Curing without compromise

Dual-curing adhesives offer you the benefits of light-curing without compromising reliability, bond strength or processing quality. They also ensure that, ultimately, the adhesive is fully cured. Additionally, they offer a high degree of flexibility in production and allow more freedom as you develop your production process.

Most manufacturing companies prefer light-curing adhesives to achieve high production yield. However, light-curing processes have their own set of limitations. Therefore, DELO focused on pushing these limits further by developing dozens of dual-curing DELO DUALBOND products.

In a vast number of industries, including automotive, electronics, and mechanical engineering, bonding has gained preferability due to adhesives’ lightweight construction, miniaturization, and multi-material design. Adhesive are also increasingly being used as sealants to protect components from environmental influences.

Companies which mass-produce their goods prefer light-curing adhesives, as their high positioning accuracy—allowing components to instantly fix upon first contact—promotes high yields. Once applied, the adhesive does not creep beyond the bondline, which can happen with, for example, oven-cured products.

Light-cured adhesives achieve full strength within seconds when irradiated; in special cases, even less than one. This is achieved with high-intensity LED lamps that generate 100–1000 times that of normal daylight within their specific light spectrum. These adhesives, however, still have their limits given some of their applications can reach temperatures of more than 150 °C and make regular contact with corrosive chemicals, oil, and acid.

Where there is light there is also a shadow

When two components are bonded, it is important that all the adhesive dispensed is fully cured. If light only reaches some of the adhesive, in shadowed areas, it will remain liquid. This puts components at risk of corrosion, or in the case of optical products, an undesirable effect on the light path. If you intend to use light-curing adhesives, your design should avoid including such shadowed areas.

The adhesives industry has developed many new dual-curing products for situations in which shadowed areas are unavoidable. Aside from light, they use a second curing mechanism so that adhesives can bond reliably, even in shadowed areas. This may either come in form of humidity, oxygen exclusion, heat, mixing the resin with hardener to create a two-component product, or in its latest version, as Activation on the Flow technology. Each option fulfills different requirements and enables various manufacturing processes. All of these products are isocyanate- and silicone-free, with the exception of UV silicones.

Light/anaerobic-curing adhesives

If your requirements are more demanding, anaerobic curing can be used instead of humidity as a secondary mechanism. Light/anaerobic-curing adhesives offer high levels of strength and temperature ranges up to 180 °C. They can be used for challenging applications in electric motors with high heat dissipation levels. They are also resistant to automotive chemicals such as brake fluid, oil, and road salt.

Light/anaerobic-curing adhesives are based on so-called “metal adhesives” widely used in mechanical engineering, such as thread lockers. Therefore, they need metal ions and oxygen exclusion to fully cure in shadowed areas. They offer two benefits compared to traditional methacrylate metal adhesives: Firstly, production yield is higher due to fast light fixation. Secondly, the adhesive cures on the fillet where air would otherwise be found. Both the light-cured and anaerobic-cured areas share similar properties. If sufficient enough metal ions are present, these adhesives do not require an additional process to cure in shadowed areas.

The third option is light/heat-curing materials, in which heat is applied to achieve full bonding strength. This group is the most diverse, as it offers products based on epoxy resins and acrylates, and other chemicals, many of which are used in optoelectronics thanks to its high transparency and low yellowing and outgassing.

Epoxides tend to display higher strength; they are harder, and because of their denser network, more resistant to chemicals and high temperatures. Some of these products are so resilient that they can be used in modules which constantly make contact with hot transmission fluid. Acrylates are softer and therefore more flexible and tension-equalizing, letting them better compensate dynamic stress. An example of this is the attachment of decorative trims and cockpit elements in cars where component tension needs to be equalized within a temperature range of -40–100 °C.

These product groups share a common trait in that they fix components with UV or visible light within a few seconds, thus ensuring high precision compared to standard products. Shifting of components both before and during heat curing is avoided.

Convection ovens are usually used to supply the heat necessary for final curing. Alternatively, tunnel, induction, or thermode ovens can be used. Typical temperatures sit at around 100 °C while the most reliable products need at least 120 °C and temperature-sensitive components can be bonded with other materials at as little as 60 °C. This way, high precision, defined production processes and short cycle times can be combined with low thermal stress.