What’s Happening at Missouri S&T:
Short Course Dates
We will be offering "Basic Composition of Coatings" September 22-26, 2014 (Fall 2014). 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.
We will be offering "Introduction to Paint Formulation" May 19-23, 2014 (Spring 2014) and October 20-24, 2014 (Fall 2014). 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.
We will be offering "Introduction to Coatings Composition and Specifications" July 21-23, 2014 (Summer 2014), course designed for the new coatings person in areas such as sales, marketing or production. The course was initiated by a number of raw material companies and distributors requesting a course with this format. This course is not as heavily technical as is our “Basic Composition of Coatings" and “Introduction to Paint Formulation" courses. The ?Introduction to Coatings Composition and Specifications" course is a two and a half day course which will discuss the types of coatings, the basic composition of coatings and the tests and specifications used by the industry. This course will allow the participant to gain the fundamentals needed to work in this industry and to communicate more clearly.
Online Short Course
We are offering "Introduction to the Coating Systems" online short course. This course is targeted for automotive and aviation type OEM companies. This self-paced seminar will cover the painting system from the composition of paints to the evaluation of the dry film. The pigments, resin, solvents and additives will be discussed including their influence on the coatings performance. Color measurement, surface profile, and other evaluation criteria will be related to composition. The importance of surface preparation and other manufacturing criteria will show the system complexity and each step's importance.
We are offering "Surface Defects: Elimination from Human and Process Contaminants" online short course. This course addresses many of the issues in prevention and minimization of defects. The course covers the defects caused by the coatings process, as well as human issues, including personal care product causes. Several of the surface defects are discussed – from basic principles and real world automotive and aircraft examples. The highly practical approach of this course will greatly aid the personnel involved in the painting operation to reduce and systematically approach issues.
We have started an employment section for our students and companies. We have a full time job section, an intern / co-op section and a graduating and alumni students section . Please explore our section on employment on our web site. Anyone wanting to have job opening listed, please contact us at (573) 341-4419 or e-mail: firstname.lastname@example.org . You can also write to us at Missouri S&T Coatings Institute, BOM #2, 651 W. 13th St., Rolla, MO 65409-1020. Our web site is http://coatings.mst.edu
Technical Insights on coatings Science
Leafing Aluminum Pigments
Sagar Vijay Gade
Graduate Research Asst., Missouri S&T Coatings Institute
Aluminum pigments have many applications in industries like coating, plastic, functional application, cosmetics, graphic art etc.1,2 They are used in automobile and maintenance coatings as these pigments give excellent weather resistance, chemical resistance and corrosion protection. The amphoteric nature of these aluminum pigments give them a high degree of chemical resistance.3 These pigments also have aesthetic and functional properties depending upon the geometry of particle, particle size and the particle size distribution of the pigment. Depending upon the manufacturing process, these lamellar flaky particles can have round or irregular perimeter. Also depending upon the type of surface treatment given during the ball milling process, these pigments can be classified as leafing and non-leafing pigments. Both leafing and non-leafing aluminum pigments are produced as powders, pastes, granules and slurries.
Seeing the orientation of the aluminum flakes in a coating, the leafing and non-leafing character of the aluminum pigments in a given coating can be easily identified. ASTM D480-88 is a commonly used test method to measure the leafing / non-leafing characteristics of a pigment. Leafing aluminum looks like polished aluminum and the degree of reflectance depends upon the particle size, surface area and the surface treatment on it. Since 1960s , solvent borne systems utilize stearic acid and mineral spirit along with aluminum in a ball mill to produce leafing flakes. The non-leafing solvent borne systems are generally ground in a ball mill along with oleic acid and mineral spirit. The non-leafing coatings have diffused metallic appearances that vary from frosty, etched aluminum and leaden grey depending upon the particle size, PVC and the surface treatment.
When stearic acid is used as the milling lubricant in the manufacturing of leafing pigments, the carboxyl groups of stearic acid get adsorbed onto the surface of the pigment, and with such orientation of adsorbed stearic acid on the surface of the pigment, the formed flakes of pigments have both hydrophobic and oleophobic properties.4,5 The degree of leafing of these surface modified flaked pigments depend upon the wetting characteristic of the coating system.
Image 1. Leafing aluminum pigment in coating
When incorporated in a suitable coating system and applied on the substrate, the evaporating solvents in the coating system form a vortex motion within the coating from the substrate to the air interface and these vertical convection currents of evaporating solvents transport the flake pigments at the coating – air interface.
The interfacial tension between the vehicle and the high aspect ratio of the particles hold the leafing flakes horizontal in the upper layer of the coating. As more solvent evaporates, the viscosity of the drying film increases which immobilizes the residual pigments in the coating matrix below. Leafing of flaked pigments depends upon i) where the stearic is present which orients the flake surface, ii) coating formulation used which will promote the leafing effect.
Milling process and selection of raw materials for coating formulation plays a key role in the leafing of pigments. Excessive dispersion can mechanically damage these pigments. Chemical desorption of stearic acid can take place if a highly polar acid with higher dissociation constant is added to the system. Compounds reacting with the stearic acid must be avoided in coating formulation, as they would change the surface characteristics that would deleaf the pigment. Instead resins with low residual acidity are preferred. Aliphatic or aromatic solvents are preferred over oxygenated solvents like alcohols, ketones and esters. Halogen containing solvents must not be used as violent reaction can take place to form hydrogen halides.2
Leafing aluminum pigments are preferably used in the solvent borne system, but with changing trends in the coating industry, now many companies are shifting towards the waterborne systems. With advancement in technology in aluminum pigment preparation and new surface treatments, these pigments can be incorporated in the waterborne systems.
However, pre-dispersed waterborne slurries from different companies are available, with lower shelf stability than the solvent borne slurries and pastes. A major concern about aluminum in water is the oxidation of aluminum in water potentially producing hydrogen gas. Factors taken into account to improve stability of dispersed pigments and shelf stability are by eliminating adverse conditions, method of incorporation, selection of wetting aids, avoiding high shearing and longer shearing times during dispersion which can bend/break aluminum flakes, reducing sparkling effect causing dull, grey, frosty colored products like non leafing pigments. The pH of the system should be maintained in the range of 8-9 and must not exceed more than 9, as at higher pH, aluminum can be oxidized by water to form aluminum oxide and flammable hydrogen gas which causes gassing and hence must be avoided. Ammonium hydroxide preferably should not be used for neutralizing, instead one can use AMP 95 or similar materials to stabilize the dispersion.2
- Koleske, J.V., Paint and Coating Testing Manual Ed.4, 1972, pp.225
- Brown, J., Paints and Coatings magazine, January 2005
- Kent, A.K., Handbook of Industrial Chemistry and Biotechnology Vol 1, 2012, pp. 1128
- Patton, T.C., Pigment Handbook Vol.1, Properties and Economics, 1973, pp.789
- Myers, R.R., Long, J.S., Treatise on Coatings Vol 3 Pigments, pp. 95
- Wiβling, P., Metallic Effect Pigments: Fundamentals and Applications, 2006, pp.97
- Buxbaum, G., Industrial Inorganic Pigments, 1998, pp. 230