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Re: [ARSCLIST] Tape baking question

Hi, Tom and Dave,

I don't have even a hypothesis on this. Let's call it a conjecture based on very incomplete facts.

(1) Acetate tapes generally used acetate as the binder.

(2) 3M 201 was a departure from that, I THINK. It used the same binder/oxide (it appears) as 202 and 203, but was acetate base film. It pins often.

(3) 175 definitely squeals - ask Doug Pomeroy. In fact, it does it enough that Art Shifrin advertises a specially modded Ampex 440 to play it on. I've had success modding a Studer A810 to play the one sample of Doug's 175 at room temp (this mod does not work with Sony PR-150).

(4) We know from Brown (cited in my AES paper) that humidity appears to be the bad actor with scission of the short chains in polyurethane,

So my conjecture is that any polyurethane can break down to the point of squealing.

My AES paper shows that the over-arching problem is soft binder syndrome and that SSS is a subset of this. The binder becomes soft and rubbery (with or without major shedding) above the Tg (see previous message) This decreases the modulus (the tape surface becomes softer) and the friction goes up. This appears to be partially due to an increase in effective surface area due to the softening of the binder. Normal practice is only a few percent surface area making real contact (at the peaks, or asperities). The lubricant loaded into the tape at manufacture is designed for the harder, lower contact area manifestation of the tape, not the degraded soft, rubbery, lower Tg manifestation that was not generally considered in the tape manufacture.

Cheers,

Richard



Quoting Tom Fine <tflists@xxxxxxxxxxxxxxxxxxx>:

Guys, I think all of that type of black oxide / no-backcoat tape can
develope this problem but it doesn't seem to be a sure thing that the
problem will develop. I've had it in small does (ie clay-like residue
on the heads and guides, but not enough to hamper playback or cause
squealing --  more like "skid marks" on some surfaces sometimes) from
early 60's Scotch 202 also.

Question that comes to mind is, did the black oxide require a different
binder or could there be something different in the oxide mix that
reacts with "traditional" binder to cause this problem sometimes?

I, too, have used dozens of reels of 175 and not had problems.

And, adding yet another depressing layer to this whole thing, Scotch
206 and 208 are supposed to "never" develop sticky-shed. Well, I've had
one reel of each do it. Both were stored for long periods in damp
enough conditions that the boxes were moldy. It's only been those two
reels and otherwise, I have 30-year-old reels of Scotch 206 that still
play back at their original levels, making them as hearty as old
AudioTape.

-- Tom Fine

----- Original Message ----- From: "David Lennick" <dlennick@xxxxxxxxxxxx>
To: <ARSCLIST@xxxxxxxxxxxxxxxx>
Sent: Tuesday, October 10, 2006 10:03 PM
Subject: Re: [ARSCLIST] Tape baking question


I have never had a problem with 175 and I've run hundreds of reels of the stuff.
On the other hand, a reel of *275* (looks identical) that came from ORTF in the
mid 70s jammed up a Studer at CBC Edmonton for a day and a half in about 1983. As
far as I can recall, that's the only defective reel I've known of that stuff as
well.

(Where do I find a fridge that will hold a Teac A3300SX-2T?)

dl

"Richard L. Hess" wrote:

Hi, David,

I invented the cold-playing process--put the player in the fridge
along with the tape...I presented that Sunday at the AES in San
Francisco.

Tapes that do not respond to baking and still squeal such as Sony
PR-150 and 3M 175 do respond to being played below their current glass
transition temperature (Tg). The binder degradation has lowered the Tg
to below room temperature.

Cold-desiccation, as I understand Peter's process, is different. I
don't think he plays the tape cold.

It seems we're all incoherent. I'm in western Nebraska on my way back
from SF. Tomorrow I pick up yet another tape recorder in Des Moines.

Cheers,

Richard

Quoting David Lennick <dlennick@xxxxxxxxxxxx>:

Lists wrote:

David:


I invented the cold-desiccation process and, while it is very helpful in
many circumstances, it is time consuming and not, always, the best
alternative.  If you simply have "sticky-shed" (binder
hydrolysis), it may
not be necessary. If you have inter-wrap adhesion or binder-base
adhesion
problems, then it can be a necessity. 

This is something I want to know about..it appears that non
back-coated Shamrock
needs this process, which explains why some tapes I loaned the CBC a
 few years
ago didn't respond to baking.

Hey..Shamrock cost $1.29 for an 1800-foot reel in the seventies and we all
bought the stuff!

dl


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