| 摘要 |
<p>The invention relates to the technology of obtaining aromatic polyimide fibres with high resistance to fire and heat, and can be used to produce articles which are exposed to open flames or are subjected to thermal shock. The technical problem addressed by the invention is that of endowing polyimide fibres with resistance to thermal shock caused by temperatures of 700-800 °C and reliable heat stability when used in a 40-70 % oxygen atmosphere in contact with open flames, as well as uniformity and stability in the fibre characteristics. This problem is solved by subjecting the fibre, which is formed from a solution of polyamide acid in an aprotic amide solvent in an aqueous/organic bath, to a two-stage heat treatment in the presence of 2-4 % by weight of the solvent and acid (phosphoric, boric, hydrochloric, benzoic, nicotinic, iso-nicotinic) until a level of 0.5-1.0 % by weight is attained per fibre; this is done either intermittently, in which case the first stage takes place in an air atmosphere, the second in a vacuum with the temperature being gradually increased from 20 to 350 °C, or in a continuous process, being made to pass through two or more pipes, in which case the first stage takes place in air at a temperature of up to 250 °C and the second in an inert medium at a temperature of between 500 and 650 °C. The polyimide fibres thus obtained have improved physical and thermo-mechanical characteristics and are very stable.</p> |
