TT in detail

TT IN DETAILS

Printing by Thermal Transfer consists of applying thermofusible ink onto a receptor using a heat source emitted by the printer.

The flexibility of TT is its capacity to meet very high demands of print quality and to provide a technical solution in keeping with user expectations. There are many variables whether from the point of view of the type of ink chosen, the nature of the printing media and finally the choice of printer technology. Each of these elements will have a big influence on the print result.

This is why to properly understand how printing by Thermal Transfer works, it is important to separate each of the elements involved in the process.

A Thermal Transfer ribbon is the consumable which contains the ink required for printing. Of virtually identical exterior appearance, TT ribbons differ through the properties of the inked ribbon (backcoating, polyester film, ink layer(s)) but also through all the components which make up the roll (core, trailer of ribbon end and leader of ribbon start).

INKED RIBBON :

ROLL COMPONENTS :

During the manufacturing process, a transparent polyester film is unwound, with on one side a single or several layers of ink applied, and on the other a protective layer called the backcoating.

Backcoating

The backcoating is the part of the ribbon which is in direct contact with the printer’s printhead. Made from silicon, the role of the backcoating is to :

protect the printhead as the ribbon unwinds,
provide excellent heat conductivity to enable the ink to transfer to the print medium,
reduce the formation of static electricity, which is harmful to the printer and its operator.

Polyester film

PET film is the basic medium for TT ribbon and is the thickest part (4.5 microns). Its principal properties are to offer excellent tear resistance which is required during the manufacturing process and subsequently during printing, and to ensure perfect heat conductivity.

Ink

Ink is made up of wax, resin or a mixture of the two, and also certain additives and colour pigments. The composition of the ink gives it very different print characteristics, making Thermal Transfer so versatile in its various fields of application.

Leader

A PET film which protects the inked part of the ribbon during transport and makes insertion into the printer easier. It may bear the customers brand name.

Trailer

Situated at the end of the ribbon, it plays an important role, namely to indicate the end of the ribbon which stops the film being unwound, thereby protecting the printhead (depending on type of printer).

Core

Normally made out of cardboard, the core is the spool on which the film is wound during manufacture and then unwound during the printing phase. Depending on the model of printer for which it is designed, the mandrel will have different properties (interior and exterior diameter, width, notches, etc.).

Drive shafts
The thermal transfer ribbon is fitted onto a rotating shaft from which it gradually unwinds. Once the inked ribbon passes under the printhead, the used TT film is automatically rewound onto a motor-driven shaft. This makes it easier to handle and to remove the TT ribbon.

Platen roller
This rotating shaft is positioned at the place where inked film and the label meet under the printhead. Its role is to exert sufficient pressure for the TT film, which is in contact with the label and the thermal head, to receive the heat needed to transfer its ink.

Ribbon detector
This system indicates the presence of the TT ribbon in the printer when it is inserted. The detector also warns the printer of the ribbon end, and stops unwinding to protect the printhead.

Printhead
The printhead is a key part of thermal transfer printers: it ensures the transfer of the ink. The part in contact with the TT ribbon is made up of a line of electrically resistant micro-heating elements, the quantity of which (between 8 and 24 points per mm) determines the resolution of the printer (between 200 and 600 dpi).

The individually-activated heating elements generate a source of heat which melts the ink onto the TT ribbon, transferring it to the receiving material with which it is in contact.

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There are several different printhead technologies: the most widespread being flathead or corner-edge/near-edge heads.
Flathead printers are mainly used for printing labels. Corner-edge technology is particularly well-suited for printing on packaging with speeds of up to 1,000mm per second.
Each type of TT ribbon is suitable for one or the other of these technologies.

One of the strengths of Thermal Transfer technology compared to other printing techniques is its capacity to print on a very wide range of media made out of different materials. The choice is made according to the requirements of the end application. Here is an overview of the main types of media.

VELLUM A standard matt medium. It’s one of the print media most commonly used in classic label applications.
COATED PAPER This material is not as rough as vellum. To mask its original unevenness, it is coated with a smooth layer based on mineral compounds. The medium appears whiter and is available in a matt or gloss finish. Coated paper is used in applications which require superior writing quality and higher resistance against certain environmental factors.
SYNTHETICS Synthetic media (polyester, polypropylene etc.) provide high quality properties for printing used in demanding environments. Synthetics offer excellent levels of resistance against the following: tear, humidity, solvents, temperature, tension, rubbing, and are long-wearing.
TEXTILES Textile media are mainly used for labelling in clothing to provide brand information, composition details or care information for a product. In view of the number of stresses to which they are exposed on a daily basis (movement, perspiration, washing, drying, ironing, detergents etc.), these materials must be particularly resistant.