Electrical properties of novel heat resistant-fast curing thermosetting resin systems

An increasing number of new applications in the electrical insulation and reinforced plastics industries are specifying a combination of unique properties. These properties include higher heat resistance, improved power factor properties at elevated temperatures at 60 cycles and at higher frequencies, improved ultraviolet resistance and weatherability, low weight loss and good retention of physical properties at temperature and after long time exposure at Class F through greater than Class H types of environments. In addition, the resin systems must have a high degree of reactivity, possess excellent handling characteristics, good compatibility, and must be readily adaptable to automation techniques. This paper describes the unique reactivity of this first series of new heat resistant, electrical grade, fast curing thermosetting resins. Two versions of these resins have been commercialized. One system is referred to as B78-156-40VT, the neat resin cut with 40% vinvltoluene to a 15 poise viscosity. The second system, still referred to as Koppers' B78-156-35VT/5DVB, contains the neat resin cut in 35% vinyltoluene and 5% divinylbenzene. This paper concentrates on highlighting the thermal and electrical properties of these new resin systems. The physical properties of castings, glass mat and glass fabric reinforced laminates at room and elevated temperatures, with and without aging are described. Weight loss data for castings and laminates over 1500 and 3500 hours subjection periods are described for Koppers' Y7000-15 and B78-156-35VT/5DVB systems. Comparison of resistance to thermal degradation over 1000 hour aging periods is shown for the new resins and other resins such as silicones, epoxies, thermosetting acrylics, polybutadienes and other polyester systems. The retention of the physical properties of glass mat reinforced laminates based on V700Ö-15 and B78-156-35VT/5DVB at 180 and 220°C. is shown. Comparison to glass fiber reinforced epoxy laminates is made at these same temperatures. Comprehensive work describing the influence of temperatures from 25°C. through 250°C. on the power factor and dielectric constant properties of these new V7000-15 and B78-156-35VT/ 5DVB resin in cast and laminate form at different frequencies and conditioning sequences is tabulated and plotted. Comparison of these same properties for cycloaliphatic and bisphenol epoxy systems is noted. Complete comparisons of V7000-15 and B78-156-35VT/5DVB resins in cast and laminate form to those of cycloaliphatic and bisphenol epoxy systems in terms of arc resistance, dielectric strength-perpendicular and parallel, power factor, dielectric constant, volume resistivity, surface resistivity, insulation resistance, chemical resistance, weather resistance, ultraviolet resistance and track resistance is emphasized.