GB/T 5019.4-2009 is the fourth part of the "Mica-based Insulation Materials" series of standards, focusing on mica paper. The standard stipulates the classification, technical requirements, test methods, inspection rules and labels, Encasement and other content of mica paper, and clearly stipulates the appearance, thickness, density, electrical insulation performance, Mechanical Property and other indicators of mica paper. Provide a normative basis for the production, mass inspection and acceptance of mica paper to ensure the quality of its insulation application.