REMEMBER when computer discs were floppy? Well, they鈥檙e back with a vengeance. A German firm has worked out how to make CDs and DVDs floppy, so you鈥檒l soon find album previews wrapped around your beer can or movie clips on DVDs you can peel off a birthday card.
The floppy medium has been developed by Sonopress, the disc-pressing plant owned by the publishing giant Bertelsmann. Sonopress is using technology developed by another Bertelsmann subsidiary, FlexStor, to produce thin and flexible optical discs that can be bent or rolled up.
Until now, it has been impossible to make CDs or DVDs from bendy plastic because it makes their data unreadable. Rigid CDs have to be 1.2 millimetres thick because the polycarbonate plastic which covers the reflective data pits鈥攈oles whose length defines the width of data pulses鈥攁cts as a lens for the laser in the CD player. If the plastic is thinner, or made from material with a different refractive index, the laser spot wanders out of focus. And if the plastic bends, it distorts the beam spot.
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FlexStor makes bendy discs by coating a roll of polyester foil, 140 micrometres thick, with a soft polymer. A stamper embosses a spiral of data pits in the soft coating, which is then hardened by ultraviolet light. Vaporised aluminium gives the disc a reflective upper coating, which is topped with a protective polymer lacquer. Flimsy discs are then cut from the roll.
In this raw state, the discs cannot be played because they flap around freely in the tray of a CD player. To play a disc it is tightly sandwiched between two halves of a reusable adaptor, shaped like a conventional 12-centimetre CD. The bottom half of the adaptor is a disc of optically pure polycarbonate, and the top is a cover of polystyrene. When the loaded adaptor is placed polycarbonate side down in the tray, the laser shines up through the clear layer which focuses it onto the polyester foil to read the data pits.
Sonopress says that the flexible discs can be pressed ten times as fast as rigid discs, and at much lower cost. And they only weigh 1.3 grams, making them cheap to post. So we can all expect a flood of multimedia junk mail any day now.