JP2009258640A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device having an improved display quality. <P>SOLUTION: The liquid crystal display device includes a pair of substrates facing each other, a liquid crystal cell interposed between the pair of substrates and including a liquid crystal cell, a pair of polarizing plates disposed on front and rear surfaces of the liquid crystal cell, an optical element disposed in the front of the liquid crystal cell, and a light source disposed at the rear of one of the pair of polarizing plates, which is disposed on the rear surface of the liquid crystal cell. The optical element refracts a component in the best visibility direction out of emitted light from the liquid crystal cell, toward normals of the pair of substrates. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device including an optical element.

  Liquid crystal display elements are known to have viewing angle characteristics (viewing angle dependency), and there are directions in which the display looks beautiful and directions in which the display does not. A vertical alignment type or twisted nematic (TN) type liquid crystal display element has a large difference in transmittance depending on the viewing angle, and has a very large viewing angle dependency particularly when driving at a high duty multiplex.

  Japanese Patent Application Laid-Open No. 2007-101874 proposes a liquid crystal display element that improves viewing angle characteristics.

JP 2007-101874 A

  In a liquid crystal display element, the visibility from the major axis direction of liquid crystal molecules is not good. For example, in a vertical alignment type liquid crystal display element, the direction in which liquid crystal molecules are tilted by voltage application is the direction in which display is most difficult to see. On the other hand, the direction opposite to the direction in which the display is most difficult to see is the direction in which the display is most easily seen (best viewing direction).

  In addition, there is a demand for obtaining the best visibility when observing the liquid crystal display element from the substrate normal direction and eliminating the portion with poor display quality when observed from a viewing angle close to the substrate normal direction.

  An object of the present invention is to provide a liquid crystal display device with improved display quality.

  According to one aspect of the present invention, a pair of opposing substrates, a liquid crystal cell including a liquid crystal layer sandwiched between the opposing pair of substrates, and a pair of polarizing plates disposed on the front and back surfaces of the liquid crystal cell An optical element disposed in front of the liquid crystal cell, and a light source disposed behind the pair of polarizing plates disposed on the back surface of the liquid crystal cell, and the optical element includes the liquid crystal A liquid crystal display device is provided that refracts the component of the best viewing azimuth of the light emitted from the cell toward the pair of substrate normals.

  According to the present invention, a liquid crystal display device with improved display quality can be provided.

  FIG. 1 is a schematic cross-sectional view of a liquid crystal display device according to a first embodiment. The inventors have provided an optical element that refracts light emitted from the liquid crystal cell in front of the liquid crystal cell so that a good display quality can be obtained when viewed from the normal direction of the substrate. Was invented.

  In the embodiment, an example of a vertically aligned liquid crystal display device will be described. The liquid crystal display device includes a liquid crystal cell 4 in which a transparent front substrate 1a and a back substrate 1b sandwich a liquid crystal layer 2, polarizing plates 5a and 5b disposed on the front and back surfaces of the liquid crystal cell 4, a light source 6, An optical element 7 is included. In the liquid crystal cell 4, the substrates 1 a and 1 b are bonded together with a sealant 3 with a gap. Liquid crystal is injected into the gap to form the liquid crystal layer 2. In the case of the vertical alignment mode, a liquid crystal having a dielectric anisotropy Δε <0 is used. The liquid crystal cell has a thickness of 5.5 μm and a retardation of 900 nm. An electrode for applying a voltage between the substrates 1a and 1b is provided on each of the substrates 1a and 1b on the liquid crystal layer 2 side.

  2A is a plan view showing the rubbing direction of the liquid crystal cell 4, and FIG. 2B is a schematic cross-sectional view taken along one-dot chain line A-A1 in FIG. 2A. FIG. 2A shows the rubbing direction of the substrate. In FIG. 2A, the direction A is defined as the upward direction when the liquid crystal display device is viewed from the substrate normal direction. In FIG. 2A, the downward arrow is the rubbing direction of the front substrate, and the upward arrow is the rubbing direction of the rear substrate. As shown in the figure, rubbing is performed on the front substrate and the rear substrate so as to be anti-parallel.

  FIG. 2B shows an arrangement of the liquid crystal molecules 2m of the rubbed liquid crystal cell. In a vertically aligned liquid crystal cell, liquid crystal molecules are not completely aligned perpendicularly to the substrate when no voltage is applied due to an alignment treatment such as rubbing, but a slight angle (pretilt angle and It is tilted and arranged with an angle called. In FIG. 2B, it is inclined about 0.5 ° to the left (the direction corresponding to the upward direction in FIG. 2A) with respect to the normal direction of the substrate. When a voltage is applied to the liquid crystal cell, the liquid crystal molecules 2m fall in the left direction in FIG. 2B.

  In the vertical alignment mode, the polarizing plates 5a and 5b are arranged so as to have absorption axis directions of −45 ° and + 45 ° with respect to the upper direction in FIG. The liquid crystal display device is displayed in normally black.

The backlight 6 is constituted by, for example, an LED or a lamp capable of multicolor display. In the embodiment, a white LED light source is used. This LED light source may be driven in a field sequential manner, or may be a mixed color white by adjusting the arrangement of red, blue and green (RGB) LEDs.
(Comparison between the case with optical element 7 and the case without optical element 7)
For comparison, in FIG. 1, the viewing angle characteristics of the transmittance of the liquid crystal display device with and without the optical element 7 will be examined.

  FIG. 3 is a graph of the viewing angle characteristic of the transmittance of the liquid crystal display device when the liquid crystal cell 4 is multiplex driven. The positive direction of the horizontal axis corresponds to the downward direction in FIG. 2A when viewed from the normal direction of the substrate. The negative direction on the horizontal axis corresponds to the upward direction. In FIG. 3, the solid line indicates the transmittance when a selection voltage (voltage applied between the upper and lower electrodes when creating a display state in multiplex drive) is applied, and the broken line indicates a non-selection voltage (non-display state in multiplex drive). This is the voltage applied between the upper and lower electrodes when it is desired to create a transmittance). The ratio of these two transmittances is the contrast ratio.

  In FIG. 3, when viewing the right side, that is, the downward direction of the liquid crystal cell 4, the transmittance when the selection voltage is applied is higher than the normal direction, and a display with a large contrast ratio can be obtained. On the other hand, when viewing the left side of FIG. 3, that is, the upper direction of the liquid crystal cell 4, the transmittance at the time of applying the selection voltage is lower than the normal direction of the substrate in the vicinity of 0 to −20 °. It is almost the same as the transmittance when a non-selection voltage is applied.

  Thus, in view of the optical characteristics of the liquid crystal cell 4 alone, in the absence of the optical element 7, a display that is difficult to see can be visually recognized only by swinging the viewing angle by about 10 from the substrate normal direction to the upward direction (so-called display crushing). Happens). This is not preferable particularly when the liquid crystal display device is often viewed from the normal direction.

  The liquid crystal molecules 2m are tilted upward in the liquid crystal cell 4 when a selection voltage is applied by orientation control. However, the major axis of the liquid crystal molecules 2m is not completely parallel to the substrate and has an average inclination of several degrees to several tens of degrees with respect to the substrate plane. With this inclination, the viewing angle at which the most easily viewable display can be visually recognized (the best viewing angle, which is distinguished from the best viewing direction) is considered to deviate from the substrate normal direction. I want to make the best visual angle as close as possible to the normal direction of the substrate.

  Therefore, in the embodiment, by arranging the optical element 7 in front of the liquid crystal cell 4, the light passing through the liquid crystal cell 4 is refracted so that the best viewing angle is brought close to the normal direction and the viewing becomes difficult to view. Keep the azimuth away from the normal direction.

  With reference to FIG. 1 again, the optical element 7 will be described. The optical element 7 is a resin prism having a refractive index of 1.7 and having a thickness of 10 mm and having a right triangular prism shape. The prism apex angle having a narrower angle (in the embodiment, this is the prism apex angle) has the best viewing direction ( Here, they are arranged so as to face in the right direction in FIG. 1 and downward in FIG. 2A. The prism apex angle is 15 ° here. In FIG. 1, the upper surface of the prism (here, the surface parallel to the cosine with respect to the prism apex angle) is arranged to be parallel to the front substrate 1a. Even when the incident surface of the prism is parallel to the substrate surface, the prism apex angle is in the best viewing direction.

  FIG. 4 is a graph of the vertical viewing angle characteristic of the transmittance of the liquid crystal display device according to the first embodiment. The horizontal axis, vertical axis, solid line graph, and broken line graph are the same as those in FIG. The transmittance-viewing angle characteristics when the selection voltage is applied in FIGS. 4 and 3 are compared. According to the solid line graph of FIG. 4, the transmittance in the vicinity of the normal direction when the selection voltage is applied is higher than that of the solid line graph of FIG. Further, the amount of change in the transmittance with respect to the viewing angle is small (the curve is gentle), and in FIG. 3, the minimum value of the transmittance that causes the display crushing that was around 10 ° in the upward direction has moved to around 22 °. Yes. Thereby, when the display of a liquid crystal display device is observed from a normal line direction, it can be visually recognized as a display with a favorable viewing angle range.

  In FIG. 4, the maximum value of the transmittance when the selection voltage is applied is slightly lower than that in FIG. This is presumably because reflection or the like was caused because a prism was inserted as the optical element 7 and light was lost to some extent. As the refractive index of the prism increases, the thickness of the prism can be reduced. However, in consideration of this reflection, the refractive index cannot be increased so much. A reasonable refractive index of the prism is 1.5 to 1.9.

  In addition, when the vertical size of the display area of the liquid crystal cell 4 is increased, the thickness of the prism must be increased. However, when the thickness of the prism increases, the observer's focus shifts and the display becomes uncomfortable. As in the first embodiment, when the prism thickness is 10 mm and the prism apex angle is 15 °, the upper limit of the vertical size of the display area as the liquid crystal cell 4 will be about 40 mm.

  The optical element 7 will be further supplemented.

  FIG. 5 is a schematic view of another example of the optical element. The optical element 7 may be an assembly of minute prisms as shown in the drawing instead of being a single prism. However, it is preferable to appropriately select the shape and size of the prism in order to prevent display blurring. Specifically, it is preferable that right prismatic prismatic microprisms are arranged in parallel at a pitch of 100 μm to 500 μm. As in the case of using one prism as the optical element, the direction of the micro prism is adjusted so that the best viewing angle of the light emitted from the liquid crystal cell that has passed through the micro prism assembly approaches the normal direction of the substrate. The exit surface is preferably parallel to the substrate surface.

  Further, a diffraction grating or a hologram may be used as the optical element 7.

  6A and 6B are schematic cross-sectional views of other examples of the liquid crystal display device according to the first embodiment. As shown in FIG. 6A, the optical element 7 may be disposed on the front surface of the front polarizing plate 5a as a part of the cover 8 of the liquid crystal display device. At this time, it is preferable in terms of design to arrange the prism so that the emission surface of the prism is parallel to the surface of the front substrate 1a. 6B is a structural example in which an assembly of microprisms described in FIG. 6A and 6B, the direction d1 is the best viewing angle, and the direction d2 is the normal direction of the substrate.

  Even when the optical element 7 is arranged in front of the front polarizing plate 5a as in the liquid crystal display device shown in FIGS. 6A and 6B, the best viewing angle d1 can be obtained by refracting light emitted from the liquid crystal cell 4. Can be moved in the vicinity of the substrate normal direction d2, and the visibility near the substrate normal can be improved.

  Next, a liquid crystal display device according to a second embodiment will be described.

  FIG. 7 is a schematic view showing a liquid crystal display device according to the second embodiment. This embodiment is different from the first embodiment shown in FIG. 1 in that a viewing angle compensation plate 9 is disposed between the liquid crystal cell 4 and the rear polarizing plate 5b.

  Although the arrangement of the front polarizing plate 5a and the optical element 7 is also different, the optical element 7 and the front polarizing plate 5a can be arranged in this order from the liquid crystal cell 4 side as in the first embodiment.

  The liquid crystal cell 4 used in the second embodiment also has the same structure as the liquid crystal cell in the first embodiment, and is rubbed in the direction shown in FIGS. 2A and 2B.

  In the vertical alignment type liquid crystal cell 4 in the second embodiment, an alignment film is formed by using a vertical alignment film material SE-1211 manufactured by Nissan Chemical Industries, Ltd., and a rayon rubbing cloth is used in FIGS. 2A and 2B. The upper and lower substrates, which are rubbed in the indicated direction, are given a pretilt angle using a gap control material having a diameter of 3.9 μm, and the birefringence Δn is 0.2 and the dielectric anisotropy between both substrates. Was produced by injecting a liquid crystal material manufactured by Merck Co., Ltd. Therefore, the retardation of the liquid crystal layer 4a is 780 nm. Further, the pretilt angle of the liquid crystal cell 4 was measured and found to be 1 °.

  The optical element 7 is a prism with an apex angle of 15 ° formed of a resin having a refractive index of 1.7, which is the same as the optical element used in the first embodiment shown in FIG. The optical element (prism) 7 is arranged so that the upper surface thereof is parallel to the substrates 1 a and 1 b and the apex angle faces the best viewing direction of the liquid crystal cell 4.

  The compensation plate 9 is formed by laminating three C plates, and all the three C plates are arranged so that the optical axis is in the normal direction of the substrate. Each C plate has a retardation of 250 nm in the thickness direction. The front and rear polarizing plates 5a and 5b each have a structure in which a triacetylcellulose (TAC) film is bonded to a polarizing layer, and the retardation in the thickness direction of the TAC film is, for example, 60 nm. Therefore, it can be considered that the liquid crystal display device according to the second embodiment performs C plate compensation equivalent to 870 nm.

  With reference to FIG. 8, the relationship between the rubbing directions of the substrates 1a and 1b and the absorption axis directions of the polarizing plates 5a and 5b in the liquid crystal display device according to the second embodiment will be described.

  The rubbing direction of the back (lower) substrate 1b is the upward direction in FIG. 8, and that of the front (upper) substrate 1a is the downward direction. When a voltage is applied to the liquid crystal cell 4, the liquid crystal molecules fall down in the rubbing direction (upward in FIG. 8) of the back (lower) substrate 1b.

  The front polarizing plate 5a and the rear polarizing plate 5b are arranged in crossed Nicols. Further, the front polarizing plate 5a has an absorption axis that forms an angle of 45 ° with the rubbing direction of the back (lower) substrate 1b (the direction in which the liquid crystal molecules fall). It arrange | positions so that it may become a 45 degree azimuth | direction clockwise. For this reason, the absorption axis direction of the back polarizing plate 5b is 45 ° in the clockwise direction from the rubbing direction of the back (lower) substrate 1b.

  The effects of the liquid crystal display device according to the second embodiment will be described with reference to FIGS. 9A to 9F.

  9A and 9B are graphs showing viewing angle characteristics of the liquid crystal display device according to the first comparative example.

  The first comparative example is a liquid crystal in which the optical element 7 is removed from the liquid crystal display device according to the second embodiment, and the compensation plate 9 is formed by laminating three C plates each having a retardation in the thickness direction of 220 nm. It is a display device. In the first comparative example, it can be considered that C plate compensation of 780 nm is performed together with the retardation of the TAC film of the polarizing plates 5a and 5b. This is a value equal to the retardation of the liquid crystal layer.

  Refer to FIG. 9A. In this figure, the horizontal axis, the vertical axis, the curve by the solid line, and the curve by the broken line mean the same as those in FIG.

  As already described in the description of the first embodiment, in the first comparative example that does not include the optical element 7, the viewing angle is swung upward by about 10 ° from the normal direction of the substrate (the negative direction of the horizontal axis of the graph). Only the display collapses.

Refer to FIG. 9B. The horizontal axis of this figure is equal to the horizontal axis of FIG. 9A. The vertical axis indicates contrast. As described above, the contrast is a value obtained by dividing the transmittance (T _on ) when a selection voltage is applied by the transmittance (T _off ) when a non-selection voltage is applied.

  It can be seen that the highest contrast is realized when observed from almost the front (viewing angle 0 ° direction, substrate normal direction).

  9C and 9D are graphs showing viewing angle characteristics of the liquid crystal display device according to the second comparative example.

  The second comparative example has a configuration in which the optical element 7 is added to the first comparative example. That is, it differs from the second embodiment in the retardation value of C plate compensation.

  Reference is made to FIG. 9C. The meanings of the horizontal axis, the vertical axis, the curve by the solid line, and the curve by the broken line are the same as those in FIG. 9A.

  As is clear from the comparison with the graph of FIG. 9A, the addition of the optical element 7 realizes good display (display with high light transmittance) in a wide viewing angle range in the observation based on the front. Recognize.

  Reference is made to FIG. 9D. The meanings of the horizontal and vertical axes are the same as those in FIG. 9B.

  Since the emitted light is refracted by the optical element 7, the viewing angle direction with high contrast is shifted to the left side of the drawing as compared with the graph of FIG. 9B, and the contrast is lowered near the front.

  9E and 9F show the viewing angle characteristics of the liquid crystal display device according to the second embodiment.

  Reference is made to FIG. 9E. The meanings of the horizontal axis, the vertical axis, the solid line curve, and the broken line curve are the same as those in FIG. 9A.

  The curve drawn with a solid line in this figure almost coincides with that in FIG. 9C. For this reason, according to the liquid crystal display device according to the second embodiment, as in the second comparative example, in the observation based on the front surface, good display (display with high light transmittance) is possible in a wide viewing angle range. It can be seen that it will be realized.

  Reference is made to FIG. 9F. The meanings of the horizontal axis and the vertical axis are the same as those in FIG. 9B.

  Compared with the graph of FIG. 9D, the contrast near the front is high. From this, it can be seen that the liquid crystal display device according to the second embodiment can perform display observed from the vicinity of the front surface with high contrast.

  That is, the liquid crystal display device according to the second embodiment is a liquid crystal display device capable of realizing both high light transmittance and high contrast during near-front observation.

  Next, the inventor of the present application changes the retardation of the compensation plate 9 of the liquid crystal display device according to the second embodiment in various ways, and provides a retardation range that can achieve both high light transmittance and high contrast during near-front observation. Examined.

  FIG. 10A shows the viewing angle dependence of the contrast when the compensation plate 9 is composed of three C plates with a retardation of 230 nm and the C plate compensation equivalent to 810 nm is performed together with the retardation of the TAC films of the polarizing plates 5a and 5b. It is a graph to show.

  Further, FIG. 10B shows that the compensation plate 9 is composed of three C plates with a retardation of 270 nm, and the contrast depends on the viewing angle when C plate compensation equivalent to 930 nm is performed together with the retardation of the TAC films of the polarizing plates 5a and 5b. It is a graph which shows sex.

  The meanings of the horizontal and vertical axes in both graphs are the same as those in FIG. 9D.

  When the graphs of the viewing angle characteristics of the contrast shown in FIGS. 10A and 10B are compared with those in FIG. 9D, it is recognized that the contrast in the vicinity of the front is high. From this, it can be seen that even when the C plate compensation corresponding to 810 nm and 930 nm is performed, high contrast display at the time of near-front observation can be realized.

  In the range where the retardation of the liquid crystal display device excluding the retardation of the liquid crystal layer (780 nm) is less than 810 nm (≈780 nm × 1.038) and exceeds 930 nm (≈780 nm × 1.192), the retardation of the liquid crystal layer Since the difference between the two increases, the light transmittance of the base is increased, and the display quality will be degraded. From this, regarding the thickness direction (substrate normal direction) of the liquid crystal display device, if the retardation of the liquid crystal display device excluding the retardation of the liquid crystal layer is 1.038 times or more and 1.192 times or less of the retardation of the liquid crystal layer, It is considered that good display quality with high light transmittance and contrast at the time of near-front observation can be realized.

  In the second embodiment, the compensation plate 9 is composed of three C plates. However, the inventor of the present application can use other configurations, for example, three biaxial plates or a combination of C plates and biaxial films. It was confirmed that the same effect was produced. As an example, the case where the compensation plate 9 is composed of two C plates and one biaxial film will be described.

  11A and 11B are graphs showing the viewing angle dependence of contrast when the compensation plate 9 is composed of two C plates and one biaxial film. The meanings of the horizontal and vertical axes in both graphs are the same as those in FIG. 9D.

  FIG. 11A shows two compensators 9 of the second embodiment, two C plates having a retardation of 250 nm and one biaxial plate having a retardation of 50 nm in the in-plane direction and 250 nm in the thickness direction. The viewing angle dependency when the liquid crystal cells 4 are sequentially stacked is shown. In this example, together with the retardation of the TAC films of the front and back polarizing plates 5a and 5b, the retardation in the thickness direction of all the films of the liquid crystal display device is 870 nm. This is 1.115 times the retardation (780 nm) of the liquid crystal layer.

  The biaxial plate and the rear polarizing plate 5b were arranged so that the former optical axis in the in-plane direction and the latter absorption axis were orthogonal to each other.

  It can be seen that a curve approximated to the contrast curve shown in FIG. 9F (when the compensation plate 9 having the same retardation in the thickness direction is constituted by three C plates) is obtained. It can be seen that even if the compensation plate 9 is configured using a biaxial film, a high-contrast display during near-front observation can be realized.

  FIG. 11B shows, as the compensation plate 9, two C plates having a retardation of 220 nm and one biaxial plate having a retardation of 50 nm in the in-plane direction and 220 nm in the thickness direction in this order from the liquid crystal cell 4 side. The viewing angle dependency when laminated is shown. In this example, together with the retardation of the TAC films of the front and rear polarizing plates 5a and 5b, the retardation in the thickness direction of all the films of the liquid crystal display device is 780 nm. This is equal to the retardation of the liquid crystal layer.

  The biaxial plate and the rear polarizing plate 5b were arranged so that the former optical axis in the in-plane direction and the latter absorption axis were orthogonal to each other.

  It can be seen that a curve approximated to the contrast curve shown in FIG. 9D (when the compensation plate 9 having the same retardation in the thickness direction is constituted by three C plates) is obtained. Even if the compensation plate 9 is configured using a biaxial film, it is considered that the same viewing angle characteristic as that when the compensation plate 9 is configured only by the C plate is realized.

  From the results shown in FIGS. 11A and 11B, even when the compensation plate 9 is configured using a biaxial film, for example, the retardation in the thickness direction of the liquid crystal display device excluding the retardation of the liquid crystal layer is the retardation of the liquid crystal layer. When the ratio is 1.038 times or more and 1.192 times or less, it may be considered that good display quality can be realized.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. In the embodiment, the vertical alignment mode is described as the liquid crystal cell, but a TN type may be used. In the embodiment, the case of multiplex driving has been described in order to make the viewing angle characteristics remarkable, but static driving may also be used. Furthermore, the present invention can be applied not only to display in the normally black mode but also to display in the normally white mode.

  In the second embodiment, the viewing angle compensation plate 9 is disposed between the liquid crystal cell 4 and the rear polarizing plate 5b. However, the viewing angle compensation plate 9 is disposed between the liquid crystal cell 4 and the front polarizing plate 5a. May be. It can also be arranged on both sides.

  Furthermore, in the second embodiment, the viewing angle compensation plate 9 is composed of three sheets using a C plate or a biaxial film, but the number of sheets is not limited.

  In the second embodiment, another example of the optical element 7 described in the first embodiment can be used. That is, for example, as shown in FIG. 5, it is possible to use an optical element, a diffraction grating, a hologram, or the like in which a large number of right-angled triangular prisms are formed on a flat plate at a pitch of 100 μm to 500 μm. is there. By these elements, the component of the emitted light on the best viewing direction side of the liquid crystal display element is deflected to the normal direction side of the liquid crystal display element.

  Furthermore, also in the second embodiment, as shown in FIGS. 6A and 6B, when a transparent cover is provided on the front surface of the liquid crystal display device, a part of the cover can be formed in a prism shape. .

The birefringence Δn is determined by using the refractive index n ₁ in the thickness direction and the refractive index n ₂ in the in-plane direction,
Δn = n ₁ −n ₂
For example, the retardation of the liquid crystal layer 4a of the liquid crystal display device according to the second embodiment shown in FIG. 7 is positive, and the retardation of the TAC film of the compensation plate 9 and the polarizing plates 5a and 5b is negative.

  Thus, when the retardation is considered including positive and negative signs, for example, in this specification, “the retardation in the thickness direction of the liquid crystal display device excluding the retardation of the liquid crystal layer is 1.038 times or more the retardation of the liquid crystal layer 1 Is 192 times or less, “the retardation in the thickness direction of the liquid crystal display device excluding the retardation of the liquid crystal layer is opposite in polarity to the retardation of the liquid crystal layer, and the absolute value of the former is It means “when the absolute value is 1.038 times or more and 1.192 times or less of the absolute value”.

  It will be apparent to those skilled in the art that other various modifications, improvements, combinations, and the like can be made.

FIG. 1 is a schematic sectional view of a liquid crystal display device according to a first embodiment. 2A is a plan view showing the rubbing direction of the liquid crystal cell 4, and FIG. 2B is a schematic cross-sectional view taken along one-dot chain line A-A1 in FIG. 2A. FIG. 3 is a graph of the viewing angle characteristic of the transmittance of the liquid crystal display device when the liquid crystal cell 4 is multiplex driven. FIG. 4 is a graph of the vertical viewing angle characteristic of the transmittance of the liquid crystal display device according to the first embodiment. FIG. 5 is a schematic view of another example of the optical element. 6A and 6B are schematic cross-sectional views of other examples of the liquid crystal display device according to the first embodiment. FIG. 7 is a schematic view showing a liquid crystal display device according to the second embodiment. FIG. 8 is a diagram for explaining the relationship between the rubbing directions of the substrates 1a and 1b and the absorption axis directions of the polarizing plates 5a and 5b in the liquid crystal display device according to the second embodiment. 9A to 9F are diagrams for explaining the effect of the liquid crystal display device according to the second embodiment. FIG. 10A and FIG. 10B are graphs showing the viewing angle dependence of contrast when the compensation plate 9 is composed of three C plates of retardation 230 nm and 270 nm, respectively. 11A and 11B are graphs showing the viewing angle dependence of contrast when the compensation plate 9 is composed of two C plates and one biaxial film.

Explanation of symbols

1a, 1b (transparent) substrate 2 liquid crystal layer 2m liquid crystal molecule 3 sealing material 4 liquid crystal cell 4a liquid crystal layer 5a, 5b polarizing plate 6 light source 7 optical element 8 cover 9 compensator

Claims (12)

A pair of opposing substrates, and a liquid crystal cell including a liquid crystal layer sandwiched between the pair of opposing substrates;
A pair of polarizing plates disposed on the front and back of the liquid crystal cell;
An optical element disposed in front of the liquid crystal cell;
A light source disposed behind one of the pair of polarizing plates disposed behind the liquid crystal cell;
The liquid crystal display device in which the optical element refracts the component of the best viewing azimuth of the light emitted from the liquid crystal cell toward the pair of substrate normals.   The liquid crystal display device according to claim 1, wherein the liquid crystal cell is a vertical alignment type. Each of the pair of polarizing plates includes a film having retardation in the thickness direction,
The pair of polarizing plates is crossed Nicol, and the absorption axis direction of each of the pair of polarizing plates has an angle of 45 ° with the direction in which the liquid crystal molecules of the liquid crystal layer collapse when a voltage is applied to the liquid crystal layer. Arranged to make
Furthermore,
Arranged between at least one of the liquid crystal cell and the polarizing plate disposed on the front surface of the liquid crystal cell, and between the liquid crystal cell and the polarizing plate disposed on the back surface of the liquid crystal cell. Including a viewing angle compensator having retardation in the thickness direction,
The sum of retardation in the thickness direction of the viewing angle compensator and the pair of polarizing plates is opposite in polarity to the retardation of the liquid crystal layer, and the absolute value is 1.038 to 1.192 times. The liquid crystal display device according to claim 2.   The liquid crystal display device according to claim 3, wherein the viewing angle compensation plate includes a C plate or a biaxial plate.   The liquid crystal display device according to claim 1, wherein the optical element is a prism.   The liquid crystal display device according to claim 1, wherein the optical element is a prism assembly in which minute prisms are arranged in parallel.   The liquid crystal display device according to claim 1, wherein an emission surface of the optical element is parallel to the pair of substrate surfaces.   The liquid crystal display device according to claim 1, wherein the optical element is disposed between the liquid crystal cell and the pair of polarizing plates disposed on the front surface.   The liquid crystal display device according to claim 1, wherein the optical element is disposed in front of the pair of polarizing plates disposed on the front surface.   The liquid crystal display device according to claim 9, wherein the optical element is disposed in front of the pair of polarizing plates disposed in front of the liquid crystal cell, and also serves as a cover. The liquid crystal display device according to claim 1, wherein the liquid crystal cell is a twisted nematic type.   The liquid crystal display device according to claim 1, wherein the liquid crystal cell is multiplex driven.

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