Bar width reduction or BWR is a method for adjusting the graphics design file of a barcode to compensate for press gain. Press gain or ink spread is one of the most common causes of poor barcode performance.
Bar width reduction is a compensation for press gain
Not all barcode design software provides for bar width reduction. Determining the appropriate amount of bar width reduction is critical and should be done with considerable care. Some barcode file e-vendors recommend applying a standard bar width reduction based on print method. This is an ill-advised approach—the time saved could become a major headache and expense later if the guesstimate is incorrect.
There are some variables to consider, all of which can contribute to press gain—and therefore the appropriate amount of bar width reduction. Ink thickness or viscosity can affect how much the ink spreads; vegetable-based inks behave differently than oil-based ink. Characteristics of the substrate vary: some substrates are porous, causing the ink to wick and spread. Non-porous substrates can cause problems of ink smearing or running. Impression pressure can influence pain. Worse still are substrates where the porosity is not consistent, such as papers made from recycled material.
Bar width reduction is best determined by measuring—not guessing
The key to controlling these and other variables is to keep careful records, documenting how a particular ink and substrate combination behave. This at least puts you in the ballpark for anticipating press gain and determining the appropriate amount of bar width reduction.
The best method for determining press gain is to measure it. Start with a barcode graphics file with a known amount of bar width reduction—or with no bar width reduction. The uncompensated width of a guard bar on a UPC symbol at 100% magnification is .0130”. Measure the width of the printed guard bars. Any deviation from .0130” is the correct amount of bar width reduction for that ink and substrate combination. Deviation will always be to the plus side unless the barcode is being reverse printed, which is very rarely done.
Bar width reduction can compensate for many variables in the print process
Be mindful of all the possible variables in the equation. Ink and substrate are just two—there could be many others. The condition of the press, the state of its bearings, the roller pressure settings, the run speed, press room temperature and humidity can all contribute to press gain. Variables are always present. The key is to know what they are and how to control—or minimize—them.
Measuring the printed image is best done with a low power microscope or magnifier. High quality bar code verifiers such as those from Axicon provide an accurate bar width measurement. It is usually unnecessary to measure all the bars in a printed barcode: they all get treated the same way by the press, unless there are some very unusual adjustments or problems with the press, in which case you have much bigger problems than press gain—and bar width reduction won’t help.
An independent bar code test lab such as Barcode-Test can do the measuring for you, and recommend the right bar width reduction values based on samples you provide.
Contact us for more information.