JP2005251655A - Light guide plate, its manufacturing method and backlight apparatus using the light guide plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin and low cost light guide plate having a high utilization efficiency of light, its manufacturing method and a backlight apparatus using the light guide plate. <P>SOLUTION: In the light guide plate in which a light incidence plane and a light outgoing plane are provided in a plate-shaped member of translucent material, and light from a light source arranged to face to the light incidence plane is emitted to a lighting object as planar lighting light; the plate-shaped member has a first refractive index, and a thin film layer of transparent material having a second refractive index larger than the first refractive index is provided on the light outgoing plane of the plate-shaped member. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a light guide plate, a manufacturing method thereof, and a backlight device using the same.

  A transmissive or transflective liquid crystal panel is provided with a backlight on the back. The backlight is roughly classified into a direct type in which a light source is arranged under a light diffusion plate and the like, and an edge light type in which a light source is arranged on a side surface of a light guide. The edge-light type backlight includes a flat light guide made of synthetic resin and having a size approximately the same as that of a liquid crystal display panel, one side of which is a light receiving surface, and a light source facing the light receiving surface. Is placed. As described above, the edge light type backlight has a configuration in which the light source is disposed on the side of the light guide, and thus can be reduced in thickness as compared with the direct type backlight, and the mobile phone or other mobile communication. Widely used in equipment.

  Hereinafter, an edge light type backlight device in the prior art will be described with reference to the drawings. FIG. 3 is a perspective view showing a main part of an edge light type backlight device in the prior art, and FIG. 4 is a partially enlarged sectional view showing the vicinity of a light incident surface of a light guide plate. As shown in FIG. 3, the edge light type backlight device has, as its basic configuration, a substantially rectangular parallelepiped light guide plate 2 made of a transparent material and three light sources 1 arranged on the side of the light guide plate 2. A light emitting diode (LED) is provided.

  The light guide plate 2 is disposed on the back surface side of the liquid crystal panel 5, and in many cases, a light reflecting sheet (not shown) for directing light from the light source 1 toward the liquid crystal panel 5 side on the lower surface side of the light guide plate 2. Is provided. Further, a diffusion sheet (not shown) and a light collecting sheet (not shown) for uniformly dispersing light from the light source 1 are often provided on the upper surface 2b side of the light guide plate 2.

  The light guide plate 2 is a plate made of a transparent member such as a colorless and transparent plastic material and has a substantially rectangular parallelepiped shape. The upper surface of the light guide plate 2 is a light emitting surface 2b, and one side surface of the light guide plate 2 is a light incident surface 2a. The light source 1 is disposed at a position facing the light incident surface 2a. Irradiated light emitted from the light source 1 is incident from the light incident surface 2a and then propagates while being repeatedly reflected inside the light guide plate toward the light output surface 2b, and a component having a critical angle or less is transmitted to the light output surface 2b of the light guide plate 2. To the outside as illumination light. The illumination light emitted to the outside illuminates the liquid crystal panel 5 from behind.

  In such an edge light type planar light source, as shown in FIG. 4, when light is emitted from the light guide plate 2 to the air layer 8, the light is refracted, and the light 3a having the incident angle θ2 is emitted from the light guide plate 2 to the emission angle θ1. Thus, the light 3b is emitted as air 3b. Here, when the refractive index of the material of the light guide plate 2 is n2, the refractive index of air 8 is n1, the incident angle of light is θ2, and the outgoing angle is θ1, according to Snell's law, n1 × sin θ1 = n2 × sin θ2. Become. When the light guide plate 2 is made of acrylic resin, the refractive index n2 = 1.5, and the refractive index n1 = 1 of the air layer 8, when the light is emitted from the light guide plate 2 to the air layer 8, the emission angle θ1 of the light 3b. Becomes larger than the incident angle θ2 of the light 3a. The critical angle of the light 3a incident at an incident angle of θ2 is about 42 degrees, and light having an incident angle θ2 of the light 3a exceeding the critical angle (about 42 degrees) is indicated by the wavy lines 7a and 7b. Are totally reflected at the light exit surface 2b. For this reason, if the thickness b of the light guide plate 2 is reduced, a large amount of light repeats total reflection in the light guide plate 2 and does not perform the backlight function. As a countermeasure, prism sheet-like reflecting means are provided on the upper and lower surfaces of the light guide plate 2. An example of forming is disclosed.

  As a first conventional example of such a light guide plate, an example of a light guide plate 10 as shown in FIG. 5 is disclosed (for example, see Patent Document 1). As shown in FIG. 5, the light guide plate 10 disposed adjacent to the linear light source 11 has a microprojection on a substrate 12 made of a resin material and a transmission surface 12 a that is substantially parallel to the liquid crystal display element 15 of the substrate 12. 14. A large number of the protrusions 14 are formed by the so-called 2P method, and the cross-sectional shape of the protrusions 14 is a substantially triangular acute triangle, and the inclination angle of the protrusions is set in the range of 90 to 150 degrees. Further, the protrusion 14 is made of a material having a refractive index larger than that of the substrate 12. Thus, since the projection 14 is formed by the 2P method, a projection shape with high dimensional accuracy is obtained, and the light guided inside the light guide plate 10 is efficiently refracted toward the liquid crystal display element 15 side.

  Moreover, an example of a backlight as shown in FIG. 6 is disclosed as a second conventional example (see, for example, Patent Document 1). As shown in FIG. 6, the backlight is disposed on the light source 21, the light guide plate 22, the light guide plate 22, the prism 23 having a higher refractive index than the light guide plate 22, and the optical fiber disposed on the prism 23. And a plate 24. The light guided into the light guide plate 22 enters the prism 23 because the refractive index of the prism 23 is larger than the refractive index of the light guide plate 22. This light is refracted when entering and exiting the prism 23, and becomes substantially perpendicular to the upper surface 22 a of the light guide plate 22. The optical fiber plate 24 is composed of a bundle of optical fibers 24F arranged substantially perpendicular to the upper surface 22a of the light guide plate 22. The light emitted from the prism 23 enters the optical fiber 24F forming the optical fiber plate 24, and is irradiated perpendicularly to the liquid crystal display element 25 to be illuminated.

JP-A-8-227015 (page 3-4, FIG. 1) JP-A-9-184922 (page 2-3, FIG. 1)

However, in the light guide plate in the first conventional example, ultraviolet rays or electron beam curable resin is used as the material of the protrusions 4 formed by the 2P method. The ultraviolet ray or electron beam curable resin has a problem that its light transmittance is inferior to that of a methacrylic resin or a polycarbonate resin. Moreover, there existed a problem that a metal mold | die and material cost were expensive and manufacturing cost became high.
In addition, the backlight in the second conventional example has a laminated structure of a light guide plate, a prism and an optical fiber plate, and the thickness of the light guide plate is 2 to 5 mm, which makes it difficult to reduce the thickness. Further, if there is even a slight gap, that is, an air layer, on the joint surface between the light guide plate and the prism, light exceeding a critical degree of about 42 degrees to the air from the light guide plate made of acrylic or the like is totally reflected on the upper surface of the light guide plate and is reflected on the prism. There was a problem that the light utilization efficiency declined.

(Object of invention)
An object of the present invention has been made in view of the above-mentioned problems of the prior art, and provides an inexpensive and thin light guide plate having high light utilization efficiency, a manufacturing method thereof, and a backlight device using the same. It is in.

In order to achieve the above object, a light guide plate of the present invention is provided with a light incident surface and a light output surface on a plate-like member made of a translucent material, and emits light from a light source arranged facing the light incident surface. In the light guide plate that emits planar illumination light from the light exit surface to the illumination object, the plate-like member has a first refractive index, and the light exit surface of the plate-like member has a first refractive index higher than the first refractive index. A thin film layer made of a transparent material having a large second refractive index is provided.
The transparent substance is characterized by being made of indium tin oxide, titanium oxide, or diamond.
The light guide plate is characterized in that the transparent material has a thickness of 100 to 1000 angstroms.

  In the light guide plate manufacturing method according to the present invention, a light incident surface and a light exit surface are provided on a plate-like member made of a translucent material, and light is emitted from a light source disposed opposite the light entrance surface. In a method for manufacturing a light guide plate that emits planar illumination light to an illumination object from a surface, a second refractive index that is higher than the first refractive index on a light emitting surface of a plate-like member having a first refractive index. A step of forming a film by printing ink containing a transparent substance with a screen printing method, and heating and baking the film together with the plate member to form a thin film layer made of the transparent substance on the light emitting surface of the plate member And a process.

In addition, the backlight device of the present invention includes a light guide plate and a light source disposed so as to face the light incident surface of the light guide plate in the vicinity or in close proximity, and illuminates light from the light source from the light emitting surface. In a backlight device that emits planar illumination light to an object, the light guide plate is used.
Further, the light guide plate has a side surface as a light incident surface and an upper surface as a light emission surface, and the light from the light source is converted into an optical path so that planar illumination light is emitted from the upper surface of the light guide plate to the illumination object. .

  As described above, the present invention is thin by providing a thin film layer made of a transparent material having a second refractive index larger than the first refractive index on the light emitting surface of the plate-like member having the first refractive index. Therefore, it is possible to provide a light guide plate that is excellent in light transmittance, has high light utilization efficiency, and is inexpensive, and a method for manufacturing the same. Further, by adopting the light guide plate, a thin backlight device can be provided at a low price.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 shows an edge light type backlight device using the light guide plate of the present embodiment, FIG. 1 (a) is a schematic sectional view showing the main part of the backlight device, and FIG. 1 (b) is FIG. It is sectional drawing which shows the light-guide plate in). Moreover, FIG. 2 is a figure which shows the manufacturing process of the light-guide plate in this embodiment. The edge light type backlight device according to the present embodiment is characterized by a light guide plate. The light guide plate is a thin plate made of a transparent material on a substrate as a plate-like member made of a transparent material and on the upper surface of the substrate which is a light emitting surface of the light guide plate. The point provided with the layer is different from the conventional example, and the other basic configuration is similar to the conventional example. Hereinafter, a description will be given based on the drawings.

  As shown in FIG. 1, the edge light type backlight device according to the present embodiment includes a light guide plate 30, a light collecting sheet 34 provided on the upper surface of the light guide plate 30, and an LED as the light source 1. The light guide plate 30 includes a substrate 32 made of translucent acrylic resin (refractive index 1.48), polycarbonate resin (refractive index 1.58), glass material (refractive index 1.5), and the like, and an upper surface of the substrate 32. And a thin film layer 33 made of a transparent material provided on the light emitting surface 32b. One side surface of the substrate 32 is a light incident surface 32a, and the light source 1 is disposed at a position facing the light incident surface 32a. Further, the lower surface facing the light emitting surface 32b is a light reflecting surface 32c. In order to reflect the light incident from the light source 1 into the light guide plate 32 toward the light emitting surface 32b, a plurality of minute surfaces are formed on the surface. A fine grain or a plurality of hemispherical dots are provided. The substrate 32 has a substantially rectangular parallelepiped shape, and the value of the plate thickness a is preferably in the range of 0.4 to 2 mm. In the present embodiment, the value is 0.5 mm.

  As the thin film layer 33 made of a transparent material, for example, indium tin oxide (refractive index 1.9), titanium oxide (refractive index 3.6), diamond (refractive index 2.7), or the like can be used. The thickness t of the thin film layer 33 is preferably in the range of 100 to 1000 angstroms. Titanium oxide has a light transmittance similar to that of glass, and the light transmittance of diamond and indium tin oxide (ITO) is slightly inferior, but there is no practical problem if the thickness t is in the range of 100 to 1000 angstroms. In the present embodiment, titanium oxide (refractive index 3.6) is used as the thin film layer 33, and the thickness is 250 angstroms. Thus, the light guide plate 30 provided with the thin film layer 33 made of a transparent material on the light output surface 32b of the substrate 32 efficiently refracts the light in the light guide plate and emits it outside, and has a high light utilization rate. It has been confirmed by experiments.

Next, the manufacturing method of the light guide plate in the present embodiment will be described by taking as an example a method of forming a transparent thin film layer of titanium oxide by a screen printing method.
As shown in FIG. 2A, the entire surface of the light emitting surface 32a, which is the upper surface of the substrate 32 having a thickness a of 0.4 to 2 mm made of transparent acrylic, polycarbonate, glass or the like, is formed on the entire surface of FIG. As shown in FIG. 4, an ink made of a paste-like organic titanium compound is printed by a screen printing method to form an organic titanium coating 33a. Organic titanium is a relatively viscous organic compound in which titanium metal is chained with an alkyl group such as a methyl group (CH3), and a flammable resin such as nitrocellulose, ethylcellulose, or rosin is added as a viscosity modifier. The ink-like viscosity is suitable for screen printing. The thickness s of the printed organic titanium film 33a is preferably 5 to 20 μm.

In the present embodiment, as the organic titanium compound paste, a water-soluble titanium compound manufactured by Matsumoto Pharmaceutical Co., Ltd., ORGATICS TC310 (R) and Orcatix TC40 (R) are used, and good results are obtained. It was.
In addition, the chemical abbreviation of ORGATICS TC 1310 (R) is “titanium lactate”
The chemical formula is (OH) ₂ Ti (C ₃ H ₅ 0 ₂ ) ₂ ,
The chemical abbreviation of ORGATICS TC400 (R) is “titanium triethanolamate”,
The chemical formula is (C ₃ H ₇ 0 ₂ ) ₂ Ti (C ₆ H ₁₄ 0 ₃ N) ₂ .
As the substrate 32, a glass material having a plate thickness a of 0.5 mm was used.

Next, the printed organic titanium-containing layer 33a is heated and fired for 20 to 40 minutes at a temperature of 180 to 220 ° C. together with the substrate 32. As shown in FIG. A thin film layer 33 made of titanium oxide having a thickness t of 500 to 1000 angstroms is formed on the upper surface 32a. After firing, the viscosity modifier such as nitrocellulose and ethylcellulose and the alkyl group are oxidized and decomposed, and only the titanium oxide (Ti ₂ 0 ₃ ) film as the thin film layer 33 remains. The thin film layer 33 made of the titanium oxide (Ti ₂ 0 ₃ ) film is colorless and transparent, and is not visually recognized from the upper surface or the lower surface of the substrate 32 when the thickness t is in the range of 500 to 1000 angstroms. The thin film layer 33 made of a titanium oxide (Ti ₂ 0 ₃ ) film is a transparent body similar to glass in appearance, but has a refractive index of about 3.6, and a general glass has a refractive index of about 1. .5 so it is very different. In this way, the thin film layer 33 made of a titanium oxide (Ti ₂ 0 ₃ ) film having a refractive index of 2 times or more is formed on the surface of the substrate 32 made of a glass material having a low refractive index, so that the light enters from the side surface of the substrate 32. The incident light is incident on the thin film layer 33 having a large refractive index on the upper surface of the substrate 32. At this time, since the refractive index of the thin film layer 33 is larger than the refractive index of the substrate 32, total reflection does not occur and the light is refracted and incident. Then, it emits outside from the thin film layer 33 and emits planar illumination light to the illumination object. As a result, the light guide plate 30 that is thin and excellent in light utilization efficiency can be obtained by the method of manufacturing the light guide plate in the present embodiment.

  The thin film layer made of indium tin oxide (ITO) and diamond can be formed by sputtering or CVD, and the film thickness is preferably in the range of 100 to 1000 angstroms.

  In the edge light type backlight device using such a light guide plate 30, as shown in FIG. 1, the irradiation light of the light source 1 incident from the light incident surface 32 a propagates inside the substrate 32 and emits light from the substrate 32. The light enters the thin film layer 33 from the surface 32b and exits to the outside as illumination light from the thin film layer 33. At this time, the illumination light is aligned vertically upward with respect to the light emission surface 32b by the light collecting sheet 34 and emitted to the outside to illuminate the liquid crystal panel 5 from behind. As a result, the edge light type backlight device according to the present embodiment forms a light emitting surface on the light emitting surface composed of the thin film layer 33 of the light guide plate 30 and forms the backlight device by the irradiation light emitted from the light source 1. It is made like that. As a result, it is possible to realize an edge-light type backlight device that has high light utilization efficiency and is inexpensive and thin.

As described above, according to the backlight device using the light guide cover of the present invention, even if the plate thickness of the light guide cover is extremely thin, for example, 0.4 mm, the light from the light source incident from the side surface of the light guide plate is used. A liquid crystal display device or the like above the light guide plate can be irradiated. Further, since the light guide plate may be a flat thin plate, it is advantageous for reducing the thickness of the backlight device, and the price can be reduced.
In the present embodiment, the edge light type backlight device has been described as an example, but the same effect can be obtained in other types of backlight devices.

FIG. 1A is a sectional view of a backlight device, and FIG. 1B is a sectional view showing a light guide plate in FIG. 1A. It is sectional drawing which shows the manufacturing process of the light-guide plate in embodiment of this invention. It is a perspective view which shows the backlight in a prior art. It is a partial expanded sectional view of the light-guide plate in a prior art. It is sectional drawing which shows the backlight apparatus in a 1st prior art example. It is sectional drawing which shows the backlight apparatus in a 2nd prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Light guide plate 2a Light incident surface 2b Light output surface 5 Liquid crystal panel 8 Air layer 10 Light guide plate 11 Light source 12 Substrate 12a Transmission surface 14 Projection 15 Liquid crystal display element 21 Light source 22 Light guide plate 22a Light guide plate upper surface 23 Prism 24 Optical fiber Plate 24F Optical fiber 25 Liquid crystal display element 30 Light guide plate 32 Substrate 32a Light incident surface 32b Light emitting surface 32c Light reflecting surface 33 Thin film layer 33a made of transparent material Film 34 Condensing sheet

Claims (6)

  A plate-like member made of a light-transmitting material is provided with a light incident surface and a light exit surface, and light from a light source arranged opposite to the light entrance surface is illuminated from the light exit surface to an illumination object. In the light guide plate that emits light, the plate member has a first refractive index, and a light emitting surface of the plate member is made of a transparent material having a second refractive index larger than the first refractive index. A light guide plate characterized in that a thin film layer is provided.   The light guide plate according to claim 1, wherein the transparent material is made of indium tin oxide, titanium oxide, or diamond.   3. The light guide plate according to claim 1, wherein a thickness of the transparent material is set in a range of 100 to 1000 angstroms.   A plate-like member made of a light-transmitting material is provided with a light incident surface and a light exit surface, and light from a light source arranged opposite to the light entrance surface is illuminated from the light exit surface to an illumination object. In a method of manufacturing a light guide plate that emits light, an ink containing a transparent substance having a second refractive index larger than the first refractive index is screened on a light emitting surface of a plate-like member having a first refractive index. A step of printing by a printing method to form a film, and a step of heating and baking the film together with the plate-like member to form a thin film layer made of the transparent material on the light emitting surface of the plate-like member. A manufacturing method of a light guide plate characterized by the above.   A light guide plate and a light source disposed so as to be close to or in close contact with the light incident surface of the light guide plate; 4. A backlight device according to claim 1, wherein the light guide plate according to any one of claims 1 to 3 is used. The planar light is emitted from the upper surface of the light guide plate to the illumination target by changing the optical path of the light from the light incident surface and the upper surface as the light emitting surface. Item 6. The backlight device according to Item 5.

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