Polyester enamels, insulation

Dual Constructions. In addition to the "basic" magnet wire insulations in which the conductor wire is coated with a single enamel, there are a number of cases where two different enamels are used one overcoated over the other. Examples include polyurethane-base insulation overcoated with poly(vinyl butyral) or with nylon, or polyester-base insulation overcoated with nylon or with polyamide imide. 

Polyurethane Enamels. Small volumes of this enamel type are used in applications for which the temperature does not rise above approximately 105 C. These enamels are made from hydroxyl-bearing polyesters and blocked isocyanates. During the heating cycle in the enameling process the isocyanates become unblocked and react with hydroxyl groups of the polyesters to form a cross-linked polyurethane film. Wires so insulated can be directly soldered, without prior removal of the polyurethane insulation. 

Wire enameled with polyester imides can be used for applications in which it is occasionally exposed to temperatures in the 155-180 C range. One of the most demanding environments is in hermetic motors used in refrigerators where the insulating enamel film is exposed at elevated temperatures to oil and refrigerants under pressure. 

Polyamide Imide Enamels. Aromatic polyamide imide insulations are made from aromatic acids and aromatic diamines. The polyamide imide polymers are primarily present in the form of polyamic acids in the Af-methyIpyrrolidone solutions. During the enameling process the polyamic acids undergo imidization and become essentially fully imidized. Whereas the polyester and polyester imide enamels contain cresylic acids as the major solvent, the polyamide imide enamels are mainly formulated with A/-methylpyrrolidone as solvent. 

Miscellaneous Extrusion-Applied Polymers. As mentioned earlier, there is a tendency to develop solventless magnet wire enamel formulations, and extrudable polymer systems would fulfill that requirement. There have been reports about extrusion of thin coatings of polyesters over copper wire. At this point, the state of the art allows extrusion of thin insulating films only with thermoplastic materials. The reliable extrusion of uniform and concentric insulating films of approximately 0.001-0.002 in. wall thickness is already an improvement over the more traditional extrusions of polyethylene, poly(vinyl chloride), and several fluoropolymers in much greater wall thicknesses. Because cross-linked insulation is ultimately required for most magnet wire applications, further materials development needs to be done to provide polymer compositions that are both extrudable as thin films and can be cross-linked in an economical process suitable for large-scale industrial application. 

Red insulating enamel (MIL-E-22118) BPA fumarate polyester (vinyl toluene ... 

Alkyd resins are often used in molding electrical or electronic articles. Components include switches, housings, connector mountings, and other insulated parts. Straight and modified alkyd resins are used in the manufacture of enamels and other finishes. They are also used in printing inks and as adhesives to bond glass fabric and other materials for polyester laminates. Surface coating is a major application for alkyd resins. 

Although an early synthetic plastic derived from cellulose was introduced in Europe in the nineteenth century, it was not until the twentieth century that the modem plastics industry was bom, with the introduction of Bakelite, which found apphcations in the manufacture of telephones, phonograph records, and a variety of varnishes and enamels. Thermoplastics, such as polyethylene, polystyrene, and polyester, can be heated and molded, and bUhons of pounds of them are produced in the United States annually. Polyethylene, a low-weight, flexible material, has many applications, including packj ing, electrical insulation, housewares, and toys. Polystyrene has found uses as an electrical insulator and, because of its clarity, in plastic optical components. Polyethylene terephthalate (PET) is an important polyester, with applications in fibers and plastic bottles. Polyvinyl chloride (PVG) is one of the most massively manufec-tured synthetic polymers. Its early apphcations were for raincoats, umbrellas, and shower cmtains, but it later found uses in pipe fittings, automotive parts, and shoe soles. 

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