The use of thermal and thermal transfer printing is a popular way to print labels with barcodes—thermal is a great technology for barcodes, especially variable or one-at-a-time label printing. Robust, industrial grade thermal printers perform well in less than pristine environments such as warehouses, packaging companies and shipping departments. But heavy duty construction and a solid,  user-friendly interface does not guarantee good labels. Here are the ten most common barcode problems in thermal label we see here in the Barcode-Test lab:

• Defects due to dirt including dirty printers, labels or ribbons. Thermal printers generate a lot of dust and particulate, much of it from the label stock and the cores on which the labels are wound. The metal or plastic enclosure can be a magnet for this dust, as can the thermal transfer ribbon, which naturally attracts it and then lays it right into the printed image, either as voids in the dark features (bars in a barcode) or as artifacts in the unprinted areas (spots in the quiet zones and spaces between the bars). The label stock itself can also be a source of dust and dirt.
• Orientation of the barcode can have a significant effect on symbol quality. Printing the barcode in ladder orientation challenges the print head timing to get bar widths precisely right. Picket fence orientation is much easier for the thermal printer to achieve bar width.
• Related to the above, print speed can drastically impact symbol quality especially if the 1D barcode must be ladder-oriented. And it can just as drastically impact the quality of a 2D symbol such as a QR Code or Data Matrix Code. Slow down the printer to maximize good print quality.
• Print head temperature must be balanced with print speed, but higher temperature is not an exact compensation for higher print speed and neither is lower print head temperature and slower print speed. Use a verifier to find the right balance.
• One size does not fit anybody– print quality results will vary according to substrate and ribbon type. What works for a paper label and a resin ribbon won’t necessarily work well for a polypropylene or coated label and a wax ribbon. Document all variables to get you into the ballpark and tweak settings to fine tune to optimal results.
• Make sure the label design software is correctly set to the printer’s resolution. Usually this is done when you configure the design application to the printer and print head DPI in set-up but don’t assume its right—check to be sure.
• Avoid using only one pixel for the X dimension (narrow bar in a 1D barcode or the element width in a 2D symbol). Not all symbologies can be accurately reproduced with multiples of one pixel, and larger symbols have more bar/space width tolerance.
• Using a marginally big enough label to save money is a risky savings strategy. The printer operator must monitor the whole print run to make sure the barcode doesn’t migrate over into quiet zone violation territory which results in a non-scanning barcode and a quantity of labels that negate any savings.
• Burned out print head pixels are always a lurking menace, and optimally oriented picket fence barcodes make them almost impossible to detect, but if you add a horizontal signal strip above or below the barcode you can easily detect burned out pixels with the naked eye. A .050” wide bar the full width of the label is all that’s needed to signal a print head that needs replacement.
• Incorrect data structure is perhaps the most subtle but devastating label mistake. You might be checking your labels with a scanner and they are scanning just fine, so you think they are OK—but if the barcode isn’t structured in accordance with the GS1 Industry Application, those labels are a liability for which you could pay dearly. You cannot rely on some verifiers to check data structure—make sure your verifier tests and reports on data structure for the labels you are producing.

Do you have other thermal printing problems or experiences to add to this discussion? We would love to hear them. Your comments are always welcome.