High Solids Polyurethane Coatings

High Solids Polyurethane/Polyurea Coatings

Traditional solventborne polyurethane coatings are typically formulated at a solid level of 30-40 percent, which would be equivalent to the volatile organic compounds (VOC) level of 5 lb/gal or above. With more stringent emission level regulations, demand for low VOC coatings and thus higher solids, has increased. This demand has led to the development of lower viscosity resins, both in the polyol and polyisocyanate components. Bayer MaterialScience supplies high solids polyol components, such as polyesters, polyacrylates and polyaspartic esters, as well as low viscosity polyisocyanates for the formulation of high solids coatings.

You can find more information about polyurethane coating chemistry in the Bayer publication, “The Chemistry of Polyurethane Coatings” by clicking here.

Additionally, learn more about waterborne coatings by browsing and downloading our collection of technical papers.

One appproach to the market's need for higher solids coatings is a new class of co-reactants, namely polyamino co-reactants. Bayer MaterialScience markets these co-reactants under the Desmophen® NH tradename.

In the past, the extremely high reactivity of primary amines has prevented their use as a viable co-reactant in coating applications. However, the significantly reduced reactivity of hindered or blocked amines, such as polyaspartic esters and aldimines (see Table 1 for structures), has allowed for a whole new family of co-reactants available to polyurethane formulators. The coatings based on these polyamino co-reactants can be formulated with solid levels in excess of 70 percent, resulting in a system with VOC levels at 2 lbs/gal or less. Table 1 also lists the advantages of polyaspartic esters and aldimines. The availability of various polyaspartic esters with vastly different reactivities and viscosity make it a more versatile co-reactant for formulators (Table 2). One can blend two or more polyaspartic esters to achieve a wide range of application viscosity and potlife. One significant characteristic of the coatings based on polyaspartic esters is that they offer extremely high hardness, balanced with a reasonable flexibility. In addition, both aldimines and polyaspartic esters are compatible with most traditional polyester or polyacrylic resins. One can easily blend polyaspartic esters with polyesters or polyacrylics to achieve the desired solid level/VOC, hardness, viscosity and cost.

(table 1 to be corrected by Web designer)

Table 2. Characteristics of Polyaspartic Esters

* Approximate gel time when mixed with an aliphatic polyisocyanate adduct, such as Desmodur® N-3300.

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