At 07:48 AM 2007-05-14, Tom Fine wrote:
>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
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.
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.