Audio and Video Tape CompositionPresentation Transcript
Audio and Video Tapes Chemical and Physical Properties By Jonas T. Sahagun
Outline Brief Background Composition and properties
Brief Background Magnetic media are one of the most widespread carriers for audio and video data. They are also used for the storage of large quantities of computer data. Beyond specific audio and video formats, magnetic media are the most prominent storage media of the IT world.
Background (cont’d) For the purpose of this report, we will concentrate on the “traditional” magnetic carriers: the audio and video tapes. All audio-specific magnetic tape formats are now, in practice, dead (Schüller, 2008). Video-specific magnetic tape formats are still in wide use, but a similar development to that which happened in the audio world is foreseeable (Schüller, 2008).
Composition and properties Magnetic tape is composed of three layers: Binder/oxide coating (magnetic layer) Base film Back coating (not on all tapes) (Hess, 2008, p.242)
Composition (cont’d) Layered structure of the magnetic tape: (Dumont, Johansen, Kilander, 1992, p.42)
The information carrier: comprising of a magnetizable element (40%), binder (40%) and minute pores (20%).
Different ferromagnetic materials are used, including pure iron oxide, iron oxide doped with cobalt, chromium dioxide with iron oxide, metallic alloys, and pure metal.
The oxide consists of a mix of magnetic particles that retain the magnetism impressed on them by the recording head.
The binder is the “glue” or matrix that holds the oxide particles to the base film.
A lubricant is added to the binder/oxide mix to reduce friction and wear.
Base film The base film is the foundation of the tape. It provides structural integrity to the tape. In the sequence of the development of magnetic tapes, the following materials were used: Acetate Polyvinyl chloride Polyester
Cellulose Acetate [AC] (1935-1972/73)
AC is derived from the naturally occurring organic compound cellulose, main structural ingredient of plants. It is manufactured out of wood pulp by purification process. It is a renewable and biodegradable substance. AC is generally robust but deteriorates with time; it becomes brittle and shrinks. Acetate tapes residing in collections are over 30-years-old, with the oldest being over 60-years-old.
Polyvinyl chloride [PVC] (1944-1972), also known as Luvitherm
PVC is an inexpensive plastic. It is one of the first synthetic product ever patented. It is not biodegradable. Have not yet shown to have systematic chemical deterioration. All PVC tape is more than 30 years old, and some of it is more than 60 years old.
Polyethylene terephthalate [PET] (1953-present) also known as Mylar, Polyester, Tenzar
PET has gradually replaced AC and PVC tapes from the late 1950s onward. It is a polyester material that is most often used to make fibers. It is mechanically robust and chemically very stable. As of approximately 1972 became the sole base film used in audio tape manufacture.
Back coating Tape back coating has been claimed to do several things: Provide a smoother wind Provide better grip for tape movement Provide for electrostatic drain Reduce print-through Back coatings generally contain carbon black and add a little strength to the overall tape.
Tape housing There are three basic methods for the immediate storage of tape: Open spool Cassette Cartridge
Open spool (cont’d) Open spools were until recently the main form of tape used for professional audio recordings. Some expensive professional digital audio formats like DASH (Digital Audio Stationary Head) and PD (ProDigi) use reel-to-reel tape and stationary head technology.
Tape in a cassette is enclosed in a shell and the two ends of the tape are securely fixed to captive spools.
Cartridge (cont’d) The primary use for cartridges is for storing computer data but a variant was extensively used to record short sound sequences for commercials, station identifications and the like. (Wheeler, 2007) (Field, 2008)
REFERENCES Dumont, J., Johansen, J. & Kilander, G. (1992). Handling and storage of recoded videotape. Retrieved from http://www.ebu.ch/fr/technical/trev/trev_254-tutorial.pdf Hess, R.L. (2008). Tape Degradation Factors and Challenges in Predicting Tape Life. ARSC Journal, 39 (2), 240-274. Retrieved from EBSCOhost Schüller, D. (2008). Audio and video carriers. Retrieved from http://www.tape-online.net/docs/audio_and_video_carriers.pdf Van Bogart, J. W.C. (1995). Magnetic Tape Storage and Handling: A Guide for Libraries and Archives. Retrieved from http://www.imaginar.org/dppd/DPPD/126%20pp%20Magnetic%20 Tape%20Storage.pdf ________. . Old IFLA website. Retrieved from http://archive.ifla.org