JP2011028008A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily improve the use efficiency of light emitted from a light source in a liquid crystal display device having a light guide plate type backlight. <P>SOLUTION: In the liquid crystal display device, light emitted from a plurality of light sources is converted to surface light by a light guide plate, and the surface light is radiated to a liquid crystal panel. With respect to the light guide plate, a reflective polarizing plate which transmits p-polarized light and reflects s-polarized light, and a spacer made of transparent resin, and a first reflecting plate which reflects the p-polarized light are laminated in this order between a potion which takes in the light, out of a first principal surface facing the liquid crystal display panel and a region from which the surface light is emitted, and a quarter-wave plate and a second reflecting plate are laminated in this order in only a region on which the s-polarized light impinges, out of a second principal surface opposite to the first principal surface, and the p-polarized light included in the light is propagated in the light guide plate as it is, and the s-polarized light included in the light is converted to p-polarized light using the quarter-wave plate and the second reflecting plate and is propagated in the light guide plate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technique effective when applied to a liquid crystal display device having a backlight unit of a light guide plate type (sometimes called an edge light type or a side light type).

  Conventionally, a liquid crystal display device having a light guide plate type backlight unit is used for a liquid crystal display of a portable information device such as a mobile phone terminal.

  In recent years, portable information devices tend to handle larger amounts of image information and moving images with a larger number of frames, for example, as the communication speed increases and the built-in memory capacity increases. As a result, medium- and small-sized liquid crystal display devices used as liquid crystal displays for portable information devices tend to have higher image quality and larger screens, and the number of pixels tends to increase. Of these, the number of pixels is increasing from the conventional QVGA (Quarter Video Gate Array) of 240 × 320 × 3 pixels to the VGA (Video Gate Array) of 480 × 620 × 3 pixels.

  In addition, for a small and medium-sized liquid crystal display device used as a liquid crystal display of a portable information device, for example, an increase in battery driving time and an improvement in brightness to improve outdoor visibility are required. An increase in the number of pixels in these liquid crystal display devices generally leads to a decrease in aperture ratio, and in particular, in a VGA type liquid crystal display device, it is difficult to increase battery driving time and improve brightness. Therefore, in recent liquid crystal display devices, improvement of the utilization efficiency of light from the backlight has been reconsidered.

  The configuration and display principle of the liquid crystal display device are summarized as follows. The liquid crystal display device mainly includes a liquid crystal display panel and a backlight disposed behind the liquid crystal display panel. At this time, the liquid crystal display panel includes a pair of substrates, a liquid crystal layer sandwiched between the pair of substrates, and a pair of polarizing plates disposed with the liquid crystal layer interposed therebetween. At this time, the pair of polarizing plates is usually arranged so as to sandwich the pair of substrates and the liquid crystal layer. In addition, the display area of the liquid crystal display panel includes a large number of pixels as described above, and each pixel includes a pixel electrode, a common electrode, and a liquid crystal layer.

  Each pixel of the liquid crystal display panel performs dark display by blocking light from the backlight, and performs bright display by transmitting light. In many cases, the pair of polarizing plates are arranged so that the absorption axes are orthogonal to each other. When the absorption axes of the pair of polarizing plates are orthogonal, the light passing through the liquid crystal layer is observed by an observer (user) unless the polarization state of the light passing through the backlight side polarizing plate is changed by the liquid crystal layer. It is completely absorbed by the polarizing plate on the side and dark display is obtained. In addition, when the absorption axes of the pair of polarizing plates are orthogonal, if the polarization state of the light passing through the backlight-side polarizing plate is changed by the liquid crystal layer, the light passing through the liquid crystal layer is The light is transmitted through the polarizing plate on the side and a bright display is obtained.

  However, since the light from the backlight in the conventional liquid crystal display device is partially polarized light that is close to natural light, usually about 60% of the light is absorbed by the polarizing plate on the backlight side. This is one of the main factors that reduce the light use efficiency from the backlight.

  In order to reduce absorption of light from the backlight by the polarizing plate, for example, a reflective polarizing plate is used in the conventional liquid crystal display device. The reflective polarizing plate is disposed, for example, between the polarizing plate on the backlight side and the backlight, and reflects the component absorbed by the polarizing plate in the light from the backlight to the backlight side. The light reflected by the reflective polarizing plate is reflected by the light guide plate of the backlight, the prism sheet, etc., and is incident on the reflective polarizing plate again. In this process, if a transmissive component is generated again in the light incident on the reflective polarizing plate, the transmissive component can pass through the reflective polarizing plate and be used for display. If all of the light reflected by the reflective polarizing plate is incident again on the reflective polarizing plate and the percentage of the transmitted component in the incident light is 100%, the light from the backlight is used. Efficiency should increase by a factor of about two. However, in the liquid crystal display device having the above configuration, the use efficiency of light due to the use of the reflective polarizing plate is about 1.3 times.

  Further, in recent light guide plate type backlights, for example, a reflection type polarizing plate is disposed in the vicinity of the light source in order to further improve the light utilization efficiency (see, for example, Patent Document 1).

  Patent Document 1 and other documents referred to in this specification are as follows.

JP 2003-007114 A

Y. Fujimura et al., “SID 91 Digest of Technical Papers”, pages 739-742. M. Born, E. Wolff, "Principles of Optics 3" Japan Society of Applied Physics, “Crystal optics”, Morikita Publishing By Tatsuta Tatsuo, "Applied Optics II", Baifukan

  When converting the light reflected by the reflective polarizing plate into light that passes through the reflective polarizing plate, the conversion efficiency can be increased by changing the polarization state that occurs when the light is reflected or refracted at the interface of the light guide plate. Instead of asking, you should use a polarization converter. At this time, the light reflected by the reflective polarizing plate should be guided along a preset optical path and reflected in the direction of the reflective polarizing plate with high efficiency.

  However, the light guide plate has a function of expanding the light emitted from the light source arranged at the end thereof into a planar shape, making the intensity distribution uniform in the plane, and guiding this to the liquid crystal layer side. For this reason, it is difficult to add a function of reflecting the light reflected by the reflective polarizing plate to the liquid crystal layer side to a normal light guide plate.

  In order to avoid such a problem, in the liquid crystal display device of Patent Document 1, a reflective plate and a quarter-wave plate are disposed in the same layer as the light source, and a reflective polarizing plate is provided between the light guide plate and the light source. It is arranged. Also, at this time, the reflection plate and the reflection type polarizing plate are not brought into close contact with each other, and the light reflected by the reflection type polarizing plate is incident on the reflection plate and the quarter wavelength plate by arranging them at a distance. Increasing.

  By the way, in a small-sized liquid crystal display device, a light source used for a light guide plate type backlight is generally a light emitting diode (LED) that can be driven at a low voltage and is small. . The shape of the light emitting diode is generally a cubic shape, and the light emitting surface is one surface of the cube, but the light emission distribution is not isotropic and is particularly strong in the normal direction of the light emitting surface, and as the distance from the normal direction increases. It quickly weakens.

  Even in the liquid crystal display device of Patent Document 1, a light emitting diode is used as a light source, but the planar distribution of the reflector and the reflective polarizing plate is not specified. If both the reflective plate and the reflective polarizing plate are arranged parallel to the four sides of the light guide plate, the strongest light emitting component of the light-emitting diode is reflected by the reflective polarizing plate, and then the reflective plate and the quarter-wave plate. Instead of going to the light-emitting diode, it goes to the light-emitting diode. Since the light emitting diode itself has no function of reflecting light or converting the polarization state, the light incident on the light emitting diode cannot be reused. For this reason, the liquid crystal display device configured as described in Patent Document 1 has a problem that the strongest light emitting component of the light emitted from the light source (light emitting diode) cannot be reused.

  Further, since a small and light liquid crystal display device used as a liquid crystal display of a portable electronic device is required to be thin and light, for example, it is not uncommon for the thickness of the light guide plate to be 1 mm or less. It is difficult to dispose a reflection-type polarizing plate, a quarter-wave plate, a reflection plate, and the like on the cross section (side surface) of such an extremely thin light guide plate. Further, since the light guide plate must be divided into two parts with the reflective polarizing plate as a boundary and assembled, the manufacturing process becomes complicated.

  As described above, in the liquid crystal display device having the conventional light guide plate type backlight, it is difficult to improve the utilization efficiency of light emitted from the light source.

  An object of the present invention is to provide a technique capable of easily improving the utilization efficiency of light emitted from a light source in a liquid crystal display device having a light guide plate type backlight.

  Another object of the present invention is to provide a technique capable of simplifying the structure and manufacturing process of a light guide plate capable of enhancing the utilization efficiency of light emitted from a light source.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  The outline of typical inventions among the inventions disclosed in the present application will be described as follows.

  In a liquid crystal display device that includes a liquid crystal display panel, a light guide plate, and a plurality of light sources, and converts the light source light emitted from the plurality of light sources into a planar light beam in the light guide plate and irradiates the liquid crystal display panel. In the liquid crystal display panel, the light incident surface of the planar light beam is substantially rectangular, and the light guide plate includes a first main surface facing the light incident surface of the liquid crystal display panel and a second main surface opposite to the first main surface. The main surface has a substantially rectangular shape, and has a surface light emitting portion that overlaps the display area of the liquid crystal display panel, and a coupling portion that guides the light source light to the surface light emitting portion, and the coupling portion is more than the surface light emitting portion. The boundary between the coupling portion and the surface light emitting portion is thick and continuously changes in thickness due to a step provided on the first main surface side. It faces the level difference of the light guide plate and has the strongest light source light intensity. The propagation direction of the main component is arranged along the coupling portion of the light guide plate in a direction substantially parallel to any one of the four sides of the light incident surface of the liquid crystal display panel, and the first main portion of the light guide plate A reflective polarizing plate that transmits P-polarized light included in the light source light and reflects S-polarized light, a spacer made of a transparent resin, and the P-polarized light are reflected on a portion of the surface where the step is provided. The first reflecting plate is laminated in this order, and on the portion of the second main surface of the light guide plate on which the S-polarized light is incident, a quarter-wave plate, The second reflecting plate is laminated in this order, and the coupling portion of the light guide plate guides the P-polarized light contained in the light source light to the surface light emitting portion while maintaining the P-polarized light, and S contained in the light source light. Polarized light is converted into P-polarized light by using the quarter-wave plate and the second reflecting plate, and the surface light emitting unit. The liquid crystal display device lead.

  According to the liquid crystal display device of the present invention, the utilization efficiency of the light emitted from the light source can be easily improved.

  In addition, according to the liquid crystal display device of the present invention, it is possible to simplify the configuration and manufacturing process of the light guide plate that can increase the utilization efficiency of the light emitted from the light source.

3 is a schematic plan view illustrating an example of a schematic configuration of a main part of the liquid crystal display device of Example 1. FIG. FIG. 2 is a schematic side cross-sectional view illustrating an example of the configuration of the liquid crystal display device when viewed in the −x direction from the line A-A ′ in FIG. 1. It is a schematic sectional side view which shows the optical path until the light which the light source emitted is guide | induced to the surface light emission part of a light-guide plate. It is a schematic cross section for demonstrating an example of the effect of making the level | step-difference part of a light-guide plate into a curved surface shape. It is a schematic cross section for demonstrating an example of the conditions of the angle of the side surface of a light-guide plate, and the shape of a level | step difference part. It is a schematic plan view which shows an example of the plane structure of the pixel of a liquid crystal display panel. It is a schematic cross section which shows an example of the cross-sectional structure in the B-B 'line | wire of FIG. It is a schematic cross section which shows an example of the cross-sectional structure in the C-C 'line of FIG. It is a typical sectional side view for demonstrating the relationship between the vibration direction of the light which injects into a quarter wavelength plate, and a slow axis azimuth. It is a schematic diagram which shows the relationship between the slow axis azimuth in the light-incidence surface of a quarter wave plate, and the incident angle dependence of the slow axis azimuth in an incident angle direction. It is a schematic diagram which shows the definition of the slow axis azimuth in an incident-light surface. It is a schematic diagram which shows the relationship between the retardation of the normal line direction of a quarter wave plate, and the incident angle dependence of the retardation in an incident angle direction. Schematic diagram showing the relationship between the incident angle and the slow axis azimuth angle in the light incident surface when the Nz coefficient of the quarter-wave plate is 1 and the slow axis azimuth angle in the incident angle direction is 45 degrees FIG. Shows the relationship between the slow axis azimuth in the incident surface where the slow axis azimuth in the incident angle direction is 45 degrees and the normal direction retardation where the retardation in the incident angle direction is a quarter wavelength. It is a schematic diagram. 6 is a schematic diagram illustrating an example of a method for forming a light guide plate used in the liquid crystal display device of Example 1. FIG. 3 is a schematic plan view illustrating an example of a relationship between an optical path of light source light and a portion having anisotropy of a light guide plate in the liquid crystal display device of Example 1. FIG. It is a schematic diagram which shows an example of schematic structure of the metal mold | die used with the formation method of the light-guide plate of Example 2 by this invention. It is a schematic diagram which shows an example of the relationship between the optical path of the light source light in the light guide plate of Example 2, and the part which has the anisotropy of a light guide plate. It is a schematic diagram for demonstrating an example of the preparation procedure of the light-guide plate of Example 3 by this invention. It is a schematic diagram which shows the relationship between the Nz coefficient of a quarter wavelength plate, and the incident angle dependence of the slow axis azimuth in an incident angle direction. Schematic diagram showing the relationship between the slow axis azimuth angle in the light incident surface when the Nz coefficient of the quarter-wave plate is 0.50 and the incident angle dependence of the slow axis azimuth angle in the incident angle direction. It is. It is a schematic diagram which shows the relationship between the retardation of the normal line direction of a quarter wave plate, and the incident angle dependence of the retardation in an incident angle direction. When the Nz coefficient of the quarter-wave plate is set to 0.50, the slow axis azimuth θ in the incident angle direction becomes 45 degrees, and the relationship between the incident angle and the slow axis azimuth in the light incident surface is shown. It is a schematic diagram. Shows the relationship between the slow axis azimuth in the incident surface where the slow axis azimuth in the incident angle direction is 45 degrees and the normal direction retardation where the retardation in the incident angle direction is a quarter wavelength. It is a schematic diagram. It is a schematic diagram which shows the relationship between the slow axis azimuth | direction angle with respect to the light which injected into the quarter wavelength plate, and the light transmittance in the 1st polarizing plate. FIG. 10 is a schematic side cross-sectional view showing an example of a schematic configuration around a coupling portion of a light guide plate in a liquid crystal display device of Example 5 according to the present invention. It is a schematic diagram which shows the relationship between a Stokes parameter, a Poincare sphere, and a polarization state. It is a schematic diagram which shows an example of the change of the polarization state of the linearly polarized light with a wavelength of 550 nm by Poincare sphere display. It is a schematic diagram which shows an example of the change of the polarization state of the linearly polarized light whose wavelength by Poincare sphere display is longer than 550 nm. It is a schematic diagram which shows an example of the change of the polarization state of the linearly polarized light whose wavelength by Poincare sphere display is shorter than 550 nm. It is the schematic diagram which showed in a plane an example of the change of the polarization state of the linearly polarized light with a wavelength of 550 nm by Poincare sphere display. It is the schematic diagram which showed another example of the change of the polarization state of the linearly polarized light with a wavelength of 550 nm by Poincare sphere display in a plane. It is a schematic diagram which shows the relationship between the Nz coefficient of a half-wave plate, and the incident angle dependence of the slow axis azimuth of an incident angle direction. It is a schematic diagram which shows the relationship between the Nz coefficient of a quarter wavelength plate, and the incident angle dependence of the slow axis azimuth of an incident angle direction. It is a schematic diagram showing the relationship between the slow axis azimuth angle in the light incident surface when the Nz coefficient of the half-wave plate is 0.25, and the incident angle dependence of the slow axis azimuth angle in the incident angle direction. . It is a schematic diagram which shows the relationship between the retardation of the normal line direction of a half-wave plate, and the incident angle dependence of the retardation of an incident angle direction. It is a schematic diagram showing the relationship between the incident angle and the slow axis azimuth angle in the light incident surface where the slow axis azimuth angle in the incident angle direction of the half-wave plate is 15 degrees. The slow axis azimuth angle of the incident angle direction of the half-wave plate is 15 degrees, and the slow axis azimuth angle in the light incident surface is normal and the retardation of the incident angle direction is a half wavelength. It is a schematic diagram which shows the relationship with retardation. It is a schematic diagram showing the relationship between the slow axis azimuth angle in the light incident surface when the Nz coefficient of the quarter wave plate is 0.80 and the incident angle dependence of the slow axis azimuth angle in the incident angle direction. is there. It is a schematic diagram which shows the relationship between the retardation of the normal line direction of a quarter wave plate, and the incident angle dependence of the retardation of an incident angle direction. It is a schematic diagram showing the relationship between the incident angle and the slow axis azimuth angle in the light incident surface where the slow axis azimuth angle in the incident angle direction of the quarter-wave plate is 75 degrees. The slow axis azimuth in the incident surface of the quarter-wave plate where the incident angle direction is 75 degrees and the normal axis where the retardation in the incident angle direction is a quarter wavelength. It is a schematic diagram which shows the relationship with the retardation of a direction. It is a schematic plan view which shows the 1st structural example of the principal part of the liquid crystal display device of Example 6 by this invention. FIG. 44 is a schematic plan view illustrating an application example of the liquid crystal display device illustrated in FIG. 43. 10 is a schematic plan view illustrating a second configuration example of a main part of a liquid crystal display device according to Example 6. FIG.

Hereinafter, the present invention will be described in detail together with embodiments (examples) with reference to the drawings.
In all the drawings for explaining the embodiments, parts having the same function are given the same reference numerals and their repeated explanation is omitted.

  In Example 1, first, an example and a principle of the schematic configuration of the liquid crystal display device of the present invention will be briefly described, and then each component will be specifically described.

1 to 5 are schematic views for explaining an example and a principle of a schematic configuration of a liquid crystal display device according to Embodiment 1 of the present invention.
FIG. 1 is a schematic plan view illustrating an example of a schematic configuration of a main part of the liquid crystal display device according to the first embodiment. FIG. 2 is a schematic side sectional view showing an example of the configuration of the liquid crystal display device when viewed in the −x direction from the line AA ′ in FIG. 1. FIG. 3 is a schematic side sectional view showing an optical path until light emitted from the light source is guided to the surface light emitting portion of the light guide plate. FIG. 4 is a schematic cross-sectional view for explaining an example of the effect of making the stepped portion of the light guide plate curved. FIG. 5 is a schematic cross-sectional view for explaining an example of conditions of the angle of the side surface of the light guide plate and the shape of the stepped portion.

  The liquid crystal display device according to the first embodiment has a light guide plate type (sometimes referred to as an edge light type) backlight. For example, as shown in FIGS. 1 and 2, the liquid crystal display panel 1 and the light guide plate 2. , A plurality of light sources 3, a first prism sheet 4, and a second prism sheet 5. In FIG. 1, the liquid crystal display panel 1, the light guide plate 2, the first prism sheet 4, and the second prism sheet 5 are shown shifted in the xy plane. The light guide plate 2, the first prism sheet 4, and the second prism sheet 5 in the actual liquid crystal display device are laminated so that the area AR 2, the area AR 4, and the area AR 5 overlap the display area AR 1 of the liquid crystal display panel 1, respectively. Is done.

  In addition, the liquid crystal display device according to the first embodiment includes, for example, an IC chip 6 for driving the liquid crystal display panel 1, a flexible wiring board 7, and an inclined base 8 for mounting the light source 3 on the flexible wiring board 7. Have.

  The liquid crystal display panel 1 is, for example, an active matrix transmission TFT liquid crystal display panel, and includes a TFT substrate 9, a counter substrate 10, a liquid crystal layer 11, a first polarizing plate 12, a second polarizing plate 13, and the like. . At this time, in the liquid crystal display panel 1, the planar shape of the surface facing the light guide plate 2 (the outer shape viewed from the z direction in FIG. 1) is approximately rectangular. Detailed description regarding the configuration of the liquid crystal display panel 1 will be described later.

  The light guide plate 2 is an optical component that converts light emitted from the light source 3 (hereinafter referred to as light source light) into a planar light beam and irradiates the liquid crystal display panel 1. At this time, the light guide plate 2 has a substantially rectangular planar shape (the outer shape viewed from the z direction in FIG. 1) of the first main surface 2a opposed to the liquid crystal display panel 1. At this time, the light guide plate 2 and the liquid crystal display panel 1 are laminated so that the relationship between the longitudinal direction and the lateral direction is the same. At this time, the plurality of light sources 3 are arranged such that the light-emitting surface of the light source light faces the side surface 2 b in the short direction of the light guide plate 2.

  The light guide plate 2 is classified into a coupling portion and a surface light emitting portion according to the function with respect to the light source light. The coupling portion is a portion that takes in the light source light, and the surface light emitting portion is a portion that emits the taken light source light toward the liquid crystal display panel 1. The light guide plate 2 emits the incorporated light source light mainly toward the liquid crystal display panel 1 from the area AR2. That is, the surface light emitting part is the area AR2 and its peripheral part in the light guide plate 2, and the coupling part is a part located between the light source 3 and the surface light emitting part in the light guide plate 2.

  In addition, the light guide plate 2 is configured such that the thickness of the surface light emitting portion is substantially uniform, and the coupling portion is thicker than the surface light emitting portion. Further, at this time, the coupling portion makes the second main surface 2c opposite to the first main surface 2a a substantially flat surface, and provides a curved step on the first main surface 2a. It is thicker than. As will be described later, the first prism sheet 4 and the second prism sheet 5 disposed between the liquid crystal display panel 1 and the light guide plate 2 are disposed between the surface light emitting portion of the light guide plate 2 and the liquid crystal display panel 1. It only has to be arranged. Therefore, by providing a step on the first main surface 2a facing the liquid crystal display panel 1 and making the coupling part thicker than the surface light emitting part, the coupling efficiency (incorporation efficiency) of the light source light is improved, and the liquid crystal display device Both reduction in thickness can be achieved.

  In addition, the light guide plate 2 is inclined in a direction in which an angle α formed by the side surface 2b that takes in the light from the light source and the second main surface 2c opposite to the first main surface 2a becomes an obtuse angle.

  In the light guide plate 2, the reflective polarizing plate 14, the transparent spacer 15, and the first reflective plate 16 are laminated in this order on the step portion of the first main surface 2a. In the light guide plate 2, a quarter-wave plate 17 and a second reflector 18 are laminated in this order at the boundary between the coupling portion of the second main surface 2c and the surface light emitting portion. Furthermore, the light guide plate 2 is provided with a large number of hollow prism-shaped protrusions 2d having an inclined surface on the light source side as a light extraction structure on the surface light emitting portion of the second main surface 2c. Detailed description regarding these configurations will be described later.

  The light source 3 is, for example, a white light emitting element such as a white LED. At this time, if the light exit surface 3a of the light source 3 is a flat surface, the light exit surface 3a can be brought into close contact with the side surface 2b of the light guide plate 2. For example, the light source light emitted from the light exit surface 3a is applied to the light guide plate 2. It is possible to prevent a decrease in the amount of light in the incident process. That is, in FIG. 2 and FIG. 3, the light exit surface 3a of the light source 3 and the side surface 2b of the light guide plate 2 are separated from each other. Further, instead of bringing the light exit surface 3a and the side surface 2b into close contact, for example, the light source 3 is arranged so that the light exit surface 3a and the side surface 2b are parallel, and a transparent spacer is provided between the light exit surface 3a and the side surface 2b. It may be interposed.

  The first prism sheet 4 and the second prism sheet 5 are optical components that adjust, for example, the incident angle to the liquid crystal display panel 1 and the surface brightness with respect to the light emitted from the surface light emitting unit. . Detailed description regarding the configuration of the first prism sheet 4 and the second prism sheet 5 will be described later.

  When the light source 3 in the liquid crystal display device of Example 1 is a white LED, the light source light emitted from the light exit surface 3a has anisotropy (angle dependency) in its intensity distribution, and the normal line of the light exit surface 3a. The strength of the direction becomes the strongest, and the strength sharply decreases as the inclination from the normal direction increases. Therefore, the principle of the liquid crystal display device according to the first embodiment will be described below by paying attention to the strongest component of the light source light, that is, the component emitted in the normal direction of the light exit surface 3a (hereinafter referred to as the main component of the light source light). Will be described.

  In the liquid crystal display device of Example 1, the main component of the light source light emitted from the light exit surface 3a proceeds in the normal direction of the side surface 2b of the light guide plate 2 as shown in FIG. The light enters the reflective polarizing plate 14 provided on the first main surface 2a. When the light source 3 is a white LED, the light source light is natural light or partially polarized light close to natural light. For this reason, P-polarized light and S-polarized light are present as main components of the light source light incident on the first main surface 2a (the reflective polarizing plate 14). The P-polarized light is linearly polarized light having a vibration direction in a plane formed by the incident direction of the light source light and the normal direction of the interface when the light source light enters the interface such as the first main surface 2a. S-polarized light is linearly polarized light whose vibration direction is perpendicular to P-polarized light.

  The reflective polarizing plate 14 has a function of transmitting linearly polarized light having a predetermined vibration direction and reflecting linearly polarized light having a vibration direction orthogonal to the vibration direction. In the liquid crystal display device of Example 1, this reflective polarizing plate 14 is arranged so that P-polarized light is transmitted and S-polarized light is reflected. The light passing through the reflective polarizing plate 14 is usually partially polarized light mainly composed of P-polarized light, and includes light having a component having a vibration direction different from that of P-polarized light. Similarly, the light reflected from the reflective polarizing plate 14 is usually partially polarized light mainly composed of S-polarized light, and includes light having a component having a vibration direction different from that of S-polarized light. However, optically, such partial polarized light is often simply referred to as polarized light. In this specification, partial polarized light mainly composed of P-polarized light and partially polarized light mainly composed of S-polarized light , P-polarized light and S-polarized light.

  S-polarized light reflected by the reflective polarizing plate 14 is converted into P-polarized light using the quarter-wave plate 17 and the second reflecting plate 18 provided on the second main surface 2c of the light guide plate 2. The S-polarized light incident on the quarter-wave plate 17 is converted into clockwise circularly-polarized light in the process of passing through the quarter-wave plate 17 and reflected by the second reflector 18. Further, the clockwise circularly polarized light reflected by the second reflecting plate 18 and incident on the quarter-wave plate 17 is converted into linearly polarized light in the process of passing through the quarter-wave plate 17, and the light guide plate Return to 2. At this time, the vibration direction of the linearly polarized light that has returned to the light guide plate 2 is rotated by 90 degrees with respect to the vibration direction of the S-polarized light reflected by the reflective polarizing plate 14, and thus becomes P-polarized light.

  On the other hand, the P-polarized light that has passed through the reflective polarizing plate 14 passes through the transparent spacer 15 and is reflected by the first reflecting plate 16, then passes again through the transparent spacer 15 and returns to the light guide plate 2. Incident on the surface 2c. At this time, if there is a quarter-wave plate 17 and a second reflector 18 in a portion of the second main surface 2c where the P-polarized light that has passed through the reflective polarizing plate 14 is incident, the P-polarized light is S It will be converted to polarized light. Therefore, the quarter-wave plate 17 and the second reflecting plate 18 are not provided in the portion where the P-polarized light having passed through the reflective polarizing plate 14 is incident, and the incident P-polarized light is totally reflected by the second main surface 2c. Let

  Further, although detailed explanation is omitted, the S-polarized light reflected from the reflective polarizing plate 14 is also the quarter-wave plate 17 and the second wavelength for the component emitted in a direction different from the normal direction of the light exit surface 3a. The light is converted to P-polarized light using the reflector 18 and then guided to the surface light emitting unit, and the P-polarized light that has passed through the reflective polarizing plate 14 is guided to the surface light emitting unit while remaining as P-polarized light.

  As described above, in the liquid crystal display device according to the first embodiment, the P-polarized light included in the light source light is guided to the surface light-emitting unit as P-polarized light, and the S-polarized light is converted to P-polarized light and guided to the surface light-emitting unit.

Moreover, the light source light emitted from the light source 3 is light that spreads radially around the normal direction of the light exit surface 3a. At this time, if the step provided on the first main surface 2a is a curved surface that is concave when viewed from the light source 3, the optical path OP2 of the main component exiting in the normal direction of the light exit surface 3a, the normal direction. The optical path OP2 _{u of the} component emitted upward and the optical path OP2 _d of the component emitted downward from the normal direction are as shown in FIG. Note that the optical path OP2, the optical path OP2 _u , and the optical path OP2 _d shown in FIG. 5 are optical paths of components that are converted from S-polarized light to P-polarized light and are guided to the surface light emitting unit among the light emitted in the respective directions. Show.

  As can be seen from FIG. 4, when the step provided on the first main surface 2a (that is, the interface between the first main surface 2a and the reflective polarizing plate 14) is curved as viewed from the light source, The S-polarized light reflected by the reflective polarizing plate 14 is converged in the process toward the quarter-wave plate 17, and the spread of the region where the S-polarized light is incident on the second main surface 2c can be suppressed. Therefore, the installation area of the quarter-wave plate 17 and the second reflector 18 can be reduced. For example, P-polarized light that has passed through the reflective polarizing plate 14 is incident on the quarter-wave plate 17. It becomes easy to prevent conversion to S-polarized light.

  As shown in FIGS. 3 and 4, if the reflecting surface of the first reflecting plate 16 is also a curved surface that is concave when viewed from the light source 3, the P-polarized light that has passed through the reflective polarizing plate 14 is After being reflected by the first reflecting plate 16, it converges in the process toward the second main surface 2 c of the light guide plate 2, and the spread of the region where the P-polarized light is incident on the second main surface 2 c can be suppressed. Therefore, it becomes easier to prevent the P-polarized light that has passed through the reflective polarizing plate 14 from entering the quarter-wave plate 17 and being converted to S-polarized light.

  Further, when the step provided on the first main surface 2a is a curved surface that is concave when viewed from the light source, by adjusting the curvature, for example, the incidence of S-polarized light that is incident on the quarter-wave plate 17 The range of angles can be narrowed. As will be described later, the quarter-wave plate 17 has an angular dependency on the slow axis azimuth and retardation, and an angular range that functions as a quarter-wave plate is limited. For this reason, the step provided on the first main surface 2a has a curved surface that is concave when viewed from the light source, and the spread of the incident angle of the S-polarized light incident on the quarter-wave plate 17 is suppressed, so that many incident components are obtained. Can be converted from S-polarized light to P-polarized light. Further, by suppressing the spread of the incident angle of the S-polarized light incident on the quarter-wave plate 17, the spread of the P-polarized light converted by the quarter-wave plate 17 and the second reflecting plate can be suppressed. .

By the way, the P-polarized light guided to the surface light emitting part is propagated in the longitudinal direction (y direction) of the light guide plate 2 while being totally reflected by the first main surface 2a and the second main surface 2c, and is emitted from the area AR2. At this time, for example, as shown in FIG. 5, the side surface 2b of the light guide plate 2 is inclined by φ ₁ degree with respect to the normal direction of the second main surface 2c, and the light exit surface 3a of the light source 3 is If it is parallel to the side surface 2 b, the traveling direction of the main component of the light source light incident from the side surface 2 b of the light guide plate 2 and traveling toward the reflective polarizing plate 14 is φ with respect to the second main surface 2 c of the light guide plate 2. Tilt only ₁ degree. Also, at this time, if the direction of the tangent at the position where the main component of the light source light is incident on the reflective polarizing plate 14 is inclined by φ ₂ degrees with respect to the second main surface 2c, the main component is The incident angle ψ _M when the included S-polarized light is incident on the quarter-wave plate 17 is {90− (φ ₁ + 2φ ₂ )} degrees. At this time, when the P-polarized light converted by the quarter-wave plate 17 and the second reflector 18 returns from the second main surface 2c to the light guide plate 2, the emission angle becomes ψ _M degrees.

If the refractive index of the light guide plate 2 is 1.5, which is the standard value of a transparent organic polymer, the incident angle (critical angle) that satisfies the total reflection condition is about 45 degrees, so S-polarized light contained in the main component In order for the P-polarized light obtained by converting to satisfy the total reflection condition, the incident angle ψ _M of the S-polarized light needs to be 45 degrees or more. Therefore, in the liquid crystal display device of Example 1, the inclination angle φ ₁ of the side surface 2b of the light guide plate 2 and the inclination angle φ ₂ of the tangent at the position where the main component of the light source light of the reflective polarizing plate 14 is incident. For example, the relationship is (φ ₁ + 2φ ₂ ) ≦ 45 degrees.

Note that the incident angle of the S-polarized light incident on the quarter-wave plate 17 is different for each component viewed in the emission direction from the light exit surface 3a of the light source 3, as shown in FIG. There is also S-polarized light whose incident angle ψ to the wave plate 17 is smaller than the incident angle ψ _M of the S-polarized light contained in the main component. Therefore, in order to convert S-polarized light having such an incident angle ψ smaller than the incident angle ψ _M of S-polarized light included in the main component into P-polarized light, for example, the inclination angle φ ₁ and the inclination angle φ ₂ can be converted. And 20 degrees ≦ (φ ₁ + 2φ ₂ ) ≦ 40 degrees, and the incident angle ψ _M of the S-polarized light contained in the main component should be 50 degrees ≦ ψ _M ≦ 70 degrees. Is desirable.

Further, although detailed description is omitted, the P-polarized light transmitted through the reflective polarizing plate 14 is similarly reflected by the first reflecting plate 16 and returned to the light guide plate 2 and is incident on the second main surface 2c. Sometimes the incident angle needs to be 45 degrees or more. Therefore, for example, the first reflector 16 has an angle φ ₂ ′ formed by the tangent at the position where P-polarized light included in the main component of the light source is incident and the second main surface 2c is (φ ₁ + 2φ ₂ ′). ) ≦ 45 degrees.

The P-polarized light guided to the surface light emitting portion in this way propagates in the longitudinal direction of the light guide plate 2 while being totally reflected by the first main surface 2a and the second main surface 2c. However, as it is, the P-polarized light propagating through the surface light emitting portion cannot be emitted to the liquid crystal display panel 1 side. Therefore, in the liquid crystal display device of Example 1, for example, as shown in FIG. 2, a hollow prism-shaped protrusion 2d (light extraction) having an inclined surface on the light source side on the second main surface 2c of the surface light emitting unit. Structure). At this time, the inclined surface of the protrusion 2d has an inclination angle from the second main surface 2c, and the incident angle when the P-polarized light reflected by the inclined surface is incident on the first main surface 2a is smaller than the critical angle. To be. At this time, it is desirable that the inclination angle of the inclined surface of the protrusion 2d is a value at which the P-polarized light incident on the inclined surface is totally reflected. Accordingly, the light guide plate 2 used in the liquid crystal display device of Example 1, from this perspective, the relationship between the inclination angle Fai_ ₂ and the inclination angle phi ₁ is the 20 ° _{≦ (φ 1 + 2φ 2)} ≦ 40 ° It is desirable that the incident angle ψ _M of the S-polarized light contained in the main component is 50 degrees ≦ ψ _M ≦ 70 degrees.

  Further, the intensity of the P-polarized light propagating through the surface light emitting portion gradually decreases as the distance from the light source 3 increases. Therefore, the protrusions 2d are arranged so as to be distributed more sparsely in the vicinity of the light source 3 having a high intensity and more densely distributed in a portion separated from the light source 3 having a low intensity, and from the area AR2 to the liquid crystal display panel 1 side. It is desirable to make the intensity of the light emitted toward the surface uniform.

  Like the light guide plate used in the conventional general liquid crystal display device, when the light source light that is natural light is directly guided to the surface light emitting part, when the light source light reflected by the light extraction structure is incident on the first main surface 2a, The light source light includes P-polarized light and S-polarized light. At this time, the P-polarized light that has entered the first main surface 2a has a low reflectance at the interface between the light guide plate and air, and thus is easily emitted to the outside of the light guide plate. On the other hand, since the S-polarized light incident on the first main surface 2a has a high reflectance at the interface between the light guide plate and air, most of the S polarized light is returned to the inside of the light guide plate and hardly emitted to the outside of the light guide plate.

  Therefore, in the liquid crystal display device of Example 1, as described above, the S-polarized light contained in the light source light incident on the light guide plate is converted to P-polarized light and then guided to the surface light emitting unit, so that the liquid crystal display from the surface light emitting unit. The amount of light emitted to the panel 1 side is increased.

  Thus, the light emitted from the surface light emitting portion of the light guide plate 2 to the liquid crystal display panel 1 side passes through the first prism sheet 4 and the second prism sheet 5 as shown in FIG. The light is incident on the liquid crystal display panel 1. At this time, the planar light beam incident on the liquid crystal display panel 1 is modulated in the liquid crystal display panel 1 and recognized as an image or an image by the observer.

  The first prism sheet 4, for example, adjusts the incident direction of a light incident on the liquid crystal display panel 1 as viewed mainly on a plane (yz plane) parallel to the longitudinal direction of the liquid crystal display panel 1. For optical parts. At this time, the first prism sheet 4 has, for example, a protrusion structure in which the cross section viewed in the longitudinal direction of the liquid crystal display panel 1 is a triangle and the planar distribution is a stripe shape on the surface facing the liquid crystal display panel 1. The protrusion structure is arranged such that the stripe direction is parallel to the short direction (x direction) of the light guide plate 2. In addition, the second prism sheet 5 is, for example, an incident direction viewed in a plane (xz plane) mainly parallel to the lateral direction of the liquid crystal display panel 1 among the incident directions of light incident on the liquid crystal display panel 1. It is an optical component for adjusting. The first prism sheet 4 has, for example, a protrusion structure in which a cross section viewed in the short direction of the liquid crystal display panel 1 is a triangle shape and a planar distribution is a stripe shape on a surface facing the liquid crystal display panel 1. The protrusions are arranged so that the stripe direction is parallel to the longitudinal direction (y direction) of the light guide plate 2.

  The light guided to the surface light emitting portion of the light guide plate 2 is P-polarized light as described above, and propagates in the longitudinal direction of the light guide plate 2 while being reflected by the first main surface 2a and the second main surface 2c. Finally, the light is refracted by the first main surface 2 a and is emitted to the outside of the light guide plate 2. At this time, for example, when the P-polarized light propagating through the surface light emitting unit is reflected or refracted by the first main surface 2a and the second main surface 2c, the polarization state may change. However, if the traveling direction of the propagating light is parallel to the longitudinal direction of the light guide plate 2 and the optical axis of the light guide plate 2 is parallel to the longitudinal direction, the first main surface 2a and the second main surface 2c. In the light reflected or refracted at, only the P-polarized component is generated, and the S-polarized component is not generated. Therefore, the light emitted from the surface light emitting portion of the light guide plate 2 toward the liquid crystal display panel 1 is light whose vibration direction is parallel to the longitudinal direction of the light guide plate 2 as shown in FIG. In addition, what is actually emitted from the surface light emitting portion is light whose main component is light whose vibration direction is parallel to the longitudinal direction of the light guide plate 2. In this specification, such light is This is called light parallel to the longitudinal direction of the light guide plate 2.

  In the first prism sheet 4 and the second prism sheet 5, the stripe direction of the protrusion structure is parallel to the short direction (x direction) and the long direction (y direction) of the light guide plate 2, respectively. At this time, the light passing through the first prism sheet 4 and the light passing through the second prism sheet 5 are refracted at the interface between the prism sheet and air, respectively. At this time, if the traveling direction of the light passing therethrough is parallel to the longitudinal direction (y direction) of the light guide plate 2 and the optical axis of the prism sheet is parallel to the longitudinal direction of the light guide plate 2, the first prism sheet In the light refracted in the fourth and second prism sheets 5, only the P-polarized component is generated, and the S-polarized component is not generated. Therefore, the vibration direction of the light passing through the first prism sheet 4 and the second prism sheet 5 toward the normal direction of the liquid crystal display panel 1 is the longitudinal direction of the light guide plate 2, that is, the longitudinal direction of the liquid crystal display panel 1. And remain parallel. That is, most of the light incident on the liquid crystal display panel 1 is light having a vibration direction parallel to the longitudinal direction of the liquid crystal display panel 1. Note that light that is actually incident on the liquid crystal display panel 1 is light whose main component is light whose vibration direction is parallel to the longitudinal direction of the liquid crystal display panel 1, but in this specification, such light is vibrated. The direction is called light parallel to the longitudinal direction of the liquid crystal display panel 1.

  In the liquid crystal display panel 1, the display area AR1 is composed of a large number of pixels, and the planar light rays from the backlight are modulated by controlling the amount of light transmitted through each pixel. At this time, the amount of light transmitted through each pixel is determined by the relationship between the polarization state and amount of light that has passed through the liquid crystal layer 11 and the direction of the transmission axis of the second polarizing plate 13. The polarization state of the light that has passed through the liquid crystal layer 11 is determined by the direction of the transmission axis of the first polarizing plate 12 and the orientation state of the liquid crystal layer 11, and the amount of light is determined by the vibration direction of the light incident on the first polarizing plate 12 and the first direction. It depends on the relationship with the direction of the transmission axis of the polarizing plate 12.

  Therefore, in order to increase the utilization efficiency of the light emitted from the backlight (light guide plate 2), for example, as shown in FIG. 1, the direction of the transmission axis 12T of the first polarizing plate 12 is set to the light guide plate 2 (liquid crystal). What is necessary is just to make it parallel to the y direction which is a longitudinal direction of the display panel 1). The direction of the transmission axis 12T of the first polarizing plate 12 is preferably parallel to the longitudinal direction of the liquid crystal display panel 1, but is not limited thereto, and is substantially parallel to the longitudinal direction of the liquid crystal display panel 1. Just do it.

  Further, in the liquid crystal display panel 1 in the liquid crystal display device of Example 1, the direction of the transmission axis LT1 of the first polarizing plate 12 is parallel or substantially parallel to the longitudinal direction of the light guide plate 2 and the liquid crystal display panel 1. Therefore, for example, the method of applying an electric field to the liquid crystal layer 11 and the pixel configuration can be changed as appropriate. In the first embodiment, an IPS liquid crystal display panel is taken as an example of the liquid crystal display panel 1.

6 to 8 are schematic views for explaining an example of a schematic configuration of the liquid crystal display panel in the liquid crystal display device of the first embodiment.
FIG. 6 is a schematic plan view illustrating an example of a planar configuration of a pixel of the liquid crystal display panel. FIG. 7 is a schematic cross-sectional view showing an example of a cross-sectional configuration taken along line BB ′ of FIG. FIG. 8 is a schematic cross-sectional view showing an example of a cross-sectional configuration taken along the line CC ′ of FIG.
6 and 7 are the same directions as the x, y, and z directions in FIG. 1, respectively.

  The pixels of the IPS liquid crystal display panel 1 are configured as shown in FIGS. 6 to 8, for example, and the pixel electrode 19 and the common electrode 20 for controlling the strength of the electric field applied to the liquid crystal layer 11 are used. Are both provided on the TFT substrate 9.

  The TFT substrate 9 has a transparent first insulating substrate 21 made of, for example, borosilicate glass. The TFT substrate 9 has a scanning signal line 22, a first insulating layer 23, a TFT element 24, a video signal line 25, and a second signal line formed on the surface of the first insulating substrate 21 facing the liquid crystal layer 11. Insulating layer 26, common electrode 20, third insulating layer 27, pixel electrode 19, first alignment film 28, and the like.

  In addition, the liquid crystal display device according to the first embodiment is a small-sized device used for, for example, a liquid crystal display of a mobile phone terminal, and the portion of the scanning signal line 22 that passes through the display area AR1 is the short side of the liquid crystal display panel 1. The portion extending in the direction (x direction) and passing through the display area AR1 of the video signal line 25 extends in the longitudinal direction (y direction) of the liquid crystal display panel 1.

  Further, the pixel electrode 19 and the common electrode 20 are stacked via a third insulating layer 27, and the planar shape of the pixel electrode 19 closer to the liquid crystal layer 11 is linear in the longitudinal direction of the liquid crystal display panel 1. It has a comb-like shape having a plurality of elongated portions (hereinafter referred to as teeth) extending in a shape. At this time, the pixel electrode 19 is connected to the source electrode of the TFT element 24 through the contact hole CH.

  The TFT element 24 has a gate electrode connected to the scanning signal line 22 and a drain electrode connected to the video signal line 25. Note that the source electrode and the drain electrode of the TFT element 24 vary depending on the bias relationship, that is, the relationship between the potential of the pixel electrode 19 and the potential of the video signal line 25 when the TFT element 24 is turned on.

  On the other hand, the counter substrate 10 has a transparent second insulating substrate 29 made of, for example, borosilicate glass. The counter substrate 10 includes a black matrix 30, a color filter 31, a planarizing film 32, a second alignment film 33, and the like formed on the surface of the second insulating substrate 29 facing the liquid crystal layer 11.

  For the liquid crystal layer 11, for example, a liquid crystal material that exhibits a nematic layer in a wide temperature range including room temperature and has positive dielectric anisotropy is used. At this time, the liquid crystal material preferably further has a high resistance.

  In the IPS liquid crystal display panel 1, the alignment of the liquid crystal layer 11 is generally homogeneous when no electric field is applied, that is, when there is no potential difference between the pixel electrode 19 and the common electrode 20. . At this time, the alignment direction of the liquid crystal layer 11 is determined by the alignment treatment applied to the first alignment film 28 and the second alignment film 33. When the planar shape of the pixel electrode 19 is a comb-like shape as shown in FIG. 6, the alignment direction in the plane of the liquid crystal layer 11 when no electric field is applied is, for example, the molecular axis direction 11M of liquid crystal molecules. The direction is inclined by an angle β with respect to the direction (y direction) in which the teeth of the signal line 25 and the pixel electrode 19 extend. This angle β is, for example, about 5 degrees.

  In this way, the direction (x direction) of the electric field applied to the liquid crystal layer 11 when a potential difference is generated between the pixel electrode 19 and the common electrode 20, and the molecular axis direction 11M of the liquid crystal molecules when no electric field is applied. And the angle of rotation of the liquid crystal molecules when an electric field is applied is increased.

  At this time, in the first polarizing plate 12 and the second polarizing plate 13, the absorption axis 12A of the first polarizing plate and the absorption axis 13A of the second polarizing plate are orthogonal to each other, and the second polarizing plate The 13 absorption axes 13A are arranged so as to coincide with the molecular axis direction 11M of the liquid crystal molecules when no electric field is applied. The first polarizing plate 12 and the second polarizing plate 13 are optical components that contain, for example, an alignment-treated iodine dye and convert natural light into polarized light due to its dichroism.

  When the absorption axis 13A of the second polarizing plate 13 is parallel to the molecular axis direction 11M of the liquid crystal molecules when no electric field is applied, the absorption axis 12A of the first polarizing plate 12 is the molecular axis of the liquid crystal molecules when no electric field is applied. It is orthogonal to the direction 11M. In each of the first polarizing plate 12 and the second polarizing plate 13, the azimuth (absorption axis) at which the absorption rate of incident light is maximum and the azimuth (transmission axis) at which the absorption is minimum are orthogonal to each other. Therefore, the transmission axis 12T of the first polarizing plate 12 is parallel to the molecular axis direction 11M of the liquid crystal molecules when no electric field is applied, and is generally parallel to the longitudinal direction (y direction) of the liquid crystal display panel 1. At this time, the transmission axis 13T of the second polarizing plate 13 is orthogonal to the molecular axis direction 11M of the liquid crystal molecules when no electric field is applied, and is substantially parallel to the short direction (x direction) of the liquid crystal display panel 1.

  In such a liquid crystal display panel 1, the polarization state of light that has passed through the liquid crystal layer 11 when no electric field is applied is substantially the same as that before passing through the liquid crystal layer 11, and the transmission axis 12T of the first polarizing plate 12 and Linearly polarized light having parallel vibration directions. Therefore, in a pixel in which there is no potential difference between the pixel electrode 19 and the common electrode 20, light emitted from the light guide plate 2 and passing through the first polarizing plate 12 and the liquid crystal layer 11 is absorbed by the second polarizing plate 13. , Black display. Note that the light passing through the first polarizing plate 12 is actually partially polarized light that is close to perfect polarization mainly composed of linearly polarized light having a vibration direction parallel to the transmission axis 12T.

  On the other hand, when a potential difference is generated between the pixel electrode 19 and the common electrode 20 to change the orientation of the liquid crystal layer 11, the polarization state of the light passing through the first polarizing plate 12 and the liquid crystal layer 11 passes through the liquid crystal layer 11. It will be in a different state than before. Therefore, in a pixel having a potential difference between the pixel electrode 19 and the common electrode 20, a part or all of the light that has passed through the first polarizing plate 12 and the liquid crystal layer 11 from the light guide plate 2 side according to the potential difference. It passes through the second polarizing plate 13 and becomes a display with a predetermined gradation (luminance) other than black. At this time, if the polarization state of the light passing through the liquid crystal layer 11 and entering the second polarizing plate 13 is the same, the luminance of the pixel increases as the amount of light passing through the first polarizing plate 12 increases. Of course.

  In the liquid crystal display device according to the first embodiment, as described above, the vibration direction of the light emitted from the light guide plate 2 and incident on the liquid crystal display panel 1 (first polarizing plate 12) is the longitudinal direction of the liquid crystal display panel 1. Parallel. Therefore, when the transmission axis 12T of the first polarizing plate 12 is made substantially parallel to the longitudinal direction of the liquid crystal display panel 1, the amount of light passing through the first polarizing plate 12 increases. Therefore, for example, the liquid crystal display device of Example 1 displays a brighter display while maintaining power consumption equivalent to that of the conventional liquid crystal display device, or consumes power consumption while maintaining brightness equivalent to that of the conventional liquid crystal display device. Can be suppressed.

  In the liquid crystal display panel 1 shown in FIGS. 6 to 8, the orientation direction of the liquid crystal layer 11 when no electric field is applied is inclined by 5 degrees with respect to the longitudinal direction (y direction). The transmission shaft 12T is also inclined by 5 degrees with respect to the longitudinal direction. On the other hand, the vibration direction of the light from the backlight (light guide plate 2) is parallel to the longitudinal direction of the liquid crystal display panel 1 as described above. Therefore, the transmission axis 12T of the first polarizing plate 12 and the vibration direction of the incident light are not parallel to each other and are shifted by 5 degrees.

However, with this degree of deviation, the light from the backlight passes through the first polarizing plate 12 with sufficiently high efficiency. This is based on the assumption that the light from the backlight is completely polarized light consisting only of linearly polarized light whose vibration direction is the longitudinal direction of the liquid crystal display panel 1, and that the first polarizing plate 12 is a complete polarizing plate. If the angle between the vibration direction of light from the light and the transmission axis 12T of the first polarizing plate 12 is β, the efficiency of the light from the backlight passing through the first polarizing plate 12 is proportional to cos ² β. Because it does. Cos ² β in the ideal case of β = 0 (degrees) is 1, whereas cos ² β in the case of β = 5 (degrees) is about 0.9924. That is, the reduction rate of the transmission efficiency when β = 5 (degrees) is about 1%. Therefore, even if the polarization state of the light incident on the first polarizing plate 12 is not linearly polarized light that is completely parallel to the transmission axis 12T, even if there is a deviation of about 5 degrees, the utilization efficiency of the light source light is improved. The effect of improving is sufficiently obtained. Note that the complete polarizing plate here is an ideal polarizing plate in which the transmittance of the absorbing component contained in the incident light is 0% and the transmittance of the transmitting component is 100%.

  Thus, in the liquid crystal display device of Example 1, by making the direction of the transmission axis 12T of the first polarizing plate 12 of the liquid crystal display panel 1 substantially parallel to the vibration direction of the light emitted from the light guide plate 2, The utilization efficiency of the light emitted from the light guide plate 2, that is, the utilization efficiency of the light source light is increased.

  Now, in the liquid crystal display device of Example 1, the light (S-polarized light) reflected by the reflective polarizing plate 14 out of the light source light incident on the light guide plate 2 is, for example, as shown in FIG. The light is converted into P-polarized light using the quarter-wave plate 17 and the second reflecting plate 18 provided on the main surface 2c.

  The quarter-wave plate 17 is a kind of optically anisotropic medium. In general, the optical anisotropy varies depending on the traveling direction of incident light, that is, the incident angle of light incident on the quarter-wave plate. To do. In the liquid crystal display device of Example 1, as shown in FIG. 3, the incident angle of the S-polarized light incident on the quarter-wave plate 17 is the light incident surface (light guide plate 2) of the quarter-wave plate 17. The second main surface 2c is inclined at a predetermined angle with respect to the normal direction of the second main surface 2c. Therefore, the quarter-wave plate 17 in the liquid crystal display device of Example 1 must function as a quarter-wave plate with respect to the S-polarized light having such an inclined optical path. That is, the quarter-wave plate 17 in the liquid crystal display device of Example 1 has a slow axis of 45 degrees with respect to the vibration direction of the S-polarized light when viewed from the incident direction of the S-polarized light, and the S-polarized light. The retardation when viewed from the incident direction must be a quarter wavelength of the S-polarized light.

  On the other hand, the retardation of the quarter-wave plate 17 is normally managed by the value in the normal direction of the light incident surface. Further, when setting the slow axis azimuth angle of the quarter-wave plate 17, usually, the slow axis azimuth angle (hereinafter referred to as the slow angle on the light entrance surface) when viewed from the normal direction of the light entrance surface. (Referred to as phase axis azimuth). Therefore, in Example 1, the retardation in the normal direction and the slow axis azimuth in the light incident plane are derived as the retardation and slow axis azimuth required for the quarter-wave plate 17.

  When a white LED is used as the light source 3, the intensity of the light source emitted from the white LED has an angle dependency, and is maximized in the normal direction of the light emitting surface and is far from the normal direction (the inclination is large). ). Therefore, in Example 1, focusing on the S-polarized light contained in the main component of the light source light, the retardation of the quarter-wave plate 17 and the slow axis azimuth required for converting the S-polarized light into the P-polarized light Is derived.

When attention is paid to the main component emitted from the light source light in the normal direction of the light exit surface, the S-polarized light contained in the main component is, for example, as shown in FIG. 5, incident angle ψ _M = {90− ( ([phi] ₁ + _{2 [} phi] ₂ )} is incident on the quarter-wave plate 17 (second main surface of the light guide plate 2). That is, in the first embodiment, the method of the quarter-wave plate 17 required for converting the S-polarized light incident on the quarter-wave plate 17 with the incident angle ψ _M with respect to the light incident surface into the P-polarized light. The retardation in the linear direction and the slow axis azimuth in the plane are derived.

  The quarter-wave plate 17 in the liquid crystal display device of Example 1 has positive uniaxial anisotropy created by stretching a transparent organic polymer film such as a cycloolefin organic polymer film, for example. Shall have. The quarter-wave plate 17 having positive uniaxial anisotropy is easy to produce and has the advantage that a thin quarter-wave plate can be produced at low cost. A quarter-wave plate having positive uniaxial anisotropy is a quarter-wave plate whose refractive index in the stretching direction is larger than its vertical direction and whose refractive index in any vertical direction is equal. That is.

9 to 14 are schematic diagrams for explaining the configuration of a quarter-wave plate in the liquid crystal display device according to the first embodiment.
FIG. 9 is a schematic side sectional view for explaining the relationship between the vibration direction of light incident on the quarter-wave plate and the slow axis azimuth angle. FIG. 10 is a schematic diagram showing the relationship between the slow axis azimuth angle in the light incident surface of the quarter-wave plate and the incident angle dependence of the slow axis azimuth angle in the incident angle direction. FIG. 11 is a schematic diagram showing the definition of the slow axis azimuth angle in the light incident surface. FIG. 12 is a schematic diagram showing the relationship between the retardation in the normal direction of the quarter-wave plate and the dependence of the retardation in the incident angle direction on the incident angle. FIG. 13 shows that the slow axis azimuth in the incident angle direction becomes 45 degrees when the Nz coefficient of the quarter-wave plate is 1, and the incident angle and the slow axis azimuth in the light incident surface are It is a schematic diagram which shows a relationship. FIG. 14 shows a slow axis azimuth angle in the light incident surface where the slow axis azimuth angle in the incident angle direction is 45 degrees, and a normal direction retardation where the retardation in the incident angle direction is a quarter wavelength. It is a schematic diagram which shows the relationship.

  A three-dimensional refractive index distribution of an optically anisotropic medium such as the quarter-wave plate 17 is generally represented by an Nz coefficient. The Nz coefficient is disclosed in Non-Patent Document 1, for example, and is defined by the following Equation 1.

_{Nz = (n s -n z)} / (n s -n f) ··· ( Equation 1)

Incidentally, in Equation 1, n _s and n _f are each a slow axis direction and the fast axis direction refractive index of in a plane which light is incident, n _z is a refractive index in the thickness direction. In the case of an optically anisotropic medium with positive uniaxial anisotropy handled in Example 1, the Nz coefficient is 1.

  Further, the slow axis angle of the optically anisotropic medium and the angle dependency of the retardation can be obtained by Lagrange's undetermined multiplier method. This calculation method is described in detail in Non-Patent Document 2, for example, and only the result is described in Example 1.

X-axis direction of the optical anisotropic medium, y-axis direction, and a refractive index in the z-axis direction, respectively, when n _x, n _y and n _z, the incident angle ψ and the azimuth in the xy plane of the optically anisotropic medium The refractive index n _{s in the} slow axis direction and the refractive index n _{f in the} fast axis direction for linearly polarized light incident at an angle Θ are expressed by the following formulas 2 to 9, respectively. The incident angle ψ is an angle from the z-axis direction (so-called polar angle), and the azimuth angle Θ is an angle from the x-axis in the xy plane.

n _s = 2A / {− B + (B ² −4AC) ^0.5 } ^0.5 (Expression 2)
_{n f = 2A / {- B} + (B 2 + 4AC) 0.5} 0.5 ··· ( Equation 3)
However,
^{_{A = n x 2 n y 2}} n z 2 ··· ( Equation 4)
^{_{B = n x 2 n z 2}} (k y 2 -1) 2 + n y 2 n z 2 (k x 2 -1) 2
+ N _x ² _ny ² (k _z ² −1) ² (Equation 5)
^{_{C = n x 2 + n y}} 2 + n z 2 -k y 2 (n x 2 + n z 2) -k x 2 (n y 2 + n z 2)
^{_{-K z 2 (n x 2 +}} n y 2) ··· ( Equation 6)
And
k _x = sinψsinΘ (Formula 7)
k _y = sinψcosΘ (Formula 8)
k _z = cosψ (Equation 9)

Further, _assuming that the direction of the slow axis is (k _sx , k _sy , k _sz ), k _sx , k _sy , and k _sz are represented by the following formulas 10 to 12, respectively.

^{_{k sx = k x n x 2}} (n y 2 -n s 2) (n z 2 -n s 2) / N os ··· ( Equation 10)
^{_{k sy = k y n y 2}} (n x 2 -n s 2) (n z 2 -n s 2) / N os ··· ( Equation 11)
^{_{k sz = k z n z 2}} (n y 2 -n s 2) (n x 2 -n s 2) / N os ··· ( Equation 12)

Note that N _os in Equations 10 to 12 is a normalization coefficient expressed by Equations 13 to 16 below.

N _os = {(k _sx ′) ² + (k _sy ′) ² + (k _sz ′) ² } ^0.5 (Formula 13)
However,
_{k sx '= k x n x} 2 (n y 2 -n s 2) (n z 2 -n s 2) ··· ( Equation 14)
_{k sy '= k y n y} 2 (n x 2 -n s 2) (n z 2 -n s 2) ··· ( Equation 15)
_{k sz '= k z n z} 2 (n y 2 -n s 2) (n x 2 -n s 2) ··· ( Equation 16)

Here, x-axis, y-axis, and the z-axis direction of the refractive index, respectively, n _x, n _y, and considering the refractive index ellipsoid is n _z, as shown in FIG. 9, the slow axis 17d The direction (k _sx , k _sy , k _sz ) is within the cross section 34 a that includes the center O of the refractive index ellipsoid 34 and is perpendicular to the direction represented by the incident angle ψ and the azimuth angle Θ. The vibration direction SPO of S-polarized light is always in the horizontal direction (in the xy plane) and parallel to the second main surface 2 c of the light guide plate 2. Therefore, the slow axis azimuth angle θ (hereinafter referred to as the slow axis azimuth angle θ in the incident angle direction) when the cross section 34a is viewed from the direction in which the linearly polarized light is incident is a counterclockwise angle, and If the direction of the phase axis 17d is defined as 0 degrees when the direction is the horizontal direction, the slow axis azimuth angle θ in the incident angle direction is an optically anisotropic medium (quarter) at the incident angle ψ as shown in FIG. The angle formed by the oscillation direction SPO of the S-polarized light incident on the one-wave plate 17) and the slow axis 17d with respect to the S-polarized light.

As described above, the incident angle ψ _M of the S-polarized light contained in the main component of the light source light should be 45 degrees or more, and is preferably 50 degrees ≦ ψ _M ≦ 70 degrees. Therefore, the inventors of the present application have determined that the slow axis azimuth angle Θ in the light incident surface of the quarter-wave plate 17 in the incident angle direction is 45 ° ≦ ψ ≦ 75 °, and the incident angle direction When the relationship between the slow axis azimuth angle θ and the incident angle dependency was examined, the relationship shown in FIG. 10 was obtained. FIG. 10 is a graph in which the horizontal axis represents the incident angle ψ (unit: degrees), and the vertical axis represents the slow axis azimuth angle θ (unit: degrees) in the incident angle direction.

Further, each of the curves F ₁ , F ₂ , F ₃ , F ₄ , and F ₅ in FIG. 10 has an Nz coefficient of 1 and a slow axis azimuth angle Θ of 57.3 degrees in the light incident surface. 6 is a curve showing the polar angle dependence of the slow axis azimuth angle θ in the incident angle direction at 60.2 degrees, 63.4 degrees, 67.1 degrees, and 71.1 degrees. At this time, the slow axis azimuth angle Θ within the light incident surface is, for example, as shown in FIG. 11, which is included in the main component of the light source light when the light incident surface is viewed from the normal direction. The angle is counterclockwise from the vibration direction SPO of the polarized light, and 0 degree when the direction of the slow axis 17d coincides with the vibration direction SPO.

As can be seen from FIG. 10, for example, when the incident angle ψ _M when the S-polarized light included in the main component of the light source light is incident on the quarter-wave plate 17 is set to 50 degrees, within the light incident surface. When the slow axis azimuth angle Θ is 57.3 degrees, the slow axis azimuth angle θ in the incident angle direction is 45 degrees. Further, when the incident angle ψ _M of the S-polarized light contained in the main component is set to any one of 55 degrees, 60 degrees, 65 degrees, and 70 degrees, the slow axis azimuth angle Θ in the light incident surface is When the angle is 60.2 degrees, 63.4 degrees, 67.1 degrees, and 71.1 degrees, respectively, the slow axis azimuth angle θ in the incident angle direction becomes 45 degrees.

  These results show that when the Nz coefficient is 1, the slow axis azimuth angle θ in the incident angle direction becomes more horizontal as observed from an oblique direction. To correct this, the slow axis azimuth in the light incident surface is corrected. This means that the angle Θ must be increased beyond 45 degrees.

  Further, if the thickness of the optically anisotropic medium is d, the retardation R of light that enters and passes through the optically anisotropic medium at an incident angle ψ (hereinafter referred to as retardation R in the incident angle direction) is expressed by the following equation: 17.

R = (n _s −n _f ) · d / cos ψ (Expression 17)

The distribution of the curves F ₁ , F ₂ , F ₃ , F ₄ , and F ₅ shown in FIG. 10 indicates that the retardation in the normal direction of the optically anisotropic medium is large if the Nz coefficient is 1. Regardless, it is unchanged. Therefore, the normal direction when the present inventors set the slow axis azimuth angle Θ in the light incident surface to 57.3 degrees, 60.2 degrees, 63.4 degrees, 67.1 degrees, and 71.1 degrees using Expression 17 When the relationship between the retardation Rz and the dependence of the retardation R on the incident angle in the incident angle direction was calculated, the results shown in FIG. 12 were obtained. FIG. 12 is a graph of the incident angle ψ (unit: degrees) on the horizontal axis and the retardation R (unit: nm) on the incident angle direction on the vertical axis.

Further, the curve F ₆ , the curve F ₇ , the curve F ₈ , the curve F ₉ , and the curve F ₁₀ in FIG. 12 are respectively obtained by comparing the slow axis azimuth Θ in the light incident surface and the retardation Rz in the normal direction. When the combination (Θ, Rz) is (57.3 degrees, 157.5 nm), (60.2 degrees, 167.5 nm), (63.4 degrees, 182.3 nm), (67.1 degrees, 205.3 nm), and (71.1 degrees, 242.4 nm) It is a curve which shows the incident angle dependence of the retardation R in the incident angle direction. In addition, curve F ₆ , curve F ₇ , curve F ₈ , curve F ₉ , and curve F ₁₀ in FIG. 12 are retardation R in the incident angle direction with respect to light having a wavelength of 550 nm at which the visibility is almost maximum among visible wavelengths. The incident angle dependence of is shown.

As can be seen from FIG. 12, for example, when the incident angle ψ _M when the S-polarized light included in the main component of the light source light is incident on the quarter-wave plate 17 is set to 50 degrees, When the slow axis azimuth angle Θ and the retardation Rz in the normal direction are 57.3 degrees and 157.5 nm, respectively, the retardation R in the incident angle direction becomes a quarter wavelength (137.5 nm). Further, when the incident angle ψ _M of the S-polarized light contained in the main component is set to any of 55 degrees, 60 degrees, 65 degrees, and 70 degrees, the slow axis azimuth angle Θ and the method The combinations (Θ, Rz) with the retardation Rz in the linear direction are (57.3 degrees, 157.5 nm), (60.2 degrees, 167.5 nm), (63.4 degrees, 182.3 nm), (67.1 degrees, 205.3 nm), and (71.1 degrees, 242.4 nm), the retardation R in the incident angle direction becomes a quarter wavelength (137.5 nm).

Further, the incident angle ψ _M of the S-polarized light included in the main component is not limited to the above-described 50 degrees, 55 degrees, 60 degrees, 65 degrees, and 70 degrees, and may be other angles. Therefore, for the intermediate incident angle ψ other than the above angle, the Nz coefficient is set to 1, and the slow axis azimuth θ in the incident angle direction is 45 degrees, and the slow axis azimuth Θ in the light incident surface is calculated. Then, for example, a result as shown in FIG. 13 is obtained. FIG. 13 is a graph in which the horizontal axis represents the incident angle ψ (unit: degrees) and the vertical axis represents the slow axis azimuth angle Θ (unit: degrees) in the light incident surface.

As can be seen from FIG. 13, the curve F ₁₁ showing the relationship between the incident angle ψ and the slow axis azimuth Θ in the light incident surface where the slow axis azimuth θ in the incident angle direction is 45 degrees is approximately It becomes a straight line. At this time, the relationship between the incident angle ψ and the slow axis azimuth angle Θ within the light incident surface is approximated by the following Equation 18.

    Θ = −3.78ψ + 40.4 (Formula 18)

Therefore, if the incident angle ψ _{M of the} S-polarized light contained in the main component of the light source light to the quarter-wave plate 17 is determined, the slow axis direction of the incident angle direction with respect to the S-polarized light is obtained from FIG. The slow axis azimuth Θ in the light incident plane required for the quarter-wave plate 17 in order to set the angle θ to 45 degrees is obtained.

  Furthermore, the slow axis azimuth θ in the light incident surface where the slow axis azimuth θ in the incident angle direction is 45 degrees and the normal direction in which the retardation R in the incident angle direction is a quarter wavelength. For example, there is a relationship as shown in FIG. 14 with the retardation Rz. FIG. 14 is a graph in which the horizontal axis represents the slow axis azimuth angle Θ (in degrees) in the light incident surface, and the vertical axis represents the normal-direction retardation Rz (in nm).

Further, the point P ₁ , the point P ₂ , the point P ₃ , the point P ₄ , and the point P ₅ shown in FIG. 14 have an incident angle ψ of 50 degrees, 55 degrees, 60 degrees, 65 degrees in FIG. This is a point showing the relationship between the slow axis azimuth angle Θ in the light incident plane and the normal direction retardation Rz at 70 and 70 degrees. A curve F ₁₂ shown in FIG. 14 is a regression curve obtained from the values of the points P ₁ , P ₂ , P ₃ , P ₄ , and P ₅ .

When the incident angle ψ _M of the S-polarized light contained in the main component is set to a certain angle, the quarter-wave plate 17 is used in order to set the slow axis azimuth angle θ in the incident angle direction with respect to the S-polarized light to 45 degrees. The slow axis azimuth angle Θ in the light incident plane required for the above can be obtained from FIG. At this time, the slow axis azimuth θ in the light incident surface where the slow axis azimuth θ in the incident angle direction with respect to the S-polarized light is 45 degrees and the retardation R in the incident angle direction are a quarter wavelength. There is a relationship as shown by a curve F ₁₂ shown in FIG. 14 between the normal direction retardation Rz. Therefore, if the incident angle ψ _M is determined and the slow axis azimuth angle Θ within the light incident surface required for the quarter-wave plate 17 is obtained from FIG. The retardation Rz in the normal direction required for the one-wave plate 17 is also obtained.

As described above, in the liquid crystal display device according to the first embodiment, the S-polarized light incident angle ψ _M included in the main component of the light source light is set in the light incident surface of the quarter-wave plate 17 to be used. By changing the slow axis azimuth angle Θ and the retardation Rz in the normal direction, the S-polarized light contained in the light source light is efficiently converted to the P-polarized light, and the utilization efficiency of the light source light is enhanced.

Note that not only S-polarized light included in the main component of the light source light but also S-polarized light included in components other than the main component are incident on the quarter-wave plate 17. At this time, the incident angle ψ of S-polarized light included in components other than the main component is different from the incident angle ψ _M of S-polarized light included in the main component. For this reason, the slow axis azimuth Θ and the normal direction retardation Rz in the light incident surface of the quarter-wave plate 17 are determined based on the incident angle ψ _M of the S-polarized light contained in the main component of the light source light. In this case, the efficiency of converting S-polarized light contained in components other than the main component into P-polarized light is lower than that of S-polarized light contained in the main component of the light source light.

However, when a white LED is used as the light source 3, the light intensity of components other than the main component decreases rapidly as the inclination of the light exit surface 3a from the normal direction increases. Further, among components other than the main component, the incident angle ψ of S-polarized light included in a component having a relatively high light intensity, that is, a component having a small inclination from the normal direction of the light exit surface 3a, is included in the main component. The difference from the incident angle ψ _M of the polarized light is small. Therefore, when the slow axis azimuth Θ and the normal direction retardation Rz in the light incident surface of the quarter-wave plate 17 are determined based on the incident angle ψ _M of the S-polarized light contained in the main component, Of the components other than the components, the S-polarized light contained in the component having a relatively high light intensity is not perfect, but the S-polarized light can be converted into the P-polarized light with relatively high efficiency.

Further, the curvature of the step provided on the first main surface 2a of the light guide plate 2 (the light incident surface of the reflective polarizing plate 14) is adjusted, and the incident angle ψ of S-polarized light contained in components other than the main component is the light source light. If the incident angle ψ _M of the S-polarized light included in the main component is substantially equal to the incident angle ψ _M , the efficiency of converting the S-polarized light included in the component other than the main component into the P-polarized light increases.

  Next, an example of a method for manufacturing a light guide plate in the liquid crystal display device of Example 1 will be briefly described.

  FIG. 15 is a schematic diagram illustrating an example of a method for forming a light guide plate used in the liquid crystal display device according to the first embodiment.

For example, the light guide plate 2 is formed by injection molding using a transparent resin such as an acrylic resin. When the light guide plate 2 is formed by injection molding, for example, as shown in FIG. 15, a mold 35 having a cavity 35a, a plurality of injection ports 35b, and an exhaust port 35c is used, and an injection port 35b of the mold 35 is used. The transparent resin 36 or the transparent resin precursor softened by heating is injected into the cavity 35a. At this time, the spatial shape of the cavity 35a is such that, for example, a coupling portion of the light guide plate 2 is formed in a region 35d near the injection port 35b, and a surface light emitting unit is formed in a region 35e between the region 35d and the exhaust port 35c. Keep the shape like this. At this time, the spatial shape of the cavity 35a is, for example, the inclination angle φ ₁ of the side surface 2b shown in FIG. 8 and the inclination angle φ of the position where the main component of the light source light is incident on the step portion of the first main surface 2A. ₂ , the incident angle ψ _M {= 90− (φ ₁ + 2φ ₂ )} when S-polarized light contained in the main component of the light source light is incident on the quarter-wave plate 17 is a predetermined value, for example, 50 degrees. Keep it at an angle between 70 degrees.

  At this time, the transparent resin 36 injected into the cavity 35a flows radially around the injection port 35b in the vicinity of the injection port 35b, and solidifies while maintaining the orientation state at the time of flow. Therefore, the obtained light guide plate 2 usually has optical anisotropy. The transparent resin 36 is generally an organic polymer, and the orientation direction of the organic polymer in the light guide plate 2 formed by injection molding generally coincides with the flow direction of the transparent resin 36. At this time, when the light guide plate 2 is divided into minute regions, each region can be regarded as a positive uniaxial anisotropic medium whose slow axis (optical axis) is the flow direction of the transparent resin 36. . At this time, if the P-polarized light propagates at an angle with respect to the flow direction of the transparent resin 36 in the formed light guide plate 2, the P-polarized light is affected by the optical anisotropy of the light guide plate 2 and is subjected to polarization conversion. As a result, an S-polarized component is generated.

  Therefore, in Example 1, by providing a large number of injection ports 35b of the mold 35 along the short direction of the light guide plate 2 as shown in FIG. The flow direction 36 f of the transparent resin 36 is set to be substantially parallel to the longitudinal direction of the light guide plate 2. Of the transparent resin 36 that has flowed into the cavity 35a from the injection port 35b, the transparent resin that flows obliquely with respect to the longitudinal direction collides with the transparent resin that flows into the adjacent injection port 35b and flows obliquely with respect to the longitudinal direction. . When the transparent resin collides with the cavity 35a in this way, the flow direction becomes the vector sum direction of both, that is, the longitudinal direction of the light guide plate 2. Therefore, by increasing the number of the injection ports 35b and narrowing the interval between the adjacent injection ports 35b, the light guide plate 2 to be formed propagates the surface light emitting unit at least in the slow axis direction of the surface light emitting unit. It can be made approximately parallel to the propagation direction of polarized light. At this time, since the surface light emitting portion of the light guide plate 2 is isotropic in appearance, the P-polarized light is not converted to S-polarized light by the optical anisotropy (birefringence) of the light guide plate 2. Thereby, the P-polarized light guided to the surface light emitting portion in the formed light guide plate 2 is maintained in the P-polarized state until it propagates through the surface light emitting portion and is emitted to the outside of the light guide plate 2.

  After the light guide plate 2 is formed, next, for example, the quarter-wave plate 17 and the second reflection plate 18 are attached to the second main surface 2c of the light guide plate 2 in this order. At this time, the quarter-wave plate 17 and the second reflecting plate 18 are attached using, for example, an optical adhesive.

As described above, the quarter-wave plate 17 uses, for example, a cycloolefin organic polymer, and is optimal for S-polarized light incident at an incident angle ψ _M , that is, S-polarized light included in the main component of the light source light. It is formed so that a retardation Rz in a normal direction can be obtained. When the quarter-wave plate 17 is formed using a cycloolefin-based organic polymer, the organic polymer film is stretched to impart uniaxial anisotropy. Therefore, in order to obtain the retardation Rz in the normal direction that is optimal for the S-polarized light incident at the incident angle ψ _M , for example, the thickness before stretching and the stretching conditions may be adjusted.

  Further, the quarter-wave plate 17 to be attached to the light guide plate 2 is usually a large-area quarter-wave plate cut into a plurality of strip-shaped quarter-wave plates. The quarter-wave plate 17 formed by stretching an organic polymer film has a slow axis that coincides with the stretching direction. Therefore, in order to obtain the slow axis azimuth angle Θ within the light incident surface obtained from FIG. 12 or Formula 18, for example, when cutting into a plurality of strip-shaped quarter-wave plates, the cutting direction and the slow axis What is necessary is just to adjust the relationship with (stretching direction).

  The second reflector 18 is formed, for example, by using a polymer film as a base material and forming a film having a high light reflectance such as an aluminum film on the surface thereof.

  Next, the reflective polarizing plate 14, the transparent spacer 15, and the first reflective plate 16 are attached in this order to the first main surface 2 a of the light guide plate 2.

The reflective polarizing plate 14 is formed, for example, by alternately laminating two kinds of polymer films having a thickness equal to one half of the wavelength of visible light passing through the inside. At this time, one of the two types of polymer films is a polymer film having in-plane refractive index anisotropy, and the other is a polymer film having no refractive index anisotropy. The polymer film having a refractive index anisotropy, either the extraordinary refractive index n _e or ordinary refractive index n _o, equal to the refractive index of the polymer film having no refractive index anisotropy. If the ordinary refractive index n _o is equal to the refractive index of the polymer film having no refractive index anisotropy, with respect to the direction and the vibration direction parallel to the polarization of the ordinary refractive index n _o, the interior of the reflective polarizer 14 Since the refractive index at is always constant, the polarized light passes through the reflective polarizing plate 14. On the other hand, at this time, with respect to the direction and the vibration direction parallel to the polarization of the extraordinary refractive index n _e, the refractive index at a wavelength of the same period in the interior of the reflective polarizing plate 14 is varied, the polarization reflective polarizing Reflected by the plate 14. Note that the reflective polarizing plate 14 is not limited to the above-described configuration, because one of the two polarized components having orthogonal incident vibration directions (P-polarized light) may be transmitted and the other (S-polarized light) may be reflected. Other configurations may be used. Therefore, the reflective polarizing plate 14 may be, for example, a wire grid polarizing plate.

  The wire grid type polarizing plate is a metal thin film patterned in a stripe shape, and has a property of reflecting a polarized light component having a vibration direction parallel to the stripe direction and transmitting a polarized light component having a vertical vibration direction. When the wire grid type polarizing plate is used as the reflective polarizing plate 14 of the liquid crystal display device of Example 1, the stripe structure is arranged so as to be parallel to the light guide plate plane (second main surface 2c). P-polarized light contained in the light can be transmitted and S-polarized light can be reflected. Moreover, when using a wire grid type polarizing plate as the reflection type polarizing plate 14 of the liquid crystal display device of Example 1, you may form directly on the 1st main surface 2a of the light-guide plate 2, or on a transparent resin film | membrane. The formed one may be attached to the light guide plate 2.

  The transparent spacer 15 is formed of, for example, a transparent resin having the same refractive index as that of the light guide plate 2, and after the reflective polarizing plate 14 is attached, the transparent spacer 15 is adhered thereon.

  Similar to the second reflector 18, the first reflector 16 is formed, for example, by using a polymer film as a base material and forming a film having a high light reflectance such as an aluminum film on the surface thereof.

  In the liquid crystal display device according to the first embodiment, in order to add a configuration for converting the S-polarized light included in the light source light incident on the light guide plate 2 to the P-polarized light, the coupling portion and the surface light emission are added. The reflection type polarizing plate 14, the transparent spacer 15, and the first reflection plate 16 are attached to the first main surface 2a of the light guide plate 2 integrally formed with the light guide plate 2, and the quarter wavelength is applied to the second main surface 2c. It is only necessary to attach the plate 17 and the second reflecting plate 18. Therefore, for example, a configuration for converting S-polarized light into P-polarized light as compared with a method in which a light guide plate is separated into a coupling portion and a surface light-emitting portion and a reflective polarizing plate is sandwiched therebetween as in Patent Document 1 Is easy to add.

  As described above, according to the liquid crystal display device of Example 1, the S-polarized component contained in the light source light can be efficiently converted into P-polarized light, and the utilization efficiency of the light source light can be increased. Therefore, it is easy to increase the luminance or reduce the power consumption of the liquid crystal display device.

  Moreover, according to the manufacturing method of the light guide plate of Example 1, it is easy to add the structure for converting the S-polarized light contained in the light source light to the P-polarized light to the light guide plate 2, and the manufacturing efficiency of the liquid crystal display device Can be suppressed and an increase in manufacturing cost can be suppressed.

  In the first embodiment, as an example of the liquid crystal display panel 1, the IPS liquid crystal display panel 1 in which the pixel electrode 19 and the common electrode 20 are stacked as shown in FIGS. However, when the IPS liquid crystal display panel 1 is used, the liquid crystal display panel 1 is not limited to this. For example, the pixel electrode 19 and the common electrode 20 may be disposed on the same surface of the insulating layer.

  Further, the liquid crystal display panel 1 used in the liquid crystal display device according to the first embodiment is not limited to the IPS method, but, for example, a VA (Vertically Aligned) method, an ECB (Electrically Controlled Birefringence) method, or an OCB (Optically Compensated Birefringence) method. Alternatively, a liquid crystal display panel that applies an electric field in the thickness direction (z direction) to the liquid crystal layer 11 may be used.

  In the first embodiment, the liquid crystal display panel 1 in which the transmission axis 12T of the first polarizing plate 12 and the transmission axis 13T of the second polarizing plate 13 are orthogonal to each other is taken as an example. If the transmission axis 12T of one polarizing plate 12 is substantially parallel to the longitudinal direction of the liquid crystal display panel 1 (light guide plate 2), that is, the vibration direction of the light emitted from the light guide plate 2 and incident on the first polarizing plate 12. Good. Therefore, the liquid crystal display panel 1 used in the liquid crystal display device of Example 1 has, for example, the transmission axis 13T of the second polarizing plate 13 parallel to the transmission axis 12T of the first polarizing plate 12, and the liquid crystal display panel. 1 may be substantially parallel to the longitudinal direction.

  In the first embodiment, as shown in FIGS. 1 and 2, the first prism sheet 4 and the second prism sheet 5 are interposed between the light guide plate 2 and the liquid crystal display panel 1. However, the present invention is not limited to this, and one prism sheet may be disposed between the light guide plate 2 and the liquid crystal display panel 1. Further, not only the prism sheet but also a light diffusion plate or the like may be interposed between the light guide plate 2 and the liquid crystal display panel 1.

  In Example 2, an example of a more preferable manufacturing method of the light guide plate 2 used in the liquid crystal display device having the configuration described in Example 1 (the configuration illustrated in FIGS. 1 to 3) will be described.

  FIG. 16 is a schematic plan view illustrating an example of a relationship between an optical path of light source light and a portion having anisotropy of a light guide plate in the liquid crystal display device according to the first embodiment.

  In the first embodiment, as an example of a method for forming the light guide plate 2, for example, a formation method by injection molding using a mold 35 having a large number of injection ports 35 b has been described. In this method, the flow direction 36f of the transparent resin 36 in the portion that becomes the surface light emitting portion of the light guide plate 2 is set to the longitudinal direction of the light guide plate 2, and at least the surface light emitting portion is apparently isotropic. ) Is maintained in the process of propagating through the surface emitting part.

  However, in the light guide plate 2 formed by injection molding, for example, as shown in FIG. 16, a portion 2e having optical anisotropy is generated at a position corresponding to between two adjacent injection ports 35b. Further, when the number of the injection ports 35b is larger than the number of the light sources 3, for example, as shown in FIG. 16, the position of the light emission surface of the light source 3 and the injection port on the incident side surface of the light guide plate 2 correspond. It is conceivable that a deviation occurs from the position and a part of the light source light passes through the anisotropic part 2e. At this time, for example, in the optical path OP through which the P-polarized light guided to the surface light emitting section passes through the portion 2e having anisotropy, an S-polarized component is generated from the P-polarized light, and the use efficiency of the light source light is reduced accordingly. That is, in the liquid crystal display device according to the first embodiment, for example, there is a concern that the use efficiency of the light source light may be reduced due to a change in the polarization state at the coupling portion of the light guide plate 2. From the above, it is desirable that the light guide plate 2 is apparently isotropic even at the coupling portion.

  In order to make the light guide plate 2 isotropic, for example, the light guide plate 2 may be formed by a casting method so that the transparent resin does not flow during the formation. In the case of producing by injection molding, a transparent resin having zero intrinsic birefringence may be used. However, at present, it is common to form a light guide plate by an injection molding method using a transparent resin having positive intrinsic birefringence, and it is difficult to completely eliminate the anisotropic portion 2e.

  Therefore, in Example 2, it can be formed by an injection molding method using a transparent resin having positive intrinsic birefringence as in the conventional case, and the coupling portion and the surface light emitting portion can be made isotropic in appearance. An example of a method for forming the light guide plate 2 will be described.

FIGS. 17 and 18 are schematic diagrams for explaining an example of a method for producing a light guide plate of Example 2 according to the present invention and effects thereof.
FIG. 17 is a schematic diagram illustrating an example of a schematic configuration of a mold used in the light guide plate forming method according to the second embodiment of the present invention. FIG. 18 is a schematic diagram illustrating an example of a relationship between an optical path of light source light in the light guide plate of Example 2 and a portion having anisotropy of the light guide plate.

  The light guide plate 2 of Example 2 is produced by an injection molding method using a transparent resin having positive intrinsic birefringence, as in Example 1. However, the mold 35 used in the manufacturing method of the second embodiment is different from the first embodiment. For example, as shown in FIG. 17, the number of injection ports 35b is the same as the number of light sources 3 used in combination. And the position is made to correspond with the arrangement position of the light source 3.

  As described in the first embodiment, the light guide plate 2 of the second embodiment thus obtained has an anisotropic portion 2e at a position corresponding to between adjacent injection ports 35b. However, the relationship between the anisotropic portion 2e in the light guide plate 2 of Example 2 and the optical path OP of the light source light is, for example, as shown in FIG.

  The distribution of the anisotropy portion 2e as shown in FIG. 18 is easy by, for example, arranging a pair of polarizing plates above and below the light guide plate 2 and observing the birefringence of the light guide plate 2. Can know. In order to observe the birefringence of the light guide plate 2 using a pair of polarizing plates, for example, the absorption axes PLA1 and PLA2 are orthogonal to each other and the directions of the absorption axes PLA1 and PLA2 are guided. It arrange | positions so that 45 degrees may be comprised with respect to the longitudinal direction (y direction) of the optical plate 2. FIG.

  At this time, in the portion where the flow direction of the transparent resin is substantially parallel to the longitudinal direction of the light guide plate 2, the slow axis is approximately 45 degrees with respect to the absorption axes PLA1 and PLA2 of the polarizing plate. appear. On the other hand, in a portion where the flow direction of the transparent resin is substantially parallel to the absorption axes PLA1 and PLA2 of the polarizing plate and a portion where the birefringence is small, the light does not pass through, so it looks dark. As a result of the above, in the light guide plate 2 formed by the method of Example 2, the light and dark distribution as shown in FIG. 18 is observed, and it can be seen that the portion that appears bright in the joint is the injection port. Actually, the brightness of the boundary between the portion 2e having the anisotropy and the portion having no anisotropy changes continuously, but in FIG. 18, this is simplified to a discontinuous distribution, Relatively bright parts are shown in white, and relatively dark parts are shown in shaded areas.

  When such a light guide plate 2 is used and the light source 3 is arranged at a position facing the injection port at the time of injection molding, the optical path OP of the light source light is normal to the light exit surface 3a of the light source 3 as shown in FIG. In both the coupling portion and the surface light emitting portion, a portion that appears bright, that is, a portion in which the flow direction (orientation direction) of the transparent resin is substantially parallel to the longitudinal direction passes. Therefore, in the light guide plate 2 of the second embodiment, the propagation direction of the light source light and the slow axis of the light guide plate 2 are almost parallel even at the coupling portion and in the vicinity thereof, and the appearance is almost isotropic. Therefore, the liquid crystal display device using the light guide plate 2 according to the second embodiment can suppress a reduction in light source light utilization efficiency due to, for example, a change in the polarization state of P-polarized light.

  As described above, according to the liquid crystal display device having the light guide plate 2 of the second embodiment, it is possible to suppress the reduction in the light source light utilization efficiency resulting from the method of manufacturing the light guide plate 2.

  In the third embodiment, in the liquid crystal display device having the configuration described in the first embodiment (the configuration illustrated in FIGS. 1 to 3), the transparent spacer 15 and the first step are formed on the step portion of the first main surface 2A of the light guide plate 2. A simpler method for providing the reflective plate 16 will be described.

FIG. 19 is a schematic diagram for explaining an example of a manufacturing procedure of the light guide plate of Example 3 according to the present invention.
In FIG. 19, the procedure for attaching the transparent spacer 15 and the first reflector 16 to the light guide plate 2 is shown in three stages (a), (b), and (c).

  The light guide plate 2 of Example 3 is formed by the injection molding described in Example 1 or Example 2. Further, the quarter-wave plate 17 and the second reflecting plate 18 are attached to the second main surface 2c of the formed light guide plate 2 by the procedure described in the first embodiment.

  Next, for example, as shown in FIG. 19A, the reflective polarizing plate 14 is attached to the step portion of the first main surface 2 </ b> A of the light guide plate 2, and then the first reflective plate 16 is The formed transparent gel film 15 ′ is pasted. The gel film 15 ′ is an optically isotropic film having a thickness of about 1 mm, for example, and has adhesiveness on the surface. Therefore, when the gel-like film 15 ′ is attached to the light guide plate 2, the shape changes along the steps of the light guide plate 2 as shown in FIG.

  At this time, as shown in FIG. 19B, the gel film 15 ′ is formed at the base of the step of the first main surface 2 a of the light guide plate 2 (the end having the same thickness as the surface light emitting portion). When a gap 37 is generated between the end portion and the first main surface 2a of the light guide plate 2, the P-polarized light reflected by the first reflection plate 16 is on the way toward the second main surface 2c of the light guide plate 2. There is a possibility that the polarization state changes due to passing through the air layer in the gap 37. Therefore, when the gap 37 is generated between the gel-like film 15 ′ and the light guide plate 2, for example, as shown in FIG. 19C, the transparent adhesive layer 38 can be permeated to fill the gap 37. desirable. At this time, the transparent adhesive layer 38 is formed using, for example, a thermosetting resin or a photocurable resin.

  At this time, if a transparent material having a refractive index substantially equal to that of the light guide plate 2 is used as the gel film 15 ′ and the transparent adhesive layer 38, the interface between the gel film 15 ′ and the transparent adhesive layer 38 and the transparent adhesive layer 38 are used. Thus, no refraction or reflection occurs at the interface between the light guide plate 2 and the P-polarized light reflected by the first reflection plate 16 can be efficiently guided to the surface light emitting unit.

  Further, in the method for manufacturing the light guide plate 2 of Example 3, instead of using the gel film 15 ′, for example, a thermosetting resin film in an intermediate stage of the curing reaction called B-stage resin is used and pasted. May be completely cured.

  In the liquid crystal display device according to the first embodiment, in order to convert the S-polarized light contained in the light source light into the P-polarized light, as described above, the quarter-wave plate 17 whose uniaxial anisotropy is positive (Nz coefficient is 1). Is used.

However, when the quarter-wave plate 17 having an Nz coefficient of 1 is used, for example, the slow axis azimuth Θ in the light incident surface in the state of being attached to the light guide plate 2 and the retardation Rz in the normal direction If there is a deviation between the design values calculated in the procedure described in Example 1, the slow axis azimuth angle θ and the retardation R in the incident angle direction change greatly, and the S-polarized light changes to the P-polarized light. There is a problem that the conversion tends to be incomplete. Further, when the quarter-wave plate 17 having an Nz coefficient of 1 is used, for example, if there is a spread (distribution) in the incident angle ψ of S-polarized light incident on the quarter-wave plate 17, the quarter wave plate 17 is used. For S-polarized light whose angle of incidence ψ to the wave plate 17 is deviated from the design value (ψ _M ), there is a problem that conversion from S-polarized light to P-polarized light tends to be incomplete. For example, as can be seen from FIGS. 10 and 12, such a problem is caused by a delay in the incident angle direction with respect to a change in the slow axis azimuth angle Θ and the normal direction retardation Rz in the light incident surface. This occurs because the phase axis azimuth angle θ and the retardation R are rapidly changed, that is, the slow axis azimuth angle θ and the retardation R in the incident angle direction are highly dependent on the incident angle.

When a white LED is used as the light source 3, the light source light (white light) is emitted radially around the normal direction of the light exit surface 3a as shown in FIGS. 8 and 18, for example. There is a spread (distribution) in the incident angle ψ of S-polarized light incident on the one-wave plate 17. At this time, the intensity of the light emitted from the light exit surface 3a decreases rapidly as the angle formed by the exit direction and the normal direction of the light exit surface 3a increases. Therefore, the intensity of the S-polarized light having a large difference between the incident angle ψ and the design value (ψ _M ) when actually incident on the quarter-wave plate 17 is sufficiently low, so that the conversion efficiency to P-polarized light is high. Even if it is low, the contribution to the light source light utilization efficiency is considered to be small.

However, when the incident angle when the S-polarized light included in the main component of the light source light is incident on the quarter-wave plate 17 deviates from the design value (ψ _M ), the S-polarized light included in the main component is changed to the P-polarized light. Conversion efficiency is reduced. Further, from the viewpoint of improving the utilization efficiency of the light source light, the S-polarized light having a large deviation between the incident angle ψ and the design value (ψ _M ) when actually entering the quarter-wave plate 17 as described above. It is desired to use it after converting it to P-polarized light.

  As described above, in the fourth embodiment, for example, the slow axis azimuth Θ and the normal direction retardation Rz in the light incident surface of the quarter-wave plate 17 deviate from the design value, or the quarter A method will be described in which the conversion from S-polarized light to P-polarized light is almost completely realized even when the incident angle ψ of the S-polarized light incident on the first wavelength plate 17 has a wide angular distribution.

  The change rate of the slow axis azimuth angle θ and the retardation R in the incident angle direction of the quarter-wave plate 17 is determined by the three-dimensional distribution of the refractive index. Therefore, in Example 4, the conversion efficiency from S-polarized light to P-polarized light is improved by obtaining the Nz coefficient that moderates these changes and using the quarter-wave plate 17 having the Nz coefficient.

20 to 24 are schematic views for explaining a schematic configuration of a quarter-wave plate in the liquid crystal display device according to Embodiment 4 of the present invention.
FIG. 20 is a schematic diagram showing the relationship between the Nz coefficient of the quarter-wave plate and the incident angle dependency of the slow axis azimuth in the incident angle direction. FIG. 21 shows the relationship between the slow axis azimuth angle in the light incident surface when the Nz coefficient of the quarter-wave plate is 0.50 and the incident angle dependence of the slow axis azimuth angle in the incident angle direction. It is a schematic diagram which shows. FIG. 22 is a schematic diagram showing the relationship between the retardation in the normal direction of the quarter-wave plate and the incident angle dependency of the retardation in the incident angle direction. FIG. 23 shows that when the Nz coefficient of the quarter-wave plate is 0.50, the slow axis azimuth angle θ in the incident angle direction is 45 degrees, and the incident angle and the slow axis azimuth angle in the light incident surface are It is a schematic diagram which shows the relationship. FIG. 24 shows a slow axis azimuth angle in the light incident surface where the slow axis azimuth angle in the incident angle direction is 45 degrees, and a normal direction retardation where the retardation in the incident angle direction is a quarter wavelength. It is a schematic diagram which shows the relationship.

Since the general light guide plate 2 has a total reflection angle of about 45 degrees on the first main surface 2a and the second main surface 2c as described above, the S-polarized light contained in the main component of the light source light is divided into four. It is desirable that the incident angle ψ _M when entering the one wavelength plate 17 is 45 degrees or more. In a general liquid crystal display device, it is considered that the distribution of the incident angles ψ of S-polarized light incident on the quarter-wave plate 17 is in the range of 50 degrees to 70 degrees. At this time, the quarter-wave plate 17 to be used is ideal if the slow axis azimuth angle θ in the incident angle direction is 45 degrees with respect to all S-polarized light having the incident angle ψ in this range. . Therefore, the inventors of the present application show the relationship between the Nz coefficient and the incident angle dependence of the slow axis azimuth angle θ in the incident angle direction while changing the Nz coefficient by 0.05 in the range of 45 degrees ≦ ψ ≦ 75 degrees. As a result of the examination, the relationship as shown in FIG. 20 was obtained. FIG. 20 is a graph in which the horizontal axis represents the incident angle ψ (unit is degrees) and the vertical axis represents the slow axis azimuth θ (angle is degrees) in the incident angle direction.

Also, the curves F ₁₄ , F ₁₅ , F ₁₆ , F ₁₇ , F ₁₈ , F ₁₉ , and F ₂₀ in FIG. ₂₀ have Nz coefficients of 0.35, 0.40, 0.45, 0.50, 0.55, It is a curve which shows the incident angle dependence of the slow axis azimuth angle (theta) in an incident angle direction when it is set to 0.60 and 0.65.

As can be seen from FIG. 20, the incident angle dependence of the slow axis azimuth angle θ in the incident angle direction varies depending on the magnitude of the Nz coefficient. When the Nz coefficient is 0.50 or less, the slow axis is increased as the incident angle ψ increases. When the azimuth angle θ increases and the Nz coefficient is 0.55 or more, the slow axis azimuth angle θ decreases as the incident angle ψ increases. Further, as a result of investigation by the inventors of the present application, the incident angle dependence of the slow axis azimuth angle θ in the range where the incident angle ψ is 50 degrees ≦ ψ ≦ 70 degrees is the most gradual, and an ideal value (θ = 45 degrees) is smaller in the curve F ₁₇ when the Nz coefficient is 0.50. Therefore, in Example 4, the Nz coefficient of the quarter-wave plate 17 is set to 0.50.

  When the Nz coefficient of the quarter-wave plate 17 is 0.50, the relationship between the slow axis azimuth angle Θ in the light incident surface and the dependence of the slow axis azimuth angle θ in the incident angle direction on the incident angle is For example, the relationship is as shown in FIG. FIG. 21 is a graph in which the horizontal axis represents the incident angle ψ (unit: degrees) and the vertical axis represents the slow axis azimuth angle θ (unit: degrees) in the incident angle direction.

Further, curve F ₂₁ , curve F ₂₂ , curve F ₂₃ , curve F ₂₄ , and curve F ₂₅ in FIG. 21 have slow axis azimuth angles Θ of 45.6 degrees, 45.7 degrees, and 45.8 degrees, respectively, in the light incident surface. 4 is a curve showing the incident angle dependence of the slow axis azimuth angle θ in each incident direction when the angle is 46.0 degrees and 46.1 degrees.

As can be seen from FIG. 21, for example, when the incident angle ψ _M when the S-polarized light contained in the main component of the light source is incident on the quarter-wave plate 17 is set to 50 degrees, within the light incident surface. When the slow axis azimuth angle Θ is 45.6 degrees, the slow axis azimuth angle θ in the incident angle direction is 45 degrees. Further, when the incident angle ψ _M of the S-polarized light contained in the main component is set to any one of 55 degrees, 60 degrees, 65 degrees, and 70 degrees, the slow axis azimuth angle Θ in the light incident surface is When the angle is 45.7 degrees, 45.8 degrees, 46.0 degrees, and 46.1 degrees, respectively, the slow axis azimuth angle θ in the incident angle direction becomes 45 degrees.

Further, the graph of FIG. 21 corresponds to the graph of FIG. However, the range of the vertical axis in the graph of FIG. 21 is one tenth of the range in the graph of FIG. That is, the incident angle dependence of the slow axis azimuth angle θ in the incident angle direction indicated by the curves F ₂₁ , F ₂₂ , F ₂₃ , F ₂₄ , and F ₂₅ is the curve shown in FIG. It is much smaller than the incident angle dependence shown by F ₁ , curve F ₂ , curve F ₃ , curve F ₄ , and curve F ₅ .

  Further, the inventors of the present application based on the above result and Expression 17, when the slow axis azimuth angle Θ in the light incident surface is 45.6 degrees, 45.7 degrees, 45.8 degrees, 46.0 degrees, and 46.1 degrees When the relationship between the retardation Rz in the normal direction and the incident angle dependence of the retardation R in the incident angle direction was calculated, for example, a result as shown in FIG. 22 was obtained. FIG. 22 is a graph of the incident angle ψ (unit: degrees) on the horizontal axis and the retardation R (unit: nm) on the incident angle direction on the vertical axis.

In addition, the curve F ₂₆ , the curve F ₂₇ , the curve F ₂₈ , the curve F ₂₉ , and the curve F ₃₀ in FIG. 22 are respectively represented by the slow axis azimuth angle Θ and the normal direction retardation Rz in the light incident surface. When the combination (Θ, Rz) is (45.6 degrees, 137.47 nm), (45.7 degrees, 137.46 nm), (45.8 degrees, 137.44 nm), (46.0 degrees, 137.42 nm), and (46.1 degrees, 137.41 nm) It is a curve which shows the incident angle dependence of the retardation R in the incident angle direction. Further, the curve F ₂₆ , the curve F ₂₇ , the curve F ₂₈ , the curve F ₂₉ , and the curve F ₃₀ in FIG. 22 are retardation R in the incident angle direction with respect to light having a wavelength of 550 nm at which the visibility is almost maximum among visible wavelengths. The incident angle dependence of is shown.

As can be seen from FIG. 22, for example, when the Nz coefficient of the quarter-wave plate 17 is set to 0.50 and the incident angle ψ _M of S-polarized light included in the main component of the light source light is set to 50 degrees, the light incident surface The retardation R in the incident angle direction becomes a quarter wavelength (137.5 nm) when the slow axis azimuth angle Θ and the retardation Rz in the normal direction are 45.6 degrees and 137.47 nm, respectively. In addition, when the incident angle ψ _M of the S-polarized light contained in the main component is set to 55 degrees, 60 degrees, 65 degrees, or 70 degrees, the slow axis azimuth angle Θ and the ray in the light incident surface When the combinations (Θ, Rz) with the direction retardation Rz are (45.7 degrees, 137.46 nm), (45.8 degrees, 137.44 nm), (46.0 degrees, 137.42 nm), and (46.1 degrees, 137.41 nm), respectively. The retardation R in the incident angle direction becomes a quarter wavelength (137.5 nm).

  Also, for an intermediate incident angle ψ other than the above angle, the slow axis azimuth θ in the light incident surface is calculated with an Nz coefficient of 0.50 and a slow axis azimuth θ of 45 ° in the incident angle direction. Then, for example, a result as shown in FIG. 23 is obtained. FIG. 23 is a graph in which the horizontal axis represents the incident angle ψ (unit: degrees), and the vertical axis represents the slow axis azimuth angle Θ (unit: degrees) in the light incident surface.

As can be seen from FIG. 23, the curve F ₃₁ indicating the relationship between the incident angle ψ and the slow axis azimuth Θ in the light incident plane where the slow axis azimuth θ in the incident angle direction is 45 degrees is approximately It becomes a straight line. At this time, the relationship between the incident angle ψ and the slow axis azimuth angle Θ within the light incident surface is approximated by the following Equation 19.

    Θ = 0.027ψ + 44.215 (Equation 19)

Therefore, if the incident angle ψ _{M of the} S-polarized light contained in the main component of the light source light to the quarter-wave plate 17 is determined, the slow axis direction in the incident angle direction with respect to the S-polarized light is obtained from FIG. The slow axis azimuth Θ in the light incident plane required for the quarter-wave plate 17 in order to set the angle θ to 45 degrees is obtained.

  Furthermore, the slow axis azimuth θ in the light incident surface where the slow axis azimuth θ in the incident angle direction is 45 degrees and the normal direction in which the retardation R in the incident angle direction is a quarter wavelength. The retardation Rz has a relationship as shown in FIG. 24, for example. FIG. 24 is a graph of the slow axis azimuth angle Θ (unit: degrees) in the light incident plane and the vertical axis retardation Rz (unit: nm) in the normal direction.

Also, the point P ₆ , the point P ₇ , the point P ₈ , the point P ₉ , and the point P ₁₀ shown in FIG. 24 have an incident angle ψ of 50 degrees, 55 degrees, 60 degrees, 65 degrees in FIG. This is a point showing the relationship between the slow axis azimuth angle Θ in the light incident plane and the normal direction retardation Rz at 70 and 70 degrees. A curve F ₃₂ shown in FIG. 24 is a regression curve obtained from the values of point P ₆ , point P ₇ , point P ₈ , point P ₉ , and point P ₁₀ .

As can be seen from FIG. 24, when the Nz coefficient is 0.50, the slow axis azimuth θ in the light incident surface where the slow axis azimuth θ in the incident angle direction becomes 45 degrees, and the retardation R in the incident angle direction. The curve F ₃₂ showing the relationship with the retardation Rz in the normal direction where becomes a quarter wavelength is substantially a straight line. At this time, the relationship between the slow axis azimuth angle Θ in the light incident surface and the normal-direction retardation Rz is approximated by the following Equation 20.

    Rz = −0.119Θ + 142.87 (Equation 20)

As in the fourth embodiment, when the Nz coefficient is set to 0.5, when the incident angle ψ _M of the S-polarized light included in the main component is set to a certain angle, the slow axis azimuth θ in the incident angle direction with respect to the S-polarized light is set to 45. In order to obtain the degree, the slow axis azimuth angle Θ in the light incident surface required for the quarter-wave plate 17 can be obtained from FIG. At this time, the slow axis azimuth θ in the light incident surface where the slow axis azimuth θ in the incident angle direction is 45 degrees and the normal direction where the retardation R in the incident angle direction is a quarter wavelength. There is a relationship like the curve F ₃₂ (Equation 20) shown in FIG. Therefore, if the incident angle ψ _M is determined and the slow axis azimuth angle Θ in the light incident surface required for the quarter-wave plate 17 is obtained from FIG. A retardation Rz in the normal direction required for the half-wave plate 17 is also obtained.

Further, as can be seen from FIGS. 21 and 23, the quarter-wave plate 17 of Example 4 has a slow axis azimuth angle in the light incident surface in the range of the incident angle ψ of 50 degrees ≦ ψ ≦ 70 degrees. The dependence of Θ on the incident angle is much smaller than that of the quarter-wave plate 17 of the first embodiment. In addition, as can be seen from FIGS. 22 and 24, the quarter-wave plate 17 of Example 4 is dependent on the incident angle dependency of the retardation Rz in the normal direction when the incident angle ψ is in the range of 50 degrees ≦ ψ ≦ 70 degrees. Also, it is much smaller than the quarter-wave plate 17 of the first embodiment. Wide which the value of the slow axis azimuthal angle Θ and the normal direction of the retardation Rz of light entering plane, is set to an optimum value for a certain incident angle [psi _M, including its angle of incidence [psi _M It means that almost complete conversion from S-polarized light to P-polarized light is possible in the angular range.

In other words, in the liquid crystal display device of Example 4, the inclination angle phi ₂ of the inclination angle phi ₁ and the reflective polarizer 14 side 2b of FIG. 5, so as to satisfy 20 degrees ≦ φ ₁ + 2φ ₂ ≦ 40 ° When the values of the slow axis azimuth angle Θ and the normal direction retardation Rz in the light incident surface of the quarter-wave plate 17 are incident angles ψ _M = {90− (φ ₁ + 2φ ₂ )} If the optimum value is set, S-polarized light having an incident angle ψ in a range of 50 ° ≦ ψ ≦ 70 ° can be converted into almost perfect P-polarized light. For example, in the liquid crystal display device of Example 4, when the incident angle ψ _{M is set} to 60 degrees (that is, φ ₁ + 2φ ₂ = 30 degrees), the Nz coefficient of the quarter-wave plate 17 is within the light incident surface. Is set to 0.5, 45.8 degrees, and 137.4 nm, respectively, the incident angle ψ to the quarter-wave plate 17 is 50 degrees ≦ ψ ≦ S-polarized light in the range of 70 degrees can be converted into almost perfect P-polarized light.

As described above, according to the liquid crystal display device of Example 4, the retardation of the slow axis azimuth Θ and the normal direction in the light incident surface of the quarter-wave plate 17 attached to the light guide plate 2 is obtained. Even when Rz deviates from the design value, it is possible to prevent a decrease in the use efficiency of the light source light due to a decrease in conversion efficiency from S-polarized light to P-polarized light. Further, according to the liquid crystal display device of Example 4, when the distribution occurs in the incident angle ψ of the S-polarized light incident on the quarter-wave plate 17, or the incident angle of the S-polarized light included in the main component of the light source light Even when deviating from the design value (ψ _M ), it is possible to prevent a decrease in the use efficiency of the light source light due to a decrease in conversion efficiency from S-polarized light to P-polarized light. Therefore, the liquid crystal display device according to the fourth embodiment can increase the light source light utilization efficiency as compared with the liquid crystal display device according to the first embodiment.

Further, as described above, the Nz coefficient of the quarter-wave plate 17 is based on the range of the incident angle ψ of S-polarized light incident on the quarter-wave plate 17 in the incident angle direction within the range. It is desirable to make the dependence of the slow axis azimuth angle θ on the incident angle as small as possible. However, as can be seen from FIG. 20, depending on the range of the incident angle ψ of the S-polarized light incident on the quarter-wave plate 17, for example, even if the Nz coefficient is other than 0.5, the slow axis azimuth in the incident angle direction. Incident angle dependency of θ is reduced. Therefore, the Nz coefficient of the quarter-wave plate 17 in the liquid crystal display device of Example 4 is set to the incident angle ψ _M = {90− (φ ₁ + 2φ ₂ )} of S-polarized light included in the main component of the light source light. Of course, it can be appropriately changed according to the range of the incident angle ψ of the S-polarized light incident on the quarter-wave plate 17.

FIG. 25 is a schematic diagram showing the relationship between the slow axis azimuth angle of light incident on the quarter-wave plate and the light transmittance of the first polarizing plate.
In FIG. 25, the horizontal axis represents the slow axis azimuth angle θ in the incident angle direction, and the vertical axis represents the relative value of the light transmittance TP in the first polarizing plate 12.

  When the vibration direction of light is converted using the quarter-wave plate 17, when the slow axis azimuth angle θ in the incident angle direction is 45 degrees, the vibration direction of S-polarized light is rotated by 90 degrees to become P-polarized light. Converted. That is, when the slow axis azimuth angle θ deviates from 45 degrees, the oscillation direction of the S-polarized light does not rotate by 90 degrees, and the S-polarized component remains in the light emitted from the quarter-wave plate 17. At this time, if the slow axis azimuth with respect to the vibration direction of a certain polarized light is θ ′, the vibration direction of the light passing through the quarter-wave plate 17 is {90−2 (45−θ ′)} degrees. Therefore, the light emitted from the light guide plate 2 and incident on the first polarizing plate 12 includes a component having such a vibration direction.

Further, if the first polarizing plate 12 is a complete polarizing plate, the first polarizing plate 12 can completely transmit this light if its transmission axis is parallel to the vibration direction of the light that has passed through the quarter-wave plate 17. However, as described above, when the transmission axis and the vibration direction of light are inclined by the angle β, the transmittance is reduced according to cos ² β.

  Therefore, in the liquid crystal display device of Example 4, the relationship between the slow axis azimuth angle θ with respect to the light incident on the quarter-wave plate 17 and the relative value of the transmittance TP of the first polarizing plate 12 is examined. A result as shown in FIG. 25 is obtained. In FIG. 25, the transmission axis of the first polarizing plate 12 is set so that the transmittance when the light whose slow axis azimuth angle θ is 45 degrees passes through the first polarizing plate 12 is maximized. It is a case relationship.

  As can be seen from FIG. 25, when the slow axis azimuth angle θ for the light incident on the quarter-wave plate 17 deviates from 45 degrees, the transmittance TP of the first polarizing plate 12 tends to decrease rapidly. . However, the transmittance TP of the first polarizing plate 12 is saturated in the range where the slow axis azimuth angle θ with respect to the light incident on the quarter-wave plate 17 is 40 degrees ≦ θ ≦ 50 degrees, and High transmittance of 95% or more.

  Therefore, in the liquid crystal display device of Example 4, the slow axis azimuth angle θ of the quarter-wave plate 17 with respect to the vibration direction of the S-polarized light included in the main component of the light source light is in the range of 40 degrees ≦ θ ≦ 50 degrees. If it exists, it can be said that it can permeate | transmit the 1st polarizing plate 12 with a sufficiently high transmittance | permeability, and can improve the utilization efficiency of light source light.

In the graph shown in FIG. 20, the slow axis azimuth θ in the incident angle direction is 40 degrees ≦ θ ≦ 50 degrees in most of the range where the incident angle ψ is 50 degrees ≦ ψ ≦ 70 degrees. The curves that fall within the range are the curves F ₁₆ , F ₁₇ , F ₁₈ , and F ₁₉ , and the range of the Nz coefficient corresponding to these curves is 0.45 or more and 0.60 or less. Therefore, in the liquid crystal display device of Example 4, the utilization efficiency of the light source light can be increased by setting the Nz coefficient of the quarter-wave plate 17 to any of 0.45 or more and 0.60 or less.

  In the fourth embodiment, the Nz coefficient of the quarter-wave plate 17 is set to 0.5. However, referring to FIG. 20, the slow axis azimuth θ in the incident angle direction is larger than when the Nz coefficient is set to 0.50. It is expected that there will be a more desirable Nz coefficient value in which the dependence on the incident angle becomes more gradual and the difference from the ideal value (45 degrees) is even smaller. Therefore, for example, the incidence angle dependence of the slow axis azimuth angle θ in the incident angle direction in the range of the Nz coefficient from 0.50 to 0.55 is examined in detail, and a more ideal Nz coefficient value is obtained. It is considered that the incident angle dependency of the slow axis azimuth angle Θ and the normal direction retardation Rz in the light incident surface of the single wavelength plate 17 can be reduced, and the utilization efficiency of the light source light can be further increased.

  In the liquid crystal display device of the present invention, as described above, a white light emitting element such as a white LED is used as the light source 3. Therefore, the light source light has a wavelength distribution over the entire visible wavelength range.

  The retardation of the quarter-wave plate 17 necessary for converting S-polarized light into circularly-polarized light or converting circularly-polarized light into P-polarized light is a quarter wavelength of the wavelength of S-polarized light, and It increases in proportion to the wavelength of S-polarized light. However, the retardation of an optically anisotropic medium such as the quarter-wave plate 17 generally has the property of decreasing with wavelength. Therefore, if the conversion from the S-polarized light to the P-polarized light is performed only by the quarter-wave plate 17 having the configuration described in the first and fourth embodiments, a wavelength range in which the S-polarized light can be completely converted to the P-polarized light is obtained. It is very narrow and it is difficult to increase the utilization efficiency of the light source.

  In the fifth embodiment, an example of a method for increasing the conversion efficiency from S-polarized light to P-polarized light over the entire wavelength range of the light source light will be described. Specifically, a broadband quarter-wave plate as described below is used as a quarter-wave plate for converting S-polarized light to P-polarized light.

  FIG. 26 is a schematic cross-sectional side view illustrating an example of a schematic configuration around the coupling portion of the light guide plate in the liquid crystal display device according to the fifth embodiment of the present invention.

  In the liquid crystal display device of Example 5, as an optical component for converting S-polarized light contained in light source light incident on the light guide plate 2 to P-polarized light, for example, as shown in FIG. A broadband quarter-wave plate 40 composed of the quarter-wave plate 17 is used. At this time, the broadband quarter-wave plate 40 is laminated in the order of the half-wave plate 39 and the quarter-wave plate 17 in this order from the side close to the second main surface 2 c of the light guide plate 2. Deploy.

  Further, the liquid crystal display device of the fifth embodiment is different from the liquid crystal display device of the first embodiment in that a broadband quarter wavelength is provided between the second main surface 2c of the light guide plate 2 and the second reflector 18. It is only the point which has arrange | positioned the board 40. FIG. Therefore, the description regarding the other structure in the liquid crystal display device of Example 5 is abbreviate | omitted.

  The setting method of the slow axis of the half-wave plate 39 and the quarter-wave plate 17 in the liquid crystal display device of Embodiment 5 can be obtained from the operating principle of the broadband quarter-wave plate 40. Therefore, first, the operating principle of the broadband quarter-wave plate 40 will be described below using Stokes parameters (S1, S2, S3) and Poincare sphere display.

  The Stokes parameters and the Poincare sphere display are described in detail in Non-Patent Document 3 and Non-Patent Document 4, for example. Therefore, in the following description, the description regarding these is kept to a minimum.

27 to 32 are schematic diagrams for explaining the operating principle of the broadband quarter-wave plate.
FIG. 27 is a schematic diagram showing the relationship between the Stokes parameter, the Poincare sphere, and the polarization state. FIG. 28 is a schematic diagram showing an example of a change in the polarization state of linearly polarized light having a wavelength of 550 nm according to Poincare sphere display. FIG. 29 is a schematic diagram showing an example of a change in the polarization state of linearly polarized light having a wavelength longer than 550 nm by Poincare sphere display. FIG. 30 is a schematic diagram showing an example of a change in the polarization state of linearly polarized light having a wavelength shorter than 550 nm by Poincare sphere display. FIG. 31 is a schematic diagram illustrating an example of a change in the polarization state of linearly polarized light having a wavelength of 550 nm according to Poincare sphere display. FIG. 32 is a schematic diagram showing another example of a change in the polarization state of linearly polarized light having a wavelength of 550 nm according to the Poincare sphere display.

  As shown in FIG. 27, when considering a three-dimensional orthogonal coordinate system having Stokes parameters (S1, S2, S3) as axes, a Poincare sphere 41 is represented by a sphere centered at the origin O of the three-dimensional orthogonal coordinate system. The In the following description, the Poincare sphere 41 is regarded as the earth, the intersection of the S3 axis and the Poincare sphere 41 is called the North Pole and the South Pole, and the intersection of the plane including the S1 axis and the S2 axis and the Poincare sphere 41 is called the equator. To.

  Each point on the surface of the Poincare sphere 41 corresponds to the polarization state of light, the north and south poles represent circularly polarized light, and each point on the equator represents linearly polarized light. The other points on the surface of the Poincare sphere 41 represent elliptically polarized light.

  Further, S1, S2, and S3 are Stokes parameters in the polarization state, respectively, and are values normalized by the Stokes parameter S0 representing the intensity.

  In the Poincare sphere display, the operation of converting linearly polarized light performed by the quarter-wave plate 17 into circularly polarized light corresponds to moving the point on the equator of the Poincare sphere 41 to the north pole or the south pole. That is, the operation of the broadband quarter-wave plate 40 in the Poincare sphere display is such that the point indicating the polarization state of linearly polarized light (S-polarized light) of each wavelength in the visible wavelength region on the equator is in the vicinity of the North Pole or the South Pole. This is equivalent to moving more concentrated.

  The broadband quarter-wave plate 40 is usually designed with reference to light having a wavelength of 550 nm that maximizes visibility. At this time, the change of the polarization state in the process in which the linearly polarized light having the wavelength of 550 nm passes through the broadband quarter-wave plate 40 designed with reference to the light having the wavelength of 550 nm can be obtained by using, for example, FIG. It is expressed by changes as shown in

  If the point PS representing the polarization state of the light incident on the broadband quarter-wave plate 40 (half-wave plate 39) is the intersection of the S1 axis and the equator, the point PS is a half wavelength. In the process of passing through the plate 39, it rotates by a half around the axis 42 corresponding to the slow axis of the half-wave plate 39 and moves to the intersection of the S2 axis and the equator. If the point PS representing the polarization state of the light emitted from the half-wave plate 39 and incident on the quarter-wave plate 17 is at the intersection of the S2 axis and the equator, the point PS is In the process of passing through the quarter-wave plate 17, it makes a quarter turn around the axis corresponding to the slow axis of the quarter-wave plate 17 (S1 axis) and moves to the North Pole. As described above, when linearly polarized light having a wavelength of 550 nm is incident on the broadband quarter-wave plate 40 designed based on light having a wavelength of 500 nm, the linearly polarized light is converted into complete circularly polarized light and is converted into the quarterly polarized light. From one wavelength plate 40.

Note that the azimuth angle θ _HW ′ of the axis 42 corresponding to the slow axis of the half-wave plate 39 in the Poincare sphere display and the slow axis azimuth angle θ _HW in the incident angle direction of the actual half-wave plate 39 And the azimuth angle θ _QW ′ of the axis 43 corresponding to the slow axis of the quarter wave plate 17 in the Poincare sphere display and the slow axis azimuth in the incident angle direction of the actual quarter wave plate 17 The relationship with the angle θ _QW will be described later.

  In addition, when linearly polarized light having a wavelength longer than 550 nm is incident on the broadband quarter-wave plate 40 designed on the basis of light having a wavelength of 550 nm, the linearly polarized light passes through the broadband quarter-wave plate 40. When the Poincare sphere display is used, the change in the polarization state during the process is represented by a change as shown in FIG. 29, for example.

  The retardation of the half-wave plate 39 and the quarter-wave plate 17 monotonously decreases with the wavelength in the visible wavelength region. Therefore, when the wavelength of light incident on the broadband quarter-wave plate 40 (half-wave plate 39) is longer than 550 nm, the point PS representing the polarization state is at the intersection of the S1 axis and the equator. Then, at the point PS, in the process of passing through the half-wave plate 39, the rotation around the axis 42 corresponding to the slow axis of the half-wave plate 39 is less than or equal to one-half rotation, and the northern hemisphere ( Move to another position on the north pole from the equator. Further, if the point PS representing the polarization state of the light emitted from the half-wave plate 39 and entering the quarter-wave plate 17 is in the northern hemisphere, the point PS is the quarter-wave plate 17. In the process of passing through, the rotation around the axis (S1 axis) corresponding to the slow axis of the quarter-wave plate 17 becomes equal to or less than a quarter rotation and moves to the vicinity of the North Pole. Thus, when linearly polarized light having a wavelength longer than 550 nm is incident on the broadband quarter-wave plate 40 designed based on light having a wavelength of 550 nm, the linearly polarized light is converted into elliptically polarized light that is close to circularly polarized light. Then, the light is emitted from the broadband quarter-wave plate 40.

  In addition, when linearly polarized light having a wavelength shorter than 550 nm is incident on the broadband quarter-wave plate 40 designed on the basis of light having a wavelength of 550 nm, the linearly polarized light passes through the broadband quarter-wave plate 40. When the Poincare sphere display is used, the change in the polarization state during the process is represented by a change as shown in FIG. 30, for example.

  The retardation of the half-wave plate 39 and the quarter-wave plate 17 monotonously decreases with the wavelength in the visible wavelength region. Therefore, when the wavelength of light incident on the broadband quarter-wave plate 40 (half-wave plate 39) is shorter than 550 nm, the point PS representing the polarization state is at the intersection of the S1 axis and the equator. Then, at the point PS, in the process of passing through the half-wave plate 39, the rotation about the axis 42 corresponding to the slow axis of the half-wave plate 39 becomes more than half, and the southern hemisphere ( Move to another position on the south pole from the equator. Further, if the point PS representing the polarization state of the light emitted from the half-wave plate 39 and entering the quarter-wave plate 17 is in the southern hemisphere, the point PS is the quarter-wave plate 17. In the process of passing through, the rotation around the axis (S1 axis) corresponding to the slow axis of the quarter-wave plate 17 becomes more than a quarter rotation, and moves to the vicinity of the North Pole. Thus, even when linearly polarized light having a wavelength shorter than 550 nm is incident on the broadband quarter wavelength plate 40 designed based on light having a wavelength of 550 nm, the linearly polarized light becomes elliptically polarized light that is close to circularly polarized light. It is converted and emitted from the broadband quarter-wave plate 40.

  As described above, the broadband quarter-wave plate 40 rotates the polarization of the half-wave plate 39 and the quarter-wave plate 17 having the same tendency of retardation wavelength dependency on the surface of the Poincare sphere 41. By laminating with an angular relationship such that the directions are approximately opposite to each other, the wavelength dependence of both retardations is offset, and the wavelength range in which linearly polarized light is converted into circularly polarized light is broadened.

  Although not described in detail, the light that has been converted to circularly polarized light or elliptically polarized light that is close to circularly polarized light by the broadband quarter-wave plate 40 is reflected by the second reflector 18, and again the broadband quarter-wave plate. When passing through the wave plate 40, rotation about an axis corresponding to the slow axis of the quarter wave plate 17 (S1 axis) and an axis 42 corresponding to the slow axis of the half wave plate 39, respectively. Is converted into linearly polarized light having a vibration direction orthogonal to the vibration direction when first incident on the broadband quarter-wave plate 40.

Now, a method of setting the slow axis azimuth angle in the normal direction of the half-wave plate 39 and the quarter-wave plate 17 in the broadband quarter-wave plate 40 that performs the above-described operation will be described with reference to FIG. Although more guided, for the sake of clarity, this will be described with reference to FIG. 31 projected onto the S1-S2 plane. At this time, the Poincare sphere 41 is represented by a circle, the center of which is the North Pole or the South Pole, and the circumference is the equator. In FIG. 31, the polarization state conversion is represented as a movement that moves counterclockwise in the northern hemisphere of the Poincare sphere 41 and reaches the north pole. At this time, if the azimuth angle θ _HW ′ of the axis 42 corresponding to the slow axis of the half-wave plate 39 is defined as a counterclockwise angle with the S1 axis being 0 degree, the value is 150 degrees. At this time, if the azimuth angle θ _QW ′ of the axis 43 corresponding to the slow axis of the quarter-wave plate 17 is defined as a counterclockwise angle with the S1 axis being 0 degree, the value is 0 degree. Become.

  In addition to the operation of the broadband quarter-wave plate 40, for example, as shown in FIG. 32, the northern hemisphere of the Poincare sphere 41 is moved clockwise to reach the North Pole (FIG. 32). (Movement of (a)), movement of the Poincare sphere moving in the counterclockwise direction to reach the South Pole (movement of (b) in FIG. 32), and movement of the Poincare sphere in the clockwise direction to reach the South Pole. (Movement (c) in FIG. 32).

When the operation of the broadband quarter-wave plate 40 moves as shown in FIG. 32A, the azimuth angle θ _HW ′ of the axis 42 corresponding to the slow axis of the half-wave plate 39 is 315. The azimuth angle θ _QW ′ of the axis 43 corresponding to the slow axis of the quarter-wave plate 17 becomes 90 degrees. When the operation of the broadband quarter-wave plate 40 moves as shown in FIG. 32B, the azimuth angle θ _HW ′ of the axis 42 corresponding to the slow axis of the half-wave plate 39 is obtained. Becomes 45 degrees, and the azimuth angle θ _QW ′ of the axis 43 corresponding to the slow axis of the quarter-wave plate 17 becomes 90 degrees. When the operation of the broadband quarter-wave plate 40 moves as shown in FIG. _32C, the azimuth angle θ _HW ′ of the axis 42 corresponding to the slow axis of the half-wave plate 39 is obtained. Becomes 135 degrees, and the azimuth angle θ _QW ′ of the axis 43 corresponding to the slow axis of the quarter-wave plate 17 becomes 0 degrees.

From these facts, the slow axis azimuth angles in the incident angle directions of the half-wave plate 39 and the quarter-wave plate 17 are θ _HW degrees and θ _QW degrees, respectively, and the light guide plate as described in the first embodiment. 2 defined as a counterclockwise angle in which the transverse direction (x direction) is 0 degree, the slow axis azimuth θ _HW degree of the half-wave plate 39 and the slow axis of the quarter wave plate 17 The relationship with the azimuth angle θ _QW degree is expressed by the following formula 21 from FIGS. 31 and 32A to 32C.

2θ _HW = ± 45 + θ _QW (Formula 21)

Note that the azimuth angle θ _HW ′ and azimuth angle θ _QW ′ in FIGS. 31 and 32A to _32C are respectively the slow axis azimuth angle θ _HW and the slow axis azimuth angle θ _QW , θ _{HW '= 2θ HW, θ QW} ' are in a relationship of = 2θ _QW. The azimuth angle has such a relationship because the Poincare sphere display includes an azimuth range that is half of real space. In other words, the Poincare sphere display is intended to indicate the polarization state and its conversion, but there is no distinction between the polarization state (vibration state of the electric vector) and the slow axis, so half the azimuth angle in real space. If there is a range, the polarization state and its conversion can be expressed. Therefore, the azimuth angle in the Poincare sphere display is twice the azimuth angle in real space as described above.

The combination of the slow axis azimuth angle θ _{HW in} the incident angle direction of the half-wave plate 39 and the slow axis azimuth angle θ _{QW in} the incident angle direction of the quarter wave plate 17 satisfying Equation 21 is Although there are many, the degree of concentration of light of each wavelength in the North Pole varies depending on the combination. When the half-wave plate 39 and the quarter-wave plate 17 made of the same material are used, the slow axis azimuth θ _HW in the incident angle direction of the half-wave plate 39 is set to 15 degrees, When minus is selected from the double sign (±) and the slow axis azimuth θ _QW in the incident angle direction of the quarter-wave plate 17 is set to 75 degrees, the degree of concentration is the best, and the visible wavelength A polarization state close to circular polarization is realized in the entire region. When the half-wave plate 39 and the quarter-wave plate 17 are made of the same material, the retardation wavelength dispersion is also the same, so that the Poincare sphere 41 is converted by polarization conversion by the half-wave plate 39 and the quarter-wave plate 17. By making the trajectories drawn on the surface of the lens have substantially the same length, the chromatic dispersion of both is canceled. That is, when the half-wave plate 39 and the quarter-wave plate 17 are made of the same material, the combination of the slow axis azimuth angles (θ _HW , θ _QW ) in each incident direction is set to the above values (15 degrees, 75 Degree), the trajectories of both become substantially the same length, and a polarization state close to circular polarization is realized in the entire visible wavelength range.

By the way, in the liquid crystal display device of Example 5, the incident angle ψ when the function of the broadband quarter-wave plate 40 is incident on the half-wave plate 39 is, for example, 50 degrees ≦ ψ ≦ 70 degrees. Must be realized for S-polarized light in the range That is, in the case where the S-polarized light of the light source light is converted into the P-polarized light using the broadband quarter-wave plate 40 as in the liquid crystal display device of Example 5, the S incident on the broadband quarter-wave plate 40 is used. Based on the distribution of the incident angle ψ of polarized light, the incident angle dependence of the slow axis azimuth angles θ _HW and θ _{QW in} the incident angle direction for each of the half-wave plate 39 and the quarter-wave plate 17 is In addition to selecting a calm Nz coefficient, it is necessary to determine the slow axis azimuth angles Θ _HW , Θ _QW and normal direction retardations Rz _HW , Rz _QW in the light incident plane that are optimum for the Nz coefficient.

FIGS. 33 to 42 show an example of a method of setting retardation in the slow axis azimuth and normal direction within the light incident surface of the half-wave plate and quarter-wave plate in the liquid crystal display device of the fifth embodiment. It is a schematic diagram for demonstrating.
FIG. 33 is a schematic diagram showing the relationship between the Nz coefficient of the half-wave plate and the incident angle dependence of the slow axis azimuth in the incident angle direction. FIG. 34 is a schematic diagram showing the relationship between the Nz coefficient of the quarter-wave plate and the incident angle dependence of the slow axis azimuth in the incident angle direction. FIG. 35 shows the relationship between the slow axis azimuth angle in the light incident surface when the Nz coefficient of the half-wave plate is 0.25, and the incident angle dependence of the slow axis azimuth angle in the incident angle direction. It is a schematic diagram. FIG. 36 is a schematic diagram showing the relationship between the retardation in the normal direction of the half-wave plate and the incident angle dependency of the retardation in the incident angle direction. FIG. 37 is a schematic diagram showing the relationship between the incident angle and the slow axis azimuth angle in the light incident surface where the slow axis azimuth angle in the incident angle direction of the half-wave plate is 15 degrees. FIG. 38 shows the retardation of the slow axis azimuth in the light incident surface where the slow axis azimuth in the incident angle direction of the half-wave plate is 15 degrees and the retardation in the incident angle direction becomes a half wavelength. It is a schematic diagram which shows the relationship with the retardation of a normal line direction. FIG. 39 shows the relationship between the slow axis azimuth angle in the light incident surface when the Nz coefficient of the quarter-wave plate is 0.80 and the incident angle dependency of the slow axis azimuth angle in the incident angle direction. It is a schematic diagram shown. FIG. 40 is a schematic diagram showing the relationship between the retardation in the normal direction of the quarter-wave plate and the incident angle dependency of the retardation in the incident angle direction. FIG. 41 is a schematic diagram showing the relationship between the incident angle and the slow axis azimuth angle in the light incident surface where the slow axis azimuth angle in the incident angle direction of the quarter-wave plate is 75 degrees. FIG. 42 shows the slow axis azimuth in the light incident surface where the slow axis azimuth in the incident angle direction of the quarter-wave plate is 75 degrees and the retardation in the incident angle direction is a quarter wavelength. It is a schematic diagram which shows the relationship with the retardation of the normal line direction which becomes.

First, a method for optimizing the Nz coefficient of the half-wave plate 39 will be described. As described above, the incident angle ψ of the light source light (S-polarized light) incident on the half-wave plate 39 is considered to be in the range of 50 degrees ≦ ψ ≦ 70 degrees. Further, the slow axis azimuth angle θ _{HW in} the incident angle direction of the half-wave plate 39 is ideally 15 degrees as described above. For this reason, the inventors of the present application changed the Nz coefficient by 0.05 in the range of 45 ° ≦ ψ ≦ 75 °, and the relationship between the Nz coefficient and the incident angle dependency of the slow axis azimuth θ _{HW in} the incident angle direction. As a result, a result as shown in FIG. 33 was obtained. FIG. 33 is a graph in which the horizontal axis represents the incident angle ψ (unit is degrees), and the vertical axis represents the slow axis azimuth θ _HW (unit is degrees) of the half-wave plate 39 in the incident angle direction.

33, the curve F ₃₃ , the curve F ₃₄ , the curve F ₃₅ , the curve F ₃₆ , the curve F ₃₇ , the curve F ₃₈ , and the curve F ₃₉ have Nz coefficients of 0.10, 0.15, 0.20, 0.25, 0.30, 6 is a curve showing the dependence of the slow axis azimuth θ _{HW on} the incident angle direction of the half-wave plate 39 on the incident angle when 0.35 and 0.40 are set.

As can be seen from FIG. 33, the incident angle dependence of the slow axis azimuth angle θ _{HW in} the incident angle direction of the half-wave plate 39 varies depending on the Nz coefficient, and when the Nz coefficient is 0.20, 0.25, 0.30, S The maximum point is shown within the range of the incident angle ψ of polarized light (50 degrees ≦ ψ ≦ 70 degrees), and the change of the slow axis azimuth angle θ _{HW in} the range becomes gentle. In particular, when the Nz coefficient is set to 0.25, the local maximum point is located approximately at the center in the range of 50 degrees ≦ ψ ≦ 70 degrees, and the variation amount of the slow axis azimuth angle θ _{HW in} the range is the smallest. Therefore, in Example 5, the Nz coefficient of the half-wave plate is set to 0.25.

Next, a method for optimizing the Nz coefficient of the quarter wave plate 17 will be described. Although the light incident on the quarter-wave plate 17 is linearly polarized light converted by the half-wave plate 39, the incident angle ψ is considered to be in the range of 50 degrees ≦ ψ ≦ 70 degrees. . Further, the slow axis azimuth angle θ _QW of the quarter-wave plate 17 is ideally 75 degrees as described above. For this reason, the inventors of the present application changed the Nz coefficient by 0.05 in the range of 45 degrees ≦ ψ ≦ 75 degrees, and the relationship between the Nz coefficient and the incident angle dependence of the slow axis azimuth angle θ _{QW in} the incident angle direction. As a result, a result as shown in FIG. 34 was obtained. FIG. 34 is a graph in which the horizontal axis represents the incident angle ψ (unit: degrees), and the vertical axis represents the slow axis azimuth θ _QW (unit: degrees) in the incident angle direction of the quarter-wave plate 17.

Also, the curves F ₄₀ , F ₄₁ , F ₄₂ , F ₄₃ , F ₄₄ , F ₄₅ , F ₄₆ , and F ₄₇ of FIG. 34 have Nz coefficients of 0.55, 0.60, 0.65, 6 is a curve showing the dependence of the slow axis azimuth θ _{QW on} the incident angle direction of the quarter-wave plate 17 on the incident angle when 0.70, 0.75, 0.80, 0.85, and 0.90 are set.

As can be seen from FIG. 34, the incident angle dependence of the slow axis azimuth angle θ _{QW in} the incident angle direction of the quarter-wave plate 17 varies depending on the Nz coefficient, and when the Nz coefficient is 0.75, 0.80, 0.85, The minimum point is shown within the range of the incident angle ψ of linearly polarized light (50 ° ≦ ψ ≦ 70 °), and the change of the slow axis azimuth θ _{QW in} the range becomes gentle. In particular, when the Nz coefficient is 0.80, the local maximum point is located approximately in the center of the range of 50 ° ≦ ψ ≦ 70 °, and the variation amount of the slow axis azimuth θ _QW within the range is the smallest. Therefore, in Example 5, the Nz coefficient of the quarter-wave plate 17 is set to 0.80.

Next, a method for optimizing the slow axis azimuth angle Θ _HW and the normal retardation Rz _HW in the light incident surface of the half-wave plate 39 will be described.

When the Nz coefficient of the half-wave plate 39 is 0.25, the relationship between the slow axis azimuth Θ _HW in the light incident surface and the dependence of the slow axis azimuth θ _{HW in} the incident angle direction on the incident angle is For example, the relationship is as shown in FIG. FIG. 35 is a graph in which the horizontal axis represents the incident angle ψ (unit: degrees), and the vertical axis represents the slow axis azimuth θ _HW (unit: degrees) in the incident angle direction.

35, the curve F ₄₈ , the curve F ₄₉ , the curve F ₅₀ , the curve F ₅₁ , and the curve F ₅₂ respectively represent the slow axis azimuth Θ _HW in the light incident surface of the half-wave plate 39. It is a curve showing the dependence of the slow axis azimuth angle θ _{HW in} the incident angle direction on the incident angle when the angle is 13.3 degrees, 13.2 degrees, 13.3 degrees, 13.6 degrees, and 14.4 degrees.

As can be seen from FIG. 35, for example, when the Nz coefficient of the half-wave plate 39 is set to 0.25 and the incident angle ψ _M of S-polarized light included in the main component of the light source light is set to 50 degrees, When the slow axis azimuth angle Θ _HW at 13.3 is 13.3 degrees, the slow axis azimuth angle θ _{HW in} the incident angle direction of the half-wave plate 39 is 15 degrees. When the incident angle ψ _M of the S-polarized light contained in the main component is set to 55 degrees, 60 degrees, 65 degrees, or 70 degrees, the slow axis azimuth angle Θ _HW in the light incident surface is set to When the angles are 13.2, 13.3, 13.6, and 14.4 degrees, respectively, the slow axis azimuth angle θ _{HW in} the incident angle direction of the half-wave plate 39 becomes 15 degrees.

Note that the curves F ₄₈ and F ₅₀ in FIG. 35 are actually curves having a maximum point in the vicinity of the polar angle of 55 degrees, and the distribution is within a range of the incident angle ψ of 45 degrees to 75 degrees. Generally agree. However, the curve F ₄₈ and the curve F ₅₀ are both curves obtained by setting the slow axis azimuth angle Θ _HW in the light incident surface to 13.3 degrees, but the way of obtaining and the meaning thereof are different. Therefore, in FIG. 35, the curve when the slow axis azimuth angle Θ _HW in the light incident surface is 13.3 degrees is divided into a curve F ₄₈ and a curve F ₅₀ , and only the meaningful part is shown. ing.

Further, the inventors of the present invention based on the above results, set the slow axis azimuth angle Θ _HW within the incident light of the half-wave plate 39 to 13.3 degrees, 13.2 degrees, 13.3 degrees, 13.6 degrees, and 14.4 degrees. When the relation between the retardation Rz _{HW in the} normal direction and the incident angle dependence of the retardation R _{HW in} the incident angle direction was calculated, a result as shown in FIG. 36, for example, was obtained. FIG. 36 is a graph of the incident angle ψ (unit is degrees) on the horizontal axis and the retardation R _HW (unit is nm) in the incident angle direction on the vertical axis.

In addition, the curve F ₅₃ , the curve F ₅₄ , the curve F ₅₅ , the curve F ₅₆ , and the curve F ₅₇ in FIG. 36 respectively represent the slow axis azimuth Θ _HW and the normal direction retardation Rz _{HW in the} light incident surface. (Θ _HW , Rz _HW ) (13.3 degrees, 320.8 nm), (13.2 degrees, 324.6 nm), (13.3 degrees, 324.5 nm), (13.6 degrees, 318.2 nm), and (14.4 degrees, 302.9 nm) Is a curve showing the incident angle dependence of the retardation R _HW in the incident angle direction. In addition, the curve F ₅₃ , the curve F ₅₄ , the curve F ₅₅ , the curve F ₅₆ , and the curve F ₅₇ in FIG. _The dependence of _{HW on} the incident angle is shown.

As can be seen from FIG. 36, for example, when the Nz coefficient of the half-wave plate 39 is set to 0.25 and the S-polarized light incident angle ψ _M included in the main component of the light source light is set to 50 degrees, When the slow axis azimuth angle Θ _HW and the retardation Rz _{HW in the} normal direction are 13.3 degrees and 320.8 nm, respectively, the retardation R _{HW in the} incident angle direction becomes a half wavelength (275 nm). Further, when the incident angle ψ _M of the S-polarized light contained in the main component is set to any one of 55 degrees, 60 degrees, 65 degrees, and 70 degrees, the slow axis azimuth angle Θ _{HW in the} light incident plane is The combinations (Θ _HW , Rz _HW ) with retardation Rz _{HW in the} normal direction are (13.2 degrees, 324.6 nm), (13.3 degrees, 324.5 nm), (13.6 degrees, 318.2 nm), and (14.4 degrees, 302.9 nm), the retardation R _HW in the incident angle direction becomes a half wavelength (275 nm).

Note that the curves F ₅₄ and F ₅₅ in FIG. 36 are actually curves having a maximum point between the incident angle ψ of 55 degrees and 60 degrees, and the incident angle ψ of 45 degrees to 75 degrees. In the range, the distribution is almost the same. However, the curve F ₅₄ and the curve F ₅₅ are different from each other in terms of numerical values used and meanings. Therefore, in FIG. 36, the curve F ₅₄ and the curve F _55, respectively, shows only the portion meaningful.

Further, the incident angle ψ of intermediate other than the above angle, the slow axis azimuth angle theta _HW incident angle direction of 15 degrees and calculating the slow axis azimuth angle theta _HW at the light incident plane, for example, The result as shown in FIG. 37 is obtained. FIG. 37 is a graph in which the horizontal axis represents the incident angle ψ (unit: degrees) and the vertical axis represents the slow axis azimuth angle Θ _HW (unit: degrees) in the light incident surface.

As can be seen from Figure 37, the slow axis azimuth angle theta _HW incidence angle direction of 15 degrees, the relationship between the slow axis azimuth angle theta _HW at the incident angle ψ and the light incident plane, the fold line F ₅₈ It becomes a relationship like this. Therefore, for example, the incident angle ψ _M when the S-polarized light included in the main component of the light source light, that is, the light emitted in the normal direction of the light exit surface of the light source, is incident on the half-wave plate 39 is set as 50. When the angle is other than 55 degrees, 55 degrees, 60 degrees, 65 degrees, and 70 degrees, for example, from the relationship of the polygonal line F ₅₈ shown in FIG. The phase axis azimuth Θ _HW may be determined.

Furthermore, law and the slow axis azimuth angle theta _HW in the light incident surface of the slow axis azimuthal angle theta _HW at the entrance angle direction of 15 degrees, the retardation R _HW incident angle direction is wave-half For example, there is a relationship as shown in FIG. 38 between the retardation Rz _{HW in the} linear direction. FIG. 38 is a graph in which the horizontal axis represents the slow axis azimuth angle Θ _HW (unit: degrees) in the light incident surface, and the vertical axis represents the normal direction retardation Rz _HW (unit: nm).

Further, point P ₁₁ , point P ₁₂ , point P ₁₃ , point P ₁₄ , and point P ₁₅ shown in FIG. 38 have incident angles ψ of 50 degrees, 55 degrees, 60 degrees, 65 degrees, and 70 degrees, respectively. This is a point showing the relationship between the slow axis azimuth angle Θ _HW in the light incident surface and the retardation Rz _{HW in the} normal direction.

In Example 5, when the incident angle ψ _M of the S-polarized light included in the main component of the light source light is set to a certain angle, the slow axis azimuth θ _HW in the incident angle direction with respect to the S-polarized light is set to 15 degrees. The slow axis azimuth angle Θ _HW in the light incident surface required for the half-wave plate 39 can be obtained from the polygonal line F _{58 in} FIG. Then, the slow axis azimuth θ _HW in the incident surface where the slow axis azimuth θ _HW in the incident angle direction is 15 degrees, and the normal direction where the retardation R _{HW in the} incident angle direction is a half wavelength The retardation Rz _HW has a relationship as shown in FIG. Therefore, if the incident angle ψ _M is determined, the retardation Rz _HW in the normal direction required for the half-wave plate 39 is also obtained.

Finally, a method for optimizing the slow axis azimuth Θ _QW and the normal direction retardation Rz _QW in the light incident surface of the quarter-wave plate 17 will be described.

When the Nz coefficient of the quarter-wave plate 17 is 0.80, the relationship between the slow axis azimuth Θ _QW in the light incident surface and the dependence of the slow axis azimuth θ _{QW in} the incident angle direction on the incident angle For example, the relationship is as shown in FIG. FIG. 39 is a graph of the incident angle ψ (unit: degrees) on the horizontal axis and the slow axis azimuth angle θ _QW (unit: degrees) in the incident angle direction on the vertical axis.

In addition, curve F ₅₉ , curve F ₆₀ , curve F ₆₁ , curve F ₆₂ , and curve F ₆₃ in FIG. 39 have the slow axis azimuth angle θ _QW in the light incident plane of 77.2 degrees, 77.3 degrees, and 77.5, respectively. 5 is a curve showing the dependence of the slow axis azimuth angle θ _{QW in} the incident angle direction on the incident angle when the angle is 7 °, 77.4 °, and 76.8 °.

The incident angle of the linearly polarized light that passes through the half-wave plate 39 and enters the quarter-wave plate 17 is approximately equal to the incident angle ψ of S-polarized light that enters the half-wave plate 39. Therefore, as can be seen from FIG. 39, for example, when the incident angle ψ _M of the S-polarized light included in the main component of the light source light is set to 50 degrees, the slow axis azimuth Θ _QW in the light incident surface is set to 77.2. When the angle is set, the slow axis azimuth θ _QW in the incident angle direction is 75 degrees. In addition, when the incident angle ψ _M of the S-polarized light contained in the main component is set to 55 degrees, 60 degrees, 65 degrees, or 70 degrees, the slow axis azimuth Θ _QW in the light incident surface is set to When the angles are 77.3 degrees, 77.5 degrees, 77.4 degrees, and 76.8 degrees, respectively, the slow axis azimuth angle θ _QW in the incident angle direction becomes 75 degrees.

Further, the inventors of the present application based on the above results, when the slow axis azimuth angle Θ _QW in the light incident surface is 77.2 degrees, 77.2 degrees, 77.5 degrees, 77.4 degrees, and 76.8 degrees, When the relationship between the retardation Rz _{QW in the} linear direction and the incident angle dependency of the retardation R _{QW in} the incident angle direction was calculated, for example, a result as shown in FIG. 40 was obtained. FIG. 40 is a graph of the incident angle ψ (unit is degrees) on the horizontal axis and the retardation R _QW (unit is nm) in the incident angle direction on the vertical axis.

Further, curve F ₆₄ , curve F ₆₅ , curve F ₆₆ , curve F ₆₇ , and curve F ₆₈ in FIG. 40 are respectively represented by slow axis azimuth Θ _QW and normal direction retardation Rz _{QW in the} light incident surface. (Θ _QW , Rz _QW ) (77.2 degrees, 153.2 nm), (77.3 degrees, 154.7 nm), (77.5 degrees, 154.7 nm), (77.4 degrees, 152.1 nm), and (76.8 degrees, 145.5 nm) ) _Is a curve showing the dependence of the retardation _RQW in the incident angle direction on the incident angle. Further, the curve F ₅₃ , the curve F ₅₄ , the curve F ₅₅ , the curve F ₅₆ , and the curve F ₅₇ in FIG. 40 are retardation R in the incident angle direction with respect to light having a wavelength of 550 nm at which the visibility is almost maximum among visible wavelengths. _It shows the incident angle dependence of _QW .

As can be seen from FIG. 40, for example, when the Nz coefficient of the quarter-wave plate 17 is set to 0.80 and the incident angle ψ _M of S-polarized light included in the main component of the light source light is set to 50 degrees, the light incident surface When the slow axis azimuth angle Θ _QW and the retardation Rz _{QW in the} normal direction are 77.2 degrees and 153.2 nm, respectively, the retardation R _{QW in the} incident angle direction becomes a quarter wavelength (137.5 nm). When the incident angle ψ _M of the S-polarized light contained in the main component is set to 55 °, 60 °, 65 ° or 70 °, the slow axis azimuth Θ _{QW in the} light incident plane is The combinations (Θ _QW , Rz _QW ) with retardation Rz _{QW in the} normal direction are (77.3 degrees, 154.7 nm), (77.5 degrees, 154.7 nm), (77.4 degrees, 152.1 nm), and (76.8 degrees, If you 145.5nm), the retardation R _QW incident angle direction is quarter wavelength (137.5 nm).

Note that the curves F ₆₅ and F ₆₆ in FIG. 40 are actually curves having a minimum point between the incident angle ψ of 55 degrees and 60 degrees, and the incident angle ψ of 45 degrees to 75 degrees. In the range, the distribution is almost the same. However, the curve F ₆₅ and the curve F ₆₆ are different in the numerical values and meanings used in the determination. Therefore, in FIG. 40, only the meaningful part is shown about the curve _F65 and the curve _F66 , respectively.

Further, when calculating the slow axis azimuth Θ _QW in the light incident surface where the slow axis azimuth θ _QW in the incident angle direction becomes 75 degrees at an intermediate incident angle ψ other than the above angle, for example, The result as shown in FIG. 41 is obtained. FIG. 41 is a graph in which the horizontal axis represents the incident angle ψ (unit: degrees) and the vertical axis represents the slow axis azimuth angle Θ _QW (unit: degrees) in the light incident surface.

As can be seen from FIG. 41, the slow axis azimuth angle θ _QW in the incident angle direction is 75 degrees, and the relationship between the incident angle ψ and the slow axis azimuth angle Θ _QW in the light incident surface is represented by the broken line F ₆₉ . It becomes a relationship like this. Therefore, for example, the incident angle ψ _M of the S-polarized light included in the main component of the light source light, that is, the light emitted in the normal direction of the light exit surface 3a of the light source 3 is set to the above-described 50 degrees, 55 degrees, 60 degrees, 65 degrees. When the angle other than 70 degrees is set, for example, the slow axis azimuth angle Θ _QW in the light incident surface of the quarter-wave plate 17 is determined from the relationship of the broken line F ₆₉ shown in FIG. Good.

Still further, the slow axis azimuth θ _{QW in the} light incident surface where the slow axis azimuth θ _QW in the incident angle direction becomes 75 degrees and the retardation R _{QW in the} incident angle direction become a quarter wavelength. The relationship with the normal direction retardation Rz _QW is, for example, as shown in FIG. FIG. 42 is a graph of the slow axis azimuth angle Θ _QW in the light incident plane on the horizontal axis and the retardation Rz _{QW in} the normal direction on the vertical axis.

Further, the point P ₁₆ , the point P ₁₇ , the point P ₁₈ , the point P ₁₉ , and the point P ₂₀ shown in FIG. 42 have the incident angles ψ of 50 degrees, 55 degrees, 60 degrees, 65 degrees, and 70 degrees, respectively. This is a point showing the relationship between the slow axis azimuth angle Θ _QW in the light incident surface and the retardation Rz _{QW in the} normal direction.

In the fifth embodiment, when the incident angle ψ _M of the S-polarized light included in the main component of the light source light is set to a certain angle, the slow axis azimuth θ _QW in the incident angle direction with respect to the S-polarized light is set to 75 degrees. The slow axis azimuth angle Θ _QW in the light incident surface required for the quarter-wave plate 17 can be obtained from the polygonal line F _{69 in} FIG. Then, the slow axis azimuth θ _{QW in the} light incident surface where the slow axis azimuth θ _QW in the incident angle direction is 75 degrees and the normal line where the retardation R _{QW in the} incident angle direction is a quarter wavelength. There is a relationship as shown in FIG. 42 between the direction retardation Rz _QW . Therefore, if the incident angle ψ _M is determined, the retardation Rz _QW in the normal direction required for the quarter-wave plate 17 is also obtained.

With the above procedure, the Nz coefficient of the half-wave plate 39 and the quarter-wave plate 17, the slow axis azimuth angles Θ _HW and Θ _QW in the light incident surface, and the normal direction retardations Rz _HW and Rz _QW The broadband quarter-wave plate 40 having the half-wave plate and the quarter-wave plate is reflected by the reflective polarizing plate 14 and incident at an incident angle ψ. It functions as a quarter-wave plate for polarized light.

  As described above, in the liquid crystal display device according to the fifth embodiment, the S-polarized light contained in the light source light is converted into the P-polarized light using the broadband quarter-wave plate 40, so that the entire wavelength region in the visible wavelength region is used. Conversion efficiency from S-polarized light to P-polarized light can be improved. Therefore, the utilization efficiency of the light source light is further increased as compared with the liquid crystal display devices of the first to fourth embodiments.

  FIG. 43 is a schematic plan view showing a first configuration example of a main part of the liquid crystal display device according to the sixth embodiment of the present invention.

  The configuration of the liquid crystal display device described in the first embodiment is an example of a configuration of a small-sized liquid crystal display device used as a liquid crystal display such as a mobile phone terminal. The planar shape of the liquid crystal display panel 1 is a video signal line 25. Is a substantially rectangular shape in which the extending direction (y direction) is the longitudinal direction. At this time, in the liquid crystal display panel 1, the transmission axis 12 </ b> T of the first polarizing plate 12 on which the light emitted from the light guide plate 2 is first incident is substantially parallel to the longitudinal direction of the liquid crystal display panel 1. Therefore, in the liquid crystal display device according to the first embodiment, the plurality of light sources 3 are arranged along the side (side surface 2b) in the short direction of the light guide plate 2 that coincides with the short direction of the liquid crystal display panel 1.

  However, the light guide plate type backlight used in the liquid crystal display device of the present invention can also be applied to, for example, a liquid crystal display device used in a display unit of a notebook computer or a car navigation system.

  The planar shape of the liquid crystal display panel 1 of these liquid crystal display devices is usually the same as in the liquid crystal display panel of the first embodiment, assuming that the scanning signal line 22 extends in the x direction and the video signal line 25 extends in the y direction. As shown in FIG. 43, it becomes a substantially rectangular shape with the x direction (the direction in which the scanning signal lines extend) as the longitudinal direction. At this time, if the pixel configuration of the liquid crystal display panel 1 is, for example, as shown in FIGS. 5 to 7, the transmission axis 12T of the first polarizing plate 12 is shorter than the liquid crystal display panel 1. The transmission axis 13T of the second polarizing plate 13 is substantially parallel to the longitudinal direction of the liquid crystal display panel 1.

  Further, as shown in FIG. 43, the planar shape of the light guide plate 2 combined with the liquid crystal display panel 1 has a substantially rectangular shape in which the extending direction (x direction) of the scanning signal lines 22 is the longitudinal direction. At this time, in order to increase the utilization efficiency of the light source light, the vibration direction of the light emitted from the light guide plate 2 toward the liquid crystal display panel 1 is parallel to the short direction (y direction) of the liquid crystal display panel 1. It is desirable to do.

  Therefore, when the transmission axis 12T of the first polarizing plate 12 is substantially parallel to the short side direction of the liquid crystal display panel 1, a plurality of light sources 3 are arranged along the longitudinal sides of the light guide plate 2, and the light guide plate 2 A reflective polarizing plate 14, a transparent spacer 15, a first reflecting plate 16, and a quarter-wave plate 17 between the coupling portion, that is, the side where the light source 3 is disposed and the surface light emitting portion (area AR 2). A second reflector 18 and the like are disposed. By doing so, the vibration direction of the P-polarized light included in the light source light taken into the light guide plate 2 is substantially parallel to the short direction of the light guide plate 2, so that the light is emitted from the light guide plate 2 toward the liquid crystal display panel 1. The light oscillation direction is substantially parallel to the transmission axis 12T of the first polarizing plate 12, so that the light source light utilization efficiency can be improved.

  FIG. 44 is a schematic plan view showing an application example of the liquid crystal display device shown in FIG.

  As an example of the liquid crystal display device of Example 6, in the configuration shown in FIG. 43, the light source 3 is arranged only on one of the two sides in the longitudinal direction (y direction) of the light guide plate 2. In this case, when the dimension of the display area AR1 of the liquid crystal display panel 1 is increased and the area of the surface light emitting portion (area AR2) of the light guide plate 2 is increased, for example, the side opposite to the side where the light source 3 is disposed. The amount of light in the vicinity of

  Therefore, when the area of the display area AR1 (surface light emitting portion of the light guide plate 2) of the liquid crystal display panel 1 is large, for example, the light sources 3 are provided on both the two sides in the longitudinal direction of the light guide plate 2 as shown in FIG. You may arrange. At this time, it is desirable that the plurality of light sources 3 arranged on one side and the plurality of light sources 3 arranged on the other side have the same number and arrangement interval, for example.

  FIG. 45 is a schematic plan view illustrating a second configuration example of a main part of the liquid crystal display device according to the sixth embodiment.

  Conventional liquid crystal display devices are usually used in such an orientation that the direction in which the scanning signal lines 22 extend is horizontal. That is, the liquid crystal display devices shown in FIGS. 1, 43, and 44 are often used in an orientation in which the x direction in which the scanning signal lines extend becomes the horizontal direction. At this time, if the first polarizing plate 12 and the second polarizing plate 13 are arranged so that their transmission axes 12T and 13T are orthogonal to each other, the transmission axis 13T of the second polarizing plate 13 is in the horizontal direction. And become almost parallel. At this time, the vibration direction of the light that is modulated by the liquid crystal display panel 1 and reaches the observer is substantially parallel to the horizontal direction.

  When the liquid crystal display device having a light guide plate type backlight according to the present invention is used as the liquid crystal display of the portable information device as described above, the portable information device is often used outdoors.

  Light from an external light source (such as the sun or a lighting device) that enters the human eye outdoors includes, for example, reflected light from a road or water surface in addition to the light directly emitted from the external light source. This reflected light is, for example, a hindrance during driving or fishing of an automobile, but both are reflected light from a horizontal surface, and are linearly polarized light whose vibration direction is in a horizontal plane. Therefore, in order to remove these linearly polarized light, in recent years, polarized sunglasses having a polarizing plate having an absorption axis in the horizontal direction have become widespread.

  However, when an observer wearing polarized sunglasses uses a liquid crystal display device with the transmission axis 13T of the second polarizing plate 13 substantially parallel to the horizontal direction, the light is emitted from the liquid crystal display device (liquid crystal display panel 1). The light is absorbed by polarized sunglasses, and images and images cannot be observed.

  Therefore, when the present invention is applied to a liquid crystal display device expected to be used outdoors, it is desirable that the liquid crystal display device has a configuration that allows an observer wearing polarized sunglasses to observe. That is, when the present invention is applied to a liquid crystal display device expected to be used outdoors, the transmission axis 13T of the second polarizing plate 13 facing the observer (user) side is sufficiently inclined from the horizontal direction. Desirably, it is ideal if it is perpendicular to the horizontal direction.

  In the case of a liquid crystal display device that is assumed to be used in a state in which the direction (x direction) in which the scanning signal line 22 extends is a horizontal direction, an observer wearing polarized sunglasses can observe, for example, As shown in FIG. 45, the transmission axis 13T of the second polarizing plate 13 may be parallel to the direction (y direction) in which the video signal line 25 extends. 45, as in the liquid crystal display panel 1 of FIGS. 43 and 44, the x direction is the direction in which the scanning signal lines 22 extend, and the y direction is the direction in which the video signal lines 25 extend. .

  At this time, if the first polarizing plate 12 and the second polarizing plate 13 are arranged so that their transmission axes 12T and 13T are orthogonal to each other, the transmission axis 12T of the first polarizing plate 12 is a scanning signal. It becomes parallel to the direction (x direction) where the line 22 extends. Therefore, when the planar shape of the liquid crystal display panel 1 is a substantially rectangular shape whose longitudinal direction is the direction in which the scanning signal lines extend as shown in FIG. 45, the first polarizing plate 12 on which the light from the light guide plate 2 first enters. The transmission axis 12T of the liquid crystal display panel 1 is parallel to the longitudinal direction of the liquid crystal display panel 1.

  Further, as shown in FIG. 45, the planar shape of the light guide plate 2 combined with the liquid crystal display panel 1 has a substantially rectangular shape in which the extending direction (x direction) of the scanning signal lines 22 is the longitudinal direction.

  At this time, as shown in FIG. 45, a plurality of light sources 3 are arranged along the short side of the light guide plate 2, and the coupling portion of the light guide plate 2, that is, the side where the light source 3 is arranged and the surface light emission. When the reflective polarizing plate 14, the transparent spacer 15, the first reflective plate 16, the quarter-wave plate 17, the second reflective plate 18, and the like are disposed between the light guide plate 2 and the region (area AR <b> 2). The vibration direction of the light emitted toward the liquid crystal display panel 1 is substantially parallel to the transmission axis 12T of the first polarizing plate 12. At this time, the vibration direction of the light that is modulated by the liquid crystal display panel 1 and reaches the observer is parallel to the short direction of the liquid crystal display panel 1.

  Therefore, when the liquid crystal display device having the configuration shown in FIG. 45 is used outdoors, if the liquid crystal display panel 1 (display area AR1) is used so that the longitudinal direction thereof faces the horizontal direction, observation with polarized sunglasses is performed. Even a person can observe the displayed video and images.

  45 shows a configuration example in which the display area AR1 of the liquid crystal display panel 1 is horizontally long, and therefore, a plurality of light sources 3 are arranged on the side of the light guide plate 2 in the short direction. On the other hand, for example, as shown in FIG. 1, when the display area AR1 of the liquid crystal display panel 1 is vertically long, in order to make it possible for an observer wearing polarized sunglasses to observe, for example, FIG. A plurality of light sources 3 are arranged on the side in the longitudinal direction of the light guide plate 2 shown, the transmission axis 12T of the first polarizing plate 12 is substantially parallel to the short direction of the liquid crystal display panel 1, and the second polarizing plate 13 Of course, the transmission axis 13T of the liquid crystal display panel 1 may be substantially parallel to the longitudinal direction of the liquid crystal display panel 1.

  The present invention has been specifically described above based on the above-described embodiments. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention. is there.

  The backlight unit of the liquid crystal display device described in the above embodiment is a surface-emitting illumination device that converts light source light emitted from a plurality of light sources 3 into planar light rays. Therefore, the configuration described in the above embodiment is not limited to the backlight unit of the liquid crystal display device, and can be applied to, for example, a lighting device for indoor lighting or a light box used when observing a photographic film. Conceivable.

DESCRIPTION OF SYMBOLS 1 Liquid crystal display panel 2 Light guide plate 2a 1st main surface 2b Side surface 2c 2nd main surface 2d Protrusion 3 Light source 3a Light emission surface 4 1st prism sheet 5 2nd prism sheet 6 IC chip 7 Flexible wiring board 8 Tilting base DESCRIPTION OF SYMBOLS 9 TFT substrate 10 Counter substrate 11 Liquid crystal layer 12 1st polarizing plate 13 2nd polarizing plate 12T, 13T Transmission axis 14 Reflective polarizing plate 15 Transparent spacer 15 'Gel-like film 16 1st reflecting plate 17 1/4 Wavelength plate 17d Delay axis 18 Second reflecting plate 19 Pixel electrode 20 Common electrode 21 First insulating substrate 22 Scanning signal line 23 First insulating layer 24 TFT element 25 Video signal line 26 Second insulating layer 27 Third Insulating layer 28 First alignment film 29 Second insulating substrate 30 Black matrix 31 Color filter 32 Flattening film 33 Second alignment film 34 Refractive index Circle 35 Mold 35a Cavity 35b Inlet 35c Exhaust port 36 Transparent resin 37 Gap 38 Transparent adhesive layer 39 Half-wave plate 40 Broadband quarter-wave plate 41 Poincare sphere 42 (Slow axis of half-wave plate Axis 43 (corresponding to the slow axis of the quarter-wave plate) axis

Claims (9)

In a liquid crystal display device that includes a liquid crystal display panel, a light guide plate, and a plurality of light sources, and converts the light source light emitted from the plurality of light sources into a planar light beam in the light guide plate and irradiates the liquid crystal display panel.
In the liquid crystal display panel, the light incident surface of the planar light beam is approximately rectangular,
In the light guide plate, the first main surface facing the light incident surface of the liquid crystal display panel and the second main surface opposite to the first main surface are substantially rectangular and the surface light emission overlaps the display region of the liquid crystal display panel. And a coupling part for guiding the light source light to the surface light emitting part,
The coupling portion is thicker than the surface light emitting portion, and the boundary between the coupling portion and the surface light emitting portion is continuously changed in thickness by a step provided on the first main surface side. And
In the light source, the light source light is directed to the step of the light guide plate, and the propagation direction of the main component having the highest intensity of the light source light is substantially parallel to any one of the four sides of the light incident surface of the liquid crystal display panel. Arranged along the coupling portion of the light guide plate in the direction of
A reflective polarizing plate that transmits the P-polarized light and reflects the S-polarized light included in the light source light and a transparent resin on the portion of the light guide plate on which the step is provided. And a first reflector that reflects the P-polarized light are laminated in this order,
On the portion of the second main surface of the light guide plate on which the S-polarized light is incident, a quarter-wave plate and a second reflecting plate are laminated in this order,
The coupling portion of the light guide plate guides the P-polarized light contained in the light source light to the surface light emitting portion while maintaining the P-polarized light, and the S-polarized light contained in the light source light reflects the quarter-wave plate and the second reflection. A liquid crystal display device characterized in that it is converted into P-polarized light using a plate and led to the surface light emitting section. In the coupling portion of the light guide plate, a light incident surface of the light source light is flat, and an angle formed with the second main surface is an obtuse angle with respect to a thickness direction of the light guide plate. Tilted,
The liquid crystal display device according to claim 1, wherein the light source is disposed such that an emission surface of the light source light is substantially parallel to the plane of the coupling portion.   2. The liquid crystal display device according to claim 1, wherein each of the reflective polarizing plate and the first reflective plate has a concave curved surface when viewed from the light source.   In the light source and the reflective polarizing plate, an incident angle when S-polarized light contained in the main component is incident on an interface between the light guide plate and the quarter-wave plate is 50 degrees or more and 70 degrees or less. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is disposed on the liquid crystal display device. In the coupling portion of the light guide plate, a light incident surface of the light source light is flat, and an angle formed with the second main surface is an obtuse angle with respect to a thickness direction of the light guide plate. Tilted,
Each of the reflective polarizing plate and the first reflective plate is a concave curved surface when viewed from the light source,
From the second main surface of the light guide plate, the inclination angle of the plane of the coupling portion from the thickness direction of the light guide plate is φ ₁ , and the tangential line at the position where the main component of the reflective polarizing plate is incident _2. The liquid crystal display device according to claim 1, wherein φ ₁ + 2φ ₂ is 20 degrees or more and 40 degrees or less, when an inclination angle of φ is φ ₂ . The light guide plate is made of a transparent resin and formed by an injection molding method,
The one or more light sources of the plurality of light sources are arranged so that a light exit surface faces an injection port of the resin when the light guide plate is formed. Liquid crystal display device. The light guide plate is made of an organic polymer,
2. The liquid crystal display device according to claim 1, wherein an orientation direction of the organic polymer in a portion of the coupling surface where the light source light propagates is substantially parallel to a propagation direction of the light source light. The quarter-wave plate has an Nz coefficient of 0.45 or more and 0.6 or less, and
The retardation in the incident direction of S-polarized light contained in the main component of the light source light is set based on a quarter wavelength of any wavelength in the visible wavelength region. A liquid crystal display device according to 1. The quarter-wave plate is a laminate of a half-wave plate and a quarter-wave plate, and the half-wave plate on the second main surface of the light guide plate, A broadband quarter wave plate laminated in the order of the quarter wave plate;
The vibration direction of S-polarized light contained in the main component of the light source light is set to 0 degree,
When the slow axis azimuth angles of the half-wave plate and the quarter-wave plate viewed from the incident direction of the S-polarized light are θ _HW and θ _QW respectively, the two slow axis azimuth angles θ _HW, theta between the _QW, the liquid crystal display device according to claim 1, characterized in that there is a relation of 2θ _HW = ± 45 degrees + theta _QW.

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