Thermal Printer Technology:   Direct Thermal
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How they work
Direct Thermal labels are made from chemically sensitized paper or synthetics that turn black when heated.  A roller advances the labels and squeezes them against the printhead, which contains a row of miniature solid-state heating elements.  The printer's internal microprocessor turns the elements on and off to form the image.   Depending on the resolution of the printer, there can be from 150 to 600 elements per inch.

Pros & Cons
The printing process is simple so the printers can be compact, fairly low in cost, and easy to load.  A disadvantage is that direct thermal labels tend to fade over time (6 months to a year), and this process can be accelerated by  heat, humidity, and exposure to sunlight.  The surface of most direct thermal labels tend to be slightly abrasive, causing printheads to wear more rapidly than thermal transfer.

Applications
Excellent for point of sale or shipment labeling applications where labels are needed in random quantites at irregular intervals and where the labels have a limited life expectancy.