JP2007178581A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device with high luminance by taking out light, without forming a reflection member on a light guide, and using the light guide which controls light with high directivity. <P>SOLUTION: The light guide is formed with a multilayer structure of which the refractive indexes are different between adjacent layers. Thus, the directivity of light emitted from the light guide and an interval/position of emission is controlled. Because the refractive index layer width and the refractive index value of each of the layers are made suitably changeable, corresponding to an emission state from the light guide, the liquid crystal display device which is easily manufactured and which is superior in visibility is materialized. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light guide, an illumination device, and a liquid crystal display device.

  In recent years, a color liquid crystal display device has been widely used in various fields as a portable notebook personal computer, a portable liquid crystal TV using a color liquid crystal panel, or a video integrated liquid crystal TV. In addition, with the increase in the amount of information processing, diversification of needs, compatibility with multimedia, and the like, liquid crystal display devices have been increased in size and definition. The liquid crystal display device basically includes a backlight and a liquid crystal display element. As the backlight, there are a direct light method in which a light source is provided directly under a liquid crystal display element and an edge light method in which a light source is provided on a side surface of a light guide, and the edge light method is frequently used because of a compact liquid crystal display device. This edge light system is a backlight of a system in which a light source is disposed on a side surface portion of a plate-shaped light guide to emit light over the entire surface of the light guide.

  FIG. 9 schematically shows a cross-sectional configuration of a conventional liquid crystal display device. As shown in the drawing, a backlight 14 is disposed on the back side of the transmissive or transflective liquid crystal element 7. The backlight 14 causes light from the light source 1 such as a white LED, which is a substantially point light source, to enter the plate-shaped light guide plate 15 from its incident surface (side surface) 16 a and to face the liquid crystal element 7 of the light guide plate 15. It is comprised so that it may radiate | emit from the output surface (upper surface) 16b (for example, refer patent document 1).

On the surface (lower surface) 16c opposite to the exit surface 16b of the light guide plate 15, a reflective member 17 made of a large number of white or reflective projections or dot-like planar patterns is formed, so that light reflectivity is achieved. Has been granted. When the reflection member 17 as described above is provided on the lower surface 16 c of the light guide plate 15, luminance unevenness occurs, so that a uniform luminance can be obtained by disposing the diffusion sheet 18 on the emission surface 16 b of the light guide plate 15. ing. However, since the range in which light is emitted is too wide in the diffusion sheet 18, the two prism sheets 12 a and 12 b are sequentially laminated on the diffusion sheet 18. FIG. 10 schematically shows the configuration of the prism sheet. As shown in the figure, the prism sheet has a base material layer formed with a series of cross-section triangular protrusions 19 and a series of cross-section wedge-shaped grooves 20. The two prism sheets 12a and 12b are arranged such that the extending direction of the ridge line of the protruding portion 19 of one prism sheet differs from the extending direction of the ridge line of the protruding portion 19 of the other prism sheet by 90 degrees (in other words, Then, the prism structures are arranged so as to be orthogonal to each other). With such a configuration, light in a certain direction out of the light emitted from the emission surface 16b of the light guide plate 15 is transmitted through one prism sheet 12a. Therefore, the emitted light L1 is condensed and emitted at a viewing angle within a certain angle range (for example, up to 70 degrees). Further, the light in the other direction is transmitted through the other prism sheet 12b, so that it is condensed at a viewing angle within a certain angle range (for example, up to 70 degrees) and emitted as the emitted light L2.
Japanese National Patent Publication No. 11-500071 (2nd page, Fig. 1)

  According to the configuration of the conventional lighting device, the light that propagates inside the light guide plate 15 is extracted from the light guide plate while being scattered by the reflecting member 17, so that the presence of light rays that do not contribute to the light collection on the prism sheet, It has been pointed out that brightness unevenness occurs such that the emitted light decreases as the depth of the light guide increases. In order to solve this problem, conventionally, the dot size and distribution of the reflecting member 17 are adjusted to improve the degree of uniformity in the back of the light guide, and the purpose of diffusion is to improve the degree of uniformity on the upper surface of the light guide plate 15. Although a configuration that minimizes the occurrence of luminance unevenness by adopting a method such as arranging the sheet 18 is adopted, the state of light incident on the prism sheet is sparse, and since a scattering plate is used, it is in the front direction. There is a problem that it is difficult to obtain the brightness.

  Furthermore, along with the recent trend of thinning, there is a demand for thinning of the light guide member. However, when the light guide is thinned, there is an adverse effect that the transferability of the reflecting member decreases, and a material for improving the transferability. There were problems such as requiring improvement and complicated optical simulation.

  Accordingly, an object of the present invention is to provide an illumination device using a light guide including a technique for extracting light without forming a reflecting member on the light guide by a relatively simple method and a method capable of controlling high directivity. And providing a liquid crystal display device.

  Therefore, a multilayer structure having different refractive indexes between adjacent layers is formed on the light guide. Here, the layer width and refractive index value of the refractive index of each layer can be appropriately changed according to the emission state from the light guide. Since it can be realized even if the refractive index difference between adjacent layers is relatively small, it can be made of a composite material that does not require processing difficulty, such as cycloolefin polymer resin, polycarbonate resin, and acrylic resin, as an example. .

  Since the light guide having such a configuration has a strong directivity to the emitted light, it is particularly well-matched with a combination of a total reflection type illumination device using a single prism sheet and high light extraction efficiency. Can be taken. Further, even in a system using two prism sheets, since the entire light guide is emitted as aligned light, a diffusion sheet in the sense of improving uniformity is not necessary, and a reduction in luminance can be reduced.

  Regarding the refractive index in the light guide, the refractive index of the first stage and the subsequent stage of the layer to which the refractive index is changed is arranged to be larger than the refractive index, but the light output angle from the light guide is the light output region and one of them. Since it is determined by the refractive index ratio in the previous region, it can be changed as appropriate according to the light emission situation.

  In addition, as a lamination | stacking method of a multilayer structure, although it laminates | stacks perpendicularly seeing from the cross section of a light guide, the structure laminated | stacked diagonally may be sufficient.

  In this way, by using a light guide having two or more regions having different refractive indexes in the light guide, the directionality of light emitted from the light guide and the emission interval and position can be easily controlled. Can do. For this reason, in a conventional total light reflection type liquid crystal display device in which the reflecting member has a groove structure, for example, the light guide is required to optimize the groove structure in order to avoid the influence of the bright line caused by the groove. The light guide of the invention does not require these processing difficulties, and also eliminates the difficulty of processing to match the light directivity and the emission interval, thereby providing a liquid crystal display device that is easy to manufacture and excellent in visibility. it can.

  In the light guide of the present invention, since the light output angle from the light guide is determined by the refractive index ratio between the light output region and the previous region, it is easy to change the refractive index layer width and refractive index of each layer. It is possible to control the directionality of light emitted from the light guide and the emission interval and position. For this reason, the matching of the light beam state is particularly good when combined with a total reflection illumination device, and the light extraction efficiency is high. In addition, it does not require the difficulty of processing seen in conventional light guides with reflective members, and is free from the problem of transferability when thinned, making it easier to manufacture, high brightness, and excellent visibility. A liquid crystal display device can be provided.

  Hereinafter, embodiments of a liquid crystal display device to which the light guide of the present invention is applied will be described in detail with reference to FIGS.

  FIG. 1 is a configuration diagram showing an example of a liquid crystal display device to which the light guide of the present invention is applied. In the liquid crystal display device of the present embodiment, as shown in the drawing, the reflection sheet 3 that reflects the light emitted below the light guide plate 2 to the inside of the light guide plate 2 is below the light guide plate 2, the LED light source 1, and the light guide plate 2. Is arranged. An optical sheet layer 4 a that changes the angle of light emitted from the light guide plate in the front direction of the liquid crystal element is provided between the light guide plate 2 and the liquid crystal element 7. The light guide plate 2 forms a multilayer structure made of two or more materials having different refractive indexes, and the refractive indexes of adjacent layers are different from each other. The optical sheet layer 4 a is disposed above the light exit surface 5 of the light guide plate 2 and has an inverted prism shape in which prism peaks 4 b are formed at a predetermined interval on the surface facing the light exit surface 5. By using the reverse prism-shaped optical sheet layer 4a, the vertical component of the light incident on the liquid crystal display panel is increased. Therefore, the front brightness of the light is improved.

Next, the behavior of light in this liquid crystal display device will be described with reference to FIGS. FIG. 2 is a schematic diagram for explaining a liquid crystal display device to which the light guide of the present invention is applied, in which the boundary of the refractive index of the light guide plate 2 can be understood. FIG. 3 is an enlarged view of the refractive index regions n1 and n2 in FIG. 2 and 3, the same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted here. Further, θc appearing in the following description represents a critical angle, and θ _{0 to} θ ₅ represent incident angles at respective positions of the light guide shown in FIG. The light incident on the light guide plate 2 from the LED light source 1 is incident on the back surface 6 (or the light exit surface 5) at an angle shallower than the critical angle in the refractive index region n1 (θ ₀ <θc). Although light is totally reflected (m1 in the figure), the light reaching the refractive index region n2 exceeds the critical angle at the interface of the refractive indexes n1 and n2 (θ ₁ = 90 ° −θ ₀ > θc). According to Snell's law, it proceeds by bending at an angle corresponding to the refractive index ratio (m2 in the figure).

Now, if the refractive index n2 is made slightly smaller than n1, light traveling through the refractive index region n2 and reaching the light exit surface 5 enters the interface at an angle larger than the critical angle (θ ₃ = 90). ([Deg.]-[Theta] ₂ > [theta] c), part of which is emitted from the light guide plate 2 without being totally reflected (m3 in the figure), and the other part is reflected into the light guide plate 2 (m4 in the figure)

The reflected light further reaches the refractive index region n3 (θ ₄ = 90 ° −θ ₃ <θc). By taking the refractive index n3 so as to be slightly larger than n2, all the light is reflected at the interface. It bends at an angle corresponding to the refractive index ratio without reflection (m5 in the figure).

  Then, the light totally reflected by the back surface 6 in the refractive index region n3 proceeds to be refracted at the interface of the refractive index n4 and reaches the light output surface 5, and part of the light is emitted to the outside of the light guide plate 2 (in the drawing). m6) and others are reflected into the light guide plate 2 (m7 in the figure). In the same manner, a part of the light is extracted from the light exit surface 5 to the outside of the light guide plate 2 and the other light is reflected into the light guide plate 2 in the same manner (by optimizing the refractive index in the adjacent layer). . The light extracted from each position on the light exit surface 5 is totally reflected by the slope of the prism crest 4b of the optical sheet layer 4a (m8 and m9 in the figure), and changes its angle to the front direction of the backlight, resulting in luminance in the front direction. Has improved.

In the liquid crystal display device of this method (hereinafter referred to as a total reflection method) to which the light guide of the present invention is applied, the layer structure (width and refractive index) of the refractive index region is compared with the case where a conventional light guide is applied. ) Can be appropriately changed, and the directionality of the light emitted from the light guide and the emission interval / position can be easily controlled. For this reason, in a conventional light guide with a total reflection type liquid crystal display device in which the reflecting member has a groove structure, for example, the return light (m1 in the figure) from the end face of the light guide 9 is grooved as shown in FIG. 8 irradiation. There is a problem that a bright line appears when the reflected light reaches the light exit surface 5 (m2 in the figure). Conventionally, the groove structure has to be optimized to solve this problem. Further, in the shape shown in FIG. 5, as a measure for improving luminance unevenness on the anti-incident light side, a technique for forming a variable reflection groove that takes a groove shape deeper toward the back of the light guide is required. The light guide does not require such processing difficulties.
Furthermore, luminance unevenness and difficulty in processing for matching the light directivity with the output interval when other reflecting members are applied (for example, a non-uniformly spaced pitch is used with a reflecting member having a V-groove structure). Therefore, a liquid crystal display device that is easy to manufacture and excellent in visibility can be provided.

  FIG. 6 is a block diagram showing an embodiment of a second liquid crystal display device to which the light guide of the present invention is applied. As shown in FIG. 6, the liquid crystal display device of the present embodiment is disposed below the light guide plate 2 and the LED light sources 1 and 11 disposed on both side end surfaces of the light guide plate 2 and below the light guide plate 2. The first prism sheet 12a and the second prism sheet 12a for condensing the light emitted from the light exit surface 5 of the light guide plate 2 in the x direction and the y direction, respectively. The prism sheet 12b and the liquid crystal element 7 are provided.

  Here, non-reflective coating layers (AR coating) 13 a and 13 b for removing unnecessary reflected light are attached to both end faces of the light guide plate 2. The non-reflective coating layer (AR coating) is an optical film that acts on a specific light wavelength component to effectively reduce the reflectance thereof, and has a reflection characteristic shown in FIG. 7 as an example. For this reason, the state of the light emitted from the two pairs of LED light sources disposed on both end faces of the light guide plate 2 through the light guide 2 is determined by the non-reflective coating layers 13a and 13b on both end faces from the light guide. Since the return light component is reduced, the light having directivity in the shape shown in FIG. 8 is emitted as being almost symmetrical (m1, m2 in the figure). The emitted light is refracted and condensed by the prism sheets arranged in the upper and lower two sheets (m3 and m4 in the figure), and the brightness in the front direction of the light is improved. Here, the operation from the LED light source until light is emitted from the light exit surface 5 of the light guide plate 2 is the same as that in FIG. 2 described in the first embodiment, and the description thereof is omitted here.

  This type of liquid crystal display device to which the light guide of the present invention is applied is characterized in that the light emitted from the light guide has a directivity compared to that of the conventional example shown in FIG. Since the light is emitted as aligned light as a whole, the diffusion sheet 18 in the sense of improving the uniformity becomes unnecessary, and the reduction in luminance can be reduced. In addition, since the LED light sources are provided on both end faces of the light guide plate 2, the luminous intensity and the amount of light that can be effectively used can be doubled. Furthermore, since the light emitted from the light guide has directivity, it is possible to avoid the presence of light rays that do not contribute to an increase in brightness, such as return light in the prism sheet and multiple reflections, resulting in a high-brightness liquid crystal display device Can be provided.

  The present invention was devised with the intention of increasing the brightness of a small portable information device, but it is free from the problem of transferability associated with the reduction in thickness because no reflecting member is formed on the light guide. In addition to cost reduction in manufacturing, it is possible to apply conventional, easy-to-manufacture members (eg polycarbonate, cycloolefin polymer, acrylic resin, etc.) as they are at relatively low cost. This is useful for improving the brightness of liquid crystal display devices.

It is sectional drawing which shows typically the liquid crystal display device to which the light guide of this invention is applied. It is a schematic diagram explaining the liquid crystal display device to which the light guide of this invention is applied. It is a schematic diagram explaining the light guide of this invention. It is a schematic diagram explaining a bright line generation mechanism in a conventional light guide having a groove structure. It is a schematic diagram explaining the conventional light guide which comprises a variable reflection groove. It is sectional drawing which shows typically the liquid crystal display device to which the light guide of this invention is applied. It is a graph which shows the reflective characteristic with respect to the wavelength of a non-reflective coating layer. It is a schematic diagram explaining the liquid crystal display device to which the light guide of this invention is applied. It is sectional drawing which shows the conventional liquid crystal display device typically. It is a schematic diagram explaining the light condensing principle in a prism sheet with the conventional liquid crystal display device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 LED light source 2 Light guide plate 3 Light reflecting plate 4a Optical sheet layer, 4b Prism mountain 5 Light guide plate surface (light emission surface)
6 Rear surface of light guide plate 7 Liquid crystal element 8 Groove groove 9 Conventional light guide plate 10 Conventional light guide plate 11 LED light source 12a, 12b Prism sheet (refractive means)
13a, 13b Non-reflective coating layer (AR coating layer)
14 Backlight (lighting device)
15 Light guide plate (conventional)
16a End face of light guide plate (light incident surface)
16b Light guide plate surface (light exit surface)
16c Rear surface of light guide plate 17 Reflecting member (lighting means)
18 Diffusion sheet (scattering means)
19 Prism sheet protrusion 20 Prism sheet wedge-shaped groove L1, L2 Ray

Claims (3)

  A liquid crystal display device comprising a liquid crystal element, a light source, and a light guide plate that guides light incident from the light source to the liquid crystal element, wherein the light guide plate is laminated in the incident direction of the incident light A liquid crystal display device having a structure, wherein each layer constituting the multilayer structure has a refractive index different from that of an adjacent layer.   The liquid crystal display device according to claim 2, wherein the multilayer structure is stacked obliquely as viewed from a cross section of the light guide plate.   The liquid crystal display device according to claim 1, wherein the light guide plate is provided with a non-reflective coating layer that acts on a specific light wavelength component to reduce the reflectance thereof.

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