Datacard SP25 ID Card Printers

THE BASICS OF REWRITABLE CARD PRINTING

What makes rewritable card printing possible is a special rewritable card stock that features a clear layer of heat-sensitive material which overlays a conventional PVC or PET substrate. Embedded within the heat-sensitive layer are a unique dye and developer that chemically bond when heated to a specific temperature and rapidly cooled. When the substances bond, the result is a visible dot. In the same way, when the substances are heated to a specific lower temperature and slowly cooled, the chemical bond breaks and the heat-sensitive material becomes clear again.

This temperature-controlled reaction effectively enables the printer to erase the card (breaking all the chemical bonds) and then rewrite the card (forming new chemical bonds) with new information.

In a rewritable card printer, heat is applied with the same printhead used in conventional full-color card printing. Unlike conventional card printing, however, the printhead comes into direct contact with the card surface. (Normally, a dye sublimation ribbon would be situated in between the printhead and the card.) Direct contact allows the heating elements of the printhead to erase and rewrite each pixel on the card.

The process of erasing and writing a card is referred to as one rewrite cycle. Typical rewritable cards can withstand at least 500 rewrite cycles before image quality begins to deteriorate. Rewritable card printing is monochromatic. In other words, all the pixels on a rewritable card are the same hue.

Rewritable card printing can achieve image quality as high as 300 dots per inch (dpi), which provides ample resolution to reproduce photos, graphics and text, including fonts as small as six points. Although rewritable card printers can print bar codes, it is not recommended. The contrast will not be as high as with a conventional black-and-white bar code, and scanning a rewritable bar code will be more challenging than normal.

THE ANATOMY OF A REWRITABLE CARD

Because rewritable cards are essentially conventional plastic cards, they can be personalized with many of the same technologies as other cards, including magnetic stripes. Rewritable cards have three layers (see diagram below). The heat-sensitive layer contains the embedded dye and developer for rewritable printing. The middle layer is a PVC or PET substrate. The third layer, which forms the opposite side of the card, is clear PVC suitable for dye-sublimation printing. In many cases, the dye-sublimation layer features a color photo, while the rewritable side features text.

Rewritable cards should only be handled by the edges, because fingerprints, skin oils and other residue can degrade image quality. To make card handling easier for operators, most rewritable cards typically feature a matte finish that makes it simple to tell which side of the card is rewritable.