Page 620 - Book Hosokawa Nanoparticle Technology Handbook

APPLICATIONS 40 EVALUATION AND APPLICATIONS OF DISPERSING CNT IN THE POLYMERS
Fig. 40.5a. As the amount of filler fibers increases in resistance as that with conventional electroconductive
the resin, a continuous structure, called electrocon- fillers. It results in less degradation of the composite
ductive path, is formed due to the inter-contacts as properties. In addition, the surface resistance is easy
shown in Fig. 40.5b. to control with less scattering, because its percolation
The electroconductivity does not increase propor- curve as shown in Fig. 40.5 is not steep.
tionally with the filler amount but goes up suddenly. Furthermore, CNT hardly drops off from the com-
This phenomenon is called percolation and the critical posites due to the locking effect caused by its fibrous
filler concentration is defined as the percolation shape. Apart from the semiconductor industry, there
threshold. are a number of applications where the electrostatic
Comparing the percolation curves of CNT and con- problems need to be mediated. CNT seems to have a
ventional electroconductive fillers, it is found that the big potential market if its price becomes reasonable.
electroconductivity of composites is more control- CNT has excellent features in mechanical
lable with CNT than with the conventional fillers, strength and heat conductivity in addition to the
because the percolation tends to take place at the sur- electroconductivity and is expected to be used in
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face resistance around 10 –10 /sq as required by various areas. Its dispersion method should be
the antistatic materials. selected considering the shape and properties of
CNT. It is important to evaluate the dispersion state
with proper parameters.
7. Development of CNT composite resin materials
Although there are still many obstacles to overcome
The most potential application of CNT composites is to in the dispersion technology as well as the price and
avoid electro-static discharge (ESD). The recent quality, CNT composite is regarded as its nearest
advanced semiconductors and hard disks often suffered commercial application on a mass basis.
from the problems caused by the ESD. For reducing the
surface resistance down to the above-mentioned value
to eliminate the electrostatic charging, conventional References
electroconductive carbon fillers have to overcome the
following problems and are required to meet severe [1] S. Iijima: Nature, 354, 56 (1991).
specifications as follows. [2] Nikkei Mechanical, 567, 36 (2001).
Problems: [3] Y. Saito: J. Nanosci. Nanotechnol., 3, 39 (2003).
[4] S. Fan, M.C. Chapline, N.R. Franklin, T.W. Tombler,
• The properties of composites including their flat-
A.M. Cassell and H. Dai: Science, 283, 512 (1999).
ness degrade with an increase in high filler
[5] Y. Nakayama: Ultramicroscopy, 91, 49 (2002).
content.
[6] S. Akita, Y. Nakayama, S. Mizooka, Y. Takano,
• The surface resistance of composites fluctuates T. Okawa, Y. Miyatake, S. Yamanaka, M. Tsuji and
and leads to instability because of the percola- T. Nosaka: Appl. Phys. Lett., 79, 1691 (2001).
tion. [7] A.C. Dillon, K.M. Jones, T.A. Bekkedahl,
• The filler particles drop off from the composites C.H. Kiang, D.S. Bethune and M.H. Heben: Nature,
because of their high concentration and particle 386, 377 (1997).
shape. These free filler particles contaminate the [8] X.B. Wu, O. Chen, J. Lin and K.L. Tan: Int. J. Hydrogen
clean room and adhere onto the devices causing Energy, 25, 261 (2000).
the short circuit of wiring. [9] H. Kato: Plastics, 52 (9), 75 (2001).
[10] H. Palmgren: Rubber Chem. Technol., 48, 462 (1975).
Required specifications: [11] S. Hashizume: Resin/Filler Mixing & Dispersion, 2,
50, Technical Information Institute (2000).
• The surface resistance needs to be controllable [12] H. Takase, Y. Mikata, S. Matsuda and A. Murakami:
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arbitrarily in the range of 10 10 /sq with an Seikei-Kakou, 14(2), 126 (2002).
accuracy of less than 10 1 /sq. [13] H. Takase, M. Furukawa, H. Kishi and A. Murakami:
• There should be no surface resistance fluctuation Seikei-Kakou, 17(1), 50 (2005).
at different locations. [14] H. Takase, Y. Mikata, S. Matsuda and A. Murakami:
• There should be no degradation of composite Seikei-Kakou, 15(1), 80 (2003).
properties. [15] K. Mitsuishi, M. Kawano and N. Nagayama: Seikei-
• The drop-off of fillers needs to be reduced. Kakou, 8(3), 183 (1996).
[16] K. Terashita, K. Miyanami, N. Yabe, K. Izumida:
It is possible to reduce the filler amount down to one- Zairyou, 37(422), 1344 (1988).
tenth with CNT while keeping the same surface [17] ASTM-D-2663-89.

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