On 1/24/22 11:05, Paul Koning via cctalk wrote: > Looking at that spec some items pop out. > > The coating is quite thin, much thinner than the backing. Not too surprising > actually, if it were thick it would reduce the max possible bit density. > > There is a coating wear spec (as a ratio of wear resistance relative to an > ordinary tape) but no other specs on the coating, such as solvent resistance. > > There also is no description of what the coating is. I also used to think of > DECtape "sandwich" tape as mylar/oxide/mylar, but the documentation doesn't > say that. And at a coating thickness of 0.04 mils, it clearly isn't another > mylar ribbon layer. It sounds more like some sort of sprayed-on coating of > some sort of abrasion-resistent material. It might well be porous, which > would be a possible explanation for the oxide coming off when rubbed with > solvent.
I think you're pretty close on this. My guess was a lubricant coating; perhaps with some graphite included. It would make sense, as it, not the mylar base is the thing that gets the wear. I have to take a look at some 3M "Black Watch" 1/2" tape, which I (may, allowing for neuron rot) has a similar dark coating on the business side. --Chuck