Hi Richard,

Charlie Richardson's assertion (as I understand it) is that the
back-coating, introduced to reduce static buildup, absorbs humidity by
design. Being in contact with each adjacent layer of the oxide, the
humidity absorbing back-coating promotes binder hydrolysis.

Fascinating thread. Thanks to all who have contributed.

Cheers!

Corey
Corey Bailey Audio Engineering

On 1/21/2016 5:52 PM, Richard L. Hess wrote:
> On 1/21/2016 7:55 PM, Tom Fine wrote:
>> And this once again circles back to one of my main questions -- if
>> sticky shed is due to problems with the binder, then why would removing
>> the back-coat seem to first of all make a tape un-sticky and second keep
>> it un-sticky for a long period of time, if not permanently?
>
> Hi, Tom,
>
> This is a VERY good question that I have asked myself (and others) for
> many years. No one except Richardson blames the back-coating.
>
> So, here is one thought I have had about this. I am not saying that
> the chemistry is the same, but I'm saying it MIGHT be a similar effect.
>
> Do you recall how vinyl sheet protectors will weld to electrostatic
> copier printing and pull it off? There is something in the vinyl that
> is attacking the electrostatic "ink" which is really plastic which is
> melted onto the paper. So, it appears to be a plastic-to-plastic
> reaction.
>
> OK, we have plastic binder on the front and plastic binder on the back
> in touch with each other. Could a similar reaction be occurring?
>
> Here is a complicating factor and a possible alternate explanation to
> the above conjecture. I believe the carbon black in the back coating
> is highly hygroscopic so it can act as a moisture concentrator that
> slurps moisture from the edge of the tape pack and wicks it across the
> full width. That moisture then accelerates the hydrolysis of the binder.
>
> But accelerates is different than starts. Well, I'm sure you've
> noticed some tapes when wiped have degradation products and/or dirt
> coming off just at the edges? Without the carbon black to wick the
> moisture into the pack, perhaps the edges degrade first?
>
> Now, this conjecture raises another issue and that is what type of a
> reaction is binder hydrolysis? Is it a linear no threshold reaction or
> is there a threshold of moisture below which hydrolysis will not occur.
>
> This is similar to ionizing radiation where study upon study shows
> that up to a point radiation is actually beneficial and then becomes
> harmful. Some scientists are saying the government mandated linear no
> threshold model for radiation is flawed and wastes huge sums of money.
>
> I realize one is chemical and one is biological, but still, some
> reactions need a catalyst to start or keep going.
>
> There is more here that we don't understand (on both counts).
>
> So, here is a post full of thinking out loud, but why not? If it
> triggers someone who cares and has access to an analytical lab and
> funding, perhaps it might go some place. Better to throw it out there.
>
> Remember, do not rely on anything I said in this message. Use it only
> as a basis for further analysis. I do not know what's true. I know
> what I'd want to check out given a white coat, glassware, and other
> things I have no real knowledge of. My last chem class was Grade 11. I
> did well and enjoyed it, but that was a long time ago.
>
> Cheers,
>
> Richard
>