Video's long player


By Barry Fox A JAPANESE company has developed super-thin videotape that boosts the recording capacity of digital camcorder cassettes by 50 per cent. Matsushita’s manufacturing process evaporates pure cobalt at high temperature in a vacuum and deposits it on the tape. The thin “metal-evaporated” (ME) tape is then strengthened by a material that Matsushita calls “diamond-like carbon” (DLC). Matsushita and its rivals Sony and TDK have been developing ME tape for 20 years, but it has only been used for broadcast-quality digital recording because it is so expensive. ME tape is very thin, allowing more video to be stored in a small cassette. But this makes it inefficient for recording analogue signals, which require a thick magnetic layer to capture low frequencies. The latest consumer video format, digital video (DV), records both sound and vision as high-frequency digital code, which can be faithfully captured in a very thin magnetic coating. Matsushita thinks DV users will pay a premium for cassettes that increase recording time from 80 to 120 minutes. The new ME tape is made by drawing a roll of clear polymer film made of polyethylene naphthalate through a vacuum chamber (see Diagram). An electron beam evaporates cobalt in a crucible by heating it to 2000 °C. The vapour settles on the film as it clings to a moving drum. The drum is cooled to 0 °C, which allows the cobalt to bond to the film as a smooth, mirror-like coating without melting the polymer. For strength, carbon is then deposited in a similar manner to create a layer of DLC over the cobalt. Matsushita refuses to elaborate on the formulation of DLC, which it has spent 20 years developing. Finally, a layer of fluorine-based lubricant is deposited on top of the carbon to help the tape move smoothly over the tape heads. Previous ME tapes have needed a backing 7 micrometres thick to withstand the strain of travelling through a video recorder. This has limited tape length in the cassette to 80 minutes. With the DLC backing, Matsushita can make do with 4.8 micrometres,
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