Introduction
For 40,000 years people have been using paints and coatings for decoration, protection, and camouflage in daily life routines. Early paints contained naturally occurring dyes and used egg yolks, linseed oil, waxes, or other natural binders to help it adhere to surfaces. Changes have been made since early formulation, but the paints and coatings industry was revolutionized following World War II when toxic components, such as lead and mercury, began to be removed.
Today synthetic polymers, resins, and solvents are used for paint production. These materials outperform their historic predecessors, showing an increased resiliency for weathering effects such as acid exposure, extreme heating and cooling, and water exposure from rain or snow.
Paint is a three component material made of a pigment, a vehicle, and carrier. High quality paints are made from high quality materials, and manufactures need to test materials to ensure that consumers will be happy with the products they purchase. To ensure that they have the right blend of components a manufacturer will run loss on drying assays, which examines the amount of material that will volatilize once it is heated.
Traditional testing methods
ASTM International has dedicated method D2369 for determining volatile content of coatings using an oven method testing. First approved in 1965, this method effectively determines the volatile content, but is not able to take advantage of new technology that reduces testing and throughput times, which would allow manufacturers to improve the efficiency of their metrology process and allow them to reduce product manufacturing times. Additionally, this method is not able to provide real?time results for analysis, which would be helpful to immediately diagnose possible manufacturing problems.
Rapid loss-on-drying
Because of technological advancement in traditional loss?on?drying techniques, ASTM International adopted method D7232 in 2006. This method is designed to produce the same result obtained from testing using method D2369, but reduces testing time from 2+ hours to minutes. Additionally, the Computrac® MAX® 4000XL Analyzer provides in?situ measurements, giving metrologists the ability to diagnose manufacturing problems immediately.
Testing and Results
For this experiment 3 different materials were tested using ASTM method D2369 and D7232. For method D2369 a convection oven was used and for D7232 a Computrac® MAX® 4000XLinstrument was used. Between sample testsusing the MAX® 4000XL the coatings and pigment were shaken in their containers. A flat pan with paper was used for each test and the materials were placed onto the pan using a 5mL plastic syringe.
The data from the tables above show that the two methods provide similar results. Additionally, the MAX® 4000XL showed a significantly tighter testing result range for 2 of the 3 sets of testing.
From the graph, the resin begins to volatilize around 100 seconds, suggesting that the idle temperature is cool enough to prevent the material from evaporating prior to data collection. Also, the tail of the rate graph shows that the material has lost all volatile content and the test is allowed to end. This is a typical graph for all 3 materials that were examined.
Conclusion
For testing paints and coatings, rapid loss?on?drying methods prove to be more desirable than traditional testing methods. Both testing methods were able to provide similar results, but the MAX® 4000XL was able to reduce testing times when compared to the convection oven, and gives a complete profile of the materials as they are being analyzed. This technology can be used to reduce manufacturing throughput times, and provide quality improvement with more information should formulation problems arise.
James A. Moore, Research Chemist
Arizona Instrument LLC