Some of the most popular choices for bar code printing are dot matrix, ink jet, laser and thermal printing. These print technologies each relate to Component 1 of the barcoding requirements mentioned earlier in section 2. To understand how each technology varies in execution and strength, let us take a moment to review each print method in detail assessing their respective strengths and weaknesses.

Dot Matrix Printing
Dot matrix print technology is one of the oldest techniques used for on-site label printing. The typical dot matrix bar code printer is a modified line printer requiring pin feed paper stock. Solenoid driven needles impact an ink coated nylon ribbon, transferring ink onto the paper or label. The image is built up dot-by-dot in a matrix as the needle and paper are moved relative to one another.

Advantages
Dot matrix printers are readily accessible and inexpensive to purchase.

They can print on virtually any type of form, check or document and can print on wide-web, multi-part (carbon) forms.

Dot matrix printers use multi-pass ribbons which can result in reduced overall cost for ribbons and the label material.

Limitations
Dot matrix printers print low to medium density bar codes that may not meet certain end-user guidelines. The dot size on the matrix printer limits the narrow element size and density of the barcode. The following example, compares sufficient dot overlap versus unacceptable dot overlap on a dot matrix printer used to print bar codes.

Continuous ribbon re-use on dot matrix printers requires continuous monitoring of ribbon condition to ensure adequate bar code contrast. Ribbon ink that has become exhausted can also produce an image that is inadequate for scanning, resulting in a low read rate and high error rate.

Ink saturation can result in paper "bleed" which can cause image distortion.

A dot matrix printed label is only as durable as a photocopy of paper. They commonly cannot produce chemical or water-resistant labels.

Printing of single, individualized labels results in significant waste. The design of the matrix printer’s print carriage, sitting far below the media, also does not enable one to adequately maximize one’s label space.

Dot matrix printing offers NO graphic print capability.

Print speed is greatly reduced when printing bar codes if greatest ink deposit and best print quality is desirable.

Ink Jet Printing
Ink jet printing is a common direct marking process and a favorite on high speed production lines. Ink droplets are selectively deflected between a moving product and an ink return channel. Ink jet printing is frequently used for coding products and cartons with human readable data and lot codes at very high speed and for case coding of cartons with bar codes.

Advantages

Common direct marking process on a product or carton that involves only one step compared to label printing which requires two steps: printing a bar code label and adhering it to the product.

A favorite on high speed production lines due to its "mark-on-the-fly" capability. "Mark-on-the-fly" being an affectionate term to describe this print process within the industry.

Used primarily for industrial use amongst large conglomerate organizations due to the affordability issue and high product volumes.

Limitations
Costly system installation designed for high volume of product labeling – not for individual or small batch label bar code printing.

Routine maintenance and supervision required to ensure consistent print quality and to prevent ink jet "clogging".

Limited dot placement accuracy and bar code density due to ink splatters and product being in continual motion.

Material to print on is restricted due to the advent of ink bleed on some materials.

Poor contrast of bar codes on corrugated box materials due to their dark backgrounds.

Properly matched scanning devices must be chosen to ensure bar code reliability.

Laser Printing
The laser printer works much like a photocopier projecting controlled streams of ions onto the surface of a print drum resulting in a charged image. The charged image then selectively attracts toner particles, transferring the image onto the paper substrate by means of pressure. The pressure from the print-head and drum then fuse the image to the paper, creating the image.

Advantages
Laser printers are good at producing bar code labeled documents on plain paper.

They can print high quality text and graphics on paper documents and can double as a document printer when not being used to print bar codes.

Bar code density is also quite high on laser printers resulting in a scannable code at virtually any wavelength using an infrared scanner.

Limitations
Laser printers are not well suited for industrial labeling applications or individual product labeling applications. Here, they prove inadequate and wasteful as it is impossible to produce single or small labels. (A minimum of a ½ a page of media is typically required for the printer to maintain control of the sheet. Unless the label is at least that size or multiple labels are needed at once, the remainder is wasted).

Laser printer labeling adhesives must be carefully selected to ensure stability under the heat and pressure of the fuser. Otherwise, it may extrude onto the printer mechanism, where it will capture stray toner or "curl" at the edges. Because of the pressures used in the laser printer image transfer process, many laminated label materials are not compatible with this technique. Those materials that are compatible may not always be available in sheet form for the laser printer to be able to print on.

A laser printed label is only as durable as a photocopy of paper. They commonly cannot produce chemical or water-resistant labels with the image longevity of a thermal printer.

Cost of laser toner cartridges for bar code printing is significant and can be costly. A 5% black density, for example, is commonly required for standard word processing versus a 15-30% black density for bar code printing. Bar code printing on a laser, therefore, is 6 x’s more expensive than standard word processing printing!

Direct Thermal Printing
Direct thermal printing is an old technology originally designed for low cost copiers and fax machines that utilizes chemically coated paper. It has since been transformed into a highly successful technology for bar coding. The thermal print-head is typically a long linear array of tiny resistive heating elements (about 100 to 300 per inch) that are arranged perpendicular to the paper flow. Each thermal print-head element locally heats an area on the chemically coated paper directly under the print element. This induces a chemical reaction which causes a black dot to form in that area. The image, itself, is formed by building it from dot rows as the media passes underneath the active edge of the print-head.

Advantages
Direct thermal printing is an excellent choice for many bar code applications because of the consistent, sharp edge image print quality that they can generate.

Direct thermal is ideal for applications with a short shelf life requirement – meaning the label is not required to last very long. Many packaging companies utilize direct thermal technology since the address and package tracking labels only need to last long enough to reach their destination which is typically accomplished in a few days.

Direct thermal printers provide simplicity and environmental economy with re-cycle-able materials available.

Direct thermal printers are simple to operate compared to most other print technologies – no ribbon or toners to replenish or monitor.

Low, long-term maintenance cost compared to comparable technologies.

Enables batch or single label print capability with virtually no waste.

Direct thermal is durable compared to other comparable print technologies.

Office and/or limited industrial application usage, though more limited in application than thermal transfer due to its shorter image longevity.

Limitations
Direct thermal printing is extremely sensitive to environmental conditions – e.g. heat and light (fluorescent and/or direct sunlight).

Direct thermal paper remains chemically active after printing. Because of this, all thermal paper materials used – labels, tags or ticket stock – are top coated to resist UV light exposure, chemicals and minimal abrasion.

Thermal Transfer Printing
Thermal transfer printers use the same basic technology as direct thermal printers, but with the elimination of chemically-coated media material in favor of a non-sensitized face stock and a special inked ribbon. A durable, polyester ribbon film coated with a dry thermal transfer ink is placed between the thermal print-head and label. The thermal print-head is used to transcribe the ink onto the label surface, where it cools and anchors to the media surface. The polyester ribbon is then peeled away, leaving behind a stable, passive image

Advantages
High contrast, crisp image bar code print quality with a durable, long-life and archival image stability.

Ideal for batch or individual label print capability – with virtually no waste.

Low, long-term maintenance cost compared to comparable technologies.

Maximum readability and IR scannability.

High contrast text, graphic and bar code print capability.

Durable for operation in office or industrial applications.

Capable of printing on an unlimited variety of media stock – except multi-form.

Limitations
Cannot print on media without use of ribbon – resulting in higher supply costs over direct thermal which, by comparison, only requires media to operate and no ribbon.

Single pass thermal transfer ribbon can be wasteful if little is printed on it.

Ink transfer ribbon is a poor candidate for re-cycling

To obtain optimum print quality in thermal transfer, the ribbon and media substrate MUST be compatible. Otherwise, the heat from the print-head could melt the ribbon onto the label causing internal printer problems.

BAR CODE PRINT TECHNOLOGY MATRIX