As I indicated in an earlier post, binder hydrolysis is not the only decay vector in magnetic tape. Baking will not cure 100% of the problems. I listed in my post about half a dozen other decay residues that have been detected and analyzed in the laboratory that were not binder hydrolysis. The interaction of different residues may have effects that have not been tested. Unfortunately, with the demise of tape, the huge labs with the expensive equipment set up to analyze these issues (often at a considerable cost) are not as readily available. We know a lot about hydrolysis since it was detected as a major issue and studied. It is not, however, the only issue.
Here is a weird one that I cannot come up with a scientific answer for:
If a tape (backcoated or not- happens to both types) throws a loop or cinches- and the oxide from one wrap is pressed tightly against the oxide from the adjacent wrap in the pack- and remains that way for a while (timing not determined); the oxide layers that are touching each other will occasionally fall off the tape when the tape is unwound. It falls off in a "sheet" across the entire width of the tape and for as far along the tape as the two oxide layers are in contact. This is not an issue of the oxide layer cracking where it is folded over and "peeling" off as the heads hit the crack/crease. We have unwound some of these tapes by hand (very slowly) and the oxide layer just falls off the tape. It is also not an issue of the oxide layers sticking together, overcoming the oxide/base adhesion and ripping off. The "sheets" of oxide are not adhering to the base layer and are not adhering to each other. They appear not to be adhering to anything- they just fall off- very strange.
The only thing I can come up with is that the oxide layers and the backcoat have different frictional properties. In addition to all the other ingredients, the oxide layer of many tapes have an abrasive. It is possible that the frictional coefficient of the oxide layers cause them to "lock" together to some degree when they are pressed tightly together inside the pack. If the tape is exposed to temperature changes, the expansion/contraction of the pack, with these two contacting oxide layers "locked together" might, eventually, be enough to loosen the binder adhesion to the base. This is pure speculation but I can't come up with another explanation. Any guesses?
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From: Association for Recorded Sound Discussion List [mailto:[log in to unmask]] On Behalf Of Richard L. Hess
Sent: Monday, January 25, 2016 10:52 AM
To: [log in to unmask]
Subject: Re: [ARSCLIST] One more sticky-shed data point - Richardson treated tape
The lowering of the Tg is a symptom and has to be caused by something.
It is not as if there were a "Tg knob" to turn that down. There has to be a cause.
I do not know whether or not hydrolysis is the engine behind the lowering of the Tg. Tg is like body temperature. You might find a way to lower your temperature, but the doctor would like to find the underlying
I'm not ruling out Tg drops begin caused by hydrolysis...what other degradation modality might cause this? I will accept that hydrolysis may not always result in sticky shedding.
That is why I started to create a symptom- and cure-based taxonomy of failure modes and why I thought "Soft Binder Syndrome" (caused by hydrolysis or not) was a good over-arching category with the Venn diagram circle for traditional sticky-shed syndrome included completely within the SBS circle.
On 1/25/2016 9:44 AM, Shai Drori wrote:
> No, I think Richards theory about the Tg is accurate about cold play.
> These tapes do not show any of the signs of SSS but do respond to other methods.
> Have I missed anything and someone was able to play them fine after baking?
> Shai Drori
> Expert digitization services for Audio Video Hi Res scanning for film
> 8mm-35mm www.audiovideofilm.com [log in to unmask]
> On Mon, Jan 25, 2016 at 2:45 PM, Tom Fine <[log in to unmask]> wrote:
>> I'm wondering if this is an extreme case of what I've been
>> theorizing about the surface getting degraded from going sticky and then being baked.
>> Maybe the Sony and 3M tape that Richard has to cold-play have a
>> surface so screwed up, either because it goes very un-smooth or
>> something happens where binder material "dries out" so it doesn't
>> shed but remains somewhat "rubbery" right at the surface have a
>> chemistry that makes hydrolysis particularly damaging to the physics of the material?
>> -- Tom Fine
>> ----- Original Message ----- From: "Shai Drori" <[log in to unmask]>
>> To: <[log in to unmask]>
>> Sent: Monday, January 25, 2016 1:03 AM
>> Subject: Re: [ARSCLIST] One more sticky-shed data point - Richardson
>> treated tape
>> High Richard
>>> I think we had a discussion about these two in the past. The PR-150
>>> has some batches that run fine but most do squeal. I haven't even
>>> tried baking them except once just for the hell of it and of course
>>> no luck. Double speed playback works when possible but I haven't had
>>> any lately so haven't tried cold play yet.
>>> Shai Drori
>>> Expert digitization services for Audio Video Hi Res scanning for
>>> film 8mm-35mm www.audiovideofilm.com [log in to unmask]
>>> On Mon, Jan 25, 2016 at 6:10 AM, Richard L. Hess <
>>> [log in to unmask]>
>>> Hi, John,
>>>> This is indeed true. HOWEVER, my success rate for baking tapes that
>>>> are suffering from squealing and/or deposition that are not back
>>>> coated is much lower.
>>>> This raises another question. If all binder breakdown is
>>>> hydrolysis, then why doesn't baking cure it 100%? I'm thinking of Sony PR-150 and 3M-175.
>>>> These two seem to show the falling Tg, but don't have the shedding.
>>>> They are outliers and inconsistent.
>>>> On 1/24/2016 3:41 PM, John Schroth wrote:
>>>> Back-coating may instigate or speed up the hydrolysis process but I
>>>>> cannot ignore the fact that there are still obscure instances
>>>>> where the tape had no back-coating and suffered from SS. Richard,
>>>>> you have noted this in the past and I have had this happen in at
>>>>> least two instances that I can recall. I'm at home today so I
>>>>> don't have access to my notes, but it was clearly sticky shed on
>>>>> tapes that had no back-coating. So one should not "always" equate back-coating with sticky shed.
>>>>> Just my two cents...
>>>>> John Schroth
>>>> Richard L. Hess email: [log in to unmask]
>>>> Aurora, Ontario, Canada 647 479 2800
>>>> Quality tape transfers -- even from hard-to-play tapes.
Richard L. Hess email: [log in to unmask]
Aurora, Ontario, Canada 647 479 2800
Quality tape transfers -- even from hard-to-play tapes.