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Home  > Forum  > Special problems & miscellaneous  > Gloss retention increase with 2K PU

Tuesday, 21 May 2019

Gloss retention increase with 2K PU

1 Post

Philippe Dufour

Tuesday 06 November 2018 12:58:38 pm

Can one suggest why some 2K PU topcoats (ie pigmented, cross-linked systems) may undergo ‘gloss retention increase’ under QUV ageing. Example: (60°) gloss before exposure is 74, then keep increasing by 4 units/1000h. Thanks.

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Vasilis Mouratidis

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Thursday 22 November 2018 10:42:33 am

If the coating is freshly applied then the heat or light generated from the lamps might be speeding up the curing process (usually polymerization of a coating continues for weeks after it is applied) and this means that the physical characteristics of the film change, it becomes more densely crosslinked and the surface increases in gloss.

If it is old then maybe some of the ingredients of the coating that have migrated to the surface are softened by the light itself or the heat generated by the lamps and this changes the surface properties of the film.

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