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Thermal transfer printing
Thermal transfer printing is a unique process unmatched among other variable imaging technologies for barcode label solutions. Unlike anything in its class, thermal transfer printing offers fail-safe durability, versatility, and high-quality image output. This is why label printers usually use thermal technology.
In thermal transfer printers, the process does not take place on the substrate, but on the ribbon. When the ribbon and substrate come into contact with the printhead, the heat from the printhead melts the ink in the ribbon and releases (transfers) the ink directly onto the substrate. The inks used in this process are generally composed of waxes, resins or wax/resin composites, depending on the needs of the project. Wax ribbon is a less expensive and less durable label material and is better suited for short-term projects; resin ribbon is a premium transfer and the best choice for long-term, high-durability needs.
Thermal transfer printing produces dense, high-resolution images (color or black and white) that can be used on a variety of media. Since the ribbon is used as a transfer agent, the images produced by this process are highly chemical resistant and very durable. This helps improve the overall readability of printed labels, making them ideal for a variety of use cases, including product identification. Thermal transfer printers work at high speeds and require little maintenance.
The main disadvantage of this technique is that each ribbon can only be used once. However, thermal transfer ribbons can be easily disposed of and are relatively more environmentally friendly to dispose of than the other printing technologies discussed below.
It is the most suitable solution for barcode label printing in the industry. Extremely versatile thermal transfer technology produces sharp, resilient images on virtually unlimited substrates—a primary requirement for most barcode projects, such as shipping labels. For an absolute guarantee of quality and reliability, there is no alternative.
Direct Thermal Printing VS Thermal Transfer Printing
While thermal printing and thermal transfer printing use nearly the same process, there is one key difference: Thermal printers don’t use ribbon. In this case, the thermal process takes place in the paper substrate itself – a specially coated thermal paper is required for optimum performance. The heat generated by the direct thermal printhead chemically reacts with the top layer of the coated paper, burning the transferred image onto the paper.
Direct thermal label printing produces crisp, clear images in a machine that is inexpensive, simple to operate, and easy to maintain. Thermal printing for barcode labels is certainly an improvement over inkjet and laser technologies, especially in terms of speed and resolution.
Thermal images are far less durable than thermal transfer printed images, and the technology is limited by substrate limitations. The coated paper required is very sensitive to environmental conditions such as direct sunlight, extreme temperatures and abrasion – limiting the range of applications for short-term projects. The resulting image is not chemically resistant and has a short lifespan. The main usage is “Point-A-to-Point-B” applications such as airport bag drop or package delivery. This technology is not well suited for barcode projects that require durable images and substrate flexibility.
Much like photocopying, laser printing uses a light source to produce an exact copy of the image it receives. A light source (laser beam) creates an electrostatic image, which is then charged onto a photoreceptor; the electrostatic charge from the photoreceptor attracts toner to produce the printed image.
The laser process produces beautiful, dense, high-resolution images for text and graphics.
When comparing heat vs. laser for barcoding purposes, the technology’s most severe limitation is its substrate limitation. Laser printers are only good for certain types and sizes of labels – certainly not working directly on any non-paper surface such as plastic or metal. It’s also not the fastest option, and laser images are nowhere near as durable as thermal print images. The toner cartridges and drum kits used in this process are very expensive and can be dangerous if mishandled. While laser printers produce much cleaner images than inkjet printers, their lack of versatility, durability, and environmental safety—combined with high unit and maintenance costs—typical of laser printers undoubtedly make them less efficient barcodes replacement of.
Dot matrix printing
One of the first printing technologies developed, dot matrix uses tiny circular hammers to tap ink from a coated fabric ribbon onto a substrate—usually paper—that must be needle-fed into the printer. Typically dot matrix printers use one or two columns of dot hammers – the more dot hammers on the print head, the higher the resolution.
Dot-matrix printers are easy to use and very inexpensive—most commonly used to print forms, checks, and other documents that need to be copied. This process is useful for record keeping as the pressure exerted by the printhead transfers the ribbon to the paper to help create a carbon copy. The ribbons used for these are relatively inexpensive due to the multiple channels.
Major drawbacks include low print quality, limited graphics capabilities, very slow print speeds, noisy operation, and lack of chemical resistance. Especially for barcode labels, a defined image is crucial. The edge definition of bitmap images is rarely clean or linear – greatly compromising the integrity of the barcode. This poor image quality, combined with low speed and inability to resist chemical solvents, can severely impact performance—a serious problem that can add significant costs to manufacturers.
There are basically two types of inkjet applications for barcode printing – direct printing applications and labeling applications. Direct inkjet printing is very effective for printing barcodes and expiration dates directly on canned foods, liquid bottles, etc. For these purposes, special direct inkjet printers are required – these machines are very expensive and are usually integrated directly into the assembly line. Inkjet technology can also generate barcodes on labels using standard office printers.
This printing technique is conceptually very similar to a dot matrix—ink is applied to a substrate by pressure in the form of droplets above and below or side by side—however, the actual delivery method is quite different. When comparing thermal and inkjet printers, inkjet devices do not use direct pressure during the transfer process, nor do they rely on ribbons – instead, they use a combination of liquid ink, ultrasonic pressure, and an electrostatic field. They create images by propelling ink into highly controllable tiny jets and onto a substrate. The quality of the image depends on the size of the ink droplets – small ink droplets produce sharper lines, larger ink droplets tend to blur.
Inkjet printing is almost the only solution for direct printing on a wide variety of substrates – from cartons and cans to plastic, glass and paper. Assembly line setups can be printed at high speeds and coded in high volumes in seconds. It is the most efficient method for alphanumeric encoding of consumer goods.
While these printers do offer users greater flexibility, their low image resolution, limited durability, and high unit price make them a less attractive option for barcoding purposes. Although in-line inkjet printing serves a large audience, it is a very niche application, and printers tend to be very expensive. The process is also less resistant to solvents, and high-speed assembly-line printing requires specialty inks—a factor that requires costly maintenance and frequent routine maintenance. The ability to print directly on many substrates makes inkjet a very useful technology; however, for barcode projects that require high quality, high resolution and good durability, thermal transfer is by far the better choice.