Postcure preheating

The TH-600, in the form of a finely precipitated powder, was held in a vacuum oven at 100°C for several days to remove solvent and absorbed moisture. Preweighed quantities were then introduced into a preheated (235°C) mold and 100 psi pressure was immediately applied using a hydraulic press. After dwelling for 1/2 hour at these conditions, a consolidated and partially cured bar 0.1" x 0.5" x 3" was removed from the mold. Bars made in this manner were later postcured to the conditions shown in Table 1. 

Once cleaned, the metal surfaces are coated with a primer prepared by rollmilling 200 g of adhesive composition and 5(X) g of methanol. A first layer of primer is appUed to the metal parts, dried for 10 min at 90°C, covered with a second layer of primer and finally dried at 90°C for 1 h in an air circulating oven. The adhesive film is inserted between the two primed metal surfaces and the assembly is placed between the platens of a hydraulic press preheated to 316°C. A pressure of 0.3-0.5 MPa is applied and the test specimens are cured at 316°C for 1.5 h, before cooling down to 100°C under pressure. The assemblies are removed from the press and postcured in an air circulating oven as follows the temperature is raised from 20 to 300°C in 1 h, then from 300 to 350°C in 5 h and left at 350°C for 5 h. The lap shear strength values determined at different temperatures are plotted in Fig. 29 for TU-2 Ti/li assemblies [curve (a)] and ZIO CNT 1810 stainless steel coupons [curve (b)]. 

Processing is normally carried out in a preheated press at 370 °C with pressure maintained at 0.03 MPa for 30 s. The pressure is then increased to 0.6—1.4 MPa, and the glue line temperature is maintained at 370 °C for 3 h. The temperature is then reduced to 260 °C or less, and the assembly is removed from the press. Autoclave techniques can also be employed. For improved mechanical properties, postcuring in an inert atmosphere (nitrogen, helium, or vacuum oven) is recommended. The desirable conditions are 24 h each at 316 °C, 345 °C, 370 C, and 400 °C followed by 8 h at 427 °C in air to achieve maximum properties. Obviously, these literature recommendations should be checked against manufacturers recommendations, but they provide a starting point for PBI processing. 

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