|Content Type||Conference Paper|
|Title||Temperature Effects on Pot Life of Epoxy Coating Systems|
|Authors||P. Standa, Wisconsin Protective Coatings|
|Source||CORROSION 2000, March 26 - 31, 2000 , Orlando, Fl|
|Copyright||2000. NACE International|
Climatic conditions, particularly temperature, can have a direct bearing upon the workable pot life of 2-pack epoxies. Pot life can vary from seconds up to 24 hours or more depending on chemistry. If for example, a formulation which has desired properties for a service condition has approximately a one hour pot life, the temperature at which the coating is stored prior to use (along with temperature during application) can have an effect of either increasing or decreasing its pot life. By understanding that heat is generated during the cross-linking of epoxies with amines, a study was conducted in which the storage temperature of both epoxy and amine was controlled along with controlling the temperature after mixing the two components. By varying the storage temperatures, it is possible to narrow down pot life ranges in order to give an applicator more pinpoint workable pot life times.
Pot life of 2-pack epoxy coating systems is one of a number of physical properties in which a coating's formulator and applicator must deal with on a daily basis. If a workable pot life is too short under certain temperature conditions, an application could be delayed or worse, canceled, resulting in the loss of the application and an unhappy end customer. For example, a certain system performs well in a particular chemical environment for a customer, but the chemistry of the system along with warm application temperatures (>80°F) shortens the pot life to an impractical time frame. What options are there? The customer may ask for an alternative coating, but this probably would require requalification in the chemical environment which most likely would be too time consuming. A relatively simple alternative would be to lower the temperature of the coating to a predetermined temperature, which will lengthen the workable pot life.
The coating used for this experiment was an 85% volume solids, bisphenol-F epoxy, cycloaliphatic amine cured. The system has approximately a one hour pot life at 70°F.
A one gallon sample (total of Parts A and B) was weighed off and placed into a refrigerator at the desired temperature and allowed to stabilize to temperature.
Both parts were mixed and initial temperature and viscosity were measured. Viscosity measurement was performed on a Brookfield Viscometer, Model RVT. Temperature was measured by simply placing a mercury thermometer into the gallon of coating while the viscosity was performed on a pint sample taken from the gallon container and then remixed into the gallon after measurement. The gallon of coating was outside of the refrigerator for the amount of time required to read the temperatures and viscosities. This was usually three to five minutes.
Readings were measured periodically until viscosity approximately doubled (usually at this point in this particular coating's pot life, application properties deteriorate) and/or until the coating began to solidify in the can.
The following temperatures were utilized to help illustrate the findings: 40°F, 50°F, 60°F, 70°F and 80°F. The 40°F and 50°F settings were entered in this study to illustrate more of an extreme low temperature range. The 80°F setting illustrates how pot life decreases with warmer temperatures. It should be noted that the starting viscosities at 40°F and 50°F are elevated simply because the material is cold and will naturally be more viscous.
40°F Controlled Temperature
At this controlled temperature, the mixed material only increased 30°F (40°F - 70°F) in the first four hours while viscosity increased 2,500 cps. Between four and six hours, the viscosity just about doubled, which made s
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