Sticky-shed syndrome

Sticky-shed syndrome is a condition created by the deterioration of the binders in a magnetic tape, which hold the iron oxide magnetizable coating to its plastic carrier, or which hold the thinner back-coating on the outside of the tape. This deterioration renders the tape unusable. Some kinds of binder are known to break down over time, due to the absorption of moisture (hydrolysis).

The symptoms of this breakdown can be immediately obvious even when rewinding the tape: tearing sounds and sluggish behavior. If a tape with sticky-shed syndrome is played, the reels will make screeching or squeaking sounds, and the tape will leave dusty, rusty particles on the guides and heads. In some cases, particularly with digital tapes, the symptoms are more subtle, causing intermittent dropouts.

Some tapes may deteriorate because of a breakdown in the binder (the glue) that holds the oxide particles on the tape, or the back coating on the reverse side, if the tape was from any of the tape manufacturers who had inadvertently used an unstable binder formulation. That binder contained polyurethane that soaks up water and causes the urethane to rise to the tape's surface. This problem became known as the 'sticky-shed syndrome'. One explanation was offered that short strands of urethane were most commonly used in tapes - until it was discovered that middle-sized strands are better and were good at absorbing moisture. Baking the tape temporarily restores the tape by driving the water molecules from the binder so that it can be safely copied to another tape or a different format. After baking, the tape usually remains in good condition for approximately a month. If the tape re-deteriorates, it may be possible to bake the tape again.

Many tapes affected by sticky-shed are those that were made by Ampex/Quantegy such as 406/407, 456/457, 499, and consumer/audiophile grade back coated tapes such as Grand Master and 20-20+.

Tapes made by Scotch/3M are also affected and the most common offenders here are the "pro" tapes such as 206/207, 226/227, 808, and 986 as well as audiophile tapes such as "Classic" and "Master-XS".

Though less common, many Sony branded tapes such as PR-150, SLH, ULH, and FeCr have also been reported to suffer from sticky-shed.

Blank cassettes from the 70's-90's are unaffected because the hygroscopic binder was not used in cassette formulations. However, some cassette tape formulations do suffer from a similar problem caused by fatty acids working to the surface of the tape that can cause sticking to heads and guides and severe modulation of signals through the playback head until it is cleaned.

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Wikipedia