JP2008134371A - Optical sheet applied to direct back light for liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical member which uniformizes the luminance distribution of light radiated on liquid crystal panel, when applied to a direct backlight unit, gives a desired front face luminance and contributes to make a liquid crystal apparatus thinner and to reduce manufacturing cost. <P>SOLUTION: An optical path control sheet 10 includes an optical path adjustment section composed of unit components (unit lenses 7) arranged in parallel on both faces, which are composed of columnar components which converge or diverge light by the refractive index difference with air, and has a structure in which a light beam radiated from a cold-cathode tube is diffused so that the luminance distribution becomes uniform over substantially a whole face. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an improvement in an optical sheet used for illumination light path control in a direct backlight unit for a display mainly using a liquid crystal display element.

  In recent years, liquid crystal display devices (LCDs) using liquid crystal panels have been used in image display means for notebook personal computers and personal computer displays in the OA field, information terminal equipment, etc., as well as image display means for information appliances such as large-screen TVs, Has been used in various fields as an image display means for mobile phones and personal digital assistants (PDAs).

In a display represented by a liquid crystal display device (LCD), a type having a built-in light source necessary for recognizing provided information is remarkably widespread.
Such a liquid crystal display device is a transmissive type, and a light source is provided on the back side of the liquid crystal panel, and a surface light source device that irradiates the liquid crystal panel by converting light from the light source into surface light emission, a so-called backlight is provided. It has been adopted.

  The backlight system is roughly divided into a cold cathode fluorescent tube (CCFT) and other light sources attached along the side edge of a flat light guide plate made of acrylic resin with excellent light transmission. There are a light guide plate light guide method (edge light method) that multi-reflects light from the light guide plate and a direct type method in which a light source is arranged on the back surface of the liquid crystal panel without using the light guide plate.

Recently, for small liquid crystal display devices with a screen size of 20 inches or less used for notebook personal computers, personal digital assistants, etc., it has become mainstream to adopt an edge light system that can reduce power consumption and can be easily thinned. In medium to large liquid crystal display devices having a screen size of 20 inches or more, the direct type is the mainstream.
In a battery-powered device such as a laptop computer, the power consumed by the light source occupies a substantial portion of the power consumed by the entire battery-powered device.
Thus, reducing the total power required to provide a given brightness increases battery life, which is particularly desirable for battery powered devices.

  Liquid crystal display devices of 20 inches or more are required to be thinner, have a low viewing angle dependency, have high brightness, and have low power consumption. There is a need to deal with realization.

  In a direct type backlight with multiple cold cathode tubes arranged in parallel, a cold cathode tube (CCFT) or an LED (Light Emitting Diode) as a light source passes through a diffusion plate that diffuses the emitted light, and the emitted light source Since the shape can be directly recognized, a resin plate having a very strong light scattering property is used as the diffusion plate. This diffuser plate usually needs to have a thickness of about 1 mm to 3 mm in order to have a strong diffusivity, and because of the thickness, there is a considerable amount of light absorption, and the amount of light from the light source is reduced, resulting in a liquid crystal display. There is a problem of darkening (Patent Documents 1 and 2).

In addition, there are many cases where a light diffusion sheet or a brightness enhancement sheet is used together in order to further uniform the brightness distribution and improve the front brightness, thereby preventing the slim shape of the entire liquid crystal display device and increasing costs. There are also problems such as.
Japanese Patent Publication No. 1-378001 JP-A-6-102506

  As shown in FIG. 1, the direct type backlight unit is made of a resin having a very light scattering property so that the shape of the light source (cold cathode tube) 5 in the lamp house (light reflecting sheet) 6 is not directly recognized. A diffusion plate 4 is used. Since the diffusion plate 4 usually requires a thickness of about 1 mm to 3 mm in order to give strong diffusibility, there is a problem that light absorption occurs, and the liquid crystal screen display becomes dark.

  Further, in order to make the luminance distribution more uniform, it is often necessary to interpose the light diffusion sheets 1 and 3 and the luminance control member 2 between the light diffusion plate 4 and the liquid crystal panel. Inhibition of slimming itself and increased costs are also problems.

  Therefore, the luminance distribution control member for illumination light in the backlight unit of the liquid crystal display device is required to have high light diffusibility and high total light transmittance.

The present invention has been made in view of the above problems, and the invention according to claim 1 is used for illumination light path control in a backlight unit for a display, and has light on both sides in the thickness direction by a difference in refractive index with air. An optical sheet provided with an optical path adjustment unit in which a plurality of unit lenses for converging or diverging extend in parallel with each other, and the extending direction of the unit lens formed on one of the two surfaces And the direction of extension of the unit lens formed on the other surface is different.
In other words, the invention according to claim 1 is an optical sheet used for controlling the luminance distribution of illumination light in a direct-type backlight unit for display, and has a columnar shape that converges or diverges light on both sides by a difference in refractive index from air. It has a lens part in which unit lenses composed of parts are arranged in parallel, and the crossing angle of stripes in which columnar parts (unit lenses) are arranged in parallel is not 0 ° between the surfaces. .

  The optical sheet is made of a transparent material to diffuse light emitted from the cold cathode tube by refraction of light by a columnar portion (unit lens) that converges or diverges light due to a difference in refractive index with air, and is made of a transparent material. The attenuation of light is less than that of a conventional light diffusing plate mixed with an agent, and a total light transmittance of 75% or more is realized.

  In the optical sheet according to the present invention, the angle of the columnar portion layer that converges or diverges light by the refractive index difference between the light incident surface from the light source and the air on the light exit surface to the liquid crystal panel (the direction in which the unit lens extends) Because of the different structure, the light emitted from the cold-cathode tube is diffused by the refraction of light by the columnar part (unit lens) that converges or diverges light due to the difference in refractive index with air, and the luminance distribution is uniform over almost the entire surface. Become. Further, since the optical path control sheet is made of a transparent resin, the amount of light attenuation is small and a high total light transmittance can be secured.

  In addition, the light diffusion sheet for backlights that are currently popular has a tendency that the luminance when observed from an angled direction in the horizontal direction is lower than the front luminance, but an example of the optical sheet according to the present invention Since the luminance is maintained at a wide angle in the horizontal direction and the luminance becomes maximum at about 40 °, it is useful for use in a dual-viewer navigation system.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
2A and 2B are explanatory views of the optical sheet according to the present embodiment, in which FIG. 2A is a perspective view and FIG. 2B is an exploded perspective view.

The optical sheet 10 according to the present embodiment is used for illumination light path control in a display backlight unit, and a plurality of unit lenses 7 for converging or diverging light according to a difference in refractive index with air on both surfaces in the thickness direction. An optical sheet provided with an optical path adjusting portion formed extending in parallel, the extending direction of the unit lens 7 formed on one of the two surfaces and the unit formed on the other surface The direction is different from the extending direction of the lens 7.
In other words, the optical sheet 10 according to the present embodiment has an optical path adjusting unit in which unit parts (unit lenses 7) including columnar parts 7 that converge or diverge light according to a difference in refractive index with air are arranged on both sides. Accordingly, the light emitted from the cold-cathode tube is diffused by utilizing the refraction of light at the light incident surface and the light exit surface, thereby ensuring the uniformity of the luminance distribution over substantially the entire surface.
The cross section in the direction orthogonal to the extending direction of the unit lens 7 may be configured by a semicircular or wavy curve, or may be configured by a plurality of straight lines having different directions such as a cross section of a prism. Alternatively, it may be configured by a combination of a curve and a straight line.
Further, the extending direction of the unit lens 7 formed on one surface of both surfaces of the optical sheet 10 and the extending direction of the unit lens 7 formed on the other surface have an intersection angle θ, When the crossing angle θ is defined as the narrower angle among the angles formed by the unit lenses on both sides, the crossing angle θ is greater than 0 ° and 90 ° or less.

  The optical sheet 10 according to the present embodiment is formed by light irradiation, press molding, or melt extrusion molding using a UV curable resin or a thermoplastic resin.

  The double-sided optical path adjustment unit is formed as an integrated type by the above method, or an optical path control sheet having one flat surface is prepared by the above method, and the single-side optical path control sheet is adhered or adhered to the substantially flat surface. Can be formed.

  At this time, if a diffusion layer is inserted between the single-sided optical path control sheets, the function as a light diffusion sheet is improved.

FIG. 3 is an explanatory diagram showing an outline of an example of the relationship between the angles of stripes composed of the cold cathode tube 5 as a light source and the unit portion (unit lens 7) on one side 8 of the optical sheet 10 according to the present invention.
The angle of the lens stripe on the cold cathode tube 5 side is preferably between 0 ° and 45 ° with respect to the cold cathode tube 5.

  The pitch of the unit parts (unit lens 7) on both sides of the optical sheet 10 according to the present invention can be applied to the same or random pitch in the same plane and between different planes.

  The light diffusibility improves as the pitch of the unit parts (unit lens 7) on each surface becomes finer.

  As an example showing the performance of the optical sheet 10 according to the present invention, a front luminance distribution of the optical sheet 10 having the configuration shown in FIG. 5 is shown in FIG.

  FIG. 6 shows the visibility of the cold cathode tube shadow through the optical sheet 10. In either case, as a comparison, the measurement results of a high diffusion sheet that is widely used as a light diffusion sheet used in combination with the light diffusion plate are also shown. These examples are a part of the optical sheet 10 according to the present invention, and the optical sheet 10 according to the present invention is not limited thereto.

Explanatory drawing which shows the backlight unit using the luminance control member which concerns on a prior art. It is explanatory drawing of the optical sheet by this embodiment, (A) is a perspective view, (B) is a disassembled perspective view. Explanatory drawing which shows the angle relationship of the optical sheet and light source by this invention. The graph which shows the optical characteristic of the optical sheet by this invention. The table | surface which shows the structural example of the optical sheet by this invention. The table | surface which shows the characteristic of the structural example of Table 1.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Polarization separation sheet or light diffusion sheet, 2 ... Prism sheet, 3 ... Light diffusion sheet, 4 ... Light diffusion plate, 5 ... Light source lamp, 6 ... Lamp house (light reflection sheet), 7 ... A columnar portion that converges or diverges light by a refractive index difference from air, 8... One side of the optical sheet according to the present invention (cold cathode tube side), 10.

Claims (14)

An optical path adjustment unit that is used for illumination optical path control in a backlight unit for a display and has a plurality of unit lenses extending in parallel with each other for converging or diverging light due to a difference in refractive index with air on both sides in the thickness direction. An optical sheet provided with
The direction in which the extending direction of the unit lens formed on one surface of the both surfaces is different from the extending direction of the unit lens formed on the other surface,
An optical sheet characterized by that. The optical sheet makes the luminance of light transmitted through the optical sheet uniform by diffusing light from the light source of the backlight unit for display, over substantially the entire surface.
The optical sheet according to claim 1.   The optical sheet according to claim 1, wherein a cross section in a direction perpendicular to the extending direction of the unit lens is configured by a semicircular or wavy curve.   The optical sheet according to claim 1, wherein a cross section in a direction perpendicular to the extending direction of the unit lens is configured by a plurality of straight lines having different directions such as a cross section of a prism.   2. The optical sheet according to claim 1, wherein a cross section in a direction orthogonal to the extending direction of the unit lens is configured by a combination of a curve and a straight line.   The optical sheet according to any one of claims 1 to 5, wherein the unit lens is a molded body formed by light irradiation to a UV curable resin, press molding of a thermoplastic resin, or melt extrusion molding.   The extending direction of the unit lens formed on one surface of the both surfaces and the extending direction of the unit lens formed on the other surface have an intersection angle θ. 6. The optical sheet according to any one of 6 above. The extending direction of the unit lens formed on one surface of the both surfaces and the extending direction of the unit lens formed on the other surface have an intersection angle θ,
The crossing angle θ is larger than 0 ° and not larger than 90 ° when the crossing angle θ is defined as a narrower angle among the angles formed by the unit lenses on both sides. The optical sheet according to any one of Items 1 to 7. The light source of the display backlight unit is composed of a cold cathode tube,
The extending direction of the unit lens formed on the surface in the thickness direction of the optical sheet facing the cold cathode tube has an intersection angle ψ with respect to the cold cathode tube. 8. The optical sheet according to any one of items 8. The light source of the display backlight unit is composed of a cold cathode tube,
The extending direction of the unit lens formed on the surface in the thickness direction of the optical sheet facing the cold cathode tube has a crossing angle ψ with respect to the cold cathode tube,
The intersection angle ψ is 0 ° or more and 45 ° or less when the intersection angle ψ is defined as a narrower angle among the angles formed by the cold-cathode tube and the unit lenses. Item 10. The optical sheet according to any one of Items 1 to 9.   The optical sheet according to any one of claims 1 to 10, wherein the pitch of the unit lenses is the same or random in the same plane and on both sides.   The optical sheet according to any one of claims 1 to 11, wherein the optical sheet is formed as a single unit by light irradiation to a UV curable resin, pressing of a thermoplastic resin, or melt extrusion. A first optical sheet is provided in which the unit lens is formed on one of the two surfaces in the thickness direction on a substantially flat surface by light irradiation to a UV curable resin, pressing or melt extrusion of a thermoplastic resin. ,
A second optical sheet in which the unit lens of the other surface in the thickness direction is formed on a substantially flat surface by light irradiation on a UV curable resin, pressing or melt extrusion of a thermoplastic resin is provided. ,
13. The optical sheet according to claim 1, wherein the substantially flat surface of the first optical sheet and the substantially flat surface of the second optical sheet are bonded to each other. The optical sheet described.   The optical sheet according to any one of claims 1 to 13, wherein the total light transmittance is 75% or more.

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