Pitch-based Carbon Fiber

No. 383
February
2011
Published monthly by
Public Relations Center
General Administration Div.
Nippon Steel Corporation
More about Nippon Steel
http://www.nsc.co.jp/en
In this issue
Feature Story
The Genesis of Product Making
Pitch-based Carbon Fiber
―Raising the Added Value of Carbon Materials Derived from Coal Tar―
Operating Roundup
ECOKOTE-S Adopted in Fuel Tanks
Nippon Steel has accepted orders for its specially-developed “ECOKOTE-STM” for fuel tanks for
Chevrolet Volt electric vehicle. It is a tin-zinc-coated corrosion-resistant steel sheet that contains
no lead or other environment-loading substances.
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Investment in Cold Rolling Mill in Nigeria
Nippon Steel and Marubeni-Itochu Steel Inc. have reached an agreement with Midland Rolling
Mills Limited in Nigeria in regard to equity investment in MRM. Each of Japanese companies is to
respectively invest US$ 3 million in MRM which manufactures cold-rolled steel in Nigeria.
NSSC FW2: Highly Corrosion-resistant Ferritic Stainless Steel
Nippon Steel & Sumikin Stainless Steel Corporation has newly developed NSSC® FW2 (Forward
Two), a “highly corrosion resistant, low-interstitial ferritic stainless steel”, having corrosion resistance equal or superior to SUS304. It features 40% reduction in rare metals through use of tin (Sn).
Resumption of Delivery of Galvanized Steel Pipes
Nippon Steel confirms that the delivery of galvanized steel pipes, which had been suspended as
previously announced, has resumed since late September of 2010. The company has since taken
measures to ensure stable manufacturing conditions and revised its inspection system.
Operating Roundup
ECOKOTE-S Adopted in Fuel Tanks
Back to Top
Investment in Cold Rolling Mill in Nigeria
No. 383 February 2011
NSSC FW2: Highly Corrosion-resistant Ferritic Stainless Steel
Resumption of Delivery of Galvanized Steel Pipes
Feature Story
The Genesis of Product Making
Pitch-based Carbon Fiber
—Raising the Added Value of Carbon Materials Derived from Coal Tar—
Nippon Graphite Fiber Corporation, a Nippon Steel Group company, produces pitch-based carbon fiber with considerably higher
added value. This type of fiber is produced using carbon materials
(impregnated pitch) derived from coal tar, which is a byproduct of
blast-furnace ironmaking. Due to its high performance with regard
to strength and modulus, pitch-based carbon fiber is increasingly
being applied in a wide range of fields—industry, construction,
space and aircraft, and sports and leisure.
The current issue highlights the production technology used to
make pitch-based carbon fiber and the strengths of Nippon Graphite Fiber Corporation, together with suggestions regarding the future direction of related application development.
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Operating Roundup
ECOKOTE-S Adopted in Fuel Tanks
Back to Top
Back
Next
Investment in Cold Rolling Mill in Nigeria
No. 383 February 2011
NSSC FW2: Highly Corrosion-resistant Ferritic Stainless Steel
Resumption of Delivery of Galvanized Steel Pipes
Feature Story
Production of Differentiated Carbon Fiber Using High-quality Impregnated Pitch
plant at its Hirohata Works to accumulate production technology knowhow related to carbon
fibers. In 1995, Nippon Steel and Nippon Oil Co.
(currently JX Nippon Oil & Energy), the latter of
which is strong in the development of carbon fiber materials for space, sports and leisure fields,
integrated their carbon fiber-related businesses
to establish NGF (currently a group company of
Nippon Steel Materials Co., Ltd.). Since then, NGF
has supplied high-quality pitch-based carbon fiber for diversifying and emerging markets.
PAN-based carbon fibers are the mainstay of
the entire carbon fiber market. However, PANbased carbon fiber has a standard value of 240
GPa (300 GPa for aircraft) for its modulus, which
indicate anti-deformability, and is difficult to produce with a high modulus of 500 GPa or more.
Consequently, the production of fiber having such
a high modulus inevitably requires higher cost.
On the other hand, with pitch-based carbon
fiber, it is comparatively easy to properly produce
fibers having moduli ranging from 50 GPa to 900
GPa. In order to distinguish these from 300 GPa-
class products, a strong field for PAN-based fiber,
NGF is directing its efforts towards the development of carbon fiber in the low and high modulus
ranges. (Refer to Fig. 1)
Fig. 1 Comparison of Physical Properties between
PAN- and Pitch-based Carbon Fibers
7,000
PAN-based high-strength grade
6,000
Tensile strength (MPa)
Two kinds of carbon fiber are produced: PANbased fiber employing acrylic fibers used for
cloths; and pitch-based carbon fiber employing
byproduct materials derived from the coal carbonization process in ironmaking and from the
oil refining process. Nippon Graphite Fiber (NGF)
produces carbon fiber employing the impregnated pitch contained in coal tar, a byproduct generated during coal carbonization. Impregnated
pitch is a hard (heavy) pitch that is produced by
heat-treating the high-purity pitch used for needle
coke and, further, by volatilizing lightweight components. NGF procures all the necessary impregnated pitch used as raw material for carbon fiber
from the Hirohata Works of C-Chem Co., Ltd. (a
joint company between Nippon Steel Chemical
and Sumikin Chemical).
In 1981, Nippon Steel started the technological development of pitch-based carbon fiber for
use in the construction and machinery industries,
with the aim of promoting advanced applications
of byproducts derived from coal carbonization
in ironmaking. In 1985, the company built a pilot
High modulus/high thermal
conductivity grade
5,000
4,000
3,000
2,000
Low modulus grade
Pitch-based (NGF)
PAN-based
1,000
0
0
100 200 300 400 500 600 700 800 900 1,000
Tensile modulus (GPa)
Operating Roundup
ECOKOTE-S Adopted in Fuel Tanks
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Investment in Cold Rolling Mill in Nigeria
NSSC FW2: Highly Corrosion-resistant Ferritic Stainless Steel
No. 383 February 2011
Resumption of Delivery of Galvanized Steel Pipes
Feature Story
Modification into Spinning Material Appropriate for Carbon Fiber Employing Hydrogen
In order to modify the impregnated pitch procured
from C-Chem into spinning material suitable for
the production of carbon fiber, after hydrogenation, the pitch is first subjected to thermal polymerization*1, in which lightweight substances are
blown off by means of high-precision distillation,
and are then removed of minute impurities by
means of filtration (Fig. 2). The hydrogen plays
two roles: to remove the sulfur and nitrogen conFig. 2 Raw Material Modification Process
C-Chem
NGF
Coal tar
Hydrogenation
Distillation
Thermal polymerization
De-QI (U process)
High-precision distillation
Heat treatment, distillation
Filtration
Impregnated pitch
Spinning material pitch
tained in coal tar, and to change the molecular
structure of the impregnated pitch so as to convert
it into 6-membered ring carbon*2 in which graphite crystals can easily grow. The 6-membered ring
carbon is converted to graphite crystals by means
of heating, and as the crystals grow, their strength
and modulus increase. Impregnated pitch in its
original form cannot be sufficiently converted to
graphite crystals, and even when subjected to
heat treatment, a fully developed graphite structure does not result (isotropic pitch). However, a
regularly-aligned molecular (liquid crystal) structure can be produced, even in a liquid state, by
adding hydrogen to adjust the molecular structure of the impregnated pitch (mesophase pitch).
Mesophase pitch that is liquid-crystallized in a well
balanced manner has a softening point (the temperature at which the substance starts to melt) below the thermal decomposition temperature and,
therefore, can be used as a material for producing
high-quality carbon fiber (Photo 1). (Isotropic pitch
can be used for producing general-purpose low
modulus carbon fiber.)
Photo 1 Change of Carbon Fiber Structures due to
Difference of Material Pitch
Isotropic pitch
Mesophase pitch
5nm
5nm
5μm
Section
5μm
Section
*1 Polymerization: Forming of compounds larger in size than
the original substance through the chemical bonding of
two or more molecules composed of one or more kinds of
substances
*2 6-membered ring: Chemical material having 6 atoms bonded
in a ring state
Operating Roundup
ECOKOTE-S Adopted in Fuel Tanks
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Investment in Cold Rolling Mill in Nigeria
No. 383 February 2011
NSSC FW2: Highly Corrosion-resistant Ferritic Stainless Steel
Resumption of Delivery of Galvanized Steel Pipes
Feature Story
Control of Crystals in the Spinning Process to Further Improve Strength and Modulus by Heat Treatment
Pitch modified as the spinning material becomes
carbon fiber via the production process shown
in Fig. 3. In the spinning process by which pitch
is converted to fibers having a diameter of about
10 µm (one-tenth of a hair), the pitch crystals are
aligned longitudinally by means of die (nozzle)
configuration and the stirring method; at the same
time, physical properties such as modulus and
strength are optimized by controlling the method
used to align and laminate the layers in which the
crystals are arranged or by controlling the sectional structure (Fig. 4). Only three companies in
the world can produce high-strength and highmodulus carbon fiber employing mesophase
pitch as the spinning material. Among them, only
NGF can produce pitch-based carbon fiber having a crystal orientation controlled so as not to allow cross-sectional cracking of the fiber, a quality
defect (Photo 2).
Yarn produced by the spinning of as many
as 12,000 ultrafine, non-processed pitch-based
carbon fibers has a low softening point (300°C),
which causes melting when the fibers are sub-
Fig. 3 Production Process for Pitch-based Carbon Fiber
Raw material pitch
modification
(Fig. 2)
Fig. 4 Crystal Orientation of Mesophase Pitch in
Spinning Process
Component separation,
hydrogenation treatment,
thermal polymerization,
refining filtration
Spinning material pitch
Spinning
Melt spinning @300∼400℃
Pitch fiber
Infusibilization treatment
Gaseous phase oxidation @100∼400℃
Infusibilized fiber
Carbonization
∼1,400℃ nitrogen gas
The pitch crystals are aligned longitudinally by means of die (nozzle)
conf iguration and the stirring
method and physical properties
are optimized by controlling the
method used to align and laminate
the crystal layers.
Photo 2 Carbon Fiber with Cross-sectional Cracking
Carbon fiber
Graphitization
∼3,000℃ nitrogen gas or argon gas
Graphite fiber
Surface treatment
Product
Oxidation and sizing treatment
Fiber cross section cracking leads
to the quality defect.
Operating Roundup
ECOKOTE-S Adopted in Fuel Tanks
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Investment in Cold Rolling Mill in Nigeria
No. 383 February 2011
NSSC FW2: Highly Corrosion-resistant Ferritic Stainless Steel
Resumption of Delivery of Galvanized Steel Pipes
Feature Story
jected to high-temperature heat treatment. To
solve this problem, oxygen and other elements
are added in advance to eliminate hydrogen and
other elemental impurities, while at the same time
the molecular bonding capability is improved by
precisely controlling the chemical reaction used
to raise the softening point (infusibilization treatment by means of gaseous phase oxidation). The
resulting infusibilized fiber is heated and baked
in an oxygen-free state to remove impurities and
elements other than carbon in order to raise the
carbon density (carbonization). Following this,
the carbon crystals are regularly rearranged by
further raising the heat-treatment temperature to
improve the modulus and strength (graphitization;
the same crystal structure found in pencil lead).
Because the carbon fiber thus manufactured is
most commonly applied in concert with resin, the
fiber is subjected to surface treatment to improve
its bonding capacity with resin and its workability
during secondary processing.
Commonly, pitch-based carbon fiber material
is produced by bundling 6,000~12,000 carbon
fibers with a diameter of 10 µm (Photo 3). To meet
the need for lighter weight, NGF has initiated
the industrial production of carbon fiber material manufactured by bundling 400 fibers with the
world’s finest diameter of 7 µm and modulus similar to that of 10 µm-diameter carbon fibers.
Photo 3 Carbon Fiber Production Line
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Operating Roundup
ECOKOTE-S Adopted in Fuel Tanks
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Investment in Cold Rolling Mill in Nigeria
NSSC FW2: Highly Corrosion-resistant Ferritic Stainless Steel
No. 383 February 2011
Resumption of Delivery of Galvanized Steel Pipes
Feature Story
New Market Development Capitalizing on the Superior Physical Properties peculiar to Pitch-based Carbon Fibers
In order to meet various applications, NGF supplies a variety of pitch-based carbon fibers of different moduli, such as yarn, fabric, and prepreg
manufactured by impregnating thermosetting
resins (Photo 4). Extensive application development of carbon fiber, such as the CFRP composite
material developed by Nippon Steel Composites
Company (established in 1988 and integrated
into Nippon Steel Materials in 2010), is one of the
strengths of the new market development program
being promoted by NGF.
Currently, carbon fiber with a low modulus
(50~150 GPa class) is increasingly being applied
in golf club shafts and fishing rods. On the other
hand, high-modulus carbon fiber (600 GPa or
more), which is difficult to produce for PAN-based
carbon fiber, is used in various rolls for printing
and film production, in the arms of liquid crystal
Photo 4 High-performance Pitch-based Carbon Fiber Products
GRANOC® prepreg
GRANOC® cloth
and semiconductor transfer robots and in construction reinforcing members by fully capitalizing
on such performances as zero thermal deformation, lightness of weight and high strength. (Refer
to Photo 5) More recently, high modulus material
is applied in racing bicycle frames requiring both
lightness of weight and high rigidity.
The fields with high expectations for expanded
application growth include the shafts of machine
Photo 5 Examples of Conventional Applications
GRANOC® yarn
Golf club
Reinforcing members
(Courtesy: SRI Sports) used in construction
Rolls for printing machine
Operating Roundup
ECOKOTE-S Adopted in Fuel Tanks
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Investment in Cold Rolling Mill in Nigeria
NSSC FW2: Highly Corrosion-resistant Ferritic Stainless Steel
No. 383 February 2011
Resumption of Delivery of Galvanized Steel Pipes
Feature Story
tool motors, and robot arms and beams. In particular, the long beams of large-capacity machine
tools are heavy and suffer reduced fabrication accuracy due to vibration. Thus, fabrication accuracy
improves with the adoption of lightweight carbon
fiber-reinforced plastic with high vibration damping
capacity (Photo 6).
High modulus carbon fiber has high thermal
conductivity (ease of thermal conduction), and its
coefficient of thermal expansion can be minimized
to zero by composite use with other materials (Figs.
5 and 6). Due to these characteristic performances, pitch-based carbon fiber has recently been adopted for the heat radiation members of electronic
equipment, solar panel members, and the antenna
members of artificial satellites operating in space
under temperature fluctuations as great as 200°C
or more, depending on the extent of exposure to
sun light (Photo 7).
Pitch-based carbon fiber offers characteristic
performances such as high elasticity (900 GPa)
and high thermal conductivity (900 W) not found
Fig. 5 Thermal Conductivity of Pitch-based Carbon Fiber
Magnesium alloy
Photo 6 Automobile Panel Fabrication Equipment
Fig. 6 Coefficient of Thermal Expansion of
Various Materials
70
Aluminum alloy
200
Metal
Copper
400
PAN (high modulus grade)
70
PAN (regular grade)
Carbon
Carbon
fiber
fiber
10
XN80 (NGF)
Ceramic
Resin
320
XN90 (NGF)
Coefficient of thermal expansion
of carbon fiber: Small absolute
value, negative value
500
XN100 (NGF)
1,000
0
200
400
600
800
Thermal conductivity (W/mk)
1000
-10
0
10
20
300
40
50
200
Coefficient of thermal expansion × 10 °C
-6
-1
When lightweight carbon fiber is adopted, the self
weight reduces and the vibration damping performance during operation is improved.
Operating Roundup
ECOKOTE-S Adopted in Fuel Tanks
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Investment in Cold Rolling Mill in Nigeria
NSSC FW2: Highly Corrosion-resistant Ferritic Stainless Steel
No. 383 February 2011
Resumption of Delivery of Galvanized Steel Pipes
Feature Story
in any other materials in practical use. NGF is promoting the market development of these fibers in
two directions.
One is to replace metallic materials with carbon
fiber in industrial applications. With energy savings
being called for in diverse industrial fields, lightweight pitch-based carbon fiber with high rigidity
can contribute to the reduction of weight in production equipment and devices.
Another direction of market development is application development in the consumer product
field, which capitalizes on such performances of
pitch-based carbon fiber as high thermal conduc-
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tivity and zero C.T.E. (coefficient of thermal expansion). For example, with the growing need for higher functionality and higher density in electronic
equipment devices, carbon fiber is seen to have a
high heat-radiation capacity, which is required of
high thermal-conducting electronic materials capable of improving device reliability.
On the strength of reinforced supply capacity
realized by the startup of new production lines in
the fall of 2010, NGF is further promoting new market development for high-performance pitch-based
carbon fiber.
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Photo 7 Artificial Satellite Antenna
Because of the complicated inner configuration required to send waves with pinpoint accuracy to a
specified area, zero thermal deformation is inevitably
necessary as a member performance value.
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