 Clinton Braganza, Mauricio Echeverri, Kim Kammer, Andrey Dyshko, Erica Montbach, Asad Khan and J. William Doane Kent Displays, Inc., 343 Portage Blvd., Kent, OH 44240 Abstract A new eye catching and fun eWriter that has the ability to reveal multi colored writing lines has been developed. The color of the written line changes across the writing surface mimicking scratch art paper technologies without creating messy residues or chemical application to reveal colors and patterns. Author Keywords Cholesteric LCD (Ch-LCD), Bistable Displays, eWriter, Boogie Board 1. Objective and Background Boogie Board ® eWriters are made using flexible substrates that allow pressure from a writing instrument to be transmitted to a polymeric dispersion of cholesteric liquid crystals. The writing pressure of the stylus induces flow in the liquid crystal layer that reorients the liquid crystal molecules from a non-reflecting, weakly scattering focal conic texture to a bright reflecting planar texture [1]. The bright texture is produced without polarizers, compensators, backlights or color filters [2, 3]. To enhance the contrast between the bright reflective state and the scattering state, the back substrate can be coated with an absorber. The color and absorbance of the coating is a matter of preference, but in a commercially available Boogie Board eWriter like the JOT 8.5 shown in Figure 1(a) below, a black absorbing layer is used. The color of the writing is uniform across the writing surface. As this Boogie Board is a single pixel device, the whole written image can be erased by applying a small field across the cholesteric liquid crystal layer, to reset it to the weakly scattering focal conic texture, returning it to the color of the absorbing background or pattern [4]. In this work, writing on the eWriter with a uniform color background reveals bright iridescent colors that change across the writing surface. The writing surface is the color of the absorbing background until written on, at which time the color of the writing will depend on the color reflected by the cholesteric liquid crystal layer and the absorbing background at that particular writing location as shown in Figure 1(b). Although it is also possible to change the color of the writing across the display by patterning the absorbing background with multiple colors [4], the color of the background will always be visible after the written image is erased, significantly reducing the appeal of this form of eWriter. Indeed, one could combine the two approaches and have the color of the writing change across a color patterned background. This writing mimics scratch art paper that uses the removal of opaque wax coatings to reveal a hidden colors or patterns without the messy waxy residue [5] or application of a wet reducing agent [6]. In addition, the colorful writing or drawing can be simply erased and reused for hours and hours of fun. To further enhance the appeal of this eWriter as a fun and exciting toy, the reflectivity and the pressure sensitivity was greatly increased to allow pressure from a rubber stamp or roller to create images while maintaining palm rejection. 2. Display Design To create an eWriter whose writing color changes by location requires changing the peak Bragg reflection wavelength of the planar texture of the cholesteric liquid crystal at that location. The peak wavelength of the cholesteric,   , is dependent upon,  , which is the the average refractive index of the nematic liquid crystal molecules used,  , the concentration of the chiral dopant molecule used to induce a uniform twist in the nematic liquid crystal so that it can Bragg reflect, and  is the Helical Twisting Power of the chiral dopant according to equation (1).   =    (1) (a) (b) Figure 1: Photographs of writing and stamping on (a) commercially available Boogie Board eWriter whose writing and background colors are the same across the writing area, and (b) and an eWriter that reveals different colors depending on the writing location. P-110 / C. Braganza SID 2016 DIGEST • 1539 ISSN 0097-966X/16/4703-1539-$1.00 © 2016 SID