Technique development and measurement of Poisson's ratio, lateral creep behavior, and thermal and hygroscopic expansion of individual layers in magnetic tapes

Abstract

An experimental technique was developed to measure the Poisson's ratio (lateral contraction over longitudinal elongation), lateral creep, and both thermal and hygroscopic expansion of thin polymeric films. A so-called profile-matching method was developed to measure the lateral and longitudinal deformation with the help of a laser scan micrometer. A thermomechanical analyzer was used to measure the coefficient of thermal expansion (CTE). The laser scan technique was also used to measure the coefficient of hygroscopic expansion (CHE). The measurements were performed on magnetic tapes, substrates, and tapes with front coat or back coat, or with both coats stripped. A model based on the rule of mixtures was developed to determine the Poisson's ratio, lateral and longitudinal deformation behavior, and thermal expansion of the front coat and back coat. To investigate the mechanical degradation of the substrates during tape manufacturing, the data for substrate with the front and back coats removed from the tape, were compared with the data for the never-coated virgin film. The relationship between the molecular structure and the degradation mechanism of the substrates is discussed. The magnetic tapes used in this research include two metal particle (MP) tapes and two metal evaporated (ME) tapes that use polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) substrates. Longitudinal and lateral deformation tests were performed at 25 Ϯ 0.5°C and 50 Ϯ 2%RH, and thermal expansion was measured from 15 to 70°C. The CHE was measured at 25 Ϯ 0.5°C and 15-80%RH.

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

“…Figure 3 (a) shows the schematic diagram of the experimental apparatus developed to conduct the Poisson's ratio measurement 9–11. An opaque sample, 280 mm long and 12.7 mm wide, loaded at one end, and fixed to a microgauge at the other end, was wrapped over a curved quartz glass (85 mm radius).…”

“… Schematic of (a) lateral profile measurement apparatus, (b) details of the curved glass for lateral profile measurement, (c) details of the curved glass with a plastic support for hygroscopic/thermal expansion measurements, and (d) functional block diagram of the measurement system 11…”

“… Effect of (a) temperature and (b) relative humidity on the width change of Al foil sample for calibration of the test apparatus. “T” and “RH” represent temperature and relative humidity, respectively 11…”

“…The first author's group extensively studied the viscoelastic properties and dimensional stability of ultrathin polymeric films and tapes 1, 3–12. This includes the creep, shrinkage, dynamic mechanical behavior, Poisson's ratio, thermal and hygroscopic expansion of polymeric substrates, tapes, and stripped tapes without front coat and/or back coat.…”

“…This includes the creep, shrinkage, dynamic mechanical behavior, Poisson's ratio, thermal and hygroscopic expansion of polymeric substrates, tapes, and stripped tapes without front coat and/or back coat. Weick and Bhushan,5, 6 Ma and Bhushan11, 12 modeled the magnetic tape as a three‐layer composite: front coat, substrate, and back coat. By performing tests on the combined layers and applying the rule of mixtures, storage modulus, complex modulus, lateral creep compliance, and coefficient of thermal expansion of each individual layer were obtained.…”