Лако-красочные материалы — производство

Besides setting via heat, several other physical effects like absence of oxygen in the glue line or presence of moisture at the adherent surfaces can be utilized in order to initiate a curing reaction. The most common one-part adhesives are based on an initiation by irradiation (e. g. UV light), by an absence of oxygen (anaerobic), or by exposure to moisture (see Section 5.7). Owing to the precise control of the curing process, systems setting under the influence of UV light or light (most of which are based on acrylates or epoxy resins) have been increasingly used to date. In low- molecular base resins, photoinitiators are dissolved or chemically incorporated

which initiate the crosslinking process under irradiation with UV light or visible light. Two such groups of adhesive may be distinguished: (i) those that set exclusively under continuous irradiation (radical reaction mechanism); and (ii) those in which crosslinking is initiated by short irradiation of the open bond-line and continues to take place after joining, without further irradiation (ionic reaction mechanism; see Section 5.7.2).

Cold-setting, one-part adhesives which crosslink under the effect of moisture (e. g. one-part polyurethane and silicon resin systems) are often used as sealing com­pounds. In the noncured state these adhesives are low-molecular and noncros — slinked. However, at the bond-line they are set by the effect of moisture diffusing from the outside, which results in a three-dimensionally, chemically crosslinked system with high plasticity. Silicon resins, for example, have a high plasticity and are characterized by the fact that their strength and deformation properties are virtually unaffected over a temperature range from -55 to + 250 °C (see Section 5.6.3.1).

4.3.4