Pendulum hardness is one of the static measurement methods of viscoelasticity, and the hardness values measured at different temperatures cannot be compared. The damping in the determination of pendulum hardness mainly comes from the absorption of mechanical energy by the paint film, that is, the loss modulus. The loss modulus is lower in both the glass and rubber regions, and higher in the fly. The hardness of the pendulum is related to the thickness of the paint film. When it is too thin, the substrate will be affected. The advantage of the pendulum damping test method is that it does not damage the coating film.
Common pendulum damping Testers include Konig pendulum, referred to as K pendulum; Persoz pendulum, referred to as P pendulum. These two Testers have been adopted by my country's national standard GB1730-88 "Determination of Paint Film Hardness Pendulum Damping Test".
The pendulum damping hardness method uses two steel balls embedded under the pendulum bar to contact the coating film sample. When the pendulum bar swings, the fixed mass of the pendulum bar is the most oppressive on the film, making the film produce resistance. According to starting from a larger angle The time Cs) required for swing damping to a smaller angle is used to determine the hardness of the coating film, K swings from 6° to 3° 'p swings from 12° to 4°. The standard time for K to be placed on a polished flat glass plate is 250s ± 10s, and for P to be 420s. Both Testers are equipped with a photoelectric control counting device to automatically record the damping time.
When the coating is measured by a pendulum damping Tester, the main cause of the swing attenuation is the absorption of mechanical energy by the coating, and the swing decay time is inversely proportional to the loss mode, which is most used to indicate the ability of the coating to absorb mechanical energy. The loss modulus is highest in the Tg transition region and is low in both the high Tg and low Tg regions. Therefore, the loss modulus is lower in the glassy and rubbery regions, where the swing decay time is longer, and softer rubber coatings have longer decay times.
A general conversion relationship cannot be established between the measurement results of these two pendulums. Usually only other pendulum instruments are specified for product testing. The results of the pendulum damping test are related to the environment during the test, and should be carried out under controlled temperature and humidity conditions without the influence of airflow. The thickness of the coating film and the material of the substrate also have an influence on the damping time.
