Labelling on blister packs

Unlike many other pharmaceutical packaging, blister packaging places special demands on the labelling process. The limited labelling area, high production rates, and the packaging design mean that both labelling technology and machine solutions must be adapted to the production line.

At Logimark, we have worked with industrial labelling solutions in many different types of pharmaceutical production. A recurring experience is that the choice of labelling technology is rarely about which printer is best – but about how the blister pack is manufactured, transported and handled throughout the entire production process.

The function of blister packaging

A blister pack normally consists of two materials:

• a shaped plastic film where the tablets or capsules are placed
• a pre-printed aluminum foil that is heat-sealed to the plastic

The aluminium foil acts as both a barrier against oxygen and moisture and as an information carrier. The product name, strength, manufacturer and other static information are usually already printed on the foil before the blister pack is manufactured. Once the blister pack is complete, it is normally transferred to a cardboard box together with a package insert, where the secondary labelling and serialisation takes place.

Since the aluminum foil also acts as the surface the patient presses through when taking out the medication, it is not possible to apply a label on top of the blister pack. A label would make it difficult to take out the tablets and would come into direct contact with the medication when the aluminum foil is broken.

For this reason, direct labelling is used almost exclusively on the blister pack itself.

The real challenge is not speed – but breadth

Many people imagine that blister packs are transported one by one through the production line. In practice, the process is often completely different. In most blister machines, blister packs are first produced in large continuous sheets. A wide plastic material is formed with several rows of blister pockets at the same time, filled with tablets and then sealed with aluminum foil.

Only later in the process is the sheet punched or cut into individual blister packs. This means that the labelling system often does not work against a single blister pack, but against a significantly wider sheet where several blisters are produced in parallel.

When discussing pharmaceutical production, the focus often falls on line speed. For blister production, it is just as important to understand how many products are being produced at once. For example, a blister machine can feed a sheet of ten blister packs side by side.

The marking must then be applied to all blisters before the next production cycle begins. This means that the challenge is not always how fast the printer can print. Instead, it is about how the marking system reaches all positions across the wide product path.

There are several ways to solve this. The most cost-effective is often to use a movable print head mounted on a linear axis. When the blister sheet stops for the next process step – such as welding or punching – the print head moves horizontally across the sheet and applies the marking to the respective blister position.

The production line then continues to the next cycle. Since the blister machine still has a natural stop between each feed, there is usually enough time for labelling without affecting the production rate.

When are multiple printheads required?

Not all blister lines operate with intermittent feeding. On some high-speed lines, production is continuous. If the blister sheets never stop, there is no longer time to move a print head between different positions. In these cases, each blister row needs to have its own print head instead.

This means that a line with ten blister rows may require ten separate printheads working simultaneously. Technically this is entirely possible, but it means a significantly higher investment cost, more consumables and more advanced service.

Therefore, when the production process allows, the primary goal is to achieve a solution where one or a few print heads can service the entire product width.