JP2010066729A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device of excellent display quality without causing the deterioration of a manufacture yield. <P>SOLUTION: The liquid crystal display device has a liquid crystal display panel 2, a first polarizing plate PL1 and an illumination unit 15 for illuminating the liquid crystal display panel. The illumination unit 15 includes: a light transmission plate 22 having a first main plane 22a and a second main plane 22b facing the first main plane; an optical sheet 26 having a first optical sheet 26A disposed at the first main plane side of the light transmission plate and a second optical sheet 26B disposed at the second main plane side; a second polarizing plate PL2 laminated on the first optical sheet and disposed so as to face a second substrate and overlap with the display area of the liquid crystal display panel; and a front cover 23A disposed at the first main plane side and a back cover 23B disposed at the second main plane side for holding the light transmission plate, the optical sheet and the second polarizing plate. The front cover and the outer surface of an array substrate are bonded through an adhesive member 30. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device including an illumination unit having a polarizing plate.

  Liquid crystal display devices include a reflective type that selectively reflects external light and displays an image, a transmissive type that selectively transmits backlight and displays an image, and both a reflective type and a transmissive type. A semi-transmission type module having the above functions has been developed.

  Among these, a transmissive or transflective liquid crystal display device includes a transmissive liquid crystal display panel and an illumination unit (that is, a backlight). The liquid crystal display panel is fixed to the lighting unit with double-sided tape or the like.

For example, according to Patent Document 1, for the purpose of holding an LCD module including an LCD, the holding surface for holding the LCD module in the LCD backlight module has a second level corresponding to the first step of the LCD module. A structure having a step is disclosed. In particular, on the holding surface, the upper step with the second step as a boundary is bonded to the back glass with a double-sided tape to hold the back glass, and the lower step with the second step as a boundary is back polarized with the double-sided tape. The back polarizing plate is held by being adhered to the plate.
JP 2007-206125 A

  In a normal liquid crystal display device, polarizing plates are attached to the outer surfaces of the liquid crystal display panel. The polarizing plate has a size smaller than the outer shape of the liquid crystal display panel in consideration of variations in the accuracy of attaching the polarizing plate to the insulating substrate of the liquid crystal display panel and variations in the outer shape of the insulating substrate.

  In a liquid crystal display device having a structure in which a liquid crystal display panel is fixed to an illumination unit by an adhesive member such as a double-sided tape through a polarizing plate attached to the back surface of the liquid crystal display panel, the narrow frame of the liquid crystal display device In response to the demand for the reduction, the bonding area of the bonding member for bonding the liquid crystal display panel to the lighting unit also tends to be reduced. Furthermore, the adhesive member may not stick due to variations in position due to the accuracy of attaching the polarizing plate and variations in position of the liquid crystal display panel. In addition, the adhesive member attached across the step between the polarizing plate and the insulating substrate floats at the step portion, and there is a possibility that sufficient adhesive force cannot be obtained.

  As a result, the liquid crystal display device may rattle and generate abnormal noise. In addition, a gap may be formed between the liquid crystal display panel and the lighting unit, and foreign matter may enter between the two. As described above, there is a possibility that the manufacturing yield of the liquid crystal display device is lowered and the display quality of the liquid crystal display device is lowered.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a liquid crystal display device with good display quality without causing a decrease in manufacturing yield.

A liquid crystal display device according to an aspect of the present invention includes:
A liquid crystal display panel comprising a display region composed of a plurality of pixels and having a liquid crystal layer held between the first substrate and the second substrate;
A first polarizing plate arranged to cover the display area on the outer surface of the first substrate;
An illumination unit that illuminates the liquid crystal display panel from the second substrate side,
The lighting unit is:
A light guide plate having a first main plane that emits light from the light source, and a second main plane that faces the first main plane;
An optical sheet having a first optical sheet disposed on the first main plane side of the light guide plate and a second optical sheet disposed on the second main plane side;
A second polarizing plate laminated on the first optical sheet, facing the second substrate and disposed so as to overlap the display area of the liquid crystal display panel;
A front cover disposed on the first main plane holding the light guide plate, the optical sheet and the second polarizing plate, and a back cover disposed on the second main plane.
The front cover and the outer surface of the second substrate are bonded through an adhesive member.

  According to the present invention, it is possible to provide a liquid crystal display device with good display quality without causing a decrease in manufacturing yield.

  A liquid crystal display device according to an embodiment of the present invention will be described below with reference to the drawings. Here, a transmissive liquid crystal display device that selectively transmits backlight light from a backlight that is an illumination unit and displays an image will be described.

  As shown in FIG. 1, the liquid crystal display device 1 includes a liquid crystal display panel 2 having a liquid crystal layer 5 held between an array substrate (second substrate) 3 and a counter substrate 4 (first substrate), and the array substrate 3 side. To the liquid crystal display panel 2. The array substrate 3 and the counter substrate 4 are formed using a light-transmitting insulating substrate such as a glass substrate.

  In the liquid crystal display panel 2, the array substrate 3 and the counter substrate 4 are bonded together via a sealing material (not shown). The liquid crystal display panel 2 includes a substantially rectangular display area 6 for displaying an image on the inner side surrounded by the sealing material. The display area 6 is composed of a plurality of pixels PX arranged in a matrix.

  In the display area 6, the array substrate 3 includes a plurality of scanning lines Y (1, 2,...), A plurality of signal lines X (1, 2,...), A switching element 7 disposed in each pixel PX, and each pixel PX. The pixel electrode 8 connected to the switching element 7 is provided. The pixel electrode 8 is formed of a light-transmitting conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO).

  Each scanning line Y extends along the row direction of the pixel PX. Each signal line X extends along the column direction of the pixels PX so as to intersect with each scanning line Y through an insulating layer. Each switching element 7 is disposed in a region including an intersection of the scanning line Y and the signal line X.

  The switching element 7 is composed of, for example, a thin film transistor (TFT) provided with a semiconductor layer formed of amorphous silicon, polysilicon, or the like. The gate electrode 7G of the switching element 7 is electrically connected to the corresponding scanning line Y (or formed integrally with the scanning line Y). The source electrode 7S of the switching element 7 is electrically connected to the corresponding signal line X (or formed integrally with the signal line X). The drain electrode 7D of the switching element 7 is electrically connected to the pixel electrode 8 of the corresponding pixel PX.

  The common electrode 9 for applying a voltage to the liquid crystal layer 5 due to a potential difference with the pixel electrode 8 may be provided on the array substrate 3 or on the counter substrate 4. That is, in the horizontal electric field mode mainly using the horizontal electric field (electric field substantially parallel to the main surface of the substrate), the array substrate 3 has the common electrode 9 that is electrically insulated from the pixel electrode 8 and opposed to the pixel electrode 8. I have. In the vertical electric field mode mainly using the vertical electric field (electric field substantially perpendicular to the main surface of the substrate), the counter substrate 4 includes a common electrode 9 that faces the pixel electrode 8 with the liquid crystal layer 5 interposed therebetween. Similar to the pixel electrode 8, the common electrode 9 is formed of a light-transmitting conductive material.

  The surfaces of the array substrate 3 and the counter substrate 4 that are in contact with the liquid crystal layer 5 are each covered with an alignment film (not shown). The array substrate 3 and the counter substrate 4 are bonded to each other with the alignment films facing each other through a spacer (not shown). At this time, a predetermined gap is formed between the array substrate 3 and the counter substrate 4 by a spacer. The liquid crystal layer 5 is formed of a liquid crystal composition sealed in the gap between the array substrate 3 and the counter substrate 4.

  In the color display type liquid crystal display device, the liquid crystal display panel 2 has a plurality of types of pixels in the display area 6, for example, a red pixel that displays red (R), a green pixel that displays green (G), and a blue (B ) Is displayed. That is, the red pixel includes a red color filter that transmits light having a red main wavelength. The green pixel includes a green color filter that transmits light having a green dominant wavelength. The blue pixel includes a blue color filter that transmits light having a blue main wavelength. These color filters are arranged on the main surface of the array substrate 3 or the counter substrate 4.

  The liquid crystal display device 1 includes a first polarizing plate on the outer surface of the counter substrate 4 (that is, the surface opposite to the surface in contact with the liquid crystal layer 5 of the insulating substrate constituting the counter substrate 4) in the liquid crystal display panel 2. PL1 is adhered. The first polarizing plate PL1 is disposed so as to cover the display area 6. The polarization direction of the first polarizing plate PL1 and the second polarizing plate PL2, which will be described later, is set in accordance with the characteristics of the liquid crystal layer 5. The liquid crystal display device 1 displays an image by polarizing light from the illumination unit 15 with the first polarizing plate PL1 and the second polarizing plate PL2.

  The liquid crystal display device 1 includes a bezel cover 11 having a rectangular frame shape. The bezel cover 11 includes a rectangular window portion 11A that exposes the display area 6 of the liquid crystal display panel 2, and a rectangular frame-shaped main body portion 11B that defines the window portion 11A. The liquid crystal display panel 2 configured as described above is sandwiched between the illumination unit 15 and the bezel cover 11. At this time, the illumination unit 15 is arranged with its surface facing the back side of the liquid crystal display panel 2 (that is, the array substrate 3 side), and illuminates the liquid crystal display panel 2 from the back side.

  As shown in FIGS. 2 and 3, the illumination unit 15 includes a light source 21, a light guide plate 22, a front cover 23A, a back cover 23B, an optical sheet 26, and the like.

  Here, the light source 21 is configured by a light emitting diode (LED) that is a plurality of point light sources. The light emitting diode 21 is a semiconductor light emitting element having a light emitting surface. The plurality of light emitting diodes 21 are arranged side by side at a predetermined interval.

  The light guide plate 22 has a function of guiding the emitted light from the light emitting diode 21 toward the liquid crystal display panel 2. The light guide plate 22 is made of a light-transmissive resin material such as acrylic resin or polycarbonate resin. The light guide plate 22 includes a wedge-type plate having a thin portion at one end and a thick portion at the other end opposed to the thin portion, and a flat plate type having a substantially uniform thickness over the whole. However, in this embodiment, a rectangular flat plate type is adopted.

  The light guide plate 22 includes a rectangular first main plane 22a facing the array substrate 3 side of the liquid crystal display panel 2, a rectangular second main plane 22b facing the first main plane 22a, and the first main plane 22b. It has four rectangular end faces that connect the first main plane 22a and the second main plane 22b. The one end surface 22c functions as an incident surface on which the light emitting surface of the light emitting diode 21 faces. Further, the first main plane 22 a functions as an emission surface that emits light toward the liquid crystal display panel 2.

  The optical sheet 26 includes a first optical sheet 26 </ b> A disposed on the first main plane 22 a side of the light guide plate 22 and a second optical sheet 26 </ b> B disposed on the second main plane 22 b side of the light guide plate 22. It has been. The first optical sheet 26 </ b> A is, for example, a condensing sheet or a diffusion sheet, and imparts predetermined optical characteristics to the light emitted from the light guide plate 22 and guides it to the liquid crystal display panel 2. The second optical sheet 26 </ b> B is a reflection sheet, and reflects light leaking from the second main plane 22 b of the light guide plate 22 toward the light guide plate 22 again.

  The illumination unit 15 further includes a second polarizing plate PL2. The second polarizing plate PL2 is laminated on the first optical sheet 26A. A plurality of first optical sheets 26A are usually stacked on the first main plane 22a side, and the second polarizing plate PL2 is the uppermost first optical sheet (that is, the first optical sheet closest to the liquid crystal display panel 2). Optical sheet) 26A. In other words, the second polarizing plate PL <b> 2 is an optical sheet positioned on the uppermost surface of the illumination unit 15, and faces the insulating substrate constituting the array substrate 3. Such a second polarizing plate PL2 is arranged so as to overlap the display region 6 similarly to the first polarizing plate PL1. That is, the second polarizing plate PL2 is disposed so as to face the first polarizing plate PL1 with the liquid crystal display panel 2 interposed therebetween.

  The front cover 23A and the back cover 23B hold the light guide plate 22, the optical sheet 26, and the second polarizing plate PL2. The front cover 23 </ b> A is disposed on the first main plane 22 a side of the light guide plate 22, and the back cover 23 </ b> B is disposed on the second main plane 22 b side of the light guide plate 22. The front cover 23A and the back cover 23B are made of, for example, a resin material.

  The front cover 23A includes a rectangular window portion 23A1 for illuminating the liquid crystal display panel 2. The front cover 23A is bonded to the array substrate 3 (more precisely, an insulating substrate constituting the array substrate) via an adhesive member 30. The adhesive member 30 is a double-sided tape or the like, and is disposed so as not to overlap the display area 6.

  When the second polarizing plate PL2 is disposed on the outer surface of the array substrate 3 (that is, the surface opposite to the surface in contact with the liquid crystal layer 5 of the insulating substrate constituting the array substrate), the array substrate 3 and the second polarizing plate A step is formed with PL2.

  For this reason, when the second polarizing plate PL2 is bonded to the front cover 23A via the adhesive member 30, in the narrow frame liquid crystal display panel 2, the area of the second polarizing plate PL2 outside the display region is small. The bonding area of the bonding member 30 that bonds the liquid crystal display panel 2 to the lighting unit 15 is small, and there is a possibility that the bonding force is insufficient.

  On the other hand, in the present embodiment, the second polarizing plate PL2 is provided in the illumination unit 15. Since the second polarizing plate PL2 is not disposed on the back side of the liquid crystal display panel 2, the outer surface of the array substrate 3, that is, the surface facing the illumination unit 15 of the insulating substrate is flat. Thereby, the adhesion area | region of the adhesive member 30 which fixes the liquid crystal display panel 2 to the illumination unit 15 becomes large, and the adhesive force which adhere | attaches both becomes large.

  For this reason, the outer surface of the array substrate 3 and the front cover 23A are bonded to the adhesive member 30 regardless of variations in position due to the bonding accuracy of the second polarizing plate PL2 and variations in the installation position of the liquid crystal display panel 2 with respect to the illumination unit 15. The liquid crystal display panel 2 can be stably fixed to the lighting unit 15 with sufficient strength.

  By increasing the adhesive force between the liquid crystal display panel 2 and the illumination unit 15, the liquid crystal display panel 2 is securely fixed to the illumination unit 15, and thus it is possible to prevent the liquid crystal display panel 2 from rattling. . Further, since the liquid crystal display panel 2 and the lighting unit 15 are securely bonded via the bonding member 30, it is possible to prevent foreign matter from entering between them.

  As described above, according to the present embodiment, it is possible to provide a liquid crystal display device with good quality without causing a decrease in manufacturing yield.

  As shown in FIG. 4, the first optical sheet 26 </ b> A may include a polarizing sheet 26 </ b> Aa (for example, DBEF manufactured by Sumitomo 3M Limited). Such a polarizing sheet 26 </ b> Aa is disposed on the uppermost surface among the plurality of first optical sheets 26 </ b> A stacked on the first main plane 22 a side of the light guide plate 22. In this case, the polarizing sheet 26Aa is in contact with the second polarizing plate PL2 (that is, the second polarizing plate PL2 is laminated directly on the polarizing sheet 26Aa). By providing the polarizing sheet 26Aa as described above, the luminance of the illumination unit 15 can be improved.

  The transmission axis of the second polarizing plate PL2 is preferably parallel to the transmission axis of the polarizing sheet 26Aa. By making the transmission axis of the second polarizing plate PL2 and the transmission axis of the polarizing sheet 26Aa parallel, the luminance of the illumination unit 15 can be further improved.

  In the illumination unit 15 including the polarizing sheet 26Aa, the second polarizing plate PL2 and the polarizing sheet 26Aa may be configured integrally. That is, as shown in FIG. 5, the second polarizing plate PL <b> 2 usually has a configuration in which the polarizing layer 28 </ b> X <b> 1 is sandwiched between a pair of cover members 28. The polarizing sheet 26 </ b> Aa also has a configuration in which the polarizing layer 28 </ b> X <b> 2 is sandwiched between the pair of cover members 28.

  As shown in FIG. 6, in the state where the cover material 28 on the polarizing plate 26Aa side of the second polarizing plate PL2 is deleted and the cover material 28 on the second polarizing plate PL2 side of the polarizing sheet 26Aa is deleted, both polarizing layers 28X1 In addition, the second polarizing plate PL2 and the polarizing sheet 26Aa may be integrally formed by pasting together and 28X2.

  Thus, by integrally forming the second polarizing plate PL2 and the polarizing sheet 26Aa, the cover material is eliminated, so that the light absorbed by the cover material 28 is reduced, and the luminance can be further improved. It becomes.

  In addition, this invention is not limited to the said embodiment itself, In the stage of implementation, it can change and implement a component within the range which does not deviate from the summary. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

  In the above-described embodiment, the example of the light emitting diode has been described as the light source 21 of the illumination unit 15. However, the present invention is not limited to this example, and the light source 21 may be a cold cathode tube.

  In the above-described embodiment, the transmissive liquid crystal display device has been described. However, the present invention is not limited to this example, and the transmissive liquid crystal display device can be applied to a transflective liquid crystal display device.

FIG. 1 is an exploded perspective view schematically showing the structure of a liquid crystal display device according to an embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing the structure of the liquid crystal display device shown in FIG. FIG. 3 is an exploded perspective view schematically showing structures of a light guide plate, a light source, a second polarizing plate, and an optical sheet in the illumination unit shown in FIGS. 1 and 2. FIG. 4 is a cross-sectional view schematically showing another structure of the liquid crystal display device applicable to this embodiment. FIG. 5 is a cross-sectional view schematically showing structures of the second polarizing plate and the polarizing sheet. FIG. 6 is a cross-sectional view schematically showing the structure of the integrally formed second polarizing plate and polarizing sheet.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device 2 ... Liquid crystal display panel 3 ... Array substrate 4 ... Opposite substrate PL1 ... 1st polarizing plate PL2 ... 2nd polarizing plate 15 ... Illumination unit 21 ... Light source 22 ... Light guide plate 22a ... 1st main plane 22b ... 1st 2 main planes 23A ... front cover 23B ... back cover 26 ... optical sheet 26A ... first optical sheet, 26B ... second optical sheet 30 ... adhesive member

Claims (5)

A liquid crystal display panel comprising a display region composed of a plurality of pixels and having a liquid crystal layer held between the first substrate and the second substrate;
A first polarizing plate arranged to cover the display area on the outer surface of the first substrate;
An illumination unit that illuminates the liquid crystal display panel from the second substrate side,
The lighting unit is:
A light guide plate having a first main plane that emits light from the light source, and a second main plane that faces the first main plane;
An optical sheet having a first optical sheet disposed on the first main plane side of the light guide plate and a second optical sheet disposed on the second main plane side;
A second polarizing plate laminated on the first optical sheet, facing the second substrate and disposed so as to overlap the display area of the liquid crystal display panel;
A front cover disposed on the first main plane holding the light guide plate, the optical sheet and the second polarizing plate, and a back cover disposed on the second main plane.
The liquid crystal display device, wherein the front cover and the outer surface of the second substrate are bonded via an adhesive member.   The liquid crystal display device according to claim 1, wherein the adhesive member is disposed so as not to overlap the display area.   The liquid crystal display device according to claim 1, wherein the first optical sheet is a polarizing sheet in contact with the second polarizing plate.   The liquid crystal display device according to claim 3, wherein a transmission axis of the second polarizing plate is parallel to a transmission axis of the polarizing sheet.   The liquid crystal display device according to claim 1, wherein the second polarizing plate is integral with the polarizing sheet.

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