Many factors will determine the barcode printing and finishing technology to be used.
The quality and performance required, size, the end-use application, whether the barcoded information is static (all codes within the run or batch have the same value) or dynamic (the code values run consecutively), compliance requirements, the volume of labels to be produced, and whether the barcode will require protection from rubbing, scuffing, scratching, moisture, oil, grease, etc.
An example of barcode static information would be that found on EAN/UPC retail labels, while dynamic information can be found on sequential coded or numbered labels in which each label carries a different code.
If the label or product packaging carries a EAN/UPC barcoded label, then it is usually printed during the normal label or package printing run.
The label or package printer will have to obtain a barcode master from one of the specialist vendors. Some label printers using graphic arts pre-press system (e.g. Esko) to produce their press files will also be able to use the system software to produce the barcode themselves.
There are also many barcoding software packages available.
One of the major considerations when selecting the barcode printing process is the size of the barcode symbology. The minimum size (magnification) and correct Bar Width Reduction (BWR) for a symbol varies by printing process and even from press to press. Printing companies should establish a minimum symbol size (magnification) and BWR to achieve acceptable and repeatable quality results.
For the volume production of barcoded labels that carry static coded information, then web- or sheet-fed analogue printing processes that include flexography, letterpress, offset lithography and gravure are regularly used.
More recently, digital label printing using electrophotographic (wet or dry toner) and inkjet technology has gained much favor. Digital also has the benefit of being able to produce sequential, variable or random coding, rather than just fixed data.
It should perhaps be noted that many printing processes require barcodes to be printed in a specific orientation to the feed direction of the web or sheet. For example when printing by flexography it is proposed that the bars should run parallel to the press direction. If the bars are required to run perpendicular to the press direction then the barcode symbol should be checked to ensure that it is not distorted.
When using either silk screen or rotogravure printing processes, the symbol should be aligned parallel to the cell structure on the screen or gravure plate cylinder to provide the smoothest bar edge possible.
In applications where only a small volume of barcoded labels is required, or where there is a need to print barcoded labels with dynamic sequential or variable information, then these are most likely to be produced on an on-demand computer-driven thermal transfer or thermal direct printer in the label, retail, pre-packing or industrial environment.
Figure 7.1 - On-demand labels produced on a thermal transfer printer
Up until the mid 1990s, the only barcode masters available were film masters. These were the original, first-generation barcode symbols imaged with a laser or other light source directly on to film, and the only sources of barcode film masters were specialized companies that had invested in the specially programed computers and vector photo-plotters necessary to make such high-precision images.
These 'true' barcode film masters were 'plate-ready' photographic film images of a specified barcode symbology, including all the necessary numbers, letters, other characters, start and stop bars, etc. They were, and still are, used when individual barcodes are to be printed by label or package printers using offset lithography, letterpress, flexography or others printing processes.
Today, barcode masters are supplied in a variety of formats that include email and disc, rather than just in a film format. Because barcodes are nothing more than a series of varying-width bars or lines, it is critical that they are produced – whether photographically or electronically – with precise widths and spacing and that high quality barcodes are printed on to the packages or labels.
There are numerous vendors of these types of barcode masters that printers can go to, while some printers are able to generate the necessary barcodes in-house using their own graphic arts pre-press system. Vendors of barcode film master services generate the required barcode and send it to the printer in a format of choice, either by post as a negative or positive film, or electronically as a PDF or Tiff.
It is important that barcode masters, whether digital or film, are strictly controlled for dimensional accuracy, and their quality must be assessed at the earliest stage so that fundamental problems with the original image can be identified and corrected before incurring the time and expense of additional pre-press and on-press work, the quality of which would be substandard, if not unacceptable, from the start.
As mentioned earlier, the production of true barcode masters was the purview of the few specialist companies that had the knowledge, expertise, and sophisticated software and hardware necessary to produce them. That's all now changed.
Today, the fast-evolving digital-imaging revolution – with the necessary barcode software – has provided the ability for almost any label or package printer to generate barcode images to standards such as ISO/IEC 15419:2001.
This standard; for example, describes in detail the software design requirements for controlling indirect imaging devices such as image-setters, whether used to generate first-generation film, printing plates (direct-to-plate), or even final paper images.
Another barcode standard, ISO/IEC 15416 Barcode Print Quality Test Specifications for Linear Symbols describes a method for assessing the quality of barcode symbols after they are printed.
Search the internet and it is soon becomes possible to find many different vendors of barcode software, barcode solutions, barcode desktop and stand-alone barcode printers that are available to suite almost any type of barcode application, from designing and creating barcoded labels, right through to the computer-generated printing of the barcodes.
There are a number of barcode software packages that are perfect for small to medium-sized businesses. They are generally easy to use with any computer-generated label or barcode printer application and can quickly create barcode asset labels, barcode inventory labels, barcode invoices, and other documents that require printed barcodes.
Many of the software packages enable barcodes to be generated through, say, Microsoft Office applications, using a range of different barcode symbologies from linear codes (asset tracking to retail), to 2D barcodes. Vendors include software from Wasp, NiceLabel, Teklynx, BarTender, etc., while some barcode software suppliers like Barillo, offer a free barcode generation program for creating UPC-A and EAN-13 barcode graphics.
Another option, the Enfocus 'Instant Barcode' downloadable plug-in, allows creative professionals to easily create, verify, fix and read barcodes directly within Adobe Illustrator. Instant Barcode supports the most commonly used barcode systems, including EAN-8, ISSN and ISBN, making it easy to integrate into any design.
Instant Barcode automatically verifies that barcodes are accurate and provides warnings when they don't meet correct parameters. The advanced barcode preflighting capabilities enable users to check a wide range of parameters such as barcode types, height, scaling overprint setting, and color use. Instant Barcode allows users to save preflight profiles for reuse at a later stage.
There are also barcode online subscription services which enable the generation of barcode images on a smartphone, tablet or computer for the most common linear or 2D barcodes. Subscribers can create images using the online barcode generator and then have it instantly e-mailed to them in any of the following formats: BMP, GIF, JPG, PNG, or TIF bitmap formats or EPS or WMF vector formats. Images may be created for resolutions at up to 1200 dpi.
The barcode generator will also remember the barcode settings, meaning that in most cases when it is returned to, it is only necessary to change the barcode data to create subsequent barcode images.
Another common approach is to design a label file that is formatted in the programing language of the printer straight to the label printer with no label software involved. This is often used in large enterprises, where the company’s ERP or other software is set up to send a formatted file to the label printer when an event needing a particular label occurs.
Certainly, each of the different label printer manufacturers have developed their own programing language. By virtue of having the largest market share in barcode printers, Zebra’s ZPL programing language has become very much a standard for developing label files. Of course, not wanting to be left out, the other printer manufacturers have their own programing languages as well; DLP for Datamax and IPL (Fingerprint, too) for Intermec are just two examples.
For end users of the various label printers, getting locked into the language of one printer company or another, may mean it can be hard to switch the brand of printer – even though there might be a good reason to change; the aggravation of reformatting a whole lot of label files can be too much.
To try and overcome this, most label print engine companies have developed emulation firmware that can allow their product to work with label files designed for other brands of printer. This can enable a user to send, for example, a Datamax DPL file to a Zebra printer. The printer software will then convert this to compatible Zebra language and produce the correct label . a solution which seems to work most of the time.
Unless there are really compelling reason to switch, it is generally advisable to stay with the brand of printer that the original label file was designed for.
For the volume production of static barcodes (where all codes within the run or batch have the same value), such as for label or product packaging that carries a EAN/UPC barcoded label, then these are usually printed during the normal label or package printing run on flexographic, offset, letterpress or gravure presses.
However, in applications where only a small volume of barcoded labels is required, or where there is a need to print barcoded labels with dynamic sequential or variable information then these are most likely to be produced on an on-demand computer driven thermal transfer or thermal direct printer in the label plant, retail, pre-packing or industrial environment. Examples of on-demand barcode printers are shown in the illustrations in Figure 7.2.
Figure 7.2 - Some of the many on-demand thermal barcode printers available today
Today, there are barcode table, bench-top and standalone barcode printers available for creating everything from shipping barcode labels to product barcode labels, inventory labels, location labels, asset tags and a variety of compliance labeling requirements, using printers designed to meet light- to medium-duty barcode printing requirements right up to heavy duty industrial applications.
Barcode printers are also incorporated into many label applications lines, into print apply equipment, and in to weigh-price packaging and labeling lines.
Some of the most commonly used barcode label printers include those produced by:
There are also a number of manufacturers of portable barcode printers from some of the above producers, as well as from Epson and ONeil.
As mentioned earlier, on-demand computer-driven barcode label printers are most commonly printed by the thermal direct or thermal transfer process, both of which are described in more detail below.
THERMAL DIRECT PRINTING
Thermal direct printing uses a special heat-sensitive chemically coated label substrate into which the print images are ‘burned’ at standard printer temperature and pressure settings. Heating of the thermal material is with a print head consisting of very many miniature heating elements distributed along its printing width which turns the image areas dark to create the required printed label (see Figure 7.3). The elements are selectively heated by pulses of energy which create points or dots of black (other colors are possible with appropriate paper) in the thermal coating and these dots create the image required from the computer’s memory.
Figure 7.3 - Principle of direct thermal printing. The special heat-sensitive chemical coating on the label substrate darkens under the action of the heating elements
Direct thermally printed images can be variable text, barcodes, or diagrams used for frozen or fresh food labels in supermarkets, industrial barcoded labels and tags, or a range of other market sectors. May also be called chemi-thermal labels.
Thermally coated substrates are of course heat sensitive so cannot be used for applications where the label may be exposed to sun, heat, abrasion, etc. However, there are thermally coated substrates with different reaction temperatures that can be used to minimize or overcome some types of heat sensitivity issues.
THERMAL TRANSFER PRINTING
Thermal transfer printing is a very similar indirect printing process to thermal direct printing, but with a heat sensitive ribbon replacing the heat sensitive thermal paper.
Very smooth and receptive conventional paper, or a suitable film, is printed by means of an electronically-controlled printing head which transfers variable data – including barcodes – to the label, ticket or tag face material via a heat-sensitive printer ribbon placed between the printing head and the face material.
Figure 7.4 - Examples of Ricoh thermal transfer ribbons
The thermal transfer printing head (Figure 7.5) makes use of very small resistors or elements which are arranged across the printing width, which are selectively heated and cooled. The heated elements come into contact with a thin film one-pass ribbon, which carries a heat-activated ink or coating on the underside.
By rapidly heating and cooling the resistor dots on the print-head in the required formation, the required character or image is created and so transfers the selected heat-activated ink coating from the film carrier to the substrate according to the pattern or shape of the heated elements.
Figure 7.5 - The thermal transfer printing head enables the black heat-activated coating on the ribbon to transfer to the substrate
Apart from the printing of barcodes, thermal transfer printing is used for the variable information printing of batch codes, date codes, sequential numbers, variable text and graphics, etc, onto pallet, carton or box end labels, for warehousing and distribution requirements, for bakery labels, for DIY and industrial labeling, and for a variety of tickets and tags. It has applications in a range of markets from food to industrial and pallet labeling.
Thermal transfer desktop barcode label printers today are becoming ever more sophisticated to meet the growing use of smart devices. An example is the Bixolon SLP-TX420, which is compatible with Mac-based PCs, Android-based tablet PCs, Windows and Linux, as well as supporting USB dongle-type WLAN wireless communication and basic wired communication.
Figure 7.6 - The Bixolon SLP-TX420 thermal transfer printer
BARCODE PRINTING SUBSTRATES
While static barcodes printed in volume on paper or film for retail applications will normally be sheet- or reel-fed printed on labelstocks suitable for application and performance on bottles, jars, cans, etc., thermal transfer barcoded labels for use in a wide variety of industrial applications are likely to require more careful selection of facestock and adhesive to match performance requirements.
Paper labels will normally perform best in controlled environments and in applications such as product and price labeling. Where labels will be exposed to harsh environments or subject to long life and hard conditions, then paper labels may no longer be the most suitable. Synthetic labelstocks that include polyester, polypropylene, vinyl and synthetic papers are then more likely to give a better performance than paper.
Adhesives too, may need to be carefully selected to give the best performance in industrial and harsh environments or performance conditions.
Barcoded labels that require resistance to temperature extremes, high humidity, chemicals or outdoor use, are most likely to require a permanent adhesive.
Some surfaces to which barcoded labels may need to be applied can be difficult to label and will then require specific adhesive formulations; others may need to be removed, re-applied, or require to have tamper-resistant or tamper-evident capabilities.
Labels substrates and adhesive will therefore need to be carefully matched to meet each label performance and application requirement.
PRINTED BARCODE PROTECTION
With many types of industrial barcoded labels it may be necessary to provide protection over the label surface and barcode to protect against moisture, water, oil, grease, chemicals, weathering, abrasion and scuffing, or harsh work or handling environments.
There are a variety of possible protection solutions available to the label converter for improving label performance including varnishes, laminates, coatings and sprays. Special top coatings are available that will enhance image performance and label/code durability.
When choosing a suitable protection method, care needs to be taken that labels still meet reflectivity and contrast requirements and can be scanned with both contact and non-contact scanners.