A method of minimizing kogation of a heater element in a thermal inkjet printhead. The method includes the steps of: (i) supplying an inkjet ink to a nozzle chamber of the printhead; and (ii) repeatedly actuating a heater element in the nozzle chamber so as to heat a portion of the ink to a temperature sufficient to form a bubble therein, thereby causing droplets of ink to be ejected from a nozzle opening associated with the nozzle chamber. The ink includes a styrene-acrylic copolymer having a glass transition temperature (Tg) in the range of 5 to 30° C. and acid value in the range of 100 180 mgKOH/g, said styrene-acrylic copolymer minimizes kogation of the heater element.