With thermal labels there are two very different processes (direct thermal and thermal transfer) and it is very important to understand what sort of printer the labels are to be used in. In the most basic format the difference between direct thermal and the thermal transfer process is that thermal transfer printers require a ribbon, direct thermal printers do not. Sharp Labels Ltd produce labels to be used with both processes.
Direct thermal labels
The direct thermal process uses a substrate which has a heat reactive coating containing a dye and developer to create the image. Formally known as Chemi-Thermal, the substrate coating is exposed to the heat from an electronically controlled print head that cause the dye and developer to come into contact forming the thermal images – text/barcode etc. No heat is applied to non-image areas so the dye and developer remain apart leaving that area blank.
As the chemical bond between the dye and developer is quite fragile, exposure to water, oil etc can have a detrimental effect to the image. Depending on what level of resistance you require there are three types of material available:
Eco – Recommended for a short label life in a non-hostile environment e.g. office.
Semi – Good resistance, recommended for logistic label type applications.
Top – Excellent resistance against chemical, mechanical stress and high humidity.
Thermal transfer labels
Thermal transfer also uses heat to print the image areas just as direct thermal does. The difference however is the label stock does not have a thermo sensitive coating to create an image so a filmic ribbon is used instead. The ribbon is run between the print head and the label stock, and as with direct thermal print heads, the image areas are heated. The heat passes through the solid ink on the ribbon transferring the image onto the receptive substrate.
Although most pressure sensitive materials can be used for this the best results are achieved by carefully selecting the type of stock and ribbon required for the end application.
As with direct thermal there are different levels of resistance, these can be achieved through a careful combination of substrate and ribbon. There are three main types of ribbon which are generally used as follows:
Wax Ribbons – Commonly used ribbon for use with uncoated face papers.
Wax/Resin Ribbons – Good resistance level. Usually used with non-absorbent materials like films, but can also be used with absorbent papers where high resistance is required.
Resin Ribbons – Used for very demanding applications in conjunction with filmic materials.
When deciding which type of direct material or label stock and ribbon to use, be sure to decide what is acceptable for the end label requirement, but also what type of printer is being used. There are many different printers combining different speeds and print resolutions depending on what is required.
Sharp Labels would always recommend completing successful trials before full production on thermal labels.