1. What are multi-layer labels?

Multi-layer labels belong to the category of special labels, they consist of several label layers on top of each other, which are located behind a cover label. The content of the label is only visible after opening the top label. The top label layer is also printed with text and image information. The special thing about multi-layer labels is that much more information can be placed on and in the label than with a single-layer label.

2. What types of multi-layer labels are there?

2.1 Sandwich labels/ peel-off labels/ double layer labels

Sandwich labels, or peel-off labels, consist of two or three label layers made of label paper or plastic film. The bottom layer, the so-called liner label, has a permanent adhesive. The upper label layer, the top label, can be peeled off from the liner label to the firmly sealed bundle (peel-off) and glued back on later. Sandwich labels are also called double-layer labels because of their multi-layer structure.

Sandwich labels can be printed with information on all sides of the label layers, except for the adhesive side of the liner label. In this way, a great deal of information in text and image form can be printed on and in the sandwich label. Variable data, such as prize codes or coupons, can also be printed on the sandwich label.

2.2 Booklet labels/ Leporello labels

Booklet labels consist of a base label, a paper booklet (a mini leaflet glued to the base label) and a laminate film as face material. The base label and the paper booklet are produced and printed separately. The paper booklet for the booklet label is offset printed on sheets of label paper. After printing, many individual pages are folded into a small booklet and bound. The carrier label is produced by the label printing company as a normal roll adhesive label in digital printing, offset printing or flexographic printing.

In a booklet machine, the basic label and the booklet are brought together and finally covered with laminate film. To make it easier to open the booklet label later, additional grip tabs can optionally be punched out of the laminate. The laminate film protects the booklet label from external influences and allows the label to be resealed.

As a low-cost alternative, there are booklet labels where the booklet is glued directly onto the backing label. With this variant, the laminate film is dispensed with. A perforation of the surface of the booklet is necessary to open it. These booklet labels cannot be resealed. In the case of booklet labels for round containers, e.g. cans or bottles, the base label must be shortened so that the label adheres securely and does not open by itself.

Another special form of booklet label is the so-called Leporello label. With this label, the booklet is provided with an accordion or zigzag fold (leporello fold). The zig-zag fold is a form of parallel fold in which two or more parts of the folded sheet are folded in alternating directions. When opened and unfolded, the typical zig-zag structure of this fold then results. The fanfold label offers a lot of space for information in a very small space. The fanfold label is often punched out in a special shape, such as a circle.

2.3 Wrap-around labels/banderoles

The wrap-around label was specially developed for round packs. It is attached to the pack with an adhesive surface and can be wrapped around the pack several times. It is easy to open, unroll and reseal several times and can be dispensed by machine. Wrap-around labels are made of label paper or plastic film and are either permanently adhesive or removable. Optionally, a transparent laminate provides protection against tearing, moisture and other external influences.

The special highlight of the wrap-around labels:
The printable area on the label is doubled by the possibility to print on the reverse side as well. The production costs of a wrap-around label with a printable reverse side are lower than those of a booklet label due to the simpler structure.

2.4 Wet glue multi-layer labels

If multi-layer labels are not produced from self-adhesive roll material, but in sheet-fed offset, and only coated with a wet glue immediately before product labelling on the labelling line, then these are referred to as wet glue multi-layer labels.

The wet glue process is traditionally used mainly in the beverage industry, e.g. for bottle labels for wine, beer, spirits and for labelling round containers such as glasses, paint, lacquer and aerosol cans. Wet-glue paper labels are inexpensive, suitable for labelling large quantities of products and easy to remove. Wet-glue multi-layer labels are processed by machine using wet-glue labellers without the need for special conversion of the systems.

3. How are multi-layer labels produced?

When printing multi-layer labels, there are many factors that influence their structure and properties. These factors include the material used, the printing technology, further processing, finishing and other optional production steps, such as personalisation. But the most important factor guiding all production steps is the purpose, the task that the labels are to fulfil.

3.1 Printing process

Three main printing processes are used in the production of multi-layer labels: offset printing, flexographic printing or digital printing. All three printing processes guarantee an excellent print image and differ essentially in the necessary consumables and tools, in the print costs that depend on the print run and in the possibility of personalisation with variable print data. There are also other printing processes that are used to print labels, such as screen printing or letterpress printing.

For the production of multi-layer labels, sometimes different printing processes have to be combined; this is the case with booklet labels, for example.

Flexographic printing: Flexographic printing is a letterpress process. Flexo printing can also be used to process low-viscosity inks with good surface coverage. Halftones are perfectly reproduced. Flexo printing is fully rotary and suitable for medium to high label runs.

Offset printing is a flat printing process. It is an indirect printing process in which the print is not applied directly from the printing plate to the material to be printed (e.g. paper), but indirectly via a so-called blanket. Offset printing enables a sharp-edged printout without pinched or frayed edges and a smooth paper reverse without embossing or shading. A distinction is made between sheet-fed offset and web offset.

Digital printing: Short runs, last-minute changes to the motif or the printing of variable data are unbeatable in terms of price with digital printing. The printed image is transferred directly from a computer to the digital press. Since no printing plates, clichés or screens are needed, printing individual multi-layer labels using digital printing is attractively priced. The special advantages of digital printing, the ease of personalisation and the unbeatable cost benefits for short and medium runs, come into their own with multi-layer labels. Digital printing is increasingly gaining market share over conventional printing methods.

Here you can find  more information about the production. (GER)

3.1.1 Materials

3.1.1.1 Paper multi-layer labels

Thanks to its physical properties such as gloss, writability, porosity and air permeability, label paper can be printed, processed and recycled in excellent quality. Paper is a renewable natural product and therefore quite cost-effective for printing multi-layer labels. However, label papers have the disadvantage that they are very sensitive to liquids, oils, greases, light and mechanical stress (tears and pulls)..

Without additional protection on the surface, the durability of multi-layer labels made of paper is short-lived. This is especially true for outdoor use. Provided with a lacquer or laminate coating, multi-layer labels not only get good protection but also an attractive appearance. The paper booklet for a booklet label is also offset printed on sheets of label paper. Printing the motif on label paper is basically possible in all colours of the Euroscale and in special colours. The choice of label paper is extremely varied and ranges from a very thin paper with a grammage of 60g to a 135g image printing paper. A rough distinction is made between the types of paper used for multi-layer labels, coated and uncoated label papers.

3.1.1.2 Film multi-layer labels

When it comes to weather resistance, robustness and temperature resistance of multi-layer labels, film labels are better suited for product labelling than paper labels, because the surface material of film labels consists of a very thin, resistant plastic. Foil labels are made from the following plastics in most label printing companies: Polyester (PET), Polyethylene (PE), Polypropylene (PP) and Polyvinylchloride (PVC). Due to the specific properties of polypropylene, this plastic is very often used for multi-layer labels.

Polyester labels (PET) are adhesive labels made of polyester film. This film is very durable and particularly resistant to water, petrol, grease, oils, alcohol, acids and alkalis. Polyester is the most stable plastic material for labels. Labels made of polyester film (PET film) have the great advantage of being particularly temperature-resistant. In the temperature range from -60°C to +150°C they neither expand nor shrink.

Polyethylene (PE) is an organic thermoplastic that contains no plasticisers, heavy metals or silicones and is easy to recycle. Polyethylene is the cheapest and most common type of film used in a label printer. Not only is it easy to print on, it is also easy to die-cut or further process after label printing. PE labels are food-compatible and are used where a certain formability is necessary.

Polypropylene and PP labels made from it have a higher stiffness and transparency than PE labels and are suitable for both indoor and outdoor use. They are particularly resistant to grease, solvents, alkalis or acids and can withstand temperatures from -15°C to +80°C without any problems. Thanks to its particularly brilliant transparency, this film is often used in label printing as a laminating film or for labels in the so-called "no-label look", for example for plastic and glass packaging.

Polyvinyl chloride (PVC) labels are very supple. Due to a certain proportion of PE material, they are less tear-resistant than PP labels. However, they adapt very well to curves and edges when sticking and can also be stuck securely to uneven surfaces. They are resistant to water, oil, alkalis and UV radiation and adhere securely at temperatures from -40°C to +80°C.

Here you can find more information about film labels from labelprint24.

 3.1.1.3 Adhesives for multi-layer labels

The range of label adhesives is as wide as the materials for the label layers are varied. Based on the adhesive properties, pressure-sensitive adhesives for multi-layer labels can generally be divided into two different groups.

On the one hand, the label printer speaks of permanent adhesion and, on the other, of removable adhesion. A combination of both are so-called semi-permanent pressure-sensitive adhesives, which can be easily removed at the beginning, but later adhere firmly to certain materials. For the adhesive strength of "removable labels", adhesive force limits of 3 N/25 mm (equivalent to 1.2 N/10 mm) are standard market practice. For permanently adhesive labels, the specified adhesive forces are 9 N/25 mm (corresponds to 3.6 N/10 mm).

While in the case of self-adhesive labels the label glue is already on the back of the label material before the label is printed, wet-glue labels are only provided with label glue shortly before they are affixed. This gluing technique is used as cold glue or hot glue labelling.

3.1.2 Further processing

After all the individual label layers, including the backing label, have been printed, further processing of the label webs begins. Depending on the customer's requirements, various further processing technologies can be used.

3.1.2.1 Personalisation

Personalisation of multi-layer labels means the printing of variable data on the inside of the labels. This variable data can be sequential barcodes, alphanumeric codes, personal phrases or other individual motifs. Digital printing systems are predestined for this process. They can be used to profitably print each individual label as a unique specimen without having to produce printing plates. The individual motifs become visible as soon as the lid label is opened at the grip flap or by means of a perforation.

3.1.2.2 Finishing/ Lamination/ Lamination/ Embossing

During lamination, the upper label layer is bonded with a thin, transparent film laminate. After this finishing process, the laminated surface is water-resistant and protected against soiling. The laminate seals the multi-layer labels. A grip tab punched out of the laminate makes it easy to open and reseal the multi-layer label. In principle, the grip tab can be applied to any side and corner of the label.

Immediately after printing, many multi-layer labels are fully or partially finished with UV-curable varnish and/or embossed using hot foil or cold foil. The purpose of these finishes is to give the multi-layer labels a noble, high-quality appearance. Digital printing also offers favourable alternatives for finishing: Metallic effects are created by printing on silver or gold foil. By partially underprinting white, it is possible to make individual design elements appear "metallic".

Another type of finishing is the so-called blind embossing. In blind embossing, the element to be embossed is pressed out of the substrate with an embossing die. The embossed elements can be felt by hand.

Relief embossing uses a negative die to transfer the transfer layer of a foil onto the label. This finishing produces a three-dimensional deformation of the substrate with a striking plastic effect.

3.1.2.3 Braille/ tactile warning triangle

Finishing of multi-layer labels is not always due to purely visual enhancement. Haptically legible information on multi-layer labels is a deliberate effect to make labels legible for the blind or visually impaired. The dots of Braille can be embossed into the cover label or realised as a structure on the multi-layer labels by means of spot-applied layers of lacquer. These two methods are also used to provide labels with a tactile warning triangle. This type of labelling for packaging with hazardous substances has been regulated in a European standard since 2004 - BS EN ISO 11683.

This states that products that are to be classified as very toxic, toxic, corrosive, harmful, extremely flammable or highly flammable according to Directive 1999/45/EC must be provided with a tactile warning sign in addition to the visible GHS hazard symbols.

Here you can find more information on chemical labels, hazardous substances and GHS

3.1.2.4 Folding/ Perforation

In the production of multi-layer labels, finishing is followed by folding, perforating and die-cutting, although not every one of these steps is necessary for every label.

Folding is the process of folding the label material to a predefined format. For example, the paper booklet of a booklet label is folded to a previously exactly defined number of pages. Folding is done mechanically in a folding machine, whose folding units must be set up with millimetre precision. Precise folding is an important step on the way to the finished multi-layer label. Professional craftsmanship is required here, because folding is precision work. The individual pages have to be folded in such a way that the printed sheet turns into a small book. There are many different types of folds in paper technology. The most common types of folds in the production of multi-layer labels are the spiral fold, the altar fold, the parallel fold, the cross fold, the window fold and the leporello fold (zigzag fold).

Fold gluing is the name given to a step in print finishing where the individual pages of a paper booklet are glued together at the binding instead of being joined with staples through the spine.

Perforation is a slit or hole punched in the label surface. Perforation is necessary, for example, so that the finished multi-layer label can be opened at one or more perforation lines without tearing the label.

3.2 The collation / fold gluing

In order to create a multi-layer label from the individual label layers, all the label layers have to be assembled. This step is carried out in a sandwich or booklet machine. The reels with the liner label, the paper booklet, additional label layers and the laminate are inserted into the machine and glued together synchronously at the collar. This process requires the highest mechanical precision when positioning the labels and is controlled via sensors. After joining, the laminate film closes the multi-layer label.

Another method for joining individual label layers is fold gluing. Here, a glue line is applied to the collar during the folding process, thus firmly joining the individual layers of the multi-layer label.

3.2.1 The die-cutting

After collating in the sandwich or booklet machine, the contours of the printed and finished multi-layer labels are punched out of the upper material of the label roll. Now the labels get their final shape. The die-cutting is done either with the help of a sharp-edged, mechanical die-cutting tool made of metal (cylinder die-cutter) or with a laser die-cutter.

The laser die-cutter cuts out the contours with a laser beam without cutting through the liner. By using the laser, the labels can be "cut" in free contours without incurring die-cutting costs. Immediately after die-cutting, the surface material around the multi-layer labels is pulled away upwards and rolled up. This process is called "weeding" because the material looks like a grid or net without the die-cut labels.

However, the laser die-cutter can only be used for wrap-around labels, because when cutting several layers of labels arranged on top of each other, the heat of the laser causes the materials to fuse.

3.2.2 The re-rolling

As there are the most diverse models of label dispensers for labelling products in industrial packaging practice, the finished multilayer labels are wound in a previously defined number of pieces onto roll cores with different core and outer diameters.

This re-rolling is done by a label rewinder. It is not only the number of labels that is important, but also the direction in which the labels are wound, because the label dispensers are designed, depending on the manufacturer and model, in such a way that the multi-layer labels must lie on the inside or outside of the liner when they are dispensed. Once the label rolls have been wound, they are packaged and dispatched.

4. Labelling of multi-layer labels

The dispensing of multi-layer labels to the exact position directly on the product or on the product packaging is carried out by manual or automatic label dispensers, as they are also used for single-layer roll labels. For industrial dispensing of labels with several sides (on large product quantities), automatic labelling machines with a wide range of speed classes are used, which are usually integrated into the manufacturers' packaging lines. A conveyor belt guides the products past the labeller, and light barriers detect the optimum labelling position. The printed labels are controlled by a microprocessor and attached with pinpoint accuracy on, under or on the sides of the product packaging. There are high-speed labellers that can apply up to 5,000 labels per minute to packages.

5. Significance, trends and application examples

In addition to the digital transformation in label production, the demand for multi-layer labels such as booklet labels and sandwich labels is one of the top trends in the international packaging industry. In view of the increasing information obligations and increased cost pressure among manufacturers, it is worthwhile for many industries to analyse the entire packaging process and think about needs-based and cost-effective packaging solutions.

• Multi-layer labels are one such packaging solution because they offer the most space of all label types. They embody the label and package inserts in one composite and save brand manufacturers and consumers additional product brochures or outer packaging.
• Multi-layer labels are suitable for all types of packaging, enhance them and, thanks to die-cut shapes, they adapt to any container, even with difficult shapes and when there is little space on the container.
• Multi-layer labels can be produced and customised more and more cost-effectively with digital printing technologies; their production is therefore also profitable for smaller runs.
• Multi-layer labels can be produced and customised more and more cost-effectively with digital printing technologies; their production is therefore also profitable for smaller runs.Multi-layer labels can be produced and customised more and more cost-effectively with digital printing technologies; their production is therefore also profitable for smaller runs.

Multi-layer labels, such as sandwich labels or booklet labels, are increasingly used, for example, in the pharmaceutical-chemical industry for the packaging of paint buckets and oil containers or for the precise labelling of cosmetic products and organic foods. They are ideal for conveying multilingual instructions for use or storage instructions in the smallest possible space on the product.

Furthermore, the multi-layer label in all the forms described above is also increasingly used in food retailing for so-called on-pack promotions. A multilayer label has a decisive advantage. Frequently changing marketing campaigns can be easily realised without cost-intensive redesigns of the entire packaging design. The corporate identity is always maintained, and the cooperation partners for competitions and other promotions also have enough space to present their brand on the packaging. With a single-layer label, the in-house effort and resources in the departments are much greater when redesigning the label.

Here you can read more about multi-layer labels von labelprint24 erfahren.

For more information and expert advice on customised multi-layer labels for your product, please contact info@labelprint24.com or visit our website at www.labelprint24.com.