Question about DECtape formulation

[Paul Koning]

> 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.

	paul