JP3822027B2 - Transmission type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a liquid crystal display device in which alignment disorder does not have an influence on display and display quality is hardly decreased even when alignment directions of liquid crystal molecules are controlled so as to be different from one another in pixels. SOLUTION: In the liquid crystal display device 1, circularly polarized light passed through a λ/4 plate 23a is made incident to a liquid crystal layer 21 exhibiting radial tilt alignment in which the alignment direction changes continuously when voltage is applied. As a result, the liquid crystal molecules can contribute to the display as far as the alignment direction and the visual angle of the liquid crystal molecules are not coincident with each other not only about an in-plane component but also about a substrate normal component even if the alignment state of the liquid crystal molecules is disordered. Thus as a result of using the liquid crystal layer in which the alignment directions of the liquid crystal molecules are controlled so as to be different from one another in the pixel for securing a wide visual field angle, the liquid crystal display device 1 having high display quality without roughness can be realized, even though not only the edge region of a pixel electrode but also the boundary region of domains exist.

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is controlled such that the alignment directions of the liquid crystal molecules are different from each other in the pixel, such as radial tilt alignment and multi-domain alignment.Transmission typeWith regard to liquid crystal display devices, in particular, it is possible to improve display quality by suppressing roughness caused by disorder of alignment state, etc.Transmission typeThe present invention relates to a liquid crystal display device.
[0002]
[Prior art]
For example, a liquid crystal display device used as a display screen of a notebook computer or a word processor has a narrower viewing angle than a display device such as a CRT because of the optical anisotropy of the liquid crystal. The quality tends to decline. Therefore, for example, Japanese Patent Application Laid-Open No. 11-258605 and Japanese Patent Application Laid-Open No. 11-109391 propose a so-called multi-domain method in which a plurality of regions are formed in the liquid crystal alignment direction.
[0003]
As an example of a multi-domain liquid crystal display device, a vertical alignment mode liquid crystal display device using a vertical alignment film and a liquid crystal having negative dielectric anisotropy will be described. The liquid crystal molecules are aligned in the vertical direction. When linearly polarized light is incident on the liquid crystal layer in this state from the polarizing plate, since the liquid crystal layer has almost no birefringence anisotropy, the linearly polarized light is output while maintaining the polarization state, and is opposite to the liquid crystal layer. Is absorbed by the polarizing plate disposed in the plate. As a result, the liquid crystal display device can display black.
[0004]
On the contrary, when a voltage is applied, as shown in FIG. 18, in the liquid crystal layer 121c of the liquid crystal display device 101, the liquid crystal molecules M are tilted according to the applied voltage. In the figure, the case of radial tilt alignment in which the alignment direction of the liquid crystal molecules M continuously changes is shown. Even in the same pixel, the alignment direction of the liquid crystal molecules M is the central axis A of the radial tilt. Is different from each other in one region A101 and the other region A102. In this state, when linearly polarized light enters the liquid crystal layer 121c from the polarizing plate 122a, the liquid crystal layer 121c can give a phase difference to the transmitted light, and can change the polarization state of the transmitted light. Therefore, the light emitted from the liquid crystal cell 121 generally changes to elliptically polarized light.
[0005]
When the elliptically polarized light is incident on the polarizing plate 122b disposed on the emission side of the liquid crystal cell 121, the amount of light corresponding to the phase difference given by the liquid crystal layer 121c is transmitted unlike when no voltage is applied. Therefore, by controlling the voltage applied to the liquid crystal layer 121c and adjusting the alignment direction of the liquid crystal molecules M, the amount of light emitted from the liquid crystal display device 101 can be changed, and gradation display is possible.
[0006]
Here, in the liquid crystal display device 101, since the alignment directions of the liquid crystal molecules M are different from each other even in one pixel, the amount of light emitted through a certain liquid crystal molecule M is reduced when viewed from an oblique direction. However, among the other liquid crystal molecules M having an alignment direction different from that of the liquid crystal molecules M, there are those that increase the amount of emitted light. As a result, the regions where the liquid crystal molecules M having different alignment directions exist are optically compensated for each other, improving the display quality when viewed from an oblique direction and expanding the viewing angle.
[0007]
[Problems to be solved by the invention]
However, when the alignment direction in the pixel is separately controlled as in the liquid crystal display device 101 having the above-described configuration, alignment disorder is likely to occur. Therefore, for example, an alignment disturbance occurs due to a slight factor that does not cause a problem in the case of a single alignment direction, such as an external electric field from a source signal line or a gate signal line. Here, when the location where the alignment disorder occurs due to the alignment disorder becomes dark, the alignment disorder is different for each location or each pixel, so that roughness is observed in the display and the display quality is deteriorated.
[0008]
Further, when the orientation directions are controlled so as to be different from each other as compared with the case of the single orientation, under the two polarizing plates, as shown in FIG. The brightness of the entire pixel is also reduced as compared with the case where the planned transmittance is maintained at this point. As a result, the light utilization efficiency (effective aperture ratio) of the liquid crystal display device also decreases.
[0009]
Here, the resolution and the number of gradations of a liquid crystal display device are improving year by year, and there is a demand for a liquid crystal display device that can display more gradations even when the area of one pixel is reduced. However, if the effective aperture ratio is reduced due to the above-mentioned disorder of orientation, the luminance at the time of white display is lowered and it is difficult to improve the number of gradations. Note that when the pixel area is enlarged, the luminance can be improved, but it is difficult to improve the resolution.
[0010]
The present invention has been made in view of the above-described problems, and the purpose of the present invention is to prevent the alignment disorder from affecting the display even when the alignment directions of the liquid crystal molecules are controlled to be different from each other in the pixel. Display quality is unlikely to deteriorate.Transmission typeIt is to realize a liquid crystal display device.
[0011]
[Means for Solving the Problems]
  In order to solve the above problems, a transmissive liquid crystal display device according to the present invention includes a first substrate provided with a pixel electrode corresponding to a pixel, a second substrate provided with a counter electrode, and a gap between the two substrates. Provided, when the voltage between the pixel electrode and the counter electrode is at least a predetermined value, the alignment direction of the liquid crystal molecules isPresents a continuously varying radial gradient orientationA liquid crystal layer, an analyzer disposed on the exit side of the liquid crystal layer, and the liquid crystal layerAt a wavelength of 550 nmCircular polarization means for setting the incident light in a substantially circular polarization state, provided between the liquid crystal layer and the analyzer, retardation in the in-plane direction,95nm or more, 175nm or lessAnd a first retardation layer set to (1).
[0014]
Each of the above configurationsTransmission typeIn the liquid crystal display device, AntiAs in a projection type liquid crystal display device, the exit side and the entrance side may be the same.
[0015]
Each of the above configurationsTransmission typeIn the liquid crystal display device, substantially circular polarized light is incident on the liquid crystal layer, and the light emitted from the liquid crystal layer is incident on the analyzer after being given a phase difference of a quarter wavelength by the first retardation layer. Is done.
[0016]
When the liquid crystal molecules of the liquid crystal layer are aligned in the substrate normal direction (vertical), the liquid crystal layer cannot give a phase difference to the transmitted light. As a result, the transmitted light is emitted while maintaining substantially circularly polarized light. The emitted light is converted into linearly polarized light by the first retardation layer, and then input to the analyzer to limit transmission. As a result,Transmission typeThe liquid crystal display device can display black. On the other hand, when the voltage between the pixel electrode and the counter electrode is a predetermined voltage, such as the initial alignment state when a voltage is applied or when no voltage is applied, the alignment directions of the liquid crystal molecules are different from each other in the pixel. Be controlled. In this state, since the liquid crystal layer gives the transmitted light a phase difference corresponding to the alignment state, the circularly polarized light is converted into elliptically polarized light. Therefore, even if it passes through the first retardation layer, it does not return to linearly polarized light, and part of the emitted light from the first retardation layer is emitted from the analyzer. As a result, the amount of light emitted from the analyzer can be controlled according to the applied voltage, and gradation display is possible.
[0017]
In addition, since the alignment directions of the liquid crystal molecules are different from each other in the pixel, regions where the liquid crystal molecules having different alignment directions are present can optically compensate for each other. As a result, the display quality when viewed from an oblique direction can be improved and the viewing angle can be expanded.
[0018]
Here, in the liquid crystal layer, as a result of controlling the alignment directions of the liquid crystal molecules to be different from each other in the pixel in order to ensure a wide viewing angle, disorder of the alignment state is likely to occur. Therefore, in the case of a conventional liquid crystal display device in which linearly polarized light is incident on the liquid crystal layer and light emitted from the liquid crystal layer is incident on the analyzer, the alignment of the liquid crystal molecules is disturbed, and the in-plane component in the alignment direction is reduced. When coincident with the absorption axis of the analyzer, the liquid crystal molecules cannot give a phase difference to the transmitted light regardless of the component in the normal direction of the substrate. Here, the manner in which the alignment state is disturbed differs from pixel to pixel, and varies depending on the location even within the same pixel, resulting in roughness. Further, since the liquid crystal molecules whose in-plane components in the alignment direction coincide with the absorption axis of the analyzer cannot contribute to the improvement in brightness, the light utilization efficiency (effective aperture ratio) is lowered. As a result, it becomes difficult to ensure the contrast ratio and increase the number of gradations.
[0019]
In contrast, according to the present inventionTransmission typeIn the liquid crystal display device, since substantially circularly polarized light is incident on the liquid crystal layer, there is no anisotropy in the alignment direction of the liquid crystal layer, and the alignment direction of the liquid crystal molecules and transmitted light are in-plane components and the substrate normal direction. As long as they do not coincide with each other, the liquid crystal molecules can give a phase difference to the transmitted light. Therefore, as a result of controlling the alignment direction of the liquid crystal molecules to be different from each other in the pixel in order to ensure a wide viewing angle, the alignment direction of the liquid crystal molecules whose alignment is disturbed despite the fact that the alignment state is likely to be disturbed. As long as it does not match, it can contribute to the improvement of brightness. As a result, high light utilization efficiency can be ensured while maintaining a wide viewing angle, and an improvement in contrast ratio and an increase in the number of gradations can be realized.
[0020]
In addition to the above configuration, the circular polarization unit sets light having a wavelength of 550 nm to a substantially circular polarization state, and the first retardation layer has a retardation in an in-plane direction of approximately ¼ nm. Is preferably set to 1.
[0021]
In this configuration, substantially circularly polarized light is incident on a wavelength of 550 nm, which has the highest human visibility, and it is possible to prevent a decrease in brightness and occurrence of roughness of light having the wavelength. As a result, compared with the case where substantially circularly polarized light is incident only at other wavelengths, it is difficult to visually recognize a decrease in brightness and roughness.Transmission typeA liquid crystal display device can be realized.
[0022]
The circularly polarized light means only needs to be able to enter circularly polarized light. However, it is sufficient that the circularly polarized light can be incident to such an extent that the reduction in brightness and roughness are not noticeable. In addition, the retardation of the first retardation layer may be perfectly matched with the quarter wavelength of the transmitted light. However, the retardation of the first retardation layer may be about a quarter wavelength to such an extent that the above-described decrease in brightness and roughness are not noticeable. That's fine.
[0023]
  Specifically, when the light having a wavelength of 550 nm is set as a reference, the in-plane retardation of the first retardation layer is set to 95 nm or more and 175 nm or less.The
[0024]
In the above configuration, since the retardation is set to 95 nm or more and 175 nm or less, even if the brightness is reduced, the overall brightness reduction and the brightness reduction in the region of orientation disorder are about 10%. It can be suppressed. As a result, compared with the case where other ranges are set, it is difficult to visually recognize a decrease in brightness and roughness.Transmission typeA liquid crystal display device can be realized.
[0025]
Further, in addition to the above configuration, the circularly polarizing means is a selective reflection layer that is provided on the incident side of the liquid crystal layer and transmits circularly polarized light in a predetermined turning direction and reflects circularly polarized light that rotates in the opposite direction. Some are desirable.
[0026]
In this configuration, of the incident light to the selective reflection layer, circularly polarized light in a predetermined turning direction is transmitted through the selective reflection layer. On the other hand, circularly polarized light that rotates in a direction opposite to the direction is reflected by the selective reflection layer, so that it is reused by being returned to the backlight source, for example, unlike the case of being absorbed by the polarizer. it can. As a result, it is possible to improve the light utilization efficiency although substantially circular polarized light can be incident on the liquid crystal layer.
[0027]
On the other hand, instead of using a selective reflection layer as the circularly polarizing means, the circularly polarizing means is disposed between the polarizer provided on the incident side of the liquid crystal layer and the polarizer and the liquid crystal layer, and has an in-plane direction. The retardation may comprise a second retardation layer set to a wavelength that is approximately a quarter of the wavelength of the transmitted light. Even in this case, since the linearly polarized light emitted from the polarizer is converted into substantially circularly polarized light by the second retardation layer, substantially circularly polarized light can be incident on the liquid crystal layer. The incident side and the emission side of the liquid crystal display device may be the same side or the opposite side, but in the case of the same side, the analyzer and the polarizer or the first and second phase differences You can share layers.
[0028]
Further, in addition to the above configuration, the analyzer is disposed on one side of the liquid crystal layer, the polarizer is disposed on the other side, and the transmission axis of the analyzer and the slow phase of the first retardation layer are disposed. The analyzer, the polarizer, and the first and first axes so that the axis forms an angle of 45 degrees, and the transmission axis of the polarizer and the slow axis of the second retardation layer form an angle of 45 degrees. It is desirable that two retardation layers are provided.
[0029]
In this configuration, the transmission axis of the analyzer and the slow axis of the first retardation layer form an angle of 45 degrees, and the transmission axis of the polarizer and the slow axis of the second retardation layer are 45. Since the angle is at a degree, linearly polarized light and circularly polarized light can be efficiently converted into each other.
[0030]
In the case of the configuration including the first and second retardation layers, the analyzer is disposed on one of the liquid crystal layers, the polarizer is disposed on the other, and the first and second positions are arranged. The phase difference layer is preferably arranged so that the respective slow axes are orthogonal to each other, and the analyzer and the polarizer are preferably arranged so that the respective transmission axes are orthogonal to each other.
[0031]
In the above configuration, the slow axes of the first and second retardation layers are arranged so as to be orthogonal to each other. Therefore, the wavelength dispersions of refractive index anisotropy possessed by both retardation layers cancel each other. As a result, in a black display state, transmitted light in a wider wavelength range is absorbed by the analyzer. Thereby, a better black display can be realized.
[0032]
Further, in any configuration, the phase difference provided between the analyzer and the polarizer and provided by the liquid crystal layer depends on the tilt angle from the normal direction of the first substrate to the viewing angle. It is desirable to provide a viewing angle compensation layer in which the refractive index anisotropy is set so as to cancel the phase difference that fluctuates.
[0033]
In this configuration, the phase difference provided by the liquid crystal layer is canceled by the viewing angle compensation layer depending on the tilt angle of the viewing angle. Therefore, it is possible to suppress the dependency of the viewing angle and to have a good contrast ratio in a wider viewing angle range.Transmission typeA liquid crystal display device can be realized.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
[First Embodiment]
An embodiment of the present invention will be described below with reference to FIGS. For example, as a liquid crystal layer whose alignment direction is not constant, a liquid crystal layer that is aligned perpendicularly to the substrate when no voltage is applied and that exhibits a radially inclined alignment in which the alignment direction continuously changes when a voltage is applied is taken as an example. As shown in FIG. 1, a liquid crystal panel 2 of the liquid crystal display device 1 according to the embodiment includes a TFT (Thin Film Transistor) substrate 21a, a counter substrate 21b, and the liquid crystal layer 21c sandwiched between the substrates 21a and 21b. 21, polarizing plates 22a and 22b disposed on both sides of the liquid crystal cell 21, and a λ / 4 plate (second retardation layer) 23a disposed between the polarizing plate 22a on the TFT substrate 21a side and the liquid crystal cell 21. And a λ / 4 plate 23b (first retardation layer) disposed between the polarizing plate 22b and the liquid crystal layer 21c on the counter substrate 21b side. The two substrates 21a and 21b correspond to the first and second substrates described in the claims. The polarizing plate 22a corresponds to a polarizer, and the polarizing plate 22b corresponds to an analyzer.
[0035]
The liquid crystal cell 21 is a vertical alignment (VA) type liquid crystal cell, in which pixel electrodes 31 (described later) formed of ITO (Indium Tin Oxide) or the like and thin film transistor elements (not shown) are arranged in a matrix. After applying a vertical alignment film (not shown) to the counter substrate 21b having the counter electrode 21a and the counter electrode, the substrates 21a and 21b are bonded together, and a negative dielectric anisotropy is formed in the gap between the substrates 21a and 21b. For example, the liquid crystal layer 21c is prepared. As a result, when no voltage is applied, the liquid crystal molecules M of the liquid crystal layer 21c are aligned substantially vertically as shown in FIG. 1, and when a voltage is applied, the liquid crystal molecules are tilted and horizontally aligned as shown in FIG. it can.
[0036]
Furthermore, in the liquid crystal cell 21c according to the present embodiment, as shown in FIG. 3, a resin 32a in which a circular hole 32 is formed is provided on each pixel electrode 31 provided on the TFT substrate 21a. As shown in FIG. 4, the wall surface H of the hole 32 is inclined, and in the vicinity of the wall surface H, the liquid crystal molecules M are aligned so as to be perpendicular to the surface of the wall surface H. In addition, when a voltage is applied, the electric field near the wall surface H is inclined in a direction parallel to the surface of the wall surface H. As a result, when the liquid crystal molecules M are tilted when a voltage is applied, the liquid crystal molecules M tend to tilt radially in the in-plane direction around the center of the hole 32 as shown by arrows in FIG. Each liquid crystal molecule M of the layer 21c can be radially inclined and aligned. Further, when the applied voltage is further increased, the inclination angle with respect to the normal direction of the substrate is increased, and each liquid crystal molecule M is substantially parallel to the display screen and is radially aligned in the plane. The resin 32a in which the hole 32 is formed can be formed by applying a photosensitive resin on the TFT substrate 21a and processing it in a photolithography process.
[0037]
In addition, for example, when the pixel pitch is increased, if only the hole portions 32 are provided in the pixel electrode 31 one by one, the alignment regulating force in the center region of the hole portions 32 is weakened, and the alignment may be unstable. is there. Therefore, when the alignment regulating force in the center region is insufficient, it is desirable to provide a plurality of holes 32 on each pixel electrode 31 as shown in FIG. In the figure, 33 is a source wiring, and 34 is a gate wiring.
[0038]
On the other hand, the λ / 4 plates 23a and 23b shown in FIG. 1 are formed of a material having birefringence anisotropy such as a uniaxially stretched polymer film, and the optical path difference between ordinary rays and extraordinary rays is incident light. The thickness (length in the normal direction of the substrate) is set to be a quarter wavelength. Thereby, linearly polarized light having a polarization direction of 45 degrees with respect to the slow axis can be converted into circularly polarized light. Further, when circularly polarized light is incident, it can be converted into linearly polarized light having a polarization direction of 45 degrees with respect to the slow axis of the λ / 4 plate 23a (23b). When the liquid crystal layer 21c is formed, when a chiral agent is added and the liquid crystal layer 21c is axially symmetrically aligned, a twist angle is generated in the liquid crystal layer 21c. Therefore, in this case, it is desirable to shift the optical path difference of the λ / 4 plate 23a (23b) from the quarter wavelength in consideration of the twist angle of the liquid crystal layer 21c.
[0039]
In the liquid crystal panel 2 according to the present embodiment, the transmission axis PAa (PAb) of the polarizing plate 22a (22b) and the slow axis SLa (SLb) of the λ / 4 plate 23a (23b) are shown in FIG. It is set in such a direction. Specifically, the slow axis SLa of the λ / 4 plate 23a is arranged to form an angle of 45 degrees with the transmission axis PAa of the polarizing plate 22a. Further, the slow axis SLb of the λ / 4 plate 23b is arranged to form 45 degrees with the transmission axis PAb of the polarizing plate 22b in the same direction as when the angles of the slow axis SLa and the transmission axis PAa are set. ing. In FIG. 6, as an example, a case where the angle is 45 degrees clockwise when viewed from the counter substrate 21 b side along the substrate normal direction is illustrated. In the same figure, no voltage is applied, and the liquid crystal molecules M are aligned substantially vertically.
[0040]
Furthermore, in the liquid crystal display device 1 according to the present embodiment, as shown in FIG. 1, a backlight 3 serving as a light source of the liquid crystal display device 1 is disposed on one of both surfaces of the liquid crystal panel 2. In the example of FIG. 1, the case where the backlight 3 is arranged on the TFT substrate 21a side is illustrated.
[0041]
In the above configuration, while no voltage is applied between the pixel electrode 31 and the counter electrode (not shown), the liquid crystal molecules M of the liquid crystal layer 21c are minor molecules near the wall surface H of the hole 32 as shown in FIG. Except for, it is in a vertical alignment state. In this state (when no voltage is applied), the light incident on the liquid crystal panel 2 from the backlight 3 passes through the polarizing plate 22a, and is linearly polarized light whose polarization direction is 45 degrees with respect to the slow axis SLa of the λ / 4 plate 23a. It becomes. Furthermore, the linearly polarized light is converted into circularly polarized light by passing through the λ / 4 plate 23a.
[0042]
Here, the liquid crystal molecules M do not give a phase difference to light incident in a direction parallel to the alignment direction. Therefore, the liquid crystal layer 21c cannot give a phase difference to light perpendicularly incident on the liquid crystal layer 21c from the backlight 3, and has almost no birefringence.
[0043]
As a result, the circularly polarized light emitted from the λ / 4 plate 23a passes through the liquid crystal layer 21c while maintaining the polarization state, and is incident on the λ / 4 plate 23b. When the circularly polarized light passes through the λ / 4 plate 23b, the circularly polarized light has a polarization direction of 45 degrees with respect to the slow axis SLb of the λ / 4 plate 23b, that is, orthogonal to the transmission axis PAb of the polarizing plate 22b. Converted to linearly polarized light in the direction. Therefore, the linearly polarized light is absorbed by the polarizing plate 22b, and the liquid crystal display device 1 can display black in a state where no voltage is applied.
[0044]
On the other hand, when a voltage is applied between the pixel electrode 31 and the counter electrode, the liquid crystal molecules M of the liquid crystal layer 21c are radially inclined and aligned as shown in FIGS. Even in this state, the polarization state is converted from the backlight 3 to the liquid crystal cell 21 in the same manner as when no voltage is applied, and circularly polarized light is incident on the liquid crystal layer 21c.
[0045]
However, when a voltage is applied, the alignment direction of the liquid crystal molecules M changes, and the alignment is radially inclined. Here, the liquid crystal molecules M do not give a phase difference to light incident in a direction parallel to the alignment direction, but when the alignment direction and the incident direction are different, the phase difference corresponding to the angle between the two is given. Can be given to transmitted light.
[0046]
As a result, in the case of light perpendicularly incident on the liquid crystal cell 21, the liquid crystal layer 21c, except for a few regions where the liquid crystal molecules M are aligned in the normal direction of the substrate, such as the center region of the hole 32, A phase difference can be given to the transmitted light, and the polarization state of the transmitted light can be changed. Accordingly, light emitted from the liquid crystal cell 21 generally changes to elliptically polarized light. Even when this elliptically polarized light passes through the λ / 4 plate 23b, it does not become linearly polarized light, unlike when no voltage is applied. Therefore, a part of the light provided from the liquid crystal cell 21 to the polarizing plate 22b through the λ / 4 plate 23b can pass through the polarizing plate 22b. Here, the amount of polarized light transmitted through the polarizing plate 22b depends on the magnitude of the phase difference provided by the liquid crystal layer 21c. Therefore, by controlling the voltage applied to the liquid crystal layer 21c and adjusting the alignment direction of the liquid crystal molecules M, the amount of light emitted from the liquid crystal display device 1 can be changed, and gradation display is possible.
[0047]
In the above configuration, the liquid crystal layer 21c is radially inclined and aligned. Therefore, even when the liquid crystal panel 2 is viewed from directions (in-plane orientations) in which in-plane components are different from each other, the entire liquid crystal molecules M related to display of a certain pixel have substantially the same phase difference given to transmitted light. As a result, a wider viewing angle can be secured as compared with the case where all the liquid crystal molecules M related to the display of a certain pixel are inclined and aligned in a single specific direction.
[0048]
Here, as in the liquid crystal display device 101 illustrated in FIG. 18, in order to ensure a wide viewing angle, even when the liquid crystal layer 121 c is radially inclined and aligned, linearly polarized light is incident on the liquid crystal layer 121 c. In this case, there is a liquid crystal molecule group in which the in-plane component in the alignment direction is inclined and aligned in a direction that matches the direction of linearly polarized light. Here, since these liquid crystal molecule groups cannot give a phase difference to transmitted light regardless of the normal direction component of the alignment direction, the light transmitted through the liquid crystal molecule groups is emitted in the same manner as in the vertical alignment. It is absorbed by the polarizing plate 122b on the side.
[0049]
As a result, the transmittance of the region along the direction of linearly polarized light and the region along the direction perpendicular to the direction of the linearly polarized light with the center position of the hole portion 32 as the center decreases. Further, for example, as shown in FIG. 19, in the edge region of the pixel electrode 31, the orientation of the liquid crystal molecules M is disturbed due to the influence of an external electric field and the like, and the disorder of the orientation varies depending on the location. End up.
[0050]
On the other hand, in the configuration of the present embodiment, since the circularly polarized light is incident on the liquid crystal cell 21, a phase difference is given to the transmitted light even though a wide viewing angle is ensured by the radially inclined orientation. The liquid crystal molecules M that cannot be used are only the liquid crystal molecules M that are aligned perpendicular to the substrate surface when viewed from the front. Further, when viewed obliquely, only the liquid crystal molecules M are aligned in the same direction as the viewing angle direction. As a result, the number of liquid crystal molecules that cannot contribute is reduced, and a phase difference can be provided unless both the in-plane component and the normal direction component are the same as the viewing angle. Therefore, as shown in FIG. 8, the area where the shadow is displayed is only the center position of the hole 32 and the intermediate position between the adjacent holes 32 and 32, and the shadow area is also displayed in the edge area of the pixel electrode 31. The area where is displayed can be greatly reduced. Further, the number of liquid crystal molecules M that can give a phase difference to transmitted light increases regardless of whether or not a shadow is visually recognized. As a result, as shown in FIG. 9, the transmission intensity T1 of the liquid crystal display device 1 according to the present embodiment is higher than the transmission intensity T101 of the conventional liquid crystal display device 101 on which linearly polarized light is incident, and the light use efficiency is increased. (Effective aperture ratio) and brightness can be improved. In FIG. 9, the horizontal axis represents the voltage [V] applied to the liquid crystal layer of each of the liquid crystal display devices 1 and 101, and the theoretical maximum transmittance in the liquid crystal display device (50% of the air transmittance) The ratio (transmission intensity) of each transmittance is illustrated.
[0051]
In the above, the retardation of the λ / 4 plates 23a and 23b is set so that the incident light becomes circularly polarized light. However, even if it is not completely circularly polarized light, the brightness does not decrease so much, and it is rough. If the deviation does not occur, substantially circularly polarized elliptically polarized light may be used. Specifically, for example, when the transmittance at the wavelength (550 nm) with the highest visibility is measured (simulated) while changing the retardation of the λ / 4 plates 23a and 23b in the configuration of FIG. As shown. Here, if the change rate of the brightness is within 10%, that is, if the transmittance is 0.9 or more, the decrease in brightness is hardly recognized by the observer, and the roughness is not easily recognized. Therefore, the retardation of the λ / 4 plates 23a and 23b is optimal if it is 135 nm with respect to light in the vicinity of 550 nm, and if it is in the range of 95 nm or more and 175 nm or less, it may not be completely circularly polarized. A similar effect can be obtained. In addition, when it is out of the above range, the brightness is drastically lowered and the roughness due to the poor alignment region is easily observed.
[0052]
By the way, if the λ / 4 plates 23a and 23b can mutually convert circularly polarized light or elliptically polarized light close to circularly polarized light and linearly polarized light at the wavelength with the highest visibility, that is, approximately the above numerical range at the wavelength. If the λ / 4 condition is satisfied, it is effective for improving the brightness and preventing the roughness. However, in particular, when performing display that emphasizes color tone, circularly polarized light or circularly polarized light is applied over the entire visible light band. It is preferable that elliptically polarized light and linearly polarized light close to each other can be converted into each other. However, in general, it is difficult to completely eliminate chromatic dispersion with the single-layer λ / 4 plates 23a and 23b. For example, when a λ / 4 plate prepared so as to satisfy the λ / 4 condition for light having the highest visibility (550 nm) as the λ / 4 plates 23a and 23b, the light wavelength is 550 nm. As it deviates from λ / 4, the λ / 4 condition is deviated. As a result, in order to realize black display, even if the applied voltage is set to a value at which light of 550 nm is blocked, visible light shifted from 550 nm may pass through the polarizing plate 22b and a coloring phenomenon may occur. .
[0053]
Therefore, when suppression of the coloring phenomenon is required, such as in the case of color display, the transmission axis PAa of the polarizing plate 22a and the transmission axis PAb of the polarizing plate 22b are orthogonal to each other as shown in FIG. Preferably, the slow axis SLa of the / 4 plate 23a and the slow axis SLb of the λ / 4 plate 23b are orthogonal to each other. The angle between the transmission axis PAa and the slow axis SLa and the angle between the transmission axis PAb and the slow axis SLb are set to 45 degrees in the same direction as in FIG.
[0054]
In the liquid crystal display device 1a according to the modification, the slow axis SLa of the λ / 4 plate 23a and the slow axis SLb of the λ / 4 plate 23b are orthogonal to each other, so that each of the λ / 4 plates 23a and 23b. The chromatic dispersions of refractive index anisotropy of each cancel each other. As a result, in the black display state, transmitted light in a wider wavelength range can be absorbed by the polarizing plate 22b, and a good black display without coloring can be realized.
[0055]
Although both λ / 4 plates 23a and 23b may be formed of λ / 4 plates made of different materials, at least the same material, preferably using λ / 4 plates manufactured by the same manufacturing method, is used. However, a color-free liquid crystal display device can be realized at a lower cost than using a broadband λ / 4 plate.
[0056]
By the way, in the above description, the case where light enters the liquid crystal layer 21c perpendicularly during black display has been described. However, in particular, in the transmissive liquid crystal display device 1, although vertical incident light contributes most to the display, it is from an oblique direction (a direction inclined from the normal direction of the display surface of the liquid crystal display device 1) with respect to the liquid crystal layer 21 c. Incident light also contributes to the display. Here, the oblique incident light is also given a phase difference by the vertically aligned liquid crystal layer 21c. Therefore, when the display surface of the liquid crystal display device 1 is viewed from an oblique direction, light leakage may occur and the contrast ratio of the display may be lowered despite the vertical alignment state that should be the black display state. is there.
[0057]
Therefore, when an improvement in the contrast ratio in the oblique direction is required, the refractive index anisotropy is set so as to cancel the phase difference with respect to the oblique incident light as in the liquid crystal display device 1b shown in FIG. It is desirable to further provide a viewing angle compensation plate (viewing angle compensation layer) 24 made of a phase difference plate. In FIG. 12, as an example, the case where the viewing angle compensation plate 24 made of a single retardation plate is provided outside the TFT substrate 21a (the side farthest from the liquid crystal layer 21c) is illustrated. The viewing angle compensation plate 24 may be formed by stacking a plurality of retardation plates. Further, the position where the viewing angle compensation plate 24 is provided is not limited to the outside of the TFT substrate 21a, and may be provided outside the counter substrate 21b or outside the both substrates 21a and 21b.
[0058]
In any case, the total phase difference by the viewing angle compensation plate 24 is set so as to cancel out the phase difference with respect to the obliquely incident light, so that the light leakage in the oblique direction can be suppressed and the contrast ratio is improved. it can. Thereby, a liquid crystal display device having a good contrast ratio in any viewing angle range can be realized.
[0059]
By the way, in the above description, the radial inclined orientation is realized by the holes 32, but the present invention is not limited to this. For example, as in the liquid crystal display device 1c shown in FIG. 13, the radial inclined alignment can be realized even when the substantially hemispherical protrusion 35 is provided on the pixel electrode 31 instead of the hole portion 32. Even in this case, the liquid crystal molecules M in the vicinity of the protrusion 35 are aligned perpendicularly to the surface of the protrusion 35, and the electric field in the vicinity of the protrusion 35 is inclined in a direction parallel to the surface of the protrusion 35 when a voltage is applied. As a result, the liquid crystal molecules M are likely to be inclined in a radial manner around the protrusions 35 in the in-plane direction, as indicated by arrows in the figure, as in the configuration of FIG. It can be tilted radially. Each protrusion 35 can be formed by applying a photosensitive resin and processing it by a photolithography process.
[0060]
In the above description, the case where each liquid crystal molecule M of the liquid crystal layer 21c tilts and the alignment directions of the liquid crystal molecules M continuously change from each other when voltage is applied has been described as an example. It is not limited to. As shown in FIGS. 14 to 16, it is also effective to divide the liquid crystal layer into a plurality of domains and use a liquid crystal layer having a configuration (multi-domain alignment) in which the alignment directions are different from each other when a voltage is applied.
[0061]
For example, in the liquid crystal display device 1 d illustrated in FIG. 14, a square pyramid-shaped projection 35 a is formed on the pixel electrode 31 instead of the hemispherical projection 35 illustrated in FIG. 13. Even in this configuration, the liquid crystal molecules M are aligned so as to be perpendicular to the inclined surfaces in the vicinity of the protrusions 35a. In addition, when a voltage is applied, the electric field at the portion of the protrusion 35a is inclined in a direction parallel to the slope of the protrusion 35a. As a result, when a voltage is applied, the in-plane component of the orientation angle of the liquid crystal molecules M becomes equal to the in-plane component (direction P1, P2, P3 or P4) in the normal direction of the nearest slope. Therefore, the pixel region is divided into four domains D1 to D4 having different alignment directions at the time of inclination. As a result, when the liquid crystal display device 1d is viewed from a certain domain side, even if the transmittance of the domain decreases, the transmittance of the remaining domain does not decrease, and the decrease in the overall transmittance can be suppressed. Thereby, the brightness of the liquid crystal display device 1d is less likely to depend on the in-plane orientation of the viewing angle.
[0062]
Here, in the 4-domain multi-domain alignment, the in-plane component in the alignment direction is limited. Therefore, unlike the case of the above-mentioned radial tilt alignment, even when linearly polarized light is incident, the transmitted light is set by setting the angle between the directions P1 to P4 and the direction of the linearly polarized light to be 45 degrees. It is possible to reduce the number of liquid crystal molecules that cannot give a phase difference to.
[0063]
However, even if such a setting is made, the alignment state of the liquid crystal molecules M tends to be disturbed in the boundary region B12, B23, B34 or B41 between the domains, or in the outer edge region of the pixel electrode 31, so that the alignment state Due to this disturbance, the direction of linearly polarized light coincides with the in-plane component in the alignment direction, which may increase the number of liquid crystal molecules that cannot give a phase difference to transmitted light.
[0064]
Specifically, in the boundary region, the liquid crystal molecules M are aligned so as to be supported by the liquid crystal molecules M present in the domains on both sides, so the alignment of the liquid crystal molecules M is not fixed and is in an unstable state. As a result, when the balance of the alignment regulating force from the domains on both sides is broken by a slight trigger, the alignment state of the boundary region changes (inclines). Here, the balance changes not only due to a slight variation in the orientation regulating force in the manufacturing process but also due to a lateral electric field caused by a voltage applied to the gate signal line and the source signal line, deterioration with time, and the like. Therefore, the change in the orientation state is not only different for each part in the boundary region, but is also different for each picture element. As a result, when linearly polarized light is incident, there is a possibility that it will be visually recognized as rough.
[0065]
In the edge region, the alignment state changes continuously, and is more susceptible to an external electric field, such as an electric field from a source signal line or a gate signal line, than the central portion of the pixel electrode 31. In addition, when the orientation is controlled by the wall structure, it is easily subjected to three-dimensional strain. As described above, since the edge region is easily affected by the surroundings, the alignment regulating force is likely to be non-uniform, and the alignment state of the liquid crystal molecules is likely to change (tilt). This change in the orientation state is not only different for each part in the boundary region, but is also different for each pixel. As a result, when linearly polarized light is incident on a liquid crystal layer having a multi-domain configuration, the alignment state may be visually perceived as rough.
[0066]
On the other hand, in the present embodiment, circularly polarized light is incident on the multi-domain aligned liquid crystal cell by the λ / 4 plate 23a. As a result, even if the alignment state of the liquid crystal molecules M is disturbed, as in the case of the radially inclined alignment, as long as the alignment direction and the viewing angle of the liquid crystal molecules M do not match not only the in-plane component but also the substrate normal component, the liquid crystal The molecule M can contribute to the display. Thus, as a result of using a multi-domain alignment liquid crystal layer to ensure a wide viewing angle, not only the edge region of the pixel electrode 31 but also the boundary region of the domain exists, and there is no roughness and the display A high-quality liquid crystal display device can be realized.
[0067]
In the liquid crystal display device 1d shown in FIG. 14, the projections 35a are provided to realize multi-domain alignment. For example, like the liquid crystal display device 1e shown in FIG. The stripe-shaped convex portions 36... Whose in-plane shape bends substantially at right angles to the zigzag are provided on the pixel electrode 31, and the counter electrode of the counter substrate 21 b can also be provided with a convex portion 37 having the same shape. The spacing in the in-plane direction of both the convex portions 36 and 37 is arranged such that the normal line of the slope of the convex portion 36 and the normal line of the slope of the convex portion 37 coincide. Each of the convex portions 36 and 37 can be formed by applying a photosensitive resin on the pixel electrode 31 and the counter electrode and processing it in a photolithography process, like the projections 35 and 35a.
[0068]
In the structure described above, in the line portion L1 (L2) other than the corner portion C of the convex portion 36, the liquid crystal molecules M in the regions D1 and D2 (D3 and D4) in the vicinity of the line portion are aligned along both mountain-shaped slopes. To do. The two line portions L1 and L2 are orthogonal to each other. As a result, each pixel can be divided into a plurality of domains D1 and D2 (D3 and D4) having different alignment directions.
[0069]
Even in this configuration, the domain boundary regions B13 and B24 exist so as to connect the corners C. Further, domain boundary regions B12 and B34 exist along the line portions L1 and L2. Therefore, when linearly polarized light is incident on the liquid crystal cell, even if the direction of the line portions L1 and L2 in the plane is inclined by 45 degrees with respect to the linearly polarized light, the alignment direction in the boundary regions B13, B24, B12, and B34 There is a possibility that the disorder of the state is visually recognized as roughness. The boundary regions B13 and B24 connecting the corners C are regions that are shielded from light, such as auxiliary capacitance wiring made of metal formed on the TFT substrate 21a and a light shielding film provided on the counter substrate 21b as a color filter substrate. However, the boundary regions B12 and B34 along the line portions L1 and L2 cannot be hidden unless an extra light shielding film is provided.
[0070]
In addition, the method for realizing multi-domain alignment is not limited to the method using protrusions, and the pixel electrode 31 or the counter electrode may be provided with a slit to perform alignment division. For example, in the liquid crystal display device 1 f shown in FIG. 16, as in the liquid crystal cell described in JP-A-11-109391, a Y-shaped slit is formed on the counter electrode of the counter substrate 21 b in the vertical direction (in the plane, approximately An alignment control window 38 is provided that is symmetrically connected in a direction parallel to any side of the pixel electrode 31 having a shape.
[0071]
In this configuration, in the region immediately below the alignment control window 38 in the surface of the counter substrate 21b, an electric field sufficient to incline the liquid crystal molecules M is not applied, and the liquid crystal molecules M are aligned vertically. On the other hand, in the region around the orientation control window 38 on the surface of the counter substrate 21b, an electric field is generated that spreads away from the orientation control window 38 as the counter substrate 21b is approached. As a result, the liquid crystal molecules M are inclined in the direction in which the major axis is perpendicular to the electric field, and the in-plane component in the alignment direction of the liquid crystal molecules M is substantially perpendicular to each side of the alignment control window 38 as indicated by arrows in the drawing. become. Thereby, a plurality of domains D1 to D4 can be formed in one pixel. Although not shown in the figure for convenience of explanation, in practice, a TFT in which the gate electrode is connected to the gate signal line 34, the source electrode is connected to the source signal line 33, and the drain is connected to the pixel electrode 31. An element is provided.
[0072]
However, even in this case, the alignment direction of the liquid crystal molecules M is likely to be disturbed in the boundary region of each domain (the region immediately below the alignment control window 38), and the disclination line DL may be visually recognized. As in the above publication, when the distance between the adjacent pixel electrodes 31 is Wp, the distance between the pixel electrode 31 and the counter electrode is d, and the slit width of the orientation control window 38 is Ws, Wp> d / 2, And / or if Ws> d / 2 is set, the appearance location of the disclination line DL can be made uniform, but there is no change in the presence of the boundary region, so that the orientation abnormality can be completely reduced. difficult.
[0073]
In any case, in a multi-domain liquid crystal cell, a plurality of domains are provided in one pixel in order to increase the viewing angle, and therefore a boundary region exists in the pixel (in the display region). Therefore, when linearly polarized light is incident, a disclination line DL along the direction of the absorption axis of the polarizing plate 22a (22b) (crossed Nicol) is generated in the alignment control window 38 due to disorder of the alignment state in the boundary region. Since the state of the disclination line DL differs from place to place and from pixel to pixel, there is a risk that roughness will be visible.
[0074]
In contrast, in the present embodiment, circularly polarized light is incident on a multi-domain aligned liquid crystal cell. Thereby, as a result of using a multi-domain alignment liquid crystal cell to ensure a wide viewing angle, not only the edge region of the pixel electrode 31 but also the boundary region of the domain is present in the alignment control window 38. The disclination line becomes difficult to observe. Therefore, the liquid crystal display device 1 having no display roughness and high display quality can be realized.
[0075]
In the present embodiment, as an example of the liquid crystal cell, the liquid crystal cell has negative dielectric anisotropy, and as an initial alignment, the liquid crystal molecule M is aligned perpendicular to the substrate surface, and the liquid crystal molecules M in the pixel are applied when a voltage is applied. The case of using a liquid crystal layer tilted in multiple directions has been described as an example, but a liquid crystal layer having positive dielectric anisotropy and oriented in multiple directions in the horizontal direction with respect to the substrate surface is used at the initial alignment. May be.
[0076]
In any case, a liquid crystal display using a liquid crystal layer in which the orientation direction is controlled so that in-plane components in the orientation direction of the liquid crystal molecules M are different from each other in one pixel in a state where a certain voltage is applied. If it is an apparatus, the effect substantially the same as this embodiment is acquired.
[0077]
Further, even in the liquid crystal layer in which the alignment direction of the liquid crystal molecules M is controlled so that the alignment direction of the liquid crystal molecules M in the pixel is a single direction, at the edge portion of the pixel, for example, a source signal line or a gate There is a possibility that the orientation direction is disturbed by an oblique electric field from a bus wiring such as a signal line. Therefore, a certain degree of effect can be obtained if the liquid crystal display device uses liquid crystal layers having different in-plane components in the alignment direction of each liquid crystal molecule M in one pixel with a certain voltage applied.
[0078]
However, the liquid crystal layer in which the alignment direction is controlled such that the in-plane components of the alignment direction of the liquid crystal molecules M are different from each other within one pixel in a state where a certain voltage is applied, such as multi-domain alignment and radial gradient alignment. If so, as compared with a liquid crystal layer in which the alignment direction is controlled so as to be a single direction, the alignment state is likely to be disturbed, and the display quality is likely to deteriorate. Therefore, the display quality can be further improved when the circularly polarized light is incident on the liquid crystal layer.
[0079]
In addition, a vertical alignment type liquid crystal cell has a higher display contrast and a faster monochrome level response speed than a TN (Twisted Nematic) type liquid crystal cell. Furthermore, the in-plane orientation dependence of the viewing angle can be suppressed by combining radial tilt orientation or multi-domain orientation. Therefore, liquid crystal satisfying all of contrast, response speed, viewing angle, in-plane orientation dependence of viewing angle and display quality by entering circularly polarized light into a multi-domain or radially tilted liquid crystal cell in the vertical alignment method. A display device can be realized. In particular, the radial tilt alignment is easier to visually recognize when combined with linearly polarized light than the multi-domain alignment, but has less in-plane orientation dependency. Therefore, as in the present embodiment, the liquid crystal display device with less in-plane orientation dependency can be realized without degrading the display quality by making the circularly polarized light incident and suppressing the roughness.
[0080]
[Second Embodiment]
By the way, in the said 1st Embodiment, when the polarizing plate 22a and (lambda) / 4 board 23a are provided between the backlight 3 and the liquid crystal cell 21 as a circularly polarized light means for injecting circularly polarized light into the liquid crystal cell 21 Explained. However, since the polarizing plate 22a absorbs vibration components other than the transmission axis PAa, the amount of light emitted from the polarizing plate 22a is limited to about 40% to 60% of the amount of incident light.
[0081]
On the other hand, in the liquid crystal display device 1g according to the present embodiment, as shown in FIG. 17, a selective reflection layer 25 is provided as a circularly polarizing means instead of the members 22a and 23a. The selective reflection layer 25 is characterized in that it transmits circularly polarized light rotating in one direction out of incident light and reflects circularly polarized light rotating in the opposite direction, and can be formed of, for example, a cholesteric liquid crystal film. . The cholesteric liquid crystal film has a helical structure. For example, in the case of a cholesteric liquid crystal film having a left-handed helical structure, incident light is separated into left circularly polarized light and right circularly polarized light in the process of passing through the helical structure. At the same time, the left circularly polarized light is reflected and the right circularly polarized light is transmitted. In contrast, right-handed helical cholesteric liquid crystals reflect right-handed circularly polarized light and transmit left-handed circularly polarized light. As a result, the circularly polarized light in the required turning direction can be extracted. Moreover, selective reflection can be performed in a wide band by using films having different helical pitches in the thickness direction. The cholesteric liquid crystal film can be produced, for example, by irradiating a bifunctional cholesteric monomer and a monofunctional nematic monomer with ultraviolet rays and utilizing a difference in speed of photocrosslinking. The selective reflection layer 25 is desired to have selective reflectivity at a wide wavelength range. However, if this is difficult, the selective reflection layer 25 is adjusted to the emission spectrum of the backlight 3 so that the light from the backlight 3 can be selectively reflected. Thus, a wavelength that can be selectively reflected may be set. For example, when a three-wavelength tube is used for the backlight 3, the selective reflection layer 25 only needs to have selective reflectivity at the three wavelengths.
[0082]
  In the liquid crystal display device 1 g configured as described above, the light emitted from the backlight 3 is transmitted through the selective reflection layer 25 to become circularly polarized light in a desired turning direction, and is incident on the liquid crystal cell 21. On the other hand, the circularly polarized light rotating in the opposite direction is reflected by the selective reflection layer 25 and returned to the backlight 3. Here, part of the circularly polarized light returned to the backlight 3 has its polarization state broken inside the backlight 3 and is emitted from the backlight 3 to the selective reflection layer 25 again. Therefore, in the liquid crystal display device 1g according to the present embodiment, a part of the light from the backlight 3 absorbed by the polarizing plate 22a of the liquid crystal display device 1 of FIG. 1 can be reused. As a result, the light utilization efficiency of the backlight 3 can be improved, and a brighter liquid crystal display device can be realized.
As described above, the liquid crystal display device is provided between the first substrate provided with the pixel electrode corresponding to the pixel, the second substrate provided with the counter electrode, and the pixel electrode. A liquid crystal layer in which the orientation directions of the liquid crystal molecules are controlled to be different from each other in the pixel when the voltage between the electrodes is at least a predetermined value; and an analyzer disposed on the output side of the liquid crystal layer; The circularly polarizing means for setting the incident light to the liquid crystal layer in a substantially circular polarization state, and provided between the liquid crystal layer and the analyzer, the in-plane retardation is approximately 4 minutes of the wavelength of the transmitted light. And a first retardation layer set to one wavelength. Further, the liquid crystal display device includes a multi-domain alignment liquid crystal layer, an analyzer disposed on an emission side of the liquid crystal layer, a circular polarization unit that sets incident light to the liquid crystal layer in a substantially circular polarization state, A first retardation layer is provided between the liquid crystal layer and the analyzer, and the retardation in the in-plane direction is set to approximately a quarter wavelength of the wavelength of the transmitted light.
[0083]
【The invention's effect】
  As described above, the transmissive liquid crystal display device according to the present invention has the alignment direction of the liquid crystal molecules.Presents a continuously varying radial gradient orientationA liquid crystal layer, an analyzer disposed on the exit side of the liquid crystal layer, and the liquid crystal layerAt a wavelength of 550 nmCircular polarization means for setting the incident light in a substantially circular polarization state, provided between the liquid crystal layer and the analyzer, retardation in the in-plane direction,95nm or more, 175nm or lessAnd a first retardation layer set in (1).
[0086]
Each of the above configurationsTransmission typeIn the liquid crystal display device, since substantially circularly polarized light is incident on the liquid crystal layer, there is no anisotropy in the alignment direction of the liquid crystal layer, and the alignment direction of the liquid crystal molecules and transmitted light are in-plane components and the substrate normal direction. As long as they do not coincide with each other, the liquid crystal molecules can give a phase difference to the transmitted light. Therefore, as a result of controlling the alignment direction of the liquid crystal molecules to be different from each other in the pixel in order to ensure a wide viewing angle, the alignment direction of the liquid crystal molecules whose alignment is disturbed despite the fact that the alignment state is likely to be disturbed. As long as it does not match, it can contribute to the improvement of brightness. As a result, while maintaining a wide viewing angle, high light utilization efficiency can be ensured, and an effect of improving the contrast ratio and increasing the number of gradations can be achieved.
[0087]
According to the present inventionTransmission typeAs described above, in the liquid crystal display device, in addition to the above configuration, the circular polarization unit sets light having a wavelength of 550 nm to a substantially circular polarization state, and the first retardation layer has an in-plane retarder. The foundation is set to approximately one quarter of 550 nm.
[0088]
In this configuration, substantially circularly polarized light is incident on a wavelength of 550 nm, which has the highest human visibility, and it is possible to prevent a decrease in brightness and occurrence of roughness of light having the wavelength. As a result, compared with the case where substantially circularly polarized light is incident only at other wavelengths, it is difficult to visually recognize a decrease in brightness and roughness.Transmission typeThe liquid crystal display device can be realized.
[0089]
According to the present inventionTransmission typeAs described above, in the liquid crystal display device, in addition to the above configuration, the in-plane retardation of the first retardation layer is set to 95 nm or more and 175 nm or less.
[0090]
In the above configuration, since the retardation is set to 95 nm or more and 175 nm or less with respect to light having a wavelength of 550 nm, even in the case where the brightness is lowered, the brightness is lowered in the general region and the brightness in the orientation disorder region. The decrease in height is suppressed to about 10%. As a result, compared with the case where other ranges are set, it is difficult to visually recognize a decrease in brightness and roughness.Transmission typeThe liquid crystal display device can be realized.
[0091]
According to the present inventionTransmission typeAs described above, in the liquid crystal display device, in addition to the above-described configuration, the circularly polarizing means is provided on the incident side of the liquid crystal layer, and transmits circularly polarized light in a predetermined turning direction and rotates in a reverse direction. It is the structure which is a selective reflection layer which reflects polarized light.
[0092]
In this configuration, the circularly polarized light that rotates in the direction opposite to the predetermined direction is reflected by the selective reflection layer, so that it can be reused unlike the case of being absorbed by the polarizer. As a result, although the substantially circular polarized light can be incident on the liquid crystal layer, the light use efficiency can be improved.
[0093]
According to the present inventionTransmission typeAs described above, the liquid crystal display device is arranged between the polarizer provided on the incident side of the liquid crystal layer and the polarizer and the liquid crystal layer instead of the selective reflection layer, and has an in-plane retardation. And a second retardation layer set to approximately a quarter wavelength of the wavelength of transmitted light.
[0094]
Even in this configuration, since the linearly polarized light emitted from the polarizer is converted into substantially circularly polarized light by the second retardation layer, substantially circularly polarized light can be incident on the liquid crystal layer. As a result, while maintaining a wide viewing angle, high light utilization efficiency can be ensured, and an effect of improving the contrast ratio and increasing the number of gradations can be achieved.
[0095]
According to the present inventionTransmission typeAs described above, in the liquid crystal display device, in the above configuration, the analyzer is arranged on one side of the liquid crystal layer, the polarizer is arranged on the other side, and the transmission axis of the analyzer and the first axis The retardation axis of the retardation layer forms an angle of 45 degrees, and the transmission axis of the polarizer and the retardation axis of the second retardation layer form an angle of 45 degrees.
[0096]
In this configuration, the transmission axis of the analyzer and the slow axis of the first retardation layer form an angle of 45 degrees, and the transmission axis of the polarizer and the slow axis of the second retardation layer are 45. Since the angle of the angle is formed, there is an effect that the linearly polarized light and the circularly polarized light can be efficiently converted into each other.
[0097]
According to the present inventionTransmission typeAs described above, in the liquid crystal display device, in the above configuration, the analyzer is disposed on one of the liquid crystal layers, the polarizer is disposed on the other, and the first and second retardation layers are provided. Are arranged such that their slow axes are orthogonal to each other, and the analyzer and polarizer are arranged so that their transmission axes are orthogonal to each other.
[0098]
In this configuration, the slow axes of the first and second retardation layers are arranged so as to be orthogonal to each other. Therefore, the wavelength dispersions of refractive index anisotropy possessed by both retardation layers cancel each other. As a result, in a black display state, transmitted light in a wider wavelength range is absorbed by the analyzer. As a result, there is an effect that a better black display can be realized.
[0099]
According to the present inventionTransmission typeAs described above, the liquid crystal display device is provided between the analyzer and the polarizer in addition to the above-described components, and out of the phase difference provided by the liquid crystal layer, from the normal direction of the first substrate. This is a configuration including a viewing angle compensation layer in which refractive index anisotropy is set so as to cancel a phase difference that varies depending on an inclination angle up to a viewing angle.
[0100]
In this configuration, the phase difference provided by the liquid crystal layer is canceled by the viewing angle compensation layer depending on the tilt angle of the viewing angle. Therefore, it is possible to suppress the dependency of the viewing angle and to have a good contrast ratio in a wider viewing angle range.Transmission typeThe liquid crystal display device can be realized.
[Brief description of the drawings]
FIG. 1, showing an embodiment of the present invention, is a schematic diagram showing a configuration of a main part of a liquid crystal display device when no voltage is applied.
FIG. 2 is a schematic diagram illustrating a configuration of a main part of the liquid crystal display device when a voltage is applied.
FIG. 3 is a perspective view showing a configuration example of a liquid crystal cell of the liquid crystal display device and showing a pixel electrode.
4 is a cross-sectional view taken along line α-α showing the vicinity of the pixel electrode of the liquid crystal cell. FIG.
FIG. 5 is a plan view showing a pixel electrode, showing another configuration example of the liquid crystal cell.
FIG. 6 shows the liquid crystal display device, and is an explanatory diagram showing the relationship between the alignment state of liquid crystal molecules when no voltage is applied, the slow axis of a λ / 4 plate, and the transmission axis of a polarizing plate. .
FIG. 7 shows the liquid crystal display device, and is an explanatory diagram showing the relationship between the alignment state of liquid crystal molecules when a voltage is applied, the slow axis of a λ / 4 plate, and the transmission axis of a polarizing plate.
FIG. 8 is an explanatory diagram illustrating a display example of the liquid crystal display device.
FIG. 9 is a graph showing the transmission intensity of the liquid crystal display device and the transmission intensity of a conventional liquid crystal display device.
FIG. 10 is a graph showing the relationship between retardation and transmittance of a λ / 4 plate.
FIG. 11 shows a modification of the liquid crystal display device, and is an explanatory diagram showing the relationship between the slow axis of a λ / 4 plate and the transmission axis of a polarizing plate.
FIG. 12 is a schematic diagram showing a configuration of a main part of the liquid crystal display device, showing a modification of the liquid crystal display device.
FIG. 13 is a perspective view showing still another configuration example of the liquid crystal cell and showing a pixel electrode.
FIG. 14 is a perspective view showing a pixel electrode according to another configuration example of the liquid crystal cell.
FIG. 15 is a plan view showing the vicinity of a pixel electrode, showing another configuration example of the liquid crystal cell.
FIG. 16 is a plan view showing the vicinity of a pixel electrode, showing still another configuration example of the liquid crystal cell.
FIG. 17, showing another embodiment of the present invention, is a schematic diagram showing a configuration of a main part of a liquid crystal display device.
FIG. 18 shows a conventional example and is a schematic diagram showing a main configuration of a liquid crystal display device.
FIG. 19 is an explanatory diagram showing a display example of the liquid crystal display device.
[Explanation of symbols]
1.1a to 1g liquid crystal display device
21a TFT substrate (first substrate)
21b Counter substrate (second substrate)
31 Pixel electrode
21c Liquid crystal layer
22a Polarizing plate (polarizer; circularly polarizing means)
22b Polarizing plate (analyzer)
23a λ / 4 plate (second retardation layer; circularly polarizing means)
23b λ / 4 plate (first retardation layer)
24 viewing angle compensation plate (viewing angle compensation layer)
25 selective reflection layer (circular polarization means)

Claims (6)

A first substrate provided with a pixel electrode corresponding to the pixel;
A second substrate provided with a counter electrode;
A liquid crystal layer that is provided between the substrates and exhibits a radially inclined alignment in which the alignment direction of the liquid crystal molecules continuously changes when the voltage between the pixel electrode and the counter electrode is at least a predetermined value;
An analyzer disposed on the exit side of the liquid crystal layer;
Circularly polarizing means for setting incident light having a wavelength of 550 nm to the liquid crystal layer in a substantially circular polarization state;
A transmissive liquid crystal display device comprising: a first retardation layer provided between the liquid crystal layer and the analyzer and having an in-plane retardation of 95 nm or more and 175 nm or less. . The circularly polarizing means is a selective reflection layer that is provided on the incident side of the liquid crystal layer and transmits circularly polarized light in a predetermined turning direction and reflects circularly polarized light that rotates in the opposite direction. 2. The transmissive liquid crystal display device according to 1. The circularly polarizing means includes a polarizer provided on the incident side of the liquid crystal layer,
  The second retardation layer is provided between the polarizer and the liquid crystal layer, and the retardation in the in-plane direction is set to approximately a quarter wavelength of the wavelength of transmitted light. The transmissive liquid crystal display device according to claim 1. The analyzer is disposed on one side of the liquid crystal layer, and the polarizer is disposed on the other side.
  The transmission axis of the analyzer and the slow axis of the first retardation layer form an angle of 45 degrees,
  In addition, the analyzer, the polarizer, and the first and second retardation layers are arranged so that the transmission axis of the polarizer and the slow axis of the second retardation layer form an angle of 45 degrees. The transmissive liquid crystal display device according to claim 3. The analyzer is disposed on one side of the liquid crystal layer, and the polarizer is disposed on the other side.
  The first and second retardation layers are arranged so that their slow axes are orthogonal to each other,
  4. The transmission type liquid crystal display device according to claim 3, wherein the analyzer and the polarizer are arranged so that their transmission axes are orthogonal to each other. Among the phase difference provided between the analyzer and the polarizer and provided by the liquid crystal layer, so as to cancel the phase difference that varies depending on the tilt angle from the normal direction to the viewing angle of the first substrate. The transmissive liquid crystal display device according to claim 1, further comprising a viewing angle compensation layer in which refractive index anisotropy is set.

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