question of coating technology-8

kba420

Copper patina is well known as the green oxidation product seen on statues and copper roofs. Antifouling paints which contain around 40% copper oxide as a functional pigment can also develop patina on the surface given the right conditions. Patina on vessels is most notable on the ˜boottop˜              

area     “which is intermittently wet and dry and often exposed to splashing as the vessel moves through water. This patina can be seen as white, green or blue patterning on the surface. Although patina is not thought to have a negative effect on antifouling performance, it can be unsightly and difficult to remove, resulting in poor overcoat ability and customer dissatisfaction, particularly where it occurs during fitting out at new building. A program is in development to find the best method of reproducing patina in the laboratory environment enabling a better understanding of the phenomena and developing improved products - and services - to deal with the issue. There are a number of questions which relate to this task: 1. how can we best reproduce patina formation in the laboratory? Chemical routes (e.g. surface washes or alternative immersion media) Physical routes (e.g. wet / dry cycling or alternative exposure criteria) 2. How can we safely and effectively remove patina in service? Chemical routes (e.g. surface treatment or wash media) Physical routes (e.g. washing, scrubbing) 3. How can we prevent patina formation in service, particularly at New Building, without reducing overall performance? Formulation route so Non-formulation routes

八戒

Hide the effect. Use a thin film, bright colour, high polishing copper-free coating for fitting out and sea-trials. Designed to polish off within 1-4 months of service

八戒

The formation of patina at NB generally occurs during sea trials when the boottop is being splashed with sea water while being exposed to the environment. It occurs on our competitors products also.As for how to reduce it, produce a reduced copper oxide antifouling for boottops, however this increases SKU's and makes painting the vessel more complex. One other option is to use Cuprous Thiocyanate antifouling for boottop coatings however I am not sure what will happen to the chemistry.

八戒

The patina should be composed of rather complex Cu-salts. It might be possible to generate it by spraying the panel with a (much) diluted HCl (or other acid) and place it in a humid and warm environment-possibly CO2 enriched as well.For removal you might try a complex former like EDTA but this might create a waste problem