Low pressure process for continuous fiber reinforced polyamic acid resin matrix composite laminates

A low pressure process for preparing a consolidated polyimide composite laminate comprising:

• a. forming prepreg plies from unidirectional fibers and a polyamic acid resin solution;
• b. placing molding stops at the sides of a matched metal mold set wherein one of the mold halves has a cavity therein;
• c. cutting the prepreg plies shorter than the length of the mold in an in-plane lateral direction;
• d. stacking the cut prepreg plies between the molding stops to a height which is higher than the molding stops wherein at least 2 prepreg plies are consecutively stacked in one direction in forming a cross-ply laminate;
• e. compressing the stacked prepreg plies to the height of the molding stops;
• f. heating the compressed prepreg plies to a temperature of about 150.degree. C. to 250.degree. C. for about 0.25 to 1.50 hours to start an imidization reaction and to allow volatiles to escape;
• g. removing the molding stops from the mold;
• h. increasing the temperature to a temperature of about 275.degree. C. to 370.degree. C. and applying a pressure to the prepreg plies of about 0 p.s.i. to 500 p.s.i. for about 0.25 to 1.50 hours to complete the imidization reaction and to enhance resin flow throughout the matrix;
• and
• i. further heating while applying a pressure of about 100 p.s.i. to 600 p.s.i. to the prepreg plies for about 0.25 to 1.50 hours to form a consolidated polyimide composite laminate.