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
2001-09-14
2003-03-04
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...
C524S439000, C524S440000, C524S441000
Reexamination Certificate
active
06528572
ABSTRACT:
BACKGROUND OF THE INVENTION
This disclosure relates to conductive polymeric resin compositions.
Articles made from thermoplastic resins are commonly utilized in material-handling and electronic devices such as packaging, chip carriers, printers and photocopier components where electrostatic dissipation is an important requirement. Electrostatic dissipation (hereinafter ESD) is defined as a transfer of electrostatic charge between bodies at different potentials caused by direct contact or induced by an electrostatic field. As electronic devices become smaller and faster, their sensitivity to static discharge increases and the necessity for increased rates of ESD becomes vital.
Conductive fillers such as carbon and graphite fibers are often incorporated into polymeric resins to modify the electrical properties and achieve ESD. The ESD provided by carbon and graphite fiber filled resins is very rapid. However, because of their macroscopic nature, the dissipation of charge is usually not complete. Localized residual charges in excess of 10 volts are generally observed, which can be harmful to electronic devices.
There accordingly remains a need in the art for conductive thermoplastic composition s having rapid ESD, together with more-complete dissipation of electrostatic change.
SUMMARY OF THE INVENTION
A conductive resin composition comprises a polymeric resin; an electrically conductive filler; and an antistatic agent. Such conductive compositions have good electrostatic dissipation properties, i.e.; residual surface voltage of less than about 5 volts, when measured about 8 seconds after application of a charge greater than about 1000 volts. Such compositions can be manufactured using conventional processing techniques and are capable of rapidly dissipating large amounts of surface charge.
DETAILED DESCRIPTION
When conductive fillers such as carbon fibers or carbon black are combined with antistatic agents in polymeric resins, the resulting composition displays an ability to rapidly dissipate any surface charge or voltage. Localized residual charges are also reduced to very low levels of less than 5 volts. The synergistic interaction between carbon fibers or carbon black and antistatic agents also allow for reductions in the quantities of these conductive components, thereby reducing material and production costs.
The polymeric resin used in the conductive compositions may be selected from a wide variety of thermoplastic resins and elastomers, blend of thermoplastic resins, or thermosetting resins. Specific non-limiting examples of thermoplastic resins include polyacetal, polyacrylic, styrene acrylonitrile, acrylonitrile-butadiene-styrene (ABS), polycarbonates, polystyrenes, polyethylene, polypropylenes, polyethylene terephthalate, polybutylene terephthalate, nylons (nylon 6, nylon 6,6, nylon 6,10, nylon 6,12, nylon 11 or nylon 12), polyamideimides, polyarylates, polyurethanes, ethylene propylene diene rubber(EPR), ethylene propylene diene monomer (EPDM), polyarylsulfone, polyethersulfone, polyphenylene sulfide, polyvinyl chloride, polysulfone, polyetherimide, polytetrafluoroethylene, fluorinated ethylene propylene, perfluoroalkoxy, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyetherketone, polyether etherketone, polyether ketone ketone, and mixtures comprising any one of the foregoing thermoplastic resins.
Specific non-limiting examples of blends of thermoplastic resins include acrylonitrile-butadiene-styrene
ylon, polycarbonate/acrylonitrile-butadiene-styrene, acrylonitrile butadiene styrene/polyvinyl chloride, polyphenylene ether/polystyrene, polyphenylene ether
ylon, polysulfone/acrylonitrile-butadiene-styrene, polycarbonate/thermoplastic urethane, polycarbonate/polyethylene terephthalate, polycarbonate/polybutylene terephthalate, thermoplastic elastomer alloys, nylon/elastomers, polyester/elastomers, polyethylene terephthalate/polybutylene terephthalate, acetal/elastomer, styrene-maleicanhydride/acrylonitrile-butadiene-styrene, polyether etherketone/polyethersulfone, polyethylene
ylon, polyethylene/polyacetal, and mixtures comprising any one of the foregoing blends of thermoplastic resins.
Specific non-limiting examples of polymeric thermosetting materials include polyurethanes, natural rubber, synthetic rubber, epoxy, phenolic, polyesters, polyamides, silicones, and mixtures comprising any one of the foregoing thermosetting resins. Blends of thermosetting resins, as well as blends of thermoplastic resins with thermosetting resins can also be utilized.
The polymeric resin or resin blend is generally used in amounts greater than or equal to about 10 weight percent (wt %), preferably greater or equal to about 30 wt %, more preferably greater than or equal to about 40 wt % of the total composition. The polymeric resins are furthermore generally used in amounts less than or equal to about 99 weight percent wt %, preferably less than or equal to about 85 wt %, more preferably less than or equal to about 55 wt % of the total weight of the composition.
The carbon fibers employed in the conductive compositions may be a conductive carbon fiber that is known for use in modifying the ESD properties of polymeric resins. Various types of conductive carbon fibers known in the art, and are classified according to their diameter, morphology, and degree of graphitization (morphology and degree of graphitization being interrelated) may also be used. For example, carbon fibers having diameters down to about 3 micrometers, graphene ribbons parallel to the fiber axis (in radial, planar, or circumferential arrangements) and produced commercially by pyrolysis of organic precursors such as phenolics, polyacrylonitrile (PAN), or pitch may be used. The carbon fibers are generally chopped having an initial length (before compounding) from about (0.1 to about 2.0 inches.) Unchopped carbon fibers may also be used. Fibers may be sized or unsized. Sized fibers are conventionally coated on at least a portion of their surfaces with a sizing composition selected for compatibility with the polymeric thermoplastic matrix material. The sizing composition facilitates wet-out and wet-through of the matrix material upon the fiber strands and assists attaining desired physical properties in the composite. Such fibers are sold under a variety of trade names, including but not limited to Fortafil CA and Fortafil CM available from Fortafil Fibers, Inc., Zoltek HT available from Zoltek Corporation, Toray available from Toray Industries Inc., and Grafil available from Mitsubishi.
Carbon fibers are generally used in amounts greater than or equal to about 2 wt %, preferably greater or equal to about 4 wt %, more preferably greater than or equal to about 6 wt % of the total composition. The carbon fibers are furthermore generally used in amounts less than or equal to about 40 wt %, preferably less than or equal to about 25 wt %, more preferably less than or equal to about 10 wt % of the total weight of the composition
Small graphitic or partially graphitic carbon fibers, also referred to as vapor grown carbon fibers (VGCF), having diameters of about 3.5 to about 500 nanometers (nm) and an aspect ratio greater than or equal to about 5 may be used. When VGCF are used, diameters of about 3.5 to about 70 nm are preferred, with diameters of about 3.5 to about 50 nm being more preferred. It is also preferable to h ave average aspect ratios greater than or equal to about 100 and more preferably greater than or equal to about 1000. Representative VGCF are described in, for example, U.S. Pat. Nos. 4,565,684 and 5,024,818 to Tibbetts et al.; U.S. Pat. No. 4,572,813 to Arakawa; U.S. Pat. Nos. 4,663,230 and 5,165,909 to Tennent; U.S. Pat. No. 4,816,289 to Komatsu et al.; U.S. Pat. No. 4,876,078 to Arakawa et al.; U.S. Pat. No. 5,589,152 to Tennent et al.; and U.S. Pat. No. 5,591,382 to Nahass et al.
VGCF are generally used in amounts greater than or equal to about 0.25 wt %, preferably greater or equal to about 0.5 wt %, more preferably greater than or equal to about 1 wt % of the total composition
Balfour Kim G.
Patel Niraj C.
Cain Edward J.
General Electric Company
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