Лако-красочные материалы — производство

The typical base monomer of this adhesive group is methyl methacrylate (MMA). This has a very good wetting behavior and easily ‘etches’ plastic materials, thus allowing excellent diffusion bonding. MMA is also capable of wetting metals and glass. MMA homopolymers have outstanding mechanical properties and are highly durable; however, in order to reduce the brittleness of these adhesive systems, acrylonitrile-butadiene copolymers, liquid isoprene rubber systems or chlorosulfo — nated rubber systems are often added to toughen them [37]. Impact toughness — modified adhesives easily reach a shear stress strength by tensile loading of 30 N mm~2. A peroxide (e. g. benzoyl peroxide or t-butyl perbenzoate) is typically added as a hardener in combination with an amine accelerator (e. g. N, N-dimethyl-p-toluidine) as an accelerator (Figure 5.24) [38].

The adhesives are available at a ratio of 1: 1 or 10: 1 in double-chamber cartridges, ready to use. The adhesive parts are mixed in a static mixing tube and applied as if it were a one-part system. As the reaction takes place as a poly­merization, and not as a polyaddition, the systems are rather tolerant to incorrect mixing. For automated applications, the adhesive parts can be applied using dose dispensers for two-part systems. Generally, the pot life of these systems is rather short — that is, the adhesive must be applied rapidly after mixing (Figure 5.25).

Two-part systems are also available as ‘no-mix’ adhesives where the hardener is applied to one adherent surface, and the resin to the other. The substrates are then joined to each other, thereby mixing the adhesive parts, and the curing takes place. The advantage of these systems is that no pot life must be observed, although perfect bonding is only obtained with thin bond-lines.