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This part of ISO 7391 establishes a system of designation for polycarbonate thermoplastic material, which may be used as the basis for specifications. The types of polycarbonate plastic are differentiated from each other by a classification system based on appropriate levels of the designatory properties a) viscosity number; b) melt volume-flow rate; c) Charpy impact strength; and on information about the intended application and/or method of processing, important properties, additives, colorants, fillers and reinforcing materials. This part of ISO 7391 is applicable to thermoplastic polyesters of carbonic acid and aromatic dihydroxy compounds. The polyester may be a homopolymer, a copolymer or a mixture of the two. It applies to materials ready for normal use in the form of powder, granules or pellets and to materials unmodified or modified by colorants, additives, fillers, etc. It is not intended to imply that materials having the same designation give necessarily the same performance. This part of ISO 7391 does not provide engineering data, performance data or data on processing conditions which may be required to specify a material for a particular application and/or method of processing. If such additional properties are required, they shall be determined in accordance with the test methods specified in Part 2 of this International Standard, if suitable. In order to specify a thermoplastic material for a particular application or to ensure reproducible processing, additional requirements may be given in data block 5 (see 3.1). processing, additional requirements may be given in data block 5 (see 3.1).