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

Abstract

The coffee-ring effect of a coated narrow stripe approximately 350 lm 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. V C 2010Wiley Periodicals, Inc. J Appl Polym Sci 120: [1555][1556][1557][1558][1559][1560][1561][1562][1563][1564][1565] 2011

Suppression of the Coffee Ring Effect by Hydrosoluble Polymer Additives

“…Coffee ring phenomenon is commonly observed during evaporating droplet containing nonvolatile solutes resulted from a combination of capillary flow and pinning of the contact line (CL) and has attracted great research interest because of its broad practical applications in inkjet printing, − functional coating, spot test analysis, , color filter, chromatography, , etc. The physical mechanisms behind it are rather complex and have been extensively studied experimentally and theoretically. − The method for suppressing coffee ring effect presents one of the most fundamental issues and plays an utmost important role in high-resolution inkjet printing technique because of the usual non-uniformity of deposited structures.…”

Operating windows of stripe coating

“…A new and better approach is to coat narrow RGB stripes directly on a large piece of glass, whereby most of the RGB solution is preserved . A recent survey on drying of stripe color filter materials reveals that coffee rings could form under certain drying conditions . Hence, a thorough understanding of the coating mechanism of narrow stripes is required before this new approach can be accepted as a reliable production means.…”