Peter Brothers:
The microwave process is called the XT process. It is patented,
That´s correct.
I have saved this from the ARSC list in 2004 that gave some more information coming directly from Terry O´Kelly of BASF:
-----------------------------------------
ctrelby@xxxxxxxxxxxxxxx 9/28/2004 5:06:38 PM >>>
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
--------------------------------------------------------------
-- Best,
Goran Finnberg The Mastering Room AB Goteborg Sweden
E-mail: mastering@xxxxxxxxx
Learn from the mistakes of others, you can never live long enough to make them all yourself. - John Luther