Yes they did. I don't have the patent # here, but I've posted it here someplace. The inventor was Russell. I have some diagrams and the patent reference in my book.
I don't believe that the curtain coater was patented or disclosed. I think it was a manufacturing secret. At least I never saw a patent on it, nor was I allowed to see one in operation. My work only used it one time IIRC. Of course, I used the slide coater quite frequently, sometimes every other week.
Hah. after I put this up, I remembered that one example in a patent of mine used the curtain coater and probably referenced a patent if there was one. I'll have to look that up!