JP4693556B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device including a light diffusing element for diffusing light emitted from a liquid crystal display panel.

  In recent years, portable electronic devices represented by portable telephones and PDAs (Personal Digital Assistants) have been widely used. A liquid crystal display device having advantages such as thinness, light weight, and low power consumption is used for a display portion of a portable electronic device.

  Unlike a self-luminous display device such as a CRT or PDP (plasma display panel), a liquid crystal display device does not emit light. Therefore, in a transmissive liquid crystal display device, an illumination element called a backlight is provided on the back side of the liquid crystal display element, and the liquid crystal display element controls the amount of transmitted illumination light from the backlight for each pixel. The image is displayed by.

  Various types of liquid crystal display devices are known. However, some methods (for example, a method using a TN type or STN type liquid crystal display element) have a disadvantage that the viewing angle is narrow, and various technical developments have been made to solve the problem. Yes.

  As a typical technique for improving the viewing angle characteristics of a liquid crystal display device, there is a method of adding an optical compensator. Further, as disclosed in Patent Documents 1, 2, and 3, the light emitted from the backlight is made incident on the liquid crystal display element after increasing its directivity (parallelism) and passed through the liquid crystal display element. A system in which light is diffused by a light diffusing element disposed in front of the liquid crystal display element is also known.

  FIG. 19 shows a liquid crystal display device 500 disclosed in Patent Document 1. The liquid crystal display device 500 includes a liquid crystal display panel 520, a backlight 510 disposed on the back side of the liquid crystal display panel 520, and a lenticular lens sheet 530 disposed on the viewer side of the liquid crystal display panel 520.

  The backlight 510 includes a light source 501, a light guide plate 502 that guides light emitted from the light source 501 to the liquid crystal display panel 520, and a reflective layer 504 that reflects light leaking from the light guide plate 502 toward the light guide plate 502. Yes. The light guide plate 502 has an emission surface that emits light toward the liquid crystal display panel 520 and a back surface facing the emission surface, and a plurality of prisms 502a are formed on the back surface.

  The light emitted from the light source 501 is reflected on the liquid crystal display panel 520 side by the prism 502a on the back surface while propagating through the light guide plate 502, and is emitted from the emission surface. The prism 502a on the back surface has two inclined surfaces inclined at predetermined angles different from each other with respect to the emission surface, so that the light emitted from the backlight 510 is in the normal direction of the display surface (front direction). ) Is significantly stronger. That is, the light emitted from the backlight 510 is given high directivity.

  Since the liquid crystal display panel 520 is designed to have the highest contrast ratio with respect to light incident in parallel to the normal direction of the display surface, light having high directivity as described above is incident on the liquid crystal display panel 520. As a result, the contrast ratio can be improved. In addition, the light that has passed through the liquid crystal display panel 520 is diffused by the lenticular lens sheet 530, thereby widening the viewing angle. In this way, the liquid crystal display device 500 achieves both a high contrast ratio and a wide viewing angle characteristic.

As for the liquid crystal display devices disclosed in Patent Documents 2 and 3, similarly to the liquid crystal display device disclosed in Patent Document 1, light having high directivity is incident on the liquid crystal layer and modulated by the liquid crystal layer. Is diffused by the light diffusing element to improve display quality. Patent Document 2 discloses a wave lens film as a light diffusing element, and Patent Document 3 discloses a light diffusing element including spherical fine particles.
JP-A-9-22011 Japanese Patent No. 2809089 Japanese Patent No. 3517975

  However, in the liquid crystal display devices disclosed in Patent Documents 1, 2, and 3, the problem of blurred display occurs. The reason why the display is blurred will be described below.

  As already described, in order to increase the contrast ratio, it is preferable that light having as high directivity as possible is incident on the liquid crystal layer. That is, it is preferable to increase the light incident on the liquid crystal layer perpendicularly as much as possible and reduce the light incident obliquely on the liquid crystal layer as much as possible. However, as a matter of course, in reality, there is not a little light incident obliquely on the liquid crystal layer, and there is also light having a large incident angle on the liquid crystal layer. Light having a large incident angle to the liquid crystal layer is light that is not sufficiently modulated by the liquid crystal layer or the retardation plate. Therefore, when such light is diffused in the front direction by the light diffusing element, the display is blurred.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a liquid crystal display device that can reduce display blur due to a light diffusing element and perform high-quality display.

  A liquid crystal display device according to the present invention is a liquid crystal display device including a light source, a liquid crystal display panel that modulates light emitted from the light source, and a light diffusing element that is disposed closer to the viewer than the liquid crystal display panel. The light diffusing element diffuses light incident at an angle within a specific angle range more strongly than light incident at another angle, and the specific angle range is a first parallel to the normal direction of the display surface. And the second plane that is parallel to the normal direction of the display surface and intersects the first plane, and the specific angle range in the first plane is A, the second plane The specific angle range in the plane is B, the viewing angle range in which the contrast ratio of the liquid crystal display panel is 1 or more in the first plane is C, and the contrast ratio of the liquid crystal display panel is in the second plane. When the viewing angle range is 1 or more, The ratio A / B between the specific angle range A in the first plane and the specific angle range B in the second plane is such that the viewing angle range C in the first plane and the second plane Is approximately equal to the ratio C / D with the viewing angle range D, thereby achieving the above object.

  In a preferred embodiment, the first surface and the second surface are substantially orthogonal.

  In a preferred embodiment, a viewing angle range in which the contrast ratio of the liquid crystal display panel is 1 or more is the widest in the first plane and the narrowest in the second plane, and the light diffusion element is The specific angle range in which light is strongly diffused is the widest in the first plane and the narrowest in the second plane.

  In a preferred embodiment, the specific angular range A in the first plane is substantially equal to or narrower than the viewing angle range C in the first plane, and in the second plane. The specific angle range B is substantially equal to or narrower than the viewing angle range D in the second plane.

  In a preferred embodiment, the light diffusing element has a haze value of 5 or more with respect to light incident at an angle within the specific angle range.

  In a preferred embodiment, the light diffusing element includes a plurality of prisms, and a cross section parallel to the first surface and a cross section parallel to the second surface of each of the plurality of prisms are different from each other. have.

  In a preferred embodiment, the light diffusing element includes a plurality of anisotropic diffusion layers each diffusing light anisotropically and having different light diffusion characteristics.

  In a preferred embodiment, the liquid crystal display panel includes a pair of substrates and a liquid crystal layer provided between the pair of substrates.

  In a preferred embodiment, the liquid crystal display panel further includes at least one phase difference compensation element.

  In a preferred embodiment, the liquid crystal display device according to the present invention includes a first polarizing element disposed closer to the viewer than the light diffusing element.

  In a preferred embodiment, the liquid crystal display device according to the present invention includes a second polarizing element disposed between the liquid crystal layer and the light diffusing element, the transmission axis of the first polarizing element, The transmission axis of the second polarizing element is substantially parallel.

  In a preferred embodiment, the liquid crystal display device according to the present invention includes a third polarizing element provided on the opposite side to the observer side with respect to the liquid crystal layer.

  In a preferred embodiment, the liquid crystal display device according to the present invention includes an illumination element including the light source.

  In a preferred embodiment, the illumination element has a light distribution such that luminance in a direction forming an angle of 30 ° or more with respect to the normal direction of the display surface is 13% or less of luminance in the normal direction of the display surface. Have

  In a preferred embodiment, the illumination element has a light distribution such that luminance in a direction forming an angle of 30 ° or more with respect to the normal direction of the display surface is 3% or less of luminance in the normal direction of the display surface. Have

  In a preferred embodiment, the illumination element includes a directivity control element that controls the directivity of light emitted from the light source.

  The light diffusing element included in the liquid crystal display device according to the present invention diffuses light incident at an angle within a specific angle range more strongly than light incident at another angle. That is, the light diffusing element has an incident angle dependency on the light diffusion characteristics. Further, the specific angle range (high diffusion angle range) in which the light diffusing element diffuses light strongly is in the first plane parallel to the display surface normal direction and parallel to the display surface normal direction. It differs in the 2nd surface which cross | intersects. That is, the high diffusion angle range has azimuth angle dependency.

  Furthermore, the azimuth angle dependency of the high diffusion angle range is set according to the contrast characteristics of the light modulator. Specifically, the high diffusion angle range in the first plane is A, the high diffusion angle range in the second plane is B, and the viewing angle range in which the contrast ratio of the liquid crystal display panel is 1 or more in the first plane. Where C is the viewing angle range in which the contrast ratio of the liquid crystal display panel is 1 or more in the second plane, and the ratio A / B between the high diffusion angle range A and the high diffusion angle range B is the viewing angle range C Is substantially equal to the ratio C / D of the viewing angle range D.

  As described above, the light diffusing element in the present embodiment has a three-dimensional anisotropy in the light diffusion characteristics, and the three-dimensional anisotropy is modulated by the light modulation unit. It is set according to the characteristics of light. Therefore, in the liquid crystal display device according to the present invention, display blurring is effectively prevented, and high-quality display can be easily realized.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment.

  FIG. 1 shows a liquid crystal display device 100 according to this embodiment. As shown in FIG. 1, the liquid crystal display device 100 is disposed on the viewer side with respect to an illumination element (backlight) 10, a liquid crystal display panel 20 that modulates light emitted from the illumination element 10, and the liquid crystal display panel 20. The light diffusing element 30 is provided.

  The liquid crystal display panel 20 includes a pair of substrates 21 and 22 and a liquid crystal layer 23 provided therebetween. Below, the board | substrate 21 arrange | positioned at the illumination element 10 side with respect to the liquid crystal layer 23 is called a "back substrate", and is arrange | positioned with respect to the liquid crystal layer 23 on the opposite side (namely, observer side). The substrate 22 is referred to as a “front substrate”.

  On the surface of the back substrate 21 and the front substrate 22 on the liquid crystal layer 23 side, an electrode for applying a voltage to the liquid crystal layer 23 and an alignment film for defining the alignment direction of the liquid crystal molecules contained in the liquid crystal layer 23 (whichever (Not shown) is also formed. In the present embodiment, the color filter 24 is provided on the liquid crystal layer 23 side of the front substrate 22.

  A phase difference compensation element 25 and a polarizing plate 26 are provided in this order on the illumination element 10 side of the rear substrate 21, and a phase difference compensation element 27 and a polarizing plate 28 are provided in this order also on the viewer side of the front substrate 22. Is provided. As the phase difference compensating elements 25 and 27, various known phase difference plates are used. The number and arrangement of the phase difference compensation elements are not limited to those exemplified here.

  The light diffusing element 30 is disposed on a polarizing plate 28 provided on the observer side of the front substrate 22. The light diffusing element 30 diffuses light emitted from the liquid crystal display panel 20. In the present embodiment, a polarizing plate 41 is further provided on the viewer side with respect to the light diffusing element 30.

  Hereinafter, for the sake of simplicity of description, the polarizing plate 41 disposed on the viewer side with respect to the light diffusing element 30 is referred to as a “first polarizing plate” and is interposed between the light diffusing element 30 and the liquid crystal layer 23. The disposed polarizing plate 28 is referred to as a “second polarizing plate”, and the polarizing plate 26 disposed between the liquid crystal layer 23 and the illumination element 10 (on the side opposite to the viewer side with respect to the liquid crystal layer 23). This will be referred to as “third polarizing plate”.

  The first polarizing plate 41 and the second polarizing plate 28 are arranged so that their transmission axes are substantially parallel to each other. Further, the third polarizing plate 26 is arranged so that its transmission axis forms a predetermined angle with the transmission axes of the first polarizing plate 41 and the second polarizing plate 28 according to the display mode of the liquid crystal display panel 20. ing.

  By modulating the light emitted from the illumination element 10 by the liquid crystal display panel 20, the amount of light emitted to the viewer side through the first polarizing plate 41 and the second polarizing plate 28 is controlled for each pixel. As a result, an image is displayed. In the present specification, among the components of the liquid crystal display panel 20, those that modulate light by giving a phase difference to the light, that is, the liquid crystal layer 23 and the phase difference compensation elements 25 and 27 are collectively referred to as “light modulator”. .

  FIG. 2 shows an example of a specific configuration of the lighting element 10. The illumination element 10 shown in FIG. 2 includes a light source 1 and a light guide plate 2 that guides light emitted from the light source 1 to the liquid crystal display panel 20. The light source 1 is, for example, a light emitting diode (LED) or a cold cathode tube. The light guide plate 2 has a structure for emitting light emitted from the light source 1 and entering the light guide plate 2 to the liquid crystal display panel 20 side. For example, a prism or a texture is formed on at least one of the two main surfaces of the light guide plate 2.

  The illumination element 10 further includes a prism sheet 3 that controls the directivity of light emitted from the light guide plate 2. The prism sheet 3 functioning as a directivity control element is provided between the light guide plate 2 and the liquid crystal display panel 20.

  The prism sheet 3 has a plurality of prisms 3a formed on the main surface on the light guide plate 2 side, and displays the light emitted from the light guide plate 2 using a total reflection phenomenon, as shown in FIG. Direct in the surface normal direction. Thus, the light emitted from the light guide plate 2 is given high directivity by the prism sheet 3. The prism sheet 3 exemplified here is also referred to as a “total reflection prism sheet”. Further, when a light guide plate having a microlens array formed on the main surface based on the normal vector theory is used as the light guide plate 2, light propagating in the light guide plate is efficiently totally reflected. Since it can radiate | emit to the prism sheet (directivity control element) 3, it is preferable.

  If the light emitted from the illumination element 10 has high directivity, the light passing through the liquid crystal layer 23 can be uniformly modulated (that is, the light passing through the liquid crystal layer 23 is given uniform retardation). Therefore, the viewing angle dependency of the display quality due to the refractive index anisotropy of the liquid crystal molecules can be reduced. The light passing through the liquid crystal layer 23 has high directivity as it is and has a large bias in luminance (the luminance in the normal direction of the display surface is extremely high and the luminance in the oblique direction is low). In addition, by being diffused by the light diffusing element 30 arranged on the viewer side, the luminance deviation is reduced, and the viewing angle is thereby widened.

  The function of the light diffusing element 30 in this embodiment will be described with reference to FIGS. 4, 5 (a), and (b). FIG. 4 is a perspective view schematically showing the light diffusing element 30. In FIG. 4, two directions X and Y that are parallel to the display surface and orthogonal to each other, and a direction (display surface normal direction) Z perpendicular to the display surface are shown. 5A is a diagram showing a cross section parallel to directions X and Z in FIG. 4, and FIG. 5B is a diagram showing a cross section parallel to directions Y and Z in FIG. is there.

  As shown in FIG. 4, the light diffusing element 30 diffuses the light modulated by the light modulation unit. At this time, as shown in FIGS. 5A and 5B, the light diffusing element 30 diffuses light incident at a specific angle range more strongly than light incident at another angle. Specifically, the light diffusing element 30 strongly diffuses light incident at a relatively small incident angle (angle formed by the incident light and the normal direction of the display surface), and weakly diffuses light incident at a relatively large incident angle. To do.

  Since the light diffusing element 30 has the above-described incident angle dependency on the light diffusing characteristic, the light incident on the liquid crystal layer 23 at a large incident angle is hardly diffused and is incident on the liquid crystal layer 23 vertically. Diffused light and incident light with a small incident angle. Therefore, blurring of the display due to the light incident on the liquid crystal layer 23 having a large incident angle being diffused in the front direction is prevented.

  Further, as can be seen by comparing FIG. 5A and FIG. 5B, the angle range in which the light diffusing element 30 diffuses light strongly (referred to as “high diffusion angle range”) is the direction X and There is a difference between a plane parallel to Z and a plane parallel to directions Y and Z. That is, the high diffusion angle range of the light diffusing element 30 varies depending on the orientation in the display surface. In other words, the high diffusion angle range of the light diffusing element 30 has azimuth angle dependency. In the present embodiment, the case where the high diffusion angle range in the plane parallel to the directions X and Z is the widest and the high diffusion angle range in the plane parallel to the directions Y and Z is the smallest is illustrated.

  As described above, the light diffusing element 30 in the present embodiment has the incident angle dependency in the light diffusion characteristic, and the high diffusion angle range has the azimuth angle dependency. That is, the light diffusing element 30 has three-dimensional anisotropy in the light diffusing characteristic. Further, the three-dimensional anisotropy is set according to the characteristics of the light modulated by the light modulation unit, as will be described later. Therefore, in the liquid crystal display device 100 according to the present embodiment, display blurring is effectively prevented, and high-quality display can be easily realized. Hereinafter, the relationship between the characteristics of the light modulated by the light modulation unit and the three-dimensional anisotropy of the light diffusion characteristics will be described in detail.

  The inventor of the present application pays attention to the ratio between the luminance in the white display state and the luminance in the black display state, that is, the contrast ratio as a parameter for evaluating the characteristic of the light modulated by the light modulation unit, and according to the contrast characteristic of the light modulation unit. It has been found that the display quality can be greatly improved by setting the high diffusion angle range of the light diffusing element 30.

  FIG. 6 shows an example of contrast characteristics of the light modulator. FIG. 6 is a diagram showing the relationship between the orientation in the display surface and the contrast ratio. The hatched portion in FIG. 6 shows a viewing angle range in which the contrast ratio is 1 or more. This portion is hereinafter referred to as a contrast cone.

  As can be seen from FIG. 6, the width of the contrast cone differs depending on the orientation in the display surface. In the example shown in FIG. 6, the contrast cone has the widest width along the direction X and the narrowest width along the direction Y. As described above, the contrast characteristics of the light modulator have azimuth dependency.

  A contrast ratio of less than 1 means that the luminance in the black display state is higher than the luminance in the white display state, and that light is not suitably modulated by the light modulation unit. On the other hand, a contrast ratio of 1 or more indicates that light is suitably modulated by the light modulation unit. Therefore, by setting the azimuth angle dependency of the high diffusion angle range of the light diffusing element 30 according to the azimuth angle dependency of the contrast cone, display blur can be effectively improved.

  Specifically, the light diffusing characteristic of the light diffusing element 30 is defined as a high diffusion angle range A (see FIG. 5A) in a certain plane parallel to the normal direction of the display surface (referred to as “first surface”). Reference), a high diffusion angle range in a plane (referred to as “second plane”) that is parallel to the normal direction of the display plane and intersects the first plane (refer to FIG. 5B), When the viewing angle ranges in which the contrast ratio in the plane and the second plane is 1 or more are C and D (see FIG. 6), the ratio A / B of A and B is the ratio C / D of C and D. Is set to be approximately equal to That is, in the direction in which the width of the contrast cone is relatively narrow, the high diffusion angle range of the light diffusion element 30 is also relatively narrow, and in the direction in which the width of the contrast cone is relatively wide, the high diffusion of the light diffusion element 30. The angle range is also relatively wide. Therefore, the light diffusing element 30 can diffuse light that is suitably modulated by the light modulating unit without diffusing light that has not been suitably modulated by the light modulating unit, thereby effectively preventing display blurring. Can be improved. In the present embodiment, the case where the first surface and the second surface are substantially orthogonal to each other is illustrated, but the present invention is not limited to this.

  In order to increase the effect of improving display blurring, the high diffusion angle range A in the first plane is substantially equal to or narrower than the viewing angle range C in which the contrast ratio in the first plane is 1 or more. The high diffusion angle range B in the second plane is preferably substantially equal to or narrower than the viewing angle range D having a contrast ratio in the second plane of 1 or more. By adopting such a configuration, it is possible to substantially diffuse only light within the contrast cone (light in a viewing angle range with a contrast ratio of 1 or more), and to effectively improve display blur. it can.

Next, a preferable relationship between the contrast characteristics of the light modulation unit and the light diffusion characteristics of the light diffusion element 30 will be described more specifically. 7, 8, and 9 show examples of preferable combinations of the contrast cone of the light modulation unit and the light diffusion characteristics of the light diffusion element 30. 7 (a), 8 (a) and 9 (a) show the contrast cone of the light modulator, whereas FIGS. 7 (b), 8 (b) and 9 (b) show the contrast cone. The light diffusion characteristics of the light diffusing element 30 are shown. In FIG. 7B, FIG. 8B, and FIG. 9B, the dependence of the haze value on the incident angle in the first surface (a plane parallel to the directions X and Z) is indicated by a curve L _1. and has incident angle dependency of haze in the (a plane parallel to the direction Y and Z) the second surface is shown by the curve L _2.

The contrast cone shown in FIG. 7A has a relatively wide width along the direction X and a relatively narrow width along the direction Y. Corresponding to this, as shown in FIG. 7B, the curve L ₁ representing the incident angle dependence of the haze value in the first plane is dependent on the incident angle of the haze value in the second plane. It has a broader shape than the curve L ₂ representing the property. That is, as shown in FIG. 7A, the viewing angle range C having a contrast ratio of 1 or more in the first plane is wider than the viewing angle range D having a contrast ratio of 1 or more in the second plane, Further, as shown in FIG. 7B, the high diffusion angle range A in the first plane is wider than the high diffusion angle range B in the second plane. In FIG. 7B, an angle range having a haze value of 5 or more is shown as a high diffusion angle range.

  7A and 7B, the high diffusion angle range A in the first plane is smaller than the viewing angle range C having a contrast ratio of 1 or more in the same plane. Further, the high diffusion angle range B in the second plane is smaller than the viewing angle range D having a contrast ratio of 1 or more in the same plane.

  Thus, by setting the incident angle dependence of the haze value of the light diffusing element 30 according to the shape of the contrast cone, display blur can be suppressed and display quality can be greatly improved.

  For the combinations shown in FIGS. 8A and 8B and the combinations shown in FIGS. 9A and 9B, the haze value of the light diffusing element 30 is appropriately set according to the shape of the contrast cone. Therefore, the same effect can be obtained.

  Next, a specific example of the light diffusing element 30 having three-dimensional anisotropy will be described.

  FIG. 10 shows an example of the light diffusing element 30 having the light diffusing characteristic shown in FIG. The light diffusing element 30 shown in FIG. 10 is a prism array sheet including a plurality of prisms 31 arranged in a matrix. A planarizing layer 32 is formed so as to cover the plurality of prisms 31. The prism 31 and the planarization layer 32 are formed so as to have different refractive indexes. Each prism 31 has a truncated quadrangular pyramid shape (quadratic pyramid shape) as shown in FIG.

  A cross section parallel to the directions X and Z of the prism 31 is shown in FIG. 11A, and a cross section parallel to the directions Y and Z of the prism 31 is shown in FIG. As shown in FIGS. 11A and 11B, the prism 31 has a top surface 31a and a bottom surface 31b, and inclined side surfaces 31c, 31d, 31e and 31f. In this embodiment, the inclined side surfaces 31c and 31d shown in FIG. 11A are both inclined at an angle of 35 ° with respect to the bottom surface 31b. In contrast, the inclined side surface 31e shown in FIG. 11 (b) is inclined at an angle of 70 ° with respect to the bottom surface 31b, and the inclined side surface 31f shown in FIG. It is inclined at an angle of 45 °.

  The light incident on the light diffusing element 30 is refracted at the interface between the inclined side surfaces 31c, 31d, 31e and 31f and the planarizing layer 32, and is diffused thereby. Since the refraction angle and the incident angle have a correlation, the light diffusing element 30 using such refraction at the prism 31 has an incident angle dependency on the light diffusion characteristics. In addition, since the cross section parallel to the first surface of the prism 31 and the cross section parallel to the second surface have different shapes, a high diffusion angle is obtained between the first surface and the second surface. The range is different. That is, the light diffusing element 30 has azimuth angle dependency in its high diffusion angle range.

  The light diffusing element 30 shown in FIG. 10 can be manufactured as follows, for example. First, a prism 31 having a predetermined shape is formed by a photolithography process using an ultraviolet curable resin. Next, the planarizing layer 32 is formed by applying a thermosetting resin so as to cover the prism 31 by a spin coating method, a second coating method, or the like, followed by thermosetting. For example, when an ultraviolet curable resin having a refractive index of about 1.50 is used and a thermosetting resin having a refractive index of about 1.30 is used, the refractive index difference is about 0.2. In this case, the light in the front direction (display surface normal direction) incident on the inclined side surfaces 31c, 31d, 31e, and 31f is the display surface normal line as illustrated in FIGS. 11 (a) and 11 (b). The light is refracted in directions inclined by 15 °, 15 °, 35 °, and 25 ° from the direction.

  FIG. 12 shows another example of the light diffusing element 30. The light diffusing element 30 shown in FIG. 12 is different from the light diffusing element 30 shown in FIG. 10 in that an isotropic diffusion layer 33 that diffuses light isotropically is further provided on the planarizing layer 32. Yes. The light diffusivity of the light diffusing element 30 shown in FIG. 10 depends on the refractive indexes of the materials of the prism 31 and the planarizing layer 32 and the inclination angles of the inclined side surfaces 31c, 31d, 31e, and 31f. Therefore, in the light diffusing element 30 shown in FIG. 10, it may be difficult to sufficiently widen the viewing angle depending on the material used. As shown in FIG. 12, by further providing the isotropic diffusion layer 33, it is possible to further diffuse the light diffused at the interface between the prism 31 and the planarization layer 32 and further widen the viewing angle.

  The isotropic diffusion layer 33 is a diffusion film using internal scattering as shown in FIG. 13, for example. The diffusion film 33 shown in FIG. 13 (sometimes referred to as a “diffuser”) is dispersed in the matrix 33a and a matrix 33a formed of a resin material, as shown in an enlarged view in FIG. Particles 33b. The refractive index of the matrix 33a and the refractive index of the particles 33b are different from each other, so that light is diffused isotropically.

  FIG. 14 shows still another example of the light diffusing element 30. The light diffusing element 30 shown in FIG. 14 has a laminated structure in which four anisotropic diffusing layers 35a, 35b, 35c, and 35d that diffuse light anisotropically are laminated. These anisotropic diffusion layers 35a, 35b, 35c and 35d have different light diffusion characteristics.

FIG. 15 schematically shows the high diffusion angle range of the anisotropic diffusion layers 35a, 35b, 35c and 35d. As shown in FIG. 15, the anisotropic diffusion layers 35a, 35b, 35c and 35d each diffuse light only in a specific direction. Specifically, when the display surface is regarded as a clock face, the high diffusion angle range of the anisotropic diffusion layer 35a is θ ₁ from the normal direction of the display surface to 3 o'clock, and the anisotropic diffusion layer The high diffusion angle range of 35b is θ ₂ from the normal direction of the display surface to 9 o'clock. Further, the high diffusion angle range of the anisotropic diffusion layer 35c is θ ₃ from the display surface normal direction to 12 o'clock, and the high diffusion angle range of the anisotropic diffusion layer 35d is 6 from the display surface normal direction. when the direction is θ _4. θ ₁ , θ ₂ , θ _3, and θ ₄ are appropriately set according to the contrast cone of the light modulation unit. Thus, the light diffusing element 30 having three-dimensional anisotropy can also be obtained by combining the anisotropic diffusion layers 35a, 35b, 35c and 35d that diffuse light only in a specific direction. As the anisotropic diffusion layers 35a, 35b, 35c, and 35d, for example, Lumisty manufactured by Sumitomo Chemical Co., Ltd. can be used.

  Further, in the liquid crystal display device 100 according to the present embodiment, as shown in FIG. 1, the first polarizing plate 41 is arranged on the viewer side with respect to the light diffusing device 30, so that the light diffusing device from the viewer side. External light (ambient light) incident on the light is absorbed by the first polarizing plate 41, and the amount thereof is reduced. Therefore, reflection of external light on the surface of the light diffusing element 30 and total reflection of external light incident on the light diffusing element 30 at the interface between the light diffusing element 30 and other layers are reduced. Therefore, glare on the display surface is suppressed and high-quality display is realized.

  Further, when the light diffusing element is provided on the viewer side of the liquid crystal display panel, when the light that has passed through the liquid crystal display panel enters the light diffusing element, there is light traveling toward the liquid crystal display panel due to backscattering. This light is called stray light and causes a reduction in display quality.

  In the liquid crystal display device 100, since the second polarizing plate 28 is disposed between the liquid crystal layer 23 and the light diffusing element 30, such stray light is reduced by being absorbed by the second polarizing plate 28. Is done. Therefore, the display quality deterioration due to stray light is suppressed. Further, when the color filter 24 is provided on the front substrate 22 as in the present embodiment, a part of the stray light can be absorbed by the color filter 24, so that the effect of suppressing deterioration in display quality is high. .

  As described above, in the case of providing the second polarizing plate 28 for suppressing the deterioration of display quality due to stray light in addition to the first polarizing plate 41 for suppressing the deterioration of display quality due to reflection of external light. In order to efficiently use the light that has passed through the liquid crystal layer 23, the transmission axis of the first polarizing plate 41 and the transmission axis of the second polarizing plate 28 are preferably substantially parallel.

  One of the first polarizing plate 41 and the second polarizing plate 28 may be omitted. For example, the first polarizing plate 41 may be omitted as in the liquid crystal display device 200 shown in FIG. 16, or the second polarizing plate 28 is omitted as in the liquid crystal display device 300 shown in FIG. It may be.

  In the liquid crystal display device 200 shown in FIG. 16, a deterioration in display quality due to stray light is suppressed by the polarizing plate 28 provided between the light diffusing element 30 and the liquid crystal layer 23. On the other hand, in the liquid crystal display device 300 shown in FIG. 17, glare of the display surface is suppressed by the polarizing plate 41 disposed on the viewer side with respect to the light diffusing element 30.

  In the liquid crystal display device 100 shown in FIG. 1, an antireflection film may be disposed between the liquid crystal layer 23 and the light diffusing element 30 instead of the second polarizing plate 28. By providing the antireflection film between the liquid crystal layer 23 and the light diffusing element 30, reflection of stray light can be suppressed, and deterioration of display quality due to stray light can be suppressed. As the antireflection film, various films known as so-called AR films can be used. For example, a multilayer interference film including a plurality of layers having different refractive indexes can be used.

  Although various backlights can be used as the illumination element 10, in order to obtain a higher contrast ratio, it is preferable to use an element that can emit light with higher directivity. Specifically, the illumination element 10 has a light distribution such that the luminance in a direction that forms an angle of 30 ° or more with respect to the normal direction of the display surface is 3% or less of the luminance in the normal direction of the display surface. A sufficiently high contrast ratio can be easily realized.

  FIGS. 18A and 18B show examples of preferable light distribution of the illumination element 10. In the light distribution shown in FIG. 18A, the luminance in the normal direction of the display surface is the highest, and the luminance suddenly decreases as the angle increases. On the other hand, in the light distribution shown in FIG. 18B, a relatively high luminance is maintained from the normal direction of the display surface to around 30 °. In both of the light distributions shown in FIGS. 18A and 18B, the luminance in the direction forming an angle of 30 ° or more with respect to the display surface normal direction is the luminance in the display surface normal direction (0 °). 3% or less. Therefore, excellent display quality can be obtained by using the illumination element 10 having such a light distribution.

  Another example of the light distribution is shown in FIG. In the light distribution shown in FIG. 18C, the luminance in a direction that forms an angle of 30 ° or more with respect to the display surface normal direction is 8% to 13% or less of the luminance in the display surface normal direction (0 °). It is. Even when the illumination element 10 having such a light distribution is used, an optical modulation pattern (that is, the shape of the contrast cone) by the light modulation unit (the liquid crystal layer 23 and the phase difference compensation elements 25 and 27) is appropriately selected. Therefore, a sufficiently excellent display quality can be obtained.

  The light distribution shown in FIGS. 18A, 18B, and 18C (referred to as light distributions A, B, and C, respectively), FIG. 7A, FIG. 8A, and FIG. Table 1 shows the suitability of the combination with the contrast cone shown in a) (referred to as contrast cones A, B and C, respectively). In Table 1, “◯” indicates that the combination is better than “Δ”, and “◎” indicates that the combination is better.

  As can be seen from Table 1, the light distribution A shown in FIG. 18A and the light distribution B shown in FIG. 18B are very well combined with any of the contrast cones A, B, and C. . Table 1 also shows that the light distribution C shown in FIG. 18C is preferably combined with the contrast cone B and more preferably combined with the contrast cone C than the contrast cone A.

  As can be seen from these facts, in order to suitably perform optical modulation, the peak portion (high-brightness portion) of the light distribution of the illumination element 10 becomes a contrast cone (angle range indicated by the contrast cone). It is preferable that they are substantially coincident or located within the contrast cone. If the peak portion of the light distribution distribution protrudes outside the contrast cone, optical modulation may not be performed properly.

  The directivity of the degree shown in FIG. 18C can be easily realized by using, for example, the illumination element 10 including the total reflection type prism sheet 3 shown in FIG. Further, the directivity of the degree shown in FIGS. 18A and 18B can be realized by using a backlight disclosed in US Pat. No. 5,499,933 and US Pat. No. 5,598,281. The above-mentioned US Pat. No. 5,499,933 discloses an edge light type backlight in which a lenticular microprism is provided on the main surface of a light guide plate. In addition, the above-mentioned US Pat. No. 5,598,281 discloses a direct type backlight that allows light emitted from a light source to enter a microcollimator and a microlens through an opening.

The contrast cone shown in FIG. 7A can be realized by combining, for example, an STN mode liquid crystal layer and a phase difference plate NRF (Nz coefficient is 1.0) manufactured by Nitto Denko Corporation. The contrast cone shown in FIG. 7B is realized by combining, for example, an STN mode liquid crystal layer and a phase difference plate NRZ (Nz coefficient is 0.5 to 0.8) manufactured by Nitto Denko Corporation. it can. The contrast cone shown in FIG. 7C can be realized by combining, for example, an STN mode liquid crystal layer and a phase difference plate NRZ (Nz coefficient is 0 to 0.4) manufactured by Nitto Denko Corporation. Incidentally, Nz coefficient is one of the indices representing the refractive index component of the phase difference plate n _x, n _y, the magnitude relation of n _z.

  According to the present invention, display blur due to the light diffusing element can be reduced, and high-quality display can be performed. The present invention is suitably used for transmissive liquid crystal display devices in general, and in particular, it is suitably used for liquid crystal display devices in display modes (for example, STN mode, TN mode, and ECB mode) with low viewing angle characteristics.

  In a display mode using birefringence such as the STN mode, the display is adversely affected by light obliquely incident on the liquid crystal layer. Therefore, highly directional light is incident on the liquid crystal layer and modulated by the liquid crystal layer. It is preferable to use a viewing angle widening technique in which light is diffused by a light diffusing element.

It is sectional drawing which shows typically the liquid crystal display device 100 in suitable embodiment of this invention. 3 is a side view showing an example of an illumination element (backlight) included in the liquid crystal display device 100. FIG. It is a figure for demonstrating the function of the total reflection type prism sheet with which the illumination element shown in FIG. 2 is provided. FIG. 4 is a diagram for explaining a function of a light diffusing element included in the liquid crystal display device 100. (A) And (b) is a figure for demonstrating the function of a light-diffusion element. It is a figure which shows an example of the contrast characteristic of a light modulation part, and is a figure which shows the relationship between the azimuth | direction in a display surface, and contrast ratio. (A) And (b) is a figure which shows the preferable combination of the contrast cone of a light modulation part, and the light-diffusion characteristic of a light-diffusion element. (A) And (b) is a figure which shows the preferable combination of the contrast cone of a light modulation part, and the light-diffusion characteristic of a light-diffusion element. (A) And (b) is a figure which shows the preferable combination of the contrast cone of a light modulation part, and the light-diffusion characteristic of a light-diffusion element. It is a perspective view which shows the example of a light-diffusion element. (A) And (b) is sectional drawing which shows typically the prism with which the light-diffusion element shown in FIG. 10 is provided. It is sectional drawing which shows the other example of a light-diffusion element. It is a figure which shows the example of the isotropic diffusion layer with which the light-diffusion element shown in FIG. 12 is provided. It is sectional drawing which shows another example of a light-diffusion element. It is a figure for demonstrating the function of the anisotropic diffusion layer contained in the light-diffusion element shown in FIG. It is sectional drawing which shows typically the other liquid crystal display device 200 in suitable embodiment of this invention. It is sectional drawing which shows typically the other liquid crystal display device 300 in suitable embodiment of this invention. (A), (b) and (c) is a graph which shows the example of the light distribution of the light radiate | emitted from the illumination element 10. FIG. It is a perspective view which shows the conventional liquid crystal display device 500 typically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Light guide plate 3 Prism sheet 3a Prism 10 Illumination element (backlight)
DESCRIPTION OF SYMBOLS 20 Liquid crystal display panel 21 Back substrate 22 Front substrate 23 Liquid crystal layer 24 Color filter 25, 27 Phase difference compensation element 26 Polarizing plate (3rd polarizing plate)
28 Polarizing plate (second polarizing plate)
30 Light diffusing element 31 Prism 31a Top surface of prism 31b Bottom surface of prism 31c, 31d, 31e and 31f Inclined side surface of prism 32 Flattening layer 33 Isotropic diffusion layer 33a Matrix 33b Particles 35a, 35b, 35c, 35d Anisotropic diffusion layer 41 Polarizing plate (first polarizing plate)
100, 200, 300 Liquid crystal display device

Claims (16)

A light source;
A liquid crystal display panel that modulates light emitted from the light source;
A light diffusing element disposed closer to the viewer than the liquid crystal display panel;
A liquid crystal display device comprising:
The light diffusing element diffuses light incident at an angle within a specific angle range more strongly than light incident at another angle;
The specific angle range is different between a first plane parallel to the display surface normal direction and a second plane parallel to the display surface normal direction and intersecting the first surface;
The specific angle range in the first plane is A, the specific angle range in the second plane is B, and the viewing angle in which the contrast ratio of the liquid crystal display panel is 1 or more in the first plane When the range is C, and the viewing angle range in which the contrast ratio of the liquid crystal display panel is 1 or more in the second plane is D,
The ratio A / B between the specific angle range A in the first plane and the specific angle range B in the second plane is the viewing angle range C in the first plane and the second range. A liquid crystal display device substantially equal to a ratio C / D with respect to the viewing angle range D in the plane.   The liquid crystal display device according to claim 1, wherein the first surface and the second surface are substantially orthogonal to each other. The viewing angle range in which the contrast ratio of the liquid crystal display panel is 1 or more is the widest in the first plane and the narrowest in the second plane,
3. The liquid crystal display device according to claim 1, wherein the specific angle range in which the light diffusing element diffuses light strongly is the widest in the first plane and the narrowest in the second plane.   The specific angle range A in the first plane is substantially equal to or narrower than the viewing angle range C in the first plane, and the specific angle range B in the second plane is 4. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is substantially equal to or narrower than the viewing angle range D in the second plane.   The liquid crystal display device according to claim 1, wherein a haze value of the light diffusing element with respect to light incident at an angle within the specific angle range is 5 or more.   The light diffusing element includes a plurality of prisms, and each of the plurality of prisms has a shape in which a cross section parallel to the first surface and a cross section parallel to the second surface are different from each other. The liquid crystal display device according to any one of 1 to 5.   6. The liquid crystal display device according to claim 1, wherein the light diffusing element includes a plurality of anisotropic diffusion layers each diffusing light anisotropically and having mutually different light diffusion characteristics.   The liquid crystal display device according to claim 1, wherein the liquid crystal display panel includes a pair of substrates and a liquid crystal layer provided between the pair of substrates.   The liquid crystal display device according to claim 8, wherein the liquid crystal display panel further includes at least one phase difference compensation element.   The liquid crystal display device according to claim 8, further comprising a first polarizing element disposed closer to an observer than the light diffusing element. A second polarizing element disposed between the liquid crystal layer and the light diffusing element;
The liquid crystal display device according to claim 10, wherein a transmission axis of the first polarizing element and a transmission axis of the second polarizing element are substantially parallel.   The liquid crystal display device according to claim 9, further comprising a third polarizing element provided on a side opposite to the viewer side with respect to the liquid crystal layer.   The liquid crystal display device according to claim 1, further comprising an illumination element including the light source.   The lighting device has a light distribution such that the luminance in a direction forming an angle of 30 ° or more with respect to the normal direction of the display surface is 13% or less of the luminance in the normal direction of the display surface. Liquid crystal display device.   The lighting device has a light distribution such that the luminance in a direction forming an angle of 30 ° or more with respect to the normal direction of the display surface is 3% or less of the luminance in the normal direction of the display surface. Liquid crystal display device.   The liquid crystal display device according to claim 13, wherein the illumination element includes a directivity control element that controls directivity of light emitted from the light source.

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