For around half a century, barcodes have been a ubiquitous part of international commerce. Although they were first developed in the 1940s, it took until the 1970s for barcodes to assume the form and function that we use today. Since then, retailers and trade networks around the world have integrated barcodes into their daily business practices to increase traceability and streamline various processes. 

Today, barcodes are everywhere, including on food packaging, drink labels, pharmaceutical products, cleaning supplies, and more. To regulate the use of barcodes in all of these different fields, government bodies and international organizations maintain strict guidelines regarding label placement and appearance. Written to address the needs of specific industries and products, these rules and regulations are stringent and are enforced under the threat of fines, recalls, and other costly penalties.

Consequently, companies must take code compliance seriously and ensure that all of their products are labeled with high-quality, machine-scannable barcodes. One of the best ways to accomplish this task is to use thermal transfer printing, which has been used by many industries for high-quality barcode creation since the 1980s. The primary benefit of barcodes is the "precise identification" of an item. The use of barcodes eliminates the possibility of an operator (for example, a cashier at a grocery store) keying in the wrong item number, as they can simply scan the barcode.

Here, we take a look at how thermal transfer printers work and examine how their operating principles contribute to barcoding success.

Thermal Transfer Operating Principles

Before delving into the ins and outs of thermal transfer printing barcodes, let’s review some important operational information. Thermal transfer printing is performed with a thermal transfer overprinter, or TTO for short. Thermal transfer overprinters were first introduced to the market in the early 1980s as an improvement on direct thermal printing. 

It’s important to distinguish between TTO and TT (thermal transfer) printers. Thermal transfer overprinters became relevant in the early 1990s when Compular produced the first commercially successful TTO machine called Jaguar, which was capable of marking barcodes using thermal transfer technology on flexible packaging film. 

On the other hand, TT printers replaced dot-matrix (impact printers), and some of the earliest fax machines used thermal transfer technology with either transfer ribbon or direct thermal on reactive thermal paper. Thermal transfer printers were developed before thermal transfer overprinters because TT printers control both the choice of substrate and the speed of substrate, making it an easier product to develop. In a desktop TT printer, a ribbon was matched to a paper label stock in a device with a four- to six-inch-per-second controlled image transfer speed.

TT printers use "contact printing" in which the ribbon (the ink carrier) is sandwiched between the thermal printhead and the label stock. Sometimes, the ribbon was removed, and a thermal label stock replaced paper labels, changing color under the thermal printhead. In TTO machines, neither the speed of the substrate nor the choice of substrate is controlled by the printer; slow 4-6 ips transfer speeds can now be up to 28 ips depending on the labeler or packaging machine. The substrate is developed for marketing appeal, product protection, and sealability (not for ease of overprinting).

Both thermal transfer printing and direct thermal printing are forms of thermal printing. As such, they do share a few similarities related to operation and application possibilities, including:

1. Utilizing heating element-equipped printheads to mark materials.
2. Specializing in creating high-contrast markings and images.

However, beyond these shared traits, they differ in some major ways.

Direct thermal printers are designed to apply heat directly onto heat-sensitive pieces of paper to create images and designs. One of the most visible examples of a modern direct thermal printer is the point-of-sale receipt printer. 

On the other hand, thermal transfer overprinters don’t apply heat directly onto the substrate, nor do they utilize heat-sensitive paper. Instead, TTO printheads apply heat to an ink-covered ribbon that separates the heating elements from the substrate. As the heating elements cause the ink on the ribbon to melt, the printer uses the melted ink to create the desired image/code on the substrate. 

In our next section, we will see how this operating principle benefits the barcode printing process. 

Reasons to Choose Thermal Transfer Printing for Barcode Applications

Compared to other printing methods, thermal transfer overprinters offer several benefits that make them particularly well-suited for barcode applications. For one, the thick, durable ink used to make thermal ribbons is ideal for barcoding. Although liquid ink sources can also be used to make barcodes, the barcodes made by TTO models are on average:

• Longer-lasting.
• Higher resolution.
• Better capable of withstanding high temperatures, chemical presence, and sun exposure.

In addition to excellent code quality, other thermal transfer overprinter benefits include:

• Industrial speed capabilities: Although TTO models don’t offer the high speeds of a continuous inkjet printer or laser marking system, that doesn’t mean they’re slow. For example, Videojet’s DataFlex 6530 can transfer images on continuous motion substrates moving up to 39 inches per second. With these speed capabilities, line operators can maximize code quality while still maintaining high levels of efficiency.
• Substrate variety: Thermal transfer overprinters are compatible with many of today’s most popular packaging materials, including flexible film, paper, and textiles. Comparatively, direct thermal printers are only able to mark specially-coated pieces of paper, preventing them from being able to mark any product packaging.
• Environmental resistance: Both TTO machinery and their created barcodes are made to last. Many of today’s top thermal transfer models are built with the same levels of ingress protection offered by leading inkjet and laser printers, promising long periods of uninterrupted uptime. 
• Diverse ink options: Thermal transfer ink ribbons are available in a variety of forms, including many specialty options. Unique ink properties can include heat, light, moisture, and solvent resistance. Further, ink selections come in a variety of colors (although black is best for barcode applications).

Intuitive usage: TTO printers are intuitive and make updating code information fast and easy. As a form of digital printing, many advanced TTO models even offer auto-updating tools that make appropriate variable data changes in real-time.

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