U.S. patent application number 16/374982 was filed with the patent office on 2019-08-01 for acrylonitrile swollen fiber for carbon fiber, precursor fiber bundle, stabilized fiber bundle, carbon fiber bundle and productio.
This patent application is currently assigned to MITSUBISHI CHEMICAL CORPORATION. The applicant listed for this patent is MITSUBISHI CHEMICAL CORPORATION. Invention is credited to Yasuyuki FUJII, Hiroshi HASHIMOTO, Masahiro HATA, Akito HATAYAMA, Akiyoshi KOGAME, Hiroko MATSUMURA, Takahiro OKUYA, lsao OOKI, Naoki SUGIURA, Kazunori SUMIYA, Kouki WAKABAYASHI.
Application Number | 20190233975 16/374982 |
Document ID | / |
Family ID | 43308935 |
Filed Date | 2019-08-01 |
United States Patent
Application |
20190233975 |
Kind Code |
A1 |
HASHIMOTO; Hiroshi ; et
al. |
August 1, 2019 |
ACRYLONITRILE SWOLLEN FIBER FOR CARBON FIBER, PRECURSOR FIBER
BUNDLE, STABILIZED FIBER BUNDLE, CARBON FIBER BUNDLE AND PRODUCTION
METHODS THEREOF
Abstract
Provided is a carbon fiber bundle for obtaining a
fiber-reinforced plastic having high mechanical characteristics. An
acrylonitrile swollen fiber for a carbon fiber having openings of
10 nm or more in width in the circumference direction of the
swollen fiber at a ratio in the range of 0.3 openings/.mu.m.sup.2
or more and 2 openings/.mu.m.sup.2 or less on the surface of the
swollen fiber, and the swollen fiber is not treated with a
finishing oil agent. A precursor fiber obtained by treating the
swollen fiber with a silicone-based finishing oil agent has a
silicon content of 1700 ppm or more and 5000 ppm or less, and the
silicon content is 50 ppm or more and 300 ppm or less after the
finishing oil agent is washed away with methyl ethyl ketone by
using a Soxhlet extraction apparatus for 8 hours. The fiber is
preferably an acrylonitrile copolymer containing acrylonitrile in
an amount of 96.0 mass % or more and 99.7 mass % or less and an
unsaturated hydrocarbon having at least one carboxyl group or ester
group in an amount of 0.3 mass % or more and 4.0 mass % or
less.
Inventors: |
HASHIMOTO; Hiroshi;
(Otake-shi, JP) ; SUGIURA; Naoki; (Toyohashi-shi,
JP) ; FUJII; Yasuyuki; (Otake-shi, JP) ;
MATSUMURA; Hiroko; (Otake-shi, JP) ; OKUYA;
Takahiro; (Otake-shi, JP) ; OOKI; lsao;
(Otake-shi, JP) ; HATA; Masahiro; (Toyohashi-shi,
JP) ; WAKABAYASHI; Kouki; (Toyohashi-shi, JP)
; KOGAME; Akiyoshi; (Otake-shi, JP) ; SUMIYA;
Kazunori; (Otake-shi, JP) ; HATAYAMA; Akito;
(Toyohashi-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MITSUBISHI CHEMICAL CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
MITSUBISHI CHEMICAL
CORPORATION
Tokyo
JP
|
Family ID: |
43308935 |
Appl. No.: |
16/374982 |
Filed: |
April 4, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13377207 |
Dec 9, 2011 |
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PCT/JP2010/059827 |
Jun 10, 2010 |
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16374982 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D01D 5/247 20130101;
D01F 6/18 20130101; Y10T 428/2975 20150115; D01F 9/22 20130101;
Y10T 428/298 20150115; Y10T 428/2978 20150115 |
International
Class: |
D01F 6/18 20060101
D01F006/18; D01F 9/22 20060101 D01F009/22; D01D 5/247 20060101
D01D005/247 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 10, 2009 |
JP |
2009-139337 |
Claims
1-3. (canceled)
4. A method of producing a swollen fiber, comprising: (i) preparing
a dope at a temperature of 50.degree. C. or more and 70.degree. C.
or less by dissolving an acrylonitrile-based copolymer, which is
obtained by copolymerizing acrylonitrile in an amount of 96.0 mass
% or more and 99.7 mass % or less and an unsaturated hydrocarbon
having at least one carboxyl group or ester group in an amount of
0.3 mass % or more and 4.0 mass % or less, as essential components,
in an organic solvent in a concentration in the range of 20 mass %
or more and 25 mass % or less; (ii) obtaining a coagulated fiber
bundle containing the organic solvent by ejecting the dope from
ejection holes into the air by use of a dry-wet spinning method,
followed by coagulating in a coagulation bath constituted of an
aqueous solution containing an organic solvent in a concentration
of 78.0 mass % or more and 82.0 mass % or less, at a temperature of
-5.degree. C. or more and 20.degree. C. or less; (iii) drawing the
coagulated fiber bundle in the air at a ratio in the range of 1.0
time or more and 1.25 times or less, followed by further drawing in
a warm aqueous solution containing an organic solvent, a total draw
ratio of both drawing processes being 2.6 times or more and 4.0
times or less; and (iv) subsequently removing the solvent with warm
water and further drawing in hot water at a ratio of 0.98 times or
more and 2.0 times or less.
5. The method according to claim 4, wherein the organic solvent is
either dimethyl formamide or dimethyl acetamide.
6. The method according to claim 4, wherein a draw ratio in the
warm aqueous solution is 2.5 times or more and 4.0 times or
less.
7-8. (canceled)
9. A method of producing a precursor fiber bundle for a carbon
fiber, comprising applying a finishing oil agent containing
silicone compounds as main components to a bundle of the swollen
fiber obtained by claim 4, in an amount of 0.8 mass % or more and
1.6 mass % or less based on 100 mass % of the swollen fiber,
followed by drying and then drawing by a heat drawing method or a
steam drawing method at a ratio in the range of 1.8 times or more
and 6.0 times or less.
10. The method according to claim 9, wherein as the silicone
compound, an amino-modified silicone compound satisfying the
following conditions (1) and (2) is used: (1) kinematic viscosity
at 25.degree. C. is 50 cSt or more and 5000 cSt or less, and (2)
amino equivalent mass is 1,700 g/mol or more and 15,000 g/mol or
less.
11. A method of producing a precursor fiber bundle for a carbon
fiber by applying a finishing oil agent containing silicone
compounds as main components to a bundle of an acrylonitrile
swollen fiber for a carbon fiber having openings of 10 nm or more
in width in the circumference direction of the swollen fiber at a
ratio in the range of 0.3 openings/.mu.m.sup.2 or more and 2
openings/.mu.m.sup.2 or less on the surface of the swollen fiber,
and that is not treated with a finishing oil agent.
12. A method of producing a stabilized fiber bundle comprising
feeding the precursor fiber bundle obtained by the method according
to claim 11 to a hot-air circulation type oven for stabilization at
a temperature of 220 to 260.degree. C. for 30 minutes or more and
100 minutes or less, thereby applying heat treatment at an
extension rate of 0% or more and 10% or less under an oxidizing
atmosphere, and the method satisfying the following conditions: (1)
intensity ratio (B/A) of peak A (2.theta.=25.degree.) and peak B
(2.theta.=17.degree.) in the equatorial-line direction, which is
determined by wide angle x-ray diffraction measurement of the fiber
bundle, is 1.3 or more, (2) orientation degree of peak B is 80% or
more, (3) orientation degree of peak A is 79% or more, and (4)
density is 1.335 g/cm.sup.3 or more and 1.360 g/cm.sup.3 or
less.
13. A method of producing a stabilized fiber bundle comprising
feeding a precursor fiber bundle to a hot-air circulation type oven
for stabilization at a temperature of 220 to 260.degree. C. for 30
minutes or more and 100 minutes or less, thereby applying heat
treatment at an extension rate of 0% or more and 10% or less under
an oxidizing atmosphere, and the method satisfying the following
conditions: (1) intensity ratio (B/A) of peak A
(2.theta.=25.degree.) and peak B (2.theta.=17.degree.) in the
equatorial-line direction, which is determined by wide angle x-ray
diffraction measurement of the fiber bundle, is 1.3 or more, (2)
orientation degree of peak B is 80% or more, (3) orientation degree
of peak A is 79% or more, and (4) density is 1.335 g/cm.sup.3 or
more and 1.360 g/cm.sup.3 or less, wherein, prior to the feeding,
the precursor fiber bundle is obtained by copolymerizing
acrylonitrile in an amount of 96.0 mass % or more and 99.7 mass %
or less and an unsaturated hydrocarbon having at least one carboxyl
group or ester group in an amount of 0.3 mass % or more and 4.0
mass % or less, as essential components, and having a silicon
content of 1700 ppm or more and 5000 ppm or less when the fiber
bundle is treated with a finishing oil agent containing silicone
compounds as main components, wherein the silicon content is 50 ppm
or more and 300 ppm or less after the finishing oil agent is washed
away with methyl ethyl ketone by using a Soxhlet extraction
apparatus for 8 hours.
14. The method of producing the stabilized fiber bundle according
to claim 12, wherein extension treatment is separately performed in
at least three sets of conditions: an extension rate of 3.0% or
more and 8.0% or less at a fiber density in the range of 1.200
g/cm.sup.3 or more and 1.260 g/cm.sup.3 or less; an extension rate
at 0.0% or more and 3.0% or less at a fiber density in the range of
1.240 g/cm.sup.3 or more and 1.310 g/cm.sup.3 or less; and an
extension rate of -1.0% or more and 2.0% or less at a fiber density
in the range of 1.300 g/cm.sup.3 or more and 1.360 g/cm.sup.3 or
less.
15-20. (canceled)
21. A method of producing a carbon fiber bundle, comprising
treating the precursor fiber bundle obtained by the method
according to claim 9 with heat under an oxidizing atmosphere to
obtain a stabilized fiber bundle having a density of 1.335
g/cm.sup.2 or more and 1.355 g/cm.sup.3 or less; then performing
heating in a first carbonization furnace having a temperature
gradient of 300.degree. C. or more and 700.degree. C. or less under
an inert atmosphere while extending the extension rate to a rate of
2% or more and 7% or less for 1.0 minute or more to 3.0 minutes or
less; and subsequently performing a heat treatment in at least one
carbonization furnace having a temperature gradient from
1000.degree. C. to a desired temperature under an inert atmosphere
while extending the extension rate to a rate of -6.0% or more and
2.0% or less for 1.0 minute or more and 5.0 minutes or less.
Description
TECHNICAL FIELD
[0001] The present invention relates to a carbon fiber bundle that
has excellent mechanical characteristics and that can be used to
obtain a high-quality and high-performance fiber-reinforced plastic
particularly for airplane use, industrial use, etc., and the
invention relates to a swollen fiber, a precursor fiber bundle and
a stabilized fiber bundle for use in producing the same.
BACKGROUND ART
[0002] In order to improve the mechanical characteristics of
resin-base molded products, a resin has been commonly used in
combination with a fiber serving as a reinforcement material. In
particular, a composite molding material formed of a carbon fiber
that is excellent in specific strength and specific elasticity in
combination with a high-performance resin develops extremely
excellent mechanical characteristics. Because of this, such a
molding material has been willingly used as a constructional
material for airplanes, high speed moving bodies, etc. Furthermore,
there is a demand for developing a material that is stronger and
that has higher rigidity as well as having excellent specific
strength and specific rigidity. Given these circumstances, the
desire is for further improvement of the performance of carbon
fiber, such as improved strength and elastic modulus.
[0003] What is required in order to produce such a high performance
carbon fiber includes obtaining an acrylonitrile precursor fiber
bundle for a carbon fiber having excellent strength and carbonizing
the precursor fiber bundle under optimal conditions. In particular,
research has been conducted for densifying a precursor fiber bundle
structure, completely removing points from which defects start, and
finding carbonizing conditions under which defects are rarely
formed. For example, Patent Literature 1 proposes a method of
drawing a coagulated fiber that still contains a solvent in a
solvent-containing drawing bath, thereby improving uniformity in
structure and orientation, in order to obtain a precursor fiber
bundle by a dry-wet spinning method. Drawing a coagulated fiber in
a bath containing a solvent is a method commonly known as a solvent
drawing technique that enables a stable drawing process by using
solvent plasticization. Accordingly, this method is considered as
an extremely excellent technique for obtaining a fiber that has
high uniformity in structure and orientation. However, if a fiber
bundle that is in a swollen state due to the presence of a solvent
is drawn, the solvent within a filament is rapidly squeezed out
from the filament simultaneously upon drawing. The resultant
structure of the filament tends to be less dense and thus a desired
filament that has a dense structure cannot be obtained. As a
result, it has been difficult to obtain a carbon fiber bundle
having high strength.
[0004] Furthermore, Patent Literature 2, which pays attention to
fine pores distributed in a coagulated fiber, proposes a technique
for obtaining a precursor fiber in which excellent strength is
developed by dry densification of a coagulated fiber that has a
high-dense structure. The fine pore distribution, which is obtained
by a mercury press-in method, reflects the bulk state from the
surface layer to the interior of the filament. This is an extremely
excellent method for evaluating the overall density of a fiber
structure. From the precursor fiber bundle that has at least a
certain level density as a whole, a very strong carbon fiber can be
obtained in which defect formation is prevented. However,
observation of fractures in the carbon fiber shows that fractures
have originated from near the surface layer at an extremely high
ratio. This means that a defect is present near the surface layer.
In other words, this technique is insufficient for manufacturing a
precursor fiber bundle that is excellent in density near the
surface layer.
[0005] Patent Literature 3 proposes a method for manufacturing an
acrylonitrile-based precursor fiber bundle that is not only high in
whole density but also that is extremely high in surface density.
Furthermore, Patent Literature 4 proposes, taking into
consideration that a finishing oil agent enters the surface-layer
portion of a fiber and inhibits densification, a technique for
preventing permeation of a finishing oil agent by focusing on
microscopic voids of the surface-layer portion. However, a
technique for preventing entry of a finishing oil agent and a
technique for preventing defect formation are both difficult to put
into practical use since very complicated steps are required.
Therefore, in the techniques discussed above, the effect of stably
preventing the entry of a finishing oil agent into the surface
layer portion is insufficient and the effect of reinforcing a
carbon fiber is still far from a sufficient level.
CITATION LIST
Patent Literature
Patent Literature 1: JP05-5224A
Patent Literature 2: JP04-91230A
Patent Literature 3: JP06-15722B
Patent Literature 4: JP11-124744A
SUMMARY OF INVENTION
Technical Problem
[0006] An object of the present invention is to provide a carbon
fiber bundle for obtaining fiber-reinforced plastic that has high
mechanical characteristics.
Solution to Problem
[0007] The present inventors conducted research with the view to
attaining the aforementioned object. They clarified proper forms
and properties of an acrylonitrile swollen fiber for a carbon fiber
and precursor fiber bundle; at the same time, they found that a
swollen fiber having a dense inner structure and capable of
preventing permeation of a finishing oil agent near a surface layer
can be obtained by optimizing coagulation conditions and drawing
conditions for spun fiber.
[0008] The aforementioned object can be attained by the following
inventions.
[0009] A first invention is directed to an acrylonitrile swollen
fiber for a carbon fiber having openings of 10 nm or more in width
in the circumference direction of the swollen fiber at a ratio in
the range of 0.3 openings/.mu.m.sup.2 or more and 2
openings/.mu.m.sup.2 or less on the surface of the swollen fiber,
in which the swollen fiber is not treated with a finishing oil
agent.
[0010] A second invention is directed to a method of producing a
swollen fiber, including
[0011] [1] a step of preparing a dope at a temperature of
50.degree. C. or more and 70.degree. C. or less by dissolving an
acrylonitrile-based copolymer, which is obtained by copolymerizing
acrylonitrile in an amount of 96.0 mass % or more and 99.7 mass %
or less and an unsaturated hydrocarbon having at least one carboxyl
group or ester group in an amount of 0.3 mass % or more and 4.0
mass % or less, as essential components, in an organic solvent in a
concentration in the range of 20 mass % or more and 25 mass % or
less,
[0012] [2] a step of obtaining a coagulated fiber bundle containing
the organic solvent by ejecting the dope from ejection holes into
the air by use of a dry-wet spinning method, followed by
coagulating in a coagulation bath constituted of an aqueous
solution containing an organic solvent in a concentration of 78.0
mass % or more and 82.0 mass % or less, at a temperature of
-5.degree. C. or more and 20.degree. C. or less,
[0013] [3] a step of drawing the coagulated fiber bundle in the air
at a ratio in the range of 1.0 time or more and 1.25 times or less,
followed by further drawing in a warm aqueous solution containing
an organic solvent, wherein a total draw ratio in both drawing
processes is 2.6 times or more and 4.0 times or less, and
[0014] [4] a step of subsequently removing the solvent with warm
water and further drawing in hot water at a ratio of 0.98 times or
more and 2.0 times or less.
[0015] A third invention is directed to a precursor fiber bundle
for a carbon fiber formed of an acrylonitrile copolymer, which is
obtained by copolymerizing acrylonitrile in an amount of 96.0 mass
% or more and 99.7 mass % or less and an unsaturated hydrocarbon
having at least one carboxyl group or ester group in an amount of
0.3 mass % or more and 4.0 mass % or less, as essential components,
and having a silicon content of 1700 ppm or more and 5000 ppm or
less when the fiber bundle is treated with a finishing oil agent
containing silicone compounds as main components, wherein the
silicon content is 50 ppm or more and 300 ppm or less after the
finishing oil agent is washed away with methyl ethyl ketone by
using a Soxhlet extraction apparatus for 8 hours.
[0016] A fourth invention is directed to a method of producing a
precursor fiber bundle for a carbon fiber including applying a
finishing oil agent containing silicone compounds as main
components to a bundle of the swollen fiber in an amount of 0.8
mass % or more and 1.6 mass % or less based on 100 mass % of the
swollen fiber, followed by drying and then drawing by a heat
drawing method or by a steam drawing method at a ratio in the range
of 1.8 times or more and 6.0 times or less.
[0017] A fifth invention is directed to a method of producing a
stabilized fiber bundles including feeding the precursor fiber
bundle to a hot-air circulation type oven for stabilization at a
temperature of 220 to 260.degree. C. for 30 minutes or more and 100
minutes or less, thereby applying heat treatment at an extension
rate of 0% or more and 10% or less under an oxidizing atmosphere,
the method satisfying the following 4 conditions:
(1) intensity ratio (B/A) of peak A (2.theta.=25.degree.) and peak
B (2.theta.=17.degree.) in the equatorial-line direction, which is
determined by wide angle x-ray diffraction measurement of the fiber
bundle, is 1.3 or more, (2) orientation degree of peak B is 80% or
more, (3) orientation degree of peak A is 79% or more and (4)
density is 1.335 g/cm.sup.3 or more and 1.360 g/cm.sup.3 or
less.
[0018] A sixth invention is directed to a carbon fiber bundle,
wherein the strength of a strand impregnated with a resin is 6000
MPa or more, the strand elastic modulus measured by an ASTM method
is 250 to 380 GPa, the ratio of the major axis and the minor axis
(major axis/minor axis) of a cross section of a single fiber
perpendicular to the fiber-axis direction is 1.00 to 1.01, the
diameter of a single fiber is 4.0 .mu.m to 6.0 .mu.m, and the
number of voids having a diameter of 2 nm or more and 15 nm or less
present in the cross section of a single fiber perpendicular to the
fiber-axis direction is 1 or more and 100 or less.
[0019] A seventh invention is directed to a method of producing a
carbon fiber bundle including treating the precursor fiber bundle
with heat under an oxidizing atmosphere to obtain a stabilized
fiber bundle having a density of 1.335 g/cm.sup.3 or more and 1.355
g/cm.sup.3 or less; then performing heating in a first
carbonization furnace having a temperature gradient of 300.degree.
C. or more and 700.degree. C. or less under an inert atmosphere
while extending the extension rate to a rate of 2% or more and 7%
or less for 1.0 minute or more to 3.0 minutes or less; and
subsequently performing a heat treatment in at least one
carbonization furnace having a temperature gradient from
1000.degree. C. to a desired temperature under an inert atmosphere
while extending the extension rate to a rate of -6.0% or more and
2.0% or less for 1.0 minute or more and 5.0 minutes or less.
Advantageous Effects of Invention
[0020] The swollen fiber of the present invention is capable of
preventing silicone oil serving as main components of a finishing
oil agent from permeating into a surface layer portion of a
precursor fiber. The carbon fiber bundle, which is obtained by
subjecting the precursor fiber bundle to stabilization and
carbonization treatment, has excellent mechanical performance and
can provide a fiber-reinforced plastic having high mechanical
characteristics.
DESCRIPTION OF EMBODIMENTS
[0021] In the present invention, the coagulated fiber refers to a
fiber that is undergoing processing and that is removed from a
coagulant and not yet subjected to drawing treatment. The swollen
fiber refers to a fiber that is undergoing processing and that is
obtained by applying drawing treatment and washing treatment to a
coagulated fiber, in other words, a fiber that is undergoing
processing before finishing oil agent attachment and dry treatment
are applied.
[Swollen Fiber]
[0022] The acrylonitrile swollen fiber for a carbon fiber
(hereinafter appropriately referred to as "swollen fiber") of the
present invention has openings of 10 nm or more in width in the
circumferential direction of a fiber within the ratio in the range
of 0.3 openings/.mu.m.sup.2 or more and 2 openings/.mu.m.sup.2 or
less on the surface of a single fiber before oil finishing
treatment is applied. The swollen fiber, to which a finishing oil
agent containing silicone compounds is applied, is dried and is
then subjected to a drawing step to provide a precursor fiber
bundle. Since the swollen fiber has such a surface, permeation of
the oil components into the swollen-fiber surface layer portion can
be significantly prevented.
[0023] As the polymer constituting a swollen fiber, an
acrylonitrile-based copolymer is preferred, which contains an
acrylonitrile unit (96.0 mass % or more and 99.7 mass % or less)
and an unsaturated hydrocarbon unit having at least one carboxyl
group or ester group (0.3 mass % or more and 4.0 mass % or less) as
essential components. Since the content of acrylonitrile unit is
set to be 96.0 mass % or more and 99.7 mass % or less, structural
irregularity of a ladder polymer formed by a stabilization reaction
can be reduced. Consequently, during the following high-temperature
treatment, a decomposition reaction can be prevented to provide a
dense carbon fiber having few defects, which lower strength.
Furthermore, the unsaturated hydrocarbon component having a
carboxyl group or an ester group is known to serve as a starting
point of a stabilization reaction in a stabilization step. If the
content thereof is set to be 0.3 mass % or more and 4.0 mass % or
less, stabilized fiber suitable for obtaining a carbon fiber at
high yield, which is formed of a Graphene laminate structure having
few structural irregularity and defects, can be obtained.
[0024] The swollen fiber can be evaluated for whether it has a
surface layer portion capable of preventing permeation of a
finishing oil agent component by applying a predetermined amount of
a finishing oil agent containing predetermined silicone-based
compounds, applying dry densification to it, extracting and washing
away the finishing oil agent with methyl ethyl ketone for 8 hours,
and quantifying the remaining silicone-based compounds.
[Evaluation of Permeability of Swollen Fiber with Finishing Oil
Agent]
[0025] The permeability of a swollen fiber with a finishing oil
agent can be evaluated as follows:
[0026] First, the following (1) amino-modified silicone oil and (2)
an emulsifier are blended and subjected to a phase-transfer
emulsification process to prepare an aqueous dispersion (a
water-based finishing oil agent for fibers). The water based
finishing oil agent for fibers is applied onto a swollen fiber.
[0027] (1) Amino-modified silicone; KF-865 (manufactured by
Shin-Etsu Chemical Co., Ltd., mono amino modified side-chain type,
kinematic viscosity: 110 cSt (25.degree. C.), amino equivalent
mass: 5,000 g/mol): 85 mass %,
[0028] (2) Emulsifier; NIKKOL BL-9EX (manufactured by Nikko
Chemicals Co., Ltd., POE (9) lauryl ether): 15 mass %.
[0029] Subsequently, a dry process is performed by a dry roll to
completely vaporize water and the swollen fiber is drawn twofold
between heated rolls. In this manner, a fiber bundle containing
silicon in an amount of 1700 ppm or more and 5000 ppm or less
determined by a fluorescent X-ray apparatus is obtained. Then, the
fiber bundle, from which the finishing oil agent is extracted and
washed with methyl ethyl ketone in a Soxhlet extraction apparatus
for 8 hours, is measured for silicon content by the fluorescent
X-ray apparatus.
[0030] For the swollen fiber of the present invention, the silicon
content (residual amount), after finishing oil agent is extracted
and washed, is preferably 50 ppm or more and 300 ppm or less. This
value is more preferably 50 ppm or more and 200 ppm or less.
[0031] The silicon content of more than 300 ppm in the fiber
bundle, after finishing oil agent is extracted and washed, means
that the surface layer portion, which prevents permeation of a
finishing oil agent component into the surface layer portion, does
not have sufficient density. The resultant carbon fiber obtained
through a carbonization step will have many voids in the surface
layer portion. As a result, a desired high-strength carbon fiber
cannot be obtained. In contrast, the silicon content of less than
50 ppm means that the amount of finishing oil agent that permeates
into the surface layer portion of a swollen fiber is extremely low.
This is considered because a highly density skin layer is formed in
the surface layer portion of a fiber in a coagulation bath.
[0032] Furthermore, the swollen fiber of the present invention more
preferably has a swelling degree of 80 mass % or less, which is
measured in accordance with the method, i. e., [2. Method of
measuring swelling degree of swollen fiber], which will be
described later. The swelling degree of more than 80 mass % means
that the density of the inner-layer structure of a swollen fiber
slightly decreases. In this case, even if formation of defects is
successfully prevented in the surface layer portion, the
possibility of forming defects in an inner layer portion is high.
As a result, a carbon fiber having high mechanical performance
cannot be obtained. A further preferable swelling degree is 75 mass
% or less.
[0033] Furthermore, the density of swollen fiber can also be
evaluated by measurement of a fine pore distribution within a
fiber. The average fine pore size of the swollen fiber of the
present invention is 55 nm or less and the total fine pore volume
is preferably 0.55 ml/g or less. The average fine pore size is more
preferably 50 nm or less and further preferably 45 nm or less.
Furthermore, the total fine pore volume is more preferably 0.50
ml/g or less and further preferably 0.45 ml/g or less. Such a
swollen fiber has no large voids within the fiber, and further, the
ratio occupied by voids is low. Thus, the fiber is dense. If a
dense skin layer is formed in a fiber surface in a coagulation
bath, the size and volume of fine pores within the fiber tend to
increase. To obtain a desired high strength carbon fiber, it is
preferable to satisfy the both conditions in which the permeation
of a finishing oil agent is prevented by densifying the surface
layer portion of a swollen fiber, as mentioned above, and in which
the swollen fiber has a dense structure that has few voids within
the fiber. Note that, the fine pore distribution of a swollen fiber
is measured in accordance with the method, i. e., [4. Method of
measuring fine pore distribution of swollen fiber], which will be
described later.
[Method of Producing Swollen Fiber]
[0034] The swollen fiber of the present invention can be produced
by subjecting a dope containing an acrylonitrile-based copolymer
and an organic solvent to wet spinning or dry-wet spinning.
[0035] Examples of the acrylonitrile-based copolymer include an
acrylonitrile-based copolymer obtained by copolymerizing
acrylonitrile and an unsaturated hydrocarbon having at least one
carboxyl group or ester group as essential components. Examples of
the unsaturated hydrocarbon having at least one carboxyl group or
ester group include acrylic acid, methacrylic acid, itaconic acid,
methyl acrylate, methyl methacrylate and ethyl acrylate. An
acrylonitrile copolymer obtained by copolymerizing any one of these
or two or more compounds of these (0.3 mass % or more and 4.0 mass
% or less) and acrylonitrile (96.0 mass % or more and 99.7 mass %
or less) is preferably used. The acrylonitrile content is more
preferably 98 mass % or more.
[0036] An unsaturated hydrocarbon having a carboxyl group or an
ester group is known to serve as a starting point of a
stabilization reaction in a stabilization step. If the content
thereof is excessively low, the stabilization reaction does not
sufficiently proceed, interfering with formation of the structure
of a stabilized fiber. In contrast, if the content is excessively
large, a reaction rapidly occurs due to the presence of many
reaction starting points. As a result, a coarse structural form is
formed and a carbon fiber having high performance cannot be
obtained. If the content is set to be 0.3 mass % or more and 4.0
mass % or less, the stabilization reaction starting point and the
rate of the reaction are well balanced and a dense structure
results. In addition, formation of a structural irregularity, which
will become a defect in a carbonization step, can be prevented.
Furthermore, a stabilization reaction can be caused in a relatively
low temperature range since the reaction system has moderate
reactivity. From both economic and safety aspects, stabilization
can be carried out. Accordingly, a stabilized fiber suitable for
obtaining a carbon fiber formed of a Graphene laminate structure
having few structural irregularities and defects at high yield can
be obtained.
[0037] As the third component, an acryl amide derivative such as
acrylamide, methacrylamide, N-methylol acrylamide, N,N-dim ethyl
acrylamide, vinyl acetate, etc. may be used. As an appropriate
method for copolymerizing a monomer mixture, any polymerization
method may be used, including, for example, redox polymerization
performed in an aqueous solution, suspension polymerization
performed in non-homogeneous system and emulsion polymerization
using a dispersant. Difference between the polymerization methods
does not limit the present invention.
[0038] In the spinning step, first, an acrylonitrile-based
copolymer is dissolved in an organic solvent in a concentration of
20 to 25 mass % to prepare a dope having a temperature of 50 to
70.degree. C. The solid-substance concentration of the dope is
preferably 20 mass % or more and more preferably 21 mass % or more.
If the solid-substance concentration is set to be 20% or more, the
amount of solvent migrating from the inside of a filament during a
coagulation process can be reduced to obtain a coagulated fiber
having the requisite density. In contrast, if the solid-substance
concentration is set to be 25 mass % or less, a dope having the
appropriate viscosity can be prepared, with the result that the
dope can be stably ejected from a nozzle, rendering production
easier. In short, if the solid-substance concentration is set to be
20 to 25 mass %, a coagulated fiber having a highly dense and
uniform structure can be stably produced.
[0039] Furthermore, if the temperature of a dope is set to be
50.degree. C. or more, the dope having the appropriate viscosity
can be obtained without reducing the solid-substance concentration.
Furthermore, if the temperature of a dope is set to be 70.degree.
C. or less, the difference in temperature between the dope and the
coagulant can be reduced. More specifically, if the temperature of
a dope is 50 to 70.degree. C., a coagulated fiber having a highly
dense and uniform structure can be stably produced.
[0040] The organic solvent is not particularly limited; however,
dimethylformamide, dimethylacetamide or dimethylsulfoxide is more
preferably used. More preferably, dimethylformamide which has
excellent solubility for an acrylonitrile-based copolymer is
used.
[0041] The spinning method may be either wet spinning or dry-wet
spinning. More preferably, dry-wet spinning is employed. This is
because it is easy to form a dense coagulated fiber and, in
particular, because the density of the surface layer portion can be
enhanced. In dry-wet spinning, the dope prepared is spun from a
spinneret having numerous nozzle holes arranged therein into the
air and then ejected in a coagulant filled with a solution mixture
of an organic solvent and water and controlled in temperature to
coagulate. The coagulated fiber is removed. The coagulant used
herein preferably has a temperature of -5 to 20.degree. C. and a
concentration of an organic solvent of 78 to 82 mass %. This is
because a dense coagulated fiber can be easily formed within the
range and, in particular, because the density of the surface layer
portion can be enhanced. A more preferable temperature range of the
aqueous solution is -5.degree. C. to 10.degree. C. and a more
preferable concentration range of the organic solvent is 78.5 mass
% or more and 81.0 mass % or less. If the organic solvent
concentration of the coagulant is set to be 81.0 mass % or less,
the density of the surface layer portion can be maintained and
permeation of a finishing oil agent into a fiber surface layer
portion can be prevented. Furthermore, if the organic solvent
concentration is set to be 78.5 mass % or more, rapid coagulation
of the surface layer during a coagulation process can be prevented,
with the result that formation of a skin layer can be prevented.
Furthermore, coagulation relatively slowly proceeds and thus an
inner density does not decrease. More specifically, if the organic
solvent concentration of the coagulant is set to be 78.5 to 81.0
mass %, a coagulated fiber that is dense not only in the surface
layer portion but also in the inner portion of a fiber can be
obtained.
[0042] The coagulated fiber is subjected to drawing and washing
treatment. The order of the drawing and washing treatment is not
particularly limited. Drawing may be applied, followed by washing,
and drawing and washing may be simultaneously performed. Any
washing method may be employed as long as a solvent can be removed.
In a particularly preferable drawing and washing treatment for a
coagulated fiber, drawing is performed in a pre-drawing tank
containing a liquid that has a lower solvent concentration and
higher temperature than a coagulant. Owing to this, a coagulated
fiber having a uniform fibril structure can be formed.
[0043] Conventionally, drawing a coagulated fiber in a bath
containing a solvent has been generally known as a solvent drawing
technique, which enables stable drawing treatment due to solvent
plasticization, with the result that a fiber having high uniformity
in structure as well as in orientation can be obtained. However, if
a fiber bundle containing a solvent in a swollen state is subjected
to drawing, as is, sufficient formation of a fibril structure and
sufficient orientation of the structure by drawing cannot be
obtained. Furthermore, since a finishing oil agent is also rapidly
squeezed out from the inside of the filament, the resultant
filament tends to have a non-dense structure and thus a swollen
fiber that has a desired dense structure cannot be obtained. In the
present invention, the temperature and concentration of a dope and
a coagulant are optimally set. Based on this, if solvent drawing
treatment is performed by optimally combining the conditions for a
solvent drawing tank with draw ratio, a dense fibril structure can
be formed.
[0044] A coagulated fiber bundle containing an organic solvent is
first drawn in the air, subsequently drawn in a drawing tank
containing a warm aqueous solution that contains an organic
solvent. The temperature of the warm aqueous solution preferably
ranges from 40.degree. C. or more to 80.degree. C. or less. If the
temperature is set to be 40.degree. C. or more, a good drawing
property can be ensured, rendering formation of a uniform fibril
structure easier. Furthermore, if the temperature is set to be
80.degree. C. or less, removal of the solvent from the surface of a
fiber proceeds moderately without causing an excessive plasticizing
action. Uniform drawing results. As a result, the quality of
swollen fiber is improved. A more preferable temperature is
55.degree. C. or more and 75.degree. C. or less.
[0045] Furthermore, concentration of the organic solvent in the
warm aqueous solution that contains an organic solvent is
preferably 30 mass % or more and 60 mass % or less. In the range of
concentration, stable drawing treatment can be performed and a
dense and uniform fibril structure can be formed in the inside and
the surface layer. A more preferable concentration is 40 mass % or
more and 50 mass % or less.
[0046] In a preferable drawing method of a coagulated fiber, the
draw ratio in the air is set to be 1.0 time or more and 1.25 times
or less, and the sum of draw ratios in the air and in the warm
aqueous solution is set to be 2.6 times or more and 4.0 times or
less. The coagulated fiber has a swollen fibril structure
containing a large amount of solvent. If the coagulated fiber
formed of such a structure is drawn at a draw ratio of 1.0 time or
more and 1.25 times or less in the air, formation of a non-dense
fibril structure can be avoided. Furthermore, if the draw ratio is
set to be 1.0 time or more, non-uniform shrinkage can be
prevented.
[0047] Furthermore, if the sum of draw ratios in the air and in a
warm aqueous solution is set to be 2.6 times or more, sufficient
drawing can be applied and a desired fibril structure having
orientation in the fiber-axis direction can be formed. Furthermore,
if the sum of draw ratios is set to be 4.0 times or less, a
precursor fiber bundle having a dense structural form can be
obtained without breakage of the fibril structure itself. In short,
a dense fibril structure having orientation in the fiber-axis
direction can be formed in the range of 2.6 times or more and 4.0
times or less. A more preferable sum of draw ratios is 2.7 times or
more and 3.5 times or less.
[0048] Furthermore, more preferably, drawing is performed in a warm
aqueous solution containing an organic solvent at a draw ratio of
2.5 times or more. This is because drawing can be performed without
collapse at the structure since the drawing in the warm aqueous
solution that contains an organic solvent is performed at a
relatively high temperature. Therefore, regarding the proportion of
a draw ratio between the drawings in the air and in the warm
aqueous solution that contains an organic solvent, the draw ratio
in the warm aqueous solution that contains an organic solvent is
preferably set to be higher. More preferably, the draw ratio in the
air is 1.0 time or more and 1.15 times or less.
[0049] In this manner, a swollen fiber having a dense surface layer
portion can be obtained. A more preferable dense swollen fiber is
produced by using a coagulated fiber bundle containing an organic
solvent with a swelling degree of 160 mass % or less in accordance
with the aforementioned drawing method. This is because the
coagulated fiber has a dense inner structure.
[0050] After drawing treatment, the fiber bundle is washed with
warm water of 50.degree. C. or more and 95.degree. C. or less to
remove the organic solvent. Furthermore, after washing, if a fiber
bundle that is in a swollen state and that lacks a solvent is drawn
in hot water, the orientation of the fiber can be further enhanced.
Alternatively, if relaxing treatment is slightly performed,
distortion due to drawing can be removed. Preferably, drawing is
performed at a ratio of 0.98 times or more and 2.0 times or less in
hot water at a temperature of 70 to 95.degree. C. Drawing performed
at a draw ratio of 0.98 times or more and less than 1.0 time is a
relaxation treatment. Removing distortion, which is produced by
drawing in the previous step performed at a high draw ratio, from a
fiber bundle is effective for stable drawing in the later drawing
step. If drawing is performed in the range of a draw ratio of 1.0
time or more and 2.0 times or less, the orientation degree of the
fibril structure can be improved and the density of the surface
layer can be increased. More preferably, drawing is performed at a
ratio of 0.99 times or more and 1.5 times or less.
[0051] Swollen fiber can be obtained by applying drawing treatment
and washing treatment to a coagulated fiber in this manner.
[Heat Drawing]
[0052] A predetermined amount of finishing oil agent is applied to
a swollen fiber and subjected to dry densification. The method for
dry densification is not particularly limited, and drying and
densification are performed in accordance with a known dry method.
A method of passing a swollen fiber through a plurality of heated
rolls is preferably used. After dry densification, the fiber bundle
is drawn in a pressurized steam of 130 to 200.degree. C., in a dry
heat medium of 100 to 200.degree. C., between heated rolls of 150
to 220.degree. C. or on a heated plate of 150 to 220.degree. C. to
further improve orientation and to perform densification.
Thereafter, the bundle is wound to obtain a precursor fiber
bundle.
[Precursor Fiber Bundle]
[0053] A precursor fiber bundle for a carbon fiber (hereinafter
appropriately referred to as a "precursor fiber bundle") of the
present invention is formed of an acrylonitrile copolymer obtained
by copolymerizing acrylonitrile (96.0 mass % or more and 99.7 mass
% or less) and an unsaturated hydrocarbon having at least one
carboxyl group or ester group (0.3 mass % or more and 4.0 mass % or
less) as essential components. The precursor fiber bundle has a
silicon content of 1700 ppm or more and 5000 ppm or less after
being treated with a finishing oil agent containing silicone-based
compounds as main components and a silicon content of 50 ppm or
more and 300 ppm or less after the finishing oil agent is washed
away with methyl ethyl ketone by using a Soxhlet extraction
apparatus for 8 hours. The silicon content is measured by a
fluorescent X-ray apparatus. Furthermore, the silicon content after
the finishing oil agent is washed away is a measured value based on
evaluation in the above section [Evaluation of permeability of
swollen fiber with finishing oil agent] performed through the steps
of applying a finishing oil agent and washing finishing oil
agent.
[0054] After treatment with a finishing oil agent, if the silicon
content of a precursor fiber bundle is 1700 ppm to 5000 ppm or
less, fusion between filaments in a stabilization step does not
occur; however, oxygen diffusion into a filament is inhibited by
the presence of an excessive amount of silicone compounds in the
surface layer. Consequently, there are no portions at which a
stabilization reaction is not sufficiently performed and the
occurrence of fiber breakage can be prevented in a step of
carbonization treatment performed at a higher temperature. As a
result, it is ensured that the fiber bundle stably passes through a
manufacturing process.
[0055] The precursor fiber bundle of the present invention has a
silicon content of 300 ppm or less after a finishing oil agent is
extracted and washed away. A silicon content of more than 300 ppm
means that oil of silicone-based compounds permeates into a surface
layer portion and the amount of oil that is present therein
increases. As a result, the silicone oil that is present in the
surface layer portion remains without being scattered in a
stabilization step and in a first-half carbonization step
(800.degree. C. or less) of a carbonization step, and is scattered
in a second-half carbonization step (more than 800.degree. C.). As
a result, many voids are formed in the surface layer portion of the
final carbon fiber. Accordingly, a desired high-strength carbon
fiber cannot be obtained. In contrast, the silicon content of the
fiber bundle being 300 ppm or less after a finishing oil agent is
extracted and washed away means that the silicon compounds applied
to a precursor fiber permeates into the surface layer portion and
is present near the outermost surface in the surface layer portion
of the precursor fiber. Thus, because the amount of the silicon
compounds that are difficult to extract is low, the silicon
compounds are present in the outermost surface layer portion. If
such a state is present, silicone-based compounds can be scattered
from the outermost surface layer portion in a stabilization step
and in a carbonization step of a carbonization step, without
forming defects. More preferable silicon content after a finishing
oil agent is extracted and washed away is 200 ppm or less by
mass.
[0056] In the precursor fiber bundle, preferably the fineness of a
single fiber is 0.5 dtex or more and 1.0 dtex or less; a ratio of
the major axis and the minor axis (major axis/minor axis) of a
cross-section of a single fiber is 1.00 or more and 1.01 or less;
an uneven surface structure extending in the fiber-axis direction
of a single fiber is not present; the difference in height (Rp-v)
between a highest portion and a lowest portion is 30 nm or more and
100 nm or less; and a center-line average roughness (Ra) is 3 nm or
more and 10 nm or less. If an (Rp-v) value is 30 nm or more or an
(Ra) value is 3 nm or more, the smoothness of the surface of a
precursor fiber filament is not excessive. This means that small
breakage of a surface-layer fibril does not occur because of the
low drawing property in a spinning step due to the skin layer
formed in a coagulation step. Thus, formation of micro defects can
be avoided. In addition, non-uniform stabilization can be avoided,
which is caused by inhibition of oxygen diffusion into an inner
portion of a filament in a stabilization step due to excessive
converging of a fiber bundle, which is an assembly of filaments. In
contrast, if the (Rp-v) value is set to be 100 nm or less or if the
(Ra) value is set to be 10 nm or less, the density of a structure
near a surface layer can be conceivably set to a sufficient level.
In short, if a filament has a surface that satisfies an (Rp-v)
value of 30 nm or more and 100 nm or less and an (Ra) value of 3 nm
or more and 10 nm or less, the structure of the filament will have
a sufficient density near the surface layer and sufficient drawing
property. The probability of defect formation near a surface layer
from a spinning step to a carbonization step can be reduced. As a
result, a high-strength carbon fiber bundle can be obtained.
[0057] The uneven surface structure extending in the fiber-axis
direction herein refers to a wrinkle structure that has a length of
0.6 .mu.m or more and that is present almost parallel to the
fiber-axis direction. The acrylonitrile fiber bundle causes volume
shrinkage usually due to coagulation and the following drawing
treatment. As a result, a wrinkle structure that extends in the
fiber-axis direction is formed on the surface. Formation of the
wrinkle structure can be prevented by preventing formation of a
rigid skin layer in a coagulation step, thereby realizing gradual
volume shrinkage. Furthermore, it is known that formation of the
wrinkle structure is significantly prevented by dry-wet spinning.
Preferably, the precursor fiber bundle does not have such a wrinkle
structure having a length of 0.6 .mu.m or more.
[0058] A fiber having a ratio of the major axis and the minor axis
(major axis/minor axis) of a single-fiber cross-section of 1.00 to
1.01, is a single fiber having a complete circular or nearly
complete circular cross-section and is excellent in structural
uniformity near the fiber surface. A more preferable ratio of the
major axis and the minor axis (major axis/minor axis) is 1.00 to
1.005.
[0059] A fiber having a fineness of a single fiber within the range
of 0.5 to 1.0 dtex has a small fiber diameter. Thus, the degree of
structural non-uniformity developed in the cross-section direction
in a carbonization step can be reduced. A more preferable range is
0.5 to 0.8 dtex.
[Method of Producing Precursor Fiber Bundle]
[0060] A precursor fiber bundle containing silicon in the
aforementioned predetermined amount can be produced by applying a
finishing oil agent that contains silicone compounds as main
components to the swollen fiber of the present invention and drying
it, and then by applying a drawing treatment in accordance with hot
drawing or steam drawing.
[0061] The silicone compound that serves as the main component of
the finishing oil agent is not particularly limited; however,
taking into consideration interaction with an acrylonitrile-based
copolymer, an amino-modified polydimethyl siloxane or an
epoxy-modified polydimethyl siloxane is preferably used. In
particular, since the swollen fiber of the present invention has a
highly dense surface layer portion, taking into account the ease of
coating the surface layer, and further, taking into account the
difficulty of removing the finishing oil agent from the surface
layer, an amino-modified polydimethyl siloxane is preferred.
[0062] Furthermore, in the case where methyl groups of a
polydimethyl siloxane skeleton are partly substituted with phenyl
groups, such a compound is excellent in view of the heat resistance
characteristics of the compound. The most preferable amino-modified
polydimethyl siloxane has a kinematic viscosity of 50 to 5,000 cSt
at 25.degree. C. and an amino equivalent mass of 1,700 to 15,000
g/mol.
[0063] The type of modification with an amino acid is not
particularly limited; however, a mono amino modified side-chain
type, a diamino modified side-chain type and a two-end modification
type are preferred. Furthermore, a mixture of these or a mixture of
a plurality of types can be used. If the kinematic viscosity at
25.degree. C. is 50 cSt or more, such a compound is non-volatile
and has a sufficient molecular weight. In this case, scattering
from a fiber can be prevented throughout the stabilization step and
the finishing oil agent plays the role that is required in the
process, with the result that a carbon fiber can be stably
produced. Furthermore, if the kinematic viscosity at 25.degree. C.
is set to be 5000 cSt or less, part of the finishing oil agent is
transferred from a fiber bundle to a roll etc. in a stabilization
step. If the finishing oil agent transferred is treated with heat
for a relatively long time, the viscosity thereof increases and
becomes sticky, with the result that part of a fiber bundle is
wound around a roll. Such trouble frequently occurs. Furthermore,
if an amino equivalent mass is set to be 1,700 g/mol or more, heat
reactivity of silicone is prevented. As a result, the occurrence of
problems, i.e., winding of part of a fiber bundle around a roll
caused by a finishing oil agent transferred from the fiber bundle
to a roll etc. can be avoided. If the amino equivalent mass is set
to be 15,000 g/mol or less, due to sufficient affinity of a
precursor fiber for silicone, scattering from a fiber can be
prevented throughout the stabilization step. In short, if the
kinematic viscosity of a finishing oil agent at 25.degree. C. is 50
to 5,000 cSt and if the amino equivalent mass falls within the
range of 1,700 to 15,000 g/mol, a process from spinning to
stabilization can be continuously and stably performed for a long
time without any problem being caused by a finishing oil agent
being transferred to a roll etc., such as winding of a fiber around
the roll and abrupt scattering of the finishing oil agent in a
stabilization step.
[0064] Examples of amino-modified polydimethyl siloxane of the mono
amino modified side-chain type include KF-864, KF-865, KF-868, and
KF-8003 (all are manufactured by Shin-Etsu Chemical Co., Ltd.).
Examples of amino-modified polydimethyl siloxane of the diamino
modified side-chain type include KF-859, KF-860, KF-869, and
KF-8005 (all are manufactured by Shin-Etsu Chemical Co., Ltd.).
Examples of amino-modified polydimethyl siloxane of the two-end
modification type include Silaplane FM-3311, FM-3221, FM-3325 (all
are manufactured by Chisso Corporation) and KF-8012 (manufactured
by Shin-Etsu Chemical Co., Ltd.).
[0065] The finishing oil agent is constituted of compounds such as
a surfactant for forming an aqueous emulsion, and a softening agent
and a lubricant agent for imparting excellent processability. As
the surfactant, a nonionic surfactant is mainly used. Pluronic type
and EO/PO adduct of a higher alcohol are used. In particular,
polyoxyethylene/polyoxypropylene block polymers, namely, NEWPOL
PE-78, PE-108, and PE-128 (all are products by Sanyo Chemical
Industries, Ltd.) are preferred.
[0066] As the softening agent and lubricant agent, an ester
compound and a urethane compound are used. The content of silicone
compounds in a finishing oil agent is 30 mass % to 90 mass %. If
the content is 30 mass % or more, fusion is sufficiently prevented
in a stabilization step. Furthermore, if the content is 90 mass %
or less, an emulsion of the finishing oil agent can be easily
stabilized at a sufficient level and a precursor fiber can be
stably produced. In short, if the content of silicone-based
compounds in a finishing oil agent is 30 mass % to 90 mass %, even
in a precursor fiber having a dense surface, as in the present
invention, fusion will be sufficiently prevented in a stabilization
step, and stability in a finishing oil agent attachment step as
well as a uniform application state can be realized. Therefore,
performance of the resultant carbon fiber can be stably
developed.
[0067] The applied amount of a finishing oil agent containing
silicone compounds as main components is 0.8 mass % to 1.6 mass %.
After the finishing oil agent is applied, the fiber is subjected to
dry densification. The dry densification is not particularly
limited and dry densification can be performed in accordance with a
known drying method. Preferably, a method of passing a fiber
through a plurality of heated rolls is employed. If the applied
amount of finishing oil agent is set to be 0.8 to 1.6 mass %,
fusion of fibers that are caused by insufficient coating with the
finishing oil agent and structural irregularity of a stabilized
fiber that is caused by insufficient diffusion of oxygen due to
excessive application of a finishing oil agent can be reduced, with
the result that carbon fiber having high strength can be
produced.
[0068] The fiber bundle after the dry densification process is, if
necessary, drawn in a pressurized steam at a temperature of 130 to
200.degree. C., in a dry heat medium, between heated rolls or on a
heated plate at a ratio of 1.8 to 6.0 times to further improve
orientation and to perform densification. In this manner, a
precursor fiber bundle is obtained. A more preferable draw ratio is
2.4 to 6.0 times and further preferably 2.6 to 6.0 times.
[Method of Producing a Stabilized Fiber Bundle]
[0069] A precursor fiber bundle is fed to a hot-air circulation
type oven for stabilization at a temperature of 220 to 260.degree.
C. for 30 minutes or more and 100 minutes or less to apply heat
treatment under an oxidizing atmosphere at an extension rate of 0%
or more and 10% or less. In this manner, a stabilized fiber bundle
having a density of 1.335 g/cm.sup.3 or more and 1.360 g/cm.sup.3
or less can be obtained. The stabilization reaction includes a
cyclization reaction with heat and an oxidation reaction with
oxygen. It is important to balance the two reactions. To balance
the two reactions, the amount of time for conducting stabilization
is preferably 30 minutes or more to 100 minutes or less. If the
reaction time is less than 30 minutes, a portion of a single fiber
in which the oxidation reaction does not sufficiently proceed, is
present within the single fiber, with the result that a large
structural plaque is generated in the cross-section direction of
the single fiber. As a result, the obtained carbon fiber has a
non-uniform structure and fails to develop high mechanical
performance. In contrast, if the reaction time exceeds 100 minutes,
a larger amount of oxygen is present near the surface of a single
fiber. Thereafter, in the following heat treatment performed at a
high temperature, a reaction that consumes an excessive amount of
oxygen occurs, which results in a defect. As a result, a carbon
fiber having high strength cannot be obtained.
[0070] A more preferable stabilization time is 40 minutes or more
and 80 minutes or less. If the density of a stabilized fiber is
less than 1.335 g/cm.sup.3, stabilization will be insufficient. In
the following heat treatment performed at a high temperature, a
decomposition reaction occurs resulting in the formation of a
defect. Because of this, a carbon fiber having high strength cannot
be obtained. If the density of a stabilized fiber exceeds 1.360
g/cm.sup.3, the oxygen content of the fiber increases. In the
following heat treatment performed at a high temperature, a
reaction that consumes an excessive amount of oxygen occurs,
resulting in the formation of a defect. Because of this, a carbon
fiber having high strength cannot be obtained. A more preferable
density range of a stabilized fiber is 1.340 g/cm.sup.3 or more and
1.350 g/cm.sup.3 or less.
[0071] Appropriate extension of a fiber performed in an oven for
stabilization is required in order to maintain and improve
orientation of a fibril structure constituting the fiber. If the
extension is less than 0%, the orientation of a fibril structure
cannot be maintained; orientation along the fiber axis does not
sufficiently develop during the formation of a carbon fiber
structure; and excellent mechanical performance will not develop.
In contrast, if the extension exceeds 10%, a fibril structure
itself will be broken, with the result that formation of a carbon
fiber structure will be impaired. In addition, since a fracture
point becomes a defect, a carbon fiber having high strength cannot
be obtained. A more preferable extension rate is 3% or more and 8%
or less.
[0072] In a preferable method of producing a stabilized fiber
bundle, a precursor fiber bundle is treated with heat under the
aforementioned oxidizing atmosphere to obtain a stabilized fiber
bundle that satisfies an intensity ratio (B/A) of peak A
(2.theta.=25.degree.) and peak B (2.theta.=17.degree.) in the
equatorial-line direction when the fiber bundle is measured by
wide-angle X-ray: 1.3 or more; an orientation degree of peak A: 79%
or more; an orientation degree of peak B: 80% or more; and a
density: 1.335 g/cm.sup.3 or more and 1.360 g/cm.sup.3 or less.
[0073] The crystal structure derived from reflection by
polyacrylonitrile (100) at peak B (2.theta.=17.degree.) is closely
related to formation of the structure of a carbon fiber. If the
orientation degree of a crystal and crystallinity are once lowered
during the process for producing a carbon fiber, it will be
difficult to return to the original states, with the result that
development of performance of the carbon fiber will tend to
decrease. The (100) used herein indicates the orientation of a
crystal. In particular, a stabilization step is a step in which the
structure of a precursor fiber significantly changes and a graphite
crystal group, which is a fundamental structure of a carbon fiber,
is formed. The crystal structure derived from reflection by
polyacrylonitrile (100) at peak B (2.theta.=17.degree.) is
significantly changed by a stabilization step and the degree of
changes significantly varies depending upon the set conditions of
the stabilizing process. To obtain a stabilized fiber having a high
orientation, an appropriate treatment must be applied. Furthermore,
the orientation degree is closely related with crystallinity. More
specifically, crystallinity is significantly reduced as the degree
of orientation is reduced. Conversely to say, if a high orientation
can be maintained, a high crystalline fiber can accordingly be
obtained. For the reason, a stabilized fiber bundle preferably has
a crystal structure that satisfies an intensity ratio (B/A) of 1.3
or more, a peak-A orientation degree of 79% or more and a peak-B
orientation degree of 80% or more.
[0074] The aforementioned stabilized fiber bundle can be relatively
easily obtained by using a precursor fiber bundle of the present
invention. Furthermore, in a step of treating a precursor fiber
bundle with heat under an oxidizing atmosphere, stabilizing
conditions are preferably set so as to perform extension treatment
separately under at least three sets of conditions: an extension
rate of 3.0% or more and 8.0% or less at a fiber density in the
range of 1.200 g/cm.sup.3 or more and 1.260 g/cm.sup.3 or less; an
extension rate at 0.0% or more and 3.0% or less at a fiber density
in the range of 1.240 g/cm.sup.3 or more and 1.310 g/cm.sup.3 or
less; and an extension rate of -1.0% or more and 2.0% or less at a
fiber density in the range of 1.300 g/cm.sup.3 or more and 1.360
g/cm.sup.3 or less.
[Carbon Fiber]
[0075] Next, a stabilized fiber bundle is heat treated for 1.0
minute to 3.0 minutes in a first carbonization furnace having a
temperature gradient of 300.degree. C. or more and 800.degree. C.
or less under an inert gas atmosphere such as nitrogen while
extending the extension rate to a rate of 2% or more to 7% or less.
A preferable processing temperature is 300.degree. C. to
800.degree. C. and the stabilized fiber bundle is processed in
linear temperature gradient conditions. In consideration of the
temperature in the previous step of stabilization, the initiation
temperature is preferably 300.degree. C. or more. If the highest
temperature exceeds 800.degree. C., the fiber becomes very fragile
and will be barely transferred to the following step. A more
suitable temperature range is 300 to 750.degree. C. More preferable
temperature range is 300 to 700.degree. C.
[0076] The temperature gradient is not particularly limited;
however a linear gradient is preferably employed. If the extension
rate is less than 2%, orientation of a fibril structure cannot be
maintained and orientation along the fiber axis in formation of a
carbon fiber structure will not be sufficient, with the result that
excellent mechanical performance cannot develop. In contrast, if
the extension rate exceeds 7%, the fibril structure itself will be
broken, with the result that subsequent formation of the carbon
fiber structure will be impaired. In addition, since a fracture
point becomes a defect, a carbon fiber having high strength cannot
be obtained. A more preferable extension rate is 3% or more and 5%
or less. The preferable treatment time is 1.0 minute to 3.0
minutes. If the treatment time is less than 1.0 minute, the
temperature will abruptly increase, and this will be accompanied by
a severe decomposition reaction. As a result, a carbon fiber having
high strength cannot be obtained. If the treatment time exceeds 3.0
minutes, the effect of plasticization in the first half of the step
will be produced, with the result that orientation degree of a
crystal will tend to decrease. As a result, the mechanical
performance of the resultant carbon fiber will be impaired. The
more preferable treatment time is 1.2 to 2.5 minutes.
[0077] Subsequently, heat treatment is performed under tension in a
second carbonization furnace that is capable of setting a
temperature gradient in the range of 1000 to 1600.degree. C. under
an inert atmosphere such as nitrogen to obtain a carbon fiber.
Furthermore, if necessary, heat treatment is additionally performed
under an inert atmosphere under tension in a third carbonization
furnace having a desired temperature gradient. Temperature is set
depending upon the desired elastic modulus of the carbon fiber. To
obtain a carbon fiber having high mechanical performance, the
highest temperature of carbonization treatment is preferably low.
Furthermore, since the elastic modulus can be increased by
increasing the treatment time, the highest temperature can be
lowered. Moreover, the temperature gradient can be set so as to
increase slowly by increasing the treatment time. This is effective
in preventing defect formation.
[0078] The temperature of the second carbonization furnace varies
depending upon the temperature condition in the first carbonization
furnace; however, the temperature is satisfactorily 1000.degree. C.
or more and preferably 1050.degree. C. or more. The temperature
gradient is not particularly limited; however a linear gradient is
preferably employed. The treatment time is preferably 1.0 minute to
5.0 minutes and more preferably 1.5 minutes to 4.2 minutes. In the
heat treatment, the fiber bundle significantly shrinks. Thus, it is
important to perform the heat treatment under tension. The
extension rate is preferably -6.0% to 2.0%. If the extension rate
is less than -6.0%, the orientation of a crystal in the fiber-axis
direction will be unsatisfactory and sufficient performance cannot
be obtained. In contrast, if the extension rate exceeds 2.0%, the
structure so far formed itself will be broken and many defects will
be formed, with the result that the strength will be significantly
reduced. More preferable extension rate falls within the range of
-5.0% to 0.5%.
[0079] The carbon fiber bundle thus obtained is subjected to
surface oxidization treatment. Examples of the surface treatment
method include known methods, i.e., oxidation treatments such as
electrolytic oxidation, chemical oxidation and air oxidation. Any
one of these methods may be employed. The electrolytic oxidation
treatment that is used widely in industry is the most preferable
method since surface oxidization treatment can be stably performed
and the surface treatment state can be controlled by varying the
amount of electricity. In this case, even if the amount of
electricity is the same, the state of the surface varies
significantly depending upon the electrolyte and the concentration
thereof that is employed; however, oxidation treatment is
preferably performed in an aqueous alkaline solution that has a pH
of more than 7 with a carbon fiber as an anode while supplying an
electric quantity of 10 to 200 coulomb/g. Examples of electrolyte
that is preferably used include ammonium carbonate, ammonium
bicarbonate, calcium hydroxide, sodium hydroxide and potassium
hydroxide.
[0080] Next, the carbon fiber bundle is subjected to sizing
treatment. The sizing agent is dissolved in an organic solvent or
dispersed in water with the help of an emulsifier to prepare an
emulsion. The above preparation is applied to a carbon fiber bundle
in accordance with a roller dip method, a roller contact method,
etc. Subsequently, the carbon fiber bundle is dried. In this
manner, sizing treatment can be performed. Note that the applied
amount of the sizing agent that is applied to the surface of a
carbon fiber can be controlled by controlling the concentration of
the sizing agent solution and the amount of the sizing agent that
is squeezed. Furthermore, drying can be performed by use of e.g.,
hot air, a hot plate, a heated roller and various infrared heaters.
Subsequently, the sizing agent is applied and dried, and then, the
carbon fiber bundle is wound onto a bobbin.
[0081] The aforementioned carbonization method is applied to the
precursor fiber bundle and stabilized fiber bundle of the present
invention to obtain a carbon fiber bundle that has excellent
mechanical performance.
[0082] In the carbon fiber bundle of the present invention, the
strength of a strand impregnated with a resin is 6000 MPa or more;
the strand elastic modulus measured by the ASTM method is 250 to
380 GPa; the ratio of the major axis and the minor axis (major
axis/minor axis) of a cross-section of a single fiber perpendicular
to the fiber-axis direction is 1.00 to 1.01; a single-fiber
diameter is 4.0 to 6.0 .mu.m; and the number of voids having a
diameter of 2 nm or more and 15 nm or less and present in the
cross-section of a single fiber in the direction perpendicular to
the fiber-axis direction is 1 or more and 100 or less. Since the
number of voids is as low as 100 or less, a carbon fiber bundle
that has extremely high strand strength can be obtained. In
particular, in a carbon fiber bundle that has a high elastic
modulus, a high strand strength can be developed. More preferably,
the number of voids is 50 or less.
[0083] In a further preferable carbon fiber bundle, the average
diameter of voids that satisfies a diameter range from 2 to 15 nm
and that are observed in the cross-section of a single fiber
perpendicular to the fiber-axis direction is 6 nm or less. The
average diameter of 6 nm or less means that a finishing oil agent
was uniformly present on a precursor fiber bundle without causing a
large amount of local permeation. By ensuring an average diameter
of 6 nm or less, the strength of a carbon fiber can be developed
stably.
[0084] In the carbon fiber bundle of the present invention, the sum
A (nm.sup.2) of areas of voids present in the cross-section of a
single fiber perpendicular to the fiber-axis direction is
preferably 2,000 nm.sup.2 or less. Furthermore, voids corresponding
to 95% or more of the sum A (nm.sup.2) are preferably present in
the area from the surface of a fiber to a depth of 150 nm. The
presence of such a structure in a single fiber means that a
finishing oil agent is present only immediately near the surface
layer in a precursor fiber bundle.
[0085] In the present invention, the knot tenacity, which is
obtained by dividing the tensile breaking stress of a knotted
carbon fiber bundle by the cross-sectional area of the fiber bundle
(mass and density of a bundle per unit length), is preferably 900
N/mm.sup.2 or more. More preferably, the knot tenacity is 1000
N/mm.sup.2 or more and further preferably, 1100 N/mm.sup.2 or more.
The knot tenacity can serve as an index reflecting mechanical
performance of a fiber bundle in a direction other than the
fiber-axis direction. In particular, performance in the direction
perpendicular to the fiber axis can be simply checked by the knot
tenacity. In the composite material, since a material is often
formed by pseudo-isotropic lamination, a complicated stress field
is formed. At this time, other than tensile and compression stress
in the fiber-axis direction, stress is also generated in a
direction other than in the fiber-axis direction. Furthermore, if a
relatively high-speed strain is produced, as is in an impact test,
the state of the stress that is generated within the material is
highly complicated. Thus, the strength in a direction different
from the fiber-axis direction becomes important. Accordingly, if
the knot tenacity is less than 900 N/mm.sup.2, sufficient
mechanical performance will not develop in a pseudo-isotropic
material.
EXAMPLES
[0086] Now, the present invention will be described in detail by
way of Examples. Note that, the performance of fibers in Examples
is measured and evaluated in accordance with the following
method.
[1. Measurement of Swelling Degree of Coagulated Fiber]
[0087] A fiber bundle that is running in a spinning step is taken.
Immediately the fiber bundle is placed in a sealable polyethylene
bag and then the bag is stored in a refrigerator of 5.degree. C. or
less. The time from initiation of storage to completing measurement
of the degree of swelling is set to fall within 8 hours.
[0088] After weighing a weighing bottle that has been previously
dried, is carried out by a direct-reading balance, about 3 g of
sample is taken from the fiber bundle and placed in the weighing
bottle and measured. The sample is placed in a dewatering cylinder
for a desktop centrifuge and placed in the centrifuge. After
centrifugal treatment (rough dewatering) is performed at a rotation
rate of 3000 rotation/minute for 10 minutes, the dewatered sample
is transferred to a weighing bottle and measured. The mass measured
herein is regarded as wet mass A.
[0089] In the case where the roughly dewatered sample still
contains a solvent, the sample will be sufficiently washed with
water and dewatered. The roughly dewatered sample or the sample
that has been further washed and dewatered is transferred to a
weighing bottle and dried in a drier of 105.degree. C. for 3 hours
without a lid. The weighing bottle having the dried sample therein
is transferred to a desiccator, gradually cooled for 20 to 30
minutes, and thereafter, the mass of the weighing bottle is
measured. The mass measured herein is regarded as dry mass B.
[0090] The degree of swelling is measured in accordance with the
following expression:
The degree of swelling (%)=(A-B)/B.times.100%
[2. Method of Measuring the Degree of Swelling of Swollen
Fiber]
[0091] Swollen fiber taken in the spinning step is used as a sample
and measured in the same manner as the degree of swelling of
coagulated fiber is measured.
[3. Observation of Surface Configuration of Swollen Fiber]
[0092] Swollen fiber taken in the spinning step is used as a
sample. The solvent contained in the swollen fiber is replaced with
t-butanol and the swollen fiber is rapidly frozen with liquid
nitrogen. Thereafter, the fiber sample is maintained at a
temperature of -30 to -25.degree. C. and lyophilized under reduced
pressure of about 3 Pa for 24 hours. The fiber sample thus dried is
fixed on a sample stand for SEM observation with carbon paste, and
then platinum is sputtered to a thickness of about 3 nm with a
sputter apparatus. The configuration of the surface is observed by
a scanning electron microscope (product name: JSM-7400F
manufactured by JEOL Ltd.) at an acceleration voltage of 3 kV and
an observation magnification of 50,000 times.
[0093] Voids, i.e., openings of the fiber surface are measured for
determining the width in the circumference direction. The number of
voids having a width of more than 10 nm is counted. Swollen fibers
of 50 or more are subjected to the same measurement. The total
number of voids is obtained and the observation area is measured to
obtain the average number of voids per unit area (1 .mu.m.sup.2)
(average number of openings).
[4. Method of Measuring Fine Pore Distribution of Swollen
Fiber]
[0094] The swollen fiber taken in the spinning step is dried in
accordance with the following treatment method. To describe this
more specifically, a swollen fiber is fixed to have a predetermined
length so that it is not deformed due to shrinkage during the
drying process, and is then soaked sequentially in solution
mixtures containing water/t-butanol in a ratio of 80/20, 50/50,
20/80, 0/100, each for 30 minutes to replace the solvent contained
in the swollen fiber with t-butanol. Subsequently, the swollen
fiber sample is placed in a flask and is rapidly frozen in liquid
nitrogen. Thereafter, while the temperature of the sample is
maintained in the range of -30 to -20.degree. C., the sample is
lyophilized under reduced pressure of 100 Pa or less for 24 to 72
hours.
[0095] The sample of the swollen fiber bundle that has been
lyophilized is cut into pieces of about 10 mm in length. About 0.15
g of the swollen fiber pieces are weighed, and a fine pore
distribution is measured by a mercury porosimeter (product name:
AutoPore IV manufactured by Shimadzu Corporation) under the
conditions of atmospheric pressure to a maximum pressure of 30,000
psia. The average fine pore size (nm) is obtained as a
volume-average fine pore size, which is fine pore size weighted by
fine pore volume. Furthermore, the total fine pore volume V (ml/g)
is obtained from mercury intrusion amount V1 (ml/g) obtained at a
pressure corresponding to a fine pore size of 500 nm and mercury
intrusion amount V2 (ml/g) obtained at a pressure corresponding to
a fine pore size of 10 nm, in accordance with the following
expression:
V=V2-V1
[5. Measurement of Silicon Content of Precursor Fiber Bundle]
[Measuring Apparatus]
[0096] Fluorescent X-ray spectrometer: product name: ZSX100e
manufactured by
Rigaku Industrial Corp.,
[0097] Target: Rh (end-window type) 4.0 kW, Dispersive crystal:
RX4, Detector: PC (proportional counter),
Slit: Std.,
[0098] Diaphragm: 10 mm.PHI., 2.theta.: 144.681 deg, Measurement
line: Si--K.alpha., Excitation voltage: 50 kV, Exciting current: 70
mA.
[Measurement Method]
[0099] A precursor fiber bundle is uniformly wound around an
acrylic resin board of 20 mm in height, 40 mm in length and 5 mm in
width, without leaving space, to prepare a measurement sample and
is placed in the apparatus. The intensity of fluorescent X-ray of
silicon is measured by a conventional fluorescent X-ray analysis
method. From the resultant intensity of fluorescent X-ray of
silicon of the precursor fiber bundle, the silicon content of the
fiber bundle is obtained by use of a calibration curve. The
intensity values of the measured samples (n=10) are averaged and
used as a measurement value.
[6. Measurement of Uneven Surface Structure of Precursor Fiber]
[0100] A single fiber of a precursor fiber bundle is fixed at both
ends on a metal sample-holder plate applied to a scanning probe
microscopic apparatus with carbon paste and measured under the
following conditions by the scanning probe microscope. First, the
shape image of a single fiber is measured by using a scanning probe
microscope. The measured image is subjected to image analysis. Ten
cross-section profiles in the direction perpendicular to the
fiber-axis are selected and measured to obtain the difference in
height (Rp-v) between a highest portion and a lowest portion of a
contouring curve and the center-line average roughness Ra. Ten
single fibers are subjected to measurement to obtain an average
value.
[Measurement Conditions]
[0101] Apparatus: SPI4000 probe station, SPA400 (unit manufactured
by SII NanoTechnology Inc., Scanning mode: Dynamic force mode (DFM)
(shape image measurement), Probe: SI-DF-20 manufactured by SII
NanoTechnology Inc., Rotation: 90.degree. (scan in the direction
perpendicular to the fiber-axis direction), Scanning speed: 1.0 Hz,
Number of pixels: 512.times.512, Measurement environment: Room
temperature, in the air.
[0102] A single image is obtained per single fiber according to the
above conditions and analyzed by image analysis software (SPIWin)
under the following conditions.
[Image Analysis Conditions]
[0103] The shape image thus obtained is subjected to [flat
treatment], [median 8 treatment] and [cubic slope correction]. In
this manner, a curved-surface image is corrected to a flat-surface
image by fitting correction. The flat-surface image thus corrected
is analyzed for surface roughness. The profile of a cross-section
in the direction perpendicular to the fiber-axis is measured to
obtain the difference in height (Rp-v) between a highest portion
and a lowest portion of a contouring curve and to obtain a
center-line average roughness Ra.
[Flat Treatment]
[0104] This is a treatment for removing distortion and undulation
in the Z-axis direction, that appears in an image data by lift,
vibration, creep of a scanner, etc., in other words, a treatment
for removing strains of data on SPM measurement caused by an
apparatus.
[Median 8 Treatment]
[0105] In a matrix of 3.times.3 around a data-point S to be
treated, calculation is performed between S and D1 to D8 to replace
Z data of S. In this manner, a filter effect such as smoothing and
noise removal is obtained.
[0106] In the median 8 treatment, a medium value of Z data of 9
points consisting of S and D1 to D8 is obtained to replace S.
[Cubic Slope Correction]
[0107] Slope correction is correction of slope by obtaining a
curved surface from all data of the image to be treated by least
squares approximation, followed by carrying out fitting of a cubic
curved surface. The terms (linear) (quadric) and (cubic) represent
dimensions of the curved surface to be fitted. In the cubic
correction, fitting of a cubic curved surface is carried out. Owing
to the cubic slope correction, curvature of a fiber from data is
eliminated to obtain a flat image.
[7. Measurement of X-Ray Diffraction Intensity and Crystal
Orientation Degree of Stabilized Fiber Bundle]
[0108] A stabilized fiber bundle is cut at arbitrary sites to
obtain fiber pieces that are 5 cm in length. Of them, fiber pieces
(12 mg) are weighed as sample fiber pieces and unidirectionally
arranged such that sample fiber pieces are accurately parallel to
the fiber axis. More precisely, a fiber bundle is prepared so as to
satisfy the conditions: width, which is the size of the fiber in
the direction perpendicular to the longitudinal direction: 2 mm;
and thickness, which is the size of the fiber in the direction
perpendicular not only to the width direction but also to the
longitudinal direction: uniform. The fiber bundle is fixed by
impregnating both ends of the fiber bundle with a vinyl
acetate/methanol solution, so that the shape of the bundle will not
be lost. This is used as the sample fiber bundle to be subjected to
measurement.
[0109] This is fixed on a sample stand for wide-angle X-ray
diffraction. The diffraction intensity in the equatorial-line
direction is measured by a transmission method to obtain a
diffraction intensity profile (the vertical axis: diffraction
intensity, the horizontal axis: 20 (unit: .degree.)). From the
obtained profile, diffraction intensity peak-top values in the
proximity of 2.theta.=17.degree. corresponding to reflection by
polyacrylonitrile (100) and 2.theta.=25.degree. corresponding to
reflection by graphite (002) are detected. The values each are
regarded as peak intensity.
[0110] Furthermore, crystal orientation degree is obtained by
measuring diffraction profile at each of reflection-peak positions
in the azimuthal-angle direction to obtain a half band-width "W" of
the peak (unit: .degree.) and by calculating in accordance with the
following expression.
Degree of crystal orientation (%)={(180-W)/180}.times.100
[0111] Degree of crystal orientation is measured by taking three
sample fiber bundles in the longitudinal direction of the fiber
bundle to be measured, measuring a degree of crystal orientation of
each of them and obtaining an average value of them.
[0112] Note that, X-ray diffraction is measured by a CuK.alpha.
beam X-ray generation apparatus (using Ni filter) manufactured by
Rigaku Corporation (trade name: TTR-III, rotary counter cathode
type X-ray generation apparatus) used as an X-ray source. A
diffraction intensity profile is detected by a scintillation
counter manufactured by Rigaku Corporation. Output is 50 kV-300
mA.
[8. Evaluation of the Cross-Sectional Shapes of Precursor Fiber and
Carbon Fiber]
[0113] The ratio of the major axis and the minor axis (major
axis/minor axis) of a cross-section of each of single fibers that
constitute a fiber bundle is determined as follows:
[0114] A fiber bundle for measurement is passed through a tube
formed of a vinyl chloride resin that has an inner diameter of 1
mm. The tube is then cut in the shape of a circle by a knife to
prepare samples. Subsequently, the sample is allowed to adhere to a
SEM sample stand so that the cross-section of a fiber faces up; Au
is sputtered to a thickness of about 10 nm; and a fiber
cross-section is observed by an electron microscope (product name:
XL20 scanning type, manufactured by Philips) under the following
conditions: an acceleration voltage of 7.00 kV and a migration
distance of 31 mm, to measure the major axis and minor axis of the
cross-section of the single fiber.
[9. Evaluation of Strand Physical-Property of Carbon Fiber
Bundle]
[0115] Preparation of a strand test-sample of a carbon fiber bundle
impregnated with a resin and measurement of the strength of the
sample are performed in accordance with JIS R7608. However, the
elastic modulus is calculated in the range of strain in accordance
with ASTM.
[10. Evaluation of Voids in Cross-Section of Carbon Fiber
Bundle]
[0116] A single fiber is removed from a carbon fiber bundle. To
this, platinum is sputtered on surface of the single fiber to a
thickness of 2 to 5 nm by using a sputtering apparatus and then
carbon is coated on the resultant single fiber to a thickness of
100 to 150 nm by using a carbon coater apparatus. Thereafter, a
tungsten protection film is deposited on the resultant single fiber
by using a focused ion beam processing apparatus (product name:
FB-2000A manufactured by Hitachi High-Technologies Corporation) to
a thickness of about 500 nm. Moreover, etching is performed by
using a focused ion beam at an acceleration voltage of 30 kV to
obtain a thin piece (thickness: 100 to 150 nm) of fiber having the
cross-section.
[0117] The thin piece (i.e., a cross-section of a single fiber) is
observed by a transmission electron microscope (product name:
H-7600, manufactured by Hitachi High-Technologies Corporation)
under the following conditions: an acceleration voltage of 100 kV
and a magnification of 150,000 to 200,000 times.
[0118] Furthermore, void portions, which look bright in a TEM image
are extracted by using image analysis software (product name:
Image-Pro PLUS, manufactured by Nippon Roper K.K.). In this manner,
the number of voids "N" is counted in the overall cross-section and
simultaneously the area of each void is measured to obtain an
equivalent circle diameter "d" (nm). Furthermore, the sum "A"
(nm.sup.2) of areas of voids and average void diameter "D" (nm) are
obtained.
[0119] Furthermore, the depth "T" (nm) of voids is obtained as
follows. The area of a void is sequentially and cumulatively
calculated from a void near the fiber surface toward a void that is
present in the direction of the center of the fiber. When the sum
of the above area reaches 95% of area "A," the distance between the
position of the last void and the fiber surface is "T." In other
words, when a circle is drawn on the cross-section of the single
fiber so that the area of all voids that are present between the
fiber surface and the circle is 0.95 A, and when the radius of the
circle is "r" and the radius of the single fiber is "R", then "T"
can be obtained in accordance with the following expression:
T=R-r.
[0120] With respect to 5 fibers, the above measurement is carried
out to obtain the average value.
[11. Measurement of Knot Tenacity of Carbon Fiber Bundle]
[0121] To both ends of a carbon fiber bundle of 150 mm in length, a
grip portion of 25 mm in length is applied to prepare a test
sample. In preparing a test sample, a weight of 0.1.times.10.sup.-3
N/denier is applied to uni-directionally arranged carbon fiber
bundles. In the test sample a single knot is formed virtually at
the center. Tension is performed at a crosshead rate of 100 mm/min.
A value of knot tenacity is obtained by dividing tensile breaking
stress by the cross-sectional area (mass and density of a bundle
per unit length) of a fiber bundle. Twelve bundles are used for a
test. The smallest value and the largest value are eliminated and
an average value of 10 bundles is used as knot tenacity.
Example 1 and Comparative Examples 1 to 3
[Preparation of Swollen Fiber and Precursor Fiber]
[0122] Acrylonitrile and methacrylic acid were polymerized in
accordance with an aqueous suspended polymerization to obtain an
acrylonitrile-based copolymer formed of an acrylonitrile
unit/methacrylic acid unit (98/2 mass %). The resultant polymer was
dissolved in dimethyl formamide to prepare a dope having a
concentration of 23.5 mass %.
[0123] The dope was ejected from a spinneret having 2000 ejection
holes of 0.13 mm in diameter arranged therein in the air, passed
through a space of about 4 mm and then ejected in a coagulant
filled with an aqueous solution containing 79.5 mass % dimethyl
formamide and controlled at a temperature of 15.degree. C. to
coagulate and to obtain a coagulated fiber. Subsequently, the
coagulated fiber was drawn (1.1 to 1.3 times) in the air and drawn
(1.1 to 2.9 times) in a drawing tank filled with an aqueous
solution containing 30 mass % dimethyl formamide and controlled at
a temperature of 60.degree. C. After the drawing process, the fiber
bundle in which a solvent was present was washed with clean water
and then drawn (1.2 times to 2.2 times) in hot water of 95.degree.
C.
[0124] Sequentially, to the fiber bundle, a finishing oil agent
containing amino-modified silicones as main components was applied
so as to apply 1.1 mass %, dried and densified. After the drying
and densification step, the fiber bundle was drawn (2.2 times to
3.0 times) between heated rolls of 180.degree. C. to further
improve the orientation and to perform densification. Thereafter,
the bundle was wound to obtain a precursor fiber bundle. The
fineness of the precursor fiber was 0.77 dtex. Furthermore, the
ratio of the major axis and the minor axis (major axis/minor axis)
of a cross-section of a single fiber was 1.005.
[0125] In this case, as the finishing oil agent containing
amino-modified silicones as main components, the followings were
used.
[0126] Amino-modified silicone; KF-865 (mono amino modified
side-chain type manufactured by Shin-Etsu Chemical Co., Ltd.,
viscosity: 110 cSt (25.degree. C.), amino equivalent mass: 5,000
g/mol, 85 mass %.
[0127] Emulsifier; NIKKOL BL-9EX (POE (9) lauryl ether,
manufactured by Nikko Chemicals Co., Ltd.), 15 mass %.
[Stabilization, Carbonization Treatment]
[0128] Next, a plurality of precursor fiber bundles were arranged
in parallel and introduced in an oven for stabilization. Air heated
to 220.degree. C. to 280.degree. C. was sprayed to the precursor
fiber bundles. In this manner, stabilization of the precursor fiber
bundles was performed to obtain stabilized fiber bundles having a
density of 1.342 g/cm.sup.3. In this case, 5.0%-extension was
performed in the density range of 1.200 g/cm.sup.3 to 1.250
g/cm.sup.3. Furthermore, 1.5%-extension was performed in the
density range of 1.250 g/cm.sup.3 to 1.300 g/cm.sup.3. Moreover,
-0.5%-extension was performed in the density range of 1.300
g/cm.sup.3 to 1.340 g/cm.sup.3. The total extension rate was set to
be 6% and the stabilization time was set to be 70 minutes.
[0129] Next, the stabilized fiber bundle was fed to a first
carbonization furnace having a temperature gradient of 300 to
700.degree. C. in nitrogen while the extension rate was increased
by 4.5%. The temperature gradient was set to be linear. The
treatment time was set to be 1.9 minutes.
[0130] Furthermore, heat treatment was performed using a second
carbonization furnace in which the temperature gradient was set to
be 1000 to 1250.degree. C., in a nitrogen atmosphere at an
extension rate of -3.8%. Subsequently, heat treatment was performed
using a third carbonization furnace in which the temperature
gradient was set to be 1250 to 1500.degree. C., in a nitrogen
atmosphere at an extension rate of -0.1% to obtain a carbon fiber
bundle. The total extension rate of the carbon fiber bundles
through the treatments in the second carbonization furnace and
third carbonization furnace was set to be -3.9% and the treatment
time was set to be 3.7 minutes.
[Surface Treatment of Carbon Fiber]
[0131] Subsequently, the bundles were fed to a 10 mass % aqueous
ammonium bicarbonate solution. Current was supplied between a
carbon fiber bundle serving as an anode and a counter pole so as to
obtain a quantity of electricity of 40 coulombs per carbon fiber (1
g) to be treated, washed with warm water of 90.degree. C. and then
dried. Next, HYDRAN N320 (manufactured by DIC Corporation) was
applied in the amount of 0.5 mass % and wound by a bobbin to obtain
a carbon fiber bundle. In Example 1 and Comparative Examples 1 to
3, the ratio of the major axis and the minor axis (major axis/minor
axis) of a cross-section of a single carbon fiber was 1.005 and the
diameter of the fiber was 4.9 .mu.m.
[Preparation of Uni-Direction Prepreg]
[0132] Onto a mold-releasing paper coated with epoxy resin #410
(that can be cured at 180.degree. C.) in the B stage, 156 carbon
fibers of the bundle released from a bobbin were uni-directionally
arranged and passed through a heat compression roller. In this
manner, the carbon fiber bundles were impregnated with epoxy resin.
A protecting film was laminated on the resultant fiber bundles to
prepare prepregs arranged in a uni-direction (hereinafter referred
to as a "UD prepreg") having a resin content of about 33 mass %, a
carbon fiber density of 125 g/m.sup.2 and a width of 500 mm.
[Molding of a Laminate Board and Evaluation of Mechanical
Performance]
[0133] A laminate board was prepared by using the above UD prepregs
and the tensile strength of the laminate board at angle 0.degree.
was evaluated by the evaluation method in accordance with ASTM
D3039.
[0134] The drawing conditions in the spinning step are shown in
Table 1.
TABLE-US-00001 TABLE 1 Spinning conditions Drawing tank (containing
warm Coagulation bath aqueous solution of organic solvent) In hot
Temper- Concen- In the air Temper- Concen- water Heat ature tration
Draw ature tration Draw Draw drawing (.degree. C.) (%) ratio
(.degree. C.) (%) ratio ratio Ratio Example 1 15 79.5 1.1 60 30 3.0
1.2 2.6 Compar. ex. 1 15 79.5 1.2 60 30 1.1 2.2 3.0 Compar. ex. 2
15 79.5 1.3 60 30 1.7 1.8 2.2 Compar. ex. 15 79.5 1.3 60 30 2.0 1.5
2.6 Example 2 10 79.5 1.1 60 30 2.5 1.4 2.6 Example 3 10 79.5 1.1
60 30 3.0 1.2 2.6 Example 4 5 79.5 1.1 60 30 3.0 1.2 2.6 Example 5
0 79.5 1.1 60 30 3.0 1.2 2.6 Example 6 -5 79.5 1.1 60 30 3.0 1.2
2.6 Example 7 20 79.5 1.1 60 30 3.0 1.2 2.6 Example 8 10 78.0 1.1
60 30 3.0 1.2 2.6 Example 9 10 79.0 1.1 60 30 3.0 1.2 2.6 Example
10 10 81.0 1.1 60 30 3.0 1.2 2.6 Example 11 10 79.5 1.1 50 30 3.0
1.2 2.6 Example 12 10 79.5 1.1 75 30 3.0 1.2 2.6 Example 13 10 79.5
1.1 60 40 3.0 1.2 2.6 Example 14 10 79.5 1.1 70 40 3.0 1.2 2.6
Example 15 10 79.5 1.1 70 60 3.5 1.3 2.8 Example 16 10 79.5 1.1 60
60 3.5 1.3 2.8 Compar. ex. 4 10 79.5 1.1 60 20 3.0 1.2 2.6 Compar.
ex. 5 10 79.5 1.1 35 30 3.0 1.2 2.6 Compar. ex. 6 25 79.5 1.1 60 30
3.0 1.2 2.6 Compar. ex. 7 15 83.0 1.1 60 30 3.0 1.2 2.6 Compar. ex.
8 10 76.0 1.1 60 30 3.0 1.2 2.6 Compar. ex. 9 5 77.0 1.1 60 0 2.0
2.0 1.9 Example 29 10 78.5 1.1 60 30 3.0 1.2 2.6 Example 30 10 80.5
1.1 60 30 3.0 1.2 2.6 Example 31 10 79.5 1.1 60 30 3.0 0.99 3.0
[Evaluation of Fiber]
[0135] Measurement of swelling degree of the coagulated fibers and
swollen fibers obtained, measurement of surface opening width of
swollen fibers, measurement of wide-angle X-ray of the precursor
fiber bundles, TMA evaluation, measurement of wide-angle X-ray of
the stabilized fiber, measurement of the strand strength and the
elastic modulus of carbon fibers, observation of voids in the
cross-section of carbon fibers and measurement of knot tenacy were
performed. The results are shown in Table 2. It was confirmed that
a carbon fiber of Example 1 has high mechanical performance.
TABLE-US-00002 TABLE 2 Swollen fiber Stabilized fiber bundle
Coagulated Average Precursor fiber bundle Wide-angle X-ray fiber
Average Total number Residual AFM Surface diffraction measurement
Swelling Swelling fine pore fine of pores amount of Si
configuration Orientation Orientation degree degree size pore
pores/.mu. after extraction Rp-v Ra degree degree mass % mass % nm
ml/g m.sup.2 ppm (nm) (nm) B/A (17.degree.) (25.degree.) Example 1
118 74 40.9 0.4 0.4 254 70 7.2 1.39 81.3 79.7 Compar. ex. 1 118 90
45 0.48 5.5 458 45 5 1.16 77.8 77.5 Compar. ex. 2 118 82 44.1 0.46
5 432 55 6 1.24 77.6 77.9 Compar. ex. 3 118 75 43.2 0.46 3.3 305 65
7 1.33 80.2 79 Example 2 115 80 40.3 0.43 1.5 142 61 6.7 1.36 80.8
79.4 Example 3 115 72 38.7 0.41 1.9 137 63 7.1 1.38 81.5 79.8
Example 4 114 70 36.2 0.4 0.6 137 61 6.6 1.37 81.6 79.8 Example 5
110 66 35 0.41 0.6 127 56 6.2 1.36 81.6 79.6 Example 6 100 63 35.1
0.39 0.6 122 51 5.9 1.38 81.7 79.9 Example 7 140 77 39.1 0.43 1 295
90 9.1 1.35 80.9 79.2 Example 8 155 96 54.1 0.54 0.3 117 45 4.2
1.37 81.6 79.8 Example 9 130 84 47.9 0.49 1.8 122 55 6.1 1.36 81.4
79.8 Example 10 115 71 33.4 0.34 2 142 50 5.2 1.35 80.7 79.5
Example 11 115 71 36.7 0.4 1.8 117 59 6.7 1.35 81.3 79.7 Example 12
115 74 40.7 0.4 1.4 127 72 7.9 1.34 81.2 79.7 Example 13 115 69
38.8 0.39 1.1 112 67 7.6 1.34 81.1 79.3 Example 14 115 68 38.1 0.4
1.2 117 75 8.2 1.35 81.2 79.4 Example 15 115 67 39.4 0.42 0.9 122
86 9.3 1.41 82.2 80.2 Example 16 115 67 38.6 0.41 0.5 112 81 8.6
1.42 82.1 80.3 Compar. ex. 4 115 81 36.6 0.41 4 315 51 5.2 1.28 80
78.8 Compar. ex. 5 115 66 35 0.37 4.8 330 54 5.5 1.25 79.8 78.9
Compar. ex. 6 165 90 45.4 0.44 5.2 447 110 11.6 1.25 79.8 78.5
Compar. ex. 7 110 69 37 0.28 3.1 315 103 10.4 1.27 79.4 78.1
Compar. ex. 8 190 105 69.1 0.63 0.2 40 25 2.5 1.25 79.2 78.2
Compar. ex. 9 170 110 58.1 0.57 0.2 49 32 2.9 1.14 77.4 76.9
Example 29 140 86 48 0.48 0.7 128 50 4.7 1.36 81.5 79.8 Example 30
115 71 32.5 0.37 1.8 140 52 5 1.36 81.1 79.6 Example 31 115 70 37.1
0.39 1.7 130 60 6.9 1.38 81.5 79.8 Tensile strength Carbon fiber
bundle of laminate Strand Average board at 0.degree. Strand elastic
Number diameter Sum of Depth of Knot (in terms of strength modulus
of voids of voids areas void strength 60 vol %) MPa GPa voids nm
nm.sup.2 nm N/mm2 MPa Example 1 6790 319 66 5.6 1,800 23 1100 3370
Compar. ex. 1 5300 320 525 6.3 24,400 168 750 2550 Compar. ex. 2
5780 320 284 6.3 8,900 72 800 2800 Compar. ex. 3 6410 320 96 5.6
1,900 65 950 3150 Example 2 6670 322 55 5 900 33 980 Example 3 6880
321 30 4.7 580 25 1080 3500 Example 4 6570 319 35 5.5 830 40 1030
Example 5 6520 320 37 5.5 850 26 1010 Example 6 6530 321 33 5.4 820
15 980 Example 7 6570 322 90 5.6 1750 30 1020 Example 8 6230 320 21
5.1 440 17 1050 3120 Example 9 6640 321 36 4.8 660 23 1100 3350
Example 10 6430 322 98 5.1 2,100 55 990 Example 11 6920 321 64 5.2
1,500 45 1070 3520 Example 12 6820 320 13 5.2 310 20 1090 Example
13 6950 320 37 4.7 680 15 1120 Example 14 7050 321 50 5.3 1,300 31
1120 3600 Example 15 7110 322 44 5.1 1,100 33 1110 3600 Example 16
7080 322 29 4.5 590 36 1130 Compar. ex. 4 5590 319 400 6.3 6,000 59
780 2710 Compar. ex. 5 5850 318 210 6.3 7,500 46 850 2830 Compar.
ex. 6 5290 321 480 6.4 23,000 182 760 2540 Compar. ex. 7 5780 320
220 6.4 8,000 161 790 2780 Compar. ex. 8 5700 318 16 5 300 9 860
2800 Compar. ex. 9 5850 319 18 5 480 12 820 Example 29 6580 321 26
5.1 500 21 1060 Example 30 6620 320 80 5.1 1700 45 1030 Example 31
6750 320 28 4.6 560 23 1050
Examples 2 to 16 and Comparative Examples 4 to 9
[0136] Swollen fibers and precursor fiber bundles were obtained in
the same manner as in Example 1 except that conditions of the
spinning step were partly changed. The fineness of a precursor
fiber was set to be 0.77 dtex and the ratio of the major axis and
the minor axis (major axis/minor axis) of a cross-section of a
single fiber was 1.005. Subsequently, carbon fiber bundles were
produced in the same carbonization conditions. The ratio of the
major axis and the minor axis (major axis/minor axis) of a
cross-section of a single carbon fiber was 1.005 and the diameter
of the fiber was 4.9 .mu.m.
[0137] The conditions for the spinning step are shown in Table 1
and the evaluation results of individual fiber bundles are shown in
Table 2, collectively.
Examples 17 to 20
[0138] Carbon fiber bundles were prepared in the same conditions as
in Example 14 by using the precursor fiber bundle obtained in
Example 14 except that only heat treatment conditions of the second
and third carbonization furnaces were changed. The heat treatment
conditions and properties of the carbon fiber bundles are shown in
Table 3.
TABLE-US-00003 TABLE 3 Example Example Example Example Carbon fiber
bundle 17 18 19 20 Temperature conditions 1050-1300 1050-1250
1100-1450 1100-1550 of second carbonization furnace (.degree. C.)
Extension rate in -3.6% -3.7% -3.5% -3.3% second carbonization
furnace (%) Temperature conditions -- 1350-1550 1500-1700 1600-1850
of third carbonization furnace (.degree. C.) Extension rate in
third -- -0.1% 0.0% 0.5% carbonization furnace (%) Total treatment
time in 1.9 3.7 3.7 3.7 carbonization furnaces (min) Major
axis/minor axis 1.005 1.005 1.005 1.005 of cross-section Diameter
of single 5.0 4.9 4.8 4.7 fiber (.mu.m) Strand strength (MPa) 6300
6550 6300 6150 Strand elastic modulus 260 335 355 375 (GPa) Number
of voids N 56 45 32 24 (voids) Average diameter of 5.4 5.1 4.5 3.0
voids (nm) Sum of areas (nm.sup.2) 1400 990 500 210 Depth of void
(nm) 31 35 28 16 Knot tenacity (N/mm.sup.2) 1190 1150 1010 950
Examples 21 to 25 and Reference Examples 1 and 2
[0139] A precursor fiber bundle was obtained in the same spinning
conditions as in Example 14 except that only the fineness of a
single fiber was changed. Carbon fiber bundles were prepared in the
same carbonization conditions as in Example 15 by using the
precursor fiber bundle obtained above except that only the heat
treatment conditions of the second and third carbonization furnaces
were changed. The precursor fibers, heat treatment conditions and
properties of carbon fiber bundles are shown in Table 4.
TABLE-US-00004 TABLE 4 Reference Reference Carbon fiber bundle
Example 21 Example 22 Example 23 Example 24 Example 25 Example 1
Example 2 Fineness of single 0.52 0.6 0.70 0.9 1.0 0.45 1.1
precursor fiber (dtex) Temperature conditions of second 1000-1250
1000-1250 1000-1250 1000-1250 1000-1250 1000-1250 1000-1250
carbonization furnace (.degree. C.) Extension rate in second -3.8%
-3.8% -3.8% -3.8% -3.8% -3.8% -3.8% carbonization furnace (%)
Temperature conditions of third 1250-1400 1250-1430 1250-1450
1250-1550 1250-1600 1250-1380 1250-1650 carbonization furnace
(.degree. C.) Extension rate in third -0.1% -0.1% -0.1% -0.1% -0.1%
-0.1% -0.1% carbonization furnace (%) Total treatment time in 3.7
3.7 3.7 3.7 3.7 3.7 3.7 carbonization furnaces (min) Major
axis/minor axis 1.005 1.005 1.005 1.005 1.005 1.005 1.005 of
cross-section Strand strength (MPa) 6350 6700 7250 6700 6200 5700
5750 Strand elastic modulus (GPa) 318 320 322 318 317 321 319
Number of voids N (voids) 26 21 39 43 68 35 65 Average diameter of
voids (nm) 5.1 4.7 6.1 4.8 5.6 5.0 4.8 Sum of areas (nm.sup.2) 886
510 1200 990 1500 880 1400 Depth of void (nm) 25 30 39 35 32 22 37
Knot tenacity (N/mm.sup.2) 920 1090 1120 1050 950 760 810
Examples 26 to 28 and Reference Examples 3 and 4
[0140] A precursor fiber bundles was prepared in the same
conditions as in Example 14 except that types of amino-modified
silicones of finishing oil agents were changed, and subsequently
carbon fiber bundles were prepared. The type of amino-modified
silicones used and properties of the precursor fibers and carbon
fiber bundles are shown in Table 5.
TABLE-US-00005 TABLE 5 Reference Reference Example 26 Example 27
Example 28 Example 3 Example 4 Amino- Product No. KF-868 KF-860
KF-861 KF-393 KF-8004 modifted Manufacturer Shin-Etsu Shin-Etsu
Shin-Etsu Shin-Etsu Shin-Etsu silicone Chemical Chemical Chemical
Chemical Chemical Co., Ltd. Co., Ltd. Co., Ltd. Co., Ltd. Co., Ltd.
Type Mono amino Diamino Diamino Diamino Diamino modified side-
modified modified modified modified chain type side-chain
side-chain side-chain side-chain type type type type Kinematic
viscosity cSt (25.degree. C.) 90 250 3500 70 800 Amino equivalent
g/mol 8800 7600 2000 350 1500 weight Precursor Residual Si amount
ppm 125 105 100 250 190 fiber bundle after extraction Carbon Strand
strength MPa 6980 7060 7100 Production Production fiber Strand
elastic GPa 321 320 321 failure, due to failure, due to bundle
modulus winding of winding of Number of voids voids 60 45 20 fiber
in an fiber in an Average diameter nm 5.4 5.1 4.2 oven for oven for
of voids stabilization stabilization Sum of areas nm.sup.2 1,600
1,100 400 Depth of void nm 28 19 14 Knot strength N/mm.sup.2 1080
1100 1150
Examples 29 to 31
[0141] Swollen fibers and precursor fiber bundles were obtained in
the same manner as in Example 1 except that the conditions of the
spinning step were partly changed. The fineness of the precursor
fibers was set to be 0.77 dtex. The ratio of the major axis and the
minor axis (major axis/minor axis) of a cross-section of a single
fiber was 1.005. Subsequently, carbon fiber bundles were produced
in the same carbonization conditions. The ratio of the major axis
and the minor axis (major axis/minor axis) of a cross-section of a
single carbon fiber was 1.005 and the diameter of the fiber was 4.9
.mu.m.
[0142] The conditions of the spinning step are shown in Table 1 and
the evaluation results of individual fiber bundles are shown in
Table 2.
INDUSTRIAL APPLICABILITY
[0143] The carbon fiber bundle of the present invention can be used
as a constructional material for airplanes, high speed moving
bodies, etc.
* * * * *