U.S. patent application number 13/377289 was filed with the patent office on 2012-04-12 for carbon fiber bundle that develops high mechanical performance.
This patent application is currently assigned to MITSUBISHI RAYON CO., LTD. Invention is credited to Hiroshi Hashimoto, Masahiro Hata, Akito Hatayama, Hiroko Matsumura, Takahiro Okuya, Isao Ooki, Naoki Sugiura, Kouki Wakabayashi.
Application Number | 20120088103 13/377289 |
Document ID | / |
Family ID | 43308936 |
Filed Date | 2012-04-12 |
United States Patent
Application |
20120088103 |
Kind Code |
A1 |
Sugiura; Naoki ; et
al. |
April 12, 2012 |
CARBON FIBER BUNDLE THAT DEVELOPS HIGH MECHANICAL PERFORMANCE
Abstract
Provided is a carbon fiber bundle for obtaining a
fiber-reinforced resin having high mechanical characteristics. A
carbon fiber bundle formed of single carbon fibers, each of which
has no uneven surface structure of 0.6 .mu.m or more in length
extending in the longitudinal direction of the single fiber; which
has an uneven structure having a difference in height (Rp-v) of 5
to 25 nm between the highest portion and the lowest portion of the
surface of the single fiber and having an average roughness Ra of 2
to 6 nm; and which has a ratio of the major axis to the minor axis
(major axis/minor axis) of a cross-section of the single fiber of
1.00 to 1.01, wherein a mass of the single fiber per unit length
falls within the range of 0.030 to 0.042 mg/m; a strand strength is
5900 MPa or more; a strand elastic modulus measured by the ASTM
method is 250 to 380 GPa; and a knot tenacity is 900 N/mm.sup.2 or
more.
Inventors: |
Sugiura; Naoki; (Aichi,
JP) ; Okuya; Takahiro; (Hiroshima, JP) ;
Hashimoto; Hiroshi; (Hiroshima, JP) ; Ooki; Isao;
(Hiroshima, JP) ; Matsumura; Hiroko; (Hiroshima,
JP) ; Hata; Masahiro; (Aichi, JP) ;
Wakabayashi; Kouki; (Aichi, JP) ; Hatayama;
Akito; (Aichi, JP) |
Assignee: |
MITSUBISHI RAYON CO., LTD
Tokyo
JP
|
Family ID: |
43308936 |
Appl. No.: |
13/377289 |
Filed: |
June 10, 2010 |
PCT Filed: |
June 10, 2010 |
PCT NO: |
PCT/JP10/59828 |
371 Date: |
December 9, 2011 |
Current U.S.
Class: |
428/367 |
Current CPC
Class: |
D01F 6/18 20130101; D06M
15/53 20130101; Y10T 428/2918 20150115; D06M 10/06 20130101; D01F
9/32 20130101; D01F 11/16 20130101; D06M 15/55 20130101; D01F 11/14
20130101; D06M 10/10 20130101; D06M 15/568 20130101; D06M 11/76
20130101; D01F 9/22 20130101; D01F 11/12 20130101; D06M 2101/40
20130101 |
Class at
Publication: |
428/367 |
International
Class: |
D02G 3/22 20060101
D02G003/22; D02G 3/36 20060101 D02G003/36; D02G 3/02 20060101
D02G003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 10, 2009 |
JP |
2009-139336 |
Claims
1. A carbon fiber bundle formed of the single carbon fiber: each
single carbon fiber having has no uneven surface structure that has
a length of 0.6 .mu.m or more and that extends in the longitudinal
direction of the single fiber, each single carbon fiber having an
uneven structure in which the difference in height (Rp-v) between a
highest portion and a lowest portion of the surface of the single
fiber is 5 to 25 nm, and in which an average roughness Ra is 2 to 6
nm, and each of which has a ratio of 1.00 to 1.01 of a major axis
to a minor axis (major axis/minor axis) of a cross-section of the
single fiber; wherein a mass of the single fiber per unit length
falls within the range of 0.030 to 0.042 mg/m; a strand strength is
5900 MPa or more; a strand elastic modulus measured by the ASTM
method is 250 to 380 GPa; and a knot tenacity is 900 N/mm.sup.2 or
more.
2. A carbon fiber bundle formed of the single carbon fiber: each
single carbon fiber having no uneven surface structure that has a
length of 0.6 .mu.m or more and that extends in the longitudinal
direction of the single fiber, each single carbon fiber having an
uneven structure that has a length of 300 nm or less in which the
difference in height (Rp-v) between a highest portion and a lowest
portion of the surface of the single fiber is 5 to 25 nm, and in
which an average roughness Ra is 2 to 6 nm, and each of which has a
ratio of 1.00 to 1.01 of a major axis to a minor axis (major
axis/minor axis) of a cross-section of the single fiber; wherein a
mass of the single fiber per unit length falls within the range of
0.030 to 0.042 mg/m; a strand strength is 5900 MPa or more; a
strand elastic modulus measured by the ASTM method is 250 to 380
GPa; and a knot tenacity is 900 N/mm.sup.2 or more.
3. The carbon fiber bundle according to claim 1 or 2, wherein a
hemispherical defect having a size within a predetermined range is
formed on a single fiber surface by a laser, the fiber is broken at
the hemispherical defective site by a tensile test, and "surface
energy of surface formed by fracture" obtained from breaking
strength of the fiber and the size of the hemispherical defect in
accordance with the Griffith Equation (1) is 30 N/m or more,
wherein .sigma. is a breaking strength; E is an ultrasonic elastic
modulus of a carbon fiber bundle; and C is a size of a
hemispherical defect. .sigma.=(2E/.pi.C).sup.1/2.times.(surface
energy of surface formed by fracture).sup.1/2 (1)
4. The carbon fiber bundle according to any of claims 1 to 3,
wherein an ipa value obtained by an electrochemical measuring
method (cyclic voltammetry) is 0.05 to 0.25 .mu.A/cm.sup.2, and an
amount of an oxygen-containing functional group (O1S/C1S) in a
carbon fiber surface obtained by X-ray photoelectron spectroscopy
falls within the range of 0.05 to 0.15.
5. The carbon fiber bundle according to any of claims 1 to 4,
wherein a Si amount measured by ICP emission spectrometry is 200
ppm or less.
6. The carbon fiber bundle according to any of claims 1 to 5, sized
by a sizing agent composition comprising a urethane modified epoxy
resin, which is a reaction product of (a) an epoxy resin having a
hydroxy group, (b) a polyhydroxy compound and (c) a diisocyanate
containing an aromatic ring, or sized by a sizing agent composition
comprising a mixture of the urethane modified epoxy resin and (a)
an epoxy resin having a hydroxy group and/or (d) an epoxy resin
having no hydroxy group.
7. The carbon fiber bundle according to claim 6, wherein (a) the
epoxy resin having a hydroxy group is a bisphenol type epoxy
resin.
8. The carbon fiber bundle according to claim 6 or 7, wherein (b)
the polyhydroxy compound is any one from among an adduct of a
bisphenol-A with an alkylene oxide, an aliphatic polyhydroxy
compound and a polyhydroxy monocarboxy compound or a mixture
thereof.
9. The carbon fiber bundle according to any of claims 6 to 8,
wherein (c) the diisocyanate containing an aromatic ring is toluene
diisocyanate or xylene diisocyanate.
10. The carbon fiber bundle according to any of claims 1 to 9,
wherein a total content of metals including an alkaline metal, an
alkaline earth metal, zinc, iron and aluminum is 50 ppm or less.
Description
TECHNICAL FIELD
[0001] The present invention relates to a carbon fiber bundle that
has excellent mechanical characteristics and that is particularly
used for obtaining a fiber-reinforced resin using a high-tenacity
heat resistant resin as a matrix for use in the construction of
airplanes.
BACKGROUND ART
[0002] Conventionally, in order to improve the mechanical
characteristics of resin-base molded products, a resin has been
commonly used in combination with a fiber serving as a
reinforcement material. In particular, a composite molding material
formed of a carbon fiber that is excellent in specific strength and
specific elasticity in combination with a high-performance resin
develops extremely high mechanical characteristics. Because of
this, such a molding material has been willingly used as a
constructional material for airplanes, high speed moving bodies,
etc. Furthermore, there is a demand for developing a material that
is stronger and that has higher rigidity as well as having
excellent specific strength and specific rigidity. Given these
circumstances, the desire is for further improvement of the
performance of carbon fiber, such as improved strength and elastic
modulus.
[0003] For example, Patent Literature 1 proposes a method of
drawing a coagulated fiber that still contains a solvent in a
solvent-containing drawing bath, thereby improving uniformity in
structure and orientation, in order to obtain an acrylic fiber
bundle used as a precursor of a carbon-fiber by a dry-wet spinning
method. Drawing a coagulated fiber in a bath containing a solvent
is a method commonly known as a solvent drawing technique that
enables a stable drawing process by using solvent plasticization.
Accordingly, this method is considered as an extremely excellent
technique for obtaining a fiber that has high uniformity in
structure and orientation. However, if a fiber bundle that is in a
swollen state due to the presence of a solvent is drawn, the
solvent within a filament is rapidly squeezed out from the filament
simultaneously upon drawing. The resultant structure of the
filament tends to be less dense and thus a desired filament that
has a dense structure cannot be obtained.
[0004] Furthermore, Patent Literature 2, which pays attention to
fine pores distributed in a coagulated fiber, proposes a technique
for obtaining a precursor fiber in which excellent strength is
developed by dry-densification of a coagulated fiber that has a
high-dense structure. The fine pore distribution, which is obtained
by a mercury press-in method, reflects the bulk state from the
surface layer to the interior of the filament. This is an extremely
excellent method for evaluating the overall density of a fiber
structure. From the precursor fiber bundle that has at least a
certain level density as a whole, a very strong carbon fiber can be
obtained in which defect point formation is suppressed. However,
observation of fractures in the carbon fiber shows that fractures
have originated from near the surface layer at an extremely high
ratio. This means that a defective point is present near the
surface layer. In other words, this technique is insufficient for
manufacturing a precursor fiber bundle that is excellent in density
near the surface layer.
[0005] Patent Literature 3 proposes a method for manufacturing an
acrylonitrile-based precursor fiber bundle that is not only high in
whole density but that is also extremely high in surface density.
Furthermore, Patent Literature 4 proposes, taking into
consideration that an oil solution enters the surface-layer portion
of a fiber and inhibits densification, a technique for suppressing
permeation of an oil solution by focusing on microscopic voids of
the surface-layer portion. However, a technique for suppressing the
entry of an oil solution and a technique for suppressing defective
point formation are both difficult to put into practical use since
very complicated steps are required. Therefore, in the techniques
discussed above, the effect of stably suppressing the entry of an
oil solution into the surface layer portion is insufficient and the
effect of reinforcing a carbon fiber is still far from a sufficient
level.
CITATION LIST
Patent Literatures
[0006] Patent Literature 1: JP05-5224A [0007] Patent Literature 2:
JP04-91230A [0008] Patent Literature 3: JP06-15722A [0009] Patent
Literature 4: JP11-124744A
SUMMARY OF INVENTION
Technical Problem
[0010] An object of the present invention is to provide a carbon
fiber bundle for obtaining a fiber-reinforced resin that has high
mechanical characteristics.
Solution to Problem
[0011] The object is attained by the invention set forth below.
[0012] The present invention is directed to a carbon fiber bundle
formed of single carbon fibers, each of which has no surface uneven
structure of 0.6 .mu.m or more in length extending in the
longitudinal direction of the single fiber; which has an uneven
structure having a difference in height (Rp-v) of 5 to 25 nm
between the highest portion and the lowest portion of the surface
of the single fiber and an average roughness Ra of 2 to 6 nm, and
which has a ratio of the major axis to the minor axis (major
axis/minor axis) of a cross-section of the single fiber of 1.00 to
1.01, in which a mass of the single fiber per unit length falls
within the range of 0.030 to 0.042 mg/m, a strand strength is 5900
MPa or more, a strand elastic modulus measured by the ASTM method
is 250 to 380 GPa and a knot tenacity is 900 N/mm.sup.2 or
more.
[0013] Note that the knot tenacity can be obtained by dividing the
tensile breaking stress of a knotted carbon fiber bundle by the
cross-sectional area of the fiber bundle (mass and density per unit
length).
Advantageous Effects of Invention
[0014] According to the carbon fiber bundle of the present
invention, it is possible to provide a fiber-reinforced resin that
has high mechanical characteristics.
[0015] Furthermore, a carbon fiber bundle that has even better
performance is obtained by acquiring "surface energy of surface
formed by fracture" such that it reaches 30N/m or more.
[0016] Moreover, a carbon-fiber composite material that has
extremely high mechanical performance can be obtained by forming a
carbon fiber bundle which has an ipa value of 0.05 to 0.25
.mu.A/cm.sup.2 that is obtained by an electrochemical measuring
method (cyclic voltammetry), and in which the amount of an
oxygen-containing functional group (O1S/C1S) in a carbon fiber
surface, that is obtained by X-ray photoelectron spectroscopy, is
within the range of 0.05 to 0.10.
DESCRIPTION OF EMBODIMENTS
[0017] The uneven surface structure present on the surface of a
carbon fiber and extending in the longitudinal direction thereof
and a sizing agent attached onto the surface play very important
roles in developing mechanical characteristics of a
fiber-reinforced resin material that uses the carbon fiber as a
reinforcement material. This is because the uneven surface
structure and the sizing agent attached onto the surface are
directly involved in formation of the interfacial phase between a
carbon fiber and a resin as well as characteristics thereof. The
mechanical performance of the fiber-reinforced resin material is
influenced by the performance of each of the three constituent
factors, i.e., the fiber, the matrix resin and the interfacial
phase. Even if only one of the three factors is unsatisfactory, the
fiber-reinforced resin material cannot develop excellent mechanical
performance.
(Uneven Surface Structure of a Single Fiber Extending in the
Longitudinal Direction)
[0018] A carbon fiber obtained by a general manufacturing method
for a carbon fiber bundle generally has an uneven surface structure
that is formed almost parallel to the fiber-axis direction. The
uneven structure has an undulation structure that is almost
parallel to the fiber axis and that extends in the fiber axis. The
depth of the uneven structure is usually about 50 nm to several
hundreds of nm and the length thereof is usually about 0.6 .mu.m to
several .mu.m and sometimes, several tens of .mu.m. Such an uneven
surface structure is usually called as surface wrinkle.
[0019] The carbon fiber bundle of the present invention does not
have an uneven surface structure that has a length of 0.6 .mu.m or
more and that extends in the longitudinal direction of a single
fiber.
[0020] In contrast, the carbon fiber bundle of the present
invention has an uneven structure that is smaller than the uneven
structure mentioned above on the surface of a single fiber. The
depth of the uneven surface structure present on a single carbon
fiber is defined by the difference in height (Rp-v) between the
highest portion and the lowest portion on the surface of a fiber
and the average roughness Ra, in an area range surrounded by a
length of 1.0 .mu.m in the fiber-circumference direction and a
length 1.0 .mu.m in the fiber-axis direction. The (Rp-v) and Ra can
be obtained by scanning the surface of a single fiber by use of a
scanning atomic force microscope (AFM). It is desirable that the
difference in height (Rp-v) be 5 to 25 nm and that the average
roughness Ra be 2 to 6 nm. It is more preferable that the
difference in height (Rp-v) be 5 to 18 nm and that Ra be 2 to 5
nm.
[0021] In the present invention, each of the single fibers that
constitutes a carbon fiber has no uneven surface structure that has
a length of 0.6 .mu.m or more and that extends in the longitudinal
direction of the fiber, on the surface of a single fiber. In the
interfacial phase of a composite material, stress tends to be
concentrated on such a large uneven surface structure. In addition,
the fracture toughness of carbon fiber tissue around such an uneven
structure is low. Accordingly, in the uneven surface structure of
this size, interfacial failure tends to originate from a point near
the uneven structure even if the level of stress applied to a
composite material is not very large. As a result, mechanical
performance of the composite material significantly decreases.
[0022] A more specific embodiment of the uneven surface structure
of each of the single fibers constituting a carbon fiber bundle of
the present invention is as follows.
[0023] Usually, carbon-fiber surface has an uneven structure of 0.6
.mu.m or more in length called a wrinkle structure, that has an
assembly of several fibrils as a unit and that extends in the
longitudinal direction of the fiber, and an uneven microscopic
structure that is smaller than the uneven structure called a
wrinkle structure and that is present in each fibril body
itself.
[0024] On the contrary, on the surface of each of the single fibers
constituting a carbon fiber bundle of the present invention, an
uneven structure that has a length of 0.6 .mu.m or more and that
extends in the longitudinal direction of a fiber is not present but
only an uneven microscopic structure that is smaller than the
uneven structure and that is present in each fibril body itself is
present. Furthermore, such an uneven microscopic structure has a
length of 300 nm or less. The uneven structure is defined by (Rp-v)
and Ra as mentioned above. To be specific, the uneven structure is
an undulation structure having a difference in height (Rp-v) of 5
to 25 nm and an average roughness Ra of 2 to 6 nm, which are
present in an area range surrounded by a length (1.0 .mu.m) in the
fiber-circumference direction of a single-fiber surface and a
length (1.0 .mu.m) in the fiber-axis direction. Preferably, (Rp-v)
is 5 to 18 nm and Ra is 2 to 5 nm. The direction of the uneven
microscopic structure is not particularly limited and may be
parallel or perpendicular to the fiber-axis direction or may be
present at an angle with the fiber-axis direction.
(Cross-Section of Single Fiber)
[0025] Furthermore, the ratio of the major axis and the minor axis
(major axis/minor axis) of a single fiber cross-section is 1.00 to
1.01. This means that the single fiber must have a complete
circular or nearly complete circular cross-section. This is because
if the cross-section is a complete circle, the portion near the
fiber surface has excellent structural uniformity, with the result
that concentration of stress can be reduced. The ratio is
preferably 1.00 to 1.005. Furthermore, for the same reason, the
mass of the single fiber per unit length is 0.030 to 0.042 mg/m. If
the mass of the single fiber per unit length (single fiber weight
per unit area) is low, the fiber diameter is small, and structural
irregularity along the cross-section is small. This means that
mechanical performance in the direction perpendicular to the fiber
axis is high. Accordingly, in a composite material, tolerance to
stress applied in the direction perpendicular to the fiber axis is
improved and the mechanical performance of a composite material can
be enhanced.
(Carbon Fiber Bundle)
[0026] In the present invention, to obtain a fiber-reinforced resin
having excellent mechanical characteristics, the strand strength of
a carbon fiber bundle must be 5900 MPa or more. The strand strength
of a carbon fiber bundle is preferably 6000 MPa or more and more
preferably 6100 MPa or more. The higher the strand strength, the
better; however, taken into consideration the balance between the
strand strength and the compressive strength of a composite
material, 10000 MPa is sufficient. Furthermore, in the present
invention, to obtain a fiber-reinforced resin having excellent
mechanical characteristics, the strand elastic modulus of a carbon
fiber bundle must be 250 to 380 GPa, which are values measured by
the ASTM method. If the elastic modulus is less than 250 GPa, the
elastic modulus of a carbon fiber bundle will be insufficient and
sufficient mechanical characteristics cannot develop. In contrast,
if the elastic modulus exceeds 380 GPa, the graphite crystal size
of the surface and interior of a carbon fiber will increase. In
accordance with this, the strength along the cross-section of the
fiber and the compressive strength in the fiber-axis direction
decrease and performance balance between tension and compression of
a composite material cannot be maintained. As a result, excellent
composite material cannot be obtained. In addition, inactivation of
the surface proceeds as the graphite crystal size increases, and
the adhesiveness with a matrix resin decreases. As a result,
mechanical performance such as tensile strength of the composite
material in the direction of 90.degree., interlayer shearing
strength, in-plane shearing strength and 0.degree. compressive
strength significantly decreases.
[0027] Furthermore, in the present invention, it is important that
the knot tenacity, which is obtained by dividing the tensile stress
at break of a knotted carbon fiber bundle by the cross-sectional
area of the fiber bundle (mass and density per unit length), is 900
N/mm.sup.2 or more. More preferably, the knot tenacity is 1000
N/mm.sup.2 or more and further preferably, 1100 N/mm.sup.2 or more.
The knot tenacity serves as an index that reflects the mechanical
performance of a fiber bundle except in the fiber-axis direction.
In particular, the performance in the direction perpendicular to
the fiber axis can be simply checked by the knot tenacity. In the
composite material, since a material is often formed by
pseudo-isotropic lamination, a complicated stress field is formed.
At this time, other than tension and compression stress in the
fiber-axis direction, stress is also generated in the fiber-axis
direction. Furthermore, if a relatively high-speed strain is
applied, as is in an impact test, the state of the stress that is
generated within the composite material is considerably complicated
and the strength in the direction that is different from the
strength in the fiber-axis direction becomes important.
Accordingly, if the knot tenacity is less than 900 N/mm.sup.2,
sufficient mechanical performance does not develop in a
pseudo-isotropic material. On the other hand, if the knot tenacity
exceeds 3000 N/mm.sup.2, the degree of orientation in the
fiber-axis direction must be reduced. Accordingly, the knot
strength should be controlled to be 3000 N/mm.sup.2 or less.
[0028] Furthermore, in the carbon fiber bundle of the present
invention, a "surface energy of surface formed by fracture" is
preferably 30 N/m or more. The surface energy of surface formed by
fracture is obtained by forming a hemispherical defect having a
predetermined size by a laser on the surface of a single fiber, and
by breaking the fiber at the hemispherical defective site in a
tensile test and by calculating from the breaking strength of the
fiber and the size of the hemispherical defect in accordance with
the following Griffith Equation (1).
.sigma.=(2E/.pi.C).sup.1/2.times.(surface energy of surface formed
by fracture).sup.1/2 (1)
Here, ".sigma." is the breaking strength; "E" is the ultrasonic
elastic modulus of a carbon fiber bundle; and "C" is the size of a
hemispherical defect. The "surface energy of surface formed by
fracture" is more preferably, 31 N/m or more and further preferably
32 N/m or more.
[0029] The surface energy of surface formed by fracture herein is
used as a break-proof index of a carbon fiber for representing
substrate strength. The carbon fiber is a material showing brittle
fracture and the tensile strength is controlled by the defective
point. If carbon fibers have the same defective points, the
breaking strength increases as the substrate strength increases.
Furthermore, a matrix resin for a high-performance composite
material often has high adhesiveness with a carbon fiber, with the
result that the critical fiber length, which serves as an index for
stress transfer, diminishes. As a result, the strength in a further
shorter length is reflected in the strength of the composite
material. Thus, the substrate strength is conceivably an important
index. In contrast, if the surface energy produced by breaking
exceeds 50 N/m, it is necessary to reduce the degree of orientation
in the fiber-axis direction. Accordingly, the surface energy
produced by breaking should be 50 N/m or less.
[0030] In the present invention, the ipa value obtained by an
electrochemical measuring method (cyclic voltammetry) is preferably
0.05 to 0.25 .mu.A/cm.sup.2. The ipa value is influenced by the
number of oxygen-containing functional groups of a carbon fiber,
surface roughness involved in formation of an electric double layer
and the microscopic graphite structure of a carbon fiber surface.
In particular, a carbon fiber whose surface is largely etched and a
carbon fiber that has an intercalation compound which is formed by
inserting an anion between layers of a graphite crystal have a
large ipa value. In developing composite material that has
excellent mechanical performance, the interface between a carbon
fiber and a resin is important. In particular, a carbon fiber that
has a surface in which an appropriate oxygen-containing functional
group is present and in which a small electric double layer is
formed, is found to form the most appropriate interface. If an ipa
value is 0.05 .mu.A/cm.sup.2 or more, it indicates that the surface
has a sufficient number of oxygen-containing functional groups, and
it exhibits sufficient adhesiveness to an interface. In contrast,
if an ipa value is 0.25 .mu.A/cm.sup.2 or less, the surface is not
excessively etched and an intercalation compound is not formed.
Such a surface can tightly adhere to a matrix resin, with the
result that the surface can sufficiently adhere to the interface
with a resin. The ipa value is more preferably 0.07 to 0.20
.mu.A/cm.sup.2 and further preferably 0.10 to 0.18
.mu.A/cm.sup.2.
[0031] Furthermore, in the present invention, it is desirable that
the amount of an oxygen containing functional group in a carbon
fiber surface (obtained by X-ray photoelectron spectroscopy) be
within the range of 0.05 to 0.15. This is because it is important
to have an appropriate adhesiveness with a matrix resin at the
interface.
[0032] Furthermore, in the present invention, a Si amount measured
by ICP emission spectrometry is desirably 200 ppm or less. In order
to manufacture a high-strength carbon fiber, usually an oil
solution containing silicone oil is attached onto a precursor fiber
bundle. Silicone oil has extremely excellent heat resistance
properties and can impart excellent mold release characteristics.
Thus, silicone oil is considered most suitable as an oil solution
for a carbon-fiber precursor bundle, which is a multifilament
bundle formed by assembling a large number of filaments each having
an extremely small diameter and each being further subjected to a
high-temperature treatment performed at a temperature of
200.degree. C. or more for several tens of minutes to several
hours. However, in carbonization treatment performed after
stabilization treatment, the silicone oil is mostly decomposed and
scattered. Consequently, the amount of silicone compound remaining
on the surface of a carbon fiber becomes extremely low.
Furthermore, the remaining silicone compound, which is present near
the surface of a carbon fiber, has been found to contribute to the
formation of voids. Therefore, if the amount of such a silicone
compound is reduced as much as possible, carbon fiber having few
voids can be manufactured. As a result, the strength of a carbon
fiber bundle can be increased. The more preferable Si amount is 150
ppm or less and a further preferable Si amount is 100 ppm or
less.
(Precursor Fiber Bundle and Manufacturing Method Thereof)
[0033] The starting material for obtaining a carbon fiber bundle of
the present invention is not particularly limited; however, the
starting material that can be obtained from an acrylonitrile-based
precursor fiber (hereinafter, appropriately referred to as
"precursor fiber") is preferred from the viewpoint of developing
mechanical performance.
[0034] The acrylonitrile-based copolymer constituting the precursor
fiber is obtained from acrylonitrile (96 mass % or more) and
several types of copolymerizable monomers. More preferably, the
composition ratio of acrylonitrile is 97 mass % or more. Examples
of copolymer components except acrylonitrile that are properly used
include acrylic acid derivatives such as acrylic acid, methacrylic
acid, itaconic acid, methyl acrylate and methyl methacrylate; and
acryl amide derivatives such as acryl amide, methacryl amide,
N-methyolacrylamide and N,N-dimethyl acrylamide and vinyl acetate.
These may be used alone or in combination. A preferable copolymer
is an acrylonitrile-based copolymer obtained by copolymerization of
a monomer that has one or more carboxyl groups as an essential
component.
[0035] As an appropriate method for copolymerizing a monomer
mixture, any polymerization method may be used, including, for
example, redox polymerization performed in an aqueous solution,
suspension polymerization performed in non-homogeneous system and
emulsion polymerization using a dispersant. Difference between the
polymerization methods does not limit the present invention. The
precursor fiber is preferably manufactured by dissolving the
aforementioned acrylonitrile based polymer in an organic solvent
such as dimethyl acetamide, dimethyl sulfoxide or dimethyl
formamide to prepare dope. Since these organic solvents do not
contain a metal component, the content of a metal component in the
resultant carbon fiber bundle can be reduced. The solid substance
concentration of the dope is preferably 20 mass % or more and more
preferably 21 mass % or more.
[0036] The spinning method may be either wet spinning or dry-wet
spinning. More preferably, dry-wet spinning is employed. In dry-wet
spinning, the dope that is prepared is at first spun from a
spinneret having numerous ejection holes arranged therein into the
air and is then introduced into a congealed liquid filled with a
solution mixture of an organic solvent and water whose temperature
is controlled so that the dope will coagulate. The coagulated fiber
is taken out, washed and drawn. As a washing method, any method may
be used as long as the solvent can be removed. Note that, before
the coagulated fiber that has been taken out is washed, if drawing
is performed in the pre-drawing tank that contains a solvent whose
concentration is lower than in congealed liquid and whose
temperature is higher than that of congealed liquid, a fibril
structure can be formed. When a coagulated fiber is drawn, the
temperature of the drawing tank preferably falls within the range
of 40 to 80.degree. C. If the temperature is less than 40.degree.
C., a stable drawing cannot be secured and it causes the drawing to
be poor, with the result that a uniform fibril structure cannot be
formed. In contrast, if the temperature exceeds 80.degree. C.,
excessively strong plasticizing action occurs by heat, and a
solvent is rapidly removed from a fiber surface and the result is
nonuniform drawing. Therefore, the quality of the precursor fiber
bundle deteriorates. A more preferable temperature is 50 to
75.degree. C. Furthermore, the concentration of the drawing tank is
preferably 30 to 60 mass %. This is because if the concentration is
less than 30 mass %, a stable drawing cannot be secured; whereas,
if the concentration is beyond 60 mass %, an excessively large
plasticization effect is obtained and interference with a stable
drawing occurs. A more preferable concentration is 33 to 55 mass
%.
[0037] The draw ratio in the drawing tank is preferably 2 to 4
times. If the draw ratio is less than twice, drawing is
insufficient and a desired fibril structure cannot be formed. In
contrast, if the draw ratio is beyond 4 times, a fibril structure
itself is broken. The result is a precursor fiber bundle that has
extremely low density. The draw ratio is more preferably 2.2 to 3.8
times and further preferably, 2.5 to 3.5 times.
[0038] Furthermore, after washing, if a fiber bundle that is
processed in a swollen state without solvent is drawn in hot water,
the orientation degree of the fiber can be further enhanced. If a
relaxing step is slightly performed, distortion caused by drawing
in the previous step can be removed. Preferably, in order to
improve the orientation degree of a fiber by increasing the total
draw ratio, drawing is performed in hot water at a ratio of 1.1 to
2.0 times.
[0039] Next, an oil solution composed of a silicone-based compound
is attached so as to apply 0.8 to 1.6 mass % and the resultant
fiber is subjected to dry densification. The dry densification is
not particularly limited as long as dry densification is performed
by a known drying method. Preferably, a method of passing a fiber
through a plurality of heated rolls is employed.
[0040] The acrylic fiber bundle after the dry densification process
has been performed, is, if necessary, drawn in pressurized steam of
130 to 200.degree. C., in a dry heat medium of 100 to 200.degree.
C., between heated rolls of 150 to 220.degree. C. or on a heat
board up to 1.8 to 6.0 times. After the orientation degree is
further improved and densification is performed, the fiber bundle
is rolled up to obtain a precursor fiber bundle.
[0041] Furthermore, a carbon fiber bundle of the present invention
can be manufactured from the above-mentioned precursor fiber bundle
as follows. The precursor fiber bundle is fed to an oven for
stabilization that is a type of furnace that circulates hot air at
a temperature of 220 to 260.degree. C. for 30 to 100 minutes to
obtain a stabilized fiber having a density of 1.335 to 1.360
g/cm.sup.3. At this time, an operation for extending the fiber by 0
to 10% is performed. The stabilization reaction consists of a
cyclization reaction with heat and an oxidation reaction with
oxygen. It is important to balance the two reactions. In order to
balance the two reactions, time for performing stabilization
treatment is preferably 30 to 100 minutes. If the reaction time is
less than 30 minutes, a single fiber has a portion in which the
oxidation reaction does not sufficiently proceed, within the fiber,
with the result that a large structural variety is generated along
the cross-section of the single fiber. As a result, the obtained
carbon fiber has a structure that is non-uniformly formed and fails
to develop high mechanical performance. In contrast, if the
reaction time exceeds 100 minutes, a larger amount of oxygen will
be present near the surface of a single fiber. Thereafter, in the
following heat treatment performed at a high temperature, a
reaction that consumes an excessive amount of oxygen occurs to form
a defective point. Because of this, high strength cannot be
obtained. A more preferable stabilization treatment time is 40 to
80 minutes.
[0042] In the case where the density of a stabilized fiber is less
than 1.335 g/cm.sup.3, stabilization treatment is insufficient. In
the following heat treatment performed at a high temperature, a
decomposition reaction occurs to form a defective point. Because of
this, high strength cannot be obtained. If the density of a
stabilized fiber exceeds 1.360 g/cm.sup.3, the oxygen content of
the fiber increases. In the following heat treatment performed at a
high temperature, a reaction that consumes an excessive amount of
oxygen occurs to form a defective point. Because of this, high
strength cannot be obtained. A more preferable density range of a
stabilized fiber is 1.340 to 1.350 g/cm.sup.3.
[0043] Appropriate extension of a fiber performed in an oven for
stabilization is required in order to maintain and improve the
orientation degree of a fibril structure that constitute a fiber.
If the extension is less than 0%, the orientation degree of a
fibril structure cannot be maintained; the orientation degree along
the fiber axis is not sufficient for forming a carbon fiber
structure; excellent mechanical performance cannot develop. In
contrast, if the extension exceeds 10%, the fibril structure itself
will be broken, with the result that formation of a carbon fiber
structure will be impaired and the fracture point will change to a
defective point. As a result, a carbon fiber that has high strength
cannot be obtained. A more preferable extension rate is 3 to
8%.
[0044] Next, a stabilized fiber is passed through a first
carbonization furnace of an inert atmosphere such as nitrogen that
has a temperature gradient of 300 to 800.degree. C., while
extending it by 2 to 7%. A preferable processing temperature is 300
to 800.degree. C. and the stabilized fiber is processed under
linear temperature gradient conditions. Taking into consideration
the temperature in the stabilization treatment step, the initiation
temperature is preferably 300.degree. C. or more. If the highest
temperature exceeds 800.degree. C., the fiber that is processed
becomes very fragile and it is difficult to operate the following
step. A more preferable temperature range is 300 to 750.degree. C.
The temperature gradient is not particularly limited; however a
linear gradient is preferably employed.
[0045] If the extension rate is less than 2%, orientation of a
fibril structure cannot be maintained and the orientation degree
along the fiber axis in formation of a carbon fiber structure will
not be sufficient, with the result that excellent mechanical
performance cannot develop. In contrast, if the extension rate
exceeds 7%, a fibril structure itself is broken, with the result
that formation of a carbon fiber structure will be impaired and a
fracture point will change to a defective point. As a result, a
carbon fiber having high strength cannot be obtained. A more
preferable extension rate is 3 to 5%.
[0046] In the first carbonization furnace, a preferable heat
treatment time is 1.0 to 3.0 minutes. If the treatment time is less
than 1.0 minute, the temperature will abruptly increase, and this
will be accompanied by a severe decomposition reaction. As a
result, a carbon fiber that has high strength cannot be obtained.
If the treatment time exceeds 3.0 minutes, effect of plasticization
in the former step will be produced, with the result that the
orientation degree of a crystal will tend to decrease. As a result
the mechanical performance of the resultant carbon fiber will be
impaired. A more preferable heat treatment time is 1.2 to 2.5
minutes.
[0047] Furthermore, the stabilized fiber is subjected to a second
carbonization furnace that has an inert atmosphere such as nitrogen
having a temperature gradient of 1000 to 1600.degree. C. and is
treated under heat under tension to obtain a carbon fiber.
Furthermore, if necessary, the carbon fiber is optionally subjected
to a third carbonization furnace having a desired temperature
gradient and is treated with heat in an inert atmosphere under
tension.
[0048] The temperature for carbonization treatment is determined
depending upon the desired elastic modulus of a carbon fiber. In
order to obtain a carbon fiber that has high strength property, the
highest temperature of carbonization treatment is preferably low.
Furthermore, elastic modulus can be increased by increasing the
treatment time. As a result, the highest temperature can be
reduced. Moreover, the gradient of temperature can be set to change
gradually by increasing the treatment time. This is effective in
suppressing defective point formation. The temperature of the
second carbonization furnace varies depending upon the temperature
of the first carbonization furnace; however, the temperature is
acceptable as long as it is a temperature of 1000.degree. C. or
more and preferably 1050.degree. C. or more. The temperature
gradient is not particularly limited; however it is preferably set
to change linearly.
[0049] In the second carbonization furnace, the heat treatment time
is preferably 1.3 to 5.0 minutes and more preferably 2.0 to 4.2
minutes. In the heat treatment, the fiber significantly shrinks
during processing. Thus, it is important to perform heat treatment
under tension.
[0050] An extension rate is preferably -6.0 to 0.0%. If the
extension rate is less than -6.0%, the orientation of a crystal in
the fiber-axis direction is not satisfactory and sufficient
performance cannot be obtained. In contrast, if the extension rate
exceeds 0.0%, the structure so far formed itself is broken and
defective points are significantly formed, with the result that the
strength is significantly reduced. More preferably, the extension
rate ranges -5.0% to -1.0%.
[0051] Next, the carbon fiber bundle is subjected to surface
oxidization treatment. Examples of the surface treatment method
include known methods, i.e., oxidation treatments such as
electrolytic oxidation, chemical oxidation and air oxidation. Any
one of these methods may be employed. The electrolytic oxidation
treatment industrially widely used is preferred since surface
oxidization treatment can be stably performed. In addition, to
control the ipa value, which represents a preferable surface
treatment state in the present invention, so that the ipa value
falls within the aforementioned range, performing the electrolytic
oxidation treatment while varying electric quantity is the simplest
method. In this case, even if the electric quantity is the same,
the ipa value significantly varies depending upon the electrolyte
and the concentration thereof that is used. In the present
invention, electrolytic oxidation treatment can be performed
preferably in an aqueous alkaline solution of pH>7 with a carbon
fiber as an anode while supplying an electric quantity of 10 to 200
coulomb/g. By using oxidation treatment, the ipa value of 0.05 to
0.25 .mu.A/cm.sup.2 can be obtained. Examples of electrolyte that
is preferably used include ammonium carbonate, ammonium
bicarbonate, calcium hydroxide, sodium hydroxide and potassium
hydroxide.
[0052] Next, the carbon fiber bundle of the present invention is
subjected to sizing treatment. The sizing agent is dissolved in an
organic solvent or dispersed in water with the help of an
emulsifier to prepare an emulsion solution. The above preparation
is applied to a carbon fiber bundle in accordance with a roller dip
method, a roller contact method, etc. Subsequently, the carbon
fiber bundle is dried. In this manner, sizing treatment can be
performed. Note that the amount of the sizing agent attached to the
surface of a carbon fiber can be controlled by controlling the
concentration of the sizing agent solution and the squeeze amount
thereof. Furthermore, drying can be performed by use of hot air, a
hot plate, a heating roller and various infrared heaters.
[0053] The most preferable sizing agent composition to be applied
to the surface of the carbon fiber of the present invention is a
urethane modified epoxy resin, which is a reaction product of (a)
an epoxy resin that contains a hydroxy group (hereinafter
appropriately referred to as a component (a)), (b) a polyhydroxy
compound (hereinafter appropriately referred to as a component (b))
and (c) a diisocyanate that contains an aromatic ring (hereinafter
appropriately referred to as a component (c)). Furthermore, a
mixture of a urethane modified epoxy resin, which is a reaction
product that is obtained by introducing a larger amount of
component (a) than is required for a reaction system, and component
(a) that remains is mentioned.
[0054] Moreover, a mixture of a urethane modified epoxy resin
obtained by using an epoxy resin having no hydroxy group
(hereinafter appropriately referred to as component (d)) and
component (d) is mentioned. Also, a mixture of a urethane modified
epoxy resin, component (a) and component (d) is mentioned.
[0055] An epoxy group has a very strong interaction with an
oxygen-containing functional group present in a carbon fiber
surface and thus can strongly allow a sizing-agent component to
adhere to the carbon fiber surface. Furthermore, since a urethane
bonding unit, which is produced from a polyhydroxy compound and a
diisocyanate that contains an aromatic ring, is contained,
flexibility and strong interaction with a carbon fiber surface due
to the polarity of a urethane bond and an aromatic ring can be
imparted. Accordingly, the urethane modified epoxy resin that has
an epoxy group and the above urethane bonding unit is a compound
that is capable of strongly bonding to a carbon fiber surface and
that has flexibility. In other words, such a sizing agent
composition forms a flexible interface layer that strongly adheres
to a carbon fiber surface. Thus, the mechanical performance of the
composite material obtained by impregnating a carbon fiber with a
matrix resin and cuing the resin can be improved.
[0056] The component (a) is not particularly limited, and the
number of hydroxy groups contained in the component (a) is not
limited. For example, glycidol, methyl glycidol, bisphenol type F
epoxy resin, bisphenol type A epoxy resin and oxycarboxylic acid
glycidyl ester epoxy resin can be used. A particular preferable
resin is a bisphenol type epoxy resin. Since these resins have an
aromatic ring, they interact strongly with a carbon fiber surface.
Furthermore, in view of heat resistance and rigidity, an epoxy
resin having an aromatic ring is often used as the matrix resin in
a composite material. This is because compatibility with such a
matrix resin is excellent.
[0057] As component (a), two types or more epoxy resins can be
used.
[0058] Furthermore, component (b) is preferably constituted of any
one from among an adduct of bisphenol A with an alkylene oxide, an
aliphatic polyhydroxy compound and a polyhydroxymonocarboxy
compound or a mixture of these. This is because these compounds can
soften the aforementioned urethane modified epoxy resins. Specific
examples thereof include an adduct of bisphenol A with 4 to 14 mol
of ethylene oxide, an adduct of bisphenol A with 2 to 14 mol of
propylene oxide, an adduct of bisphenol A with ethylene
oxide-propylene oxide block copolymer, polyethylene glycol,
trimethylolpropane and dimethylolpropionic acid.
[0059] Furthermore, component (c) is not particularly limited and a
particular preferable component is toluene diisocyanate or xylene
diisocyanate.
[0060] Furthermore, an epoxy resin that serves as component (d) is
not particularly limited. Preferably, an epoxy resin having two or
more epoxy groups in a molecule is employed. This is because the
surface of a carbon fiber strongly interacts with an epoxy group
and thus these compounds strongly adhere to the surface. The type
of epoxy group is not particularly limited and a glycidyl type, an
alicyclic epoxy group, etc. can be employed. Examples of preferable
epoxy resin that can be used include a bisphenol type-F epoxy
resin, a bisphenol type-A epoxy resin, a novolak-type epoxy resin,
a dicyclopentadiene type epoxy resin (Epiclon HP-7200 series:
manufactured by DIC Corporation), tris(hydroxyphenyl)methane-type
epoxy resin (Epicoat 1032H60, 1032S50: manufactured by Japan Epoxy
Resins Co., Ltd.), DPP Novolak type epoxy resin (Epicoat 157S65,
157S70: manufactured by Japan Epoxy Resins Co., Ltd.) and bisphenol
A alkylene oxide-added epoxy resin.
[0061] In manufacturing the mixture that contains component (d),
when component (a), component (b) and component (c) are reacted,
component (d) may be added simultaneously with component (a).
Alternatively, after completion of the urethanization reaction,
component (d) may be added. As a water dispersion that contains
these compounds, HYDRAN N320 (manufactured by DIC) is
mentioned.
[0062] The carbon fiber bundle of the present invention that has a
strand elastic modulus of 250 GPa or more is obtained through a
carbonizing process performed at relatively high temperature.
Accordingly, it is beneficial that the carbon fiber is obtained
from a precursor fiber that contains as few impurities such as a
metal as possible. The amount of metal content in the resultant
carbon fiber bundle is preferable small. In particular, the total
amount of metal components including alkaline metal, alkaline earth
metal, zinc, iron and aluminum is preferably 50 ppm or less. These
metals react with carbon, melt or vaporize at a temperature beyond
1000.degree. C., and this constitutes a reason why defective points
are formed. Highly strong carbon fiber cannot be manufactured.
EXAMPLES
[0063] Now, the present invention will be described in detail by
way of Examples. Note that, performance of a carbon fiber bundle in
Examples was measured and evaluated in accordance with the
following method.
[0064] <1. Measurement of Uneven Surface Structure of Single
Fiber>
[0065] The uneven surface structure can be measured based on the
shape of the surface as follows:
[0066] Several single-fibers of a carbon fiber bundle were placed
on a sample stand and immobilized at both ends. Furthermore, Dotite
was applied around the fibers to prepare a measurement sample. A
range of 1000 nm in the circumference direction of a single fiber
was scanned by an atomic force microscope (SPI3700/SPA-300 (trade
name) manufactured by Seiko Instruments Inc.) using a cantilever
formed of silicon nitride, in an AFM mode while sliding little by
little at a distance of 1000 nm in the fiber-axis direction. From
the resultant measured image, a low-frequency component was cut off
in accordance with a two-dimensional Fourier transform and
thereafter subjected to inverse transformation. From the resultant
planar image of a cross-section from which curvature of the single
fiber was removed, an area range surrounded by a length of 1.0
.mu.m in the fiber-circumference direction and a length of 1.0
.mu.m in the fiber-axis direction was selected and the difference
in height between the highest portion and the lowest portion was
read out, and Ra is obtained by making a calculation in accordance
with the following expression (2).
Ra={1/(Lx.times.Ly)}.intg..sup.Ly.sub.0.intg..sup.LX.sub.0|f(x,y)|dxdy
(2)
[0067] "Center surface": A plane which is parallel to the plane
that has a minimum deviation of the height from the place to the
actual surface and that divides the actual surface equally into two
based on volume. In other words, the portion that is surrounded by
the plane and the actual surface, volumes V1 and V2 that correspond
to both side portions of the plane are equal to each other.
[0068] "f(x, y)": Difference in height between the actual surface
and the center surface,
[0069] "Lx, Ly": Size of the XY plane.
[0070] Furthermore, when an atomic force microscope was used to
take measurements, the presence or absence of an uneven structure
of 0.6 .mu.m or more in length was checked and the length of an
uneven structure of 300 nm or less in length was measured.
[0071] <2. Evaluation of a Cross-Sectional Shape of Single
Fiber>
[0072] The ratio of the major axis and the minor axis (major
axis/minor axis) of the cross section of single fibers that
constitute a carbon fiber bundle was determined as follows:
[0073] A carbon fiber bundle for measurement was passed through a
tube formed of a vinyl chloride resin that has an inner diameter of
1 mm. The tube was cut in the shape of a circle by a knife to
prepare samples. Subsequently, each sample was allowed to adhere to
a SEM sample stand so that the cross-section faced up; Au was
deposited in a thickness of about 10 nm by sputtering; and a fiber
cross-section was observed by a scanning electron microscope
(product name: XL20, manufactured by Philips) under the following
conditions: an acceleration voltage of 7.00 kV and a migration
distance of 31 mm to measure the major axis and minor axis of the
cross section of the single fiber.
[0074] <3. Evaluation of Strand Physical Properties of Carbon
Fiber Bundle>
[0075] Preparation of a strand test sample of a carbon fiber bundle
impregnated with a resin and measurement of the strength of the
sample were performed in accordance with JIS R7601. However, the
elastic modulus was calculated in the range of strain in accordance
with ASTM.
[0076] <4. Measurement of Knot Tenacity of Carbon Fiber
Bundle>
[0077] Knot tenacity was measured as follows:
[0078] To both ends of a carbon fiber bundle of 150 mm in length, a
grip portion of 25 mm in length was attached to prepare a test
sample. In preparing the test sample, a load of 0.1.times.10.sup.-3
N/denier was applied to unidirectionally arrange carbon fiber
bundles. In the test sample, a single knot was formed almost in the
center. Tension was performed at a crosshead rate of 100 mm/min.
Twelve bundles were used for a test. The smallest value and the
largest value were removed and the average value of 10 bundles was
obtained and used as a measurement value.
[0079] <5. Evaluation of "Surface Energy of Surface Formed by
Fracture" of Carbon Fiber Bundle>
[0080] A single carbon fiber was cut into pieces in the length of
20 cm. Each of the single-fiber pieces was allowed to adhere and
immobilize onto a mount for a tensile test for a single fiber of
10-mm sample length shown in JIS R7606. An extra portion extruded
from the mount was cut and removed. In this manner, samples were
prepared.
[0081] Next, these samples that were fixed to the mount were
irradiated with a laser to obtain a hemispherical defect. As a
laser interface system, MicroPoint (pulse energy 300 .mu.J)
manufactured by Photonic Instruments Co., Ltd. were used. As the
optical microscope required for converging laser light, ECLIPSE
LV100 manufactured by Nikon was used. The aperture stop of the
optical microscope was set to a minimum and an object lens was set
at 100 times. Under the conditions, a laser (one pulse) having a
wavelength of 435 nm, the intensity of which was attenuated by 10%
by an attenuator, was applied to the center of a sample in the
fiber-axis direction and in the perpendicular direction of the
fiber axis to form a hemispherical defect.
[0082] To avoid shrinkage break of a sample carbon fiber, the
sample that was attached to a mount was further sandwiched by films
and the space within the films was filled with viscous liquid and
then subjected to a tensile test. To describe more specifically, a
film of about 5 mm in width and about 15 mm in length was prepared
and allowed to adhere to the upper portion of both surfaces of the
sample mount with an adhesive and sandwiched so as to wrap the
sample including the mount. The space within the film was filled
with an aqueous glycerin solution (glycerin:water=1:2). A tensile
test was performed at a tension rate of 0.5 mm/min to measure the
breaking load.
[0083] Next, a sample of a pair of pieces, which was divided into
two pieces in the tensile test, was removed from the mount,
carefully washed with water and naturally dried. Subsequently, a
sample piece was immobilized onto a SEM sample stand with carbon
paste so that the fracture was in a face up position to enable the
preparation of a sample for SEM observation. The fracture surface
of the obtained sample for SEM observation was observed by SEM,
i.e., JSM6060 (acceleration voltage: 10 to 15 kV, magnification:
10000 to 15000) manufactured by JEOL Ltd.
[0084] The obtained SEM image was imported into a personal computer
and analyzed by image analyzing software. In this manner, the size
of a hemispherical defect and the cross-sectional area of a fiber
were measured.
[0085] Next, breaking strength (a) (breaking load/fiber
cross-sectional area) and the size of a hemispherical defect (C)
were plotted. The slope of the data was obtained.
.sigma.=(2E/.pi.C).sup.1/2.times.(surface energy of surface formed
by fracture).sup.1/2 (1)
[0086] In accordance with Equation (1), surface energy of surface
formed by fracture was obtained from the slope and ultrasonic
elastic modulus (E) of a carbon fiber bundle.
[0087] <6. Measurement of Ipa of Carbon Fiber Bundle>
[0088] An Ipa value was measured by the following method.
[0089] An electrolyte is adjusted to pH3 with a 5% aqueous
phosphoric acid solution and bubbled with nitrogen to eliminate the
effect of dissolved oxygen. A sample carbon fiber was dipped in the
electrolyte as one of the electrodes, whereas, a platinum electrode
having a sufficient surface area is used as the other electrode.
Herein, as a reference electrode, an Ag/AgCl electrode was
employed. A sample was formed of a 12000-filament tow having a
length of 50 mm. The potential to be applied between the carbon
fiber electrode and the platinum electrode ranges from -0.2 V from
+0.8 V and a scanning speed thereof was set to be 2.0 mV/sec. A
current-voltage curve was drawn by an X-Y recorder. After sweeping
was performed three times or more to obtain a stable curve, a
current value i was read with a potential of +0.4 V applied to the
Ag/AgCl reference electrode that was used as a reference potential,
and an ipa value was calculated in accordance with the following
expression (3).
ipa=1(.mu.A)/sample length(cm).times.{4.pi..times.weight per unit
area(g/cm).times.number of filaments/density(g/cm.sup.3)}.sup.1/2
(3)
[0090] The apparent surface area was calculated from sample length,
sample density obtained by the method described in JIS R7601 and
mass per unit area. Current value i was divided by the obtained
value to obtain an ipa value. The measurement was performed by
cyclic voltammetry analyzer Type P-1100 manufactured by Yanagimoto
Mfg. Co., Ltd.
[0091] <7. Measurement of Si Amount of Carbon Fiber
Bundle>
[0092] A sample of a carbon fiber bundle was placed in a platinum
crucible whose tare was known and calcified in a muffle furnace of
600 to 700.degree. C. The mass thereof was measured to obtain ash
content. Subsequently, a predetermined amount of sodium carbonate
was added, and the mixture was melted by a burner and dissolved
with deionized water in a 50 ml poly measuring flask. The sample
was measured by ICP emission spectrometry to determine the amount
of Si.
Production Examples 1 to 7 of Precursor Fiber Bundle
Precursor Fiber (1)
[0093] An acrylonitrile based polymer containing acrylonitrile (98
mass %) and methacrylic acid (2 mass %) was dissolved in
dimethylformamide to prepare a 23.5 mass % dope.
[0094] The dope was ejected from a spinneret having 0.15 mm
diameter with 2000 ejection holes arranged therein in a dry-wet
spinning manner. To explain more specifically, the dope was ejected
into the air, passed through a space of about 5 mm and then
solidified in a congealed liquid filled with an aqueous solution
containing 79.0 mass % dimethyl formamide and controlled at a
temperature of 10.degree. C. to obtain a coagulated fiber.
Subsequently, the coagulated fiber was drawn (1.1 times) in the air
and drawn (2.5 times) in a drawing tank filled with an aqueous
solution containing 35 mass % dimethyl formamide and controlled at
60.degree. C. After the drawing process, the fiber bundle in which
a solvent was present was washed with clean water and then drawn
(1.4 times) in hot water of 95.degree. C. Sequentially, to the
fiber bundle, an oil solution containing an amino modified silicone
as a main component was attached so as to apply 1.1 mass %, dried
and densified. After the drying and densification step, the fiber
bundle was drawn (2.6 times) between heated rolls to further
improve the orientation degree and densification. Thereafter, the
bundle was wound up to obtain an acrylonitrile-based precursor
fiber bundle. The denier of the fiber was 0.77 dtex.
Precursor Fiber (2)
[0095] Precursor fiber bundle (2) was obtained under the same
conditions as in precursor fiber bundle (1) except that the draw
ratio before washing with water was set to be 2.9 times and the
draw ratio in hot water after washing was set to be 1.2 times.
Precursor Fiber (3)
[0096] Precursor fiber bundle (3) was obtained under the same
conditions as in precursor fiber bundle (2) except that the denier
of the precursor fiber was set to be 0.67 dtex.
Precursor Fiber (4)
[0097] Precursor fiber bundle (4) was obtained under the same
conditions as in precursor fiber bundle (2) except that the denier
of the precursor fiber was set to be 0.90 dtex.
Precursor Fiber (5)
[0098] Precursor fiber bundle (5) was obtained under the same
conditions as in precursor fiber bundle (1) except that the draw
ratio before washing with water was set to be 4.1 times, the draw
ratio in hot water after washing was set to be 0.9 times and
drawing that was performed between heated rolls was set to be 2.4
times.
Precursor Fiber (6)
[0099] Precursor fiber bundle (6) was obtained under the same
conditions as in precursor fiber bundle (1) except that the draw
ratio before washing with water was set to be 1.9 times and the
draw ratio in hot water after washing was set to be 2.0 times.
Precursor Fiber (7)
[0100] Precursor fiber bundle (7) was obtained under the same
conditions as in precursor fiber bundle (2) except that the denier
of the precursor fiber was set to be 1.0 dtex.
[0101] The manufacturing conditions for precursor fiber bundles (1)
to (7) are shown in Table 1.
TABLE-US-00001 TABLE 1 Spinning conditions Precursor Coagulation
bath In the air Draw tank Hot water Dry heat fiber Precursor
Temperature Concentration Draw Temperature Concentration Draw Draw
drawing Denier fiber (.degree. C.) (%) ratio (.degree. C.) (%)
ratio ratio Ratio dtex Precursor 10 79.0 1.1 60 35 2.5 1.4 2.6 0.77
(1) Precursor 10 79.0 1.1 60 35 2.9 1.2 2.6 0.77 (2) Precursor 10
79.0 1.1 60 35 2.9 1.2 2.6 0.67 (3) Precursor 10 79.0 1.1 60 35 2.9
1.2 2.6 0.90 (4) Precursor 10 79.0 1.1 60 35 4.1 0.99 2.4 0.77 (5)
Precursor 10 79.0 1.1 60 35 1.9 2.0 2.4 0.77 (6) Precursor 10 79.0
1.1 60 35 2.9 1.2 2.6 1.00 (7) Precursor 5 77.0 1.3 60 0 2.0 2.0
1.9 0.77 (8)
Examples 1 to 7, Comparative Examples 1 to 4
Preparation of Carbon Fiber Bundle
[0102] A plurality of precursor fiber bundles (1), (2), (3), (4),
(5), (6) or (7) were arranged in parallel and introduced in an oven
for stabilization. Air heated to 220 to 280.degree. C. was sprayed
to the precursor fiber bundles to perform stabilization treatment.
In this manner, stabilized fiber bundles having a density of 1.345
g/cm.sup.3 were obtained. The extension rate was set to be 6% and
stabilization treatment time was 70 minutes.
[0103] Next, the stabilized fiber bundles were passed through a
first carbonization furnace having a temperature gradient of 300 to
700.degree. C. in nitrogen while the extension rate was increased
by 4.5%. The temperature gradient was set so as to change linearly.
The treatment time was 2.0 minutes.
[0104] Furthermore, heat treatment was performed using a second
carbonization furnace having a nitrogen atmosphere in which the
temperature gradient of 1000 to 1600.degree. C. could be set, at
the predetermined temperatures shown in Table 2 or Table 3.
Subsequently, heat treatment was performed using a third
carbonization furnace having a nitrogen atmosphere in which the
temperature gradient of 1200 to 2400.degree. C. could be set, at
the predetermined temperatures shown in Table 2 or Table 3 to
obtain carbon fiber bundles. The total extension rate of the fiber
bundles through the treatments in the second carbonization furnace
and third carbonization furnace was -4.0%, and the treatment time
in total was set to be 3.5 minutes.
[0105] Subsequently, the fiber bundles were fed to a 10 mass %
aqueous ammonium bicarbonate solution. Current was supplied between
a carbon fiber bundle serving as an anode and a counter pole so as
to obtain a quantity of electricity of 40 coulombs per carbon fiber
(1 g) to be treated. Then, the fiber bundles were washed with warm
water of 90.degree. C. and dried.
[0106] Next, Hydran N320 (hereinafter referred to as "sizing agent
1") was attached onto the fiber bundles in the amount of 0.5 mass %
and wound by a bobbin to obtain a carbon fiber bundle.
(Preparation of UniDirectional Prepreg)
[0107] Onto a mold-releasing paper coated with epoxy resin #410
(that can be used at 180.degree. C.) [manufactured by Mitsubishi
Rayon Co., Ltd.] in the B stage, 156 carbon fiber bundles released
from a bobbin were arranged in parallel and passed through a heat
compression roller. In this manner, the carbon fiber bundles were
impregnated with epoxy resin. A protecting film was laminated on
the resultant bundles to prepare a prepreg arranged in a
unidirection (hereinafter referred to as a "UD prepreg") having a
resin content of about 33 mass %, a carbon fiber mass per unit area
of 125 g/m.sup.2 and a width of 500 mm.
(Molding of a Laminate Board and Evaluation of Mechanical
Performance)
[0108] A laminate board was prepared by using the UD prepreg and
the tensile strength of the laminate board at angle 0.degree. was
evaluated by the evaluation method in accordance with ASTM
D3039.
[0109] The manufacturing conditions for a carbon fiber bundle and
the evaluation results are shown in Table 2 and Table 3.
[0110] Note that it was confirmed that in any of Examples, a single
fiber does not have an uneven surface structure that has a length
of 0.6 .mu.m or more and that extends in the longitudinal direction
of a fiber but has a microscopic uneven structure that has a length
of 300 nm or less.
TABLE-US-00002 TABLE 2 Carbon fiber bundle Example 1 Example 2
Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Type of
precursor fiber Precursor Precursor Precursor Precursor Precursor
Precursor Precursor Precursor bundle (1) (2) (3) (4) (2) (2) (2)
(2) Conditions of second 1250-1300 1250-1300 1250-1300 1250-1300
1050-1250 1100-1301 1200-1500 1050-1250 carbonization furnace
(.degree. C.) Conditions of third 1350-1550 1350-1550 1350-1550
1350-1550 1250-1450 1300-1501 1550-1800 -- carbonization furnace
(.degree. C.) Difference in height (Rp - v) 12 15 14 16 15 15 15 15
(nm) Ra (nm) 3 4 3 4 4 4 4 4 Major axis/minor axis of 1.005 1.005
1.005 1.005 1.005 1.005 1.005 1.005 cross-section Weight per unit
area of 0.035 0.035 0.030 0.041 0.035 0.035 0.035 0.035 single
fiber (mg/m) Strand strength (MPa) 6050 6300 6400 6100 6700 6500
6050 6350 Strand elastic modulus 330 335 345 325 305 325 355 260
(GPa) Knot tenacity (N/mm.sup.2) 950 1040 1100 1000 1200 1100 910
1250 Surface energy of surface 32 33 34 33 35 34 30 36 formed by
fracture (N/m) iPa (.mu.A/cm.sup.2) 0.15 0.15 0.15 0.15 0.17 0.16
0.09 0.18 O1S/C1S 0.09 0.09 0.09 0.09 0.11 0.1 0.07 0.13 Si amount
(ppm) 150 120 110 130 120 120 125 120 Metal content (ppm) 40 40 40
40 40 40 40 40 Tensile strength of 3000 3150 3180 3100 3400 3300
3020 3240 laminate board at 0.degree. C. (in terms of 60 vol %)
MPa
TABLE-US-00003 TABLE 3 Comparative Comparative Comparative
Comparative Comparative Carbon fiber bundle Example 1 Example 2
Example 3 Example 4 Example 5 Type of precursor fiber bundle
Precursor (5) Precursor (6) Precursor (7) Precursor (6) Precursor
(8) Conditions of second carbonization 1250-1300 1250-1300
1250-1300 1200-1500 1250-1300 furnace (.degree. C.) Conditions of
third carbonization 1350-1550 1350-1550 1350-1550 1550-1800
1350-1550 furnace (.degree. C.) Difference in height(Rp - v) (nm)
29 13 23 13 8 Ra (nm) 8 3 6 3 2 Major axis/minor axis of
cross-section 1.005 1.005 1.005 1.005 1.005 Weight per unit area of
single fiber (mg/m) 0.035 0.035 0.045 0.045 0.045 Strand strength
(MPa) 5400 5700 5750 5200 5950 Strand elastic modulus (GPa) 330 330
315 355 325 Knot tenacity (N/mm.sup.2) 650 750 850 630 790 Surface
energy of surface formed by 29 30 30 28 29 fracture (N/m) iPa
(.mu.A/cm.sup.2) 0.18 0.15 0.15 0.09 0.15 O1S/C1S 0.12 0.10 0.09
0.07 0.11 Si amount (ppm) 300 220 160 210 230 Metal content (ppm)
40 40 40 40 40 Tensile strength of laminate board at 0.degree. C.
2650 2700 2700 2400 2850 (in terms of 60 vol %) MPa
Production Example 8 of Precursor Fiber Bundle
[0111] A dope, which was prepared in the same manner as in
Production Example 1, was ejected from a spinneret having 0.13 mm
diameter with 2000 of ejection holes arranged therein in a dry-wet
spinning manner. To explain more specifically, the dope was ejected
into the air, passed through a space of about 5 mm and then
solidified in a congealed liquid filled with an aqueous solution
containing 77.0 mass % dimethyl formamide and controlled at a
temperature of 5.degree. C. to obtain a coagulated fiber.
Subsequently, the coagulated fiber was drawn (1.3 times) in the air
and drawn (2.0 times) in a drawing tank filled with an aqueous
solution controlled at 60.degree. C. After the drawing process, the
fiber bundle in which a solvent was present was washed with clean
water and then drawn (2.0 times) in hot water of 95.degree. C.
Sequentially, to the fiber bundle, an oil solution containing an
amino modified silicone as a main component was attached so as to
apply 1.0 mass %, dried and densified. After the drying and
densification step, the fiber bundle was drawn (1.9 times) between
heated rolls to further improve the orientation degree and
densification. Thereafter, the bundle was wound up to obtain the
precursor fiber bundle. The denier of the fiber was 0.77 dtex.
Example 8
[0112] A carbon fiber bundle was prepared under the same
carbonizing conditions as in Example 5 except that the third
carbonization furnace was not used. Furthermore, a laminate board
was prepared in the same manner and mechanical performance was
evaluated to obtain the results shown in Table 2. Note that, it was
confirmed that the single fiber has no uneven surface structure
having a length of 0.6 .mu.m or more and extending in the
longitudinal direction of the fiber and has an uneven microscopic
structure having a length of 300 nm or less.
Examples 9 to 11, Comparative Examples 6 to 8
[0113] Carbon fiber bundles were obtained in the same manner as in
Example 2 except that the carbonizing conditions were changed. The
evaluation results are shown in Table 4. Note that, in any one of
Examples, it was confirmed that the single fiber has no uneven
surface structure having a length of 0.6 .mu.m or more and
extending in the longitudinal direction of the fiber and has an
uneven microscopic structure having a length of 300 nm or less.
TABLE-US-00004 TABLE 4 Comparative Comparative Comparative Carbon
fiber bundle Example 9 Example 6 Example 10 Example 7 Example 11
Example 8 Conditions changed from Stabilized Stabilized First First
Second, third Second, third Example 2 fiber extension fiber
extension carbonated carbonated carbonated carbonated rate rate
fiber extension fiber extension fiber extension fiber extension
rate rate rate rate 8.0% 10.5% 6.5% 7.2% -5.2% -6.5% Difference in
height(Rp - v) (nm) 13 12 14 13 15 16 Ra (nm) 4 4 4 4 4 4 Major
axis/minor axis of cross- 1.005 1.005 1.005 1.005 1.005 1.005
section Weight per unit area of single fiber 0.034 0.033 0.034
0.033 0.035 0.035 (mg/m) Strand strength (MPa) 6000 5300 5900 5400
6050 5500 Strand elastic modulus (GPa) 338 340 336 336 327 310
Surface energy of surface formed 990 700 970 750 990 800 by
fracture (N/m) Knot tenacity (N/mm.sup.2) 31 27 30 28 31 30 iPa
(.mu.A/cm.sup.2) 0.15 0.15 0.15 0.15 0.15 0.15 O1S/C1S 0.09 0.09
0.09 0.09 0.09 0.09 Si amount (ppm) 120 120 120 120 120 120 Metal
content (ppm) 40 40 40 40 40 40 Tensile strength of laminate board
at 3000 2550 2950 2500 2980 2600 0.degree. C. (in terms of 60 vol
%) MPa
Examples 12 and 13
[0114] Carbon fiber bundles were obtained in the same manner as in
Example 5 except that the surface treatment conditions were
changed. The evaluation results are shown in Table 5. Note that in
any of the Examples, it was confirmed that the single fiber has no
uneven surface structure having a length of 0.6 .mu.m or more and
extending in the longitudinal direction of the fiber and has an
uneven microscopic structure having a length of 300 nm or less.
Examples 14 to 16
[0115] Carbon fiber bundles were obtained in the same manner as in
Example 5 except that the types and amounts attached of sizing
agents were changed. The evaluation results are shown in Table 5.
Note that in any one of the Examples, it was confirmed that the
single fiber has no uneven surface structure having a length of 0.6
.mu.m or more and extending in the longitudinal direction of the
fiber and has an uneven microscopic structure having a length of
300 nm or less.
[0116] Note that, sizing agent 2, sizing agent 3 and sizing agent 4
were prepared as follows:
(Sizing Agent 2)
[0117] "Epicoat 828" (80 parts by mass) manufactured by Japan Epoxy
Resins Co., Ltd. as a main agent and "Pluronic F88" (20 parts by
mass) manufactured by ADEKA Corporation as an emulsifier were
blended to obtain an aqueous dispersion by phase-transfer
emulsification.
(Sizing Agent 3)
[0118] In a flask, polyol (3.2 mol) consisting of 1.8 mol of an
adduct of bisphenol A with 8 mol of propylene oxide, 0.8 mol of
trimethylolpropane and 0.6 mol of dimethyloipropionic acid were
placed. Furthermore, 0.5 g of 2,6-di(t-butyl) 4-methylphenol (BHT)
as a reaction inhibitor and 0.2 g of dibutyltin dilaurate as a
reaction catalyst were added and stirred until a homogeneous
mixture was obtained. Herein, if necessary, methyl ethyl ketone was
added as a viscosity moderator. To the mixture homogeneously
dissolved, metaxylene diisocyanate (3.4 mol) was added dropwise and
polymerization of a urethane prepolymer was performed while
stirring at a reaction temperature of 50.degree. C. for a reaction
time of 2 hours. Then, Epicoat 834 (manufactured by JER) (0.25 mol)
was added and reacted with an isocyanate group at an end of the
urethane prepolymer to obtain an epoxy modified urethane resin.
[0119] The epoxy modified urethane resin (90 parts by mass) and
"Pluronic F88" (10 parts by mass) manufactured by ADEKA Corporation
as an emulsifier were blended to prepare an aqueous dispersion.
(Sizing Agent 4)
[0120] To a flask, polyethylene glycol 400 (2.5 mol) and Epicoat
834 (manufactured by JER) (0.7 mol) were placed and further
2,6-di(t-butyl)-4-methylphenol (BHT) (0.25 g) as a reaction
inhibitor, and dibutyl tin dilaurate (0.1 g) as a reaction catalyst
were added. The mixture was stirred until it became homogeneous.
Herein, if necessary, methyl ethyl ketone was added as a viscosity
moderator. To the mixture homogeneously dissolved, a metaxylene
diisocyanate (2.7 mol) was added dropwise. The reaction was
performed at a temperature of 40.degree. C. for 2 hours while
stirring to obtain an epoxy modified urethane resin.
[0121] The epoxy modified urethane resin (80 parts by mass) and
Pluronic F88 (20 parts by mass) manufactured by ADEKA Corporation
as an emulsifier were mixed to prepare an aqueous dispersion.
TABLE-US-00005 TABLE 5 Carbon fiber bundle Example 12 Example 13
Example 14 Example 15 Example 16 Conditions changed from Example 5
Surface Surface Sizing agent Sizing agent Sizing agent treatment
treatment 8% Ammonium Ammonium Sizing agent 2 Sizing agent 3 Sizing
agent 4 carbonate bicarbonate (amount (amount (amount 20 coulomb/g
200 coulomb/g attached, 0.4 attached, 0.4 attached, 0.4 mass %)
mass %) mass %) Strand strength (MPa) 6,400 6,700 6,700 6,700 6,700
iPa (.mu.A/cm.sup.2) 0.40 0.24 0.17 0.17 0.17 O1S/C1S 0.19 0.16
0.11 0.11 0.11 Tensile strength of laminate board at 3000 3280 3050
3410 3350 0.degree. C. (in terms of 60 vol %) MPa
INDUSTRIAL APPLICABILITY
[0122] The carbon fiber bundle of the present invention can be used
as a constructional material for airplanes and high speed moving
bodies.
* * * * *