JP4817741B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device that includes a liquid crystal layer containing homogeneously aligned liquid crystal molecules and displays an image using at least one of external light and backlight light.

  Liquid crystal display devices are widely used as displays for OA equipment, portable information terminals, and the like because they are thin, light, and have low power consumption. In particular, an active matrix liquid crystal display device in which a switching element is arranged for each pixel has excellent display characteristics, and is becoming a mainstream display device, and research and development have been actively conducted.

Among such liquid crystal display devices, there is a liquid crystal display device that includes a polarization control element that controls the polarization state of light on the outer surface of an array substrate and a counter substrate that constitute a liquid crystal display panel. This polarization control element includes a polarizing plate and two types of retardation plates (a half-wave plate that gives a half-wave phase difference between ordinary rays and extraordinary rays with respect to light of a predetermined wavelength, and A so-called broadband circularly polarizing film having a small wavelength dependency in combination with a quarter-wave plate that gives a quarter-wave phase difference is formed (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2004-271786

  The liquid crystal display device configured as described above includes a polarization control element having a structure in which a plurality of films are laminated. The polarizing plate generally has a structure in which a polarizer formed of polyvinyl alcohol (PVA) is sandwiched between a support made of a pair of triacetate cellulose (TAC). Furthermore, since a plurality of retardation plates are combined to increase the bandwidth (relaxation of the wavelength dependence of the retardation plates), the entire polarization control element becomes thick, and such polarization control elements are placed on both sides of the liquid crystal display panel. There is a problem that the entire liquid crystal display device provided becomes thick, and the polarization control element that requires a plurality of retardation plates leads to an increase in the cost of the entire device.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a liquid crystal display device having good display quality and capable of reducing the overall thickness and cost of the device. There is to do.

According to this embodiment,
A liquid crystal display device having a plurality of pixels arranged in a matrix, wherein a liquid crystal display having a liquid crystal layer containing liquid crystal molecules that are homogeneously aligned between a first substrate and a second substrate arranged to face each other A panel, a first support layer disposed on one outer surface of the liquid crystal display panel, a polarizer layer disposed on the first support layer, and a second support disposed on the polarizer layer A first optical element including a body layer, a third support layer provided on the other outer surface of the liquid crystal display panel, an analyzer layer disposed on the third support layer, and the analyzer layer And a second optical element including a fourth support layer disposed on the substrate, and an acute angle formed by an absorption axis of the polarizer layer and a slow axis of the first support layer is 25 degrees or more and 40 Within the range of less than 45 degrees or greater than 45 degrees and less than or equal to 65 degrees, The acute angle formed by the absorption axis of the layer and the slow axis of the third support layer is in the range of 25 degrees or more and less than 40 degrees or in the range of 45 degrees to 65 degrees, the first optical element and Each of the second optical elements controls a polarization state so that light having an elliptical polarization state is incident on the liquid crystal layer and has a wavelength range of 450 nm to 450 nm having an elliptical polarization state incident on the liquid crystal layer. The ellipticity of light at 650 nm is such that the difference between the maximum value and the minimum value is smaller than 0.15, and the ellipticity of light having a wavelength of 550 nm having the elliptical polarization state is 0.5 or more and 0.85 or less. The polarization state is controlled so that the first support layer and the third support layer are formed of a cycloolefin-based polymer and transmit light having a predetermined wavelength that passes through the fast axis and the slow axis. 1/4 in between It provides a phase difference of length, the second support layer and the fourth substrate layer, a liquid crystal display device characterized by being formed by a cycloolefin-based polymer of the unstretched is provided.

  According to the present invention, it is possible to provide a liquid crystal display device having good display quality and capable of reducing the thickness and cost of the entire device.

  A liquid crystal display device according to an embodiment of the present invention will be described below with reference to the drawings. Here, a transflective liquid crystal display device having, as examples, a reflective portion that displays an image using external light and a transmissive portion that displays an image using backlight is described as an example. Not limited to. For example, a reflective liquid crystal display device in which each pixel has only a reflective portion, a transmissive liquid crystal display device in which each pixel has only a transmissive portion, a part of pixels constituting the display region have a reflective portion and other pixels are transmissive The present invention can be applied to various types of liquid crystal display devices such as a liquid crystal display device having a portion.

  As shown in FIGS. 1 and 2, the liquid crystal display device is an active matrix type transflective color liquid crystal display device and includes a liquid crystal display panel LPN. The liquid crystal display panel LPN includes an array substrate (first substrate) AR, a counter substrate (second substrate) CT arranged opposite to the array substrate AR, and between the array substrate AR and the counter substrate CT. And a held liquid crystal layer LQ.

  Further, the liquid crystal display device includes a first optical element OD1 provided on one outer surface of the liquid crystal display panel LPN (that is, the outer surface opposite to the surface holding the liquid crystal layer LQ of the array substrate AR), and the liquid crystal display panel. A second optical element OD2 provided on the other outer surface of the LPN (that is, the outer surface opposite to the surface holding the liquid crystal layer LQ of the counter substrate CT) is provided. Further, the liquid crystal display device includes a backlight unit BL that illuminates the liquid crystal display panel LPN from the first optical element OD1 side.

  Such a liquid crystal display device includes a plurality of pixels PX arranged in a matrix of m × n in a display area DSP that displays an image. Each pixel PX displays (transmits) an image by selectively transmitting backlight light from the backlight unit BL and a reflection unit PR that displays (reflects) an image by selectively reflecting outside light. Display portion).

  The array substrate AR is formed using an insulating substrate 10 having optical transparency such as a glass plate or a quartz plate. That is, the array substrate AR includes m × n pixel electrodes EP arranged for each pixel in the display area DSP, and n scanning lines Y (Y1) respectively formed along the row direction of the pixel electrodes EP. To Yn), m signal lines X (X1 to Xm) respectively formed along the column direction of the pixel electrodes EP, and arranged in the vicinity of the intersection position of the scanning line Y and the signal line X in each pixel PX. There are provided m × n switching elements W (for example, thin film transistors), an auxiliary capacitance line AY that is capacitively coupled to the pixel electrode EP so as to form an auxiliary capacitance CS in parallel with the liquid crystal capacitance CLC.

  The array substrate AR is further connected to at least a part of the scanning line driver YD connected to the n scanning lines Y and the m signal lines X in the driving circuit area DCT around the display area DSP. At least a part of the signal line driver XD. The scanning line driver YD sequentially supplies scanning signals (driving signals) to the n scanning lines Y based on control by the controller CNT. Further, the signal line driver XD supplies video signals (drive signals) to the m signal lines X at the timing when the switching elements W in each row are turned on by the scanning signal based on the control by the controller CNT. Thereby, the pixel electrode EP of each row is set to a pixel potential corresponding to the video signal supplied via the corresponding switching element W.

  Each switching element W is, for example, an N-channel thin film transistor, and includes a polysilicon semiconductor layer 12 disposed on the insulating substrate 10. The polysilicon semiconductor layer 12 has a source region 12S and a drain region 12D on both sides of the channel region 12C. The polysilicon semiconductor layer 12 is covered with a gate insulating film 14.

  The gate electrode WG of the switching element W is connected to one scanning line Y (or formed integrally with the scanning line Y), and is disposed on the gate insulating film 14 together with the scanning line Y and the auxiliary capacitance line AY. . The gate electrode WG, the scanning line Y, and the auxiliary capacitance line AY are covered with an interlayer insulating film 16.

  The source electrode WS and the drain electrode WD of the switching element W are disposed on both sides of the gate electrode WG on the interlayer insulating film 16. The source electrode WS is connected to one signal line X (or formed integrally with the signal line X) and is in contact with the source region 12S of the polysilicon semiconductor layer 12. The drain electrode WD is connected to one pixel electrode EP (or formed integrally with the pixel electrode EP) and is in contact with the drain region 12D of the polysilicon semiconductor layer 12. The source electrode WS, the drain electrode WD, and the signal line X are covered with the organic insulating film 18.

  The pixel electrode EP includes a reflective electrode EPR provided corresponding to the reflective part PR and a transmissive electrode EPT provided corresponding to the transmissive part PT. The reflective electrode EPR is disposed on the organic insulating film 18 and is electrically connected to the drain electrode WD. The reflective electrode EPR is formed of a metal film having light reflectivity such as aluminum. The transmissive electrode EPT is disposed on the interlayer insulating film 16 and is electrically connected to the reflective electrode EPR. The transmissive electrode EPT is formed of a metal film having optical transparency such as indium tin oxide (ITO). The pixel electrodes EP corresponding to all the pixels PX are covered with the alignment film 20.

  On the other hand, the counter substrate CT is formed using an insulating substrate 30 having optical transparency such as a glass plate or a quartz plate. That is, the counter substrate CT includes a black matrix 32 that partitions each pixel PX in the display area DSP, a color filter 34 disposed in each pixel surrounded by the black matrix 32, a counter electrode ET, and the like.

  The black matrix 32 is disposed so as to face wiring portions such as the scanning lines Y and the signal lines X provided on the array substrate AR. The color filter 34 is formed of a plurality of different colors, for example, colored resins colored in three primary colors such as red, blue, and green. The red colored resin, the blue colored resin, and the green colored resin are disposed corresponding to the red pixel, the blue pixel, and the green pixel, respectively.

  The color filter 34 may be formed so that the optical density is different between the reflection part PR and the transmission part PT. That is, outside light that contributes to display passes through the color filter 34 twice in the reflection part PR, whereas backlight light that contributes to display passes only once through the color filter 34 in the transmission part PT. is there. Therefore, in order to adjust the color between the reflection part PR and the transmission part PT, it is desirable that the optical density of the colored resin arranged in the reflection part PR is about half that of the colored resin arranged in the transmission part PT.

  The counter electrode ET is disposed so as to face the pixel electrodes EP of all the pixels PX. The counter electrode ET is formed of a light-transmitting metal film such as indium tin oxide (ITO). The counter electrode ET is covered with an alignment film 36.

  When the counter substrate CT and the array substrate AR as described above are arranged so that the alignment films 20 and 36 face each other, a predetermined gap is formed by a spacer (not shown) arranged therebetween. The At this time, a gap of about half of the transmission part PT is formed in the reflection part PR. In this embodiment, the gap of the reflection part PR is about 2.8 μm, and the gap of the transmission part PT is set to about 4.8 μm.

  The liquid crystal layer LQ is composed of a liquid crystal composition including liquid crystal molecules 40 enclosed in a gap formed between the alignment film 20 of the array substrate AR and the alignment film 36 of the counter substrate CT. In this embodiment, the liquid crystal layer LQ includes liquid crystal molecules 40 having a twist angle of 0 deg (homogeneous alignment).

  As shown in FIG. 3, the first optical element OD1 and the second optical element OD2 control the polarization state of the light that has passed through them. That is, the first optical element OD1 controls the polarization state of light passing through the liquid crystal layer LQ so that light having an elliptical polarization state is incident on the liquid crystal layer LQ. Therefore, the polarization state of the backlight light incident on the first optical element OD1 is converted into elliptically polarized light when passing through the first optical element OD1. Thereafter, the backlight light emitted from the first optical element OD1 is incident on the liquid crystal layer LQ while maintaining the polarization state of elliptically polarized light.

  Similarly, the second optical element OD2 controls the polarization state of the light passing through the liquid crystal layer LQ so that the light having the polarization state of elliptical polarization enters the liquid crystal layer LQ. Therefore, the polarization state of the external light incident on the second optical element OD2 is converted into elliptically polarized light when passing through the second optical element OD1. Thereafter, the external light emitted from the second optical element OD2 enters the liquid crystal layer LQ while maintaining the polarization state of elliptically polarized light.

  The first optical element OD1 has a structure in which a polarizer layer 53 is sandwiched between a first support layer 51 and a second support layer 52. That is, the first support layer 51 is disposed on the outer surface of the array substrate AR in the liquid crystal display panel LPN. The first support layer 51 may be disposed so as to contact the outer surface of the array substrate AR, or another optical element may be interposed therebetween. The polarizer layer 53 is disposed on the first support layer 51. The polarizer layer 53 is bonded to the first support layer 51 through an adhesive, for example. The second support layer 52 is disposed on the polarizer layer 53. The second support layer 52 is bonded to the polarizer layer 53 via an adhesive, for example.

  The second optical element OD2 has a structure in which an analyzer layer 63 is sandwiched between a third support layer 61 and a fourth support layer 62. That is, the third support layer 61 is disposed on the outer surface of the counter substrate CT in the liquid crystal display panel LPN. The third support layer 61 may be disposed in contact with the outer surface of the counter substrate CT, or another optical element may be interposed therebetween. The analyzer layer 63 is disposed on the third support layer 61. The analyzer layer 63 is bonded to the third support layer 61 via an adhesive, for example. The fourth support layer 62 is disposed on the analyzer layer 63. The fourth support layer 62 is bonded to the analyzer layer 63 via an adhesive, for example.

  The first support layer 51 and the third support layer 61 are formed of a cycloolefin polymer such as Zeonore (manufactured by Optes Co., Ltd.), Arton (manufactured by JSR Co., Ltd.), Essina (manufactured by Sekisui Chemical Co., Ltd.), or the like. It has a function of giving a phase difference of ¼ wavelength between light of a predetermined wavelength that passes through the fast axis and slow axis. That is, the first support layer 51 and the third support layer 61 have a function as a retardation plate in addition to the function as an original support.

  The polarizer layer 53 and the analyzer layer 63 are made of, for example, polyvinyl alcohol (PVA) that has been stretched and dyed. The second support layer 52 and the fourth support layer 62 are made of, for example, triacetate cellulose (TAC).

  The polarizer layer 53 and the analyzer layer 63 described above have an absorption axis and a transmission axis orthogonal to each other in a plane orthogonal to the light traveling direction. The polarizer layer 53 and the analyzer layer 63 extract light having a vibration surface in one direction parallel to the transmission axis, that is, light having a polarization state of linearly polarized light, from light having a vibration surface in a random direction. is there.

  The first support layer 51 converts linearly polarized light transmitted through the polarizer layer 53 into elliptically polarized light. The third support layer 61 converts linearly polarized light transmitted through the analyzer layer 63 into elliptically polarized light.

  In the following description, for the polarizer layer 53 and the analyzer layer 63, the respective arrangements are specified by the respective absorption axes A1 and A2, and for the first support layer 51 and the third support layer 61, The respective arrangements are specified by the respective slow axes D1 and D3.

  Here, as shown in FIG. 4, in the liquid crystal display device according to this embodiment, when viewed from the counter substrate side, it is convenient in a plane parallel to the main surface of the array substrate AR (or counter substrate CT). The X axis and Y axis orthogonal to each other are defined, and the normal direction of this plane is defined as the Z axis. In-plane corresponds to a plane defined by the X-axis and the Y-axis. Here, the X axis corresponds to the horizontal direction of the screen, and the Y axis corresponds to the vertical direction of the screen. Further, the positive (+) direction (0 ° azimuth) of the X axis corresponds to the right side of the screen, and the negative (−) direction (180 ° azimuth) of the X axis corresponds to the left side of the screen. Furthermore, the positive (+) direction (90 ° azimuth) of the Y axis corresponds to the upper side of the screen, and the negative (−) direction (270 ° azimuth) of the Y axis corresponds to the lower side of the screen.

  The first support layer 51 and the third support layer 61 have a slow axis and a fast axis that are orthogonal to each other. In discussing birefringence, the slow axis corresponds to an axis having a relatively large refractive index, and the fast axis corresponds to an axis having a relatively small refractive index. The slow axis coincides with the vibration plane of the extraordinary ray. The fast axis coincides with the plane of vibration of ordinary rays. When the refractive indexes of ordinary ray and extraordinary ray are respectively no and ne, and the thickness of the retardation plate along the traveling direction of each ray is d, the retardation value Δn · d (nm) of the retardation plate is (Ne · d−no · d) (that is, Δn = ne−no).

  The first support layer 51 and the third support layer 61 are so-called quarter-wave plates that give a quarter-wave phase difference between light of a predetermined wavelength that passes through the fast axis and the slow axis. That is, by arranging the first support layer 51 so that its slow axis forms a predetermined angle (acute angle) with respect to the absorption axis (or transmission axis) of the polarizer layer 53 in the plane, It has a function of converting linearly polarized light transmitted through the polarizer layer 53 into elliptically polarized light having a predetermined ellipticity (= amplitude in the minor axis direction / amplitude in the major axis direction). Similarly, the third support layer 61 is arranged so that its slow axis forms a predetermined angle (acute angle) with respect to the absorption axis (or transmission axis) of the analyzer layer 63 in the plane. The linearly polarized light transmitted through the analyzer layer 63 has a function of converting it into elliptically polarized light having a predetermined ellipticity.

  In general, the birefringent material constituting the retardation plate has characteristics in which the refractive index no for ordinary light and the refractive index ne for extraordinary light depend on the wavelength of light. For this reason, the retardation value Δn · d of the phase difference plate depends on the wavelength of light passing therethrough. For this reason, at least two types of retardation plates (1/2 wavelength plate and 1/4 wavelength plate) are used to form circularly polarized light by providing a predetermined retardation in all wavelength ranges used for color display. ) To reduce the wavelength dependence of the retardation value of the retardation plate.

  On the other hand, in this embodiment, the polarizer layer 53 and a single retardation layer (the first support layer 51 functioning as a quarter-wave plate) are combined, and the analyzer layer 63 and the single layer are combined. Combined with one retardation layer (third support layer 61 functioning as a quarter-wave plate), the angle between the absorption axis of the polarizer layer or the analyzer layer and the slow axis of the retardation layer is optimized. By doing so, elliptically polarized light having a substantially constant ellipticity regardless of the wavelength of incident light is formed. Here, as the optimization condition, for the first optical element OD1, the acute angle θ formed by the absorption axis A1 of the polarizer layer 53 and the slow axis D1 of the first support layer 51 is 25 degrees or more and 70. It is set within the range of degrees. Similarly, for the second optical element OD2, the acute angle θ formed by the absorption axis A2 of the analyzer layer 63 and the slow axis D3 of the third support layer 61 is in the range of 25 degrees to 70 degrees. Is set.

  Hereinafter, a more desirable range of the angle θ will be considered.

  The ellipticity of light of specific wavelengths (for example, 470 nm (blue), 550 nm (green), and 610 nm (red)) used for color display is the angle (or absorption axis) formed by the absorption axis A1 and the slow axis D1. It depends on the angle θ between A2 and the slow axis D3. In order to achieve good display quality, it is desirable to set the ellipticity to be substantially the same for all light of a specific wavelength.

  When the angle θ is 45 °, the difference in ellipticity between light having a wavelength of 550 nm and light having a wavelength of 470 nm is about 0.15, and optical characteristics are deteriorated. On the other hand, when the angle θ is smaller than 40 degrees, or when the angle θ is an acute angle larger than 45 degrees, the difference in ellipticity obtained with light of each wavelength can be made sufficiently small. This means that a polarization state with a substantially uniform ellipticity can be formed for light in the entire wavelength range (450 nm to 650 nm) used for color display. Thereby, the tendency of the improvement of an optical characteristic is seen.

  More desirably, by setting the angle θ to 30 degrees or less, or the angle θ to an acute angle of 50 degrees or more, the ellipticity of the light in the entire wavelength range (450 nm to 650 nm) used for color display is improved. Elliptical polarized light having a difference of 0.1 or less can be formed, and further improvement of optical characteristics can be expected.

  Therefore, when the first optical element OD1 and the second optical element OD2 configured as described above are applied to the liquid crystal display device according to this embodiment, the angle θ is an angle smaller than 40 degrees or an acute angle larger than 45 degrees. More preferably, the angle θ is set to an acute angle of 30 degrees or less or 50 degrees or more. As a result, the ellipticity of light having an elliptical polarization state incident on the liquid crystal layer and having a wavelength in the range of 450 nm to 650 nm is such that the difference between the maximum value and the minimum value is less than 0.15, preferably 0.1 or less. The optical characteristics can be improved and good display quality can be realized.

  When attention is paid to green light having a relatively high relative visibility, for example, light having a wavelength of 550 nm, the ellipticity of elliptically polarized light formed through the first optical element OD1 (or the second optical element OD2) is 0. If it is smaller than 65, the difference from the ellipticity of light of other wavelengths can be reduced (that is, the wavelength dependency can be reduced). However, in the transflective liquid crystal display device including the first optical element OD1 (or the second optical element OD2), the reflectance by the reflecting portion is significantly reduced. In particular, when the ellipticity is less than 0.5, the reflectance by the reflecting portion is reduced by 10% or more, and the quality of the image displayed when used as a reflective liquid crystal display device is significantly reduced, which is preferable. Absent.

  Similarly, when the ellipticity of elliptically polarized light formed by passing through the first optical element OD1 (or the second optical element OD2) for light having a wavelength of 550 nm exceeds 0.8, the wavelength dependence is as described above. Therefore, the difference in ellipticity with light of other wavelengths is expanded to about 0.15. In particular, when the ellipticity exceeds 0.85, the white color displayed when used as a reflective liquid crystal display device is colored yellow, and the quality of the displayed image is remarkably deteriorated. .

  As described above, in order to set the ellipticity of light having a wavelength of 550 nm to 0.5 to 0.85, the angle θ in the first optical element OD1 (or the second optical element OD2) is 25 degrees to 65 degrees. Is set. Desirably, in order to set the ellipticity of light having a wavelength of 550 nm to 0.65 or more and 0.8 or less, the angle θ in the first optical element OD1 (or the second optical element OD2) is 28 degrees or more and 40 degrees or less. Or it is set to 48 degrees or more and 57 degrees or less.

  Therefore, when the first optical element OD1 (or the second optical element OD2) having the above-described configuration is applied to the liquid crystal display device according to this embodiment, the liquid crystal layer is set by setting the angle θ to the above-described range. The ellipticity of light having a wavelength of 550 nm having an elliptical polarization state incident on the light is set to 0.5 or more and 0.85 or less, preferably 0.65 or more and 0.8 or less, thereby improving optical characteristics. And good display quality can be realized.

  From the above, θ in the first optical element OD1 and the second optical element OD2 is set in the range of 25 degrees to 65 degrees, the difference in ellipticity (less than 0.15), and the ellipticity of light at 550 nm In consideration of the range (0.5 or more and 0.85 or less), it is desirable that θ is set to a range of 25 degrees or more and less than 40 degrees, or greater than 45 degrees and 65 degrees or less.

  Thus, the acute angle formed by the absorption axis of the polarizer layer (or analyzer layer) and the slow axis of the retardation layer (that is, the first support layer or the third support layer) is set within the above range. By doing so, a polarization state having an ellipticity in a predetermined range can be formed for light in the entire wavelength range used for color display, for example, a wavelength range of 450 nm to 650 nm, and elliptical polarization having a substantially uniform ellipticity. Can be used. That is, the optical characteristics are deteriorated due to the wavelength dependence of the retardation value in a single retardation layer (¼ wavelength plate) without combining a plurality of retardation layers, that is, a ½ wavelength plate and a ¼ wavelength plate. Can also be prevented.

  The optical element disposed on the outer surface of the liquid crystal display panel functions as a first functional layer that functions as a polarizer (or analyzer), a support disposed between the functional layer and the liquid crystal display panel, and a position. It has a three-layer structure including a second functional layer that functions as a phase difference plate, and a third functional layer that functions as a protective layer that sandwiches the first functional layer with the second functional layer. Such an optical element can be made thinner overall than an optical element having a structure in which a retardation plate is laminated in addition to a polarizing plate in which a first functional layer is sandwiched between a pair of TAC layers. In addition, the entire liquid crystal display device including such an optical element can be thinned. Furthermore, since the configuration of the optical element can be simplified, the cost can be reduced.

  The second functional layer is made of a cycloolefin polymer. This cycloolefin-based polymer has excellent characteristics in terms of photoelastic coefficient and moisture permeability as compared with TAC. That is, as shown in FIG. 5, when the value of TAC is 1 for the photoelastic coefficient corresponding to the rate of change in optical characteristics when stress (especially heat) is applied, the cycloolefin polymer is 1 / 3, indicating that the characteristic change with respect to stress is small. Further, regarding the moisture permeability, when the TAC value is 1, the cycloolefin polymer is 1/30 of that, and it is understood that the resistance to humidity is high.

  In other words, by forming the second functional layer from a cycloolefin polymer, it is possible to provide a highly durable optical element that is difficult to peel off from the liquid crystal display panel even when used in a high temperature and high humidity environment. It becomes.

  In the above-described embodiment, the example in which only the second functional layer between the first functional layer and the liquid crystal display panel is formed of the cycloolefin polymer has been described. However, the third functional layer is disposed on the outer surface of the first functional layer. The functional layer (that is, the second support layer 52 and the fourth support layer 62 described above) may also be formed of a cycloolefin polymer. This makes it difficult for moisture from the outside to pass through the first functional layer, and it is possible to further improve the durability of the optical element against heat and humidity. The third functional layer is preferably formed of an unstretched cycloolefin polymer and substantially does not have a function as a retardation plate. That is, it is desirable that the third functional layer is configured to have characteristics that do not disturb the optimization conditions of the first functional layer and the second functional layer.

  Next, operations of reflective display and transmissive display by the transflective liquid crystal display device whose display mode is normally white mode will be described in more detail with reference to FIG.

  First, the light passing through the liquid crystal layer LQ in the reflection part PR operates as follows when no potential difference is applied to the liquid crystal layer LQ, that is, when no voltage is applied. That is, external light incident from the counter substrate CT side is converted to have a polarization state of, for example, clockwise elliptically polarized light by passing through the second optical element OD2, and then the liquid crystal layer LQ through the counter substrate CT. Is incident on. This elliptically polarized light reaches the reflective electrode EPR after being given a phase difference of π / 2 when passing through the liquid crystal layer LQ. The reflected light reflected by the reflective electrode EPR is given a phase difference of π at that time, and given a phase difference of π / 2 when passing through the liquid crystal layer LQ again. That is, the elliptically polarized light reciprocating through the liquid crystal layer LQ is given a phase difference of 2π. Therefore, the reflected light reflected by the reflecting part PR passes through the counter substrate CT while maintaining the polarization state of clockwise elliptically polarized light. Since the elliptically polarized light can pass through the second optical element OD2, it contributes to bright display of a single color that matches the color of the color filter 34.

  On the other hand, the light passing through the liquid crystal layer LQ in the reflection part PR operates as follows when a potential difference is applied to the liquid crystal layer LQ, that is, when a voltage is applied. That is, as in the case of no voltage application, outside light incident from the counter substrate CT side is converted to have a polarization state of, for example, clockwise elliptically polarized light by passing through the second optical element OD2, and the counter substrate CT Through the liquid crystal layer LQ. This elliptically polarized light is not affected by the phase difference when passing through the liquid crystal layer LQ when the residual retardation of the liquid crystal layer LQ at the time of voltage application is 0, so that the polarization state is maintained as it is in the reflective electrode EPR. Reach. The reflected light reflected by the reflective electrode EPR is given a phase difference of π at that time as described above and passes through the liquid crystal layer LQ again, but is not affected by the phase difference, and thus reciprocated through the liquid crystal layer LQ. The elliptically polarized light is given a phase difference of π. That is, the reflected light reflected by the reflecting part PR is converted to a counterclockwise elliptically polarized light state and passes through the counter substrate CT. This elliptically polarized light does not pass through the second optical element OD2. For this reason, it becomes dark display, ie, black display.

  Note that when a voltage is applied to the liquid crystal layer LQ, the liquid crystal molecules at the substrate interface do not completely stand out due to the alignment regulating force (anchoring), so the residual retardation of the liquid crystal layer LQ when the voltage is applied is not zero. In general, it has a residual retardation of about several to several tens of nm. In that case, by reducing the retardation value of any of the layers constituting the second optical element OD2 by the residual retardation of the liquid crystal layer LQ, the polarization state of the light reaching the reflective electrode EPR is changed to the residual retardation of the liquid crystal layer LQ. Is the same as when 0 is zero, and black display can be performed by the same mechanism as described above.

  As described above, the reflection part PR displays an image by selectively reflecting external light.

  The light passing through the liquid crystal layer LQ in the transmissive part PT operates as follows when no voltage is applied. That is, the backlight light emitted from the backlight unit BL is converted to have, for example, a counterclockwise elliptically polarized state by passing through the first optical element OD1, and the liquid crystal layer passes through the array substrate AR. Incident to LQ. This elliptically polarized light is given a phase difference of π when passing through the liquid crystal layer LQ in the transmission part PT having a gap about twice that of the reflection part PR. That is, the transmitted light that has passed through the transmission part PT is converted to have a clockwise elliptically polarized state, and passes through the counter substrate CT. Since the elliptically polarized light can pass through the second optical element OD2, it contributes to bright display of a single color that matches the color of the color filter 34.

  On the other hand, the light passing through the liquid crystal layer LQ in the transmission part PT operates as follows when a voltage is applied. That is, as in the case of no voltage application, the backlight light incident from the array substrate AR side is converted to have, for example, a counterclockwise elliptically polarized state by passing through the first optical element OD1, and the array The light enters the liquid crystal layer LQ through the substrate AR. For example, when the residual retardation of the liquid crystal layer when voltage is applied is 0, this elliptically polarized light is not affected by the phase difference when passing through the liquid crystal layer LQ. pass. This elliptically polarized light does not pass through the second optical element OD2. For this reason, it becomes dark display, ie, black display.

  Thus, in the transmissive part PT, an image is displayed by selectively transmitting the backlight light.

(Example)
The liquid crystal layer LQ is composed of a liquid crystal composition including homogeneously aligned liquid crystal molecules 40. For example, MJ041113 (Merck, Δn = 0.065) was applied as the liquid crystal composition. At this time, the director (the major axis direction of the liquid crystal molecules) 40D of the liquid crystal molecules 40 is set parallel to the Y axis in the XY plane shown in FIG. When the X-axis is used as a reference (when the positive direction on the X-axis is a 0 ° azimuth), the director 40D corresponds to a 270 ° azimuth.

  That is, as shown in FIG. 6, the method when the liquid crystal display panel is tilted in the positive (+) direction of the Y axis with respect to the normal Z in the YZ plane including the normal line Z and the Y axis of the liquid crystal display panel. The angle Θ (deg) made with the line Z is positive (+), and the angle Θ made with the normal Z when it falls in the negative (−) direction of the Y axis with respect to the normal Z is negative (−). , The director 40D of the liquid crystal molecules 40 has an angle Θ formed with the normal Z in a negative range. Here, the range where the director 40D of the liquid crystal molecules 40 exists, that is, the range where Θ is from 0 ° to −90 ° is the main viewing angle direction (the lower side of the screen), and the range where the director 40D of the liquid crystal molecules 40 does not exist, ie, Θ is 0. The range from ° to + 90 ° is the anti-main viewing angle direction (upper side of the screen).

  The polarizer layer 53 is disposed at an angle θ1 (deg) formed between the absorption axis A1 and the X axis. As described above, the first support layer 51 is optimized to form elliptically polarized light having a predetermined ellipticity in cooperation with the polarizer layer 53, and between the slow axis D1 and the X axis. Are arranged at an angle θ2 (deg) formed (that is, θ1 and θ2 are selected so that | θ2−θ1 | is within a range of 25 degrees to 70 degrees).

  Similarly, the analyzer layer 63 is disposed so that the absorption axis A2 thereof and the absorption axis A1 of the polarizer layer 53 are substantially orthogonal, and here is disposed at an angle θ5 (deg) formed between the analyzer layer 63 and the X axis. . As described above, the third support layer 61 is optimized so as to form elliptically polarized light having a predetermined ellipticity in cooperation with the analyzer layer 63, and between the slow axis D3 and the X axis. Are arranged at an angle θ6 (deg) formed (that is, θ5 and θ6 are selected so that | θ6-θ5 | is within a range of 25 degrees to 70 degrees).

  In this example, the first support layer 51 and the third support layer 61 employ ZEONOR (manufactured by Optes Co., Ltd.), which is a uniaxial quarter wave plate (in-plane retardation is 145 nm). The second support layer 52 and the fourth support layer 62 employ TAC. At this time, θ1 = 1 °, θ2 = 36 °, θ5 = 91.5 °, and θ6 = 145 °.

  According to such an embodiment, the ellipticity of the light having a wavelength of 550 nm transmitted through the polarizer layer 53 and the first support layer 51 is 0.75, and the light having a wavelength range of 450 nm to 650 nm is substantially equal. The ellipticity was obtained. Further, the ellipticity of the light having a wavelength of 550 nm transmitted through the analyzer layer 63 and the third support layer 61 is also 0.75, and almost the same ellipticity is obtained for the light in the wavelength range of 450 nm to 650 nm. It was.

  Further, when the viewing angle dependency of contrast in the transmission part was simulated, a characteristic diagram as shown in FIG. 7 was obtained. In such a characteristic diagram, the center corresponds to the normal direction of the liquid crystal display panel, the 0 ° (deg) azimuth is the positive (+) direction on the X axis, and the 180 (deg) azimuth is the negative ( -) Direction, 90 (deg) azimuth is positive (+) direction on the Y-axis (upper side of screen: anti-main viewing angle direction), 270 (deg) azimuth is negative (-) direction on the Y-axis (bottom of screen) Side: main viewing angle direction). Concentric circles centered on the normal direction are tilt angles with respect to the normal, and correspond to 20 °, 40 °, 60 °, and 80 °, respectively. This characteristic diagram is obtained by connecting angles at which equal contrast is obtained in each direction.

  As can be seen from FIG. 7, it was confirmed that the high-contrast region can be enlarged in almost all directions, and in particular, the contrast reduction in the main viewing angle direction of the screen can be improved. It was also confirmed that gradation inversion was suppressed over all directions.

  The present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the components without departing from the scope of the invention in the stage of implementation. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine the component covering different embodiment suitably.

  For example, the example in which the switching element W is configured by an N-channel thin film transistor has been described, but other configurations may be used as long as the same various drive signals can be generated.

  In the above-described embodiment, each of the first support layer and the third support layer employs ZEONOR, which is a uniaxial retardation plate. However, a similar uniaxial retardation plate or biaxial retardation plate is used. It can be appropriately employed depending on required performance such as a phase difference plate and phase difference to be compensated.

FIG. 1 schematically shows a configuration of a liquid crystal display device according to an embodiment of the present invention. FIG. 2 is a diagram schematically showing a cross-sectional structure of the liquid crystal display device shown in FIG. FIG. 3 is a diagram schematically showing the configuration of the first optical element and the second optical element of the liquid crystal display device shown in FIG. FIG. 4 is a diagram for explaining the positional relationship between the first optical element and the second optical element with reference to the director of liquid crystal molecules in the liquid crystal display device shown in FIG. FIG. 5 is a diagram showing a comparison result of characteristics between cycloolefin polymer and TAC. FIG. 6 is a diagram for explaining directors of liquid crystal molecules. FIG. 7 is a characteristic diagram of the viewing angle dependence of contrast in the liquid crystal display device of the example.

Explanation of symbols

    LPN ... liquid crystal display panel, AR ... array substrate, CT ... counter substrate, LQ ... liquid crystal layer, PT ... transmission part, PR ... reflection part, OD1 ... first optical element, OD2 ... second optical element, 51 ... first support Body layer (second functional layer) 52. Second support layer (third functional layer) 53 53 Polarizer layer (first functional layer) 61 Third support layer (second functional layer) 62 ... 4th support layer (3rd functional layer), 63 ... Analyzer layer (1st functional layer), BL ... Backlight unit, PX ... Pixel

Claims (3)

A liquid crystal display device having a plurality of pixels arranged in a matrix,
A liquid crystal display panel holding a liquid crystal layer containing homogeneously aligned liquid crystal molecules between a first substrate and a second substrate disposed to face each other;
A first support layer disposed on one outer surface of the liquid crystal display panel; a polarizer layer disposed on the first support layer; and a second support layer disposed on the polarizer layer. A first optical element comprising:
A third support layer provided on the other outer surface of the liquid crystal display panel; an analyzer layer disposed on the third support layer; and a fourth support layer disposed on the analyzer layer. A second optical element including,
The acute angle formed by the absorption axis of the polarizer layer and the slow axis of the first support layer is in the range of 25 degrees or more and less than 40 degrees, or in the range of more than 45 degrees and 65 degrees or less, and the analyzer The acute angle formed by the absorption axis of the layer and the slow axis of the third support layer is in the range of 25 degrees or more and less than 40 degrees or in the range of 45 degrees to 65 degrees;
Each of the first optical element and the second optical element controls a polarization state so that light having an elliptical polarization state is incident on the liquid crystal layer and also has an elliptical polarization state incident on the liquid crystal layer. The ellipticity of light having a wavelength range of 450 nm to 650 nm having a difference between the maximum value and the minimum value is smaller than 0.15, and the ellipticity of light having a wavelength of 550 nm having the elliptical polarization state is 0.5. The polarization state is controlled to be 0.85 or less,
The first support layer and the third support layer are formed of a cycloolefin-based polymer, and a phase difference of ¼ wavelength between light of a predetermined wavelength that passes through the fast axis and the slow axis. a given,
The liquid crystal display device, wherein the second support layer and the fourth support layer are formed of an unstretched cycloolefin polymer .   The liquid crystal display device according to claim 1, further comprising a backlight unit that illuminates the liquid crystal display panel from the first optical element side.   The liquid crystal display device according to claim 1, wherein the display mode is normally white.

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