Journal of the Japan Society of Colour Material

The effects of resin compositions of unsaturated polyester-monomer systems on the curing rate were studied. Two polyesters were prepared either from maleic anhydride 2 moles, phthalic anhydride 1 mole, and propylene glycol 3.3 moles, or from fumaric acid 2 moles, phtharic anhydride 1 mole, and propylene glycol 3. 3 moles, both with the acid value of 30. The monomers employed were styrene, methyl methacrylate and acrylonitrile. A linear accelerator manufactured by High Voltage Engineering Co. was used, and the dose levels employed were from 1. 5 to 9 M.rad.
It was found that the curing rate depended on the reactivity ratios between polyester and monomer, and that the addition of monomer to polyester was proportional to the concentration of unsaturated acids in the polyester. The presence of additives such as metal soap and redox catalizer had no appreciable effect on the curing rate.

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The effects of air/paint ratio and the paint properties on the paint atomization by high speed air streams were studied using the microflash technique.
An acrylic white enamel with the viscosity of 30 cp was sprayed at the enamel velocity of 1. 7 m/sec with the air velocity of 27. 0 to 91. 7 m/sec, both velocities being measured at the spray-gun nozzle, and the patterns of enamel atomization were obserbed with the photographs. The enamel particle size became smaller with the increase in the velocity of air stream, and the shape changed from rodlike to sphere-like at the same time. The extent of atomization increased as the distance of enamel particles from the spray-gun was increased.
An amino-alkyd white enamel with the viscosity of 115 cp and the surface tension of 27.2 dyne/cm was sprayed, and the enamel particles were captured through a shutter by aqueous alcoholic solution of hydroxy propyl methyl cellulose with the viscosity of 2170 cp and surfae tension of 25. 3 dyne/cm, and the optical micrograph was taken to determine the particle size distribution, which was found to follow the Nukiyama-Tanazawa equation, f (x)= ax^p exp (-bx^q) where a, b, p and q are constants and x the particle diameter. The distance of spray-gun from the place where the enamel particles were collected was changed, and it was found that the Sauter's diameter of enamel particles became smaller until the distance of 25 cm was reached from where no further change was observed. The change further in solids concentration of the collected enamel particles was also determined.
The effects of viscosity and degree of polymerization on the Sauter's diameter of particles were studied using an acrylic clear enamel, of which viscosity was varied from 20 to 200 cp with xylene at the constant velocity of air streams. The atomization was not perfect when the (air/100 cp enamel) volume ratio was less than 2500, and no perfect atomization was obtained with the 200 cp enamel. The degree of polymerization of the acrylic resin had no effect on the Sauter's diameter when sprayed at the constant viscosity of 30 cp.
The effects of surface tension on the atomization were studied using the aqueous alcoholic solutions of methyl cellulose, and the extent of atomization became slightly better as the surface tension was decreased from 50 to 30 dyne/cm.
From these experimental results the optimum conditions of paint spraying process are discussed.

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