MULTILAYER LABELS – A CLOSER LOOK

Multi-layer labels, also known as peel-off labels, offer comprehensive information, without overloading the design. In multi-web label production, the Gallus Labelmaster demonstrates an impressive interplay of efficiency, precision and flexibility. Multi-layer labels are characterised by a large amount of space in a very small area. These labels enable highly efficient communication for retailers with constantly growing information requirements. 

Multi-layer labels are firmly established in all market segments. In the pharmaceutical sector, they can be found on folding cartons, vials, cans and blister wallets. Their purpose is to clearly communicate dosage instructions, warnings and ingredients information. In the food sector, multi-layer labels enable precise labelling of ingredients, additives, origin information and allergens. For multi-lingual versions, in particular, multi-layer labels provide the necessary space to concisely convey information in all language variants. On household product packaging, multi-layer labels convey important warning and handling instructions. 

In the security sector, multi-layer labels are used as void labels. Any attempt to remove the label irreversibly separates the film and adhesive. This reveals a void message or pattern as clear evidence of tampering. In logistics and e-commerce, they facilitate product tracking and returns management. New multi-layer label applications are continuing to grow.

“New multi-layer label applications are continuing to grow”

The simplest way to explain the differences in the production process of multi-layer labels is to look at the substrates. A common production method is based on a single-substrate web. Firstly, the reverse side of the substrate is printed, followed by the front. Secondly, the web is slit into narrower webs. These are then configured on top of each other to create a multi-layer label. The maximum label width is limited to approximately one-third of the original web width.

The manufacturing process differs when using a machine with multiple unwinders. In this case, production is carried out with several substrate webs. This method allows for the use of different printing materials and enables high-volume production.

Modular printing presses can be equipped with up to three unwinders and often feature 12 or more inline printing units. Additionally, a rail system above the printing units can accommodate applications, such as cold- or hot-foil stamping. These provide further options for unwinding and rewinding.

In multi-web applications, precise web transport is crucial. Only with utmost precision can different substrates such as polypropylene, polyethylene and paper webs be accurately combined to form a single label. This is achieved through a highly precise machine-control system. The system adjusts the unwinding and web tension of the materials according to their respective E-modulus. This is a crucial factor, as the stretch properties of these materials vary greatly.

With register control in the longitudinal and traverse alignment, one web is defined as the master and the other webs are synchronised to it. This ensures that all webs are perfectly aligned, enabling precise and stable further processing.

To expand Gallus Labelmaster press systems for multi-web label production, the ‘System to Compose’ – a modular design – offers the necessary options. Each machine system can be upgraded with flexographic and screen-printing units. For example, to enable reverse printing as the first production step, as well as for haptic effects or the application of braille lettering.

Adding a digital-printing unit allows for variable-data printing in one to four colours, with an optional colour gamut expansion, including orange and violet. Additionally, die-cutting units can be retrofitted – often a requirement between printing units in multi-web applications.

The production of multi-layer labels differs from that of traditional pressure-sensitive labels (PSL). The printing sequence often begins with reverse printing. For this, the web is unwound with the liner facing up. The substrate and liner are separated and the open adhesive back is printed in the first flexographic printing unit, as shown in the sample label ‘Body Sport’. Subsequently, both layers are recombined, pressed together and the web is turned over for front printing. The four-colour design is then printed in four flexographic printing units (CMYK).

The next step is a cold-foil transfer and, most importantly, the neutralisation of the adhesive on the back. Various processes are available for this, such as release varnish or glue killer. In this case, a release varnish is applied to the front so that the individual sides of the multi-layer label can be opened easily. 

Following this, haptic effects are applied in a screen-printing unit before the webs are cut and precisely superimposed to form the multi-layer label. 

The production of multi-layer labels places high demands on the machine configuration. Fast and flexible changeover of the machine system is an essential factor for efficient production. Multi-layer label designs require very different processing sequences. Flexo- and screen-printing units – as well as die-cutting units – must be able to be placed at different positions in the machine. Where one job might require a screen-printing unit in the machine sequence, the next might require a die-cutting unit in that position. Efficiency in production is therefore achieved by ensuring that modules can be exchanged with ease, speed and flexibility.

Other features, crucial for efficient multi-layer label production, include easy operation and control of the machine via the human machine interface (HMI). Especially with longer machines, the system supports the operator by providing real-time information at all times. The status of the printing units, register accuracy and the processes on the rail above the printing units are all available. This includes parameters such as tension or the status of web-tension units and web-edge guides – regardless of the operator’s location at the machine.

Particularly in the production of multi-layer labels with long web paths, waste plays a key role in effective and sustainable production. With the Gallus Labelmaster, this aspect is optimised with a short web path of just 1.4m between the printing units. In addition, a compact arrangement of all key processes on the primary level. This eliminates additional web paths of 4–6m that would arise when changing to other machine levels. This results in reduced waste, time and costs, especially with frequent job changes. 

At the same time, short web paths lead to a high level of stability in the production process. Short web paths optimise the use of materials in multi-layer labelling, as well as ensuring simple operation and high efficiency.