By Tom Colella, Engineering Manager
The demise of polystyrene capacitors began in 1990 when the suppliers felt that thin-sheet capacitor dielectric material was too much effort for such a small part of their product line. At the time, the majority of their effort was manufacturing Styrofoam cups, containers and other materials. Capacitor manufacturers placed large onetime orders to satisfy the demand for this precision-type of dielectric material. Now that the worldwide stock has been diminished or depleted, what are the options?
Polystyrene was developed by a German apothecary in 1839 from the resin of the American sweet gum tree. After the tree’s distillation, it left an oily substance that came to be known as Styrol. After a few days, it thickened into a jelly called Styroloxyd. Eighty years later, it was realized that heating this Styrol started a chain reaction that caused macromolecules to form. Further development led to the substance we now call polystyrene.
A company in Germany began manufacturing polystyrene in 1931 in pellet form. In 1937, Dow Chemical introduced polystyrene products into the United States as an insulating material and developed a synthetic version. Around the time of World War II, polystyrene was combined with isobutylene, and the result was foam polystyrene. In the early to mid-1950s, insulating sheet material was developed and, thus, the use in film and foil capacitor designs was introduced.
Polystyrene as a Capacitor Dielectric
The polystyrene capacitor was the device of choice for precision-tuned circuits due to the extreme stability in the 0°C thru +50°C range as well as long-term stability. The major drawback of this dielectric was the maximum operating temperature of +85°C, the glass transition temperature of ~95°C, and a fluid temperature of +100°C, making applications for this device limited. This type of capacitor was only available as a film and foil construction. There was an attempt to develop a metallized version of polystyrene. However, due to the low melting point of the dielectric, it was unsuccessful.
Where Do We Go From Here?
Polystyrene film capacitors are gone. But, there are alternatives. First, there is a combination film capacitor that takes the temperature coefficient of two different dielectrics to provide a near 0% change between 0°C thru +50°C. Electrocube’s 730D Series capacitor is a metallized capacitor and the size is extremely small in comparison to the original polystyrene film and foil design.
A second alternative is the Polystyrene Substitute Combination Dielectric (PSCD) film-foil series which is a hybrid capacitor that is stable in the 0°C to +50°C range and similar in size to the original polystyrene designs.
Finally, a third alternate capacitor is the polypropylene and foil capacitor – Electrocube’s 950D series – which is relatively stable at +25°C, has a high insulation resistance and low dissipation factor. The size is comparable to the original polystyrene and foil design.
Depending on the application, environment and specifications, there are viable – even better – alternatives for replacing polystyrene capacitors. Many customers have already successfully made the move. Contact Electrocube’s engineering department to discuss particular applications and find new solutions.