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

-- 
Richard L. Hess                   email: [log in to unmask]
Aurora, Ontario, Canada                             647 479 2800
http://www.richardhess.com/tape/contact.htm
Quality tape transfers -- even from hard-to-play tapes.