JP2007047409A - Liquid crystal display device, and mobile electronic apparatus with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device which is easily made thiner in thickness and can display more high-quality image than heretofore, and to provide a mobile electronic apparatus with the liquid crystal display device. <P>SOLUTION: The liquid crystal display device comprises: a first substrate 10; a second substrate 20 disposed nearer to an observer than the first substrate 10; a liquid crystal layer 30 between the substrates; a light diffusing element 24 disposed nearer to the observer than the liquid crystal layer 30; and a light source 2 disposed in the side of the first substrate 10. The first substrate 10 comprises a selective reflection layer 14 which selectively reflects linearly polarized light in a specified polarization direction from the light entering the side face 10a into the inside of the substrate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device suitably used for a portable electronic device.

  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.

  Since the liquid crystal display device is a non-light-emitting display element, the liquid crystal display device includes an illumination device called a backlight, and performs display using light from the backlight. The backlight is generally composed of a light source, a reflector, a light guide plate, a lens sheet, and the like. Since the thickness of the backlight greatly affects the thickness of the entire liquid crystal display device, it is necessary to make the backlight thin in order to reduce the thickness of the liquid crystal display device.

  Backlights are broadly classified into “direct type” as disclosed in Patent Document 1 and “edge light type” as disclosed in Patent Document 2. The “direct type” is a system in which a plurality of light sources 702 such as cold cathode tubes are arranged directly below the liquid crystal display panel 701 as shown in FIG. On the other hand, in the “edge light type”, as shown in FIG. 25, a light source 802 is disposed on the side of a light guide plate 803 provided immediately below the liquid crystal display panel 801, and light from the light source 802 is liquid crystal by the light guide plate 803. This is a system that leads to the display panel 801.

Since the edge light type backlight can be easily reduced in thickness as compared with the direct type backlight, the edge light type backlight is currently used in many small liquid crystal display devices.
JP 2003-215585 A JP-A-8-94444

  However, recently, with the explosive spread of portable electronic devices, liquid crystal display devices are required to be thinner. In recent years, there has been a demand for higher quality displays for small liquid crystal display devices used in portable electronic devices. Even if a conventional edge light type backlight is used, these requirements cannot be sufficiently met.

  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 be made thinner and can display higher quality than before, and a portable electronic device including the liquid crystal display device. There is.

  A liquid crystal display device according to the present invention includes a first substrate, a second substrate disposed closer to the viewer than the first substrate, and a liquid crystal layer provided between the first substrate and the second substrate. A light diffusing element disposed closer to the viewer than the liquid crystal layer, and a light source that is provided on a side of the first substrate and emits light toward a side surface of the first substrate. Includes a selective reflection layer that selectively reflects linearly polarized light in a specific polarization direction among light incident on the inside of the first substrate from the side surface of the first substrate, thereby achieving the above object. .

  In a preferred embodiment, the first substrate is formed on a transparent substrate having two main surfaces facing each other and a main surface on the liquid crystal layer side of the two main surfaces of the transparent substrate, A low refractive index layer having a refractive index lower than that of the transparent substrate.

  In a preferred embodiment, the selective reflection layer is provided on a main surface opposite to the liquid crystal layer side of the two main surfaces of the transparent substrate.

  In a preferred embodiment, the selective reflection layer includes a dielectric film.

  In a preferred embodiment, the dielectric film is inclined at an angle of 48 ° or more and 54 ° or less with respect to the main surface of the transparent substrate on the liquid crystal layer side.

  In a preferred embodiment, the dielectric film includes an inclined portion inclined at an angle of 48 ° or more and 54 ° or less with respect to the liquid crystal side main surface of the transparent substrate.

  In a preferred embodiment, the light diffusing element has a Fresnel reflectance of 4% or less with respect to light incident on the light diffusing element from the liquid crystal layer side.

In a preferred embodiment, the light diffusing element includes a first layer and a second layer having different refractive indexes in this order from the liquid crystal layer side, and the first layer has a refractive index n ₁ and the second layer. The refractive index n _{2 of the} layer satisfies the relationship of n ₁ <n ₂ , 1.3 ≦ n ₁ ≦ 1.7 and 1.3 ≦ n ₂ ≦ 1.7.

  In a preferred embodiment, the light diffusing element is a lens sheet including a plurality of lenses, and an interface between the first layer and the second layer is a lens surface of the plurality of lenses.

  In a preferred embodiment, the liquid crystal display device according to the present invention further includes a polarizing plate having a transmission axis substantially parallel to the specific polarization direction and provided between the light source and a side surface of the first substrate. Prepare.

  In a preferred embodiment, the liquid crystal display device according to the present invention has a reflector provided on the side opposite to the observer side with respect to the selective reflection layer, and a transmission axis substantially parallel to the specific polarization direction. And a polarizing plate provided between the selective reflection layer and the reflection plate.

  A portable electronic device according to the present invention includes a liquid crystal display device having the above-described configuration, thereby achieving the above-described object.

  According to the present invention, it is possible to provide a liquid crystal display device that can be made thinner and display higher quality than before and a portable electronic device including such a liquid crystal display device.

  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 schematically shows a liquid crystal display device 100 according to this embodiment. As shown in FIG. 1, the liquid crystal display device 100 includes a pair of substrates 10 and 20 facing each other, and a liquid crystal layer 30 provided therebetween. Hereinafter, the substrate 10 disposed on the back side is referred to as a “rear substrate”, and the substrate 20 disposed on the front side (that is, the observer side relative to the back substrate 10) is referred to as a “front substrate”.

  A linear light source 2 is provided on the side of the back substrate 10. The linear light source 2 emits light toward the side surface 10 a of the back substrate 10. The linear light source 2 may be, for example, a cold cathode tube, or may be a combination of a point light source such as a light emitting diode (LED) and a linear light guide.

  The back substrate 10 includes a transparent substrate (for example, a glass substrate or a plastic substrate) 11 and a low refractive index layer 12 formed on the main surface 11a of the transparent substrate 11 on the liquid crystal layer 30 side (observer side). Yes. The low refractive index layer 12 has a refractive index lower than that of the transparent substrate 11. On the low refractive index layer 12, an electrode for applying a voltage to the liquid crystal layer 30 and an alignment film are formed (both not shown).

  Further, the back substrate 10 includes a selective reflection layer 14 that selectively reflects linearly polarized light in a specific polarization direction out of light incident on the inside of the back substrate 10 from the side surface 10a. The selective reflection layer 14 is formed on the main surface 11b on the opposite side of the transparent substrate 11 from the liquid crystal layer 30 side.

  The selective reflection layer 14 in the present embodiment includes a plurality of dielectric films 15 therein. The plurality of dielectric films 15 are inclined at a predetermined angle with respect to the main surfaces 11a and 11b of the transparent substrate 11, and are arranged at a predetermined interval (pitch). These dielectric films 15 have a refractive index different from that of the surrounding material, and are single-layer or multi-layer thin films formed to have a predetermined thickness.

  At the interface between the dielectric film 15 and the surrounding material, the light reflectance has a polarization dependency. Specifically, the reflectance of S-polarized light whose polarization direction is perpendicular to the incident surface (a plane including the normal line and the ray of the interface) is high, and the reflectance of P-polarized light whose polarization direction is parallel to the incident surface is low. In particular, for light incident at an angle close to the Brewster angle, the reflectance of P-polarized light is substantially zero and only S-polarized light is reflected. Accordingly, linearly polarized light having a specific polarization direction is selectively reflected at the interface between the dielectric film 15 and the surrounding material as shown in an enlarged manner in FIG. In the present embodiment, as shown in FIG. 1, the selective reflection layer 14 reflects linearly polarized light whose polarization direction is substantially parallel to the main surfaces 11 a and 11 b of the transparent substrate 11 (perpendicular to the paper surface of FIG. 1).

  The front substrate 20 has a transparent substrate 21 disposed so as to face the back substrate 10. A color filter 22 is provided on the main surface 21 a of the transparent substrate 21 on the liquid crystal layer 30 side. On the main surface 21a, an electrode for applying a voltage to the liquid crystal layer 30 and an alignment film are also formed (both not shown).

  On the main surface 21b on the observer side of the transparent substrate 21, a retardation plate 23, a light diffusing element 24, and a polarizing plate 25 are laminated in this order. The light diffusing element 24 arranged on the viewer side with respect to the liquid crystal layer 30 diffuses the light that has passed through the liquid crystal layer 30.

The light diffusing element 24 in the present embodiment is a lenticular lens sheet having a plurality of semi-cylindrical lenticular lenses 24 'as shown in FIG. The light diffusing element 24, which is a lenticular lens sheet, has a first layer 24a and a second layer 24b having different refractive indexes in this order from the liquid crystal layer 30 side, and the first layer 24a and the second layer 24b The interface constitutes the lens surface of the lenticular lens 24 '. In order to suitably diffuse light on the lens surface, the refractive index n ₁ of the first layer 24a is lower than the refractive index n ₂ of the second layer 24b (that is, the relationship of n ₁ <n ₂ is satisfied). ) Is set.

  In the liquid crystal display device 100 according to the present embodiment, light emitted from the linear light source 2 and incident on the back substrate 10 through the side surface 10a is the main surface 11a on the observer side of the transparent substrate 11 and the selective reflection layer 14. It propagates in the back substrate 10 while repeating total reflection with the surface 14a opposite to the viewer side. The low-refractive index layer 12 is provided in order to efficiently totally reflect light on the observer-side main surface 11 a of the transparent substrate 11. A part of the light propagating in the back substrate 10 is reflected toward the observer side (the liquid crystal layer 30 side) by the dielectric film 15 provided in the selective reflection layer 14 and is emitted from the back substrate 10. The light emitted from the back substrate 10 is modulated by the liquid crystal layer 30, thereby displaying.

  Thus, in the liquid crystal display device 100 according to the present embodiment, the back substrate 10 including the selective reflection layer 14 is used, and the back substrate 10 also functions as a light guide plate. Therefore, compared with the case of using a conventional edge light type backlight, it is possible to reduce the thickness and cost by not providing the light guide plate. Further, since the selective reflection layer 14 of the back substrate 10 selectively reflects linearly polarized light (light having a specific polarization state) in a specific polarization direction, it is necessary to provide a separate polarizing plate on the back side of the liquid crystal layer 30. Therefore, it is possible to further reduce the thickness and cost.

  Moreover, when the selective reflection layer 14 including the dielectric film 15 is used as in the present embodiment, high directivity can be imparted to the light emitted from the back substrate 10. That is, the luminance in the normal direction of the display surface (front direction) of the light emitted from the back substrate 10 can be remarkably increased. If the light emitted from the back substrate 10 has high directivity, the light that is obliquely incident on the liquid crystal layer 30 is small, so that the light passing through the liquid crystal layer 30 can be uniformly modulated. That is, uniform retardation can be given to the light passing through the liquid crystal layer 30. Therefore, the viewing angle dependence of display quality due to the refractive index anisotropy of liquid crystal molecules can be reduced. In general, the liquid crystal display device is designed to have the highest contrast ratio for the light incident in parallel to the normal direction of the display surface, so that the light having high directivity as described above is incident on the liquid crystal layer 30. By doing so, the contrast ratio can be improved.

  The light having passed through the liquid crystal layer 30 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). The light diffusing element 24 disposed on the viewer side of the liquid crystal layer 30 reduces the luminance deviation of the light that has passed through the liquid crystal layer 30 and widens the viewing angle. Therefore, in the liquid crystal display device 100, both a high contrast ratio and a wide viewing angle characteristic are realized.

  As described above, the liquid crystal display device 100 according to the present embodiment can not only achieve a thinner and lower cost than conventional ones, but can also display a high quality display. Hereinafter, a preferred configuration for realizing higher quality display in the liquid crystal display device 100 will be described.

  First, in order to display with a low viewing angle dependency and a high contrast ratio, it is preferable that light emitted from the back substrate 10 has higher directivity. Specifically, as shown in FIG. 2, the light distribution of the light emitted from the back substrate 10 has a half-value angle of ± 3 ° or less (an angle at which the luminance is 50% or less of the luminance in the normal direction of the display surface). With this, the viewing angle dependency can be made sufficiently small, and a sufficiently high contrast ratio can be realized.

  The inventor of the present application examined in detail the relationship between the light distribution of the light emitted from the back substrate 10 and the configuration of the dielectric film 15 of the selective reflection layer 14, and as shown in FIG. By setting the inclination angle (inclination angle with respect to the main surface 11a of the transparent substrate 11 on the liquid crystal layer 30 side) α to 48 ° or more and 54 ° or less, light can be reflected within ± 3 ° from the normal direction of the display surface. It was found that the half-value angle of the light distribution can be made ± 3 ° or less.

  Further, from the viewpoint of realizing a high contrast ratio, it is preferable to suppress backscattering of the light diffusing element 24. As shown in FIG. 4, a part of the light that passes through the liquid crystal layer 30 and enters the light diffusing element 24 is the interface between the phase difference plate 23 and the first layer 24a or the first layer 24a and the second layer 24b. Backscattered by Fresnel reflection at the interface. Backscattered light is called stray light and causes a reduction in contrast ratio.

  The inventor of the present application can greatly suppress the reduction in the contrast ratio by setting the Fresnel reflectance of the light diffusing element 24 to the light incident on the light diffusing element 24 from the liquid crystal layer 30 side to a predetermined value or less. I found it. Table 1 and FIG. 5 show the relationship between the Fresnel reflectance of the light diffusing element 24 and the contrast ratio.

  As can be seen from Table 1 and FIG. 5, when the Fresnel reflectivity exceeds 4%, the contrast ratio rapidly decreases. On the other hand, by setting the Fresnel reflectance to 4% or less, it is possible to suppress a decrease in contrast ratio and keep the contrast ratio at 90% or more. Further, by setting the Fresnel reflectance to 3% or less, it is possible to further suppress the reduction in contrast ratio and keep the contrast ratio at 95% or more.

The inventor of the present application has also made extensive studies on a preferable configuration for setting the Fresnel reflectance of the light diffusing element 24 to 4% or less. As a result, the refractive indexes n ₁ and n ₂ of the first layer 24a and the second layer 24b constituting the light diffusing element 24 are set to 1.3 ≦ n ₁ ≦ 1.7 and 1.3 ≦ n ₂ ≦ 1.7. It was found that the Fresnel reflectance of the light diffusing element 24 can be reduced to 4% or less by setting so as to satisfy the above relationship. Hereinafter, the examination results will be described in more detail.

First, as can be seen from FIG. 4, the Fresnel reflectance R representing the degree of backscattering of the light diffusing element 24 is the Fresnel reflectance R ₁ at the interface between the phase difference plate 23 and the first layer 24a, and the first layer. This is the sum of the Fresnel reflectivity R ₂ at the interface between 24a and the second layer 24b.

The Fresnel reflectivity R ₁ at the interface between the retardation film 23 and the first layer 24a is expressed by the following equation (1), where n ₃ is the refractive index of the retardation film 23.
R ₁ = [(n ₁ −n ₃ ) / (n ₁ + n ₃ )] ² (1)

Further, the Fresnel reflectivity R ₂ at the interface between the first layer 24a and the second layer 24b is expressed by the following equation (2).
R ₂ = [(n ₂ −n ₁ ) / (n ₂ + n ₁ )] ² (2)

Accordingly, the Fresnel reflectivity R of the light diffusing element 24 is expressed by the following expression (3) from the above expressions (1) and (2).
R = R ₁ + R ₂
= [(N ₁ −n ₃ ) / (n ₁ + n ₃ )] ² + [(n ₂ −n ₁ ) / (n ₂ + n ₁ )] ² ... (3)

Tables 2 to 9 below show the relationship between the refractive indices n ₁ , n ₂ and n _{3 of} the first layer 24a, the second layer 24b and the retardation plate 23 and the Fresnel reflectivity R, R ₁ and R _2. . The relationships shown in Tables 2 to 9 are shown as graphs in FIGS. 6 to 13, the refractive index n ₁ of the first layer 24 a and the refractive index n ₃ of the phase difference plate 23 are set to constant values, and the refractive index n ₂ of the second layer 24 _b is from 1.3 to 1.7. It is a graph which shows the change of the Fresnel reflectance R of the light-diffusion element 24 when making it change.

Tables 2 to 4 show cases where the refractive index n ₁ of the first layer 24 a is ₁ to 1.2 and the relationship of 1.3 ≦ n ₁ ≦ 1.7 is not satisfied. In such a case, as can be seen from FIGS. 6 to 8, the Fresnel reflectivity R of the light diffusing element 24 may exceed 4%.

In contrast, in Tables 5 to 9, the refractive index n ₂ of the refractive index n ₁ and a second layer 24b of the first layer 24a is 1.3 ≦ n ₁ ≦ 1.7 and 1.3 ≦ n ₂ ≦ The case where the relationship of 1.7 is satisfied is shown. In such a case, as can be seen from FIGS. 9 to 13, the Fresnel reflectance R of the light diffusing element 24 can be 4% or less. Therefore, so as to satisfy the relationship of refractive index n ₂ of 1.3 ≦ n ₁ ≦ 1.7 and 1.3 ≦ n ₂ ≦ 1.7 in refractive index n ₁ and a second layer 24b of the first layer 24a By setting, it is possible to realize a high-quality display in which a decrease in contrast ratio due to backscattering is suppressed.

  Next, preferred configurations and modifications of the rear substrate 10 and the light diffusing element 24 of the liquid crystal display device 100 will be described.

First, a preferable configuration of the low refractive index layer 12 of the back substrate 10 will be described. In order to propagate light efficiently in the back substrate 10, the difference between the refractive index of the low refractive index layer 12 and the refractive index of the transparent substrate 11 is preferably about 0.1 or more, and about 0.18. More preferably, it is the above. Examples of the material for the low refractive index layer 12 include MgF ₂ (refractive index is about 1.38), perfluoro resin (refractive index is about 1.34), and silicon oxide (refractive index is about 1.3). Can be used.

  Next, a preferable configuration and modification of the selective reflection layer 14 of the back substrate 10 will be described.

  As an optical element that utilizes the polarization dependence of the reflectance on the surface of a dielectric film, a polarization beam splitter or the like is known. Similarly to the dielectric films of the optical elements, the dielectric film 15 of the selective reflection layer 14 is formed to have a thickness that satisfies a predetermined condition with respect to the wavelength of light to be reflected. The reflectance of polarized light can be lowered and the reflectance of S-polarized light can be increased.

As described above, the inclination angle α of the dielectric film 15 (inclination angle with respect to the main surface 11a on the viewer side of the transparent substrate 11) reduces the viewing angle dependency and displays a high contrast ratio. It is preferably 48 ° or more and 54 ° or less. Further, as the material of the dielectric film 15, various materials such as MgF ₂ , SiO ₂ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ can be used.

  The shape of the dielectric film 15 (the shape seen from the layer normal direction of the liquid crystal layer 30) can be an arbitrary shape. For example, the dielectric film 15 may be formed in a line shape (strip shape) as shown in FIG. 14A, or may be formed in an island shape (dot shape) as shown in FIG. 14B. May be. 14A and 14B are views of the linear light source 2 and the back substrate 10 as viewed from the normal direction of the display surface.

  The ratio of the area obtained by projecting the dielectric film 15 onto the main surface 11a with respect to the area of the main surface 11a of the transparent substrate 11 is constant in the main surface 11a as shown in FIGS. 14 (a) and 14 (b). Or may not be constant. For example, as shown in FIGS. 15A and 15B, the ratio of the dielectric film 15 may increase as the distance from the linear light source 2 increases. The amount of light propagating in the back substrate 10 decreases as the distance from the linear light source 2 increases. However, the distance from the linear light source 2 increases as the distance from the linear light source 2 increases, as shown in FIGS. When the ratio is increased, the intensity distribution of light emitted from the back substrate 10 can be made more uniform. In order to increase the ratio of the dielectric film 15 as the distance from the linear light source 2 increases, the area of the dielectric film 15 formed at a constant repetition pitch as shown in FIGS. The distance from the linear light source 2 may be increased, or the repetition pitch of the dielectric films 15 formed so as to have substantially the same area may be decreased as the distance from the linear light source 2 is increased.

  The selective reflection layer 14 is formed as follows, for example.

  First, as shown in FIG. 16 (a), on a flat film 16 formed of a resin (for example, ZEONOR manufactured by Nippon Zeon Co., Ltd. having a refractive index of 1.53), a plurality of cross sections having a right triangle shape are formed. The convex portion 17 is formed using a resin (for example, an ultraviolet curable resin having a refractive index of 1.53).

Next, as shown in FIG. 16 (b), a dielectric material (for example, refractive index) is formed on the inclined surface of the convex portion 17 (the surface inclined with respect to the main surface of the flat film 16) via the mask 3. The dielectric film 15 is formed by vapor-depositing TiO _{2 having a} refractive index of 2.2 and ZrO ₂ having a refractive index of 2.0. The thickness (for example, 70 nm) and the pitch P (for example, 60 μm) of the dielectric film 15 are appropriately determined according to the type of the dielectric material.

  Subsequently, as shown in FIG. 16C, an adhesive material (for example, an ultraviolet curable resin having a refractive index of 1.53 or an adhesive material) is applied so as to cover the convex portion 17 to form the adhesive layer 18. To do.

  Thereafter, as shown in FIG. 16 (d), the adhesive layer 18 is brought into contact with the main surface 11b of the transparent substrate (for example, a glass substrate having a refractive index of 1.52), and the adhesive layer 18 is cured. The selective reflection layer 14 is formed on the 11 major surfaces 11b.

  The selective reflection layer 14 is also formed as follows.

  First, as shown in FIG. 17A, a plurality of convex portions 17 having a right triangle shape in cross section are formed on a flat film 16 made of resin using a resin. In the process shown in FIG. 16A, the convex portions 17 are arranged on the film 16 without a gap, whereas here, the convex portions 17 are arranged at a predetermined interval. Moreover, the convex part 17 is formed so that the space | interval of the adjacent convex part 17 becomes so narrow that it distances from the light source 2 arrange | positioned later.

  Next, as shown in FIG. 17B, a dielectric film 15 is formed by vapor-depositing a dielectric material on the film 16 on which the convex portions 17 are formed. At this time, the dielectric film 15 is formed on the inclined surface of the convex portion 17 and on the portion of the film 16 where the convex portion 17 is not formed.

  Subsequently, as shown in FIG. 17C, an adhesive layer 18 is formed by applying an adhesive material so as to cover the dielectric film 15.

  Thereafter, as shown in FIG. 17D, the selective reflection layer 14 is formed on the main surface 11 b of the transparent substrate 11 by bringing the adhesive layer 18 into contact with the main surface 11 b of the transparent substrate 11 and curing the adhesive layer 18. Form.

  The dielectric film 15 of the selective reflection layer 14 formed as shown in FIGS. 17A to 17D is an inclined portion 15a inclined with respect to the main surface 11a of the transparent substrate 11 and parallel to the main surface 11a. Among them, the inclined portion 15a reflects light propagating through the back substrate 10 toward the main surface 11a of the transparent substrate 11 at an angle that does not satisfy the total reflection condition. It is the inclined portion 15a that contributes to extracting light from the main surface 11a. That is, only the inclined portion 15a functions as a substantial selective reflection film.

  In the formation process shown in FIGS. 16A to 16D, it is necessary to control the arrangement of the dielectric film 15 using the mask 3, whereas the process shown in FIGS. 17A to 17D is performed. In the formation process, the arrangement process of the inclined portions 15a that substantially function as the selective reflection film can be controlled simply by appropriately setting the arrangement of the convex portions 17, so that the formation process can be simplified.

  The inclination angle α of the inclined portion 15a of the dielectric film 15 shown in FIG. 17D is entirely inclined with respect to the main surface 11a of the transparent substrate 11 as shown in FIG. Like the inclination angle α of the dielectric film 15 (which is an inclined portion), it is preferably 48 ° or more and 54 ° or less.

  In the present embodiment, the selective reflection layer 14 having the dielectric film 15 therein is exemplified. However, the selective reflection layer 14 is not limited to those exemplified here, and selectively reflects linearly polarized light in a specific polarization direction. What can be used can be widely used. The selective reflection layer 14 including the dielectric film 15 as exemplified in the present embodiment can be manufactured by a simple manufacturing process, and the difference between the reflectance of P-polarized light and the reflectance of S-polarized light is increased. It is easy to set a high reflectance. Furthermore, it is easy to give high directivity to the light emitted from the back substrate 10.

  The selective reflection layer 14 formed as described above has a degree of polarization as compared with a normal polarizing plate formed by adsorbing and stretching a dichroic dye such as iodine or dye on a PVA film. May be low. Therefore, from the viewpoint of obtaining a high contrast ratio, a further polarizing plate may be provided in addition to the polarizing plate 25 provided on the front substrate 20.

  FIG. 18 shows a liquid crystal display device 200 having a further polarizing plate. The liquid crystal display device 200 is different from the liquid crystal display device 100 shown in FIG. 1 in that a polarizing plate 42 and a reflection plate 44 are provided on the back side of the selective reflection layer 14.

  As shown in FIG. 18, the liquid crystal display device 200 is provided between the selective reflection layer 14 and the reflective plate 44 provided on the side opposite to the observer, and between the selective reflective layer 14 and the reflective plate 44. And a polarizing plate 42. The reflection plate 44 is made of silver alloy, aluminum, or the like. The polarizing plate 42 is disposed so that the transmission axis is substantially parallel to the polarization direction of the light reflected by the selective reflection layer 14.

  In the liquid crystal display device 100 shown in FIG. 1, the dielectric film 15 of the selective reflection layer 14 is inclined so as to reflect the light propagating in the back substrate 10 toward the liquid crystal layer 30 side. On the other hand, in the liquid crystal display device 200, as shown in FIG. 18, the dielectric film 15 of the selective reflection layer 14 reflects the light propagating in the back substrate 10 to the side opposite to the liquid crystal layer 30, that is, the polarizing plate 42 side. So as to be inclined.

  In the liquid crystal display device 200 having the above-described configuration, part of the light propagating through the back substrate 10 and the selective reflection layer 14 is once opposite to the liquid crystal layer 30 by the dielectric film 15 of the selective reflection layer 14, that is, polarized. The light is reflected toward the plate 42 side, reflected by the reflection plate 44, passes through the polarizing plate 42 again, and then exits from the back substrate 10.

  In the liquid crystal display device 200, since the light reflected by the selective reflection layer 14 passes through the polarizing plate 42 before entering the liquid crystal layer 30, a high contrast ratio is obtained even when the polarization degree of the selective reflection layer 14 is low. be able to.

  However, when a configuration such as the liquid crystal display device 200 is adopted, the light reflected by the selective reflection layer 14 passes through the polarizing plate 42 twice before entering the liquid crystal layer 30, so that the luminance decreases. May end up.

  By adopting a configuration such as the liquid crystal display device 300 shown in FIG. 19, it is possible to suppress a decrease in luminance while obtaining a high contrast ratio. The liquid crystal display device 300 is different from the liquid crystal display device 100 shown in FIG. 1 in that it includes a polarizing plate 46 provided between the light source 2 and the side surface of the back substrate 10. The polarizing plate 46 has a transmission axis substantially parallel to the polarization direction of the light reflected by the selective reflection layer 14.

  In the liquid crystal display device 300, since the light emitted from the light source 2 passes through the polarizing plate 46 before entering the back substrate 10, a high contrast ratio can be obtained even when the selective reflection layer 14 itself has a low degree of polarization. it can. Further, in the liquid crystal display device 300, the light emitted from the light source 2 passes through the polarizing plate 46 only once before entering the liquid crystal layer 30, so that the luminance is reduced as compared with the liquid crystal display device 200 shown in FIG. Can be suppressed.

  In the liquid crystal display device 300 shown in FIG. 19, the light emitted from the light source 2 passes through the polarizing plate 46 before entering the back substrate 10, and thus enters the back substrate 10 as linearly polarized light. Therefore, the selective reflection layer 14 of the liquid crystal display device 300 is replaced with a simple light reflection structure, that is, a structure that reflects light at a predetermined angle toward the liquid crystal layer regardless of the polarization direction (for example, a microprism array). However, it can be displayed once. However, the linearly polarized light incident on the back substrate is slightly depolarized while propagating through the back substrate. In such a configuration, the depolarized component is also reflected to the liquid crystal layer side by the light reflecting structure. As a result, the contrast ratio decreases. On the other hand, since the selective reflection layer 14 is used in the liquid crystal display device 300, it is possible to suppress a decrease in contrast ratio due to depolarization that occurs in the process in which linearly polarized light propagates through the back substrate 10. According to the study of the present inventor, when the configuration of the liquid crystal display device 300 is adopted, a contrast ratio of about 6 times or more can be obtained as compared with the configuration in which the selective reflection layer 14 of the liquid crystal display device 300 is replaced with a simple light reflection structure. I understood it.

  Next, a preferred configuration and modification examples of the light diffusing element 24 will be described.

  In the present embodiment, a lenticular lens sheet is exemplified as the light diffusing element 24. Since the lenticular lens 24 'mainly diffuses light in a direction orthogonal to the extending direction thereof, the extending direction of the lenticular lens 24' is appropriately set according to the light distribution of the light emitted from the back substrate 10. The The light reflected by the selective reflection layer 14 including the dielectric film 15 is a light incident surface on the dielectric film 15 (a plane including normal lines and light rays at the interface between the dielectric film 15 and the surrounding material). Therefore, the extending direction of the lenticular lens 24 ′ is substantially perpendicular to the light incident surface to the dielectric film 15 as shown in FIG. 1 and the like. Is preferred.

  The light diffusing element 24 is not limited to the lenticular lens sheet exemplified here, and various known elements can be used. For example, as the light diffusing element 24, a prism sheet (for example, a total reflection prism sheet) having a plurality of prisms may be used.

  Alternatively, a diffusion film 26 using internal scattering as shown in FIG. 20 may be used as the light diffusing element 24. The diffusion film 26 (sometimes referred to as a “diffuser”) includes a matrix 26a formed of a resin material and particles 26b dispersed in the matrix 26a, as shown in an enlarged view in FIG. Have. The particles 26b have a refractive index different from that of the matrix 26a.

  Further, as shown in FIG. 21, a combination of the diffusion film 26 and the lens sheet 24 may be used, or a combination of the diffusion film 26 and the prism sheet may be used. While the lens sheet 24 and the prism sheet diffuse light anisotropically, the diffusion film 26 diffuses light relatively isotropically. Therefore, a desired light distribution can be easily realized by using these in combination.

  In the present embodiment, as shown in FIG. 1 and the like, the configuration in which the polarizing plate 25 is provided on the viewer side with respect to the light diffusing element 24 is illustrated, but the arrangement of the polarizing plates is limited to this. It is not a thing. A polarizing plate 27 may be provided between the light diffusing element 24 and the liquid crystal layer 30 as in the liquid crystal display device 400 illustrated in FIG. When the polarizing plate 27 is provided between the light diffusing element 24 and the liquid crystal layer 30, the stray light generated by the back scattering in the light diffusing element 24 can be absorbed by the polarizing plate 27, so that the display quality due to the stray light is improved. The decrease can be suppressed.

  However, in the liquid crystal display device 400, the display surface may be glaring. The cause of the glare is that external light (ambient light) is reflected on the surface of the light diffusing element 24, or external light incident on the light diffusing element 24 is totally reflected at the interface between the light diffusing element 24 and other layers. There is to be.

  As shown in FIG. 1 and the like, when the polarizing plate 25 is disposed closer to the viewer than the light diffusing element 24, external light (ambient light) incident on the light diffusing element 24 from the viewer is absorbed by the polarizing plate 25. The amount is reduced. Therefore, glare on the display surface can be prevented.

  Further, as in the liquid crystal display device 500 shown in FIG. 23, the polarizing plate 25 disposed on the viewer side with respect to the light diffusing element 24 and the polarizing plate 27 disposed between the light diffusing element 24 and the liquid crystal layer 30. If both are provided, it is possible to prevent display quality from being deteriorated due to stray light while preventing glare on the display surface. In this case, in order to use light efficiently, it is preferable that the transmission axes of the two polarizing plates 25 and 27 are substantially parallel to each other.

  The liquid crystal display device according to the present invention can be made thinner than conventional ones and can perform high-quality display. The liquid crystal display device according to the present invention is suitably used for various electronic devices, and particularly suitably for portable electronic devices such as portable telephones and PDAs.

It is sectional drawing which shows typically the liquid crystal display device 100 in suitable embodiment of this invention. It is a graph which shows the preferable light distribution of the light radiate | emitted from a back substrate. It is a figure for demonstrating the preferable inclination | tilt angle (alpha) of a dielectric material film. It is a figure which shows typically a mode that backscattering generate | occur | produces in a light-diffusion element. It is a graph which shows the relationship between the Fresnel reflectance (%) of a light-diffusion element, and contrast ratio (%). A light diffusing element when the refractive index n ₁ of the first layer is 1, the refractive index n ₃ of the retardation plate is 1.48, and the refractive index n ₂ of the second layer is changed from 1.3 to 1.7. It is a graph which shows the change of Fresnel reflectance R of. Light when the refractive index n ₁ of the first layer is 1.1, the refractive index n ₃ of the retardation film is 1.48, and the refractive index n ₂ of the second layer is changed from 1.3 to 1.7. It is a graph which shows the change of the Fresnel reflectance R of a diffusion element. Light when the refractive index n ₁ of the first layer is 1.2, the refractive index n ₃ of the retardation film is 1.48, and the refractive index n ₂ of the second layer is changed from 1.3 to 1.7. It is a graph which shows the change of the Fresnel reflectance R of a diffusion element. Light when the refractive index n ₁ of the first layer is 1.3, the refractive index n ₃ of the retardation plate is 1.48, and the refractive index n ₂ of the second layer is changed from 1.3 to 1.7. It is a graph which shows the change of the Fresnel reflectance R of a diffusion element. Light when the refractive index n ₁ of the first layer is 1.4, the refractive index n ₃ of the retardation plate is 1.48, and the refractive index n ₂ of the second layer is changed from 1.3 to 1.7. It is a graph which shows the change of the Fresnel reflectance R of a diffusion element. Light when the refractive index n ₁ of the first layer is 1.5, the refractive index n ₃ of the retardation film is 1.48, and the refractive index n ₂ of the second layer is changed from 1.3 to 1.7. It is a graph which shows the change of the Fresnel reflectance R of a diffusion element. Light when the refractive index n ₁ of the first layer is 1.6, the refractive index n ₃ of the retardation film is 1.48, and the refractive index n ₂ of the second layer is changed from 1.3 to 1.7. It is a graph which shows the change of the Fresnel reflectance R of a diffusion element. Light when the refractive index n ₁ of the first layer is 1.7, the refractive index n ₃ of the retardation plate is 1.48, and the refractive index n ₂ of the second layer is changed from 1.3 to 1.7. It is a graph which shows the change of the Fresnel reflectance R of a diffusion element. (A) And (b) is a top view which shows an example of the shape of a dielectric film. (A) And (b) is a top view which shows another example of the shape of a dielectric film. (A)-(d) is process sectional drawing which shows the formation process of a selective reflection layer typically. (A)-(d) is process sectional drawing which shows the formation process of a selective reflection layer typically. 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. It is sectional drawing which shows the example of the other light-diffusion element used for the liquid crystal display device of this invention. It is sectional drawing which shows the example of the other light-diffusion element used for the liquid crystal display device of this invention. It is sectional drawing which shows typically the other liquid crystal display device 400 in suitable embodiment of this invention. It is sectional drawing which shows typically the other liquid crystal display device 500 in suitable embodiment of this invention. It is sectional drawing which shows typically the liquid crystal display device provided with the general direct type | mold backlight. It is sectional drawing which shows typically the liquid crystal display device provided with the general edge light type backlight.

Explanation of symbols

2 linear light source 10 rear substrate 11 transparent substrate 12 low refractive index layer 14 selective reflection layer 15 dielectric film 15a inclined portion of dielectric film 15b parallel portion of dielectric film 20 front substrate 21 transparent substrate 22 color filter 23 phase difference plate 24 light diffusing element 24 ′ lenticular lens 24a first layer 24b second layer 25 polarizing plate 26 diffusing film 27 polarizing plate 30 liquid crystal layer 42 polarizing plate 44 reflecting plate 46 polarizing plate 100, 200, 300, 400, 500 liquid crystal display device

Claims (12)

A first substrate;
A second substrate disposed closer to the viewer than the first substrate;
A liquid crystal layer provided between the first substrate and the second substrate;
A light diffusing element disposed closer to the viewer than the liquid crystal layer;
A light source provided on a side of the first substrate and emitting light toward a side surface of the first substrate;
With
The liquid crystal display device, wherein the first substrate includes a selective reflection layer that selectively reflects linearly polarized light having a specific polarization direction among light incident on the inside of the first substrate from a side surface of the first substrate.   The first substrate is formed on a transparent substrate having two main surfaces facing each other and a main surface on the liquid crystal layer side of the two main surfaces of the transparent substrate, and the refractive index of the transparent substrate The liquid crystal display device according to claim 1, further comprising a low refractive index layer having a low refractive index.   The liquid crystal display device according to claim 2, wherein the selective reflection layer is provided on a main surface opposite to the liquid crystal layer side of the two main surfaces of the transparent substrate.   The liquid crystal display device according to claim 1, wherein the selective reflection layer includes a dielectric film.   The liquid crystal display device according to claim 4, wherein the dielectric film is inclined at an angle of 48 ° to 54 ° with respect to a main surface of the transparent substrate on the liquid crystal layer side.   5. The liquid crystal display device according to claim 4, wherein the dielectric film includes an inclined portion inclined at an angle of 48 ° to 54 ° with respect to a main surface of the transparent substrate on the liquid crystal side.   The liquid crystal display device according to claim 1, wherein the light diffusing element has a Fresnel reflectance of 4% or less with respect to light incident on the light diffusing element from the liquid crystal layer side. The light diffusing element has a first layer and a second layer having different refractive indexes in this order from the liquid crystal layer side, and the refractive index n ₁ of the first layer and the refractive index n ₂ of the second layer are , N ₁ <n ₂ , 1.3 ≦ n ₁ ≦ 1.7 and 1.3 ≦ n ₂ ≦ 1.7 are satisfied, The liquid crystal display device according to claim 1.   The liquid crystal display device according to claim 8, wherein the light diffusing element is a lens sheet including a plurality of lenses, and an interface between the first layer and the second layer is a lens surface of the plurality of lenses.   The liquid crystal display device according to claim 1, further comprising a polarizing plate having a transmission axis substantially parallel to the specific polarization direction and provided between the light source and a side surface of the first substrate. . A reflector provided on the side opposite to the observer side with respect to the selective reflection layer;
The liquid crystal display according to claim 1, further comprising: a polarizing plate having a transmission axis substantially parallel to the specific polarization direction and provided between the selective reflection layer and the reflection plate. apparatus.   A portable electronic device comprising the liquid crystal display device according to claim 1.

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