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More on Tape Baking

More culinary information. Who cares why the dough rises so long as it makes a great cake? In response to our recent tip on tape baking (inSync 5/22/00) we’ve received a message that helps clear up some misconceptions (some of which are ours) about the process.

To answer several questions about the baking of tape:

The goal is NOT to drive out humidity; the goal is to heat several of the chemical constituents above their “glass temperatures” so they will be in a liquid enough form to migrate back into the tape dispersion-binder mix and continue to play the role they were designed to do. That’s why if the tapes fail again, they can be reheated as many times as necessary and will always recover to full playability. The hygroscopic nature of the chemicals involved makes it seem as if it were a humidity problem, but it is not. It’s just that the pH of the chemicals (when they migrate out of the binder) makes them attract water. The presence of excess moisture on the tapes is the symptom, not the disease.

The use of a vacuum oven will not likely improve matters as I have said in the 1st paragraph. Heating to a high enough temperature to allow the offending chemicals to liquefy is all that is necessary. The moisture that has been picked up will evaporate of its own accord.

I hope this helps clear up a few misconceptions!

Bill Lund
3M Tech Service
St. Paul, MN

Editor’s Note: As mentioned in the earlier Tech Tip the baking of tapes does do some damage to them. There are some newer techniques for restoring old tapes that do not involve oven heating. The use of vacuum or dehumidification techniques may not be addressing the “real” problem, but all we are looking to do is make the tape playable while incurring the least amount of damage. Roger Nichols talks about this some at his Digital Atomics Web page (of course he also provides the service so keep that in mind). Either way it is known that the tape will return to its unplayable state after a time.

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