Tips for better flexible film coding: optimizing results from TTO printers

Flexible film is the fastest growing packaging category today and is used for a wide range of products. Thermal Transfer Overprinting, or TTO, is a digital technology designed specifically for flexible film that offers many advantages over alternatives. However, to avoid unnecessary maintenance costs, undersized production speeds and poor printing, manufacturers must choose the right combination of printhead and ribbon.

Why TTO?

Our first tip is to use TTO. Compared to mechanical approaches, such as hot stamping and rotary coders, TTO offers more uptime and less waste, while meeting the market demand for better traceability by recording real-time data.

TTO not only prints data better and more easily, but it also makes interim changes faster.

Compared to other digital technologies, such as continuous and thermal inkjet printers, TTO is typically easier to integrate into the packaging machine and delivers better print quality. It also offers a more flexible, and larger, printing surface. In addition, TTO is extremely reliable, with a relatively low initial investment, and low maintenance and operating costs. There is virtually no warm-up time for the equipment, which is usually ready for use within 60 seconds of turning on. The method produces no odor or dirt and requires no drying time. There is also no danger of perforation of the film, unlike mechanical methods where broken stamps can puncture the package. The limitations of TTO technology are the need to print on unfilled packages and slower maximum speeds.

For more information on the "pros" and "cons" of different methods, read our white paper:
“Choosing the right coding technology for flexible film“.

How TTO works

Before discussing how TTO printing can be optimized, it is important to first understand the technology.

TTO is best suited for marking on flexible films that are flat, before the packages or pouches are filled, where the printer is mounted close to the packaging station of it.

The main elements of a TTO printer are the print head, ink ribbon and roll, or flat plate for intermittent applications. The print head consists of small heating elements within a ceramic unit. Each heating element can be heated separately to form characters, such as letters and numbers.

When the print head receives a signal to print a predetermined code, it lowers, pressing the ribbon and packaging film against the roll, which moves in the same direction as the packaging.

Understanding Thermal Transfer Overprinting (TTO).

The heating elements related to that coding warm up on the print head, melt the ink on the ribbon, and the melted ink is then transferred from the ribbon to the packaging film. When the message is printed, the print head returns to its starting position within the TTO coder. The printer is then ready to repeat the process with the same or a different code, depending on the need. Heating and cooling of the printhead's heating elements occurs quickly and frequently.

With a high resolution of approximately 300 dpi and a quality that approximates pre-printed packaging, TTO offers design versatility, allowing for barcodes, logos and 2D codes. Depending on the situation, average packaging speeds of up to 120-160 packs per minute (ppm) or 1,200 millimeters/second (mm/s) are obtained, although more advanced devices can achieve up to 455 ppm, or 1,800 mm/s.

The wide selection of available ribbons allows all applications to be met in terms of mechanical resistance, light resistance, water resistance, heat resistance and solvent resistance. Most thermal transfer ribbons (TTRs) are some form of mixed wax/resin formula. In some situations, however, these ribbons are unsuitable.

The heating elements related to that coding warm up on the print head, melt the ink on the ribbon, and the melted ink is then transferred from the ribbon to the packaging film. When the message is printed, the print head returns to its starting position within the TTO coder. The printer is then ready to repeat the process with the same or a different code, depending on the need. Heating and cooling of the printhead's heating elements occurs quickly and frequently.

With a high resolution of approximately 300 dpi and a quality that approximates pre-printed packaging, TTO offers design versatility, allowing for barcodes, logos and 2D codes. Depending on the situation, average packaging speeds of up to 120-160 packs per minute (ppm) or 1,200 millimeters/second (mm/s) are obtained, although more advanced devices can achieve up to 455 ppm, or 1,800 mm/s.

The wide selection of available ribbons allows all applications to be met in terms of mechanical resistance, light resistance, water resistance, heat resistance and solvent resistance. Most thermal transfer ribbons (TTRs) are some form of mixed wax/resin formula. In some situations, however, these ribbons are unsuitable.

Oils inherent in the production of nuts, chips and popcorn, for example, can form a barrier between the packaging material and the applied code, causing poor adhesion. Chemical solvents, such as those used in the manufacture of antibacterial wipes, are equally problematic because they can dissolve the code.

Choosing the right printhead for your application needs

Freezing temperatures also hinder adhesion, while extreme heat can cause code smearing. In such situations, a ribbon with a high resin content is recommended because it provides the resistance needed to overcome these factors.

Tips for optimal printhead and ribbon selection

TTO printheads can generally be divided into standard, robust and premium, reflecting their suitability for different applications. These categories are based on the robustness of the coding equipment and the required durability of the code, given the expected production and market conditions.

As mentioned earlier, the heating elements crucial to character creation are encased in a ceramic coating. This protects the heating elements as they transfer heat to the inked ribbon and print the message. These ceramic coatings differ in their ability to resist repeated heating and cooling cycles, as well as wear and tear. Both factors affect print head life and coding speed.

Standard printheads are robust enough for clean film applications in normal factory environments, such as when printing many food and beverage products.

Robust printheads, with stronger ceramic coatings, support printing in more challenging environments, such as coding potato bags on a farm, where dirt and rocks pose a high risk of scratching the ceramic surface. Using a standard print head here would result in a greater number of problematic prints, not to mention having to replace the print head more often.

In normal situations, the print speed of these two print heads is comparable to 1,200 mm/s. In the more difficult applications mentioned earlier - oily products, extreme temperatures, use of solvents - which require resin-rich TTRs to ensure crisp durable codes, the speed is usually reduced to about 300 mm/s. This is because more energy and heat must be applied to resin-rich TTRs to successfully print codes. As a result, the heating and cooling process between prints takes longer, limiting throughput. Equipment wear is also greater, so printheads wear out sooner.

A new option, the premium printhead, has been launched to increase coding speed for resin-rich ribbons without compromising quality. Such technology is currently only available in Markem-Imaje's SmartDate® Xtreme Plus printhead. This innovative printhead technology, which handles heat fluctuations better, enables coding speeds of 600 mm/s. That is twice as fast as what is achievable with most other printheads when using high resin content resins, at a comparable level of quality.

Further tips for better TTO coding

Using the print heads properly will give you better quality prints for longer and extend the life of the print head, reducing costs and downtime.

You can also improve uptime and durability by using long TTR rolls. For example, our ribbons are 50 to 83% longer than industry average. With 80% more prints per roll, they require less frequent replacement, less roll waste and lower energy consumption.

Avoid ribbons from outside parties. While they may seem cheaper than the coding vendor's offerings, they may void the warranty and are more likely to wear out the printheads prematurely, leading to additional equipment expenses that outweigh the benefit of consumable costs. For example, our ribbons have a proven back coating that can double the life of the printhead compared to ribbons without that coating.

Regular cleaning of printheads is also essential. It may sound obvious, but in our experience, line operators don't do this often enough. Inadequate cleaning leads to a buildup of dust, dirt and grit on the printhead, which in turn leads to bad and possibly unreadable codes.
Because the heat from the print head has to break through the layer of dirt, the heat is less likely to reach the ink, thus reducing print quality.

Cleaning the printhead at every ribbon change prevents such problems. Operators can easily remember to do it while minimizing downtime consequences.

Printhead life can also be affected by print mode, printhead pressure, intensity setting and print volume. Operator training can save companies money by minimizing printhead replacement through better use of the equipment.

For example, if the ribbon has been used for some time, the printed characters may show streaks, gaps or fading. Some customers try to remedy this by increasing the intensity (darker). This is normally set from 80 to 100%, but users have been known to set it to 140%, the maximum setting. While this will improve the print, the extra heat involved will shorten the life of the print head. A better solution is usually to move the print head slightly so that the heating elements are in better contact with the film. This produces the improved print without additional stress on the components. Finally, choose a supplier that offers a standard print head warranty to further minimize your maintenance costs.

For more information - contact Kees Bink - T. +31 651 528 973