AronAlpha Blog

Understanding How Cyanoacrylate Industrial Adhesives Work

Posted by Mark Tansky on Jan 26, 2018 3:12:52 PM

As modern adhesive technologies advance, manufacturers are progressively interested in understanding the use of adhesives in product assembly applications and what benefits are offered over mechanical assembly methods such as welding, rivets and threaded fasteners. This post will help you gain a better understanding of how cyanoacrylates work and why they are a good choice as it relates to alternative fastening techniques. 

Industrial adhesives are frequently specified in the design phase of product assembly development by Design Engineers.  Often Process Engineers and Quality Engineers will circle back to adhesives in order to correct or overcome a design flaw or process bottleneck during the fine tuning stage of product launch in a manufacturing environment.  Adhesives are frequently used in bonding automotive subassemblies, aerospace components, musical instruments, appliance part assembly and even in disposable medical device applications. These industries have learned to employ adhesives due to their ease of use, low cost, low weight, fast cure speed, robust bonding performance, and aesthetic appearance or to unlock new possibilities that are not possible when using “traditional” AAcyanoFamily_2-1-216x300.jpgAAcyanoFamily_2-1-216x300.jpgfasteners. As an overview, Cyanoacrylate is the chemical name for what is commonly known as “Krazy Glue” or “Super Glue”. In fact, the term cyanoacrylate generally describes a one part, room temperature curing adhesive that are available in a wide range of viscosities from water thin liquids to thixotropic no run gels.  When cyanoacrylates are pressed into a thin film between two mating substrates, they cure rapidly to form rigid thermoplastics with excellent adhesion to many substrates used in today’s product assembly environment. The main ingredient in instant adhesive is cyanoacrylate esters (ethyl are the most common), which is an acrylic monomer (liquid) that transforms to a polymer (solid) state after curing. Cyanoacrylate adhesives also differ from traditional glue due to their special bonding conditions. Where as water-based and solvent based adhesives evaporate during the curing process or epoxy requires a two part system to initiate cure, cyanoacrylate relies on the atmospheric and surface (humidity) moisture as its catalyst.  This means if the adhesive is placed on a perfectly dry surface, it will be a challenge to change from a liquid to a solid and create a strong, durable bond.

In contrast, when any amount of moisture is present, the molecules in the cyanoacrylate adhesive will react with the moisture to form long polymeric chains in between the two surfaces in contact. This reaction generates exothermic heat and occurs instantly, which differs from traditional glue bonding that occurs by evaporation of the base fluid. Curing is an important component for all adhesive types and should be considered when choosing the right type of adhesive for specific applications.

Broadly speaking, curing is defined as the process where a chemical reaction takes place to form harder and tougher linkages in a chemical substance. For some materials, this process will only occur at specific temperatures or humidity levels. For many non-cyanoacrylate glues, curing can be facilitated by radiation, heat, mixing, evaporation or UV light.

As mentioned above, curing for cyanoacrylate glues is facilitated by the presence of moisture and occurs almost instantly at ambient temperatures. The bonds formed during curing are also extremely rigid but very strong, hence its nickname of “super (strong) glue”.    

Like all other products, there are potential issues to consider when deciding if cyanoacrylate glue is the right choice for your application. One of the main problems is the possible lack of bonding occurring between the glue and a surface. This may be due to an absence of moisture on the surface or atmosphere, acidic nature of the substrate or the chemical composition of the substrate (polyolefin and other difficult to bond plastics such as fluoropolymers and acetal resins) which makes it inert and tough to bond.

These types of issues can be overcome by utilizing complementary chemistries called accelerators (setters) which speed the cure of cyanoacrylates on dry or acidic surfaces while a surface primer can be used on polyolefin plastics (polypropylene or polyethylene) which enable cyanoacrylate to form strong bonds.

Another problem you may experience is cyanoacrylate’s tendency to form strong bonds with undesirable surfaces, such as your operator’s skin. This is a common problem, because the human skin is constantly perspiring and generates a layer of moisture, creating conditions for the cyanoacrylate glue to cure.

This problem can be easily solved with the help of acetone, commonly known as nail polish remover. Acetone can chemically dissolve the strong bonds occurring in the cyanoacrylate adhesive without harming your skin. It can also be used to remove residue from any surface. 

The last issue with cyanoacrylate adhesives stems from its chemical composition. Because they are so strong and fast-acting, cyanoacrylate glues have a relatively short shelf-life and should only be purchased when needed for your assembly process. Specifically, they have an average shelf life of one year from the date of manufacturing, and one month once the glue has been opened and exposed to your manufacturing environment. Do not purchase them in bulk or stockpile for future use.

Summary

Cyanoacrylate adhesives are the proper name for a type of glue commonly known as Super Glue or Krazy Glue or Instant Adhesive. Their name derives from the strong bond they can form with any surface in the presence of moisture.  Advantages include one-part adhesive system, solvent free, rapid room temperature curing, excellent adhesion to many substrates, easy to dispense in automated systems, wide range of viscosities, excellent shear and tensile strength.

Disadvantages include poor peel strength, limited gap cure, poor solvent resistance, low temperature resistance (up to 250 F) and bonds skin instantly.

For more information on selecting the right cyanoacrylate industrial adhesive and how you can improve your productivity in your assembly process, contact us at 1-800-338-5192 or email us at sales@aronalpha.net.  You can also visit us on the web at www.aronalpha.net.

Topics: Cyanoacrylate, Instant Adhesives