On Jan 24, 2022, at 2:46 PM, Chuck Guzis via cctalk
<cctalk at classiccmp.org> wrote:
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.
I thought Black Watch has coating on the back, as others mentioned. DECtape is not black
but brown, so graphite doesn't seem to be involved.