How long to cure fresh paint before applying vinyl?

[signbrad]

The problem you had was that it wasnt cured at all, clearcoat is catalyzed and isocyanates stop working around 65 degrees.

Temperature can easily interfere with paint catalyzation. If the paint booth is too cold when the painting is done or the vehicle is painted and then rolled outside where it is too cold, catalyzing slows dramatically. You could very easily have a situation where a mask tries to bond to a finish that has not had sufficient cure time due to a lower temperature.

How cold is too cold? Most dry times and pot life times are given at 70-75 degrees at 50% relative humidity. At the Matthews Paint school, they told us the 15 Degree Rule. For every 15 degree increase in temperature, the dry time and pot life can be cut in half. But for every 15 degree decrease in temperature, the dry time will double.

Is 65 degrees too cold for Matthews Polyurethane? I am very leery about spraying at that temperature. And at some point below 65 the catalyzing stops. And once catalyzing stops, it doesn't start back up again. It dies. And once it dies, if the cross-linking was not finished, the film is as hard as it's going to get. It will have reduced resistance to UV radiation, water absorption, and abrasion resistance. I suspect this is true for most polyurethanes and urethanes. Probably epoxies, too.

If Matthews paint is mixed exactly according their instructions and properly applied, it does not require a cure time of weeks before vinyl can be applied. I can't say that all polyurethanes are exactly like Matthews, but a paint shop should be familiar enough with the product they use to give good advice on how much wait time is required.


From Matthews' website

2007 Sign Builder Illustrated article with some info on curing:
http://www.matthewspaint.com/getmedia/cbd27018-0baf-4e9e-ae0a-1335eefefc2d/mpc_durability.pdf.aspx

Matthews Training Manual
This should link to a downloadable pdf of the entire manual. Section 16 on Troubleshooting has a wealth of information on cure times, temperatures needed, etc.
http://www.matthewspaint.com/getmed...034-4cb076f00f25/mpc-training-manual.pdf.aspx

I know I sound like a Matthews rep but I'm not. It is just the paint I have used for many years and I am familiar with it. I have been to their two-day school twice and I would go every year if my boss gave me the time off.

Brad in Kansas City

 

[S'N'S]

From SignBrads first link, the underlined bits says it all.

“Typically urethanes can take between
five to seven days to reach full cure,
unless the sign is being baked or accel-
erated,” says Sawar. “One of the reasons
the industry has come up with accelera-
tors is to speed up the polimerization
process (the paint/catalyst reaction). For
example, using an accelerator enables
the sign builder to apply vinyl in hours
rather than days.”