Bar Width Reduction
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
Virtually every barcode design software provides for press gain compensation. Determining the appropriate amount of BWR is critical and should be done with considerable care. Some barcode file websites recommend applying a standard bar width reduction based on the X dimension (narrow element width) or on the physical size or magnification of the barcode. 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 BWR. 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 BWR.
The best method for determining press gain is to measure it. Start with a barcode graphics file with a known amount of BWR—or with no BWR. 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 controls an important set of variables in the print process
Be mindful of all the possible variables in the equation. Ink and substrate are just two and there could be many others. The condition of the press, the state of its bearings, the roller pressure settings, the run speed, even the 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. Very few barcode verifiers measure and report bar widths. 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’ve got much bigger problems than press gain—and BWR won’t help.