One of the most common types of cyanoacrylates used as instant adhesives are ethyl cyanoacrylates. Years ago, I was told to use methyl cyanoacrylates for metal and ethyl for everything else. That simple saying served me well for many years. Permabond 910 was the original methyl cyanoacrylate. It was formulated over 60 years ago and is still sourced to meet aerospace, automotive, and many other company-specific specifications. Permabond 101 followed not too long after that. Permabond 101 is an ethyl cyanoacrylate that forms strong bonds to most plastics. It too is still sourced for aerospace, automotive, and other industry specifications.
That begs the question, “if the 910 bonds metal and the 101 bonds virtually everything else, why do you keep formulating new grades?” There are currently so many grades of these types of cyanoacrylates and others, as well as blends of types and tougheners, etc., that we no longer categorize cyanoacrylates by their chemical type but by their properties.
Standard ethyl cyanoacrylates are brittle. Toughened ethyl cyanoacrylates are preferred if the assembly will need to withstand vibration, impact, or flexing stresses. Although these are ethyl based, they can have higher shear strength on steel than a standard methyl cyanoacrylate. Permabond 731 and 735 exhibit shear strength on steel to 4400 psi (30 MPa). Although these are marketed as toughened cyanoacrylates, they have some added benefits, namely slower set time and higher temperature resistance. Cyanoacrylates or instant adhesives are often desired due to their fast set time – often less than 5 seconds. In other applications where accurate alignment or a larger area is to be bonded, the super-fast cure time can make processing difficult. Depending on the metal, gap, and humidity, Permabond 735 can take up to 50 seconds to cure on metal. Regarding temperature resistance, most cyanoacrylates have a lower service temperature limit of -65°F (-55°C), and the higher temperature limit varies as listed below:
- Standard Ethyl and Low Odor Ethyl 180°F (82°C)
- Standard Methyl 195°F (90°C)
- Toughened Ethyl 250°F (120°C)
- Modified Ethyl 390°F (200°C)
- Allyl 480°F (250°C) – To achieve the high temperature resistance a secondary heat cure process is needed. After curing at room temperature for 4 hours, heat the clamped parts at 302F (150C) for 2 hours. Note without the secondary cure process, these cyanoacrylates resist 180°F (82°C).
Permabond Alkoxyethyl cyanoacrylates are low-odor, non-fogging, non-frosting, and non-blooming. They are ideal for dark surfaces. Specialty grades are available for infiltrating 3D Granular Print Models (3D10, 3D30, 3D90). This process can involve dipping the model into an open cyanoacrylate bath.
Cyanoacrylates cure by reacting to small traces of moisture on the surface of the substrates being bonded. Porous and acidic surfaces like wood, leather, and paper can be challenging for standard ethyl cyanoacrylates. Permabond surface insensitive ethyl cyanoacrylates (including 790, 792, 795, 799, 2011) overcome these challenges.
In short, the answer to the question “Why do you keep formulating new grades?” is because we love a challenge and love to push the limits of technology but mostly because our customers ask us to.