Solvent shrinkage epoxy resin

Epoxy resins offer a unique combination of properties for adhesive applications. These include the ability to formulate liquid systems without solvents or carriers, the ability to convert these systems to cured products without the production of low-molecular-weight by-products, the ability to bond dissimilar or nonporous surfaces, and the ability to produce thick sections without subsequent stress cracking due to shrinkage. 

Although epoxy resin and hardener may be used in unmodified form in adhesive systems, most systems will consist of components that have been modified by incorporation of various additives to achieve specific effects. Formulators will add catalysts or blend hardeners to obtain a specific usable life of the mix and to control the curing temperature. Reactive diluents may be added to modify viscosity or flexibility. Fillers impart improved compression strength and reduce shrinkage and cost. Solvents may be used to reduce viscosity or improve adhesion. Various additives may be added, usually at a low percentage, to reduce aeration, improve adhesion to difficult surfaces, or minimize settlement of fillers. Depending on the application, particular properties such as flame retardency. 

Epoxy resins have proven very popular because of their versatility, excellent adhesion, low cure shrinkage, good electrical properties, compatibility with many other materials, resistance to weathering and chemicals, dependability, and ability to cure under adverse conditions. The most widely used epoxy resins in the casting field are the bisphenol-A and cycloaliphatic epoxies. Novolac epoxy resins have higher heat deflection temperatures, but they require high-temperature cure. The novolacs also have excellent resistance to solvents and chemicals. Epoxy castings are often used in electrical/electronic applications. (5ee also epoxy resin.)... 

Diluents. These are generally incorporated to reduce the viseosity of the freshly mixed adhesive to offset the effect of the filler. This may be required to improve handling and spreading characteristics or to allow filler additions which tend to reduce cost. Other properties of the fresh and hardened adhesive can be affected by the use of diluents, for example pot life, flexibility and glass transition temperature. If the diluent is non-reactive, such as solvents which remain in the cured system, the net result is a deterioration of chemical and mechanical properties such as increased shrinkage and reduced adhesion. Reactive diluents containing epoxy compounds are capable of combining chemically with the resin/hardener system. 

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