n.a form of degradation affecting magnetic tape, resulting from the deterioration of the binder and characterized by the deposit of a gummy residue on the tape heads during playbackAMIA 2000The chemical breakdown of videotape binders or coatings due to hydrolysis has been well documented. The binders absorb atmospheric moisture and release acids and alcohols that act as catalysts hastening deterioration. Acids may be present from the tape itself or contracted from common pollutant gases. Aged tapes are more hygroscopic than newer tapes in their ability to absorb moisture. Hydrolysis weakens the binder causing particle shedding, dropouts, and eventual loss of the tape through severe degradation. High humidity increases the rate of moisture absorption; it increases tape pack stresses, distortion, tightness, and dropouts form debris and exudations; and, it results in clogging, sticky shed syndrome or “stiction”, scoring, and head wear. High temperatures can also cause damage such as increased tape tightness, pressure, distortion, dropouts from wound in debris, layer to layer adhesion, changes in dimensions, all of which promote tracking errors.Ritzenthaler 2010, 170–171Sticky shed syndrome (also referred to as “sticktion”) is a condition resulting from the deterioration of the binder in magnetic tape, which leaves gummy residue on tape heads during playback. Sticky shed appears primarily in audio, video, and computer tapes manufactured in the United States between mid-1970s and mid-1980s. The binder used to hold the metallic particles on the base can absorb water and weaken. When the tape is played back, the oxide particles rub off the tape, build up on the equipment, and cause loss of information. Preservation options include duplication, cleaning, and baking.Hobaica 2012, 135Sticky-shed syndrome is a condition caused by degradation of audio magnetic tape that results in the deposition of a gummy residue on the tape heads and guides during playback. It causes severe contamination of tape decks, which need to be cleaned before the tape can be played further. Thus, tapes with sticky-shed should be treated before playing to avoid possible damage to the tape.Heller 2017, 64Sticky shed syndrome is a form of archival decay. It is a deteriorative condition that affects reel-to-reel tape collections from the late twentieth century. The problem arises in a substance known as the binder, an adhesive glue used to attach the magnetic oxide (where the audio is stored) to the polyester backing material of the tape itself (see Figure 1). Starting in the early 1970s, manufacturers began experimenting with new binder formulas in an effort to improve tape’s frequency response. While they succeeded in achieving better sound, problems began to surface when the tapes were kept in long-term storage. Over time, these new binders absorbed moisture from the air, transforming the solid adhesive into a viscous, gummy substance. In minor occurrences, the sticky backing will simply prevent the tapes from playing, causing the reel to stick together and refuse to turn. But in the most extreme cases, playing the tape will cause the oxide layer to flake away or “shed” from the backing, permanently destroying the item. Often this disintegration is accompanied by a distinctive, high-pitched squeal from the playback deck.Harvey and Mahard 2020, 233High humidity can promote binder hydrolysis, a chemical reaction in which the binder (typically polyurethane) absorbs ambient moisture and becomes soft and sticky. In moderate cases, this may cause the tape to chatter or squeal when played. In more severe cases, it may cause the magnetic layer to pull away from the tape base (a condition commonly referred to as “sticky shed syndrome”) and clog playback equipment with a gummy residue that can lead to a significant loss of high frequencies.Byrum 2004The Preservation Research and Testing Division has been conducting research to better characterize long term stability and playability concerns related to sound and moving image recordings on magnetic tapes, with particular focus on “sticky shed syndrome”. With sticky shed degradation, tapes deposit a residue on playback equipment which can both damage equipment and impact the sound or video signal layer. The phenomenon appears most common in analog audio and video tapes manufactured using polyester-urethane (PEU) binders beginning in the 1970s. Unanswered questions remain regarding the causes, detection, and treatment of the problem.
Notes
The gummy or sticky residue is caused by the deterioration of the binder that holds the metallic particles containing the recorded information to the base layer of the tape. The condition, caused by the absorption of moisture from the air, affects audio, video, and computer tapes manufactured since the 1970s. The shedding during playback causes loss of information, so typically affected tapes are treated by baking or cleaning before they are played.
