Two-Component Coatings

Question:

I need literature on high gloss problems concerning liquid paint and conventional oven curing. We are having gloss fluctuation with the liquid paint. Parts are not coming out of the oven at consistent gloss levels. The mixing ratio of the paint has been checked and doubled checked. There is no mixing problem that we have found.

Can you provide me with a breakdown of catalyst ounces vs. gloss? Example, if mixing ratio of paint is 4:1 and the gloss of the paint is 35+/-10 deg and 1 more ounce of catalyst is added, how many more degrees will that 1 ounce increase the gloss? The catalyst in question being used is polyurethane. T.B.

Answer:

I'm good T.B., but I'm not that good. If I were, I'd be rich instead of famous. My first comment is that a 35 degree gloss is not a high gloss. Instead, a high gloss is 80 to 90 degrees. Furthermore, I think your +/-10 deg variation in a 35 deg gloss is too great. If that is the supplier's specification on your paint, you could produce glosses of 25 and 45 and still be in spec.

There is no true, safe or reasonable relationship between catalyst ounces and gloss that you or anyone else should even think about when using two-component coatings. It is well known that modern paints are engineering materials. Some bright kid spent weeks in the laboratory developing the formulation for the paint you are using. It is formulated to be mixed in the ration of 4:1, that is, four parts of the pigmented part to one part of the catalyst. Any variation in that ration may very well cause a difference in gloss, but that is the good news. The bad news is that it may not cure properly, and worse, will most likely cause a difference in the performance properties. I don't like to give advice, but if I were you, I wouldn't mess with the mix ratio to solve your gloss fluctuation problem. Instead, I would look elsewhere.

Some common causes of gloss variations in cured paint films are the following:

Infrequent and improper mixing of the pigmented portion of the paint;
Infrequent mixing of the catalyzed paint;
Unstable oven temperature;
Spraying too wet or too dry (this can result from different solvent reductions and from different gun to product differences); and
Painter technique (there can be gloss differences from one painter to the next).

These are some of the causes. I'm sure that if I thought about it long enough, I could come up with others. In any event, this gives you something to think about.