Hand Writing
By far the quickest and least expensive way to label a disc is to simply write on its top surface. Using a soft fiber or felt-tipped permanent marker is preferable but be aware that the solvents in some types of inks can potentially damage the disc and, even though the plastic dummy substrate of a single-sided writable DVD disc affords some protection, caution is still in order. Avoid using ballpoint pens, pencils or other sharp writing instruments. As with CD-R and CD-RW the part of the disc least vulnerable to injury is the center clamping or hub area. Double-sided writable DVD discs can be marked only in this region. Some discs are specially coated to accommodate handwritten labels and even special markers are available and intended for such use.
Adhesive Labels
A more attractive way to label a disc is to apply an adhesive label. Several manufacturers offer permanent marker, inkjet, solid ink and laser printer compatible products specifically designed for labeling discs as well as positioning devices to help with centering. Other options include various surface colors and finishes including matte, glossy, foil, holographic and glow in the dark as well as special coatings that can be repeatedly written on with permanent marker and dry erased. Full surface or "donut-style" labels are preferable to partial stickers but be careful as any adhesive label can potentially upset the balance of a disc when playing back. This is especially true at high speeds, resulting in excessive noise, vibration and data retrieval problems. Heat, humidity, sunlight, handling and the passage of time can also compromise the stability of adhesive labels resulting in separation from the disc surface and even interference with the drive. Sticky labels may not be the best choice when archiving important data as some types of label adhesives can react with and undermine the disc over time. Remember too that, once applied, labels should never be removed or repositioned. Even smoothing air bubbles can concentrate physical stresses in a small area and potentially damage the disc.
Specialized Disc Printers
Specialized disc printing devices are available to label discs in larger numbers and for imparting a more polished appearance. Currently, desktop products employing inkjet, thermal transfer and re-transfer technologies are available for directly labeling on the disc surface.
Inkjet
Inkjet printing technology has been available for many years and has proven extremely popular with consumers due to its high quality and cost effectiveness. Inkjet printers function by ejecting liquid ink from a print head onto the surface of a specially coated "inkjet-printable" disc. These special discs have an extra coating, called an Ink Absorption Layer (IAL), which receives the ink from the printer and allows it to stay in place long enough to properly dry. Some discs are even available decorated with screen printed images and areas left blank for desktop inkjet labeling. Inkjet printers produce high-resolution full color images but there is a downside in that resulting labels are subject to being smudged by high humidity or damp fingers and thus are not suitable for use in automotive or other harsh environments. Inkjet printed discs should not be stored or shipped in flexible plastic envelopes as the chemicals used to keep the package materials supple can interact with the inks and cause the label to stick to the sleeve resulting in additional physical stresses upon disc removal. Using jewel cases or other containers that do not directly contact the printed surface is best.
Thermal Transfer
Unlike inkjet printers that spray liquid ink, thermal transfer printers convey solid pigment from a coated ribbon onto the surface of a disc through a combination of heat and pressure. Typically used to produce monochrome and spot color labels, thermal transfer printing does not require specially coated discs to accept the ink from the printing process. The results are, as well, reasonably durable. However, some disc surfaces give better results than others. Consequently, discs are available which feature special coatings optimized for thermal transfer printing. But be aware that writable DVD discs often have a raised ring in their center hub or clamping area that interferes with and can damage the printer's labeling head. It is possible to print above and below this area to avoid the difficulty and there are some discs specially manufactured without this ring to provide an unobstructed surface. For labeling situations where discs share a largely common background appearance but vary slightly from disc to disc or among groups of discs some thermal transfer solutions can align and overprint their output onto partial images already printed onto the surface of the disc.
Re-transfer
More recently, re-transfer printers have come to market and function by applying heat and pressure to convey solid resins from an ink ribbon to an intermediate film and then to the surface of the disc. Typically re-transfer systems produce photo-realistic color labels that are smooth and highly durable. Only certain types of disc surfaces are suitable for re-transfer printing including those optimized for thermal transfer use as well as some inkjet-printable surfaces and "crystal" protective coatings. Some additionally offer coated center hubs that allow for full surface printing.
This course brought to you by the Optical Storage Technology Association. www.osta.org
