Bar Width Reduction
Bar width reduction or BWR is compensation in the bar code data file for press or dot gain. The act of putting ink onto a substrate almost always results in that image spreading. Scanning a bar code is negatively impacted by fattened bars and thinned spaces. Bar width reduction factors the design file, reducing bar width but retaining bar positions, in anticipation of the print processes restoring the bars to nominal widths and if done correctly, cancelling the negative effect of ink spread.
Bar Width Reduction is the Most Important Thing that Can Be Done to Assure Bar Code Quality
Bar width reduction is arguably the simplest and most important thing that can be done to assure that a printed bar code will scan successfully. But bar width reduction is also one of the most misunderstood and misapplied factors in bar code quality. Why is this?
Bar width reduction is sometimes confused with scaling the bar code. BWR does not change the locations of the bars and spaces; it changes the width of the as-yet-unprinted bars but does not move them closer together on their centers, as scaling does.
Scaling the symbol to a larger size will increase the tolerance of the bar code to press gain. This may be where the confusion between scaling and bar width reduction comes from. But scaling the symbol to a smaller size will decrease the tolerance of the bar code to press gain. And scaling a bar code can introduce a host of other problems to the integrity of the bar code image well beyond its tolerance to press gain.
Some of the confusion is because of the nature of process compensation. Bar width reduction is a prediction of something that will happen in the future, not something that is completely known in the present time.
Bar Width Reduction is a Prediction of Something That Will Happen in the Future
Predicting the right amount of bar width reduction is not a complicated process—but neither is it a formula or a look-up on a chart. The best predictions always come from accurate historical data; the more data, the better. The interaction of different types of inks and substrates is a whole set of variables that must be measured and documented before bar width reduction can be predicted. Press set-up including blanket characteristics, roller pressure, plate durometer and other factors all contribute. Press condition is another consideration. The best way to control these variables is to document them and build a database that, over time, will include all possible combinations of factors and the results they yielded in bar code quality.
With diligence, over time, predicting bar width reduction becomes less of an art and more of a science. But where do you begin? Start with a bar code file with no bar width reduction. Document every step in the process and measure the results. If the bar code has gained .0015” in bar width, that is the bar width reduction for every future bar code printed on that press under those conditions, until something changes.
Bar Width Reduction is a Matter of Documenting Process Variables Over Time
Many of the press gain-related problems I’ve seen over the years are the result of not knowing how a bar code file has been bar width reduced. This is especially prevalent in customer-supplied bar code files. By documenting everything, whatever is not documented, such as the bar width reduction of a customer-supplied file, becomes obvious.
A diligently documented process over time produces amazing results: surprises disappear, quality improves, waste and cost and delays decrease and customers become more loyal.