Over the last twenty years there has been a revolution in print technology. Bar code applications are very sensitive to the ability of printers to present their special messages in high contrast, well dimensioned bars and spaces. The continued growth of new bar code applications in retail and industrial projects has benefited greatly from the steady advances in printer capability. Today, any Mac chooseable printer will print a bar code with the proper print composition software application. Through Apple Script, this label printing process can be initiated and controlled by another application program.

If all the supermarket packages created since the grocery industry's adoption of bar code in 1973 are counted, then more bar code is printed off-site than in-house. Eliminating this retail point-of-sale application, the division of label production shifts the other way, with about 40% of labels printed by off-site vendors and 60% of labels printed by the bar code user in close coordination with scanning applications.

The oldest and most common form of printing transfers ink from a master plate, which holds a positive or negative representation of the image, to the paper or other media to be printed on. Once a master image is created, usually by photographic means, the printing of repeated copies of this image is fast and very inexpensive. Most UPC labels are created by generating a photographic image of the bar code, called a film master, usually in reverse image. This film master is used to create an etched plate or drum which physically transfers ink to paper or other compatible label media.

Newer production printing processes have come along and added flexibility to the creation of bar code labels off-site. Probably the most precise labels produced today are created by photocomposition printing. In this process images are created by CRT electron projection onto photosensitive paper. CRT typesetters are extremely fast and capable of very high image resolution. If your application requires a small "X" dimension, you might consider this label production technique. These labels can be laminated for durability and have adhesive backing added. Library systems and circuit board manufacturers have shown a preference for this print technology, among others. Label cost will be higher than for ink based printing, however.

Bar code applications have become more integrated into the real time processes and events of the industrial and commercial world. As a result the need for demand printed bar code labels to express and carry control messages has grown rapidly. As with scanning devices, there are legitimate reasons to mix printer types in a responsive bar code plan, as some bar code applications will benefit from one print technology, and other applications or locations will benefit from another print technology. What is important to retain is constant label quality and system design integrity.

There are actually two approaches to dot matrix printer design. The faster printers employ a hammer bank spanning the width of the page to be printed. This mechanism shuttles slightly to the left and right under computer control precisely releasing the pins that create the dots forming each element of a bar code and the paper passes underneath. The other approach to designing a dot matrix printer employs a moving print head riding on a track and moving back and forth across the page. The print head usually has 9 or 24 pins which are released in clusters to form the bar code elements. Apple Imagewriters are of this type. However, several cautions are worth noting when printing bar code by an Imagewriter or similar printer. Since these printers use multipass ribbons, it is possible to exhaust the ribbon and not deposit enough ink (carbon) to permit dependable scanning. Dot Matrix printers will usually offer two or three print speeds. The label area containing the bar code should be printed at the highest resolution, or multipass (graph) mode. This assures the greatest ink deposit in each bar, and the smallest voids.

Thermal printing is not a new technology, but it has been adopted as a popular method of printing bar code for ten years or so. Recent advances in print heads and thermal papers have combined to make this a practical technology for producing demand labels with inexpensive printers. The thermal printer is very simple in design, and the label paper is the only moving component in the system.

To create a thermal printed label, heat sensitive label stock passes across the face of a print head of the same width as the paper. The print head is called a linear thermal array and can momentarily heat any position along its length under digital or computer control. As the timed passage of the label progresses, tiny dark dots are created under the heated array elements and these dots combine to produce a bar code, as well as human readable text and graphic label enhancements. The label stock has to be specially treated and matched to the print head carefully to assure the proper heat level and application time.

Thermal transfer printers are closely related to direct thermal printers. They employ a thermal array print head, but instead of heating specially coated paper to change its color, they melt a wax-like ink off a transfer ribbon running between the print head and the label stock to create a dot. Some of the industrial conditions that limit the use of direct thermal printed labels are avoided with thermal transfer technology. Direct sunlight will not shorten the life of this label, and the "X" dimension is printable to about 5 mils (smaller than usually recommended.)

Desktop publishing using the Macintosh and a page based laser printer have become one of the most familiar combinations in a modern business. For an investment of several hundred dollars a Mac can produce precise and appealing text and graphics running under inexpensive word processing packages. The temptation to use laser printers to produce bar code labels seems irresistible. The resolution of the laser page printer permits minimum "X" dimension printing to 5-6 mils, and the carbon toner gives excellent contrast for reliable scanning. On the other hand, for extensive production or warehouse applications the page format is usually less adaptable to automatic label application than a continuous spool of labels. However, bar code menus and labels produced of Avery label stock provide excellent bar codes for scanned data input.

Ink jet printing results from the precise projection of drops of ink a short distance to a media surface. It is a non-contact print method based on either continuous projection of ink, or controlled pulses of ink. In continuous ink jet systems the ink is broken into tiny droplets by ultrasonic vibration. These droplets are electrostatically charged and deflected to the media under computer control. Ink can be projected by a single nozzle or a bank of nozzles. Ink jet printers are now appearing in the desktop publishing field as a less expensive alternative to the laser printer. They can produce bar code with "X" dimensions down to 10-12 mils. As with laser printers, Mac choosable ink jet printers create good bar code labels. However, some inks are water soluble, which limits the bar code from use in many commercial applications.

Label printing software is a subject that should be addressed in the early planning stages of a bar code data collection program. There are two methods of providing "canned" bar code label printing capability: it can be a barcode software application written to run on a Mac host, or bar codes can be generated from fonts. A great deal of care must be taken to insure proper bar code data composition and bar code geometry is fonts are used.

Pre-written bar code label packages should support the bar code symbologies described previously, as well as several more you may run into in certain industries. You should also be sure that Code 128 is optimized for density before you purchase any package, and that Code UCC/EAN-128 is included. All software packages do not print every symbology with equal accuracy and efficiency. You should insist on a sample label print out from the printer you intend to use as a proof of symbology exactness. The most common host for printer software is the PC, but popular packages are also available to run on Macintosh, DEC minicomputers, and IBM mainframes.

Copyright ©2001 Data Capture Institute, Inc.