JP2006208535A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device on which a moire fringe is inconspicuous even when a prism sheet of which the prism ridge lines are arranged in a direction parallel or perpendicular to a direction of rows in a liquid crystal cell is used. <P>SOLUTION: In the liquid crystal display device comprising: a backlight set 14; a lower side polarizing plate 13; a liquid crystal cell 12 having a plurality of pixels arrangned in row and column directions; and an upper side polarizing plate 11, sequentially arranged toward an upward direction, the backlight set 14 is constructed with: a light source 21; a light guide plate 19 to take in light from the light source 21; and a first diffusion sheet 18, a first prism sheet 16 with the prism ridge lines arranged in the direction parallel or perpendicular to the direction of rows in the liquid crystal cell, and a second diffusion sheet 15 sequentially arranged on the upper surface of the light guide plate 19, wherein the haze value of the second diffusion sheet 15 is 60-80%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device in which ridge lines of a prism are provided as a prism sheet in a direction parallel to or perpendicular to the row direction of a liquid crystal cell and the occurrence of moire fringes is small. .

  The transmissive liquid crystal display device includes various optical sheets such as a diffusion sheet, a lens sheet, a prism sheet, and a deflection film between a liquid crystal cell and a backlight light source. Among them, the prism sheet is used for condensing light from the backlight light source in the vertical direction of the light-emitting surface of the light guide plate (normal angle is 0 degree) in order to improve the front luminance of the liquid crystal cell. It is what has been. As shown in FIG. 4, the prism sheet 50 is formed of a transparent sheet having a fine prism surface on the front surface 51 and a smooth surface on the back surface 52. Are provided with parallel V-shaped grooves 53 and inverted V-shaped ridges 54 formed at a pitch p (see Patent Document 1 below).

  In general, each RGB pixel in the active matrix type liquid crystal cell has a rectangular shape as shown in FIG. 5, and each RGB pixel has a constant value in the row and column directions of the liquid crystal cell. Many are repeatedly arranged at a pitch.

  Accordingly, when the prism sheet is disposed between the liquid crystal cell and the backlight source, as shown in FIG. 6A, each of RGB arranged in the row direction and the column direction at a constant pitch of the liquid crystal cell. The V-shaped grooves or inverted V-shaped ridgelines 54 (the V-shaped grooves in FIG. 6 are omitted in FIG. 6) are almost parallel to the pixels and the prism sheet. If so arranged, so-called moire fringes (interference fringes) are generated due to interference between the two, which is very disturbing. Therefore, as shown in FIG. 6B, the prism sheet is inclined by a predetermined angle θ so that the direction of the ridge line 54 of the prism is not parallel to or orthogonal to the row direction of the liquid crystal cell. The angle formed by each side and the ridge line 54 of the prism is inclined by a predetermined angle θ.

  When the predetermined angle θ gradually increases from θ = 0 degrees, the moire fringe interval gradually decreases in proportion to the size, and finally the moire fringe interval cannot be recognized by human eyes. So it looks like there are virtually no moire fringes.

In this case, the same effect can be obtained by tilting the arrangement direction of each pixel of the liquid crystal cell or tilting the ridge line of the prism sheet, but each pixel of the liquid crystal cell is generally arranged in the row direction of the substrate of the liquid crystal cell. In addition, since it is easier to incline the direction of the ridge line of the prism sheet than to incline the arrangement direction of each pixel of the liquid crystal cell, the direction of the ridge line of the prism sheet is generally set. A prism sheet inclined by θ = about 45 degrees from each side of the prism sheet is often used. In particular, for liquid crystal display devices for mobile phones or personal computers, two prism sheets have respective ridge lines in order to increase surface brightness and narrow the viewing angle so that they cannot be seen by the surrounding people. Used in combination so as to be orthogonal.
JP-A-8-68997 (claims, paragraphs [0028] to [0030], [0061] to [0075], FIGS. 1 to 6) JP-A-11-52372 (Claims, paragraphs [0017] to [0027], FIGS. 1 to 2)

  However, if an angle formed by each side of the prism sheet and the ridge line of the prism sheet is inclined by a predetermined angle θ, it is usually from the original plate on which the prism is formed in the vertical direction or the horizontal direction of θ = 0 degrees. Since it is manufactured by cutting in a direction inclined by a predetermined angle θ by a mold, a rectangular prism sheet cannot be obtained at the end of the original plate. For this reason, there is a problem that the cost of each prism sheet is increased because an extra portion is formed on the original plate of the prism sheet.

  In addition, since the ridge line of the prism sheet is attached in a direction inclined with respect to the arrangement direction of each pixel of the liquid crystal cell, the ridge line crosses the light-transmitting portion of each pixel in an oblique direction, so that the luminance decreases. There are also problems.

  On the other hand, if the prism ridge line of the prism sheet is parallel or perpendicular to each side of the prism sheet with θ = 0 degrees, the above-mentioned problem of the cost and brightness of the prism film is solved. However, since the row direction of the liquid crystal cell and the ridge line of the prism of the prism sheet are parallel or close to a right angle, moire fringes are generated due to interference between the two, and this countermeasure against moire fringes is indispensable.

  The present invention has been made to solve the above-mentioned problems of the prior art, and the object of the present invention is to provide a prism ridge line as a prism sheet in order to solve the problems related to the cost and brightness reduction of the prism sheet. An object of the present invention is to provide a liquid crystal display device in which moire fringes are not noticeable even when a liquid crystal cell provided in a direction parallel or orthogonal to the row direction is used.

  The above object of the present invention can be achieved by the following configurations. That is, the invention of the liquid crystal display device according to claim 1 is a liquid crystal display device in which a backlight set, a lower polarizing plate, a liquid crystal cell, and an upper polarizing plate are sequentially arranged in the upward direction. A light source, a light guide plate for taking in light from the light source, a first diffusion sheet sequentially disposed on an upper surface of the light guide plate, and a ridge line of the prism in a direction parallel or orthogonal to the row direction of the liquid crystal cell The second diffusion sheet is provided with a first prism sheet and a second diffusion sheet provided, and the second diffusion sheet has a haze value of 60% to 80%.

  The haze value (Th) is the degree of an unclear cloudy appearance inside or on the surface of the transparent plastic, and the numerical value is also called “cloudy value”. This haze value is obtained as Th = (Td / Tt) × 100 (%) by measuring the total light transmittance (Tt) and the scattered light transmittance (Td).

  According to a second aspect of the present invention, in the liquid crystal display device according to the first aspect, a second prism sheet is disposed between the first prism sheet and the first diffusion sheet, and the second The ridge line of the prism sheet is orthogonal to the ridge line of the first prism sheet.

  Furthermore, in the invention of the liquid crystal display device according to claim 3, the backlight set, the lower polarizing plate, the liquid crystal cell having a plurality of pixels arranged in the row direction and the column direction, and the upper polarizing plate are in the upward direction. The backlight set includes a light source, a light guide plate that takes in light from the light source, a diffusion sheet that is sequentially arranged on an upper surface of the light guide plate, and a prism ridge line. And a first prism sheet and an optical sheet provided in a direction parallel to or perpendicular to the row direction, and a light diffusing material is mixed in the optical sheet.

  According to a fourth aspect of the present invention, in the liquid crystal display device according to the third aspect, the optical sheet includes a transparent sheet mixed with a light diffusing material on at least one surface of the brightness enhancement film. Features. The brightness enhancement film selectively reflects the polarization component absorbed by the polarizing plate disposed below the liquid crystal cell in the visible light from the backlight source based on the reflective polarization technology. The liquid crystal cell is reused over the entire viewing angle. Moreover, the transparent sheet mixed with the light diffusing material may be provided only on one surface of the brightness enhancement film or on both surfaces.

  The invention according to claim 5 is the liquid crystal display device according to claim 3 or 4, wherein a second prism sheet is disposed between the first prism sheet and the diffusion sheet, and the second prism sheet is provided. The ridge line of the prism sheet is orthogonal to the ridge line of the first prism sheet.

  Furthermore, the invention of the liquid crystal display device according to claim 6 is directed to a backlight set, a lower polarizing plate, a liquid crystal cell having a plurality of pixels arranged in a row direction and a column direction, and an upper polarizing plate. The backlight set includes a light source, a light guide plate that takes in light from the light source, a diffusion sheet and a prism ridge line that are sequentially arranged on the upper surface of the light guide plate. A first prism sheet provided in a direction parallel to or perpendicular to the row direction of the light source, and the diffusion sheet is formed by forming a light diffusion layer containing transparent fine particles on the upper surface of a transparent base sheet. It is characterized by becoming.

  The invention according to claim 7 is the liquid crystal display device according to claim 6, wherein a second prism sheet is disposed between the first prism sheet and the diffusion sheet, and the second prism sheet. The ridge line is perpendicular to the ridge line of the first prism sheet.

  The present invention provides the following excellent effects by having the above configuration. That is, according to the first aspect of the present invention, since the prism ridge line is provided in a direction parallel to or perpendicular to the row direction of the liquid crystal cell, there is no more portion than the original plate of the prism sheet. Since the prism sheet cut out without waste can be used, the cost is reduced.

  In addition, light having a haze value of 60% to 80%, which has a higher light diffusion efficiency than the second diffusion sheet that is conventionally used as the second diffusion sheet, is used. Since the incident direction is highly scattered because it is scattered again by the second diffusion sheet after being scattered by the first diffusion sheet, the ridge line of the prism as the prism sheet is in the row direction of the liquid crystal cell. In other words, the moiré fringes that are inevitably generated by the use of those provided in parallel or orthogonal directions are difficult to visually recognize. In addition, since the ridge line of the prism is not inclined with respect to the arrangement direction of the pixels of the liquid crystal cell, the luminance of the liquid crystal display device is increased.

  Since the light scattering effect is small when the haze value is less than 60%, the prism sheet has a prism ridge line provided in a direction parallel or orthogonal to the row direction of the liquid crystal cell. The moiré fringes that inevitably occur are conspicuous. On the other hand, when the haze value exceeds 80%, moire fringes due to the large light scattering effect become inconspicuous, but the luminance of the liquid crystal display device decreases because the light transmittance decreases.

  Further, according to the invention according to claim 2, since two prism sheets are provided, the brightness of the liquid crystal display device is improved as compared with the single sheet, and the viewing angle is narrowed so that it can be seen by others. An optimum liquid crystal display device can be obtained as a display device for a portable telephone or a personal computer that is not desired.

  According to the invention of claim 3, since the prism ridge line is provided in a direction parallel or orthogonal to the row direction of the liquid crystal cell, there is no more portion than the prism sheet original plate. Since the prism sheet cut out without waste can be used, the cost is reduced. In addition, since the light diffusion material is mixed in the optical sheet, the light incident on the liquid crystal cell is scattered by the light diffusion material in the optical sheet again after being scattered by the diffusion sheet. Since it is scattered, it is difficult to visually recognize the moire fringes that are inevitably generated by using a prism sheet in which the prism ridge is provided in a direction parallel or orthogonal to the row direction of the liquid crystal cell. In addition, since the ridge line of the prism is not inclined with respect to the arrangement direction of the pixels of the liquid crystal cell, the luminance of the liquid crystal display device is increased.

  According to the invention of claim 4, the brightness enhancement film reflects the polarization component that is absorbed by the lower polarizing plate in the visible light from the backlight source, and this reflected light is re-reflected by the reflection sheet. Since it is converted into polarized light that is not absorbed by the lower polarizing plate and reused, the amount of light that passes through the lower polarizing plate increases. Therefore, even with only one prism sheet, the luminance is high and the viewing angle is high. A wide liquid crystal display device suitable for an image display device such as a monitor or a television can be obtained.

  Further, according to the invention of claim 5, a liquid crystal display device that produces the same effect as that of the invention of claim 2 while obtaining the effect of the invention of claim 3 or 4 can be obtained.

  Furthermore, according to the invention according to claim 6, since the prism ridge line is provided in a direction parallel or orthogonal to the row direction of the liquid crystal cell, there is no more portion than the prism sheet original plate. Since the prism sheet cut out without waste can be used, the cost is reduced.

  In addition, the diffusion sheet in which the light diffusion layer containing transparent fine particles is formed on the surface of the transparent base sheet has a high light scattering efficiency and a large light scattering efficiency. In order to obtain a liquid crystal display device having a wide viewing angle and high brightness, it is necessary to use a prism sheet in which prism ridges are provided in a direction parallel or perpendicular to the row direction of the liquid crystal cell. Moiré fringes that are generated automatically become difficult to see. In addition, since the ridge line of the prism is not inclined with respect to the arrangement direction of the pixels of the liquid crystal cell, the luminance of the liquid crystal display device is increased.

  Further, according to the invention of claim 7, a liquid crystal display device that produces the same effect as that of the invention of claim 2 while obtaining the effect of the invention of claim 6 can be obtained.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the embodiments and FIGS. 1 to 3. The embodiments described below are liquid crystals for embodying the technical idea of the present invention. The display device is illustrated, and is not intended to specify the present invention in this embodiment. The present invention has been variously modified without departing from the technical idea shown in the claims. It can be equally applied to things.

  A liquid crystal display device 10A of Example 1 will be described with reference to FIG. The liquid crystal display device 10A of Example 1 is roughly formed by laminating an upper polarizing plate 11, a liquid crystal cell 12, a lower polarizing plate 13, and a backlight set 14. Of these, the upper polarizing plate 11, the liquid crystal cell 12, and the lower polarizing plate 13 are illustrated as being separated from each other, but are actually in close contact with both surfaces of the liquid crystal cell 12.

  On the other hand, the backlight set 14 includes, in order from the liquid crystal cell 12 in the downward direction, the second diffusion sheet 15, the first and second prism sheets 16, 17 arranged in the direction in which the ridge lines of the prisms are orthogonal to each other, 1, a diffusion sheet 18, a light guide plate 19, and a reflection sheet 20 are arranged, and a light source 21 made of a tubular cold cathode tube or a light emitting diode is arranged on the side of the light guide plate 19.

  In FIG. 1, the second diffusion sheet 15, the first and second prism sheets 16, 17, the first diffusion sheet 18, the light guide plate 19, and the reflection sheet 20 are not in contact with each other for easy understanding. These components are configured to contact each other when the liquid crystal display device 10A is assembled in a frame member (not shown).

  Among these, in Example 1, as the first and second prism sheets 16 and 17, the ridge lines of the prisms are parallel or orthogonal to the sides of the prism sheet as shown in FIG. The provided one is used, and the second diffusion sheet 15 has a haze value of 60% to 80%.

  Thus, when a prism sheet having a prism ridge line parallel or orthogonal to each side of the prism sheet is used, the prism ridge line is parallel or orthogonal to the row direction of the liquid crystal cell. In the prior art, moire fringes are conspicuous. However, in Example 1, as the second diffusion sheet 15, a sheet having a haze value of 60% to 80% having a light scattering property larger than that of the first diffusion sheet 18 that is conventionally used normally is used. The light incident on the liquid crystal cell is scattered again by the first diffusion sheet 15 after being scattered by the second diffusion sheet 18, so that the moire fringes are not noticeable because the incident direction is highly scattered. .

  In this case, if the haze value of the second diffusion sheet 15 is less than 60%, the light scattering effect is small, so that moire fringes are conspicuous. If the haze value exceeds 80%, the light scattering effect is large. In addition, the moire fringes are inconspicuous, but the brightness of the liquid crystal display device is lowered because the light transmittance is lowered. In addition, since the ridgeline of the prism sheet is provided in a direction parallel to or orthogonal to each side of the prism sheet, the prism sheet can be cut out without waste so that there is no excess part from the original plate of the prism sheet. A liquid crystal display device 10A with less generation of moire fringes can be obtained while using an inexpensive prism sheet.

  In the first embodiment, two prism sheets are used, but one prism sheet may be used. When two prism sheets are provided, the luminance is improved and the viewing angle is narrower than in the case of one prism sheet, and the liquid crystal display device is optimal as a display device for a mobile phone or a personal computer that is not desired to be seen by others. Is obtained. On the contrary, if the number of the prism sheets is one, the luminance is lowered as compared with the case where the number of the prism sheets is two, but the viewing angle is widened, so that it is suitable for an image display device such as a monitor or a television.

  A liquid crystal display device 10B of Example 2 will be described with reference to FIG. However, in FIG. 2, the same components as those of the liquid crystal display device 10A according to the first embodiment shown in FIG. The difference between the liquid crystal display device 10B of the second embodiment and the liquid crystal display device 10A of the first embodiment is that the backlight set 14 is replaced with the second diffusion sheet 15 on both surfaces of the brightness enhancement film 22. The optical sheet 15 ′ having transparent sheets 23 and 24 mixed with a light diffusing material is used, and the other configuration is the same as that of the liquid crystal display device 10A of the first embodiment.

  The brightness enhancement film 22 is a well-known product marketed as DBEF (trade name, manufactured by Sumitomo 3M Co., Ltd.). In Example 2, a light diffusing material is mixed into the surface of the brightness enhancement film 22 described above. An optical sheet 15 ′ having transparent sheets 23 and 24 is used. As the optical sheet 15 ′ having such a configuration, a commercially available DBEF-D400 (trade name, manufactured by Sumitomo 3M Limited) can be used as it is.

  When this optical sheet 15 ′ is used, the brightness enhancement film 22 reflects the polarization component absorbed by the lower polarizing plate 13 in the visible light from the backlight light source, but this reflected light is re-reflected by the reflection sheet 20. Since the light is converted into polarized light that is not absorbed by the lower polarizing plate 13 and reused, the amount of light transmitted through the lower polarizing plate 13 is increased, and the transparent sheets 23 and 24 mixed with a light diffusing material. As a result, the light incident on the liquid crystal cell 12 is more highly scattered.

  Therefore, according to the liquid crystal display device 10B of the second embodiment, the luminance of the optical sheet 15 ′ can be achieved even when a prism sheet having prism ridge lines provided in a direction parallel to or orthogonal to each side of the prism sheet is used. Although the same effect as that of the liquid crystal display device 10A of the first embodiment is obtained by the ascending effect and the light scattering effect, the liquid crystal display device 10B having higher luminance can be obtained. In this case, the transparent sheets 23 and 24 mixed with the light diffusing material may be provided only on one surface of the brightness enhancement film 22 or may be provided on both surfaces. Further, in the second embodiment, two prism sheets are used, but a single prism sheet may be used as in the first embodiment.

  A liquid crystal display device 10C of Example 3 will be described with reference to FIG. In FIG. 3, the same components as those of the liquid crystal display device 10B according to the second embodiment shown in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted. The liquid crystal display device 10C of the third embodiment is different from the liquid crystal display device 10B of the second embodiment in that the optical sheet 15 ′ used in the liquid crystal display device 10B of the second embodiment is not used, and The high-intensity diffusion sheet 18 ′ is used in place of the diffusion sheet 18, and the other configuration is the same as that of the liquid crystal display device 10B of the second embodiment.

  This high-intensity diffusion sheet 18 ′ is obtained by forming a light diffusion layer 26 containing transparent fine particles on one surface of a transparent substrate sheet 25. Here, a transparent substrate is used as the high-intensity diffusion sheet 18 ′. A commercially available product having a back coat layer 27 having an anti-sticking action or an anti-static action on the other surface of the sheet 25, for example, Opulse BS series (trade name, manufactured by Eiwa Co., Ltd.), Light-up GM3 series (product) Name, manufactured by Kimoto Co., Ltd.) and the like can be selected as appropriate. The high-intensity diffusion sheet 18 'has a feature that it has a high total light transmittance and can obtain highly scattered light as compared with a conventional diffusion sheet that is generally used.

  Therefore, according to the liquid crystal display device 10C of the third embodiment, even when a prism sheet having a prism ridge line provided in a direction parallel to or orthogonal to each side of the prism sheet is used, the high brightness diffusion sheet 18 ′. Due to the brightness increasing effect and the light scattering effect, the liquid crystal display device 10C having higher brightness can be obtained while achieving the same effect as the liquid crystal display device 10A of the first embodiment. In this case, the light diffusion layer 26 containing transparent fine particles may be provided only on one surface of the transparent base sheet 25 or on both surfaces. Furthermore, in the second embodiment, two prism sheets are used. However, as in the first embodiment, one prism sheet may be used.

1 is a longitudinal sectional view of a liquid crystal display device of Example 1. FIG. 6 is a longitudinal sectional view of a liquid crystal display device of Example 2. FIG. 6 is a longitudinal sectional view of a liquid crystal display device of Example 3. FIG. It is an enlarged vertical sectional view of a prism sheet. It is an enlarged plan view of each pixel part of a liquid crystal cell. It is a top view for demonstrating the direction of the groove | channel or ridgeline of a prism sheet.

Explanation of symbols

10A, 10B, 10C Liquid crystal display device 11 Upper polarizing plate 12 Liquid crystal cell 13 Lower polarizing plate 14 Backlight set 15, 18 Diffusion sheet 15 'Optical sheet 16, 17 Prism sheet 18' High-intensity diffusion sheet 19 Light guide plate 20 Reflecting sheet DESCRIPTION OF SYMBOLS 21 Backlight light source 22 Brightness enhancement film 23, 24 Transparent sheet mixed with diffusing material 25 Transparent substrate sheet 26 Light diffusing layer containing transparent fine particles 27 Back coat layer

Claims (7)

In the liquid crystal display device in which a backlight set, a lower polarizing plate, a liquid crystal cell having a plurality of pixels arranged in the row direction and the column direction, and an upper polarizing plate are sequentially arranged in the upward direction, the backlight set Are a light source, a light guide plate for taking in light from the light source, a first diffusion sheet sequentially arranged on the upper surface of the light guide plate, and a direction in which the ridge lines of the prisms are parallel or orthogonal to the row direction of the liquid crystal cell A liquid crystal display device comprising: a first prism sheet and a second diffusion sheet provided on the second diffusion sheet, wherein the second diffusion sheet has a haze value of 60% to 80%. A second prism sheet is disposed between the first prism sheet and the first diffusion sheet, and the ridge line of the second prism sheet is orthogonal to the ridge line of the first prism sheet. The liquid crystal display device according to claim 1. In the liquid crystal display device in which a backlight set, a lower polarizing plate, a liquid crystal cell having a plurality of pixels arranged in the row direction and the column direction, and an upper polarizing plate are sequentially arranged in the upward direction, the backlight set Is provided with a light source, a light guide plate for taking in light from the light source, a diffusion sheet sequentially disposed on the upper surface of the light guide plate, and a ridge line of the prism in a direction parallel or orthogonal to the row direction of the liquid crystal cell. A liquid crystal display device comprising: a first prism sheet and an optical sheet, wherein a light diffusing material is mixed in the optical sheet.   4. The liquid crystal display device according to claim 3, wherein the optical sheet includes a transparent sheet in which a light diffusing material is mixed on at least one surface of the brightness enhancement film. A second prism sheet is disposed between the first prism sheet and the diffusion sheet, and a ridge line of the second prism sheet is orthogonal to a ridge line of the first prism sheet. The liquid crystal display device according to claim 3. In the liquid crystal display device in which a backlight set, a lower polarizing plate, a liquid crystal cell having a plurality of pixels arranged in the row direction and the column direction, and an upper polarizing plate are sequentially arranged in the upward direction, the backlight set Is provided with a light source, a light guide plate for taking in light from the light source, and a ridge line of a diffusion sheet and a prism sequentially arranged on the upper surface of the light guide plate in a direction parallel or orthogonal to the row direction of the liquid crystal cell. A liquid crystal display device comprising: a first prism sheet, wherein the diffusion sheet is formed by forming a light diffusion layer containing transparent fine particles on an upper surface of a transparent substrate sheet. A second prism sheet is disposed between the first prism sheet and the diffusion sheet, and a ridge line of the second prism sheet is orthogonal to a ridge line of the first prism sheet. The liquid crystal display device according to claim 6.

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