Bar code symbols may be produced in a variety of ways: by direct marking,
as with laser etching or with ink jet printing; or, more commonly by imaging
or printing the bar code symbol onto a separate label. For our purposes,
the terms "print" and "printer" refer to the production
of a bar code whether the image is printed, etched, or imaged. The importance
of precise bar code printing cannot be overstated; success of the whole set
of integrated technologies that comprise an entire bar code system depends
upon bar code print quality.
Bar code printing applications fall into two categories - ON-SITE user-controlled
printing and OFF-SITE label supplier-controlled printing.
On-site Printing
On-site printing generally takes place at or near the point of use. The data encoded is usually variable, entered by an operator through a keyboard or downloaded from the host computer. The most common bar code print technologies for on-site use are:
- Direct Thermal — Heating elements in the printhead are selectively
heated to form an image made from overlapping dots on a heat-sensitive
substrate.
-
Thermal Transfer — Thermal transfer technology uses much the same type
of printhead as direct thermal, except that an intervening ribbon with resin-based
or wax-based ink is heated and transfers the image from the ribbon to the
substrate.
-
Dot Matrix Impact — A moving printhead, with one or more vertical rows
of hammers, produces images by multiple passes over a ribbon. These passes
create rows of overlapping dots on the substrate to form an image. Serial
dot matrix printers produce images character by character; high-volume dot
matrix line printers print an entire line in one pass.
-
Ink Jet — This technology uses a fixed printhead with a number of tiny
orifices that project tiny droplets of ink onto a substrate to form an image
made up of overlapping dots. Ink jet printers are used for in-line direct
marking on products or containers.
- Laser (Xerographic) — The image is formed on an electrostatically charged, photo-conductive drum using a controlled laser beam. The charged areas attract toner particles that are transferred and fused onto the substrate.
- Large copy-machine-size dot matrix line printers, in-line ink jet printers,
or in-line thermal transfer printer applicators for
high-volume applications
- Desk-top dot matrix, laser, direct thermal, and thermal transfer printers
for variable-demand print jobs
- Wireless direct thermal or thermal transfer printers for portable and field applications
Clearly, with the staggering range of choices available, users need to carefully determine their application parameters before going to purchase a bar code printer.
On-site printing most often involves purchasing label-design software as well as printer hardware. Bar code printers come with their own proprietary programming languages that support all the standard symbologies, and they are capable of printing simple data-static or serialized bar code labels on their own. However, labels that require additional formatted text, graphics, or multiple fields will require a separate label-design software package. Currently, more than 100 packages exist that are designed for a wide range of platforms and have a wider range of features. Once the purview of programmers, label design can now be accomplished by nonprogrammers via easy-to-use WYSIWYG graphical interfaces.
Off-site Printing
Generally speaking, commercial label printers may use flexographic,
letterpress, offset lithographic, rotogravure, photocomposition,
hot stamping, laser etching, or digital processes to produce
a consistently higher-grade
label than those labels produced by on-site printers. If
the content of the bar code symbol is known ahead of use, a commercial
label supplier
is generally
the best choice. However, there are tradeoffs. Commercially
supplied labels have to be ordered, stocked, and placed in
inventory.
A business with frequent
product line changes and/or label changes will have to weigh
its options carefully.