Every now and then, when I print designs the length of the platen, some of my shirts come out with an outline of the neck of the platen on them.
I know it's from where I press the squeegee on the part of the screen that overlaps the shoulders of the platen, but in some instances (i.e., when the design is the size of the platen), this is unavoidable.
(1) What's causing this? My best guess is that it's from adhesive build-up, but I really don't know.
I'm going to make the assumption that you have actual INK on the shirt that is the outline of the platen. If that is the case, it sounds like your emulsion might be breaking at the edges of the platen and allowing ink to be pushed through with the print stroke. You can: 1) use less squeegie pressure, 2) make a thicker stencil with more coats of emulsion, 3) make sure your screen is tight in the frame, 4) put some tape on the shirt side of the stencil where it comes in contact with the edges of the platen, 5) round & smooth the edges of your platen more to eliminate any sharp edge that might be breaking through your emulsion.
is the outline the color of the shirt or the ink being used? Shirts will sometimes leave some of the dyed cotton at places and builds up faster around the area where seams are.
sounds like this might be happening. should be any real problem for you.
I apologize for not making myself totally clear. The outline is not the color of the ink used, but it is a gray-ish outline of the neck of the platen. (That's why I wasn't sure if it had anything to do with adhesive build-up....but I've since ruled that out.) I can spot remove it, but I'd rather not have to.
Like I said, it's only when I press the squeegee the total length of the platen. When I am printing a design that is small enough so I don't have to swipe the squeegee all the way up the platen, the line doesn't appear.
Platen outline on shirts 
