HOUSTON, October ,17 2000 Lyondell (NYSE:LYO) In an effort to further reduce urban ozone and air toxics, EPA and State regulatory Agencies continue to reduce the allowable VOC and HAP contents for a variety of coating categories. These stricter regulations are making it increasingly difficult for coating suppliers to offer compliant products that also meet customer performance and cost requirements.
Raw material suppliers are working to assist their customers in balancing these sometimes conflicting requirements. In a paper entitled "New Tools for Formulating Ultra-Low VOC, High Performance 2K Polyurethane Coatings," presented at the 2000 International Coatings Exposition, a conceptual approach to low VOC formulation is presented by Lyondell Chemical.
The new tools alluded to in the title are: ACRYFLOW P120, a solvent-free liquid acrylic polyol; Luxate® HA-500, a highly functional, low-viscosity isocyanate crosslinker; and TBAc (tertiary butyl acetate), a non-HAP and proposed VOC-exempt solvent. These materials were shown to be useful in formulating ultra-low VOC (1 pound/gallon) and HAP-free 2K urethane coatings that perform like their medium solids counterparts.
A discussion of the development, performance characteristics and benefits of each of these materials is given. The low-VOC liquid acrylic polyol, based on a proprietary polymerization process, has a low molecular weight with few non- or mono-functional impurities and an OH number of 130 mg KOH/gram. In addition, the allylic monomer-based polymers do not lose functionality as the polymer molecular weight decreases and feature an almost ideal distribution of functionality.
Also discussed are the benefits of a novel approach to resin formulation: combining two acrylic polyols, one with a low Tg and one with a high Tg. These benefits include low viscosity, lower demand for expensive isocyanates, and comparable cost, performance and durability.
New low-viscosity isocyanate crosslinkers are also described. Unlike other low-viscosity versions of HDI that have been commercialized, these new adducts offer cost and performance comparable to that of trimer. Molecular structures are shown for common adducts and comparative physical properties for Lyondell's new HA-300 and HA-500 adducts are given.
A discussion of the impact of these adducts' high functionality, essential for high crosslink density and cure speed, is given. The dry-times of low-viscosity HDI adducts compared to that of HDI dimer and trimer are graphically presented.
Information also is presented on new tert-butyl acetate (TBAc) solutions of the most popular isocyanate crosslinkers, now available from Lyondell.
Solvent contributions to final film properties are discussed, and a comparison of the benefits, limitations and uses of VOC exempt solvents is given. TBAc is included in this list, due to its exemption proposed by EPA. With intermediate evaporation rate and good solvency properties, TBAc will be an important tool for formulating compliant coatings.
A list of general performance requirements for 2K urethane coatings is presented and a discussion of the trade-offs made to achieve compliance with VOC content regulations given. Five formulations were prepared using high and low Tg acrylic polyols, low viscosity isocyanate crosslinkers and tertiary butyl acetate. The formulation with the best performance is given.
Finally, comparative performance information is presented for this ultra low-VOC formulation and the best commercial benchmark. Initial coating properties, appearance and chemical resistance properties are compared as well as performance under 2,000 hours of accelerated weathering. The ultra-low VOC formulation was found to give a harder coating with physical properties and weatherability comparable to that of the best commercial benchmark.
Lyondell is a leading worldwide manufacturer and marketer of propylene oxide and derivatives and other intermediate chemicals. Its products are used in a wide range of consumer goods including home furnishings, athletic equipment, personal care products, paints and coatings, automotive components, antifreeze and reformulated gasoline as well as in industrial, construction and mining applications.
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