JP2005126518A - Optical sheet and back light unit using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet for effectively utilizing light emitted from a light source without increasing the consumption electric power of the light source, especially an optical sheet which is used for a back light unit and can improve the brightness of a liquid crystal display device without increasing the consumption electric power of the back light unit of the liquid crystal display device, and to provide the back light unit using the same. <P>SOLUTION: The optical sheet for converting UV rays emitted from a light source into visible light is characterized by containing an organic compound which absorbs the UV rays to emit phosphorescence. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical sheet for converting ultraviolet light emitted from a light source into visible light, and particularly to an optical sheet incorporated in a backlight unit of a liquid crystal display device and a backlight unit using the same.

  Examples of the optical sheet include a hologram sheet, a polarizing sheet, a light reflection preventing sheet, a light reflecting sheet, a light partially reflecting partially transmissive sheet, a diffraction grating sheet, an interference filter sheet, a color filter sheet, a light wavelength conversion sheet, and a light diffusion sheet. is there. Examples of the optical sheet incorporated in the backlight unit of the liquid crystal display device include a light guide plate, a light diffusion sheet, and a prism sheet.

  In a liquid crystal display device, a backlight method in which a liquid crystal layer is illuminated from the back surface is widely used. In such a backlight method, a backlight unit is provided on the lower surface side of the liquid crystal layer. A schematic diagram of the backlight unit is shown in FIG. In general, the backlight unit 20 includes a light source 21 such as a cold cathode tube or an LED, and a plurality of optical sheets 22 such as a light guide plate 23, a light diffusion sheet 24, and a prism sheet 25.

  A light beam incident on the light guide plate 23 from the light source 21 provided on the side surface of the backlight unit 20 is a microdot disposed on the bottom surface of the light guide plate or a reflection sheet disposed on the bottom surface or side surface of the light guide plate. Reflected by (not shown) and emitted from the surface of the light guide plate 23. The light beam emitted from the light guide plate 23 enters the light diffusion sheet 24, diffuses, and is emitted from the surface of the light diffusion sheet 24. Thereafter, the light beam emitted from the light diffusing sheet 24 enters the prism sheet 25, and is emitted substantially upward by the prism portion 25 a formed on the surface of the prism sheet 25.

  Some backlight units 20 are provided with a plurality of prism sheets 25 and a light diffusion sheet 24 in order to improve the light collecting property.

  By the way, in order to display a still image and a moving image clearly, it is necessary to improve the brightness | luminance of a liquid crystal display device. Means for that purpose include improving the light quantity of the light source 21 and improving various optical properties of the light diffusion sheet 24 and the prism sheet 25. However, portable electronic devices such as mobile phones and notebook computers that use liquid crystal display devices have limited power consumption to enable long-term use, and limit the amount of light emitted from the light source 21. There is.

As a means for improving the brightness of the liquid crystal display device without increasing the power consumption of the backlight unit, a fluorescent dye is added to the resin layer of the light diffusion sheet (see, for example, Patent Document 1), and the backlight unit is equipped. Various proposals have been made such as containing an optically active ion for converting light other than visible wavelengths into visible light (for example, see Patent Document 2). However, even with these technologies, it has not been possible to sufficiently improve the luminance of the liquid crystal display device to the level currently required.
Japanese Patent No. 2698898 Japanese Patent Laid-Open No. 2001-21885

  Accordingly, an object of the present invention is to provide an optical sheet for effectively using light emitted from a light source without increasing the power consumption of the light source. In particular, an object of the present invention is to provide an optical sheet for a backlight unit capable of improving the luminance of the liquid crystal display device without increasing the power consumption of the backlight unit of the liquid crystal display device, and a backlight unit using the same. Is to provide.

  As a result of intensive studies, the present inventors have increased the amount of light in the visible region by absorbing the ultraviolet light contained in the light emitted from the light source into the phosphorescent substance from the excited triplet state and releasing it as visible light. As a result, the present invention has been completed.

  That is, the present invention provides an optical sheet for converting ultraviolet light emitted from a light source into visible light, comprising an organic compound that emits phosphorescence by absorbing ultraviolet light. is there.

  When the optical sheet of the present invention is used, for example, in a backlight unit of a liquid crystal display device, it is possible to convert ultraviolet rays contained in the light emitted from the light source into visible light with high efficiency. Even without increasing the brightness, the brightness of the liquid crystal display device can be improved by the amount of visible light converted from ultraviolet rays. Therefore, it is not necessary to increase the power consumption to improve the brightness of the liquid crystal display device, use a portable electronic device such as a mobile phone or a notebook computer using the backlight unit for a long time, and still images and moving images. It becomes possible to display more clearly.

  When the optical sheet of the present invention is used, the ultraviolet rays contained in the light emitted from the light source can be efficiently converted into visible light, and high-luminance display can be achieved without increasing the power consumption of the light source. Therefore, when the optical sheet of the present invention is used for a backlight unit of a liquid crystal display element, ultraviolet rays contained in light rays emitted from a light source such as a cold cathode tube or an LED can be converted into visible rays. Only the brightness of the liquid crystal display device can be improved. Therefore, it is possible to display still images and moving images more clearly.

  The organic compound that emits phosphorescence by absorbing ultraviolet rays used in the present invention is a substance that emits light when electrons transition from the excited triplet state to the ground singlet state. Specific examples include transition metal complexes, Examples include benzophenone, 4-methyl-benzoic acid, dibenzothiophene and the like. Moreover, as a transition metal used for a transition metal complex, Cr, Mn, Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt etc. can be illustrated, for example. Examples of the ligand used in the transition metal complex include acetylacetonate, 2,2′-bipyridine, 4,4′-dimethyl-2,2′-bipyridine, 1,10-phenanthroline, and 2-phenylpyridine. And porphyrin, phthalocyanine, and the like. One kind or a plurality of kinds of these ligands may be coordinated with respect to one complex.

  Among these, the organic compound that emits phosphorescence by absorbing the ultraviolet rays used in the present invention is preferably a platinum or iridium complex. Furthermore, a compound represented by the following formula (I), formula (II), formula (III), formula (IV), formula (V), or formula (VI) is more preferable. In particular, a compound represented by Formula (II), Formula (V), or Formula (VI) is preferable.

The converted visible light is preferably white light when used in a backlight unit or the like. The emission colors of the above compounds are as follows.
Compounds of formula (I); green compounds of formula (II); green compounds of formula (III); compounds of red formula (IV); compounds of yellow formula (V); compounds of red formula (VI); In the optical sheet of the present invention, it is preferable to mix an appropriate amount of the compound of the formula (V) and the compound of the formula (VI), since the color of visible light obtained by wavelength conversion of ultraviolet light becomes white light.

  In the optical sheet of the present invention, it is preferable to take the following means in order to prevent the organic compound that emits phosphorescence by absorbing ultraviolet rays from causing non-radiative transition and lowering the phosphorescence efficiency. One of the causes of inactivation of the excited triplet state and causing non-radiative transition is an interaction between excitons called concentration quenching that occurs when the concentration of a phosphorescent substance in the medium is increased. Another cause of the non-radiative transition caused by the deactivation of the excited triplet state is the presence of oxygen. In order to suppress non-radiative transition due to concentration quenching or oxygen intervention, for example, transition metal complexes include a method in which a complex molecule is surrounded by a conductive polymer such as polyparaphenylene and a method in which the complex molecule is enclosed in a medium such as glass. .

  In the present invention, it is preferable to encapsulate an organic compound that emits phosphorescence in glass. Glass is preferable as a medium for stably dispersing various substances, and can impart optical properties such as refraction and diffusion. Considering the dispersibility in the resin, the shape of the optical glass is preferably spherical.

  As a method of encapsulating an organic compound that emits phosphorescence by absorbing ultraviolet rays in an optical glass, it is preferable to use a sol-gel method. According to the sol-gel method, glass can be produced from a liquid raw material without undergoing high-temperature melting. Therefore, an organic compound that emits phosphorescence can be contained in the glass. As a method for producing encapsulated particles of an organic compound that emits phosphorescence by a sol-gel method, silicon alkoxide compounds such as tetraethoxysilane and tetramethoxysilane, alcohol compounds such as ethanol, methanol, propanol, and butanol, and water are used. The ratio includes, for example, (alkoxide compound) to (alcohol compound) to (water) in a ratio of about (1) to (1-20) to (1-20), and further contains hydrochloric acid, nitric acid, ammonia, and the like. A sol solution containing a small amount as a catalyst is produced, and an organic compound that emits phosphorescence by absorbing ultraviolet rays is added to the sol solution. Thereafter, hydrolysis and polycondensation reaction are caused at room temperature to about 100 ° C. for about 1 to 200 hours for gelation, and sintering is further performed at a high temperature of about 200 to 800 ° C. for about 5 to 200 hours. By this, particles encapsulating an organic compound that emits phosphorescence with glass can be produced. The particle shape of the encapsulated particles is preferably 0.05 to 100 μm, more preferably 0.1 to 50 μm, and particularly preferably 0.1 to 20 μm.

  Particles encapsulating an organic compound that emits phosphorescence with glass can be made spherical by pulverization or pulverization or polishing in a polishing apparatus. The particle diameter of the spherical glass is appropriately adjusted depending on the grinding and polishing conditions.

  Hereinafter, an example in which the optical sheet of the present invention is used in a backlight unit of a liquid crystal display element will be described. FIG. 1 is a schematic cross-sectional view showing an optical sheet for a backlight unit according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing an optical sheet according to a different form from the optical sheet of FIG.

  FIG. 1 shows a case where the optical sheet of the present invention is used as an optical sheet 1 called a prism sheet or a lens sheet. The optical sheet 1 includes a sheet portion 2 and a plurality of prism portions 3 formed in parallel and adjacent to the surface of the sheet portion 2. By the prism portion 3, the optical sheet 1 has an optical property of condensing the peak direction of the light beam emitted from the light guide plate and diffused by the light diffusion sheet in a substantially upward direction.

  The optical sheet 1 is formed of a synthetic resin 4 and glass particles 5 encapsulating an organic compound that emits phosphorescence by absorbing ultraviolet rays. The glass particles 5 are uniformly dispersed in the synthetic resin 4. The glass particles are preferably spherical particles.

  The synthetic resin 4 is preferably a colorless and transparent material, and examples thereof include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, and weather resistant vinyl chloride.

  A light guide plate 23, a light diffusing sheet 24, and a prism sheet 25 as shown in FIG. 3 are laminated, and a light beam emitted from the light source 21 is uniformly diffused and sent to an upper liquid crystal display element (not shown) or the like. In the unit 20, when the optical sheet 1 is used for the prism sheet 25, the ultraviolet rays contained in the light emitted from the light source 21 can be converted into visible light, and as a result, the liquid crystal display provided with the backlight unit 20. The brightness of the device can be improved.

  The optical sheet 6 in FIG. 2 is a light diffusing sheet, and is a sheet having an optical property of uniformly diffusing transmitted light. Specifically, the optical sheet 6 includes a base material layer 7, a light diffusion layer 8 laminated on the front side of the base material layer 7, and a sticking prevention layer 9 laminated on the back surface of the base material layer 7. It is configured.

  Since the base material layer 7 is required to transmit light, it is preferable that the base material layer 7 is formed of a transparent, particularly colorless and transparent synthetic resin. The synthetic resin used for the base material layer 7 is not particularly limited, and examples thereof include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, and weather resistant vinyl chloride. .

  The light diffusion layer 8 is composed of a binder resin 10 and resin beads 11 dispersed in the binder resin 10. By dispersing the resin beads 11 in this way, the light beam that passes through the light diffusion layer 8 can be uniformly diffused. Further, by providing a resin bead 11 whose upper end protrudes from the binder resin 10 or is embedded in the binder resin 10, the light beam can be diffused better.

  Examples of the resin used for the binder resin 10 include ionizing radiation curable resins such as acrylic resins, polyurethanes, polyesters, fluorine resins, silicone resins, polyamideimides, epoxy resins, and ultraviolet curable resins. . In addition to the above-described resin, for example, a plasticizer, a stabilizer, a dispersant, and the like may be blended in the binder resin 10. Since the binder resin needs to transmit light, it is transparent, and colorless and transparent is particularly preferable.

  The resin beads are substantially spherical, and examples of the material thereof include acrylic resin, polyurethane, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamide, polymethyl methacrylate, and the like. The resin beads 11 are preferably transparent in order to increase the amount of transmitted light, and particularly preferably colorless and transparent.

  The anti-sticking layer 9 is composed of a binder resin 12 and resin beads 13 dispersed in the binder resin 12. The materials of the binder resin 12 and the resin beads 13 are the same as those used for the light diffusion layer 8. Since the anti-sticking layer 9 is intended to prevent sticking with the light guide plate (see FIG. 3), the blending amount of the resin beads 13 is relatively small. Therefore, the resin beads are separated from each other in the binder resin 12. Are distributed.

  As in the optical sheet 1, fine glass particles 14 encapsulating an organic compound that emits phosphorescence by absorbing ultraviolet rays are dispersed in the binder resin 12. The optical sheet 6 exhibits a wavelength conversion function for converting ultraviolet light into visible light by the anti-sticking layer 9 containing such fine glass particles 14 in a dispersed manner. Therefore, by using the optical sheet 6 as the light diffusion sheet of the backlight unit, the amount of visible light transmitted to the liquid crystal surface can be increased, and as a result, the luminance of the liquid crystal display device can be increased without increasing the power consumption. Can be improved.

  In addition, the optical sheet of this invention is not limited to the said embodiment, For example, it is also possible to disperse | distribute the said fine glass particle in a light-guide plate. In the optical sheet 6, the fine glass particles 14 may be dispersed in the binder resin 10 or the base material layer 7 of the light diffusion layer 8.

  The optical sheet of the present invention is not limited to the use as an optical sheet incorporated in a backlight unit of a liquid crystal display device. For example, a hologram sheet, a polarizing sheet, a light reflection preventing sheet, a light reflection sheet, and a part of light It can be used in applications such as a partially reflective sheet, diffraction grating sheet, interference filter sheet, color filter sheet, light wavelength conversion sheet, and light diffusion sheet.

(Example 1)
On the surface of a 100 μm-thick polyester film (Lumilar T60 manufactured by Toray Industries, Inc.), acrylic polyol (Acridick A-807 manufactured by Dainippon Ink and Chemicals, Inc.) as a resin and polystyrene particles (Techpolymer manufactured by Sekisui Plastics Co., Ltd.) as beads. SBX-8) was used to prepare a light diffusion layer having a dry film thickness of 15 μm in which 150 parts by mass of beads were dispersed with respect to 100 parts by mass of the acrylic polyol. Next, on the back surface of the polyester film, 5 parts by mass of silica (Nibsei E-220A manufactured by Nippon Kagaku Kogyo Co., Ltd.) with respect to 100 parts by mass of the acrylic polyol, and a mixture of two types of Ir complexes by the sol-gel method (the above formula A glass containing a compound of (VI) and the compound of formula (V) is prepared, and further pulverized and polished to obtain 3 parts by mass of spherical glass particles having a particle diameter of 500 nm (compound of formula (VI) 1. A light-diffusion sheet with a sticking-preventing layer was prepared by preparing a sticking-preventing layer having a dry film thickness of 2 μm in which 58 parts by weight and 0.02 parts by weight of the compound of the formula (V) were dispersed.
(Example 2)
In Example 1, a light diffusion sheet with a sticking prevention layer was prepared in the same manner as in Example 1 except that 1.6 parts by mass of the compound of the formula (II) was contained in the spherical glass as an Ir complex.
(Comparative Example 1)
In Example 1, 1 part by mass of a fluorescent dye (Nikka Flow OB manufactured by Nippon Kagaku Kogyo Co., Ltd.) is contained in the light diffusion layer, and a mixture of two types of Ir complexes (1.58 mass of the compound of the formula (VI) is used in the anti-sticking layer. Part and a spherical glass containing 0.02 parts by mass of the compound of the formula (VI) were prepared in the same manner as in Example 1 to prepare a light diffusion sheet with a sticking prevention layer.
(Comparative Example 2)
In Example 1, a spherical glass containing a mixture of two types of Ir complexes (1.58 parts by mass of the compound of formula (VI) and 0.02 parts by mass of the compound of formula (V)) is not dispersed in the anti-sticking layer. Except for the above, a light diffusion sheet with a sticking prevention layer was prepared in the same manner as in Example 1.

The obtained four types of light diffusion sheets were incorporated into the backlight unit, and the brightness was visually determined from the upper surface of the backlight unit.
Example 1: ○ (good)
Example 2: Good (good)
Comparative Example 1: Δ (somewhat inferior)
Comparative Example 2: X (Inferior)

It is typical sectional drawing which shows the optical sheet for backlight units which concerns on one Embodiment of this invention. It is typical sectional drawing which shows the optical sheet for backlight units of a form different from the optical sheet of FIG. It is a typical perspective view which shows a general backlight unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical sheet 2 Sheet part 3 Prism part 4 Synthetic resin 5 Glass particle 6 Optical sheet 7 Base material layer 8 Light-diffusion layer 9 Sticking prevention layer 10 Binder resin 11 Resin bead 12 Binder resin 13 Resin bead 14 Glass particle 20 Backlight unit 21 Light source 22 Optical sheet 23 Light guide plate 24 Light diffusion sheet 25 Prism sheet 25a Prism unit

Claims (6)

An optical sheet for converting ultraviolet light emitted from a light source into visible light, comprising an organic compound that emits phosphorescence by absorbing ultraviolet light. The optical sheet according to claim 1, wherein the phosphorescent organic compound is a platinum or iridium complex. The phosphorescent organic compound has the formula (I),

Formula (II),

Formula (III),

Formula (IV),

Formula (V),

Or formula (VI)

The optical sheet according to claim 1, which is a compound represented by the formula: The optical sheet according to claim 1, wherein the phosphorescent organic compound is encapsulated with glass. The optical sheet according to claim 1, which is used for a backlight unit of a liquid crystal display device. A backlight unit for a liquid crystal display device using the optical sheet according to claim 1.

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