Curing of polyurethane coatings

With a minimum of analytical measurements, the effect of several parameters on the curing of polyurethane coatings can be studied using the presented model. 

This reaction has great significance in the preparation of polyurethane products as it causes chain extension and branching, provides the carbon dioxide necessary for foaming and forms the basis of air curing of polyurethane coatings. 

Table 2.8 summarizes different types of polyurethane coating systems, their compositions, curing mechanism and ASTM classification. 

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. 

The addition of small amounts of fluorinated polyols to conventional aqueous polyurethane coatings can improve their water resistance and mechanical properties considerably 47 FEVE resins can be applied as water-based coatings and cured at 160°C (320°F) for 25 min to produce coatings with high gloss and good water and weather resistance.48 They may also be cured with water-based hardeners.49... 

Most of the radiation curable raw material technology is based on acrylic or methacrylic acid deritive but may also include modified epoxies, polyesters, and polyurethanes. Thus the backbones of radiation curing and conventional coatings are similar. 

The electron beam curing of coatings has for some time attracted a great deal of attention since It Is claimed that coatings can be fully cured In a fraction of a — second. The coatings are primarily based on the cross-linking of acrylic or epoxy resins In a polyurethane or polyester base (l.e., modified paints). 

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