Mechanical, hygroscopic, and thermal properties of metal particle and metal evaporated tapes and their individual layers

Abstract

Mechanical and thermal properties of magnetic tapes and their individual layers strongly affect the tribology of magnetic head-tape interface and reliability of tape drives. Dynamic mechanical analysis, longitudinal creep, lateral creep, Poisson's ratio, the coefficient of hygroscopic expansion (CHE), and the coefficient of thermal expansion (CTE) tests were performed on magnetic tapes, tapes with front coat or back coat removed, substrates (with front and back coats removed), and never-coated virgin films of the substrates. Storage modulus and loss tangent values were obtained at a frequency range from 0.016 to 28 Hz, and at a temperature range from Ϫ50 to 150 or 210°C. Longitudinal creep tests were performed at 25°C/50% RH, 40°C/25% RH, and 55°C/10% RH for 50 h. The Poisson's ratio and lateral creep were measured at 25°C/50% RH. CHE was measured at 25°C/15-80% RH. CTE values of various samples were measured at a temperature range from 30 to 70°C. The tapes used in this research included two magnetic particle (MP) tapes and two metal evaporated (ME) tapes that were based on poly(ethylene terephthalate) and poly(ethylene naphthalate) substrates. The master curves of storage modulus and creep compliance for these samples were generated for a frequency range from 10 Ϫ20 to 10 15 Hz. The effect of tape manufacturing process on the various mechanical properties of substrates was analyzed by comparing the data for the substrates (with front and back coats removed) and the never-coated virgin films. A model based on the rule of mixtures was developed to determine the storage modulus, complex modulus, creep compliance, and CTE for the front coat and back coat of MP and ME tapes.

Dynamic mechanical analysis of magnetic tapes at ultra‐low frequencies

“…Previous experiments conducted with commercial DMA equipment have shown these trends, as the storage modulus slope is fairly stable until it reaches an elevated temperature near 100°C, when more energy is released, and the slope of the elastic modulus becomes more negative 3, 6–8, 17. This is also reflected in the loss tangent plots, where the peak of the α‐peak aligns with the temperature at which the storage modulus slope changes.…”

“…By performing experiments at different temperatures, information about the magnetic tape samples' thermal properties, such as their glass transition temperatures, could be extracted. Experiments from commercial DMAs have shown shifts in the relaxation peaks (α, β, and β*) to lower temperatures, associated with decreased strain application frequencies 3, 6, 7, 17. Therefore, by performing ULDMA experiments along frequency and temperature sweeps, the storage modulus, loss modulus, and loss tangent values can be plotted against temperature, demonstrating how decreased frequencies influence these peaks.…”

Non-contact tape tension measurement and correlation of lateral tape motion and tape tension transients

“…Hu and Hollman (1984) examined the case of a curved tape segment and noted that a tension gradient will develop across the tape width as a result of uneven stretching. Bhushan (1992) concluded that uneven tension across the tape width can cause tape vibration over the guide bearings. Our experimental results showed that a correlation exists between tape tension transients and LTM, although no prediction could be made about the direction of the motion resulting from a tension transient.…”

“…If one edge of a tape is shorter than the other, the tape is curved (Bhushan 1992). Curvature can be characterized by the radius of curvature, denoted as r in Fig.…”

“…It is apparent, however, that tape transients lead to transverse motion of the tape in the wide span between supports due to tape curvature (Bhushan 1992). Tape tension in a tape drive is generally measured using pressure transducers (Hu and Hollman 1984).…”