Dynamic mechanical analysis of magnetic tapes at ultra‐low frequencies

Abstract

A custom, ultra-low frequency, dynamic mechanical analyzer (ULDMA) has been developed to study the correlated effects of temperature and frequency on the viscoelastic behavior of magnetic tapes. It has been used to acquire data needed for the development of future magnetic tapes that require an archival life of up to 100 years. A range of elevated temperatures is used to simulate real-world storage environments, which enables the investigation of how the viscoelastic characteristics of tape samples influence the extent to which the tape deforms. The experiments and subsequent analysis examine the influence of the molecular structure on the viscoelasticity of magnetic tapes. Experiments were performed on a variety of magnetic tapes, including poly(ethylene terephthalate) (PET), poly(ethylene naphthalate) (PEN), metalized PET (M-PET), and metalized Spaltan (M-SPA). Additional experiments examined PEN and PET substrates by removing the front and back magnetic layers from the tape sample. Because of the viscoelastic behavior of the tapes, a time delay was present between the strain and stress signals, which was determined using a Fourier transform program. The elastic modulus (E), storage modulus (E 0 ), loss modulus (E 00 ), and loss tangent (tan d) were obtained from the time delay for each of the ULDMA experiments at 25, 50, and 70 C over the frequency range of 0.0100-0.0667 Hz. Plots of these mechanical characteristics demonstrate the ability of frequency and temperature to affect trends associated with mechanical and thermal properties. Finally, some samples displayed an initial relaxation during the ULDMA experiments, which, when modeled using Maxwell's viscoelastic model, provided an insight into the relaxation characteristics of the samples.

Dynamic mechanical analysis of barium ferrite magnetic tapes with aramid and poly(ethylene naphthalate) substrates

“…The frequency effects on the storage modulus appear to be inconsequential, because the grouping is so tight. The gradual decline matches the expected decay of the material under these conditions based on past experiments . The decline is not as extreme for the PEN substrate.…”

“…Rummel and Weick describe the ultra‐low frequency dynamic mechanical analyzer (ULDMA) used in this study. Because of their viscoelastic characteristics, magnetic tapes demonstrate a phase lag between the applied strain, and measured stress .…”

“…Berry and Rummel describe the detailed procedure used to perform the ULDMA experiments using magnetic tape and substrate samples. Repeatability of the experimental apparatus and reproducibility of results are addressed in their work and in the article by Rummel and Weick . Data sets were acquired using a National Instruments data acquisition board and LabView software.…”

“…A custom‐built dynamic mechanical analyzer capable of performing experiments at ultra‐low frequencies was used to study the viscoelastic properties of the BaFe PEN and BaFe aramid tapes and their respective substrates. Rummel and Weick describe the need for ULDMA due to transitions observed in magnetic tape materials at near‐room temperature conditions. Weick also observed these transitions in earlier work using commercial DMA equipment, and noted that such transitions could lead to problems with archival storage of magnetic tapes due to changes in stress‐strain characteristics as the tape is stored in a roll.…”

“…The investigation was therefore carried‐out using temperatures in the 25–70°C range, and frequencies of 0.006–0.065 Hz within this temperature range. Representative peak elastic modulus curves could then be studied using raw data . Next, using Fourier frequency analysis, data sets were broken‐down into frequency content to enable the determination of coherence and time delays or phase angles between the stress and strain.…”