Labels for packaging
This chapter discusses the importance of the label in the packaging process. The different types of labels are outlined along with trends in types of labels and the substrates used. Basic specification requirements are listed. The market for labels and the opportunities for the future are mentioned.
Labels are an integral part of the packaging industry and have been for well over 100 years. in the early days they were simple, handwritten and used for identifying bales of cloth by batch and colour. Their use spread quickly and nowadays they are used in a variety of ways and applications.
The label is a versatile tool with the basic function of providing information, be it brand recognition, legislative information, as a selling tool or for many security applications. The most important information which a label can contain includes weight, usage instructions, hazardous warnings, etc. Labels are produced in many shapes and sizes often with focused, defined characteristics as we will see later in this chapter.
Wherever you look, labels are in evidence. A trip to the local supermarket will reinforce how important the label is to product recognition and thereby to the selling function. Look at the many bottles, jars or cartons which use the humble label. The end use markets (consumers) for labels include food, pharmaceutical, cosmetic, industrial, wine and spirits etc. (see Fig. 17.1), each requiring specific characteristics, e.g. resistance against chemicals, abrasion, freezing, water, etc. in addition to normal labels, derivatives include in-mould, sleeves and pouches. ‘Smart’ labels are able to indicate the freshness of a food product, some can provide oxygen scavenging properties, while others offer anti-counterfeiting measures and tamper evidence. They can even be applied directly onto fresh food products like apples, oranges and bananas.
An expanding and developing market is the use of RFID (radio frequency identification) tags which are becoming more widely used as they are becoming cheaper to produce. These tags are used in a variety of tracking and security applications, e.g. libraries, retails shops and for tracking products through a supply chain. They will gradually replace bar codes for pricing and promotional campaigns.
When all the information required cannot be contained on a single label, multipage labels can be produced which may be used to supply information in several languages or the many contra-indications required in the pharmaceutical industry. A very recent application is the provision of Braille characters which has become a mandatory requirement on all retail medicines.
Although label purists would say that shrink sleeves are not part of the label world, they do play an important role in decorating bottles which are an unusual shape and they are, in general, manufactured using a narrow web press.
For the first half of the twentieth century glue applied labels were the only method of application, until the 1950s when Stanton Avery ‘invented’ the self-adhesive (pressure sensitive) label. Figure 17.2 shows the current usage of self-adhesive labels compared to other types of labelling techniques. In-mould labels and sleeves now feature prominently in the label industry.
This type of label is now by far the most popular and has taken a significant market share from wet glue applications during the past 10 years. They can be used in a wide range of applications as they can be applied to the product more quickly and can be printed on many different substrates. With modern printing presses and finishing equipment, very fast changeovers from one design to another can be achieved quickly and easily.
The label face material, which can be paper or a film composite (there are more than 1,200 different face materials available that can be used in label production), is provided in roll form with an adhesive on the back. It can be printed using several printing techniques although there are still labels which are provided with no printing on initially. For visual effect, the finished label can be laminated or varnished.
In order to stop the material sticking to itself, a backing sheet or liner is used which is discarded when the label is applied to the product. The composition of the liner is very important as it must have enough tack to keep the label on the liner yet release it easily when it is applied to the pack or container. A silicone coating is the normal means of preventing the label sticking to the backing sheet.
When the label is printed, it is usually cut to shape using hardened metal dies which can be in a flat bed or rotary configuration. Laser cutting technology is gradually replacing metal dies as it is faster and can be adjusted to the desired shape of the label much quicker and it is easier to produce complicated designs. An important factor in die cutting is that the die must only cut through the face stock and not the liner otherwise, when it comes to the application stage, the liner would come away with the actual label.
When the label has been printed and die cut, the finished label is separated from the selvedge or waste (the skeleton which is the area not required for the actual label) and wound up ready for use on the labelling machine, the waste being collected for disposal or recycling if possible.
Once the label manufacturer has determined the end use for the label, he will purchase the label stock to the correct specification, already coated with the appropriate adhesive on the back and the liner in place. It is then printed on the face material with the required design in exact register, not only with the multiple colour images but also the die cutting position. During the production run the label is cut to shape in line by means of a rotary (usually) cutting die which, as already mentioned, must be carefully set so that it only cuts through the face material and the adhesive, and not the silicone layer or the carrier web. If this happens the web can break during label application, causing downtime and loss of product. Labels may be butt-cut, with no space between each one on the carrier web or, more frequently, die cut to a specific shape with a defined space between each label.
Labels for semi-automatic and automatic application are invariably required to be spaced on the carrier web, as determined by the requirements of the application machine. Labels are normally supplied on reels.
Paper was the first material used for self-adhesive labels and is still widely used. Factors governing choice of paper will be covered in Section 17.5.
• Only plastic films can offer a ‘no label’ look on transparent containers such as glass and PET bottles. This type of label is becoming increasingly popular especially for spirits and water bottles. The total cost is much less than decorating the bottle (usually glass but not always) by any other means. It also means that one type of bottle can be utilised for a wide range of products simply by changing the label. This reduces storage space requirements for incoming packaging materials and enables a more cost effective solution to be offered for the filling company.
• Plastic films offer improved product resistance where there is likely to be product spillage down the sides of the container and/or the product is likely to be handled in dirty or damp conditions such as garages and gardens.
As well as selecting the most desirable face material for a given end use, it is also necessary to select the correct adhesive from a range of standard options. Selection criteria are based on the requirements of the substrates and the performance expected from the final product, including a consideration of whether or not the label is meant to be a permanent feature of the pack. A label applied to a pharmaceutical product is almost certainly required to be permanent, whereas an information label on a decorative tin of biscuits may be designed to be peelable so that it can be removed when the initial use is complete. Self-adhesive labels are available in permanent and peelable options, as well as water removable for reusable containers or recycling purposes. Depending on the storage conditions of the product and the substrate to which the label is applied, even peelable labels can be difficult to remove over time and so-called permanent labels can peel off.
Self-adhesive labels are normally applied by semi or fully automatic labelling equipment, depending on the speed required. In fully automatic systems, the label applicator is an integral part of the packaging line and speeds in excess of 600 packs per minute and more are possible. A sensor detects the presence of the item to be labelled, causing the label to be automatically dispensed from the backing paper. The label is picked up by direct contact with the item, or blown on (common in the application of top ‘saddle’ labels). The label is then wiped firmly onto the container to ensure full adhesion with the substrate.
Fully automatic systems require special tooling known as a ‘beak’ which is specific to the label dimensions and shape. The purpose of the beak is to fold the carrier web back on itself, allowing the adhesive-coated edge of the label to be exposed, ready to be picked up by the container. The carrier web is wound up separately and disposed of using specialist disposal contractors.
Self-adhesive labels should be used (once printed) within a reasonable period of time after their manufacture, preferably not more than six months depending on storage conditions. There are two reasons for this: firstly, the adhesive tends to bleed slightly around the die-cut edge, which means that adhesive can offset onto the back of the release paper, which will cause unwinding problems on the application machine. This is made worse by storing the reels of labels in warm conditions. Reels must always be stored horizontally on the flat, cut edge and never on the face. This applies to part reels removed from production as well as to new material from the supplier, which should be left in its individual reel wrapping and stored in cool, dry conditions. A second potential problem associated with long-term storage is that, like any reeled material, the labels can take on a permanent curvature, which becomes more pronounced towards the core. This can lead to the label not standing out sufficiently from the beak to be picked up by the container at the point of application.
This type of label can be produced on paper or film and, in general, requires the application of an adhesive to allow it to be attached to a product container. This technique has enjoyed widespread use (and still does in some areas) in fixing labels to bottles, primarily in the beer and spirits markets. They used to be used almost exclusively for wine bottles, but in recent years this market has given way to self-adhesive labels. They are still used widely for wraparound labels on canned goods and some soft drinks applications.
The labels are normally pre-printed and delivered to the filler machinery in stacks, pre-cut to the right shape and dimension. A stack of labels is placed into a magazine on the filling machine and a label picked from the stack using glued pickers or vacuum transfer over a glued roller, and then applied to the container. The container must be firmly gripped to prevent excessive movement which would result in mis-applied labels. The label is wiped onto the container with rollers or brushes. For wraparound labels on cylindrical containers (e.g. cans), a line of adhesive is applied to the can and this acts as the pick-up mechanism for the label. The can rotates to wrap the label around the surface and a second line of adhesive is applied to the overlap. The usage of adhesive is thus kept to a minimum which also makes the label easier to remove for recycling.
Printed paper is the most economical choice for labels for canned goods, while beers and spirits are more likely to be labelled using film laminate structures, aluminium foil/paper laminates or metallised paper. Embossing and foil-blocking are good ways to add visual effects to a label and give a wide range of special effects.
The selection of suitable papers for ungummed (and other) labels is dependent not only on the aesthetic effects required but also on the environment in which it will be used. For example, if the label is to be used in freezing conditions then the label must stay on the container until it is defrosted and the contents used. Some might require resistance to scuffing, others to being re-wet constantly as in shampoo bottles. The economics of producing and placing a label on a product can be an important feature of the whole production chain.
Papers can be clay coated for surface smoothness and opacity giving high quality finishes suitable for high quality printing processes. Where this is not important a lower, cheaper grade of paper can be chosen. As with all other packaging materials, the packaging technologist should seek out the most cost effective solution, commensurate with meeting all the other requirements of the product pack.
Paper selection is also governed by the label application method to be used. For instance, where a vacuum pick-up is to be used, the paper’s porosity to air is important as is the degree of stiffness with regard to application to tightly-radiused surfaces. Where the curvature of a container is tight, a lightweight, flexible label is easier to apply – and more likely to remain in place – than a heavier weight, stiffer material. Moisture absorbency (measured by the Cobb value) will affect the speed of wetting out of the adhesive and thus the speed of application.
An important property of paper in its use for labels is its degree of curl. When paper is wetted during the application of ungummed labels, the fibres swell due to the absorption of water, the degree of swelling being greater in the cross direction than the machine direction which causes the paper to curl parallel to the machine direction, away from the wetted surface. The effects of paper curl can be minimised by the choice of paper and by keeping the amount of water used in the adhesive application process to a minimum. The grain direction required should always be specified to the supplier. Usually, but not always, the grain direction is parallel to the base of the label.
Wraparound labelling of PET bottles for soft drinks uses paper or plastic labels, the latter providing better flexibility on the flexible bottle, less wrinkling due to moisture absorbency and good aesthetic effects. Other benefits of plastic versus paper are improved scuff resistance of the print (by reverse-printing the label) and resistance to tearing and damage during use. Plastic film labels on bottles destined for refilling are more easily removed intact than paper labels, which are likely to disintegrate in the cleaning process leaving a slurry which is difficult to clean out.
A wide range of materials is used in the label market. Paper substrates are by far the most popular followed by plastic films as shown in Fig. 17.3. Film labels are usually supplied on the reel, which eliminates the cutting stage during label production and are easier to handle and are less prone to damage than stacks of cut single labels. A cutter on the label applicator cuts the label to size as it is applied.
In-mould labels are applied to a container during the manufacturing process. A pre-printed label is placed in the mould and the label becomes an integral part of the finished item, with no requirement for label application equipment on the filling line.
In-mould labelling (IML) is carried out on blow mouldings such as polyethylene and polypropylene containers or bottles. The label substrate can be paper, in which case it is coated with a heat sensitive adhesive, or films such as polypropylene which fuse directly to the blow moulded container.
In-mould labelling of injection mouldings most commonly uses film labels, which are placed into the injection mould. The molten plastic is injected and the label fuses to the component surface. Good, all-round decoration can be obtained using this method, which is currently used for tubs for butter and margarine, and for large containers for biscuits. A similar process exists for in-mould labelling during thermoforming.
The pre-printed and die-cut labels are delivered to the moulder in stacks and are usually picked up and placed automatically into the mould during the opening cycle. Accuracy of label placement in the mould is critical for good finished effects.
Shrink sleeve labelling is a relatively low volume but fast-growing sector of the market, offering all-round decoration of a container, scuff resistance (by printing on the reverse side of the film) and the option of tamper evidence, by extending the sleeve over the closure of a container. Shrink sleeves are also used to combine two packs together as one sales unit, often as a promotional offer. Where tamper evidence is required, it is usual to incorporate a tear-strip (either as a separate tape, or by the use of two lines of vertical perforations) to gain access to the closure, and horizontal perforations around the sleeve to avoid removing the entire label when opening the product.
Shrink sleeves are made from a flat web of plastic material, usually PET, OPP or PS. PVC has been used in the past and has good shrink characteristics, with minimal distortion at low temperatures but has some environmental issues. Therefore PET and OPP are gaining market share. PET shrinks very quickly and requires tight control of the shrink tunnel temperatures to avoid distortion. OPP shrinks more slowly, requiring a longer dwell time.
• The loosely sleeved container is then transferred to a shrink tunnel which may use hot air, radiant heat, or steam to apply heat to the sleeve to shrink the label onto the container in the correct position. The direction of the heat onto specific areas is important to provide an even and correct level of shrinkage without excessive distortion.
Labels may be printed by rotary letterpress, flexo, gravure, screen or litho, depending on quantity and quality requirements, and may be foil blocked and/or embossed for special effects (Fig. 17.4). The use of digital printing for labels is expanding rapidly, as it enables the brand owner to enter a market with the minimum of waiting time and minimises development costs. ‘Spur of the moment’ promotional campaigns can be mounted quickly in response to changing market conditions. Shrink sleeves are printed in the reel prior to tubing, using flexography or gravure.
Ink jet printing is an ‘on demand’ process which is more commonly used for online printing of date codes, ‘best before’ data, batch identification, etc., directly onto packaging components such as tins and bottles. This application is not considered to be high quality, as the main consideration is that the information is legible. It is a non-contact process, with special ink being dispersed into very fine droplets through a nozzle, giving the familiar dot matrix appearance.
Printed labels can be dated, coded and given variable information by ink jet printing, in which case, if the label is lacquered, an area must be left unlacquered for satisfactory adhesion of the ink droplets. On high-speed lines where the capital cost can be justified, laser printing of additional information can be carried out. The laser effectively etches the printed surface, leaving the label substrate exposed.
Printed labels must meet all the requirements of any printed surface for a particular application, such as resistance to fading, scuffing, specific products, etc. They must be easy to read under the normal usage conditions within which the product is used. This must be a prime consideration at the design stage. Bar codes must be guaranteed to be readable at the point of sale and at any other relevant points in the distribution process, and should be verified at some stage in the production cycle.
Label dimensions, reel dimensions, core dimensions and unwinding direction must be specified before the label is printed to allow the maximum compatibility with the downstream operations. Reels should be carefully wrapped to protect them from damage during transit to the filling machine. Storage conditions should be carefully monitored to ensure that the labels arrive in good condition ready to be used and to minimise excessive waste.
Labels must meet all the service requirements of the final product and have good adhesion to the relevant surface on which it will be mounted. Any particular requirement must be met during the useful life of the product, e.g. a shampoo bottle (continual wet and damp conditions), tinned vegetables (long shelf storage), etc., and finally disposal/recycling. This means that during the packaging development process, the label must be regarded as an integral part of the product/pack mix and be fully tested to ensure that it conforms to all requirements.
The current (2009) FINAT Technical Handbook outlines 27 test methods which can be used to test many aspects of self-adhesive label materials for specification and production. Although these are not ‘official’ standards, they are widely used by suppliers and printers throughout the world. They are perceived as a universal standard for determining certain characteristics. This publication, together with the FINAT Educational Handbook, provide a very useful source of information on label production for the student.
It is important to get the production of the label right first time as the further down the production chain a problem arises, the more expensive it is to put right and the longer it takes to produce. The opportunity cost of re-printing can be very expensive. Apart from technical problems during the printing and finishing stages, there are many areas where disputes can occur between the parties involved in the production process. It is essential that proofs are signed off at each stage of the production process; in this way everyone knows what is expected of them and corrections or modifications can be made early in the process.
Starting well before printing and pre-press artwork is produced, it is imperative that the specification of the label is accurate and accepted, and is understood and signed off by all parties. This will include the brand owner, the designer, the printer and the filling company. This stage is essential and time should be taken to ensure that everyone in the supply chain understands what is expected at each stage in production. This is the time when the specification of the substrate and adhesive is agreed. This is also when the end use of the label is specified, the type of container, the printing process, the method of filling, and the expected life of the label on the product, to name just a few criteria.
One of the most important factors for the brand owner is colour consistency not only from pack to pack but from batch to batch over a prolonged period of production. Meeting the colour specification is probably one of the greatest areas of contention between brand owner and printer, which is why exact colours must be specified if possible using a ‘standard’ colour system such as Pantone as a reference.
Another problem area is the actual printing. Although the label is a transitory element in the life cycle of a product, it must be presented to the highest quality commensurate with the type of end product it is to be used on. The biggest single fault is mis-register between one colour and the next. This of course has to be within accepted tolerances. For example, this may not matter on a tin of peas, but if this occurs on a pharmaceutical label, this could prevent the information from being easily read. This also applies to ‘heavy’ printing where overimpression or overinking can make some typefaces (especially 4 pt and below) illegible.
There is increasing globalisation of suppliers to the industry and their customers, and major brand owners are also becoming more global. This means that these brand owners are looking for global converters/printers who can supply labels in the locality of the product manufacture. There are relatively few global printers which indicates that there are potential business opportunities available.
Self-adhesive labels dominate the label converting sector which is also increasingly producing other types of labels. Sleeves are seen as a potential expansion area as are wraparound film labels. As mentioned elsewhere, wet glue applied labels are steadily losing market share even though their market volume is increasing. In-mould labels are still perceived as a relatively small niche market. The boundary between flexible packaging and label converting is becoming less distinct.
During the past few years flexography has become the dominant process worldwide with UV flexo growing rapidly. In addition digital printing has become a mainstream process in most developed markets. Letterpress continues to decline in volume yet offset litho is enjoying a revival. Foiling is becoming more popular due to the introduction of cold foil techniques.
Almost every aspect of label production has a digital input at some stage: design and artwork, scanning and cameras, proofing and page make-up, plate-making, printing, finishing, quality inspection and die cutting. More than 12% of new label presses are digital or have a digital unit. Stand alone digital presses are being introduced which operate at commercially acceptable speeds to make them viable alternatives to conventional printing techniques. The ultimate would be control of all the operations digitally through management information systems (MIS).
The use of digital printing of labels and tags will become more widespread. RFID and other smart technologies will grow rapidly. The use of label printing technology will become widely used in the new and evolving ‘printing for electronics’ market; this is seen as an additional segment not as a replacement technology. Anti-counterfeit and product authentication applications are growing to respond to the enormous current counterfeiting activities. There are major new advances in nano-materials which will influence the way labels are employed on high value and pharmaceutical products along with developments in anti-microbial and anti-bacterial label products. Techniques are in the development stage to use labels to detect MRSA, E-coli, BSE, Asian bird flu and many other viruses. There will be nano sensors to track food from the farm to the plate. As these techniques are introduced so the importance of security inks and materials will become more important. Smart, active and intelligent labels will offer new opportunities.
Labels and Labelling International magazine (monthly). Visit http://www.labelsandlabelling.com
NarroWebTech magazine (quarterly). Visit http://www.flexo.de