JP2004258527A - Liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transflective liquid crystal display in which favorable display quality with sufficient intensity of light can be obtained in both of transmissive display and reflective display without having a defocused image. <P>SOLUTION: A rough base layer 16 is formed on the inner face of a back side transparent substrate 12 and in a part corresponding to the reflective part Dr of a pixel region Dp, and a scattering reflective layer 17 is deposited thereon. A color filter layer 18 is formed to cover the scattering reflective layer 17. A pixel electrode 13 and a thin film transistor 14 are arranged in each pixel region Dp on the inner face of a front side transparent substrate 11, and a liquid crystal layer is sealed between the transparent substrates 11, 12. Front and back and front retardation plates 4, 5 and front and back polarizing plates 2, 3 are successively layered as interposing the liquid crystal cell 1 to constitute a liquid crystal display element LD. Then a surface light source back light BL with a light guide plate is disposed in the back side of the liquid crystal display element LD. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device capable of performing both transmissive display and reflective display.
[0002]
[Prior art]
2. Description of the Related Art In recent years, a transflective liquid crystal display device with low power consumption has been widely used as a display suitable for a portable tool such as a mobile phone or a portable information terminal. This transflective liquid crystal display device uses a reflective display that uses external light where there is abundant external light obtained from the usage environment such as natural light or indoor lighting, and uses a built-in lighting device where the external light is weak. This is a liquid crystal display device in which power consumption mainly consumed by the lighting device is reduced by switching to the transparent display.
[0003]
Such a transflective liquid crystal display device generally includes a liquid crystal cell provided with a transflective layer, and a forward scattering film and a polarizing plate laminated on a front side, which is a side on which the liquid crystal cell is observed, and a rear side. A liquid crystal display element is formed by laminating a polarizing plate on the liquid crystal display, and a backlight is provided on the rear side of the liquid crystal display element. In this case, the transflective layer provided in the liquid crystal cell may be a transflective plate type that reflects and transmits incident light at a predetermined ratio, or a reflective portion provided with a partial reflective film in the pixel region. And a transmissive portion. The transflective layer is provided between the rear substrate of the liquid crystal cell and the liquid crystal layer. Further, the forward scattering film is provided to suppress strong mirror reflection specific to the mirror surface and reflection of the outside scene when the reflection surface of the semi-transmissive reflection layer is a mirror reflection surface in order to increase the reflection efficiency (for example, Patent Document 1).
[0004]
[Patent Document 1]
JP-A-2002-303865 (pages 3 and 4, FIGS. 13A and 13B)
[0005]
[Problems to be solved by the invention]
However, in the transflective liquid crystal display device, each pixel light corresponding to different information in each adjacent pixel is scattered by the forward scattering film when emitted from the liquid crystal display element, and the boundary of the display image is reduced. So-called image blurring tends to occur. In the transmissive display, the light emitted from the backlight is condensed and made incident on the liquid crystal display element. However, when the incident light is emitted, it is scattered by the forward scattering film, so that the light intensity decreases. Display becomes dark.
[0006]
The present invention not only suppresses reflection and mirror reflection in reflective display, but also achieves transflective display and good display quality with sufficient light intensity without image blur in both transmissive display and reflective display. It is an object to provide a reflection type liquid crystal display device.
[0007]
[Means for Solving the Problems]
In the liquid crystal display device of the present invention, a liquid crystal layer is provided between a front substrate that is a display observation side and a rear substrate that is disposed to face the front substrate, and the inner surfaces of the front substrate and the rear substrate that face each other. At least one electrode is provided on one side, and a plurality of electrodes for forming a plurality of pixels are provided on the other inner surface so as to face the at least one electrode, respectively, and the liquid crystal layer and the rear substrate are connected to each other. A reflective film is provided in the other region except for one predetermined region for each of the plurality of pixels, and the other of the plurality of pixels is provided with the reflective film. A reflection portion that reflects light incident from the front side by the region and emits the light to the front side by the reflection film, and a transmission portion that emits light incident from the rear side to the front side by one region where the reflection film is not provided. Formed liquid Element, a front polarizing plate and a rear polarizing plate disposed on the front side and the rear side of the liquid crystal element, respectively, and a backlight disposed on the rear side of the rear polarizing plate. A base layer having an uneven surface formed on at least the other area corresponding to the reflective portion on the inner surface side of the rear substrate; and the reflective film is formed on the uneven surface of the base layer. It is characterized by having.
[0008]
According to this liquid crystal display device, a reflective film selectively disposed in a region corresponding to a reflective portion between the liquid crystal layer and the rear transparent substrate is formed on an underlayer having an uneven surface to form an uneven reflective film. Since the liquid crystal layer is transmitted after the reflection and the scattering are performed at the same time, image blur is prevented in the reflective display. Also, in the transmissive display, since there is no uneven surface in front of the liquid crystal layer, image blur does not occur and loss due to light scattering when the uneven underlying layer exists is small. Accordingly, not only mirror reflection and reflection in the reflective display are prevented, but also in both the transmissive display and the reflective display, a good display quality with sufficient light intensity without image blur can be obtained.
[0009]
In the liquid crystal display device according to the present invention, it is preferable that a color filter of a predetermined color is formed on at least the entire pixel region so as to cover the base layer and the reflective film as described in claim 2, thereby forming a mirror. A good reflection color display without reflection or image blur can be obtained. In this case, as described in claim 3, the underlayer is provided at least in a region excluding the transmission part, and the color filter is formed such that the film thickness in the reflection part is smaller than the film thickness in the transmission part. Therefore, it is easy to provide a liquid crystal display device in which the thickness of the color filter in the reflection part is smaller than the thickness of the transmission part in order to make the display quality of the transmission color display and the reflection color display substantially the same. Can be manufactured.
[0010]
In the liquid crystal display device according to the present invention, it is preferable that the color filter is provided with a through hole in a region corresponding to the reflection portion, thereby providing a sufficiently bright reflective color display. Is obtained, and it is possible to obtain a white color closer to pure white in the reflective display by optimally setting the opening area ratio of the through holes for each pixel of each color.
[0011]
Further, as set forth in claim 5, the liquid crystal element includes a plurality of pixel electrodes in which electrodes provided on the inner surface of the front substrate are arranged in a matrix for each pixel and a thin film transistor as a switching element is connected to each pixel. It is preferable to use an active matrix type liquid crystal element which is an active matrix type liquid crystal display device, whereby a base layer in which irregularities are randomly formed without regularity is transferred to a rear substrate on which a thin film transistor is not formed in an active matrix type liquid crystal display device. Active matrix liquid crystal display that can be easily formed by a method or printing method, prevents defective coloring due to interference of reflected light in reflective display, and has good display quality without image blur in both reflection and transmission. The device can be manufactured with high yield.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
A liquid crystal display device according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is an exploded perspective view showing a liquid crystal display device of the present embodiment, and FIG. 2 is a schematic cross-sectional view showing a configuration of a main part thereof.
[0013]
The liquid crystal display device of this example is a transflective color liquid crystal display device used as a display of a mobile phone. As shown in FIG. 1, the liquid crystal display device is roughly divided into a liquid crystal display element LD and a rear side (non-observation side). Surface light source backlight BL. The liquid crystal display element LD includes a liquid crystal cell 1, a front polarizing plate 2 and a rear polarizing plate 3 disposed on the front side (display observation side) and the rear side of the liquid crystal cell 1, respectively. It comprises a front retardation plate 4 disposed between the liquid crystal cell 1 and the rear polarizing plate 3, and a rear retardation plate 5 disposed between the liquid crystal cell 1 and the rear polarizing plate 3.
[0014]
In the liquid crystal cell 1, as shown in FIG. 2, a front transparent substrate 11 and a rear transparent substrate 12 are joined to each other with a predetermined gap maintained by a sealing material arranged in a frame shape (not shown). A liquid crystal Lc is sealed between the two transparent substrates 11 and 12 surrounded by.
[0015]
The liquid crystal display element LD of this example is an active matrix type liquid crystal display element, and the liquid crystal layer Lc formed by enclosing liquid crystal between the transparent substrates 11 and 12 is a TN (twisted nematic) liquid crystal layer. . Therefore, a plurality of pixel electrodes 13 are arranged in a matrix on a surface (hereinafter referred to as an inner surface) facing the rear transparent substrate 12 of the front transparent substrate 11. Each pixel electrode 13 is provided with a TFT (thin film transistor) 14 as a switching element of an applied voltage. Each of these TFTs 14 is connected to a gate wiring and a drain wiring (not shown), and each TFT 14 is turned on / off according to various drive voltages applied through these wirings, and a signal voltage is applied to each pixel electrode 13. A pre-alignment film 15 is provided so as to cover all the pixel electrodes 13 and the thin film transistors 14. The surface of the pre-alignment film 15 that is in contact with the liquid crystal is subjected to an alignment process in a predetermined direction by a method such as rubbing in order to twist-align the liquid crystal molecules of the liquid crystal layer Lc.
[0016]
On the other hand, a base layer 16 is arranged on the inner surface of the rear transparent substrate 12 so as to correspond to each pixel electrode 13 of the front transparent substrate 11. These underlayers 16 are respectively arranged in regions facing the region from each thin film transistor 14 on the front transparent substrate 11 to about half of each pixel electrode 13 connected thereto. Each surface (the surface facing the liquid crystal layer Lc side) of the underlayer 16 is formed as a fine uneven surface. In FIG. 2, the unevenness is shown larger than the actual one.
[0017]
Then, a thin film made of a metal such as aluminum, silver, or a silver-palladium alloy is formed on the uneven surface of each underlayer 16 by a sputtering method or a vapor deposition method, and the scattering reflection layer 17 is formed. In this case, the scattering reflection layer 17 is formed to have a small thickness of about 1000 to 1500 °, whereby the surface of the scattering reflection layer 17 also becomes a fine uneven surface following the uneven surface of the base layer 16. In order to randomly reflect the incident light so that the reflected light does not interfere with the scattering reflection surface having the fine unevenness, the unevenness is required to be a random unevenness having no regularity.
[0018]
It is extremely difficult to obtain the scattering reflection layer 17 having such a random uneven reflection surface by forming the underlayer 16 by photolithography. However, in the active matrix type liquid crystal display element LD of this example, since the thin film transistor 14 is provided on the front transparent substrate 11, as a method of forming the base layer 16 on the rear transparent substrate 12, a transfer method other than photolithography or printing is used. Method can be used. If a transfer method or a printing method is used, the underlayer 16 having a desired random uneven surface can be easily formed. Therefore, the base layer 16 having a random uneven surface is formed on the rear transparent substrate 12 on which the thin film transistor 14 is not formed by using a transfer method, and a metal thin film is formed thereon by the sputtering method or the like as described above. Thereby, a scattering reflection layer having a desired random uneven reflection surface can be easily obtained. The front transparent substrate 11 is a normal active matrix substrate in which thin film transistors 14 and pixel electrodes 13 are simply provided in a matrix. As a result, it becomes possible to manufacture an active matrix type liquid crystal display device having a scattering reflection layer having a random uneven reflection surface at a high yield.
[0019]
A color filter layer 18 is laminated on and covers each of the scattering reflection layers 17 described above. The color filter layer 18 of this example includes red, green, and blue color filter elements 18R, 18G, and 18B. Each color filter element 18R, 18G, and 18B is provided for each pixel region Dp in which the pixel electrode 13 is disposed. They are arranged in a predetermined arrangement. Therefore, in one pixel region Dp, for example, the reflection part Dr on which the corresponding red filter element 18R is laminated on the diffuse reflection layer 17 and the same red filter element 18R are directly laminated on the inner surface of the rear transparent substrate 12. And a transmission portion Dt. Here, the film thickness of the portion corresponding to the reflection part Dr of the red filter element 18R is formed smaller than the film thickness of the part corresponding to the transmission part Dt. The thickness of each filter in the transmission part Dt and the reflection part Dr is set so that the color characteristics of each color display in the transmission part Dt and the reflection part Dr are optimized.
[0020]
That is, the filter film thickness of the reflection part Dr is such that light that enters the reflection part Dr from the front side of the liquid crystal display element LD, is reflected by the scattering reflection layer 17 and exits to the front side, for example, a thin part (the reflection part Dr) of the red filter element 18R. Is set to a thickness such that the light Ra1 and the like which are transmitted and reciprocated through the liquid crystal display element LD are emitted as colored light having sufficiently high color purity and intensity, and are incident on the transmission part Dt from the rear side of the liquid crystal display element LD. Then, the light Rb1 transmitted through the transmission portion Dt and emitted to the front side, for example, the light Rb1 transmitted through the thick portion (corresponding to the transmission portion Dt) of the red filter element 18R in one direction and emitted is subjected to color purity. And the thickness is set to a thickness at which the light is emitted as a sufficiently high colored light. This film thickness configuration is similarly applied to the other green and blue color filter elements 18G and 18B.
[0021]
On the color filter layer 18, a transparent flattening protective layer 19 is laminated. The flattening protective layer 19 is provided for absorbing the unevenness of the surface of the color filter layer 18 caused by the uneven underlayer 16 and the scattering / reflection layer 17 selectively arranged for each reflection part Dr to obtain a flat surface. In this example, the color filter layer 18 is formed by uniformly applying an acrylic resin material on the color filter layer 18 by spin coating.
[0022]
On the flat surface of the flattening protective film 19, a single transparent opposing electrode 20 is laminated, and a rear alignment film 21 is uniformly laminated thereon. Therefore, the surface of the rear alignment film 21 is a flat surface parallel to the rear transparent substrate 12, and the distance between the front and rear alignment films 15 and 21 in the pixel region Dp, that is, the liquid crystal layer thickness d is equal to the thickness of the reflecting portion. In both regions of the Dr and the transmissive portion Dt, d0 is constant.
[0023]
The rear alignment film 21 is subjected to an alignment process by rubbing along a predetermined direction in order to twist-align the liquid crystal molecules of the liquid crystal layer Lc, like the front alignment film 15 facing the liquid crystal layer Lc. .
[0024]
In the liquid crystal layer Lc formed by enclosing the liquid crystal between the front and rear alignment films 15 and 21, the liquid crystal layer when no electric field is applied between the pixel electrode 13 and the counter electrode 20 is applied. The twist angle in the initial alignment state of the liquid crystal molecules in Lc, the refractive index anisotropy Δn in the initial alignment state, and the liquid crystal layer thickness d in the pixel region Dp are set as follows.
[0025]
First, in the absence of an electric field in which the liquid crystal molecules are in the initial twist alignment state, the liquid crystal molecules have a refractive index anisotropy so as to have a retardation that gives a phase difference of 1/4 wavelength between the ordinary light and the extraordinary light. The product Δnd of Δn and the layer thickness d is set. In this case, Δnd is preferably in the range of 195 ± 10 nm to 235 ± 10 nm, and is set to 195 ± 10 nm in this example, and the twist angle of the liquid crystal molecule is preferably 60 ° to 70 °, and is 64 ° in this example. Is set to In order to obtain the twist angle of 64 °, in this example, as shown in FIG. 1, the alignment processing directions of the front and rear alignment films 15 and 21 are set.
[0026]
That is, the orientation direction 11a applied to the alignment film 15 on the front transparent substrate 11 is parallel to the horizontal axis x of the screen of the liquid crystal display device (the front surface of the front polarizer 2) and directed in the direction of the arrow (from right to left in the figure). And the direction of the alignment treatment 12a applied to the alignment film 21 on the rear transparent substrate 12 side is a direction crossing the horizontal axis x at 64 ° and heading in the direction of the arrow. As a result, the liquid crystal molecules are twisted in a counterclockwise (counterclockwise) direction by 64 ° when viewed from the front transparent substrate 11.
[0027]
Here, the slow axis 1a of the liquid crystal layer Lc in which the liquid crystal molecules are aligned as described above exists in a direction crossing the horizontal axis x at an angle of 45 °, as indicated by a two-dot chain line.
[0028]
With respect to the liquid crystal cell 1 configured as described above, the transmission axis 2a of the front polarizing plate 2 installed on the front side thereof is parallel to the alignment processing direction 11a on the front transparent substrate 11 side of the liquid crystal cell 1. The rear polarizing plate 3 installed on the rear side is disposed in such a manner that its transmission axis 3a is orthogonal to the transmission axis 2a of the front polarizing plate 2.
[0029]
Both the front retardation plate 4 and the rear retardation plate 5 disposed between the liquid crystal cell 1 and the polarizing plates 2 and 3 have a quarter wavelength between the transmitted ordinary light and the extraordinary light. A λ / 4 retardation plate that provides a phase difference, and is installed such that each slow axis 4a, 5a crosses each transmission axis 2a, 3a of the adjacent polarizing plate 2, 3 at 45 ° before and adjacent thereto. ing. Therefore, the slow axis 4a of the front retarder 4 is orthogonal to the virtual slow axis 1a of the liquid crystal cell 1, and the slow axis 5a of the rear retarder 5 is parallel to the virtual slow axis 1a. The optical axes are arranged such that the slow axes 4a and 5a are orthogonal to each other.
[0030]
The surface light source backlight BL installed on the rear side of the rear polarizing plate 3 includes a light guide plate 30 made of a transparent plate such as an acrylic resin and an LED (light emitting diode) or the like disposed opposite to one end surface thereof. And a plurality of light emitting elements 31.
[0031]
In the surface light source backlight BL, light emitted from the light emitting element 31 is guided by the light guide plate 30 and emitted in a planar manner from the front surface thereof. While traveling in the light guide plate 30 while repeating total reflection at the interface between the front and rear surfaces of the light guide plate 30 and the outer air phase, and from the front surface toward the rear polarizing plate 3 from the entire front surface. Light is irradiated in a planar manner. The light source of the backlight BL is not limited to a light emitting element such as an LED, but may be a linear light source such as a cold cathode tube.
[0032]
According to the liquid crystal display device configured as described above, under conditions where the illuminance of the external light, which is light in the use environment, is sufficient, reflection display using the external light is performed, and the illuminance of the external light is insufficient. In a dark environment, it is possible to perform transmissive display using light emitted from the built-in surface light source backlight BL.
[0033]
First, a reflection display operation using external light will be described. In the liquid crystal cell 1, for each pixel region Dp to which a drive voltage is applied in accordance with input information, an electric field is not formed between the electrodes, and the liquid crystal molecules are in an initial twist alignment state. ) And a pixel region Dp (hereinafter, referred to as an ON pixel) in which an electric field of a predetermined strength is formed between the electrodes and liquid crystal molecules are vertically aligned. Incidentally, in FIG. 2, the pixel region Dp1 corresponding to the red filter element 18R is an off pixel, and both the pixel regions Dp2 and Dp3 corresponding to the green filter element 18G and the blue filter element 18B are on pixels.
[0034]
In FIG. 2, external light (non-polarized light) Ra1 incident on the reflection part Dr of the pixel area Dp1 provided with, for example, the red filter element 18R of the off pixel is transmitted through the front polarizer 2 so that its vibration direction is transmitted. It becomes linearly polarized light along the axis 2a and enters the front retardation plate 4. The linearly polarized light that has entered the front phase difference plate 4 is transmitted therethrough, is given a phase difference of λ / 4, becomes circularly polarized light, and enters the liquid crystal cell 1.
[0035]
The above-mentioned circularly polarized light incident on the liquid crystal cell 1 is transmitted through the liquid crystal layer Lc in the off state, in which the liquid crystal molecules are initially twisted over 64 ° and have a retardation (Δnd) corresponding to a phase difference of λ / 4. Here, when the liquid crystal layer Lc is in the off state in which the liquid crystal molecules are initially twist-aligned as described above, the transmission axis 1a exists in a direction orthogonal to the slow axis 4a of the front retardation plate 4. By transmitting the light, the phase difference of λ / 4 is cancelled, and the linearly polarized light has the same vibration direction as the original linearly polarized light.
[0036]
The linearly polarized light passes through the red filter element 18R and is colored red, and then enters the scattering reflection layer 17 and is scattered and reflected. In the diffuse reflection, the reflection direction is irregularly scattered according to the incident position, but the change in the polarization state is slight.
[0037]
The linearly polarized light scattered and reflected by the scattering / reflection layer 17 travels on a return path in the reverse order of the outward light path up to the scattering / reflection layer 17. That is, after passing through the red filter element 18R, the light passes through the liquid crystal layer Lc and the front retardation plate 4 in the off state. The liquid crystal layer Lc and the phase difference plate 4 in the OFF state cancel each other out of the phase difference in the reverse light path similarly to the outgoing light path, so that the oscillation direction is transmitted through the front polarizing plate 2. Is emitted from the front phase difference plate 4 as the same linearly polarized light as above, and enters the front polarizing plate 2. Since the oscillation direction of the incident linearly polarized light is along the transmission axis 2a of the front polarizer 2, the incident linearly polarized light is transmitted through the front polarizer 2 without being absorbed as it is, and is efficiently emitted forward on the observation side. Are displayed in red with sufficient light intensity.
[0038]
The external light Ra1 incident on the transmission portion of the pixel region Dp1 passes through the liquid crystal layer Lc in the OFF state in the liquid crystal cell 1 and returns to linearly polarized light. And is emitted to the rear side. Thereafter, the linearly polarized light passes through the rear retardation plate 5 to become circularly polarized light, the polarized component light along the absorption axis of the rear polarizer 3 is absorbed, and only the polarized component light along the transmission axis is transmitted to the rear side. It is transmitted and eventually disappears.
[0039]
On the other hand, the external light (non-polarized light) Ra2 incident on the reflection portion Dr of the pixel region Dp3 provided with the blue filter element 18B, which is an ON-state pixel region, transmits through the front polarizer 2 and passes through the front retarder 4 , And becomes a circularly polarized light as in the case of the above-described pixel region in the off state, and enters the liquid crystal layer Lc in the on state.
[0040]
In the liquid crystal layer Lc in the ON state, the liquid crystal molecules are vertically oriented by the electric field formed between the electrodes. Since the liquid crystal layer Lc in the rising orientation has substantially zero retardation (Δnd) with respect to light transmitted in the layer thickness direction, incident circularly polarized light is emitted as the circularly polarized light and is scattered and reflected by the scattering reflection layer 16. The light passes through the liquid crystal layer Lc in the ON state again as circularly polarized light, and enters the front phase difference plate 4. The circularly polarized light that has entered the front phase difference plate 4 is given a phase difference of λ / 4 here and is emitted as linearly polarized light. A plane along the oscillation direction of the emitted linearly polarized light (hereinafter, referred to as a polarization plane) is given a phase difference of λ / 2 to the linearly polarized light transmitted through the front polarizer 2 on the outward optical path and emitted. The polarization plane is rotated by 90 °, and becomes a direction along an absorption axis (not shown) orthogonal to the transmission axis 2a of the front polarizer 2. Accordingly, the linearly polarized light emitted to the front side from the front phase difference plate 4 enters the front polarizing plate 2 and is absorbed and is not emitted to the observation side (front side), and the pixel corresponding to the pixel region Dp3 in the ON state. Indicates a black display.
[0041]
The transmissive portion Dt of the pixel region Dp3 in the ON state is provided between the pair of front and rear polarizers 2 and 3 before and after the retardation plates are arranged with the same retardation value and their slow axes are orthogonal to each other. Since the liquid crystal panels 4 and 5 have a configuration in which the liquid crystal layer Lc having a retardation of about 0 is interposed therebetween, the external light transmitted through the transmission section Dt transmits only two polarizing plates whose transmission axes are orthogonal to each other. This is the same as in the case, and all are absorbed by both polarizing plates 2 and 3.
[0042]
As described above, in the reflection display by the liquid crystal display device of this example, the scattering reflection layer 17 is provided on the rear side of the liquid crystal layer Lc, and the image display is performed by the reflected light that has been scattered and reflected and then transmitted through the liquid crystal layer Lc again. Therefore, since the reflected light is emitted to the observation side without being scattered after passing through the liquid crystal layer Lc, the occurrence of so-called image blur which blurs the display is prevented. The reflective display is a so-called normally white display in which the pixels in the ON state are displayed in black, but the loss of light by the front polarizer 2 is minimized in the OFF state, and the incident light is reduced in the ON state. Since it is almost completely absorbed by the front and rear polarizers 2 and 3, a color reflection display with high contrast can be obtained. Further, the film thickness of the portion corresponding to the reflection portion Dr of each color filter element is set to a thickness that allows light that reciprocates through the light to be emitted as colored light having sufficiently high color purity and light intensity. A color display with sufficiently high purity and strength can be obtained. Therefore, according to the liquid crystal display device of the reflective display mode of the present example, color purity, light intensity and contrast are sufficiently high, and glare peculiar to reflection and specular reflection is caused without causing image blur due to the scattering reflection layer. Suppressed and favorable color reflection display is obtained.
[0043]
Next, a transmissive display operation by the liquid crystal display device of this example will be described.
2, among the backlight light emitted from the light emitting element 31 (see FIG. 1) and incident on the light guide plate 30, the backlight light (non-polarized light) Rb1 emitted toward the pixel region Dp1 in the OFF state is The light passes through the rear polarizing plate 3 and becomes a linearly polarized light whose polarization plane is along the transmission axis 3 a, and enters the rear retardation plate 5. The linearly polarized light passes through the rear retardation plate 5 to become circularly polarized light, enters the liquid crystal cell 1, passes through a portion of the red filter element 18R corresponding to the transmission portion Dt, and is colored red, and is turned off. To the liquid crystal layer Lc. The circularly polarized light colored red is given a phase difference of λ / 4 when transmitting through the liquid crystal layer Lc in the off state, becomes linearly polarized light, and exits the liquid crystal cell 1. The output linearly polarized light is a linearly polarized light that is rotated by 90 ° from the point when the polarization plane has passed through the rear polarizer 3 and is along the x-axis. The linearly polarized light has a phase difference of λ / 4 and the slow axis is on the x-axis. On the other hand, the light passes through the front phase difference plate 4 crossed at 45 ° to be circularly polarized. This circularly polarized light is incident on the front polarizer 2, and only the polarized component light whose polarization plane is along the transmission axis 2a is emitted to the front side. As a result, the off pixel is displayed in red by the transmitted polarization component light colored red.
[0044]
On the other hand, the backlight Rb2 incident on the transmission portion Dt of the pixel region Dp3 provided with the blue filter element 18B, which is the ON-state pixel region, also undergoes the same operation as the above-described OFF-state pixel region Dp1. The light becomes blue circularly polarized light and is incident on the liquid crystal layer Lc in the ON state. Since the liquid crystal layer Lc in the ON state has a retardation (Δnd) of substantially 0, the incident circularly polarized light is transmitted as it is, exits from the liquid crystal cell 1, and enters the front phase difference plate 4. Since the front retardation plate 4 and the rear retardation plate 5 are arranged so that the slow axes are orthogonal to each other and cancel out the phase difference given to each other, the incident circularly polarized light must pass through the front retardation plate 4. As a result, the plane of polarization returns to the original linearly polarized light along the transmission axis of the rear polarizer 3, and since this linearly polarized light is linear in the direction along the absorption axis of the front polarizer 2, Incident and absorbed. Therefore, the pixels corresponding to the pixel region Dp3 in the ON state perform black display. In addition, since the scattering reflection layer 17 of this example is a reflection layer that does not substantially transmit incident light, the backlight Rb does not transmit through the reflection portion of each pixel region, and therefore, there is no leak light. A black display is obtained.
[0045]
As described above, the transmissive display by the liquid crystal display device of the present example is also a normally white display in which the pixels in the on state are black, and the incident light is the front and rear polarizers in the transmission part Dt of the pixel region Dp3 in the on state. Since the light is absorbed almost completely by the two or three, a color transmission display with high contrast can be obtained. Further, since there is no scattering / reflection layer in the transmission portion of each pixel region, the transmitted light is not scattered, so that the image is not blurred and the light intensity, that is, the luminance of the color display is not reduced.
[0046]
Next, a second embodiment of the present invention will be described with reference to FIG. In the following embodiments, the same components as those in the above-described first embodiment are denoted by the same reference numerals, and description thereof is omitted.
[0047]
The liquid crystal display of this example has a structure in which the flattening protective layer 19 interposed between the color filter layer 18 and the counter electrode 20 in the liquid crystal display of the first embodiment is omitted. Then, the layer thicknesses of the uneven underlayer 16 and the like are adjusted, and the liquid crystal layer thicknesses (gap) d1 and d2 of the reflection part Dr and the transmission part Dt in each pixel region Dp are individually and optimally set as follows. .
[0048]
That is, when the product Δn · d1 of the liquid crystal layer thickness d1 of the reflection part Dr and the refractive index anisotropy Δn of the liquid crystal is λ, the wavelength of transmitted light is λ, and a positive integer including 0 is k,
Δn · d1 = λ (2k + 1) / 4
Set so that
[0049]
On the other hand, the liquid crystal layer thickness d2 of the transmission portion Dt is the product Δn · d2 of the thickness d2 and the refractive index anisotropy Δn when the liquid crystal molecules are in the off-state alignment state, and the wavelength of the transmitted light includes λ and 0. When a positive integer is k ′,
Δn · d2 = λ (2k ′ + 1) / 2
Set so that
[0050]
In the present example, the liquid crystal layer thickness d1 of the reflection part Dr is set to a value such that Δn · d1 of the liquid crystal layer of the reflection part Dr becomes λ / 4 as in the first embodiment, and the liquid crystal layer thickness d2 of the transmission part Dr is set to the value. Δn · d2 is a value that becomes λ / 2. In order to obtain such a liquid crystal layer thickness configuration, the thickness of the uneven underlayer 16 is made larger than that of the first embodiment. Other configurations such as the film thickness ratio between the reflection part and the transmission part of each color filter element 18R, 18G, 18B are the same as those of the first embodiment.
[0051]
The operation of the liquid crystal display device configured as described above is almost the same as the operation in the first embodiment, except for the transmissive display function in the off pixels.
[0052]
In the transmissive portion Dt of the off-pixel region Dp1 in the liquid crystal display device of the present example, the phase difference between the phase difference plates 4 and 5 is λ / 2 before and after the slow axes are orthogonal to each other and cancel out the phase difference of the same value. Is arranged such that its slow axis 1a is aligned parallel to the slow axis of one of the phase difference plates, so that light passing through these layers has a λ / 2 order. The difference is given. Therefore, the linearly polarized light transmitted through the rear polarizer 3 is rotated by 90 ° by transmitting the linearly polarized light, and becomes a linearly polarized light along the transmission axis 2a (see FIG. 1) of the front polarizer 2. And is emitted. The emitted linearly polarized light passes through the pre-polarizing plate 2 without being absorbed, and bright colored light colored by each color filter element is emitted to the front of the liquid crystal display device on the observation side. In this case, the intensity of the outgoing colored light in this case is higher than that of the colored light that is made to enter the pre-polarizing plate 2 as circularly polarized light, transmits only the polarized component light along the transmission axis, and is emitted in the first embodiment. High and extremely bright colored display is provided. Therefore, according to the liquid crystal display device of this example, a high-quality transmissive color display having higher contrast and sufficiently high color purity and light intensity than the transmissive color display obtained in the first embodiment can be obtained.
[0053]
Therefore, according to the liquid crystal display device of the second embodiment, in both the reflective display and the transmissive display, not only the image blur and the decrease in the light intensity due to the light scattering are eliminated, but also the color purity and the light intensity are reduced. Good color display quality with high and very high contrast is obtained.
[0054]
Next, a third embodiment of the present invention will be described with reference to FIG.
The liquid crystal display device of this example is different from the liquid crystal display device of the first embodiment in that a cylindrical or prismatic through hole h1 of a predetermined size is provided in a portion corresponding to each reflective portion Dr of each color filter element 18R, 18G, 18B. To h3 are partially perforated. In this case, the opening area of each of the through holes h1 to h3 provided in each of the color filter elements 18R, 18G, and 18B is preferably 50% or less of the entire area (total area) of the reflection section Dr. As described above, by providing the through-holes in the color filter element portion of the reflection section, the display quality in the reflection color display is further improved.
[0055]
That is, the reflective display uses a smaller amount of incident light than the transmissive display that uses built-in illumination light to utilize external light, and tends to have a lower display brightness because of the reciprocating transmission through the color filter layer. Therefore, as in the first and second embodiments, the layer thickness of the color filter in the reflection section is made smaller than that of the transmission section by a predetermined thickness. Cannot be made thinner than the minimum thickness required to obtain Therefore, in the liquid crystal display device of this example, the above-described through holes h1 to h3 are formed. The external light that has entered the through holes h1 to h3 is reflected by the scattering reflection film 17, and is uncolored when emitted from the same through hole, and is colored when emitted from the surrounding color filter element. The light is emitted as light, and each emitted light has a higher intensity than the light that has transmitted and reciprocated through the color filter element. Therefore, the light emitted from the color filter element is colored light having both sufficiently high color purity and intensity, which is a mixture of light having high color purity transmitted and reciprocated and light having high intensity through the through-hole.
[0056]
In the liquid crystal display device of the present example, the opening area of the through hole (hereinafter, referred to as the through hole of the green pixel) h2 provided in the green filter element 18G is provided in the other red and blue filter elements 18R and 18G. The opening areas of the through holes (hereinafter, referred to as red pixel through holes and blue pixel through holes) h1 and h3 are set to be larger than the opening areas. This is for compensating for the difference in the luminosity of the green light among the luminosity of the red, green and blue colored lights, and thereby, the reflection of each of the red, green and blue is performed. The visibility of the colored light is corrected, and the white light due to the additive color mixture becomes light closer to pure white. That is, the white point is improved. In this case, the opening area of the through-hole h2 of the green pixel is 5% to 50% of the total area of the portion corresponding to the reflection portion Dr of the green filter element 18G (hereinafter, referred to as the green reflection portion total area), and each of red and blue. The opening area of each of the through holes h1 and h3 of the pixel is preferably 0 to 50% of the total area of the red and blue reflecting portions, and among them, the opening area ratio of the through hole h2 of the green pixel is 20 to 40%, and the red and blue portions. The opening area ratio of each of the through holes h1 and h3 of each pixel is more preferably 0 to 30%. In this example, the opening area ratio of the through hole h2 of the green pixel is 30%, and the through hole h1 of each of the red and blue pixels is set. , H3 is 1%.
[0057]
As described above, according to the liquid crystal display device of the present example, in both the reflective display and the transmissive display, not only the image blur is prevented, but also the color purity and the intensity are both sufficiently high and the white point is improved. Good color image display can be obtained.
[0058]
Next, a fourth embodiment of the present invention will be described with reference to FIG.
The liquid crystal display device of this example is the same as the liquid crystal display device of the second embodiment, except that the uneven underlayer 16 is an uneven underlayer 16 ′ formed uniformly over substantially the entire inner surface of the rear transparent substrate 12, and a color filter layer. The transparent gap adjusting layer 22 is provided between the pixel electrode 18 'and the counter electrode 20 except for the transmission part Dt in the pixel region Dp, and the gaps in the reflection part Dr and the transmission part Dt, that is, the liquid crystal layer thicknesses d1 and d2 are set to the second embodiment. It has been optimized as well.
[0059]
Since the uneven underlayer 16 ′ of this example is uniformly laminated on the inner surface of the rear transparent substrate 11, irregularities having a uniform size but no regularity and a random arrangement are formed on the reflective portion Dr. It can be easily formed by a transfer method or a printing method as compared with the case where it is selectively provided.
[0060]
A scattering / reflection layer 17 'is formed on the uneven base layer 16' in a region other than a portion corresponding to the transmission portion Dt of the pixel region Dp. In this way, by arranging the scattering reflection layer 17 ′ not only in the region corresponding to the reflection part Dr but also in the region facing the thin film transistor 14, the irradiation of the backlight Rb to the thin film transistor 14 is cut off and the malfunction occurs. Can be prevented.
[0061]
On the uneven base layer 16 'on which the scattering / reflecting layers 17' are selectively arranged, the color filter layers 18 'are evenly stacked including those on the scattering / reflecting layers 17'. Accordingly, the layer thicknesses of the respective color filter elements 18'R, 18'G, 18'B are equal, and the layer thicknesses of the individual color filter elements are constant without distinction between the reflection part Dr and the transmission part Dt. As described above, the color filter layer 18 'of this example has a constant layer thickness without distinction between the color filter elements 18'R, 18'G, and 18'B and the reflection portion Dr and the transmission portion Dt. Can be laminated.
[0062]
The constant layer thickness is set to a thickness that allows sufficient color purity and intensity to be obtained in a transmission color display. For this reason, in the reflective color display, simply forming the layer thickness of the color filter element of the reflective portion Dr to the same layer thickness as the transmissive portion Dt results in an unnecessarily large layer thickness, and the color purity is sufficient but the intensity is sufficient. Is insufficient, resulting in a dark color display. Therefore, in the present embodiment, through holes h1 to h3 are respectively formed in portions corresponding to the reflection portions Dr of the respective color filter elements 18'R, 18'G, 18'B, as in the third embodiment. Similarly, the opening area ratio of each of the through holes h1 to h3 is set such that the through hole h2 of the green filter element 18G is larger than the other through holes h1 and h3 at a predetermined same ratio. Thereby, even in the reflection color display, it is possible to obtain good color display quality with sufficient color purity and intensity and improved white characteristics.
[0063]
Further, the color filter layer 18 'of this example is formed using a material having a refractive index substantially the same as that of the uneven base layer 16'. For example, when the material of the uneven base layer 16 'is an acrylic resin having a refractive index of about 1.5, an acrylic resin base material having a refractive index of about 1.5 is used as a base material of the color filter layer. Thus, it is possible to prevent the backlight Rb transmitted from the uneven base layer 16 'of the transmission portion Dt to the color filter layer 18' from being scattered at the uneven interface between the uneven base layer 16 'and the color filter layer 18'. it can. As a result, light scattering in the transmissive display is substantially eliminated, and image blur and a decrease in light intensity are more significantly suppressed.
[0064]
In this example on the color filter layer 18 ′, a gap adjusting layer 22 made of a transparent resin material such as an acrylic resin is provided over substantially the entire region except for the region corresponding to the transmission portion Dt. The gap adjustment layer 22 is provided for appropriately setting the gap of the reflection portion Dr in each pixel region Dp, that is, the liquid crystal layer thickness d1, and therefore, may be provided at least in a region corresponding to the reflection portion Dr. . Then, the counter electrode 20 and the rear alignment film 21 are sequentially laminated so as to cover the gap adjusting layer 22 and the color filter layer 18 ′ therebetween.
[0065]
In the liquid crystal display device of the present example formed as described above, the respective thicknesses of the reflective portion Dr and the transmissive portion Dt, that is, the liquid crystal layer thickness are adjusted by appropriately adjusting the thicknesses of the uneven underlayer 16 ′ and the gap adjusting layer 22. d1 and d2 are optimally set as in the second embodiment.
[0066]
That is, the liquid crystal layer thickness d1 of the reflection part Dr is set so that the product Δn · d1 of this and the refractive index anisotropy Δn of the liquid crystal becomes λ / 4, and the liquid crystal layer thickness d2 of the transmission part Dt is: The product Δn · d2 of this and the refractive index anisotropy Δn of the liquid crystal is set to be λ / 2.
[0067]
By setting the respective liquid crystal layer thicknesses of the reflective part Dr and the transmissive part Dt as described above, color display with high contrast can be obtained in both reflective display and transmissive display as in the second embodiment. Therefore, in both reflective display and transmissive display, a transflective color liquid crystal display device with sufficiently high color purity and light intensity, high contrast, and good color display without image blur can be manufactured more easily. It can be easily manufactured by a process.
[0068]
Note that the liquid crystal display device of the present invention is not limited to the first to fourth embodiments.
For example, the liquid crystal layer is not limited to a TN alignment having a twist alignment angle of 64 °, but may be a so-called STN (Super Twist Nematic) having a twist alignment angle of 180 ° or more, or a liquid crystal layer having a homogeneous alignment other than the twist alignment.
[0069]
Further, the front and rear retardation plates are not limited to the retardation plates providing a phase difference of λ / 4, and may be omitted as appropriate. Further, each optical axis of the retardation plate, the polarizing plate, the liquid crystal layer, The arrangement in the alignment processing direction is not limited to the arrangement in the above embodiment.
[0070]
That is, in each of the reciprocating reflection display optical path by external light and the transmissive display optical path by built-in backlight light, the difference in the amount of light emitted to the observation side (front side) according to ON / OFF of the liquid crystal layer, that is, the display contrast is maximized. Optical conditions such as the arrangement of the phase difference and the slow axis of the front and rear retardation plates, the arrangement of the transmission axes of the front and rear polarizers, the twist angle of the liquid crystal layer and the direction of the alignment treatment, etc. The optimal setting may be used.
[0071]
Further, in the above-described embodiment, substantially half of each pixel region is a reflection portion and the remaining substantially half region is a transmission portion. However, the reflection portion and the transmission portion may have any shape according to the application of the liquid crystal display device. May be formed to have an arbitrary area ratio, or one or both of the reflection part and the transmission part may be formed in one pixel.
[0072]
Further, the color filter layer of each embodiment and the gap adjusting layer of the fourth embodiment may be provided on the inner surface of the front transparent substrate.
[0073]
In addition, the liquid crystal display device is not limited to the active matrix type, but may be a simple matrix type liquid crystal display device.
[0074]
【The invention's effect】
According to the liquid crystal display device of the present invention, a reflective film selectively disposed in a region corresponding to the reflective portion between the liquid crystal layer and the rear transparent substrate is formed on the underlayer having the uneven surface to form an uneven reflective film. Since the liquid crystal layer is transmitted after the reflection and scattering of light are performed at the same time, image blur is prevented in the reflective display. Also, in the transmissive display, since there is no uneven surface in front of the liquid crystal layer, image blur does not occur and loss due to light scattering when the uneven underlying layer exists is small. Accordingly, not only mirror reflection and reflection in the reflective display are prevented, but also in both the transmissive display and the reflective display, a good display quality with sufficient light intensity without image blur can be obtained.
[0075]
In the liquid crystal display device according to the present invention, as described in claim 2, by forming a color filter of a predetermined color over at least the entire pixel region so as to cover the base layer and the reflective film, mirror reflection and image formation can be achieved. Good reflection color display without blur can be obtained. In this case, as described in claim 3, the base layer is provided at least in a region excluding the transmission part, and the color filter is formed so that the film thickness in the reflection part is smaller than the film thickness in the transmission part. In addition, it is possible to easily manufacture a liquid crystal display device in which the thickness of the color filter in the reflection part is smaller than the thickness of the transmission part in order to make each display quality of the transmission color display and the reflection color display substantially the same.
[0076]
Further, as described in claim 4, by forming a through-hole in a region corresponding to the reflection portion of the color filter, a sufficiently bright reflective color display can be obtained, and the through-hole of each pixel of each color can be obtained. By setting the aperture area ratio optimally, it is possible to obtain a white color closer to pure white in the reflective display.
[0077]
Further, as set forth in claim 5, the liquid crystal element includes a plurality of pixel electrodes in which electrodes provided on the inner surface of the front substrate are arranged in a matrix for each pixel and a thin film transistor as a switching element is connected to each pixel. By using an active matrix type liquid crystal element that is an active matrix type liquid crystal display device, a base layer in which irregularities are randomly formed without regularity is transferred or printed on a rear substrate on which a thin film transistor is not formed in an active matrix type liquid crystal display device. In this manner, an active matrix type liquid crystal display device having a good display quality which is free from image blurring in both reflection and transmission is prevented, and defective coloration due to interference of reflected light is prevented in a reflective display. can do.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view showing a liquid crystal display device according to a first embodiment of the present invention.
FIG. 2 is a schematic sectional view showing a configuration of a main part of the first embodiment.
FIG. 3 is a schematic cross-sectional view illustrating a configuration of a main part of a liquid crystal display device according to a second embodiment of the invention.
FIG. 4 is a schematic cross-sectional view illustrating a configuration of a main part of a liquid crystal display device according to a third embodiment of the invention.
FIG. 5 is a schematic cross-sectional view illustrating a configuration of a main part of a liquid crystal display device according to a fourth embodiment of the invention.
[Explanation of symbols]
1: Liquid crystal cell
2. Front polarizing plate
3: Post-polarizing plate
4: Front retardation plate
5. Rear retardation plate
11 Front transparent substrate
12 Rear transparent substrate
13: Pixel electrode
14 ... Thin film transistor (TFT)
15 ... Pre-alignment film
16, 16 ': uneven underlayer
17, 17 ': scattering reflection layer
18, 18 ': color filter layer
19: Flattening protective film
20: Counter electrode
21 ... post-alignment film
22 ... Gap adjusting layer
LD: Liquid crystal display element
Lc: liquid crystal layer
Dp: Pixel area
Dr ... Reflector
Dt ... Transmissive part

Claims (5)

A liquid crystal layer is provided between a front substrate on which a display is viewed and a rear substrate opposed to the front substrate, and at least one electrode is provided on one of the opposing inner surfaces of the front substrate and the rear substrate. However, a plurality of electrodes for forming a plurality of pixels facing the at least one electrode are provided on the other inner surface, and the plurality of pixels are provided between the liquid crystal layer and the rear substrate. For each pixel, a reflection film is provided on the other region except for one predetermined region, and for each of the plurality of pixels, light is incident from the front side by the other region provided with the reflection film. A liquid crystal element in which a reflection part for reflecting light by the reflection film and emitting the light to the front side and a transmission part for emitting light incident from the rear side to the front side are formed by one of the regions where the reflection film is not provided. When,
A front polarizer and a rear polarizer disposed on the front side and the rear side of the liquid crystal element, respectively.
A backlight disposed on the rear side of the rear polarizing plate,
A liquid crystal display device comprising:
At least the other region corresponding to the reflection portion on the inner surface side of the rear substrate is provided with an underlayer having an uneven surface, and the reflection film is formed on the uneven surface of the underlayer. A liquid crystal display device characterized by the above-mentioned. 2. The liquid crystal display device according to claim 1, wherein a color filter of a predetermined color is formed on at least the entire pixel region so as to cover the base layer and the reflection film. 3. The liquid crystal display device according to claim 2, wherein the underlayer is provided at least in a region excluding the transmission portion, and a film thickness of the color filter in the reflection portion is smaller than a film thickness in the transmission portion. 4. . 4. The liquid crystal display device according to claim 2, wherein the color filter has a through-hole formed in a region corresponding to the reflection unit. 5. The liquid crystal element is an active matrix type liquid crystal element in which electrodes provided on the inner surface of the front substrate are arranged in a matrix for each pixel and a plurality of pixel electrodes each connected to a thin film transistor as a switching element. The liquid crystal display device according to claim 1, wherein:

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