Evaporation of Solvents from Resin Solutions

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  • 溶剤の蒸発速度
  • ヨウザイ ノ ジョウハツ ソクド

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The rates of evaporation of pure solvents and of solvents from resin solutions were studied. The solvents chosen were toluene, xylene, methyl iso-butyl ketone, n-butyl acetate and cellosolve acetate, and the rate of evaporation was studied in the ranges, temperature 20-30°C, relative humidity 55-83 %, and wind velocity 0. 25-1. 7 m/sec. The resins chosen were coconut and soya modified alkyd resins and ethyl celluloses which were dissolved in the above solvents, and the concentration range studied was 30-70%. It was found that the rates of evaporation of pure solvents follow the Langmuir-Knudsen and Gardner equations, and there existed a linear relationship between the rate of evaporation and the wind velocity, although this was not the case with such highly volatile solvents as toluene and methyl iso-butyl ketone especially in high humidity range. The deviation from the linear relationship was attributed to the temperature drop near the solvent surface caused by the rapid evaporation and to the condensation of moisture. The rate of evaporation of solvent from resin solutions, W (mg. cm-2. min-1), was constant until a certain critical concentration was reached. Below this critical concentration the viscosity or the molecular weight of ethyl cellulose did not affect the W-value. The addition of a plasticizer, dioctyl phthalate, to the alkyd resin solutions resulted in an increase in the W-value. Comparison of the W-values for the pure solvents and for the resin solutions suggested that the rate-controlling steps for the evaporation were the diffusion steps through the surface film as well as the stagnant vapor phase. The critical concentrations were 50-70% for the alkyds and 25-40% for the ethyl cellulose, beyond which the W-value decreased gradually with the increase in concentration. The Bloms equation appeared to hold only in the region transient to the more concentrated region where the internal diffusion is now rate-controlling.

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