Novolac Epoxy Resins:
Novolac epoxy resins generally contain multiple epoxide groups. The number of epoxide groups per molecule depends upon the number of phenolic hydroxyl groups in the starting phenolic novolac resin, the extent to which they reacted and the degree of low molecular species being polymerised during synthesis. The multiple epoxide groups allow these resins to achieve high cross-link density resulting in excellent temperature, chemical and solvent resistance. Novolac epoxy resins are widely used to formulate the moulding compounds for microelectronics packaging because of their superior performance at elevated temperature, excellent mouldability, and mechanical properties, superior electrical properties, and heat and humidity resistance.
Resins for flooring
Almost 90 % of epoxy resins used for industrial epoxy flooring are Bisphenol A epoxies.Novolac epoxy resins have greatly improved chemical and heat resistance compared to the much more common Bis A epoxies.They have higher heat distortion temperatures. Generally Bis A epoxies will begin to soften in the 50-70 degree °C range. Novolac epoxies initially raise this value by about 14 degrees °C . All epoxies will reharden when the elevated temperatures fall below this transition temperature. However, Bis Novolac epoxies will continue to cure when exposed to temperatures of about 65 degrees °C for a few hours. After this 'additional curing' they generally can withstand about 150 degrees °C (dry environment) without problems.
The chemical resistance test shows that epoxy floor made with good quality Bis A epoxy are persistant to 70% sulfuric acid and epoxy floor laid with novolac epoxy are persistant to 98% sulfuric acid. Because of all this improved characteristics Novolac epoxy resins are much more expensive than regular epoxies.
More about epoxy resins you can find in "The Best Web Epoxy Links" eBook.