Compositions – Electrically conductive or emissive compositions – Elemental carbon containing
Reexamination Certificate
1999-11-16
2001-04-24
Buttner, David J. (Department: 1712)
Compositions
Electrically conductive or emissive compositions
Elemental carbon containing
C524S505000, C524S538000, C523S351000, C525S397000
Reexamination Certificate
active
06221283
ABSTRACT:
FEDERALLY SPONSORED RESEARCH
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of making a conductive thermoplastic composition containing at least one dispersed phase polymer with a continuous phase polymer and at least one conductivity imparting agent wherein the bulk resistivity of the composition is at least partially determined by the particle size of the dispersed phase within the continuous phase. The thermoplastic composition preferably comprises a compatibilized blend of at least one polyphenylene ether resin, at least one polyamide resin, and at least one conductivity imparting agent, and optionally, one or more of impact modifiers, stabilizers, antioxidants, lubricants, and fillers. In one embodiment, this invention provides a method of controlling the bulk resistivity of a compatibilized blend of at least one polyphenylene ether resin and at least one polyamide resin, wherein the polyphenylene ether resin is a dispersed phase and wherein the method comprises varying the compatibilizing agent content and/or the level of level of copolymers between the polyphenylene ether resin and polyamide resin and/or the dispersed phase particle size.
The invention also relates to the conductive compositions of the method and articles made from the conductive compositions of the method.
2. Brief Description of the Related Art
Automobile manufacturers have for a number of years investigated the use of plastic body panels to replace stamped sheet metal panels. The motivation for the replacement has included weight reduction in addition to enhanced performance through elimination of dings and corrosion of the panels.
In the automotive assembly process, it is often desirable to assemble plastic panels and metal body panels onto the automotive frame in the same operation. An undercoating is subsequently applied through an electro-deposition process to afford corrosion resistance to the metal components. Subsequent to this process, paint is applied through an electrostatic process to insure a high transfer rate of the paint onto the panels. Each of these processes involves a baking step at elevated temperatures, often in excess of 180° C. and the high temperatures have been partly responsible for the limited success of plastics in these applications.
Plastic components are in general not sufficiently conductive for electrostatic paint processes. It is known in the art, however, that conductive additives can be formulated into the resin composition to increase the conductivity of the resin. These conductive additives are generally expensive, difficult to handle, and often adversely affect other critical properties such as ductility. Optimization of the quantity of conductive additive necessary for a particular application is desirable to avoid these and other adverse affects.
It is therefore apparent that a need continues to exist for methods of making conductive thermoplastic compositions.
SUMMARY OF THE INVENTION
The instant invention provides a method for making conductive thermoplastic compositions containing at least two polymers, a dispersed phase polymer and a continuous phase polymer, and at least one conductivity imparting agent wherein the bulk resistivity of the compositions is controlled at least in part, by varying the particle size of the dispersed phase polymer within the continuous phase polymer. The resin composition preferably comprises a compatibilized blend of at least one polyphenylene ether resin and at least one polyamide resin wherein the polyphenylene ether resin is a dispersed phase. The resin composition also comprises a conductivity impacting agent comprising either (a) a conductive carbon black powder present in an amount between about 0.5% by weight and about 3.0% by weight based on the entire weight of the resin composition, (b) a conductive carbon fibril present in an amount between about 0.2% by weight and about 3.0% by weight based on the entire weight of the resin composition, or (c) a combination of a conductive carbon black powder and a conductive carbon fibril present in a combined amount between about 0.2% by weight and about 3.0% by weight based on the entire weight of the resin composition wherein the conductivity impacting agent is present predominantly in the polyamide resin.
DETAILED DESCRIPTION OF THE INVENTION
The thermoplastic compositions of the present invention are made from resins able to withstand paint process oven temperatures. Useful resins include various polymer blends and alloys such as, for example, polycarbonate containing blends and alloys and polyphenylene ether containing blends and alloys. Examples of such polymer blends and alloys include polycarbonate/ABS, polyphenylene ether/polyester, polyphenylene ether/polyphenylene sulfide, and polyphenylene ether/polyamide. The resin composition is preferably a resin composition comprising a compatibilized blend of a polyphenylene ether resin and a polyamide resin.
Compatibilized blends of polyphenylene ether resin and polyamide resin are generally known in the art. These blends are typically made through reactive compounding techniques involving addition of a compatibilizing agent to compositions containing polyphenylene ether resin and polyamide resin. The compatibilizing agent is thought to result in reaction products between the polyphenylene ether resin and a polyamide resin and that these reaction products improve the compatibility between the polyphenylene ether resin and polyamide resin. The reaction products are believed to play a role in the reduction and stabilization of the dispersed phase particle size, key indices of compatibility. The improved compatibility results in enhanced physical properties such as, for example, increased ductility. Illustrative compatibilizing agents for blends of polyphenylene ether resin and polyamide resin include citric acid, maleic anhydride, fumaric acid, malic acid as well as various derivatives of the foregoing.
The polyphenylene ether resins (hereinafter referred to as “PPE”) useful in the present invention include all known polyphenylene ether resins. Preferable resins include poly(2,6-dimethylphenylene ether) as well as the copolymer resins of 2,6-dimethylphenol and 2,3,6-trimethylphenol. In compositions wherein high heat resistance is desired to accommodate, for example, paint cure ovens, PPE having a glass transition temperature (i.e. Tg) higher than the oven temperature are desirable as is use of a polyamide resin having a melting point (i.e. Tm) greater than the oven temperature. The intrinsic viscosity is typically between about 0.20 and about 0.60 dl/g as measured in chloroform at 25° C. Other variations in the resins are also useful based upon similar principles.
The ratio of PPE to polyamide resin can vary widely but is preferably adjusted so that the polyamide resin remains the continuous phase. Preferably the polyamide is at least about 40% by weight of the total resin composition. Increasing the level of the polyamide results in enhanced ductility and flow and is often preferred. The resin compositions may contain more than one type of polyamide resin such as a blend of nylon 6 and nylon 6,6. When a mixture of nylon 6 and nylon 6,6 is used, it is often preferred to have a limited amount of nylon 6 in order to maximize the heat resistance of the compatibilized blend of PPE and polyamide resins. Minor amounts of nylon 6 are often useful at improving certain physical properties, for example, ductility. Moreover, the amine to acid endgroup ratio of the polyamide resin or mixture of polyamide resins may also be varied as well as the relative viscosity of the polyamide contained within the resin composition. Such variations are useful for fine-tuning certain physical properties desired in the final composition. These and other variations of the polyamide and the polyphenylene ether resins do not detract from the present invention.
The compositions of the invention may additionally contain various property modifiers such as elastomers for ductility enhancement. Useful elastom
Dharmarajan Raja
Hossan Robert
Keulen Jan P H
Koevoets Christiaan H.
Majumdar Biswaroop
Buttner David J.
General Electric Company
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