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Methods of Printing and Types of Printers
Off-site methods are generally those used by printing
companies or large manufacturers to print large volumes or
labels well in advance of use. Several types of wet-ink
printing are commonly used in this manner. The popular
in-house methods discussed below included direct thermal and
thermal transfer, charged image, ink jet, dot matrix, and
formed character and drum printing. These methods are used
to print labels in small to mediums-sized amounts close to
the time and place they are to be used.
Wet-Ink (Off-Site)
Wet-ink techniques include letterpress, offset
lithography, flexography, rotogravure, and inking wheels.
The basic wet-ink technique is to create a photographic
image or film master of the labels, make a printing plate
from the master, and apply ink to the plate to transfer the
image to label facestock.
Direct Thermal (In-House)
Direct thermal printers contain a print head that applies
heat to coated stock, which turns black to create the text
of the label. This type of printing saves money by not
requiring printer ribbons and provides good quality bar code
symbols.
However, if the print head does not supply sufficient
steady heat, symbols may vary in darkness, which prevents
quick, accurate scanning. The coated facestock is also more
expensive than other paper facestock and is sensitive to
temperature, light, water, chemicals, and hard use. The life
expectancy of these labels is usually less than a year.
Direct thermal labels serve best for short-term or indoor
uses such as products with short shelf lives, shipping, or
indoor storage with little handling involved. Thermal
transfer printing (described below) is usually more
effective for labels that must remain readable for longer
than a year or under rough conditions.
Thermal Transfer (In-House)
Thermal transfer printing is the most widely used method
for bar code printing. The print head applies heat to
printer ribbons that transfer the ink to the paper to create
the symbol. This method improves on direct thermal printing
in several ways. Thermal transfer print heads often last
longer. A wide variety of both paper and synthetic label
materials may be used with both black and colored ribbons.
Print quality is high and lasting. Symbols can be read by
both infrared and visible light scanners.
A wide variety of ribbons are available, and it is
important to match your application closely. Three basic
types of thermal transfer ribbons are available:
Wax-based ribbons are low in cost and suitable
for most applications, but labels may be scratched in
use or smear if overheated.
Resin-based ribbons produce labels that are much
more resistant to wear and extreme conditions. Some
resin inks used on certain stocks can withstand
temperatures over 1,000 degrees F.
Wax/resin ribbons produce labels with higher
durability than wax-based ribbons and lower cost than
resin-based ribbons.
Whichever ribbon you choose, be sure that it:
Conducts heat well enough to allow the ink on the
ribbon to melt, keeping the overall heat level low and
protecting the print head.
Has a combination of tensile strength and smooth
surface that will allow high-speed printing and will not
tear, stick, or slip during printing, wear down the
print head, or cause ink build-up.
Carries a type of ink that can be applied
uniformly and binds well to the facestock.
Charged Image (In-House)
This general type of printing includes xerographic
(similar to photocopying), laser, electrostatic, ion
deposition, and magnetographic printing. These printers
apply an electric charge to an image of the character to be
printed. The charged image attracts ink toner to form the
image, which is then heat- or pressure-fused to the label.
Charged image printers can rapidly produce bar code
symbols of very high quality. However, high initial and
maintenance costs, and the possibility that the labels may
fade over time, are drawbacks. In addition, improper toner
settings can blur the edges of the bars and make the spaces
too small. Be sure to adjust these printers to meet your
requirements.
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