Multicoat systems

In the majority of cases maximum durability will be produced by a multicoat system comprising priming and finishing paints only. Other considerations, however, such as uniformity of colour and smoothness of surface, may make it desirable to introduce intermediate coats, e.g. putty, filler and undercoat. The appearance of the final film or of the final painted structure is of some importance, and a final colour coat, which may contribute very little resistance to corrosion, may be necessary. 

A multicoat system provides a higher probability of ensuring complete, uniform coverage of the corrodible substrate. Maintenance of interlayer adhesion is crucial. The multilayer structure might allow incorporation of many desirable properties in the outer coatings system, such as ... 

Figure 9.6 The scratch resistances of the reference and hybrid system have been evaluated. The test has been performed in accordance to ISO 1518 standard (Paints and Varnishes - Scratch test) [62]. This standard specifies a test method for determining under defined conditions the resistance of a single coating or a multicoat system of paint, varnish or related product to penetration by scratching with a hemispherically tipped needle. Scratch resistance has been determined as the minimum load in grams required to cut through the film until the substrate. (Courtesy, Celine de Lame, CoRl).

For barrier coatings to be effective it is necessary to have (i) good adhesion of the barrier film on the metal surface (this is generally accomplished by multicoat procedure to a certain extent) (ii) proper choice of the polymers to control the permeability of oxygen and (iii) optimum film thickness achieved by multicoats or thin-film system, depending upon the envisaged application. 

Finish systems can be one coat or multicoat that use primers, intermediate coats, and topcoats. Primers provide adhesion, corrosion protection, passivation, and solvent resistance to substrates. Topcoats provide weather, chemical, and physical resistance, and generally... 

The Anglian Water Authority lock gates at Little Paxton were similarly grit-blasted and sprayed with zinc to 100 p.m plus a multicoat paint system. 

Acrylics may be formulated as lacquers, enamels, and emulsions. Lacquers and baking enamels are used as automotive and appliance finishes. In both these industries acrylics are used as top coats in multicoat finishing systems. 

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