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Polyurea spray coatings technology is a recent development in the polyurethane coatings industry. Polyurethane chemistry has been in existence for approximately 60 years, while elastomeric urethane coatings have been available since the 1970s. Polyurea elastomer technology was introduced some 10 years later. The two main application areas are Reaction Injection Moulding (RlM) and sprayable coatings.
Polyurea coatings combine extreme application properties such as rapid cure (even at temperatures well below O [degrees]C)1 and insensitivity to humidity, with exceptional physical properties such as high hardness, flexibility, tear and tensile strength, and chemical and water resistance. This results in good weathering and abrasion resistance. The systems are 100% solids, making them compliant with the strictest VOC regulations. Due to its specific curing profile and exceptional film properties, the polyurea spray coating technique has been introduced into many areas, including corrosion protection, containment, membranes, linings and caulks.
Definitions
The term 'polyurea' has been wrongly used in the past. Urethane coatings chemistry can be divided into three segments: polyurethane coatings; polyurea coatings; and hybrid polyurethane/polyurea coatings. all three are linked to different isocyanate reactions (Figure 1). Each of these segments deals with systems that can be aromatic, aliphatic, or a blend of both aromatic and aliphatic. Pigments, fillers, solvents and/or additives can be introduced to all of them.
* A polyurethane coating is the result of a reaction between an isocyanate component and a resin blend made with only hydroxyl-containing resins. The final coating film will contain no intentional urea groups. A polyurethane system will most probably contain one or more catalysts.
* A polyurea coating is the result of a one-step reaction between an isocyanate component and a resin-blend component. The isocyanate can be monomer based, a prepolymer, a polymer or a blend. For the prepolymer, amine- and/or hydroxyl-terminated resins can be used. On the other hand, the resin blend should only contain amine-terminated resins and/or chain extenders and not any hydroxyl reactive polymer components. all the polyurea coatings mentioned in the paper comply with this requirement.
* A polyurethane/polyurea hybrid coating has a composition that is a combination of the above-mentioned two-coating systems. The isocyanate component can be the same as the "pure" polyurea systems. The resin blend is a blend of amine-terminated and hydroxyl-terminated polymer...