Direct-to-Card printing is the process by which a thermal print head is lowered onto the ribbon, and pushes the ribbon into contact with the card. The print head then heats up the ribbon, and in the case of colour printing turns the ribbon to gas, which sublimates into the surface of the card (dye-sublimation). For this process to work well, the card needs to be made of laminated PVC, as Laminated PVC at a microscopic level contains many grooves for the ink to sublimate. When printing in black (or other single colour) the ribbon is typically a wax resin, that is melted onto the card. This process is a little more forgiving on the card surface, though still performs best on PVC.
Direct-to-Card is the most popular technology, due to;
- a low cost to manufacture
- a low printing cost, and
- potentially high speed printing capability
There are drawbacks however. The two most important issues in relation to the purchase of a card printer, are print head scratching and poor print quality.
While these issues are not as troublesome as they were 15 years ago, they are still a factor to be aware of.
Print Head Scratches: When the print head pushes the ribbon against the card and the card is moving back and forth across the head any foreign material such as a grain of sand, or gritty dust can scratch the print head. A print head scratch will be seen as a thin white line across the printing length of the card (typically the long edge). Depending on where the scratch is it may not cause a problem, but if it is through the middle of a photo or persons name, the print head will need to be replaced at a cost of $700 -$1200 or more.
Poor Quality Print: It is difficult to sublimate colour ribbon to an uncontrolled surface such as a PVC card. Different cards absorb different levels on ink and the changes can be significant from different card manufacturers. Some manufacturers use recycled PVC, giving the card a purple hue, others polish the pvc to save on the cost of having a clear PVC laminate over the card. Because of this difficulty it the quality of print on cards can vary significantly and may require adjustments. There is also a limitation that the print head cannot fill in gaps and groves in the card. These can be often found in smart cards over where the aerial or chip are positioned beneath the surface of the card, resulting in blemishes.
However as time goes on and with improved scratch resistance of heads and improved thermal conductivity during the print process, these issues are less significant.