A barcode, as defined in the Polish standard PN-EN 1556: 2001 “Barcodes. Terminology”, is a “pattern of parallel rectangular bars and spaces, arranged according to the coding rules contained in the descriptions of individual symbologies, in order to represent data in a machine-readable form”.
In printing houses, barcodes are usually printed together with the graphic design of the entire packaging or label. However, these codes are not just a simple decorative or informational element printed on the packaging. They require very high printing accuracy, as they are an element of the packaging that must be read automatically using barcode scanners.
The requirements regarding the precision of barcode printing can be evidenced by the fact that the traditional method of barcode quality verification specifies that the deviation in the width of EAN/UPC code bars with a magnification factor of 0.80 should not exceed +/- 35
In the case of incorrect barcode quality, the printing house may face a complaint about the printed packaging, which usually involves high costs and may also result in the loss of customers. In turn, the manufacturer whose products contain such incorrect codes may be exposed to returns from a customer, e.g., from a retail chain, for an entire incorrectly coded delivery.
EAN-13 and EAN-8 barcodes, which are codes commonly placed on unit packaging, can be printed using any printing technique. However, the most accurate of these is the flat printing technique, e.g., offset, lithography, and the least accurate: flexography and screen printing. In the brochure “Printing EAN. UCC Barcodes”, developed jointly by the Central Research and Development Centre of the Printing Industry and the Institute of Logistics and Warehousing, available on the website www.gs1pl.org, Table 3 contains the recommended minimum magnification factors for codes depending on the printing technique and the type of printing substrate. According to the PN-EN 1556 standard “Barcodes. Terminology”, the magnification factor is a constant multiplier (for EAN/UPC codes it ranges from 0.80 to 2.00) used for the nominal dimensions of the barcode symbol in order to obtain the actual dimensions of the code in which it is to be printed.
If, for example, the nominal height of EAN-13 code bars is 22.85 mm, then for a code with a magnification factor of 0.80, the height of the code bars will be 0.80 x 22.85 = 18.28 mm accordingly.
According to Table 1, offset printing allows for the printing of good quality codes with a factor of 0.80, which is the smallest allowed by the standard. On the other hand, flexographic printing is usually the least accurate: here the code magnification factor should not be less than 1.60 when printing on corrugated cardboard or 1.30 –
when printing on foil or paper.
Of course, these are only recommendations, because if one possesses a modern and precise machine park, appropriate inks and printing substrates, high staff skills, and appropriate devices for verifying the quality of the printed code, the applied barcode magnification factors can be smaller. The author of the article has encountered printing houses that were able to print good quality barcodes using the flexographic method with the minimum permissible magnification factor, i.e., 0.80. Therefore, every printing house should determine for itself the minimum code magnification factor for the printing technique used, at which it is able to guarantee its customers the printing of good quality barcodes. This must be done experimentally, by performing a series of tests with various printing parameters that can be adjusted in the printing process, such as the pressure force of the printing plate (too much pressure force can, for example, in flexography cause over-impression visible as a doubling of the code bar edges). The barcodes produced during such tests should be thoroughly examined. In principle, the only tool that enables this is a barcode quality verifier.
A barcode quality verifier is a device consisting of a barcode scanner and an analysis program. The analysis program can be placed either in a separate device to which the scanner is connected or saved on the hard drive of a computer, on whose monitor the analysis results will be displayed. A printing house can purchase such a verifier itself, but it can also send samples for analysis to a company that owns such a device.
The practice often used by printing houses of checking the readability of barcodes using only a scanner does not give any guarantee that the code read by this scanner will also be read by scanners of other types and other companies. The wear and tear of mechanical and optical components, e.g., wear of the mirror bearing, scratching of the surface of the counter scanner glass, etc., has a large impact on the reading capabilities of barcode scanners. Besides, scanners have different “intelligence” of decoding software. Thus, the only reliable device ensuring an objective assessment of barcode quality is a barcode verifier.
The article comes from the magazine “Logistyka” 1/2006.