I apologize! I think now we are all in violent agreement here, then.
Thank you for a clear explanation and also thank you for noting that the
resulting polymers after baking are more likely to revert.
I'm not trying to cause trouble, I'm trying to understand...still.
Yes, the packing was a major consideration in the back coating
design...allowing a path for entrained air to escape.
Wasn't 3M first with back coating with 206/207 in 1969 (3M date
confirmed via the late Del Eiler's spreadsheet at aes.org/aeshc/)?
I think that was billed at the time as static drain, better escape of
entrained air, and better guidance, but I could be wrong. Anyone have
data sheets / ads going back to then?
Thanks for sharing all this information.
On 1/22/2016 8:48 PM, lists wrote:
> Arrgh, Richard:
> You did exactly what I asked "please" not to get into in my early post. Oh well- I said quite that hydrolysis is NOT REVERASBLE it is BI-DIRECTIONAL. People keep trying to prove the wrong thing- it is not reversible, it is not reversible, it is not reversible- it is bi-directional! The oligomers cross-link back into polymers. We and others have proven this in the lab- not just Cuddihy.
> They don't cross-link back into the original polymers (not reversible!). In addition, the polymers that are created by the cross-linking are almost always shorter than the originals- which means they are more subject to hydrolysis breakdown in the future than the originals-but they are still polymers and aren't "sticky".
> Sorry for the "rant".
> As for the carbon black, my contact at AMPEX who helped work on tape development indicated that the backcoating was not done as a static barrier but as a method to allow to tape to pack more smoothly.
> -----Original Message-----
> From: Association for Recorded Sound Discussion List [mailto:[log in to unmask]] On Behalf Of Richard L. Hess
> Sent: Friday, January 22, 2016 1:29 PM
> To: [log in to unmask]
> Subject: Re: [ARSCLIST] One more sticky-shed data point - Richardson treated tape
> On 1/22/2016 12:05 PM, lists wrote:
>> remember, hydrolysis is a bi-directional chemical reaction. Not only
>> is there a threshold at which hydrolysis will occur, there is also a
>> threshold at which hydrolysis will run in the other direction and the
>> oligomers will cross-link back into polymers.
> Hi, Peter,
> That was definitely Bertram and Cuddihy's conjecture, but in the work that Ric Bradshaw did at IBM, he has seen evidence that this is not the case. As I understand it, he draws the following distinction:
> In basic chemical theory, the reaction is bidirectional, but in the filled matrix that is the recording tape binder, there is little likelihood that the ends of the severed long chain molecules will find receptive "landing sites" [RLH's phrase, not RWB's] and even less likelihood that they will find the original points from which they were severed.
> So, while there may be some random cross linking, the physical presence of the magnetic particles, lubricants, and other components of the mag coat matrix interferes with the reversing of the process. I believe I can state Bradshaw's conjecture as: yes, there may be some re-linking, but it never will come close to the original condition on day of manufacture. In other words, once it goes down this path, it's never coming all the way back.
> Thank you for the clarification of Richardson's hypothesis. I don't think I ever got that out of what I've read of his, but I have not read all of the material he sent as some was sent under non-disclosure and I do not recall opening it. I felt if I read it and integrated it into my understanding, I might inadvertently disclose something. At one point in my past life, I commented, "I have signed so many NDAs that I can't even talk to myself!"
> Also, thanks for confirming the existence of a threshold in the onset of hydrolysis. That makes sense.
> One other question. One of your recent posts seems to suggest that the hydrophilic nature of the carbon black or other back-coating materials was part of the plan. Was it? Or was carbon black chosen to be conductive to dissipate the static charge which, under certain conditions can spark over and print a "tick" to the tape? Perhaps the hydrophilic nature of carbon black was either ignored or not known by the designers--or they thought that it wouldn't be an issue. It would be much more expensive to deposit a copper or silver (and probably even
> aluminum) thin film on the back side of the base film to provide that conductivity.
Richard L. Hess email: [log in to unmask]
Aurora, Ontario, Canada 647 479 2800
Quality tape transfers -- even from hard-to-play tapes.