Two-Component (2-C)

Two-Component (2-C)

Two component adhesives are 100% solids systems that obtain their storage stability by separating the reactive components. They are supplied as “resin” and “hardener” in separate containers. It is important to maintain the prescribed ratio of the resin and hardener in order to obtain the desired cure and physical properties of the adhesive. The two components are only mixed together to form the adhesive a short time before application with cure occurring at room temperature. Since the reaction typically begins immediately upon mixing the two components, the viscosity of the mixed adhesive increases with time until the adhesive can no longer be applied to the substrate or bond strength is decreased due to diminished wetting of the substrate. Formulations are available with a variety of cure speeds providing various working times (worklife) after mixing and rates of strength build-up after bonding. Final strength is reached in minutes to weeks after bonding depending on the formulation. Adhesive must be cleaned from mixing and application equipment before cure has progressed to the point where the adhesive is no longer soluble. Depending on worklife, two component adhesives can be applied by trowel, bead or ribbon, spray, or roller. Assemblies are usually fixtured until sufficient strength is obtained to allow further processing. If faster rate of cure (strength build-up) is desired, heat can be used to accelerate the cure. This is particularly useful when parts need to be processed more quickly after bonding or additional worklife is needed but a slower rate of strength build-up cannot be accommodated. When cured, two component adhesives are typically tough and rigid with good temperature and chemical resistance.

Two component adhesives can be mixed and applied by hand for small applications. However, this requires considerable care to insure proper ratio of the components and sufficient mixing to insure proper cure and performance. There is usually considerable waste involved in hand mixing as well. As a result, adhesive suppliers have developed packaging that allows the components to remain separate for storage and also provides a means for dispensing mixed adhesive, e.g. side-by-side syringes, concentric cartridges. The package is typically inserted into an applicator handle and the adhesive is dispensed through a disposable mixing nozzle. The proper ratio of components is maintained by virtue of the design of the package and proper mixing is insured by use of the mixing nozzle. Adhesive can be dispensed from these packages multiple times provided the time between uses does not exceed the worklife of the adhesive. If the worklife is exceeded, a new mixing nozzle must be used. For larger applications, meter-mix equipment is available to meter, mix, and dispense adhesive packaged in containers ranging from quarts to drums.

Four major types of two component adhesives include:

  1. Epoxies
  2.  Methyl Methacrylates
  3. Silicone Adhesives
  4. Urethanes

1. Epoxies

Two component epoxy resin based systems are the most widely used structural adhesives. They can be formulated into fast curing systems with 2 to 5 minute worklife that give rigid bond lines which are somewhat brittle. Longer worklife systems usually contain additives to provide flexible or tough bond lines. Two component epoxy adhesives are used to bond metal, plastic, fiber reinforced plastic (FRP), glass, and some rubbers.

2. Methyl Methacrylates

Methyl methacrylate (MMA) adhesives can provide faster strength build-up than epoxy adhesives and are more tolerant of oil on the substrate. MMA adhesives are used for bonding plastics to each other and for bonding metals to plastics. Classic applications for this type of adhesive are in the automotive industry and in rail car manufacturing.

3. Silicone Adhesives

Two component silicones are generally used for production line assembly, e.g. in electronics and the electrical industry as well as in the production of household appliances, in the automotive industry, and for window manufacture. Cured properties are similar to single component moisture curing silicones. Two component silicones are used instead of single component silicones when adhesive film thicknesses of over 0.25 inches (6 mm) are required or for large bonding areas. This type of silicone adhesive is also used when the available humidity in the air does not suffice for the complete curing of single component silicone.

4. Urethanes

Two component urethane adhesives can be formulated with a wide range of cured properties ranging from soft and flexible, to tough and elastic, to hard and rigid. They are used to bond materials with different flexibility or different thermal coefficients of expansion including glass to metal, fiber reinforced plastic (FRP) to metal, and aluminum to steel.

For additional information on Chemically Curing Adhesives, visit: