Aspects Related to Chemistry

The carboxy/epoxy system displays a very fast lacquer type dry but, in comparison to a 2 pack polyurethane, relatively slow through cure. Tertiary amines can be used to enhance the cure of the coating. However, careful selection of the catalyst is critical since some amines can also make the coating water sensitive. There is also the potential to catalyse the system internally by incorporating an amine functional monomer onto the backbone of the acrylic resin by copolymeiisation of amine functional acrylic or vinyl monomers. 

Ketimine systems cure by a two stage process. The first reaction involves a reaction of the ketimine with atmospheric moisture to produce a ketone and a highly reactive amine. The amine can then react with either an acetoacetate functional acrylic, or an unsaturated acrylic polymer. The cure reaction is extremely quick and would result in rapid gelation if the amine crosslinker was not blocked with a ketone. The chemical linkage produced 

Primary and secondary amine functional systems require a phenolic catalyst to react at ambient temperature and are characterised by a relatively slow cure. Tertiary amines are also used to crosslink qwxy functional acrylics. However, the reaction will only occur in the presence of a protonating agent, such as an acid or moisture. The slow cure of this system can be compensated for by using relatively hard polymers to give good physical drying. 

The curing of a coating will not only depend on the chemistry, but also on the application in which it is utilised. In general, like 2K acrylic/isocyanate systems, the non-isocyanate acrylic must display good cure under ambient temperature and low bake (60-80°C) conditions. The minimum cure requirements, specific to the main end use sectors, have been summarised in table 6-2  

Vehicle Refinish Ambient/low bake Reduced dirt pick up, good polishing characteristics, rapid development of resistance properties 

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