JP5077873B2 - Liquid crystal display element - Google Patents

Description

  The present invention relates to a liquid crystal display element, and more particularly to a liquid crystal display element having a vertical alignment type liquid crystal cell and viewing angle compensated by an optical compensator (biaxial film) having negative biaxial optical anisotropy.

  The “vertical alignment” liquid crystal display element in which the liquid crystal molecular alignment in the liquid crystal layer of the liquid crystal cell is perpendicular to the substrate has a very good black level when no voltage is applied. By introducing an optical compensator having negative optical anisotropy having appropriate parameters into one or both between the liquid crystal cell and the lower polarizing plate, a very good viewing angle characteristic can be obtained. Have.

  As a viewing angle compensation method, Patent Document 1 discloses a method using an optical compensation plate (so-called (negative) C plate) having negative uniaxial optical anisotropy. The C plate is disposed between one or both of the upper polarizing plate and the glass substrate of the liquid crystal cell adjacent thereto, and the lower polarizing plate and the glass substrate of the liquid crystal cell adjacent thereto. By this method, it is possible to cancel the optical anisotropy of the vertically aligned liquid crystal layer and eliminate the viewing angle characteristic when no voltage is applied.

  Since the polarizing plates bonded to the upper and lower surfaces of the liquid crystal cell are arranged in crossed Nicols, a good black state can be realized during frontal observation. However, when the viewing angle is changed, light leakage is observed particularly when observed from a direction deviated by 45 ° from the absorption axis of the upper and lower polarizing plates. This is a phenomenon that appears because the “viewing angle characteristic of the polarizing plate” exists, and it is known that this deteriorates the viewing angle characteristic.

  As a method for solving this, a method using an optical compensator (biaxial film) having negative biaxial optical anisotropy disclosed in Patent Document 1 has been proposed. Patent Document 2 discloses a parameter example of a particularly effective biaxial film. In this method, a biaxial film is disposed between one of the upper polarizing plate and the glass substrate of the liquid crystal cell adjacent thereto, or between the lower polarizing plate and the glass substrate of the liquid crystal cell adjacent thereto. Furthermore, Patent Document 3 discloses a method of arranging a biaxial film between both the upper and lower polarizing plates and the glass substrate of the liquid crystal cell.

  With these technologies using a biaxial film, the viewing angle characteristics caused by the polarizing plate, which has become a problem when using the C plate as described above, can be eliminated, and the liquid crystal display element can be obliquely oriented at 45 ° from the polarizing plate absorption axis. Even when observed, it is possible to realize a black display substantially equivalent to that in frontal observation.

  In addition, in the patent document 4, the present inventors have proposed a vertical alignment type liquid crystal display element that realizes uniform monodomain alignment by rubbing treatment. Of course, the viewing angle compensation method described above can be applied to this element as it is.

  The improvement in viewing angle characteristics of a polarizing plate using a biaxial film as described above is a positive uniaxial optical difference in which the in-plane retardation Re of the optical compensation plate and the optical axis expressed in the liquid crystal layer are in the thickness direction. It is realized by exquisitely combining optical characteristics that exhibit directionality. The optical compensator is required to exhibit a double effect of simultaneously compensating the viewing angle characteristics of the liquid crystal layer, so that the negative (two in the thickness direction) retardation can be set freely. An optical compensator (biaxial film) having axial optical anisotropy is used.

Patent 2047880 specification Japanese Patent No. 3330574 JP 11-163119 A JP 2005-234254 A

  However, in a vertical alignment type liquid crystal display device compensated for viewing angle with a biaxial film, when no voltage is applied, when observed under a deep polar angle condition at a 45 ° azimuth from the polarizing member absorption axis, a light-through state colored in blue or purple is observed. May be observed. A technique for suppressing such coloring is desired.

  An object of the present invention is to provide a liquid crystal display element that includes a vertical alignment type liquid crystal cell, has a viewing angle compensated by a biaxial film, and suppresses coloring that occurs when observed from a deep polar angle when no voltage is applied. It is.

According to one aspect of the present invention, a first polarizing layer, a vertical alignment type liquid crystal cell disposed above the first polarizing layer, and a first polarizing layer disposed above the liquid crystal cell. Arranged in at least one of a second polarizing layer arranged in crossed Nicols with respect to the layer, between the first polarizing layer and the liquid crystal cell, and between the second polarizing layer and the liquid crystal cell. An optical compensator having negative biaxial optical anisotropy, and the liquid crystal cell is disposed on the first and second substrates, the first and second substrates being opposed to each other . A transparent electrode formed between each of the first and second substrates, and at least one of the first and second substrates on the entire surface of the liquid crystal layer side. Provided is a liquid crystal display element in which irregularities with random in-plane distribution and height distribution are formed.

  In a liquid crystal display element having a vertical alignment type liquid crystal cell and viewing angle compensation by a biaxial film, by forming random irregularities on the inner surface of the substrate of the liquid crystal cell, compared to the case where random irregularities are not formed, It is possible to achieve achromatic coloring that occurs when observed from a deep polar angle when no voltage is applied.

  Before describing the liquid crystal display element according to the embodiment of the present invention, first, as a comparative example, simulation analysis performed on a liquid crystal display element of the prior art will be described. As described above, in a vertical alignment type liquid crystal display device having an optical compensator having negative biaxial optical anisotropy (referred to as a biaxial film), the polarizing member absorption axis is applied when no voltage is applied. When observed under a deep polar angle condition in a 45 ° azimuth direction, a light-out state colored in blue or purple may be observed.

  As a first comparative example, a simulation for specifically grasping this phenomenon was performed. Further, for comparison with this simulation, as a second comparative example, a viewing angle is obtained with an optical compensator having negative uniaxial optical anisotropy (hereinafter referred to as C plate) as disclosed in Patent Document 1. We also performed a simulation for compensation.

  FIG. 11 is an exploded perspective view schematically showing the liquid crystal display element of the first comparative example. The simulation conditions of the first comparative example will be described with reference to FIG. For the simulation, a liquid crystal display simulator LCDMASTER 6.0 manufactured by Shintec was used.

  As shown in FIG. 11, a coordinate system indicating the orientation in the liquid crystal layer plane is set. A vertically aligned liquid crystal cell 111 is disposed on the polarizing plate 101, and a polarizing plate 131 with a viewing angle compensation plate is disposed on the liquid crystal cell 111. The polarizing plate 101 has a structure in which a TAC film 103 which is a protective film made of triacetyl cellulose (TAC) is laminated on the liquid crystal cell 111 side (upper side) of the polarizing layer 102. The polarizing plate 131 with a viewing angle compensation plate has a structure in which a biaxial film 121 is laminated on the liquid crystal cell 111 side (lower side) of the polarizing layer 133. A TAC film is not formed on the polarizing plate 131 with a viewing angle compensation plate.

  The lower polarizing layer 102 and the upper polarizing layer 133 are arranged in crossed Nicols. The direction of the absorption axis of the lower polarizing layer 102 is 45 ° (the direction of 45 ° -225 ° is simply called the 45 ° direction), and the direction of the absorption axis of the upper polarizing layer 133 is 135 ° (135 ° − The 315 ° direction is simply called the 135 ° orientation). As a material of both polarizing layers, SKN18243T manufactured by Polatechno was assumed.

  The liquid crystal cell 111 includes a lower glass substrate 112, an upper glass substrate 118, and a liquid crystal layer 115 sandwiched between both glass substrates. The liquid crystal layer 115 is assumed to have a monodomain alignment structure set at a pretilt angle of 89 °, and the orientation of the pretilt angle is 90 ° at the center of the liquid crystal layer. The retardation (thickness direction retardation) in the thickness cross section of the liquid crystal layer 115 was about 320 nm.

  The in-plane retardation Re of the biaxial film 121 was 55 nm, and the thickness direction retardation Rth was 220 nm. The in-plane slow axis direction of the biaxial film 121 was set to 45 ° orthogonal to the absorption axis of the polarizing layer 133 which is the nearest polarizing layer. As a material of the biaxial film 121, a norbornene plastic film was assumed.

  The TAC layer is generally known to function as a C plate. The thickness direction retardation Rth of the TAC film 103 included in the polarizing plate 101 was about 60 nm.

  FIG. 12 is an exploded perspective view schematically showing a liquid crystal display element of a second comparative example. The simulation conditions of the second comparative example will be described with reference to FIG. Differences from the first comparative example will be described.

  In the first comparative example, the polarizing plate 131 with a viewing angle compensator having a biaxial film is used as the upper polarizing plate. However, in the second comparative example, the TAC film 232 is disposed on the polarizing layer 233 on the liquid crystal layer 111 side. Is used, a normal polarizing plate 231 is used. A C plate 221 is disposed between the polarizing plate 231 and the liquid crystal cell 111. The thickness direction retardation Rth of the C plate 221 was 180 nm. As the material of the C plate 221, a norbornene-based plastic film was assumed in the same manner as the biaxial film 121 of the first comparative example. Other conditions are the same as in the first comparative example.

  Next, simulation results of the first and second comparative examples will be described with reference to FIGS. FIG. 13 shows a spectrum when no voltage is applied when observed from an azimuth of 0 ° and a polar angle of 50 °. Here, the normal direction of the display element is defined as a polar angle of 0 °. The horizontal axis of the graph of FIG. 13 is the wavelength expressed in nm, and the vertical axis is the transmittance expressed in%. The solid line is the spectral spectrum of the first comparative example (when biaxial film is used), and the broken line is the spectral spectrum of the second comparative example (when C plate is used).

  When a biaxial film is used, a state in which there is almost no light transmission is obtained in the vicinity of about 530 nm, but the light leakage tends to increase as it shifts from there to the short wavelength side and the long wavelength side. The maximum transmittance remains at about 0.2% in the wavelength range of 450 nm to 700 nm, for example.

  On the other hand, when the C plate is used, it can be seen that although the light leakage is much larger than that of the biaxial film, the light is flat in a wide range. For example, in the range of about 450 nm to 700 nm, the transmittance is about 0.7% and is almost constant.

  When a biaxial film is used, the overall light leakage is smaller than that of the C plate, but the viewing angle characteristics of the polarizing plate cannot be completely eliminated in all wavelength ranges, and light leakage occurs in a specific wavelength range. Further, coloring corresponding to this is observed. Depending on the parameters of the biaxial film and the liquid crystal layer, it may be colored in various colors. In addition, parameter variations of the liquid crystal layer or the biaxial film remarkably appear as a change in color tone, which easily causes display unevenness.

  On the other hand, when the C plate is used, luminance unevenness can be considered, but the change in color tone is greatly reduced as compared with the case of using a biaxial film, and the margin of each parameter is large. When a liquid crystal display element using a C plate was actually manufactured under the same conditions and observed, no light was observed although the light leakage was large.

Next, the viewing angle characteristics in the 0 ° and 180 ° azimuths that are the horizontal orientations of the liquid crystal display element are compared.
14 and 15 show polar angles of the liquid crystal display elements of the first comparative example (when using a biaxial film) and the second comparative example (when using a C plate) with respect to 0 ° and 180 ° azimuth, respectively. It is the spectral spectrum observed from 50 degrees. In FIG. 14 and FIG. 15, the solid line is a spectral spectrum with an azimuth of 0 °, and the broken line is a spectral spectrum with an azimuth of 180 °. As in FIG. 13, the horizontal axis of both graphs represents the wavelength in nm units, and the vertical axis represents the transmittance in% units.

  There is a characteristic that a difference is observed in the spectrum during left-right observation both when the biaxial film is used and when the C plate is used. This tendency is a phenomenon seen only in the case of monodomain vertical alignment having a pretilt angle in the liquid crystal layer. If the pretilt angle is 90 °, there is no difference in viewing angle characteristics between the 0 ° and 180 ° azimuths, but the difference (asymmetrical on the left and right) increases as the pretilt angle becomes smaller than 90 °.

  Naturally, in a monodomain vertical alignment type liquid crystal display element, a good display state cannot be obtained unless the pretilt angle is made smaller than 90 °. In the column of “Best Mode for Carrying Out the Invention” in Patent Document 4 (Japanese Patent Application Laid-Open No. 2005-234254), the inventors of the present application, as a pretilt angle of a liquid crystal layer bulk for obtaining good display characteristics, It is proposed that the angle is preferably 89.5 ° or less. Thus, since the pretilt angle is smaller than 90 °, the left-right asymmetry described above cannot be completely eliminated.

  When using a biaxial film and when using a C plate, left and right asymmetry is observed in the spectrum, but as will be explained below, the left and right asymmetry is particularly problematic. In this case, a biaxial film is used.

  As shown in FIG. 15, when the C plate is used, since the spectrum is relatively flat, the difference between the left and right observations is only the difference in luminance. However, as shown in FIG. 14, when a biaxial film is used, the wavelength at which the minimum transmittance can be obtained is different on the left and right sides, so that there is a concern that the color tone may appear to be clearly different in the left and right observations. In addition, when a liquid crystal display element using a biaxial film similar to that shown in FIG. 11 was actually produced and observed, a difference in color tone was clearly observed in the left-right direction.

  As described above, when the biaxial plate is used, although the size of the light omission is suppressed as a whole, the light transmission is lost only in a specific wavelength region, so that coloring is observed. In addition, a difference in color tone is also observed during left-right observation. On the other hand, when the C plate is used, although the size of light leakage is larger than when the biaxial plate is used, the light transmittance is almost constant in a wide wavelength region, and coloring is suppressed. For this reason, a difference in color tone between left and right observations hardly occurs.

  In addition, as an optical compensator that compensates the viewing angle characteristics of recent vertical alignment type liquid crystal display elements, priority is given to the numerical viewing angle characteristics, so a method using a biaxial film with good luminance viewing angle characteristics Is widely used. As biaxial films, for example, Konica Minolta Op's optical film n-TAC stretched based on TAC materials and Optes' new ZEONOR using norbornene-based cyclic olefin materials are marketed in large quantities. ing.

  On the other hand, VAC films manufactured by Sumitomo Chemical Co., Ltd. have been put on the market as optical films having optical properties equivalent to those of C plates, but the market distribution volume has been rapidly decreasing and it is becoming difficult to obtain them. .

  It is desired to use a biaxial film to realize a liquid crystal display element that is inferior in color tone as compared with, for example, a C plate. In addition, it is desirable that the size of light leakage can be suppressed as compared with the case where a C plate is used, for example.

  Next, the liquid crystal display element of the first embodiment will be described. FIG. 1A is a schematic cross-sectional view showing the configuration of the liquid crystal display element of the first embodiment. A vertically aligned liquid crystal cell 11 is disposed on the polarizing plate 1, a biaxial film 21 is disposed on the liquid crystal cell 11, and a polarizing plate 31 is disposed on the biaxial film 21.

  Each of the polarizing plate 1 and the polarizing plate 31 has a structure in which a TAC film is laminated on the liquid crystal cell side of the polarizing layer. The polarizing layer 2 and the TAC film 3 constitute the polarizing plate 1, and the polarizing layer 33 and the TAC film 32 constitute the polarizing plate 31.

  The liquid crystal cell 11 is configured to include the lower glass substrate 12, the lower transparent electrode 13, the lower vertical alignment film 14, the liquid crystal layer 15, the upper vertical alignment film 16, the upper transparent electrode 17, and the upper glass substrate 18. The A liquid crystal layer 15 is sandwiched between the lower glass substrate 12 and the upper glass substrate 18 facing each other.

  Random irregularities (unevenness with random in-plane distribution of the positions of the irregularities) are formed over the entire inner surface (the surface on the liquid crystal layer 15 side) of the lower glass substrate 12. A lower transparent electrode 13 is formed on the inner surface of the lower glass substrate 12, and a lower vertical alignment film 14 is applied on the inner surface of the lower transparent electrode 13 (above the liquid crystal layer side of the lower glass substrate 12). Has been.

  The thickness of the laminated layer of the lower transparent electrode 13 and the lower vertical alignment film 14 is preferably not more than the difference in height between the most convex part and the most concave part of the irregularities on the inner surface of the lower glass substrate 12. As a result, the vertical alignment film 14 serving as the uppermost surface of the lower substrate also has a structure in which the uneven shape of the lower glass substrate 12 is reflected without filling the unevenness.

  The inner surface of the upper glass substrate 18 is a plane. An upper transparent electrode 17 is formed on the inner surface of the upper glass substrate 18, and an upper vertical alignment film 16 is applied on the inner surface of the upper transparent electrode 17 (above the liquid crystal layer side of the upper glass substrate 18).

The upper and lower vertical alignment films 14 and 16 are subjected to an alignment treatment for imparting a desired pretilt angle to the liquid crystal molecules of the liquid crystal layer 15. For example, as a vertical alignment film, the surface free energy is 35 m N / m to 39 m N / m as disclosed in the column “Best Mode for Carrying Out the Invention” of JP-A-2005-234254. Can be used for appropriate rubbing treatment as disclosed in the same column.

  Further, for example, as disclosed in Japanese Patent No. 3054076, a pretilt angle may be imparted to the vertical alignment film by performing a treatment of irradiating polarized or non-polarized ultraviolet rays obliquely from the substrate. A uniform monodomain alignment can be obtained by applying anti-parallel conditions or the like between the upper and lower vertical alignment films.

  As a method for forming a random uneven shape on one surface of a glass substrate, a method known as a frosting treatment or a frosting treatment of the glass surface can be used. For example, a method in which one side of a glass is immersed in an aqueous solution containing hydrogen fluoride and hydrochloric acid to obtain irregularities by chemical etching, or sand blasting that performs physical etching by spraying silica sand or the like on a glass surface with high-pressure air or the like. Laws are known.

  Japanese Patent Laid-Open No. 2-172844 discloses that a silicon alkoxide coating material is applied to a glass substrate and baked to gel the silicon alkoxide and form irregularities on the substrate surface in a state where fine particles are dispersed. A method is disclosed. In addition, the surface irregularities are formed by dispersing silica-based fine particles having a particle size of about 0.1 μm to 3 μm on a substrate and applying and baking a polysilane-based hard coat material thereon. Is also possible. Furthermore, it is also possible to form irregularities on the surface by dispersing and dispersing these fine particles in a polysilane-based hard coat material, followed by firing.

  The liquid crystal display element of the first example was subjected to a simulation analysis for examining optical characteristics as in the comparative example.

  In the simulation model of the first comparative example described with reference to FIG. 11, the liquid crystal cell is replaced with the liquid crystal cell of the first embodiment in which random irregularities are formed on the inner surface of the lower glass substrate, and the upper polarized light is changed. The plate is replaced with a polarizing plate with a viewing angle compensation plate from a polarizing plate with a normal TAC film, and a structure in which a biaxial film is disposed between the liquid crystal cell and the upper polarizing plate is the simulation model of the first embodiment. did. The coordinate system indicating the in-plane orientation of the liquid crystal layer is also set in the same manner as in the first comparative example. In the simulation, a liquid crystal display simulator LCDMASTER 6.0 manufactured by Shintec was used as in the comparative example.

  The lower polarizing layer 2 and the upper polarizing layer 33 are arranged in crossed Nicols. The direction of the absorption axis of the lower polarizing layer 2 is 45 °, and the direction of the absorption axis of the upper polarizing layer 33 is 135 °. As a material for both polarizing layers, SKN18243T manufactured by Polatechno is assumed.

  The liquid crystal layer 15 has a monodomain vertical alignment that has been subjected to an alignment process having a certain pretilt angle so as to be antiparallel to the upper and lower substrates, the orientation direction of the pretilt angle of the liquid crystal layer center molecule is 90 °, and the pretilt angle is 89 °. It was. The birefringence anisotropy Δn of the liquid crystal material used for the liquid crystal layer 15 was about 0.091.

  The in-plane retardation Re of the biaxial film 21 was 55 nm, and the thickness direction retardation Rth was 220 nm. The in-plane slow axis direction of the biaxial film 21 was set to 45 ° orthogonal to the absorption axis direction of the polarizing layer 33 which is the nearest polarizing layer. The thickness direction retardation Rth of each of the upper and lower TAC films 3 and 32 was 68 nm.

  Here, the center cell thickness and the maximum unevenness distance are defined. As in the liquid crystal cell structure shown in FIG. 1A, when unevenness is formed on the surface of one substrate and the surface of the counter substrate is a flat surface, the most convex and concave portions of the unevenness of the substrate on which the unevenness is formed. The distance from the center height to the counter substrate surface (liquid crystal layer thickness) is defined as the center cell thickness.

  Using the height of the center of the most convex part and the most concave part as a reference, the distance to the most convex part is equal to the distance to the most concave part. The distance from the center height to the most convex part is, for example, a positive distance with a sign, and the distance from the center height to the most concave part is, for example, a negative distance with a sign. It is defined as the maximum unevenness distance. The distance from the center height to the most convex part and the size of the distance from the center height to the most concave part will be referred to as an absolute value of the maximum unevenness distance.

  For example, when the distance from the center height to the most convex part is +0.5 μm and the distance from the center height to the most concave part is −0.5 μm, the maximum unevenness distance is ± 0.5 μm. In this example, the difference in height between the most convex part and the most concave part is 1 μm. The cell thickness distribution in the liquid crystal layer can be expressed as the sum of the center cell thickness and the maximum unevenness distance.

  First, the simulation was performed by setting the center cell thickness to 3.5 μm and the thickness direction retardation corresponding to the center cell thickness to about 320 nm.

  Next, how the spectral spectrum changes as the maximum unevenness distance is increased from 0 μm to ± 0.8 μm when observed at an azimuth of 0 ° and a polar angle of 50 ° will be described. The maximum unevenness distance of 0 μm corresponds to the conventional liquid crystal cell structure.

  FIG. 2 shows a spectral spectrum. The horizontal axis of the graph is the wavelength in nm, and the vertical axis is the transmittance in% (this is the same for the graphs of FIGS. 4 and 6 below). Curves A1 to A5 are spectra when the maximum unevenness distance is 0 μm, ± 0.2 μm, ± 0.4 μm, ± 0.6 μm, and ± 0.8 μm, respectively.

  As a comparison, the spectrum of the conventional example (structure shown in FIG. 12) in the case of using a C plate (C plate of Rth = 180 nm and one TAC film on the polarizing layer surface) instead of the biaxial film is also shown. The curve B1 is shown in FIG.

  The shape of the spectrum of the example is almost similar without depending on the maximum unevenness distance, but the transmittance tends to increase as the maximum unevenness distance increases. Moreover, the tendency that the transmittance increase on the short wavelength side is larger than the transmittance increase on the long wavelength side is seen. Even when the maximum unevenness distance is set to ± 0.8 μm, it is considered that the flatness in a wide wavelength region is slightly lowered as compared with the case of the C plate. However, it can be expected that the luminance transmittance may be lowered from the transmittance near the wavelength of 550 nm.

  The spectral transmittance of the example using the biaxial film generally increases as the maximum unevenness distance increases. From this, it is considered that the coloring that has occurred due to the absence of light transmission in the specific wavelength region can be alleviated by increasing the maximum unevenness distance.

  Next, the maximum unevenness distance dependency of CIE1931xy chromaticity when azimuths of 0 ° and 180 ° are observed at a polar angle of 50 ° will be described. As a light source, a standard light source D65 was assumed.

  The chromaticity coordinates in FIG. 3 show the chromaticity at azimuths of 0 ° and 180 ° when the maximum unevenness distance is increased by ± 0.1 μm from 0 μm to ± 0.7 μm. For comparison, chromaticity coordinates of 0 ° and 180 ° in the conventional example using the C plate instead of the biaxial film are also shown.

  In the case of the conventional structure having the maximum unevenness distance of 0 μm, it can be seen that the color tone when observed from the azimuths of 0 ° and 180 °, that is, from the left and right azimuth is greatly different. As the maximum concavo-convex distance increases, it can be seen that the azimuth 0 ° and 180 ° move toward a certain chromaticity coordinate that is close to an achromatic color, and the chromaticity distance between the 0 ° azimuth and 180 ° azimuth approaches. There is a tendency to go.

  The chromaticity coordinates when using the C plate are almost the same at azimuths of 0 ° and 180 °. In the element of the example using the biaxial film, the chromaticity coordinates that finally go when the maximum unevenness distance is increased are different from the chromaticity at the azimuths of 0 ° and 180 ° when the C plate is used. . However, it is clear that by increasing the maximum unevenness distance, the appearance coloring state is greatly improved, and the difference between the left and right color tones is alleviated.

  In addition, the chromaticity change accompanying the maximum uneven | corrugated distance change is large until the maximum uneven | corrugated distance reaches +/- 0.4micrometer. In the range of the maximum unevenness distance of ± 0.4 μm or more, there is a tendency that the change in chromaticity accompanying the change in the maximum unevenness distance is small. Therefore, it may be effective that the maximum unevenness distance is ± 0.4 μm or more. That is, it would be effective to have a cell thickness distribution having a cell thickness difference of ± 0.4 μm or more with respect to the center cell thickness. In other words, it may be effective that the difference in height between the most convex part and the most concave part of the irregularities on the substrate surface is 0.8 μm or more.

  Furthermore, in order to realize chromaticity close to the liquid crystal display element of the C plate use structure in which the cell thickness condition is the optimum condition of 3.5 μm, the liquid crystal display element of the example is examined to optimize the center cell thickness. went. It was found that when the chromaticity is completely equal, the center cell thickness needs to be reduced from 3.5 μm by about 0.6 μm to 2.9 μm. It was found that the thickness direction retardation needs to be reduced by about 55 nm.

  FIG. 4 shows a spectrum at the time of observation at an azimuth of 0 ° and a polar angle of 50 ° with respect to the liquid crystal display element of the example in which the center cell thickness is 2.9 μm and the maximum unevenness distance is ± 0.4 μm. FIG. 4 also shows the spectrum of the element using the C plate shown in FIG. Curve A6 is the spectrum of the example, and curve B2 is the spectrum of the element using the C plate.

  The spectrum of the element using the C plate shows a substantially flat shape at a wavelength of about 450 nm to 700 nm. On the other hand, the spectrum of the example also shows a substantially flat shape in a similar wavelength range. Thus, the element of the Example using a biaxial film can be made into the thing of the characteristic which is not inferior to a C plate use element at the point of a color tone.

  Furthermore, the overall transmittance level is lower for the element of the example than for the element using the C plate. It can be seen that the device of the example is superior in terms of luminance transmittance. In the element of the example, although the transmittance increases as a whole with achromatic color, the increase width is suppressed.

  However, if the center cell thickness is made too thin, there is a concern that the maximum transmittance in the electro-optical characteristics is lowered. The center cell thickness and retardation are set between the cell thickness of 3.5 μm and the retardation of about 320 nm, which are optimum in the conventional structure, to the cell thickness of 2.9 μm and the retardation of about 270 nm, and the maximum unevenness distance is set to ± 0.4 μm or more. In this case, the viewing angle characteristics when no voltage is applied can be made relatively achromatic, and the electro-optical characteristics during frontal observation can be prevented from being significantly lowered as compared with the conventional element structure. In order to prove this, it was confirmed what chromaticity change can be obtained at a cell thickness of 3.2 μm, which is between 3.5 μm and 2.9 μm.

FIG. 5 shows chromaticity coordinates indicating the maximum uneven distance dependency of CIE1931xy chromaticity when the central cell thickness is 3.2 μm and the azimuths of 0 ° and 180 ° are observed at a polar angle of 50 °.
The maximum unevenness distance was increased from 0 μm to ± 0.5 μm. Similarly to FIG. 3, the chromaticity coordinates of the C plate using element are also shown.

  Similar to the case shown in FIG. 3, as the maximum unevenness distance increases, achromatic color is achieved, and the difference between the left and right color tones is less likely to be recognized. The maximum unevenness distance was ± 0.5 μm, and the closest color tone was obtained when the C plate was used.

  FIG. 6 shows a spectrum at the time of observation at an azimuth of 0 ° and a polar angle of 50 ° when the maximum unevenness distance is ± 0.5 μm. The spectrum of the element using the C plate shown in FIG. 2 is also shown. Curve A7 is the spectrum of the example, and curve B3 is the spectrum of the element using the C plate. It can be seen that even when the center cell thickness is 3.2 μm, a substantially flat spectrum is obtained and achromatic color is realized. Further, it can be seen that the transmittance is significantly lower than that in the case of using the C plate, and a good contrast characteristic can be obtained.

  In addition, although the example which performs an alignment process by rubbing or ultraviolet irradiation to both the upper and lower vertical alignment films of the liquid crystal cell has been described, the alignment process may be performed on at least one vertical alignment film. Even when only one vertical alignment film is subjected to the alignment treatment, it is possible to achieve achromatic color with good contrast characteristics. When the alignment process is applied only to the vertical alignment film on one side, the alignment process is not applied to the vertical alignment film on the flat counter substrate side, and the alignment process is not applied to the vertical alignment film on the substrate side on which random irregularities are formed. It is preferable to apply.

  In the above-described cell structure, random irregularities are formed on one glass substrate, but random irregularities may be formed on both upper and lower glass substrates.

  FIG. 1B is a schematic cross-sectional view of a liquid crystal display element having a liquid crystal cell 11a in which random irregularities are formed on the upper and lower glass substrates. Also on the upper glass substrate 18a, random irregularities are formed on the inner surface, the transparent electrode 17a is formed on the surface, and the vertical alignment film 16a is applied to the transparent electrode 17a. Other structures are similar to those of the liquid crystal display element described with reference to FIG.

  As for the liquid crystal display element having such a cell structure, when a simulation analysis was performed, as in the case where the unevenness was formed on the substrate on one side, the coloring was achromatic, and while reducing the difference in color tone during left-right observation, It was found that the overall increase in light transmission can be suppressed.

  In addition, for such a cell structure, the distance from the height of the center of the convex and concave portions of one substrate to the height of the central portion of the concave and convex portions of the counter substrate ( The liquid crystal layer thickness) is defined as the center cell thickness.

  In the case of such a cell structure, a difference in cell thickness of ± 0.4 μm or more with respect to the center cell thickness may be covered by unevenness on both the upper and lower substrates. For this reason, the maximum unevenness distance of each of the upper and lower substrates is half that when the unevenness is formed only on one side substrate, and is preferably ± 0.2 μm or more. In other words, for each of the upper and lower substrates, it is preferable that the difference in height between the most convex and concave portions of the unevenness is 0.4 μm or more.

  Even in the case where irregularities are formed on the substrates on both sides of the liquid crystal cell, the alignment treatment may be performed on at least the vertical alignment film on the substrate on one side.

  In the above embodiment, one biaxial film is used, but a configuration using a plurality of biaxial films is also possible. For example, two biaxial films can be used in an overlapping manner. FIG. 7 is an exploded perspective view schematically showing the liquid crystal display device having such a configuration. The point that two biaxial films are arranged between the upper substrate of the liquid crystal cell and the upper polarizing layer is that the liquid crystal display element described with reference to FIG. It is different from the liquid crystal display element described with reference to (B). Note that the liquid crystal cell 11 has random unevenness on one substrate (see FIG. 1A), and the liquid crystal cell 11a has random unevenness on both substrates (FIG. 1B). )reference).

  In this configuration, the upper polarizing plate 31b is a polarizing plate with a viewing angle compensation plate in which the biaxial film 21b is laminated on the polarizing layer 33b. The absorption axis direction of the polarizing layer 33b of the polarizing plate 31b with a viewing angle compensation plate and the in-plane slow axis direction of the biaxial film 21b are parallel. Further, the absorption axis direction of the second biaxial film 41b arranged on the liquid crystal cell 11 (or 11a) side is orthogonal to the absorption axis direction of the biaxial film 21b on the polarizing layer 33b side.

  For example, the structure which arrange | positions a biaxial film on both sides of a liquid crystal cell is also possible. FIG. 8 is an exploded perspective view schematically showing a liquid crystal display device having such a configuration. In this liquid crystal display element, both the upper and lower polarizing plates of the liquid crystal cell 11 (or 11a) are polarizing plates with viewing angle compensation plates using biaxial films.

  In the lower polarizing plate 1c, the absorption axis direction of the polarizing layer 2c and the in-plane slow axis direction of the biaxial film 41c are orthogonal to each other, and in the upper polarizing plate 31c, the absorption axis direction of the polarizing layer 33c and the biaxial film. The in-plane slow axis direction of 21c is orthogonal. The in-plane slow axis orientation of the lower biaxial film 41c is orthogonal to the in-plane slow axis orientation of the upper biaxial film 21c. The absorption axis orientation of the upper and lower polarizing layers is the same as that of the element described with reference to FIG.

  In the element using two biaxial films as shown in FIGS. 7 and 8, the thickness direction retardation Rth of each biaxial film is set to the thickness of the biaxial film of the element using one biaxial film. What is necessary is just to set to about half of direction retardation.

  In the above description, for example, the orientation control by rubbing or ultraviolet light irradiation has been described. However, as another example of the orientation control, it is described in the “Embodiment of the Invention” column of JP-A-2004-252298. Technology is also available. In this technique, a plurality of rectangular or parallelogram-shaped openings (slits) are provided at regular intervals on the transparent electrodes on the upper and lower substrates of the liquid crystal cell. In plan view (within the display surface), the slits on the upper transparent electrode and the slits on the lower transparent electrode are alternately arranged at regular intervals. It is also possible to control the alignment direction of the liquid crystal molecules by generating an oblique electric field with such a structure. In such a configuration, it is not necessary to perform alignment treatment such as rubbing on the vertical alignment film.

  Next, the liquid crystal display element of the second embodiment will be described. In the liquid crystal display element of the first example, the thickness direction retardation of the liquid crystal layer was assumed to be around 320 nm. If there is retardation in the vicinity, it is considered that a good display state can be obtained by static driving (active matrix driving) or ˜¼ duty multiplex driving.

  The liquid crystal display element of the second embodiment is assumed to be suitable for driving conditions of 1/8 duty or more (the denominator is 8 or more) in multiplex driving, and the thickness of the liquid crystal layer is larger than that of the first embodiment. The vertical retardation is large.

  FIG. 9 is an exploded perspective view schematically showing the liquid crystal display element of the second embodiment. A difference in configuration from the liquid crystal display element of the first embodiment shown in FIG. 1A will be described. In the device of the first embodiment, one biaxial film is disposed between the liquid crystal cell and the upper polarizing plate. However, in the second embodiment, the liquid crystal cell 11d and the upper polarizing plate are disposed. A single C plate 51 and a single biaxial film 21d are disposed between them.

  A C plate 51 is disposed on the liquid crystal cell 11d side, and a biaxial film 21d is disposed on the upper polarizing plate 31 side. The in-plane slow axis direction of the biaxial film 21d is parallel to the absorption axis direction of the polarizing layer 33 of the upper polarizing plate 31, which is the nearest polarizing layer. The thickness direction retardation Rth of the C plate 51 is 220 nm.

  The birefringence anisotropy Δn of the liquid crystal material in the liquid crystal layer of the liquid crystal cell 11d is approximately 0.15. Using this liquid crystal material, the optimum cell thickness of a liquid crystal cell having a conventional structure with no irregularities is 4 μm. The liquid crystal cell 11d is obtained by forming random irregularities on a substrate on one side, like the liquid crystal display element of the first embodiment shown in FIG. An alignment process is performed on at least one of the upper and lower vertical alignment films of the liquid crystal cell 11d to form a monodomain vertical alignment having a desired pretilt angle.

  In addition, the liquid crystal display element of the second embodiment is made in the same manner as the first embodiment described with reference to FIG. 1A with respect to the conditions such as the absorption axis orientation of the upper and lower polarizing layers and the retardation of the biaxial film. A simulation was performed. The definitions of the center cell thickness and the maximum unevenness distance are the same as in the first embodiment.

FIG. 10 shows chromaticity coordinates indicating the maximum uneven distance dependency of CIE1931xy chromaticity when the central cell thickness is 4 μm and the azimuths of 0 ° and 180 ° are observed at a polar angle of 50 °.
The maximum unevenness distance was increased from 0 μm to ± 0.5 μm. Also shown is the chromaticity coordinates of a conventional structure element using only the C plate.

  As in the case of the first embodiment, as the maximum unevenness distance increases, the chromaticity coordinates tend to shift in the direction of the achromatic color, and it can be confirmed that the color tone difference between the left and right is improved. When the optimum cell thickness of 4 μm in the conventional structure is set as the center cell thickness, it can be seen that the chromaticity is deviated from the conventional structure using the C plate as in the first embodiment.

  Also in this example, it was confirmed that by shifting the center cell thickness to a smaller one, the characteristics of the C plate using element were approached. A good center cell thickness is approximately 3.4 μm to 4 μm, and a corresponding thickness direction retardation is approximately 510 nm to 600 nm. The maximum unevenness distance is preferably set to ± 0.4 μm or more (retardation is ± 60 nm or more). As in the first embodiment, the liquid crystal cell may have a configuration in which irregularities are formed on the upper and lower substrates. In this case, the maximum unevenness distance is preferably set to ± 0.2 μm or more for each of the upper and lower substrates.

  From the first and second embodiments, when a common place of the optimum range of the center cell thickness and the maximum unevenness distance is found, when the optimum cell thickness corresponding to the optimum retardation of the conventional structure is used as a reference, the center cell thickness is The absolute value of the maximum concavo-convex distance is set to approximately 80% to 100%, and the absolute value of the maximum concavo-convex distance is approximately 10% or more (when there is unevenness only on one side substrate), or approximately 5% or more (when both sides have unevenness) It is preferable to set for each of the substrates.

  Therefore, the absolute value of the maximum unevenness distance is about 10% or more of the center cell thickness (when there is unevenness only on one side of the substrate), or about 5% or more (for each substrate when both sides have unevenness). It is preferable to set. The upper limit of the absolute value of the maximum unevenness distance is the center cell thickness.

  In addition, the difference in height between the most convex part and the most concave part of the concave and convex portions on the inner surface of the cell substrate is preferably 0.8 μm or more when the concave and convex portions are formed only on one side substrate, and the concave and convex portions are formed on both side substrates. When forming, it is preferable to set it as 0.4 micrometer or more about each board | substrate. Note that the in-plane pitch of the unevenness is preferably randomly distributed at about 1 μm to 20 μm (it is preferable that a region where the unevenness is distributed at such a pitch is included).

  As described above in the first and second embodiments, in the vertical alignment type liquid crystal display element in which at least one biaxial film is disposed between the polarizing layer and the liquid crystal layer as the viewing angle compensation means, the liquid crystal By forming random irregularities on the inner surface of at least one substrate of the cell, it is possible to achieve achromatic coloration that is seen when observing at a deep viewing angle when no voltage is applied. In addition, it is also possible to suppress the luminance better than when the C plate is used. In the liquid crystal display element using the monodomain vertical alignment cell, there is also an effect of reducing the asymmetry of the coloring degree of the left and right color tones. When the biaxial film is disposed only on one side of the liquid crystal cell, it can be disposed on either the upper side or the lower side of the liquid crystal cell as necessary.

  Examples of liquid crystal display elements to which the technology of the embodiment can be applied include, for example, a segment display static drive liquid crystal display element, a segment display simple matrix drive liquid crystal display element, a dot matrix display simple matrix drive display element, and one liquid crystal display element. Examples include a liquid crystal display element including a segment display static drive liquid crystal display element part and a segment display simple matrix drive liquid crystal display element part, an active matrix drive liquid crystal display element including a thin film transistor (TFT) drive, and the like.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

FIG. 1A is a schematic cross-sectional view of the liquid crystal display element of the first embodiment, and FIG. 1B is a schematic cross-sectional view of a liquid crystal display element of a modification of the first embodiment. FIG. 2 is a spectral spectrum of the liquid crystal display element of the first embodiment in which the center cell thickness is 3.5 μm. FIG. 3 is a chromaticity diagram showing CIE1931xy chromaticity of the liquid crystal display element of the first embodiment in which the center cell thickness is 3.5 μm. FIG. 4 is a spectral spectrum of the liquid crystal display element of the first embodiment in which the center cell thickness is 2.9 μm. FIG. 5 is a chromaticity diagram showing CIE1931xy chromaticity of the liquid crystal display element of the first embodiment in which the center cell thickness is 3.2 μm. FIG. 6 is a spectral spectrum of the liquid crystal display element of the first embodiment in which the center cell thickness is 3.2 μm. FIG. 7 is an exploded perspective view schematically showing a liquid crystal display element of another modification of the first embodiment. FIG. 8 is an exploded perspective view schematically showing a liquid crystal display element of still another modification of the first embodiment. FIG. 9 is an exploded perspective view schematically showing the liquid crystal display element of the second embodiment. FIG. 10 is a chromaticity diagram showing CIE1931xy chromaticity of the liquid crystal display element of the second embodiment. FIG. 11 is an exploded perspective view schematically showing the liquid crystal display element of the first comparative example. FIG. 12 is an exploded perspective view schematically showing a liquid crystal display element of a second comparative example. FIG. 13 shows spectral spectra of the liquid crystal display elements of the first and second comparative examples. FIG. 14 is a spectrum when the liquid crystal display element of the first comparative example is observed from 0 ° and 180 ° azimuths. FIG. 15 is a spectrum obtained when the liquid crystal display element of the second comparative example is observed from 0 ° and 180 ° azimuths.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polarizing plate 2 Polarizing layer 3 TAC film 11 Liquid crystal cell 12 Lower glass substrate 13 Lower transparent electrode 14 Lower vertical alignment film 15 Liquid crystal layer 16 Upper vertical alignment film 17 Upper transparent electrode 18 Upper glass substrate 21 Biaxial film 31 Polarization Plate 32 TAC film 33 Polarizing layer

Claims (10)

A first polarizing layer;
A vertical alignment type liquid crystal cell disposed above the first polarizing layer;
A second polarizing layer disposed above the liquid crystal cell and arranged in crossed Nicols with respect to the first polarizing layer;
An optical compensator having negative biaxial optical anisotropy disposed between at least one of the first polarizing layer and the liquid crystal cell and between the second polarizing layer and the liquid crystal cell; Have
The liquid crystal cell is sandwiched between a first substrate and a second substrate disposed opposite to each other, a transparent electrode formed on each of the first and second substrates, and the first and second substrates. A liquid crystal display element, wherein at least one of the first and second substrates is provided with irregularities with random in- plane distribution and height distribution over the entire surface on the liquid crystal layer side.   The unevenness is formed on the first surface of the first substrate on the liquid crystal layer side, and the second surface of the second substrate on the liquid crystal layer side is a plane, and the first surface When the center cell thickness is defined as the distance from the center height of the most convex part and the most concave part of the surface irregularities to the second surface, the distance from the center height to the most convex part, and 2. The liquid crystal display element according to claim 1, wherein the distance from the central height to the most concave portion is 10% or more of the central cell thickness.   The unevenness is formed on the first surface of the first substrate on the liquid crystal layer side, and the second surface of the second substrate on the liquid crystal layer side is a plane, and the first surface The liquid crystal display element according to claim 1, wherein a difference in height between the most convex part and the most concave part of the unevenness on the surface is 0.8 μm or more.   The unevenness is formed on both the first surface on the liquid crystal layer side of the first substrate and the second surface on the liquid crystal layer side of the second substrate, and the first surface When the distance from the center height of the most convex part and the most concave part of the concave and convex parts to the center height of the convex part and the most concave part of the concave and convex parts on the second surface is defined as the center cell thickness, For each of the first and second surfaces, the distance from the central height to the most convex part and the distance from the central height to the most concave part are both 5% or more of the central cell thickness. The liquid crystal display element according to claim 1.   The unevenness is formed on both the first surface on the liquid crystal layer side of the first substrate and the second surface on the liquid crystal layer side of the second substrate, and the first surface The difference in height between the most convex part and the most concave part of the concave and convex parts and the difference in height between the convex part and the most concave part of the concave and convex parts on the second surface are both 0.4 μm or more. 5. A liquid crystal display element according to 1 or 4. The first of said liquid crystal layer side of the surface of the substrate, and the surface of the second liquid crystal layer side, are respectively the vertical alignment film and is formed on the formed concavo-convex surface the thickness of the lamination of the transparent conductive Goku及 beauty vertical alignment film, liquid crystal display according to any one of the thin claims 1-5 than the difference in height between the top protrusion and the uppermost recess uneven element.   Vertical alignment films are formed above the liquid crystal layer side of the first substrate and above the liquid crystal layer side of the second substrate, respectively, and one of the first and second substrates is formed. The vertical alignment film on the substrate side is subjected to an alignment treatment so that a pretilt angle is expressed, and the vertical alignment film on the other substrate side is not subjected to the alignment treatment. The liquid crystal display element as described.   The unevenness is formed on the surface of the first substrate on the liquid crystal layer side, the surface of the second substrate on the liquid crystal layer side is a flat surface, and the liquid crystal layer side of the first substrate is A vertical alignment film is formed above the second substrate and above the liquid crystal layer side of the second substrate, and the vertical alignment film on the second substrate side is aligned so that a pretilt angle is expressed. The liquid crystal display element according to claim 1, wherein the liquid crystal display element is subjected to a treatment, and the vertical alignment film on the first substrate side is not subjected to the alignment treatment.   The liquid crystal display element according to claim 7, wherein the alignment treatment is performed by rubbing or ultraviolet irradiation. Wherein the first and second transparent electrodes on the substrate, each of the plurality of being rectangular or parallelogram-shaped openings formed, in a plan view, the opening of the transparent electrodes of the first substrate side parts and an opening of the transparent electrodes of the second substrate side, the liquid crystal display device according to any one of claims 1 to 6 are arranged alternately.

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