PRINT GAIN PROBLEMS

A packaging designer specified a high-tech look for the rollout of a hot new electronics product. They created a box with black barcodes printed on a crisp white substrate. Visually the barcodes looked great but failed to scan.

• Linear and 2D barcodes share a common characteristic: they must have uniform dark and light values with at least a?minimum reflective difference.

Symbol Contrast is the parameter in the ISO standard that reports this reflective difference, and the verification report showed an ISO 4.0 (A) grade. Why are these symbols failing?

The remainder of the highest detected reflectance value minus the lowest detected reflectance value is the Symbol Contrast value.

Variations in the reflectance values are reported in the ISO parameter Modulation. How could there be reflectance variations in a black barcode on a clean, white substrate?

Print gain is the most common cause.

• Print gain is the spreading of the printed image—in this case, the black bars in a barcode. When the bars gain or spread, they crowd the spaces between them, making them smaller.

The reflectance value is lowered in spaces squeezed by print gain. The high reflectance value is no longer uniform. "Why is this a problem?” Barcode scanners decode a barcode by detecting the reflective differences in bar and space patterns.? When bars get fatter and spaces get thinner, the reflective differences decrease. If the bars grow excessively, a scanner may incorrectly decode the barcode, or fail to decode it altogether.

Fortunately for the electronics company, this problem was detected before the product rollout. The solution: bar width reduction of the design file. Bar width reduction (BWR) thins the bars so anticipated print gain returns them to their nominal width. This preserves the full reflectance value of the spaces and reassures high scanning rates.