Non-isothermal viscosity behaviours of a thermosetting acrylic powder coating during initial stage of curing reaction have been studied using a cone-plate type rheometer and a computer simulation technique to obtain better understandings for leveling processes of coating film. Isothermal viscosity behaviours have been measured at a constant share rate (0. 148 1/sec) in rotation mode. Thus, the following empirical equation of non-isothermal behaviours of viscosity is derived : In η=ln ηI+∫toSTEP (Pnon) ·K·dt where η is non-isothermal viscosity, ηI initial viscosity, Pnon non-isothermal starting time of increase of viscosity, K increasing rate of viscosity, STEP step function, and t stoving time. The temperature dependence of both ηI and K are found to be the Andrade's and the Arrhenius' type, respectively, and each apparent activation energy for these parameters are 42.7 and 17.5 Kcal/ mole, those of which are comparable with the reported values. Pnon is given by P multiplied of a correction factor on thermal hysteresis of non-isothermal history herein P being isothermal starting time of increase of viscosity, whose temperature dependence shows the Arrhenius' type with apparent activation energy of 21.8 Kcal/mole. Based on above equation, viscosity behaviours under non-isothermal conditions have been computed using a continuous systems simulation program. Non-isothermal behaviours are found to be “V shape” curves having a minimum value called the minimum viscosity ηmin comparable with the results of recent studies which used very different methods and equations. From the analysis of simulations on various parameters, the following facts can be observed : 1) Both ηmin and the time of min obtained (tmin) decrease with increasing of either heating rate or initial temperature in fine agreement with previous data. 2) ηmin also decreases with decreasing of ηI, while tmin does not. 3) When either K decreases or P increases, ηmin decreases and tmin increases. The curvature of “V shape” curve, on the other hand, becomes large with decreasing of K. In addition, the practical senses of the transformation from isothermal changes to non-isothermal behaviours are considered from a geometrical viewpoint using the concept of “viscosity surface” which consists of the viscosity curves. In fact, a contour map and solid drawings of “viscosity surface” have been designed by X Y digital plotter to estimate the shape of this surface.
On the test of protective coatings for the power transmission towers at the 600 kV Shiobara Testing Laboratory of Central Research Institute of Electric Power Industry, the results of inspection after six years were given in the previous reports. And this report is concerned with the result of inspection in 1975 after fifteen years exposure. Conclusions of the inspection are as follows ; 1) Zinc rich paint systems in these coatings showed more excellent result than other kinds of coatings at the atmospheric exposures except that in the industrial environment. 2) The gloss of paint films faded rapidly in early one or two years, but after that slowly. 3) The states of steel surface with surface preparation had a great influence on the durability of paint films. And the treatment of steel surface with the phosphoric acid pickling showed more excellent result than other kinds of treatments. 4) The deterioration of the paint films on the test panels agreed with that on the towers. 5) Protective coatings prevented towers from corrosion more than six years. 6) Zinc galvanized tower showed excellent result after fifteen years exposure.