Лако-красочные материалы — производство

While construction applications usually require reactive hardener systems to give good room-temperature cure, many metal bonding applications require strength at elevated temperatures. Usually, however, they also permit heat curing and postcuring. Surface preparation is crucial to achieving high bond strength and will always involve at least degreasing and abrading. Because of the high strength of the substrates, joint design is also very important and should always aim to provide the largest practicable bonded areas. Since high-strength epoxies are generally hard, joint design should aim to produce bonds that are in tension or compression rather than shear or peel.

Solvent-free systems may include adhesion promoters such as silicones, flexibilizers such as liquid polysulfide rubbers, and reinforcing fillers, either fibrous or micronized. Room-temperature to mildly elevated-temperature systems will be cured with amidopo — lyamine hardeners, often at ratios considerably in excess of stoichiometric requirements. This increase in hardener quantity improves flexibility and adhesion at the expense of tensile strength and heat distortion temperature. For applications at higher temperatures, use is made of more reactive polyamine hardeners, often with metal powder as filler. These will have postcuring cycles of several hours at temperatures that are increased in steps up to 150 to 180° C. Alternatively, solvent-based hybrid systems can be formulated, incorpor­ating phenolic resins, nitrile rubbers, and poly(vinyl acetals). These solvent-based systems are typically single-component, applied to both mating surfaces. After the solvent has flashed off, the assembly is clamped and cured at elevated temperature. This type of system is particularly suited to applications such as bonding of brake linings to their backing pads (Section VI. C).