Thermal Aging Program 熱老化測試-The materials covered by this program have, in many cases, been investigated with respect to retention of certain critical properties (e.g. dielectric, tensile, impact, and the like) as part of a long-time thermal-aging program conducted in accordance with Underwriters Laboratories Inc. Standard for Polymeric Materials-Long Term Property Evaluations, UL746B. The end-of-life of a material at each test temperature in this program has been assumed to be the time when the value of the critical property had decreased to 50 percent of its original (as received) value. If a material has been investigated under the thermal aging program, the Relative Temperature Index (RTI), in degrees C shown is based on a comparison with a material which has acceptable service experience and correlates numerically with the temperatures above which the material is likely to degrade prematurely. If a material has not been investigated under the thermal aging program, the temperature index shown is based on the generic class of the material. A tabulation of the temperature indices according to generic material class is included in UL746B and is based on past field-test performance and chemical structure.

More than one RTI may be appropriate for a given material depending on the property requirements for a given application. In certain cases, higher temperatures are permitted if so specified by the end-use product standard.