Adjustment of Print-head Temperature / Print Speed
Since thermal transfer printing involves imaging through tiny heated pins contacting a ribbon onto a label, the print head temperature has a dramatic effect on symbol quality. If the heat setting is too high, the bars will print too heavy. Conversely, if the setting is too cool, the bars within a symbol will print too light. The heat setting can be adjusted either as a printer function or through a software setting. Adjustment control will vary between software and printers.
Symbol Orientation
It is highly recommended that barcode symbols be printed in the direction of the printer. Barcodes printed with bars perpendicular to the print direction tend to yield dimensional errors.
Printer Maintenance
The quality of printed symbols tends to degrade as deposits build up on the thermal print head. Regular cleaning of the print head and guide surface in accordance with the manufacturer’s recommendation is highly advised.
Thermal Print heads eventually wear out to the point where one or more dot elements fail to heat properly. When this occurs, the printed symbol may no longer be scannable. Obviously, if printed symbols are routinely checked by a barcode print verifier, print head wears will be easily detected. Another procedure we recommend is to print a symbol with a horizontal bar going across the top of the label. Any defective element module will be easy to recognize.
Source: Bar Code Graphics, Inc.(http://www.barcode-us.com/upc/printingTips.html)