Liquid crystal display device

Abstract

To provide a liquid crystal display device which costs less, can increase the contrast ratio and the angle of field, and also is useful as well as an in-cell type touch panel capable of displaying in a reflection mode.SOLUTION: The liquid crystal display device sequentially includes a first substrate, a liquid crystal layer, a second substrate, a phase difference layer, and a polarizer from the back surface side, and has a plurality of pixels arranged in a matrix. The first substrate includes a reflective layer reflecting light, a first electrode and a second electrode capable of generating a lateral electric field in the liquid crystal layer, and a first horizontal orientation film in contact with the liquid crystal layer. The second substrate has a second horizontal orientation film in contact with the liquid crystal layer. The liquid crystal layer takes on a twist orientation when no voltages are being applied. The phase difference layer has a λ / 4 plate, a λ / 2 plate, and a positive C-plate.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The following disclosure relates to liquid crystal displays. [Background technology]

[0002] Liquid crystal display devices are display devices that use liquid crystal material for display, and are generally broadly classified into transmissive liquid crystal display devices and reflective liquid crystal display devices according to the display method. Transmissive liquid crystal display devices are devices that perform display in a transmissive mode using transmitted light from a backlight behind the screen, while reflective liquid crystal display devices are devices that perform display in a reflective mode using external light (also called ambient light) instead of backlight light. As a display device that combines these characteristics, a semi-transmissive liquid crystal display device has been proposed in which each pixel has an area that performs display in a transmissive mode and an area that performs display in a reflective mode (see, for example, Patent Document 1).

[0003] Liquid crystal display devices can also be broadly classified according to the liquid crystal driving method, and there are known liquid crystal display devices of a vertical electric field type that drives a liquid crystal layer with an electric field in a direction approximately perpendicular to the substrate surface to perform display, and a horizontal electric field type that drives a liquid crystal layer with an electric field in a direction approximately parallel to the substrate surface to perform display. Examples of the vertical electric field type include the twisted nematic (TN) mode and the multi-domain vertical alignment (MVA) mode, and examples of the horizontal electric field type include the in-plane switching (IPS) mode and the fringe field switching (FFS) mode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5767195 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, liquid crystal display devices used in smartphones, tablets, and the like are usually provided with a touch sensor function. There are various types of touch sensors known, such as resistive film type, electrostatic capacitance type, and optical type. Liquid crystal display devices equipped with a touch sensor (also called touch panel) include a type in which the touch sensor is attached externally (external type) and a type in which the touch sensor is built-in (built-in type). The built-in type touch panel is advantageous in terms of narrowing the frame, reducing the thickness, and reducing the weight, etc., compared to the external type touch panel, and also has the advantage of increasing the light transmittance.

[0006] Built-in touch panels are classified into on-cell type and in-cell type. The cell means a display panel (also called a liquid crystal panel) that includes an active matrix substrate, typically a thin film transistor (TFT) substrate, an opposing substrate arranged to face the active matrix substrate, and a liquid crystal layer arranged between the substrates. In general, in the in-cell type, a layer that performs the touch sensor function is arranged in the display panel, while in the on-cell type, a layer that performs the touch sensor function is arranged between the display panel and a polarizing plate arranged on the observation surface side of the display panel. Among these, the in-cell type can theoretically realize the thinnest and lightest touch panel. In addition, liquid crystal display devices capable of displaying in a reflective mode are suitable for outdoor use, so that an in-cell type touch panel capable of displaying in a reflective mode is required, but has not yet been realized.

[0007] The reason why this has not been realized is believed to be that in the current reflective liquid crystal display device, one of a pair of electrodes (also called the opposing electrode or common electrode) for applying a voltage to the liquid crystal layer is arranged on the opposing substrate side. Therefore, the inventors thought that if a horizontal electric field method such as the FFS mode is used, both of the pair of electrodes are provided only on the active matrix substrate side, so that an in-cell type touch panel capable of displaying in the reflective mode can be realized. However, after further investigation, it was found that even if the conventional horizontal electric field method is simply adopted in a reflective liquid crystal display device, the reflectance is low, for example, about 60% of the reflectance when a VA mode, which is a type of vertical electric field method, is adopted. If the reflectance is low like this, the contrast ratio becomes small, and it is considered that it cannot be used practically as an in-cell type touch panel.

[0008] As a result of intensive research, the present inventors have found that a liquid crystal display device having a first substrate, a liquid crystal layer, a second substrate, a retardation layer, and a polarizing plate in this order from the rear side, and having a plurality of pixels arranged in a matrix, the first substrate having a reflective layer that reflects light, a first electrode and a second electrode that can generate a transverse electric field in the liquid crystal layer, and a first horizontal alignment film in contact with the liquid crystal layer, the second substrate having a second horizontal alignment film in contact with the liquid crystal layer, and the liquid crystal layer having a twisted alignment when no voltage is applied, can improve the contrast ratio even though it is a transverse electric field type liquid crystal display device, and is useful as an in-cell type touch panel capable of displaying in a reflective mode. However, it has been found that this device has a new problem of being expensive because a special retardation plate is preferably used as the retardation layer. On the other hand, it has also been found that the use of a general-purpose retardation plate causes problems in terms of physical properties such as viewing angle and contrast (see, for example, Test Example 2 described later). In order to reduce costs in the field of optical films, it is possible to use films that are widely distributed and produced, to reduce material loss, to improve productivity, and so on.

[0009] The present invention has been made in consideration of the above-mentioned current situation, and aims to provide a liquid crystal display device that is low-cost, has an improved contrast ratio and viewing angle, and is also useful as an in-cell touch panel capable of displaying in a reflective mode. [Means for solving the problem]

[0010] (1) One embodiment of the present invention is a liquid crystal display device comprising a first substrate, a liquid crystal layer, a second substrate, a retardation layer, and a polarizing plate, in that order from the rear side, and having a plurality of pixels arranged in a matrix, wherein the first substrate has a reflective layer that reflects light, a first electrode and a second electrode that can generate a transverse electric field in the liquid crystal layer, and a first horizontal alignment film in contact with the liquid crystal layer, the second substrate has a second horizontal alignment film in contact with the liquid crystal layer, the liquid crystal layer has a twisted alignment when no voltage is applied, and the retardation layer includes a λ / 4 plate, a λ / 2 plate, and a positive C plate.

[0011] (2) Moreover, in addition to the configuration of (1) above, an embodiment of the present invention is a liquid crystal display device, wherein the liquid crystal layer contains a positive type liquid crystal material or a negative type liquid crystal material.

[0012] (3) Furthermore, in one embodiment of the present invention, in addition to the configuration of (2) above, when the liquid crystal layer contains the positive type liquid crystal material, the angle between the polarization axis of the polarizer and the alignment direction of the liquid crystal molecules defined by the first horizontal alignment film is 63.5° or more and 71.5° or less, and when the liquid crystal layer contains the negative type liquid crystal material, the angle between the polarization axis of the polarizer and the alignment direction of the liquid crystal molecules defined by the first horizontal alignment film is 20.5° or more and 26° or less.

[0013] (4) Furthermore, an embodiment of the present invention is a liquid crystal display device having the configuration of (1), (2), or (3) above, wherein the positive C plate is located between the λ / 4 plate and the λ / 2 plate.

[0014] (5) Furthermore, in an embodiment of the present invention, in addition to the configuration of (1), (2), (3), or (4), the positive C plate has an absolute value of a thickness direction retardation Rth (nm) of 150 to 270 nm.

[0015] (6) Furthermore, in an embodiment of the present invention, in addition to the configuration of (1), (2), (3), (4), or (5), the retardation layer further includes a second positive C plate, and the second positive C plate is located between the λ / 2 plate and the polarizing plate.

[0016] (7) Moreover, in addition to the configuration (6), another embodiment of the present invention is a liquid crystal display device, wherein the second positive C plate has an absolute value of a thickness direction retardation Rth (nm) of 50 to 130 nm.

[0017] (8) Furthermore, one embodiment of the present invention is a liquid crystal display device having the configuration of (1), (2), (3), (4), (5), (6) or (7), wherein the twist angle of the liquid crystal layer when no voltage is applied is 70° or more and 85° or less.

[0018] (9) Furthermore, an embodiment of the present invention is a liquid crystal display device, in which, in addition to the configuration of (2), (3), (4), (5), (6), (7) or (8), when the liquid crystal layer contains the positive liquid crystal material, the product (dΔn) of the thickness d of the liquid crystal layer and the birefringence Δn of the liquid crystal material is 218 nm or more and 255 nm or less.

[0019] (10) Furthermore, in one embodiment of the present invention, in addition to the configuration of (2), (3), (4), (5), (6), (7), (8) or (9), when the liquid crystal layer contains the positive liquid crystal material, an angle between the in-plane slow axis of the λ / 2 plate and the alignment direction of the liquid crystal material defined by the first horizontal alignment film is 47.5° or more and 52.5° or less.

[0020] (11) Furthermore, an embodiment of the present invention is a liquid crystal display device, in which, in addition to the configuration of (1), (2), (3), (4), (5), (6), (7), (8), (9) or (10) above, when the liquid crystal layer contains the negative type liquid crystal material, the product (dΔn) of the thickness d of the liquid crystal layer and the birefringence Δn of the liquid crystal material is 230 nm or more and 260 nm or less.

[0021] (12) Furthermore, in one embodiment of the present invention, in addition to the configuration of (1), (2), (3), (4), (5), (6), (7), (8), (9), (10) or (11), when the liquid crystal layer contains the negative type liquid crystal material, an angle between the in-plane slow axis of the λ / 2 plate and the alignment direction of the liquid crystal material defined by the first horizontal alignment film is 38.5° or more and 42.5° or less.

[0022] (13) Furthermore, in one embodiment of the present invention, in addition to the configuration of (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11) or (12), at least one of the first electrode and the second electrode has a plurality of strip-shaped portions and a slit located between two adjacent strip-shaped portions of the plurality of strip-shaped portions.

[0023] (14) Furthermore, one embodiment of the present invention is a liquid crystal display device having the configuration described above in (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (12) or (13), and further having a single domain orientation.

[0024] (15) Furthermore, an embodiment of the present invention is a liquid crystal display device that performs display in a normally black mode in addition to the configuration of (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (12), (13), or (14) above.

[0025] (16) Furthermore, in an embodiment of the present invention, in addition to the configuration of (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (12), (13), (14), or (15), one of the first electrode and the second electrode is a pixel electrode provided in each of the plurality of pixels, and the other is a common electrode including a plurality of segments each capable of functioning as a touch sensor electrode, and the first substrate has a plurality of touch wirings each connected to a corresponding one of the touch sensor electrodes.

[0026] (17) Furthermore, in one embodiment of the present invention, in addition to the configuration of (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (12), (13), (14), (15), or (16), the first substrate has a thin film transistor provided in each of the plurality of pixels and including an oxide semiconductor layer, and the oxide semiconductor layer includes an In-Ga-Zn-O based semiconductor.

[0027] (18) Furthermore, in one embodiment of the present invention, in addition to the configuration of (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (12), (13), (14), (15), (16), or (17), a liquid crystal display device further includes a light source. Effect of the Invention

[0028] According to the present invention, it is possible to provide a liquid crystal display device which is low in cost, has an improved contrast ratio and viewing angle, and is also useful as an in-cell touch panel capable of displaying in a reflective mode. [Brief description of the drawings]

[0029] [Figure 1] 1 is a schematic cross-sectional view of a liquid crystal display device 1. FIG. [Diagram 2] FIG. 2 is a schematic cross-sectional view showing the liquid crystal display device 1 in more detail. [Diagram 3] FIG. 1 is a schematic plan view of the entire liquid crystal display device 1 as viewed from the observation surface side. [Figure 4] In a liquid crystal display device 1 having, in order from the rear side, a first substrate 10, a liquid crystal layer 20, a second substrate 30, a λ / 4 plate 41, a λ / 2 plate 42, and a polarizing plate 50, this is a plan view conceptually showing the relationship between the long axis direction of liquid crystal molecules 21 in the liquid crystal layer 20 when no voltage is applied, the in-plane slow axis 41SA of the λ / 4 plate 41, the in-plane slow axis 42SA of the λ / 2 plate 42, and the polarization axis 50AA of the polarizing plate 50. [Figure 5A] 1 is a schematic plan view of a first substrate 10 as viewed from the first horizontal alignment film 140 side. [Figure 5B] FIG. 2 is a schematic plan view of the second substrate 30 as viewed from the second horizontal alignment film 340 side. [Figure 5C] FIG. 1 is a schematic plan view of a liquid crystal panel 1X after the first substrate 10 and the second substrate 30 are bonded together, as viewed from the second substrate 30 side. [Figure 6] 1 is a diagram conceptually showing the setting of the optical axis for minimizing the black reflectance, and is also a diagram conceptually showing the optical axis setting in Example 1. [Figure 7] 13 is a graph showing evaluation results of black luminance. [Figure 8] 13 is a graph showing the evaluation results of contrast. [Figure 9] In a liquid crystal display device 1 having, in order from the rear side, a first substrate 10, a liquid crystal layer 20, a second substrate 30, a λ / 4 plate 41, a λ / 2 plate 42, and a polarizing plate 50, this is a plan view conceptually showing the relationship between the long axis direction of liquid crystal molecules 21 in the liquid crystal layer 20 when no voltage is applied, the in-plane slow axis 41SA of the λ / 4 plate 41, the in-plane slow axis 42SA of the λ / 2 plate 42, and the polarization axis 50AA of the polarizing plate 50. [Figure 10A] 1 is a schematic plan view of a first substrate 10 as viewed from the first horizontal alignment film 140 side. [Figure 10B] FIG. 2 is a schematic plan view of the second substrate 30 as viewed from the second horizontal alignment film 340 side. [Figure 10C] FIG. 1 is a schematic plan view of a liquid crystal panel 1X after the first substrate 10 and the second substrate 30 are bonded together, as viewed from the second substrate 30 side. [Figure 11] 13 is a diagram conceptually showing the setting of the optical axis for minimizing the black reflectance, and is also a diagram conceptually showing the optical axis setting of Example 3. [Figure 12A] FIG. 13 is a diagram showing a simulation result in the case where the liquid crystal material is a positive type. [Figure 12B] FIG. 13 is a diagram showing a simulation result in the case where the liquid crystal material is a positive type. [Figure 13] FIG. 13 is a diagram showing simulation results for Examples 1 and 3. [Figure 14] 1 is a graph showing the distribution of maximum black luminance values ​​for Examples 1 to 4. [Figure 15] FIG. 13 is a diagram showing a simulation result in the case where the liquid crystal material is a negative type. [Figure 16] 13 is a graph showing the distribution of maximum black luminance values ​​for Examples 11 to 14. [Figure 17] 2 is a plan view illustrating a schematic arrangement of touch sensor electrodes TX and touch wirings TL included in the liquid crystal display device 1. FIG. [Figure 18] FIG. 2 is a schematic cross-sectional view showing the liquid crystal display device 1 in more detail. [Figure 19] 1 is a schematic cross-sectional view of a liquid crystal display device 1. FIG. [Figure 20] FIG. 13 is a diagram showing a simulation result in the case where the liquid crystal material is a positive type. [Figure 21] 13 is a graph showing the distribution of maximum black luminance values ​​for Examples 21 to 23. [Figure 22] FIG. 13 is a diagram showing a simulation result in the case where the liquid crystal material is a negative type. [Diagram 23] 13 is a graph showing the distribution of maximum black luminance values ​​for Examples 31 to 33. [Figure 24] 1 is a schematic cross-sectional view of a liquid crystal display device 1. FIG. [Diagram 25]1 is a schematic plan view conceptually illustrating that each pixel P in a liquid crystal display device 1 has a reflective region Rf and a transmissive region Tr. [Figure 26] FIG. 1 is a schematic cross-sectional view of a liquid crystal display device. [Figure 27A] 1 is a schematic plan view showing the structure of a liquid crystal cell 1100 when viewed from the front. [Figure 27B] 27B is a schematic cross-sectional view (cross-sectional view taken along line AA') in FIG. 27A. [Figure 28] FIG. 1 is a schematic cross-sectional view of a test cell 1000. [Figure 29A] FIG. 1 is a schematic plan view showing the structure of a test cell 3000 (and a liquid crystal cell 3100) viewed from the front. [Figure 29B] 29B is a schematic cross-sectional view (cross-sectional view taken along line AA') in FIG. 29A. [Diagram 30] FIG. 3 is a schematic cross-sectional view of a test cell 3000. [Diagram 31] FIG. 13 is a diagram conceptually illustrating the setting of optical axes in Test Example 5. [Figure 32A] FIG. 1 is a diagram showing the results of Test Examples 1 and 2. [Figure 32B] FIG. 1 shows the results of Test Examples 3 and 4. [Figure 32C] FIG. 13 is a diagram showing the results of Test Example 5. [Figure 33A] FIG. 1 is a diagram showing the results of Test Examples 1 and 2. [Figure 33B] FIG. 1 shows the results of Test Examples 3 and 4. [Figure 33C] FIG. 13 is a diagram showing the results of Test Example 5. [Diagram 34] FIG. 2 is a diagram conceptually illustrating an azimuth angle. [Diagram 35] This is an image taken from the front. [Figure 36A] FIG. 1 is a diagram showing the results of Test Examples 1 and 2. [Figure 36B] FIG. 1 shows the results of Test Examples 3 and 4. [Figure 36C] FIG. 13 is a diagram showing the results of Test Example 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] (Definition of terms) In this specification, the observation side means the side closer to the screen (display surface) of the liquid crystal display device, and the rear side means the side farther from the screen (display surface) of the liquid crystal display device.

[0031] The no-voltage-applied state refers to a state in which the voltage applied to the liquid crystal layer is less than the threshold voltage (including no voltage application). The voltage-applied state refers to a state in which the voltage applied to the liquid crystal layer is equal to or greater than the threshold voltage. In this specification, the no-voltage-applied state is also referred to as when no voltage is applied, and the voltage-applied state is also referred to as when a voltage is applied.

[0032] The polar angle means the angle between the direction of interest (for example, the measurement direction) and the normal direction of the screen of the liquid crystal panel. The azimuth refers to the direction when the target direction is projected onto the screen of the liquid crystal panel, and is expressed as the angle (azimuth angle) between the target direction and a reference direction. Here, the reference direction (0°) is set to the horizontal right direction on the screen of the liquid crystal panel. For angles and azimuth angles, positive angles are counterclockwise from the reference orientation, and negative angles are clockwise from the reference orientation. Both counterclockwise and clockwise refer to the direction of rotation when the LCD panel screen is viewed from the observation side (front). Additionally, angles refer to values ​​measured when the LCD panel screen is viewed in a flat view, and refer to acute angles unless otherwise specified, such as the direction of rotation.

[0033] The axial direction of the optical film means the direction of the polarization axis of the polarizing plate if it is a polarizing plate, and means the direction of the slow axis if it is a retardation layer. The polarization axis of the polarizing plate means the absorption axis if it is an absorption type polarizing plate, and means the reflection axis if it is a reflection type polarizing plate. The axial direction of the retardation layer means the direction of the in-plane slow axis of the retardation layer, unless otherwise specified.

[0034] The retardation layer means a layer in which at least one of the in-plane retardation (also referred to as in-plane phase difference) Re and the thickness-direction retardation (also referred to as thickness-direction phase difference) Rth has a value of 10 nm or more. Preferably, it means a layer having a value of 20 nm or more. In the present specification, the numerical values described as Re and Rth are absolute values unless otherwise specified.

[0035] The in-plane phase difference Re is defined as Re = (nx - ny) × d. The thickness-direction phase difference Rth is defined as Rth = {nz - (nx + ny) / 2} × d. nx represents the principal refractive index in the direction of the slow axis in the plane of each retardation layer. ny represents the principal refractive index in the direction of the fast axis in the plane of each retardation layer. nz represents the principal refractive index in the direction perpendicular to the plane of each retardation layer. The slow axis direction is the azimuth in which the refractive index is maximum, and the fast axis direction is the azimuth in which the refractive index is minimum. d indicates the thickness of the retardation layer.

[0036] An A plate is a retardation plate that satisfies "nx > ny ≒ nz". Among C plates, a positive C plate (also referred to as +C-plate) is a retardation plate that satisfies "nz > nx ≒ ny", and Rth shows a positive value. A negative C plate (also referred to as -C-plate) is a retardation plate that satisfies "nz < nx ≒ ny", and Rth shows a negative value.

[0037] Unless otherwise specified, the measurement wavelength of optical parameters such as refractive index and phase difference is 550 nm.

[0038] "Approximately parallel" means that the angle (absolute value) between the two is within the range of 0°±10°, and this angle is preferably within the range of 0°±5°, and more preferably 0° (i.e., parallel in the narrow sense). "Approximately perpendicular" (or approximately perpendicular) means that the angle (absolute value) between the two is within the range of 90°±10°, and this angle is preferably within the range of 90°±5°, and more preferably 90° (i.e., orthogonal or perpendicular in the narrow sense).

[0039] Hereinafter, a liquid crystal display device according to an embodiment of the present invention will be described. The present invention is not limited to the contents described in the following embodiment, and appropriate design changes can be made within the scope of the configuration of the present invention.

[0040] (Embodiment 1) FIG. 1 is a schematic cross-sectional view of a liquid crystal display device 1 according to an example of the present embodiment, and FIG. 2 is a schematic cross-sectional view showing the liquid crystal display device 1 according to an example of the present embodiment in more detail. FIG. 3 is a schematic plan view of the entire liquid crystal display device 1 according to an example of the present embodiment, as viewed from the observation surface side. As shown in FIG. 1, the liquid crystal display device 1 includes, in order from the rear side, a first substrate 10, a liquid crystal layer 20, a second substrate 30, a retardation layer 40, and a polarizing plate 50. The retardation layer 40 includes a positive C plate 43 in addition to a λ / 4 plate 41 and a λ / 2 plate 42. In this embodiment, a TFT substrate is used as the first substrate 10. Note that a portion or structure having a structure in which the liquid crystal layer 20 is sandwiched between the first substrate 10 and the second substrate 30 is also referred to as a liquid crystal panel 1X.

[0041] As shown in Fig. 3, the liquid crystal display device 1 has a plurality of pixels P arranged in a matrix. The plurality of pixels P typically include three types of pixels, namely red pixels, green pixels, and blue pixels, but the number of types of pixels may be two or less, or may be four or more. Each pixel P includes a thin film transistor (TFT) 110, and a first electrode 121 and a second electrode 122 capable of generating a transverse electric field in the liquid crystal layer 20. A gate electrode of the TFT 110 is electrically connected to a corresponding gate line (also referred to as a scanning line) GL, and a source electrode of the TFT 110 is electrically connected to a corresponding source line (also referred to as a signal line) SL. A drain electrode of the TFT 110 is electrically connected to the second electrode 122.

[0042] <First substrate> As shown in FIG. 2, the first substrate 10 has, in order from the back side to the observation side, a reflective layer 130 that reflects light, a first electrode 121, a second electrode 122, and a first horizontal alignment film 140 that contacts the liquid crystal layer 20. The first substrate 10 preferably further has a support substrate 100 and a backplane circuit BP on the back side of the reflective layer 130. An insulating layer (also called an insulating film) is provided between each layer, etc., as necessary. For example, a first interlayer insulating layer 151 is provided so as to cover the backplane circuit BP, a second interlayer insulating layer 152 is provided on the first interlayer insulating layer 151 with the reflective layer 130 sandwiched therebetween, and a dielectric layer (also called a third interlayer insulating layer) 153 is provided between the first electrode 121 and the second electrode 122.

[0043] The supporting substrate 100 is preferably transparent and insulating, and examples of the supporting substrate 100 include a glass substrate and a plastic substrate.

[0044] The backplane circuit BP is provided on a support substrate 100. The backplane circuit BP is a circuit for driving a plurality of pixels P, and includes a TFT 110, a gate line GL, a source line SL, etc. Usually, the backplane circuit BP also includes a gate insulating film.

[0045] The TFT 110 is provided in each of the pixels P. The TFT 110 is preferably one including an oxide semiconductor layer as an active layer (also referred to as an oxide semiconductor TFT). The oxide semiconductor included in the oxide semiconductor layer has been attracting attention in recent years as an active layer material to replace amorphous silicon and polycrystalline silicon, and has a higher mobility than amorphous silicon. Therefore, the oxide semiconductor TFT can operate at a higher speed than the amorphous silicon TFT. In addition, the oxide semiconductor layer can be formed by a simpler process than the polycrystalline silicon layer, and can be applied to devices requiring a large area.

[0046] Since oxide semiconductor TFTs also have excellent off-leak characteristics, a driving method can be used to display images by reducing the frequency of rewriting. For example, when displaying a still image, image data can be rewritten once per second. This type of driving method is called pause driving or low-frequency driving, and can significantly reduce the power consumption of a liquid crystal display device. By employing pause driving and performing touch detection during periods when images are not being rewritten, it is possible to suppress a decrease in sensitivity of touch operations due to noise from the driving circuit, and the S / N ratio (signal-to-noise ratio) can be increased, for example, to about 10 times that of conventional devices.

[0047] The oxide semiconductor TFT is also advantageous in terms of reducing the size of the TFT, and therefore can suitably realize a configuration in which a memory circuit is provided for each pixel P (also referred to as MIP (Memory In Pixels)).

[0048] The oxide semiconductor may be an amorphous oxide semiconductor or a crystalline oxide semiconductor having a crystalline portion. Examples of the crystalline oxide semiconductor include a polycrystalline oxide semiconductor, a microcrystalline oxide semiconductor, and a crystalline oxide semiconductor whose c-axis is oriented substantially perpendicular to the layer surface.

[0049] The oxide semiconductor layer may be a single layer or may have a laminated structure of two or more layers. The oxide semiconductor layer having a laminated structure may include an amorphous oxide semiconductor layer and a crystalline oxide semiconductor layer, may include a plurality of crystalline oxide semiconductor layers having different crystal structures, or may include a plurality of amorphous oxide semiconductor layers. When the oxide semiconductor layer has a two-layer structure including an upper layer and a lower layer, the energy gap of the oxide semiconductor included in the lower layer may be different from the energy gap of the oxide semiconductor included in the upper layer.

[0050] The materials and structures of the amorphous oxide semiconductor and each crystalline oxide semiconductor, the film formation method, and the configuration of the oxide semiconductor layer having a laminated structure are described in, for example, JP 2014-007399 A. For reference, the entire disclosure of JP 2014-007399 A is incorporated herein by reference.

[0051] Specifically, the oxide semiconductor layer preferably contains at least one metal element selected from In (indium), Ga (gallium), and Zn (zinc). Among them, an oxide semiconductor film containing a ternary oxide of In, Ga, and Zn is more preferable. A preferred example of the ternary oxide of In, Ga, and Zn is indium gallium zinc oxide. A semiconductor containing a ternary oxide of In, Ga, and Zn is called an In-Ga-Zn-O-based semiconductor, and the ratio (composition ratio) of In, Ga, and Zn in this semiconductor is not particularly limited, and examples thereof include In:Ga:Zn=2:2:1, In:Ga:Zn=1:1:1, and In:Ga:Zn=1:1:2.

[0052] The In-Ga-Zn-O based semiconductor may be amorphous or crystalline. As a crystalline In-Ga-Zn-O based semiconductor, one in which the c-axis is oriented approximately perpendicular to the layer surface is preferable.

[0053] The crystal structure of the crystalline In-Ga-Zn-O-based semiconductor is disclosed in, for example, JP 2014-007399 A, JP 2012-134475 A, JP 2014-209727 A, etc. For reference, the entire disclosures of JP 2012-134475 A and JP 2014-209727 A are incorporated herein by reference. Since a TFT having an In-Ga-Zn-O-based semiconductor layer has high mobility (more than 20 times that of an a-Si TFT) and low leakage current (less than 1 / 100 that of an a-Si TFT), it is suitable for use as a driving TFT (for example, a TFT included in a driving circuit provided on the same substrate as the display area around a display area including a plurality of pixels) and a pixel TFT (a TFT provided in a pixel).

[0054] The oxide semiconductor layer may contain an oxide semiconductor other than an In-Ga-Zn-O-based semiconductor. For example, a ternary oxide of In, Sn (tin) and Zn may be mentioned, and for example, In2O3-SnO2-ZnO; InSnZnO is preferably exemplified. A semiconductor containing a ternary oxide of In, Sn and Zn is called an In-Sn-Zn-O-based semiconductor. Alternatively, the oxide semiconductor layer may include an In-Al-Zn-O based semiconductor, an In-Al-Sn-Zn-O based semiconductor, a Zn-O based semiconductor, an In-Zn-O based semiconductor, a Zn-Ti-O based semiconductor, a Cd-Ge-O based semiconductor, a Cd-Pb-O based semiconductor, CdO (cadmium oxide), an Mg-Zn-O based semiconductor, an In-Ga-Sn-O based semiconductor, an In-Ga-O based semiconductor, a Zr-In-Zn-O based semiconductor, an Hf-In-Zn-O based semiconductor, an Al-Ga-Zn-O based semiconductor, a Ga-Zn-O based semiconductor, an In-Ga-Zn-Sn-O based semiconductor, or the like.

[0055] The first interlayer insulating layer 151 is provided so as to cover the backplane circuit BP. The surface of the first interlayer insulating layer 151 on the reflective layer 130 side preferably has an uneven shape (also referred to as an uneven surface structure). This allows the reflective layer 130 to have an uneven surface structure that reflects this shape. The first interlayer insulating layer 151 having an uneven surface structure can be suitably formed using a photosensitive resin, for example, as described in Japanese Patent No. 3394926.

[0056] The reflective layer (also referred to as a reflective film) 130 is provided on the first interlayer insulating layer 151. The reflective layer 130 is formed from a material that reflects light. In particular, it is preferable that the reflective layer 130 is formed from a metal material having a high reflectance. Examples of materials for the reflective layer 130 include a silver alloy, an aluminum alloy, and an aluminum alloy.

[0057] The reflective layer 130 preferably has an uneven shape that reflects the uneven surface structure that the first interlayer insulating layer 151 preferably has. That is, the reflective layer 130 also preferably has an uneven surface structure. This uneven surface structure is also called MRS (Micro Reflective Structure) and is provided to diffusely reflect ambient light and realize a white display close to paper white. The uneven surface structure is preferably composed of a plurality of convex parts p arranged randomly so that the center distance between adjacent convex parts p is 5 μm or more and 50 μm or less. The center distance between adjacent convex parts p is more preferably 10 μm or more and 20 μm or less. The shape of the convex parts p is preferably approximately circular or approximately polygonal when viewed from the normal direction of the support substrate. The area of ​​the convex parts p that occupies one pixel P is preferably, for example, about 20 to 40%, and the height of the convex parts p is preferably, for example, 1 μm or more and 5 μm or less.

[0058] The second interlayer insulating layer 152 is provided on the first interlayer insulating layer 151 so as to cover the reflective layer 130. That is, the reflective layer 130 is disposed between the first interlayer insulating layer 151 and the second interlayer insulating layer 152.

[0059] Here, the first interlayer insulating layer 151 and the second interlayer insulating layer 152 are preferably formed from an organic insulating material or an inorganic insulating material. For example, organic insulating films obtained using an organic insulating material include organic films (relative dielectric constant ε=2 to 5) of acrylic resin, polyimide resin, novolac resin, etc., and laminates thereof. The thickness of the organic insulating film is not particularly limited, but is, for example, 2 μm or more and 4 μm or less. For example, inorganic insulating films obtained using an inorganic insulating material include inorganic films (relative dielectric constant ε=5 to 7) of silicon nitride (SiNx), silicon oxide (SiO2), etc., and laminates thereof. The thickness of the inorganic insulating film is not particularly limited, but is, for example, 1500 Å or more and 3500 Å or less. Alternatively, the inorganic insulating film may be a laminate of an organic insulating film and an inorganic insulating film. Among them, it is preferable that the first interlayer insulating layer 151 and the second interlayer insulating layer 152 are organic insulating films.

[0060] From the viewpoint of manufacturing, it is preferable that the interlayer insulating layers 151 and 152 are highly transparent, and it is suitable to form them from the same material with high transmittance. Also, the first interlayer insulating layer 151, which is farther from the observation surface side than the reflective layer 130, may have a low transmittance or may be opaque. From the viewpoint of light utilization efficiency, the second interlayer insulating layer 152 may have a high transparency, and may be made of a material with high transmittance different from that of the first interlayer insulating layer 151.

[0061] The first electrode 121 is disposed on the reflective layer 130 via the second interlayer insulating layer 152, and a dielectric layer 153 is disposed between the first electrode 121 and the second electrode 122. Therefore, the reflective layer 130 is located on the opposite side of the liquid crystal layer 20 with respect to the first electrode 121 and the second electrode 122 (i.e., on the rear side of the first electrode 121 and the second electrode 122). In this embodiment, of the first electrode 121 and the second electrode 122, the second electrode 122 is located relatively closer to the observation surface, and the first electrode 121 is located on the rear surface. The electrode located relatively closer to the observation surface is also referred to as an upper layer electrode, and the electrode located relatively closer to the rear surface is also referred to as a lower layer electrode.

[0062] One of the first electrode 121 and the second electrode 122 is a pixel electrode PE, and the other is a common electrode CE. The pixel electrode is provided in each of the multiple pixels P. The pixel electrode is electrically connected to the backplane circuit BP. In this embodiment, the first electrode 121 (lower layer electrode) is the common electrode CE, and the second electrode 122 (upper layer electrode) is the pixel electrode PE.

[0063] At least one of the first electrode 121 and the second electrode 122 preferably has a plurality of strip portions SP and a slit Sl located between two adjacent strip portions among the plurality of strip portions. The strip portion SP corresponds to an electrode portion, and the slit Sl corresponds to an opening, and such an electrode is also called a slit electrode or a finger electrode. From the viewpoint of easily generating a transverse electric field, it is preferable that at least the upper layer electrode (pixel electrode PE in this embodiment) is a slit electrode. In this case, the lower layer electrode (common electrode CE in this embodiment) may be a planar electrode, that is, a so-called solid electrode, or may be a slit electrode.

[0064] The extension directions of the multiple strip portions SP constituting the slit electrode are preferably approximately parallel to each other. Also, it is preferable that they have a linear shape extending in the same direction. A linear shape means that the center line of the strip portion SP, not the outer edge of the strip portion SP, is linear, and the center line of the strip portion SP means a line that divides the strip portion SP in half in the width direction. The width direction means a direction approximately perpendicular to the direction in which the strip portion SP extends in a plan view. Note that the strip portion SP may have a bent portion (also called a kink portion) in the middle (for example, at the end portion), but it is preferable that the strip portion SP does not have a bent portion.

[0065] The extension direction of the strip portions SP may be different for each pixel, but is preferably the same for two or more adjacent pixels, and is most preferably the same for all pixels from the viewpoint of maximizing display performance.

[0066] In addition, in a plan view, the angle (also referred to as the finger angle) between the alignment direction of the liquid crystal molecules 21 defined by the first horizontal alignment film 140 and the extension direction of the multiple strip portions SP may be 0° or may be greater than 0° and less than or equal to 30°. A mode in which the finger angle is 0° is a mode in which the alignment direction of the liquid crystal molecules 21 defined by the first horizontal alignment film 140 and the extension direction of the multiple strip portions SP are approximately parallel. Note that it is preferable to consider the finger angle in consideration of the twist angle, which will be described later, and the like.

[0067] The width L of each strip-shaped portion SP differs depending on the applied voltage, etc., but is preferably, for example, 0.3 to 10 μm, and more preferably 1 to 5 μm. The interval between two adjacent strip-shaped portions SP (i.e., the interval between the center lines of each strip-shaped portion) also differs depending on the applied voltage, etc., but is preferably, for example, 0.3 to 10 μm, and more preferably 1 to 5 μm.

[0068] In the present embodiment, the pixel electrode PE is provided above the common electrode CE. However, in a relatively large liquid crystal display device, that is, in a liquid crystal display device in which the area of ​​the pixel P is relatively large, it is preferable that the pixel electrode PE is provided above the common electrode CE. In this configuration (also referred to as the V2 structure), since there is no need to form a slit in the common electrode CE, which is the lower electrode, the increase in resistivity (sheet resistivity) of the common electrode CE is suppressed more than in the configuration (also referred to as the V3 structure) in which the common electrode CE is provided above the pixel electrode PE, and therefore the fringe electric field applied to the liquid crystal layer 20 is suppressed from weakening. In this configuration (V2 structure), when the pixel electrode PE is a slit electrode, the resistivity of the pixel electrode PE increases, but since an externally input voltage is applied to the pixel electrode PE, it is easy to reduce the effect of the increase in resistivity (i.e., to suppress the fringe electric field from weakening). In order to suppress the increase in resistivity of the common electrode CE, it is possible to use low-resistance wiring made of a metal material (for example, connecting the low-resistance wiring to the common electrode). However, in such a configuration, adverse effects on the display due to specular reflection from the low-resistance wiring (for example, glare, rainbow-colored diffraction, interference patterns) may occur, making it necessary to block light with a black matrix or the like, and it may not be possible to sufficiently improve the reflective aperture ratio.

[0069] In the configuration in which the pixel electrode PE is provided above the common electrode CE, the common electrode CE is not present in the region in which the second contact hole CH2 is formed, and the region does not contribute to reflective display, so that the reflectance may be lower than in the configuration in which the common electrode CE is provided above the pixel electrode PE. Since the area of ​​the region that does not contribute to reflective display, such as the contact hole, is required to a certain extent regardless of the size of the area of ​​the pixel P, the ratio of the region that does not contribute to reflective display in the pixel P increases as the area of ​​the pixel P decreases (i.e., the resolution increases), and the above-mentioned decrease in reflectance increases. In other words, in a relatively large liquid crystal display device, the ratio of the region that does not contribute to reflective display in the pixel P is easier to reduce, so that the above-mentioned decrease in reflectance is easier to suppress. For these reasons, in a relatively large liquid crystal display device, a configuration in which the pixel electrode PE is provided above the common electrode CE is advantageous.

[0070] On the other hand, as described above, the reduction in reflectance due to the region in which the second contact hole CH2 is formed not contributing to the reflective display becomes greater as the area of ​​the pixel P becomes smaller (i.e., as the resolution increases). Therefore, in a relatively high-resolution liquid crystal display device, i.e., a liquid crystal display device in which the area of ​​the pixel P is relatively small, it is preferable that the common electrode CE is provided above the pixel electrode PE (see Variant 1 of Embodiment 1 described below).

[0071] The first electrode 121 and the second electrode 122 are preferably each made of a transparent conductive material, such as indium tin oxide (ITO), indium zinc oxide (IZO (registered trademark)), a mixture thereof, or the like.

[0072] In the embodiment shown in FIG. 2, the pixel electrode PE (the second electrode 122 in this embodiment) is electrically connected to the backplane circuit (more specifically, to the drain electrode of the TFT 110) via the contact electrode 160. The contact electrode 160 is formed in the same layer as the reflective film 130 and is made of the same material (metal film, etc.) as the reflective film 130. The first interlayer insulating layer 151 is formed with a first contact hole CH1 that exposes a part of the backplane circuit BP (more specifically, at least a part of the drain electrode of the TFT 110), and the contact electrode 160 is connected to the backplane circuit BP at the first contact hole CH1. The second interlayer insulating layer 152 is formed with a second contact hole CH2 that exposes a part of the contact electrode 160, and the pixel electrode PE (the second electrode 122 in this embodiment) is connected to the contact electrode 160 at the second contact hole CH2.

[0073] The dielectric layer 153 is provided so as to cover the first electrode 121. The dielectric layer 153 is preferably formed from an inorganic insulating material. The inorganic insulating film obtained using the inorganic insulating material is as described above.

[0074] The first horizontal alignment film 140 is provided on the second electrode 122 and is in contact with the liquid crystal layer 20. Therefore, it can be said that the first electrode 121 and the second electrode 122 are disposed between the second interlayer insulating layer 152 and the first horizontal alignment film 140.

[0075] The first horizontal alignment film 140 and the second horizontal alignment film 340 described later are each subjected to an alignment treatment, and define the alignment direction (also referred to as the alignment direction) of the liquid crystal molecules 21 contained in the liquid crystal layer 20. For example, the alignment treatment is preferably performed by a photo-alignment treatment or a rubbing treatment. In the photo-alignment treatment, a photodecomposition type photo-alignment film material can be used, and in the rubbing treatment, it is preferable to use an alignment film material such as polyimide.

[0076] Both the first horizontal alignment film 140 and the second horizontal alignment film 340 are horizontal alignment films that align the liquid crystal molecules 21 in a direction horizontal to the first substrate 10 and the second substrate 30 when no voltage is applied to the liquid crystal layer 20. That is, the liquid crystal molecules 21 are horizontally aligned when no voltage is applied to the liquid crystal layer 20. The pretilt angle is substantially 0°.

[0077] The alignment direction of the liquid crystal molecules 21 determined by the first horizontal alignment film 140 is different from the alignment direction of the liquid crystal molecules 21 determined by the second horizontal alignment film 340. Therefore, the liquid crystal layer 20 has a twisted alignment when no voltage is applied (see FIG. 2). When a voltage is applied to the liquid crystal layer 20, that is, when a transverse electric field is generated in the liquid crystal layer 20 by the first electrode 121 and the second electrode 122, the alignment state of the liquid crystal layer 20 changes due to the transverse electric field (fringe electric field).

[0078] <Liquid crystal layer> The liquid crystal layer 20 is located between the first substrate 10 and the second substrate 30, and contains a positive type liquid crystal material or a negative type liquid crystal material. The positive type liquid crystal material means a nematic liquid crystal material having a positive dielectric anisotropy Δε, and the negative type liquid crystal material means a nematic liquid crystal material having a negative dielectric anisotropy Δε. The dielectric anisotropy Δε is the dielectric constant ε in the long axis direction of the liquid crystal molecules 21. / / and the dielectric constant in the minor axis direction ε ⊥(i.e., ε / / -ε ⊥ ).

[0079] In the case of a positive-type liquid crystal material, the birefringence Δn of the liquid crystal material is preferably, for example, 0.12 or less, and more preferably 0.119 or less. From the viewpoint of manufacturing (yield rate, etc.), the thickness d of the liquid crystal layer 20 is preferably 2 μm or more, and in this case, it is suitable that Δn is 0.119 or less. More preferably, d is 2.5 μm or more and Δn is 0.095 or less. However, from the viewpoint of response, a smaller cell thickness is preferable. Also, the dielectric anisotropy Δε of the liquid crystal material is preferably, for example, 10 or more.

[0080] In the case of a negative type liquid crystal material, the birefringence Δn of the liquid crystal material is preferably, for example, 0.123 or less, and more preferably 0.12 or less. In particular, it is suitable that the thickness d of the liquid crystal layer 20 is 2 μm or more and Δn is 0.123 or less. More preferably, d is 2.5 μm or more and Δn is 0.098 or less. In addition, it is preferable that the dielectric anisotropy Δε of the liquid crystal material is, for example, -5 or less. Note that the smaller Δε (or the larger the absolute value of Δε), the more the VR curve (threshold value, maximum reflectance value, etc.) shifts to the low voltage side.

[0081] When selecting positive or negative type, it is preferable to consider the application and desired performance. For example, from the viewpoint of realizing flickerless (also called flicker-free), it is preferable to use a negative type liquid crystal material. This is for the following reason. In the in-plane electric field method of FFS mode using positive type liquid crystal material, flexopolarization occurs spontaneously in the liquid crystal layer due to the influence of fine slit electrodes on the electrodes (i.e., fringe electric field) when voltage is applied. Since the liquid crystal responds according to this flexopolarization, the luminance changes when the polarity is inverted, which is considered to be easily recognized as flicker. In addition, from the viewpoint of reliability, it is preferable to use a positive type liquid crystal material.

[0082] The liquid crystal layer 20 may further include a chiral agent, if necessary. The liquid crystal layer 20 can be formed by, for example, a dropping method.

[0083] The thickness d of the liquid crystal layer 20 (also referred to as the cell gap or cell thickness) is preferably 3.6 μm or less, and more preferably 2.0 to 3.4 μm. From the viewpoint of response speed, it is preferably 3 μm or less. A smaller cell thickness is preferable from the viewpoint of cost reduction, since it allows the number of materials to be reduced. However, if the cell thickness is too small, the display quality may not be improved due to unevenness in the cell thickness or foreign matter, resulting in a trade-off with the occurrence rate of defective display quality. From the viewpoint of yield, it is preferable that the cell thickness is 2 μm or more, as described above.

[0084] The liquid crystal layer 20 may have a multi-domain alignment such as a dual-domain alignment, but is preferably a single-domain alignment (also called a mono-domain alignment) from the viewpoint of maximizing the liquid crystal mode reflection efficiency and the liquid crystal mode transmission efficiency.

[0085] <Second board> The second substrate 30 is disposed opposite the first substrate 10 with the liquid crystal layer 20 interposed therebetween, and has a second horizontal alignment film 340 in contact with the liquid crystal layer 20. The second substrate 30 preferably further has a support substrate 300 and a color filter layer 310. For example, as shown in FIG. 2, the second substrate 30 has, in order from the liquid crystal layer 20 side, the second horizontal alignment film 340, the color filter layer 310, and the support substrate 300. The second substrate 30 preferably also has a plurality of columnar spacers (not shown). Note that the first substrate 10 may have a plurality of columnar spacers.

[0086] The support substrate 300 is preferably transparent and insulating, and examples of the support substrate 300 include a glass substrate and a plastic substrate. A high-resistance transparent conductive film may be formed on the surface of the support substrate 300 opposite to the liquid crystal layer 20 (for example, in FIG. 2, the surface of the support layer 300 on the retardation layer 40 side) to prevent static electricity from sticking to the liquid crystal cell. This high-resistance transparent conductive film may have a multi-layer structure in consideration of suppressing a decrease in transmittance and suppressing an increase in reflectance.

[0087] The color filter layer 310 typically includes a red color filter provided in an area corresponding to a red pixel and transmitting red light, a green color filter provided in an area corresponding to a green pixel and transmitting green light, and a blue color filter provided in an area corresponding to a blue pixel and transmitting blue light. However, the number of types of color filters may be two or less, or four or more. If color display is not performed, the color filter layer 310 is omitted.

[0088] If necessary, an overcoat layer (also called a planarizing layer) may be provided to cover the color filter layer 310. Note that the white display may have a yellowish tinge depending on the material (e.g., transparent conductive material) forming the electrodes, the material forming the interlayer insulating layer and the dielectric layer, and the material forming the alignment film. In that case, the chromaticity of the white display may be adjusted (i.e., blue shift) by forming the overcoat layer from a blue resist, so that the chromaticity of the white display may be brought closer to that of a D65 light source, for example. The D65 light source is the CIE standard illuminant D65.

[0089] <Retardation layer> The retardation layer 40 is located between the second substrate 30 and the polarizing plate 50, and includes a λ / 4 plate 41, a λ / 2 plate 42, and a positive C plate 43 (see FIG. 1 and FIG. 2). By providing the retardation layer 40 with the positive C plate 43 in addition to the λ / 4 plate 41 and the λ / 2 plate 42, it is possible to improve both the viewing angle and the contrast ratio at a high level, which is extremely useful. In particular, the luminance floating during black display (also called black floating) is sufficiently suppressed, and the viewing angle during black display is expanded. From the viewpoint of further exerting such effects, it is preferable that the λ / 4 plate 41, the λ / 2 plate 42, and the positive C plate 43 are arranged in the order of the λ / 4 plate 41, the positive C plate 43, and the λ / 2 plate 42 from the liquid crystal layer 20 (and the second substrate 30) side (see FIG. 1).

[0090] The λ / 4 plate means a retardation plate that imparts an in-plane phase difference of 1 / 4 wavelength to incident light of wavelength λ, and is also called a λ / 4 wave plate or QWP (Quarter-Wave Plate). Specifically, the λ / 4 plate 41 can convert linearly polarized light into circularly polarized light or circularly polarized light into linearly polarized light. For example, linearly polarized light incident on the λ / 4 plate 41 becomes circularly polarized light when it is output from the λ / 4 plate 41.

[0091] The λ / 2 plate means a retardation plate that imparts an in-plane phase difference of 1 / 2 wavelength to incident light of wavelength λ, and is also called a λ / 2 wave plate, a half wave plate, or an HWP (Half-Wave Plate). Specifically, the λ / 2 plate 42 can rotate the vibration direction of the incident light beam by approximately 90°. For example, the circularly polarized light incident on the λ / 2 plate 42 becomes circularly polarized light with the rotation direction reversed when it is output.

[0092] A general-purpose retardation plate can be used as the λ / 4 plate 41 and the λ / 2 plate 42. More specifically, it is preferable to use a retardation plate that is generally distributed as a circular polarizing plate of an anti-reflection film, for example. In the present invention, preferably, as described later, by controlling the angle between the polarization axis of the polarizing plate and the alignment direction of the liquid crystal molecules defined by the first horizontal alignment film 140 within a predetermined range, even if a general-purpose retardation plate is used as the λ / 4 plate 41 and the λ / 2 plate 42 instead of a special retardation plate, the contrast ratio and viewing angle can be improved while being a liquid crystal display device of the horizontal electric field type, and it is also useful as an in-cell type touch panel capable of displaying in a reflective mode, so that cost reduction can be achieved. In particular, from the user's perspective, it is very useful because it can reduce the total cost. Cost reduction can be achieved similarly when the liquid crystal display device of the present invention is used not only as a built-in touch panel such as an in-cell type, but also as an external touch panel.

[0093] Specifically, it is preferable to use uniaxial A-plates as the λ / 4 plate 41 and the λ / 2 plate .

[0094] The positive C plate 43 (and the positive C plate 44 described later) may be made of a single film, or may be a laminate of two or more retardation films.

[0095] As the positive C plate 43 (and 44), it is preferable to use, for example, a film containing a material with negative intrinsic birefringence as a component, which is biaxially stretched lengthwise and widthwise, or a film coated with a liquid crystal material such as nematic liquid crystal, etc. Examples of materials with negative intrinsic birefringence include resin compositions containing acrylic resins and styrene resins, polystyrene, polyvinyl naphthalene, polyvinyl biphenyl, polyvinyl pyridine, polymethyl methacrylate, polymethyl acrylate, N-substituted maleimide copolymers, polycarbonates having a fluorene skeleton, triacetyl cellulose (especially those with a low degree of acetylation), etc.

[0096] Specific examples of the positive C plate 43 (and 44) ​​include a positive C plate manufactured by ENEOS Corporation or Hayashi Telempu Corporation, and a Positive-C retardation film manufactured by Nippon Kayaku Co., Ltd.

[0097] In order to enhance the viewing angle improving effect, the thickness direction retardation Rth of the positive C plate 43 is preferably 150 to 270 nm, more preferably 160 to 250 nm, and further preferably 170 to 240 nm.

[0098] The thickness of the positive C plate 43 is preferably, for example, 0.1 to 100 μm. Within this range, the mechanical strength and display uniformity are superior. The thickness is more preferably 0.1 to 80 μm, and even more preferably 0.1 to 50 μm. When the positive C plate 43 has a laminated structure, it is preferable to set the total thickness of the whole to be within the above range, and the thicknesses of the respective retardation films may be the same or different.

[0099] <Polarizing plate> The polarizing plate 50 is located closer to the observation surface than the retardation layer 40 (see Figs. 1 and 2). The polarizing plate 50 may be a circular polarizing plate or a linear polarizing plate. Here, the linear polarizing plate means a polarizing plate having a function of extracting polarized light (linearly polarized light) that vibrates only in a specific direction from unpolarized light (natural light), partially polarized light, or polarized light, and is distinguished from a circular polarizing plate. Among them, a linear polarizing plate is preferable.

[0100] The polarizing plate 50 may be either an absorptive polarizing plate or a reflective polarizing plate. An absorptive polarizing plate is a polarizing plate that has the function of absorbing light that vibrates in a specific direction and transmitting polarized light (linearly polarized light) that vibrates in a direction perpendicular thereto. A reflective polarizing plate is a polarizing plate that has the function of reflecting light that vibrates in a specific direction and transmitting polarized light (linearly polarized light) that vibrates in a direction perpendicular thereto. Among these, an absorptive polarizing plate is preferred. It is particularly suitable to use an absorptive linear polarizing plate.

[0101] Examples of the absorptive polarizing plate include a polarizing plate obtained by dyeing and adsorbing an anisotropic material such as an iodine complex (or dye) on a polyvinyl alcohol film and then stretching and aligning the film. In general, in order to ensure mechanical strength and resistance to moist heat, the polyvinyl alcohol film is used in practical use with a protective film such as a triacetyl cellulose film laminated on both sides. Examples of the reflective polarizing plate include a film in which multiple dielectric thin films are laminated, a film in which multiple thin films with different refractive index anisotropy are laminated, a nanowire grid polarizing plate, and a polarizing plate using selective reflection of a cholesteric liquid crystal.

[0102] <Other configurations etc.> In the liquid crystal display device 1 of this embodiment, display is performed in a lateral electric field mode in which the liquid crystal layer 20 has a twisted orientation when no voltage is applied. This makes it possible to sufficiently improve the contrast ratio of the reflective display. The twist angle θ1 of the liquid crystal layer 20 when no voltage is applied is preferably 70° or more and 85° or less. A more preferable range will be described later.

[0103] The twist angle θ1 of the liquid crystal layer 20 is the angle between the alignment direction of the liquid crystal molecules 21 determined by the first horizontal alignment film 140 and the alignment direction of the liquid crystal molecules 21 determined by the second horizontal alignment film 340. That is, it is the angle between the long axis direction of the liquid crystal molecules 21A (also referred to as the liquid crystal molecules 21A on the first substrate 10 side when no voltage is applied) near the first horizontal alignment film 140 and the long axis direction of the liquid crystal molecules 21B (also referred to as the liquid crystal molecules 21B on the second substrate 30 side when voltage is applied) near the second horizontal alignment film 340.

[0104] From the viewpoint of increasing the contrast ratio, the liquid crystal display device 1 is preferably in a normally black mode. The normally black mode is a display mode in which black is displayed when no voltage is applied and white is displayed when a voltage is applied.

[0105] The liquid crystal display device 1 is also configured with a plurality of components, such as the above-mentioned components, external circuits such as a TCP (tape carrier package) and a PCB (printed wiring board), optical films such as a viewing angle widening film and a brightness enhancing film, and a bezel (frame), and some of the components may be incorporated into other components. These are not particularly limited, and those commonly used in the field of liquid crystal display devices can be used, so their explanation will be omitted.

[0106] <Examples of favorable optical settings> In the following, the preferred settings of the twist angle of the liquid crystal layer 20, the optical axis settings of each optical film (i.e., the polarizing plate 50 and the retardation layer 40), the retardation dΔn of the liquid crystal layer 20, and the verification results leading to the settings will be further described for the cases where the liquid crystal material constituting the liquid crystal layer 20 is a positive type and a negative type. An absorption type polarizing plate is used as the polarizing plate 50. Note that the slow axis angle of the positive C plate 43 is in the film normal direction (i.e., 90° when the alignment direction of the liquid crystal molecules 21A defined by the first horizontal alignment film 140 is 0°), so that the positive C plate was not provided. The preferred settings are the same when a positive C plate is provided.

[0107] (i) When the liquid crystal material is a positive type (i-1) Preferred Settings Below, examples of optical settings that are particularly preferable from the viewpoint of improving the contrast ratio are shown. 4 is a plan view conceptually showing the relationship between the long axis direction of the liquid crystal molecules 21 in the liquid crystal layer 20 when no voltage is applied, the in-plane slow axis 41SA of the λ / 4 plate 41, the in-plane slow axis 42SA of the λ / 2 plate 42, and the polarization axis 50AA of the polarizing plate 50 in the liquid crystal display device 1 including, in order from the rear side, a first substrate 10, a liquid crystal layer 20, a second substrate 30, a λ / 4 plate 41, a λ / 2 plate 42, and a polarizing plate 50. In FIG. 4, the liquid crystal molecules 21A near the first horizontal alignment film 140 and the liquid crystal molecules 21B near the second horizontal alignment film 340 are shown as the liquid crystal molecules 21.

[0108] In the following description, the angle when the reference orientation is 0° refers to the angle when Fig. 4 is likened to a clock face, the reference orientation, i.e., the orientation orientation of the liquid crystal molecules 21A defined by the first horizontal alignment film 140, is set to the 0° direction (3 o'clock direction) and the twist direction is set to the positive (counterclockwise). The twist direction means the direction twisted from the orientation orientation of the liquid crystal molecules 21 defined by the first horizontal alignment film 140 to the orientation orientation of the liquid crystal molecules 21 defined by the second horizontal alignment film 340 when the liquid crystal display device 1 is viewed from the observation surface side.

[0109] The twist angle θ1 of the liquid crystal layer 20 when no voltage is applied is preferably 70° or more and 85° or less, more preferably 75° or more and 85° or less, even more preferably 80° or more and 85° or less, particularly preferably 81° or more and 84° or less, and most preferably around 83° (approximately 83°).

[0110] The angle θ2 between the polarization axis 50AA of the polarizing plate 50 and the alignment direction of the liquid crystal molecules 21A defined by the first horizontal alignment film 140 is preferably 63.5° or more and 71.5° or less. More preferably, it is 64.5° or more and 71.5° or less, and in this case, it is possible to easily achieve a contrast ratio of 20 or more. In addition, 63.5° or more and 70.5° or less is also one of the preferred ranges. More preferably, it is 64.5° or more and 70.5° or less, and particularly preferably, it is 66.3° or more and 70° or less. In addition, when the reference direction is 0° and the twist direction (counterclockwise) is positive, it is preferably -71.5° or more and -63.5° or less, more preferably -71.5° or more and -64.5° or less, even more preferably -70.5° or more and -64.5° or less, and particularly preferably -70° or more and -66.3° or less.

[0111] The angle θ3 between the in-plane slow axis 42SA of the λ / 2 plate 42 and the alignment direction of the liquid crystal molecules 21A defined by the first horizontal alignment film 140 is preferably 47.5° or more and 52.5° or less. More preferably, it is 48° or more and 52° or less, even more preferably, it is 49° or more and 51° or less, and particularly preferably, it is 49° or more and 50° or less. In addition, when the reference direction is 0° and the twist direction (counterclockwise) is positive, it is preferably -52.5° or more and -47.5° or less, more preferably -52° or more and -48° or less, even more preferably, it is -51° or more and -49° or less, and particularly preferably, it is -50° or more and -49° or less.

[0112] The angle θ4 between the in-plane slow axis 41SA of the λ / 4 plate 41 and the alignment direction of the liquid crystal molecules 21A defined by the first horizontal alignment film 140 is preferably 20° or more and 30° or less. More preferably, it is 22° or more and 28° or less, even more preferably, it is 23° or more and 26° or less, and particularly preferably, it is 24° or more and 25.5° or less. In addition, when the reference direction is 0° and the twist direction (counterclockwise) is positive, it is preferably -30° or more and -20° or less, more preferably -28° or more and -22° or less, even more preferably, it is -26° or more and -23° or less, and particularly preferably, it is -25.5° or more and -24° or less.

[0113] The retardation of the liquid crystal layer 20, i.e., the product (dΔn) of the thickness d of the liquid crystal layer 20 and the birefringence Δn of the liquid crystal material, is preferably 218 nm or more and 255 nm or less. In particular, from the viewpoint of improving the response performance, the retardation dΔn is preferably 252 nm or less. From the viewpoint of further improving the contrast ratio, it is more preferably 224 nm or more and 252 nm or less, even more preferably 230 nm or more and 250 nm or less, and particularly preferably 236 nm or more and 248 nm or less.

[0114] (i-2) Verification results by optical simulation The above-mentioned preferable settings were found by the inventors of the present application through verification using optical simulations. The verification results will be described below.

[0115] A liquid crystal display device 1 was assumed to have a configuration including a reflective liquid crystal panel 1X using a positive liquid crystal material, a λ / 4 plate 41, a λ / 2 plate 42, and a polarizing plate 50. For the optical simulation, a liquid crystal layer having a monodomain structure (a liquid crystal layer performing normally black display) as shown in FIG. 5A, FIG. 5B, and FIG. 5C was assumed. FIG. 5A is a plan view schematic diagram of a first substrate 10 (TFT substrate) viewed from the first horizontal alignment film 140 side. FIG. 5B is a plan view schematic diagram of a second substrate 30 (opposing substrate) viewed from the second horizontal alignment film 340 side. FIG. 5C is a plan view schematic diagram of the liquid crystal panel 1X after the first substrate 10 and the second substrate 30 are bonded together viewed from the second substrate 30 side.

[0116] 5A, 5B, and 5C are likened to the dial of a clock, and the reference direction, that is, the alignment direction of the liquid crystal molecules 21A defined by the first horizontal alignment film 140, is set to the 0° direction (the 3 o'clock direction). In FIGS. 5A and 5B, the alignment direction of the liquid crystal molecules 21 is indicated by an arrow.

[0117] The upper layer electrode was a slit electrode (see Figures 5A and 5B). The direction in which the strip portions SP of the slit electrode extended (which also corresponds to the direction in which each slit Sl extended) was +10° relative to the reference direction (0°). That is, the finger angle was 10°. In addition, in a plan view, the width of each strip portion SP was 1.6 μm, and the distance between two adjacent strip portions SP was 3 μm. The alignment direction of the liquid crystal molecules 21B defined by the second horizontal alignment film 340 was +97° in Figure 5B and +83° in Figure 5C. That is, the twist angle θ1 was +83°.

[0118] First, a simulation was performed using an LCD Master 1D manufactured by Shintech Co., Ltd., and the following parameter conditions were optimized to minimize the reflectance of black display (also called black reflectance). Cell thickness d:3.2~3.6μm Twist angle θ1: 70~85° Axial orientation of optical films (polarizing plate 50, λ / 2 plate 42, λ / 4 plate 41): ±90° A uniaxial retardation plate with a retardation of 140 nm was used as the λ / 4 plate 41, and a uniaxial retardation plate with a retardation of 270 nm was used as the λ / 2 plate 42, and the wavelength dispersion of these retardation plates was set to be flat. The calculations were repeated while varying only one of the above parameters and fixing the other parameters.

[0119] FIG. 6 shows the optical axis settings of the λ / 4 plate 41, the λ / 2 plate 42, and the polarizing plate 50 that minimize the black reflectance. FIG. 6 is a conceptual diagram showing the optical axis settings that minimize the black reflectance. As shown in FIG. 6, the optimal setting of the polarization axis 50AA of the polarizing plate 50 was the -68.3° direction (also called the +111.7° direction). The optimal setting of the slow axis 42SA of the λ / 2 plate 42 was the -49.5° direction (also called the +130.5° direction), and the optimal setting of the slow axis 41SA of the λ / 4 plate 41 was the -24.9° direction (also called the +155.1° direction).

[0120] Next, we performed a simulation using LCD Master 2D manufactured by Shintech Co., Ltd. to examine the preferred range of optical conditions. In this simulation, we varied the value of the parameter of interest (the parameter for which we were trying to find the preferred range) around the optimal value (reference value) while keeping the other parameters fixed at their optimal values.

[0121] It was found that the response performance may not be improved when the retardation dΔn exceeds 252 nm, i.e., when the birefringence Δn of the liquid crystal material is 0.07 and the cell thickness d exceeds 3.6 μm. It was also found that the response performance may not be improved when the twist angle θ1 exceeds 85°. Considering the response performance, it was found that the optimal setting of the twist angle θ1 is 83°, the optimal setting of the retardation dΔn is 245 nm, and the optimal setting of the optical axes of the λ / 4 plate 41, the λ / 2 plate 42, and the polarizing plate 50 is the setting shown in FIG. 6.

[0122] In order to study the influence of retardation dΔn and twist angle θ1 on the luminance during black display (also referred to as black luminance) and contrast, a simulation was performed by varying retardation dΔn within the range of 224 to 252 nm and twist angle θ1 within the range of 70 to 85°. The evaluation results of black luminance are shown in Table 1 and FIG. 7, and the evaluation results of contrast are shown in Table 2 and FIG. 8. From these results, it was found that the preferable range of twist angle θ1 is 70° or more and 85° or less, and the preferable range of retardation dΔn is 236 nm or more and 252 nm or less. FIG. 7 is a graph showing the evaluation results of black luminance, and FIG. 8 is a graph showing the evaluation results of contrast.

[0123] In addition, when the liquid crystal layer conditions of retardation dΔn = 217 nm (Δn = 0.069928 at a wavelength of 550 nm), cell thickness = 3.11 μm, and twist angle θ1 = 74° were combined with special phase difference plates (a λ / 4 plate with a retardation of 110 nm and a λ / 2 plate with a retardation of 260 nm), the black luminance and contrast were calculated to be 0.02 (au) and 1789, respectively.

[0124] [Table 1]

[0125] [Table 2]

[0126] (ii) When the liquid crystal material is negative type (ii-1) Preferred Settings Below, examples of optical settings that are particularly preferable from the viewpoint of improving the contrast ratio are shown. 9 is a plan view conceptually showing the relationship between the long axis direction of the liquid crystal molecules 21 in the liquid crystal layer 20 when no voltage is applied, the in-plane slow axis 41SA of the λ / 4 plate 41, the in-plane slow axis 42SA of the λ / 2 plate 42, and the polarization axis 50AA of the polarizer 50 in a liquid crystal display device 1 including, in order from the rear side, a first substrate 10, a liquid crystal layer 20, a second substrate 30, a λ / 4 plate 41, a λ / 2 plate 42, and a polarizer 50. In FIG. 9, liquid crystal molecules 21A near a first horizontal alignment film 140 and liquid crystal molecules 21B near a second horizontal alignment film 340 are shown as the liquid crystal molecules 21.

[0127] In the following explanation, the angle when the reference orientation is 0° refers to the angle when Figure 9 is likened to a clock face, the reference orientation, i.e., the alignment orientation of liquid crystal molecules 21A defined by the first horizontal alignment film 140, is set to the 0° direction (3 o'clock direction) and the twist direction is positive (counterclockwise).

[0128] The twist angle θ1 of the liquid crystal layer 20 when no voltage is applied is preferably 70° or more and 85° or less, more preferably 75° or more and 85° or less, even more preferably 80° or more and 85° or less, particularly preferably 81° or more and 84° or less, and most preferably around 83° (approximately 83°).

[0129] The angle θ2 between the polarization axis 50AA of the polarizing plate 50 and the alignment direction of the liquid crystal molecules 21A defined by the first horizontal alignment film 140 is preferably 64° or more and 69.5° or less. More preferably, it is 65° or more and 69.3° or less, even more preferably 66° or more and 69° or less, and particularly preferably 67° or more and 68.7° or less. Even when the reference direction is taken as 0° and the twist direction (counterclockwise) is taken as positive, it is preferable that the angle θ2 is within the above range (all positive values).

[0130] The angle θ3 between the in-plane slow axis 42SA of the λ / 2 plate 42 and the alignment direction of the liquid crystal molecules 21A defined by the first horizontal alignment film 140 is preferably 47.5° or more and 51.5° or less. More preferably, it is 48° or more and 51° or less, even more preferably 40° or more and 41.5° or less, and particularly preferably 48.5° or more and 50.0° or less. Even when the reference direction is taken as 0° and the twist direction (counterclockwise) is taken as positive, it is preferable that the angle θ3 is within the above range (all positive values).

[0131] The angle θ4 between the in-plane slow axis 41SA of the λ / 4 plate 41 and the alignment direction of the liquid crystal molecules 21A defined by the first horizontal alignment film 140 is preferably 15° or more and 35° or less. More preferably, it is 17° or more and 32° or less, even more preferably, it is 20° or more and 30° or less, and particularly preferably, it is 24° or more and 28° or less. Even when the reference direction is 0° and the twist direction (counterclockwise) is positive, it is preferable that the angle θ4 is within the above range (all positive values).

[0132] The retardation dΔn of the liquid crystal layer 20, i.e., the product of the thickness d of the liquid crystal layer 20 and the birefringence Δn of the liquid crystal material, is preferably 230 nm or more and 260 nm or less. From the viewpoint of further improving the contrast ratio, it is more preferably 232 nm or more and 250 nm or less, even more preferably 235 nm or more and 246 nm or less, and particularly preferably 236 nm or more and 245 nm or less.

[0133] (ii-2) Verification results by optical simulation The above-mentioned preferable settings were found by the inventors of the present application through verification using optical simulations. The verification results will be described below.

[0134] A liquid crystal display device 1 was assumed to have a configuration including a reflective liquid crystal panel 1X using a negative liquid crystal material, a λ / 4 plate 41, a λ / 2 plate 42, and a polarizing plate 50. For the optical simulation, a liquid crystal layer having a monodomain structure (a liquid crystal layer performing normally black display) as shown in FIG. 10A, FIG. 10B, and FIG. 10C was assumed. FIG. 10A is a plan view schematic diagram of a first substrate 10 (TFT substrate) viewed from the first horizontal alignment film 140 side. FIG. 10B is a plan view schematic diagram of a second substrate 30 (opposing substrate) viewed from the second horizontal alignment film 340 side. FIG. 10C is a plan view schematic diagram of a liquid crystal panel 1X after the first substrate 10 and the second substrate 30 are bonded together viewed from the second substrate 30 side.

[0135] In the following description, each of Figures 10A, 10B, and 10C is likened to a clock face, with the 3 o'clock direction being 0°, clockwise being negative, and counterclockwise being positive. In Figures 10A and 10B, the alignment direction of liquid crystal molecules 21 is indicated by an arrow.

[0136] In this example, the upper layer electrode is a slit electrode (see Figs. 10A and 10B). The alignment direction of the liquid crystal molecules 21A defined by the first horizontal alignment film 140 is the 90° direction (12 o'clock direction), and the direction in which the strip portions SP of the upper layer electrode (slit electrode) extend (which also corresponds to the direction in which each slit Sl extends) is the +10° direction. That is, the finger angle is 10°. In addition, in a plan view, the width of each strip portion SP is 1.6 μm, and the interval between two adjacent strip portions SP is 3 μm. The alignment direction of the liquid crystal molecules 21B defined by the second horizontal alignment film 340 is the +7° direction in Fig. 10B, and the +83° direction in Fig. 10C. That is, the twist angle θ1 is +83°.

[0137] Using LCD Master 1D manufactured by Shintech Co., Ltd., the twist angle θ1 was fixed at 83°, and the conditions for minimizing the black reflectance were determined, including the cell thickness d, the angle of the polarization axis 50AA of the polarizing plate 50, the angle and retardation of the slow axis 42SA of the λ / 2 plate 42, and the angle and retardation of the slow axis 41SA of the λ / 4 plate 41. Note that the calculations were repeated while changing only one of the above parameters and fixing the other parameters.

[0138] FIG. 11 shows the optical axis settings of the λ / 4 plate 41, the λ / 2 plate 42, and the polarizing plate 50 that minimize the black reflectance. FIG. 11 is a conceptual diagram showing the optical axis settings that minimize the black reflectance. As shown in FIG. 11, the optimal setting of the polarization axis 50AA of the polarizing plate 50 was the +21.7° direction (also called the -158.3° direction). The optimal setting of the slow axis 42SA of the λ / 2 plate 42 was the +40.5° direction (also called the -139.5° direction), and the optimal setting of the slow axis 41SA of the λ / 4 plate 41 was the +65.1° direction (also called the -114.9° direction).

[0139] <Simulation verification results> The effects of including the positive C plate 43 described above were found by the inventors of the present application through verification using optical simulation. The verification results will be explained below separately for the cases where the liquid crystal material constituting the liquid crystal layer 20 is of the positive type and the negative type. Note that an absorptive polarizing plate is used as the polarizing plate 50.

[0140] (i) When the liquid crystal material is a positive type In the liquid crystal display device 1 having a configuration including a reflective liquid crystal panel 1X using a positive type liquid crystal material, a retardation layer 40, and a polarizing plate 50, the retardation layer 40 is assumed to have a three-layer structure of a λ / 4 plate 41, a λ / 2 plate 42, and a positive C plate 43 or a negative C plate 43R, and the position of the C plate is changed to study the effect of adding the C plate on the viewing angle. LCD Master 1D by Shintech Co., Ltd. was used as the simulation software. A uniaxial retardation plate with a retardation of 140 nm was used as the λ / 4 plate 41, and a uniaxial retardation plate with a retardation of 270 nm was used as the λ / 2 plate 42, and the wavelength dispersion of these retardation plates was set to be flat. The other settings were the optimal settings obtained in (i) of the above <Preferred optical setting example> when the liquid crystal material is a positive type. The results are shown in Figures 12A and 12B.

[0141] 12A and 12B are diagrams showing simulation results for the present embodiment in which the liquid crystal material is a positive type. An example not including a C-plate is shown as Example 1. The upper parts of FIGS. 12A and 12B show schematic cross-sectional views of the liquid crystal display device 1 in each example (only the reflective layer 130 is shown separately from the liquid crystal panel 1X), and the lower parts show the viewing angle (when light is incident at a polar angle of 30°) in black display (0V). The thickness direction retardation Rth of the C-plate used in each example is shown in parentheses after the reference numeral 43 or 43R representing the C-plate (the same applies to other similar figures).

[0142] 12A and 12B, it can be seen that the examples (Examples 2, 3, and 4) in which the retardation layer 40 includes the positive C plate 43 are more excellent in the viewing angle improvement effect than the examples (Examples 5, 6, and 7) in which the retardation layer 40 includes the negative C plate 43R. Among them, in the example (Example 3) in which the positive C plate 43 is located between the λ / 4 plate 41 and the λ / 2 plate 42, the black floating is significantly improved, and the viewing angle improvement effect can be significantly confirmed. In addition, when a test cell having the same arrangement as in Example 3 was fabricated using an actual positive C plate (Rth: 200 nm) and examined, it was confirmed that the viewing angle improvement effect was also visually observed. To make the comparison easier to understand, FIG. 13 shows schematic cross-sectional views of the liquid crystal display devices 1 of Examples 1 and 3 and the viewing angle (when light is incident at a polar angle of 30°) in black display (0 V). FIG. 13 is a diagram showing the simulation results for Examples 1 and 3.

[0143] In addition, for an embodiment in which the retardation layer 40 includes a positive C plate 43 in addition to the λ / 4 plate 41 and the λ / 2 plate 42, the optical conditions were optimized to minimize black floating. That is, for each of the configuration examples of Examples 1 to 4, in a black display (0V) state, the luminance distribution was analyzed at azimuth angles of 0 to 360° (15° steps) and polar angles of 0 to 80° (10° steps) with incident light at a polar angle of 30°. The results are shown in FIG. 14. FIG. 14 is a graph showing the distribution of maximum black luminance for Examples 1 to 4. In FIG. 14, the horizontal axis represents Rth (nm) of the positive C plate 43, and the vertical axis represents the maximum black luminance.

[0144] From Fig. 14, it is clear that the maximum black luminance is the lowest in Example 3 among Examples 1 to 4. In addition, it was found that, based on the value (indicated by an arrow) at which the vertical axis (maximum black luminance) is the minimum in the distribution curve of Example 3, the Rth of the positive C plate 43 is within 30% when the Rth is 150 nm or more and 270 nm or less, the Rth is within 15% when the Rth is 160 nm or more and 250 nm or less, and the Rth is within 10% when the Rth is 170 nm or more and 240 nm or less. Based on this result, it was found that the preferable range of the thickness direction retardation Rth is as described above.

[0145] (ii) When the liquid crystal material is negative type In the liquid crystal display device 1 having a configuration including a reflective liquid crystal panel 1X using a negative type liquid crystal material, a retardation layer 40, and a polarizing plate 50, the retardation layer 40 is assumed to have a three-layer structure of a λ / 4 plate 41, a λ / 2 plate 42, and a positive C plate 43 or a negative C plate 43R, and the position of the C plate is changed to study the effect of adding the C plate on the viewing angle. LCD Master 1D by Shintech Co., Ltd. was used as the simulation software. A uniaxial retardation plate with a retardation of 140 nm was used as the λ / 4 plate 41, and a uniaxial retardation plate with a retardation of 270 nm was used as the λ / 2 plate 42, and the wavelength dispersion of these retardation plates was set to be flat. The other settings were the optimal settings obtained in (ii) of the above <Preferred optical setting example> when the liquid crystal material is negative type.

[0146] As a result, almost the same tendency as when the liquid crystal material is positive type (see FIG. 12A and FIG. 12B) was obtained, so FIG. 15 shows only the simulation results of an example (Example 13) in which the positive C plate 43 is located between the λ / 4 plate 41 and the λ / 2 plate 42, and an example (Example 11) in which no C plate is included. FIG. 15 shows the simulation results of the present embodiment in which the liquid crystal material is negative type. The upper part of FIG. 15 shows a schematic cross-sectional view of the liquid crystal display device 1 in each example (however, only the reflective layer 130 is shown separately from the liquid crystal panel 1X), and the lower part shows the viewing angle in black display (0V) (when light is incident at a polar angle of 30°).

[0147] In addition, for an embodiment in which the retardation layer 40 includes a positive C plate 43 in addition to the λ / 4 plate 41 and the λ / 2 plate 42, the optical conditions were optimized to minimize black floating. That is, for each of the configuration examples of Examples 11 to 14 below, in a black display (0V) state, the luminance distribution was analyzed at azimuth angles of 0 to 360° (15° steps) and polar angles of 0 to 80° (10° steps) with incident light at a polar angle of 30°. The results are shown in FIG. 16. FIG. 16 is a graph showing the distribution of maximum black luminance for Examples 11 to 14. In FIG. 16, the horizontal axis represents Rth (nm) of the positive C plate 43, and the vertical axis represents the maximum black luminance. Example 11: Example without C-plate. Example 12: An example in which the retardation plates are arranged as follows from the observation surface side: a positive C plate 43 (thickness direction retardation Rth: 50 nm), a λ / 2 plate 42, and a λ / 4 plate 41. Example 13: An example in which the retardation plates are arranged, in order from the observation surface side, as a λ / 2 plate 42, a positive C plate 43 (thickness direction retardation Rth: 210 nm), and a λ / 4 plate 41. Example 14: An example in which the retardation plates are arranged, in order from the observation surface side, as a λ / 2 plate 42, a λ / 4 plate 41, and a positive C plate 43 (thickness direction retardation Rth: 10 nm).

[0148] From FIG. 16, it is clear that the maximum black luminance is the lowest in Example 13 among Examples 11 to 14. In addition, in the distribution curve of Example 13, it was found that the value (with an arrow) at which the vertical axis (maximum black luminance) is the minimum is within 30% when the Rth of the positive C plate 43 is 150 nm or more and 270 nm or less, the value is within 15% when the Rth is 160 nm or more and 250 nm or less, and the value is within 10% when the Rth is 170 nm or more and 240 nm or less. In other words, the same tendency as when the liquid crystal material is a positive type (see FIG. 14) was obtained. Based on this result, it was found that the preferable range of the thickness direction retardation Rth is as described above.

[0149] <Application Examples> The liquid crystal display device 1 of the present embodiment is suitable for various applications. In particular, it is preferably applicable to touch panels. Whether it is applied to an external touch panel or a built-in touch panel, it is useful because it can be produced at a lower cost than conventional touch panels and has an improved contrast ratio. In particular, it is preferably applicable to a built-in touch panel, and is particularly preferably applicable to an in-cell touch panel. In this way, by using the liquid crystal display device 1 of the present embodiment, it is possible to preferably realize an in-cell touch panel capable of displaying in a reflective mode, which has not been possible until now.

[0150] By realizing an in-cell touch panel capable of displaying in reflective mode, for example, a frame wiring area required for an external touch panel is not required, so that a narrow frame can be achieved, and since the touch panel function can be installed without a cover glass, it contributes to a thinner and lighter touch panel. In addition, since the touch function and the display function are driven in a time-division manner, the touch panel is not affected by LCD (liquid crystal display) noise, which can be the largest noise source in a touch panel. In other words, since no killer pattern occurs, tuning (adjustment) of the touch signal is easy. Furthermore, the loss of reflected light is sufficiently small, and a more natural and natural display can be obtained when writing with a pen. Moreover, compared to an external touch panel, a total cost reduction can be achieved from the user's perspective. Moreover, it is possible to combine finger input with pen input using the electromagnetic induction method (EMR), which allows for highly accurate pen writing.

[0151] An example in which the liquid crystal display device 1 is used in an in-cell touch panel will be further described. Fig. 17 is a plan view schematic illustrating the arrangement relationship between the touch sensor electrodes TX and the touch wirings TL included in the liquid crystal display device 1. As shown in Fig. 17, the liquid crystal display device 1 has a display area DR and a non-display area FR. The display area DR is defined by a plurality of pixels P (see Fig. 3, for example) arranged in a matrix. The non-display area FR is located on the periphery of the display area DR and is also referred to as a peripheral area or a frame area.

[0152] In the display region DR, the common electrode CE is divided into a plurality of segments TX. Each segment (common electrode portion) TX functions as a touch sensor electrode. In the example shown in FIG. 17, each touch sensor electrode TX is provided corresponding to two or more pixels P.

[0153] The liquid crystal display device 1 (more specifically, the first substrate 10) has a plurality of touch wirings TL. Each touch sensor electrode TX is electrically connected to a corresponding touch wiring TL. A connection portion TC between the touch sensor electrode TX and the touch wiring TL is also referred to as a touch wiring contact portion TC.

[0154] The touch wiring TL is connected to a touch driving unit TD provided in the non-display region FR. The touch driving unit TD is configured to switch, for example, between a display mode in which a plurality of touch sensor electrodes TX function as a common electrode CE and a touch detection mode in which the touch sensor electrodes TX function as the touch sensor electrodes TX in a time-division manner. For example, in the display mode, the touch driving unit TD applies a common signal to the touch sensor electrodes TX (common electrodes CE) via the touch wiring TL. On the other hand, in the touch detection mode, the touch driving unit TD applies a touch driving signal to the touch sensor electrodes TX via the touch wiring TL.

[0155] 17, the touch wirings TL extend in the column direction (the same direction as the source wirings SL). Some of the touch wirings TL extend to the corresponding touch sensor electrodes TX, crossing one or more other touch sensor electrodes TX.

[0156] Focusing on a certain touch sensor electrode TX, a first touch wiring TL1 that supplies a signal to the touch sensor electrode TX extends to a touch wiring contact portion TC, and a second touch wiring TL2 that supplies a signal to another touch sensor electrode TX extends across the touch sensor electrode TX. The second touch wiring TL2 and the touch sensor electrode TX overlap with each other via an insulating layer. Depending on the position of the touch sensor electrode TX, two or more touch wirings TL may be arranged to extend across the touch sensor electrode TX, or no touch wiring TL may be arranged to cross the touch sensor electrode TX.

[0157] In addition to the touch drive unit TD, the non-display area FR is provided with peripheral circuits including drive circuits such as a gate driver that supplies gate signals to the gate bus lines (gate wiring) GL and a source driver that supplies source signals to the source bus lines (source wiring) SL (not shown). These drive circuits may be mounted on the first substrate (TFT substrate) 10, for example, or may be formed integrally (monolithically). A semiconductor chip including some or all of the drive circuits may be mounted on the non-display area FR.

[0158] In an in-cell touch panel, it is particularly preferable to use an In-Ga-Zn-O based semiconductor as the TFT 110. From the viewpoint of achieving flickerless (also called flicker-free), it is particularly preferable to use a negative type liquid crystal material. This is for the following reason. In the in-plane electric field method of the FFS mode using a positive type liquid crystal material, flexoelectric polarization occurs spontaneously in the liquid crystal layer due to the influence of the fine slit electrodes on the electrodes when a voltage is applied (i.e., the fringe electric field). Since the liquid crystal responds according to this flexoelectric polarization, the luminance changes when the polarity is inverted, which is thought to be easily visually recognized as flicker.

[0159] (Modification 1 of the first embodiment) In the first embodiment, the first electrode 121, which is a lower layer electrode, is the common electrode CE, and the second electrode 122, which is an upper layer electrode, is the pixel electrode PE. However, the second electrode 122 may be the common electrode CE, and the first electrode 121 may be the pixel electrode PE. In this example, the second electrode 122 (upper layer electrode) is the common electrode CE, and the first electrode 121 (lower layer electrode) is the pixel electrode PE (see FIG. 18).

[0160] FIG. 18 is a schematic cross-sectional view showing the liquid crystal display device 1 of this example in more detail. In this example as well, from the viewpoint of easily generating a transverse electric field, it is preferable that at least the upper layer electrode (common electrode CE in this example) is a slit electrode. The lower layer electrode (pixel electrode PE in this example) may be a planar electrode, i.e., a so-called solid electrode, or may be a slit electrode. As described above, the liquid crystal display device 1 of this modified example is particularly suitable as a relatively high-definition liquid crystal display device, i.e., a liquid crystal display device in which the area of ​​the pixel P is relatively small.

[0161] (Modification 2 of the first embodiment) In the first embodiment, an FFS mode liquid crystal display device has been described, but an IPS mode liquid crystal display device may also be used (however, the liquid crystal layer 20 has a twisted orientation when no voltage is applied). This modification is an IPS mode liquid crystal display device. In this modification, the first electrode 121 and the second electrode 122 are provided in the same layer, and it is preferable that both the first electrode 121 and the second electrode 122 are slit electrodes.

[0162] (Embodiment 2) In this embodiment, features unique to this embodiment will be mainly described, and descriptions of contents overlapping with the above-mentioned embodiment 1 will be omitted. This embodiment is substantially the same as embodiment 1, except that the retardation layer 40 includes another positive C plate 44 in addition to the positive C plate 43. For convenience, the positive C plate 43 described above in embodiment 1 will also be referred to as the first positive C plate 43, and the positive C plate 44 added in this embodiment will also be referred to as the second positive C plate 44.

[0163] Fig. 19 is a schematic cross-sectional view of a liquid crystal display device 1 as an example of this embodiment. As shown in Fig. 19, the liquid crystal display device 1 includes, in order from the rear side, a first substrate 10, a liquid crystal layer 20, a second substrate 30, a retardation layer 40, and a polarizing plate 50. The retardation layer 40 includes a first positive C plate 43 and a second positive C plate 44 in addition to a λ / 4 plate 41 and a λ / 2 plate 42. The positive C plate 44 may be made of a single film or may be a laminate of two or more retardation films.

[0164] When the retardation layer 40 includes the first positive C plate 43 and the second positive C plate 44, it is possible to achieve both a further improvement in the viewing angle and an improvement in the contrast ratio. In particular, the black floating is further suppressed than in the second embodiment. From the viewpoint of further exerting such an effect, it is preferable that the second positive C plate 44 is located between the λ / 2 plate 42 and the polarizing plate 50. That is, it is preferable that the retardation layer 40 has the λ / 4 plate 41, the first positive C plate 43, the λ / 2 plate 42, and the second positive C plate 44 located in this order from the liquid crystal layer 20 (and second substrate 30) side (see FIG. 19).

[0165] The second positive C plate 44 may be the same as the first positive C plate 43 (having the same physical properties and thickness, etc.) or different from the first positive C plate 43 as long as it is a retardation plate that satisfies "nz>nx≈ny". However, from the viewpoint of further exerting the viewing angle improving effect, the thickness direction retardation Rth (absolute value) of the second positive C plate 44 is preferably 50 to 130 nm, more preferably 70 to 120 nm, and further preferably 80 to 115 nm.

[0166] The thickness of the second positive C plate 44 is preferably, for example, 0.1 to 100 μm. Within this range, the mechanical strength and display uniformity are superior. The thickness is more preferably 0.1 to 80 μm, and even more preferably 0.1 to 50 μm. When the positive C plate 44 has a laminated structure, it is preferable to set the total thickness of the whole to be within the above range, and the thicknesses of the respective retardation films may be the same or different.

[0167] The effects of including the first positive C plate 43 and the second positive C plate 44 were found by the inventors of the present application through verification using optical simulation. The verification results will be explained below separately for the cases where the liquid crystal material constituting the liquid crystal layer 20 is of the positive type and the negative type. Note that an absorptive polarizing plate is used as the polarizing plate 50.

[0168] (i) When the liquid crystal material is a positive type In the liquid crystal display device 1 having a configuration including a reflective liquid crystal panel 1X using a positive type liquid crystal material, a retardation layer 40, and a polarizing plate 50, the retardation layer 40 is assumed to have a four-layer structure in which a λ / 2 plate 42, a first positive C plate 43 (thickness direction retardation Rth: 210 nm), a λ / 4 plate 41, and a second positive C plate 44 (thickness direction retardation Rth: 110 nm) are arranged in order from the observation surface side, and the influence of the addition of the second positive C plate 44 on the viewing angle was examined (Example 23). LCD Master 1D by Shintech Co., Ltd. was used as the simulation software. A uniaxial retardation plate with a retardation of 140 nm was used as the λ / 4 plate 41, and a uniaxial retardation plate with a retardation of 270 nm was used as the λ / 2 plate 42, and the wavelength dispersion of these retardation plates was set to be flat. The other settings were the optimal settings obtained in the first embodiment when the liquid crystal material was a positive type. The results are shown in FIG. 20.

[0169] Fig. 20 is a diagram showing a simulation result for the present embodiment in which the liquid crystal material is a positive type. An example not including a C plate is set as Example 21, and an example including a first positive C plate 43 but not a second positive C plate 44 is set as Example 22. The upper part of Fig. 20 shows a schematic cross-sectional view of the liquid crystal display device 1 in each example (however, only the reflective layer 130 is shown separately from the liquid crystal panel 1X), and the lower part shows the viewing angle in black display (0V) (when light is incident at a polar angle of 30°).

[0170] Furthermore, for Examples 21 to 23, the luminance distribution was analyzed in the black display (0 V) state, with incident light at a polar angle of 30° and at azimuth angles of 0 to 360° (15° steps) and polar angles of 0 to 80° (10° steps). The results are shown in Fig. 21. Fig. 21 is a graph showing the distribution of maximum black luminance for Examples 21 to 23. In Fig. 21, the horizontal axis represents Rth (nm) of the second positive C plate 44, and the vertical axis represents the maximum black luminance.

[0171] 21, it was found that the distribution curve of Example 22 was within 30% of the minimum value (marked with an arrow) of the vertical axis (maximum black luminance) when the Rth of the second positive C plate 44 was 50 nm or more and 130 nm or less, within 15% when the Rth was 70 nm or more and 120 nm or less, and within 10% when the Rth was 80 nm or more and 115 nm or less. Based on this result, it was found that the preferable range of the thickness direction retardation Rth of the second positive C plate 44 is as described above.

[0172] (ii) When the liquid crystal material is negative type In the liquid crystal display device 1 having a configuration including a reflective liquid crystal panel 1X using a negative type liquid crystal material, a retardation layer 40, and a polarizing plate 50, the retardation layer 40 is assumed to have a four-layer structure in which a λ / 2 plate 42, a first positive C plate 43 (thickness direction retardation Rth: 210 nm), a λ / 4 plate 41, and a second positive C plate 44 (thickness direction retardation Rth: 110 nm) are arranged in order from the observation surface side, and the influence of the addition of the second positive C plate 44 on the viewing angle was examined (Example 33). LCD Master 1D by Shintech Co., Ltd. was used as the simulation software. A uniaxial retardation plate with a retardation of 140 nm was used as the λ / 4 plate 41, and a uniaxial retardation plate with a retardation of 270 nm was used as the λ / 2 plate 42, and the wavelength dispersion of these retardation plates was set to be flat. The other settings were the optimal settings obtained in the first embodiment when the liquid crystal material was a positive type. The results are shown in FIG. 22.

[0173] Fig. 22 is a diagram showing a simulation result for the present embodiment in which the liquid crystal material is a negative type. An example not including a C plate is designated as Example 31, and an example including a first positive C plate 43 but not a second positive C plate 44 is designated as Example 32. The upper part of Fig. 22 shows a schematic cross-sectional view of the liquid crystal display device 1 in each example (however, only the reflective layer 130 is shown separately from the liquid crystal panel 1X), and the lower part shows the viewing angle in black display (0V) (when light is incident at a polar angle of 30°).

[0174] Furthermore, for Examples 31 to 33, the luminance distribution was analyzed in a black display (0 V) state, with incident light at a polar angle of 30°, at azimuth angles of 0 to 360° (15° steps) and polar angles of 0 to 80° (10° steps). The results are shown in Fig. 23. Fig. 23 is a graph showing the distribution of maximum black luminance for Examples 31 to 33. In Fig. 23, the horizontal axis represents Rth (nm) of the second positive C plate 44, and the vertical axis represents the maximum black luminance.

[0175] From Fig. 23, it was found that the distribution curve of Example 32 was within 30% of the minimum value (marked with an arrow) of the vertical axis (maximum black luminance) when the Rth of the second positive C plate 44 was 50 nm or more and 130 nm or less, within 15% when the Rth was 70 nm or more and 120 nm or less, and within 10% when the Rth was 80 nm or more and 115 nm or less. In other words, the same tendency as when the liquid crystal material was a positive type (see Fig. 21) was obtained. Based on this result, it was found that the preferable range of the thickness direction retardation Rth of the second positive C plate 44 is as described above.

[0176] (Embodiment 3) In this embodiment, features unique to this embodiment will be mainly described, and descriptions of contents overlapping with the above-mentioned embodiment 1 will be omitted. In embodiment 1, a reflective liquid crystal display device was exemplified and described, but in this embodiment, a semi-transmissive liquid crystal display device will be described. The liquid crystal display device of this embodiment differs from the liquid crystal display device of embodiment 1 mainly in that a light source is provided on the rear side of the liquid crystal layer 20.

[0177] Fig. 24 is a cross-sectional schematic diagram of a liquid crystal display device 1 as an example of this embodiment. The liquid crystal display device 1 further includes a light source 61 (also referred to as a backlight) on the rear side of the liquid crystal layer 20. In addition, it is preferable that the liquid crystal display device 1 further includes a polarizing plate 50' and a retardation layer 40'. More preferably, as shown in Fig. 24, the liquid crystal display device 1 includes, in order from the rear side, the light source 61, the polarizing plate 50', the retardation layer 40', the first substrate 10, the liquid crystal layer 20, the second substrate 30, the retardation layer 40, and the polarizing plate 50. In this embodiment, a TFT substrate is also suitable as the first substrate 10.

[0178] The light source 61 (backlight) is not particularly limited as long as it irradiates light, and may be a direct type, an edge type, or any other type. Specifically, for example, it is preferable that the light source has a light emitting diode (LED) or other such light source, a light guide plate, and a reflective sheet, and may further have a diffusion sheet or a prism sheet.

[0179] The polarizing plate 50' is disposed on the rear side of the liquid crystal layer 20. More specifically, it is disposed on the rear side of the first substrate 10. The polarizing plate 50' may be a circular polarizing plate or a linear polarizing plate, but is preferably a linear polarizing plate. Also, it may be an absorptive polarizing plate or a reflective polarizing plate, but is preferably an absorptive polarizing plate. In particular, it is preferable to use an absorptive linear polarizing plate.

[0180] The polarization axis of the polarizing plate 50' may be arranged so as to be approximately perpendicular to or approximately parallel to the polarization axis of the polarizing plate 50. That is, the polarizing plate 50' may be arranged in a crossed Nicol state or a parallel Nicol state with the polarizing plate 50. Among these, the crossed Nicol state is preferable.

[0181] The retardation layer 40' is disposed between the polarizing plate 50' and the liquid crystal layer 20. More specifically, it is disposed between the polarizing plate 50' and the first substrate 10. The retardation layer 40' may include, for example, a λ / 4 plate and a λ / 2 plate. The arrangement order of these is preferably, for example, the λ / 2 plate and the λ / 4 plate from the rear side.

[0182] In the liquid crystal display device 1 of this embodiment, each pixel P has a reflective region Rf for performing display in a reflective mode and a transmissive region Tr for performing display in a transmissive mode (see FIG. 25). FIG. 25 is a schematic plan view conceptually showing that each pixel P has a reflective region Rf and a transmissive region Tr in the liquid crystal display device 1 of this embodiment. A reflective layer 130 (see FIG. 2, for example) is arranged in the reflective region Rf, but the reflective layer 130 is not arranged in the transmissive region Tr. The proportion of the area of ​​the transmissive region Tr in each pixel P can be appropriately set depending on the application, etc., but is preferably, for example, 20% or more and 90% or less. The position and shape of the transmissive region Tr in the pixel P can also be appropriately set depending on the application, etc.

[0183] In the liquid crystal display device of this embodiment, i.e., the semi-transmissive liquid crystal display device, similarly to the reflective liquid crystal display device, the contrast ratio of the reflective display can be sufficiently improved by performing display in the lateral electric field mode in which the liquid crystal layer 20 has a twisted orientation when no voltage is applied. Therefore, the liquid crystal display device 1 of this embodiment is also useful as an in-cell touch panel capable of displaying in the reflective mode at low cost and with an improved contrast ratio.

[0184] (Embodiment 4) In this embodiment, features unique to this embodiment will be mainly described, and descriptions of contents overlapping with the above-mentioned embodiment 1 will be omitted. The liquid crystal display device of this embodiment mainly differs from the liquid crystal display device of embodiment 1 in that a light source is provided on the observation surface side of the liquid crystal layer 20. The liquid crystal display device of this embodiment is a reflective liquid crystal display device.

[0185] Fig. 26 is a cross-sectional schematic diagram of a liquid crystal display device 1 as one example of this embodiment. The liquid crystal display device 1 of this embodiment further includes a light source 62 (also referred to as a front light) on the observation surface side of the liquid crystal layer 20. More preferably, as shown in Fig. 26, the liquid crystal display device 1 includes, in this order from the rear side, a first substrate 10, a liquid crystal layer 20, a second substrate 30, a retardation layer 40, a polarizing plate 50, and a light source 62. In this embodiment as well, a TFT substrate is suitable as the first substrate 10.

[0186] The light source 62 (front light) is not particularly limited as long as it can irradiate light. Specifically, for example, it is preferable that the light source has a light emitting diode (LED) or other light source and a light guide plate. By further including the light source 62, the reflective liquid crystal display device 1 can perform bright reflective display even in an environment where sufficient ambient light cannot be obtained.

[0187] Although the embodiments of the present invention have been described above, the individual matters described above can all be applied to the present invention as a whole.

[0188] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the following, an absorptive polarizing plate is used as the polarizing plate 50.

[0189] (Test Examples 1 to 4) As shown in Fig. 27B, the liquid crystal cell 1100 for obtaining the test cell 1000 includes a first substrate 10, a second substrate 30, and a liquid crystal layer 20 provided between these substrates. Fig. 27A is a plan view showing the structure of the liquid crystal cell 1100 as viewed from the front. Fig. 27B is a cross-sectional view taken along line A-A' in Fig. 27A (cross-sectional view taken along line A-A').

[0190] As shown in FIG. 27B, the first substrate 10 includes a glass substrate 100, and includes a common electrode CE as the first electrode 121, a dielectric layer 153, a pixel electrode PE as the second electrode 122, and a first horizontal alignment film 140 on the glass substrate in this order. The common electrode CE is made of ITO, and has a thickness of 100 nm. The dielectric layer 153 is made of silicon nitride (SiNx), and has a thickness of 300 nm. The pixel electrode PE is made of ITO, and has a thickness of 100 nm. The pixel electrode PE has a plurality of strip portions SP and a plurality of slits Sl. The width of each strip portion SP is 3 μm, and the width of each slit Sl (the distance between two adjacent strip portions SP) is 5 μm. Each strip portion SP is bent in a dogleg shape. That is, each strip portion SP includes a first portion SPa extending in a certain direction (first direction) and a second portion SPb extending in a direction (second direction) different from the first direction. The bending angle (the angle that the first portion SPa and the second portion SPb of the strip portion SP make with respect to the left-right direction in FIG. 27A) is 7°.

[0191] The second substrate 30 has a glass substrate 300 and a second horizontal alignment film 340 provided on the glass substrate 300, as shown in FIG. 27B.

[0192] The thickness (cell gap) of the liquid crystal layer 20 is determined by plastic beads (not shown).

[0193] The alignment treatment for the first horizontal alignment film 140 and the second horizontal alignment film 340 was carried out by a photo-alignment treatment or a rubbing treatment.

[0194] When photo-alignment treatment was performed, a photodecomposition type photo-alignment film material was used. The photo-alignment film material was applied by spin coating, and the thickness of the alignment film was 1000 Å (i.e., 100 nm). The non-polarized UV light emitted from the UV lamp unit was converted to polarized UV light by a wire grid polarizer, and the alignment film was irradiated with the polarized UV light to perform the photo-alignment treatment. The extinction ratio of the wire grid polarizer was 100:1. The wavelength of UV light effective for photo-alignment was 220 to 260 nm, and the irradiation energy was 300 mJ / cm. 2 The alignment direction of the liquid crystal molecules is a direction substantially perpendicular to the transmission axis direction of the polarized UV light (particularly preferably at 90°).

[0195] When rubbing treatment is used, a horizontal alignment film is formed and then rubbed with a rubbing roller (e.g., a roller wrapped with cloth) to perform the alignment treatment. This results in a uniaxial alignment direction of the liquid crystal molecules. As an alignment film material suitable for operating the liquid crystal molecules with a transverse electric field, a polyimide-based material is suitable. In addition, a material that does not generate a pretilt due to the rubbing treatment is suitable, and such materials are commercially available. The liquid crystal molecules are aligned approximately parallel to the rubbing direction.

[0196] For the liquid crystal cell 1100 having the above structure, first, the retardation of the liquid crystal layer 20 was measured using a polarimeter ("AxoScan" manufactured by Axometrics Co., Ltd.) Next, the cell thickness was measured using a cell gap inspection device ("RetQC" manufactured by Otsuka Electronics Co., Ltd.).

[0197] 28, a λ / 4 plate 41, a λ / 2 plate 42 and a polarizing plate 50 were attached in this order to the second substrate 30 side of the liquid crystal cell 1100 (adhesive layer not shown).

[0198] Then, a drop of matching oil mo for reducing loss due to interface reflection was dropped on the reflector 130 having a concave-convex surface structure (MRS), and the liquid crystal cell 1100 was placed on the reflector 130 with the first substrate 10 side facing down. In this way, the test cell 1000 was produced. In addition, in this state, the reflectance was measured by changing the voltage applied between the pixel electrode PE and the common electrode CE. The voltage was applied to the pixel electrode PE and the common electrode CE using a function generator ("AFG1022" manufactured by TEKTRONIX) capable of applying a voltage of 0V to 10V with a square wave of 30Hz. The reflectance was measured using a spectrophotometer ("CM-2600d" manufactured by MINOLTA). FIG. 28 is a schematic cross-sectional view of the test cell 1000.

[0199] In addition, test cell 2000 was prepared in the same manner as test cell 1000, except that the process of attaching an optical film to liquid crystal cell 1100 during the preparation process of test cell 1000 was changed to a process of attaching a λ / 4 plate 41, a positive C plate 43, a λ / 2 plate 42 and a polarizing plate 50 to the second substrate 30 side of liquid crystal cell 1100.

[0200] As the λ / 4 plate 41, Nitto Denko Corporation's "NZF-UF01A" (retardation: 140 nm) was used in Test Examples 2 and 3, and Nitto Denko Corporation's "NZF-UF01A" (retardation: 110 nm) was used in Test Examples 1 and 4. As the λ / 2 plate 42, Nitto Denko Corporation's "NZF-UF01A" (retardation: 270 nm) was used in Test Examples 2 and 3, and Nitto Denko Corporation's "NZF-UF01A" (retardation: 260 nm) was used in Test Examples 1 and 4. As the positive C plate 43, one with Rth of 200 nm was used.

[0201] In Test Examples 1, 2, and 4, the above-mentioned Test Cell 1000 was used, and in Test Example 3, the above-mentioned Test Cell 2000 was used to carry out the following studies on (a) and (b). In Test Examples 1 to 3, the liquid crystal material was positive type, and the display mode was TW-FFS mode. In Test Example 4, the liquid crystal material was negative type, and the display mode was TW-FFS mode. The optical axis settings (initial settings) and specifications of Test Examples 1 to 4 are shown in Table 11 and FIG. 6. FIG. 6 is also a diagram conceptually illustrating the optical axis settings of Test Examples 1 to 4 (excluding the positive C plate).

[0202] [Table 3]

[0203] (Test Example 5) As shown in Fig. 29B, the liquid crystal cell 3100 for obtaining the test cell 3000 includes a first substrate 10, a second substrate 30, and a liquid crystal layer 20 provided between these substrates. Fig. 29A is a plan view showing the structure of the test cell 3000 (and the liquid crystal cell 3100) as viewed from the front. Fig. 29B is a cross-sectional view (cross-sectional view taken along line A-A') in Fig. 29A.

[0204] The first substrate 10 includes a glass substrate 100, on which a pixel electrode PE and a first vertical alignment film (not shown) are disposed in this order. The second substrate 30 includes a glass substrate 300, on which a common electrode CE and a second vertical alignment film (not shown) are disposed in this order. Of the vertical alignment films, only the second vertical alignment film disposed on the observation surface side is subjected to a photo-alignment treatment. The alignment direction of the liquid crystal molecules 21 determined by the first vertical alignment film is the 90° direction (the pretilt angle is 88.4°).

[0205] As shown in FIG. 30, the λ / 4 plate 41, the first λ / 2 plate 42a, the second λ / 2 plate 42b, and the polarizing plate 50 were attached in this order to the second substrate 30 side of the liquid crystal cell 3100 (adhesive layer is not shown). The polarizing plate 50 was "NPF-CRT1794KDUHC3" manufactured by Nitto Denko Corporation, the λ / 4 plate 41 was "NZF-UF01A" (retardation: 110 nm) manufactured by Nitto Denko Corporation, and the λ / 2 plates 42a and 42b were "NZF-UF01A" (retardation: 260 nm) manufactured by Nitto Denko Corporation. Then, a drop of matching oil mo was dropped on the reflecting plate 130 having the MRS, and the liquid crystal cell 3100 was placed on the reflecting plate 130 with the first substrate 10 side facing down. In this manner, the test cell 3000 was produced. FIG. 30 is a schematic cross-sectional view of the test cell 3000.

[0206] In Test Example 5, the above-mentioned Test Cell 3000 was used to examine the following items (a) and (b). In Test Example 5, the liquid crystal material is a negative type with negative dielectric anisotropy, and the display mode is a VA mode. The optical axis setting (initial setting) and specifications of Comparative Example 1 are shown in Table 4 and FIG.

[0207] [Table 4]

[0208] In the following discussion, normalized reflectance is calculated using the following formula: Normalized reflectance (%) = (n-level reflectance - 0-level reflectance) / (255-level reflectance - 0-level reflectance) x 100 It was calculated by:

[0209] (a) Oblique gamma characteristic evaluation The γ curve was analyzed with a polar angle of 50°. The results are shown in Figures 32A to 32C. In these figures, the upper part shows a schematic cross-sectional view of the test cell in each example, the middle part shows a graph of the γ curve, and the lower part shows a distribution diagram of the reflected luminance at a grayscale level of 255 in white display. In the graph in the middle part, the horizontal axis shows the grayscale (0 to 255 levels) when viewed from the front, and the vertical axis shows the normalized reflectance. The front was corrected to γ ​​= 2.2. In each graph, the angle attached to each γ curve (the azimuth is defined as 0° at 3 o'clock, and the polar angle is defined as 0° in the normal direction of the observation surface of the panel) means the angle in the azimuth direction (however, the polar angle is defined as 50°). For example, in Test Example 1, "75°" indicates the gamma curve at an azimuth direction of 75° and a polar angle of 50°, "210°" indicates the gamma curve at an azimuth direction of 210° and a polar angle of 50°, and "285°" indicates the gamma curve at an azimuth direction of 285° and a polar angle of 50°. Figures 32A to 32C are diagrams showing the results of Test Examples 1 to 5.

[0210] The γ curve was analyzed by changing the polar angle. The results are shown in Figures 33A to 33C. In these figures, the upper graph shows the case where the polar angle is 30°, the middle graph shows the case where the polar angle is 40°, and the lower graph shows the case where the polar angle is 50°. In each graph, the horizontal axis represents the gray scale (0 to 255 gray scale) when viewed from the front, and the vertical axis represents the normalized reflectance. Figures 33A to 33C also show the results of Test Examples 1 to 5.

[0211] 32A to 32C and 33A to 33B show that in the positive-type liquid crystal materials (Test Examples 1 to 4), when the polar angle is 30°, the oblique γ characteristics are almost equivalent, but when the polar angle is 40° or more, the oblique γ characteristics become an issue in Test Example 3. However, a comparison between Test Example 2 and Test Example 3 shows that the oblique γ characteristics are improved by adding the positive C plate 43.

[0212] (b) Simulation evaluation from an oblique direction The oblique γ characteristics were evaluated relative to the γ characteristics when viewed from the front, and an image simulation was performed when the display screen was viewed from an oblique direction. Specifically, a color original image was displayed on each test cell, and the displayed image was photographed by a camera from each azimuth shown in FIG. 34 (each azimuth was photographed from a polar angle of 50 degrees). The results are shown in FIG. 36A to FIG. 36C. For comparison, an image photographed from the front (also referred to as an original image) is shown in FIG. 35. FIG. 34 is a diagram conceptually showing the azimuth angle, FIG. 35 is an image photographed from the front, and FIG. 36A to FIG. 36C are diagrams showing the results of Test Examples 1 to 5.

[0213] 35 and 36A to 36C, column (I) lists the simulation image and its orientation (angle) where the image is most prominent, and column (II) lists the simulation image and its orientation (angle) where the image is most recessed. "Image is prominent" means that the gradation is higher than that from the front, and "image is recessed" means that the gradation is lower than that from the front.

[0214] 36A to 36C, among Test Examples 1 to 5, Test Example 3 was the best-balanced example from the three viewpoints of whiteout, blackout, and natural color (saturation of facial color, etc.). Whiteout refers to a phenomenon in which a bright part becomes uniformly bright. For example, if the change in the γ curve is smaller than γ=2.2, the image floats and whiteout becomes large. Blackout refers to a phenomenon in which a dark part becomes uniformly dark. For example, if the change in the γ curve is larger than γ=2.2, the image sinks and blackout becomes large. For example, in Test Example 5, the simulation image in which the image floats the most had large whiteout (see s in FIG. 36C), and the simulation image in which the image sinks the most had unnatural facial color (see FIG. 36C).

[0215] In Figures 36A and 36B, a comparison between Test Example 2 and Test Example 3 reveals that the addition of the positive C plate 43 suppresses whiteout and blackout (see s and t in Figure 36A).

[0216] The above-described aspects of the present invention may be combined as appropriate without departing from the gist of the present invention. [Explanation of symbols]

[0217] 1:LCD display device 1X: LCD panel 10, 30: PCB 20: Liquid crystal layer 21, 21A, 21B: Liquid crystal molecules 40, 40': Retardation layer 41:λ / 4 plate 42, 42a, 42b: λ / 2 plate 41SA, 42SA, 42aSA, 42bSA: In-plane slow axis 43, 43R, 44: Positive C plate 50, 50': Polarizing plate 50AA: Polarization axis 61, 62: Light source 100, 300: Support substrate 110: TFT 121, 122: Electrode 130: Reflective layer 140, 340: Horizontal alignment film 151, 152: Interlayer insulating layer 153: Dielectric layer 160: Contact electrode 210, 310: color filter layer 1000, 2000, 3000: Test cell 1100, 3100: Liquid crystal cell BP: Backplane circuit CE: Common electrode PE: Pixel electrode CH1, CH2: Contact hole DR:Display area FR: Hidden area GL: Gate wiring SL: Source wiring p: protruding part P: Pixel Rf:Reflection area Tr:Transmission area Sl: Slit SP, SPa, SPb: Band TC: Touch wiring contact part TD: Touch drive unit TL, TL1, TL2: Touch wiring TX: Touch sensor electrode

Claims

1. A liquid crystal display device including a first substrate, a liquid crystal layer, a second substrate, a retardation layer, and a polarizing plate in this order from a rear surface side, and having a plurality of pixels arranged in a matrix, the first substrate has a reflective layer that reflects light, a first electrode and a second electrode that can generate a transverse electric field in the liquid crystal layer, and a first horizontal alignment film that is in contact with the liquid crystal layer; the second substrate has a second horizontal alignment film in contact with the liquid crystal layer, The liquid crystal layer has a twisted orientation when no voltage is applied, The retardation layer includes a λ / 4 plate, a λ / 2 plate, and a positive C plate. A liquid crystal display device comprising:

2. The liquid crystal layer includes a positive type liquid crystal material or a negative type liquid crystal material.

2. The liquid crystal display device according to claim 1 .

3. When the liquid crystal layer contains the positive type liquid crystal material, an angle between a polarization axis of the polarizer and an alignment direction of liquid crystal molecules defined by the first horizontal alignment film is 63.5° or more and 71.5° or less; When the liquid crystal layer contains the negative type liquid crystal material, the angle between the polarization axis of the polarizer and the alignment direction of the liquid crystal molecules defined by the first horizontal alignment film is 20.5° or more and 26° or less.

3. The liquid crystal display device according to claim 2.

4. The positive C plate is located between the λ / 4 plate and the λ / 2 plate.

2. The liquid crystal display device according to claim 1 .

5. The positive C plate has a thickness direction retardation Rth (nm) of 150 to 270 nm in absolute value.

2. The liquid crystal display device according to claim 1 .

6. The retardation layer further includes a second positive C plate, The second positive C plate is located between the λ / 2 plate and the polarizing plate.

2. The liquid crystal display device according to claim 1 .

7. The second positive C plate has a thickness direction retardation Rth (nm) of 50 to 130 nm in absolute value.

7. The liquid crystal display device according to claim 6.

8. The twist angle of the liquid crystal layer when no voltage is applied is 70° or more and 85° or less.

2. The liquid crystal display device according to claim 1 .

9. When the liquid crystal layer contains the positive type liquid crystal material, the product (dΔn) of the thickness d of the liquid crystal layer and the birefringence Δn of the liquid crystal material is 218 nm or more and 255 nm or less.

3. The liquid crystal display device according to claim 2.

10. When the liquid crystal layer contains the positive type liquid crystal material, the angle between the in-plane slow axis of the λ / 2 plate and the alignment direction of the liquid crystal material defined by the first horizontal alignment film is 47.5° or more and 52.5° or less.

3. The liquid crystal display device according to claim 2.

11. When the liquid crystal layer contains the negative type liquid crystal material, the product (dΔn) of the thickness d of the liquid crystal layer and the birefringence Δn of the liquid crystal material is 230 nm or more and 260 nm or less.

3. The liquid crystal display device according to claim 2.

12. When the liquid crystal layer contains the negative type liquid crystal material, the angle between the in-plane slow axis of the λ / 2 plate and the alignment direction of the liquid crystal material defined by the first horizontal alignment film is 38.5° or more and 42.5° or less.

3. The liquid crystal display device according to claim 2.

13. At least one of the first electrode and the second electrode has a plurality of strip portions and a slit located between two adjacent strip portions of the plurality of strip portions.

2. The liquid crystal display device according to claim 1 .

14. Single domain orientation 2. The liquid crystal display device according to claim 1 .

15. Display in normally black mode 2. The liquid crystal display device according to claim 1 .

16. One of the first electrode and the second electrode is a pixel electrode provided in each of the plurality of pixels, and the other is a common electrode including a plurality of segments each capable of functioning as a touch sensor electrode; The first substrate has a plurality of touch wirings each connected to a corresponding one of the touch sensor electrodes.

2. The liquid crystal display device according to claim 1 .

17. the first substrate has a thin film transistor provided in each of the plurality of pixels and including an oxide semiconductor layer; The oxide semiconductor layer includes an In—Ga—Zn—O based semiconductor.

2. The liquid crystal display device according to claim 1 .

18. Further, a light source is provided.

18. The liquid crystal display device according to claim 1,

Images