Methyl Methacrylate adhesives have become a standard for use in the automotive and transportation industry. They combine the strength of a structural adhesive with a unique cure profile that allows them to be applied over large areas and differing materials. In an industry always looking for lightweight and streamlined solutions, MMAs provide an optimal fit.
Ideal "Snap-cure" profile
The most attractive part of MMAs for the automotive industry is their "snap-cure" property. Rather than building up strength slowly over the cure process like epoxies or other adhesives, MMAs remain workable and then cure to a fixture strength in a matter of minutes. That open workable time, as well as curing time, can be tailored to the exact application by changing formulation and mixing ratios. This allows time for large panels of heavy trucks or equipment to be coated with adhesive, and then fixtured as quickly as possible. Use of MMAs in this way can significantly speed up production time by allowing quicker adhering and less time waiting for cure. Full cure is usually reached in 4-24 hours at room temperature.
"MMAs remain workable and then cure to a fixture strength in a matter of minutes."
Flexibility of applications
MMAs also have a number of other properties that make them well -suited to automotive assembly. Importantly, they are insensitive to many common contaminants found in automotive production, like grease and oil. Being able to adhere pieces without first going through a rigorous cleaning process can further streamline production. MMAs can bond with differing surfaces including metal, some plastics and composites in any combination, allowing their use in many different automotive applications. The use of adhesive instead of metal rivets can also create a lighter vehicle, reducing fuel and material costs. It also distributes the stress through the bond area vs localized points. Aesthetically, MMAs can reduce bond-line read-through (BLRT), creating a smoother appearance than rivets or some other adhesives.
MMAs are two-part adhesives that can be applied in a number of ways - including meter mix equipment or mixing nozzles. In some formulations one part can be applied to each surface separately and combined through joining the pieces, known as "bead on bead" application. The ratios can vary according to formulation and desired cure. They are a structural adhesive, with up to 80 or 90 percent the strength of epoxies. MMAs can withstand temperatures up to 120C, and toughened formulations can provide good impact and excellent peel resistance.