August 1, 2014
Note: Low-cure coatings are sometimes referred to as low-bake coatings, or ultra low-bake coatings (ULB). There’s no single standard for these terms, so we use them here interchangeably.
Why use a low-cure coating?
Most of the time, a low-cure coating is needed because the part – or some section of the part – won’t hold up under high cure temperatures. Cure cycles are based on the temperature of the substrate, not the temperature inside the oven. And many cure schedules for standard coatings require the substrate to reach temperatures above 700°F. But that’s not always possible. For example, we’ve got a part in right now that has a neoprene edge on it – the part can’t go over 200°F.
Another reason to use a low-cure coating – we see this occasionally, but not frequently – is to save on cost. Reduced baking requirements mean lower energy costs.
What low-cure coating options exist?
A number of coating manufacturers have reformulated their most popular coatings in a low-bake formula. These coatings typically cure at temperatures between 275°F and 375°F. Some of the most common low-cure formulations are for epoxy, polyester, and other powders.
But even non “low-bake” coatings like the Xylan® 1000 series can be low-bake – in a sense. We’ve had parts that we’ve coated in Xylan and cured at temperatures around 200°F. But there are some pretty big tradeoffs involved in curing at low temperatures like that.
What are the drawbacks of low-cure coatings?
If you’re talking about the reformulated low-cure coatings, they achieve the low-cure formulation by using additives, often a polyamide-imide. Depending on the functionality you need out of the part, these may be fine. But additives always mean that you are sacrificing some performance.
The same thing happens when you cure a normal coating at lower temperatures. You’ll probably get fine mechanical performance – toughness, weatherability – but the chemical resistance and nonstick properties will suffer. Whitford has a chart that illustrates how this works, but it’s true with almost all coatings – if you want really good chemical resistance, you’ve got to be able to get up into the 500°F range, and even higher if you want to get any nonstick.
(Check out Whitford’s chart on page 3 of this document.)
What are some of the advantages of low-cure coatings?
Aside from the cost savings, which we already discussed, really just not damaging your part is the big advantage.
The thing to be aware of here is that if you’re just looking for good weatherability and cosmetic finish, there are a lot of good options. But if you need properties such as chemical resistance and/or nonstick, your options are going to be pretty limited, despite what some coating manufacturers may say. At that point, you need an experienced coater that will give you real-world advice, so that you don’t end up with a bunch of part failures down the line.