Volume 2 Issue 8

What’s Happening at Missouri S&T:

Professor Philip Whitefield Appointed Chemistry Department Chair at Missouri S&T

Dr. Philip Whitefield, Chair, Missouri S&T Chemistry Department

The Missouri S&T Coatings Institute is a part of the Chemistry Department here at Missouri S&T. Dr. Philip Whitefield was recently appointed the new Chairman of the Chemistry Department. Dr. Whitefield’s research is in the elucidation of particle formation in exhaust plumes such as factory exhaust and jet and space shuttle contrails.

Michael Van De Mark, Director

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

Why Does Hide Not Improve With Added Titanium Dioxide After About 20% PVC?
By Michael Van De Mark, Director, Missouri S&T Coatings Institute

The PVC of a coating is the pigment volume concentration of the pigment in the dry film. The opacity or hide is the ability of a coating to prevent the substrate from being seen through the coating. Hide is caused by the scattering of light which is enhanced by the refractive index difference between the pigment and the resin. The higher the difference in refractive index, the better the pigment scatters or hides. The particle size of the pigment will also alter the scattering ability of a pigment. It should be noted that the scattering ability of the pigment may be wavelength dependent. If a pigment scatters blue more than red, a color shift may be observed. It is highly desirable to minimize these scattering differences as a function of light wavelength. Light can be scattered down to the surface and back up giving a shadow or some view of the substrate although blurred. If the amount of hiding pigment is increased from zero to 10% PVC, we see a clear increase in hide. As we increase the PVC toward 20% PVC, the hide continues to increase and plateaus. Increasing the PVC from 20% to 30%, or higher, has minimal effect but does increase the cost considerably. Typically the hide will be between 97 and 98.5% at 20% PVC. The hide of most good paints is between 99.3 and 99.7% even for lower cost paints. The remainder of the hide cannot come from scatter but must be obtained from absorption. In addition to scatter, absorption of light will also prevent the surface from being seen. Typically burnt umber, carbon black or similar dark pigment is added in trace amount to absorb light scattered back from the substrate. This will increase hide to the desired value. Typically as little as 0.25 lbs. of a pre-dispersed carbon black will increase the hide from 98% to 99.5% without significantly reducing the whiteness of the paint. Hide is generally determined by measuring the Y (in the CIE scale) or L* (in the L*a*b* scale) color value over the white area and over the black area of a panel that was coated using a fixed gap draw down bar. We usually use a 3 mil bird bar which has a 6 mil gap and typically produces about a 3 mil dry film thickness for a typical architectural coating.

%Hide = [Y(over black area) * 100] / Y(over white area)

The End User

Clean is a Necessity!
By Michael Van De Mark, Director, Missouri S&T Coatings Institute

Surface cleaning is a very high priority step in the coating process. Various washing, de-greasing and de-oxidation treatments have been used. No matter what process is used, problems can still arise. One of the most common sources of surface contamination is not process dependent, but is a result of the employees. These contaminants are due primarily to the personal care products and cosmetics of the employees.

A key ingredient in many personal care products, such as deodorants, is silicones. If a can of deodorant is used near a coating line, it can cause craters in the coating. Even if it were applied at the employee’s home, transfer to their hands and subsequent transfer to the surface is a problem. The result is random coating defects. Mineral oil and silicones are common ingredients in many cosmetic products. It is important to define to employees a list of ingredients to avoid in these products. Also the use of make-up, body oils, shaving cream, hair dressings, and hand lotions should be limited. Touching the face, neck or any part of the skin with their gloves can result in transfer of these components to the substrate. The workers' gloves should be kept free of these components through proper education of the employees as to the potential problems and, if necessary, repercussions which may result from ignoring the rules. Rework of parts due to these problems costs the OEM industry significantly each year. It is interesting to note that, in general, most unions will work with management to help eliminate potentially contaminating products both from the work place and from use by employees before they come to work. It is in everyone’s best interest to have as little rework as possible.

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