FLAT CLEAR FINISHES

Q. My company manufactures illuminated control panels for aircraft cockpit usage. These are normally fabricated from a MIL SPEC grade of clear cast acrylic.

Back-lit graphics are applied to the front of the panels to denote the various switch and display functions. The colors used are quite limited, with the majority being black and to a lesser degree a couple of shades of gray and some browns.

To cut down on glare, the topcoat colors are normally specified from the flat grouping of FED STD 595. Depending on where the panels are finally mounted in the cockpit, wear and tear can range from light to heavy. As a final step in their process, most manufacturers apply a clear coat of some sort to the panel faces and edges for added durability.

I’ve been searching for years for the “ideal” clear coat for this type of product. Suffice to say, two-component urethanes are the most durable. But no matter what the type of vehicle system being used, there seem to always be trade-offs somewhere.
Mar resistance is a big issue with me. Resistance to fingernail burnishing is seemingly difficult to achieve. I’m sure there is more than one material used to make paints flat. Does any one stand out as being more resistant to burnishing?

Another issue is the amount of flatting agent used. I’ve seen some loading so heavy that blacks no longer look black. They turn grayish. Most panel manufacturers rely on the flat clear to hide little cosmetic “sins” that occur during processing. So some hiding power is good but again, not to the point of changing the paint color.

Are different agents more efficient in their ability to create a flat finish? What would be your formula for the perfect clear coat?
I’ve read your column for years. Keep up the good work. C.H.

 

A. According to what I read in the literature, you should be looking at clear coats containing silica or silicates for improved mar resistance.

Another approach is clears containing nano-particles.

Although I can’t quote chapter and verse on who supplies what to whom, I can suggest you contact the coatings suppliers listed in the 2008 PRODUCTS FINISHING DIRECTORY AND TECHNOLOGY GUIDE.