SYNOPSISViscoelastic and shrinkage characteristics of five ultrathin polymeric films are presented. These films include poly(ethy1ene terephthalate) or PET, poly(ethy1ene naphthalate) or PEN, an aromatic polyamide (ARAMID), a polyimide (PI), and poly(benzoxazo1e) or PBO. PET film is currently the standard substrate used for magnetic tapes, and the other four films represent alternative substrates with improved material properties. Thicknesses of the films range from 14.4 pm for P E T to 4.4 pm for ARAMID. A creep apparatus is used to measure the viscoelastic and shrinkage characteristics of the films. The largest amount of creep compliance was measured for P E T followed by PI, PEN, ARAMID, and PBO. Creep velocity was highest for P E T and PI, followed by ARAMID, PEN, and PI. Shrinkage measurements a t 50°C for 100 h show that PEN shrinks more than all the other substrates. Time-temperature superposition is used to predict long-term creep behavior, and relationships between polymeric structure and viscoelastic behavior are also discussed. Based on their relative cost and creep behavior, PEN and ARAMID substrates appear to be suitable alternatives to PET. 0 1995 John Wiley & Sons, Inc.

ABSTRACT:Creep-compliance behavior of specially prepared magnetic tape materials was measured at elevated temperature levels to facilitate the use of a time-temperature superposition (TTS) process. This TTS process allowed for the construction of master curves at a reference temperature of 30°C, which were used to predict the long-term viscoelastic behavior of the magnetic particle (MP) and metal-evaporated (ME) tapes used in the study. The specially prepared samples allowed for the use of a rule of mixtures technique to determine the long-term creep compliance of the front coat and back coat used for the magnetic tapes. To test the validity of this procedure, the front coat, substrate, and back coat data determined through separate experiments were used to calculate creep compliances of simulated tapes. These calculated creepcompliance curves were then compared to measured data for the actual magnetic tapes. After determination and validation of the front coat, substrate, and back coat creepcompliance data sets, they were used to determine strain distributions when the tapes are stored in a reel. Strain distributions were calculated for two cases, which reflect how tapes are stored in different drives: (1) the front coat (magnetic ϩ nonmagnetic layer) is oriented away from the hub, and (2) the front coat is oriented toward the hub. Results showed that strain in the critical front coat of a tape is lower if it is stored with the front coat oriented toward the hub. In addition, the use of the creep-compliance data showed that the MP tape front coat is more susceptible to creep than the ME tape front coat. The strain distributions in future magnetic tapes were also simulated by reducing the thickness and compliance of the layers. Results showed the importance of using lower compliance front coat, substrate, and back coat materials if thinner tapes are to be developed to increase the volume of information that can be stored in a magnetic tape reel.

Creep compliance, shrinkage, and dynamic mechanical analysis (DMA) results are presented and discussed for developmental magnetic tapes made from PEN and metalized PET (Spaltan V R ) substrates as well as PEN substrate samples cut from wide-stock in the machine and transverse directions. Curve fit parameters from the Kelvin-Voigt model are discussed to shed light on the creepcompliance characteristics, particularly the roll-off characteristics observed at elevated temperatures and long time periods. Characteristic peaks observed in storage and loss moduli measured using DMA that correspond with molecular movement provide information that assists with the understanding of creep-compliance and shrinkage behavior for these materials. Such movement corresponds with dimensional instabilities that need to be understood for future generations of advanced digital magnetic tapes.

ABSTRACT:Creep-compliance experiments were performed for three representative magnetic tapes. Two of these tapes used a magnetic particle (MP) coating, and one used a metal-evaporated (ME) coating. The MP tapes used the following polyester substrates: semitensilized poly(ethylene naphthalate) (PEN) and supertensilized poly(ethylene terephthalate). The ME tape used an aromatic poly(amide) or aramid substrate. Time-temperature superposition was used to make creep-compliance predictions at 30 and 50°C reference temperatures. Comparisons were made with dimensional stability requirements based on position error signal (PES) specifications for magnetic tape drives along with in-cartridge creep specifications based on PES measurements. Circumferential and lateral creep strains were determined that account for storage of the tapes in a reel, and creep strains were predicted for future tapes with thinner, lower compliance coatings. A rule of mixtures method was also used to extract compliance information for individual layers of MP-PEN tapes, and stress profiles through the thickness of the tapes were determined. Additional measurements and analyses were performed to determine the creep recovery and shrinkage characteristics for the magnetic tapes.

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AbstreViscoelastic and shrinkage characteristics of alternative substrates for magnetic tapes are presented. The substrates evaluated include two polyesters (PET & PEN), an aromatic polyamide (ARAMID), a polyimide (PI), and poly(benzoxazo1e) or PBO. Thicknesses of the films range from 14.4 pm for PET to 4.4 pm for ARAMID. Results are also presented for ultra-thin magnetic tapes which use PET, PEN, or ARAMID as substrates. Based on their creep behavior (and relative cost), PEN or ARAMID appear to be suitable alternative substrates to PET.

in Wiley Online Library (wileyonlinelibrary.com).ABSTRACT: A viscoelastic computational model is developed that uses experimentally determined viscoelastic material properties as input and can be used to predict the behavior of a tape material in a wound roll as stresses relax over time. Experimental creep test results are used to find best-fit creep-compliance parameters to describe two high density data storage tape media. The two tapes used in the analysis are a developmental tape with a poly(ethylenenaphthalate) (PEN) substrate and metal particle (MP) front coat similar to linear tape open (LTO4) (referred to in this work as ''Tape C''), and LTO3, a commercially available tape with a PEN substrate and MP front coat. Sets of best-fit creep-compliance parameters are determined for both tapes. The differences between the predicted behavior using three-, five-, and sevenparameter Kelvin-Voigt models are evaluated, both for a benchmark case and in a viscoelastic wound roll model.The choice of material model is found to significantly influence the predictions of the wound roll model. The differences between different material models for the same material are on the order of the differences found between the two different materials. A material model with a higher number of creep-compliance parameters, although more computationally expensive, produces better results, particularly over long spans of time. The relative differences between the three-, five-, and seven-parameter models are shown to be qualitatively consistent for several variations in the computational model setup, allowing predictions to be made based on simple benchmarks.

Viscoelastic characteristics of magnetic tapes with poly(ethylene naphthalate) substrates were studied using experimental techniques. Measurements were made using samples cut from commercially available tapes, and solvents were used to remove front and/or back coat layers to obtain substrates and dual-layer samples. Experimental results allowed for fundamental compliance and viscosity parameters to be determined using a Kelvin-Voigt model. Rates of creep-compliance were also predicted, and comparisons were made with results for tapes that used poly(ethylene terephthalate) and aromatic poly(amide) substrates.Dynamic mechanical analysis (DMA) was used to help make correlations between viscous characteristics measured from the creep-compliance results and molecular characteristics of the substrates. Time-temperature superposition (TTS) was used to predict creep-compliance over extended time periods, and a rule-of-mixtures method was used to predict the compliance of constitutive layers.