Addition Level of Polyfunctional Aziridine
PZ-28, PZ-33, and PZBI-25 are typically added at levels of 1% to 3% to finished formulated coatings, inks, or adhesives or at a level of 5% on the acid functional resin in the formulation. Through experimentation, it is best to determine the ideal level of polyfunctional aziridine to be used in each system to achieve the desired end results.
Method of Adding Polyfunctional Aziridine
The PZ-28 or PZ-33 is added to the formulated coating, adhesive, or ink just prior to use. PZ-28 and PZ-33 are a two-part system not a one-part system. Whereas, PZBI-25 is a dispersion that has a potential of being a one-part system, but needs to be tested. The polyfunctional aziridine is added slowly and under good agitation and allowed to continue agitation for a minimum of 10 minutes after all of the cross-linker has been added. The cross-linker can be added neat into the system or it can be premixed into a solution, which can be added to the system. If added in a solution, a solvent without active hydrogen is ideal. However, water can be used a long as the premix solution is added to the system immediately. A premix solution with water cannot sit since the polyfunctional aziridine will react with the water very quickly and cause an exothermic reaction.
As a general rule, it is best to add the polyfunctional aziridine into the formulated system at ambient temperature to maintain the pot-life. It is important to realize that when either PZ-28 or PZ-33 is added to the aqueous system, it will have a pot-life. Typical formulated systems will have a pot-life of 12 to 24 hours for PZ-28 and 4-8 hours for PZ-33 at pH levels of 0 to 9.5. Even though the reaction with water is slower than with the carboxylic acid of the resin, it will react with the water over time in the pot. It is recommended that each system be tested for length of the pot-life to achieve the desired properties. PZBI-25 has a significantly longer pot-life and has the potential of being a one-part system.