When designing a manufacturing process with adhesives in mind, one of the first questions that arises is “Will the adhesive be one component or two?” (I.e. will it just be one liquid, or will there need to be two that are some how mixed together?). Often it is assumed that one part processes are more efficient and easier to control. Although this is often true, many engineers are surprised to learn the process flexibility two component adhesives offer.
One part adhesives cure through a variety of means, including; moisture, heat, and light. So although they come as one “component” the second “component” is the external factor that affects the cure such as moisture, heat, or light. Two part adhesives cure when combined, and generally, no external factor such as moisture, heat, or light is required.
Generally speaking, 2 component adhesives have a longer shelf life at ambient temperatures. Single component adhesives may have a shorter shelf life and require care to protect against moisture, heat, or light.
In addition to the obvious strength and environmental resistance requirements of the finished bond, application, and process preferences assist in product type selection. Types of single component adhesives include cyanoacrylate, epoxy, and UV light cure. Cyanoacrylates cure with a small amount of moisture on the surface of the substrates and very quickly bond a variety of substrates. Although they are ideal for many applications, but not for applications that require aligning the components after assembly, as the cure occurs too quickly. For those types of applications, UV light cure adhesives offer more control. However, if light curing isn’t an option due to opaque substrates, single component epoxies may be in order, providing the components can withstand the heat required to cure. If not, two components may be more suitable.
A variety of epoxy and acrylic adhesives are manufactured as two component systems. There are several means of combining the parts.
The most common is the standard 1:1 ratio two component epoxy, acrylic, or toughened acrylic. You can hand mix them or purchase as pre-packaged in a dual cartridge and dispense via a static mixing nozzle. This method offers the advantage of dispensing only one bead of adhesive.
Other products are available that you can dispense on top of each other – commonly called bead on bead acrylics. To use, dispense a bead of one part on top of a bead of the other part. The assembly immediately.
A third option, called two part no mix or surface activated acrylics, offers more time between dispensing and assembly. Apply a thin film of activator to one surface and a bead of adhesive on the other. When assembled the spreading action that occurs when the bead of adhesive squeezes thin mixes the adhesive with the activator.
So keep in mind that one component doesn’t always mean one step, and two component doesn’t always require two steps.
