ABSTRACT:Tensile and dynamic mechanical properties of improved ultrathin polymeric films for magnetic tapes are presented. These films include poly(ethylene terephthalate) or PET, poly(ethylene naphthalate) or PEN, and aromatic polyamide (ARAMID). PET film is currently the standard substrate used for magnetic tapes; thinner tensilized-type PET, PEN, and ARAMID were recently used as alternate substrates with improved material properties. The thickness of the films ranges from 6.2 to 4.8 m.Young's modulus of elasticity, F5 value, strain-at-yield, breaking strength, and strainat-break were obtained at low strain rates by using a tensile machine. Storage (or elastic) modulus, EЈ, and the loss tangent, tan ␦, which is a measurement of viscous energy dissipation, are measured by using a dynamic mechanical analyzer at temperature ranges of Ϫ50 to 150°C (for PET), and Ϫ50 to 210°C (for PEN and ARAMID), and at a frequency range of 0.016 to 29 Hz. Frequency-temperature superposition was used to predict the dynamic mechanical behavior of the films over a 28 decade frequency range. Results show that ARAMID and tensilized films tend to have higher strength and moduli than standard PET and PEN. The rates of decrease of storage modulus as a function of temperature are lower for PET films than those for PEN and ARAMID films. Storage modulus for PEN films are higher than that for PET films at high frequencies, but this relationship reverses at low frequencies. ARAMID has the highest modulus and strength among the films in this study. The relationship between polymeric structure and mechanical properties are also discussed.

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Long-term creep-deformation and shrinkage characteristics of improved ultrathin polymeric films for magnetic tapes are presented. These films include poly-(ethylene terephthalate) (PET), poly(ethylene naphthalate) (PEN), and aromatic polyamide (ARAMID). PET film is currently the standard substrate used for magnetic tapes, and thinner tensilized-type PET, PEN, and ARAMID have recently been used as alternate substrates with improved material properties. The thickness of the films ranges from 6.2 to 4.8 m. More dimensional stability is required for advanced magnetic tapes, and the study of creep and shrinkage behavior is important for estimating the dimensional stability. Creep measurements were performed on all available substrates at 25, 40, and 55°C for 100 h. Based on these data, master curves were generated using time-temperature superposition to predict dimensional stability after several years. The amount of creep deformation is considerably smaller for ARAMID and tensilized-type PET than for PEN, although Standard PET shows the largest amount of creep. In addition, creep measurements under high humidity also show similar trends. Shrinkage measurements at 55°C for 100 h show that the shrinkage of ARAMID is lower than that of PET and PEN. The relationship between the polymeric structure and dimensional stability are also discussed. Based on the creep and shrinkage behavior, ARAMID and tensilized-type PET seem to be suitable for advanced magnetic tapes.

The novel concept and significance of a nano-alloyed polymer, which includes nano-dispersed domains, is proposed, and a biaxially stretched nano-alloyed film is developed. The developed film has a higher glass transition temperature and improved dimensional stability compared with regular poly(ethylene terephthalate) (PET) films. Nano-sized polyimide domains are dispersed with our original melting extrusion process, which produces highly concentrated polyimide master batches at much lower temperatures than the regular processing temperature of the polyimide. The biaxially stretched film has been industrialized for use as a substrate for data storage tapes and can additionally be applied to materials in the fields of electronic devices, automobile, environmental and energy devices. Polymer Journal (2012) 44, 1170-1178; doi:10.1038/pj.2012.96; published online 13 June 2012Keywords: biaxially stretched film; glass transition temperature; nano alloy; nanostructure control technology; polyester; polyimide INTRODUCTION Development of a biaxially stretched nano-alloyed film Biaxially stretched polyester films, which are represented by poly (ethylene terephthalate) (PET) films, are currently the most widely used polymeric substrate materials in the fields of display technologies, electronic devices, storage media, electronic insulators, automobile, molding, package, printing and architecture. This widespread use is a result of the films possessing high strength, durability, transparency, flexibility and good surface properties. Information and telecommunications equipment have recently required more compactness and portability as well as excellent film properties, such as higher heat resistance and dimensional stability, especially in the field of electronics, environment and energy. It has been difficult for conventional biaxially stretched PET films to meet the future demand, and outstanding films with cost effectiveness are required.We have created a biaxially stretched nano-alloyed PET film that has a higher glass transition temperature, which is an intrinsic property of polymers, compared with regular biaxially stretched PET films. 1 The technical points from our development are the following. First, the novel concept and significance of nano-alloyed polymers have been proposed. Secondly, nanostructure control technology has been developed for the nano-sized dispersion of polyimide, which is a different organic polymeric material than polyester. Finally, the processing conditions for the biaxially stretched nano-alloyed films have been established. In this paper, we describe the design of a nano-alloyed polymer and biaxially stretched films.

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