Volume 6 Issue 4
What’s Happening at Missouri S&T:
Fall Short Course Dates
This fall we will be offering ?Basic Composition of Coatings" September 20-24, 2010. The Basic Composition course is intended for new personnel in the coatings profession. It targets the components of coatings (resin, pigments, extenders, solvents and additives), testing and specifications, general formulation and manufacturing methods. Basic Composition is primarily a lecture course with several laboratory demonstrations. For more information see our web site at http://coatings.mst.edu/index.html and to register contact Michael Van De Mark at firstname.lastname@example.org or call 573-341-4419. **This course is held on the Rolla campus**
This fall we will be offering ?Introduction to Paint Formulation" October 18-22 , 2010. This course is intended to give the person a fundamental knowledge of how to approach a starting formulation and troubleshoot it. This course involves both lecture and laboratory work. For more information see our web site at http://coatings.mst.edu/index.html and to register contact Michael Van De Mark at email@example.com or call 573-341-4419. **This course is held on the Rolla campus**
Technical Insights on Coatings Science
- How does Tg (glass transition temperature) affect the gloss of emulsion paints?
Most gloss emulsion coatings are formulated using excess of coalescing aid in a high Tg emulsion1. The PVC (pigment volume concentration) of such coatings is low (15-20%) and even with best efforts, it is difficult to achieve gloss levels of 60. The Tg of the emulsions is typically over 50 oC. This is lowered by addition of coalescing aid, which in turn adds to the VOC (volatile organic component/compound) of the coating. To get better hiding, most of the pigment is TiO2, with very little, or no filler which could reduce gloss. Such coatings are quite popular in household applications and wood finishing in western countries where medium gloss is acceptable to consumers. Emulsion polymers, being thermoplastics, give non-convertible coatings which have low resistance to solvents, detergents, soap, water and aging.
Several of these drawbacks have been addressed by high-performance stoving finishes. Two stage cure ( 80 oC for 2 min., followed by 15 min. at 180 oC) high gloss VOC coatings have been developed by using a high Tg emulsion (Tg > 60 oC) with highly reactive functional groups in the polymer 2,3. These resins have been crosslinked by means of hexamethoxymethylmelamine. Efforts have been made to synthesize crosslinkable emulsions by introducing allylic double bonds on the surface, which reacts with the atmospheric oxygen to give crosslinked coatings, thereby resisting solvents to some extent. Dispersion coatings of saturated polyesters, electro-deposition coatings, 2 component polyurethanes and epoxy emulsions have successfully replaced solvent based coatings (which usually give high gloss) in industrial sectors where high temperature curing is possible. The waterborne urethane dispersions which have seen significant success in clear floor finishes are now being used in pigmented high gloss architectural applications. These can be used as is or crosslinked with aziridines.
1.) V.C. Malshe and Meenal Sikchi; Basics of Paint Technology; Chapter VIII, Water Borne Coatings, Pp 176-177.
2.) M.A. Winnik, P. Pineq, C. Kruger, J. Zhang and P.V. Yanef; J. Coat. Tech.; 71. (892); 47-60, 1999.
3.) R.C. Mhamne, Ph.D. (Tech.), Thesis, Univ. of Mumbai (India), 2001.
- A Quick “Touch” on Computer and Related Screen Coatings
These days we want it all from our electronics: amazing applications, faster operating systems and new bright and crystal clear screens. The screens we rely on everyday need to be extremely durable, scratch and abrasion resistant, water repellent, transparent, and even fingerprint free! The world of touch screen has lead researchers looking for new hydro-oleophobic coatings. To achieve such characteristics, perfluoroalkyl chains (C n F2 n +1, n = 8–10) are the functional groups that provide the most desirable results. Unfortunately, the perfluoroalkyl chains are also stable and lipophilic, meaning they can accumulate in wildlife and the environment.
Another polymer that offers promising traits is perfluoropolyether (PFPE). This polymer exhibited low toxicity, high chemical resistance, and thermal stability.1 A PFPE oligomer based organic-inorganic hybrid material, prepared by the sol-gel process has been used to coat glass. The PFPE functionalized glass exhibited both strong hydrophobic and oleophobic characteristics.2 Though the PFPE based material was successful, another research team has made PFPE functionalized micro-nanoscale binary structures with even more promising results of hydro-oleophobic properties.1 As the need for keyboard coatings decrease the need for touch screen coatings increase. You may want to stop and think about what you are really “looking through” as you continue to read through our newsletter!
1. Yu Gao, Yangen Huang, Shijun Feng, Guotuan Gu, Feng-Ling Qing. Novel superhydrophobic PFPE-modified silica nanocomposite. Journal of Materials Science Letters. 5 October 2009
2. P. Fabbri, M. Messori, F. Pilati, R. Taurino. Hydrophobic and oleophobic coatings based on perfluoropolyether/silica hybrids by the Sol-Gel Method. Advances in Polymer Technology, Vol. 26, No. 3, 182-190 (2007)