Page 323 - Engineering Plastics Handbook

Polyamide-imide (PAI) 281

TABLE 12.2 Diluents for PAI Polymer Solutions
Diluent Percent of total solvent (maximum)
Aromatic hydrocarbons 40–50
Ethyl acetate 40–50
Acetone 60
Cyclohexanone 80

toluene are often employed. Because solution viscosity is such an impor-
tant variable for formulators and applicators, different molecular weights
of polyamide-imide powders are available. The starting solution viscos-
ity will also depend on the percent polymer solids.

Torlon AI-10 polymer solutions
In Fig. 12.21, the solution viscosity is illustrated for Torlon AI-10 dissolved
in NMP at various percent solids and measured at different temperatures.
NMP is most commonly used due to its high solvency power, its low odor,
and a relatively low level of toxicity. Diluents may be added up to the level
provided in Table 12.2 to lower viscosity and formulation cost.
Alternatively, Torlon AI-10 powder may be formulated using a mixed
organic aqueous system, where water is the major solvent component, as
shown in Table 12.3 [26]. AI-10 is approximately 50% imidized along the
polymer backbone. The remaining amic acid groups can form hydrophilic
ammonium complexes, allowing a high portion of water in the formulation.
Alternatively, Torlon AI-30 and AI-50 are amenable to aqueous systems
when formulated with a tertiary amine Table 12.4 [27]. Due to the very
low degree of imidization compared to AI-10 or polyamide-imides pro-
duced in the isocyanate process, these polymers can form stable, low-
viscosity solutions in water at low to moderate polymer solids. Generally
the polymer solids are 5 to 15%, depending on the polyamide-imide used,
and provide solutions with a viscosity in the range of 50 to 2000 cP.

Injection molding
By using standard injection-molding equipment and the right set points,
polyamide-imide molding resins may be routinely processed. A short

TABLE 12.3 Torlon AI-10 in
Mixed Organic Aqueous System

Torlon AI-10 15%
Water 50%
Diethylaminoethanol 4%
Triethylamine 2%
Furfuryl alcohol 18%
N-methylpyrrolidone 10%