Adhesive bonding
The first use of adhesives by humans can be dated to around 220,000 B.C., when tar from birch tree bark was used to glue stone arrowheads to a shaft.
Therefore, good wetting of the materials to be joined by the adhesive in its liquid state is required to produce a high quality bond.
This leads to an increased mobility of the plastic's polymer chains, which in turn allows penetration by those of the adhesive.
Due to the short range of the adhesion forces, the nature of the surface layer of the substrate is crucial.
Likewise, contaminants, especially those which, due to their low surface tension, counteract wetting by the adhesive (for example, oils, release agents, etc.)
They allow the gluing of sheet metal parts with corrosion protection and drawing oils without previous cleaning; The curing of the adhesive takes place in the furnaces used subsequently for hardening the lacquer at temperatures between approximately 150 and 200 °C.
Therefore, when planning a bonding operation, in addition to the actual environmental conditions, their possible long-term effects on the adhesive and substrate must also be taken into account.
As with any joining technique, bonding technology not only offers a wide range of possibilities and many advantages, but also has limitations that must be considered when planning and designing adhesive processes.
This film ensures among other things that the windscreen remains intact as a unit after fracture, thus minimising the risk of injury from glass fragments.
This is only possible through the use of an adhesive with the correct mechanical properties for the application; on the one hand, the adhesive offers sufficient strength to secure the windscreen to the bodywork and, on the other hand, it is sufficiently elastic to compensate for relative movements between the bodywork and windscreen during driving, thus preventing breakage.
Due to the small size of the control devices, sensors, cameras, etc., the capabilities of conventional joining technologies are soon exceeded.
In order to ensure the proper functioning of the control units and associated sensors, the electronics must be safely protected from external influences, such as moisture, salt, fuel and other automotive fluids.
To ensure adequate EMC, metal housing is used in which the lid is glued by means of special fillers containing adhesives.
Based on the fact that the wafers are not in direct contact, this procedure enables the use of different substrates, e.g. silicon, glass, metals and other semiconductor materials.
A drawback is that small structures become wider during patterning which hampers the production of an accurate intermediate layer with tight dimension control.
[6] Further, the possibility of corrosion due to out-gassed products, thermal instability and penetration of moisture limits the reliability of the bonding process.
[7] Another disadvantage is the missing possibility of hermetically sealed encapsulation due to higher permeability of gas and water molecules while using organic adhesives.
The simple plaster for example has to have good adhesion to a variety of skin types, but also be as painless as possible to remove.
In addition, transdermal patches deliver medication over a longer period of time through the skin into the bloodstream, others are used for the long-term attachment of sensors used for example for the continuous measurement of blood sugar levels.
These patches must stick securely for up to 14 days, sometimes under extreme conditions, for example, when showering, swimming, exercising or in a sauna.
Often, light-curing adhesives are used, which attain sufficient strength after a few seconds of irradiation with light of a certain wavelength and are able to survive the subsequent sterilisation process, during which they can be subjected to superheated steam, ethylene oxide or gamma radiation.
For example, temperature-stable silicone adhesives are used in the production of ceramic hobs or sealing windows in oven doors.
Compared to fastening by means of a metal clamping ring, gluing offers advantages in the manufacturing process by avoiding breaking the jugs.
The adhesive used must, among other things, have enough strength, be dishwasher safe, and have sufficient elasticity to compensate for the different thermal expansion behaviour of glass and the plastic material of the handle to prevent glass breakage, and it has to maintain this performance over the entire life of the coffee machine, even at temperatures up to 100 °C.
In addition, the production of multifunction devices, such as those that facilitate cooking, stirring, kneading, mixing and grinding, would be impossible in their current form without modern adhesives.
Light-curing adhesives ensure that the rotor and stator, the two main components of the motor, form a robust unit.
The curing of the adhesive takes place within a very short time, so that high quantities of the device can be produced cost-effectively.
This is achieved by the use of molecules of naturally occurring polymers, such as cellulose and starch, which can be degraded to water, carbon dioxide and biomass by microorganisms using enzymes.
At that time, stamp adhesives consisted of naturally occurring raw materials such as molasses, potato starch and occasionally fish glue, but these performed poorly.
With the growing use of bonding technology in industry and professional trades, and the resulting, increasing demands on the quality and durability of glued products, comprehensive national and international standards have been developed for, amongst other things, the characterisation, classification and testing of adhesives and adhesive bonds.
