HOW TO CHOOSE AN ADHESIVE
There are many different adhesive types out on the market. These adhesives are not all created equal! Knowing how to choose an adhesive is a science in itself.
In this blog post we thought it would be useful to breakdown info on the technical details and show you more about adhesive types and examples how they are used in manufacturing. If you’d like to learn more about how we can help you automate an adhesive process contact us today.
Using the term acrylics can be a bit misleading as some types of anaerobic, UV curable, and cyanoacrylate adhesives are often based on acrylic chemistry. Acrylics are often used for structural applications to replace welding, bolting, or riveting. See below for additional details and examples of anaerobic, UV cure, and cyanoacrylate adhesives.
Anaerobic adhesives are single part adhesives that are free of solvents. These adhesives cure in the presence of air and metal ions. An anaerobic adhesive will stay liquid (or paste) until it is isolated from oxygen in the presence of metals like iron or steel. Anaerobic adhesives can be a challenge for robotic dispensing in high volumes as contacting metal can start the cure process.
Thread locker and mating or gasketing of automotive components are common uses of anaerobic adhesives.
Brazing pastes are used in the brazing process and are a combination of flux and a filler metal(s). Solder pastes help to limit contamination to a brazing joint and uses capillary action to distribute throughout a joint. Brazing alloys can include tin, silver, copper, aluminum, nickel, and gold.
Conductive epoxies are typically two part adhesive that are often used in electronics manufacturing. An epoxy alone is typically non-conductive. A secondary additive, like silver, is used to give epoxy conductive properties. Changing the ratios of the mixture can lead to a variety of compounds depending on the required electrical and mechanical requirements. Conductive epoxies can often be very thick and difficult to dispense.
Cyanoacrylates are typically what most people associate as “super glue.” Cyanoacrylates have a wide variety of uses for medical (wound closure), industrial, and around the home. Cyanoacrylates typically cure quickly and are typically activate by moisture in the air. Biocompatible capable cyanoacrylates are often used in medical device manufacturing.
Epoxy adhesives may be the most versatile of all available adhesives. Epoxies are able to adhere many different types of materials and are high strength. They hold up to chemicals and harsh environments. Epoxies can come in single part or two part varieties. Epoxies have applications in nearly every possible industry including automotive, composites, electronics, food processing, energy, medical, transportation, and construction.
Potting compounds are most widely known for their use in the electronics industry. A potting material, often an epoxy or silicone, is applied to protect internal electronics components from damage due to shock or vibrations. The potting agent is used to “fill up” the component using a mold. After the potting compound has cured or hardened internal components are secured and protected.
Silicone adhesives are flexible and remain highly flexible at high temperatures. Most silicone compounds are inert to interactions with other chemicals and are often used in implantable medical devices. Silicone adhesives tend to be weaker than other adhesives and as a result, silicone is used to seal components rather than being used for bond strength. Silicon adhesives are often used in construction applications, electronics potting and electronics staking, automotive gasket sealing, marine applications, and medical applications.
Silicones use humidity to cure and cure time can be affected by the thickness of the adhesive and the ambient temperature. They can be packaged and delivered as single part or two part varieties that are often easily setup to dispense with robotic adhesive dispensing systems.
Solvent Based Adhesives:
Solvent based adhesive are a mixture of chemicals that can be tuned for desired final performance of the adhesive and how the solvent is applied (liquid, tape, paste). Most solvent based adhesives have a flammable component that evaporates. The remaining film provides the bond between the two materials.
Solvent bonding is a process that uses a solvent to soften or dissolve the material where the materials mix/dissolve together. The solvent evaporates leaving a bond between the two materials. Solvent bonding is often used when a water or air tight seal is required. A wide variety of plastic materials can be solvent bonded including ABS, polycarbonate, polystyrene, PVC, and others.
Room Temperature Vulcanizing (RTV) adhesives are typically a two part silicone compound that cures at room temperature. The resulting cured product is a flexible rubber type compound that can be used as an adhesive, a sealant, potting compound, or gasket sealer.
There are two main types of RTV silicones: platinum cure and tin cure. Platinum cure is often more expensive and cures without the need for moisture. The cure time of platinum cure RTV’s can be sped up with the addition of heat. Tin cure RTVs require moisture to cure and can also be described as condensation cure.
A UV curable adhesive is one that requires a ultraviolet (UV) light source to harden the adhesive. UV cure adhesives are popular in the medical device industry as they can be easy to apply with automated or robotic adhesive dispensing and the UV cure process leaves a consistent and repeatable adhesive joint. UV adhesives join most types of materials and are available with a clear appearance after cure.
One major downside to a UV cure adhesive is that it is typically reserved for applications that allow for line-of-site application of the UV cure light source. As a result, an adhesive trapped between components or that is not visible through clear plastics are not good candidates for a UV cure adhesive.
Urethanes are good all-around adhesives that perform well in a variety of environments. These types of adhesive have good shear and pull strength properties making them tough and resistant to shock and vibration. They are good for bonding dissimilar materials and can come as unmixed two part applications or premixed single part formulas. Urethanes can be provided in small syringe cartridges and up to 55 gallon drums.
Urethane adhesives are used in Hot Melt applications. See next section for more detail.
Hot melt adhesives are what most people commonly refer to as glue guns. Hot melt adhesive have many industrial applications across a variety of industries. Hot melt materials come as a solid at room temperature and soften as heat is applied. Hot melt adhesive are typically fast setting. Hot melt adhesives make good candidates for automated and robotic processing.
There are a wide variety of adhesives on the market and we recommend discussing application with adhesive manufacturers as early in the development process as possible. Use the technical experts… they can guide you how to choose an adhesive. We regularly see poorly chosen adhesives that set manufactures up for long term process and quality issues.
Do you have an adhesive process that is causing headaches for your manufacturing team? Contact us to get some help!