Multi-layer or leaflet labels are increasingly used in situations where standard labels are inadequate, but as Chris Lindley-Smith of Newman Labelling Systems reveals, they can lead to application issues.
Dual or multi-layer labels are commonly known as leaflet labels, booklet labels or fix-a-form labels and are constituted from a single- or multi-page leaflet (sometimes up to 40 pages) incorporated on top of a self-adhesive label with another self-adhesive cover. They are increasingly being used for applications where the product space available is inadequate for presenting the required information on a standard label format.
From a pharmaceutical industry perspective, multi-page labels have been especially noticeable, as strict regulatory control has increased the need for more product information, often in multiple languages.
Leaflet labels are commonly found on a variety of pharmaceutical products including over-the-counter (OTC) medicines, prescription-based solid dose products, clinical trial products and unit dose injectables. The production of these products requires the application of such leaflet labels onto glass and plastic bottles, square pots, vials and even ampoules.
In practice, these labels can cause production problems for many automatic application systems, as their initial design did not consider the use of anything other than a single-ply label.
With a ‘standard’ reel of paper labels, the reel might be 300–400mm in diameter and contain several thousand labels die cut with radiused corners. They are lightweight, flexible and only a few microns in thickness. Compare this with a similar-sized reel of leaflet or multi-layer labels. The same diameter reel will contain only a few hundred labels; the labels are relatively heavy, inflexible and can be several millimetres thick. In addition, leaflet labels have been designed to allow the user to open them and this requires that the label cover layer adhesive is non-permanent and forms a relatively weak bond.
complex rollers
Taking each feature in turn we must first consider the quantity issue. For example, a labelling machine operating in a production line at 100 bottles per minute will continue for 50 min with 5,000 labels. If the production is changed to leaflet labels at the same speed, it is quite possible that the label reel will only hold 1,000 labels, giving the operator just 10 min of production between label reel changes. This smaller reel capacity causes significantly lower line efficiencies, especially if buffer feeding systems are not used on either side of the labelling system.
The next potential issue is the label thickness. A typical labeller will rely on the use of a fork-style sensor or even a microswitch system to measure the distances between the labels on the carrier paper and hence allow accurate control of the label steps as they are dispensed onto the product. Such sensors are also used to recognise and signal when the label reel has run out. Fork sensors by their very nature have a limited gap size, which is often smaller than the label thickness so alternatives must be found.
Label thickness may also affect the way the labeller is able to drive the labels towards the product. Many label-dispensing systems use a nip roller system to push and pull the labels but this struggles with the big steps between the label and backing paper of leaflet labels as the labels pass through. This causes unreliable feeding, especially at elevated speeds and in the long term adds extra loading and premature wear to the drive system. This type of positive drive is also quite likely to force the leaflet labels to open up within the dispenser – the cover layer of the label is designed to be peelable by the end user and hence uses a low tack adhesive; but this is also peelable by the applicator.
Along with the additional label thickness come significant rigidity and material memory. Many label applicators feature a relatively complex series of rollers to control the movement of the labels through the dispensing phase. The labels may effectively be required to move though a series of tight turns as they negotiate these rollers. Unfortunately, leaflet labels have a tendency to delaminate from the carrier web. This basically means that the web material is flexible and may form a curve around each roller easily, whereas the label does not follow and peels away from its carrier within the labelling system. Once again this causes mechanical jamming and ongoing maintenance.
flexibility
The label material ‘memory’ is also something to watch for, especially if the leaflet label is being applied to a square or rectangular product with small radius corners. Although many leaflet labels are designed with some flexibility to allow application onto round products, the material memory when ‘stretched’ around the corners of a square product may cause the label cover piece to spring open even after the label has been applied effectively and passed by quality controls. Once again the low tack adhesive on the label cover does not help this situation because it sometimes cannot overcome the force generated by the material’s memory.
Although many leaflet labels are designed with some flexibility to allow application onto round products, the material memory when ‘stretched’ around the corners of a square product may cause the label cover piece to spring open
The weight of leaflet labels is another area that may cause difficulties. It is possible that some leaflet labels will fall open under their own weight while in position on a label dispenser during machine start up – generally these labels can be closed again during the labelling phase but this is not to be relied upon as the application tolerance is not good. The application tolerance problem is compounded further if a ‘flag and wrap’ style of application is used. In this case the label is applied onto one side of a product and dispensed so that it looks like a flag, the system will then wrap the label around the product within a side belt applicator system or similar. When heavy leaflet labels are applied in this way they have a tendency to sag before they are wrapped, which may cause label creasing and a skewed application.
The label overprint must also be considered. Standard labels have a flat clear overprint area, which is important for contact printers such as hot foil or thermal transfer technologies. A thick leaflet label cannot be overprinted onto the leaflet portion as this gives inconsistent results so the overprint code must be positioned onto the trailing edge of the label where it is flat and single layered. It is critical that this area is large enough for the required text but when using a thermal transfer coding system the printhead must engage the label vertically to allow enough ‘run in’ to the coding phase. It is important that the coder printhead can retract far enough from the print surface between codes to allow the thick booklet section to pass to the coder.
A thick leaflet label cannot be overprinted onto the leaflet portion as this gives inconsistent results
As multi-layer labels usage is likely to increase, selecting label application systems that can cope with large variations in label thicknesses without any serious modification work is a high priority. So what should manufacturers look for to minimise the risk?
One of the key factors in meeting this is the design of the label drive. Ideally the system should not drive the backing material until the label has already been removed from the web; this will ensure that the labels do not open up during the process and will avoid damage to the label finish. Newman Labelling Systems achieves this by the use of a drive roller system, which controls the label backing paper only, leaving the labels untouched on the carrier web until the point of application onto the product.
Another important means of identifying a system that can genuinely handle heavy, inflexible labels is the label path. Ideally the label web path from the reel unwinder to the applicator plate should be straight and unhindered by rollers or drive points.
Good access to the label dispensing area should also be considered; a clear area with plenty of space for ancillary equipment such as coders, sensors and cameras is important.
A clear area with plenty of space for ancillary equipment such as coders, sensors and cameras is important
The system must also have robust control throughout the application phase to ensure the best possible placement accuracy of the label. For booklet labels applied onto round products, the flag and wrap method of application should be avoided. It is much better that the label dispensing is synchronised with the label application to minimise label sagging and ensure the application tolerance is kept to a minimum.
With leaflet labels offering real advantages to the manufacturer, we can expect increased usage over the coming years. But you cannot automatically expect your existing label application methods to cope with the demands they place on machinery, in terms of line efficiency, quality application and increased maintenance, especially if you haven’t purchased at the quality end of the market. Well designed and manufactured labelling systems should not find the majority of leaflet labels an issue as they have been designed to accommodate label variety through a short label path and appropriate label drive design.
