Thermoset Rigid Laminates
Thermoset rigid laminates are composite materials in the "plastics" family. Generally speaking, plastic materials can be classified as either thermoset or thermoplastic. By definition, thermoset materials maintain their dimensional stability at elevated temperatures while most thermoplastic material melt (or lose dimensional stability) at elevated temperatures.
Because thermoset materials maintain their dimensional stability at elevated temperatures, these materials have been used in electrical insulating applications since their discovery. Electrical equipment tends to generate a tremendous amount of heat due to the concentration of moving electrons in a small space. The passage of electricity through electrical wires creates thermal energy or heat due to the resistance offered by copper or aluminum to the passage of electrons through their valence structures. Thus, the materials that insulate the copper or aluminum conductors must be able to withstand the thermal energy created without deforming or melting. For this reason, thermoset plastics find common application in electrical equipment and other applications where dimensional stability at elevated temperatures is required.
Themoset rigid laminates are composite materials. By definition, composite materials consist of two or more materials. In the case of most thermoset rigid laminates, the primary materials include a substrate or base material such a paper, cotton cloth, or glass cloth along with a resin or adhesive such as epoxy, melamine, or silicone. To make a thermoset laminate, the base material is coated with the adhesive so that layers of material can be pressed into sheet form under heat and pressure.
A simple formula for understanding the construction of thermoset laminates is:
The following chart provides an example of the construction of several thermoset laminate materials. Due to the use of these materials in electrical equipment, the National Electric Manufacturers Association or NEMA has established the industry standards for the minimum test values by property for each material. Thermoset materials are commonly referenced using the NEMA grade designation.
|Substrate or Base Material||Resin or Adhesive||Final Composite|
|Paper||Phenolic||Paper Phenolic, NEMA Grade XXX|
|Cotton Cloth||Phenolic||Canvas Phenolic, NEMA Grade CE|
|Glass Cloth||Epoxy||Glass Epoxy, NEMA Grade G-10/FR4|
Glass Polyester, NEMA GPO-3