Page 327 - Engineering Plastics Handbook

Polyamide-imide (PAI) 285

TABLE 12.8 Polyimide-imide Cure Schedules
Coatings
Torlon AI-10
( 25 µm, 25% in NMP)

Time, min Temperature, °C Temperature, °F
60 149 300
15 260 500
5 315 600
Molded parts

Torlon injection- Parts with max.
molded grades (4203L, cross-sectional
4301, 4275, 4435, thickness of
5030,7130) [29] 0.3 in (7.6 mm)
Days Temperature, °C Temperature, °F
1 149 300
1 191 375
1 204 400
1 218 425
1 232 450
1 243 470
1 252 485
10 260 500

Curing process
Polyamide-imide polymers require a thermal cure cycle to achieve max-
imum properties after they have been formed into the final article,
whether it is a coating or injection-molded part. Polyamide-imides have
relatively low molecular weight to facilitate melt processing or coating
applications. The articles themselves, before cure, are actually weak,
brittle, and poor in chemical and wear resistance, and they do not have
optimum thermal resistance. The curing process involves heating the
polyamide-imide material in a batch process such as a forced-air oven;
or, in the case of coatings, they may cured in a continuous process due
to the shorter time scale involved. The cure cycle is dependent on the
thickness of the polyamide-imide article and its geometry. For parts the
temperature cycle is ramped slowly upward to allow stress relaxation and
diffusion of moisture, created in the curing reactions, out of the part.
Different cure cycles may be required, depending on the application
requirements.
During the curing process, the molecular weight of the polymer
increases by chain extension, any remaining amic acids will imidize,
and cross-links are created between the polymer chains. These reactions