JP6878265B2 - 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.

A conventional technique for solving such a problem is described in, for example, Patent Document 1. A transmission display area and a reflection display area are provided in the same display surface, a step structure is provided between the portion corresponding to the transmission display area and the portion corresponding to the reflection display area, and the dielectric anisotropy of the liquid crystal material is 10. A semi-transmissive liquid crystal display element having a retardation value of ~ 15 and a retardation value of the liquid crystal layer in the transmission display region of 170 to 300 nm has been proposed.

Further, in Patent Document 2, a first polarizing plate, a liquid crystal display panel, a first retardation plate, and a second polarizing plate are arranged from the backlight side, and the absorption axis of the first polarizing plate and the absorption of the second polarizing plate are arranged. The axes are orthogonal, the orientation direction of the liquid crystal molecules in the liquid crystal layer of the liquid crystal display panel is orthogonal to the slow axis of the first retardation plate, and the first retardation plate has biaxial double-polarizing anisotropy. However, a liquid crystal display device having a retardation equivalent to that of the liquid crystal layer when no electric field is applied has been proposed.

Japanese Unexamined Patent Publication No. 2009-36803 Japanese Unexamined Patent Publication No. 2010-32787

According to the prior art described in Patent Document 1, the dielectric anisotropy of a liquid crystal material is 10 to 15 in a birefringence control (abbreviated as ECB) type transflective liquid crystal display element. Since the retardation value of the liquid crystal layer in the transmissive display region is 170 to 300 nm and the retardation value in the reflective display region is 140 nm to 170 to 180 nm, light leakage caused by the step portion between the transmissive display portion and the reflective display portion is prevented. We propose a normally white transflective liquid crystal display element that can be prevented, the setting margin of black display conditions can be expanded, and has high contrast. However, there is no description about a configuration in which both the reflection region and the transmission region are normally black and a configuration in which the viewing angle is improved.

Further, in the prior art described in Patent Document 2 above, in the same double-refractive-index (ECB) type liquid crystal display device, the absorption axis of the first polarizing plate and the absorption axis of the second polarizing plate are orthogonal to each other. The orientation direction of the liquid crystal molecules in the liquid crystal layer of the liquid crystal display panel is orthogonal to the slow axis of the first retardation plate, and the first retardation plate has biaxial compound refractive anisotropy, and when no electric field is applied. We have proposed a semi-transmissive liquid crystal display device that can expand the viewing angle not only in the transmission display in the transmission part but also in the reflection display in the reflection part by having the same retardation as the retardation of the liquid crystal layer of. However, there is no description about the arrangement configuration of the reflecting portion, the operating principle of the liquid crystal display device when no electric field is applied and when the electric field is applied at the reflecting portion, and the configuration in which the reflecting portion becomes normally black. That is, according to the configuration of Patent Document 2, it is considered that the operation is as follows. Light incident on the liquid crystal layer from the second polarizing plate side when no electric field is applied passes through the second polarizing plate and becomes linearly polarized light. In this linearly polarized light, the slow axis of the first retardation plate having the same retardation and the orientation direction of the liquid crystal molecules of the liquid crystal layer are orthogonal to each other, and the retardation of the first retardation plate and the retardation of the liquid crystal layer are cancelled. In addition, it passes through the first retardation plate and the liquid crystal layer with linearly polarized light. Assuming that there is a reflecting portion near the liquid crystal layer, the linearly polarized light reflected by the reflecting portion passes through the liquid crystal layer and the first retardation plate as linearly polarized light, and is the same as the polarization direction of the second polarizing plate. Therefore, the light passes through and becomes a white display, that is, normally white. When the reflecting portion is between the first polarizing plate and the backlight, the operating principle of the transmitting portion is the same, and when no electric field is applied to the liquid crystal layer, a black display, that is, normally black is displayed.

In a birefringence-controlled liquid crystal display device, liquid crystal molecules are parallel to the surface of the substrate in a state where no electric field is 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 value is obtained. When the electric field is exceeded, 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 a birefringence-controlled liquid crystal display device in which a light reflecting portion is arranged near a liquid crystal layer and both the light reflecting portion and the light transmitting portion are displayed in normal black. The purpose of the present invention is to provide a liquid crystal display device capable of achieving a level, suppressing black floating, and further improving a viewing angle.

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, and is a light reflection that reflects light incident from the liquid crystal layer and the liquid crystal layer that has passed through the liquid crystal layer. A liquid crystal display panel having a portion, a light transmitting portion for transmitting light incident from the counter-display surface side to the liquid crystal layer, and a first polarizing plate arranged on the display surface side of the liquid crystal display panel. A first 1/2 wavelength plate provided between the liquid crystal display panel and the first polarizing plate, a second polarizing plate arranged on the counter-display surface side of the liquid crystal display panel, and the liquid crystal. A second 1/2 wavelength plate provided between the display panel and the second polarizing plate is provided, and a portion of the liquid crystal layer corresponding to the light reflecting portion has a phase difference of the first. The phase difference of the part corresponding to the light transmitting portion in the liquid crystal layer is set in the range of 1/4 or more and 4/9 or less of the phase difference of the 1/2 wavelength plate of 1. The phase difference is set to be equal to or less than the phase difference of the / 2 wavelength plate, and each of the first 1/2 wavelength plate and the second 1/2 wavelength plate is a liquid crystal when its slow axis is no electric field applied. It intersects the alignment axis of the molecule, and in the first polarizing plate and the second polarizing plate, their absorption axes intersect with each other and intersect with the alignment axis of the liquid crystal molecule when no electric field is applied. The first 1/2 wavelength plate and the second 1/2 wavelength plate have a configuration in which their slow axes intersect with each other.

In the liquid crystal display device of the present invention, preferably, the phase difference of the portion of the liquid crystal layer corresponding to the light transmitting portion is in the range of 7/9 or more and 1 times or less the phase difference of the first 1/2 wave plate. Is set to.

Further, in the liquid crystal display device of the present invention, preferably, the first 1/2 wave plate has a refractive index of nx1 and ny1 in the plane orthogonal to each other and a refractive index of nz1 in the thickness direction thereof. The second 1/2 wave plate has nx1>nz1> ny1 and nx2 when the refractive indexes in the planes orthogonal to each other are nx2 and ny2 and the refractive index in the thickness direction is nz2, respectively. The relationship of>nz2> ny2 is satisfied .

Further, in the liquid crystal display device of the present invention, preferably, the relationship of nx1, ny1, nz1 in the first 1/2 wave plate is represented by Nz1 = (nx1-nz1) / (nx1-ny1), and the second When the relationship of nx2, ny2, nz2 in the 1/2 wave plate is expressed by Nz2 = (nx2-nz2) / (nx2-ny2), Nz1 and Nz2 are set in the range of more than 0 and 0.7 or less, respectively. ing.

Further, in the liquid crystal display device of the present invention, preferably, the slow phase axis of the first 1/2 wave plate and the orientation axis of the liquid crystal molecules when no electric field is applied are at an intersection angle of 50 ° or more and 75 ° or less. It intersects .

Further, in the liquid crystal display device of the present invention, preferably, the slow phase axis of the second 1/2 wave plate and the orientation axis of the liquid crystal molecules when no electric field is applied are at an intersection angle of 65 ° or more and 90 ° or less. It intersects.

Further, in the liquid crystal display device of the present invention, preferably, the light reflecting portion includes a light-shielding layer and a columnar portion overlapping the light-transmitting portion and in the liquid crystal layer at an end portion on the side of the light transmitting portion .

According to the present invention, the birefringence control type liquid crystal display device that displays in normal black operates as follows. In the light reflection mode, which is the operation mode of the liquid crystal layer of the light reflection part, the phase difference of the liquid crystal layer of the light reflection part (the part corresponding to the light reflection part in the liquid crystal layer) is approximately 1/4 wave plate when no electric field is applied. Function. Therefore, the circularly polarized light emitted from the first 1/2 wave plate and the liquid crystal layer becomes a wide band circularly polarized light.

When an electric field is applied to the liquid crystal layer of the light reflecting portion, it becomes linearly polarized light through the first 1/2 wave 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 of the light reflecting portion 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.

No electric field is applied to the liquid crystal layer of the light reflecting part When no electric field is applied, the first 1/2 wave plate and the liquid crystal layer function as approximately 1/4 wave plates, and the circularly polarized light emitted from the liquid crystal layer of the light reflecting part is , Wide-band circularly polarized light is obtained, and the circularly polarized light is reflected by the light reflecting portion to become reflected light. The circularly polarized reflected light passes through the liquid crystal layer of the light reflecting portion and the first 1/2 wavelength 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, in the light transmission mode, which is the operation mode of the liquid crystal layer of the light transmitting portion, the light incident from the side opposite to the display surface with respect to the liquid crystal display panel is the light incident on the liquid crystal layer of the light transmitting portion (in the liquid crystal layer). The part corresponding to the light transmitting part) is transmitted. The slow axis of the second 1/2 wave plate intersects the alignment axis of the liquid crystal molecules when no electric field is applied, and the alignment axis of the liquid crystal molecules when no electric field is applied and the slow phase of the first 1/2 wave plate. When the axes intersect and the intersection angle between the slow axis of the second 1/2 wave plate and the slow axis of the first 1/2 wave plate is 30 ° or more and 50 ° or less, the liquid crystal display is displayed. The light incident from the side of the counter-display surface of the panel is linearly polarized by the second polarizing plate, and this linear polarization is the phase difference of the second 1/2 wave plate and the position of the liquid crystal layer of the light transmitting portion. After passing through the second 1/2 wave plate, the liquid crystal layer of the light transmitting portion, and the first 1/2 wave plate in order to cancel the phase difference and the phase difference of the first 1/2 wave plate. , Linear polarization. The polarization direction of this linearly polarized light is orthogonal to the polarization direction of the first polarizing plate. As a result, when no electric field is applied, the linearly polarized light orthogonal to the polarization direction of the first polarizing plate is not emitted to the outside from the first polarizing plate, and a black display of normally black with high display quality can be obtained, so-called. A semi-transmissive reflection type liquid crystal display device can be realized.

According to the present invention, the phase difference between the portion corresponding to the light reflection portion in a liquid crystal layer is set to 1/4 or more 4/9 or less of the range of the phase difference between the first half-wave plate, It is possible to improve the viewing angle dependence and realize a black display of normal black with a wide viewing angle and high display quality.

Further, according to the present invention, when the phase difference of the portion corresponding to the light transmitting portion in the liquid crystal layer is set in the range of 7/9 or more and 1 times or less the phase difference of the first 1/2 wave plate. Can achieve a black level with high display quality even when light is transmitted (light transmission mode), and the visibility of black display is improved.

Further, according to the present invention, the first 1/2 wave plate has a refractive index of nx1 and ny1 in the plane perpendicular to each other and a refractive index of nz1 in the thickness direction thereof, respectively, and the second one The / 2 wave plate has a relationship of nx1> nz1> ny1 and nx2> nz2> ny2 when the refractive indexes in the planes orthogonal to each other are nx2 and ny2 and the refractive index in the thickness direction is nz2. When it is satisfied, the viewing angle dependence can be 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, the relationship of nx1, ny1, nz1 in the first 1/2 wave plate is represented by Nz1 = (nx1-nz1) / (nx1-ny1), and nx2 in the second 1/2 wave plate. When the relationship between, ny2 and nz2 is expressed by Nz2 = (nx2-nz2) / (nx2-ny2), Nz1 and Nz2 are further set in the range of more than 0 and 0.7 or less, respectively. It is possible to improve the viewing angle dependence and realize a black display of normal black with a wide viewing angle and high display quality.

Further, according to the present invention, when the intersection angle between the slow phase axis of the first 1/2 wave plate and the orientation axis of the liquid crystal molecules when no electric field is applied is 50 ° or more and 75 ° or less, it is further displayed. It is possible to realize a high-quality normal black black display.

Further, according to the present invention, when the intersection angle between the slow phase axis of the second 1/2 wave plate and the orientation axis of the liquid crystal molecules when no electric field is applied is 65 ° or more and 90 ° or less, it is further displayed. It is possible to realize a high-quality normal black black 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 light transmission part of the liquid crystal display device. It is a figure which shows the shaft arrangement and the phase difference value of the light transmission part of a liquid crystal display device. It is a figure for demonstrating the operation when the electric field is not applied and the electric field is applied of the light reflection part of the liquid crystal display device. It is a figure which shows the shaft arrangement and the phase difference value of the light reflection part of a liquid crystal display device. It is a figure which shows the relationship of each refractive index of the 1st and 2nd 1/2 wave plates used in the liquid crystal display device of another embodiment of this invention.

FIG. 1 is a cross-sectional view showing the configuration of the liquid crystal display device according to the embodiment of the present invention, and FIG. 2 is a diagram for explaining the operation of the light transmitting portion of the liquid crystal display device when no electric field is applied and when an electric field is applied. Yes, FIG. 3 is a diagram showing the axial arrangement and the phase difference value of the light transmitting portion of the liquid crystal display device.

The liquid crystal display device 1 of the present embodiment is a birefringence control type semi-transmissive reflection type liquid crystal display device that displays in normal black. The liquid crystal display device 1 has a liquid crystal layer 32 of a light reflecting portion, and also has a light reflecting layer 4 that reflects light incident from the display surface 3 side and passing through the liquid crystal layer 32 of the light reflecting portion. A first 1/2 wavelength plate 7 is provided between the first polarizing plate 6 arranged on the display surface 3 side of the liquid crystal display panel 5 and the liquid crystal display panel 5 and the first polarizing plate 6. .. The phase difference of the liquid crystal layer 32 of the light reflecting portion is smaller than 1/2 of the phase difference of the first 1/2 wave plate 7, and the slow axis of the first 1/2 wave plate 7 is an electric field. It intersects the orientation axis of the liquid crystal molecules when no application is applied.

Further, the liquid crystal display device 1 has a liquid crystal layer 2 of a light transmitting portion, and also has a liquid crystal display panel 5 and a liquid crystal display panel 5 that allow light incident from the counter-display surface 43 side to pass through the liquid crystal layer 2 of the light transmitting portion. A second 1/2 wavelength plate 50 is provided between the second polarizing plate 44 arranged on the counter-display surface 43 side of the liquid crystal display panel 5 and the second polarizing plate 44. The phase difference of the liquid crystal layer 2 of the light transmitting portion is equal to or less than, preferably equal to, the phase difference of the first 1/2 wave plate 7 and the same phase difference of the second 1/2 wave plate 50. Or set slightly smaller. The phase difference between the first 1/2 wave plate 7 and the second 1/2 wave plate 50 do not have to be completely equal, and are displaced within a certain range (within a range of about ± 10 nm). May be.

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 (abbreviated as 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 (abbreviated as 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 ₂ ) or silicon nitride (SiN _x ). 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 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 that allows a current to flow through the semiconductor layer 30 (channel portion 29) 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. Functions as a (gate 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 intersection angle between 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 is not necessarily 90 °. It does not have to be. In the present embodiment, the crossing angle is arranged at 85 ° or more and 120 ° or less, preferably 102 °.

The liquid crystal display panel 5 is of the birefringence control (Electrically Controlled Birefringence; abbreviated as ECB) type, and has a liquid crystal layer 32 (a portion of the liquid crystal layer corresponding to the light reflecting portion) and a liquid crystal layer 2 (liquid crystal) of the light transmitting portion. Horizontal alignment processing so that the liquid crystal molecules are parallel to the opposing surfaces of the first and second substrates 10 and 28 in the initial orientation state in which an electric field is not applied to the portion of the layer corresponding to the light transmitting portion). Use the one with. 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).

Since the light waves incident on the liquid crystal layer 32 of the light reflecting portion and emitted from them have different velocities on the X-axis and the Y-axis, the phases are out of phase on the X-axis and the Y-axis. That is. Here, assuming that the wavelength of the incident light is λ, the thickness of the liquid crystal layer 32 of the light reflecting portion 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 32 of the light reflecting portion is the phase difference (1/2) of the first 1/2 wavelength plate 7. Wavelength. 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 the case (270 nm in the present embodiment) (for example, the present embodiment). It was found that the color of normally black (degree of blackness) was good (close to pure black) at 105 nm in the form. 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, the present inventor has a phase difference between the first and second 1/2 wave plates 7, 50 (1/2 wavelength, for example, a wavelength of 550 nm) of the liquid crystal layer 2 of the light transmitting portion. In this case, the phase difference of the first 1/2 wave plate 7 is about 275 nm. In this embodiment, it is set to be equal to or less than, preferably equal to or slightly smaller than 270 nm), and is added to the liquid crystal display panel 5. It has been found that a high contrast ratio can be obtained even at the time of transmission by arranging the slow axes of the second 1/2 wave plates 7 and 50 in a predetermined direction.

The present inventor prepared a sample of the liquid crystal display device of Example 1 in order to confirm that the visibility of the normally black is improved in the light reflection mode and the light transmission mode. Hereinafter, Example 1 will be described.

With reference to FIGS. 1, 3 and 5, the direction when the liquid crystal display panel 5 is viewed from the display surface 3 side, that is, the direction orthogonal to the initial orientation direction (= rubbing direction) when no electric field is applied to the liquid crystal molecules is used as a reference. Assuming that the axis (= 0 °) and the counterclockwise angle from the reference axis to each axis are angles such as the 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 second 1/2 wavelength plate 50 is 10 ° (phase difference value Δnd = 270 nm), and the angle θp2 of the absorption axis of the second polarizing plate 44 is 65 °.

As the first 1/2 wave plate 7 and the second 1/2 wave plate 50, a product name "Zeonoa film" manufactured by Nippon Zeon Corporation was used. For nx1, ny1, nz1, nz2, ny2, nz2, nx1 = nz2, ny1 = ny2, nz1 = nz2, nx1> ny1 = nz1, Nz1 = Nz2 = 1.0, nx1 = 1.52794, ny1 = 1.52 , Nz1 = 1.52.

As the first polarizing plate 6 and the second polarizing plate 44, a product name "TEG1465DUHC" manufactured by Nitto Denko KK was used. Further, the phase difference value of the liquid crystal layer 32 of the light reflecting portion was set to 105 nm, and the phase difference value of the liquid crystal layer 2 of the light transmitting portion was set to 260 nm. Then, for this sample, the reflectance of black display, the reflectance of white display, and the reflection contrast ratio were measured using a spectrocolorimeter "CM-2600d" manufactured by Konica Minolta Japan Co., Ltd., and Topcon Techno House Co., Ltd. The transmission contrast ratio was measured using a color luminance meter "BM-5AS" manufactured by Japan.

As a result of the experiment, in Example 1, the reflectance of the black display was 0.35%, the reflectance of the white display was 14.0%, the reflection contrast ratio was 40: 1, and the transmission contrast ratio was 180: 1. It was confirmed that good visibility can be obtained with the black display of normal black in both the reflection mode and the light transmission mode.

Further, when the phase difference of the liquid crystal layer 32 of the light reflecting portion is made smaller than 1/2 of the phase difference of the first 1/2 wavelength plate 7, the black level with high display quality can be obtained, and the black display can be visually recognized. It was confirmed that the sex was improved. 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 32 of the light reflecting portion is 65 nm, the reflection contrast ratio becomes 8: 1. The visibility of the black display tended to decrease. Accordingly, the phase difference of the liquid crystal layer 32 of the light reflecting portion is 1/4 or more on 4/9 The following phase difference between the first half-wave plate 7.

If the phase difference of the liquid crystal layer 2 of the light transmitting portion is set to be equal to or slightly smaller than the phase difference of the first 1/2 wave plate 7, the black level with high display quality can be obtained even during transmission, and black is obtained. It was confirmed that the visibility of the display was improved. However, when it is smaller than 7/9 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 of the light transmitting portion is 200 nm, the transmission contrast ratio becomes 15: 1. The visibility of the black display tended to decrease. Therefore, the phase difference of the liquid crystal layer 2 of the light transmitting portion is preferably 7/9 or more and 1 times or less the phase difference of the first 1/2 wavelength plate 7.

The phase difference of the liquid crystal layer 32 of the light reflecting portion functions as a approximately 1/4 wave plate when no electric field is applied. The circularly polarized light emitted from the first 1/2 wave plate 7 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. 4 and 5, 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 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. 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).

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 crossing 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 arranged at 50 ° or more and 75 ° or less, and more preferably 62 ° ( It is arranged at 152 ° -90 °). 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. 4. The incident light c1 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 results in linearly polarized light (referred to as linearly polarized light c2). When no electric field is applied, the linearly polarized light c2 becomes wide-band circularly polarized light (referred to as circularly polarized light c3) when it passes through the first 1/2 wave plate 7 and the liquid crystal layer 32 of the light reflecting portion.

On the other hand, when an electric field is applied to the liquid crystal layer 32 of the light reflecting portion, the phase difference of the liquid crystal layer 32 of the light reflecting portion becomes 0, so that the first 1/2 wave plate 7 and the liquid crystal layer of the reflecting portion It passes through 32 and becomes linearly polarized light c4, which is reflected by the light reflecting layer 4. The reflected light d3 of the linearly polarized light c4 passes through the liquid crystal layer 2 and the first 1/2 wave plate 7 again, becomes linearly polarized light d4 which is the same as the polarization direction of the first polarizing plate 6, and is displayed in white. ..

Further, when no electric field is applied to the liquid crystal layer 32 of the light reflecting portion, the light passing through the liquid crystal layer 32 of the light reflecting portion to become a wide-band circularly polarized light c3, and the light-reflecting layer 4 reflects the wide-band circularly polarized light c3. It becomes the reflected light d1. The circularly polarized reflected light d1 passes through the liquid crystal layer 32 of the reflecting portion and the first 1/2 wavelength plate 7 again, becomes linearly polarized light d2 orthogonal to the polarization direction of the first polarizing plate 6, and becomes normally black. It is possible to obtain a black display having a high tint, that is, a high display quality, that is, a so-called black floating is suppressed.

Next, an embodiment of the light transmission mode will be described. FIG. 1 is a cross-sectional view showing the configuration of the liquid crystal display device 1 according to the embodiment of the present invention, and FIG. 2 is for explaining the operation of the light transmitting portion of the liquid crystal display device 1 when no electric field is applied and when an electric field is applied. FIG. 3 is a diagram showing an axial arrangement of a light transmitting portion of the liquid crystal display device 1. The same reference numerals are given to the parts corresponding to the above-mentioned form of the light reflecting portion, and the duplicated description will be omitted.

The liquid crystal display device 1 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 second 1/2 wavelength plate 50 is further provided, and a light transmitting portion 46 for transmitting light incident from the side of the counter-display surface 43 of the liquid crystal display panel 5 is provided including the liquid crystal layer 2, and is a so-called semi-transmissive type. It is realized as a liquid crystal display device 1 (which includes both a light reflecting unit 47 and a light transmitting unit 46). Basically, the backlight device is not required on the counter-display surface 43 side, but it may be present.

The slow-phase axis of the second 1/2 wave plate 50 and the orientation axis of the liquid crystal molecules when no electric field is applied intersect. The crossing angle between the slow axis of the second 1/2 wave plate 50 and the orientation axis of the liquid crystal molecules when no electric field is applied is preferably 65 ° or more and 90 ° or less, and more preferably 80 ° (Fig.). (Calculated from 90 ° -10 ° from θf2 = 10 ° shown in 3). 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 120 ° or less, more preferably 102 °. As a result, a black display with a high display quality can be obtained even when light is transmitted (light transmission mode), and the tint (degree of blackness) of normal black can be improved.

Next, the display of the light transmitting portion 46 of the liquid crystal display device 1 will be described with reference to FIG. 2. In the liquid crystal display panel 5, the liquid crystal layer 2 is formed on the light transmitting portion 46 that transmits the light incident from the counter-display surface 43 side. Since the light is contained and passes through the liquid crystal layer 2, the light incident from the side of the counter-display surface 43 of the liquid crystal display panel 5 is the second polarizing plate when no electric field is applied to the liquid crystal layer 2. The linearly polarized light a1 is obtained by 44. This straight line because the phase difference is canceled by the liquid crystal layer 2, the phase difference of the second 1/2 wave plate 50 as the retardation plate, and the phase difference and each axis arrangement of the first 1/2 wavelength plate 7. The polarized light a1 becomes linearly polarized light a2 after passing through the second 1/2 wave plate 50, the liquid crystal layer 2, and the first 1/2 wave plate 7. The polarization direction of the linearly polarized light a2 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 1 in which the linearly polarized light a2 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, when 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 b1. The linearly polarized light b1 becomes elliptically polarized light b2 after passing through the second 1/2 wavelength plate 50, the liquid crystal layer 2, and the first 1/2 wavelength plate 7. Only the light in the polarization direction of the first polarizing plate 6 passes through the elliptically polarized light b2, and the display becomes white.

FIG. 6 is a diagram showing the relationship between the refractive indexes of the first 1/2 wave plate 7 and the second 1/2 wave plate 50 used in the liquid crystal display device of another embodiment of the present invention. .. The first 1/2 wave plate 7 has a refractive index of nx1 and ny1 in the plane orthogonal to each other, and a refractive index of nz1 in the thickness direction thereof, and the second 1/2 wave plate 50 has a refractive index of nz1. When the refractive indexes in the planes orthogonal to each other are nx2 and ny2, and the refractive index in the thickness direction is nz2, and when the relations of nx1> nz1> ny1 and nx2> nz2> ny2 are satisfied, It is possible to improve the viewing angle dependence and realize a black display of normal black with a wide viewing angle and high display quality.

Further, the relationship of nx1, ny1, nz1 in the first 1/2 wave plate 7 is represented by Nz1 = (nx1-nz1) / (nx1-ny1), and nx2, ny2 in the second 1/2 wave plate 50. When the relationship of nz2 is expressed by Nz2 = (nx2-nz2) / (nx2-ny2), when Nz1 and Nz2 are set in the range of more than 0 and 0.7 or less, respectively, the viewing angle dependence is further increased. It can be improved, and a black display of normal black with a wide viewing angle and high display quality can be realized.

The present inventor prepared a sample of the liquid crystal display device of Example 2 in order to confirm that the viewing angle of the normal black is improved in the light reflection mode and the light transmission mode. Hereinafter, the second embodiment will be described.

With reference to FIGS. 1, 3 and 5, the direction when the liquid crystal display panel 5 is viewed from the display surface 3 side, that is, the direction orthogonal to the initial orientation direction (= rubbing direction) when no electric field is applied to the liquid crystal molecules is used as a reference. Assuming that the axis (= 0 °) and the counterclockwise angle from the reference axis to each axis are angles such as the 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 second 1/2 wavelength plate 50 is 10 ° (phase difference value Δnd = 270 nm), and the angle θp2 of the absorption axis of the second polarizing plate 44 is 65 °.

As the first 1/2 wave plate 7 and the second 1/2 wave plate 50, a product name "NAZ film" manufactured by Nitto Denko KK was used. For nx1, ny1, nz1, nz2, ny2, nz2, nx1 = nz2, ny1 = ny2, nz1 = nz2, nx1> nz1> ny1, Nz1 = Nz2 = 0.5, nx1 = 1.52196, ny1 = 1.52 , Nz1 = 1.52098.

For the first polarizing plate 6 and the second polarizing plate 44, a product name "TEG1465DUHC" manufactured by Nitto Denko KK was used. Further, the phase difference value of the liquid crystal layer 32 of the light reflecting portion was set to 105 nm, and the phase difference value of the liquid crystal layer 2 of the light transmitting portion was set to 260 nm. Then, for this sample, the reflectance of black display, the reflectance of white display, and the reflection contrast ratio were measured using a spectrocolorimeter "CM-2600d" manufactured by Konica Minolta Japan Co., Ltd., and Topcon Techno House Co., Ltd. The transmission contrast ratio was measured using a color luminance meter "BM-5AS" manufactured by Japan.

As a result of the experiment, in Example 2, the reflectance of the black display was 0.30%, the reflectance of the white display was 13.5%, the reflection contrast ratio was 45: 1, and the transmission contrast ratio was 200: 1. It was confirmed that good visibility can be obtained with the black display of normal black in both the reflection mode and the light transmission mode.

The first and second 1/2 wave plates 7 and 50 satisfy the relationship of nx1> nz1> ny1 and nx2> nz2> ny2, and Nz1 and Nz2 are in the range of more than 0 and 0.7 or less, respectively. It is set, and more preferably Nz1 and Nz2 are set in the range of 0.3 or more and 0.7 or less, respectively. As a result, black floating when the display surface 3 is viewed from an oblique direction (about 50 ° from the front) in the vertical and horizontal directions from the front of the liquid crystal display panel 5 is controlled, and the normal black with a wide viewing angle and high display quality is used. Black display can be realized.

1 Liquid crystal display device 2 Liquid crystal layer of light transmitting part 3 Display surface 4 Light reflecting layer 5 Liquid crystal display panel 6 First polarizing plate 7 First 1/2 wavelength plate 10 First substrate 11 Light-shielding layer 12 Color filter layer 13 Common electrode 14 First alignment layer 15 Columnar portion 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 insulating layer 25 First interlayer insulating layer 26 Second gate insulating layer 27 First gate insulating layer 28 Second substrate 29 Channel portion 30 Semiconductor layer 31 Gate electrode 32 Liquid crystal layer of light reflecting portion 43 Reverse display surface 44 Second liquid crystal 46 Light transmission part 47 Light reflection part 50 Second 1/2 wavelength plate

Claims (7)

It is a birefringence control type liquid crystal display device that displays in normal black.
A liquid crystal display having a liquid crystal layer, a light reflecting portion that reflects light incident from the display surface side and passing through the liquid crystal layer, and a light transmitting portion that transmits light incident from the counter-display surface side to the liquid crystal layer. With the panel
A first polarizing plate arranged on the display surface side of the liquid crystal display panel,
A first 1/2 wave plate provided between the liquid crystal display panel and the first polarizing plate, and
A second polarizing plate arranged on the counter-display surface side of the liquid crystal display panel,
A second 1/2 wave plate provided between the liquid crystal display panel and the second polarizing plate is provided.
The portion of the liquid crystal layer corresponding to the light reflecting portion is set in a range in which the phase difference is 1/4 or more and 4/9 or less of the phase difference of the first 1/2 wave plate, and the liquid crystal layer. The phase difference of the portion corresponding to the light transmitting portion in the above is set to be equal to or less than the phase difference of the first 1/2 wave plate.
The slow-phase axis of each of the first 1/2 wave plate and the second 1/2 wave plate intersects the orientation axis of the liquid crystal molecules when no electric field is applied .
In the first polarizing plate and the second polarizing plate, their absorption axes intersect each other and the orientation axis of the liquid crystal molecules when no electric field is applied.
The first 1/2 wave plate and the second 1/2 wave plate are liquid crystal display devices whose slow axes intersect with each other. Phase difference of the portion corresponding to the light transmitting portion of the liquid crystal layer, according to claim 1 which is set to 7/9 or more 1 times the range of the phase difference of the first half-wave plate Liquid crystal display device. The first 1/2 wave plate has a refractive index of nx1 and ny1 in the plane orthogonal to each other and a refractive index of nz1 in the thickness direction thereof, and the second 1/2 wave plate has a refractive index of nz1. When the refractive indexes in the planes orthogonal to each other are nx2 and ny2, and the refractive indexes in the thickness direction are nz2, the relationship of nx1>nz1> ny1 and nx2>nz2> ny2 is satisfied. 1 or the liquid crystal display device according to claim 2. The relationship of nx1, ny1, nz1 in the first 1/2 wave plate is represented by Nz1 = (nx1-nz1) / (nx1-ny1), and the relationship of nx2, ny2, nz2 in the second 1/2 wave plate When the relationship is represented by Nz2 = (nx2-nz2) / (nx2-ny2), Nz1 and Nz2 are any one of claims 1 to 3 set in the range of more than 0 and 0.7 or less, respectively. The liquid crystal display device according to item 1. Wherein the first and the slow axis of the half wave plate and the orientation axis of the liquid crystal molecules when the no electric field applied, of claims 1 to 4 intersect at an intersection angle of 50 ° or more 75 ° or less The liquid crystal display device according to any one item. The second and the slow axis of the half wave plate and the orientation axis of the liquid crystal molecules when the no electric field applied, of claims 1 to 5 intersect at the following intersection angle 65 ° or more 90 ° The liquid crystal display device according to any one item. The light-reflecting portion according to any one of claims 1 to 6, further comprising a light-shielding layer and a columnar portion overlapping the light-transmitting portion on the side of the light-transmitting portion and in the liquid crystal layer. The liquid crystal display device described.

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