Thermal Printing, commonly known as TT Printing or DT Printing, has been around since the 1940s and still has widespread use in label packaging today. Thermal Transfer printing or TT printing employs the use of a heat transferrable thermal ribbon, whereas direct thermal printing is a process where a heated print head activates a heat sensitive direct thermal material to acheive the desired image in black.
Thermal printers operate in conjunction with a PC or laptop computer that has any number of label design software applications installed on it and communicate with the printer as one would with a common desktop printer. The difference being, the label design software allows the user to typeset copy, revise fonts, add black and white images, sequential numbers and barcodes in a variable or sequential fashion as needed.
Thermal Transfer Label Printing in the Digital Age
With the widespread adoption of digital label printing, the need for on demand thermal printing has been reduced to some degree but continues to have a strong presence in the marketplace for specific uses.
Digital printing can replace many of the capabilities thermal printing has to offer specific to custom label packaging, such as adding sequential barcodes, serial numbers, or expiration dates. Now, with digital printing's ability to incorporate variable data and imaging, this type of information can be added directly on the press during the initial label run. While Digital Printing may not address the on demand needs of a grocery store chain's deli department, that was never its intended use.
With conventional TT Printing a company might order a moderate quantity of a single label design and size, produced on a flexographic press. This label would likely have a specific defined area or window used to add a barcode (static or sequential), consecutive numbers, or a unique product name. The printed labels could then be processed through a Thermal Transfer printer in smaller quantities to meet the client's specific requirements. The purpose for doing so, beyond the need to revise any one of these additions on the fly and provide "just in time" label inventory within the client's operation, is commonly to reduce the inherent plate charges associated with multiple items.
How It's Made
The illustration above is an example of the thermal printing process transferring an image to pre-printed and diecut series of labels through the use of a heated print head. This process is similar to transferring an image with a typewriter ribbon. In the case of the direct thermal printing process (not pictured) the ribbon is replaced by a heat activated label material that when activated by an electronic print head produces the desired image in black. Thermal printers (one example shown in the image below) can utilize both a wax or wax/resin ribbon or non-ribbon direct thermal type of printer to produce average quality labels. The choice of ribbon and material type is dependent upon the expected use of the labels and the application.
Advantages of TT Printing Labels
The primary advantage of Thermal Transfer printing is on-demand print capabilities, an easy and affordable way to serve customers at a place of business. It's also a more cost effective method for short-run labels than digital label printing.
Disadvantages of TT Printing Labels
The greatest disadvantage to thermal transfer and direct thermal printing relate directly to the image quality produced. The lower print head dpi or "dots per inch" is the limiting factor to producing high end type print images on a thermal printer. For this reason most thermal printer users utilize TT printing for simple black text, numbering, or barcodes. In the case of direct thermal printing on a heat activated material, exposure to heat or prolonged sunlight will eventually turn the entire label black and render it useless.
Printing speed can also be limited for thermal printing making it less than ideal for medium to large production of on-demand labels. For these higher quantity orders we recommend digitally printed labels in smaller quantities as required. Needless to say, there are limits and specific uses for thermal printing that should not be ignored.
If you plan to purchase your own thermal printer, you will need to order labels that are engineered to be compatible with your specific printer model and brand. Information such as your intended label use, the correct ribbon type for such use, the maximum roll diameter for your printer and the minimum required gap spaces between your labels is required. These are just a few very important things to be aware of. Because thermal printing takes place after a blank or printed label has been produced by your label supplier (with or without a varnish or lamination), the labels must first be engineered and produced in a way that will allow for a clean, legible thermal print transfer that will adhere strongly to the label surface.
Special finishes or laminations are commonly used to both protect your pre-printed labels and to ensure thermal printing compatibility. Specifications vary between thermal printers brands, so if you are using your own thermal printer always notify your label provider of the type and brand so they can engineer a label that's right for your equipment and the ribbon you plan to use.