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RE: [AV Media Matters] Detailed look at history of sticky tapesyndrome


We have three tapes in-house right now that are hydrolyzed and are
exhibiting "sticky shed" that have no back coating.  These are early 2"
video tapes, however, not audio tapes.

To help complicate matters, we have seen tapes with badly hydrolyzed
recording layers that show very little deterioration of the back
coating. We have also seen tapes with badly deteriorating back
coating that show little or no deterioration of the recording layer.
I do not, on the other hand, remember ever seeing a tape with a
badly hydrolyzed recording layer that had NO deterioration of the
back coating- that is, of course, excepting tapes that had no a back
coating to begin with.

Peter Brothers
Tape Restoration and Disaster Recovery Since 1983

> -----Original Message-----
> From: rohre@ARLUT.UTEXAS.EDU [mailto:rohre@ARLUT.UTEXAS.EDU]
> Sent: Friday, November 15, 2002 6:49 PM
> To: AV Media Matters
> Subject: [AV Media Matters] Detailed look at history of sticky tape
> syndrome
> I am soliciting input of anyone who has worked with old analog magnetic
> tapes that have developed stiction.  First some background:
> Stiction in Mylar based magnetic tapes first came to industry attention in
> the scientific community in the 1980's.  It was found that exposure to
> modest ambient humidity, in even office environments, could cause a
> hydrolysis of the binder holding the back coating to tapes.  Some tapes
> eventually developed failures of the binder holding the magnetic oxide, and
> the oxide would depart the base film, leaving clear film.
> Ampex Tape Division developed a technique that could be safely done to
> recover the tapes to playability, at least long enough for new copies to be
> made from Masters.  This was a low heat, baking process.  In the science
> community, environmental chambers were used which controlled the temperature
> for the 24 to 48 hour process very exactly.  (24 baking, 24 cooling).
> However, Ampex personnel also found that a consumer grade convection oven
> was adequate for this process for smaller size reels used in the audio
> industry and very large archives were processed for that customer base.
> In my scientific instrumentation recording use; I have also experienced the
> occasional sticky tape.  Some seem prone to it from certain batches of tape.
> In one famous incident, a batch of tape used for the Galileo space probe
> became sticky during the mission past Jupiter, but JPL successfully applied
> tape command techniques remotely, to free the tape and continue to use it.
> This overcame a failure of their high speed data link, and allowed use of
> the lower speed link, by the recorder serving as an analog buffer memory.
> This command was, once tape stuck to guides or heads, to reverse the tape
> motion, and it would free itself.  As long as the tape movement was continued, you often could play back data just fine.
> Examination of my own sticky tape incidents has now lead me to believe this
> problem always starts with the back coating on tapes.  Back coating was
> applied widely to instrumentation and top of the line audio tapes to reduce
> print through artifacts, reduce cinching in storage, and reduce friction
> between tape layers.  It is thicker than oxide coatings, and thus has in my
> opinion, larger area to absorb moisture.  (It is possible its binder differs
> from the binder that is used with oxide particles, but I have no confirmation of that.)
> In any case, the sticky syndrome has always seemed to start with the back
> coating causing sticking to tape guides, and this migrates around and
> sometimes coats the head to tape interface as well.  I have several times
> managed to clean sticky residue from guides and heads and completed playback
> of such tapes in mild cases of "sticky shed" as it is called.
> Once the baking formula was perfected, I have recovered tapes that were even
> shedding the oxide by the baking process.  Then in 30 days we reproduced the
> tapes and had time to transfer wanted data or audio.
> Now my question to the tape users is; has anyone else noticed that this
> failure starts first with the back coating?   I have three 27 year old tapes
> that seem to have excellent oxide and base film condition, but the back
> coating is sticky when played over tape guides.  My impression is in any
> tape over 25 years, one might well want to bake it first, to save the debris
> buildup on the tape playback equipment.
> Incidentally, the manual tape stiction check was done before mounting the
> tape, ie it, and its fellow tapes, unwind easily by hand rotation of the
> reel allowing gravity to pull the tape from the reel.  No tendency to adhere
> to the adjacent layer is seen with that easy test.  Of course, stiction can
> be a depth- in- the- tape reel dependent failure as well, but as a first
> check, the outer layer test is a good beginning.
> Has anyone experienced sticky tapes without back coatings?  And has anyone
> noticed back coating failure before oxide failure or delamination?
> Thank you,
> Stuart M. Rohre
> Applied Research Labs, Tape Archives
> Univ. of Tx., Austin

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