Stripe coating with a coffee-ring effect for color filter solutions

摘要

The coffee-ring effect of a coated narrow stripe approximately 350 μm wide was examined. The coating solution was based on a new formulation with a specific application for the production of color filters used in liquid-crystal display panels. The basic components of this formulation were color pigments, solvents, and a novel alkali solution resin. The resin was a copolymer consisting of methacrylic acid, hydroxyl ethyl methacrylate, and methyl methacrylate. Three solvents with different boiling points were used: propylene glycol methyl ether acetate, methyl ethyl ketone, and tetrahydrofuran. The formation of a coffee ring on the coated stripe was mainly dependent on the solvent evaporation rate and the acid value of the copolymer. The acid value determined the strength of the hydrogen bonding of the copolymer. Fourier transform infrared analysis revealed that the intramolecular hydrogen bonding of the carbonyl groups of hydroxyl ethyl methacrylate was one of the critical factors affecting the formation of a coffee ring. The other factor was the rate of solvent evaporation. A proper adjustment of the acid value combined with a highly volatile solvent could effectively eliminate the formation of a coffee ring.