If the 19th century relative to joining techniques is determined by mechanical means like bolts, nuts, screws and nails for assembling steam engines, ships, bridges and wooden structures, the 20th century parallel to rapid progress in industrialization, transportation and metallurgy added thermal joining processes like welding and soldering. So-to-speak the 20th century was determined by thermal bonding thus representing the era of welding. Adhesives and therefore chemical bonds played a minor role only, with woodworking, paper packaging and book binding being early exemptions.
Adhesives no matter if natural or petro based with no exemption represent macromolecular structures, with rapid progress in polymer and surface science in the 1930th and after WW2 directly promoting adhesive bonding. Although first all-bonded aircraft took off in the 1960th already, all-bonded wooden structures pioneered at the same time in construction, it took until the 1990th to see first mass applications in structural sealing and adhesion. Progress was slowed by liability issues, lack of long-term experience, improper design of joints and widely lacking education of workers applying adhesives.
Final breakthrough of adhesive bonding came with on-going progress in polymer science and curing mechanisms, in appropriate design and preparation of joining parts, in ever more sophisticated dispensing equipment and radiation cure technologies plus their smooth integration in serial production processes, the permanent addition of new functionalities and constantly toughening environmental, safety and health requirements all favouring the use of adhesives and sealants, as does micronisation in electronics, light weighting in transportation, renewable energy generation, etc. In most cases representing less than 1% to manufacturing costs of industrial goods, adhesives across all market segments these days grow over-proportional to GDP, and represent key enablers of sustainable living and consumption in future.
Relative to bonding, the presentation will span from the first industrial revolution to tomorrow’s world of digitalized industrial manufacturing, and how this translates into ever more intelligent adhesive bonding solutions. It will also shed light on upcoming lifestyle & living trends and their consequence on adhesives. Recycling, composting, re-use, re-manufacture and re-furbishing of adhesive bonded goods will become commonplace to increase resource efficiency and rigorous cut on carbon footprint – best accomplished with adhesive bonding. Rationales will be given to the on-going replacement of mechanical by chemical bonds, as will be discussed the driving forces for future growth.
Thus all speaks to rightly expecting the on-going century to become an era of adhesive dominated bonding, which will apart from technical and regulatory rationales also be discussed by presenting today’s and tomorrow’s global market outlook for adhesives and sealants across segments spanning from household and DIY all the way to industrial use in hygiene and packaging, transportation, white goods, electrics and electronics, woodworking and construction, and beyond to ever more sophisticated fields like medical.
In most business areas there is a clear trend visible to utilize the full lightweight and performance potential of all available materials, including FRP and non-ferrous metals. These materials and material combinations require optimized joining technologies and create new challenges for designers, material developers and modeling specialists. As an adhesive and composite resin supplier we constantly have to translate our customer's requirements into new materials. For this we rely, like most industrial areas today, on reliable and validated models and numerical tools to understand the underlying principles and relationships.
This talk will give an introduction into the topic and highlight some of the most recent developments in terms of the mechanics background, design consequences, material development and modeling challenges and will give an overview about the possibilities we have today when using numerical modeling to support material and process development and to predict residual stresses which are locally superimposed with the stresses from external loads.. This will cover the mismatch of thermal expansions between the different materials which plays an increasingly important role, especially if a hot-curing adhesive is used, temperature changes during service are strong or components have large dimensions.
The trend to the transparency just as to the dematerialization of the building envelope is of continuous interest in architecture. Point fittings supported these topics and will therefore often used for glass facades. Novel applications of adhesive joints represent an alternative to the currently used mechanical fixed point fittings.
However, permanent adhesive joints are only realizable with special qualities of the adherent surfaces. Thereby, the surface structure, inherent moisture or contaminants have a decisive influence on the adhesion properties. The surfaces of the materials and thus their adhesive behaviour can be modified by specific cleaning and surface treatments. But due to deactivation processes on the modified surfaces, a fast bonding after the pretreatment is recommended. Since the value chain of the manufacturing of a building envelope is distributed to multiple companies, it makes sense to separate the pretreatment as special process from the adhesive bonding. Hence, to increase quality and economic efficiency of the industrial production of adhesive glass fixings, a temporally and locally separation of the individual manufacturing steps should be aimed. In consequence, a long-term stability of the surface modifications or an appropriate surface protection has to be ensured.
Therefore, the stability of the surface pretreatment with atmospheric plasma used on different stainless steels, commonly used in glass constructions, have been investigated before and after long term storages under specified atmospheric conditions and vacuum. The experimental study included contact angle measurements for the determination of the wettability and the surface energy of untreated and pretreated as well as of unstored and stored stainless steel surfaces. Furthermore, the adhesion of pretreated and stored specimens was determined by the tensile-strength-test of butt joints (according to EN 15780).
Understanding the molecular details of adhesion and adhesive failure is challenging and progress in this field is slow. Whether it is adhesion and delamination of paints and glues, adhesion on metals, oxides and compound materials used in light weight applications, or adhesive interactions in tissue gluing: Empirical trial and error dominates the engineering world, while knowledge-based structure property design is limited by a lack of fundamental understanding.
Experimentally and theoretically, it is very challenging to understand and predict interactions at adhesive interfaces from a molecular viewpoint. In particular, predicting adhesion and adhesive failure relies on understanding the scaling of single molecule interactions towards integral interactions at the meso- and macroscopic scale. Single molecule experiments at interfaces are by now state-of-the art in fundamental science, yet bridging the gap to realistic interfaces where multiple molecules interact simultaneously was a fundamentally difficult task.
I will discuss our recent exciting advances that allow us to directly predict the scaling of individual single molecular interactions towards the macroscopic level, where a large number of bonds interacts simultaneously. We developed a synergistic experimental and theoretical approach combining macroscopic adhesion experiments, single molecule adhesion measurements and scaling theories based on non-equilibrium thermodynamics. I will in detail discuss how the adhesive interaction of acid/base bonds, metal/amine bonds and hydrophobic interactions on the single molecular level can be measured and utilized to predict macroscopic level adhesion. In addition, I will also demonstrate how one particular adhesive bond can be incorporated into an adhesive interface in a variety of different molecular geometries giving rise to quite different adhesive strengths. As such, I will highlight how understanding of adhesion relies on both understanding interaction free energies (thermodynamic quantities) as well as unbinding energy landscapes (path dependent kinetic properties) of individual bonds.
Our novel and unique experimental strategy provides a framework for the knowledge-based molecular design of any adhesive interface. We can effectively predict and in the very near future also tune properties of adhesive interfaces based on single molecule energy landscapes and scaling laws that can be measured quite efficiently with our current technology.
The wide acceptance of glass as a building material encourages many requests for transparent, almost dematerialized appearing building envelopes. This requires glass structures, which are increasingly involved in the load transfer. However, glass is a brittle material. Adhesively bonded connections allow substance‐to‐substance bonds of the adherend parts with a homogeneous distribution of forces while reducing local stress peaks. Besides the usual mechanical connections, load bearing, structural bonds therefore becoming considerably important for glass as appropriate for the involved material.
Epoxy resin adhesives are especially suited for structural bonding for point fixings. A variety of commercially available epoxy resin adhesives is known and has different areas of application, like automotive industry, mechanical engineering as well as construction engineering. For point fixings in glass constructions, e.g. façades or railings, transparent adhesives will be best suited. According to our research and investigations an optimally appropriate adhesive could not be identified so far. Especially the thermal stability and resistance to ageing is insufficient for outdoor applications. Beginning with basic formulations for epoxy resin adhesives, proper starting materials are determined by examination of the thermo‐mechanical, mechanical and chemical properties. This is followed by the study of the ageing stability of the different formulations. The basic formulations are then modified by the addition of fillers and additives. This influenced the mechanical strength and the thermal stability as well as the location of the glass transition region. Even the ageing behavior could be positively changed by these modifications.
Since 1978 with the commercial launch of the silane terminated polyethers or Kaneka MS PolymerTM, Kaneka has been continuously developing new polymers with differentiating properties to expand the application area. The newest generation is the high strength silane terminated polymers, so-called HS Polymers, which will close some existing gaps with other technologies.
It will be shown that the new HS Polymers are upgraded versions of the standard DMS-MS and TMS-MS types. An overview will be given of formulations examples, such as high strength adhesives for DIY repair, (semi-)structural applications, parquet, and more specific improved properties will be shown.
Besides the new polymer grades Kaneka wants to show that the standard MS PolymerTM grades remain a key technology for future. Assembly of light-weight materials with adhesives, joining hybrid materials, etc. becomes more and more important. It will be shown that the properties of MS PolymerTM will overcome the difficulties which arise when plastics or hybrid materials need to be adhered.
Polyurethanes have been used for many years to produce high-performance materials. Croda has extended its range of bio-based polyester polyols, to meet the industry need towards durable and environmentally sustainable materials. The bio-based polyols are valuable for reactive polyurethane adhesives and thermoplastic hot-melts. Furthermore, Croda offers a range of additives from natural resources to prevent blocking or undesired adhesion.
The bio-based polyols show enhanced wetting of the substrate and offer (low temperature) flexibility. The dimer fatty acid based hydrocarbon character imparts an affinity for a wide range of substrates, and offers a unique combination of hydrolytic, thermo-oxidative and UV stability for demanding applications like electronics, sportswear and construction adhesives.
The new polyols are liquid for ease of handling, with a balanced choice of ingredients to improve compatibility with other polyols or (bio-) polymers and enable improvement over commercially available polyester polyols. One grade gives adhesion to dissimilar substrates which matches well with the market trend to lightweight construction in transportation, where metal is combined with composites and plastics. One grade offers extreme flexibility, combined with adhesion to higher polarity plastics and wood, which makes it suitable for lamination, construction and sports goods.
In this presentation an overview about bio based raw materials for the formulation of hot melt adhesives is given. Currently used solutions that are already known to the market are covered as well as recent activities. A future outlook is critically discussed. As an example from Jowat R&D, the development of hot melt pressure sensitive adhesives based on PLA derived polymers will be presented. It will be shown how it was realized to use PLA, which is tough and brittle as pure material, as backbone polymer in pressure sensitive hot melt formulations.
In biological systems, especially our body, healing is a normal reaction without the involvement of any activity. The immune system normally knows exactly when and what to do in order to fight against a damage. The protein fibrin, for example, acts as a curing adhesive in the plasmatic clotting and forms a network that closes the wound. The situation is different in synthetic systems. They are designed to withstand any external influences. They should be permanently stable and should not change their characteristics over the life time. A drawback of this behavior is that they cannot react if any damage occurs.
Self-healing mechanisms, which are incorporated into the material, should eliminate this deficiency. Several approaches have been developed in recent years. This papers deals with different strategies and possibilities of self-healing technologies which can be built in adhesives and in general polymeric materials. An overview about recent developments will be given.
The presentation provides a basic overview on UV technology and explains how it can help medical device manufacturers to improve their production process and quality control. In comparison to heat-curable or solvent-based adhesives, light curing adhesives cure on demand within seconds and allow faster assembly processes resulting in greater throughput. Additional biocompatible additives included in many light-curing materials such as cure indicator and fluorescence, enable further optimization of validation-, production- and quality control processes. With focus on medical devices, the presentation will provide examples on those technologies. For manufacturers, the cure indicator allows destruction-free process validation and easier quality control. A special red fluorescence, patented by Dymax, offers several advantages over traditional blue fluorescing materials. Another topic the presentation will cover is the current trend of switching from broad spectrum lamps to LED curing systems to achieve additional process savings. According to latest developments on the chemistry side LED systems can be used without loss of adhesive quality. In addition, cure indicator and fluorescing technology can be combined and allow manufacturers to fully exploit all advantages these additives provide.
LED light is the future of adhesive curing. Until recently LED-hardening adhesives were limited to free-radical curing acrylates with photo initiators in the UV and visible light wavelength spectrum. With the recent development of new and innovative photo initiators, cationic curing epoxy systems can now also be hardened within seconds.
For acrylates, innovative LED systems were developed which enable curing with longwave UV and Visible light. This technology opens up new fields and applications by allowing adhesives to be cured through opaque and UV-blocked substrates.
Just as with traditional free-radical curing acrylates, speed of cure is dependent on LED light intensity. Fortunately, the new generation of LED curing technology can achieve extremely high output intensities, which leads to faster curing and shorter production times. The combination of innovative LED equipment and newly developed epoxies and acrylates reduces the curing times for adhesives and coatings significantly. Curing depths and bond strength of LED cured adhesives are similar to adhesives cured with traditional broad spectrum UV systems.
Adhesives manufacturers and users have many opportunities to explore in today's world. Crucial is the ability to quickly evaluate new recipes,optimise existing ones, find alternative raw materials. Ultimately there is a need to predict the performance of recipes. We want to show that rheology, or the study of the flow characteristics of materials, is one effective tool to do this. We can use rheology as a central tool enabling a quick, accurate, and straightforward identification of, and even start to predict, adhesive properties. The use of rheology significantly shortens the development process, thereby allowing formulators to create better adhesive systems faster. Rheology also improves the quality and predictability of the data generated when compared with other techniques.
We are on a path to use the combination of Design of Experiments (DoE) plus Rheology (DMA). In a series of lectures, of which this one is the first, we will slowly lift the veil of what the power of this combination is. “The Ideal PSA” model is currently constructed by combining DoE, DMA and standard adhesive testing.
In todays paper we will show the DMA basis - the Luth-Burgers model - describing the rheological response of HMPSA adhesives, display several examples demonstrating the effectiveness of the rheology tool.
Current UV technology is largely used for labels, medical & low end tapes applications. Because of environmental pressure, tapes manufacturers have also been looking for these solventfree products to use them in high performance tapes and close the gap with SB acrylics. The expertise of Henkel in UV curing, acrylic polymer design and historical know how in Hot melt technology were successfully combined into an innovative UV curable hotmelt product family. These products now have the correct adhesion cohesion balance and can finally compete with the performance of solvent based acrylics. They can be tackified if needed and used in applications such as foils, foam, double sided tapes, high shear tapes … Thanks to this patented technology it is now also possible to coat thick layers tapes in one pass, faster curing time and consume less energy. Creating competitive advantage for our customers!
A major share of pressure sensitive adhesives - tapes, labels and films – are being produced with acrylic dispersions or UV-acrylic hotmelts.
Within adhesives tapes however, there are high performance applications which are dominated by solvent-borne acrylics despite some economical and ecological disadvantages.
Consequently, it is a challenging but rewarding task to develop solvent-free alternatives, be it dispersions or hotmelts.
This presentation gives an insight into the toolbox of polymer design which can be applied in the development of solvent-free technologies and shows corresponding application examples.
Adhesives in film form enjoy a variety of application advantages compared to liquid, pasteous or conventional hot melt adhesive systems. With the adjustable, predefined thickness, adhesive films provide a consistent amount of adhesive to the bond line. Adhesive films are tackfree and can be delivered in single or multi-layer constructions. To establish the bond, adhesive films typically require temperature, pressure and time. Within the thermoplastic nature of adhesive films lies also the major limitation which makes them only partially suitable in application areas where high strength at elevated temperatures are required. To bridge the gap between reactive adhesive performance and the easy to use delivery form of adhesive films, latent reactive adhesives were developed and promise a multitude of opportunities. The thermoplastic matrix allows a storage stable pre-application of the adhesive, crosslinking is initiated upon bonding by the thermal activation of a chemically protected reactive component. The presentation will give an introduction to latent reactive as well as thermoplastic adhesive films, their application, uses and benefits.