Cyanoacrylate adhesives (CA adhesives) — also called “super glues” or instant adhesives — are popular in many industrial and domestic applications.
Cyanoacrylates are molecularly composed of acrylic monomers stabilized by a weak acid. When an acidic stabilizer is neutralized by a weak base, typically water, polymerization into a long-chain polymer occurs. CAs can be made from a variety of monomers, but the most common is ethyl cyanoacrylate (ECA) and methoxyethyl cyanoacrylate (MECA).
These glues are simple to use, cure quickly, have a high throughput, and can be used to bond a variety of substrates such as metals, plastics, elastomers, ceramics, and porous materials. They are the only single-component fast-bonding adhesives curing in ambient conditions without the need for an external energy source.
However, there are still myths about CA adhesives due to their unusual properties and quirks. We debunk some cyanoacrylate adhesive myths here.
1. Same properties for every cyanoacrylate adhesives
Be noted that consumer CAs found at your local hardware store do not represent the capabilities of all cyanoacrylate materials. Newer market entrants aimed at industrial and technical markets have been developed to overcome some of the historical challenges and broaden the applications of CAs.
Cyanoacrylates are manufactured in a variety of formulations, each with its own set of viscosity, thixotropy, cure time, bond strength, and other characteristics. There are materials available for every application, from hobbyist woodworkers to electronics manufacturing to medical-grade skin bonding materials for wound closure.
2. Brittle
While cyanoacrylate adhesives are brittle in general, some are less brittle than conventional products. Rubber-toughened formulations may provide advanced impact resistance. When compared to other grades, these formulations have better shock resistance and peel strength, as well as a longer setting time while being specially formulated to achieve the toughest possible bond between well-mated, non-porous surfaces. They provide more flexible bonds by offering better resistant to impact, humidity, and temperature.
3. Low maximum operating temperature – around 80 ˚C
While most CA glues have a maximum recommended operating temperature of 80˚C, there are several products on the market that offer higher temperature resistance up to 200°C.
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4. Blooming issue
Blooming is the name given to the chalky white residue that appears on the surface of the part as a result of CA’s volatility. While blooming has no effect on bond integrity, it can be aesthetically unappealing. CAs based on MECA monomers are less susceptible to blooming because they are less volatile than ECA products.
Recent advancements have developed low-blooming MECA materials with fewer compromises and an additional light-curing mechanism. It combines the fast-curing properties of ECA-based CAs with the low-blooming properties of MECA-based CAs.
5. Unpleasant odor
Cyanoacrylate adhesives are noticeable for their distinct odor. It is critical to work with traditional CAs in a well-ventilated area and with the proper protective equipment. An appropriate dispensing methodology can reduce the need for handling while also improving health and safety. However, not all CAs have a strong odor; low-bloom formulations have a low odor as well.
6. Manual dispensing techniques only
It is not necessary to apply a CA directly from the tube or bottle. Cyanoacrylates can be dispensed as part of a manual, semi-automated, or fully automated process, depending on the level of accuracy and repeatability required, as well as the throughput of the application.
For instance, for a semi-automated and precise dispensing technique, you can combine a pressure pot or reservoir with a suitable diaphragm dispensing valve. Mounting this equipment on a robot to fully automate will result in a methodology requiring very little operator intervention.
Finding an adhesives supplier who is also experienced with the relevant dispensing and automation equipment is the key to establishing a successful dispensing methodology.
7. Gap filling not available
Because most cyanoacrylate adhesives have a low, runny viscosity, they don’t work well when there are gaps to fill, the parts are porous, or the bond line orientation causes the adhesive to drip or run out.
Nevertheless, now CAs are available in a variety of viscosities for gap filling. The high viscosity formulation prevents running on inclined or vertical surfaces during the 3 to 60-second fixture time, allows for gap filling of up to 0.5 mm or more, and minimizes adhesive absorption into porous substrates to ensure a good bond.
8. Poor moisture and solvent resistance
This is generally true, and it has limited their use in many industrial applications in the past. Actually, these glues are more resistant to non-polar solvents like IPA. And while it may seem counterintuitive, cyanoacrylate adhesives are more chemically resistant to petrol than they are to water.
However, recent advances in chemistry, such as hybrid chemistry, provide superior moisture resistance with a very small reduction in adhesive strength after 1000 hours in water and significantly improved compatibility with polar solvents.
9. Invalid for structural adhesive
CA bond strength has previously been compromised by temperature and moisture/humidity, limiting their use in load-bearing applications. Advanced formulations, on the other hand, have extremely high impact resistance and toughness. It exhibits structural bonding performance to steel, ABS, PVC, phenolic, and polycarbonate, among other substrates, and has exceptional adhesion to aluminum. It is a good candidate for testing for a structural industrial application due to its higher temperature, moisture, and solvent resistance.
