Direct Printing of Barcodes on Corrugated: Challenges
Direct printing of barcodes on corrugated presents some very special challenges. Some developments in the industry are increasing these challenges: increased use of recycled materials make barcode printing more difficult; reducing the use of corrugated by packaging on shrink pads presents other challenges.
Recycled materials make direct printing of barcodes on corrugated a challenge
Bare corrugated made with non-recycled materials is a relatively low reflectance substrate for a barcode. The industry generally accepts an ANSI/ISO grade of D for the parameter Symbol Contrast because of this. Recycled materials can be worse, for several reasons.
Corrugated made of recycled material can tend to be even darker than virgin corrugated, making Symbol Contrast even lower, sometimes pushing it into an ANSI/ISO F.
Recycled corrugated often has a surface with an inconsistent contrast, that varies from relatively reflective in one area to lower reflectivity in adjacent areas. Direct printing of barcodes on corrugated with variable reflectivity can wreak havoc with the scanner.
Most verifiers cannot report specific problems in direct printing of barcodes on corrugated
One of the reasons the quiet zones are so critical to successful scanning is that these are the areas where the scanner calibrates itself to the high reflectance value for that barcode. If it then encounters areas within the barcode where the high reflectance values are different than the calibrated value, the scanner may struggle or fail to decode the symbol.
A verifier will signal these problems in the parameters Modulation and/or Decodability in addition to downgrading Symbol Contrast. Most verifiers do not have the ability to report variable light reflectance issues, so diagnosing these occurrences can be challenging.
Recycled corrugated can also exhibit variability in surface tension and/or wax content. This affects substrate acceptance of the pigment. Some areas may be highly receptive, and the image will wick. Adjacent areas may be resistive to the pigment, minimizing wicking or even tending to smear. Verifiers are not equipped to signal these problems specifically.
Corrugated from recycled materials can also be prone to warping, which is not necessarily a problem with contact post printing methods such as flexography. But warping can be a major problem with non-contact printing such as ink jet, where the distance and tolerance from the print head to the corrugated substrate is small. Contact with the jets is a problem and so is too much distance.
Beyond the printing process, other problems include shrink wrap, which is highly reflective even when taut, and refractive when wrinkled or slack over the barcode. While this is not within the scope of an article on post printing, it is exacerbated by warped corrugated by creating a distance between the shrink wrap and the barcode.
Problems with direct printing of barcodes on corrugated are made worse with shrink wrap
Finally, a word about the flexographic post print process. When text or other graphics are also being printed on the corrugated it is tempting to include the GTIN14 or ITF14 barcode on the same plate. This is an ill advised practice, as the barcode often requires a different—usually higher—impression than graphics to get a good result.
It is recommended to use a separate plate and an additional station to control and optimize direct printing of barcodes on corrugated.