We have learned from our last article that a structural adhesive, according to 3M, is one that can create a bond with at least 1,000 psi of overlap shear strength to aluminum. Today we are going to go over the different families of structural adhesives 3M has to offer and the differences, strengths and potential weaknesses of each.
Rigid epoxy adhesives are epoxies with less flexibility or ‘stretch’ after they have been cured. They offer tremendous strength between ‘like’ substrates, especially metal. Rigid epoxies are not the best option for dissimilar substrates that are going to contract and expand at different rates.
Flexible epoxies are, you guessed it, more flexible after cure. They may not be quite as strong as rigid epoxies between two similar substrates like metal, but offer stronger bonds between two surfaces that may contract and expand at different rates, like metal to plastic. This ‘stretchiness’ in the bond also gives flexible epoxies a much higher peel strength and great adhesion to most plastics.
Toughened epoxies are exactly what their name implies, tough. They are not particularly flexible but offer extreme bond strength at given elongations and offer excellent fatigue, vibration and shock resistance. Toughened epoxies also have excellent peel strength.
- 3M DP420NS
- 3M DP920 – bonds to metals, oily surfaces
Heat cured epoxies have excellent strength, especially at high temperatures. These adhesives have to be heated themselves to cure. Cure time on heat cured epoxies is 40-60 minutes at around 300 Degrees F.
- 3M 2214
MMA adhesives (also known as methyl metharylates) are a good all-around adhesives for a wide range of substrates. They bond well to most plastics and have high impact resistance on metal bonds. They also require less surface preparation as they are tolerant of many substrate contaminations.
A newer product line from 3M, low odor acrylics are a cutting edge adhesive technology that were formulated to improve on the odor of the traditional MMA without sacrificing strength or cure characteristics. They bond to a wide range of substrates like metals and plastics and have great impact resistance. Like traditional MMA’s, this low odor adhesive is also tolerant of many surface contaminations.
- 3M DP8805NS
- 3M DP810
LSE acrylic adhesives (short for Low Surface Energy) are great for plastics. They are formulated to bond well to Thermoplastic Olefins and plastics like polypropylene and polyethylene. LSE acrylics should bond well with little or no surface preparation.
- 3M DP8010
Urethanes are naturally more flexible than epoxies. These semi-rigid urethanes are formulated to be more rigid with greater long term holding power and strength to like substrates.
- 3M DP600
Flexible urethanes have great elongation properties or ‘stretch’ which makes them perfect for bonding just about any type of plastic. UV resistance and a faster cure time also separate Urethanes from Epoxies.
- 3M DP604NS