Printing Tips

Since the dependence on barcoded information is continually growing, the ramifications for non-scannable barcode symbols are severe. In addition to print quality, there are other factors, which affect the scanning performance/ acceptance of barcode symbols. In fact, a recent retail scanning performance study illustrated that one third of all barcode rejections were caused by factors other than print quality. Many of these problems resulted from errors in the design or origination stages.

Design Stage Considerations:

Quiet Zones

Barcodes require an area of free space on both the left and right of a symbol. These spaces need to be clear of any stray marks or graphics that the scanner may interpret as an errant bar.

Quiet Zone measures .125” width on the left and right hand sides of a barcode symbol.

Print Contrast (Color)

A scanner reads a barcode by distinguishing the differences between the bars and spaces. The spaces must be light colored (highly reflective) and the bars must be dark (less reflective). The best color combination is black bars on a white background, but other color combinations will work as long as the contrast between the bars and spaces is adequate. If the contrast gets too low, the scanner can not differentiate between the bars and spaces, therefore the bars code appears invisible.

Height

Truncation (shortening of symbol height) should only be used as a last alternative. The shorter the barcode height, the more difficult it is to scan the code in most scanning environments. Truncation has a dramatic effect on UPC symbols, and some retailers penalize suppliers for reducing the height of a barcode on a package which has the space for a standard symbol.

Encodation

This simply insures that the bars and spaces match the human readable characters when a barcode is scanned. The human readable characters should not be omitted or abbreviated.

Printing Suggestions

Barcodes can be printed from a multitude of printing methods ranging from wet ink processes to on-demand digital printers. Symbol print quality will vary depending on the printing process. Flexographic, offset lithography, and silk screening qualify as “wet ink” printing processes, whereas laser and thermal transfer printers are typical on-demand printers. The following suggestions will help maximize barcode print quality

Wet Ink Process:

Precision Barcode Artwork

All wet ink printing utilizes either printing plates or screens. In order for a printing plate to accurately duplicate a barcode image, the original barcode artwork must be precise and be properly compensated for print growth. (For further information go to Pre-Press Products.)

Height

If it is too thick, the bars of a symbol usually print thin, because less ink transfers from the plate to the substrate. Conversely, if it is too thin, the bars print wide because the ink is slapped against the substrate, spreading the ink outward. For flexible packaging, it is ink viscosity, which causes the most problems with barcode print quality. When the law required the removal of lead from ink, the opaque characteristics of the ink has dropped. Barcode symbols are read by having the bars absorb scanner beam of light, while the spaces between the bars reflect the light. If white ink is printed on flexible packaging under the symbol and the white ink is not opaque, the scanner beam passes through the white instead of reflecting off it. Thus, the contrast between the dark bars and light spaces is lost.

Plate Impression

When printing flexographically, you want to use just enough impression to achieve a clean, sharp detail with appropriate ink coverage. This holds true for the barcode symbol as well. Too much impression will cause the bars to print wide and too little results in thin bars. Watch other graphics that print on the same plate for indications of inappropriate plate impression. When printing large solids or reverses, barcode symbols will usually print wide because the impression is increased to get suitable ink coverage.

Symbol Orientation

The decision to run barcode symbols with or against the web direction is a concern. We normally recommend running symbols in the same directions as the press (picket fence orientation). However, proper distortion can allow barcodes to be printed in a ladder orientation.

Suggestions for Digital Printing (Thermal Transfer)

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.