JP2007108229A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device of which the thickness is reduced and which has excellent display quality. <P>SOLUTION: The liquid crystal display device is equipped with: a liquid crystal display panel constructed by holding a liquid crystal layer between an array substrate and a counter substrate; a first polarizing plate disposed on the outside surface of the array substrate; a second polarizing plate disposed on the outside surface of the counter substrate; and a surface light source device to illuminate the liquid crystal display panel from the array substrate side via the first polarizing plate, and is characterized by having the coefficient of dynamic friction of a surface of the first polarizing plate PL1 facing the surface light source device is less than that of the surface light source device facing the first polarizing plate PL1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device including a transmissive liquid crystal display panel and a surface light source device.

  In a liquid crystal display device that selectively transmits light emitted from a surface light source device and displays an image, the surface light source is used in order to improve the utilization efficiency of the emitted light from the light source in order to meet the demand for higher brightness. Increasingly, optical sheets having a diffusion function, a brightness enhancement function, and the like are arranged on the surface of the apparatus, that is, the surface facing the liquid crystal display panel. This optical sheet has a thin thickness of about 0.1 to 0.2 mm and has flexibility, so that it bends and swells due to environmental conditions such as high temperature and high humidity, or electrostatic charging. Is likely to occur.

  In recent years, demands for thinning liquid crystal display devices have increased, and the distance between a liquid crystal display panel and a surface light source device is often set to be very thin, about 0.1 to 0.2 mm. For this reason, it becomes difficult to keep the distance between the liquid crystal display panel and the surface light source device constant, and when the optical sheet is slightly bent and swung, the liquid crystal display panel is disposed on the surface facing the surface light source device. The optical sheet may stick locally to the applied polarizing plate. Such local sticking between the optical sheet and the polarizing plate forms a portion where both are in close contact with each other, and a non-contact portion of the display screen causes non-uniformity of display called a Newton ring, There is a risk of degrading the display quality.

For such a problem, the surface of the polarizing plate facing the surface light source device is formed as a rough surface having fine irregularities (surface having irregularities), so that the adhesion between the polarizing plate and the optical sheet is temporarily prevented, and display unevenness There is a method of making it difficult to visually recognize (see, for example, Patent Document 1 and Patent Document 2).
Japanese Patent Laid-Open No. 10-96922 JP-A-10-240143

  By the measures described in Patent Document 1 and Patent Document 2 described above, it was possible to suppress the sticking between the polarizing plate and the optical sheet, but the rough surface of the surface of the polarizing plate was a large number of dispersed and mixed in the adhesive. It is formed by coating silica particles. The silica particles have a high hardness of about 3H in terms of pencil hardness. For this reason, in a configuration in which the distance between the liquid crystal display panel and the surface light source device is set to be extremely thin, a rough surface with high hardness comes into contact with the optical sheet due to vibration or impact, and the optical sheet is easily damaged. If the optical sheet is damaged, the functions unique to the optical sheet cannot be obtained sufficiently, and the display quality may be deteriorated.

  There has also been proposed a method in which at least one film having an uneven surface is interposed between an optical sheet and a polarizing plate to prevent sticking between the two, but such a method is used in a liquid crystal display device. Contrary to the demand for thinning.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a liquid crystal display device that can be thinned and has a good display quality.

A liquid crystal display device according to an aspect of the present invention includes:
A liquid crystal display panel configured to hold a liquid crystal layer between the array substrate and the counter substrate;
A first polarizing plate disposed on the outer surface of the array substrate;
A second polarizing plate disposed on the outer surface of the counter substrate;
A liquid crystal display device comprising: a surface light source device that illuminates the liquid crystal display panel from the array substrate side through the first polarizing plate;
The dynamic friction coefficient of the surface of the first polarizing plate facing the surface light source device is smaller than the dynamic friction coefficient of the surface of the surface light source device facing the first polarizing plate.

  According to the present invention, it is possible to provide a liquid crystal display device which can be thinned and has a good display quality.

  A liquid crystal display device according to an embodiment of the present invention will be described below with reference to the drawings.

  As shown in FIG. 1, the liquid crystal display device 1 includes a transmissive liquid crystal display panel 2. The liquid crystal display panel 2 includes a pair of substrates, that is, an array substrate 3 and a counter substrate 4, and a liquid crystal layer LQ held as a light modulation layer between the pair of substrates. The liquid crystal display panel 2 has a substantially rectangular effective display portion 8 for displaying an image. The effective display unit 8 is composed of a plurality of display pixels PX arranged in a matrix.

  The array substrate 3 includes a switching element SW such as a thin film transistor disposed for each display pixel PX in the vicinity of the intersection of the scanning line Sc and the signal line Sg, a pixel electrode PE connected to the switching element SW, and the like. The counter substrate 4 includes a counter electrode CE and the like. Both the pixel electrode PE and the counter electrode CE are formed of a light-transmitting conductive material. The array substrate 3 and the counter substrate 4 are arranged with the pixel electrode PE and the counter electrode CE facing each other, and a gap is formed between them. The liquid crystal layer LQ is formed of a liquid crystal composition sealed in the gap between the array substrate 3 and the counter substrate 4.

  Further, on the outer surface of the liquid crystal display panel 2, that is, the outer surface of the array substrate 3 and the outer surface of the counter substrate 4, a first polarizing plate PL1 and a second polarizing plate PL2 whose polarization directions are set according to the characteristics of the liquid crystal layer LQ, respectively. Is arranged.

  In the color display type liquid crystal display device, the liquid crystal display panel 2 includes a plurality of types of display pixels, for example, a red pixel that displays red (R), a green pixel that displays green (G), and a blue that displays blue (B). Has pixels. 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 panel 2 having such a configuration is disposed between the bezel cover 11 and a backlight 15 as a surface light source device. That is, the rectangular frame-shaped bezel cover 11 is attached to the surface side of the liquid crystal display panel 2 (that is, the counter substrate side). The bezel cover 11 includes a rectangular window portion 12 that exposes the effective display portion 8 of the liquid crystal display panel 2, and a frame-shaped main body portion 13 that defines the window portion 12.

  A driver circuit 5 that supplies a drive signal to the liquid crystal display panel 2 is electrically connected to one side edge of the liquid crystal display panel 2 via a plurality of flexible printed wiring boards 6 and 7. The driver circuit 5 is arranged on the back side of the backlight 15 by curving the printed wiring boards 6 and 7 toward the back side of the backlight 15.

  The backlight 15 is housed in the bezel cover 11 together with the liquid crystal display panel 2 with the surface thereof facing the back side of the liquid crystal display panel 2 (that is, the array substrate side). Illuminate.

  As shown in FIG. 2, the backlight 15 includes a light source 22 and a light guide 26 having a substantially rectangular flat plate shape that converts the emitted light emitted from the light source 22 into a planar shape and emits the light. In this embodiment, the backlight 15 includes an elongated cylindrical cold cathode tube as the light source 22. The cold cathode tube is attached to a lamp holder fitted to both ends thereof. The light source 22 is not limited to a cold cathode tube but may be a light emitting diode (LED).

  The light guide 26 has a first main surface 26b and a second main surface 26d that face each other, and a first side surface 26a and a second side surface 26e that connect the first main surface 26b and the second main surface 26d. is doing. The first side surface 26 a faces the light source 22 and corresponds to an incident surface on which radiated light from the light source 22 enters. The first main surface 26b and the second main surface 26d are surfaces from which incident light incident from the incident surface can be emitted. In particular, the first main surface 26b emits incident light toward the liquid crystal display panel 2. This corresponds to the exit surface.

  In this embodiment, the light guide 26 is made of a light-transmitting acrylic resin or polycarbonate resin. Further, in this embodiment, the light guide 26 is formed in a wedge shape such that the thickness gradually decreases from the first side surface 26a toward the second side surface (non-light incident surface) 26e. Here, the thickness of the light guide 26 corresponds to the height along the normal direction of the first main surface 26b. With such a shape, the light incident from the first side surface 26a of the light guide 26 is uniformly reflected toward the first main surface 26b, and the second main surface located on the second side surface 26e side of the light guide 26 is used. An accommodation space for the driver circuit 5 and the like is secured on the surface 26d side. In particular, the wedge-shaped light guide is desirably employed in an edge light type backlight that illuminates a large liquid crystal display panel.

  The backlight 15 further includes a reflector 31 that reflects the emitted light emitted from the light source 22 toward the first side surface 26 a of the light guide 26. The reflector 31 is disposed so as to surround the periphery of the light source 22 disposed so as to face the first side surface 26a of the light guide 26 in a state where the cross section is curved in a substantially C shape.

  The reflector 31 forms an opening 32 for taking out the radiated light from the light source 22. The opening 32 faces the first side surface 26 a of the light guide 26. The opening 32 is formed between the tip 37 and the tip 39 of the reflector 31. The tip portions 37 and 39 oppose each other, and sandwich the light guide 26 in the thickness direction.

  The optical sheet 27 is disposed so as to cover the first main surface 26 b of the light guide 26. The optical sheet 27 gives predetermined optical characteristics to the outgoing light emitted from the first main surface 26b of the light guide 26. For example, the optical sheet 27 condenses the outgoing light from the first main surface 26b. A film having a function of diffusing light emitted from the first main surface 26b, and a liquid crystal display panel by efficiently guiding the light emitted from the first main surface 26b to the liquid crystal layer And a brightness enhancement film having a function of improving the brightness. As this optical sheet 27, a plurality of films may be combined and arranged, or a plurality of films may be integrated.

  The optical sheet 29 is disposed on the second main surface 26 d side of the light guide 26. The optical sheet 29 is a reflection sheet that reflects light leaking from the inside of the light guide 26 to the outside through the second main surface 26 d toward the first main surface 26 b of the light guide 26.

  The light source 22, the light guide 26, the optical sheet 27, the optical sheet 29, and the reflector 31 are accommodated in a substantially rectangular frame 40.

  By the way, with the demand for thinning of the liquid crystal display device, the distance between the liquid crystal display panel 2 and the backlight 15 is set to be extremely thin. That is, the distance between the first polarizing plate PL1 disposed on the outer surface of the array substrate 3 of the liquid crystal display panel 2 and the optical sheet 27 disposed closest to the liquid crystal display panel 2 of the backlight 15 is also extremely thin. The first polarizing plate PL1 is bonded to the array substrate 3 over almost the entire surface, but the optical sheet 27 is only partially bonded to the frame 40 and is not completely fixed. For this reason, the optical sheet 27 may be bent or swelled, which causes display due to local sticking between the optical sheet 27 and the first polarizing plate PL1, damage to the optical sheet 27 due to contact between the two, or the like. There is a risk of degrading the quality. In particular, when the optical sheet 27 is a brightness enhancement film, there is a risk that sticking may not realize a sufficient brightness enhancement function due to damage or the like.

  Therefore, in this embodiment, the first polarizing plate PL1 is configured such that the dynamic friction coefficient of the surface facing the backlight 15 is smaller than the dynamic friction coefficient of the surface of the backlight 15 facing the first polarizing plate PL1. Yes. More specifically, as shown in FIG. 3, the first polarizing plate PL1 is for bonding the effective portion 50 as the polarizing plate and the effective portion 50 to the outer surface of the liquid crystal display panel 2 (that is, the outer surface of the array substrate 3). The adhesive layer 51, the release layer 52 that protects the adhesive layer 51, the protective layer 53 for preventing the surface of the effective portion 50 from being stained and damaged, and the liquid crystal display panel 2 disposed on the protective layer 53 as a backlight 15, the coating layer 54 corresponding to the surface facing the backlight 15 is laminated.

  The effective portion 50 includes, for example, a polarizer (or analyzer) layer 50A formed of stretched and dyed polyvinyl alcohol (PVA), and a polarizer layer 50A formed of, for example, triacetate cellulose (TAC). It is comprised by the support body layers 50B and 50C to perform.

  As shown in FIG. 4, the coating layer 54 has a concavo-convex shape having a low friction characteristic on the surface thereof. That is, the coating layer 54 is a base material in a state in which spherical bodies (resin spheres) 54P formed using, for example, a light-transmitting resin material such as acrylic resin or silicon resin are dispersed in the binder resin 54B. It can form by apply | coating on the protective layer 53 used.

  According to the first polarizing plate PL1 in which the coating layer 54 having such a configuration is arranged, the low roughness and the low characteristics that are the characteristics of the coating layer 54 are obtained even when the backlight 15 is arranged at a minute interval. The smoothness due to the frictional property can suppress sticking of the backlight 15 to the optical sheet 27 corresponding to the surface facing the first polarizing plate PL1, and damage to the optical sheet 27 even if the two come into contact with each other. It becomes possible to prevent.

  Further, the dynamic friction coefficient of the coating layer 54 is smaller than the dynamic friction coefficient of the optical sheet 27. Furthermore, the coefficient of dynamic friction of the coating layer 54 is desirably less than 0.2. These dynamic friction coefficients are values measured when the coating layer 54 or the optical sheet 27 are brought into contact with the reference object under the same conditions. In this embodiment, the coating layer 54 or the optical sheet 27 is used as the reference object. It is a measured value when it is contacted at a speed of 300 mm / min with a load of 500 g.

Next, the effect of this embodiment was verified. As a comparative example, a spherical body (silica sphere) formed using silica (SiO ₂ ) having a hardness higher than that of a resin sphere was applied on the protective layer 53 in a state of being dispersed in a binder resin, thereby forming a coating layer 54. It compared with the structure at the time of applying a polarizing plate.

  As shown in FIG. 5, in the comparative example, the average roughness of the coating layer 54 was 0.31, whereas in the embodiment, the average roughness of the coating layer 54 was lower than that of the comparative example. Was 0.16. Further, in the comparative example, the dynamic friction coefficient of the coating layer 54 was 0.25 to 0.28, whereas in the embodiment, the friction coefficient was lower than that of the comparative example, and the dynamic friction coefficient of the coating layer 54 was 0. It was 18-0.20.

  Due to the difference in characteristics, in the comparative example, it was possible to improve the adhesion of the optical sheet 27 to the first polarizing plate PL1, but the hardness of the surface of the first polarizing plate PL1 (that is, silica) due to the contact between them. The optical sheet 27 was damaged by the influence of the hardness of the sphere), roughness, and high frictional properties.

  On the other hand, in the embodiment, it is possible to improve the sticking of the optical sheet 27 to the first polarizing plate PL1, and even if they are in contact with each other, the surface of the first polarizing plate PL1 has low hardness and low roughness. The optical sheet 27 was not damaged due to the low friction. In particular, defining the dynamic friction coefficient of the coating layer 54 to be less than 0.2 is extremely effective in creating a low-friction characteristic while preventing the optical sheet 27 from being damaged while having an uneven shape on the surface of the coating layer. is important.

  As described above, according to the liquid crystal display device according to this embodiment, when the transmissive liquid crystal display panel and the surface light source device are arranged so as to overlap each other, the second liquid crystal display panel disposed on the surface light source device side of the liquid crystal display panel. The dynamic friction coefficient of the surface facing the surface light source device of one polarizing plate is set smaller than the dynamic friction coefficient of the surface facing the first polarizing plate of the surface light source device. For this reason, with the demand for thinning, the distance between the liquid crystal display panel and the surface light source device (more precisely, the distance between the first polarizing plate and the optical sheet arranged closest to the liquid crystal display panel of the surface light source device) is increased. Even if it is set to a small value, it is possible to prevent the optical sheet from sticking to the first polarizing plate and prevent damage to the optical sheet without interposing another film therebetween. . As a result, it is possible to reduce the thickness of the apparatus without deteriorating the quality, and it is possible to prevent the display quality from deteriorating due to sticking or damage of the optical sheet.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the spirit of the invention in the stage of implementation. In addition, 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, an example in which the wedge-shaped light guide 26 is applied has been described. However, a flat light guide 26 having a substantially uniform thickness may be applied.

  In the above-described embodiment, the case where the brightness enhancement film is disposed as the optical sheet on the surface facing the first polarizing plate of the surface light source device has been described. However, the film having other functions is the first polarizing plate. May correspond to the opposite surface.

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 a surface light source device (backlight) applied to the liquid crystal display device shown in FIG. FIG. 3 is a cross-sectional view schematically showing the structure of a polarizing plate applied to the liquid crystal display device shown in FIG. FIG. 4 is a diagram schematically showing the structure of the surface (coating layer) of the polarizing plate shown in FIG. FIG. 5 is a diagram illustrating a verification result of the effect according to the embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device, 2 ... Liquid crystal display panel, 3 ... Array substrate, 4 ... Opposite substrate, 15 ... Back light, 22 ... Light source, 26 ... Light guide, 27 ... Optical sheet, 29 ... Optical sheet, PL1 ... No. DESCRIPTION OF SYMBOLS 1 polarizing plate, PL2 ... 2nd polarizing plate, 50 ... Effective part, 51 ... Adhesive layer, 52 ... Release layer, 53 ... Protective layer, 54 ... Coating layer, LQ ... Liquid crystal layer, PX ... Display pixel

Claims (4)

A liquid crystal display panel configured to hold a liquid crystal layer between the array substrate and the counter substrate;
A first polarizing plate disposed on the outer surface of the array substrate;
A second polarizing plate disposed on the outer surface of the counter substrate;
A liquid crystal display device comprising: a surface light source device that illuminates the liquid crystal display panel from the array substrate side through the first polarizing plate;
A liquid crystal display device, wherein a coefficient of dynamic friction of a surface of the first polarizing plate facing the surface light source device is smaller than a coefficient of dynamic friction of a surface of the surface light source device facing the first polarizing plate.   The liquid crystal display device according to claim 1, wherein a coefficient of dynamic friction of a surface of the first polarizing plate facing the surface light source device is less than 0.2.   The liquid crystal display device according to claim 1, wherein the first polarizing plate has a coating layer in which resin spheres are dispersed on a surface facing the surface light source device. The surface light source device includes a light source,
A light guide including an incident surface on which radiated light emitted from the light source is incident, a first main surface and a second main surface facing each other, on which incident light incident from the incident surface is emitted;
An optical sheet disposed on the first main surface side of the light guide and having a brightness enhancement function facing the first polarizing plate;
The liquid crystal display device according to claim 1, further comprising:

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