Note: Descriptions are shown in the official language in which they were submitted.
CA 02764661 2011-12-06
Description
Title of Invention:
ACRYLONITRILE SWOLLEN FIBER FOR CARBON FIBER, PRECURSOR
FIBER BUNDLE, STABILIZED FIBER BUNDLE, CARBON FIBER BUNDLE
AND PRODUCTION METHODS THEREOF
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
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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
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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
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[0006]
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
[0007]
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
[0008]
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.
[0009]
The aforementioned object can be attained by the following
inventions.
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/ m2 or more and 2 openings/ m2 or less on the surface of the
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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
[1] a step of preparing a dope at a temperature of 50 C or more and
70 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,
[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 C or more and 20 C or less,
[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
[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.
[0011]
A third invention is directed to a precursor fiber bundle for a carbon
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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.
[0012]
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.
[0013]
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 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 (20 = 25 ) and peak B (20 = 17 ) 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,
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(3) orientation degree of peak A is 79% or more and
(4) density is 1.335 g/cm3 or more and 1.360 g/cm3 or less.
[0014]
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 m to 6.0 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.
[0015]
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/cm3 or more and 1.355 g/cm3 or less; then performing
heating in a first carbonization furnace having a temperature gradient of
300 C or more and 700 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 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
[0016]
The swollen fiber of the present invention is capable of preventing
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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
[0017]
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.
[0018]
[Swollen fiber]
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/ m2 or more and 2
openings/ m2 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.
[0019]
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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.
[0020]
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.
[0021]
[Evaluation of permeability of swollen fiber with finishing oil agent]
The permeability of a swollen fiber with a finishing oil agent can be
evaluated as follows:
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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.
(1) Amino-modified silicone; KF-865 (manufactured by Shin-Etsu
Chemical Co., Ltd., mono amino modified side-chain type, kinematic
viscosity: 110 cSt (25 C), amino equivalent mass: 5,000 g/mol): 85
mass %,
(2) Emulsifier; NIKKOL BL-9EX (manufactured by Nikko Chemicals
Co., Ltd., POE (9) lauryl ether): 15 mass %.
[0022]
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.
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.
[0023]
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
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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.
[0024]
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.
[0025]
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
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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.
[0026]
[Method of producing swollen fiber]
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.
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.
[0027]
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
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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.
[0028]
As the third component, an acryl amide derivative such as
acrylamide, methacrylamide, N-methylol acrylamide, N,N-dimethyl
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.
[0029]
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 C. The solid-substance
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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.
[0030]
Furthermore, if the temperature of a dope is set to be 50 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 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 C, a coagulated fiber
having a highly dense and uniform structure can be stably produced.
[0031]
The organic solvent is not particularly limited; however,
dimethylformamide, dimethylacetamide or dimethylsuIfoxide is more
preferably used. More preferably, dimethylformamide which has
excellent solubility for an acrylonitrile-based copolymer is used.
[0032]
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
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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 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 C to 10 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.
[0033]
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
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solvent concentration and higher temperature than a coagulant. Owing
to this, a coagulated fiber having a uniform fibril structure can be formed.
[0034]
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.
[0035]
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 C or more to 80 C
or less. If the temperature is set to be 40 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 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
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temperature is 55 C or more and 75 C or less.
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.
[0036]
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.
[0037]
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.
[0038]
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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.
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.
[0039]
After drawing treatment, the fiber bundle is washed with warm water
of 500C or more and 95 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 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
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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.
Swollen fiber can be obtained by applying drawing treatment and
washing treatment to a coagulated fiber in this manner.
[0040]
[Heat drawing]
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 C, in a dry heat medium of 100 to 200 C, between heated rolls of 150
to 220 C or on a heated plate of 150 to 220 C to further improve
orientation and to perform densification. Thereafter, the bundle is wound
to obtain a precursor fiber bundle.
[0041]
[Precursor fiber bundle]
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
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CA 02764661 2011-12-06
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.
[0042]
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.
[0043]
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 C or less) of a carbonization step, and is scattered in a second-half
carbonization step (more than 800 C). As a result, many voids are
- 20 -
CA 02764661 2011-12-06
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.
[0044]
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
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CA 02764661 2011-12-06
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.
[0045]
The uneven surface structure extending in the fiber-axis direction
herein refers to a wrinkle structure that has a length of 0.6 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 m or more.
[0046]
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
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CA 02764661 2011-12-06
preferable ratio of the major axis and the minor axis (major axis/minor
axis) is 1.00 to 1.005.
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.
[0047]
[Method of producing precursor fiber bundle]
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.
[0048]
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.
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 C and an amino
equivalent mass of 1,700 to 15,000 g/mol.
- 23 -
CA 02764661 2011-12-06
[0049]
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 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 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 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
- 24 -
CA 02764661 2011-12-06
step.
[0050]
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.).
[0051]
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.
[0052]
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
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CA 02764661 2011-12-06
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.
[0053]
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.
[0054]
The fiber bundle after the dry densification process is, if necessary,
drawn in a pressurized steam at a temperature of 130 to 200 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.
[0055]
[Method of producing a stabilized fiber bundle]
A precursor fiber bundle is fed to a hot-air circulation type oven for
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CA 02764661 2011-12-06
stabilization at a temperature of 220 to 260 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/cm3 or more
and 1.360 g/cm3 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.
[0056]
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/cm3, 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/cm3, the oxygen content of the fiber increases. In
the following heat treatment performed at a high temperature, a reaction
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CA 02764661 2011-12-06
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/cm3 or more and 1.350 g/cm3 or less.
[0057]
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.
[0058]
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 (20 = 25 ) and peak B (20 = 17 ) 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/cm3 or
more and 1.360 g/cm3 or less.
[0059]
The crystal structure derived from reflection by polyacrylonitrile
(100) at peak B (20 = 17 ) is closely related to formation of the structure
of a carbon fiber. If the orientation degree of a crystal and crystallinity
- 28 -
CA 02764661 2011-12-06
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 (20 = 17 ) 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.
[00601
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/cm3 or more and 1.260 g/cm3 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/cm3 or more and 1.310 g/cm3 or less; and an extension
rate of -1.0% or more and 2.0% or less at a fiber density in the range of
- 29 -
CA 02764661 2011-12-06
1.300 g/cm3 or more and 1.360 g/cm3 or less.
[0061]
[Carbon fiber]
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 C or more and 800 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 C to 800 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 C or more. If
the highest temperature exceeds 800 C, the fiber becomes very fragile
and will be barely transferred to the following step. A more suitable
temperature range is 300 to 750 C. More preferable temperature range
is 300 to 700 C.
[0062]
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
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CA 02764661 2011-12-06
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.
[0063]
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 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.
[0064]
The temperature of the second carbonization furnace varies
depending upon the temperature condition in the first carbonization
furnace; however, the temperature is satisfactorily 1000 C or more and
preferably 1050 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
- 31 -
CA 02764661 2011-12-06
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%.
[0065]
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.
[0066]
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
- 32 -
CA 02764661 2011-12-06
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.
[0067]
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.
[0068]
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 p.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.
[0069]
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CA 02764661 2011-12-06
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.
[0070]
In the carbon fiber bundle of the present invention, the sum A (nm2)
of areas of voids present in the cross-section of a single fiber
perpendicular to the fiber-axis direction is preferably 2,000 nm2 or less.
Furthermore, voids corresponding to 95% or more of the sum A (nm2) 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.
[0071]
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/mm2 or more. More preferably, the knot
tenacity is 1000 N/mm2 or more and further preferably, 1100 N/mm2 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
- 34 -
CA 02764661 2011-12-06
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/mm2, sufficient mechanical performance will not develop in a pseudo-
isotropic material.
Examples
[0072]
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.
[0073]
[1. Measurement of swelling degree of coagulated fiber]
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 C or less. The time from
initiation of storage to completing measurement of the degree of swelling
is set to fall within 8 hours.
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.
- 35 -
CA 02764661 2011-12-06
[0074]
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 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.
The degree of swelling is measured in accordance with the following
expression:
The degree of swelling (A - B) / B x 100%
[0075]
[2. Method of measuring the degree of swelling of swollen fiber]
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.
[0076]
[3. Observation of surface configuration of swollen fiber]
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 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
- 36 -
CA 02764661 2011-12-06
magnification of 50,000 times.
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 m2) (average number of
openings).
[0077]
[4. Method of measuring fine pore distribution of swollen fiber]
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 C, the sample is lyophilized under reduced pressure of 100
Pa or less for 24 to 72 hours.
[0078]
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
- 37 -
CA 02764661 2011-12-06
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
[0079]
[5. Measurement of silicon content of precursor fiber bundle]
[Measuring apparatus]
Fluorescent X-ray spectrometer: product name: ZSX100e manufactured by
Rigaku Industrial Corp.,
Target: Rh (end-window type) 4.0 kW,
Dispersive crystal: RX4,
Detector: PC (proportional counter),
Slit: Std.,
Diaphragm: 10 mm4,
20: 144.681 deg,
Measurement line: Si-Ka,
Excitation voltage: 50 kV,
Exciting current: 70 mA.
[0080]
[Measurement method]
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.
- 38 -
CA 02764661 2011-12-06
The intensity values of the measured samples (n = 10) are averaged and
used as a measurement value.
[0081]
[6. Measurement of uneven surface structure of precursor fiber]
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.
[0082]
[Measurement conditions]
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 Sli NanoTechnology Inc.,
Rotation: 90 (scan in the direction perpendicular to the fiber-axis
direction),
Scanning speed: 1.0 Hz,
Number of pixels: 512 x 512,
Measurement environment: Room temperature, in the air.
A single image is obtained per single fiber according to the above
conditions and analyzed by image analysis software (SPIWin) under the
following conditions.
- 39 -
CA 02764661 2011-12-06
[0083]
[Image analysis conditions]
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.
[0084]
[Flat treatment]
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.
[0085]
[Median 8 treatment]
In a matrix of 3 x 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.
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.
[0086]
[Cubic slope correction]
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
- 40 -
CA 02764661 2011-12-06
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.
[0087]
[7. Measurement of X-ray diffraction intensity and crystal orientation
degree of stabilized fiber bundle]
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.
[0088]
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: )). From the
obtained profile, diffraction intensity peak-top values in the proximity of 20
= 17 corresponding to reflection by polyacrylonitrile (100) and 20 = 25
corresponding to reflection by graphite (002) are detected. The values
each are regarded as peak intensity.
[0089]
Furthermore, crystal orientation degree is obtained by measuring
- 41 -
CA 02764661 2011-12-06
diffraction profile at each of reflection-peak positions in the azimuthal-
angle direction to obtain a half band-width "W" of the peak (unit: ) and by
calculating in accordance with the following expression.
Degree of crystal orientation (%) = {(180 - W) / 180} x 100
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.
Note that, X-ray diffraction is measured by a CuKa 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.
[0090]
[8. Evaluation of the cross-sectional shapes of precursor fiber and carbon
fiber]
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:
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
- 42 -
CA 02764661 2011-12-06
the cross-section of the single fiber.
[0091]
[9. Evaluation of strand physical-property of carbon fiber bundle]
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.
[0092]
[10. Evaluation of voids in cross-section of carbon fiber bundle]
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.
[0093]
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.
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
- 43 -
CA 02764661 2011-12-06
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"(nm2) of areas of voids and average void
diameter "D" (nm) are obtained.
[0094]
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 0.95A, 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.
With respect to 5 fibers, the above measurement is carried out to
obtain the average value.
[0095]
[11. Measurement of knot tenacity of carbon fiber bundle]
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 x 10"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
- 44 -
CA 02764661 2011-12-06
and an average value of 10 bundles is used as knot tenacity.
[0096]
(Example 1 and Comparative Examples 1 to 3)
[Preparation of swollen fiber and precursor fiber]
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 %.
[0097]
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 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 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 C.
[0098]
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 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
- 45 -
CA 02764661 2011-12-06
of the major axis and the minor axis (major axis/minor axis) of a cross-
section of a single fiber was 1.005.
In this case, as the finishing oil agent containing amino-modified
silicones as main components, the followings were used.
[0099]
,.Amino-modified silicone; KF-865 (mono amino modified side-chain type
manufactured by Shin-Etsu Chemical Co., Ltd., viscosity: 110 cSt (25 C),
amino equivalent mass: 5,000 g/mol, 85 mass %.
..Emulsifier; NIKKOL BL-9EX (POE (9) lauryl ether, manufactured by Nikko
Chemicals Co., Ltd.), 15 mass %.
[0100]
[Stabilization, carbonization treatment]
Next, a plurality of precursor fiber bundles were arranged in parallel
and introduced in an oven for stabilization. Air heated to 220 C to 280 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/cm3. In this case, 5.0%-extension
was performed in the density range of 1.200 g/cm3 to 1.250 g/cm3.
Furthermore, 1.5%-extension was performed in the density range of 1.250
g/cm3 to 1.300 g/cm3. Moreover, -0.5%-extension was performed in the
density range of 1.300 g/cm3 to 1.340 g/cm3. The total extension rate
was set to be 6% and the stabilization time was set to be 70 minutes.
[0101]
Next, the stabilized fiber bundle was fed to a first carbonization
furnace having a temperature gradient of 300 to 700 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.
[0102]
Furthermore, heat treatment was performed using a second
- 46 -
CA 02764661 2011-12-06
carbonization furnace in which the temperature gradient was set to be
1000 to 1250 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 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.
[0103]
[Surface treatment of carbon fiber]
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 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 m.
[0104]
[Preparation of uni-direction prepreg]
Onto a mold-releasing paper coated with epoxy resin #410 (that can
be cured at 180 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
- 47 -
CA 02764661 2011-12-06
uni-direction (hereinafter referred to as a "UD prepreg") having a resin
content of about 33 mass %, a carbon fiber density of 125 g/m2 and a
width of 500 mm.
[0105]
[Molding of a laminate board and evaluation of mechanical performance]
A laminate board was prepared by using the above UD prepregs and
the tensile strength of the laminate board at angle 00 was evaluated by
the evaluation method in accordance with ASTM D3039.
The drawing conditions in the spinning step are shown in Table 1.
[0106]
[Table 1]
48 -
CA 02764661 2011-12-06
Table 1
Spinning conditions
Drawing tank (containing In hot H eat
Coagulation bath in the air warm aqueous solution of water drawing
organic solvent)
Tempe- Conce- Tempe- Conce-
Draw Draw Draw
rature ntration rature ntration Ratio
( C) (%) ratio ( C) (%) ratio ratio
Example 1 15 79.5 1.1 60 30 3.0 1.2 2.6
Com ar.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
[0107]
[Evaluation of fiber]
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
- 49 -
CA 02764661 2011-12-06
mechanical performance.
[0108]
[Table 2]
50 -
CA 02764661 2011-12-06
O
_ N U o htn Old -It W ) o
- t# >~ y ti'i T N t- h 0~ 0\ O~ C O\ 6 0 00 00 00 00 00 '.0 CC 0\ 0'
>~ cj^, C1 N h h h N h[ [~ h h h h r- h h [N N 00 00 N h r- N h h h h h
c~ N O N
0 M 001p N00 to 10110 h Ot 1D~ hMN~NN~ 0000 'C}'Nd'tn ~r to
t
Ca y '-' h r.: O O =--i .-~ .--i ..r p ri ..~ o r.+ -4 00 O\ 01 Ol ON h
.Ni b v 00 h h 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 N h N h N 00 00
00
~' 01 "0 Nr m 10 00 r` 10 00 in h 10 to to kn .-r N 00 'r V1 N N It '.D \p 00
,'d Q en - N M M M M M M M M M M M M M M ~' V' N N N N N ^'~ M M M
OC
U cc3 qC N h~IONC'-N--~Nhrnl0NcnloNtr tno~h O\
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.~ n rL.(
..U ptntoL( -.M.-+11p.-+Otntn000NN '.0=--~r.+~t9en NCNCD
O h V to 10 10 1D 10 to to O\ to to to h 1D h o0 00 to to N Mtn to 10
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to to M O -' M M N N -' N :t - N --~ --~ N - en e ~t - O a, N d. M.
N d' d' M r .r N M d' M
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cd O N Orn r. N M r: N - - - Ql 11t h h 00 .-.'et 1010 ~t r. to r 00 1~
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= a y~y...~~ o
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X X X N Md'tn110ho0ON ~^t ~..r. X X X X X X N M
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CA 02764661 2011-12-06
[Table 2-2]
Table 2-2
Tensile
Carbon fiber bundle strength of
laminate board
at 0
Strand Strand Number Average Sum of Depth of Knot (in terms of 60
strength elastic of voids diameter of areas void strength vol%)
modulus voids
MPa GPa voids nm nm2 nm N/mm2 MPa
Example 1 6790 319 66 5.6 1,800 23 1100 3370
Compar.exl 5300 320 525 6.3 24,400 168 750 2550
Compar.ex2 5780 320 284 6.3 8,900 72 800 2800
Compar.ex3 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.ex4 5590 319 400 6.3 6,000 59 780 2710
Compar.ex5 5850 318 210 6.3 7,500 46 850 2830
Compar.ex6 5290 321 480 6.4 23,000 182 760 2540
Compar.ex7 5780 320 220 6.4 8,000 161 790 2780
Compar.ex8 5700 318 16 5 300 9 860 2800
Compar.ex9 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
CA 02764661 2011-12-06
[0109]
(Examples 2 to 16 and Comparative Examples 4 to 9)
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 m.
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.
[0110]
(Examples 17 to 20)
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.
[0111]
[Table 3]
- 53 -
CA 02764661 2011-12-06
Table 3
Carbon fiber bundle Example Example Example Example
17 18 19 20
Temperature conditions 1050- 1050- 1100- 1100-
of second carbonization 1300 1250 1450 1550
furnace ( C)
Extension rate in -3.6% -3.7% -3.5% -3.3%
second carbonization
furnace (%)
Temperature conditions - 1350- 1500- 1600-
of third carbonization 1550 1700 1850
furnace ( 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 ( 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) 1400 990 500 210
Depth of void (nm) 31 35 28 16
Knot tenacity (N/mm) 1190 1150 1010 950
[0112]
(Examples 21 to 25 and Reference Examples 1 and 2)
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
54 -
CA 02764661 2011-12-06
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.
[0113]
[Table 4]
- 55 -
CA 02764661 2011-12-06
N N O O
N O O ~_ 00 O O
,~ ~/'1 lIl O l~
40, " ~ O O O M " I M 00
N O N
N r O O
N v~ - o o p 0 - p 0 O
o 0 00 M 00 o M p O N c~
0 N
CD 1 M 00 r-
Ga O N
O O
N v1 O
O
kn C>
O ~ N O p r 00 Q O N
00 M O O M N l/) r+ M Q\
O N
N O O
N Ln
0 0
N N \ \ c/'1 p 00 O
CL -, 00 i - I~ O p - ~r 00 kn t/7
CD p M p c+~ O M d ~} M O
O N
O O
kn 41
0 0
C14 Irl c,
00 i. \ N v N ^' O O\ N
C>
N M ~p N M
O O M N O M M =- -
N O O
N (P1 M
0 0
O O M O O M O N M N M O
O N
N O
N p O 00 ~p O
00 O M N --= 00 1.) N
O O M O O M r+ \O M N 00 N
O N
O O
U Q O U ,
r. Cl) 0 0 c 0 Q cn ~. b rn
= 4? O 4~ .p O u O .0 cd ~..i O ==O
U U c~ U A`=+ v> > OC
U cd c0 U U 4., '~'~
;3 Z
Q k w O `~ O w y `-' O ^O cd O
b0 ~' Q vUi cUd O 0 cUd U > ccd 4~
o r.
c. 0 C y. 4~ U U U ~+
cd cd .D y O O
M O s. O C +- N s.. -p CJ~ Q
w H ' F-+ o d
w w ~' ~
CA 02764661 2011-12-06
[0114]
(Examples 26 to 28 and Reference Examples 3 and 4)
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.
[0115]
[Table 5]
CA 02764661 2011-12-06
00 ILI
f~u~jxEU a 3wo
N
0-0.- O N O
21 40.
t-- L N O ,C'S -O N M N - y O s~ y
f1+ x rYi On u U Q O' -O O
00
N O O O O
LL oo U O 00 00 p N p N O
O ... O M N M
W rw C/~ U U Q N ~~
con o -':j
Q oo W' a w ' 0 00
cd "o N N p O M O
UU Q b
N ~j Ei 0 (1)
v N
A a) 00 El)
ro 00 W U b y O 00 000 O d O 00 00
.0 Z 0 O, 00 ON M \O - N O
T7 00 \O
-0 0
U
0
~= rG
z
U
a+ 0
z r
~, 0 C N
U ,> C .9 U 0 E co d .C
Q co 4'.
b a' c. cd
,~s=õ+
a N co 7~C O N bA 4r O 4. 0
O 15 O-c3
O N c0 Q sue. +~+ a+
O
>
i C/) V) G Z Q > Q ~4
c,
U
CA 02764661 2011-12-06
[0116]
(Examples 29 to 31)
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 m.
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
[0117]
The carbon fiber bundle of the present invention can be used as a
constructional material for airplanes, high speed moving bodies, etc.
