Лако-красочные материалы — производство

As mentioned previously, in structural aircraft manufacture, phenolic resin adhe­sives are used which may today be applied in the form ofprefabricated, supported or unsupported films. Furthermore, epoxy resin film systems supported with fabrics or mats are used which are processed on anticorrosive primers (also described previ­ously). In order to obtain plastication, the epoxy resin matrices of these adhesives, which are cured at 120 °C, are modified by means of epoxy-terminated butadiene — acrylonitrile rubber components (CTBN) that segregate in the form of globular particles when the epoxy resin cures in the bond-line; in this way they act not only as a plasticizer but also as a crack stopper. For higher-temperature environments, other thermoplastic materials such as polysulfone resins also are used, whilst polyamide (which was used in former times) is still being used to produce adhesives for use in low-temperature environments. The epoxy resin component itself is produced from oxirane-terminated bis-phenol-A monomers and other oligomeric fractions; these are sometimes modified with regards to fire risk, smoke development in case offire, and toxicity. Dicyandiamides continue to predominate the curing systems; at room temperature they have a crystalline form so that they are not able to react, and elevated temperatures are required for them to dissolve in the adhesive (albeit to a limited extent) and to have them react. Originally, a temperature of 170 °C was required for this purpose, but today specific accelerators in the form of amines make it possible to obtain the same results with a temperature of only 120 °C. Polyimide adhesives may also be used in very high-temperature environments — for example, close to the engines — as they resist temperatures of250 °C and higher, at least for short periods of time.

With the exception of the longitudinal joints bonded by Fokker (see Sec­tion 8.2.1.1), cold-setting adhesives — for example, two-part epoxy resin systems which generally are cured at approximately 60 °C in order to improve their strength and resistance — have not yet been used in aircraft structures. However, they will increasingly be used in the future in combination with carbon fiber-reinforced plastics. Today, even cold-setting epoxy resin systems can be modified to obtain a globular rubber formation in the bond-line, which will result in an increased toughness. As a consequence, this type of adhesive may also be used in application areas where the temperatures are 80 °C or higher, thus offering an important development potential in the structural field.