Paint systems thermosetting acrylics

Uses Adduct monomer for preparation of thermosetting acrylic resins with improved flexibility for paint systems also used in photopolymer production and adhesive applies. 

Synonyms Polypropylene glycol (5) methacrylate Uses Prep, of thermosetting acrylic resins for paint systems photopolymer prod. adhesive applies. 

DR pigments are used in paint applications where their properties are required, such as high-temperature paints and coil-coating paint systems based on fluoropoly-mers, silicone-polyester, and plastisol. The NiSbTi and CrSbTi DR pigments are used in trade sale paints including acrylic house paints, general industrial paints in polyester systems, and fleet colors in thermoset acrylic, thermoplastic acrylic, and polyurethane systems. They are also used in polyester-based powder coating applications. 

In the early days, although paint manufacturers flirted with acrylamide chemistry for automotive topcoats, their higher curing temperatures of 150 C and above precluded commercialisation in this end use. Carboxy functional acrylics have inferior weathering performance. Consequently, thermosetting acrylic topcoats are almost exclusively based on hydroxyl functional polymers. These are crosslinked with either alkylated melamine formaldehyde resins or as 2 component (2K) systems, with aliphatic isocyanate adducts. The 2 component systems are an extremely important class used mainly in automotive repair applications and warrant a chapter in their own right (see Chapter V on component isocyanate curing systems). 

Whilst there are some thermoset acrylic emulsions cormnerdally available, the bulk of the thermoset resins, used as the main binder system, are produced in solution. Some may then be made waterborne by neutralisation and inversion (dispersion) into a water phase. Lower molecular weights favour this qrproach. The rate of conversion from solvent based to waterborne industrial thermoset coating systems has been, and is, much slower than the conversion from architectural alkyd paints to emulsion altonatives. There are two principle reasons for this. Firstly there are problems of application and substrate wetting of many waterborne systems. Secondly, the modifications frequently required to induce water dispersibility reduce one or more of the essential performance properties required from the cured film, compared to a solvent based system. Water resistance, with many films having an increased tendency for blushing is one example. However, for some applications, such as electrodeposition, only waterborne systems will work. 

The selection of TSA systems and functional monomers are generally made on the basis of performance criteria for the final paint system. For example, curing temperatures and the performance of different thermosetting acrylic resin systems vary depending on the type of curing mechanism. Such a dependence, compared to older alkyd-melamine systems, has been demonstrated by Brendly et alP and can be summarized as in Table 4. 

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