JP5066902B2 - Optical sheet - Google Patents

Description

  The present invention relates to an optical sheet having a brightness enhancement function. The optical sheet of the present invention is particularly used for illumination light path control in a backlight unit for a display represented by an image display device (liquid crystal display) incorporating a liquid crystal display element.

Since the liquid crystal display is not self-luminous type like other image display devices (plasma display panel, organic EL display, field emission display, etc.), a light source, that is, a backlight unit is almost always required. In this case, the power consumption of the backlight unit is added to the power consumption necessary for driving the liquid crystal display element.
Therefore, in order to reduce the power consumption of the backlight unit as much as possible, an attempt is made to reduce the total power consumption of the display by using an optical sheet having a brightness enhancement function.

  As a brightness enhancement sheet for reducing the power consumption of the backlight unit, a brightness enhancement film (BEF) developed by 3M USA is known.

The BEF is a film in which unit prisms 72 having a triangular cross section are periodically arranged in one direction on a member 70 as shown in FIG. The prism 72 has a size (pitch) larger than the wavelength of light. BEF collects light from “off-axis” and redirects this light “on-axis” or “recycle” towards the viewer. To do. When using the display (when observing), the BEF increases the on-axis brightness by reducing the off-axis brightness. Here, “on-axis” is a direction that coincides with the visual direction of the viewer, and is generally the normal direction to the display screen (direction F shown in FIG. 3).
A technique that employs a brightness control member having a repetitive array structure of prisms 72 typified by BEF in a display is disclosed in, for example, Patent Document 1.

On the other hand, a light guide plate type that has been conventionally used for liquid crystal displays is known (see, for example, Patent Documents 2 and 3 below).
A general light guide plate method does not use a light-transmitting film having a prism shape and uses a diffusion film, and therefore has a drawback that the amount of light is insufficient when used as a backlight for a liquid crystal display. It was.

In view of this, the present applicant has proposed an optical sheet that can make light emitted from a light source uniform without increasing the amount of light emitted unnecessarily and control the diffusion range (see Patent Document 4).
In this optical sheet, in order from the incident light incident side, at least (a) a light scattering layer that scatters incident light to the exit surface side that is the non-incident surface side, (b) an adhesive layer or an adhesive layer, (c) A light-reflecting layer that has a highly light-reflective surface facing the exit surface side of the light-scattering layer (a), and reflects light scattered by the light-scattering layer to the light-scattering layer side; (d) light A lens sheet in which a back surface (flat surface) is fixed to the other surface of the reflective layer (c) and a plurality of unit lenses are arranged on the surface, and is a structure in which they are integrated, and reflects light. The layer (c) has an opening corresponding to each unit lens of the lens sheet (d) in a ratio of 1: 1 so that a perpendicular line extending from the vertex of the convex portion of each unit lens to the flat surface on the back surface of the lens sheet passes. It has the part.
JP-A-6-102506 Japanese Patent Laid-Open No. 3-190004 JP-A-3-201304 JP 2006-208930 A

In the technique disclosed in Patent Document 4, it is essential to provide an opening in the light reflection layer in terms of lens design. Specifically, a reflective layer having a plurality of regular openings (air layers) is fixed to the emission surface of the diffusion layer with an adhesive. However, in such a structure, there is a possibility that the shape of the opening is collapsed, in that case, the light distribution characteristics of the optical sheet is different from the target, and unevenness is observed on the surface of the liquid crystal display device, A reduction in brightness occurs, making it impossible to obtain characteristics expected as a brightness-enhancing optical sheet.
An object of the present invention is to reliably maintain the shape of the opening, satisfy the designed light distribution characteristics, not reduce the brightness of illumination light in the backlight unit for display, and the number of manufacturing steps. It is in the provision of the optical sheet which enables reduction of this, or utilization of the existing manufacturing process.

The invention according to claim 1 is an optical sheet used for illumination light path control in a backlight unit for display.
In order from the incident light incident side, at least,
The incident light is scattered on the exit surface side, which is the non-incident surface side, and the light scattering layer having a striped uneven structure on the exit surface side, and the adhesiveness provided on the convex portion of the striped uneven structure Or a light scattering sheet comprising an adhesive white layer, and a transparent sheet in which a plurality of unit lenses are arranged on a transparent support,
The light-scattering sheet has a structure in which an exit surface side of the light-scattering sheet and a back side of a surface of the transparent sheet on which a unit lens of the transparent support is disposed are bonded by an adhesive or sticky white layer. It is an optical sheet.
According to a second aspect of the present invention, in the optical sheet according to the first aspect, the white layer having adhesiveness or tackiness is a mixture of an adhesive or pressure-sensitive adhesive and a white pigment or white dye. is there.
The invention according to claim 3 is characterized in that the striped uneven structure is formed on the surface of the material forming the light scattering layer by a molding method selected from extrusion molding, scratch molding and emboss molding. The optical sheet according to claim 1 or 2 .
According to a fourth aspect of the invention, the material for forming the light scattering layer, methyl methacrylate - according to claim 3, wherein the styrene copolymer resin, a material selected from polyethylene terephthalate resin and glass It is an optical sheet.

  In the optical sheet having the brightness enhancement function according to the present invention, since the stripe-shaped uneven structure is formed on the surface of the light scattering layer, the shape of the opening (recess) serving as the reflective layer changes during and after the processing. There is nothing to do. Therefore, it is possible to freely set the depth of the groove of the concavo-convex structure, to securely hold the shape of the opening, satisfy the designed light distribution characteristics, and to improve the illumination light in the display backlight unit. Provided is an optical sheet that does not reduce brightness and that can reduce the number of manufacturing processes or use existing manufacturing processes.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiment 1 is a reference example.
<Embodiment 1>
FIG. 1 is a cross-sectional view illustrating a main part of the laminated structure of the optical sheet according to the first embodiment.

  The optical sheet according to Embodiment 1 scatters incident light sequentially from the incident light incident side to the exit surface side, which is the non-incident surface side, and has a striped uneven structure on the exit surface side. 2 and a light scattering sheet comprising a white layer 3 provided on the convex portion of the striped concavo-convex structure. FIG. 3 is a plan view of the light scattering layer 2 for explaining the striped uneven structure. As shown in FIG. 3, in the light scattering layer 2, concave portions 21 that form openings, white layers are provided on the top, and convex portions 22 are alternately and regularly provided in a stripe shape.

  The material for forming the light scattering layer 2 is preferably a material selected from methyl methacrylate-styrene copolymer resin, polyethylene terephthalate resin, and glass.

  Examples of a method for forming a striped uneven structure on the surface of the light scattering layer 2 include methods such as extrusion molding, scratch molding, cutting, and emboss molding on the surface of the material forming the light scattering layer 2. From the viewpoint that the size of the concavo-convex structure can be easily and freely set, extrusion molding, scratch molding and emboss molding are preferable.

  The size of the striped concavo-convex structure is not particularly limited. For example, the cross-sectional shape may be a square, the depth may be 3 μm or more, and the width may be 30 μm or more.

  A white layer 3 is provided on the convex portions of the striped concavo-convex structure. The white layer 3 is formed from a white paint whose main component is a white pigment or a white dye. The white layer 3 has a reflection function. For the reflective layer 3, a white paint is selectively applied only to the convex portions of the striped concavo-convex structure, or the white paint 3 is applied before forming the concavo-convex structure, and then cutting, scratch molding, embossing is performed. You may make it form the white layer 3 only in the convex part of a striped uneven structure by methods, such as shaping | molding. The thickness of the white layer 3 is not particularly limited, but can be, for example, 1 μm or more.

  The optical sheet according to Embodiment 1 includes the transparent sheet 1 in which a plurality of unit lenses are arranged on a transparent support. The transparent support is preferably formed from a material selected from methyl methacrylate-styrene copolymer resin, polyethylene terephthalate resin, polycarbonate resin and glass.

  Moreover, the transparent sheet 1 has a plurality of unit lenses arranged on a transparent support. Examples of the unit lens include a cylindrical lens and a prism, which can be easily formed integrally on the transparent support by curing the radiation curable resin.

The optical sheet according to Embodiment 1 is formed by a bonded body 4 in which an emission surface side of the light scattering sheet and a back side of a surface on which the unit lens of the transparent support of the transparent sheet is disposed are made of an adhesive or an adhesive. It has a joined structure. Various methods such as gravure coating, die coating, and roll coating can be applied as the method of applying the bonded body 4.
Examples of the bonded body 4 include UV curable, solvent-diluted, water-dispersed, or acrylic adhesives or pressure-sensitive adhesives. The bonded body is less likely to be buried in a striped uneven structure and has excellent smoothness. From the viewpoint, a UV curable adhesive or pressure-sensitive adhesive is preferred. In the present invention, the terms adhesive and pressure-sensitive adhesive are almost synonymous.
The optical sheet according to the first embodiment formed in this manner has a structure in which the light scattering sheet and the transparent sheet are independent from each other, and a structure in which these are integrated. In addition, since the stripe-shaped uneven structure is formed in the light scattering layer itself having sufficient mechanical strength, the shape of the opening (recess) serving as the reflective layer may change during and after processing. Absent.
The thickness of the joined body 4 is not particularly limited, but can be 3 μm or more and 50 μm or less.

  The opening (recess) in the striped uneven structure is formed on the straight line drawn from the apex of the unit lens (cylindrical lens) formed in the transparent sheet along the thickness direction of the optical sheet. It is preferable that the groove width center be formed.

A further specific example of the optical sheet according to <Embodiment 1> will be described.
The pitch of the cylindrical lens in the transparent sheet 1 was 140 μm, and a 75 μm thick polyethylene terephthalate film (Toyobo A4300) was used as the transparent support.
In the light scattering sheet, a 2 mm thick methyl methacrylate-styrene copolymer resin plate was used for the light scattering layer 2, and grooves having a depth of 20 μm and a width of 59 μm were formed on the surface every 81 μm.
The white layer 3 was formed using a white paint mainly composed of TiO ₂ and had a thickness of 5 μm.
As the joined body 4, a UV curable adhesive having a thickness of 10 μm was used.

<Embodiment 2>
FIG. 2 is a cross-sectional view illustrating a main part of the laminated structure of the optical sheet according to the second embodiment.

  The optical sheet according to Embodiment 2 scatters incident light sequentially from the incident light incident side to the exit surface side, which is the non-incident surface side, and has a striped uneven structure on the exit surface side. 6 and a light scattering sheet comprising a white layer 7 provided on the convex portion of the striped concavo-convex structure. The striped uneven structure is the same as that of the first embodiment. In addition, the optical sheet according to Embodiment 2 includes a transparent sheet 5 in which a plurality of unit lenses are arranged on a transparent support. The structure of the transparent sheet 5 is the same as that of the first embodiment.

  The optical sheet according to the second embodiment is provided with the white layer 7 having adhesiveness or tackiness on the convex portion of the striped concavo-convex structure without providing the joined body 4 with the optical sheet according to the first embodiment. Has characteristics. The white layer 7 can be a mixture of a white pigment or a white dye in an adhesive or pressure-sensitive adhesive. As a method for applying the white layer 7, various methods such as a gravure coating, a die coating, and a roll coating method can be adopted. According to the second embodiment, since it is not necessary to provide the joined body 4, the manufacturing process can be simplified.

A further specific example of the optical sheet according to <Embodiment 2> will be described.
The pitch of the cylindrical lens in the transparent sheet 5 was 140 μm, and a 75 μm thick polyethylene terephthalate film (Toyobo A4300) was used as the transparent support.
In the light scattering sheet, a 2 mm thick methyl methacrylate-styrene copolymer resin plate was used for the light scattering layer 6, and grooves having a depth of 20 μm and a width of 59 μm were formed on the surface every 81 μm.
The white layer 7 is an adhesive white ink layer and has a thickness of 10 μm. The white ink layer is prepared by mixing a binder made of an acrylic resin and a white pigment made of titanium dioxide having a volume ratio of 1 with respect to the binder, and further adding an additive (urethane-modified copolymer polyester resin: Toyobo Co., Ltd. trade name Byron UR-3200) is added at a weight ratio of 2%.

  The optical sheet of the present invention can freely set the depth of the groove of the concavo-convex structure, securely hold the shape of the opening, satisfy the designed light distribution characteristics, Since the brightness of the illuminating light in the unit is not reduced, and the number of manufacturing processes can be reduced or existing manufacturing processes can be used. It is useful for illumination light path control in a backlight unit for a display.

3 is a cross-sectional view illustrating a main part of a laminated structure of an optical sheet according to Embodiment 1. FIG. 6 is a cross-sectional view illustrating a main part of a laminated structure of an optical sheet according to Embodiment 2. FIG. It is a top view of the light-scattering layer for demonstrating stripe-shaped uneven structure. It is a perspective view for demonstrating a brightness enhancement film (BEF: Brightness Enhancement Film).

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,5 ... Transparent sheet, 2, 6 ... Light-scattering layer, 3, 7 ... White layer, 4 ... Assembly.

Claims (4)

In an optical sheet used for illumination light path control in a backlight unit for display,
In order from the incident light incident side, at least,
The incident light is scattered on the exit surface side, which is the non-incident surface side, and the light scattering layer having a striped uneven structure on the exit surface side, and the adhesiveness provided on the convex portion of the striped uneven structure Or a light scattering sheet comprising an adhesive white layer, and a transparent sheet in which a plurality of unit lenses are arranged on a transparent support,
The light-scattering sheet has a structure in which an exit surface side of the light-scattering sheet and a back side of a surface of the transparent sheet on which a unit lens of the transparent support is disposed are bonded by an adhesive or sticky white layer. Optical sheet. The adhesive or white layer having adhesiveness, the optical sheet of claim 1 wherein the a mixture of the adhesive or pressure-sensitive adhesive white pigment or a white dye. The striped uneven structure on the surface of the material forming the light scattering layer, extrusion, according to claim 1 or 2, characterized in that it is formed by a molding method selected from scratch molding and embossing Optical sheet. The optical sheet according to claim 3 , wherein the material forming the light scattering layer is a material selected from methyl methacrylate-styrene copolymer resin, polyethylene terephthalate resin, and glass.

Images