B-stage epoxies are partially cured polymer adhesives that are solid at room temperature. The incomplete polymer material contains all the reactive ingredients necessary for 100% polymerization, however, this reaction is designed to advance very slowly at room temperature. As a result, these solid materials can be easy applied to your desired interface weeks or months after the intitial partial cure. The solid material can then be wet back out and completely polymerized with heat.
Is a B-stage epoxy right for your application? This blog post will dive deeper into B-stage epoxies and explore some of the benefits of this type of adhesive system.
B-Stageable Vs. B-Stage Epoxy
First thing we should explain is the difference between these two types of B-stage systems.
A B-stageable epoxy is a LIQUID product that can undergo a controlled partial cure to from a B-stage epoxy. To reitereate, these products are LIQUID and it is up to the end user to advance the system to the partially cured solid state. As a result, this type of product requires a higher level of involvement from the end user. However, if a specific geometry is required for your B-stage material, this type of product might be best for you.
B-stage epoxies, on the other hand, are SOLID products normally refered to as a film. As described above, these products are partially cured and require heat in order for the polymerization to complete. Unlike their liquid counterparts, these products will need to be cut to the correct geometry in order to be application ready.
Controlled Bond Line
This is where B-stage epoxies really shine. Unlike liquid adhesives, solid B-stage films can be applied to form an extremely precise bond line. With the correct adhesive manufacturer nearly any specified dimensions can be achieved. If your application requires high levels of precision, like in some micro-elctronics, composites and robotics applications, then a B-stage epoxy may be the adhesive choice for you.
Higher Performance Properties
The second biggest advantage of a B-stage system is the ability to achieve very high levels of performance filler materials. Specialty adhesive formulations rely on filler materials to achieve certain performance properties such as thermal and electrical conductivity. In general higher levels of filler in the product formulation result in higher levels of these specific performance properties. However, these filler materials also increase the viscosity of liquid formulations. As a result most formulations can only tolerate a specific amount of filler before the viscosity becomes prohibitively high.
In a B-stage material, however, solvents can be used to keep the viscosity of the liquid product low, allowing for higher filler levels. During the partial cure stage, these solvents can be flashed off, leaving behind the highly loaded, partially cured epoxy adhesive. If your application requires exceptionally high levels of thermal or electrical conductivity in your adhesive material, a B-stage epoxy may be the choice for you.