U.S. patent application number 15/309430 was filed with the patent office on 2017-06-01 for polybenzimidazole carbon fiber and method for manufacturing same.
The applicant listed for this patent is NATIONAL INSTITUTE OF ADVANCED INDUSTRIAL SCIENCE AND TECHNOLOGY. Invention is credited to Hiroaki HATORI, Toshihira IRISAWA, Masaya KODAMA, Yasushi SONEDA.
Application Number | 20170152612 15/309430 |
Document ID | / |
Family ID | 54392476 |
Filed Date | 2017-06-01 |
United States Patent
Application |
20170152612 |
Kind Code |
A1 |
IRISAWA; Toshihira ; et
al. |
June 1, 2017 |
POLYBENZIMIDAZOLE CARBON FIBER AND METHOD FOR MANUFACTURING
SAME
Abstract
The present application provides polybenzimidazole carbon fiber
that does not require infusibilization treatment and method for
producing same.
Inventors: |
IRISAWA; Toshihira;
(Ibaraki, JP) ; HATORI; Hiroaki; (Ibaraki, JP)
; SONEDA; Yasushi; (Ibaraki, JP) ; KODAMA;
Masaya; (Ibaraki, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NATIONAL INSTITUTE OF ADVANCED INDUSTRIAL SCIENCE AND
TECHNOLOGY |
Tokyo |
|
JP |
|
|
Family ID: |
54392476 |
Appl. No.: |
15/309430 |
Filed: |
April 24, 2015 |
PCT Filed: |
April 24, 2015 |
PCT NO: |
PCT/JP2015/062604 |
371 Date: |
November 7, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D01F 6/74 20130101; D01F
9/24 20130101 |
International
Class: |
D01F 9/24 20060101
D01F009/24; D01F 6/74 20060101 D01F006/74 |
Foreign Application Data
Date |
Code |
Application Number |
May 8, 2014 |
JP |
2014-096576 |
Claims
1. A polybenzimidazole carbon fiber comprising: a structure
obtained by turning a precursor fiber including polybenzimidazole
into a carbon fiber under application of heat, wherein the
polybenzimidazole includes a structure represented by General
Formula (1) or General Formula (2) below as a structural unit, and
wherein the polybenzimidazole carbon fiber has an elastic modulus
in tension of 100 GPa or more and a tensile strength of 0.8 GPa or
more: ##STR00009## where in the General Formulas (1) and (2),
R.sup.1 and R.sup.3 each represent a trivalent or tetravalent group
of one selected from the group consisting of aryl groups and
unsaturated heterocyclic groups that are expressed by any one of
Structural Formulas (1) to (10) below, and R.sup.2 represents a
bivalent group of one selected from the group consisting of aryl
groups and unsaturated heterocyclic groups that are expressed by
any one of the Structural Formulas (1) to (10), alkenylene groups
including from 2 to 4 carbon atoms, an oxygen atom, a sulfur atom,
and a sulphonyl group: ##STR00010##
2. The polybenzimidazole carbon fiber according to claim 1, wherein
the polybenzimidazole carbon fiber is a continuous fiber having a
fiber diameter of 8 .mu.m or more.
3. A method for producing a polybenzimidazole carbon fiber, the
method comprising: spinning, in an acid solution, a polymer
including polybenzimidazole including a structure represented by
General Formula (1) or General Formula (2) below as a structural
unit, to thereby obtain a first precursor fiber of the polymer;
contacting the first precursor fiber with a basic solution, and
neutralizing the acid solution remaining in the first precursor
fiber to be removed, to thereby obtain a second precursor fiber;
and heating the second precursor fiber at a temperature of from
1,000.degree. C. to 1,600.degree. C. under an inert gas, to thereby
turn the second precursor fiber into a carbon fiber: ##STR00011##
where in the General Formulas (1) and (2), R.sup.1 and R.sup.3 each
represent a trivalent or tetravalent group of one selected from the
group consisting of aryl groups and unsaturated heterocyclic groups
that are expressed by any one of Structural Formulas (1) to (10)
below, and R.sup.2 represents a bivalent group of one selected from
the group consisting of aryl groups and unsaturated heterocyclic
groups that are expressed by any one of the Structural Formulas (1)
to (10), alkenylene groups including from 2 to 4 carbon atoms, an
oxygen atom, a sulfur atom, and a sulphonyl group: ##STR00012##
4. The method for producing a polybenzimidazole carbon fiber
according to claim 3, wherein the acid solution is polyphosphoric
acid and the basic solution is an ethanol solution of
triethylamine.
5. The method for producing a polybenzimidazole carbon fiber
according to claim 4, wherein the contacting is allowing the first
precursor fiber to pass through a bath of the ethanol solution of
triethylamine for from 5 seconds to 30 seconds to neutralize the
polyphosphoric acid remaining in the first precursor fiber to be
removed.
6. The method for producing a polybenzimidazole carbon fiber
according to claim 3, wherein the spinning further comprises:
coagulating, in a coagulation bath, a reaction solution of the
polymer obtained through polymerization in a first acid solution,
to thereby obtain a first coagulated matter of the polymer;
contacting the first coagulated matter with a first basic solution
to neutralize the first acid solution remaining in the first
coagulated matter to be removed, to thereby obtain a second
coagulated matter; and dissolves the second coagulated matter in a
second acid solution to prepare a raw liquid for spinning, and
spins the raw liquid for spinning, to thereby obtain a first
precursor fiber of the polymer, and wherein the contacting is
contacting the first precursor fiber with a second basic solution,
and neutralizing the second acid solution remaining in the first
precursor fiber to be removed, to thereby obtain a second precursor
fiber.
7. The method for producing a polybenzimidazole carbon fiber
according to claim 6, wherein the first acid solution is
polyphosphoric acid, the first basic solution is an aqueous sodium
hydrogen carbonate solution, the second acid solution is
methanesulfonic acid, and the second basic solution is an ethanol
solution of triethylamine.
8. The method for producing a polybenzimidazole carbon fiber
according to claim 7, wherein the contacting is allowing the first
precursor fiber to pass through a bath of the ethanol solution of
triethylamine for from 5 seconds to 30 seconds, and neutralizing
the methanesulfonic acid remaining in the first precursor fiber to
be removed.
9. The method for producing a polybenzimidazole carbon fiber
according to claim 3, wherein a heating temperature of the heating
is a temperature of from 1,200.degree. C. to 1,400.degree. C.
Description
TECHNICAL FIELD
[0001] The present invention relates to a polybenzimidazole carbon
fiber made from a fiber material that is a precursor fiber
including polybenzimidazole; and a method for producing the
same.
BACKGROUND ART
[0002] Carbon fibers have been used in a wide variety of
applications from aircraft to building materials. If their
productivity is improved and their cost is lowered more and more,
they can be materials in place of stainless steel plates also in
automobile body and the like. At present, carbon fibers are mainly
produced using polyacrylonitrile (PAN) fibers and pitch fibers as
fiber raw materials (fiber precursor fibers).
[0003] These precursor fibers, however, require a pre-treatment
called an infusibilization treatment prior to carbonization, and
this treatment is a major obstacle to reduction in cost and energy
required for their production, and to increase in productivity.
[0004] Specifically, because PAN fibers and pitch fibers are fused
in the course of a carbonization treatment (a high-temperature
thermal treatment of 1,000.degree. C. or more) and cannot maintain
their fiber shapes, they are changed to infusible, flame-resistant
fibers by an air oxidization treatment called an infusibilization
treatment and then are subjected to carbonization, to thereby
obtain carbon fibers. In this infusibilization treatment, it is
necessary to uniformly control oxidation reaction and also strictly
manage temperature conditions for suppressing thermal runaway due
to exothermic reaction, and moreover its treatment time is long
(about 30 minutes to about 1 hour).
[0005] Therefore, the present inventors have studied various
precursor fibers that do not require the infusibilization
treatment, and have presented research reports of PBI carbon fibers
obtained from polybenzimidazole (hereinafter referred to as "PBI")
fiber serving as precursor fibers (see NPL 1). The PBI fibers can
be carbonized while maintaining their fiber shape without
performing the infusibilization treatment.
[0006] In existing reports, it is known that PBI fibers are spun
and carbonized to thereby obtain carbon fibers having an elastic
modulus of 80 GPa and a strength of 670 MPa (see PTL 1). Moreover,
it is known that carbon fibers having a diameter of more than 100
.mu.m can be produced by treating PBI fibers being basic with an
acid solvent to thereby form salts. Moreover, it is believed that
the above-described PBI fibers have an elastic modulus of 100 GPa
and a strength of 420 MPa (see PTL 2).
[0007] However, the PBI carbon fibers obtained by carbonizing the
PBI fibers have low elastic modulus and low strength, which is
problematic. Therefore, the PBI carbon fibers are required to be
improved in both elastic modulus and strength for practical
applications.
[0008] On the other hand, known is a method for removing, from
fibers, polyphosphoric acid used in production of polymers by
contacting the PBI fibers with a neutralization solution as a
method for improving the PBI fibers serving as a precursor fiber in
strength (see, for example, PTL 3).
[0009] However, carbon fibers obtained from the above-described PBI
fibers serving as precursor fibers have not been known. Moreover,
the PBI carbon fibers having sufficient elastic modulus and
strength for practical applications have not been found yet. That
is, elastic modulus and strength of a precursor fiber do not always
correspond to elastic modulus and strength of a carbon fiber
obtained by carbonizing this precursor fiber. Moreover, whether the
carbon fiber can achieve intended elastic modulus and strength is
unknown. Therefore, there has been a demand that the PBI carbon
fibers having sufficient elastic modulus and strength for practical
applications are newly developed.
CITATION LIST
Patent Literature
[0010] PTL 1: U.S. Pat. No. 3,528,774 [0011] PTL 2: U.S. Pat. No.
3,903,248 [0012] PTL 3: Japanese Patent Application Laid-Open
(JP-A) No. 2008-507637
Non-Patent Literature
[0012] [0013] NPL 1: Proceedings of the 39th Annual Meeting of The
Carbon Society of Japan, 3B02, 3B03 (2012)
SUMMARY OF INVENTION
Technical Problem
[0014] The present invention aims to solve the above problems in
the existing technique and achieve the following object. That is,
an object of the present invention is to provide: a PBI carbon
fiber that can be efficiently produced without an infusibilization
treatment and is excellent in elastic modulus and strength; and a
method for producing the PBI carbon fiber.
Solution to Problem
[0015] Means for solving the above problems are as follows.
[0016] <1> A polybenzimidazole carbon fiber including:
[0017] a structure obtained by turning a precursor fiber including
polybenzimidazole into a carbon fiber under application of
heat,
[0018] wherein the polybenzimidazole includes a structure
represented by General Formula (1) or General Formula (2) below as
a structural unit, and
[0019] wherein the polybenzimidazole carbon fiber has an elastic
modulus in tension of 100 GPa or more and a tensile strength of 0.8
GPa or more:
##STR00001##
[0020] where in the General Formulas (1) and (2), R.sup.1 and
R.sup.3 each represent a trivalent or tetravalent group of one
selected from the group consisting of aryl groups and unsaturated
heterocyclic groups that are expressed by any one of Structural
Formulas (1) to (10) below, and R.sup.2 represents a bivalent group
of one selected from the group consisting of aryl groups and
unsaturated heterocyclic groups that are expressed by any one of
the Structural Formulas (1) to (10), alkenylene groups including
from 2 to 4 carbon atoms, an oxygen atom, a sulfur atom, and a
sulphonyl group:
##STR00002##
[0021] <2> The polybenzimidazole carbon fiber according to
<1>, wherein the polybenzimidazole carbon fiber is a
continuous fiber having a fiber diameter of 8 .mu.m or more.
[0022] <3> A method for producing a polybenzimidazole carbon
fiber, the method including:
[0023] spinning, in an acid solution, a polymer including
polybenzimidazole including a structure represented by General
Formula (1) or General Formula (2) below as a structural unit, to
thereby obtain a first precursor fiber of the polymer;
[0024] contacting the first precursor fiber with a basic solution,
and neutralizing the acid solution remaining in the first precursor
fiber to be removed, to thereby obtain a second precursor fiber;
and
[0025] heating the second precursor fiber at a temperature of from
1,000.degree. C. to 1,600.degree. C. under an inert gas, to thereby
turn the second precursor fiber into a carbon fiber:
##STR00003##
[0026] where in the General Formulas (1) and (2), R.sup.1 and
R.sup.3 each represent a trivalent or tetravalent group of one
selected from the group consisting of aryl groups and unsaturated
heterocyclic groups that are expressed by any one of Structural
Formulas (1) to (10) below, and R.sup.2 represents a bivalent group
of one selected from the group consisting of aryl groups and
unsaturated heterocyclic groups that are expressed by any one of
the Structural Formulas (1) to (10), alkenylene groups including
from 2 to 4 carbon atoms, an oxygen atom, a sulfur atom, and a
sulphonyl group:
##STR00004##
[0027] <4> The method for producing a polybenzimidazole
carbon fiber according to <3>, wherein the acid solution is
polyphosphoric acid and the basic solution is an ethanol solution
of triethylamine.
[0028] <5> The method for producing a polybenzimidazole
carbon fiber according to <4>, wherein the contacting is
allowing the first precursor fiber to pass through a bath of the
ethanol solution of triethylamine for from 5 seconds to 30 seconds
to neutralize the polyphosphoric acid remaining in the first
precursor fiber to be removed.
[0029] <6> The method for producing a polybenzimidazole
carbon fiber according to <3>,
[0030] wherein the spinning further includes: coagulating, in a
coagulation bath, a reaction solution of the polymer obtained
through polymerization in a first acid solution, to thereby obtain
a first coagulated matter of the polymer; contacting the first
coagulated matter with a first basic solution to neutralize the
first acid solution remaining in the first coagulated matter to be
removed, to thereby obtain a second coagulated matter; and
dissolves the second coagulated matter in a second acid solution to
prepare a raw liquid for spinning, and spins the raw liquid for
spinning, to thereby obtain a first precursor fiber of the polymer,
and
[0031] wherein the contacting is contacting the first precursor
fiber with a second basic solution, and neutralizing the second
acid solution remaining in the first precursor fiber to be removed,
to thereby obtain a second precursor fiber.
[0032] <7> The method for producing a polybenzimidazole
carbon fiber according to <6>, wherein the first acid
solution is polyphosphoric acid, the first basic solution is an
aqueous sodium hydrogen carbonate solution, the second acid
solution is methanesulfonic acid, and the second basic solution is
an ethanol solution of triethylamine.
[0033] <8> The method for producing a polybenzimidazole
carbon fiber according to <7>, wherein the contacting is
allowing the first precursor fiber to pass through a bath of the
ethanol solution of triethylamine for from 5 seconds to 30 seconds,
and neutralizing the methanesulfonic acid remaining in the first
precursor fiber to be removed.
[0034] <9> The method for producing a polybenzimidazole
carbon fiber according to any one of <3> to <8>,
wherein a heating temperature of the heating is a temperature of
from 1,200.degree. C. to 1,400.degree. C.
Advantageous Effects of Invention
[0035] According to the present invention, it is possible to solve
the above problems in the existing technique and to provide: a PBI
carbon fiber that can be efficiently produced without an
infusibilization treatment and is excellent in elastic modulus and
strength; and a method for producing the PBI carbon fiber.
BRIEF DESCRIPTION OF DRAWINGS
[0036] FIG. 1A is an image presenting cross sections of PBI carbon
fibers according to Example 3 obtained through an electron
microscope.
[0037] FIG. 1B is an image presenting cross sections of PBI carbon
fibers according to Example 10 obtained through an electron
microscope.
[0038] FIG. 1C is an image presenting cross sections of PBI carbon
fibers according to Comparative Example 1 obtained through an
electron microscope.
[0039] FIG. 1D is an image presenting cross sections of PBI carbon
fibers according to Comparative Example 1 obtained through an
electron microscope.
[0040] FIG. 2A is a graph presenting measurement results of elastic
modulus in tension.
[0041] FIG. 2B is a graph presenting measurement results of tensile
strength.
[0042] FIG. 3 is an explanatory view presenting presumption
conditions of reachable strength.
[0043] FIG. 4A is an image presenting cross sections of PBI carbon
fibers according to Example 15 obtained through an electron
microscope.
[0044] FIG. 4B is an image presenting cross sections of PBI carbon
fibers according to Example 16 obtained through an electron
microscope.
[0045] FIG. 5 is a graph presenting measurement results of
density.
[0046] FIG. 6A is a schematic view presenting plane interval c/2 of
carbon network planes and stack thickness L.sub.c of carbon network
planes in a graphite crystal.
[0047] FIG. 6B is a schematic view presenting an optical system in
measuring wide angle X-ray diffraction profile.
[0048] FIG. 7 is a graph presenting a relationship between plane
interval c/2 and stack thickness Lc of carbon network planes.
[0049] FIG. 8 is a graph presenting measurement results of
cross-sectional areas of microvoids.
[0050] FIG. 9 is a graph presenting measurement results of volume
percentages of microvoids.
DESCRIPTION OF EMBODIMENTS
[0051] (PBI Carbon Fiber)
[0052] A polybenzimidazole (PBI) carbon fiber of the present
invention includes a structure obtained by turning a precursor
fiber including PBI into a carbon fiber under application of heat.
The PBI includes a structure represented by the following General
Formula (1) or General Formula (2) as a structural unit. The PBI
carbon fiber has an elastic modulus in tension of 100 GPa or more
and a tensile strength of 0.8 GPa or more.
##STR00005##
[0053] In the General Formulas (1) and (2), R.sup.1 and R.sup.3
each represent a trivalent or tetravalent group of one selected
from the group consisting of aryl groups and unsaturated
heterocyclic groups that are expressed by any one of the following
Structural Formulas (1) to (10), and R.sup.2 represents a bivalent
group of one selected from the group consisting of aryl groups and
unsaturated heterocyclic groups that are expressed by any one of
the Structural Formulas (1) to (10), alkenylene groups including
from 2 to 4 carbon atoms, an oxygen atom, a sulfur atom, and a
sulphonyl group.
##STR00006##
[0054] Examples of the alkenylene group include a vinylene
group.
[0055] The precursor fiber including the above PBI (PBI precursor
fiber) can be carbonized while maintaining its fiber shape even
without an infusibilization treatment. Therefore, the carbon fibers
can be efficiently produced compared to carbon fibers obtained from
precursor fibers such as PAN fibers or pitch fibers, which require
the infusibilization treatment.
[0056] In addition, the PBI precursor fiber can be carbonized with
high carbonization yield. Therefore, it is possible to suppress
distortion of structures due to pyrolysis gas generated and
released during carbonization, and/or generation of voids (pores)
(including foaming) which would reduce the mechanical strength of
carbon fibers. Moreover, partly because the carbonization yield is
high; i.e., the amount of gas and/or tar released by pyrolysis
during carbonization is small, even in the case where carbonization
is performed under rapid heating, it is possible to avoid instant
generation of a large amount of decomposition gas, which makes it
possible to perform carbonization treatment very rapidly. Thereby,
it is possible to carbonize thick fibers having large volumes
relative to their outer surfaces so that gas does not easily escape
during carbonization.
[0057] The PBI carbon fiber has an elastic modulus in tension of
100 GPa or more and a tensile strength of 0.8 GPa or more; i.e., it
is excellent in both elastic modulus and strength.
[0058] The reason why the PBI carbon fiber can achieve the
above-described elastic modulus and strength is because an acid
solution in the PBI precursor fiber is neutralized by a basic
solution to be removed in the below-described production method.
The invention of the PBI carbon fiber is based on the finding that
the precursor fiber obtained through the above-described
neutralization for removal can be turned into a carbon fiber while
maintaining a fiber structure of the precursor fiber.
[0059] Here, the elastic modulus in tension and the tensile
strength can be measured by a single fiber tensile test according
to the JIS7606 method.
[0060] As described above, the PBI carbon fiber can maintain high
elastic modulus and high strength even if a thick fiber is
carbonized to have a larger diameter. Commercially available
products of carbon fibers (e.g., PAN carbon fibers) generally have
a fiber diameter of about 7 .mu.m. However, the PBI carbon fiber
can maintain high elastic modulus and high strength not only when
the fiber diameter is a small diameter of from 2 .mu.m to 8 .mu.m
(exclusive) but also when the fiber diameter is 8 .mu.m or more,
and is further increased to a large thickness of 16 .mu.m or more.
Here, the upper limit of the fiber diameter is about 30 .mu.m.
[0061] Moreover, the PBI carbon fiber can be a continuous fiber
(filament).
[0062] The above-described PBI carbon fiber according to the
present invention can be produced by a method for producing the PBI
carbon fiber according to present invention, which will be
described hereinafter.
[0063] (Method for Producing PBI Carbon Fiber)
[0064] The method for producing the PBI carbon fiber includes a
step of obtaining a first precursor fiber, a step of obtaining a
second precursor fiber, and a step of producing a carbon fiber.
[0065] <Step of Obtaining First Precursor Fiber>
[0066] The step of obtaining a first precursor fiber is a step of
spinning, in an acid solution, a polybenzimidazole-including
polymer having a structure expressed by the General Formula (1) or
(2) as a structural unit, to thereby obtain a first precursor fiber
of the polymer.
##STR00007##
[0067] In the General Formulas (1) and (2), R.sup.1 and R.sup.3
each represent a trivalent or tetravalent group of one selected
from the group consisting of aryl groups and unsaturated
heterocyclic groups that are expressed by any one of Structural
Formulas (1) to (10) below, and R.sup.2 represents a bivalent group
of one selected from the group consisting of aryl groups and
unsaturated heterocyclic groups that are expressed by any one of
the Structural Formulas (1) to (10), alkenylene groups including
from 2 to 4 carbon atoms, an oxygen atom, a sulfur atom, and a
sulphonyl group.
##STR00008##
[0068] Examples of the alkenylene group include a vinylene
group.
[0069] The PBI may be a commercially available product or may be
synthesized.
[0070] When the PBI is synthesized, it can be obtained by allowing,
in the acid solution, terephthalic acid (available from, for
example, Wako Pure Chemical Industries, Ltd.) and
4,4'-bephenyl-1,1',2,2'-tetramine (available from, for example,
Aldrich) as starting materials to proceed to polycondensation
reaction.
[0071] The polymer may be the PBI itself. Alternatively, the
polymer may be a copolymer formed of a structural unit of the PBI
and another structural unit, or a polymer blend material obtained
by combining the PBI with another polymer so long as the effects of
the present invention are not deteriorated.
[0072] The precursor fiber may be a fiber material obtained from
the polymer itself. However, the precursor fiber may be a fiber
material obtained by adding any substituent to a terminal of the
polymer so long as the effects of the present invention are not
deteriorated.
[0073] Examples of the any substituent include an ester group, an
amide group, an imide group, a hydroxyl group, and a nitro
group.
[0074] Methods of the spinning can be roughly divided into the
following two methods: a first method and a second method. The
first method can be performed by directly spinning, as a raw liquid
for spinning, a reaction solution obtained by allowing the polymer
to proceed to polycondensation reaction in the acid solution. The
second method can be performed in the following manner.
Specifically, the acid solution constituting the reaction solution
is regarded as a first acid solution. A coagulated matter of the
polymer is first obtained from the reaction solution, and then the
coagulated matter is dissolved in a second acid solution for
spinning, to thereby obtain a reaction solution as a raw liquid for
spinning. Then, the raw liquid for spinning is spun.
[0075] The acid solution used for the first method is not
particularly limited so long as it can dissolve the starting
materials and the polymer to be produced and can serve as a
catalyst that promotes polymerization. Specific examples of the
acid solution include polyphosphoric acid, polyphosphate ester,
diphenyl cresyl phosphate, and methanesulfonic acid in which
diphenyl cresyl phosphate or diphosphorus pentaoxide is dissolved.
Among them, the polyphosphoric acid is preferable in terms of
controlling the polymerization reaction.
[0076] When the spinning is performed by the second method, the
step of obtaining a first precursor fiber includes a step of
obtaining a first coagulated matter and a step of obtaining a
second coagulated matter. In addition, the step of obtaining a
first precursor fiber is a step of obtaining a first precursor
fiber of the polymer by spinning a raw liquid for spinning, the raw
liquid for spinning being prepared by dissolving, in a second acid
solution, the second coagulated matter obtained in the step of
obtaining a second coagulated matter.
[0077] --Step of Obtaining First Coagulated Matter--
[0078] The step of obtaining a first coagulated matter is a step of
coagulating, in the first acid solution, the reaction solution of
the polymer obtained through polymerization in a coagulation bath,
to thereby obtain a first coagulated matter of the polymer.
[0079] The first acid solution can be the same one as the acid
solution used in the first method.
[0080] A coagulation liquid in the coagulation bath is not
particularly limited so long as the polymer can be coagulated.
Examples of the coagulation liquid include water, alcohol,
methanesulfonic acid, polyphosphoric acid, and dilute sulfuric
acid. Among them, the water is preferable.
[0081] --Step of Obtaining Second Coagulated Matter--
[0082] The step of obtaining a second coagulated matter is a step
of contacting the first coagulated matter with a first basic
solution, and neutralizing the first acid solution remaining in the
first coagulated matter to be removed, to thereby obtain a second
coagulated matter.
[0083] The first basic solution is not particularly limited so long
as it neutralizes the first acid solution. Examples of the first
basic solution include an aqueous sodium hydrogen carbonate
solution, an aqueous sodium hydroxide solution, potassium
hydroxide, and an ethanol solution of triethylamine. Among them,
the aqueous sodium hydrogen carbonate solution is preferable
because reduction in a degree of polymerization can be
prevented.
[0084] Here, the coagulated matter may be washed with water or
alcohol before or after washed with the first basic solution.
[0085] When the spinning is performed by the second method as
described above, the second coagulated matter that has been washed
is dissolved in the second acid solution to prepare the raw liquid
for spinning.
[0086] The second acid solution is not particularly limited so long
as the second coagulated matter can be dissolved. Examples of the
second acid solution include methanesulfonic acid, polyphosphoric
acid, and concentrated sulfuric acid. Among them, the
methanesulfonic acid is preferable because it can impart viscosity
suitable for the spinning to the raw liquid for spinning.
[0087] The spinning method in the first method and the second
method is not particularly limited and may be appropriately
selected depending on the intended purpose. Examples of the
spinning method include known wet-type spinning methods and known
dry-type spinning methods.
[0088] Note that, the first precursor fiber and a second precursor
fiber that will be described hereinafter may be subjected to
drawing treatment.cndot.thermal treatment if necessary. Regarding
the drawing treatment, spun yarn may be directly drawn in a
coagulation bath, or wound yarn may be washed with water and then
drawn in the bath. The drawing treatment and the thermal treatment
may be performed at the same time. Regarding the thermal treatment,
an atmosphere is not particularly limited, but the thermal
treatment is preferably performed in air or in a nitrogen
atmosphere. A temperature and time of the thermal treatment may be
appropriately selected, but the temperature of the thermal
treatment is preferably from 200.degree. C. to 600.degree. C.
Moreover, a draw ratio is preferably from about 1.2 times to about
10 times.
[0089] As described above, the first precursor fiber can be
obtained.
[0090] <Step of Obtaining Second Precursor Fiber>
[0091] The step of obtaining a second precursor fiber is a step of
contacting the first precursor fiber with a basic solution, and
neutralizing the acid solution remaining in the first precursor
fiber to be removed, to thereby obtain a second precursor
fiber.
[0092] When the step of obtaining a first precursor fiber is
performed by the first method, the basic solution used in the step
of obtaining a second precursor fiber is not particularly limited
so long as it neutralizes the acid solution. Examples of the basic
solution include an ethanol solution of triethylamine, an aqueous
sodium hydrogen carbonate solution, an aqueous sodium hydroxide
solution, and potassium hydroxide. The ethanol solution of
triethylamine is preferable because an excess amount of alkali
remaining in fibers after neutralization reaction is easily
removed.
[0093] Moreover, a method of the contacting is not particularly
limited and may be performed by spraying the basic solution to the
first precursor fiber. However, the first precursor fiber is
preferably allowed to pass through a bath of the basic
solution.
[0094] In particular, when the step of obtaining a first precursor
fiber is performed by the first method, and when the acid solution
is the polyphosphoric acid and the basic solution is the ethanol
solution of triethylamine, it is preferable that the first
precursor fiber be allowed to pass through a bath of the ethanol
solution of triethylamine for from 5 seconds to 30 seconds.
[0095] The above-described method can effectively neutralize the
acid solution in the first precursor fiber to be removed.
[0096] Here, the precursor fiber may be washed with water or
alcohol before or after washed with the basic solution.
[0097] When the step of obtaining a first precursor fiber is
performed by the second method, the step of obtaining a second
precursor fiber is performed as a step of contacting the first
precursor fiber with a second basic solution, and neutralizing the
second acid solution remaining in the first precursor fiber to be
removed, to thereby obtain a second precursor fiber.
[0098] The second basic solution is not particularly limited so
long as it can neutralize the second acid solution. Examples of the
second basic solution include an ethanol solution of triethylamine,
an aqueous sodium hydrogen carbonate solution, an aqueous sodium
hydroxide solution, and potassium hydroxide. Among them, the
ethanol solution of triethylamine is preferable because excess of
alkali remaining in fibers after neutralization reaction is easily
removed.
[0099] A method of the contacting is not particularly limited and
may be performed by spraying the second basic solution to the first
precursor fiber. However, the first precursor fiber is preferably
allowed to pass through a bath of the second basic solution.
[0100] In particular, when the second acid solution is the
methanesulfonic acid and the second basic solution is the ethanol
solution of triethylamine, the first precursor fiber is preferably
allowed to pass through a bath of the ethanol solution of
triethylamine for from 5 seconds to 30 seconds.
[0101] The above-described method can effectively neutralize the
second acid solution in the first precursor fiber to be
removed.
[0102] Here, the precursor fiber may be washed with water or
alcohol before or after washed with the second basic solution.
[0103] <Step of Producing Carbon Fibers>
[0104] The step of producing carbon fibers is a step of heating the
second precursor fiber at a temperature of from 1,000.degree. C. to
1,600.degree. C. in an inert gas atmosphere to turn the second
precursor fiber into a carbon fiber.
[0105] When a heating temperature in the step of producing carbon
fibers is from 1,200.degree. C. to 1,400.degree. C., the PBI carbon
fibers that are more excellent in elastic modulus and strength can
be produced.
[0106] Moreover, as described above, the PBI fibers have property
of maintaining their fiber shapes even if the PBI fibers are
subjected to high-speed carbonization treatment at a rapid
temperature increasing rate.
[0107] Therefore, a temperature increasing rate in the heating is
not particularly limited and can be the following: from such a
low-speed temperature increasing rate as 5.degree. C./min through
such a high-speed temperature increasing rate as a range of from
15.degree. C./sec to 1,000.degree. C./sec.
[0108] Here, the inert gas is not particularly limited. Examples of
the inert gas include nitrogen and argon gas.
[0109] The method for producing the PBI carbon fiber may further
include a step of graphitizing the PBI carbon fibers. This step is
performed by heating the PBI carbon fibers at higher temperature
after the step of producing carbon fibers or successively after the
step of producing carbon fibers, in order to control mechanical
properties (e.g., elastic modulus and strength) of the PBI carbon
fibers obtained through the carbonization.
[0110] A heating temperature in the graphitizing step (a heating
step to be performed successively with the carbonization step in
some cases) is not particularly limited but is preferably from
2,000.degree. C. to 3,200.degree. C. Setting the heating
temperature in such a range makes it possible to produce the carbon
fibers having sufficient mechanical properties at high
carbonization yield and high density.
[0111] Note that, the graphitizing step is preferably performed in
an inert gas similar to the step of producing carbon fibers.
[0112] Note that, the method for producing the PBI carbon fiber may
further include a surface treatment and a step of performing
application of sizing performed in known processes of producing
carbon fibers.
EXAMPLES
(Preparation of Precursor Fiber)
<PBI Precursor Fiber 1>
[0113] First, terephthalic acid (1 mol) (available from Wako Pure
Chemical Industries, Ltd., Distributor Code No. 208-08162) and
4,4'-bephenyl-1,1',2,2'-tetraamine (1 mol) (available from Aldrich,
Distributor Code No. D12384), each of which is a raw material of a
polymer, were allowed to proceed to polycondensation reaction in
polyphosphoric acid (available from Sigma-Aldrich, Distributor Code
No. 208213) serving as a first acid solution, to thereby prepare a
reaction solution including
poly2,2'-(p-phenylene)-5,5'-bibenzimidazole as a PBI polymer.
[0114] Next, the reaction solution was charged into a water bath
serving as a coagulation bath. Then, the PBI polymer was coagulated
so as to have a fiber shape, to thereby obtain a first coagulated
matter (step of obtaining a first coagulated matter).
[0115] The first coagulated matter was stirred in dimethylacetamide
(DMAc) to wash impurities. Then, the first coagulated matter was
stirred in an aqueous sodium hydrogen carbonate solution
(concentration: 5 wt %) to neutralize the first acid solution in
the first coagulated matter to be removed, to thereby obtain a
second coagulated matter of the PBI polymer. Next, the second
coagulated matter was washed with water and alcohol, and was dried
at 240.degree. C. under vacuum for 1 day (step of obtaining a
second coagulated matter).
[0116] Note that, it is known that polycondensation reaction of the
PBI polymer proceeds in a substantially quantitative manner. It was
confirmed that when the step of obtaining a second coagulated
matter was omitted and the first coagulated matter was directly
dried, a yield; i.e., an amount relative to a theoretically
determined amount of the PBI polymer in the first coagulated matter
was 110% or more, which means that the first acid solution
(polyphosphoric acid) remained in the PBI polymer. When the step of
obtaining a second coagulated matter was performed, the yield was
about 98%.
[0117] Next, the second coagulated matter was dissolved in
methanesulfonic acid (available from Wako Pure Chemical Industries,
Ltd., Distributor Code No. 138-01576) serving as a second acid
solution, to thereby prepare a raw liquid for spinning, the raw
liquid including the second coagulated matter in an amount of 3.2
wt %.
[0118] By wet-type spinning, the raw liquid for spinning was
charged into a water bath serving as a coagulation bath, and was
allowed to pass through a multi-hole nozzle member including 402
nozzle holes, to thereby eject a fiber bundle of 402 fibers. The
fiber bundle was wound by a winding device, to thereby obtain a
first precursor fiber of the PBI polymer (step of obtaining a first
precursor fiber). Here, the wet-type spinning was performed under
application of tension so that a jet stretch ratio represented by
winding speed/discharge linear velocity was 1.5. Moreover, a
diameter of each of the nozzle holes of the multi-hole nozzle
member was set so that a diameter of one first precursor fiber
constituting the fiber bundle was 20 .mu.m.
[0119] Next, the first precursor fiber was allowed to pass through
a bath of an ethanol solution of triethylamine serving as a second
basic solution for 30 seconds. Then, the second acid solution in
the first precursor fiber was neutralized to be removed, to thereby
obtain a second precursor fiber of the PBI polymer. After that, the
second precursor fiber was washed with water and was dried (step of
obtaining a second precursor fiber).
[0120] In order to confirm whether the second acid solution in the
obtained second precursor fiber remains or not, CHNS elemental
analysis was performed. Here, the CHNS elemental analysis is
performed by detecting a sulfur component (S component) in the
methanesulfonic acid serving as the second acid solution.
[0121] As a result of the analysis, it was confirmed that the
sulfur component (S component) was not detected in the second
precursor fiber and the methanesulfonic acid was completely
neutralized to be removed.
[0122] As described above, PBI precursor fiber 1 serving as the
second precursor fiber was prepared.
[0123] <PBI Precursor Fiber 2>
[0124] PBI precursor fiber 2 was prepared in the same manner as in
the method for preparing the PBI precursor fiber 1 except that a
diameter of each of the nozzle holes of the multi-hole nozzle
member was changed for adjustment so that a diameter of one fiber
was 11 .mu.m.
[0125] <PBI Precursor Fiber 3>
[0126] In the preparation of the PBI precursor fiber 1, the step of
obtaining a second precursor fiber was omitted and was replaced
with the following procedures. Specifically, the first precursor
fiber was allowed to pass through a bath of water for 30 seconds.
Then, the first precursor fiber was washed with water and was
dried, to thereby obtain the second precursor fiber.
[0127] PBI precursor fiber 3 was prepared in the same manner as in
the method for preparing the PBI precursor fiber 1 so that a
diameter of one fiber was 11 .mu.m.
[0128] When the PBI precursor fiber 3 was subjected to the CHNS
analysis, it was confirmed that about 8% of the sulfur component (S
component) was detected in the second precursor fiber and the
methanesulfonic acid was not completely neutralized to be
removed.
[0129] <PBI Precursor Fiber 4>
[0130] PBI precursor fiber 4 was prepared in the same manner as in
the preparation of the PBI precursor fiber 1 except that some
procedures were changed in the following manners. Specifically, the
multi-hole nozzle member was replaced with a single hole nozzle
member having a diameter of a nozzle hole was 250 .mu.m. A fiber
was obtained so that one fiber was adjusted to have a fiber
diameter of 40 .mu.m. The fiber was not subjected to the step of
obtaining a second precursor fiber and was directly dried, to
thereby obtain PBI precursor fiber 4.
[0131] (Carbonization of Precursor Fiber)
Example 1
[0132] The PBI precursor fiber 1 serving as the second precursor
fiber was heated from room temperature to a predetermined heating
temperature of 1,000.degree. C. at a temperature increasing rate of
10.degree. C./min in a nitrogen atmosphere. Moreover, the PBI
precursor fiber 1 was continued in heating for 10 minutes at the
predetermined heating temperature and was turned into carbon
fibers, to thereby produce PBI carbon fibers according to Example 1
(step of producing carbon fibers). Here, the PBI carbon fibers
according to Example 1 each had a diameter of 16 .mu.m. Moreover,
the PBI carbon fibers according to Examples 2 to 7, which will be
described hereinafter, each had the same diameter as the above.
Example 2
[0133] PBI carbon fibers according to Example 2 were produced in
the same manner as in the step of producing carbon fibers of
Example 1 except that the predetermined heating temperature was
changed from 1,000.degree. C. to 1,100.degree. C.
Example 3
[0134] PBI carbon fibers according to Example 3 were produced in
the same manner as in the step of producing carbon fibers of
Example 1 except that the predetermined heating temperature was
changed from 1,000.degree. C. to 1,200.degree. C.
Example 4
[0135] PBI carbon fibers according to Example 4 were produced in
the same manner as in the step of producing carbon fibers of
Example 1 except that the predetermined heating temperature was
changed from 1,000.degree. C. to 1,300.degree. C.
Example 5
[0136] PBI carbon fibers according to Example 5 were produced in
the same manner as in the step of producing carbon fibers of
Example 1 except that the predetermined heating temperature was
changed from 1,000.degree. C. to 1,400.degree. C.
Example 6
[0137] PBI carbon fibers according to Example 6 were produced in
the same manner as in the step of producing carbon fibers of
Example 1 except that the predetermined heating temperature was
changed from 1,000.degree. C. to 1,500.degree. C.
Example 7
[0138] PBI carbon fibers according to Example 7 were produced in
the same manner as in the step of producing carbon fibers of
Example 1 except that the predetermined heating temperature was
changed from 1,000.degree. C. to 1,600.degree. C.
Example 8
[0139] The PBI precursor fiber 2 serving as the second precursor
fiber was heated from room temperature to a predetermined heating
temperature of 1,000.degree. C. at a temperature increasing rate of
10.degree. C./min in a nitrogen atmosphere. Moreover, the PBI
precursor fiber 2 was continued in heating for 10 minutes at the
predetermined heating temperature and was turned into carbon
fibers, to thereby produce PBI carbon fibers according to Example 8
(step of producing carbon fibers). Here, the PBI carbon fibers
according to Example 8 each had a diameter of 9 .mu.m. Moreover,
the PBI carbon fibers according to Examples 9 to 14, which will be
described hereinafter, each had the same diameter as the above.
Example 9
[0140] PBI carbon fibers according to Example 9 were produced in
the same manner as in the step of producing carbon fibers of
Example 8 except that the predetermined heating temperature was
changed from 1,000.degree. C. to 1,100.degree. C.
Example 10
[0141] PBI carbon fibers according to Example 10 were produced in
the same manner as in the step of producing carbon fibers of
Example 8 except that the predetermined heating temperature was
changed from 1,000.degree. C. to 1,200.degree. C.
Example 11
[0142] PBI carbon fibers according to Example 11 were produced in
the same manner as in the step of producing carbon fibers of
Example 8 except that the predetermined heating temperature was
changed from 1,000.degree. C. to 1,300.degree. C.
Example 12
[0143] PBI carbon fibers according to Example 12 were produced in
the same manner as in the step of producing carbon fibers of
Example 8 except that the predetermined heating temperature was
changed from 1,000.degree. C. to 1,400.degree. C.
Example 13
[0144] PBI carbon fibers according to Example 13 were produced in
the same manner as in the step of producing carbon fibers of
Example 8 except that the predetermined heating temperature was
changed from 1,000.degree. C. to 1,500.degree. C.
Example 14
[0145] PBI carbon fibers according to Example 14 were produced in
the same manner as in the step of producing carbon fibers of
Example 8 except that the predetermined heating temperature was
changed from 1,000.degree. C. to 1,600.degree. C.
Comparative Example 1
[0146] PBI carbon fibers according to Comparative Example 1 were
produced in the same manner as in the step of producing carbon
fibers of Example 1 except that the PBI precursor fiber 1 was
changed to the PBI precursor fiber 3 and the PBI precursor fiber 3
was turned into carbon fibers.
Comparative Example 2
[0147] PBI carbon fibers according to Comparative Example 2 were
produced in the same manner as in the step of producing carbon
fibers of Example 6 except that the PBI precursor fiber 1 was
changed to the PBI precursor fiber 4 and the PBI precursor fiber 4
was turned into carbon fibers.
[0148] <Confirmation of Structure Using Electron
Microscope>
[0149] FIGS. 1A to 1D are images (SEM images) presenting cross
sections of the PBI carbon fibers according to Example 3, Example
10, and Comparative Example 1, which are obtained through an
electron microscope. Here, FIG. 1A is an image presenting cross
sections of the PBI carbon fibers according to Example 3 obtained
through an electron microscope; FIG. 1B is an image presenting
cross sections of the PBI carbon fibers according to Example 10
obtained through an electron microscope; and FIGS. 1C and 1D are
images presenting cross sections of the PBI carbon fibers according
to Comparative Example 1, which are obtained through an electron
microscope.
[0150] As presented in FIGS. 1A to 1D, it is confirmed that the PBI
carbon fibers according to Examples 3 and 10 each have a
cross-sectional shape of nearly perfect circle and are carbon
fibers each of which is hardly adhered to another fiber. Meanwhile,
it is confirmed that the PBI carbon fibers according to Comparative
Example 1 have a cross-sectional shape of ellipse and are carbon
fibers each of which is strongly adhered to another fiber.
[0151] <Single Fiber Tensile Test>
[0152] One fiber of each of the PBI carbon fibers according to
Examples 1 to 14 was subjected to a single fiber tensile test
according to the JIS7606 method to measure the fiber for elastic
modulus in tension and tensile strength.
[0153] Measurement results are presented in FIGS. 2A and 2B. Here,
FIG. 2A is a graph presenting measurement results of elastic
modulus in tension, and FIG. 2B is a graph presenting measurement
results of tensile strength. Each value in FIGS. 2A and 2B is
presented by a histogram and is an average value determined from
values of the tests performed 10 times. The error bars present both
maximum values and minimum values during the test.
[0154] As presented in these FIGS. 2A and 2B, it is confirmed that
all of the PBI carbon fibers according to Examples 1 to 14 have an
elastic modulus in tension of 100 GPa or more, which is a high
value, and have an elastic modulus in tension of 150 GPa or more,
which is a higher value. Moreover, it is confirmed that all of the
PBI carbon fibers have an elastic modulus in tension of 0.8 GPa or
more, which is a high value. It is believed that the PBI carbon
fibers of the present invention can achieve the above-described
high values of elastic modulus in tension and tensile strength even
if each of the PBI carbon fibers has a large diameter (e.g., 9
.mu.m and 16 .mu.m), which is advantageous. Among them, it is
confirmed that the PBI carbon fibers according to Examples 3 to 5
and 10 to 12, which were obtained at a carbonization treatment
temperature of from 1,200.degree. C. to 1,400.degree. C., could
achieve relatively high elastic modulus in tension and relatively
high tensile strength.
[0155] Note that, a single fiber could not be extracted from the
PBI carbon fibers according to Comparative Example 1 because each
fiber was strongly adhered to another fiber. Therefore, the PBI
carbon fibers according to Comparative Example 1 could not be
measured for elastic modulus in tension and tensile strength. It is
believed that the obtained carbon fibers have low elastic modulus
in tension and low tensile strength. This is because when solvent
molecules remaining thereon as salts are released through a thermal
treatment, some defects are generated in the carbon fibers, and the
above-described defects serve as a starting point of breakage in
the carbon fibers.
[0156] Moreover, when the PBI carbon fibers according to
Comparative Example 2 were subjected to the single fiber tensile
test, the PBI carbon fibers had an elastic modulus in tension of 85
GPa and a tensile strength of 720 MPa.
[0157] <Presumption of Reachable Strength>
[0158] The PBI carbon fibers according to Example 11 (a
carbonization treatment temperature is 1,300.degree. C.), which are
particularly excellent in both elastic modulus in tension and
tensile strength, were used to performed presumption of reachable
strength based on the following Referential Document 1. FIG. 3 is
an explanatory view presenting presumption conditions of the
reachable strength. Here, the reachable strength means a
defect-free strength presumed in the following manner in
consideration of a notch tip portion at which stress is
concentrated. Specifically, as presented in FIG. 3, a surface notch
is introduced into carbon fibers through focused ion beams. The
obtained carbon fibers are subjected to the aforementioned single
fiber tensile test, to thereby obtain the reachable strength. This
reachable strength can be calculated by the following Mathematical
Formulas (1) and (2).
.sigma. N = 1 .alpha. .sigma. 0 ( 1 ) .alpha. = 1 + 2 c .rho. ( 2 )
##EQU00001##
[0159] Here, in the Mathematical Formulas (1) and (2),
.sigma..sub.0 represents reachable strength, .sigma..sub.N
represents a value obtained by dividing a tensile load by a
cross-sectional area of the fiber, .alpha. represents a percentage
of stress concentration, c represents a notch depth, and .rho.
represents a radius of curvature of a notch tip portion.
[0160] When the PBI carbon fibers according to Example 11 were
measured for the above reachable strength, it was confirmed that a
presumption value of its reachable strength was 5.2 GPa, which was
a considerably high value. This is because defects in the fibers
can be reduced by optimizing the conditions of the step of
obtaining a first precursor fiber and the step of obtaining a
second precursor fiber. Thereby, it can be expected to achieve a
value of tensile strength that is larger than the values obtained
in the Examples.
[0161] Referential Document 1; M. Shioya, H. Inoue, Y. Sugimoto,
Carbon, v65, 63-70 (2013)
[0162] (Rapid Carbonization)
Example 15
[0163] The PBI precursor fiber 1 serving as the second precursor
fiber was subjected to rapid carbonization in the following manner.
Specifically, the PBI precursor fiber 1 was rapidly heated from
room temperature to 1,040.degree. C. for 0.2 seconds in a nitrogen
atmosphere using Curie Point Pyrolyzer (available from Japan
Analytical Industry Co., Ltd.) and was retained for 5 seconds.
Thereby, PBI carbon fibers according to Example 15 were
produced.
Example 16
[0164] PBI carbon fibers according to Example 16 were produced in
the same manner as in the method for producing the PBI carbon
fibers according to Example 15 except that the PBI precursor fiber
1 was changed to the PBI precursor fiber 2.
[0165] <Confirmation of Structure Using Electron
Microscope>
[0166] FIGS. 4A to 4B are images (SEM images) presenting cross
sections of the PBI carbon fibers according to Examples 15 and 16,
which are obtained through an electron microscope. Here, FIG. 4A is
an image presenting cross sections of the PBI carbon fibers
according to Example 15 obtained through an electron microscope,
and FIG. 4B is an image presenting cross sections of the PBI carbon
fibers according to Example 16 obtained through an electron
microscope.
[0167] As presented in FIGS. 4A and 4B, the PBI carbon fibers
according to Examples 15 and 16 each have a cross-sectional shape
of nearly perfect circle and are carbon fibers each of which is
hardly adhered to another fiber.
(Properties of PBI Carbon Fibers)
[0168] The PBI carbon fibers of the present invention were measured
for density, crystallinity, and microvoids (pores) in order to
verify that properties of the PBI carbon fibers were different from
properties of other carbon fibers.
[0169] <Measurement of Density>
[0170] The PBI carbon fibers according to Examples 1 to 6 and 8 to
13 were each measured for density by a sink-float method.
Measurement results of the obtained densities are presented in FIG.
5.
[0171] As presented in this FIG. 5, among the densities of the PBI
carbon fibers according to Examples 1 to 6 and 8 to 13, the highest
density was about 1.7 g/cm.sup.3 at most.
[0172] It is found that each of the PBI carbon fibers according to
the present invention has a density lower than densities of other
carbon fibers because densities of commercially available products
of PAN carbon fibers are within a range of from 1.75 g/cm.sup.3 to
1.85 g/cm.sup.3.
[0173] <Measurement of Crystallinity>
[0174] First, plane interval c/2 of carbon network planes and stack
thickness L.sub.c of carbon network planes were measured as
parameters indicating graphite crystallinity of carbon fibers. FIG.
6A is a schematic view presenting plane interval c/2 of carbon
network planes and stack thickness L.sub.c of carbon network planes
in a graphite crystal. Note that, reference signs 1a, 1b and 1c in
FIG. 6A represent carbon network planes.
[0175] The measurement of the plane interval c/2 of the carbon
network planes and the stack thickness L.sub.c of the carbon
network planes was performed by measuring a wide angle X-ray
diffraction profile with an X-ray diffraction device using
CuK.alpha. rays monochromatized with a Ni filter as an X-ray
source. Specifically, in the optical system for an equatorial
direction illustrated in FIG. 6B, the plane interval c/2 of carbon
network planes and the stack thickness L.sub.c of carbon network
planes were obtained from the peak of (002) observed at
2.theta.=26.degree. in the equatorial direction profile. Note that,
FIG. 6B is a schematic view indicating an optical system in
measuring a wide angle X-ray diffraction profile, where the
equatorial direction is a direction in which the detector is
perpendicular to the fiber axis.
[0176] The plane intervals c/2 and the stack thicknesses Lc of the
PBI carbon fibers according to Examples 6 and 13 (carbonization
treatment temperature of 1,500.degree. C.) are presented in Table 1
described below.
[0177] Moreover, the plane intervals c/2 and the stack thicknesses
Lc of the PBI carbon fibers according to Examples 6 and 13, which
were obtained through a graphitization treatment under heating at a
graphitization temperature of 2,800.degree. C., are also presented
in Table 1 described below.
TABLE-US-00001 TABLE 1 Carbonization .cndot. graphitization
temperature (.degree. C.) c/2 (nm) Lc (nm) Example 13 (9 .mu.m)
1,500 0.355 1.47 Example 6 (16 .mu.m) 1,500 0.352 1.56 Example 13
(9 .mu.m) 2,800 0.342 9.41 Example 6 (16 .mu.m) 2,800 0.341
9.43
[0178] The plane intervals c/2 and the stack thicknesses Lc of the
PBI carbon fibers according to Examples 6 and 13 described in Table
1 were substantially the same values as the plane intervals c/2 and
the stack thicknesses Lc of PAN carbon fibers subjected to almost
the same carbonization treatment (carbonization treatment of
1,500.degree. C.) as the above, which are described in the
below-described Referential Document 2 and Referential Document 3.
However, the PBI carbon fibers of the present invention can be
distinguished from the pitch carbon fibers because the PBI carbon
fibers have wider plane intervals c/2 and smaller stack thicknesses
Lc than those of pitch carbon fibers subjected to almost the same
carbonization treatment as the above. That is, the PBI carbon
fibers according to the present invention have wider plane
intervals c/2 and smaller stack thicknesses Lc than those of the
pitch carbon fibers.
[0179] Moreover, as presented in FIG. 7, the plane intervals c/2
and the stack thicknesses Lc of the PBI carbon fibers according to
Examples 6 and 13, which were subjected to a graphitization
treatment at 2,800.degree. C., have narrower stack thicknesses Lc
compared to PAN graphite fibers and pitch graphite fibers, which
were subjected to almost the same graphitization treatment as
described in the below-described Referential Document 2 and
Referential Document 3. Therefore, the PBI carbon fibers can be
distinguished from the PAN carbon fibers and the pitch carbon
fibers.
[0180] Referential Document 2; E. Fitzer, Carbon 27, 5, 621
(1989)
[0181] Referential Document 3; A. Takaku, et al., J. Mater. Sci.,
25, 4873 (1990)
[0182] <Measurement of Microvoids>
[0183] As parameters evaluating the carbon fibers for microvoids
(pores), volumes and average cross-sectional areas of microvoids in
the carbon fibers were measured. The measurement of the volumes and
the average cross-sectional areas of the microvoids in the carbon
fibers was performed by measuring a small angle X-ray diffraction
profile with an X-ray diffraction device using CuK.alpha. rays
monochromatized with a Ni filter as an X-ray source. Specifically,
in the optical system for an equatorial direction illustrated in
FIG. 6B, the volumes and the average cross-sectional areas of the
microvoids were determined from the scattering patterns observed in
the equatorial direction profile of a range of 2.theta.=0.5.degree.
through 8.degree.. Here, the analysis method and the calculation
method were performed according to the methods described in the
Referential Document 3.
[0184] Regarding the volume and the average cross-sectional area of
the microvoids, T300 (available from Toray Industries, Inc.)
(Referential Example 1) and IMS 60 (available from Toho Tenax Co.,
Ltd.) (Referential Example 2) as commercially available products of
typical PAN carbon fibers were used for comparison.
[0185] First, volume percentages of the microvoids of the PBI
carbon fibers according to Examples 1 to 6 and 8 to 13 are
presented in FIG. 8. As presented in FIG. 8, compared to values of
the Referential Example 1 and the Referential Example 2
(Referential Example 1: 4.9%, Referential Example 2: 5.7%), the
volumes of the microvoids of the PBI carbon fibers according to
Examples 1 to 6 and 8 to 13 are similar to the above values or are
lower than the above values, which indicates that occurrence of
microvoids causing breakage is low.
[0186] Next, average cross-sectional areas of the microvoids of the
PBI carbon fibers according to Examples 1 to 6 and 8 to 13 are
presented in FIG. 9. As presented in FIG. 9, a considerable
difference among the average cross-sectional areas of the
microvoids of the PBI carbon fibers according to Examples 1 to 6
and 8 to 13 cannot be found. However, the values of the average
cross-sectional areas of the microvoids presented in FIG. 9 are
considerably low; i.e., about half the values of Referential
Example 1 and Referential Example 2 (Referential Example 1: 2.52
nm.sup.2, Referential Example 2: 2.11 nm.sup.2).
REFERENCE SIGNS LIST
[0187] 1a, 1b, 1c Carbon network planes [0188] c/2 Plane interval
of carbon network planes [0189] L.sub.c Stack thickness of carbon
network planes
* * * * *