Paint evaluation

The fine technical assistance of Mr. Arthur H. Marsh and Ms. Ella B. Yezrielev in conducting the polymer syntheses and paint evaluation is gratefully acknowledged. The author should also like to thank Union Carbide Corporation for permission to publish this work. 

The chart on the following page may assist in paint evaluation it lists coil-coating finishes and comparative properties of some of the most popular generic coating types. It is available to assist prospective users of prepainted metal in a number of ways. 

Metal surface preparation processes and paint evaluation... 

Rheology is perhaps one of the most powerful techniques for paint evaluation during its formulation as well as in its manufacture. Before a paint is manufactured, its appUcation is known and it is essential to control its flow properties for best operation and application. To control the flow properties of the paint, a rheometer must be selected to make flow measurements which permits good interpretation of the flow properties of the paint. This allows the manufacturer to decide whether two batches of the same material or of different materials will have equal flow behavior under all conditions of operational application. The manufacturer could also predict from these flow measurements whether there is any difference in physical properties on paint application. In the preoperational stage, physical effects which occur in manufacturing and storing, such as temperature effects, evaporation, mixing procedures and shelf life must be studied. These physical effects can be correlated to the flow characteristics of the paint formulation. This allows one to achieve a more efficient and better controlled operation in manufacture and application. 

Have there been previous lead-based paint evaluations ... 

Because of the risk of lead poisoning, the exposure of children to lead-based paint is a significant public health concern. The first step in the quantitative analysis of lead in dried paint chips is to dissolve the sample. Corl evaluated several dissolution techniques. " In this study, samples of paint were collected and pulverized with a Pyrex mortar and pestle. Replicate portions of the powdered paint were then taken for analysis. Results for an unknown paint sample and for a standard reference material, in which dissolution was accomplished by a 4-6-h digestion with HNO3 on a hot plate, are shown in the following table. 

S. ColHs, The Development and Evaluation of Paint Remover Used bj the US. AirTorce Air Force Technical Report 5714, Suppl. 1, Jan. 1955. 

An important property of a pigment is its ability to maintain its color when exposed to light, weather, heat, and chemicals. This property is seldom measured for pigments alone. Rather it is determined for the dispersion of a pigment in a desired medium, eg, paints or plastics, and in many cases it is compared to the performance of a standard pigment. The observed changes are the result of complex pigment and media reactions and their possible interactions. In aH evaluations, time of exposure plays a role. 

Both prototypal questions related illustrate the need for a successhil technical service professional to have a strong understanding of the customer s apphcations and processes, within proper intellectual property considerations. This need for a thorough understanding is not always straightforward. A common example of the complications that can arise is provided from the paint (qv) industry (11). If, for instance, a calcium carbonate suppHer would like a paint manufacturer to use their material versus a competitive one, the onus is on the suppHer to show that the material can be successfully used in the paint formula of interest. However, many such formulas are held as proprietary. The technical service professional therefore does not know the components of the paint. This would lead to an unworkable situation from an evaluation standpoint save for the fact that the paint company may supply a miHbase or other intermediate form of the paint to allow a proper comparison of carbonates to be carried out. Thus mutual benefits can result and no loss of proprietary information occur. 

New product introductions are generally heavily supported by the technical service function. Many customers using chemical feedstocks to produce multicomponent products for the consumer market require extensive on-line evaluations of new raw materials prior to their acceptance for use. An example of this would be the use of a new engineering polymer for the fabrication of exterior automobile stmctural panels. Full-scale fabrication of the part foUowed by a detailed study of parameters, such as impact strength, colorant behavior, paint receptivity, exterior photodurabiHty, mar resistance, and others, would be required prior to making a raw materials change of this nature. 

Abrasion Resistance. Porcelain enamel is the most scratch resistant and hardest of commercial coatings (see Hardness). This property is used to distinguish between porcelain enamel and organic enamel or painted coatings. The rate of abrasive wear in surface abrasion increases with time, and the subsurface abrasion which follows exhibits a higher, but constant rate of wear. Abrasion resistance can be evaluated by loss of gloss or weight (35). 

Standard method for evaluation of painted or coated specimens subjected to corrosive environments Standard test method of salt spray (FOG) testing... 

Brown and Fessler have conducted a laboratory evaluation of conductive mastics that can be brushed or sprayed onto the concrete surface to achieve the necessary thickness. However, the most extensive study on conductive paints for cathodic protection purposes has been undertaken by the Federal Highway AuthorityA total of nine commercially available resins were evaluated in this work. It was shown that neither thermal cycling, freeze thawing nor the application of cathodic protection currents... 

The main value of salt-spray tests is in the evaluation of the effectiveness of phosphate coatings in restricting the spread of rust from scratches or other points of damage in a paint film. This feature is of particular interest to the motorcar industry, as vehicles are often exposed to marine atmospheres and to moisture and salt when the latter is used to disperse ice and frost from road surfaces. Great care is needed in the interpretation of a salt-spray test, as it has been found to favour thin iron phosphate coatings more than is justified by experience with natural weathering. In the motorcar industry the present custom is to use zinc phosphate coatings on the car bodies and all other parts exposed to the outside atmosphere. 

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