Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-10-26
2002-02-05
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S495000
Reexamination Certificate
active
06344513
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a resin composition giving a molded article having small shrinkage anisotropy, resistant to accumulation of static charge and exhibiting excellent static charge dissipation property to quickly attenuate the electrostatic voltage in case of accumulating static charge and a transportation jig made thereof, especially a silicon wafer carrier.
BACKGROUND ARTS
It is known that a thermoplastic resin composition can be imparted with antistaticity by compounding a low-molecular antistatic agent such as an alkylsulfonic acid phosphonium salt or compounding a high-polymer antistatic agent such as a polyether ester amide. Although the initial antistatic effect is high in the case of compounding a low-molecular antistatic agent, the performance is lowered by the variation of environment and the antistaticity is eliminated by wiping or washing. On the other hand, the application of the process for compounding a high-polymer antistatic agent to an engineering plastic such as polyester often causes insufficient heat-resistance and melt stability and it is difficult to attain a saturated static voltage of 1 KV or below and a half-life period of static voltage of 10 sec or shorter (impressed voltage: 10 KV) simply by increasing the compounding amount of the agent. Even if such performance can be achieved, the other physical properties are deteriorated and a problem arises in productivity.
Another known method for imparting a thermoplastic resin with antistaticity is the compounding of carbon fiber (JP-A 8-88266). The resistivity and saturated static voltage can be decreased by increasing the compounding amount of carbon fiber in the case of exclusive compounding of carbon fiber, however, it is difficult to decrease the half-life period of static voltage to 10 seconds or shorter (impressed voltage: 10 KV).
Satisfactory results are attained on the above-mentioned characteristics by compounding a carbon fiber or a stainless steel fiber in combination with a conductive filler or powder having extremely small aspect ratio, however, the composition is unsuitable as a transportation jig in the field of electronics since conductive powder dust is generated in the molding of the composition. Furthermore, the control of the surface resistivity of antistatic level is difficult in the system.
DISCLOSURE OF THE INVENTION
When a silicon wafer carrier is formed with a resin composition produced by simply adding a high-polymer antistatic agent to a thermoplastic resin, sufficient antistatic performance cannot be attained in spite of desirable results comprising suppressed lowering of antistaticity in washing stage and low contamination of the silicon wafer with dissolved metal.
The integration degree of integrated circuit is increasing day by day to decrease the particle size causing static hazard on a silicon wafer for integrated circuit and, accordingly, the present antistatic performance (surface resistivity: 10
12
to 10
13
&OHgr;) became insufficient.
When a resin composition compounded with a low-molecular antistatic agent is used as a transportation jig in electronic field, a large amount of dissolved metal is generated in washing stage, etc., and the metal is attached to the silicon wafer to cause the crystal defect and the deterioration of electric characteristics of the device.
A thermoplastic resin compounded with carbon fiber (which may be abbreviated as CF hereinafter) cannot cope with varied forms of the transportation jigs and it is sometimes difficult, dependent on the form of the transportation jig, to attain stable electric conductivity even by mixing a large amount of CF, supposedly owing to the poor dispersibility of CF. Furthermore, the compounding of CF results in the generation of shrinkage anisotropy of the molded article caused by the orientation of CF and is unsuitable for a transportation jig required to have accurate dimensions.
A resin compounded with a carbon black, e.g. with 7% by weight of ketjenblack not only generates large amount of conductive powder dust but also causes the remarkable deterioration of mechanical properties and the use of the composition as a transportation jig is impossible.
The object of the present invention is to solve the above-mentioned problems of conventional techniques.
A concrete object of the present invention is to provide a resin composition having desirable and permanent antistaticity, exhibiting excellent static charge dissipating performance and having extremely small variations of antistatic properties (saturated static voltage and half-life period of static voltage) on the surface of a molded article.
Another object of the present invention is to provide a transportation jig for electronic field made of a resin composition having excellent static charge dissipating performance, giving uniform and excellent antistaticity on the surface of a transportation jig and having small shrinkage anisotropy.
Still further objects and advantages of the present invention will become apparent by the following explanation.
The present invention comprises a resin composition produced by compounding (A) 100 parts by weight of a thermoplastic resin with (B) 1 to 30 parts by weight of a carbon fiber having a diameter of 1 nm to 1 &mgr;m, a length of 1 &mgr;m to 3 mm and a volume resistivity of smaller than 1 &OHgr;cm and (C) 5 to 200 parts by weight of an antistatic polymer having a surface resistivity of 10
8
to 10
11
&OHgr; (measured under impressed voltage of 500V), a melting point of 100° C. or above, an apparent melt viscosity of 10 to 1,000 Pa·s at apparent shearing rate of 1,000 sec
−1
at 260° C. and an apparent melt viscosity ratio of the antistatic polymer to the thermoplastic resin of 0.01 to 1.3 under the above condition.
The present invention further comprises a transportation jig for electronic field, especially a silicon wafer carrier, made of the above resin composition.
The transportation jig means, e.g. a silicon wafer carrier, a silicon wafer cassette, a silicon wafer carrier box, a silicon wafer pressing rod, an IC tray, a carrier for transportation of liquid crystal substrate and transportation jig for HDD and LCD-relating parts.
The present invention will be described in detail as follows.
<Thermoplastic Resin>
The thermoplastic resin (A) is, for example, a thermoplastic polyester, a polyolefin, a polycarbonate, an acrylic resin, a thermoplastic polyurethane resin, a polyvinyl chloride, a fluororesin, a polyamide, a polyacetal, a polysulfone, a polyphenylene sulfide, a polyether ether ketone or a styrene resin, preferably a thermoplastic polyester.
The thermoplastic polyester of the thermoplastic resin (A) is composed of a dicarboxylic acid component and a diol component. The dicarboxylic acid component is, for example,, terephthalic acid and 2,6-naphthalenedicarboxylic acid. Examples of the diol component are ethylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol and neopentyl glycol.
The thermoplastic polyester of the thermoplastic resin (A) is preferably polybutylene terephthalate, polypropylene terephthalate, polyethylene terephthalate, polybutylene-2,6-naphthalenedicarboxylate or polyethylene-2,6-naphthalenedicarboxylate, especially preferably polybutylene terephthalate from the viewpoint of high crystallization rate.
The thermoplastic polyester of the thermoplastic resin (A) may be copolymerized with a copolymerization component in an amount of 30 mol % or less, preferably 20 mol % or less and further preferably 10 mol % or less based, on the total dicarboxylic acid component.
Examples of such copolymerization component are aromatic dicarboxylic acid, e.g. terephthalic acid, isophthalic acid and phthalic acid; alkyl-substituted phthalic acids such as methylterephthalic acid and methylisophthalic acid; naphthalenedicarboxylic acids such as 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid and 1,5-naphthalenedicarboxylic acid; diphenyldicarboxylic acids such as 4,4′-diphenyldicarboxylic acid and 3,4′-diphenyldicarboxy
Cain Edward J.
Teijin Limited
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