There are many things to consider when printing barcode labels with variable data. Most of them are practical concerns: Which variable label data like text, graphic elements or barcodes should be on the labels? Which font size do you want? Which parts should be pre-printed, and which information should the printer add as variable data?
Which barcode labels are suitable for my application?
Don’t forget to to consider the technical constraints of your labeling system. What is the maximum label width your label printer can handle? Do you need to turn a broad label by 90 degrees so that the narrow side comes out of the printer first? Or can you use a label printer that is wide enough for your purpose without having to rotate the label? Are the ribbon and labels compatible, and does the printing result comply with readability and durability requirements?
All these factors determine the position and orientation of the barcode on the label. Either it leaves the printer by the long edge and looks like a picket fence, or the barcode is printed along the length of the label and looks like a ladder.
The printing direction has a direct impact on the legibility of the barcode. Here’s why:
Printing direction impacts barcode legibility
Thermal-direct and thermal-transfer printers have a fixed, built-in printhead that covers the entire width of the label. Each printhead contains numerous tiny heating elements. They are tightly spaced – with up to 23 elements per millimetre.
The heating elements are electronically switched on and off, generating pressure pulses. Tiny dots create the actual print.
The printer moves the label material along while printing. In one approach, the label material itself darkens at the right spots (thermal-direct printing). Or there is a temperature-sensitive ribbon between the label and the thermal printing head (thermal-transfer printing). Heating elements melt the coating of the ribbon, transferring the ink to the label.
Continuous printing quality is imperative for barcodes. Missing or faulty bars are unacceptable, as they make barcodes unscannable. To prevent build-ups, you need to regularly clean your printheads.
However, and despite all care, at some point even the best printhead will succumb to wear and tear. Individual ink dots will not escape. Or maybe clogged printheads will keep occasional dots from being fully printed even before it’s time for the next cleaning run.
Such issues can go undetected. To be on the safe side, you can always set up a barcode scanner behind the printer to check the legibility of every code. However, while this is an option for more complex set-ups, simper processes often do not have room for it.
Here’s a trick: Print a thick bar over the barcode
Often, there’s a trick to help you out: If you add a thick solid bar over the barcode on the label, you can easily see with the naked eye whether the row of printheads is working properly along the entire width of the barcode. No scanner needed!
If possible, you can rotate the layout of the barcode (as well as the entire label contents) by 90 degrees. That way, a faulty dot would influence the entire print of the barcode, making it impossible to miss.
A warning about rotating barcodes
Rotating barcodes comes at a technical price that we don’t want to hide: Dots are turned on and off in rapid succession at very high printing speeds. From an electronic perspective, the speed is not a problem. However, the heating elements have a certain lag. Even after being turned off, they are still a little warm.
At very high printing speeds, lines can look a little blurry. This can cause a legibility problem for barcodes, in particular because scanners need the bars and blank spaces in between to have very crisp edges. You should therefore check whether it is even a viable option to rotate the barcode with the materials you are using and the printing speeds you need.