STICKING UP FOR THE FUTURE
A conference on adhesives and coatings gave interesting insights into some major and highly topical aspects of self adhesive technology.
‘Towards 2000 – Pressure Sensitive Adhesives for Today and Tomorrow’, held in Amsterdam highlighted the diverse nature of self adhesive technology. Twenty papers were given at the two-day event. The support it attracted, and clear interest in the subjects discussed, may prompt its regular appearance in the conference calendar organised by Cowise Management & Training Services.
Edited coverage in this issue concentrates on roll-label market trends, special applications, filmic trends, linerless technology, repulpable adhesives and permanent adhesive trends.
Better than expected growth for labelstocks
Mikael Airas of Raflatac presented a market review for 1993 on behalf of EPSMA (European Pressure Sensitive Manufacturers Association). It reported a 4.4 per cent growth in total volumes of pressure-sensitive reel and sheet labelstocks for 1993. This proved much better than a forecast of 1 per cent (against an actual 8 per cent in 1992).
Non-paper rolls (filmics and other synthetics) showed the highest increase with 8 per cent actual growth. This is modest compared with 1982’s increase of 28 per cent. Paper sheet materials at –2.4 per cent continued to lose ground, mainly from reduced promotional work and the growing shift from sheet to roll label production. Rolls accounted for 87 per cent of volumes.
Overall, the European labelstock market grew from 2,195 million sq metres in 1992 to 2,292 million sq metres in 1993. Roughly half the growth cane from the Western area (UK and Ireland) with a strong 9 per cent increase. This reflected a 2 per cent growth in GDP, compared with negative increases in most European countries; Germany’s declined to –1.5 per cent.
Most European labelstock markets grew by 1 per cent. EPSMA’s figures showed a ‘surprising’ growth of 10 per cent for the former Comecon countries against a forecast decrease of –23 per cent. This was attributed to a change of statistical areas, such as including the former GDR in German volumes.
Mikael Airas said a previewed European GDP growth of 1.5 per cent and members’ sales figures support 1994’s forecast for a total average growth of 5-7 per cent. Rolls grow in most areas by some 5 per cent, while sheets are near static (20 per cent growth for rolls and 10 per cent for sheets in East European countries).
The labelstock industry’s main threat is from increased raw material prices. Pulp costs have increased by 54 per cent in a year. Price pressures of this nature will be hard to absorb by everybody in the supply chain. They will trickle down to end-users, which could harm the industry. Nevertheless, recovery shows a positive outlook for the industry at large.
Non-paper roll labelstocks will continue to grow (10 per cent in 1994), with a new generation of products appearing in the mid 1990s, showing improved super-clear aesthetic capabilities. Repulpable adhesives will soon become standard for paper recycling. Adhesives will also have a higher performance, with cheaper general-purpose adhesives increasing from 50 to 70-80 per cent for a wider range of applications.
Pressure-sensitive usage in speciality markets
Consultant Alexander Watson told delegates the estimated pressure-sensitive materials market in 1993 comprised 7,300 million sq metres. Tapes took up 55 per cent, labelstocks were 34 per cent and special products 11 per cent. Tapes will decline to 52 per cent, with labelstocks growing to 37 per cent by 1996.
Although near-static, speciality grades offered the PSA industry some attractive niche market opportunities, particularly products for medical applications and personal hygiene products. Other important PSA sectors include automotive, building and insulation, protective films and specialised courier envelopes and bags.
Tom Alexander of Phazar Technologies gave examples of special uses for pressure-sensitive materials in commerce. For example, envelopes with PSA stripe closures, and individual release tapes, were growing alternatives conventional remoistenable gum or latex seals. Hot melt PSAs were now widely use for resealable or permanent closures on plastic bags.
Referring to the growth in form/label applications, he described a design that uses the forms’ entire width to avoid uneven packs. A slot die applies hot melt adhesive to one side. The labels are die cut in the normal manner. Oriented polypropylene (OPP) release liners – as thin as to 30 microns – are preferred to paper. Besides improving the presentation, with no unsightly thick wedges, their ultra-smooth surface enhances adhesive tack by up to 30 per cent.
The form’s paper web is also the label’s face material, offering considerable cost savings over conventional coated facestocks. By creating their own labelstock in-line, producers can cut costs by up to 50 per cent. Hot melt coating and liner lamination take place at normal press speeds.
Other commercial pressure-sensitive applications include removable stick-on notes. One company combines carbonless and low-tack adhesives to create message pads. A silicone formulation, from Phazer Technologies, did not react to the carbonless coating.
Postage stamps presented an interesting PSA development. Canada has issued stamps with a 90gsm one-side coated paper facestock, an emulsion adhesive and 90gsm liner. The world’s first filmic stamps, issued by the US Post Office, used a 36-micron white polyester facestock, adhesive, a phosphorescent tagging varnish for electronic sorting, and watersoluble primer.
Australian ‘peel and stick’ stamps in 1991 had an adhesive with a release coat allowing philatelists to peel off the stamps. A simulated serration applied by rotary die cutters gave a perforated edge.
Britain’s Royal Mail is currently test marketing such stamps, sold in books of 20. Die cutting with simulated perforations, including ellipses and phosphor bars matching those on conventional stamps, helps prevent forgeries. The 92gsm facestock has an acrylic adhesive and a water-soluble layer to aid removal by soaking. The booklet’s cover comprises a 160gsm coated board with a light silicone coating, doubling as the stamps’ release paper.
Better than expected growth for labelstocks
Paper’s limitations had helped foster the recent rapid growth in filmics for self-adhesive labels, said Steve Langstaff of UCB Filmics. They were a jungle for the uninitiated. Although they looked alike, each has different mechanical properties, also different coatings, limitations and prices.
Filmic facestocks offer many advantages. They have a high resistance to mechanical scuffing or tearing, while squeezability allows most filmic labels to deform in the same manner as a plastic container. High resistance is given to both harsh environmental conditions and a container’s contents. Most films resist most chemicals, but the polyolefins (polyethylene and polypropylene) are the most inert of common facestock materials.
Aesthetic considerations extend beyond whether a label is scuffed or not. Filmics gave marketers eyecatching labels with different levels of gloss for specific applications thet obviated the cost of overlaminating paper. Clear labels with high quality graphics offered a unique ‘no label’ look that emulated a direct printed effect. Polyester (PET) and oriented polypropylene (OPP) facestocks, in particular, gave excellent clarity.
There was widespread uncertainty and a lack of cohesion regarding environmental issues for both filmics and paper. Steve Langstaff said the argument boiled down to one question: incinerate or recycle? Incineration with energy recovery is favoured by many, but recycling has probably more fans.
The former does not offer much of an environmental driving force away from paper, except that filmics have higher calorific values. Paper’s calorific value is 16 MJ/kg, PVC’s is 18 MJ/KG, while polyolefins reach 47 MJ/kg. Questions surround the burning of certain films, particularly PVC, and the emission of dioxins at certain temperatures.
Where recycling is favoured, paper labelling acts as a contaminate where substrate identical labelling is essential. Slight miss-matches in polymers are not critical for technically unsophisticated products, like blow-moulded bottles, made from recycled materials demand a correct polymer mix.
Besides the constituents, the relative volumes also decide a particular polymer mix.
Why use filmic liners?
When it came to release liners, any move from paper to filmics followed the same considerations as facestocks: mechanical performance, aesthetic and environment.
In view of the differences between filmics, only PET and OPP have the necessary stiffness and temperature resistance. This applies particularly to thermally-cured systems. Compared with paper, e resistance to tearing was an advantage, with implications at all production stages and end use. If tearing does happen it is non-fibrous, which is critical in certain industries.
Regarding aesthetics, filmic liners improved the ‘non-label’ look possibilities due to their surface smoothness: adhesives applied to the release web took the impression of the liner’s surface. Being smooth, the adhesives were invisible on the label substrate. Paper, by contrast, gave a rougher adhesive layer, easily visible through the label.
On environmental issues, Steve Langstaff asked what other industry throws away half of the original component (the release web)? Many parties had made great efforts to recycle the release liner, either as fuel or ‘new’ paper. Again, the same argument of recycling versus incineration applied. Consequently, any swing towards incineration would show no environmental driving force for moving towards filmic liners.
If recycling is preferred, polymers once again have an advantage. Recycling silicone-coated paper, with the inevitable adhesive contamination, is difficult because it forms stickies and reduces friction between the fibres.
With filmics, reprocessing volatises most adhesive contamination. Any remaining impurities do not effect the production of low-tech products. With polypropylene the silicone is said to aid reprocessing, so some companies prefer it to virgin polymer.
The five main filmics
PVC was the first high-volume filmic and remained the benchmark product. However, environmental issues had left many unanswered question, resulting in a shrinking market share.
As a replacement, PE had grown rapidly in usage due to low cost and compatibility with most blow-moulded containers. Each of the several different densities available had their own mechanical properties. Converters usually used a medium density product. Corona treatment gave a high surface energy. It was readily printable, however top-coated PE further improved this feature.
Laminating, die cutting and stripping were good. When dispensed, PE offered a fully-squeezable product. Despite poor clarity, stiffness and temperature resistance, it had a promising future.
Steve Langstaff said he could not understand why polystyrene (PS) had made such an impact in the self-adhesive labelling industry. Although clear and stiff, it had poor mechanical features and low temperature resistance.
PET, however, had a high temperature range, excellent optical properties and good mechanical properties. High costs and a lack of recyclability with polyolefins left it more suited for high added-value applications.
OPP is the dominant polypropylene film, offering many properties at an affordable price. The bubble, or blown, version, gives excellent die cutting and stripping performance. Its clarity approaches that of PET, while having a higher service temperature than PE. Being readily recycled with other polyolefins, it could become the dominant filmic facestock.
Breaking through the linerless barrier
Linerless, pressure-sensitive substrates reduced backing waste, silicone and adhesives. Doug Smith of Ko-Pack International said a logical consequence of the technology reduced materials by 50 per cent to give significant savings. Evaluating laminate costs alone usually justified its comparative cost-effectiveness.
Linerless technology was still in its infancy. Its long term success would depend upon technological expertise and communication. One barrier to success would be the market’s inability to perceive its capabilities and benefits, both for the converter and end-user.
Attempts to introduce linerless products were first made in 1962. In 1989 Monoweb patented a system requiring end-users to die cut and apply the preprinted laminate. It was essentially for long runs with fixed information as a wet-glue applied replacement.
Ko-Pack’s development of commercially-acceptable linerless labels was first patented in 1991. The aim was not to replace or compete with conventional pressure-sensitive labels, but instead complement them to meet specific applications.
Production is handled in one-pass on a multi-colour Ko-Pack 004 press. It converts both sides of the web, using silicone and hot melt adhesive coatings. Users can convert plain bonded paper into primary or multi-layered labels and specialist products, without using a pre-coated silicone carrier web. Instead a regular pattern of silicone and adhesive allows back-to-back presentation of labels.
Linerless labels for overprinting come in three formats: back-to-back with same-size labels, or individually-sized labels to match the overall size. Alternatively, a label could fold on to itself to provide a single large label. They all give several fixed or variable data thermal overprinting options, including bar codes.
A basic application is security-checked baggage labels, but more involved constructions included their usage as part of business form sets. Doug Smith said the concept offered end-users flexibility in design, label construction and overprint combinations. No waste meant lower material costs and no waste disposal problems and costs at point of use. Ko-Pack, with its associate KoBel, is giving priority to developing an automatic applicator.
A laminator’s perspective on pressure-sensitive recycling
European legislation to reduce waste volumes has forced industries to adopt positive and responsible attitudes towards recycling. John Kortram of Fasson Roll Division Europe described the reason behind the development of FasRoll S2025. The patented acrylic emulsion PSA is repulpable and compatible with recycling processes.
Wastepaper streams naturally include pressure-sensitive materials. Unfortunately, they are hard to separate, resulting in contaminating stickies that also cause problems in paper recycling processes. Therefore, mills have avoided waste containing PSAs.
The label waste stream includes industrial waste: from the laminator, the converter and end-user. The fourth stage ends as post-consumer waste. Projects run by FINAT address the first three stages, while the latter is typically handled through dual stream principles. Their effectiveness depends upon individual awareness and discipline in separating, sorting and grading waste.
John Kortram said Fasson’s aim was to develop repulpable PSAs that eliminated the need to separate or sort wastepaper containing PSA from existing post-consumer waste streams. Besides going through paper recycling processes without producing stickies, they would pass standard test methods. Because none were available, fasson ‘borrowed’ methods developed for de-inking processes and repulpable splicing tapes.
The company has set up a carefully-controlled ‘closed loop’ recycling project with Sibille-Dalle. Products included facestocks suitable for office and computer-imprintable applications. Including matrix waste that contains the S2025 adhesive is seen to underscore the project’s success.
Expanding on Sibille-Dalle’s involvement, Yves Mazuel said 17 per cent of its annual 320,000 tonne production of speciality papers was for self-adhesive laminates. Recycled fibres ended up in one third of total production, using 60,000 tonnes of wastepaper at four recycling plants.
Another approach to repulpable label adhesives came from Jean Yves Caylus of Rohm & Haas European Laboratories. He expanded on the problems papermakers had with stickies. Physically separating or screening adhesives during repulping sounded good, but the presence of proprietary cleaning systems at different mills made it impractical.
The case for water-soluble adhesives also seemed sound. However, since all mills reuse their water, a build up of adhesives in the system would only post-pone the problem. Redispersable adhesives disperse into small particles, which remain buried in the pulp acting as an inner filler in the final product.
Certain properties, such as peel, sheer, tack and shelf stability, could be sensitive to humidity changes with this approach to adhesive design.
Jean Yves Caylus said the term, ‘water-based’ bore no relation as to whether an adhesive was repulpable or recyclable. Developing one that was depended upon the film formation process of the emulsion polymer and the morphology of the resulting film.
He described his company’s testing of a repulpable PSA with a prototype emulsion. Designed to redisperse during pulping, it leaves small and non-tacky particles that do not interfere with any papermaking process.
Wider applications for permanent adhesives
Advances in water-based acrylic PSAs had broadened their range of properties. They also brought forward the idea of a single permanent PSA for all standard applications, bringing considerable benefits for laminators and converters. Standard applications now account for over 50 per cent of consumption of permanent adhesives.
According to Håken Saxen, Raflatac’s R&D manager (in a paper read by Tom Saxberg), evaluating their adhesive properties was difficult using standard test methods. For example, adhesion to moist substrates, adhesion at low temperatures and adhesive bleeding during cutting and slitting.
A wider range of raw materials, such as tackifiers and plasticisers, had improved the properties of water-based PSAs. Further progress would depend upon advances in polymers, perhaps using new raw materials.
In addition to general-purpose permanent PSAs, a need would exist for PSAs with special formulations. Examples include labelling for wash-off bottle labels, pharmaceuticals, deep freeze products and certain foods.
Recent improvements to general-purpose PSAs included high adhesion to PE facestocks and adhesives with high heat resistance. The aim was to overcome the traditional shortcomings of acrylics, such as low adhesion to non-polar substrates, especially in chill areas and where moisture was present.
Factors influencing the development of permanent adhesives include growth in filmics and synthetic substrates and increasing demand for repulpable adhesives. Applications will expand further, while laminators will focus more attention on reducing adhesive odour.
The behaviour of PSAs during coating and drying will come under closer scrutiny. Overall versatility will also depend upon expanding the range of raw materials, involving closer co-operation with chemicals companies.