JP6882132B2 - Liquid crystal display device - Google Patents

Description

The present invention relates to a liquid crystal display device that can be suitably implemented as a display device of various electronic devices such as mobile phones.

Conventionally, in an active matrix type liquid crystal display device, the light transmittance of the liquid crystal display panel at the time of black display is not minimized, and the black level of normally black with high display quality cannot be obtained, so-called black floating problem is solved. Technology is required.

Patent Document 1 describes an example of a conventional technique for solving such a problem. Patent Document 1 describes a first polarizing plate arranged outside one cell substrate of a liquid crystal cell, a second polarizing plate arranged outside the other cell substrate, and between the first polarizing plate and the liquid crystal cell. A first retardation plate having an in-plane retardation value Ro of 200 nm or more and 400 nm or less is provided, and the angle in the counterclockwise direction is expressed as positive with respect to the absorption axis of the first polarizing plate. The absorption axes of the two polarizing plates are arranged at an angle within 0 ° ± 10 °, and the first retardation plate has an angle from the absorption axis of the first polarizing plate to the absorption axis of the second polarizing plate. A liquid crystal display device in which the slow axis is arranged within a predetermined angle range, and a liquid crystal display device in which a second retardation plate is arranged on at least one surface of the first retardation plate is proposed. Has been done.

Further, another example of the prior art for solving the above problem is described in Patent Document 2. Patent Document 2 provides a pair of polarizing plates having a reflection region and a transmission region in the pixel, and having a pair of polarizing plates facing each other with a liquid crystal layer interposed therebetween, and a transverse electric field driven semi-transmissive liquid crystal display device. A semi-transmissive liquid crystal display device having a 1/2 wavelength plate between a polarizing plate common to a reflection region and a transmission region and a liquid crystal layer among the plates has been proposed.

Japanese Unexamined Patent Publication No. 2009-31402 JP-A-2007-240752

The prior art described in Patent Document 1 described above is a Twisted Nematic (TN) type, Vertical Aligned (VA) type, and In Plane Switching (IPS) type liquid crystal display device. It is targeted. That is, Patent Document 1 does not propose any technique for preventing black floating in a wide band and further improving the viewing angle for a birefringence control (ECB) type liquid crystal display device.

Further, the conventional technique described in Patent Document 2 relates to an IPS type liquid crystal display device, and the IPS type liquid crystal display device displays liquid crystal molecules by rotating them in a direction parallel to a substrate by applying an electric field. As a result, a wider viewing angle can be realized as compared with the TN type liquid crystal display device. In this conventional technique, when the transmission region is normally black, the reflection region becomes normally white. Therefore, the common signal between the transmission region and the reflection region is inverted, and the display is inverted between the transmission region and the reflection region (black display). It proposes a technology to improve coloring and light leakage by solving the problem of white display inversion) and providing a 1/2 wavelength plate between the polarizing plate and the liquid crystal layer, and it is a reflection region and transmission. No technique has been proposed for making the area normally black, or for preventing black floating on the ECB type liquid crystal display device in a wide band and further improving the viewing angle.

In the ECB type liquid crystal display device, liquid crystal molecules are parallel to the surface of the substrate in a state where an electric field is not applied to the liquid crystal layer (initial orientation state), and when the electric field applied to the liquid crystal layer is gradually increased, a certain threshold electric field is generated. When it exceeds, the liquid crystal molecules gradually start to rise with respect to the surface of the substrate, and are driven in an operation mode in which the orientation direction of the liquid crystal molecules becomes perpendicular to the surface of the substrate at a high voltage.

An object of the present invention is an ECB-type liquid crystal display device that displays in normal black, a liquid crystal display capable of achieving a black level with high display quality in a wide band, suppressing black floating, and further improving the viewing angle. To provide a device.

The liquid crystal display device of the present invention is a double-refractive index control type liquid crystal display device that displays in normal black, has a liquid crystal layer, and reflects light incident from the display surface side and passing through the liquid crystal layer. Between the liquid crystal display panel having a light reflecting portion, the first polarizing plate arranged on the display surface side of the liquid crystal display panel, and the liquid crystal display panel and the first polarizing plate, the first A first 1/2 wavelength plate and an optical compensation plate, which are provided in order from the side of the polarizing plate, are provided, and the liquid crystal layer has a phase difference of the first 1/2 wavelength plate when no electric field is applied. The first 1/2 wavelength plate, which is smaller than 1/2 of the phase difference, has its slow axis intersecting the orientation axis of the liquid crystal molecules when no electric field is applied, and is orthogonal to each other in the plane. When the refractive indexes of the above are nx1 and ny1, and the refractive index in the thickness direction is nz1, the relationship of nx1> ny1 = nz1 is satisfied, and the optical compensating plates are in the planes orthogonal to each other. When the refractive index is nx2 and ny2, respectively, and the refractive index in the thickness direction is nz2, the configuration satisfies the relationship of nz2> nz2 = ny2.

The liquid crystal display device of the present invention preferably has 0.3 ≦ RD1 when the in-plane phase difference of the first 1/2 wave plate is RD1 and the phase difference in the thickness direction of the optical compensation plate is RD2. / RD2 ≦ 0.9.

Further, in the liquid crystal display device of the present invention, preferably, the liquid crystal display panel has a light transmitting portion that allows light incident from the counter-display surface side to pass through the liquid crystal layer, and the counter-display surface of the liquid crystal display panel. A second polarizing plate arranged on the side and a 1/4 wave plate provided between the liquid crystal display panel and the second polarizing plate are further provided, and a slow axis of the 1/4 wave plate is provided. And the orientation axis of the liquid crystal molecules when no electric field is applied intersect at approximately 90 °.

Further, the liquid crystal display device of the present invention preferably includes a second 1/2 wave plate provided between the 1/4 wave plate and the second polarizing plate, and is slower than the 1/4 wave plate. The phase axis and the orientation axis of the liquid crystal molecules when no electric field is applied intersect at 90 °, and the slow axis of the second 1/2 wave plate and the slow axis of the first 1/2 wave plate Crosses at 85 ° or more and 110 ° or less.

Further, in the liquid crystal display device of the present invention, preferably, the phase difference of the light transmitting portion when no electric field is applied is larger than the phase difference of the light reflecting portion when no electric field is applied.

According to the present invention, in a birefringence-controlled liquid crystal display device that displays in normal black, the phase difference of the liquid crystal layer functions as a 1/4 wave plate. Further, in a state where an electric field is not applied to the liquid crystal layer, the circularly polarized light emitted from the first 1/2 wave plate, the optical compensation plate, and the liquid crystal layer becomes wide-band circularly polarized light.

When an electric field is applied to the liquid crystal layer, it becomes linearly polarized light through the first 1/2 wave plate, the optical compensation plate, and the liquid crystal layer, and is reflected by the light reflecting portion. The reflected light of linearly polarized light passes through the liquid crystal layer, the optical compensation plate, and the first 1/2 wave plate again, and becomes linearly polarized light in the same polarization direction as that of the first polarizing plate, so that it is displayed in white.

When no electric field is applied to the liquid crystal layer, the first 1/2 wave plate, the optical compensation plate, and the liquid crystal layer function as 1/4 wave plates, and the circularly polarized light emitted from the liquid crystal layer becomes wide-band circularly polarized light. The circularly polarized light is reflected by the light reflecting part and becomes reflected light. The circularly polarized reflected light passes through the liquid crystal layer, the optical compensation plate and the first 1/2 wave plate again, becomes linearly polarized light orthogonal to the polarization direction of the first polarizing plate, and has a wide band of normally black tint. That is, a black level with high display quality, that is, a black display in which so-called black floating is suppressed.

Further, according to the present invention, when the refractive index of the first 1/2 wave plate in the plane orthogonal to each other is nx1 and ny1, and the refractive index in the thickness direction is nz1, nx1> The relationship of ny1 = nz1 is satisfied. Further, when the refractive index in the plane orthogonal to each other is nx2 and ny2 and the refractive index in the thickness direction is nz2, the optical compensating plate satisfies the relationship of nz2> nx2 = ny2. In the present invention, preferably, the in-plane phase difference of the first 1/2 wave plate is RD1 (= (nx1-ny1) × d1; d1 is the thickness of the first 1/2 wave plate), and the optics. When the phase difference in the thickness direction of the compensation plate is RD2 (= (nz2-nx2) × d2; d2 is the thickness of the optical compensation plate), the viewing angle is 0.3 ≦ RD2 / RD1 ≦ 0.9. The dependency can be greatly improved, and a black display of normally black with a wide viewing angle and high display quality can be realized.

Further, according to the present invention, in the liquid crystal display panel, the light incident from the counter-display surface side is transmitted through the liquid crystal layer included in the light transmitting portion. When the crossing angle between the slow axis of the 1/4 wave plate and the alignment axis of the liquid crystal molecules when no electric field is applied is approximately 90 °, the light incident from the side of the counter-display surface of the liquid crystal display panel is second. It becomes linearly polarized light by the polarizing plate. This linearly polarized light becomes circularly polarized light when it passes through the 1/4 wave plate, and this circularly polarized light becomes linearly polarized light after passing through the liquid crystal layer, the optical compensation plate, and the first 1/2 wave plate. The polarization direction of this linearly polarized light is orthogonal to the polarization direction of the first polarizing plate. As a result, it is possible to realize a so-called semi-transmissive reflection type liquid crystal display device in which linearly polarized light is not emitted from the first polarizing plate to the outside and a black display of normally black having high display quality can be obtained.

Further, according to the present invention, in the liquid crystal display panel, the light incident from the counter-display surface side is transmitted through the liquid crystal layer included in the light transmitting portion. The crossing angle between the slow axis of the 1/4 wave plate and the orientation axis of the liquid crystal molecules when no electric field is applied is 90 °, and the slow axis of the second 1/2 wave plate and the first 1/2 wavelength. When the intersection angle of the plate with the slow axis is 85 ° or more and 110 ° or less, the light incident from the side of the counter-display surface of the liquid crystal display panel is linearly polarized by the second polarizing plate. The linearly polarized light becomes circularly polarized light in a wide band when it passes through the second 1/2 wave plate and the 1/4 wave plate. This circularly polarized light becomes linearly polarized light after passing through the liquid crystal layer, the optical compensation plate, and the first 1/2 wavelength plate. The polarization direction of this linearly polarized light is orthogonal to the polarization direction of the first polarizing plate. As a result, it is possible to realize a so-called semi-transmissive reflection type liquid crystal display device in which linearly polarized light is not emitted from the first polarizing plate to the outside and a black display of normally black having high display quality can be obtained.

Further, according to the present invention, since the phase difference of the light transmitting portion when no electric field is applied is larger than the phase difference of the light reflecting portion when no electric field is applied, the phase difference between the light transmitting portion and the light reflecting portion of the liquid crystal layer is adjusted. It is possible to provide a multi-gap for this purpose, that is, a layer thickness adjusting layer of the liquid crystal layer, whereby high contrast can be realized in both the reflection display and the transmission display.

It is sectional drawing which shows the structure of the liquid crystal display device of one Embodiment of this invention. It is a figure for demonstrating the operation when the electric field is not applied and the electric field is applied of the liquid crystal display device. It is a figure which shows the shaft arrangement and the phase difference value of a liquid crystal display device. (A) is a diagram showing the relationship of each refractive index of the first 1/2 wave plate of the present invention, and (b) is a diagram showing the relationship of each refractive index of the optical compensation plate of the present invention. It is sectional drawing which shows the structure of the liquid crystal display device of another embodiment of this invention. It is a figure for demonstrating the operation when the electric field is not applied and the electric field is applied of the liquid crystal display device of another embodiment. It is a figure which shows the shaft arrangement and the phase difference value of the liquid crystal display device of another embodiment. It is a figure for demonstrating the operation when the electric field is not applied and the electric field is applied of the liquid crystal display device of another embodiment. It is a figure which shows the shaft arrangement and the phase difference value of the liquid crystal display device of another embodiment.

FIG. 1 is a cross-sectional view showing the configuration of a liquid crystal display device according to an embodiment of the present invention, and FIG. 2 is a diagram for explaining the operation of the liquid crystal display device when no electric field is applied and when an electric field is applied. Is a diagram showing the axial arrangement and the phase difference value of the liquid crystal display device, and FIG. 4 is a diagram showing the relationship between the refractive indexes of the first 1/2 wave plate and the optical compensation plate of the present invention.

The liquid crystal display device 1 of the present embodiment is a birefringence control type reflective liquid crystal display device that displays in normal black. The liquid crystal display device 1 has a liquid crystal display panel 5 having a liquid crystal layer 2 and a light reflecting layer 4 that reflects light incident from the display surface 3 side and passing through the liquid crystal layer 2, and a display of the liquid crystal display panel 5. A first 1/2 wavelength plate 7 and an optical compensation plate 8 are provided between the first polarizing plate 6 arranged on the surface 3 side and the liquid crystal display panel 5 and the first polarizing plate 6.

The phase difference of the liquid crystal layer 2 is smaller than 1/2 of the phase difference of the first 1/2 wave plate 7, and its slow phase axis intersects with the orientation axis of the liquid crystal molecules when no electric field is applied. ..

The liquid crystal display panel 5 includes a first substrate 10, a light-shielding layer 11, a color filter layer 12, a common electrode 13, a first alignment layer 14, a columnar portion 15, a liquid crystal layer 2, a second alignment layer 16, and a transparent electrode 17. , Fifth interlayer insulating layer 18, light reflecting layer 4, fourth interlayer insulating layer 19, drain electrode 20, source electrode 21, interlayer connecting portion 22, third interlayer insulating layer 23, second interlayer insulating layer 24. The first interlayer insulating layer 25, the second gate insulating layer 26, the first gate insulating layer 27, the second substrate 28, the channel portion 29, the semiconductor layer 30, and the gate electrode 31 are provided.

The drain electrode 20, the source electrode 21, the interlayer connection portion 22, the channel portion 29, the semiconductor layer 30, and the gate electrode 31 constitute a thin film transistor (TFT) as an active element. The drain electrode 20 is connected to the light reflecting layer 4 which is a pixel electrode by an interlayer connection portion 22 or the like. The gate signal line connected to the gate electrode 31 is provided for each row of pixels, and the source signal line connected to the source electrode 21 is provided for each column of pixels, and each of the gate signal line and the source signal line is provided. Pixels are formed at the intersections.

The first substrate 10 and the second substrate 28 are realized by a glass substrate. The light-shielding layer 11 constitutes a black matrix and is provided between pixels in a plan view seen from above in FIG. 1 to partition each pixel. The common electrode 13 is made of indium tin oxide (ITO) or the like, and constitutes a transparent electrode layer. The first alignment layer 14 and the second alignment layer 16 are made of polyimide or the like. The fourth interlayer insulating layer 19 is made of an acrylic resin or the like. The first to third interlayer insulating layers 25, 24, 23 and the first and second gate insulating layers 26, 27 are made of silicon oxide (SiO) or silicon nitride (SiN). The light reflecting layer 4 is made of molybdenum (Mo), aluminum (Al), or the like, and has, for example, a structure in which an Al layer is laminated on the Mo layer.

The thin film transistor has a semiconductor layer 30 made of amorphous silicon (a-Si), low-temperature poly silicon (LTPS), etc., and is a three-terminal element consisting of a gate electrode 31, a source electrode 21, and a drain electrode 20. A switching element (gate) that allows a current to flow through the semiconductor layer 30 (channel) between the source electrode 21 and the drain electrode 20 by applying a voltage of a predetermined potential (for example, 3V, 6V) to the gate electrode 31. It functions as a transfer element).

The first polarizing plate 6 is a linear polarizing plate, and is linearly polarized light that coincides with the light transmission axis (hereinafter, also referred to as the transmission axis) from randomly polarized light (elliptical polarized light) incident on the display surface 3 from the outside. Only transparent. The light transmission axis (or light absorption axis (hereinafter, also referred to as absorption axis)) of the first polarizing plate 6 and the light transmission axis (or light absorption axis) of the second polarizing plate 44 (see FIG. 4) described later. The crossing angle of is not necessarily 90 °. In the present embodiment, the crossing angle is arranged at 85 ° or more and 130 ° or less, preferably 102 °.

The liquid crystal display panel 5 is of the birefringence control (ECB) type, and in an initial orientation state in which an electric field is not applied to the liquid crystal layer 2, liquid crystal molecules are placed on each other of the first and second substrates 10, 28. The one that has been subjected to horizontal alignment treatment so as to be parallel to each of the opposing surfaces is used. When the voltage applied to the liquid crystal display panel 5 is gradually increased, the liquid crystal molecules gradually start to rise with respect to the surfaces of the first and second substrates 10 and 28 when a certain threshold voltage is exceeded. At a high voltage equal to or higher than the specified value, the orientation direction of the liquid crystal molecules becomes perpendicular to the surfaces of the substrates 10 and 28.

Since the liquid crystal is a refractive index anisotropic medium, the traveling speed differs between the light wave in the orientation axis direction (X axis) of the liquid crystal molecule and the light wave in the direction orthogonal to the orientation axis (Y axis) of the liquid crystal molecule. The refractive index of the light wave is different between the X-axis and the Y-axis. The difference between the refractive index (nx) on the X-axis and the refractive index (ny) on the Y-axis is called the birefringence Δn (= nx−ny).

The light wave incident on the liquid crystal layer 2 and emitted from it has different velocities on the X-axis and the Y-axis, so that the phase shifts on the X-axis and the Y-axis, and this phase shift is called a phase difference or retardation. Here, assuming that the wavelength of the incident light is λ, the thickness of the liquid crystal layer 2 is d, and the birefringence is Δn, the phase difference δ is expressed by the following equation (1). It is also represented by Δn · d (nm).
δ = 2π ・ Δn ・ d / λ… (1)

The inventor of the present invention is a birefringence control type, and in the normally black liquid crystal display device 1, the phase difference of the liquid crystal layer 2 is the phase difference (1/2 wavelength) of the first 1/2 wave plate 7. For example, when the wavelength is 550 nm, the phase difference of the first 1/2 wave plate 7 is about 275 nm. In the present embodiment, it is smaller than 1/2 of (270 nm in the present embodiment) (for example, 105 nm in the present embodiment). It was found that the color of normal black (degree of blackness) was good (close to pure black). Then, they have found that the tint of normally black can be improved by arranging the slow-phase axis of the first 1/2 wave plate 7 added to the liquid crystal display panel 5 in a predetermined direction.

Further, as shown in FIGS. 4A and 4B, the first 1/2 wave plate 7 has refractive indexes of nx1 and ny1 in the planes orthogonal to each other, respectively, in the thickness direction thereof. When the refractive index is nz1, it is set so as to satisfy the relationship of nx1> ny1 = nz1, and the optical compensation plate 8 has the refractive indexes in the planes orthogonal to each other nx2 and ny2, respectively, and its thickness. When the refractive index in the direction is nz2, it is set so as to satisfy the relationship of nz2> nx2 = ny2. Further, the optical compensation plate 8 preferably sets the in-plane phase difference of the first 1/2 wave plate 7 to RD1 (= (nx1-ny1) × d1; d1 is that of the first 1/2 wave plate 7. When the phase difference in the thickness direction of the optical compensation plate 8 is RD2 (= (nz2-nx2) × d2; d2 is the thickness of the optical compensation plate 8), 0.3 ≦ RD2 / RD1 ≦ 0.9. As a result, in the composite retardation plate formed by the first 1/2 wavelength plate 7 and the optical compensation plate 8, the in-plane phase difference and the thickness direction phase difference are set in a suitable range. It was found that this can greatly improve the viewing angle dependence. That is, when the value of RD2 / RD1 is less than 0.3 and the value of Nz exceeds 0.9, it tends to be difficult to improve the viewing angle dependence. More preferably, 0.3 ≦ RD2 / RD1 ≦ 0.7. For example, when RD1 is 270 nm, RD2 is preferably about 80 nm to 240 nm, more preferably about 80 nm to 190 nm. The direction of nx1 of the first 1/2 wave plate 7 is the same as the slow axis.

The present inventor prepared samples of the liquid crystal display devices of Example 1 and Comparative Example 1 in order to confirm that the visibility of the normally black was improved, and set the phase difference value of the liquid crystal layer 2 to 105 nm. As the first polarizing plate 6, a polarizing plate manufactured by Nitto Denko Corporation and having a product name of "TEG1465DUHC" was used. Further, in Example 1, as the first 1/2 wave plate 7, the one having a phase difference value of 270 nm and nx1> ny1 = nz1 of the product name “Zeonoa Film” manufactured by Nippon Zeon Corporation (nx1 = 1. 52794, ny1 = 1.52, nz1 = 1.52) was used. The optical compensating plate 8 has a thickness of 1.5 μm, a liquid crystal having Δn = 0.09 is vertically oriented, and a retardation value of 135 nm, nz2> nz2 = ny2 (nx2 = ny2 = 1.482, nz2 =). 1.572) was used. RD2 / RD1 is 0.5.

In Comparative Example 1, the optical compensation plate 8 was not used. Then, for each sample of Example 1 and Comparative Example 1, a spectrophotometer "CM-2600d" manufactured by Konica Minolta Japan Co., Ltd. was used to determine the reflectance of black display, the reflectance of white display, and the reflection contrast ratio. I measured it.

As a result of the experiment, in Example 1, the reflectance of the black display was 0.45%, the reflectance of the white display was 17.2%, and the reflection contrast ratio was 38: 1. On the other hand, in Comparative Example 1, the reflectance of black display was 0.58%, the reflectance of white display was 17.6%, and the reflection contrast ratio was 30: 1. It was confirmed that better visibility was obtained in the black display as compared with the sample of. Further, in Example 1, even when viewed from the front of the sample of the liquid crystal display device in an oblique direction (about 50 ° from the front) in the vertical and horizontal directions, the black floating is further improved as compared with Comparative Example 1, and more. Good visibility was obtained.

Further, when the phase difference of the liquid crystal layer 2 is made smaller than 1/2 of the phase difference of the first 1/2 wave plate 7, the black level with high display quality can be obtained and the visibility of the black display is improved. It was confirmed that. However, when it is smaller than 1/4 of the phase difference of the first 1/2 wave plate 7, for example, when the phase difference value of the liquid crystal layer 2 is 65 nm, the reflection contrast ratio becomes 8: 1, and the black display is visually recognized. The sex tended to decrease. Therefore, the phase difference of the liquid crystal layer 2 is preferably 1/4 or more and smaller than 1/2 of the phase difference of the first 1/2 wave plate 7. More preferably, it is 1/4 or more and 4/9 or less.

The phase difference of the liquid crystal layer 2 functions as a 1/4 wave plate. The circularly polarized light emitted from the first 1/2 wave plate 7, the optical compensation plate 8, and the liquid crystal layer 2 becomes a wide-band circularly polarized light. However, when the circularly polarized light emitted from the liquid crystal layer 2 is reflected by the light reflecting layer 4, it becomes circularly polarized light whose rotation direction is reversed.

With reference to FIGS. 2, 3 and 4, the direction orthogonal to the initial orientation direction (= rubbing direction) when the liquid crystal display panel 5 is viewed from the display surface 3 side, that is, when no electric field is applied to the liquid crystal molecules. Assuming that the reference axis (= 0 °) and the counterclockwise angle from the reference axis to each axis are angles such as the slow axis, for example, the angle θp1 of the absorption axis of the first polarizing plate 6 is 167 °. .. The angle θf1 of the slow axis of the first 1/2 wave plate 7 is 152 ° (phase difference value Δnd = 270 nm).

Further, when the refractive index of the first 1/2 wave plate 7 in the plane perpendicular to each other is nx1 and ny1, and the refractive index in the thickness direction is nz1, nx1> ny1 = nz1. The optical compensating plate 8 is set so as to satisfy the relationship, and when the refractive indexes in the planes orthogonal to each other are nx2 and ny2, respectively, and the refractive index in the thickness direction is nz2, nz2> nx2 = It is set to satisfy the relationship of ny2. Further, preferably, it is set in the range of 0.3 ≦ RD2 / RD1 ≦ 0.9. As a result, black floating when viewed from the front of the liquid crystal display panel 5 in an oblique direction (about 50 ° from the front) is controlled, and a black display with a wide viewing angle and a high display quality can be obtained. , The viewing angle dependence in normal black can be improved.

Since the liquid crystal layer 2 of the liquid crystal display panel 5 is rubbed in the vertical direction, the liquid crystal molecules are oriented in the vertical direction. When the liquid crystal display panel 5 is tilted upward or downward from the front, the Δn of the liquid crystal becomes smaller and the phase difference of the liquid crystal layer 2 becomes smaller. On the other hand, when the liquid crystal 2 is tilted to the left or right from the front, the Δn of the liquid crystal 2 does not change, the thickness of the liquid crystal layer 2 becomes large, and the phase difference of the liquid crystal layer 2 becomes large.

When only the first 1/2 wave plate 7 satisfying the relationship of nx1> ny1 = nz1 is used without using the optical compensation plate 8, the liquid crystal display panel intersects the orientation axis of the liquid crystal layer 2. When 5 is tilted upward or downward from the front surface, the phase difference of the first 1/2 wave plate 7 becomes large. When tilted to the left or right from the front, the phase difference of the first 1/2 wave plate 7 becomes smaller.

In this case, the phase difference of the liquid crystal layer 2 needs to be smaller than 1/2 of the phase difference of the first 1/2 wave plate 7, and preferably the position of the first 1/2 wave plate 7. It is preferable that the phase difference is 1/4 or more and smaller than 1/2, but there is a difference between the angle dependence of the phase difference of the liquid crystal layer 2 and the angle dependence of the phase difference of the first 1/2 wave plate 7. Depending on the tilt angle from the front, the phase difference of the liquid crystal layer 2 becomes 1/2 or more or smaller than 1/4 of the phase difference of the first 1/2 wave plate 7, so that black floating occurs. The viewing angle dependence becomes large, and the visibility is lowered.

The liquid crystal display device of the present invention preferably uses the optical compensation plate 8 set in the range of 0.3 ≦ RD2 / RD1 ≦ 0.9, so that the liquid crystal layer can be changed depending on the tilt angle from the front. The phase difference of 2 is 1/4 or more and smaller than 1/2 of the phase difference of the first 1/2 wave plate 7. As a result, it is possible to control black floating in a direction tilted from the front, obtain a black display with a wide viewing angle and a high display quality, and improve the viewing angle dependence in normal black.

The slow-phase axis of the first 1/2 wave plate 7 and the orientation axis of the liquid crystal molecules when no electric field is applied intersect at an intersection angle α1. The intersection angle α1 between the slow axis of the first 1/2 wave plate 7 and the orientation axis of the liquid crystal molecules when no electric field is applied is preferably 52 ° or more and 72 ° or less, more preferably 62 °. Be placed. As a result, a black display with a high display quality and a black level can be obtained, and the color tone (degree of blackness) of normal black can be improved.

Next, the display of the liquid crystal display device 1 will be described with reference to FIG. 2. The light a1 of randomly polarized light (elliptical polarized light) incident on the display surface 3 side of the liquid crystal display device 1 from the outside is the first polarizing plate 6. It becomes linearly polarized light (referred to as linearly polarized light a2). When the linearly polarized light a2 passes through the first 1/2 wave plate 7, the optical compensation plate 8, and the liquid crystal layer 2, it becomes wide-band circularly polarized light (referred to as circularly polarized light a3).

When an electric field is applied to the liquid crystal layer 2, the phase difference of the liquid crystal layer 2 becomes 0, so that the linearly polarized light a4 is obtained through the first 1/2 wave plate 7, the optical compensation plate 8, and the liquid crystal layer 2. It is reflected by the light reflecting layer 4. The reflected light b3 of the linearly polarized light a4 passes through the liquid crystal layer 2, the optical compensation plate 8 and the first 1/2 wave plate 7 again, and becomes linearly polarized light b4 which is the same as the polarization direction of the first polarizing plate 6. It is displayed in white.

Further, in a state where an electric field is not applied to the liquid crystal layer 2, it passes through the liquid crystal layer 2 and becomes a wide-band circularly polarized light a3, and is reflected by the light reflecting layer 4 as the wide-band circularly polarized light a3 to become reflected light b1. The circularly polarized reflected light b1 passes through the liquid crystal layer 2, the optical compensation plate 8 and the first 1/2 wave plate 7 again, becomes linearly polarized light b2 orthogonal to the polarization direction of the first polarizing plate 6, and becomes normal. It is possible to obtain a black tint, that is, a black level having a high display quality, that is, a black display in which so-called black floating is suppressed.

FIG. 5 is a cross-sectional view showing a liquid crystal display device according to another embodiment of the present invention, FIG. 6 is a view for explaining the operation of the liquid crystal display device when no electric field is applied and when an electric field is applied, and FIG. 7 is a diagram for explaining the operation of the liquid crystal display device. It is a figure which shows the shaft arrangement of a liquid crystal display device. The same reference numerals are given to the parts corresponding to the above-described embodiments, and duplicate description will be omitted.

The liquid crystal display device 1a of the present embodiment is arranged between the second polarizing plate 44 arranged on the counter-display surface 43 side of the liquid crystal display panel 5 and the liquid crystal display panel 5 and the second polarizing plate 44. A 1/4 wavelength plate 45 and a second 1/2 wavelength plate 50 are further provided, and a light transmitting portion 46 that transmits light incident from the side of the counter-display surface 43 of the liquid crystal display panel 5 includes the liquid crystal layer 2. It is provided and is realized as a so-called semi-transmissive type liquid crystal display device 1a (which includes both a light reflecting portion and a light transmitting portion). Basically, the backlight device is not required on the counter-display surface 43 side, but it may be present.

Since the slow-phase axis of the 1/4 wave plate 45 and the orientation axis of the liquid crystal molecules when no electric field is applied are orthogonal to each other, the phase difference can be canceled out. In this way, between the liquid crystal display panel 5 and the second polarizing plate 44, a 1/4 wave plate 45 and a second 1/2 wavelength plate 50 are provided in this order from the side of the liquid crystal display panel 5. Further, the slow axis of the second 1/2 wave plate 50 and the slow axis of the first 1/2 wave plate 7 intersect at an intersection angle of 85 ° or more and 110 ° or less.

Next, the display of the liquid crystal display device 1a will be described with reference to FIG. 6. In the liquid crystal display panel 5, the liquid crystal layer 2 is included in the light transmitting portion 46 that transmits the light incident from the counter-display surface 43 side, and the light is emitted. Since it is transmitted through the liquid crystal layer 2, in a state where an electric field is not applied to the liquid crystal layer 2, the light incident from the side of the counter-display surface 43 of the liquid crystal display panel 5 becomes linearly polarized light c1 by the second polarizing plate 44. .. When the linearly polarized light c1 passes through the second 1/2 wave plate 50 and the 1/4 wave plate 45, it becomes a wide-band circularly polarized light c2. The wide-band circularly polarized light c2 becomes linearly polarized light c3 after passing through the liquid crystal layer 2, the optical compensation plate 8, and the first 1/2 wave plate 7. The polarization direction of the linearly polarized light c3 is orthogonal to the polarization direction of the first polarizing plate 6. As a result, it is possible to realize a so-called semi-transmissive liquid crystal display device in which the linearly polarized light c3 does not emit to the outside from the first polarizing plate 6 and a black display of normally black having high display quality can be obtained.

Further, in a state where an electric field is applied to the liquid crystal layer 2, the incident light from the counter-display surface 43 side passes through the second polarizing plate 44 and becomes linearly polarized light d1. The light of the linearly polarized light d1 becomes a wide-band circularly polarized light d2 by the second 1/2 wave plate 50 and the 1/4 wave plate 45. The wide-band circularly polarized light d2 passes through the liquid crystal layer 2, the optical compensation plate 8 and the first 1/2 wave plate 7 to become elliptically polarized light d3, and the elliptically polarized light d3 is light in the polarization direction of the first polarizing plate 6. Only passes and becomes white.

With reference to FIGS. 6 and 7, the reference axis (= rubbing direction) is the direction orthogonal to the initial orientation direction (= rubbing direction) when the liquid crystal display panel 5 is viewed from the display surface 3 side, that is, when no electric field is applied to the liquid crystal molecules. = 0 °), and the counterclockwise angle from the reference axis to each axis is an angle such as a slow axis, the angle θp1 of the absorption axis of the first polarizing plate 6 is 167 °. The angle θf1 of the slow axis of the first 1/2 wave plate 7 is 152 ° (phase difference value Δnd = 270 nm). The angle θf2 of the slow axis of the 1/4 wave plate 45 is 0 ° (phase difference value Δnd = 140 nm), and the angle θf3 of the slow axis of the second 1/2 wave plate 50 is 56 ° (phase difference value). Δnd = 270 nm), and the angle θp2 of the absorption axis of the second polarizing plate 44 is 65 °. The 1/4 wave plate 45 is manufactured by Nippon Zeon Co., Ltd. and has a product name of "Zeonoa film". The refractive index in the in-plane direction orthogonal to each other is nx3, ny3, and the refractive index in the thickness direction is nz3. In this case, the one in which nx3> ny3 = nz3 (nx = 1.52424, ny = 1.52, nz = 1.52) was used. The second 1/2 wave plate 50 is manufactured by Nippon Zeon Co., Ltd. and has a product name of "Zeonor film". The refractive index in the in-plane direction orthogonal to each other is nx4, ny4, and the refractive index in the thickness direction is set. When nz4 was used, the one having nz4> ny4 = nz4 (nx = 1.52794, ny = 1.52, nz = 1.52) was used. For the second polarizing plate 44, a product name "TEG1465DUHC" manufactured by Nitto Denko KK was used.

The crossing angle between the slow axis of the first 1/2 wave plate 7 and the orientation axis of the liquid crystal molecules when no electric field is applied is preferably selected to be 52 ° or more and 72 ° or less, and more preferably 62 °. Is done. The crossing angle between the orientation axis of the liquid crystal molecules and the slow axis of the 1/4 wave plate 45 when no electric field is applied is 90 °, and the slow axis of the second 1/2 wave plate 50 and the first 1/1 /. The crossing angle (θf3-θf1) of the two-wave plate 7 with the slow axis is preferably selected to be 85 ° or more and 110 ° or less, more preferably 96 °. Further, the intersection angle (θp1-θp2) between the absorption axis of the first polarizing plate 6 and the absorption axis of the second polarizing plate 44 is preferably selected to be 85 ° or more and 130 ° or less, more preferably 102 °.

As a result, it is possible to realize a black display of normally black having a high black level display quality.

Further, the phase difference of the light transmitting portion 46 is made larger than the phase difference of the light reflecting portion 47, and the light transmitting portion 46 and the light reflecting portion 47 of the liquid crystal layer 2 are made into a multi-gap, that is, the layer thickness of the liquid crystal layer 2. An adjusting layer can be provided. As a result, high contrast can be realized in both the reflection display and the transmission display.

FIG. 8 is a diagram for explaining the operation of the liquid crystal display device of another embodiment when no electric field is applied and when an electric field is applied, and FIG. 9 is a diagram showing the shaft arrangement of the liquid crystal display device.

A second polarizing plate 44 arranged on the opposite side of the liquid crystal display panel 5 and a 1/4 wavelength plate 45 arranged between the liquid crystal display panel 5 and the second polarizing plate 44 are further provided. A liquid crystal layer 2 is included in a light transmitting portion that transmits light incident from the counter-display surface side of the liquid crystal display panel 5, and is a so-called semi-transmissive type (providing both a light reflecting portion and a light transmitting portion) liquid crystal. It is realized as a display device. Basically, the backlight device is not required on the counter-display surface side, but it may be present.

Since the slow-phase axis of the 1/4 wave plate 45 and the orientation axis of the liquid crystal molecules when no electric field is applied are substantially orthogonal to each other, the phase difference can be canceled out. In this way, a 1/4 wave plate 45 is provided between the liquid crystal display panel 5 and the second polarizing plate 44.

In a state where an electric field is not applied to the liquid crystal layer 2, the light incident from the counter-display surface side of the liquid crystal display panel 5 becomes linearly polarized light e1 by the second polarizing plate 44, and the linearly polarized light e1 is 1. When it passes through the / 4 wave plate 45, it becomes circularly polarized light e2. The circularly polarized light e2 becomes linearly polarized light e3 after passing through the liquid crystal layer 2, the optical compensation plate 8, and the first 1/2 wavelength plate 7. The polarization direction of the linearly polarized light e3 is orthogonal to the polarization direction of the first polarizing plate 6. As a result, it is possible to realize a so-called semi-transmissive liquid crystal display device in which the linearly polarized light e3 does not emit to the outside from the first polarizing plate 6 and a black display of normally black having high display quality can be obtained.

Further, in a state where an electric field is applied to the liquid crystal layer 2, the incident light from the counter-display surface side passes through the second polarizing plate 44 and becomes linearly polarized light g1. The light of the linearly polarized light g1 becomes circularly polarized light g2 by the quarter wave plate 45. The circularly polarized light g2 passes through the liquid crystal layer 2, the optical compensation plate 8 and the first 1/2 wave plate 7 to become elliptically polarized light g3, and the elliptically polarized light g3 is only the light in the polarization direction of the first polarizing plate 6. After passing through, it becomes white.

With reference to FIGS. 8 and 9, the reference axis (=) is the direction orthogonal to the initial orientation direction (= rubbing direction) when the liquid crystal display panel 5 is viewed from the display surface side, that is, when no electric field is applied to the liquid crystal molecules. 0 °), and if the counterclockwise angle from the reference axis to each axis is an angle such as a slow axis, the angle θp1 of the absorption axis of the first polarizing plate 6 is 167 °. The angle θf1 of the slow axis of the first 1/2 wave plate 7 is 152 ° (phase difference value Δnd = 270 nm). The angle θf2 of the slow axis of the 1/4 wave plate 45 is 1 ° (phase difference value Δnd = 140 nm), and the angle θp2 of the absorption axis of the second polarizing plate 44 is 46 °. The 1/4 wave plate 45 is manufactured by Nippon Zeon Co., Ltd. and has a product name of "Zeonoa film". The refractive index in the in-plane direction orthogonal to each other is nx5, ny5, and the refractive index in the thickness direction is nz5. In this case, the one in which nx5> ny5 = nz5 is used (nx = 1.52244, ny = 1.52, nz = 1.52), and the second polarizing plate 44 is manufactured by Nitto Denko Co., Ltd. and has a product name. "TEG1465 DUHC" was used.

The crossing angle between the slow axis of the first 1/2 wave plate 7 and the orientation axis of the liquid crystal molecules when no electric field is applied is preferably selected to be 52 ° or more and 72 ° or less, and more preferably 62 °. Is done. The crossing angle between the orientation axis of the liquid crystal molecules and the slow axis of the 1/4 wave plate 45 when no electric field is applied is selected to be 91 °. This intersection angle is selected within the range of about 90 ° ± 3 °, more preferably within the range of about 90 ° ± 1 °. Further, the intersection angle (θp1-θp2) between the absorption axis of the first polarizing plate 6 and the absorption axis of the second polarizing plate 44 is preferably selected to be 85 ° or more and 130 ° or less, more preferably 121 °.

As a result, it is possible to realize a black display of normally black having a high black level display quality.

1,1a Liquid crystal display device 2 Liquid crystal layer 3 Display surface 4 Light reflection layer 5 Liquid crystal display panel 6 First polarizing plate 7 First 1/2 wave plate 8 Optical compensation plate 10 First substrate 11 Light-shielding layer 12 Color filter Layer 13 Common electrode 14 First alignment layer 15 Columnar part 16 Second alignment layer 17 Transparent electrode 18 Fifth interlayer insulation layer 19 Fourth interlayer insulation layer 20 Drain electrode 21 Source electrode 22 Interlayer connection part 23 Third Interlayer insulation layer 24 Second interlayer insulation layer 25 First interlayer insulation layer 26 Second gate insulation layer 27 First gate insulation layer 28 Second substrate 29 Channel portion 30 Semiconductor layer 31 Gate electrode 43 Non-display surface 44 Second polarizing plate 45 1/4 wave plate 46 Light transmitting part 47 Light reflecting part 50 Second 1/2 wave plate

Claims (5)

It is a birefringence control type liquid crystal display device that displays in normal black.
A liquid crystal display panel having a liquid crystal layer and a light reflecting portion that reflects light incident from the display surface side and passing through the liquid crystal layer.
A first polarizing plate arranged on the display surface side of the liquid crystal display panel,
A first 1/2 wavelength plate and an optical compensation plate, which are provided in order from the side of the first polarizing plate, are provided between the liquid crystal display panel and the first polarizing plate.
The liquid crystal layer has a phase difference when no electric field is applied, which is smaller than 1/2 of the phase difference of the first 1/2 wave plate.
The slow phase axis of the first 1/2 wave plate intersects the orientation axis of the liquid crystal molecules when no electric field is applied, and the refractive indexes in the planes orthogonal to each other are set to nx1 and ny1, respectively. When the refractive index in the thickness direction is nz1, the relationship of nx1> ny1 = nz1 is satisfied.
When the refractive index in the plane orthogonal to each other is nx2 and ny2 and the refractive index in the thickness direction is nz2, the liquid crystal display satisfies the relationship of nz2> nx2 = ny2. apparatus. Claim 1 is 0.3 ≦ RD2 / RD1 ≦ 0.9 when the in-plane phase difference of the first 1/2 wave plate is RD1 and the phase difference in the thickness direction of the optical compensation plate is RD2. The liquid crystal display device described in 1. The liquid crystal display panel has a light transmitting portion that allows light incident from the counter-display surface side to pass through the liquid crystal layer.
A second polarizing plate arranged on the counter-display surface side of the liquid crystal display panel,
A 1/4 wave plate provided between the liquid crystal display panel and the second polarizing plate is further provided.
The liquid crystal display device according to claim 1 or 2, wherein the slow phase axis of the 1/4 wave plate and the orientation axis of the liquid crystal molecules when no electric field is applied intersect at approximately 90 °. A second 1/2 wave plate provided between the 1/4 wave plate and the second polarizing plate is provided.
The slow axis of the 1/4 wave plate and the orientation axis of the liquid crystal molecules when no electric field is applied intersect at 90 °.
The liquid crystal display device according to claim 3, wherein the slow axis of the second 1/2 wave plate and the slow axis of the first 1/2 wave plate intersect at 85 ° or more and 110 ° or less. The liquid crystal display device according to claim 3 or 4, wherein the phase difference of the light transmitting portion when no electric field is applied is larger than the phase difference of the light reflecting portion when no electric field is applied.

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