return to the Main page
The glass transition temperature (Tg) is one of the most vital characteristics of the coating. For a coating to possess reasonable mechanical properties the Tg must be above the use temperature. If the Tg is below the use temperature the coating will be soft and often tacky. The last thing you want to happpen after the coating is applied and dries is for the coating to pick up dirt. Dirt pick up is a mahor problem with coatings that are soft and tacky. If the Tg is above the use temperature, the coating may exibit excellent non-blocking characteristics, but the coating with be brittle, and have poor impact resistance. When you paint a window sill and close the window sticks and wont open, that is called blocking. When two objects are painted and when put together they stick together. This is a very undesirable characteristic. The Tg must be high enough that blocking does not occur, but if the Tg is too high it may be brittle. Some coatings, when applied to wood, will crack over time. This is because the coating is not flexible enough to move with the wood, therefore the coating is too brittle. The value of the desirable Tg for a coatings application is dependent on the specific characteristics of the polymer used in the coating. Every application requires a different coating and every different coating requires a different Tg.
The Tg Effects the Following Properties of a Coating
return to the Main page