Title of Invention	IN-PLANE SWITCHING LIQUID CRYSTAL DISPLAY
Abstract	The present invention relates to an in-plane switching liquid crystal display (1PSLCD) including a compensation film. To improve the contrast characteristics when viewed from the front thereof, and at a predetermined inclination angle of the in-plane switching liquid crystal display while minimizing a color shift according to viewing angles in the black state, the present invention is characterized in that the in-plane switching liquid crystal display uses at least one A-plate (11, 13) and adjusts the optical axis direction (12, 14) and the retardation value of the A-plate.

Title of Invention

IN-PLANE SWITCHING LIQUID CRYSTAL DISPLAY

Abstract

The present invention relates to an in-plane switching liquid crystal display (1PSLCD) including a compensation film. To improve the contrast characteristics when viewed from the front thereof, and at a predetermined inclination angle of the in-plane switching liquid crystal display while minimizing a color shift according to viewing angles in the black state, the present invention is characterized in that the in-plane switching liquid crystal display uses at least one A-plate (11, 13) and adjusts the optical axis direction (12, 14) and the retardation value of the A-plate.

Full Text	Technical Field [1 ] The present invention relates to a liquid crystal display (LCD). More particularly, the present invention relates to an in-plane switching liquid crystal display (IPS-LCD) including a compensation film employing at least one A-plate while adjusting an optical axis direction and a retardation value thereof in order to improve a viewing angle characteristic of the IPS-LCD filled with liquid crystal of positive dielectric anisotropy (Δ ε >0) or negative dielectric anisotropy ( Δ ε Background Art [2] IPS-LCDs are disclosed in US Patent No. 3,807,831, but this patent does not disclose the use of viewing-angle compensation films. IPS-LCDs including no viewing-angle compensation films have a disadvantage in that they have a low contrast ratio due to a relatively great amount of light leakage in the dark state at inclination angle. Disclosure [3] It is an object of the present invention to provide an IPS-LCD representing a superior contrast characteristic and a low color shift at a front and at a predetermined inclination angle of the IPS-LCD by minimizing light leakage in a black state of the IPS-LCD at the predetermined inclination angle. [4] The viewing angle characteristic of the IPS-LCD may be lowered due to a dependency of an orthogonality between the absorption axes of two polarizer plates to the viewing angle and a dependency of a birefringence of an IPS-LCD panel to the viewing angle. [5] The present inventors have found that +A-plates with an optical axis direction and a retardation value adjusted according to an alignment order thereof are necessary to solve the above problems lowering the viewing angle characteristic of the IPS-LCD. On the basis of this finding, the present invention has been completed. 6] Accordingly, the present invention provides an in-plane switching liquid crystal display comprising: a first polarizer plate; a liquid crystal cell, which is filled with liquid crystal of positive dielectric anisotropy (Δ ε >0) or negative dielectric anisotropy ( Δ ε being aligned in-plane in parallel to a polarizer plate; and a second polarizer plate, wherein an absorption axis of the first polarizer plate is perpendicular to an absorption axis of the second polarizer plate, and the optical axis of the liquid crystal filled in the liquid crystal cell is parallel to the absorption axis of the first polarizer plate, wherein at least one A-plate is interposed between the polarizer plate and the liquid crystal cell in order to compensate for a viewing angle, and an optical axis direction and an in- plane retardation value of the A-plate are adjusted according to an alignment order of the A-plate. [7] The present invention is characterized by using upper and lower polarizer plates and at least one A-plate with the optical axis direction and the retardation value thereof adjusted according to the alignment order to the A-plate in order to compensate for the viewing angle of the IPS-LCD in the black state. [8 J The contrast ratio value is an index representing a degree of definition for an image, and a higher contrast ratio value allows a higher definition image. The IPS- LCD presents the lowest contrast characteristic at an inclination angle of 70 ° . If the contrast characteristic of the IPS-LCD can be improved at the inclination angle of 70 ° , the contrast characteristic of the IPS-LCD can be improved at all viewing angles. When the IPS-LCD exclusively uses the polarizer plate, a minimum contrast ratio value of the IPS-LCD at the inclination angle of 70 ° is identical to or less than 10:1. The present invention can improve the minimum contrast ratio value by using the A-1 plate. Description of Accompanying Drawings [9] FIG. 1 is a view illustrating a basic structure of an IPS-LCD. [ 10] FIG. 2 is a view illustrating the arrangement of the absorption axes of polarizer plates and the optical axis of liquid crystals of an IPS-LCD panel in the basic structure of FIG. 1. [11] FIG. 3 is a view illustrating a refractive index of a retardation film. [12] FIG. 4 is a view illustrating a structure of a first IPS-LCD including a viewing angle compensation film according to one embodiment of the present invention. [13] FIG. 5 is a view illustrating a structure of a second IPS-LCD including a viewing angle compensation film according to one embodiment of the present invention. [14] FIG. 6 is a view illustrating a structure of a third IPS-LCD including a viewing angle compensation film according to one embodiment of the present invention. [15] FIG. 7 is a view illustrating a structure of a fourth IPS-LCD including a viewing angle compensation film according to one embodiment of the present invention. [ 16] FIG. 8 is a view illustrating a structure of a fifth IPS-LCD including a viewing angle compensation film according to one embodiment of the present invention. [17] FIG. 9 is a graph representing a simulation result obtained from the first IPS-LCD including a viewing angle compensation film according to one embodiment of the present invention. [ 18] FIG. 10 is a graph representing a simulation result obtained from the second IPS- LCD including a viewing angle compensation film according to one embodiment of the present invention. Mode for Invention [ 19] Reference will now be made in detail to the preferred embodiments of the present invention. [20] FIG. 1 is a view illustrating a basic structure of an IPS-LCD. [21 ] The IPS-LCD includes a First polarizer plate, a second polarizer plate and a liquid crystal cell. An absorption axis 4 of the First polarizer plate is aligned in perpendicular to the an absorption axis 5 of the second polarizer plate and the absorption axis 4 of the first polarizer plate is parallel to an optical axis 6 of liquid crystal of an IPS-panel. In FIG. 2, two absorption axes 4 and 5 of two polarizer plates and one optical axis 6 of the liquid crystal are shown. [22] The liquid crystal display using a compensation Film according to the present invention includes the first polarizer plate 1, the liquid crystal cell 3, which is Homo- geneously aligned between two glass substrates and Filled with liquid crystal of positive dielectric anisotropy ( Δ ε the second polarizer plate 2. The optical axis 6 of the liquid crystal filled in the liquid crystal cell is aligned in-plane in parallel to the first and second polarizer plates 1 and 2. The absorption axis 4 of the First polarizer plate 1 is aligned in perpendicular to the absorption axis 5 of the second polarizer plate 2 and the absorption axis 4 of the first polarizer plate 1 is parallel to the optical axis 6 of the liquid crystal filled in the IPS- panel. In addition, according to the liquid crystal display of the present invention, one of first and second substrates 15 and 16 includes an active matrix drive electrode having a pair of electrodes, which is formed on a surface of the substrate adjacent to a liquid crystal layer. [23] A retardation value of the liquid crystal layer formed in the liquid crystal cell of the IPS-LCD according to the present invention is preferably 200nm to 350nm at a wavelength of 550nm. [24] In order to obtain the white state when voltage is applied to the IPS-panel, light which is linearly polarized at an angle of 90 ° by passing through the first polarizer plate must be linearly polarized at an angle of 0 ° by passing through the liquid crystal layer. To this end, the retardation value of the liquid crystal layer of the IPS-panel must be set to a half of 589nm, wherein 589nm is a wavelength of monochromatic light providing highest brightness for people. In order to obtain a white color, the retardation value of the liquid crystal layer can be adjusted slightly shorter than or longer than the half of the 589nm. Therefore, preferably, the liquid crystal layer has the retardation value of about 295nm, which is about a half of the 589nm. [25] The LCD according to the present invention may align the liquid crystal in mu lti- domains, or the liquid crystal may be divided into multi-domains as voltage is applied thereto. [26] The LCDs can be classified into IPS (In-Plane Switching) LCDs, Super-IPS (Super-In-Plane Switching) LCDs and FFS (Fringe-Field Switching) LCDs according to modes of the active matrix drive electrode including a pair of electrodes. In the present invention, the IPS-LCD may include the Super-IPS LCD, the FFS LCD, or a reverse TN IPS LCD. [27] FIG. 3 illustrates a refractive index of a retardation film used for compensating for a viewing angle of the IPS-LCD. Referring to FIG. 3, an in-plane refractive index in an x-axis direction having a higher refractive index is n (8), an in-plane refractive index in a y-axis direction having a smaller refractive index is n (9), and a thickness refractive y index in a z-axis direction is n (10). Depending on the magnitudes of the refractive indexes, the characteristics of the retardation films will be determined. [28] A film where the refractive indexes in the two-axis directions among the refractive indexes in the three-axis directions are different from each other is referred to as an uniaxial film. A film with n > n -n is referred to as a positive A-plate, the in-plane x v r retardation value of which is defined using the difference between two refractive indexes lying in a plane, and the thickness of the film as given in the following equation 1. [29] (Equation 1) [30] R =dx(n -n ) wherein d represents the thickness of the film. in x y [31 ] FIGS. 4 to 8 show structures of viewing angle compensation films including the A- plate according to the present invention. [32] An IPS-panel 3 is interposed between two orthogonal polarizer plates 1 and 2, wherein liquid crystal molecules 7 of the IPS-panel are aligned in parallel to an IPS- LCD panel substrate in a rubbing direction, which is formed on the substrate by surface-treating the substrate such that liquid crystal molecules are aligned in one direction. [33] In order to obtain the viewing angle compensation function, the retardation film must be interposed between the liquid crystal cell 3 and the polarizer plates. [34] An optical axis (or a slow axis) of the retardation film is determined according to the structure of the retardation film. The optical axis of the retardation film can be aligned in perpendicular to or parallel to an absorption axis of an adjacent polarizer plate. [35] The retardation value of the retardation film is determined according to an alignment order of the retardation film. [36] FIGS. 4 to 7 show structures of the IPS-LCDs including the viewing angle com- pensalion films according to the present invention. Herein, it should be noted that a relative position between a backlight unit and an observer must not be inter-changed. The A-plate can be represented with a non-diagonalized matrix at a predetermined in- clination angle because the non-diagonalized matrix may output different results depending on a multiplication order. [37] According to a first embodiment of the present invention, there is provided an LCD including an A-plate 11 interposed between a second polarizer plate 2 and a liquid crystal cell 3, wherein an optical axis 12 of the A-plate 11 is parallel to an absorption axis 5 of the second polarizer plate 2 and the A-plate 11 has an in-plane retardation value in a range of 250nm to 450nm at a wavelength of 550nm. (38] In order to allow the A-plate to compensate for the retardation caused by the IPS- liquid crystal cell, the optical axis of the IPS-liquid crystal cell must be aligned perpen- dicularly to the optical axis of the A-plate in a black state of the IPS-LCD. Therefore, the optical axis 12 of the A-plate 11 must be aligned in parallel to the absorption axis 5 of the second polarizer plate 2. [39] The A-plate 11 has the in-plane retardation value in a range of 250nm to 450nm at a wavelength of 550nm due to the following reason. [40] The IPS-liquid crystal cell interposed between the orthogonal polarizer plates is converted into the white state only when the light, which has been linearly polarized at an angle of 0 ° , is linearly polarized at an angle of 90 ° after passing through the liquid crystal cell when voltage is applied to the IPS-panel under the conditions in which the retardation value of the liquid crystal cell is a half ( λ/2) of 589nm and the optical axis of the liquid crystal cell is inclined at an angle of 45 ° with respect to the absorption axis of the polarizer plate. However, since the design value may vary depending on wavelength dispersion characteristics of the liquid crystal, the above function can be obtained only when the retardation value of the A-plate is in a range of 250nm to 450nm. [41] The first embodiment of the present invention is shown in FIG. 4. [42] Table 1 shows a simulation result obtained from the first IPS-LCD structure as shown in FIG. 4 when the design value of the retardation film is actually applied to the first IPS-LCD structure. [43] Table 1 [44] When the IPS-LCD exclusively uses the polarizer plate, the minimum contrast ratio value of the IPS-LCD is identical to or less than 10:1 at an inclination angle of 70 ° . Since the minimum contrast ratio value can be obtained in all viewing angles at the in- clination angle of 70 ° , the improvement of the contrast ratio value at the inclination angle of 70 ° means the improvement of the contrast ratio value in all viewing angles. [45] Table 1 shows the improvement result of the viewing angle characteristic (contrast characteristic) by using the A-plate, in which the most superior viewing angle char- acteristic can be obtained when the minimum contrast ratio at the inclination angle of 70 ° has a maximum value. [46] According to a second embodiment of the present invention, there is provided an LCD including an A-plate 11 interposed between a second polarizer plate 2 and a liquid crystal cell 3, wherein an optical axis 12 of the A-plate 11 is perpendicular to an absorption axis 5 of the second polarizer plate 2 and the A-plate 11 has an in-plane re- tardation value in a range of 50nm to 150nm at a wavelength of 550nm. [47] Herein, the optical axis 12 of the A-plate 11 must be perpendicular to the absorption axis 5 of the second polarizer plate 2 and the A-plate 11 must have the in- plane retardation value in a range of 50nm to 150nm at a wavelength of 550nm due to the following reason. [48] When the optical axis of the IPS-liquid crystal cell is aligned in parallel to the optical axis of the A-plate, the total retardation value(sum of retardation value of IPS- Panel and A-Plate) is 3/4X. at a wavelength of 550nrn. In addition, if a 1/4 λ retardation film or a 3/4X retardation film is aligned perpendicularly to the absorption axis of the polarizer plate, light leakage generated at a predetermined inclination angle caused by the polarizer plates can be minimized. Therefore, in order to allow the A-plate to perform the above function together with the IPS-Liquid crystal cell, the A-plate is designed such that the total retardation value of the A-plate and the IPS-liquid crystal cell is set to 3/4 λ at the wavelength of 550nm. That is, since the design value may vary depending on the wavelength dispersion characteristics of the IPS-liquid Crystal cell and the A-plate, the retardation value of the A-plate is set to the above range in order to obtain the total retardation value of 3/4 λ. [49] The second embodiment of the present invention is shown in FIG. 5. [50] Table 2 shows a simulation result obtained from the second IPS-LCD structure as shown in FIG. 5 when the design value of the retardation film is actually applied to the second IPS-LCD structure. [51] [52] According to a third embodiment of the present invention, there is provided an LCD including an A-plate 11 interposed between a first polarizer plate 1 and a liquid crystal cell 3, wherein an optical axis 12 of the A-plate 11 is parallel to an absorption axis 4 of the first polarizer plate 1 and the A-plate 11 has an in-plane retardation value in a range of 40nm to 150nm at a wavelength of 550nm. [53] Herein, the optical axis 12 of the A-plate 11 must be parallel to the absorption axis 4 of the first polarizer plate 1 and the A-plate 11 must have the in-plane retardation value in a range of 40nm to 150nm at a wavelength of 550nm due to the following reason. [54] When the optical axis of the EPS-liquid crystal cell is aligned in parallel to the optical axis of the A-plate, the total retardation value is 3/4 λ at a wavelength of 550nm. In addition, if a 1/4 λ retardation film or a 3/4 λ retardation film is aligned per- pendicularly to the absorption axis of the polarizer plate, light leakage generated at a predetermined inclination angle caused by the polarizer plates can be minimized. Therefore, in order to allow the A-plate to perform the above function together with the IPS-Liquid Crystal cell, the A-plate is designed such that the total retardation value of the A-plate and the IPS-liquid crystal cell is set to 3/4 λ at the wavelength of 550nm. That is, since the design value may vary depending on the wavelength dispersion char- acteristics of the IPS-liquid Crystal cell and the A-plate, the retardation value of the A- plate is set to the above range in order to obtain the total retardation value of 3/4 λ. [55] The third embodiment of the present invention is shown in FIG. 6. [56] Table 3 shows a simulation result obtained from the third IPS-LCD structure as shown in FIG. 6 when the design value of the retardation film is actually applied to the third IPS-LCD structure. [57] [58] According to a fourth embodiment of the present invention, there is provided an LCD including a first A-plate 11 interposed between a first polarizer plate 1 and a liquid crystal cell 3 and a second A-plate 13 interposed between the liquid crystal cell 3 and a second polarizer plate 2, wherein an optical axis 12 of the first A-plate 11 is parallel to an absorption axis 4 of the first polarizer plate I, an optical axis 14 of the second A-plate 13 is parallel to an absorption axis 5 of the second polarizer plate 2, the First A-plate 11 has an in-plane retardation value in a range of 100nm to 150nm at a wavelength of 550nm, and the second A-plate 13 has an in-plane retardation value in a range of 350nm to 450nm at a wavelength of 550nm. [59] Herein, the optical axis 12 of the first A-plate 11 must be parallel to the absorption axis 4 of the first polarizer plate I, the optical axis 14 of the second A-plate 13 must be parallel to the absorption axis 5 of the second polarizer plate 2, the first A-plate 11 must have the in-plane retardation value in a range of 100nm to 150nm at a wavelength of 550nm, and the second A-plate 13 must have the in-plane retardation value in a range of 350nm to 450nm at a wavelength of 550nm due to the following reason. [60] In order to minimize light leakage caused by the orthogonal polarizer plates at a predetermined inclination angle by using the A-plate, a 1/4 λ retardation film or a 3/4 λ retardation film at the wavelength of 550nm is used. To this end, the first and second A-plates have the above retardation values such that the total retardation value of the IPS-liquid crystal cell, which is a kind of the A-plates, and the A-plates is set to 1/4 λ at the wavelength of 550nm. In the wavelength of 550nm, the first A-plate plays a role of a 1/4 λ A-plate, the IPS-liquid crystal cell plays a role of a 1/2 λ A-plate, and the second A-plate plays a role of a -1/2 λ A-plate. Accordingly, the total in-plane re- tardation value is set to 1/4 λ. That is, according to the fourth embodiment of the present invention, after forming an A-plate unit including the first and second A-plates and the IPS-liquid crystal cell such that the A-plate unit has the total in-plane re- tardation value of 1/4 λ, the A-plate unit is aligned perpendicularly to the absorption axis of the first polarizer plate. [61) The fourth embodiment of the present invention is shown in FIG. 7. [62] Table 4 shows a simulation result obtained from the fourth IPS-LCD structure as shown in FIG. 7 when the design value of the retardation film is actually applied to the third IPS-LCD structure. [63] [64] According to a fifth embodiment of the present invention, there is provided an LCD including first and second A-plates 11 and 13 interposed between a second polarizer plate 2 and a liquid crystal cell 3, wherein the second A-plate film 13 is adjacent to the second polarizer plate 2, an optical axis (n )12 of the first A-plate 11 is perpendicular to an absorption axis 5 of the second polarizer plate 2, an optical axis 14 of the second A-plate 13 is parallel to an absorption axis 5 of the second polarizer plate 2, the first A-plate 11 has an in-plane retardation value in a range of 100nm to 150nm at a wavelength of 550nm, and the second A-plate 13 has an in-plane retardation value in a range of 350nm to 450nm at a wavelength of 550nm. [65] Herein, the optical axis of the first A-plate must be perpendicular to the absorption axis 5 of the second polarizer plate 2, the optical axis 14 of the second A-plate 13 must be parallel to the absorption axis 5 of the second polarizer plate 2, the first A-plate 11 must have the in-plane retardation value in a range of 100nm to I50nm at a wavelength of 550nm, and the second A-plate 13 must have the in-plane retardation value in a range of 350nm to 450nm at a wavelength of 550nm due to the following reason. [661 The first and second A-plates are designed such that the total retardation value of the IPS-liquid crystal cell and the first and second A-plates is set to 3/4 λ at the wavelength of 550nm. That is, at the wavelength of 550nm, the IPS-liquid crystal cell plays a role of a 1/2 \ A-plate, the first A-plate plays a role of a -1/4 λ A-plate, and the second A-plate plays a role of a 1/2 λ A-plate. That is, according to the fifth embodiment of the present invention, after forming an A-plate unit including the first and second A-plates and the IPS-liquid crystal cell such that the A-plate unit has the total in-plane retardation value of 3/4 λ, the A-plate unit is aligned perpendicularly to the absorption axis of the first polarizer plate, thereby minimizing light leakage at a predetermined inclination angle caused by the polarizer plates. [67] The fifth embodiment of the present invention is shown in FIG. 8. [68] Table. 5 shows a simulation result obtained from the fifth IPS-LCD structure as shown in FIG. 8 when the design value of the retardation film is actually applied to the third IPS-LCD structure. [69] [70] The polarizer plates may include protective films used for protecting a polarizer element made from stretched PVA (polyvinyl alcohol) doped with iodine. In addition, the protective film can be made from TAC (triacetate cellulose) having a thickness re- tardation value, such as 400 TAC or 80 D TAC , PNB (polynorbomene) or COP (cyclo olefin) having no thickness retardation value. The viewing angle compensation char- acteristic of the IPS-LCD may be influenced by the protective film used for protecting the polarizer element. [71 ] According to the present invention, the A-plate can be made from polymer or a cured liquid crystal film. [72] In addition, according to the present invention, the A-plate film can be used as an internal protective film for at least one polarizer plate. Since the internal protective film of the polarizer plate is used for protecting the polarizer element, a transparent material having the polarizer element protecting function is used as the internal protective film. That is, since the A-plate is made from the transparent material having the polarizer element protecting function, the A-plate film can be used as a retardation film having the polarizer element protecting function. [73] Embodiments [74] Hereinafter, preferred embodiments of the present invention will be described. However, it is noted that the preferred embodiments described below are used for il- lustrative purpose only and the present invention is not limited thereto. [75] Embodiment 1 [76] The IPS-LCD shown in FIG. 4 includes the IPS-liquid crystal cell 3 filled with the liquid crystal having a cell gap of 2.9 D, a prelilt angle of 3 ° , dielectric anisotropy of A E = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate 11 is fabricated by using stretched m-PC (modified-polycarbonate) and has an in-plane re- tardation value R = 395nm at a wavelength of 550nm. The internal protective film for in the first polarizer plate is made from non-oriented COP (COP without stretching) having no retardation value , and the internal protective film for the second polarizer plate is made from TAC (Triacetate Cellulose) having a thickness of about 80 and a thickness retardation value R = -65nm. FIG. 9 shows the simulation result for the lh contrast ratio value of the IPS-LCD at all inclination angles for all azimuthal angles when the A-plate is used as the viewing angle compensation film under the above cir- cumstance. [77] Referring to FIG. 9, a center of a circle corresponds to an inclination angle of 0, and the inclination angle increases as a radius of the circle becomes enlarged. Numerals 20, 40,60 and 80 marked along the radius of the circle in FIG. 9 represent the inclination angles. [78] In addition, numerals 0 to 330 marked along a circumference of the circle represent the azimuthal angles. FIG. 9 shows the contrast characteristic in all viewing directions (inclination angles of 0 ° to 80 ° and azimuthal angles of 0 ° to 360 ° ) when an upper polarizer plate is aligned in a direction of an azimuthal angle of 0 ° , and a lower polarizer plate is aligned in a direction of an azimuthal angle of 90 ° . The conventional IPS-LCD, which exclusively uses the polarizer plates, may represent a contrast ratio equal to or less than 10:1 at an inclination angle of 70 ° . However, the IPS-LCD of the present invention represents a superior contrast ratio above 30:1 at an inclination angle of 70 ° as shown in FIG. 9 and Table 1. [79] Embodiment 2 [80] The IPS-LCD shown in FIG. 4 includes the IPS-liquid crystal cell 3 filled with the liquid crystal having a cell gap of 2.9 ⌂, a pretilt angle of 3 °, dielectric anisotropy of Δ ε - +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate 11 is fabricated by using stretched m-PC (modified-polycarbonate) and has an in-plane re- tardation value R = 412nm at a wavelength of 550nm. The internal protective film for the first polarizer plate 1 is made from TAC (Triacetate Cellulose) having a thickness of about 40 D and a thickness retardation value R = -32nm, and the internal protective film for the second polarizer plate 2 is made from TAC (Triacetate Cellulose) having a thickness of about 80 Q and a thickness retardation value R = -65nm. When the above lh viewing angle compensation film and polarizer plates are employed, the minimum contrast ratio value of the IPS-LCD at an inclination angle of 70 ° for all azimuthal angles is 75:1 (see, Table 4). [81] Embodiment 3 [82] The IPS-LCD shown in FIG. 5 includes the IPS-liquid crystal cell 3 filled with the liquid crystal having a cell gap of 2.9 D, a pretilt angle of 3 °, dielectric anisotropy of A e = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate 11 is fabricated by using stretched m-PC (modified-polycarbonate) and has an in-plane re- tardation value R = 110nm at a wavelength of 550nm. The internal protective film for in ~ the first polarizer plate 1 is made from TAC (Triacetate Cellulose) having a thickness of about 40 0 and a thickness retardation value R = -32nm, and the internal protective film for the second polarizer plate 2 is made from COP having a retardation value of about 0. When the above viewing angle compensation film and polarizer plates are employed, the minimum contrast ratio value of the IPS-LCD at an inclination angle of 70 ° for all azimuthal angles is 20:1 (see, Table 2). [83] Embodiment 4 [84] The IPS-LCD shown in FIG. 5 includes the IPS-liquid crystal cell 3 filled with the liquid crystal having a cell gap of 2.9 0, a pretilt angle of 3 °, dielectric anisotropy of A ε = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate 11 is fabricated by using stretched m-PC (modified-polycarbonate) and has an in-plane re- tardation value R = 117nm at a wavelength of 550nm. The internal protective film for the first polarizer plate 1 is made from TAC (Triacetate Cellulose) having a thickness of about 80 0 and a thickness retardation value R = -65nm, and the internal protective film for the second polarizer plate 2 is made from COP having a retardation value of about 0. When the above viewing angle compensation film and polarizer plates are employed, the minimum contrast ratio value of the IPS-LCD at an inclination angle of 70 ° for all azimuthal angles is 25:1 (see, Table 2). [85] Embodiment 5 [86] The IPS-LCD shown in FIG. 5 includes the IPS-liquid crystal cell 3 filled with the liquid crystal having a cell gap of 2.9 D, a pretilt angle of 3 °, dielectric anisotropy of A e = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate 11 is fabricated by using stretched m-PC (modified-polycarbonate) and has an in-plane re- tardation value R = 50nm at a wavelength of 550nm. The internal protective film for in the first polarizer plate 1 is made from TAC (Triacetate Cellulose) having a thickness of about 80 0 and a thickness retardation value R = -65nm, and the internal protective ih film for the second polarizer plate 2 is made from TAC (Triacetate Cellulose) having a thickness of about 80 D and a thickness retardation value R = -65nm. When the above lb viewing angle compensation film and polarizer plates are employed, the minimum contrast ratio value of the IPS-LCD at an inclination angle of 70 ° for all azimuthal angles is 15:1 (see, Table 2). [87] Embodiment 6 [88] The IPS-LCD shown in FIG. 6 includes the IPS-liquid crystal cell 3 filled with the liquid crystal having a cell gap of 2.9 D, a pretilt angle of 3 ° , dielectric anisotropy of A e = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate 11 is fabricated by using stretched m-PC (modified-polycarbonate) and has an in-plane re- tardation value R = 85nm at a wavelength of 550nm. The internal protective film for in the first polarizer plate 1 is made from TAC (Triacetate Cellulose) having a thickness of about 40 D and a thickness retardation value R = -32nm, and the internal protective lb film for the second polarizer plate 2 is made from COP having a retardation value of about 0. When the above viewing angle compensation film and polarizer plates are employed, the minimum contrast ratio value of the IPS-LCD at an inclination angle of 70 ° for all azimuthal angles is 15:1 (see, Table 3). [89] Embodiment 7 [90] The IPS-LCD shown in FIG. 6 includes the IPS-liquid crystal cell 3 filled with the liquid crystal having a cell gap of 2.9 D, a pretilt angle of 3 ° .dielectric anisotropy of Δ ε = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate 11 is fabricated by using stretched m-PC (modified-polycarbonate) and has an in-plane re- tardation value R = 105nm at a wavelength of 550nm. The internal protective film for in the first polarizer plate 1 is made from TAC (Triacetate Cellulose) having a thickness of about 80 D and a thickness retardation value R = -65nm, and the internal protective tb film for the second polarizer plate 2 is made from COP having a retardation value of about 0. When the above viewing angle compensation film and polarizer plates are employed, the minimum contrast ratio value of the IPS-LCD at an inclination angle of 70 ° for all azimuthal angles is 20:1 (see, Table 3). [91] Embodiment 8 [92] The IPS-LCD shown in FIG. 6 includes the IPS-liquid crystal cell 3 filled with the liquid crystal having a cell gap of 2.9 D, a pretilt angle of 3 ° , dielectric anisotropy of Δ ε = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate 11 is fabricated by using stretched m-PC (modified-polycarbonate) and has an in-plane re- tardation value R = 70nm at a wavelength of 550nm. The internal protective film for in the first polarizer plate 1 is made from TAC (Triacetate Cellulose) having a thickness of about 80 D and a thickness retardation value R = -65nm, and the internal protective film for the second polarizer plate 2 is made from TAC (Triacetate Cellulose) having a thickness of about 40 D and a thickness retardation value R = -32nm. When the above viewing angle compensation Film and polarizer plates are employed, the minimum contrast ratio value of the IPS-LCD at an inclination angle of 70 ° for all azimuthal angles is 20:1 (see, Table 3). [93] Embodiment 9 [941 The IPS-LCD shown in FIG. 7 includes the IPS-liquid crystal cell 3 filled with the liquid crystal having a cell gap of 2.9 0, a pretilt angle of 3 ° , dielectric anisotropy of A e = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate is fabricated by using stretched m-PC (modified-polycarbonate) and includes a first A- plate 11 having an in-plane retardation value R = 105nm at a wavelength of 550nm in and a second A-plate 13 having an in-plane retardation value R = 380nm at a in wavelength of 550nm. The internal protective film for the first polarizer plate I is made from TAC (Triacetate Cellulose) having a thickness of about 40 0 and a thickness retardation value R = -32nm, and the internal protective film for the second polarizer plate 2 is made from TAC (Triacetate Cellulose) having a thickness of about 40 D and a thickness retardation value R = -32nm. FIG. 10 shows the simulation result for the lh contrast ratio value at inclination angles for all azimuthal angles. When the above viewing angle compensation film and polarizer plates are employed, the minimum contrast ratio value of the IPS-LCD at an inclination angle of 70 ° for all azimuthal angles is 55:1 (see, Table 4). [95] Embodiment 10 [96] The IPS-LCD shown in FIG. 7 includes the IPS-liquid crystal cell 3 filled with the liquid crystal having a cell gap of 2.9 D, a pretilt angle of 3 ° , dielectric anisotropy of Δ ε = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate is fabricated by using stretched m-PC (modified-polycarbonate) and includes a first A- plate 11 having an in-plane retardation value R = 115nm at a wavelength of 550nm in and a second A-plate 13 having an in-plane retardation value R = 380nm at a in wavelength of 550nm. The internal protective film for the first polarizer plate 1 is made from TAC (Triacetate Cellulose) having a thickness of about 80 D and a thickness retardation value R = -65nm, and the internal protective film for the second polarizer plate 2 is made from TAC (Triacetate Cellulose) having a thickness of about 80 D and a thickness retardation value R = -65nm. When the above viewing angle compensation lh film and polarizer plates are employed, the minimum contrast ratio value of the IPS- LCD at an inclination angle of 70 ° for all azimuthal angles is 20:1 (see, Table 4). [97] Embodiment 11 [98] The IPS-LCD shown in FIG. 7 includes the EPS-liquid crystal cell 3 filled with the liquid crystal having a cell gap of 2.9 D, a pretilt angle of 3 ° , dielectric anisotropy of Δ ε = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate is fabricated by using stretched m-PC (modified-polycarbonate) and includes a first A- plate 11 having an in-plane retardation value R = 120nm at a wavelength of 550nm in and a second A-plate 13 having an in-plane retardation value R = 380nm at a in wavelength of 550nm. The internal protective film for the first polarizer plate 1 is made from TAC (Triacetate Cellulose) having a thickness of about 80 0 and a thickness retardation value R = -65nm, and the internal protective film for the second polarizer th plate 2 is made from TAC (Triacetate Cellulose) having a thickness of about 40 D and a thickness retardation value R - -32nm. When the above viewing angle compensation film and polarizer plates are employed, the minimum contrast ratio value of the IPS- LCD at an inclination angle of 70 ° for all azimuthal angles is 50:1 (see, Table 4). [99] Embodiment 12 [100] The IPS-LCD shown in FIG. 8 includes the IPS-liquid crystal cell 3 filled with the liquid crystal having a cell gap of 2.9 0, a pretilt angle of 3 ° , dielectric anisotropy of A e = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate is fabricated by using stretched m-PC (modified-polycarbonate) and includes a first A- plate 11 having an in-plane retardation value R = 125nm at a wavelength of 550nm in ~ and a second A-plate 13 having an in-plane retardation value R = 395nm at a in wavelength of 550nm. The internal protective film for the first polarizer plate 1 is made from TAC (Triacetate Cellulose) having a thickness of about 40 D and a thickness retardation value R = -32nm, and the internal protective film for the second polarizer plate 2 is made from TAC (Triacetate Cellulose) having a thickness of about 40 D and a thickness retardation value R = -32nm. When the above viewing angle compensation film and polarizer plates are employed, the minimum contrast ratio value of the IPS- LCD at an inclination angle of 70 ° for all azimuthal angles is 75:1 (see, Table 5). [101] Embodiment 13 [102] The IPS-LCD shown in FIG. 8 includes the IPS-liquid crystal cell 3 filled with the liquid crystal having a cell gap of 2.9 D, a pretilt angle of 3 ° , dielectric anisotropy of A e = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate is fabricated by using stretched m-PC (modified-polycarbonate) and includes a first A- plate 11 having an in-plane retardation value R = 125nm at a wavelength of 550nm in and a second A-plate 13 having an in-plane retardation value R = 395nm at a in wavelength of 550nm. The internal protective film for the first polarizer plate 1 is made from TAC (Triacetate Cellulose) having a thickness of about 40 D and a thickness retardation value R = -32nm, and the internal protective film for the second polarizer plate 2 is made from TAC (Triacetate Cellulose) having a thickness of about 80 0 and a thickness retardation value R = -65nm. When the above viewing angle compensation film and polarizer plates are employed, the minimum contrast ratio value of the IPS- LCD at an inclination angle of 70 ° for all azimuthal angles is 43:1 (see, Table 5). [103] Embodiment 14 [104] The IPS-LCD shown in FIG. 8 includes the IPS-liquid crystal cell 3 filled with the liquid crystal having a cell gap of 2.9 0, a pretilt angle of 3 D , dielectric anisotropy of Δ ε = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate is fabricated by using stretched m-PC (modified-polycarbonate) and includes a first A- plate 11 having an in-plane retardation value R = 125nm at a wavelength of 550nm in and a second A-plate 13 having an in-plane retardation value R = 390nm at a in wavelength of 550nm. The internal protective film for the first polarizer plate 1 is made from TAC (Triacetate Cellulose) having a thickness of about 80 0 and a thickness retardation value R = -65nm, and the internal protective film for the second polarizer th plate 2 is made from TAC (Triacetate Cellulose) having a thickness of about 80 D and a thickness retardation value R = -65nm. When the above viewing angle compensation th film and polarizer plates are employed, the minimum contrast ratio value of the IPS- LCD at an inclination angle of 70 ° for all azimutha] angles is 15:1 (see, Table 5). [ 105J While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment and the drawings, but, on the contrary, it is intended to cover various modifications and variations within the spirit and scope of the appended claims. Industrial Applicability [106] As described above, the in-plane switching liquid crystal display using at least one A-plate according to the present invention can improve the contrast characteristic at a front and at a predetermined inclination angle thereof by adjusting the optical axis direction and the retardation value of the A-plate while minimizing a color shift according to viewing angles in the black state. WE CLAIM: 1. An in-plane switching liquid crystal display comprising: a first polarizer plate (1); a liquid crystal cell (3), which is filled with liquid crystal of positive dielectric anisotropy (Δ ε > 0) or negative dielectric anisotropy (Δ ε liquid crystal filled in the liquid crystal cell (3) being aligned in-plane in parallel to a polarizer plate; and a second polarizer plate (2), wherein an absorption axis of the first polarizer plate (1) is perpendicular to an absorption axis(5) of the second polarizer plate (2), and the optical axis of the liquid crystal filled in the liquid crystal cell is parallel to the absorption axis of the first polarizer plate(l), wherein a first A-plate (11) is interposed between the first polarizer plate (1) and the liquid crystal cell (3), a second A-plate (13) is interposed between the liquid crystal cell (3) and the second polarizer plate (2), an optical axis (12) of the first A- plate (11) is parallel to the absorption axis (4) of the first polarizer plate (1), an optical axis (14) of the second A-plate (13) is parallel to the absorption axis (5) of the second polarizer plate (2), an in-plane retardation value of the first A-plate (11) is in a range of 100 nm to 150 nm at a wavelength of 550 nm and an in-plane retardation value of the second A-plate (13) is in a range of 350 nm to 450 nm at a wavelength of 550 nm. 2. An in-plane switching liquid crystal display comprising: a first polarizer plate (1); a liquid crystal cell (3), which is filled with liquid crystal of positive dielectric anisotropy (Δ ε > 0) or negative dielectric anisotropy (Δ ε liquid crystal filled in the liquid crystal cell (3) being aligned in-plane in parallel to a polarizer plate; and a second polarizer plate (2), wherein an absorption axis of the first polarizer plate (1) is perpendicular to an absorption axis of the second polarizer plate (2), and the optical axis of the liquid crystal filled in the liquid crystal cell (3) is parallel to the absorption axis of the first polarizer plate (1), wherein first and second A-plates (11; 13) are interposed between the liquid crystal cell (3) and the second polarizer plate (2), the second A-plate (13) is aligned adjacent to the second polarizer plate (2), an optical axis (12) of the first A-plate (13) is perpendicular to the absorption axis (5) of the second polarizer plate (2), an optical axis (14) of the second A-plate (13) is parallel to the absorption axis (5) of the second polarizer plate (2), an in-plane retardation value of the first A-plate is in a range of 100 nm to 150 nm at a wavelength of 550 run and an in-plane retardation value of the second A-plate (11) is in a range of 350 nm to 450 nm at a wavelength of 550 nm. 3. The in-plane switching liquid crystal display as claimed in claim 1 or 2, wherein the retardation value of the liquid crystal cell (3) is in a range of 200 nm to 350 nm at a wavelength of 550 nm. ABSTRACT IN-PLANE SWITCHING LIQUID CRYSTAL DISPLAY The present invention relates to an in-plane switching liquid crystal display (1PSLCD) including a compensation film. To improve the contrast characteristics when viewed from the front thereof, and at a predetermined inclination angle of the in-plane switching liquid crystal display while minimizing a color shift according to viewing angles in the black state, the present invention is characterized in that the in-plane switching liquid crystal display uses at least one A-plate (11, 13) and adjusts the optical axis direction (12, 14) and the retardation value of the A-plate.

Full Text

Technical Field
[1 ] The present invention relates to a liquid crystal display (LCD). More particularly,
the present invention relates to an in-plane switching liquid crystal display (IPS-LCD)
including a compensation film employing at least one A-plate while adjusting an
optical axis direction and a retardation value thereof in order to improve a viewing
angle characteristic of the IPS-LCD filled with liquid crystal of positive dielectric
anisotropy (Δ ε >0) or negative dielectric anisotropy ( Δ ε Background Art
[2] IPS-LCDs are disclosed in US Patent No. 3,807,831, but this patent does not
disclose the use of viewing-angle compensation films. IPS-LCDs including no
viewing-angle compensation films have a disadvantage in that they have a low contrast
ratio due to a relatively great amount of light leakage in the dark state at inclination
angle.
Disclosure
[3] It is an object of the present invention to provide an IPS-LCD representing a
superior contrast characteristic and a low color shift at a front and at a predetermined
inclination angle of the IPS-LCD by minimizing light leakage in a black state of the
IPS-LCD at the predetermined inclination angle.
[4] The viewing angle characteristic of the IPS-LCD may be lowered due to a
dependency of an orthogonality between the absorption axes of two polarizer plates to
the viewing angle and a dependency of a birefringence of an IPS-LCD panel to the
viewing angle.
[5] The present inventors have found that +A-plates with an optical axis direction and
a retardation value adjusted according to an alignment order thereof are necessary to
solve the above problems lowering the viewing angle characteristic of the IPS-LCD.
On the basis of this finding, the present invention has been completed.
6] Accordingly, the present invention provides an in-plane switching liquid crystal
display comprising: a first polarizer plate; a liquid crystal cell, which is filled with
liquid crystal of positive dielectric anisotropy (Δ ε >0) or negative dielectric
anisotropy ( Δ ε being aligned in-plane in parallel to a polarizer plate; and a second polarizer plate,
wherein an absorption axis of the first polarizer plate is perpendicular to an absorption

axis of the second polarizer plate, and the optical axis of the liquid crystal filled in the
liquid crystal cell is parallel to the absorption axis of the first polarizer plate, wherein
at least one A-plate is interposed between the polarizer plate and the liquid crystal cell
in order to compensate for a viewing angle, and an optical axis direction and an in-
plane retardation value of the A-plate are adjusted according to an alignment order of
the A-plate.
[7] The present invention is characterized by using upper and lower polarizer plates
and at least one A-plate with the optical axis direction and the retardation value thereof
adjusted according to the alignment order to the A-plate in order to compensate for the
viewing angle of the IPS-LCD in the black state.
[8 J The contrast ratio value is an index representing a degree of definition for an
image, and a higher contrast ratio value allows a higher definition image. The IPS-
LCD presents the lowest contrast characteristic at an inclination angle of 70 ° . If the
contrast characteristic of the IPS-LCD can be improved at the inclination angle of 70 °
, the contrast characteristic of the IPS-LCD can be improved at all viewing angles.
When the IPS-LCD exclusively uses the polarizer plate, a minimum contrast ratio
value of the IPS-LCD at the inclination angle of 70 ° is identical to or less than 10:1.
The present invention can improve the minimum contrast ratio value by using the A-1
plate.
Description of Accompanying Drawings
[9] FIG. 1 is a view illustrating a basic structure of an IPS-LCD.
[ 10] FIG. 2 is a view illustrating the arrangement of the absorption axes of polarizer
plates and the optical axis of liquid crystals of an IPS-LCD panel in the basic structure
of FIG. 1.
[11] FIG. 3 is a view illustrating a refractive index of a retardation film.
[12] FIG. 4 is a view illustrating a structure of a first IPS-LCD including a viewing
angle compensation film according to one embodiment of the present invention.
[13] FIG. 5 is a view illustrating a structure of a second IPS-LCD including a viewing
angle compensation film according to one embodiment of the present invention.
[14] FIG. 6 is a view illustrating a structure of a third IPS-LCD including a viewing
angle compensation film according to one embodiment of the present invention.
[15] FIG. 7 is a view illustrating a structure of a fourth IPS-LCD including a viewing
angle compensation film according to one embodiment of the present invention.
[ 16] FIG. 8 is a view illustrating a structure of a fifth IPS-LCD including a viewing
angle compensation film according to one embodiment of the present invention.
[17] FIG. 9 is a graph representing a simulation result obtained from the first IPS-LCD
including a viewing angle compensation film according to one embodiment of the
present invention.

[ 18] FIG. 10 is a graph representing a simulation result obtained from the second IPS-
LCD including a viewing angle compensation film according to one embodiment of
the present invention.
Mode for Invention
[ 19] Reference will now be made in detail to the preferred embodiments of the present
invention.
[20] FIG. 1 is a view illustrating a basic structure of an IPS-LCD.
[21 ] The IPS-LCD includes a First polarizer plate, a second polarizer plate and a liquid
crystal cell. An absorption axis 4 of the First polarizer plate is aligned in perpendicular
to the an absorption axis 5 of the second polarizer plate and the absorption axis 4 of the
first polarizer plate is parallel to an optical axis 6 of liquid crystal of an IPS-panel. In
FIG. 2, two absorption axes 4 and 5 of two polarizer plates and one optical axis 6 of
the liquid crystal are shown.
[22] The liquid crystal display using a compensation Film according to the present
invention includes the first polarizer plate 1, the liquid crystal cell 3, which is Homo-
geneously aligned between two glass substrates and Filled with liquid crystal of
positive dielectric anisotropy ( Δ ε the second polarizer plate 2. The optical axis 6 of the liquid crystal filled in the liquid
crystal cell is aligned in-plane in parallel to the first and second polarizer plates 1 and
2. The absorption axis 4 of the First polarizer plate 1 is aligned in perpendicular to the
absorption axis 5 of the second polarizer plate 2 and the absorption axis 4 of the first
polarizer plate 1 is parallel to the optical axis 6 of the liquid crystal filled in the IPS-
panel. In addition, according to the liquid crystal display of the present invention, one
of first and second substrates 15 and 16 includes an active matrix drive electrode
having a pair of electrodes, which is formed on a surface of the substrate adjacent to a
liquid crystal layer.
[23] A retardation value of the liquid crystal layer formed in the liquid crystal cell of the
IPS-LCD according to the present invention is preferably 200nm to 350nm at a
wavelength of 550nm.
[24] In order to obtain the white state when voltage is applied to the IPS-panel, light
which is linearly polarized at an angle of 90 ° by passing through the first polarizer
plate must be linearly polarized at an angle of 0 ° by passing through the liquid crystal
layer. To this end, the retardation value of the liquid crystal layer of the IPS-panel must
be set to a half of 589nm, wherein 589nm is a wavelength of monochromatic light
providing highest brightness for people. In order to obtain a white color, the retardation
value of the liquid crystal layer can be adjusted slightly shorter than or longer than the
half of the 589nm. Therefore, preferably, the liquid crystal layer has the retardation
value of about 295nm, which is about a half of the 589nm.

[25] The LCD according to the present invention may align the liquid crystal in mu lti-
domains, or the liquid crystal may be divided into multi-domains as voltage is applied
thereto.
[26] The LCDs can be classified into IPS (In-Plane Switching) LCDs, Super-IPS
(Super-In-Plane Switching) LCDs and FFS (Fringe-Field Switching) LCDs according
to modes of the active matrix drive electrode including a pair of electrodes. In the
present invention, the IPS-LCD may include the Super-IPS LCD, the FFS LCD, or a
reverse TN IPS LCD.
[27] FIG. 3 illustrates a refractive index of a retardation film used for compensating for
a viewing angle of the IPS-LCD. Referring to FIG. 3, an in-plane refractive index in an
x-axis direction having a higher refractive index is n (8), an in-plane refractive index in
a y-axis direction having a smaller refractive index is n (9), and a thickness refractive
y
index in a z-axis direction is n (10). Depending on the magnitudes of the refractive
indexes, the characteristics of the retardation films will be determined.
[28] A film where the refractive indexes in the two-axis directions among the refractive
indexes in the three-axis directions are different from each other is referred to as an
uniaxial film. A film with n > n -n is referred to as a positive A-plate, the in-plane
x v r
retardation value of which is defined using the difference between two refractive
indexes lying in a plane, and the thickness of the film as given in the following
equation 1.
[29] (Equation 1)
[30] R =dx(n -n ) wherein d represents the thickness of the film.
in x y
[31 ] FIGS. 4 to 8 show structures of viewing angle compensation films including the A-
plate according to the present invention.
[32] An IPS-panel 3 is interposed between two orthogonal polarizer plates 1 and 2,
wherein liquid crystal molecules 7 of the IPS-panel are aligned in parallel to an IPS-
LCD panel substrate in a rubbing direction, which is formed on the substrate by
surface-treating the substrate such that liquid crystal molecules are aligned in one
direction.
[33] In order to obtain the viewing angle compensation function, the retardation film
must be interposed between the liquid crystal cell 3 and the polarizer plates.
[34] An optical axis (or a slow axis) of the retardation film is determined according to
the structure of the retardation film. The optical axis of the retardation film can be
aligned in perpendicular to or parallel to an absorption axis of an adjacent polarizer
plate.
[35] The retardation value of the retardation film is determined according to an
alignment order of the retardation film.
[36] FIGS. 4 to 7 show structures of the IPS-LCDs including the viewing angle com-

pensalion films according to the present invention. Herein, it should be noted that a
relative position between a backlight unit and an observer must not be inter-changed.
The A-plate can be represented with a non-diagonalized matrix at a predetermined in-
clination angle because the non-diagonalized matrix may output different results
depending on a multiplication order.
[37] According to a first embodiment of the present invention, there is provided an LCD
including an A-plate 11 interposed between a second polarizer plate 2 and a liquid
crystal cell 3, wherein an optical axis 12 of the A-plate 11 is parallel to an absorption
axis 5 of the second polarizer plate 2 and the A-plate 11 has an in-plane retardation
value in a range of 250nm to 450nm at a wavelength of 550nm.
(38] In order to allow the A-plate to compensate for the retardation caused by the IPS-
liquid crystal cell, the optical axis of the IPS-liquid crystal cell must be aligned perpen-
dicularly to the optical axis of the A-plate in a black state of the IPS-LCD. Therefore,
the optical axis 12 of the A-plate 11 must be aligned in parallel to the absorption axis 5
of the second polarizer plate 2.
[39] The A-plate 11 has the in-plane retardation value in a range of 250nm to 450nm at
a wavelength of 550nm due to the following reason.
[40] The IPS-liquid crystal cell interposed between the orthogonal polarizer plates is
converted into the white state only when the light, which has been linearly polarized at
an angle of 0 ° , is linearly polarized at an angle of 90 ° after passing through the liquid
crystal cell when voltage is applied to the IPS-panel under the conditions in which the
retardation value of the liquid crystal cell is a half ( λ/2) of 589nm and the optical axis
of the liquid crystal cell is inclined at an angle of 45 ° with respect to the absorption
axis of the polarizer plate. However, since the design value may vary depending on
wavelength dispersion characteristics of the liquid crystal, the above function can be
obtained only when the retardation value of the A-plate is in a range of 250nm to
450nm.
[41] The first embodiment of the present invention is shown in FIG. 4.
[42] Table 1 shows a simulation result obtained from the first IPS-LCD structure as
shown in FIG. 4 when the design value of the retardation film is actually applied to the
first IPS-LCD structure.
[43] Table 1

[44] When the IPS-LCD exclusively uses the polarizer plate, the minimum contrast ratio
value of the IPS-LCD is identical to or less than 10:1 at an inclination angle of 70 ° .
Since the minimum contrast ratio value can be obtained in all viewing angles at the in-
clination angle of 70 ° , the improvement of the contrast ratio value at the inclination
angle of 70 ° means the improvement of the contrast ratio value in all viewing angles.
[45] Table 1 shows the improvement result of the viewing angle characteristic (contrast
characteristic) by using the A-plate, in which the most superior viewing angle char-
acteristic can be obtained when the minimum contrast ratio at the inclination angle of
70 ° has a maximum value.
[46] According to a second embodiment of the present invention, there is provided an
LCD including an A-plate 11 interposed between a second polarizer plate 2 and a
liquid crystal cell 3, wherein an optical axis 12 of the A-plate 11 is perpendicular to an
absorption axis 5 of the second polarizer plate 2 and the A-plate 11 has an in-plane re-
tardation value in a range of 50nm to 150nm at a wavelength of 550nm.
[47] Herein, the optical axis 12 of the A-plate 11 must be perpendicular to the
absorption axis 5 of the second polarizer plate 2 and the A-plate 11 must have the in-
plane retardation value in a range of 50nm to 150nm at a wavelength of 550nm due to
the following reason.
[48] When the optical axis of the IPS-liquid crystal cell is aligned in parallel to the
optical axis of the A-plate, the total retardation value(sum of retardation value of IPS-
Panel and A-Plate) is 3/4X. at a wavelength of 550nrn. In addition, if a 1/4 λ retardation
film or a 3/4X retardation film is aligned perpendicularly to the absorption axis of the
polarizer plate, light leakage generated at a predetermined inclination angle caused by
the polarizer plates can be minimized. Therefore, in order to allow the A-plate to

perform the above function together with the IPS-Liquid crystal cell, the A-plate is
designed such that the total retardation value of the A-plate and the IPS-liquid crystal
cell is set to 3/4 λ at the wavelength of 550nm. That is, since the design value may vary
depending on the wavelength dispersion characteristics of the IPS-liquid Crystal cell
and the A-plate, the retardation value of the A-plate is set to the above range in order to
obtain the total retardation value of 3/4 λ.
[49] The second embodiment of the present invention is shown in FIG. 5.
[50] Table 2 shows a simulation result obtained from the second IPS-LCD structure as
shown in FIG. 5 when the design value of the retardation film is actually applied to the
second IPS-LCD structure.
[51]
[52] According to a third embodiment of the present invention, there is provided an
LCD including an A-plate 11 interposed between a first polarizer plate 1 and a liquid
crystal cell 3, wherein an optical axis 12 of the A-plate 11 is parallel to an absorption
axis 4 of the first polarizer plate 1 and the A-plate 11 has an in-plane retardation value
in a range of 40nm to 150nm at a wavelength of 550nm.
[53] Herein, the optical axis 12 of the A-plate 11 must be parallel to the absorption axis
4 of the first polarizer plate 1 and the A-plate 11 must have the in-plane retardation
value in a range of 40nm to 150nm at a wavelength of 550nm due to the following
reason.
[54] When the optical axis of the EPS-liquid crystal cell is aligned in parallel to the
optical axis of the A-plate, the total retardation value is 3/4 λ at a wavelength of
550nm. In addition, if a 1/4 λ retardation film or a 3/4 λ retardation film is aligned per-
pendicularly to the absorption axis of the polarizer plate, light leakage generated at a
predetermined inclination angle caused by the polarizer plates can be minimized.
Therefore, in order to allow the A-plate to perform the above function together with
the IPS-Liquid Crystal cell, the A-plate is designed such that the total retardation value

of the A-plate and the IPS-liquid crystal cell is set to 3/4 λ at the wavelength of 550nm.
That is, since the design value may vary depending on the wavelength dispersion char-
acteristics of the IPS-liquid Crystal cell and the A-plate, the retardation value of the A-
plate is set to the above range in order to obtain the total retardation value of 3/4 λ.
[55] The third embodiment of the present invention is shown in FIG. 6.
[56] Table 3 shows a simulation result obtained from the third IPS-LCD structure as
shown in FIG. 6 when the design value of the retardation film is actually applied to the
third IPS-LCD structure.
[57]
[58] According to a fourth embodiment of the present invention, there is provided an
LCD including a first A-plate 11 interposed between a first polarizer plate 1 and a
liquid crystal cell 3 and a second A-plate 13 interposed between the liquid crystal cell
3 and a second polarizer plate 2, wherein an optical axis 12 of the first A-plate 11 is
parallel to an absorption axis 4 of the first polarizer plate I, an optical axis 14 of the
second A-plate 13 is parallel to an absorption axis 5 of the second polarizer plate 2, the
First A-plate 11 has an in-plane retardation value in a range of 100nm to 150nm at a
wavelength of 550nm, and the second A-plate 13 has an in-plane retardation value in a
range of 350nm to 450nm at a wavelength of 550nm.
[59] Herein, the optical axis 12 of the first A-plate 11 must be parallel to the absorption
axis 4 of the first polarizer plate I, the optical axis 14 of the second A-plate 13 must be
parallel to the absorption axis 5 of the second polarizer plate 2, the first A-plate 11
must have the in-plane retardation value in a range of 100nm to 150nm at a wavelength
of 550nm, and the second A-plate 13 must have the in-plane retardation value in a
range of 350nm to 450nm at a wavelength of 550nm due to the following reason.
[60] In order to minimize light leakage caused by the orthogonal polarizer plates at a
predetermined inclination angle by using the A-plate, a 1/4 λ retardation film or a 3/4 λ
retardation film at the wavelength of 550nm is used. To this end, the first and second

A-plates have the above retardation values such that the total retardation value of the
IPS-liquid crystal cell, which is a kind of the A-plates, and the A-plates is set to 1/4 λ
at the wavelength of 550nm. In the wavelength of 550nm, the first A-plate plays a role
of a 1/4 λ A-plate, the IPS-liquid crystal cell plays a role of a 1/2 λ A-plate, and the
second A-plate plays a role of a -1/2 λ A-plate. Accordingly, the total in-plane re-
tardation value is set to 1/4 λ. That is, according to the fourth embodiment of the
present invention, after forming an A-plate unit including the first and second A-plates
and the IPS-liquid crystal cell such that the A-plate unit has the total in-plane re-
tardation value of 1/4 λ, the A-plate unit is aligned perpendicularly to the absorption
axis of the first polarizer plate.
[61) The fourth embodiment of the present invention is shown in FIG. 7.
[62] Table 4 shows a simulation result obtained from the fourth IPS-LCD structure as
shown in FIG. 7 when the design value of the retardation film is actually applied to the
third IPS-LCD structure.
[63]
[64] According to a fifth embodiment of the present invention, there is provided an
LCD including first and second A-plates 11 and 13 interposed between a second
polarizer plate 2 and a liquid crystal cell 3, wherein the second A-plate film 13 is
adjacent to the second polarizer plate 2, an optical axis (n )12 of the first A-plate 11 is
perpendicular to an absorption axis 5 of the second polarizer plate 2, an optical axis 14
of the second A-plate 13 is parallel to an absorption axis 5 of the second polarizer plate
2, the first A-plate 11 has an in-plane retardation value in a range of 100nm to 150nm
at a wavelength of 550nm, and the second A-plate 13 has an in-plane retardation value
in a range of 350nm to 450nm at a wavelength of 550nm.
[65] Herein, the optical axis of the first A-plate must be perpendicular to the absorption
axis 5 of the second polarizer plate 2, the optical axis 14 of the second A-plate 13 must
be parallel to the absorption axis 5 of the second polarizer plate 2, the first A-plate 11

must have the in-plane retardation value in a range of 100nm to I50nm at a wavelength
of 550nm, and the second A-plate 13 must have the in-plane retardation value in a
range of 350nm to 450nm at a wavelength of 550nm due to the following reason.
[661 The first and second A-plates are designed such that the total retardation value of
the IPS-liquid crystal cell and the first and second A-plates is set to 3/4 λ at the
wavelength of 550nm. That is, at the wavelength of 550nm, the IPS-liquid crystal cell
plays a role of a 1/2 \ A-plate, the first A-plate plays a role of a -1/4 λ A-plate, and the
second A-plate plays a role of a 1/2 λ A-plate. That is, according to the fifth
embodiment of the present invention, after forming an A-plate unit including the first
and second A-plates and the IPS-liquid crystal cell such that the A-plate unit has the
total in-plane retardation value of 3/4 λ, the A-plate unit is aligned perpendicularly to
the absorption axis of the first polarizer plate, thereby minimizing light leakage at a
predetermined inclination angle caused by the polarizer plates.
[67] The fifth embodiment of the present invention is shown in FIG. 8.
[68] Table. 5 shows a simulation result obtained from the fifth IPS-LCD structure as
shown in FIG. 8 when the design value of the retardation film is actually applied to the
third IPS-LCD structure.
[69]
[70] The polarizer plates may include protective films used for protecting a polarizer
element made from stretched PVA (polyvinyl alcohol) doped with iodine. In addition,
the protective film can be made from TAC (triacetate cellulose) having a thickness re-
tardation value, such as 400 TAC or 80 D TAC , PNB (polynorbomene) or COP (cyclo
olefin) having no thickness retardation value. The viewing angle compensation char-
acteristic of the IPS-LCD may be influenced by the protective film used for protecting
the polarizer element.
[71 ] According to the present invention, the A-plate can be made from polymer or a
cured liquid crystal film.
[72] In addition, according to the present invention, the A-plate film can be used as an

internal protective film for at least one polarizer plate. Since the internal protective
film of the polarizer plate is used for protecting the polarizer element, a transparent
material having the polarizer element protecting function is used as the internal
protective film. That is, since the A-plate is made from the transparent material having
the polarizer element protecting function, the A-plate film can be used as a retardation
film having the polarizer element protecting function.
[73] Embodiments
[74] Hereinafter, preferred embodiments of the present invention will be described.
However, it is noted that the preferred embodiments described below are used for il-
lustrative purpose only and the present invention is not limited thereto.
[75] Embodiment 1
[76] The IPS-LCD shown in FIG. 4 includes the IPS-liquid crystal cell 3 filled with the
liquid crystal having a cell gap of 2.9 D, a prelilt angle of 3 ° , dielectric anisotropy of A
E = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate 11 is
fabricated by using stretched m-PC (modified-polycarbonate) and has an in-plane re-
tardation value R = 395nm at a wavelength of 550nm. The internal protective film for
in
the first polarizer plate is made from non-oriented COP (COP without stretching)
having no retardation value , and the internal protective film for the second polarizer
plate is made from TAC (Triacetate Cellulose) having a thickness of about 80 and a
thickness retardation value R = -65nm. FIG. 9 shows the simulation result for the
lh
contrast ratio value of the IPS-LCD at all inclination angles for all azimuthal angles
when the A-plate is used as the viewing angle compensation film under the above cir-
cumstance.
[77] Referring to FIG. 9, a center of a circle corresponds to an inclination angle of 0,
and the inclination angle increases as a radius of the circle becomes enlarged.
Numerals 20, 40,60 and 80 marked along the radius of the circle in FIG. 9 represent
the inclination angles.
[78] In addition, numerals 0 to 330 marked along a circumference of the circle represent
the azimuthal angles. FIG. 9 shows the contrast characteristic in all viewing directions
(inclination angles of 0 ° to 80 ° and azimuthal angles of 0 ° to 360 ° ) when an upper
polarizer plate is aligned in a direction of an azimuthal angle of 0 ° , and a lower
polarizer plate is aligned in a direction of an azimuthal angle of 90 ° . The conventional
IPS-LCD, which exclusively uses the polarizer plates, may represent a contrast ratio
equal to or less than 10:1 at an inclination angle of 70 ° . However, the IPS-LCD of the
present invention represents a superior contrast ratio above 30:1 at an inclination angle
of 70 ° as shown in FIG. 9 and Table 1.
[79] Embodiment 2
[80] The IPS-LCD shown in FIG. 4 includes the IPS-liquid crystal cell 3 filled with the

liquid crystal having a cell gap of 2.9 ⌂, a pretilt angle of 3 °, dielectric anisotropy of Δ
ε - +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate 11 is
fabricated by using stretched m-PC (modified-polycarbonate) and has an in-plane re-
tardation value R = 412nm at a wavelength of 550nm. The internal protective film for
the first polarizer plate 1 is made from TAC (Triacetate Cellulose) having a thickness
of about 40 D and a thickness retardation value R = -32nm, and the internal protective
film for the second polarizer plate 2 is made from TAC (Triacetate Cellulose) having a
thickness of about 80 Q and a thickness retardation value R = -65nm. When the above
lh
viewing angle compensation film and polarizer plates are employed, the minimum
contrast ratio value of the IPS-LCD at an inclination angle of 70 ° for all azimuthal
angles is 75:1 (see, Table 4).
[81] Embodiment 3
[82] The IPS-LCD shown in FIG. 5 includes the IPS-liquid crystal cell 3 filled with the
liquid crystal having a cell gap of 2.9 D, a pretilt angle of 3 °, dielectric anisotropy of A
e = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate 11 is
fabricated by using stretched m-PC (modified-polycarbonate) and has an in-plane re-
tardation value R = 110nm at a wavelength of 550nm. The internal protective film for
in *~
the first polarizer plate 1 is made from TAC (Triacetate Cellulose) having a thickness
of about 40 0 and a thickness retardation value R = -32nm, and the internal protective
film for the second polarizer plate 2 is made from COP having a retardation value of
about 0. When the above viewing angle compensation film and polarizer plates are
employed, the minimum contrast ratio value of the IPS-LCD at an inclination angle of
70 ° for all azimuthal angles is 20:1 (see, Table 2).
[83] Embodiment 4
[84] The IPS-LCD shown in FIG. 5 includes the IPS-liquid crystal cell 3 filled with the
liquid crystal having a cell gap of 2.9 0, a pretilt angle of 3 °, dielectric anisotropy of A
ε = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate 11 is
fabricated by using stretched m-PC (modified-polycarbonate) and has an in-plane re-
tardation value R = 117nm at a wavelength of 550nm. The internal protective film for
the first polarizer plate 1 is made from TAC (Triacetate Cellulose) having a thickness
of about 80 0 and a thickness retardation value R = -65nm, and the internal protective
film for the second polarizer plate 2 is made from COP having a retardation value of
about 0. When the above viewing angle compensation film and polarizer plates are
employed, the minimum contrast ratio value of the IPS-LCD at an inclination angle of
70 ° for all azimuthal angles is 25:1 (see, Table 2).
[85] Embodiment 5
[86] The IPS-LCD shown in FIG. 5 includes the IPS-liquid crystal cell 3 filled with the
liquid crystal having a cell gap of 2.9 D, a pretilt angle of 3 °, dielectric anisotropy of A

e = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate 11 is
fabricated by using stretched m-PC (modified-polycarbonate) and has an in-plane re-
tardation value R = 50nm at a wavelength of 550nm. The internal protective film for
in
the first polarizer plate 1 is made from TAC (Triacetate Cellulose) having a thickness
of about 80 0 and a thickness retardation value R = -65nm, and the internal protective
ih
film for the second polarizer plate 2 is made from TAC (Triacetate Cellulose) having a
thickness of about 80 D and a thickness retardation value R = -65nm. When the above
lb
viewing angle compensation film and polarizer plates are employed, the minimum
contrast ratio value of the IPS-LCD at an inclination angle of 70 ° for all azimuthal
angles is 15:1 (see, Table 2).
[87] Embodiment 6
[88] The IPS-LCD shown in FIG. 6 includes the IPS-liquid crystal cell 3 filled with the
liquid crystal having a cell gap of 2.9 D, a pretilt angle of 3 ° , dielectric anisotropy of A
e = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate 11 is
fabricated by using stretched m-PC (modified-polycarbonate) and has an in-plane re-
tardation value R = 85nm at a wavelength of 550nm. The internal protective film for
in
the first polarizer plate 1 is made from TAC (Triacetate Cellulose) having a thickness
of about 40 D and a thickness retardation value R = -32nm, and the internal protective
lb
film for the second polarizer plate 2 is made from COP having a retardation value of
about 0. When the above viewing angle compensation film and polarizer plates are
employed, the minimum contrast ratio value of the IPS-LCD at an inclination angle of
70 ° for all azimuthal angles is 15:1 (see, Table 3).
[89] Embodiment 7
[90] The IPS-LCD shown in FIG. 6 includes the IPS-liquid crystal cell 3 filled with the
liquid crystal having a cell gap of 2.9 D, a pretilt angle of 3 ° .dielectric anisotropy of Δ
ε = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate 11 is
fabricated by using stretched m-PC (modified-polycarbonate) and has an in-plane re-
tardation value R = 105nm at a wavelength of 550nm. The internal protective film for
in
the first polarizer plate 1 is made from TAC (Triacetate Cellulose) having a thickness
of about 80 D and a thickness retardation value R = -65nm, and the internal protective
tb
film for the second polarizer plate 2 is made from COP having a retardation value of
about 0. When the above viewing angle compensation film and polarizer plates are
employed, the minimum contrast ratio value of the IPS-LCD at an inclination angle of
70 ° for all azimuthal angles is 20:1 (see, Table 3).
[91] Embodiment 8
[92] The IPS-LCD shown in FIG. 6 includes the IPS-liquid crystal cell 3 filled with the
liquid crystal having a cell gap of 2.9 D, a pretilt angle of 3 ° , dielectric anisotropy of Δ
ε = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate 11 is

fabricated by using stretched m-PC (modified-polycarbonate) and has an in-plane re-
tardation value R = 70nm at a wavelength of 550nm. The internal protective film for
in
the first polarizer plate 1 is made from TAC (Triacetate Cellulose) having a thickness
of about 80 D and a thickness retardation value R = -65nm, and the internal protective
film for the second polarizer plate 2 is made from TAC (Triacetate Cellulose) having a
thickness of about 40 D and a thickness retardation value R = -32nm. When the above
viewing angle compensation Film and polarizer plates are employed, the minimum
contrast ratio value of the IPS-LCD at an inclination angle of 70 ° for all azimuthal
angles is 20:1 (see, Table 3).
[93] Embodiment 9
[941 The IPS-LCD shown in FIG. 7 includes the IPS-liquid crystal cell 3 filled with the
liquid crystal having a cell gap of 2.9 0, a pretilt angle of 3 ° , dielectric anisotropy of A
e = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate is
fabricated by using stretched m-PC (modified-polycarbonate) and includes a first A-
plate 11 having an in-plane retardation value R = 105nm at a wavelength of 550nm
in
and a second A-plate 13 having an in-plane retardation value R = 380nm at a
in
wavelength of 550nm. The internal protective film for the first polarizer plate I is
made from TAC (Triacetate Cellulose) having a thickness of about 40 0 and a thickness
retardation value R = -32nm, and the internal protective film for the second polarizer
plate 2 is made from TAC (Triacetate Cellulose) having a thickness of about 40 D and a
thickness retardation value R = -32nm. FIG. 10 shows the simulation result for the
lh
contrast ratio value at inclination angles for all azimuthal angles. When the above
viewing angle compensation film and polarizer plates are employed, the minimum
contrast ratio value of the IPS-LCD at an inclination angle of 70 ° for all azimuthal
angles is 55:1 (see, Table 4).
[95] Embodiment 10
[96] The IPS-LCD shown in FIG. 7 includes the IPS-liquid crystal cell 3 filled with the
liquid crystal having a cell gap of 2.9 D, a pretilt angle of 3 ° , dielectric anisotropy of Δ
ε = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate is
fabricated by using stretched m-PC (modified-polycarbonate) and includes a first A-
plate 11 having an in-plane retardation value R = 115nm at a wavelength of 550nm
in
and a second A-plate 13 having an in-plane retardation value R = 380nm at a
in
wavelength of 550nm. The internal protective film for the first polarizer plate 1 is
made from TAC (Triacetate Cellulose) having a thickness of about 80 D and a thickness
retardation value R = -65nm, and the internal protective film for the second polarizer
plate 2 is made from TAC (Triacetate Cellulose) having a thickness of about 80 D and a
thickness retardation value R = -65nm. When the above viewing angle compensation
lh
film and polarizer plates are employed, the minimum contrast ratio value of the IPS-

LCD at an inclination angle of 70 ° for all azimuthal angles is 20:1 (see, Table 4).
[97] Embodiment 11
[98] The IPS-LCD shown in FIG. 7 includes the EPS-liquid crystal cell 3 filled with the
liquid crystal having a cell gap of 2.9 D, a pretilt angle of 3 ° , dielectric anisotropy of Δ
ε = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate is
fabricated by using stretched m-PC (modified-polycarbonate) and includes a first A-
plate 11 having an in-plane retardation value R = 120nm at a wavelength of 550nm
in
and a second A-plate 13 having an in-plane retardation value R = 380nm at a
in
wavelength of 550nm. The internal protective film for the first polarizer plate 1 is
made from TAC (Triacetate Cellulose) having a thickness of about 80 0 and a thickness
retardation value R = -65nm, and the internal protective film for the second polarizer
th
plate 2 is made from TAC (Triacetate Cellulose) having a thickness of about 40 D and a
thickness retardation value R - -32nm. When the above viewing angle compensation
film and polarizer plates are employed, the minimum contrast ratio value of the IPS-
LCD at an inclination angle of 70 ° for all azimuthal angles is 50:1 (see, Table 4).
[99] Embodiment 12
[100] The IPS-LCD shown in FIG. 8 includes the IPS-liquid crystal cell 3 filled with the
liquid crystal having a cell gap of 2.9 0, a pretilt angle of 3 ° , dielectric anisotropy of A
e = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate is
fabricated by using stretched m-PC (modified-polycarbonate) and includes a first A-
plate 11 having an in-plane retardation value R = 125nm at a wavelength of 550nm
in *~
and a second A-plate 13 having an in-plane retardation value R = 395nm at a
in
wavelength of 550nm. The internal protective film for the first polarizer plate 1 is
made from TAC (Triacetate Cellulose) having a thickness of about 40 D and a thickness
retardation value R = -32nm, and the internal protective film for the second polarizer
plate 2 is made from TAC (Triacetate Cellulose) having a thickness of about 40 D and a
thickness retardation value R = -32nm. When the above viewing angle compensation
film and polarizer plates are employed, the minimum contrast ratio value of the IPS-
LCD at an inclination angle of 70 ° for all azimuthal angles is 75:1 (see, Table 5).
[101] Embodiment 13
[102] The IPS-LCD shown in FIG. 8 includes the IPS-liquid crystal cell 3 filled with the
liquid crystal having a cell gap of 2.9 D, a pretilt angle of 3 ° , dielectric anisotropy of A
e = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate is
fabricated by using stretched m-PC (modified-polycarbonate) and includes a first A-
plate 11 having an in-plane retardation value R = 125nm at a wavelength of 550nm
in
and a second A-plate 13 having an in-plane retardation value R = 395nm at a
in
wavelength of 550nm. The internal protective film for the first polarizer plate 1 is
made from TAC (Triacetate Cellulose) having a thickness of about 40 D and a thickness

retardation value R = -32nm, and the internal protective film for the second polarizer
plate 2 is made from TAC (Triacetate Cellulose) having a thickness of about 80 0 and a
thickness retardation value R = -65nm. When the above viewing angle compensation
film and polarizer plates are employed, the minimum contrast ratio value of the IPS-
LCD at an inclination angle of 70 ° for all azimuthal angles is 43:1 (see, Table 5).
[103] Embodiment 14
[104] The IPS-LCD shown in FIG. 8 includes the IPS-liquid crystal cell 3 filled with the
liquid crystal having a cell gap of 2.9 0, a pretilt angle of 3 D , dielectric anisotropy of Δ
ε = +7, and a birefringence of An = 0.1 at a wavelength of 550nm. The A-plate is
fabricated by using stretched m-PC (modified-polycarbonate) and includes a first A-
plate 11 having an in-plane retardation value R = 125nm at a wavelength of 550nm
in
and a second A-plate 13 having an in-plane retardation value R = 390nm at a
in
wavelength of 550nm. The internal protective film for the first polarizer plate 1 is
made from TAC (Triacetate Cellulose) having a thickness of about 80 0 and a thickness
retardation value R = -65nm, and the internal protective film for the second polarizer
th
plate 2 is made from TAC (Triacetate Cellulose) having a thickness of about 80 D and a
thickness retardation value R = -65nm. When the above viewing angle compensation
th
film and polarizer plates are employed, the minimum contrast ratio value of the IPS-
LCD at an inclination angle of 70 ° for all azimutha] angles is 15:1 (see, Table 5).
[ 105J While this invention has been described in connection with what is presently
considered to be the most practical and preferred embodiment, it is to be understood
that the invention is not limited to the disclosed embodiment and the drawings, but, on
the contrary, it is intended to cover various modifications and variations within the
spirit and scope of the appended claims.
Industrial Applicability
[106] As described above, the in-plane switching liquid crystal display using at least one
A-plate according to the present invention can improve the contrast characteristic at a
front and at a predetermined inclination angle thereof by adjusting the optical axis
direction and the retardation value of the A-plate while minimizing a color shift
according to viewing angles in the black state.

WE CLAIM:
1. An in-plane switching liquid crystal display comprising:
a first polarizer plate (1);
a liquid crystal cell (3), which is filled with liquid crystal of positive dielectric
anisotropy (Δ ε > 0) or negative dielectric anisotropy (Δ ε liquid crystal filled in the liquid crystal cell (3) being aligned in-plane in parallel to a
polarizer plate; and
a second polarizer plate (2),
wherein an absorption axis of the first polarizer plate (1) is perpendicular to an
absorption axis(5) of the second polarizer plate (2), and the optical axis of the liquid
crystal filled in the liquid crystal cell is parallel to the absorption axis of the first
polarizer plate(l),
wherein a first A-plate (11) is interposed between the first polarizer plate (1)
and the liquid crystal cell (3), a second A-plate (13) is interposed between the liquid
crystal cell (3) and the second polarizer plate (2), an optical axis (12) of the first A-
plate (11) is parallel to the absorption axis (4) of the first polarizer plate (1), an optical
axis (14) of the second A-plate (13) is parallel to the absorption axis (5) of the second
polarizer plate (2), an in-plane retardation value of the first A-plate (11) is in a range
of 100 nm to 150 nm at a wavelength of 550 nm and an in-plane retardation value of
the second A-plate (13) is in a range of 350 nm to 450 nm at a wavelength of 550 nm.
2. An in-plane switching liquid crystal display comprising:
a first polarizer plate (1);
a liquid crystal cell (3), which is filled with liquid crystal of positive dielectric
anisotropy (Δ ε > 0) or negative dielectric anisotropy (Δ ε liquid crystal filled in the liquid crystal cell (3) being aligned in-plane in parallel to a
polarizer plate; and

a second polarizer plate (2),
wherein an absorption axis of the first polarizer plate (1) is perpendicular to an
absorption axis of the second polarizer plate (2), and the optical axis of the liquid
crystal filled in the liquid crystal cell (3) is parallel to the absorption axis of the first
polarizer plate (1),
wherein first and second A-plates (11; 13) are interposed between the liquid
crystal cell (3) and the second polarizer plate (2), the second A-plate (13) is aligned
adjacent to the second polarizer plate (2), an optical axis (12) of the first A-plate (13)
is perpendicular to the absorption axis (5) of the second polarizer plate (2), an optical
axis (14) of the second A-plate (13) is parallel to the absorption axis (5) of the second
polarizer plate (2), an in-plane retardation value of the first A-plate is in a range of 100
nm to 150 nm at a wavelength of 550 run and an in-plane retardation value of the
second A-plate (11) is in a range of 350 nm to 450 nm at a wavelength of 550 nm.
3. The in-plane switching liquid crystal display as claimed in claim 1 or 2,
wherein the retardation value of the liquid crystal cell (3) is in a range of 200 nm to
350 nm at a wavelength of 550 nm.

ABSTRACT

IN-PLANE SWITCHING LIQUID CRYSTAL DISPLAY
The present invention relates to an in-plane switching liquid crystal display (1PSLCD)
including a compensation film. To improve the contrast characteristics when viewed from the
front thereof, and at a predetermined inclination angle of the in-plane switching liquid crystal
display while minimizing a color shift according to viewing angles in the black state, the
present invention is characterized in that the in-plane switching liquid crystal display uses at
least one A-plate (11, 13) and adjusts the optical axis direction (12, 14) and the retardation
value of the A-plate.

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02199-kolnp-2006-correspondence others-1.1.pdf

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02199-kolnp-2006-form-1.pdf

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2199-KOLNP-2006-(04-11-2011)-ABSTRACT.pdf

2199-KOLNP-2006-(04-11-2011)-AMANDED CLAIMS.pdf

2199-KOLNP-2006-(04-11-2011)-CORRESPONDENCE.pdf

2199-KOLNP-2006-(04-11-2011)-DESCRIPTION (COMPLETE).pdf

2199-KOLNP-2006-(04-11-2011)-DRAWINGS.pdf

2199-KOLNP-2006-(04-11-2011)-FORM 1.pdf

2199-KOLNP-2006-(04-11-2011)-FORM 2.pdf

2199-KOLNP-2006-(04-11-2011)-OTHERS.pdf

2199-KOLNP-2006-(04-11-2011)-PETITION UNDER RULR 137.pdf

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2199-KOLNP-2006-(20-01-2012)-CORRESPONDENCE.pdf

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2199-KOLNP-2006-CORRESPONDENCE 1.1.pdf

2199-KOLNP-2006-CORRESPONDENCE.pdf

2199-KOLNP-2006-EXAMINATION REPORT.pdf

2199-KOLNP-2006-FORM 18.pdf

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Patent Number

253538

Indian Patent Application Number

2199/KOLNP/2006

PG Journal Number

31/2012

Publication Date

03-Aug-2012

Grant Date

30-Jul-2012

Date of Filing

03-Aug-2006

Name of Patentee

LG CHEM, LTD.

Applicant Address

LG TWIN TOWER 20, YOIDO-DONG, YOUNGDUNGPO-GU, SEOUL, 150-721

Inventors:

#	Inventor's Name	Inventor's Address
1	JEON ,BYOUNG KUN	203, LG CHEMICAL SHINYEOLRIP APARTMENT DORYONG-DONG, YUSEONG-GU, DAEJEON, 305-340
2	YU, JEONG SU	107-1501, HANWOOL APARTMENT, SHINSUNG-DONG, YUSEONG-GU, DAEJEON, 305-707,
3	MALIMONENKO, NIKOLAY	6-203, LG CHEMICAL APARTMENT, DORYONG-DONG, YUSEONG-GU, DAEJEON, 305-340
4	JANG, JUN WON	103, LG CHEMICAL SHINYEOLRIP APARTMENT, 388-11, DORYONG-DONG, YUSEONG-GU, DAEJEON, 305-340
5	BELYAEV, SERGEY	6-201, LG CHEMICAL APARTMENT, DORYONG-DONG, YUSEONG-GU, DAEJEON 305-340

PCT International Classification Number

G02F1/13363

PCT International Application Number

PCT/KR2005/000906

PCT International Filing date

2005-03-29

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	10-2004-0021202	2004-03-29	Republic of Korea