Barcode Printing Methods and Print Quality Requirements

Barcodes sit on almost every packaged product, carton, and shipping label, and their print quality decides whether a scanner reads the code on the first pass or forces a manual key-in. This guide covers the printing methods used for barcodes and the technical and material requirements that keep printed codes readable.

Printing Methods for Barcodes

Barcodes can be printed by offset lithography, letterpress, gravure, and plateless (inkjet) methods. Whatever process is chosen, the printed result has to meet a high quality standard. The main points are:

• For correct scanning, printed bars must be clean and sharp, with no obvious missing segments (defects) in the bars and no leftover ink spots in the spaces. In practice the maximum diameter of a defect or spot should be no more than 0.4 times the narrowest nominal bar width.
• Controlling the dimensional error of the code raises the first-read rate and lowers the decoding error rate. This calls for tighter plate-making and printing quality as well as suitable tolerances in the reading device.
• Reliable reading needs a clear contrast signal between bars and spaces. The greater the contrast, the better the reading performance.
• Printing tolerances must be strictly controlled, otherwise reading performance drops.
• Edge roughness matters. When roughness is too high, the code cannot be read.
• The ink layer thickness for bars and spaces is generally kept within 0.1 mm. If it is thicker, the bars and spaces sit on different scanning planes, which harms reading accuracy.

Printing Requirements

To keep barcode printing quality under control, the process and the materials have to meet a set of requirements:

• Size scaling. Barcodes are normally printed at their original size. When scaling is needed, it is best handled by the organization that supplies the barcode film master.
• Color combination. Black ink is the safest bar color and white the safest space color. When other colors are used, choose the combination according to the red-light response of the colors.
• Substrate. Optically, the material should scatter light well rather than produce mirror reflection. For dimensional stability, choose a stock with good weather resistance, stable dimensions under load, good color receptivity, moderate ink spread, low penetration, and moderate smoothness and finish.
• Ink. Take ink color shift into account when matching inks. Because barcode printing is solid-area printing, the reflection density it reaches depends on the ink's optical properties and the ink layer thickness. During printing, reflection density rises as the ink layer thickens, then saturates once the layer passes a certain value, so watch both ink concentration and layer thickness. Ink viscosity should not be too low, and ink supply and pressure should not be too high, as all of these affect barcode printing precision.