Product Formulation

Adhesives are a classic example of a ‘reactive formulation’: they need a stimulus to invoke curing, whether this is deliberately applied (such as heat or pressure) or spontaneous (such as a redox-activated cure on contact with a metal surface).

I’ve spent much of my career immersed in the design of adhesives and their components, with particular focus on cyanoacrylates (CAs), the well-known active components of instant adhesives. I know this chemistry in great detail, and am happy to share that knowledge.

As a very mature field, it could be considered that there is little left to do with cyanoacrylates, but this is never the case, and new markets await those who are prepared to apply fresh thinking – such as the radiation-sensitive formulations described in the examples below.

Although cyanoacrylate (CA) adhesives cure instantly on contact with a surface, reliable volume curing requires the action of UV light – a technology that has been applied in industry for over 20 years. But could consumers benefit from the same concept? As well as performance-based and regulatory requirements, other challenges are the unpleasant odour of standard industrial CAs, and the need to avoid powerful UV light sources.

But by using odour-free CAs, an initiating system receptive to a low-powered blue LED (described in this patent), and an innovative product design, we were able to overcome these issues during my time at Afinitica. The resulting ‘Fix & Flash’ product created a significant market opportunity, and has been very well received by customers.

It is commonplace for plastic components to be laser-welded together, but the mechanical clamps that are used to temporarily hold the parts together are time-consuming to set up, and inherently restricted to flat-topped parts.

To resolve this, when I was part of the team at Henkel we used existing IR dyes with instant adhesives to provide a novel (and patented) infrared-absorbing CA formulation. This acts as a ‘chemical clamp’, streamlining the manufacturing process, and allowing the processing of complex part shapes – such as stylised automotive lamp clusters whose curves can be tracked by laser-welding robots.

Breaking into new application areas demands ever more from the components of a formulation. Such formulations comprise not just the monomers themselves, but co-monomers to modify properties, initiators to trigger a change, viscosity modifiers, plasticisers, and functional additives.

Understanding how these components will interact in particular scenarios is challenging. Reactive formulations are expected to remain shelf- or pot-stable until used, but raised expectations lead to the need for more ‘tinkering’ with fundamental components, which may provoke unwanted instability.

It’s not an easy task to find a balance between economically integrating new product features, ensuring stable formulations, and creating enduring value. But it pays dividends when achieved, and I can help find that balance in your product developments.

The adhesive ‘threadlockers’ used in industry only act in contact with metal and in the absence of air. But this redox-based chemical signalling only extends tiny distances from the metal surface, meaning that an incomplete cure can result if the joint is not perfect or the parts are not microscopically flat.

Within my position at Loctite, we were able to overcome this issue by using certain onium salts, which allowed the chemical signals to extend further into the bondline – so-called ‘centerline’ curing. Monitoring the efficiency of this cascading effect was the subject of the first industrial Ph.D. project I initiated, published in this journal article and this patent.