Printing Compliant GS1 Barcodes

If the U.S. Consumer Packaged Goods (CPG) industry is ever going to benefit from sharing supply chain information between trading partners, the current status of the quality of GS1 GTIN bar codes on shipping cartons must be addressed. The advantages to all trading partners are well documented - see Global Commerce Initiative www.gci-net.org.

The Global Trade Item Number - GTIN - is a family of data structures supported by GS1 that are used to identify items, cartons, and pallets throughout the supply chain. These data structures consist of up to 14 digits that are encoded in a number of different bar codes - EAN/UPC - being the most familiar. The GS1 GTIN structure for shipping cartons can be encoded either in ITF-14 (Interleaved 2-of-5) or a GS1-128 bar code. For more information on GS1 GTIN's see www.gs1.org.

Walking through any large retailer distribution center will highlight the problem - many of the GS1 GTIN bar codes printed on shipping cartons do not conform to printing standards. By having non-compliant GS1 GTIN bar codes in the supply chain both CPGs and retailers lose. The CPG's lose because they are spending a lot of money on GS1 GTIN compliance with no return and both lose because of the lack of information regarding location, inventory levels, and consumption of products throughout the supply chain.

To compound the problem, the shipping carton is changing such that in the future it will be even more difficult to direct print compliant GS1 bar code symbols. According to a recent research report from the Packaging Machinery Manufacturers Institute (PMMI), the future trend for secondary packaging is for a decrease in the amount of corrugate. An extreme example is shrink pads - consumer products on sheets of corrugate enclosed in shrink wrap. There is no corrugate on the side of the secondary package. The PMMI reports also notes an increase in the amount of recycled content in corrugated containers.

Decreasing the amount of corrugate will reduce the available real estate on a shipping container for printing bar codes. The smallest X dimension for printing the GS1 GTIN directly on a carton is 25 mils (0.025 inch). The shorter cartons may require that the bar code be truncated, reducing the vertical redundancy and may result in the bar code being outside the scan pattern. The reduction in corrugate will have an impact on both flexographic printing and ink jet printing.

Increasing the use of shrink wrap can lead to scanning problems if the shrink wrap is placed over the GS1 barcode symbol. Both the material used for shrink wrapping and the air gap between the shrink wrap and the bar code can cause scanning problems. This is a risky proposition, since the air gap between the shrink wrap and the bar code will change with each carton. If applying shrink wrap over a bar code, the GS1 barcode symbol should be verified after the shrink wrapping process. If you are verifying according to a sampling plan, you will not be able to determine with any certainty that the entire batch of bar codes are compliant.

An increase in the amount of recycled content of corrugate will decrease the symbol contrast for direct printing. Recycled material tends to be darker than virgin board. A corrugate with a higher recycled content also has an increased chance of warping. Considering the limited throw distance of most ink jet printers, this will cause bar and space distortion.

This white paper discusses three technologies commonly used to print GS1 compliant bar codes on shipping cartons - flexographic printing, ink jet printing, and label printing. Please note that not all of these technologies are accepted worldwide as a solution for printing GS1 compliant bar codes. Woolworth's, the largest retailer in Australia, moving approximately 750 million cartons and 9 million pallets through their distribution centers annually, will not permit bar codes printed with ink jet technology in their supply chain. Woolworth's barcode specification states the following:
"INKJET BAR CODES ARE CURRENTLY NOT ACCEPTABLE TO WOOLWORTHS" (Packaging Barcode Spec V8.0, 2008, page 44, Section 6.4.1.7.) Note: All caps are part of the spec!

Printing Options
To start, you need to decide if you want to print the bar codes off-site or on-site. If the decision is to print off-site, the most common option is flexographic printing - either directly on to the shipping carton or preprinted bar code labels.

If you elect to print on-site, the predominant methods are ink jet printing and industrial thermal or thermal transfer label printing. The label printing option would include label print and apply.

Flexographic Printing Directly on Corrugate
If your SKU is of sufficient volume then off-site printing the GS1 bar code symbol directly on to the shipping container may be the most economical solution. The cartons are printed at the carton manufacturer on flexographic printing presses. This requires a printing plate. Bar code and text changes are accomplished by changing the printing plate. The flexographic printing process is ideal for large runs. Because of the nature of the printing process, flexographic printing typically provides the best GS1 barcode symbol print quality for direct printing. The black flexographic inks provide good symbol contrast against the brown corrugated. Symbol contrast is even better if printing on a mottled white corrugate board.

Direct printing on corrugated does have its challenges. Placing the GS1 barcode symbol on the same printing plate as other text and graphics can cause print issues. The impression required for proper ink laydown for the GS1 barcode symbol may be different than the impression required for the other information on the printing plate. The press operator may compromise the impression setting. The result is a non-conforming GS1 barcode symbol. One way around this is to separate the GS1 GTIN bar code from the other images by placing the bar code on another printing plate and mounting the plate on an additional print station. This will increase costs slightly.

Bearer bars - the box that surrounds the barcode symbol and the quiet zone - are required for ITF-14 symbols printed directly on corrugated. Bars across the top and bottom of the symbol are required for other printing processes. The bearer bar provides two benefits when printing on corrugated. It provides additional mechanical support to the bar code image to offset any increased plate impression. The second benefit from the bearer bar applies to scanning the ITF-14 symbols. The design of the ITF symbology will, under certain conditions, permit a successful partial scan. The scanning path can exit the ITF bar code without scanning both the Start and Stop characters and get a successful read. However, this should not pose a problem to those systems scanning the GS1 barcode symbol. GS1 compliant scanning systems are typically set up with a scanning data profile that will only accept the scan if 14 digits are read and the check digit is correct.

The trend, mention in the PMMI research, toward smaller corrugate will reduce the available space for printing the GS1 barcode systems. Printing a smaller GS1 barcode symbol is an option, but you will be limited in reducing the bar code X dimension for the specific GS1 symbology as specified in the GS1 General Specifications (see Symbol Specification Table)

The second trend mentioned in the research, that of an increase in recycled material in corrugate, will result in the bar code symbol contrast being reduced. This is already an issue but will become more of an issue in the future. One of the reasons that bar codes printed directly on corrugate - both flexo and ink jet - receive a low ISO grade is the poor bar code symbol contrast.

The disadvantage to off-site printing is that each carton will be dedicated to a particular SKU. It will have its own unique GS1 barcode symbol. Small print runs are not economical and inventory control for stock-outs is more of an issue. Obsolescence and write-offs as a result of product SKU changes need to be considered.

By having the bar codes preprinted, carton handling becomes less of an issue at the plant. Benefits include higher conveyor speeds; no need to control carton skew at printing locations along the conveyor; no production slow down to accommodate labeling speeds; and the responsibility for the quality of the GS1 barcode symbol resides with the supplier.

Ink Jet Printing
Printing GS1 barcode symbols with industrial ink jet printers is considered a low cost on-site solution. However, ink jet printing does have its challenges.

Corrugate is composed of new fiber and recycled fiber. The new fiber to recycled fiber ratio changes with each batch of corrugate. For the most part, new fibers are long but lighter in color. Long fibers tend to promote bar width growth. Recycled fibers are short but dark in color. The dark color negatively impacts print contrast. The result is that bar width growth and print contrast can change with each shipment.

An option worth considering to improve the symbol contrast is having the shipping container manufactured out of mottled white corrugate. The inks tend not to migrate and the symbol contrast is superior to standard corrugate.

Poor dimensional tolerances of corrugate shipping container can cause GS1 barcode symbol printing problems. The trend to increased use of recycled corrugate will increase the occurrence of carton warp. Ink jet throw distance now becomes an issue. Throw distance is the distance a drop can travel in a straight line from the print head to the surface to be printed. In most of the ink jet systems used to print GS1 barcode symbologies on corrugate, the throw distance is approximately 1/8" to ¼". Variations in the distance from the print head to the corrugate surface from carton warp and improper carton orientation from poor material handling can result in the throw distance exceeding ¼". The result is a decrease in overall symbol contrast and poor edge contrast.

An additional factor is the type of conveyor used. Fluctuations in conveyor speed and carton bounce from roller conveyors all add to the difficulty in producing a conformant GS1 GTIN bar code. Most successful ink jet printing installations use a belt conveyor.
Ink is another issue. The corrugate surfaces receptivity to ink, called surface tension, will change with each shipment of corrugated containers. Surface wax, which can change the surface from porous to non-porous, is one of the culprits. Poor ink adhesion will cause ink to run.

In addition, many inks are oil based - they don't dry - so the possibility exists for the inks to continue to migrate in the corrugate surface long after the time of application. Some waterbased inks suffer from the same problem with humidity changes. The result is bar width growth over time.

Some inks are dye based inks and do not provide sufficient print contrast between the bars and the spaces. To address this problem, chemical additives to the ink can provide the necessary ink properties that will enhance the print contrast. As mentioned previously, another method to improve symbol contrast is to use a mottled white corrugate.

Other inks are waxed based. They provide better print contrast than most waterbased and oil based inks. Throw distance is still an issue. Since the inks don't penetrate the corrugate surface abrasion resistance is less than the other inks.

Purchasing inks from other than the ink jet printer manufacturer, in addition to voiding the warranty, can cause the ink jet valves to clog and system performance to decrease.
According to the PMMI research report, "recycled corrugate also limits color usage and printability on boxes which was mentioned by 31% of the companies" in the research report. As stated previously, ink jet printing GS1 barcode symbols is not a globally accepted solution. Woolworth's Australia will not accept ink jet bar codes.

Label Printing and Applying
Printing and applying the GS1 barcode symbols using labels is the most expensive alternative of the three discussed. Labels can be either preprinted or printed on site. If printed on-site it is normally accomplished with either direct thermal or thermal transfer labels. Both direct thermal and thermal transfer printing is available in all industrial label printer and label printer applicators. There is a trend to direct thermal labels for print and apply GS1 bar code symbols because direct thermal printing reduces the supply change to the label roll only.

Preprinted labels are produced by a commercial flexographic printer. The labels can either be hand applied or automatically applied. Preprinted labels require a printing plate and are subject to similar printing impression issues as outlined in preprinted corrugate. The X dimensions can be smaller - to 20 mils.

An industrial labeling system is less sensitive to changes in corrugate material. However, label adhesion can vary as a result of batch to batch variation in surface wax.
Labels do not change reflectivity from one shipment to another. Symbol contrast is the highest of the three technologies. The bar codes have sharp well defined edges. The label printing speed is under precise control of the printer.

Automated print and apply equipment will require attention to carton skewness on the conveyor. Skewed cartons can result in labels not applied or if applied may not be in the required location.

Label print and apply equipment is limited in the number of applications per minute. Typically 60 to 70 applications per minute is the maximum. Conveyor speeds to 300 fpm are possible.

Non-conforming bar codes can occur as a result of normal print head wear for both direct thermal and thermal transfer printing. Wrinkled ribbons are at times the culprit with thermal transfer printing. Expect from 2 million to 5 million linear inches of printed labels from a print head. The accumulation of dust and dirt can shorten print head life significantly. Because of lubricants applied to thermal transfer ribbon, thermal transfer print heads tend to last longer than direct thermal.

If printing the GS1 barcode symbol parallel to the direction of web travel, missing dots result in a non-conforming symbol. One simple method to visually highlight a missing dot when printing in this orientation is to print a bar - akin to the bearer bar mentioned previously - above or below the bar code perpendicular to the bars of the symbol. Missing dots will result in white spaces in the bar.

If the GS1 barcode symbol is rotated on the label, printing the bar code perpendicular to the direction of web travel, a missing dot will result in a white line through the entire bar code. Because of the vertical redundancy of bar codes, the bar code will probably conform and scanning will not be an issue.

The drawback to printing the bar code perpendicular to the direction of web travel is reduced printing speed. Most label printers can print bar codes parallel to the direction of web travel at speeds to 12 inches per second (ips). Rotating the bar code and printing perpendicular to the direction of web travel will reduce print speeds to as low as 2 ips, depending on the X dimension.

This bar code print orientation is sometimes referred to as picket fence or stepladder bar code orientation. However, the picket fence or step ladder nomenclature refers to the orientation of the bar code on the carton as it moves along the conveyor and not how the label is printed. A label printer applicator can be mounted such that the bar code is printed parallel to the direction of web travel and be applied to the carton either in a picket fence or a stepladder orientation.

The labels, ribbons, and even print heads - the most expensive components in any labeling system - can be sourced from a multitude of vendors. This does not imply that sourcing labels and ribbons doesn't have pitfalls. Using the incorrect ribbon for the printer or the label material will produce non-conforming symbols. If either ribbon or label material is changed, printer heat settings may need adjusted.

If using print and apply equipment, the labels must be converted properly. Deep die cuts, probably the most common defect, can cause the adhesive to ooze and the labels not dispense properly.

Verification vs. Scanning
No matter how the bar codes are produced, they need to be verified in order to determine if they can be scanned throughout the supply chain. Verification is the process whereby a printed bar code is compared to the bar code specification and a determination is made as to the bar code level - or grade - of compliance relative to the specification. All industry or company standards will specify the acceptable grade.

Verifying bar codes on the carton at conveyor speeds has historically been challenging and expensive. The most common solution is to mount a scanner on the line. However, mounting a commercial bar code scanner on the conveyor to check the GS1 barcode symbols will not guarantee that the bar code meets the GS1 specification. Commercial scanners have very aggressive decoding algorithms - they can read practically anything. Using a commercial scanner to check the GS1 bar code will provide two pieces of information - that a bar code is on the carton and that it can be scanned. It will not determine if the symbol passes the ISO grade and as such cannot assure that the GS1 bar code will be scanned anywhere in the supply chain. Compliance to the ISO grade can only be provided by a bar code verifier.

The ISO specification measures eight different criteria to determine the symbol grade, anywhere from a grade of 4 - very good - to 0 for a failing grade. A quality control verification policy should include a sampling plan, written documentation of the results, and a periodic calibration procedure. This policy should apply to GS1 bar codes printed on-site as well as printed off-site. Don't assume that all off-site printers produce GS1 barcode symbols that conform to GS1 specifications.

Some bar codes printed with ink jet technology can continue to change dimensionally for a period of time after printing. This can be due to additional ink wicking from the type of corrugate or - in the case of water-based inks - from changes in humidity or moisture as the carton moves through the supply chain. Ideally, samples should be collected from the manufacturer to the retailer and verified for compliance.

If you want an independent source to check your GS1 bar code symbols - GS1 will verify the bar codes. For a fee of $15 - $5 for a partner - GS1 US will verify your bar code and provide a report - see www.barcodes.gs1.org.

Operator Training
Last, but not least, a continuous operating training program needs to be established. The training agenda should include bar code basics, variables that can impact bar code print quality, issues that are indigenous to the technology used - things like ink throw distance if using ink jet and proper print head adjustment if using label printers. The training programs need to be ongoing. My experience is that on-site printing system performance tends to deteriorate six to eight months after the install.

In Conclusion
The retail industry can benefit from GS1 bar code symbols that are printed in conformance with the standards by all CPG manufacturers. The current quality of the bar codes in the supply chain is unacceptable. CPG's are spending a lot of money with little or not return. What can be expected from a supply chain that insists on conforming symbols? Woolworth's achieves a 99.3% successful scan on about 750 million cartons annually.

About the Author
Rick Fox is President and CEO of FOX IV Technologies, Inc. a manufacturer and integrator of automated labeling systems. FOX IV Technologies was listed as one of the twelve leading companies involved in RFID in the book "RFID for Dummies."

Rick has over 25 years experience in bar code printing technologies including flexography, ink jet, direct thermal and thermal transfer printing. He also has experience in bar code and RFID systems integration into complex manufacturing and warehouse/distribution environments.

He is a member of GS1's (formerly the Uniform Code Council) Global BarCodes and Identification Technical Advisory Group. Rick was also a member of the North American Healthcare Group that developed guidelines for the use of the Reduced Space Symbology (RSS) for healthcare. He has written many articles and presented papers on bar code printing and RFID implementation. He co-authored the chapter "Smart RFID Labeling Approaches" in the RFID Labeling Book.

Rick was elected to membership in the AIDC 100 - an international organization of automatic identification and data capture professionals who have significantly contributed to the growth and advancement of the AIDC industry. He serves on the Advisory Committee for the School of Engineering at Robert Morris University, Pittsburgh, PA.

Rick is currently a member of the Packaging Machinery Manufacturers Institute (PMMI) board of directors and Chairman of the Show Committee.