Question about DECtape formulation

[Chuck Guzis]

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