Understanding Surface Insensitive and How It Relates to Cyanoacrylate Adhesives
Regular Cyanoacrylate Adhesives (CAs) have certain traits that can inhibit cure times. However, when companies formulate a surface insensitive CA, they react much faster than traditional glues. The speed of reaction does not relate to inactive or active surfaces, nor does it relate to ambient, or surface, temperatures.
Characteristics of Cyanoacrylates
Cyanoacrylate Adhesives require a weak base, or moisture, to react, as these types of glues are acid-stabilized. For traditional Cyanoacrylates, this means that any acidic substrate, such as paper, or acidic residues, like lemon juice or vinegar, or certain types of steel, can inhibit the adhesion. The curing time may increase, and the bond may not strengthen.
However, overall Cyanoacrylates are among the fastest and most robust adhesives available. When scientists first developed super glue, the first Cyanoacrylate widely recognized by the public, the quick fixture times and usefulness were very attractive to consumers.
Developed in the 1950s and sold to the Loctite Corporation in 1960, over the ensuing decade, scientists refined the formulas and developed new products for different target markets.
For example, rubber-toughened Cyanoacrylates had tougher resistance to impact and a greater peel strength than the original formula. Other types included thermally resistant Cyanoacrylates that allowed the use of these special adhesive mixtures in environments where temperatures reached as high as 250 degrees Fahrenheit.
Surface Insensitive Cyanoacrylates
One of the most popular and useful developments came in the form of surface insensitive cyanoacrylate adhesives. Surface insensitive means that the acids in substrates does not affect the cure rate like the general-purpose cyanoacrylates.
These glues had the advantage of offering very quick cure and fixture rates, even on very acidic surfaces like wood and dechormated metals. They also have high shear and tensile strengths.
Advantages of Surface Insensitive Cyanoacrylates
Surface insensitive Cyanoacrylates provide consistent and reliable curing. This makes them ideal for manufacturing applications and assembly lines. Surface insensitive glues have an additive called crown ether, which neutralizes surface acids on the substrates, and requires much less moisture to combine and form the bond. This vastly increased the effectiveness and ability of this type of Cyanoacrylate to bond together substrates that regular Cyanoacrylates had difficulties with due to the acid content.
Blooming and Surface Insensitive Cyanoacrylates
Small, volatile monomers in Cyanoacrylates, when a bead line is formed during application, results in outgassing when curing. The volatiles, as they are called, fall onto the surface of the assembly line substrate, causing a hazy white color, or blooming. In electronics, blooming causes malfunctions and can lower quality control percentages significantly. Newer types of surface insensitive Cyanoacrylates, called low odor/low bloom, minimize or eliminate this problem, increasing productivity for end users.
Cyanoacrylates had some limitations in the early years due to the somewhat brittle nature and lack of flexibility. New products have been developed, and now many of the different formulations of Cyanoacrylates are classified as highly flexible. This important characteristic translates to fewer tears on stress concentration points.
Types of Surface Insensitive Glues
Loctite produces several kinds of surface insensitive glues ideal for commercial use.
This Henkel Loctite formulation has low viscosity with excellent peel strength and flexibility. It provides strong adhesive bonds between metals, plastics, wood, paper, leather and fabric. Loctite 435 has excellent shock and vibration resistance, making it ideal for certain manufacturing applications. It is also CFIA listed for food packaging. Full cure time is 24 hours at a full cure temperature of 77 degrees Fahrenheit.
This very versatile, all-weather adhesive works on just about any surface and dries within 30 seconds of application. The clear adhesive cures at room temperature and strengthens the bond by as much as 3500 psi. The non-foaming formula, with a low odor, makes it suitable for many different commercial purposes, both indoors and outdoors.
This is another low-odor and low-blooming super glue. Clear, with a fixture time of 40 seconds, this Cyanoacrylate is also considered non-sag, meaning the adhesive will not drip during application. The full cure time is 24 hours. You can also purchase Loctite 455 in a 10-gram syringe, 20-gram tube or in an 850-gram cartridge and case pricing is available, as well.
This rapid repair glue withstands a wide temperature range, providing a quick and sure bond wherever needed. It has excellent wide-gap filling properties. Since it is non-sag, the repaired surface remains rigid, allowing better accuracy during application.
It is a two-compound formulation, great for general purpose repairs on things like various plastics, rubber, wood or other porous materials. Many companies use Loctite 3092 for auto repairs including mounting brackets, tail lamps, headlamps, and interior and exterior trim parts.