I am curious about the influence of the cross-linking process on the diffusivity of a powder coating. The powder coating is applied to a metallic substrate and the thermal properties is measured with a coatmaster Atline measurement system. The cross-linking process shall be thermally activated without changing the volume of the coating.
Dear Dr. Nils A. Reinke,
relationship between the particle size distribution of the powder and the powder coating film formation during the application process to enable the formation of smooth, non-porous films the powder deposited during the application process should be as densely packed as possible onto the substrate surface prior to fusion and cross-linking in the oven. This will ensure that shrinkage and the formation of voids, pinholes and orange peel should be minimised.
The importance of the relationship between the powder particle size and the coating film thickness after curing is great. It could be difficult in achieving a uniform 25 micron coating layer with particles larger than 50-75 microns (unless the polymer has exceptionally good flow out). Packed, uniform spheres result in void spaces of up to 48%. Thermosetting powders however consist of irregular multi-sided particles of varying size and psd. When these powder particles are deposited in a layer the void volume will be greater. Therefore, before melting and cross-linking the powder film can be between three and seven times the actual thickness of the final coating film after curing.
The technology is not yet available to reduce the void volume in the deposited layer using existing methods. However, it is generally easier to obtain a smoother coating film with a lower particle size and a smaller psd. Unfortunately, it is extremely difficult to apply these smaller particle sizes.
For more details, please see the very interesting and complete source at: http://www.powdercoatingservices.co.nz/Powder+Coating/Resources+and+Useful+Links/Properties+and+Selection.html
Good reading and best regards, Pierluigi Traverso.
Dear Pierluigi
Thank you for your detailed answer. In this matter I am not aiming to get a smooth film, but to start the crosslinking process without melting the particles. Here I would like to investigate the influence of the degree of cross-linking on the diffusivity of the non-melted particle-layer.
BR Nils
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