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ARSCLIST  May 2007

ARSCLIST May 2007

Subject:

Re: 'New' solution for stickey shed

From:

"Richard L. Hess" <[log in to unmask]>

Reply-To:

Association for Recorded Sound Discussion List <[log in to unmask]>

Date:

Mon, 14 May 2007 13:59:12 -0400

Content-Type:

text/plain

Parts/Attachments:

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text/plain (98 lines)

At 07:48 AM 2007-05-14, Tom Fine wrote:
>Hi Konrad:
>
>Some of what this guy says is simply not right about sticky-shed. I 
>can't comment on his "cure". I'll stick with baking tapes, which is 
>proven to work.
>
>I'm hoping Richard Hess posts a long missive on this one. With this 
>topic well-addressed many other places, I wonder why so much 
>mythology persists?

Hello, Tom, Konrad,

Peter Brothers has posted an excellent hypothesis as to why the 
chemical technique may work. If we consider that the short (broken) 
chains which is the lower molecular weight, sticky stuff ends up 
partially adsorbing to the magnetic particles when water is driven 
out, then this mystery chemical could also be a water "magnet" and 
can pull the water out of the coating allowing sites for the short 
chains to adsorb. This is consistent with the baking process.

We certainly have seen tapes suffering from binder hydrolysis -- what 
I'm starting to call "Soft Binder Syndrome" (SBS). With 
non-back-coated tapes there is a large population (not 100%, but 
close) that do not respond to baking. These are the SBS without SSS 
tapes. We used to call them "loss of lubricant" (LoL) until we found 
out there was still ample lubricant in the tapes.

What we are seeing with the non-back-coated tapes that have SBS (and 
squeal) is that they are in a rubbery phase at room temperature 
because the breakdown of the polymers has caused the temperature at 
which the surface turns from smooth to rubbery (called the GLASS 
TRANSITION TEMPERATURE or Tg) has fallen to below room temperature. 
What we do in these cases is play the tapes with the tape and the 
player below the current Tg of the tape.

Measuring Tg is not easy -- you need to measure the Youngs Modulus of 
the Coating (alone not on the basefilm) at various temperatures and 
from that plot you can extract the Tg.

It all comes down to the tapes decaying and for all of the 
polyester-polyurethane tapes it appears that moisture is the catalyst 
for the breakdown -- hence as Peter says, it's all hydroysis.

Incubation/baking appears to cause enough movement in the tape pack 
to break the layer-to-layer bonds that form under pressure 
(especially near the hub) that causes pinning and pullouts. I have 
found that slow (1.88 in/s) playback of the tape also helps in that regard.

I think our goal here is to use reliable, tested processes and 
digitize the content. I spent a substantial amount of effort working 
on tapes that squealed and did not respond to baking. My cold playing 
technique (which I encourage all of you to try and respond back) 
should, in theory, work with SSS tape as well as SBS (and I suggest 
that SSS is a subset of SBS), but the massive amounts of debris 
generated by the backcoat/magcoat combination overwhelms the 
capability of cold playback (at least right now) and at pro play 
speeds, pullout is exacerbated due to the bonding between backcoat and magcoat.

I do not think we've yet seen a documented case of LoL so thankfully 
that myth is being put to bed. We used to think the squealing Sony 
PR-150 and 3M 175 was LoL, but we now see that it is SBS. By the way, 
the Tg of one sample of 175 was about +8C or about 46F.

Keeping polyester polyurethane tapes dry (<40% RH) is a good way to 
keep them feeling OK. I had a non-backcoated tape of this type that 
had been peaking at 75% RH in storage "heal" after three months 
storage at about 40% RH.

By the way, it is approximately a minute:day relationship between 
thermal and moisture equilibrium--or at least that's a convenient way 
to think of it. In other words if a tape takes 90 minutes to reach 
thermal equilibrium throughout the pack, then it takes 90 days to 
reach moisture equilibrium. This is based on work with 1-inch tapes 
so 1/4-inch tapes might not be as bad, but it seems to match my experience.

My AES paper cites the reference for that.

In general, I am less happy with a chemical approach than a 
physical/state approach (within limits) to the SBS/SSS problem as 
there is a great chance of unknown, long-term damage from any 
chemical approach. With that said, I have tried approaches to SBS 
based on the LoL hypothesis and they were abysmal failures.

Konrad: we did have a belated success in your neck of the woods with 
playing a tape in a fridge. Paul or Mike have the details. I think it 
needed 48 hours of cold soak before it played.

Cheers,

Richard


Richard L. Hess                   email: [log in to unmask]
Aurora, Ontario, Canada       (905) 713 6733     1-877-TAPE-FIX
Detailed contact information: http://www.richardhess.com/tape/contact.htm
Quality tape transfers -- even from hard-to-play tapes. 

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