Thermal Transfer Printing, How it Works?

Thermal transfer printing involves the transfer of ink from a ribbon substrate onto a paper or film/polyester label stock through a combination of heat & pressure process. The ink is transferred to the paper or film/polyester as it passes between the printhead and pressure roller in a thermal transfer printer. (Avery, Datamax, Citizen, TEC etc.) See the illustration giveN below.

Thermal Transfer Printer Mechanism

Thermal transfer ribbon is constructed of a high-density tissue coated on one side with either a wax base ink, wax-resin base ink or a resin based ink. The non-ink side of the ribbon is coated with a lubricating agent that helps prevent wear or damage to the printer's printhead. A release tab and leader tape precede these imaging components, while a trailer tape may or may not be at the end of the

ribbon roll.

 

The basic mechanics are the same between both printers, i.e. there is a printhead, ribbon, and substrate. The main differences are the ink transfer process and the printhead design. Performance and price are also issues to consider when choosing between a near edge and flat head printer

In flat head printing, the printhead is horizontal, and the heating element is in the center of the printhead. The ribbon passes over the heating element and the ink is transferred. The ribbon continues to travel in the horizontal plane for about a centimeter before emerging from the front of the printer, where it is directed up to the printer’s take-up spindle. This centimeter of travel is very important, as it allows the ink to fully adhere to the printed surface and then release from the ribbon.

In near edge printing, the printhead is angled approximately 45º and the heating elements are located near the edge of the printhead. The ribbon has limited contact with the substrate. It only touches the substrate when it passes under the printhead’s heating elements. The transfer process must both adhere and release at the same time. This requires a change in the ribbon’s formulation, particularly the release layer, explaining the need for additional ribbon

formulations specifically for near edge printers.

A flat head printer usually produces labels at speeds up to 12 IPS. Near edge printers double that print speed and can be used with a broader range of media, such as tags and other card-based stocks. Near edge printers also perform better on smooth print surfaces such as polypropylene,

polyester and polyethylene films.

Basically there are only three types of ribbons and the selection of the most appropriate ribbon ink type depends on the requirements of the end-user application.

• Wax-based ribbons - economical choice typically used for general purpose applications where long range durability is not an issue.
• Wax/Resin-based ribbons - an appropriate selection where both durability and economy are important.
• Resin-based ribbons - the ideal selection where extra smudge/scratch or chemical/environmental resistance is important.

Thermal Transfer Ribbon Construction

Leader Tape
The leader tape may be blue, silver, gold, clear or custom. There are several functions of the leader tape. They include:

• Ease of use - leader tape aides in the loading of the ribbon into the printer.
• Customization - allows for the application of a customer name or logo. Helps with identification, marketing and promotion.
• Protection - guards against damage to the ribbon.

Substrate
Imaging components of the ribbon include the ink, a primer, the base film and a backcoating.

• Topcoat - a top coating can also be applied to improve the adhesion of the ink to the application surface or to increase chemical/environmental resistance.
• Ink Layer - the ink layer gives us the printed image and can be manipulated to match the application requirements (chemical resistance, environmental resistance and smudge/scratch resistance).
• Primer - helps ensure consistent release of the ink from the film.
• Base Film - the base film carries the ink and primer through the coating/printing process and helps promote heat transfer.
• Backcoat - the back coating is applied to reduce static and protect the printhead while providing consistent heat transfer. 

 Trailer Tape
The trailer tape is essentially a ribbon sensing mechanism. It allows the printer to sense the end of the ribbon. The printer type determines the type of trailer tape to be used. There are three different types of trailer tapes:

• Aluminum (Silver) - designed for reflective type sensor that reflects light indicating that the ribbon is at its end.
• Transparent (Clear) - designed for transmissive type sensor that allows light to shine through to indicate to the printer that the ribbon is at its end.
• None - this is for a mechanical type sensor where the printer's response to tension tells that the ribbon is at its end.

Ribbon Cores
Cores are either fiber or plastic, depending on OEM specifications and customer needs.

Advantages & Disadvantages of Various Printing Methods

Ink Jet Printing

Advantages

Mechanically simple

Large gamut of specialty colors

Ink and substrate flexibility

Very good initial print quality

Non-contact printing for special applications

Disadvantages

Cost of consumables

Limited print speeds

Average reliability

Poor image stability

Lamination needed for durability

Quality decreases over long runs

Laser Printing

Advantages

Good print quality

Good print durability

Excellent graphics

Best for “Batch Oriented” applications

Prints full pages

Continuing hardware cost decline will spur growth

Disadvantages

High machine entry costs

Mechanically complex

High transaction costs

Limited selection of substrates

Slow speeds

Low reliability

Machine size is often not suitable for applications

High price consumables

Impact Printing

Advantages

Oldest Technology

User friendly

Reliability

Inexpensive

Minimal software requirements

Disadvantages

Maximum resolution 240 dpi

Monochrome only

Not “variable friendly” batch oriented

Limited resolution

Declining number of installations

Direct Thermal
Advantages

Single consumable

High-speed capability

Extremely portable

Technology is improving

Durability improving

Low cost of entry

Disadvantages

Media tends to discolor

Poor durability

Poor UV stability

High energy required

Printhead cost high with excessive wear

Label stock high cost

Lower image density

Limited selection of substrate

Thermal Transfer Printing
Advantages

Excellent durability

High bar code integrity

Wide font range, size and style

High resolution

Portable

Low cost of entry

Disadvantages

Cost of consumables

Initial setup can be time consuming

Print Head Cleaning

Maintaining a barcode printer, cleaning it regularly and replacing parts as when required is necessary to ensure high print quality and consistent print performance. The print head is the most critical component of a barcode printer and without proper cleaning and maintenance, it will produce less than desirable print quality that can cause operational down time and wastages as well. 90% of print quality problems result directly from improper use or care of the print head.

Clean your print heads

Cleaning print heads at regular intervals can extend their life considerably. As a general rule, print heads should be cleaned every time the ribbon is replaced. Cleaning is fairly quick and easy with cleaning pens, swabs or cards and is very inexpensive compared to constantly replacing print heads.