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"Lacquer yellowing"





January 8, 2010

Hi all,

Have a problem with polyurethane coating which assumes a brown-yellow colour when undergoing a tropical test in contact with leather. Coating protects Brass zipper teeth.

The problem occurs even when coating is put over white carton.

Does anybody have any ideas ?.

Thanks

Gordon Reina
Continuous Improvement - Varese, Lombardia, ITALY
^


January 20, 2010

I've heard our lacquer supplier who said that yellowing might be due to the % of catalyst. Does anybody have any other suggestions ?

Your advice is welcomed.

Gordon Reina
- Varese, Lombardia, Italy
^


January 22, 2010

Could it the tannin from the leather? However, it is more likely that the lacquer is not yellowing but the brass substrate being affected by UV light rays. Try to add some UV absorber to the lacquer if it does not have some already included.

Terry Hickling
Birmingham, United Kingdom
^


February 12, 2010

You inform me that it yellows (private e-mail) without UV interference ... unless you keep it protected natural sunlight will yellow some resin systems. Try to purchase a lacquer based on an acrylic resin system ... if I remember I think paraloid acrylic resins dissolved in solvents would be the basis for a suitable varnish.

Terry Hickling
Birmingham, United Kingdom
^


March 9, 2010

Dear Terry,

I thank you for your suggestions.
Do you know if any commercial product exists with the properties you mentioned ?

Regards

Gordon Reina
- Varese, Lombardia, Italy
^


March 17, 2010

Try Paraloid B 44 acryl resin dissolved in toluene(you can use less toxic solvent/or solvent mixture too).7,5-10% must be ok.I think that italian company CTS Srl. sells it(conservation of metals is one of applications).Baked epoxy based clearcoat(special coating for brass/aluminium hardware) can be very good too(Austrian producer is Lorenz Industrielacke,Purkersdorf).Hope it helps and good luck!

Goran Budija
- Zagreb, Croatia
^

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