The most important parameter which decides the Throwing Power of an electrodeposition coating is the resistance of freshly electrodeposited matter. Authors investigated the change of electric re-sistance during electrodeposition. Nive MMA-MAA Copolymers (Acid equivalent=1,2,3, meq/g Mn= 4000, 8000, 12000) were synthesized, partially neutralized by TEA, and dispersed into water to prepare coating solutions. The conductivity of these solutions and molar conductivity of TEA in these solu-tions were measured. The voltage was applied smoothly and rapidly, and the current was measured by oscilograph. Current-voltage curves were investigated and following results were obtained. 1. The molar conductivity of TEA is approximately 20 Scm2/mol, being independent of the mole-cular weight of resin, but depends slightly on the acid equivalent of resin. 2. When the molecular weight of resin is high, and its acid equivalent is low, the electrodeposited matter changes to insulator with much delayed time, and the quantity of required for the insulator formation is large. 3. When the temperature of coating solutions is higher than critical value Tc, the electrodeposited matter changes to insulator without delayed time. The quantity of electricity required for the insula-tor formation corresponds to the coagulation of colloid particles and increased according to amine concentration of solutions. 4. Tc lowers by the addition of organic solvent, and corresponds to the minimum film formation temperature (MFT).
The effects of spraying conditions on specific charge (charge to mass ratio), diameter of paint particles and transfer efficiency were studied with a high-speed electrostatic rotary atomizer. On the basis of these results, the effect of specific charge and particle diameter on transfer efficiency was discussed. The results are summarized as follows : 1. Specific charge is almost independent of cup rotational speed and air flow rate for spray pattern adjustment. However, specific charge increases with the increase of applied voltage, and with the decrease of paint flow rate and paint viscosity. The contribution of the factors to the increase of the charge is in the following order ; applied voltage>>paint flow rate>paint viscosity. 2. The diameter of paint particles is little influenced by applied voltage and air flow rate. However, the diameter decreases with the increase of rotational speed, and with the decrease of paint flow rate and paint viscosity. The contribution of the factors to the decrease of the diameter is in the following order ; paint flow rate>rotational speed>paint viscosity. 3. When specific charge is less than that of the practical use, transfer efficiency increases to 90% with specific charge. In the low specific charge region within the practical use, transfer efficiency is more than 90%, and depends on specific charge and diameter of paint particles. In the high specific charge region, transfer efficiency gradually increases only with the diameter.