Paint / varnish yellowing

[Madsci]

Hi peoples!

I'm working for a "glass decorating" company for alcoholic drinks and cosmetics. Recently, we had a problem with a new green apple acrylic varnish: We can't get a perfect color-match.

The color demanded by the client is a "green bottle" with a slight blueish tint inside. However, after curing (conventional heat oven), the color we have is "bottle green" with a slight yellowish color. We've asked to the paint manufacturer to adjust the pigment loading and color. After three tries, we still have the same problem: the little yellow shade/tint is still present. I tried to have more informations on the varnish, but paint manufacturers are so secretive about their paint formulations and we bought a lot of that stuff.

Is it possible that we over-bake it? I've heard that acrylic varnishes could be yellowing if they are over-baked.


Regards,


Daniel Picard, P.Chem.
Sérigraphie Richford

 

[rhodie]

What you are suggesting is possible; the bake time may need to be looked at. Look just as hard at "under-baking" time as "over-baking".

You might also look at other variables in the process such as:

1. After baking, does the color composition of the glass in the bottle changed at all?
2. Do the chemicals used to prepare the glass surface for paint change the desired color at all?
3. Is the varnish stored according to the manufacturer's guidelines? Sometimes humidity and other ambient factors can affect acrylic based coatings.


Just some random ideas for you to consider...