JP4805335B2 - Reflective liquid crystal display - Google Patents

Description

  The present invention relates to a reflective liquid crystal display device, and for example, suppresses a reduction in contrast caused by interface reflection or the like in a reflective liquid crystal display device used in a low power consumption device such as a portable terminal without degrading display quality. The present invention relates to a reflection type liquid crystal display device characterized by a configuration for the purpose.

  Since the liquid crystal display device has features such as small size, light weight, and low power consumption, it is widely used as a display monitor for information equipment terminals, televisions, portable information equipment terminals, video cameras, and the like.

  Since the liquid crystal material is not a self-luminous element, some kind of light source is necessary to use it as a display device. In particular, in the case of a reflective liquid crystal display device used for low power consumption devices such as portable terminals, indoor lighting or the like is a light source Or a front light as a light source (see, for example, Patent Document 1).

Here, a conventional reflective liquid crystal display device will be described with reference to FIG.
FIG. 10 is a schematic sectional view of a conventional reflective liquid crystal display device, in which a liquid crystal panel 80 having a liquid crystal layer 82 sandwiched between a TFT substrate 81 and a CF (color filter) substrate 83; The front light 90 is configured to be fixed and held on the frame 85 so as to face each other through a slight gap, that is, an air layer 96.

  The front light 90 includes a light source 91, a reflector 92 that reflects and collects light from the light source 91 toward the light guide plate 93, and the light guide plate 93. A prism 94 is engraved and reflects part of the light being guided toward the liquid crystal panel 80 side. In general, an antireflection film 95 is provided on the back surface of the front light 90, while a polarizing plate 84 is provided on the surface side of the liquid crystal panel 80.

  The pitch of the prisms 94 is set so that it is difficult to see moire with respect to the pixel pitch of the liquid crystal panel 80. For example, the same pitch as the pixel pitch is set so that the moire pitch is infinite, or the prism pitch is set so that the moire is very fine.

  In general, the liquid crystal panel 80 has a structure in which the reflectance is increased in order to realize a bright display. In particular, in a small application such as a mobile phone or a PDA, the viewing angle may be narrow. Often a high reflectivity design is taken.

  In such a reflective liquid crystal display device, a circularly polarizing plate is usually used as a polarizing plate, and this circularly polarizing plate is composed of a retardation plate and a polarizing plate. When light is reflected in front of the liquid crystal panel, the reflected light is absorbed by the circularly polarizing plate and is not emitted.

  This is because the circularly polarizing plate first converts the incident light into linearly polarized light by the polarizing plate, then converts it to circularly polarized light by the phase difference plate, and then the circularly polarized light reflected by the interface is incident on the phase difference plate again and is polarized. This is because the light is converted into linearly polarized light rotated by 90 °, and the reflected light composed of the linearly polarized light rotated by 90 ° is absorbed by the polarizing plate and is not emitted.

As the arrangement structure of the circularly polarizing plates, the following three types of configurations shown in FIG. 11 can be considered.
FIG. 11A is a conceptual configuration diagram when a circularly polarizing plate is bonded to the liquid crystal panel side, and a circularly polarizing plate 100 including a polarizing plate 101 and a retardation plate 102 on the display surface side of the liquid crystal panel 80. Are bonded together by the pressure-sensitive adhesive 103, and an air layer 96 is interposed between the light guide plate 93.

  FIG. 11B is a conceptual configuration diagram when a circularly polarizing plate is bonded to the light guide plate side. A circularly polarizing plate 100 including a polarizing plate 101 and a retardation plate 102 is provided on the back side of the light guide plate 93. The air layer 96 is interposed between the adhesive 104 and the liquid crystal panel 80.

  FIG. 11C is a conceptual configuration diagram when both surfaces of the circularly polarizing plate are adhered. The circularly polarizing plate 100 including the polarizing plate 101 and the retardation plate 102 on the back side of the light guide plate 93 is the adhesive 103. And 104 are attached to the liquid crystal panel 80 and the light guide plate 93. In this case, the air layer is not interposed.

FIG. 12 is an explanatory diagram of reflected light components at the air layer interface. The refractive index n ₂ of the air layer 96 in the above configuration is n ₂ = 1, and the refractive indexes n ₁ and n ₃ of the constituent members such as the liquid crystal panel 80, the circularly polarizing plate 100, the light guide plate 93, or the adhesives 103 and 104. Is about 1.4 to 1.6, the interface between the component member and the air layer 96 has the largest refractive index difference, and the incident light 105 is greatly refracted at this interface.

  If it is refracted greatly, the interface reflection becomes large, and if it is refracted beyond the critical angle, it is totally reflected, so that the contrast is lowered. For example, in the configuration shown in FIG. 11A, the contrast is only about 5 to 10, the color reproduction range is narrow due to the contrast and the reduction, and the display quality is very poor.

  Therefore, in principle, the configuration shown in FIG. 11C is preferable, but when the light guide plate 93 and the liquid crystal panel 80 having different coefficients of thermal expansion are bonded, peeling occurs due to thermal shock, and when rigid bodies are bonded, bubbles are mixed. Therefore, it is difficult to apply to applications other than small applications.

Therefore, with the configuration of FIG. 11B, the circularly polarizing plate 100 is placed on the light guide plate 93 side so that the interface reflected light 106 due to the interface reflection of the air layer 96 is absorbed by the polarizing plate 101 constituting the circularly polarizing plate 100. It has been proposed to increase the contrast (see, for example, Patent Document 2).
JP 2001-108986 A JP-A-11-259007

  However, in the configuration of FIG. 11B described above, the moire between the prism 94 of the light guide plate 93 and the pixels of the liquid crystal panel 80 and the interference rainbow due to the interference between the reflective structure of the liquid crystal panel 80 and the pixels become easier to see. The problem that occurred.

This is probably because the angle of light guided through the light guide plate 93 is narrowed by bonding the circularly polarizing plate 100 to the light guide plate 93, and the diffusion component light is reduced.
Conversely, if the diffuse component light is strong, moire and interference are averaged and weakened.

In addition, since the light 107 refracted at a critical angle or more at the interface with the air layer 96 is totally reflected, the contrast is lowered.
Furthermore, there is a problem that the circularly polarizing plate 100 and the liquid crystal panel 80 are rubbed by an external pressure such as pen input and the circularly polarizing plate 100 is damaged.

  Therefore, an object of the present invention is to suppress a reduction in contrast due to interface reflection caused by an air layer without reducing display quality.

  In order to solve the above problems, according to the present invention, in the reflective liquid crystal display device, at least the reflective liquid crystal panel, the first retardation plate, the second retardation plate, the polarizing plate, and the light guide plate are arranged in this order. The first retardation plate is bonded or bonded to the reflective liquid crystal panel side, the second retardation plate and the polarizing plate are bonded to the light guide plate side, and the first retardation plate and the second retardation plate are bonded to each other. The retardation plate and the polarizing plate constitute a circular polarizer.

  In this case, by attaching the first retardation plate to the reflective liquid crystal panel side, antireflection, flaw prevention and diffusion functions can be added, and the second retardation plate and the polarizing plate are connected to the light guide plate side. By attaching to the polarizing plate, the light emitted from the second retardation plate is brought close to the circularly polarized light and absorbed by the polarizing plate as much as possible at the interface of the air layer, or reflected by reducing the wavelength dispersion of the in-plane retardation. The reflected light from the liquid crystal panel can be efficiently absorbed by the polarizing plate.

  In addition, by forming a circular polarizer with the first retardation plate, the second retardation plate, and the polarizing plate, the in-plane retardation of the first retardation plate and the second retardation plate is added together. The desired phase difference, that is, 95 nm or more and 195 nm or less, which is ¼ of the visible light wavelength range, is set to circularly polarized light emitted from the first phase difference plate, and reflected light from the reflective liquid crystal panel is polarized. Can be absorbed efficiently. Note that a circular polarizer means an element that converts the polarization state of incident light into roughly circular polarization, but even if the polarization state of emitted light deviates from circular polarization, the observer is related to the reflective liquid crystal panel. If the light emitted to the side is linearly polarized light rotated by approximately 90 °, it can be regarded as a circular polarizer.

  With the above configuration, it is possible to reduce the reflection intensity of black display and increase the contrast. That is, the light emitted from the first retardation plate constituting the interface with the air layer is deviated from the circularly polarized light. However, when comparing the reflection from the interface and the reflection type liquid crystal panel, the latter has a higher reflection intensity. The contrast can be increased by using circularly polarized light emitted from the second retardation plate.

  In this case, when the λ / 4 plate is configured such that the sum of the in-plane retardations of the first retardation plate and the second retardation plate is 95 nm or more and 195 nm or less, which is ¼ of the visible light wavelength range, The angle formed by the slow axis of the first retardation plate and the second retardation plate may be 0 ° or more and 30 ° or less. In this case, the in-plane retardation of the first retardation plate is preferably made as small as possible so that the in-plane retardation of the second retardation plate approaches ¼ of the visible light wavelength region.

  If the slow axes of the first retardation plate and the second retardation plate are substantially parallel, a circular polarizer can be formed by adding the in-plane retardations, but there is a retardation in the thickness direction. If it remains, it will deviate from circularly polarized light, but this deviation can be corrected by setting the angle formed by the slow axis to 0 ° or more and 30 ° or less.

  With such a configuration, the light emitted from the second phase difference plate is converted to circularly polarized light or light emitted to the observer side in relation to the reflective liquid crystal panel is linearly polarized light rotated by approximately 90 °, and the contrast is increased. be able to. Note that if there is a phase difference in the thickness direction, it will deviate from linearly polarized light rotated by 90 °. However, if the reflection intensity is small, it can be regarded as a circular polarizer because the action is the same. .

  Alternatively, when the λ / 4 plate is configured such that the in-plane retardation difference between the first retardation plate and the second retardation plate is 95 nm or more and 195 nm or less, which is ¼ of the visible light wavelength region. The angle formed by the slow axis of one retardation plate and the second retardation plate may be 60 ° or more and 90 ° or less.

  If the slow axes of the first retardation plate and the second retardation plate are approximately orthogonal, a circular polarizer can be constructed by subtracting the in-plane retardation of each, but there is a retardation in the thickness direction. If there is, it will deviate from circularly polarized light, but this deviation can be corrected by shifting the slow axis by approximately 30 ° from orthogonal, that is, by making the angle formed by the slow axis 60 ° or more and 90 ° or less. Can do.

  Even with this configuration, the light emitted from the second retardation plate is converted into linearly polarized light obtained by rotating the light emitted to the observer side by approximately 90 ° in relation to the circularly polarized light or the reflective liquid crystal panel, thereby increasing the contrast. Can do. In this case as well, if there is a phase difference in the thickness direction, it will deviate from linearly polarized light rotated by 90 °. However, if the reflection intensity is reduced, the action is the same, so that the circular polarizer and Can be considered.

  In each configuration described above, the angle between the absorption axis of the polarizing plate and the slow axis of the second retardation plate is θ, and the angle between the absorption axis of the polarizing plate and the slow axis of the first retardation plate is approximately 2θ + 45. It is desirable to set it as °.

  By configuring in this manner, a broadband λ / 4 plate can be configured by using the second retardation plate as a λ / 2 plate and the first retardation plate as a λ / 4 wavelength plate. That is, by setting the angle formed by the absorption axis of the polarizing plate and the slow axis of the first retardation plate to approximately 2θ + 45 °, the polarization direction of the linearly polarized light is retarded on the λ / 2 plate regardless of the slow axis direction. The λ / 4 plate can be rotated circularly with linearly polarized light incident from approximately 45 ° or 135 ° with respect to the slow axis. .

  With this configuration, the wavelength dispersion of the in-plane retardation can be reduced and the reflected light from the reflective liquid crystal panel can be efficiently absorbed by the polarizing plate. In this configuration, the interface reflection from the air layer cannot be suppressed. However, when the interface reflection and the reflected light from the reflective liquid crystal panel are compared, the latter has a higher reflection intensity, so that the contrast can be increased.

  In the case of the above-described configuration, a third retardation plate having an in-plane retardation of 190 nm or more and 390 nm or less, which is a half of the visible light wavelength range, is disposed between the polarizing plate and the second retardation plate. Is desirable.

  With such a configuration, the first to third retardation plates can form a broadband λ / 4 plate, or a broadband λ / 4 plate and an optical compensator, thereby achieving in-plane retardation wavelength dispersion. Therefore, the polarizing plate can efficiently absorb the reflected light from the reflective liquid crystal panel.

  Further, if the in-plane retardation of the first retardation plate is made as small as possible, the light emitted from the second retardation plate can be brought close to circularly polarized light so that most of the interface reflection of the air layer can be absorbed by the polarizing plate. , The contrast can be made higher. The optical compensation is to cancel the positive phase difference generated in the thickness direction of the reflective liquid crystal panel by the negative phase difference generated in the thickness direction of the phase difference plate.

  In this case, the angle between the absorption axis of the polarizing plate and the slow axis of the third retardation plate is θ, and the angle between the absorption axis of the polarizing plate and the slow axis of the second retardation plate is approximately 2θ + 45 °. The in-plane retardation difference between the third retardation plate and the first and second retardation plates is desirably 95 nm or more and 195 nm or less, which is a quarter of the visible light wavelength range.

  With this configuration, the third retardation plate is a λ / 2 plate, the first and second retardation plates are λ / 4, and the first to third retardation plates are broadband λ / 4 plates. Can be configured. Preferably, the in-plane retardation of the first retardation plate is made as small as possible so that the in-plane retardation of the second retardation plate approaches ¼ of the visible light wavelength region.

  Alternatively, the angle between the absorption axis of the polarizing plate and the slow axis of the third retardation plate is θ, the angle between the absorption axis of the polarizing plate and the slow axis of the second retardation plate is approximately 2θ + 45 °, The angle between the slow axis of the second retardation plate and the slow axis of the first retardation plate is substantially orthogonal, and the difference between the in-plane retardation of the second retardation plate and the first retardation plate Is preferably not less than 95 nm and not more than 195 nm, which is 1/4 of the visible light wavelength region.

With this configuration, the second and third retardation plates can be λ / 2 plates, the first retardation plate can be a λ / 4 plate, and a broadband λ / 4 plate can be combined with an optical compensation plate.
That is, the second retardation plate is equivalent to a λ / 4 plate having the same slow axis, and the third retardation plate and one λ / 4 plate form a broadband λ / 4 plate. The retardation plate and the other λ / 4 plate constitute an optical compensation plate.

  As a result, the wavelength dispersion of the in-plane retardation can be reduced, the reflected light from the reflective liquid crystal panel can be efficiently absorbed by the polarizing plate, and the thickness direction retardation of the vertically aligned liquid crystal layer can be canceled. I will explain this situation.

  In the vertical alignment mode using a circularly polarizing plate, black is displayed when no voltage is applied or below the threshold voltage, so the in-plane retardation is almost zero, and in principle the contrast can be increased. Since the used horizontal alignment mode displays black when voltage is applied, the in-plane phase difference is minimized but does not become zero, so the contrast is relatively low. This is because the anchoring effect by the alignment film is strong in the horizontal alignment mode, and the liquid crystal layer does not rise at the substrate interface even after the voltage is applied.

  However, even in the vertical alignment mode, a phase difference in the thickness direction occurs for obliquely incident light. However, if an optical compensation plate equivalent to a configuration in which λ / 4 plates are arranged so that their slow axes are orthogonal to each other is arranged. Since the in-plane retardation is canceled by each, the retardation in the thickness direction can be used for optical compensation of the reflective liquid crystal panel.

  In this way, by combining the broadband λ / 4 plate and the optical compensator, the light emitted to the observer side in relation to the reflective liquid crystal panel becomes linearly polarized light rotated by approximately 90 °. It can be regarded as a circular polarizer. In this configuration, the interface reflection from the air layer cannot be suppressed. However, when the interface reflection and the reflected light from the reflective liquid crystal panel are compared, the latter has a higher reflection intensity, so that the contrast can be increased.

  In the above-described configuration, the third and fourth retardation plates having an in-plane retardation of 190 nm or more and 390 nm or less, which is ½ of the visible light wavelength range, between the polarizing plate and the second retardation plate. It is desirable to dispose a retardation plate, whereby the first to fourth retardation plates can constitute a broadband λ / 4 plate and an optical compensation plate.

  With this configuration, the wavelength dispersion of the in-plane retardation is reduced so that the reflected light from the reflective liquid crystal panel can be efficiently absorbed by the polarizing plate, and the retardation in the thickness direction of the vertically aligned liquid crystal layer is canceled. be able to.

  Also, if the in-plane retardation of the first retardation plate is made as small as possible, the light emitted from the second retardation plate can be brought close to circularly polarized light and most of the interface reflection of the air layer can be absorbed by the polarizing plate. , The contrast can be the highest.

  In this case, the angle between the absorption axis of the polarizing plate and the slow axis of the fourth retardation plate is θ, the angle between the absorption axis of the polarizing plate and the slow axis of the third retardation plate is approximately 2θ + 45 °, The angle formed by the slow axis of the third retardation plate and the slow axis of the second retardation plate is substantially orthogonal, and in-plane between the third retardation plate and the first and second retardation plates The difference in phase difference is desirably 95 nm or more and 195 nm or less, which is ¼ of the visible light wavelength region.

  With this configuration, the third and fourth retardation plates are λ / 2 plates, the first and second retardation plates are λ / 4 plates, and a broadband λ / 4 plate is combined with an optical compensation plate. be able to. Preferably, the in-plane retardation of the first retardation plate is made as small as possible so that the in-plane retardation of the second retardation plate approaches ¼ of the visible light wavelength region.

  In each of the above structures, it is desirable to use an unstretched film as the first retardation plate.

  That is, in order to suppress the interface reflection from the air layer, it is necessary to make the light emitted from the second retardation plate circularly polarized, but the first phase is between the second retardation plate and the reflective liquid crystal panel. In the configuration in which the phase difference plate is arranged, it is deviated from the circularly polarized light.

  In order to reduce this shift and increase the contrast, it is desirable to make the first retardation plate as small as possible so that the in-plane retardation of the second retardation plate approaches ¼ of the visible light wavelength region. For this purpose, an in-plane retardation is set to about several nanometers using an unstretched film for the first retardation plate, and the in-plane retardation of the second retardation plate is set to ¼ of the visible light wavelength region. Accordingly, the light emitted from the second retardation plate approaches circularly polarized light, and most of the interface reflection generated at the interface with the air layer is absorbed by the polarizing plate, so that the contrast can be increased.

  In each of the above configurations, it is desirable to provide an antireflection film on at least the surface of the first retardation plate.

  In general, it is ideal that an antireflection film is formed on both interfaces of the first retardation plate and the circularly polarizing plate. However, an antireflection film is formed on at least the surface of the first retardation plate. As a result, the interface reflection is approximately 0 to 1/4, and a reduction in contrast due to total reflection can be suppressed. The reason why the surface of the first phase difference plate is given priority is that the surface of the first phase difference plate is the interface where total reflection is first performed, and this is more effective in suppressing total reflection.

  In each configuration described above, it is desirable that the adhesive layer provided between the polarizing plate and the light guide plate has a light diffusion function.

  With this configuration, when display unevenness mainly caused by the light guide plate such as Newton rings or moire occurs, it can be mitigated by imparting a light diffusion function to the interface on the light guide plate side. The addition of the light diffusing function is effective in alleviating display unevenness, but at the same time it causes a decrease in contrast and image blur, so it is necessary to keep it to the minimum necessary.

  In each of the above configurations, it is desirable that the adhesive layer provided between the first retardation plate and the reflective liquid crystal panel has a light diffusion function.

  With this configuration, when display unevenness mainly caused by the reflective liquid crystal panel, such as interference fringes with the reflective electrode of the reflective liquid crystal panel, occurs, by providing a light diffusion function to the interface on the reflective liquid crystal panel side, Can be relaxed. In this case as well, the provision of the light diffusing function is effective in alleviating display unevenness, but at the same time it causes a decrease in contrast and image blurring, so it must be kept to the minimum necessary.

  In each of the above-described configurations, it is desirable that the opposing surfaces of the first retardation plate and the second retardation plate are smooth.

  There is a method of imparting a light diffusion function by making the interface in contact with the air layer an uneven structure, but if the uneven structure is used, the circular polarizing plate and the reflective liquid crystal panel are rubbed by external pressure such as pen input, and each interface is damaged. There is a risk of it. However, by using a smooth surface, even if an external pressure such as pen input is applied, each interface is not damaged.

  In each of the above configurations, it is desirable to arrange a viewing angle control plate that diffuses incident light from a specific direction between the light guide plate and the reflective liquid crystal panel.

  The main cause of display unevenness is a diffraction phenomenon due to adjacent light. For example, even if the prism shape of the light guide plate is optimized so that diffraction is not visible in the front direction, the light is visible in a certain observation direction. Since the diffraction phenomenon occurs in the direction where adjacent light is in phase, that is, the interval is an integral multiple of the wavelength, even if the prism pitch is designed so that the phase of the light is deviated from the front, the phase of the light is Diffraction phenomenon occurs in the direction of fitting.

  In this case, the use of an adhesive having a light diffusing function can alleviate the diffraction phenomenon, but it is necessary to control the light diffusing function because of a trade-off with a decrease in contrast and image blur due to multiple diffusion.

  However, if a viewing angle control plate that diffuses incident light from a specific direction as in this configuration is used, a light diffusion function can be given only in a specific direction where the diffraction phenomenon becomes significant. Since there is no light diffusion function, it is possible to suppress a decrease in contrast and image blur.

  According to the present invention, moire and interference rainbow can be reduced, so that it is possible to improve the display quality of a reflective liquid crystal display device using a front light, and in particular, a high-quality reflective liquid crystal display device especially for medium and large size. The place that contributes to the realization of

  Here, an embodiment of the present invention will be described. In the reflective liquid crystal display device, at least the reflective liquid crystal panel, the first retardation plate, the second retardation plate, the polarizing plate, and the light guide plate are laminated in this order, and the first retardation is provided. A plate is bonded or adhered to the reflective liquid crystal panel side, a second retardation plate and a polarizing plate are bonded to the light guide plate side, and the first retardation plate, the second retardation plate and the polarizing plate are circularly polarized. It constitutes a child.

  Here, with reference to FIG.1 and FIG.2, the reflection type liquid crystal display device of Example 1 of this invention is demonstrated. FIG. 1 is a schematic cross-sectional view showing a basic configuration of a reflective liquid crystal display device which is a premise of Embodiment 1 of the present invention. FIG. 1 shows a TFT substrate 11 provided with an alignment film on a glass substrate via a reflective electrode. The liquid crystal panel 10 is formed by sandwiching the liquid crystal layer 12 between the glass substrate and the CF substrate 13 provided with an alignment film via a transparent electrode on the glass substrate, and the front light 20. The frame 15 is fixed and held facing each other through a slight gap.

  The front light 20 includes a light source 21 composed of a cold cathode tube in which a trace amount of Hg is mixed in Ar or Ne gas, a reflector 22 that reflects / condenses light from the light source 21 toward a light guide plate (manufactured by Fujitsu Chemical), The polarizing element 30 is bonded to the back surface of the light guide plate 23, that is, the liquid crystal panel surface side with an adhesive.

In addition, a prism 24 is engraved on the surface of the light guide plate 23, that is, on the viewer side, and reflects part of the light being guided toward the liquid crystal panel 10 side.
In this case, the pitch of the prisms 24 is set so that moiré is not easily seen with respect to the pixel pitch of the liquid crystal panel 10.

  Also, the surface sandblasting of the liquid crystal panel 10 forms a rough surface 14 with, for example, a fine scratch having a height of 100 μm or less between the top and bottom of the irregularities. The degree of scratching in this case may be set to a level where interference rainbows and moire can be tolerated. For example, haze (cloudiness value) H may be equal to or less than about H to 50%, and if too much is added, brightness, The contrast is reduced and the display is blurred.

The haze (haze value) H is expressed by the ratio of the diffuse transmittance T _d [%] and the total light transmittance T _t [%] measured using an integrating sphere light transmittance measuring device. Indicator,
H [%] = (T _d / T _t ) × 100
And displays up to one decimal place.

  When the polarizing element 30 is provided on the light guide plate 23 side in order to increase the contrast, the light incident on the liquid crystal panel 10 generates an interference rainbow due to interference between the reflection surface inside the liquid crystal panel 10 and the pixel portion. The interference rainbow is diffused by the rough surface 14 provided on the surface of the panel 10, and the interference rainbow entering the observer's eyes can be reduced.

  Next, the reflective liquid crystal display device according to the first embodiment of the present invention will be described with reference to FIG. 2, but the basic configuration is the same as the configuration shown in FIG. The explanation is centered. FIG. 2A is a conceptual configuration diagram of the polarizing element of the reflective liquid crystal display device according to the first embodiment of the present invention. The first retardation plate 61 is provided on the liquid crystal panel 10 with an adhesive layer containing a light diffusing material. At the same time, the anti-reflection film 63 is provided on the first retardation plate 61.

  On the other hand, on the light guide plate 23, a polarizing plate 66 in which the second retardation plate 64 is bonded with the adhesive layer 65 is bonded with the light diffusion material-containing adhesive layer 67, and both are opposed to each other through the air layer 68. Is. In this case, a circular polarizer 69 is constituted by the first retardation plate 61, the second retardation plate 64, and the polarizing plate 66.

  As shown in FIG. 2B, when the phase difference of the first phase difference plate 61 is A, the phase difference of the second phase difference plate 64 is λ / 4 plate ± A, so that It can function as a λ / 4 plate. Alternatively, the first retardation plate 61 may be a λ / 4 plate and the second retardation plate 64 may be a λ / 2 plate, thereby functioning as a broadband λ / 4 plate as a whole.

  In the first embodiment, by attaching the first retardation plate 61 to the liquid crystal panel 10 side, antireflection, flaw prevention and diffusion functions can be added, and the second retardation plate 64 and the polarization are added. By sticking the plate 66 to the light guide plate 23 side, the light emitted from the second retardation plate 64 can be made close to circularly polarized light, and the interface reflection of the air layer can be increased and absorbed by the polarizing plate 66 as much as possible. Will improve.

  Alternatively, by functioning as a broadband λ / 4 plate as a whole, the wavelength dispersion of the in-plane retardation can be reduced and the reflected light from the liquid crystal panel 10 can be efficiently absorbed by the polarizing plate 66.

  Next, a reflective liquid crystal display device according to a second embodiment of the present invention will be described with reference to FIG. 3. The basic configuration is the same as that of the first embodiment, and in this case, the second phase difference is described. A third retardation plate is inserted between the plate and the polarizing plate. FIG. 3A is a conceptual configuration diagram of the reflective liquid crystal display device according to the second embodiment of the present invention. As in the first embodiment, the first retardation plate 61 is provided on the liquid crystal panel 10. The anti-reflection film 63 is provided on the first retardation plate 61 while being bonded together by the light diffusion material-containing adhesive layer 62.

  On the other hand, the third retardation plate 70 is bonded between the second retardation plate 64 and the polarizing plate 66 by the adhesive layer 65 and the adhesive layer 71, and is bonded to the light guide plate 23 by the adhesive layer 67 containing the light diffusing material. The two are opposed to each other through the air layer 68. In this case, the first polarizer 61, the second retardation plate 64, the third retardation plate 70, and the polarizing plate 66 constitute a circular polarizer 69.

  As shown in FIG. 3B, when the phase difference of the first phase difference plate 61 is A, the phase difference of the second phase difference plate 64 is λ / 4 plate ± A, and the third phase difference plate. By making 70 a λ / 2 plate, it can function as a broadband λ / 4 plate as a whole. Alternatively, the first retardation plate 61 is a λ / 4 plate, the second retardation plate 64 is a λ / 2 plate, and the third retardation plate 70 is a λ / 2 plate. It can function as four plates and an optical compensator.

  In Example 2, the wavelength dispersion of the in-plane retardation can be reduced and the reflected light from the reflective liquid crystal panel 1 can be efficiently absorbed by the polarizing plate. Note that the antireflection, scratch prevention, diffusion function, and the action of bringing the light emitted from the second retardation plate 64 closer to circularly polarized light are the same as in the first embodiment.

  Next, a reflective liquid crystal display device according to a third embodiment of the present invention will be described with reference to FIG. 4, but the basic configuration is the same as that of the first embodiment. A third retardation plate and a fourth retardation plate are inserted between the retardation plate and the polarizing plate. FIG. 4A is a conceptual configuration diagram of the reflective liquid crystal display device according to the third embodiment of the present invention. As in the first embodiment, the first retardation plate 61 is provided on the liquid crystal panel 10. The anti-reflection film 63 is provided on the first retardation plate 61 while being bonded together by the light diffusion material-containing adhesive layer 62.

  On the other hand, the third retardation plate 70 and the fourth retardation plate 72 are bonded together by the adhesive layer 65, the adhesive layer 71, and the adhesive layer 73 between the second retardation plate 64 and the polarizing plate 66, and light diffusion is performed. It is bonded to the light guide plate 23 by an adhesive layer 67 containing a material, and both are opposed to each other through an air layer 68. In this case, the first polarizer 61, the second retardation plate 64, the third retardation plate 70, the fourth retardation plate 72, and the polarizing plate 66 constitute a circular polarizer 69. It will be.

  The configuration and effects of Example 3 will be described in detail including the slow axis. First, the first retardation plate 61 in this case uses an unstretched TAC film and has an in-plane retardation of about several nanometers, for example, 5.5 nm. The surface of the TAC film is a hard coat / low reflection (HCLR). ) To form a smooth antireflection film 63.

  On the other hand, the second retardation plate 64 is 132 to 143 nm so that the in-plane retardation approaches λ / 4, and the slow axis of the first retardation plate 61 and the retardation of the second retardation plate 64 are slow. The angle formed by the phase axis was set to 0 to 180 °.

  The in-plane retardation of the third retardation plate 70 and the fourth retardation plate 72 is 275 nm, respectively, and the angle θ formed by the absorption axis of the polarizing plate 66 and the slow axis of the fourth retardation plate 72 is set. 10 °, the angle formed by the slow axis of the fourth phase plate 72 and the slow axis of the third phase plate 70 is 55 °, and the slow axis of the third phase plate 70 and the second phase difference The angle formed by the slow axis of the plate 64 was 90 °. Therefore, the angle formed by the absorption axis of the polarizing plate 66 and the slow axis of the third retardation plate 70 is 65 °, that is, 2θ + 45 °.

  The results of measuring the reflection intensity and contrast at a polar angle of 45 ° for this reflection type liquid crystal display device are shown in FIGS. The reflection intensity shown in the figure is the reflection intensity of black display with reference to a standard white plate, while the contrast is the reflection intensity ratio of monochrome display.

In this case, relates to a retardation in the thickness direction, a case where the absolute value of the phase difference _{[Delta] R THF} phase difference _{[Delta] R ThLC} the retarder of the liquid crystal layer is matched _{[Delta] R} th = 0 nm, the phase difference _{[Delta] R ThLC} of the liquid crystal layer position retardation plate _{[Delta] R THF} case 50nm less than the phase difference _{[Delta] R} th = -50 nm, the phase difference _{[Delta] R ThLC} of the liquid crystal layer shows a case 50nm greater than the phase difference _{[Delta] R THF} retarder as _{[Delta] R} th = 50nm.

That is, the ideal optical compensation in the vertical alignment mode is ΔR _th = 0 nm, but ΔR _th varies when there is a variation in film thickness between the liquid crystal layer and the retardation plate. Assuming that there is approximately%, the optimum value was determined in the range of ΔR _th = ± 50 nm. Here, the retardation in the thickness direction is 137.5 to 275 nm for the liquid crystal layer and 137.5 to 275 nm for the retardation plate.

Since the liquid crystal layer is vertically aligned, the phase difference ΔR _thLC of the liquid crystal layer is such that the refractive index in the major axis direction of the liquid crystal molecule is n _e , the refractive index in the minor axis direction of the liquid crystal molecule is n _o , and the liquid crystal layer If the optical path, i.e., the cell gap was set to d _LC in,
ΔR _thLC = (n _e −n _o ) × d _LC = Δn × d _LC
It becomes. However, when the reflective electrode has a concavo-convex structure, the liquid crystal layer is tilted and the incident / exit optical path _dLC is different, so that the refractive index n and the optical path _dLC need to be corrected.

On the other hand, the phase difference [Delta] R _THF phase difference plate, n _x, the refractive index in the plane direction of the retardation plate n _y, a n _z the thickness direction of the refractive index, the optical path of the phase plate, i.e., the film thickness d _{If F}
[Delta] R _THF = _{[(n x -n y) / 2} -n z ] × _{d F}
It becomes.

  FIGS. 5A and 5B show the measurement results when the in-plane retardation of the second retardation plate is 132 nm. Here, the visible light wavelength λ is 550 nm near the visibility peak, This corresponds to a value obtained by subtracting the in-plane retardation of 5.5 nm of the TAC film as the first retardation plate from 137.5 nm which is the retardation of λ / 4.

When ΔR _th = 0 nm, the angle formed by the slow axis of the first retardation plate and the slow axis of the second retardation plate is 0 ° or 180 °, the reflection intensity of black display is minimum, and the contrast CR is maximum. Further, when ΔR _th = ± 50 nm, an angle of 30 ° or 150 °, that is, 0 ° (180 °) ± 30 °, the reflection intensity of black display is minimum, and CR is maximum.

  If the phase difference in the thickness direction is not shifted, the slow axis is almost parallel and the incident light is circularly polarized. If the phase difference in the thickness direction is shifted, the slow axis is changed from parallel. It shows that the shift of the phase difference can be corrected by shifting within a range of about 30 °.

  6 (a) and 6 (b) are measurement results when the in-plane retardation of the second retardation plate is 138 nm. Again, the visible light wavelength λ is 550 nm near the visibility peak, and This corresponds to a phase difference of λ / 4 of 137.5 nm, and the in-plane retardation of the TAC film as the first retardation plate is not considered.

When ΔR _th = 0 nm, there is no large difference in all angle ranges, and when ΔR _th = ± 50 nm, the reflection intensity of black display is minimum and the CR is maximum at an angle of 45 ° or 135 °.

This means that if there is no deviation in the thickness direction retardation, the incident light is averagely deviated from the circularly polarized light in all directions, and if there is a deviation in the thickness direction retardation, the slow axis is further changed from parallel. It shows that the shift of the phase difference can be corrected by shifting. However, since the phase difference condition of the liquid crystal layer and the retardation plate is set to be ΔR _{th =} 0nm, ΔR _{th =} no merit in 0 nm, but has a merit exits configuration only if [Delta] R _th is shifted The maximum CR obtained with this configuration is 1/10 to 1/20 when the in-plane retardation of the second retardation plate shown in FIG. 5 is 132 nm.

  FIGS. 7A and 7B are measurement results when the in-plane retardation of the second retardation plate is set to 143 nm. Again, the visible light wavelength λ is 550 nm near the visibility peak, and This corresponds to a value obtained by adding the in-plane retardation of 5.5 nm of the TAC film as the first retardation plate to 137.5 nm which is the retardation of λ / 4.

At ΔR _th = 0 nm, the angle formed by the slow axis of the first retardation plate and the slow axis of the second retardation plate is 90 °, the reflection intensity of black display is minimum, the contrast CR is maximum, and ΔR _{At th} = ± 50 nm, the angle formed by 60 ° or 120 °, that is, 90 ° ± 30 °, the reflection intensity of black display is minimum, and CR is maximum.

  This means that when the phase difference in the thickness direction is not shifted, the slow axis is orthogonal and the incident light is circularly polarized. When the phase difference in the thickness direction is shifted, the slow axis is from orthogonal to approximately 30. It shows that it can be corrected by shifting within the range of °.

  From the results shown in FIGS. 5 to 7, the circular polarizer 69 is configured in consideration of the TAC film serving as the first retardation plate, that is, the surfaces of the first retardation plate and the second retardation plate. It is understood that the contrast CR can be greatly improved by configuring the circular polarizer 69 in consideration of the internal phase difference and the slow axis.

  Next, a reflective liquid crystal display device according to a fourth embodiment of the present invention will be described. In the reflection type liquid crystal display device of the fourth embodiment, the antireflection film 63 provided on the surface of the first retardation plate 61 in Example 3 is omitted.

Here, the in-plane retardation of the second retardation plate 64 is 132 nm, the angle formed by the slow axes of the first retardation plate 61 and the second retardation plate 64 is 0 °, and the polar angle is 45. As a result of measuring the reflection intensity at 0 °, the reflection intensity of black display at ΔR _th = 0 nm was about four times that of the tenth embodiment, and the CR was reduced to 1/4.

  This indicates that the interface with the air layer is dominant with respect to the interface reflection, and the contrast can be considerably improved if the reflection at this interface is suppressed by using an antireflection film. The reflective liquid crystal display device according to the eleventh embodiment is inferior in characteristics to the liquid crystal display device according to the tenth embodiment, but has improved contrast as compared with the conventional example.

Next, a reflective liquid crystal display device according to a fifth embodiment of the present invention will be described with reference to FIG.
The reflective liquid crystal display device according to the fifth embodiment includes a light diffusing material-containing adhesive layer 62 on the liquid crystal panel 10 side and a light diffusing material-containing adhesive on the light guide plate 23 side in the reflective liquid crystal display device of Example 3 described above. The haze value (cloudiness value) of the layer 67 is 20 to 60%.

  FIG. 8 is an explanatory diagram of a Newton ring or moire interference fringe at each haze value and an improvement result of the interference rainbow by the reflective electrode. For comparison, a reflection type liquid crystal display device in which a light diffusing material is not put in each adhesive layer and a reflection in which fine irregularities are formed on the surface of the first retardation plate 61 and only anti-glare (AG) treatment is applied. Type liquid crystal display device was produced.

  As is apparent from the figure, by using the light diffusion material-containing adhesive layer 67 on the light guide plate 23 side, display unevenness mainly caused by the light guide plate such as Newton rings and moire is reduced, while on the liquid crystal panel 10 side. By using the adhesive layer 61 with the light diffusing material, display unevenness mainly due to the reflective liquid crystal panel such as an interference rainbow with the reflective electrode is reduced.

  In this case, if each haze value is increased, the light diffusion function is increased, and thus display unevenness can be further reduced. However, if the haze value is set to 60% or more, contrast reduction and image blurring become stronger.

  Therefore, a light diffusing material having a diffusivity with a haze value of about 40 [%] is present in both or at least one of the light diffusing material-containing adhesive layer 62 on the liquid crystal panel 10 side and the light diffusing material-containing adhesive layer 67 on the light guide plate 23 side. It is preferable to apply an adhesive layer.

  On the other hand, all the display unevenness was confirmed in the reflection type liquid crystal display device in which no light diffusing material was put in the adhesive layer for comparison. Further, in the reflection type liquid crystal display device in which fine irregularities are formed on the surface of the first retardation plate 61 and the anti-glare (AG) treatment is performed, the interference fringes are reduced, but the first retardation having irregularities on the surface. A scratch was generated by rubbing the plate 61 and the second retardation plate having a flat surface.

Next, a reflective liquid crystal display device according to a sixth embodiment of the present invention will be described with reference to FIG.
In the reflective liquid crystal display device according to the sixth embodiment, a viewing angle control plate 74 that diffuses incident light from a specific direction between the light guide plate 23 and the polarizing plate 66, such as Lumisti (trade name, manufactured by Sumitomo Chemical Co., Ltd.). ) Is arranged, and other than that is the same as the third embodiment.

  FIG. 9 is an explanatory diagram of the diffusion characteristics of the viewing angle control plate 74. The viewing angle control plate 74 transmits the incident light as it is within a range of ± 25 ° from the vertical direction of the substrate, and within a range of ± 25 ° to 55 °. Incident light is designed to diffuse.

  In addition, although the angle range which spread | diffuses can be set arbitrarily, since generation | occurrence | production of the display nonuniformity was especially severe in this angle range, it set to this angle range. This is because the cause of display unevenness is due to the diffraction phenomenon, and even if the prism shape or the like is optimized so that the diffraction is not visible in the front direction, it can be seen in a certain observation direction.

  As a result of observing how the display unevenness looks, in the range of ± 25 ° from the substrate vertical direction which is the observer direction, there is slight display unevenness, but the contrast is high and no image blur occurs. On the other hand, ± 25 ° Since the display unevenness is almost invisible in the range of ˜55 °, it was confirmed that the discomfort caused by the display unevenness entering the visual field range can be reduced.

  As mentioned above, although each embodiment of the present invention has been described, the present invention is not limited to the configuration described in each embodiment, and various modifications can be made. For example, in the description of the first embodiment, the surface of the liquid crystal panel is scratched by sandblasting, but the scratching method is not limited to sandblasting.

  In each of the above embodiments, the polarizing plate and the light guide plate or the phase difference plate and the liquid crystal panel are bonded using the adhesive layer. However, the adhesive layer is not limited to UV curing. The polarizing plate and the light guide plate or the phase difference plate and the liquid crystal panel may be integrated with an adhesive such as an adhesive.

  Further, although the detailed configuration is not disclosed in the first and second embodiments described above, it is based on the third embodiment described above, and is described in the above-mentioned “Means for Solving the Problems” section. Each configuration is adopted.

Here, the detailed features of the present invention will be described.
(Appendix 1) At least a reflective liquid crystal panel, a first retardation plate, a second retardation plate, a polarizing plate, and a light guide plate are laminated in this order, and the first retardation plate is the reflective liquid crystal. The second retardation plate and the polarizing plate are bonded or bonded to the light guide plate side on the panel side, and the first retardation plate, the second retardation plate, and the polarizing plate constitute a circular polarizer. A reflection-type liquid crystal display device.
(Additional remark 2) The angle which the slow axis of said 1st phase difference plate and said 2nd phase difference plate makes is 0 degree or more and 30 degrees or less, and said 1st phase difference plate and said 2nd phase difference The reflective liquid crystal display device according to appendix 1, wherein the sum of the in-plane retardation of the plate is 95 nm or more and 195 nm or less, which is a quarter of the visible light wavelength range.
(Additional remark 3) The angle | corner which the slow axis of the said 1st phase difference plate and the said 2nd phase difference plate makes is 60 degrees or more and 90 degrees or less, The said 1st phase difference plate and the said 2nd phase difference The reflection type liquid crystal display device according to supplementary note 1, wherein a difference in in-plane retardation of the plate is 95 nm or more and 195 nm or less which is ¼ of a visible light wavelength region.
(Supplementary Note 4) The angle between the absorption axis of the polarizing plate and the slow axis of the second retardation plate is θ, and the angle between the absorption axis of the polarizing plate and the slow axis of the first retardation plate is It is approximately 2θ + 45 °, and the in-plane phase difference between the first retardation plate and the second retardation plate is 95 nm or more and 195 nm or less, which is ¼ of the visible light wavelength range. The reflective liquid crystal display device according to appendix 1.
(Supplementary Note 5) A third retardation plate having an in-plane retardation of 190 nm or more and 390 nm or less, which is a half of a visible light wavelength region, is disposed between the polarizing plate and the second retardation plate. The reflection type liquid crystal display device according to appendix 1.
(Supplementary Note 6) The angle between the absorption axis of the polarizing plate and the slow axis of the third retardation plate is θ, and the angle between the absorption axis of the polarizing plate and the slow axis of the second retardation plate is It is approximately 2θ + 45 °, and the difference in in-plane retardation between the third retardation plate and the first and second retardation plates is 95 nm or more and 195 nm or less, which is ¼ of the visible light wavelength range. The reflective liquid crystal display device according to appendix 5.
(Supplementary Note 7) The angle between the absorption axis of the polarizing plate and the slow axis of the third retardation plate is θ, and the angle between the absorption axis of the polarizing plate and the slow axis of the second retardation plate is The angle between the slow axis of the second retardation plate and the slow axis of the first retardation plate is substantially orthogonal, and the second retardation plate and the first retardation plate are approximately 2θ + 45 °. 6. The reflective liquid crystal display device according to appendix 5, wherein the difference in in-plane retardation of the retardation plate is 95 nm or more and 195 nm or less, which is a quarter of the visible light wavelength range.
(Additional remark 8) Between the said polarizing plate and the said 2nd phase difference plate, the 3rd phase difference plate and the 4th phase difference which have an in-plane phase difference of 190 nm or more and 390 nm or less which are 1/2 of a visible light wavelength range. The reflective liquid crystal display device according to appendix 1, wherein a plate is disposed.
(Supplementary Note 9) The angle formed by the absorption axis of the polarizing plate and the slow axis of the fourth retardation plate is θ, and the angle formed by the absorption axis of the polarizing plate and the slow axis of the third retardation plate is The angle between the slow axis of the third retardation plate and the slow axis of the second retardation plate is substantially orthogonal, and the third retardation plate and the first retardation plate 9. The reflective liquid crystal display device according to appendix 8, wherein a difference in in-plane retardation of the second retardation plate is 95 nm or more and 195 nm or less which is a quarter of a visible light wavelength region.
(Additional remark 10) The reflection type liquid crystal display device of Additional remark 1 thru | or 9 using the unstretched film for said 1st phase difference plate.
(Additional remark 11) The reflection type liquid crystal display device of Additional remark 1 thru | or 9 provided with the anti-reflective film at least on the surface of the said 1st phase difference plate.
(Additional remark 12) The reflection type liquid crystal display device of Additional remark 1 thru | or 9 with which the adhesion layer provided between the said polarizing plate and the said light-guide plate has a light-diffusion function.
(Supplementary note 13) The reflective liquid crystal display device according to supplementary notes 1 to 9, wherein the adhesive layer provided between the first retardation plate and the reflective liquid crystal panel has a light diffusion function.
(Supplementary Note 14) The reflective liquid crystal display device according to any one of Supplementary notes 1 to 9, wherein surfaces of the first retardation plate and the second retardation plate facing each other are smooth.
(Supplementary note 15) The reflective liquid crystal display device according to any one of supplementary notes 1 to 9, wherein a viewing angle control plate that diffuses incident light from a specific direction is disposed between the light guide plate and the reflective liquid crystal panel.

It is a schematic sectional drawing which shows the basic composition of the reflection type liquid crystal display device used as the premise of Example 1 of this invention. It is explanatory drawing of the polarizing element of the reflection type liquid crystal display device of Example 1 of this invention. It is explanatory drawing of the reflection type liquid crystal display device of Example 2 of this invention. It is explanatory drawing of the reflection type liquid crystal display device of Example 3 of this invention. It is explanatory drawing of the reflection intensity and contrast in 45 degrees of polar angles when the in-plane phase difference of the 2nd phase difference plate of the reflection type liquid crystal display device of Example 3 of this invention is 132 nm. It is explanatory drawing of the reflection intensity and contrast in 45 degrees of polar angles when the in-plane phase difference of the 2nd phase difference plate of the reflection type liquid crystal display device of Example 3 of this invention is 138 nm. It is explanatory drawing of the reflection intensity and contrast in 45 degrees of polar angles when the in-plane phase difference of the 2nd phase difference plate of the reflection type liquid crystal display device of Example 3 of this invention is 143 nm. It is explanatory drawing of the improvement result of the Newton ring or moire interference fringe in each haze value, and an interference rainbow. It is explanatory drawing of the diffusion characteristic of a viewing angle control board. It is a schematic sectional drawing of the conventional reflection type liquid crystal display device. It is explanatory drawing of the arrangement structure of a circularly-polarizing plate. It is explanatory drawing of the reflected light component in an air layer interface.

Explanation of symbols

10 liquid crystal panel 11 TFT substrate 12 liquid crystal layer 13 CF substrate 14 rough surface 15 frame 20 front light 21 light source 22 reflector 23 light guide plate 24 prism 30 polarizing element 61 first retardation plate 62 adhesive layer 63 antireflection film 64 second Retardation plate 65 Adhesive layer 66 Polarizing plate 67 Adhesive layer 68 containing light diffusing material Air layer 69 Circular polarizer 70 Third retardation plate 71 Adhesive layer 72 Fourth retardation plate 73 Adhesive layer 74 Viewing angle control plate 80 Liquid crystal panel 81 TFT substrate 82 Liquid crystal layer 83 CF substrate 84 Polarizing plate 85 Frame 90 Front light 91 Light source 92 Reflector 93 Light guide plate 94 Prism 95 Antireflection film 96 Air layer 100 Circular polarizing plate 101 Polarizing plate 102 Phase difference plate 103 Adhesive 104 Adhesive 105 incident light 106 interface reflected light 107 light

Claims (3)

At least a reflective liquid crystal panel, a first retardation plate, a second retardation plate, a polarizing plate, and a light guide plate are laminated in this order, and the first retardation plate is on the reflective liquid crystal panel side, The second retardation plate and the polarizing plate are bonded or bonded to the light guide plate side, and the first retardation plate, the second retardation plate, and the polarizing plate constitute a circular polarizer. Reflective liquid crystal display device. The third retardation plate having an in-plane retardation of 190 nm or more and 390 nm or less, which is a half of the visible light wavelength range, is disposed between the polarizing plate and the second retardation plate. 1. A reflective liquid crystal display device according to 1. Between the polarizing plate and the second retardation plate, a third retardation plate and a fourth retardation plate having an in-plane retardation of 190 nm or more and 390 nm or less, which is a half of the visible light wavelength range, are arranged. The reflective liquid crystal display device according to claim 1, wherein

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