GB2393262A - :New mode LCD comprising an A-plate or O-plate retardation film - Google Patents

Abstract

A new mode LCD comprising at least one polariser 3 and an LC layer 1 whose initial alignment has the LC molecules aligned parallel to the substrates and are untwisted, is provided with an optical compensator comprising an A-plate and/or an O-plate retardation film 2, the optical compensator is used to improve the optical performance of the new mode LCD.

Description

( - 1 New Mode LCD comprising an A Plate or O Plate Retardation Film Field

of the Invention

The invention relates to a compensator for use in new mode liquid crystal displays, comprising an A plate and/or an O plate retardation film, and to a new mode liquid crystal display comprising such a compensator. Background and Prior Art

The liquid-crystal display (LCD) devices typically used in prior art are

for example TN ( wisted nematic) LCDs, for example in accordance 15 with Schadt, M. and Helfrich, W. Appl. Phys. Lett.18, pp.127 ff (1974) and in particular in their special form with low optical retardation d.An in the range from 150 nm to 600 nm in accordance with DE 30 22 818, STN (super wisted nematic) LCDs, such as, for example, in accordance with GB 2.123. 163, Waters, C. M., Brimmel, 20 V, and Raynes, E. Pproc.3rd Int. Display Research Conference, Kobe 1983, pp. 396 ff and Proc. SID 25/4, pp. 261 ff, 1984, Scheffer, T. J. and Nehring, J. Appl. Phys. Lett. 45, pp.1021 ff, 1984 and J. Appl. Phys. 58, pp. 3022 ff,1985, DE 34 31 871, DE 36 08 911 and EP 0 260 450, IPS (in-olane switching) LCDs, as described, for 25 example, in DE 40 00 451 and EP 0 588 568, and VA or VAN (_ertically aligned nematic) LCDs, as described, for example, in Tanaka, Y. et al. Taniguchi, Y., Sasaki, T., Takeda, A., Koibe, Y., and Okamoto, K. SID 99 Digest pp.206 ff (1999), Koma, N., Noritake, K., Kawabe, M., and Yoneda, K., International Display Workshop (IDW) 30,97 pp.789 ff (1997) and Kim, K.H., Lee, K., Park, S.B., Song, J.K., Kim, S., and Suk, J.H., Asia Display 98, pp. 383 ff, (1998).

In LCD devices which were known hitherto and are for the most part already commercially available, the optical appearance is 35 inadequate, at least for demanding applications. In particular the contrast, especially in the case of coloured displays, the brightness,

( - 2 the colour saturation and the viewing-angle dependence of these parameters are in clear need of improvement and have to be improved if the display devices are to compete with the performance features of the widespread CRTs(_athode ay ubes). Further 5 disadvantages of the LCD devices of prior art are often their poor

spatial resolution and inadequate response times, in particular in the case of STN, but also in the case of TN or IPS and VA LCDs, in the case of the latter especially if they are to be used for the reproduction of video, such as, for example, in multimedia applications on 10 computer display screens or in the case of television sets.

Particularly for this purpose, but also even for the display of rapid cursor movements, short response times are desired.

Recently a new type of LCDs has been reported in prior art. These

15 displays, which are disclosed for example in WO 01/07962, are hereinafter shortly referred to as "new mode" LCDs. The LCDs of the new mode contain an electro-optical liquid-crystal (LC) switching element comprising at least one polariser and an LC layer which has an initial alignment in which the LC molecules are aligned essentially 20 parallel to the substrates, and are essentially untwisted, i.e. essentially parallel or antiparallel to one another. The realignment of the LC molecules from their initial alignment essentially parallel to the substrates is caused by a corresponding electric field. In case of LC

materials of negative dielectric anisotropy, the electric field is aligned

25 essentially parallel to the substrates. In case of LC materials of positive dielectric anisotropy the electric field is aligned essentially

perpendicular to the substrates. The LC layer has an extremely low optical retardation d.An in the range from 0.05 Em to 0.46 Sum. The LC switching element preferably contains, in addition to the LC layer, 30 a further birefringent layer, preferably a \/4 layer or two \/4 layers or a \/2 layer. The two \/4 layers may replace the \/2 layer.

The LCDs of the new mode were found to have a good contrast and at the same time good viewing-angle dependence of the contrast, to 35 allow the display both of gray shades and of half-tone colours over a broad range of observation angles, and fast response times that are

- 3 in particular adequate for video reproduction. In particular, they are highly suitable for applications with display of grey shades, such as, for example, television sets, computer monitors and multimedia equipment. Both mains-independent operation and also operation on 5 the mains are possible. Mains operation is often preferred.

The new mode LCDs are, inter alla, display screens of television sets, computers, such as, for example, notebook computers or desktop computers, central control units and of other equipment, for 10 example gambling machines, electro-optical displays, such as displays of watches, pocket calculators, electronic (pocket) games, portable data banks, such as PDAs (personal digital assistants) or of mobile telephones.

15 The new mode LCDs, details on their assembly and suitable components and LO media to be used therefor are described in WO 01/07962, the entire disclosure of which is incorporated into this

application by reference.

20 However, it has turned out that new mode LCDs in some cases show properties, such as the viewing angle characteristics, in particular the contrast at different viewing angles and directions, that still leave some room for further improvement when used in specific applications. It has now been found that the properties of new mode LCDs, especially the viewing angle characteristics, can be further improved by using a compensator comprising one or more retardation films of specific types and in specific arrangements as described in the 30 following invention.

One aim of the present invention is to provide a compensator for an LCD, in particular for an LCD of the new mode, that improves the optical performance of the LCD, in particular the gray level stability at 35 wide viewing angles, is easy to manufacture, and allows economic fabrication even at large scales.

- 4 Another aim of this invention is to provide an advantageous use of the compensator according to this invention.

5 Further aims of this invention relate to LCDs, in particular to new mode LCDs, comprising an inventive compensator which show advantageous properties such as good contrast, reduced colour shift and wide viewing angles.

10 Other aims of the present invention are immediately evident to the person skilled in the art from the following detailed description.

The above aims can be achieved by providing compensators and LCDs according to the present invention.

Definition of Terms In connection with polarization, compensation and retardation layers, films or plates as described in the present application, the following 20 definitions of terms as used throughout this application are given.

The term 'film' as used in this application includes self-supporting, i.e. free-standing, films that show more or less pronounced mechanical stability and flexibility, as well as coatings or layers on a supporting 25 substrate or between two substrates.

The term 'liquid crystal or mesogenic materiel' or'liquid crystal or mesogenic compound' should denote materials or compounds comprising one or more rod-shaped, board-shaped or disk-shaped 30 mesogenic groups, i.e. groups with the ability to induce liquid crystal phase behaviour. Liquid crystal (LC) compounds with rod-shaped or board-shaped groups are also known in the art as 'calamitic' liquid crystals. Liquid crystal compounds with a disk-shaped group are also known in the art as 'discotic' liquid crystals. The compounds or 35 materials comprising mesogenic groups do not necessarily have to exhibit a liquid crystal phase themselves. It is also possible that they

- 5 show liquid crystal phase behaviour only in mixtures with other compounds, or when the mesogenic compounds or materials, or the mixtures thereof, are polymerized.

5 For the sake of simplicity, the term 'liquid crystal material' is used hereinafter for both liquid crystal materials and mesogenic materials, and the term 'mesogen' is used for the mesogenic groups of the material.

The term 'director' is known in prior art and means the preferred

10 orientation direction of the long molecular axes (in case of calamitic compounds) or short molecular axis (in case of discotic compounds) of the mesogens in a liquid crystal material.

The term 'planar structure' or 'planer orientation' refers to a film 15 wherein the optical axis is substantially parallel to the film plane.

The term 'homeotropic structure' or'homeotropic orientation' refers to a film wherein the optical axis is substantially perpendicular to the film plane, i.e. substantially parallel to the film normal.

The terms 'tilted structure' or 'tilted orientation' refers to a film wherein the optical axis is tilted at an angle between O and 90 degrees relative to the film plane.

25 The term 'splayed structure' or 'splayed orientation' means a tilted orientation as defined above, wherein the tilt angle additionally varies monotonuously in the range from O to 90 a, preferably from a minimum to a maximum value, in a direction perpendicular to the film plane.

30 The tilt angle of a splayed film hereinafter is given as the average tilt angle Dave, unless stated otherwise.

The average tilt angle (have iS defined as follows d 0'(d) 35 _ d'=0 ave d

( - 6 wherein 6'(d') is the local tilt angle at the thickness d' within the film, and d is the total thickness of the film.

5 In planar, homeotropic and tilted optical films comprising uniaxially positive birefringent liquid crystal material with uniform orientation, the optical axis of the film is given by the director of the liquid crystal material. 10 The term 'helically twisted structure' relates to a film comprising one or more layers of liquid crystal material wherein the mesogens are oriented with their main molecular axis in a preferred direction within molecular sublayers, said preferred orientation direction in different sublayers being twisted at an angle around a helix axis. The term 15 'helically twisted structure with planar orientation' means a film with helically twisted structure as described above, wherein the helix axis is substantially perpendicular to the film plane, i.e. substantially parallel to the film normal.

20 The term 'A plate' refers to an optical retarder utilizing a layer of uniaxially birefringent material with its extraordinary axis oriented parallel to the plane of the layer, and its ordinary axis (also called 'a axis') oriented perpendicular to the plane of the layer, i.e. Darallel to the direction of normally incident light.

The term 'C plate' refers to an optical retarder utilizing a layer of a uniaxially birefringent material with its extraordinary axis (also called c-axis') perpendicular to the plane of the layer, i.e. parallel to the direction of normally incident light.

The term 'O plate' refers to an optical retarder utilizing a layer of a uniaxially birefringent material with its extraordinary axis oriented at an oblique angle with respect to the plane of the layer.

( - 7 In A-, C- and O-plates comprising optically uniaxial birefringent liquid crystal material with uniform orientation, the optical axis of the film is given by the direction of the extraordinary axis.

5 An A plate or C plate comprising optically uniaxial birefringent material with positive birefringence is also referred to as '+ A/C plate' or positive A/C plate'. An A plate or C plate comprising a film of optically uniaxial birefringent material with negative birefringence is also referred to as '- A/C plate' or 'negative AIC plate'.

A retardation film with positive or negative birefringence is also shortly referred to as 'positive' or 'negative' retardation film, respectively.

A transmissive or transflective LCD according to the present 15 invention preferably contains a polariser and an analyser, which are arranged on opposite sides of the arrangement of LC layer and birefringent layer.

Polariser and Analyser are jointly referred to as "polarizers" in this 20 application. Summary of the Invention

The present invention relates to a compensator for use in new mode 25 liquid crystal displays, comprising at least one retardation film having an optical axis that is substantially parallel to the film plane (A plate) and/or at least one retardation film having an optical axis that is tilted at an angle between 0 and 90 relative to the film plane (O plate).

30 The present invention further relates to a liquid crystal display comprising a liquid crystal layer having an initial alignment which is essentially parallel to the substrates and is essentially untwisted, at least one polariser, a device for generating an electric field, which is

aligned essentially parallel to the substrates in the case of liquid 35 crystal materials of negative dielectric anisotropy and is aligned essentially perpendicular to the substrates in the case of liquid-crystal

- 8 materials of positive dielectric anisotropy, and, if desired, at least one birefringent layer, said liquid crystal layer having an optical retardation [(d.An)Lc] in the range from 0.05,um to 0.46,um (new mode liquid crystal display), characterized in that the liquid crystal display comprises a compensator according to the present invention as described above and below.

Detailed Description of the Invention

The compensator according to the present invention comprises one or more A plates, preferably positive A plates, and/or one or more O plates, preferably positive O plates. Further preferred is a compensator comprising one or more C plates, preferably negative C plates.

Suitable optical films for use as A plate retarders are known in prior art, like for example uniaxially stretched polymer films such as polyethyleneterephthalate (PET), polyvinylalcohol (PVA) or polycarbonate (PC) films.

Suitable optical films for use as O plate retarders are known in prior art, and can be obtained for example by oblique vapour deposition of a thin film, e.g. of an inorganic material such as Ta2O5, as described for example in US 5,196,953 and WO 96/10773. It is also possible to 25 use as O plate an LC film as described in WO 96/10770, which is prepared from a polymerisable LC material with a smectic A or C phase and a nematic phase at higher temperatures, by applying the LC material in its nematic phase onto a substrate optionally covered with an alignment layer of obliquely deposited SiO, lowering the 30 temperature into the smectic C phase of the material so that the LC material adopts its naturally tilted smectic C structure, and fixing the tilted structure by polymerization of the LC material.

Suitable optical films for use as negative C plate retarders are known 35 in prior art, like for example stretched or uniaxially compressed

plastic films like DAC or TAC as described for example in US

( - 9 - 4,701,028, inorganic thin films obtained by physical vapour deposition as described for example in US 5,196,953, or negatively birefringent polyimide films as described for example in US 5,480,964 and US 5,395,918.

Preferably the retardation films comprise polymerized or crosslinked LC material.

The A plate retardation film preferably comprises polymerised LC 10 material with planar structure as described for example in WO 98/04651, the entire disclosure of which is incorporated by reference.

The tilted or splayed O plate retarder preferably comprises a polymerised liquid crystal material with tilted or splayed structure, as 15 described for example in US 5,619,352, WO 97/44409, WO 97/44702, WO 97/44703 or WO 98/12584, the entire disclosure of

which is incorporated by reference.

The negative C plate retarder preferably comprises polymerized 20 chiral LC, in particular cholesteric LC (CLC) material with a short pitch and a reflection in the UV range, such as a UVCLC film or highly twisted A plate as described for example in GB 2,315,072, WO 01/20393 and WO 01/20394, the entire disclosure of which is

incorporated by reference.

Especially preferred are the following embodiments - the compensator comprises at least two O plates wherein the tilt angle varies in a direction perpendicular to the film plane (splayed O plates), - the compensator comprises at least four A plates, - comprises at least two O plates wherein the tilt angle varies in a direction perpendicular to the film plane (splayed O plates) and at least two A plates, 35 - the compensator in addition to the A and or O plates comprises at least one negative C plate,

- 10 - the A plate, O plate and/or C plate comprise a polymerised or crosslinked LC material, - the A plate comprises a polymerized or crosslinked achiral LC material with planar orientation, - the O plate comprises a polymerised or crosslinked achiral LC material with titled or splayed orientation, - the negative C plate comprises a polymerised or crosslinked cholesteric LC (CLC) material with helically twisted structure and 10 planar orientation, - the helical pitch of the CLC material in the negative retardation film is smaller than 250 nm, - the reflection wavelength of the CLC material in the negative 15 retardation film is smaller than 375 nm, - the thickness of the A plate is from 0.1 to 1,um, preferably from 0.13 to 0.65,um, - the optical retardation of the A plate is from 12 to 115 nm, preferably from 15 to 75 nm, - the thickness of the O plate is from 0.4 to 1.5 m, preferably from 0.5 to O.9, um, - the optical retardation of the O plate is from 46 to 173 nm, preferably from 58 to 104 nm, 25 - the thickness of the negative C plate is from 0.5 to 2,um, preferably from 1 to 1.5,um, - the optical retardation of the negative C plate is from 29 to 116 nm, preferably from 58 to 87 nm.

Especially preferred compensator stacks are shown in table 1. Therein, LC denotes the liquid crystal cell, O denotes a tilted or splayed O plate, A denotes a planar,A plate, and -C denotes a negative C plate. For the case where the O plate is a splayed O plate, the arrow is denoting the 35 preferred direction of increasing tilt angle.

- 11 For sake of simplicity, the polarisers are omitted in table 1. A display for practical applications will, however, further comprise a pair of polarisers sandwiching the stack as shown in table 1.

5 In the stack formats as shown in table 1 the single retarder components are arranged symmetrically, therefore incoming light may enter the stack from either side.

The single A,O and C plates in a compensator according to the 10 present invention and also in the stacks shown in table 1 can be laminated directly onto each other or separated by a transparent intermediate film, like for example a TAC film. "(TAC)" in table 1 indicates the preferred positions of optional TAC films.

15 Table 1 - Preferred compensator stacks in inventive disoIaYs _11_ (TAC) O _ A _ A O _

2) (TAC) O A (TAC) LC (TAC) A O (TAC)

20 3) O (TAC) (TAC) A LC A (TAC) (TAC) I O

4) O (TAC) A (TAC) LC (TAC) A (TAC) I O

5) (TAC) A (TAC) O LC O (TAC) A (TAC)

6) (TAC) A O (TAC) LC (TAC) O A (TAC)

7) A (TAC) O (TAC) (TAC) O (TAC) A

25 8) A (TAC) (TAC) O LC O (TAC) (TAC) A

- (TAC) A (TAC) A LC A (TAC) A (TAC)

10) A (TAC) (TAC) A LC A (TAC) (TAC) A

11) (TAC) A A (TAC) LC (TAC) A A (TAC)

1 A (TAC) A (TAC) LC (TAC) A (TAC) I A

30 _ (TAC) O O (TAC)

14) i O (TAC) LC (TAC) O Particularly preferred are compensator stacks of type 1) above.

3 The LCDs according to the present invention may further comprise one or more further optical components such as polarisers or

- 12 compensation or retardation films, like for example one or more quarter wave retardation films (QWF, \/4 films) or half wave retardation films (HOOF, \/2 films), positive or negative A, O or C plates or retardation films with twisted, homeotropic, planar, tilted or 5 splayed structure. Particularly preferred are optical films comprising polymerized or crosslinked LC material. Homeotropic LC films are described for example in WO 98/00475.

The LCD according to the present invention may be a reflective or 10 transmissive display, and may further comprise a light source, like a conventional backlight, or a reflective layer on the side of the LC cell opposite to that of the first linear polarizer. In case of a reflective display with a reflective layer on one side of the LC cell the second linear polariser may be omitted.

The negative and positive retarders and A, O and C plates of the compensator according to the present invention are preferably prepared from a polymerisable LC material by in-situ polymerization.

In a preferred method of preparation the polymerisable LC material is 20 coated onto a substrate, oriented into the desired orientation and subsequently polymerised for example by exposure to heat or actinic radiation as described for example in WO 01/20394, GB 2,315,072 or WO 98/04651.

25 Alternatively it is possible to prepare the retardation films from a readily synthesized LC polymer that is applied onto a substrate, for example at a temperature above its glass transition temperature or its melting point, or from solution e.g. in an organic solvent, aligned into the desired orientation, and solidified for example by evaporating 30 the solvent or by cooling below the glass temperature or melting point of the LC polymer. If for example a LC polymer with a glass temperature that is higher than ambient temperature is used, evaporation of the solvent or cooling leaves a solid LC polymer film.

If for example an LC polymer with a high melting point is used, the 35 LC polymer can be applied as a melt onto the substrate which solidifies upon cooling. LC side chain polymers or LC main chain

! - 13 polymers can be used, preferably LC side chain polymers. The LC polymer should preferably be selected such that its glass transition or melting temperature is significantly higher than the operating tempature of the retarder. For example, LC side chain polymers 5 comprising a polyacrylate, polymethacrylate, polysiloxane, polystyrene or epoxide backbone with laterally attached mesogenic side chains can be used. The LC polymer may also comprise side chains with reactive groups that can be crosslinked after or during evaporation of the solvent to permanently fix the orientation. The LC 10 polymer may also be subjected to mechanical or heat treatment after application to the substrate to improve alignment. The above methods and suitable materials are known to those skilled in the art.

The compensator according to the present invention is especially 15 suitable for use in LCDs of the new mode as described for example in WO 01/07962. However, it can also be used for compensation of conventional LCDs, in particular those of the DAP (deformation of aligned phases) or VA (vertically aligned) mode, like e.g. ECB (electrically controlled birefringence), CSH (colour super 20 homeotropic), VAN or VAC (vertically aligned nematic or cholesteric) displays, MVA (multi-domain vertically aligned) or PVA (patterned vertically aligned) displays, in displays of the bend mode or hybrid type displays, like e.g. OCB (optically compensated bend cell or optically compensated birefringence), R-OCB (reflective OCB), HAN 25 (hybrid aligned nematic) or pi-cell (-cell) displays, furthermore in displays of the TN (twisted nematic), HTN (highly twisted nematic) or STN (super twisted nematic) mode, in AMD-TN (active matrix driven TN) displays, or in displays of the IPS (in plane switching) mode which are also known as 'super TFT' displays.

The examples below serve to illustrate the invention without limiting it. Therein, the following abbreviations are used: tilt angle [degrees] 35 twist angle [degrees] p helical pitch [nary]

- 14 ne extraordinary refractive index (at 20 C and 589 nm) nO ordinary refractive index (at 20 C and 589 nm) Eat dielectric constant parallel to the long molecular axis (at 20 C and 1 kHz) 5 el dielectric constant perpendicular to the long molecular axis (at 20 C and 1 kHz) K,, first elastic constant K22 second elastic constant K33 third elastic constant 10 Von threshold voltage M Voff saturation voltage M d layer thickness [am] ret. retardation [nary] 15 The uncompensated and compensated displays described in the following examples, unless explicitly stated otherwise, contain the following components: A plate Planar polymerised LC film with the following parameters ne 1.610 d 0.1-5.0 nO 1.495 ret. 12 - 575 O elate Splayed polymerized LC film with the following parameters 30 Dmin 2 d 0.1 - 5.0 Dmax 88 ret. 6 - 300 Dave 45 ne,1.610 nO 1.495 Nenative C plate (-C plate)

- 15 Highly twisted polymerised LC film with the following parameters ne 1.610 d 0.1 - 5.0 5 nO 1.495 p < 250 TAC Slightly anisotropic TAC film with the following parameters nx 1.48147 nz 1.48108 ny 1.48145 d 80 LC cell New mode LC cell with the following cell parameters surface rubbing anti-parallel Elf 15.1 surface pre-tilt 3 al 4.8 20 d 4.5 K,, 12. 5 An 0.06 K22 6 no 1.525 K33 17.7 nO 1.465 Voff 0.5 Von 5 25 QWF

Planar A plate with polymerised LC material with a retardation of close to / of a wavelength of the light which is passing through the system, typically in the region of 135nm for visible light.

Polarisers Standard type stretched dichroic polarisers, the stretch axis being indicated in the Figures by double headed arrows.

l - 1 6 The display configurations shown in the following Figures also contain a light source, like for example a backlight on the left side of the display (not shown).

5 The values and plots of the So-contrast and grey levels in the following examples are obtained by modelling and measurement, respectively, using berreman matrix methods for optical simulations I and Eldim EZContrast equipment for viewing angle measurement.

10 Example 1 - Comparative Example An uncompensated new mode display of prior art comprises one LC

cell (1), one quarter wave foil (QWF) (2), and two crossed polarisers (3) with a configuration as shown in Figure 1A. The backlight (not 15 shown) is on the left side of the display.

The orientation of the LC molecules in the LC cell (1) and the QWF (2) is schematically depicted by the mesogens (1a, 2a). The dashed lines (1b, 2b) represent the orientation direction of the mesogens (1a, 20 2a) that are adjacent to the surface of the LC cell (1) and QWF (2).

Figure 1 B shows the iso-contrast plot modelled for a Von value of 7.0 and a Voe value of 0.5. Figure 1C shows one real measurement of the Socontrast plot for the same values of Von and Voff (7.0/0.5) to 25 demonstrate the accuracy of the modelled results.

Figure 1D shows the So-contrast plot measured for a Von value of 5.0 and a Voff value of 0.5. Figure 1 E shows the So-contrast plot measured for a Von value of 4.0 and a Voff value of 1.0. For the case 30 Von = 5 the on axis contrast is calculated to be 10-20:1. The 10:1 contrast area extends to '10/ -40 vertically and +50 / -50 horizontally. For the case Von = 4 the on axis contrast is calculated to be 10-1:1. The 10:1 contrast area extends to +0 / -60 vertically and +60 / -60 horizontally.

- 17 The grey level diagrams are shown in Figure 1F for the horizontal and Figure 1G for the vertical directions. Grey scale inversion is present in both the horizontal and vertical directions, especially in the black and lower grey levels.

Examole 2 A compensated display according to the present invention comprises an LO cell (1), two splayed O-plates on TAC (2, 2') with a retardation 10 of 732 nm and an orientation of the optical axis of 125 (2) and 235 (2'), respectively, and two crossed polarisers (3, 3') oriented at 45 (3) and 135 (3'), respectively. The configuration is shown in Figure 2A. Figure 2B shows the iso-contrast plots modelled for a Von of 5.0 and Voe of 0.5. The on axis contrast is calculated to be greater than 15 100:1. The 10:1 contrast area extends to +43/ -70 vertically end +60 /-60 horizontally. The 100:1 contrast area extends to +20 /-40 vertically and +33 / -33 horizontally.

Example 3

A compensated display according to the present invention comprises an LO cell (1), two splayed O-plates on TAC (2, 2') with a retardation of 636 nm and an orientation of the optical axis of 142 (2) and 218 (2'), respectively, two planar A-plates on TAC (3, 3') with a 25 retardation of 239 nm and an orientation of the optical axis of 270 (3) and 90 (3'), respectively, and two crossed polarisers (4, 4') oriented at 45 (4) and 135 (4'), respectively. The configuration is shown in Figure 3A. Figure 3B shows the iso-contrast plots modelled for a Von of 5.0 and Voe of 0.5. The on axis contrast is 30 calculated to be greater then 100:1. The 10:1 contrast area extends to +55/ -70 vertically and +80 / -80 horizontally. The 100:1 contrast area extends to +40 / -40 vertically and +45 / -45 horizontally.

Example 4

- 18 A compensated display according to the present invention comprises an LC cell (1), two splayed O-plates on TAC (2, 2') with a retardation of 576 nm and an orientation of the optical axis of 180 , two planar A plates on TAC (3, 3') with a retardation of 434 nm and an orientation 5 of the optical axis of 270 (3) and 90 (3'), respectively, and two crossed polarisers (4, 4') oriented at 45 (4) and 135 (4'), respectively. The configuration is shown in Figure 4A. Figure 4B shows the So-contrast plots modelled for a Van of 5.0 and Voff of 0.5.

The on axis contrast is calculated to be greater then 100:1. The 10:1 10 contrast area extends to +50/ -60 vertically and +60 / -60 horizontally. The 100:1 contrast area extends to +30 / -30 vertically and +30 /-30 horizontally.

Example 5

A compensated display according to the present invention comprises an LC cell (1), two splayed O-plates (2, 2') with a retardation of 545 nm and an orientation of the optical axis of 180 , two planar A-plates on TAC (3, 3') with a retardation of 434 nm and an orientation of the 20 optical axis of 270 (3) and 90 (3'), respectively, and two crossed polarisers (4, 4') oriented at 45 (4) and 135 (4'), respectively. The configuration is shown in Figure 5A. Figure 5B shows the iso contrast plots modelled for a Von of 5.0 and Voff of 0.5. The on axis contrast is calculated to be greater than 100:1. The 10:1 contrast 25 area extends to +50/ -60 vertically and +60 / -60 horizontally. The 100:1 contrast area extends to +30 / -30 vertically and +30 / -30 horizontally. Example 6

A compensated display according to the present invention comprises an LC cell (1), two splayed O-plates (2, 2') with a retardation of 545 nm and an orientation of the optical axis of 180 , two planar A-plates (3, 3') with a retardation of 434 nm and an orientation of the optical 35 axis of 270 (3) and 90 (3'), two negative C plates (highly twisted A plates) (4, 4') with a retardation of 1168 nm and an orientation of the

- 1 9 optical axis of 270 (4) and 90 (4'), respectively, and two crossed polarisers (5, 5') oriented at 45 (5) and 135 (5'), respectively. The configuration is shown in Figure 6A. Figure 6B shows the iso-contrast plots modelled for a Von of 5.0 and Voff of 0.5. The on axis contrast is 5 calculated to be greater than 100:1. The 10:1 contrast area extends to +50/ -60 vertically and +60 / -60 horizontally. The 100:1 contrast area extends to +35 / -30 vertically and +35 / -35 horizontally.

Example 7

A compensated display according to the present invention comprises an LC cell (1), two splayed O-plates (2, 2') with a retardation of 827 nm and an orientation of the optical axis of 180 (2) and 218 (2'), respectively, two planar A-plates on TAC (3, 3') with a retardation of 15 642 nm and an orientation of the optical axis of 270 (3) and 90 (3'), respectively, and two crossed polarisers (4, 4') oriented at 45 (4) and 135 (4'), respectively. The configuration is shown in Figure 7A.

Figure 7B shows the iso-contrast plots modelled for a Von of 4.0 and Voff of 1.0. The on axis contrast is calculated to be greater than 20 100:1. The 10:1 contrast area extends to +50/ -60 vertically and +70 / -70 horizontally. The 100:1 contrast area extends to +30 / -30 vertically and +35 / -35 horizontally. The grey level diagrams are shown in Figure 7C for the horizontal and Figure 7D for the vertical directions. No black state inversion is present in the horizontal 25 direction and extent of grey level inversion in the vertical direction is improved on the uncompensated display.

Examole 8 30 A compensated display according to the present invention comprises an LC cell (1), two planar A-plates (2, 2') with a retardation of 481 nm and an orientation of the optical axis of 31 1 (2) and 49 (2') , respectively, two planar A-plates on TAC (3, 3') with a retardation of 138 nm and an orientation of the optical axis of 265 (3) and 138 35 (3') , respectively, and two crossed polarisers (4, 4') oriented at 45 (4) and 135 (4'), respectively. The configuration is shown in Figure

- 20 8A. Figure 8B shows the iso-contrast plots modelled for a Von of 5.0 and Voff of 0.5. The on axis contrast is calculated to be greater than 100:1. The 10:1 contrast area extends to +50/ -30 vertically and +80 / 80 horizontally. The 100:1 contrast area extends to +15 / -10 5 vertically and +55 / -55 horizontally.

Claims (9)

l- Claims

1. A compensator for use in new mode liquid crystal displays, characterized in that it comprises at least one retardation film s having an optical axis that is substantially parallel to the film plane (A plate) and/or at least one retardation film having an optical axis that is tilted at an angle between 0 and 90 relative to the film plane (O plate) .

to

2. A compensator as claimed in claim 1, which comprises at least two O plates wherein the tilt angle varies in a direction perpendicular to the film plane.

3. A compensator as claimed in claim 1, which comprises at least four Is A plates.

4. A compensator as claimed in claim 2, which further comprises at least two A plates.

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5. A compensator as claimed in any of the preceding claims, which additionally comprises at least one negative C plate.

6. A compensator as claimed in any of the preceding claims, wherein the A plate(s) and/or O plate(s) and/or C plate(s) comprise :, polymerized or crosslinked liquid crystal material.

7. A compensator substantially as hereinbefore described with reference to any of Examples 2 to

8.

to 8. A liquid crystal display comprising a liquid crystal layer having an initial alignment which is essentially parallel to the substrates and is essentially untwisted, at least one polariser, a device for generating

an electric field which is aligned essentially parallel to the

substrates in the case of liquid crystal materials of negative dielectric anisotropy and is aligned essentially perpendicular to the substrates in the case of liquid crystal materials of positive dielectric 5 anisotropy, and, if desired, at least one birefringent layer, said liquid crystal layer having an optical retardation [d.An)Lc] in the range from 0.05 Am to 0.46 m, characterized in that the display further comprises a compensator to as claimed in any of the preceding claims.

9. Use of a compensator as claimed in any of claims 1 to 7 in a new mode liquid crystal display.