When using direct thermal or thermal transfer printers for barcode labels, the orientation of the barcode—whether in a picket fence or ladder orientation—can significantly impact the quality and readability of the printed barcode. Here is a quick explanation of why the picket fence orientation generally produces better barcodes than the ladder orientation.
How Thermal Label Printers Work
Regardless of whether you use direct thermal labels (no ribbon needed) or thermal transfer (with a transfer ribbon), the principle of printing is the same and both techniques use the same printheads.
The thermal printhead is built with a row of printing elements protected by a thin ceramic coating.
Thermal printheads are available in several widths, with 4 inches and 6 inches the most common for labeling applications.
The number of printing elements determines the print density, or dots per inch, of the label printer.
For general logistics label printing, eight dots per millimeter (203 dots per inch) is most commonly used, and 12 dots per millimeter (300 dots per inch) is often used as well, especially for printing higher-density barcodes, such as GS1-128.
600 dpi printheads are also available for printing very small barcodes, which are often found in electronics and other industries.
Note that thermal printheads are treated as consumable items—over time, they will wear and need to be replaced. Regular cleaning helps extend the printhead’s life.
When using direct thermal labels, printheads tend to have a shorter lifespan, since they are in contact directly with the abrasive paper surface.
Picket Fence vs Ladder Orientation
Picket Fence Orientation
In the picket fence orientation, the lines of the barcode are printed parallel to the substrate’s (label) movement through the printer. This means the barcode lines are vertical as they move through the printer.
As the label moves past the printhead, the appropriate elements are turned on at the start of each and held at the correct temperature until the end.
Advantages:
Crisper and Straighter Edges: The printhead heats continuously as the substrate moves, allowing each line of the barcode to be printed in one steady motion. This results in straighter lines and crisper edges because the printhead elements are heated evenly for a set period.
Higher Print Quality: The continuous heating process helps produce high-quality barcodes with less risk of jagged edges or distortions, which are critical for ensuring the barcode is readable by scanners.
Barcodes printed in the picket fence orientation usually have the best verification scores, which helps avoid chargebacks for non-compliant barcodes.
Higher Printing Speeds: The printer can be operated at high speeds, while maintaining print quality. This helps with keeping up with production demands.
Disadvantages:
Vulnerability to Printhead Damage: If a single heater element in the printhead fails, it will reduce the width of the bar it was printing. While this might not be easily noticeable to the human eye, it can render the barcode unreadable by scanners.
This is why setting up barcode scanners on your packaging line is important to ensure that each barcode is readable.
Ladder Orientation
In the ladder orientation, the barcode is printed perpendicular to the movement of the substrate. This means the barcode lines are horizontal as they move through the printer.
As each print element is printing, it needs to be turned on and off rapidly to build up the barcode image.
Advantages:
Detectable Printhead Issues: If a heater element fails, it creates a white space across the entire barcode, easily detectable by the human eye.
This is a blemish on the package, so it will need attention shortly.
Disadvantages:
Lower Print Quality: The printhead must turn on and off rapidly to print each line, resulting in less crisp lines and potentially harder-to-read barcodes.
Increased Wear on Printhead: The rapid heating and cooling required can cause increased wear, leading to more frequent maintenance and replacements, particularly in high-speed printing applications.
Lower Printing Speeds: Barcode print quality will decline as printing speeds increase. Reducing printing speed can rectify this, but it might lead to lower production rates.
Conclusion
The picket fence orientation is generally preferred for thermal transfer printing because it produces higher-quality barcodes with crisper and straighter edges, which are essential for ensuring readability by scanners.
However, monitoring the printhead for potential failures affecting barcode readability is important to ensure the printed barcodes meet GS1 and customer standards.
Whichever print orientation you use, it’s important to regularly clean your printhead to get the best results and to prolong its life.
