In addition, PS labels are capable of being converted into a range of added value products including booklet labels, ‘smart’ labels with RFID inlays, 2-side printed clear films and many more.
These clever combinations are made possible by the equally rapid development of narrow web press technology able to perform a wide variety of converting operations in a single pass, including de- and re-laminating, web turning and printing on the adhesive side and the ability to run in multiple webs.
Other value-added processes ideal for the self-adhesive label format include hot foiling and embossing, cold foiling, hologram insertion, rotary and flatbed screen and much more.
In this series of articles we look in detail at each component of the self-adhesive label laminate including the release coated liner, the difference between paper and film face stocks, adhesive manufacture and performance, to the specification, performance and testing of the finished label laminate.
We also look at the sustainability aspects of self-adhesive materials, a subject which has assumed greater importance in recent years as legislators and brands turn their attention to eliminating landfill waste from the packaging production chain.
We can trace the birth of the modern self-adhesive label industry back to the 1930s, when Stan Avery patented a system to die-cut labels to shape and then apply them automatically on a packaging line. In 1935 with capital of less than $100, Avery created Kum- Kleen Adhesive Products Co. to produce self- adhesive labels using machinery he had developed while working at the Adhere Paper Company.
Stan Avery did not invent self-adhesive technology. As early as 1892 self-adhesive medical plasters had been developed with industrial tapes available from the 1890s. His genius was pulling together existing technology developments and refashioning them into a totally new industrial system.
Avery’s initial trials used an adhesive ‘coater’ fashioned from a cigar box and a simple die-punch. From this, he pioneered the technique from which virtually all of the self-adhesive graphic and industrial fastening products used worldwide have evolved. His first products were the Kum-Kleen pricing labels (Figure 1.2).
Figure 1.1 Stanton R Avery, founder of today’s self-adhesive labels industry
Figure 1.2 Kum-Kleen stickers
These first self-adhesive labels were not technically die-cut but rather were die-punched using a male die which came up through a guiding plate and which die-cut two 3⁄4 inch round discs of adhesive coated paper. Carrying them through a female die and sticking them side by side on a strip of backing paper, Stan Avery made his 3⁄4 inch Kum-Kleen price labels for antique and gift shops before expanding to other retail establishments.
When the limitation of the die-punched method began to restrict both the production and volume sales of self-adhesive labels, he had the idea to make a sandwich of the backing, the face paper and the adhesive and then, as a separate process, die-cut the required label shape through the face paper only.
To create the first cutters, Stan Avery used the edge of a very thin strip of watch spring. Supported on edge in a thin metal plate with only a fraction of an inch or so exposed for cutting, Avery was able to make dies of any desired shape with uniformly thin cutting edges. It was then only necessary to work the die between absolutely flat ground steel surfaces to make perfect cuts every time.
By 1937 Avery had developed the first synthetic-based pressure-sensitive adhesive and, using a second-hand dough mixer purchased for $10, started his own adhesive production. It was many years later before he purchased his first high-speed mixer. Then, in 1938, Avery Adhesives as it was renamed, suffered a fire that destroyed all of its equipment – except a stock of labels. It was while rebuilding the factory that Stan Avery implemented the changes in his die-cutting machinery.
In 1938, Sessions of York started converting the first Avery Kum-Kleen labels in England under license. These were manufactured on the company’s roll-label seal presses which were used to stamp out printed labels from slit-back Kum-Kleen tape purchased in 41⁄2 inch (112mm) rolls – the full width of Stan Avery’s original tape-based plant.
During World War II Avery Adhesives received wartime government contracts for self-adhesive labels that replaced metal identification tags and also for instructional labels for assembly-line workers. Among the products being produced at this time were waterproof labels bearing ‘SOS’ in Morse code that were stuck on rescue radios.
When World War II ended, Avery Adhesives changed its business focus and markets from retail labels to one that encompassed much broader markets. The war economy had without doubt hastened market acceptance of pressure-sensitive labels.
In Europe, the post-war years saw UK-based Samuel Jones – which had built its business on gummed labels – building experimental coating equipment and selling self-adhesive laminate. These self-adhesive laminates were based on non-silicone release coatings using a castor oil and shellac varnish.
Early silicone coatings were initially water-based, moving rapidly to petroleum-based – a far cry from today’s solvent-free silicones. Adhesives were solvent-based and, judging by the formulation, were not especially aggressive, which was just as well bearing in mind the absence of silicone release coatings.
It was researchers at Dow Corning, formed in 1943, who first saw the potential of silicones for releasing self-adhesive materials, and the company built this business from the 1950s onwards.
The next significant advance in self-adhesive label technology came about in 1949. Killing time on a train journey, Stan Avery used a wooden matchbox to satisfy himself that if the backing paper of a roll of labels is pulled away at a sharp angle, the labels on the roll will always detach themselves. Here the first automatic on-roll label dispensing system was born. Today’s sophisticated label dispensing equipment still uses that basic simple principle developed by Avery.
Another key development took place in 1951when Heinrich Hermann developed a process for coating adhesive paper, setting up Herma to commercialize the technology.
Meanwhile, other players were emerging. In Germany, Werner Jackstädt had joined his father’s wholesale paper business in 1947 producing self-adhesive sheets and postcard materials. By 1954, the Jackstädt business had started to dispatch the first sample rolls of self-adhesive paper to printers in Europe and the Jac organization eventually grew to become the world’s largest privately-owned manufacturer of self-adhesive papers, films and labels before being acquired by Avery Dennison in 2002.
Today’s other dominant player, UPM Raflatac, traces its origins to 1972, when Juhani Stromberg, a young chemist at a company called Raf. Haarla, based in Tampere, Finland, developed a water-based adhesive as an alternative to the solvent-based adhesives which prevailed in the label industry at that time. Raf Haarla’s first laminating machine was built in 1976, the same year Raf. Haarla merged with United Paper Mills Ltd., with label production becoming a separate unit called Raflatac. UPM then acquired the self-adhesive operation of the Kymmene-Stromberg Corporation (Kymtac Oy), to further strengthen the position of the combined Raf Haarla and Sterling (now UPM Raflatac) business within Europe.
In 1985 UPM Raflatac began to globalize its operations with production and sales in the US.
There is not enough space in this here for a full corporate history of the self-adhesive label industry, which saw the emergence of companies like Ritrama, Herma, Mactac and others, and the interested reader is directed to Mike Fairley’s excellent and comprehensive book The History of Labels, available through the Label Academy.
Figure 1.3 Key dates in the evolution of pressure-sensitive labels
GLOBAL LABEL MARKET
Pressure-sensitive (PS) labels today account for around 40 percent of total global label demand. Wet-glue labels represent the second biggest label technology at around 35 percent, having been progressively displaced by PS labels over the last two decades, a trend which sees no sign of letting up (Figure 1.4).
Figure 1.4 PS labels represent 40% of global volume, split equally between VIP and Prime (Source- AWA)_PORTRAIT
As a general rule, the percentage of PS against wet-glue labels increases with the level of economic development. In the US, for example, wet-glue labels now represent less than 20 percent of overall label demand. In Europe, that figure is closer to 50/50, but this conceals major differences between the developing economies of Eastern and Southern Europe – where wet-glue remains for now the predominant technology – and Western, Central and Northern Europe, where PS labels long ago eclipsed wet-glue.
The fastest growing label technology is sleeving, predominantly heat-shrinkable sleeves, which now account for almost one fifth of the world market by volume and growing by 8 percent year on year. But this has to be put into perspective. Individual shrink sleeve labels are bigger than PS labels since they have to wrap 360 degrees around a container, so volume comparisons need to take this into account (Figure 1.5).
Figure 1.5 Relative growth rate of different label technologies (source AWA)
In terms of PS market growth, we see a distinct difference between lower growth rates of 1-3 percent in developed markets and growth of anything up to 10 percent in developing markets such as China, India and ASEAN, with an average global growth of 5 percent.
Once again, we need to be cautious about seeing Europe as one market. While lower growth rates have characterized Europe’s developed economies, markets like Poland and Turkey have been growing until recently in double digits (Figure 1.6).
Figure 1.6 Long term European PS labelstock growth trends (source- FINAT)
It is noteworthy that PS growth anywhere in the world and in any decade, closely tracks the rate of GDP growth. Indeed, analysis conducted by FINAT demonstrates that PS labels are a leading indicator, or predictor, of economic growth trends. This reflects the fact that label growth is itself highly sensitive to trends in wider consumer and industrial markets. This can be seen by looking at the main end user markets for PS labels: (in rough order of growth) beverage, pharma, industrial chemicals, personal care, food, household chemicals, transport and logistics, automotive and retail (Figure 1.7)
Figure 1.7 Self-adhesive growth rates are a leading indicator for wider GDP growth (source- FINAT)
Another measure of PS penetration is per capita consumption. The region with the highest PS consumption, 17 sqm per capita, is Scandinavia, and this figures plummets to below 1 percent per capita in India and China, demonstrating the huge potential for future volume growth in developing markets.
We have already noted that PS represents 40 percent of global label consumption. But less than half of this volume goes to the prime label market.
Around 44 percent of global PS production is in fact accounted for by VIP (variable information printing) labels. Typical applications would be tracking labels for parcels, pallet labels, address labels and so on.
A further six percent is accounted for by functional or security labels, and five percent are promotional labels. This leaves some 45 percent of global PS production going to the prime label market.
For the prime label market then, wet-glue is still, by far, the biggest label technology globally, accounting for 46 percent of the market, compared to 24 percent for PS and 24 percent for sleeving (Figure 1.8).
Figure 1.8 Wet-glue remains the main form of prime label decoration (source AWA)
FILM VS PAPER
Another key trend is the increased use of filmic materials compared to paper. The market for which we have the best statistics is Europe, where FINAT (and prior to that EPSMA) has been collecting detailed data on the pressure-sensitive label market for over 50 years. FINAT’s figures show that in 2018 of a total European consumption of 7.49 billion sqm, non-paper roll label materials accounted for 27 percent of the total, up from 15 percent in 2000. This represents a growth rate almost four times that of paper face materials and demonstrates a continued trend towards high value-added applications in the consumer FMCG markets and an increased demand for clear-on-clear products.
With growing global awareness of sustainability issues, PS label technology has come under the spotlight on three fronts: non-removeable label adhesive can contaminate a plastics container waste recycling stream; waste created when the label is die-cut and the matrix skeleton is stripped away is non-recyclable; and the liner waste left when the label is applied to the container, whether paper or plastics-based, is still mostly thrown into landfill.
Although currently incineration for energy is still an allowable route for dealing with matrix and liner waste, increasingly legislatures and bodies like the EU are adopting ‘circular economy’ policies, where raw material used to create a product must be ‘upcycled’ and used to recreate new versions of that product, or a product of equivalent value. This is opposed to ‘recycle’, where processed reclaimed waste usually ends up in secondary applications such as insulation, plastic park benches and traffic cones.
Of all the process waste produced in the PS life cycle, filmic liners are the easiest to upcycle in a way compatible with circular economy thinking.
Providing they are properly sorted, recycled PET liners provide excellent feedstock for new PET liners, and this value allows recyclers to pay for collection and reprocessing.
Paper-based liners present challenges, since the silicone coating must be removed before they can be reprocessed. The technology does exist and has been commercialized, but there are only a handful of sites with the appropriate technology.
A bigger issue for both film and glassine liners is the lack of large-scale sortation and collection of liner waste by major end user companies.
Label organizations in both Europe and the US have sponsored collection and recycling systems and some industry suppliers and global brands have been proactive in making such systems work. But there is a long way to go before the industry as a whole can be counted as sustainable.
Matrix waste provides an even more intractable problem if the goal is a circular economy. Currently it is not possible to cleanly separate the laminate components after they have been tightly wound into a roll. The only feasible non-landfill disposal path remains pelletization as a feedstock for industrial furnaces and waste-to-energy schemes.
Adhesive contamination of PET containers means that after the label is removed, a layer of adhesive remains on the surface which does not allow clean separation of the PET material. This is an issue which has received attention from materials suppliers. Avery Dennison’s CleanFlake is an excellent example of this kind of a ‘switchable’ adhesive which deactivates in the presence of the fluids found in container recycling systems.
In terms of sustainable PS face materials, the two schemes focused on label papers have proved very successful. These are run by the PEFC (Program for the Endorsement of Forest Certification) and FSC (Forest Stewardship Council) organizations. They ensure the papers are sourced from biodiverse and sustainable plantations and are not sourced from old growth forests.
For PS face films there are a growing number of biomass-based non-fossil fuel alternatives, as well as bio and photo-degradable films.
VIP VS PRIME LABELS
There are two main categories of self-adhesive labels from an end user point of view: Prime (or Primary) labels and VIP (variable information print, sometimes called Variable Data Printed, or VDP) labels.
Prime labels are found mainly in fast moving consumer goods (FMCG) applications, generally placed in a prominent position on the top or front of a product. It is usually decorative and eye-catching, and includes only the most important pieces of information about the product. There may also be a back label where legal, nutritional, recycling and other information will be found.
Prime labels can be either filmic or paper, and can incorporate a range of surface printed effects. The main printing methods for prime labels include flexography offset, letterpress, gravure, Screen and digital (toner and liquid electrophotography and water-based and UV inkjet).
VIP labels are found mainly in the supply chain where products and packages need to be identified for track and trace or addressing purposes.
Many in-plant logistics systems – warehousing, distribution, shipping, storage, tracking – use labels that are printed with variable data. This variable information printing may be in the form of variable text, barcodes, sequential numbers, batch codes, date codes, etc. Variable information or data printing on labels is undertaken with non-impact laser, thermal transfer, or inkjet printers, or with impact printing systems such as dot-matrix printers.
It is important to understand the imaging processes involved as they directly impact the properties required in the self-adhesive laminate (Figure 1.10).
Figure 1.10 Variable information printing technologies
The main VIP print processes include:
Laser printing. This electrophotographic printing process, which is also widely used in photocopiers, uses fine toner particles to provide the image.
The laser beam in the printer creates the image, point by point, controlled by a computer, into a charged pattern on to a pre-sensitized belt or drum.
This pattern has opposite polarity to the toner powder and so attracts it, forming the image.
Paper or label material held against the photoreceptor collects the toner image which is then passed through a fusing system to bond the toner to the labelstock.
Most fusing systems use heat in a pressure nip, but variations include radiant heat fusing and flash fusion using halogen and xenon lamps. The latter are also called ‘cold’ or ‘cool’ lasers because only the dark toner is heated during the flash fusion process.
Variations of how the image is created from the computer’s memory include magnetography and ion deposition (now renamed as Electron Beam Imaging or EBI. technology).
Direct thermal printing. The main process used for adding price-weight information, product description and barcodes to supermarket frozen and fresh produce labels – meat, fish, cheese, fruit, vegetables, etc. – which are weighed and priced at food packers, remote from the supermarket, but also in the store for delicatessen, bread and produce labeling.
The print head for direct thermal printing consists of numerous elements in the form of a grid or matrix that are heated and cooled selectively by a microprocessor controller. A special heat-sensitive coated paper is required which, when heated by these elements changes color within the areas of contact to form the required letters, words, numbers or codes.
As the special thermally printable coating is heat- sensitive, direct thermal printing is primarily used for fresh and chill cabinet products that have a short shelf-life in store of several days. It is not normally used for long shelf-life labeled products or in warm or hot conditions.
Direct thermal labels can be unprotected, or have both a top coating and a barrier coating to protect the image from contamination from both sides.
They are still only recommended for short term labeling as the thermal coating is sensitive to both heat and light so the coating will darken with age and this can adversely affect the print contrast signal (PCS) of printed barcodes, so they cannot be scanned.
Thermal transfer printing. The most commonly used variable data printing process and again makes use of elements which are heated and cooled selectively. However, this time, rather than using a special thermally-sensitive coated paper; the elements come into contact with a filmic one-pass ribbon (of which there are different types), which carries a heat-activateable ink coating.
The required image is therefore created by transferring the heat-activated ink coating from the film carrier to the substrate according to the pattern or shape of the heated elements.
Thermal transfer printing is used for variable information printing of batch codes, date codes, sequential numbers, text, diagrams and barcodes onto pallet, carton or box end labels, for warehousing and distribution requirements, for bakery labels and for DIY and industrial labeling. Printers may be incorporated into packaging and/or weighing lines or be stand-alone. Some are also print-and-apply systems.
Inkjet printers. There are two inkjet printing systems, continuous inkjet (CIJ) and impulse, also called ‘drop on demand’ (DOD) inkjet printing.
Continuous inkjet printing is widely used for printing batch numbers and ‘sell by’ dates or barcodes directly onto products or in-line, on label printing and continuous stationery machines. This inkjet printing method uses minute droplets of solvent-based inks, usually MEK, which are activated and fired at a label surface by means of electrical charges to form the desired image.
Continuous inkjet printing utilizing piezo-electric technology can print in multiple colors at press speed. ‘Impulse’ or ‘Drop on demand’ inkjet is used for office A4 printers with both thermal ink-jet and piezo electric methods used to create the ink droplets.
In thermal inkjet (Canon ‘Bubble-jet’ and Hewlett Packard ‘Desk-jet’) each ink drop is generated when it is needed, by the activation of an electric current to a resistor in the wall of each ink chamber. This heats water in the ink causing it to vaporize and expand. A bubble is created, which forces ink out of the chamber nozzle as the pressure increases.
Dye based inks are being replaced by pigmented inks, where improved water resistance and light fastness are needed.
Piezo electric inkjet systems can utilize either water-based or hotmelt/solid inks. This technology is also fired by an electrical pulse which is applied to a piece of piezo crystal along the wall of the ink chamber. The pulse causes the crystal to deform and reduce the area inside the chamber, thereby forcing an ink droplet out through the nozzle.
It is important to note that film labels must be provided with a special coating in order to ensure optimum ink absorption and ink keying properties, as well as sharpness of image, this being an essential requirement for the printing of barcodes.
Prime labels in higher value-added markets often make use of metallized materials, and can be either filmic or paper. They have been coated on one side with a very thin layer of metal (about 1 micron thick), usually aluminum. Metallizing is produced by melting and vaporizing the aluminum in a vacuum while passing a web or paper or film around a chilled roller and over the point of vaporization. The vaporized molecules then collect on the cool web, so providing the paper or film with a metallic finish.
Metallizing may be carried out by direct metallizing onto the material surface, or by transfer metallizing where the vaporized metal particles are attracted in the vacuum chamber to a very smooth plastic carrier web and then transferred to the chosen substrate under pressure. This gives a higher finish than direct vacuum metallizing.
Metallic foil is a thin, flexible layer of metal – most commonly aluminum – which is used as a label face material. Some thinner gages are often laminated to paper for improved strength.
Alternative ways of metallizing self-adhesive face materials include metallic inks and cold and hot foiling.
Linerless labels consist of a roll of self-wound material, most commonly a direct thermal coated and top coated label. The surface to be printed is coated with a release coating and the reverse side with a pressure-sensitive adhesive. When the roll is wound up the face stock functions as the release surface. The labels are then butt cut – or may have limited shapes cut to the top or bottom – and applied on a print-apply label applicator or for prime labels by a proprietary applicator system.
Linerless labels are most commonly found in the form of pressure-sensitive labels for the blank label industry, as well as thermal labels used in print and apply weigh-price label dispensers and applicators for meat, poultry, and seafood packaging.
Linerless pressure-sensitive labels for prime label applications first came to the fore in the early 1980s when Waddingtons in the United Kingdom developed its Monoweb coating technology to produce linerless labels which were used by major brands including Heinz.
A specially designed applicator system die-cut and applied the label in one pass on the production line. Today a number of companies offer proprietary linerless technology and applicator systems for both primary and secondary product decoration labels.