JP2008139364A - Optical sheet and backlight unit and display using the same - Google Patents

Abstract

In an improvement of an optical sheet used for illumination light path control in a backlight unit for a display using a liquid crystal display element, the angle between the optical element and the end face of the optical sheet is limited to limit the optical element caused by heat or vibration. An optical sheet that does not peel off is provided.
An optical sheet in which a plurality of unit optical elements for controlling at least one of a direction, a range, a color, and a luminance distribution extend in parallel with each other on one surface in a thickness direction. The inclination of the unit optical element is in the range of 0 ° to 10 ° or 80 ° to 90 ° with respect to the end face of the shape of the optical sheet.
[Selection] Figure 10

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.

Therefore, the light intensity distribution emitted from the optical sheet using the BEF as shown in FIGS. 1 and 2 has a viewer's visual direction F, that is, an angle with respect to the visual direction F, as shown in FIG. Although the light intensity in the upper direction is the highest, as shown as a small light intensity peak around ± 90 ° shown on the horizontal axis in the figure, there is a problem that the amount of light emitted from the horizontal direction is increased. is there.
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 ° is more 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). In FIG. 4, reference numerals 21 and 27 denote reflection plates, and reference numeral 26 denotes a cold cathode tube.

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, light control functions 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 element. Further, the diffusion film or DBEF 80, the prism sheet or optical film 81, the diffusion film 82, and the diffusion plate 83 are referred to as unit sheets having optical performance.

  However, as the price and size of displays increase, the integration of the diffuser plate and the optical element is desired from the viewpoint of reducing the number of members and improving the rigidity of the optical sheet. In this case, the laminated structure form of the backlight unit is as shown in FIG. 8, and a diffusion film or DBEF 80 / diffusion plate integrated optical element 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 diffuser integrated optical element 86 is disposed on the lamp house 85 in which the light source 84 is housed as shown in FIG. 9 is most desirable.

  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, the peeling of the optical elements caused by the influence of high heat generated when the backlight is lit, the vibration of transportation, and the synergistic effect due to the rigidity of the optical sheet becomes a serious problem. The peeling of the optical element occurs when the end of the optical element facing the end face of the optical sheet is caught by another member due to vibration during transportation of the optical sheet, impact during high temperature when the backlight is lit, or vibration during transportation of the backlight. . The diffuser plate-integrated optical element 86 is characteristic in comparison with the prior art, because the diffuser plate-integrated optical element 86 itself is rigid, and thus is easily affected by the vibration.

  As a method for solving peeling, there are methods of making the optical element smaller than the plate in order to eliminate the catching part, and a method of heat-treating the end face, but these treatments have a high effect of suppressing peeling, but the optical element is not used when creating the optical sheet. There is a demerit of complicating the process, such as removing or post-processing the optical sheet once created.

  In order to achieve the above object, according to the present invention, a plurality of unit optical elements for controlling at least one of direction, range, color, and luminance distribution are formed to extend in parallel with each other on one surface in the thickness direction. In the optical sheet, the unit optical element extends with an inclination in a range of 0 ° to 10 ° or 80 ° to 90 ° with respect to an edge of the optical sheet.

  An eighth aspect is a backlight using the optical sheet according to any one of the first to seventh aspects, and a ninth aspect is a liquid crystal display using the backlight according to the eighth aspect.

  According to the present invention, in the configuration using the diffusion plate-integrated optical element 86 as shown in FIGS. 8 and 9, vibration during transportation of the optical sheet, impact during high temperature when the backlight is lit, and vibration during backlight transportation. Thus, it is possible to realize a backlight and a liquid crystal display that do not have a display defect due to peeling of the optical element.

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

  The optical sheet of the present invention includes a diffusion plate-integrated optical element 86, and the diffusion plate-integrated optical element 86 can be obtained by simply joining the diffusion plate and the optical element, or a part or all of the functions of the diffusion plate. In other words, it is also included in the case where it is joined to a slightly diffusing plate or a 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.

  The diffusion plate and optical element can be joined by directly applying the optical element to the diffusion plate with a thermoplastic or UV curable material. The method of apply | coating directly is mention | raise | lifted. 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 Examples of the diffusing agent include titanium dioxide and barium sulfate.

  As another bonding method, a method of applying an optical element on a base material of PET, PC (polycarbonate) or acrylic with a thermoplastic or UV curable material as described above, a binder of beads or a diffusing agent is used. There is also a method of joining the base material and the diffusion plate through a method of dissolving in a solvent together with the resin to be applied and applying the solution onto the base material. As a method for joining the base material and the diffusion plate, there are a method using a pressure sensitive adhesive or an adhesive well known in the field, and a method for directly joining the base material and the plate with heat or pressure after surface treatment with an excimer laser. Can be mentioned.

The optical sheet of the present invention includes a unit sheet in which a plurality of unit optical elements are formed to extend in parallel to each other, and the unit optical element is 0 ° to 10 ° with respect to an edge of the optical sheet or In this embodiment, the optical sheet is an optical element 86 with an integrated diffuser plate.
In other words, the present invention is characterized in that the inclination of the unit optical element of the diffuser integrated optical element 86 includes a range of 0 ° to 10 ° or 80 ° to 90 ° with respect to the end face of the shape of the optical sheet. . Ideally, it should be in the range of 0 ° to 10 ° or 80 ° to 90 ° for all end faces, but if the display design is not possible, as many ranges as possible are 0 ° to 10 ° or Include within 80 ° to 90 °.

  The angle can be set by forming the optical element directly on the diffuser plate adjusted to a predetermined shape in advance, or two types of optical elements formed on the base material on the plate adjusted to a predetermined shape at a predetermined angle. The method of joining is mentioned. Alternatively, there is a method in which an optical element is appropriately formed or bonded to a plate larger than a predetermined optical sheet shape, and then processed so as to have a predetermined angle.

  The optical sheet prepared as in the present invention was incorporated into a backlight or a liquid crystal display device, and it was difficult to cause an impact while the light source was turned on, or to be peeled off during a transportation test in the state of the optical sheet or display.

  FIG. 10 shows the shape of an embodiment of the present invention. The black solid line from the shape A to the shape C indicates the shape of the optical sheet, and the thick line portion indicates the side as a reference for the tilt of the optical element. Although there is no particular size limitation in the present invention, in the examples, the maximum width (a) of the shapes A-1 to C was unified to 415 mm and the maximum length (b) 730 mm and verified. The short side cuts of shapes A-1 and A-2 were 10 mm wide and 10 mm deep, and the long side cuts were 10 mm wide and 5 mm deep. The cut of shape B was 10 mm wide and 5 mm deep for the short side cut, 20 mm wide and 10 mm deep for the long side cut, and the two corners with the corners inclined at 45 ° with respect to the other sides. All corners of shape C were 90 °. As the material of the plate, two types of polycarbonate, styrene, acrylic and styrene copolymer, having a haze of 92% and a total light transmittance of 65% were used.

  As an optical element, a cylindrical lens was made of UV curable acrylic resin on PET. Thereafter, as disclosed in JP-A-2000-284268, a white reflective layer was formed. Alternatively, a prism was formed of UV curable acrylic resin on PET.

  The inclination of the optical element was 0 °, 90 °, 5 ° and 10 ° for shape A, and 0 ° and 45 ° for shapes B and C. Two types of optical elements formed on PET were joined to a plate cut in advance from shape A to C at a predetermined angle with an acrylic adhesive.

  The sample prepared as above was wrapped in a plastic bag, placed in a cardboard box, tested at a frequency of 5-50HZ and acceleration of 1.0G for 60 minutes in the Z direction, 15 minutes in the X direction, and 15 minutes in the Y direction. . As a result, in the case of shape A-1, all samples with an inclination of 10 ° were peeled regardless of the plate material and the type of optical element, and other than that, no peeling occurred. No peeling occurred in the shape A-2. In shape B, peeling occurred at 45 ° with respect to the thick line regardless of the plate material and optical element type. Part of the shape B with 0 ° with respect to the thick line was peeled off. The part peeled off was at 45 ° with respect to the end face of the plate, and the part at 0 ° with respect to the end face of the plate did not peel off regardless of the plate material and the type of optical element. In shape C, peeling at 0 ° with respect to the thick line did not occur regardless of the plate material and the type of optical element. Peeling occurred at 45 ° with respect to the thick line regardless of the plate material and optical element type.

  Also, in order to test the vibration state due to transportation, the created optical sheet is incorporated into the liquid crystal display device, and when 2 hours have passed since the light source is turned off or turned on, the vibration frequency is 5 to 50 Hz and the acceleration is 1.0 G in the Z direction. The test was performed for 60 minutes, 15 minutes in the X direction and 15 minutes in the Y direction. As a result, in the case of shape A-1, all samples with an inclination of 10 ° were peeled regardless of the plate material and the type of optical element, and other than that, no peeling occurred. No peeling occurred in the shape A-2. In shape B, peeling occurred at 45 ° with respect to the thick line regardless of the plate material and optical element type. The shape B having a 0 ° with respect to the thick line had a partial rise. The part peeled off was at 45 ° with respect to the end face of the plate, and the part at 0 ° with respect to the end face of the diffuser plate did not peel regardless of the material of the plate and the type of optical element. In shape C, peeling at 0 ° with respect to the thick line did not occur regardless of the plate material and optical element type. Peeling occurred at 45 ° with respect to the thick line regardless of the plate material and optical element type.

  From the above results, it was found that the ease of peeling of the optical element formed on the optical sheet depends on the angle formed by the optical element and the end face of the optical sheet. 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, by controlling the angle formed between the optical element and the end face of the optical sheet, peeling occurs due to vibration during transportation of the optical sheet, impact during high temperature when the backlight is lit, and vibration during backlight transportation. It becomes possible to provide an optical sheet that does not.

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 a component reduction type backlight. Explanatory drawing of a diffuser plate integrated optical element. Explanatory drawing of a diffuser plate integrated optical element. Explanatory drawing of the Example of this invention.

Explanation of symbols

  20 ... Light source, 23 ... Light source, 26 ... Diffusion plate, 27 ... Reflection plate, 38 ... Optical sheet, 40 ... Backlight unit, 42 ... Liquid crystal panel, 44 ... Lens portion, 46 ... Opening portion 48... Reflective material having striped pattern, 70... Member, 72... Unit prism, 80 .. diffusion film or DBEF, 81 ... prism sheet or optical film, 82. ...... Diffusion plate, 84 ... Light source, 85 ... Lamp house, 86 ... Plate integrated optical element.

Claims (9)

In the optical sheet in which a plurality of unit optical elements for controlling at least one of the direction, range, color, and luminance distribution are formed to extend in parallel with each other on one surface in the thickness direction.
The unit optical element extends with an inclination in a range of 0 ° to 10 ° or 80 ° to 90 ° with respect to an edge of the optical sheet.
An optical sheet characterized by that. One surface in the thickness direction of the optical sheet is an entrance surface, and the other surface in the thickness direction is an exit surface,
The unit optical element is formed on the exit surface;
The optical sheet according to claim 1. The optical sheet is configured by laminating and integrating a plurality of unit sheets having optical performance,
The unit optical element is formed on the exit surface;
The unit sheet constituting the incident surface is a diffusion plate;
The optical sheet according to claim 1. The optical sheet is configured by laminating and integrating a plurality of unit sheets having optical performance,
One surface in the thickness direction of the optical sheet is an entrance surface, and the other surface in the thickness direction is an exit surface,
The unit optical element is formed on the exit surface;
The unit sheet constituting the incident surface is a diffusion plate,
The total thickness of the optical sheet is 1.5 mm or more,
The optical sheet according to claim 1. The optical sheet is configured by laminating and integrating a plurality of unit sheets having optical performance,
The unit optical element is formed on the exit surface;
The unit sheet constituting the incident surface is a diffusion plate,
5. The optical sheet according to claim 1, wherein the unit sheet adjacent to the diffusion plate is bonded to the diffusion plate by an adhesive, an adhesive, or excimer bonding. The optical sheet is configured by laminating and integrating a plurality of unit sheets having optical performance,
One surface in the thickness direction of the optical sheet is an entrance surface, and the other surface in the thickness direction is an exit surface,
The unit optical element is formed on the exit surface;
The unit optical element extends linearly,
The unit sheet constituting the emission surface is a prism or a lens.
The optical sheet according to any one of claims 1 to 5, wherein: The optical sheet is configured by laminating and integrating a plurality of unit sheets having optical performance,
One surface in the thickness direction of the optical sheet is an entrance surface, and the other surface in the thickness direction is an exit surface,
The unit optical element is formed on the exit surface;
The unit optical elements are arranged in stripes,
The unit sheet constituting the emission surface is a diffusion layer or a reflection layer.
The optical sheet according to any one of claims 1 to 5, wherein:   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 cold cathode tube or LED light source;
A display comprising the backlight unit according to claim 8.

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