JP2008210645A - Downright backlight unit and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain display unevenness in case an optical plate made by integrating a plurality of layers with different functions is used for a downright backlight unit. <P>SOLUTION: The backlight unit includes an optical layer and a light source separated from the optical layer and illuminating a rear face of a liquid crystal display panel through the optical layer. A face opposed to the rear face of the backlight unit is structured of a surface of the optical layer, with only an air layer existing between the optical layer and the light source, and the optical layer consists only of an optical plate 23 equipped with an optical function layer 231 with a plurality of convex parts 231a constituting lenses or prisms provided at one main face and with the other main face faced to the light source, a diffusion plate 232 facing the other main face and with a total light-beam transmittance of 55% or less, and a reflecting layer 233 intercalated between the optical function layer 231 and the diffusion plate 232 and with an opening fitted. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal display technology using a direct type backlight unit.

  Patent Document 1 describes an optical sheet used in a liquid crystal display device. This optical sheet includes a lens sheet in which a plurality of convex portions each constituting a lens are provided on the front surface, a light scattering layer facing the back surface, and a light reflecting layer interposed therebetween. The light reflecting layer has an opening at a position corresponding to the center of the lens.

  When the light scattering layer of the optical sheet is illuminated, the light scattering layer emits scattered light. Of this scattered light, the light traveling toward the center of the lens enters the lens sheet, and the light traveling toward the peripheral edge of the lens is reflected by the reflective layer. The scattered light reflected by the reflective layer changes its traveling direction by being further scattered by the light scattering layer, and finally enters the lens sheet. Scattered light incident on the lens sheet is emitted from the lens sheet with its divergence angle controlled by the lens.

  As is clear from this, the light reflection layer suppresses the incidence of scattered light on the peripheral edge of the lens. Therefore, this optical sheet emits less light toward the wide-angle side due to reflection at the interface between the peripheral edge of the lens and the air layer. Further, as described above, the light reflected by the light reflecting layer finally enters the central portion of the lens. Therefore, when this optical sheet is used, desired directivity and high light utilization efficiency can be achieved.

  Further, the optical sheet can be provided with sufficient rigidity to prevent a large deformation when it is supported on a frame by using a diffusion plate as a light scattering layer. That is, this optical sheet can be made into an optical plate by using a diffusion plate as a light scattering layer. Since this optical plate is formed by integrating a plurality of layers having different functions, the number of parts of the backlight unit can be reduced by using this optical plate. Therefore, the assembly can be facilitated and the cost can be reduced.

However, the present inventor has found the following facts in making the present invention. That is, this optical plate exhibits excellent performance when used in an edge type backlight unit. However, when this is used in a direct type backlight unit, display unevenness may occur.
JP 2006-106197 A

  An object of the present invention is to suppress display unevenness when an optical plate formed by integrating a plurality of layers having different functions is used in a direct type backlight unit.

  According to a first aspect of the present invention, there is provided a direct type backlight unit used for illuminating the back surface of a liquid crystal display panel, wherein the back surface unit is separated from the optical layer and the optical layer is interposed between the optical layer and the back surface. A light source that illuminates, and a surface of the backlight unit facing the back surface is formed by a surface of the optical layer, and only an air layer exists between the optical layer and the light source, and the optical layer Is provided with a plurality of convex portions each constituting a lens or a prism on one main surface, the other main surface facing the light source, and the other main surface facing the other main surface and 60% or less. An optical plate provided with a diffuser plate having a total light transmittance, a reflective layer interposed between the optical functional layer and the diffuser plate and provided with an opening, and the optical plate between Faced with the light source Direct type backlight unit, characterized in that it consists only diffusing film is provided.

  According to a second aspect of the present invention, there is provided a direct type backlight unit used for illuminating the back surface of a liquid crystal display panel, wherein the back surface unit is spaced apart from the optical layer and the optical layer is interposed between the optical layer and the back surface. A light source that illuminates, and a surface of the backlight unit facing the back surface is formed by a surface of the optical layer, and only an air layer exists between the optical layer and the light source, and the optical layer Is provided with a plurality of convex portions each constituting a lens or a prism on one main surface and the other main surface facing the light source, and the other main surface facing the other main surface and 55% or less. The optical plate comprises only a diffusion plate having a total light transmittance, and a reflection layer interposed between the optical functional layer and the diffusion plate and provided with an opening. Direct type backlight unit Tsu door is provided.

  According to a third aspect of the present invention, there is provided a liquid crystal display comprising: a direct type backlight unit according to the first or second aspect; and a liquid crystal display panel having a back face facing the direct type backlight unit. An apparatus is provided.

  According to the present invention, it is possible to suppress display unevenness when an optical plate formed by integrating a plurality of layers having different functions is used in a direct type backlight unit.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same referential mark is attached | subjected to the component which exhibits the same or similar function, and the overlapping description is abbreviate | omitted.

  FIG. 1 is a perspective view schematically showing a liquid crystal display device according to a first embodiment of the present invention. FIG. 2 is an exploded perspective view of the liquid crystal display device shown in FIG. FIG. 3 is a cross-sectional view schematically showing a part of the liquid crystal display device shown in FIG. In each figure, the X1 direction indicates a direction parallel to one side of the liquid crystal display panel 1 to be described later, the Y1 direction indicates a direction parallel to the side intersecting with the previous side of the liquid crystal display panel 1, and the Z direction indicates X1. The direction orthogonal to the direction and the Y1 direction is shown.

  The liquid crystal display device shown in FIGS. 1 to 3 includes a liquid crystal display panel 1, a backlight unit 2, and a front frame 3.

  The liquid crystal display panel 1 is typically a transmissive liquid crystal display panel. The liquid crystal display panel 1 may be a transflective liquid crystal display panel.

  The backlight unit 2 is a direct type backlight unit. The backlight unit 2 illuminates the back surface of the liquid crystal display panel 1.

  As shown in FIGS. 2 and 3, the backlight unit 2 includes a structure 21, a plurality of fluorescent lamps 22 that are light sources, an optical plate 23, a diffusion film 24, and a resin frame 25.

  The structural body 21 supports the fluorescent lamp 22, the optical plate 23, and the diffusion film 24 together with the resin frame 25. In the example shown in FIGS. 2 and 3, the structure 21 constitutes a substantially box-shaped lamp house, and includes a back plate 211 and a pair of lamp holders 212.

  The back plate 211 is made of, for example, a metal material. As shown in FIG. 2, the pair of edge portions of the back plate 211 that are spaced apart from each other are bent so that thin grooves having a substantially bowl shape extending in the X1 direction are formed. Thereby, a thick groove is formed between the thin grooves.

  The lamp holder 212 is made of resin, for example. These lamp holders 212 are respectively attached to both ends of the back plate 211.

  The back plate 211 and the lamp holder 212 form a recess 21a and a flat surface 21b surrounding the opening. A fluorescent lamp 22 is disposed in the recess 21a, and an optical plate 23 is placed on the flat surface 21b.

  A plurality of recesses into which the fluorescent lamp 22 is inserted are provided on each facing surface of the lamp holder 212. At least one of the lamp holders 212 includes, for example, a circuit for electrically connecting the fluorescent lamp 22 and the power supply circuit, or a power supply circuit for supplying power to the fluorescent lamp 22. Yes.

  The structure 21 may further include one or more spacer pins extending from the bottom surface of the recess toward the opening. When the top part of the spacer pin is substantially in the same plane as the flat surface 21b, for example, the center part of the optical plate 23 can be supported by the spacer pin. Therefore, it can suppress that the optical plate 23 bends.

  The reflective layer is, for example, a layer formed on the bottom surface or side wall of the thick groove formed by the back plate 211. Alternatively, the reflective layer is a sheet having a substantially bowl shape corresponding to the thick groove formed by the back plate 211. The reflective layer may have light scattering properties.

  The fluorescent lamp 22 is inserted into a recess provided in the lamp holder 212. Each fluorescent lamp 22 is typically a cold cathode discharge lamp and has, for example, a substantially U shape. When the fluorescent lamp 22 has a substantially U shape, both end portions of each fluorescent lamp 22 are inserted into the recesses of the lamp holder 212 containing the above circuit, and the folded portion of each fluorescent lamp 22 is the other lamp holder. Insert into the recess 212.

  Although a plurality of fluorescent lamps 22 are arranged here, only one fluorescent lamp 22 may be installed. Further, instead of the fluorescent lamp 22, another light source such as a light emitting diode may be used.

  The optical plate 23 is placed on the flat surface 21 b of the structure 21. Specifically, the peripheral edge of the optical plate 23 is supported by the flat surface 21 b of the structure 21. The optical plate 23 has a function of scattering the light emitted from the fluorescent lamp 22 and a function of controlling the directivity of the scattered light. The structure of the optical plate 23 will be described later.

  The diffusion film 24 is placed on the optical plate 23. The diffusion film 24 is a light scattering layer. The diffusion film 24 has, for example, a structure in which transparent fine particles having a refractive index different from that of the transparent resin are dispersed, or a structure in which a concave portion and / or a convex portion are provided on at least one main surface. is doing.

  The optical plate 23 and the diffusion film 24 constitute an optical layer. One main surface of the optical layer is a surface facing the liquid crystal display panel 1 of the backlight unit 2. Further, only an air layer exists between the optical layer and the fluorescent lamp 22. The light scattering ability of the diffusion film 24 is typically much smaller than the light scattering ability of the optical plate 23. For example, the haze of the diffusion film 24 is in the range of about 35% to about 75%, while the haze of the optical plate 23 is about 90% or more. That is, the diffusion film 24 plays a role of finely adjusting the optical characteristics of the previous optical layer.

  The resin frame 24 includes a front plate provided with an opening and a plurality of side plates supported on the outer peripheral edge portion thereof. The front plate has larger dimensions in the X1 direction and the Y1 direction than the structure 21. The opening provided in the front plate has smaller dimensions in the X1 direction and the Y1 direction than the optical plate 23 and the diffusion film 24.

  The resin frame 24 is fitted with the structure 21. The resin frame 24 and the structure 21 sandwich the peripheral portions of the optical plate 23 and the diffusion film 24. The liquid crystal display panel 1 is placed on the resin frame 24.

  The front frame 3 is made of, for example, a metal material. The front frame 3 is fitted with the resin frame 25. The front frame 3 and the resin frame 24 sandwich the periphery of the liquid crystal display panel 1.

  FIG. 4 is a perspective view schematically showing an example of an optical plate that can be used in the liquid crystal display device shown in FIG. FIG. 5 is a cross-sectional view taken along line VV of the optical plate shown in FIG.

  In each figure, the X2 direction indicates a direction orthogonal to the Z direction described above, and the Y2 direction indicates a direction orthogonal to the Z direction and intersecting the X2 direction. The X2 direction may be parallel to the X1 direction, may be parallel to the Y1 direction, or may be oblique to at least one of the X1 direction and the Y1 direction.

  The optical plate 23 includes an optical functional layer 231, a diffusion plate 232, and a reflective layer 233 interposed therebetween. In the previous liquid crystal display device, the optical plate 23 is installed so that the diffusion plate 232 faces the fluorescent lamp 22. The optical plate 23 typically has a thickness of 1.5 mm or more.

  The optical function layer 231 is made of a transparent material such as a transparent resin. The optical functional layer 231 may have a single layer structure or a multilayer structure.

  On one main surface of the optical function layer 231, a plurality of convex portions 231a each constituting a lens are provided. Each of the convex portions 231a has a shape extending in the X2 direction, and is arranged in the Y2 direction. That is, these convex portions 231a constitute a lens group in which lenticulars whose longitudinal directions are equal to the X2 direction are arranged in the Y2 direction. When the optical plate 23 is used in the previous liquid crystal display device, the main surface provided with the convex portion 231 a of the optical function layer 231 is a light emitting surface that emits scattered light toward the liquid crystal display panel 1.

  The other main surface of the optical functional layer 231 is typically a flat surface. When the optical plate 23 is used in the previous liquid crystal display device, the flat surface of the optical functional layer 231 is a light incident surface on which light emitted from the fluorescent lamp 22 is incident.

  The optical function layer 231 can be formed by, for example, extrusion molding, injection molding, or hot press molding. In this case, as a material of the optical function layer 231, for example, polyethylene terephthalate, polycarbonate, polymethyl methacrylate, or cycloolefin polymer can be used.

  Alternatively, the optical functional layer 231 can be formed by applying a photocurable resin on a transparent substrate and exposing the mold in a state where a mold is pressed against the coating film. In this case, as a material for the transparent substrate, for example, polyethylene terephthalate, polypropylene, polycarbonate, polymethyl methacrylate, or polyethylene can be used. Moreover, as a photocurable resin, an ultraviolet curable resin can be used, for example.

  The diffusion plate 232 faces the flat surface of the optical function layer 231. The diffusion plate 232 has, for example, a structure in which transparent particles having a refractive index different from that of the transparent resin are dispersed, or a structure in which at least one main surface is provided with a recess and / or a protrusion. is doing. As the transparent resin, for example, polycarbonate, acrylic resin, polypropylene, or cycloolefin can be used. As the transparent particles, inorganic particles and / or organic particles made of glass and silica can be used.

  The reflective layer 233 is a layer that reflects light traveling from the diffuser plate 232 toward the optical functional layer 231. The reflective layer 233 has openings at positions corresponding to the center of the convex portion 231a. This opening is filled with a gas such as air. The reflective layer 233 is, for example, a white layer or a metal layer. As a material for the white layer, for example, a composite material in which a white pigment made of an inorganic substance such as titanium dioxide, barium sulfate, and magnesium oxide is dispersed in a transparent resin can be used. As the metal layer, for example, a vapor deposition layer made of a material having high reflectivity and low light absorption such as silver and aluminum can be used.

  As described above, in this embodiment, the optical layer of the backlight unit 2 is composed of only the optical plate 23 and the diffusion film 24. Further, in general backlight units, a diffusion plate having a total light transmittance of about 65% or more is used in consideration of light use efficiency and the cost of the diffusion plate. As the 232, those having a total light transmittance of 60% or less are used, and those having 55% or less are typically used. In other words, in this embodiment, the optical layer of the backlight unit 2 is composed of only the optical plate 23 and the diffusion film 24 having a small total light transmittance.

  When this configuration is adopted, display unevenness can be suppressed. For example, it is possible to prevent the luminance unevenness corresponding to the shape of the fluorescent lamp 22 from being visually recognized when the backlight unit 2 is turned on and the display surface of the liquid crystal display device is observed. In addition, there is almost no decrease in luminance due to the use of the diffuser plate 232 having a small total light transmittance instead of the diffuser plate having a large total light transmittance. Therefore, when this configuration is adopted, the assembly of the backlight unit is facilitated, and bright display is possible with almost no display unevenness.

Next, the second aspect of the present invention will be described.
FIG. 6 is an exploded perspective view schematically showing a liquid crystal display device according to the second embodiment of the present invention. This liquid crystal display device has the same structure as the liquid crystal display device described with reference to FIGS. 1 to 5 except that the following configuration is adopted.

  That is, in the liquid crystal display device of FIG. 6, the diffusion film 24 is omitted. In this liquid crystal display device, the diffuser plate 232 shown in FIGS. 4 and 5 uses a plate having a total light transmittance of 55% or less, and typically a plate having a light transmittance of 50% or less.

  When this configuration is adopted, display unevenness can be suppressed. For example, it is possible to prevent the luminance unevenness corresponding to the shape of the fluorescent lamp 22 from being visually recognized when the backlight unit 2 is turned on and the display surface of the liquid crystal display device is observed. In addition, there is almost no decrease in luminance due to the use of the diffuser plate 232 having a small total light transmittance instead of the diffuser plate having a large total light transmittance. Therefore, when this configuration is adopted, the assembly of the backlight unit is facilitated, and bright display is possible with almost no display unevenness.

  As the diffusing plate 232, one having a total light transmittance of, for example, 45% or more is used. If the total light transmittance is small, the luminance of the backlight unit 2 may be insufficient due to light absorption by the diffusion plate 232 and / or a member located on the back side thereof.

The optical plate 23 can be variously modified.
In the optical functional layer 231 shown in FIGS. 4 and 5, the convex portion 231a constitutes a lens group in which lenticulars whose longitudinal directions are equal to the X2 direction are arranged in the Y2 direction. Instead, the convex portion 231a may constitute a lens group in which lenses are arranged in the X2 direction and the Y2 direction.

  The opening provided in the reflective layer 233 does not have to be a band shape. For example, the reflective layer 233 may be provided with a plurality of openings arranged in the X2 direction and the Y2 direction. Further, the reflective layer 233 may be provided with an opening at a position shifted from a position corresponding to the boundary between the adjacent convex portions 231a.

The optical plate 23 can be further modified.
FIG. 7 is a perspective view schematically showing a modification of the optical plate shown in FIG. FIG. 8 is a sectional view taken along line VIII-VIII of the optical plate shown in FIG.

  In this optical plate 23, a plurality of convex portions 231a, each of which constitutes a prism, are provided on one main surface of the optical function layer 231. Each of the convex portions 231a has a shape extending in the X2 direction, and is arranged in the Y2 direction. That is, these convex portions 231a constitute a prism group in which prisms whose longitudinal directions are equal to the X2 direction are arranged in the Y2 direction. The optical plate 23 shown in FIGS. 7 and 8 is the same as the optical plate 23 shown in FIGS. 4 and 5 except that the above structure is adopted for the optical function layer 231.

  Thus, the convex part 231a may comprise a prism instead of constituting a lens. In this case, the convex portion 231a may constitute a prism group in which prisms are arranged in the X2 direction and the Y2 direction. Further, the reflective layer 233 may be omitted.

Examples of the present invention will be described below.
(Example 1)
In this example, for the liquid crystal display device described with reference to FIGS. 1 to 5, the relationship between the total light transmittance of the diffusion plate 232 and display unevenness was examined by the method described below.

  First, an acrylic ultraviolet curable resin was applied on a polyethylene terephthalate sheet as a base material, and the optical functional layer 231 was formed by exposing in a state where a mold was pressed against the coating film. That is, the optical functional layer 231 has a two-layer structure of a polyethylene terephthalate sheet and an acrylic resin layer that constitutes a lens group composed of a plurality of lenticulars.

  Next, the optical functional layer 231 and the photosensitive resin film were bonded so that the base material of the optical functional layer 231 faced the photosensitive resin film. As this photosensitive resin film, a DuPont chromalin (registered trademark) film having adhesiveness was used. Next, the photosensitive resin film was exposed to ultraviolet rays through the optical function layer 231. The lenticular caused a distribution of the exposure amount on the photosensitive resin film. As a result, the adhesive strength of the photosensitive resin film was greatly reduced in the focal point of the lenticular and in the vicinity thereof as compared with other regions. Then, the laminated body of the optical function layer 231 and the photosensitive resin film was pressed against the reflective layer formed on the release paper. As a material for the reflective layer, a mixture containing urethane resin and titanium dioxide was used. Next, this laminate was peeled from the release paper. As a result, the reflective layer was transferred only to the region of the photosensitive resin film where the adhesive force was greater. As described above, a reflective layer 233 was obtained.

Next, an adhesive was applied to the reflective layer 233, and the optical functional layer 231 and the diffusion plate 232 were bonded to each other through these. As the diffusion plate 232, a sheet made of an acrylic styrene copolymer (MS), having a haze of 92%, and a size of 415 mm × 730 mm × 2 mm was used.
As described above, a plurality of optical plates 23 having different total light transmittances were manufactured.

  Next, the liquid crystal display device described with reference to FIGS. 1 to 5 was assembled using these optical plates 23. As the diffusion film 24, a film made by Eiwa Co., Ltd. having a haze of 48% was used.

  A white image, a red image, a green image, and a blue image were displayed on these liquid crystal display devices, and the presence or absence of display unevenness corresponding to the fluorescent lamp 22 was examined. In addition, the case where display nonuniformity did not arise in all of a white image, a red image, a green image, and a blue image was determined as "pass", and the case other than that was determined as "fail". The results are summarized in the following table.

(Example 2)
In this example, the relationship between the total light transmittance of the diffusion plate 232 and the display unevenness was examined for the liquid crystal display device described with reference to FIG. 6 by the same method as described in Example 1. That is, in this example, a plurality of liquid crystal display devices having different total light transmittances of the diffusion plate 232 were prepared by the same method as described in Example 1 except that the diffusion film 24 was omitted. These liquid crystal display devices were examined for the presence or absence of display unevenness by the same method as described in Example 1. The results are summarized in the following table.

(Comparative example)
In this example, the same method as described in Example 1 except that the diffusion plate 232, the diffusion film, and the prism sheet are sequentially placed instead of placing the optical plate 23 on the flat surface 21b of the structure 21. Thus, a plurality of liquid crystal display devices having different total light transmittances of the diffusion plate 232 were prepared. As a diffusion film interposed between the diffusion plate 232 and the prism sheet, a film with 89% haze made by Eiwa Co., Ltd. was used. As the prism sheet, BEFIII manufactured by 3M was used.

These liquid crystal display devices were examined for the presence or absence of display unevenness by the same method as described in Example 1. The results are summarized in the following table.

  As shown in the above table, in the liquid crystal display device of Example 3, the total light transmittance of the diffusion plate 232 did not affect display unevenness. On the other hand, in the liquid crystal display devices of Examples 1 and 2, display unevenness occurs when the total light transmittance of the diffuser plate 232 is large, and display unevenness occurs when the diffuser plate 232 with a small total light transmittance is used. I was able to prevent it.

1 is a perspective view schematically showing a liquid crystal display device according to a first aspect of the present invention. The disassembled perspective view of the liquid crystal display device shown in FIG. FIG. 2 is a cross-sectional view schematically showing a part of the liquid crystal display device shown in FIG. 1. FIG. 2 is a perspective view schematically showing an example of an optical plate that can be used in the liquid crystal display device shown in FIG. 1. Sectional drawing along the VV line of the optical plate shown in FIG. The disassembled perspective view which shows schematically the liquid crystal display device which concerns on the 2nd aspect of this invention. The perspective view which shows roughly the modification of the optical plate shown in FIG. Sectional drawing along the VIII-VIII line of the optical plate shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display panel, 2 ... Backlight unit, 3 ... Front frame, 21 ... Structure, 21a ... Recessed part, 21b ... Flat surface, 22 ... Fluorescent lamp, 23 ... Optical plate, 24 ... Diffusing film, 25 ... Resin frame , 211 ... back plate, 212 ... lamp holder, 231 ... optical functional layer, 231a ... convex part, 232 ... diffuser plate, 233 ... reflective layer.

Claims (4)

A direct-type backlight unit used to illuminate the back of a liquid crystal display panel,
An optical layer; and a light source that is spaced apart from the optical layer and that illuminates the back surface through the optical layer, wherein a surface facing the back surface of the backlight unit is configured by a surface of the optical layer, There is only an air layer between the optical layer and the light source,
The optical layer is
A plurality of convex portions each constituting a lens or a prism are provided on one main surface and the other main surface faces the light source, and the other main surface faces the other main surface and 60% or less. An optical plate comprising a diffuser plate having light transmittance, a reflective layer interposed between the optical functional layer and the diffuser plate and provided with an opening, and sandwiching the optical plate A direct type backlight unit comprising only a diffusion film facing the light source. A direct-type backlight unit used to illuminate the back of a liquid crystal display panel,
An optical layer; and a light source that is spaced apart from the optical layer and that illuminates the back surface through the optical layer, wherein a surface facing the back surface of the backlight unit is configured by a surface of the optical layer, There is only an air layer between the optical layer and the light source,
The optical layer is provided with a plurality of convex portions each constituting a lens or a prism on one main surface, the optical functional layer having the other main surface facing the light source, and the other main surface. It consists only of an optical plate having a diffuser plate having a total light transmittance of 55% or less, and a reflective layer interposed between the optical functional layer and the diffuser plate and provided with an opening. Characteristic direct type backlight unit.   The backlight unit according to claim 1, wherein each of the plurality of convex portions is a lenticular.   4. A liquid crystal display device comprising: the direct type backlight unit according to claim 1; and a liquid crystal display panel having a back surface facing the direct type backlight unit.

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