Viscosity Behavior of Phenol-Epoxy Clear Enamel Under High Shear Rate
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概要
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Viscosity is of importance to the paint applicability. The shear rate of enamel under application is very high, reaching above 6×10<SUP>4</SUP>sec<SUP>-1</SUP> in such a case as roller coating. The viscosity of clear enamels was studied as a function of shear rate with a Burrel-Severs type viscometer, which was compared with a # 4 Ford Cup Viscometer. Clear enamels of a phenol-epoxy thermosetting resin were used at the solids contents of 30, 26. 7, 24. 1 and 19.9%. Solvents used were four binnry systems, butyl cellosolve-solvesso # 100, isophorone-solvesso # 150, butyl cellosolve-xylene and isophorone-xylene. Viscosities were measured at temperatures of 0 to 50°:C.<BR>At the solids content 30% the enamel was a Newtonian at temperatures above 20°:C and a non-Newtonian at 0°:C. The relationship between concentration and logarithm of viscosity below the solids content 30% was expressed by log ηa = AC + log η<SUB>0</SUB><BR>where ηa, is the apparent viscosity in poises of the enamel, ηa the viscosity of the solvent, C the concentration (wt. %) and A a constant. Apparent activation energies for the flow of solvents and enamels were about 3 and 7 kcal/mol, respectively. These values were not appreciably affected by the kind of solvent and concentration. A good agreement was obtained between the viscosity values determined with the two viscometers at higher temperatures and lower concentrations. Little cor relation was found between the solvent viscosity and the enamel viscosity. Solubility of the enamel in the solvent appeared to be important, and a good correlation was found between the solubility parameter of the resin and those of the solvents.
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