High-temperature resins development

Because of this continued emphasis on adhesive bonding technology development over the years, the airframes of modem front-line aircraft such as the B-2 bomber and the F-117 and F-22 fighters are largely structurally bonded advanced composites. They tend to be comprised of materials that are more advanced (expensive) than commercial aircraft such as carbon and boron fiber reinforcements with cyanate esters, bismaleimides, polyimides or other high-temperature resin matrices and adhesives. 

Although polyimides are the largest class of high temperature resin systems, other resins have been developed that are used for specialist applications or, alternatively, were never developed commercially, perhaps due to cost considerations. 

The American ThermalWorks company has developed a new carbon fibre composite printed circuit board and substrate material, STABLCOR, which comprises a high temperature resin incorporating carbon fibre sandwiched between two very thin layers of copper. The material has a Tg of 170 "C. However, the company is developing a version with a Tg of 240 C. The material is designed as a plane , or non-signal carrying layer in a ply stack with other dielectric layers to make a composite PCB or device substrate. The carbon composite material has a dielectric constant of approximately 13.4 which makes it electrically conductive. This material allows the user to tailor the coefficient of thermal expansion of a PCB down to 3 ppm/°C to match that of silicon. 

Although many organizations have been involved in high temperature adhesive development for captive use and as a service to their customers, most of this information is proprietary and the remainder is seldom published. An example of a promising adhesive with the potential for high temperature application is the cured resin from 1,3-dicyanatobenzene (resorcinol dicyanate) as shown in Eq. (7) ... 

In the 1960s, CIBA Products Co. marketed and manufactured glycidylated o-cresol novolak resins, which had been developed by Koppers Co. as high temperature-resistant polymers. Dow offered glycidylated phenol novolak resins, SheU introduced polyglycidyl ethers of tetrafunctional phenols, and Union Carbide developed a triglycidyl p- am in oph en o1 resin. 

Not all the epoxy resins are equally efficacious and all have to be stoved at a relatively high temperature (180-220°C) in order to develop the requisite... 

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