Tert-Butyl Acetate: VOC-Exempt Solvent for Coatings
Why Regulate VOCs in Coatings?
• Volatile Organic Compounds (VOCs) contribute to ground level ozone (smog) formation • Ozone is a lung irritant and criteria pollutant • Major sources (biogenic, cars and truck) are difficult to reduce • Coating operations are a minor but visible source of VOCs • Low-VOC coating technologies exist
– Water-based
– Energy curable (UV and powder)
– High solids
– Exempt solvents
VOC Regulations in the US and Canada
• US lowers ozone standard to 75 ppb in 2008 • Effective 9/30/09, TBAC is VOC-exempt in Canada for architectural and automotive coatings • US and Canadian Regulations based on photochemical reactivity
– Only photochemically reactive compounds are regulated
– Negligibly reactive compounds are exempt:
• Acetone, methyl acetate, TBAC, many halogenated solvents. • Many halogenated compounds are regulated under the Montreal protocol because they deplete stratospheric ozone
Resins Soluble in TBAC • Acrylics and styrene acrylics • Urethanes and isocyanates • Alkyds and polyesters • Modified alkyds (silicone, oil-modified urethanes, acrylic and phenolic) • Nitrocellulose and other cellulosic resins • Some chlorinated resins (not PVC) • Epoxies and their amino and amido-amine curatives • Melamine and urea-formaldehyde • Phenolic and styrenated • Silicones and silanes
Formulating with TBAC • TBAC is a medium-fast evaporating solvent (2.8 times n-BuAc) • Solvent blend must contain ~30% slow solvent for optimum flow, leveling and appearance (e.g. MAK, EEP, PMA, xylene) • TBAC blush resistance superior to acetone and methyl acetate • Slow solvents should be used for pigment grinding • TBAC can be used with isocyanates and amido curatives • TBAC is stable in acid-catalyzed varnishes • Coating properties are unaffected because TBAC evaporates first
Conclusion :
- Coating VOC regulations are spreading and becoming stricter
- VOC-exempt solvents like TBAC are useful formulating tools for cost-effective, high performance coatings
• TBAC is suitable for a wide range of coating technologies • Solvent-based coatings require less energy to produce, apply, and cure than other low-VOC coatings • Solvent-based coatings with TBAC can meet stringent VOC-content limits as well as qualify for green building environmental credits