U.S. patent application number 12/166479 was filed with the patent office on 2010-01-07 for carbon fiber.
This patent application is currently assigned to TOHO TENAX CO., LTD.. Invention is credited to Harumitsu Enomoto, Taro Oyama, Takaya Suzuki, HIDEKAZU YOSHIKAWA.
Application Number | 20100003186 12/166479 |
Document ID | / |
Family ID | 41432981 |
Filed Date | 2010-01-07 |
United States Patent
Application |
20100003186 |
Kind Code |
A1 |
YOSHIKAWA; HIDEKAZU ; et
al. |
January 7, 2010 |
CARBON FIBER
Abstract
According to the present invention, there is disclosed a carbon
fiber having a strand tensile strength of 6,100 MPa or more, a
strand tensile modulus of 340 GPa or more and a density of 1.76
g/cm.sup.3 or more and possessing, on the surface, striations
oriented in a direction parallel to the fiber axis, wherein the
distance between striations in a 2.times.2 .mu.m area of the carbon
fiber surface when observed by a scanning probe microscope is 0.1
to 0.3 .mu.m, the root mean square surface roughness Rms (5 .mu.m)
in a 5.times.5 .mu.m area of the carbon fiber surface when observed
by a scanning probe microscope is 20 to 40 nm, and the root mean
square surface roughness Rms (0.5 .mu.m) when measured in a
0.5.times.0.5 .mu.m area is 2 to 12 nm.
Inventors: |
YOSHIKAWA; HIDEKAZU;
(Shizuoka, JP) ; Oyama; Taro; (Shizuoka, JP)
; Suzuki; Takaya; (Shizuoka, JP) ; Enomoto;
Harumitsu; (Shizuoka, JP) |
Correspondence
Address: |
LONDA, BRUCE S.
875 THIRD AVE, 8TH FLOOR
NEW YORK
NY
10022
US
|
Assignee: |
TOHO TENAX CO., LTD.
Tokyo
JP
|
Family ID: |
41432981 |
Appl. No.: |
12/166479 |
Filed: |
July 2, 2008 |
Current U.S.
Class: |
423/447.2 |
Current CPC
Class: |
D01F 9/22 20130101; D01F
9/12 20130101 |
Class at
Publication: |
423/447.2 |
International
Class: |
D01F 9/12 20060101
D01F009/12 |
Claims
1. A carbon fiber having a strand tensile strength of 6,100-6,400
MPa, a strand tensile modulus of 340-370 GPa, an average diameter
of the carbon fiber of 4.5 to 6.0 .mu.m and a density of 1.76-1.80
g/cm.sup.3 and possessing, on the surface, striations oriented in a
direction parallel to the fiber axis, wherein the distance between
striations in a 2.times.2 .mu.m area of the carbon fiber surface
when observed by a scanning probe microscope is 0.1 to 0.3 .mu.m,
the root mean square surface roughness Rms (5 .mu.m) in a 5.times.5
.mu.m area of the carbon fiber surface when observed by a scanning
probe microscope is 20 to 40 nm, and the root mean square surface
roughness Rms (0.5 .mu.m) when measured in a 0.5.times.0.5 .mu.m
area is 2 to 12 nm.
2. (canceled)
3. The carbon fiber according to claim 1, wherein the surface
oxygen concentration (O/C) of carbon fiber when measured by an
X-ray photoelectron spectrometer is 0.13 or more, the surface
nitrogen concentration (N/C) of carbon fiber when measured by the
spectrometer is 0.05 or less, the crystallite size measured by
wide-angle X-ray diffractometry is 2 nm or more, and the band
intensity ratio (D/G) of 1,360 cm.sup.-1 band intensity (D) and
1,580 cm.sup.-1 band intensity (G) when measured by Raman
spectrometry is 1.3 or less.
4. The carbon fiber according to claim 1, which is obtained by
subjecting, to an oxidation treatment and a carbonization
treatment, an acrylic fiber having an orientation degree of 90.5%
or less when measured by wide-angle X-ray diffractometry
(diffraction angle: 17.degree.).
5. The carbon fiber according to claim 1, which is obtained by
firing an oxidized fiber showing a mass reduction ratio of 7% or
less when immersed in dimethylformamide for 12 hours.
Description
TECHNICAL FIELD
[0001] The present invention relates to a carbon fiber which can be
compounded with a resin to be made into a composite material of
high performance.
BACKGROUND ART
[0002] As the process for production of carbon fiber, there is a
well-known process which comprises subjecting a raw material fiber
[e.g. a polyacrylonitrile (PAN)] used as a precursor fiber, to an
oxidation treatment and then to a carbonization treatment to obtain
a carbon fiber (see, for example, Patent Literature 1). The carbon
fiber obtained thus has good properties such as high tensile
strength, high tensile modulus and the like.
[0003] In recent years, composite materials produced using a carbon
fiber [e.g. a carbon fiber-reinforced plastic (CFRP)] are finding
ever increasing applications in various industries. The following
requirements are becoming stronger particularly in industries such
as sport, leisure, aerospace, automobile and the like. [0004] (1)
Higher performance (high strength and high modulus) [0005] (2)
Lighter weight (light fiber weight and low fiber content) [0006]
(3) Exhibition of higher properties in compounding of composite
material (improvement in carbon fiber surface property and
interface property)
[0007] In order to obtain a composite material of higher
performance in compounding of a carbon fiber and a matrix material
(e.g. a resin), it is important that the matrix material is
improved in properties; further, it is essential that the carbon
fiber per se is improved in surface property, strength and modulus.
That is, a composite material of higher performance (high strength
and high modulus) can be obtained by compounding a carbon fiber
having a high adhesivity to matrix material, with a matrix material
to uniformly disperse the carbon fiber in the matrix material.
[0008] Investigations have been made heretofore on the improvement
of carbon fiber in surface property, strength and modulus (see, for
example, Patent Literature 2).
[0009] However, conventional carbon fibers are insufficient in
performance for use in production of a composite material
satisfying the above-mentioned higher performance.
[0010] Patent Literature 1: JP-A-2001-131833 (Claims, page 5)
[0011] Patent Literature 2: JP-A-2003-73932 (Claims)
DISCLOSURE OF THE INVENTION
[0012] The present inventor made a study in order to solve the
above-mentioned problems. In the course of the study, the present
inventor found that a carbon fiber having a tensile strength, a
tensile modulus and a density, each of a given range and
possessing, on the surface, striations oriented in the fiber axis
direction shows good adhesivity to a matrix material and gives a
composite material of high performance. The finding has led to the
completion of the present invention.
[0013] Hence, the present invention aims at providing a carbon
fiber which has alleviated the conventional problems.
[0014] The present invention, which has achieved the above aim, is
as described below. [0015] [1] A carbon fiber having a strand
tensile strength of 6,100 MPa or more, a strand tensile modulus of
340 GPa or more and a density of 1.76 g/cm.sup.3 or more and
possessing, on the surface, striations oriented in a direction
parallel to the fiber axis. [0016] [2] The carbon fiber according
to [1], wherein the distance between striations in a 2.times.2
.mu.m area of the carbon fiber surface when observed by a scanning
probe microscope is 0.1 to 0.3 .mu.m, the root mean square surface
roughness Rms (5 .mu.m) in a 5.times.5 .mu.m area of the carbon
fiber surface when observed by a scanning probe microscope is 20 to
40 nm, and the root mean square surface roughness Rms (0.5 .mu.m)
when measured in a 0.5.times.0.5 .mu.m area is 2 to 12 nm. [0017]
[3] The carbon fiber according to [1], wherein the surface oxygen
concentration (O/C) of carbon fiber when measured by an X-ray
photoelectron spectrometer is 0.13 or more, the surface nitrogen
concentration (N/C) of carbon fiber when measured by the
spectrometer is 0.05 or less, the crystallite size measured by
wide-angle X-ray diffractometry is 2 nm or more, and the band
intensity ratio (D/G) of 1,360 cm.sup.-1 band intensity (D) and
1,580 cm.sup.-1 band intensity (G) when measured by Raman
spectrometry is 1.3 or less. [0018] [4] The carbon fiber according
to [1], which is obtained by subjecting, to an oxidation treatment
and a carbonization treatment, an acrylic fiber having an
orientation degree of 90.5% or less when measured by wide-angle
X-ray diffractometry (diffraction angle: 17.degree.). [0019] [5]
The carbon fiber according to [1], which is obtained by firing an
oxidized fiber showing a mass reduction ratio of 7% or less when
immersed in dimethylformamide for 12 hours.
[0020] The carbon fiber of the present invention is high in strand
tensile strength, strand tensile modulus and density and moreover
possesses striations oriented in the fiber axis direction on the
surface of the carbon fiber; therefore, the carbon fiber, when
compounded with a matrix material and made into a composite
material, functions as a reinforcing material showing good
adhesivity to the matrix material. The present carbon fiber is low
in fluffing and end breakage.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a partially sectional schematic drawing of an
example of the carbon fiber of the present invention.
[0022] FIG. 2 is a graph showing the change of the modulus of a
PAN-based oxidized fiber, relative to the temperature increase, in
the primary stretching of first carbonization step.
[0023] FIG. 3 is a graph showing the change of the crystallite size
of a PAN-based oxidized fiber, relative to the temperature
increase, in the primary stretching of first carbonization
step.
[0024] FIG. 4 is a graph showing the change of the density of a
fiber subjected to the primary stretching treatment of first
carbonization step, relative to the temperature increase, in the
secondary stretching of first carbonization step.
[0025] FIG. 5 is a graph showing the change of the density of a
fiber subjected to a first carbonization treatment, relative to the
temperature increase, in the primary stretching of second
carbonization step.
[0026] FIG. 6 is a graph showing the change of the crystallite size
of a fiber subjected to a first carbonization treatment, relative
to the temperature increase, in the primary stretching of second
carbonization step.
[0027] FIG. 7 is a graph showing the change of the density of a
fiber subjected to the primary treatment of second carbonization
step, relative to the temperature increase, in the secondary
stretching of second carbonization step.
[0028] In FIG. 1, 2 is a carbon fiber; 4 is a wave-shaped mountain;
6 is a wave-shaped valley; a is a distance between wave-shaped
mountains (a distance between striations); b is a height difference
between wave-shaped mountain and wave-shaped valley (a striation
roughness); and c is a surface roughness in a very small surface
area.
BEST MODE FOR CARRYING OUT THE INVENTION
[0029] The present invention is described in detail below.
[0030] The carbon fiber of the present invention fiber has a strand
tensile strength of 6,100 MPa or more, preferably 6,150 to 6,400
MPa, a strand tensile modulus of 340 GPa or more, preferably 340 to
370 GPa, and a density of 1.76 g/cm.sup.3 or more, preferably 1.76
to 1.80 g/cm.sup.3, and possesses, on the surface, striations
oriented in a direction parallel to the fiber axis. Incidentally,
in the present specification, strand tensile strength may be
described simply as strength, and strand tensile modulus may be
described simply as modulus.
[0031] FIG. 1 is a partially sectional schematic drawing showing an
example of the section of the carbon fiber of the present invention
obtained by cutting the fiber vertically relative to the fiber
axis. As shown in FIG. 1, the carbon fiber 2 of the present example
has, on the surface, striations oriented in a direction parallel to
the fiber axis. That is, the present carbon fiber 2 has a
wave-shaped surface wherein bending is repeated along the periphery
of the fiber section obtained by cutting the fiber by an arbitrary
plane intersecting the fiber axis at right angles. In FIG. 1, 4
indicates a wave-shaped mountain and 6 indicates a wave-shaped
valley.
[0032] a indicates a distance between wave-shaped mountains, i.e. a
striation distance. b indicates a height difference between
wave-shaped mountain and wave-shaped valley, i.e. a striation
roughness. c indicates a surface roughness of very small fiber
surface area. The striation distance a and the striation roughness
b can be measured using a scanning probe microscope.
[0033] The striations can be formed by controlling the shape of the
nozzle hole for discharging a spinning solution. Also, the
striations can be formed spontaneously by employing wet spinning or
wet on dry spinning. The shape, etc. of striations can be
controlled by controlling spinning conditions and/or post-treatment
conditions.
[0034] In the carbon fiber of the present invention, the striation
distance a is preferably 0.1 to 0.3 .mu.m. The striation distance a
is a measurement value obtained by observing a length and width
area of 2.times.2 .mu.m of carbon fiber surface using a scanning
probe microscope. The detail thereof is described in Examples which
appear later.
[0035] The striation roughness b is preferably 20 to 40 nm. The
striation roughness b indicates a root mean square surface
roughness Rms (5.mu.) calculated from the measurement data obtained
by observing a length and width area 5.times.5 .mu.m of carbon
fiber surface using a scanning probe microscope. The detail thereof
is described in Examples which appear later.
[0036] The surface roughness c is preferably 2 to 12 nm. The
surface roughness c indicates a root mean square surface roughness
Rms (0.5.mu.) calculated from the measurement data obtained by
observing a length and width area 0.5.times.0.5 .mu.m of carbon
fiber surface using a scanning probe microscope. The detail thereof
is described in Examples which appear later. The surface roughness
c can be controlled by controlling the quantity of electricity
required for surface treatment.
[0037] The average diameter of the carbon fiber is preferably 4.5
to 6.0 .mu.m, more preferably 5.0 to 6.0 .mu.m.
[0038] The surface oxygen concentration (O/C) and surface nitrogen
concentration (N/C) of the carbon fiber are measured by an X-ray
photoelectron spectrometer (ESCA). The surface oxygen concentration
(O/C) of the carbon fiber is preferably 0.13 or more, more
preferably 0.13 to 0.26. When the surface oxygen concentration
(O/C) is less than 0.13, the adhesivity between carbon fiber and
matrix resin is inferior, causing a reduction in the physical
properties of the composite material obtained. Meanwhile, when the
surface oxygen concentration (O/C) of the carbon fiber is more than
0.26, the carbon fiber is low in strength.
[0039] The surface nitrogen concentration (N/C) is preferably 0.05
or less. When the surface nitrogen concentration (N/C) is more than
0.05, it is impossible to obtain the required physical properties
of carbon fiber. The surface oxygen concentration (O/C) and surface
nitrogen concentration (N/C) can be controlled by controlling the
conditions of surface treatment.
[0040] The crystallite size can be measured by wide-angle X-ray
diffractometry. The crystallite size is preferably 2 nm or more,
more preferably 2.1 to 2.5 nm. The carbon fiber of the present
invention has a structure in which crystalline portions formed by
growth of graphite surface and carbonaceous amorphous portions are
mixed with each other. When the crystallite size is less than 2 nm,
the growth of graphite surface is weak and no carbon fiber of high
strength can be obtained.
[0041] The band strength ratio (D/G) of 1,360 cm.sup.-1 band
strength (D) and 1,580 cm.sup.-1 band strength (G), measured by
Raman spectrometry is preferably 1.3 or less, more preferably 0.95
to 1.3.
[0042] The amorphous portions show a peak of band strength (D) at
1,360 cm.sup.-1, and the crystalline portions formed by growth of
graphite surface show a peak of band strength (G) at 1,580
cm.sup.-1. When the band strength ratio (D/G) is more than 1.3, the
growth of graphite surface is weak and no carbon fiber of high
strength can be obtained. When the band strength ratio (D/G) is
less than 0.95, the growth of graphite surface is striking. In this
case, the flexibility of carbon fiber structure is impaired, which
is not preferred.
[0043] The crystallite size can be controlled by the operating
conditions of carbonization furnace, described later. As the
temperature of carbonization furnace is made higher, the
crystallite size tends to become larger.
[0044] The carbon fiber of the present invention is preferably
obtained by subjecting an acrylic fiber having an orientation
degree of 90.5% or less, preferably 89 to 90% when measured by
wide-angle X-ray diffractometry (diffraction angle: 17.degree.), to
an oxidation treatment and a carbonization treatment. When the
orientation degree is more than 90%, the drawing ratio of the
acrylic fiber used as a raw material for carbon fiber needs to be
made high (large) and there is a fear of occurrence of end
breakage; therefore, such an orientation degree is not
preferred.
[0045] The carbon fiber of the present invention is preferably
obtained by using, as a raw material, an oxidized fiber showing a
mass reduction ratio of 7% or less when immersed in
dimethylformamide (DMF) for 12 hours and subjecting the oxidized
fiber to a carbonization treatment. When the mass reduction ratio
is larger than 7%, the oxidized fiber is insufficient in oxidation
of precursor fiber. Such an insufficient oxidized fiber is not
preferred because it invites end breakage in carbonization step and
gives a carbon fiber low in strength.
[0046] The carbon fiber of the present invention can be produced,
for example, by the following process.
<Precursor Fiber>
[0047] As the precursor fiber used in production of the present
carbon fiber, there can be used, with no restriction, a pitch-based
fiber, a tar-based fiber and an acrylonitrile-based fiber, which
are all known. Of these, an acrylic fiber is preferred and more
preferred is an acrylic fiber having an orientation degree of 90.5%
or less when measured by wide-angle X-ray diffractometry
(diffraction angle: 17.degree.). Specifically explaining, a monomer
containing acrylonitrile in an amount of 90 mass % or more,
preferably 95 mass % or more is homo-polymerized or copolymerized
with other monomer; the spinning solution of the resulting
(co)polymer is spun to prepare a raw material for carbon fiber. As
the other monomer used in copolymerization, there can be mentioned,
for example, acrylic acid, methyl acrylate, itaconic acid, methyl
methacrylate and acrylamide. As the spinning method, there can be
used any of wet spinning and wet on dry spinning. With wet
spinning, the carbon fiber obtained has, on the surface, striations
formed spontaneously; therefore, wet spinning is preferred
particularly. A carbon fiber having striations is preferred because
it has good adhesivity to a matrix resin. In the wet spinning, the
spinning solution is discharged into a coagulating solution; the
resulting coagulated acrylic fiber is then subjected appropriately
to known steps such as water washing, drying, drawing and the like;
thereby, a precursor fiber is obtained.
<Oxidation Treatment>
[0048] The precursor fiber is then subjected to an oxidation
treatment in a heated air of 200 to 280.degree. C. In this
treatment, stretching is conducted at a stretching ratio of 0.85 to
1.30. In order to obtain a carbon fiber of high strength and high
modulus, the stretching ratio is preferably 0.95 or more. In this
oxidation treatment, the precursor fiber as a raw material is
converted into an oxidized fiber having a fiber density of 1.3 to
1.5 g/cm.sup.3. As to the stretching proportion in the oxidation
treatment, there is no particular restriction. The stretching ratio
may be in the above range in total.
<First Carbonization Treatment>
[0049] In the process for production of the present carbon fiber,
in the first carbonization treatment step, the above-obtained
oxidized fiber is subjected to a primary stretching treatment at a
stretching ratio of 1.03 to 1.06 in an inert atmosphere in a
temperature range of 300 to less than 800.degree. C. Then, the
oxidized fiber subjected to the primary stretching treatment is
subjected to a secondary stretching treatment at a stretching ratio
of 0.9 to 1.01 in an inert atmosphere in a temperature range of 300
to less than 800.degree. C., to obtain a first carbonization
treatment fiber having a fiber density of 1.50 to 1.70
g/cm.sup.3.
<First Carbonization Treatment.cndot.Primary Stretching
Treatment>
[0050] In the first carbonization treatment step, the oxidized
fiber is subjected to gradual temperature elevation, in the
above-mentioned temperature range, from a low temperature
(300.degree. C.) to a high temperature (less than 800.degree. C.).
In this step, the modulus, density, crystallite size, etc. of the
fiber, described in the following (1) to (3) change.
[0051] In the primary stretching treatment of the first
carbonization treatment step, the oxidized fiber is subjected to
temperature elevation and, while the fiber is in the following
temperature elevation ranges, stretching is conducted at a total
stretching ratio of 1.03 to 1.06.
[0052] (1) A temperature elevation range from when the modulus of
oxidized fiber has dropped to the minimum, to when the modulus
increases to 9.8 GPa.
[0053] (2) A temperature elevation range up to when the density of
oxidized fiber reaches 1.5 g/cm.sup.3.
[0054] (3) A temperature elevation range up to when the crystallite
size of oxidized fiber as measured by wide-range X-ray
diffractometry (diffraction angle: 26.degree.) reaches 1.45 nm.
[0055] The temperature elevation range from when the modulus of
oxidized fiber has dropped to the minimum, to when the modulus
increases to 9.8 GPa, is a range .beta. shown in FIG. 2.
[0056] By conducting stretching (1.03 to 1.06 times) in the
temperature elevation range from when the modulus of oxidized fiber
has dropped to the minimum, to when the modulus increases to 9.8
GPa, end breakage is suppressed, the low-modulus portions of
oxidized fiber are stretched efficiently and high orientation is
achieved, and a primary stretching treatment fiber of high density
can be obtained.
[0057] Meanwhile, stretching to 1.03 times or more before the
modulus of oxidized fiber drops to the minimum, that is, in a range
.alpha., is not preferred because end breakage increases and the
primary stretching treatment fiber obtained is strikingly low in
strength.
[0058] Also, when stretching is conducted to 1.03 times or more
after the modulus dropped to the minimum and then has increased to
9.8 GPa, that is, in a range .gamma., the modulus of the resulting
fiber is high and forced stretching is conducted and, therefore,
fiber defects and voids increase, impairing the effect of
stretching. Hence, the primary stretching treatment is conducted in
the above modulus range.
[0059] By conducting stretching (1.03 to 1.06 times) in a
temperature elevation range up to when the density of oxidized
fiber reaches 1.5 g/cm.sup.3, an increase in orientation degree is
realized while the generation of voids is suppressed, and a primary
stretching treatment fiber of high quality can be obtained.
[0060] In contrast, when the primary stretching is conducted to
1.03 times or more in a high density range of more than 1.5
g/cm.sup.3, generation of voids is promoted by forced stretching
and the final carbon fiber comes to have structural defects and a
low density; therefore, such stretching is not preferred. Hence,
the primary stretching treatment is conducted in the above density
range.
[0061] Incidentally, when the stretching ratio in primary
stretching is less than 1.03 times, the effect of stretching is low
and no carbon fiber of high strength can be obtained. When the
stretching ratio is higher than 1.06 times, end breakage occurs and
no carbon fiber of high quality and high strength can be
obtained.
<First Carbonization Treatment.cndot.Secondary Stretching
Treatment>
[0062] In the secondary stretching treatment of the first
carbonization treatment step, the fiber after primary stretching
treatment is subjected to temperature elevation and, during the
temperature elevation, stretched at 0.9 to 1.01 times in (1) a
temperature elevation range in which the density of the fiber
continues to increase and (2) a temperature elevation range in
which the crystallite size of the fiber observed by wide-angle
X-ray diffractometry (diffraction angle: 26.degree.) is not larger
than 1.45 nm.
[0063] In the secondary stretching treatment of the first
carbonization treatment step, there are, as shown in FIG. 4, three
conditions in which the density of fiber changes, i.e. a condition
in which the density shows no increase with an increase in
carbonization temperature, a condition in which the density
continues to increase, and a condition in which the density
increases and then decreases.
[0064] When the secondary stretching treatment is conducted at a
stretching ratio of 0.9 to 1.01 times under one of the above three
conditions, i.e. the condition in which the density of the fiber
after primary stretching treatment continues to increase, the
generation of voids is suppressed and there can be obtained a final
carbon fiber of high density. The condition in which the density
continues to increase, can be realized by controlling the
temperature condition in the secondary stretching.
[0065] In contrast, when the secondary stretching treatment is
conducted in a period of fiber density decrease, the generation of
voids in carbon fiber is promoted and no carbon fiber of high
density can be obtained. Further, when a period of no change of
fiber density is included in the secondary stretching treatment,
there is no density improvement in the secondary stretching
treatment and there can be obtained no final carbon fiber of high
strength. Therefore, the secondary stretching treatment is
conducted in a temperature elevation range in which the fiber
density continues to increase.
[0066] Further, the secondary stretching treatment is conducted at
a stretching ratio of 0.9 to 1.01 times in a temperature elevation
range in which the crystallite size of the fiber after primary
stretching treatment when measured by wide-angle X-ray
diffractometry (diffraction angle: 26.degree.) is 1.45 nm or less.
By such stretching treatment, the fiber is made more dense with no
crystal growth, the generation of voids is suppressed, and there
can be obtained a final carbon fiber of high density.
[0067] When the secondary stretching treatment is conducted in a
temperature elevation range in which the crystallite size becomes
larger than 1.45 nm, the carbon fiber obtained has an increased
number of voids. Moreover, the obtained fiber is lower in quality
owing to end breakage and there can be obtained no carbon fiber of
high strength. Therefore, the secondary stretching treatment is
carried out in the above-mentioned range of crystallite size.
[0068] Incidentally, when the stretching ratio is less than 0.9
times in the secondary stretching treatment, the first
carbonization treatment fiber is strikingly low in orientation
degree when measured by wide-angle X-ray diffractometry
(diffraction angle: 26.degree.), making it impossible to obtain a
carbon fiber of high strength. When the stretching ratio is higher
than 1.01 times, end breakage is incurred and there can be obtained
no carbon fiber of high quality and high strength. Therefore, in
the secondary stretching treatment, the stretching ratio is
preferred to be in a range of 0.9 to 1.01 times.
[0069] In order to obtain a carbon fiber of high strength, the
first carbonization treatment fiber preferably has an orientation
degree of 76.0% or more when measured by wide-angle X-ray
diffractometry (diffraction angle: 26.degree.).
[0070] When the orientation degree is less than 76.0%, no carbon
fiber of high strength can be obtained. In order to obtain an
orientation degree of 76.0% or more, it is necessary that a
stretching ratio of 0.95 or more is employed in the oxidation
treatment and the above-mentioned conditions are employed in the
first carbonization step.
[0071] In the first carbonization treatment step, there are
conducted the primary stretching treatment and secondary stretching
treatment of oxidized fiber, under the above-mentioned conditions,
whereby a first carbonization treatment fiber can be obtained. The
first carbonization treatment step may be conducted, using one or
more furnaces, continuously or in two or more stages.
<Second Carbonization Treatment>
[0072] In the second carbonization treatment step, the first
carbonization treatment fiber is stretched in an inert atmosphere
in a temperature range of 800 to 1,600.degree. C. with temperature
elevation, to obtain a second carbonization treatment fiber. The
second carbonization treatment step consists of primary stretching
treatment and secondary stretching treatment.
<Second Carbonization Treatment.cndot.Primary Stretching
Treatment>
[0073] In the primary stretching treatment of the second
carbonization treatment step, the first carbonization treatment
fiber is stretched with temperature elevation in a temperature
elevation range in which the density of the fiber continues to
increase, in a temperature elevation range in which the nitrogen
content of the fiber is kept at 10 mass % or more, and in a
temperature elevation range in which the crystallite size of the
fiber when measured by wide-angle X-ray diffractometry (diffraction
angle: 26.degree.) is 1.47 nm or less.
[0074] The changes of density and crystallite size when measured by
wide-angle X-ray diffractometry (diffraction angle: 26.degree.), in
the primary stretching treatment of second carbonization treatment
step of the first carbonization treatment fiber are shown
respectively in FIGS. 5 and 6.
[0075] Incidentally, in the primary stretching treatment of second
carbonization treatment step, fiber tension (F MPa) depends upon
the sectional area (S mm.sup.2) of the fiber after first
carbonization step; therefore, in the present invention, fiber
stress (B mN) is used as tension factor.
[0076] In the present invention, the range of the fiber stress B
lies in a range satisfying the following formula.
1.24>B>0.46
wherein B=F.times.S and S=.pi.D.sup.2/4 [D is the diameter (mm) of
first carbonization treatment fiber].
[0077] Here, the fiber sectional area is calculated as follows.
First, fiber diameter is measured at a repetition number n of 20 by
the method using a micrometer microscope, specified by JIS R 7601.
Then, an average of the measured fiber diameters is calculated.
Using the calculated average of fiber diameters, an area of true
circle is calculated. The calculated area of true circle is taken
as fiber sectional area.
<Second Carbonization Treatment.cndot.Secondary Stretching
Treatment>
[0078] Subsequently, the above-obtained primary stretching
treatment fiber of second carbonization treatment step is subjected
to the following secondary stretching treatment.
[0079] In the secondary stretching treatment, the primary
stretching treatment fiber is stretched with temperature elevation,
in a temperature elevation range in which the density of the fiber
shows no change or in a temperature elevation range in which the
fiber density decreases.
[0080] The change of the density of primary stretching treatment
fiber, in its secondary stretching treatment is shown in FIG.
7.
[0081] Incidentally, in the secondary stretching treatment of
second carbonization treatment step, as in the primary stretching
treatment, fiber tension (H MPa) depends upon the sectional area (S
mm.sup.2) of the fiber after first carbonization step. In the
present invention, fiber stress (E mN) is used as tension factor.
The range of the fiber stress E lies in a range satisfying the
following formula.
0.60>E>0.23
wherein E=H.times.S and S=.pi.D.sup.2/4 [D is the diameter (mm) of
first carbonization treatment fiber].
[0082] The thus-obtained second carbonization treatment fiber has
an elongation of preferably 2.10% or more, more preferably 2.20% or
more. Also, the fiber preferably has a diameter of 5 to 6.5
.mu.m.
<Third Carbonization Treatment>
[0083] In the third carbonization treatment step, the
above-obtained second carbonization treatment fiber is carbonized
in an inert atmosphere at 1,600 to 2,100.degree. C. to obtain a
third carbonization treatment fiber. The carbonization treatment is
conducted under the following conditions.
[0084] In the third carbonization treatment step, the tension of
fiber (J MPa) depends upon the sectional area (K mm.sup.2) of the
fiber after second carbonization treatment. In the present
invention, fiber stress (G mN) is used as tension factor. In the
present invention, the fiber stress needs to satisfy following
formula.
2.80>G>0.65
wherein G=J.times.K and K=.pi.L.sup.2/4 [L is the diameter (mm) of
second carbonization treatment fiber].
[0085] The carbonization treatment step may be conducted
continuously using one carbonization treatment furnace, or may be
conducted continuously using a plurality of carbonization treatment
furnaces.
<Surface Treatment>
[0086] The third carbonization treatment fiber is then subjected to
a surface treatment. The surface treatment includes a gas-phase
treatment and a liquid-phase treatment. The surface treatment is
preferred, from the standpoints of easy process control and high
productivity, to be a liquid-phase treatment employing an
electrolytic oxidation reaction. In the surface treatment, there is
no particular restriction as to the pH of electrolytic solution;
however, the pH is preferably 0 to 5.5. The oxidation reduction
potential (ORP) is set at +400 mV or more, preferably at +500 mV or
more.
[0087] The product of pH and ORP is controlled preferably at 0 to
2,300, more preferably at 100 or less.
[0088] As the electrolytic solution, an aqueous solution of
inorganic acid, inorganic acid salt or the like can be used.
However, an inorganic acid (e.g. sulfuric acid, nitric acid or
hydrochloric acid) or an aqueous solution thereof is preferred and
an aqueous nitric acid solution is particularly preferred.
<Sizing Treatment>
[0089] Preferably, the resulting third carbonization treatment
fiber is subjected to a sizing treatment and made into a form of
carbon fiber strand superior in handleability. The number of single
fibers constituting the strand is preferably 500 to 40,000, more
preferably 1,000 to 20,000. The sizing can be conducted by a known
method. A sizing agent having a known composition can be used
appropriately depending upon the application of the final carbon
fiber obtained. The sizing treatment is conducted appropriately by
attaching a sizing agent uniformly to the third carbonization
treatment fiber, followed by drying. The drying is preferably
conducted by passing the sizing agent-attached carbon fiber through
an air atmosphere of 100 to 220.degree. C.
EXAMPLES
[0090] The present invention is described more specifically by way
of Examples and Comparative Examples. The testing methods for
properties of precursor fiber, oxidized fiber and carbon fiber are
explained below.
<Density>
[0091] The density of each fiber was measured by the Archimedes
method. Each fiber was deaerated in acetone and then measured for
density.
<Crystallite Size by Wide-Angle X-Ray Diffractometry
(Diffraction Angle: 17.degree. C. or 26.degree.) and Orientation
Degree>
[0092] The diffraction pattern of a fiber was obtained using an
X-ray diffractometer (RINT 1200 L produced by Rigaku Denki) and a
computer (Hitachi 2050/32). A crystallite size at diffraction angle
of 17.degree. or 26.degree. was calculated from the diffraction
pattern. The orientation degree of a fiber was determined using the
half value width.
<Single Fiber Modulus>
[0093] A primary stretching treatment fiber of first carbonization
treatment step was measured for single fiber modulus according to
the method specified by JIS R 7606 (2000).
<Strand Strength and Modulus>
[0094] Each second carbonization treatment fiber and each third
carbonization treatment fiber were measured for strand strength and
modulus according to the method specified by JIS R 7601.
<Surface Oxygen Concentration O/C and Surface Nitrogen
Concentration N/C of Carbon Fiber>
[0095] The surface oxygen concentration O/C and surface nitrogen
concentration N/C of each carbon fiber were determined using XPS
(ESCA) according to the following procedure.
[0096] A carbon fiber was cut. The cut fiber pieces were arranged
apart on a stainless steel-made, sample support. The photoelectron
escaping angle of XPS was set at 900. An X-ray source of MgK.alpha.
was used. The inside of a sample chamber was kept at a vacuum of
1.times.10.sup.-6 Pa. In order to correct the peak caused by the
electrification during measurement, first, the bonding energy (BE)
of the main peak of C.sub.1s was adjusted to 284.6 eV. In the chart
obtained, a linear baseline was drawn in a range of 394 to 406 eV,
to determine an N.sub.1s peak area. An O.sub.1s peak area was
determined by drawing a linear baseline in a range of 528 to 540
eV. A C.sub.1s peak area was determined by drawing a linear
baseline in a range of 282 to 296 eV. A ratio of the O.sub.1s peak
area and the C.sub.1s peak area was determined, and this value was
taken as the surface oxygen concentration O/C of the carbon fiber.
A ratio of the N.sub.1s peak area and the C.sub.1s peak area was
determined, and this value was taken as the surface nitrogen
concentration N/C of the carbon fiber.
<Band Intensity Ratio (D/G)>
[0097] As a Raman spectrometer, there was used Single Microscope
Laser Raman Spectrometer T 64000 produced by JOBIN YVON
Corporation. As an excitation light source, an Ar.sup.+ laser
(.lamda.=514.5 nm) was used. The output of the Ar.sup.+ laser was
20 mW. Baseline correction was made for the chart obtained, after
which a 1360 cm.sup.-1 band intensity (D) and a 1580 cm.sup.-1 band
intensity (G) were calculated. Using these intensities, a band
intensity ratio (D/G) was calculated. The same measurement were
repeated three times and an average of three measurements was
determined. This average was taken as the band intensity ratio
(D/G) of the material measured.
<Shape of Carbon Fiber>
[0098] The striation roughness (height difference between mountain
and valley) and surface roughness in very small surface area,
formed on the surface of a carbon fiber are each determined as root
mean square surface roughness. For these measurements, a scanning
probe microscope (SPM Nanoscope III produced by DI) was used. A
carbon fiber sample to be examined was put on a stainless
steel-made disc for measurement; the two ends of the sample were
fixed; and measurement was conducted in Tapping Mode.
[0099] The data obtained was subjected to secondary curve
correction using a program attached to the scanning probe
microscope and a root mean square surface roughness was
determined.
[0100] As to the distance between striations (distance between
mountains in wave shape), of a carbon fiber, a surface area of
2.times.2 .mu.m was observed using the same scanning probe
microscope, and the distance between striations was measured from
the image obtained. The same measurement was repeated five times,
an average was calculated, and the average was taken as distance
between striations.
Example 1
[0101] A spinning solution of a copolymer composed of 95 mass % of
acrylonitrile, 4 mass % of methyl acrylate and 1 mass % of itaconic
acid was subjected to wet spinning, followed by water washing,
drying, drawing and oiling, to obtain an acrylic precursor fiber
having a fiber diameter of 9.1 .mu.m and an orientation degree of
89.7% when measured by wide-angle X-ray diffractometry (diffraction
angle: 17.degree.). This fiber was subjected to an oxidation
treatment in hot air in an oxidation furnace of hot-air circulation
type, of inlet temperature (minimum temperature) of 200.degree. C.
and outlet temperature (maximum temperature) of 260.degree. C., to
obtain an acrylic oxidized fiber having a fiber density of 1.34
g/cm.sup.3 and a mass reduction ratio of 5.0% when immersed in DMF
for 12 hours.
[0102] Then, the oxidized fiber was subjected to primary and
secondary stretching treatments using a first carbonization
furnace, under the conditions shown in Table 1. The first
carbonization furnace contained inside an inert atmosphere and had
an inlet temperature (minimum temperature) of 300.degree. C. and an
outlet temperature (maximum temperature) of 800.degree. C. The
inside of the carbonization furnace had such a temperature gradient
that the inside temperature became gradually higher from the inlet
toward the outlet.
[0103] The primary stretching was conducted in a range .beta. shown
in FIG. 2 at a stretching ratio of 1.05 times. The fiber after the
primary stretching treatment (primary stretching treatment fiber)
had a single fiber modulus of 8.8 GPa, a density of 1.40 g/cm.sup.3
and a crystallite size of 1.20 nm and showed no end breakage.
[0104] Then, the primary stretching treatment fiber was subjected
to secondary stretching of first carbonization step. The secondary
stretching was carried out in a temperature elevation range in
which the density of the fiber continued to increase (FIG. 4) and
the crystallite size thereof was not larger than 1.45 nm (FIG. 3).
The stretching ratio was 1.00 time. By the secondary stretching
treatment, there was obtained a first carbonization treatment fiber
having a density of 1.70 g/cm.sup.3, an orientation degree of
79.0%, a fiber diameter of 5.9 .mu.m and a fiber sectional area of
2.73.times.10.sup.-5 mm.sup.2. The first carbonization treatment
fiber shows no end breakage.
[0105] Then, the first carbonization treatment fiber was subjected
to primary and secondary stretching treatments using a second
carbonization furnace, step under the following conditions. The
second carbonization furnace contained inside an inert atmosphere
and had an inlet temperature (minimum temperature) of 800.degree.
C. and an outlet temperature (maximum temperature) of 1,550.degree.
C. The inside of the carbonization furnace had such a temperature
gradient that the inside temperature became gradually higher from
the inlet toward the outlet.
[0106] First, the first carbonization treatment fiber was subjected
to primary stretching at a fiber tension of 29.9 MPa and a fiber
stress of 0.817 mN while the density and crystallite size of the
fiber were respectively in primary stretching treatment condition
ranges of FIG. 5 and FIG. 6, to obtain a primary treatment fiber.
That is, as shown in FIG. 5, stretching was conducted in a period
in which the density of the fiber increased with temperature
elevation and reached the maximum 1.9 g/cm.sup.3. Further, as shown
in FIG. 6, stretching was conducted in a period in which the
crystallite size of the fiber decreased once with temperature
elevation, then began to increase and reached 1.47 nm.
[0107] Then, the primary stretching treatment fiber was subjected
to secondary stretching treatment of second carbonization step. The
secondary stretching treatment was conducted at a fiber tension of
14.9 MPa at a fiber stress of 0.408 mN under a density range shown
in FIG. 7, to obtain a second carbonization treatment fiber.
[0108] The fiber had a diameter of 5.2 .mu.m, a sectional area of
2.12.times.10.sup.-5 mm.sup.2, a density of 1.805 g/cm.sup.3 and an
elongation of 2.20%.
[0109] Then, the second carbonization treatment fiber was subjected
to a third carbonization treatment using a third carbonization
furnace. The third carbonization furnace contained inside an inert
atmosphere and had an inlet temperature (minimum temperature) of
1,600.degree. C. and an outlet temperature (maximum temperature) of
1,900.degree. C. In the third carbonization treatment, stretching
was conducted at a fiber tension of 76.9 MPa and a fiber stress of
1.633 mN and a third carbonization treatment fiber was
obtained.
[0110] Then, the third carbonization treatment fiber was subjected
to a surface treatment by an electrolytic oxidation reaction using
an electrolytic solution (an aqueous nitric acid solution) in which
the pH was set at 0.1, the oxidation reduction potential (ORP) was
set at +600 mV and the product of pH and ORP was set at 60.
[0111] Subsequently, a sizing agent was applied to the third
carbonization treatment fiber by a known method, followed by
drying, to obtain a carbon fiber strand having a density of 1.77
g/cm.sup.3, a fiber diameter of 5.1 .mu.m, a strand strength of
6,130 MPa, a strand modulus of 343 GPa, an orientation of 84.2% and
a crystallite size of 2.2 nm.
[0112] In the fiber, striations were observed on the surface; the
distance between striations was 0.20 .mu.m; the striation roughness
Rms (5.mu.) was 25.0 nm; the surface roughness Rms (0.5.mu.) was
6.2 nm; the surface oxygen concentration (O/C) was 0.14; the
surface nitrogen concentration (N/C) was 0.025; and the band
intensity ratio (D/G) was 1.293. This carbon fiber had properties
suitable as a carbon fiber for use in production of composite
material.
Examples 2 to 3 and Comparative Examples 1 to 14
[0113] The oxidized fiber obtained in Example 1 was subjected to a
first carbonization treatment, a second carbonization treatment, a
third carbonization treatment, a surface treatment and a sizing
treatment, in the same manners as in Example 1 except that the
treatments were conducted under the conditions shown in Tables 1 to
6, whereby were obtained carbon fibers after first carbonization
treatment, second carbonization treatment, third carbonization
treatment, surface treatment and sizing treatment, having
properties shown in Tables 1 to 6.
[0114] However, in Comparative Examples 4 and 10, the steps after
second carbonization step could not be run and, in Comparative
Examples 5 and 6, the steps after first carbonization secondary
stretching treatment step could not be run.
[0115] As shown in Table 1, the carbon fibers obtained in Examples
2 to 3, similarly to the carbon fiber obtained in Example 1, showed
properties suitable as a carbon fiber for composite material. In
contrast, in Comparative Examples 1 to 3, 7 to 9 and 11 to 14, the
carbon fibers shown in Tables 1 to 6 were obtained but showed
properties insufficient as a carbon fiber for composite
material.
Examples 4 and Comparative Examples 15 to 16
[0116] The second carbonization fiber obtained in Example 1 was
subjected to a third carbonization treatment, a surface treatment
and a sizing treatment in the same manners as in Example 1 except
that the third carbonization treatment was conducted under a
temperature condition shown in Table 7, whereby carbon fibers after
surface treatment and sizing treatment, having properties shown in
Table 7 were obtained.
[0117] As a result, the carbon fiber obtained in Example 4,
similarly to that of Example 1, showed properties suitable as a
carbon fiber for composite material, as shown in Table 7. In
contrast, the carbon fibers obtained in Comparative Examples 15 to
16 showed no properties sufficient as a carbon fiber for composite
material, as shown in Table 7.
Examples 5 to 8 and Comparative Examples 17 to 23
[0118] The third carbonization fiber obtained in Example 1 was
subjected to a surface treatment and a sizing treatment in the same
manners as in Example 1 except that the surface treatment was
conducted under conditions shown in Tables 8 to 10, whereby carbon
fibers after surface treatment and sizing treatment, having
properties shown in Tables 8 to 10 were obtained.
[0119] The carbon fibers obtained in Examples 5 to 8, similarly to
that of Example 1, showed properties suitable as a carbon fiber for
composite material, as shown in Tables 8 to 10. In contrast, the
carbon fibers obtained in Comparative Examples 17 to 23 showed
properties insufficient as a carbon fiber for composite material,
as shown in Tables 8 to 10.
TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Precursor
fiber Orientation degree (%) 89.7 89.7 89.7 Oxidized fiber Density
(g/cm.sup.3) 1.34 1.34 1.34 Mass reduction by DMF (%) 5.0 5.0 5.0
First Primary Range of FIG. 1 .beta. .beta. .beta. carbonization
stretching Stretching ratio (times) 1.05 1.06 1.05 step conditions
Single fiber modulus (GPa) 8.8 8.4 8.8 Density (g/cm.sup.3) 1.40
1.39 1.40 Crystallite size (nm) 1.20 1.10 1.20 Secondary Change of
density Continuous Continuous Continuous stretching increase
increase increase conditions Crystallite size (nm) 1.45 or less
1.45 or less 1.45 or less Stretching ratio (times) 1.00 1.01 1.00
After Density (g/cm.sup.3) 1.70 1.75 1.52 first Orientation degree
(%) 79.0 79.5 77.0 carbonization Fiber diameter (.mu.m) 5.9 5.5 6.8
Second Primary Fiber tension F (MPa) 29.9 44.7 18.0 carbonization
treatment Fiber stress B (mN) 0.817 1.062 0.653 step Secondary
Fiber tension H (MPa) 14.9 15.5 11.2 treatment Fiber stress E (mN)
0.408 0.368 0.408 After Density (g/cm.sup.3) 1.805 1.810 1.800
second Fiber diameter (.mu.m) 5.2 5.1 5.2 carbonization Elongation
(%) 2.21 2.23 2.20 Third Fiber tension J (MPa) 76.9 80.0 76.9
carbonization Fiber stress G (mN) 1.633 1.633 1.633 step Carbon
Strand form Good Good Good fiber Density (g/cm.sup.3) 1.77 1.79
1.76 Fiber diameter (.mu.m) 5.1 5.0 5.1 Strand strength (MPa) 6150
6200 6100 Strand modulus (GPa) 343 345 342 Orientation degree (%)
84.2 84.3 84.2 Crystallite size (nm) 2.2 2.2 2.2 Presence of
surface striations Yes Yes Yes Distance between striations (.mu.m)
0.20 0.20 0.20 Striation roughness Rms (5.mu.) (nm) 25.0 26.0 25.5
Surface roughness Rms (0.5.mu.) (nm) 6.2 6.0 6.5 Surface oxygen
concentration (O/C) 0.14 0.14 0.14 Surface nitrogen concentration
(N/C) 0.025 0.022 0.026 Band intensity ratio (D/G) 1.293 1.295
1.294
TABLE-US-00002 TABLE 2 Comparative Comparative Comparative Example
1 Example 2 Example 3 Precursor fiber Orientation degree (%) 89.7
89.7 89.7 Oxidized fiber Density (g/cm.sup.3) 1.34 1.34 1.34 Mass
reduction by DMF (%) 5.0 5.0 5.0 First Primary Range of FIG. 1
.beta. .beta. .beta. carbonization stretching Stretching ratio
(times) 1.05 1.05 1.06 step conditions Single fiber modulus (GPa)
8.8 8.8 8.8 Density (g/cm.sup.3) 1.40 1.40 1.40 Crystallite size
(nm) 1.20 1.20 1.20 Secondary Change of density Continuous
Continuous Continuous stretching increase increase increase
Conditions Crystallite size (nm) 1.45 or less 1.45 or less 1.45 or
less Stretching ratio (times) 1.00 1.00 1.01 After Density
(g/cm.sup.3) 1.70 1.70 1.70 first Orientation degree (%) 79.0 79.0
79.0 carbonization Fiber diameter (.mu.m) 5.9 5.9 5.9 Second
Primary Fiber tension F (MPa) 50.8 14.9 29.9 carbonization
treatment Fiber stress B (mN) 1.388 0.408 0.817 step Secondary
Fiber tension H (MPa) 14.9 14.9 23.9 treatment Fiber stress E (mN)
0.408 0.408 0.653 After Density (g/cm.sup.3) 1.795 1.800 1.800
second Fiber diameter (.mu.m) 5.1 5.3 5.0 carbonization Elongation
(%) 2.10 2.10 2.15 step Third Fiber tension J (MPa) 80.0 74.0 83.2
carbonization Fiber stress G (mN) 1.633 1.633 1.633 step Carbon
Strand form Good Good Good fiber Density (g/cm.sup.3) 1.75 1.76
1.76 Fiber diameter (.mu.m) 5.0 5.2 5.1 Strand strength (MPa) 5900
6000 5950 Strand modulus (GPa) 342 341 345 Orientation degree (%)
84.2 84.1 84.3 Crystallite size (nm) 2.2 2.2 2.2 Presence of
surface striations Yes Yes Yes Distance between striations (.mu.m)
0.21 0.22 0.21 Striation roughness Rms (5.mu.) (nm) 26.0 25.5 27.0
Surface roughness Rms (0.5.mu.) (nm) 7.0 6.5 6.5 Surface oxygen
concentration (O/C) 0.14 0.14 0.14 Surface nitrogen concentration
(N/C) 0.023 0.024 0.022 Band intensity ratio (D/G) 1.297 1.293
1.290
TABLE-US-00003 TABLE 3 Comparative Comparative Comparative Example
4 Example 5 Example 6 Precursor fiber Orientation degree (%) 89.7
89.7 89.7 Oxidized fiber Density (g/cm.sup.3) 1.34 1.34 1.34 Mass
reduction by DMF (%) 5.0 5.0 5.0 First Primary Range of FIG. 1
.beta. .alpha. .gamma. carbonization stretching Stretching ratio
(times) 1.05 1.05 1.05 step conditions Single fiber modulus (GPa)
8.8 9.2 10.3 Density (g/cm.sup.3) 1.40 1.37 1.52 Crystallite size
(nm) 1.20 0.90 1.45 Secondary Change of density Continuous No
passing No passing Stretching increase trough step through step
conditions Crystallite size (nm) 1.45 or less Stretching ratio
(times) 1.00 After Density (g/cm.sup.3) 1.70 first Orientation
degree (%) 79.0 carbonization Fiber diameter (.mu.m) 5.9 Second
Primary Fiber tension F (MPa) 29.9 carbonization treatment Fiber
stress B (mN) 0.817 step Secondary Fiber tension H (MPa) 6.0
treatment Fiber stress E (mN) 0.163 After Density (g/cm.sup.3)
1.805 second Fiber diameter (.mu.m) 5.2 carbonization Elongation
(%) 2.20 Third Fiber tension J (MPa) No passing carbonization
through step step Fiber stress G (mN) Carbon Strand form Fiber
Density (g/cm.sup.3) Fiber diameter (.mu.m) Strand strength (MPa)
Strand modulus (GPa) Orientation degree (%) Crystallite size (nm)
Presence of surface striations Distance between striations (.mu.m)
Striation roughness Rms (5.mu.) (nm) Surface roughness Rms
(0.5.mu.) (nm) Surface oxygen concentration (O/C) Surface nitrogen
concentration (N/C) Band intensity ratio (D/G)
TABLE-US-00004 TABLE 4 Comparative Comparative Comparative Example
7 Example 8 Example 9 Precursor fiber Orientation degree (%) 89.7
89.7 89.7 Oxidized fiber Density (g/cm.sup.3) 1.34 1.34 1.34 Mass
reduction by DMF (%) 5.0 5.0 5.0 First Primary Range of FIG. 1
.beta. .beta. .beta. carbonization stretching Stretching ratio
(times) 1.06 1.05 1.02 step conditions Single fiber modulus (GPa)
8.8 8.8 8.8 Density (g/cm.sup.3) 1.40 1.40 1.38 Crystallite size
(nm) 1.20 1.20 1.20 Secondary Change of density Increase and No
increase Continuous stretching then decrease increase Conditions
Crystallite size (nm) 1.47 1.45 or less 1.45 or less Stretching
ratio (times) 1.00 1.00 1.00 After Density (g/cm.sup.3) 1.80 1.50
1.63 first Orientation degree (%) 79.8 76.5 77.5 carbonization
Fiber diameter (.mu.m) 5.4 6.9 6.1 Second Primary Fiber tension F
(MPa) 35.7 21.8 27.9 carbonization treatment Fiber stress B (mN)
0.817 0.817 0.817 step Secondary Fiber tension H (MPa) 17.8 10.9
14.0 treatment Fiber stress E (mN) 0.408 0.408 0.408 After Density
(g/cm.sup.3) 1.790 1.802 1.798 second Fiber diameter (.mu.m) 5.0
5.0 5.2 carbonization Elongation (%) 2.05 2.15 2.20 Third Fiber
tension J (MPa) 83.2 83.2 76.9 carbonization Fiber stress G (mN)
1.633 1.633 1.633 step Carbon Strand form Good Good Good Fiber
Density (g/cm.sup.3) 1.74 1.76 1.76 Fiber diameter (.mu.m) 4.9 4.9
5.1 Strand strength (MPa) 5800 5950 5850 Strand modulus (GPa) 338
343 336 Orientation degree (%) 84.0 84.2 83.9 Crystallite size (nm)
2.2 2.2 2.1 Presence of surface striations Yes Yes Yes Distance
between striations (.mu.m) 0.19 0.20 0.21 Striation roughness Rms
(5.mu.) (nm) 24.0 25.0 26.0 Surface roughness Rms (0.5.mu.) (nm)
6.6 6.3 6.0 Surface oxygen concentration (O/C) 0.15 0.14 0.15
Surface nitrogen concentration (N/C) 0.026 0.023 0.022 Band
intensity ratio (D/G) 1.293 1.294 1.299
TABLE-US-00005 TABLE 5 Comparative Comparative Comparative Example
10 Example 11 Example 12 Precursor fiber Orientation degree (%)
89.7 89.7 89.7 Oxidized fiber Density (g/cm.sup.3) 1.34 1.34 1.34
Mass reduction by DMF (%) 5.0 5.0 5.0 First Primary Range of FIG. 1
.beta. .beta. .beta. carbonization stretching Stretching ratio
(times) 1.07 1.05 1.05 step conditions Single fiber modulus (GPa)
8.8 8.8 8.8 Density (g/cm.sup.3) 1.39 1.39 1.39 Crystallite size
(nm) 1.20 1.20 1.20 Secondary Change of density Continuous
Continuous Continuous stretching increase increase increase
conditions Crystallite size (nm) 1.45 or less 1.45 or less 1.45 or
less Stretching ratio (times) 1.00 0.85 1.03 After Density
(g/cm.sup.3) 1.68 1.71 1.70 first Orientation degree (%) 79.1 78.5
79.2 carbonization Fiber diameter (.mu.m) 5.7 6.0 5.8 Second
Primary Fiber tension F (MPa) 32.0 28.9 30.9 carbonization
treatment Fiber stress B (mN) 0.817 0.817 0.817 step Secondary
Fiber tension H (MPa) 16.0 14.4 15.5 treatment Fiber stress E (mN)
0.408 0.408 0.408 After Density (g/cm.sup.3) 1.795 1.800 1.790
second Fiber diameter (.mu.m) 4.9 5.2 4.9 carbonization Elongation
(%) 2.20 2.05 2.10 Third Fiber tension J (MPa) No passing 76.9 86.6
carbonization through step step Fiber stress G (mN) 1.633 1.633
Carbon Strand form Good Good fiber Density (g/cm.sup.3) 1.76 1.74
Fiber diameter (.mu.m) 5.1 4.8 Strand strength (MPa) 5750 5500
Strand modulus (GPa) 335 336 Orientation degree (%) 83.8 83.9
Crystallite size (nm) 2.1 2.2 Presence of surface striations Yes
Yes Distance between striations (.mu.m) 0.21 0.19 Striation
roughness Rms (5.mu.) (nm) 26.0 23.5 Surface roughness Rms
(0.5.mu.) (nm) 6.9 7.5 Surface oxygen concentration (O/C) 0.14 0.14
Surface nitrogen concentration (N/C) 0.024 0.023 Band intensity
ratio (D/G) 1.299 1.298
TABLE-US-00006 TABLE 6 Comparative Comparative Example 13 Example
14 Precursor fiber Orientation degree (%) 89.7 89.7 Oxidized fiber
Density (g/cm.sup.3) 1.34 1.34 Mass reduction by DMF 5.0 5.0 (%)
First Primary Range of Fig. 1 .beta. .beta. carboni- stretching
Stretching ratio (times) 1.05 1.05 zation conditions Single fiber
modulus 8.8 8.8 step (GPa) Density (g/cm.sup.3) 1.40 1.40
Crystallite size (nm) 1.20 1.20 Secondary Change of density
Continuous Continuous stretching increase increase conditions
Crystallite size (nm) 1.45 or less 1.45 or less Stretching ratio
(times) 1.00 1.00 After Density (g/cm.sup.3) 1.70 1.70 first
Orientation degree (%) 79.0 79.0 carboni- Fiber diameter (.mu.m)
5.9 5.9 zation Second Primary Fiber tension F (MPa) 29.9 29.9
carboni- treatment Fiber stress B (mN) 0.817 0.817 zation Secondary
Fiber tension H (MPa) 14.9 14.9 step treatment Fiber stress B (mN)
0.408 0.408 After Density (g/cm.sup.3) 1.805 1.805 second Fiber
diamener (.mu.m) 5.2 5.2 carboni- Elongation (%) 2.21 2.21 zation
Third Fiber tension J (MPa) 26.9 153.8 carboni- Fiber stress G (mN)
0.572 3.267 zation step Carbon Strand form Good Bad Fiber Density
(g/cm.sup.3) 1.76 1.75 Fiber diameter (.mu.m) 5.2 4.9 Strand
strength (MPa) 6050 5850 Strand modulus (GPa) 340 348 Orientation
degree (%) 84.1 84.4 Crystallite size (nm) 2.2 2.2 Presence of
surface striations Yes Yes Distance between striations (.mu.m) 0.20
0.20 Striation roughness Rms (5 .mu.) (nm) 24.5 26.5 Surface
roughness Rms (0.5 .mu.) 6.3 7.0 (nm) Surface oxygen concentration
0.14 0.14 (O/C) Surface nitrogen concentration 0.025 0.028 (N/C)
Band intensity ratio (D/G) 1.293 1.290
TABLE-US-00007 TABLE 7 Comparative Comparative Example 15 Example 1
Example 4 Example 16 Maximum temperature in third 1800 1900 2000
2100 carbonization step (.degree. C.) Carbon Strand form Good Good
Good Good fiber Density (g/cm.sup.3) 1.79 1.77 1.76 1.79 Fiber
diameter (.mu.m) 5.2 5.1 5.1 5.0 Strand strength (MPa) 6250 6150
6100 5850 Strand modulus (GPa) 325 343 360 381 Orientation degree
(%) 83.5 84.2 85.0 85.6 Crystallite size (nm) 2.1 2.2 2.4 2.6
Presence of surface striations Yes Yes Yes Yes Distance between
striations (.mu.m) 0.22 0.20 0.20 0.19 Striation roughness Rms 27.0
25.0 23.0 21.5 (5.mu.) (nm) Surface roughness Rms 7.5 6.2 8.0 9.0
(0.5.mu.) (nm) Surface oxygen concentration 0.16 0.14 0.13 0.12
(O/C) Surface nitrogen concentration 0.038 0.025 0.018 0.010 (N/C)
Band intensity ratio (D/G) 1.31 1.293 1.130 1.005
TABLE-US-00008 TABLE 8 Comparative Comparative Comparative Example
1 Example 17 Example 18 Example 19 Surface PH 0.1 0.1 0.1 0.1
treatment ORP (mV) +600 +600 +600 +600 conditions PH .times. ORP 60
60 60 60 Kind of chemical Nitric acid Nitric acid Nitric acid
Nitric acid Electricity amount for 200 0 50 100 surface treatment
(C/g) Carbon Strand form Good Good Good Good fiber Density
(g/cm.sup.3) 1.77 1.77 1.77 1.77 Fiber diameter (.mu.m) 5.1 5.1 5.1
5.1 Strand strength (MPa) 6150 5650 5850 6000 Strand modulus (GPa)
343 345 345 344 Orientation degree (%) 84.2 84.3 84.2 84.2
Crystallite size (nm) 2.2 2.2 2.2 2.2 Presence of surface Yes Yes
Yes Yes striations Distance between striations 0.20 0.14 0.14 0.23
(.mu.m) Striation roughness Rms 25.0 11.0 16.6 21.7 (5.mu.) (nm)
Surface roughness Rms 6.2 2.0 4.8 5.4 (0.5.mu.) (nm) Surface oxygen
concentration 0.14 0.05 0.08 0.10 (O/C) Surface nitrogen 0.025
0.033 0.031 0.043 concentration (N/C) Band intensity ratio (D/G)
1.293 0.916 1.211 1.248
TABLE-US-00009 TABLE 9 Comparative Example 5 Example 6 Example 7
Example 20 Surface PH 0.1 0.1 0.1 0.1 treatment ORP (mV) +600 +600
+600 +600 conditions PH .times. ORP 60 60 60 60 Kind of chemical
Nitric acid Nitric acid Nitric acid Nitric acid Electricity amount
for 150 250 300 350 surface treatment (C/g) Carbon Strand form Good
Good Good Good fiber Density (g/cm.sup.3) 1.77 1.77 1.77 1.77 Fiber
diameter (.mu.m) 5.1 5.1 5.0 5.0 Strand strength (MPa) 6100 6300
6250 6000 Strand modulus (GPa) 344 343 343 342 Orientation degree
(%) 84.2 84.3 84.4 84.4 Crystallite size (nm) 2.2 2.2 2.2 2.2
Presence of surface Yes Yes Yes Yes striations Distance between
striations 0.21 0.23 0.25 0.27 (.mu.m) Striation roughness Rms 22.5
34.5 37.4 41.0 (5.mu.) (nm) Surface roughness Rms 9.9 4.3 8.7 12.1
(0.5.mu.) (nm) Surface oxygen concentration 0.13 0.14 0.15 0.16
(O/C) Surface nitrogen 0.042 0.036 0.021 0.02 concentration (N/C)
Band intensity ratio (D/G) 1.296 1.294 1.300 1.305
TABLE-US-00010 TABLE 10 Comparative Comparative Comparative Example
21 Example 8 Example 22 Example 23 Surface PH 5.5 0.1 5.5 10
treatment ORP (mv) +400 +600 +300 +200 conditions PH .times. ORP
2200 60 1650 2000 Kind of chemical Ammonium Sulfuric Ammonium
Ammonium nitrate acid sulfate hydrogen- carbonate Electricity
amount for 150 150 150 150 surface treatment (C/g) Carbon Strand
form Good Good Good Good fiber Density (g/cm.sup.3) 1.77 1.79 1.76
1.75 Fiber diameter (.mu.m) 5.1 5.1 5.1 5.1 Strand strength (MPa)
5950 6100 5800 5700 Strand modulus (GPa) 344 343 341 339
Orientation degree (%) 84.3 84.3 84.4 84.4 Crystallite size (nm)
2.2 2.2 2.2 2.2 Presence of surface Yes Yes Yes Yes striations
Distance between striations 0.18 0.20 0.16 0.14 (.mu.m) Striation
roughness Rms 20.5 23.5 16.0 13.0 (5.mu.) (nm) Surface roughness
Rms 6.8 8.7 3.8 2.5 (0.5.mu.) (nm) Surface oxygen concentration
0.14 0.13 0.13 0.10 (O/C) Surface nitrogen 0.028 0.03 0.032 0.031
concentration (N/C) Band intensity ratio (D/G) 1.250 1.293 1.158
1.09
* * * * *