Volume 3 Issue 1

What’s Happening at Missouri S&T:

Spring Short Courses

This spring we will be offering “Basic Composition of Coatings¿? March 13-17, 2006 and “Introduction to Paint Formulation¿? May 15-19, 2006. 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. The Introduction to Formulation 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 and to register contact Michael Van De Mark at coatings@mst.edu or call 573-341-4419.

Summer Interns

Remember to contact us early if you are planning to hire a summer intern next year. We will make sure that our students are informed of the opportunity.

Technical Insights on Coatings Science

Special Effect Pigments
By Katherine A. Durham, Missouri S&T Coatings Institute

Special effect pigments have applications ranging from security to automotive coatings. Because of their eye-catching appeal, they are often used in a decorative capacity. There are three main uses of special effect pigments in decorative applications. The first is to create an illusion of depth. Light reflects at the interfacing of a multitude of pigment particles and the binder, causing this effect. Effect pigments can also be used to create angle-dependent color, as well as an imitation of natural pearl.(1) The global market for effect pigments is growing at a rate of approximately 7% a year, with an estimated worth of $1.287 billion in 2004.(2)

Two major classifications of effect pigments are substrate-free pigments and substrate-based pigments. Pigments are considered substrate-free if their platelets are made up of an optically homogeneous material. Substrate-based pigments have layers of optically different materials.

Metal effect pigments are a large category of substrate-free pigments. They are composed of flakes of metal that reflect light from their surfaces. Larger flakes result in increased brilliance.(1) Metal effect pigments can be either leafing or non-leafing. Leafing pigments reside at or near the surface of the film matrix, while the non-leafing variety is contained within the film matrix.(3)

Other substrate-free effect pigments are used less often than metal effect pigments. A naturally effect pigment, natural pearl essence, creates a high, soft luster. Because it must be extracted from fish scales, skin or bladder, it is expensive and rare. Another pigment, basic lead carbonate is toxic. Bismuth oxychloride, micaceous iron oxide, and titanium dioxide flakes generally have limited stability. Pigments based on liquid crystal polymers can create angle-dependent optical effects at thickness levels of over 4 um.(1)

Although substrate-free effect pigments are in wide use, they can be mechanically unstable. Substrate-based pigments use their substrate as a supporting scaffold. This adds to their mechanical stability. Substrate-based pigments are classified according to the substrate.

Mica-based effect pigments can produce a high level of angle-dependent color. Mica is naturally-occurring, plentiful, and relatively inexpensive. Generally, mica-based pigments are a combination of metal oxide layers on mica platelets. Common pigments of this type are titanium dioxide-mica, and iron oxide-mica pigments. However, the optical effect depends considerably on the thickness of the layers, which must be carefully regulated. Alumina-based pigments can exhibit a distinctively directed reflection, which appears as a sparkle. Good quality alumina crystal flakes can be produced using controlled growth system. Silica-based pigments have an advantage in that thin silica flakes can be manufactured with consistency. Pigments based on silica flakes often show color travel effects such as red to gold, and gold to blue. Glass flake-based pigments are composed of metal coated glass flakes. These can appear pearlescent or as a sparkle. However, they generally have a broad thickness that prevents color travel effects. Iron oxide flakes can be used as a substrate for metal oxides. When layered with iron oxide and silica, the pigment produces an angle dependent purple to gold effect. Aluminum flakes can be used as a substrate for iron oxide, resulting in pigments that show gold, orange and red metallic effects.(1)

In addition to chemical composition and particle size, flake orientation contributes heavily to appearance. This can lead to problems with reproducibility between applications. Other challenges associated with effects pigments are increasing durability, lowering VOCs in coatings, and increasing the ease of preparation and application.(2) Special effect pigments have a decorative appeal that is in demand. As the effect pigment industry continues to grow, further innovations will increase the already wide range of possible applications.

References:
1. Maile, Frank J., Pfaff, Gerhard, Reynders, Peter. (2005). Effect Pigments—Past, Present, and Future. Progress in Organic Coatings, 54(3), 150-163.

2. Challenger, Cynthia. (2004). Pigments II: Growing Demand for Specialty Effect Pigments. Journal of Coatings Technology: Coatings Tech, 1(7), 38-42.

3. Ferguson, Russell L. (2004). Today’s Aluminum Pigments. Journal of Coatings Technology: Coatings Tech, 1(7), 48-50.

The End User

How are Special Effect Pigments Characterized as to Color?
By Michael Van De Mark, Director, Missouri S&T Coatings Institute

The typical spectrophotometer used in retail stores is unidirectional. It only utilizes one spectral angle for measurement which will not properly define the color of most special effect pigments. In special effect pigments, the color is angle dependent between the light source and the observer. Therefore, spectrophotometer manufacturers had to manufacture spectrometers which would be able to measure the reflected light at several different angles. This approach has resulted in good agreement between the color measurement and the customer. The science of color measurement in these special effect pigments is still developing and we should see major improvements over the next several years.

Is there a topic you would like discussed? Contact us by e-mail at coatings@mst.edu.