Tribology and Mechanics of Magnetic Storage Devices By Bharat Bhushan (Springer, 1990 1st edition p 43-45; 1996 2nd edition ISBN 978-0-387-94627-6) quote obtained via Google Books by Herb Johnson 3/2019 used with permission of Bharat Bhushan 3/4/2019 1.4.4.1 Flexible Media Flexible media (tapes and floppy disks) mostly have particulate coatings. The base film is typically made of polyethylene terephthalate (PET) 12 to 36um thick for tapes (Fig. l.l2) and 76 to 102um thick for floppy disks. The base film has a magnetic coating, typically 2 to 5um thick, composed of acicular mag- netic particles [such as y-Fe2O3, Co-doped y-Fe2O3, CrO2, and Fe (metal) for horizontal recording] or hexagonal platelets of barium ferrite (for vertical recording), polymeric binders [such as polyester-polyurethane, polyether- polyurethane, nitrocellulose, poly-(vinyl chloride), poly-(vinyl alcohol-vinyl acetate), poly-(vinylidene chloride), phenoxy, and epoxy], lubricants (such as fatty acid esters, e.g., butyl stearate, butyl palmitate, stearic acid), a cross linker or curing agent (such as functional isocyanates), a dispersant or wet- ting agent (such as lecithin), and solvents (such as tetrahydrofuran and methyl isobutylketone). Magnetic particles are typically 60-80% by weight (or 37-50% by volume} of the total coating. Floppy disks operate in physical contact with the head; therefore, load bearing Al2O3 or Cr2O3 particles are sometimes added to increase the wear resistance of the media. Floppy disks are packaged inside a polyvinyl chloride (PVC) jacket or a hard jacket (only for 95-mm size). Inside the jacket, a soft liner, a protective fabric is used to minimize wear or abrasion of the media. The wiping action of the liner on the media coating removes and entrap particulate contaminants which may originate from the diskette mannfactur- ing process, the jacket, head-disk contact (wear debris), and the external environment. The liner is made of nonwoven fibers of polyester (polyethylene terephthalate) or rayon. The liner fibers are thermally or fusion bonded to the PVC plastic jacket at spots (Ostrowski, 1933; Tse and Lewis, 1986]. Most flexible media-binder materials have their glass-transition tempera- ture below the operating temperature (that is, they are in the rubbery stale] to provide desired flexibility. Some block copolymer binders, such as polyester-polyurethanes, have one segment in the rubbery state and another in the glass state (Ferry, 1980). Most magnetic tapes have a backcoating for antistatic protection (Fig. 1.12]. The backcoat may have the same composition as the front coat or merely a polyester-polyurethane coating containing conductive carbon black. For further details, sec Tochihara (1932). Typical physical properties of components of magnetic media are presented in Table 1.8a [density, Young's modulus, Knoop microhardness]. ------------------ White, R. M. (1985) Introduction to Magnetic Recording. IEEE PRess, New York. Tse, M.K. and Lewis, A.F. (1986) Triboacoustics of nonwoven fabric/floppy disk dynamic contact. in Tribiology and Mechanics of Magnetic Storage Systems" Vol 3 (B Bhushan and N. S Eiss eds), pp 61-73 SP-21 ASLE, Park Ridge IL. Tochihara, S. (1982) Magnetic coatings and their applications in Japan. Progress in Organic Coatings, 10, 195-204 Bhushan, B. (1990) "Reliability of Flexible Magnetic Media", Springer-Verlag in preparation. --------------- Notes by Herb Johnson Mylar (a trade name of Dupont), also known as BoPET (Biaxially-oriented polyethylene terephthalate) is a polyester film made from stretched polyethylene terephthalate (PET). Epoxy is either any of the basic components or the cured end products of epoxy resins; or a colloquial name for the epoxide functional group. Phenoxy resins are amorphous thermoplastic polymers and thermosetting resins. These polymers have terminal hydroxyl groups as well as hydroxyl groups in every repeat unit and thus can be classified as polyhydroxyethers. Phenoxy resins are often blended with epoxy and phenolic resins to enhance their performance properties. (https://polymerdatabase.com/polymer%20classes/Phenoxy%20type.html)