Polyamide-imide compression molding

Polyamide-imides enjoy, as the name suggests, a positive synergy of properties from both polyamides and poljdmides, such as flexibility, melt processability, elongation, dimensional stability, and toughness. Polyamide-imide polymers can be processed into a wide variety of forms, from injection- or compression-molded parts and ingots to coatings, films, fibers, and adhesives. Generally these articles reach their maximum properties with a subsequent thermal cure process. 

Due to the specialty nature and niche applications for polyamide-imide parts, many of these low-volume pieces are machined from preformed stock shapes. Toray, based in Japan, is producer of polyamide-imide resin that it converts to polyamide-imide parts and stock shapes, largely for the Asian markets. In the United States, Quadrant EPP supplies extruded Torlon polyamide-imide rod and plate stock as well as compression-molded ingots and shapes. Drake Plastics extrudes custom profiles in addition to standard shapes from Torlon resins. Injection-molded Torlon polyamide-imide stock shapes are available through Parkway Products. 

Polyamide-imide powders may be compression-molded into standard shapes and geometries. This operation produces parts that may be used as is or further machined into intricate parts. The mechanical properties of compression-molded parts are somewhat less than those of the corresponding injection-molded grades. The tjtpical compression-molding operation uses a fine particle size of polyamide-imide powder. The powder material should have particles which are 100% less than 150 pm and 95% less than 75 pm. Polyamide-imide powders may also be used as an additive or adhesive binder in the sintering of other shapes based on PTFE powders, metal powders, or abrasive materials. 

One example of the compression-molding process is outlined in Table 12.7 [28]. Polyamide-imide powder particles with a maximum particle size of 150 jm and a median particle size in the range of 10 to 50 pm are preheated in an oven for 1 to 24 h at 260 to 316°C. The purpose is to increase molecular weight and complete the imidization processes, both of which create water and can lead to voids in the compression-molded article. The compression-molding schedule depends on the size and geometry of the mold. A pressure-molding schedule for a 14.0 cm X 1.6 cm disk mold is shown in Table 12.8, where the mold temperature is set in the range of 315 to 329°C. 

Polyamide-imides (PAIs) are thermoplastic amorphous polymers prepared by the condensation of an aromatic diamine, such as methylene diamine, and an anhydride, such as trimellitic add chloride. PAIs have good mechanical, thermal, chemical resistance, high strength, melt processability, and high heat capacity. They can be processed into a variety of forms, such as injection or compression molded articles, coatings, films, fiber, and adhesives. The typical heat deflection temperature for neat molded PAI is 278°C,but reinforcements are often used to improve mechanical properties. PAIs are generally soluble in strong aprotic solvents such as NMP and DMAc, and thus misdble blends with PBI are feasible. 

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