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No. 383February 2011Published monthly by Public Relations Center General Administration Div. Nippon Steel Corporation

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The Genesis of Product Making

Pitch-based Carbon Fiber―Raising the Added Value of Carbon Materials Derived from Coal Tar―

In this issue Feature Story

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.

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 resis-tance 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 confi rms 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.

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ECOKOTE-S Adopted in Fuel Tanks

Investment in Cold Rolling Mill in Nigeria

NSSC FW2: Highly Corrosion-resistant Ferritic Stainless Steel

Resumption of Delivery of Galvanized Steel Pipes

The Genesis of Product Making

—Raising the Added Value of Carbon Materials Derived from Coal Tar—Pitch-based Carbon Fiber

Nippon Graphite Fiber Corporation, a Nippon Steel Group com-pany, produces pitch-based carbon fi ber with considerably higher added value. This type of fi ber 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 fi ber 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 fi ber and the strengths of Nippon Graph-ite Fiber Corporation, together with suggestions regarding the fu-ture direction of related application development.

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No. 383 February 2011

Feature Story

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Two kinds of carbon fiber are produced: PAN-based fiber employing acrylic fibers used for cloths; and pitch-based carbon fiber employing byproduct materials derived from the coal car-bonization process in ironmaking and from the oil refi ning process. Nippon Graphite Fiber (NGF) produces carbon fi ber employing the impregnat-ed pitch contained in coal tar, a byproduct gen-erated 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 com-ponents. NGF procures all the necessary impreg-nated pitch used as raw material for carbon fi ber 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 technologi-cal 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

Production of Differentiated Carbon Fiber Using High-quality Impregnated Pitch

plant at its Hirohata Works to accumulate pro-duction technology knowhow related to carbon fi bers. In 1995, Nippon Steel and Nippon Oil Co. (currently JX Nippon Oil & Energy), the latter of which is strong in the development of carbon fi -ber materials for space, sports and leisure fi elds, 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 fi-ber for diversifying and emerging markets.

PAN-based carbon fibers are the mainstay of the entire carbon fiber market. However, PAN-based carbon fiber has a standard value of 240 GPa (300 GPa for aircraft) for its modulus, which indicate anti-deformability, and is diffi cult to pro-duce with a high modulus of 500 GPa or more. Consequently, the production of fi ber having such a high modulus inevitably requires higher cost.

On the other hand, with pitch-based carbon fi ber, it is comparatively easy to properly produce fi bers having moduli ranging from 50 GPa to 900 GPa. In order to distinguish these from 300 GPa-

class products, a strong fi eld for PAN-based fi ber, NGF is directing its efforts towards the develop-ment of carbon fi ber in the low and high modulus ranges. (Refer to Fig. 1)

0 100 200 300 400 500 600 700 800 900 1,000

7,000

6,000

5,000

4,000

3,000

2,000

1,000

0

Tens

ile s

tren

gth

(MP

a)

Tensile modulus (GPa)

PAN-based high-strength grade

High modulus/high thermal conductivity grade

Low modulus grade

Pitch-based (NGF)PAN-based



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Fig. 1 Comparison of Physical Properties between PAN- and Pitch-based Carbon Fibers









In order to modify the impregnated pitch procured from C-Chem into spinning material suitable for the production of carbon fiber, after hydrogena-tion, the pitch is fi rst subjected to thermal polym-erization*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 con-

Modifi cation into Spinning Material Appropriate for Carbon Fiber Employing Hydrogen

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 graph-ite 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 struc-ture does not result (isotropic pitch). However, a regularly-aligned molecular (liquid crystal) struc-ture can be produced, even in a liquid state, by adding hydrogen to adjust the molecular struc-ture of the impregnated pitch (mesophase pitch). Mesophase pitch that is liquid-crystallized in a well balanced manner has a softening point (the tem-perature at which the substance starts to melt) be-low the thermal decomposition temperature and, therefore, can be used as a material for producing high-quality carbon fi ber (Photo 1). (Isotropic pitch can be used for producing general-purpose low modulus carbon fi ber.)



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5nm5nm

5μm5μm

Isotropic pitch Mesophase pitch

Section Section

C-Chem NGF

Coal tar

Distillation

De-QI (U process)

Heat treatment, distillation

Impregnated pitch

Hydrogenation

Thermal polymerization

High-precision distillation

Filtration

Spinning material pitch

*1

*2

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 substances6-membered ring: Chemical material having 6 atoms bonded in a ring state

Photo 1 Change of Carbon Fiber Structures due to Difference of Material Pitch

Fig. 2 Raw Material Modifi cation Process









Pitch modifi ed 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 fi bers having a diameter of about 10 µm (one-tenth of a hair), the pitch crystals are aligned longitudinally by means of die (nozzle) confi guration 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 sec-tional structure (Fig. 4). Only three companies in the world can produce high-strength and high-modulus carbon fiber employing mesophase pitch as the spinning material. Among them, only NGF can produce pitch-based carbon fi ber hav-ing a crystal orientation controlled so as not to al-low cross-sectional cracking of the fi ber, 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-

Control of Crystals in the Spinning Process to Further Improve Strength and Modulus by Heat Treatment



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Component separation, hydrogenation treatment, thermal polymerization, refining filtration

Spinning

Infusibilization treatment

Carbonization

Graphitization

Surface treatment

Product

Spinning material pitch

Pitch fiber

Infusibilized fiber

Carbon fiber

Graphite fiber

Raw material pitch modification

(Fig. 2)

Oxidation and sizing treatment

～3,000℃ nitrogen gas or argon gas

～1,400℃ nitrogen gas

Gaseous phase oxidation @100～400℃

Melt spinning @300～400℃

Fig. 3 Production Process for Pitch-based Carbon Fiber Fig. 4 Crystal Orientation of Mesophase Pitch in Spinning Process

Photo 2 Carbon Fiber with Cross-sectional Cracking

Fiber cross section cracking leads to the quality defect.

The pitch crystals are aligned lon-gitudinally by means of die (nozzle) conf igurat ion and the st irr ing method and physical properties are optimized by controlling the method used to align and laminate the crystal layers.









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 treat-ment 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 fi ber thus manufactured is

most commonly applied in concert with resin, the fi ber 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 fi bers with a diameter of 10 µm (Photo 3). To meet the need for lighter weight, NGF has initiated the industrial production of carbon fiber mate-rial manufactured by bundling 400 fi bers with the world’s fi nest diameter of 7 µm and modulus simi-lar to that of 10 µm-diameter carbon fi bers.



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Photo 3 Carbon Fiber Production Line









In order to meet various applications, NGF sup-plies a variety of pitch-based carbon fi bers of dif-ferent moduli, such as yarn, fabric, and prepreg manufactured by impregnating thermosetting resins (Photo 4). Extensive application develop-ment of carbon fi ber, 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

New Market Development Capitalizing on the Superior Physical Properties peculiar to Pitch-based Carbon Fibers

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 fi shing rods. On the other hand, high-modulus carbon fiber (600 GPa or more), which is diffi cult to produce for PAN-based carbon fiber, is used in various rolls for printing and fi lm production, in the arms of liquid crystal

and semiconductor transfer robots and in con-struction reinforcing members by fully capitalizing on such performances as zero thermal deforma-tion, 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 fi elds with high expectations for expanded application growth include the shafts of machine



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Golf club(Courtesy: SRI Sports)

Reinforcing members used in construction

Rolls for printing machine

Photo 4 High-performance Pitch-based Carbon Fiber Products Photo 5 Examples of Conventional Applications

GRANOC® prepreg GRANOC® cloth GRANOC® yarn









tool motors, and robot arms and beams. In par-ticular, the long beams of large-capacity machine tools are heavy and suffer reduced fabrication ac-curacy due to vibration. Thus, fabrication accuracy improves with the adoption of lightweight carbon fi ber-reinforced plastic with high vibration damping capacity (Photo 6).

High modulus carbon fiber has high thermal conductivity (ease of thermal conduction), and its coeffi cient of thermal expansion can be minimized to zero by composite use with other materials (Figs.

5 and 6). Due to these characteristic performanc-es, pitch-based carbon fi ber has recently been ad-opted for the heat radiation members of electronic equipment, solar panel members, and the antenna members of artificial satellites operating in space under temperature fl uctuations 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

0 200 400 600 800 1000

Thermal conductivity (W/mk)

70

200

400

500

70

10

320

1,000

Magnesium alloy

Aluminum alloy

Copper

PAN (high modulus grade)

PAN (regular grade)

XN80 (NGF)

XN90 (NGF)

XN100 (NGF)

Carbonfiber

0-10 10 20 300 40 50 200

Metal

Ceramic ResinCarbonCarbon

fiberfiberCarbon

fiber

Coefficient of thermal expansion of carbon fiber: Small absolute value, negative value

Coefficient of thermal expansion × 10-6 °C -1

Fig. 5 Thermal Conductivity of Pitch-based Carbon Fiber Fig. 6 Coeffi cient of Thermal Expansion of Various Materials



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Photo 6 Automobile Panel Fabrication Equipment

When lightweight carbon fiber is adopted, the self weight reduces and the vibration damping perfor-mance during operation is improved.









in any other materials in practical use. NGF is pro-moting the market development of these fi bers in two directions.

One is to replace metallic materials with carbon fi ber in industrial applications. With energy savings being called for in diverse industrial fields, light-weight pitch-based carbon fiber with high rigidity can contribute to the reduction of weight in pro-duction equipment and devices.

Another direction of market development is ap-plication development in the consumer product field, which capitalizes on such performances of pitch-based carbon fi ber as high thermal conduc-

tivity and zero C.T.E. (coeffi cient of thermal expan-sion). For example, with the growing need for high-er functionality and higher density in electronic equipment devices, carbon fi ber is seen to have a high heat-radiation capacity, which is required of high thermal-conducting electronic materials ca-pable 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 mar-ket development for high-performance pitch-based carbon fi ber.

Photo 7 Artifi cial Satellite Antenna

Because of the complicated inner confi guration re-quired to send waves with pinpoint accuracy to a specifi ed area, zero thermal deformation is inevitably necessary as a member performance value.

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More about Nippon Steel on the website: http://www.nsc.co.jp/en

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