Feature 40 years of fastenings & adhesives
Sticking with history
where more traditional adhesives would soak in to the substrates. This formulation was also especially helpful for overhead applications, where a liquid CA might drip.
The 1980s also saw the introduction of Polyolefin primers. Prior to this innovation, the bonding of certain plastics with CAs was difficult. The primer meant that cyanoacrylates could be used as a reliable bonding solution for both polypropylene and other polyolefin materials.
The next major innovation saw manufacturers like Henkel introduce a range of light curing cyanoacrylates. These versatile adhesives combine the capability of curing joints that are exposed to a suitable light source with the assurance of the standard cyanoacrylate mechanism in areas shadowed from light.
Adhesives have been around for 6000 years, and yet they are still continuing to evolve and improve. Colin Chapman of Henkel reflects on developments in adhesive technology over the last 40 years
dhesives have been around for a great deal longer than Design Solutions magazine – about 6000 years in fact. Nevertheless, it is fair to say that since the launch of this magazine, there have been a number of significant developments that have greatly benefitted designers and engineers.
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The basic purpose of adhesives has remained the same – to bond two surfaces in such a way that a joint remains secure. However, the expecta- tions involved in that goal have changed over the years – particularly with regards to the introduction of dif- ferent substrates, the need to reduce costs, and the requirements to consider the environmental impact of materials. Although there are a number of adhesive technologies available, for the purpose of this history we are focussing on three product areas: cyanoacrylates, anaerobics and epox- ies. With these, there have been some significant developments over the past four decades.
Design Solutions 1971-2011 Cyanoacrylates
These Instant Adhesives – sometimes referred to as Super Glues – have been around since the 1940s. At first, the cyanoacryate (CA) technology was not thought acceptable on the grounds that it was ‘too sticky’. While this shouldn’t be a dilemma for an adhesive, the speed of cure did present problems. Fortunately, though, for designers who have now come to rely on these adhesives for many areas of their work, new formulations in the 1950s saw their re-emergence as a viable bonding medium, and developments have continued since that time.
The 1970s saw the introduction of chemistry that would meet the need for even faster curing times. This reformulation also fulfilled the need for longer shelf life. Move forward around ten years, and the next major development hit the market – a gel cyanoacrylate. With its high viscosity, this product rapidly found support from those who needed to bond porous materials in circumstances
- 40TH ANNIVERSARY SUPPLEMENT -
This picture, taken about 30 years ago, shows that sheet metal bonding adhesives have stood the test of time – similar products are still being used today
Beyond those developments, CAs have been launched that can be used on high temperature applications, up to 120°C in some cases. Such products are chiefly suitable for bonding compo- nents in loudspeakers, transformers, drill motors, disk drives, automotive parts and household equipment. Within the last couple of years, a new cyanoacrylate has been developed that significantly increases the versatility of instant adhesives. This pioneering two-part product provides all the long-established benefits – an initial bond within seconds, clear bondline, high strength and easy dispensing – but also allows any exposed adhesive remaining outside of the joint to harden within two to four minutes. This further advantage removes the need for a post-assembly activator.
Furthermore, larger gap sizes can be readily accommodated. The new adhesive, known as Loctite 3090, will bond together close fitting parts in 20 seconds. Even where the gap is 3mm, bonding is achieved in less than 90 seconds. The product can also be used where a gap of up to 5mm is involved. It can be used on a variety of substrates, including plastic, rubber, wood, stone, leather, fabric or metal, is capable of withstanding a force of some 20N/mm2. Application is very easy – with the adhesive available in a pack containing a dual syringe with seven mixer nozzles. These syringes not only ensure a clean application, but also that the correct ratio of each component part of the adhesive is always applied. Its gel viscosity means the adhesive can be used for vertical or overhead applica- tion, and it can be used in a temperature range of between -20°C and +80°C.
Anaerobics
This adhesive technology came into existence about 20 years before Design Solutions first hit the streets. The basic
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