Re: [ARSCLIST] powder-like substance from open reel tapes

[Claus Trelby <ctrelby@xxxxxxxxxxxxxxx>]

Hi John,

Welcome to the 70?s tape pit. I?m sure you have heard about sticky-shed
syndrome etc.

Environmental law changes forced most tape manufactures to change the
formula of their binder in the early 70?s. This has left us with resulting
sticky-shed and other artifacts. Scotch/3M I have found not to exhibit
sticky-shed unless it was stored VERY poorly, but? A fine white powder will
in many cases be released and distribute itself on the tape path and heads.
It is very hard to see, and in many cases you have to look at the erase head
(it?s black) to see this. The powder is fine enough that it will slowly
deteriorate the Hi frequency play-back response during a pass.
The baking of tapes is not a fix-all solution. It was specifically developed
by a group of engineers from Ampex to solve the sticky-shed issues. AGFA
developed their own solution to the same problem. (I?ll include an email
from a BASF engineer to our Video Director at the end of this posting). No
such study was done by Scotch/3M to my knowledge but I have found that a
pass or two on a pellon based cleaning machine with light tension will clear
off the powder and render the tape playable. This process can also be done
by hand if you are very careful.

I know this doesn?t answer your question about TDK, but I have not
encountered tapes from the 70?s from TDK, and have no direct solution for
you. It sounds like and cleaning pass is in order for you, BUT PROCEED WITH
CAUTION, and test on lengths of tape with no audio, since you might damage
the tape in trying to find your solution.

The following excerpt is from and email from Terry O'Kelly, formerly of BASF
to Pat Shevlin, Xepa Digital. (130 @ 8hrs refers to 10.5? dia, 2? tape - I
would still suggest this process is done by engineers with experience to
assure a successful result)?

...


?I do have good records of the Agfa XT process and the AMPEX process for
driving water molecules out of the polyurethane binder.  Agfa used a
microwave, but the oven had to be so carefully controlled over a short
period of time that it was not generally recommended for users.  IDT in West
Palm Beach licensed the Afga method, but I don't know if they are still
around.

The Ampex method used a convection oven with an internal fan that moved
heated air around the tape.  The tape was slowly brought to a temperature of
130 degrees F. for a period of about 8 hours.  Plastic reels could be used,
but it was better to have transferred the tape to a metal reel.  The
transfer process itself helps to redistribute tension in the tape pack to
make it more uniform.  More than one tape required a spacer such as an empty
metal reel.  Once the tapes had cooled to the touch, they were good for
about 30 days; but copying the data as soon as possible was safest.  The
binder would begin to absorb water again after 30 days, but the linking
structure of the binder would be damaged enough that a second baking may not
have prevented the oxide/binder combination from delaminating or rubbing off
altogether.

The goals of both the Ampex and Agfa methods were the same: drive the water
molecules out.  The XT process was faster but more difficult without a very
controlled environment.  The Ampex process was slower but easy to follow for
most people.?

...

I hope you find this helpful.

Claus.

Claus Trelby
Managing Engineer/Partner

XEPA Digital
1137 Branchton Road, 19-N-3
Boyers, PA 16020-0137
www.xepadigital.com
ctrelby@xxxxxxxxxxxxxxx
P:724-794-3686
F:724-794-3292
C:805-490-1730



-----Original Message-----
From: Association for Recorded Sound Discussion List
[mailto:ARSCLIST@xxxxxxx]On Behalf Of John Loy
Sent: Tuesday, September 28, 2004 3:40 PM
To: ARSCLIST@xxxxxxxxxxxx
Subject: [ARSCLIST] powder-like substance from open reel tapes


I was wondering if anyone had experienced a powderlike substance from
open reel tapes from the early to mid 1970's. The brand of tapes are
TDK. The powder has been gumming up the machine's transport yet has not
impeded play or audio quality. When I go to rewind a tape however, it
slows the machine and prevents a full rewind at which time I have to
clean the machine. The powder is a yellowish-brown and while it is on
the guides and heads of the machine looks organized but scrapes off
into a power. If you have heard of or experienced this problem please
respond and let me know what I can do about it or what effect it may
have on my machines or the tapes in a long term storage situation.
Please ONLY helpful, polite inquiries.



  thanks,
John A. Loy
Audio Preservation Engineer
Southern Folklife Collection
UNC Chapel Hill

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