How Do You Want to Print Bar Codes?
As discussed previously, there are a variety of scanning techniques that should be investigated as well as a number of printing techniques for bar code labeling. This section focuses specifically on
in-house printing techniques and considerations for reproducing labels on-site. While there are several printers that support bar coding on-site, only four printers stand-out as the most
wide spread in this industry: dot matrix, laser, thermal transfer, and direct thermal. The table below compares the common features among the different printers.
Printing bar code labels in advance is often inconvenient and sometimes impossible to plan. Inconvenience and minimum orders are generally the driving forces for printing labels on-site. When considering on-site printing, startup and operating costs must be taken into account. This includes the printing equipment, consumables (labels and ribbons), personnel, and computers to support such a task.
Dot Matrix printers are currently the most common printers among all businesses. Dot Matrix printers are inexpensive, impact printers that can provide draft, near letter quality, and letter quality printing. The image is formed by a head striking a carbon ribbon onto a single or multipart form. Typically, the print head has 9 or 24 pins which create the image. When generating bar codes with a dot matrix printer, a low resolution or density provides the best scanning results. Some 24 pin dot matrix printers can generate acceptable medium density bar codes.
Laser printing is becoming the most familiar technology in the modern business setting. The most common laser printers support 600 dpi. Other laser printers can support 1200 dpi with special toner cartridges. Laser printers work very well with most off-the-shelf labeling packages and are the best choices for office environment that need to share a common printer. For applications requiring high density bar codes, a 600 dpi or 1200 dpi laser printer is sufficient.
Thermal transfer printing uses a high carbon, thermal transfer ribbon (see the Ribbons and Labels section for additional information) which passes between a printhead and facestock. The heat from the printhead causes the ribbon's ink to be released and bind to the stock or label. Thermal transfer is the most effective way of producing rugged labels.
Direct Thermal Printers
Direct thermal printing uses no ribbon. A heat sensitive paper comes into contact with a printhead and causes the paper to turn black similar to a fax machine. Direct thermal paper is sensitive to heat and sunlight and therefore is recommended for indoor, general purpose labeling. The life expectancy of the label is approximately 12 months.
Thermal Printer Options
There are many Printer Options that are available to meet your application needs (for example, if your labels will be printed in one location and then distributed to different locations to be applied, consider purchasing a printer that offers a rewind option). Here is a list of some of the most common options that are available.
- Label Peel: For demand label applications, each label is printed, peeled and ready to apply. Some
models will take up the excess backing and rewind to a spindle.
- Cutter: For applications requiring cut labels either sets of preformed labels/tags or variable length
labels from continuous media.
- Media Rewind: Internal or external option to rewind the full label roll while media is printing. Ideal for
applications where labels are printed in advance and stored for multicolor passes. Some internal
rewinders double as a line/backing rewinder in applications using the peeling option.
- Memory: Store longer label formats, multiple label jobs or detailed graphics with memory expansions.
- Unwinder: Used with larger rolls of stock. Normally, mounted behind the printer, labels are fed through a rear opening in the printer.
Labeling software for the most part is separated into two distinct categories: off-the-shelf and custom. Off-the-shelf programs are generic applications that produce labels on demand. There are many DOS and Windows applications that allow custom labels to be generated on demand using WYSIWYG (What You See Is What You Get) interfaces. These labels are generally produced off-line and do not need to be created from the host program. This software is available for dot matrix, laser, and thermal printers. If it is necessary to integrate bar code printing with your current applications, consider custom or "on-line" program callable printing.
Program callable printing generates labels through custom programming usually requiring simple modifications to your existing software. Printing directly to either a thermal transfer or direct thermal printers requires a basic knowledge of the syntax of the printer commands used to format the label. Usually, each manufacturer has a different command set and among them some instruction sets are much easier to use and are more robust.
Windows Printer Drivers
Historically, nearly all thermal transfer and direct thermal printers have utilized proprietary, programming languages to “drive” the label printer. This responsibility typically required a programmer to either modify or generate host code. In comparison to the tools that are available today, changes were relatively difficult to make since every change to the label required a programming change. In addition, the label program was specific for the printer since each manufacturer had a different programming language. Most label manufacturers today support Windows print drivers which are similar to the Windows print drivers for a dot matrix printers. There are many advantages of using a Windows print driver for a label printer. (1) any Windows application can print to the printer, (2) any user can make changes to the label, and (3) the application is not tied to a specific printer.
Unfortunately, some manufacturers do not provide Windows print drivers at this time, but most will have them available in the near future. Certainly, there are benefits with the traditional approach. Printing speed is the primary advantage. If a label printer was purchased to print only one or two labels at a time, then programming the print language direct would increase performance substantially because only a stream of printer commands (or codes) are passed through the parallel or serial line as opposed to an entire image of label. An image file can easily be over one megabyte in size and thus take longer to transfer than a stream of several hundred characters. Most label print drivers, however, support an option to generate copies of a label so that the label image is initially transferred only one time, loaded into the printer memory, and extracted from memory to generate the specified number of copies. Obviously, this is much more efficient and the way most label printers are currently designed today.
In summary, if the label printer must create distinct labels on every label run (e.g. one-up-number to serialize a product), make sure that your application directly utilizes the programming print language. There are some software applications that do this very thing, however, they are generally very expensive. Eventually, these programming languages will no longer be supported as new printers are introduced into the market. There are even some label printers today that only support Windows print drivers.
External Bar Code Printer Interfaces
Bar code printer interfaces attach to the serial or parallel port of a PC and connect directly to a dot matrix or laser printer. These printer interfaces require simple command strings to be embedded within the application software similar to control character strings. Bar code controllers virtually transform an ordinary printer into a bar code and labeling printer.
Bar code verifiers make sure that the bar codes that are printed are readable, have good contrast, and comply fully with the parameters of the bar code symbology. Bar codes are typically verified using an “A” to “F” or PASS/FAIL grading system.
Verifying the quality of readability of your bar code is essential when you are printing new packaging or labels for a product you are shipping to some retail outlets or distributors. A non-readable bar code could mean fines or return of the entire product lot.