JP2008180881A - Optical sheet, backlight unit using the same and display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet which does not cause the stripping due to heat or vibration with respect to improvement of the optical sheet used for illumination optical path control in a backlight unit for display using a liquid crystal display element. <P>SOLUTION: The optical sheet 10 is constituted by bonding an optical functional member 12 and a plate (diffusion plate or optical unit sheet) 14. As shown in Fig.10 (A), (B), edge surfaces 12A, 14A of the members 12, 14 are integrated by heat treatment. Otherwise, as shown in Fig.10(C), the edge surfaces 12A, 14A of the members 12, 14 are integrated with a resin film 16. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an improvement of an optical sheet used for illumination light path control in a display backlight unit mainly using a liquid crystal display element, and relates to a backlight unit and a display on which the sheet is mounted.

A display typified by a liquid crystal display device (LCD) is remarkably widespread in a type including a light source necessary for recognizing provided information. 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.

  A brightness enhancement film (BEF) which is a registered trademark of 3M Corporation of the United States is widely used as an optical sheet for solving this problem.

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 (direction F shown in FIG. 1) side with respect to the display screen.

  When the repetitive array structure of the prisms 72 is arranged in only one direction, only the direction change or recycling in the parallel direction is possible, and in order to control the luminance of the display light in the horizontal and vertical directions, the prism groups are arranged in parallel. Two sheets are stacked and combined so that the directions are substantially orthogonal to each other.

The adoption of BEF allows display designers to achieve the desired on-axis brightness while reducing power consumption.
As patent documents disclosing that a brightness control member having a repetitive array structure of prisms 72 typified by BEF is adopted for a display, many are known as exemplified in Patent Documents 1 to 3. ing.
Japanese Patent Publication No. 1-378001 JP-A-6-102506 Japanese National Patent Publication No. 10-506500

In the optical sheet using the BEF as a brightness control member as described above, the light P from the light source 20 is finally emitted at a controlled angle φ by the refraction action x as shown in FIG. Thus, it is possible to control to increase the intensity of light in the visual direction F of the viewer.
However, at the same time, the light component due to the reflection / refraction action y is unnecessarily emitted in the lateral direction without proceeding in the visual direction F of the viewer.

Accordingly, the light intensity distribution emitted from the optical sheet using the BEF as shown in FIGS. 1 and 2 is such that the viewer's visual direction F, that is, the angle with respect to the visual direction F is 0 °, as indicated by B in FIG. Although the light intensity in the (on the axial direction) is the highest, as shown as a small light intensity peak around ± 90 ° shown in the horizontal axis in the figure, the light emitted from the horizontal direction is increased. There's a problem.
The graph of FIG. 3 shows the light intensity distribution when only one prism sheet is used, and the curve indicated by “vertical distribution” in the figure corresponds to the direction in which the prisms 72 are arranged in parallel, and is indicated by “horizontal distribution”. The curved line corresponds to the longitudinal direction of the prism 72.
In general, a usage form in which two prism sheets are used in combination so that the directions in which the prisms 72 are arranged in parallel is substantially orthogonal.
A luminance distribution having such a light intensity peak is not desirable, and a smooth luminance distribution having no light intensity peak around ± 90 ° as shown by A in FIG. 3 is desirable.
In addition, if only the on-axis brightness is excessively increased, the width of the peaks in the graph (especially in the vertical distribution curve) becomes extremely narrow and the viewing area is extremely limited. Therefore, it is necessary to newly use a light diffusing film which is a separate member from the prism sheet, which is accompanied by an increase in the number of members.

In order to overcome such a drawback, as shown in FIG. 4, there is also a backlight unit 40 using an optical film 38 having a repetitive array structure of unit lenses instead of a prism (Patent Document 4).
4 and 6, reference numeral 21 denotes a lamp house, reference numeral 23 denotes a light source (cold cathode tube), and reference numeral 27 denotes a light reflecting sheet (light reflecting plate).

A lens 44 for guiding the light traveling in the optical film 38 to the liquid crystal panel 42 is provided on the surface of the transparent base 39 of the optical film 38 on the liquid crystal panel 42 side. As shown in the perspective view of FIG. 5, the lens 44 has a plurality of unit lenses repeatedly forming an array structure.
Further, on the other surface, a reflector 48 having a stripe pattern having an opening 46 in the vicinity of the focal plane of the lens 44 is provided.

The reflecting material 48 is obtained by mixing a mixture of white titanium dioxide (TiO ₂ ) powder in a solution such as a transparent adhesive with a predetermined pattern (when the unit lens is a semi-cylindrical convex cylindrical lens group, each unit lens Is formed in a stripe shape having an opening corresponding to 1: 1).

FIG. 6 is an explanatory diagram showing optical path control characteristics of the backlight when the optical sheet of FIGS. 4 and 5 is applied to the backlight unit.
Of the light emitted from the diffusion film 32, only the light that has passed through the opening 46 enters the lens 44 and is emitted after being condensed in a certain direction by the lens 44.
Then, the light enters the polarizing plate 49 and only light having a predetermined polarization component is guided to the liquid crystal panel 42.

  On the other hand, the light that could not pass through the opening 46 is reflected by the reflecting material 48, returned to the diffusion plate 26 side, and guided to the reflecting plate 27. Then, the light is incident on the diffusion plate 26 again by being reflected by the reflection plate 27 and is diffused again on the diffusion plate 26. 6 and is emitted by the lens 44 after being narrowed within a predetermined angle φ as shown in FIG.

In the backlight unit 40 using such an optical film 38, the size and the position of the opening 46 of the optical film 38 are adjusted to increase the light use efficiency, and the light is emitted from the lens 44 in the front direction S. Can be controlled to increase the proportion of light emitted.
JP 2000-284268 A

  In the case of a display having a large screen such as a monitor for a liquid crystal TV or a personal computer instead of a display having a relatively small screen such as a mobile phone or a mobile terminal, in order to make the luminance distribution in the screen uniform. It is preferable to adopt a direct backlight unit in which a light source is housed in a lamp house behind the screen, rather than a backlight unit using an edge light to a light guide plate.

  As shown in FIG. 7, the backlight unit in the liquid crystal display device is in the form of a laminated structure of each element, and the diffusion film or DBEF80 / prism sheet or optical film 81 / diffusion film 82 / diffusion plate 83 is a light source. It is arranged on 84 lamp houses 85 accommodated. Hereinafter, the light control sheets such as the diffusion film or DBEF 80, the prism sheet or optical film 81, and the diffusion film 82 are collectively referred to as an optical functional member.

  However, as the price of displays increases and the size increases, integration of the diffuser plate and the optical functional member is desired from the viewpoint of reducing the number of members and improving the rigidity of the optical functional member. In this case, the laminated structure form of the backlight unit is as shown in FIG. 8, and a diffusion film or DBEF 80 / plate integrated optical functional member 86 is disposed on the lamp house 85 in which the light source 84 is housed. If the required performance is met, a simple configuration in which only the plate-integrated optical functional member 86 is disposed on the lamp house 85 in which the light source 84 is housed as shown in FIG.

  Although the configuration as described above is an ideal form, various problems due to the simplification of the configuration have not been solved, so there are no sales examples as actual products. In particular, peeling of the optical functional member and the diffusion plate due to the influence of high heat generated when the backlight is turned on or vibration of transportation becomes a serious problem.

In order to achieve the above object, the present invention relates to an optical sheet in which an optical functional member for controlling at least one of the direction, range, color, and luminance distribution of light is bonded to a diffusion plate. And an end face of the diffusion plate are integrated.
The present invention also relates to an optical device in which an optical functional member that controls at least one of the direction, range, color, and luminance distribution of light emission is joined to an optical unit sheet having optical performance different from that of the optical functional member. In the sheet, the end face of the optical functional member and the end face of the optical unit sheet are integrated.

  Claims 4 to 5 refer to an optical sheet whose end face is protected by heat treatment or coating of a resin film.

  Further, claim 8 is a backlight using the optical sheet according to claims 1 to 7, and claim 9 is a liquid crystal display using the backlight according to claim 8.

  According to the present invention, in the configuration using the plate-integrated optical functional member 86 as shown in FIG. 8 and FIG. A liquid crystal display can be realized.

  Embodiments of the present invention will be described below with reference to the drawings.

  As the plate-integrated optical functional member 86 that is the optical sheet of the present invention, the diffuser plate and the optical functional member are simply joined together, and the functions of the diffuser plate are partially or entirely integrated into the optical functional member. Also included are those that are joined to simple transparent plates. Therefore, in the present invention, examples of the optical unit sheet having optical performance different from that of the optical functional member include the above-described fine diffusion plate and simple transparent plate.

  Examples of the material for the diffusion plate, the fine diffusion plate, and the transparent plate include polycarbonate, acrylic, polystyrene, or a mixture of these materials in an arbitrary ratio, which are well known in the art.

  As a method of joining the plate and optical functional member, a method in which an optical functional part is directly provided on the plate with a thermoplastic or UV curable material, a bead or a diffusing agent is dissolved in a solvent together with a resin serving as a binder and directly applied on the plate How to do. As thermoplastic materials, UV curable materials, binder resins, polycarbonate, acrylic, polypropylene, cycloolefin polymers well known in the field, as beads and diffusing agents, inorganic fillers such as glass and silica, organic fillers Etc.

  As another bonding method, a method of adding an optical functional part on a base material of the above-mentioned thermoplastic or UV curable material to a base material of PET, PC (polycarbonate) or acrylic, beads or a diffusing agent are used. There is also a method of joining the substrate and the plate through a method of dissolving in a solvent together with a resin serving as a binder and applying the solution onto the substrate. Examples of the method for bonding the substrate and the plate include a method using a pressure-sensitive adhesive or adhesive well known in the art, and a method for directly bonding the substrate and the plate with heat or pressure after surface treatment with an excimer laser. It is done.

In the present invention, as shown in FIGS. 10A and 10B, the end faces 12A and 14A of the members 12 and 14 constituting the optical sheet 10 are integrated by heat treatment, or a resin as shown in FIG. 10C. It is characterized by being integrated by the film 16.
Here, one member 12 constituting the optical sheet 10 is an optical functional member, and the other member 14 is an optical unit sheet having optical performance different from that of the diffusion plate or the optical functional member 12.

The heat treatment refers to fusing the optical functional member 12 and the plate (diffusion plate or optical unit sheet) 14 at the end faces 12A and 14A. Means include heating the end face of the cut optical sheet, punching with a heated Thomson blade, or processing while cutting with a laser.
In the case shown in FIG. 10A, only the end face 14A of one member 14 is melted and welded as shown by the scattered point range, and in the case shown in FIG. 10B, the scattered point range. As shown, the end faces 12A and 14A of both the members 12 and 14 are melted and welded.

The part to be heat-treated may be all or part of the end face.
There are also methods in which the end face of the cut optical sheet is punched with a partially heated Thomson blade or processed while being cut with a laser. In particular, by treating only the portion that is easily peeled off or the contact portion with the backlight or panel that begins to peel off, the cost and labor for heat treatment can be reduced.

As shown in FIG. 10C, when the end surfaces 12A and 14A of the members 12 and 14 constituting the optical sheet 10 are integrated by the resin film 16, the resin is spread over the end surfaces 12A and 14A of both the members 12 and 14. This is done by attaching the membrane 16.
The coating of the resin film 16 is preferably resistant to water, heat, and solvents, and examples thereof include acrylic resins, urethane resins, phenol resins, epoxy resins, melamine resins, urea resins, unsaturated polyesters, alkyd resins, and the like. The part coated with the resin film 16 may be all or part of the end face. In particular, by treating only the portion that is easily peeled off or the contact portion with the backlight or panel that begins to peel off, the cost and labor required for coating the resin film 16 can be reduced.

  The optical sheet prepared as described above was incorporated into a backlight or a liquid crystal display device, and the light source was turned on for a long time, and peeling did not occur even during a transportation test.

  FIG. 11 shows the shape of an embodiment of the present invention. A solid black line from the shape A to the shape C indicates the shape of the optical sheet 10, and a thick line portion G indicates a heat-treated end face or location. Although there is no particular size limitation in the present invention, in the examples, the maximum width (a) of the shape A to the shape C was unified to 415 mm and the maximum length (b) 730 mm and verified. The short side cut of shape A was 10 mm wide and 10 mm deep, and the long side cut was 10 mm wide and 5 mm deep. The cut of shape B was 10 mm × 10 mm. The round hole of shape C was 5mm in diameter. As the material for the plate, two types of styrene, a copolymer of acryl and styrene, having a haze of 92% and a total light transmittance of 65% were used. Moreover, the thing of the shape A which does not end-process as a reference was also created.

  As the optical functional member 12, a cylindrical lens was made of UV curable acrylic resin on PET. Thereafter, as disclosed in JP-A-2005-37694, a white reflective layer was formed. This was joined to the plate with an acrylic adhesive.

  For those not subjected to the end face treatment, the produced optical sheet 10 was cut with a round blade cutter. Regarding what is coated with the resin film 16, the produced optical sheet 10 was cut with a round blade cutter, and a commercially available one-component curable sealing agent was applied to the treated surface. As for a part to be heat-treated, after cutting other than the treated surface with a round blade cutter, it was cut into a predetermined shape with a laser cutter. All heat-treated items were created using a laser cutter from the beginning.

  The sample prepared as described above was tested under the two conditions of 80 ° C. for 500 hours and 80 ° C. for 1 day and at room temperature for 2 days. These conditions assume the temperature when the backlight is turned on and off. As a result, the shapes A to C did not peel off regardless of the end face processing method. In addition, the shape A that had not been subjected to the end face treatment peeled off from the cut portion.

  In order to test the vibration state due to transportation, the created optical sheet 10 is incorporated into a liquid crystal display device, the frequency is 5 to 50 Hz, the acceleration is 1.0 G, 69 minutes in the Z direction, 18 minutes in the X direction, 18 minutes in the Y direction. For 18 minutes. As a result, the shapes A to C did not peel off regardless of the end face processing method. In addition, the shape A that had not been subjected to the end face treatment peeled off from the cut portion.

  Shape A to shape C are examples of optical sheet shapes, and the present invention is not limited to such shapes.

  As described above, according to the present invention, it is possible to provide an optical sheet that does not peel off due to heat generated from a light source of a backlight or a liquid crystal display device or vibration during transportation.

Explanatory drawing which shows "BEF" which is an optical sheet which concerns on a prior art. Explanatory drawing which shows the optical path control characteristic of the backlight by BEF. The graph which shows the optical path control characteristic of the backlight by BEF. Explanatory drawing which shows the optical sheet which concerns on another type of prior art from BEF. The perspective view which shows the optical sheet | seat of FIG. Explanatory drawing which shows the optical path control characteristic of the backlight by the optical sheet of FIG. Explanatory drawing which shows an example of a backlight. Explanatory drawing which shows a component reduction type backlight. Explanatory drawing which shows a component reduction type backlight. The figure which shows the implementation shape of this invention. The figure which shows the implementation shape of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Optical sheet, light source 20 ... Light source, 23 ... Light source, 26 ... Diffusing plate, 27 ... Reflecting plate, 38 ... Optical sheet, 40 ... Backlight unit, 42 ... Liquid crystal panel, 44 ... ... lens part, 46 ... opening, 48 ... reflector made of stripe pattern, 70 ... member, 72 ... unit prism, 80 ... diffusion film or DBEF, 81 ... prism sheet or optical film, 82 …… Diffusion film, 83 …… Diffusion plate, 84 …… Light source, 85 …… Lamp house, 86… Plate integrated optical functional member.

Claims (9)

In an optical sheet in which an optical functional member that controls at least one of the direction, range, color, and luminance distribution of light is bonded to a diffusion plate,
The end surface of the optical function member and the end surface of the diffusion plate are integrated.
An optical sheet characterized by that. In an optical sheet in which an optical functional member that controls at least one of the direction, range, color, and luminance distribution of light is joined to an optical unit sheet that is different in optical performance from the optical functional member,
The end face of the optical functional member and the end face of the optical unit sheet are integrated.
An optical sheet characterized by that. The total thickness of the optical sheet is 1.5 mm or more,
The optical sheet according to claim 1 or 2, wherein The integration is performed by heat-treating both end faces or one end face and melting the end faces.
The optical sheet according to any one of claims 1 to 3, wherein: The integration is performed by attaching a resin film over both end faces.
The optical sheet according to any one of claims 1 to 3, wherein:   The optical sheet according to any one of claims 1, 3, 4, and 5, wherein the optical functional member and the diffusing plate are joined by a pressure-sensitive adhesive, an adhesive, or an excimer.   The optical sheet according to any one of claims 2 to 5, wherein the optical functional member and the optical unit sheet are bonded by an adhesive, an adhesive, or an excimer.   A display backlight unit comprising at least a direct light source and the optical sheet according to claim 1. An image display element comprising a liquid crystal display element that defines a display image according to transmission / shading in pixel units;
A light source using a cold cathode ray tube or LED;
A display comprising the backlight unit according to claim 8.

Images