One Component Or Two?
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 component 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 component 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 component adhesives cure when they are combined and generally no external factor such as moisture, heat, or light is required.
Generally speaking, two component adhesives have 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 the small amount of moisture on the surface of the components and very quickly bond a variety of substrates. Although they are ideal for many applications, they are not suited 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 maybe more suitable.
A variety of epoxy and acrylic adhesives are manufactured as two component systems. When it comes to two components there are several means of combining. The most common is the standard 1:1 ratio two component epoxy, acrylic, or toughened acrylic which can be hand mixed or pre-packaged in a dual cartridge and dispensed via a static mixing nozzle. This method offers the advantage of dispensing only one bead of adhesive. Other products are available that are designed to be dispensed on top of each other – commonly called bead on bead acrylics. This method eliminates concerns over pot life as the adhesive is not pre-mixed. A bead of one part is dispensed on top of a bead of the other part. Parts should be assembled immediately after the second bead is dispensed. A third option called two part no mix or surface activated acrylics offer more time between dispensing and assembly as the activator is applied in a very thin film to one surface and the adhesive is applied in a bead on the other. When the components are 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.