount thereof was 0.5 %
to the yarn.
While unwinding from the bobbin, the pitch fiber
was continuously introduced in linear form into a continuously
infusibilizing furnace in oxygen-rich atmosphere (oxygen/-
nitrogen = 60/40) having such temperature gradient as the
furnace inlet temperature of 180 C and the maximum
temperature of 295 C. The rate of elevating temperature
was 6 C/min, and the period of time for the infusibilizing
process was 19 minutes. The tension loaded onto the fiber
was 0.007 g per filament which corresponds to 20 g to a
fiber composed of 3,000 filaments. The oxygen concentration
in the infusibilized fiber after the infusibilizing process
was 9O5 ~ by weight.
During the infusibilizing process, the pitch fiber
was smoothly unwound from the bobbin, with no break of the
fiber in the infusibilizing furnace. Thus, the infusibilizing
process progressed in such smooth manner~
The infusibilized fiber obtained in such manner was
fed to the furnace of thermal treatment maintained at 450 C,
prior to the supply thereof to the furnace of pre-carbonization.
Tension of 0.007 g per filament was loaded onto the fiber.
Air was introduced inside the furnace.
In the above configuration, the period of time
- 28 -
- 2~3~
required for the thermal treatment of the infusibilized
fiber was 25 seconds.
The thermal treatment was smoothly effected with
no fiber break in the furnace of thermal treatment.
The stretching ratio of the fiber at thermal treatment
was 20 %.
The fiber thermally processed in oxygen-containing
atmosphere was continuously introduced in linear form into
a furnace of pre-carbonization in oxygen-containing
atmosphere (oxygen/nitrogen = 5/95) having such temperature
gradient as the furnace inlet temperature of 400 C and
the maximum temperature of 600 C. Tension of 0~017 g per
filament was loaded onto the fiber. The stretching ratio
was 15 %. The period of time for pre-carbonization was
25 secondsO Continuous treatment was effected for 24 hours,
but with no break of the fiber inside the furnace.
The pre~carbonized fiber was heated up to 2,500 ~
in argon-gas atmosphere, to obtain carbon fiber. The fiber
(filament~ diameter was 8.7 ~m.
The characteristic properties of the carbon fiber
are shown in Table 1.
Example 2
By employing the same materials and method as in
Example 1, an infusibilized fiber was produced.
~s in Example 1, the infusibilized fiber was fed to a
- 29 -
furnace of thermal treatment, main-tained at 450 C, prior
to the supply thereof to a furnace of pre-carbonization.
Tension of 0.007 g per filament was loaded onto the fiber,
which was then subjected to thermal treatment for 25 seconds.
Air was introduced inside the furnace.
The thermal treatment was smoothly effected with
no fiber break in the furnace of thermal treatment.
The stretching ratio of the fiber at thermal treatment was
20 %.
The fiber thermally processed in oxygen-containing
atmosphere was continuously introduced in linear form into
a furnace of pre-carbonization in oxygen-containing atmosphere
(oxygen/nitrogen = 5/95) having such temperature gradient
as the furnace inlet temperature of 400 C and the maximum
temperature of 600 C. Differently from Example 1, tension
of 0.067 g per filament was loaded onto the fiber.
The stretching ratio was 19~. The period of time for pre-
carbonization was 25 seconds. Continuous treatment was
effected for 24 hours, but without any break of fiber
inside the furnace.
The pre-carbonized fiber was heated up to 2,800 C
in argon-gas atmosphere, to obtain carbon fiber.
The fiber (filament) diameter was 8.4 ~m.
The characteristic properties of the carbon fiber
are shown in Table 1.
- 30 -
3~
E r- ~;r
E -- a) c~
'~4 C~
C
O
0 ~ ~
U ,_1 0 0 O O o ~o
O c V (~ r. a~
Ul f~
~1
V
~ ~ v r~ a~ ~ o
C V ~
E~ ~n
_ :~` _
~.C <~
E v O o o O
UU)
C
O O
'v ~
0~ ~.
e '~ ~ ~ ~ ~
~ ~ 3
..~
_, I C ~ ~ o o o o
0 R ") 6 E
0 0 X ~ ~ ~1 ~ ~ .
_.. . _
~ 3
U o
c u V
v E v h
V C) C C~
u) ~ O E r~ r r.
_ C -I o o o
( S u o o O
C E O O o
In ' ~a ~O o c~ I
0 ~
_ C ~
C O O O O O
'11 ~V, ''V~ N N I ~
C VC V 1.1
U V V
E~ ,~0 ~ o o o
~ d~ o o o
0,1 l
~4 ~ E~ o o o
_
,I N 'V _ ''I ~ -- 3 1
~ ~ a
x ~ u u
~3~
Comparative Example 1
By employing the same materials and method as in
Example 1, an infusibilized fiber was producedO Without
effecting the thermal treatment of the infusibilized fiber
prior to pre-carbonization~ the infusibilized fiber was
directly introduced in linear form continuously to a furnace
of pre-carbonization in oxygen-containing atmosphere
(oxygen/nitrogen -- 5/95) for pre-carbonization. The furnace
of pre-carbonization had such temperature gradient as the
furnace inlet temperature of 400C and the maximum temperature
of 900C. The process of pre-carbonization was continued
over 250 seconds. Tension of 0.017 g per filament was
loaded onto the fiber. The stretching ratio then was 15 %.
The pre-carbonized fiber was heated up to 2,500 C
in argon-gas atmosphere, to obtain carbon fiber. The fiber
(filament~ diameter was 9.5 ~m.
~ l~he characteristic properties of the carbon fiber
are shown in Table 1.
Comparative Example 2
By employing the same materials and method as in
Example 1, an infusibilized fiber was produced. As in
Example 1, the infusibilized fiber was fed to a furnace
of thermal treatment, maintained at 450 C. Tension of
0.007 g per filament was loaded onto the fiber, which was
then subjected to thermal treatment for 25 seconds.
- 32 -
2 ~
Air was introduced inside the furnace. The fiber stretching
ratio at the thermal treatment was 20 %.
Differently from Example 1, the fiber thermally
processed in oxygen-containing atmosphere was directly
heated up to 2,500 C in argon-gas atmosphere, to obtain
carbon fiber. The fiber (filament) diameter was 9.2 ~m.
The characteristic properties of the carbon fiber
are shown in Table 1.
Example 3
By employing the same materials and method as in
Example 1, a pre-carbonized fiber was produced.
The pre-carbonized fiber was cor.tinuously fed in
linear form to a furnace of carbonization in argon-gas
atmosphere at the maximum temperature of 2,800 C.
Tension of 0.3 g per filament was loacled onto the fiber.
The stretching ratio was 9 %. The period of time for
carbonization was 10 minutes. The fiber (filament)diameter
was 8.3 ~m.
The characteristic properties of the carbon fiber
are shown in ~able 2.
Example 4
By employing the same materials and method as in
Example 1, an infusibilized fiber was produced.
As in Example 1, the infusibilized fiber was fed to a
furnace of thermal treatment maintained at 450 C, prior to
~3~
the supply thereof to a furnace of pre-carbonization.
Tension of 0.007 g per filament was loaded onto the fiber,
which was then subjected to thermal treatment for 25 seconds.
Air was introduced inside the furnace.
The thermal treatment was smoothly effected with
no fiber break in the furnace of thermal treatment.
The stretching ratio of the fiber at thermal treatment was
20 %.
The fiber thermally processed in oxygen-containing
atmosphere was continuously introduced in linear form into
a furnace of pre-carbonization in oxygen-containing
atmosphere (oxygen/nitrogen = 5/95) having such temperature
gradient as the furnace inlet temperature of 400 C and
the maximum temperature of 600 C. Differently from Example 1,
tension of 0.06~ g per filament was loaded onto the fiber.
The stretching ratio was then 19%. The period of time for
pre-carbonization was 25 seconds. Continuous treatment
was effected for 24 hours, ~ut with no break of fiber
inside the furnace.
The pre-carbonized fiber was continuously introduced
in linear form to a furnace of carbonization in argon-gas
atmosphere at the maximum temperature of 3,000 C.
Tension of 0.4 g per filament was loaded onto the fiber.
The stretching ratio was 10 %. The period of time for
carbonization was 12 minutes. The fiber (filament) diameter
- 34 -
2~3~3~
was 8~1 ~m.
The characteristic properties of the carbon ~iber
are shown in Table 2.
- 35 -
~ l ~ i~
_1 ~ E ~ 3 & !~ ~
_I O ~O G 1`
~'v
~C
r~
~ C O O O
" a~n
v a ,~ _
a o~
O ~n O O
JO _ r~ _
" V ~ o o o
_ _
O ,U, O C~ O ~
o ~ a . .
o c~ o o o
' e o o o
c e e cc o
a ~ E~ ~ rlN
_ C~
U O.n o~ v~
C C V ~
V8 C
[ . _~ 19 O O O
~ ~ 5 ~ o o o
o~ .~ ~ o ~ o~
~: ~ _
c~
~a u o o o
a v v N r~l I
C V V 1<
'C V O~
v a
v ~ o 8 r r~
~ ~ 5 ~ o o
, ~ 8 ~ ~ ~
_ _ C~ ~
a u ~ ~ ~ 3 6
~i eD'
~, x 9
~3~
Comparative Example 3
By employing the same materials and method as in
Example 1, an infusibilized fiber was produced. Without
effecting the thermal treatment of the infusibilized fiber
prior to pre-carbonization, the infusibilized fiber was
directly introduced in linear form continuously to a
furnace of pre-carbonization in oxygen~containing atmosphere
(oxygen/nitrogen = 5/95) for pre-carbonization.
The furnace of pre-carbonization had such temperature gradient
as the furnace inlet temperature of 400C and the maximum
temperature of 900C. The process of pre-carbonization
was continued over 250 seconds. Tension of 0.017 g per
filament was loaded onto the fiber. The stretching ratio
then was 15 %.
The pre-carbonized fiber was continuously introduced
into a furnace of carbonization at the maximum temperature
of 2,800 C in argon-gas atmosphere. Tension of 0.3 g per
filament was loaded onto the fiber. The stretching ratio
was 8 ~. The period of time for carbonization was 10 minutes.
The fiber (filament) diameter was 9.1 ~m.
The characteristic properties of the carbon fiber
are shown in Table 2.
53~
Effects of the Invention:
As has been described above, the high thermal
conduct~vity pitch-type carbon fiber in accordance with
the present invention has characteristic features, such
that the thermal conductivity is extremely high without
causing deterioration of the tensile strength and tensile
elastic modulus thereof, that the compressive strength is
also high, and that the yarn handleability is excellent.
- 38 -
