JP2008140698A - Backlight unit, and liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight unit which has flexibility (bending performance) without significantly changing an existing structure, and to provide a liquid crystal display equipped with the backlight unit. <P>SOLUTION: A backlight unit 10 having flexibility includes a light guide plate 5 which is made of a silicone rubber, and light sources 1a, 1b, 1c, 1d, 1e, 1f, 1g which are arranged along at least one lateral side of the light guide plate 5. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a flexible backlight device and a bendable liquid crystal display device including the backlight device.

  In recent years, as a display device used in an electronic device represented by a digital camera, a digital video camera, a mobile phone, a mobile device, a notebook personal computer, etc., a liquid crystal display device having a backlight device is mainly used. . In addition, a cold cathode fluorescent tube (CCFL) has been used so far for these backlight devices, but recently, those mainly using light emitting diode elements have become mainstream.

  Here, as shown in FIG. 7, the optical member used in the conventional backlight device includes a light guide plate 95 that guides the light from the light source 91, a reflection sheet 97 for efficiently guiding the light to the liquid crystal panel side, a guide. There is a functional optical sheet 96 such as a diffusion sheet for efficiently diffusing the light propagated through the optical plate and entering the liquid crystal panel, and a light source such as a CCFL or a light emitting diode installed on one side or both sides of the light guide plate The light 91 is efficiently incident on the liquid crystal panel, and the light emission luminance is controlled to be uniform over the entire screen in the observed screen.

  On the other hand, as a display device that is expected to replace a flat panel display typified by a liquid crystal display device based on a conventional glass substrate or to generate a new market, a flexible display device having flexibility (flexibility) is known. There have been proposed light-emitting elements such as thin film transistor arrays and organic EL, which are expected to be applied to flexible display devices, or display elements using electronic paper (for example, Non-Patent Document 1). , 2).

  Currently, display elements using self-luminous elements do not require a backlight device as a light source because they can generate an image by light emission of each element, but there are problems of various technical studies being reported Although most of the electronic devices are commercialized as display devices for some electronic devices, liquid crystal display devices are used in most electronic devices. A liquid crystal display device requires a backlight device (or front light device) as a light source because of its configuration, but there are several reports on flexible backlight devices, but there are reports on using optical members with a light guiding function. There is almost no (for example, refer nonpatent literature 3 and 4).

  In addition, in order to eliminate the air layer generated between the cold cathode tube and the light guide plate as the light source, and between the light guide plate and each optical sheet, a transparent elastic particle is added to the rubber elastic body for the purpose of improving the light utilization efficiency. A rubber elastic body having a shape for efficiently guiding light emitted from a cold-cathode tube serving as a light source was used for the purpose of uniformly illuminating an object to be irradiated such as a light plate (see Patent Document 1) or a liquid crystal panel. A light guide plate has been proposed (see Patent Document 2). However, these light guide plates are used to improve the adhesion between the light source and the light guide plate, or the light guide plate and each optical sheet by combining the cold cathode tube and the light guide plate, and to make the light of the cold cathode enter the light guide plate efficiently. It is about the shape, not the purpose of giving flexibility.

Y. Fujisaki, H. Sato, H. Fujikake, Y. Inoue, S. Tokito and T. Kurita; “Flexible crystal display cells on plastic substrate driven by low-voltage organic thin-film transistor wit improved gate insulator and passivation layer” , Jpn. J. Appl. Phys., Vol.44, No.6A, pp.3728-3732 (2005) M. Suzuki, T. Suzuki, T. Tsuzuki, S. Tokito, T. Kurita, F. Sato; “Flexible Color OLED Display using White Light-Emitting Layer based on Phosphorescent Polymers”, IDW'04 DIGEST, pp.1277− 1280 (2004) P. Slikkerveer, P. Bouten, P. Cirkel, J. de Goede, H. Jagt, N. Kooyman, G. Nisato, R. van Rijswijk and R. Duineveld; “A Fully Flexible Color Display”, SID 04 DIGEST, pp.770-773 (2004) A. Nagawasa and K. Fujisawa; “An Ultra Slim Backlight System using Optical-Patterned Film”, SID 05 DIGEST, pp.570-573 (2005) Japanese Patent No. 3657305 JP 9-211122 A

  The present invention has been made in view of the above problems in the prior art, and a backlight device having flexibility (flexibility) without greatly changing the conventional structure, and a liquid crystal including the backlight device. An object is to provide a display device.

  The present invention provided to solve the above problems includes a flexible light guide plate made of silicone resin and a plurality of light emitting elements arranged on at least one side surface of the light guide plate, and has flexibility. This is a backlight device.

  Here, the light source is preferably a light emitting diode element or a cold cathode tube.

  Moreover, it is preferable that the refractive index of the said light-guide plate is 1.4 or more, and the unevenness | corrugation which shows a light-diffusion function is provided in the surface of the said light-guide plate.

  In addition, it is preferable that the light emitting element is disposed on a side surface of the light guide plate that is parallel to a direction in which the backlight device bends.

  Moreover, it is good to provide the optical sheet which adjusts the optical characteristic of the light radiate | emitted from the said light emitting element, and is guide | induced to the said light-guide plate.

  The present invention provided to solve the problems is a liquid crystal display device comprising the backlight device according to any one of claims 1 to 6 and a flexible liquid crystal panel.

According to the first and second aspects of the invention, by using a light guide plate made of silicone resin, it has flexibility, a function of guiding light from the light source, and a function of efficiently emitting the guided light. And a backlight device having an excellent function of propagating light.
According to the invention of claim 3, since the difference in refractive index from the sealing resin of the light emitting diode is small, the light from the light source can be efficiently used as a backlight device.
According to the invention of claim 4, since the diffusion sheet can be omitted from the optical sheet, the number of parts of the backlight device can be reduced, and the thickness of the entire device can be reduced.
According to the invention of claim 5, even when the backlight device is curved, the loss of light from the light source is reduced, and light emission with high luminance can be obtained.
According to the sixth aspect of the invention, the optical characteristics of the light emitted from the apparatus can be adjusted appropriately, so that uniform and high-luminance emission can be obtained.
According to the seventh aspect of the present invention, a flexible liquid crystal display device can be provided because both the backlight device and the liquid crystal panel have flexibility.

The configuration of the backlight device according to the present invention will be described below.
FIG. 1 is a perspective view showing a configuration of a backlight device according to the present invention, and FIG. 2 is a perspective view when the backlight device 10 is bent.
The backlight device 10 includes a light source unit 20 and a light guide plate 5. Specifically, the optical sheet 6 on the front surface (light emitting surface) side of the light guide plate 5, a flexible sheet-shaped light guide plate 5, and the reflective sheet 7 on the back side of the light guide plate 5 are laminated. Each of the light sources 1a, 1b, 1c, 1d, 1e, 1f, and 1g (hereinafter referred to as the light sources 1a, 1b, 1c, 1e, 1f, and 1g) The light source unit 1) is arranged and a frame is provided on the short side of the light guide plate 5 so as to cover the end surfaces of the optical sheet 6, the light guide plate 5, and the reflection sheet 7, and the backlight. The entire device is flexible in at least one direction (the arrow direction in the figure).

  When the backlight device 10 is driven, power is supplied to the light sources 1a, 1b, 1c, 1d, 1e, 1f, and 1g via the wiring board 2, and the light sources 1a, 1b, 1c, 1d, 1e, and 1f are supplied. , 1 g is emitted to the side surface of the light guide plate 5, and then the light incident on the light guide plate 5 propagates in the light guide plate 5 and is guided by the reflection sheet 7 so as to spread in the light guide plate 5. Lighted. The guided light is emitted from the main surface of the light guide plate 5 by the function of the light guide plate 5 to emit efficiently. Next, the light emitted from the light guide plate 5 is adjusted to a predetermined optical characteristic by the optical sheet 6 and then emitted as uniform light from the light emitting surface 8.

  Here, the light source unit 1 consists of a light emitting diode element (LED) or a cold cathode tube (CCFL), and emits white light. In the case where the light source unit 1 is composed of LEDs, any configuration of white LEDs, or red LEDs, green LEDs, and blue LEDs that mix light emitted from the respective LEDs and emit white light to the outside may be used. Moreover, it is preferable that several LED is arrange | positioned along with the one side surface (end surface) of the light-guide plate 5 like FIG. At this time, the light source (LED) 1 is mounted on a flexible wiring board (flexible wiring board) 2 so that electric power is supplied, and this wiring board 2 serves as a light incident surface of the light guide plate 5. The light source unit 1 is installed on the edge of the light guide plate 5 so that the light source unit 1 is disposed on the side surface.

  The light guide plate 5 is formed by integrally molding a silicone rubber resin by molding and has flexibility. Here, the material of the light guide plate 5 is a polycarbonate resin (PC), which is a transparent thermoplastic resin conventionally used in terms of high permeability, moldability, low water absorption (moisture absorption), environmental resistance, and low birefringence. It is preferable to use a silicone rubber resin material whose performance is equal to or higher than that of acrylic resin (polymethyl methacrylate (PMMA)) and the molded product is flexible. For example, polydimethylsiloxane (PDMS), polyalkylalkenylsiloxane, polyalkyl Examples include phenylsiloxane. Thereby, the transparency and refractive index of the light guide plate 5 become appropriate, and as a result, the light guide plate 5 has an excellent function of guiding light. Particularly, the case where the constituent material is polydimethylsiloxane (PDMS) is suitable, and the light guide plate 5 is transparent and has a refractive index of 1.4 or more, and has a function of guiding light better than the conventional light guide plate. Become a thing.

  Further, the light guide plate 5 is excellent in the function of efficiently emitting the guided light. This is because the surface of the light guide plate 5 has a predetermined patterned shape, and is controlled to have such a shape when the surface is formed. The surface shape is optically designed based on the light distribution characteristics of the light source unit 1 and the like. This surface shape needs to be optimized depending on the final size of the liquid crystal display device, the type and number of light sources constituting the light source unit 1, and the like.

  FIG. 3 shows an example of the surface shape for the function of efficiently emitting the light guided by the light guide plate 5. In FIG. 3, fine convex portions 5b are provided at a constant pitch on the light emitting surface side surface of the light guide plate 5A (FIG. 3A), and fine concave portions 5a having a variable pitch are provided on the reflective sheet 7 side (FIG. 3). (B)) A function of efficiently emitting the guided light is provided.

  Further, the light guide plate 5 may be provided with unevenness indicating the light diffusion function on the surface on the light exit surface side. An example is shown in FIG. FIG. 4A is a perspective view of the light guide plate 5B, and FIG. 4B is a cross-sectional view of a light emission surface area of a backlight device using the light guide plate 5B. In the light guide plate 5B, fine concave portions 5b are provided at a constant pitch on the surface opposite to the light emitting surface 8, and unevenness 5c indicating a light diffusion function is provided on the surface on the light emitting surface side. Thereby, it is possible to omit the diffusion sheet 6c in the optical sheet 6 described later.

  In producing the light guide plate 5, when polydimethylsiloxane (PDMS) is used as a constituent material, the light guide plate 5 is generally molded by curing using a polymerization reaction by mixing two liquids. For example, SYLGARD 184 manufactured by Toray Dow Corning Silicone may be used, but it is possible to easily obtain the light guide plate 5 having a desired shape by using a master mold as the material. Or it is also possible to use the fine metal mold | die used for preparation of the light-guide plate made from the conventional polycarbonate (PC) or acrylic resin PMMA (polymethylmethacrylate). In addition, when providing the unevenness showing the light diffusion function on the light emitting surface side surface like the light guide plate 5B, it is the same as the method for producing the relief plate used in the micro contact printing method as a kind of fine patterning. A glass substrate finely processed by photolithography may be used as a master mold. Specifically, a fine structure of a resist is formed on a substrate by photolithography to form a stamp mold, and the fine structure is transferred to the surface of the light guide plate 5 by the stamp mold (reference document: A. Kumar, GM). Whitesides; Appl. Phys. Lett., Vol. 63, pp. 2002-2004 (1993)).

  The optical sheet 6 is for adjusting the optical characteristics of light emitted from each light source unit 1 and guided to the light guide plate 5, and is a prism sheet for adjusting the outgoing direction of incident light, and a diffusion for scattering light. Sheets are stacked to enable display with uniform luminance distribution and high front luminance. An example is shown in FIG. Here, the optical sheet 6 is formed by laminating prism sheets 6a and 6b for adjusting the emission direction of incident light and a diffusion sheet 6c for scattering light.

  1 and 2 show a configuration in which the light source unit 20 is disposed on a side surface of the light guide plate 5 that is parallel to the direction in which the backlight device 10 bends (bending direction, arrow direction in the figure). However, the present invention is not limited to this, and the backlight device 10 may be arranged at a right angle to the direction in which the backlight device 10 bends (bending direction, arrow direction in the figure) or at the corner of the light guide plate 5. When a cold cathode tube is used as the light source, the backlight device 10 is also bent when placed on a side surface perpendicular to the direction in which the backlight device 10 bends (bending direction, arrow direction in the figure). It is preferable that light incident on the light guide plate 5 is efficiently emitted from the light emitting surface 8.

  Further, the light source unit 1 and the light guide plate 5 may be in a state where they are just in contact with each other, but both may be bonded with an adhesive having the same refractive index as that of the light guide plate 5 in order to improve the light utilization efficiency of the light source unit 1. Alternatively, the light source unit 1 may be integrally formed with the light guide plate 5 so as to be included in the light guide plate 5. In that case, the silicone rubber may be cured even though the light source unit 1 is installed at a desired position before the silicone rubber is cured. Further, it is preferable to apply a reflection film or a reflection sheet to the end face of the light guide plate 5 facing the light source unit 20 or the portions of the frames 3 and 4 that are in contact with the light guide plate 5 in order to improve the light use efficiency.

Next, FIG. 5 shows a conceptual cross-sectional view of the liquid crystal display device of the present invention.
The liquid crystal display device of the present invention is a transmissive liquid crystal display device, and includes the above-described backlight device 10 and a liquid crystal panel 30 mounted on the backlight device 10. Here, the liquid crystal panel 30 has flexibility, the direction in which the liquid crystal panel 30 can be bent is aligned with the direction in which the backlight device 10 is bent, and the liquid crystal display device as a whole can be bent.
The basic configuration of the liquid crystal panel 30 relating to the liquid crystal display may be the same as that conventionally known.

Although the example which implemented this invention is demonstrated below, this invention is not limited to this.
(Example 1)
In this example, the backlight device 10 shown in FIG. 1 was produced.
The light guide plate has the structure of the light guide plate 5A shown in FIG. 3A, and a glass substrate on which a concavo-convex pattern is formed by a photolithography method is used as a master mold, and PDMS (Toray Dow Corning SYLGARD184) manufactured by Silicone Co. was used. Specifically, the base material of SYLGARD 184 and the polymerization initiator are mixed and stirred, then vacuum (reduced pressure) defoaming treatment is performed to remove bubbles in the liquid agent, and the mixture is poured into the master mold, and then at 60 ° C. for 12 hours. Then, after performing the heat polymerization in a thermostat, the hardened material from the master mold was peeled off to obtain a light guide plate 5A. The thickness of the light guide plate 5A can be adjusted by inserting a spacer between the upper and lower master molds into which the PDMS liquid is poured, and is 0.5 mm here. The obtained light guide plate 5A had a refractive index of 1.41 and was transparent to visible light.
Further, in this embodiment, a glass plate is used as a master mold as a simple method, but a metal mold that is a conventional light guide plate manufacturing method may be used as long as a desired shape can be obtained. However, fine processing techniques such as nanoimprinting may be applied.

Next, the backlight device 10 shown in FIG. 1 was assembled using the obtained sample of the light guide plate 5A. Here, a backlight device for a 4-inch diagonal liquid crystal display device is used in consideration of application to a portable display device. Moreover, white LED was used as the light source of the light source unit 1, and the optical sheet 6 was composed of prism sheets 6a and 6b and a diffusion sheet 6c shown in FIG. At this time, the thickness of each of the diffusion sheet 6c, the reflection sheet 7, and the prism sheets 6a and 6b is 200 μm or less even in the conventional product, and since it already has flexibility, a commercially available one was used. When the backlight device 10 was manufactured with the above-described configuration, it was confirmed that the backlight device 10 was flexible enough for practical use. Further, when the backlight device 10 was driven, uniform and high luminance light emission was obtained on the entire light emitting surface 8.
Incidentally, the light guide plate in the conventional product is usually made of a resin such as PC or PMMA, and in recent years its thickness is 1 mm or less, but it is difficult to give flexibility because the material itself is hard.

(Example 2)
In Example 1, the configuration of the light guide plate is changed to the light guide plate 5B shown in FIG. 4 instead of the light guide plate 5A, the diffusion sheet 6c is omitted, and the rest is shown in FIG. A backlight device was produced.
The light guide plate is configured as shown in FIG. 4A, and the light diffusion function 5c can be imparted to the surface of the light guide plate 5B on the light emitting surface 8 side by roughening the surface. In the production, a rough surface is formed in advance on the master mold on the liquid crystal panel side by using etching or the like among the master molds, and a liquid agent of PDMS is poured into the master mold and hardened in the same manner as in the first embodiment. However, in this embodiment, a light guide plate having a smooth surface is prepared, and then a metal (for example, Al) is sputtered and etched on the surface having a diffusion function. When a metal film is formed on a light guide plate made of PDMS using a sputtering method or the like, the surface becomes a fine and random uneven shape, and by removing the metal by etching, the width is several μm and the depth is several tens to several hundred μm. It becomes possible to form fine and irregular irregularities. The surface state of the light guide plate 5B produced in this example is shown in FIG. In this embodiment, the smooth surface is roughened, but this formation method is not limited to the smooth light guide plate surface shape, and can be formed on a surface shape with a shape that can obtain an optical function. It is.

  When the backlight device 10 was manufactured with the above-described configuration, it was confirmed that the backlight device 10 was flexible enough for practical use. Further, when the backlight device 10 was driven, uniform and high luminance light emission was obtained on the entire light emitting surface 8. Further, by using the sample of the light guide plate 5B, it is possible to have a function of guiding light from the light source unit 1 and a function of diffusing light incident on the prism sheets 6a and 6b. Since the film 6c is omitted, it is possible to reduce the number of parts and the overall thickness of the constituent members of the backlight device 10.

  The present invention is not limited to the above-described embodiments, and various changes can be made in the configuration of the flexible liquid crystal display device. For example, the light source unit 1 may be a cold cathode tube (CCFL) as long as the side surface of the light guide plate is perpendicular to the direction in which the backlight device bends. In addition, a light guide plate manufactured by PDMS may be wedge-shaped. Furthermore, the pattern formed on the light guide plate may not be a pattern as in the present embodiment as long as it has an optical light guiding function. The size of the liquid crystal display device to be implemented is not limited to the present embodiment, and can be combined according to the size of various liquid crystal display panels.

It is a perspective view which shows the structure of the backlight apparatus which concerns on this invention. It is a perspective view which shows the state which bent the backlight apparatus which concerns on this invention. It is the schematic which shows the structure (1) in the light emission surface area | region of the light-guide plate used by this invention, and the backlight apparatus using this light-guide plate. It is the schematic which shows the structure (2) in the light emission surface area | region of the light-guide plate used by this invention, and the backlight apparatus using this light-guide plate. 1 is a schematic cross-sectional view showing a configuration of a liquid crystal display device according to the present invention. 6 is an external view showing a surface state of a light guide plate of Example 2. FIG. It is sectional drawing which shows the conventional structure of a backlight apparatus.

Explanation of symbols

1, 91... Light source unit, 1 a, 1 b, 1 c, 1 d, 1 e, 1 f, 1 g ... light source, 2, 92 ... wiring board, 3, 4, 94 ... frame, 5, 5 A, 5B, 95: Light guide plate, 6, 96: Optical sheet, 6a, 6b: Prism sheet, 6c: Diffusion sheet, 7, 97: Reflective sheet, 8: Light emitting surface, DESCRIPTION OF SYMBOLS 10,90 ... Backlight apparatus, 20 ... Light source part, 30 ... Liquid crystal panel

Claims (7)

  A backlight device comprising a flexible light guide plate made of silicone resin and a light source disposed on at least one side surface of the light guide plate, and having flexibility.   The backlight device according to claim 1, wherein the light source is a light emitting diode element or a cold cathode tube.   The backlight device according to claim 1, wherein a refractive index of the light guide plate is 1.4 or more.   The backlight device according to claim 1, wherein the light guide plate is provided with unevenness indicating a light diffusion function.   The backlight device according to claim 1, wherein the light source is disposed on a side surface of the light guide plate that is parallel to a direction in which the backlight device bends.   The backlight device according to claim 1, further comprising an optical sheet that adjusts optical characteristics of light emitted from the light source and guided to the light guide plate. A liquid crystal display device comprising the backlight device according to claim 1 and a flexible liquid crystal panel.

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