Label Implementation Guide (LIG)
Bar Code Print Quality
Overview to Printing and Applying Bar Codes
One reason that bar code
technology has grown so rapidly is that bar codes can be printed with many
different methods. Bar codes can be printed with impact printers, thermal
printers, toner-based printers (lasers), ink jet printers, and virtually any
photographic or wet ink process on almost any surface.
Deciding Which Printing Technology to Use
One of the first decisions a project team must
make is how they are going to print each different type of bar code they need to
create. For economic, logistical or technical reasons, different printing
methods might be used to print each of the three different types of labels
described in the GS1 standards:
The GTIN-12 (formerly UPC-A) item label applied to individual consumer units.
The 14 digit GTIN-14 is applied to intermediate packs and shipping containers.
The 18 digit SSCC serial number applied to cartons and shipping containers.
In general terms, each symbol / label can be:
- Printed directly (no label) on the item, package or the
- Printed on a label applied to the item or carton.
Labels can be produced using a variety of
printing techniques including:
years past, impact printers including dot matrix and industrial quality shuttle
printers (less popular; lower definition) could be found in use.
Thermal printers, both direct thermal and thermal transfer (quite popular
providing greater print definition).
Toner-based printers including laser and LED printers.
Furthermore, labels can be produced in-house
or purchased through a service bureau.
This chapter discusses each of these
techniques and the very important topic of Bar Code Print Quality.
7.3 Bar Code Quality
into the different methods of printing bar codes, it's important to discuss bar
code print quality. Just because a bar code looks good to our eye, doesn't mean
that it is actually printed properly and should be readable by various scanning
devices throughout the supply chain. This is such an important issue that some
retailers have resorted to fines or "charge backs" for out-of-specification bar
Bar code print
quality is always the responsibility of the supplier. Regardless of whether the
supplier prints bar code symbols or a service bureau provides bar codes to the
supplier. In any event, the supplier needs to be sure that the bar codes are
readable throughout all aspects of the shipping process to the final user.
The cost of creating bad bar
codes can be extremely high. Ask the candy company that printed hundreds of
thousands of red bar codes on candy wrappers for a Christmas promotion and had
to call them all back because red bars are invisible to most bar code scanners.
Or ask the company that was charged $30,000 by its customer for marking its
products with unreadable bar codes.
Bar code "quality"
involves the actual print quality and several other important issues that
combine to determine if a bar code is in or out of specification.
in the appendix, bar codes encode data in much the same way that Morse Code
works, using a series of wide and narrow bars and spaces instead of dots and
dashes to encode each character.
The widths of
the bars and spaces are critical. If the widths are wrong, the bar code could be
unreadable or, even worse, could be decoded improperly.
readers need to be able to tell the difference between a bar and a space. If the
contrast between them is not great enough, the bar code may not be readable.
Bar codes are
supposed to have "quiet zones" on either side of the symbol. Quiet
zones are blank areas, free of any printing, typically 10 times the width of the
narrowest bar or space in the bar code. Failure to allow adequate space on
either side of the symbol for quiet zones can make it impossible to read the bar
verifiers are instruments that analyze the bar code print quality to determine
if it should be readable by a bar code scanner using a specified light source
and spot size. They cost between $1,000 and $3,500. Considering the
penalties for supplying out-of-spec bar codes, this is a necessary piece of
equipment that should be used often enough to ensure that your printing
processes are working properly and that service bureaus are supplying in-spec
Some retailers have selected a
specific brand of verification equipment for their testing and don’t accept
results from any other brand of verifier. This situation is not common and is
usually a legacy from before the ANSI X3.182 Quality Standard, but it’s a good
idea to check with the customer to see if they have a preferred brand of testing
ANSI Print Quality
American National Standards Institute has published a bar code print quality
specification. Named ANSI X3.182, this specification uses 8 categories of
measurement criteria to grade bar code print quality using letter grades ranging
from A to F. Any grade other than an "F" is considered passing. As a
rule of thumb, the higher the letter score, the easier it will be to read. Some
bar code specifications reference this specification and specify that labels
must receive a specific letter grade or better, i.e. "C" or better.
Some bar code verifiers can test to the ANSI print quality test. As standards
are updated, inclusion of ANSI print
quality references will grow. Verifier manufacturers are offering more options
that incorporate the ANSI print quality measurement.
The ANSI print quality grading
method is based on the relationship between the printed symbol and the way bar
code scanners interpret the symbol. Scanning performance is key to the process.
In order to determine how well a bar code will perform in typical situations, a
number of measurements are performed by a verifier to determine the final grade
of the symbol.
Similarly, a European standard was
developed a number of years ago. Fortunately, a worldwide common specification
has evolved and accepted as the common ANSI/ISO/CEN standard.
The first key measurement is
decode. This is a test to decipher the bars and spaces into meaningful data.
Assuming that the decode test passes, the other checks are graded from A through
F. If the symbol cannot be decoded, it fails and automatically receives a grade
of F. Other measurements include:
This is a measurement that tests
the printing accuracy of the symbol. In general, the higher level of
decodability, the better a scanner can be expected to perform.
A measurement between the largest
and smallest reflectances in a scan profile. In general, the lighter the spaces
and darker the bars, the better the symbol contrast. Colored symbols are
acceptable if they provide adequate contrast.
The ratio of the minimum edge
contrast to the symbol contrast. This test looks at the edges of the bars and
compares them to the "clarity" of the spaces and also looks at the
edges to be sure that they are not wavy or fuzzy.
It also grades the extent to which narrower bars and spaces are
“visible” to the scanner and verifier.
The irregularities found within
elements and quiet zones. Most often these are spots (dark blots in the middle
of a light space) or voids (light blots in the middle of a dark bar) in the
This a measure of the amount of
light reflected from an illuminated source. Light is reflected from the spaces
and absorbed by the bars and this measurement checks the spaces and quiet zones
to be sure that ample light is being reflected so that a scanner can pick up the
bar and space elements in a bar code.
Other factors also contribute to
the determination of how a symbol is graded such as label material opacity,
surface gloss measurement, and the effect of over-laminates.
For most compliance applications,
hand held laser scanners will be used. This is an application where ANSI Grade
"C" or better is acceptable and the mandate will typically specify this
measurement. Note that ANSI grade “C” or better is specified for all UPC-A
symbol use. Interleaved 2 of 5 (ITF-14) may have a grade as low as “D” for the
Reflectance grading parameter only, and only when printed directly on corrugate
with a wet ink process in an Off-Line process or an Ink Jet technology in an
On-Line process. Ink Jet may be considered when cartons (with NO pre-printing)
Even if the bar
code is printed properly, if the human readable data below it doesn't match the
decoded bar code, the label is out of specification because the human readable
interpretation and the bar code must agree.
if the bar code and human readable match, if the symbol is affixed to the wrong
item, it’s also out of specification.
If the label
adhesive is not correct, the label can fall off during storage or shipment.
If the label
materials are too translucent, too much of a dark background can show through
the material, making the spaces difficult to identify and causing the label to
fail a print contrast test. Therefore, print quality testing should be done
after the label has been applied to the package.
are selected for their required durability and abrasion resistance, surface
smoothness to create a sharp image, the surface they will be applied to for
adhesive selection, maximum and minimum exposure temperatures and application
temperatures for substrate selection, opacity to ensure adequate print contrast
and, finally, budget.
of the Label
If the label is
placed improperly, making it unreadable, it's out of specification.
label inside a clear package containing many items to show through is also not
permitted because the wrong symbol could inadvertently be scanned.
Bar code labels
placed on the top of a shipping container that will be stacked will be
specifications define where the label / symbol should be affixed on an item or
carton. Failure to comply results in an out-of-spec label.
Verification tests the symbol for
its characteristics but to comply with the specification, quality procedures
that check for the correct human readable interpretation and label placement as
well as test for label adhesion are needed.
All quality checks need to be
documented and kept on file in case future quality questions arise.
In summary, procedures to monitor
the quality of the bar code printing and placement must be written and approved
by IT and Operations.
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