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Direct Thermal Printer Labels – How do they work?


direct thermal printer labels and direct thermal labelsDirect Thermal Printer Labels use a well-established technology common in till receipt printers, older fax machines and point of sale terminals. The printing system works by activating a pigment present in the paper rolls used in the printer. Direct Thermal printer labels work by having the pigment ‘cure’ and change colour when heat is applied. Direct thermal printer labels have the advantage of requiring no inks, toners or ribbons. The printers themselves can be compact and lightweight too so many practical applications exist. They can also be built for industrial use due to their reliability and capacity to do long print runs.

Direct Thermal Printer Labels Usage

This print technology is ideal for situations where labels will not be exposed to harsh environmental conditions and where the label lifespan is a matter of months. Of course, the harsher the environment, the shorter the durability in any case.

The technology is not suitable for wet or high humidity environments, hot environments or high UV environments (i.e. exposure to direct sunlight for prolonged periods). A similar system using so-called thermal transfer is a parallel technology for such circumstances and idea for chemical labelling.

Direct Thermal Label Printers

The direct thermal printer print head has a series of tiny ceramic print heads. These can be heated and cooled very quickly which in turn heats the paper passing under the print head. The thermal paper is passed under the print head at a constant and known speed, perpendicular to the print head. In turn, each ceramic head can be switched on and off (i.e. pulsed) to heat and cool for different lengths of time. The result is individual dark lines recorded in the material to create an image or text. Therefore, if all the ceramic discs are heated simultaneously, the paper can be turned from white to black.

Resolution

A direct thermal printer will commonly come with 200 ceramic discs per inch of print head – this is referred to as dots per inch or dpi – in other words, the resolution. 200dpi resolution is perfectly suitable for receipts, courier labels or sandwich labels.

Printers are also available in 300 and 600 dpi versions should a higher resolution be needed. 300 dpi versions are about twice the price of 200 dpi versions. 600dpi versions are twice as expensive again.

Print Speed

As well as expense, generally speaking, the more dpi a printer has, the slower it will work. 200dpi printers can run at up to 14 inches per second (350mm/sec). 600dpi printers will struggle to muster themselves past 3 inches per second. As with most technologies, compromises are part of the solution.

Print Width

Printers come in a range of print widths. Commonly 2,4,6 and 8-inch print heads are used with 8 inch being capable of printing A4 in portrait mode and useful for odette labelling or A4 parcel labels.

In terms of cost, prices kind of double with every factor that is increased. The wider the head, the more the cost, the faster the head the more the cost, the higher the resolution, the more the cost. You can’t have high speed and high resolution so generally, A4 laser printers are often a better technology to turn to for high-speed high resolution, low cost.

Direct Thermal Paper

Direct Thermal Printer Labels use paper prepared by having a colourless pigment applied to it which solidifies as a crystallised matrix with an organic acid. This pigment and acid is stored in a solid form but has a relatively low melting point. When the pigment crystals melt from the heat of the print head, they react with the acid which changes the pigment’s molecular structure, changing its colour. The pigment then re-solidifies in that form. This process is known as tautomerization.
Direct Thermal Printing Paper Diagram

Pigments have now been developed in a range of colours but the tautomerization process is the same irrespective of colour. As a result, labels can be manufactured to have certain areas change to specific colours. These cannot be combined to create full-colour images in this specific industrial printing process. Using single colour direct thermal printer labels, it is not possible to print a photograph in full colour but a black and white rendition can be quite satisfactory.

On a side note, Kodak developed a full colour system in the late 1990’s caling “Zero Ink” or Zink for trademark purposes. This is used specifically in instant cameras and not suited to industrial printing.

Eco v Semi-Top Coat
Whilst ‘eco’ direct thermal printer label paper will not have a specialised coating applied to the top of the material, premium grade material will. This has a number of benefits.

  • Reduced fading of material after printing
  • Acts as a lubricant for the print head giving smoother performance, reduced wear and longer print head lifespan
  • Reduced transfer of coatings from paper to print head giving better output and less need for cleaning
  • Targets the heat to the pigment layer for darker, crisper print
  • Provide a key for overprinting plain labels with ink i.e. pre-printing

In some cases, the surface coating can provide better water and oil resistance for the labels although this is marginal.

You can buy any sort of direct thermal printer label from Positive ID Labelling and we produce a wide range of labels for specific uses in the food and chemicals industries. For more information on buying direct thermal printer labels, call us on 01332 864895 or fill in the enquiry form below:







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