(877) 678-8726 - 1 WEST CAMERON AVENUE - KELLOGG, IDAHO 83837

What Is Polyaspartic?

Polyaspartic chemistry was first introduced in the early 1990's making it a relatively new technology. The patents were issued to Bayer in Germany and Miles Corporation in the USA. Pure polyurea reacts extremely quickly making them almost unusable without plural component spray equipment. Polyaspartic technology utilizes a partially blocked amine to react more slowly with the isocyanates and thus produce a modified polyurea. The amine/diamine or even triamine functional coreactant for aliphatic polyisocyanate is typically reacted with a maleate. Polyaspartic esters as they are often called, initially found use in conventional solvent-borne two-component polyurethane coatings.

The Properties

To manufacture the aspartic, an amine is reacted with diethyl or dibutyl maleate by the Michael reaction[6]. This converts the primary amine to secondaries and also introduces bulky groups to the molecule which causes steric hindrance. As the molecule is now much bigger this alters the reaction kinetics with isocyanates(polyisocyantes) slowing the curing reaction down.
The productivity increases are not based on fast curing speeds alone. This technology has permitted for some basic changes as to how the finished coating is produced. Polyaspartic technology has made it possible in some instances to move from a conventional three-layered paint system (zinc-rich primer/epoxy/polyurethane topcoat) to a two-layer system consisting of the zinc-rich primer/polyaspartic topcoat. This has been achieved in the highly demanding corrosion protection on steel application. Direct-to-metal (DTM) coating applications are also possible with polyaspartics, and productivity is improved with the elimination of a primer step. The DTM process produced a 30% reduction in labor time in a railcar application. A generic structure for the polyaspartic ester is shown below.

The Chemistry

The reactive groups are the secondary amines. The sterically hindered environment of these groups reduces their reactivity compared to the reaction of typical secondary amines with polyisocyanates. The overall reactivity of the aspartates can be adjusted by changing the “X” group to influence the degree of steric hindrance. In general, the reactivity falls between the very fast curing of a polyurea polymer and the slower reaction rate of a typical polyurethane. The available grades of polyaspartic esters were designed to produce different reaction rates and can be blended to achieve the desired curing profile. The degree of steric hindrance has a limited influence on the film properties of the coating film.
The curing rate of a polyaspartic ester coating is strongly influenced by environmental conditions. As with most systems, the curing rate increases with temperature, but in this instance the rate is also greatly accelerated with increasing humidity. The second generation of polyaspartic ester technology produces formulations that are more robust and show more consistent curing times over a range of humidity levels.

Applications

Polyaspartic ester coatings formulations are unique in that they cure at a relatively high rate, but at the same time have a long enough pot life that they can be applied without the need for plural-component impingement mixing equipment. The pot life in general terms is comparable to the drying time of the coating. Once the coating is applied to the substrate, it is exposed to the catalytic influence of ambient water and the curing reaction accelerates. This curing profile permits polyaspartic coatings to be applied manually with a brush or roller. Polyaspartic coating technology should be considered if the application calls for a high-performance coating with a long open time and a fast cure profile.
The advantages of using polyaspartic esters as the main component of the co-reactant for reaction with an aliphatic polyisocyanate in low to zero volatile organic compound (VOC) coatings was realized. The rate of reaction of polyaspartic esters can be manipulated, thus extending the pot-life and controlling the cure rate of aliphatic coatings. This allows formulators to create high solids coatings systems which are user-friendly with longer working times and still maintain a fast-cure. Traditional aliphatic polyurea formulations required high-pressure, high-temperature plural component spray systems to be applied due to fast initial reaction rates. Aliphatic polyaspartics can be formulated with slower reaction rates to accommodate batch-mixing and application by roller-applied methods or spray-applied through conventional single components paint sprayers without the use of solvent. As with aliphatic polyurethane or acrylic coatings, polyaspartic coatings made with aliphatic isocyanates and derivatives are UV and light stable and have a low yellowing tendency. When coating concrete, polyaspartics can be installed in both clear and pigmented form. Additionally, broadcast media such as quartz, vinyl paint chips can be incorporating, as well as metallic pigments.