JP2004326137A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a gradation inverting phenomenon without depending on observing direction in a liquid crystal display device having liquid crystal regions where liquid crystal molecules are axis-symmetrically aligned in every pixel region, excellent visual field angle characteristics and high contrast. <P>SOLUTION: A phase difference compensation element having negative double refractivity and the relation n<SB>x</SB>>n<SB>y</SB>>n<SB>z</SB>about main refractive indices n<SB>x</SB>and n<SB>y</SB>in an intra-surface direction and the main refractive index n<SB>z</SB>in the thickness direction is disposed between a liquid crystal cell wherein liquid crystal molecules are nearly vertically aligned when no voltage is applied and liquid crystal molecules are axis-symmetrically aligned in every liquid crystal region and a polarizing plate disposed in a orthogonally crossed nicols state. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display device. In particular, the present invention relates to a liquid crystal display device having a wide viewing angle characteristic suitably used for a flat display such as a personal computer, a word processor, an amusement device, a television device, and a display device using a shutter effect.

  As a liquid crystal display device having the above-described wide viewing angle characteristics, the present inventors disclosed a display mode (Axially Symmetric Aligned Microcell Mode: ASM mode) in which liquid crystal molecules are axially symmetrically arranged for each picture element. No. 120728. In this method, liquid crystal molecules are axially symmetrically aligned by using phase separation from a mixture of liquid crystal and a photocurable resin. This is a display mode using an Np-type liquid crystal material that is vertically aligned.

  In this conventional ASM mode liquid crystal display device, a liquid crystal material having a positive dielectric anisotropy Δε is used. This display mode has excellent display characteristics in all directions because the liquid crystal molecules are axially symmetrically aligned.However, when the absorption axis of the polarizing plate is in a crossed Nicol state, the viewing angle characteristics tend to decrease. is there. In addition, there is a problem that the area of the light shielding portion of the BM (black matrix) must be set large in order to prevent light leakage when the voltage is turned off. Furthermore, this conventional ASM mode is difficult to manufacture because it uses a phase separation process that requires complicated temperature control in order to obtain an axisymmetric alignment of liquid crystal molecules, and the obtained axisymmetric alignment is unstable. In particular, there is a problem that reliability is low at high temperatures.

  As a means for solving these problems, the present inventors have disclosed in Japanese Patent Application No. 8-341590 that each pixel region has a liquid crystal region in which liquid crystal molecules are axially symmetrically aligned, and has excellent omnidirectional viewing angle characteristics. Proposed a high-contrast liquid crystal display device and a method for manufacturing the same relatively easily.

  In the proposed liquid crystal display device, a liquid crystal layer composed of liquid crystal molecules having negative dielectric anisotropy (Δε <0) is sandwiched between a pair of substrates, and a vertical alignment layer is provided on a surface of both substrates in contact with the liquid crystal layer. Is provided. Also, at least one substrate is provided with a projection so as to surround the picture element region. Further, a pair of polarizing plates are disposed with the absorption axes orthogonal to each other with the pair of substrates interposed therebetween. According to this liquid crystal display device, the liquid crystal molecules are oriented substantially perpendicularly to the pair of substrates when no voltage is applied, and the liquid crystal molecules are aligned in each pixel region when voltage is applied, without requiring a complicated manufacturing process. It is possible to realize an alignment state in which the alignment is performed in an axially symmetric manner.

  According to the above-described proposed liquid crystal display device, when no voltage is applied, the liquid crystal molecules are oriented in a direction substantially perpendicular to the pair of substrates, so that the viewing angle direction parallel to the normal direction of the substrates is good. A black state is obtained, and a high-contrast display is obtained. However, when the observation is performed while changing the viewing angle, (i) the viewing angle dependency is caused by the characteristics of the polarizing plate itself, and (ii) the retardation value of the vertically aligned liquid crystal molecules changes depending on the direction. Due to the viewing angle dependence of the retardation value of the liquid crystal layer, light leakage is observed and the contrast ratio decreases.

  Among them, the viewing angle dependency due to the characteristics of the polarizing plate itself is as follows. When the light incident on the liquid crystal display device in the wide viewing angle mode from the direction of the polarization axis (transmission axis) of the polarizing plate crosses the refractive index ellipsoid of the liquid crystal layer, it has only ordinary light or only extraordinary light. However, when light incident from an oblique direction whose azimuth is shifted by 45 ° from the absorption axis of the polarizing plate crosses the refractive index ellipsoid of the liquid crystal layer, it becomes elliptically polarized light because it has both components of ordinary light and extraordinary light. Apparently, light leakage becomes remarkable in a state where the absorption axes of the polarizing plates orthogonal to each other are open to each other.

  The viewing angle dependence of the retardation value of the liquid crystal layer is as follows. In the above liquid crystal display device, when no voltage is applied, the liquid crystal molecules are oriented in a direction substantially perpendicular to the pair of substrates, so that when viewed obliquely, the retardation value differs depending on the viewing angle, and the viewing angle dependence is observed. Will be done.

  Due to such a synergistic effect of the viewing angle dependency of the polarizing plate itself and the viewing angle dependency of the liquid crystal layer, a region having particularly poor viewing angle characteristics occurs in a direction shifted by 45 ° from the absorption axis of the polarizing plate which is orthogonal to each other. is there. For example, in the direction of 45 ° with respect to the absorption axis direction of the polarizing plate, there is a problem that the contrast is remarkably reduced at a viewing angle in a certain direction, for example, about 35 ° to 50 °, and further, the gradation characteristic is inverted. In particular, display characteristics deteriorated significantly at the time of halftone display.

  The present invention has been made in order to solve the above-described problems of the related art, and provides a liquid crystal display device that eliminates deterioration of viewing angle characteristics due to a deviation from an absorption axis and has a substantially axially symmetric viewing angle characteristic. The purpose is to do.

A liquid crystal display device of the present invention includes a liquid crystal cell sandwiched between a pair of substrates and having a liquid crystal layer made of liquid crystal molecules having negative dielectric anisotropy, and an absorption axis of a polarizing plate that sandwiches the liquid crystal cell and is orthogonal to each other. A pair of polarizing plates, and a phase difference compensating element provided on at least one of the pair of polarizing plates and the liquid crystal cell; the liquid crystal layer has a plurality of liquid crystal regions; A liquid crystal display device having a vertical alignment layer on the surface of the liquid crystal layer side, wherein the liquid crystal molecules are axially symmetrically aligned for each of the plurality of liquid crystal regions when a voltage is applied; has a negative birefringence, x orthogonal to each other respectively, y, and z-axis to the three principal refractive indices n _x, a n _y, a n _z, the main-plane direction of the liquid crystal cell the refractive index n _x, and n _y, when a principal refractive index in the thickness direction of the liquid crystal cell and n _z, Seki n _x> n _y> n _z Have the above object is met.

  The phase difference compensating elements may be provided one by one between the pair of polarizing plates and the liquid crystal cell.

  The phase difference compensating element is formed by laminating a biaxial film having retardation in the in-plane direction and the thickness direction, or a uniaxial film having retardation in the in-plane direction and a uniaxial film having retardation in the thickness direction. It may be composed of a laminated film.

  It is preferable that the x-axis direction of the phase difference compensating element is arranged to be substantially orthogonal to the absorption axis of the polarizing plate adjacent to the phase difference compensating element.

  It is preferable that the deviation between the x-axis direction of the phase difference compensating element and the direction orthogonal to the absorption axis of the polarizing plate be 1 ° or less.

The birefringence index of the liquid crystal molecules [Delta] n, when the average thickness of the liquid crystal layer d _LC, and the thickness of the retardation compensation element and d _f, the retardation retardation value d in the plane direction of the compensating element it is preferable _f (n _x -n _y) is smaller than the retardation value d _LC · [Delta] n of the liquid crystal layer.

The retardation compensation element preferably satisfies the _{0.035 ≦ {d f (n x} -n y)} / (d LC · Δn) ≦ 0.15.

The birefringence index of the liquid crystal molecules [Delta] n, when the average thickness of the liquid crystal layer to be d _LC, and the thickness of the retardation compensation element d _f, the retardation retardation value d in the thickness direction of the compensation element it is preferable _f (n _x -n _z) is smaller than the retardation value d _LC · [Delta] n of the liquid crystal layer.

It is preferable retardation value d _f a thickness direction of the retardation compensation element (n _x -n _z) is greater than 0. Furthermore, it is preferable that the ratio between the in-plane direction of the retardation compensation element retardation value d _f (n _x -n _y) and thickness direction retardation values d _f (n _x -n _z) is 2 or more , that the ratio between the in-plane direction of the retardation compensation element retardation value d _f (n _x -n _y) and thickness direction retardation values d _f (n _x -n _z) is 3 to 6 Even more preferred.

  It is preferable that the phase difference compensating element has an average refractive index of 1.4 or more and 1.7 or less.

The liquid crystal layer preferably has a retardation value d _LC · Δn in the range of 300 to 550 nm.

  An anti-reflection film or an anti-glare anti-glare layer may be provided on the surface of the polarizing plate on the viewer side among the pair of polarizing plates. It is preferable that an antireflection film is provided on the surface of the antiglare antiglare layer.

  Hereinafter, the operation of the present invention will be described.

According to the present invention, in a liquid crystal display device in which liquid crystal molecules are vertically aligned when no voltage is applied and are axially symmetric or concentric for each pixel region when voltage is applied, a pair of polarizing plates arranged in an orthogonal crossed Nicols state between at least one polarizing plate of the substrate adjacent thereto has a negative birefringence, the principal refractive indices n _x in the plane direction, n _y, and the thickness direction for the principal refractive index n _z the n _x> n _y> be provided (retardation film or the retardation plate typically) retardation compensation element having a relationship of n _z, the retardation value of the viewing angle dependence and the liquid crystal layer due to the characteristics of the polarizing plate itself By compensating for viewing angle dependency, it is possible to make the isocontrast contour curve circular regardless of the observation direction. In addition, the liquid crystal layer has excellent viewing angle characteristics because it changes between vertical alignment and axially symmetric alignment depending on the voltage. Further, since a normally black mode display in which a liquid crystal material having a negative dielectric anisotropy takes a vertical alignment state when no voltage is applied is performed, a high-contrast display is possible.

  The phase difference compensating element may be provided between one of the pair of polarizing plates and a substrate adjacent thereto, and one between each pair of polarizing plates and the substrate adjacent thereto. It may be provided.

  This retardation compensation element may be a biaxial film having retardation in an in-plane direction and a thickness direction, a laminated film of two biaxial films, or a retardation in an in-plane direction. A laminated structure in which a uniaxial film having the film and a uniaxial film having a retardation in the thickness direction can be similarly used.

The retardation compensation element, by placing by substantially orthogonal to the absorption axis of the polarizing plate adjacent the direction of n _x of its principal refractive index in the retardation compensation element, the viewing angle dependence of compensation Can be fully exhibited.

  As will be described in an embodiment to be described later, when the difference between the slow axis of the phase difference compensating element and the direction orthogonal to the absorption axis of the polarizing plate is larger than 1 °, the degree of polarization performance under the polarizing plate crossed Nicols is reduced. As a result, light leakage occurs and sufficient black level and contrast cannot be obtained. Therefore, the difference between the slow axis of the phase difference compensating element and the direction perpendicular to the absorption axis of the polarizing plate is 1 ° or less. Is desirable.

Birefringence Δn of the liquid crystal molecules, the average thickness of the liquid crystal layer d _LC, and the retardation compensation element with respect to the thickness d _f, plane retardation value d _f of the phase difference compensating element (n _x -n _y) By making the retardation value d _LC · Δn of the liquid crystal layer smaller, the effect of compensating for the viewing angle dependency can be increased. In particular, when the in-plane retardation value d _f of the phase difference compensating element (n _x -n _y) in the range of 3.5% to 15% of the retardation value d _LC · [Delta] n of the liquid crystal layer, as shown in FIG. 35 to be described later Thus, it is possible to obtain a display with high contrast.

Birefringence Δn of the liquid crystal molecules, the average thickness d _LC of the liquid crystal layer, and the thickness d _f of the phase compensation element, a retardation value in the thickness direction of the phase compensation element d _f (n _x -n _z Is smaller than the retardation value d _LC · Δn of the liquid crystal layer, the effect of compensating the viewing angle dependency can be increased. In particular, when the thickness direction of the retardation value d _f (n _x -n _z) of the phase difference compensating element in the range of 30% to 80% of the retardation value d _LC · [Delta] n of the liquid crystal layer, the effect of the retardation compensation element It is possible to obtain a display having a large size and good color characteristics.

The ratio of the retardation values in the plane direction of the retardation compensation element d _f (n _x -n _y) and thickness direction retardation values _{d f (n x -n z)} ( or refractive index difference ratio) is from 0 Is also desirable. This is because, as shown in an embodiment described later, when the ratio between the two retardation values is larger than 0, that is, when the retardation value in the thickness direction is not 0, the viewing angle compensation effect occurs. In particular, when the ratio of both retardation values is 2 or more, a favorable display state with a viewing angle of 60 ° or more at a contrast ratio of 10 can be realized. Further, when the ratio of the two retardation values is 3 or more and 6 or less, a more excellent display state with a contrast ratio of 20 and a viewing angle of 60 ° or more can be realized. In addition, a polymer material such as polycarbonate having an average refractive index of 1.4 or more and 1.7 or less can be used as a material of the phase difference compensating element, and a transparent (transmissivity of 90% or more) phase difference in a visible light region can be used. A compensating element is obtained.

Here, by setting the retardation value d _LC · Δn of the liquid crystal layer in the range of 300 to 550 nm, it is possible to improve the viewing angle characteristics at the time of applying a voltage and to prevent grayscale inversion. Thus, a good display state with a viewing angle of 60 ° or more at a contrast ratio of 10 can be obtained.

  By providing an anti-reflection film or an anti-glare anti-glare layer on the surface of the polarizing plate on the front side of the pair of polarizing plates, the effect of compensating for the viewing angle dependence can be increased. Further, by providing an antireflection film thereon, the effect of compensating for the viewing angle dependency can be further increased.

  When a phase difference compensating element is provided, coloring may occur in a wide viewing angle direction.However, an anti-glare anti-glare layer is provided on the front surface of the polarizing plate, and an anti-reflection film is further provided on the surface. Can compensate for this coloring.

  As described in detail above, according to the present invention, when no voltage is applied, the liquid crystal molecules are oriented substantially perpendicular to the substrate, and when the voltage is applied, the liquid crystal molecules are axially symmetric or concentrically aligned for each pixel. In the liquid crystal display device having the above, since the gradation inversion phenomenon can be prevented regardless of the observation direction, it is possible to obtain a high-contrast display in a wide viewing angle region. Note that the liquid crystal region is typically formed for each picture element, but a plurality of liquid crystal regions may be formed in a picture element.

  The liquid crystal display device of the present invention having such excellent characteristics is suitably used for a flat panel display such as a personal computer, a word processor, an amusement device, and a television device, a display plate using a shutter effect, a window, a door, and a wall. Can be

Hereinafter, embodiments of the present invention will be described.
(basic action)
The operation principle of the liquid crystal display device 100 according to the present invention will be described with reference to FIG. 1A and 1B show a state when no voltage is applied, and FIGS. 1C and 1D show a state when a voltage is applied. 1 (a) and 1 (c) are cross-sectional views, and FIGS. 1 (b) and 1 (d) are views showing the results of observing the upper surface with a crossed Nicol state polarizing microscope.

  In the liquid crystal display device 100, a liquid crystal layer 40 composed of liquid crystal molecules 42 having a negative dielectric anisotropy (Δε) (Nn type) is sandwiched between a pair of substrates 32 and 34. Vertical alignment layers 38a and 38b are formed on the surfaces of the pair of substrates 32 and 34 that are in contact with the liquid crystal layer 40. In addition, a convex portion 36 is formed on at least one surface of the pair of substrates 32 and 34 on the liquid crystal layer 40 side. Due to the convex portions 36, the liquid crystal layer 40 has two different thicknesses of dout and din. As a result, as described later, a liquid crystal region exhibiting an axially symmetric orientation when a voltage is applied is defined as a region surrounded by the protrusion 36. In FIG. 1, electrodes formed on the pair of substrates 32 and 34 for applying a voltage to the liquid crystal layer 40 are omitted.

  In the liquid crystal display device 100, when no voltage is applied, as shown in FIG. 1A, the liquid crystal molecules 42 are aligned in a direction perpendicular to the substrate by the alignment control force of the vertical alignment layers 38a and 38b. Observation of the picture element region in the state where no voltage is applied by a polarizing microscope in a crossed Nicol state shows a dark field as shown in FIG. 1B (normally black mode).

  On the other hand, when a voltage is applied to the liquid crystal display device 100, a force acts on the liquid crystal molecules 42 having negative dielectric anisotropy to orient the major axis of the liquid crystal molecules perpendicularly to the direction of the electric field. As shown in ()), it is inclined from the direction perpendicular to the substrate (halftone display state). In FIG. 1C, reference numeral 44 denotes a central axis. When the picture element region in this state is observed with a crossed Nicols polarizing microscope, an extinction pattern is observed in a direction along the absorption axis as shown in FIG.

  FIG. 2 shows a voltage transmittance curve of the liquid crystal display device 100 according to the present invention. The horizontal axis represents the voltage applied to the liquid crystal layer, and the vertical axis represents the relative transmittance.

  As the voltage is increased from the normally black state when no voltage is applied, the transmittance gradually increases. Here, the voltage at which the relative transmittance becomes 10% is called Vth (threshold voltage). When the voltage is further increased, the transmittance further increases and reaches saturation. The voltage at which the transmittance is saturated is called Vst. When the voltage applied to the liquid crystal layer 40 is between 1/2 Vth and Vst, the transmittance reversibly changes within the operating range shown in FIG. When a voltage of about 1/2 Vth is applied, the liquid crystal molecules are almost vertically aligned with the substrate, but the symmetry of the liquid crystal molecules with respect to the central axis of the axisymmetric alignment is recorded. Is considered to reversibly return to the axisymmetric alignment state when. However, when the applied voltage is lower than 1/2 Vth, the liquid crystal molecules return to a substantially vertical alignment state. When the voltage is applied again, the direction in which the liquid crystal molecules fall is not uniquely determined. Because of the presence, the transmittance is not stable.

  At the stage when the Nn-type liquid crystal material is injected into the liquid crystal cell, the behavior is the same as when the applied voltage is lower than 1/2 Vth. Therefore, once a voltage of 1/2 Vth or more is applied, a plurality of central axes become one in a region surrounded by the convex portion 36 (corresponding to a pixel region), and the voltage transmission shown in FIG. It shows rate characteristics.

  In addition, “picture element” is generally defined as a minimum unit for performing display. In the specification of the present application, “picture element area” indicates a partial area of a liquid crystal display element corresponding to “picture element”. In the case of a picture element having a large aspect ratio (long picture element), a plurality of picture element areas may be formed for one long picture element. Is preferably as small as possible as long as the axially symmetric orientation can be formed stably. In the specification of the present application, “axially symmetric orientation” refers to an orientation state such as radial, concentric (tangential), or spiral.

(Liquid crystal material)
The liquid crystal material used in the present invention is a so-called Nn-type liquid crystal material having negative dielectric anisotropy (Δε <0). The magnitude of the absolute value of Δε can be appropriately set depending on the application, and generally, it is preferable to have a large absolute value from the viewpoint of reducing the drive voltage.

D _LC · Δn (retardation) at the time of applying a voltage is an important factor that determines important characteristics of the device such as transmittance and viewing angle characteristics of the device. In the display mode of the present invention, they need not necessarily be limited to the optimum value of the liquid crystal cell specific retardation determined by the product of the liquid crystal material specific Δn and liquid crystal layer thickness d _LC.

FIG. 3 shows a voltage transmittance curve of the liquid crystal display device having a retardation value larger than the optimum value of the retardation (first minimum condition for maximizing the transmittance: d _LC · Δn = 550 nm).

  In such a liquid crystal display device, it is not necessary to use a region exceeding the maximum point of the relative transmittance, and the liquid crystal display device may be driven in a region where the relative transmittance monotonously increases. That is, the voltage at which the relative transmittance becomes maximum in FIG. 3 may be set as the maximum drive voltage (Vmax).

In the present invention, the retardation value at the maximum drive voltage used is important. Here, the product d _LC · Δn (retardation value) of the apparent Δn (anisotropy of the refractive index: the value at the maximum driving voltage) of the liquid crystal molecules and the average thickness d _LC of the liquid crystal layer when the liquid crystal cell is manufactured. ) Is preferably about 300 nm to 550 nm, and more preferably 300 nm to 500 nm. In this range, the transmittance when voltage is applied and the viewing angle characteristics when no voltage is applied are good, and the so-called gradation inversion (contrast inversion) phenomenon in which the relationship between the magnitude of the applied voltage and the transmittance is reversed depending on the viewing angle does not occur.

  On the other hand, there is a second minimum condition (retardation value: 1000 nm to 1400 nm) where the transmittance is maximized. However, in this range, the viewing angle characteristics when no voltage is applied are inferior, and further, the gradation inversion (contrast inversion) phenomenon occurs. May cause.

Hereinafter, d _LC · Δn will be described in more detail with reference to two simulation results performed by the present inventors.

(1) First, Δn of the liquid crystal material is fixed to about 0.08, and the cell thickness of the liquid crystal cell is changed from 4 μm to 8 μm so that the equal contour viewing angle characteristic is maximized for each d _LC · Δn. In order to optimize the biaxial phase difference compensating element, an electro-optical experiment (simulation) was performed. Then, the viewing angle characteristics, gradation inversion, and the relationship between the transmittance and the retardation were evaluated. In the calculation of the contrast ratio, the voltage at the time of the applied voltage (10 V) at which the transmittance is saturated is set to 100%, the voltage of the transmittance of 0.1% is applied to the black level, and the voltage of the transmittance of 95% is applied to the white level. Using.

4 and 5 are plots of viewing angles θ of contrast ratios 10 and 20, FIG. 6 is a plot of contrast inversion angle θ, and FIG. 7 is a plot of transmittance at 10 V applied with respect to the retardation d _LC · Δn of the liquid crystal cell. It is. Here, as the phase difference compensating element, one having a ratio of the in-plane refractive index difference to the refractive index difference in the thickness direction (normal direction) of 4.5 was used. Here, the azimuth angle Φ = 0 is defined as the absorption axis direction of the lower polarizing plate.

From the results of FIG. 4, it is found that when the contrast ratio is 10, the region of d _LC · Δn having a characteristic that the omnidirectional viewing angle is 60 ° or more is 300 nm to 550 nm, and d _LC · Δn is within this range. Is preferable.

Furthermore, if the contrast ratio is 20, as shown in FIG. 5, it can be seen that the viewing angle decreases with d _LC · [Delta] n is increased. FIG. 6 shows that the reversal angle is 60 ° or more in all directions, and the range in which a substantially circular viewing angle characteristic is obtained is a range of 300 nm to 400 nm. Therefore, and if such a contrast ratio of 20 is required, the use in the preferred range as substantially circular required viewing angle characteristics, d _LC · [Delta] n is 300 nm to 400 nm.

On the other hand, it is generally known that when the retardation of the liquid crystal cell exceeds the first minimum condition, the display performance (viewing angle, inversion angle characteristics) is remarkably deteriorated. However, as shown in FIG. The resulting d _LC · Δn is 550 nm. Therefore, this point is the first minimum of the liquid crystal material, and it is understood that sufficient display performance cannot be obtained under the condition of the liquid crystal cell exceeding 550 nm.

(2) Next, the cell thickness of the liquid crystal cell is fixed at 5 μm, the material Δn is changed from 0.07 to 0.1, and the equal contour viewing angle characteristic is maximized for each d _LC · Δn. In order to optimize the biaxial phase difference compensating element as described above, an electro-optical experiment (simulation) was performed. Then, the viewing angle characteristics, gradation inversion, and the relationship between transmittance and retardation were evaluated. In the calculation of the contrast ratio, the voltage at the time of the applied voltage (10 V) at which the transmittance is saturated is set to 100%, and the voltage of the transmittance 0.1% is applied to the black level, and the voltage of the transmittance 95% is applied to the white level. Using.

8 and 9 show the viewing angles θ of the contrast ratios 10 and 20, FIG. 10 shows the contrast inversion angle θ, and FIG. 11 shows the transmittance when 10 V is applied with respect to the retardation d _LC · Δn of the liquid crystal cell. It is. Here, as the phase difference compensating element, one having a ratio of the in-plane refractive index difference to the refractive index difference in the thickness direction (normal direction) of 4.5 was used.

From the results in FIG. 8, when the contrast ratio is 10, the region of d _LC · Δn having a characteristic that the viewing angle in all directions is 60 ° or more is 300 nm to 550 nm, and d _LC · Δn is within this range. Is preferred.

Furthermore, if the contrast ratio is 20, as shown in FIG. 9, it can be seen that the viewing angle decreases with d _LC · [Delta] n is increased. FIG. 10 shows that the inversion angle is 60 ° or more in all directions, and the range in which a substantially circular viewing angle characteristic can be obtained is a range of 300 nm to 400 nm. Therefore, and if such a contrast ratio of 20 is required, the use in the preferred range as substantially circular required viewing angle characteristics, d _LC · [Delta] n is 300 nm to 400 nm.

  On the other hand, as shown in FIG. 11, as the retardation of the liquid crystal cell increases, the transmittance when 10 V is applied increases.

From the simulation results of (1) and (2) above, it can be said that the optimal d _LC · Δn region in the liquid crystal display device of the present invention is 300 nm to 550 nm, and more preferably 300 nm to 400 nm.

  The twist angle of the liquid crystal molecules in the liquid crystal layer is also one of the important factors that determine the transmittance of the liquid crystal display device. In the present invention, the twist angle at the maximum driving voltage is important as in the retardation value.

  The twist angle when the maximum drive voltage is applied is preferably 45 to 110 °, and more preferably 100 ° from the viewpoint of transmittance.

  Since the present invention uses Nn-type liquid crystal molecules, the apparent twist angle of the liquid crystal molecules depends on the voltage. The twist angle when no voltage is applied is almost 0 °, and the twist angle increases with an increase in the voltage. When a sufficient voltage is applied, the twist angle approaches the twist angle inherent to the liquid crystal material.

  It is preferable that the twist angle and the retardation value at the maximum drive voltage are both within preferable ranges. In this case, the transmittance can be more effectively brought close to the maximum value.

(Photocurable resin)
As described above with reference to FIG. 2, it is preferable to constantly apply a voltage of Ｖ Vth or more to the liquid crystal display device of the present invention.

  When a voltage is applied to liquid crystal molecules oriented perpendicular to the substrate, the direction in which the liquid crystal molecules fall is not uniquely determined, and as a result, a phenomenon occurs in which a plurality of central axes are transiently formed. On the other hand, when the voltage is continuously applied, only one central axis is formed in the region defined by the convex portion, and this state is stably present as long as the voltage of 1/2 Vth or more is applied.

  Therefore, by applying a voltage of 1/2 Vth or more to stabilize the axially symmetric alignment, the photocurable resin previously mixed in the liquid crystal material is cured, so that the surface in contact with the liquid crystal layer can be fixed. A symmetric alignment fixed layer can be formed, whereby the axially symmetric alignment of liquid crystal molecules can be stabilized. After curing the photocurable resin, even if the voltage of 1/2 Vth or more is removed, a plurality of central axes are not formed, and an axially symmetric orientation is formed with good reproducibility.

  As the photocurable resin, acrylate, methacrylate, styrene, and derivatives thereof can be used. By adding a photopolymerization initiator to these resins, the photocurable resin can be more efficiently cured. Further, a thermosetting resin can also be used.

  The addition amount of the curable resin is not particularly limited in the present invention because the optimum value differs depending on the material, but the resin content (% based on the total weight including the liquid crystal material) is about 0.1% to 5%. Is preferred. If it is less than about 0.1%, the axisymmetric alignment state cannot be stabilized by the cured resin, and if it exceeds about 5%, the effect of the vertical alignment layer is hindered, and the liquid crystal molecules deviate from the vertical alignment. The rate increases (light leakage), and the black state when the voltage is turned off deteriorates.

(Phase difference compensation element)
As described in the description of the related art, when a vertically aligned liquid crystal material is sandwiched between two orthogonal polarizing plates, a good black state is obtained in the front direction, and a high-contrast display is obtained. However, when observation is performed while changing the viewing angle, light leakage is observed due to (i) the viewing angle dependence due to the characteristics of the polarizing plate itself, and (ii) the viewing angle dependence due to the retardation of the liquid crystal layer, and the contrast ratio decreases. Happens.

  Therefore, in the present invention, a phase difference compensating element is disposed between at least one of the pair of polarizing plates and a substrate adjacent thereto. The phase difference compensating element is composed of a phase difference plate or a plurality of phase difference plates. Further, the retardation plate includes a retardation film.

FIG. 12 is a perspective view showing the direction of the main refractive index of the phase difference compensating element used in the present invention. Here, a plane parallel to the surface of the retardation compensation element defining an orthogonal coordinate system with the x-y plane, the three principal refractive indices of the index ellipsoid of the phase difference compensating element n _x, n _y, n _z . Main refractive index in the plane direction is defined as n _x, n _y, the main refractive index in the thickness direction is defined as n _z. The retardation compensation element has a negative birefringence, with the relationship between the in-plane direction of the principal refractive indices n _x, n _y, and a main refractive index in the thickness direction n _z for n _x> n _y> n _z . In the phase difference compensating element satisfies this relationship, the direction of n _x is the largest principal refractive index (x-axis direction) is the direction of the slow axis.

  Examples of the material of such a retardation compensating element or a retardation plate or a retardation film constituting the same include, for example, visible light such as polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate (PMMA), liquid crystalline polymer, and cellulose triacetate. High molecular materials which are transparent in the optical region (transmittance of 90% or more) are mentioned, and these materials have an average refractive index of about 1.4 or more and about 1.7 or less.

  The retardation compensating element may be a laminated retardation film obtained by laminating a plurality of retardation films with different azimuths of respective optical axes. Even when a laminated retardation film obtained by laminating a uniaxial film having retardation in the in-plane direction and a uniaxial film having retardation in the thickness direction is used, a film having retardation in the in-plane direction and in the thickness direction can be obtained. Even when an axial film is used, the effect of improving the viewing angle characteristics can be obtained similarly. Alternatively, a film obtained by laminating two biaxial retardation films may be used.

  As shown in FIG. 13A, polarizing plates 132a and 132b are arranged so as to sandwich both sides of a liquid crystal cell 134, and biaxial retardation films 133a and 133b are provided between the polarizing plates 132a and 132b and the liquid crystal cell 134. In a liquid crystal display device in which the backlight 131 is disposed on the rear side of the polarizing plate 132a, for example, the following configuration may be adopted.

  As shown in FIGS. 13B and 13C, at least one of the polarizing plates 132a and 132b has the polarizing layers 136a and 136b sandwiched between a pair of supporting films 135a and 137a or a pair of supporting films 135b and 137b, respectively. A polarizing plate 132a, 132b having a retardation in the plane or in the normal direction of the plane (e.g., obtained from Nitto Denko Corporation or Sumitomo Chemical Co., Ltd.). (Possible). In this case, the retardation of the phase difference compensating element used for the viewing angle compensation in the liquid crystal display device of the present invention includes the retardation of the polarizing plates 132a and 132b. By adjusting the value of the retardation according to the present invention, the viewing angle characteristics can be improved. The effect is obtained. In the above example, the support films are provided on both sides of the polarizing layer, but may be provided on one side.

  As the support film, for example, TAC (triacetic acid cellulose), PET (polyethylene phthalate), PETG (polyethyleneglycol), PMMA (polymethylmethacrylate, PMMA (polymethylmethacrylate), PC (PolymethylMethacrylate), PC (PolyethylMethanacryl), and PC (PolyZnA) are available. Can be used. In particular, TAC is suitably used as a support film because it is harder than a retardation film. The support film made of TAC has, for example, a retardation of about 50 to about 60 nm in a normal direction and a retardation of about 5 to about 10 nm in an in-plane direction.

  The phase difference compensating element may be provided between one polarizing plate and a substrate adjacent thereto, or may be provided between both polarizing plates and a substrate adjacent thereto.

It is preferably arranged in 45 ° and 135 ° angle to the absorption axis of the polarizing plate adjacent to the direction and the phase difference compensating element n _x of the main refractive index of the retardation compensation element, 67 ° to 113 ° It is more preferable to arrange them at an angle. Further, it is preferable to make the two orthogonal to each other, since the function of compensating the viewing angle dependency due to the characteristics of the polarizing plate itself and the viewing angle dependency due to the retardation of the liquid crystal layer can be sufficiently exhibited.

The evaluation was performed under a polarizing plate crossed Nicols. As shown in FIG. 14, when the orthogonal precision between the slow axis of the phase difference compensating element and the absorption axis of the polarizing plate was larger than 1 °, the polarizing plate crossed Nicols were used. The lower polarization degree performance was lowered to cause light leakage, and sufficient black level and contrast could not be obtained. Therefore, the direction orthogonal to the absorption axis direction and the polarizing plate of the main refractive indices n _x of the phase compensation element, the deviation is desirably not more than 1 °.

Birefringence Δn of the liquid crystal molecules, the average thickness of the liquid crystal layer d _LC, when the thickness d _f of the phase difference compensating element, in-plane retardation value d _f (n _x -n _y) of the phase difference compensating element liquid crystal layer Is preferably smaller than the retardation value d _LC · Δn. More preferably, it is in the range of 3.5% to 15% of the retardation value d _LC · Δn of the liquid crystal layer. If it is less than 3.5%, the effect of improving the viewing angle characteristics is low, and if it exceeds 15%, the change in color tone when the viewing angle is reduced may be large.

Further, it is preferable that the retardation value d _f in the thickness direction of the phase compensation element (n _x -n _z) is smaller than the retardation value d _LC · [Delta] n of the liquid crystal layer. More preferably, it is in the range of 30% to 80% of the retardation value d _LC · Δn of the liquid crystal layer. If it is less than 30%, the effect of the phase difference compensating element is small, and if it is more than 80%, coloring may become large in a wide viewing angle direction.

  Hereinafter, the mechanism of the viewing angle compensation by the phase difference compensating element will be described by taking the case of the normally black mode as an example.

  In general, from the polarization characteristics of the polarizing plate and the optical characteristics of the axis-symmetric alignment of the liquid crystal molecules, it has been found that the viewing angle characteristics are deteriorated in the azimuth angle of 45 ° with respect to the absorption axis of the polarizing plate as compared with the axial direction. I have.

  As shown in FIG. 15, when the viewing angle is inclined obliquely from the front at the time of the voltage off with respect to the liquid crystal cell in which only the polarizing plate is provided without providing the phase difference compensating element, as shown in FIG. , The apparent refractive index changes due to the refractive index ellipsoid. As a result, the optical characteristics change and good viewing angle characteristics cannot be obtained.

  On the other hand, as shown in FIG. 17, even when the viewing angle is inclined obliquely from the front in the direction of 45 ° with respect to the absorption axis of the polarizing plate when the voltage is off, as shown in FIG. As shown in the figure, since the apparent refractive index ellipsoid is substantially spherical, the optical characteristics hardly change even when the liquid crystal cell is viewed obliquely. Therefore, as shown in FIGS. 19 and 20, even when the viewing angle is lowered at the time of voltage off and at the time of voltage on, the black display and the white display are apparently the same as when viewed from the front. The angular characteristics are well compensated. Further, as shown in FIGS. 21 to 24, the original viewing angle characteristics do not deteriorate in the direction of the absorption axis of the polarizing plate even if the phase difference compensating element is provided. Therefore, good viewing angle characteristics can be obtained in all directions.

In the above simulations (1) and (2), the optimum retardation film in which the ratio between the in-plane refractive index difference and the thickness direction refractive index difference of the retardation compensation element (retardation film) is 4.5. 25 and 26 show the results of evaluation of the relationship between the in-plane and normal direction retardations of the liquid crystal and the retardation of the liquid crystal cell, respectively. From these figures, it can be seen that the optimum retardation in the in-plane direction and the thickness direction increases as d _LC · Δn increases.

Incidentally, the ratio of the retardation values in the plane direction of the retardation compensation element d _f (n _x -n _y) and thickness direction retardation values _{d f (n x -n z)} ( or refractive index difference ratio) is As shown in FIG. 27 to FIG. 30, it is desirable that the value is larger than 0. This is because the viewing angle compensation effect occurs when the ratio between the two retardation values is not 0, that is, when the retardation value in the thickness direction (normal direction) is not 0.

  Further, as shown in FIGS. 27 and 29, when the refractive index difference ratio (retardation ratio) in the in-plane direction and the thickness direction is set to 2 or more, a favorable display state with a viewing angle of 60 ° or more at a contrast ratio of 10 is realized. can do.

  Here, the reason why the viewing angle is set to 60 ° or more is that the viewing angle of the TN mode liquid crystal display device which is generally used at present is 60 °. On the other hand, the reason why the contrast ratio is set to 10 is that the contrast ratio in a general wide viewing angle mode is about 10. Further, in order to realize a viewing angle of 70 ° or more in consideration of a liquid crystal display mode such as IPS or VA at a contrast ratio of 10, it is preferable to set the refractive index difference ratio to 2.5 or more.

  In particular, as shown in FIG. 28, when the refractive index difference ratio is 3 or more and 6 or less, a more excellent viewing angle compensation effect with a contrast ratio of 20 and a viewing angle of 60 ° or more can be obtained. In this graph, the portion having a refractive index difference ratio of 3 to 6 is a portion in which the characteristics in the directions of the viewing angles of 45 ° and 135 ° exceed the characteristics in the other directions. Therefore, in the range of the refractive index difference ratio of 3 or more and 6 or less, the viewing angle characteristics in the 45 ° and 135 ° directions are improved, and a substantially circular viewing angle characteristic is obtained.

  Here, the reason why the viewing angle is set to 60 ° or more is that the viewing angle of the TN mode liquid crystal display device which is generally used at present is 60 °. On the other hand, the reason why the contrast ratio 20 is defined is that good display characteristics can be realized under more severe conditions than in a general wide viewing angle mode.

(Vertical alignment layer)
The vertical alignment layer only needs to have a surface for vertically aligning liquid crystal molecules, and the material may be an inorganic material or an organic material. For example, a polyimide type (JALS204 (Nihon Synthetic Rubber) or 1211 (Nissan Chemical)) or an inorganic type (EXP-OA003 (Nissan Chemical Industries)) can be used.

(Polarizer)
By arranging the polarizing plates in a crossed Nicols state, a good black state in a normally black mode can be obtained when a vertically aligned liquid crystal material is interposed, and a high-contrast display can be obtained. As the polarizing plate, for example, iodine or a hydrophilic polymer is adsorbed on a hydrophilic polymer film such as a polyvinyl alcohol-based film, a polyvinyl formal film, a polyvinyl acetal film, and a poly (ethylene-acetic acid) copolymer-based saponified film. It is possible to use an oriented iodine-based polarizing film or a dye-based polarizing film, or a polyene-based polarizing film or the like in which a polyvinyl alcohol-based film is dehydrated or a polyvinyl chloride film is dehydrochlorinated and the polyene is oriented. it can.

  Further, by providing an anti-reflection film or an anti-glare anti-glare layer on the surface of the polarizing plate, the viewing angle characteristics in a direction shifted by 45 ° from the absorption axis direction can be further improved. In particular, this anti-glare anti-glare layer is obtained by subjecting a hard coat layer to an anti-glare treatment. As the binder resin used for the hard coat layer, any resin having a hard property and having transparency can be used, and examples thereof include a thermosetting resin and an ionizing radiation-curable resin. In the present invention, “having a hard property” or “hard coat” refers to a material having a hardness of H or more according to a pencil hardness test shown in JIS K5400.

  As the thermosetting resin, for example, a phenol resin, a urea resin, a diallyl phthalate resin, a melamine resin, a guanamine resin, an unsaturated polyester resin, a polyurethane resin, an epoxy resin, an aminoalkyd resin, a melamine-urea cocondensation resin, a silicon resin, A polysiloxane resin or the like can be used.

  The ionizing radiation-curable resin can be cured by irradiation with an electron beam or ultraviolet rays. The ionizing radiation-curable resin preferably has an acrylate-based functional group, for example, a relatively low-molecular-weight polyester resin, polyether resin, acrylic resin, epoxy resin, urethane resin, alkyd resin, spiroacetal resin, polybutadiene resin, Oligomers or prepolymers such as acrylates or methacrylates of polyfunctional compounds such as polythiol polyene resins and polyhydric alcohols can be used. Particularly preferred is a mixture of polyester acrylate and polyurethane acrylate.

  The anti-glare treatment applied to the hard coat layer is a treatment for preventing external reflected light from directly entering the observer's eyes by scattering external light by forming fine irregularities on the surface. There is a method of using or a method of adding fine particles to the binder resin.

  The method using a shaping film is performed, for example, as follows. First, an ionizing radiation-curable resin composition is applied to the surface of a polarizing plate, and a mat-like shaped film having fine irregularities on the surface is laminated on an uncured coating film. Next, after irradiating the laminated coating with ionizing radiation to completely cure the coating film, an antiglare layer having fine irregularities formed on the surface is formed by peeling off the molding film. You.

  The fine particles added to the binder resin include beads and fillers, such as amorphous silica powder, polycarbonate particles, acrylate resin beads, and methacrylate resin beads.

Further, by providing an anti-reflection film (anti-reflection coating layer) on the surface of the polarizing plate in addition to the anti-glare anti-glare layer, the viewing angle characteristics in the direction shifted by 45 ° from the absorption axis can be further improved. Can be. This antireflection film reduces reflected light by utilizing light interference. For example, a film obtained by laminating a dielectric thin film made of an inorganic material can be used. Examples of the inorganic material include LiF, MgF ₂ , 3NaF · AlF ₃ , AlF ₃ , and SiO _x (x: 1.8 <x <2.2). The method of forming a thin film made of an inorganic material is preferably a gas phase method, and examples thereof include a vacuum deposition method, a sputtering method, an ion plating method, and a plasma CVD method.

  Hereinafter, embodiments of the present invention will be described more specifically, but the present invention is not limited thereto.

(Embodiment 1)
The method for manufacturing the liquid crystal display device according to the first embodiment will be described with reference to FIG. FIG. 31A is a cross-sectional view of the liquid crystal display device according to the first embodiment, and FIG. 31B is a plan view thereof.

  First, a spacer 65 having a height of about 5 μm was formed outside the pixel region using photosensitive polyimide on a substrate 62 having a transparent electrode 63 (ITO: 100 nm) formed on the surface. Next, a convex portion 66 having a height of about 3 μm was formed using an acrylic negative resist. Here, the size of the region surrounded by the convex portion 66, that is, the size of the pixel region was 100 μm × 100 μm. A vertical alignment layer 68 was formed thereon by spin-coating JALS204 (Japanese synthetic rubber). Further, a vertical alignment layer 67 was formed on the other substrate 61 having a transparent electrode 64 (ITO: 100 μm) formed on the surface by using the same material. Thereafter, the two were bonded to each other to produce a liquid crystal cell.

In the fabricated cell, an Nn-type liquid crystal material (Δε = −4.0, Δn = 0.08, a twist angle specific to the liquid crystal material is set so as to be 90 ° twist at a cell gap of 5 μm, and a retardation value d _LC · Δn = 400 nm) and a voltage of 7 V was applied. Immediately after the application of the voltage, in the initial state, a plurality of orientation axes having an axially symmetric orientation exist, and when the voltage application state is continued, one axially symmetric orientation region (monodomain) is formed for each pixel region.

Next, as shown in FIG. 32, polarizing plates 101 and 102 and phase difference compensating elements 103 and 104 were arranged on both sides of the liquid crystal cell 100 to complete a liquid crystal display device. FIG. 32A is a layout diagram of a liquid crystal cell, a polarizing plate, and a phase difference compensating element in the present embodiment. FIG. 32B is a diagram showing the absorption axis direction of the polarizing plate and the three main refractive indices of the phase difference compensating element. It is a figure which shows the relationship with the direction of nx which is the largest principal refractive index among them, ie, the slow axis direction. As shown in FIG. 32, an upper polarizing plate 101 and a lower polarizing plate 102 are arranged on both outer sides of the liquid crystal cell 100 such that their absorption axes are orthogonal to each other. In addition, a first phase difference compensating element 103 is arranged between the upper polarizing plate 101 and the liquid crystal cell 100, and a second phase difference compensating element 104 is arranged between the lower polarizing plate 102 and the liquid crystal cell 100. . The first phase compensation element 103 and the second phase compensation element 104 are both a phase compensation element such as shown in FIG. 12, wherein the plane of the retardation values d _f (n _x -n _y) the 42 nm, and the thickness direction retardation value d _f (n _x -n _z) and 170 nm.

  In the structure of the obtained liquid crystal display device, the cross-sectional shape of the vertical alignment layer 68 is in a mortar shape as shown in FIG. 31, and changes in the thickness position (from the center of the picture element to the peripheral portion) are not affected. The derivative of the curve shown is positive, and the derivative of the curve showing the change in the thickness of the liquid crystal layer in the picture element region is negative.

  The axially symmetric orientation of the liquid crystal cell of the first embodiment is stable when a voltage of 1/2 Vth or more is applied, and when the voltage is lower than 1/2 Vth, the state of the axially symmetric orientation collapses and returns to the initial state. I have. When a voltage was applied again, the state was changed to an axially symmetric orientation state in which a plurality of central axes of the initial axis symmetry existed, and one central axis was provided for each pixel region. This phenomenon did not change even after 20 runs. Here, in order to measure the electro-optical characteristics of the liquid crystal cell of Embodiment 1, after applying a voltage of 1/2 Vth or more to form an axially symmetric state, the axially symmetric orientation is stable during the measurement of the electro-optical characteristics. The measurement was performed in the voltage range (1/2 Vth or more).

  FIG. 33 shows the electro-optical characteristics of the liquid crystal display device according to the first embodiment. As is clear from FIG. 33, in the liquid crystal display device of Embodiment 1, the transmittance in the OFF state was low, and a good contrast ratio (CR = 300: 1, 5V) was obtained.

  FIG. 34 shows the viewing angle characteristics of the contrast in the liquid crystal display device of the first embodiment. In FIG. 34, Φ is the azimuth (angle in the display plane: the absorption axis of the lower polarizing plate is 0 °), θ is the viewing angle (the inclination angle from the normal to the display plane), and the hatching indicates a contrast ratio of 20. : Indicates one or more areas. As shown in FIG. 34, in the conventional liquid crystal display device, a high contrast ratio is obtained in a wide viewing angle range including a direction shifted by 45 ° from the absorption axis of the polarizing plate, which is a particularly poor viewing angle characteristic. A substantially circular viewing angle characteristic was obtained.

(Embodiment 2)
In the second embodiment, the liquid crystal cell shown in FIG. 31 is manufactured in the same manner as in the first embodiment, and the polarizing plates 101 are disposed on both sides of the liquid crystal cell 100 in the arrangement shown in FIG. The liquid crystal display device was completed by arranging 102 and the phase difference compensating elements 103 and 104. However, in the second embodiment, the twist angle specific to the liquid crystal material is set so that the Nn-type liquid crystal material (Δε = −3.3, Δn = 0.0773, 90 ° twist at a cell gap of 6 μm), and the retardation value d _LC .DELTA.n = 450 nm).

FIG. 35 shows the results of measuring the electro-optical characteristics of the liquid crystal display device of the second embodiment in the same manner as in the first embodiment. Here, the viewing angle theta = 40 °, the azimuth angle [Phi = 45 ° and fixed, was determined by changing the retardation value d _f in the plane of the phase compensation element (n _x -n _y). As shown in FIG. 35, the range of the retardation value d _f in the plane of the retardation compensation element contrast ratio of 10 or more (n _x -n _y) is 16.0Nm～65.0Nm, retardation of the liquid crystal layer It was 3.5% to 15% of the value d _LC · Δn. Also, is when the retardation value in the plane of the contrast ratio is maximized _{(n x -n y) · d} f has a value of about 42.5 nm, about the retardation value d _LC · [Delta] n of the liquid crystal layer 9 0.5%. Further, the viewing angle theta = 40 °, the azimuth angle [Phi = 135 ° is fixed, even when measured by varying retardation value in the plane of the retardation compensation element of _{(n x -n y) · d} f, FIG. 35 The same result as was obtained.

(Comparative Example 1)
In Comparative Example 1, the liquid crystal cell shown in FIG. 31 was manufactured in the same manner as in Embodiment 1, and a pair of polarizing plates were arranged on both sides of the liquid crystal cell so that the respective absorption axes were orthogonal to each other to complete the liquid crystal display device. did. However, in Comparative Example 1, no phase difference compensating element was provided. FIG. 36 shows the viewing angle characteristics of the contrast in the liquid crystal display device of Comparative Example 1. In FIG. 36, Φ is an azimuth angle (angle in the display surface), θ is a viewing angle (angle of inclination from the normal to the display surface), and hatching indicates a region where the contrast ratio is 10: 1 or more. As shown in FIG. 36, the viewing angle characteristics in the direction shifted from the absorption axis of the polarizing plate by 45 ° (the direction shown in (a) or (b) of FIG. 36) are poor. In particular, when the viewing angle is 35 ° or more, the contrast is remarkable. Had declined.

(Comparative Example 2)
In Comparative Example 2, the liquid crystal cell shown in FIG. 31 was manufactured in the same manner as in Embodiment 1, and an upper polarizing plate and a lower polarizing plate were arranged on both sides of the liquid crystal cell such that their absorption axes were orthogonal to each other. Further, a first phase difference compensating element was arranged between the upper polarizing plate and the liquid crystal cell, and a second phase difference compensating element was arranged between the lower polarizing plate and the liquid crystal cell. However, in Comparative Example 2, the first phase difference compensating element and the second phase difference compensating element are both frisbee type phase difference compensating elements, _nx = _ny , and the retardation value d in the thickness direction is _f (n _x -n _z) was 150nm.

  FIG. 37 shows the viewing angle characteristics of contrast in the liquid crystal display device of Comparative Example 2. In FIG. 37, Φ is an azimuth angle (angle in the display surface), θ is a viewing angle (inclination angle from the display surface normal), and hatching indicates a region where the contrast ratio is 10: 1 or more. Compared with Comparative Example 1 in which the phase difference compensating element is not provided, the viewing angle characteristics in the direction shifted from the absorption axis of the polarizing plate by 45 ° are somewhat improved, but the contrast is still remarkably increased particularly when the viewing angle is 40 ° or more. Had declined.

(Embodiment 3)
In the third embodiment, the liquid crystal cell shown in FIG. 31 is manufactured in the same manner as in the first embodiment, and similarly to the first embodiment, the polarizing plates 101 are provided on both sides of the liquid crystal cell 100 in the arrangement shown in FIG. The liquid crystal display device was completed by arranging 102 and the phase difference compensating elements 103 and 104. However, in the third embodiment, an antiglare antiglare layer having a haze of 3.5% and a gloss of 80% was provided on the surface of the upper polarizing plate 101.

  FIG. 38 shows gradation characteristics of four gradations (liquid crystal drive voltage: 2.77 V, 3.74 V, 4.8 V, 7.77 V) for the liquid crystal display device of the third embodiment. FIG. 38A shows the gradation characteristics in the absorption axis direction of the upper polarizing plate 101, and FIG. 38B shows the gradation characteristics in the direction shifted by 45 ° from the absorption axis of the upper polarizing plate 101. For comparison, FIG. 39 shows the gradation characteristics of four gradations (liquid crystal driving voltage: 2.77 V, 3.74 V, 4.8 V, 7.77 V) of the liquid crystal display device of Embodiment 1. FIG. 39 (a) shows the gradation characteristics in the direction of the absorption axis of the upper polarizing plate 101, and FIG. 39 (b) shows the gradation characteristics in the direction shifted by 45 ° from the absorption axis of the upper polarizing plate 101.

  As shown in FIGS. 38 and 39, by providing the anti-glare antiglare layer on the polarizing plate, it was possible to suppress an increase in the black level which appears as the viewing angle was lowered. In particular, the increase in black level at a viewing angle of 60 ° in a direction shifted by 45 ° from the absorption axis was significantly suppressed, and the viewing angle characteristics could be improved by improving the contrast ratio.

(Embodiment 4)
In the fourth embodiment, the liquid crystal cell shown in FIG. 31 is manufactured in the same manner as in the third embodiment, and similarly to the third embodiment, the polarizing plates 101 are provided on both sides of the liquid crystal cell 100 in the arrangement shown in FIG. The liquid crystal display device was completed by arranging 102 and the phase difference compensating elements 103 and 104. However, in the fourth embodiment, an antiglare antiglare layer having a haze of 13% and a gloss of 40% was provided on the surface of the upper polarizing plate 101.

  FIG. 40 shows gradation characteristics of four gradations (liquid crystal drive voltage: 2.77 V, 3.74 V, 4.8 V, 7.77 V) of the liquid crystal display device of the fourth embodiment. FIG. 40A shows the gradation characteristics in the direction of the absorption axis of the upper polarizing plate 101, and FIG. 40B shows the gradation characteristics in the direction shifted from the absorption axis of the upper polarizing plate 101 by 45 °.

  As shown in FIG. 40, as in Embodiment 3, by providing an anti-glare antiglare layer on a polarizing plate, it was possible to suppress an increase in the black level that appears as the viewing angle is reduced. In the fourth embodiment, by increasing the haze, the increase in the black level at a viewing angle of 60 °, particularly in the direction shifted by 45 ° from the absorption axis, is significantly suppressed as compared with the third embodiment. The viewing angle characteristics could be improved by increasing the ratio.

(Embodiment 5)
In the fifth embodiment, the liquid crystal cell shown in FIG. 31 is manufactured in the same manner as in the third embodiment, and similarly to the third embodiment, the polarizing plates 101 are provided on both sides of the liquid crystal cell 100 in the arrangement shown in FIG. The liquid crystal display device was completed by arranging 102 and the phase difference compensating elements 103 and 104. However, in Embodiment 5, an anti-glare anti-glare layer having a haze of 3.5% and a gloss of 80% was provided on the surface of the upper polarizing plate 101, and an anti-reflection film was further provided.

  FIG. 41 shows gradation characteristics of four gradations (liquid crystal drive voltage: 2.77 V, 3.74 V, 4.8 V, 7.77 V) of the liquid crystal display device of the fifth embodiment. FIG. 41A shows the gradation characteristics in the absorption axis direction of the upper polarizing plate 101, and FIG. 41B shows the gradation characteristics in the direction shifted from the absorption axis of the upper polarizing plate 101 by 45 °.

  As shown in FIG. 41, by providing the anti-reflection film, it is possible to further suppress the increase in the black level that appears when the viewing angle is lowered as compared with the third embodiment, and further improve the contrast ratio to improve the viewing angle characteristics. Could be improved.

(Embodiment 6)
In the sixth embodiment, the liquid crystal cell shown in FIG. 31 is manufactured in the same manner as in the third embodiment, and the polarizing plates 101 are disposed on both sides of the liquid crystal cell 100 in the arrangement shown in FIG. The liquid crystal display device was completed by arranging 102 and the phase difference compensating elements 103 and 104. However, in the sixth embodiment, an anti-glare antiglare layer having a haze of 13% and a gloss of 40% is provided on the surface of the upper polarizing plate 101, and an antireflection film is further provided.

  FIG. 42 shows the gradation characteristics of four gradations (liquid crystal drive voltage: 2.77 V, 3.74 V, 4.8 V, 7.77 V) for the liquid crystal display device of the sixth embodiment. 42A shows the gradation characteristics in the direction of the absorption axis of the upper polarizing plate 101, and FIG. 42B shows the gradation characteristics in the direction shifted from the absorption axis of the upper polarizing plate 101 by 45 °.

  As shown in FIG. 42, by providing an anti-reflection film, an increase in black level that appears when the viewing angle is reduced can be further suppressed as compared with the fourth embodiment, and the viewing angle characteristics can be further improved by further improving the contrast ratio. Could be improved.

(Embodiment 7)
With reference to FIG. 43, a method for manufacturing the liquid crystal display of the seventh embodiment will be described. Since the liquid crystal cell of the liquid crystal display device of the present embodiment has the same structure as the liquid crystal cell of FIG. 31, it will be described with reference to FIG.

  First, on a substrate having a transparent electrode (for example, an ITO film having a thickness of about 100 nm) formed on the surface, a spacer having a height of about 6 μm was formed outside the picture element region using photosensitive polyimide. Next, a convex portion 66 having a height of about 3 μm was formed using an acrylic negative resist. Here, the size of the region surrounded by the convex portion 66, that is, the size of the pixel region was 100 μm × 100 μm. A vertical alignment layer 68 was formed thereon by spin-coating JALS204 (Japanese synthetic rubber). Further, a vertical alignment layer 67 was formed on the other substrate 61 having a transparent electrode 64 (ITO: 100 μm) formed on the surface by using the same material. Thereafter, the two were bonded to each other to produce a liquid crystal cell.

In the fabricated cell, an Nn-type liquid crystal material (Δε = −3.0, Δn = 0.073, a twist angle specific to the liquid crystal material is set so as to be 90 ° twist at a cell gap of 6 μm, and a retardation value d _LC · Δn = 450 nm) and a voltage of 7 V was applied. Immediately after the application of the voltage, in the initial state, a plurality of orientation axes having an axially symmetric orientation exist, and when the voltage application state is continued, one axially symmetric orientation region (monodomain) is formed for each pixel region.

Next, as shown in FIG. 43, a polarizing plate and a phase difference compensating element were arranged on both sides of the liquid crystal cell to complete a liquid crystal display device. FIG. 43 is a layout diagram of the liquid crystal cell, the polarizing plate, and the phase difference compensating element in the present embodiment, and shows the absorption axis direction of the polarizing plate and the maximum main refractive index among the three main refractive indexes of the phase difference compensating element. It is a figure which shows the relationship with the direction of nx, ie, the slow axis direction. As shown in FIG. 43, an upper polarizing plate and a lower polarizing plate were arranged on both outer sides of the liquid crystal cell such that their absorption axes were orthogonal to each other. Further, a phase difference compensating element was arranged between the upper polarizing plate and the liquid crystal cell. The retardation compensation element of the present embodiment was formed by a biaxial stretching method using a polycarbonate material. This was 42nm-plane retardation values _{d f (n x -n y)} , the thickness direction retardation value d _f (n _x -n _z) and 191 nm.

  The difference from the other embodiments is that the phase difference compensating element is provided only on one side (one side) of the liquid crystal cell. In this embodiment, a single phase difference compensating element having retardation in the biaxial direction is used as the phase difference compensating element. However, the present invention is not limited to this. That is, as long as the refractive index nx, ny and nz in the x, y and z-axis directions satisfy the condition of nx> ny> nz, as in the other embodiments.

  FIG. 44 shows the viewing angle characteristics of the contrast ratio of the liquid crystal display device of the present embodiment. Hatching indicates a region where the contrast ratio is 10: 1 or more. In the liquid crystal display device of the present embodiment, the case where there is no phase difference compensating element in the 45 ° direction sandwiched between the absorption axes of both polarizing plates, which is a region where the viewing angle characteristics are poor, due to the influence of the polarizing plates arranged in a crossed Nicols state The viewing angle with a contrast ratio of 1.7, which is 1.7 times as wide as that of, was widened, and a high contrast ratio could be obtained in all directions. In the seventh embodiment, the phase difference compensating element is disposed between the front polarizer and the liquid crystal cell. However, the same viewing angle characteristics can be obtained even when the retardation compensator is disposed between the rear polarizer and the liquid crystal cell. Was done.

  Further, in the viewing angle compensation in the direction of 45 ° with respect to the absorption axis of the polarizing plate, an in-plane compensation of the phase difference compensating element was obtained in which the effect of compensating the viewing angle more than 1 times was obtained as compared with the case without the phase difference compensating element. And the conditions of the normal direction retardation were in the range of about 5 nm to about 70 nm and about 60 nm to about 280 nm, respectively.

(Embodiment 8)
In the present embodiment, the same liquid crystal cell as in Embodiment 7 is used, and two retardation plates produced by a biaxial stretching method as retardation compensating elements are provided between the two polarizing plates and the liquid crystal cell, respectively. The liquid crystal display devices arranged one by one will be described. The phase difference compensating element in accordance with the present embodiment, the retardation value d _f in the plane (n _x -n _y) is 43 nm, the thickness direction retardation value d _f (n _x -n _z) is a polycarbonate material 191nm The following phase difference compensating element was used. The liquid crystal cell in the present embodiment also has a liquid crystal layer in which liquid crystal molecules are aligned substantially perpendicularly to the substrate when no voltage is applied, and are axially symmetrical about an axis perpendicular to the substrate when voltage is applied.

  FIG. 45 shows the configuration of the liquid crystal display device of the present embodiment. The pair of phase difference compensating elements are arranged such that their slow axes are orthogonal to each other. Further, the polarizing plate is disposed so that the slow axis of one phase difference compensating element is orthogonal to the absorption axis of the polarizing plate, and the pair of polarizing plates is such that the respective absorption axes are orthogonal to each other. (Cross Nicols state).

  FIG. 46 shows the viewing angle characteristics of the contrast ratio of the liquid crystal display device of the present embodiment. Hatching indicates a region where the contrast ratio is 10: 1 or more. In the liquid crystal display device of the present embodiment, the case where there is no phase difference compensating element in the 45 ° direction sandwiched between the absorption axes of both polarizing plates, which is a region where the viewing angle characteristics are poor, due to the influence of the polarizing plates arranged in a crossed Nicols state The viewing angle with a contrast ratio of 2.3, which is 2.3 times wider than that of, was widened, and a high contrast ratio was obtained in all directions.

  Further, in the viewing angle compensation in the direction of 45 ° with respect to the absorption axis of the polarizing plate, an in-plane compensation of the phase difference compensating element was obtained in which the effect of compensating the viewing angle more than 1 times was obtained as compared with the case without the phase difference compensating element. And the conditions of the normal direction retardation were in the range of about 5 nm to about 70 nm and about 60 nm to about 280 nm, respectively.

FIG. 3 is a diagram illustrating the operation principle of the liquid crystal display device according to the present invention. (A) and (b) show a state when no voltage is applied, (c) and (d) show a state when a voltage is applied, (a) and (c) show cross-sectional views, and (b) and (D) shows the result of observing the upper surface with a polarizing microscope in a crossed Nicols state. FIG. 3 is a diagram illustrating a voltage transmittance curve of the liquid crystal display device. FIG. 4 is a diagram illustrating a voltage transmittance curve of a liquid crystal display device having a retardation value larger than an optimal value of retardation. Shows the d _LC · [Delta] n was changed to 4μm~8μm the d _LC of the liquid crystal [Delta] n as .0773, [Phi = 0 °, 45 °, the relationship between the viewing angle of a contrast ratio of 10 at 90 ° and 135 ° It is. Shows the d _LC · [Delta] n was changed to 4μm~8μm the d _LC of the liquid crystal [Delta] n as .0773, [Phi = 0 °, 45 °, the relationship between the viewing angle contrast ratio 20 at 90 ° and 135 ° It is. And d _LC · [Delta] n was changed to 4μm~8μm the d _LC of the liquid crystal [Delta] n as 0.0773, [Phi = 0 °, 45 °, a diagram showing the relationship between the inversion angle of 90 ° and 135 °. And d _LC · [Delta] n of varying d _LC in 4μm~8μm the liquid crystal [Delta] n as 0.0773 is a diagram showing the relationship between the transmittance when a voltage 10V is applied. The difference between d _LC · Δn in which Δn was changed from 0.07 to 0.1 with the thickness d _{LC of the} liquid crystal layer being 5 μm and the viewing angle of the contrast ratio 10 at φ = 0 °, 45 °, 90 ° and 135 °. It is a figure showing a relation. The difference between d _LC · Δn in which Δn is changed from 0.07 to 0.1 with the thickness d _{LC of the} liquid crystal layer being 5 μm and the viewing angle of the contrast ratio 20 at Φ = 0 °, 45 °, 90 ° and 135 °. It is a figure showing a relation. Shows the d _LC · [Delta] n was varied [Delta] n as 5μm to 0.07 to 0.1 the thickness d _LC of the liquid crystal layer, [Phi = 0 °, 45 °, the relationship between the inversion angle of 90 ° and 135 ° It is. Shows the d _LC · [Delta] n in which the thickness d _LC of the liquid crystal layer to change the [Delta] n as 5μm to 0.07 to 0.1, the relationship between the transmittance in the voltage of 10V is applied. FIG. 3 is a perspective view showing a direction of a main refractive index of a phase difference compensating element used in the present invention. (A) to (c) are cross-sectional views showing examples of other phase difference compensating elements that can be used in the present invention. FIG. 7 is a diagram illustrating a relationship between a shift from a direction perpendicular to a slow axis of a phase difference compensating element and an absorption axis of a polarizing plate and a light leakage amount. FIG. 4 is a diagram for explaining a mechanism of viewing angle compensation by a phase difference compensating element, and is a diagram showing a polarizing plate absorption axis direction. FIG. 4 is a diagram for explaining a mechanism of viewing angle compensation by a phase difference compensating element, and is a diagram showing an image of a refractive index ellipsoid in a polarizing plate absorption axis direction. It is a figure for explaining the mechanism of viewing angle compensation by a phase difference compensating element, and is a figure showing 45 degrees from a polarizing plate absorption axis direction. FIG. 4 is a diagram for explaining a mechanism of viewing angle compensation by a phase difference compensating element, and is a diagram showing an image of a refractive index ellipsoid in a direction at 45 ° from a polarizing plate absorption axis direction. FIG. 18 is a diagram for explaining the mechanism of viewing angle compensation by the phase difference compensating element, and is a diagram showing a case where the screen of FIG. 17 is viewed obliquely when the voltage is off. FIG. 18 is a diagram for explaining a mechanism of viewing angle compensation by a phase difference compensating element, and is a diagram showing a case where the screen of FIG. 17 is viewed obliquely when a voltage is turned on. FIG. 4 is a diagram for explaining a mechanism of viewing angle compensation by a phase difference compensating element, and is a diagram showing a polarizing plate absorption axis direction. FIG. 4 is a diagram for explaining a mechanism of viewing angle compensation by a phase difference compensating element, and is a diagram showing an image of a refractive index ellipsoid in a polarizing plate absorption axis direction. FIG. 22 is a diagram for explaining the mechanism of viewing angle compensation by a phase difference compensating element, and is a diagram showing a case where the screen of FIG. 21 is viewed obliquely when the voltage is off. FIG. 22 is a diagram for explaining a mechanism of viewing angle compensation by a phase difference compensating element, and is a diagram showing a case where the screen of FIG. 21 is viewed obliquely when a voltage is turned on. Optimum phase difference films and d _LC · [Delta] n of varying d _LC in 4μm~8μm the liquid crystal [Delta] n as 0.0773, the ratio between the refractive index difference of the in-plane refractive index difference and the thickness direction and 4.5 FIG. 4 is a diagram showing the relationship between the in-plane and normal-direction retardations of FIG. And d _LC · [Delta] n in which the thickness d _LC of the liquid crystal layer to change the [Delta] n as 5μm to 0.07 to 0.1, the ratio of the refractive index difference of the in-plane refractive index difference and the thickness direction is 4.5 It is a figure which shows the relationship with the in-plane and normal-direction retardation of an optimal retardation film. The relationship between the ratio of the refractive index difference in the normal direction to the in-plane refractive index difference (0.001) of the phase difference compensating element and the viewing angle of the contrast ratio 10 at Φ = 0 °, 45 °, 90 ° and 135 °. FIG. The relationship between the ratio of the refractive index difference in the normal direction to the in-plane refractive index difference (0.001) of the phase difference compensating element and the viewing angle of the contrast ratio 20 at Φ = 0 °, 45 °, 90 ° and 135 °. FIG. It is a figure which shows the relationship between the refractive index difference ratio of the normal direction with respect to the in-plane refractive index difference (0.001) of a phase difference compensation element, and the inversion angle in (phi) = 0 degree, 45 degree, 90 degree, and 135 degree. . In a liquid crystal cell having d _LC · Δn of 390 nm, the in-plane of the phase difference compensating element when the refractive index difference ratio in the normal direction to the in-plane refractive index difference (0.001) of the phase difference compensating element is changed FIG. 6 is a diagram illustrating a relationship between the retardation in the normal direction and the normal direction. 1A is a cross-sectional view of the liquid crystal display device of Embodiment 1, and FIG. 1B is a plan view thereof. (A) a liquid crystal cell in the first embodiment, a layout view of a polarizing plate and a retardation compensation element, (b) is the n _x is the largest principal refractive index of the absorption axis direction and the phase difference compensating element of the polarizer It is a figure showing the relation with a direction. FIG. 3 is a diagram illustrating electro-optical characteristics of the liquid crystal display device according to the first embodiment. FIG. 3 is a diagram illustrating viewing angle characteristics of contrast in the liquid crystal display device according to the first embodiment. FIG. 9 is a diagram illustrating electro-optical characteristics of the liquid crystal display device according to the second embodiment. FIG. 9 is a diagram illustrating viewing angle characteristics of contrast in the liquid crystal display device of Comparative Example 1. FIG. 9 is a diagram illustrating viewing angle characteristics of contrast in the liquid crystal display device of Comparative Example 2. FIG. 14 is a diagram illustrating four gradation characteristics of the liquid crystal display device according to the third embodiment. (A) is the gradation characteristic in the direction of the absorption axis of the upper polarizing plate, and (b) is the gradation characteristic in the direction shifted by 45 ° from the absorption axis of the upper polarizing plate. FIG. 4 is a diagram illustrating four gradation characteristics of the liquid crystal display device according to the first embodiment. (A) is the gradation characteristic in the direction of the absorption axis of the upper polarizing plate, and (b) is the gradation characteristic in the direction shifted by 45 ° from the absorption axis of the upper polarizing plate. FIG. 14 is a diagram illustrating four gradation characteristics of the liquid crystal display device according to the fourth embodiment. (A) is the gradation characteristic in the direction of the absorption axis of the upper polarizing plate, and (b) is the gradation characteristic in the direction shifted by 45 ° from the absorption axis of the upper polarizing plate. FIG. 14 is a diagram illustrating four gradation characteristics of the liquid crystal display device according to the fifth embodiment. (A) is the gradation characteristic in the direction of the absorption axis of the upper polarizing plate, and (b) is the gradation characteristic in the direction shifted by 45 ° from the absorption axis of the upper polarizing plate. FIG. 14 is a diagram illustrating four gradation characteristics of the liquid crystal display device according to the sixth embodiment. (A) is the gradation characteristic in the direction of the absorption axis of the upper polarizing plate, and (b) is the gradation characteristic in the direction shifted by 45 ° from the absorption axis of the upper polarizing plate. FIG. 14 is a layout diagram of a liquid crystal cell, a polarizing plate, and a phase difference compensating element in Embodiment 7. FIG. 15 is a diagram illustrating viewing angle characteristics of contrast in the liquid crystal display device of Embodiment 7. FIG. 15 is a layout diagram of a liquid crystal cell, a polarizing plate, and a phase difference compensating element in Embodiment 8. FIG. 15 is a diagram illustrating viewing angle characteristics of contrast in the liquid crystal display device of Embodiment 8.

Explanation of reference numerals

Reference Signs List 100 liquid crystal display device, liquid crystal cell 101, 102 polarizing plate 103, 104 phase difference compensating element 32, 34, 61, 62 substrate 38a, 38b, 67, 68 vertical alignment layer 36, 66 convex part 40 liquid crystal layer 42 liquid crystal molecule 63, 64 Transparent electrode 65 Spacer

Claims (1)

A liquid crystal cell sandwiched between a pair of substrates and having a liquid crystal layer made of liquid crystal molecules having negative dielectric anisotropy,
A pair of polarizing plates sandwiching the liquid crystal cell and having absorption axes of the polarizing plates orthogonal to each other,
A liquid crystal display device comprising: a pair of polarizing plates; and a phase difference compensating element provided one by one between the liquid crystal cell,
The liquid crystal molecules are oriented in a direction substantially perpendicular to the pair of substrates when no voltage is applied,
Phase difference compensating element has a negative birefringence, x orthogonal to each other respectively, y, and z-axis to the three principal refractive indices n _x, n _y, has a n _z, of the liquid crystal cell the main refractive index in the plane direction n _x, and n _y, the main refractive index in the thickness direction of the liquid crystal cell when a n _z, has a relation of _{n x> n y> n z} ,
The phase difference compensating element is arranged such that an x-axis direction of the phase difference compensating element is substantially orthogonal to an absorption axis of a polarizing plate adjacent to the phase difference compensating element,
Phase difference ratio between the retardation value d _f retardation values d _f in the plane direction of the compensating element (n _x -n _y) and thickness direction (n _x -n _z) is 2 or more, a liquid crystal display device.

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