Liquid crystal reflective display

Abstract

This invention relates to a liquid crystal display device, comprising at least one retardation film ( 4 ), a nematic liquid crystal layer ( 5 ), and a light reflecting RGB patterned cholesteric colour filter ( 6 ), for reflecting either essentially left-circular or right-circular polarised light, being characterised in that said liquid crystal layer ( 5 ) is a super twisted nematic liquid crystal layer having a twist angle in the interval 180-270 degrees, and in that the summed retardation R of the retardation film or retardation films and the liquid crystal layer is equal to approximately R=(3+2n)λ/4, where n=0,1,2,3.

1 . A liquid crystal display device, comprising: a polariser ( 1 ), at least one retardation film ( 4 ), a nematic liquid crystal layer ( 5 ), and a, preferably cross-linked, light reflecting RGB patterned cholesteric colour filter ( 6 ), characterized in that said liquid crystal layer ( 5 ) is a super twisted nematic liquid crystal layer having a twist angle in the interval 180-270 degrees, and in that the summed retardation R of the retardation film or the retardation films and the liquid crystal layer is equal to approximately R=(3+2n)λ/4, where n=0,1,2,3 . . . .  
   
   
       2 . A liquid crystal display device as in  claim 1 , wherein said at least one retardation film ( 4 ) is arranged between said polariser ( 1 ) and said super twisted nematic liquid crystal layer ( 5 ).  
   
   
       3 . A liquid crystal display device as in  claim 2 , wherein said at least one retardation film ( 4 ) comprises a quarterwave plate.  
   
   
       4 . A liquid crystal display device as in  claim 2 , wherein said at least one retardation film comprises a wideband quarterwave plate.  
   
   
       5 . A liquid crystal display device as in  claim 4 , wherein said wideband quarterwave plate consists of two retardation films with different optical axes and retardations.  
   
   
       6 . A liquid crystal display device as in  claim 1 , wherein the polariser ( 1 ), the at least one retardation film ( 4 ), the liquid crystal layer ( 5 ), and the, preferably cross-linked, light reflecting RGB patterned cholesteric colour filter ( 6 ) are arranged on each other in sequence.  
   
   
       7 . A liquid crystal display device as in  claim 1 , wherein the absorption axis of said polariser ( 1 ) makes an angle of about 105°-115° with the vertical y-axis of the device, 
 wherein said device comprises a first and a second retardation film ( 2 , 3 ), said first retardation film ( 2 ) having a retardation of essentially 280 nm and making an angle of essentially 170° with said vertical y-axis, and said second retardation film ( 3 ) having a retardation of esentially 140 nm and having a slow axis making an angle of about 25°-35° with said vertical y-axis,said first and second retardation films together constituting a wide-band quarter-wave plate resulting in an improved overall dark state, whereby the liquid crystal layer ( 5 ) is switchable over essentially 315 nm (≈{fraction (l/2)}·λ)and comprises a right-handed 235°-245° twisted nematic layer with an optical thickness of essentially 0,76 μm, and whereby a left-handed colour filter is arranged on the top of a back substrate ( 8 ).    
   
   
       8 . A liquid crystal display device as in  claim 1 , wherein the absorption axis of said polariser ( 1 ) makes an angle of about 115°-125° with the vertical y-axis of the device, wherein said device comprises a first and a second retardation film ( 2 , 3 ), said first retardation film ( 2 ) having a retardation of essentially 280 nm and making an angle of about ±5° with said vertical y-axis, and said second retardation film ( 3 ) having a retardation of esentially 140 nm and having a slow axis making an angle of about 25°-35° with said vertical y-axis,said first and second retardation films together constituting a wide-band quarter-wave plate resulting in an improved overall dark state, whereby the liquid crystal layer ( 5 ) is switchable over essentially 315 nm (≈½·λ)and comprises a right-handed essentially 235°-245° twisted nematic layer with an optical thickness of essentially 0,76 μm, and wherby a left-handed colour filter is arranged on the top of a back substrate ( 8 ).  
   
   
       9 . A liquid crystal display device as in  claim 1 , wherein said device comprises a further retardation film being a twisted nematic polymeric layer.  
   
   
       10 . A liquid crystal display device, wherein said twisted nematic polymeric layer and said super twisted nematic layer ( 5 ) have mutually opposite twist directions.  
   
   
       11 . A liquid crystal display device as in  claim 9  or  10 , wherein the absorption axis of the polariser ( 1 ) makes an angle of essentially 115°-125° with the vertical y-axis of the device, wherein said device comprises a first and a second retardation film ( 2 , 3 ), said first retardation film ( 2 ) having a retardation of essentially 280 nm and making an angle of essentially 0° with said vertical y-axis, and said second retardation film ( 3 ) having a retardation of esentially 140 nm and having a slow axis making an angle of esentially 25°-35° with said vertical y-axis,said first and second retardation films together constituting a wide-band quarter-wave plate resulting in an improved overall dark state, whereby said twisted nematic polymeric layer, being placed closer to the polariser than said liquid crystal layer ( 5 ), comprises a right-handed 230-250° twisted nematic layer with an optical thickness of 0,75-0,85 μm, said liquid crystal layer being switchable over essentially 315 nm (≈½·λ)and comprises a left-handed essentially −235°-−245° twisted nematic layer with an optical thickness of essentially 0,82 μm, and whereby a left-handed colour filter is arranged on the top of a back substrate ( 8 ).