Direct thermal printing uses label material with a heat sensitive coating. When heated by the print head of your printer, the thermal coating turns black to create the image/text required.
Thermal transfer printing uses a thermal transfer ribbon (i.e. an ink ribbon also known as a carbon ribbon). The print head heats the ribbon and ink is deposited onto the label material to create the image/text required.
Some small desktop printers such as the Zebra GC420d are direct thermal only, but most thermal printers will operate in thermal transfer or direct thermal mode. The cost of consumables is similar for the two methods of printing. Direct thermal labels are generally a little more expensive, but when you add the cost of thermal transfer labels and ribbons together, the costs are similar.
The advantages and disadvantages of the two methods of printing are as follows:
Direct Thermal Printing
Advantages of Direct Thermal Printing:
• Simpler for the operator to load the media (you only have to load the roll of labels).
• It can be easier to obtain a good print quality during the initial setup (you do not need to match the ribbon type to the label material).
• Environmentally better as you do not have to dispose of used ink ribbons (generally you can only use thermal ribbons once).
Disadvantages of Direct Thermal Printing:
• The print will fade in time, especially if exposed to direct sunlight.
• The label material will discolour in time, especially if exposed to direct sunlight.
• The label material is prone to marking if rubbed or scuffed.
• Cannot be used in high temperature applications (generally specified to 50°C), as the labels will quickly turn black.
• There is a limited range of direct thermal label materials, compared to thermal transfer (although it is possible to obtain direct thermal card tag material and some synthetic materials such as polypropylene).
• Direct thermal labels will cause greater wear to the print head compared to thermal transfer printing. You can therefore expect the replace the print head more often with direct thermal printing if you are printing high volumes of labels.
The problem of print fading and the label material marking when scuffed are reduced when using top coated direct thermal labels. Top coated direct thermal labels are more expensive, but also provide limited resistance to moisture and water damage. If direct thermal labels are to be used in a freezer (with a freezer adhesive), it is advisable to use top coated label material.
Thermal Transfer Printing
Advantages of Thermal Transfer Printing:
• Thermal transfer printing produces a permanent print, which has excellent resistance to fading, even when subjected to direct sunlight.
• The durability of thermal transfer print can be determined by the choice of ribbon type. The most popular (and lowest cost) grade is wax, which has limited smudge resistance. The next grade up is wax/resin, which has good smudge resistance, but limited scratch resistance. The top grade is resin, which is scratch and water resistant and resistant to many chemicals (see the ribbon specification for information on which chemicals a particular ribbon is resistant to).
• There are a much wider choice of label materials available for thermal transfer printing compared to direct thermal. The choice of label materials varies from uncoated and coated papers and card through to cloth and a wide range of synthetic materials, including polyethylene, polypropylene, polyester and polyimide. The choice of adhesives is also greater with thermal transfer labels, in particular for very low temperature applications (-196°C) and very high temperatures (+ 575°C).
• There are a good range of coloured ribbons available for thermal transfer printing.
• Thermal ribbons have a silicon coating on the print head side to protect the print head against excessive wear.
Disadvantages of Thermal Transfer Printing:
• Thermal transfer printing takes a little more time to load the media compared to direct thermal printing.
• You need to take care that the grade of ribbon matches the label material you are using. If you are using relatively coarse, uncoated paper labels, a wax ribbon will give a better print quality (the soft wax will flow into the rough material). However if you use a wax ribbon on a coated synthetic material, it will rub off very easily. Here a resin ribbon would be the preferred choice.
• On some lower grade ribbons, the print head will need cleaning more often as there can be build up of ink.
• You need to dispose of the used ribbons, which is less environmentally friendly compared to direct thermal printing.
When starting a new project with thermal transfer printing, it is always advisable to ask your supplier for a sample ribbon to ensure you have a good match between the ribbon and label material.
To enquire about direct thermal or thermal transfer printing, call our sales office on 01482 485001 or visit our website www.labelsexpress.co.uk