24 Jan
2022
24 Jan
'22
11:05 a.m.
On Jan 23, 2022, at 8:40 PM, Noel Chiappa via
cctalk<cctalk at classiccmp.org> 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.
paul
From: Gary Oliver
I've always thought the physical tape wound on a DECtape spool was a
fairly conventional 'sandwich' of mylar/oxide/mylar ...
Was there some kind of 'lubricating' coat on the data side? It makes
sense, but none of my DEC documents or Googling has any mention of
lubrication ...
If someone has some detail information on the tape construction, I'd am
curious to see it.
Dunno if you know of this:
http://www.bitsavers.org/pdf/dec/dectape/3M_DECtape_Spec_Nov66.pdf
but it doesn't mention any lubrication, just a "Protective Overlay" layer,
over the "Coating" (which I assume is the oxide). I'm a bit surprised that
"some of the data side of the tape came off on the wipe", though, unless the
"various concentrations of isopropanol/water" dissolved the Protective
Overlay.