High Brightness Bichromal Display by Molecular Level Controlling Elastomer Swelling
Publication Date: 2005-Nov-08
The IP.com Prior Art Database
This disclosure describes methods for preparing perfluorosilioxane oil for bichromal displays through hydrosilylation reaction between perfluoroalkyl ethylene and hydridosiloxane. The physical properties the of oil (e.g., boiling point, density, viscosity and swelling effect on silicone elastomer) can be tuned at molecular level. Oil with high fluorocarbon to siloxane ratio has low swelling effect whereas oil with low fluorocarbon to siloxane ratio has high swelling effect. Oil with an optimum ratio of fluorocarbon to siloxane could be used to achieve increased display brightness.
One concept for electronic paper displays is based on a bichromal black/white wax ball rotation inside an oil-swollen silicone elastomer. One major shortcoming in this type of display is the low in whiteness (ca. 20%). The root cause is the increased distance between beads caused by swelling of the silicone elastomer from the silicone oil in which the balls are suspended. An alternative suspension agent based on poly(trifluorochloroethylene) oil has been shown to reduce swelling to about 14% from about 25% with the silicone oil. However, this oil has a specific density 1.8 which significantly changes the ball rotation mechanicsand so the driving voltage shifts from 80V to 150V.
Fluorocarbon is well-known a non-swelling solvent for silicone elastomer. However, there is no off-the-shelf transparent fluorocarbon suitable for bichromal display application. Pure flurocarbons (CnF2n+2) do not swell the bichromal display media and some of perfluoroalkylethers (CnF2n+1OCH3) have very low boiling point <80C.
This disclosure describes methods for preparing perfluorosilioxane oil through hydrosilylation reaction between perfluoroalkyl ethylene and hydridosiloxane. The physical properties of oil (e.g., boiling point, density, viscosity and swelling effect on silicone elastomer) can be tuned at molecular level. Oil with high fluorocarbon to siloxane ratio has low swelling effect whereas oil with low fluorocarbon to siloxane ratio has high swelling effect. Oil with an optimum ratio of fluorocarbon to siloxane could be used for high brightness bichromal display.
Silicone elastomer is usually cross-linked by condensation or addition curing. Condensation curing involves the reaction between two hydrolytic active functional groups (e.g. hydroxy or ethoxy). Addition curing involves a platinum catalyzed addition reaction between hydridosilicone and vinylsilicone. Therefore, there are no side-products formed in addition curing. For bichromal devices, the formulation is optimized in 1.5/10 curing agent/resin ratio to provide a good optical performance with 25% linear expansion upon swelling. Too large a swelling gives low optical performance due to low bead density inside given area of media. Further increase in curing agent/resin formulation does not lower the swelling.
In order to achieve high whiteness in bichromal devices, one approach is to lower the swelling of the silicone elastomer. An early approach to control swelling (US6441946) is by mixing a solvent system of perfluoroalkyl ether/silicone oil. One major disadvantage of this solvent system is its low boiling point (61°C). With such low boiling point, it is difficult to fabricate the swollen sheet device; furthermore outdoor applications are
not possible. Therefore, one needs to design a new swelling fluid for the silicone elastomer which the swelling ratio is controlled...